WorldWideScience

Sample records for stiffness tests

  1. Contributions of Hamstring Stiffness to Straight-Leg-Raise and Sit-and-Reach Test Scores.

    Science.gov (United States)

    Miyamoto, Naokazu; Hirata, Kosuke; Kimura, Noriko; Miyamoto-Mikami, Eri

    2018-02-01

    The passive straight-leg-raise (PSLR) and the sit-and-reach (SR) tests have been widely used to assess hamstring extensibility. However, it remains unclear to what extent hamstring stiffness (a measure of material properties) contributes to PSLR and SR test scores. Therefore, we aimed to clarify the relationship between hamstring stiffness and PSLR and SR scores using ultrasound shear wave elastography. Ninety-eight healthy subjects completed the study. Each subject completed PSLR testing, and classic and modified SR testing of the right leg. Muscle shear modulus of the biceps femoris, semitendinosus, and semimembranosus was quantified as an index of muscle stiffness. The relationships between shear modulus of each muscle and PSLR or SR scores were calculated using Pearson's product-moment correlation coefficients. Shear modulus of the semitendinosus and semimembranosus showed negative correlations with the two PSLR and two SR scores (absolute r value≤0.484). Shear modulus of the biceps femoris was significantly correlated with the PSLR score determined by the examiner and the modified SR score (absolute r value≤0.308). The present findings suggest that PSLR and SR test scores are strongly influenced by factors other than hamstring stiffness and therefore might not accurately evaluate hamstring stiffness. © Georg Thieme Verlag KG Stuttgart · New York.

  2. Wing Torsional Stiffness Tests of the Active Aeroelastic Wing F/A-18 Airplane

    Science.gov (United States)

    Lokos, William A.; Olney, Candida D.; Crawford, Natalie D.; Stauf, Rick; Reichenbach, Eric Y.

    2002-01-01

    The left wing of the Active Aeroelastic Wing (AAW) F/A-18 airplane has been ground-load-tested to quantify its torsional stiffness. The test has been performed at the NASA Dryden Flight Research Center in November 1996, and again in April 2001 after a wing skin modification was performed. The primary objectives of these tests were to characterize the wing behavior before the first flight, and provide a before-and-after measurement of the torsional stiffness. Two streamwise load couples have been applied. The wing skin modification is shown to have more torsional flexibility than the original configuration has. Additionally, structural hysteresis is shown to be reduced by the skin modification. Data comparisons show good repeatability between the tests.

  3. Effect of Shoes on Stiffness and Energy Efficiency of Ankle-Foot Orthosis: Bench Testing Analysis.

    Science.gov (United States)

    Kobayashi, Toshiki; Gao, Fan; LeCursi, Nicholas; Foreman, K Bo; Orendurff, Michael S

    2017-12-01

    Understanding the mechanical properties of ankle-foot orthoses (AFOs) is important to maximize their benefit for those with movement disorders during gait. Though mechanical properties such as stiffness and/or energy efficiency of AFOs have been extensively studied, it remains unknown how and to what extent shoes influence their properties. The aim of this study was to investigate the effect of shoes on stiffness and energy efficiency of an AFO using a custom mechanical testing device. Stiffness and energy efficiency of the AFO were measured in the plantar flexion and dorsiflexion range, respectively, under AFO-alone and AFO-Shoe combination conditions. The results of this study demonstrated that the stiffness of the AFO-Shoe combination was significantly decreased compared to the AFO-alone condition, but no significant differences were found in energy efficiency. From the results, we recommend that shoes used with AFOs should be carefully selected not only based on their effect on alignment of the lower limb, but also their effects on overall mechanical properties of the AFO-Shoe combination. Further study is needed to clarify the effects of differences in shoe designs on AFO-Shoe combination mechanical properties.

  4. The influence of testing apparatus stiffness on the source properties of laboratory stick-slip

    Science.gov (United States)

    Kilgore, B. D.; McGarr, A.; Beeler, N. M.; Lockner, D. A.

    2016-12-01

    Stick-slip experiments were performed to determine the influence of the testing apparatus stiffness on source properties, to develop methods to relate stick-slip to natural earthquakes, and to examine the hypothesis of McGarr [2012] that the product of unloading stiffness, k, and slip duration, T, is both scale-independent and approximately constant for both laboratory and natural earthquakes. A double-direct shear load frame was used with Sierra White Granite samples at 2 MPa normal stress, and a remote loading rate of 0.2 µm/s. The stiffness of the test apparatus was varied by more than an order of magnitude by inserting disk springs into the shear loading column adjacent to the granite samples. Servo-controlling slip at a point between the forcing ram and the shear force load cell, produced repeatable slip events. Slip and slip duration decrease as k increases, as they do for natural earthquakes. In contrast to earthquakes, stress drop and slip rate decrease with increasing k, and the product kT for these experiments is not constant, but decreases with k. These data, collected over a range of k, do not conform to McGarr's [2012] hypothesis. However, analysis of stick-slip studies from other testing apparatuses is consistent with McGarr's hypothesis; kT is scale-independent, similar to that of earthquakes, equal to the ratio of static stress drop to average slip velocity, and similar to the ratio of shear modulus to wavespeed of rock. These properties result from conducting experiments over a range of sample sizes, using rock samples with the same elastic properties as the Earth, and using testing machines whose stiffnesses decrease, and characteristic periods increase with scale. A consequence of our experiments and analysis is that extrapolation of lab scale earthquake source properties to the Earth is more difficult than previously thought, requiring an accounting for the properties of the testing machines and additional research beyond that reported here.

  5. Effects of vehicle front-end stiffness on rear seat dummies in NCAP and FMVSS208 tests.

    Science.gov (United States)

    Sahraei, Elham; Digges, Kennerly; Marzougui, Dhafer

    2013-01-01

    This study is devoted to quantifying changes in mass and stiffness of vehicles tested by the National Highway Traffic Safety Administration (NHTSA) over the past 3 decades (model years 1982 to 2010) and understanding the effect of those changes on protection of rear seat occupants. A total of 1179 tests were used, and the changes in their mass and stiffness versus their model year was quantified. Additionally, data from 439 dummies tested in rear seats of NHTSA's full frontal crashes were analyzed. Dummies were divided into 3 groups based on their reference injury criteria. Multiple regressions were performed with speed, stiffness, and mass as predicting variables for head, neck, and chest injury criteria. A significant increase in mass and stiffness over model year of vehicles was observed, for passenger cars as well as large platform vehicles. The result showed a significant correlation (P-value < .05) between the increase in stiffness of the vehicles and increase in head and chest injury criteria for all dummy sizes. These results explain that stiffness is a significant contributor to previously reported decreases in protection of rear seat occupants over model years of vehicles.

  6. Stiffness modulus of Polyethylene Terephthalate modified asphalt mixture: A statistical analysis of the laboratory testing results

    International Nuclear Information System (INIS)

    Baghaee Moghaddam, Taher; Soltani, Mehrtash; Karim, Mohamed Rehan

    2015-01-01

    Highlights: • Effect of PET modification on stiffness property of asphalt mixture was examined. • Different temperatures and loading amounts were designated. • Statistical analysis was used to find interactions between selected variables. • A good agreement between experimental results and predicted values was obtained. • Optimal amount of PET was calculated to achieve the highest mixture performance. - Abstract: Stiffness of asphalt mixture is a fundamental design parameter of flexible pavement. According to literature, stiffness value is very susceptible to environmental and loading conditions. In this paper, effects of applied stress and temperature on the stiffness modulus of unmodified and Polyethylene Terephthalate (PET) modified asphalt mixtures were evaluated using Response Surface Methodology (RSM). A quadratic model was successfully fitted to the experimental data. Based on the results achieved in this study, the temperature variation had the highest impact on the mixture’s stiffness. Besides, PET content and amount of stress showed to have almost the same effect on the stiffness of mixtures. The optimal amount of PET was found to be 0.41% by weight of aggregate particles to reach the highest stiffness value

  7. A novel mechatronic system for measuring end-point stiffness: mechanical design and preliminary tests.

    Science.gov (United States)

    Masia, L; Sandini, G; Morasso, P G

    2011-01-01

    Measuring arm stiffness is of great interest for many disciplines from biomechanics to medicine especially because modulation of impedance represents one of the main mechanism underlying control of movement and interaction with external environment. Previous works have proposed different methods to identify multijoint hand stiffness by using planar or even tridimensional haptic devices, but the associated computational burden makes them not easy to implement. We present a novel mechanism conceived for measuring multijoint planar stiffness by a single measurement and in a reduced execution time. A novel mechanical rotary device applies cyclic radial perturbation to human arm of a known displacement and the force is acquired by means of a 6-axes commercial load cell. The outcomes suggest that the system is not only reliable but allows obtaining a bi-dimensional estimation of arm stiffness in reduced amount of time and the results are comparable with those reported in previous researches. © 2011 IEEE

  8. A STUDY OF DISPLACEMENT-LEVEL DEPENDENCY OF VERTICAL STIFFNESS OF PILE - COMPARISONS BETWEEN STATIC LOADING TEST AND MEASUREMENTS DURING TRAIN PASSING -

    Science.gov (United States)

    Nihei, Tatsuya; Nishioka, Hidetoshi; Kawamura, Chikara; Nishimura, Masahiro; Edamatsu, Masayuki; Koda, Masayuki

    In order to introduce the performance based design of pile foundation, vertical stiffness of pile is one of the important design factors. Although it had been es timated the vertical stiffness of pile had the displacement-level dependency, it had been not clarified. We compared the vertical stiffness of pile measured by two loading conditions at pile foundation of the railway viaduct. Firstly, we measured the vertical stiffness at static loading test under construction of the viaduct. Secondly, we measured the vertical stiffness at the time of train passing. So, we recognized that the extrapolation of the displacement level dependency in static loading test could evaluate the vertical stiffness of pile during train passing.

  9. Development of procedures for calculating stiffness and damping properties of elastomers in engineering applications. Part 4: Testing of elastomers under a rotating load. [resonance testing

    Science.gov (United States)

    Darlow, M. S.; Smalley, A. J.

    1977-01-01

    A test rig designed to measure stiffness and damping of elastomer cartridges under a rotating load excitation is described. The test rig employs rotating unbalance in a rotor which runs to 60,000 RPM as the excitation mechanism. A variable resonant mass is supported on elastomer elements and the dynamic characteristics are determined from measurements of input and output acceleration. Five different cartridges are considered: three of these are buttons cartridges having buttons located in pairs, with 120 between each pair. Two of the cartridges consist of 360 elastomer rings with rectangular cross-sections. Dynamic stiffness and damping are measured for each cartridge and compared with predictions at different frequencies and different strains.

  10. ELF-test less accurately identifies liver cirrhosis diagnosed by liver stiffness measurement in non-Asian women with chronic hepatitis B

    NARCIS (Netherlands)

    Harkisoen, S.; Boland, G. J.; van den Hoek, J. A. R.; van Erpecum, K. J.; Hoepelman, A. I. M.; Arends, J. E.

    2014-01-01

    The enhanced liver fibrosis test (ELF-test) has been validated for several hepatic diseases. However, its performance in chronic hepatitis B virus (CHB) infected patients is uncertain. This study investigates the diagnostic value of the ELF test for cirrhosis identified by liver stiffness

  11. Stiff Hands

    Science.gov (United States)

    ... All Topics A-Z Videos Infographics Symptom Picker Anatomy Bones Joints Muscles Nerves Vessels Tendons About Hand Surgery What is a Hand Surgeon? What is a Hand Therapist? Media Find a Hand Surgeon Home Anatomy Stiff Hands Email to a friend * required fields ...

  12. Relationship between liver tissue stiffness and histopathological findings analyzed by shear wave elastography and compression testing in rats with non-alcoholic steatohepatitis.

    Science.gov (United States)

    Ogawa, Saori; Moriyasu, Fuminori; Yoshida, Keiko; Oshiro, Hisashi; Kojima, Mayumi; Sano, Takatomo; Furuichi, Yoshihiro; Kobayashi, Yoshiyuki; Nakamura, Ikuo; Sugimoto, Katsutoshi

    2016-07-01

    The aim of the present study was to investigate two methods of determining liver stiffness in rats with various degrees of non-alcoholic steatohepatitis induced by a methionine- and choline-deficient (MCD) diet by comparing each finding with reference to histopathological liver findings. Twenty male Wister rats were fed an MCD diet for up to 32 weeks, and four were fed a normal diet. Ultrasound-based shear wave elastography (SWE) and mechanical compression testing using an Instron Universal Testing machine were performed on each rat at designated time points. After each examination, liver histopathology was analyzed to evaluate the degrees of steatosis, inflammation, and fibrosis based on non-alcoholic fatty liver disease (NAFLD) activity score, and each finding was compared with reference to liver histopathologic findings. Median liver stiffness values measured using SWE showed a stepwise increase with increasing histological inflammation score (P = 0.002), hepatic fibrosis stage (P = 0.029), ballooning score (P = 0.012), and steatosis grade (P = 0.030). Median liver stiffness measured using an Instron machine showed a stepwise increase only with increasing histological fibrosis stage (P = 0.033). Degree of liver stiffness measured by SWE and the Instron machine differed. SWE reflected mainly inflammation, whereas Instron machine-derived values primarily reflected fibrosis. This is the main source of discrepancies between measurements made with these two modalities.

  13. Trabecular meshwork stiffness in glaucoma.

    Science.gov (United States)

    Wang, Ke; Read, A Thomas; Sulchek, Todd; Ethier, C Ross

    2017-05-01

    Alterations in stiffness of the trabecular meshwork (TM) may play an important role in primary open-angle glaucoma (POAG), the second leading cause of blindness. Specifically, certain data suggest an association between elevated intraocular pressure (IOP) and increased TM stiffness; however, the underlying link between TM stiffness and IOP remains unclear and requires further study. We here first review the literature on TM stiffness measurements, encompassing various species and based on a number of measurement techniques, including direct approaches such as atomic force microscopy (AFM) and uniaxial tension tests, and indirect methods based on a beam deflection model. We also briefly review the effects of several factors that affect TM stiffness, including lysophospholipids, rho-kinase inhibitors, cytoskeletal disrupting agents, dexamethasone (DEX), transforming growth factor-β 2 (TGF-β 2 ), nitric oxide (NO) and cellular senescence. We then describe a method we have developed for determining TM stiffness measurement in mice using a cryosection/AFM-based approach, and present preliminary data on TM stiffness in C57BL/6J and CBA/J mouse strains. Finally, we investigate the relationship between TM stiffness and outflow facility between these two strains. The method we have developed shows promise for further direct measurements of mouse TM stiffness, which may be of value in understanding mechanistic relations between outflow facility and TM biomechanical properties. Copyright © 2016 Elsevier Ltd. All rights reserved.

  14. A Test Set for stiff Initial Value Problem Solvers in the open source software R: Package deTestSet

    NARCIS (Netherlands)

    Mazzia, F.; Cash, J.R.; Soetaert, K.

    2012-01-01

    In this paper we present the R package deTestSet that includes challenging test problems written as ordinary differential equations (ODEs), differential algebraic equations (DAEs) of index up to 3 and implicit differential equations (IDES). In addition it includes 6 new codes to solve initial value

  15. Arterial stiffness

    Directory of Open Access Journals (Sweden)

    Ursula Quinn

    2012-09-01

    Full Text Available Measurements of biomechanical properties of arteries have become an important surrogate outcome used in epidemiological and interventional cardiovascular research. Structural and functional differences of vessels in the arterial tree result in a dampening of pulsatility and smoothing of blood flow as it progresses to capillary level. A loss of arterial elastic properties results a range of linked pathophysiological changes within the circulation including increased pulse pressure, left ventricular hypertrophy, subendocardial ischaemia, vessel endothelial dysfunction and cardiac fibrosis. With increased arterial stiffness, the microvasculature of brain and kidneys are exposed to wider pressure fluctuations and may lead to increased risk of stroke and renal failure. Stiffening of the aorta, as measured by the gold-standard technique of aortic Pulse Wave Velocity (aPWV, is independently associated with adverse cardiovascular outcomes across many different patient groups and in the general population. Therefore, use of aPWV has been proposed for early detection of vascular damage and individual cardiovascular risk evaluation and it seems certain that measurement of arterial stiffness will become increasingly important in future clinical care. In this review we will consider some of the pathophysiological processes that result from arterial stiffening, how it is measured and factors that may drive it as well as potential avenues for therapy. In the face of an ageing population where mortality from atheromatous cardiovascular disease is falling, pathology associated with arterial stiffening will assume ever greater importance. Therefore, understanding these concepts for all clinicians involved in care of patients with cardiovascular disease will become vital.

  16. Estimating Gear Teeth Stiffness

    DEFF Research Database (Denmark)

    Pedersen, Niels Leergaard

    2013-01-01

    The estimation of gear stiffness is important for determining the load distribution between the gear teeth when two sets of teeth are in contact. Two factors have a major influence on the stiffness; firstly the boundary condition through the gear rim size included in the stiffness calculation...... and secondly the size of the contact. In the FE calculation the true gear tooth root profile is applied. The meshing stiffness’s of gears are highly non-linear, it is however found that the stiffness of an individual tooth can be expressed in a linear form assuming that the contact length is constant....

  17. The stiffness change and the increase in the ultimate capacity for a stiff pile resulting from a cyclic loading

    DEFF Research Database (Denmark)

    Lada, Aleksandra; Ibsen, Lars Bo; Nicolai, Giulio

    In the paper the experimental results of small-scale tests on a stiff monopile are presented to outline the change in stiffness during the cyclic loading and the change in the ultimate pile capacity. The results confirm the increase of stiffness and the increase in bearing capacity resulting from...

  18. Posttraumatic stiff elbow

    Directory of Open Access Journals (Sweden)

    Ravi Mittal

    2017-01-01

    Full Text Available Posttraumatic stiff elbow is a frequent and disabling complication and poses serious challenges for its management. In this review forty studies were included to know about the magnitude of the problem, causes, pathology, prevention, and treatment of posttraumatic stiff elbow. These studies show that simple measures such as internal fixation, immobilization in extension, and early motion of elbow joint are the most important steps that can prevent elbow stiffness. It also supports conservative treatment in selected cases. There are no clear guidelines about the choice between the numerous procedures described in literature. However, this review article disproves two major beliefs-heterotopic ossification is a bad prognostic feature, and passive mobilization of elbow causes elbow stiffness.

  19. Observer-Based Human Knee Stiffness Estimation.

    Science.gov (United States)

    Misgeld, Berno J E; Luken, Markus; Riener, Robert; Leonhardt, Steffen

    2017-05-01

    We consider the problem of stiffness estimation for the human knee joint during motion in the sagittal plane. The new stiffness estimator uses a nonlinear reduced-order biomechanical model and a body sensor network (BSN). The developed model is based on a two-dimensional knee kinematics approach to calculate the angle-dependent lever arms and the torques of the muscle-tendon-complex. To minimize errors in the knee stiffness estimation procedure that result from model uncertainties, a nonlinear observer is developed. The observer uses the electromyogram (EMG) of involved muscles as input signals and the segmental orientation as the output signal to correct the observer-internal states. Because of dominating model nonlinearities and nonsmoothness of the corresponding nonlinear functions, an unscented Kalman filter is designed to compute and update the observer feedback (Kalman) gain matrix. The observer-based stiffness estimation algorithm is subsequently evaluated in simulations and in a test bench, specifically designed to provide robotic movement support for the human knee joint. In silico and experimental validation underline the good performance of the knee stiffness estimation even in the cases of a knee stiffening due to antagonistic coactivation. We have shown the principle function of an observer-based approach to knee stiffness estimation that employs EMG signals and segmental orientation provided by our own IPANEMA BSN. The presented approach makes realtime, model-based estimation of knee stiffness with minimal instrumentation possible.

  20. Current front stiffness of European vehicles with regard to compatibility

    NARCIS (Netherlands)

    Huibers, J.; Beer, E. de

    2001-01-01

    EuroNCAP tests are carried out since 1997. The test procedure in general is comparable to the EC Directive 96/79 with a test speed of 64 km/h. This increased test speed implies a higher frontal stiffness for new vehicle designs in order to achieve a high ranking. This frontal stiffness is one of the

  1. Prospective validation of FibroTest in comparison with liver stiffness for predicting liver fibrosis in Asian subjects with chronic hepatitis B.

    Directory of Open Access Journals (Sweden)

    Beom Kyung Kim

    Full Text Available Diagnostic values of FibroTest (FT for hepatic fibrosis have rarely been assessed in Asian chronic hepatitis B (CHB patients. We aimed to validate its diagnostic performances in comparison with liver stiffness (LS.From 2008 to 2010, 194 CHB patients who underwent liver biopsies along with FT and transient elastography were prospectively enrolled. Fibrosis stage was assessed according to the Batts and Ludwig system.To predict significant fibrosis (F≥2, advanced fibrosis (F≥3, and cirrhosis (F = 4, areas under receiver operating characteristic curves (AUROCs of FT were 0.903, 0.907, and 0.866, comparable to those of LS (0.873, 0.897, and 0.910, respectively. Optimized cutoffs of FT to maximize sum of sensitivity and specificity were 0.32, 0.52, and 0.68 for F≥2, F≥3, and F = 4, while those of LS were 8.8, 10.2, and 14.1 kPa, respectively. According to FT and LS cutoffs, 123 (63.4% and 124 (63.9% patients were correctly classified consistent with histological fibrosis (F1, F2, F3, and F4, respectively. Overall concordance between each fibrosis stage estimated by FT and LS was observed in 111 patients, where 88 were correctly classified with histological results. A combination formula adding LS to FT (LS+FT showed similar AUROC levels (0.885, 0.905, and 0.915, while another multiplying LS by FT (LS×FT showed the best AUROCs (0.941, 0.931, and 0.929 for F≥2, F≥3, and F4, respectively.FT provides good fibrosis prediction, with comparable outcomes to LS in Asian CHB patients. FT substantially reduces need for liver biopsy, especially when used in combination with LS.

  2. Diagnostic accuracy and prognostic significance of blood fibrosis tests and liver stiffness measurement by FibroScan in non-alcoholic fatty liver disease.

    Science.gov (United States)

    Boursier, Jérôme; Vergniol, Julien; Guillet, Anne; Hiriart, Jean-Baptiste; Lannes, Adrien; Le Bail, Brigitte; Michalak, Sophie; Chermak, Faiza; Bertrais, Sandrine; Foucher, Juliette; Oberti, Frédéric; Charbonnier, Maude; Fouchard-Hubert, Isabelle; Rousselet, Marie-Christine; Calès, Paul; de Lédinghen, Victor

    2016-09-01

    NAFLD is highly prevalent but only a small subset of patients develop advanced liver fibrosis with impaired liver-related prognosis. We aimed to compare blood fibrosis tests and liver stiffness measurement (LSM) by FibroScan for the diagnosis of liver fibrosis and the evaluation of prognosis in NAFLD. Diagnostic accuracy was evaluated in a cross-sectional study including 452 NAFLD patients with liver biopsy (NASH-CRN fibrosis stage), LSM, and eight blood fibrosis tests (BARD, NAFLD fibrosis score, FibroMeter(NAFLD), aspartate aminotransferase to platelet ratio index (APRI), FIB4, FibroTest, Hepascore, FibroMeter(V2G)). Prognostic accuracy was evaluated in a longitudinal study including 360 NAFLD patients. LSM and FibroMeter(V2G) were the two best-performing tests in the cross-sectional study: AUROCs for advanced fibrosis (F3/4) were, respectively, 0.831±0.019 and 0.817±0.020 (p⩽0.041 vs. other tests); rates of patients with ⩾90% negative/positive predictive values for F3/4 were 56.4% and 46.7% (ptests); Obuchowski indexes were 0.834±0.014 and 0.798±0.016 (p⩽0.036 vs. other tests). Two fibrosis classifications were developed to precisely estimate the histological fibrosis stage from LSM or FibroMeter(V2G) results without liver biopsy (diagnostic accuracy, respectively: 80.8% vs. 77.4%, p=0.190). Kaplan-Meier curves in the longitudinal study showed that both classifications categorised NAFLD patients into subgroups with significantly different prognoses (pfibrosis classification, the worse was the prognosis. LSM and FibroMeter(V2G) were the most accurate of nine evaluated tests for the non-invasive diagnosis of liver fibrosis in NAFLD. LSM and FibroMeter(V2G) fibrosis classifications help physicians estimate both fibrosis stage and patient prognosis in clinical practice. The amount of liver fibrosis is the main determinant of the liver-related prognosis in patients with non-alcoholic fatty liver disease (NAFLD). We evaluated eight blood tests and Fibro

  3. Stiffness of Railway Soil-Steel Structures

    Directory of Open Access Journals (Sweden)

    Machelski Czesław

    2015-12-01

    Full Text Available The considerable influence of the soil backfill properties and that of the method of compacting it on the stiffness of soil-steel structures is characteristic of the latter. The above factors (exhibiting randomness become apparent in shell deformation measurements conducted during construction and proof test loading. A definition of soil-shell structure stiffness, calculated on the basis of shell deflection under the service load, is proposed in the paper. It is demonstrated that the stiffness is the inverse of the deflection influence function used in structural mechanics. The moving load methodology is shown to be useful for testing, since it makes it possible to map the shell deflection influence line also in the case of group loads (concentrated forces, as in bridges. The analyzed cases show that the shell’s span, geometry (static scheme and the height of earth fill influence the stiffness of the structure. The soil-steel structure’s characteristic parameter in the form of stiffness k is more suitable for assessing the quality of construction works than the proposed in code geometric index ω applied to beam structures. As shown in the given examples, parameter k is more effective than stiffness parameter λ used to estimate the deformation of soil-steel structures under construction. Although the examples concern railway structures, the methodology proposed in the paper is suitable also for road bridges.

  4. Stiffness of Railway Soil-Steel Structures

    Science.gov (United States)

    Machelski, Czesław

    2015-12-01

    The considerable influence of the soil backfill properties and that of the method of compacting it on the stiffness of soil-steel structures is characteristic of the latter. The above factors (exhibiting randomness) become apparent in shell deformation measurements conducted during construction and proof test loading. A definition of soil-shell structure stiffness, calculated on the basis of shell deflection under the service load, is proposed in the paper. It is demonstrated that the stiffness is the inverse of the deflection influence function used in structural mechanics. The moving load methodology is shown to be useful for testing, since it makes it possible to map the shell deflection influence line also in the case of group loads (concentrated forces), as in bridges. The analyzed cases show that the shell's span, geometry (static scheme) and the height of earth fill influence the stiffness of the structure. The soil-steel structure's characteristic parameter in the form of stiffness k is more suitable for assessing the quality of construction works than the proposed in code geometric index ω applied to beam structures. As shown in the given examples, parameter k is more effective than stiffness parameter λ used to estimate the deformation of soil-steel structures under construction. Although the examples concern railway structures, the methodology proposed in the paper is suitable also for road bridges.

  5. Development of a stiffness-angle law for simplifying the measurement of human hair stiffness.

    Science.gov (United States)

    Jung, I K; Park, S C; Lee, Y R; Bin, S A; Hong, Y D; Eun, D; Lee, J H; Roh, Y S; Kim, B M

    2018-04-01

    This research examines the benefits of caffeine absorption on hair stiffness. To test hair stiffness, we have developed an evaluation method that is not only accurate, but also inexpensive. Our evaluation method for measuring hair stiffness culminated in a model, called the Stiffness-Angle Law, which describes the elastic properties of hair and can be widely applied to the development of hair care products. Small molecules (≤500 g mol -1 ) such as caffeine can be absorbed into hair. A common shampoo containing 4% caffeine was formulated and applied to hair 10 times, after which the hair stiffness was measured. The caffeine absorption of the treated hair was observed using Fourier-transform infrared spectroscopy (FTIR) with a focal plane array (FPA) detector. Our evaluation method for measuring hair stiffness consists of a regular camera and a support for single strands of hair. After attaching the hair to the support, the bending angle of the hair was observed with a camera and measured. Then, the hair strand was weighed. The stiffness of the hair was calculated based on our proposed Stiffness-Angle Law using three variables: angle, weight of hair and the distance the hair was pulled across the support. The caffeine absorption was confirmed by FTIR analysis. The concentration of amide bond in the hair certainly increased due to caffeine absorption. After caffeine was absorbed into the hair, the bending angle and weight of the hair changed. Applying these measured changes to the Stiffness-Angle Law, it was confirmed that the hair stiffness increased by 13.2% due to caffeine absorption. The theoretical results using the Stiffness-Angle Law agree with the visual examinations of hair exposed to caffeine and also the known results of hair stiffness from a previous report. Our evaluation method combined with our proposed Stiffness-Angle Law effectively provides an accurate and inexpensive evaluation technique for measuring bending stiffness of human hair. © 2018

  6. Stiff quantum polymers

    OpenAIRE

    Kleinert, H.

    2009-01-01

    At ultralow temperatures, polymers exhibit quantum behavior, which is calculated here for the second and fourth moments of the end-to-end distribution in the large-stiffness regime. The result should be measurable for polymers in wide optical traps.

  7. Relationship between Static Stiffness and Modal Stiffness of Structures

    Directory of Open Access Journals (Sweden)

    Tianjian Ji Tianjian Ji

    2010-02-01

    Full Text Available This paper derives the relationship between the static stiffness and modal stiffness of a structure. The static stiffness and modal stiffness are two important concepts in both structural statics and dynamics. Although both stiffnesses indicate the capacity of the structure to resist deformation, they are obtained using different methods. The former is calculated by solving the equations of equilibrium and the latter can be obtained by solving an eigenvalue problem. A mathematical relationship between the two stiffnesses was derived based on the definitions of two stiffnesses. This relationship was applicable to a linear system and the derivation of relationships does not reveal any other limitations. Verification of the relationship was given by using several examples. The relationship between the two stiffnesses demonstrated that the modal stiffness of the fundamental mode was always larger than the static stiffness of a structure if the critical point and the maximum mode value are at the same node, i.e. for simply supported beam and seven storeys building are 1.5% and 15% respectively. The relationship could be applied into real structures, where the greater the number of modes being considered, the smaller the difference between the modal stiffness and the static stiffness of a structure.

  8. On gear tooth stiffness evaluation

    DEFF Research Database (Denmark)

    Pedersen, Niels Leergaard; Jørgensen, Martin Felix

    2014-01-01

    The estimation of gear stiffness is important for determining the load distribution between the gear teeth when two sets of teeth are in contact. Two factors have a major influence on the stiffness; firstly the boundary condition through the gear rim size included in the stiffness calculation...

  9. Analysis of Dynamic Stiffness of Bridge Cap-Pile System

    Directory of Open Access Journals (Sweden)

    Jinhui Chu

    2018-01-01

    Full Text Available In order to investigate the applicability of dynamic stiffness for bridge cap-pile system, a laboratory test was performed. A numerical model was also built for this type of system. The impact load was applied on the cap top and the dynamic stiffness was analysed. Then, the effect of the effective friction area between pile and soil was also considered. Finally, the dynamic stiffness relationship between the single pile and the cap-pile system was also compared. The results show that the dynamic stiffness is a sensitive index and can well reflect the static characteristics of the pile at the elastic stage. There is a significant positive correlation between the vertical dynamic stiffness index and bearing capacity of the cap-pile system in the similar formation environment. For the cap-pile system with four piles, the dynamic stiffness is about four times as large as the single pile between 10 and 20 Hz.

  10. Stiffness, resilience, compressibility

    Energy Technology Data Exchange (ETDEWEB)

    Leu, Bogdan M. [Argonne National Laboratory, Advanced Photon Source (United States); Sage, J. Timothy, E-mail: jtsage@neu.edu [Northeastern University, Department of Physics and Center for Interdisciplinary Research on Complex Systems (United States)

    2016-12-15

    The flexibility of a protein is an important component of its functionality. We use nuclear resonance vibrational spectroscopy (NRVS) to quantify the flexibility of the heme iron environment in the electron-carrying protein cytochrome c by measuring the stiffness and the resilience. These quantities are sensitive to structural differences between the active sites of different proteins, as illustrated by a comparative analysis with myoglobin. The elasticity of the entire protein, on the other hand, can be probed quantitatively from NRVS and high energy-resolution inelastic X-ray scattering (IXS) measurements, an approach that we used to extract the bulk modulus of cytochrome c.

  11. Pharmacological modulation of arterial stiffness.

    LENUS (Irish Health Repository)

    Boutouyrie, Pierre

    2011-09-10

    Arterial stiffness has emerged as an important marker of cardiovascular risk in various populations and reflects the cumulative effect of cardiovascular risk factors on large arteries, which in turn is modulated by genetic background. Arterial stiffness is determined by the composition of the arterial wall and the arrangement of these components, and can be studied in humans non-invasively. Age and distending pressure are two major factors influencing large artery stiffness. Change in arterial stiffness with drugs is an important endpoint in clinical trials, although evidence for arterial stiffness as a therapeutic target still needs to be confirmed. Drugs that independently affect arterial stiffness include antihypertensive drugs, mostly blockers of the renin-angiotensin-aldosterone system, hormone replacement therapy and some antidiabetic drugs such as glitazones. While the quest continues for \\'de-stiffening drugs\\

  12. Dynamic stiffness of suction caissons

    DEFF Research Database (Denmark)

    Ibsen, Lars Bo; Liingaard, Morten; Andersen, Lars

    The purpose of this report is to evaluate the dynamic soil-structure interaction of suction caissons for offshore wind turbines. The investigation is limited to a determination of the vertical dynamic stiffness of suction caissons. The soil surrounding the foundation is homogenous with linear...... viscoelastic properties. The dynamic stiffness of the suction caisson is expressed by dimensionless frequency-dependent dynamic stiffness coefficients corresponding to the vertical degree of freedom. The dynamic stiffness coefficients for the foundations are evaluated by means of a dynamic three...

  13. Limit cycles and stiffness control with variable stiffness actuators

    NARCIS (Netherlands)

    Carloni, Raffaella; Marconi, L.

    2012-01-01

    Variable stiffness actuators realize highly dynamic systems, whose inherent mechanical compliance can be properly exploited to obtain a robust and energy-efficient behavior. The paper presents a control strategy for variable stiffness actuators with the primarily goal of tracking a limit cycle

  14. Efficient Method for Calculating the Composite Stiffness of Parabolic Leaf Springs with Variable Stiffness for Vehicle Rear Suspension

    Directory of Open Access Journals (Sweden)

    Wen-ku Shi

    2016-01-01

    Full Text Available The composite stiffness of parabolic leaf springs with variable stiffness is difficult to calculate using traditional integral equations. Numerical integration or FEA may be used but will require computer-aided software and long calculation times. An efficient method for calculating the composite stiffness of parabolic leaf springs with variable stiffness is developed and evaluated to reduce the complexity of calculation and shorten the calculation time. A simplified model for double-leaf springs with variable stiffness is built, and a composite stiffness calculation method for the model is derived using displacement superposition and material deformation continuity. The proposed method can be applied on triple-leaf and multileaf springs. The accuracy of the calculation method is verified by the rig test and FEA analysis. Finally, several parameters that should be considered during the design process of springs are discussed. The rig test and FEA analytical results indicate that the calculated results are acceptable. The proposed method can provide guidance for the design and production of parabolic leaf springs with variable stiffness. The composite stiffness of the leaf spring can be calculated quickly and accurately when the basic parameters of the leaf spring are known.

  15. Artificial muscles with adjustable stiffness

    International Nuclear Information System (INIS)

    Mutlu, Rahim; Alici, Gursel

    2010-01-01

    This paper reports on a stiffness enhancement methodology based on using a suitably designed contact surface with which cantilevered-type conducting polymer bending actuators are in contact during operation. The contact surface constrains the bending behaviour of the actuators. Depending on the topology of the contact surface, the resistance of the polymer actuators to deformation, i.e. stiffness, is varied. As opposed to their predecessors, these polymer actuators operate in air. Finite element analysis and modelling are used to quantify the effect of the contact surface on the effective stiffness of a trilayer cantilevered beam, which represents a one-end-free, the-other-end-fixed polypyrrole (PPy) conducting polymer actuator under a uniformly distributed load. After demonstrating the feasibility of the adjustable stiffness concept, experiments were conducted to determine the stiffness of bending-type conducting polymer actuators in contact with a range (20–40 mm in radius) of circular contact surfaces. The numerical and experimental results presented demonstrate that the stiffness of the actuators can be varied using a suitably profiled contact surface. The larger the radius of the contact surface is, the higher is the stiffness of the polymer actuators. The outcomes of this study suggest that, although the stiffness of the artificial muscles considered in this study is constant for a given geometric size, and electrical and chemical operation conditions, it can be changed in a nonlinear fashion to suit the stiffness requirement of a considered application. The stiffness enhancement methodology can be extended to other ionic-type conducting polymer actuators

  16. Arterial stiffness and cognitive impairment.

    Science.gov (United States)

    Li, Xiaoxuan; Lyu, Peiyuan; Ren, Yanyan; An, Jin; Dong, Yanhong

    2017-09-15

    Arterial stiffness is one of the earliest indicators of changes in vascular wall structure and function and may be assessed using various indicators, such as pulse-wave velocity (PWV), the cardio-ankle vascular index (CAVI), the ankle-brachial index (ABI), pulse pressure (PP), the augmentation index (AI), flow-mediated dilation (FMD), carotid intima media thickness (IMT) and arterial stiffness index-β. Arterial stiffness is generally considered an independent predictor of cardiovascular and cerebrovascular diseases. To date, a significant number of studies have focused on the relationship between arterial stiffness and cognitive impairment. To investigate the relationships between specific arterial stiffness parameters and cognitive impairment, elucidate the pathophysiological mechanisms underlying the relationship between arterial stiffness and cognitive impairment and determine how to interfere with arterial stiffness to prevent cognitive impairment, we searched PUBMED for studies regarding the relationship between arterial stiffness and cognitive impairment that were published from 2000 to 2017. We used the following key words in our search: "arterial stiffness and cognitive impairment" and "arterial stiffness and cognitive impairment mechanism". Studies involving human subjects older than 30years were included in the review, while irrelevant studies (i.e., studies involving subjects with comorbid kidney disease, diabetes and cardiac disease) were excluded from the review. We determined that arterial stiffness severity was positively correlated with cognitive impairment. Of the markers used to assess arterial stiffness, a higher PWV, CAVI, AI, IMT and index-β and a lower ABI and FMD were related to cognitive impairment. However, the relationship between PP and cognitive impairment remained controversial. The potential mechanisms linking arterial stiffness and cognitive impairment may be associated with arterial pulsatility, as greater arterial pulsatility

  17. Stiffness of desiccating insect wings

    International Nuclear Information System (INIS)

    Mengesha, T E; Vallance, R R; Mittal, R

    2011-01-01

    The stiffness of insect wings is typically determined through experimental measurements. Such experiments are performed on wings removed from insects. However, the wings are subject to desiccation which typically leads to an increase in their stiffness. Although this effect of desiccation is well known, a comprehensive study of the rate of change in stiffness of desiccating insect wings would be a significant aid in planning experiments as well as interpreting data from such experiments. This communication presents a comprehensive experimental analysis of the change in mass and stiffness of gradually desiccating forewings of Painted Lady butterflies (Vanessa cardui). Mass and stiffness of the forewings of five butterflies were simultaneously measured every 10 min over a 24 h period. The averaged results show that wing mass declined exponentially by 21.1% over this time period with a time constant of 9.8 h, while wing stiffness increased linearly by 46.2% at a rate of 23.4 μN mm -1 h -1 . For the forewings of a single butterfly, the experiment was performed over a period of 1 week, and the results show that wing mass declined exponentially by 52.2% with a time constant of 30.2 h until it reached a steady-state level of 2.00 mg, while wing stiffness increased exponentially by 90.7% until it reached a steady-state level of 1.70 mN mm -1 . (communication)

  18. Stiffness of desiccating insect wings

    Energy Technology Data Exchange (ETDEWEB)

    Mengesha, T E; Vallance, R R [Department of Mechanical Engineering, The George Washington University, 738 Phillips Hall, 801 22nd St NW, Washington, DC 20052 (United States); Mittal, R, E-mail: vallance@gwu.edu [Department of Mechanical Engineering, Johns Hopkins University, 126 Latrobe Hall, 3400 N Charles Street, Baltimore, MD 21218 (United States)

    2011-03-15

    The stiffness of insect wings is typically determined through experimental measurements. Such experiments are performed on wings removed from insects. However, the wings are subject to desiccation which typically leads to an increase in their stiffness. Although this effect of desiccation is well known, a comprehensive study of the rate of change in stiffness of desiccating insect wings would be a significant aid in planning experiments as well as interpreting data from such experiments. This communication presents a comprehensive experimental analysis of the change in mass and stiffness of gradually desiccating forewings of Painted Lady butterflies (Vanessa cardui). Mass and stiffness of the forewings of five butterflies were simultaneously measured every 10 min over a 24 h period. The averaged results show that wing mass declined exponentially by 21.1% over this time period with a time constant of 9.8 h, while wing stiffness increased linearly by 46.2% at a rate of 23.4 {mu}N mm{sup -1} h{sup -1}. For the forewings of a single butterfly, the experiment was performed over a period of 1 week, and the results show that wing mass declined exponentially by 52.2% with a time constant of 30.2 h until it reached a steady-state level of 2.00 mg, while wing stiffness increased exponentially by 90.7% until it reached a steady-state level of 1.70 mN mm{sup -1}. (communication)

  19. Fitness as a determinant of arterial stiffness in healthy adult men: a cross-sectional study.

    Science.gov (United States)

    Chung, Jinwook; Kim, Milyang; Jin, Youngsoo; Kim, Yonghwan; Hong, Jeeyoung

    2018-01-01

    Fitness is known to influence arterial stiffness. This study aimed to assess differences in cardiorespiratory endurance, muscular strength, and flexibility according to arterial stiffness, based on sex and age. We enrolled 1590 healthy adults (men: 1242, women: 348) who were free of metabolic syndrome. We measured cardiorespiratory endurance in an exercise stress test on a treadmill, muscular strength by a grip test, and flexibility by upper body forward-bends from a standing position. The brachial-ankle pulse wave velocity test was performed to measure arterial stiffness before the fitness test. Cluster analysis was performed to divide the patients into groups with low (Cluster 1) and high (Cluster 2) arterial stiffness. According to the k-cluster analysis results, Cluster 1 included 624 men and 180 women, and Cluster 2 included 618 men and 168 women. Men in the middle-aged group with low arterial stiffness demonstrated higher cardiorespiratory endurance, muscular strength, and flexibility than those with high arterial stiffness. Similarly, among men in the old-aged group, the cardiorespiratory endurance and muscular strength, but not flexibility, differed significantly according to arterial stiffness. Women in both clusters showed similar cardiorespiratory endurance, muscular strength, and flexibility regardless of their arterial stiffness. Among healthy adults, arterial stiffness was inversely associated with fitness in men but not in women. Therefore, fitness seems to be a determinant for arterial stiffness in men. Additionally, regular exercise should be recommended for middle-aged men to prevent arterial stiffness.

  20. Real-Time Vision-Based Stiffness Mapping †.

    Science.gov (United States)

    Faragasso, Angela; Bimbo, João; Stilli, Agostino; Wurdemann, Helge Arne; Althoefer, Kaspar; Asama, Hajime

    2018-04-26

    This paper presents new findings concerning a hand-held stiffness probe for the medical diagnosis of abnormalities during palpation of soft-tissue. Palpation is recognized by the medical community as an essential and low-cost method to detect and diagnose disease in soft-tissue. However, differences are often subtle and clinicians need to train for many years before they can conduct a reliable diagnosis. The probe presented here fills this gap providing a means to easily obtain stiffness values of soft tissue during a palpation procedure. Our stiffness sensor is equipped with a multi degree of freedom (DoF) Aurora magnetic tracker, allowing us to track and record the 3D position of the probe whilst examining a tissue area, and generate a 3D stiffness map in real-time. The stiffness probe was integrated in a robotic arm and tested in an artificial environment representing a good model of soft tissue organs; the results show that the sensor can accurately measure and map the stiffness of a silicon phantom embedded with areas of varying stiffness.

  1. Real-Time Vision-Based Stiffness Mapping †

    Directory of Open Access Journals (Sweden)

    Angela Faragasso

    2018-04-01

    Full Text Available This paper presents new findings concerning a hand-held stiffness probe for the medical diagnosis of abnormalities during palpation of soft-tissue. Palpation is recognized by the medical community as an essential and low-cost method to detect and diagnose disease in soft-tissue. However, differences are often subtle and clinicians need to train for many years before they can conduct a reliable diagnosis. The probe presented here fills this gap providing a means to easily obtain stiffness values of soft tissue during a palpation procedure. Our stiffness sensor is equipped with a multi degree of freedom (DoF Aurora magnetic tracker, allowing us to track and record the 3D position of the probe whilst examining a tissue area, and generate a 3D stiffness map in real-time. The stiffness probe was integrated in a robotic arm and tested in an artificial environment representing a good model of soft tissue organs; the results show that the sensor can accurately measure and map the stiffness of a silicon phantom embedded with areas of varying stiffness.

  2. Determination of Ankle and Metatarsophalangeal Stiffness During Walking and Jogging.

    Science.gov (United States)

    Mager, Fabian; Richards, Jim; Hennies, Malika; Dötzel, Eugen; Chohan, Ambreen; Mbuli, Alex; Capanni, Felix

    2018-05-29

    Forefoot stiffness has been shown to influence joint biomechanics. However, little or no data exists on metatarsophalangeal stiffness. Twenty-four healthy rearfoot strike runners were recruited from a staff and student population at the University of Central Lancashire. Five repetitions of shod, self-selected speed level walking and jogging were performed. Kinetic and kinematic data were collected using retro-reflective markers placed on the lower limb and foot, to create a three-segment foot model using the Calibrated Anatomical System Technique. Ankle and metatarsophalangeal moments and angles were calculated. Stiffness values were calculated using a linear best fit line of moment versus of angle plots. Paired t-tests were used to compare values between walking and jogging conditions. Significant differences were seen in ankle range of motion (ROM), but not in metatarsophalangeal ROM. Maximum moments were significantly greater in the ankle during jogging, but these were not significantly different at the metatarsophalangeal joint. Average ankle joint stiffness exhibited significantly lower stiffness when walking compared to jogging. However, the metatarsophalangeal joint exhibited significantly greater stiffness when walking compared to jogging. A greater understanding of forefoot stiffness may inform the development of footwear, prosthetic feet and orthotic devices, such as ankle-foot orthoses for walking and sporting activities.

  3. Stiff-Person Syndrome and Graves’ Disease

    Directory of Open Access Journals (Sweden)

    Lais Moreira Medeiros MD

    2016-12-01

    Full Text Available A 9-year-old female child presented with a history of falls, weight loss, diffuse leg pain, and progressive gait disorder, following 1 previous event described as a tonic–clonic seizure. She had increased thyroid volume, brisk symmetric reflexes, abnormal gait, and painful spasms of the paraspinal musculature. Thyroid function tests indicated biochemical hyperthyroidism, and thyrotropin receptor antibodies were positive. Her electromyography showed continuous activation of normal motor units of the paraspinal and proximal lower extremity muscles. The patient had a diagnosis of Graves’ disease with associated stiff-person syndrome, with elevated anti–glutamic acid decarboxylase antibody levels. After intravenous immunoglobulin therapy, her ambulation was substantially improved and the symptoms of stiff-person syndrome decreased dramatically.

  4. Rotational and peak torque stiffness of rugby shoes.

    Science.gov (United States)

    Ballal, Moez S; Usuelli, Federico Giuseppe; Montrasio, Umberto Alfieri; Molloy, Andy; La Barbera, Luigi; Villa, Tomaso; Banfi, Giuseppe

    2014-09-01

    Sports people always strive to avoid injury. Sports shoe designs in many sports have been shown to affect traction and injury rates. The aim of this study is to demonstrate the differing stiffness and torque in rugby boots that are designed for the same effect. Five different types of rugby shoes commonly worn by scrum forwards were laboratory tested for rotational stiffness and peak torque on a natural playing surface generating force patterns that would be consistent with a rugby scrum. The overall internal rotation peak torque was 57.75±6.26 Nm while that of external rotation was 56.55±4.36 Nm. The Peak internal and external rotational stiffness were 0.696±0.1 and 0.708±0.06 Nm/deg respectively. Our results, when compared to rotational stiffness and peak torques of football shoes published in the literature, show that shoes worn by rugby players exert higher rotational and peak torque stiffness compared to football shoes when tested on the same natural surfaces. There was significant difference between the tested rugby shoes brands. In our opinion, to maximize potential performance and lower the potential of non-contact injury, care should be taken in choosing boots with stiffness appropriate to the players main playing role. Copyright © 2014 Elsevier Ltd. All rights reserved.

  5. Measurement and Treatment of Passive Muscle Stiffness

    DEFF Research Database (Denmark)

    Kirk, Henrik

    , which aimed to investigate: 1) The development of a clinical method to evaluate and distinguish neural (reflex mediated stiffness) and non-neural (passive muscle stiffness) components of muscle stiffness in adults with CP by objective and reliable measurements. 2) The association between increased...... and reliability of the method, and argue for the use of the method in the clinical practice. The device is able to distinguish between passive muscle stiffness and reflex-mediated stiffness in subjects with CP. It shows good high intrarater and interrater reliability in evaluation of passive muscle stiffness...... to measure muscle stiffness, and distinguish between passive muscle stiffness and reflex-mediated stiffness. Furthermore, it is a reliable device to measure changes in passive ROM. Treatment of passive muscle stiffness should be directed towards intense training, comprising many repetitions with a functional...

  6. Exchange stiffness of Ca-doped YIG

    Science.gov (United States)

    Avgin, I.; Huber, D. L.

    1994-05-01

    An effective medium theory for the zero-temperature exchange stiffness of uncompensated Ca-doped YIG is presented. The theory is based on the assumption that the effect of the Ca impurities is to produce strong, random ferromagnetic interactions between spins on the a and d sublattices. In the simplest version of the theory, a fraction, x, of the ad exchange integrals are large and positive, x being related to the Ca concentration. The stiffness is calculated as function of x for arbitrary perturbed ad exchange integral, Jxad. For Jxad≳(1/5)‖8Jaa+3Jdd‖, with Jaa and Jdd denoting the aa and dd exchange integrals, respectively, there is a critical concentration, Xc, such that when x≳Xc, the stiffness is complex. It is suggested that Xc delineates the region where there are significant departures from colinearity in the ground state of the Fe spins. Extension of the theory to a model where the Ca doping is assumed to generate Fe4+ ions on the tetrahedral sites is discussed. Possible experimental tests of the theory are mentioned.

  7. Association of Parental Hypertension With Arterial Stiffness in Nonhypertensive Offspring

    DEFF Research Database (Denmark)

    Andersson, Charlotte; Quiroz, Rene; Enserro, Danielle

    2016-01-01

    High arterial stiffness seems to be causally involved in the pathogenesis of hypertension. We tested the hypothesis that offspring of parents with hypertension may display higher arterial stiffness before clinically manifest hypertension, given that hypertension is a heritable condition. We compa......, in this community-based sample of young, nonhypertensive adults, we observed greater arterial stiffness in offspring of parents with hypertension. These observations are consistent with higher vascular stiffness at an early stage in the pathogenesis of hypertension.......High arterial stiffness seems to be causally involved in the pathogenesis of hypertension. We tested the hypothesis that offspring of parents with hypertension may display higher arterial stiffness before clinically manifest hypertension, given that hypertension is a heritable condition. We...... compared arterial tonometry measures in a sample of 1564 nonhypertensive Framingham Heart Study third-generation cohort participants (mean age: 38 years; 55% women) whose parents were enrolled in the Framingham Offspring Study. A total of 468, 715, and 381 participants had 0 (referent), 1, and 2 parents...

  8. Determining the concrete stiffness matrix through ultrasonic testing Determinação da matriz de rigidez do concreto utilizando ultrassom

    Directory of Open Access Journals (Sweden)

    Raquel Gonçalves

    2011-06-01

    Full Text Available The determination of the modulus tangent (Eci and of the modulus secant (Ecs of the concrete can be done using compression test but, to be simpler, it is used relations with characteristic strength (f ck. Relations are also used to determine the transversal modulus (Gc and, in the case of the Poisson's ratio (ν, a fixed value 0.20 is established. The objective of this research was to evaluate the use of the ultrasonic propagation waves to determine these properties. For the tests were used specimens with f ck varying from 10 to 35 MPa. For the ultrasonic tests were used cylindrical and cubic specimens. The modulus of deformation obtained by ultrasound was statistically equivalent to the obtained by compression tests. The results of modules obtained using the relations with f ck was far away from those obtained by ultrasound or by compression tests. The Poisson's ratio obtained by ultrasound was superior to the fixed value. We can conclude that the concrete characterization by ultrasound is consistent and, to this characterization the cylindrical specimen, normally used to determine f ck, can be used.A determinação dos módulos de deformação tangente (Eci e secante (Ecs do concreto pode ser realizada por meio do ensaio de compressão, mas, por facilidade, utilizam-se relações com a resistência característica (f ck. Relações são também utilizadas na determinação do módulo de elasticidade transversal (Gc e, no caso do coeficiente de Poisson (ν, um valor fixo de 0,20 é adotado. O objetivo do trabalho foi avaliar o uso de propagação de ondas de ultrassom na determinação dessas propriedades. Para os ensaios, foram utilizados corpos de prova com f ck variando de 10 a 35 MPa. No caso do ultrassom, os corpos de prova foram cilíndricos e cúbicos. Os valores de módulo de deformação obtidos por ultrassom foram estatisticamente equivalentes aos obtidos por compressão e, no caso do ultrassom, os corpos de prova cúbicos e cil

  9. Effects of mechanical properties and geometric conditions on stiffness of Hyperboloid Shallow Shell

    Directory of Open Access Journals (Sweden)

    Zhao Lihong

    2015-01-01

    Full Text Available The experiment models based on the hyperboloid shallow shells that represent automobile panel's surface features are established. The effects of material properties and geometric conditions condition on the stiffness of hyperboloid shallow shell are investigated experimentally. The influences of panel thickness and geometric conditions on stiffness are very obvious. Stiffness increases with increasing of the panel thickness, and stiffness doubled as increasing in thickness with 0.1 mm. The effect of thickness on stiffness is far greater than that of blank holding force. The greater the arc height of punch, the greater the stiffness. And stiffness increases nearly by five times with arc height of punch is from 3mm to 9mm. The effect of arc height of punch on stiffness is far greater than that of materials mechanical properties. The stiffness is varied with different panel material properties by the same forming and stiffness test conditions. The decrease of yield strength is beneficial to the panel stiffness. The appropriate choice of materials and forming process condition is important in meeting necessary requirements for the energy-saving, lightweight and reducing wind resistance design in automotive industry.

  10. Association of Gastrocnemius Muscle Stiffness With Passive Ankle Joint Stiffness and Sex-Related Difference in the Joint Stiffness.

    Science.gov (United States)

    Chino, Kintaro; Takashi, Hideyuki

    2017-11-15

    Passive ankle joint stiffness is affected by all structures located within and over the joint, and is greater in men than in women. Localized muscle stiffness can be assessed by ultrasound shear wave elastography, and muscle architecture such as fascicle length and pennation angle can be measured by B-mode ultrasonography. Thus, we assessed localized muscle stiffness of the medial gastrocnemius (MG) with consideration of individual variability in the muscle architecture, and examined the association of the muscle stiffness with passive ankle joint stiffness and the sex-related difference in the joint stiffness. Localized muscle stiffness of the MG in 16 men and 17 women was assessed at 10° and 20° plantar flexion, neutral anatomical position, 10° and 20° dorsiflexion. Fascicle length and pennation angle of the MG were measured at these joint positions. Passive ankle joint stiffness was determined by the ankle joint angle-torque relationship. Localized MG muscle stiffness was not significantly correlated with passive ankle joint stiffness, and did not show significant sex-related difference, even when considering the muscle architecture. This finding suggest that muscle stiffness of the MG would not be a prominent factor to determine passive ankle joint stiffness and the sex-related difference in the joint stiffness.

  11. Sex Differences in Limb and Joint Stiffness in Recreational Runners

    Directory of Open Access Journals (Sweden)

    Sinclair Jonathan

    2015-09-01

    Full Text Available Purpose. Female runners are known to be at greater risk from chronic running injuries than age-matched males, although the exact mechanisms are often poorly understood. The aim of the current investigation was to determine if female recreational runners exhibit distinct limb and joint stiffness characteristics in relation to their male counterparts. Methods. Fourteen male and fourteen female runners ran over a force platform at 4.0 m · s-1. Lower limb kinematics were collected using an eight-camera optoelectric motion capture system operating at 250 Hz. Measures of limb and joint stiffness were calculated as a function of limb length and joint moments divided by the extent of limb and joint excursion. All stiffness and joint moment parameters were normalized to body mass. Sex differences in normalized limb and knee and ankle joint stiffness were examined statistically using independent samples t tests. Results. The results indicate that normalized limb (male = 0.18 ± 0.07, female = 0.37 ± 0.10 kN · kg · m-1 and knee stiffness (male = 5.59 ± 2.02, female = 7.34 ± 1.78 Nm · kg · rad-1 were significantly greater in female runners. Conclusions. On the basis that normalized knee and limb stiffness were shown to be significantly greater in female runners, the findings from the current investigation may provide further insight into the aetiology of the distinct injury patterns observed between sexes.

  12. The study of stiffness modulus values for AC-WC pavement

    Science.gov (United States)

    Lubis, AS; Muis, Z. A.; Iskandar, T. D.

    2018-02-01

    One of the parameters of the asphalt mixture in order for the strength and durability to be achieved as required is the stress-and-strain showing the stiffness of a material. Stiffness modulus is a very necessary factor that will affect the performance of asphalt pavements. If the stiffness modulus value decreases there will be a cause of aging asphalt pavement crack easily when receiving a heavy load. The high stiffness modulus asphalt concrete causes more stiff and resistant to bending. The stiffness modulus value of an asphalt mixture material can be obtained from the theoretical (indirect methods) and laboratory test results (direct methods). For the indirect methods used Brown & Brunton method, and Shell Bitumen method; while for the direct methods used the UMATTA tool. This study aims to determine stiffness modulus values for AC-WC pavement. The tests were conducted in laboratory that used 3 methods, i.e. Brown & Brunton Method, Shell Bitumen Method and Marshall Test as a substitute tool for the UMATTA tool. Hotmix asphalt made from type AC-WC with pen 60/70 using a mixture of optimum bitumen content was 5.84% with a standard temperature variation was 60°C and several variations of temperature that were 30, 40, 50, 70 and 80°C. The stiffness modulus value results obtained from Brown & Brunton Method, Shell Bitumen Method and Marshall Test which were 1374,93 Mpa, 235,45 Mpa dan 254,96 Mpa. The stiffness modulus value decreases with increasing temperature of the concrete asphalt. The stiffness modulus value from the Bitumen Shell method and the Marshall Test has a relatively similar value.The stiffness modulus value from the Brown & Brunton method is greater than the Bitumen Shell method and the Marshall Test, but can not measure the stiffness modulus value at temperature above 80°C.

  13. Multi-fingered haptic palpation utilizing granular jamming stiffness feedback actuators

    International Nuclear Information System (INIS)

    Li, Min; Sareh, Sina; Seneviratne, Lakmal D; Wurdemann, Helge A; Althoefer, Kaspar; Ranzani, Tommaso; Dasgupta, Prokar

    2014-01-01

    This paper describes a multi-fingered haptic palpation method using stiffness feedback actuators for simulating tissue palpation procedures in traditional and in robot-assisted minimally invasive surgery. Soft tissue stiffness is simulated by changing the stiffness property of the actuator during palpation. For the first time, granular jamming and pneumatic air actuation are combined to realize stiffness modulation. The stiffness feedback actuator is validated by stiffness measurements in indentation tests and through stiffness discrimination based on a user study. According to the indentation test results, the introduction of a pneumatic chamber to granular jamming can amplify the stiffness variation range and reduce hysteresis of the actuator. The advantage of multi-fingered palpation using the proposed actuators is proven by the comparison of the results of the stiffness discrimination performance using two-fingered (sensitivity: 82.2%, specificity: 88.9%, positive predicative value: 80.0%, accuracy: 85.4%, time: 4.84 s) and single-fingered (sensitivity: 76.4%, specificity: 85.7%, positive predicative value: 75.3%, accuracy: 81.8%, time: 7.48 s) stiffness feedback. (paper)

  14. Accurate spring constant calibration for very stiff atomic force microscopy cantilevers

    Energy Technology Data Exchange (ETDEWEB)

    Grutzik, Scott J.; Zehnder, Alan T. [Field of Theoretical and Applied Mechanics, Cornell University, Ithaca, New York 14853 (United States); Gates, Richard S.; Gerbig, Yvonne B.; Smith, Douglas T.; Cook, Robert F. [Nanomechanical Properties Group, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

    2013-11-15

    There are many atomic force microscopy (AFM) applications that rely on quantifying the force between the AFM cantilever tip and the sample. The AFM does not explicitly measure force, however, so in such cases knowledge of the cantilever stiffness is required. In most cases, the forces of interest are very small, thus compliant cantilevers are used. A number of methods have been developed that are well suited to measuring low stiffness values. However, in some cases a cantilever with much greater stiffness is required. Thus, a direct, traceable method for calibrating very stiff (approximately 200 N/m) cantilevers is presented here. The method uses an instrumented and calibrated nanoindenter to determine the stiffness of a reference cantilever. This reference cantilever is then used to measure the stiffness of a number of AFM test cantilevers. This method is shown to have much smaller uncertainty than previously proposed methods. An example application to fracture testing of nanoscale silicon beam specimens is included.

  15. Accurate spring constant calibration for very stiff atomic force microscopy cantilevers

    International Nuclear Information System (INIS)

    Grutzik, Scott J.; Zehnder, Alan T.; Gates, Richard S.; Gerbig, Yvonne B.; Smith, Douglas T.; Cook, Robert F.

    2013-01-01

    There are many atomic force microscopy (AFM) applications that rely on quantifying the force between the AFM cantilever tip and the sample. The AFM does not explicitly measure force, however, so in such cases knowledge of the cantilever stiffness is required. In most cases, the forces of interest are very small, thus compliant cantilevers are used. A number of methods have been developed that are well suited to measuring low stiffness values. However, in some cases a cantilever with much greater stiffness is required. Thus, a direct, traceable method for calibrating very stiff (approximately 200 N/m) cantilevers is presented here. The method uses an instrumented and calibrated nanoindenter to determine the stiffness of a reference cantilever. This reference cantilever is then used to measure the stiffness of a number of AFM test cantilevers. This method is shown to have much smaller uncertainty than previously proposed methods. An example application to fracture testing of nanoscale silicon beam specimens is included

  16. Properties and determination of the interface stiffness

    International Nuclear Information System (INIS)

    Du Danxu; Zhang Hao; Srolovitz, David J.

    2007-01-01

    The chemical potential of a curved interface contains a term that is proportional to the product of the interface curvature and the interface stiffness. In crystalline materials, the interface stiffness is a tensor. This paper examines several basic issues related to the properties of the interface stiffness, especially the determination of the interface stiffness in particular directions (i.e. the commonly used scalar form of the interface stiffness). Of the five parameters that describe an arbitrary grain boundary, only those describing the inclination are crucial for the scalar stiffness. We also examine the influence of crystal symmetry on the stiffness tensor for both free surfaces and grain boundaries. This results in substantial simplifications for cases in which interfaces possess mirror or rotational symmetries. An efficient method for determining the interface stiffness tensor using atomistic simulations is proposed

  17. Stiffness of the ligaments of the human wrist joint

    NARCIS (Netherlands)

    Savelberg, H.H.C.M.; Kooloos, J.G.M.; Huiskes, H.W.J.; Kauer, J.M.G.

    1992-01-01

    The stiffnesses of the superficial ligaments of 14 human cadaver wrist joints have been determined. In these experiments the tested, fresh-frozen carpal joints are divided into a number of bone-ligament-bone complexes, which are loaded in a tensile testing machine at a rate of 66% of the ligaments'

  18. Experimental Investigation of Stiffness Characteristics and Damping Properties of a Metallic Rubber Material

    Science.gov (United States)

    Lu, Ch. Zh.; Li, Jingyuan; Zhou, Bangyang; Li, Shuang

    2017-09-01

    The static stiffness and dynamic damping properties of a metallic rubber material (MR) were investigated, which exhibited a nonlinear deformation behavior. Its static stiffness is analyzed and discussed. The effects of structural parameters of MR and experimental conditions on its shock absorption capacity were examined by dynamic tests. Results revealed excellent elastic and damping properties of the material. Its stiffness increased with density, but decreased with thickness. The damping property of MR varied with its density, thickness, loading frequency, and amplitude.

  19. Shoulder Stiffness : Current Concepts and Concerns

    NARCIS (Netherlands)

    Itoi, Eiji; Arce, Guillermo; Bain, Gregory I.; Diercks, Ronald L.; Guttmann, Dan; Imhoff, Andreas B.; Mazzocca, Augustus D.; Sugaya, Hiroyuki; Yoo, Yon-Sik

    Shoulder stiffness can be caused by various etiologies such as immobilization, trauma, or surgical interventions. The Upper Extremity Committee of ISAKOS defined the term "frozen shoulder" as idiopathic stiff shoulder, that is, without a known cause. Secondary stiff shoulder is a term that should be

  20. Dynamic stiffness of suction caissons

    DEFF Research Database (Denmark)

    Ibsen, Lars Bo; Liingaard, Morten; Andersen, Lars

    This report concerns the dynamic soil-structure interaction of steel suction caissons applied as foundations for offshore wind turbines. An emphasis is put on torsional vibrations and coupled sliding/rocking motion, and the influence of the foundation geometry and the properties of the surrounding...... soil is examined. The soil is simplified as a homogenous linear viscoelastic material and the dynamic stiffness of the suction caisson is expressed in terms of dimensionless frequency-dependent coefficients corresponding to the different degrees of freedom. The dynamic stiffness coefficients...... for the skirted foundation are evaluated by means of a three-dimensional coupled boundary element/finite element model. Comparisons with known analytical and numerical solutions indicate that the static and dynamic behaviour of the foundation are predicted accurately with the applied model. The analysis has been...

  1. Increased muscle belly and tendon stiffness in patients with Parkinson's disease, as measured by myotonometry.

    Science.gov (United States)

    Marusiak, Jarosław; Jaskólska, Anna; Budrewicz, Sławomir; Koszewicz, Magdalena; Jaskólski, Artur

    2011-09-01

    Based on Davis's law, greater tonus of the muscle belly in individuals with Parkinson's disease can create greater tension in the tendon, leading to structural adjustment and an increase in tendon stiffness. Our study aimed to separately assess passive stiffness in the muscle belly and tendon in medicated patients with Parkinson's disease, using myotonometry. We tested 12 patients with Parkinson's disease and 12 healthy matched controls. Passive stiffness of muscle belly and tendon was estimated by myotonometry, electromyography, and mechanomyography in relaxed biceps and triceps brachii muscles. Compared with controls, patients with Parkinson's disease had higher stiffness in the muscle belly and tendon of the biceps brachii and in the tendon of the triceps brachii. In patients with Parkinson's disease, there was a positive correlation between muscle belly stiffness and parkinsonian rigidity in the biceps brachii. Patients with Parkinson's disease have higher passive stiffness of the muscle belly and tendon than healthy matched controls. Copyright © 2011 Movement Disorder Society.

  2. Verification and sensitivity analysis on the elastic stiffness of the leaf type holddown spring assembly

    International Nuclear Information System (INIS)

    Song, Kee Nam

    1998-01-01

    The elastic formula of leaf type hold down spring(HDS) assembly is verified by comparing the values of elastic stiffness with the characteristic test results of the HDS's specimens. The comparisons show that the derived elastic stiffness formula is useful in reliably estimating the elastic stiffness of leaf type HDS assembly. The elastic stiffness sensitivity of leaf type HDS assembly is analyzed using the formula and its gradient vectors obtained from the mid-point formula. As a result of sensitivity analysis, the elastic stiffness sensitivity with respect to each design variable is quantified and design variables of large sensitivity are identified. Among the design variables, leaf thickness is identified as the most sensitive design variable to the elastic of leaf type HDS assembly. In addition, the elastic stiffness sensitivity, with respect to design variable, is in power-law type correlation to the base thickness of the leaf. (author)

  3. [Metabolic syndrome and aortic stiffness].

    Science.gov (United States)

    Simková, A; Bulas, J; Murín, J; Kozlíková, K; Janiga, I

    2010-09-01

    The metabolic syndrome (MS) is a cluster of risk factors that move the patient into higher level of risk category of cardiovascular disease and the probability of type 2 diabetes mellitus manifestation. Definition of MS is s based on the presence of selected risk factors as: abdominal obesity (lager waist circumpherence), atherogenic dyslipidemia (low value of HDL-cholesterol and increased level of triglycerides), increased fasting blood glucose (or type 2 DM diagnosis), higher blood pressure or antihypertensive therapy. In 2009 there were created harmonizing criteria for MS definition; the condition for assignment of MS is the presence of any 3 criteria of 5 mentioned above. The underlying disorder of MS is an insulin resistance or prediabetes. The patients with MS more frequently have subclinical (preclinical) target organ disease (TOD) which is the early sings of atherosclerosis. Increased aortic stiffness is one of the preclinical diseases and is defined by pathologically increased carotidofemoral pulse wave velocity in aorta (PWV Ao). With the aim to assess the influence of MS on aortic stiffness we examined the group of women with arterial hypertension and MS and compare them with the group of women without MS. The aortic stiffness was examined by Arteriograph--Tensiomed, the equipment working on the oscillometric principle in detection of pulsations of brachial artery. This method determines the global aortic stiffness based on the analysis of the shape of pulse curve of brachial artery. From the cohort of 49 pts 31 had MS, the subgroups did not differ in age or blood pressure level. The mean number of risk factors per person in MS was 3.7 comparing with 1.7 in those without MS. In the MS group there was more frequently abdominal obesity present (87% vs 44%), increased fasting blood glucose (81% vs 22%) and low HDL-cholesterol level. The pulse wave velocity in aorta, PWV Ao, was significantly higher in patients with MS (mean value 10,19 m/s vs 8,96 m

  4. Dynamically tuned magnetostrictive spring with electrically controlled stiffness

    Science.gov (United States)

    Scheidler, Justin J.; Asnani, Vivake M.; Dapino, Marcelo J.

    2016-03-01

    This paper presents the design and testing of an electrically controllable magnetostrictive spring that has a dynamically tunable stiffness (i.e., a magnetostrictive Varispring). The device enables in situ stiffness tuning or stiffness switching for vibration control applications. Using a nonlinear electromechanical transducer model and an analytical solution of linear, mechanically induced magnetic diffusion, Terfenol-D is shown to have a faster rise time to stepped voltage inputs and a significantly higher magnetic diffusion cut-off frequency relative to Galfenol. A Varispring is manufactured using a laminated Terfenol-D rod. Further rise time reductions are achieved by minimizing the rod’s diameter and winding the electromagnet with larger wire. Dynamic tuning of the Varispring’s stiffness is investigated by measuring the Terfenol-D rod’s strain response to dynamic, compressive, axial forces in the presence of sinusoidal or square wave control currents. The Varispring’s rise time is \\lt 1 ms for 1 A current switches. Continuous modulus changes up to 21.9 GPa and 500 Hz and square wave modulus changes (dynamic {{Δ }}E effect) up to 12.3 GPa and 100 Hz are observed. Stiffness tunability and tuning bandwidth can be considerably increased by operating about a more optimal bias stress and improving the control of the electrical input.

  5. Evaluating pulp stiffness from fibre bundles by ultrasound

    Science.gov (United States)

    Karppinen, Timo; Montonen, Risto; Määttänen, Marjo; Ekman, Axel; Myllys, Markko; Timonen, Jussi; Hæggström, Edward

    2012-06-01

    A non-destructive ultrasonic tester was developed to measure the stiffness of pulp bundles. The mechanical properties of pulp are important when estimating the behaviour of paper under stress. Currently available pulp tests are tedious and alter the fibres structurally and mechanically. The developed tester employs (933 ± 15) kHz tweezer-like ultrasonic transducers and time-of-flight measurement through (9.0 ± 2.5) mm long and (0.8 ± 0.1) mm thick fibre bundles kept at (19.1 ± 0.4) °C and (62 ± 1)% RH. We determined the stiffness of soft wood pulps produced by three kraft pulping modifications: standard kraft pulp, (5.2 ± 0.4) GPa, prehydrolysis kraft pulp, (4.3 ± 0.4) GPa, and alkali extracted prehydrolysis kraft pulp, (3.3 ± 0.4) GPa. Prehydrolysis and alkali extraction processes mainly lowered the hemicellulose content of the pulps, which essentially decreased the fibre-wall stiffness hence impairing the stiffness of the fibre networks. Our results indicate that the method allows ranking of pulps according to their stiffness determined from bundle-like samples taken at an early phase of the papermaking process.

  6. Modelling, simulation and experiment of the spherical flexible joint stiffness

    Directory of Open Access Journals (Sweden)

    S. Li

    2018-02-01

    Full Text Available The spherical flexible joint is extensively used in engineering. It is designed to provide flexibility in rotation while bearing vertical compression load. The linear rotational stiffness of the flexible joint is formulated. The rotational stiffness of the bonded rubber layer is related to inner radius, thickness and two edge angles. FEM is used to verify the analytical solution and analyze the stiffness. The Mooney–Rivlin, Neo Hooke and Yeoh constitutive models are used in the simulation. The experiment is taken to obtain the material coefficient and validate the analytical and FEM results. The Yeoh model can reflect the deformation trend more accurately, but the error in the nearly linear district is bigger than the Mooney–Rivlin model. The Mooney–Rivlin model can fit the test result very well and the analytical solution can also be used when the rubber deformation in the flexible joint is small. The increase of Poisson's ratio of the rubber layers will enhance the vertical compression stiffness but barely have effect on the rotational stiffness.

