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Sample records for boundary stiffness regulates

  1. Extracellular Matrix Stiffness Regulates Osteogenic Differentiation through MAPK Activation.

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    Jun-Ha Hwang

    Full Text Available Mesenchymal stem cell (MSC differentiation is regulated by the extracellular matrix (ECM through activation of intracellular signaling mediators. The stiffness of the ECM was shown to be an important regulatory factor for MSC differentiation, and transcriptional coactivator with PDZ-binding motif (TAZ was identified as an effector protein for MSC differentiation. However, the detailed underlying mechanism regarding the role of ECM stiffness and TAZ in MSC differentiation is not yet fully understood. In this report, we showed that ECM stiffness regulates MSC fate through ERK or JNK activation. Specifically, a stiff hydrogel matrix stimulates osteogenic differentiation concomitant with increased nuclear localization of TAZ, but inhibits adipogenic differentiation. ERK and JNK activity was significantly increased in cells cultured on a stiff hydrogel. TAZ activation was induced by ERK or JNK activation on a stiff hydrogel because exposure to an ERK or JNK inhibitor significantly decreased the nuclear localization of TAZ, indicating that ECM stiffness-induced ERK or JNK activation is important for TAZ-driven osteogenic differentiation. Taken together, these results suggest that ECM stiffness regulates MSC differentiation through ERK or JNK activation.

  2. The focal adhesion: a regulated component of aortic stiffness.

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    Robert J Saphirstein

    Full Text Available Increased aortic stiffness is an acknowledged predictor and cause of cardiovascular disease. The sources and mechanisms of vascular stiffness are not well understood, although the extracellular matrix (ECM has been assumed to be a major component. We tested here the hypothesis that the focal adhesions (FAs connecting the cortical cytoskeleton of vascular smooth muscle cells (VSMCs to the matrix in the aortic wall are a component of aortic stiffness and that this component is dynamically regulated. First, we examined a model system in which magnetic tweezers could be used to monitor cellular cortical stiffness, serum-starved A7r5 aortic smooth muscle cells. Lysophosphatidic acid (LPA, an activator of myosin that increases cell contractility, increased cortical stiffness. A small molecule inhibitor of Src-dependent FA recycling, PP2, was found to significantly inhibit LPA-induced increases in cortical stiffness, as well as tension-induced increases in FA size. To directly test the applicability of these results to force and stiffness development at the level of vascular tissue, we monitored mouse aorta ring stiffness with small sinusoidal length oscillations during agonist-induced contraction. The alpha-agonist phenylephrine, which also increases myosin activation and contractility, increased tissue stress and stiffness in a PP2- and FAK inhibitor 14-attenuated manner. Subsequent phosphotyrosine screening and follow-up with phosphosite-specific antibodies confirmed that the effects of PP2 and FAK inhibitor 14 in vascular tissue involve FA proteins, including FAK, CAS, and paxillin. Thus, in the present study we identify, for the first time, the FA of the VSMC, in particular the FAK-Src signaling complex, as a significant subcellular regulator of aortic stiffness and stress.

  3. Mechanism of regulation of stem cell differentiation by matrix stiffness.

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    Lv, Hongwei; Li, Lisha; Sun, Meiyu; Zhang, Yin; Chen, Li; Rong, Yue; Li, Yulin

    2015-05-27

    Stem cell behaviors are regulated by multiple microenvironmental cues. As an external signal, mechanical stiffness of the extracellular matrix is capable of governing stem cell fate determination, but how this biophysical cue is translated into intracellular signaling remains elusive. Here, we elucidate mechanisms by which stem cells respond to microenvironmental stiffness through the dynamics of the cytoskeletal network, leading to changes in gene expression via biophysical transduction signaling pathways in two-dimensional culture. Furthermore, a putative rapid shift from original mechanosensing to de novo cell-derived matrix sensing in more physiologically relevant three-dimensional culture is pointed out. A comprehensive understanding of stem cell responses to this stimulus is essential for designing biomaterials that mimic the physiological environment and advancing stem cell-based clinical applications for tissue engineering.

  4. Deleterious localized stress fields: the effects of boundaries and stiffness tailoring in anisotropic laminated plates.

    Science.gov (United States)

    Groh, R M J; Weaver, P M

    2016-10-01

    The safe design of primary load-bearing structures requires accurate prediction of stresses, especially in the vicinity of geometric discontinuities where deleterious three-dimensional stress fields can be induced. Even for thin-walled structures significant through-thickness stresses arise at edges and boundaries, and this is especially precarious for laminates of advanced fibre-reinforced composites because through-thickness stresses are the predominant drivers in delamination failure. Here, we use a higher-order equivalent single-layer model derived from the Hellinger-Reissner mixed variational principle to examine boundary layer effects in laminated plates comprising constant-stiffness and variable-stiffness laminae and deforming statically in cylindrical bending. The results show that zigzag deformations, which arise due to layerwise differences in the transverse shear moduli, drive boundary layers towards clamped edges and are therefore critically important in quantifying localized stress gradients. The relative significance of the boundary layer scales with the degree of layerwise anisotropy and the thickness to characteristic length ratio. Finally, we demonstrate that the phenomenon of alternating positive and negative transverse shearing deformation through the thickness of composite laminates, previously only observed at clamped boundaries, can also occur at other locations as a result of smoothly varying the material properties over the in-plane dimensions of the laminate.

  5. Mechanosensitive Kinases Regulate Stiffness-Induced Cardiomyocyte Maturation

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    Young, Jennifer L.; Kretchmer, Kyle; Ondeck, Matthew G.; Zambon, Alexander C.; Engler, Adam J.

    2014-01-01

    Cells secrete and assemble extracellular matrix throughout development, giving rise to time-dependent, tissue-specific stiffness. Mimicking myocardial matrix stiffening, i.e. ~10-fold increase over 1 week, with a hydrogel system enhances myofibrillar organization of embryonic cardiomyocytes compared to static hydrogels, and thus we sought to identify specific mechanosensitive proteins involved. Expression and/or phosphorylation state of 309 unique protein kinases were examined in embryonic cardiomyocytes plated on either dynamically stiffening or static mature myocardial stiffness hydrogels. Gene ontology analysis of these kinases identified cardiogenic pathways that exhibited time-dependent up-regulation on dynamic versus static matrices, including PI3K/AKT and p38 MAPK, while GSK3β, a known antagonist of cardiomyocyte maturation, was down-regulated. Additionally, inhibiting GSK3β on static matrices improved spontaneous contraction and myofibril organization, while inhibiting agonist AKT on dynamic matrices reduced myofibril organization and spontaneous contraction, confirming its role in mechanically-driven maturation. Together, these data indicate that mechanically-driven maturation is at least partially achieved via active mechanosensing at focal adhesions, affecting expression and phosphorylation of a variety of protein kinases important to cardiomyogenesis. PMID:25236849

  6. Matrix stiffness regulates endothelial cell proliferation through septin 9.

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    Yi-Ting Yeh

    Full Text Available Endothelial proliferation, which is an important process in vascular homeostasis, can be regulated by the extracellular microenvironment. In this study we demonstrated that proliferation of endothelial cells (ECs was enhanced on hydrogels with high stiffness (HSG, 21.5 kPa in comparison to those with low stiffness (LSG, 1.72 kPa. ECs on HSG showed markedly prominent stress fibers and a higher RhoA activity than ECs on LSG. Blockade of RhoA attenuated stress fiber formation and proliferation of ECs on HSG, but had little effect on ECs on LSG; enhancement of RhoA had opposite effects. The phosphorylations of Src and Vav2, which are positive RhoA upstream effectors, were higher in ECs on HSG. The inhibition of Src/Vav2 attenuated the HSG-mediated RhoA activation and EC proliferation but exhibited nominal effects on ECs on LSG. Septin 9 (SEPT9, the negative upstream effector for RhoA, was significantly higher in ECs on LSG. The inhibition of SEPT9 increased RhoA activation, Src/Vav2 phosphorylations, and EC proliferation on LSG, but showed minor effects on ECs on HSG. We further demonstrated that the inactivation of integrin α(vβ(3 caused an increase of SEPT9 expression in ECs on HSG to attenuate Src/Vav2 phosphorylations and inhibit RhoA-dependent EC proliferation. These results demonstrate that the SEPT9/Src/Vav2/RhoA pathway constitutes an important molecular mechanism for the mechanical regulation of EC proliferation.

  7. On the Influence of Force Distribution and Boundary Condition on Helical Gear Stiffness

    DEFF Research Database (Denmark)

    Pedersen, Niels Leergaard

    2015-01-01

    The gear stiffness has a direct influence on the dynamic response of transmission systems that include a gear box, the stiffness also controls the load distribution among the teeth in mesh. The stiffness of a gear tooth varies non-linearly as the contact line with the meshing gear tooth moves along...... influence on the stiffness. These two factors are the rim thickness included in the stiffness calculation and the contact zone size. In the contact zone the distribution of the load is also shown to be important. Simple possible simplications in relation to the contact load distribution are presented....... The gear stiffness is found using the elastic energy of the loaded tooth. In the nite element calculation the true gear tooth root profile is applied....

  8. Amputee locomotion: Spring-like leg behavior and stiffness regulation using running-specific prostheses

    Science.gov (United States)

    Hobara, Hiroaki; Baum, Brian S; Kwon, Hyun-Joon; Miller, Ross H; Ogata, Toru; Kim, Yoon Hyuk; Shim, Jae Kun

    2013-01-01

    Carbon fiber running-specific prostheses (RSPs) have allowed individuals with lower extremity amputation (ILEA) to participate in running. It has been established that as running speed increases, leg stiffness (Kleg) remains constant while vertical stiffness (Kvert) increases in able-bodied runners. The Kvert further depends on a combination of the torsional stiffnesses of the joints (joint stiffness; Kjoint) and the touchdown joint angles. Thus, an increased understanding of spring-like leg function and stiffness regulation in ILEA runners using RSPs is expected to aid in prosthetic design and rehabilitation strategies. The aim of this study was to investigate stiffness regulation to various overground running speeds in ILEA wearing RSPs. Eight ILEA performed overground running at a range of running speeds. Kleg, Kvert and Kjoint were calculated from kinetic and kinematic data in both intact and prosthetic limbs. Kleg and Kvert in both limbs remained constant when running speed increased, while intact limbs in ILEA running with RSPs have a higher Kleg and Kvert than residual limbs. There were no significant differences in Kankle, Kknee and touchdown knee angle between the legs at all running speeds. Hip joints in both legs did not demonstrate spring-like function; however, distinct impact peaks were observed only in the intact leg hip extension moment at early stance phase, indicating that differences in Kvert between limbs in ILEA are due to attenuating shock with the hip joint. Therefore, these results suggest that ILEA using RSPs have a different stiffness regulation between the intact and prosthetic limbs during running. PMID:23953671

  9. Amputee locomotion: spring-like leg behavior and stiffness regulation using running-specific prostheses.

    Science.gov (United States)

    Hobara, Hiroaki; Baum, Brian S; Kwon, Hyun-Joon; Miller, Ross H; Ogata, Toru; Kim, Yoon Hyuk; Shim, Jae Kun

    2013-09-27

    Carbon fiber running-specific prostheses (RSPs) have allowed individuals with lower extremity amputation (ILEA) to participate in running. It has been established that as running speed increases, leg stiffness (Kleg) remains constant while vertical stiffness (Kvert) increases in able-bodied runners. The Kvert further depends on a combination of the torsional stiffnesses of the joints (joint stiffness; Kjoint) and the touchdown joint angles. Thus, an increased understanding of spring-like leg function and stiffness regulation in ILEA runners using RSPs is expected to aid in prosthetic design and rehabilitation strategies. The aim of this study was to investigate stiffness regulation to various overground running speeds in ILEA wearing RSPs. Eight ILEA performed overground running at a range of running speeds. Kleg, Kvert and Kjoint were calculated from kinetic and kinematic data in both the intact and prosthetic limbs. Kleg and Kvert in both the limbs remained constant when running speed increased, while intact limbs in ILEA running with RSPs have a higher Kleg and Kvert than residual limbs. There were no significant differences in Kankle, Kknee and touchdown knee angle between the legs at all running speeds. Hip joints in both the legs did not demonstrate spring-like function; however, distinct impact peaks were observed only in the intact leg hip extension moment at the early stance phase, indicating that differences in Kvert between limbs in ILEA are due to attenuating shock with the hip joint. Therefore, these results suggest that ILEA using RSPs has a different stiffness regulation between the intact and prosthetic limbs during running. Copyright © 2013 Elsevier Ltd. All rights reserved.

  10. Past matrix stiffness primes epithelial cells and regulates their future collective migration through a mechanical memory.

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    Nasrollahi, Samila; Walter, Christopher; Loza, Andrew J; Schimizzi, Gregory V; Longmore, Gregory D; Pathak, Amit

    2017-11-01

    During morphogenesis and cancer metastasis, grouped cells migrate through tissues of dissimilar stiffness. Although the influence of matrix stiffness on cellular mechanosensitivity and motility are well-recognized, it remains unknown whether these matrix-dependent cellular features persist after cells move to a new microenvironment. Here, we interrogate whether priming of epithelial cells by a given matrix stiffness influences their future collective migration on a different matrix - a property we refer to as the 'mechanical memory' of migratory cells. To prime cells on a defined matrix and track their collective migration onto an adjoining secondary matrix of dissimilar stiffness, we develop a modular polyacrylamide substrate through step-by-step polymerization of different PA compositions. We report that epithelial cells primed on a stiff matrix migrate faster, display higher actomyosin expression, form larger focal adhesions, and retain nuclear YAP even after arriving onto a soft secondary matrix, as compared to their control behavior on a homogeneously soft matrix. Priming on a soft ECM causes a reverse effect. The depletion of YAP dramatically reduces this memory-dependent migration. Our results present a previously unidentified regulation of mechanosensitive collective cell migration by past matrix stiffness, in which mechanical memory depends on YAP activity. Copyright © 2017 Elsevier Ltd. All rights reserved.

  11. Biophysical Regulation of Cell Behavior—Cross Talk between Substrate Stiffness and Nanotopography

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    Yong Yang

    2017-02-01

    Full Text Available The stiffness and nanotopographical characteristics of the extracellular matrix (ECM influence numerous developmental, physiological, and pathological processes in vivo. These biophysical cues have therefore been applied to modulate almost all aspects of cell behavior, from cell adhesion and spreading to proliferation and differentiation. Delineation of the biophysical modulation of cell behavior is critical to the rational design of new biomaterials, implants, and medical devices. The effects of stiffness and topographical cues on cell behavior have previously been reviewed, respectively; however, the interwoven effects of stiffness and nanotopographical cues on cell behavior have not been well described, despite similarities in phenotypic manifestations. Herein, we first review the effects of substrate stiffness and nanotopography on cell behavior, and then focus on intracellular transmission of the biophysical signals from integrins to nucleus. Attempts are made to connect extracellular regulation of cell behavior with the biophysical cues. We then discuss the challenges in dissecting the biophysical regulation of cell behavior and in translating the mechanistic understanding of these cues to tissue engineering and regenerative medicine.

  12. Nucleoskeletal stiffness regulates stem cell migration and differentiation through lamin A/C.

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    Chen, Liujing; Jiang, Fulin; Qiao, Yini; Li, Hong; Wei, Zhangming; Huang, Tu; Lan, Jingxiang; Xia, Yue; Li, Juan

    2017-12-07

    Stem cell-based tissue engineering provides a prospective strategy to bone tissue repair. Bone tissue repair begins at the recruitment and directional movement of stem cells, and ultimately achieved on the directional differentiation of stem cells. The migration and differentiation of stem cells are regulated by nucleoskeletal stiffness. Mechanical properties of lamin A/C contribute to the nucleoskeletal stiffness and consequently to the regulation of cell migration and differentiation. Nuclear lamin A/C determines cell migration through the regulation of nucleoskeletal stiffness and rigidity and involve in nuclear-cytoskeletal coupling. Moreover, lamin A/C is the essential core module regulating stem cell differentiation. The cells with higher migration ability tend to have enhanced differentiation potential, while the optimum amount of lamin A/C in migration and differentiation of MSCs is in conflict. This contrary phenomenon may be the result of mechanical microenvironment modulation. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

  13. A Stiffness Reduction Method for efficient absorption of waves at boundaries for use in commercial Finite Element codes.

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    Pettit, J R; Walker, A; Cawley, P; Lowe, M J S

    2014-09-01

    Commercially available Finite Element packages are being used increasingly for modelling elastic wave propagation problems. Demand for improved capability has resulted in a drive to maximise the efficiency of the solver whilst maintaining a reliable solution. Modelling waves in unbound elastic media to high levels of accuracy presents a challenge for commercial packages, requiring the removal of unwanted reflections from model boundaries. For time domain explicit solvers, Absorbing Layers by Increasing Damping (ALID) have proven successful because they offer flexible application to modellers and, unlike the Perfectly Matched Layers (PMLs) approach, they are readily implemented in most commercial Finite Element software without requiring access to the source code. However, despite good overall performance, this technique requires the spatial model to extend significantly outside the domain of interest. Here, a Stiffness Reduction Method (SRM) has been developed that operates within a significantly reduced spatial domain. The technique is applied by altering the damping and stiffness matrices of the system, inducing decay of any incident wave. Absorbing region variables are expressed as a function of known model constants, helping to apply the technique to generic elastodynamic problems. The SRM has been shown to perform significantly better than ALID, with results confirmed by both numerical and analytical means. Copyright © 2013 Elsevier B.V. All rights reserved.

  14. UK: disputing boundaries of biotechnology regulation

    OpenAIRE

    Les Levidow; Susan Carr

    1996-01-01

    UK biotechnology regulation has developed ‘precautionary controls’ for GMO releases. Stringent legislation was drafted and eventually implemented by the Department of Environment (DoE). In parallel, the DoE established a broadly-based advisory committee, which included ecologists and an implicit public-interest representation. The committee was assigned the task to advise on the release of all “novel organisms” — a term which implies an analogy between GMOs and non-indigenous organisms. Copyr...

  15. Stiff mutant genes of Phycomyces target turgor pressure and wall mechanical properties to regulate elongation growth rate

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    Joseph K. E. Ortega

    2012-05-01

    Full Text Available Regulation of cell growth is paramount to all living organisms. In plants, algae and fungi, regulation of expansive growth of cells is required for development and morphogenesis. Also, many sensory responses of stage IVb sporangiophores of Phycomyces blakesleeanus are produced by regulating elongation growth rate (growth responses and differential elongation growth rate (tropic responses. Stiff mutant sporangiophores exhibit diminished tropic responses and are found to be defective in at least four genes; madD, madE, madF and madG. Prior experimental research suggests that the defective genes affect growth regulation, but this was not verified. All the growth of the single-celled stalk of the stage IVb sporangiophore occurs in a short region termed the growth zone. Prior experimental and theoretical research indicates that elongation growth rate of the stage IVb sporangiophore can be regulated by controlling the cell wall mechanical properties within the growth zone and the magnitude of the turgor pressure. A quantitative biophysical model for elongation growth rate is required to elucidate the relationship between wall mechanical properties and turgor pressure during growth regulation. In this study, it is hypothesized that the mechanical properties of the wall within the growth zone of stiff mutant sporangiophores are different compared to wild type. A biophysical equation for elongation growth rate is derived for fungal and plant cells with a growth zone. Two strains of stiff mutants are studied, C149 madD120 (- and C216 geo- (-. Experimental results demonstrate that turgor pressure is larger but irreversible deformation rates of the wall within the growth zone and growth zone length are smaller for stiff mutant sporangiophores compared to wild type. These findings explain the diminished tropic responses of the stiff mutant sporangiophores and suggest that the defective genes affect the amount of wall-building material delivered to the inner

  16. Interplay of Matrix Stiffness and Cell-Cell Contact in Regulating Differentiation of Stem Cells.

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    Ye, Kai; Cao, Luping; Li, Shiyu; Yu, Lin; Ding, Jiandong

    2016-08-31

    Stem cells are capable of sensing and responding to the mechanical properties of extracellular matrixes (ECMs). It is well-known that, while osteogenesis is promoted on the stiff matrixes, adipogenesis is enhanced on the soft ones. Herein, we report an "abnormal" tendency of matrix-stiffness-directed stem cell differentiation. Well-defined nanoarrays of cell-adhesive arginine-glycine-aspartate (RGD) peptides were modified onto the surfaces of persistently nonfouling poly(ethylene glycol) (PEG) hydrogels to achieve controlled specific cell adhesion and simultaneously eliminate nonspecific protein adsorption. Mesenchymal stem cells were cultivated on the RGD-nanopatterned PEG hydrogels with the same RGD nanospacing but different hydrogel stiffnesses and incubated in the induction medium to examine the effect of matrix stiffness on osteogenic and adipogenic differentiation extents. When stem cells were kept at a low density during the induction period, the differentiation tendency was consistent with the previous reports in the literature; however, both lineage commitments were favored on the stiff matrices at a high cell density. We interpreted such a complicated stiffness effect at a high cell density in two-dimensional culture as the interplay of matrix stiffness and cell-cell contact. As a result, this study strengthens the essence of the stiffness effect and highlights the combinatory effects of ECM cues and cell cues on stem cell differentiation.

  17. Regulation of matrix stiffness on the epithelial-mesenchymal transition of breast cancer cells under hypoxia environment

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    Lv, Yonggang; Chen, Can; Zhao, Boyuan; Zhang, Xiaomei

    2017-06-01

    Substrate stiffness and hypoxia are associated with tumor development and progression, respectively. However, the synergy of them on the biological behavior of human breast cancer cell is still largely unknown. This study explored how substrate stiffness regulates the cell phenotype, viability, and epithelial-mesenchymal transition (EMT) of human breast cancer cells MCF-7 under hypoxia (1% O2). TRITC-phalloidin staining showed that MCF-7 cells transformed from round to irregular polygon with stiffness increase either in normoxia or hypoxia. While being accompanied with the upward tendency from a 0.5- to a 20-kPa substrate, the percentage of cell apoptosis was significantly higher in hypoxia than that in normoxia, especially on the 20-kPa substrate. Additionally, it was hypoxia, but not normoxia, that promoted the EMT of MCF-7 by upregulating hypoxia-inducible factor-1α (HIF-1α), vimentin, Snail 1, and matrix metalloproteinase 2 (MMP 2) and 9 (MMP 9), and downregulating E-cadherin simultaneously regardless of the change of substrate stiffness. In summary, this study discovered that hypoxia and stiffer substrate (20 kPa) could synergistically induce phenotype change, apoptosis, and EMT of MCF-7 cells. Results of this study have an important significance on further exploring the synergistic effect of stiffness and hypoxia on the EMT of breast cancer cells and its molecular mechanism.

  18. Substrate stiffness and oxygen as regulators of stem cell differentiation during skeletal tissue regeneration: a mechanobiological model.

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    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.

  19. Triceps surae short latency stretch reflexes contribute to ankle stiffness regulation during human running.

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    Neil J Cronin

    Full Text Available During human running, short latency stretch reflexes (SLRs are elicited in the triceps surae muscles, but the function of these responses is still a matter of controversy. As the SLR is primarily mediated by Ia afferent nerve fibres, various methods have been used to examine SLR function by selectively blocking the Ia pathway in seated, standing and walking paradigms, but stretch reflex function has not been examined in detail during running. The purpose of this study was to examine triceps surae SLR function at different running speeds using Achilles tendon vibration to modify SLR size. Ten healthy participants ran on an instrumented treadmill at speeds between 7 and 15 km/h under 2 Achilles tendon vibration conditions: no vibration and 90 Hz vibration. Surface EMG from the triceps surae and tibialis anterior muscles, and 3D lower limb kinematics and ground reaction forces were simultaneously collected. In response to vibration, the SLR was depressed in the triceps surae muscles at all speeds. This coincided with short-lasting yielding at the ankle joint at speeds between 7 and 12 km/h, suggesting that the SLR contributes to muscle stiffness regulation by minimising ankle yielding during the early contact phase of running. Furthermore, at the fastest speed of 15 km/h, the SLR was still depressed by vibration in all muscles but yielding was no longer evident. This finding suggests that the SLR has greater functional importance at slow to intermediate running speeds than at faster speeds.

  20. Regulation of proximal tubular cell differentiation and proliferation in primary culture by matrix stiffness and ECM components.

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    Chen, Wan-Chun; Lin, Hsi-Hui; Tang, Ming-Jer

    2014-09-15

    To explore whether matrix stiffness affects cell differentiation, proliferation, and transforming growth factor (TGF)-β1-induced epithelial-mesenchymal transition (EMT) in primary cultures of mouse proximal tubular epithelial cells (mPTECs), we used a soft matrix made from monomeric collagen type I-coated polyacrylamide gel or matrigel (MG). Both kinds of soft matrix benefited primary mPTECs to retain tubular-like morphology with differentiation and growth arrest and to evade TGF-β1-induced EMT. However, the potent effect of MG on mPTEC differentiation was suppressed by glutaraldehyde-induced cross-linking and subsequently stiffening MG or by an increasing ratio of collagen in the soft mixed gel. Culture media supplemented with MG also helped mPTECs to retain tubular-like morphology and a differentiated phenotype on stiff culture dishes as soft MG did. We further found that the protein level and activity of ERK were scaled with the matrix stiffness. U-0126, a MEK inhibitor, abolished the stiff matrix-induced dedifferentiation and proliferation. These data suggest that the ERK signaling pathway plays a vital role in matrix stiffness-regulated cell growth and differentiation. Taken together, both compliant property and specific MG signals from the matrix are required for the regulation of epithelial differentiation and proliferation. This study provides a basic understanding of how physical and chemical cues derived from the extracellular matrix regulate the physiological function of proximal tubules and the pathological development of renal fibrosis. Copyright © 2014 the American Physiological Society.

  1. 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....

  2. Influence of visual feedback in the regulation of arm stiffness following stroke.

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    Piovesan, Davide; Casadio, Maura; Morasso, Pietro; Giannoni, Psiche

    2011-01-01

    Stroke survivors strongly rely on visual feedback to control their movements, since segmental reflexes are characterized by an inherent hyper-excitability. To test the effect of visual feedback on the modulation of arm stability we estimated the stiffness of the paretic arm in nine stroke survivors during robot mediated therapy, where subjects trained with and without vision. While several studies found a negligible effect in unimpaired individuals, our results highlighted a marked reduction of stroke survivors' arm stiffness in absence of visual feedback.

  3. Seasonal regulation of primary production in eastern boundary upwelling systems

    Science.gov (United States)

    Messié, Monique; Chavez, Francisco P.

    2015-05-01

    The regulation of seasonal satellite-derived primary production (PP) was investigated within a 150 km coastal box in four eastern boundary upwelling systems (EBUS): California, Peru, Northwest Africa and Benguela. The following regulating factors were considered: (1) wind-driven nitrate supply; (2) iron supply inferred from proxies (shelf mud belt width, modeled atmospheric iron deposition, river discharge); (3) temperature; (4) light and (5) physical export consisting of offshore export, eddy-driven and wind-driven subduction. The ratio of potential new production (carbon-equivalent of nitrate supply) to primary production, termed the N-ratio, is shown to be an indicator of PP limitation by nitrate supply (low N-ratios) vs. inhibition by other factors (high N-ratios). The factors regulating PP were assessed by analyzing the N-ratios and computing spatial correlations between PP and each factor each month. The regulation of primary production was found to vary spatially, seasonally and from one EBUS to another. Macronutrient supply is shown to be the dominant regulating factor off Northwest Africa and during some seasons and locations in other systems. Light regulation within the mixed layer occurs in all EBUS in winter but may only inhibit PP (high N-ratios) off Peru and Benguela. Evidence for iron limitation was found in each EBUS (except Northwest Africa) at varying levels and was greatest off Peru during austral winter when iron demand by phytoplankton increases due to low light levels. Rapid offshore advection combined with wind-driven and/or eddy-driven subduction may inhibit PP off California. A simple generalization regarding the regulation of primary production in EBUS is not forthcoming.

  4. 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...

  5. Actin and myosin regulate cytoplasm stiffness in plant cells: a study using optical tweezers

    NARCIS (Netherlands)

    Honing, van der H.S.; Ruijter, de N.C.A.; Emons, A.M.C.; Ketelaar, T.

    2010-01-01

    Here, we produced cytoplasmic protrusions with optical tweezers in mature BY-2 suspension cultured cells to study the parameters involved in the movement of actin filaments during changes in cytoplasmic organization and to determine whether stiffness is an actin-related property of plant cytoplasm.

  6. Loss of muscle strength during sepsis is in part regulated by glucocorticoids and is associated with reduced muscle fiber stiffness

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    Alamdari, Nima; Toraldo, Gianluca; Aversa, Zaira; Smith, Ira; Castillero, Estibaliz; Renaud, Guillaume; Qaisar, Rizwan; Larsson, Lars; Jasuja, Ravi

    2012-01-01

    Sepsis is associated with impaired muscle function but the role of glucocorticoids in sepsis-induced muscle weakness is not known. We tested the role of glucocorticoids in sepsis-induced muscle weakness by treating septic rats with the glucocorticoid receptor antagonist RU38486. In addition, normal rats were treated with dexamethasone to further examine the role of glucocorticoids in the regulation of muscle strength. Sepsis was induced in rats by cecal ligation and puncture, and muscle force generation (peak twitch and tetanic tension) was determined in lower extremity muscles. In other experiments, absolute and specific force as well as stiffness (reflecting the function of actomyosin cross bridges) were determined in isolated skinned muscle fibers from control and septic rats. Sepsis and treatment with dexamethasone resulted in reduced maximal twitch and tetanic force in intact isolated extensor digitorum longus muscles. The absolute and specific maximal force in isolated muscle fibers was reduced during sepsis together with decreased fiber stiffness. These effects of sepsis were blunted (but not abolished) by RU38486. The results suggest that muscle weakness during sepsis is at least in part regulated by glucocorticoids and reflects loss of contractility at the cellular (individual muscle fiber) level. In addition, the results suggest that reduced function of the cross bridges between actin and myosin (documented as reduced muscle fiber stiffness) may be involved in sepsis-induced muscle weakness. An increased understanding of mechanisms involved in loss of muscle strength will be important for the development of new treatment strategies in patients with this debilitating consequence of sepsis. PMID:23019215

  7. Inactive Mineral Filler as a Stiffness Modulus Regulator in Foamed Bitumen-Modified Recycled Base Layers

    Science.gov (United States)

    Buczyński, Przemyslaw; Iwański, Marek

    2017-10-01

    The article presents the results of a cold recycled mix test with a foam bitumen including the addition of the inactive mineral filler as a dust of basalt. Basalt dust was derived from dedusting system by extraction of aggregates in the mine. Assessment of the impact of a basalt dust on the properties of a recycled base layer was carried out in terms of the amount of mineral filler (basalt) in the composition of the mineral mixture. This experiment involved a dosing of mineral filler in range from 5 to 20% with steps of 7.5% in the mineral mixture composition. The foamed bitumen was performed at optimum foaming process settings (ie. bitumen temperature, air pressure) and at 2.5% of the water content. The amount of a hydraulic binder as a Portland cement was 2.0%. The evaluation of rheological properties allowed to determine whether the addition of inactive mineral fillers can act as a stiffness modulus controller in the recycled base layer. The analysis of the rheological properties of a recycled base layer in terms of the amount of inactive fillers was performed in accordance with given standard EN 12697-26 Annex D. The study was carried out according to the direct tension-compression test methodology on cylindrical samples. The sample was subjected to the oscillatory sinusoidal strain ε0 allow to conclude that the use of an inactive filler can reduce the stiffness of an appropriate designed mixes of the cold recycled foundation. In addition, the analysis of the relation E‧-E″ showed a similar behaviour of a recycled base, regardless of the amount of inactive fillers in the mix composition, at high temperatures/high frequency of induced load.

  8. Aortic and carotid arterial stiffness and epigenetic regulator gene expression changes precede blood pressure rise in stroke-prone Dahl salt-sensitive hypertensive rats.

    Directory of Open Access Journals (Sweden)

    Victoria L Herrera

    Full Text Available Multiple clinical studies show that arterial stiffness, measured as pulse wave velocity (PWV, precedes hypertension and is an independent predictor of hypertension end organ diseases including stroke, cardiovascular disease and chronic kidney disease. Risk factor studies for arterial stiffness implicate age, hypertension and sodium. However, causal mechanisms linking risk factor to arterial stiffness remain to be elucidated. Here, we studied the causal relationship of arterial stiffness and hypertension in the Na-induced, stroke-prone Dahl salt-sensitive (S hypertensive rat model, and analyzed putative molecular mechanisms. Stroke-prone and non-stroke-prone male and female rats were studied at 3- and 6-weeks of age for arterial stiffness (PWV, strain, blood pressure, vessel wall histology, and gene expression changes. Studies showed that increased left carotid and aortic arterial stiffness preceded hypertension, pulse pressure widening, and structural wall changes at the 6-week time-point. Instead, differential gene induction was detected implicating molecular-functional changes in extracellular matrix (ECM structural constituents, modifiers, cell adhesion, and matricellular proteins, as well as in endothelial function, apoptosis balance, and epigenetic regulators. Immunostaining testing histone modifiers Ep300, HDAC3, and PRMT5 levels confirmed carotid artery-upregulation in all three layers: endothelial, smooth muscle and adventitial cells. Our study recapitulates observations in humans that given salt-sensitivity, increased Na-intake induced arterial stiffness before hypertension, increased pulse pressure, and structural vessel wall changes. Differential gene expression changes associated with arterial stiffness suggest a molecular mechanism linking sodium to full-vessel wall response affecting gene-networks involved in vascular ECM structure-function, apoptosis balance, and epigenetic regulation.

  9. miR-181b regulates vascular stiffness age dependently in part by regulating TGF-β signaling.

    Directory of Open Access Journals (Sweden)

    Daijiro Hori

    Full Text Available Endothelial dysfunction and arterial stiffening play major roles in cardiovascular diseases. The critical role for the miR-181 family in vascular inflammation has been documented. Here we tested whether the miR-181 family can influence the pathogenesis of hypertension and vascular stiffening.qPCR data showed a significant decrease in miR-181b expression in the aorta of the older mice. Eight miR-181a1/b1-/- mice and wild types (C57BL6J:WT were followed weekly for pulse wave velocity (PWV and blood pressure measurements. After 20 weeks, the mice were tested for endothelial function and aortic modulus. There was a progressive increase in PWV and higher systolic blood pressure in miR-181a1/b1-/- mice compared with WTs. At 21 weeks, aortic modulus was significantly greater in the miR-181a1/b1-/- group, and serum TGF-β was found to be elevated at this time. A luciferase reporter assay confirmed miR-181b targets TGF-βi (TGF-β induced in the aortic VSMCs. In contrast, wire myography revealed unaltered endothelial function along with higher nitric oxide production in the miR-181a1/b1-/- group. Cultured VECs and VSMCs from the mouse aorta showed more secreted TGF-β in VSMCs of the miR-181a1/b1-/- group; whereas, no change was observed from VECs. Circulating levels of angiotensin II were similar in both groups. Treatment with losartan (0.6 g/L prevented the increase in PWV, blood pressure, and vascular stiffness in miR-181a1/b1-/- mice. Immunohistochemistry and western blot for p-SMAD2/3 validated the inhibitory effect of losartan on TGF-β signaling in miR-181a1/b1-/- mice.Decreased miR-181b with aging plays a critical role in ECM remodeling by removing the brake on the TGF-β, pSMAD2/3 pathway.

  10. Biomaterial stiffness determines stem cell fate.

    Science.gov (United States)

    Lv, Hongwei; Wang, Heping; Zhang, Zhijun; Yang, Wang; Liu, Wenbin; Li, Yulin; Li, Lisha

    2017-06-01

    Stem cells have potential to develop into numerous cell types, thus they are good cell source for tissue engineering. As an external physical signal, material stiffness is capable of regulating stem cell fate. Biomaterial stiffness is an important parameter in tissue engineering. We summarize main measurements of material stiffness under different condition, then list and compare three main methods of controlling stiffness (material amount, crosslinking density and photopolymeriztion time) which interplay with one another and correlate with stiffness positively, and current advances in effects of biomaterial stiffness on stem cell fate. We discuss the unsolved problems and future directions of biomaterial stiffness in tissue engineering. Copyright © 2017. Published by Elsevier Inc.

  11. Elasticity of Stiff Biopolymers

    OpenAIRE

    Ghosh, Abhijit; Samuel, Joseph; Sinha, Supurna

    2007-01-01

    We present a statistical mechanical study of stiff polymers, motivated by experiments on actin filaments and the considerable current interest in polymer networks. We obtain simple, approximate analytical forms for the force-extension relations and compare these with numerical treatments. We note the important role of boundary conditions in determining force-extension relations. The theoretical predictions presented here can be tested against single molecule experiments on neurofilaments and ...

  12. Regulating time commitments in healthcare organizations: managers' boundary approaches at work and in life.

    Science.gov (United States)

    Tengelin, Ellinor; Arman, Rebecka; Wikström, Ewa; Dellve, Lotta

    2011-01-01

    The purpose of this paper is to explore managers' boundary setting in order to better understand their handling of time commitment to work activities, stress, and recovery during everyday work and at home. The paper has qualitatively-driven, mixed method design including observational data, individual interviews, and focus group discussions. Data were analyzed according to Charmaz' view on constructivist grounded theory. A first step in boundary setting was to recognize areas with conflicting expectations and inexhaustible needs. Second, strategies were formed through negotiating the handling of managerial time commitment, resulting in boundary-setting, but also boundary-dissolving, approaches. The continuous process of individual recognition and negotiation could work as a form of proactive coping, provided that it was acknowledged and questioned. These findings suggest that recognition of perceived boundary challenges can affect stress and coping. It would therefore be interesting to more accurately assess stress, coping, and health status among managers by means of other methodologies (e.g. physiological assessments). In regulating managers' work assignments, work-related stress and recovery, it seems important to: acknowledge boundary work as an ever-present dilemma requiring continuous negotiation; and encourage individuals and organizations to recognize conflicting perspectives inherent in the leadership assignment, in order to decrease harmful negotiations between them. Such awareness would benefit more sustainable management of healthcare practice. This paper highlights how managers can handle ever-present boundary dilemmas in the healthcare sector by regulating their time commitments in various ways.

  13. THE DIFFERENTIAL REGULATION OF CELL MOTILE ACTIVITY THROUGH MATRIX STIFFNESS AND POROSITY IN THREE DIMENSIONAL COLLAGEN MATRICES

    Science.gov (United States)

    Miron-Mendoza, Miguel; Seemann, Joachim; Grinnell, Frederick

    2010-01-01

    In three dimensional collagen matrices, cell motile activity results in collagen translocation, cell spreading and cell migration. Cells can penetrate into the matrix as well as spread and migrate along its surface. In the current studies, we quantitatively characterize collagen translocation, cell spreading and cell migration in relationship to collagen matrix stiffness and porosity. Collagen matrices prepared with 1 to 4 mg/ml collagen exhibited matrix stiffness (storage modulus measured by oscillating rheometry) increasing from 4 to 60 Pa and matrix porosity (measured by scanning electron microscopy) decreasing from 4 to 1 μm2. Over this collagen concentration range, the consequences of cell motile activity changed markedly. As collagen concentration increased, cells no longer were able to cause translocation of collagen fibrils. Cell migration increased and cell spreading changed from dendritic to more flattened and polarized morphology depending on location of cells within or on the surface of the matrix. Collagen translocation appeared to depend primarily on matrix stiffness, whereas cell spreading and migration were less dependent on matrix stiffness and more dependent on collagen matrix porosity. PMID:20537378

  14. Uncertainty quantification of inflow boundary condition and proximal arterial stiffness-coupled effect on pulse wave propagation in a vascular network.

    Science.gov (United States)

    Brault, Antoine; Dumas, Laurent; Lucor, Didier

    2017-10-01

    This work aims at quantifying the effect of inherent uncertainties from cardiac output on the sensitivity of a human compliant arterial network response based on stochastic simulations of a reduced-order pulse wave propagation model. A simple pulsatile output form is used to reproduce the most relevant cardiac features with a minimum number of parameters associated with left ventricle dynamics. Another source of significant uncertainty is the spatial heterogeneity of the aortic compliance, which plays a key role in the propagation and damping of pulse waves generated at each cardiac cycle. A continuous representation of the aortic stiffness in the form of a generic random field of prescribed spatial correlation is then considered. Making use of a stochastic sparse pseudospectral method, we investigate the sensitivity of the pulse pressure and waves reflection magnitude over the arterial tree with respect to the different model uncertainties. Results indicate that uncertainties related to the shape and magnitude of the prescribed inlet flow in the proximal aorta can lead to potent variation of both the mean value and standard deviation of blood flow velocity and pressure dynamics due to the interaction of different wave propagation and reflection features. Lack of accurate knowledge in the stiffness properties of the aorta, resulting in uncertainty in the pulse wave velocity in that region, strongly modifies the statistical response, with a global increase in the variability of the quantities of interest and a spatial redistribution of the regions of higher sensitivity. These results will provide some guidance in clinical data acquisition and future coupling of arterial pulse wave propagation reduced-order model with more complex beating heart models. Copyright © 2016 John Wiley & Sons, Ltd.

  15. Keratin 8/18 regulation of cell stiffness-extracellular matrix interplay through modulation of Rho-mediated actin cytoskeleton dynamics.

    Directory of Open Access Journals (Sweden)

    François Bordeleau

    Full Text Available Cell mechanical activity generated from the interplay between the extracellular matrix (ECM and the actin cytoskeleton is essential for the regulation of cell adhesion, spreading and migration during normal and cancer development. Keratins are the intermediate filament (IF proteins of epithelial cells, expressed as pairs in a lineage/differentiation manner. Hepatic epithelial cell IFs are made solely of keratins 8/18 (K8/K18, hallmarks of all simple epithelia. Notably, our recent work on these epithelial cells has revealed a key regulatory function for K8/K18 IFs in adhesion/migration, through modulation of integrin interactions with ECM, actin adaptors and signaling molecules at focal adhesions. Here, using K8-knockdown rat H4 hepatoma cells and their K8/K18-containing counterparts seeded on fibronectin-coated substrata of different rigidities, we show that the K8/K18 IF-lacking cells lose their ability to spread and exhibit an altered actin fiber organization, upon seeding on a low-rigidity substratum. We also demonstrate a concomitant reduction in local cell stiffness at focal adhesions generated by fibronectin-coated microbeads attached to the dorsal cell surface. In addition, we find that this K8/K18 IF modulation of cell stiffness and actin fiber organization occurs through RhoA-ROCK signaling. Together, the results uncover a K8/K18 IF contribution to the cell stiffness-ECM rigidity interplay through a modulation of Rho-dependent actin organization and dynamics in simple epithelial cells.

  16. 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.

  17. Activation of Yes-Associated Protein in Low-Grade Meningiomas Is Regulated by Merlin, Cell Density, and Extracellular Matrix Stiffness.

    Science.gov (United States)

    Tanahashi, Kuniaki; Natsume, Atsushi; Ohka, Fumiharu; Motomura, Kazuya; Alim, Adiljan; Tanaka, Ichidai; Senga, Takeshi; Harada, Ichiro; Fukuyama, Ryuichi; Sumiyoshi, Naoyuki; Sekido, Yoshitaka; Wakabayashi, Toshihiko

    2015-07-01

    The NF2 gene product Merlin is a protein containing ezrin, radixin, and moesin domains; it is a member of the 4.1 protein superfamily associated with the membrane cytoskeleton and also interacts with cell surface molecules. The mammalian Hippo cascade, a downstream signaling cascade of merlin, inactivates the Yes-associated protein (YAP). Yes-associated protein is activated by loss of the NF2 gene and functions as an oncogene in meningioma cells; however, the factors controlling YAP expression, phosphorylation, and subcellular localization in meningiomas have not been fully elucidated. Here, we demonstrate that merlin expression is heterogeneous in 1 NF2 gene-negative and 3 NF2 gene-positive World Health Organization grade I meningiomas. In the NF2 gene-positive meningiomas, regions with low levels of merlin (tumor rims) had greater numbers of cells with nuclear YAP versus regions with high merlin levels (tumor cores). Merlin expression and YAP phosphorylation were also affected by cell density in the IOMM-Lee and HKBMM human meningioma cell lines; nuclear localization of YAP was regulated by cell density and extracellular matrix (ECM) stiffness in IOMM-Lee cells. These results suggest that cell density and ECM stiffness may contribute to the heterogeneous loss of merlin and increased nuclear YAP expression in human meningiomas.

  18. A comparison of the regulation of health professional boundaries across OECD countries

    National Research Council Canada - National Science Library

    Bourgeault, Ivy Lynn; Grignon, Michel

    2013-01-01

    .... Our case studies focus on the inter-professional boundary negotiation between medicine and nursing and the intraprofessional boundary negotiation between domestic and internationally trained physicians...

  19. 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)

  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. 'Stiff-person'-syndroom

    NARCIS (Netherlands)

    Vogels, R. L.; van Orshoven, N. P.; de Koning-Tijssen, M. A.; Wouda, E. J.

    2003-01-01

    In two patients, a man aged 54 years and a woman aged 49 years, stiff-person syndrome was diagnosed. This is a rare disorder of the central nervous system, with signs of an autoimmune pathogenesis. Patients present with pain and stiffness of the lower back, a complaint that is regularly seen in

  2. Vibration Control via Stiffness Switching of Magnetostrictive Transducers

    Science.gov (United States)

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

    2016-01-01

    This paper presents a computational study of structural vibration control that is realized by switching a magnetostrictive transducer between high and low stiffness states. Switching is accomplished by either changing the applied magnetic field with a voltage excitation or changing the shunt impedance on the transducer's coil (i.e., the magnetostrictive material's magnetic boundary condition). Switched-stiffness vibration control is simulated using a lumped mass supported by a damper and the magnetostrictive transducer (mount), which is represented by a nonlinear, electromechanical model. Free vibration of the mass is calculated while varying the mount's stiffness according to a reference switched-stiffness vibration control law. The results reveal that switching the magnetic field produces the desired change in stiffness, but also an undesired actuation force that can significantly degrade the vibration control. Hence, a modified switched-stiffness control law that accounts for the actuation force is proposed and implemented for voltage-controlled stiffness switching. The influence of the magnetomechanical bias condition is also discussed. Voltage-controlled stiffness switching is found to introduce damping equivalent to a viscous damping factor up to about 0.25; this is shown to primarily result from active vibration reduction caused by the actuation force. The merit of magnetostrictive switched-stiffness vibration control is then quantified by comparing the results of voltage- and shunt-controlled stiffness switching to the performance of optimal magnetostrictive shunt damping.

  3. Macroscopic stiffness of breast tumors predicts metastasis.

    Science.gov (United States)

    Fenner, Joseph; Stacer, Amanda C; Winterroth, Frank; Johnson, Timothy D; Luker, Kathryn E; Luker, Gary D

    2014-07-01

    Mechanical properties of tumors differ substantially from normal cells and tissues. Changes in stiffness or elasticity regulate pro-metastatic behaviors of cancer cells, but effects have been documented predominantly in isolated cells or in vitro cell culture systems. To directly link relative stiffness of tumors to cancer progression, we combined a mouse model of metastatic breast cancer with ex vivo measurements of bulk moduli of freshly excised, intact tumors. We found a high, inverse correlation between bulk modulus of resected tumors and subsequent local recurrence and metastasis. More compliant tumors were associated with more frequent, larger local recurrences and more extensive metastases than mice with relatively stiff tumors. We found that collagen content of resected tumors correlated with bulk modulus values. These data establish that relative differences in tumor stiffness correspond with tumor progression and metastasis, supporting further testing and development of tumor compliance as a prognostic biomarker in breast cancer.

  4. Line tension at lipid phase boundaries regulates formation of membrane vesicles in living cells

    DEFF Research Database (Denmark)

    Vind-Kezunovic, Dina; Helix Nielsen, Claus; Wojewodzka, Urszula

    2008-01-01

    on these observations we describe the energetic requirements for plasma membrane vesiculation. We propose that the decrease in total 'L-o/L-d' boundary line tension arising from the coalescence of smaller L-d-like domains makes it energetically favourable for L-d-like domains to bend from flat mu m-sized surfaces...... to cap-like budding vesicles. Thus living cells may utilize membrane line tension energies as a control mechanism of exocytic events....

  5. Cholesterol Regulates Syntaxin 6 Trafficking at trans-Golgi Network Endosomal Boundaries

    Directory of Open Access Journals (Sweden)

    Meritxell Reverter

    2014-05-01

    Full Text Available Inhibition of cholesterol export from late endosomes causes cellular cholesterol imbalance, including cholesterol depletion in the trans-Golgi network (TGN. Here, using Chinese hamster ovary (CHO Niemann-Pick type C1 (NPC1 mutant cell lines and human NPC1 mutant fibroblasts, we show that altered cholesterol levels at the TGN/endosome boundaries trigger Syntaxin 6 (Stx6 accumulation into VAMP3, transferrin, and Rab11-positive recycling endosomes (REs. This increases Stx6/VAMP3 interaction and interferes with the recycling of αVβ3 and α5β1 integrins and cell migration, possibly in a Stx6-dependent manner. In NPC1 mutant cells, restoration of cholesterol levels in the TGN, but not inhibition of VAMP3, restores the steady-state localization of Stx6 in the TGN. Furthermore, elevation of RE cholesterol is associated with increased amounts of Stx6 in RE. Hence, the fine-tuning of cholesterol levels at the TGN-RE boundaries together with a subset of cholesterol-sensitive SNARE proteins may play a regulatory role in cell migration and invasion.

  6. Line tension at lipid phase boundaries regulates formation of membrane vesicles in living cells

    DEFF Research Database (Denmark)

    Vind-Kezunovic, D.; Nielsen, C.H.; Wojewodzka, U.

    2008-01-01

    Ternary lipid compositions in model membranes segregate into large-scale liquid-ordered (L(o)) and liquid-disordered (L(d)) phases. Here, we show mum-sized lipid domain separation leading to vesicle formation in unperturbed human HaCaT keratinocytes. Budding vesicles in the apical portion of the ...... mum-sized surfaces to cap-like budding vesicles. Thus living cells may utilize membrane line tension energies as a control mechanism of exocytic events Udgivelsesdato: 2008/11....... Based on these observations we describe the energetic requirements for plasma membrane vesiculation. We propose that the decrease in total 'L(o)/L(d)' boundary line tension arising from the coalescence of smaller L(d)-like domains makes it energetically favourable for L(d)-like domains to bend from flat...

  7. China’s New Urban Space Regulation Policies: A Study of Urban Development Boundary Delineations

    Directory of Open Access Journals (Sweden)

    Zhuzhou Zhuang

    2016-12-01

    Full Text Available China’s rapid urbanisation has led to ecological deterioration and reduced the land available for agricultural production. The purpose of this study is to develop an urban development boundary delineation (UDBD model using the high-tech manufacturing area of Xinbei in the District of Changzhou as a case study, and by applying remote sensing, GIS, and other technologies. China’s UDBD policies are reviewed, spatiotemporal changes since 1985 are documented, and future expansion is modelled to 2020. The simulated urban-growth patterns are analysed in relation to China’s policies for farmland preservation, ecological redlines protection areas, and housing developments. The UDBD model developed in this study satisfies regional farmland and ecological space protection constraints, while being consistent with urban development strategies. This study provides theoretical references and technological support for the implementation of land management policies that will optimize land allocations for urban growth, agriculture, and ecological protection.

