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Sample records for dynamic stress effects

  1. Static and dynamic effective stress coefficient of chalk

    DEFF Research Database (Denmark)

    Alam, M. Monzurul; Fabricius, Ida Lykke; Christensen, Helle Foged

    2012-01-01

    Deformation of a hydrocarbon reservoir can ideally be used to estimate the effective stress acting on it. The effective stress in the subsurface is the difference between the stress due to the weight of the sediment and a fraction (effective stress coefficient) of the pore pressure. The effective...... elastic deformation caused by pore pressure buildup, for example, during waterflooding. By contrast, during the increase in differential stress, as in the case of pore pressure depletion due to production, n increases with stress while α decreases.......Deformation of a hydrocarbon reservoir can ideally be used to estimate the effective stress acting on it. The effective stress in the subsurface is the difference between the stress due to the weight of the sediment and a fraction (effective stress coefficient) of the pore pressure. The effective...... stress coefficient is thus relevant for studying reservoir deformation and for evaluating 4D seismic for the correct pore pressure prediction. The static effective stress coefficient n is estimated from mechanical tests and is highly relevant for effective stress prediction because it is directly related...

  2. Timing matters: temporal dynamics of stress effects on memory retrieval.

    Science.gov (United States)

    Schwabe, Lars; Wolf, Oliver T

    2014-09-01

    Stress may impair memory retrieval. This retrieval impairment has been attributed to the action of the stress hormone cortisol, which is released with a delay of several minutes after a stressful encounter. Hence, most studies tested memory retrieval 20-30 min after stress, when the stress-induced cortisol increase peaks. In the present experiment, we investigated whether retrieval impairments can also be found at later intervals after stress. To this end, participants learned a list of words on day 1. Twenty-four hours later, they were first exposed to a stressor or a nonstressful control manipulation and completed a recognition test for the words either immediately thereafter, 25 min later, or 90 min later. Our findings showed that stress did not impair memory retrieval when memory was tested immediately after the stressor, before cortisol levels were elevated. However, retrieval performance was impaired 25 min after stress, when cortisol levels peaked, as well as 90 min after the stressor, when cortisol levels had already returned to baseline. The retrieval impairment 90 min after stress appeared to be even stronger than the one after 25 min. These findings suggest that the detrimental effects of stress on retrieval performance may last longer than is usually assumed.

  3. Effect of Magnetohydrodynamic Couple Stresses on Dynamic Characteristics of Exponential Slider Bearing

    Directory of Open Access Journals (Sweden)

    N.B. Naduvinamani

    2017-05-01

    Full Text Available The effect of couple stresses on static and dynamic characteristics of exponential slider bearing in the presence of magnetic field considering squeeze action is theoretically analyzed in this paper. The modified magnetohydrodynamic couple stress Reynolds type equation is derived on the basis of Stokes couple stress model and closed form expressions are obtained for static and dynamic character coefficients. Comparing with bearing lubricated with non-conducting Newtonian lubricants, the magnetohydrodynamic couple stress lubrication provides the higher steady load carrying capacity, dynamic stiffness and damping coefficient. The exponential bearing shows higher efficiency for small film thickness at higher value of couple stress parameter and Hartmann number.

  4. Prediction of Stress Concentration effect under Thermal and Dynamic loads on a High Pressure Turbine Rotor

    Directory of Open Access Journals (Sweden)

    R.Nagendra Babu

    2010-08-01

    Full Text Available Geometric discontinuities cause a large variation of stress and produce a significant increase in stress. The high stress due to the variation of geometry is called as ‘stress concentration’. This will increase when the loads are further applied. There are many investigators who have studied the stress distribution around the notches, grooves, and other irregularities of various machine components. This paper analyses the effects of thermal and fatigue load on a steam turbine rotor under the operating conditions. Stresses due to thermal and dynamic loads of High Pressure Steam Turbine Rotor of 210MW power station are found in two stages. A source code is developed for calculating the nominal stress at each section of HPT rotor. Maximum stress is obtained using FEA at the corresponding section. Thermal and Fatigue Stress Concentration Factors at each section are calculated. It is observed that the SCFdue to the combined effect of thermal and dynamic loads at the temperatures beyond 5400C is exceeding the safe limits.

  5. Effects of moving dynamic tyre loads on tyre-pavement contact stresses

    CSIR Research Space (South Africa)

    Steyn, WJvdM

    2002-01-01

    Full Text Available The purpose of this paper is to indicate the effect that moving dynamic tyre loads has on the tyre-pavement contact stresses used in pavement analysis. Traditionally tyre loads (in pavement analysis) are modelled as constant loads applied through...

  6. Effect of speaking rate and contrastive stress on formant dynamics and vowel perception.

    Science.gov (United States)

    Pitermann, M

    2000-06-01

    Vowel formants play an important role in speech theories and applications; however, the same formant values measured for the steady-state part of a vowel can correspond to different vowel categories. Experimental evidence indicates that dynamic information can also contribute to vowel characterization. Hence, dynamically modeling formant transitions may lead to quantitatively testable predictions in vowel categorization. Because the articulatory strategy used to manage different speaking rates and contrastive stress may depend on speaker and situation, the parameter values of a dynamic formant model may vary with speaking rate and stress. In most experiments speaking rate is rarely controlled, only two or three rates are tested, and most corpora contain just a few repetitions of each item. As a consequence, the dependence of dynamic models on those factors is difficult to gauge. This article presents a study of 2300 [iai] or [i epsilon i] stimuli produced by two speakers at nine or ten speaking rates in a carrier sentence for two contrastive stress patterns. The corpus was perceptually evaluated by naive listeners. Formant frequencies were measured during the steady-state parts of the stimuli, and the formant transitions were dynamically and kinematically modeled. The results indicate that (1) the corpus was characterized by a contextual assimilation instead of a centralization effect; (2) dynamic or kinematic modeling was equivalent as far as the analysis of the model parameters was concerned; (3) the dependence of the model parameter estimates on speaking rate and stress suggests that the formant transitions were sharper for high speaking rate, but no consistent trend was found for contrastive stress; (4) the formant frequencies measured in the steady-state parts of the vowels were sufficient to explain the perceptual results while the dynamic parameters of the models were not.

  7. Effect of stress-triaxiality on void growth in dynamic fracture of metals: a molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Seppala, E T; Belak, J; Rudd, R E

    2003-10-07

    The effect of stress-triaxiality on growth of a void in a three dimensional single-crystal face-centered-cubic (FCC) lattice has been studied. Molecular dynamics (MD) simulations using an embedded-atom (EAM) potential for copper have been performed at room temperature and using strain controlling with high strain rates ranging from 10{sup 7}/sec to 10{sup 10}/sec. Strain-rates of these magnitudes can be studied experimentally, e.g. using shock waves induced by laser ablation. Void growth has been simulated in three different conditions, namely uniaxial, biaxial, and triaxial expansion. The response of the system in the three cases have been compared in terms of the void growth rate, the detailed void shape evolution, and the stress-strain behavior including the development of plastic strain. Also macroscopic observables as plastic work and porosity have been computed from the atomistic level. The stress thresholds for void growth are found to be comparable with spall strength values determined by dynamic fracture experiments. The conventional macroscopic assumption that the mean plastic strain results from the growth of the void is validated. The evolution of the system in the uniaxial case is found to exhibit four different regimes: elastic expansion; plastic yielding, when the mean stress is nearly constant, but the stress-triaxiality increases rapidly together with exponential growth of the void; saturation of the stress-triaxiality; and finally the failure.