  7. Online Identification and Verification of the Elastic Coupling Torsional Stiffness

    Directory of Open Access Journals (Sweden)

    Wanyou Li

    2016-01-01

    Full Text Available To analyze the torsional vibration of a diesel engine shaft, the torsional stiffness of the flexible coupling is a key kinetic parameter. Since the material properties of the elastic element of the coupling might change after a long-time operation due to the severe working environment or improper use and the variation of such properties will change dynamic feature of the coupling, it will cause a relative large calculation error of torsional vibration to the shaft system. Moreover, the torsional stiffness of the elastic coupling is difficult to be determined, and it is inappropriate to measure this parameter by disassembling the power unit while it is under normal operation. To solve these problems, this paper comes up with a method which combines the torsional vibration test with the calculation of the diesel shafting and uses the inherent characteristics of shaft torsional vibration to identify the dynamic stiffness of the elastic coupling without disassembling the unit. Analysis results show that it is reasonable and feasible to identify the elastic coupling dynamic torsional stiffness with this method and the identified stiffness is accurate. Besides, this method provides a convenient and practical approach to examine the dynamic behavior of the long running elastic coupling.

  8. Determination of rolling resistance coefficient based on normal tyre stiffness

    Science.gov (United States)

    Rykov, S. P.; Tarasuyk, V. N.; Koval, V. S.; Ovchinnikova, N. I.; Fedotov, A. I.; Fedotov, K. V.

    2018-03-01

    The purpose of the article is to develop analytical dependence of wheel rolling resistance coefficient based on the mathematical description of normal tyre stiffness. The article uses the methods of non-holonomic mechanics and plane section methods. The article shows that the abscissa of gravity center of tyre stiffness expansion by the length of the contact area is the shift of normal road response. It can be used for determining rolling resistance coefficient. When determining rolling resistance coefficient using ellipsis and power function equations, one can reduce labor costs for testing and increase assessment accuracy.

  9. Coupling between the Output Force and Stiffness in Different Variable Stiffness Actuators

    Directory of Open Access Journals (Sweden)

    Amir Jafari

    2014-08-01

    Full Text Available The fundamental objective in developing variable stiffness actuators is to enable the actuator to deliberately tune its stiffness. This is done through controlling the energy flow extracted from internal power units, i.e., the motors of a variable stiffness actuator (VSA. However, the stiffness may also be unintentionally affected by the external environment, over which, there is no control. This paper analysis the correlation between the external loads, applied to different variable stiffness actuators, and their resultant output stiffness. Different types of variable stiffness actuators have been studied considering springs with different types of nonlinearity. The results provide some insights into how to design the actuator mechanism and nonlinearity of the springs in order to increase the decoupling between the load and stiffness in these actuators. This would significantly widen the application range of a variable stiffness actuator.

  10. Influence of stiffness on CHF for horizontal tubes under LPLF conditions

    Energy Technology Data Exchange (ETDEWEB)

    Baburajan, P.K. [Nuclear Safety Analysis Division, AERB, Niyamak Bhavan, 400094 (India); Bisht, Govind Singh [Department of Mechanical Engineering, IIT Bombay, 400076 (India); Gaikwad, Avinash J. [Nuclear Safety Analysis Division, AERB, Niyamak Bhavan, 400094 (India); Prabhu, S.V., E-mail: svprabhu@iitb.ac.in [Department of Mechanical Engineering, IIT Bombay, 400076 (India)

    2014-10-01

    Highlights: • Effect of stiffness on the CHF in horizontal tube under LPLF conditions is studied. • CHF increases with the increase in stiffness. • Correlation for the prediction of CHF as a function of stiffness is developed. • Correlation for mass flux at CHF in terms of stiffness and initial mass flux is given. • RELAP5 is capable of predicting the effect of stiffness on CHF. - Abstract: Studies reported in the past on critical heat flux (CHF) are mostly limited to vertical flow, large channel diameter, high pressure and high mass flux. Since horizontal flow is commonly encountered in boiler tubes, refrigerating equipments and nuclear reactor fuel channels (PHWR), there is a need to understand horizontal flow CHF, generate sufficient experimental database and to develop reliable predictive method. Few studies are reported on the effect of upstream flow restrictions on flow instabilities and CHF. The present work investigates the effect of upstream flow restriction on CHF in horizontal flow at near atmospheric pressure conditions. In the present study, stiffness is defined as the ratio of upstream flow restriction pressure drop to the test section pressure drop. The classification of a flow boiling system as soft or stiff on the basis of quantification of the stiffness is attempted. Experimental data shows an increase in the CHF with the increase in the stiffness for a given initial mass flux. A correlation for the prediction of CHF under various stiffness conditions is developed. A correlation is suggested to predict the mass flux at CHF as a function of stiffness and initial mass flux. Modeling and transient analysis of the stiffness effect on CHF is carried out using the thermal hydraulic system code RELAP5. The predicted phenomena are in agreement with the experimental observations.

  11. Comparison of cervical spine stiffness in individuals with chronic nonspecific neck pain and asymptomatic individuals.

    Science.gov (United States)

    Ingram, Lewis A; Snodgrass, Suzanne J; Rivett, Darren A

    2015-03-01

    Clinical measurement, cross-sectional. To determine if spinal joint stiffness is different in individuals with nonspecific neck pain, and whether stiffness magnitude is associated with pain intensity and disability. Manual therapists commonly evaluate spinal joint stiffness in patients presenting with nonspecific neck pain. However, a relationship between stiffness and neck pain has not yet been demonstrated. Spinal stiffness at C7 was objectively measured in participants with chronic nonspecific neck pain whose symptomatic spinal level was identified as C7 (n = 12) and in age- and sex-matched asymptomatic controls (n = 12). Stiffness (slope of the linear region of the force-displacement curve) was quantified using a device that applied 5 standardized mechanical force cycles to the C7 spinous process, while concurrently measuring displacement and resistance to movement. Stiffness was compared between groups using an independent t test. Spearman rho and Pearson r were used to determine the extent to which stiffness magnitude was associated with pain intensity (visual analog scale) and level of disability (Neck Disability Index), respectively, in the group with neck pain. Participants with nonspecific neck pain had greater spinal joint stiffness at C7 compared with asymptomatic individuals (mean difference, 1.78 N/mm; 95% confidence interval: 0.28, 3.27; P = .022). However, stiffness magnitude in the group with neck pain was not associated (P>.05) with pain intensity or level of disability. These preliminary results suggest that cervical spine stiffness may be greater in the presence of nonspecific neck pain. However, judgments regarding pain intensity and level of disability should not be inferred from examinations of spinal joint stiffness.

  12. Response of stiff piles in sand to long-term cyclic lateral loading

    DEFF Research Database (Denmark)

    Bakmar, Christian LeBlanc; Houlsby, Guy T.; Byrne, Byron W.

    2010-01-01

    . To address this, a series of laboratory tests were conducted where a stiff pile in drained sand was subjected to between 8000 and 60000 cycles of combined moment and horizontal loading. A typical design for an offshore wind turbine monopile was used as a basis for the study, to ensure that pile dimensions...... and loading ranges were realistic. A complete non-dimensional framework for stiff piles in sand is presented and applied to interpret the test results. The accumulated rotation was found to be dependent on relative density and was strongly affected by the characteristics of the applied cyclic load. The pile...... stiffness increased with number of cycles, which contrasts with the current methodology where static p - y curves are degraded to account for cyclic loading. Methods are presented to predict the change in stiffness and the accumulated rotation of a stiff pile due to long-term cyclic loading. The use...

  13. The Effect of Shoe Insole Stiffness on Leg Stiffness during Stance Phase of Running in Two Different Speeds ‎among Active Men

    Directory of Open Access Journals (Sweden)

    Zeinab Tazike-Lemeski

    2016-08-01

    Full Text Available Introduction: The effect of shoe insoles with different characteristics and in different running speeds on lower-limb stiffness is still ‎controversial. The aim of this study was to investigate the effect of two types of insoles (soft and semi-rigid in two ‎different running speeds on leg stiffness during stance phase of running among active men.‎ Materials and Methods: ‎15 male students without any background of lower extremity injury were selected. Subjects were asked to run with ‎two controlled velocities of 3.0 ± 0.2 and 5.0 ± 0.1 m/s in control and insole conditions (soft and semi-rigid on a ‎force plate, placed on the middle of 15-meter runway. The cinematics and cinetics of motion were measured and ‎calculated using 5 video cameras and one force plate. The leg stiffness was achieved via dividing the vertical ‎ground reaction force by leg compression. Two-factor repeated measures ANOVA was used to test the hypothesis at ‎the significance level of P £ 0.050.‎ Results: There was a significant difference between the two types of insoles on leg stiffness. In fact, semi-rigid insole significantly increased leg stiffness (P < 0.001. However, this discrepancy was not related to the running speed (P = 0.999. In addition, there was no significant difference between the two different speeds on leg stiffness (P = 0.632. Conclusion: It seems that the increase in shoe insole stiffness may increase the leg stiffness. Furthermore, the effect of insole ‎stiffness is not related to the running speed, and leg stiffness will remains constant in low to medium running speeds.‎

  14. Artificial neural networks for stiffness estimation in magnetic resonance elastography.

    Science.gov (United States)

    Murphy, Matthew C; Manduca, Armando; Trzasko, Joshua D; Glaser, Kevin J; Huston, John; Ehman, Richard L

    2018-07-01

    To investigate the feasibility of using artificial neural networks to estimate stiffness from MR elastography (MRE) data. Artificial neural networks were fit using model-based training patterns to estimate stiffness from images of displacement using a patch size of ∼1 cm in each dimension. These neural network inversions (NNIs) were then evaluated in a set of simulation experiments designed to investigate the effects of wave interference and noise on NNI accuracy. NNI was also tested in vivo, comparing NNI results against currently used methods. In 4 simulation experiments, NNI performed as well or better than direct inversion (DI) for predicting the known stiffness of the data. Summary NNI results were also shown to be significantly correlated with DI results in the liver (R 2  = 0.974) and in the brain (R 2  = 0.915), and also correlated with established biological effects including fibrosis stage in the liver and age in the brain. Finally, repeatability error was lower in the brain using NNI compared to DI, and voxel-wise modeling using NNI stiffness maps detected larger effects than using DI maps with similar levels of smoothing. Artificial neural networks represent a new approach to inversion of MRE data. Summary results from NNI and DI are highly correlated and both are capable of detecting biologically relevant signals. Preliminary evidence suggests that NNI stiffness estimates may be more resistant to noise than an algebraic DI approach. Taken together, these results merit future investigation into NNIs to improve the estimation of stiffness in small regions. Magn Reson Med 80:351-360, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  15. Intraventricular filling under increasing left ventricular wall stiffness and heart rates

    Science.gov (United States)

    Samaee, Milad; Lai, Hong Kuan; Schovanec, Joseph; Santhanakrishnan, Arvind; Nagueh, Sherif

    2015-11-01

    Heart failure with normal ejection fraction (HFNEF) is a clinical syndrome that is prevalent in over 50% of heart failure patients. HFNEF patients show increased left ventricle (LV) wall stiffness and clinical diagnosis is difficult using ejection fraction (EF) measurements. We hypothesized that filling vortex circulation strength would decrease with increasing LV stiffness irrespective of heart rate (HR). 2D PIV and hemodynamic measurements were acquired on LV physical models of varying wall stiffness under resting and exercise HRs. The LV models were comparatively tested in an in vitro flow circuit consisting of a two-element Windkessel model driven by a piston pump. The stiffer LV models were tested in comparison with the least stiff baseline model without changing pump amplitude, circuit compliance and resistance. Increasing stiffness at resting HR resulted in diminishing cardiac output without lowering EF below 50% as in HFNEF. Increasing HR to 110 bpm in addition to stiffness resulted in lowering EF to less than 50%. The circulation strength of the intraventricular filling vortex diminished with increasing stiffness and HR. The results suggest that filling vortex circulation strength could be potentially used as a surrogate measure of LV stiffness. This research was supported by the Oklahoma Center for Advancement of Science and Technology (HR14-022).

  16. Extension of elastic stiffness formula for leaf type holddown spring assembly

    Energy Technology Data Exchange (ETDEWEB)

    Song, Kee Nam; Kang, Heung Seok; Yoon, Kyung Ho; Kim, Hyung Kyu [Korea Atomic Energy Research Institute, Taejon (Korea)

    1998-09-01

    Based on the Euler beam theory and the strain energy method, an elastic stiffness formula of the holddown spring assembly consisting of several leaves was previously derived. The formula was known to be useful to estimate the elastic stiffness of the holddown spring assembly only with the geometric data and the material properties of the leaf. Recently, it was reported that the elastic stiffness from the formula deviated much from the test results as the number of leaves was increased. In this study, in order to resolve such an increasing deviation as the increasing number of leaves, the formula has been extended to be able to consider normal forces and friction forces acting on interfaces between the leaves. The elastic stiffness analysis on specimens of leaf type holddown springs has been carried out using the extended formula and the analysis results are compared with the test results. As a result of comparisons, it is found that the extended formula is able to evaluate the elastic stiffness of the holddown spring assembly within an error range of 10%, irrespective of the number of leaves. In addition, it is found that the effect of shear forces and axial forces on the elastic stiffness of the holddown spring assembly is only below 0.2% of the elastic stiffness, and therefore the greatest portion of the elastic stiffness of the holddown spring assembly is attributed to the bending moment. (author). 13 refs., 10 figs., 12 tabs.

  17. Stiffness Coefficients of Mortise and Tenon Joints used on Wooden Window Profiles

    Directory of Open Access Journals (Sweden)

    Milan Podlena

    2016-04-01

    Full Text Available Samples of corner joints of wooden rectangular windows, with widths of 78 and 92 mm, were used to determine the stiffness of tenon and mortise joints. Two series of samples were loaded statically in the angular plane of compression and tension, so that the bending moment could be derived. The objective of the experiment was to determine the existing correlations between the stiffness in maximum strength and the stiffness in the elastic area for both types of tests. After strength tests were carried out, the annual ring width of the samples was measured to determine whether this factor affects the stiffness of the joints. The results showed that there was a relatively strong correlation between the stiffness in the elastic area and the maximum load. A two-factor analysis of variance confirmed that the type of load did not affect the stiffness of the joint, but the type of joint (width does significantly affect the stiffness. Therefore, the width of annual rings was positively correlated with the stiffness of the joints.

  18. A variable stiffness joint with electrospun P(VDF-TrFE-CTFE) variable stiffness springs

    NARCIS (Netherlands)

    Carloni, Raffaella; Lapp, Valerie I.; Cremonese, Andrea; Belcari, Juri; Zucchelli, Andrea

    This letter presents a novel rotational variable stiffness joint that relies on one motor and a set of variable stiffness springs. The variable stiffness springs are leaf springs with a layered design, i.e., an electro-active layer of electrospun aligned nanofibers of poly(vinylidene

  19. Load to Failure and Stiffness

    Science.gov (United States)

    Esquivel, Amanda O.; Duncan, Douglas D.; Dobrasevic, Nikola; Marsh, Stephanie M.; Lemos, Stephen E.

    2015-01-01

    Background: Rotator cuff tendinopathy is a frequent cause of shoulder pain that can lead to decreased strength and range of motion. Failures after using the single-row technique of rotator cuff repair have led to the development of the double-row technique, which is said to allow for more anatomical restoration of the footprint. Purpose: To compare 5 different types of suture patterns while maintaining equality in number of anchors. The hypothesis was that the Mason-Allen–crossed cruciform transosseous-equivalent technique is superior to other suture configurations while maintaining equality in suture limbs and anchors. Study Design: Controlled laboratory study. Methods: A total of 25 fresh-frozen cadaveric shoulders were randomized into 5 suture configuration groups: single-row repair with simple stitch technique; single-row repair with modified Mason-Allen technique; double-row Mason-Allen technique; double-row cross-bridge technique; and double-row suture bridge technique. Load and displacement were recorded at 100 Hz until failure. Stiffness and bone mineral density were also measured. Results: There was no significant difference in peak load at failure, stiffness, maximum displacement at failure, or mean bone mineral density among the 5 suture configuration groups (P row rotator cuff repair to be superior to the single-row repair; however, clinical research does not necessarily support this. This study found no difference when comparing 5 different repair methods, supporting research that suggests the number of sutures and not the pattern can affect biomechanical properties. PMID:26665053

  20. Study of stiffness and bearing capacity degradation of reinforced concrete beams under constant-amplitude fatigue.

    Science.gov (United States)

    Liu, Fangping; Zhou, Jianting; Yan, Lei

    2018-01-01

    For a reinforced concrete beam subjected to fatigue loads, the structural stiffness and bearing capacity will gradually undergo irreversible degeneration, leading to damage. Moreover, there is an inherent relationship between the stiffness and bearing capacity degradation and fatigue damage. In this study, a series of fatigue tests are performed to examine the degradation law of the stiffness and bearing capacity. The results pertaining to the stiffness show that the stiffness degradation of a reinforced concrete beam exhibits a very clear monotonic decreasing "S" curve, i.e., the stiffness of the beam decreases significantly at the start of the fatigue loading, it undergoes a linear decline phase in the middle for a long loading period, and before the failure, the bearing capacity decreases drastically again. The relationship between the residual stiffness and residual bearing capacity is determined based on the assumption that the residual stiffness and residual bearing capacity depend on the same damage state, and then, the bearing capacity degradation model of the reinforced concrete beam is established based on the fatigue stiffness. Through the established model and under the premise of the known residual stiffness degradation law, the degradation law of the bearing capacity is determined by using at least one residual bearing capacity test data, for which the parameters of the stiffness degradation function are considered as material constants. The results of the bearing capacity show that the bearing capacity degradation of the reinforced concrete beam also exhibits a very clear monotonic decreasing "S" curve, which is consistent with the stiffness degradation process and in good agreement with the experiment. In this study, the stiffness and bearing capacity degradation expressions are used to quantitatively describe their occurrence in reinforced concrete beams. In particular, the expression of the bearing capacity degradation can mitigate numerous

  1. Stiffness and damping in mechanical design

    National Research Council Canada - National Science Library

    Rivin, Eugene I

    1999-01-01

    ... important conceptual issues are stiffness of mechanical structures and their components and damping in mechanical systems sensitive to and/or generating vibrations. Stiffness and strength are the most important criteria for many mechanical designs. However, although there are hundreds of books on various aspects of strength, and strength issues ar...

  2. Experimental study on vertical static stiffnesses of polycal wire rope isolators

    Science.gov (United States)

    Balaji, P. S.; Moussa, Leblouba; Khandoker, Noman; Yuk Shyh, Ting; Rahman, M. E.; Hieng Ho, Lau

    2017-07-01

    Wire rope isolator is one of the most effective isolation system that can be used to attenuate the vibration disturbances and shocks during the operation of machineries. This paper presents the results of investigation on static elastic stiffnesses (both in tension and in compression) of Polycal Wire Rope Isolator (PWRI) under quasi-static monotonic loading conditions. It also studied effect of variations in height and width of PWRI on its static stiffnesses. Suitable experimental setup was designed and manufactured to meet the test conditions. The results show that their elastic stiffnesses for both tension and compression loading conditions are highly influenced by their geometric dimensions. It is found that their compressive stiffness reduced by 55% for an increment of 20% in their height to width ratio. Therefore, the stiffness of PWRI can be fine-tuned by controlling their dimensions according to the requirements of the application.

  3. SILICOMB PEEK Kirigami cellular structures: mechanical response and energy dissipation through zero and negative stiffness

    International Nuclear Information System (INIS)

    Virk, K; Marsh, M; Monti, A; Trehard, T; Hazra, K; Boba, K; Remillat, C D L; Scarpa, F; Farrow, I R

    2013-01-01

    The work describes the manufacturing, testing and parametric analysis of cellular structures exhibiting zero Poisson’s ratio-type behaviour, together with zero and negative stiffness effects. The cellular structures are produced in flat panels and curved configurations, using a combination of rapid prototyping techniques and Kirigami (Origami and cutting) procedures for PEEK (Polyether Ether Ketone) thermoplastic composites. The curved cellular configurations show remarkable large deformation behaviours, with zero and negative stiffness regimes depending also on the strain rate applied. These unusual stiffness characteristics lead to a large increase of energy absorption during cyclic tests. (paper)

  4. Force and stiffness characteristics of superconducting bearing prototype

    International Nuclear Information System (INIS)

    Matveev, V.; Nizhelskiy, N.; Poluschenko, O.

    2004-01-01

    The radial-axial superconducting bearing prototype was designed, fabricated and tested. The YBaCuO high-temperature superconducting (HTS) monodomain disks diameter 28 mm and thickness of h = 4; 6; 8; 10 mm, capable to trap magnetic field 1 T, were fabricated to be employed in bearing prototype. Force interaction of single field cooled HTS disks with NdFeB magnets depending on disk thickness under 1 mm magnet air gap was studied. It was found that the increase in disk thickness results in reducing radial stiffness and in growing axial one. The results obtained were used for optimization of HTS-PM arrangement, and for developing the bearing design. The designed bearing incorporates a rotor with 7 HTS disks of 4 mm thickness, total mass 90 g, and stator with two pairs of permanent annular magnets of NdFeB. It is established that the force-displacement dependencies of the bearing have three zones: non-hysteresis (elastic) zone with high stiffness up to 560 N/mm; zone of elastic interaction with stiffness 190 N/mm; hysteretic zone with stiffness 150 N/mm in which a rotor residual displacement being observed after unloading. The outer bearing diameter is 130 mm, thickness 30 mm, and mass 1.8 kg. The maximal radial load capacity of the bearing is 190 N at the rotor displacement of 1.3 mm, and the maximal axial load capacity is 85 N at the displacement of 1 mm

  5. The endogenous fluorescence of fibroblast in collagen gels as indicator of stiffness of the extracellular matrix

    Science.gov (United States)

    Padilla-Martinez, J. P.; Ortega-Martinez, A.; Franco, W.

    2016-03-01

    The stiffness or rigidity of the extracellular matrix (ECM) regulates cell response. Established mechanical tests to measure stiffness, such as indentation and tensile tests, are invasive and destructive to the sample. Endogenous or native molecules to cells and ECM components, like tryptophan and cross-links of collagen, display fluorescence upon irradiation with ultraviolet light. Most likely, the concentration of these endogenous fluorophores changes as the stiffness of the ECM changes. In this work we investigate the endogenous fluorescence of collagen gels containing fibroblasts as a non-invasive non-destructive method to measure stiffness of the ECM. Human fibroblast cells were cultured in three-dimensional gels of type I collagen (50,000 cells/ml). This construct is a simple model of tissue contraction. During contraction, changes in the excitation-emission matrix (a fluorescence map in the 240-520/290-530 nm range) of constructs were measured with a spectrofluoremeter, and changes in stiffness were measured with a standard indentation test over 16 days. Results show that a progressive increase in fluorescence of the 290/340 nm excitation-emission pair correlates with a progressive increase in stiffness (r=0.9, α=0.5). The fluorescence of this excitation-emission pair is ascribed to tryptophan and variations in the fluorescence of this pair correlate with cellular proliferation. In this tissue model, the endogenous functional fluorescence of proliferating fibroblast cells is a biomechanical marker of stiffness of the ECM.

  6. Topology optimization under stochastic stiffness

    Science.gov (United States)

    Asadpoure, Alireza

    Topology optimization is a systematic computational tool for optimizing the layout of materials within a domain for engineering design problems. It allows variation of structural boundaries and connectivities. This freedom in the design space often enables discovery of new, high performance designs. However, solutions obtained by performing the optimization in a deterministic setting may be impractical or suboptimal when considering real-world engineering conditions with inherent variabilities including (for example) variabilities in fabrication processes and operating conditions. The aim of this work is to provide a computational methodology for topology optimization in the presence of uncertainties associated with structural stiffness, such as uncertain material properties and/or structural geometry. Existing methods for topology optimization under deterministic conditions are first reviewed. Modifications are then proposed to improve the numerical performance of the so-called Heaviside Projection Method (HPM) in continuum domains. Next, two approaches, perturbation and Polynomial Chaos Expansion (PCE), are proposed to account for uncertainties in the optimization procedure. These approaches are intrusive, allowing tight and efficient coupling of the uncertainty quantification with the optimization sensitivity analysis. The work herein develops a robust topology optimization framework aimed at reducing the sensitivity of optimized solutions to uncertainties. The perturbation-based approach combines deterministic topology optimization with a perturbation method for the quantification of uncertainties. The use of perturbation transforms the problem of topology optimization under uncertainty to an augmented deterministic topology optimization problem. The PCE approach combines the spectral stochastic approach for the representation and propagation of uncertainties with an existing deterministic topology optimization technique. The resulting compact representations

  7. A Stewart isolator with high-static-low-dynamic stiffness struts based on negative stiffness magnetic springs

    Science.gov (United States)

    Zheng, Yisheng; Li, Qingpin; Yan, Bo; Luo, Yajun; Zhang, Xinong

    2018-05-01

    In order to improve the isolation performance of passive Stewart platforms, the negative stiffness magnetic spring (NSMS) is employed to construct high static low dynamic stiffness (HSLDS) struts. With the NSMS, the resonance frequencies of the platform can be reduced effectively without deteriorating its load bearing capacity. The model of the Stewart isolation platform with HSLDS struts is presented and the stiffness characteristic of its struts is studied firstly. Then the nonlinear dynamic model of the platform including both geometry nonlinearity and stiffness nonlinearity is established; and its simplified dynamic model is derived under the condition of small vibration. The effect of nonlinearity on the isolation performance is also evaluated. Finally, a prototype is built and the isolation performance is tested. Both simulated and experimental results demonstrate that, by using the NSMS, the resonance frequencies of the Stewart isolator are reduced and the isolation performance in all six directions is improved: the isolation frequency band is increased and extended to a lower-frequency level.

  8. Big bang nucleosynthesis with a stiff fluid

    International Nuclear Information System (INIS)

    Dutta, Sourish; Scherrer, Robert J.

    2010-01-01

    Models that lead to a cosmological stiff fluid component, with a density ρ S that scales as a -6 , where a is the scale factor, have been proposed recently in a variety of contexts. We calculate numerically the effect of such a stiff fluid on the primordial element abundances. Because the stiff fluid energy density decreases with the scale factor more rapidly than radiation, it produces a relatively larger change in the primordial helium-4 abundance than in the other element abundances, relative to the changes produced by an additional radiation component. We show that the helium-4 abundance varies linearly with the density of the stiff fluid at a fixed fiducial temperature. Taking ρ S10 and ρ R10 to be the stiff fluid energy density and the standard density in relativistic particles, respectively, at T=10 MeV, we find that the change in the primordial helium abundance is well-fit by ΔY p =0.00024(ρ S10 /ρ R10 ). The changes in the helium-4 abundance produced by additional radiation or by a stiff fluid are identical when these two components have equal density at a 'pivot temperature', T * , where we find T * =0.55 MeV. Current estimates of the primordial 4 He abundance give the constraint on a stiff fluid energy density of ρ S10 /ρ R10 <30.

  9. Dynamic stiffness of suction caissons - vertical vibrations

    Energy Technology Data Exchange (ETDEWEB)

    Ibsen, Lars Bo; Liingaard, M.; Andersen, Lars

    2006-12-15

    The dynamic response of offshore wind turbines are affected by the properties of the foundation and the subsoil. The purpose of this report is to evaluate the dynamic soil-structure interaction of suction caissons for offshore wind turbines. The investigation is limited to a determination of the vertical dynamic stiffness of suction caissons. The soil surrounding the foundation is homogenous with linear viscoelastic properties. The dynamic stiffness of the suction caisson is expressed by dimensionless frequency-dependent dynamic stiffness coefficients corresponding to the vertical degree of freedom. The dynamic stiffness coefficients for the foundations are evaluated by means of a dynamic three-dimensional coupled Boundary Element/Finite Element model. Comparisons are made with known analytical and numerical solutions in order to evaluate the static and dynamic behaviour of the Boundary Element/Finite Element model. The vertical frequency dependent stiffness has been determined for different combinations of the skirt length, Poisson's ratio and the ratio between soil stiffness and skirt stiffness. Finally the dynamic behaviour at high frequencies is investigated. (au)

  10. INFLUENCE OF PIEZOELECTRIC TRANSDUCER TO GLASS FIBER REINFORCED COMPOSITE STIFFNESS

    Directory of Open Access Journals (Sweden)

    Witold Rządkowski

    2015-08-01

    Full Text Available The main goal was to determine if transducers based on piezoelectric materials are suitable for strain calculations in thin GFRP specimens. Numerous experimental studies, both physical and numerical, performed by the authors, have shown that there is a huge influence of bonded piezoelectric transducer on the overall stiffness of the measured object. The paper presents tensile test performed on strength machine with Digital Image Correlation strain and deflection observations. Test were compared with FEM models for detailed investigation. The main conclusion is piezoelectric transducers has huge influence on local stiffness of measured object. That is critical especially when they are used as strain sensors, when presence of sensor is influencing to measured results.

  11. Knee joint stiffness in individuals with and without knee osteoarthritis: a preliminary study.

    Science.gov (United States)

    Oatis, Carol A; Wolff, Edward F; Lennon, Sandra K

    2006-12-01

    Descriptive, case-matched comparison. To compare the knee joint stiffness and damping coefficients of individuals with knee osteoarthritis (KOA) to those of age- and gender-matched individuals without KOA. A secondary purpose was to investigate relationships between these coefficients and complaints of stiffness in individuals with KOA. KOA is a leading cause of disability, and stiffness is a common complaint in individuals with KOA. Yet the most common method of assessing knee joint stiffness is through a self-report questionnaire. Stiffness and damping coefficients at the knee were calculated in 10 volunteers (mean age +/- SD, 64.1+/-15.5 years) with KOA and compared to coefficients from age-and gender-matched individuals without KOA, collected in a previous study (mean age +/- SD, 62.1+/-13.9 years). Stiffness and damping coefficients were calculated from the angular motion of the knee during a relaxed oscillation. Spearman correlation coefficients were calculated between stiffness and damping coefficients and WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) scores for subjects with KOA. Independent 2-tailed t tests revealed significantly larger damping coefficients (P = .035) among those with KOA (95% CI, 0.10-2.32 Nm s/rad). Spearman rank correlations revealed a significant positive relationship (r = .85, P = .003) between the damping coefficient and the stiffness subscore of the WOMAC. This study offers preliminary data demonstrating the feasibility of measuring stiffness and damping coefficients in individuals with KOA. Additionally, the damping coefficient is increased in people with KOA when compared to age- and gender-matched individuals without KOA. The damping coefficient appears to be associated with the complaints of stiffness reported by the WOMAC.

  12. Dynamic Bending and Torsion Stiffness Derivation from Modal Curvatures and Torsion Rates

    Science.gov (United States)

    MAECK, J.; DE ROECK, G.

    1999-08-01

    In order to maintain the reliability of civil engineering structures, considerable effort is currently spent on developing a non-destructive vibration testing method for monitoring the structural integrity of constructions. The technique must be able to observe damage, secondly to localize the damage; and finally to give an idea of the severity of the damage. Within the framework of relating changes of measured modal parameters to changes in the integrity of the structure, it is important to be able to determine the dynamic stiffness in each section of the structure from measured modal characteristics.A damaged structure results in a dynamic stiffness reduction of the cracked sections. The dynamic stiffnesses provide directly an indication of the extension of the cracked zones in the structure. The dynamic stiffness reduction can also be associated with a degree of cracking in a particular zone.In an experimental programme, a concrete beam of 6 m length is subjected to an increasing static load to produce cracks. After each static perload, the beam is tested dynamically in a free-free set-up. The change in modal parameters is then related to damage in the beam.The technique that will be presented in the paper to predict the damage location and intensity is a direct stiffness derivation from measured modal displacement derivatives. Using the bending modes, the dynamic bending stiffness can be derived from modal curvatures. Using the torsional modes, the dynamic torsion stiffness can be derived from modal torsion rates.

  13. Passive stiffness of rat skeletal muscle undernourished during fetal development

    Directory of Open Access Journals (Sweden)

    Ana Elisa Toscano

    2010-01-01

    Full Text Available OBJECTIVES: The aim of the study was to investigate the effect of fetal undernutrition on the passive mechanical properties of skeletal muscle of weaned and young adult rats. INTRODUCTION: A poor nutrition supply during fetal development affects physiological functions of the fetus. From a mechanical point of view, skeletal muscle can be also characterized by its resistance to passive stretch. METHODS: Male Wistar rats were divided into two groups according to their mother's diet during pregnancy: a control group (mothers fed a 17% protein diet and an isocaloric low-protein group (mothers fed a 7.8% protein diet. At birth, all mothers received a standardized meal ad libitum. At the age of 25 and 90 days, the soleus muscle and extensor digitorum longus (EDL muscles were removed in order to test the passive mechanical properties. A first mechanical test consisted of an incremental stepwise extension test using fast velocity stretching (500 mm/s enabling us to measure, for each extension stepwise, the dynamic stress (σd and the steady stress (σs. A second test consisted of a slow velocity stretch in order to calculate normalized stiffness and tangent modulus from the stress-strain relationship. RESULTS: The results for the mechanical properties showed an important increase in passive stiffness in both the soleus and EDL muscles in weaned rat. In contrast, no modification was observed in young adult rats. CONCLUSIONS: The increase in passive stiffness in skeletal muscle of weaned rat submitted to intrauterine undernutrition it is most likely due to changes in muscle passive stiffness.

  14. Finite element based nonlinear normalization of human lumbar intervertebral disc stiffness to account for its morphology.

    Science.gov (United States)

    Maquer, Ghislain; Laurent, Marc; Brandejsky, Vaclav; Pretterklieber, Michael L; Zysset, Philippe K

    2014-06-01

    Disc degeneration, usually associated with low back pain and changes of intervertebral stiffness, represents a major health issue. As the intervertebral disc (IVD) morphology influences its stiffness, the link between mechanical properties and degenerative grade is partially lost without an efficient normalization of the stiffness with respect to the morphology. Moreover, although the behavior of soft tissues is highly nonlinear, only linear normalization protocols have been defined so far for the disc stiffness. Thus, the aim of this work is to propose a nonlinear normalization based on finite elements (FE) simulations and evaluate its impact on the stiffness of human anatomical specimens of lumbar IVD. First, a parameter study involving simulations of biomechanical tests (compression, flexion/extension, bilateral torsion and bending) on 20 FE models of IVDs with various dimensions was carried out to evaluate the effect of the disc's geometry on its compliance and establish stiffness/morphology relations necessary to the nonlinear normalization. The computed stiffness was then normalized by height (H), cross-sectional area (CSA), polar moment of inertia (J) or moments of inertia (Ixx, Iyy) to quantify the effect of both linear and nonlinear normalizations. In the second part of the study, T1-weighted MRI images were acquired to determine H, CSA, J, Ixx and Iyy of 14 human lumbar IVDs. Based on the measured morphology and pre-established relation with stiffness, linear and nonlinear normalization routines were then applied to the compliance of the specimens for each quasi-static biomechanical test. The variability of the stiffness prior to and after normalization was assessed via coefficient of variation (CV). The FE study confirmed that larger and thinner IVDs were stiffer while the normalization strongly attenuated the effect of the disc geometry on its stiffness. Yet, notwithstanding the results of the FE study, the experimental stiffness showed consistently

  15. Observed variations of monopile foundation stiffness

    DEFF Research Database (Denmark)

    Kallehave, Dan; Thilsted, C.L.; Diaz, Alberto Troya

    2015-01-01

    full-scale measurements obtained from one offshore wind turbine structure located within Horns Reef II offshore wind farm. Data are presented for a 2.5 years period and covers normal operating conditions and one larger storm event. A reduction of the pile-soil stiffness was observed during the storm...... events, followed by a complete regain to a pre-storm level when the storm subsided. In additional, no long term variations of the pile-soil stiffness was observed. The wind turbine is located in dense to very dense sand deposits.......The soil-structure stiffness of monopile foundations for offshore wind turbines has a high impact on the fatigue loading during normal operating conditions. Thus, a robust design must consider the evolution of pile-soil stiffness over the lifetime of the wind farm. This paper present and discuss...

  16. Damper modules with adapted stiffness ratio

    Energy Technology Data Exchange (ETDEWEB)

    Sonnenburg, R.; Stretz, A. [ZF Sachs AG, Entwicklungszentrum, Schweinfurt (Germany)

    2011-07-15

    A mechanism for the excitation of piston rod vibrations in automotive damper modules is discussed by a simple model. An improved nonlinear model based on elasticity effects leads to good simulation results. It is shown theoretically and experimentally that the adaptation of the stiffness of the piston rod bushing to the ''stiffness'' of the damper force characteristic can eliminate the piston rod oscillations completely. (orig.)

  17. OroSTIFF: Face-referenced measurement of perioral stiffness in health and disease.

    Science.gov (United States)

    Chu, Shin-Ying; Barlow, Steven M; Kieweg, Douglas; Lee, Jaehoon

    2010-05-28

    A new device and automated measurement technology known as OroSTIFF is described to characterize non-participatory perioral stiffness in healthy adults for eventual application to patients with orofacial movement disorders associated with neuromotor disease, traumatic injury, or congenital clefts of the upper lip. Previous studies of perioral biomechanics required head stabilization for extended periods of time during measurement, which precluded sampling patients with involuntary body/head movements (dyskinesias), or pediatric subjects. The OroSTIFF device is face-referenced and avoids the complications associated with head-restraint. Supporting data of non-participatory perioral tissue stiffness using OroSTIFF are included from 10 male and 10 female healthy subjects. The OroSTIFF device incorporates a pneumatic glass air cylinder actuator instrumented for pressure, and an integrated subminiature displacement sensor to encode lip aperture. Perioral electromyograms were simultaneously sampled to confirm passive muscle state for the superior and inferior divisions of the orbicularis oris muscles. Perioral stiffness, derived as a quotient from resultant force (DeltaF) and interangle span (DeltaX), was modeled with multilevel regression techniques. Real-time calculation of the perioral stiffness function demonstrated a significant quadratic relation between imposed interangle stretch and resultant force. This stiffness growth function also differed significantly between males and females. This study demonstrates the OroSTIFF 'proof-of-concept' for cost-effective non-invasive stimulus generation and derivation of perioral stiffness in a group of healthy unrestrained adults, and a case study to illustrate the dose-dependent effects of Levodopa on perioral stiffness in an individual with advanced Parkinson's disease who exhibited marked dyskinesia and rigidity. Copyright 2010 Elsevier Ltd. All rights reserved.

  18. Effect of Acute Resistance Exercise on Carotid Artery Stiffness and Cerebral Blood Flow Pulsatility

    Directory of Open Access Journals (Sweden)

    Wesley K Lefferts

    2014-03-01

    Full Text Available Arterial stiffness is associated with cerebral flow pulsatility. Arterial stiffness increases following acute resistance exercise (RE. Whether this acute RE-induced vascular stiffening affects cerebral pulsatility remains unknown. Purpose: To investigate the effects of acute RE on common carotid artery (CCA stiffness and cerebral blood flow velocity (CBFv pulsatility. Methods: Eighteen healthy men (22 ± 1 yr; 23.7 ± 0.5 kg∙m-2 underwent acute RE (5 sets, 5-RM bench press, 5 sets 10-RM bicep curls with 90 s rest intervals or a time control condition (seated rest in a randomized order. CCA stiffness (β-stiffness, Elastic Modulus (Ep and hemodynamics (pulsatility index, forward wave intensity and reflected wave intensity were assessed using a combination of Doppler ultrasound, wave intensity analysis and applanation tonometry at baseline and 3 times post-RE. CBFv pulsatility index was measured with transcranial Doppler at the middle cerebral artery (MCA. Results: CCA β-stiffness, Ep and CCA pulse pressure significantly increased post-RE and remained elevated throughout post-testing (p 0.05. There were significant increases in forward wave intensity post-RE (p0.05. Conclusion: Although acute RE increases CCA stiffness and pressure pulsatility, it may not affect CCA or MCA flow pulsatility. Increases in pressure pulsatility may be due to increased forward wave intensity and not pressure from wave reflections.

  19. Dynamic Stiffness Transfer Function of an Electromechanical Actuator Using System Identification

    Science.gov (United States)

    Kim, Sang Hwa; Tahk, Min-Jea

    2018-04-01

    In the aeroelastic analysis of flight vehicles with electromechanical actuators (EMAs), an accurate prediction of flutter requires dynamic stiffness characteristics of the EMA. The dynamic stiffness transfer function of the EMA with brushless direct current (BLDC) motor can be obtained by conducting complicated mathematical calculations of control algorithms and mechanical/electrical nonlinearities using linearization techniques. Thus, system identification approaches using experimental data, as an alternative, have considerable advantages. However, the test setup for system identification is expensive and complex, and experimental procedures for data collection are time-consuming tasks. To obtain the dynamic stiffness transfer function, this paper proposes a linear system identification method that uses information obtained from a reliable dynamic stiffness model with a control algorithm and nonlinearities. The results of this study show that the system identification procedure is compact, and the transfer function is able to describe the dynamic stiffness characteristics of the EMA. In addition, to verify the validity of the system identification method, the simulation results of the dynamic stiffness transfer function and the dynamic stiffness model were compared with the experimental data for various external loads.

  20. STIFFNESS MODIFICATION OF COTTON IN CHITOSAN TREATMENT

    Directory of Open Access Journals (Sweden)

    CAMPOS Juan

    2017-05-01

    Full Text Available Chitosan is a biopolymer obtained from chitin, and among their most important aspects highlights its applications in a lot of industrial sectors due to its intrinsic properties, especially in the textile sector. In the last years, chitosan is widely used in the cotton and wool finishing processes due to its bond between them and its properties as an antifungical and antimicrobial properties. In this paper three different molecular weight chitosan are used in the finishing process of cotton to evaluate its influence in the surface properties modification. In order to evaluate the effect of the treatment with chitosan, flexural stiffness test is performed in warp and weft direction, and then the total value is calculated. The cotton fabric is treated with 5 g/L of different types of chitosan in an impregnation bath. This study shows the extent of surface properties modification of the cotton provided by three types of chitosan treatment. The results show that all types of chitosan modify the cotton flexural rigidity properties but the one which modifies it in a relevant manner is chitosan originated from shrimps. Chitosan, textile, flexural stiffnes, chitin, cotton.

  1. Assessment of clay stiffness and strength parameters using index properties

    Directory of Open Access Journals (Sweden)

    Sayed M. Ahmed

    2018-06-01

    Full Text Available A new approach is developed to determine the shear wave velocity in saturated soft to firm clays using measurements of the liquid limit, plastic limit, and natural water content with depth. The shear wave velocity is assessed using the site-specific variation of the natural water content with the effective mean stress. Subsequently, an iterative process is envisaged to obtain the clay stiffness and strength parameters. The at-rest earth pressure coefficient, as well as bearing capacity factor and rigidity index related to the cone penetration test, is also acquired from the analyses. Comparisons are presented between the measured clay parameters and the results of corresponding analyses in five different case studies. It is demonstrated that the presented approach can provide acceptable estimates of saturated clay stiffness and strength parameters. One of the main privileges of the presented methodology is the site-specific procedure developed based on the relationships between clay strength and stiffness parameters, rather than adopting direct correlations. Despite of the utilized iterative processes, the presented approach can be easily implemented using a simple spreadsheet, benefiting both geotechnical researchers and practitioners. Keywords: Soft to firm clays, Atterberg limits, Shear wave velocity, Small-strain shear modulus, Constrained modulus, Undrained shear strength, Effective friction angle, Cone penetration test

  2. Test of numerical methods for the integration of kinetic equations in tropospheric chemistry; Confronto di metodi numerici per l'integrazione di sistemi di equazioni differenziali ordinarie di tipo STIFF inserite nel modello fotochimico Calgrid

    Energy Technology Data Exchange (ETDEWEB)

    Lorenzini, R.; Passoni, L. [ENEA, Centro Ricerche Ezio Clementel, Bologna (Italy). Dipt. Ambiente

    1999-07-01

    The integration of ordinary differential equations systems (ODEs) is of significant concern to tropospheric and stratospheric chemistry modelers. The solution of the ODEs requires a large computational effort because of their stiff nature; in a three-dimensional photochemical model the solution of the ODEs required at least 70% of the total CPU time. Several numerical integration techniques exist which attempt to provide accurate and computationally efficient solutions. In this work it is presented a comparison of some of the techniques in terms of solution accuracy and required computational time. It has been compared the Hybrid Solver (Young and Boris, 1977), the Quasi Steady-State Approximation method (Hesstvedt et al., 1978) and the Chemical Solver for Ordinary Differential Equations (Aro, 1996), by using the CALGRID photochemical model. The accuracy is evaluated by comparing the results of every method with the solutions obtained by the Livermore Solver for Ordinary Differential Equations (Hindmarsh, 1980). The comparison has been made varing the parameters of the error tolerances, and taking into account the trade-off between solution accuracy and computational efficiency. [Italian] L'integrazione di sistemi di equazioni differenziali ordinarie (ODEs), e' un problema significativo per i modellisti della chimica troposferica e stratosferica. A causa della loro natura stiff la soluzione degli ODEs richiese un notevole sforzo computazionale; in un modello fotochimico tridimensionale la soluzione degli ODEs richiede almeno il 70% del tempo totale di CPU. Esistono diverse tecniche di integrazione numerica che possono fornire soluzioni accurate e computazionalmente efficienti: in questo lavoro presentiamo un confronto fra alcune tecniche in termini di accuratezza della soluzione e tempo computazionale richiesto. Si sono confrontati il Solver Ibrido (Young and Boris, 1977), il metodo Quasi Steady-State Approximation (Hesstvedt et al., 1978) ed il Chemical

  3. Measurements of the weak bonding interfacial stiffness by using air-coupled ultrasound

    Directory of Open Access Journals (Sweden)

    Wen-Lin Wu

    2017-12-01

    Full Text Available An air-coupled ultrasonic method, focusing on the problem that weak bonding interface is difficult to accurately measure using conventional nondestructive testing technique, is proposed to evaluate the bond integrity. Based on the spring model and the potential function theory, a theoretical model is established to predict the through-transmission spectrum in double-layer adhesive structure. The result of a theoretical algorithm shows that all the resonant transmission peaks move towards higher frequency with the increase of the interfacial stiffness. The reason for these movements is related to either the normal stiffness (KN or the transverse stiffness (KT. A method to optimize the measurement parameters (i.e. the incident angle and testing frequency is put forward through analyzing the relationship between the resonant transmission peaks and the interfacial spring stiffness at the frequency below 1MHz. The air-coupled ultrasonic testing experiments at the normal and oblique incident angle respectively are carried out to verify the theoretical analysis and to accurately measure the interfacial stiffness of double-layer adhesive composite plate. The experimental results are good agreement with the results from the theoretical algorithm, and the relationship between bonding time and interfacial stiffness is presented at the end of this paper.

  4. The bending stiffness of shoes is beneficial to running energetics if it does not disturb the natural MTP joint flexion.

    Science.gov (United States)

    Oh, Keonyoung; Park, Sukyung

    2017-02-28

    A local minimum for running energetics has been reported for a specific bending stiffness, implying that shoe stiffness assists in running propulsion. However, the determinant of the metabolic optimum remains unknown. Highly stiff shoes significantly increase the moment arm of the ground reaction force (GRF) and reduce the leverage effect of joint torque at ground push-off. Inspired by previous findings, we hypothesized that the restriction of the natural metatarsophalangeal (MTP) flexion caused by stiffened shoes and the corresponding joint torque changes may reduce the benefit of shoe bending stiffness to running energetics. We proposed the critical stiffness, k cr , which is defined as the ratio of the MTP joint (MTPJ) torque to the maximal MTPJ flexion angle, as a possible threshold of the elastic benefit of shoe stiffness. 19 subjects participated in a running test while wearing insoles with five different bending stiffness levels. Joint angles, GRFs, and metabolic costs were measured and analyzed as functions of the shoe stiffness. No significant changes were found in the take-off velocity of the center of mass (CoM), but the horizontal ground push-offs were significantly reduced at different shoe stiffness levels, indicating that complementary changes in the lower-limb joint torques were introduced to maintain steady running. Slight increases in the ankle, knee, and hip joint angular impulses were observed at stiffness levels exceeding the critical stiffness, whereas the angular impulse at the MTPJ was significantly reduced. These results indicate that the shoe bending stiffness is beneficial to running energetics if it does not disturb the natural MTPJ flexion. Copyright © 2017 Elsevier Ltd. All rights reserved.

  5. Single motor–variable stiffness actuator using bistable switching mechanisms for independent motion and stiffness control

    NARCIS (Netherlands)

    Groothuis, Stefan; Carloni, Raffaella; Stramigioli, Stefano

    This paper presents a proof of concept of a variable stiffness actuator (VSA) that uses only one (high power) input motor. In general, VSAs use two (high power) motors to be able to control both the output position and the output stiffness, which possibly results in a heavy, and bulky system. In

  6. Efficient reanalysis of structures by a direct modification method. [local stiffness modifications of large structures

    Science.gov (United States)

    Raibstein, A. I.; Kalev, I.; Pipano, A.

    1976-01-01

    A procedure for the local stiffness modifications of large structures is described. It enables structural modifications without an a priori definition of the changes in the original structure and without loss of efficiency due to multiple loading conditions. The solution procedure, implemented in NASTRAN, involved the decomposed stiffness matrix and the displacement vectors of the original structure. It solves the modified structure exactly, irrespective of the magnitude of the stiffness changes. In order to investigate the efficiency of the present procedure and to test its applicability within a design environment, several real and large structures were solved. The results of the efficiency studies indicate that the break-even point of the procedure varies between 8% and 60% stiffness modifications, depending upon the structure's characteristics and the options employed.

  7. Specific adaptations of neuromuscular control and knee joint stiffness following sensorimotor training.

    Science.gov (United States)

    Gruber, M; Bruhn, S; Gollhofer, A

    2006-08-01

    The aim of this study was to examine how fixations of the ankle joint during sensorimotor training (SMT) influence adaptations in mechanical stiffness and neuromuscular control of the knee joint. Sixty-three healthy subjects were randomly assigned to three training groups that differed in their degree of ankle joint fixation, which was either barefooted, with an ankle brace or with a ski boot. Mechanical knee joint stiffness and reflex control of m. vastus medialis, m. vastus lateralis, m. biceps femoris, and m. semitendinosus were tested during force controlled anterior tibial displacements. This force was applied as both a fast and a slow stimulus. After the training period the group that trained barefooted showed an increase in mechanical stiffness of the knee joint from 79 +/- 21 (Mean +/- SD) N/mm to 110 +/- 38 N/mm (p boots was able to improve knee joint stiffness from 67 +/- 26 N/mm to 96 +/- 47 N/mm (p knee joint injuries.

  8. On the Adhesive JKR Contact and Rolling Models for Reduced Particle Stiffness Discrete Element Simulations

    DEFF Research Database (Denmark)

    Hærvig, Jakob; Kleinhans, Ulrich; Wieland, Christoph

    2017-01-01

    particle stiffness to experimental data. Then two well-defined test cases are investigated to show the applicability of the guidelines. When introducing a reduced particle stiffness in DEM simulations by reducing the effective Young's modulus from E to Emod, the surface energy density γ in the adhesive......, this criterion can be used to estimate how much the time step size can be changed when a reduced particle stiffness is introduced. Introducing particles with a reduced particle stiffness has some limitations when strong external forces are acting to break-up formed agglomerates or re-entrain particles deposited...... on a surface out into the free stream. Therefore, care should be taken in flows with high local shear to make sure that an external force, such as a fluid drag force, acting to separate agglomerated particles, is several orders of magnitude lower than the critical force required to separate particles....

  9. Brain tissue stiffness is a sensitive marker for acidosis.

    Science.gov (United States)

    Holtzmann, Kathrin; Gautier, Hélène O B; Christ, Andreas F; Guck, Jochen; Káradóttir, Ragnhildur Thóra; Franze, Kristian

    2016-09-15

    Carbon dioxide overdose is frequently used to cull rodents for tissue harvesting. However, this treatment may lead to respiratory acidosis, which potentially could change the properties of the investigated tissue. Mechanical tissue properties often change in pathological conditions and may thus offer a sensitive generic readout for changes in biological tissues with clinical relevance. In this study, we performed force-indentation measurements with an atomic force microscope on acute cerebellar slices from adult rats to test if brain tissue undergoes changes following overexposure to CO2 compared to other methods of euthanasia. The pH significantly decreased in brain tissue of animals exposed to CO2. Concomitant with the drop in pH, cerebellar grey matter significantly stiffened. Tissue stiffening was reproduced by incubation of acute cerebellar slices in acidic medium. Tissue stiffness provides an early, generic indicator for pathophysiological changes in the CNS. Atomic force microscopy offers unprecedented high spatial resolution to detect such changes. Our results indicate that the stiffness particularly of grey matter strongly correlates with changes of the pH in the cerebellum. Furthermore, the method of tissue harvesting and preparation may not only change tissue stiffness but very likely also other physiologically relevant parameters, highlighting the importance of appropriate sample preparation. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

  10. Strength and stiffness reduction factors for infilled frames with openings

    Science.gov (United States)

    Decanini, Luis D.; Liberatore, Laura; Mollaioli, Fabrizio

    2014-09-01

    Framed structures are usually infilled with masonry walls. They may cause a significant increase in both stiffness and strength, reducing the deformation demand and increasing the energy dissipation capacity of the system. On the other hand, irregular arrangements of the masonry panels may lead to the concentration of damage in some regions, with negative effects; for example soft story mechanisms and shear failures in short columns. Therefore, the presence of infill walls should not be neglected, especially in regions of moderate and high seismicity. To this aim, simple models are available for solid infills walls, such as the diagonal no-tension strut model, while infilled frames with openings have not been adequately investigated. In this study, the effect of openings on the strength and stiffness of infilled frames is investigated by means of about 150 experimental and numerical tests. The main parameters involved are identified and a simple model to take into account the openings in the infills is developed and compared with other models proposed by different researchers. The model, which is based on the use of strength and stiffness reduction factors, takes into account the opening dimensions and presence of reinforcing elements around the opening. An example of an application of the proposed reduction factors is also presented.

  11. VARIABLE STIFFNESS HAND PROSTHESIS: A SYSTEMATIC REVIEW

    Directory of Open Access Journals (Sweden)

    S. Cecilia Tapia-Siles

    2017-06-01

    Full Text Available Prosthetics is an important field in engineering due to the large number of amputees worldwide and the associated problems such as limited functionality of the state of the art. An important functionality of the human hand is its capability of adjusting the stiffness of the joints depending on the currently performed task. For the development of new technology it is important to understand the limitations of existing resources. As part of our efforts to develop a variable stiffness grasper for developing countries a systematic review was performed covering technology of body powered and myoelectric hand prosthesis. Focus of the review is readiness of prosthetic hands regarding their capability of controlling the stiffness of the end effector. Publications sourced through three different digital libraries were systematically reviewed on the basis of the PRISMA standard. We present a search strategy as well as the PRISMA assessment of the resulting records which covered 321 publications. The records were assessed and the results are presented for the ability of devices to control their joint stiffness. The review indicates that body powered prosthesis are preferred to myoelectric hands due to the reduced cost, the simplicity of use and because of their inherent ability to provide feedback to the user. Stiffness control was identified but has not been fully covered in the current state of the art. In addition we summarise the identified requirements on prosthetic hands as well as related information which can support the development of new prosthetics.

  12. A Novel Variable Stiffness Mechanism Capable of an Infinite Stiffness Range and Unlimited Decoupled Output Motion

    Directory of Open Access Journals (Sweden)

    Stefan Groothuis

    2014-06-01

    Full Text Available In this paper, a novel variable stiffness mechanism is presented, which is capable of achieving an output stiffness with infinite range and an unlimited output motion, i.e., the mechanism output is completely decoupled from the rotor motion, in the zero stiffness configuration. The mechanism makes use of leaf springs, which are engaged at different positions by means of two movable supports, to realize the variable output stiffness. The Euler–Bernoulli leaf spring model is derived and validated through experimental data. By shaping the leaf springs, it is shown that the stiffness characteristic of the mechanism can be changed to fulfill different application requirements. Alternative designs can achieve the same behavior with only one leaf spring and one movable support pin.

  13. Factors influencing the stiffness of fibroadenomas at shear wave elastography

    International Nuclear Information System (INIS)

    Elseedawy, M.; Whelehan, P.; Vinnicombe, S.; Thomson, K.; Evans, A.

    2016-01-01

    Aim: To identify which features of fibroadenomas are associated with false-positive findings at shear wave elastography (SWE). Materials and methods: A total of 151 patients with histologically confirmed fibroadenomata were identified from a prospective database, from a single breast unit. The following features were assessed by two observers who were unaware of the SWE findings: patient age, grey-scale ultrasound lesion diameter (<15 or ≥15 mm), distance from the lesion to skin, composition of surrounding tissue (fatty, mixed or dense), and source of referral (screening or symptomatic). Statistical analysis was carried out using the chi-square test. Results: A statistically significant positive association was found between grey-scale ultrasound lesion size and lesion stiffness. Twenty-nine of 70 (41%) lesions ≥15 mm were stiff, versus 10 of 81 (12%) <15 mm (p=0.001). Patient age, distance from the lesion to skin, make-up of surrounding tissue, and source were not significantly associated with stiffness. Conclusion: Fibroadenomas giving false-positive SWE results tend to be larger in size than those that do not. More compression of adjacent normal tissue is assumed to be the cause of the present findings. As previous studies have shown that large cancers tend to be stiffer than smaller cancers, it may be appropriate to vary the quantitative cut-off value used for benign/malignant differentiation in SWE according to lesion size. - Highlights: • Fibroadenomas giving false positive SWE results tend to be larger in size. • More compression of adjacent normal tissue is assumed to be the cause of our findings. • The age of the patient is not related to fibroadenoma stiffness.

  14. Analysis of results of surgical treatment of posttraumatic stiff elbow

    Directory of Open Access Journals (Sweden)

    Rex Chandrabose

    2008-01-01

    Full Text Available Background: Surgical management of posttraumatic elbow stiffness has been reported with poor outcome following treatment. Sequential release in earlier stages of stiffness yielded much better results. The goal of our study was to assess the outcome in improvement of the range of motion of the elbow after surgical release and to analyze a tailor-made approach according to individual needs to yield good result. Materials and Methods: A prospective study was conducted in 47 cases of elbow stiffness due to various types of injuries. All the cases were treated with sequential release if there was no progress after adequate supervised conservative management except in unreduced dislocations. All the cases were followed up for a minimum period of 24 months. Overall outcome was rated with the functional scoring system by Mayo Clinic Performance Index. Results: Twenty-five (44.68% out of 47 patients had excellent results with a mean preoperative range of motion of 33.9° and postoperative range of motion of 105° with net gain in range of motion of 71.1° (′ t ′ test value is 19.27, P < 0.01. None of the patients had elbow instability. Patients not having heterotopic ossification, who underwent surgery from three to six months post injury had a mean gain of 73.5°. In patients who waited for more than six months had mean gain of 66.8°. However, the results in cases having heterotopic ossification followed a slightly different pattern. In cases where release was performed from three months to six months had mean gain of 77.5°. Cases in which release was performed after six months had gain of 57.1°. Conclusions: In cases of posttraumatic elbow stiffness after a failed initial conservative treatment, early arthrolysis with sequential surgical soft tissue release yields good result than delayed surgery.

  15. Derivation of the extended elastic stiffness formula of the holddown spring assembly comprised of several leaves

    International Nuclear Information System (INIS)

    Song, Kee Nam; Kang, H. S.; Yoon, K. H.

    1999-01-01

    Based on the Euler beam theory and the elastic strain energy method, the elastic stiffness formula of the holddown spring assembly consisting of several leaves was previously derived. Even though the previous formula was known to be useful to estimate the elastic stiffness of the holddown spring assembly, recently it was reported that the elastic stiffness from the previous formula deviated greatly from the test results as the number of leaves was increased. The objective of this study is to extend the previous formula in order to resolve such an increasing deviation when increasing the number of leaves. Additionally, considering the friction forces acting on the interfaces between the leaves, we obtained an extended elastic stiffness formula. The characteristic test and the elastic stiffness analysis on the various kinds of specimens of the holddown spring assembly have been carried out; the validity of the extended formula has been verified by the comparison of their results. As a result of comparisons, it is found that the extended formula is able to evaluate the elastic stiffness of the holddown spring assembly within the maximum error range of +12%, irrespective of the number of the leaves. (author). 9 refs., 5 figs., 1 tab

  16. Defining normal liver stiffness range in a normal healthy Chinese population without liver disease.

    Directory of Open Access Journals (Sweden)

    James Fung

    Full Text Available BACKGROUND: For patients with chronic liver disease, different optimal liver stiffness cut-off values correspond to different stages of fibrosis, which are specific for the underlying liver disease and population. AIMS: To establish the normal ranges of liver stiffness in the healthy Chinese population without underlying liver disease. METHODS: This is a prospective cross sectional study of 2,528 healthy volunteers recruited from the general population and the Red Cross Transfusion Center in Hong Kong. All participants underwent a comprehensive questionnaire survey, measurement of weight, height, and blood pressure. Fasting liver function tests, glucose and cholesterol was performed. Abdominal ultrasound and transient elastography were performed on all participants. RESULTS: Of the 2,528 subjects, 1,998 were excluded with either abnormal liver parenchyma on ultrasound, chronic medical condition, abnormal blood tests including liver enzymes, fasting glucose, fasting cholesterol, high body mass index, high blood pressure, or invalid liver stiffness scan. The reference range for the 530 subjects without known liver disease was 2.3 to 5.9 kPa (mean 4.1, SD 0.89. The median liver stiffness was higher in males compared with females (4.3 vs 4.0 kPa respectively, p55 years (p=0.001. CONCLUSIONS: The healthy reference range for liver stiffness in the Chinese population is 2.3 to 5.9 kPa. Female gender and older age group was associated with a lower median liver stiffness.

  17. The influence of artificially increased trunk stiffness on the balance recovery after a trip.

    Science.gov (United States)

    van der Burg, J C E; Pijnappels, M; van Dieën, J H

    2007-07-01

    Falls occur frequently in the growing population of elderly. Since trunk control is critical for maintaining balance, the higher trunk stiffness in elderly people compared to the general population has been associated with their increased fall-risk. Theoretically, trunk stiffness may be beneficial for balance recovery in walking, i.e. after a trip. A stiff joint may provide a torque that restricts the perturbation effects and thereby reduces the probability of a fall. The aim of this study was to test whether trunk stiffness impaired or assisted balance recovery after a trip during walking. An orthopedic corset was used to simulate trunk stiffness in 11 young male adults. Subjects walked over a platform, with or without the corset on, and were occasionally tripped over a hidden obstacle. Kinematics of the tripping reaction were measured. Initial trunk accelerations were significantly attenuated by the corset, which indicates a positive effect of the stiffening corset. However, no subsequent effects on peak trunk inclination and on the peak moment arm of gravity on the trunk were found. The pattern of trunk motion allowed ample time for triggered or voluntary muscle responses to be generated, before a substantial inclination occurred. It appears that such active responses were sufficient in the young subjects tested to obtain a similar net effect with or without the increased trunk stiffness induced by the corset.

  18. A variable stiffness mechanism for steerable percutaneous instruments: integration in a needle.

    Science.gov (United States)

    De Falco, Iris; Culmone, Costanza; Menciassi, Arianna; Dankelman, Jenny; van den Dobbelsteen, John J

    2018-06-04

    Needles are advanced tools commonly used in minimally invasive medical procedures. The accurate manoeuvrability of flexible needles through soft tissues is strongly determined by variations in tissue stiffness, which affects the needle-tissue interaction and thus causes needle deflection. This work presents a variable stiffness mechanism for percutaneous needles capable of compensating for variations in tissue stiffness and undesirable trajectory changes. It is composed of compliant segments and rigid plates alternately connected in series and longitudinally crossed by four cables. The tensioning of the cables allows the omnidirectional steering of the tip and the stiffness tuning of the needle. The mechanism was tested separately under different working conditions, demonstrating a capability to exert up to 3.6 N. Afterwards, the mechanism was integrated into a needle, and the overall device was tested in gelatine phantoms simulating the stiffness of biological tissues. The needle demonstrated the capability to vary deflection (from 11.6 to 4.4 mm) and adapt to the inhomogeneity of the phantoms (from 21 to 80 kPa) depending on the activation of the variable stiffness mechanism. Graphical abstract ᅟ.

  19. A novel magnetorheological elastomer isolator with negative changing stiffness for vibration reduction

    International Nuclear Information System (INIS)

    Yang, J; Sun, S S; Li, W H; Alici, G; Du, H; Deng, H X

    2014-01-01

    Magneto-rheological elastomers (MREs) have attracted notable credits in the development of smart isolators and absorbers due to their controllable stiffness and damping properties. For the purpose of mitigating unwanted structural and/or machinery vibrations, the traditional MRE-based isolators have been generally proven effective because the MR effect can increase the stiffness when the magnetic field is strengthened. This study presents a novel MRE isolator that experienced reduced stiffness when the applied current was increased. This innovative work was accomplished by applying a hybrid magnet (electromagnet and permanent magnets) onto a multilayered MRE structure. To characterise this negative changing stiffness concept, a multilayered MRE isolator with a hybrid magnet was first designed, fabricated and then tested to measure its properties. An obvious reduction of the effective stiffness and natural frequency of the proposed MRE isolator occurred when the current was continuously adjusted. This device could also work as a conventional MRE isolator as its effective stiffness and natural frequency also increased when a negative current was applied. Further testing was carried out on a one-degree-of-freedom system to assess how effectively this device could isolate vibration. In this experiment, two cases were considered; in each case, the vibration of the primary system was obviously attenuated under ON-OFF control logic, thus demonstrating the feasibility of this novel design as an alternative adaptive vibration isolator. (paper)

  20. Tuning the Stiffness Balance Using Characteristic Frequencies as a Criterion for a Superconducting Gravity Gradiometer

    Science.gov (United States)

    Liu, Xikai; Ma, Dong; Chen, Liang; Liu, Xiangdong

    2018-01-01

    Tuning the stiffness balance is crucial to full-band common-mode rejection for a superconducting gravity gradiometer (SGG). A reliable method to do so has been proposed and experimentally tested. In the tuning scheme, the frequency response functions of the displacement of individual test mass upon common-mode accelerations were measured and thus determined a characteristic frequency for each test mass. A reduced difference in characteristic frequencies between the two test masses was utilized as the criterion for an effective tuning. Since the measurement of the characteristic frequencies does not depend on the scale factors of displacement detection, stiffness tuning can be done independently. We have tested this new method on a single-component SGG and obtained a reduction of two orders of magnitude in stiffness mismatch. PMID:29419796

  1. Plant fibre composites - porosity and stiffness

    DEFF Research Database (Denmark)

    Madsen, Bo; Thygesen, Anders; Lilholt, Hans

    2009-01-01

    Plant fibre composites contain typically a relatively large amount of porosity which influences their performance. A model, based on a modified rule of mixtures, is presented to include the influence of porosity on the composite stiffness. The model integrates the volumetric composition...... of the composites with their mechanical properties. The fibre weight fraction is used as an independent parameter to calculate the complete volumetric composition. A maximum obtainable stiffness of the composites is calculated at a certain transition fibre weight fraction, which is characterised by a best possible...... combination of high fibre volume fraction and low porosity. The model is validated with experimental data from the literature on several types of composites. A stiffness diagram is presented to demonstrate that the calculations can be used for tailoring and design of composites with a given profile...

  2. Steel Rack Connections: Identification of Most Influential Factors and a Comparison of Stiffness Design Methods.

    Directory of Open Access Journals (Sweden)

    S N R Shah

    Full Text Available Steel pallet rack (SPR beam-to-column connections (BCCs are largely responsible to avoid the sway failure of frames in the down-aisle direction. The overall geometry of beam end connectors commercially used in SPR BCCs is different and does not allow a generalized analytic approach for all types of beam end connectors; however, identifying the effects of the configuration, profile and sizes of the connection components could be the suitable approach for the practical design engineers in order to predict the generalized behavior of any SPR BCC. This paper describes the experimental behavior of SPR BCCs tested using a double cantilever test set-up. Eight sets of specimens were identified based on the variation in column thickness, beam depth and number of tabs in the beam end connector in order to investigate the most influential factors affecting the connection performance. Four tests were repeatedly performed for each set to bring uniformity to the results taking the total number of tests to thirty-two. The moment-rotation (M-θ behavior, load-strain relationship, major failure modes and the influence of selected parameters on connection performance were investigated. A comparative study to calculate the connection stiffness was carried out using the initial stiffness method, the slope to half-ultimate moment method and the equal area method. In order to find out the more appropriate method, the mean stiffness of all the tested connections and the variance in values of mean stiffness according to all three methods were calculated. The calculation of connection stiffness by means of the initial stiffness method is considered to overestimate the values when compared to the other two methods. The equal area method provided more consistent values of stiffness and lowest variance in the data set as compared to the other two methods.

  3. Steel Rack Connections: Identification of Most Influential Factors and a Comparison of Stiffness Design Methods

    Science.gov (United States)

    Shah, S. N. R.; Sulong, N. H. Ramli; Shariati, Mahdi; Jumaat, M. Z.

    2015-01-01

    Steel pallet rack (SPR) beam-to-column connections (BCCs) are largely responsible to avoid the sway failure of frames in the down-aisle direction. The overall geometry of beam end connectors commercially used in SPR BCCs is different and does not allow a generalized analytic approach for all types of beam end connectors; however, identifying the effects of the configuration, profile and sizes of the connection components could be the suitable approach for the practical design engineers in order to predict the generalized behavior of any SPR BCC. This paper describes the experimental behavior of SPR BCCs tested using a double cantilever test set-up. Eight sets of specimens were identified based on the variation in column thickness, beam depth and number of tabs in the beam end connector in order to investigate the most influential factors affecting the connection performance. Four tests were repeatedly performed for each set to bring uniformity to the results taking the total number of tests to thirty-two. The moment-rotation (M-θ) behavior, load-strain relationship, major failure modes and the influence of selected parameters on connection performance were investigated. A comparative study to calculate the connection stiffness was carried out using the initial stiffness method, the slope to half-ultimate moment method and the equal area method. In order to find out the more appropriate method, the mean stiffness of all the tested connections and the variance in values of mean stiffness according to all three methods were calculated. The calculation of connection stiffness by means of the initial stiffness method is considered to overestimate the values when compared to the other two methods. The equal area method provided more consistent values of stiffness and lowest variance in the data set as compared to the other two methods. PMID:26452047

  4. Variable stiffness and damping MR isolator

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, X Z; Wang, X Y; Li, W H; Kostidis, K [University of Wollongong, School of Mechanical, Materials and Mechatronic Engineering, NSW 2522 (Australia)], E-mail: weihuali@uow.edu.au

    2009-02-01

    This paper presents the development of a magnetorheological (MR) fluid-based variable stiffness and damping isolator for vibration suppressions. The MR fluid isolator used a sole MR control unit to achieve the variable stiffness and damping in stepless and relative large scope. A mathematical model of the isolator was derived, and a prototype of the MR fluid isolator was fabricated and its dynamic behavior was measured in vibration under various applied magnetic fields. The parameters of the model under various magnetic fields were identified and the dynamic performances of isolator were evaluated.

  5. Use of the dynamic stiffness method to interpret experimental data from a nonlinear system

    Science.gov (United States)

    Tang, Bin; Brennan, M. J.; Gatti, G.

    2018-05-01

    The interpretation of experimental data from nonlinear structures is challenging, primarily because of dependency on types and levels of excitation, and coupling issues with test equipment. In this paper, the use of the dynamic stiffness method, which is commonly used in the analysis of linear systems, is used to interpret the data from a vibration test of a controllable compressed beam structure coupled to a test shaker. For a single mode of the system, this method facilitates the separation of mass, stiffness and damping effects, including nonlinear stiffness effects. It also allows the separation of the dynamics of the shaker from the structure under test. The approach needs to be used with care, and is only suitable if the nonlinear system has a response that is predominantly at the excitation frequency. For the structure under test, the raw experimental data revealed little about the underlying causes of the dynamic behaviour. However, the dynamic stiffness approach allowed the effects due to the nonlinear stiffness to be easily determined.

  6. LSODE, 1. Order Stiff or Non-Stiff Ordinary Differential Equations System Initial Value Problems

    International Nuclear Information System (INIS)

    Hindmarsh, A.C.; Petzold, L.R.