  8. Collaborative jurisdiction in the regulation of electric utilities: A new look at jurisdictional boundaries

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1991-12-31

    This conference is one of several activities initiated by FERC, DOE and NARUC to improve the dialogue between Federal and State regulators and policymakers. I am pleased to be here to participate in this conference and to address, with you, electricity issues of truly national significance. I would like to commend Ashley Brown and the NARUC Electricity Committee for its foresight in devising a conference on these issues at this critical juncture in the regulation of the electric utility industry. I also would like to commend Chairman Allday and the FERC for their efforts to improve communication between Federal and State electricity regulators; both through FERC`s Public Conference on Electricity Issues that was held last June, and through the FERC/NARUC workshops that are scheduled to follow this conference. These collaborative efforts are important and necessary steps in addressing successfully the many issues facing the electric utility industry those who regulate it, and those who depend upon it - in other words, about everyone.

  9. 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.

  10. Vibration Control via Stiffness Switching of Magnetostrictive Transducers

    Science.gov (United States)

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

    2016-01-01

    In this paper, a computational study is presented of structural vibration control that is realized by switching a magnetostrictive transducer between high and low stiffness states. Switching is accomplished by either changing the applied magnetic field with a voltage excitation or changing the shunt impedance on the transducer's coil (i.e., the magnetostrictive material's magnetic boundary condition). Switched-stiffness vibration control is simulated using a lumped mass supported by a damper and the magnetostrictive transducer (mount), which is represented by a nonlinear, electromechanical model. Free vibration of the mass is calculated while varying the mount's stiffness according to a reference switched-stiffness vibration control law. The results reveal that switching the magnetic field produces the desired change in stiffness, but also an undesired actuation force that can significantly degrade the vibration control. Hence, a modified switched-stiffness control law that accounts for the actuation force is proposed and implemented for voltage-controlled stiffness switching. The influence of the magneto-mechanical bias condition is also discussed. Voltage-controlled stiffness switching is found to introduce damping equivalent to a viscous damping factor up to about 0.13; this is shown to primarily result from active vibration reduction caused by the actuation force. The merit of magnetostrictive switched-stiffness vibration control is then quantified by comparing the results of voltage- and shunt-controlled stiffness switching to the performance of optimal magnetostrictive shunt damping. For the cases considered, optimal resistive shunt damping performed considerably better than both voltage- and shunt-controlled stiffness switching.

  11. Procedural justice and social regulation across group boundaries: does subgroup identity undermine relationship-based governance?

    Science.gov (United States)

    Huo, Yuen J

    2003-03-01

    The relational model of authority suggests that people are inclined to accept the decisions of ethnic outgroup authorities when they identify with a superordinate category they share with the authority, and when the authority satisfies their relational justice concerns. Using responses from a random sample of African Americans, Latinos, and Whites about their cross-ethnic interactions with legal authorities, the findings indicated that those who are highly identified with the superordinate category of America indicate greater reliance on relational concerns and less on instrumental concerns when evaluating the authority's decision. In contrast, identification with one's ethnic subgroup did not moderate the linkage between relational concerns and acceptance. Across all ethnic groups, there were positive rather than negative correlations between measures of American and ethnic identity. Together, these findings indicate that subgroup identity does not undermine the relational basis of social regulation and that relationship-based governance is compatible with multiculturalism.

  12. 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.

  13. Members of the LATERAL ORGAN BOUNDARIES DOMAIN transcription factor family are involved in the regulation of secondary growth in Populus.

    Science.gov (United States)

    Yordanov, Yordan S; Regan, Sharon; Busov, Victor

    2010-11-01

    Regulation of secondary (woody) growth is of substantial economic and environmental interest but is poorly understood. We identified and subsequently characterized an activation-tagged poplar (Populus tremula × Populus alba) mutant with enhanced woody growth and changes in bark texture caused primarily by increased secondary phloem production. Molecular characterization of the mutation through positioning of the tag and retransformation experiments shows that the phenotype is conditioned by activation of an uncharacterized gene that encodes a novel member of the LATERAL ORGAN BOUNDARIES DOMAIN (LBD) family of transcription factors. Homology analysis showed highest similarity to an uncharacterized LBD1 gene from Arabidopsis thaliana, and we consequently named it Populus tremula × Populus alba (Pta) LBD1. Dominant-negative suppression of Pta LBD1 via translational fusion with the repressor SRDX domain caused decreased diameter growth and suppressed and highly irregular phloem development. In wild-type plants, LBD1 was most highly expressed in the phloem and cambial zone. Two key Class I KNOTTED1-like homeobox genes that promote meristem identity in the cambium were downregulated, while an Altered Phloem Development gene that is known to promote phloem differentiation was upregulated in the mutant. A set of four LBD genes, including the LBD1 gene, was predominantly expressed in wood-forming tissues, suggesting a broader regulatory role of these transcription factors during secondary woody growth in poplar.

  14. 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\\

  15. 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...

  16. 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-β2 (TGF-β2), 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.

  17. Limit cycles and stiffness control with variable stiffness actuators

    NARCIS (Netherlands)

    Carloni, Raffaella; Marconi, Lorenzo

    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

  18. The posttraumatic stiff elbow.

    Science.gov (United States)

    Morrey, Bernard F

    2005-02-01

    The development of joint contracture is a well-recognized complication of elbow injury. Precise causes of the propensity of this joint for ankylosis are understood poorly. Yet, treatment is emerging and therefore the indications and willingness on the part of the surgeon to address this problem is improving. Limited open procedures have emerged during the past several years that are safe and effective by improving arcs of motion of 50-70 degrees in approximately 80-90% of patients. For severe injuries that involve the articular surface, interposition arthroplasty is less documented but has been shown to be effective but constitutes one of the most challenging technical procedures. Joint replacement arthroplasty generally should not be considered as a treatment for posttraumatic stiffness unless the patient is older than 65 years. The experience with this procedure indicates that with linked semiconstrained implants, approximately 80% of patients will achieve a near functional arc of motion. Arthroscopic intervention shows the greatest activity of investigation and clinical expansion. The learning curve is defined by a concern of complications to the neural structures and the fear of this complication has limited the application but the emerging documentation of the safeness of this option also has been associated with improved effectiveness. Therefore, arthroscopic intervention for the stiff elbow, particularly those with soft tissue extrinsic involvement, is emerging as the treatment of choice in many instances. The investigation regarding the medical treatment of altering the tendency of the soft tissue to go through such intense contracture is in its infancy but suggests that this could be a long-term solution at least for many patients.

  19. 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

  20. 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)

  1. Morphological Computation of Haptic Perception of a Controllable Stiffness Probe.

    Directory of Open Access Journals (Sweden)

    Nantachai Sornkarn

    Full Text Available When people are asked to palpate a novel soft object to discern its physical properties such as texture, elasticity, and even non-homogeneity, they not only regulate probing behaviors, but also the co-contraction level of antagonistic muscles to control the mechanical impedance of fingers. It is suspected that such behavior tries to enhance haptic perception by regulating the function of mechanoreceptors at different depths of the fingertips and proprioceptive sensors such as tendon and spindle sensors located in muscles. In this paper, we designed and fabricated a novel two-degree of freedom variable stiffness indentation probe to investigate whether the regulation of internal stiffness, indentation, and probe sweeping velocity (PSV variables affect the accuracy of the depth estimation of stiff inclusions in an artificial silicon phantom using information gain metrics. Our experimental results provide new insights into not only the biological phenomena of haptic perception but also new opportunities to design and control soft robotic probes.

  2. HIV infection and aortic stiffness.

    Science.gov (United States)

    Leite, Luisa Helena Maia; Cohen, Ariel; Boccara, Franck

    People living with human immunodeficiency virus (HIV) infection and receiving antiretroviral therapy now have the same life expectancy as the general population. However, they have a higher risk of atherosclerotic cardiovascular events because of a complex and polyfactorial vasculopathy, combining the effects of antiretroviral therapy, the HIV virus itself, immune activation, chronic inflammation and metabolic disturbances. Whether people living with HIV infection experience increased vascular aging compared with the general population remains controversial. To summarize current knowledge of the association between HIV infection and aortic stiffness as a marker of vascular aging. This review included 18 clinical studies in adult populations, published between 2009 and 2016, and identified on PubMed/MEDLINE or other databases. Search terms were aortic stiffness, arterial stiffness, vascular aging, pulse wave velocity and HIV. All 18 studies were observational, and compared groups infected (HIV+) and not infected (HIV-) with HIV. Ten studies (55%) reported no significant differences in aortic stiffness between HIV+ groups and age-matched HIV- control groups. The main reported determinants of aortic stiffness were age, blood pressure, smoking, metabolic syndrome and HIV-related variables, including CD4/CD8 ratio, current T-CD4 count < 200/mm 3 and nadir T-CD4+ count < 200/mm 3 . We found discordant results regarding whether HIV+ patients had increased aortic stiffness compared with HIV- controls. However, HIV-related conditions were associated with vascular health. This association has been confirmed in recent prospective studies. There is emerging evidence that HIV itself and immune activity affect vascular health and the large arteries. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

  3. Lase Ultrasonic Web Stiffness tester

    Energy Technology Data Exchange (ETDEWEB)

    Tim Patterson, Ph.D., IPST at Ga Tech

    2009-01-12

    The objective is to provide a sensor that uses non-contact, laser ultrasonics to measure the stiffness of paper during the manufacturing process. This will allow the manufacturer to adjust the production process in real time, increase filler content, modify fiber refining and as result produce a quality product using less energy. The sensor operates by moving back and forth across the paper web, at pre-selected locations firing a laser at the sheet, measuring the out-of-plane velocity of the sheet then using that measurement to calculate sheet stiffness.

  4. 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.

  5. Quasi-stationary mechanics of elastic continua with bending stiffness wrapping on a pulley system

    Science.gov (United States)

    Kaczmarczyk, S.; Mirhadizadeh, S.

    2016-05-01

    In many engineering applications elastic continua such as ropes and belts often are subject to bending when they pass over pulleys / sheaves. In this paper the quasi-stationary mechanics of a cable-pulley system is studied. The cable is modelled as a moving Euler- Bernoulli beam. The distribution of tension is non-uniform along its span and due to the bending stiffness the contact points at the pulley-beam boundaries are not unknown. The system is described by a set of nonlinear ordinary differential equations with undetermined boundary conditions. The resulting nonlinear Boundary Value Problem (BVP) with unknown boundaries is solved by converting the problem into the ‘standard’ form defined over a fixed interval. Numerical results obtained for a range of typical configurations with relevant boundary conditions applied demonstrate that due to the effects of bending stiffness the angels of wrap are reduced and the span tensions are increased.

  6. [From stiff man syndrome to stiff person spectrum disorders].

    Science.gov (United States)

    Meinck, H-M; Balint, B

    2018-02-01

    The identification of new variants of the stiff man syndrome (SMS) and of new, probably pathogenic neuronal autoantibodies has led to the concept of stiff man (or person) spectrum disorders (SPSD). This is an expanding group of rare chronic autoimmune inflammatory diseases of the central nervous system (CNS) that have in common the main symptoms of fluctuating rigidity and spasms with pronounced stimulus sensitivity. These core symptoms are mandatory and can be accompanied by a wide variety of other neurological signs. The SPSDs are associated with autoantibodies directed against neuronal proteins that attenuate excitability. Neither clinical phenotypes nor the course of SPSD correlate closely with the antibody status. The treatment of these diseases aims at maintaining mobility and is pragmatically oriented to the degree of impediment and comprises antispastic, anticonvulsant and immunomodulating or immunosuppressive medication strategies.

  7. Energy-Efficient Variable Stiffness Actuators

    NARCIS (Netherlands)

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

    2011-01-01

    Variable stiffness actuators are a particular class of actuators that is characterized by the property that the apparent output stiffness can be changed independent of the output position. To achieve this, variable stiffness actuators consist of a number of elastic elements and a number of actuated

  8. 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

  9. Ground boundaries

    Science.gov (United States)

    Balluffi, R. W.; Bristowe, P. D.

    The present document is a progress report describing the work accomplished on the study of grain boundaries in Ag, Au, Ni, Si, and Ge. Research was focused on the following four major efforts: study of the atomic structure of grain boundaries by means of x-ray diffraction, transmission electron microscopy and computer modeling; grain boundary migration; short-circuit diffusion along grain boundaries; and development of Thin-Film Deposition/Bonding Apparatus for the manufacture of high purity bicrystals.

  10. Negative stiffness in gear contact

    Directory of Open Access Journals (Sweden)

    Půst L.

    2015-12-01

    Full Text Available The tooth contact stiffness is very often included in dynamic mathematical models of gear drives. It is an important value for calculation of torsion eigenfrequencies as well as the dynamic properties of the whole transmission systems. Planetary gear drives have several advantages over simple parallel axis gears, especially due to theirs compact design and great torque-to-weight ratio caused by multiple parallel paths. However, the dimensional or mounting errors can cause that some planets have the tendency to take more load than the others. One of the ways how to improve load sharing is the application of flexible planetary pins or by using a free central wheel. However in such cases, the wheels motion is defined in one rotation coordinate and two translation coordinates — tangential and radial. The reaction force at radial change of axis distance is usually neglected. The focus of this contribution is to derive the stiffness of this radial connection and to analyse the influence of radial stiffness on planetary gear dynamics.

  11. Crossing boundaries: a comprehensive survey of medical licensing laws and guidelines regulating the interstate practice of pathology.

    Science.gov (United States)

    Hiemenz, Matthew C; Leung, Stanley T; Park, Jason Y

    2014-03-01

    In the United States, recent judicial interpretation of interstate licensure laws has found pathologists guilty of malpractice and, more importantly, the criminal practice of medicine without a license. These judgments against pathologists highlight the need for a timely and comprehensive survey of licensure requirements and laws regulating the interstate practice of pathology. For all 50 states, each state medical practice act and state medical board website was reviewed. In addition, each medical board was directly contacted by electronic mail, telephone, or US registered mail for information regarding specific legislation or guidelines related to the interstate practice of pathology. On the basis of this information, states were grouped according to similarities in legislation and medical board regulations. This comprehensive survey has determined that states define the practice of pathology on the basis of the geographic location of the patient at the time of surgery or phlebotomy. The majority of states (n=32) and the District of Columbia allow for a physician with an out-of-state license to perform limited consultation to a physician with the specific state license. Several states (n=5) prohibit physicians from consultation without a license for the specific state. Overall, these results reveal the heterogeneity of licensure requirements between states. Pathologists who either practice in multiple states, send cases to out-of-state consultants, or serve as consultants themselves should familiarize themselves with the medical licensure laws of the states from which they receive or send cases.

  12. Shoulder stiffness and rotator cuff repair.

    Science.gov (United States)

    Papalia, Rocco; Franceschi, Francesco; Vasta, Sebastiano; Gallo, Andrea; Maffulli, Nicola; Denaro, Vincenzo

    2012-01-01

    Shoulder stiffness is a frequent complication of surgical repair of rotator cuff tears. Post-operative stiffness negatively affects surgical outcomes leading to a substantial comorbidity and to the failure of surgical treatment. Also, a stiff shoulder could commonly be concomitant with an rotator cuff tear (RCT). We performed a comprehensive search of CINAHL, Embase, Medline and the Cochrane Central Registry of Controlled Trials, from inception of the database to 31 July 2011. Sixteen articles published in peer-reviewed journals were included in this comprehensive review. The management of shoulder stiffness is still controversial. The role of rehabilitation programs (standard versus early passive mobilization) after RCT repair on the development of stiffness is not clear, while the role of arthroscopic capsular release for post-operative stiffness is better defined, although a threshold of decreased the range of movement for which capsular release is advised has not been identified. Several factors have been identified to predispose the development of shoulder stiffness. There is also evidence in favor of surgical management of RCTs even when accompanied by shoulder stiffness, and there are strong evidences that arthroscopic capsular release is reliable and effective in managing shoulder stiffness. The post-operative rehabilitation protocol remains controversial. We are still far from definitive guidelines for the management of pre- and post-operative stiffness, and prospective double-blinded randomized clinical trials are needed to obtain evidence allowing to establish a reliable and effective management plan for shoulder stiffness.

  13. The wave equation for stiff strings and piano tuning

    CERN Document Server

    Gràcia, Xavier

    2016-01-01

    We study the wave equation for a string with stiffness. We solve the equation and provide a uniqueness theorem with suitable boundary conditions. For a pinned string we compute the spectrum, which is slightly inharmonic. Therefore, the widespread scale of 12 equal divisions of the just octave is not the best choice to tune instruments like the piano. Basing in the theory of dissonance, we provide a way to tune the piano in order to improve its consonance. A good solution is obtained by tuning a note and its fifth by minimizing their beats.

  14. Ground boundaries

    Energy Technology Data Exchange (ETDEWEB)

    Balluffi, R.W.; Bristowe, P.D.

    1990-01-01

    The present document is a progress report describing the work accomplished on the study of grain boundaries in Ag, Au, Ni, Si, and Ge. Research was focused on the following four major efforts: study of the atomic structure of grain boundaries by means of x-ray diffraction, transmission electron microscopy and computer modeling; grain boundary migration; short-circuit diffusion along grain boundaries; and development of Thin-Film Deposition/Bonding Apparatus for the manufacture of high purity bicrystals. 10 refs., 1 fig.

  15. Vascular Aging and Arterial Stiffness

    Directory of Open Access Journals (Sweden)

    Luana de Rezende Mikael

    Full Text Available Abstract Cardiovascular diseases (CVD account annually for almost one third of all deaths worldwide. Among the CVD, systemic arterial hypertension (SAH is related to more than half of those outcomes. Type 2 diabetes mellitus is an independent risk factor for SAH because it causes functional and structural damage to the arterial wall, leading to stiffness. Several studies have related oxidative stress, production of free radicals, and neuroendocrine and genetic changes to the physiopathogenesis of vascular aging. Indirect ways to analyze that aging process have been widely studied, pulse wave velocity (PWV being considered gold standard to assess arterial stiffness, because there is large epidemiological evidence of its predictive value for cardiovascular events, and it requires little technical knowledge to be performed. A pulse wave is generated during each cardiac contraction and travels along the arterial bed until finding peripheral resistance or any bifurcation point, determining the appearance of a reflected wave. In young individuals, arteries tend to be more elastic, therefore, the reflected wave occurs later in the cardiac cycle, reaching the heart during diastole. In older individuals, however, the reflected wave occurs earlier, reaching the heart during systole. Because PWV is an important biomarker of vascular damage, highly valuable in determining the patient’s global cardiovascular risk, we chose to review the articles on vascular aging in the context of cardiovascular risk factors and the tools available to the early identification of that damage.

  16. The effect of matrix stiffness on biomechanical properties of chondrocytes.

    Science.gov (United States)

    Zhang, Quanyou; Yu, Yang; Zhao, Hucheng

    2016-10-01

    The behavior of chondrocytes is regulated by multiple mechanical microenvironmental cues. During development and degenerative disease of articular cartilage, as an external signal, the extracellular matrix stiffness of chondrocytes changes significantly, but whether and how this biophysical cue affects biomechanical properties of chondrocytes remain elusive. In the present study, we designed supporting-biomaterials as  mimics of native pericellular matrix to study the effect of matrix stiffness on chondrocyte morphology and F-actin distribution. Furthermore, the active mechanical behavior of chondrocytes during sensing and responding to different matrix stiffness was quantitatively investigated using atom force microscope technique and theoretical model. Our results indicated that stiffer matrix tends to increase the cell spreading area, the percentage of irregular cell shape distribution and mechanical parameters including elastic modulus (Eelastic), instantaneous modulus (E0), relaxed modulus (ER) and apparent viscosity (μ) of chondrocytes. Knowledge of matrix stiffness-dependent biomechanical behaviors of chondrocytes has important implications for optimizing matrix material and advancing chondrocyte-based applications for functional tissue engineering. © The Author 2016. Published by Oxford University Press on behalf of the Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  17. Gradual stiffness versus magnetic imaging-guided variable stiffness colonoscopes: A randomized noninferiority trial.

    Science.gov (United States)

    Garborg, Kjetil; Wiig, Håvard; Hasund, Audun; Matre, Jon; Holme, Øyvind; Noraberg, Geir; Løberg, Magnus; Kalager, Mette; Adami, Hans-Olov; Bretthauer, Michael

    2017-02-01

    Colonoscopes with gradual stiffness have recently been developed to enhance cecal intubation. We aimed to determine if the performance of gradual stiffness colonoscopes is noninferior to that of magnetic endoscopic imaging (MEI)-guided variable stiffness colonoscopes. Consecutive patients were randomized to screening colonoscopy with Fujifilm gradual stiffness or Olympus MEI-guided variable stiffness colonoscopes. The primary endpoint was cecal intubation rate (noninferiority limit 5%). Secondary endpoints included cecal intubation time. We estimated absolute risk differences with 95% confidence intervals (CIs). We enrolled 475 patients: 222 randomized to the gradual stiffness instrument, and 253 to the MEI-guided variable stiffness instrument. Cecal intubation rate was 91.7% in the gradual stiffness group versus 95.6% in the variable stiffness group. The adjusted absolute risk for cecal intubation failure was 4.3% higher in the gradual stiffness group than in the variable stiffness group (upper CI border 8.1%). Median cecal intubation time was 13 minutes in the gradual stiffness group and 10 minutes in the variable stiffness group (p < 0.001). The study is inconclusive with regard to noninferiority because the 95% CI for the difference in cecal intubation rate between the groups crosses the noninferiority margin. (ClinicalTrials.gov identifier: NCT01895504).

  18. Research on Detection of Machine Stiffness

    OpenAIRE

    Wang Li-Jie; Shi Wei-Chao; Xu De-Kai

    2015-01-01

    Machine tool stiffness is a principal factor affecting machine tool precision, traditional methods can only be used to detect limited categories of machine tools. The paper introduces a new scheme to detect machine tool stiffness on the basis of dynamic detection of machine tool stiffness considering its characteristics and stress state during processing. An experiment conducted in turn-milling machining center CH7516GS indicated by comparison that statics analysis of finite elements matched ...

  19. Negotiating boundaries

    DEFF Research Database (Denmark)

    Aarhus, Rikke; Ballegaard, Stinne Aaløkke

    2010-01-01

    to maintain the order of the home when managing disease and adopting new healthcare technology. In our analysis we relate this boundary work to two continuums of visibility-invisibility and integration-segmentation in disease management. We explore five factors that affect the boundary work: objects......To move treatment successfully from the hospital to that of technology assisted self-care at home, it is vital in the design of such technologies to understand the setting in which the health IT should be used. Based on qualitative studies we find that people engage in elaborate boundary work......, activities, places, character of disease, and collaboration. Furthermore, the processes are explored of how boundary objects move between social worlds pushing and shaping boundaries. From this we discuss design implications for future healthcare technologies for the home....

  20. Boundary Spanning

    DEFF Research Database (Denmark)

    Zølner, Mette

    The paper explores how locals span boundaries between corporate and local levels. The aim is to better comprehend potentialities and challenges when MNCs draws on locals’ culture specific knowledge. The study is based on an in-depth, interpretive case study of boundary spanning by local actors...... in the period of post-acquisition when their organization is being integrated into the acquiring MNC. The paper contributes to the literature on boundary spanning in three ways: First, by illustrating that boundary spanning is performed by numerous organizational actors in a variety of positions in MNCs......, inclusively by locals in subsidiaries. Second, by showing that boundary spanning is ‘situated’ in the sense that its result depends on the kind of knowledge to be transmitted and the attitude of the receivers. A third contribution is methodological. The study illustrates that combining bottom-up grounded...

  1. Microenvironmental stiffness enhances glioma cell proliferation by stimulating epidermal growth factor receptor signaling.

    Directory of Open Access Journals (Sweden)

    Vaibhavi Umesh

    Full Text Available The aggressive and rapidly lethal brain tumor glioblastoma (GBM is associated with profound tissue stiffening and genomic lesions in key members of the epidermal growth factor receptor (EGFR pathway. Previous studies from our laboratory have shown that increasing microenvironmental stiffness in culture can strongly enhance glioma cell behaviors relevant to tumor progression, including proliferation, yet it has remained unclear whether stiffness and EGFR regulate proliferation through common or independent signaling mechanisms. Here we test the hypothesis that microenvironmental stiffness regulates cell cycle progression and proliferation in GBM tumor cells by altering EGFR-dependent signaling. We began by performing an unbiased reverse phase protein array screen, which revealed that stiffness modulates expression and phosphorylation of a broad range of signals relevant to proliferation, including members of the EGFR pathway. We subsequently found that culturing human GBM tumor cells on progressively stiffer culture substrates both dramatically increases proliferation and facilitates passage through the G1/S checkpoint of the cell cycle, consistent with an EGFR-dependent process. Western Blots showed that increasing microenvironmental stiffness enhances the expression and phosphorylation of EGFR and its downstream effector Akt. Pharmacological loss-of-function studies revealed that the stiffness-sensitivity of proliferation is strongly blunted by inhibition of EGFR, Akt, or PI3 kinase. Finally, we observed that stiffness strongly regulates EGFR clustering, with phosphorylated EGFR condensing into vinculin-positive focal adhesions on stiff substrates and dispersing as microenvironmental stiffness falls to physiological levels. Our findings collectively support a model in which tissue stiffening promotes GBM proliferation by spatially and biochemically amplifying EGFR signaling.

  2. Microenvironmental Stiffness Enhances Glioma Cell Proliferation by Stimulating Epidermal Growth Factor Receptor Signaling

    Science.gov (United States)

    Umesh, Vaibhavi; Rape, Andrew D.; Ulrich, Theresa A.; Kumar, Sanjay

    2014-01-01

    The aggressive and rapidly lethal brain tumor glioblastoma (GBM) is associated with profound tissue stiffening and genomic lesions in key members of the epidermal growth factor receptor (EGFR) pathway. Previous studies from our laboratory have shown that increasing microenvironmental stiffness in culture can strongly enhance glioma cell behaviors relevant to tumor progression, including proliferation, yet it has remained unclear whether stiffness and EGFR regulate proliferation through common or independent signaling mechanisms. Here we test the hypothesis that microenvironmental stiffness regulates cell cycle progression and proliferation in GBM tumor cells by altering EGFR-dependent signaling. We began by performing an unbiased reverse phase protein array screen, which revealed that stiffness modulates expression and phosphorylation of a broad range of signals relevant to proliferation, including members of the EGFR pathway. We subsequently found that culturing human GBM tumor cells on progressively stiffer culture substrates both dramatically increases proliferation and facilitates passage through the G1/S checkpoint of the cell cycle, consistent with an EGFR-dependent process. Western Blots showed that increasing microenvironmental stiffness enhances the expression and phosphorylation of EGFR and its downstream effector Akt. Pharmacological loss-of-function studies revealed that the stiffness-sensitivity of proliferation is strongly blunted by inhibition of EGFR, Akt, or PI3 kinase. Finally, we observed that stiffness strongly regulates EGFR clustering, with phosphorylated EGFR condensing into vinculin-positive focal adhesions on stiff substrates and dispersing as microenvironmental stiffness falls to physiological levels. Our findings collectively support a model in which tissue stiffening promotes GBM proliferation by spatially and biochemically amplifying EGFR signaling. PMID:25000176

  3. Measurement and Treatment of Passive Muscle Stiffness

    DEFF Research Database (Denmark)

    Kirk, Henrik

    This PhD thesis is based on research conducted at the University of Copenhagen and Helene Elsass Center from 2012 to 2015. Measurements and treatment of passive muscle stiffness in people with cerebral palsy (CP) comprise the focus of the thesis. The thesis summarizes the results from four studies...... stiffness. I introduce how to evaluate and distinguish between passive muscle stiffness and reflex-mediated stiffness in research and in clinical practice. Furthermore, I present ”the Portable Spasticity Assessment Device”, which was developed as a part of the PhD study. I discuss the validity...

  4. A new approach to determine press stiffness

    DEFF Research Database (Denmark)

    Arentoft, Mogens; Wanheim, Tarras

    2004-01-01

    A new procedure is proposed for measuring press stiffness, including separated horizontal and vertical loading of the press frame. The load can be eccentrically positioned for measuring rotational stiffnesses. Two loading devices and corresponding measuring equipment for registration of press...... deflections are designed. The press stiffness is presented as a 6 by 6 flexibility matrix. The approach has been tested by measuring the stiffness of a 5000 kN O-frame, ring element, hydraulic press, a 10000 kN O-frame, pillar element, hydraulic press and a 10000 kN O-frame, ring element mechanical press...

  5. Extracellular matrix stiffness causes systematic variations in proliferation and chemosensitivity in myeloid leukemias

    Science.gov (United States)

    Shin, Jae-Won; Mooney, David J.

    2016-01-01

    Extracellular matrix stiffness influences biological functions of some tumors. However, it remains unclear how cancer subtypes with different oncogenic mutations respond to matrix stiffness. In addition, the relevance of matrix stiffness to in vivo tumor growth kinetics and drug efficacy remains elusive. Here, we designed 3D hydrogels with physical parameters relevant to hematopoietic tissues and adapted them to a quantitative high-throughput screening format to facilitate mechanistic investigations into the role of matrix stiffness on myeloid leukemias. Matrix stiffness regulates proliferation of some acute myeloid leukemia types, including MLL-AF9+ MOLM-14 cells, in a biphasic manner by autocrine regulation, whereas it decreases that of chronic myeloid leukemia BCR-ABL+ K-562 cells. Although Arg-Gly-Asp (RGD) integrin ligand and matrix softening confer resistance to a number of drugs, cells become sensitive to drugs against protein kinase B (PKB or AKT) and rapidly accelerated fibrosarcoma (RAF) proteins regardless of matrix stiffness when MLL-AF9 and BCR-ABL are overexpressed in K-562 and MOLM-14 cells, respectively. By adapting the same hydrogels to a xenograft model of extramedullary leukemias, we confirm the pathological relevance of matrix stiffness in growth kinetics and drug sensitivity against standard chemotherapy in vivo. The results thus demonstrate the importance of incorporating 3D mechanical cues into screening for anticancer drugs. PMID:27790998

  6. Stiffness control of balance in quiet standing.

    Science.gov (United States)

    Winter, D A; Patla, A E; Prince, F; Ishac, M; Gielo-Perczak, K

    1998-09-01

    Our goal was to provide some insights into how the CNS controls and maintains an upright standing posture, which is an integral part of activities of daily living. Although researchers have used simple performance measures of maintenance of this posture quite effectively in clinical decision making, the mechanisms and control principles involved have not been clear. We propose a relatively simple control scheme for regulation of upright posture that provides almost instantaneous corrective response and reduces the operating demands on the CNS. The analytic model is derived and experimentally validated. A stiffness model was developed for quiet standing. The model assumes that muscles act as springs to cause the center-of-pressure (COP) to move in phase with the center-of-mass (COM) as the body sways about some desired position. In the sagittal plane this stiffness control exists at the ankle plantarflexors, in the frontal plane by the hip abductors/adductors. On the basis of observations that the COP-COM error signal continuously oscillates, it is evident that the inverted pendulum model is severely underdamped, approaching the undamped condition. The spectrum of this error signal is seen to match that of a tuned mass, spring, damper system, and a curve fit of this "tuned circuit" yields omega n the undamped natural frequency of the system. The effective stiffness of the system, Ke, is then estimated from Ke = I omega n2, and the damping B is estimated from B = BW X I, where BW is the bandwidth of the tuned response (in rad/s), and I is the moment of inertia of the body about the ankle joint. Ten adult subjects were assessed while standing quietly at three stance widths: 50% hip-to-hip distance, 100 and 150%. Subjects stood for 2 min in each position with eyes open; the 100% stance width was repeated with eyes closed. In all trials and in both planes, the COP oscillated virtually in phase (within 6 ms) with COM, which was predicted by a simple 0th order spring

  7. 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 sutures in the repair should be considered to judge the strength of the repair. Clinical Relevance: Previous in vitro studies have shown the double-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

  8. Grain boundaries

    Energy Technology Data Exchange (ETDEWEB)

    Balluffi, R.W.; Bristowe, P.D.

    1991-01-01

    The present document is a progress report describing the work accomplished to date during the second year of our four-year grant (February 15, 1990--February 14, 1994) to study grain boundaries. The research was focused on the following three major efforts: Study of the atomic structure of grain boundaries by means of x-ray diffraction, transmission electron microscopy and computer modeling; study of short-circuit diffusion along grain boundaries; and development of a Thin-film Deposition/Bonding Apparatus for the manufacture of high purity bicrystals.

  9. Grain boundaries

    Science.gov (United States)

    Balluffi, R. W.; Bristowe, P. D.

    The present document is a progress report describing the work accomplished to date during the second year of our four-year grant (February 15, 1990 to February 14, 1994) to study grain boundaries. The research was focused on the following three major efforts: study of the atomic structure of grain boundaries by means of x-ray diffraction, transmission electron microscopy and computer modeling; study of short-circuit diffusion along grain boundaries; and development of a Thin-film Deposition/Bonding Apparatus for the manufacture of high purity bicrystals.

  10. Matrix Stiffness Modulates Proliferation, Chemotherapeutic Response and Dormancy in Hepatocellular Carcinoma Cells

    OpenAIRE

    Schrader, Joerg; Gordon-Walker, Timothy T; Aucott, Rebecca L; van Deemter, Marielle; Quaas, Alexander; Walsh, Shaun; Benten, Daniel; Stuart J. Forbes; Wells, Rebecca G.; John P. Iredale

    2011-01-01

    There is increasing evidence that the physical environment is a critical mediator of tumor behavior. Hepatocellular carcinoma (HCC) develops within an altered biomechanical environment, and increasing matrix stiffness is a strong predictor of HCC development. The aim of this study was to establish whether changes in matrix stiffness, which are characteristic of inflammation and fibrosis, regulate HCC cell proliferation and chemotherapeutic response. Using an in vitro system of "mechanically t...

  11. Curvature dependent modulation of fish fin stiffness

    Science.gov (United States)

    Nguyen, Khoi; Yu, Ning; Bandi, Mahesh; Venkadesan, Madhusudhan; Mandre, Shreyas

    Propulsion and maneuvering ability of fishes depends on the stiffness of their fins. However, increasing stiffness by simply adding material to thicken the fin would incur a substantial energetic cost associated with flapping the fin. We propose that fishes increase stiffness of the fin not by building thicker fins, but by geometrically coupling out-of-plane bending of the fin's rays with in-plane stretching of a stiff membrane that connects the rays. We present a model of fin elasticity for ray-finned fish, where we decompose the fin into a series of elastic beams (rays) with springy interconnections (membrane). In one limit, where the membranes are infinitely extensible, the fin's stiffness is no more than the sum of the stiffness of individual rays. At the other limit of an inextensible membrane, fin stiffness reaches an asymptotic maximum. The asymptote value increases monotonically with curvature. We propose that musculature at the base of the fin controls fin curvature, and thereby modulates stiffness.

  12. Embodying Desired Behavior in Variable Stiffness Actuators

    NARCIS (Netherlands)

    Visser, L.C.; Stramigioli, Stefano; Bicchi, Antonio

    2011-01-01

    Variable stiffness actuators are a class of actuators with the capability of changing their apparent output stiffness independently from the actuator output position. This is achieved by introducing internally a number of compliant elements, and internal actuated degrees of freedom that determine

  13. 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...

  14. Foil Bearing Stiffness Estimation with Pseudospectral Scheme

    Directory of Open Access Journals (Sweden)

    Sankar Balaji

    2016-01-01

    Full Text Available Compliant foil gas lubricated bearings are used for the support of light loads in the order of few kilograms at high speeds, in the order of 50,000 RPM. The stiffness of the foil bearings depends both on the stiffness of the compliant foil and on the lubricating gas film. The stiffness of the bearings plays a crucial role in the stable operation of the supported rotor over a range of speeds. This paper describes a numerical approach to estimate the stiffness of the bearings using pseudo spectral scheme. Methodology to obtain the stiffness of the foil bearing as a function of weight of the shaft is given and the results are presented.

  15. Stiffness Control of Surgical Continuum Manipulators.

    Science.gov (United States)

    Mahvash, Mohsen; Dupont, Pierre E

    2011-04-01

    This paper introduces the first stiffness controller for continuum robots. The control law is based on an accurate approximation of a continuum robot's coupled kinematic and static force model. To implement a desired tip stiffness, the controller drives the actuators to positions corresponding to a deflected robot configuration that produces the required tip force for the measured tip position. This approach provides several important advantages. First, it enables the use of robot deflection sensing as a means to both sense and control tip forces. Second, it enables stiffness control to be implemented by modification of existing continuum robot position controllers. The proposed controller is demonstrated experimentally in the context of a concentric tube robot. Results show that the stiffness controller achieves the desired stiffness in steady state, provides good dynamic performance, and exhibits stability during contact transitions.

  16. Determination of 6 stiffnesses for a press

    DEFF Research Database (Denmark)

    Arentoft, Mogens; Eriksen, Morten; Wanheim, Tarras

    2000-01-01

    the workpiece will result in deflections of the press, which will decrease the tolerances of the component. At present, it is possible to measure the reaction forces from the workpiece, for instance by use of the model material technique as described in [1-2]. If the stiffness and clearances of the press...... is known too, the final dimensions can be predicted by divide the force by the stiffness and add the clearance. If the stiffness of the press is known, it is possible to optimize the orientation of the workpiece too, so the direction, in which the best tolerances is demanded, is equal to the direction...... in which the press has the highest stiffness. Furthermore, knowledge about the stiffnesses of all presses in a production system makes it possible to choose the press which best fit to a specific process....

  17. Validity and reliability of three methods of stiffness assessment

    National Research Council Canada - National Science Library

    Elizabeth C.Pruyn Mark L.Watsford Aron J.Murphy

    2016-01-01

    ... and reliability of 3 in vivo methods of stiffness assessment using 1 cohort of participants.Methods:To determine inter-day reliability,15 female netballers were assessed for stiffness twice within 1 week using unilateral hopping(vertical stiffness...

  18. 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.

  19. Blurring Boundaries

    DEFF Research Database (Denmark)

    Neergaard, Ulla; Nielsen, Ruth

    2010-01-01

    This article builds on the results obtained in the so-called Blurring Boundaries project which was undertaken at the Law Department, Copenhagen Business School, in the period from 2007 to 2009. It looks at the sustainability of the Danish welfare state in an EU law context and on the integration...... of welfare functions into EU law both from an internal market law and a constitutional law perspective. The main problem areas covered by the Blurring Boundaries project were studied in sub-projects on: 1) Internal market law and welfare services; 2) Fundamental rights and non-discrimination law aspects......; and 3) Services of general interest. In the Blurring Boundaries project, three aspects of the European Social Model have been particularly highlighted: the constitutionalisation of the European Social Model, its multi-level legal character, and the clash between market access justice at EU level...

  20. Research on Detection of Machine Stiffness

    Directory of Open Access Journals (Sweden)

    Wang Li-Jie

    2015-01-01

    Full Text Available Machine tool stiffness is a principal factor affecting machine tool precision, traditional methods can only be used to detect limited categories of machine tools. The paper introduces a new scheme to detect machine tool stiffness on the basis of dynamic detection of machine tool stiffness considering its characteristics and stress state during processing. An experiment conducted in turn-milling machining center CH7516GS indicated by comparison that statics analysis of finite elements matched the experimental result well, which provided precise original data for design of improved machine tool precision and access to design of precision detection equipment for other types of machine tools.

  1. Interplay of matrix stiffness and protein tethering in stem cell differentiation.

    Science.gov (United States)

    Wen, Jessica H; Vincent, Ludovic G; Fuhrmann, Alexander; Choi, Yu Suk; Hribar, Kolin C; Taylor-Weiner, Hermes; Chen, Shaochen; Engler, Adam J

    2014-10-01

    Stem cells regulate their fate by binding to, and contracting against, the extracellular matrix. Recently, it has been proposed that in addition to matrix stiffness and ligand type, the degree of coupling of fibrous protein to the surface of the underlying substrate, that is, tethering and matrix porosity, also regulates stem cell differentiation. By modulating substrate porosity without altering stiffness in polyacrylamide gels, we show that varying substrate porosity did not significantly change protein tethering, substrate deformations, or the osteogenic and adipogenic differentiation of human adipose-derived stromal cells and marrow-derived mesenchymal stromal cells. Varying protein-substrate linker density up to 50-fold changed tethering, but did not affect osteogenesis, adipogenesis, surface-protein unfolding or underlying substrate deformations. Differentiation was also unaffected by the absence of protein tethering. Our findings imply that the stiffness of planar matrices regulates stem cell differentiation independently of protein tethering and porosity.

  2. Programmable variable stiffness 2D surface design

    Science.gov (United States)

    Trabia, Sarah; Hwang, Taeseon; Yim, Woosoon

    2014-03-01

    Variable stiffness features can contribute to many engineering applications ranging from robotic joints to shock and vibration mitigation. In addition, variable stiffness can be used in the tactile feedback to provide the sense of touch to the user. A key component in the proposed device is the Biased Magnetorheological Elastomer (B-MRE) where iron particles within the elastomer compound develop a dipole interaction energy. A novel feature of this device is to introduce a field induced shear modulus bias via a permanent magnet which provides an offset with a current input to the electromagnetic control coil to change the compliance or modulus of a base elastomer in both directions (softer or harder). The B-MRE units can lead to the design of a variable stiffness surface. In this preliminary work, both computational and experimental results of the B-MRE are presented along with a preliminary design of the programmable variable stiffness surface design.

  3. Stiff Neck, Torticollis, and Pseudotumor Cerebri

    Directory of Open Access Journals (Sweden)

    J Gordon Millichap

    2002-05-01

    Full Text Available Three prepubertal children diagnosed with pseudotumor cerebri and presenting with stiff neck and torticollis are reported from Schneider Children’s Medical Center, Sackler School of Medicine, Tel Aviv, Israel.

  4. Strength and stiffness of engineering systems

    CERN Document Server

    Leckie, Frederick A

    2009-01-01

    This book on the stiffness and strength of engineering systems integrates a wide array of topics into a unified text, including plasticity, fracture, composite materials, energy approaches, and mechanics of microdevices (MEMs)..

  5. 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.

  6. 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)

  7. Closed-Form Formula of the Transverse Dynamic Stiffness of a Shallowly Inclined Taut Cable

    Directory of Open Access Journals (Sweden)

    Dan-hui Dan

    2014-01-01

    Full Text Available The segmented vibration-governed equations and their general solutions for cables acted upon by intermediate transverse forces are derived by applying Hamilton’s principle. Including the effects of sagging, flexible stiffness, clamped boundary conditions, and inclination angle of the cable, the element-wise dynamic stiffness for each cable segment, split into segments having unique transverse forces, is derived. By using methods from the global stiffness assembly process of FEM, the global level of the cables’ dynamic equilibrium equation is obtained, and, as a result, the final closed-form formula of transverse dynamic stiffness is derived. Additionally, the corresponding analytic form, without considering sagging effects, is also obtained. Case studies are conducted on the aspects of accuracy, rationality of the distribution on the spatial field, and frequency domains of dynamic stiffness calculations. By comparison with the Guyan-based static FEM reduction method, it is shown that the result obtained from the proposed closed-form solution, which includes sagging effects, is exact and rational, thus creating a powerful tool in transverse vibration analysis.

  8. Albedo Boundary

    Science.gov (United States)

    2003-01-01

    MGS MOC Release No. MOC2-510, 11 October 2003The sharp, nearly straight line that runs diagonally across the center of this April 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image is an albedo boundary. Albedois a term that refers to reflectance of sunlight. A surface with a low albedo is one that appears dark because it reflects less light than a high albedo (bright) surface. On Mars, albedo boundaries occur between two materials of differing texture, particle size, or composition, or some combination of these three factors. The boundary shown here is remarkable because it is so sharp and straight. This is caused by wind. Most likely, the entire surface was once covered with the lower-albedo (darker) material that is now seen in the upper half of the image. At some later time, wind stripped away this darker material from the surfaces in the lower half of the image. The difference in albedo here might be related to composition, and possibly particle size. This picture is located near the southwest rim of Schiaparelli Basin at 5.5oS, 345.9oW. The picture covers an area 3 km (1.9 mi) wide and is illuminated by sunlight from the left.

  9. 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...

  10. Integration of acoustic radiation force and optical imaging for blood plasma clot stiffness measurement.

    Directory of Open Access Journals (Sweden)

    Caroline W Wang

    Full Text Available Despite the life-preserving function blood clotting serves in the body, inadequate or excessive blood clot stiffness has been associated with life-threatening diseases such as stroke, hemorrhage, and heart attack. The relationship between blood clot stiffness and vascular diseases underscores the importance of quantifying the magnitude and kinetics of blood's transformation from a fluid to a viscoelastic solid. To measure blood plasma clot stiffness, we have developed a method that uses ultrasound acoustic radiation force (ARF to induce micron-scaled displacements (1-500 μm on microbeads suspended in blood plasma. The displacements were detected by optical microscopy and took place within a micro-liter sized clot region formed within a larger volume (2 mL sample to minimize container surface effects. Modulation of the ultrasound generated acoustic radiation force allowed stiffness measurements to be made in blood plasma from before its gel point to the stage where it was a fully developed viscoelastic solid. A 0.5 wt % agarose hydrogel was 9.8-fold stiffer than the plasma (platelet-rich clot at 1 h post-kaolin stimulus. The acoustic radiation force microbead method was sensitive to the presence of platelets and strength of coagulation stimulus. Platelet depletion reduced clot stiffness 6.9 fold relative to platelet rich plasma. The sensitivity of acoustic radiation force based stiffness assessment may allow for studying platelet regulation of both incipient and mature clot mechanical properties.

  11. On the Free Vibration Modeling of Spindle Systems: A Calibrated Dynamic Stiffness Matrix

    Directory of Open Access Journals (Sweden)

    Omar Gaber

    2014-01-01

    Full Text Available The effect of bearings on the vibrational behavior of machine tool spindles is investigated. This is done through the development of a calibrated dynamic stiffness matrix (CDSM method, where the bearings flexibility is represented by massless linear spring elements with tuneable stiffness. A dedicated MATLAB code is written to develop and to assemble the element stiffness matrices for the system’s multiple components and to apply the boundary conditions. The developed method is applied to an illustrative example of spindle system. When the spindle bearings are modeled as simply supported boundary conditions, the DSM model results in a fundamental frequency much higher than the system’s nominal value. The simply supported boundary conditions are then replaced by linear spring elements, and the spring constants are adjusted such that the resulting calibrated CDSM model leads to the nominal fundamental frequency of the spindle system. The spindle frequency results are also validated against the experimental data. The proposed method can be effectively applied to predict the vibration characteristics of spindle systems supported by bearings.

  12. The Static WKB Solution to Catenary Problems with Large Sag and Bending Stiffness

    Directory of Open Access Journals (Sweden)

    Yuhung Hsu

    2014-01-01

    Full Text Available Large sag with a bending stiffness catenary is a subject that draws attention in the realm of fatigue analysis, estimation of suspension cable sag for bridge cable hoisting, and ocean engineering of the employment of mooring systems. However, the bending stiffness is the cause of boundary layers at the anchorage of cables, thereby finding a solution of the differential equation can be extremely difficult. Previous studies have tackled this problem with the perturbation method; yet, due to the complexity of the matching process and solution finding, the method might not be an ideal solution for engineering applications. Moreover, the finite difference method and the finite element method in numerical analysis can often be ineffective because of inappropriate parameter configuration and the drastic variation of functions in the boundary layers. Therefore, this study proposed a novel bending moment expression of a large sag catenary. The expression was derived from the sag identified using bending moment equations, and a solution was found by applying the WKB method (Wentzel-Kramers-Brillouin method to overcome the complex problem of boundary layers. Consequently, a simple solution of various mechanical properties in a cable with bending stiffness and large sag could be obtained.

  13. 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

    2018-01-25

    This research examines the benefits of caffeine absorption on hair stiffness. In order 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) 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. This

  14. Boundary issues

    Science.gov (United States)

    Townsend, Alan R.; Porder, Stephen

    2011-03-01

    What is our point of no return? Caesar proclaimed 'the die is cast' while crossing the Rubicon, but rarely does modern society find so visible a threshold in our continued degradation of ecosystems and the services they provide. Humans have always used their surroundings to make a living— sometimes successfully, sometimes not (Diamond 2005)—and we intuitively know that there are boundaries to our exploitation. But defining these boundaries has been a challenge since Malthus first prophesied that nature would limit the human population (Malthus 1798). In 2009, Rockström and colleagues tried to quantify what the 6.8 billion (and counting) of us could continue to get away with, and what we couldn't (Rockström et al 2009). In selecting ten 'planetary boundaries', the authors contend that a sustainable human enterprise requires treating a number of environmental thresholds as points of no return. They suggest we breach these Rubicons at our own peril, and that we've already crossed three: biodiversity loss, atmospheric CO2, and disruption of the global nitrogen (N) cycle. As they clearly hoped, the very act of setting targets has provoked scientific inquiry about their accuracy, and about the value of hard targets in the first place (Schlesinger 2009). Such debate is a good thing. Despite recent emphasis on the science of human-ecosystem interactions, understanding of our planetary boundaries is still in its infancy, and controversy can speed scientific progress (Engelhardt and Caplan 1987). A few weeks ago in this journal, Carpenter and Bennett (2011) took aim at one of the more controversial boundaries in the Rockström analysis: that for human alteration of the global phosphorus (P) cycle. Rockström's group chose riverine P export as the key indicator, suggesting that humans should not exceed a value that could trigger widespread marine anoxic events—and asserting that we have not yet crossed this threshold. There are defensible reasons for a marine

  15. boundary dissipation

    Directory of Open Access Journals (Sweden)

    Mehmet Camurdan

    1998-01-01

    are coupled by appropriate trace operators. This overall model differs from those previously studied in the literature in that the elastic chamber floor is here more realistically modeled by a hyperbolic Kirchoff equation, rather than by a parabolic Euler-Bernoulli equation with Kelvin-Voight structural damping, as in past literature. Thus, the hyperbolic/parabolic coupled system of past literature is replaced here by a hyperbolic/hyperbolic coupled model. The main result of this paper is a uniform stabilization of the coupled PDE system by a (physically appealing boundary dissipation.

  16. 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

  17. Stiff collagen matrices increase tumorigenic prolactin signaling in breast cancer cells.

    Science.gov (United States)

    Barcus, Craig E; Keely, Patricia J; Eliceiri, Kevin W; Schuler, Linda A

    2013-05-03

    Clinically, circulating prolactin levels and density of the extracellular matrix (ECM) are individual risk factors for breast cancer. As tumors develop, the surrounding stroma responds with increased deposition and cross-linking of the collagen matrix (desmoplasia). In mouse models, prolactin promotes mammary carcinomas that resemble luminal breast cancers in women, and increased collagen density promotes tumor metastasis and progression. Although the contributions of the ECM to the physiologic actions of prolactin are increasingly understood, little is known about the functional relationship between the ECM and prolactin signaling in breast cancer. Here, we examined consequences of increased ECM stiffness on prolactin signals to luminal breast cancer cells in three-dimensional collagen I matrices in vitro. We showed that matrix stiffness potently regulates a switch in prolactin signals from physiologic to protumorigenic outcomes. Compliant matrices promoted physiological prolactin actions and activation of STAT5, whereas stiff matrices promoted protumorigenic outcomes, including increased matrix metalloproteinase-dependent invasion and collagen scaffold realignment. In stiff matrices, prolactin increased SRC family kinase-dependent phosphorylation of focal adhesion kinase (FAK) at tyrosine 925, FAK association with the mitogen-activated protein kinase mediator GRB2, and pERK1/2. Stiff matrices also increased co-localization of prolactin receptors and integrin-activated FAK, implicating altered spatial relationships. Together, these results demonstrate that ECM stiffness is a powerful regulator of the spectrum of prolactin signals and that stiff matrices and prolactin interact in a feed-forward loop in breast cancer progression. Our study is the first reported evidence of altered ECM-prolactin interactions in breast cancer, suggesting the potential for new therapeutic approaches.