  8. Quantifying the effect of heat stress on daily milk yield and monitoring dynamic changes using an adaptive dynamic model.

    Science.gov (United States)

    André, G; Engel, B; Berentsen, P B M; Vellinga, Th V; Lansink, A G J M Oude

    2011-09-01

    Automation and use of robots are increasingly being used within dairy farming and result in large amounts of real time data. This information provides a base for the new management concept of precision livestock farming. From 2003 to 2006, time series of herd mean daily milk yield were collected on 6 experimental research farms in the Netherlands. These time series were analyzed with an adaptive dynamic model following a Bayesian method to quantify the effect of heat stress. The effect of heat stress was quantified in terms of critical temperature above which heat stress occurred, duration of heat stress periods, and resulting loss in milk yield. In addition, dynamic changes in level and trend were monitored, including the estimation of a weekly pattern. Monitoring comprised detection of potential outliers and other deteriorations. The adaptive dynamic model fitted the data well; the root mean squared error of the forecasts ranged from 0.55 to 0.99 kg of milk/d. The percentages of potential outliers and signals for deteriorations ranged from 5.5 to 9.7%. The Bayesian procedure for time series analysis and monitoring provided a useful tool for process control. Online estimates (based on past and present only) and retrospective estimates (determined afterward from all data) of level and trend in daily milk yield showed an almost yearly cycle that was in agreement with the calving pattern: most cows calved in winter and early spring versus summer and autumn. Estimated weekly patterns in terms of weekday effects could be related to specific management actions, such as change of pasture during grazing. For the effect of heat stress, the mean estimated critical temperature above which heat stress was expected was 17.8±0.56°C. The estimated duration of the heat stress periods was 5.5±1.03 d, and the estimated loss was 31.4±12.2 kg of milk/cow per year. Farm-specific estimates are helpful to identify management factors like grazing, housing and feeding, that affect the

  9. Nonlinear effect of elastic vortexlike motion on the dynamic stress state of solids

    Science.gov (United States)

    Shilko, Evgeny V.; Grinyaev, Yurii V.; Popov, Mikhail V.; Popov, Valentin L.; Psakhie, Sergey G.

    2016-05-01

    We present a theoretical analysis of the dynamic stress-strain state of regions in a solid body that are involved in a collective elastic vortexlike motion. It is shown that the initiation of elastic vortexlike motion in the material is accompanied by the appearance of dilatancy and equivalent strain, the magnitudes of which are proportional to the square of the ratio of linear velocity on the periphery of the elastic vortex to the velocity of longitudinal elastic waves (P wave). Under conditions of dynamic loading the described dynamic effects are able to initiate inelastic deformation or destruction of the material at loading speeds of a few percent of the P -wave speed. The obtained analytical estimates suggest that dynamic nonlinear strains can make a significant contribution in a number of widely studied nonlinear dynamic phenomena in solids. Among them are the effect of acoustic (dynamic) dilatancy in solids and granular media, which leads to the generation of longitudinal elastic waves by transverse waves [V. Tournat et al., Phys. Rev. Lett. 92, 085502 (2004), 10.1103/PhysRevLett.92.085502] and the formation of an array of intense "hot spots" (reminiscent of shear-induced hydrodynamic instabilities in fluids) in adiabatic shear bands [P. R. Guduru et al., Phys. Rev. E 64, 036128 (2001), 10.1103/PhysRevE.64.036128].

  10. Effect of Initial Principal Stress Direction on the Dynamic Characteristics of Carbonate Sand

    Institute of Scientific and Technical Information of China (English)

    Yu Haizhen; Zhao Wenguang; Wang Ren; Li Jianguo; He Yang

    2005-01-01

    The dynamic characteristics of carbonate sand under wave loads are very important for constructions on the ocean floor. The initial principal stress direction has been known to exert some influence on the dynamic characteristics of sand during cyclic loading. In an effort to investigate this aspect of the problem, several series of cyclic undrained tests were carried out on a saturated and loose sample of carbonate sand using a geotechnical static and dynamic universal triaxial shear apparatus. In this test apparatus, a hollow cylindrical sand specimen is subjected to a simultaneous application of both triaxial and torsional modes of shear stresses, which brings about the continuous rotation of principal stress axes. The test results indicated that the initial principal stress direction has a considerable influence on the dynamic strength of loose carbonate sand and with the increase of initial orientation of principal stress, dynamic strength will be reduced, the cyclic pore pressure increased, but the residual pore pressure reduced.

  11. Memory dynamics under stress.

    Science.gov (United States)

    Quaedflieg, Conny W E M; Schwabe, Lars

    2017-06-19

    Stressful events have a major impact on memory. They modulate memory formation in a time-dependent manner, closely linked to the temporal profile of action of major stress mediators, in particular catecholamines and glucocorticoids. Shortly after stressor onset, rapidly acting catecholamines and fast, non-genomic glucocorticoid actions direct cognitive resources to the processing and consolidation of the ongoing threat. In parallel, control of memory is biased towards rather rigid systems, promoting habitual forms of memory allowing efficient processing under stress, at the expense of "cognitive" systems supporting memory flexibility and specificity. In this review, we discuss the implications of this shift in the balance of multiple memory systems for the dynamics of the memory trace. Specifically, stress appears to hinder the incorporation of contextual details into the memory trace, to impede the integration of new information into existing knowledge structures, to impair the flexible generalisation across past experiences, and to hamper the modification of memories in light of new information. Delayed, genomic glucocorticoid actions might reverse the control of memory, thus restoring homeostasis and "cognitive" control of memory again.

  12. The effect of fracture density and stress state on the static and dynamic bulk moduli of Westerly granite

    Science.gov (United States)

    Blake, O. O.; Faulkner, D. R.

    2016-04-01

    Elastic properties are key parameters during the deformation of rocks. They can be measured statically or dynamically, but the two measurements are often different. In this study, the static and dynamic bulk moduli (Kstatic and Kdynamic) were measured at varying effective stress for dry and fluid-saturated Westerly granite with controlled fracture densities under isotropic and differential stress states. Isotropic fracturing of different densities was induced in samples by thermal treatment to 250, 450, 650, and 850°C. Results show that fluid saturation does not greatly affect static moduli but increases dynamic moduli. Under isotropic loading, high fracture density and/or low effective pressure results in a low Kstatic/Kdynamic ratio. For dry conditions Kstatic/Kdynamic approaches 1 at low fracture densities when the effective pressure is high, consistent with previous studies. Stress-induced anisotropy exists under differential stress state that greatly affects Kstatic compared to Kdynamic. As a result, the Kstatic/Kdynamic ratio is higher than that for the isotropic stress state and approaches 1 with increasing axial loading. The effect of stress-induced anisotropy increases with increasing fracture density. A key omission in previous studies comparing static and dynamic properties is that anisotropy has not been considered. The standard methods for measuring static elastic properties, such as Poisson's ratio, Young's and shear modulus, involve subjecting the sample to a differential stress state that promotes anisotropy. Our results show that stress-induced anisotropy resulting from differential stress state is a major contributor to the difference between static and dynamic elasticity and is dominant with high fracture density.