    2005-01-01

    1 - Description of program or function: LSODE (Livermore Solver for Ordinary Differential Equations) solves stiff and non-stiff systems of the form dy/dt = f. In the stiff case, it treats the Jacobian matrix df/dy as either a dense (full) or a banded matrix, and as either user-supplied or internally approximated by difference quotients. It uses Adams methods (predictor-corrector) in the non-stiff case, and Backward Differentiation Formula (BDF) methods (the Gear methods) in the stiff case. The linear systems that arise are solved by direct methods (LU factor/solve). The LSODE source is commented extensively to facilitate modification. Both a single-precision version and a double-precision version are available. 2 - Methods: It is assumed that the ODEs are given explicitly, so that the system can be written in the form dy/dt = f(t,y), where y is the vector of dependent variables, and t is the independent variable. LSODE contains two variable-order, variable- step (with interpolatory step-changing) integration methods. The first is the implicit Adams or non-stiff method, of orders one through twelve. The second is the backward differentiation or stiff method (or BDF method, or Gear's method), of orders one through five. 3 - Restrictions on the complexity of the problem: The differential equations must be given in explicit form, i.e., dy/dt = f(y,t). Problems with intermittent high-speed transients may cause inefficient or unstable performance

  7. Comparative study of diastolic filling under varying left ventricular wall stiffness

    Science.gov (United States)

    Mekala, Pritam; Santhanakrishnan, Arvind

    2014-11-01

    Pathological remodeling of the human cardiac left ventricle (LV) is observed in hypertensive heart failure as a result of pressure overload. Myocardial stiffening occurs in these patients prior to chronic maladaptive changes, resulting in increased LV wall stiffness. The goal of this study was to investigate the change in intraventricular filling fluid dynamics inside a physical model of the LV as a function of wall stiffness. Three LV models of varying wall stiffness were incorporated into an in vitro flow circuit driven by a programmable piston pump. Windkessel elements were used to tune the inflow and systemic pressure in the model with least stiffness to match healthy conditions. Models with stiffer walls were comparatively tested maintaining circuit compliance, resistance and pump amplitude constant. 2D phase-locked PIV measurements along the central plane showed that with increase in wall stiffness, the peak velocity and cardiac output inside the LV decreased. Further, inflow vortex ring propagation toward the LV apex was reduced with increasing stiffness. The above findings indicate the importance of considering LV wall relaxation characteristics in pathological studies of filling fluid dynamics.

  8. Acute changes in arterial stiffness following exercise in people with metabolic syndrome.

    Science.gov (United States)

    Radhakrishnan, Jeyasundar; Swaminathan, Narasimman; Pereira, Natasha M; Henderson, Keiran; Brodie, David A

    This study aims to examine the changes in arterial stiffness immediately following sub-maximal exercise in people with metabolic syndrome. Ninety-four adult participants (19-80 years) with metabolic syndrome gave written consent and were measured for arterial stiffness using a SphygmoCor (SCOR-PVx, Version 8.0, Atcor Medical Private Ltd, USA) immediately before and within 5-10min after an incremental shuttle walk test. The arterial stiffness measures used were pulse wave velocity (PWV), aortic pulse pressure (PP), augmentation pressure, augmentation index (AI), subendocardial viability ratio (SEVR) and ejection duration (ED). There was a significant increase (pexercise. Exercise capacity had a strong inverse correlation with arterial stiffness and age (pExercise capacity is inversely related to arterial stiffness and age in people with metabolic syndrome. Exercise induced changes in arterial stiffness measured using pulse wave analysis is an important tool that provides further evidence in studying cardiovascular risk in metabolic syndrome. Copyright © 2016 Diabetes India. Published by Elsevier Ltd. All rights reserved.

  9. Finite Element Analysis of Single Cell Stiffness Measurements Using PZT-Integrated Buckling Nanoneedles.

    Science.gov (United States)

    Rad, Maryam Alsadat; Tijjani, Auwal Shehu; Ahmad, Mohd Ridzuan; Auwal, Shehu Muhammad

    2016-12-23

    This paper proposes a new technique for real-time single cell stiffness measurement using lead zirconate titanate (PZT)-integrated buckling nanoneedles. The PZT and the buckling part of the nanoneedle have been modelled and validated using the ABAQUS software. The two parts are integrated together to function as a single unit. After calibration, the stiffness, Young's modulus, Poisson's ratio and sensitivity of the PZT-integrated buckling nanoneedle have been determined to be 0.7100 N·m -1 , 123.4700 GPa, 0.3000 and 0.0693 V·m·N -1 , respectively. Three Saccharomyces cerevisiae cells have been modelled and validated based on compression tests. The average global stiffness and Young's modulus of the cells are determined to be 10.8867 ± 0.0094 N·m -1 and 110.7033 ± 0.0081 MPa, respectively. The nanoneedle and the cell have been assembled to measure the local stiffness of the single Saccharomyces cerevisiae cells The local stiffness, Young's modulus and PZT output voltage of the three different size Saccharomyces cerevisiae have been determined at different environmental conditions. We investigated that, at low temperature the stiffness value is low to adapt to the change in the environmental condition. As a result, Saccharomyces cerevisiae becomes vulnerable to viral and bacterial attacks. Therefore, the proposed technique will serve as a quick and accurate process to diagnose diseases at early stage in a cell for effective treatment.

  10. Aging impairs smooth muscle-mediated regulation of aortic stiffness: a defect in shock absorption function?

    Science.gov (United States)

    Gao, Yuan Z.; Saphirstein, Robert J.; Yamin, Rina; Suki, Bela

    2014-01-01

    Increased aortic stiffness is an early and independent biomarker of cardiovascular disease. Here we tested the hypothesis that vascular smooth muscle cells (VSMCs) contribute significantly to aortic stiffness and investigated the mechanisms involved. The relative contributions of VSMCs, focal adhesions (FAs), and matrix to stiffness in mouse aorta preparations at optimal length and with confirmed VSMC viability were separated by the use of small-molecule inhibitors and activators. Using biomechanical methods designed for minimal perturbation of cellular function, we directly quantified changes with aging in aortic material stiffness. An alpha adrenoceptor agonist, in the presence of NG-nitro-l-arginine methyl ester (l-NAME) to remove interference of endothelial nitric oxide, increases stiffness by 90–200% from baseline in both young and old mice. Interestingly, increases are robustly suppressed by the Src kinase inhibitor PP2 in young but not old mice. Phosphotyrosine screening revealed, with aging, a biochemical signature of markedly impaired agonist-induced FA remodeling previously associated with Src signaling. Protein expression measurement confirmed a decrease in Src expression with aging. Thus we report here an additive model for the in vitro biomechanical components of the mouse aortic wall in which 1) VSMCs are a surprisingly large component of aortic stiffness at physiological lengths and 2) regulation of the VSMC component through FA signaling and hence plasticity is impaired with aging, diminishing the aorta's normal shock absorption function in response to stressors. PMID:25128168

  11. Measurement of passive ankle stiffness in subjects with chronic hemiparesis using a novel ankle robot

    Science.gov (United States)

    Roy, Anindo; Bever, Christopher T.; Forrester, Larry W.; Macko, Richard F.; Hogan, Neville

    2011-01-01

    Our objective in this study was to assess passive mechanical stiffness in the ankle of chronic hemiparetic stroke survivors and to compare it with those of healthy young and older (age-matched) individuals. Given the importance of the ankle during locomotion, an accurate estimate of passive ankle stiffness would be valuable for locomotor rehabilitation, potentially providing a measure of recovery and a quantitative basis to design treatment protocols. Using a novel ankle robot, we characterized passive ankle stiffness both in sagittal and in frontal planes by applying perturbations to the ankle joint over the entire range of motion with subjects in a relaxed state. We found that passive stiffness of the affected ankle joint was significantly higher in chronic stroke survivors than in healthy adults of a similar cohort, both in the sagittal as well as frontal plane of movement, in three out of four directions tested with indistinguishable stiffness values in plantarflexion direction. Our findings are comparable to the literature, thus indicating its plausibility, and, to our knowledge, report for the first time passive stiffness in the frontal plane for persons with chronic stroke and older healthy adults. PMID:21346215

  12. An acoustic startle alters knee joint stiffness and neuromuscular control.

    Science.gov (United States)

    DeAngelis, A I; Needle, A R; Kaminski, T W; Royer, T R; Knight, C A; Swanik, C B

    2015-08-01

    Growing evidence suggests that the nervous system contributes to non-contact knee ligament injury, but limited evidence has measured the effect of extrinsic events on joint stability. Following unanticipated events, the startle reflex leads to universal stiffening of the limbs, but no studies have investigated how an acoustic startle influences knee stiffness and muscle activation during a dynamic knee perturbation. Thirty-six individuals were tested for knee stiffness and muscle activation of the quadriceps and hamstrings. Subjects were seated and instructed to resist a 40-degree knee flexion perturbation from a relaxed state. During some trials, an acoustic startle (50 ms, 1000 Hz, 100 dB) was applied 100 ms prior to the perturbation. Knee stiffness, muscle amplitude, and timing were quantified across time, muscle, and startle conditions. The acoustic startle increased short-range (no startle: 0.044 ± 0.011 N·m/deg/kg; average startle: 0.047 ± 0.01 N·m/deg/kg) and total knee stiffness (no startle: 0.036 ± 0.01 N·m/deg/kg; first startle 0.027 ± 0.02 N·m/deg/kg). Additionally, the startle contributed to decreased [vastus medialis (VM): 13.76 ± 33.6%; vastus lateralis (VL): 6.72 ± 37.4%] but earlier (VM: 0.133 ± 0.17 s; VL: 0.124 ± 0.17 s) activation of the quadriceps muscles. The results of this study indicate that the startle response can significantly disrupt knee stiffness regulation required to maintain joint stability. Further studies should explore the role of unanticipated events on unintentional injury. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  13. Soft Robotic Haptic Interface with Variable Stiffness for Rehabilitation of Neurologically Impaired Hand Function

    Directory of Open Access Journals (Sweden)

    Frederick Sebastian

    2017-12-01

    Full Text Available The human hand comprises complex sensorimotor functions that can be impaired by neurological diseases and traumatic injuries. Effective rehabilitation can bring the impaired hand back to a functional state because of the plasticity of the central nervous system to relearn and remodel the lost synapses in the brain. Current rehabilitation therapies focus on strengthening motor skills, such as grasping, employ multiple objects of varying stiffness so that affected persons can experience a wide range of strength training. These devices have limited range of stiffness due to the rigid mechanisms employed in their variable stiffness actuators. This paper presents a novel soft robotic haptic device for neuromuscular rehabilitation of the hand, which is designed to offer adjustable stiffness and can be utilized in both clinical and home settings. The device eliminates the need for multiple objects by employing a pneumatic soft structure made with highly compliant materials that act as the actuator of the haptic interface. It is made with interchangeable sleeves that can be customized to include materials of varying stiffness to increase the upper limit of the stiffness range. The device is fabricated using existing 3D printing technologies, and polymer molding and casting techniques, thus keeping the cost low and throughput high. The haptic interface is linked to either an open-loop system that allows for an increased pressure during usage or closed-loop system that provides pressure regulation in accordance to the stiffness the user specifies. Preliminary evaluation is performed to characterize the effective controllable region of variance in stiffness. It was found that the region of controllable stiffness was between points 3 and 7, where the stiffness appeared to plateau with each increase in pressure. The two control systems are tested to derive relationships between internal pressure, grasping force exertion on the surface, and displacement using

  14. Elastin in large artery stiffness and hypertension

    Science.gov (United States)

    Wagenseil, Jessica E.; Mecham, Robert P.

    2012-01-01

    Large artery stiffness, as measured by pulse wave velocity (PWV), is correlated with high blood pressure and may be a causative factor in essential hypertension. The extracellular matrix components, specifically the mix of elastin and collagen in the vessel wall, determine the passive mechanical properties of the large arteries. Elastin is organized into elastic fibers in the wall during arterial development in a complex process that requires spatial and temporal coordination of numerous proteins. The elastic fibers last the lifetime of the organism, but are subject to proteolytic degradation and chemical alterations that change their mechanical properties. This review discusses how alterations in the amount, assembly, organization or chemical properties of the elastic fibers affect arterial stiffness and blood pressure. Strategies for encouraging or reversing alterations to the elastic fibers are addressed. Methods for determining the efficacy of these strategies, by measuring elastin amounts and arterial stiffness, are summarized. Therapies that have a direct effect on arterial stiffness through alterations to the elastic fibers in the wall may be an effective treatment for essential hypertension. PMID:22290157

  15. Diagram of state of stiff amphiphilic macromolecules

    NARCIS (Netherlands)

    Markov, Vladimir A.; Vasilevskaya, Valentina V.; Khalatur, Pavel G.; ten Brinke, Gerrit; Khokhlov, Alexei R.

    2007-01-01

    We studied coil-globule transitions in stiff-chain amphiphilic macromolecules via computer modeling and constructed phase diagrams for such molecules in terms of solvent quality and persistence length. We showed that the shape of the phase diagram essentially depends on the macromolecule degree of

  16. Advanced damper with negative structural stiffness elements

    International Nuclear Information System (INIS)

    Dong, Liang; Lakes, Roderic S

    2012-01-01

    Negative stiffness is understood as the occurrence of a force in the same direction as the imposed deformation. Structures and composites with negative stiffness elements enable a large amplification in damping. It is shown in this work, using an experimental approach, that when a flexible flat-ends column is aligned in a post-buckled condition, a negative structural stiffness and large hysteresis (i.e., high damping) can be achieved provided the ends of the column undergo tilting from flat to edge contact. Stable axial dampers with initial modulus equivalent to that of the parent material and with enhanced damping were designed and built using constrained negative stiffness effects entailed by post-buckled press-fit flat-ends columns. Effective damping of approximately 1 and an effective stiffness–damping product of approximately 1.3 GPa were achieved in such stable axial dampers consisting of PMMA columns. This is a considerable improvement for this figure of merit (i.e., the stiffness–damping product), which generally cannot exceed 0.6 GPa for currently used damping layers. (paper)

  17. The effect of sex, menstrual cycle phase, and monophasic oral contraceptive pill use on local and central arterial stiffness in young adults.

    Science.gov (United States)

    Priest, Stacey E; Shenouda, Ninette; MacDonald, Maureen J

    2018-04-20

    Arterial stiffness is associated with increased cardiovascular disease risk. Previous sex-based investigations of local and central stiffness report inconsistent findings and have not controlled for menstrual cycle phase in women. There is also evidence that sex hormones influence the vasculature, but their impact on arterial stiffness across a natural menstrual (NAT) or oral contraceptive pill (OCP) cycle has been understudied. This study sought to 1) examine potential sex differences in local and central stiffness, 2) compare stiffness profiles between NAT and OCP cycles, and 3) investigate the relationship between duration of OCP use and arterial stiffness. Fifty-three healthy adults (22{plus minus}3 years; 20 men, 15 NAT, 18 OCP) underwent assessments of sex hormone concentrations, β-stiffness index (local stiffness), and carotid-femoral pulse wave velocity (cfPWV, central stiffness). All participants were tested three times (men: same day and time one week apart; NAT: menstrual, mid-follicular, luteal; OCP: placebo, early and late active pill). Men had higher β-stiffness than NAT and OCP (p0.05 for all) and were not associated with duration of OCP use (β-stiffness: r=0.003, p=0.99; cfPWV: r =-0.26, p=0.30). The apparent sex-differences in local, but not central stiffness highlight the importance of assessing both indices when comparing men and women. Furthermore, fluctuating sex hormones do not appear to influence β-stiffness or cfPWV. Therefore, these stiffness indices may only need to be assessed during one cycle phase in women in future investigations.

  18. Effect of waste plastic bottles on the stiffness and fatigue properties of modified asphalt mixes

    International Nuclear Information System (INIS)

    Modarres, Amir; Hamedi, Hamidreza

    2014-01-01

    Highlights: • PET reduced the mix stiffness at both temperatures of 5 and 25 °C. • PET improved the fatigue behavior at both testing temperatures. • At more than 210 microstrain, adding temperature resulted in higher fatigue life. • SBS modified mixes showed better fatigue behavior than PET modified ones. • Overall PET had comparable effects to SBS on the stiffness and fatigue behavior. - Abstract: Nowadays, the use of recycled waste materials as modifier additives in asphalt mixes could have several economic and environmental benefits. The main purpose of this research was to investigate the effect of waste plastic bottles (Polyethylene Terephthalate (PET)) on the stiffness and specially fatigue properties of asphalt mixes at two different temperatures of 5 and 20 °C. Likewise, the effect of PET was compared to styrene butadiene styrene (SBS) which is a conventional polymer additive which has been vastly used to modify asphalt mixes. Different PET contents (2–10% by weight of bitumen) were added directly to mixture as the method of dry process. Then the resilient modulus and fatigue tests were performed on cylindrical specimens with indirect tensile loading procedure. Overall, the mix stiffness reduced by increasing the PET content. Although stiffness of asphalt mix initially increased by adding lower amount of PET. Based on the results of resilient modulus test, the stiffness of PET modified mix was acceptable and warranted the proper deformation characteristics of these mixes at heavy loading conditions. At both temperatures, PET improved the fatigue behavior of studied mixes. PET modified mixes revealed comparable stiffness and fatigue behavior to SBS at 20 °C. However, at 5 °C the fatigue life of SBS modified mixes was to some extent higher than that of PET modified ones especially at higher strain levels of 200 microstrain

  19. Measurement of gastrocnemius muscle elasticity by shear wave elastography: association with passive ankle joint stiffness and sex differences.

    Science.gov (United States)

    Chino, Kentaro; Takahashi, Hideyuki

    2016-04-01

    Passive joint stiffness is an important quantitative measure of flexibility, but is affected by muscle volume and all of the anatomical structures located within and over the joint. Shear wave elastography can assess muscle elasticity independent of the influences of muscle volume and the other nearby anatomical structures. We determined how muscle elasticity, as measured using shear wave elastography, is associated with passive joint stiffness and patient sex. Twenty-six healthy men (24.4 ± 5.9 years) and 26 healthy women (25.2 ± 4.8 years) participated in this study. The passive ankle joint stiffness and tissue elasticity of the medial gastrocnemius (MG) were quantified with the ankle in 30° plantar flexion (PF), a neutral anatomical position (NE), and 20° dorsiflexion (DF). No significant difference in passive joint stiffness by sex was observed with the ankle in PF, but significantly greater passive ankle joint stiffness in men than in women was observed in NE and DF. The MG elasticity was not significantly associated with joint stiffness in PF or NE, but it was significantly associated with joint stiffness in DF. There were no significant differences in MG elasticity by sex at any ankle position. Muscle elasticity, measured independent of the confounding effects of muscle volume and the other nearby anatomical structures, is associated with passive joint stiffness in the joint position where the muscle is sufficiently lengthened, but does not vary by sex in any joint position tested.

  20. Non-invasive evaluation of liver stiffness after splenectomy in rabbits with CCl4-induced liver fibrosis.

    Science.gov (United States)

    Wang, Ming-Jun; Ling, Wen-Wu; Wang, Hong; Meng, Ling-Wei; Cai, He; Peng, Bing

    2016-12-14

    To investigate the diagnostic performance of liver stiffness measurement (LSM) by elastography point quantification (ElastPQ) in animal models and determine the longitudinal changes in liver stiffness by ElastPQ after splenectomy at different stages of fibrosis. Liver stiffness was measured in sixty-eight rabbits with CCl 4 -induced liver fibrosis at different stages and eight healthy control rabbits by ElastPQ. Liver biopsies and blood samples were obtained at scheduled time points to assess liver function and degree of fibrosis. Thirty-one rabbits with complete data that underwent splenectomy at different stages of liver fibrosis were then included for dynamic monitoring of changes in liver stiffness by ElastPQ and liver function according to blood tests. LSM by ElastPQ was significantly correlated with histologic fibrosis stage ( r = 0.85, P fibrosis, moderate fibrosis, and cirrhosis, respectively. Longitudinal monitoring of the changes in liver stiffness by ElastPQ showed that early splenectomy (especially F1) may delay liver fibrosis progression. ElastPQ is an available, convenient, objective and non-invasive technique for assessing liver stiffness in rabbits with CCl 4 -induced liver fibrosis. In addition, liver stiffness measurements using ElastPQ can dynamically monitor the changes in liver stiffness in rabbit models, and in patients, after splenectomy.

  1. Parametric study of roof diaphragm stiffness requirements

    International Nuclear Information System (INIS)

    Jones, W.D.; Tenbus, M.A.

    1991-01-01

    A common assumption made in performing a dynamic seismic analysis for a building is that the roof/floor system is open-quotes rigidclose quotes. This assumption would appear to be reasonable for many of the structures found in nuclear power plants, since many of these structures are constructed of heavily reinforced concrete having floor/roof slabs at least two feet in thickness, and meet the code requirements for structural detailing for seismic design. The roofs of many Department of Energy (DOE) buildings at the Oak Ridge Y-12 Plant in Oak Ridge, Tennessee, have roofs constructed of either metal, precast concrete or gypsum plank deck overlaid with rigid insulation, tar and gravel. In performing natural phenomena hazard assessments for one such facility, it was assumed that the existing roof performed first as a flexible diaphragm (zero stiffness) and then, rigid (infinitely stiff). For the flexible diaphragm model it was determined that the building began to experience significant damage around 0.09 g's. For the rigid diaphragm model it was determined that no significant damage was observed below 0.20 g's. A Conceptual Design Report has been prepared for upgrading/replacing the roof of this building. The question that needed to be answered here was, open-quotes How stiff should the new roof diaphragm be in order to satisfy the rigid diaphragm assumption and, yet, be cost effective?close quotes. This paper presents a parametric study of a very simple structural system to show that the design of roof diaphragms needs to consider both strength and stiffness (frequency) requirements. This paper shows how the stiffness of a roof system affects the seismically induced loads in the lateral, vertical load resisting elements of a building and provides guidance in determining how open-quotes rigidclose quotes a roof system should be in order to accomplish a cost effective design

  2. Correlation study of spleen stiffness measured by FibroTouch with esophageal and gastric varices in patients with liver cirrhosis

    Directory of Open Access Journals (Sweden)

    WEI Yutong

    2015-03-01

    Full Text Available ObjectiveTo explore the correlation of spleen stiffness measured by FibroScan with esophageal and gastric varices in patients with liver cirrhosis. MethodsSpleen and liver stiffness was measured by FibroScan in 72 patients with liver cirrhosis who received gastroscopy in our hospital from December 2012 to December 2013. Categorical data were analyzed by χ2 test, and continuous data were analyzed by t test. Pearson's correlation analysis was used to investigate the correlation between the degree of esophageal varices and spleen stiffness. ResultsWith the increase in the Child-Pugh score in patients, the measurements of liver and spleen stiffness showed a rising trend. Correlation was found between the measurements of spleen and liver stiffness (r=0.367, P<0.05. The differences in measurements of spleen stiffness between patients with Child-Pugh classes A, B, and C were all significant (t=5.149, 7.231, and 6.119, respectively; P=0031, 0.025, and 0.037, respectively. The measurements of spleen and liver stiffness showed marked increases in patients with moderate and severe esophageal and gastric varices. The receiver operating characteristic (ROC curve analysis showed that the area under the ROC curve, sensitivity, and specificity for spleen stiffness were significantly higher than those for liver stiffness and platelet count/spleen thickness. ConclusionThe spleen stiffness measurement by FibroScan shows a good correlation with the esophageal and gastric varices in patients with liver cirrhosis. FibroScan is safe and noninvasive, and especially useful for those who are not suitable for gastroscopy.

  3. A quantitative method for evaluating inferior glenohumeral joint stiffness using ultrasonography.

    Science.gov (United States)

    Tsai, Wen-Wei; Lee, Ming-Yih; Yeh, Wen-Lin; Cheng, Shih-Chung; Soon, Kok-Soon; Lei, Kin Fong; Lin, Wen-Yen

    2013-02-01

    Subluxation of the affected shoulder in post-stroke patients is associated with nerve disorders and muscle fatigue. Clinicians must be able to accurately and reliably measure inferior glenohumeral subluxation in patients to provide appropriate treatment. However, quantitative methods for evaluating the laxity and stiffness of the glenohumeral joint (GHJ) are still being developed. The aim of this study was to develop a new protocol for evaluating the laxity and stiffness of the inferior GHJ using ultrasonography under optimal testing conditions and to investigate changes in the GHJ from a commercially available humerus brace and shoulder brace. Multistage inferior displacement forces were applied to create a glide between the most cephalad point on the visible anterosuperior surface of the humeral head and coracoid process in seven healthy volunteers. GHJ stiffness was defined as the slope of the linear regression line between the glides and different testing loads. The testing conditions were defined by different test loading mechanisms (n=2), shoulder constraining conditions (n=2), and loading modes (n=4). The optimal testing condition was defined as the condition with the least residual variance of measured laxity to the calculated stiffness under different testing loads. A paired t-test was used to compare the laxity and stiffness of the inferior GHJ using different braces. No significant difference was identified between the two test loading mechanisms (t=0.218, p=0.831) and two shoulder constraining conditions (t=-0.235, p=0.818). We concluded that ultrasonographic laxity measurements performed using a pulley set loading mechanism was as reliable as direct loading. Additionally, constraining the unloaded shoulder was proposed due to the lower mean residual variance value. Moreover, pulling the elbow downward with loading on the upper arm was suggested, as pulling the elbow downward with the elbow flexed and loading on the forearm may overestimate stiffness

  4. Comparison and evaluation of flexible and stiff piping systems

    International Nuclear Information System (INIS)

    Hahn, W.; Tang, H.T.; Tang, Y.K.

    1983-01-01

    An experimental and numerical study was performed on a piping system, with various support configurations, to assess the difference in piping response for flexible and stiff piping systems. Questions have arisen concerning a basic design philosophy employed in present day piping designs. One basic question is, the reliability of a flexible piping system greater than that of a stiff piping system by virtue of the fact that a flexible system has fewer snubber supports. With fewer snubbers, the pipe is less susceptible to inadvertent thermal stresses introduced by snubber malfunction during normal operation. In addition to the technical issue, the matter of cost savings in flexible piping system design is a significant one. The costs associated with construction, in-service inspection and maintenance are all significantly reduced by reducing the number of snubber supports. The evaluation study, sponsored by the Electric Power Research Institute, was performed on a boiler feedwater line at Consolidated Edison's Indian Point Unit 1. In this study, the boiler feedwater line was tested and analyzed with two fundamentally different support systems. The first system was very flexible, employing rod and spring hangers, and represented the 'old' design philosophy. The pipe system was very flexible with this support system, due to the long pipe span lengths between supports and the fact that there was only one lateral support. This support did not provide much restraint since it was near an anchor. The second system employed strut and snubber supports and represented the 'modern' design philosophy. The pipe system was relatively stiff with this support system, primarily due to the increased number of supports, including lateral supports, thereby reducing the pipe span lengths between supports. The second support system was designed with removable supports to facilitate interchange of the supports with different support types (i.e., struts, mechanical snubbers and hydraulic

  5. Arterial stiffness and functional outcome in acute ischemic stroke.

    Science.gov (United States)

    Lee, Yeong-Bae; Park, Joo-Hwan; Kim, Eunja; Kang, Chang-Ki; Park, Hyeon-Mi

    2014-03-01

    Arterial stiffness is a common change associated with aging and can be evaluated by measuring pulse wave velocity (PWV) between sites in the arterial tree, with the stiffer artery having the higher PWV. Arterial stiffness is associated with the risk of stroke in the general population and of fatal stroke in hypertensive patients. This study is to clarify whether PWV value predicts functional outcome of acute ischemic stroke. ONE HUNDRED PATIENTS WERE ENROLLED WITH A DIAGNOSIS OF ACUTE ISCHEMIC STROKE AND CATEGORIZED INTO TWO GROUPS: large-artery atherosclerosis (LAAS) or small vessel disease (SVD) subtype of Trial of Org 10172 in Acute Stroke Treatment (TOAST) classification. Each group was divided into two sub-groups based on the functional outcome of acute ischemic stroke, indicated by modified Rankin Scale (mRS) at discharge. Poor functional outcome group was defined as a mRS ≥ 3 at discharge. Student's t-test or Mann-Whitney U-test were used to compare maximal brachial-ankle PWV (baPWV) values. Twenty-four patients whose state was inadequate to assess baPWV or mRS were excluded. There were 38 patients with good functional outcome (mRS vs. 1,789.80 ± 421.91, p = 0.022), while there was no significant difference of baPWV among patients with LAAS subtype (2,071.76 ± 618.42 vs. 1,878.00 ± 365.35, p = 0.579). Arterial stiffness indicated by baPWV is associated with the functional outcome of acute ischemic stroke. This finding suggests that measurement of baPWV predicts functional outcome in patients with stroke especially those whose TOAST classification was confirmed as SVD subtype.

  6. Mixed, Nonsplit, Extended Stability, Stiff Integration of Reaction Diffusion Equations

    KAUST Repository

    Alzahrani, Hasnaa H.

    2016-01-01

    A tailored integration scheme is developed to treat stiff reaction-diffusion prob- lems. The construction adapts a stiff solver, namely VODE, to treat reaction im- plicitly together with explicit treatment of diffusion. The second-order Runge

  7. The stable stiffness triangle - drained sand during deformation cycles

    DEFF Research Database (Denmark)

    Sabaliauskas, Tomas; Ibsen, Lars Bo

    2017-01-01

    Cyclic, drained sand stiffness was observed using the Danish triaxial appa- ratus. New, deformation dependant soil property (the stable stiffness triangle) was detected. Using the the stable stiffness triangle, secant stiffness of drained sand was plausible to predict (and control) even during ir...... findings can find application in off-shore, seismic and other engi- neering practice, or inspire new branches of research and modelling wherever dynamic, cyclic or transient loaded sand is encountered....

  8. Is chronic obstructive pulmonary disease associated with increased arterial stiffness?

    DEFF Research Database (Denmark)

    Janner, Julie H; McAllister, David A; Godtfredsen, Nina S

    2012-01-01

    We hypothesize that airflow limitation is associated with increasing arterial stiffness and that having COPD increases a non-invasive measure of arterial stiffness - the aortic augmentation index (AIx) - independently of other CVD risk factors.......We hypothesize that airflow limitation is associated with increasing arterial stiffness and that having COPD increases a non-invasive measure of arterial stiffness - the aortic augmentation index (AIx) - independently of other CVD risk factors....

  9. A Rapid Aeroelasticity Optimization Method Based on the Stiffness characteristics

    OpenAIRE

    Yuan, Zhe; Huo, Shihui; Ren, Jianting

    2018-01-01

    A rapid aeroelasticity optimization method based on the stiffness characteristics was proposed in the present study. Large time expense in static aeroelasticity analysis based on traditional time domain aeroelasticity method is solved. Elastic axis location and torsional stiffness are discussed firstly. Both torsional stiffness and the distance between stiffness center and aerodynamic center have a direct impact on divergent velocity. The divergent velocity can be adjusted by changing the cor...

  10. A novel energy-efficient rotational variable stiffness actuator

    NARCIS (Netherlands)

    Rao, S.; Carloni, Raffaella; Stramigioli, Stefano

    This paper presents the working principle, the design and realization of a novel rotational variable stiffness actuator, whose stiffness can be varied independently of its output angular position. This actuator is energy-efficient, meaning that the stiffness of the actuator can be varied by keeping

  11. Direct measurement of the intrinsic ankle stiffness during standing

    NARCIS (Netherlands)

    Vlutters, Mark; Vlutters, M.; Boonstra, Tjitske; Schouten, Alfred Christiaan; van der Kooij, Herman

    2015-01-01

    Ankle stiffness contributes to standing balance, counteracting the destabilizing effect of gravity. The ankle stiffness together with the compliance between the foot and the support surface make up the ankle-foot stiffness, which is relevant to quiet standing. The contribution of the intrinsic

  12. Measuring multi-joint stiffness during single movements: numerical validation of a novel time-frequency approach.

    Science.gov (United States)

    Piovesan, Davide; Pierobon, Alberto; DiZio, Paul; Lackner, James R

    2012-01-01

    This study presents and validates a Time-Frequency technique for measuring 2-dimensional multijoint arm stiffness throughout a single planar movement as well as during static posture. It is proposed as an alternative to current regressive methods which require numerous repetitions to obtain average stiffness on a small segment of the hand trajectory. The method is based on the analysis of the reassigned spectrogram of the arm's response to impulsive perturbations and can estimate arm stiffness on a trial-by-trial basis. Analytic and empirical methods are first derived and tested through modal analysis on synthetic data. The technique's accuracy and robustness are assessed by modeling the estimation of stiffness time profiles changing at different rates and affected by different noise levels. Our method obtains results comparable with two well-known regressive techniques. We also test how the technique can identify the viscoelastic component of non-linear and higher than second order systems with a non-parametrical approach. The technique proposed here is very impervious to noise and can be used easily for both postural and movement tasks. Estimations of stiffness profiles are possible with only one perturbation, making our method a useful tool for estimating limb stiffness during motor learning and adaptation tasks, and for understanding the modulation of stiffness in individuals with neurodegenerative diseases.

  13. Measuring multi-joint stiffness during single movements: numerical validation of a novel time-frequency approach.

    Directory of Open Access Journals (Sweden)

    Davide Piovesan

    Full Text Available This study presents and validates a Time-Frequency technique for measuring 2-dimensional multijoint arm stiffness throughout a single planar movement as well as during static posture. It is proposed as an alternative to current regressive methods which require numerous repetitions to obtain average stiffness on a small segment of the hand trajectory. The method is based on the analysis of the reassigned spectrogram of the arm's response to impulsive perturbations and can estimate arm stiffness on a trial-by-trial basis. Analytic and empirical methods are first derived and tested through modal analysis on synthetic data. The technique's accuracy and robustness are assessed by modeling the estimation of stiffness time profiles changing at different rates and affected by different noise levels. Our method obtains results comparable with two well-known regressive techniques. We also test how the technique can identify the viscoelastic component of non-linear and higher than second order systems with a non-parametrical approach. The technique proposed here is very impervious to noise and can be used easily for both postural and movement tasks. Estimations of stiffness profiles are possible with only one perturbation, making our method a useful tool for estimating limb stiffness during motor learning and adaptation tasks, and for understanding the modulation of stiffness in individuals with neurodegenerative diseases.

  14. A Discrete-Time Algorithm for Stiffness Extraction from sEMG and Its Application in Antidisturbance Teleoperation

    Directory of Open Access Journals (Sweden)

    Peidong Liang

    2016-01-01

    Full Text Available We have developed a new discrete-time algorithm of stiffness extraction from muscle surface electromyography (sEMG collected from human operator’s arms and have applied it for antidisturbance control in robot teleoperation. The variation of arm stiffness is estimated from sEMG signals and transferred to a telerobot under variable impedance control to imitate human motor control behaviours, particularly for disturbance attenuation. In comparison to the estimation of stiffness from sEMG, the proposed algorithm is able to reduce the nonlinear residual error effect and to enhance robustness and to simplify stiffness calibration. In order to extract a smoothing stiffness enveloping from sEMG signals, two enveloping methods are employed in this paper, namely, fast linear enveloping based on low pass filtering and moving average and amplitude monocomponent and frequency modulating (AM-FM method. Both methods have been incorporated into the proposed stiffness variance estimation algorithm and are extensively tested. The test results show that stiffness variation extraction based on the two methods is sensitive and robust to attenuation disturbance. It could potentially be applied for teleoperation in the presence of hazardous surroundings or human robot physical cooperation scenarios.

  15. An analytical study on the static vertical stiffness of wire rope isolators

    Energy Technology Data Exchange (ETDEWEB)

    Balaji, P. S.; Rahman, M. E.; Ho, Lau Hieng [Curtin University Sarawak, Miri (Malaysia); Moussa, Leblouba [University of Sharjah, Sharjah (United Arab Emirates)

    2016-01-15

    The vibrations caused by earthquake ground motions or the operations of heavy machineries can affect the functionality of equipment and cause damages to the hosting structures and surrounding equipment. A Wire rope isolator (WRI), which is a type of passive isolator known to be effective in isolating shocks and vibrations, can be used for vibration isolation of lightweight structures and equipment. The primary advantage of the WRI is that it can provide isolation in all three planes and in any orientation. The load-supporting capability of the WRI is identified from the static stiffness in the loading direction. Static stiffness mainly depends on the geometrical and material properties of the WRI. This study develops an analytical model for the static stiffness in the vertical direction by using Castigliano's second theorem. The model is validated by using the experimental results obtained from a series of monotonic loading tests. The flexural rigidity of the wire ropes required in the model is obtained from the transverse bending test. Then, the analytical model is used to conduct a parametric analysis on the effects of wire rope diameter, width, height, and number of turns (loops) on vertical stiffness. The wire rope diameter influences stiffness more than the other geometric parameters. The developed model can be accurately used for the evaluation and design of WRIs.

  16. Model-Based Estimation of Ankle Joint Stiffness

    Directory of Open Access Journals (Sweden)

    Berno J. E. Misgeld

    2017-03-01

    Full Text Available We address the estimation of biomechanical parameters with wearable measurement technologies. In particular, we focus on the estimation of sagittal plane ankle joint stiffness in dorsiflexion/plantar flexion. For this estimation, a novel nonlinear biomechanical model of the lower leg was formulated that is driven by electromyographic signals. The model incorporates a two-dimensional kinematic description in the sagittal plane for the calculation of muscle lever arms and torques. To reduce estimation errors due to model uncertainties, a filtering algorithm is necessary that employs segmental orientation sensor measurements. Because of the model’s inherent nonlinearities and nonsmooth dynamics, a square-root cubature Kalman filter was developed. The performance of the novel estimation approach was evaluated in silico and in an experimental procedure. The experimental study was conducted with body-worn sensors and a test-bench that was specifically designed to obtain reference angle and torque measurements for a single joint. Results show that the filter is able to reconstruct joint angle positions, velocities and torque, as well as, joint stiffness during experimental test bench movements.

  17. Model-Based Estimation of Ankle Joint Stiffness.

    Science.gov (United States)

    Misgeld, Berno J E; Zhang, Tony; Lüken, Markus J; Leonhardt, Steffen

    2017-03-29

    We address the estimation of biomechanical parameters with wearable measurement technologies. In particular, we focus on the estimation of sagittal plane ankle joint stiffness in dorsiflexion/plantar flexion. For this estimation, a novel nonlinear biomechanical model of the lower leg was formulated that is driven by electromyographic signals. The model incorporates a two-dimensional kinematic description in the sagittal plane for the calculation of muscle lever arms and torques. To reduce estimation errors due to model uncertainties, a filtering algorithm is necessary that employs segmental orientation sensor measurements. Because of the model's inherent nonlinearities and nonsmooth dynamics, a square-root cubature Kalman filter was developed. The performance of the novel estimation approach was evaluated in silico and in an experimental procedure. The experimental study was conducted with body-worn sensors and a test-bench that was specifically designed to obtain reference angle and torque measurements for a single joint. Results show that the filter is able to reconstruct joint angle positions, velocities and torque, as well as, joint stiffness during experimental test bench movements.

  18. Model-Based Estimation of Ankle Joint Stiffness

    Science.gov (United States)

    Misgeld, Berno J. E.; Zhang, Tony; Lüken, Markus J.; Leonhardt, Steffen

    2017-01-01

    We address the estimation of biomechanical parameters with wearable measurement technologies. In particular, we focus on the estimation of sagittal plane ankle joint stiffness in dorsiflexion/plantar flexion. For this estimation, a novel nonlinear biomechanical model of the lower leg was formulated that is driven by electromyographic signals. The model incorporates a two-dimensional kinematic description in the sagittal plane for the calculation of muscle lever arms and torques. To reduce estimation errors due to model uncertainties, a filtering algorithm is necessary that employs segmental orientation sensor measurements. Because of the model’s inherent nonlinearities and nonsmooth dynamics, a square-root cubature Kalman filter was developed. The performance of the novel estimation approach was evaluated in silico and in an experimental procedure. The experimental study was conducted with body-worn sensors and a test-bench that was specifically designed to obtain reference angle and torque measurements for a single joint. Results show that the filter is able to reconstruct joint angle positions, velocities and torque, as well as, joint stiffness during experimental test bench movements. PMID:28353683

  19. The Stress and Stiffness Analysis of Diaphragm

    Directory of Open Access Journals (Sweden)

    Qu Dongyue

    2017-01-01

    Full Text Available Diaphragm coupling with its simple structure, small size, high reliability, which can compensate for its input and output displacement deviation by its elastic deformation, is widely used in aerospace, marine, and chemical etc. This paper uses the ANSYS software and its APDL language to analysis the stress distribution when the diaphragm under the load of torque, axial deviation, centrifugal force, angular deviation and multiple loads. We find that the value of maximum stress usually appears in the outer or inner transition region and the axial deviation has a greater influence to the distribution of the stress. Based on above, we got three kinds of stiffness for axial, angular and torque, which the stiffness of diaphragm is nearly invariable. The results can be regard as an important reference for design and optimization of diaphragm coupling.

  20. Electrothermally Actuated Microbeams With Varying Stiffness

    KAUST Repository

    Tella, Sherif Adekunle

    2017-11-03

    We present axially loaded clamped-guided microbeams that can be used as resonators and actuators of variable stiffness, actuation, and anchor conditions. The applied axial load is implemented by U-shaped electrothermal actuators stacked at one of the beams edges. These can be configured and wired in various ways, which serve as mechanical stiffness elements that control the operating resonance frequency of the structures and their static displacement. The experimental results have shown considerable increase in the resonance frequency and mid-point deflection of the microbeam upon changing the end conditions of the beam. These results can be promising for applications requiring large deflection and high frequency tunability, such as filters, memory devices, and switches. The experimental results are compared to multi-physics finite-element simulations showing good agreement among them.

  1. Music decreases aortic stiffness and wave reflections.

    Science.gov (United States)

    Vlachopoulos, Charalambos; Aggelakas, Angelos; Ioakeimidis, Nikolaos; Xaplanteris, Panagiotis; Terentes-Printzios, Dimitrios; Abdelrasoul, Mahmoud; Lazaros, George; Tousoulis, Dimitris

    2015-05-01

    Music has been related to cardiovascular health and used as adjunct therapy in patients with cardiovascular disease. Aortic stiffness and wave reflections are predictors of cardiovascular risk. We investigated the short-term effect of classical and rock music on arterial stiffness and wave reflections. Twenty healthy individuals (22.5±2.5 years) were studied on three different occasions and listened to a 30-min music track compilation (classical, rock, or no music for the sham procedure). Both classical and rock music resulted in a decrease of carotid-femoral pulse wave velocity (PWV) immediately after the end of music listening (all pclassical or rock music in a more sustained way (nadir by 6.0% and 5.8%, respectively, at time zero post-music listening, all pmusic preference was taken into consideration, both classical and rock music had a more potent effect on PWV in classical aficionados (by 0.20 m/s, p=0.003 and 0.13 m/s, p=0.015, respectively), whereas there was no effect in rock aficionados (all p=NS). Regarding wave reflections, classical music led to a more potent response in classical aficionados (AIx decrease by 9.45%), whereas rock led to a more potent response to rock aficionados (by 10.7%, all pMusic, both classical and rock, decreases aortic stiffness and wave reflections. Effect on aortic stiffness lasts for as long as music is listened to, while classical music has a sustained effect on wave reflections. These findings may have important implications, extending the spectrum of lifestyle modifications that can ameliorate arterial function. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  2. On the elastic stiffness of grain boundaries

    International Nuclear Information System (INIS)

    Zhang Tongyi; Hack, J.E.

    1992-01-01

    The elastic softening of grain boundaries is evaluated from the starting point of grain boundary energy. Several examples are given to illustrate the relationship between boundary energy and the extent of softening. In general, a high grain boundary energy is associated with a large excess atomic volume in the boundary region. The consequent reduction in grain boundary stiffness can represent a significant fraction of that observed in bulk crystals. (orig.)

  3. Arthrodiastasis for stiff hips in young patients

    OpenAIRE

    Cañadell, J.M. (J. M.); Gonzales, F. (F.); Barrios, R.H. (Raúl H.); Amillo, S. (Santiago)

    1993-01-01

    Joint distraction (arthrodiastasis) with a unilateral fixator was used to treat 9 patients with stiffness of the hip which had followed Perthes' disease (3), epiphysiolysis (2), congenital dysplasia (2), tuberculosis (1) and idiopathic chondrolysis (1). Their average age was 14 years, and they all had pain, limp and shortening of the leg. Distraction of 0.5 to 1 cm was maintained for an average of 94 days. The average range of movement subsequently was 65 degrees compared with 20 degrees befo...

  4. Stiff modes in spinvalve simulations with OOMMF

    Energy Technology Data Exchange (ETDEWEB)

    Mitropoulos, Spyridon [Department of Computer and Informatics Engineering, TEI of Eastern Macedonia and Thrace, Kavala (Greece); Tsiantos, Vassilis, E-mail: tsianto@teikav.edu.gr [Department of Electrical Engineering, TEI of Eastern Macedonia and Thrace, Kavala, 65404 Greece (Greece); Ovaliadis, Kyriakos [Department of Electrical Engineering, TEI of Eastern Macedonia and Thrace, Kavala, 65404 Greece (Greece); Kechrakos, Dimitris [Department of Education, ASPETE, Heraklion, Athens (Greece); Donahue, Michael [Applied and Computational Mathematics Division, NIST, Gaithersburg, MD (United States)

    2016-04-01

    Micromagnetic simulations are an important tool for the investigation of magnetic materials. Micromagnetic software uses various techniques to solve differential equations, partial or ordinary, involved in the dynamic simulations. Euler, Runge-Kutta, Adams, and BDF (Backward Differentiation Formulae) are some of the methods used for this purpose. In this paper, spinvalve simulations are investigated. Evidence is presented showing that these systems have stiff modes, and that implicit methods such as BDF are more effective than explicit methods in such cases.

  5. Water retention properties of stiff silt

    Directory of Open Access Journals (Sweden)

    Barbara Likar

    2017-06-01

    Full Text Available Recent research into the behaviour of soils has shown that it is in fact much more complex than can be described by the mechanics of saturated soils. Nowadays the trend of investigations has shifted towards the unsaturated state. Despite the signifiant progress that has been made so far, there are still a lot of unanswered questions related to the behaviour of unsaturated soils. For this reason, in the fild of geotechnics some new concepts are developed, which include the study of soil suction. Most research into soil suction has involved clayey and silty material, whereas up until recently no data have been available about measurements in very stiff preconsolidated sandy silt. Very stiff preconsolidated sandy silt is typical of the Krško Basin, where it is planned that some very important geotechnical structures will be built, so that knowledge about the behaviour of such soils at increased or decreased water content is essential. Several different methods can be used for soil suction measurements. In the paper the results of measurements carried out on very stiff preconsolidated sandy silt in a Bishop - Wesley double-walled triaxial cell are presented and compared with the results of soil suction measurements performed by means of a potentiometer (WP4C. All the measurement results were evaluated taking into account already known results given in the literature, using the three most commonly used mathematical models. Until now a lot of papers dealing with suction measurements in normal consolidated and preconsolidated clay have been published. Measurements on very stiff preconsolidated sandy silt, as presented in this paper were not supported before.

  6. Cryotherapy induces an increase in muscle stiffness.

    Science.gov (United States)

    Point, M; Guilhem, G; Hug, F; Nordez, A; Frey, A; Lacourpaille, L

    2018-01-01

    Although cold application (ie, cryotherapy) may be useful to treat sports injuries and to prevent muscle damage, it is unclear whether it has adverse effects on muscle mechanical properties. This study aimed to determine the effect of air-pulsed cryotherapy on muscle stiffness estimated using ultrasound shear wave elastography. Myoelectrical activity, ankle passive torque, shear modulus (an index of stiffness), and muscle temperature of the gastrocnemius medialis were measured before, during an air-pulsed cryotherapy (-30°C) treatment of four sets of 4 minutes with 1-minute recovery in between and during a 40 minutes postcryotherapy period. Muscle temperature significantly decreased after the second set of treatment (10 minutes: 32.3±2.5°C; Pcryotherapy induces an increase in muscle stiffness. This acute change in muscle mechanical properties may lower the amount of stretch that the muscle tissue is able to sustain without subsequent injury. This should be considered when using cryotherapy in athletic practice. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  7. Static stiffness modeling of a novel hybrid redundant robot machine

    International Nuclear Information System (INIS)

    Li Ming; Wu Huapeng; Handroos, Heikki

    2011-01-01

    This paper presents a modeling method to study the stiffness of a hybrid serial-parallel robot IWR (Intersector Welding Robot) for the assembly of ITER vacuum vessel. The stiffness matrix of the basic element in the robot is evaluated using matrix structural analysis (MSA); the stiffness of the parallel mechanism is investigated by taking account of the deformations of both hydraulic limbs and joints; the stiffness of the whole integrated robot is evaluated by employing the virtual joint method and the principle of virtual work. The obtained stiffness model of the hybrid robot is analytical and the deformation results of the robot workspace under certain external load are presented.

  8. Lower Body Stiffness Modulation Strategies in Well Trained Female Athletes.

    Science.gov (United States)

    Millett, Emma L; Moresi, Mark P; Watsford, Mark L; Taylor, Paul G; Greene, David A

    2016-10-01

    Millett, EL, Moresi, MP, Watsford, ML, Taylor, PG, and Greene, DA. Lower body stiffness modulation strategies in well trained female athletes. J Strength Cond Res 30(10): 2845-2856, 2016-Lower extremity stiffness quantifies the relationship between the amount of leg compression and the external load to which the limb are subjected. This study aimed to assess differences in leg and joint stiffness and the subsequent kinematic and kinetic control mechanisms between athletes from various training backgrounds. Forty-seven female participants (20 nationally identified netballers, 13 high level endurance athletes and 14 age and gender matched controls) completed a maximal unilateral countermovement jump, drop jump and horizontal jump to assess stiffness. Leg stiffness, joint stiffness and associated mechanical parameters were assessed with a 10 camera motion analysis system and force plate. No significant differences were evident for leg stiffness measures between athletic groups for any of the tasks (p = 0.321-0.849). However, differences in joint stiffness and its contribution to leg stiffness, jump performance outcome measures and stiffness control mechanisms were evident between all groups. Practitioners should consider the appropriateness of the task utilised in leg stiffness screening. Inclusion of mechanistic and/or more sports specific tasks may be more appropriate for athletic groups.

  9. Modelling of Asphalt Concrete Stiffness in the Linear Viscoelastic Region

    Science.gov (United States)

    Mazurek, Grzegorz; Iwański, Marek

    2017-10-01

    Stiffness modulus is a fundamental parameter used in the modelling of the viscoelastic behaviour of bituminous mixtures. On the basis of the master curve in the linear viscoelasticity range, the mechanical properties of asphalt concrete at different loading times and temperatures can be predicted. This paper discusses the construction of master curves under rheological mathematical models i.e. the sigmoidal function model (MEPDG), the fractional model, and Bahia and co-workers’ model in comparison to the results from mechanistic rheological models i.e. the generalized Huet-Sayegh model, the generalized Maxwell model and the Burgers model. For the purposes of this analysis, the reference asphalt concrete mix (denoted as AC16W) intended for the binder coarse layer and for traffic category KR3 (5×105 controlled strain mode. The fixed strain level was set at 25με to guarantee that the stiffness modulus of the asphalt concrete would be tested in a linear viscoelasticity range. The master curve was formed using the time-temperature superposition principle (TTSP). The stiffness modulus of asphalt concrete was determined at temperatures 10°C, 20°C and 40°C and at loading times (frequency) of 0.1, 0.3, 1, 3, 10, 20 Hz. The model parameters were fitted to the rheological models using the original programs based on the nonlinear least squares sum method. All the rheological models under analysis were found to be capable of predicting changes in the stiffness modulus of the reference asphalt concrete to satisfactory accuracy. In the cases of the fractional model and the generalized Maxwell model, their accuracy depends on a number of elements in series. The best fit was registered for Bahia and co-workers model, generalized Maxwell model and fractional model. As for predicting the phase angle parameter, the largest discrepancies between experimental and modelled results were obtained using the fractional model. Except the Burgers model, the model matching quality was

  10. Elastic dynamic research of high speed multi-link precision press considering structural stiffness of rotation joints

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Feng Feng; Sun, Yu; Peng, Bin Bin [School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing (China)

    2016-10-15

    An elastic dynamic model of high-speed multi-link precision press considering structural stiffness of rotation joints was established by the finite element method. In the finite element model, rotation joint was established by four bar elements with equivalent stiffness, and connected link was established by beam element. Then, the elastic dynamics equation of the system was established, and modal superposition method was used to solve the dynamic response. Compared with the traditional elastic dynamic model with perfect constraint of the rotation joints, the elastic dynamic response value of the improved model is larger. To validate the presented new method of elastic dynamics analysis with stiffness of rotation joints, a related test of slider Bottom dead center (BDC) position in different speed was designed. The test shows that the model with stiffness of rotation joints is more reasonable. So it provides a reasonable theory and method for dynamic characteristics research of such a multi-link machine.

  11. Endoscopic add-on stiffness probe for real-time soft surface characterisation in MIS.

    Science.gov (United States)

    Faragasso, A; Stilli, A; Bimbo, J; Noh, Y; Liu, H; Nanayakkara, T; Dasgupta, P; Wurdemann, H A; Althoefer, K

    2014-01-01

    This paper explores a novel stiffness sensor which is mounted on the tip of a laparoscopic camera. The proposed device is able to compute stiffness when interacting with soft surfaces. The sensor can be used in Minimally Invasive Surgery, for instance, to localise tumor tissue which commonly has a higher stiffness when compared to healthy tissue. The purely mechanical sensor structure utilizes the functionality of an endoscopic camera to the maximum by visually analyzing the behavior of trackers within the field of view. Two pairs of spheres (used as easily identifiable features in the camera images) are connected to two springs with known but different spring constants. Four individual indenters attached to the spheres are used to palpate the surface. During palpation, the spheres move linearly towards the objective lens (i.e. the distance between lens and spheres is changing) resulting in variations of their diameters in the camera images. Relating the measured diameters to the different spring constants, a developed mathematical model is able to determine the surface stiffness in real-time. Tests were performed using a surgical endoscope to palpate silicon phantoms presenting different stiffness. Results show that the accuracy of the sensing system developed increases with the softness of the examined tissue.

  12. Breast tissue stiffness estimation for surgical guidance using gravity-induced excitation.

    Science.gov (United States)

    Griesenauer, Rebekah H; Weis, Jared A; Arlinghaus, Lori R; Meszoely, Ingrid M; Miga, Michael I

    2017-06-21

    Tissue stiffness interrogation is fundamental in breast cancer diagnosis and treatment. Furthermore, biomechanical models for predicting breast deformations have been created for several breast cancer applications. Within these applications, constitutive mechanical properties must be defined and the accuracy of this estimation directly impacts the overall performance of the model. In this study, we present an image-derived computational framework to obtain quantitative, patient specific stiffness properties for application in image-guided breast cancer surgery and interventions. The method uses two MR acquisitions of the breast in different supine gravity-loaded configurations to fit mechanical properties to a biomechanical breast model. A reproducibility assessment of the method was performed in a test-retest study using healthy volunteers and was further characterized in simulation. In five human data sets, the within subject coefficient of variation ranged from 10.7% to 27% and the intraclass correlation coefficient ranged from 0.91-0.944 for assessment of fibroglandular and adipose tissue stiffness. In simulation, fibroglandular content and deformation magnitude were shown to have significant effects on the shape and convexity of the objective function defined by image similarity. These observations provide an important step forward in characterizing the use of nonrigid image registration methodologies in conjunction with biomechanical models to estimate tissue stiffness. In addition, the results suggest that stiffness estimation methods using gravity-induced excitation can reliably and feasibly be implemented in breast cancer surgery/intervention workflows.

  13. Differentiation between non-neural and neural contributors to ankle joint stiffness in cerebral palsy.

    Science.gov (United States)

    de Gooijer-van de Groep, Karin L; de Vlugt, Erwin; de Groot, Jurriaan H; van der Heijden-Maessen, Hélène C M; Wielheesen, Dennis H M; van Wijlen-Hempel, Rietje M S; Arendzen, J Hans; Meskers, Carel G M

    2013-07-23

    Spastic paresis in cerebral palsy (CP) is characterized by increased joint stiffness that may be of neural origin, i.e. improper muscle activation caused by e.g. hyperreflexia or non-neural origin, i.e. altered tissue viscoelastic properties (clinically: "spasticity" vs. "contracture"). Differentiation between these components is hard to achieve by common manual tests. We applied an assessment instrument to obtain quantitative measures of neural and non-neural contributions to ankle joint stiffness in CP. Twenty-three adolescents with CP and eleven healthy subjects were seated with their foot fixated to an electrically powered single axis footplate. Passive ramp-and-hold rotations were applied over full ankle range of motion (RoM) at low and high velocities. Subject specific tissue stiffness, viscosity and reflexive torque were estimated from ankle angle, torque and triceps surae EMG activity using a neuromuscular model. In CP, triceps surae reflexive torque was on average 5.7 times larger (p = .002) and tissue stiffness 2.1 times larger (p = .018) compared to controls. High tissue stiffness was associated with reduced RoM (p therapy.

  14. On the Value of Estimating Human Arm Stiffness during Virtual Teleoperation with Robotic Manipulators.

    Science.gov (United States)

    Buzzi, Jacopo; Ferrigno, Giancarlo; Jansma, Joost M; De Momi, Elena

    2017-01-01

    Teleoperated robotic systems are widely spreading in multiple different fields, from hazardous environments exploration to surgery. In teleoperation, users directly manipulate a master device to achieve task execution at the slave robot side; this interaction is fundamental to guarantee both system stability and task execution performance. In this work, we propose a non-disruptive method to study the arm endpoint stiffness. We evaluate how users exploit the kinetic redundancy of the arm to achieve stability and precision during the execution of different tasks with different master devices. Four users were asked to perform two planar trajectories following virtual tasks using both a serial and a parallel link master device. Users' arm kinematics and muscular activation were acquired and combined with a user-specific musculoskeletal model to estimate the joint stiffness. Using the arm kinematic Jacobian, the arm end-point stiffness was derived. The proposed non-disruptive method is capable of estimating the arm endpoint stiffness during the execution of virtual teleoperated tasks. The obtained results are in accordance with the existing literature in human motor control and show, throughout the tested trajectory, a modulation of the arm endpoint stiffness that is affected by task characteristics and hand speed and acceleration.

  15. On the Value of Estimating Human Arm Stiffness during Virtual Teleoperation with Robotic Manipulators

    Directory of Open Access Journals (Sweden)

    Jacopo Buzzi

    2017-09-01

    Full Text Available Teleoperated robotic systems are widely spreading in multiple different fields, from hazardous environments exploration to surgery. In teleoperation, users directly manipulate a master device to achieve task execution at the slave robot side; this interaction is fundamental to guarantee both system stability and task execution performance. In this work, we propose a non-disruptive method to study the arm endpoint stiffness. We evaluate how users exploit the kinetic redundancy of the arm to achieve stability and precision during the execution of different tasks with different master devices. Four users were asked to perform two planar trajectories following virtual tasks using both a serial and a parallel link master device. Users' arm kinematics and muscular activation were acquired and combined with a user-specific musculoskeletal model to estimate the joint stiffness. Using the arm kinematic Jacobian, the arm end-point stiffness was derived. The proposed non-disruptive method is capable of estimating the arm endpoint stiffness during the execution of virtual teleoperated tasks. The obtained results are in accordance with the existing literature in human motor control and show, throughout the tested trajectory, a modulation of the arm endpoint stiffness that is affected by task characteristics and hand speed and acceleration.

  16. A case of stiff-person syndrome due to secondary adrenal insufficiency.

    Science.gov (United States)

    Mizuno, Yuri; Yamaguchi, Hiroo; Uehara, Taira; Yamashita, Kenichiro; Yamasaki, Ryo; Kira, Jun-Ichi

    2017-06-28

    We report a case of flexion contractures in a patient's legs secondary to postpartum hypopituitarism. A 56-year-old woman presented with a 3-year history of worsening flexion contractures of the hips and knees. On admission, her hips and knees could not be extended, and she had muscle stiffness and tenderness to palpation of the lower extremities. We first suspected stiff-person syndrome or Isaacs' syndrome because of her muscle stiffness. However, multiple hormones did not respond to stimulation tests, and an MRI of the brain showed atrophy of the pituitary gland with an empty sella. A subsequent interview revealed that she had suffered a severe hemorrhage while delivering her third child. She was diagnosed with panhypopituitarism and started on cortisol replacement therapy. After 1 week of treatment with hydrocortisone (10 mg/day), her symptoms quickly improved. We then added 75 μg/day of thyroid hormone. During the course of her treatment, autoantibodies against VGKC complex were found to be weakly positive. However, we considered the antibodies to be unrelated to her disease, because her symptoms improved markedly with low-dose steroid treatment. There are a few reports describing flexion contractures of the legs in patients with primary and secondary adrenal insufficiency. As these symptoms are similar to those seen in stiff-person syndrome, adrenal and pituitary insufficiency should be taken into account to achieve the correct diagnosis and treatment in patients with flexion contractures and muscle stiffness.

  17. Prediction of Bending Stiffness for Laminated CFRP and Its Application to Manufacturing of Roof Reinforcement

    Directory of Open Access Journals (Sweden)

    Jeong-Min Lee

    2014-05-01

    Full Text Available Recently, carbon fiber reinforced plastic (CFRP with high strength, stiffness, and lightweight is used widely in number of composite applications such as commercial aircraft, transportation, machinery, and sports equipment. Especially, it is necessary to apply lightweight materials to car components for reducing energy consumption and CO2 emissions. In case of car roof reinforcement manufactured using CFRP, superior strength and bending stiffness are required for the safety of drivers in the rollover accident. Mechanical properties of CFRP laminates are generally dependent on the stacking sequence. Therefore, research of stacking sequence using CFRP prepreg is required for superior bending stiffness. In this study, the 3-point bending FE-analysis for predicting the bending stiffness of CFRP roof reinforcement was carried out on three cases [0PW∘]5, [0PW°/0UD°/0-PW°]s, and [0UD∘]5. Material properties that the six independent elastic constants are E11, E22, G12, G23, G13, and ν12 used in FE-analysis were evaluated by the tensile test in 0°, 45°, and 90° directions. Through structural strength analysis of the automobile roof reinforcement fabricated using CFRP, the effect of the stacking sequence on the bending stiffness was evaluated and validated through experiments under the same conditions as the analysis.

  18. Breast tissue stiffness estimation for surgical guidance using gravity-induced excitation

    Science.gov (United States)

    Griesenauer, Rebekah H.; Weis, Jared A.; Arlinghaus, Lori R.; Meszoely, Ingrid M.; Miga, Michael I.

    2017-06-01

    Tissue stiffness interrogation is fundamental in breast cancer diagnosis and treatment. Furthermore, biomechanical models for predicting breast deformations have been created for several breast cancer applications. Within these applications, constitutive mechanical properties must be defined and the accuracy of this estimation directly impacts the overall performance of the model. In this study, we present an image-derived computational framework to obtain quantitative, patient specific stiffness properties for application in image-guided breast cancer surgery and interventions. The method uses two MR acquisitions of the breast in different supine gravity-loaded configurations to fit mechanical properties to a biomechanical breast model. A reproducibility assessment of the method was performed in a test-retest study using healthy volunteers and was further characterized in simulation. In five human data sets, the within subject coefficient of variation ranged from 10.7% to 27% and the intraclass correlation coefficient ranged from 0.91-0.944 for assessment of fibroglandular and adipose tissue stiffness. In simulation, fibroglandular content and deformation magnitude were shown to have significant effects on the shape and convexity of the objective function defined by image similarity. These observations provide an important step forward in characterizing the use of nonrigid image registration methodologies in conjunction with biomechanical models to estimate tissue stiffness. In addition, the results suggest that stiffness estimation methods using gravity-induced excitation can reliably and feasibly be implemented in breast cancer surgery/intervention workflows.

  19. VCODE, Ordinary Differential Equation Solver for Stiff and Non-Stiff Problems

    International Nuclear Information System (INIS)

    Cohen, Scott D.; Hindmarsh, Alan C.

    2001-01-01

    1 - Description of program or function: CVODE is a package written in ANSI standard C for solving initial value problems for ordinary differential equations. It solves both stiff and non stiff systems. In the stiff case, it includes a variety of options for treating the Jacobian of the system, including dense and band matrix solvers, and a preconditioned Krylov (iterative) solver. 2 - Method of solution: Integration is by Adams or BDF (Backward Differentiation Formula) methods, at user option. Corrector iteration is by functional iteration or Newton iteration. For the solution of linear systems within Newton iteration, users can select a dense solver, a band solver, a diagonal approximation, or a preconditioned Generalized Minimal Residual (GMRES) solver. In the dense and band cases, the user can supply a Jacobian approximation or let CVODE generate it internally. In the GMRES case, the pre-conditioner is user-supplied

  20. Improving stability and curving passing performance for railway vehicles with a variable stiffness MRF rubber joint

    Science.gov (United States)

    Harris, B. J.; Sun, S. S.; Li, W. H.

    2017-03-01

    With the growing need for effective intercity transport, the need for more advanced rail vehicle technology has never been greater. The conflicting primary longitudinal suspension requirements of high speed stability and curving performance limit the development of rail vehicle technology. This paper presents a novel magnetorheological fluid based joint with variable stiffness characteristics for the purpose of overcoming this parameter conflict. Firstly, the joint design and working principle is developed. Following this, a prototype is tested by MTS to characterize its variable stiffness properties under a range of conditions. Lastly, the performance of the proposed MRF rubber joint with regard to improving train stability and curving performance is numerically evaluated.

  1. Strength and stiffness of uniaxially tensioned reinforced concrete panels subjected to membrane shear. Technical report

    International Nuclear Information System (INIS)

    Hilmy, S.I.; White, R.N.; Gergely, P.

    1982-06-01

    This report presents experimental and analytical results on internal pressurization effects and seismic shear effects in a concrete containment vessel that is cracked by tension in one direction only. The experimental program, which was restricted to 6 in. thick flat specimens with two-way reinforcement, included establishment of (a) extensional stiffness for uniaxially tensioned specimens stressed to 0.6fy, and (b) shear strength and stiffness of these cracked specimens with tension levels ranging from 0 to 0.9fy; values were about 10 to 15 percent higher than in similar biaxially tensioned specimens. Eleven (11) specimens were tested (6 in monotonic shear and 5 in reversing cyclic shear)

  2. Evaluation of the stiffness characteristics of rapid palatal expander screws

    Directory of Open Access Journals (Sweden)

    Luca Lombardo

    2016-11-01

    Full Text Available Abstract Background The aim of this study is to evaluate the mechanical properties of the screws used for rapid expansion of the upper jaw. Methods Ten types of expansion screw were assessed, seven with four arms: Lancer Philosophy 1, Dentaurum Hyrax Click Medium, Forestadent Anatomic Expander type “S”, Forestadent Anatomic Expander type “S” for narrow palates, Forestadent Memory, Leone A 2620-10 with telescopic guide, and Leone A 0630-10 with orthogonal arms; and three with two arms: Dentaurum Variety S.P., Target Baby REP Veltri, and Leone A 362113. A test expander with the mean dimensions taken from measurements on a sample of 100 expanders was constructed for each screw. The test expanders were connected to the supports of an Instron 4467 (Instron Corp., USA mechanical testing machine equipped with a 500 N load cell, and the compression force exerted after each activation was measured. The mean forces expressed by the two- and four-arm expanders were then compared. Results After five activations, the forces expressed by the two-arm devices were double than those expressed by the four-arm devices on average (224 ± 59.9 N vs. 103 ± 32.9 N, and such values remained high after subsequent activations. Conclusions The expanders tested demonstrated stiffness characteristics compatible with opening of the palatine sutures in pre-adolescent patients. The stiffness of such devices can be further increased during the construction phase.

  3. STRETCHING EXERCISES - EFFECT ON PASSIVE EXTENSIBILITY AND STIFFNESS IN SHORT HAMSTRINGS OF HEALTHY-SUBJECTS

    NARCIS (Netherlands)

    HALBERTSMA, JPK; GOEKEN, LNH

    Passive muscle stretch tests are common practice in physical therapy and rehabilitation medicine. However, the effects of stretching exercises are not well known. With an instrumental straight-leg-raising set-up the extensibility, stiffness, and electromyographic activity of the hamstring muscles

  4. Estimating bridge stiffness using a forced-vibration technique for timber bridge health monitoring

    Science.gov (United States)

    James P. Wacker; Xiping Wang; Brian Brashaw; Robert J. Ross

    2006-01-01

    This paper describes an effort to refine a global dynamic testing technique for evaluating the overall stiffness of timber bridge superstructures. A forced vibration method was used to measure the frequency response of several simple-span, sawn timber beam (with plank deck) bridges located in St. Louis County, Minnesota. Static load deflections were also measured to...

  5. The link between exercise and titin passive stiffness.

    Science.gov (United States)

    Lalande, Sophie; Mueller, Patrick J; Chung, Charles S

    2017-09-01

    What is the topic of this review? This review focuses on how in vivo and molecular measurements of cardiac passive stiffness can predict exercise tolerance and how exercise training can reduce cardiac passive stiffness. What advances does it highlight? This review highlights advances in understanding the relationship between molecular (titin-based) and in vivo (left ventricular) passive stiffness, how passive stiffness modifies exercise tolerance, and how exercise training may be therapeutic for cardiac diseases with increased passive stiffness. Exercise can help alleviate the negative effects of cardiovascular disease and cardiovascular co-morbidities associated with sedentary behaviour; this may be especially true in diseases that are associated with increased left ventricular passive stiffness. In this review, we discuss the inverse relationship between exercise tolerance and cardiac passive stiffness. Passive stiffness is the physical property of cardiac muscle to produce a resistive force when stretched, which, in vivo, is measured using the left ventricular end diastolic pressure-volume relationship or is estimated using echocardiography. The giant elastic protein titin is the major contributor to passive stiffness at physiological muscle (sarcomere) lengths. Passive stiffness can be modified by altering titin isoform size or by post-translational modifications. In both human and animal models, increased left ventricular passive stiffness is associated with reduced exercise tolerance due to impaired diastolic filling, suggesting that increased passive stiffness predicts reduced exercise tolerance. At the same time, exercise training itself may induce both short- and long-term changes in titin-based passive stiffness, suggesting that exercise may be a treatment for diseases associated with increased passive stiffness. Direct modification of passive stiffness to improve exercise tolerance is a potential therapeutic approach. Titin passive stiffness itself may

  6. Constitutive Modelling of Resins in the Stiffness Domain

    Science.gov (United States)

    Klasztorny, M.

    2004-09-01

    An analytic method for inverting the constitutive compliance equations of viscoelasticity for resins is developed. These equations describe the HWKK/H rheological model, which makes it possible to simulate, with a good accuracy, short-, medium- and long-term viscoelastic processes in epoxy and polyester resins. These processes are of first-rank reversible isothermal type. The time histories of deviatoric stresses are simulated with three independent strain history functions of fractional and normal exponential types. The stiffness equations are described by two elastic and six viscoelastic constants having a clear physic meaning (three long-term relaxation coefficients and three relaxation times). The time histories of axiatoric stresses are simulated as perfectly elastic. The inversion method utilizes approximate constitutive stiffness equations of viscoelasticity for the HWKK/H model. The constitutive compliance equations for the model are a basis for determining the exact complex shear stiffness, whereas the approximate constitutive stiffness equations are used for determining the approximate complex shear stiffness. The viscoelastic constants in the stiffness domain are derived by equating the exact and approximate complex shear stiffnesses. The viscoelastic constants are obtained for Epidian 53 epoxy and Polimal 109 polyester resins. The accuracy of the approximate constitutive stiffness equations are assessed by comparing the approximate and exact complex shear stiffnesses. The constitutive stiffness equations for the HWKK/H model are presented in uncoupled (shear/bulk) and coupled forms. Formulae for converting the constants of shear viscoelasticity into the constants of coupled viscoelasticity are given as well.

  7. Arterial stiffness assessment in patients with phenylketonuria

    Science.gov (United States)

    Hermida-Ameijeiras, Alvaro; Crujeiras, Vanesa; Roca, Iria; Calvo, Carlos; Leis, Rosaura; Couce, María-Luz

    2017-01-01

    Abstract In patients with phenylketonuria (PKU) compliant to diet greater tendency to overweight and higher inflammatory biomarkers levels than controls were reported. Although this could lead to atherogenesis, the elastic properties of large arteries in PKU patients have never been assessed. The aim of this study was to assess arterial stiffness measured by applanation tonometry in PKU patients compared to healthy controls. We carried out a cross-sectional study in 41 PKU patients (range age: 6–50 years old) and 41 age- and gender-matched healthy controls. Evaluated data included pharmacological treatment with sapropterin, clinical, and biochemical parameters. Aortic stiffness was assessed noninvasively by applanation tonometry measuring central blood pressure, aortic augmentation index (Aix@HR75), augmentation pressure (AP), and pulse wave velocity (PWV). We found higher PWV in classic PKU patients (6.60 m/second vs 5.26 m/second; P: .044). Percentage of PKU patients with PWV above 90 percentile was higher than controls (14.63% vs 2.32%; P: .048). A positive relationship was observed between the annual Phe median and PWV (r: 0.496; P: .012). PKU subjects with lower Phe tolerance showed more body weight (67.6 kg vs 56.8 kg; P: .012) and more PWV than those with higher Phe tolerance (6.55 m/second vs 5.42 m/second; P: .044). Our data show increased aortic stiffness in PKU patients, measured by applanation tonometry, when compared to healthy controls. Higher Phe levels are associated with a bigger PWV increase, which is not present in those subjects compliant to diet or under sapropterin treatment. These results could have marked effects in both research and clinical daily practice for a proper evaluation of cardiovascular risk in PKU subjects. PMID:29390507

  8. Ambulatory Arterial Stiffness Indexes in Cushing's Syndrome.

    Science.gov (United States)

    Battocchio, Marialberta; Rebellato, Andrea; Grillo, Andrea; Dassie, Francesca; Maffei, Pietro; Bernardi, Stella; Fabris, Bruno; Carretta, Renzo; Fallo, Francesco

    2017-03-01

    Long-standing exposure to endogenous cortisol excess is associated with high cardiovascular risk. The aim of our study was to investigate arterial stiffness, which has been recognized as an independent predictor of adverse cardiovascular outcome, in a group of patients with Cushing's syndrome. Twenty-four patients with Cushing's syndrome (3 males, mean age 49±13 years; 20 pituitary-dependent Cushing's disease and 4 adrenal adenoma) underwent 24-h ambulatory blood pressure monitoring (ABPM) and evaluation of cardiovascular risk factors. The Ambulatory Arterial Stiffness Index (AASI) and symmetric AASI (sAASI) were derived from ABPM tracings. Cushing patients were divided into 8 normotensive (NOR-CUSH) and 16 hypertensive (HYP-CUSH) patients, and were compared with 8 normotensive (NOR-CTR) and 16 hypertensive (HYP-CTR) control subjects, matched for demographic characteristics, 24-h ABPM and cardiometabolic risk factors. The AASI and sAASI indexes were significantly higher in Cushing patients than in controls, either in the normotensive (p=0.048 for AASI and p=0.013 for sAASI) or in the hypertensive (p=0.004 for AASI and p=0.046 for sAASI) group. No difference in metabolic parameters was observed between NOR-CUSH and NOR-CTR or between HYP-CUSH and HYP-CTR groups. AASI and sAASI were both correlated with urinary cortisol in patients with endogenous hypercortisolism (Spearman's rho=0.40, p=0.05, and 0.61, p=0.003, respectively), while no correlation was found in controls. Both AASI and sAASI are increased in Cushing syndrome, independent of BP elevation, and may represent an additional cardiovascular risk factor in this disease. The role of excess cortisol in arterial stiffness has to be further clarified. © Georg Thieme Verlag KG Stuttgart · New York.