  18. 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...

  19. Electrochemical stiffness in lithium-ion batteries

    Science.gov (United States)

    Tavassol, Hadi; Jones, Elizabeth M. C.; Sottos, Nancy R.; Gewirth, Andrew A.

    2016-11-01

    Although lithium-ion batteries are ubiquitous in portable electronics, increased charge rate and discharge power are required for more demanding applications such as electric vehicles. The high-rate exchange of lithium ions required for more power and faster charging generates significant stresses and strains in the electrodes that ultimately lead to performance degradation. To date, electrochemically induced stresses and strains in battery electrodes have been studied only individually. Here, a new technique is developed to probe the chemomechanical response of electrodes by calculating the electrochemical stiffness via coordinated in situ stress and strain measurements. We show that dramatic changes in electrochemical stiffness occur due to the formation of different graphite-lithium intercalation compounds during cycling. Our analysis reveals that stress scales proportionally with the lithiation/delithiation rate and strain scales proportionally with capacity (and inversely with rate). Electrochemical stiffness measurements provide new insights into the origin of rate-dependent chemomechanical degradation and the evaluation of advanced battery electrodes.

  20. Substrate stiffness orchestrates epithelial cellular heterogeneity with controlled proliferative pattern via E-cadherin/β-catenin mechanotransduction.

    Science.gov (United States)

    Wang, Bingjie; Qin, Peng; Zhao, Hui; Xia, Tie; Wang, Jingyu; Liu, Longwei; Zhu, Lu; Xu, Jing; Huang, Chenyu; Shi, Yan; Du, Yanan

    2016-09-01

    Epithelial cellular heterogeneity has been observed in pathological tissues with abnormal matrix stiffness and cells cultured on rigid substrates. However, it remains unclear how matrix stiffness influences cellular heterogeneity formation in multi-cellular population. Here, we demonstrated that cellular heterogeneity regulated by substrate stiffness is evident starting from the initial single-cell stage (indicated by cellular Young's modulus and morphology) until the resulting multi-cellular stage (indicated by cellular functions) through distinguished proliferative patterns. Epithelial cells on soft substrate proliferated in a neighbor-dependent manner with stronger E-cadherin expression and more homogeneous E-cadherin/β-catenin localization compared to those on coverslips, which resulted in reduced heterogeneity in downstream cellular functions of the multi-cellular population. In particular, decreased heterogeneity in human embryonic stem cells upon expansion and endodermal induction was achieved on soft substrate. Overall, our work provides new insights on mechanotransduction during epithelial proliferation which regulates the formation of cellular heterogeneity and potentially provides a highly efficient approach to regulate stem cell fate by fine-tuning substrate stiffness. This study demonstrates that cellular heterogeneity regulated by substrate stiffness is evident starting from the initial single-cell stage until the resulting multi-cellular stage through distinguished proliferative patterns. During this process, E-cadherin/β-catenin mechanotransduction is found to play important role in substrate stiffness-regulated epithelial cellular heterogeneity formation. In particular, decreased heterogeneity in human embryonic stem cells upon expansion and endodermal induction is achieved on soft substrate. Hence, we believe that this work not only provides new insights on mechanotransduction of E-cadherin/β-catenin which regulates the formation of cellular

  1. Elastic stiffness of a Skyrmion crystal.

    Science.gov (United States)

    Nii, Y; Kikkawa, A; Taguchi, Y; Tokura, Y; Iwasa, Y

    2014-12-31

    We observe the elastic stiffness and ultrasonic absorption of a Skyrmion crystal in the chiral-lattice magnet MnSi. The Skyrmion crystal lattice exhibits a stiffness 3 orders of magnitude smaller than that of the atomic lattice of MnSi, being as soft as the flux line lattice in type-II superconductors. The observed anisotropic elastic responses are consistent with the cylindrical shape of the Skyrmion spin texture. Phenomenological analysis reveals that the spin-orbit coupling is responsible for the emergence of anisotropic elasticity in the Skyrmion lattice.

  2. Increased blood pressure and aortic stiffness among abusers of anabolic androgenic steroids

    DEFF Research Database (Denmark)

    Rasmussen, Jon J; Schou, Morten; Madsen, Per L

    2018-01-01

    BACKGROUND: Abuse of anabolic androgenic steroids (AAS) is prevalent among recreational athletes and adverse effects on blood pressure (BP) and arterial stiffness could be substantial. Testosterone decreases natriuretic peptides which are key components in BP-regulation and may impair BP...

  3. Breaking Boundaries

    DEFF Research Database (Denmark)

    produce desperate attempts to maintain old or create new differences. Political and sociological research into these complex processes has been mainly guided by structural and normative concerns. Faced with growing evidence about the instability of world order and domestic social structures alike, policy....... As a fundamental human experience, liminality transmits cultural practices, codes, rituals, and meanings in-between aggregate structures and uncertain outcomes. As a methodological tool it is well placed to overcome disciplinary boundaries, which often direct attention to specific structures or sectors of society....... Its capacity to provide explanatory accounts of seemingly unstructured situations provides an opportunity to link experience-based and culture-oriented approaches not only to contemporary problems but also to undertake comparisons across historical periods. From a perspective of liminality...

  4. Detonation capturing for stiff combustion chemistry

    NARCIS (Netherlands)

    Berkenbosch, A.C.; Kaasschieter, E.F.; Klein, R.

    1998-01-01

    This paper contributes to the topic of unphysical one-cell-per-time-step travelling combustion wave solutions in numerical computations of detonation waves in the presence of stiff chemical source terms. These false weak detonation solutions appear when a gas-dynamics-chemistry operator-splitting

  5. Alcohol consumption and arterial stiffness in men

    NARCIS (Netherlands)

    Sierksma, A.; Muller, M.; Schouw, Y.T. van der; Grobbee, D.E.; Hendriks, H.F.J.; Bots, M.L.

    2004-01-01

    Objective: Moderate alcohol consumption has been proposed to be anti-atherogenic and protect against coronary heart disease. Arterial stiffness provides a summary measure of atherosclerotic arterial damage and cardiovascular risk. A vascular protective effect of moderate alcohol consumption would be

  6. Bipedal walking gait with variable stiffness knees

    NARCIS (Netherlands)

    Roozing, W.; Carloni, Raffaella

    The Segmented Spring-Loaded Inverted Pendulum model is analysed, and it is shown that it exhibits walking gait. We propose a control architecture that exploits control of the knee stiffness to provide robustness of the system with respect to changes in gait. This controller is extended for a

  7. Robust Bipedal Walking with Variable Leg Stiffness

    NARCIS (Netherlands)

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

    The bipedal spring-mass model embodies important characteristics of human walking, and therefore serves as an important starting point in studying human-like walking for robots. In this paper, we propose to extend the bipedal spring-mass model with variable leg stiffness and exploit the potential of

  8. Fuzzy variable impedance control based on stiffness identification for human-robot cooperation

    Science.gov (United States)

    Mao, Dachao; Yang, Wenlong; Du, Zhijiang

    2017-06-01

    This paper presents a dynamic fuzzy variable impedance control algorithm for human-robot cooperation. In order to estimate the intention of human for co-manipulation, a fuzzy inference system is set up to adjust the impedance parameter. Aiming at regulating the output fuzzy universe based on the human arm’s stiffness, an online stiffness identification method is developed. A drag interaction task is conducted on a 5-DOF robot with variable impedance control. Experimental results demonstrate that the proposed algorithm is superior.

  9. Stiff person syndrome in South Asia.

    Science.gov (United States)

    Chang, Thashi; Lang, Bethan; Vincent, Angela

    2016-10-18

    Stiff person syndrome is a highly disabling, progressive autoimmune disorder of the central nervous system characterized by muscle rigidity and spasms. Stiff person syndrome is rare, but is believed to be under diagnosed with only 14 cases been reported among a 1.7 billion population in South Asia. We report the first authenticated case from Sri Lanka. A 55-year-old Sri Lankan female presented with difficulty in walking and recurrent falls due to progressive muscular rigidity in her lower limbs and trunk with superimposed muscle spasms that occurred in response to unexpected noise, startle or emotional upset. She had anxiety and specific phobias to open spaces, walking unaided and being among crowds of people. She had insulin-dependent diabetes mellitus and was on thyroxine replacement. On examination, she had hyperlordosis combined with board-like rigidity of her anterior abdomen and rigidity of her lower limbs bilaterally. Upper limbs were normal. Magnetic resonance imaging of her neuraxis was normal. Electromyography showed continuous motor unit activity at rest. Glutamic acid decarboxylase antibodies were detected in her serum at a titre of 15,500 IU/ml (normal <5). She showed a remarkable and sustained improvement to treatment with intravenous immunoglobulins, immunosuppressive and muscle relaxant medications, regaining independent ambulation. Diagnosis of stiff person syndrome remains clinical, supported by electromyography and serology for glutamic acid decarboxylase antibodies, facilitated by a high index of clinical suspicion. An autoimmune basis lends stiff person syndrome amenable to treatment highlighting the importance of diagnosis. This case adds to map the worldwide distribution of stiff person syndrome.

  10. The Role of the Regulated Sector in the UK Anti-Money Laundering Framework: Pushing the Boundaries of the Private Police

    Directory of Open Access Journals (Sweden)

    Mo Egan

    2010-06-01

    Full Text Available This article argues that the conceptualisation of private police in current academic literature requires expansion to accommodate the role of the regulated sector in the Anti- Money Laundering (AML framework. Firstly, it evaluates the literature on ‘private police’ and argues that its current parameters are too narrow to accommodate the ‘policing’ role of the regulated sector. Secondly, it lays out the legislative framework that has developed to deal with the problem of money laundering. Thirdly, it contextualises the role of the regulated sector, examining the domestic inter-agency policing relationships within the suspicious activity regime as operationalised in Scotland. Finally, it takes a closer look at how the courts have interpreted the ‘failure to report offence’ under s330 of the Proceeds of Crime Act (POCA 2002 and its consequential effect on the engagement of the regulated sector with the SARs regime.

  11. 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....

  12. Stiffness analysis and experimental validation of robotic systems

    Science.gov (United States)

    Carbone, Giuseppe

    2011-06-01

    Stiffness can be considered of primary importance in order to guarantee the successful use of any robotic system for a given task. Therefore, this paper proposes procedures for carrying out both numerical and experimental estimations of stiffness performance for multibody robotic systems. The proposed numerical procedure is based on models with lumped parameters for deriving the Cartesian stiffness matrix. Stiffness performance indices are also proposed for comparing stiffness performance. Then, an experimental procedure for the evaluation stiffness performance is proposed as based on a new measuring system named as Milli-CATRASYS (Milli Cassino Tracking System) and on a trilateration technique. Cases of study are reported to show the soundness and engineering feasibility of both the proposed numerical formulation for stiffness analysis and experimental validation of stiffness performance.

  13. Nondiabetic Glucometabolic Status and Progression of Aortic Stiffness

    DEFF Research Database (Denmark)

    McEniery, Carmel M; Wilkinson, Ian B; Johansen, Nanna B

    2017-01-01

    OBJECTIVE Aortic stiffness is an important predictor of futuremorbidity andmortality. Diabetes is associated with increased aortic stiffness, but the importance of nondiabetic glucometabolic status for accelerated aortic stiffening is unclear. We tested the hypothesis that adverse glucometabolic ...

  14. Animals prefer leg stiffness values that may reduce the energetic cost of locomotion.

    Science.gov (United States)

    Shen, ZhuoHua; Seipel, Justin

    2015-01-07

    Despite the neuromechanical complexity and wide diversity of running animals, most run with a center-of-mass motion that is similar to a simple mass bouncing on a spring. Further, when animals׳ effective leg stiffness is measured and normalized for size and weight, the resulting relative leg stiffness that most animals prefer lies in a narrow range between 7 and 27. Understanding why this nearly universal preference exists could shed light on how whole animal behaviors are organized. Here we show that the biologically preferred values of relative leg stiffness coincide with a theoretical minimal energetic cost of locomotion. This result strongly implies that animals select and regulate leg stiffness in order to reduce the energy required to move, thus providing animals an energetic advantage. This result also helps explain how high level control targets such as energy efficiency might influence overall physiological parameters and the underlying neuromechanics that produce it. Overall, the theory presented here provides an explanation for the existence of a nearly universal preferred leg stiffness. Also, the results of this work are beneficial for understanding the principles underlying human and animal locomotion, as well as for the development of prosthetic, orthotic and robotic devices. Copyright © 2014 Elsevier Ltd. All rights reserved.

  15. Stiffness-activated GEF-H1 expression exacerbates LPS-induced lung inflammation.

    Directory of Open Access Journals (Sweden)

    Isa Mambetsariev

    Full Text Available Acute lung injury (ALI is accompanied by decreased lung compliance. However, a role of tissue mechanics in modulation of inflammation remains unclear. We hypothesized that bacterial lipopolysacharide (LPS stimulates extracellular matrix (ECM production and vascular stiffening leading to stiffness-dependent exacerbation of endothelial cell (EC inflammatory activation and lung barrier dysfunction. Expression of GEF-H1, ICAM-1, VCAM-1, ECM proteins fibronectin and collagen, lysyl oxidase (LOX activity, interleukin-8 and activation of Rho signaling were analyzed in lung samples and pulmonary EC grown on soft (1.5 or 2.8 kPa and stiff (40 kPa substrates. LPS induced EC inflammatory activation accompanied by expression of ECM proteins, increase in LOX activity, and activation of Rho signaling. These effects were augmented in EC grown on stiff substrate. Stiffness-dependent enhancement of inflammation was associated with increased expression of Rho activator, GEF-H1. Inhibition of ECM crosslinking and stiffening by LOX suppression reduced EC inflammatory activation and GEF-H1 expression in response to LPS. In vivo, LOX inhibition attenuated LPS-induced expression of GEF-H1 and lung dysfunction. These findings present a novel mechanism of stiffness-dependent exacerbation of vascular inflammation and escalation of ALI via stimulation of GEF-H1-Rho pathway. This pathway represents a fundamental mechanism of positive feedback regulation of inflammation.

  16. The passive stiffness of the wrist and forearm

    Science.gov (United States)

    Charles, Steven K.; Zollo, Loredana; Guglielmelli, Eugenio; Hogan, Neville; Krebs, Hermano I.

    2012-01-01

    Because wrist rotation dynamics are dominated by stiffness (Charles SK, Hogan N. J Biomech 44: 614–621, 2011), understanding how humans plan and execute coordinated wrist rotations requires knowledge of the stiffness characteristics of the wrist joint. In the past, the passive stiffness of the wrist joint has been measured in 1 degree of freedom (DOF). Although these 1-DOF measurements inform us of the dynamics the neuromuscular system must overcome to rotate the wrist in pure flexion-extension (FE) or pure radial-ulnar deviation (RUD), the wrist rarely rotates in pure FE or RUD. Instead, understanding natural wrist rotations requires knowledge of wrist stiffness in combinations of FE and RUD. The purpose of this report is to present measurements of passive wrist stiffness throughout the space spanned by FE and RUD. Using a rehabilitation robot designed for the wrist and forearm, we measured the passive stiffness of the wrist joint in 10 subjects in FE, RUD, and combinations. For comparison, we measured the passive stiffness of the forearm (in pronation-supination), as well. Our measurements in pure FE and RUD agreed well with previous 1-DOF measurements. We have linearized the 2-DOF stiffness measurements and present them in the form of stiffness ellipses and as stiffness matrices useful for modeling wrist rotation dynamics. We found that passive wrist stiffness was anisotropic, with greater stiffness in RUD than in FE. We also found that passive wrist stiffness did not align with the anatomical axes of the wrist; the major and minor axes of the stiffness ellipse were rotated with respect to the FE and RUD axes by ∼20°. The direction of least stiffness was between ulnar flexion and radial extension, a direction used in many natural movements (known as the “dart-thrower's motion”), suggesting that the nervous system may take advantage of the direction of least stiffness for common wrist rotations. PMID:22649208

  17. A review of shear strength models for rock joints subjected to constant normal stiffness

    Directory of Open Access Journals (Sweden)

    Sivanathan Thirukumaran

    2016-06-01

    Full Text Available The typical shear behaviour of rough joints has been studied under constant normal load/stress (CNL boundary conditions, but recent studies have shown that this boundary condition may not replicate true practical situations. Constant normal stiffness (CNS is more appropriate to describe the stress–strain response of field joints since the CNS boundary condition is more realistic than CNL. The practical implications of CNS are movements of unstable blocks in the roof or walls of an underground excavation, reinforced rock wedges sliding in a rock slope or foundation, and the vertical movement of rock-socketed concrete piles. In this paper, the highlights and limitations of the existing models used to predict the shear strength/behaviour of joints under CNS conditions are discussed in depth.

  18. How Crouch Gait Can Dynamically Induce Stiff-Knee Gait

    NARCIS (Netherlands)

    Van der Krogt, M.M.; Bregman, D.J.J.; Wisse, M.; Doorenbosch, C.A.M.; Harlaar, J.; Collins, S.H.

    Children with cerebral palsy frequently experience foot dragging and tripping during walking due to a lack of adequate knee flexion in swing (stiff-knee gait). Stiff-knee gait is often accompanied by an overly flexed knee during stance (crouch gait). Studies on stiff-knee gait have mostly focused on

  19. How Crouch Gait Can Dynamically Induce Stiff-Knee Gait

    NARCIS (Netherlands)

    van der Krogt, M.M.; Bregman, D.J.J.; Wisse, M.; Doorenbosch, C.A.M.; Harlaar, J.

    2010-01-01

    Children with cerebral palsy frequently experience foot dragging and tripping during walking due to a lack of adequate knee flexion in swing (stiff-knee gait). Stiff-knee gait is often accompanied by an overly flexed knee during stance (crouch gait). Studies on stiff-knee gait have mostly focused on

  20. A 2-DOF joint with coupled variable output stiffness

    NARCIS (Netherlands)

    Tan, Daniel J.; Brouwer, Dannis Michel; Fumagalli, Matteo; Carloni, Raffaella

    This paper presents a 2-degree-of-freedom (DOF) joint with coupled variable output stiffness that makes use of three actuators, i.e., two for the 2-D joint motions and one for the joint stiffness adjustment. By base-mounting the actuators and the variable stiffness module that contains the passive

  1. Technology for Boundaries

    DEFF Research Database (Denmark)

    Bødker, Susanne; Kristensen, Jannie Friis; Nielsen, Christina

    2003-01-01

    This paper presents a study of an organisation, which is undergoing a process transforming organisational and technological boundaries. In particular, we shall look at three kinds of boundaries: the work to maintain and change the boundary between the organisation and its customers; boundaries.......After analysing the history and the current boundary work, the paper will propose new technological support for boundary work. In particular the paper will suggest means of supporting boundaries when these are productive and for changing boundaries when this seems more appropriate. In total, flexible technologies...... seem a core issue when dealing with technology for boundaries....

  2. 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.

  3. Dispersive Stiffness of Dzyaloshinskii Domain Walls

    Science.gov (United States)

    Pellegren, J. P.; Lau, D.; Sokalski, V.

    2017-07-01

    It is well documented that subjecting perpendicular magnetic films that exhibit the interfacial Dzyaloshinskii-Moriya interaction to an in-plane magnetic field results in a domain wall (DW) energy σ , which is highly anisotropic with respect to the orientation of the DW in the film plane Θ . We demonstrate that this anisotropy has a profound impact on the elastic response of the DW as characterized by the surface stiffness σ ˜ (Θ )=σ (Θ )+σ''(Θ ) and evaluate its dependence on the length scale of deformation. The influence of stiffness on DW mobility in the creep regime is assessed, with analytic and numerical calculations showing trends in σ ˜ that better represent experimental measurements of domain wall velocity in magnetic thin films compared to σ alone. Our treatment provides experimental support for theoretical models of the mobility of anisotropic elastic manifolds and makes progress toward a more complete understanding of magnetic domain wall creep.

  4. Exact dynamic stiffness matrix for flexural vibration of three-layered sandwich beams

    Science.gov (United States)

    Howson, W. P.; Zare, A.

    2005-04-01

    An exact dynamic member stiffness matrix (exact finite element), which defines the flexural motion of a three-layered sandwich beam with unequal faceplates, is developed from the closed form solution of the governing differential equation. This enables the powerful modelling features associated with the finite element technique to be utilised, including the ability to account for nodal masses, spring support stiffnesses and non-classical boundary conditions. However, such a formulation necessitates the solution of a transcendental eigenvalue problem. This is accomplished using the Wittrick-Williams algorithm, which enables the required natural frequencies to be converged upon to any required accuracy with the certain knowledge that none have been missed. The accuracy of the method is confirmed by comparison with three sets of published results and a final example indicates its range of application.

  5. 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.

  6. 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...

  7. 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.

  8. Stiffness and design for strength of trapezoidal Belleville springs

    DEFF Research Database (Denmark)

    Pedersen, Niels Leergaard; Pedersen, Pauli

    2011-01-01

    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...... 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...

  9. One-dimensional analysis of thin-walled beams with diaphragms and its application to optimization for stiffness reinforcement

    Science.gov (United States)

    Jung, Joon Hee; Jang, Gang-Won; Shin, Dongil; Kim, Yoon Young

    2017-08-01

    This paper presents a method to analyze thin-walled beams with quadrilateral cross sections reinforced with diaphragms using a one-dimensional higher-order beam theory. The effect of a diaphragm is reflected focusing on the increase of static stiffness. The deformations on the beam-interfacing boundary of a thin diaphragm are described by using deformation modes of the beam cross section while the deformations inside the diaphragm are approximated in the form of complete cubic polynomials. By using the principle of minimum potential energy, its stiffness that significantly affects distortional deformation of a thin-walled beam can be considered in the one-dimensional beam analysis. It is shown that the accuracy of the resulting one-dimensional analysis is comparable with that by a shell element based analysis. As a means to demonstrate the usefulness of the present approach for design, position optimization problems of diaphragms for stiffness reinforcement of an automotive side frame are solved.

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

    Energy Technology Data Exchange (ETDEWEB)

    Li Ming, E-mail: hackingming@gmail.com [Laboratory of Intelligent Machines, Lappeenranta University of Technology (Finland); Wu Huapeng; Handroos, Heikki [Laboratory of Intelligent Machines, Lappeenranta University of Technology (Finland)

    2011-10-15

    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.

  11. Regional brain stiffness changes across the Alzheimer's disease spectrum

    Directory of Open Access Journals (Sweden)

    Matthew C. Murphy

    2016-01-01

    Full Text Available Magnetic resonance elastography (MRE is an MRI-based technique to noninvasively measure tissue stiffness. Currently well established for clinical use in the liver, MRE is increasingly being investigated to measure brain stiffness as a novel biomarker of a variety of neurological diseases. The purpose of this work was to apply a recently developed MRE pipeline to measure regional brain stiffness changes in human subjects across the Alzheimer's disease (AD spectrum, and to gain insights into the biological processes underlying those stiffness changes by correlating stiffness with existing biomarkers of AD. The results indicate that stiffness changes occur mostly in the frontal, parietal and temporal lobes, in accordance with the known topography of AD pathology. Furthermore, stiffness in those areas correlates with existing imaging biomarkers of AD including hippocampal volumes and amyloid PET. Additional analysis revealed preliminary but significant evidence that the relationship between brain stiffness and AD severity is nonlinear and non-monotonic. Given that similar relationships have been observed in functional MRI experiments, we used task-free fMRI data to test the hypothesis that brain stiffness was sensitive to structural changes associated with altered functional connectivity. The analysis revealed that brain stiffness is significantly and positively correlated with default mode network connectivity. Therefore, brain stiffness as measured by MRE has potential to provide new and essential insights into the temporal dynamics of AD, as well as the relationship between functional and structural plasticity as it relates to AD pathophysiology.

  12. Research on static angular stiffness measurement of flexible joint

    Directory of Open Access Journals (Sweden)

    Yongchao HUANG

    2016-10-01

    Full Text Available Measurement accuracy of the angular stiffness of flexible joint is directly related to the control accuracy and sensitivity of gyro, but the traditional measurement methods have many problems. According to the principle of angular stiffness measurement of flexible joint, two static measurement methods of angular stiffness are proposed based on different loading ways, namely mechanical loading angular stiffness measurement and piezoelectric loading angular stiffness measurement. The mechanical loading angular stiffness measurement system is built by using a motor driven indexing feeding tilting table, the measure experiment if the angular stiffness of flexible joint is conducted, and the angular stiffness of flexible joint is measured. For the excessive fluctuation problem of the measure result in mechanical load test, a piezoelectric loading structure is designed and a measurement method employing piezoelectric actuator is proposed for angular stiffness measurement of flexible joint. Based on ANSYS Workbench, the displacement output of the piezoelectric loading structure is analyzed by simulations. The simulation results illustrate that the displacement output meets the requirement of static loading angular stiffness measurement of flexible joint, and the theoretical feasibility of piezoelectric loading angular stiffness measurement method is validated.

  13. Definition and Validation of a Methodology to Measure the Local Static Stiffness of Large Appendages Interfaces Using Dynamic Measurements

    Science.gov (United States)

    Bernasconi, M.; Rodriguez Senin, A.; Laduree, G.

    2014-06-01

    This paper describes the methodology developed under the Sentinel 1 spacecraft structure project to measure the local static stiffness of synthetic aperture radar antenna (SAR-A) interfaces using dynamic measurements. The methodology used consists in measuring accelerance [acceleration/force] frequency response functions (FRF) at the SAR-A interfaces and at several points selected as boundary conditions used for the derivation of the local stiffness [1]. The accelerance FRF is used to calculate the flexibility FRF [displacement/force] from which the static term of the flexibility is extracted. The static term is obtained via a least squares approximation at low frequency of the real part of the flexibility FRF (curve fitting approach) and extrapolation of the curve down to 0 Hz.Since the test was performed with the launch vehicle adapter ring clamped, the direct results of these measurements lead to global stiffness values. To calculate the local stiffness values the results were post- processed to subtract the contribution of the global deformation of the spacecraft structure. The local flexibility matrix at the SAR-A interfaces is calculated by imposing zero displacement at those points selected as virtual boundary conditions. Then, the local stiffness components were obtained inverting the diagonal terms of the local flexibility matrix for the three translational and the two in-plane rotational degrees of freedom in 9 SAR-A interfaces.The results obtained using this methodology were validated with a classical static test at one of the interfaces showing a good correlation between static and dynamic tests results. It was concluded that this methodology is suitable for the verification of static stiffness of large appendages interfaces and it can be applied to future missions that carry large payloads with critical structural interfaces.

  14. Cosmology with a stiff matter era

    Science.gov (United States)

    Chavanis, Pierre-Henri

    2015-11-01

    We consider the possibility that the Universe is made of a dark fluid described by a quadratic equation of state P =K ρ2 , where ρ is the rest-mass density and K is a constant. The energy density ɛ =ρ c2+K ρ2 is the sum of two terms: a rest-mass term ρ c2 that mimics "dark matter" (P =0 ) and an internal energy term u =K ρ2=P that mimics a "stiff fluid" (P =ɛ ) in which the speed of sound is equal to the speed of light. In the early universe, the internal energy dominates and the dark fluid behaves as a stiff fluid (P ˜ɛ , ɛ ∝a-6). In the late universe, the rest-mass energy dominates and the dark fluid behaves as pressureless dark matter (P ≃0 , ɛ ∝a-3). We provide a simple analytical solution of the Friedmann equations for a universe undergoing a stiff matter era, a dark matter era, and a dark energy era due to the cosmological constant. This analytical solution generalizes the Einstein-de Sitter solution describing the dark matter era, and the Λ CDM model describing the dark matter era and the dark energy era. Historically, the possibility of a primordial stiff matter era first appeared in the cosmological model of Zel'dovich where the primordial universe is assumed to be made of a cold gas of baryons. A primordial stiff matter era also occurs in recent cosmological models where dark matter is made of relativistic self-gravitating Bose-Einstein condensates (BECs). When the internal energy of the dark fluid mimicking stiff matter is positive, the primordial universe is singular like in the standard big bang theory. It expands from an initial state with a vanishing scale factor and an infinite density. We consider the possibility that the internal energy of the dark fluid is negative (while, of course, its total energy density is positive), so that it mimics anti-stiff matter. This happens, for example, when the BECs have an attractive self-interaction with a negative scattering length. In that case, the primordial universe is nonsingular and

  15. Boundary Layer Effect on Behavior of Discrete Models

    Directory of Open Access Journals (Sweden)

    Jan Eliáš

    2017-02-01

    Full Text Available The paper studies systems of rigid bodies with randomly generated geometry interconnected by normal and tangential bonds. The stiffness of these bonds determines the macroscopic elastic modulus while the macroscopic Poisson’s ratio of the system is determined solely by the normal/tangential stiffness ratio. Discrete models with no directional bias have the same probability of element orientation for any direction and therefore the same mechanical properties in a statistical sense at any point and direction. However, the layers of elements in the vicinity of the boundary exhibit biased orientation, preferring elements parallel with the boundary. As a consequence, when strain occurs in this direction, the boundary layer becomes stiffer than the interior for the normal/tangential stiffness ratio larger than one, and vice versa. Nonlinear constitutive laws are typically such that the straining of an element in shear results in higher strength and ductility than straining in tension. Since the boundary layer tends, due to the bias in the elemental orientation, to involve more tension than shear at the contacts, it also becomes weaker and less ductile. The paper documents these observations and compares them to the results of theoretical analysis.

  16. Boundary Layer Effect on Behavior of Discrete Models.

    Science.gov (United States)

    Eliáš, Jan

    2017-02-10

    The paper studies systems of rigid bodies with randomly generated geometry interconnected by normal and tangential bonds. The stiffness of these bonds determines the macroscopic elastic modulus while the macroscopic Poisson's ratio of the system is determined solely by the normal/tangential stiffness ratio. Discrete models with no directional bias have the same probability of element orientation for any direction and therefore the same mechanical properties in a statistical sense at any point and direction. However, the layers of elements in the vicinity of the boundary exhibit biased orientation, preferring elements parallel with the boundary. As a consequence, when strain occurs in this direction, the boundary layer becomes stiffer than the interior for the normal/tangential stiffness ratio larger than one, and vice versa. Nonlinear constitutive laws are typically such that the straining of an element in shear results in higher strength and ductility than straining in tension. Since the boundary layer tends, due to the bias in the elemental orientation, to involve more tension than shear at the contacts, it also becomes weaker and less ductile. The paper documents these observations and compares them to the results of theoretical analysis.

  17. Effects of altered corneal stiffness on native and postoperative LASIK corneal biomechanical behavior: A whole-eye finite element analysis.

    Science.gov (United States)

    Roy, Abhijit Sinha; Dupps, William J

    2009-10-01

    To investigate the impact of corneal elasticity on corneal shape changes before and after simulated LASIK with and without consideration of whole-eye biomechanics. A finite element whole-eye model of a human eye was constructed. The cornea was modeled as hyperelastic and incompressible using experimental data representing a range of corneal stiffness. The corneal response to intraocular pressure loading and LASIK for 2.00, 4.00, and 6.00 diopters of spherical myopia was analyzed as a function of corneal stiffness and limbal boundary conditions. Myopic LASIK produced different degrees of central flattening and postoperative ametropia in low-stiffness and high-stiffness corneas. Although a cornea-only model demonstrated maximum stresses and displacements in the central cornea and predicted residual myopia, a whole-eye model with equivalent corneal stiffness predicted greater paracentral displacements and less myopic undercorrection. In a whole-eye model with a stiffer cornea, maximum displacements shifted further toward the limbus, favoring additional mechanically mediated central flattening and refractive overcorrection (hyperopia). In postoperative LASIK models thinned by high myopic corrections, corneal stiffening caused central cornea flattening. Differences in the corneoscleral stiffness relationship affect simulated refractive outcomes after LASIK and may be a source of individual variation in refractive surgery outcomes. A whole-eye model allowing limbal motion illustrates a stiffness-dependent biomechanical balance between central corneal flattening and pre-ectatic weakening of the corneal apex not demonstrated in previous computational models and provides insight into under- and overcorrection in myopic LASIK and the previously unexplained phenomenon of corneal flattening after therapeutic collagen cross-linking for keratoconus. Copyright 2009, SLACK Incorporated.

  18. Boundary definition of a multiverse measure

    OpenAIRE

    Bousso, Raphael; Freivogel, Ben; Leichenauer, Stefan; Rosenhaus, Vladimir

    2010-01-01

    We propose to regulate the infinities of eternal inflation by relating a late time cut-off in the bulk to a short distance cut-off on the future boundary. The light-cone time of an event is defined in terms of the volume of its future light-cone on the boundary. We seek an intrinsic definition of boundary volumes that makes no reference to bulk structures. This requires taming the fractal geometry of the future boundary, and lifting the ambiguity of the conformal factor. We propose to work in...

  19. Thompson′s quadricepsplasty for stiff knee

    Directory of Open Access Journals (Sweden)

    Kundu Z

    2007-01-01

    Full Text Available Background : Stiffness of the knee after trauma and/or surgery for femoral fractures is one of the most common complications and is difficult to treat. Stiffness in extension is more common and can be reduced by vigorous physiotherapy. If it does not improve then quadricepsplasty is indicated. The present study was undertaken to evaluate the results of Thompsons quadricepsplasty. Materials and Methods : 22 male patients (age range 20-45 years with posttraumatic knee stiffness following distal femoral fractures underwent Thompson′s quadricepsplasty where knee flexion range was less than 45°. The index injury in these patients was treated with plaster cast (n=5, plates (n=3, intramedullary nailing (n=3 and external fixator for open fractures (n=9. Thompson′s quadricepsplasty was performed in all the patients using anterior approach, with incision extending from upper thigh to tibial tubercle. Release of rectus femoris from underlying vastus intermedius and release of intraarticular adhesions were performed. After surgery the patients needed parentral analgesia for three days and then oral analgesics for three weeks. Active assisted knee mobilization exercises were started on the first post-operative day. Continous passive motion machine was used from the same day. Supervised physiotherapy was continued in hospital for six weeks followed by intensive knee flexion and extension exercise including cycling at home for atleast another six months. Results : Out of 22 patients, 20 had excellent to good results and two patients had poor results using criteria devised by Judet. One poor result was due to peroperative fracture of patella which was then internally fixed and hence the flexion of knee could not be started immediately. There was peroperative avulsion of tibial tuberosity in another patient who finally gained less than 50° knee flexion and hence a poor result. Conclusion : Thompsons quadricepsplasty followed by a strict and rigourous

  20. Biomechanical response to ankle-foot orthosis stiffness during running.

    Science.gov (United States)

    Russell Esposito, Elizabeth; Choi, Harmony S; Owens, Johnny G; Blanck, Ryan V; Wilken, Jason M

    2015-12-01

    The Intrepid Dynamic Exoskeletal Orthosis (IDEO) is an ankle-foot orthosis developed to address the high rates of delayed amputation in the military. Its use has enabled many wounded Service Members to run again. During running, stiffness is thought to influence an orthosis' energy storage and return mechanical properties. This study examined the effect of orthosis stiffness on running biomechanics in patients with lower limb impairments who had undergone unilateral limb salvage. Ten patients with lower limb impairments underwent gait analysis at a self-selected running velocity. 1. Nominal (clinically-prescribed), 2. Stiff (20% stiffer than nominal), and 3. Compliant (20% less stiff than nominal) ankle-foot orthosis stiffnesses were tested. Ankle joint stiffness was greatest in the stiffest strut and lowest in the compliant strut, however ankle mechanical work remained unchanged. Speed, stride length, cycle time, joint angles, moments, powers, and ground reaction forces were not significantly different among stiffness conditions. Ankle joint kinematics and ankle, knee and hip kinetics were different between limbs. Ankle power, in particular, was lower in the injured limb. Ankle-foot orthosis stiffness affected ankle joint stiffness but did not influence other biomechanical parameters of running in individuals with unilateral limb salvage. Foot strike asymmetries may have influenced the kinetics of running. Therefore, a range of stiffness may be clinically appropriate when prescribing ankle-foot orthoses for active individuals with limb salvage. Published by Elsevier Ltd.

  1. MEMS Variable Stiffness Spring and Its Application in Fuze

    Directory of Open Access Journals (Sweden)

    Li Sui

    2014-04-01

    Full Text Available MEMS processing technology can manufacture any complex structures in a plane, using this point, a variable stiffness design idea for the planar micro-spring is proposed. That is, using one type of structure named contact pairs to achieve stiffness change during the micro-spring’s stretching process. Using contact pairs, three types of variable stiffness springs are designed: stiffness increase spring, stiffness decrease spring and stiffness hump spring. Finally, the variable stiffness springs’ application for fuze setback arming device is discussed. When the three types of springs are used in setback arming device, the stiffness decrease spring is better than the other two springs from security analysis. Kinematic analysis shows that, if the variable stiffness spring’s design is reasonable, the setback arming device not only can effectively solve the safety and reliability issues for rocket fuze, but also applies in small caliber grenade fuze’s working environment without changing the setback arming device’s size and structure. Analysis result indicate that the setback arming device based on MEMS variable stiffness spring is universal for rocket fuze and small caliber grenade fuze.

  2. Vertical Dynamic Stiffness of Offshore Foundations

    DEFF Research Database (Denmark)

    Latini, Chiara; Cisternino, Michele; Zania, Varvara

    2016-01-01

    Nowadays, pile and suction caisson foundations are widely used to support offshore structures which are subjected to vertical dynamic loads. The dynamic soil-structure interaction of floating foundations (foundations embedded in a soil layer whose height is greater than the foundation length......) is investigated by numerical analyses of representative finite element models. The 3D numerical model is compared and validated with existing analytical solutions. A parametric study is carried out analyzing the effect of the slenderness ratio Hp/d and the height and the stiffness of the soil layer on the dynamic...

  3. Chorein Sensitivity of Actin Polymerization, Cell Shape and Mechanical Stiffness of Vascular Endothelial Cells

    Directory of Open Access Journals (Sweden)

    Ioana Alesutan

    2013-09-01

    Full Text Available Background/Aims: Endothelial cell stiffness plays a key role in endothelium-dependent control of vascular tone and arterial blood pressure. Actin polymerization and distribution of microfilaments is essential for mechanical cell stiffness. Chorein, a protein encoded by the VPS13A gene, defective in chorea-acanthocytosis (ChAc, is involved in neuronal cell survival as well as cortical actin polymerization of erythrocytes and blood platelets. Chorein is expressed in a wide variety of further cells, yet nothing is known about the impact of chorein on cells other than neurons, erythrocytes and platelets. The present study explored whether chorein is expressed in human umbilical vein endothelial cells (HUVECs and addressed the putative role of chorein in the regulation of cytoskeletal architecture, stiffness and survival of those cells. Methods: In HUVECs with or without silencing of the VPS13A gene, VPS13A mRNA expression was determined utilizing quantitative RT-PCR, cytoskeletal organization visualized by confocal microscopy, G/F actin ratio and phosphorylation status of focal adhesion kinase quantified by western blotting, cell death determined by flow cytometry, mechanical properties studied by atomic force microscopy (AFM and cell morphology analysed by scanning ion conductance microscopy (SICM. Results: VPS13A mRNA expression was detectable in HUVECs. Silencing of the VPS13A gene attenuated the filamentous actin network, decreased the ratio of soluble G-actin over filamentous F-actin, reduced cell stiffness and changed cell morphology as compared to HUVECs silenced with negative control siRNA. These effects were paralleled by a significant decrease in FAK phosphorylation following VPS13A silencing. Moreover, silencing of the VPS13A gene increased caspase 3 activity and induced necrosis in HUVECs. Conclusions: Chorein is a novel regulator of cytoskeletal architecture, cell shape, mechanical stiffness and survival of vascular endothelial cells.

  4. Grain boundaries: Progress report

    Energy Technology Data Exchange (ETDEWEB)

    Balluffi, R.W.; Bristowe, P.D.

    1988-02-01

    Quantitative measurements of grain boundary structure factors using x-ray diffraction have been performed on low angle (001) twist boundaries in gold. Also, a computer atomistic simulation program is being implemented to examine the equilibrium properties of a series of boundaries in gold. Simulation of boundaries at room temperature have been performed. Electron microscopy of grain boundary melting in aluminum was also performed. Results indicated an absence of melting. (CBS)

  5. Síndrome stiff skin: relato de caso Stiff skin syndrome: case report

    Directory of Open Access Journals (Sweden)

    Adriana Gutstein da Fonseca Amorim

    2011-08-01

    Full Text Available Síndrome stiff skin é doença rara, esclerodermiforme, de etiologia desconhecida, caracterizada por endurecimento pétreo da pele, hipertricose leve e limitação da mobilidade articular. Não há tratamento efetivo até o momento. Exercícios e reabilitação são importantes para manter a qualidade de vida do paciente. Os autores apresentam caso de um menino de dois anos de idade com endurecimento cutâneo progressivo desde os oito meses de idade e restrição secundária da mobilidade articular, diagnosticado como Síndrome stiff skinStiff skin syndrome is a rare scleroderma-like disorder of unknown etiology characterized by stone-hard indurations of skin, mild hypertrichosis and limited joint mobility. No effective treatment has yet been found. Exercises and rehabilitative therapy are important in maintaining the patient's quality of life. The authors present a case of a two-year-old boy with progressive skin hardening since he was eightmonth old and secondary restricted joint mobility, diagnosed as Stiff skin syndrome

  6. Oxidized low-density lipoprotein alters the effect of matrix stiffness on the formation of endothelial networks and capillary lumens.

    Science.gov (United States)

    Gundavaram, Madhu S; Shentu, Tzu Pin; Kowalsky, Gregory B; Volkov, Suncica; Schraufnagel, Dean E; Levitan, Irena

    2013-09-01

    Abstract Formation of new blood vessels is essential for vascular repair and remodeling, and it is known that biomechanical properties of extracellular matrix play a major role in this process. Our earlier studies have also shown that exposing endothelial cells to oxidized modification of low-density lipoproteins (oxLDL) increases endothelial stiffness and facilitates their ability to form cellular networks, suggesting that it facilitates endothelial angiogenic potential. The goal of this study, therefore, was to test the interrelationship between matrix stiffness and oxLDL in the regulation of angiogenesis. Our results show that, as expected, an increase in matrix stiffness inhibited endothelial network formation and that exposure to oxLDL significantly facilitated this process. We also show, however, that oxLDL-induced facilitation of endothelial networks was observed only in stiff (3 mg/mL) but not in soft (1 mg/mL) collagen gels, resulting in blunting the effect of matrix stiffness. Also unexpectedly, we show that an increase in matrix stiffness results in a significant increase in the number of capillary lumens that are formed by single cells or pairs of cells, suggesting that while endothelial connectivity is impaired, formation of single-cell lumens is facilitated. oxLDL facilitates lumen formation, but this effect is also matrix dependent and is observed only in soft gels and not in stiff gels. Finally, an increase in both matrix stiffness and oxLDL exposure results in changes in capillary morphology, with the formation of larger capillary lumens. Overall, our study suggests that oxLDL plays an important role in formation of new capillaries and their morphology and that this effect is critically dependent on the extracellular environment's compliance, thereby underlining the importance of the interdependence of these parameters.

  7. 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.

  8. STIFF: Converting Scientific FITS Images to TIFF

    Science.gov (United States)

    Bertin, Emmanuel

    2011-10-01

    STIFF is a program that converts scientific FITS1 images to the more popular TIFF2 format for illustration purposes. Most FITS readers and converters do not do a proper job at converting FITS image data to 8 bits. 8-bit images stored in JPEG, PNG or TIFF files have the intensities implicitely stored in a non-linear way. Most current FITS image viewers and converters provide the user an incorrect translation of the FITS image content by simply rescaling linearly input pixel values. A first consequence is that the people working on astronomical images usually have to apply narrow intensity cuts or square-root or logarithmic intensity transformations to actually see something on their deep-sky images. A less obvious consequence is that colors obtained by combining images processed this way are not consistent across such a large range of surface brightnesses. Though with other software the user is generally afforded a choice of nonlinear transformations to apply in order to make the faint stuff stand out more clearly in the images, with the limited selection of choices provides, colors will not be accurately rendered, and some manual tweaking will be necessary. The purpose of STIFF is to produce beautiful pictures in an automatic and consistent way.

  9. 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.

  10. 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.

  11. Stiffness-Controlled Thermoresponsive Hydrogels for Cell Harvesting with Sustained Mechanical Memory.

    Science.gov (United States)

    Fan, Xingliang; Zhu, Lu; Wang, Ke; Wang, Bingjie; Wu, Yaozu; Xie, Wei; Huang, Chengyu; Chan, Barbara Pui; Du, Yanan

    2017-03-01

    Most mechanobiological investigations focused on in situ mechanical regulation of cells on stiffness-controlled substrates with few downstream applications, as it is still challenging to harvest and expand mechanically primed cells by enzymatic digestion (e.g., trypsin) without interrupting cellular mechanical memory between passages. This study develops thermoresponsive hydrogels with controllable stiffness to generate mechanically primed cells with intact mechanical memory for augmented wound healing. No significant cellular property alteration of the fibroblasts primed on thermoresponsive hydrogels with varied stiffness has been observed through thermoresponsive harvesting. When reseeding the harvested cells for further evaluation, softer hydrogels are proven to better sustain the mechanical priming effects compared to rigid tissue culture plate, which indicates that both the stiffness-controlled substrate and thermoresponsive harvesting are required to sustain cellular mechanical memory between passages. Moreover, epigenetics analysis reveals that thermoresponsive harvesting could reduce the rearrangement and loss of chromatin proteins compared to that of trypsinization. In vivo wound healing using mechanically primed fibroblasts shows featured epithelium and sebaceous glands, which indicates augmented skin recovery compared with trypsinized fibroblasts. Thus, the thermoresponsive hydrogel-based cell harvesting system offers a powerful tool to investigate mechanobiology between cell passages and produces abundant cells with tailored mechanical priming properties for cell-based applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Oncogenes induce a vimentin filament collapse mediated by HDAC6 that is linked to cell stiffness.

    Science.gov (United States)

    Rathje, Li-Sophie Z; Nordgren, Niklas; Pettersson, Torbjörn; Rönnlund, Daniel; Widengren, Jerker; Aspenström, Pontus; Gad, Annica K B

    2014-01-28

    Oncogenes deregulate fundamental cellular functions, which can lead to development of tumors, tumor-cell invasion, and metastasis. As the mechanical properties of cells govern cell motility, we hypothesized that oncogenes promote cell invasion by inducing cytoskeletal changes that increase cellular stiffness. We show that the oncogenes simian virus 40 large T antigen, c-Myc, and cyclin E induce spatial reorganization of the vimentin intermediate filament network in cells. At the cellular level, this reorganization manifests as increased width of vimentin fibers and the collapse of the vimentin network. At nanoscale resolution, the organization of vimentin fibers in these oncogene-expressing cells was more entangled, with increased width of the fibers compared with control cells. Expression of these oncogenes also resulted in up-regulation of the tubulin deacetylase histone deacetylase 6 (HDAC6) and altered spatial distribution of acetylated microtubules. This oncogene expression also induced increases in cellular stiffness and promoted the invasive capacity of the cells. Importantly, HDAC6 was required and sufficient for the structural collapse of the vimentin filament network, and was required for increased cellular stiffness of the oncogene-expressing cells. Taken together, these data are consistent with the possibility that oncogenes can induce cellular stiffness via an HDAC6-induced reorganization of the vimentin intermediate filament network.

  13. Lower-extremity arterial stiffness vs. aortic stiffness in the general population.

    Science.gov (United States)

    Wohlfahrt, Peter; Krajčoviechová, Alena; Seidlerová, Jitka; Galovcová, Markéta; Bruthans, Jan; Filipovský, Jan; Laurent, Stéphane; Cífková, Renata

    2013-08-01

    While determinants of aortic pulse wave velocity (aPWV) are well known, much less is known about factors affecting lower-extremity pulse wave velocity (lePWV). Unlike aPWV, increased lePWV does not predict cardiovascular risk, but limits lower-extremity blood flow and is associated with increased left ventricular mass. The aim of this study was to compare the effect of cardiovascular risk factors on aPWV and lePWV. A total of 911 individuals from the Czech post-MONICA study (a randomly selected 1% representative population sample, mean age 54±13.5 years, 47% men) were examined. Pulse wave velocity was measured using the SphygmoCor device. Aging had a large effect on aPWV, but only a small effect on lePWV. After adjustment for covariates, we observed that hypertension, diabetes, chronic kidney disease and dyslipidemia were positively and significantly associated with aPWV. However, only hypertension had a significant effect on lePWV. Increased ankle systolic blood pressure was associated with increased aPWV independently of brachial blood pressure. Ankle systolic blood pressure was more closely related to aPWV than lePWV. Subjects with an ankle-brachial index lower lePWV compared with individuals with a normal ankle-brachial index. Lower-extremity arterial stiffness is affected by age and cardiovascular risk factors to a lesser extent than aortic stiffness. Increased ankle systolic blood pressure is linked not only to increased lower-extremity arterial stiffness, but also increased aortic stiffness. In subjects with a low ankle-brachial index, lower-extremity arterial stiffness is spuriously decreased.

  14. Ambulatory arterial stiffness index and its role in assessing arterial stiffness in dialysis patients.

    Science.gov (United States)

    Liu, Wenjin; Zhou, Jiajun; Chen, Jianping; Meng, Meijuan; Li, Xiurong; Gao, Chaoqing; Zhou, Jianmei; Wang, Liang; Sun, Zhuxing; Chu, Hong; Fan, Wei; Bai, Youwei; Yang, Junwei

    2017-06-01

    Ambulatory arterial stiffness index (AASI) is a parameter derived from ambulatory blood pressure (ABP) readings. It is calculated as 1 minus the linear slope of DBP on SBP. We tested its value in assessing arterial stiffness in dialysis patients. We performed a cross-sectional analysis of the baseline data from a cohort study. A total of 344 patients on maintenance hemodialysis from six tertiary hospitals were included. All patients underwent ABP monitoring and carotid-femoral pulse wave velocity (cfPWV) measurement. Clinical determinants of AASI were analyzed, and the ability of AASI for assessing arterial stiffness was compared with ambulatory pulse pressure (PP). Multiple regression analysis revealed that ambulatory PP (β = 0.003), current smoker (β = -0.069), age (β = 0.003) and ambulatory SBP (β = 0.001) were independent determinants of AASI. Ambulatory PP correlates better with cfPWV than AASI (r = 0.28 for AASI and 0.59 for PP; P for difference: <0.001). When cfPWV was treated as a categorical variable, receiver operating characteristic curve analysis also showed a more potent predictive value of PP over AASI (area under the curve: 0.64 for AASI, 0.80 for PP; P for difference: <0.001). Net reclassification improvement and integrated discrimination improvement analysis demonstrated no added predictive value of AASI to PP (net reclassification improvement = -2.2%, P = 0.26; integrated discrimination improvement = 0.001, P = 0.51). Sensitivity analysis in patients with more ABP readings (≥49) yielded similar results. For dialysis patients, AASI has very limited value in assessing arterial stiffness, whether used alone or added to PP. Our results suggest that this index should not be used as a surrogate marker of arterial stiffness for dialysis patients in future practice and studies.