  13. Ultrasonic Dynamic Vector Stress Sensor

    Science.gov (United States)

    Heyman, Joseph S.; Froggatt, Mark

    1992-01-01

    Stress inferred from measurements in specimens rather than in bonded gauges. Ultrasonic dynamic vector stress sensor (UDVSS) measures changes in dynamic directional stress occurring in material or structure at location touched by device when material or structure put under cyclic load. Includes phase-locked loop, synchronous amplifier, and contact probe. Useful among manufacturers of aerospace and automotive structures for stress testing and evaluation of designs.

  14. Coseismic temporal changes of slip direction: the effect of absolute stress on dynamic rupture

    Science.gov (United States)

    Guatteri, Mariagiovanna; Spudich, P.

    1998-01-01

    We investigate the dynamics of rupture at low-stress level. We show that one main difference between the dynamics of high- and low-stress events is the amount of coseismic temporal rake rotation occurring at given points on the fault. Curved stations on exposed fault surfaces and earthquake dislocation models derived from ground-motion inversion indicate that the slip direction may change with time at a pointon the fault during dynamic rupture. We use a 3D boundary integral method to model temporal rake variations during dynamic rupture propagation assuming a slip-weakening friction law and isotropic friction. The points at which the slip rotates most are characterized by an initial shear stress direction substantially different from the average stress direction over the fault plane. We show that for a given value of stress drop, the level of initial shear stress (i.e., the fractional stress drop) determines the amount of rotation in slip direction. We infer that seismic events that show evidence of temporal rake rorations are characterized by a low initial shear-stress level with spatially variable direction on the fault (possibly due to changes in fault surface geometry) and an almost complete stress drop. Our models motivate a new interpretation of curved and cross-cutting striations and put new constraints on their analysis. The initial rake is in general collinear with the initial stress at the hypocenter zone, supporting the assumptions made in stress-tensor inversion from first-motion analysis. At other points on the fualt, especially away from the hypocenter, the initial slip rake may not be collinear with the initial shear stress, contradicting a common assumption of structural geology. On the other hand, the later part of slip in our models is systematically more aligned withi the average stress direction than the early slip. Our modeling suggests that the length of the straight part of curved striations is usually an upper bound of the slip

  15. The effect of stress and stress hormones on dynamic colour-change in a sexually dichromatic Australian frog.

    Science.gov (United States)

    Kindermann, Christina; Narayan, Edward J; Wild, Francis; Wild, Clyde H; Hero, Jean-Marc

    2013-06-01

    Rapid colour changes in vertebrates have fascinated biologists for centuries, herein we demonstrate dynamic colour change in an anuran amphibian, the stony creek frog (Litoria wilcoxii), which turns from brown to bright (lemon) yellow during amplexus. We show this by comparing the colour of baseline (unpaired males) and amplecting (paired) males. We also investigate the possible role of stress and stress hormones on this colour change. Frogs were subjected to four different levels of stressors (handling, toe-clipping, saline injection and adrenocorticotropic hormone [ACTH] injection) and the colour change was measured using digital photography. A comparison of baseline colour and stress hormone (corticosterone) levels was also conducted to give further insight to this topic. From the images, the Red Blue Green (RGB) colour values were calculated, and a principal components analysis (PCA) was used to create a single colour metric (the major axis) as an index of colour in the visible spectrum. A moderate stressor (toe-clipping) led to a significant change in colour (within 10 min) similar to that of amplecting males. Surprisingly, neither a mild stressor (handling and saline injection) nor the maximum stressor (handling and ACTH injection) led to a lightening response. This study confirms that the dynamic male colour change in this species in response to medium stressors adds new knowledge to the understanding of the functional mechanisms of dynamic colour change in amphibians.

  16. Static and dynamic stresses

    DEFF Research Database (Denmark)

    Tishin, A.M.; Spichkin, Yu.I.; Bohr, Jakob

    1999-01-01

    In this chapter we shall consider the properties of lanthanide metals, their alloys and compounds which can be studied using static and alternating mechanical stresses. The main attention will be paid to the effects related to magnetoelastic interactions. These interactions in magnetic materials...... to the appearance of anomalies in elastic constants, as well as to additional damping of sound oscillations in the lanthanide materials. The importance of understanding the nature of magnetoelastic interactions and related effects arises from the scientific desire to gather a better knowledge of magnetism, as well...

  17. Finite-size effect on the dynamic and sensing performances of graphene resonators: the role of edge stress

    OpenAIRE

    Chang-Wan Kim; Mai Duc Dai; Kilho Eom

    2016-01-01

    We have studied the finite-size effect on the dynamic behavior of graphene resonators and their applications in atomic mass detection using a continuum elastic model such as modified plate theory. In particular, we developed a model based on von Karman plate theory with including the edge stress, which arises from the imbalance between the coordination numbers of bulk atoms and edge atoms of graphene. It is shown that as the size of a graphene resonator decreases, the edge stress depending on...

  18. Effects of Pre-Stress State and Rupture Velocity on Dynamic Fault Branching

    Science.gov (United States)

    Kame, N.; Rice, J. R.; Dmowska, R.

    2002-12-01

    We consider a mode II rupture which propagates along a planar main fault and encounters an intersection with a branching fault that makes an angle with the main fault. Within a formulation that allows the failure path to be dynamically self-chosen, we study the following questions: Does the rupture start along the branch? Does it continue? Which side is most favored for branching, the extensional or compressional? Does rupture continue on the main fault too? What path is finally self-chosen? Failure in the modeling is described by a slip-weakening law for which the peak and residual strength, and strength at any particular amount of slip, is proportional to normal stress. We use the elastodynamic boundary integral equation method to allow simulations of rupture along the branched fault system. Our results show that dynamic stresses around the rupturing fault tip, which increase with rupture velocity at locations off the main fault plane, relative to those on it, could initiate rupture on a branching fault. As suggested by prior work [Poliakov, Dmowska and Rice, 2002, http://esag.harvard.edu/dmowska/PDR.pdf], whether a branching rupture, once begun, can be continued to a larger scale depends on principal stress directions in the pre-stress state and on rupture velocity. The most favored side for rupture transferring on a branching fault switches from the extensional side to the compressive side as we consider progressively shallower angles of the direction of maximum pre-compression with the main fault. Simultaneous rupturing on both faults is usually difficult for a narrow branching angle due to strong stress interaction between faults, which discourages rupture continuation on the other side. However, it can be activated by enhanced dynamic stressing when the rupture velocity is very near the limiting velocity (Rayleigh wave velocity for mode II). It can also be activated when the branching angle is wide because of decreasing stress interaction between faults

  19. Effectiveness of Selected Fitness Exercises on Stress of Femoral Neck using Musculoskeletal Dynamics Simulations and Finite Element Model.