  9. Analysis of bearing stiffness variations, contact forces and vibrations in radially loaded double row rolling element bearings with raceway defects

    Science.gov (United States)

    Petersen, Dick; Howard, Carl; Sawalhi, Nader; Moazen Ahmadi, Alireza; Singh, Sarabjeet

    2015-01-01

    A method is presented for calculating and analyzing the quasi-static load distribution and varying stiffness of a radially loaded double row bearing with a raceway defect of varying depth, length, and surface roughness. The method is applied to ball bearings on gearbox and fan test rigs seeded with line or extended outer raceway defects. When balls pass through the defect and lose all or part of their load carrying capacity, the load is redistributed between the loaded balls. This includes balls positioned outside the defect such that good raceway sections are subjected to increased loading when a defect is present. The defective bearing stiffness varies periodically at the ball spacing, and only differs from the good bearing case when balls are positioned in the defect. In this instance, the stiffness decreases in the loaded direction and increases in the unloaded direction. For an extended spall, which always has one or more balls positioned in the defect, this results in an average stiffness over the ball spacing period that is lower in the loaded direction in comparison to both the line spall and good bearing cases. The variation in bearing stiffness due to the defect produces parametric excitations of the bearing assembly. The qualitative character of the vibration response correlates to the character of the stiffness variations. Rapid stiffness changes at a defect exit produce impulses. Slower stiffness variations due to large wavelength waviness features in an extended spall produce low frequency excitation which results in defect components in the velocity spectra. The contact forces fluctuate around the quasi-static loads on the balls, with rapid stiffness changes producing high magnitude impulsive force fluctuations. Furthermore, it is shown that analyzing the properties of the dynamic model linearized at the quasi-static solutions provides greater insight into the time-frequency characteristics of the vibration response. This is demonstrated by relating

  10. Intestinal lymphangiectasia and reversible high liver stiffness.

    Science.gov (United States)

    Milazzo, Laura; Peri, Anna Maria; Lodi, Lucia; Gubertini, Guido; Ridolfo, Anna Lisa; Antinori, Spinello

    2014-08-01

    Primary intestinal lymphangiectasia (PIL) is a protein-losing enteropathy characterized by tortuous and dilated lymph channels of the small bowel. The main symptoms are bilateral lower limb edema, serosal effusions, and vitamin D malabsorption resulting in osteoporosis. We report here a case of long-lasting misdiagnosed PIL with a peculiar liver picture, characterized by a very high stiffness value at transient elastography, which decreased with clinical improvement. The complex interplay between lymphatic and hepatic circulatory system is discussed. © 2014 by the American Association for the Study of Liver Diseases.

  11. Relative stiffness of flat conductor cables

    Science.gov (United States)

    Hankins, J. D.

    1976-01-01

    The measurement of the bending moment required to obtain a given deflection in short lengths of flat conductor cable (FCC) is presented in this report. Experimental data were taken on 10 different samples of FCC and normalized to express all bending moments (relative stiffness factor) in terms of a cable 5.1 cm (2.0 in.) in width. Data are presented in tabular and graphical form for the covenience of designers who may be interested in finding torques exerted on critical components by short lengths of FCC.

  12. Pipe elbow stiffness coefficients including shear and bend flexibility factors for use in direct stiffness codes

    International Nuclear Information System (INIS)

    Perry, R.F.

    1977-01-01

    Historically, developments of computer codes used for piping analysis were based upon the flexibility method of structural analysis. Because of the specialized techniques employed in this method, the codes handled systems composed of only piping elements. Over the past ten years, the direct stiffness method has gained great popularity because of its systematic solution procedure regardless of the type of structural elements composing the system. A great advantage is realized with a direct stiffness code that combines piping elements along with other structural elements such as beams, plates, and shells, in a single model. One common problem, however, has been the lack of an accurate pipe elbow element that would adequately represent the effects of transverse shear and bend flexibility factors. The purpose of the present paper is to present a systematic derivation of the required 12x12 stiffness matrix and load vectors for a three dimensional pipe elbow element which includes the effects of transverse shear and pipe bend flexibility according to the ASME Boiler and Pressure Vessel Code, Section III. The results are presented analytically and as FORTRAN subroutines to be directly incorporated into existing direct stiffness codes. (Auth.)

  13. Stiffness Evolution in Frozen Sands Subjected to Stress Changes

    KAUST Repository

    Dai, Sheng; Santamarina, Carlos

    2017-01-01

    Sampling affects all soils, including frozen soils and hydrate-bearing sediments. The authors monitor the stiffness evolution of frozen sands subjected to various temperature and stress conditions using an oedometer cell instrumented with P-wave transducers. Experimental results show the stress-dependent stiffness of freshly remolded sands, the dominant stiffening effect of ice, creep after unloading, and the associated exponential decrease in stiffness with time. The characteristic time for stiffness loss during creep is of the order of tens of minutes; therefore it is inevitable that frozen soils experience sampling disturbances attributable to unloading. Slow unloading minimizes stiffness loss; conversely, fast unloading causes a pronounced reduction in stiffness probably attributable to the brittle failure of ice or ice-mineral bonding.

  14. Stiffness Evolution in Frozen Sands Subjected to Stress Changes

    KAUST Repository

    Dai, Sheng

    2017-04-21

    Sampling affects all soils, including frozen soils and hydrate-bearing sediments. The authors monitor the stiffness evolution of frozen sands subjected to various temperature and stress conditions using an oedometer cell instrumented with P-wave transducers. Experimental results show the stress-dependent stiffness of freshly remolded sands, the dominant stiffening effect of ice, creep after unloading, and the associated exponential decrease in stiffness with time. The characteristic time for stiffness loss during creep is of the order of tens of minutes; therefore it is inevitable that frozen soils experience sampling disturbances attributable to unloading. Slow unloading minimizes stiffness loss; conversely, fast unloading causes a pronounced reduction in stiffness probably attributable to the brittle failure of ice or ice-mineral bonding.

  15. Elastic metamaterial beam with remotely tunable stiffness

    Energy Technology Data Exchange (ETDEWEB)

    Qian, Wei [University of Michigan–Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240 (China); Yu, Zhengyue [School of Naval Architecture, Ocean & Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Wang, Xiaole [School of Electronic Information and Electrical Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Lai, Yun [College of Physics, Optoelectronics and Energy & Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006 (China); Yellen, Benjamin B., E-mail: yellen@duke.edu [University of Michigan–Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240 (China); Department of Mechanical Engineering and Materials Science, Duke University, P.O. Box 90300, Hudson Hall, Durham, North Carolina 27708 (United States)

    2016-02-07

    We demonstrate a dynamically tunable elastic metamaterial, which employs remote magnetic force to adjust its vibration absorption properties. The 1D metamaterial is constructed from a flat aluminum beam milled with a linear array of cylindrical holes. The beam is backed by a thin elastic membrane, on which thin disk-shaped permanent magnets are mounted. When excited by a shaker, the beam motion is tracked by a Laser Doppler Vibrometer, which conducts point by point scanning of the vibrating element. Elastic waves are unable to propagate through the beam when the driving frequency excites the first elastic bending mode in the unit cell. At these frequencies, the effective mass density of the unit cell becomes negative, which induces an exponentially decaying evanescent wave. Due to the non-linear elastic properties of the membrane, the effective stiffness of the unit cell can be tuned with an external magnetic force from nearby solenoids. Measurements of the linear and cubic static stiffness terms of the membrane are in excellent agreement with experimental measurements of the bandgap shift as a function of the applied force. In this implementation, bandgap shifts by as much as 40% can be achieved with ∼30 mN of applied magnetic force. This structure has potential for extension in 2D and 3D, providing a general approach for building dynamically tunable elastic metamaterials for applications in lensing and guiding elastic waves.

  16. Impact of matrix stiffness on fibroblast function

    Energy Technology Data Exchange (ETDEWEB)

    El-Mohri, Hichem; Wu, Yang; Mohanty, Swetaparna; Ghosh, Gargi, E-mail: gargi@umich.edu

    2017-05-01

    Chronic non-healing wounds, caused by impaired production of growth factors and reduced vascularization, represent a significant burden to patients, health care professionals, and health care system. While several wound dressing biomaterials have been developed, the impact of the mechanical properties of the dressings on the residing cells and consequently on the healing of the wounds is largely overlooked. The primary focus of this study is to explore whether manipulation of the substrate mechanics can regulate the function of fibroblasts, particularly in the context of their angiogenic activity. A photocrosslinkable hydrogel platform with orthogonal control over gel modulus and cell adhesive sites was developed to explore the quantitative relationship between ECM compliance and fibroblast function. Increase in matrix stiffness resulted in enhanced fibroblast proliferation and stress fiber formation. However, the angiogenic activity of fibroblasts was found to be optimum when the cells were seeded on compliant matrices. Thus, the observations suggest that the stiffness of the wound dressing material may play an important role in the progression of wound healing. - Highlights: • Proliferation and stress fiber formation of fibroblasts increase with increasing matrix mechanics. • Cell area correlates with the growth of fibroblasts. • Angiogenic activity of fibroblasts optimum when cells seeded on compliant gels.

  17. Multifunctional Stiff Carbon Foam Derived from Bread.

    Science.gov (United States)

    Yuan, Ye; Ding, Yujie; Wang, Chunhui; Xu, Fan; Lin, Zaishan; Qin, Yuyang; Li, Ying; Yang, Minglong; He, Xiaodong; Peng, Qingyu; Li, Yibin

    2016-07-06

    The creation of stiff yet multifunctional three-dimensional porous carbon architecture at very low cost is still challenging. In this work, lightweight and stiff carbon foam (CF) with adjustable pore structure was prepared by using flour as the basic element via a simple fermentation and carbonization process. The compressive strength of CF exhibits a high value of 3.6 MPa whereas its density is 0.29 g/cm(3) (compressive modulus can be 121 MPa). The electromagnetic interference (EMI) shielding effectiveness measurements (specific EMI shielding effectiveness can be 78.18 dB·cm(3)·g(-1)) indicate that CF can be used as lightweight, effective shielding material. Unlike ordinary foam structure materials, the low thermal conductivity (lowest is 0.06 W/m·K) with high resistance to fire makes CF a good candidate for commercial thermal insulation material. These results demonstrate a promising method to fabricate an economical, robust carbon material for applications in industry as well as topics regarding environmental protection and improvement of energy efficiency.

  18. Elastic metamaterial beam with remotely tunable stiffness

    Science.gov (United States)

    Qian, Wei; Yu, Zhengyue; Wang, Xiaole; Lai, Yun; Yellen, Benjamin B.

    2016-02-01

    We demonstrate a dynamically tunable elastic metamaterial, which employs remote magnetic force to adjust its vibration absorption properties. The 1D metamaterial is constructed from a flat aluminum beam milled with a linear array of cylindrical holes. The beam is backed by a thin elastic membrane, on which thin disk-shaped permanent magnets are mounted. When excited by a shaker, the beam motion is tracked by a Laser Doppler Vibrometer, which conducts point by point scanning of the vibrating element. Elastic waves are unable to propagate through the beam when the driving frequency excites the first elastic bending mode in the unit cell. At these frequencies, the effective mass density of the unit cell becomes negative, which induces an exponentially decaying evanescent wave. Due to the non-linear elastic properties of the membrane, the effective stiffness of the unit cell can be tuned with an external magnetic force from nearby solenoids. Measurements of the linear and cubic static stiffness terms of the membrane are in excellent agreement with experimental measurements of the bandgap shift as a function of the applied force. In this implementation, bandgap shifts by as much as 40% can be achieved with ˜30 mN of applied magnetic force. This structure has potential for extension in 2D and 3D, providing a general approach for building dynamically tunable elastic metamaterials for applications in lensing and guiding elastic waves.

  19. Direct measurement of the intrinsic ankle stiffness during standing.

    Science.gov (United States)

    Vlutters, M; Boonstra, T A; Schouten, A C; van der Kooij, H

    2015-05-01

    Ankle stiffness contributes to standing balance, counteracting the destabilizing effect of gravity. The ankle stiffness together with the compliance between the foot and the support surface make up the ankle-foot stiffness, which is relevant to quiet standing. The contribution of the intrinsic ankle-foot stiffness to balance, and the ankle-foot stiffness amplitude dependency remain a topic of debate in the literature. We therefore developed an experimental protocol to directly measure the bilateral intrinsic ankle-foot stiffness during standing balance, and determine its amplitude dependency. By applying fast (40 ms) ramp-and-hold support surface rotations (0.005-0.08 rad) during standing, reflexive contributions could be excluded, and the amplitude dependency of the intrinsic ankle-foot stiffness was investigated. Results showed that reflexive activity could not have biased the torque used for estimating the intrinsic stiffness. Furthermore, subjects required less recovery action to restore balance after bilateral rotations in opposite directions compared to rotations in the same direction. The intrinsic ankle-foot stiffness appears insufficient to ensure balance, ranging from 0.93±0.09 to 0.44±0.06 (normalized to critical stiffness 'mgh'). This implies that changes in muscle activation are required to maintain balance. The non-linear stiffness decrease with increasing rotation amplitude supports the previous published research. With the proposed method reflexive effects can be ruled out from the measured torque without any model assumptions, allowing direct estimation of intrinsic stiffness during standing. Copyright © 2015 Elsevier Ltd. All rights reserved.

  20. Ultrasound shear wave elastography in the assessment of passive biceps brachii muscle stiffness: influences of sex and elbow position.

    Science.gov (United States)

    Chen, Johnson; O'Dell, Michael; He, Wen; Du, Li-Juan; Li, Pai-Chi; Gao, Jing

    To assess differences in biceps brachii muscle (BBM) stiffness as evaluated by ultrasound shear wave elastography (SWE). The passive stiffness of the BBM was quantified with shear wave velocity (SWV) measurements obtained from 10 healthy volunteers (5 men and 5 women, mean age 50years, age range 42-63 years) with the elbow at full extension and 30° flexion in this IRB-approved study. Potential differences between two depths within the muscle, two elbow positions, the two arms, and sexes were assessed by using two-tailed t-test. The reproducibility of SWV measurements was tested by using intraclass correlation coefficient (ICC). Significantly higher passive BBM stiffness was found at full elbow extension compared to 30° of flexion (p≤0.00006 for both arms). Significantly higher passive stiffness in women was seen for the right arm (p=0.04 for both elbow positions). Good correlation of shear wave velocity measured at the different depths. The ICC for interobserver and intraobserver variation was high. SWE is a reliable quantitative tool for assessing BBM stiffness, with differences in stiffness based on elbow position demonstrated and based on sex suggested. Copyright © 2017 Elsevier Inc. All rights reserved.

  1. Formal Solutions for Polarized Radiative Transfer. III. Stiffness and Instability

    Science.gov (United States)

    Janett, Gioele; Paganini, Alberto

    2018-04-01

    Efficient numerical approximation of the polarized radiative transfer equation is challenging because this system of ordinary differential equations exhibits stiff behavior, which potentially results in numerical instability. This negatively impacts the accuracy of formal solvers, and small step-sizes are often necessary to retrieve physical solutions. This work presents stability analyses of formal solvers for the radiative transfer equation of polarized light, identifies instability issues, and suggests practical remedies. In particular, the assumptions and the limitations of the stability analysis of Runge–Kutta methods play a crucial role. On this basis, a suitable and pragmatic formal solver is outlined and tested. An insightful comparison to the scalar radiative transfer equation is also presented.

  2. Finite Element Analysis of Single Cell Stiffness Measurements Using PZT-Integrated Buckling Nanoneedles

    Directory of Open Access Journals (Sweden)

    Maryam Alsadat Rad

    2016-12-01

    Full Text Available This paper proposes a new technique for real-time single cell stiffness measurement using lead zirconate titanate (PZT-integrated buckling nanoneedles. The PZT and the buckling part of the nanoneedle have been modelled and validated using the ABAQUS software. The two parts are integrated together to function as a single unit. After calibration, the stiffness, Young’s modulus, Poisson’s ratio and sensitivity of the PZT-integrated buckling nanoneedle have been determined to be 0.7100 N·m−1, 123.4700 GPa, 0.3000 and 0.0693 V·m·N−1, respectively. Three Saccharomyces cerevisiae cells have been modelled and validated based on compression tests. The average global stiffness and Young’s modulus of the cells are determined to be 10.8867 ± 0.0094 N·m−1 and 110.7033 ± 0.0081 MPa, respectively. The nanoneedle and the cell have been assembled to measure the local stiffness of the single Saccharomyces cerevisiae cells The local stiffness, Young’s modulus and PZT output voltage of the three different size Saccharomyces cerevisiae have been determined at different environmental conditions. We investigated that, at low temperature the stiffness value is low to adapt to the change in the environmental condition. As a result, Saccharomyces cerevisiae becomes vulnerable to viral and bacterial attacks. Therefore, the proposed technique will serve as a quick and accurate process to diagnose diseases at early stage in a cell for effective treatment.

  3. Lamb Wave Stiffness Characterization of Composites Undergoing Thermal-Mechanical Aging

    Science.gov (United States)

    Seale, Michael D.; Madaras, Eric I.

    2004-01-01

    The introduction of new, advanced composite materials into aviation systems requires a thorough understanding of the long term effects of combined thermal and mechanical loading upon those materials. Analytical methods investigating the effects of intense thermal heating combined with mechanical loading have been investigated. The damage mechanisms and fatigue lives were dependent on test parameters as well as stress levels. Castelli, et al. identified matrix dominated failure modes for out-of-phase cycling and fiber dominated damage modes for in-phase cycling. In recent years, ultrasonic methods have been developed that can measure the mechanical stiffness of composites. To help evaluate the effect of aging, a suitably designed Lamb wave measurement system is being used to obtain bending and out-of-plane stiffness coefficients of composite laminates undergoing thermal-mechanical loading. The system works by exciting an antisymmetric Lamb wave and calculating the velocity at each frequency from the known transducer separation and the measured time-of-flight. The same peak in the waveforms received at various distances is used to measure the time difference between the signals. The velocity measurements are accurate and repeatable to within 1% resulting in reconstructed stiffness values repeatable to within 4%. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the dispersion curve. A mechanical scanner is used to move the sensors over the surface to map the time-of-flight, velocity, or stiffnesses of the entire specimen. Access to only one side of the material is required and no immersion or couplants are required because the sensors are dry coupled to the surface of the plate. In this study, the elastic stiffnesses D(sub 11), D(sub 22), A(sub 44), and A(sub 55) as well as time-of-flight measurements for composite samples that have undergone combined thermal and mechanical aging for

  4. A novel variable stiffness mechanism for dielectric elastomer actuators

    Science.gov (United States)

    Li, Wen-Bo; Zhang, Wen-Ming; Zou, Hong-Xiang; Peng, Zhi-Ke; Meng, Guang

    2017-08-01

    In this paper, a novel variable stiffness mechanism is proposed for the design of a variable stiffness dielectric elastomer actuator (VSDEA) which combines a flexible strip with a DEA in a dielectric elastomer minimum energy structure. The DEA induces an analog tuning of the transverse curvature of the strip, thus conveniently providing a voltage-controllable flexural rigidity. The VSDEA tends to be a fully flexible and compact structure with the advantages of simplicity and fast response. Both experimental and theoretical investigations are carried out to reveal the variable stiffness performances of the VSDEA. The effect of the clamped location on the bending stiffness of the VSDEA is analyzed, and then effects of the lengths, the loading points and the applied voltages on the bending stiffness are experimentally investigated. An analytical model is developed to verify the availability of this variable stiffness mechanism, and the theoretical results demonstrate that the bending stiffness of the VSDEA decreases as the applied voltage increases, which agree well with the experimental data. Moreover, the experimental results show that the maximum change of the relative stiffness can reach about 88.80%. It can be useful for the design and optimization of active variable stiffness structures and DEAs for soft robots, vibration control, and morphing applications.

  5. Stiffness and the automatic selection of ODE codes

    International Nuclear Information System (INIS)

    Shampine, L.F.

    1984-01-01

    The author describes the basic ideas behind the most popular methods for the numerical solution of ordinary differential equations (ODEs). He takes up the qualitative behavior of solutions of ODEs and its relation ot the propagation of numerical error. Codes for ODEs are intended either for stiff problems or for non-stiff problems. The difference is explained. Users of codes do not have the information needed to recognize stiffness. A code, DEASY, which automatically recognizes stiffness and selects a suitable method is described

  6. Fatigue crack paths under the influence of changes in stiffness

    Directory of Open Access Journals (Sweden)

    G. Kullmer

    2016-02-01

    Full Text Available An important topic of the Collaborative Research Centre TRR 30 of the Deutsche Forschungsgemeinschaft (DFG is the crack growth behaviour in graded materials. In addition, the growth of cracks in the neighbourhood of regions and through regions with different material properties belongs under this topic. Due to the different material properties, regions with differing stiffness compared to the base material may arise. Regions with differing stiffness also arise from ribs, grooves or boreholes. Since secure findings on the propagation behaviour of fatigue cracks are essential for the evaluation of the safety of components and structures, the growth of cracks near changes in stiffness has to be considered, too. Depending on the way a crack penetrates the zone of influence of such a change in stiffness and depending on whether this region is more compliant or stiffer than the surrounding area the crack may grow towards or away from this region. Both cases result in curved crack paths that cannot be explained only by the global loading situation. To evaluate the influence of regions with differing stiffness on the path of fatigue cracks the paths and the stress intensity factors of cracks growing near and through regions with differing stiffness are numerically determined with the program system ADAPCRACK3D. Therefore, arrangements of changes in stiffness modelled as material inclusions with stiffness properties different from the base material or modelled as ribs and grooves are systematically varied to develop basic conclusions about the crack growth behaviour near and through changes in stiffness.

  7. On prestress stiffness analysis of bolt-plate contact assemblies

    DEFF Research Database (Denmark)

    Pedersen, Niels Leergaard; Pedersen, Pauli

    2008-01-01

    , but with finite element (FE) and contact analysis, it is possible to find the stiffness of the member. In the case of many connections and for practical applications, it is not suitable to make a full FE analysis. The purpose of the present paper is to find simplified expressions for the stiffness of the member......, including the case when the width of the member is limited. The calculation of the stiffness is based on the FE, including the solution to the contact problem, and we express the stiffness as a function of the elastic energy in the structure, whereby the definition of the displacements related...

  8. Ball Bearing Stiffnesses- A New Approach Offering Analytical Expressions

    Science.gov (United States)

    Guay, Pascal; Frikha, Ahmed

    2015-09-01

    Space mechanisms use preloaded ball bearings in order to withstand the severe vibrations during launch.The launch strength requires the calculation of the bearing stiffness, but this calculation is complex. Nowadays, there is no analytical expression that gives the stiffness of a bearing. Stiffness is computed using an iterative algorithm such as Newton-Raphson, to solve the nonlinear system of equations.This paper aims at offering a simplified analytical approach, based on the assumption that the contact angle is constant. This approach gives analytical formulas of the stiffness of preloaded ball bearing.

  9. Low frequency noise reduction using stiff light composite panels

    Institute of Scientific and Technical Information of China (English)

    DENG Yongchang; LIN Weizheng

    2003-01-01

    The experiment presented in this paper is to investigate and analyze the noise reduction at low frequency using stiff light composite panels. Since these composite panels are made of lightweight and stiff materials, this actuation strategy will enable the creation of composite panels for duct noise control without using traditional heavy structural mass. The results suggest that the mass-spring resonance absorption in the case of a comparatively stiff thick panel with a thin flexible plate is more efficient with minimum weight, when subjected to low-frequency (<500 Hz). The efficiency of the panel absorber depends on the mass of the thin flexible plate and the stiffness of the panel.

  10. [Odontoid bending stiffness after anterior fixation with a single lag screw: biomechanical study].

    Science.gov (United States)

    Buchvald, P; Čapek, L; Barsa, P

    2015-01-01

    PURPOSE OF THE STUDY The aim of the experiment was to compare the bending stiffness of an intact odontoid process with bending stiffness after its simulated type II fracture was fixed with a single lag screw. The experiment was done with a desire to answer the question of whether a single osteosynthetic screw is sufficient for good fixation of a type II odontoid fracture. MATERIAL AND METHODS The C2 vertebrae of six cadavers were used. With simultaneous measurement of odontoid bending stiffness, the occurrence of a fracture (type IIA, Grauer's modification of the Anderson- D'Alonzo classification) was simulated using action exerted by a tearing machine in the direction perpendicular to the odontoid axis. Each odontoid fracture was subsequently treated by direct osteosynthesis with a single lag screw inserted in the axial direction by a standard surgical procedure in order to provide conditions similar to those achieved by routine surgical management. The treated odontoid process was subsequently subjected to the same tearing machine loading as applied to it at the start of the experiment. The bending stiffness measured was then compared with that found before the fracture occurred. The results were statistically evaluated by the t-test for paired samples at the level of significance α = 0.05. RESULTS The average value of bending stiffness for odontoid processes of intact vertebrae at the moment of fracture occurrence was 318.3 N/mm. After single axial lag screw fixation of the fracture, the average bending stiffness for the odontoid processes treated was 331.3 N/mm. DISCUSSION Higher values of bending stiffness after screw fixation were found in all specimens and, in comparison with the values recorded before simulated fractures, the increase was statistically significant. CONCLUSIONS The results of our measurements suggest that the single lag screw fixation of a type IIA odontoid fracture will provide better stability for the fracture fragment-C2 body complex on

  11. Estimation of axial stiffness of plant fibres from compaction of non-woven mats

    International Nuclear Information System (INIS)

    Gamstedt, E K; Bommier, E; Madsen, B

    2014-01-01

    Plant fibres are known to show a large variability in stiffness, which makes it time-consuming to experimentally characterize this property by conventional tensile testing. In this work, an alternative method is used, where the average fibre stiffness is back-calculated from compaction tests of in-plane randomly oriented fibre mats. The model by Toll is used to relate the load–displacement curve from the test to the Young modulus of the fibre, taking into account the natural variability in fibre cross section. Several tests have been performed on hemp fibre mats and compared with results from single-fibre tensile testing. The average back-calculated Young's modulus of the fibres was 45 GPa, whereas the average value from tensile testing ranged from 30 to 60 GPa. The straightforward compaction test can be useful in ranking of fibre stiffness, provided that the mat is composed of well-separated fibres and not of twisted yarns. (paper)

  12. Pulling a polymer with anisotropic stiffness near a sticky wall

    International Nuclear Information System (INIS)

    Tabbara, R; Owczarek, A L

    2012-01-01

    We solve exactly a two-dimensional partially directed walk model of a semi-flexible polymer that has one end tethered to a sticky wall, while a pulling force away from the adsorbing surface acts on the free end of the walk. This model generalizes a number of previously considered adsorption models by incorporating individual horizontal and vertical stiffness effects, in competition with a variable pulling angle. A solution to the corresponding generating function is found by means of the kernel method. While the phases and related phase transitions are similar in nature to those found previously the analysis of the model in terms of its physical variables highlights various novel structures in the shapes of the phase diagrams and related behaviour of the polymer. We review the results of previously considered sub-cases, augmenting these findings to include analysis with respect to the model’s physical variables—namely, temperature, pulling force, pulling angle away from the surface, stiffness strength and the ratio of vertical to horizontal stiffness potentials, with our subsequent analysis for the general model focusing on the effect that stiffness has on this pulling angle range. In analysing the model with stiffness we also pay special attention to the case where only vertical stiffness is included. The physical analysis of this case reveals behaviour more closely resembling that of an upward pulling force acting on a polymer than it does of a model where horizontal stiffness acts. The stiffness–temperature phase diagram exhibits re-entrance for low temperatures, previously only seen for three-dimensional or co-polymer models. For the most general model we delineate the shift in the physical behaviour as we change the ratio of vertical to horizontal stiffness between the horizontal-only and the vertical-only stiffness regimes. We find that a number of distinct physical characteristics will only be observed for a model where the vertical stiffness dominates

  13. The relationship between various measures of obesity and arterial stiffness in morbidly obese patients

    Directory of Open Access Journals (Sweden)

    Røislien J

    2011-02-01

    Full Text Available Abstract Background Obesity is associated with increased risk of cardiovascular disease. Arterial stiffness assessed by carotid femoral pulse wave velocity (PWV is an independent predictor of cardiovascular morbidity and mortality. We aimed to investigate how various measures of body composition affect arterial stiffness. Methods This is an analysis of cross-sectional baseline data from a controlled clinical trial addressing changes in arterial stiffness after either surgery or lifestyle intervention in a population of morbidly obese patients. High-fidelity applanation tonometry (Millar®, Sphygmocor® was used to measure pulse wave velocity (PWV. Carotid femoral PWV is a direct measure of arterial stiffness and is considered to be the gold standard method. The Inbody 720 Body Composition Analyzer was used for bioelectrical impedance analysis (BIA. Spearman's correlation, independent samples t-test, chi-square tests, Fisher's exact test and multiple linear regression analyses were used as statistical methods. Results A total of 133 patients (79 women, with a mean (SD age of 43 (11 years were included in the study. Men had a significantly higher prevalence of obesity related comorbidities and significantly higher PWV, 9.1 (2.0 m/s vs. 8.1 (1.8 m/s, p = 0.003, than women. In the female group, PWV was positively correlated with WC, WHtR, BMI and visceral fat area. In the male group, PWV was negatively correlated with BMI. Multiple linear regression analysis showed that increasing BMI, WC, WHtR, visceral fat area and fat mass were independently associated with higher PWV in women, but not in men, after adjustment for age, hypertension and type 2 diabetes. Conclusion Most measures of general and abdominal obesity were predictors of arterial stiffness in female morbidly obese patients. Trial registration ClinicalTrials.gov Identifier NCT00626964

  14. Salt-induced aggregation of stiff polyelectrolytes

    International Nuclear Information System (INIS)

    Fazli, Hossein; Mohammadinejad, Sarah; Golestanian, Ramin

    2009-01-01

    Molecular dynamics simulation techniques are used to study the process of aggregation of highly charged stiff polyelectrolytes due to the presence of multivalent salt. The dominant kinetic mode of aggregation is found to be the case of one end of one polyelectrolyte meeting others at right angles, and the kinetic pathway to bundle formation is found to be similar to that of flocculation dynamics of colloids as described by Smoluchowski. The aggregation process is found to favor the formation of finite bundles of 10-11 filaments at long times. Comparing the distribution of the cluster sizes with the Smoluchowski formula suggests that the energy barrier for the aggregation process is negligible. Also, the formation of long-lived metastable structures with similarities to the raft-like structures of actin filaments is observed within a range of salt concentration.

  15. Discrete computational mechanics for stiff phenomena

    KAUST Repository

    Michels, Dominik L.

    2016-11-28

    Many natural phenomena which occur in the realm of visual computing and computational physics, like the dynamics of cloth, fibers, fluids, and solids as well as collision scenarios are described by stiff Hamiltonian equations of motion, i.e. differential equations whose solution spectra simultaneously contain extremely high and low frequencies. This usually impedes the development of physically accurate and at the same time efficient integration algorithms. We present a straightforward computationally oriented introduction to advanced concepts from classical mechanics. We provide an easy to understand step-by-step introduction from variational principles over the Euler-Lagrange formalism and the Legendre transformation to Hamiltonian mechanics. Based on such solid theoretical foundations, we study the underlying geometric structure of Hamiltonian systems as well as their discrete counterparts in order to develop sophisticated structure preserving integration algorithms to efficiently perform high fidelity simulations.

  16. Effect of exercise on arterial stiffness

    DEFF Research Database (Denmark)

    Montero, David; Andersen, Andreas Breenfeldt; Oberholzer, Laura

    2017-01-01

    points (P = 0.196) although a linear decreasing trend was detected (P = 0.016). CONCLUSIONS: Central AS augments during a conventional ET intervention that effectively enhances aerobic exercise capacity in young individuals. This suggests that normal, healthy elastic arteries are not amendable......BACKGROUND: Whether arterial stiffness (AS) can be improved by regular exercise in healthy individuals remains equivocal according to cross-sectional and longitudinal studies assessing arterial properties at discrete time points. The purpose of the present study was to pinpoint the time course......), in 9 previously untrained healthy normotensive adults (27 ± 4 years) with no history of cardiovascular disease. Exercise capacity was assessed by maximal oxygen consumption (VO2max) elicited by incremental ergometry. RESULTS: VO2max increased throughout the ET intervention (+12% from week 0 to week 8...

  17. Temperature Effects on Stiffness Moduli of Reservoir Sandstone from the Deep North Sea

    DEFF Research Database (Denmark)

    Orlander, Tobias; Andreassen, Katrine Alling; Fabricius, Ida Lykke

    We investigate effect of testing temperature on the dynamic frame stiffness of quartz-bearing North Sea sandstone from depths of 5 km. We show that at low stress levels, the rock frame stiffens with increasing temperature and we propose an explanation for the controlling mechanisms. While...... temperature. This is unfortunate and hence, we designed a testing program with the intension of separating and quantifying effects of temperature and stress, specifically for the sandstone material subject to this study....

  18. A comparative study on free vibration analysis of delaminated torsion stiff and bending stiff composite shells

    International Nuclear Information System (INIS)

    Dey, Sudip; Karmakar, Amit

    2013-01-01

    This paper presents a finite element method to compare the effects of delamination on free vibration of graphite-epoxy bending stiff and torsion stiff composite pretwisted shallow conical shells. The generalized dynamic equilibrium equation is derived from Lagrange's equation of motion neglecting the Coriolis effect for moderate rotational speeds. An eight noded isoparametric plate bending element is employed incorporating rotary inertia and effects of transverse shear deformation based on Mindlin's theory. The multipoint constraint; algorithm is utilized to ensure the compatibility of deformation and equilibrium of resultant forces and moments at the delamination crack front. The standard eigen value problem is solved by applying the QR iteration algorithm. Mode shapes for typical configurations are also depicted. Numerical results obtained are the first known non-dimensional frequencies which could serve as reference solutions for the future investigators.

  19. Mechanically stiff, electrically conductive composites of polymers and carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Worsley, Marcus A.; Kucheyev, Sergei O.; Baumann, Theodore F.; Kuntz, Joshua D.; Satcher, Jr., Joe H.; Hamza, Alex V.

    2017-10-17

    Using SWNT-CA as scaffolds to fabricate stiff, highly conductive polymer (PDMS) composites. The SWNT-CA is immersing in a polymer resin to produce a SWNT-CA infiltrated with a polymer resin. The SWNT-CA infiltrated with a polymer resin is cured to produce the stiff and electrically conductive composite of carbon nanotube aerogel and polymer.

  20. Mechanically stiff, electrically conductive composites of polymers and carbon nanotubes

    Science.gov (United States)

    Worsley, Marcus A.; Kucheyev, Sergei O.; Baumann, Theodore F.; Kuntz, Joshua D.; Satcher, Jr., Joe H.; Hamza, Alex V.

    2015-07-21

    Using SWNT-CA as scaffolds to fabricate stiff, highly conductive polymer (PDMS) composites. The SWNT-CA is immersing in a polymer resin to produce a SWNT-CA infiltrated with a polymer resin. The SWNT-CA infiltrated with a polymer resin is cured to produce the stiff and electrically conductive composite of carbon nanotube aerogel and polymer.

  1. A prototype of a novel energy efficient variable stiffness actuator

    NARCIS (Netherlands)

    Visser, L.C.; Carloni, Raffaella; Klijnstra, F.; Stramigioli, Stefano

    In this work, we present a proof of concept of a novel variable stiffness actuator. The actuator design is based on the conceptual design proposed in earlier work, and is such that the apparent output stiffness of the actuator can be changed independently of the output position and without any

  2. Optimization of a quasi-zero-stiffness isolator

    International Nuclear Information System (INIS)

    Carrella, A.; Brennan, M. J.; Waters, T. P.

    2007-01-01

    The frequency range over which a mount can isolate a mass from a vibrating base (or vice versa) is often limited by the mount stiffness required to support the weight of the mass. This compromise can be made more favourable by employing non-linear mounts with a softening spring characteristic such that small excursions about the static equilibrium position result in small dynamic spring forces and a correspondingly low natural frequency. This paper concerns the force-displacement characteristic of a so-called quasi-zero-stiffness (QZS) mechanism which is characterised by an appreciable static stiffness but very small (theoretically zero) dynamic stiffness. The mechanism studied comprises a vertical spring acting in parallel with two further springs which, when inclined at an appropriate angle to the vertical, produce a cancelling negative stiffness effect. Analysis of the system shows that a QZS characteristic can be obtained if the systems parameters (angle of inclination and ratio of spring stiffness) are opportunely chosen. By introducing the additional criterion that the displacement of the system be largest without exceeding a desired (low) value of stiffness an optimal set of parameter values is derived. Under sufficiently large displacements the stiffness of the QZS mechanism can eventually exceed that of the simple mass-spring system and criteria for this detrimental scenario to arise are presented

  3. Arterial Stiffness in Children: Pediatric Measurement and Considerations

    Science.gov (United States)

    Savant, Jonathan D.; Furth, Susan L.; Meyers, Kevin E.C.

    2014-01-01

    Background Arterial stiffness is a natural consequence of aging, accelerated in certain chronic conditions, and predictive of cardiovascular events in adults. Emerging research suggests the importance of arterial stiffness in pediatric populations. Methods There are different indices of arterial stiffness. The present manuscript focuses on carotid-femoral pulse wave velocity and pulse wave analysis, although other methodologies are discussed. Also reviewed are specific measurement considerations for pediatric populations and the literature describing arterial stiffness in children with certain chronic conditions (primary hypertension, obesity, diabetes, chronic kidney disease, hypercholesterolemia, genetic syndromes involving vasculopathy, and solid organ transplant recipients). Conclusions The measurement of arterial stiffness in children is feasible and, under controlled conditions, can give accurate information about the underlying state of the arteries. This potentially adds valuable information about the functionality of the cardiovascular system in children with a variety of chronic diseases well beyond that of the brachial artery blood pressure. PMID:26587447

  4. Relationship between glycaemic levels and arterial stiffness in non-diabetic adults.

    Science.gov (United States)

    Cavero-Redondo, Iván; Martínez-Vizcaíno, Vicente; Álvarez-Bueno, Celia; Recio-Rodríguez, José Ignacio; Gómez-Marcos, Manuel Ángel; García-Ortiz, Luis

    2018-01-23

    To examine, in a non-diabetic population, whether the association between arterial stiffness and glycaemic levels depends on the test used as a glycaemic indicator, fasting plasma glucose (FPG) or glycated haemoglobin A1c (HbA1c). A cross-sectional analysis of a 220 non-diabetic subsample from the EVIDENT II study in which FPG, HbA1c and arterial stiffness-related parameters (pulse wave velocity, radial and central augmentation index, and central pulse pressure) were determined. Mean differences in arterial stiffness-related parameters by HbA1c and FPG tertiles were tested using analysis of covariance. All means of arterial stiffness-related parameters increased by HbA1c tertiles, although mean differences were only statistically significant in pulse wave velocity (p ≤.001), even after controlling for potential confounders (HbA1c <5.30% = 6.88 m/s; HbA1c 5.30%-5.59% = 7.06 m/s; and HbA1c ≥5.60% = 8.16 m/s, p =.004). Conversely, mean differences in pulse wave velocity by FPG tertiles did not reach statistically significant differences after controlling for potential confounders (FPG 4.44 mmol/l = 7.18 m/s; FPG 4.44 mmol/l-4.87 mmol/l = 7.26 m/s; and FPG ≥4.88 mmol/l = 7.93 m/s, p =.066). Glucose levels in a non-diabetic population were associated with arterial stiffness but better when levels were determined using HbA1c. Copyright © 2017 Elsevier España, S.L.U. All rights reserved.

  5. Indentation stiffness does not discriminate between normal and degraded articular cartilage.

    Science.gov (United States)

    Brown, Cameron P; Crawford, Ross W; Oloyede, Adekunle

    2007-08-01

    Relative indentation characteristics are commonly used for distinguishing between normal healthy and degraded cartilage. The application of this parameter in surgical decision making and an appreciation of articular cartilage biomechanics has prompted us to hypothesise that it is difficult to define a reference stiffness to characterise normal articular cartilage. This hypothesis is tested for validity by carrying out biomechanical indentation of articular cartilage samples that are characterised as visually normal and degraded relative to proteoglycan depletion and collagen disruption. Compressive loading was applied at known strain rates to visually normal, artificially degraded and naturally osteoarthritic articular cartilage and observing the trends of their stress-strain and stiffness characteristics. While our results demonstrated a 25% depreciation in the stiffness of individual samples after proteoglycan depletion, they also showed that when compared to the stiffness of normal samples only 17% lie outside the range of the stress-strain behaviour of normal samples. We conclude that the extent of the variability in the properties of normal samples, and the degree of overlap (81%) of the biomechanical properties of normal and degraded matrices demonstrate that indentation data cannot form an accurate basis for distinguishing normal from abnormal articular cartilage samples with consequences for the application of this mechanical process in the clinical environment.

  6. Effects of no stiffness inside unbonded tendon ducts on the behavior of prestressd concrete containment vessels

    Energy Technology Data Exchange (ETDEWEB)

    Noh, Sang Hoon; Kwak, Hyo Gyong [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of); Jung, Rae Young; Noh, Sang Hoon [Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of)

    2016-06-15

    The numerical simulation methodologies to evaluate the structural behaviors of prestressed concrete containment vessels (PCCVs) have been substantially developed in recent decades. However, there remain several issues to be investigated more closely to narrow the gap between test results and numerical simulations. As one of those issues, the effects of no stiffness inside unbonded tendon ducts on the behavior of PCCVs are investigated in this study. Duct holes for prestressing cables' passing are provided inside the containment wall and dome in one to three directions for general PCCVs. The specific stress distribution along the periphery of the prestressing duct hole and the loss of stiffness inside the hole, especially in an unbonded tendon system, are usually neglected in the analysis of PCCVs with the assumption that the duct hole is filled with concrete. However, duct holes are not small enough to be neglected. In this study, the effects of no stiffness inside the unbonded tendon system on the behaviors of PCCVs are evaluated using both analytical and numerical approaches. From the results, the effects of no stiffness in unbonded tendons need to be considered in numerical simulations for PCCVs, especially under internal pressure loading.

  7. Accuracy and reproducibility of bending stiffness measurements by mechanical response tissue analysis in artificial human ulnas.

    Science.gov (United States)

    Arnold, Patricia A; Ellerbrock, Emily R; Bowman, Lyn; Loucks, Anne B

    2014-11-07

    Osteoporosis is characterized by reduced bone strength, but no FDA-approved medical device measures bone strength. Bone strength is strongly associated with bone stiffness, but no FDA-approved medical device measures bone stiffness either. Mechanical Response Tissue Analysis (MRTA) is a non-significant risk, non-invasive, radiation-free, vibration analysis technique for making immediate, direct functional measurements of the bending stiffness of long bones in humans in vivo. MRTA has been used for research purposes for more than 20 years, but little has been published about its accuracy. To begin to investigate its accuracy, we compared MRTA measurements of bending stiffness in 39 artificial human ulna bones to measurements made by Quasistatic Mechanical Testing (QMT). In the process, we also quantified the reproducibility (i.e., precision and repeatability) of both methods. MRTA precision (1.0±1.0%) and repeatability (3.1 ± 3.1%) were not as high as those of QMT (0.2 ± 0.2% and 1.3+1.7%, respectively; both pstiffness was indistinguishable from the identity line (p=0.44) and paired measurements by the two methods agreed within a 95% confidence interval of ± 5%. If such accuracy can be achieved on real human ulnas in situ, and if the ulna is representative of the appendicular skeleton, MRTA may prove clinically useful. Copyright © 2014 Elsevier Ltd. All rights reserved.

  8. Effects of no stiffness inside unbonded tendon ducts on the behavior of prestressd concrete containment vessels

    International Nuclear Information System (INIS)

    Noh, Sang Hoon; Kwak, Hyo Gyong; Jung, Rae Young; Noh, Sang Hoon

    2016-01-01

    The numerical simulation methodologies to evaluate the structural behaviors of prestressed concrete containment vessels (PCCVs) have been substantially developed in recent decades. However, there remain several issues to be investigated more closely to narrow the gap between test results and numerical simulations. As one of those issues, the effects of no stiffness inside unbonded tendon ducts on the behavior of PCCVs are investigated in this study. Duct holes for prestressing cables' passing are provided inside the containment wall and dome in one to three directions for general PCCVs. The specific stress distribution along the periphery of the prestressing duct hole and the loss of stiffness inside the hole, especially in an unbonded tendon system, are usually neglected in the analysis of PCCVs with the assumption that the duct hole is filled with concrete. However, duct holes are not small enough to be neglected. In this study, the effects of no stiffness inside the unbonded tendon system on the behaviors of PCCVs are evaluated using both analytical and numerical approaches. From the results, the effects of no stiffness in unbonded tendons need to be considered in numerical simulations for PCCVs, especially under internal pressure loading

  9. Experimental Challenges to Stiffness as a Transport Paradigm

    Science.gov (United States)

    Luce, T. C.

    2017-10-01

    Transport in plasmas is treated experimentally as a relationship between gradients and fluxes in analogy to the random-walk problem. Gyrokinetic models often predict strong increases in local flux for small increases in local gradient when above a threshold, holding all other parameters fixed. This has been named `stiffness'. The radial scalelength is then expected to vary little with source strength as a result of high stiffness. To probe the role of ExB shearing on stiffness in the DIII-D tokamak, two neutral beam injection power scans in H-mode plasmas were specially crafted-one with constant, low torque and one with increasing torque. The ion heat, electron heat, and ion toroidal momentum transport do not show expected signatures of stiffness, while the ion particle transport does. The ion heat transport shows the clearest discrepancy; the normalized heat flux drops with increasing inverse ion temperature scalelength. ExB shearing affects the transport magnitude, but not the scalelength dependence. Linear gyrofluid (TGLF) and nonlinear gyrokinetic (GYRO) predictions show stiff ion heat transport around the experimental profiles. The ion temperature gradient required to match the ion heat flux with increasing auxiliary power is not correctly described by TGLF, even when parameters are varied within the experimental uncertainties. TGLF also underpredicts transport at smaller radii, but overpredicts transport at larger radii. Independent of the theory/experiment comparison, it is not clear that the theoretical definition of stiffness yields any prediction about parameter scans such as the power scans here, because the quantities that must be held fixed to quantify stiffness are varied. A survey of recent literature indicated that profile resilience is routinely attributed to stiffness, but simple model calculations show profile resilience does not imply stiffness. Taken together, these observations challenge the use of local stiffness as a paradigm for explaining

  10. Effects of circumferential ankle pressure on ankle proprioception, stiffness, and postural stability: a preliminary investigation.

    Science.gov (United States)

    You, Sung H; Granata, Kevin P; Bunker, Linda K

    2004-08-01

    Cross-sectional repeated-measures design. Determine the effects of circumferential ankle pressure (CAP) intervention on proprioceptive acuity, ankle stiffness, and postural stability. The application of CAP using braces, taping, and adaptive shoes or military boots is widely used to address chronic ankle instability (CAI). An underlying assumption is that the CAP intervention might improve ankle stability through increased proprioceptive acuity and stiffness in the ankle. METHOD AND MEASURES: A convenience sample of 10 subjects was recruited from the local university community and categorized according to proprioceptive acuity (high, low) and ankle stability (normal, CAI). Proprioceptive acuity was measured when blindfolded subjects were asked to accurately reproduce a self-selected target ankle position before and after the application of CAP. Proprioceptive acuity was determined in 5 different ankle joint position sense tests: neutral, inversion, eversion, plantar flexion, and dorsiflexion. Joint position angles were recorded electromechanically using a potentiometer. Passive ankle stiffness was computed from the ratio of applied static moment versus angular displacement. Active ankle stiffness was determined from biomechanical analyses of ankle motion following a mediolateral perturbation. Postural stability was quantified from the center of pressure displacement in the mediolateral and the anteroposterior directions in unipedal stance. All measurements were recorded with and without CAP applied by a pediatric blood pressure cuff. Data were analyzed using a separate mixed-model analysis of variance (ANOVA) for each dependent variable. Post hoc comparison using Tukey's honestly significant difference (HSD) test was performed if significant interactions were obtained. Significance level was set at P<.05 for all analyses. Significant group (high versus low proprioceptive acuity) x CAP interactions were identified for postural stability. Passive ankle stiffness was

  11. Intraoperative cervix location and apical support stiffness in women with and without pelvic organ prolapse.

    Science.gov (United States)

    Swenson, Carolyn W; Smith, Tovia M; Luo, Jiajia; Kolenic, Giselle E; Ashton-Miller, James A; DeLancey, John O

    2017-02-01

    It is unknown how initial cervix location and cervical support resistance to traction, which we term "apical support stiffness," compare in women with different patterns of pelvic organ support. Defining a normal range of apical support stiffness is important to better understand the pathophysiology of apical support loss. The aims of our study were to determine whether: (1) women with normal apical support on clinic Pelvic Organ Prolapse Quantification, but with vaginal wall prolapse (cystocele and/or rectocele), have the same intraoperative cervix location and apical support stiffness as women with normal pelvic support; and (2) all women with apical prolapse have abnormal intraoperative cervix location and apical support stiffness. A third objective was to identify clinical and biomechanical factors independently associated with clinic Pelvic Organ Prolapse Quantification point C. We conducted an observational study of women with a full spectrum of pelvic organ support scheduled to undergo gynecologic surgery. All women underwent a preoperative clinic examination, including Pelvic Organ Prolapse Quantification. Cervix starting location and the resistance (stiffness) of its supports to being moved steadily in the direction of a traction force that increased from 0-18 N was measured intraoperatively using a computer-controlled servoactuator device. Women were divided into 3 groups for analysis according to their pelvic support as classified using the clinic Pelvic Organ Prolapse Quantification: (1) "normal/normal" was women with normal apical (C -5 cm and Ba and/or Bp ≥ 0 cm). Demographics, intraoperative cervix locations, and apical support stiffness values were then compared. Normal range of cervix location during clinic examination and operative testing was defined by the total range of values observed in the normal/normal group. The proportion of women in each group with cervix locations within and outside the normal range was determined. Linear regression

  12. Experimental verification of the axial and lateral stiffness of large W7-X rectangular bellows

    International Nuclear Information System (INIS)

    Reich, J.; Cardella, A.; Koppe, T.; Missal, B.; Capriccioli, A.; Loehrer, W.; Langone, S.; Sassone, P.C.

    2006-01-01

    The WENDELSTEIN 7-X (W7-X) is a super-conducting helical advanced stellarator. W7-X is provided with 299 ports, which connect the plasma vessel with the outer vessel. All the ports are equipped with bellows, which, during bake-out and final adjustment, compensate the relative movements of the vessels. The bellows have different shapes and dimensions ranging from 100 mm circular to 1170 x 570 mm rectangular sizes. During various load-cases the axial and lateral stiffness of all bellows will create a resulting spring-force which acts on the supports of the vessels directly. The higher the stiffness the more is the significant influence on the supports. The lateral stiffness which was calculated with the established standard EJMA-code (Expansion Joint Manufacturers Association) seemed to be relatively small. This appeared to be not correct in particular for non circular bellows. That is why the stiffness of rectangular, multi-layer bellows have then been re-calculated with the Finite Element Method (FEM) code ANSYS. The maximum difference between the FEM and EJMA code resulted to be up to 250 % in particular with movements along the longer side of the bellows. In order to clarify the differences a test-campaign with the largest rectangular bellows was performed. A special test rack allowed predefined displacements in pure lateral and axial directions taking into consideration of the friction in the moving elements. During the tests the load-displacement diagram was recorded permanently. The outcome of the FEM-results was then verified by the tests in axial and lateral directions. The EJMA-code is well proved for circular bellows. The tests showed that instead any calculation of rectangular bellows has to be confirmed by experiments. The paper summarises the calculation, describes the test activities, the apparatus and reports the final results. (author)

  13. Drilling the near cortex with elongated figure-of-8 holes to reduce the stiffness of a locking compression plate construct.

    Science.gov (United States)

    Chen, Jerry Yongqiang; Zhou, Zhihong; Ang, Benjamin Fu Hong; Yew, Andy Khye Soon; Chou, Siaw Meng; Chia, Shi-Lu; Koh, Joyce Suang Bee; Howe, Tet Sen

    2015-12-01

    To compare the stiffness of locking compression plate (LCP) constructs with or without drilling the near cortex with elongated figure-of-8 holes. 24 synthetic bones were sawn to create a 10-mm gap and were fixed with a 9-hole 4.5-mm narrow LCP. In 12 bones, the near cortex of the adjacent holes to the LCP holes was drilled to create elongated figure-of-8 holes before screw insertion. The stiffness of LCP constructs under axial loading or 4-point bending was assessed by (1) dynamic quasi-physiological testing for fatigue strength, (2) quasi-static testing for stiffness, and (3) testing for absolute strength to failure. None of the 24 constructs had subcatastrophic or catastrophic failure after 10 000 cycles of fatigue loading (p=1.000). The axial stiffness reduced by 16% from 613±62 to 517±44 N/mm (p=0.012) in the case group, whereas the bending stiffness was 16±1 Nm2 in both groups (p=1.000). The maximum axial load to catastrophic failure was 1596±84 N for the control group and 1627±48 N for the case group (p=0.486), whereas the maximum bending moment to catastrophic failure was 79±12 and 80±10 Nm, respectively (p=0.919). Drilling the near cortex with elongated figure-of-8 holes reduces the axial stiffness of the LCP construct, without compromising its bending stiffness or strength.

  14. Stiffness Matrices and Anisotropy in the Trapezoidal Corrugated Composite Sheets

    Directory of Open Access Journals (Sweden)

    Mohammad Golzar

    2013-10-01

    Full Text Available In the some applications like as morphing technology, high strain and anisotropic behavior are essential design requirements. The corrugated composite sheets due to their special geometries have potential to high deflection under axial loading through longitudinal direction of corrugation. In this research, the strain and the anisotropic behavior of corrugated composite sheets are investigated by fabricating glass/epoxy samples with trapezoidal geometries. For evaluation of the mechanical behavior of the composites the samples were subjected to tension and flexural tests in the longitudinal and transverse directions of corrugation. In order to determine anisotropic behavior of the corrugated sheets, two approaches were introduced: (1 tensile anisotropic (E* and (2 flexural anisotropic (D*. The anisotropic behavior and ultimate deflections were investigated theoretically and experimentally. In this paper, mechanical behaviors based on theoretical and experimental analysis including the elastic constants and stiffness matrices of trapezoidal corrugated composite sheets were studied and the results were verified by finite element method. The results of the numerical and analytical solutions were compared with those of experimental tests. Finally, the load-displacement curves of tensile tests in longitudinal direction of corrugation, the ultimate deflection and anisotropy behavior of these exclusive composite sheets in the corrugated composite sheets were studied experimentally. The experimental results of the trapezoidal corrugated sheets showed that one of the most important parameters in the ultimate strain was amplitude of the corrugation elements. Generally, increasing the amplitude and element per length unit of trapezoidal corrugated specimen led to higher ultimate strain.

  15. Training haptic stiffness discrimination: time course of learning with or without visual information and knowledge of results.

    Science.gov (United States)

    Teodorescu, Kinneret; Bouchigny, Sylvain; Korman, Maria

    2013-08-01

    In this study, we explored the time course of haptic stiffness discrimination learning and how it was affected by two experimental factors, the addition of visual information and/or knowledge of results (KR) during training. Stiffness perception may integrate both haptic and visual modalities. However, in many tasks, the visual field is typically occluded, forcing stiffness perception to be dependent exclusively on haptic information. No studies to date addressed the time course of haptic stiffness perceptual learning. Using a virtual environment (VE) haptic interface and a two-alternative forced-choice discrimination task, the haptic stiffness discrimination ability of 48 participants was tested across 2 days. Each day included two haptic test blocks separated by a training block Additional visual information and/or KR were manipulated between participants during training blocks. Practice repetitions alone induced significant improvement in haptic stiffness discrimination. Between days, accuracy was slightly improved, but decision time performance was deteriorated. The addition of visual information and/or KR had only temporary effects on decision time, without affecting the time course of haptic discrimination learning. Learning in haptic stiffness discrimination appears to evolve through at least two distinctive phases: A single training session resulted in both immediate and latent learning. This learning was not affected by the training manipulations inspected. Training skills in VE in spaced sessions can be beneficial for tasks in which haptic perception is critical, such as surgery procedures, when the visual field is occluded. However, training protocols for such tasks should account for low impact of multisensory information and KR.

  16. Martial arts training attenuates arterial stiffness in middle aged adults.

    Science.gov (United States)

    Douris, Peter C; Ingenito, Teresa; Piccirillo, Barbara; Herbst, Meredith; Petrizzo, John; Cherian, Vincen; McCutchan, Christopher; Burke, Caitlin; Stamatinos, George; Jung, Min-Kyung

    2013-09-01

    Arterial stiffness increases with age and is related to an increased risk of coronary artery disease. Poor trunk flexibility has been shown to be associated with arterial stiffness in middle-aged subjects. The purpose of our research study was to measure arterial stiffness and flexibility in healthy middle-aged martial artists compared to age and gender matched healthy sedentary controls. Ten martial artists (54.0 ± 2.0 years), who practice Soo Bahk Do (SBD), a Korean martial art, and ten sedentary subjects (54.7 ± 1.8 years) for a total of twenty subjects took part in this cross-sectional study. Arterial stiffness was assessed in all subjects using pulse wave velocity (PWV), a recognized index of arterial stiffness. Flexibility of the trunk and hamstring were also measured. The independent variables were the martial artists and matched sedentary controls. The dependent variables were PWV and flexibility. There were significant differences, between the SBD practitioners and sedentary controls, in PWV (P = 0.004), in trunk flexibility (P= 0.002), and in hamstring length (P= 0.003). The middle-aged martial artists were more flexible in their trunk and hamstrings and had less arterial stiffness compared to the healthy sedentary controls. The flexibility component of martial art training or flexibility exercises in general may be considered as a possible intervention to reduce the effects of aging on arterial stiffness.

  17. Simvastatin Ameliorates Matrix Stiffness-Mediated Endothelial Monolayer Disruption.

    Directory of Open Access Journals (Sweden)

    Marsha C Lampi

    Full Text Available Arterial stiffening accompanies both aging and atherosclerosis, and age-related stiffening of the arterial intima increases RhoA activity and cell contractility contributing to increased endothelium permeability. Notably, statins are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA reductase inhibitors whose pleiotropic effects include disrupting small GTPase activity; therefore, we hypothesized the statin simvastatin could be used to attenuate RhoA activity and inhibit the deleterious effects of increased age-related matrix stiffness on endothelial barrier function. Using polyacrylamide gels with stiffnesses of 2.5, 5, and 10 kPa to mimic the physiological stiffness of young and aged arteries, endothelial cells were grown to confluence and treated with simvastatin. Our data indicate that RhoA and phosphorylated myosin light chain activity increase with matrix stiffness but are attenuated when treated with the statin. Increases in cell contractility, cell-cell junction size, and indirect measurements of intercellular tension that increase with matrix stiffness, and are correlated with matrix stiffness-dependent increases in monolayer permeability, also decrease with statin treatment. Furthermore, we report that simvastatin increases activated Rac1 levels that contribute to endothelial barrier enhancing cytoskeletal reorganization. Simvastatin, which is prescribed clinically due to its ability to lower cholesterol, alters the endothelial cell response to increased matrix stiffness to restore endothelial monolayer barrier function, and therefore, presents a possible therapeutic intervention to prevent atherogenesis initiated by age-related arterial stiffening.

  18. Subspace methods for identification of human ankle joint stiffness.

    Science.gov (United States)

    Zhao, Y; Westwick, D T; Kearney, R E

    2011-11-01

    Joint stiffness, the dynamic relationship between the angular position of a joint and the torque acting about it, describes the dynamic, mechanical behavior of a joint during posture and movement. Joint stiffness arises from both intrinsic and reflex mechanisms, but the torques due to these mechanisms cannot be measured separately experimentally, since they appear and change together. Therefore, the direct estimation of the intrinsic and reflex stiffnesses is difficult. In this paper, we present a new, two-step procedure to estimate the intrinsic and reflex components of ankle stiffness. In the first step, a discrete-time, subspace-based method is used to estimate a state-space model for overall stiffness from the measured overall torque and then predict the intrinsic and reflex torques. In the second step, continuous-time models for the intrinsic and reflex stiffnesses are estimated from the predicted intrinsic and reflex torques. Simulations and experimental results demonstrate that the algorithm estimates the intrinsic and reflex stiffnesses accurately. The new subspace-based algorithm has three advantages over previous algorithms: 1) It does not require iteration, and therefore, will always converge to an optimal solution; 2) it provides better estimates for data with high noise or short sample lengths; and 3) it provides much more accurate results for data acquired under the closed-loop conditions, that prevail when subjects interact with compliant loads.

  19. Cross-linking in collagen by nonenzymatic glycation increases the matrix stiffness in rabbit achilles tendon.

    Science.gov (United States)

    Reddy, G Kesava

    2004-01-01

    Nonenzymatic glycation of connective tissue matrix proteins is a major contributor to the pathology of diabetes and aging. Previously the author and colleagues have shown that nonenzymatic glycation significantly enhances the matrix stability in the Achilles tendon (Reddy et al., 2002, Arch. Biochem. Biophys., 399, 174-180). The present study was designed to gain further insight into glycation-induced collagen cross-linking and its relationship to matrix stiffness in the rabbit Achilles tendon. The glycation process was initiated by incubating the Achilles tendons (n = 6) in phosphate-buffered saline containing ribose, whereas control tendons (n = 6) were incubated in phosphate-buffered saline without ribose. Eight weeks following glycation, the biomechanical attributes as well as the degree of collagen cross-linking were determined to examine the potential associations between matrix stiffness and molecular properties of collagen. Compared to nonglycated tendons, the glycated tendons showed increased maximum load, stress, strain, Young's modulus of elasticity, and toughness indicating that glycation increases the matrix stiffness in the tendons. Glycation of tendons resulted in a considerable decrease in soluble collagen content and a significant increase in insoluble collagen and pentosidine. Analysis of potential associations between the matrix stiffness and degree of collagen cross-linking showed that both insoluble collagen and pentosidine exhibited a significant positive correlation with the maximum load, stress, and strain, Young's modulus of elasticity, and toughness (r values ranging from.61 to.94) in the Achilles tendons. However, the soluble collagen content present in neutral salt buffer, acetate buffer, and acetate buffer containing pepsin showed an inverse relation with the various biomechanical attributes tested (r values ranging from.22 to.84) in the Achilles tendons. The results of the study demonstrate that glycation-induced collagen cross

  20. Detailed investigation on the effect of wall spring stiffness on velocity profile in molecular dynamics simulation

    International Nuclear Information System (INIS)

    Namvar, S; Karimian, S M H

    2012-01-01

    In this paper, motion of 576 monatomic argon molecules is studied in a channel with two 2-layered wall molecules. The effect of wall spring stiffness (K) on maximum value of velocity profile is investigated in the channel. It was observed that for K −2 , there is a decrease in the maximum value of velocity profile with an increase in K. This observation has been already reported by Sofos et al. To investigate a wider range of spring stiffness, in this paper the value of K was increased to more than 500εσ −2 . In this range of wall spring stiffness the behavior of maximum value of velocity profile changed; it increased with an increase in K. In a separate simulation the external force applied to the molecules was also increased and the same non-monotonic behavior of maximum value of velocity was observed. To clarify the reason of this behavior, the concepts of original and effective wall are introduced and through several test it is inferred that the mentioned concepts are not successful to demonstrate the reason of such behavior. It is suggested to obtain non-dimensional parameters governing the simulation in order to investigate the effect of every involved parameter on such a behavior. It is finally concluded that while wall spring stiffness affects the maximum velocity magnitude within the flow, the interaction of the two has not been clearly shown yet. The behavior of the maximum velocity is non-monotonic with the change of K. This is why no specific criterion has been reported for suitable value of wall spring stiffness in molecular dynamics simulation.

  1. Large strain variable stiffness composites for shear deformations with applications to morphing aircraft skins

    Science.gov (United States)

    McKnight, G. P.; Henry, C. P.

    2008-03-01

    Morphing or reconfigurable structures potentially allow for previously unattainable vehicle performance by permitting several optimized structures to be achieved using a single platform. The key to enabling this technology in applications such as aircraft wings, nozzles, and control surfaces, are new engineered materials which can achieve the necessary deformations but limit losses in parasitic actuation mass and structural efficiency (stiffness/weight). These materials should exhibit precise control of deformation properties and provide high stiffness when exercised through large deformations. In this work, we build upon previous efforts in segmented reinforcement variable stiffness composites employing shape memory polymers to create prototype hybrid composite materials that combine the benefits of cellular materials with those of discontinuous reinforcement composites. These composites help overcome two key challenges for shearing wing skins: the resistance to out of plane buckling from actuation induced shear deformation, and resistance to membrane deflections resulting from distributed aerodynamic pressure loading. We designed, fabricated, and tested composite materials intended for shear deformation and address out of plane deflections in variable area wing skins. Our designs are based on the kinematic engineering of reinforcement platelets such that desired microstructural kinematics is achieved through prescribed boundary conditions. We achieve this kinematic control by etching sheets of metallic reinforcement into regular patterns of platelets and connecting ligaments. This kinematic engineering allows optimization of materials properties for a known deformation pathway. We use mechanical analysis and full field photogrammetry to relate local scale kinematics and strains to global deformations for both axial tension loading and shear loading with a pinned-diamond type fixture. The Poisson ratio of the kinematically engineered composite is ~3x higher than

  2. Effect of Reduced Stiffness Dance Flooring on Lower Extremity Joint Angular Trajectories During a Ballet Jump.

    Science.gov (United States)

    Hackney, James; Brummel, Sara; Newman, Mary; Scott, Shannon; Reinagel, Matthew; Smith, Jennifer

    2015-09-01

    We carried out a study to investigate how low stiffness flooring may help prevent overuse injuries of the lower extremity in dancers. It was hypothesized that performing a ballet jump (sauté) on a reduced stiffness dance floor would decrease maximum joint flexion angles and negative angular velocities at the hips, knees, or ankles compared to performing the same jump on a harder floor. The participants were 15 young adult female dancers (age range 18 to 28, mean = 20.89 ± 2.93 years) with at least 5 years of continuous ballet experience and without history of serious lower body injury, surgery, or recent pain. They performed sautés on a (low stiffness) Harlequin ® WoodSpring Floor and on a vinyl-covered hardwood on concrete floor. Maximum joint flexion angles and negative velocities at bilateral hips, knees, and ankles were measured with the "Ariel Performance Analysis System" (APAS). Paired one-tailed t-tests yielded significant decreases in maximum knee angle (average decrease = 3.4° ± 4.2°, p = 0.026) and angular negative velocity of the ankles (average decrease = 18.7°/sec ± 27.9°/sec, p = 0.009) with low stiffness flooring. If the knee angle is less acute, then the length of the external knee flexion moment arm will also be shorter and result in a smaller external knee flexion moment, given an equal landing force. Also, high velocities of eccentric muscle contraction, which are necessary to control negative angular velocity of the ankle joint, are associated with higher risk of musculotendinous injury. Hence, our findings indicate that reduced floor stiffness may indeed help decrease the likelihood of lower extremity injuries.

  3. Design, Development and Scaling Analysis of a Variable Stiffness Magnetic Torsion Spring

    Directory of Open Access Journals (Sweden)

    Angelo Sudano

    2013-10-01

    Full Text Available In this paper we report on the design, modeling, experimental testing and scaling analysis of a novel MAgnetic Variable stiffnEess spRIng-Clutch (MAVERIC device, which may be used as the elastic element of Variable Stiffness Actuators (VSAs. The device, comprising two co-axial diametrically magnetized hollow cylinders, has two degrees of freedom: a rotation of the two cylinders around the common axis and a relative translation along the same axis. For small rotations, the torque arising from the magnetic interaction of the two cylinders is almost linearly proportional to their relative rotation, as in mechanical torsion springs. In addition, the stiffness of the equivalent spring can be varied continuously from a maximum value down to exactly zero by changing the axial overlap of the two cylinders. In this way the proposed device can be used both as a clutch (i.e., perfectly compliant element and as a variable stiffness torsion spring. A prototype, designed after magnetostatic FEM simulations, has been built and experimentally characterized. The developed MAVERIC has an experimentally determined maximum transmissible torque of 109.81mNm, while the calculated maximum stiffness is 110.2mNmrad−1. The amplitude of the torque-angle characteristic can be tuned linearly with a sensitivity of 12.63mNmmm−1 rad−1. Further simulations have been computed parameterizing the geometry and the number of pole pairs of the magnets. The maximum torque density reached for one pole pair is 47.21 · 103 Nm m−3, whereas for a fixed geometry similar to that of the developed prototype, the maximum torque is reached for seven pole pairs. Overall, compared to mechanical springs, MAVERIC has no fatigue or overloading issues. Compared to other magnetic couplers, torsion stiffness can be varied continuously from a maximum value down to exactly zero, when the device acts as a disengaged clutch, disconnecting the load from the actuator.

  4. Roles of Arterial Stiffness and Blood Pressure in Hypertension-Associated Cognitive Decline in Healthy Adults.

    Science.gov (United States)

    Hajjar, Ihab; Goldstein, Felicia C; Martin, Greg S; Quyyumi, Arshed A

    2016-01-01

    Although there is strong evidence that hypertension leads to cognitive decline, especially in the executive domain, the relationship between blood pressure and cognition has been conflicted. Hypertension is characterized by blood pressure elevation and increased arterial stiffness. We aimed at investigating whether arterial stiffness would be superior to blood pressure in predicting cognitive decline and explaining the hypertension-executive decline association. A randomly selected asymptomatic population (n=591, age=49.2 years, 70% women, 27% black, and education=18 years) underwent annual vascular and cognitive assessments. Cognition was assessed using computerized versions commonly used cognitive tests, and principal component analysis was used for deriving cognitive scores for executive function, memory, and working memory. Arterial stiffness was measured by carotid-femoral pulse wave velocity (PWV). Higher PWV, but not blood pressure, was associated with a steeper decline in executive (P=0.0002), memory (P=0.05), and working memory (P=0.02) scores after adjusting for demographics, education, and baseline cognitive performance. This remained true after adjusting for hypertension. Hypertension was associated with greater decline in executive score (P=0.0029) and those with combined hypertension and elevated PWV (>7 m/s) had the greatest decline in executive score (P value hypertension×PWV=0.02). PWV explained the association between hypertension and executive function (P value for hypertension=0.0029 versus 0.24 when adjusting for PWV). In healthy adults, increased arterial stiffness is superior to blood pressure in predicting cognitive decline in all domains and in explaining the hypertension-executive function association. Arterial stiffness, especially in hypertension, may be a target in the prevention of cognitive decline. © 2015 American Heart Association, Inc.

  5. Biomechanical constraints on the feedforward regulation of endpoint stiffness.

    Science.gov (United States)

    Hu, Xiao; Murray, Wendy M; Perreault, Eric J

    2012-10-01

    Although many daily tasks tend to destabilize arm posture, it is still possible to have stable interactions with the environment by regulating the multijoint mechanics of the arm in a task-appropriate manner. For postural tasks, this regulation involves the appropriate control of endpoint stiffness, which represents the stiffness of the arm at the hand. Although experimental studies have been used to evaluate endpoint stiffness control, including the orientation of maximal stiffness, the underlying neural strategies remain unknown. Specifically, the relative importance of feedforward and feedback mechanisms has yet to be determined due to the difficulty separately identifying the contributions of these mechanisms in human experiments. This study used a previously validated three-dimensional musculoskeletal model of the arm to quantify the degree to which the orientation of maximal endpoint stiffness could be changed using only steady-state muscle activations, used to represent feedforward motor commands. Our hypothesis was that the feedforward control of endpoint stiffness orientation would be significantly constrained by the biomechanical properties of the musculoskeletal system. Our results supported this hypothesis, demonstrating substantial biomechanical constraints on the ability to regulate endpoint stiffness throughout the workspace. The ability to regulate stiffness orientation was further constrained by additional task requirements, such as the need to support the arm against gravity or exert forces on the environment. Together, these results bound the degree to which slowly varying feedforward motor commands can be used to regulate the orientation of maximum arm stiffness and provide a context for better understanding conditions in which feedback control may be needed.