  15. Arterial stiffness, hypertension, and rational use of nebivolol

    Directory of Open Access Journals (Sweden)

    Enrico Agabiti-Rosei

    2009-05-01

    Full Text Available Enrico Agabiti-Rosei, Enzo Porteri, Damiano RizzoniClinica Medica, Department of Medical and Surgical Sciences, University of Brescia, ItalyAbstract: Arterial stiffness plays a key role in the pathophysiology of the cardiovascular system. Some indices of arterial stiffness (pulse wave velocity, augmentation index, characteristics of central blood pressure waveform may be presently calculated and evaluated in the clinical setting. Age and blood pressure are the two major clinical determinants of increased arterial stiffness, while molecular determinants of arterial stiffness are related to fibrotic components of the extracellular matrix, mainly elastin, collagen and fibronectin. Increased arterial stiffness has been consistently observed in conditions such as hypertension, dyslipidemia and diabetes. Arterial stiffness evaluated by means of carotid-femoral pulse wave velocity yielded prognostic significance beyond and above traditional risk factors. A more favorable effect of calcium channel blockers, diuretics and ACE inhibitors compared with β-blockers on indices of arterial stiffness was observed in several studies. It is conceivable that newer β-blockers with additional vasodilating properties, such as nebivolol, which has favorable effects on carbohydrate and lipid metabolism, as well as on endothelial function and on oxidative stress, may have favorable effects on arterial stiffness, compared with atenolol. In fact, in recent studies, nebivolol was demonstrated to improve artery stiffness to a greater extent than older β-blockers. Because endothelial dysfunction and increased arterial stiffness play an important role in the early atherosclerotic processes and are associated with poor outcomes and increased mortality, independently of blood pressure, the ability of nebivolol to enhance release of endothelium-derived nitric oxide, and consequently improve endothelial function and arterial stiffness, may have significant clinical

  16. Quantification of Magnetically Induced Changes in ECM Local Apparent Stiffness

    OpenAIRE

    Herath, Sahan C.B.; Yue, Du; Hui, Shi; Kim, Min-Cheol; Wang, Dong-An; Wang, Qingguo; Van Vliet, Krystyn J.; Asada, Harry; Chen, Peter C.Y.

    2014-01-01

    The stiffness of the extracellular matrix (ECM) is known to influence cell behavior. The ability to manipulate the stiffness of ECM has important implications in understanding how cells interact mechanically with their microenvironment. This article describes an approach to manipulating the stiffness ECM, whereby magnetic beads are embedded in the ECM through bioconjugation between the streptavidin-coated beads and the collagen fibers and then manipulated by an external magnetic field. It als...

  17. Physically Inspired Models for the Synthesis of Stiff Strings with Dispersive Waveguides

    Directory of Open Access Journals (Sweden)

    Testa I

    2004-01-01

    Full Text Available We review the derivation and design of digital waveguides from physical models of stiff systems, useful for the synthesis of sounds from strings, rods, and similar objects. A transform method approach is proposed to solve the classic fourth-order equations of stiff systems in order to reduce it to two second-order equations. By introducing scattering boundary matrices, the eigenfrequencies are determined and their dependency is discussed for the clamped, hinged, and intermediate cases. On the basis of the frequency-domain physical model, the numerical discretization is carried out, showing how the insertion of an all-pass delay line generalizes the Karplus-Strong algorithm for the synthesis of ideally flexible vibrating strings. Knowing the physical parameters, the synthesis can proceed using the generalized structure. Another point of view is offered by Laguerre expansions and frequency warping, which are introduced in order to show that a stiff system can be treated as a nonstiff one, provided that the solutions are warped. A method to compute the all-pass chain coefficients and the optimum warping curves from sound samples is discussed. Once the optimum warping characteristic is found, the length of the dispersive delay line to be employed in the simulation is simply determined from the requirement of matching the desired fundamental frequency. The regularization of the dispersion curves by means of optimum unwarping is experimentally evaluated.

  18. Synthesis of stiffness and mass matrices from experimental vibration modes.

    Science.gov (United States)

    Ross, R. G., Jr.

    1971-01-01

    With highly complex structures, it is sometimes desirable to derive a dynamic model of the system from experimental vibration data. This paper presents algorithms for synthesizing the mass and stiffness matrices from experimentally derived modal data in a way which preserves the physical significance of the individual mass and stiffness elements. The synthesizing procedures allow for the incorporation of other mass and stiffness data, whether empirical or based on the analyst's insight. The mass and stiffness matrices are derived for a cantilever beam example and are compared with those obtained using earlier techniques.

  19. Variable stiffness mechanisms of dual parameters changing magnetorheological fluid devices

    Science.gov (United States)

    Deng, Huaxia; Wang, Mingxian; Han, Guanghui; Zhang, Jin; Ma, Mengchao; Zhong, Xiang; Yu, Liandong

    2017-12-01

    Magnetorheological fluid (MRF) dampers are widely used as the variable damping devices in the semi-active vibration control system. In order to further improve the vibration reduction performance, a variable stiffness MRF damper with two chambers and two springs has been proposed recently. According to the test results, both of the damping and stiffness of the device can be controllable by changing the applied current independently. However, the mechanisms of variable stiffness for this device are still not clear. In this paper, the force transmissions of the parts of the variable stiffness MRF damper are analyzed, which reveals the variable stiffness mechanisms of dual parameters changing MRF devices. There are three stages for the variable stiffness MRF damper due to the friction and the yield of MR fluid. These stages can be controlled by the applied current of the different chambers, which changes the equivalent stiffness of the device. The proposed modelling of the device is verified by simulations and tests. In addition, the relationships between the equivalent stiffness and the parameters of the device are derived, which provide the design guidance for the variable stiffness MRF dampers.

  20. Nonlinear stiffness profiles of external fixators constructed with composite rods.

    Science.gov (United States)

    Carlson, Kimberly R; Kraus, Karl H; Kowaleski, Michael P

    2006-12-01

    To determine if composite connecting rods confer nonlinear stiffness characteristics on unilateral and bilateral external skeletal fixators (ESF) in cranial-caudal bending and axial loading. Mechanical testing performed on models. Six models of 6-pin ESF constructs composed of birch dowels, a commercial ESF system, and composite connecting rods. Unilateral and bilateral ESF configurations were assembled using either specially designed composite titanium and silicone (composite group) or solid titanium (solid group) connecting rods. Mechanical testing was performed in axial loading and 4-point cranial-caudal bending. Stiffness was determined at a low and high-load range, and was considered increasing and nonlinear if the stiffness at high loads was greater than at low loads. The stiffness of the solid group was linear in all testing modes and configurations. Bilateral composite fixators had a nonlinear increasing stiffness in axial loading and cranial-caudal bending. Unilateral composite fixators had a nonlinear increasing stiffness in axial loading, but not cranial-caudal bending. Solid connecting rods conferred a higher stiffness in all testing modes and configurations. Composite connecting rods resulted in nonlinear increasing axial and bending stiffness in bilateral fixators, and in axial load in unilateral fixators. Conventional ESF can be constructed so that the stiffness increases as load increases. This provides the surgeon with additional options to control the local mechanical environment of a healing fracture, which may be used to enhance fracture healing.

  1. 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.

  2. 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.

  3. Effect of exercise on arterial stiffness

    DEFF Research Database (Denmark)

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

    2017-01-01

    ), 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......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...... 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...

  4. Tissue Transglutaminase Modulates Vascular Stiffness and Function Through Crosslinking-Dependent and Crosslinking-Independent Functions.

    Science.gov (United States)

    Steppan, Jochen; Bergman, Yehudit; Viegas, Kayla; Armstrong, Dinani; Tan, Siqi; Wang, Huilei; Melucci, Sean; Hori, Daijiro; Park, Sung Yong; Barreto, Sebastian F; Isak, Abraham; Jandu, Sandeep; Flavahan, Nicholas; Butlin, Mark; An, Steven S; Avolio, Alberto; Berkowitz, Dan E; Halushka, Marc K; Santhanam, Lakshmi

    2017-02-03

    The structural elements of the vascular wall, namely, extracellular matrix and smooth muscle cells (SMCs), contribute to the overall stiffness of the vessel. In this study, we examined the crosslinking-dependent and crosslinking-independent roles of tissue transglutaminase (TG2) in vascular function and stiffness. SMCs were isolated from the aortae of TG2-/- and wild-type (WT) mice. Cell adhesion was examined by using electrical cell-substrate impedance sensing and PicoGreen assay. Cell motility was examined using a Boyden chamber assay. Cell proliferation was examined by electrical cell-substrate impedance sensing and EdU incorporation assays. Cell micromechanics were studied using magnetic torsion cytometry and spontaneous nanobead tracer motions. Aortic mechanics were examined by tensile testing. Vasoreactivity was studied by wire myography. SMCs from TG2-/- mice had delayed adhesion, reduced motility, and accelerated de-adhesion and proliferation rates compared with those from WT. TG2-/- SMCs were stiffer and displayed fewer cytoskeletal remodeling events than WT. Collagen assembly was delayed in TG2-/- SMCs and recovered with adenoviral transduction of TG2. Aortic rings from TG2-/- mice were less stiff than those from WT; stiffness was partly recovered by incubation with guinea pig liver TG2 independent of crosslinking function. TG2-/- rings showed augmented response to phenylephrine-mediated vasoconstriction when compared with WT. In human coronary arteries, vascular media and plaque, high abundance of fibronectin expression, and colocalization with TG2 were observed. TG2 modulates vascular function/tone by altering SMC contractility independent of its crosslinking function and contributes to vascular stiffness by regulating SMC proliferation and matrix remodeling. © 2017 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.

  5. State Agency Administrative Boundaries

    Data.gov (United States)

    Kansas Data Access and Support Center — This database comprises 28 State agency boundaries and point of contact. The Kansas Geological Survey collected legal descriptions of the boundaries for various...

  6. Allegheny County Municipal Boundaries

    Data.gov (United States)

    Allegheny County / City of Pittsburgh / Western PA Regional Data Center — This dataset demarcates the municipal boundaries in Allegheny County. Data was created to portray the boundaries of the 130 Municipalities in Allegheny County the...

  7. HUD GIS Boundary Files

    Data.gov (United States)

    Department of Housing and Urban Development — The HUD GIS Boundary Files are intended to supplement boundary files available from the U.S. Census Bureau. The files are for community planners interested in...

  8. Political State Boundary (National)

    Data.gov (United States)

    Department of Transportation — State boundaries with political limit - boundaries extending into the ocean (NTAD). The TIGER/Line Files are shapefiles and related database files (.dbf) that are an...

  9. Mechanical stiffness: a global parameter associated to elite sprinters performance

    Directory of Open Access Journals (Sweden)

    Fernando López Mangini

    Full Text Available Abstract This study analyzes vertical stiffness as a global parameter that could be directly associated to sprinter's performance. We evaluated vertical stiffness, performance, heart rate and lactate concentration on fifteen male sprinters that ran on a treadmill at gait transition speed and 13 km h−1. Vertical Stiffness was determined by the ratio of the vertical acceleration peak and maximum displacement of the center of mass. Physiological parameters were measured throughout the experimental procedure and performance was estimated by athlete's time records on 100 m track race. As expected, vertical stiffness and heart rate increased with running speed. We found a high correlation between heart rate and vertical stiffness at gait transition speed. However, at 13 km h−1, lactate peak showed a higher correlation with vertical stiffness, suggesting a greater participation of the anaerobic system. An inverse relationship between performance and vertical stiffness was found, where faster athletes were the stiffer ones. Performance and lactate peak presented the same inverse relationship; faster athletes had higher lactate peaks. As a result, faster athletes were stiffer and consume more energy. All in all, these findings suggest that mechanical stiffness could be a potential global parameter to evaluate performance in sprinters.

  10. A novel stiffness control method for series elastic actuator

    Science.gov (United States)

    Lin, Guangmo; Zhao, Xingang; Han, Jianda

    2017-01-01

    Compliance plays an important role in human-robot cooperation. However, fixed compliance, or fixed stiffness, is difficult to meet the growing needs of human machine collaboration. As a result, the robot actuator is demanded to be able to adjust its stiffness. This paper presents a stiffness control scheme for a single DOF series elastic actuator (SEA) with a linear spring mounted in series in the mechanism. In this proposed method, the output angle of the spring is measured and used to calculate the input angle of the spring, thus the equivalent stiffness of the robot actuator revealed to the human operator can be rendered in accordance to the desired stiffness. Since the techniques used in this method only involve the position information of the system, there is no need to install an expensive force/torque sensor on the actuator. Further, the force/torque produced by the actuator can be estimated by simply multiplying the deformation angle of the spring and its constant stiffness coefficient. The analysis of the stiffness controller is provided. Then a simulation that emulates a human operates the SEA while the stiffness controller is running is carried out and the results also validate the proposed method.

  11. 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.

  12. Alcohol intake and aortic stiffness in young men and women

    NARCIS (Netherlands)

    Elzen, A.P. van den; Sierksma, A.; Oren, A.; Vos, L.E.; Witteman, J.C.; Grobbee, D.E.; Hendriks, H.F.; Uiterwaal, C.S.; Bots, M.L.

    2005-01-01

    Background: Moderate alcohol consumption has been shown to protect against cardiovascular disease. Aortic stiffness can be regarded as a marker of cardiovascular disease risk. Previously we have shown an inverse to J-shaped association between alcohol intake and aortic stiffness in middle-aged and

  13. 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.

  14. A fourth order exponentially-fitted multiderivative method for Stiff ...

    African Journals Online (AJOL)

    A fourth order exponentially-fitted multiderivative method for Stiff initial value problems. ... Journal of the Nigerian Association of Mathematical Physics ... implemented and preliminary numerical results indicate that the approach compares favourably with other existing methods that have solved the same set of stiff problems.

  15. A review on in situ stiffness adjustment methods in MEMS

    NARCIS (Netherlands)

    de Laat, M.L.C.; Perez Garza, H.H.; Herder, J.L.; Ghatkesar, M.K.

    2016-01-01

    In situ stiffness adjustment in microelectromechanical systems is used in a variety of applications such as radio-frequency mechanical filters, energy harvesters, atomic force microscopy, vibration detection sensors. In this review we provide designers with an overview of existing stiffness

  16. Three-Dimensional Stiffness of the Carpal Arch

    Science.gov (United States)

    Gabra, Joseph N.; Li, Zong-Ming

    2015-01-01

    The carpal arch of the wrist is formed by irregularly shaped carpal bones interconnected by numerous ligaments, resulting in complex structural mechanics. The purpose of this study was to determine the three-dimensional stiffness characteristics of the carpal arch using displacement perturbations. It was hypothesized that the carpal arch would exhibit an anisotropic stiffness behavior with principal directions that are oblique to the conventional anatomical axes. Eight (n = 8) cadavers were used in this study. For each specimen, the hamate was fixed to a custom stationary apparatus. An instrumented robot arm applied three-dimensional displacement perturbations to the ridge of trapezium and corresponding reaction forces were collected. The displacement-force data were used to determine a three-dimensional stiffness matrix using least squares fitting. Eigendecomposition of the stiffness matrix was used to identify the magnitudes and directions of the principal stiffness components. The carpal arch structure exhibited anisotropic stiffness behaviors with a maximum principal stiffness of 16.4 ± 4.6 N/mm that was significantly larger than the other principal components of 3.1 ± 0.9 and 2.6 ± 0.5 N/mm (p articulation between the trapezium and scaphoid. This study provides advanced characterization of the wrist's three-dimensional structural stiffness for improved insight into wrist biomechanics, stability, and function. PMID:26617368

  17. Integrated Stiffness Analysis of Redundant Parallel Manipulator Based on Finite Element Method

    NARCIS (Netherlands)

    Wang, S.; Cheng, G.; Pang, Y.; Lodewijks, G.

    2015-01-01

    An integrated stiffness model is established for a Planar Parallel Manipulator (PPM) with actuation redundancy based on Finite Element Method (FEM), and the static stiffness, dynamitic stiffness and moving stiffness of the PPM are analyzed according to the integrated stiffness model. Firstly, a

  18. Stiffness and Adhesivity Control Aortic Valve Interstitial Cell Behavior within Hyaluronic Acid Based Hydrogels

    Science.gov (United States)

    Duan, Bin; Hockaday, Laura A.; Kapetanovic, Edi; Kang, Kevin H.; Butcher, Jonathan T.

    2013-01-01

    Bioactive and biodegradable hydrogels that mimic the extracellular matrix and regulate valve interstitial cells (VIC) behavior are of great interest as three dimensional (3D) model systems for understanding mechanisms of valvular heart disease pathogenesis in vitro and the basis for regenerative templates for tissue engineering. However, the role of stiffness and adhesivity of hydrogels in VIC behavior remains poorly understood. This study reports synthesis of oxidized and methacrylated hyaluronic acid (Me-HA and MOHA) and subsequent development of hybrid hydrogels based on modified HA and methacrylated gelatin (Me-Gel) for VIC encapsulation. The mechanical stiffness and swelling ratio of the hydrogels were tunable with molecular weight of HA and concentration/composition of precursor solution. The encapsulated VIC in pure HA hydrogels with lower mechanical stiffness showed more spreading morphology comparing to stiffer counterparts and dramatically upregulated alpha smooth muscle actin expression indicating more activated myofibroblast properties. The addition of Me-Gel in Me-HA facilitated cell spreading, proliferation and VIC migration from encapsulated spheroids and better maintained VIC fibroblastic phenotype. The VIC phenotype transition during migration from encapsulated spheroids in both Me-HA and Me-HA/Me-Gel hydrogel matrix was also observed. These findings are important for the rational design of hydrogels for controlling VIC morphology, and for regulating VIC phenotype and function. The Me-HA/Me-Gel hybrid hydrogels accommodated with VIC are promising as valve tissue engineering scaffolds and 3D model for understanding valvular pathobiology. PMID:23648571

  19. Position-dependent characterization of passive wrist stiffness.

    Science.gov (United States)

    Pando, Autumn L; Lee, Hyunglae; Drake, Will B; Hogan, Neville; Charles, Steven K

    2014-08-01

    Because the dynamics of wrist rotations are dominated by stiffness, understanding wrist rotations requires a thorough characterization of wrist stiffness in multiple degrees of freedom. The only prior measurement of multivariable wrist stiffness was confined to approximately one-seventh of the wrist range of motion (ROM). Here, we present a precise nonlinear characterization of passive wrist joint stiffness over a range three times greater, which covers approximately 70% of the functional ROM of the wrist. We measured the torque-displacement vector field in 24 directions and fit the data using thin-plate spline smoothing optimized with generalized cross validation. To assess anisotropy and nonlinearity, we subsequently derived several different approximations of the stiffness due to this multivariable vector field. The directional variation of stiffness was more pronounced than reported previously. A linear approximation (obtained by multiple linear regression over the entire field) was significantly more anisotropic (eigenvalue ratio of 2.69 ± 0.52 versus 1.58 ± 0.39; ) though less misaligned with the anatomical wrist axes (12.1 ± 4.6° versus 21.2 ± 9.2°; ). We also found that stiffness over this range exhibited considerable nonlinearity-the error associated with a linear approximation was 20-30%. The nonlinear characterization over this greater range confirmed significantly greater stiffness in radial deviation compared to ulnar deviation. This study provides a characterization of passive wrist stiffness better suited to investigations of natural wrist rotations, which cover much of the wrist's ROM. It also provides a baseline for the study of neurological and/or orthopedic disorders that result in abnormal wrist stiffness.

  20. Geometric and architectural contributions to hamstring musculotendinous stiffness.

    Science.gov (United States)

    Blackburn, J Troy; Pamukoff, Derek N

    2014-01-01

    Greater hamstring musculotendinous stiffness is associated with lesser anterior cruciate ligament loading mechanisms during both controlled joint perturbations and dynamic tasks, suggesting a potential protective mechanism. Additionally, lesser hamstring stiffness has been reported in females, potentially contributing to their greater risk of anterior cruciate ligament injury. However, the factors which contribute to high vs. low stiffness are unclear. Muscle geometry and architecture influence force production and may, therefore, influence stiffness. The purpose of this investigation was to evaluate the contributions of geometric and architectural muscle characteristics to hamstring stiffness. Thirty healthy individuals (15 males, 15 females) volunteered for participation. Biceps femoris long head cross-sectional area, pennation angle, fiber length, tendon stiffness, and posterior thigh fat thickness were assessed via ultrasound imaging, and strength was measured via isometric contraction. Stiffness was assessed via the damped oscillatory technique. Following normalization to anthropometric factors, only strength (r=0.535) and posterior thigh fat thickness (Spearman ρ=-0.305) were correlated with stiffness. Normalized tendon stiffness (0.06 vs. 0.10N/m·kg(-1)) and strength (7.1 vs. 10.0N·kg(-1)) were greater in males, while posterior thigh fat thickness (10.4 vs. 5.0mm) was greater in females. Greater posterior thigh fat thickness may influence stiffness by contributing to greater intramuscular fat and shank segment mass, and lesser muscle per unit mass in the thigh segment. These findings suggest that training designed to increase hamstring strength and decrease fat mass may be beneficial for anterior cruciate ligament injury prevention. © 2013.

  1. 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

  2. Potential effect of matrix stiffness on the enrichment of tumor initiating cells under three-dimensional culture conditions.

    Science.gov (United States)

    Liu, Chang; Liu, Yang; Xu, Xiao-xi; Wu, Hao; Xie, Hong-guo; Chen, Li; Lu, Ting; Yang, Li; Guo, Xin; Sun, Guang-wei; Wang, Wei; Ma, Xiao-jun; He, Xin

    2015-01-01

    Cancer stem cell (CSC) or tumor initiating cell (TIC) plays an important role in tumor progression and metastasis. Biophysical forces in tumor microenvironment have an important effect on tumor formation and development. In this study, the potential effect of matrix stiffness on the biological characteristics of human head and neck squamous cell carcinoma (HNSCC) TICs, especially the enrichment of HNSCC TICs, was investigated under three-dimensional (3D) culture conditions by means of alginate gel (ALG) beads with different matrix stiffnesses. ALG beads with soft (21 kPa), moderate (70 kPa) and hard (105 kPa) stiffness were generated by changing alginate concentration. It was found that significant HNSCC TIC enrichment was achieved in the ALG beads with moderate matrix stiffness (70 kPa). The gene expression of stemness markers Oct3/4 and Nanog, TIC markers CD44 and ABCG2 was enhanced in cells under this moderate (70 kPa) stiffness. HNSCC TIC proportion was also highly enriched under moderate matrix stiffness, accompanying with higher tumorigenicity, metastatic ability and drug resistance. And it was also found that the possible molecular mechanism underlying the regulated TIC properties by matrix stiffness under 3D culture conditions was significantly different from 2D culture condition. Therefore, the results achieved in this study indicated that 3D biophysical microenvironment had an important effect on TIC characteristics and alginate-based biomimetic scaffolds could be utilized as a proper platform to investigate the interaction between tumor cells and 3D microenvironment. Copyright © 2014 Elsevier Inc. All rights reserved.

  3. Substrate stiffness-modulated registry phase correlations in cardiomyocytes map structural order to coherent beating

    Science.gov (United States)

    Dasbiswas, K.; Majkut, S.; Discher, D. E.; Safran, Samuel A.

    2015-01-01

    Recent experiments show that both striation, an indication of the structural registry in muscle fibres, as well as the contractile strains produced by beating cardiac muscle cells can be optimized by substrate stiffness. Here we show theoretically how the substrate rigidity dependence of the registry data can be mapped onto that of the strain measurements. We express the elasticity-mediated structural registry as a phase-order parameter using a statistical physics approach that takes the noise and disorder inherent in biological systems into account. By assuming that structurally registered myofibrils also tend to beat in phase, we explain the observed dependence of both striation and strain measurements of cardiomyocytes on substrate stiffness in a unified manner. The agreement of our ideas with experiment suggests that the correlated beating of heart cells may be limited by the structural order of the myofibrils, which in turn is regulated by their elastic environment.

  4. 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.

  5. 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.

  6. Tuning the dependency between stiffness and permeability of a cell encapsulating hydrogel with hydrophilic pendant chains.

    Science.gov (United States)

    Cha, Chaenyung; Jeong, Jae Hyun; Shim, Jongwon; Kong, Hyunjoon

    2011-10-01

    The mechanical stiffness of a hydrogel plays a significant role in regulating the phenotype of cells that adhere to its surface. However, the effect of hydrogel stiffness on cells cultured within its matrix is not well understood, because of the intrinsic inverse dependency between the permeability and stiffness of hydrogels. This study therefore presents an advanced biomaterial design strategy to decrease the inverse dependency between permeability and stiffness of a cell encapsulating hydrogel. Hydrogels were made by cross-linking poly(ethylene glycol) diacrylate (PEGDA) and poly(ethylene glycol) monoacrylate (PEGMA), with PEGMA acting as a pendant polymer chain. Increasing the mass fraction of PEGMA while keeping the total polymer concentration constant led to a decrease in the elastic modulus (E) of the hydrogel, but caused a minimal increase in the swelling ratio (Q). The size and hydrophobicity of the end groups of pendant PEG chains further fine tuned the dependency between Q and E of the hydrogel. Pure PEGDA hydrogels with varying molecular weights, which show the same range of E but a much greater range of Q, were used as a control. Fibroblasts encapsulated in PEGDA-PEGMA hydrogels displayed more significant biphasic dependencies of cell viability and vascular endothelial growth factor (VEGF) expression on E than those encapsulated in pure PEGDA hydrogels, which were greatly influenced by Q. Overall, the hydrogel design strategy presented in this study will be highly useful to better regulate the phenotype and ultimately improve the therapeutic efficacy of a wide array of cells used in various biology studies and clinical settings. Copyright © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  7. Keratins significantly contribute to cell stiffness and impact invasive behavior.

    Science.gov (United States)

    Seltmann, Kristin; Fritsch, Anatol W; Käs, Josef A; Magin, Thomas M

    2013-11-12

    Cell motility and cell shape adaptations are crucial during wound healing, inflammation, and malignant progression. These processes require the remodeling of the keratin cytoskeleton to facilitate cell-cell and cell-matrix adhesion. However, the role of keratins for biomechanical properties and invasion of epithelial cells is only partially understood. In this study, we address this issue in murine keratinocytes lacking all keratins on genome engineering. In contrast to predictions, keratin-free cells show about 60% higher cell deformability even for small deformations. This response is compared with the less pronounced softening effects for actin depolymerization induced via latrunculin A. To relate these findings with functional consequences, we use invasion and 3D growth assays. These experiments reveal higher invasiveness of keratin-free cells. Reexpression of a small amount of the keratin pair K5/K14 in keratin-free cells reverses the above phenotype for the invasion but does not with respect to cell deformability. Our data show a unique role of keratins as major players of cell stiffness, influencing invasion with implications for epidermal homeostasis and pathogenesis. This study supports the view that down-regulation of keratins observed during epithelial-mesenchymal transition directly contributes to the migratory and invasive behavior of tumor cells.

  8. Decoupled control of stiffness and permeability with a cell-encapsulating poly(ethylene glycol) dimethacrylate hydrogel.

    Science.gov (United States)

    Cha, Chaenyung; Kim, So Youn; Cao, Lan; Kong, Hyunjoon

    2010-06-01

    Hydrogels are increasingly used as a cell encapsulation and transplantation device. The successful use of a hydrogel greatly relies on an ability to control hydrogel stiffness which affects structural integrity and regulates cellular phenotypes. However, conventional strategies to increase the gel stiffness lead to decrease in the gel permeability and subsequently deteriorate the viability of cells encapsulated in a gel matrix. This study presents a strategy to decouple the inversed dependency of permeability on the stiffness of a hydrogel by chemically cross-linking methacrylic alginate with poly(ethylene glycol) dimethacrylate (PEGDA). As expected, gel stiffness represented by elastic modulus was tuned over one order of magnitude with the concentration of methacrylic alginate and the degree of substitution of methacrylic groups. In contrast, swelling ratio of the hydrogel indicative of gel permeability was minimally changed because of multiple hydrophilic groups of alginate, similar to function of proteoglycans in a natural extracellular matrix. Furthermore, viability of neural cells encapsulated in a hydrogel of PEGDA and methacrylic alginate rather increased with hydrogel stiffness. Overall, the results of this study demonstrate an advanced biomaterial design paradigm which allows one to culture cells in a 3D matrix of varying rigidity. This study will therefore greatly expedite the use of a hydrogel system in both fundamental studies and clinical settings of cell therapies. (c) 2010 Elsevier Ltd. All rights reserved.

  9. 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.

  10. Stiffness Modulation of Rayed Fins by Curvature

    Science.gov (United States)

    Nguyen, Khoi; Yu, Ning; Venkadesan, Madhusudhan; Bandi, Mahesh; Mandre, Shreyas

    2016-11-01

    Fishes with rayed fins comprise over 99% of all extant fish species. Multifunctional use of fins, from propulsion to station holding, requires substantial modulation of stiffness. We propose that fishes stiffen the fin by curving it transverse to its length. This effect is similar to stiffening a dollar bill by curling it because of curvature-induced coupling of out-of-plane bending with in-plane stretching. Unlike a piece of paper, rayed fins are a composite of rays and membranes. We model this as parallel elastic beams (rays) with springy interconnections (membranes). Our analysis shows that the key parameters stiffening the fin are the ray anisotropy to bending, the misalignment of principal bending directions of adjacent rays, and the membrane elasticity. The composite fin stiffens when the principal bending directions of adjacent rays are misaligned due to fin curvature, which necessarily causes the membrane to stretch. Unlike a homogenous thin sheet, composite rayed structures are able to mimic curvature-induced stiffening by using misaligned rays even if the fin appears geometrically flat. Preliminary radiographic evidence from the rays of fish fins supports such a mechanism. Funding by Human Frontier Science Program.

  11. Simvastatin Ameliorates Matrix Stiffness-Mediated Endothelial Monolayer Disruption

    Science.gov (United States)

    Lampi, Marsha C.; Faber, Courtney J.; Huynh, John; Bordeleau, Francois; Zanotelli, Matthew R.; Reinhart-King, Cynthia A.

    2016-01-01

    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. PMID:26761203

  12. 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.

  13. 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.

  14. Influence of Compression and Stiffness Apparel on Vertical Jump Performance.

    Science.gov (United States)

    Wannop, John W; Worobets, Jay T; Madden, Ryan; Stefanyshyn, Darren J

    2016-04-01

    Compression apparel alters both compression of the soft tissues and the hip joint stiffness of athletes. It is not known whether it is the compression elements, the stiffness elements, or some combination that increases performance. Therefore, the purpose of this study was to determine how systematically increasing upper leg compression and hip joint stiffness independently from one another affects vertical jumping performance. Ten male athletes performed countermovement vertical jumps in 8 concept apparel conditions and 1 control condition (loose fitting shorts). The 8 apparel conditions, 4 that specifically altered the amount of compression exerted on the thigh and 4 that altered the hip joint stiffness by means of elastic thermoplastic polyurethane bands, were tested on 2 separate testing sessions (one testing the compression apparel and the other testing the stiffness apparel). Maximum jump height was measured, while kinematic data of the hip, knee, and ankle joint were recorded with a high-speed camera (480 Hz). Both compression and stiffness apparel can have a positive influence on vertical jumping performance. The increase in jump height for the optimal compression was due to increased hip joint range of motion and a trend of increasing the jump time. Optimal stiffness also increased jump height and had the trend of decreasing the hip joint range of motion and hip joint angular velocity. The exact mechanisms by which apparel interventions alter performance is not clear, but it may be due to alterations to the force-length and force-velocity relationships of muscle.

  15. Investigation of the torsional stiffness of flexible disc coupling

    Science.gov (United States)

    Buryy, A.; Simonovsky, V.; Obolonik, V.

    2017-08-01

    Calculation of flexible coupling torsional stiffness is required when analyzing the torsional vibrations of the reciprocating machinery train. While having the lowest torsional stiffness of all the elements of the train, flexible coupling has a significant influence on the natural frequencies of torsional vibration. However, considering structural complexity of coupling, precise definition of its torsional stiffness is quite a difficult task. The paper presents a method for calculating the torsional stiffness of flexible disc coupling based on the study of its finite element model response under the action of torque. The analysis of the basic parameters that quantitatively and qualitatively affect the coupling torsional stiffness has been also provided. The results of the calculation as well as model adequacy, sufficient for practical application, have been confirmed at the experimental measurement of flexible disc coupling torsional stiffness. The obtained elastic characteristics (dependences of applied torque and torsional stiffness versus twist angle) are nonlinear in the initial stage of loading. This feature should be taken into account when creating reliable mathematical models of torsional vibrations of reciprocating machinery trains containing flexible disc couplings.

  16. Stiffness Is the Cardinal Symptom of Inflammatory Musculoskeletal Diseases, Yet Still Variably Measured: Report from the OMERACT 2016 Stiffness Special Interest Group.

    Science.gov (United States)

    Halls, Serena; Sinnathurai, Premarani; Hewlett, Sarah; Mackie, Sarah L; March, Lyn; Bartlett, Susan J; Bingham, Clifton O; Alten, Rieke; Campbell, Ina; Hill, Catherine L; Holt, Robert J; Hughes, Rod; Kirwan, John R; Leong, Amye L; Leung, Ying Ying; Lyddiatt, Anne; Neill, Lorna; Orbai, Ana-Maria

    2017-12-01

    The objectives of the Outcome Measures in Rheumatology (OMERACT) Stiffness special interest group (SIG) are to characterize stiffness as an outcome in rheumatic disease and to identify and validate a stiffness patient-reported outcome (PRO) in rheumatology. At OMERACT 2016, international groups presented and discussed results of several concurrent research projects on stiffness: a literature review of rheumatoid arthritis (RA) stiffness PRO measures, a qualitative investigation into the RA and polymyalgia rheumatica patient perspective of stiffness, data-driven stiffness conceptual model development, development and testing of an RA stiffness PRO measure, and a quantitative work testing stiffness items in patients with RA and psoriatic arthritis. The literature review identified 52 individual stiffness PRO measures assessing morning or early morning stiffness severity/intensity or duration. Items were heterogeneous, had little or inconsistent psychometric property evidence, and did not appear to have been developed according to the PRO development guidelines. A poor match between current stiffness PRO and the conceptual model identifying the RA patient experience of stiffness was identified, highlighting a major flaw in PRO selection according to the OMERACT filter 2.0. Discussions within the Stiffness SIG highlighted the importance of further research on stiffness and defined a research agenda.

  17. The Dynamic Stiffness of Surface Footings for Offshore Wind Turbines

    DEFF Research Database (Denmark)

    Vahdatirad, Mohammadjavad; Andersen, Lars; Clausen, Johan

    2011-01-01

    This study concerns the dynamic stiffness of foundations for large offshore wind turbines. Especially, the purpose of the analysis is to quantify the uncertainties related to the first natural frequency of a turbine supported by a surface footing on layered soil. The dynamic properties...... due to sediment transportation. Further, the stiffness and density of the materials within a single layer is subject to uncertainties. This leads to uncertainties of the dynamic stiffness of the foundation and therefore the natural frequencies. The aim of the study is to quantify the level...

  18. 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.

  19. Understanding perceptual boundaries in laparoscopic surgery.

    Science.gov (United States)

    Lamata, Pablo; Gomez, Enrique J; Hernández, Félix Lamata; Oltra Pastor, Alfonso; Sanchez-Margallo, Francisco Miquel; Del Pozo Guerrero, Francisco

    2008-03-01

    Human perceptual capabilities related to the laparoscopic interaction paradigm are not well known. Its study is important for the design of virtual reality simulators, and for the specification of augmented reality applications that overcome current limitations and provide a supersensing to the surgeon. As part of this work, this article addresses the study of laparoscopic pulling forces. Two definitions are proposed to focalize the problem: the perceptual fidelity boundary, limit of human perceptual capabilities, and the Utile fidelity boundary, that encapsulates the perceived aspects actually used by surgeons to guide an operation. The study is then aimed to define the perceptual fidelity boundary of laparoscopic pulling forces. This is approached with an experimental design in which surgeons assess the resistance against pulling of four different tissues, which are characterized with both in vivo interaction forces and ex vivo tissue biomechanical properties. A logarithmic law of tissue consistency perception is found comparing subjective valorizations with objective parameters. A model of this perception is developed identifying what the main parameters are: the grade of fixation of the organ, the tissue stiffness, the amount of tissue bitten, and the organ mass being pulled. These results are a clear requirement analysis for the force feedback algorithm of a virtual reality laparoscopic simulator. Finally, some discussion is raised about the suitability of augmented reality applications around this surgical gesture.

  20. Characterizations of boundary pluripolar hulls

    NARCIS (Netherlands)

    Djire, I.K.; Wiegerinck, J.

    2016-01-01

    We present some basic properties of the so-called boundary relative extremal function and discuss boundary pluripolar sets and boundary pluripolar hulls. We show that for B-regular domains the boundary pluripolar hull is always trivial on the boundary of the domain and present a “boundary version”

  1. Grain Boundary Complexions

    Science.gov (United States)

    2014-05-01

    deter- mine bulk materials behavior and properties such as superplasticity, creep, fatigue, corrosion , strength and conductivity [2]. Grain boundary...interface (i.e. lattice mismatch accommodated by interface dislocations ), wetting transitions will not occur. A wetting transition is possible in the case...melting only starts around dislocations at low- angle grain boundaries; the grain boundary structure con- sists of isolated liquid pools separated by

  2. Stable Boundary Layer Issues

    OpenAIRE

    Steeneveld, G.J.

    2012-01-01

    Understanding and prediction of the stable atmospheric boundary layer is a challenging task. Many physical processes are relevant in the stable boundary layer, i.e. turbulence, radiation, land surface coupling, orographic turbulent and gravity wave drag, and land surface heterogeneity. The development of robust stable boundary layer parameterizations for use in NWP and climate models is hampered by the multiplicity of processes and their unknown interactions. As a result, these models suffer ...

  3. Oxygen boundary crossing probabilities.

    Science.gov (United States)

    Busch, N A; Silver, I A

    1987-01-01

    The probability that an oxygen particle will reach a time dependent boundary is required in oxygen transport studies involving solution methods based on probability considerations. A Volterra integral equation is presented, the solution of which gives directly the boundary crossing probability density function. The boundary crossing probability is the probability that the oxygen particle will reach a boundary within a specified time interval. When the motion of the oxygen particle may be described as strongly Markovian, then the Volterra integral equation can be rewritten as a generalized Abel equation, the solution of which has been widely studied.

  4. Arterial pressure suffices to increase liver stiffness.

    Science.gov (United States)

    Piecha, Felix; Peccerella, Teresa; Bruckner, Tom; Seitz, Helmut-Karl; Rausch, Vanessa; Mueller, Sebastian

    2016-11-01

    Noninvasive measurement of liver stiffness (LS) has been established to screen for liver fibrosis. Since LS is also elevated in response to pressure-related conditions such as liver congestion, this study was undertaken to learn more about the role of arterial pressure on LS. LS was measured by transient elastography (μFibroscan platform, Echosens, Paris, France) during single intravenous injections of catecholamines in anesthetized rats with and without thioacetamide (TAA)-induced fibrosis. The effect of vasodilating glycerol trinitrate (GTN) on LS was also studied. Pressures in the abdominal aorta and caval and portal veins were measured in real time with the PowerLab device (AD Instruments, Dunedin, New Zealand). Baseline LS values in all rats (3.8 ± 0.5 kPa, n = 25) did not significantly differ from those in humans. Epinephrine and norepinephrine drastically increased mean arterial pressure (MAP) from 82 to 173 and 156 mmHg. Concomitantly, LS almost doubled from 4 to 8 kPa, while central venous pressure remained unchanged. Likewise, portal pressure only showed a slight and delayed increase. In the TAA-induced fibrosis model, LS increased from 9.5 ± 1.0 to 25.6 ± 14.7 kPa upon epinephrine injection and could efficiently be decreased by GTN. We finally show a direct association in humans in a physiological setting of elevated cardiac output and MAP. During continuous spinning at 200 W, MAP increased from 84 ± 8 to 99 ± 11 mmHg while LS significantly increased from 4.4 ± 1.8 to 6.7 ± 2.1 kPa. In conclusion, our data show that arterial pressure suffices to increase LS. Moreover, lowering MAP efficiently decreases LS in fibrotic livers that are predominantly supplied by arterial blood. Copyright © 2016 the American Physiological Society.

  5. A single gene connects stiffness in glaucoma and the vascular system.

    Science.gov (United States)

    Borrás, Teresa

    2017-05-01

    Arterial calcification results in arterial stiffness and higher systolic blood pressure. Arterial calcification is prevented by the high expression of the Matrix-Gla gene (MGP) in the vascular smooth muscle cells (VSMC) of the arteries' tunica media. Originally, MGP, a gene highly expressed in cartilage and VSMC, was found to be one of the top expressed genes in the trabecular meshwork. The creation of an Mgp-lacZ Knock-In mouse and the use of mouse genetics revealed that in the eye, Mgp's abundant expression is localized and restricted to glaucoma-associated tissues from the anterior and posterior segments. In particular, it is specifically expressed in the regions of the trabecular meshwork and of the peripapillary sclera that surrounds the optic nerve. Because stiffness in these tissues would significantly alter outflow facility and biomechanical scleral stress in the optic nerve head (ONH), we propose MGP as a strong candidate for the regulation of stiffness in glaucoma. MGP further illustrates the presence of a common function affecting key glaucomatous parameters in the front and back of the eye, and thus offers the possibility for a sole therapeutic target for the disease. Copyright © 2016. Published by Elsevier Ltd.

  6. A Variable Stiffness Concept For Efficient Aircraft Vertical Tail Design

    National Research Council Canada - National Science Library

    Cooper, Jonathan E; Sensburg, O; Amprikidis, M

    2003-01-01

    This report results from a contract tasking University of Manchester as follows: The contractor will investigate using a variable stiffness vertical tail attachment to control aeroelastic performance over a range of dynamic pressures...

  7. Operator-Based Preconditioning of Stiff Hyperbolic Systems

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-02-09

    We introduce an operator-based scheme for preconditioning stiff components encoun- tered 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 char- acteristic 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.

  8. Arterial Stiffness and Renal Replacement Therapy: A Controversial Topic.

    Science.gov (United States)

    Fischer, Edmundo Cabrera; Zócalo, Yanina; Galli, Cintia; Wray, Sandra; Bia, Daniel

    2015-01-01

    The increase of arterial stiffness has been to have a significant impact on predicting mortality in end-stage renal disease patients. Pulse wave velocity (PWV) is a noninvasive, reliable parameter of regional arterial stiffness that integrates the vascular geometry and arterial wall intrinsic elasticity and is capable of predicting cardiovascular mortality in this patient population. Nevertheless, reports on PWV in dialyzed patients are contradictory and sometimes inconsistent: some reports claim the arterial wall stiffness increases (i.e., PWV increase), others claim that it is reduced, and some even state that it augments in the aorta while it simultaneously decreases in the brachial artery pathway. The purpose of this study was to analyze the literature in which longitudinal or transversal studies were performed in hemodialysis and/or peritoneal dialysis patients, in order to characterize arterial stiffness and the responsiveness to renal replacement therapy.

  9. Arterial Stiffness and Renal Replacement Therapy: A Controversial Topic

    Directory of Open Access Journals (Sweden)

    Edmundo Cabrera Fischer

    2015-01-01

    Full Text Available The increase of arterial stiffness has been to have a significant impact on predicting mortality in end-stage renal disease patients. Pulse wave velocity (PWV is a noninvasive, reliable parameter of regional arterial stiffness that integrates the vascular geometry and arterial wall intrinsic elasticity and is capable of predicting cardiovascular mortality in this patient population. Nevertheless, reports on PWV in dialyzed patients are contradictory and sometimes inconsistent: some reports claim the arterial wall stiffness increases (i.e., PWV increase, others claim that it is reduced, and some even state that it augments in the aorta while it simultaneously decreases in the brachial artery pathway. The purpose of this study was to analyze the literature in which longitudinal or transversal studies were performed in hemodialysis and/or peritoneal dialysis patients, in order to characterize arterial stiffness and the responsiveness to renal replacement therapy.

  10. Torque-stiffness-controlled dynamic walking with central pattern generators.

    Science.gov (United States)

    Huang, Yan; Vanderborght, Bram; Van Ham, Ronald; Wang, Qining

    2014-12-01

    Walking behavior is modulated by controlling joint torques in most existing passivity-based bipeds. Controlled Passive Walking with adaptable stiffness exhibits controllable natural motions and energy efficient gaits. In this paper, we propose torque-stiffness-controlled dynamic bipedal walking, which extends the concept of Controlled Passive Walking by introducing structured control parameters and a bio-inspired control method with central pattern generators. The proposed walking paradigm is beneficial in clarifying the respective effects of the external actuation and the internal natural dynamics. We present a seven-link biped model to validate the presented walking. Effects of joint torque and joint stiffness on gait selection, walking performance and walking pattern transitions are studied in simulations. The work in this paper develops a new solution of motion control of bipedal robots with adaptable stiffness and provides insights of efficient and sophisticated walking gaits of humans.

  11. Dynamic Stiffness Analysis of Curved Thin-Walled Beams

    Directory of Open Access Journals (Sweden)

    A.Y.T. Leung

    1993-01-01

    Full Text Available The natural vibration problem of curved thin-walled beams is solved by the dynamic stiffness method. The dynamic stiffness of a curved open thin-walled beam is given. The computed natural frequencies of the beam are compared with those obtained by a completely analytical method to show the high accuracy of the present method. The interaction of in-plane and out-of-plane modes is emphasized.

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

    OpenAIRE

    Venkata Giri Kumar, P.; Deshpande, Sudheer; Joshi, Aniruddha; More, Pooja; Nagendra, H.R.

    2017-01-01

    Background The variations in Tridoshas are the basis for disease diagnosis and treatment in Ayurveda. The doshas are assessed by sensing the pulse manually with fingers which depends on skill of the physician. There is a need to measure doshas using instruments and study them objectively. Objective Arterial stiffness is well established pulse parameter in modern medicine and is closely associated to kathinya in the context of Ayurveda. The aim of our study was to measure arterial stiffness us...

  13. Importance of arterial stiffness in predicting cardiovascular events

    Directory of Open Access Journals (Sweden)

    Ecobici Monica

    2017-03-01

    Full Text Available Introduction. Cardiovascular events represent an important cause of morbidity and mortality in the entire population. Arterial stiffness is currently considered one of the most important risk factors for the development of cardiovascular events. The gold-standard for evaluating arterial stiffness is pulse wave velocity (PWV. Recent studies have demonstrated that PWV is an independent risk factor regarding the development of cardiovascular events, especially in certain categories of patients.

  14. Relationship between increased carotid artery stiffness and idiopathic subjective tinnitus.

    Science.gov (United States)

    Bayraktar, C; Taşolar, S

    2017-05-01

    Tinnitus is defined as perception of sound with no external stimulus, and can separate into pulsatile and non-pulsatile types. Arterial stiffness is a parameter that can predict the cardiovascular event and associated with incidence of stroke. It has been shown that increased arterial stiffness may lead to microvascular damage in brain. Our aim was to assess the arterial stiffness of the carotid system in the development and severity of idiopathic subjective tinnitus. Forty subjective tinnitus patients and 40 age- and sex-matched controls were enrolled in the study. The parameters obtained from the participants included pure tone hearing (dB), serum lipid profile (mg/dl), fasting glucose (mg/dl), blood pressure (mmHg), and body mass index (BMI, kg/m2). The common carotid artery (CCA) stiffness index, Young's elastic modulus (YEM), common carotid intima-media thickness (CIMT), peak systolic velocity (PSV), end-diastolic velocity (EDV), resistive index (RI), pulsatility index (PI), vessel diameter, mean velocity (MV), and volume flow (VF) were measured in both the right and left common carotid arteries in both groups. The CCA stiffness index, YEM measurements, right CIMT, and left PI were found to be significantly higher in the patients than those in the control group (p tinnitus and the patient characteristics, there was a significant positive correlation with the CCA stiffness index, YEM measurements, left CIMT, and neutrophil-to-lymphocyte ratio (NLR). However, only the right and left CCA stiffness parameters were found to be statistically significant in the multivariate analysis as independent predictors of a moderate to high degree of tinnitus. The increased stiffness index of the common carotid arteries was significantly associated with the formation and severity of tinnitus. Therefore, an assessment of the carotideal system may be helpful in these patients.

  15. Method Suitable for Updating the Boundary Condition of Continuous Beam Bridges

    Science.gov (United States)

    Cao, JianXin; Zheng, Honglan; Liu, Yang

    2017-10-01

    The boundary support conditions of continuous beam bridges play the great influence on the results of the structural analysis, but it is difficult to accurately model the boundaries owing to the complexity structure of constraint conditions. To address this issue, a parameterized method is proposed to update the boundary support conditions in this study. First, the connection stiffness at boundary is considered as the optimization variable, and then the optimization problem of updating the boundary conditions are described in detail based on the theory of finite element model updating. Second, for verifying the proposed method, a loading test was conducted on an actual three-span continuous beam bridge. With the proposed method, the discrepancy between the measured modal parameters and the analytical results are greatly reduced; therefore, it is shown that the proposed method is effective for updating the boundary support conditions of actual continuous beam bridges.

  16. Leg stiffness of sprinters using running-specific prostheses

    Science.gov (United States)

    McGowan, Craig P.; Grabowski, Alena M.; McDermott, William J.; Herr, Hugh M.; Kram, Rodger

    2012-01-01

    Running-specific prostheses (RSF) are designed to replicate the spring-like nature of biological legs (bioL) during running. However, it is not clear how these devices affect whole leg stiffness characteristics or running dynamics over a range of speeds. We used a simple spring–mass model to examine running mechanics across a range of speeds, in unilateral and bilateral transtibial amputees and performance-matched controls. We found significant differences between the affected leg (AL) of unilateral amputees and both ALs of bilateral amputees compared with the bioL of non-amputees for nearly every variable measured. Leg stiffness remained constant or increased with speed in bioL, but decreased with speed in legs with RSPs. The decrease in leg stiffness in legs with RSPs was mainly owing to a combination of lower peak ground reaction forces and increased leg compression with increasing speeds. Leg stiffness is an important parameter affecting contact time and the force exerted on the ground. It is likely that the fixed stiffness of the prosthesis coupled with differences in the limb posture required to run with the prosthesis limits the ability to modulate whole leg stiffness and the ability to apply high vertical ground reaction forces during sprinting. PMID:22337629

  17. 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.