    Science.gov (United States)

    Qian, Jing-Guang; Li, Zhaoxia; Zhang, Hong; Bian, Rong; Zhang, Songning

    2014-06-28

    The purpose of the study was to establish a dynamics model and a three-dimensional (3D) finite element model to analyze loading characteristics of femoral neck during walking, squat, single-leg standing, and forward and lateral lunges. One male volunteer performed three trials of the five movements. The 3D kinematic data were captured and imported into the LifeMOD to establish a musculoskeletal dynamics model to obtain joint reaction and muscle forces of iliacus, gluteus medius, gluteus maximus, psoas major and adductor magnus. The loading data LfeMOD were imported and transformed into a hip finite-element model. The results of the finite element femur model showed that stress was localized along the compression arc and the tension arc. In addition, the trabecular bone and tension lines of the Ward's triangle also demonstrated high stress. The compact bone received the greatest peak stress in the forward lunge and the least stress in the squat. However, the spongy bone in the femoral neck region had the greatest stress during the walk and the least stress in the squat. The results from this study indicate that the forward lunge may be an effective method to prevent femoral neck fractures. Walking is another effective and simple method that may improve bone mass of the Ward's triangle and prevent osteoporosis and femoral neck fracture.

  20. Effectiveness of Selected Fitness Exercises on Stress of Femoral Neck using Musculoskeletal Dynamics Simulations and Finite Element Model

    Directory of Open Access Journals (Sweden)

    Qian Jing-Guang

    2014-07-01

    Full Text Available The purpose of the study was to establish a dynamics model and a three-dimensional (3D finite element model to analyze loading characteristics of femoral neck during walking, squat, single-leg standing, and forward and lateral lunges. One male volunteer performed three trials of the five movements. The 3D kinematic data were captured and imported into the LifeMOD to establish a musculoskeletal dynamics model to obtain joint reaction and muscle forces of iliacus, gluteus medius, gluteus maximus, psoas major and adductor magnus. The loading data LfeMOD were imported and transformed into a hip finite-element model. The results of the finite element femur model showed that stress was localized along the compression arc and the tension arc. In addition, the trabecular bone and tension lines of the Ward's triangle also demonstrated high stress. The compact bone received the greatest peak stress in the forward lunge and the least stress in the squat. However, the spongy bone in the femoral neck region had the greatest stress during the walk and the least stress in the squat. The results from this study indicate that the forward lunge may be an effective method to prevent femoral neck fractures. Walking is another effective and simple method that may improve bone mass of the Ward's triangle and prevent osteoporosis and femoral neck fracture.

  1. Finite-size effect on the dynamic and sensing performances of graphene resonators: the role of edge stress.

    Science.gov (United States)

    Kim, Chang-Wan; Dai, Mai Duc; Eom, Kilho

    2016-01-01

    We have studied the finite-size effect on the dynamic behavior of graphene resonators and their applications in atomic mass detection using a continuum elastic model such as modified plate theory. In particular, we developed a model based on von Karman plate theory with including the edge stress, which arises from the imbalance between the coordination numbers of bulk atoms and edge atoms of graphene. It is shown that as the size of a graphene resonator decreases, the edge stress depending on the edge structure of a graphene resonator plays a critical role on both its dynamic and sensing performances. We found that the resonance behavior of graphene can be tuned not only through edge stress but also through nonlinear vibration, and that the detection sensitivity of a graphene resonator can be controlled by using the edge stress. Our study sheds light on the important role of the finite-size effect in the effective design of graphene resonators for their mass sensing applications.

  2. THE EFFECTS OF ACUTE AND CHRONIC STRESS ON ERYTHROCYTE DYNAMIC IN COMBINATION WITH ß–ADRENERGIC RECEPTORS BLOCKADE IN RATS

    Directory of Open Access Journals (Sweden)

    Lucian Hritcu

    2005-08-01

    Full Text Available : 3 consecutive days propranolol hydrochloride administration (5 mg/kg b.w., subcutaneous injections under acute and chronic stress conditions causes changes of peripheral erythrocyte distribution in rats. The effects of acute stress and its combination with ȕ-adrenergic receptor blockade on erythrocyte dynamic were more pregnant beside the effects of chronic stress and its combination with ȕ-adrenergic receptor blockade, respectively. ȕ-adrenergic mechanisms were shown to be involved in regulation of erythrocyte dynamic in acute and chronic stress response.

  3. Effects of Pre-Stress State and Propagation Velocity on Dynamic Fault Branching

    Science.gov (United States)

    Kame, N.; Rice, J. R.; Dmowska, R.

    2001-12-01

    Major earthquakes seldom rupture along single planar faults. Instead there exist geometric complexities, including fault bends, branches and stepovers, which affect the rupture process, including nucleation and arrest. Here we consider a mode II rupture which propagates along a planar fault and encounters an intersection with a branching fault that makes an angle with the main fault. Analyses based on elastic stress fields near propagating ruptures suggest that whether a branch path will be followed or not, and whether branching to the extensional or compressional side is favored, depend on both the rupture propagation velocity as the branch is approached and on the pre-stress state before rupture arrives. See Kame and Yamashita (GJI, 139, 345-358, 1999) and Poliakov, Dmowska and Rice (JGR subm. 2001, http://esag.harvard.edu/dmowska/PDR.pdf). The latter predicted that branching to the extensional side would be favored in all pre-stress states except for those in which the direction of maximum pre-compression Smax makes a shallow angle ψ with the fault plane. Angles ψ 45 ° result when the ratio is less than unity. Thus it is anticipated that the most favored side for rupture branching should switch from the extensional to the compressive side as we consider progressively larger σ oxx/σ oyy (which means progressively smaller ψ ). In order to test that and other predictions, we have adapted the elastodynamic boundary integral equation methodology of Kame and Yamashita to 2-dimensional Mode II ruptures along branched fault systems, to allow simulations of rupture in which the failure path is dynamically self-chosen. Failure in the modeling is described by a slip-weakening law for which the peak and residual strength, and strength at any particular amount of slip, is proportional to normal stress (-σ nn). Our current results are preliminary. Nevertheless, by comparing results for σ oxx/σ oyy = 0.8 with those for 1.4, we have established, e.g., that a 15

  4. Dynamics of chemically stressed populations: the deduction of population consequences from effects on individuals

    Energy Technology Data Exchange (ETDEWEB)

    Kooijman, S.A.; Metz, J.A.

    1984-06-01

    A general, simple, and explicit model for the age-dependent growth and reproduction of individuals as a function of food supply is presented. The model assumes a Holling-type functional response coupled with a von Bertalanffy body growth law, a fixed ratio between the energy utilized for reproduction and respiration, and a juvenile stage that ends as soon as the animal attains a sufficient weight. This model is shown to fit the available data on the development of Daphnia magna quite well. The model is used as a basis for studying the effects of chemicals on population growth rate, given the effects on individuals. Effects on individual growth and reproduction are reflected in a concentration-dependent relative reduction of the population growth rate. Effects on feeding rate, digestion, basal metabolism, and survival work out much more dramatically at low natural population growth rates. This already follows from a much simpler model that assumes age-independent reproduction, as exemplified to a good approximation by the rotifer Brachionus rubens. The theoretical results are supplemented with experimental evidence, implying that the stress on a population at a certain concentration of a chemical may indeed be strongly dependent on the feeding state of that population.