  6. Hormones and arterial stiffness in patients with chronic kidney disease.

    Science.gov (United States)

    Gungor, Ozkan; Kircelli, Fatih; Voroneanu, Luminita; Covic, Adrian; Ok, Ercan

    2013-01-01

    Cardiovascular disease constitutes the major cause of mortality in patients with chronic kidney disease. Arterial stiffness is an important contributor to the occurrence and progression of cardiovascular disease. Various risk factors, including altered hormone levels, have been suggested to be associated with arterial stiffness. Based on the background that chronic kidney disease predisposes individuals to a wide range of hormonal changes, we herein review the available data on the association between arterial stiffness and hormones in patients with chronic kidney disease and summarize the data for the general population.

  7. Superfluid phase stiffness in electron doped superconducting Gd-123

    Science.gov (United States)

    Das, P.; Ghosh, Ajay Kumar

    2018-05-01

    Current-voltage characteristics of Ce substituted Gd-123 superconductor exhibits nonlinearity below a certain temperature below the critical temperature. An exponent is extracted using the nonlinearity of current-voltage relation. Superfluid phase stiffness has been studied as a function of temperature following the Ambegaokar-Halperin-Nelson-Siggia (AHNS) theory. Phase stiffness of the superfluid below the superconducting transition is found to be sensitive to the change in the carrier concentration in superconducting system. There may be a crucial electron density which affects superfluid stiffness strongly. Electron doping is found to be effective even if the coupling of the superconducting planes is changed.

  8. Experimental measure of arm stiffness during single reaching movements with a time-frequency analysis

    OpenAIRE

    Piovesan, Davide; Pierobon, Alberto; DiZio, Paul; Lackner, James R.

    2013-01-01

    We tested an innovative method to estimate joint stiffness and damping during multijoint unfettered arm movements. The technique employs impulsive perturbations and a time-frequency analysis to estimate the arm's mechanical properties along a reaching trajectory. Each single impulsive perturbation provides a continuous estimation on a single-reach basis, making our method ideal to investigate motor adaptation in the presence of force fields and to study the control of movement in impaired ind...

  9. Cardiorespiratory fitness and age-related arterial stiffness in women with systemic lupus erythematosus.

    Science.gov (United States)

    Montalbán-Méndez, Cristina; Soriano-Maldonado, Alberto; Vargas-Hitos, José A; Sáez-Urán, Luis M; Rosales-Castillo, Antonio; Morillas-de-Laguno, Pablo; Gavilán-Carrera, Blanca; Jiménez-Alonso, Juan

    2018-03-01

    The aim of this study was twofold: (i) to examine the association of cardiorespiratory fitness with arterial stiffness in women with systemic lupus erythematosus; (ii) to assess the potential interaction of cardiorespiratory fitness with age on arterial stiffness in this population. A total of 49 women with systemic lupus erythematosus (mean age 41.3 [standard deviation 13.8] years) and clinical stability during the previous 6 months were included in the study. Arterial stiffness was assessed through pulse wave velocity (Mobil-O-Graph® 24 hours pulse wave velocity monitor). Cardiorespiratory fitness was estimated with the Siconolfi step test and the 6-minute walk test. Cardiorespiratory fitness was inversely associated with pulse wave velocity in crude analyses (P fitness × age interaction effect on pulse wave velocity, regardless of the test used to estimate cardiorespiratory fitness (P fitness was associated with a lower increase in pulse wave velocity per each year increase in age. The results of this study suggest that cardiorespiratory fitness might attenuate the age-related arterial stiffening in women with systemic lupus erythematosus and might thus contribute to the primary prevention of cardiovascular disease in this population. As the cross-sectional design precludes establishing causal relationships, future clinical trials should confirm or contrast these findings. © 2018 Stichting European Society for Clinical Investigation Journal Foundation.

  10. Experimental Characterization of Stress- and Strain-Dependent Stiffness in Grouted Rock Masses.

    Science.gov (United States)

    Kim, Ji-Won; Chong, Song-Hun; Cho, Gye-Chun

    2018-03-29

    Grouting of fractured rock mass prior to excavation results in grout-filled discontinuities that govern the deformation characteristics of a site. The influence of joint characteristics on the properties of grouted rocks is important in assessing the effects of grouting on jointed rock mass. However, grouting remains a predominantly empirical practice and the effects of grouting on rock joint behavior and material properties have yet to be accurately assessed. Granular materials, including jointed rocks, typically display nonlinear strain-dependent responses that can be characterized by the shear modulus degradation curve. In this study, the effects of grouting on the strain-dependent shear stiffness of jointed rock mass were investigated at the small-strain (below 10 -5 ) and mid-strain (10 -5 to 10 -3 ) ranges using the quasi-static resonant column test and rock mass dynamic test devices. The effects of curing time, axial stress, initial joint roughness, and grouted joint thickness were examined. The results show that (1) grouting of rock joints leads to decreased stress sensitivity and increased small-strain shear stiffness for all tested samples; (2) the grouted rock samples display similar modulus degradation characteristics as the applied grout material; (3) the initial joint roughness determines the stress-dependent behaviors and general stiffness range of the jointed and grouted rocks, but the strain-dependent behaviors are dependent on the properties of the grout material; (4) increased grouted joint thickness results in larger contribution of the grout properties in the overall grouted rock mass.

  11. Strength and Stiffness Development in Soft Soils: A FESEM aided Soil Microstructure Viewpoint

    Science.gov (United States)

    Wijeyesekera, D. C.; Ho, M. H.; Bai, X.; Bakar, I.

    2016-07-01

    This paper opens with an overview of the debatable definition of soft soil that goes beyond a (CH) organic / inorganic clay and OH peat to include weakly cemented periglacial deposits of loess and alike. It then outlines the findings obtained from stiffness test on cement-stabilised soft clay. The findings are complemented with a microstructure viewpoint obtained using field emission scanning electron microscope (FESEM). Research also comprised of making cylindrical stabilised clay samples, prepared in the laboratory with various rubber chips contents and cement, and then aged for 28 days. The samples were then subjected to unconfined compressive strength (UCS) test and observations were also made of its microstructure using the FESEM. The impact of the soil microstructure on the stiffness result was studied both with the stabilized soil and also of some of the natural undisturbed loess soils. Sustainability aspect and the potential of the use of rubber chips and sand as additives to cement stabilisation are also discussed. The overall test results indicated that rubber chips and sand contributed to the improvement in unconfined compressive strength (qu). The derogatory influence of moisture on the stiffness of the stabilised clay was studied simultaneously. SEM micrographs are presented that show bonding of cement, rubber chips/ sand and soft clay, granular units and aggregated / agglomerated units in loess. The paper concludes with observations on the dependence of soil microstructure on the soil strength and deformability and even collapsibility of the loess. Current practices adopted as engineering solutions to these challenging soils are outlined.

  12. Negative stiffness honeycombs as tunable elastic metamaterials

    Science.gov (United States)

    Goldsberry, Benjamin M.; Haberman, Michael R.

    2018-03-01

    Acoustic and elastic metamaterials are media with a subwavelength structure that behave as effective materials displaying atypical effective dynamic properties. These material systems are of interest because the design of their sub-wavelength structure allows for direct control of macroscopic wave dispersion. One major design limitation of most metamaterial structures is that the dynamic response cannot be altered once the microstructure is manufactured. However, the ability to modify wave propagation in the metamaterial with an external stimulus is highly desirable for numerous applications and therefore remains a significant challenge in elastic metamaterials research. In this work, a honeycomb structure composed of a doubly periodic array of curved beams, known as a negative stiffness honeycomb (NSH), is analyzed as a tunable elastic metamaterial. The nonlinear static elastic response that results from large deformations of the NSH unit cell leads to a large variation in linear elastic wave dispersion associated with infinitesimal motion superposed on the externally imposed pre-strain. A finite element model is utilized to model the static deformation and subsequent linear wave motion at the pre-strained state. Analysis of the slowness surface and group velocity demonstrates that the NSH exhibits significant tunability and a high degree of anisotropy which can be used to guide wave energy depending on static pre-strain levels. In addition, it is shown that partial band gaps exist where only longitudinal waves propagate. The NSH therefore behaves as a meta-fluid, or pentamode metamaterial, which may be of use for applications of transformation elastodynamics such as cloaking and gradient index lens devices.

  13. A new variable stiffness suspension system: passive case

    Directory of Open Access Journals (Sweden)

    O. M. Anubi

    2013-02-01

    Full Text Available This paper presents the design, analysis, and experimental validation of the passive case of a variable stiffness suspension system. The central concept is based on a recently designed variable stiffness mechanism. It consists of a horizontal control strut and a vertical strut. The main idea is to vary the load transfer ratio by moving the location of the point of attachment of the vertical strut to the car body. This movement is controlled passively using the horizontal strut. The system is analyzed using an L2-gain analysis based on the concept of energy dissipation. The analyses, simulation, and experimental results show that the variable stiffness suspension achieves better performance than the constant stiffness counterpart. The performance criteria used are; ride comfort, characterized by the car body acceleration, suspension deflection, and road holding, characterized by tire deflection.

  14. Molecular Cues Guiding Matrix Stiffness in Liver Fibrosis

    Directory of Open Access Journals (Sweden)

    Takaoki Saneyasu

    2016-01-01

    Full Text Available Tissue and matrix stiffness affect cell properties during morphogenesis, cell growth, differentiation, and migration and are altered in the tissue remodeling following injury and the pathological progression. However, detailed molecular mechanisms underlying alterations of stiffness in vivo are still poorly understood. Recent engineering technologies have developed powerful techniques to characterize the mechanical properties of cell and matrix at nanoscale levels. Extracellular matrix (ECM influences mechanical tension and activation of pathogenic signaling during the development of chronic fibrotic diseases. In this short review, we will focus on the present knowledge of the mechanisms of how ECM stiffness is regulated during the development of liver fibrosis and the molecules involved in ECM stiffness as a potential therapeutic target for liver fibrosis.

  15. Role of flexural stiffness of leukocyte microvilli in adhesion dynamics

    Science.gov (United States)

    Wu, Tai-Hsien; Qi, Dewei

    2018-03-01

    Previous work reported that microvillus deformation has an important influence on dynamics of cell adhesion. However, the existing studies were limited to the extensional deformation of microvilli and did not consider the effects of their bending deformation on cell adhesion. This Rapid Communication investigates the effects of flexural stiffness of microvilli on the rolling process related to adhesion of leukocytes by using a lattice-Boltzmann lattice-spring method (LLM) combined with adhesive dynamics (AD) simulations. The simulation results reveal that the flexural stiffness of microvilli and their bending deformation have a profound effect on rolling velocity and adhesive forces. As the flexural stiffness of the microvilli decreases, their bending angles increase, resulting in an increase in the number of receptor-ligand bonds and adhesive bonding force and a decrease in the rolling velocity of leukocytes. The effects of flexural stiffness on deformation and adhesion represent crucial factors involved in cell adhesion.

  16. Operator-Based Preconditioning of Stiff Hyperbolic Systems

    International Nuclear Information System (INIS)

    Reynolds, Daniel R.; Samtaney, Ravi; Woodward, Carol S.

    2009-01-01

    We introduce an operator-based scheme for preconditioning stiff components encountered in implicit methods for hyperbolic systems of partial differential equations posed on regular grids. The method is based on a directional splitting of the implicit operator, followed by a characteristic decomposition of the resulting directional parts. This approach allows for solution to any number of characteristic components, from the entire system to only the fastest, stiffness-inducing waves. We apply the preconditioning method to stiff hyperbolic systems arising in magnetohydro- dynamics and gas dynamics. We then present numerical results showing that this preconditioning scheme works well on problems where the underlying stiffness results from the interaction of fast transient waves with slowly-evolving dynamics, scales well to large problem sizes and numbers of processors, and allows for additional customization based on the specific problems under study

  17. Finding trap stiffness of optical tweezers using digital filters.

    Science.gov (United States)

    Almendarez-Rangel, Pedro; Morales-Cruzado, Beatriz; Sarmiento-Gómez, Erick; Pérez-Gutiérrez, Francisco G

    2018-02-01

    Obtaining trap stiffness and calibration of the position detection system is the basis of a force measurement using optical tweezers. Both calibration quantities can be calculated using several experimental methods available in the literature. In most cases, stiffness determination and detection system calibration are performed separately, often requiring procedures in very different conditions, and thus confidence of calibration methods is not assured due to possible changes in the environment. In this work, a new method to simultaneously obtain both the detection system calibration and trap stiffness is presented. The method is based on the calculation of the power spectral density of positions through digital filters to obtain the harmonic contributions of the position signal. This method has the advantage of calculating both trap stiffness and photodetector calibration factor from the same dataset in situ. It also provides a direct method to avoid unwanted frequencies that could greatly affect calibration procedure, such as electric noise, for example.

  18. Assessment of pathologic increase in liver stiffness enables earlier diagnosis of CFLD: Results from a prospective longitudinal cohort study.

    Directory of Open Access Journals (Sweden)

    Victoria Klotter

    Full Text Available About 30% of patients with Cystic Fibrosis (CF develop CF-associated liver disease (CFLD. Recent studies have shown that transient elastography (TE, as a method to quantify liver stiffness, allows non-invasive diagnosis of CFLD in adults and children with CF. Within this study we aimed to prospectively identify patients at risk for development of CFLD by longitudinal analysis of liver stiffness and fibrosis scores in a 5-year follow-up. 36 pediatric and 16 adult patients with initial liver stiffness below the cut-off value indicative of CFLD (6.3 kPa were examined by transient elastography for 4-5 years. TE, APRI-, and FIB-4-scores were assessed and compared by Kruskal-Wallis test and receiver operating characteristic (ROC-analysis. Frequencies were compared by Chi2-test. Among the 36 patients participating in this study, a subgroup of 9 patients developed liver stiffness >6.3 kPa after 4-5 years with an increase of ΔTE >0.38 kPa/a (the group with increasing liver stiffness was labelled TEinc. APRI- and FIB-4 scores confirmed the rationale for grouping. The frequency of CFLD assessed by conventional diagnosis was significantly higher in TEinc-group compared to the control group (TEnorm. None of the adult CF patients matched criteria for TEinc-group. For the first time it was shown that the non-invasive longitudinal assessment of TE allows identification of patients with progression of CFLD in a subgroup of juvenile but not in adult CF patients. Comparing TE to conventional fibrosis-scores underlined the strength of the continuous assessment of liver stiffness for the exact diagnosis of progressive CFLD. The newly described cut-off for pathologic increase of liver stiffness, ΔTEcutoff = 0.38kPa/a, might enable to detect developing CFLD using consequent follow up TE measurements before reaching the level of stiffness indicating established CFLD. Nevertheless, the limited size of the analyzed cohort should encourage a prospective, multi

  19. Arterial Stiffness and Functional Outcome in Acute Ischemic Stroke

    OpenAIRE

    Lee, Yeong-Bae; Park, Joo-Hwan; Kim, Eunja; Kang, Chang-Ki; Park, Hyeon-Mi

    2014-01-01

    Objective Arterial stiffness is a common change associated with aging and can be evaluated by measuring pulse wave velocity (PWV) between sites in the arterial tree, with the stiffer artery having the higher PWV. Arterial stiffness is associated with the risk of stroke in the general population and of fatal stroke in hypertensive patients. This study is to clarify whether PWV value predicts functional outcome of acute ischemic stroke. Methods One hundred patients were enrolled with a diagnosi...

  20. MINIMUM BRACING STIFFNESS FOR MULTI-COLUMN SYSTEMS: THEORY

    OpenAIRE

    ARISTIZÁBAL-OCHOA, J. DARÍO

    2011-01-01

    A method that determines the minimum bracing stiffness required by a multi-column elastic system to achieve non-sway buckling conditions is proposed. Equations that evaluate the required minimum stiffness of the lateral and torsional bracings and the corresponding “braced" critical buckling load for each column of the story level are derived using the modified stability functions. The following effects are included: 1) the types of end connections (rigid, semirigid, and simple); 2) the bluepr...

  1. Potential Relationship between Passive Plantar Flexor Stiffness and Running Performance.

    Science.gov (United States)

    Ueno, Hiromasa; Suga, Tadashi; Takao, Kenji; Tanaka, Takahiro; Misaki, Jun; Miyake, Yuto; Nagano, Akinori; Isaka, Tadao

    2018-02-01

    The present study aimed to determine the relationship between passive stiffness of the plantar flexors and running performance in endurance runners. Forty-eight well-trained male endurance runners and 24 untrained male control subjects participated in this study. Plantar flexor stiffness during passive dorsiflexion was calculated from the slope of the linear portion of the torque-angle curve. Of the endurance runners included in the present study, running economy in 28 endurance runners was evaluated by measuring energy cost during three 4-min trials (14, 16, and 18 km/h) of submaximal treadmill running. Passive stiffness of the plantar flexors was significantly higher in endurance runners than in untrained subjects. Moreover, passive plantar flexor stiffness in endurance runners was significantly correlated with a personal best 5000-m race time. Furthermore, passive plantar flexor stiffness in endurance runners was significantly correlated with energy cost during submaximal running at 16 km/h and 18 km/h, and a trend towards such significance was observed at 14 km/h. The present findings suggest that stiffer plantar flexors may help achieve better running performance, with greater running economy, in endurance runners. Therefore, in the clinical setting, passive stiffness of the plantar flexors may be a potential parameter for assessing running performance. © Georg Thieme Verlag KG Stuttgart · New York.

  2. A multiwell platform for studying stiffness-dependent cell biology.

    Science.gov (United States)

    Mih, Justin D; Sharif, Asma S; Liu, Fei; Marinkovic, Aleksandar; Symer, Matthew M; Tschumperlin, Daniel J

    2011-01-01

    Adherent cells are typically cultured on rigid substrates that are orders of magnitude stiffer than their tissue of origin. Here, we describe a method to rapidly fabricate 96 and 384 well platforms for routine screening of cells in tissue-relevant stiffness contexts. Briefly, polyacrylamide (PA) hydrogels are cast in glass-bottom plates, functionalized with collagen, and sterilized for cell culture. The Young's modulus of each substrate can be specified from 0.3 to 55 kPa, with collagen surface density held constant over the stiffness range. Using automated fluorescence microscopy, we captured the morphological variations of 7 cell types cultured across a physiological range of stiffness within a 384 well plate. We performed assays of cell number, proliferation, and apoptosis in 96 wells and resolved distinct profiles of cell growth as a function of stiffness among primary and immortalized cell lines. We found that the stiffness-dependent growth of normal human lung fibroblasts is largely invariant with collagen density, and that differences in their accumulation are amplified by increasing serum concentration. Further, we performed a screen of 18 bioactive small molecules and identified compounds with enhanced or reduced effects on soft versus rigid substrates, including blebbistatin, which abolished the suppression of lung fibroblast growth at 1 kPa. The ability to deploy PA gels in multiwell plates for high throughput analysis of cells in tissue-relevant environments opens new opportunities for the discovery of cellular responses that operate in specific stiffness regimes.

  3. A multiwell platform for studying stiffness-dependent cell biology.

    Directory of Open Access Journals (Sweden)

    Justin D Mih

    Full Text Available Adherent cells are typically cultured on rigid substrates that are orders of magnitude stiffer than their tissue of origin. Here, we describe a method to rapidly fabricate 96 and 384 well platforms for routine screening of cells in tissue-relevant stiffness contexts. Briefly, polyacrylamide (PA hydrogels are cast in glass-bottom plates, functionalized with collagen, and sterilized for cell culture. The Young's modulus of each substrate can be specified from 0.3 to 55 kPa, with collagen surface density held constant over the stiffness range. Using automated fluorescence microscopy, we captured the morphological variations of 7 cell types cultured across a physiological range of stiffness within a 384 well plate. We performed assays of cell number, proliferation, and apoptosis in 96 wells and resolved distinct profiles of cell growth as a function of stiffness among primary and immortalized cell lines. We found that the stiffness-dependent growth of normal human lung fibroblasts is largely invariant with collagen density, and that differences in their accumulation are amplified by increasing serum concentration. Further, we performed a screen of 18 bioactive small molecules and identified compounds with enhanced or reduced effects on soft versus rigid substrates, including blebbistatin, which abolished the suppression of lung fibroblast growth at 1 kPa. The ability to deploy PA gels in multiwell plates for high throughput analysis of cells in tissue-relevant environments opens new opportunities for the discovery of cellular responses that operate in specific stiffness regimes.

  4. Evaluation of arterial stiffness in nondiabetic chronic kidney disease patients

    Directory of Open Access Journals (Sweden)

    Bodanapu Mastanvalli

    2017-01-01

    Full Text Available Chronic kidney disease (CKD is a growing problem worldwide. Clinical and epidemiologic studies have shown that structural and functional changes that occur in major arteries are a major contributing factor to the high mortality in uremic patients. Recent studies have shown a stepwise increase of the carotid-femoral pulse wave velocity (cfPWV from CKD Stage 1 to Stage 5. We evaluated the cfPWV and augmentation index (AIx, as indirect markers of arterial stiffness in patients with nondiabetic CKD and compared the values with normal population; we also evaluated the relationship between various stages of CKD and arterial stiffness markers. This cross-sectional study was carried out in the Department of Nephrology for a duration of two years from January 15, 2012, to January 14, 2014. Fifty patients with nondiabetic CKD were studied along with 50 healthy volunteers who did not have CKD, who served as controls. Assessment of arterial stiffness (blood pressure, PWV, heart rate, aortic augmentation pressure, and AIx was performed using the PeriScope device. PWV positively correlated with systolic and diastolic blood pressure, mean aortic arterial pressure, serum creatinine, and serum uric acid and negatively correlated with estimated glomerular filtration rate. Arterial stiffness increased as CKD stage increased and was higher in nondiabetic CKD group than in the general population. Arterial stiffness progressed gradually from CKD Stage 2 to 5, and then abruptly, in dialysis patients. Measures to decrease the arterial stiffness and its influence on decreasing cardiovascular events need further evaluation.

  5. Identification of sudden stiffness changes in the acceleration response of a bridge to moving loads using ensemble empirical mode decomposition

    Science.gov (United States)

    Aied, H.; González, A.; Cantero, D.

    2016-01-01

    The growth of heavy traffic together with aggressive environmental loads poses a threat to the safety of an aging bridge stock. Often, damage is only detected via visual inspection at a point when repairing costs can be quite significant. Ideally, bridge managers would want to identify a stiffness change as soon as possible, i.e., as it is occurring, to plan for prompt measures before reaching a prohibitive cost. Recent developments in signal processing techniques such as wavelet analysis and empirical mode decomposition (EMD) have aimed to address this need by identifying a stiffness change from a localised feature in the structural response to traffic. However, the effectiveness of these techniques is limited by the roughness of the road profile, the vehicle speed and the noise level. In this paper, ensemble empirical mode decomposition (EEMD) is applied by the first time to the acceleration response of a bridge model to a moving load with the purpose of capturing sudden stiffness changes. EEMD is more adaptive and appears to be better suited to non-linear signals than wavelets, and it reduces the mode mixing problem present in EMD. EEMD is tested in a variety of theoretical 3D vehicle-bridge interaction scenarios. Stiffness changes are successfully identified, even for small affected regions, relatively poor profiles, high vehicle speeds and significant noise. The latter is due to the ability of EEMD to separate high frequency components associated to sudden stiffness changes from other frequency components associated to the vehicle-bridge interaction system.

  6. Dynamic shear stiffness and damping ratio of marine calcareous and siliceous sands

    Science.gov (United States)

    Javdanian, Hamed; Jafarian, Yaser

    2018-03-01

    Shear stiffness and damping ratio of two marine calcareous and siliceous sands were evaluated through an experimental program. Resonant column and cyclic triaxial experiments were conducted to measure the dynamic properties of the sands in small and large shear strain amplitudes. The tests were conducted under various initial stress-density conditions. The influence of effective confining pressure on the dynamic properties of the sands was assessed and compared in a preceding paper. It was shown that the calcareous sand has higher shear stiffness and lower damping ratio in comparison to the siliceous sand. In this note, the results are presented in more details and the dynamic behavior curves of the studied sands are compared with some available models, mostly developed based on the laboratory data of siliceous sands. This comparative study reveals that the previous models predict the dynamic properties of the calcareous sand in less precision than those of the siliceous sand.

  7. A Numerical Analysis of the Resistance and Stiffness of the Timber and Concrete Composite Beam

    Science.gov (United States)

    Szumigała, Ewa; Szumigała, Maciej; Polus, Łukasz

    2015-03-01

    The article presents the results of a numerical analysis of the load capacity and stiffness of the composite timber and concrete beam. Timber and concrete structures are relatively new, they have not been thoroughly tested and they are rarely used because of technological constraints. One of the obstacles to using them is difficulty with finding a method which would allow successful cooperation between concrete and timber, which has been proposed by the authors of the present article. The modern idea of sustainable construction design requires the use of new more environmentally-friendly solutions. Wood as an ecological material is easily accessible, less energy-consuming, and under certain conditions more corrosion-resistant than steel. The analysis presented in the article showed that cooperation between a wooden beam and a concrete slab on profiled steel sheeting is possible. The analysed composite beam has a greater load capacity and stiffness than the wooden beam.

  8. Effect of relative pile’s stiffness on lateral pile response under loading of large eccentricity

    DEFF Research Database (Denmark)

    Zania, Varvara; Hededal, Ole; Klinkvort, R.T.

    2015-01-01

    The wide application of monopiles as foundations for offshore wind turbines has raised the issue of the suitability of the p –y curves proposed by API for lateral pile loading, since the latter were developed after full-scale tests on flexible and slender piles. This study investigates the role...... of the relative pile’s stiffness, when it is subjected to lateral load of large eccentricity. Employing centrifuge experiments, a hollow steel pile well instrumented with strain gauge pairs has been subjected to lateral load. The bending moment distribution of the model pile embedded in uniform, dense, dry sand...... was obtained under two different stress levels and two different embedment depths. Hence, the p – y curves were obtained providing an insight into the effect of the relative pile’s stiffness on the soil – pile interaction, while the effect of the installation process could also be evaluated....

  9. Response of stiff piles to random two-way lateral loading

    DEFF Research Database (Denmark)

    Bakmar, Christian LeBlanc; Byrne, B.W.; Houlsby, G. T.

    2010-01-01

    A model for predicting the accumulated rotation of stiff piles under random two-way loading is presented. The model is based on a strain superposition rule similar to Miner's rule and uses rainflow-counting to decompose a random time-series of varying loads into a set of simple load reversals. Th....... The method is consistent with the work of LeBlanc et al. (2010) and is supported by 1g laboratory tests. An example is given for an offshore wind turbine indicating that accumulated pile rotation during the life of the turbine is dominated by the worst expected load.......A model for predicting the accumulated rotation of stiff piles under random two-way loading is presented. The model is based on a strain superposition rule similar to Miner's rule and uses rainflow-counting to decompose a random time-series of varying loads into a set of simple load reversals...

  10. Unidirectional variable stiffness hydraulic actuator for load-carrying knee exoskeleton

    Directory of Open Access Journals (Sweden)

    Jun Zhu

    2017-01-01

    Full Text Available This article presents the design and experimental testing of a unidirectional variable stiffness hydraulic actuator for load-carrying knee exoskeleton. The proposed actuator is designed for mimicking the high-efficiency passive behavior of biological knee and providing actively assistance in locomotion. The adjustable passive compliance of exoskeletal knee is achieved through a variable ratio lever mechanism with linear elastic element. A compact customized electrohydraulic system is also designed to accommodate application demands. Preliminary experimental results show the prototype has good performances in terms of stiffness regulation and joint torque control. The actuator is also implemented in an exoskeleton knee joint, resulting in anticipant human-like passive compliance behavior.

  11. A Numerical Analysis of the Resistance and Stiffness of the Timber and Concrete Composite Beam

    Directory of Open Access Journals (Sweden)

    Szumigała Ewa

    2015-03-01

    Full Text Available The article presents the results of a numerical analysis of the load capacity and stiffness of the composite timber and concrete beam. Timber and concrete structures are relatively new, they have not been thoroughly tested and they are rarely used because of technological constraints. One of the obstacles to using them is difficulty with finding a method which would allow successful cooperation between concrete and timber, which has been proposed by the authors of the present article. The modern idea of sustainable construction design requires the use of new more environmentally-friendly solutions. Wood as an ecological material is easily accessible, less energy-consuming, and under certain conditions more corrosion-resistant than steel. The analysis presented in the article showed that cooperation between a wooden beam and a concrete slab on profiled steel sheeting is possible. The analysed composite beam has a greater load capacity and stiffness than the wooden beam.

  12. A new pneumatic suspension system with independent stiffness and ride height tuning capabilities

    Science.gov (United States)

    Yin, Zhihong; Khajepour, Amir; Cao, Dongpu; Ebrahimi, Babak; Guo, Konghui

    2012-12-01

    This paper introduces a new pneumatic spring for vehicle suspension systems, allowing independent tuning of stiffness and ride height according to different vehicle operating conditions and driver preferences. The proposed pneumatic spring comprises a double-acting pneumatic cylinder, two accumulators and a tuning subsystem. This paper presents a detailed description of the pneumatic spring and its working principle. The mathematical model is established based on principles of thermo and fluid dynamics. An experimental setup has been designed and fabricated for testing and evaluating the proposed pneumatic spring. The analytical and experimental results confirm the capability of the new pneumatic spring system for independent tuning of stiffness and ride height. The mathematical model is verified and the capabilities of the pneumatic spring are further proved. It is concluded that this new pneumatic spring provides a more flexible suspension design alternative for meeting various conflicting suspension requirements for ride comfort and performance.

  13. Impact attenuation properties of jazz shoes alter lower limb joint stiffness during jump landings.

    Science.gov (United States)

    Fong Yan, Alycia; Smith, Richard M; Hiller, Claire E; Sinclair, Peter J

    2017-05-01

    To quantify the impact attenuation properties of the jazz shoes, and to investigate the in-vivo effect of four jazz shoe designs on lower limb joint stiffness during a dance-specific jump. Repeated measures. A custom-built mechanical shoe tester similar to that used by athletic shoe companies was used to vertically impact the forefoot and heel region of four different jazz shoe designs. Additionally, dancers performed eight sautés in second position in bare feet and the shoe conditions. Force platforms and 3D-motion capture were used to analyse the joint stiffness of the midfoot, ankle, knee and hip during the jump landings. Mechanical testing of the jazz shoes revealed significant differences in impact attenuation characteristics among each of the jazz shoe designs. Gross knee and midfoot joint stiffness were significantly affected by the jazz shoe designs in the dancers' jump landings. The tested jazz shoe designs altered the impact attenuating capacity of jump landing technique in dancers. The cushioned jazz shoes are recommended particularly for injured dancers to reduce impact on the lower limb. Jazz shoe design should consider the impact attenuation properties of the forefoot region, due to the toe-strike landing technique in dance movement. Copyright © 2016 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

  14. Impact of hypertension severity on arterial stiffness, cerebral vasoreactivity, and cognitive performance

    Science.gov (United States)

    Muela, Henrique Cotchi Simbo; Costa-Hong, Valeria A.; Yassuda, Monica Sanches; Machado, Michel Ferreira; Nogueira, Ricardo de Carvalho; Moraes, Natalia C.; Memória, Claudia Maia; Macedo, Thiago A.; Bor-Seng-Shu, Edson; Massaro, Ayrton Roberto; Nitrini, Ricardo; Bortolotto, Luiz A.

    2017-01-01

    ABSTRACT. Aging, hypertension (HTN), and other cardiovascular risk factors contribute to structural and functional changes of the arterial wall. Objective: To evaluate whether arterial stiffness (AS) is related to cerebral blood flow changes and its association with cognitive function in patients with hypertension. Methods: 211 patients (69 normotensive and 142 hypertensive) were included. Patients with hypertension were divided into 2 stages: HTN stage-1 and HTN stage-2. The mini-mental state examination (MMSE), Montreal Cognitive Assessment (MoCA) and a battery of neuropsychological (NPE) tests were used to determine cognitive function. Pulse wave velocity was measured using the Complior®. Carotid properties were assessed by radiofrequency ultrasound. Central arterial pressure and augmentation index were obtained using applanation tonometry. Middle cerebral artery flow velocity was measured by transcranial Doppler ultrasonography. Results: Both arterial stiffness parameters and cerebral vasoreactivity worsened in line with HTN severity. There was a negative correlation between breath holding index (BHI) and arterial stiffness parameters. Cognitive performance worsened in line with HTN severity, with statistical difference occurring mainly between the HTN-2 and normotension groups on both the MMSE and MoCA. The same tendency was observed on the NPE tests. Conclusion: Hypertension severity was associated with higher AS, worse BHI, and lower cognitive performance. PMID:29354219

  15. Dynamics of compressible gas-liquid flows with a stiff density ratio

    International Nuclear Information System (INIS)

    Cortes, Julien

    1999-01-01

    This work is devoted to the study of transient two-phase flows when the ratio of the two densities is stiff. At first, we review briefly some of the basic principles about two-phase flow, hyperbolicity and the finite volume method. Then we develop a perturbation method, based on the stiffness of the density ratio, to examine the Eigen-structure of two-fluid models. Indeed, in such models, complex phasic interactions yield a complex Eigen-structure which may raise numerous problems in simulations. We show that our approach provides a convenient frame to study the hyperbolicity of such models. At this stage, advanced numerical tests are computed showing the efficiency of our approach in the context of unstructured multidimensional meshes. Our tests are validated for non-equilibrium flows using experimental data or through mesh refinements. At last, we use the scaling of the densities to analyse how momentum is transferred between phases in the context of bubbly flows. We study the relevance of a stiff relaxation term related to the ratio of the densities using linear stability properties and Chapman-Enskog expansions. Our results and some numerical computations tends to show that such a system is apparently well-posed despite being 'weakly' hyperbolic. (author) [fr

  16. Pneumatic Artificial Muscles Force Modelling and the Position and Stiffness Control on the Knee Joint of the Musculoskeletal Leg

    Directory of Open Access Journals (Sweden)

    Jingtao Lei

    2017-03-01

    Full Text Available Pneumatic artificial muscles (PAMs have properties similar to biological muscle and are widely used in robotics as actuators. A musculoskeletal leg mechanism driven by PAMs is presented in this paper. The joint stiffness of the musculoskeletal bionic leg for jumping movement needs to be analysed. The synchronous control on the position and stiffness of the joint is important to improve the flexibility of leg. The accurate force model of PAM is the foundation to achieving better control and dynamic jumping performance. The experimental platform of PAM is conducted, and the static equal pressure experiments are performed to obtain the PAM force model. According to the testing data, parameter identification method is adopted to determine the force model of PAM. A simulation on the position and stiffness control of the knee joint is performed, and the simulation results show the effectiveness of the presented method.

  17. Interlimb symmetry of dynamic knee joint stiffness and co-contraction is maintained in early stage knee osteoarthritis.

    Science.gov (United States)

    Collins, A T; Richardson, R T; Higginson, J S

    2014-08-01

    Individuals with knee OA often exhibit greater co-contraction of antagonistic muscle groups surrounding the affected joint which may lead to increases in dynamic joint stiffness. These detrimental changes in the symptomatic limb may also exist in the contralateral limb, thus contributing to its risk of developing knee osteoarthritis. The purpose of this study is to investigate the interlimb symmetry of dynamic knee joint stiffness and muscular co-contraction in knee osteoarthritis. Muscular co-contraction and dynamic knee joint stiffness were assessed in 17 subjects with mild to moderate unilateral medial compartment knee osteoarthritis and 17 healthy control subjects while walking at a controlled speed (1.0m/s). Paired and independent t-tests determined whether significant differences exist between groups (pknees compared to the healthy group (p=0.051). Subjects with mild to moderate knee osteoarthritis maintain symmetric control strategies during gait. Copyright © 2014 Elsevier Ltd. All rights reserved.

  18. A new method of measuring the stiffness of corpus cavernosum penis with ShearWave™ Elastography.

    Science.gov (United States)

    Zhang, J-J; Qiao, X-H; Gao, F; Li, F; Bai, M; Zhang, H-P; Liu, Y; Du, L-F; Xing, J-F

    2015-04-01

    To evaluate the feasibility of measuring the stiffness of corpus cavernosum penis (CCP) with ShearWave™ Elastography (SWE; SuperSonic Imagine, Aix-en-Provence, France). 40 healthy volunteers with ages ranging from 19 to 81 years (mean, 36 years; standard deviation, 17 years) were selected in this study. The ultrafast ultrasound device Aixplorer(®) (SuperSonic Imagine) was used for the research and the probe selected was SuperLinear™ SL15-4 (SuperSonic Imagine). The shear wave stiffness (SWS) of CCP was measured using SWE images. The measurement indexes of SWS included (1) SWS of CCP measured in the transverse section (SWS-T), (2) SWS of CCP measured in the longitudinal section (SWS-L) and (3) mean of SWS-T and SWS-L (SWS-M). The interval between hormone test and SWE examination of each subject was less than 7 days. The paired t-test was used to analyse the differences between SWS-T and SWS-L. The Pearson correlation was used to analyse the correlation of SWS of CCP with age as well as with sex hormone levels. There was no significant difference between SWS-T and SWS-L (p > 0.05). SWS (SWS-T, SWS-L, SWS-M) was negatively correlated with age and oestradiol value, and SWS (SWS-T, SWS-L, SWS-M) was positively correlated with testosterone value. SWE could serve as a new non-invasive method of evaluating the stiffness of CCP. It is the first time that we have discussed the feasibility of measuring the stiffness of CCP with SWE and analysed the correlation of SWS of CCP with age as well as with sex hormone levels.

  19. A simplified procedure for mass and stiffness estimation of existing structures

    Science.gov (United States)

    Nigro, Antonella; Ditommaso, Rocco; Carlo Ponzo, Felice; Salvatore Nigro, Domenico

    2016-04-01

    This work focuses the attention on a parametric method for mass and stiffness identification of framed structures, based on frequencies evaluation. The assessment of real structures is greatly affected by the consistency of information retrieved on materials and on the influence of both non-structural components and soil. One of the most important matter is the correct definition of the distribution, both in plan and in elevation, of mass and stiffness: depending on concentrated and distributed loads, the presence of infill panels and the distribution of structural elements. In this study modal identification is performed under several mass-modified conditions and structural parameters consistent with the identified modal parameters are determined. Modal parameter identification of a structure before and after the introduction of additional masses is conducted. By considering the relationship between the additional masses and modal properties before and after the mass modification, structural parameters of a damped system, i.e. mass, stiffness and damping coefficient are inversely estimated from these modal parameters variations. The accuracy of the method can be improved by using various mass-modified conditions. The proposed simplified procedure has been tested on both numerical and experimental models by means linear numerical analyses and shaking table tests performed on scaled structures at the Seismic Laboratory of the University of Basilicata (SISLAB). Results confirm the effectiveness of the proposed procedure to estimate masses and stiffness of existing real structures with a maximum error equal to 10%, under the worst conditions. Acknowledgements This study was partially funded by the Italian Civil Protection Department within the project DPC-RELUIS 2015 - RS4 ''Seismic observatory of structures and health monitoring''.

  20. Hydration Status Is Associated with Aortic Stiffness, but Not with Peripheral Arterial Stiffness, in Chronically Hemodialysed Patients

    Directory of Open Access Journals (Sweden)

    Daniel Bia

    2015-01-01

    Full Text Available Background. Adequate fluid management could be essential to minimize high arterial stiffness observed in chronically hemodialyzed patients (CHP. Aim. To determine the association between body fluid status and central and peripheral arterial stiffness levels. Methods. Arterial stiffness was assessed in 65 CHP by measuring the pulse wave velocity (PWV in a central arterial pathway (carotid-femoral and in a peripheral pathway (carotid-brachial. A blood pressure-independent regional arterial stiffness index was calculated using PWV. Volume status was assessed by whole-body multiple-frequency bioimpedance. Patients were first observed as an entire group and then divided into three different fluid status-related groups: normal, overhydration, and dehydration groups. Results. Only carotid-femoral stiffness was positively associated (P<0.05 with the hydration status evaluated through extracellular/intracellular fluid, extracellular/Total Body Fluid, and absolute and relative overhydration. Conclusion. Volume status and overload are associated with central, but not peripheral, arterial stiffness levels with independence of the blood pressure level, in CHP.

  1. Quantitative Maximum Shear-Wave Stiffness of Breast Masses as a Predictor of Histopathologic Severity.

    Science.gov (United States)

    Berg, Wendie A; Mendelson, Ellen B; Cosgrove, David O; Doré, Caroline J; Gay, Joel; Henry, Jean-Pierre; Cohen-Bacrie, Claude

    2015-08-01

    The objective of our study was to compare quantitative maximum breast mass stiffness on shear-wave elastography (SWE) with histopathologic outcome. From September 2008 through September 2010, at 16 centers in the United States and Europe, 1647 women with a sonographically visible breast mass consented to undergo quantitative SWE in this prospective protocol; 1562 masses in 1562 women had an acceptable reference standard. The quantitative maximum stiffness (termed "Emax") on three acquisitions was recorded for each mass with the range set from 0 (very soft) to 180 kPa (very stiff). The median Emax and interquartile ranges (IQRs) were determined as a function of histopathologic diagnosis and were compared using the Mann-Whitney U test. We considered the impact of mass size on maximum stiffness by performing the same comparisons for masses 9 mm or smaller and those larger than 9 mm in diameter. The median patient age was 50 years (mean, 51.8 years; SD, 14.5 years; range, 21-94 years), and the median lesion diameter was 12 mm (mean, 14 mm; SD, 7.9 mm; range, 1-53 mm). The median Emax of the 1562 masses (32.1% malignant) was 71 kPa (mean, 90 kPa; SD, 65 kPa; IQR, 31-170 kPa). Of 502 malignancies, 23 (4.6%) ductal carcinoma in situ (DCIS) masses had a median Emax of 126 kPa (IQR, 71-180 kPa) and were less stiff than 468 invasive carcinomas (median Emax, 180 kPa [IQR, 138-180 kPa]; p = 0.002). Benign lesions were much softer than malignancies (median Emax, 43 kPa [IQR, 24-83 kPa] vs 180 kPa [IQR, 129-180 kPa]; p masses. Despite overlap in Emax values, maximum stiffness measured by SWE is a highly effective predictor of the histopathologic severity of sonographically depicted breast masses.

  2. Meal ingestion markedly increases liver stiffness suggesting the need for liver stiffness determination in fasting conditions.

    Science.gov (United States)

    Alvarez, Daniel; Orozco, Federico; Mella, José María; Anders, Maria; Antinucci, Florencia; Mastai, Ricardo

    2015-01-01

    The introduction of noninvasive liver stiffness (LS) determination has heralded a new stage in the diagnosis and treatment of liver fibrosis. We evaluated the effect of food intake on LS in patients with different degrees of liver disease. We evaluated 24 patients (F≤1, n=11 and F> 1, n=13). LS (Fibroscan®) and portal blood flow (PBF) (Doppler ultrasound) were studied before and 30min after ingestion of a standard liquid meal. Food intake increased PBF (51±10%, p1). Hemodynamic and LS values returned to baseline pre-meal levels within 2hours. LS increases markedly after ingestion of a standard meal, irrespective of the degree of fibrosis. Our results strongly suggest that LS should be measured in fasting conditions. Copyright © 2015 Elsevier España, S.L.U. and AEEH y AEG. All rights reserved.

  3. Evaluation of stiffness and plastic deformation of active ceramic self-ligating bracket clips after repetitive opening and closure movements.

    Science.gov (United States)

    Carneiro, Grace Kelly Martins; Roque, Juliano Alves; Segundo, Aguinaldo Silva Garcez; Suzuki, Hideo

    2015-01-01

    The aim of this study was to assess whether repetitive opening and closure of self-ligating bracket clips can cause plastic deformation of the clip. Three types of active/interactive ceramic self-ligating brackets (n = 20) were tested: In-Ovation C, Quicklear and WOW. A standardized controlled device performed 500 cycles of opening and closure movements of the bracket clip with proper instruments and techniques adapted as recommended by the manufacturer of each bracket type. Two tensile tests, one before and one after the repetitive cycles, were performed to assess the stiffness of the clips. To this end, a custom-made stainless steel 0.40 x 0.40 mm wire was inserted into the bracket slot and adapted to the universal testing machine (EMIC DL2000), after which measurements were recorded. On the loading portion of the loading-unloading curve of clips, the slope fitted a first-degree equation curve to determine the stiffness/deflection rate of the clip. The results of plastic deformation showed no significant difference among bracket types before and after the 500 cycles of opening and closure (p = 0.811). There were significant differences on stiffness among the three types of brackets (p = 0.005). The WOW bracket had higher mean values, whereas Quicklear bracket had lower values, regardless of the opening/closure cycle. Repetitive controlled opening and closure movements of the clip did not alter stiffness or cause plastic deformation.

  4. Arterial Stiffness and Walk Time in Patients with End-Stage Renal Disease

    Directory of Open Access Journals (Sweden)

    Abbi D. Lane

    2013-04-01

    Full Text Available Background: End-stage renal disease patients experience increased prevalence of cardiovascular disease. Heart-artery interaction may be shifted, impacting blood pressure lability, and exercise tolerance. The coupling ratio consists of the ratio of indexed arterial elastance (EaI, arterial load to ElvI, a measure of cardiac contractility or stiffness. Our purpose was to explore the relationship between elastances and functional capacity. We hypothesized that arterial stiffness (central pulse wave velocity, PWV and elastances would be correlated to shuttle walk time. Methods: We used applanation tonometry, ultrasonography, and a shuttle walk test to evaluate our hypothesis. Spearman's correlations were used to assess relationships between variables. Block regression was also performed. Results: Forty-two subjects on maintenance hemodialysis participated. Average age=44±5 years, body surface area=2.01 kg/m2. Mean EaI=4.45 and mean ElvI=6.89; the coupling ratio=0.82. Mean aortic pulse pressure=51 mmHg and PWV=9.6 m/s. PWV(r=-0.385 and EaI (r=-0.424 were significantly and inversely related to walking time while stroke volume index (SVI was positively correlated to shuttle walk time (r=0.337, pConclusions: We conclude that, like other clinical populations, both arterial and heart function predict walking ability and represent potential targets for intervention; arterial stiffness and SVI are strongly related to shuttle walk time in patients with ESRD.

  5. Generating random walks and polygons with stiffness in confinement

    International Nuclear Information System (INIS)

    Diao, Y; Ernst, C; Saarinen, S; Ziegler, U

    2015-01-01

    The purpose of this paper is to explore ways to generate random walks and polygons in confinement with a bias toward stiffness. Here the stiffness refers to the curvature angle between two consecutive edges along the random walk or polygon. The stiffer the walk (polygon), the smaller this angle on average. Thus random walks and polygons with an elevated stiffness have lower than expected curvatures. The authors introduced and studied several generation algorithms with a stiffness parameter s>0 that regulates the expected curvature angle at a given vertex in which the random walks and polygons are generated one edge at a time using conditional probability density functions. Our generating algorithms also allow the generation of unconfined random walks and polygons with any desired mean curvature angle. In the case of random walks and polygons confined in a sphere of fixed radius, we observe that, as expected, stiff random walks or polygons are more likely to be close to the confinement boundary. The methods developed here require that the random walks and random polygons be rooted at the center of the confinement sphere. (paper)

  6. Three Days of Intermittent Fasting: Repeated-Sprint Performance Decreased by Vertical-Stiffness Impairment.

    Science.gov (United States)

    Cherif, Anissa; Meeusen, Romain; Farooq, Abdulaziz; Ryu, Joong; Fenneni, Mohamed Amine; Nikolovski, Zoran; Elshafie, Sittana; Chamari, Karim; Roelands, Bart

    2017-03-01

    To examine the effects of 3 d of intermittent fasting (3d-IF: abstaining from eating/drinking from dawn to sunset) on physical performance and metabolic responses to repeated sprints (RSs). Twenty-one active males performed an RS test (2 sets: 5 × 5-s maximal sprints with 25 s of recovery between and 3 min of recovery between sets on an instrumented treadmill) in 2 conditions: counterbalanced fed/control session (CS) and fasting session (FS). Biomechanical and biochemical markers were assessed preexercise and postexercise. Significant main effects of IF were observed for sprints: maximal speed (P = .016), mean speed (P = .015), maximal power (P = .035), mean power (P = .049), vertical stiffness (P = .032), and vertical center-of-mass displacement (P = .047). Sprint speed and vertical stiffness decreased during the 1st (P = .003 and P = .005) and 2nd sprints (P = .046 and P = .048) of set 2, respectively. Postexercise insulin decreased in CS (P = .023) but not in FS (P = .230). Free-fatty-acid levels were higher in FS than in CS at preexercise (P < .001) and at postexercise (P = .009). High-density lipoprotein cholesterol (HDL-C) was higher at postexercise in FS (1.32 ± 0.22 mmol/L) than in CS (1.26 ± 0.21 mmol/L, P = .039). The triglyceride (TG) concentration was decreased in FS (P < .05) compared with CS. 3d-IF impaired speed and power through a decrease in vertical stiffness during the initial runs of the 2nd set of RS. The findings of the current study confirmed the benefits of 3d-IF: improved HDL-C and TG profiles while maintaining total cholesterol and low-density lipoprotein cholesterol levels. Moreover, improving muscle power might be a key factor to retain a higher vertical stiffness and to partly counteract the negative effects of intermittent fasting.

  7. Acute effects of repeated bouts of aerobic exercise on arterial stiffness after glucose ingestion.

    Science.gov (United States)

    Kobayashi, Ryota; Hashimoto, Yuto; Hatakeyama, Hiroyuki; Okamoto, Takanobu

    2018-03-22

    The aim of this study was to investigate the acute repeated bouts of aerobic exercise decrease leg arterial stiffness. However, the influence of repeated bouts of aerobic exercise on arterial stiffness after glucose ingestion is unknown. The present study investigates the acute effects of repeated bouts of aerobic exercise on arterial stiffness after the 75-g oral glucose tolerance test (OGTT). Ten healthy young men (age, 23.2 ± 0.9 years) performed repeated bouts of aerobic exercise trial (RE, 65% peak oxygen uptake; two 15 min bouts of cycling performed 20 min apart) and control trial (CON, seated and resting in a quiet room) at 80 min before the 75-g OGTT on separate days in a randomized, controlled crossover fashion. Carotid-femoral (aortic) and femoral-ankle (leg) pulse wave velocity, carotid augmentation index, brachial and ankle blood pressure, heart rate and blood glucose and insulin levels were measured before (baseline) and 30, 60 and 120 min after the 75-g OGTT. Leg pulse wave velocity, ankle systolic blood pressure and blood glucose levels increased from baseline after the 75-g OGTT in the CON trial, but not in the RE trial. The present findings indicate that acute repeated bouts of aerobic exercise before glucose ingestion suppress increases in leg arterial stiffness following glucose ingestion. RE trial repeated bouts of aerobic exercise trial; CON trial control trial; BG blood glucose; VO 2peak peak oxygen uptake; PWV Pulse wave velocity; AIx carotid augmentation index; BP blood pressure; HR heart rate; CVs coefficients of variation; RPE Ratings of perceived exertion; SE standard error.

  8. Inverse axial mounting stiffness design for lithographic projection lenses.

    Science.gov (United States)

    Wen-quan, Yuan; Hong-bo, Shang; Wei, Zhang

    2014-09-01

    In order to balance axial mounting stiffness of lithographic projection lenses and the image quality under dynamic working conditions, an easy inverse axial mounting stiffness design method is developed in this article. Imaging quality deterioration at the wafer under different axial vibration levels is analyzed. The desired image quality can be determined according to practical requirements, and axial vibrational tolerance of each lens is solved with the damped least-squares method. Based on adaptive interval adjustment, a binary search algorithm, and the finite element method, the axial mounting stiffness of each lens can be traveled in a large interval, and converges to a moderate numerical solution which makes the axial vibrational amplitude of the lens converge to its axial vibrational tolerance. Model simulation is carried out to validate the effectiveness of the method.

  9. Mixed, Nonsplit, Extended Stability, Stiff Integration of Reaction Diffusion Equations

    KAUST Repository

    Alzahrani, Hasnaa H.

    2016-07-26

    A tailored integration scheme is developed to treat stiff reaction-diffusion prob- lems. The construction adapts a stiff solver, namely VODE, to treat reaction im- plicitly together with explicit treatment of diffusion. The second-order Runge-Kutta- Chebyshev (RKC) scheme is adjusted to integrate diffusion. Spatial operator is de- scretised by second-order finite differences on a uniform grid. The overall solution is advanced over S fractional stiff integrations, where S corresponds to the number of RKC stages. The behavior of the scheme is analyzed by applying it to three simple problems. The results show that it achieves second-order accuracy, thus, preserving the formal accuracy of the original RKC. The presented development sets the stage for future extensions, particularly, to multidimensional reacting flows with detailed chemistry.

  10. Mass and stiffness calibration of nanowires using thermally driven vibration

    International Nuclear Information System (INIS)

    Kiracofe, D R; Raman, A; Yazdanpanah, M M

    2011-01-01

    Cantilevered or suspended nanowires show promise for force or mass sensing applications due to their small mass, high force sensitivity and high frequency bandwidth. To use these as quantitative sensors, their bending stiffness or mass must be calibrated experimentally, often using thermally driven vibration. However, this can be difficult because nanowires are slightly asymmetric, which results in two spatially orthogonal bending eigenmodes with closely spaced frequencies. This asymmetry presents problems for traditional stiffness calibration methods, which equate the measured thermal vibration spectrum near a resonance to that of a single eigenmode. Moreover, the principal axes may be arbitrarily rotated with respect to the measurement direction. In this work, the authors propose a method for calibrating the bending stiffness and mass of such nanowires' eigenmodes using a single measurement taken at an arbitrary orientation with respect to the principal axes.

  11. Analytical study of a quasi-zero stiffness coupling using a torsion magnetic spring with negative stiffness

    Science.gov (United States)

    Zheng, Yisheng; Zhang, Xinong; Luo, Yajun; Zhang, Yahong; Xie, Shilin

    2018-02-01

    By now, many translation quasi-zero stiffness (QZS) mechanisms have been proposed to overcome the restriction between the isolation frequency range and the load bearing capacity of linear isolators. The couplings of rotor systems undertake the functions of transmitting static driving torque and isolating disturbing torque simultaneously, which creates the demand of torsion QZS mechanisms. Hence a QZS coupling is presented in this paper, where a torsion magnetic spring (TMS) composed of two coaxial ring magnet arrangements in repulsive configuration is employed to produce negative torsion stiffness to counteract the positive stiffness of a rubber spring. In this paper, the expressions of magnetic torque and stiffness are given firstly and verified by finite element simulations; and the effect of geometric parameters of the TMS on its stiffness characteristic is analyzed in detail, which contributes to the optimal design of the TMS. Then dynamic analysis of the QZS coupling is performed and the analytical expression of the torque transmissibility is achieved based on the Harmonic Balance Method. Finally, simulation of the torque transmissibility is carried out to reveal how geometric parameters of the TMS affect the isolation performance.

  12. Modifiable risk factors for increased arterial stiffness in outpatient nephrology.

    Directory of Open Access Journals (Sweden)

    Usama Elewa

    Full Text Available Arterial stiffness, as measured by pulse wave velocity (PWV, is an independent predictor of cardiovascular events and mortality. Arterial stiffness increases with age. However, modifiable risk factors such as smoking, BP and salt intake also impact on PWV. The finding of modifiable risk factors may lead to the identification of treatable factors, and, thus, is of interest to practicing nephrologist. We have now studied the prevalence and correlates of arterial stiffness, assessed by PWV, in 191 patients from nephrology outpatient clinics in order to identify modifiable risk factors for arterial stiffness that may in the future guide therapeutic decision-making. PWV was above normal levels for age in 85/191 (44.5% patients. Multivariate analysis showed that advanced age, systolic BP, diabetes mellitus, serum uric acid and calcium polystyrene sulfonate therapy or calcium-containing medication were independent predictors of PWV. A new parameter, Delta above upper limit of normal PWV (Delta PWV was defined to decrease the weight of age on PWV values. Delta PWV was calculated as (measured PWV - (upper limit of the age-adjusted PWV values for the general population. Mean±SD Delta PWV was 0.76±1.60 m/sec. In multivariate analysis, systolic blood pressure, active smoking and calcium polystyrene sulfonate therapy remained independent predictors of higher delta PWV, while age, urinary potassium and beta blocker therapy were independent predictors of lower delta PWV. In conclusion, arterial stiffness was frequent in nephrology outpatients. Systolic blood pressure, smoking, serum uric acid, calcium-containing medications, potassium metabolism and non-use of beta blockers are modifiable factors associated with increased arterial stiffness in Nephrology outpatients.

  13. Betel nut chewing associated with increased risk of arterial stiffness.

    Science.gov (United States)

    Wei, Yu-Ting; Chou, Yu-Tsung; Yang, Yi-Ching; Chou, Chieh-Ying; Lu, Feng-Hwa; Chang, Chih-Jen; Wu, Jin-Shang

    2017-11-01

    Betel nut chewing is associated with certain cardiovascular outcomes. Subclinical atherosclerosis may be one link between betel nut chewing and cardiovascular risk. Few studies have examined the association between chewing betel nut and arterial stiffness. The aim of this study was thus to determine the relationship between betel nut chewing and arterial stiffness in a Taiwanese population. We enrolled 7540 eligible subjects in National Cheng Kung University Hospital from October 2006 to August 2009. The exclusion criteria included history of cerebrovascular events, coronary artery disease, and taking lipid-lowering drugs, antihypertensives, and hypoglycemic agents. Increased arterial stiffness was defined as brachial-ankle pulse wave velocity (baPWV) ≥1400cm/s. According to their habit of betel nut use, the subjects were categorized into non-, ex-, and current chewers. The prevalence of increased arterial stiffness was 32.7, 43.3, and 43.2% in non-, ex- and current chewers, respectively (p=0.011). Multiple logistic regression analysis revealed that ex-chewers (odds ratio [OR] 1.69, 95% confidence interval (CI)=1.08-2.65) and current chewers (OR 2.29, 95% CI=1.05-4.99) had elevated risks of increased arterial stiffness after adjustment for co-variables. Both ex- and current betel nut chewing were associated with a higher risk of increased arterial stiffness. Stopping betel nut chewing may thus potentially be beneficial to reduce cardiovascular risk, based on the principals of preventive medicine. Copyright © 2017 Elsevier B.V. All rights reserved.

  14. Evaluation of Stiffness Changes in a High-Rise Building by Measurements of Lateral Displacements Using GPS Technology

    Science.gov (United States)

    Choi, Se Woon; Kim, Ill Soo; Park, Jae Hwan; Kim, Yousok; Sohn, Hong Gyoo; Park, Hyo Seon

    2013-01-01

    The outrigger truss system is one of the most frequently used lateral load resisting structural systems. However, little research has been reported on the effect of installation of outrigger trusses on improvement of lateral stiffness of a high-rise building through full-scale measurements. In this paper, stiffness changes of a high-rise building due to installation of outrigger trusses have been evaluated by measuring lateral displacements using a global positioning system (GPS). To confirm the error range of the GPS measurement system used in the full-scale measurement tests, the GPS displacement monitoring system is investigated through a free vibration test of the experimental model. Then, for the evaluation of lateral stiffness of a high-rise building under construction, the GPS displacement monitoring system is applied to measurements of lateral displacements of a 66-story high-rise building before and after installation of outrigger truss. The stiffness improvement of the building before and after the installation is confirmed through the changes of the natural frequencies and the ratios of the base shear forces to the roof displacements. PMID:24233025

  15. Evaluation of Stiffness Changes in a High-Rise Building by Measurements of Lateral Displacements Using GPS Technology

    Directory of Open Access Journals (Sweden)

    Se Woon Choi

    2013-11-01

    Full Text Available The outrigger truss system is one of the most frequently used lateral load resisting structural systems. However, little research has been reported on the effect of installation of outrigger trusses on improvement of lateral stiffness of a high-rise building through full-scale measurements. In this paper, stiffness changes of a high-rise building due to installation of outrigger trusses have been evaluated by measuring lateral displacements using a global positioning system (GPS. To confirm the error range of the GPS measurement system used in the full-scale measurement tests, the GPS displacement monitoring system is investigated through a free vibration test of the experimental model. Then, for the evaluation of lateral stiffness of a high-rise building under construction, the GPS displacement monitoring system is applied to measurements of lateral displacements of a 66-story high-rise building before and after installation of outrigger truss. The stiffness improvement of the building before and after the installation is confirmed through the changes of the natural frequencies and the ratios of the base shear forces to the roof displacements.

  16. An analysis of valve train behavior considering stiffness effects

    International Nuclear Information System (INIS)

    Chun, Dong Joon; Lee, Jin Kab

    2000-01-01

    To maintain the specific volumetric efficiency of a heavy-duty diesel engine, an understanding of the behavior of each part of the valve train system is very important. The stiffness of the valve train system has a strong influence on the behavior of the valve train than value clearance, heat-resistance, or the durability of parts. In this study, a geometrical cam design profile using a finite element model of the valve train system is suggested. The results of the valve behavior according to the change in stiffness is analyzed for further tuning of the valve train system

  17. Arterial stiffness and sedentary lifestyle: Role of oxidative stress.

    Science.gov (United States)

    Lessiani, Gianfranco; Santilli, Francesca; Boccatonda, Andrea; Iodice, Pierpaolo; Liani, Rossella; Tripaldi, Romina; Saggini, Raoul; Davì, Giovanni

    2016-04-01

    Sedentary lifestyle is a risk factor for the development of cardiovascular disease, and leads to a quantifiable impairment in vascular function and arterial wall stiffening. We tested the hypothesis of oxidative stress as a determinant of arterial stiffness (AS) in physically inactive subjects, and challenged the reversibility of these processes after the completion of an eight-week, high-intensity exercise training (ET). AS was assessed before and after ET, measuring carotid to femoral pulse wave velocity (PWV) with a Vicorder device. At baseline and after ET, participants performed urine collection and underwent fasting blood sampling. Urinary 8-iso-PGF2α, an in vivo marker of lipid peroxidation, total, HDL and LDL cholesterol, and triglyceride concentrations were measured. ET was associated with significantly reduced urinary 8-iso-PGF2α(p<0.0001) levels. PWV was significantly reduced after ET completion (p<0.0001), and was directly related to urinary 8-iso-PGF2α(Rho=0.383, p=0.021). After ET, cardiovascular fitness improved [peak oxygen consumption (p<0.0001), peak heart rate (p<0.0001)]. However, no improvement in lipid profile was observed, apart from a significant reduction of triglycerides (p=0.022). PWV and triglycerides were significantly related (Rho=0.466, p=0.005) throughout the study period. PWV levels were also related to urinary 8-iso-PGF2α in our previously sedentary subjects. We conclude that regular physical exercise may be a natural antioxidant strategy, lowering oxidant stress and thereby the AS degree. Copyright © 2015 Elsevier Inc. All rights reserved.

  18. Increased arterial stiffness in children with congenital heart disease.

    Science.gov (United States)

    Häcker, Anna-Luisa; Reiner, Barbara; Oberhoffer, Renate; Hager, Alfred; Ewert, Peter; Müller, Jan

    2018-01-01

    Objective Central systolic blood pressure (SBP) is a measure of arterial stiffness and strongly associated with atherosclerosis and end-organ damage. It is a stronger predictor of cardiovascular events and all-cause mortality than peripheral SBP. In particular, for children with congenital heart disease, a higher central SBP might impose a greater threat of cardiac damage. The aim of the study was to analyse and compare central SBP in children with congenital heart disease and in healthy counterparts. Patients and methods Central SBP was measured using an oscillometric method in 417 children (38.9% girls, 13.0 ± 3.2 years) with various congenital heart diseases between July 2014 and February 2017. The test results were compared with a recent healthy reference cohort of 1466 children (49.5% girls, 12.9 ± 2.5 years). Results After correction for several covariates in a general linear model, central SBP of children with congenital heart disease was significantly increased (congenital heart disease: 102.1 ± 10.2 vs. healthy reference cohort: 100.4 ± 8.6, p congenital heart disease subgroups revealed higher central SBP in children with left heart obstructions (mean difference: 3.6 mmHg, p congenital heart disease have significantly higher central SBP compared with healthy peers, predisposing them to premature heart failure. Screening and long-term observations of central SBP in children with congenital heart disease seems warranted in order to evaluate the need for treatment.

  19. Evaluation of Fatigue Life of CRM-Reinforced SMA and Its Relationship to Dynamic Stiffness

    Directory of Open Access Journals (Sweden)

    Nuha Salim Mashaan

    2014-01-01

    Full Text Available Fatigue cracking is an essential problem of asphalt concrete that contributes to pavement damage. Although stone matrix asphalt (SMA has significantly provided resistance to rutting failure, its resistance to fatigue failure is yet to be fully addressed. The aim of this study is to evaluate the effect of crumb rubber modifier (CRM on stiffness and fatigue properties of SMA mixtures at optimum binder content, using four different modification levels, namely, 6%, 8%, 10%, and 12% CRM by weight of the bitumen. The testing undertaken on the asphalt mix comprises the dynamic stiffness (indirect tensile test, dynamic creep (repeated load creep, and fatigue test (indirect tensile fatigue test at temperature of 25°C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400 kPa. Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture.

  20. Evaluation of fatigue life of CRM-reinforced SMA and its relationship to dynamic stiffness.

    Science.gov (United States)

    Mashaan, Nuha Salim; Karim, Mohamed Rehan; Abdel Aziz, Mahrez; Ibrahim, Mohd Rasdan; Katman, Herda Yati; Koting, Suhana

    2014-01-01

    Fatigue cracking is an essential problem of asphalt concrete that contributes to pavement damage. Although stone matrix asphalt (SMA) has significantly provided resistance to rutting failure, its resistance to fatigue failure is yet to be fully addressed. The aim of this study is to evaluate the effect of crumb rubber modifier (CRM) on stiffness and fatigue properties of SMA mixtures at optimum binder content, using four different modification levels, namely, 6%, 8%, 10%, and 12% CRM by weight of the bitumen. The testing undertaken on the asphalt mix comprises the dynamic stiffness (indirect tensile test), dynamic creep (repeated load creep), and fatigue test (indirect tensile fatigue test) at temperature of 25°C. The indirect tensile fatigue test was conducted at three different stress levels (200, 300, and 400 kPa). Experimental results indicate that CRM-reinforced SMA mixtures exhibit significantly higher fatigue life compared to the mixtures without CRM. Further, higher correlation coefficient was obtained between the fatigue life and resilient modulus as compared to permanent strain; thus resilient modulus might be a more reliable indicator in evaluating the fatigue life of asphalt mixture.

  1. Identification of stiffness variations in supporting substances of a human canine tooth with a bracket-beam-piezoelectric sensor and its electromechanical impedance

    Directory of Open Access Journals (Sweden)

    Hector A. Tinoco

    2017-06-01

    Full Text Available In this paper, an experimental method is described to identify the stiffness variations produced by drillings done in different supporting substances of a human canine tooth. To measure the supporting substances parameters through of a canine, a sensor-actuator system was developed. The sensor-actuator device was composed of a stainless steel bracket bonded to a steel wire attached to two piezoelectric transducers, with a concentrated mass attached to the end of the wire. To excite the device, high frequency voltage (between 5 and 10 KHz was applied through the piezo-transducers, which affects the tooth by means of the vibration of the wire. High frequency mechanical vibrations allowed the appraisal of the mechanical response from the supporting substances. Mechanical responses associated with the stiffness of the support were quantified with the electrical impedance of the piezo-transducers. The device was coupled to the crown of a canine tooth simulating a condition of fixing as in the bone, the tooth was fastened by the root portion inside the supporting substance. Four supporting substances were characterized for the tests. After establishing base values of the stiffness of each supporting substance, the stiffness variations were assessed in two stages (two drillings; these were made perpendicularly to the longitudinal axis of the tooth, Results show that it is possible to assess stiffness variations with the proposed methodology as well as to quantify the stiffness differences, by means of variation indexes.

  2. Introduction of Two Novel Stiffness Parameters and Interpretation of Air Puff-Induced Biomechanical Deformation Parameters With a Dynamic Scheimpflug Analyzer.

    Science.gov (United States)

    Roberts, Cynthia J; Mahmoud, Ashraf M; Bons, Jeffrey P; Hossain, Arif; Elsheikh, Ahmed; Vinciguerra, Riccardo; Vinciguerra, Paolo; Ambrósio, Renato

    2017-04-01

    To investigate two new stiffness parameters and their relationships with the dynamic corneal response (DCR) parameters and compare normal and keratoconic eyes. Stiffness parameters are defined as Resultant Pressure at inward applanation (A1) divided by corneal displacement. Stiffness parameter A1 uses displacement between the undeformed cornea and A1 and stiffness parameter highest concavity (HC) uses displacement from A1 to maximum deflection during HC. The spatial and temporal profiles of the Corvis ST (Oculus Optikgeräte, Wetzlar, Germany) air puff were characterized using hot wire anemometry. An adjusted air pressure impinging on the cornea at A1 (adjAP1) and an algorithm to biomechanically correct intraocular pressure based on finite element modelling (bIOP) were used for Resultant Pressure calculation (adjAP1 - bIOP). Linear regression analyses between DCR parameters and stiffness parameters were performed on a retrospective dataset of 180 keratoconic eyes and 482 normal eyes. DCR parameters from a subset of 158 eyes of 158 patients in each group were matched for bIOP and compared using t tests. A P value of less than .05 was considered statistically significant. All DCR parameters evaluated showed significant differences between normal and keratoconic eyes, except peak distance. Keratoconic eyes had lower stiffness parameter values, thinner pachymetry, shorter applanation lengths, greater absolute values of applanation velocities, earlier A1 times and later second applanation times, greater HC deformation amplitudes and HC deflection amplitudes, and lower HC radius of concave curvature (greater concave curvature). Most DCR parameters showed a significant relationship with both stiffness parameters in both groups. Keratoconic eyes demonstrated less resistance to deformation than normal eyes with similar IOP. The stiffness parameters may be useful in future biomechanical studies as potential biomarkers. [J Refract Surg. 2017;33(4):266-273.]. Copyright 2017

  3. Experimental Characterization of Stress- and Strain-Dependent Stiffness in Grouted Rock Masses

    Directory of Open Access Journals (Sweden)

    Ji-Won Kim

    2018-03-01

    Full Text Available Grouting of fractured rock mass prior to excavation results in grout-filled discontinuities that govern the deformation characteristics of a site. The influence of joint characteristics on the properties of grouted rocks is important in assessing the effects of grouting on jointed rock mass. However, grouting remains a predominantly empirical practice and the effects of grouting on rock joint behavior and material properties have yet to be accurately assessed. Granular materials, including jointed rocks, typically display nonlinear strain-dependent responses that can be characterized by the shear modulus degradation curve. In this study, the effects of grouting on the strain-dependent shear stiffness of jointed rock mass were investigated at the small-strain (below 10−5 and mid-strain (10−5 to 10−3 ranges using the quasi-static resonant column test and rock mass dynamic test devices. The effects of curing time, axial stress, initial joint roughness, and grouted joint thickness were examined. The results show that (1 grouting of rock joints leads to decreased stress sensitivity and increased small-strain shear stiffness for all tested samples; (2 the grouted rock samples display similar modulus degradation characteristics as the applied grout material; (3 the initial joint roughness determines the stress-dependent behaviors and general stiffness range of the jointed and grouted rocks, but the strain-dependent behaviors are dependent on the properties of the grout material; (4 increased grouted joint thickness results in larger contribution of the grout properties in the overall grouted rock mass.

  4. Dynamic stiffness of pile groups in a multilayered soil. Part 1

    International Nuclear Information System (INIS)

    Ohta, Y.; Hijikata, K.; Kobayashi, Y.

    1989-01-01

    For evaluating the dynamic stiffness of the pile group foundations, forced vibration tests are executed on pile group foundation models. Two types of test models are used, one is a single pile model and the other a four-pile model. Dividing the tests into 4 steps, the forced vibration tests are performed. Step 1 is for the single pile model, and steps 2 to 4 are for the four-pile model. In step 2 and step 3, the gap effects between the foundation bottom and the ground surface are examined. In step 4, the backfill effects are obtained. Based on the test results, the pile group effects, the gap effects and the backfill effects on the dynamic characteristics of the pile group foundations are described in this paper

  5. An L-stable method for solving stiff hydrodynamics

    Science.gov (United States)

    Li, Shengtai

    2017-07-01

    We develop a new method for simulating the coupled dynamics of gas and multi-species dust grains. The dust grains are treated as pressure-less fluids and their coupling with gas is through stiff drag terms. If an explicit method is used, the numerical time step is subject to the stopping time of the dust particles, which can become extremely small for small grains. The previous semi-implicit method [1] uses second-order trapezoidal rule (TR) on the stiff drag terms and it works only for moderately small size of the dust particles. This is because TR method is only A-stable not L-stable. In this work, we use TR-BDF2 method [2] for the stiff terms in the coupled hydrodynamic equations. The L-stability of TR-BDF2 proves essential in treating a number of dust species. The combination of TR-BDF2 method with the explicit discretization of other hydro terms can solve a wide variety of stiff hydrodynamics equations accurately and efficiently. We have implemented our method in our LA-COMPASS (Los Alamos Computational Astrophysics Suite) package. We have applied the code to simulate some dusty proto-planetary disks and obtained very good match with astronomical observations.