  18. Inflammatory Markers for Arterial Stiffness in Cardiovascular Diseases

    Directory of Open Access Journals (Sweden)

    Ioana Mozos

    2017-08-01

    Full Text Available Arterial stiffness predicts an increased risk of cardiovascular events. Inflammation plays a major role in large arteries stiffening, related to atherosclerosis, arteriosclerosis, endothelial dysfunction, smooth muscle cell migration, vascular calcification, increased activity of metalloproteinases, extracellular matrix degradation, oxidative stress, elastolysis, and degradation of collagen. The present paper reviews main mechanisms explaining the crosstalk between inflammation and arterial stiffness and the most common inflammatory markers associated with increased arterial stiffness, considering the most recent clinical and experimental studies. Diverse studies revealed significant correlations between the severity of arterial stiffness and inflammatory markers, such as white blood cell count, neutrophil/lymphocyte ratio, adhesion molecules, fibrinogen, C-reactive protein, cytokines, microRNAs, and cyclooxygenase-2, in patients with a broad variety of diseases, such as metabolic syndrome, diabetes, coronary heart disease, peripheral arterial disease, malignant and rheumatic disorders, polycystic kidney disease, renal transplant, familial Mediterranean fever, and oral infections, and in women with preeclampsia or after menopause. There is strong evidence that inflammation plays an important and, at least, partly reversible role in the development of arterial stiffness, and inflammatory markers may be useful additional tools in the assessment of the cardiovascular risk in clinical practice. Combined assessment of arterial stiffness and inflammatory markers may improve non-invasive assessment of cardiovascular risk, enabling selection of high-risk patients for prophylactic treatment or more regular medical examination. Development of future destiffening therapies may target pro-inflammatory mechanisms.

  19. 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.

  20. 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.

  1. Changes in human knee ligament stiffness secondary to osteoarthritis.

    Science.gov (United States)

    Fishkin, Zair; Miller, David; Ritter, Christopher; Ziv, Israel

    2002-03-01

    Stiffness of the medial (MCL) and lateral (LCL) collateral ligaments was compared between a group of 10 patients undergoing total knee arthroplasty for varus degenerative osteoarthritis (OAP), a group of 10 osteoarthritic cadaveric knees (OAC), and a group of 10 non-osteoarthritic cadaveric knees (NOA). A load-elongation curve was obtained for the medial and lateral compartments of each knee using an instrumented Moreland spreader. A strain gage (SG) was attached to the spreader handle and strain was calibrated to load applied against the spread distance. In extension, medial compartment stiffness of the OAP, OAC, and NOA groups was 60.7+/-16, 52.8+/-9.3 and 21.4+/-5.0 N/mm, respectively. Lateral compartment stiffness in extension was 29.2+/-9.2, 33.3+/-10.3 and 19.5+/-5.3 N/mm, for OAP, OAC, and NOA, respectively. Differences in stiffness between the OAP and OAC groups were not statistically significant (p > 0.05). However, the osteoarthritic groups (OAP and OAC) demonstrated a statistically significantly (p < 0.05) increase in ligament stiffness when compared to the NOA group. Following knee arthroplasty, stiffer medial structures in extension may lead to flexion contracture and accelerated polyethylene wear. Adequate bone resection, in conjunction with soft tissue release may alleviate the threefold increase in stiffness observed in the medial compartment secondary to OA without jeopardizing joint stability.

  2. Measurement of cadaver lumbar spine motion segment stiffness.

    Science.gov (United States)

    Brown, Mark D; Holmes, David C; Heiner, Anneliese D

    2002-05-01

    Prospective. To measure lumbar spine motion segment stiffness and relate it to the degree of disc degeneration. The association between the instability of the lumbar spine motion segment and disc degeneration remains unclear. The traditional method for determining motion segment instability at the time of decompressive surgery is a manual test performed by the surgeon. To quantify instability of the lumbar spine, a vertebrae distractor was developed in the authors' laboratory to measure motion segment stiffness by applying a defined load at a constant rate. Lumbar stiffness was measured by subjecting cadaver lumbar spine motion segments to a constant rate flexion-traction load and recording the magnitude of the resistance to distraction versus the range of motion. Disc degeneration was measured by pressure-volume discography and by grading of disc morphology. Motion segment stiffness decreased with the initial stages of disc degeneration and then increased with severe disc degeneration. This measure of motion segment stiffness correlated well with a manual stiffness measure. The observed results follow an accepted hypothesis of motion segment instability associated with disc degeneration.

  3. Leg stiffness of sprinters using running-specific prostheses.

    Science.gov (United States)

    McGowan, Craig P; Grabowski, Alena M; McDermott, William J; Herr, Hugh M; Kram, Rodger

    2012-08-07

    Running-specific prostheses (RSF) are designed to replicate the spring-like nature of biological legs (bioL) during running. However, it is not clear how these devices affect whole leg stiffness characteristics or running dynamics over a range of speeds. We used a simple spring-mass model to examine running mechanics across a range of speeds, in unilateral and bilateral transtibial amputees and performance-matched controls. We found significant differences between the affected leg (AL) of unilateral amputees and both ALs of bilateral amputees compared with the bioL of non-amputees for nearly every variable measured. Leg stiffness remained constant or increased with speed in bioL, but decreased with speed in legs with RSPs. The decrease in leg stiffness in legs with RSPs was mainly owing to a combination of lower peak ground reaction forces and increased leg compression with increasing speeds. Leg stiffness is an important parameter affecting contact time and the force exerted on the ground. It is likely that the fixed stiffness of the prosthesis coupled with differences in the limb posture required to run with the prosthesis limits the ability to modulate whole leg stiffness and the ability to apply high vertical ground reaction forces during sprinting.

  4. Stable Boundary Layer Issues

    NARCIS (Netherlands)

    Steeneveld, G.J.

    2012-01-01

    Understanding and prediction of the stable atmospheric boundary layer is a challenging task. Many physical processes are relevant in the stable boundary layer, i.e. turbulence, radiation, land surface coupling, orographic turbulent and gravity wave drag, and land surface heterogeneity. The

  5. Dynamic stiffness of horizontally vibrating suction caissons

    DEFF Research Database (Denmark)

    Latini, Chiara; Zania, Varvara; Cisternino, Michele

    2016-01-01

    The promising potential for offshore wind market is on developing wind farms in deeper waters with bigger turbines. In deeper waters the design foundation configuration may consist of jacket structures supported by floating piles or by suction caissons. Taking the soil-structure interaction effects...... of this type of foundation using the finite element method (FEM) to account for the interaction with the soil. 3D numerical models for both the soil and the suction caisson are formulated in a frequency domain. The response of the soil surrounding the foundation is considered linear viscoelastic...... with hysteretic type damping. In addition, non-reflective boundaries are included in the model. Two different soil profiles are presented, one when the rigid bedrock is set close to the seabed and the other one when it is far away. The dynamic impedances at the top of the foundation are determined and compared...

  6. An optimised stiffness reduction method for simulating infinite elastic space using commercial Finite Elements codes

    Science.gov (United States)

    Pettit, J. R.; Walker, A.; Lowe, M. J. S.

    2015-01-01

    A common goal when using Finite Element (FE) modelling in time domain wave scattering problems is to minimise model size by only considering a region immediately surrounding a scatterer or feature of interest. The model boundaries must simulate infinite space by minimising the reflection of incident waves. This is a significant and long-standing challenge that has only achieved partial success. Industrial companies wishing to perform such modelling are keen to use established commercial FE packages that offer a thorough history of validation and testing. Unfortunately, this limits the flexibility available to modellers preventing the use of popular research tools such as Perfectly Matched Layers (PML). Unlike PML, Absorbing Layers by Increasing Damping (ALID) have proven successful offering practical implementation into any solver that has representation of material damping. Despite good performance further improvements are desirable. Here, a Stiffness Reduction Method (SRM) has been developed and optimised to operate within a significantly reduced spatial domain. The technique is applied by altering damping and stiffness matrices, inducing decay of incident waves. Variables are expressed as a function of known model constants, easing implementation for generic problems. Analytical and numerical solutions have shown that SRM out performs ALID, with results approaching those of PML.

  7. Boundary definition of a multiverse measure

    Science.gov (United States)

    Bousso, Raphael; Freivogel, Ben; Leichenauer, Stefan; Rosenhaus, Vladimir

    2010-12-01

    We propose to regulate the infinities of eternal inflation by relating a late time cutoff in the bulk to a short-distance cutoff on the future boundary. The light-cone time of an event is defined in terms of the volume of its future light cone on the boundary. We seek an intrinsic definition of boundary volumes that makes no reference to bulk structures. This requires taming the fractal geometry of the future boundary and lifting the ambiguity of the conformal factor. We propose to work in the conformal frame in which the boundary Ricci scalar is constant. We explore this proposal in the Friedmann-Robertson-Walker approximation for bubble universes. Remarkably, we find that the future boundary becomes a round three-sphere, with smooth metric on all scales. Our cutoff yields the same relative probabilities as a previous proposal that defined boundary volumes by projection into the bulk along timelike geodesics. Moreover, it is equivalent to an ensemble of causal patches defined without reference to bulk geodesics. It thus yields a holographically motivated and phenomenologically successful measure for eternal inflation.

  8. Effect of crack orientation statistics on effective stiffness of mircocracked solid

    DEFF Research Database (Denmark)

    Kushch, V.I.; Sevostianov, I.; Mishnaevsky, Leon

    2009-01-01

    This paper addresses the problem of calculating effective elastic properties of a solid containing multiple cracks with prescribed orientation statistics. To do so, the representative unit cell approach has been used. The microgeometry of a cracked solid is modeled by a periodic structure...... with a unit cell containing multiple cracks: a sufficient number is taken to account for the microstructure statistics. The developed method combines the superposition principle, the technique of complex potentials and certain new results in the theory of special functions. A proper choice of potentials...... provides reducing the boundary-value problem to an ordinary, well-posed set of linear algebraic equations. The exact finite form expression of the effective stiffness tensor has been obtained by analytical averaging the strain and stress fields. The convergence study has been performed: the statistically...

  9. Dynamic Force Identification for Beamlike Structures Using an Improved Dynamic Stiffness Method

    Directory of Open Access Journals (Sweden)

    S.L. Chen

    1996-01-01

    Full Text Available In this study a procedure of dynamic force identification for beamlike structures is developed based on an improved dynamic stiffness method. In this procedure, the entire structure is first divided into substructures according to the excitation locations and the measured response sites. Each substructure is then represented by an equivalent element. The resulting model only retains the degree of freedom (DOF associated with the excitations and the measured responses and the DOF corresponding to the boundaries of the structures. Because the technique partly bypasses the processes of modal parameter extraction, global matrix inversion, and model reduction, it can eliminate many of the approximations and errors that may be introduced during these processes. The principle of the method is described in detail and its efficiency is demonstrated via numerical simulations of three different structures. The sensitivity of the estimated force to random noise is discussed and the limitation of the technique is pointed out.

  10. Computational methods for the identification of spatially varying stiffness and damping in beams

    Science.gov (United States)

    Banks, H. T.; Rosen, I. G.

    1986-01-01

    A numerical approximation scheme for the estimation of functional parameters in Euler-Bernoulli models for the transverse vibration of flexible beams with tip bodies is developed. The method permits the identification of spatially varying flexural stiffness and Voigt-Kelvin viscoelastic damping coefficients which appear in the hybrid system of ordinary and partial differential equations and boundary conditions describing the dynamics of such structures. An inverse problem is formulated as a least squares fit to data subject to constraints in the form of a vector system of abstract first order evolution equations. Spline-based finite element approximations are used to finite dimensionalize the problem. Theoretical convergence results are given and numerical studies carried out on both conventional (serial) and vector computers are discussed.

  11. 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.

  12. Seeking the boundary of boundary extension.

    Science.gov (United States)

    McDunn, Benjamin A; Siddiqui, Aisha P; Brown, James M

    2014-04-01

    Boundary extension (BE) is a remarkably consistent visual memory error in which participants remember seeing a more wide-angle image of a scene than was actually viewed (Intraub & Richardson, Journal of Experimental Psychology: Learning, Memory, and Cognition 15:179-187, 1989). Multiple stimulus factors are thought to contribute to the occurrence of BE, including object recognition, conceptual knowledge of scenes, and amodal perception at the view boundaries (Intraub, Wiley Interdisciplinary Reviews: Cognitive Science 3:117-127, 2012). In the present study, we used abstract scenes instead of images of the real world, in order to remove expectations based on semantic associations with objects and the schematic context of the view. Close-angle and wide-angle scenes were created using irregular geometric shapes rated by independent observers as lacking any easily recognizable structure. The abstract objects were tested on either a random-dot or a blank background in order to assess the influence of implied continuation of the image beyond its boundaries. The random-dot background conditions had background occlusion cues either present or absent at the image border, in order to test their influence on BE in the absence of high-level information about the scenes. The results indicate that high-level information about objects and schematic context is unnecessary for BE to occur, and that occlusion information at the image boundary also has little influence on BE. Contrary to previous studies, we also found clear BE for all conditions, despite using scenes depicting undetailed objects on a blank white background. The results highlighted the ubiquitous nature of BE and the adaptability of scene perception processes.

  13. Immersed Boundary Models for Quantifying Flow-Induced Mechanical Stimuli on Stem Cells Seeded on 3D Scaffolds in Perfusion Bioreactors.

    Directory of Open Access Journals (Sweden)

    Yann Guyot

    2016-09-01

    Full Text Available Perfusion bioreactors regulate flow conditions in order to provide cells with oxygen, nutrients and flow-associated mechanical stimuli. Locally, these flow conditions can vary depending on the scaffold geometry, cellular confluency and amount of extra cellular matrix deposition. In this study, a novel application of the immersed boundary method was introduced in order to represent a detailed deformable cell attached to a 3D scaffold inside a perfusion bioreactor and exposed to microscopic flow. The immersed boundary model permits the prediction of mechanical effects of the local flow conditions on the cell. Incorporating stiffness values measured with atomic force microscopy and micro-flow boundary conditions obtained from computational fluid dynamics simulations on the entire scaffold, we compared cell deformation, cortical tension, normal and shear pressure between different cell shapes and locations. We observed a large effect of the precise cell location on the local shear stress and we predicted flow-induced cortical tensions in the order of 5 pN/μm, at the lower end of the range reported in literature. The proposed method provides an interesting tool to study perfusion bioreactors processes down to the level of the individual cell's micro-environment, which can further aid in the achievement of robust bioprocess control for regenerative medicine applications.

  14. Genomewide analysis of LATERAL ORGAN BOUNDARIES Domain ...

    Indian Academy of Sciences (India)

    The investigation of transcription factor (TF) families is a major focus of postgenomic research. The plant-specific ASYMMETRIC LEAVES2-LIKE (ASL) / LATERAL ORGAN BOUNDARIES Domain (LBD) proteins constitute a major zincfinger-like-domain transcription factor family, and regulate diverse biological processes in ...

  15. Administrative Area Boundaries 2 (State Boundaries), Region 9, 2010, NAVTEQ

    Data.gov (United States)

    U.S. Environmental Protection Agency — NAVTEQ Administrative Area Boundaries 2 (State Boundaries) for Region 9. There are five Administrative Area Boundaries layers (1, 2, 3, 4, 5). These layers contain...

  16. Administrative Area Boundaries 4 (City Boundaries), Region 9, 2010, NAVTEQ

    Data.gov (United States)

    U.S. Environmental Protection Agency — NAVTEQ Administrative Area Boundaries 4 (City Boundaries) for Region 9. There are five Administrative Area Boundaries layers (1, 2, 3, 4, 5). These layers contain...

  17. Inverse boundary spectral problems

    CERN Document Server

    Kachalov, Alexander; Lassas, Matti

    2001-01-01

    Inverse boundary problems are a rapidly developing area of applied mathematics with applications throughout physics and the engineering sciences. However, the mathematical theory of inverse problems remains incomplete and needs further development to aid in the solution of many important practical problems.Inverse Boundary Spectral Problems develop a rigorous theory for solving several types of inverse problems exactly. In it, the authors consider the following: ""Can the unknown coefficients of an elliptic partial differential equation be determined from the eigenvalues and the boundary value

  18. Beyond the Boundary

    DEFF Research Database (Denmark)

    Gorm Hansen, Birgitte

    2011-01-01

    Whether celebratory or critical, STS research on science-industry relations has focused on the blurring of boundaries and hybridization of codes and practices. However, the vocabulary of boundary and hybrid tends to reify science and industry as separate in the attempt to map their relation...... as the negotiation of a preexisting science-industry boundary. Rather, viability is obtained through a strategy of "circumventing" the science-industry food chain and "sequestering" biotech components within the research center. Symbiosis allows academic scientists to do biology while at the same time demonstrating...

  19. Beyond the Boundary

    DEFF Research Database (Denmark)

    Gorm Hansen, Birgitte

    2012-01-01

    Whether celebratory or critical, STS research on science-industry relations has focused on the blurring of boundaries and hybridization of codes and practices. However, the vocabulary of boundary and hybrid tends to reify science and industry as separate in the attempt to map their relation...... as the negotiation of a preexisting science-industry boundary. Rather, viability is obtained through a strategy of circumventing the science-industry food chain and sequestering biotech components within the research center. Symbiosis allows academic scientists to do biology while at the same time demonstrating...

  20. Mending fences: repairing boundaries through ego state therapy.

    Science.gov (United States)

    Phillips, Maggie

    2013-07-01

    Ego state therapy has often been cited as an effective treatment to help repair fragmentation related to posttraumatic stress and dissociative disorders. This article explores how specialized work with ego states can help to clarify and strengthen internal and external boundaries, create greater boundary flexibility, and contribute to containment and self-regulation. Applications of direct and indirect hypnosis to repair boundary issues through ego state therapy are emphasized, and clinical case examples are used to illustrate results.

  1. Spurious Behavior of Shock-Capturing Methods: Problems Containing Stiff Source Terms and Discontinuities

    Science.gov (United States)

    Yee, Helen M. C.; Kotov, D. V.; Wang, Wei; Shu, Chi-Wang

    2013-01-01

    The goal of this paper is to relate numerical dissipations that are inherited in high order shock-capturing schemes with the onset of wrong propagation speed of discontinuities. For pointwise evaluation of the source term, previous studies indicated that the phenomenon of wrong propagation speed of discontinuities is connected with the smearing of the discontinuity caused by the discretization of the advection term. The smearing introduces a nonequilibrium state into the calculation. Thus as soon as a nonequilibrium value is introduced in this manner, the source term turns on and immediately restores equilibrium, while at the same time shifting the discontinuity to a cell boundary. The present study is to show that the degree of wrong propagation speed of discontinuities is highly dependent on the accuracy of the numerical method. The manner in which the smearing of discontinuities is contained by the numerical method and the overall amount of numerical dissipation being employed play major roles. Moreover, employing finite time steps and grid spacings that are below the standard Courant-Friedrich-Levy (CFL) limit on shockcapturing methods for compressible Euler and Navier-Stokes equations containing stiff reacting source terms and discontinuities reveals surprising counter-intuitive results. Unlike non-reacting flows, for stiff reactions with discontinuities, employing a time step and grid spacing that are below the CFL limit (based on the homogeneous part or non-reacting part of the governing equations) does not guarantee a correct solution of the chosen governing equations. Instead, depending on the numerical method, time step and grid spacing, the numerical simulation may lead to (a) the correct solution (within the truncation error of the scheme), (b) a divergent solution, (c) a wrong propagation speed of discontinuities solution or (d) other spurious solutions that are solutions of the discretized counterparts but are not solutions of the governing equations

  2. Higher Matrix Stiffness Upregulates Osteopontin Expression in Hepatocellular Carcinoma Cells Mediated by Integrin β1/GSK3β/β-Catenin Signaling Pathway.

    Directory of Open Access Journals (Sweden)

    Yang You

    Full Text Available Increased stromal stiffness is associated with hepatocellular carcinoma (HCC development and progression. However, the molecular mechanism by which matrix stiffness stimuli modulate HCC progress is largely unknown. In this study, we explored whether matrix stiffness-mediated effects on osteopontin (OPN expression occur in HCC cells. We used a previously reported in vitro culture system with tunable matrix stiffness and found that OPN expression was remarkably upregulated in HCC cells with increasing matrix stiffness. Furthermore, the phosphorylation level of GSK3β and the expression of nuclear β-catenin were also elevated, indicating that GSK3β/β-catenin pathway might be involved in OPN regulation. Knock-down analysis of integrin β1 showed that OPN expression and p-GSK3β level were downregulated in HCC cells grown on high stiffness substrate compared with controls. Simultaneously, inhibition of GSK-3β led to accumulation of β-catenin in the cytoplasm and its enhanced nuclear translocation, further triggered the rescue of OPN expression, suggesting that the integrin β1/GSK-3β/β-catenin pathway is specifically activated for matrix stiffness-mediated OPN upregulation in HCC cells. Tissue microarray analysis confirmed that OPN expression was positively correlated with the expression of LOX and COL1. Taken together, high matrix stiffness upregulated OPN expression in HCC cells via the integrin β1/GSK-3β/β-catenin signaling pathway. It highlights a new insight into a pathway involving physical mechanical signal and biochemical signal molecules which contributes to OPN expression in HCC cells.

  3. HUC 8 Boundaries

    Data.gov (United States)

    Kansas Data Access and Support Center — This data set is a digital hydrologic unit boundary that is at the 4-digit, 6-digit, 8-digit, and 11-digit level. The data set was developed by delineating the...

  4. FWS Approved Acquisition Boundaries

    Data.gov (United States)

    US Fish and Wildlife Service, Department of the Interior — This data layer depicts the external boundaries of lands and waters that are approved for acquisition by the U.S. Fish and Wildlife Service (USFWS) in North America,...

  5. National Forest Boundaries

    Data.gov (United States)

    Minnesota Department of Natural Resources — This theme shows the USFS national forest boundaries in the state. This data was acquired from the GIS coordinators at both the Chippewa National Forest and the...

  6. VT Telephone Exchange Boundaries

    Data.gov (United States)

    Vermont Center for Geographic Information — (Link to Metadata) The UtilityTelecom_EXCHANGE represents Vermont Telephone Exchange boundaries as defined by the VT Public Service Board. The original data was...

  7. State Park Statutory Boundaries

    Data.gov (United States)

    Minnesota Department of Natural Resources — Legislative statutory boundaries for sixty six state parks, six state recreation areas, and eight state waysides. These data are derived principally from DNR's...

  8. 500 Cities: City Boundaries

    Data.gov (United States)

    U.S. Department of Health & Human Services — This city boundary shapefile was extracted from Esri Data and Maps for ArcGIS 2014 - U.S. Populated Place Areas. This shapefile can be joined to 500 Cities...

  9. Allegheny County Parcel Boundaries

    Data.gov (United States)

    Allegheny County / City of Pittsburgh / Western PA Regional Data Center — This dataset contains parcel boundaries attributed with county block and lot number. Use the Property Information Extractor for more control downloading a filtered...

  10. Watershed Boundary Areas

    Data.gov (United States)

    Department of Homeland Security — This map layer contains hydrologic unit boundaries and codes for the United States, Puerto Rico, and the U.S. Virgin Islands. It was revised for inclusion in the...

  11. NM School District Boundaries

    Data.gov (United States)

    Earth Data Analysis Center, University of New Mexico — The dataset represents the boundaries of all public school districts in the state of New Mexico. The source for the data layer is the New Mexico Public Education...

  12. Allegheny County Boundary

    Data.gov (United States)

    Allegheny County / City of Pittsburgh / Western PA Regional Data Center — This dataset contains the Allegheny County boundary. If viewing this description on the Western Pennsylvania Regional Data Center’s open data portal...

  13. Boundary representation modelling techniques

    CERN Document Server

    2006-01-01

    Provides the most complete presentation of boundary representation solid modelling yet publishedOffers basic reference information for software developers, application developers and users Includes a historical perspective as well as giving a background for modern research.

  14. Site Area Boundaries

    Data.gov (United States)

    U.S. Environmental Protection Agency — This dataset consists of site boundaries from multiple Superfund sites in U.S. EPA Region 8. These data were acquired from multiple sources at different times and...

  15. Tax Unit Boundaries

    Data.gov (United States)

    Kansas Data Access and Support Center — The Statewide GIS Tax Unit boundary file was created through a collaborative partnership between the State of Kansas Department of Revenue Property Valuation...

  16. Severity of Osteoarthritis Is Associated with Increased Arterial Stiffness

    Directory of Open Access Journals (Sweden)

    Kaspar Tootsi

    2016-01-01

    Full Text Available Objective. Osteoarthritis (OA is associated with increased cardiovascular comorbidity and mortality. Evidence is lacking about whether arterial stiffness is involved in OA. The objective of our study was to find out associations between OA, arterial stiffness, and adipokines. Design. Seventy end-stage knee and hip OA patients (age 62±7 years and 70 asymptomatic controls (age 60±7 years were investigated using the applanation tonometry to determine their parameters of arterial stiffness. Serum adiponectin, leptin, and matrix metalloproteinase 3 (MMP-3 levels were determined using the ELISA method. Correlation between variables was determined using Spearman’s rho. Multiple regression analysis with a stepwise selection procedure was employed. Results. Radiographic OA grade was positively associated with increased carotid-femoral pulse wave velocity (cf-PWV (r=0.272, p=0.023. We found that OA grade was also associated with leptin and MMP-3 levels (rho=-0.246, p=0.040 and rho=0.235, p=0.050, resp.. In addition, serum adiponectin level was positively associated with augmentation index and inversely with large artery elasticity index (rho=0.293, p=0.006 and rho=-0.249, p=0.003, resp.. Conclusions. Our results suggest that OA severity is independently associated with increased arterial stiffness and is correlated with expression of adipokines. Thus, increased arterial stiffness and adipokines might play an important role in elevated cardiovascular risk in end-stage OA.

  17. 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.

  18. Stiffness of endodontically-treated teeth related to restoration technique.

    Science.gov (United States)

    Reeh, E S; Douglas, W H; Messer, H H

    1989-11-01

    Endodontically-treated posterior teeth are susceptible to fracture; consequently, full-occlusal-coverage restorations are recommended. We designed this study to examine the potential for alternative restorative techniques for pulpless teeth, using strain gauges mounted on extracted maxillary second premolars to measure strains generated by nondestructive occlusal loading. Cuspal stiffness was evaluated on the following sequentially performed procedures: unaltered tooth, completion of all endodontic procedures, appropriate restorative preparation, and restoration. The restorative procedures evaluated were: (1) amalgam, (2) cast gold onlay, (3) composite restoration with enamel etch, and (4) composite restoration with enamel and dentin etch. Finally, all teeth were loaded to fracture. Cast gold was the strongest restorative material tested (2.11 relative stiffness, compared with that of the unaltered tooth at 1.00), and amalgam was the weakest (0.35 relative stiffness). Composite restoration and enamel plus dentin etch were almost as strong as the unaltered tooth (0.87 relative stiffness), while enamel-etch-only yielded lower stiffness (0.51).

  19. Foundation stiffness in the linear modeling of wind turbines

    Science.gov (United States)

    Chiang, Chih-Hung; Yu, Chih-Peng; Chen, Yan-Hao; Lai, Jiunnren; Hsu, Keng-Tsang; Cheng, Chia-Chi

    2017-04-01

    Effects of foundation stiffness on the linear vibrations of wind turbine systems are of concerns for both planning and construction of wind turbine systems. Current study performed numerical modeling for such a problem using linear spectral finite elements. The effects of foundation stiffness were investigated for various combinations of shear wave velocity of soil, size of tower base plate, and pile length. Multiple piles are also included in the models such that the foundation stiffness can be analyzed more realistically. The results indicate that the shear wave velocity of soil and the size of tower base plate have notable effects on the dominant frequency of the turbine-tower system. The larger the lateral dimension, the stiffer the foundation. Large pile cap and multiple spaced piles result in higher stiffness than small pile cap and a mono-pile. The lateral stiffness of a mono-pile mainly depends on the shear wave velocity of soil with the exception for a very short pile that the end constraints may affect the lateral vibration of the superstructure. Effective pile length may be determined by comparing the simulation results of the frictional pile to those of the end-bearing pile.

  20. Arterial stiffness and wave reflections in marathon runners.

    Science.gov (United States)

    Vlachopoulos, Charalambos; Kardara, Despina; Anastasakis, Aris; Baou, Katerina; Terentes-Printzios, Dimitrios; Tousoulis, Dimitris; Stefanadis, Christodoulos

    2010-09-01

    Regular aerobic exercise has beneficial effects on the cardiovascular system. Marathon running is an aerobic and extremely vigorous exercise. Arterial stiffness and wave reflections are independent predictors of cardiovascular risk. We investigated the acute effect of marathon race on aortic stiffness and wave reflections, as well as possible chronic alterations of these indexes in marathon runners. We studied 49 marathon runners (age 38 +/- 9 years) and 46 recreationally active control subjects (age 37 +/- 5 years). To investigate the acute effect of marathon race, a subgroup of 20 runners was evaluated after the race as well. Aortic stiffness was evaluated with carotid-femoral pulse wave velocity (PWV) and wave reflections with augmentation index (AIx). Marathon runners had significantly higher systolic, diastolic, pulse (both aortic and brachial), and mean pressures compared to controls (P Marathon runners had significantly higher PWV (6.89 m/s vs. 6.33 m/s, P Marathon race caused a significant fall in both AIx (12.2% vs. -5.8%, P marathon race, whereas aortic stiffness was not altered. Moreover, marathon runners have increased aortic stiffness and pressures, whereas wave reflections indexes do not differ compared to controls.

  1. A variable stiffness dielectric elastomer actuator based on electrostatic chucking.

    Science.gov (United States)

    Imamura, Hiroya; Kadooka, Kevin; Taya, Minoru

    2017-05-14

    Dielectric elastomer actuators (DEA) are one type of promising artificial muscle; however, applications of bending-type DEA for robotic end-effectors may be limited by their low stiffness and ability to resist external loads without buckling. Unimorph DEA can produce large out-of-plane deformation suitable for use as robotic end effectors; however, design of such actuators for large displacement comes at the cost of low stiffness and blocking force. This work proposes and demonstrates a variable stiffness dielectric elastomer actuator (VSDEA) consisting of a plurality of unimorph DEA units operating in parallel, which can exhibit variable electrostatic chucking to modulate the structure's bending stiffness. The unimorph DEA units are additively manufactured using a high-resolution pneumatic dispenser, and VSDEA comprising various numbers of units are assembled. The performance of the DEA units and VSDEA are compared to model predictions, exhibiting a maximum stiffness change of 39.2×. A claw actuator comprising two VSDEA and weighing 0.6 grams is demonstrated grasping and lifting a 10 gram object.

  2. Control of the stiffness of robotic appendages using dielectric elastomers

    Science.gov (United States)

    Morton, Jeffrey

    A new robotic leg design is presented that utilizes dielectric elastomers (3M VHB 4910) to rapidly control stiffness changes for enhanced mobility and agility of a field demonstrated hexapod robot. It has been shown that stiffness changes of electro-active membranes made of dielectric elastomers can overcome challenges with other polymer materials that use heat to create modulus and stiffness changes. Applied electric fields eliminate issues with thermal transport rates and thermo-mechanical delaminatation. The dielectric elastomer is characterized uniaxially to understand its hyperelastic and viscoelastic properties. The uniaxial data is fit to a hyperelastic and viscoelastic finite deformation model. The material is then pre-stretched biaxially to stretch ratios ranging from 200%, 300% and 400%. A set of electro-mechanical transverse load experiments are then utilized to obtain up to 92% reduction in stiffness that is controlled by an electric field. The results are compared to a finite deformation membrane finite element model to understand and improve field driven stiffness changes for real-time robotic applications.

  3. Instantaneous stiffness and hysteresis of dynamic elastic response prosthetic feet.

    Science.gov (United States)

    Webber, Christina M; Kaufman, Kenton

    2017-10-01

    Dynamic elastic response prosthetic feet are designed to mimic the functional characteristics of the native foot/ankle joint. Numerous designs of dynamic elastic response feet exist which make the prescription process difficult, especially because of the lack of empirical evidence describing the objective performance characteristics of the feet. To quantify the mechanical properties of available dynamic elastic response prosthetic feet, specifically the stiffness and hysteresis. Mechanical testing of dynamic elastic response prosthetic feet. Static Proof Testing in accordance with ISO 10328 was conducted on seven dynamic elastic response prosthetic feet. Load-displacement data were used to calculate the instantaneous stiffness in both the heel and forefoot regions, as well as hysteresis associated with each foot. Heel stiffness was greater than forefoot stiffness for all feet. The heel of the glass composite prosthetic foot was stiffer than the carbon fiber feet and it exhibited less hysteresis. Two different carbon fiber feet had the stiffest forefoot regions. Mechanical testing is a reproducible method that can be used to provide objective evidence about dynamic elastic response prosthetic foot performance and aid in the prescription process. Clinical relevance The quantitative stiffness and hysteresis data from this study can be used by prosthetists to aid the prescription process and make it more objective.

  4. Axial and torsional stiffness of pediatric prosthetic feet.

    Science.gov (United States)

    Taboga, Paolo; Grabowski, Alena M

    2017-02-01

    Prosthetic stiffness likely affects the walking biomechanics of toddlers and children with leg amputations, but the actual stiffness values for prostheses are not reported by manufacturers or in standardized testing procedures. We measured axial (k A ) and torsional (k T ) stiffness from four brands of pediatric prosthetic feet (Trulife, Kingsley Mfg. Co., TRS Incorporated, and College Park Industries) over a range of foot sizes. We applied forces and torques onto prostheses with a materials testing machine that replicated those exhibited in vivo by using the kinetics measured from four non-amputee toddlers (2-3years) during walking. Across brands, k A averaged 35.2kN/m during heel loading, was more stiff during midfoot loading (121.8kN/m, Pfeet. Plantarflexion torsional stiffness (k T1 ), was not statistically different across brands. For every 1cm increase in foot size, k T1 increased 0.16kN·m/rad (Pfeet should be publically reported to health practitioners to ensure evidence-based decisions and meet the specific needs of each patient with a leg amputation. Copyright © 2017 Elsevier Ltd. All rights reserved.

  5. VT Federal Aid Urban Boundaries

    Data.gov (United States)

    Vermont Center for Geographic Information — Federal Aid Urban boundaries are defined based on US Census data. The roadways within these boundaries have urban classifications. These FAU boundaries were updated...

  6. Effect of substrate stiffness on the functions of rat bone marrow and adipose tissue derived mesenchymal stem cells in vitro.

    Science.gov (United States)

    Li, Xiaoming; Huang, Yan; Zheng, Lisha; Liu, Haifeng; Niu, Xufeng; Huang, Jin; Zhao, Feng; Fan, Yubo

    2014-04-01

    Regenerative medicine treatments that combine the use of cells and materials may open new options for tissue/organ repair and regeneration. The microenvironment of mesenchymal stem cells (MSCs) strictly regulates their self-renewal and functions. In this study, when rat bone marrow derived MSCs (rBMSCs) and rat adipose tissue derived MSCs (rAMSCs) in passages 2-4 were cultured on different substrates, they presented the cellular functions to be dependent of substrate stiffness. The cells attached better on the softer substrate than on the stiffer one. The substrate stiffness had no significant influence on the proliferation of those cells. However, the substrate stiffness significantly promoted the osteogenic differentiation of the two kinds of stem cells. Furthermore, rBMSCs cultured on the same stiffness expressed more osteoblast-related markers than rAMSCs. In addition, combined biomaterials and biochemical reagents treatment yielded a stronger effect on osteogenic differentiation of MSCs than either treatment alone. These results have significant implications for further extending our capabilities in engineering functional tissue substitutes. Copyright © 2013 Wiley Periodicals, Inc.

  7. Identities beyond Boundaries: Ethnic minority professionals’ negotiation of the boundary between work and non‐work domains

    OpenAIRE

    Van Laer, Koen; Janssens, Maddy

    2012-01-01

    Whereas most studies approach boundary work as an either/or choice between integration and segmentation of work and non-work, this study aims to develop a more complex understanding by adopting an identity perspective and drawing on the extreme case of ethnic minorities. Based on in-depth interviews, our findings show the construction of boundary transcending identities which allows individuals to combine integration and segmentation, boundary regulation by other domain members which challeng...

  8. Comparison Study on the Exact Dynamic Stiffness Method for Free Vibration of Thin and Moderately Thick Circular Cylindrical Shells

    Directory of Open Access Journals (Sweden)

    Xudong Chen

    2016-01-01

    Full Text Available Comparison study on free vibration of circular cylindrical shells between thin and moderately thick shell theories when using the exact dynamic stiffness method (DSM formulation is presented. Firstly, both the thin and moderately thick dynamic stiffness formulations are examined. Based on the strain and kinetic energy, the vibration governing equations are expressed in the Hamilton form for both thin and moderately thick circular cylindrical shells. The dynamic stiffness is assembled in a similar way as that in classic skeletal theory. With the employment of the Wittrick-Williams algorithm, natural frequencies of circular cylindrical shells can be obtained. A FORTRAN code is written and used to compute the modal characteristics. Numerical examples are presented, verifying the proposed computational framework. Since the DSM is an exact approach, the advantages of high accuracy, no-missing frequencies, and good adaptability to various geometries and boundary conditions are demonstrated. Comprehensive parametric studies on the thickness to radius ratio (h/r and the length to radius ratio (L/r are performed. Applicable ranges of h/r are found for both thin and moderately thick DSM formulations, and influences of L/r on frequencies are also investigated. The following conclusions are reached: frequencies of moderately thick shells can be considered as alternatives to those of thin shells with high accuracy where  h/r is small and L/r is large, without any observation of shear locking.

  9. Shifting Institutional Boundaries through Cross-Border Higher Education

    Science.gov (United States)

    Amaral, Alberto; Tavares, Orlanda; Cardoso, Sónia; Sin, Cristina

    2016-01-01

    Cross-border higher education (CBHE) has been changing the organizational boundaries of higher education institutions (HEIs). This study aims to analyze the shifting boundaries of Portuguese HEIs through the lens of the identity concept in organization theories, considering three contexts with different levels of regulation: African…

  10. Stiffness control of magnetorheological gels for adaptive tunable vibration absorber

    Science.gov (United States)

    Kim, Hyun Kee; Kim, Hye Shin; Kim, Young-Keun

    2017-01-01

    In this study, a stiffness feedback control system for magnetorheological (MR) gel—a smart material of variable stiffness—is proposed, toward the design of a tunable vibration absorber that can adaptively tune to a time varying disturbance in real time. A PID controller was designed to track the required stiffness of the MR gel by controlling the magnitude of the target external magnetic field pervading the MR gel. This paper proposes a novel magnetic field generator that could produce a variable magnetic field with low energy consumption. The performance of the MR gel stiffness control was validated through experiments that showed the MR gel absorber system could be automatically tuned from 56 Hz to 67 Hz under a field of 100 mT to minimize the vibration of the primary system.

  11. Stiffness of the extrafibrillar phase in staggered biological arrays.

    Science.gov (United States)

    Bar-On, Benny; Wagner, H Daniel

    2012-08-17

    A number of important biological tissues such as nacre, tendon, and bone consist of staggered structural arrays as universal motifs. Such arrays usually include stiff fibril-like (or plateletlike, or needlelike) elements embedded in an extrafibrillar (XF) phase. This work discusses the effect of the stiffness of such an XF matrix on the elastic properties of the resulting staggered composite. In the case of most biological composites, this XF stiffness is hardly accessible and very little data are available. We develop an analysis based on previous analytical formulation that results in a relation between the XF modulus and the deformations of the staggered particles. This analysis is then used to back-calculate the yet unmeasured modulus of the XF phase from experimental deformation data, thereby providing a simple alternative to potentially complex direct measurements. This is demonstrated and validated for parallel-fiber bone tissue.

  12. Output-Based Control of Robots with Variable Stiffness Actuation

    Directory of Open Access Journals (Sweden)

    Gianluca Palli

    2011-01-01

    Full Text Available The output-based control of a redundant robotic manipulator with relevant and adjustable joint stiffness is addressed. The proposed controller is configured as a cascade system that allows the decoupling of the actuators dynamics from the arm dynamics and the consequent reduction of the order of the manipulator dynamic model. Moreover, the proposed controller does not require the knowledge of the whole robot state: only the positions of the actuators and of the joints are necessary. This approach represents a significant simplification with respect to previously proposed state feedback techniques. The problem of controlling simultaneously the position trajectory and the desired stiffness in both the joint and work space is investigated, and the relations between the manipulator redundancy and the selection of both the joint and work space stiffness of the manipulator are discussed. The effectiveness of the proposed approach is verified by simulations of a 3 degrees of freedom planar manipulator.

  13. Stiffness and damping of elastomeric O-ring bearing mounts

    Science.gov (United States)

    Smalley, A. J.

    1977-01-01

    A test rig to measure the dynamic stiffness and damping of elastomer O rings was described. Test results for stiffness and loss coefficient in the frequency range from 50 Hz to 1000 Hz are presented. Results are given for three different materials, for five temperatures, for three amplitudes, for five values of squeeze for three values of stretch for three values of cross-section diameter and for three values of groove width. All test data points were plotted. In addition, trend summary plots were presented which compare the effect of material, temperature, amplitude, squeeze, stretch, cross-section diameter, and groove width. O ring deflections under a static load for different material were presented; and effective static stiffness values were compared with dynamic values.

  14. 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.

  15. Muscle stiffness and spinal stretch reflex sensitivity in the triceps surae.

    Science.gov (United States)

    Blackburn, J Troy; Padua, Darin A; Guskiewicz, Kevin M

    2008-01-01

    Greater musculotendinous stiffness may enhance spinal stretch reflex sensitivity by improving mechanical coupling of the muscle spindle and the stretch stimulus. This heightened sensitivity would correspond with a shorter latency and higher-amplitude reflex response, potentially enhancing joint stability. To compare spinal stretch reflex latency and amplitude across groups that differed in musculotendinous stiffness. Static group comparisons. Research laboratory. Forty physically active individuals (20 men, 20 women). We verified a sex difference in musculotendinous stiffness and compared spinal stretch reflex latency and amplitude in high-stiffness (men) and low-stiffness (women) groups. We also evaluated relationships between musculotendinous stiffness and spinal stretch reflex latency and amplitude, respectively. Triceps surae musculotendinous stiffness and soleus spinal stretch reflex latency and amplitude were assessed at 30% of a maximal voluntary isometric plantar-flexion contraction. The high-stiffness group demonstrated significantly greater stiffness (137.41 +/- 26.99 N/cm) than the low-stiffness group did (91.06 +/- 20.10 N/cm). However, reflex latency (high stiffness = 50.11 +/- 2.07 milliseconds, low stiffness = 48.26 +/- 2.40 milliseconds) and amplitude (high stiffness = 0.28% +/- 0.12% maximum motor response, low stiffness = 0.31% +/- 0.16% maximum motor response) did not differ significantly across stiffness groups. Neither reflex latency (r = .053, P = .746) nor amplitude (r = .073, P = .653) was related significantly to musculotendinous stiffness. A moderate level of pretension (eg, 30%) likely eliminates series elastic slack; thus, a greater change in force per unit-of-length change (ie, heightened stiffness) would have minimal effects on coupling of the muscle spindle and the stretch stimulus and, therefore, on spinal stretch reflex sensitivity. It appears unlikely that differences in musculotendinous stiffness influenced spinal stretch reflex

  16. 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.

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

    Science.gov (United States)

    Venkata Giri Kumar, P; Deshpande, Sudheer; Joshi, Aniruddha; More, Pooja; Nagendra, H R

    The variations in Tridoshas are the basis for disease diagnosis and treatment in Ayurveda. The doshas are assessed by sensing the pulse manually with fingers which depends on skill of the physician. There is a need to measure doshas using instruments and study them objectively. Arterial stiffness is well established pulse parameter in modern medicine and is closely associated to kathinya in the context of Ayurveda. The aim of our study was to measure arterial stiffness using Nadi Tarangini, a pulse acquisition system, and investigate the significant variations of stiffness across Tridosha locations. A total of 42 samples of vata, pitta and kapha pulses with proper systolic and diastolic peaks were included in the study. The arterial stiffness parameters namely stiffness index (SI) and reflection index (RI) were considered for the study. The data was analyzed using one-way ANOVA followed by Tamhane's T2 test. The changes in SI and RI between males and females were assessed using independent samples t test. SI at vata (5.669 ± 1.165) was significantly low compared to pitta (8.910 ± 3.509) and kapha (8.021 ± 2.814); RI at vata (0.846 ± 0.071) was significantly low compared to pitta (0.945 ± 0.043) and kapha (0.952 ± 0.033). SI at kapha was significantly low in females compared to males. 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. Copyright © 2017 Transdisciplinary University, Bangalore and World Ayurveda Foundation. Published by Elsevier B.V. All rights reserved.

  18. 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

    2017-11-28

    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, 2017. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  19. Ivabradine on aortic stiffness in patients with heart failure.

    Science.gov (United States)

    Nar, Gokay; Inci, Sinan; Aksan, Gokhan; Demirelli, Selami; Soylu, Korhan; Yuksel, Serkan; Gulel, Okan; Icli, Atilla

    2015-04-01

    The aim of this study was to evaluate the effect of ivabradine treatment on aortic stiffness by measuring aortic elastic parameters in patients with heart failure (HF) receiving ivabradine treatment. The study included clinical patients who were diagnosed with HF (ejection fraction, <35%), had sinus rhythm and persistent symptoms despite full medical treatment. The study group consisted of patients with a heart rate greater than 70 beats per minute and the control group consisted of patients with a heart rate less than 70 beats per minute. Echocardiographic measurements were conducted and aortic strain, aortic distensibility, and aortic stiffness index were calculated. By the end of the twelfth month, a decrease was observed in the left ventricular end-diastolic and end-systolic volumes, whereas ejection fraction was increased (P < 0.001). When aortic elastic parameters were evaluated between the 2 groups, there was no significant difference regarding aortic strain, aortic distensibility, and aortic stiffness index at the time of enrollment and during the visit at 3 months. At the twelfth month visit, aortic strain (P < 0.001) and distensibility (P < 0.001) were significantly increased, whereas there was a significant decrease in the aortic stiffness index (P < 0.001). During the follow-up at 12 months, significant improvements were observed in the left ventricular functions and aortic elastic parameters along with decreased heart rate in patients with HF receiving ivabradine treatment. This outcome may indicate that ivabradine treatment may correct aortic stiffness and may reduce aortic stiffness after 1 year of follow-up.

  20. 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.

  1. Polarization-induced stiffness asymmetry of optical tweezers.

    Science.gov (United States)

    Madadi, Ebrahim; Samadi, Akbar; Cheraghian, Mojtaba; Reihani, S Nader S

    2012-09-01

    A tightly focused, linearly polarized laser beam, so-called optical tweezers, is proven to be a useful micromanipulation tool. It is known that there is a stiffness asymmetry in the direction perpendicular to the optical axis inherited from the polarization state of the laser. In this Letter, we report our experimental results of stiffness asymmetry for different bead sizes measured at the optimal trapping condition. We also provide the results of our generalized Lorenz-Mie based calculations, which are in good agreement with our experimental results. We also compare our results with previous reports.

  2. Fast Stiffness Matrix Calculation for Nonlinear Finite Element Method

    Directory of Open Access Journals (Sweden)

    Emir Gülümser

    2014-01-01

    Full Text Available We propose a fast stiffness matrix calculation technique for nonlinear finite element method (FEM. Nonlinear stiffness matrices are constructed using Green-Lagrange strains, which are derived from infinitesimal strains by adding the nonlinear terms discarded from small deformations. We implemented a linear and a nonlinear finite element method with the same material properties to examine the differences between them. We verified our nonlinear formulation with different applications and achieved considerable speedups in solving the system of equations using our nonlinear FEM compared to a state-of-the-art nonlinear FEM.

  3. Associations between bicycling and carotid arterial stiffness in adolescents

    DEFF Research Database (Denmark)

    Ried-Larsen, M; Grøntved, A; Østergaard, Lars

    2015-01-01

    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...... modulus [standard beta -0.48 (95% CI -0.91 to -0.06)]. Similar trends were observed when investigating the association between commuter bicycling and carotid arterial stiffness. These associations were not observed in girls. Our observations suggest that increasing bicycling in adolescence may...

  4. Electroplated CoPt magnets for actuation of stiff cantilevers

    Science.gov (United States)

    Loke, Y. C.; Hofbauer, W.; Lu, P.; Ansari, K.; Tang, X. S.; O'Shea, S. J.

    2011-11-01

    A cantilever has been microfabricated for use in non-contact Atomic Force Microscopy (AFM) using a very thick magnetic film to actuate the cantilever motion. The thick magnetic block is deposited electrochemically over a defined area of the cantilever. This cantilever is particularly suitable for driving stiff AFM cantilevers in a liquid environment. Clean mechanical resonances are easily observed. Examples are given of a hard (CoPt) magnet of dimension 29 × 21 × 6 μm3 electroplated on Silicon cantilevers of stiffness ˜22 N/m, giving a static displacement of ˜0.2 nm in an applied field of 10-3 T.

  5. The Progression of Diabetic Microvascular Complications and Increased Vascular Stiffness

    Directory of Open Access Journals (Sweden)

    Georgescu Olivia

    2014-12-01

    Full Text Available In patients with type 2 diabetes mellitus it might be helpful to use, for risk stratification, non-invasive techniques as markers of early atherosclerosis. Arterial stiffness shows the functional vascular properties and can be estimated by pulse wave velocity (PWV and augmentation index (AIX. Typical for type 2 diabetes is premature arterial stiffening which appears before the onset of clinically micro or macrovascular disease and is increased in the presence of microvascular complications. Further studies are needed to determine whether therapeutic interventions for reducing vascular stiffness may decrease the cardiovascular mortality in patients with type 2 diabetes.

  6. 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...... rate 75 (AIx@HR75) were measured in 72 obese patients aged 10-18 years at baseline and after 1-year of lifestyle intervention (follow-up). We found that although the degree of obesity decreased (Delta body mass index z-score: -0.24 +/- 0.45, P ....27 +/- 0.47 ms(-1), P obesity measures. No significant change...

  7. A Novel Concept for Safe, Stiffness-Controllable Robot Links.

    Science.gov (United States)

    Stilli, Agostino; Wurdemann, Helge A; Althoefer, Kaspar

    2017-03-01

    The recent decade has seen an astounding increase of interest and advancement in a new field of robotics, aimed at creating structures specifically for the safe interaction with humans. Softness, flexibility, and variable stiffness in robotics have been recognized as highly desirable characteristics for many applications. A number of solutions were proposed ranging from entirely soft robots (such as those composed mainly from soft materials such as silicone), via flexible continuum and snake-like robots, to rigid-link robots enhanced by joints that exhibit an elastic behavior either implemented in hardware or achieved purely by means of intelligent control. Although these are very good solutions paving the path to safe human-robot interaction, we propose here a new approach that focuses on creating stiffness controllability for the linkages between the robot joints. This article proposes a replacement for the traditionally rigid robot link-the new link is equipped with an additional capability of stiffness controllability. With this added feature, a robot can accurately carry out manipulation tasks (high stiffness), but can virtually instantaneously reduce its stiffness when a human is nearby or in contact with the robot. The key point of the invention described here is a robot link made of an airtight chamber formed by a soft and flexible, but high-strain resistant combination of a plastic mesh and silicone wall. Inflated with air to a high pressure, the mesh silicone chamber behaves like a rigid link; reducing the air pressure, softens the link and rendering the robot structure safe. This article investigates a number of link prototypes and shows the feasibility of the new concept. Stiffness tests have been performed, showing that a significant level of stiffness can be achieved-up to 40 N reaction force along the axial direction, for a 25-mm-diameter sample at 60 kPa, at an axial deformation of 5 mm. The results confirm that this novel concept to linkages

  8. Effect of Augmentation Material Stiffness on Adjacent Vertebrae after Osteoporotic Vertebroplasty Using Finite Element Analysis with Different Loading Methods.