  5. Analysis of Geometric Effects on Stress Wave Propagation in Epoxy Resins of Plate-Like Structure by Dynamic Photoelasticity Combined with Strain Gauge

    Science.gov (United States)

    Hayasi, Ryoei; Masuda, Yoshiharu; Hashimoto, Shozo; Kuriyama, Shinhou

    2008-06-01

    Experimental studies have been conducted using the dynamic photoelastic technique combined with a strain gauge to investigate geometric effects on stress wave propagation in axially impacted epoxy resins of plate-like structure. Dynamic photoelasticity provides a means of visualizing the stress wave field inside a solid. A device that triggers the generation of stress waves by direct projectile impact is used to conduct high-speed photoelasticity and strain gauge measurements. This triggering is achieved by an electrical connection between projectile and sample. The geometric effects of the width-to-wavelength ratio on the propagation speed and attenuation coefficient of stress waves were analyzed for isotropic rectangular rods of different width-to-thickness ratios, the thickness being the same in each case. The experimental results for stress wave speed as a function of width-to-wavelength ratio are in reasonable agreement with theoretical predictions based on a modified Love's equation involving the geometric effects due to lateral inertia.

  6. A dynamic model of stress and sustained attention

    Science.gov (United States)

    Hancock, Peter A.; Warm, Joel S.

    2003-01-01

    This paper examines the effects of stress on sustained attention. With recognition of the task itself as the major source of cognitive stress, a dynamic model is presented that addresses the effects of stress on vigilance and, potentially, a wide variety of attention performance tasks.

  7. Modulatory effect of betaine on expression dynamics of HSPs during heat stress acclimation in goat (Capra hircus).

    Science.gov (United States)

    Dangi, Satyaveer Singh; Dangi, Saroj K; Chouhan, V S; Verma, M R; Kumar, Puneet; Singh, Gyanendra; Sarkar, Mihir

    2016-01-10

    Changing climatic scenario with expected global rise in surface temperature compelled more focus of research over decoding heat stress response mechanism of animals and mitigation of heat stress. Recently betaine, a trimethyl form of glycine has been found to ameliorate heat stress in some species of animals. To overcome deleterious effect of heat stress, an attempt was taken to investigate the effect of betaine supplementation on heat stress mitigation in goats. Eighteen female Barbari goats were taken and randomly divided into 3 groups (n=6) such as control, HS (Heat stressed), HS+B (Heat stressed administered with betaine). Except for the control group, other groups were exposed to repeated heat stress (42 °C) for 6 h for sixteen consecutive days. Blood samples were collected at the end of heat exposure on day 1 (Initial heat stress acclimation - IHSA), day 6 (Short term heat stress acclimation - STHSA) and day 16 (Long term heat stress acclimation - LTHSA). When the groups were compared between different heat stress acclimatory phases, expression of all HSPs (HSP60, HSP70, HSP90 and HSP105/110) showed a similar pattern with a first peak on IHSA, reaching a basal level on STHSA followed by second peak on LTHSA. The messenger RNA (mRNA) and protein expression of HSPs was observed to be higher (Pbetaine administration was shown to have a dwindling effect on expression of HSPs, suggesting a possible role of this chemical chaperone on heat stress amelioration.

  8. The Effect of Astaxanthin and Regular Training on Dynamic Pattern of Oxidative Stress on Male under Strenuous Exercise

    Science.gov (United States)

    Sylviana, N.; Gunawan, H.; Lesmana, R.; Purba, A.; Akbar, I. B.

    2017-03-01

    Strenuous physical activity will induced higher Reactive Oxygen Species (ROS) level in human body that can be measured by serum Malondialdehyde (MDA) level. Malondialdehyde is product of lipid peroxidation process that define as oxidative damage of lipid biomolecule by reactivity of reactive oxygen species. Still, the dynamic pattern of Malondialdehyde (MDA) level under strenuous exercise is not fully understood. Potent antioxidant such as Astaxanthin and training may be altered the level of MDA. Thus, purpose of this study is to understand effect of astaxanthin to MDA dynamic pattern on training male after strenuous physical activity. It was a double blind, experimental study, conducted on thirty young male age, divided into untrained and trained groups. Supplement Astaxanthin was given to 15 subject as well as placebo for one week after supplementation, Subjects were tested with anaerobic strenuous physical activity. The values were analyzed with ANOVA test followed by Duncan test showed that in every groups, mean of MDA before test was similar, start increase significantly after tested, begin decrease at 6th hour post test and back to baseline at 24th hour post-test ( poxidative stress condition without altered its dynamic pattern in male after strenuous physical activity

  9. The effect of Guinier-Preston zones on the dynamic yield stress of alloys under the shock-wave load

    Science.gov (United States)

    Malashenko, V. V.

    2017-05-01

    The movement of an ensemble of edge dislocations under shock-wave action on an alloy that contains the Guinier-Preston zones has been theoretically studied. The analytical expression for the contribution of the Guinier-Preston zones into the dynamic yield stress has been obtained and it has been shown that this contribution is affected by the density of mobile dislocations. The numerical estimates have shown that the formation of these zones lead to a substantial increase in the dynamic yield stress of alloys.

  10. Effects of cross-anisotropy and stress-dependency of pavement layers on pavement responses under dynamic truck loading

    Directory of Open Access Journals (Sweden)

    Rafiqul A. Tarefder

    2016-06-01

    Full Text Available Previous studies by the authors have determined pavement responses under dynamic loading considering cross-anisotropy in one layer only, either the cross-anisotropic viscoelastic asphalt concrete (AC layer or the cross-anisotropic stress-dependent base layer, but not both. This study evaluates pavement stress–strain responses considering cross-anisotropy in all layers, i.e. AC, base and subbase, using finite element modeling (FEM technique. An instrumented pavement section on Interstate I-40 near Albuquerque, New Mexico was used in ABAQUS framework as model geometry. Field asphalt cores were collected and tested in the laboratory to determine the cross-anisotropy (n-values defined by horizontal to vertical modulus ratio, and other viscoelastic parameters as inputs of the model incorporated through user defined material interface (UMAT functionality in ABAQUS. Field base and subbase materials were also collected and tested in the laboratory to determine stress-dependent nonlinear elastic model parameters, as inputs of the model, again incorporated through UMAT. The model validation task was carried out using field-measured deflections and strain values under falling weight deflectometer (FWD loads at the instrumented section. The validated model was then subjected to an actual truck loading for studying cross-anisotropic effects. It was observed that horizontal tensile strain at the bottom of the AC layer and vertical strains in all layers decreased with an increase in n-value of the asphalt layer, from n < 1 (anisotropy to n=1 (isotropy. This indicates that the increase in horizontal modulus caused the decrease in layer strains. It was also observed that if the base and subbase layers were considered stress-dependent instead of linear elastic unbound layers, the horizontal tensile strain at the bottom of the asphalt layer increased and vertical strains on top of the base and subbase also increased.