  6. Design of a Variable Stiffness Soft Dexterous Gripper

    Science.gov (United States)

    Nefti-Meziani, Samia; Davis, Steve

    2017-01-01

    Abstract This article presents the design of a variable stiffness, soft, three-fingered dexterous gripper. The gripper uses two designs of McKibben muscles. Extensor muscles that increase in length when pressurized are used to form the fingers of the gripper. Contractor muscles that decrease in length when pressurized are then used to apply forces to the fingers through tendons, which cause flexion and extension of the fingers. The two types of muscles are arranged to act antagonistically and this means that by raising the pressure in all of the pneumatic muscles, the stiffness of the system can be increased without a resulting change in finger position. The article presents the design of the gripper, some basic kinematics to describe its function, and then experimental results demonstrating the ability to adjust the bending stiffness of the gripper's fingers. It has been demonstrated that the fingers' bending stiffness can be increased by more than 150%. The article concludes by demonstrating that the fingers can be closed loop position controlled and are able to track step and sinusoidal inputs. PMID:29062630

  7. Sport stretching : Effect on passive muscle stiffness of short hamstrings

    NARCIS (Netherlands)

    Halbertsma, JPK; vanBolhuis, AI; Goeken, LNH

    Objective: To evaluate the effects of one 10-minute stretch on muscle stiffness in subjects with short hamstrings. Design: Randomized control trial. Setting: Laboratory for human movement sciences in the department of rehabilitation of a university hospital. Subjects: Sixteen students from the

  8. Terminology: resistance or stiffness for medical compression stockings?

    Directory of Open Access Journals (Sweden)

    André Cornu-Thenard

    2013-04-01

    Full Text Available Based on previous experimental work with medical compression stockings it is proposed to restrict the term stiffness to measurements on the human leg and rather to speak about resistance when it comes to characterize the elastic property of compression hosiery in the textile laboratory.

  9. Probing the stiffness of isolated nucleoli by atomic force microscopy.

    Science.gov (United States)

    Louvet, Emilie; Yoshida, Aiko; Kumeta, Masahiro; Takeyasu, Kunio

    2014-04-01

    In eukaryotic cells, ribosome biogenesis occurs in the nucleolus, a membraneless nuclear compartment. Noticeably, the nucleolus is also involved in several nuclear functions, such as cell cycle regulation, non-ribosomal ribonucleoprotein complex assembly, aggresome formation and some virus assembly. The most intriguing question about the nucleolus is how such dynamics processes can occur in such a compact compartment. We hypothesized that its structure may be rather flexible. To investigate this, we used atomic force microscopy (AFM) on isolated nucleoli. Surface topography imaging revealed the beaded structure of the nucleolar surface. With the AFM's ability to measure forces, we were able to determine the stiffness of isolated nucleoli. We could establish that the nucleolar stiffness varies upon drastic morphological changes induced by transcription and proteasome inhibition. Furthermore, upon ribosomal proteins and LaminB1 knockdowns, the nucleolar stiffness was increased. This led us to propose a model where the nucleolus has steady-state stiffness dependent on ribosome biogenesis activity and requires LaminB1 for its flexibility.

  10. Development of a variable stiffness and damping tunable vibration isolator

    CSIR Research Space (South Africa)

    Cronje, JM

    2005-03-01

    Full Text Available the amplification at resonance. A practical variable stiffness spring was developed by using a compound leaf spring with circular spring elements. A wax actuator, controlled by a hot-air gun with a closed-loop displacement and velocity feedback control system...

  11. Numerical Integration of Stiff System of Ordinary Differential ...

    African Journals Online (AJOL)

    The goal of this work is to develop, analyse and implement a K-step Implicit Rational Runge-Kutta schemes for Integration of Stiff system of Ordinary differential Equations. Its development adopted Taylor and Binomial series expansion Techniques to generate its parameters. The analysis of its basic properties adopted ...

  12. Homogeneous axisymmetric model with a limitting stiff equation of state

    International Nuclear Information System (INIS)

    Korkina, M.P.; Martynenko, V.G.

    1976-01-01

    A solution is obtained for Einstein's equations in which all metric coefficients are time functions for a limiting stiff equation of the substance state. Thr solution describes a homogeneous cosmological model with cylindrical symmetry. It is shown that the same metrics can be induced by a massless scalar only time-dependent field. Analysis of this solution is presented

  13. Contact stiffness considerations when simulating tyre/road noise

    Science.gov (United States)

    Winroth, Julia; Kropp, Wolfgang; Hoever, Carsten; Höstmad, Patrik

    2017-11-01

    Tyre/road simulation tools that can capture tyre vibrations, rolling resistance and noise generation are useful for understanding the complex processes that are involved and thereby promoting further development and optimisation. The most detailed tyre/road contact models use a spatial discretisation of the contact and assume an interfacial stiffness to account for the small-scale roughness within the elements. This interfacial stiffness has been found to have a significant impact on the simulated noise emissions but no thorough investigations of this sensitivity have been conducted. Three mechanisms are thought to be involved: The horn effect, the modal composition of the vibrational field of the tyre and the contact forces exciting the tyre vibrations. This study used a numerical tyre/road noise simulation tool based on physical relations to investigate these aspects. The model includes a detailed time-domain contact model with linear or non-linear contact springs that accounts for the effect of local tread deformation on smaller length scales. Results confirm that an increase in contact spring stiffness causes a significant increase of the simulated tyre/road noise. This is primarily caused by a corresponding increase in the contact forces, resulting in larger vibrational amplitudes. The horn effect and the modal composition are relatively unaffected and have minor effects on the radiated noise. A more detailed non-linear contact spring formulation with lower stiffness at small indentations results in a reduced high-frequency content in the contact forces and the simulated noise.

  14. Significance of arterial stiffness in Tridosha analysis: A pilot study

    Directory of Open Access Journals (Sweden)

    P. Venkata Giri Kumar

    2017-10-01

    Conclusion: The SI and RI acquired using Nadi Tarangini have shown significant variations across Tridosha locations. The framework developed to measure the arterial stiffness across Tridosha locations can be used for the interventional studies in Ayurveda which in turn can help in disease diagnosis and treatment.

  15. Cardiovascular Health and Arterial Stiffness: The Maine Syracuse Longitudinal Study

    Science.gov (United States)

    Crichton, Georgina E; Elias, Merrill F; Robbins, Michael A

    2014-01-01

    Ideal cardiovascular health is a recently defined construct by the American Heart Association (AHA) to promote cardiovascular disease reduction. Arterial stiffness is a major risk factor for cardiovascular disease. The extent to which the presence of multiple prevalent cardiovascular risk factors and health behaviors is associated with arterial stiffness is unknown. The aim of this study was to examine the association between the AHA construct of cardiovascular health and arterial stiffness, as indexed by pulse wave velocity and pulse pressure. The AHA health metrics, comprising of four health behaviors (smoking, body mass index, physical activity, and diet) and three health factors (total cholesterol, blood pressure, and fasting plasma glucose) were evaluated among 505 participants in the Maine-Syracuse Longitudinal Study. Outcome measures were carotid-femoral pulse wave velocity (PWV) and pulse pressure measured at 4 to 5-year follow-up. Better cardiovascular health, comprising both health factors and behaviors, was associated with lower arterial stiffness, as indexed by pulse wave velocity and pulse pressure. Those with at least five health metrics at ideal levels had significantly lower PWV (9.8 m/s) than those with two or less ideal health metrics (11.7 m/s) (P<0.001). This finding remained with the addition of demographic and PWV-related variables (P=0.004). PMID:24384629

  16. Pre-diabetes and arterial stiffness in uraemic patients

    DEFF Research Database (Denmark)

    Hornum, Mads; Clausen, Peter; Kjaergaard, Jesper

    2010-01-01

    In order to address factors of relevance for new onset diabetes mellitus and cardiovascular disease after kidney transplantation, we investigated the presence of pre-diabetes, arterial stiffness and endothelial dysfunction in patients with end-stage renal disease (ESRD) accepted for kidney...

  17. Stochastic dynamic stiffness of surface footing for offshore wind turbines

    DEFF Research Database (Denmark)

    Vahdatirad, Mohammadjavad; Andersen, Lars Vabbersgaard; Ibsen, Lars Bo

    2014-01-01

    Highlights •This study concerns the stochastic dynamic stiffness of foundations for large offshore wind turbines. •A simple model of wind turbine structure with equivalent coupled springs at the base is utilized. •The level of uncertainties is quantified through a sensitivity analysis. •Estimation...

  18. Stiffness and hysteresis properties of some prosthetic feet

    NARCIS (Netherlands)

    van Jaarsveld, H.W.L.; Grootenboer, H.J.; de Vries, J.; Koopman, Hubertus F.J.M.

    1990-01-01

    A prosthetic foot is an important element of a prosthesis, although it is not always fully recognized that the properties of the foot, along with the prosthetic knee joint and the socket, are in part responsible for the stability and metabolic energy cost during walking. The stiffness and the

  19. Variable stiffness actuators: the user’s point of view

    NARCIS (Netherlands)

    Grioli, Giorgio; Wolf, Sebastian; Garabini, Manolo; Catalano, Manuel; Burdet, Etienne; Caldwell, Darwin; Carloni, Raffaella; Friedl, Werner; Grebenstein, Markus; Laffranchi, Matteo; Lefeber, Dirk; Stramigioli, Stefano; Tsagarakis, Nikos; van Damme, Michael; Vanderborght, Bram; Albu-Shaeffer, Alin; Bicchi, Antonio

    Since their introduction in the early years of this century, variable stiffness actuators (VSA) witnessed a sustained growth of interest in the research community, as shown by the growing number of publications. While many consider VSA very interesting for applications, one of the factors hindering

  20. Riparian Sediment Delivery Ratio: Stiff Diagrams and Artifical Neural Networks

    Science.gov (United States)

    Various methods are used to estimate sediment transport through riparian buffers and grass jilters with the sediment delivery ratio having been the most widely applied. The U.S. Forest Service developed a sediment delivery ratio using the stiff diagram and a logistic curve to int...

  1. Substrate stiffness affects skeletal myoblast differentiation in vitro

    Directory of Open Access Journals (Sweden)

    Sara Romanazzo, Giancarlo Forte, Mitsuhiro Ebara, Koichiro Uto, Stefania Pagliari, Takao Aoyagi, Enrico Traversa and Akiyoshi Taniguchi

    2012-01-01

    Full Text Available To maximize the therapeutic efficacy of cardiac muscle constructs produced by stem cells and tissue engineering protocols, suitable scaffolds should be designed to recapitulate all the characteristics of native muscle and mimic the microenvironment encountered by cells in vivo. Moreover, so not to interfere with cardiac contractility, the scaffold should be deformable enough to withstand muscle contraction. Recently, it was suggested that the mechanical properties of scaffolds can interfere with stem/progenitor cell functions, and thus careful consideration is required when choosing polymers for targeted applications. In this study, cross-linked poly-ε-caprolactone membranes having similar chemical composition and controlled stiffness in a supra-physiological range were challenged with two sources of myoblasts to evaluate the suitability of substrates with different stiffness for cell adhesion, proliferation and differentiation. Furthermore, muscle-specific and non-related feeder layers were prepared on stiff surfaces to reveal the contribution of biological and mechanical cues to skeletal muscle progenitor differentiation. We demonstrated that substrate stiffness does affect myogenic differentiation, meaning that softer substrates can promote differentiation and that a muscle-specific feeder layer can improve the degree of maturation in skeletal muscle stem cells.

  2. Strength and stiffness capacity utilisation of timber members in roof ...

    African Journals Online (AJOL)

    C Brand Wessels, Nils-Olaf Petersen. Abstract. The main objective of this study was to determine which property, of the six strength and stiffness properties used in structural timber design, was the most influential in the design of nail-plated roof trusses. Thirty recently completed nail-plated roof truss designs were randomly ...

  3. Bone metabolism and arterial stiffness after renal transplantation.

    Science.gov (United States)

    Cseprekál, Orsolya; Kis, Eva; Dégi, Arianna A; Kerti, Andrea; Szabó, Attila J; Reusz, György S

    2014-01-01

    To assess the relationship between bone and vascular disease and its changes over time after renal transplantation. Metabolic bone disease (MBD) is common in chronic kidney disease (CKD) and is associated with cardiovascular (CV) disease. Following transplantation (Tx), improvement in CV disease has been reported; however, data regarding changes in bone disease remain controversial. Bone turnover and arterial stiffness (pulse wave velocity (PWV)) were assessed in 47 Tx patients (38 (3-191) months after Tx). Bone alkaline phosphatase (BALP), osteocalcin (OC) and beta-crosslaps were significantly higher in Tx patients, and decreased significantly after one year. There was a negative correlation between BALP, OC and steroid administered (r = -0.35; r = -0.36 respectively). PWV increased in the Tx group (1.15 SD). In patients with a follow up of bone turnover and arterial stiffness are present following kidney transplantation. While bone turnover decreases with time, arterial stiffness correlates initially with bone turnover, after which the influence of cholesterol becomes significant. Non-invasive estimation of bone metabolism and arterial stiffness may help to assess CKD-MBD following renal transplantation.

  4. Stiff person case misdiagnosed as conversion disorder: A case report.

    Science.gov (United States)

    Razmeh, Saeed; Habibi, Amir Hasan; Sina, Farzad; Alizadeh, Elham; Eslami, Monireh

    2017-01-01

    Stiff person syndrome (SPS) is a rare neurological disease resulting in stiffness and spasm of muscles. It initially affects the axial muscles and then spread to limb muscles. Emotional stress exacerbated the symptoms and signs of the disease. The pathophysiology of the disease is caused by the decreased level of the glutamic acid decarboxylase (GAD) activity due to an autoantibody against GAD that decreases the level of gamma-aminobutyric acid (GABA). In this paper, we present a case of atypical presentation of SPS with lower limb stiffness misdiagnosed as conversion disorder. We report a patient with atypical presentation of SPS with lower limb stiffness and gait disorder misdiagnosed as conversion disorder for a year. Her antithyroid peroxidase antibody (anti-TPO Ab) level was 75 IU (normal value: 0-34 IU). Intravenous immunoglobulin (IVIG) was administered (2gr/kg, 5 days) for the patient that showed significant improvement in the follow-up visit. It is essential that in any patient with bizarre gait disorder and suspicious to conversion disorder due to the reversibility of symptoms, SPS and other movement disorder should be considered.

  5. Nanocharacterization of the negative stiffness of ferroelectric materials

    Czech Academy of Sciences Publication Activity Database

    Skandani, A.A.; Čtvrtlík, Radim; Al-Haik, M.

    2014-01-01

    Roč. 105, č. 8 (2014), "082906-1"-"082906-5" ISSN 0003-6951 R&D Projects: GA TA ČR TA03010743 Institutional support: RVO:68378271 Keywords : ferroelectric materials * negative stiffness * thermomechanical environments Subject RIV: JJ - Other Materials Impact factor: 3.302, year: 2014

  6. The conundrum of arterial stiffness, elevated blood pressure, and aging.

    Science.gov (United States)

    AlGhatrif, Majd; Lakatta, Edward G

    2015-02-01

    Isolated systolic hypertension is a major health burden that is expanding with the aging of our population. There is evidence that central arterial stiffness contributes to the rise in systolic blood pressure (SBP); at the same time, central arterial stiffening is accelerated in patients with increased SBP. This bidirectional relationship created a controversy in the field on whether arterial stiffness leads to hypertension or vice versa. Given the profound interdependency of arterial stiffness and blood pressure, this question seems intrinsically challenging, or probably naïve. The aorta's function of dampening the pulsatile flow generated by the left ventricle is optimal within a physiological range of distending pressure that secures the required distal flow, keeps the aorta in an optimal mechanical conformation, and minimizes cardiac work. This homeostasis is disturbed by age-associated, minute alterations in aortic hemodynamic and mechanical properties that induce short- and long-term alterations in each other. Hence, it is impossible to detect an "initial insult" at an epidemiological level. Earlier manifestations of these alterations are observed in young adulthood with a sharp decline in aortic strain and distensibility accompanied by an increase in diastolic blood pressure. Subsequently, aortic mechanical reserve is exhausted, and aortic remodeling with wall stiffening and dilatation ensue. These two phenomena affect pulse pressure in opposite directions and different magnitudes. With early remodeling, there is an increase in pulse pressure, due to the dominance of arterial wall stiffness, which in turn accelerates aortic wall stiffness and dilation. With advanced remodeling, which appears to be greater in men, the effect of diameter becomes more pronounced and partially offsets the effect of wall stiffness leading to plateauing in pulse pressure in men and slower increase in pulse pressure (PP) than that of wall stiffness in women. The complex nature of

  7. Natural asphalt modified binders used for high stiffness modulus asphalt concrete

    Science.gov (United States)

    Bilski, Marcin; Słowik, Mieczysław

    2018-05-01

    This paper presents a set of test results supporting the possibility of replacing, in Polish climate conditions, hard road 20/30 penetration grade bitumen used in the binder course and/or base course made of high stiffness modulus asphalt concrete with binders comprising of 35/50 or 50/70 penetration grade bitumens and additives in the form of natural Gilsonite or Trinidad Epuré asphalts. For the purpose of comparing the properties of the discussed asphalt binders, values of the Performance Grade have been determined according to the American Superpave system criteria.

  8. A method for exponential propagation of large systems of stiff nonlinear differential equations

    Science.gov (United States)

    Friesner, Richard A.; Tuckerman, Laurette S.; Dornblaser, Bright C.; Russo, Thomas V.

    1989-01-01

    A new time integrator for large, stiff systems of linear and nonlinear coupled differential equations is described. For linear systems, the method consists of forming a small (5-15-term) Krylov space using the Jacobian of the system and carrying out exact exponential propagation within this space. Nonlinear corrections are incorporated via a convolution integral formalism; the integral is evaluated via approximate Krylov methods as well. Gains in efficiency ranging from factors of 2 to 30 are demonstrated for several test problems as compared to a forward Euler scheme and to the integration package LSODE.

  9. Using strong nonlinearity and high-frequency vibrations to control effective mechanical stiffness

    DEFF Research Database (Denmark)

    Thomsen, Jon Juel

    2008-01-01

    the method of direct separation of motions with results of a modified multiple scales ap-proach, valid also for strong nonlinearity, the stiffening ef-fect is predicted for a generic 1-dof system, and results are tested against numerical simulation and ((it is planned)) laboratory experiments.......High-frequency excitation (HFE) can be used to change the effective stiffness of an elastic structure, and related quanti-ties such as resonance frequencies, wave speed, buckling loads, and equilibrium states. There are basically two ways to do this: By using parametrical HFE (with or without non...

  10. Effects of combined aerobic and resistance exercise on central arterial stiffness and gait velocity in patients with chronic poststroke hemiparesis.

    Science.gov (United States)

    Lee, Yong Hee; Park, Soo Hyun; Yoon, Eun Sun; Lee, Chong-Do; Wee, Sang Ouk; Fernhall, Bo; Jae, Sae Young

    2015-09-01

    The effects of combined aerobic and resistance exercise training on central arterial stiffness and gait velocity in patients with chronic poststroke hemiparesis were investigated. Twenty-six patients with chronic poststroke hemiparesis were randomly assigned to either the combined aerobic and resistance exercise group (n = 14) or the control group (n = 12). The exercise intervention group received a combined aerobic and resistance exercise training (1 hr/day, three times/week for 16 wks), whereas the control group received usual care. Central arterial stiffness was determined by pulse wave velocity and augmentation index. Gait velocity was assessed using the 6-min walk test, 10-m walk test, and the Timed Up-and-Go test. Patients in the exercise intervention group had greater improvement of mean pulse wave velocity (P hemiparesis.

  11. Derivation of elastic stiffness formula for leaf type HDS and conceptual design of leaf type HDS of SMART FA

    Energy Technology Data Exchange (ETDEWEB)

    Song, Kee Nam; Kang, Heung Seok; Yoon, Kyung Ho; Suh, Jung Min; Lee, Jin Seok

    1997-12-01

    Based on the strain energy method and Euler beam theory, an elastic stiffness formula for the leaf type HDS, now widely used as the holddown spring for the FA of Westinghouse type PWRs, has been derived. Through comparisons with the characteristic test results of the test produced HDSs, it has been found that the derived formula is useful to reliably estimate an elastic stiffness with material properties and the geometric data of an HDS. Through sensitivity analysis of HDS`s elastic stiffness, the elastic stiffness sensitivity with respect to different design variables was identified, as well as the design variables having remarkable sensitivity. In addition, finite element analysis using surface-to-surface contact elements on the contact surface between the leaves shows that the analysis results are in good agreement with the elastic stiffness determined from the derived formula. It is therefore expected that the finite element model and the analysis method will be useful in the analysis of the elasto-plastic behavior of the leaf type HDS in the future. To both reduce the cobalt content, which is considered to be the source of radioactive contamination in the reactor core, and to design the HDS to meet the holddown requirements of the SMART FA, a conceptual design for the HDS of the SMART FA has been performed through two analyses of the elastic characteristics of the HDS : the possibility of substitution of the leaf spring`s material from Inconel 718 to Zircaloy and the effects on the HDS`s elastic characteristics according to the variation of leaf thickness and the number of leaves composing the HDS. (author). 34 refs., 33 tabs., 37 figs.

  12. Stiffness and frictional resistance of a superelastic nickel-titanium orthodontic wire with low-stress hysteresis.

    Science.gov (United States)

    Liaw, Yu-Cheng; Su, Yu-Yu M; Lai, Yu-Lin; Lee, Shyh-Yuan

    2007-05-01

    Stress-induced martensite formation with stress hysteresis that changes the elasticity and stiffness of nickel-titanium (Ni-Ti) wire influences the sliding mechanics of archwire-guided tooth movement. This in-vitro study investigated the frictional behavior of an improved superelastic Ni-Ti wire with low-stress hysteresis. Improved superelastic Ni-Ti alloy wires (L & H Titan, Tomy International, Tokyo, Japan) with low-stress hysteresis were examined by using 3-point bending and frictional resistance tests with a universal test machine at a constant temperature of 35 degrees C, and compared with the former conventional austenitic-active superelastic Ni-Ti wires (Sentalloy, Tomy International). Wire stiffness levels were derived from differentiation of the polynomial regression of the unloading curves, and values for kinetic friction were measured at constant bending deflection distances of 0, 2, 3, and 4 mm, respectively. Compared with conventional Sentalloy wires, the L & H Titan wire had a narrower stress hysteresis including a lower loading plateau and a higher unloading plateau. In addition, L & H Titan wires were less stiff than the Sentalloy wires during most unloading stages. Values of friction measured at deflections of 0, 2, and 3 mm were significantly (P Sentalloy wires at all bending deflections (P <.05). Stress-induced martensite formation significantly reduced the stiffness and thus could be beneficial to decrease the binding friction of superelastic Ni-Ti wires during sliding with large bending deflections. Austenitic-active alloy wires with low-stress hysteresis and lower stiffness and friction offer significant potential for further investigation.

  13. Arterial Stiffness in Nonhypertensive Type 2 Diabetes Patients in Ghana

    Directory of Open Access Journals (Sweden)

    Kwame Yeboah

    2016-01-01

    Full Text Available Background. Increased arterial stiffness is an independent cardiovascular risk factor in diabetes patients and general population. However, the contribution of diabetes to arterial stiffness is often masked by coexistent obesity and hypertension. In this study, we assessed arterial stiffness in nonhypertensive, nonobese type 2 diabetes (T2DM patients in Ghana. Methods. In case-control design, 166 nonhypertensive, nonobese participants, comprising 96 T2DM patients and 70 nondiabetes controls, were recruited. Peripheral and central blood pressure (BP indices were measured, and arterial stiffness was assessed as aortic pulse wave velocity (PWVao, augmentation index (AIx, cardioankle vascular index (CAVI, and heart-ankle pulse wave velocity (haPWV. Results. With similar peripheral and central BP indices, T2DM patients had higher PWVao (8.3 ± 1 versus 7.8 ± 1.3, p=0.044 and CAVI (7.9 ± 1.2 versus 6.9 ± 0.7, p=0.021 than nondiabetic control. AIx and haPWV were similar between T2DM and nondiabetic controls. Multiple regression models showed that, in the entire study participants, the major determinants of PWVao were diabetes status, age, gender, systolic BP, and previous smoking status (β = 0.22, 0.36, 0.48, 0.21, and 0.25, resp.; all p<0.05; the determinants of CAVI were diabetes status, age, BMI, heart rate, HbA1c, total cholesterol, HDL cholesterol, and previous smoking status (β = 0.21, 0.38, 0.2, 0.18, 0.24. 0.2, −0.19, and 0.2, resp.; all p<0.05. Conclusion. Our findings suggest that nonhypertensive, nonobese T2DM patients have increased arterial stiffness without appreciable increase in peripheral and central pressure indices.

  14. Stiffness analysis for the micromagnetic standard problem No. 4

    International Nuclear Information System (INIS)

    Tsiantos, Vassilios D.; Suess, Dieter; Schrefl, Thomas; Fidler, Josef

    2001-01-01

    In this article solutions to micromagnetic standard problem No. 4, a 500-nmx125-nm-wide NiFe film, are presented. A three-dimensional-finite element simulation based on the solution of the Gilbert equation has been used. The simulations show that two different reversal mechanisms occur for the two different applied fields. For a field at 170 degree counterclockwise from the saturation direction there is a nonuniform rotation of magnetization towards the direction of the applied field, with the magnetization at the ends rotating faster than the magnetization in the center. For a field at 190 degree counterclockwise from the saturation direction the magnetization at the ends and in the center rotate in opposite directions leading to the formation of a 360 degree wall after 0.22 ns associated with a peak in the exchange energy. Moreover, the time for the magnetization component parallel to the long axis to cross the zero is 0.136 and 0.135 ns for field 1 and field 2, respectively. The stiffness of the problem has been investigated solving the system of ordinary differential equations with a nonstiff method (Adams) and a stiff one (backward differentiation formula, BDF). For the measure of stiffness the ratio of the total number of time steps (nst) taken by the two solvers, that is nst(Adams)/nst(BDF), has been used. This ratio is 0.784 for field 1 and 0.593 for field 2, which means that the nonstiff method (Adams) uses larger time steps than the stiff method (BDF) and consequently the systems are not stiff. The average time step for the Adams method was 0.2 ps for both fields. [copyright] 2001 American Institute of Physics

  15. Development of procedures for calculating stiffness and damping properties of elastomers. Part 3: The effects of temperature, dissipation level and geometry

    Science.gov (United States)

    Smalley, A. J.; Tessarzik, J. M.

    1975-01-01

    Effects of temperature, dissipation level and geometry on the dynamic behavior of elastomer elements were investigated. Force displacement relationships in elastomer elements and the effects of frequency, geometry and temperature upon these relationships are reviewed. Based on this review, methods of reducing stiffness and damping data for shear and compression test elements to material properties (storage and loss moduli) and empirical geometric factors are developed and tested using previously generated experimental data. A prediction method which accounts for large amplitudes of deformation is developed on the assumption that their effect is to increase temperature through the elastomers, thereby modifying the local material properties. Various simple methods of predicting the radial stiffness of ring cartridge elements are developed and compared. Material properties were determined from the shear specimen tests as a function of frequency and temperature. Using these material properties, numerical predictions of stiffness and damping for cartridge and compression specimens were made and compared with corresponding measurements at different temperatures, with encouraging results.

  16. On the role of CFRP reinforcement for wood beams stiffness

    Science.gov (United States)

    Ianasi, A. C.

    2015-11-01

    In recent years, carbon fiber composites have been increasingly used in different ways in reinforcing structural elements. Specifically, the use of composite materials as a reinforcement for wood beams under bending loads requires paying attention to several aspects of the problem such as the number of the composite layers applied on the wood beams. Study consolidation of composites revealed that they are made by bonding fibrous material impregnated with resin on the surface of various elements, to restore or increase the load carrying capacity (bending, cutting, compression or torque) without significant damage of their rigidity. Fibers used in building applications can be fiberglass, aramid or carbon. Items that can be strengthened are concrete, brick, wood, steel and stone, and in terms of structural beams, walls, columns and floors. This paper describes an experimental study which was designed to evaluate the effect of composite material on the stiffness of the wood beams. It proposes a summary of the fundamental principles of analysis of composite materials and the design and use. The type of reinforcement used on the beams is the carbon fiber reinforced polymer (CFRP) sheet and plates and also an epoxy resin for bonding all the elements. Structural epoxy resins remain the primary choice of adhesive to form the bond to fiber-reinforced plastics and are the generally accepted adhesives in bonded CFRP-wood connections. The advantages of using epoxy resin in comparison to common wood-laminating adhesives are their gap-filling qualities and the low clamping pressures that are required to form the bond between carbon fiber plates or sheets and the wood beams. Mechanical tests performed on the reinforced wood beams showed that CFRP materials may produce flexural displacement and lifting increases of the beams. Observations of the experimental load-displacement relationships showed that bending strength increased for wood beams reinforced with CFRP composite plates

  17. Stiffness Evaluation of High Temperature Superconductor Bearing Stiffness for 10 kWh Superconductor Flywheel Energy Storage System

    International Nuclear Information System (INIS)

    Park, B. J.; Jung, S. Y.; Lee, J. P.; Park, B. C.; Kim, C. H.; Han, S. C.; Du, S. G.; Han, Y. H.; Sung, T. H.

    2009-01-01

    A superconductor flywheel energy storage(SFES) system is mainly act an electro-mechanical battery which transfers mechanical energy into electrical form and vice versa. SFES system consists of a pair of non-contacting High Temperature Superconductor (HTS) bearings with a very low frictional loss. But it is essential to design an efficient HTS bearing considering with rotor dynamic properties through correct calculation of stiffness in order to support a huge composite flywheel rotor with high energy storage density. Static properties of HTS bearings provide data to solve problems which may occur easily in a running system. Since stiffness to counter vibration is the main parameter in designing an HTS bearing system, we investigate HTS bearing magnetic force through static properties between the Permanent Magnet(PM) and HTS. We measured axial / radial stiffness and found bearing stiffness can be easily changed by activated vibration direction between PM and HTS bulk. These results are used to determine the optimal design for a 10 kWh SFES.

  18. Matrix stiffness and oxigen tension modulate epigenetic conversion of mouse dermal fibroblasts into insulin producing cells.

    Directory of Open Access Journals (Sweden)

    Alessandro Zenobi

    2017-05-01

    Full Text Available In vivo, cells are surrounded by a three-dimensional (3-D organization of supporting matrix, neighboring cells and a gradient of chemical and mechanical signals (Antoni, et al., 2015. However, the present understanding of many biological processes is mainly based on two-dimensional (2-D systems that typically provides a static environment. In the present study, we tested two different 3-D culture systems and apply them to the epigenetic conversion of mouse dermal fibroblasts into insulin producing-cells (Pennarossa, et al., 2013; Brevini, et al., 2015, combining also the use of two oxygen tensions. In particular, cells were differentiated using the Polytetrafluoroethylene micro-bioreactor (PTFE and the Polyacrylamide (PAA gels with different stiffness (1 kPa; 4 kPa, maintained either in the standard 20% or in the more physiological 5% oxygen tensions. Standard differentiation performed on plastic substrates was assessed as a control. Cell morphology (Fig.1A, insulin expression and release were analyzed to evaluate the role of both stiffness and oxygen tension in the process. The results obtained showed that 1 kPa PAA gel and PTFE system induced a significantly higher insulin expression and release than plastic and 4 kPa PAA gel, especially in low oxygen condition (Fig.1B. Furthermore, comparing the efficiency of the two systems tested, 1 kPa PAA gel ensured a higher insulin transcription than PTFE (Fig.1C. Recent studies show the direct influence of substrates on lineage commitment and cell differentiation (Engler, et al., 2006; Evans, et al., 2009. The evidence here presented confirm that the use of an appropriate stiffness (similar to the pancreatic tissue, combined with a physiological oxygen tension, promote β-cell differentiation, with beneficial effects on cell functional activity and insulin release. The present results highlight the importance of 3-D cell rearrangement and oxigen tension to promote in vitro epigenetic conversion of

  19. Controlling cyclic stiffness of a foundation, by manipulating the deformation history

    DEFF Research Database (Denmark)

    Sabaliauskas, Tomas; Ibsen, Lars Bo

    2018-01-01

    Offshore wind turbines are slender structures, dynamic response of which depends on foundation stiffness. Unfortunately, foundations embedded in sand can become disturbed, their stiffness can increase and decrease episodically. To investigate the phenomenon governing loss and recovery of stiffnes...

  20. The design of and chronic tissue response to a composite nerve electrode with patterned stiffness

    Science.gov (United States)

    Freeberg, M. J.; Stone, M. A.; Triolo, R. J.; Tyler, D. J.

    2017-06-01

    Objective. As neural interfaces demonstrate success in chronic applications, a novel class of reshaping electrodes with patterned regions of stiffness will enable application to a widening range of anatomical locations. Patterning stiff regions and flexible regions of the electrode enables nerve reshaping while accommodating anatomical constraints of various implant locations ranging from peripheral nerves to spinal and autonomic plexi. Approach. Introduced is a new composite electrode enabling patterning of regions of various electrode mechanical properties. The initial demonstration of the composite’s capability is the composite flat interface nerve electrode (C-FINE). The C-FINE is constructed from a sandwich of patterned PEEK within layers of pliable silicone. The shape of the PEEK provides a desired pattern of stiffness: stiff across the width of the nerve to reshape the nerve, but flexible along its length to allow for bending with the nerve. This is particularly important in anatomical locations near joints or organs, and in constrained compartments. We tested pressure and volume design constraints in vitro to verify that the C-FINE can attain a safe cuff-to-nerve ratio (CNR) without impeding intraneural blood flow. We measured nerve function as well as nerve and axonal morphology following 3 month implantation of the C-FINE without wires on feline peripheral nerves in anatomically constrained areas near mobile joints and major blood vessels in both the hind and fore limbs. Main Results. In vitro inflation tests showed effective CNRs (1.93  ±  0.06) that exceeded the industry safety standard of 1.5 at an internal pressure of 20 mmHg. This is less than the 30 mmHg shown to induce loss of conduction or compromise blood flow. Implanted cats showed no changes in physiology or electrophysiology. Behavioral signs were normal suggesting healthy nerves. Motor nerve conduction velocity and compound motor action potential did not change significantly

  1. Stiffness Analysis and Comparison of 3-PPR Planar Parallel Manipulators with Actuation Compliance

    DEFF Research Database (Denmark)

    Wu, Guanglei; Bai, Shaoping; Kepler, Jørgen Asbøl

    2012-01-01

    In this paper, the stiffness of 3-PPR planar parallel manipulator (PPM) is analyzed with the consideration of nonlinear actuation compliance. The characteristics of the stiffness matrix pertaining to the planar parallel manipulators are analyzed and discussed. Graphic representation of the stiffn...... of the stiffness characteristics by means of translational and rotational stiffness mapping is developed. The developed method is illustrated with an unsymmetrical 3-PPR PPM, being compared with its structure-symmetrical counterpart....

  2. Test

    DEFF Research Database (Denmark)

    Bendixen, Carsten

    2014-01-01

    Bidrag med en kortfattet, introducerende, perspektiverende og begrebsafklarende fremstilling af begrebet test i det pædagogiske univers.......Bidrag med en kortfattet, introducerende, perspektiverende og begrebsafklarende fremstilling af begrebet test i det pædagogiske univers....

  3. Longitudinal relaxation of initially straight flexible and stiff polymers

    Science.gov (United States)

    Dimitrakopoulos, Panagiotis; Dissanayake, Inuka

    2004-11-01

    The present talk considers the relaxation of a single flexible or stiff polymer chain from an initial straight configuration in a viscous solvent. This problem commonly arises when strong flows are turned off in both industrial and biological applications. The problem is also motivated by recent experiments with single biopolymer molecules relaxing after being fully extended by applied forces as well as by the recent development of micro-devices involving stretched tethered biopolymers. Our results are applicable to a wide array of synthetic polymers such as polyacrylamides, Kevlar and polyesters as well as biopolymers such as DNA, actin filaments, microtubules and MTV. In this talk we discuss the mechanism of the polymer relaxation as was revealed through Brownian Dynamics simulations covering a broad range of time scales and chain stiffness. After the short-time free diffusion, the chain's longitudinal reduction at early intermediate times is shown to constitute a universal behavior for any chain stiffness caused by a quasi-steady relaxation of tensions associated with the deforming action of the Brownian forces. Stiff chains are shown to exhibit a late intermediate-time longitudinal reduction associated with a relaxation of tensions affected by the deforming Brownian and the restoring bending forces. The longitudinal and transverse relaxations are shown to obey different laws, i.e. the chain relaxation is anisotropic at all times. In the talk, we show how from the knowledge of the relaxation mechanism, we can predict and explain the polymer properties including the polymer stress and the solution birefringence. In addition, a generalized stress-optic law is derived valid for any time and chain stiffness. All polymer properties which depend on the polymer length are shown to exhibit two intermediate-time behaviors with the early one to constitute a universal behavior for any chain stiffness. This work was supported in part by the Minta Martin Research Fund. The

  4. Effects of forefoot bending stiffness of badminton shoes on agility, comfort perception and lower leg kinematics during typical badminton movements.

    Science.gov (United States)

    Park, Sang-Kyoon; Lam, Wing-Kai; Yoon, Sukhoon; Lee, Ki-Kwang; Ryu, Jiseon

    2017-09-01

    This study investigated whether an increase in the forefoot bending stiffness of a badminton shoe would positively affect agility, comfort and biomechanical variables during badminton-specific movements. Three shoe conditions with identical shoe upper and sole designs with different bending stiffness (Flexible, Regular and Stiff) were used. Elite male badminton players completed an agility test on a standard badminton court involving consecutive lunges in six directions, a comfort test performed by a pair of participants conducting a game-like practice trial and a biomechanics test involving a random assignment of consecutive right forward lunges. No significant differences were found in agility time and biomechanical variables among the three shoes. The players wearing the shoe with a flexible forefoot outsole demonstrated a decreased perception of comfort in the forefoot cushion compared to regular and stiffer conditions during the comfort test (p badminton-specific tasks. It was concluded that an optimisation of forefoot structure and materials in badminton shoes should consider the individual's perception to maximise footwear comfort in performance.

  5. Optimization of a variable-stiffness skin for morphing high-lift devices

    NARCIS (Netherlands)

    Thuwis, G.A.A.; Abdalla, M.M.; Gürdal, Z.

    2010-01-01

    One of the possibilities for the next generation of smart high-lift devices is to use a seamless morphing structure. A passive composite variable-stiffness skin as a solution to the dilemma of designing the structure to have high enough stiffness to withstand aerodynamic loading and low stiffness to

  6. Comparative numerical solutions of stiff Ordinary differential equations using magnus series expansion method

    Directory of Open Access Journals (Sweden)

    SURE KÖME

    2014-12-01

    Full Text Available In this paper, we investigated the effect of Magnus Series Expansion Method on homogeneous stiff ordinary differential equations with different stiffness ratios. A Magnus type integrator is used to obtain numerical solutions of two different examples of stiff problems and exact and approximate results are tabulated. Furthermore, absolute error graphics are demonstrated in detail.

  7. Source and Message Factors in Persuasion: A Reply to Stiff's Critique of the Elaboration Likelihood Model.

    Science.gov (United States)

    Petty, Richard E.; And Others

    1987-01-01

    Answers James Stiff's criticism of the Elaboration Likelihood Model (ELM) of persuasion. Corrects certain misperceptions of the ELM and criticizes Stiff's meta-analysis that compares ELM predictions with those derived from Kahneman's elastic capacity model. Argues that Stiff's presentation of the ELM and the conclusions he draws based on the data…

  8. Characterizing Axial Stiffness of Individual Batter Piles with Emphasis on Elevated, Laterally Loaded, Clustered Pile Groups

    Science.gov (United States)

    2016-11-01

    using the appropriate stiffness based on the direction of the calculated pile load. 1...load cases. CPGA utilizes the stiffness method (Saul 1968) of three-dimensional pile group analysis for user-specified static loadings. The pile...CPGA analysis and coordinate systems (global and pile) As discussed in Chapter 1, the CPGA software utilizes the stiffness method (Saul 1968) of

  9. The impact of intervention strategies that target arterial stiffness in end-stage renal disease: a systematic review protocol.

    Science.gov (United States)

    Rodriguez, Rosendo A; Shea, Beverley; Hae, Richard; Burns, Kevin D

    2016-07-19

    Vascular damage contributes to the high cardiovascular morbidity and mortality in end-stage renal disease (ESRD). Increased aortic stiffness measured by carotid-femoral pulse wave velocity (cf-PWV) is a strong and independent predictor of the cardiovascular risk in ESRD patients. Recently, there has been considerable interest in developing strategies to lessen the progression of arterial stiffness in ESRD patients using cf-PWV as a tool to monitor therapeutic responses, but their benefit on the long-term cardiovascular risk is not known. Appraisal of the effects of existing stiffness-based interventions on the cf-PWV would facilitate selecting optimal therapies to be tested in randomized clinical trials. The aim of this systematic review will be to evaluate the impact of arterial stiffness-based interventions on the cf-PWV in ESRD patients. Secondarily, for each intervention, we will determine the minimal duration needed to achieve a significant reduction of cf-PWV, the minimal cf-PWV reduction threshold or effect size, and adverse events. This review will be conducted using MEDLINE, EMBASE, and EBM Reviews. We will select clinical trials and observational studies (cohort, case-control, and before/after studies and case series) that evaluated pharmacologic or non-pharmacologic interventions in which the primary effect is to improve structural and/or dynamic components of arterial stiffness in adults with stage 5 chronic kidney disease. The primary outcome of interest will be cf-PWV. Study selection and data collection will be performed by two reviewers. Validated tools will be used to assess the methodological quality and risk of bias among different study designs. We will describe all included citations according to study characteristics, methodological quality, and outcomes. Suitability for meta-analysis will be determined by the degree of clinical and statistical heterogeneity between studies. If appropriate, we will calculate effect estimates by obtaining the

  10. Modeling, Control, and Numerical Simulations of a Novel Binary-Controlled Variable Stiffness Actuator (BcVSA

    Directory of Open Access Journals (Sweden)

    Irfan Hussain

    2018-06-01

    Full Text Available This research work aims at realizing a new compliant robotic actuator for safe human-robotic interaction. In this paper, we present the modeling, control, and numerical simulations of a novel Binary-Controlled Variable Stiffness Actuator (BcVSA aiming to be used for the development of a novel compliant robotic manipulator. BcVSA is the proof of concept of the active revolute joint with the variable recruitment of series-parallel elastic elements. We briefly recall the basic design principle which is based on a stiffness varying mechanism consisting of a motor, three inline clutches, and three torsional springs with stiffness values (K0, 2K0, 4K0 connected to the load shaft and the motor shaft through two planetary sun gear trains with ratios (4:1, 4:1 respectively. We present the design concept, stiffness and dynamic modeling, and control of our BcVSA. We implemented three kinds of Multiple Model Predictive Control (MPC to control our actuator. The main motivation of choosing this controller lies in the fact that working principle of multiple MPC and multiple states space representation (stiffness level of our actuator share similar interests. In particular, we implemented Multiple MPC, Multiple Explicit MPC, and Approximated Multiple Explicit MPC. Numerical simulations are performed in order to evaluate their effectiveness for the future experiments on the prototype of our actuator. The simulation results showed that the Multiple MPC, and the Multiple Explicit MPC have similar results from the robustness point of view. On the other hand, the robustness performance of Approximated Multiple Explicit MPC is not good as compared to other controllers but it works in the offline framework while having the capability to compute the sub-optimal results. We also performed the comparison of MPC based controllers with the Computed Torque Control (CTC, and Linear Quadratic Regulator (LQR. In future, we are planning to test the presented approach on the

  11. Prevalence of arterial stiffness in North China, and associations with risk factors of cardiovascular disease: a community-based study

    Directory of Open Access Journals (Sweden)

    Wang Jin-Wen

    2012-12-01

    Full Text Available Abstract Background Brachial-ankle pulse wave velocity (baPWV, which reflects the stiffness of both central and peripheral muscular arteries, has been frequently used as a simple index for assessing arterial stiffness. The aim of the present study was to investigate the prevalence of arterial stiffness in North China based on baPWV measurements, and explore the associations between increased arterial stiffness and risk factors of cardiovascular diseases (CVD. Methods Twenty-three community populations were established in North China. For each participant, parameters for calculating baPWV, including blood pressures and pressure waveforms, were measured using a non-invasive automatic device. All participants were required to respond to an interviewer-led questionnaire including medical histories and demographic data, and to receive blood tests on biochemical indictors. Results A total of 2,852 participants were finally investigated. Among them, 1,201 people with low burden of CVD risk factors were chosen to be the healthy reference sample. The cut-off point of high baPWV was defined as age-specific 90th percentile of the reference sample. Thus, the prevalence of high baPWV was found to be 22.3% and 26.4% in men and women respectively. After adjusted for age, heart rate (HR, systolic blood pressure (SBP, fasting glucose level, and smoking were significantly associated with high baPWV in men; while level of serum total cholesterol (TC, HR, SBP, and diabetes were significantly associated with high baPWV in women. Conclusions Based on the age-specific cut-off points, the middle-aged population has a higher prevalence of high baPWV in North China. There exists a difference between men and women in terms of the potential risk factors associated with arterial stiffness.

  12. PDASAC, Partial Differential Sensitivity Analysis of Stiff System

    International Nuclear Information System (INIS)

    Caracotsios, M.; Stewart, W.E.

    2001-01-01

    1 - Description of program or function: PDASAC solves stiff, nonlinear initial-boundary-value problems in a timelike dimension t and a space dimension x. Plane, circular cylindrical or spherical boundaries can be handled. Mixed-order systems of partial differential and algebraic equations can be analyzed with members of order or 0 or 1 in t, 0, 1 or 2 in x. Parametric sensitivities of the calculated states are computed simultaneously on request, via the Jacobian of the state equations. Initial and boundary conditions are efficiently reconciled. Local error control (in the max-norm or the 2-norm) is provided for the state vector and can include the parametric sensitivities if desired. 2 - Method of solution: The method of lines is used, with a user- selected x-grid and a minimum-bandwidth finite-difference approximations of the x-derivatives. Starting conditions are reconciled with a damped Newton algorithm adapted from Bain and Stewart (1991). Initial step selection is done by the first-order algorithms of Shampine (1987), extended here to differential- algebraic equation systems. The solution is continued with the DASSL predictor-corrector algorithm (Petzold 1983, Brenan et al. 1989) with the initial acceleration phase deleted and with row scaling of the Jacobian added. The predictor and corrector are expressed in divided-difference form, with the fixed-leading-coefficient form of corrector (Jackson and Sacks-Davis 1989; Brenan et al. 1989). Weights for the error tests are updated in each step with the user's tolerances at the predicted state. Sensitivity analysis is performed directly on the corrector equations of Caracotsios and Stewart (1985) and is extended here to the initialization when needed. 3 - Restrictions on the complexity of the problem: This algorithm, like DASSL, performs well on differential-algebraic equation systems of index 0 and 1 but not on higher-index systems; see Brenan et al. (1989). The user assigned the work array lengths and the output

  13. Stiff and tough: a comparative study on the tensile properties of shark skin.

    Science.gov (United States)

    Creager, Shelby B; Porter, Marianne E

    2018-02-01

    In sharks, the skin is a biological composite with mineralized denticles embedded within a collagenous matrix. Swimming performance is enhanced by the dermal denticles on the skin, which have drag reducing properties produced by regional morphological variations and changes in density along the body. We used mechanical testing to quantify the effect of embedded mineralized denticles on the quasi-static tensile properties of shark skin to failure in four coastal species. We investigated regional differences in denticle density and skin properties by dissecting skin from the underlying fascia and muscle at 10 anatomical landmarks. Hourglass-shaped skin samples were extracted in the cranial to caudal orientation. Denticle density was quantified and varied significantly among both regions and species. We observed the greatest denticle densities in the cranial region of the body for the bonnethead, scalloped hammerhead, and bull sharks. Skin samples were then tested in tension until failure, stress strain curves were generated, and mechanical properties calculated. We found significant species and region effects for all three tensile mechanical properties. We report the greatest ultimate tensile strength, stiffness, and toughness near the cranial and lateral regions of the body for all 4 of the coastal species. We also report that denticle density increases with skin stiffness but decreases with toughness. Copyright © 2017 Elsevier GmbH. All rights reserved.

  14. Stiffness and strength properties of natural fractures from north ramp drill holes

    International Nuclear Information System (INIS)

    Olsson, W.A.; Price, R.H.; Brown, S.R.

    1994-01-01

    Cores containing natural fractures were obtained from drillholes UE 25 NRG-4 and USW NRG-6 at Yucca Mountain, Nevada. Seven selected fractures were sheared at constant normal stress, either 5 or 10 MPa, in the air-dry condition. Detailed profilometer data were collected from each fracture surface before testing. The tests yielded the normal closure as a function of normal stress, and the shear stress and dilation as a function of shear offset. The constitutive properties resulting from the measurements were: normal stiffness, shear stiffness, shear strength and coefficient of friction, and dilation. Peak friction ranged from 0.89 to 1.11; residual friction ranged from 0.76 to 1.00. The lowest initial dilation angle was found to be 5.29 degrees and the highest was 11.28 degrees. The roughness characteristics of the fracture surfaces agree qualitatively with the simple mathematical model of Brown (1994) derived from fracture data in many other rock types

  15. Solving the Bateman equations in CASMO5 using implicit ode numerical methods for stiff systems

    International Nuclear Information System (INIS)

    Hykes, J. M.; Ferrer, R. M.

    2013-01-01

    The Bateman equations, which describe the transmutation of nuclides over time as a result of radioactive decay, absorption, and fission, are often numerically stiff. This is especially true if short-lived nuclides are included in the system. This paper describes the use of implicit numerical methods for o D Es applied to the stiff Bateman equations, specifically employing the Backward Differentiation Formulas (BDF) form of the linear multistep method. As is true in other domains, using an implicit method removes or lessens the (sometimes severe) step-length constraints by which explicit methods must abide. To gauge its accuracy and speed, the BDF method is compared to a variety of other solution methods, including Runge-Kutta explicit methods and matrix exponential methods such as the Chebyshev Rational Approximation Method (CRAM). A preliminary test case was chosen as representative of a PWR lattice depletion step and was solved with numerical libraries called from a Python front-end. The Figure of Merit (a combined measure of accuracy and efficiency) for the BDF method was nearly identical to that for CRAM, while explicit methods and other matrix exponential approximations trailed behind. The test case includes 319 nuclides, in which the shortest-lived nuclide is 98 Nb with a half-life of 2.86 seconds. Finally, the BDF and CRAM methods were compared within CASMO5, where CRAM had a FOM about four times better than BDF, although the BDF implementation was not fully optimized. (authors)

  16. Custom 3D Printable Silicones with Tunable Stiffness.

    Science.gov (United States)

    Durban, Matthew M; Lenhardt, Jeremy M; Wu, Amanda S; Small, Ward; Bryson, Taylor M; Perez-Perez, Lemuel; Nguyen, Du T; Gammon, Stuart; Smay, James E; Duoss, Eric B; Lewicki, James P; Wilson, Thomas S

    2018-02-01

    Silicone elastomers have broad versatility within a variety of potential advanced materials applications, such as soft robotics, biomedical devices, and metamaterials. A series of custom 3D printable silicone inks with tunable stiffness is developed, formulated, and characterized. The silicone inks exhibit excellent rheological behavior for 3D printing, as observed from the printing of porous structures with controlled architectures. Herein, the capability to tune the stiffness of printable silicone materials via careful control over the chemistry, network formation, and crosslink density of the ink formulations in order to overcome the challenging interplay between ink development, post-processing, material properties, and performance is demonstrated. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Stiff person syndrome (SPS: Literature review and case report

    Directory of Open Access Journals (Sweden)

    Erna Pretorius

    2013-11-01

    Full Text Available Stiff person syndrome (SPS is a rare, debilitating condition which presents with progressive and inconsistent neurological features. The main symptoms are stiffness and intermittent, painful muscle spasms, triggered and exacerbated by stressful and emotional stimuli. The fluctuating clinical nature of SPS, and otherwise normal neurological examination, often lead to a misdiagnosis of conversion disorder. Psychiatric symptoms frequently accompany this disorder and patients are often first seen by psychiatrists. SPS is autoimmune-based: antibodies are directed against glutamate decarboxylase, resulting in dysregulation of gamma-aminobutyric acid (GABA in the brain which is considered the cause of the neuropsychiatric symptomatology. SPS should be considered in the differential diagnosis of conversion disorder. Effective management requires early detection, a collaborative approach with GABA-ergic medication and intravenous immunoglobulins, and management of concomitant psychiatric disorders. We describe a patient with SPS. Only one other case has been reported in South Africa.

  18. Associations between bicycling and carotid arterial stiffness in adolescents

    DEFF Research Database (Denmark)

    Ried-Larsen, M; Grøntved, A; Østergaard, Lars

    2015-01-01

    Youth Heart Study. Total frequency of bicycle usage was assessed by self-report, and carotid arterial stiffness was assessed using B-mode ultrasound. After adjusting for pubertal status, body height, and objectively measured physical activity and other personal lifestyle and demographic factors, boys......The aim of the study was to investigate the associations between bicycling and carotid arterial stiffness, independent of objectively measured moderate-and-vigorous physical activity. This cross-sectional study included 375 adolescents (age 15.7 ± 0.4 years) from the Danish site of the European...... using their bicycle every day of the week displayed a higher carotid arterial compliance {standard beta 0.47 [95% confidence interval (CI) 0.07-0.87]} and distension [standard beta 0.38 (95% CI -0.04 to 0.81)]. Boys using their bicycle every day of the week furthermore displayed a lower Young's elastic...

  19. Strong, tough and stiff bioinspired ceramics from brittle constituents

    Science.gov (United States)

    Bouville, Florian; Maire, Eric; Meille, Sylvain; van de Moortèle, Bertrand; Stevenson, Adam J.; Deville, Sylvain

    2014-05-01

    High strength and high toughness are usually mutually exclusive in engineering materials. In ceramics, improving toughness usually relies on the introduction of a metallic or polymeric ductile phase, but this decreases the material’s strength and stiffness as well as its high-temperature stability. Although natural materials that are both strong and tough rely on a combination of mechanisms operating at different length scales, the relevant structures have been extremely difficult to replicate. Here, we report a bioinspired approach based on widespread ceramic processing techniques for the fabrication of bulk ceramics without a ductile phase and with a unique combination of high strength (470 MPa), high toughness (22 MPa m1/2), and high stiffness (290 GPa). Because only mineral constituents are needed, these ceramics retain their mechanical properties at high temperatures (600 °C). Our bioinspired, material-independent approach should find uses in the design and processing of materials for structural, transportation and energy-related applications.

  20. Computational singular perturbation analysis of stochastic chemical systems with stiffness

    Science.gov (United States)

    Wang, Lijin; Han, Xiaoying; Cao, Yanzhao; Najm, Habib N.

    2017-04-01

    Computational singular perturbation (CSP) is a useful method for analysis, reduction, and time integration of stiff ordinary differential equation systems. It has found dominant utility, in particular, in chemical reaction systems with a large range of time scales at continuum and deterministic level. On the other hand, CSP is not directly applicable to chemical reaction systems at micro or meso-scale, where stochasticity plays an non-negligible role and thus has to be taken into account. In this work we develop a novel stochastic computational singular perturbation (SCSP) analysis and time integration framework, and associated algorithm, that can be used to not only construct accurately and efficiently the numerical solutions to stiff stochastic chemical reaction systems, but also analyze the dynamics of the reduced stochastic reaction systems. The algorithm is illustrated by an application to a benchmark stochastic differential equation model, and numerical experiments are carried out to demonstrate the effectiveness of the construction.

  1. Sex differences in flexibility-arterial stiffness relationship and its application for diagnosis of arterial stiffening: a cross-sectional observational study.

    Directory of Open Access Journals (Sweden)

    Masato Nishiwaki

    Full Text Available Arterial stiffness might be related to trunk flexibility in middle-aged and older participants, but it is also affected by age, sex, and blood pressure. This cross-sectional observational study investigated whether trunk flexibility is related to arterial stiffness after considering the major confounding factors of age, sex, and blood pressure. We further investigated whether a simple diagnostic test of flexibility could be helpful to screen for increased arterial stiffening.According to age and sex, we assigned 1150 adults (male, n = 536; female, n = 614; age, 18-89 y to groups with either high- or poor-flexibility based on the sit-and-reach test. Arterial stiffness was assessed by cardio-ankle vascular index.In all categories of men and in older women, arterial stiffness was higher in poor-flexibility than in high-flexibility (P<0.05. This difference remained significant after normalizing arterial stiffness for confounding factors such as blood pressure, but it was not found among young and middle-aged women. Stepwise multiple-regression analysis also supported the notion of the sex differences in flexibility-arterial stiffness relationship. Receiver operating characteristic curve analysis revealed that cut-off values for sit-and-reach among men and women were 33.2 (area under the curve [AUC], 0.711; 95% confidence interval [CI], 0.666-0.756; sensitivity, 61.7%; specificity, 69.7% and 39.2 (AUC, 0.639; 95% CI, 0.592-0.686; sensitivity, 61.1%; specificity, 62.0% cm, respectively.Our results indicate that flexibility-arterial stiffness relationship is not affected by BP, which is a major confounding factor. In addition, sex differences are observed in this relationship; poor trunk flexibility increases arterial stiffness in young, middle-aged, and older men, whereas the relationship in women is found only in the elderly. Also, the sit-and-reach test can offer a simple method of predicting arterial stiffness at home or elsewhere.

  2. Contribution of collagen fibers to the compressive stiffness of cartilaginous tissues.

    Science.gov (United States)

    Römgens, Anne M; van Donkelaar, Corrinus C; Ito, Keita

    2013-11-01

    Cartilaginous tissues such as the intervertebral disk are predominantly loaded under compression. Yet, they contain abundant collagen fibers, which are generally assumed to contribute to tensile loading only. Fiber tension is thought to originate from swelling of the proteoglycan-rich nucleus. However, in aged or degenerate disk, proteoglycans are depleted, whereas collagen content changes little. The question then rises to which extend the collagen may contribute to the compressive stiffness of the tissue. We hypothesized that this contribution is significant at high strain magnitudes and that the effect depends on fiber orientation. In addition, we aimed to determine the compression of the matrix. Bovine inner and outer annulus fibrosus specimens were subjected to incremental confined compression tests up to 60 % strain in radial and circumferential direction. The compressive aggregate modulus was determined per 10 % strain increment. The biochemical composition of the compressed specimens and uncompressed adjacent tissue was determined to compute solid matrix compression. The stiffness of all specimens increased nonlinearly with strain. The collagen-rich outer annulus was significantly stiffer than the inner annulus above 20 % compressive strain. Orientation influenced the modulus in the collagen-rich outer annulus. Finally, it was shown that the solid matrix was significantly compressed above 30 % strain. Therefore, we concluded that collagen fibers significantly contribute to the compressive stiffness of the intervertebral disk at high strains. This is valuable for understanding the compressive behavior of collagen-reinforced tissues in general, and may be particularly relevant for aging or degenerate disks, which become more fibrous and less hydrated.

  3. A Novel Technique to Measure In Vivo Uterine Suspensory Ligament Stiffness

    Science.gov (United States)

    Smith, Tovia M.; Luo, Jiajia; Hsu, Yvonne; Ashton-Miller, James A.; Delancey, John O.L.

    2013-01-01

    Objective To describe a new computer-controlled research apparatus for measuring in vivo uterine ligament force-displacement behavior and stiffness and to present pilot data in women with and without prolapse. Study Design Seventeen women with varying uterine support underwent testing in the operating room (OR) after anesthetic induction. A tripod-mounted computer-controlled linear servoactuator was used to quantify force-displacement behavior of the cervix and supporting ligaments. The servoactuator applied a caudally-directed force to a tenaculum at 4 mm/s velocity until the traction force reached 17.8N (4 lbs.). Cervix location on POP-Q in clinic, in the OR at rest, and with minimal force (Ligament “stiffness” between minimum and maximum force was calculated. Results The mean (SD) subject age was 54.5 (12.7) years, parity 2.9 (1.1), BMI 29.0 (4.3) kg/m2, and POP-Q point C −3.1 (3.9) cm. POP-Q point C was most strongly correlated with cervix location at maximum force (r=+0.68, p=.003) and at rest (r=+0.62, p=.009). Associations between cervix location at minimum force (r=+0.46, p=.059) and ligament stiffness (r= −0.44,p=.079) were not statistically significant. Cervix location in the OR with minimal traction lay below the lowest point found on POP-Q for 13 women. Conclusions POP-Q point C was strongly correlated with cervix location at rest and at maximum traction force; however only 19% of the variation in POP-Q point C location was explained by ligament stiffness. The cervix location in the OR at minimal traction lay below POP-Q point C value in ¾ of women. PMID:23747493

  4. Differential fracture healing resulting from fixation stiffness variability. A mouse model

    International Nuclear Information System (INIS)

    Gardner, M.J.; Putnam, S.M.; Wong, A.; Streubel, P.N.; Kotiya, A.; Silva, M.J.

    2011-01-01

    The mechanisms underlying the interaction between the local mechanical environment and fracture healing are not known. We developed a mouse femoral fracture model with implants of different stiffness, and hypothesized that differential fracture healing would result. Femoral shaft fractures were created in 70 mice, and were treated with an intramedullary nail made of either tungsten (Young's modulus=410 GPa) or aluminium (Young's modulus=70 GPa). Mice were then sacrificed at 2 or 5 weeks. Fracture calluses were analyzed using standard microCT, histological, and biomechanical methods. At 2 weeks, callus volume was significantly greater in the aluminium group than in the tungsten group (61.2 vs. 40.5 mm 3 , p=0.016), yet bone volume within the calluses was no different between the groups (13.2 vs. 12.3 mm 3 ). Calluses from the tungsten group were stiffer on mechanical testing (18.7 vs. 9.7 N/mm, p=0.01). The percent cartilage in the callus was 31.6% in the aluminium group and 22.9% in the tungsten group (p=0.40). At 5 weeks, there were no differences between any of the healed femora. In this study, fracture implants of different stiffness led to different fracture healing in this mouse fracture model. Fractures treated with a stiffer implant had more advanced healing at 2 weeks, but still healed by callus formation. Although this concept has been well documented previously, this particular model could be a valuable research tool to study the healing consequences of altered fixation stiffness, which may provide insight into the pathogenesis and ideal treatment of fractures and non-unions. (author)

  5. Stiffness distribution in insect cuticle: a continuous or a discontinuous profile?

    Science.gov (United States)

    Rajabi, H; Jafarpour, M; Darvizeh, A; Dirks, J-H; Gorb, S N

    2017-07-01

    Insect cuticle is a biological composite with a high degree of complexity in terms of both architecture and material composition. Given the complex morphology of many insect body parts, finite-element (FE) models play an important role in the analysis and interpretation of biomechanical measurements, taken by either macroscopic or nanoscopic techniques. Many previous studies show that the interpretation of nanoindentation measurements of this layered composite material is very challenging. To develop accurate FE models, it is of particular interest to understand more about the variations in the stiffness through the thickness of the cuticle. Considering the difficulties of making direct measurements, in this study, we use the FE method to analyse previously published data and address this issue numerically. For this purpose, sets of continuous or discontinuous stiffness profiles through the thickness of the cuticle were mathematically described. The obtained profiles were assigned to models developed based on the cuticle of three insect species with different geometries and layer configurations. The models were then used to simulate the mechanical behaviour of insect cuticles subjected to nanoindentation experiments. Our results show that FE models with discontinuous exponential stiffness gradients along their thickness were able to predict the stress and deformation states in insect cuticle very well. Our results further suggest that, for more accurate measurements and interpretation of nanoindentation test data, the ratio of the indentation depth to cuticle thickness should be limited to 7% rather than the traditional '10% rule'. The results of this study thus might be useful to provide a deeper insight into the biomechanical consequences of the distinct material distribution in insect cuticle and also to form a basis for more realistic modelling of this complex natural composite. © 2017 The Author(s).

  6. Central Artery Stiffness, Baroreflex Sensitivity, and Brain White Matter Neuronal Fiber Integrity in Older Adults

    Science.gov (United States)

    Tarumi, Takashi; de Jong, Daan L.K.; Zhu, David C.; Tseng, Benjamin Y.; Liu, Jie; Hill, Candace; Riley, Jonathan; Womack, Kyle B.; Kerwin, Diana R.; Lu, Hanzhang; Cullum, C. Munro; Zhang, Rong

    2015-01-01

    Cerebral hypoperfusion elevates the risk of brain white matter (WM) lesions and cognitive impairment. Central artery stiffness impairs baroreflex, which controls systemic arterial perfusion, and may deteriorate neuronal fiber integrity of brain WM. The purpose of this study was to examine the associations among brain WM neuronal fiber integrity, baroreflex sensitivity (BRS), and central artery stiffness in older adults. Fifty-four adults (65±6 years) with normal cognitive function or mild cognitive impairment (MCI) were tested. The neuronal fiber integrity of brain WM was assessed from diffusion metrics acquired by diffusion tensor imaging. BRS was measured in response to acute changes in blood pressure induced by bolus injections of vasoactive drugs. Central artery stiffness was measured by carotid-femoral pulse wave velocity (cfPWV). The WM diffusion metrics including fractional anisotropy (FA) and radial (RD) and axial (AD) diffusivities, BRS, and cfPWV were not different between the control and MCI groups. Thus, the data from both groups were combined for subsequent analyses. Across WM, fiber tracts with decreased FA and increased RD were associated with lower BRS and higher cfPWV, with many of the areas presenting spatial overlap. In particular, the BRS assessed during hypotension was strongly correlated with FA and RD when compared with hypertension. Executive function performance was associated with FA and RD in the areas that correlated with cfPWV and BRS. These findings suggest that baroreflex-mediated control of systemic arterial perfusion, especially during hypotension, may play a crucial role in maintaining neuronal fiber integrity of brain WM in older adults. PMID:25623500

  7. Interfacial free energy and stiffness of aluminum during rapid solidification

    International Nuclear Information System (INIS)

    Brown, Nicholas T.; Martinez, Enrique; Qu, Jianmin

    2017-01-01

    Using molecular dynamics simulations and the capillary fluctuation method, we have calculated the anisotropic crystal-melt interfacial free energy and stiffness of aluminum in a rapid solidification system where a temperature gradient is applied to enforce thermal non-equilibrium. To calculate these material properties, the standard capillary fluctuation method typically used for systems in equilibrium has been modified to incorporate a second-order Taylor expansion of the interfacial free energy term. The result is a robust method for calculating interfacial energy, stiffness and anisotropy as a function of temperature gradient using the fluctuations in the defined interface height. This work includes the calculation of interface characteristics for temperature gradients ranging from 11 to 34 K/nm. The captured results are compared to a thermal equilibrium case using the same model and simulation technique with a zero gradient definition. We define the temperature gradient as the change in temperature over height perpendicular to the crystal-melt interface. The gradients are applied in MD simulations using defined thermostat regions on a stable solid-liquid interface initially in thermal equilibrium. The results of this work show that the interfacial stiffness and free energy for aluminum are dependent on the magnitude of the temperature gradient, however the anisotropic parameters remain independent of the non-equilibrium conditions applied in this analysis. As a result, the relationships of the interfacial free energy/stiffness are determined to be linearly related to the thermal gradient, and can be interpolated to find material characteristics at additional temperature gradients.

  8. Effects of Ramadan fasting on body composition and arterial stiffness.

    Science.gov (United States)

    Sezen, Yusuf; Altiparmak, Ibrahim Halil; Erkus, Muslihittin Emre; Kocarslan, Aydemir; Kaya, Zekeriya; Gunebakmaz, Ozgur; Demirbag, Recep

    2016-12-01

    To examine the effects of Ramadan fasting on body composition, arterial stiffness and resting heart rate. This prospective study was conducted at the Department of Cardiology, Harran University, Sanliurfa, Turkey, during Ramadan 2015, and comprised overweight and obese males. Body composition, arterial stiffness and echocardiography were assessed before and after Ramadan. Body composition was assessed by bioelectrical impedance analysis using segmental body composition analyser. Arterial stiffness and haemodynamic parameters were also measured. SPSS 20 was used for data analysis. Of the 100 subjects enrolled, 70(70%) were included. The overall mean age was 37±7 years. No significant changes were observed in blood pressures, resting heart rate, aortic pulse wave velocity, aortic augmentation index-75, aortic pulse pressure, brachial pulse pressure, basal metabolic rate, total body water, fat-free mass, and echocardiographic parameters (p>0.05 each). Although aortic pulse wave velocity (m/s) and augmentation index-75 (%) decreased after fasting period compared to that of before Ramadan, these reductions did not reach statistically significant levels (8.6±1.8 vs. 8.9±1.9, and 13.6±6.6 vs. 14.7±9.3, respectively; p>0.05 each). Body mass index, waist-hip ratio, body water rate, percentage of body fat mass, body fat mass, and visceral fat mass percentage were significantly reduced (pRamadan. Ramadan fasting had beneficial effects on body composition, but did not have any significant effect on arterial stiffness and resting heart rate.

  9. Influence of facing vertical stiffness on reinforced soil wall design

    OpenAIRE

    Puig Damians, Ivan; Bathurst, Richard; Josa Garcia-Tornel, Alejandro; Lloret Morancho, Antonio

    2013-01-01

    Current design practices for reinforced soil walls typically ignore the influence of facing type and foundation compressibility on the magnitude and distribution of reinforcement loads in steel reinforced soil walls under operational conditions. In this paper, the effect of the facing vertical stiffness (due to elastomeric bearing pads placed in the horizontal joints between panels) on load capacity of steel reinforced soil walls is examined in a systematic manner using a numerical modelli...

  10. Stiffness management of sheet metal parts using laser metal deposition

    Science.gov (United States)

    Bambach, Markus; Sviridov, Alexander; Weisheit, Andreas

    2017-10-01

    Tailored blanks are established solutions for the production of load-adapted sheet metal components. In the course of the individualization of production, such semi-finished products are gaining importance. In addition to tailored welded blanks and tailored rolled blanks, patchwork blanks have been developed which allow a local increase in sheet thickness by welding, gluing or soldering patches onto sheet metal blanks. Patchwork blanks, however, have several limitations, on the one hand, the limited freedom of design in the production of patchwork blanks and, on the other hand, the fact that there is no optimum material bonding with the substrate. The increasing production of derivative and special vehicles on the basis of standard vehicles, prototype production and the functionalization of components require solutions with which semi-finished products and sheet metal components can be provided flexibly with local thickenings or functional elements with a firm metallurgical bond to the substrate. An alternative to tailored and patchwork blanks is, therefore, a free-form reinforcement applied by additive manufacturing via laser metal deposition (LMD). By combining metal forming and additive manufacturing, stiffness can be adapted to the loads based on standard components in a material-efficient manner and without the need to redesign the forming tools. This paper details a study of the potential of stiffness management by LMD using a demonstrator part. Sizing optimization is performed and part distortion is taken into account to find an optimal design for the cladding. A maximum stiffness increase of 167% is feasible with only 4.7% additional mass. Avoiding part distortion leads to a pareto-optimal design which achieves 95% more stiffness with 6% added mass.

  11. Experimental exposure to diesel exhaust increases arterial stiffness in man

    Directory of Open Access Journals (Sweden)

    Newby David E

    2009-03-01

    Full Text Available Abstract Introduction Exposure to air pollution is associated with increased cardiovascular morbidity, although the underlying mechanisms are unclear. Vascular dysfunction reduces arterial compliance and increases central arterial pressure and left ventricular after-load. We determined the effect of diesel exhaust exposure on arterial compliance using a validated non-invasive measure of arterial stiffness. Methods In a double-blind randomized fashion, 12 healthy volunteers were exposed to diesel exhaust (approximately 350 μg/m3 or filtered air for one hour during moderate exercise. Arterial stiffness was measured using applanation tonometry at the radial artery for pulse wave analysis (PWA, as well as at the femoral and carotid arteries for pulse wave velocity (PWV. PWA was performed 10, 20 and 30 min, and carotid-femoral PWV 40 min, post-exposure. Augmentation pressure (AP, augmentation index (AIx and time to wave reflection (Tr were calculated. Results Blood pressure, AP and AIx were generally low reflecting compliant arteries. In comparison to filtered air, diesel exhaust exposure induced an increase in AP of 2.5 mmHg (p = 0.02 and in AIx of 7.8% (p = 0.01, along with a 16 ms reduction in Tr (p = 0.03, 10 minutes post-exposure. Conclusion Acute exposure to diesel exhaust is associated with an immediate and transient increase in arterial stiffness. This may, in part, explain the increased risk for cardiovascular disease associated with air pollution exposure. If our findings are confirmed in larger cohorts of susceptible populations, this simple non-invasive method of assessing arterial stiffness may become a useful technique in measuring the impact of real world exposures to combustion derived-air pollution.

  12. Experimental challenges to stiffness as a transport paradigm

    Science.gov (United States)

    Luce, T. C.; Burrell, K. H.; Holland, C.; Marinoni, A.; Petty, C. C.; Smith, S. P.; Austin, M. E.; Grierson, B. A.; Zeng, L.

    2018-02-01

    Two power scans were carried out in H-mode plasmas in DIII-D; one employed standard co-current neutral beam injection (NBI), while the other used a mixture of co-current and counter-current NBI to scan power while holding the torque to a low fixed value. Analysis of the ion and electron heat transport, ion toroidal angular momentum transport, and thermal deuterium transport from these scans is presented. Invariance of the gradients or gradient scalelengths, as might be expected from stiff transport, was not generally observed. When invariance was seen, it was not accompanied by a strong increase in transport, except in the case of the absolute deuterium ion transport. Conduction in the ion channel is the dominant energy loss mechanism. The variation of the ion heat transport with applied power is similar for the co-injection and fixed torque scans, indicating that E  ×  B shearing is not determining the plasma response to additional power. There is however, a quantitative difference in the transport between the two scans, indicating E  ×  B shearing does play a role in the transport. Comparison of these results with a previous experiment that directly probed stiffness at a single radius leads to the following conclusion: while local stiffness as formally defined may hold, invariance of the gradients or normalized scalelengths does not follow from stiff transport in more practical scaling experiments, such as the power scans discussed here. Possible reasons for the lack of correspondence between the local picture and the global expectations are discussed.