    Science.gov (United States)

    Cho, Ah-Reum; Cho, Sang-Bong; Lee, Jae-Ho; Kim, Kyung-Hoon

    2015-11-01

    Vertebroplasty is an effective treatment for osteoporotic vertebral fractures, which are one of the most common fractures associated with osteoporosis. However, clinical observation has shown that the risk of adjacent vertebral body fractures may increase after vertebroplasty. The mechanism underlying adjacent vertebral body fracture after vertebroplasty is not clear; excessive stiffness resulting from polymethyl methacrylate has been suspected as an important mechanism. The aim of our study was to compare the effects of bone cement stiffness on adjacent vertebrae after osteoporotic vertebroplasty under load-controlled versus displacement-controlled conditions. An experimental computer study using a finite element analysis. Medical research institute, university hospital, Korean. A three-dimensional digital anatomic model of L1/2 bone structure was reconstructed from human computed tomographic images. The reconstructed three-dimensional geometry was processed for finite element analysis such as meshing elements and applying material properties. Two boundary conditions, load-controlled and displacement-controlled methods, were applied to each of 5 deformation modes: compression, flexion, extension, lateral bending, and torsion. The adjacent L1 vertebra, irrespective of augmentation, revealed nearly similar maximum von Mises stresses under the load-controlled condition. However, for the displacement-controlled condition, the maximum von Mises stresses in the cortical bone and inferior endplate of the adjacent L1 vertebra increased significantly after cement augmentation. This increase was more significant than that with stiffer bone cement under all modes, except the torsion mode. The finite element model was simplified, excluding muscular forces and incorporating a large volume of bone cement, to more clearly demonstrate effects of bone cement stiffness on adjacent vertebrae after vertebroplasty. Excessive stiffness of augmented bone cement increases the risk of

  9. Adaptive Sentence Boundary Disambiguation

    CERN Document Server

    Palmer, D D; Palmer, David D.; Hearst, Marti A.

    1994-01-01

    Labeling of sentence boundaries is a necessary prerequisite for many natural language processing tasks, including part-of-speech tagging and sentence alignment. End-of-sentence punctuation marks are ambiguous; to disambiguate them most systems use brittle, special-purpose regular expression grammars and exception rules. As an alternative, we have developed an efficient, trainable algorithm that uses a lexicon with part-of-speech probabilities and a feed-forward neural network. After training for less than one minute, the method correctly labels over 98.5\\% of sentence boundaries in a corpus of over 27,000 sentence-boundary marks. We show the method to be efficient and easily adaptable to different text genres, including single-case texts.

  10. The Bottom Boundary Layer.

    Science.gov (United States)

    Trowbridge, John H; Lentz, Steven J

    2018-01-03

    The oceanic bottom boundary layer extracts energy and momentum from the overlying flow, mediates the fate of near-bottom substances, and generates bedforms that retard the flow and affect benthic processes. The bottom boundary layer is forced by winds, waves, tides, and buoyancy and is influenced by surface waves, internal waves, and stratification by heat, salt, and suspended sediments. This review focuses on the coastal ocean. The main points are that (a) classical turbulence concepts and modern turbulence parameterizations provide accurate representations of the structure and turbulent fluxes under conditions in which the underlying assumptions hold, (b) modern sensors and analyses enable high-quality direct or near-direct measurements of the turbulent fluxes and dissipation rates, and (c) the remaining challenges include the interaction of waves and currents with the erodible seabed, the impact of layer-scale two- and three-dimensional instabilities, and the role of the bottom boundary layer in shelf-slope exchange.

  11. Stiffness characterization of a 3-PPR planar parallel manipulator with actuation compliance

    DEFF Research Database (Denmark)

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

    2015-01-01

    This paper investigates the stiffness of a compliant planar parallel manipulator. Instead of establishing stiffness matrix directly for planar mechanisms, we adopt the modeling approach for spatial mechanisms, which allows us to derive two decoupled homogeneous matrices, corresponding to the tran......This paper investigates the stiffness of a compliant planar parallel manipulator. Instead of establishing stiffness matrix directly for planar mechanisms, we adopt the modeling approach for spatial mechanisms, which allows us to derive two decoupled homogeneous matrices, corresponding...... submatrices. In addition, the influence of the nonlinear actuation compliance to the manipulator stiffness is investigated, and the established stiffness model is experimentally verified....

  12. Stiffness Analysis and Improvement of Bolt-Plate Contact Assemblies

    DEFF Research Database (Denmark)

    Pedersen, Niels Leergaard; Pedersen, Pauli

    2008-01-01

    of stiffnesses is extended to include different material parameters by including the influence of Poisson's ratio. Two simple practical formulas are suggested and their accuracies are documented for different bolts and different material (Poisson's ratio). Secondly, the contact analysis between the bolt head...

  13. 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

  14. 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 transp...

  15. [Progress on cervical muscle strength and soft tissue stiffness testing].

    Science.gov (United States)

    Ma, Ming; Zhang, Shi-min

    2015-08-01

    Biomechanical evaluation of neck muscles has important significance in the diagnosis and treatment for cervical spondylosis, the neck muscle strength and soft tissue stiffness test is two aspects of biomechanical testing. Isometric muscle testing operation is relatively simple, the cost is lower, which can evaluate the muscle force below grade 3. However, isokinetic muscle strength testing can assess the muscle strength of joint motion in any position. It is hard to distinguish stiffness difference in different soft tissues when the load-displacement curve is used to evaluate the local soft tissue stiffness. Elasticity imaging technique can not only show the elastic differences of different tissues by images, but also quantify the elastic modulus of subcutaneous tissues and muscles respectively. Nevertheless, it is difficult to observe the flexibility of the cervical spine by means of the analysis of the whole neck stiffness. In a word, a variety of test method will conduce not only the biomechanical evaluation of neck muscles, but also making an effective biomechanics mathematical model of neck muscles. Besides, isokinetic muscle testing and the elasticity imaging technology still need further validation and optimization before they are better applied to neck muscles biomechanical testing.

  16. The Influence of Teleoperator Stiffness and Damping on Object Discrimination

    NARCIS (Netherlands)

    Christiansson, G.A.V.; Van der Linde, R.Q.; Van der Helm, F.C.T.

    2008-01-01

    Human task performance using teleoperator systems depends on the physical and controlled parameters of the system. Two teleoperated grasping tasks—size and stiffness discrimination—were studied to investigate how changes in system parameters influence human capabilities. The device characteristics

  17. Large stroke high support stiffness flexure based universal joint

    NARCIS (Netherlands)

    Naves, Mark; Aarts, R.G.K.M.; Brouwer, Dannis Michel

    2017-01-01

    Universal two degree of freedom flexure joints are often used for parallel manipulators or applications which demand transmission of torque. However, contemporary flexure-based universal joints are limited to small deflection angles caused by their strong loss of stiffness in support directions when

  18. 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...

  19. The effects of cycling shoe stiffness on forefoot pressure.

    Science.gov (United States)

    Jarboe, Nathan Edward; Quesada, Peter M

    2003-10-01

    Plantar pressure data were recorded in two different shoe types to determine the effect of cycling shoe stiffness on peak plantar forefoot pressure in cyclists. Two pairs of shoes of the same size and manufacturer, identical except for outsole material and stiffness, were tested. Shoe stiffness measurements were collected under controlled conditions and in two different configurations using a dynamic hydraulic tensile testing machine. Measurements of plantar pressure were done using Pedar capacitive-based sensor insoles while subjects pedaled in a seated position at a controlled power output. Power output was set at a constant value of 400 W across all subjects by a magnetic resistance trainer unit. The pressure distribution in carbon-fiber-composite shoes during cycling was compared to cycling shoes made with plastic soles. Carbon fiber shoes presented stiffness values 42% and 550% higher than plastic shoes in longitudinal bending and three-point bending, respectively. The shoes made with carbon fiber produced peak plantar pressures 18% higher than those of plastic design (121 kPa vs. 103 kPa, p = .005). Competitive or professional cyclists suffering from metatarsalgia or ischemia should be especially careful when using carbon fiber cycling shoes because the shoes increase peak plantar pressure, which may aggravate these foot conditions.

  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. Farber disease overlapping with stiff skin syndrome: Expanding the ...

    African Journals Online (AJOL)

    Stiff skin syndrome (SSS) (MIM %184900)1 was fi rst described by Esterly and McKusick as a disorder characterized by thickened and indurated skin of the entire body and limitation of joint mobility with fl exion contractures. Aim of the Study: Diagnosis and clarifi cation of overlapping in the clinical presentation of the studied ...

  2. 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 ...

  3. Stiffness of the healing medial collateral ligament of the mouse.

    NARCIS (Netherlands)

    Gijssen, Y.; Sierevelt, I.N.; Kooloos, J.G.M.; Blankevoort, L.

    2004-01-01

    The knee joints of mice can serve as a model for studying knee ligament properties. The goal of our study was to measure the structural stiffness of the medial collateral ligament (MCL) of the murine knee. A tensile test was developed for this purpose. First 84 femur-MCL-tibia complexes of

  4. Modeling short-range stiffness of feline lower hindlimb muscles

    NARCIS (Netherlands)

    Cui, L.; Perreault, E.J.; Maas, H.; Sandercock, T.G.

    2008-01-01

    The short-range stiffness (SRS) of skeletal muscles is a critical property for understanding muscle contributions to limb stability, since it represents a muscle's capacity to resist external perturbations before reflexes or voluntary actions can intervene. A number of studies have demonstrated that

  5. Design optimization of a twist compliant mechanism with nonlinear stiffness

    Science.gov (United States)

    Tummala, Y.; Frecker, M. I.; Wissa, A. A.; Hubbard, J. E., Jr.

    2014-10-01

    A contact-aided compliant mechanism called a twist compliant mechanism (TCM) is presented in this paper. This mechanism has nonlinear stiffness when it is twisted in both directions along its axis. The inner core of the mechanism is primarily responsible for its flexibility in one twisting direction. The contact surfaces of the cross-members and compliant sectors are primarily responsible for its high stiffness in the opposite direction. A desired twist angle in a given direction can be achieved by tailoring the stiffness of a TCM. The stiffness of a compliant twist mechanism can be tailored by varying thickness of its cross-members, thickness of the core and thickness of its sectors. A multi-objective optimization problem with three objective functions is proposed in this paper, and used to design an optimal TCM with desired twist angle. The objective functions are to minimize the mass and maximum von-Mises stress observed, while minimizing or maximizing the twist angles under specific loading conditions. The multi-objective optimization problem proposed in this paper is solved for an ornithopter flight research platform as a case study, with the goal of using the TCM to achieve passive twisting of the wing during upstroke, while keeping the wing fully extended and rigid during the downstroke. Prototype TCMs have been fabricated using 3D printing and tested. Testing results are also presented in this paper.

  6. Beam section stiffness properties usig 3D finite elements

    DEFF Research Database (Denmark)

    Couturier, Philippe; Krenk, Steen; Høgsberg, Jan Becker

    2013-01-01

    The cross-section properties of a beam is characterized by a six by six stiffness matrix, relating the six generalized strains to the conjugate section forces. The problem is formulated as a single-layer finite element model of a slice of the beam, on which the six deformation modes are imposed via...

  7. VARIABLE MESH STIFFNESS OF SPUR GEAR TEETH USING ...

    African Journals Online (AJOL)

    primary source of parametric vibration excitation in geared systems, by virtue of large magnitude change in stiffness that occurs during gear engagement. A gear mesh kinematic simulation. WIll be developeJ 1(1 simulate the meshing actIOn 01 two spur gears,. Recently, greatcr elliphasis has been played on the creation of ...

  8. 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 Nijm...

  9. 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.

  10. A note on operator splitting in a stiff linear case

    NARCIS (Netherlands)

    J.G. Verwer (Jan); B. Sportisse

    1998-01-01

    textabstractThis note is concerned with the numerical technique of operator splitting for initial value problems. Using a stiff linear ODE system as model problem, error bounds are derived for standard 1st- and 2nd-order splitting methods. The analysis focuses on deriving bounds independent of

  11. The use of approximate factorization in stiff ODE solvers

    NARCIS (Netherlands)

    P.J. van der Houwen; B.P. Sommeijer (Ben)

    1997-01-01

    textabstractWe consider implicit integration methods for the numerical solution of stiff initial-value problems. In applying such methods, the implicit relations are usually solved by Newton iteration. However, it often happens that in subintervals of the integration interval the problem is nonstiff

  12. Stiffness design of geometrically nonlinear structures using topology optimization

    DEFF Research Database (Denmark)

    Buhl, Thomas; Pedersen, Claus B. Wittendorf; Sigmund, Ole

    2000-01-01

    response. The problem is circumvented by optimizing the structures for multiple loading conditions or by minimizing the complementary elastic work. Examples show that differences in stiffnesses of structures optimized using linear and nonlinear modelling are generally small but they can be large in certain...

  13. Step-parallel algorithms for stiff initial value problems

    NARCIS (Netherlands)

    W.A. van der Veen

    1995-01-01

    textabstractFor the parallel integration of stiff initial value problems, three types of parallelism can be employed: 'parallelism across the problem', 'parallelism across the method' and 'parallelism across the steps'. Recently, methods based on Runge-Kutta schemes that use parallelism across the

  14. Treatment of Stiff Initial Value Problems using Block Backward ...

    African Journals Online (AJOL)

    ... on some standard stiff initial value Problems. The results show that the 3-point BDF step size ratio with r = 2 has the widest region of absolute stability and highest accuracy. Keywords: Zero stability, Hybrid, k –step, Block methods, first order initial value problem. Journal of the Nigerian Association of Mathematical Physics, ...

  15. 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

  16. A Multiscale Mechanical Model for Plant Tissue Stiffness

    Directory of Open Access Journals (Sweden)

    Damiano Pasini

    2013-06-01

    Full Text Available Plant petioles and stems are hierarchical cellular structures, displaying structuralfeatures defined at multiple length scales. The current work focuses on the multi-scalemodelling of plant tissue, considering two orders of structural hierarchy, cell wall and tissue.The stiffness of plant tissue is largely governed by the geometry of the tissue cells, thecomposition of the cell wall and the structural properties of its constituents. The cell wallis analogous to a fiber reinforced composite, where the cellulose microfibril (CMF is theload bearing component. For multilayered cell wall, the microfibril angle (MFA in themiddle layer of the secondary cell wall (S2 layer largely affects the longitudinal stiffnessfor values up to 40o. The MFA in turn influences the overall wall stiffness. In this work,the effective stiffness of a model system based on collenchyma cell wall of a dicotyledonousplant, the Rheum rhabarbarum, is computed considering generic MFA and volume fractions.At the cellular level, a 2-D Finite Edge Centroidal Voronoi tessellation (FECVT has beendeveloped and implemented to generate the non-periodic microstructure of the plant tissue.The effective elastic properties of the cellular tissue are obtained through finite elementanalysis (FEA of the Voronoi model coupled with the cell wall properties. The stiffness ofthe hierarchically modeled tissue is critically important in determining the overall structuralproperties of plant petioles and stems.

  17. Wide Stiffness Range Cavity Optomechanical Sensors for Atomic Force Microscopy

    CERN Document Server

    Liu, Yuxiang; Aksyuk, Vladimir; Srinivasan, Kartik

    2012-01-01

    We report on progress in developing compact sensors for atomic force microscopy (AFM), in which the mechanical transducer is integrated with near-field optical readout on a single chip. The motion of a nanoscale, doubly-clamped cantilever was transduced by an adjacent high quality factor silicon microdisk cavity. In particular, we show that displacement sensitivity on the order of 1 fm/(Hz)^(1/2) can be achieved while the cantilever stiffness is varied over four orders of magnitude (\\approx 0.01 N/m to \\approx 290 N/m). The ability to transduce both very soft and very stiff cantilevers extends the domain of applicability of this technique, potentially ranging from interrogation of microbiological samples (soft cantilevers) to imaging with high resolution (stiff cantilevers). Along with mechanical frequencies (> 250 kHz) that are much higher than those used in conventional AFM probes of similar stiffness, these results suggest that our cavity optomechanical sensors may have application in a wide variety of hig...

  18. 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.

  19. On the development of planar actuators for variable stiffness devices

    Science.gov (United States)

    Henke, Markus; Gerlach, Gerald

    2013-04-01

    This contribution describes the development, the potential and the limitations of planar actuators for controlling bending devices with variable stiffness. Such structures are supposed to be components of new smart, self-sensing and -controlling composite materials for lightweight constructions. To realize a proper stiffness control, it is necessary to develop reliable actuators with high actuation capabilities based on smart materials. Several actuator designs driven by electroactive polymers (EAPs) are presented and discussed regarding to their applicability in such structures. To investigate the actuators, variable-flexural stiffness devices based on the control of its area moment of inertia were developed. The devices consist of a multi-layer stack of thin, individual plates. Stiffness variation is caused by planar actuators which control the sliding behavior between the layers by form closure structures. Previous investigations have shown that actuators with high actuation potential are needed to ensure reliable connections between the layers. For that reason, two kinds of EAPs Danfoss PolyPower and VHB 4905 by 3M, have been studied as driving unit. These EAP-driven actuators will be compared based on experimental measurements and finite element analyses.

  20. 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

  1. 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...

  2. Stiff person syndrome (SPS): Literature review and case report

    African Journals Online (AJOL)

    Stiff person syndrome (SPS) is a rare, debilitating condition which presents with progressive and inconsistent neurological features. The main ... clinical nature of SPS, and otherwise normal neurological examination, often lead to a misdiagnosis of conversion disorder. .... vitamin B12 and red cell folate levels were normal.

  3. 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

  4. Role of β2- and β3-adrenoceptors in arterial stiffness in a state of hypertension.

    Science.gov (United States)

    Leblanc, Camille; Tabrizchi, Reza

    2017-12-06

    An increase in arterial stiffness is associated with a high risk for morbidity and mortality in a state of elevated systemic pressure. The sympathetic nervous system plays an important role in the regulation of vascular tone via activation of β-adrenoceptors. The aim of this investigation was to determine the involvement of β-adrenoceptors in the control of arterial stiffness in a state of hypertension versus normotension. Pulse wave velocity (PWV), an index of vascular stiffness, was assessed in isoflurane-anaesthetized 13-14-week-old male spontaneously hypertensive (SH) and Wistar-Kyoto (WKY) rats. At baseline, PWV was significantly higher in SH (9.2±0.9m/s) compared to WKY rats (6.7±0.4m/s). The stimulation of β2- but not β3-adrenoceptors significantly reduced PWV in SH rats despite comparable reductions in blood pressure. Stimulation of β2- or β3-adrenoceptors did not reduce PWV in WKY rats. The administration of sodium nitroprusside (SNP) also significantly reduced PWV in SH but not WKY rats. Immunofluorescence revealed the expression of β2- and β3-adrenoceptors in endothelial cells and vascular smooth muscle cells of the abdominal aorta. There were no significant differences in the distribution of the expression of β2- and β3-adrenoceptors in endothelial and/or smooth muscle cells in blood vessels of SH compared to WKY rats. The evidence suggests that β2-adrenoceptor stimulation and SNP infusion reduce PWV independently from reduction in blood pressure in a state of high systemic arterial pressure. A reduction in vascular tone of the central arteries may play a key role in decreasing PWV that is elevated due to stiffer arterial wall. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. Carotid and Aortic Stiffness in Patients with Heterozygous Familial Hypercholesterolemia.

    Directory of Open Access Journals (Sweden)

    Alexandra I Ershova

    Full Text Available The role of plasma cholesterol in impairing arterial function and elasticity remains unclear. We evaluated arterial stiffness, measured locally in the common carotid artery by high-resolution echo-tracking, and aortic stiffness, using carotid-femoral pulse wave velocity (PWV (the "gold-standard" measurement of arterial stiffness, in treatment-naive patients with heterozygous familial hypercholesterolemia (FH.The study included 66 patients with FH (10-66 years old and 57 first-degree relatives without FH (11-61 years old. Carotid-femoral PWV was determined by SphygmoCor (AtCor, Australia. The parameters of carotid stiffness β-index, Peterson elastic modulus and local PWV were assessed with regard to the common carotid artery at a distance of 1cm from the bifurcation (AlokaProsound Alpha7, Japan.FH patients showed significantly higher β-index (6.3(4.8-8.2 vs. 5.2(4.2-6.4, p = 0.005, Ep (78(53-111 kPa vs. 62(48-79 kPa, p = 0.006, local PWV (5.4(4.5-6.4 m/c vs. 4.7(4.2-5.4 m/c, p = 0.005, but comparable values of carotid-femoral PWV (6.76(7.0-7.92 m/c vs. 6.48(6.16-7.12 m/c, p = 0.138. Carotid arteries and the aorta stiffened with age in patients with FH, but after 30 years, carotid arteries stiffened more significantly than the aorta.Our study demonstrated that treatment-naive patients with FH had stiffer carotid arteries than their relatives, but showed no difference in aortic stiffness. We also found out that the rate of reduction of elasticity of the aorta and carotid arteries in FH patients varies: it is observed earlier in carotid arteries than in the aorta.

  6. Nonsteroidal antiinflammatory drugs are associated with increased aortic stiffness

    Directory of Open Access Journals (Sweden)

    Martin Claridge

    2005-07-01

    Full Text Available Martin Claridge1, Simon Hobbs1, Clive Quick2, Nick Day3, Andrew Bradbury1, Teun Wilmink11Department of Vascular Surgery, University of Birmingham, Birmingham Heartlands Hospital Birmingham, UK; 2Department of Surgery, Hinchingbrooke Hospital, Huntingdon, UK; 3Department of Epidemiology and Biostatistics, University of Cambridge, Cambridge, UKObjectives: Nonsteroidal antiinflammatory drugs (NSAIDS have been shown to retard aneurysm growth in animal models. In vitro studies have shown an inhibitory effect of NSAIDS on matrix metalloproteinase-9, interleukin-1β, and IL-6 mediated arterial wall elastolysis. The aim of this study was to investigate the effects of NSAIDs on arterial stiffness, a surrogate marker of elastolysis.Methods: 447 subjects enrolled in a community-based abdominal aortic aneurysm (AAA screening program were assessed for age, blood pressure, smoking status, and drug history. Aortic diameter and stiffness were measured by M-Mode ultrasound. The concentration of the amino-terminal propeptide of type III procollagen was used as a proxy measurement of type III collagen turnover.Results: NSAID ingestion was significantly (p = 0.006 associated with increased aortic wall stiffness after adjusting for age, aortic diameter, blood pressure, and smoking status. No such effect was seen for β-blockers, calcium channel antagonists, nitrates, angiotensin-converting enzyme inhibitors, diuretics, or antiplatelet agents.Discussion: These novel data show that NSAIDS are associated with increased aortic stiffness, possibly through the effects of cytokine mediated elastolysis. This in turn may prevent aortic expansion and the development of AAA.Keywords: nonsteroidal antiinflammatory drugs, abdominal aortic aneurysm, aortic stiffness, elastolysis

  7. Acute exercise modifies titin phosphorylation and increases cardiac myofilament stiffness

    Directory of Open Access Journals (Sweden)

    Anna Eliane Müller

    2014-11-01

    Full Text Available Titin-based myofilament stiffness is largely modulated by phosphorylation of its elastic I-band regions N2-Bus (decreases passive stiffness, PT and PEVK (increases PT. Here, we tested the hypothesis that acute exercise changes titin phosphorylation and modifies myofilament stiffness. Adult rats were exercised on a treadmill for 15min, untrained animals served as controls. Titin phosphorylation was determined by Western blot analysis using phosphospecific antibodies to Ser4099 and Ser4010 in the N2-Bus region (PKG and PKA-dependent. respectively, and to Ser11878 and Ser 12022 in the PEVK region (PKCα and CaMKIIδ-dependent, respectively. Passive tension was determined by step-wise stretching of isolated skinned cardiomyocytes to sarcomere length ranging from 1.9-2.4µm and showed a significantly increased PT from exercised samples, compared to controls. In cardiac samples titin N2-Bus phosphorylation was significantly decreased by 40% at Ser4099, however, no significant changes were observed at Ser4010. PEVK phosphorylation at Ser11878 was significantly increased, which is probably mediated by the observed exercise-induced increase in PKCα activity. Interestingly, relative phosphorylation of Ser12022 was substantially decreased in the exercised samples. Surprisingly, in skeletal samples from acutely exercised animals we detected a significant decrease in PEVK phosphorylation at Ser11878 and an increase in Ser12022 phosphorylation; however, PKCα activity remained unchanged. In summary, our data show that a single exercise bout of 15 min affects titin domain phosphorylation and titin-based myocyte stiffness with obviously divergent effects in cardiac and skeletal muscle tissues. The observed changes in titin stiffness could play an important role in adapting the passive and active properties of the myocardium and the skeletal muscle to increased physical activity.

  8. Influence of running velocity on vertical, leg and joint stiffness : modelling and recommendations for future research.

    Science.gov (United States)

    Brughelli, Matt; Cronin, John

    2008-01-01

    Human running can be modelled as either a spring-mass model or multiple springs in series. A force is required to stretch or compress the spring, and thus stiffness, the variable of interest in this paper, can be calculated from the ratio of this force to the change in spring length. Given the link between force and length change, muscle stiffness and mechanical stiffness have been areas of interest to researchers, clinicians, and strength and conditioning practitioners for many years. This review focuses on mechanical stiffness, and in particular, vertical, leg and joint stiffness, since these are the only stiffness types that have been directly calculated during human running. It has been established that as running velocity increases from slow-to-moderate values, leg stiffness remains constant while both vertical stiffness and joint stiffness increase. However, no studies have calculated vertical, leg or joint stiffness over a range of slow-to-moderate values to maximum values in an athletic population. Therefore, the effects of faster running velocities on stiffness are relatively unexplored. Furthermore, no experimental research has examined the effects of training on vertical, leg or joint stiffness and the subsequent effects on running performance. Various methods of training (Olympic style weightlifting, heavy resistance training, plyometrics, eccentric strength training) have shown to be effective at improving running performance. However, the effects of these training methods on vertical, leg and joint stiffness are unknown. As a result, the true importance of stiffness to running performance remains unexplored, and the best practice for changing stiffness to optimize running performance is speculative at best. It is our hope that a better understanding of stiffness, and the influence of running speed on stiffness, will lead to greater interest and an increase in experimental research in this area.

  9. Impact testing of the residual limb: System response to changes in prosthetic stiffness.

    Science.gov (United States)

    Boutwell, Erin; Stine, Rebecca; Gard, Steven

    2016-01-01

    Currently, it is unknown whether changing prosthetic limb stiffness affects the total limb stiffness and influences the shock absorption of an individual with transtibial amputation. The hypotheses tested within this study are that a decrease in longitudinal prosthetic stiffness will produce (1) a reduced total limb stiffness, and (2) reduced magnitude of peak impact forces and increased time delay to peak force. Fourteen subjects with a transtibial amputation participated in this study. Prosthetic stiffness was modified by means of a shock-absorbing pylon that provides reduced longitudinal stiffness through compression of a helical spring within the pylon. A sudden loading evaluation device was built to examine changes in limb loading mechanics during a sudden impact event. No significant change was found in the peak force magnitude or timing of the peak force between prosthetic limb stiffness conditions. Total limb stiffness estimates ranged from 14.9 to 17.9 kN/m but were not significantly different between conditions. Thus, the prosthetic-side total limb stiffness was unaffected by changes in prosthetic limb stiffness. The insensitivity of the total limb stiffness to prosthetic stiffness may be explained by the mechanical characteristics (i.e., stiffness and damping) of the anatomical tissue within the residual limb.

  10. Minnesota County Boundaries - lines

    Data.gov (United States)

    Minnesota Department of Natural Resources — Minnesota county boundaries derived from a combination of 1:24,000 scale PLS lines, 1:100,000 scale TIGER, 1:100,000 scale DLG, and 1:24,000 scale hydrography lines....

  11. Knowledge production at boundaries

    NARCIS (Netherlands)

    Stange, Kari

    2017-01-01

    This thesis addresses how knowledge is used and produced in stakeholder-led collaborations to make long-term management plans for European fishery management. Boundary object theory is applied and developed to explain how stakeholders from the fishing industry interact with each other, and with

  12. Environmentalists without Boundaries

    African Journals Online (AJOL)

    GREGORY

    2009-03-16

    Mar 16, 2009 ... African Journal of Environmental Science and Technology Vol. ... The most fruitful scientific endeavors invariably cross boundaries – across ... The White Man's Burden: Why the West's Efforts to Aid the Rest Have Done So Much ... cooperation and capacity (7)stimulating economic development and growth, ...

  13. Environmentalists without Boundaries

    African Journals Online (AJOL)

    GREGORY

    2009-03-16

    Mar 16, 2009 ... Hence, this is a laudable project, but Coca Cola should also be cognizant of the growing African environmental pollution problems associated with plastics disposal as they market bottled water and other juices on the continent. This is an example of a challenge associated with advertent boundary crossing ...

  14. Minnesota County Boundaries

    Data.gov (United States)

    Minnesota Department of Natural Resources — Minnesota county boundaries derived from a combination of 1:24,000 scale PLS lines, 1:100,000 scale TIGER, 1:100,000 scale DLG, and 1:24,000 scale hydrography lines....

  15. Boundaries of the universe

    CERN Document Server

    Glasby, John S

    2013-01-01

    The boundaries of space exploration are being pushed back constantly, but the realm of the partially understood and the totally unknown is as great as ever. Among other things this book deals with astronomical instruments and their application, recent discoveries in the solar system, stellar evolution, the exploding starts, the galaxies, quasars, pulsars, the possibilities of extraterrestrial life and relativity.

  16. Dual boundary spanning

    DEFF Research Database (Denmark)

    Li-Ying, Jason

    2016-01-01

    The extant literature runs short in understanding openness of innovation regarding and the different pathways along which internal and external knowledge resources can be combined. This study proposes a unique typology for outside-in innovations based on two distinct ways of boundary spanning...

  17. Environmentalists without Boundaries

    African Journals Online (AJOL)

    GREGORY

    2009-03-16

    Mar 16, 2009 ... idea that development and environmental sustainability require poverty eradication is not a shocking one, but many scholars remain skeptical about the ... in developing countries has potentially solved this boundary problem by asking for donations through the purchase of bottled water at a price that will ...

  18. Effects of Cross-Sectional Shape, Solidity, and Distribution of Heat-Transfer Coefficient on the Torsional Stiffness of Thin Wings Subjected to Aerodynamic Heating

    Science.gov (United States)

    Thomson, Robert G.

    1959-01-01

    A study has been made of the effects of varying the shape, solidity, and heat-transfer coefficient of thin wings with regard to their influence on the torsional-stiffness reduction induced by aerodynamic heating. The variations in airfoil shape include blunting, flattening, and combined blunting and flattening of a solid wing of symmetrical double-wedge cross section. Hollow double-wedge wings of constant skin thickness with and without internal webs also are considered. The effects of heat-transfer coefficients appropriate for laminar and turbulent flow are investigated in addition to a step transition along the chord from a lower to a higher constant value of heat-transfer coefficient. From the results given it is concluded that the flattening of a solid double wedge decreases the reduction in torsional stiffness while slight degrees of blunting increase the loss. The influence of chordwise variations in heat-transfer coefficient due to turbulent and laminar boundary-layer flow on the torsional stiffness of solid wings is negligible. The effect of a step transition in heat-transfer coefficient along the chord of a solid wing can, however, become appreciable. The torsional-stiffness reduction of multiweb and hollow double-wedge wings is substantially less than that calculated for a solid wing subjected to the same heating conditions.

  19. Ursodeoxycholic acid treatment is associated with improvement of liver stiffness in cystic fibrosis patients

    NARCIS (Netherlands)

    van der Feen, Cathelijne; van der Doef, Hubert P. J.; van der Ent, Cornelis K.; Houwen, Roderick H. J.

    2016-01-01

    Background: Ursodeoxycholic acid (UDCA) might prevent progression of cystic fibrosis liver disease, but objective parameters for its effect are lacking. Methods: We used liver stiffness measurements to evaluate the effect of Ursodeoxycholic acid. Results: Paired measurements of liver stiffness were

  20. Estimation of quasi-stiffness of the human knee in the stance phase of walking

    National Research Council Canada - National Science Library

    Shamaei, Kamran; Sawicki, Gregory S; Dollar, Aaron M

    2013-01-01

    .... The knee joint moment-angle relationship is approximately linear in the flexion and extension stages of stance, exhibiting nearly constant stiffnesses, known as the quasi-stiffnesses of each stage...

  1. Stromal PDGFR-α Activation Enhances Matrix Stiffness, Impedes Mammary Ductal Development, and Accelerates Tumor Growth.

    Science.gov (United States)

    Hammer, Anisha M; Sizemore, Gina M; Shukla, Vasudha C; Avendano, Alex; Sizemore, Steven T; Chang, Jonathan J; Kladney, Raleigh D; Cuitiño, Maria C; Thies, Katie A; Verfurth, Quinn; Chakravarti, Arnab; Yee, Lisa D; Leone, Gustavo; Song, Jonathan W; Ghadiali, Samir N; Ostrowski, Michael C

    2017-06-01

    The extracellular matrix (ECM) is critical for mammary ductal development and differentiation, but how mammary fibroblasts regulate ECM remodeling remains to be elucidated. Herein, we used a mouse genetic model to activate platelet derived growth factor receptor-alpha (PDGFRα) specifically in the stroma. Hyperactivation of PDGFRα in the mammary stroma severely hindered pubertal mammary ductal morphogenesis, but did not interrupt the lobuloalveolar differentiation program. Increased stromal PDGFRα signaling induced mammary fat pad fibrosis with a corresponding increase in interstitial hyaluronic acid (HA) and collagen deposition. Mammary fibroblasts with PDGFRα hyperactivation also decreased hydraulic permeability of a collagen substrate in an in vitro microfluidic device assay, which was mitigated by inhibition of either PDGFRα or HA. Fibrosis seen in this model significantly increased the overall stiffness of the mammary gland as measured by atomic force microscopy. Further, mammary tumor cells injected orthotopically in the fat pads of mice with stromal activation of PDGFRα grew larger tumors compared to controls. Taken together, our data establish that aberrant stromal PDGFRα signaling disrupts ECM homeostasis during mammary gland development, resulting in increased mammary stiffness and increased potential for tumor growth. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

  2. Stromal PDGFR-α Activation Enhances Matrix Stiffness, Impedes Mammary Ductal Development, and Accelerates Tumor Growth

    Directory of Open Access Journals (Sweden)

    Anisha M. Hammer

    2017-06-01

    Full Text Available The extracellular matrix (ECM is critical for mammary ductal development and differentiation, but how mammary fibroblasts regulate ECM remodeling remains to be elucidated. Herein, we used a mouse genetic model to activate platelet derived growth factor receptor-alpha (PDGFRα specifically in the stroma. Hyperactivation of PDGFRα in the mammary stroma severely hindered pubertal mammary ductal morphogenesis, but did not interrupt the lobuloalveolar differentiation program. Increased stromal PDGFRα signaling induced mammary fat pad fibrosis with a corresponding increase in interstitial hyaluronic acid (HA and collagen deposition. Mammary fibroblasts with PDGFRα hyperactivation also decreased hydraulic permeability of a collagen substrate in an in vitro microfluidic device assay, which was mitigated by inhibition of either PDGFRα or HA. Fibrosis seen in this model significantly increased the overall stiffness of the mammary gland as measured by atomic force microscopy. Further, mammary tumor cells injected orthotopically in the fat pads of mice with stromal activation of PDGFRα grew larger tumors compared to controls. Taken together, our data establish that aberrant stromal PDGFRα signaling disrupts ECM homeostasis during mammary gland development, resulting in increased mammary stiffness and increased potential for tumor growth.

  3. Manipulation of cell mechanotaxis by designing curvature of the elasticity boundary on hydrogel matrix.

    Science.gov (United States)

    Ueki, Ayaka; Kidoaki, Satoru

    2015-02-01

    Directional cell migration induced by the stiffness gradient of cell culture substrates is known as a subset of the mechanical-cue-induced taxis, so-called mechanotaxis, typically durotaxis toward hard region. To establish the general conditions of biomaterials to manipulate the mechanotaxis, the effect of the shape of the elasticity transition boundary between hard and soft regions of a substrate on mechanotaxis should be systematically determined as well as the conditions of elasticity gradient strength. Here, as a simplified factor of expressing variations in the shape of the elasticity boundary in living tissues, we focus on the curvature of the elasticity boundary. Mask-free photolithographic microelasticity patterning of photocurable gelatin gel was employed to systematically prepare elasticity boundaries with various curvatures, and the efficiency of mechanotaxis of fibroblast cells around each curved boundary was examined. Highly efficient usual durotaxis was induced on a convex boundary with 100 μm in radius and on a concave boundary with 750 μm in radius of curvature. Interestingly, biased migration toward soft regions of the gel, i.e., inverse durotaxis, was first observed for concave boundaries with 50 μm or 100 μm in radius of curvature, which was named as "negative mechanotaxis". The curvature of the elasticity boundary was found to markedly affect the efficiency of induction and the direction of mechanotaxis. The mechanism responsible for this phenomenon and the implication for the curvature effect in in vivo systems are discussed. Copyright © 2014 Elsevier Ltd. All rights reserved.

  4. Vascular Stiffness and Increased Pulse Pressure in the Aging Cardiovascular System

    OpenAIRE

    Jochen Steppan; Viachaslau Barodka; Berkowitz, Dan E; Daniel Nyhan

    2011-01-01

    Aging leads to a multitude of changes in the cardiovascular system, including systolic hypertension, increased central vascular stiffness, and increased pulse pressure. In this paper we will review the effects of age-associated increased vascular stiffness on systolic blood pressure, pulse pressure, augmentation index, and cardiac workload. Additionally we will describe pulse wave velocity as a method to measure vascular stiffness and review the impact of increased vascular stiffness as an in...

  5. 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

  6. Grain Boundary Segregation in Metals

    CERN Document Server

    Lejcek, Pavel

    2010-01-01

    Grain boundaries are important structural components of polycrystalline materials used in the vast majority of technical applications. Because grain boundaries form a continuous network throughout such materials, their properties may limit their practical use. One of the serious phenomena which evoke these limitations is the grain boundary segregation of impurities. It results in the loss of grain boundary cohesion and consequently, in brittle fracture of the materials. The current book deals with fundamentals of grain boundary segregation in metallic materials and its relationship to the grain boundary structure, classification and other materials properties.

  7. An Algorithm for Synthesizing Mass and Stiffness Matrices from Experimental Vibration Modes

    Science.gov (United States)

    Ross, R. G., Jr.

    1972-01-01

    An algorithm is described for synthesizing the mass and stiffness matrices from experimentally derived modal data in a way that preserves the physical significance of the individual mass and stiffness elements. The mass and stiffness matrices are derived for a rollup solar array example, and are then used to define the modal response of a modified array.

  8. Aortic stiffness and microalbuminuria in patients with chronic obstructive pulmonary disease

    Directory of Open Access Journals (Sweden)

    Alaa Refaat

    2015-07-01

    Conclusions: COPD is associated with increased aortic stiffness. MAU is independently related to aortic stiffness in patients with COPD. Further studies are necessary to investigate whether MAU could be an effective biomarker of aortic stiffness and potential cardiovascular compromise in patients with COPD.

  9. Interactions and Optimizations Analysis between Stiffness and Workspace of 3-UPU Robotic Mechanism

    Science.gov (United States)

    Zhang, Dan; Wei, Bin

    2017-04-01

    The interactions between stiffness and workspace performances are studied. The stiffness in x, y and z directions as well as the workspace of a 3-UPU mechanism are studied and optimized. The stiffness of the robotic system in every single moveable direction is measured and analyzed, and it is observed that in the case where one tries to make the x and y translational stiffness larger, the z directional stiffness will be reduced, i.e. the x and y translational stiffness contradicts with the one in z direction. Subsequently, the objective functions for the summation of the x and y translational stiffness and z directional stiffness are established and they are being optimized simultaneously. However, we later found that these two objectives are not in the same scale; a normalization of the objectives is thus taken into consideration. Meanwhile, the robotic system's workspace is studied and optimized. Through comparing the stiffness landscape and the workspace volume landscape, it is also observed that the z translational stiffness shows the same changing tendency with the workspace volume's changing tendency while the x and y translational stiffness shows the opposite changing tendency compared to the workspace volume's. Via employing the Pareto front theory and differential evolution, the summation of the x and y translational stiffness and the volume of the workspace are being simultaneously optimized. Finally, the mechanism is employed to synthesize an exercise-walking machine for stroke patients.

  10. 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.

  11. Boundary Conditions of Methamphetamine Craving

    Science.gov (United States)

    Lopez, Richard B.; Onyemekwu, Chukwudi; Hart, Carl L.; Ochsner, Kevin N.; Kober, Hedy

    2015-01-01

    Methamphetamine use has increased significantly and become a global health concern. Craving is known to predict methamphetamine use and relapse following abstinence. Some have suggested that cravings are automatic, generalized, and uncontrollable, but experimental work addressing these claims is lacking. In two exploratory studies we tested the boundary conditions of methamphetamine craving by asking: (1) is craving specific to users’ preferred route of administration? and (2) can craving be regulated by cognitive strategies? Two groups of methamphetamine users were recruited. In Study 1, participants were grouped by their preferred route of administration (intranasal vs. smoking), and rated their craving in response to photographs and movies depicting methamphetamine use (via the intranasal vs. smoking route). In Study 2, methamphetamine smokers implemented cognitive regulation strategies while viewing photographs depicting methamphetamine smoking. Strategies involved either focusing on the positive aspects of smoking methamphetamine or the negative consequences of doing so – the latter strategy based on treatment protocols for addiction. In Study 1, we found a significant interaction between group and route of administration, such that participants who preferred to smoke methamphetamine reported significantly stronger craving for smoking stimuli, whereas those who preferred the intranasal route reported stronger craving for intranasal stimuli. In Study 2, participants reported significantly lower craving when focusing on the negative consequences associated with methamphetamine use. Taken together, these findings suggest that strength of craving for methamphetamine is moderated by users’ route of administration and can be reduced by cognitive strategies. This has important theoretical, methodological, and clinical implications. PMID:26302338

  12. Effects of boundary conditions on bistable behaviour in axisymmetrical shallow shells.

    Science.gov (United States)

    Sobota, P M; Seffen, K A

    2017-07-01

    Multistable shells are thin-walled structures that have more than one stable state of self-stress. We consider isotropic axisymmetrical shallow shells of arbitrary polynomial shapes using a Föppl-von Kármán analytical model. By employing a Rayleigh-Ritz approach, we identify stable shapes from local minima in the strain energy formulation, and we formally characterize the level of influence of the boundary conditions on the critical geometry for achieving bistable inversion-an effect not directly answered in the literature. Systematic insight is afforded by connecting the boundary to ground through sets of extensional and rotational linear springs. For typical cap-like shells, it is shown that bistability is generally enhanced when the extensional spring stiffness increases and when the rotational spring stiffness decreases, i.e. when boundary movements in-plane are resisted but when their rotations are not; however, for certain other shapes and large in-plane stiffness values, bistability can be enhanced by resisting but not entirely preventing edge rotations. Our predictions are furnished as detailed regime maps of the critical geometry, which are accurately correlated against finite-element analysis. Furthermore, the suitabilities of single degree-of-freedom models, for which solutions are achieved in closed form, are evaluated and compared to our more accurate predictions.

  13. Boundary-layer theory

    CERN Document Server

    Schlichting (Deceased), Hermann

    2017-01-01

    This new edition of the near-legendary textbook by Schlichting and revised by Gersten presents a comprehensive overview of boundary-layer theory and its application to all areas of fluid mechanics, with particular emphasis on the flow past bodies (e.g. aircraft aerodynamics). The new edition features an updated reference list and over 100 additional changes throughout the book, reflecting the latest advances on the subject.

  14. Winkler boundary conditions for three-point bending tests on 1D nanomaterials

    Science.gov (United States)

    Gangadean, D.; McIlroy, David N.; Faulkner, Brian E.; Aston, D. Eric

    2010-06-01

    Bending tests with atomic force microscopes (AFM) is a common method for elasticity measurements on 1D nanomaterials. Interpretation of the force and deflection data is necessary to determine the Young's modulus of the tested material and has been done assuming either of two classic boundary conditions that represent two extreme possibilities for the rigidity of the sample-anchor interface. The elasticity results from the two boundary conditions differ by a factor of four. Furthermore, both boundary conditions ignore the effects of deflections in the anchors themselves. The Winkler model for beams on elastic foundations is developed here for three-point bending tests to provide a more realistic representation. Equations for computing sample elasticity are derived from two sets of boundary conditions for the Winkler model. Application of this model to interpret the measurement of mechanical stiffness of a silica nanowire at multiple points in a three-point bending is discussed. With the correct choice of boundary conditions, the Winkler model gives a better fit for the observed stiffness profile than the classical beam models while providing a result that differs from both by a factor of two and is comparable to the bulk elasticity.

  15. Winkler boundary conditions for three-point bending tests on 1D nanomaterials.

    Science.gov (United States)

    Gangadean, D; McIlroy, David N; Faulkner, Brian E; Aston, D Eric

    2010-06-04

    Bending tests with atomic force microscopes (AFM) is a common method for elasticity measurements on 1D nanomaterials. Interpretation of the force and deflection data is necessary to determine the Young's modulus of the tested material and has been done assuming either of two classic boundary conditions that represent two extreme possibilities for the rigidity of the sample-anchor interface. The elasticity results from the two boundary conditions differ by a factor of four. Furthermore, both boundary conditions ignore the effects of deflections in the anchors themselves. The Winkler model for beams on elastic foundations is developed here for three-point bending tests to provide a more realistic representation. Equations for computing sample elasticity are derived from two sets of boundary conditions for the Winkler model. Application of this model to interpret the measurement of mechanical stiffness of a silica nanowire at multiple points in a three-point bending is discussed. With the correct choice of boundary conditions, the Winkler model gives a better fit for the observed stiffness profile than the classical beam models while providing a result that differs from both by a factor of two and is comparable to the bulk elasticity.

  16. Measuring the Substellar Boundary

    Science.gov (United States)

    Cancino, Adolfo Andrew; Dupuy, Trent

    2018-01-01

    Brown dwarfs are not massive enough to undergo hydrogen fusion and therefore constantly lose heat and change luminosity over their lifetime. Because of this, brown dwarfs do not follow the same pattern that stars on the main sequence follow. Brown dwarfs can have similar luminosities but widely differing masses, or vice versa, while stars follow a tight relationship between mass and luminosity. In principle, mass and luminosity measurements straddling the boundary between stars and brown dwarfs could be used to directly measure this dividing line in mass. We present a method for determining this boundary accurately given a limited sample size. We tested our method with Monte Carlo simulated samples of brown dwarfs and stars with randomly drawn masses and ages, using evolutionary models to infer luminosities. In our simulation designed to mimic the largest current sample of such mass measurements (37 objects; Dupuy & Liu 2017), we find that the uncertainty in the dividing line that can be inferred from the data is ± 4 MJup. This implies that distinguishing between competing evolutionary model predictions for the boundary (~70-80 MJup) will be difficult given the current sample size of mass measurements.

  17. On the stiffness analysis of a cable driven leg exoskeleton.

    Science.gov (United States)

    Sanjeevi, N S S; Vashista, Vineet

    2017-07-01

    Robotic systems are being used for gait rehabilitation of patients with neurological disorder. These devices are externally powered to apply external forces on human limbs to assist the leg motion. Patients while walking with these devices adapt their walking pattern in response to the applied forces. The efficacy of a rehabilitation paradigm thus depends on the human-robot interaction. A cable driven leg exoskeleton (CDLE) use actuated cables to apply external joint torques on human leg. Cables are lightweight and flexible but can only be pulled, thus a CDLE requires redundant cables. Redundancy in CDLE can be utilized to appropriately tune a robot's performance. In this work, we present the stiffness analysis of CDLE. Different stiffness performance indices are established to study the role of system parameters in improving the human-robot interaction.

  18. 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.

  19. [Arterial stiffness in patients with chronic obstructive pulmonary disease].

    Science.gov (United States)

    2012-01-01

    To estimate arterial stiffness (AS) in patients with chronic obstructive pulmonary disease (COPD). A total of 112 COPD patients over 40 years of age entered a population-based trial. The patients with coronary heart diseases, peripheral vascular atherosclerosis, other severe chronic diseases in exacerbation were withdrawn. The control group consisted of 26 healthy volunteers matched by gender and age. AS was measured at arteriograph "Tensioclinic" ("Tensiomed", Hungary). COPD patients, first of all elderly ones, had abnormal properties of arterial wall. Increased arterial rigidity and pulse wave reflection (accelerated pulse wave velocity and high index of augmentation) are strongly associated with elevation of central arterial pressure. High arterial wall stiffness in COPD patients suggests an increased risk of cardiovascular diseases that necessitates examination in prospective studies.

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

    DEFF Research Database (Denmark)

    Andersson, Charlotte; Quiroz, Rene; Enserro, Danielle

    2016-01-01

    with hypertension. Parental hypertension was associated with greater offspring mean arterial pressure (multivariable-adjusted estimate=2.9 mm Hg; 95% confidence interval, 1.9-3.9, and 4.2 mm Hg; 95% confidence interval, 2.9-5.5, for 1 and 2 parents with hypertension, respectively; P... forward pressure wave amplitude (1.6 mm Hg; 95% confidence interval, 0.6-2.7, and 1.9 mm Hg; 95% confidence interval, 0.6-3.2, for 1 and 2 parents with hypertension, respectively; P=0.003 for both). Carotid-femoral pulse wave velocity and augmentation index displayed similar dose-dependent relations......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...

  1. Tuning the Range of Polyacrylamide Gel Stiffness for Mechanobiology Applications.

    Science.gov (United States)

    Denisin, Aleksandra K; Pruitt, Beth L

    2016-08-31

    Adjusting the acrylamide monomer and cross-linker content in polyacrylamide gels controls the hydrogel stiffness, yet the reported elastic modulus for the same formulations varies widely and these discrepancies are frequently attributed to different measurement methods. Few studies exist that examine stiffness trends across monomer and cross-linker concentrations using the same characterization platform. In this work, we use Atomic Force Microscopy and analyze force-distance curves to derive the elastic modulus of polyacrylamide hydrogels. We find that gel elastic modulus increases with increasing cross-link concentration until an inflection point, after which gel stiffness decreases with increasing cross-linking. This behavior arises because of the formation of highly cross-linked clusters, which add inhomogeneity and heterogeneity to the network structure, causing the global network to soften even under high cross-linking conditions. We identify these inflection points for three different total polymer formulations. When we alter gelation kinetics by using a low polymerization temperature, we find that gels are stiffer when polymerized at 4 °C compared to room temperature, indicating a complex relationship between gel structure, elasticity, and network formation. We also investigate how gel stiffness changes during storage over 10 days and find that specific gel formulations undergo significant stiffening (1.55 ± 0.13), which may be explained by differences in gel swelling resulting from initial polymerization parameters. Taken together, our study emphasizes the importance of polyacrylamide formulation, polymerization temperature, gelation time, and storage duration in defining the structural and mechanical properties of the polyacrylamide hydrogels.