  11. Effects of cross-anisotropy and stress-dependency of pavement layers on pavement responses under dynamic truck loading

    Institute of Scientific and Technical Information of China (English)

    Rafiqul A. Tarefder; Mesbah U. Ahmed; Asifur Rahman

    2016-01-01

    Previous studies by the authors have determined pavement responses under dynamic loading consid-ering cross-anisotropy in one layer only, either the cross-anisotropic viscoelastic asphalt concrete (AC) layer or the cross-anisotropic stress-dependent base layer, but not both. This study evaluates pavement stressestrain responses considering cross-anisotropy in all layers, i.e. AC, base and subbase, using finite element modeling (FEM) technique. An instrumented pavement section on Interstate I-40 near Albu-querque, New Mexico was used in ABAQUS framework as model geometry. Field asphalt cores were collected and tested in the laboratory to determine the cross-anisotropy (n-values) defined by horizontal to vertical modulus ratio, and other viscoelastic parameters as inputs of the model incorporated through user defined material interface (UMAT) functionality in ABAQUS. Field base and subbase materials were also collected and tested in the laboratory to determine stress-dependent nonlinear elastic model pa-rameters, as inputs of the model, again incorporated through UMAT. The model validation task was carried out using field-measured deflections and strain values under falling weight deflectometer (FWD) loads at the instrumented section. The validated model was then subjected to an actual truck loading for studying cross-anisotropic effects. It was observed that horizontal tensile strain at the bottom of the AC layer and vertical strains in all layers decreased with an increase in n-value of the asphalt layer, from n<1 (anisotropy) to n ¼ 1 (isotropy). This indicates that the increase in horizontal modulus caused the decrease in layer strains. It was also observed that if the base and subbase layers were considered stress-dependent instead of linear elastic unbound layers, the horizontal tensile strain at the bottom of the asphalt layer increased and vertical strains on top of the base and subbase also increased.

  12. Hot carrier injection degradation under dynamic stress

    Institute of Scientific and Technical Information of China (English)

    Ma Xiao-Hua; Cao Yan-Rong; Hao Yue; Zhang Yue

    2011-01-01

    In this paper, we have studied hot carrier injection (HCI) under alternant stress. Under different stress modes, different degradations are obtained from the experiment results. The different alternate stresses can reduce or enhance the HC effect, which mainly depends on the latter condition of the stress cycle. In the stress mode A (DC stress with electron injection), the degradation keeps increasing. In the stress modes B (DC stress and then stress with the smallest gate injection) and C (DC stress and then stress with hole injection under Vg=0V and Vd = 1.8 V), recovery appears in the second stress period. And in the stress mode D (DC stress and then stress with hole injection under Vg = -1.8 V and Vd = 1.8 V), as the traps filled in by holes can be smaller or greater than the generated interface states, the continued degradation or recovery in different stress periods can be obtained.

  13. Effects of drought stress on microbial dynamics in seasonally dry California ecosystems

    Science.gov (United States)

    Schaeffer, S. M.; Boot, C. M.; Doyle, A.; Clark, J.; Schimel, J. P.

    2008-12-01

    One of the key environmental factors controlling microbial activity is moisture. This water limitation is particularly strong in semi-arid and arid ecosystems such as those found along California's coast and interior range-lands. Cool, wet winters separated by long, dry summers present some the most challenging conditions for microbial survival and growth. Infrequent pulses of precipitation directly control microbial dynamics through soil wet-dry cycles, which in turn control the export of materials and nutrients into streams and groundwater. Recent research suggests that living microbial biomass can increase during the driest, hottest part of the year. We measured dissolved organic carbon and nitrogen (DOC, DON), microbial biomass carbon and nitrogen, inorganic nitrogen (NH4+, NO3-), and nitrification potential from July of 2007 to the present in California semi-arid grasslands. We also monitored inorganic nitrogen concentrations in soil pore water, shallow ground water, and stream water over the same period. Seasonal trends in DOC and DON show that they accumulate over the dry summer, and then decrease with the onset of the winter rains. Microbial biomass carbon showed a similar pattern, being higher in the summer and declining during winter (188.94±13.34 and 139.21±8.45 μg C g-1 dry soil respectively. However, biomass nitrogen remained unchanged over the same period (11.21±0.84 and 10.86±0.74 μg N g-1 dry soil respectively). Nitrification potentials were lowest during the winter wet season (5.26±0.40 μg N d-1 g-1 dry soil) and highest during the dry summer season (8.91±0.60 μg N d-1 g-1 dry soil). However, the seasonal patterns in NH4+ and NO3- availability suggest that net nitrification was not substantial until after the winter rains began. It is not currently known whether this increase in biomass represents actual growth of new organisms, or is a result of microbes accumulating internal solutes to avoid drying out. At the landscape-scale, these

  14. The impact of static stress change, dynamic stress change, and the background stress on aftershock focal mechanisms

    Science.gov (United States)

    Hardebeck, Jeanne L.

    2014-01-01

    The focal mechanisms of earthquakes in Southern California before and after four M ≥ 6.7 main shocks provide insight into how fault systems respond to stress and changes in stress. The main shock static stress changes have two observed impacts on the seismicity: changing the focal mechanisms in a given location to favor those aligned with the static stress change and changing the spatial distribution of seismicity to favor locations where the static stress change aligns with the background stress. The aftershock focal mechanisms are significantly aligned with the static stress changes for absolute stress changes of ≥ 0.02 MPa, for up to ~20 years following the main shock. The dynamic stress changes have similar, although smaller, effects on the local focal mechanisms and the spatial seismicity distribution. Dynamic stress effects are best observed at long periods (30–60 s) and for metrics based on repeated stress cycling in the same direction. This implies that dynamic triggering operates, at least in part, through cyclic shear stress loading in the direction of fault slip. The background stress also strongly controls both the preshock and aftershock mechanisms. While most aftershock mechanisms are well oriented in the background stress field, 10% of aftershocks are identified as poorly oriented outliers, which may indicate limited heterogeneity in the postmain shock stress field. The fault plane orientations of the outliers are well oriented in the background stress, while their slip directions are not, implying that the background stress restricts the distribution of available fault planes.

  15. Nutrients versus emerging contaminants-Or a dynamic match between subsidy and stress effects on stream biofilms.

    Science.gov (United States)

    Aristi, I; Casellas, M; Elosegi, A; Insa, S; Petrovic, M; Sabater, S; Acuña, V

    2016-05-01

    Freshwater ecosystems are threatened by multiple anthropogenic stressors, which might be differentiated into two types: those that reduce biological activity at all concentrations (toxic contaminants), and those that subsidize biological activity at low concentrations and reduce it at high concentrations (assimilable contaminants). When occurring in mixtures, these contaminants can have either antagonistic, neutral or synergistic effects; but little is known on their joint effects. We assessed the interaction effects of a mixture of assimilable and toxic contaminants on stream biofilms in a manipulative experiment using artificial streams, and following a factorial design with three nutrient levels (low, medium or high) and either presence or absence of a mixture of emerging contaminants (ciprofloxacin, erythromycin, diclofenac, methylparaben, and sulfamethoxazole). We measured biofilm biomass, basal fluorescence, gross primary production and community respiration. Our initial hypotheses were that biofilm biomass and activity would: increase with medium nutrient concentrations (subsidy effect), but decrease with high nutrient concentrations (stress effect) (i); decrease with emerging contaminants, with the minimum decrease at medium nutrient concentrations (antagonistic interaction between nutrients subsidy and stress by emerging contaminants) and the maximum decrease at high nutrient concentrations (synergistic interaction between nutrients and emerging contaminants stress) (ii). All the measured variables responded linearly to the available nutrients, with no toxic effect at high nutrient concentrations. Emerging contaminants only caused weak toxic effects in some of the measured variables, and only after 3-4 weeks of exposure. Therefore, only antagonistic interactions were observed between nutrients and emerging contaminants, as medium and high nutrient concentrations partly compensated the harmful effects of emerging contaminants during the first weeks of the