  13. Stiffness and hysteresis properties of some prosthetic feet

    OpenAIRE

    van Jaarsveld, H.W.L.; Grootenboer, H.J.; de Vries, J.; Koopman, Hubertus F.J.M.

    1990-01-01

    A prosthetic foot is an important element of a prosthesis, although it is not always fully recognized that the properties of the foot, along with the prosthetic knee joint and the socket, are in part responsible for the stability and metabolic energy cost during walking. The stiffness and the hysteresis, which are the topics of this paper, are not properly prescribed, but could be adapted to improve the prosthetic walking performance. The shape is strongly related to the cosmetic appearance a...

  14. A method for measuring exchange stiffness in ferromagnetic films

    International Nuclear Information System (INIS)

    Girt, Erol; Huttema, W.; Montoya, E.; Kardasz, B.; Eyrich, C.; Heinrich, B.; Mryasov, O. N.; Dobin, A. Yu.; Karis, O.

    2011-01-01

    An exchange stiffness, A ex , in ferromagnetic films is obtained by fitting the M(H) dependence of two ferromagnetic layers antiferromagnetically coupled across a nonmagnetic spacer layer with a simple micromagnetic model. In epitaxial and textured structures this method allows measuring A ex between the crystallographic planes perpendicular to the growth direction of ferromagnetic films. Our results show that A ex between [0001] planes in textured Co grains is 1.54 ± 0.12 x 10 -11 J/m.

  15. Running Economy: Neuromuscular and Joint Stiffness Contributions in Trained Runners.

    Science.gov (United States)

    Tam, Nicholas; Tucker, Ross; Santos-Concejero, Jordan; Prins, Danielle; Lamberts, Robert P

    2018-05-29

    It is debated whether running biomechanics make good predictors of running economy, with little known information about the neuromuscular and joint stiffness contributions to economical running gait. The aim of this study was to understand the relationship between certain neuromuscular and spatiotemporal biomechanical factors associated with running economy. Thirty trained runners performed a 6-minute constant-speed running set at 3.3 m∙s -1 , where oxygen consumption was assessed. Overground running trials were also performed at 3.3 m∙s -1 to assess kinematics, kinetics and muscle activity. Spatiotemporal gait variables, joint stiffness, pre-activation and stance phase muscle activity (gluteus medius; rectus femoris (RF); biceps femoris(BF); peroneus longus (PL); tibialis anterior (TA); gastrocnemius lateralis and medius (LG and MG) were variables of specific interest and thus determined. Additionally, pre-activation and ground contact of agonist:antagonist co-activation were calculated. More economical runners presented with short ground contact times (r=0.639, p<0.001) and greater strides frequencies (r=-0.630, p<0.001). Lower ankle and greater knee stiffness were associated with lower oxygen consumption (r=0.527, p=0.007 & r=0.384, p=0.043, respectively). Only LG:TA co-activation during stance were associated with lower oxygen cost of transport (r=0.672, p<0.0001). Greater muscle pre-activation and bi-articular muscle activity during stance were associated with more economical runners. Consequently, trained runners who exhibit greater neuromuscular activation prior to and during ground contact, in turn optimise spatiotemporal variables and joint stiffness, will be the most economical runners.

  16. Updating Stiffness and Hysteretic Damping Matrices Using Measured Modal Data

    Directory of Open Access Journals (Sweden)

    Jiashang Jiang

    2018-01-01

    Full Text Available A new direct method for the finite element (FE matrix updating problem in a hysteretic (or material damping model based on measured incomplete vibration modal data is presented. With this method, the optimally approximated stiffness and hysteretic damping matrices can be easily constructed. The physical connectivity of the original model is preserved and the measured modal data are embedded in the updated model. The numerical results show that the proposed method works well.

  17. Updating Stiffness and Hysteretic Damping Matrices Using Measured Modal Data

    OpenAIRE

    Jiashang Jiang; Yongxin Yuan

    2018-01-01

    A new direct method for the finite element (FE) matrix updating problem in a hysteretic (or material) damping model based on measured incomplete vibration modal data is presented. With this method, the optimally approximated stiffness and hysteretic damping matrices can be easily constructed. The physical connectivity of the original model is preserved and the measured modal data are embedded in the updated model. The numerical results show that the proposed method works well.

  18. Arterial stiffness, central hemodynamics, and cardiovascular risk in hypertension

    Science.gov (United States)

    Palatini, Paolo; Casiglia, Edoardo; Gąsowski, Jerzy; Głuszek, Jerzy; Jankowski, Piotr; Narkiewicz, Krzysztof; Saladini, Francesca; Stolarz-Skrzypek, Katarzyna; Tikhonoff, Valérie; Van Bortel, Luc; Wojciechowska, Wiktoria; Kawecka-Jaszcz, Kalina

    2011-01-01

    This review summarizes several scientific contributions at the recent Satellite Symposium of the European Society of Hypertension, held in Milan, Italy. Arterial stiffening and its hemodynamic consequences can be easily and reliably measured using a range of noninvasive techniques. However, like blood pressure (BP) measurements, arterial stiffness should be measured carefully under standardized patient conditions. Carotid-femoral pulse wave velocity has been proposed as the gold standard for arterial stiffness measurement and is a well recognized predictor of adverse cardiovascular outcome. Systolic BP and pulse pressure in the ascending aorta may be lower than pressures measured in the upper limb, especially in young individuals. A number of studies suggest closer correlation of end-organ damage with central BP than with peripheral BP, and central BP may provide additional prognostic information regarding cardiovascular risk. Moreover, BP-lowering drugs can have differential effects on central aortic pressures and hemodynamics compared with brachial BP. This may explain the greater beneficial effect provided by newer antihypertensive drugs beyond peripheral BP reduction. Although many methodological problems still hinder the wide clinical application of parameters of arterial stiffness, these will likely contribute to cardiovascular assessment and management in future clinical practice. Each of the abovementioned parameters reflects a different characteristic of the atherosclerotic process, involving functional and/or morphological changes in the vessel wall. Therefore, acquiring simultaneous measurements of different parameters of vascular function and structure could theoretically enhance the power to improve risk stratification. Continuous technological effort is necessary to refine our methods of investigation in order to detect early arterial abnormalities. Arterial stiffness and its consequences represent the great challenge of the twenty-first century for

  19. Stiffness compatibility of coralline hydroxyapatite bone substitute under dynamic loading

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    When hydroxyapatite bone substitutes are implanted in human bodies,bone tissues will grow into their porous structure,which will reinforce their strength and stiffness.The concept of mechanical com-patibility of bone substitutes implies that their mechanical properties are similar to the bone tissues around,as if they were part of the bone.The mechanical compatibility of bone substitutes includes both static and dynamic behavior,due to the mechanical properties of bone depending on the strain rate.In this study,split Hopkinson pressure bar technique(SHPB) was employed to determine the dy-namic mechanical properties of coralline hydroxyapatite,bones with and bones without organic com-ponents,and their dynamic stress-strain curves of the three materials were obtained.The mechanical effects of collagens in bone were assessed,by comparing the difference between the Young’s moduli of the three materials.As the implanted bone substitute becomes a part of bone,it can be regarded as an inclusion composite.The effective modulus of the composite was also evaluated in order to estimate its mechanical compatibility on stiffness.The evaluated result shows that the suitable porosity of HA is 0.8,which is in favor of both static and dynamic stiffness compatibility.

  20. Stiffness compatibility of coralline hydroxyapatite bone substitute under dynamic loading

    Institute of Scientific and Technical Information of China (English)

    REN ChaoFeng; HOU ZhenDe; ZHAO Wei

    2009-01-01

    When hydroxyapatite bone substitutes are implanted in human bodies, bone tissues will grow into their porous structure, which will reinforce their strength and stiffness. The concept of mechanical com-patibility of bone substitutes implies that their mechanical properties are similar to the bone tissues around, as if they were part of the bone. The mechanical compatibility of bone substitutes includes both static and dynamic behavior, due to the mechanical properties of bone depending on the strain rate. In this study, split Hopkinson pressure bar technique (SHPB) was employed to determine the dy-namic mechanical properties of coralline hydroxyapatite, bones with and bones without organic com-ponents, and their dynamic stress-strain curves of the three materials were obtained. The mechanical effects of collagens in bone were assessed, by comparing the difference between the Young's moduli of the three materials. As the implanted bone substitute becomes a part of bone, it can be regarded as an inclusion composite. The effective modulus of the composite was also evaluated in order to estimate its mechanical compatibility on stiffness. The evaluated result shows that the suitable porosity of HA is0.8, which is in favor of both static and dynamic stiffness compatibility.

  1. Origami tubes assembled into stiff, yet reconfigurable structures and metamaterials.

    Science.gov (United States)

    Filipov, Evgueni T; Tachi, Tomohiro; Paulino, Glaucio H

    2015-10-06

    Thin sheets have long been known to experience an increase in stiffness when they are bent, buckled, or assembled into smaller interlocking structures. We introduce a unique orientation for coupling rigidly foldable origami tubes in a "zipper" fashion that substantially increases the system stiffness and permits only one flexible deformation mode through which the structure can deploy. The flexible deployment of the tubular structures is permitted by localized bending of the origami along prescribed fold lines. All other deformation modes, such as global bending and twisting of the structural system, are substantially stiffer because the tubular assemblages are overconstrained and the thin sheets become engaged in tension and compression. The zipper-coupled tubes yield an unusually large eigenvalue bandgap that represents the unique difference in stiffness between deformation modes. Furthermore, we couple compatible origami tubes into a variety of cellular assemblages that can enhance mechanical characteristics and geometric versatility, leading to a potential design paradigm for structures and metamaterials that can be deployed, stiffened, and tuned. The enhanced mechanical properties, versatility, and adaptivity of these thin sheet systems can provide practical solutions of varying geometric scales in science and engineering.

  2. Photoplethysmographic signal waveform index for detection of increased arterial stiffness

    International Nuclear Information System (INIS)

    Pilt, K; Meigas, K; Ferenets, R; Temitski, K; Viigimaa, M

    2014-01-01

    The aim of this research was to assess the validity of the photoplethysmographic (PPG) waveform index PPGAI for the estimation of increased arterial stiffness. For this purpose, PPG signals were recorded from 24 healthy subjects and from 20 type II diabetes patients. The recorded PPG signals were processed with the analysis algorithm developed and the waveform index PPGAI similar to the augmentation index (AIx) was calculated. As a reference, the aortic AIx was assessed and normalized for a heart rate of 75 bpm (AIx@75) by a SphygmoCor device. A strong correlation (r = 0.85) between the PPGAI and the aortic AIx@75 and a positive correlation of both indices with age were found. Age corrections for the indices PPGAI and AIx@75 as regression models from the signals of healthy subjects were constructed. Both indices revealed a significant difference between the groups of diabetes patients and healthy controls. However, the PPGAI provided the best statistical discrimination for the group of subjects with increased arterial stiffness. The waveform index PPGAI based on the inexpensive PPG technology can be considered as a perspective measure of increased arterial stiffness estimation in clinical screenings. (paper)

  3. Helical growth trajectories in plant roots interacting with stiff barriers

    Science.gov (United States)

    Gerbode, Sharon; Noar, Roslyn; Harrison, Maria

    2009-03-01

    Plant roots successfully navigate heterogeneous soil environments with varying nutrient and water concentrations, as well as a variety of stiff obstacles. While it is thought that the ability of roots to penetrate into a stiff lower soil layer is important for soil erosion, little is known about how a root actually responds to a rigid interface. We have developed a laser sheet imaging technique for recording the 3D growth dynamics of plant roots interacting with stiff barriers. We find that a root encountering an angled interface does not grow in a straight line along the surface, but instead follows a helical trajectory. These experiments build on the pioneering studies of roots grown on a tilted 2D surface, which reported ``root waving,'' a similar curved pattern thought to be caused by the root's sensitivity to both gravity and the rigid surface on which it is grown. Our measurements extend these results to the more physiologically relevant case of 3D growth, where the spiral trajectory can be altered by tuning the relative strengths of the gravity and touch stimuli, providing some intuition for the physical mechanism driving it.

  4. Weight reduction and aortic stiffness in obese children and adolescents

    DEFF Research Database (Denmark)

    Hvidt, K. N.; Olsen, M. H.; Ibsen, H.

    2015-01-01

    Little is known about the effect of weight reduction on aortic stiffness and especially so in the young. The present study investigates whether weight reduction influences aortic stiffness in obese children and adolescents. Carotid-femoral pulse wave velocity (cfPWV) and augmentation index at heart...... was found in AIx@HR75 (Delta AIx@HR75: 2.10 +/- 9.73%, P = 0.072), but changes in AIx@HR75 were related to changes in abdominal fat (Delta waist/height ratio: beta = 50.3, 95% CI 6.7-94.0, P = 0.02) and changes in total body fat percent by dual energy X-ray absorptiometry scan (Delta total body fat...... (%): beta = 0.7, 95% CI 0.1-1.3, P = 0.02) when adjusted for gender and relevant baseline confounders. In conclusion, no clear effect of weight reduction was found on aortic stiffness, although changes in AIx@HR75 were associated with changes in both abdominal fat and total body fat percent. The higher cf...

  5. Wearable Vibrotactile Haptic Device for Stiffness Discrimination during Virtual Interactions

    Directory of Open Access Journals (Sweden)

    Andualem Tadesse Maereg

    2017-09-01

    Full Text Available In this paper, we discuss the development of cost effective, wireless, and wearable vibrotactile haptic device for stiffness perception during an interaction with virtual objects. Our experimental setup consists of haptic device with five vibrotactile actuators, virtual reality environment tailored in Unity 3D integrating the Oculus Rift Head Mounted Display (HMD and the Leap Motion controller. The virtual environment is able to capture touch inputs from users. Interaction forces are then rendered at 500 Hz and fed back to the wearable setup stimulating fingertips with ERM vibrotactile actuators. Amplitude and frequency of vibrations are modulated proportionally to the interaction force to simulate the stiffness of a virtual object. A quantitative and qualitative study is done to compare the discrimination of stiffness on virtual linear spring in three sensory modalities: visual only feedback, tactile only feedback, and their combination. A common psychophysics method called the Two Alternative Forced Choice (2AFC approach is used for quantitative analysis using Just Noticeable Difference (JND and Weber Fractions (WF. According to the psychometric experiment result, average Weber fraction values of 0.39 for visual only feedback was improved to 0.25 by adding the tactile feedback.

  6. Magnetic resonance elastography of the lung parenchyma in an in situ porcine model with a noninvasive mechanical driver: correlation of shear stiffness with trans-respiratory system pressures.

    Science.gov (United States)

    Mariappan, Yogesh K; Kolipaka, Arunark; Manduca, Armando; Hubmayr, Rolf D; Ehman, Richard L; Araoz, Philip; McGee, Kiaran P

    2012-01-01

    Quantification of the mechanical properties of lung parenchyma is an active field of research due to the association of this metric with normal function, disease initiation and progression. A phase contrast MRI-based elasticity imaging technique known as magnetic resonance elastography is being investigated as a method for measuring the shear stiffness of lung parenchyma. Previous experiments performed with small animals using invasive drivers in direct contact with the lungs have indicated that the quantification of lung shear modulus with (1) H based magnetic resonance elastography is feasible. This technique has been extended to an in situ porcine model with a noninvasive mechanical driver placed on the chest wall. This approach was tested to measure the change in parenchymal stiffness as a function of airway opening pressure (P(ao) ) in 10 adult pigs. In all animals, shear stiffness was successfully quantified at four different P(ao) values. Mean (±STD error of mean) pulmonary parenchyma density corrected stiffness values were calculated to be 1.48 (±0.09), 1.68 (±0.10), 2.05 (±0.13), and 2.23 (±0.17) kPa for P(ao) values of 5, 10, 15, and 20 cm H2O, respectively. Shear stiffness increased with increasing P(ao) , in agreement with the literature. It is concluded that in an in situ porcine lung shear stiffness can be quantitated with (1) H magnetic resonance elastography using a noninvasive mechanical driver and that it is feasible to measure the change in shear stiffness due to change in P(ao) . Copyright © 2011 Wiley-Liss, Inc.

  7. A comparison of muscle stiffness and musculoarticular stiffness of the knee joint in young athletic males and females.

    Science.gov (United States)

    Wang, Dan; De Vito, Giuseppe; Ditroilo, Massimiliano; Fong, Daniel T P; Delahunt, Eamonn

    2015-06-01

    The objective of this study was to investigate the gender-specific differences in peak torque (PT), muscle stiffness (MS) and musculoarticular stiffness (MAS) of the knee joints in a young active population. Twenty-two male and twenty-two female recreational athletes participated. PT of the knee joint extensor musculature was assessed on an isokinetic dynamometer, MS of the vastus lateralis (VL) muscle was measured in both relaxed and contracted conditions, and knee joint MAS was quantified using the free oscillation technique. Significant gender differences were observed for all dependent variables. Females demonstrated less normalized PT (mean difference (MD)=0.4Nm/kg, p=0.005, η(2)=0.17), relaxed MS (MD=94.2N/m, pjoint injury incidence and prevalence in females when compared to males. Copyright © 2015 Elsevier Ltd. All rights reserved.

  8. Influence of inhaled nicotine source on arterial stiffness.

    Science.gov (United States)

    Szołtysek-Bołdys, Izabela; Sobczak, Andrzej; Zielińska-Danch, Wioleta; Bartoń, Aleksandra; Koszowski, Bartosz; Kośmider, Leon

    2014-01-01

    Tobacco smoking leads to changes in hemodynamic parameters such as heart rate and systolic or diastolic blood pressure. It has a direct influence on the elasticity of blood vessels and increases arterial stiffness, which can result in development of atherosclerosis. Data show that the nicotine in tobacco smoke probably is responsible for these changes. Electronic cigarettes (e-cigarettes) were supposedly a healthier alternative to combustible cigarettes because they imitate a process of cigarettes smoking but generate nicotine aerosol without the toxic substances from tobacco combustion. However, the use of e-cigarettes is still controversial because their toxicity, safety and long term use health impact have not been sufficiently studied. The aim of this study was to evaluate changes in arterial stiffness parameters after smoking a cigarette or e-cigarette use. Fifteen healthy women, aged 19-25 years old, smoking ≥5 cigarettes per day for at least two years participated in the study. A non-invasive measurement of arterial stiffness parameters - Stiffness Index (SI) and Reflection Index (RI) - was conducted and systolic and diastolic blood pressure and heart rate were measured before and after smoking a conventional cigarette as well as use of an e-cigarette. Statistically significant changes in the SI and RI were observed before and after smoking of a conventional cigarette [SI: 6.75m/s (6.66 - 6.85, 95% CI) vs 6.56m/s (6.46 - 6.65. 95% CI), p=0.0056; RI: 54.0% (51.5 - 56.7, 95% CI) vs 49.6% (47.5 - 51.8, 95% CI), p=0.010]. The use of e-cigarettes resulted in no statistically significant changes in the SI and RI. After both product use systolic and diastolic blood pressure and heart rate increased but the changes were not statistically significant. In contrast to conventional cigarette use, the use of electronic cigarettes causes no changes in arterial stiffness. This may indicate lower bioavailability of nicotine from the e-cigarette or an additional effect of

  9. Cardiovascular autonomic dysfunction and carotid stiffness in adults with repaired tetralogy of Fallot.

    Science.gov (United States)

    Novaković, Marko; Prokšelj, Katja; Starc, Vito; Jug, Borut

    2017-06-01

    Adults after surgical repair of tetralogy of Fallot (ToF) may have impaired vascular and cardiac autonomic function. Thus, we wanted to assess interrelations between heart rate variability (HRV) and heart rate recovery (HRR), as parameters of cardiac autonomic function, and arterial stiffness, as a parameter of vascular function, in adults with repaired ToF as compared to healthy controls. In a case-control study of adults with repaired ToF and healthy age-matched controls we measured: 5-min HRV variability (with time and frequency domain data collected), carotid artery stiffness (through pulse-wave analysis using echo-tracking ultrasound) and post-exercise HRR (cycle ergometer exercise testing). Twenty-five patients with repaired ToF (mean age 38 ± 10 years) and 10 healthy controls (mean age 39 ± 8 years) were included. Selected HRR and HRV (time-domain) parameters, but not arterial stiffness were significantly reduced in adults after ToF repair. Moreover, a strong association between late/slow HRR (after 2, 3 and 4 min) and carotid artery stiffness was detected in ToF patients (r = -0.404, p = 0.045; r = -0.545, p = 0.005 and r = -0.545, p = 0.005, respectively), with statistical significance retained even after adjusting for age, gender, resting heart rate and β-blockers use (r = -0.393, p = 0.024 for HRR after 3 min). Autonomic cardiac function is impaired in patients with repaired ToF, and independently associated with vascular function in adults after ToF repair, but not in age-matched healthy controls. These results might help in introducing new predictors of cardiovascular morbidity in a growing population of adults after surgical repair of ToF.

  10. The Relationship of Carotid Arterial Stiffness and Left Ventricular Concentric Hypertrophy in Hypertension.

    Science.gov (United States)

    Jaroch, Joanna; Łoboz-Grudzień, Krystyna; Magda, Stefania; Florescu, Maria; Bociąga, Zbigniew; Ciobanu, Andrea O; Kruszyńska, Ewa; Dudek, Krzysztof; Vinereanu, Dragos

    2016-01-01

    Left ventricular hypertrophy (LVH) and geometry patterns vary in different hemodynamic profiles The concentric hypertrophy (CH) pattern has been proved to have the worst prognosis. The aim of the study was to test the hypothesis that carotid artery stiffness, as a marker of vascular damage, is associated with CH, independently of other potential determinants such as demographic factors (age, sex, BMI), clinical parameters (smoking, diabetes, creatinine level) and hemodynamic variables (blood pressure, pulse pressure [PP]). The study involved 262 subjects (89 men): 202 patients with hypertension (153 untreated, 49 on medication), aged 55.7 ± 10 years, and 60 age-matched normal controls. The subjects were examined by echocardiography and carotid ultrasound with a high-resolution echo-tracking system. Based on the left ventricular mass index (LVMI) and relative wall thickness (RWT), the patients with hypertension were divided into four patterns of LVH and geometry: normal geometry (N, n = 57), concentric remodeling (CR, n = 48), concentric hypertrophy CH (n = 62) and eccentric hypertrophy (EH, n = 35). Intima-media thickness (IMT) and the parameters of arterial stiffness were also assessed using the β stiffness index (β), Young elastic modulus (Ep), arterial compliance (AC), one-point pulse wave velocity (PWVβ) and the wave reflection augmentation index (AI). Univariate analysis showed that the following variables are significant in determining CH: β > 8.4, Ep > 136 kPa, PWVβ > 7.1 m/s, AI > 21.9%, systolic BP > 151 mm Hg, PP > 54, IMT > 0.56 and the presence of diabetes. However, by multivariate analysis only AI (OR 3.65, p = 0.003), PWVβ > 7.1 m/s (OR 2.86, p = 0.014), systolic BP (OR 3.12, p = 0037) and the presence of diabetes (OR 3.75, p = 0.007) were associated independently with the occurrence of CH. Concentric hypertrophy in hypertension is strongly associated with carotid arterial stiffness and wave reflection parameters, independently of the influence

  11. Effect of contouring on bending structural stiffness and bending strength of the 3.5 titanium SOP implant.

    Science.gov (United States)

    Rutherford, Scott; Ness, Malcolm G

    2012-11-01

    To compare the bending structural stiffness (BSS) and bending strength (BS) of the 3.5 titanium (Ti) string of pearls (SOP) plate and the 3.5 316LVM stainless steel SOP plate; and the effect of contouring on the BSS and BS of the 3.5 Ti SOP plate. In vitro experimental static 4-point bending materials testing. Twenty-five 3.5 mm Ti and five 3.5 mm 316LVM stainless steel SOP locking bone plates. Each plate was tested in 4-point bending until 10 mm of displacement was achieved. BSS and BS were then calculated for each plate. A 2-sample t-test was used to compare the mean BSS and BS of the different groups. The 3.5 Ti SOP plate had lower mean BSS (0.00263 Nm(2) ) but similar mean BS (12.8 Nm) when compared to the 3.5 316LVM SOP (0.00402 Nm(2) , 13.0 Nm). Prebending the 3.5 Ti SOP diminished its mean BSS (0.00224 Nm(2) ) and mean BS (9.4 Nm) when compared to the Ti control. Pretwisting the 3.5 Ti SOP increased its mean BSS (0.00273 Nm(2) ) but decreased its mean BS (12.4 Nm) when compared to the Ti control. The 3.5 Ti SOP is less stiff but of similar strength to the 3.5 316LVM stainless steel SOP. Prebending the Ti SOP significantly lowers its stiffness and strength. Pretwisting the SOP actually increases its stiffness but slightly lowers its strength. © Copyright 2012 by The American College of Veterinary Surgeons.

  12. Evaluation of stiffness and plastic deformation of active ceramic self-ligating bracket clips after repetitive opening and closure movements

    Directory of Open Access Journals (Sweden)

    Grace Kelly Martins Carneiro

    2015-08-01

    Full Text Available OBJECTIVE: The aim of this study was to assess whether repetitive opening and closure of self-ligating bracket clips can cause plastic deformation of the clip.METHODS: Three types of active/interactive ceramic self-ligating brackets (n = 20 were tested: In-Ovation C, Quicklear and WOW. A standardized controlled device performed 500 cycles of opening and closure movements of the bracket clip with proper instruments and techniques adapted as recommended by the manufacturer of each bracket type. Two tensile tests, one before and one after the repetitive cycles, were performed to assess the stiffness of the clips. To this end, a custom-made stainless steel 0.40 x 0.40 mm wire was inserted into the bracket slot and adapted to the universal testing machine (EMIC DL2000, after which measurements were recorded. On the loading portion of the loading-unloading curve of clips, the slope fitted a first-degree equation curve to determine the stiffness/deflection rate of the clip.RESULTS: The results of plastic deformation showed no significant difference among bracket types before and after the 500 cycles of opening and closure (p = 0.811. There were significant differences on stiffness among the three types of brackets (p = 0.005. The WOW bracket had higher mean values, whereas Quicklear bracket had lower values, regardless of the opening/closure cycle.CONCLUSION: Repetitive controlled opening and closure movements of the clip did not alter stiffness or cause plastic deformation.

  13. Theoretical Design and Characteristics Analysis of a Quasi-Zero Stiffness Isolator Using a Disk Spring as Negative Stiffness Element

    Directory of Open Access Journals (Sweden)

    Lingshuai Meng

    2015-01-01

    Full Text Available This paper presents a novel quasi-zero stiffness (QZS isolator designed by combining a disk spring with a vertical linear spring. The static characteristics of the disk spring and the QZS isolator are investigated. The optimal combination of the configurative parameters is derived to achieve a wide displacement range around the equilibrium position in which the stiffness has a low value and changes slightly. By considering the overloaded or underloaded conditions, the dynamic equations are established for both force and displacement excitations. The frequency response curves (FRCs are obtained by using the harmonic balance method (HBM and confirmed by the numerical simulation. The stability of the steady-state solution is analyzed by applying Floquet theory. The force, absolute displacement, and acceleration transmissibility are defined to evaluate the isolation performance. Effects of the offset displacement, excitation amplitude, and damping ratio on the QZS isolator and the equivalent system (ELS are studied. The results demonstrate that the QZS isolator for overloaded or underloaded can exhibit different stiffness characteristics with changing excitation amplitude. If loaded with an appropriate mass, excited by not too large amplitude, and owned a larger damper, the QZS isolator can possess better isolation performance than its ELS in low frequency range.

  14. Cardiac magnetic resonance imaging-derived pulmonary artery distensibility index correlates with pulmonary artery stiffness and predicts functional capacity in patients with pulmonary arterial hypertension

    International Nuclear Information System (INIS)

    Kang, Ki-Woon; Chang, Hyuk-Jae; Kim, Young-Jin; Choi, Byoung-Wook; Yang, Woo-In; Shim, Chi-Young; Ha, Jongwon; Chung, Namsik; Lee, Hye-Sun

    2011-01-01

    Increased stiffness of the pulmonary vascular bed is known to increase mortality in patients with pulmonary arterial hypertension (PAH); and pulmonary artery (PA) stiffness is also thought to be associated with exercise capacity. The purpose of the present study was to investigate whether cardiac magnetic resonance imaging (CMRI)-derived PA distensibility index correlates with PA stiffness estimated on right heart catheterization (RHC) and predicts functional capacity (FC) in patients with PAH. Thirty-five consecutive PAH patients (23% male, mean age, 44±13 years; 69% idiopathic) underwent CMRI, RHC, and 6-min walk test (6MWT). PA distensibility indices were derived from cross-sectional area change (%) in the transverse view, perpendicular to the axis of the main PA, on CMRI [(maximum area-minimum area)/minimum area during cardiac cycle]. Among the PA stiffness indices, pulmonary vascular resistance (PVR) and PA capacitance were calculated using hemodynamic dataset from RHC. CMRI-derived PA distensibility was inversely correlated with PVR (R 2 =0.34, P 2 =0.35, P 2 =0.61, P<0.001). Furthermore, PA distensibility <20% predicted poor FC (<400 m in 6MWT) with a sensitivity of 82% and a specificity of 94%. Non-invasive CMRI-derived PA distensibility index correlates with PA stiffness and can predict FC in patients with PAH. (author)

  15. Femoral pseudoarthrosis and knee stiffness: long-term results of a one-stage surgical approach.

    Science.gov (United States)

    Gomes, João L Ellera; Ruthner, Roberto P; Moreira, Luiz

    2010-02-01

    The objective of this study was to analyze the surgical results of the simultaneous treatment of femoral pseudoarthrosis and knee stiffness using a combined one-stage approach (quadricepsplasty + osteoperiosteal decortications + bone autografting + fracture stabilization). Twelve patients (six men) followed up for a minimum of 10 years and who had undergone surgery for these combined procedures were contacted for evaluation. Their mean age at the time of the surgery was 30 years (standard deviation, SD 15; range 22-65 years), and mean time from initial trauma was 16 months (SD 6, range 10-32 months). Mean range of motion improved from 10 degrees (SD 9) to 112 degrees (SD 13) postoperatively. Fractures healed in all patients, and improvement in their range of motion was statistically significant (Student's t-test = 31; P time interval since disease onset (Pearson correlation = -0.672; P = 0.017). Postoperative recovery was uneventful, and no deaths or severe complications occurred in this series. Despite increased tissue handling, blood loss and postoperative morbidity, the simultaneous treatment of femoral pseudoarthrosis and knee stiffness was successful, and results suggested that the earlier a combined approach is used, the better the outcome may be.

  16. Structural stiffness and Coulomb damping in compliant foil journal bearings: Theoretical considerations

    Science.gov (United States)

    Ku, C.-P. Roger; Heshmat, Hooshang

    1994-07-01

    Compliant foil bearings operate on either gas or liquid, which makes them very attractive for use in extreme environments such as in high-temperature aircraft turbine engines and cryogenic turbopumps. However, a lack of analytical models to predict the dynamic characteristics of foil bearings forces the bearing designer to rely on prototype testing, which is time-consuming and expensive. In this paper, the authors present a theoretical model to predict the structural stiffness and damping coefficients of the bump foil strip in a journal bearing or damper. Stiffness is calculated based on the perturbation of the journal center with respect to its static equilibrium position. The equivalent viscous damping coefficients are determined based on the area of a closed hysteresis loop of the journal center motion. The authors found, theoretically, that the energy dissipated from this loop was mostly contributed by the frictional motion between contact surfaces. In addition, the source and mechanism of the nonlinear behavior of the bump foil strips were examined. With the introduction of this enhanced model, the analytical tools are now available for the design of compliant foil bearings.

  17. Comparison of Nonequilibrium Solution Algorithms Applied to Chemically Stiff Hypersonic Flows

    Science.gov (United States)

    Palmer, Grant; Venkatapathy, Ethiraj

    1995-01-01

    Three solution algorithms, explicit under-relaxation, point implicit, and lower-upper symmetric Gauss-Seidel, are used to compute nonequilibrium flow around the Apollo 4 return capsule at the 62-km altitude point in its descent trajectory. By varying the Mach number, the efficiency and robustness of the solution algorithms were tested for different levels of chemical stiffness.The performance of the solution algorithms degraded as the Mach number and stiffness of the flow increased. At Mach 15 and 30, the lower-upper symmetric Gauss-Seidel method produces an eight order of magnitude drop in the energy residual in one-third to one-half the Cray C-90 computer time as compared to the point implicit and explicit under-relaxation methods. The explicit under-relaxation algorithm experienced convergence difficulties at Mach 30 and above. At Mach 40 the performance of the lower-upper symmetric Gauss-Seidel algorithm deteriorates to the point that it is out performed by the point implicit method. The effects of the viscous terms are investigated. Grid dependency questions are explored.

  18. No change in calf muscle passive stiffness after botulinum toxin injection in children with cerebral palsy.

    Science.gov (United States)

    Alhusaini, Adel A A; Crosbie, Jack; Shepherd, Roberta B; Dean, Catherine M; Scheinberg, Adam

    2011-06-01

    Stiffness and shortening of the calf muscle due to neural or mechanical factors can profoundly affect motor function. The aim of this study was to investigate non-neurally mediated calf-muscle tightness in children with cerebral palsy (CP) before and after botulinum toxin type A (BoNT-A) injection. Sixteen children with spastic CP (seven females, nine males; eight at Gross Motor Function Classification System level I, eight at level II; age range 4-10 y) and calf muscle spasticity were tested before and during the pharmaceutically active phase after injection of BoNT-A. Measures of passive muscle compliance and viscoelastic responses, hysteresis, and the gradient of the torque-angle curve were computed and compared before and after injection. Although there was a slight, but significant increase in ankle range of motion after BoNT-A injection and a small, significant decrease in the torque required to achieve plantigrade and 5° of dorsiflexion, no significant difference in myotendinous stiffness or hysteresis were detected after BoNT-A injection. Despite any effect on neurally mediated responses, the compliance of the calf muscle was not changed and the muscle continued to offer significant resistance to passive motion of the ankle. These findings suggest that additional treatment approaches are required to supplement the effects of BoNT-A injections when managing children with calf muscle spasticity. © The Authors. Developmental Medicine & Child Neurology © 2011 Mac Keith Press.

  19. Measurement Research of Motorized Spindle Dynamic Stiffness under High Speed Rotating

    Directory of Open Access Journals (Sweden)

    Xiaopeng Wang

    2015-01-01

    Full Text Available High speed motorized spindle has become a key functional unit of high speed machine tools and effectively promotes the development of machine tool technology. The development of higher speed and more power puts forward the stricter requirement for the performance of motorized spindle, especially the dynamic performance which affects the machining accuracy, reliability, and production efficiency. To overcome the problems of ineffective loading and dynamic performance measurement of motorized spindle, a noncontact electromagnetic loading device is developed. The cutting load can be simulated by using electromagnetic force. A new method of measuring force by force sensors is presented, and the steady and transient loading force could be measured exactly. After the high speed machine spindle is tested, the frequency response curves of the spindle relative to machine table are collected at 0~12000 rpm; then the relationships between stiffness and speeds as well as between damping ratio and speeds are obtained. The result shows that not only the static and dynamic stiffness but also the damping ratio declined with the increase of speed.

  20. Effects of ultrasound frequency and tissue stiffness on the histotripsy intrinsic threshold for cavitation.

    Science.gov (United States)

    Vlaisavljevich, Eli; Lin, Kuang-Wei; Maxwell, Adam; Warnez, Matthew T; Mancia, Lauren; Singh, Rahul; Putnam, Andrew J; Fowlkes, Brian; Johnsen, Eric; Cain, Charles; Xu, Zhen

    2015-06-01

    Histotripsy is an ultrasound ablation method that depends on the initiation of a cavitation bubble cloud to fractionate soft tissue. Previous work has indicated that a cavitation cloud can be formed by a single pulse with one high-amplitude negative cycle, when the negative pressure amplitude directly exceeds a pressure threshold intrinsic to the medium. We hypothesize that the intrinsic threshold in water-based tissues is determined by the properties of the water inside the tissue, and changes in tissue stiffness or ultrasound frequency will have a minimal impact on the histotripsy intrinsic threshold. To test this hypothesis, the histotripsy intrinsic threshold was investigated both experimentally and theoretically. The probability of cavitation was measured by subjecting tissue phantoms with adjustable mechanical properties and ex vivo tissues to a histotripsy pulse of 1-2 cycles produced by 345-kHz, 500-kHz, 1.5-MHz and 3-MHz histotripsy transducers. Cavitation was detected and characterized by passive cavitation detection and high-speed photography, from which the probability of cavitation was measured versus pressure amplitude. The results revealed that the intrinsic threshold (the negative pressure at which probability = 0.5) is independent of stiffness for Young's moduli (E) ultrasound frequency in the hundreds of kilohertz to megahertz range. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

  1. The Influence of Outdoor Shoe Sole Stiffness on the Metatarsophalangeal Joint Kinematics When Walking and Running in Different Conditions

    Directory of Open Access Journals (Sweden)

    Paolo Mistretta

    2018-02-01

    Full Text Available Understanding the action of the metatarsophalangeal joint (MTP is fundamental to improving the design process of a new outdoor shoe. Coming from the stated consideration, the aim of this research is to study the influence of shoe sole stiffness and terrain slope on the MTP joint angle of subjects walking in different conditions. To pursue this intent, different data collection sessions have been carried out in-vitro and in-vivo, indoor and outdoor. Two different approaches have been used to collect gait kinematics: an IMU (Inertial Measurement Unit based system for the first campaign of tests, and a 2D video analysis for the second. Major findings showed a linear correlation between shoe sole stiffness and peak MTP joint angle during gait, as well as consistency in the value of the slope of the linear regression curves corresponding to the different conditions examined.

  2. A METHOD OF DETERMINING THE COORDINATES OF THE STIFFNESS CENTER AND THE STIFFNESS PRINCIPAL AXIS OF THE VIBRATING SYSTEM WITH DAMPING

    OpenAIRE

    Dang Xuan Truong; Tran Duc Chinh

    2014-01-01

    The report presents a methodology to determine the directions of the stiffness principal axis (in this case subject to the linear displacement and forced rotation angle) of a solid object interact with the surrounding environment by resilient bearing supports. The results also show that determining the coordinates of the stiffness center in the vibrating system with damping factors is necessary in our research.

  3. Assessment of the impact of degraded shear wall stiffnesses on seismic plant risk and seismic design loads

    International Nuclear Information System (INIS)

    Klamerus, E.W.; Bohn, M.P.; Johnson, J.J.; Asfura, A.P.; Doyle, D.J.

    1994-02-01

    Test results sponsored by the USNRC have shown that reinforced shear wall (Seismic Category I) structures exhibit stiffnesses and natural frequencies which are smaller than those calculated in the design process. The USNRC has sponsored Sandia National Labs to perform an evaluation of the effects of the reduced frequencies on several existing seismic PRAs in order to determine the seismic risk implications inherent in these test results. This report presents the results for the re-evaluation of the seismic risk for three nuclear power plants: the Peach Bottom Atomic Power Station, the Zion Nuclear Power Plant, and Arkansas Nuclear One -- Unit 1 (ANO-1). Increases in core damage frequencies for seismic initiated events at Peach Bottom were 25 to 30 percent (depending on whether LLNL or EPRI hazard curves were used). At the ANO-1 site, the corresponding increases in plant risk were 10 percent (for each set of hazard curves). Finally, at Zion, there was essentially no change in the computed core damage frequency when the reduction in shear wall stiffness was included. In addition, an evaluation of deterministic ''design-like'' structural dynamic calculations with and without the shear stiffness reductions was made. Deterministic loads calculated for these two cases typically increased on the order of 10 to 20 percent for the affected structures

  4. Flexible Sensors for Pressure Therapy: Effect of Substrate Curvature and Stiffness on Sensor Performance.

    Science.gov (United States)

    Khodasevych, Iryna; Parmar, Suresh; Troynikov, Olga

    2017-10-20

    Flexible pressure sensors are increasingly being used in medical and non-medical applications, and particularly in innovative health monitoring. Their efficacy in medical applications such as compression therapy depends on the accuracy and repeatability of their output, which in turn depend on factors such as sensor type, shape, pressure range, and conformability of the sensor to the body surface. Numerous researchers have examined the effects of sensor type and shape, but little information is available on the effect of human body parameters such as support surfaces' curvature and the stiffness of soft tissues on pressure sensing performance. We investigated the effects of body parameters on the performance of pressure sensors using a custom-made human-leg-like test setup. Pressure sensing parameters such as accuracy, drift and repeatability were determined in both static (eight hours continuous pressure) and dynamic (10 cycles of pressure application of 30 s duration) testing conditions. The testing was performed with a focus on compression therapy application for venous leg ulcer treatments, and was conducted in a low-pressure range of 20-70 mmHg. Commercially available sensors manufactured by Peratech and Sensitronics were used under various loading conditions to determine the influence of stiffness and curvature. Flat rigid, flat soft silicone and three cylindrical silicone surfaces of radii of curvature of 3.5 cm, 5.5 cm and 6.5 cm were used as substrates under the sensors. The Peratech sensor averaged 94% accuracy for both static and dynamic measurements on all substrates; the Sensitronics sensor averaged 88% accuracy. The Peratech sensor displayed moderate variations and the Sensitronics sensor large variations in output pressure readings depending on the underlying test surface, both of which were reduced markedly by individual pressure calibration for surface type. Sensor choice and need for calibration to surface type are important considerations for

  5. Substrate stiffness and oxygen as regulators of stem cell differentiation during skeletal tissue regeneration: a mechanobiological model.

    Directory of Open Access Journals (Sweden)

    Darren Paul Burke

    Full Text Available Extrinsic mechanical signals have been implicated as key regulators of mesenchymal stem cell (MSC differentiation. It has been possible to test different hypotheses for mechano-regulated MSC differentiation by attempting to simulate regenerative events such as bone fracture repair, where repeatable spatial and temporal patterns of tissue differentiation occur. More recently, in vitro studies have identified other environmental cues such as substrate stiffness and oxygen tension as key regulators of MSC differentiation; however it remains unclear if and how such cues determine stem cell fate in vivo. As part of this study, a computational model was developed to test the hypothesis that substrate stiffness and oxygen tension regulate stem cell differentiation during fracture healing. Rather than assuming mechanical signals act directly on stem cells to determine their differentiation pathway, it is postulated that they act indirectly to regulate angiogenesis and hence partially determine the local oxygen environment within a regenerating tissue. Chondrogenesis of MSCs was hypothesized to occur in low oxygen regions, while in well vascularised regions of the regenerating tissue a soft local substrate was hypothesised to facilitate adipogenesis while a stiff substrate facilitated osteogenesis. Predictions from the model were compared to both experimental data and to predictions of a well established computational mechanobiological model where tissue differentiation is assumed to be regulated directly by the local mechanical environment. The model predicted all the major events of fracture repair, including cartilaginous bridging, endosteal and periosteal bony bridging and bone remodelling. It therefore provides support for the hypothesis that substrate stiffness and oxygen play a key role in regulating MSC fate during regenerative events such as fracture healing.

  6. Intracortical stiffness of mid-diaphysis femur bovine bone: lacunar-canalicular based homogenization numerical solutions and microhardness measurements.

    Science.gov (United States)

    Hage, Ilige S; Hamade, Ramsey F

    2017-09-01

    Microscale lacunar-canalicular (L-C) porosity is a major contributor to intracortical bone stiffness variability. In this work, such variability is investigated experimentally using micro hardness indentation tests and numerically using a homogenization scheme. Cross sectional rings of cortical bones are cut from the middle tubular part of bovine femur long bone at mid-diaphysis. A series of light microscopy images are taken along a line emanating from the cross-section center starting from the ring's interior (endosteum) ring surface toward the ring's exterior (periosteum) ring surface. For each image in the line, computer vision analysis of porosity is conducted employing an image segmentation methodology based on pulse coupled neural networks (PCNN) recently developed by the authors. Determined are size and shape of each of the lacunar-canalicular (L-C) cortical micro constituents: lacunae, canaliculi, and Haversian canals. Consequently, it was possible to segment and quantify the geometrical attributes of all individual segmented pores leading to accurate determination of derived geometrical measures such as L-C cortical pores' total porosity (pore volume fraction), (elliptical) aspect ratio, orientation, location, and number of pores in secondary and primary osteons. Porosity was found to be unevenly (but linearly) distributed along the interior and exterior regions of the intracortical bone. The segmented L-C porosity data is passed to a numerical microscale-based homogenization scheme, also recently developed by the authors, that analyses a composite made up of lamella matrix punctuated by multi-inclusions and returns corresponding values for longitudinal and transverse Young's modulus (matrix stiffness) for these micro-sized spatial locations. Hence, intracortical stiffness variability is numerically quantified using a combination of computer vision program and numerical homogenization code. These numerically found stiffness values of the homogenization

  7. Shaking table test and verification of development of an ...

    Indian Academy of Sciences (India)

    A full-scale multiple degrees of freedom shaking table is tested toverify the energy dissipation of this proposed AIC, including test building without control, with passive control added involving various stiffness ratios and also with synchronic control added involving various stiffness ratios. Shock absorption of displacement ...

  8. Direct structural parameter identification by modal test results

    Science.gov (United States)

    Chen, J.-C.; Kuo, C.-P.; Garba, J. A.

    1983-01-01

    A direct identification procedure is proposed to obtain the mass and stiffness matrices based on the test measured eigenvalues and eigenvectors. The method is based on the theory of matrix perturbation in which the correct mass and stiffness matrices are expanded in terms of analytical values plus a modification matrix. The simplicity of the procedure enables real time operation during the structural testing.

  9. Liver stiffness measurement by transient elastography predicts late posthepatectomy outcomes in patients undergoing resection for hepatocellular carcinoma.

    Science.gov (United States)

    Rajakannu, Muthukumarassamy; Cherqui, Daniel; Ciacio, Oriana; Golse, Nicolas; Pittau, Gabriella; Allard, Marc Antoine; Antonini, Teresa Maria; Coilly, Audrey; Sa Cunha, Antonio; Castaing, Denis; Samuel, Didier; Guettier, Catherine; Adam, René; Vibert, Eric

    2017-10-01

    .71 (95% confidence interval, 0.646-0.917), respectively. Liver stiffness measurement ≥22 kPa had 42.9% sensitivity and 92.6% specificity and hepatic venous pressure gradient ≥10 mm Hg had 28.6% sensitivity and 96.3% specificity. In selected patients undergoing liver resection for hepatocellular carcinoma, transient elastography is an easy and effective test to predict persistent hepatic decompensation preoperatively. Copyright © 2017 Elsevier Inc. All rights reserved.

  10. Influence of Passive Joint Stiffness on Proprioceptive Acuity in Individuals With Functional Instability of the Ankle.

    Science.gov (United States)

    Marinho, Hellen Veloso Rocha; Amaral, Giovanna Mendes; de Souza Moreira, Bruno; Araújo, Vanessa Lara; Souza, Thales Rezende; Ocarino, Juliana Melo; da Fonseca, Sérgio Teixeira

    2017-12-01

    Study Design Controlled laboratory study, cross-sectional. Background Deficits in ankle proprioceptive acuity have been reported in persons with functional instability of the ankle. Passive stiffness has been proposed as a possible mechanism underlying proprioceptive acuity. Objective To compare proprioceptive acuity and passive ankle stiffness in persons with and without functional ankle instability, and to assess the influence of passive joint stiffness on proprioceptive acuity in persons with functional ankle instability. Methods A sample of 18 subjects with and 18 without complaints of functional ankle instability following lateral ankle sprain participated. An isokinetic dynamometer was used to compare motion perception threshold, passive position sense, and passive ankle stiffness between groups. To evaluate the influence of passive stiffness on proprioceptive acuity, individuals in the lateral functional ankle instability group were divided into 2 subgroups: "high" and "low" passive ankle stiffness. Results The functional ankle instability group exhibited increased motion perception threshold when compared with the corresponding limb of the control group. Between-group differences were not found for passive position sense and passive ankle stiffness. Those in the functional ankle instability group with higher passive ankle stiffness had smaller motion perception thresholds than those with lower passive ankle stiffness. Conclusion Unlike motion perception threshold, passive position sense is not affected by the presence of functional ankle instability. Passive ankle stiffness appears to influence proprioceptive acuity in persons with functional ankle instability. J Orthop Sports Phys Ther 2017;47(12):899-905. Epub 7 Oct 2017. doi:10.2519/jospt.2017.7030.

  11. Tailoring the mechanical properties by molecular integration of flexible and stiff polymer networks.

    Science.gov (United States)

    Wan, Haixiao; Shen, Jianxiang; Gao, Naishen; Liu, Jun; Gao, Yangyang; Zhang, Liqun

    2018-03-28

    Designing a multiple-network structure at the molecular level to tailor the mechanical properties of polymeric materials is of great scientific and technological importance. Through the coarse-grained molecular dynamics simulation, we successfully construct an interpenetrating polymer network (IPN) composed of a flexible polymer network and a stiff polymer network. First, we find that there is an optimal chain stiffness for a single network (SN) to achieve the best stress-strain behavior. Then we turn to study the mechanical behaviors of IPNs. The result shows that the stress-strain behaviors of the IPNs appreciably exceed the sum of that of the corresponding single flexible and stiff network, which highlights the advantage of the IPN structure. By systematically varying the stiffness of the stiff polymer network of the IPNs, optimal stiffness also exists to achieve the best performance. We attribute this to a much larger contribution of the non-bonded interaction energy. Last, the effect of the component concentration ratio is probed. With the increase of the concentration of the flexible network, the stress-strain behavior of the IPNs is gradually enhanced, while an optimized concentration (around 60% molar ration) of the stiff network occurs, which could result from the dominant role of the enthalpy rather than the entropy. In general, our work is expected to provide some guidelines to better tailor the mechanical properties of the IPNs made of a flexible network and a stiff network, by manipulating the stiffness of the stiff polymer network and the component concentration ratio.

  12. Technical Validation of ARTSENS–An Image Free Device for Evaluation of Vascular Stiffness

    Science.gov (United States)

    Radhakrishnan, Ravikumar; Kusmakar, Shitanshu; Thrivikraman, Arya Sree; Sivaprakasam, Mohanasankar

    2015-01-01

    Vascular stiffness is an indicator of cardiovascular health, with carotid artery stiffness having established correlation to coronary heart disease and utility in cardiovascular diagnosis and screening. State of art equipment for stiffness evaluation are expensive, require expertise to operate and not amenable for field deployment. In this context, we developed ARTerial Stiffness Evaluation for Noninvasive Screening (ARTSENS), a device for image free, noninvasive, automated evaluation of vascular stiffness amenable for field use. ARTSENS has a frugal hardware design, utilizing a single ultrasound transducer to interrogate the carotid artery, integrated with robust algorithms that extract arterial dimensions and compute clinically accepted measures of arterial stiffness. The ability of ARTSENS to measure vascular stiffness in vivo was validated by performing measurements on 125 subjects. The accuracy of results was verified with the state-of-the-art ultrasound imaging-based echo-tracking system. The relation between arterial stiffness measurements performed in sitting posture for ARTSENS measurement and sitting/supine postures for imaging system was also investigated to examine feasibility of performing ARTSENS measurements in the sitting posture for field deployment. This paper verified the feasibility of the novel ARTSENS device in performing accurate in vivo measurements of arterial stiffness. As a portable device that performs automated measurement of carotid artery stiffness with minimal operator input, ARTSENS has strong potential for use in large-scale screening. PMID:27170892

  13. Increase in Leg Stiffness Reduces Joint Work During Backpack Carriage Running at Slow Velocities.

    Science.gov (United States)

    Liew, Bernard; Netto, Kevin; Morris, Susan

    2017-10-01

    Optimal tuning of leg stiffness has been associated with better running economy. Running with a load is energetically expensive, which could have a significant impact on athletic performance where backpack carriage is involved. The purpose of this study was to investigate the impact of load magnitude and velocity on leg stiffness. We also explored the relationship between leg stiffness and running joint work. Thirty-one healthy participants ran overground at 3 velocities (3.0, 4.0, 5.0 m·s -1 ), whilst carrying 3 load magnitudes (0%, 10%, 20% weight). Leg stiffness was derived using the direct kinetic-kinematic method. Joint work data was previously reported in a separate study. Linear models were used to establish relationships between leg stiffness and load magnitude, velocity, and joint work. Our results found that leg stiffness did not increase with load magnitude. Increased leg stiffness was associated with reduced total joint work at 3.0 m·s -1 , but not at faster velocities. The association between leg stiffness and joint work at slower velocities could be due to an optimal covariation between skeletal and muscular components of leg stiffness, and limb attack angle. When running at a relatively comfortable velocity, greater leg stiffness may reflect a more energy efficient running pattern.

  14. The relationship between passive stiffness and evoked twitch properties: the influence of muscle CSA normalization

    International Nuclear Information System (INIS)

    Ryan, E D; Thompson, B J; Sobolewski, E J; Herda, T J; Costa, P B; Walter, A A; Cramer, J T

    2011-01-01

    Passive stiffness measurements are often used as a clinical tool to examine a muscle's passive lengthening characteristics. The purpose of this study was to examine the relationship between passive stiffness and evoked twitch properties prior to and following normalization of passive stiffness to muscle cross-sectional area (CSA). Ten healthy volunteers (mean ± SD age = 23 ± 3 year) performed passive range of motion, evoked twitch, and muscle CSA assessments of the plantar flexor muscles. Passive stiffness was determined from the slope of the final 5° of the angle–torque curve. Peak twitch torque (PTT) and rate of torque development (RTD) were determined via transcutaneous electrical stimulation, and muscle CSA was assessed using a peripheral quantitative computed tomography scanner. Pearson product moment correlation coefficients (r) were used to assess the relationships between passive stiffness and PTT and RTD and normalized passive stiffness (passive stiffness . muscle CSA −1 ) and PTT and RTD. Significant positive relationships were observed between passive stiffness and PTT (P = 0.003, r = 0.828) and RTD (P = 0.003, r = 0.825). There were no significant relationships between normalized passive stiffness and PTT (P = 0.290, r = 0.372) or RTD (P = 0.353, r = 0.329) demonstrating that stiffness did not account for a significant portion of the variance in twitch properties. Passive stiffness was largely influenced by the amount of muscle tissue in this study. Future studies that examine muscle stiffness and its relationship with performance measures, among different populations, and following various interventions may consider normalizing stiffness measurements to muscle CSA

  15. Systematic profiling of spatiotemporal tissue and cellular stiffness in the developing brain.

    Science.gov (United States)

    Iwashita, Misato; Kataoka, Noriyuki; Toida, Kazunori; Kosodo, Yoichi

    2014-10-01

    Accumulating evidence implicates the significance of the physical properties of the niche in influencing the behavior, growth and differentiation of stem cells. Among the physical properties, extracellular stiffness has been shown to have direct effects on fate determination in several cell types in vitro. However, little evidence exists concerning whether shifts in stiffness occur in vivo during tissue development. To address this question, we present a systematic strategy to evaluate the shift in stiffness in a developing tissue using the mouse embryonic cerebral cortex as an experimental model. We combined atomic force microscopy measurements of tissue and cellular stiffness with immunostaining of specific markers of neural differentiation to correlate the value of stiffness with the characteristic features of tissues and cells in the developing brain. We found that the stiffness of the ventricular and subventricular zones increases gradually during development. Furthermore, a peak in tissue stiffness appeared in the intermediate zone at E16.5. The stiffness of the cortical plate showed an initial increase but decreased at E18.5, although the cellular stiffness of neurons monotonically increased in association with the maturation of the microtubule cytoskeleton. These results indicate that tissue stiffness cannot be solely determined by the stiffness of the cells that constitute the tissue. Taken together, our method profiles the stiffness of living tissue and cells with defined characteristics and can therefore be utilized to further understand the role of stiffness as a physical factor that determines cell fate during the formation of the cerebral cortex and other tissues. © 2014. Published by The Company of Biologists Ltd.

  16. Mechanical metamaterials at the theoretical limit of isotropic elastic stiffness

    Science.gov (United States)

    Berger, J. B.; Wadley, H. N. G.; McMeeking, R. M.

    2017-02-01

    A wide variety of high-performance applications require materials for which shape control is maintained under substantial stress, and that have minimal density. Bio-inspired hexagonal and square honeycomb structures and lattice materials based on repeating unit cells composed of webs or trusses, when made from materials of high elastic stiffness and low density, represent some of the lightest, stiffest and strongest materials available today. Recent advances in 3D printing and automated assembly have enabled such complicated material geometries to be fabricated at low (and declining) cost. These mechanical metamaterials have properties that are a function of their mesoscale geometry as well as their constituents, leading to combinations of properties that are unobtainable in solid materials; however, a material geometry that achieves the theoretical upper bounds for isotropic elasticity and strain energy storage (the Hashin-Shtrikman upper bounds) has yet to be identified. Here we evaluate the manner in which strain energy distributes under load in a representative selection of material geometries, to identify the morphological features associated with high elastic performance. Using finite-element models, supported by analytical methods, and a heuristic optimization scheme, we identify a material geometry that achieves the Hashin-Shtrikman upper bounds on isotropic elastic stiffness. Previous work has focused on truss networks and anisotropic honeycombs, neither of which can achieve this theoretical limit. We find that stiff but well distributed networks of plates are required to transfer loads efficiently between neighbouring members. The resulting low-density mechanical metamaterials have many advantageous properties: their mesoscale geometry can facilitate large crushing strains with high energy absorption, optical bandgaps and mechanically tunable acoustic bandgaps, high thermal insulation, buoyancy, and fluid storage and transport. Our relatively simple

  17. Effects of safflower seed extract on arterial stiffness

    Directory of Open Access Journals (Sweden)

    Katsuya Suzuki

    2010-11-01

    Full Text Available Katsuya Suzuki1, Shigekazu Tsubaki2, Masami Fujita3, Naoto Koyama1, Michio Takahashi1, Kenji Takazawa41Research Institute for Health Fundamentals, Ajinomoto Co., Inc., Kawasaki; 2Samoncho Clinic, Tokyo; 3Shinanozaka Clinic, Tokyo; 4Tokyo Medical University Hachioji Medical Center, Tokyo, JapanAbstract: Safflower seed extract (SSE contains characteristic polyphenols and serotonin derivatives (N-(p-coumaroyl serotonin and N-feruloylserotonin, which are reported to inhibit oxidation of low-density lipoprotein (LDL, formation of atherosclerotic plaques, and improve arterial stiffness as assessed by pulse wave analysis in animal models. The effects of long-term supplementation with SSE on arterial stiffness in human subjects were evaluated. This double-blind, placebo-controlled study was conducted in 77 males (35–65 years and 15 postmenopausal females (55–65 years with high-normal blood pressure or mild hypertension who were not undergoing treatment. Subjects received SSE (70 mg/day as serotonin derivatives or placebo for 12 weeks, and pulse wave measurements, ie, second derivative of photoplethysmogram (SDPTG, augmentation index, and brachial-ankle pulse wave velocity (baPWV were conducted at baseline, and at weeks 4, 8, and 12. Vascular age estimated by SDPTG aging index improved in the SSE-supplemented group when compared with the placebo group at four (P = 0.0368 and 12 weeks (P = 0.0927. The trend of augmentation index reduction (P = 0.072 versus baseline was observed in the SSE-supplemented group, but reduction of baPWV by SSE supplementation was not observed. The SSE-supplemented group also showed a trend towards a lower malondialdehyde-modified-LDL autoantibody titer at 12 weeks from baseline. These results suggest long-term ingestion of SSE in humans could help to improve arterial stiffness.Keywords: safflower, serotonin derivatives, antioxidants, augmentation index, pulse wave velocity

  18. Metacarpophalangeal joint stiffness. Still a challenge for the hand surgeon?

    Science.gov (United States)

    Jiménez, I; Muratore-Moreno, G; Marcos-García, A; Medina, J

    2016-01-01

    The aim of this study is to analyse the outcomes of the surgical treatment of metacarpophalangeal stiffness by dorsal teno-arthrolysis in our centre, and present a review the literature. This is a retrospective study of 21 cases of metacarpophalangeal stiffness treated surgically. Dorsal teno-arthrolysis was carried out on all patients. A rehabilitation programme was started ten days after surgery. An evaluation was performed on the aetiology, variation in pre- and post-operative active mobility, complications, DASH questionnaire, and a subjective satisfaction questionnaire. The mean age of the patients was 36.5 years and the mean follow-up was 6.5 years. Of the 21 cases, the most common cause was a metacarpal fracture (52.4%), followed by complex trauma of the forearm (19%). Improvement in active mobility was 30.5°, despite obtaining an intra-operative mobility 0-90° in 80% of cases. Mean DASH questionnaire score was 36.9 points. The outcome was described as excellent in 10% of our patients, good in 30%, poor in 40%, and bad in the remaining 20%. There was a complex regional pain syndrome in 9.5% of cases, and intrinsic muscle injury in 14.3%. Because of its difficult management and poor outcomes, surgical treatment of metacarpophalangeal stiffness in extension is highly complex, with dorsal teno-arthrolysis being a reproducible technique according to our results, and the results reported in the literature. Copyright © 2016 SECOT. Published by Elsevier Espana. All rights reserved.

  19. An Explicit Consistent Geometric Stiffness Matrix for the DKT Element

    Directory of Open Access Journals (Sweden)

    Eliseu Lucena Neto

    Full Text Available Abstract A large number of references dealing with the geometric stiffness matrix of the DKT finite element exist in the literature, where nearly all of them adopt an inconsistent form. While such a matrix may be part of the element to treat nonlinear problems in general, it is of crucial importance for linearized buckling analysis. The present work seems to be the first to obtain an explicit expression for this matrix in a consistent way. Numerical results on linear buckling of plates assess the element performance either with the proposed explicit consistent matrix, or with the most commonly used inconsistent matrix.

  20. A uniform quantitative stiff stability estimate for BDF schemes

    Directory of Open Access Journals (Sweden)

    Winfried Auzinger

    2006-01-01

    Full Text Available The concepts of stability regions, \\(A\\- and \\(A(\\alpha\\-stability - albeit based on scalar models - turned out to be essential for the identification of implicit methods suitable for the integration of stiff ODEs. However, for multistep methods, knowledge of the stability region provides no information on the quantitative stability behavior of the scheme. In this paper we fill this gap for the important class of Backward Differentiation Formulas (BDF. Quantitative stability bounds are derived which are uniformly valid in the stability region of the method. Our analysis is based on a study of the separation of the characteristic roots and a special similarity decomposition of the associated companion matrix.

  1. Analytical stiffness matrices with Green-Lagrange strain measure

    DEFF Research Database (Denmark)

    Pedersen, Pauli

    2005-01-01

    Separating the dependence on material and stress/strain state from the dependence on initial geometry, we obtain analytical secant and tangent stiffness matrices. For the case of a linear displacement triangle with uniform thickness and uniform constitutive behaviour closed-form results are listed...... a solution based on Green-Lagrange strain measure. The approach is especially useful in design optimization, because analytical sensitivity analysis then can be performed. The case of a three node triangular ring element for axisymmetric analysis involves small modifications and extension to four node...

  2. Evaluation of ground stiffness parameters using continuous surface wave geophysics

    DEFF Research Database (Denmark)

    Gordon, Anne; Foged, Niels

    2000-01-01

    Present day knowledge of the magnitude of the strain levels in the ground associated with geotechnical structures, together with an increasing number of projects requiring the best estimates of ground movements around excavations, has led to, inter alia, increased interest in measuring the very......-small-strain stiffness of the ground Gmax. Continuous surface wave geophysics offers a quick, non-intrusive and economical way of making such measurements. This paper reviews the continuous surface wave techniques and evaluates, in engineering terms, the applicability of the method to the site investigation industry....

  3. Estimative of relative stiffness of the exudate gum polysaccharides

    International Nuclear Information System (INIS)

    Oliveira, Marilia A.; Paula, Regina C.M.

    2001-01-01

    The Smidsrod empirical stiffness parameter (B) of A. occidentale and A. lebbeck gum were determined using the correlation of intrinsic viscosity [η] with ionic strength. The B value of 0.204 and 0.193 found respectively for A. occidentale and A. lebbeck suggests a flexible the molecule. The ionic strength has a greater influence on the [η]. The decrease of [η] increase of I, from 0.01 M to 0.1 M of NaCl, is higher for A. lebbeck (89%) than for A. occidentale (19%). (author)

  4. General procedure for the determination of foundation stiffness

    International Nuclear Information System (INIS)

    Halbritter, A.L.; Prates, C.L.M.

    1984-01-01

    A general procedure for the determination of the spring constants and damping coeficientes which represent the foundation-structure interaction is presented. According to this procedure it is possible to determine the variation of the stiffness and damping with the frequency for flexible foundation slabs by employing the equivalent rigid slab concept. It is also possible to determine the distribution of the springs along the foundation. The results obtained for the reactor building of a NPP of 1300 MW PWR of KWU type taking into account the flexibility of the foundation slab is presented as an application example of this procedure. (Author) [pt

  5. Development and assessment of a practical stiffness reduction method for the in-plane design of steel frames

    OpenAIRE

    Kucukler, M; Gardner, L; Macorini, L

    2016-01-01

    In this paper, the development and assessment of a stiffness reduction method for the in-plane design of steel frames is presented. The adopted stiffness reduction approach is implemented by reducing the flexural stiffnesses (EI) of the members of a steel frame by considering the first-order forces they are subjected to through the stiffness reduction functions and performing Geometrically Nonlinear Analysis (i.e. second-order elastic analysis). Since the presented approach uses stiffness red...

  6. Vibration Isolation System Using Negative Stiffness(Advances in Motion and Vibration Control Technology)

    OpenAIRE

    水野, 毅; 高崎, 正也

    2003-01-01

    A new vibration isolation system using negative stiffness realized by active control technique is proposed in this paper. The serial connection of a normal spring and a suspension system with negative stiffness enables the isolation system to have low stiffness for vibration from the ground and high (theoretically infinite) stiffness against direct disturbance acting on the isolation table. A control method of realizing negative stiffness with a linear actuator is presented in an analytical f...

  7. Influence of TVT properties on outcomes of midurethral sling procedures: high-stiffness versus low-stiffness tape.

    Science.gov (United States)

    Prien-Larsen, Jens Christian; Prien-Larsen, Thomas; Cieslak, Lars; Dessau, Ram B

    2016-07-01

    Although there is clear consensus on the use of monofilament polypropylene tapes for treating stress urinary incontinence (SUI), tapes differ in weight, stiffness, and elasticity. In this study, we compared outcomes of two tape types: high-stiffness Intramesh SOFT L.I.F.T versus low-stiffness Intramesh L.I.F.T. tape. Our null hypothesis was that in terms of performance, SOFT tape equaled L.I.F.T. tape. Six hundred and sixty women underwent prospective transvaginal tape (TVT) surgery for SUI: 210 had the SOFT tape placed and 450 the L.I.F.T. tape. Follow-ups were scheduled at 3 and 12 months. Objective cure at 3-months' follow-up was 87 % in the SOFT group vs 94 % in the L.I.F.T. group (p = 0.003) and at 12 months 86 vs 96 % (p = 0.0004), respectively. Subjective outcomes were equal. For SOFT tape, the objective failure rate at 3 months was especially pronounced in women older than 70 years: 31 vs 10 % (p = 0.008), and subjective failure was 24 vs 7 % (p = 0.01). At 12 months, objective failure for the SOFT tape was significantly higher in both age groups compared with L.I.F.T. [odds ratio (OR) 2.17]. Multivariate analysis showed that body mass index (BMI) ≥30 (OR 2.41), mixed incontinence (MUI) (OR 2.24), use of SOFT tape (OR 2.17), and age ≥ 70 years are significant independent risk factors for surgical failure. Outcomes with SOFT tape are significantly inferior than with L.I.F.T. tape, especially among elderly women. Therefore, the two variants of monofilament polypropylene tape are not interchangeable.

  8. Intrinsic ankle stiffness during standing increases with ankle torque and passive stretch of the Achilles tendon

    Science.gov (United States)

    Gill, Jaspret

    2018-01-01

    Individuals may stand with a range of ankle angles. Furthermore, shoes or floor surfaces may elevate or depress their heels. Here we ask how these situations impact ankle stiffness and balance. We performed two studies (each with 10 participants) in which the triceps surae, Achilles tendon and aponeurosis were stretched either passively, by rotating the support surface, or actively by leaning forward. Participants stood freely on footplates which could rotate around the ankle joint axis. Brief, small stiffness-measuring perturbations (torque or passive stretch. Sway was minimally affected by stretch or lean, suggesting that this did not underlie the alterations in stiffness. In quiet stance, maximum ankle stiffness is limited by the tendon. As tendon strain increases, it becomes stiffer, causing an increase in overall ankle stiffness, which would explain the effects of leaning. However, stiffness also increased considerably with passive stretch, despite a modest torque increase. We discuss possible explanations for this increase. PMID:29558469

  9. Differential rigor development in red and white muscle revealed by simultaneous measurement of tension and stiffness.

    Science.gov (United States)

    Kobayashi, Masahiko; Takemori, Shigeru; Yamaguchi, Maki

    2004-02-10

    Based on the molecular mechanism of rigor mortis, we have proposed that stiffness (elastic modulus evaluated with tension response against minute length perturbations) can be a suitable index of post-mortem rigidity in skeletal muscle. To trace the developmental process of rigor mortis, we measured stiffness and tension in both red and white rat skeletal muscle kept in liquid paraffin at 37 and 25 degrees C. White muscle (in which type IIB fibres predominate) developed stiffness and tension significantly more slowly than red muscle, except for soleus red muscle at 25 degrees C, which showed disproportionately slow rigor development. In each of the examined muscles, stiffness and tension developed more slowly at 25 degrees C than at 37 degrees C. In each specimen, tension always reached its maximum level earlier than stiffness, and then decreased more rapidly and markedly than stiffness. These phenomena may account for the sequential progress of rigor mortis in human cadavers.

  10. Measurement of stiffness of standing trees and felled logs using acoustics: A review.

    Science.gov (United States)

    Legg, Mathew; Bradley, Stuart

    2016-02-01

    This paper provides a review on the use of acoustics to measure stiffness of standing trees, stems, and logs. An outline is given of the properties of wood and how these are related to stiffness and acoustic velocity throughout the tree. Factors are described that influence the speed of sound in wood, including the different types of acoustic waves which propagate in tree stems and lumber. Acoustic tools and techniques that have been used to measure the stiffness of wood are reviewed. The reasons for a systematic difference between direct and acoustic measurements of stiffness for standing trees, and methods for correction, are discussed. Other techniques, which have been used in addition to acoustics to try to improve stiffness measurements, are also briefly described. Also reviewed are studies which have used acoustic tools to investigate factors that influence the stiffness of trees. These factors include different silvicultural practices, geographic and environmental conditions, and genetics.

  11. MODELING OF EQUIVALENT STIFFNESS OF A MAGNETIC SPRING OF VIBRATION EXCITER BASED ON COAXIAL-LINEAR MOTOR

    Directory of Open Access Journals (Sweden)

    G.M. Golenkov

    2015-12-01

    Full Text Available Purpose. The research of the influence of value and direction of current on the equivalent spring magnetic force based on coaxial-linear motor (CLM – MS. Methodology. We carried out investigation of the equivalent harshness of magnetic spring with determination of electromechanical propulsion performance characteristics by the methods of computer modeling and experimental research of physical model of CLM – MS. The modeling of magnetic spring of CLM – MS is carried out by the finite-element method. The challenge is met as an axisymmetric challenge in cylindrical co-ordinates in magnetostatic approach. The experimental investigattion of the propulsion performance characteristics of magnetic spring is carried out on the test bench. Results. After the computer modeling and the experimental investigation of the electromechanical propulsion performance characteristics of magnetic spring the expressions of equivalent stiffness coefficient depending on the current in winding are obtained. The results of computer modeling are confirmed experimentally. Originality. The determination of equivalent stiffness coefficient of magnetic spring of vibration exciter based on coaxial-linear motor. Practical value. The obtained determination of equivalent stiffness coefficient of magnetic spring may be used in process of designing of vibration machines with devices for change of natural oscillation frequency.

  12. Measurement model and calibration experiment of over-constrained parallel six-dimensional force sensor based on stiffness characteristics analysis

    International Nuclear Information System (INIS)

    Niu, Zhi; Zhao, Yanzhi; Zhao, Tieshi; Cao, Yachao; Liu, Menghua

    2017-01-01

    An over-constrained, parallel six-dimensional force sensor has various advantages, including its ability to bear heavy loads and provide redundant force measurement information. These advantages render the sensor valuable in important applications in the field of aerospace (space docking tests, etc). The stiffness of each component in the over-constrained structure has a considerable influence on the internal force distribution of the structure. Thus, the measurement model changes when the measurement branches of the sensor are under tensile or compressive force. This study establishes a general measurement model for an over-constrained parallel six-dimensional force sensor considering the different branch tensions and compression stiffness values. Numerical calculations and analyses are performed using practical examples. Based on the parallel mechanism, an over-constrained, orthogonal structure is proposed for a six-dimensional force sensor. Hence, a prototype is designed and developed, and a calibration experiment is conducted. The measurement accuracy of the sensor is improved based on the measurement model under different branch tensions and compression stiffness values. Moreover, the largest class I error is reduced from 5.81 to 2.23% full scale (FS), and the largest class II error is reduced from 3.425 to 1.871% FS. (paper)

  13. Remote Determination of Time-Dependent Stiffness of Surface-Degrading-Polymer Scaffolds Via Synchrotron-Based Imaging.