  2. Revision Arthroplasty for the Management of Stiffness After Primary TKA.

    Science.gov (United States)

    Moya-Angeler, Joaquin; Bas, Marcel A; Cooper, H John; Hepinstall, Matthew S; Rodriguez, Jose A; Scuderi, Giles R

    2017-06-01

    The aim of this study was to evaluate the results of revision surgery for the treatment of stiffness after total knee arthroplasty (TKA). An IRB-approved retrospective review was performed to identify patients who were revised due to stiffness after a primary TKA. Patients were included when at least one major component had to be revised due to stiffness after primary TKA with a minimum follow-up of 2 years. Patients with history of previous infection and those treated with isolated polyethylene exchange were excluded. The study group involved 42 knees. Mean follow-up was 47 months (24-109 months). Mean flexion contracture improved from 9.7° (0°-35°) preoperatively to 2.3° (0°-20°) postoperatively (P < .00). Mean flexion improved from 81.5° (10°-125°) preoperatively to 94.3° (15°-140°) postoperatively (P .02). Mean range of motion improved from 72.0° preoperatively (10°-100°) to 92° (15°-140°) postoperatively (P < .00). Mean Knee Society knee scores improved from 43.9 points (15-67) preoperatively to 72.0 points (50-93) at latest follow-up and mean Knee Society Function scores improved from 48.7 (35-80) preoperatively to 70.1 points (30-90) postoperatively. Pain improved in 73% of the patients. Revision surgery appears to be a reasonable option for patients presenting with pain and stiffness after TKA. However, the benefits may be modest as the outcomes still do not approach those achieved with primary TKA. Copyright © 2017 Elsevier Inc. All rights reserved.

  3. Stiffness analysis of 3D spheroids using microtweezers.

    Directory of Open Access Journals (Sweden)

    Devina Jaiswal

    Full Text Available We describe a novel mechanical characterization method that has directly measured the stiffness of cancer spheroids for the first time to our knowledge. Stiffness is known to be a key parameter that characterizes cancerous and normal cells. Atomic force microscopy or optical tweezers have been typically used for characterization of single cells with the measurable forces ranging from sub pN to a few hundred nN, which are not suitable for measurement of larger 3D cellular structures such as spheroids, whose mechanical characteristics have not been fully studied. Here, we developed microtweezers that measure forces from sub hundred nN to mN. The wide force range was achieved by the use of replaceable cantilevers fabricated from SU8, and brass. The chopstick-like motion of the two cantilevers facilitates easy handling of samples and microscopic observation for mechanical characterization. The cantilever bending was optically tracked to find the applied force and sample stiffness. The efficacy of the method was demonstrated through stiffness measurement of agarose pillars with known concentrations. Following the initial system evaluation with agarose, two cancerous (T47D and BT474 and one normal epithelial (MCF 10A breast cell lines were used to conduct multi-cellular spheroid measurements to find Young's moduli of 230, 420 and 1250 Pa for BT474, T47D, and MCF 10A, respectively. The results showed that BT474 and T47D spheroids are six and three times softer than epithelial MCF10A spheroids, respectively. Our method successfully characterized samples with wide range of Young's modulus including agarose (25-100 kPa, spheroids of cancerous and non-malignant cells (190-200 μm, 230-1250 Pa and collagenase-treated spheroids (215 μm, 130 Pa.

  4. Cervical Spine Stiffness and Geometry of the Young Human Male

    Science.gov (United States)

    1982-11-01

    gaged cantilever beam. A 1/32 drill was used to make a hole in the vertebra and a #20 gage hypodermic needle stock cut to length acted as the pin. At...some descriptive geometric calculations. STIFFNESS AND MATERIAL PROPERTIES OF INDIVIDUAL MOTION SEGMENTS THEORETICAL CONSIDERATIONS I. In theory , the...34-" --------------- A 1 2 0 * x 3+ -¶.• " ~CZ PLEXIGLASS BASE SCHEMATIC SHOWING THE HOLE LOCATIONS, SCRIBE MARKS AND SUPPORTING NEEDLE LOCATIONS

  5. 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.

  6. Simple Stiffness Tailoring of Balsa Sandwich Core Material

    OpenAIRE

    Kepler, J.A.

    2010-01-01

    Abstract A concept for improving the shear stiffness properties of balsa core material for sandwich structures is presented. The concept is based on utilization of the strongly orthotropic properties of the balsa wood, applying an appropriate transverse layup sequence. The effective core material shear modulus is modeled using basic laminate theory. This is subsequently validated through sandwich beam bending and lap shear experiments. Compared to the standard balsa core systems, a...

  7. Stiff fluid spike solutions from Bianchi type V seed solutions

    Science.gov (United States)

    Gregoris, D.; Lim, W. C.; Coley, A. A.

    2017-12-01

    In this paper we expand upon our previous work Coley et al (2016 Class. Quantum Grav. 33 215010) by using the entire family of Bianchi type V stiff fluid solutions as seed solutions of the Stephani transformation. Among the new exact solutions generated, we observe a number of important physical phenomena. The most interesting phenomenon is exact solutions with intersecting spikes. Other interesting phenomena are solutions with saddle states and a close-to-FL epoch.

  8. On a high-potential variable flexural stiffness device

    Science.gov (United States)

    Henke, Markus; Gerlach, Gerald

    2013-05-01

    There are great efforts in developing effective composite structures for lightweight constructions for nearly every field of engineering. This concerns for example aeronautics and spacecrafts, but also automotive industry and energy harvesting applications. Modern concepts of lightweight components try to make use of structures with properties which can be adjusted in a controllable was. However, classic composite materials can only slightly adapt to varying environmental conditions because most materials, like carbon or glass-fiber composites show properties which are time-constant and not changeable. This contribution describes the development, the potential and the limitations of novel smart, self-controlling structures which can change their mechanical properties - e.g. their flexural stiffness - by more then one order of magnitude. These structures use a multi-layer approach with a 10-layer stack of 0.75 mm thick polycarbonate. The set-up is analytically described and its mechanical behavior is predicted by finite element analysis done with ABAQUS. The layers are braided together by an array of shape memory alloy (SMA) wires, which can be activated independently. Depending on the temperature applied by the electrical current flowing through the wires and the corresponding contraction the wires can tightly clamp the layers so that they cannot slide against each other due to friction forces. In this case the multilayer acts as rigid beam with high stiffness. If the friction-induced shear stress is smaller than a certain threshold, then the layers can slide over each other and the multilayer becomes compliant under bending load. The friction forces between the layers and, hence, the stiffness of the beam is controlled by the electrical current through the wires. The more separate parts of SMA wires the structure has the larger is the number of steps of stiffness changes of the flexural beam.

  9. 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.

  10. 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.

  11. Factors associated with stiff knee gait in cerebral palsy

    OpenAIRE

    Compton, Eleanor Frances

    2015-01-01

    Stiff knee gait (SKG) is one of a few classified walking patterns which people with cerebral palsy (pwCP) can present with. The characteristic for SKG is delayed and/or reduced peak knee flexion during swing phase, which can reduce walking ability and result in functional restrictions. Through the use of both clinical and laboratory based measures this cross-sectional study aimed to identify the factors associated with SKG, suggest possible treatment options and propose potential directions f...

  12. Boundary issues and personality disorders.

    Science.gov (United States)

    Gutheil, Thomas G

    2005-03-01

    The author first presents an overview of the basic elements of boundary theory and clarifies the distinction between boundary crossings and boundary violations. The concepts of context dependence, power asymmetry, and fiduciary duty as they relate to boundary problems are also discussed. The intrinsic and extrinsic consequences of boundary problems are reviewed. The extrinsic consequences fall into three major categories: civil lawsuits, complaints to the board of registration, and complaints to professional societies. The author then reviews types of boundary issues that arise in relation to histrionic, dependent, antisocial, and borderline personality disorders. Countertransference issues that arise in working with patients with personality disorders are discussed, as well as cultural differences that may affect the perception of boundary problems. The article ends with a list of risk management principles and recommendations for avoiding boundary problems in the therapeutic relationship.

  13. Allegheny County Zip Code Boundaries

    Data.gov (United States)

    Allegheny County / City of Pittsburgh / Western PA Regional Data Center — This dataset demarcates the zip code boundaries that lie within Allegheny County. These are not clipped to the Allgeheny County boundary. If viewing this...

  14. Modeling of Axial Spring Stiffness in Active Vibration Controlled Drilling

    Directory of Open Access Journals (Sweden)

    Pao William

    2014-07-01

    Full Text Available During drilling process, substantial amount of vibration and shock are induced to the drill string. Active vibration controlled drilling is introduced to reduce the vibration and increase the efficiency of drilling process. In this system, two main components that determine the damping coefficient are magnetorheological (MR damper and spring assembly. Performance of vibration damping system is depending on the viscosity of MR fluid in the damper and spring constant of spring assembly. One of the key issues that are unclear from the design is the correlation between the axial spring stiffness configuration and the damping force which needs to be tuned actively. There has been lack of studies on how the viscosity of MR fluid on the active vibration damper affects the damping stiffness of the whole system. The objective of the project is to extract the correlations for the viscous damping coefficient, equivalent spring stiffness and power input to the system. Simplified vibration model is thus created using Simulink, together with experimental data fed from APS Technology’s in-house team. Inputs of the simulation such as force exerted, mass of mandrel, spring constant and step time are based on the experimental data and can be adjusted to suit different experiments. By having the model, behavior of the system can be studied and analyzed. From the simulation, it is also observed that the relationship between damping coefficient and power input of the system is linear.

  15. 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.

  16. Origami tubes assembled into stiff, yet reconfigurable structures and metamaterials

    Science.gov (United States)

    Filipov, Evgueni T.; Tachi, Tomohiro; Paulino, Glaucio H.

    2015-01-01

    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. PMID:26351693

  17. Cardiorespiratory fitness and age-related arterial stiffness in lupus.

    Science.gov (United States)

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

    2018-01-10

    The aim of the present study was twofold: 1) to examine the association of cardiorespiratory fitness with arterial stiffness in women with systemic lupus erythematosus; 2) 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® 24h pulse wave velocity monitor). Cardiorespiratory fitness was estimated with the Siconolfi step test and the six-minute walk test. Cardiorespiratory fitness was inversely associated with pulse wave velocity in crude analyses (Pfitness×age interaction effect on pulse wave velocity, regardless of the test used to estimate cardiorespiratory fitness (Pfitness was associated with a lower increase in pulse wave velocity per each year increase in age. The results of the present study suggest that cardiorespiratory fitness attenuates 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. Since the cross-sectional design precludes establishing causal relationships, future clinical trials should confirm or contrast these findings. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

  18. Achilles tendon stiffness is unchanged one hour after a marathon.

    Science.gov (United States)

    Peltonen, Jussi; Cronin, Neil J; Stenroth, Lauri; Finni, Taija; Avela, Janne

    2012-10-15

    Overuse-induced injuries have been proposed as a predisposing factor for Achilles tendon (AT) ruptures. If tendons can be overloaded, their mechanical properties should change during exercise. Because there data are lacking on the effects of a single bout of long-lasting exercise on AT mechanical properties, the present study measured AT stiffness before and after a marathon. AT stiffness was determined as the slope of the force-elongation curve between 10 and 80% of maximum voluntary force. AT force-elongation characteristics were measured in an ankle dynamometer using simultaneous motion-capture-assisted ultrasonography. Oxygen consumption and ankle kinematics were also measured on a treadmill at the marathon pace. All measurements were performed before and after the marathon. AT stiffness did not change significantly from the pre-race value of 197±62 N mm(-1) (mean ± s.d.) to the post-race value of 206±59 N mm(-1) (N=12, P=0.312). Oxygen consumption increased after the race by 7±10% (Pmarathon induced a change in their foot strike technique. The AT of the physically active individuals seems to be able to resist mechanical changes under physiological stress. We therefore suggest that natural loading, like in running, may not overstress the AT or predispose it to injury. In addition, decreased running economy, as well as altered foot strike technique, was probably attributable to muscle fatigue.

  19. Ontogeny of material stiffness heterogeneity in the macaque mandibular corpus.

    Science.gov (United States)

    Daegling, David J; Granatosky, Michael C; McGraw, W Scott

    2014-02-01

    Evidence is accumulating that bone material stiffness increases during ontogeny, and the role of elastic modulus in conditioning attributes of strength and toughness is therefore a focus of ongoing investigation. Developmental changes in structural properties of the primate mandible have been documented, but comparatively little is known about changes in material heterogeneity and their impact on biomechanical behavior. We examine a cross-sectional sample of Macaca fascicularis (N = 14) to investigate a series of hypotheses that collectively evaluate whether the patterning of material stiffness (elastic modulus) heterogeneity in the mandible differs among juvenile, subadult and adult individuals. Because differences in age-related activity patterns are known to influence bone stiffness and strength, these data are potentially useful for understanding the relationship between feeding behavior on the one hand and material and structural properties of the mandible on the other. Elastic modulus is shown to be spatially dependent regardless of age, with this dependence being explicable primarily by differences in alveolar versus basal cortical bone. Elastic modulus does not differ consistently between buccal and lingual cortical plates, despite likely differences in the biomechanical milieu of these regions. Since we found only weak support for the hypothesis that the spatial patterning of heterogeneity becomes more predictable with age, accumulated load history may not account for regional differences in bone material properties in mature individuals with respect to the mandibular corpus. Copyright © 2013 Wiley Periodicals, Inc.

  20. Experimental and theoretical rotordynamic stiffness coefficients for a three-stage brush seal

    Science.gov (United States)

    Pugachev, A. O.; Deckner, M.

    2012-08-01

    Experimental and theoretical results are presented for a multistage brush seal. Experimental stiffness is obtained from integrating circumferential pressure distribution measured in seal cavities. A CFD analysis is used to predict seal performance. Bristle packs are modeled by the porous medium approach. Leakage is predicted well by the CFD method. Theoretical stiffness coefficients are in reasonable agreement with the measurements. Experimental results are also compared with a three-teeth-on-stator labyrinth seal. The multistage brush seal gives about 60% leakage reduction over the labyrinth seal. Rotordynamic stiffness coefficients are also improved: the brush seal has positive direct stiffness and smaller cross-coupled stiffness.

  1. Progress report on grain boundaries

    Science.gov (United States)

    Balluffi, R. W.; Bristowe, P. D.

    1989-06-01

    The research was focused on the following three major areas: (1) study of the atomic structure of grain boundaries by means of X-ray diffraction, transmission electron microscopy and computer modeling; (2) study of grain boundary phase transitions by electron microscopy and computer modeling; (3) investigation of the mechanism of high angle grain boundary migration. Results are briefly discussed.

  2. Progress report on grain boundaries

    Energy Technology Data Exchange (ETDEWEB)

    Balluffi, R.W.; Bristowe, P.D.

    1989-06-01

    The research was focused on the following three major areas: (1) study of the atomic structure of grain boundaries by means of x-ray diffraction, transmission electron microscopy and computer modeling; (2) study of grain boundary phase transitions by electron microscopy and computer modeling; (3) investigation of the mechanism of high angle grain boundary migration. Results are briefly discussed. 20 refs.

  3. Relationship between cell stiffness and stress fiber amount, assessed by simultaneous atomic force microscopy and live-cell fluorescence imaging.

    Science.gov (United States)

    Gavara, Núria; Chadwick, Richard S

    2016-06-01

    Actomyosin stress fibers, one of the main components of the cell's cytoskeleton, provide mechanical stability to adherent cells by applying and transmitting tensile forces onto the extracellular matrix (ECM) at the sites of cell-ECM adhesion. While it is widely accepted that changes in spatial and temporal distribution of stress fibers affect the cell's mechanical properties, there is no quantitative knowledge on how stress fiber amount and organization directly modulate cell stiffness. We address this key open question by combining atomic force microscopy with simultaneous fluorescence imaging of living cells, and combine for the first time reliable quantitative parameters obtained from both techniques. We show that the amount of myosin and (to a lesser extent) actin assembled in stress fibers directly modulates cell stiffness in adherent mouse fibroblasts (NIH3T3). In addition, the spatial distribution of stress fibers has a second-order modulatory effect. In particular, the presence of either fibers located in the cell periphery, aligned fibers or thicker fibers gives rise to reinforced cell stiffness. Our results provide basic and significant information that will help design optimal protocols to regulate the mechanical properties of adherent cells via pharmacological interventions that alter stress fiber assembly or via micropatterning techniques that restrict stress fiber spatial organization.

  4. 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

  5. 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 stiffness modulus of asphalt concrete under steady-state strain was performed using the simple axial compression-tensile test under 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

  6. Boundaries and Boundary Marks - Substantive Cultural Heritage of Extensive Importance

    Science.gov (United States)

    Waldhaeusl, P.; Koenig, H.; Mansberger, R.

    2015-08-01

    The Austrian Society for surveying and Geoinformation (ASG) has proposed to submit "Boundaries and Boundary Marks" for the UNESCO World Heritage title. It was time that boundaries, borders and limits of all types as well as ownership rights would find the proper attention in the global public. Landmarks symbolize the real property and the associated rights and obligations, in a figurative sense, the property generally and all legal limits. A democratic state of law is impossible at today's population density without a functioning land administration system with surveying and jurisdiction. As monumental World Heritage representatives of the geodetic artwork "Boundaries and Boundary Marks" are specifically proposed: remaining monuments of the original cadastral geodetic network, the first pan-Austrian surveying headquarters in Vienna, and a specific selection of outstanding boundary monuments. Landmarks are monuments to the boundaries which separate rights and obligations, but also connect the neighbors peacefully after written agreement. "And cursed be he who does not respect the boundaries" you wrote already 3000 years ago. Boundaries and Boundary Marks are a real thing; they all belong to the tangible or material heritage of human history. In this context also the intangible heritage is discussed. This refers to oral tradition and expressions, performing arts; social practices, rituals and festive events; as well as to knowledge and practices handling nature and the universe. "Boundaries and Boundary Marks" do not belong to it, but clearly to the material cultural world heritage. "Boundary and Boundary Marks" is proposed to be listed according to the criteria (ii),(iv),(vi).

  7. 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.

  8. Design of a New Nonlinear Stiffness Compliant Actuator and Its Error Compensation Method

    Directory of Open Access Journals (Sweden)

    Shaobin Lan

    2016-01-01

    Full Text Available Compliant actuators are more advantageous than stiff actuators in some circumstances, for example, unstructured environment robots and rehabilitation robots. Compliant actuators are more adaptive and safe. Constant stiffness compliant actuators have some limitations in impedance and bandwidth. Variable stiffness actuators improve their performance owing to introducing an extra motor to tune the stiffness of the actuators. However, they also have some limitations such as the bulky structure and heavy weight. It was also found that there are some waste functions existing in the current variable stiffness actuators and that the fully decoupled position control and stiffness tune are not necessary, because there exist some regular phenomena during most circumstances of human interaction with the robots which are “low load, low stiffness and high load, high stiffness”. In this paper, a design method for nonlinear stiffness compliant actuator was proposed which performed the predefined deflection-torque trajectory of the regular phenomenon. A roller and a cantilever which has special curve profile constitute the basic mechanical structure of the nonlinear stiffness compliant actuators. An error compensation method was also proposed to analyze the stiffness of elastic structure. The simulation results proved that the proposed method was effective in designing a predefined nonlinear stiffness compliant actuator.

  9. 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.

  10. A classification of ecological boundaries

    Science.gov (United States)

    Strayer, D.L.; Power, M.E.; Fagan, W.F.; Pickett, S.T.A.; Belnap, J.

    2003-01-01

    Ecologists use the term boundary to refer to a wide range of real and conceptual structures. Because imprecise terminology may impede the search for general patterns and theories about ecological boundaries, we present a classification of the attributes of ecological boundaries to aid in communication and theory development. Ecological boundaries may differ in their origin and maintenance, their spatial structure, their function, and their temporal dynamics. A classification system based on these attributes should help ecologists determine whether boundaries are truly comparable. This system can be applied when comparing empirical studies, comparing theories, and testing theoretical predictions against empirical results.

  11. Transcending Organizational Boundaries

    DEFF Research Database (Denmark)

    Kringelum, Louise Tina Brøns

    This thesis explores how processes of business model innovation can unfold in a port authority by transcending organizational boundaries through inter-organizational collaboration. The findings contribute to two fields of academic inquiry: the study of business model innovation and the study of how...... by applying the engaged scholarship approach, thereby providing a methodological contribution to both port and business model research. Emphasizing the interplay of intra- and inter-organizational business model innovation, the thesis adds insight into the roles of port authorities, business model trends...

  12. Grain Boundary Energies in Copper.

    Science.gov (United States)

    Omar, Ramli

    Available from UMI in association with The British Library. Requires signed TDF. The dependence of grain boundary energy on boundary orientation was studied in copper annealed at 1000 ^circC. Grain boundary orientations and the disorientations across the boundaries were measured. A rotation matrix notation is used to interpret selected area electron channelling patterns observed in a scanning electron microscope. The Herring and Shewmon torque terms were investigated using wire specimens having a "bamboo" structure. The Herring torque terms were determined using the Hess relation. The (110) section of the Sigma 11 gamma-plot (i.e. the variation of grain boundary energy with boundary orientation) was evaluated. In this plot, minima in energies were found at the (311) and (332) mirror planes. Sigma 3 and Sigma9 boundaries were investigated in sheet specimens. The (110) and (111) sections of the Sigma3 gamma -plot were evaluated. In addition to the sharp cusps occurring at the Sigma3 {111} planes, the further shallower cusps occur at the incoherent Sigma 3 boundaries with the interfacial planes approximately parallel to {322} in one crystal and {11.44} in the other crystal. Flat and curved Sigma9 boundaries were investigated. The break up of Sigma9 boundaries into two Sigma3 boundaries and the relation between the Sigma3 and Sigma 9 gamma-plots was also examined. The (110) section of the Sigma9 gamma-plot was constructed.

  13. Telemetric ambulatory arterial stiffness index, a predictor of cardio-cerebro-vascular mortality, is associated with aortic stiffness-determining factors.

    Science.gov (United States)

    Li, Zhi-Yong; Xu, Tian-Ying; Zhang, Sai-Long; Zhou, Xiao-Ming; Xu, Xue-Wen; Guan, Yun-Feng; Lo, Ming; Miao, Chao-Yu

    2013-09-01

    Ambulatory arterial stiffness index (AASI) has been proposed as a new measure of arterial stiffness for predicting cardio-cerebro-vascular morbidity and mortality. However, there has been no research on the direct relationships between AASI and arterial stiffness-determining factors. We utilized beat-to-beat intra-aortic blood pressure (BP) telemetry to characterize AASI in Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). By determination of aortic structural components and analysis of their correlations with AASI, we provided the first direct evidence for the associations between AASI and arterial stiffness-determining factors including the collagen content and collagen/elastin. Ambulatory arterial stiffness index was positively correlated with pulse pressure in both WKY and SHR, less dependent on BP and BP variability than pulse pressure, and relatively stable, especially the number of BP readings not less than ~36. The correlations between AASI and aortic components were comparable for various AASI values derived from BP readings not less than ~36. Not only AASI but also BP variability and pulse pressure demonstrated a direct relationship with arterial stiffness. These findings indicate AASI may become a routine measure in human arterial stiffness assessment. It is recommended to use a cluster of parameters such as AASI, BP variability, and pulse pressure for evaluating arterial stiffness. © 2013 John Wiley & Sons Ltd.

  14. Reweighting twisted boundary conditions

    CERN Document Server

    Bussone, Andrea; Hansen, Martin; Pica, Claudio

    2015-01-01

    Imposing twisted boundary conditions on the fermionic fields is a procedure extensively used when evaluating, for example, form factors on the lattice. Twisting is usually performed for one flavour and only in the valence, and this causes a breaking of unitarity. In this work we explore the possibility of restoring unitarity through the reweighting method. We first study some properties of the approach at tree level and then we stochastically evaluate ratios of fermionic determinants for different boundary conditions in order to include them in the gauge averages, avoiding in this way the expensive generation of new configurations for each choice of the twisting angle, $\\theta$. As expected the effect of reweighting is negligible in the case of large volumes but it is important when the volumes are small and the twisting angles are large. In particular we find a measurable effect for the plaquette and the pion correlation function in the case of $\\theta=\\pi/2$ in a volume $16\\times 8^3$, and we observe a syst...

  15. Charismatic leadership, boundary issues, and collusion.

    Science.gov (United States)

    Dorian, B J; Dunbar, C; Frayn, D; Garfinkel, P E

    2000-01-01

    The authors suggest that a charismatic leadership style has an impact on the maintenance of boundaries and standards of practice within a department of psychiatry. They also underline the need for all members of a self-regulated professional group to assume responsibility for the maintenance of standards within the group. An overview of leadership tasks and styles, with particular emphasis on the qualities of charismatic leadership, is provided, and the impacts of boundary violations committed by members of a psychiatric department or institute on the integrity of the professional group are also elaborated. The authors then develop several hypotheses regarding the phenomenon of emotional collusion that occurs in departments in which a charismatic leader becomes sexually involved with patients. The individual internal psychological mechanisms and companion group dynamics that may allow the leader to be supported at the cost of ethical standards, principles of practice, and the ultimate creativity and viability of the group are then discussed. The authors conclude that the maintenance of standards within a self-regulating professional group must be the shared responsibility of all members. The example of boundary violations by a charismatic leader is used to illustrate the need for open debate regarding fundamental principles required to maintain a healthy functioning of critical checks and balances within the psychiatric profession.

  16. Determination of the elastic and stiffness characteristics of cross-laminated timber plates from flexural wave velocity measurements

    Science.gov (United States)

    Santoni, Andrea; Schoenwald, Stefan; Van Damme, Bart; Fausti, Patrizio

    2017-07-01

    Cross-laminated timber (CLT) is an engineered wood with good structural properties and it is also economically competitive with the traditional building construction materials. However, due to its low volume density combined with its high stiffness, it does not provide sufficient sound insulation, thus it is necessary to develop specific acoustic treatments in order to increase the noise reduction performance. The material's mechanical properties are required as input data to perform the vibro-acoustic analyses necessary during the design process. In this paper the elastic constants of a CLT plate are derived by fitting the real component of the experimental flexural wave velocity with Mindlin's dispersion relation for thick plates, neglecting the influence of the plate's size and boundary conditions. Furthermore, its apparent elastic and stiffness properties are derived from the same set of experimental data, for the plate considered to be thin. Under this latter assumption the orthotropic behaviour of an equivalent thin CLT plate is described by using an elliptic model and verified with experimental results.

  17. Association of impaired endothelial glycocalyx with arterial stiffness, coronary microcirculatory dysfunction, and abnormal myocardial deformation in untreated hypertensives.

    Science.gov (United States)

    Ikonomidis, Ignatios; Voumvourakis, Astrinos; Makavos, George; Triantafyllidi, Helen; Pavlidis, George; Katogiannis, Konstantinos; Benas, Dimitris; Vlastos, Dimitris; Trivilou, Paraskevi; Varoudi, Maria; Parissis, John; Iliodromitis, Efstathios; Lekakis, John

    2018-03-02

    We investigated the association of endothelial glycocalyx damage with arterial stiffness, impairment of coronary microcirculatory function, and LV myocardial deformation in 320 untreated hypertensives and 160 controls. We measured perfused boundary region (PBR) of the sublingual microvessels, a marker inversely related with glycocalyx thickness, coronary flow reserve (CFR), and Global Longitudinal strain (GLS) by echocardiography, pulse wave velocity (PWV), and central systolic blood pressure (cSBP). Hypertensives had higher PBR, PWV cSBP, and lower CFR and GLS than controls (P < .05). In hypertensives, increased PBR was associated with increased cSBP, PWV, and decreased CFR and GLS after adjustment for age, sex, BMI, smoking LV mass, heart rate, hyperlipidemia, and office SBP (P < .05). PBR had an additive value to PWV, CFR, and office SBP for the prediction of abnormal GLS (x 2  = 2.4-3.8, P for change = .03). Endothelial glycocalyx is impaired in untreated hypertensives and is related to arterial stiffness, coronary, and myocardial dysfunction. ©2018 Wiley Periodicals, Inc.

  18. A spectral dynamic stiffness method for free vibration analysis of plane elastodynamic problems

    Science.gov (United States)

    Liu, X.; Banerjee, J. R.

    2017-03-01

    A highly efficient and accurate analytical spectral dynamic stiffness (SDS) method for modal analysis of plane elastodynamic problems based on both plane stress and plane strain assumptions is presented in this paper. First, the general solution satisfying the governing differential equation exactly is derived by applying two types of one-dimensional modified Fourier series. Then the SDS matrix for an element is formulated symbolically using the general solution. The SDS matrices are assembled directly in a similar way to that of the finite element method, demonstrating the method's capability to model complex structures. Any arbitrary boundary conditions are represented accurately in the form of the modified Fourier series. The Wittrick-Williams algorithm is then used as the solution technique where the mode count problem (J0) of a fully-clamped element is resolved. The proposed method gives highly accurate solutions with remarkable computational efficiency, covering low, medium and high frequency ranges. The method is applied to both plane stress and plane strain problems with simple as well as complex geometries. All results from the theory in this paper are accurate up to the last figures quoted to serve as benchmarks.

  19. Vibration Analysis of a Piecewise-Smooth System with Negative Stiffness under Delayed Feedback Control

    Directory of Open Access Journals (Sweden)

    Dongmei Huang

    2017-01-01

    Full Text Available The principal resonance of a delayed piecewise-smooth (DPWS system with negative stiffness under narrow-band random excitation is investigated in aspects of multiscale analysis, design methodology of the controller, and response properties. The amplitude-frequency response and steady-state moments together with the corresponding stability conditions of the controlled stochastic system are derived, in which the degradation case is also under consideration. Then, from the perspective of the equivalent damping, the comparisons of the response characteristics of the controlled system to the uncontrolled system, such as the phenomenon of frequency island, are fulfilled. Furthermore, sensitivity of the system response to feedback gain and time delay is studied and interesting dynamic properties are found. Meanwhile, the classification of the steady-state solution is also discussed. To control the maximum amplitude, the feedback parameters are determined by the frequency response together with stability boundaries which must be utilized to exclude the combinations of the unstable parameters. For the case with small noise intensity, mean-square responses present the similar characteristics to what is discussed in the deterministic case.

  20. Circulating chemerin level is independently correlated with arterial stiffness.

    Science.gov (United States)

    Yoo, Hye Jin; Choi, Hae Yoon; Yang, Sae Jeong; Kim, Hee Young; Seo, Ji A; Kim, Sin Gon; Kim, Nan Hee; Choi, Kyung Mook; Choi, Dong Seop; Baik, Sei Hyun

    2012-01-01

    Adipokines have been implicated in the pathogenesis of obesity and obesity-related disorders, including atherosclerosis. Chemerin is a recently discovered adipokine which is closely correlated with various metabolic phenotypes in humans. We examined the association between circulating chemerin levels and arterial stiffness, as represented by the brachial ankle pulse wave velocity (baPWV). Fifty-eight obese and 62 non-obese individuals participated in the study. We measured the serum chemerin and high sensitivity C-reactive protein (hsCRP) levels, and the homeostasis model assessment of insulin resistance (HOMA-IR), as well as other cardiovascular risk factors. Vascular health was assessed by the baPWV and carotid intima-media thickness (IMT). The serum chemerin level was significantly increased in obese individuals compared with lean controls (120.14±19.43 ng/mL vs. 106.81±23.39 ng/mL, p = 0.001). The circulating chemerin level had a significant positive correlation with the body mass index, waist circumference, HOMA-IR, and low-density lipoprotein-cholesterol, triglycerides, and hsCRP levels. The serum chemerin level was significantly associated with the baPWV (r= 0.280, p= 0.002), but not the carotid IMT (r= 0.065, p= 0.504). Multiple stepwise regression analysis showed that age (p chemerin levels (p= 0.017) were definitive risk factors for arterial stiffness (r(2)=0.457). The circulating chemerin level was an independent risk factor for arterial stiffness even after adjusting for other cardiovascular risk factors.

  1. Wave reflections, arterial stiffness, heart rate variability and orthostatic hypotension.

    Science.gov (United States)

    Lu, Dai-Yin; Sung, Shih-Hsien; Yu, Wen-Chung; Cheng, Hao-Min; Chuang, Shao-Yuan; Chen, Chen-Huan

    2014-12-01

    Increased arterial stiffness and wave reflections are independently associated with orthostatic hypotension (OH). This study investigated whether heart rate variability (HRV) is also involved in the modulation of orthostatic blood pressure (BP) change. A total of 429 subjects (65.1 ± 16.4 years, 77.4% men) were enrolled in this study. OH was defined as a ⩾ 20 mm Hg decrease in brachial systolic blood pressure (SBP) or a ⩾ 10 mm Hg diastolic blood pressure (DBP) decrease upon standing. Measurements of carotid-femoral pulse wave velocity (cf-PWV) and the amplitude of the reflected pressure wave from a decomposed carotid pressure wave (Pb) were obtained by carotid tonometry in the supine position. The power spectrum from a 5-min recording of an electrocardiogram at rest was analyzed to provide components in the high frequency (HF) and low frequency (LF) ranges. Subjects with OH (n = 59, 13.8%) had significantly higher cf-PWV and Pb and significantly lower LogHF and LogLF than those without OH (n = 370). The cf-PWV, Pb, LogHF and LogLF were significantly associated with postural SBP and DBP changes. Furthermore, cf-PWV but not Pb was significantly associated with LogHF and LogLF. Multivariate analysis showed that Pb (odds ratio (OR) per 1 s.d. 1.65, 95% confidence interval (CI) 1.282-2.137; P = 0.003) and LogHF (OR 0.628, 95% CI 0.459-0.860, P = 0.004), but not cf-PWV (OR 1.279, 95% CI 0.932-1.755, P = 0.128), were significant independent determinants of OH. Increased wave reflections may predispose OH independently of arterial stiffness and HRV. In contrast, increased arterial stiffness may cause OH through the modulation of HRV.

  2. 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.

  3. 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

  4. Decreased serum bilirubin is associated with arterial stiffness in men.

    Science.gov (United States)

    Li, Y; Meng, S-y; Meng, C-c; Yu, W-g; Wang, R-t

    2013-04-01

    The brachial-ankle pulse wave velocity (baPWV) is a marker for early atherosclerotic changes. Serum total bilirubin (TB) is an effective antioxidant and has been associated with carotid intima-media thickness, cardiovascular disease, stroke and peripheral arterial disease, all of which may be caused by arteriosclerosis. This study aimed to investigate the association of TB with arterial stiffness. In this cross-sectional study, we investigated the relationship between TB and baPWV in 2207 participants (1331 men, 876 women) in a general health examination. Different metabolic parameters were compared across TB quartiles. Age-adjusted mean values of baPWV gradually decreased with TB quartiles in men (Q1 = 1348, Q2 = 1266, Q3 = 1215, and Q4 = 1154 cm/s). However, the age-adjusted means of baPWV had no significance in women according to TB quartiles. Univariate analysis showed that age, smoking status, BMI, SBP, DBP, AST, ALT, GGT, TB, TG, and HDL-C were significantly associated with baPWV in men, whereas only age, BMI, SBP, DBP, TG and FPG were significantly associated with baPWV in women. In addition, BMI, SBP, TB, age, TG, and AST were significant factors in the multivariate model with baPWV in men; only BMI and FPG were significant factors with baPWV in women. The findings show that serum total bilirubin concentration is negatively correlated to arterial stiffness in Chinese men. Early detection of abnormal bilirubin levels could potentially serve as an early biomarker for arterial stiffness. Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.

  5. Increased mean platelet volume is associated with arterial stiffness.

    Science.gov (United States)

    Wang, Rui-Tao; Li, Ying; Zhu, Xiu-Ying; Zhang, Yi-Na

    2011-01-01

    The brachial-ankle pulse wave velocity (baPWV) is a useful index of arterial stiffness. Mean platelet volume (MPV), an indicator of platelet activation, is associated with hypertension, stroke, and coronary artery disease, all of which may be caused by arteriosclerosis. However, little research has been conducted to investigate the relationship between MPV and arterial stiffness. In this cross-sectional study, we investigated the relationship between platelet count, MPV, and baPWV in 2645 apparently healthy Chinese participants (1676 men, 969 women) in a general health examination. Different metabolic parameters were compared across MPV quintiles (Q1: ≤8.1 fl, Q2: 8.2-8.5 fl, Q3: 8.6-9.6 fl, Q4: 9.7-10.7 fl, and Q5: ≥10.8 fl). Age-adjusted mean values of baPWV gradually increased with MPV quintiles (Q1 = 1124, Q2 = 1134, Q3 = 1199, Q4 = 1207, and Q5 = 1270 cm/s). Univariate analysis showed that age, sex, smoking status, body mass index (BMI), systolic blood pressure (SBP), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), fasting plasma glucose (FPG), total platelet count, and MPV were significantly associated with baPWV. In addition, age, sex, BMI, MPV, SBP, and FPG were significant factors in the multivariate model with baPWV. Notably, MPV was found to be a significant determinant for baPWV (β = 0.198; P < 0.001). The findings show that elevated MPV is positively correlated to arterial stiffness.

  6. Kinematic Characterization of Left Ventricular Chamber Stiffness and Relaxation

    Science.gov (United States)

    Mossahebi, Sina

    Heart failure is the most common cause of hospitalization today, and diastolic heart failure accounts for 40-50% of cases. Therefore, it is critical to identify diastolic dysfunction at a subclinical stage so that appropriate therapy can be administered before ventricular function is further, and perhaps irreversibly impaired. Basic concepts in physics such as kinematic modeling provide a unique method with which to characterize cardiovascular physiology, specifically diastolic function (DF). The advantage of an approach that is standard in physics, such as the kinematic modeling is its causal formulation that functions in contrast to correlative approaches traditionally utilized in the life sciences. Our research group has pioneered theoretical and experimental quantitative analysis of DF in humans, using both non-invasive (echocardiography, cardiac MRI) and invasive (simultaneous catheterization-echocardiography) methods. Our group developed and validated the Parametrized Diastolic Filling (PDF) formalism which is motivated by basic physiologic principles (LV is a mechanical suction pump at the mitral valve opening) that obey Newton's Laws. PDF formalism is a kinematic model of filling employing an equation of motion, the solution of which accurately predicts all E-wave contours in accordance with the rules of damped harmonic oscillatory motion. The equation's lumped parameters---ventricular stiffness, ventricular viscoelasticity/relaxation and ventricular load---are obtained by solving the 'inverse problem'. The parameters' physiologic significance and clinical utility have been repeatedly demonstrated in multiple clinical settings. In this work we apply our kinematic modeling approach to better understand how the heart works as it fills in order to advance the relationship between physiology and mathematical modeling. Through the use of this modeling, we thereby define and validate novel, causal indexes of diastolic function such as early rapid filling energy

  7. Task dependency of grip stiffness--a study of human grip force and grip stiffness dependency during two different tasks with same grip forces.

    Directory of Open Access Journals (Sweden)

    Hannes Höppner

    Full Text Available It is widely known that the pinch-grip forces of the human hand are linearly related to the weight of the grasped object. Less is known about the relationship between grip force and grip stiffness. We set out to determine variations to these dependencies in different tasks with and without visual feedback. In two different settings, subjects were asked to (a grasp and hold a stiffness-measuring manipulandum with a predefined grip force, differing from experiment to experiment, or (b grasp and hold this manipulandum of which we varied the weight between trials in a more natural task. Both situations led to grip forces in comparable ranges. As the measured grip stiffness is the result of muscle and tendon properties, and since muscle/tendon stiffness increases more-or-less linearly as a function of muscle force, we found, as might be predicted, a linear relationship between grip force and grip stiffness. However, the measured stiffness ranges and the increase of stiffness with grip force varied significantly between the two tasks. Furthermore, we found a strong correlation between regression slope and mean stiffness for the force task which we ascribe to a force stiffness curve going through the origin. Based on a biomechanical model, we attributed the difference between both tasks to changes in wrist configuration, rather than to changes in cocontraction. In a new set of experiments where we prevent the wrist from moving by fixing it and resting it on a pedestal, we found subjects exhibiting similar stiffness/force characteristics in both tasks.

  8. Encapsulation of chondrocytes in high-stiffness agarose microenvironments for in vitro modeling of osteoarthritis mechanotransduction.

    Science.gov (United States)

    Jutila, Aaron A; Zignego, Donald L; Schell, William J; June, Ronald K

    2015-05-01

    In articular cartilage, chondrocytes reside within a gel-like pericellular matrix (PCM). This matrix provides a mechanical link through which joint loads are transmitted to chondrocytes. The stiffness of the PCM decreases in the most common degenerative joint disease, osteoarthritis. To develop a system for modeling the stiffness of both the healthy and osteoarthritic PCM, we determined the concentration-stiffness relationships for agarose. We extended these results to encapsulate chondrocytes in agarose of physiological stiffness. Finally, we assessed the relevance of stiffness for chondrocyte mechanotransduction by examining the biological response to mechanical loading for cells encapsulated in low- and high-stiffness gels. We achieved agarose equilibrium stiffness values as large as 51.3 kPa. At 4.0% agarose, we found equilibrium moduli of 34.3 ± 1.65 kPa, and at 4.5% agarose, we found equilibrium moduli of 35.7 ± 0.95 kPa. Cyclical tests found complex moduli of ~100-300 kPa. Viability was >96% for all studies. We observed distinct metabolomic responses in >500 functional small molecules describing changes in cell physiology, between primary human chondrocytes encapsulated in 2.0 and 4.5% agarose indicating that the gel stiffness affects cellular mechanotransduction. These data demonstrate both the feasibility of modeling the chondrocyte pericellular matrix stiffness and the importance of the physiological pericellular stiffness for understanding chondrocyte mechanotransduction.

  9. MEMS measurements of single cell stiffness decay due to cyclic mechanical loading.

    Science.gov (United States)

    Barazani, Bruno; Warnat, Stephan; MacIntosh, Andrew J; Hubbard, Ted

    2017-08-25

    The goal of this study was to measure the mechanical stiffness of individual cells and to observe changes due to the application of repeated cell mechanical loads. 28 single baker's yeast cells (Saccharomyces cerevisiae) were fatigue tested and had their stiffness measured during repetitive loading cycles performed by a MEMS squeezer in aqueous media. Electrothermal micro-actuators compressed individual cells against a reference back spring; cell and spring motions were measured using a FFT image analysis technique with ~10 nm resolution. Cell stiffness was calculated based on measurements of cell elongation vs. applied force which resulted in stiffness values in the 2-10 N/m range. The effect of increased force was studied for cells mechanically cycled 37 times. Cell stiffness decreased as the force and the cycle number increased. After 37 loading cycles (~4 min), forces of 0.24, 0.29, 0.31, and 0.33 μN caused stiffness drops of 5%, 13%, 31% and 41% respectively. Cells force was then set to 0.29 μN and cells were tested over longer runs of 118 and 268 cycles. After 118 cycles (~12 min) cells experienced an average stiffness drop of 68%. After 268 cycles (~25 min) cells had a stiffness drop of 77%, and appeared to reach a stiffness plateau of 20-25% of the initial stiffness after approximately 200 cycles.

  10. A finite element formulation preserving symmetric and banded diffusion stiffness matrix characteristics for fractional differential equations

    Science.gov (United States)

    Lin, Zeng; Wang, Dongdong

    2017-10-01

    Due to the nonlocal property of the fractional derivative, the finite element analysis of fractional diffusion equation often leads to a dense and non-symmetric stiffness matrix, in contrast to the conventional finite element formulation with a particularly desirable symmetric and banded stiffness matrix structure for the typical diffusion equation. This work first proposes a finite element formulation that preserves the symmetry and banded stiffness matrix characteristics for the fractional diffusion equation. The key point of the proposed formulation is the symmetric weak form construction through introducing a fractional weight function. It turns out that the stiffness part of the present formulation is identical to its counterpart of the finite element method for the conventional diffusion equation and thus the stiffness matrix formulation becomes trivial. Meanwhile, the fractional derivative effect in the discrete formulation is completely transferred to the force vector, which is obviously much easier and efficient to compute than the dense fractional derivative stiffness matrix. Subsequently, it is further shown that for the general fractional advection-diffusion-reaction equation, the symmetric and banded structure can also be maintained for the diffusion stiffness matrix, although the total stiffness matrix is not symmetric in this case. More importantly, it is demonstrated that under certain conditions this symmetric diffusion stiffness matrix formulation is capable of producing very favorable numerical solutions in comparison with the conventional non-symmetric diffusion stiffness matrix finite element formulation. The effectiveness of the proposed methodology is illustrated through a series of numerical examples.

  11. 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....

  12. Analytical stiffness matrices with Green-Lagrange strain measure

    DEFF Research Database (Denmark)

    Pedersen, Pauli

    2005-01-01

    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......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...

  13. Static Stiffness Modeling of Parallel Kinematics Machine Tool Joints

    Directory of Open Access Journals (Sweden)

    O. K. Akmaev

    2015-09-01

    Full Text Available The possible variants of an original parallel kinematics machine-tool structure are explored in this article. A new Hooke's universal joint design based on needle roller bearings with the ability of a preload setting is proposed. The bearing stiffness modeling is carried out using a variety of methods. The elastic deformation modeling of a Hook’s joint and a spherical rolling joint have been developed to assess the possibility of using these joints in machine tools with parallel kinematics.

  14. Design of the uniaxial shaker with variable stiffness

    Directory of Open Access Journals (Sweden)

    Chlebo Ondrej

    2017-01-01

    Full Text Available During the vibration testing, various types of vibration drivers of different structures are used. Electrodynamic drivers are generally used for smaller excitation forces whereas for bigger excitation forces hydraulic drivers are used. The main disadvantage of drivers can be found in their size. One of the possibilities for size reduction may be a suitable engineering design. The paper deals with the design of a small uniaxial driver which uses an inertial driver as a source of the excitation force. The structure considers the requirements for stiffness changes of the whole system with the aim of available frequency range tuning.

  15. Teaching Neuroimages: a pediatric patient with headache and neck stiffness.

    Science.gov (United States)

    Moeck, Adam R; Pergami, Paola

    2013-09-24

    A 14-year-old right-handed boy presented with sudden onset of severe headache and neck stiffness. Physical examination showed arm asymmetry with smaller size and muscle bulk (present since childhood) and increased deep tendon reflexes on the right, but normal strength. Brain CT and lumbar puncture ruled out subarachnoid hemorrhage or infection. MRI and angiography (figure) identified an unruptured type III spinal arteriovenous malformation at the C3-C4 level, supplied by the right vertebral artery.(1) Subtle physical examination findings can indicate underlying pathology and should not be overlooked in the proper context. Vascular studies should be considered for severe headache with negative initial workup.(2.)

  16. Dynamic Stiffness Matrix for a Beam Element with Shear Deformation

    Directory of Open Access Journals (Sweden)

    Walter D. Pilkey

    1995-01-01

    Full Text Available A method for calculating the dynamic transfer and stiffness matrices for a straight Timoshenko shear beam is presented. The method is applicable to beams with arbitrarily shaped cross sections and places no restrictions on the orientation of the element coordinate system axes in the plane of the cross section. These new matrices are needed because, for a Timoshenko beam with an arbitrarily shaped cross section, deflections due to shear in the two perpendicular planes are coupled even when the coordinate axes are chosen to be parallel to the principal axes of inertia.

  17. 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.

  18. Dynamic stiffness and damping of foundations for jacket structures

    DEFF Research Database (Denmark)

    Latini, Chiara; Zania, Varvara; Johannesson, Björn

    2015-01-01

    resistance as defined by Nogami & Novak (1977) is determined, considering 3D wave propagation within linear soil layer with hysteretic damping. Thereafter, the dynamic response of the pile is estimated assuming soil pressure equal to the soil resistance and imposing displacement compatibility. A parametric...... study clarifies the role of the parameters involved i.e. the depth of the soil layer, the pile diameter and the soil layer shear wave velocity. Results are presented in terms of dimensionless graphs which highlight the frequency dependency of the dynamic stiffness and damping....

  19. Gravitational particle creation in a stiff matter dominated universe

    Science.gov (United States)

    Lankinen, Juho; Vilja, Iiro

    2017-08-01

    A scenario for gravitational particle creation in a stiff matter dominated flat Friedmann-Robertson-Walker universe is presented. The primary creation of scalar particles is calculated using quantum field theory in curved spacetime and it is found to be strongly dependent on the scalar mass and the expansion parameter of the universe. The particle creation is most effective for a very massive scalar field and large expansion parameter. We demonstrate the phenomenon by applying it to cosmological toy model scenario, where secondary particles are created by the scalar field decay.

  20. Stiffness of serial and quasi-serial manipulators: comparison analysis

    Directory of Open Access Journals (Sweden)

    Klimchik Alexandr

    2016-01-01

    Full Text Available The paper deals with comparison analysis of serial and quasi-serial manipulators. It shows a difference between stiffness behaviours of corresponding industrial robots under external loading, which is caused by machining process. The analysis is based on the estimation of compliance errors induced by cutting forces that are applied to the manipulator end-effector. We demonstrate that the quasi-seral manipulators are preferable for large-dimensional tasks while the quasi-serial ones better suit small size tasks.

  1. The Future of Boundary Plasma and Material Science

    Science.gov (United States)

    Whyte, Dennis

    2012-03-01

    The boundary of magnetic confinement devices, from the pedestal through to the surrounding surfaces, encompasses an enormous range of plasma and material physics, and their integrated coupling. It is becoming clear that due to fundamental limits of plasma stability and material response the boundary will largely define the viability of an MFE reactor. However we face an enormous knowledge deficit in stepping from present devices and ITER towards a demonstration power plant. We outline the future of boundary research required to address this deficit. The boundary should be considered a multi-scale system of coupled plasma and material science regulated through the non-linear interface of the sheath. Measurement, theory and modeling across these scales are assessed. Dimensionless parameters, often used to organized core plasma transport on similarity arguments, can be extended to the boundary plasma, plasma-surface interactions and material response. This methodology suggests an intriguing way forward to prescribe and understand the boundary issues of an eventual reactor in intermediate devices. A particularly critical issue is that the physical chemistry of the material, which is mostly determined by the material temperature, has been too neglected; pointing to the requirement for boundary plasma experiments at appropriate material temperatures. Finally the boundary plasma requirements for quiescent heat exhaust and control of transient events, such as ELMs, will be examined.

  2. Boundary Management Preferences, Boundary Control, and Work-Life Balance among Full-Time Employed Professionals in Knowledge-Intensive, Flexible Work

    Directory of Open Access Journals (Sweden)

    Christin Mellner

    2015-01-01

    Full Text Available Profound changes are taking place within working life, where established boundaries between work and personal life are challenged by increased global competition, ever-faster changing markets, and rapid development of boundary transcending information and communication technologies (ICT. The aim of this study was to investigate boundary management preferences in terms of keeping work and personal life domains separated or integrated, that is, segmenting or blending of domains, the perception of being in control of one´s preferred boundaries, and work-life balance among employees at a Swedish telecom company (N = 1,238, response rate 65%, men 73%, mean age 42 years. Psychosocial work factors, individual characteristics, sociodemographic factors, and work-life balance were investigated in relation to boundary management preferences and perceived boundary control. For high boundary control among segmenters, nearly all the studied psychosocial work factors were significant. Among integrators, this was the case only for clear expectations in work. For both groups, the individual capacity for self-regulation was associated with high boundary control. Regarding sociodemographic factors, cohabiting women with children who preferred segmentation had low boundary control. Finally, there was a main effect of boundary control on work-life balance. In particular, male segmenters perceiving high boundary control had better work-life balance than all others. Conclusions of the study are that segmenters need external boundaries in work for succesful boundary management. Moreover, self-regulation seems a crucial boundary competence in knowledge- intensive, flexible work. Results are of value for health promotion in modern work organizations in supporting employees achieving successful boundary control and subsequent work-life balance.