  16. Dynamic regulation of cerebral DNA repair genes by psychological stress

    DEFF Research Database (Denmark)

    Forsberg, Kristin; Aalling, Nadia; Wörtwein, Gitta

    2015-01-01

    for maintaining genomic integrity. The aim of the present study was to characterize the pattern of cerebral DNA repair enzyme regulation after stress through the quantification of a targeted range of gene products involved in different types of DNA repair. 72 male Sprague-Dawley rats were subjected to either...... was seen in HC, but with overall smaller effects and without the induction after acute stress. Nuclear DNA damage from oxidation as measured by the comet assay was unaffected by stress in both regions. We conclude that psychological stress have a dynamic influence on brain DNA repair gene expression...

  17. Thermal effect on dynamics of thin and thick composite laminated microbeams by modified couple stress theory for different boundary conditions

    Science.gov (United States)

    Ghadiri, Majid; Zajkani, Asghar; Akbarizadeh, Mohammad Reza

    2016-12-01

    In this article, thermal effect on free vibration behavior of composite laminated microbeams based on the modified couple stress theory is presented. The proposed anisotropic model is developed by using a variational formulation. The governing equations and boundary conditions are obtained based on a modified couple stress theory and using the principle of minimum potential energy and considering different beam theories, i.e., Euler-Bernoulli, Timoshenko and Reddy beam theories. Unlike the classical beam theories, this model contains a material length scale parameter and can capture the size effect. Free vibration of a simply supported beam is solved by utilizing Fourier series. In addition, the fundamental frequency is achieved by using the generalized differential quadrature method for four types of cross-ply laminations with clamped-clamped, clamped-hinged and hinged-hinged boundary conditions for different beam theories. For investigating different parameters including temperature changes, material length scale parameter, beam thickness, some numerical results on different cross-ply laminated beams are presented. The fundamental frequency of different thin and thick beam theories is investigated by increasing slenderness ratio and thermal loads. The results prove that the modified couple stress theory increases the natural frequency under the thermal effects for free vibration of composite laminated microbeams.

  18. [Effects of NaCl stress on photosynthesis characteristics and fast chlorophyll fluorescence induction dynamics of Pistacia chinensis leaves].

    Science.gov (United States)

    Li, Xu-Xin; Liu, Bing-Xiang; Guo, Zhi-Tao; Chang, Yue-Xia; He, Lei; Chen, Fang; Lu, Bing-She

    2013-09-01

    By using fast chlorophyll fluorescence induction dynamics analysis technique (JIP-test), this paper studied the photosynthesis characteristics and fast chlorophyll fluorescence induction dynamics of 1-year old Pistacia chinensis seedlings under the stress of NaCl at the concentrations 0% (CK), 0.15%, 0.3%, 0.45%, and 0.6%. With the increasing concentration of NaCl, the contents of Chl a, Chl b, and Chl (a+b) in the seedlings leaves decreased, the Chl a/b ratio decreased after an initial increase, and the carotenoid content increased. The net photosynthetic rate (P(n)) and stomatal conductance (g(s)) decreased gradually with increasing NaCl concentration. The decrease of P(n) was mainly attributed to the stomatal limitation when the NaCl concentration was lower than 0.3%, and to the non-stomatal limitation when the NaCl concentration was higher than 0.3%. The trapped energy flux per RC (TR0/CS0), electron transport flux per RC (ET0/CS0), density of RCs (RC/CS0), and yield or flux ratio (psi(0) or phi(E0)) decreased, but the absorption flux per CS (ABS/CS0) and the K phase (W(k)) and J phase (V) in the O-J-I-P chlorophyll fluorescence induction curves increased distinctly, indicating that NaCl stress damaged the leaf oxygen-evolving complex (OEC), donor sides, and PS II reaction centers. When the NaCl concentration reached 0.3%, the maximum photochemical efficiency (F(v)/F(m)) and performance index (PI(ABS)) decreased 17.7% and 36.6%, respectively, as compared with the control.

  19. Dynamics of active cellular response under stress

    Science.gov (United States)

    de, Rumi; Zemel, Assaf; Safran, Samuel

    2008-03-01

    Forces exerted by and on adherent cells are important for many physiological processes such as wound healing and tissue formation. In addition, recent experiments have shown that stem cell differentiation is controlled, at least in part, by the elasticity of the surrounding matrix. Using a simple theoretical model that includes the forces due to both the mechanosensitive nature of cells and the elastic response of the matrix, we predict the dynamics of orientation of cells. The model predicts many features observed in measurements of cellular forces and orientation including the increase with time of the forces generated by cells in the absence of applied stress and the consequent decrease of the force in the presence of quasi-static stresses. We also explain the puzzling observation of parallel alignment of cells for static and quasi-static stresses and of nearly perpendicular alignment for dynamically varying stresses. In addition, we predict the response of the cellular orientation to a sinusoidally varying applied stress as a function of frequency. The dependence of the cell orientation angle on the Poisson ratio of the surrounding material can be used to distinguish systems in which cell activity is controlled by stress from those where cell activity is controlled by strain. Reference: Nature Physics, vol. 3, pp 655 (2007).

  20. Effects of a father-based in-home intervention on perceived stress and family dynamics in parents of children with autism.

    Science.gov (United States)

    Bendixen, Roxanna M; Elder, Jennifer H; Donaldson, Susan; Kairalla, John A; Valcante, Greg; Ferdig, Richard E

    2011-01-01

    Parents of children with autism report high rates of stress. Parental differences in stress are inconsistent, with most research indicating that mothers report higher levels of stress than fathers. We explored parental differences before and after an in-home training program. Fathers were taught an intervention designed to improve their child's social reciprocity and communication; they then trained mothers. Stress was assessed with the Parenting Stress Index-Short Form, and family dynamics was assessed with the Family Adaptability and Cohesion Evaluation Scales II. Both mothers and fathers reported high preintervention levels of stress. After intervention, fathers' stress was reduced, but not significantly, possibly because of the variability in fathers' scores; mothers' stress scores were significantly reduced. Parenting styles were significantly different before and after intervention. Interdisciplinary teams, including occupational therapists, nurses, and special educators, can work.together to have a positive impact on the lives of families of children with autism.

  1. Dynamical theory of active cellular response to external stress

    Science.gov (United States)

    de, Rumi; Safran, Samuel A.