    Science.gov (United States)

    Bawolin, N K; Chen, X B

    2017-04-01

    Surface-degrading polymers have been widely used to fabricate scaffolds with the mechanical properties appropriate for tissue regeneration/repair. During their surface degradation, the material properties of polymers remain approximately unchanged, but the scaffold geometry and thus mechanical properties vary with time. This paper presents a novel method to determine the time-dependent mechanical properties, particularly stiffness, of scaffolds from the geometric changes captured by synchrotron-based imaging, with the help of finite element analysis (FEA). Three-dimensional (3D) tissue scaffolds were fabricated from surface-degrading polymers, and during their degradation, the tissue scaffolds were imaged via the synchrotron-based imaging to characterize their changing geometry. On this basis, the stiffness behavior of scaffolds was estimated from the FEA, and the results obtained were compared to the direct measurements of scaffold stiffness from the load-displacement material testing. The comparison illustrates that the Young's moduli estimated from the FEA and characterized geometry are in agreement with the ones of direct measurements. The developed method of estimating the mechanical behavior was also demonstrated effective with a nondegrading scaffold that displays the nonlinear stress-strain behavior. The in vivo monitoring of Young's modulus by morphology characterization also suggests the feasibility of characterizing experimentally the difference between in vivo and in vitro surface degradation of tissue engineering constructs.

  14. Integrator Performance Analysis In Solving Stiff Differential Equation System

    International Nuclear Information System (INIS)

    B, Alhadi; Basaruddin, T.

    2001-01-01

    In this paper we discuss the four-stage index-2 singly diagonally implicit Runge-Kutta method, which is used to solve stiff ordinary differential equations (SODE). Stiff problems require a method where step size is not restricted by the method's stability. We desire SDIRK to be A-stable that has no stability restrictions when solving y'= λy with Reλ>0 and h>0, so by choosing suitable stability function we can determine appropriate constant g) to formulate SDIRK integrator to solve SODE. We select the second stage of the internal stage as embedded method to perform low order estimate for error predictor. The strategy for choosing the step size is adopted from the strategy proposed by Hall(1996:6). And the algorithm that is developed in this paper is implemented using MATLAB 5.3, which is running on Window's 95 environment. Our performance measurement's local truncation error accuracy, and efficiency were evaluated by statistical results of sum of steps, sum of calling functions, average of Newton iterations and elapsed times.As the results, our numerical experiment show that SDIRK is unconditionally stable. By using Hall's step size strategy, the method can be implemented efficiently, provided that suitable parameters are used

  15. Dynamic stiffness of suction caissons - torsion, sliding and rocking

    Energy Technology Data Exchange (ETDEWEB)

    Ibsen, Lars Bo; Liingaard, M.; Andersen, Lars

    2006-12-15

    This report concerns the dynamic soil-structure interaction of steel suction caissons applied as foundations for offshore wind turbines. An emphasis is put on torsional vibrations and coupled sliding/rocking motion, and the influence of the foundation geometry and the properties of the surrounding soil is examined. The soil is simplified as a homogenous linear viscoelastic material and the dynamic stiffness of the suction caisson is expressed in terms of dimensionless frequency-dependent coefficients corresponding to the different degrees of freedom. The dynamic stiffness coefficients for the skirted foundation are evaluated by means of a three-dimensional coupled boundary element/finite element model. Comparisons with known analytical and numerical solutions indicate that the static and dynamic behaviour of the foundation are predicted accurately with the applied model. The analysis has been carried out for different combinations of the skirt length and the Poisson's ratio of the subsoil. Finally, the high-frequency impedance has been determined for future use in lumped-parameter models of wind turbine foundations in aero-elastic codes. (au)

  16. Arterial stiffness &Sri Lankan chronic kidney disease of unknown origin.

    Science.gov (United States)

    Gifford, Fiona; Kimmitt, Robert; Herath, Chula; Webb, David J; Melville, Vanessa; Siribaddana, Sisira; Eddleston, Michael; Dhaun, Neeraj

    2016-09-02

    Chronic kidney disease (CKD) is common and independently associated with cardiovascular disease (CVD). Arterial stiffness contributes to CVD risk in CKD. In many developing countries a considerable proportion of CKD remains unexplained, termed CKDu. We assessed arterial stiffness in subjects with Sri Lankan CKDu, in matched controls without CKD and in those with defined CKD. Aortic blood pressure (BP), pulse wave velocity (PWV) and augmentation index (AIx) were assessed in 130 subjects (50 with CKDu, 45 with CKD and 35 without CKD) using the validated TensioMed™ Arteriograph monitor. Brachial and aortic BP was lower in controls than in CKDu and CKD subjects but no different between CKDu and CKD. Controls had a lower PWV compared to subjects with CKDu and CKD. Despite equivalent BP and renal dysfunction, CKDu subjects had a lower PWV than those with CKD (8.7 ± 1.5 vs. 9.9 ± 2.2 m/s, p CKDu vs. CKD: 6.7 ± 0.9 vs. 8.7 ± 1.5 vs. 10.4 ± 1.5 m/s, p CKDu is associated with less arterial stiffening than defined causes of CKD. Whether this translates to lower cardiovascular morbidity and mortality long term is unclear and should be the focus of future studies.

  17. Damage severity estimation from the global stiffness decrease

    International Nuclear Information System (INIS)

    Nitescu, C; Gillich, G R; Manescu, T; Korka, Z I; Abdel Wahab, M

    2017-01-01

    In actual damage detection methods, localization and severity estimation can be treated separately. The severity is commonly estimated using fracture mechanics approach, with the main disadvantage of involving empirically deduced relations. In this paper, a damage severity estimator based on the global stiffness reduction is proposed. This feature is computed from the deflections of the intact and damaged beam, respectively. The damage is always located where the bending moment achieves maxima. If the damage is positioned elsewhere on the beam, its effect becomes lower, because the stress is produced by a diminished bending moment. It is shown that the global stiffness reduction produced by a crack is the same for all beams with a similar cross-section, regardless of the boundary conditions. One mathematical relation indicating the severity and another indicating the effect of removing damage from the beam. Measurements on damaged beams with different boundary conditions and cross-sections are carried out, and the location and severity are found using the proposed relations. These comparisons prove that the proposed approach can be used to accurately compute the severity estimator. (paper)

  18. Ambulatory arterial stiffness indices and target organ damage in hypertension

    Directory of Open Access Journals (Sweden)

    Gómez-Marcos Manuel

    2012-01-01

    Full Text Available Abstract Background The present study was designed to evaluate which arterial stiffness parameter - AASI or the home arterial stiffness index (HASI - correlates best with vascular, cardiac and renal damage in hypertensive individuals. Methods A cross-sectional study was carried out involving 258 hypertensive patients. AASI and HASI were defined as the 1-regression slope of diastolic over systolic blood pressure readings obtained from 24-hour recordings and home blood pressure over 6 days. Renal damage was evaluated by glomerular filtration rate (GFR and microalbuminuria; vascular damage by carotid intima-media thickness (IMT, pulse wave velocity (PWV and ankle/brachial index (ABI; and left ventricular hypertrophy by the Cornell voltage-duration product (VDP and the Novacode index. Results AASI and HASI were not correlated with microalbuminuria, however AASI and HASI- blood pressure variability ratio (BPVR showed negative correlation with GRF. The Cornell PDV was positively correlated with AASI- BPVR-Sleep (r = 0.15, p Conclusions After adjusting for age, gender and 24-hour heart, the variables that best associated with the variability of IMT, PWV and ABI were AASI and Awake-AASI, and with GFR was HASI-BPVR.

  19. Explicit integration of extremely stiff reaction networks: partial equilibrium methods

    International Nuclear Information System (INIS)

    Guidry, M W; Hix, W R; Billings, J J

    2013-01-01

    In two preceding papers (Guidry et al 2013 Comput. Sci. Disc. 6 015001 and Guidry and Harris 2013 Comput. Sci. Disc. 6 015002), we have shown that when reaction networks are well removed from equilibrium, explicit asymptotic and quasi-steady-state approximations can give algebraically stabilized integration schemes that rival standard implicit methods in accuracy and speed for extremely stiff systems. However, we also showed that these explicit methods remain accurate but are no longer competitive in speed as the network approaches equilibrium. In this paper, we analyze this failure and show that it is associated with the presence of fast equilibration timescales that neither asymptotic nor quasi-steady-state approximations are able to remove efficiently from the numerical integration. Based on this understanding, we develop a partial equilibrium method to deal effectively with the approach to equilibrium and show that explicit asymptotic methods, combined with the new partial equilibrium methods, give an integration scheme that can plausibly deal with the stiffest networks, even in the approach to equilibrium, with accuracy and speed competitive with that of implicit methods. Thus we demonstrate that such explicit methods may offer alternatives to implicit integration of even extremely stiff systems and that these methods may permit integration of much larger networks than have been possible before in a number of fields. (paper)

  20. Disorder-induced stiffness degradation of highly disordered porous materials

    Science.gov (United States)

    Laubie, Hadrien; Monfared, Siavash; Radjaï, Farhang; Pellenq, Roland; Ulm, Franz-Josef

    2017-09-01

    The effective mechanical behavior of multiphase solid materials is generally modeled by means of homogenization techniques that account for phase volume fractions and elastic moduli without considering the spatial distribution of the different phases. By means of extensive numerical simulations of randomly generated porous materials using the lattice element method, the role of local textural properties on the effective elastic properties of disordered porous materials is investigated and compared with different continuum micromechanics-based models. It is found that the pronounced disorder-induced stiffness degradation originates from stress concentrations around pore clusters in highly disordered porous materials. We identify a single disorder parameter, φsa, which combines a measure of the spatial disorder of pores (the clustering index, sa) with the pore volume fraction (the porosity, φ) to scale the disorder-induced stiffness degradation. Thus, we conclude that the classical continuum micromechanics models with one spherical pore phase, due to their underlying homogeneity assumption fall short of addressing the clustering effect, unless additional texture information is introduced, e.g. in form of the shift of the percolation threshold with disorder, or other functional relations between volume fractions and spatial disorder; as illustrated herein for a differential scheme model representative of a two-phase (solid-pore) composite model material.

  1. Ultra-stiff metallic glasses through bond energy density design.

    Science.gov (United States)

    Schnabel, Volker; Köhler, Mathias; Music, Denis; Bednarcik, Jozef; Clegg, William J; Raabe, Dierk; Schneider, Jochen M

    2017-07-05

    The elastic properties of crystalline metals scale with their valence electron density. Similar observations have been made for metallic glasses. However, for metallic glasses where covalent bonding predominates, such as metalloid metallic glasses, this relationship appears to break down. At present, the reasons for this are not understood. Using high energy x-ray diffraction analysis of melt spun and thin film metallic glasses combined with density functional theory based molecular dynamics simulations, we show that the physical origin of the ultrahigh stiffness in both metalloid and non-metalloid metallic glasses is best understood in terms of the bond energy density. Using the bond energy density as novel materials design criterion for ultra-stiff metallic glasses, we are able to predict a Co 33.0 Ta 3.5 B 63.5 short range ordered material by density functional theory based molecular dynamics simulations with a high bond energy density of 0.94 eV Å -3 and a bulk modulus of 263 GPa, which is 17% greater than the stiffest Co-B based metallic glasses reported in literature.

  2. Blood pressure and arterial stiffness in obese children and adolescents.

    Science.gov (United States)

    Hvidt, Kristian Nebelin

    2015-03-01

    Obesity, elevated blood pressure (BP) and arterial stiffness are risk factors for cardiovascular disease. A strong relationship exists between obesity and elevated BP in both children and adults. Obesity and elevated BP in childhood track into adult life increasing the risk of cardiovascular disease in adulthood. Ambulatory BP is the most precise measure to evaluate the BP burden, whereas carotid-femoral pulse wave velocity (cfPWV) is regarded as the gold standard for evaluating arterial (i.e. aortic) stiffness. These measures might contribute to a better understanding of obesity's adverse impact on the cardiovascular system, and ultimately a better prevention and treatment of childhood obesity. The overall aim of the present PhD thesis is to investigate arterial stiffness and 24-hour BP in obese children and adolescents, and evaluate whether these measures are influenced by weight reduction. The present PhD thesis is based on four scientific papers.  In a cross-sectional design, 104 severe obese children and adolescents with an age of 10-18 years were recruited when newly referred to the Children's Obesity Clinic, Holbæk University Hospital, and compared to 50 normal weighted age and gender matched control individuals. Ambulatory BP was measured, and cfPWV was investigated in two ways in respect to the distance measure of aorta; the previously recommended length - the so called subtracted distance, and the currently recommended length - the direct distance. In a longitudinal design, the obese patients were re-investigated after one-year of lifestyle intervention at the Children's Obesity Clinic in purpose of reducing the degree of obesity. In the cross-sectional design, the obese group had higher measures of obesity, while matched for age, gender and height, when compared to the control group. In the longitudinal design, 74% of the 72 followed up obese patients experienced a significant weight reduction. CfPWV was dependent on the method used to measure the

  3. Training Stiffness perception: Knowledge of results and modality effects

    Directory of Open Access Journals (Sweden)

    Korman Maria

    2011-12-01

    Full Text Available Perception of compliant objects demands integration of haptic and visual position information with force information. Multisensory interactions are ubiquitous in perception, even at early processing stages, and thus can potentially play a role in learning. In this study we explored humans' improvement on uni-sensory stiffness discrimination as a function of different sensory conditions and immediate knowledge of results (KR during training. Two by two design was used: subjects were trained over two days on stiffness discrimination task with either matched visual-tactile, or tactile only stimuli and either with or without immediate feedback on their performance during training trials. Training resulted in both immediate but also latent, overnight learning in the proportion of correctly discriminated pairs of targets (PC, in all groups. Discrimination decision time (DT gains were obtained only during practice, while between sessions partial deterioration was evident. Affordance of visual information during training blocks resulted in higher PC during training blocks, but lower PC in the haptic-only retests. This finding challenges the notion that long-term unisensory learning mechanisms operate optimally under multisensory training conditions, at least for the combination of the visual and haptic modalities. We didn’t find evidence that information feedback during training enhances discrimination ability in terms of PC. However, we found transient within-session effects of KR and visual-haptic trainings on DT: while visualhaptic training resulted in slower responses, KR training induced faster responses.

  4. Endothelial Estrogen Receptor-α Does Not Protect Against Vascular Stiffness Induced by Western Diet in Female Mice.

    Science.gov (United States)

    Manrique, Camila; Lastra, Guido; Ramirez-Perez, Francisco I; Haertling, Dominic; DeMarco, Vincent G; Aroor, Annayya R; Jia, Guanghong; Chen, Dongqing; Barron, Brady J; Garro, Mona; Padilla, Jaume; Martinez-Lemus, Luis A; Sowers, James R

    2016-04-01

    Consumption of a diet high in fat and refined carbohydrates (Western diet [WD]) is associated with obesity and insulin resistance, both major risk factors for cardiovascular disease (CVD). In women, obesity and insulin resistance abrogate the protection against CVD likely afforded by estrogen signaling through estrogen receptor (ER)α. Indeed, WD in females results in increased vascular stiffness, which is independently associated with CVD. We tested the hypothesis that loss of ERα signaling in the endothelium exacerbates WD-induced vascular stiffening in female mice. We used a novel model of endothelial cell (EC)-specific ERα knockout (EC-ERαKO), obtained after sequential crossing of the ERα double floxed mice and VE-Cadherin Cre-recombinase mice. Ten-week-old females, EC-ERαKO and aged-matched genopairs were fed either a regular chow diet (control diet) or WD for 8 weeks. Vascular stiffness was measured in vivo by pulse wave velocity and ex vivo in aortic explants by atomic force microscopy. In addition, vascular reactivity was assessed in isolated aortic rings. Initial characterization of the model fed a control diet did not reveal changes in whole-body insulin sensitivity, aortic vasoreactivity, or vascular stiffness in the EC-ERαKO mice. Interestingly, ablation of ERα in ECs reduced WD-induced vascular stiffness and improved endothelial-dependent dilation. In the setting of a WD, endothelial ERα signaling contributes to vascular stiffening in females. The precise mechanisms underlying the detrimental effects of endothelial ERα in the setting of a WD remain to be elucidated.

  5. [Comparison of the M and XL FibroScan(®) probes to estimate liver stiffness by transient elastography].

    Science.gov (United States)

    Herrero, José Ignacio; Iñarrairaegui, Mercedes; D'Avola, Delia; Sangro, Bruno; Prieto, Jesús; Quiroga, Jorge

    2014-04-01

    The FibroScan(®) XL probe has been specifically designed for obese patients to measure liver stiffness by transient elastography, but it has not been well tested in non-obese patients. The aim of this study was to compare the M and XL FibroScan(®) probes in a series of unselected obese (body mass index above 30 kg/m(2)) and non-obese patients with chronic liver disease. Two hundred and fifty-four patients underwent a transient elastography examination with both the M and XL probes. The results obtained with the two probes were compared in the whole series and in obese (n=82) and non-obese (n=167) patients separately. The reliability of the examinations was assessed using the criteria defined by Castéra et al. The proportion of reliable exams was significantly higher when the XL probe was used (83% versus 73%; P=.001). This significance was maintained in the group of obese patients (82% versus 55%; P<.001), but not in the non-obese patients (84% versus 83%). Despite a high correlation between the stiffness values obtained with the two probes (R=.897; P<.001), and a high concordance in the estimation of fibrosis obtained with the two probes (Cronbach's alpha value: 0.932), the liver stiffness values obtained with the XL probe were significantly lower than those obtained with the M probe, both in the whole series (9.5 ± 9.1 kPa versus 11.3 ± 12.6 kPa; P<0.001) and in the obese and non-obese groups. In conclusion, transient elastography with the XL probe allows a higher proportion of reliable examinations in obese patients but not in non-obese patients. Stiffness values were lower with the XL probe than with the M probe. Copyright © 2013 Elsevier España, S.L. and AEEH y AEG. All rights reserved.

  6. Fin Ray Stiffness and Fin Morphology Control Ribbon-Fin-Based Propulsion.

    Science.gov (United States)

    Liu, Hanlin; Taylor, Bevan; Curet, Oscar M

    2017-06-01

    Ribbon-fin-based propulsion has rich locomotor capabilities that can enhance the mobility and performance of underwater vehicles navigating in complex environments. Bony fishes using this type of propulsion send one or multiple traveling waves along an elongated fin with the actuation of highly flexible rays that are interconnected by an elastic membrane. In this work, we study how the use of flexible rays and different morphology can affect the performance of ribbon-fin propulsion. We developed a physical model composed of 15 rays that are interconnected with an elastic membrane. We tested four different ray flexural stiffness and four aspect ratios. The robotic model was tested in a low-turbulence flume under two flow conditions ([Formula: see text] wavelength/s). In two experimental sets, we measured fin kinematics, net surge forces, and power consumption. Using these data, we perform a thrust and power analysis of the undulating fin. We present the thrust coefficient, power coefficient, and propulsive efficiency. We find that the thrust generation was linear with the enclosed area swept by the fin, and square of the relative velocity between the incoming flow and traveling wave. The thrust coefficient levels off around 0.5. In addition, for our parameter range, we find that the power consumption scales by the cube of the effective tangential velocity of the rays [Formula: see text] (A is the amplitude of the ray oscillating motion, and [Formula: see text] is the angular velocity). We show that a decay in stiffness decreases both thrust production and power consumption. However, for rays with high flexural stiffness, the difference in thrust compared with rigid rays is minimal. Moreover, our results show that flexible rays can improve the propulsive efficiency compared with a rigid counterpart. Finally, we find that the morphology of ribbon fin affects its propulsive efficiency. For the aspect ratio considered in our experiments, [Formula: see text] was the most

  7. Sensitivity analysis of the stiffness between the frame structure and the frequency and vibration mode

    Science.gov (United States)

    Chen, Wenyuan

    2018-03-01

    The modal parameters such as natural frequency and vibration mode of the frame structure of the layer stiffness sensitivity is inconsistent. This article focuses on the theoretical derivation of the frequency and mode of the frame structure layer stiffness of the first-order sensitivity. The numerical examples show that the frame structure of layer stiffness higher than with the first order sensitivity vibration frequency.

  8. A diabetic patient presenting with stiff hand following fasciectomy for Dupuytren's contracture: A case report.

    Science.gov (United States)

    Fournier, Katia; Papanas, Nikolaos; Compson, Jonathan P; Maltezos, Efstratios

    2008-10-27

    Reported is the case of a 68-year-old male presenting with severe wrist and hand stiffness following surgery for a Dupuytren's contracture. Complications of surgery or rehabilitation and complex regional pain syndrome were excluded as factors explaining this stiffness. Given the patient's diabetes mellitus and the striking similarity with the typical diabetic stiff hand, it is suggested that diabetes may have contributed to the development of the complication.

  9. Evaluation of stiffness feedback for hard nodule identification on a phantom silicone model

    OpenAIRE

    Li, M.; Konstantinova, J.; Xu, G.; He, B.; Aminzadeh, V.; Xie, J.; Wurdemann, H.; Althoefer, K.

    2017-01-01

    Haptic information in robotic surgery can significantly improve clinical outcomes and help detect hard soft-tissue inclusions that indicate potential abnormalities. Visual representation of tissue stiffness information is a cost-effective technique. Meanwhile, direct force feedback, although considerably more expensive than visual representation, is an intuitive method of conveying information regarding tissue stiffness to surgeons. In this study, real-time visual stiffness feedback by slidin...

  10. Numerical and experimental analysis of a vibration isolator equipped with a negative stiffness system

    Science.gov (United States)

    Palomares, E.; Nieto, A. J.; Morales, A. L.; Chicharro, J. M.; Pintado, P.

    2018-02-01

    This paper presents a Negative Stiffness System (NSS) based on a set of two double-acting pneumatic linear actuators (PLA). The NSS is added to a system with a single degree of freedom, which consists of a sprung mass and a pneumatic spring. One end of each PLA is jointed to the sprung mass while the other end is jointed to the vibrating frame. In addition, the PLAs are symmetrically arranged so that they remain horizontal while the sprung mass is in static conditions. When the rear chamber is pressurised, the vertical component of the force applied by the PLAs will work against the pneumatic spring reducing the dynamic resonance frequency of the overall system. Experimental tests and simulations showed improvements regarding sprung mass isolation in comparison to the passive system without NSS, decreasing the resonance frequency by up to 58 % and improving the vibration attenuation for different experimental excitations.

  11. Effects of cyclic shear loads on strength, stiffness and dilation of rock fractures

    Directory of Open Access Journals (Sweden)

    Thanakorn Kamonphet

    2015-12-01

    Full Text Available Direct shear tests have been performed to determine the peak and residual shear strengths of fractures in sandstone, granite and limestone under cyclic shear loading. The fractures are artificially made in the laboratory by tension inducing and saw-cut methods. Results indicate that the cyclic shear load can significantly reduce the fracture shear strengths and stiffness. The peak shear strengths rapidly decrease after the first cycle and tend to remain unchanged close to the residual strengths through the tenth cycle. Degradation of the first order asperities largely occurs after the first cycle. The fracture dilation rates gradually decrease from the first through the tenth cycles suggesting that the second order asperities continuously degrade after the first load cycle. The residual shear strengths are lower than the peak shear strengths and higher than those of the smooth fractures. The strength of smooth fracture tends to be independent of cyclic shear loading.

  12. Whole-organ and segmental stiffness measured with liver magnetic resonance elastography in healthy adults: significance of the region of interest.

    Science.gov (United States)

    Rusak, Grażyna; Zawada, Elżbieta; Lemanowicz, Adam; Serafin, Zbigniew

    2015-04-01

    MR elastography (MRE) is a recent non-invasive technique that provides in vivo data on the viscoelasticity of the liver. Since the method is not well established, several different protocols were proposed that differ in results. The aim of the study was to analyze the variability of stiffness measurements in different regions of the liver. Twenty healthy adults aged 24-45 years were recruited. The examination was performed using a mechanical excitation of 64 Hz. MRE images were fused with axial T2WI breath-hold images (thickness 10 mm, spacing 10 mm). Stiffness was measured as a mean value of each cross section of the whole liver, on a single largest cross section, in the right lobe, and in ROIs (50 pix.) placed in the center of the left lobe, segments 5/6, 7, 8, and the parahilar region. Whole-liver stiffness ranged from 1.56 to 2.75 kPa. Mean segmental stiffness differed significantly between the tested regions (range from 1.55 ± 0.28 to 2.37 ± 0.32 kPa; P < 0.0001, ANOVA). Within-method variability of measurements ranged from 14 % for whole liver and segment 8-26 % for segment 7. Within-subject variability ranged from 13 to 31 %. Results of measurement within segment 8 were closest to the whole-liver method (ICC, 0.84). Stiffness of the liver presented significant variability depending on the region of measurement. The most reproducible method is averaging of cross sections of the whole liver. There was significant variability between stiffness in subjects considered healthy, which requires further investigation.

  13. Stiffness requirement of flexible skin for variable trailing-edge camber wing

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The method for analyzing the deformation of flexible skin under the air loads was developed based on the panel method and finite element method.The deformation of flexible skin under air pressures and effects of the local deformation on the aerodynamic characteristics were discussed.Numerical results show that the flexible skin on the upper surface of trailing-edge will bubble under the air loads and the bubble has a powerful effect on the aerodynamic pressure near the surface of local deforma-tion.Then the stiffness requirements for flexible skin of variable trailing-edge were given by using the Jacobs rule,i.e.,the maximum displacement of skin is not greater than 0.1% of wing chord.Results show that the in-plane stiffness can be reduced by increasing the ratio of bending stiffness to in-plane stiffness.Although the deformation of flexible skin increases with the in-plane stiffness decreasing,it depends on the bending stiffness.When the bending stiffness exceeds critical value,the deformation of flexible skin only depends on the bending stiffness and has nothing to do with the in-plane stiffness.The conclusions can be used for the structural design of flexible skin.

  14. Wide-range stiffness gradient PVA/HA hydrogel to investigate stem cell differentiation behavior.

    Science.gov (United States)

    Oh, Se Heang; An, Dan Bi; Kim, Tae Ho; Lee, Jin Ho

    2016-04-15

    Although stiffness-controllable substrates have been developed to investigate the effect of stiffness on cell behavior and function, the use of separate substrates with different degrees of stiffness, substrates with a narrow range stiffness gradient, toxicity of residues, different surface composition, complex fabrication procedures/devices, and low cell adhesion are still considered as hurdles of conventional techniques. In this study, a cylindrical polyvinyl alcohol (PVA)/hyaluronic acid (HA) hydrogel with a wide-range stiffness gradient (between ∼20kPa and ∼200kPa) and cell adhesiveness was prepared by a liquid nitrogen (LN2)-contacting gradual freezing-thawing method that does not use any additives or specific devices to produce the stiffness gradient hydrogel. From an in vitro cell culture using the stiffness gradient PVA/HA hydrogel, it was observed that human bone marrow mesenchymal stem cells have favorable stiffness ranges for induction of differentiation into specific cell types (∼20kPa for nerve cell, ∼40kPa for muscle cell, ∼80kPa for chondrocyte, and ∼190kPa for osteoblast). The PVA/HA hydrogel with a wide range of stiffness spectrum can be a useful tool for basic studies related with the stem cell differentiation, cell reprogramming, cell migration, and tissue regeneration in terms of substrate stiffness. It is postulated that the stiffness of the extracellular matrix influences cell behavior. To prove this concept, various techniques to prepare substrates with a stiffness gradient have been developed. However, the narrow ranges of stiffness gradient and complex fabrication procedures/devices are still remained as limitations. Herein, we develop a substrate (hydrogel) with a wide-range stiffness gradient using a gradual freezing-thawing method which does not need specific devices to produce a stiffness gradient hydrogel. From cell culture experiments using the hydrogel, it is observed that human bone marrow mesenchymal stem cells have

  15. Critical appraisal of the differential effects of antihypertensive agents on arterial stiffness

    Directory of Open Access Journals (Sweden)

    Francesca Kum

    2010-06-01

    Full Text Available Francesca Kum, Janaka KarallieddeUnit for Metabolic Medicine, Cardiovascular Division, Kings College-Waterloo Campus, King’s College London, United KingdomAbstract: Increased central arterial stiffness, involving accelerated vascular ageing of the aorta, is a powerful and independent risk factor for early mortality and provides prognostic information above and beyond traditional risk factors for cardiovascular disease (CVD. Central arterial stiffness is an important determinant of pulse pressure; therefore, any pathological increase may result in left ventricular hypertrophy and impaired coronary perfusion. Central artery stiffness can be assessed noninvasively by measurement of aortic pulse wave velocity, which is the gold standard for measurement of arterial stiffness. Earlier, it was believed that changes in arterial stiffness, which are primarily influenced by long-term pressure-dependent structural changes, may be slowed but not reversed by pharmacotherapy. Recent studies with drugs that inhibit the renin–angiotensin–aldosterone system, advanced glycation end products crosslink breakers, and endothelin antagonists suggest that blood pressure (BP-independent reduction and reversal of arterial stiffness are feasible. We review the recent literature on the differential effect of antihypertensive agents either as monotherapy or combination therapy on arterial stiffness. Arterial stiffness is an emerging therapeutic target for CVD risk reduction; however, further clinical trials are required to confirm whether BP-independent changes in arterial stiffness directly translate to a reduction in CVD events.Keywords: aortic pulse wave velocity, augmentation index, blood pressure, renin–angiotensin–aldosterone system

  16. Muscle contributions to elbow joint rotational stiffness in preparation for sudden external arm perturbations.

    Science.gov (United States)

    Holmes, Michael W R; Keir, Peter J

    2014-04-01

    Understanding joint stiffness and stability is beneficial for assessing injury risk. The purpose of this study was to examine joint rotational stiffness for individual muscles contributing to elbow joint stability. Fifteen male participants maintained combinations of three body orientations (standing, supine, sitting) and three hand preloads (no load, solid tube, fluid filled tube) while a device imposed a sudden elbow extension. Elbow angle and activity from nine muscles were inputs to a biomechanical model to determine relative contributions to elbow joint rotational stiffness, reported as percent of total stiffness. A body orientation by preload interaction was evident for most muscles (Psafety.

  17. Cellular shear stiffness reflects progression of arsenic-induced transformation during G1

    DEFF Research Database (Denmark)

    Muñoz, Alexandra; Eldridge, Will J; Jakobsen, Nina Munkholt

    2017-01-01

    epithelial cells were exposed to sodium arsenite to initiate early stages of transformation. Exposed cells were cultured in soft agar to further transformation and select for clonal populations exhibiting anchorage independent growth. Shear stiffness of various cell populations in G1 was assessed using...... reduced stiffness relative to control clonal lines, which were cultured in soft agar but did not receive arsenic treatment. The relative standard deviation of the stiffness of Arsenic clones was reduced compared to control clones, as well as to the arsenic exposed cell population. Cell stiffness...

  18. Evaluation of stiffness feedback for hard nodule identification on a phantom silicone model.

    Science.gov (United States)

    Li, Min; Konstantinova, Jelizaveta; Xu, Guanghua; He, Bo; Aminzadeh, Vahid; Xie, Jun; Wurdemann, Helge; Althoefer, Kaspar

    2017-01-01

    Haptic information in robotic surgery can significantly improve clinical outcomes and help detect hard soft-tissue inclusions that indicate potential abnormalities. Visual representation of tissue stiffness information is a cost-effective technique. Meanwhile, direct force feedback, although considerably more expensive than visual representation, is an intuitive method of conveying information regarding tissue stiffness to surgeons. In this study, real-time visual stiffness feedback by sliding indentation palpation is proposed, validated, and compared with force feedback involving human subjects. In an experimental tele-manipulation environment, a dynamically updated color map depicting the stiffness of probed soft tissue is presented via a graphical interface. The force feedback is provided, aided by a master haptic device. The haptic device uses data acquired from an F/T sensor attached to the end-effector of a tele-manipulated robot. Hard nodule detection performance is evaluated for 2 modes (force feedback and visual stiffness feedback) of stiffness feedback on an artificial organ containing buried stiff nodules. From this artificial organ, a virtual-environment tissue model is generated based on sliding indentation measurements. Employing this virtual-environment tissue model, we compare the performance of human participants in distinguishing differently sized hard nodules by force feedback and visual stiffness feedback. Results indicate that the proposed distributed visual representation of tissue stiffness can be used effectively for hard nodule identification. The representation can also be used as a sufficient substitute for force feedback in tissue palpation.

  19. Evaluation of stiffness feedback for hard nodule identification on a phantom silicone model.

    Directory of Open Access Journals (Sweden)

    Min Li

    Full Text Available Haptic information in robotic surgery can significantly improve clinical outcomes and help detect hard soft-tissue inclusions that indicate potential abnormalities. Visual representation of tissue stiffness information is a cost-effective technique. Meanwhile, direct force feedback, although considerably more expensive than visual representation, is an intuitive method of conveying information regarding tissue stiffness to surgeons. In this study, real-time visual stiffness feedback by sliding indentation palpation is proposed, validated, and compared with force feedback involving human subjects. In an experimental tele-manipulation environment, a dynamically updated color map depicting the stiffness of probed soft tissue is presented via a graphical interface. The force feedback is provided, aided by a master haptic device. The haptic device uses data acquired from an F/T sensor attached to the end-effector of a tele-manipulated robot. Hard nodule detection performance is evaluated for 2 modes (force feedback and visual stiffness feedback of stiffness feedback on an artificial organ containing buried stiff nodules. From this artificial organ, a virtual-environment tissue model is generated based on sliding indentation measurements. Employing this virtual-environment tissue model, we compare the performance of human participants in distinguishing differently sized hard nodules by force feedback and visual stiffness feedback. Results indicate that the proposed distributed visual representation of tissue stiffness can be used effectively for hard nodule identification. The representation can also be used as a sufficient substitute for force feedback in tissue palpation.

  20. Impact of morning stiffness on working behaviour and performance in people with rheumatoid arthritis.

    Science.gov (United States)

    Mattila, Kalle; Buttgereit, Frank; Tuominen, Risto

    2014-12-01

    Work disability remains a considerable problem for many patients with rheumatoid arthritis (RA). Morning stiffness is a symptom of RA associated with early retirement from work and with impaired functional ability. We aimed to explore the patient's perception of the impact of morning stiffness on the working life of patients with RA. A survey was conducted in 11 European countries. Patients of working age, with RA for ≥6 months and morning stiffness ≥3 mornings a week, were interviewed by telephone using a structured questionnaire. Responses were assessed in the total sample and in subgroups defined by severity and duration of morning stiffness and by country. A total of 1,061 respondents completed the survey, 534 were working, 224 were retired and the rest were, i.e. homemakers and unemployed. Among the 534 working respondents, RA-related morning stiffness affected work performance (47 %), resulted in late arrival at work (33 %) and required sick leave in the past month (15 %). Of the 224 retired respondents, 159 (71 %) stopped working earlier than their expected retirement age, with 64 % giving RA-related morning stiffness as a reason. There was a differential impact of increasing severity and increasing duration of morning stiffness on the various parameters studied. There were notable inter-country differences in the impact of RA-related morning stiffness on ability to work and on retirement. This large survey showed that from the patient's perspective, morning stiffness reduces the ability to work in patients with RA and contributes to early retirement.

  1. Altered arterial stiffness and subendocardial viability ratio in young healthy light smokers after acute exercise.

    Directory of Open Access Journals (Sweden)

    Robert J Doonan

    Full Text Available Studies showed that long-standing smokers have stiffer arteries at rest. However, the effect of smoking on the ability of the vascular system to respond to increased demands (physical stress has not been studied. The purpose of this study was to estimate the effect of smoking on arterial stiffness and subendocardial viability ratio, at rest and after acute exercise in young healthy individuals.Healthy light smokers (n = 24, pack-years = 2.9 and non-smokers (n = 53 underwent pulse wave analysis and carotid-femoral pulse wave velocity measurements at rest, and 2, 5, 10, and 15 minutes following an exercise test to exhaustion. Smokers were tested, 1 after 12h abstinence from smoking (chronic condition and 2 immediately after smoking one cigarette (acute condition. At rest, chronic smokers had higher augmentation index and lower aortic pulse pressure than non-smokers, while subendocardial viability ratio was not significantly different. Acute smoking increased resting augmentation index and decreased subendocardial viability ratio compared with non-smokers, and decreased subendocardial viability ratio compared with the chronic condition. After exercise, subendocardial viability ratio was lower, and augmentation index and aortic pulse pressure were higher in non-smokers than smokers in the chronic and acute conditions. cfPWV rate of recovery of was greater in non-smokers than chronic smokers after exercise. Non-smokers were also able to achieve higher workloads than smokers in both conditions.Chronic and acute smoking appears to diminish the vascular response to physical stress. This can be seen as an impaired 'vascular reserve' or a blunted ability of the blood vessels to accommodate the changes required to achieve higher workloads. These changes were noted before changes in arterial stiffness or subendocardial viability ratio occurred at rest. Even light smoking in young healthy individuals appears to have harmful effects on vascular

  2. Correlation of liver stiffness measured by FibroScan with sex and age in healthy adults undergoing physical examination

    Directory of Open Access Journals (Sweden)

    ZHAO Chongshan

    2016-04-01

    Full Text Available ObjectiveTo determine the reference range of liver stiffness in healthy population, and to investigate the influence of age and sex on liver stiffness. MethodsA total of 1794 healthy subjects who underwent physical examination in China National Petroleum Corporation Central Hospital from October 1, 2012 to October 31, 2014 were enrolled, and FibroScan was used to perform liver stiffness measurement (LSM. Since LSM value was not normally distributed, the Wilcoxon rank sum test was used to compare LSM value between male and female patients, the Kruskal-Wallis test was used to compare LSM value between different age groups, and the Spearman's rank correlation analysis was used to analyze the correlation between LSM value and age. The one-sided percentile method was used to determine the range of normal reference values in male and female subjects or in different age groups. ResultsLSM was successfully performed in 1590 patients, and the rate of successful measurement was 88.63%. A total of 107 patients were excluded due to abnormal liver enzymes. The analysis showed that LSM value showed a significant difference between male and female subjects (Z=-4.980, P<0.001, as well as between different age groups (χ2=16.983, P=0.001. Age was positively correlated with LSM value (r=0.087, P=0.001. The reference range was estimated to be ≤7.1 kPa in adults, ≤7.0 kPa in females, and ≤7.2 kPa in males. From the perspective of age, the reference range was estimated to be ≤6.8 kPa in persons aged 20-29 years, ≤6.7 kPa in persons aged 30-44 years, ≤7.8 kPa in persons aged 45-59 years, and ≤8.8 kPa in persons aged 60-74 years. ConclusionLiver stiffness value is influenced by sex and age. Sex and age should be taken into account while performing liver stiffness measurement in healthy subjects.

  3. A lightweight, biological structure with tailored stiffness: The feather vane.

    Science.gov (United States)

    Sullivan, Tarah N; Pissarenko, Andreï; Herrera, Steven A; Kisailus, David; Lubarda, Vlado A; Meyers, Marc A

    2016-09-01

    The flying feathers of birds are keratinous appendages designed for maximum performance with a minimum weight penalty. Thus, their design contains ingenious combinations of components that optimize lift, stiffness, aerodynamics, and damage resistance. This design involves two main parts: a central shaft that prescribes stiffness and lateral vanes which allows for the capture of air. Within the feather vane, barbs branch from the shaft and barbules branch from barbs, forming a flat surface which ensures lift. Microhooks at the end of barbules hold barbs tightly together, providing the close-knit, unified structure of the feather vane and enabling a repair of the structure through the reattachment of un-hooked junctions. Both the shaft and barbs are lightweight biological structures constructed of keratin using the common motif of a solid shell and cellular interior. The cellular core increases the resistance to buckling with little added weight. Here we analyze the detailed structure of the feather barb and, for the first time, explain its flexural stiffness in terms of the mechanics of asymmetric foam-filled beams subjected to bending. The results are correlated and validated with finite element modeling. We compare the flexure of single barbs as well as arrays of barbs and find that the interlocking adherence of barbs to one another enables a more robust structure due to minimized barb rotation during deflection. Thus, the flexure behavior of the feather vane can be tailored by the adhesive hooking between barbs, creating a system that mitigates damage. A simplified three-dimensional physical model for this interlocking mechanism is constructed by additive manufacturing. The exceptional architecture of the feather vane will motivate the design of bioinspired structures with tailored and unique properties ranging from adhesives to aerospace materials. Despite its importance to bird flight, literature characterizing the feather vane is extremely limited. The feather

  4. Development of procedures for calculating stiffness and damping properties of elastomers in engineering applications. Part 1: Verification of basic methods

    Science.gov (United States)

    Chiang, T.; Tessarzik, J. M.; Badgley, R. H.

    1972-01-01

    The primary aim of this investigation was verification of basic methods which are to be used in cataloging elastomer dynamic properties (stiffness and damping) in terms of viscoelastic model constants. These constants may then be used to predict dynamic properties for general elastomer shapes and operating conditions, thereby permitting optimum application of elastomers as energy absorption and/or energy storage devices in the control of vibrations in a broad variety of applications. The efforts reported involved: (1) literature search; (2) the design, fabrication and use of a test rig for obtaining elastomer dynamic test data over a wide range of frequencies, amplitudes, and preloads; and (3) the reduction of the test data, by means of a selected three-element elastomer model and specialized curve fitting techniques, to material properties. Material constants thus obtained have been used to calculate stiffness and damping for comparison with measured test data. These comparisons are excellent for a number of test conditions and only fair to poor for others. The results confirm the validity of the basic approach of the overall program and the mechanics of the cataloging procedure, and at the same time suggest areas in which refinements should be made.

  5. AFM stiffness nanotomography of normal, metaplastic and dysplastic human esophageal cells

    International Nuclear Information System (INIS)

    Fuhrmann, A; Staunton, J R; Banyai, N; Davies, P C W; Ros, R; Nandakumar, V

    2011-01-01

    The mechanical stiffness of individual cells is important in tissue homeostasis, cell growth, division and motility, and the epithelial–mesenchymal transition in the initiation of cancer. In this work, a normal squamous cell line (EPC2) and metaplastic (CP-A) as well as dysplastic (CP-D) Barrett's Esophagus columnar cell lines are studied as a model of pre-neoplastic progression in the human esophagus. We used the combination of an atomic force microscope (AFM) with a scanning confocal fluorescence lifetime imaging microscope to study the mechanical properties of single adherent cells. Sixty four force indentation curves were taken over the nucleus of each cell in an 8 × 8 grid pattern. Analyzing the force indentation curves, indentation depth-dependent Young's moduli were found for all cell lines. Stiffness tomograms demonstrate distinct differences between the mechanical properties of the studied cell lines. Comparing the stiffness for indentation forces of 1 nN, most probable Young's moduli were calculated to 4.7 kPa for EPC2 (n = 18 cells), 3.1 kPa for CP-A (n = 10) and 2.6 kPa for CP-D (n = 19). We also tested the influence of nuclei and nucleoli staining organic dyes on the mechanical properties of the cells. For stained EPC2 cells (n = 5), significant stiffening was found (9.9 kPa), while CP-A cells (n = 5) showed no clear trend (2.9 kPa) and a slight softening was observed (2.1 kPa) in the case of CP-D cells (n = 16). Some force–indentation curves show non-monotonic discontinuities with segments of negative slope, resembling a sawtooth pattern. We found the incidence of these 'breakthrough events' to be highest in the dysplastic CP-D cells, intermediate in the metaplastic CP-A cells and lowest in the normal EPC2 cells. This observation suggests that the microscopic explanation for the increased compliance of cancerous and pre-cancerous cells may lie in their susceptibility to 'crumble and yield' rather than their

  6. THE RELATIONSHIP BETWEEN STIFFNESS LOSSES AND LOSSES IN BEARINGS OF ROPE BLOCKS

    Directory of Open Access Journals (Sweden)

    V. M. Bohomaz

    2017-08-01

    Full Text Available Purpose. To determine the efficiency of rope blocks, it is necessary to determine the stiffness coefficient of the ropes of blocks, taking into account the classification group of the mechanism and the wrapping angle of a block by a rope. At this one should use well-tested values of the efficiency coefficients of the rope blocks, taking into account the wrapping angle of a block by a rope and the analytically found friction coefficients of the rolling bearings given to the trunnion. Methodology. The work presents the analytical method of determining the coefficient of bearing resistance of the block when it is rotated by both the inner and outer cages, as well as the design scheme of the bearing of the block. Findings. The analysis of the lubrication method effect, the operating mode of the mechanism and the wrapping angle of a block by a rope on losses in bearings was carried out for rope blocks. The corresponding comparative tables of losses are given. Analysis of the obtained calculation results allows us to establish: 1 the main resistance affecting the cable blocks efficiency is the resistance in bearings; 2 the second largest component is the stiffness losses, depending on the operating mode, the wrapping angle of a block by a rope, the type of bearing lubrication; 3 the block efficiency when rotating the inner cage is higher than rotating the outer one by about 3% with thick lubrication and 1M mode; 4 in the sequential location of assemblies with a rolling bearing, it is necessary to strive for the design of the assembly in which the inner cage rotates; 5 with the number of blocks up to 5, one can use the recommended definitions of block bearings in the literature with an error in the efficiency value of up to 10%. Originality. The authors obtained values of resistances in the rolling bearings of the rope blocks and stiffness losses due to the girth of the block by the rope. In this case, dependences were used to determine the coefficient

  7. Matrix Stiffness Corresponding to Strictured Bowel Induces a Fibrogenic Response in Human Colonic Fibroblasts

    Science.gov (United States)

    Johnson, Laura A.; Rodansky, Eva S.; Sauder, Kay L.; Horowitz, Jeffrey C.; Mih, Justin D.; Tschumperlin, Daniel J.; Higgins, Peter D.

    2013-01-01

    Background Crohn’s disease is characterized by repeated cycles of inflammation and mucosal healing which ultimately progress to intestinal fibrosis. This inexorable progression towards fibrosis suggests that fibrosis becomes inflammation-independent and auto-propagative. We hypothesized that matrix stiffness regulates this auto-propagation of intestinal fibrosis. Methods The stiffness of fresh ex vivo samples from normal human small intestine, Crohn’s disease strictures, and the unaffected margin were measured with a microelastometer. Normal human colonic fibroblasts were cultured on physiologically normal or pathologically stiff matrices corresponding to the physiological stiffness of normal or fibrotic bowel. Cellular response was assayed for changes in cell morphology, α-smooth muscle actin (αSMA) staining, and gene expression. Results Microelastometer measurements revealed a significant increase in colonic tissue stiffness between normal human colon and Crohn’s strictures as well as between the stricture and adjacent tissue margin. In Ccd-18co cells grown on stiff matrices corresponding to Crohn’s strictures, cellular proliferation increased. Pathologic stiffness induced a marked change in cell morphology and increased αSMA protein expression. Growth on a stiff matrix induced fibrogenic gene expression, decreased matrix metalloproteinase and pro-inflammatory gene expression, and was associated with nuclear localization of the transcriptional cofactor MRTF-A. Conclusions Matrix stiffness, representative of the pathological stiffness of Crohn’s strictures, activates human colonic fibroblasts to a fibrogenic phenotype. Matrix stiffness affects multiple pathways suggesting the mechanical properties of the cellular environment are critical to fibroblast function and may contribute to autopropagation of intestinal fibrosis in the absence of inflammation, thereby contributing to the intractable intestinal fibrosis characteristic of Crohn’s disease. PMID

  8. Variable stiffness corrugated composite structure with shape memory polymer for morphing skin applications

    Science.gov (United States)

    Gong, Xiaobo; Liu, Liwu; Scarpa, Fabrizio; Leng, Jinsong; Liu, Yanju

    2017-03-01

    This work presents a variable stiffness corrugated structure based on a shape memory polymer (SMP) composite with corrugated laminates as reinforcement that shows smooth aerodynamic surface, extreme mechanical anisotropy and variable stiffness for potential morphing skin applications. The smart composite corrugated structure shows a low in-plane stiffness to minimize the actuation energy, but also possess high out-of-plane stiffness to transfer the aerodynamic pressure load. The skin provides an external smooth aerodynamic surface because of the one-sided filling with the SMP. Due to variable stiffness of the shape memory polymer the morphing skin exhibits a variable stiffness with a change of temperature, which can help the skin adjust its stiffness according different service environments and also lock the temporary shape without external force. Analytical models related to the transverse and bending stiffness are derived and validated using finite element techniques. The stiffness of the morphing skin is further investigated by performing a parametric analysis against the geometry of the corrugation and various sets of SMP fillers. The theoretical and numerical models show a good agreement and demonstrate the potential of this morphing skin concept for morphing aircraft applications. We also perform a feasibility study of the use of this morphing skin in a variable camber morphing wing baseline. The results show that the morphing skin concept exhibits sufficient bending stiffness to withstand the aerodynamic load at low speed (less than 0.3 Ma), while demonstrating a large transverse stiffness variation (up to 191 times) that helps to create a maximum mechanical efficiency of the structure under varying external conditions.

  9. Quantitative Elastography for Cervical Stiffness Assessment during Pregnancy

    Directory of Open Access Journals (Sweden)

    A. Fruscalzo

    2014-01-01

    Full Text Available Aim. Feasibility and reliability of tissue Doppler imaging-(TDI- based elastography for cervical quantitative stiffness assessment during all three trimesters of pregnancy were evaluated. Materials and Methods. Prospective case-control study including seventy-four patients collected between the 12th and 42nd weeks of gestation. The tissue strain (TS was measured by two independent operators as natural strain. Intra- and interoperator intraclass correlation coefficient (ICC agreements were evaluated. Results. TS measurement was always feasible and exhibited a high performance in terms of reliability (intraoperator ICC-agreement = 0.93; interoperator ICC agreement = 0.89 and 0.93 for a single measurement and for the average of two measurements, resp.. Cervical TS showed also a significant correlation with gestational age, cervical length, and parity. Conclusions. TS measurement during pregnancy demonstrated high feasibility and reliability. Furthermore, TS significantly correlated with gestational age, cervical length, and parity.

  10. Cell stiffness, contractile stress and the role of extracellular matrix

    International Nuclear Information System (INIS)

    An, Steven S.; Kim, Jina; Ahn, Kwangmi; Trepat, Xavier; Drake, Kenneth J.; Kumar, Sarvesh; Ling, Guoyu; Purington, Carolyn; Rangasamy, Tirumalai; Kensler, Thomas W.; Mitzner, Wayne; Fredberg, Jeffrey J.; Biswal, Shyam

    2009-01-01

    Here we have assessed the effects of extracellular matrix (ECM) composition and rigidity on mechanical properties of the human airway smooth muscle (ASM) cell. Cell stiffness and contractile stress showed appreciable changes from the most relaxed state to the most contracted state: we refer to the maximal range of these changes as the cell contractile scope. The contractile scope was least when the cell was adherent upon collagen V, followed by collagen IV, laminin, and collagen I, and greatest for fibronectin. Regardless of ECM composition, upon adherence to increasingly rigid substrates, the ASM cell positively regulated expression of antioxidant genes in the glutathione pathway and heme oxygenase, and disruption of a redox-sensitive transcription factor, nuclear erythroid 2 p45-related factor (Nrf2), culminated in greater contractile scope. These findings provide biophysical evidence that ECM differentially modulates muscle contractility and, for the first time, demonstrate a link between muscle contractility and Nrf2-directed responses.

  11. Stiff self-interacting strings at high temperature QCD

    Science.gov (United States)

    S Bakry, A.; Chen, X.; Deliyergiyev, M.; Galal, A.; Khalaf, A.; M Pengming, P.

    2018-03-01

    We investigate the implications of Nambu-Goto (NG), Lüscher Weisz (LW) and Polyakov-Kleinert (PK) effective string actions for the Casimir energy and the width of the quantum delocalization of the string in 4-dim pure SU(3) Yang-Mills lattice gauge theory. At a temperature closer to the critical point T/Tc=0.9, we found that the next to leading-order (NLO) contributions from the expansion of the NG string in addition to the boundary terms in LW action to decrease the deviations from the lattice data in the intermediate distance scales for both the quark-antiquark QQ̅ potential and broadening of the color tube compared to the free string approximation. We conjecture possible stiffness of the QCD string through studying the effects of extrinsic curvature term in PK action and find a good fitting behavior for the lattice Monte-Carlo data at both long and intermediate quark separations regions.

  12. Cell stiffness, contractile stress and the role of extracellular matrix

    Energy Technology Data Exchange (ETDEWEB)

    An, Steven S., E-mail: san@jhsph.edu [Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, Room E-7616, Baltimore, MD 21205 (United States); Kim, Jina [Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, Room E-7616, Baltimore, MD 21205 (United States); Ahn, Kwangmi [Division of Biostatistics, Penn State College of Medicine, Hershey, PA 17033 (United States); Trepat, Xavier [CIBER, Enfermedades Respiratorias, 07110 Bunyola (Spain); Drake, Kenneth J. [Division of Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, MA 02115 (United States); Kumar, Sarvesh; Ling, Guoyu; Purington, Carolyn; Rangasamy, Tirumalai; Kensler, Thomas W.; Mitzner, Wayne [Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, Room E-7616, Baltimore, MD 21205 (United States); Fredberg, Jeffrey J. [Division of Molecular and Integrative Physiological Sciences, Harvard School of Public Health, Boston, MA 02115 (United States); Biswal, Shyam [Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, Room E-7616, Baltimore, MD 21205 (United States); Division of Pulmonary and Critical Care Medicine, Johns Hopkins School of Medicine, Baltimore, MD 21205 (United States)

    2009-05-15

    Here we have assessed the effects of extracellular matrix (ECM) composition and rigidity on mechanical properties of the human airway smooth muscle (ASM) cell. Cell stiffness and contractile stress showed appreciable changes from the most relaxed state to the most contracted state: we refer to the maximal range of these changes as the cell contractile scope. The contractile scope was least when the cell was adherent upon collagen V, followed by collagen IV, laminin, and collagen I, and greatest for fibronectin. Regardless of ECM composition, upon adherence to increasingly rigid substrates, the ASM cell positively regulated expression of antioxidant genes in the glutathione pathway and heme oxygenase, and disruption of a redox-sensitive transcription factor, nuclear erythroid 2 p45-related factor (Nrf2), culminated in greater contractile scope. These findings provide biophysical evidence that ECM differentially modulates muscle contractility and, for the first time, demonstrate a link between muscle contractility and Nrf2-directed responses.

  13. Stiffness Characteristics of Composite Rotor Blades With Elastic Couplings

    Science.gov (United States)

    Piatak, David J.; Nixon, Mark W.; Kosmatka, John B.

    1997-01-01

    Recent studies on rotor aeroelastic response and stability have shown the beneficial effects of incorporating elastic couplings in composite rotor blades. However, none of these studies have clearly identified elastic coupling limits and the effects of elastic couplings on classical beam stiffnesses of representative rotor blades. Knowledge of these limits and effects would greatly enhance future aeroelastic studies involving composite rotor blades. The present study addresses these voids and provides a preliminary design database for investigators who may wish to study the effects of elastic couplings on representative blade designs. The results of the present study should provide a basis for estimating the potential benefits associated with incorporating elastic couplings without the need for first designing a blade cross section and then performing a cross-section analysis to obtain the required beam section properties as is customary in the usual one-dimensional beam-type approach.

  14. Stiffness and design for strength of trapezoidal Belleville springs

    DEFF Research Database (Denmark)

    Pedersen, Niels Leergaard; Pedersen, Pauli

    2011-01-01

    in this paper. Finite element results are compared with analytical predictions and critically analysed in terms of the effect of Poisson ratio, overall stiffness, and stress distribution in the spring. This is done in order to verify the range of validity of design standards. Finite element analysis emerges......Belleville springs or coned disc springs are commonly used in machine design. The geometric dimensions of the spring and the determination of non-linear force–displacement curve are regulated by different standards. However, the theory behind Belleville spring design standards is founded on a study...... published in 1936. Furthermore, the common spring design with cross-sections of uniform thickness poses problems in terms of non-uniformity of stress distribution. In view of this, non-linear three-dimensional finite element analyses of spring designs including uniform or variable thickness are carried out...

  15. Stiffness of RBC optical confinement affected by optical clearing

    Science.gov (United States)

    Grishin, Oleg V.; Fedosov, Ivan V.; Tuchin, Valery V.

    2017-03-01

    In vivo optical trapping is a novel applied direction of an optical manipulation, which enables one to noninvasive measurement of mechanical properties of cells and tissues in living animals directly. But an application area of this direction is limited because strong scattering of many biological tissues. An optical clearing enables one to decrease the scattering and therefore increase a depth of light penetration, decrease a distortion of light beam, improve a resolution in imaging applications. Now novel methods had appeared for a measurement an optical clearing degree at a cellular level. But these methods aren't applicable in vivo. In this paper we present novel measurement method of estimate of the optical clearing, which are based on a measurement of optical trap stiffness. Our method may be applicable in vivo.

  16. Reproducibility of the ambulatory arterial stiffness index in hypertensive patients

    DEFF Research Database (Denmark)

    Dechering, D.G.; Steen, M.S. van der; Adiyaman, A.

    2008-01-01

    BACKGROUND: We studied the repeatability of the ambulatory arterial stiffness index (AASI), which can be computed from 24-h blood pressure (BP) recordings as unity minus the regression slope of diastolic on systolic BP. METHODS: One hundred and fifty-two hypertensive outpatients recruited...... in Nijmegen (mean age = 46.2 years; 76.3% with systolic and diastolic hypertension) and 145 patients enrolled in the Systolic Hypertension in Europe (Syst-Eur) trial (71.0 years) underwent 24-h BP monitoring at a median interval of 8 and 31 days, respectively. We used the repeatability coefficient, which...... were approximately 30%. Differences in AASI between paired recordings were correlated with differences in the goodness of fit (r2) of the AASI regression line as well as with differences in the night-to-day BP ratio. However, in sensitivity analyses stratified for type of hypertension, r2, or dipping...

  17. Central Hemodynamics and Arterial Stiffness in Systemic Sclerosis.

    Science.gov (United States)

    Bartoloni, Elena; Pucci, Giacomo; Cannarile, Francesca; Battista, Francesca; Alunno, Alessia; Giuliani, Marco; Cafaro, Giacomo; Gerli, Roberto; Schillaci, Giuseppe

    2016-12-01

    Although microvascular disease is a hallmark of systemic sclerosis (SSc), a higher prevalence of macrovascular disease and a poorer related prognosis have been reported in SSc than in the general population. The simultaneous assessment of prognostically relevant functional properties of larger and smaller arteries, and their effects on central hemodynamics, has never been performed in SSc using the state-of-the-art techniques. Thirty-four women with SSc (aged 61±15 years, disease duration 17±12 years, and blood pressure 123/70±18/11 mm Hg) and 34 healthy women individually matched by age and mean arterial pressure underwent the determination of carotid-femoral (aortic) and carotid-radial (upper limb) pulse wave velocity (a direct measure of arterial stiffness), aortic augmentation (a measure of the contribution of reflected wave to central pulse pressure), and aortobrachial pulse pressure amplification (brachial/aortic pulse pressure) through applanation tonometry (SphygmoCor). Patients and controls did not differ by carotid-femoral or carotid-radial pulse wave velocity. Aortic augmentation index corrected for a heart rate of 75 bpm (AIx@75) was higher in women with SSc (30.9±16% versus 22.2±12%; P=0.012). Patients also had a lower aortobrachial amplification of pulse pressure (1.22±0.18 versus 1.33±0.25; P=0.041). SSc was an independent predictor of AIx@75 (direct) and pulse pressure amplification (inverse). Among patients, age, mean arterial pressure, and C-reactive protein independently predicted carotid-femoral pulse wave velocity. Age and mean arterial pressure were the only predictors of AIx@75. Women with SSc have increased aortic augmentation and decreased pulse pressure amplification (both measures of the contribution of reflected wave to central waveform) but no changes in aortic or upper limb arterial stiffness. Microvascular involvement occurs earlier than large artery stiffening in SSc. © 2016 American Heart Association, Inc.

  18. A METHOD OF DETERMINING THE COORDINATES OF THE STIFFNESS CENTER AND THE STIFFNESS PRINCIPAL AXIS OF THE VIBRATING SYSTEM WITH DAMPING

    Directory of Open Access Journals (Sweden)

    Dang Xuan Truong

    2014-12-01

    Full Text Available The report presents a methodology to determine the directions of the stiffness principal axis (in this case subject to the linear displacement and forced rotation angle of a solid object interact with the surrounding environment by resilient bearing supports. The results also show that determining the coordinates of the stiffness center in the vibrating system with damping factors is necessary in our research.

  19. Cerebral Microbleeds and White Matter Hyperintensities in Cognitively Healthy Elderly: A Cross-Sectional Cohort Study Evaluating the Effect of Arterial Stiffness

    Directory of Open Access Journals (Sweden)

    Anna-Märta Gustavsson

    2015-05-01

    Full Text Available Background: Arterial stiffness reflects the ageing processes in the vascular system, and studies have shown an association between reduced cognitive function and cerebral small vessel disease. Small vessel disease can be visualized as white matter hyperintensities (WMH and lacunar infarcts but also as cerebral microbleeds on brain magnetic resonance imaging (MRI. We aimed to investigate if arterial stiffness influences the presence of microbleeds, WMH and cognitive function in a population of cognitively healthy elderly. Methods: The study population is part of the Swedish BioFinder study and consisted of 208 individuals without any symptoms of cognitive impairment, who scored >27 points on the Mini-Mental State Examination. The participants (mean age, 72 years; 59% women underwent MRI of the brain with visual rating of microbleeds and WMH. Arterial stiffness was measured with carotid-femoral pulse wave velocity (cfPWV. Eight cognitive tests covering different cognitive domains were performed. Results: Microbleeds were detected in 12% and WMH in 31% of the participants. Mean (±standard deviation, SD cfPWV was 10.0 (±2.0 m/s. There was no association between the presence of microbleeds and arterial stiffness. There was a positive association between arterial stiffness and WMH independent of age or sex (odds ratio, 1.58; 95% confidence interval, 1.04-2.40, p 0.05. Cognitive performance was not associated with microbleeds, but individuals with WMH performed slightly worse than those without WMH on the Symbol Digit Modalities Test (mean ± SD, 35 ± 7.8 vs. 39 ± 8.1, p Conclusions: Arterial stiffness was not associated with the presence of cerebral microbleeds or cognitive function in cognitively healthy elderly. However, arterial stiffness was related to the presence of WMH, but the association was attenuated when multiple adjustments were made. There was a weak negative association between WMH and performance in one specific test of attention

  20. Through Thickness Ultrasonic Testing and Its Use in Characterising ...

    African Journals Online (AJOL)

    The stiffness coefficients of different types of limestone were determined using the through thickness ultrasonic test and measurements of size and weight, and the results obtained verified using aluminium specimens of known mechanical properties. The values of density and stiffness coefficients obtained for the various ...

  1. Cellular volume regulation and substrate stiffness modulate the detachment dynamics of adherent cells

    Science.gov (United States)

    Yang, Yuehua; Jiang, Hongyuan

    2018-03-01

    Quantitative characterizations of cell detachment are vital for understanding the fundamental mechanisms of cell adhesion. Experiments have found that cell detachment shows strong rate dependence, which is mostly attributed to the binding-unbinding kinetics of receptor-ligand bond. However, our recent study showed that the cellular volume regulation can significantly regulate the dynamics of adherent cell and cell detachment. How this cellular volume regulation contributes to the rate dependence of cell detachment remains elusive. Here, we systematically study the role of cellular volume regulation in the rate dependence of cell detachment by investigating the cell detachments of nonspecific adhesion and specific adhesion. We find that the cellular volume regulation and the bond kinetics dominate the rate dependence of cell detachment at different time scales. We further test the validity of the traditional Johnson-Kendall-Roberts (JKR) contact model and the detachment model developed by Wyart and Gennes et al (W-G model). When the cell volume is changeable, the JKR model is not appropriate for both the detachments of convex cells and concave cells. The W-G model is valid for the detachment of convex cells but is no longer applicable for the detachment of concave cells. Finally, we show that the rupture force of adherent cells is also highly sensitive to substrate stiffness, since an increase in substrate stiffness will lead to more associated bonds. These findings can provide insight into the critical role of cell volume in cell detachment and might have profound implications for other adhesion-related physiological processes.

  2. A computational technique to identify the optimal stiffness matrix for a discrete nuclear fuel assembly model

    International Nuclear Information System (INIS)

    Park, Nam-Gyu; Kim, Kyoung-Joo; Kim, Kyoung-Hong; Suh, Jung-Min

    2013-01-01

    Highlights: ► An identification method of the optimal stiffness matrix for a fuel assembly structure is discussed. ► The least squares optimization method is introduced, and a closed form solution of the problem is derived. ► The method can be expanded to the system with the limited number of modes. ► Identification error due to the perturbed mode shape matrix is analyzed. ► Verification examples show that the proposed procedure leads to a reliable solution. -- Abstract: A reactor core structural model which is used to evaluate the structural integrity of the core contains nuclear fuel assembly models. Since the reactor core consists of many nuclear fuel assemblies, the use of a refined fuel assembly model leads to a considerable amount of computing time for performing nonlinear analyses such as the prediction of seismic induced vibration behaviors. The computational time could be reduced by replacing the detailed fuel assembly model with a simplified model that has fewer degrees of freedom, but the dynamic characteristics of the detailed model must be maintained in the simplified model. Such a model based on an optimal design method is proposed in this paper. That is, when a mass matrix and a mode shape matrix are given, the optimal stiffness matrix of a discrete fuel assembly model can be estimated by applying the least squares minimization method. The verification of the method is completed by comparing test results and simulation results. This paper shows that the simplified model's dynamic behaviors are quite similar to experimental results and that the suggested method is suitable for identifying reliable mathematical model for fuel assemblies

  3. A proposal for an unusually stiff and moderately ductile hard coating material: Mo2BC

    International Nuclear Information System (INIS)

    Emmerlich, J; Music, D; Braun, M; Fayek, P; Schneider, J M; Munnik, F

    2009-01-01

    The elastic properties of Mo 2 BC were studied using ab initio calculations. The calculated bulk modulus of 324 GPa is 45% larger than that of Ti 0.25 Al 0.75 N and 14% smaller than that of c-BN, indicating a highly stiff material. The bulk modulus (B) to shear modulus (G) ratio is 1.72 at the transition from brittle to ductile behaviour. This, in combination with a positive Cauchy pressure (c 12 - c 44 ), suggests moderate ductility. When compared with a typical hard protective coating such as Ti 0.25 Al 0.75 N (B = 178 GPa; B/G = 1.44; negative Cauchy pressure), Mo 2 BC displays considerable potential as protective coating for metal cutting applications. In order to test this proposal, Mo 2 BC thin films were synthesized using dc magnetron sputtering from three plasma sources on Al 2 O 3 (0 0 0 1) at a substrate temperature of ∼900 0 C. The calculated lattice parameters are in good agreement with values determined from x-ray diffraction. The measured Young's modulus values of ∼460 ± 21 GPa are in excellent agreement with the 470 GPa value obtained by calculations. Scanning probe microscopy imaging of the residual indent revealed no evidence for crack formation as well as significant pile-up, which is consistent with the moderate plasticity predicted. The apparent contradiction between moderate ductility on the one hand and indentation hardness values of 29 GPa can be understood by considering the electronic structure particularly the extreme anisotropy. The presence of stiff Mo-C and Mo-B layers with metallic interlayer bonding enables this intriguing and unexpected property combination.

  4. Influence of Abutment Design on Stiffness, Strength, and Failure of Implant-Supported Monolithic Resin Nano Ceramic (RNC) Crowns.

    Science.gov (United States)

    Joda, Tim; Huber, Samuel; Bürki, Alexander; Zysset, Philippe; Brägger, Urs

    2015-12-01

    Recent technical development allows the digital manufacturing of monolithic reconstructions with high-performance materials. For implant-supported crowns, the fixation requires an abutment design onto which the reconstruction can be bonded. The aim of this laboratory investigation was to analyze stiffness, strength, and failure modes of implant-supported, computer-assisted design and computer-aided manufacturing (CAD/CAM)-generated resin nano ceramic (RNC) crowns bonded to three different titanium abutments. Eighteen monolithic RNC crowns were produced and loaded in a universal testing machine under quasi-static condition according to DIN ISO 14801. With regard to the type of titanium abutment, three groups were defined: (1) prefabricated cementable standard; (2) CAD/CAM-constructed individualized; and (3) novel prefabricated bonding base. Stiffness and strength were measured and analyzed statistically with Wilcoxon rank sum test. Sections of the specimens were examined microscopically. Stiffness demonstrated high stability for all specimens loaded in the physiological loading range with means and standard deviations of 1,579 ± 120 N/mm (group A), 1,733 ± 89 N/mm (group B), and 1,704 ± 162 N/mm (group C). Mean strength of the novel prefabricated bonding base (group C) was 17% lower than of the two other groups. Plastic deformations were detectable for all implant-abutment crown connections. Monolithic implant crowns made of RNC seem to represent a feasible and stable prosthetic construction under laboratory testing conditions with strength higher than the average occlusal force, independent of the different abutment designs used in this investigation. © 2014 Wiley Periodicals, Inc.

  5. Objective Assessment of Joint Stiffness: A Clinically Oriented Hardware and Software Device with an Application to the Shoulder Joint.

    Science.gov (United States)

    McQuade, Kevin; Price, Robert; Liu, Nelson; Ciol, Marcia A

    2012-08-30

    Examination of articular joints is largely based on subjective assessment of the "end-feel" of the joint in response to manually applied forces at different joint orientations. This technical report aims to describe the development of an objective method to examine joints in general, with specific application to the shoulder, and suitable for clinical use. We adapted existing hardware and developed laptop-based software to objectively record the force/displacement behavior of the glenohumeral joint during three common manual joint examination tests with the arm in six positions. An electromagnetic tracking system recorded three-dimensional positions of sensors attached to a clinician examiner and a patient. A hand-held force transducer recorded manually applied translational forces. The force and joint displacement were time-synchronized and the joint stiffness was calculated as a quantitative representation of the joint "end-feel." A methodology and specific system checks were developed to enhance clinical testing reproducibility and precision. The device and testing protocol were tested on 31 subjects (15 with healthy shoulders, and 16 with a variety of shoulder impairments). Results describe the stiffness responses, and demonstrate the feasibility of using the device and methods in clinical settings.

  6. Arterial stiffness, cardiovagal baroreflex sensitivity and postural blood pressure changes in older adults: the Rotterdam Study

    NARCIS (Netherlands)

    Mattace-Raso, Francesco U. S.; van den Meiracker, Anton H.; Bos, Willem Jan; van der Cammen, Tischa J. M.; Westerhof, Berend E.; Elias-Smale, Suzette; Reneman, Robert S.; Hoeks, Arnold P. G.; Hofman, Albert; Witteman, Jacqueline C. M.

    2007-01-01

    Arterial stiffness may be involved in the impairment of the arterial baroreflex. In the present study the associations between arterial stiffness and cardiovagal baroreflex sensitivity (BRS) and between BRS and postural blood pressure (BP) changes were investigated within the framework of the

  7. Flexural Stiffness of Myosin Va Subdomains as Measured from Tethered Particle Motion

    Science.gov (United States)

    Michalek, Arthur J.; Kennedy, Guy G.; Warshaw, David M.; Ali, M. Yusuf

    2015-01-01

    Myosin Va (MyoVa) is a processive molecular motor involved in intracellular cargo transport on the actin cytoskeleton. The motor's processivity and ability to navigate actin intersections are believed to be governed by the stiffness of various parts of the motor's structure. Specifically, changes in calcium may regulate motor processivity by altering the motor's lever arm stiffness and thus its interhead communication. In order to measure the flexural stiffness of MyoVa subdomains, we use tethered particle microscopy, which relates the Brownian motion of fluorescent quantum dots, which are attached to various single- and double-headed MyoVa constructs bound to actin in rigor, to the motor's flexural stiffness. Based on these measurements, the MyoVa lever arm and coiled-coil rod domain have comparable flexural stiffness (0.034 pN/nm). Upon addition of calcium, the lever arm stiffness is reduced 40% as a result of calmodulins potentially dissociating from the lever arm. In addition, the flexural stiffness of the full-length MyoVa construct is an order of magnitude less stiff than both a single lever arm and the coiled-coil rod. This suggests that the MyoVa lever arm-rod junction provides a flexible hinge that would allow the motor to maneuver cargo through the complex intracellular actin network. PMID:26770194

  8. Effects of plyometric and isometric training on muscle and tendon stiffness in vivo.

    Science.gov (United States)

    Kubo, Keitaro; Ishigaki, Tomonobu; Ikebukuro, Toshihiro

    2017-08-01

    The purpose of this study was to compare the effects of plyometric and isometric training on tendon properties during ramp and ballistic contractions and muscle stiffness under passive and active conditions. Eleven subjects completed 12 weeks (3 days/week) of a unilateral training program for the plantar flexors. They performed plyometric training on one side (PLY) and isometric training on the other side (ISO). Active muscle stiffness in the medial gastrocnemius muscle was calculated according to changes in estimated muscle force and fascicle length during fast stretching after submaximal isometric contractions. Passive muscle stiffness was also calculated from estimated passive muscle force and fascicle length during slow passive stretching. Stiffness and hysteresis of tendon structures were measured using ultrasonography during ramp and ballistic contractions. Passive muscle stiffness and tendon hysteresis did not change for PLY or ISO Active muscle stiffness significantly i