  3. Structure and properties of grain boundaries

    Science.gov (United States)

    Balluffi, R. W.; Bristowe, P. D.

    1984-03-01

    Results were obtained in the following areas: determination of relative grain boundary energies by the rotating crystallite method; simple structural unit model for core dependent properties of tilt boundaries; twist boundary energies for metals with long ranged pairwise interatomic potentials; structural unit/grain boundary dislocation model for grain boundary structure; detection of expansion of boundaries using diffraction; effect of secondary relaxations on diffraction from high-(SIGMA) 001 twist boundaries; and mechanism of grain boundary migration.

  4. Negotiating Cluster Boundaries

    DEFF Research Database (Denmark)

    Giacomin, Valeria

    2017-01-01

    Palm oil was introduced to Malay(si)a as an alternative to natural rubber, inheriting its cluster organizational structure. In the late 1960s, Malaysia became the world’s largest palm oil exporter. Based on archival material from British colonial institutions and agency houses, this paper focuses...... on the governance dynamics that drove institutional change within this cluster during decolonization. The analysis presents three main findings: (i) cluster boundaries are defined by continuous tug-of-war style negotiations between public and private actors; (ii) this interaction produces institutional change...... within the cluster, in the form of cumulative ‘institutional rounds’ – the correction or disruption of existing institutions or the creation of new ones; and (iii) this process leads to a broader inclusion of local actors in the original cluster configuration. The paper challenges the prevalent argument...

  5. Repeated judgment sampling: Boundaries

    Directory of Open Access Journals (Sweden)

    Johannes Muller-Trede

    2011-06-01

    Full Text Available This paper investigates the boundaries of the recent result that eliciting more than one estimate from the same person and averaging these can lead to accuracy gains in judgment tasks. It first examines its generality, analysing whether the kind of question being asked has an effect on the size of potential gains. Experimental results show that the question type matters. Previous results reporting potential accuracy gains are reproduced for year-estimation questions, and extended to questions about percentage shares. On the other hand, no gains are found for general numerical questions. The second part of the paper tests repeated judgment sampling's practical applicability by asking judges to provide a third and final answer on the basis of their first two estimates. In an experiment, the majority of judges do not consistently average their first two answers. As a result, they do not realise the potential accuracy gains from averaging.

  6. Superfluid Boundary Layer.

    Science.gov (United States)

    Stagg, G W; Parker, N G; Barenghi, C F

    2017-03-31

    We model the superfluid flow of liquid helium over the rough surface of a wire (used to experimentally generate turbulence) profiled by atomic force microscopy. Numerical simulations of the Gross-Pitaevskii equation reveal that the sharpest features in the surface induce vortex nucleation both intrinsically (due to the raised local fluid velocity) and extrinsically (providing pinning sites to vortex lines aligned with the flow). Vortex interactions and reconnections contribute to form a dense turbulent layer of vortices with a nonclassical average velocity profile which continually sheds small vortex rings into the bulk. We characterize this layer for various imposed flows. As boundary layers conventionally arise from viscous forces, this result opens up new insight into the nature of superflows.

  7. Public Computation & Boundary Play

    CERN Document Server

    Sengupta, Pratim

    2016-01-01

    In this paper, we introduce 'public computation' as a genre of learning environments that can be used to radically broaden public participation in authentic, computation-enabled STEM disciplinary practices. Our paradigmatic approach utilizes open source software designed for professional scientists, engineers and digital artists, and situates them in an undiluted form, alongside live and archived expert support, in a public space. We present a case study of DigiPlay, a prototypical public computation space we designed at the University of Calgary, where users can interact directly with scientific simulations as well as the underlying open source code using an array of massive multi- touch screens. We argue that in such a space, public interactions with the code can be thought of as boundary work and play, through which public participation becomes legitimate scientific act, as the public engages in scientific creation through truly open-ended explorations with the code.

  8. Challenging the Boundaries

    DEFF Research Database (Denmark)

    Nørgaard, Nina

    2004-01-01

    to explore in the study and teaching of foreign languages. Not only may linguistics and literature be employed to shed light on each other, the insights gained may furthermore prove useful in a broader context in our foreign language studies. The article begins with a brief introduction to literary...... linguistics in general and to Hallidayan linguistics in particular. The theoretical framework thus laid out, it is exemplified how Halliday's theory of language may be employed in the analysis of literature. The article concludes by considering the possible status of literary linguistics in a broader......To many people, challenging the boundaries between the traditional disciplines in foreign language studies means doing cultural studies. The aim of this article is to pull in a different direction by suggesting how the interface between linguistics and literature may be another fertile field...

  9. The Plasmasphere Boundary Layer

    Directory of Open Access Journals (Sweden)

    D. L. Carpenter

    2004-12-01

    Full Text Available As an inner magnetospheric phenomenon the plasmapause region is of interest for a number of reasons, one being the occurrence there of geophysically important interactions between the plasmas of the hot plasma sheet and of the cool plasmasphere. There is a need for a conceptual framework within which to examine and discuss these interactions and their consequences, and we therefore suggest that the plasmapause region be called the Plasmasphere Boundary Layer, or PBL. Such a term has been slow to emerge because of the complexity and variability of the plasma populations that can exist near the plasmapause and because of the variety of criteria used to identify the plasmapause in experimental data. Furthermore, and quite importantly in our view, a substantial obstacle to the consideration of the plasmapause region as a boundary layer has been the longstanding tendency of textbooks on space physics to limit introductory material on the plasmapause phenomenon to zeroth order descriptions in terms of ideal MHD theory, thus implying that the plasmasphere is relatively well understood. A textbook may introduce the concept of shielding of the inner magnetosphere from perturbing convection electric fields, but attention is not usually paid to the variety of physical processes reported to occur in the PBL, such as heating, instabilities, and fast longitudinal flows, processes which must play roles in plasmasphere dynamics in concert with the flow regimes associated with the major dynamo sources of electric fields. We believe that through the use of the PBL concept in future textbook discussions of the plasmasphere and in scientific communications, much progress can be made on longstanding questions about the physics involved in the formation of the plasmapause and in the cycles of erosion and recovery of the plasmasphere. Key words. Magnetospheric physics (plasmasphere; plasma convection; MHD waves and instabilities

  10. The Plasmasphere Boundary Layer

    Directory of Open Access Journals (Sweden)

    D. L. Carpenter

    2004-12-01

    Full Text Available As an inner magnetospheric phenomenon the plasmapause region is of interest for a number of reasons, one being the occurrence there of geophysically important interactions between the plasmas of the hot plasma sheet and of the cool plasmasphere. There is a need for a conceptual framework within which to examine and discuss these interactions and their consequences, and we therefore suggest that the plasmapause region be called the Plasmasphere Boundary Layer, or PBL. Such a term has been slow to emerge because of the complexity and variability of the plasma populations that can exist near the plasmapause and because of the variety of criteria used to identify the plasmapause in experimental data. Furthermore, and quite importantly in our view, a substantial obstacle to the consideration of the plasmapause region as a boundary layer has been the longstanding tendency of textbooks on space physics to limit introductory material on the plasmapause phenomenon to zeroth order descriptions in terms of ideal MHD theory, thus implying that the plasmasphere is relatively well understood. A textbook may introduce the concept of shielding of the inner magnetosphere from perturbing convection electric fields, but attention is not usually paid to the variety of physical processes reported to occur in the PBL, such as heating, instabilities, and fast longitudinal flows, processes which must play roles in plasmasphere dynamics in concert with the flow regimes associated with the major dynamo sources of electric fields. We believe that through the use of the PBL concept in future textbook discussions of the plasmasphere and in scientific communications, much progress can be made on longstanding questions about the physics involved in the formation of the plasmapause and in the cycles of erosion and recovery of the plasmasphere.

    Key words. Magnetospheric physics (plasmasphere; plasma convection; MHD waves and instabilities

  11. Grain boundary melting in ice

    OpenAIRE

    Thomson, E. S.; Hansen-Goos, Hendrik; Wilen, L. A.; Wettlaufer, J. S.

    2012-01-01

    We describe an optical scattering study of grain boundary premelting in water ice. Ubiquitous long ranged attractive polarization forces act to suppress grain boundary melting whereas repulsive forces originating in screened Coulomb interactions and classical colligative effects enhance it. The liquid enhancing effects can be manipulated by adding dopant ions to the system. For all measured grain boundaries this leads to increasing premelted film thickness with increasing electrolyte concentr...

  12. Conformal boundaries of warped products

    DEFF Research Database (Denmark)

    Kokkendorff, Simon Lyngby

    2006-01-01

    In this note we prove a result on how to determine the conformal boundary of a type of warped product of two length spaces in terms of the individual conformal boundaries. In the situation, that we treat, the warping and conformal distortion functions are functions of distance to a base point....... The result is applied to produce examples of CAT(0)-spaces, where the conformal and ideal boundaries differ in interesting ways....

  13. COL4A1 Is Associated With Arterial Stiffness By Genome Wide Association Scan

    Science.gov (United States)

    Tarasov, Kirill V; Sanna, Serena; Scuteri, Angelo; Strait, James B; Orrù, Marco; Parsa, Afshin; Lin, Ping-I; Maschio, Andrea; Lai, Sandra; Piras, Maria Grazia; Masala, Marco; Tanaka, Toshiko; Post, Wendy; O’Connell, Jeffrey R.; Schlessinger, David; Cao, Antonio; Nagaraja, Ramaiah; Mitchell, Braxton D.; Abecasis, Gonçalo R.; Shuldiner, Alan R.; Uda, Manuela; Lakatta, Edward G.; Najjar, Samer S.

    2009-01-01

    Background Pulse wave velocity (PWV), a non-invasive index of central arterial stiffness, is a potent predictor of cardiovascular mortality and morbidity. Heritability and linkage studies have pointed toward a genetic component affecting PWV. We conducted a genome-wide association study to identify single nucleotide polymorphisms (SNPs) associated with PWV. Methods and Results The study cohort included participants from the SardiNIA study for whom PWV measures were available. Genotyping was performed in 4,221 individuals, using either the Affymetrix 500K or the Affymetrix 10K mapping array sets (with imputation of the missing genotypes). Associations with PWV were evaluated using an additive genetic model that included age, age2 and sex as covariates. The findings were tested for replication in an independent internal Sardinian cohort of 1,828 individuals, using a custom-chip designed to include the top 43 non-redundant SNPs associated with PWV. Of the loci that were tested for association with PWV, the nonsynonymous SNP rs3742207 in the COL4A1 gene on chromosome 13 and SNP rs1495448 in the MAGI1 gene on chromosome 3 were successfully replicated (p=7.08×10−7 and p=1.06×10−5 respectively for the combined analyses). The association between rs3742207 and PWV was also successfully replicated (p=0.02) in an independent population, the Old Order Amish, leading to an overall p=5.16×10−8. Conclusions A genome-wide association study identified a SNP in the COL4A1 gene that was significantly associated with PWV in two populations. Collagen type 4 is the major structural component of basement membranes, suggesting that previously unrecognized cell-matrix interactions may exert an important role in regulating arterial stiffness. PMID:20031579

  14. 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.

  15. The Boundary Function Method. Fundamentals

    Science.gov (United States)

    Kot, V. A.

    2017-03-01

    The boundary function method is proposed for solving applied problems of mathematical physics in the region defined by a partial differential equation of the general form involving constant or variable coefficients with a Dirichlet, Neumann, or Robin boundary condition. In this method, the desired function is defined by a power polynomial, and a boundary function represented in the form of the desired function or its derivative at one of the boundary points is introduced. Different sequences of boundary equations have been set up with the use of differential operators. Systems of linear algebraic equations constructed on the basis of these sequences allow one to determine the coefficients of a power polynomial. Constitutive equations have been derived for initial boundary-value problems of all the main types. With these equations, an initial boundary-value problem is transformed into the Cauchy problem for the boundary function. The determination of the boundary function by its derivative with respect to the time coordinate completes the solution of the problem.

  16. Analysis of turbulent boundary layers

    CERN Document Server

    Cebeci, Tuncer

    1974-01-01

    Analysis of Turbulent Boundary Layers focuses on turbulent flows meeting the requirements for the boundary-layer or thin-shear-layer approximations. Its approach is devising relatively fundamental, and often subtle, empirical engineering correlations, which are then introduced into various forms of describing equations for final solution. After introducing the topic on turbulence, the book examines the conservation equations for compressible turbulent flows, boundary-layer equations, and general behavior of turbulent boundary layers. The latter chapters describe the CS method for calculati

  17. A New Hybrid Gyroscope with Electrostatic Negative Stiffness Tuning

    Directory of Open Access Journals (Sweden)

    Xian Chu

    2013-05-01

    Full Text Available A variety of gyroscopes have been extensively studied due to their capability of precision detection of rotation rates and extensive applications in navigation, guidance and motion control. In this work, a new Hybrid Gyroscope (HG which combines the traditional Dynamically Tuned Gyroscope (DTG with silicon micromachined technology is investigated. The HG not only has the potentiality of achieving the same high precision as the traditional DTG, but also features a small size and low cost. The theoretical mechanism of the HG with a capacitance transducer and an electrostatic torquer is derived and the influence of the installation errors from the capacitance plate and the disc rotor module is investigated. A new tuning mechanism based on negative stiffness rather than the traditional dynamic tuning is proposed. The experimental results prove that the negative stiffness tuning is practicable and a tuning voltage of as high as 63 V is demonstrated. Due to the decreased installation error, the non-linearity of the scale factor is reduced significantly from 11.78% to 0.64%, as well as the asymmetry from 93.3% to 1.56% in the open loop condition. The rebalancing close-loop control is simulated and achieved experimentally, which proves that the fundamental principle of the HG is feasible.

  18. 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

  19. IRKC: An IMEX solver for stiff diffusion-reaction PDEs

    Science.gov (United States)

    Shampine, L. F.; Sommeijer, B. P.; Verwer, J. G.

    2006-11-01

    The Fortran 90 code IRKC is intended for the time integration of systems of partial differential equations (PDEs) of diffusion-reaction type for which the reaction Jacobian has real (negative) eigenvalues. It is based on a family of implicit-explicit Runge-Kutta-Chebyshev methods which are unconditionally stable for reaction terms and which impose a stability constraint associated with the diffusion terms that is quadratic in the number of stages. Special properties of the family make it possible for the code to select at each step the most efficient stable method as well as the most efficient step size. Moreover, they make it possible to apply the methods using just a few vectors of storage. A further step towards minimal storage requirements and optimal efficiency is achieved by exploiting the fact that the implicit terms, originating from the stiff reactions, are not coupled over the spatial grid points. Hence, the systems to be solved have a small dimension (viz., equal to the number of PDEs). These characteristics of the code make it especially attractive for problems in several spatial variables. IRKC is a successor to the RKC code [B.P. Sommeijer, L.F. Shampine, J.G. Verwer, RKC: an explicit solver for parabolic PDEs, J. Comput. Appl. Math. 88 (1997) 315-326] that solves similar problems without stiff reaction terms.

  20. Stiff-person syndrome: autoimmunity and the central nervous system.

    Science.gov (United States)

    Murinson, B B; Vincent, A

    2001-05-01

    Stiff-person syndrome (SPS) is a rare disease of severe progressive muscle stiffness in the spine and lower extremities with superimposed muscle spasms triggered by external stimuli. Patients with SPS are often referred for psychiatric evaluation and the psychiatrist may be the first to diagnosis SPS. Psychosocial stressors often precede the first manifestations of the disease; depression, anxiety, and alcohol abuse are comorbid illnesses. The identification of an association with antibodies to glutamic acid decarboxylase (GAD) was invaluable for definitively establishing a pathological basis for the disease; antibodies to amphiphysin and gephyrin are also found in cases of SPS but at much lower frequencies. Whether the antibodies inhibit GAD activity in vivo, target GAD-expressing neurons for immune-mediated destruction, are part of a wider immune process, or are merely a marker for destruction of GAD-expressing neurons by an independent neurodegenerative process is not yet clear. Both electromyography and the detection of GAD antibodies are useful in establishing a diagnosis of SPS. Treatment of SPS includes the use of immunomodulating therapies (plasmapheresis and intravenous immunoglobulins) and symptomatic treatment with benzodiazepines and baclofen. The use of tricyclic antidepressants and rapid withdrawal from therapy should be avoided.

  1. The effect of toothbrush bristle stiffness on nanohybrid surface roughness

    Science.gov (United States)

    Zairani, O.; Irawan, B.; Damiyanti, M.

    2017-08-01

    The surface of a restoration can be affected by toothpaste containing abrasive agents and the stiffness of toothbrush bristles. Objective: To identify the effect of toothbrush bristle stiffness on nanohybrid surface roughness. Methods: Sixteen nanohybrid specimens were separated into two groups. The first group was brushed using soft-bristle toothbrushes, and the second group was brushed using medium-bristle toothbrushes. Media such as aqua bides was used for brushing in both groups. Brushing was done 3 times for 5 minutes. Surface roughness was measured initially and at 5, 10, and 15 minutes using a surface roughness tester. Results: The results, tested with One-Way ANOVA and Independent Samples t Test, demonstrated that after brushing for 15 minutes, the soft-bristle toothbrush group showed a significantly different value (p toothbrushes showed the value of nano hybrid surface roughness significant difference after brushing for 10 minutes. Conclusion: Roughness occurs more rapidly when brushing with medium-bristle tooth brushes than when brushing with soft-bristle toothbrushes.

  2. 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.

  3. A new hybrid gyroscope with electrostatic negative stiffness tuning.

    Science.gov (United States)

    Yang, Bo; Guan, Yumei; Wang, Shourong; Zou, Qi; Chu, Xian; Xue, Haiyan

    2013-05-30

    A variety of gyroscopes have been extensively studied due to their capability of precision detection of rotation rates and extensive applications in navigation, guidance and motion control. In this work, a new Hybrid Gyroscope (HG) which combines the traditional Dynamically Tuned Gyroscope (DTG) with silicon micromachined technology is investigated. The HG not only has the potentiality of achieving the same high precision as the traditional DTG, but also features a small size and low cost. The theoretical mechanism of the HG with a capacitance transducer and an electrostatic torquer is derived and the influence of the installation errors from the capacitance plate and the disc rotor module is investigated. A new tuning mechanism based on negative stiffness rather than the traditional dynamic tuning is proposed. The experimental results prove that the negative stiffness tuning is practicable and a tuning voltage of as high as 63 V is demonstrated. Due to the decreased installation error, the non-linearity of the scale factor is reduced significantly from 11.78% to 0.64%, as well as the asymmetry from 93.3% to 1.56% in the open loop condition. The rebalancing close-loop control is simulated and achieved experimentally, which proves that the fundamental principle of the HG is feasible.

  4. 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.

  5. Dynamics of podosome stiffness revealed by atomic force microscopy

    Science.gov (United States)

    Labernadie, Anna; Thibault, Christophe; Vieu, Christophe; Maridonneau-Parini, Isabelle; Charrière, Guillaume M.

    2010-01-01

    Podosomes are unique cellular entities specifically found in macrophages and involved in cell–matrix interactions, matrix degradation, and 3D migration. They correspond to a core of F-actin surrounded at its base by matrix receptors. To investigate the structure/function relationships of podosomes, soft lithography, atomic force microscopy (AFM), and correlative fluorescence microscopy were used to characterize podosome physical properties in macrophages differentiated from human blood monocytes. Podosome formation was restricted to delineated areas with micropatterned fibrinogen to facilitate AFM analyses. Podosome height and stiffness were measured with great accuracy in living macrophages (578 ± 209 nm and 43.8 ± 9.3 kPa) and these physical properties were independent of the nature of the underlying matrix. In addition, time-lapse AFM revealed that podosomes harbor two types of overlapping periodic stiffness variations throughout their lifespan, which depend on F-actin and myosin II activity. This report shows that podosome biophysical properties are amenable to AFM, allowing the study of podosomes in living macrophages at nanoscale resolution and the analysis of their intimate dynamics. Such an approach opens up perspectives to better understand the mechanical functionality of podosomes under physiological and pathological contexts. PMID:21081699

  6. Modeling of Stiffness and Strength of Bone at Nanoscale.

    Science.gov (United States)

    Abueidda, Diab W; Sabet, Fereshteh A; Jasiuk, Iwona M

    2017-05-01

    Two distinct geometrical models of bone at the nanoscale (collagen fibril and mineral platelets) are analyzed computationally. In the first model (model I), minerals are periodically distributed in a staggered manner in a collagen matrix while in the second model (model II), minerals form continuous layers outside the collagen fibril. Elastic modulus and strength of bone at the nanoscale, represented by these two models under longitudinal tensile loading, are studied using a finite element (FE) software abaqus. The analysis employs a traction-separation law (cohesive surface modeling) at various interfaces in the models to account for interfacial delaminations. Plane stress, plane strain, and axisymmetric versions of the two models are considered. Model II is found to have a higher stiffness than model I for all cases. For strength, the two models alternate the superiority of performance depending on the inputs and assumptions used. For model II, the axisymmetric case gives higher results than the plane stress and plane strain cases while an opposite trend is observed for model I. For axisymmetric case, model II shows greater strength and stiffness compared to model I. The collagen-mineral arrangement of bone at nanoscale forms a basic building block of bone. Thus, knowledge of its mechanical properties is of high scientific and clinical interests.

  7. Targeting Fold Stiffness to Design Enhanced Origami Structures

    Science.gov (United States)

    Buskohl, Philip; Bazzan, Giorgio; Abbott, Andrew; Durstock, Michael; Vaia, Richard

    2014-03-01

    Structures with adaptive geometry are increasingly of interest for actuation, sensing and packaging applications. Origami structures, by definition, can ``shape-shift'' between multiple geometric configurations that are predefined by a pattern of folds. Plastic deformation and local failure at the fold lines transform an originally homogenous material into a grid with locally tailored mechanical properties that bias the response of the overall structure to external loading. Typically, origami structures focus on uniformly stiff fold lines with rigid facets. In this study, we discuss how localized variations in stiffness can influence global properties, including energy budget to transition from flat to folded structure, the preferred path through configuration space, and the final mechanical response of the folded architecture. A simple, bi-stable origami fold pattern is laser machined into polypropylene sheets of different compliance and the critical load of the transition is measured. We model the structure as a truss with bar elongation, folding, and facet bending in order to predict ways to enhance or mitigate the critical load. Targeting local folding properties to modify global performance directly extends to the analysis of more complex architectures.

  8. Strength and Stiffness of Stabilized Alluvial Silt under Frost Actions

    Directory of Open Access Journals (Sweden)

    Haibo Wang

    2017-01-01

    Full Text Available The Yellow River alluvial silt was stabilized into pavement base materials for cold regions. The stabilizing additives were cement, fly ash, and lime, which were included in a range of combinations and dosages when mixed with the silt. Freeze-thaw cyclic impacts were conducted on the treated samples to assess materials performance of withstanding the frost actions. The tests were conducted on samples cured for 7 days to up to 180 days. Test results show that the cement-fly ash-treated samples outperform the other two stabilization categories with respect to material strength and stiffness developed under both normal and frost conditions. Under the normal conditions, the material unconfined compressive (UC strength rises to 3.0 MPa on day 28 depending on the cement and fly ash dosage used. If subjected to frost actions, the fly ash inclusions warrant a residual UC strength value of 1.3 MPa and above. The antifrost performance of the cement-fly ash-treated samples is related to thermal buffer capacity of the fly ash particles. Water adsorption and material soundness results agree with the strength and stiffness development. An optimal dosage was 3–6% for the cement and 0.3 for cement to fly ash mass ratio.

  9. Frequency domain identification of grinding stiffness and damping

    Science.gov (United States)

    Leonesio, Marco; Parenti, Paolo; Bianchi, Giacomo

    2017-09-01

    As equivalent stiffness and damping of the grinding process dominate cutting stability, their identification is essential to predict and avoid detrimental chatter occurrence. The identification of these process constants is not easy in large cylindrical grinding machines, e.g. roll grinders, since there are no practical ways to measure cutting force normal component. This paper presents a novel frequency domain approach for identifying these process parameters, exploiting in-process system response, measured via impact testing. This method adopts a sub-structuring approach to couple the wheel-workpiece relative dynamic compliance with a two-dimensional grinding force model that entails both normal and tangential directions. The grinding specific energy and normal force ratio, that determine grinding stiffness and damping, are identified by fitting the closed loop FRF (Frequency Response Function) measured during specific plunge-grinding tests. The fitting quality supports the predictive capability of the model. Eventually, the soundness of the proposed identification procedure is further assessed by comparing the grinding specific energy identified through standard cutting power measurements.

  10. Calculation of exact vibration modes for plane grillages by the dynamic stiffness method

    Science.gov (United States)

    Hallauer, W. L., Jr.; Liu, R. Y. L.

    1982-01-01

    A dynamic stiffness method is developed for the calculation of the exact modal parameters for plane grillages which consist of straight and uniform beams with coincident elastic and inertial axes. Elementary bending-torsion beam theory is utilized, and bending translation is restricted to one direction. The exact bending-torsion dynamic stiffness matrix is obtained for a straight and uniform beam element with coincident elastic and inertial axes. The element stiffness matrices are assembled using the standard procedure of the static stiffness method to form the dynamic stiffness matrix of the complete grillage. The exact natural frequencies, mode shapes, and generalized masses of the grillage are then calculated by solving a nonlinear eigenvalue problem based on the dynamic stiffness matrix. The exact modal solutions for an example grillage are calculated and compared with the approximate solutions obtained by using the finite element method.

  11. 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......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 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....

  12. A molecular dynamics study of stiffness-dependent thermal conductivity of graphene

    Science.gov (United States)

    Huang, Jianzhang; Han, Qiang

    2017-03-01

    Non-equilibrium molecular dynamics (NEMD) simulations is used to investigate the effect of support stiffness on thermal conductivity property based on the ‘graphene-springs’ model. It shows that the support stiffness greatly influences the thermal conductivity. Thermal conductivity of graphene decreases nonlinearly as the support stiffness increases. The temperature stability of thermal conductivity property of graphene can be improved by the support stiffness. For patterned stiffness supported stripe, thermal conductivity is significantly dependent on the patterned area, angle and stripe distribution. The work in this paper reveals the possibility for designing and controlling of thermal conduction of graphene by using support stiffness, which is beneficial to the application of graphene in nanoscale devices.

  13. 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.

  14. Research regarding stiffness optimization of wires used for joints actuation from an elephant's trunk robotic arm

    Science.gov (United States)

    Ciofu, C.; Stan, G.

    2016-11-01

    Elephant's trunk robotic arms driven by wires and pulley mechanisms have issues with wires stiffness because of the entailed elastic deformations that is causing errors of positioning. Static and dynamic loads from each joint of the robotic arm affect the stiffness of driving wires and precision positioning. The influence of wires elastic deformation on precision positioning decreases with the increasing of wires stiffness by using different pre-tensioning devices. In this paper, we analyze the variation of driving wires stiffness particularly to each wire driven joint. We obtain optimum wires stiffness variation by using an analytical method that highlights the efficiency of pre-tensioning mechanism. The analysis of driving wires stiffness is necessary for taking appropriate optimization measures of robotic arm dynamic behavior and, thus, for decreasing positioning errors of the elephant's trunk robotic arm with inner actuation through wires/cables.

  15. Symbolic Boundary Work in Schools: Demarcating and Denying Ethnic Boundaries

    Science.gov (United States)

    Tabib-Calif, Yosepha; Lomsky-Feder, Edna

    2014-01-01

    This article examines the symbolic boundary work that is carried out at a school whose student population is heterogeneous in terms of ethnicity and class. Based on ethnography, the article demonstrates how the school's staff seeks to neutralize ethnic boundaries and their accompanying discourse, while the pupils try to bring ethnic…

  16. A Two-Degree of Freedom Variable Stiffness Actuator Based on the MACCEPA Concept

    OpenAIRE

    Maarten Weckx; Glenn Mathijssen; Idris Si Mhand Benali; Raphaël Furnemont; Ronald Van Ham; Dirk Lefeber; Bram Vanderborght

    2014-01-01

    The current state-of-the-art of variable stiffness actuators consists mostly of different concepts for single-degree of freedom joints. However, in bio-inspired robotic applications, multiple degrees of freedom variable stiffness actuators are often desired. Currently, this is usually achieved by cascading single-degree of freedom actuators. The innovation presented in this work is a two-degree of freedom variable stiffness actuator using the mechanically adjustable and controllable equilibri...

  17. Modeling and characterization of stiffness controlled robotic legs using dielectric elastomers

    Science.gov (United States)

    Newton, Jason; Morton, Jeffrey; Clark, Jonathan; Oates, William S.

    2012-04-01

    A new robotic leg design is presented that utilizes dielectric elastomers (3M VHB 4910) to rapidly control stiffness changes for enhanced mobility and agility of a field demonstrated hexapod robot. A set of electromechanical test are utilized to obtain up to 92% reduction in stiffness that is controlled by an electric field. The results are compared to a finite deformation membrane finite element model to understand and improve field driven stiffness changes for real-time robotic applications.

  18. Variation in Stiffness of Monopiles in Dense Sand Under Cyclic Lateral Loads

    DEFF Research Database (Denmark)

    Nicolai, Giulio; Ibsen, Lars Bo

    2016-01-01

    The stiffness of the soil-foundation system is an important parameter that is taken into account in design. Recent studies of offshore wind turbines have shown that long-term cyclic lateral loading, induced by waves and wind, may lead to an increase in the foundation stiffness during the lifetime...... on the stiffness variation of a small-scale monopile in dense saturated sand during cyclic tests of approximately 50,000 load cycles....

  19. Collaboration in Healthcare Through Boundary Work and Boundary Objects

    DEFF Research Database (Denmark)

    Meier, Ninna

    2015-01-01

    This article contributes to our understanding of how boundary work is practiced in healthcare settings. Previous studies have shown how boundaries are constantly changing, multiple, and co-existing, and can also be relatively stable cognitive and social distinctions between individuals and groups....... In highly specialized, knowledge-intensive organizations such as healthcare organizations, organizational, professional, and disciplinary boundaries mark the formal structure and division of work. Collaboration and coordination across these boundaries are essential to minimizing gaps in patient care......, but also may be challenging to achieve in practice. By drawing on data from an ethnographic study of two hospital wards, this article investigates practices of cross-disciplinary and professional collaboration and adds to our knowledge of how this kind of boundary work is produced in context. Moreover...

  20. Boundary-Layer & health

    Science.gov (United States)

    Costigliola, V.

    2010-09-01

    It has long been known that specific atmospheric processes, such as weather and longer-term climatic fluctuations, affect human health. The biometeorological literature refers to this relationship as meteorotropism, defined as a change in an organism that is correlated with a change in atmospheric conditions. Plenty of (patho)physiological functions are affected by those conditions - like the respiratory diseases - and currently it is difficult to put any limits for pathologies developed in reply. Nowadays the importance of atmospheric boundary layer and health is increasingly recognised. A number of epidemiologic studies have reported associations between ambient concentrations of air pollution, specifically particulate pollution, and adverse health effects, even at the relatively low concentrations of pollution found. Since 1995 there have been over twenty-one studies from four continents that have explicitly examined the association between ambient air pollutant mixes and daily mortality. Statistically significant and positive associations have been reported in data from various locations around the world, all with varying air pollutant concentrations, weather conditions, population characteristics and public health policies. Particular role has been given to atmospheric boundary layer processes, the impact of which for specific patient-cohort is, however, not well understood till now. Assessing and monitoring air quality are thus fundamental to improve Europe's welfare. One of current projects run by the "European Medical Association" - PASODOBLE will develop and demonstrate user-driven downstream information services for the regional and local air quality sectors by combining space-based and in-situ data with models in 4 thematic service lines: - Health community support for hospitals, pharmacies, doctors and people at risk - Public information for regions, cities, tourist industry and sporting event organizers - Compliance monitoring support on particulate

  1. (Investigations of ultrasonic wave interactions with grain boundaries and grain imperfections)

    Energy Technology Data Exchange (ETDEWEB)

    1990-01-01

    The main objective of our research is to obtain a better understanding of ultrasonic wave interaction with interfaces in polycrystalline materials. This report discusses two recently developed experimental techniques: scanning acoustic microscope and optical point sensors. As for general wave propagation problems in anisotropic media, four major topics are discussed in separate sections. First, single boundaries between large bicrystals are considered. The reflection and transmission coefficients of such interfaces are calculated for imperfect boundary conditions by using the finite interface stiffness approach. Ultrasonic transmission through multiple-grain structures are investigated by computer simulation based on the statistical evaluation of repeated acoustical wave interactions with individual grain boundaries. The number of grains interacting with the propagating acoustical wave is considered to be high enough to approximate the wave-material interaction as scattering on elastic inhomogeneities. The grain scattering induced attenuation of Rayleigh waves is investigated in polycrystalline materials. 41 refs., 43 figs.

  2. A mechanism to compensate undesired stiffness in joints of prosthetic hands.

    Science.gov (United States)

    Smit, Gerwin; Plettenburg, Dick; Van der Helm, Frans

    2014-04-01

    Cosmetic gloves that cover a prosthetic hand have a parasitic positive stiffness that counteracts the flexion of a finger joint. Reducing the required input torque to move a finger of a prosthetic hand by compensating the parasitic stiffness of the cosmetic glove. Experimental, test bench. The parasitic positive stiffness and the required input torques of a polyvinyl chloride glove and a silicone glove were measured when flexing a metacarpophalangeal finger joint for 90°. To compensate this positive stiffness, an adjustable compensation mechanism with a negative stiffness was designed and built. A MATLAB model was created to predict the optimal settings of the mechanism, based on the measured stiffness, in order to minimize the required input torque of the total system. The mechanism was tested in its optimal setting with an applied glove. The mechanism reduced the required input torque by 58% for the polyvinyl chloride glove and by 52% for the silicone glove. The total energy dissipation of the joint did not change significantly. This study shows that the undesired positive stiffness in the joint can be compensated with a relatively simple negative stiffness mechanism, which fits inside a finger of a standard cosmetic glove. Clinical relevance This study presents a mechanism that compensates the undesired stiffness of cosmetic gloves on prosthetic hands. As a result, it requires less input force, torque and energy to move the fingers. Application of this mechanism in body-powered hands will reduce the control effort of the user.

  3. Transient Elastography for Spleen Stiffness Measurement in Patients With Cirrhosis: Role in Degree of Thrombocytopenia.

    Science.gov (United States)

    Chien, Cheng-Hung; Lin, Yi-Lan; Chien, Rong-Nan; Hu, Ching-Chih; Yen, Cho-Li; Lee, Tsung-Shih; Hsieh, Po-Jen; Lin, Chih-Lang

    2016-09-01

    The purpose of our study was to evaluate the relationship between spleen stiffness measured by transient elastography and the degree of thrombocytopenia in patients with liver cirrhosis. A total of 67 patients with liver cirrhosis were prospectively enrolled in the study. All patients underwent single-day hematologic and biochemical tests, sonography, and transient elastography of the liver and spleen. Thrombocytopenia was categorized as mild (platelet count, 75,000-150,000/μL), moderate (50,000-75,000/μL), and severe (thrombocytopenia was significantly correlated with spleen stiffness (P = .001) and spleen size (P = .002) but not with liver stiffness (P = .086). In patients without splenomegaly, spleen stiffness values were significantly higher in patients with thrombocytopenia than in those without thrombocytopenia (P = .035). In patients with splenomegaly, spleen stiffness values were significantly higher in patients with moderate to severe thrombocytopenia than in those with a normal platelet count or mild thrombocytopenia (P = .007). Compared to liver stiffness, spleen stiffness showed a better and statistically significant correlation with platelet count and spleen size in patients with cirrhosis. The degree of thrombocytopenia was directly correlated with spleen stiffness, irrespective of the presence of splenomegaly. The clinical phenomenon of unexpected thrombocytopenia may be explained by a subtle or irreversible change in spleen stiffness.

  4. Measuring and Modelling the In-Plane Bending Stiffness and Wrinkling Behaviour of Engineering Fabrics

    OpenAIRE

    Harrison, Philip; Anderson, Drew; Alvarez, Marcos F.; Bali, Eshan; Mateos, Yuri

    2016-01-01

    In this investigation two simple tests are conducted to characterise the shear, out-of-plane bending stiffness and in-plane bending stiffness of engineering fabrics and to investigate their wrinkling response during shear. A cantilever bending test [1] is first used to measure the out-of-plane bending stiffness while a modified version of the uniaxial bias extension (UBE) test is used to explore both the in-plane shear and the in-plane bending stiffness of the fabric (see Figure 1a). An estim...

  5. The role of negative stiffness in semi-active control of magneto-rheological dampers

    DEFF Research Database (Denmark)

    Høgsberg, Jan Becker

    2011-01-01

    The performance of external dampers depends on the particular combination of energy dissipation and stiffness, where in general damping increases with decreasing damper stiffness. It is therefore of great interest to minimize or even introduce negative damper stiffness. The present paper proposes...... adaptive control strategies for the applied voltage of a semi-active magneto-rheological damper. From linear equivalent models obtained by harmonic averaging it is found that these control strategies introduce equivalent negative stiffness, and by numerical simulations it is illustrated that they lead...

  6. MR elastography: Spleen stiffness measurements in healthy volunteers--preliminary experience.

    Science.gov (United States)

    Mannelli, Lorenzo; Godfrey, Edmund; Joubert, Ilse; Patterson, Andrew J; Graves, Martin J; Gallagher, Ferdia A; Lomas, David J

    2010-08-01

    The purpose of this article is to establish the range of normal splenic stiffness in healthy volunteers using MR elastography (MRE) and to investigate any correlation with physiologic parameters and driver position. Sixteen volunteers (mean [+/- SD] age, 37 +/- 9 years) with no history of gastrointestinal, hepatobiliary, or cardiovascular disease were recruited. The MRI protocol included T2-weighted axial and gradient-echo MRE sequences using steady-state 60-Hz excitation. Two MRE acquisitions were performed, one with the driver placed on the right side of the abdomen and the other with the driver placed on the left side. Volunteers' body mass index (BMI), arterial mean blood pressure, age, spleen volume, and liver stiffness were also determined. Two radiologists independently measured the spleen stiffness on the MRE inversion images. The correlations between spleen stiffness and BMI, arterial mean blood pressure, age, spleen volume, and liver stiffness were quantified. Sixteen volunteers underwent MRE. With the driver placed on the right side of the abdomen, the mean splenic stiffness was 3,565 +/- 586 Pa (range, 2,353-4,442 Pa); with the driver on the left side of the abdomen, the mean splenic stiffness was significantly (p 0.05) These preliminary results in a small number of healthy volunteers show that spleen stiffness is not significantly correlated with BMI, arterial mean blood pressure, spleen volume, or liver stiffness. A significant difference was observed using different driver positions.

  7. 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

    Cancer cells consistently exhibit decreased stiffness, however the onset and progression of this change has not been characterized. To study the development of cell stiffness changes we evaluated the shear stiffness of populations of cells during transformation to a carcinogenic state. Bronchial...... 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...

  8. Contractile equilibration of single cells to step changes in extracellular stiffness.

    Science.gov (United States)

    Crow, Ailey; Webster, Kevin D; Hohlfeld, Evan; Ng, Win Pin; Geissler, Phillip; Fletcher, Daniel A

    2012-02-08

    Extracellular stiffness has been shown to alter long timescale cell behaviors such as growth and differentiation, but the cellular response to changes in stiffness on short timescales is poorly understood. By studying the contractile response of cells to dynamic stiffness conditions using an atomic force microscope, we observe a seconds-timescale response to a step change in extracellular stiffness. Specifically, we observe acceleration in contraction velocity (μm/min) and force rate (nN/min) upon a step decrease in stiffness and deceleration upon a step increase in stiffness. Interestingly, this seconds-timescale response to a change in extracellular stiffness is not altered by inhibiting focal adhesion signaling or stretch-activated ion channels and is independent of cell height and contraction force. Rather, the response timescale is altered only by disrupting cytoskeletal mechanics and is well described by a simple mechanical model of a constant velocity actuator pulling against an internal cellular viscoelastic network. Consistent with the predictions of this model, we find that an osmotically expanding hydrogel responds to step changes in extracellular stiffness in a similar manner to cells. We therefore propose that an initial event in stiffness sensing is establishment of a mechanical equilibrium that balances contraction of the viscoelastic cytoskeleton with deformation of the extracellular matrix. Copyright © 2012 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  9. Arterial stiffness, atherosclerosis and cardiovascular risk: Pathophysiologic mechanisms and emerging clinical indications.

    Science.gov (United States)

    Palombo, Carlo; Kozakova, Michaela

    2016-02-01

    Arterial stiffness results from a degenerative process affecting mainly the extracellular matrix of elastic arteries under the effect of aging and risk factors. Changes in extracellular matrix proteins and in the mechanical properties of the vessel wall related to arterial stiffening may activate number of mechanisms involved also in the process of atherosclerosis. Several noninvasive methods are now available to estimate large artery stiffness in the clinical setting, including carotid-femoral pulse wave velocity, the reference for aortic stiffness estimate, and local distensibility measures of superficial arteries, namely carotid and femoral. An independent predictive value of arterial stiffness for cardiovascular events has been demonstrated in general as well as in selected populations, and reference values adjusted for age and blood pressure have been established. Thus, arterial stiffness is emerging as an interesting tissue biomarker for cardiovascular risk stratification and estimation of the individual "biological age". This paper overviews the mechanisms accounting for development and progression of arterial stiffness and for associations between arterial stiffness, atherosclerotic burden and incident cardiovascular events, summarizes the evidence and caveat for clinical use of stiffness as surrogate marker of cardiovascular risk, and briefly outlines some emerging methods for large artery stiffness characterization. Copyright © 2015 Elsevier Inc. All rights reserved.

  10. Seismic link at plate boundary

    Indian Academy of Sciences (India)

    transfer between two major faults, and parallel to the geothermal area extension. 1. Introduction. Plate boundaries are the zones where most earth dynamics are focussed. The complexity of tectonic boundaries draws attention to them as the largest earthquakes are felt in these areas and they elicit the natural hazard of ...

  11. Exclusion Process with Slow Boundary

    Science.gov (United States)

    Baldasso, Rangel; Menezes, Otávio; Neumann, Adriana; Souza, Rafael R.

    2017-06-01

    We study the hydrodynamic and the hydrostatic behavior of the simple symmetric exclusion process with slow boundary. The term slow boundary means that particles can be born or die at the boundary sites, at a rate proportional to N^{-θ }, where θ > 0 and N is the scaling parameter. In the bulk, the particles exchange rate is equal to 1. In the hydrostatic scenario, we obtain three different linear profiles, depending on the value of the parameter θ ; in the hydrodynamic scenario, we obtain that the time evolution of the spatial density of particles, in the diffusive scaling, is given by the weak solution of the heat equation, with boundary conditions that depend on θ . If θ \\in (0,1), we get Dirichlet boundary conditions, (which is the same behavior if θ =0, see Farfán in Hydrostatics, statical and dynamical large deviations of boundary driven gradient symmetric exclusion processes, 2008); if θ =1, we get Robin boundary conditions; and, if θ \\in (1,∞), we get Neumann boundary conditions.

  12. Fuzzy Boundary and Fuzzy Semiboundary

    OpenAIRE

    Athar, M.; Ahmad, B.

    2008-01-01

    We present several properties of fuzzy boundary and fuzzy semiboundary which have been supported by examples. Properties of fuzzy semi-interior, fuzzy semiclosure, fuzzy boundary, and fuzzy semiboundary have been obtained in product-related spaces. We give necessary conditions for fuzzy continuous (resp., fuzzy semicontinuous, fuzzy irresolute) functions. Moreover, fuzzy continuous (resp., fuzzy semicontinuous, fuzzy irresolute) functions have been characterized via fuzzy...

  13. Nucleation of small angle boundaries

    CSIR Research Space (South Africa)

    Nabarro, FRN

    1996-12-01

    Full Text Available The internal stresses induced by the strain gradients in an array of lattice cells delineated by low-angle dislocation boundaries are partially relieved by the creation of new low-angle boundaries. This is shown to be a first-order transition...

  14. How Firms Make Boundary Decisions

    DEFF Research Database (Denmark)

    Dobrajska, Magdalena; Billinger, Stephan; Becker, Markus

    2014-01-01

    We report findings from an analysis of 234 firm boundary decisions that a manufacturing firm has made during a 10 year period. Extensive interviews with all major decision makers located both at the headquarters and subsidiaries allow us to examine (a) who was involved in each boundary decision...

  15. 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

  16. Vitamin E reduces liver stiffness in nonalcoholic fatty liver disease

    Science.gov (United States)

    Fukui, Aiko; Kawabe, Naoto; Hashimoto, Senju; Murao, Michihito; Nakano, Takuji; Shimazaki, Hiroaki; Kan, Toshiki; Nakaoka, Kazunori; Ohki, Masashi; Takagawa, Yuka; Takamura, Tomoki; Kamei, Hiroyuki; Yoshioka, Kentaro

    2015-01-01

    AIM: To evaluate the efficacy of vitamin E treatment on liver stiffness in nonalcoholic fatty liver disease (NAFLD). METHODS: Thirty-eight NAFLD patients were administered vitamin E for > 1 year. The doses of vitamin E were 150, 300, or 600 mg; three times per day after each meal. Responses were assessed by liver enzyme levels [aspartate aminotransferase (AST), alanine aminotranferease (ALT), and γ-glutamyl transpeptidase (γ-GTP)], noninvasive scoring systems of hepatic fibrosis-4 [FIB-4 index and aspartate aminotransferase-to-platelet index (APRI)], and liver stiffness [velocity of shear wave (Vs)] measured by acoustic radiation force impulse elastography. Vs measurements were performed at baseline and 12 mo after baseline. The patients were genotyped for the patatin-like phospholipase domain containing 3 (PNPLA3) polymorphisms and then divided into either the CC/CG or GG group to examine each group’s responses to vitamin E treatment. RESULTS: We found marked differences in the platelet count, serum albumin levels, alkaline phosphatase levels, FIB-4 index, APRI, and Vs at baseline depending on the PNPLA3 polymorphism. AST, ALT, and γ-GTP levels (all P < 0.001); FIB-4 index (P = 0.035); APRI (P < 0.001); and Vs (P < 0.001) significantly decreased from baseline to 12 mo in the analysis of all patients. In the subset analyses of PNPLA3 genotypes, AST levels (P = 0.011), ALT levels (P < 0.001), γ-GTP levels (P = 0.005), APRI (P = 0.036), and Vs (P = 0.029) in genotype GG patients significantly improved, and AST and ALT levels (both P < 0.001), γ-GTP levels (P = 0.003), FIB-4 index (P = 0.017), and APRI (P < 0.001) in genotype CC/CG patients. CONCLUSION: One year of vitamin E treatment improved noninvasive fibrosis scores and liver stiffness in NAFLD patients. The responses were similar between different PNPLA3 genotypes. PMID:26644818

  17. Vascular Stiffness in Children With Chronic Kidney Disease.

    Science.gov (United States)

    Savant, Jonathan D; Betoko, Aisha; Meyers, Kevin E C; Mitsnefes, Mark; Flynn, Joseph T; Townsend, Raymond R; Greenbaum, Larry A; Dart, Allison; Warady, Bradley; Furth, Susan L

    2017-05-01

    Carotid-femoral pulse wave velocity (cfPWV) is a measure of arterial stiffness associated with cardiovascular events in the general population and in adults with chronic kidney disease. However, few data exist regarding cfPWV in children with chronic kidney disease. We compared observed cfPWV assessed via applanation tonometry in children enrolled in the CKiD cohort study (Chronic Kidney Disease in Children) to normative data in healthy children and examined risk factors associated with elevated cfPWV. cfPWV Z score for height/gender and age/gender was calculated from and compared with published pediatric norms. Multivariable linear regression was used to assess the relationship between cfPWV and age, gender, race, body mass index, diagnosis, urine protein-creatinine ratio, mean arterial pressure, heart rate, number of antihypertensive medications, uric acid, and serum low-density lipoprotein. Of the 95 participants with measured cfPWV, 60% were male, 19% were black, 46% had glomerular cause of chronic kidney disease, 22% had urine protein-creatinine ratio 0.5 to 2.0 mg/mg and 9% had >2.0 mg/mg, mean age was 15.1 years, average mean arterial pressure was 80 mm Hg, and median glomerular filtration rate was 63 mL/min per 1.73 m2 Mean cfPWV was 5.0 m/s (SD, 0.8 m/s); mean cfPWV Z score by height/gender norms was -0.1 (SD, 1.1). cfPWV increased significantly with age, mean arterial pressure, and black race in multivariable analysis; no other variables, including glomerular filtration rate, were independently associated with cfPWV. In this pediatric cohort with mild kidney dysfunction, arterial stiffness was comparable to that of normal children. Future research is needed to examine the impact of chronic kidney disease progression on arterial stiffness and associated cardiovascular parameters in children. © 2017 American Heart Association, Inc.

  18. Prediction of dislocation boundary characteristics

    DEFF Research Database (Denmark)

    Winther, Grethe

    Plastic deformation of both fcc and bcc metals of medium to high stacking fault energy is known to result in dislocation patterning in the form of cells and extended planar dislocation boundaries. The latter align with specific crystallographic planes, which depend on the crystallographic....... Crystal plasticity calculations combined with the hypothesis that these boundaries separate domains with local differences in the slip system activity are introduced to address precise prediction of the experimentally observed boundaries. The presentation will focus on two cases from fcc metals...... orientation of the grain [1]. For selected boundaries it has been experimentally verified that the boundaries consist of fairly regular networks of dislocations, which come from the active slip systems [2]. The networks have been analyzed within the framework of Low-Energy-Dislocation-Structures (LEDS...

  19. Boundary Drawing in Clinical Work

    DEFF Research Database (Denmark)

    Meier, Ninna

    The aim of this paper is to show how health care professionals temporarily dissolve and redraw boundaries in their everyday work, in order to coordinate clinical work and facilitate collaboration in patient pathways. Boundaries are social constructions that help us make sense of our complex, social...... world. In health care, formal boundaries are important distinctions that separate health care practitioners into medical specialties, professions and organizational departments. But clinical work also relies on the ability of health care practitioners to collaborate around patients in formal...... arrangements or emergent, temporary teams. Focusing on the cognitive and social boundaries we draw to establish identity and connection (to a profession, team or person) the paper shows how health care professionals can use inter-personal relationships to temporarily dismiss formal boundaries. By redrawing...

  20. Distributed Tuning of Boundary Resources

    DEFF Research Database (Denmark)

    Eaton, Ben; Elaluf-Calderwood, Silvia; Sørensen, Carsten

    2015-01-01

    in the context of a paradoxical tension between the logic of generative and democratic innovations and the logic of infrastructural control. Boundary resources play a critical role in managing the tension as a firm that owns the infrastructure can secure its control over the service system while independent...... firms can participate in the service system. In this study, we explore the evolution of boundary resources. Drawing on Pickering’s (1993) and Barrett et al.’s (2012) conceptualizations of tuning, the paper seeks to forward our understanding of how heterogeneous actors engage in the tuning of boundary...... resources within Apple’s iOS service system. We conduct an embedded case study of Apple’s iOS service system with an in-depth analysis of 4,664 blog articles concerned with 30 boundary resources covering 6 distinct themes. Our analysis reveals that boundary resources of service systems enabled by digital...