    2008-09-01

    We present a comprehensive, theoretical treatment of the orientational response to external stress of active, contractile cells embedded in a gel-like elastic medium. The theory includes both the forces that arise from the deformation of the matrix as well as forces due to the internal regulation of the stress fibers and focal adhesions of the cell. We calculate the time-dependent response of both the magnitude and the direction of the elastic dipole that characterizes the active forces exerted by the cell, for various situations. For static or quasistatic external stress, cells orient parallel to the stress while for high frequency dynamic external stress, cells orient nearly perpendicular. Both numerical and analytical calculations of these effects are presented. In addition we predict the relaxation time for the cellular response for both slowly and rapidly varying external stresses; several characteristic scaling regimes for the relaxation time as a function of applied frequency are predicted. We also treat the case of cells for which the regulation of the stress fibers and focal adhesions is controlled by strain (instead of stress) and show that the predicted dependence of the cellular orientation on the Poisson ratio of the matrix can differentiate strain vs stress regulation of cellular response.

  2. Dynamical theory of active cellular response to external stress.

    Science.gov (United States)

    De, Rumi; Safran, Samuel A

    2008-09-01

    We present a comprehensive, theoretical treatment of the orientational response to external stress of active, contractile cells embedded in a gel-like elastic medium. The theory includes both the forces that arise from the deformation of the matrix as well as forces due to the internal regulation of the stress fibers and focal adhesions of the cell. We calculate the time-dependent response of both the magnitude and the direction of the elastic dipole that characterizes the active forces exerted by the cell, for various situations. For static or quasistatic external stress, cells orient parallel to the stress while for high frequency dynamic external stress, cells orient nearly perpendicular. Both numerical and analytical calculations of these effects are presented. In addition we predict the relaxation time for the cellular response for both slowly and rapidly varying external stresses; several characteristic scaling regimes for the relaxation time as a function of applied frequency are predicted. We also treat the case of cells for which the regulation of the stress fibers and focal adhesions is controlled by strain (instead of stress) and show that the predicted dependence of the cellular orientation on the Poisson ratio of the matrix can differentiate strain vs stress regulation of cellular response.

  3. Temporal Dynamics of Acute Stress-Induced Dendritic Remodeling in Medial Prefrontal Cortex and the Protective Effect of Desipramine

    DEFF Research Database (Denmark)

    Nava, Nicoletta; Treccani, Giulia; Alabsi, Abdelrahman;

    2015-01-01

    Stressful events are associated with increased risk of mood disorders. Volumetric reductions have been reported in brain areas critical for the stress response, such as medial prefrontal cortex (mPFC), and dendritic remodeling has been proposed as an underlying factor. Here, we investigated...

  4. Molecular Dynamic Simulation of Thin Film Growth Stress Evolution

    Science.gov (United States)

    Zheng, Haifeng

    2011-12-01

    With the increasing demand for thin films across a wide range of technology, especially in electronic and magnetic applications, controlling the stresses in deposited thin films has become one of the more important challenges in modern engineering. It is well known that large intrinsic stress---in the magnitude of several gigapascals---can result during the thin film preparation. The magnitude of stress depends on the deposition technique, film thickness, types and structures of materials used as films and substrates, as well as other factors. Such large intrinsic stress may lead to film cracking and peeling in case of tensile stress, and delamination and blistering in case of compression. However it may also have beneficial effects on optoelectronics and its applications. For example, intrinsic stresses can be used to change the electronic band gap of semiconducting materials. The far-reaching fields of microelectronics and optoelectronics depend critically on the properties, behavior, and reliable performance of deposited thin films. Thus, understanding and controlling the origins and behavior of such intrinsic stresses in deposited thin films is a highly active field of research. In this study, on-going tensile stress evolution during Volmer-Weber growth mode was analyzed through numerical methods. A realistic model with semi-cylinder shape free surfaces was used and molecular dynamics simulations were conducted. Simulations were at room temperature (300 K), and 10 nanometer diameter of islands were used. A deposition rate that every 3 picoseconds deposit one atom was chosen for simulations. The deposition energy was and lattice orientation is [0 0 1]. Five different random seeds were used to ensure average behaviors. In the first part of this study, initial coalescence stress was first calculated by comparing two similar models, which only differed in the distance between two neighboring islands. Three different substrate thickness systems were analyzed to

  5. Motional Effect on Wall Shear Stresses

    DEFF Research Database (Denmark)

    Kock, Samuel Alberg; Torben Fründ, Ernst; Yong Kim, Won

    Atherosclerosis is the leading cause of death and severe disability. Wall Shear Stress (WSS), the stress exerted on vessel walls by the flowing blood is a key factor in the development of atherosclerosis. Computational Fluid Dynamics (CFD) is widely used for WSS estimations. Most CFD simulations...... are based on static models to ease computational burden leading to inaccurate estimations. The aim of this work was to estimate the effect of vessel wall deformations (expansion and bending) on WSS levels....

  6. Factors affecting the dynamic response of pre-stressed anchors after transient excitation

    Institute of Scientific and Technical Information of China (English)

    Xu Huijun; Li Qingfeng

    2011-01-01

    The wide application of pre-stressed bolting technology in coal mine tunnels has made the nondestructive stress wave reflection method of determining bolting quality an important one.The effect of the support plate on the dynamic response of the pre-stressed anchor is of particular interest.A theoreticalanalysis and numerical simulations are used to identify the factors affecting the contact stress between the support plate and the rock wall.A formula allowing the calculation of contact stress is presented.Stress wave propagation through the nut,support plate,and rock wall are predicted.The dynamic response signals were measured in the field using prestressed anchors pre-tightened to different torques.The effects from the support plate on the dynamic response were recorded and the results compared to the predictions of pre-stressed anchor.This work provides a theoretical reference for the signal processing of dynamic reflected wave signals in anchor bolts.

  7. DYNAMIC EFFECTIVE SHEAR STRENGTH OF SATURATED SAND

    Institute of Scientific and Technical Information of China (English)

    邵生俊; 谢定义

    2002-01-01

    The dynamic effective shear strength of saturated sand under cyclic loading is discussed in this paper. The discussion includes the transient time dependency behaviors based on the analysis of the results obtained in conventional cyclic triaxial tests and cyclic torsional shear triaxial tests. It has been found that the dynamic effective shear strength is composed of effective frictional resistance and viscous resistance, which are characterized by the strain rate dependent feature of strength magnitude, the coupling of consolidation stress with cyclic stress and the dependency of time needed to make the soil strength suffciently mobilized, and can also be expressed by the extended Mohr-Coulomb's law. The two strength parameters of the dynamic effective internal frictional angle φd and the dynamic viscosity coefficient η are determined. The former is unvaried for different number of cyclic loading, dynamic stress form and consolidation stress ratio. And the later is unvaried for the different dynamic shear strain rate γt developed during the sand liquefaction, but increases with the increase of initial density of sand. The generalization of dynamic effective stress strength criterion in the 3-dimensional effective stress space is studied in detail for the purpose of its practical use.

  8. The effect of academic stress and attachment stress on stress-eaters and stress-undereaters.

    Science.gov (United States)

    Emond, Michael; Ten Eycke, Kayla; Kosmerly, Stacey; Robinson, Adele Lafrance; Stillar, Amanda; Van Blyderveen, Sherry

    2016-05-01

    It is well established that stress is related to changes in eating patterns. Some individuals are more likely to increase their overall food intake under conditions of stress, whereas others are more likely to consume less food when stressed. Attachment style has been linked to disordered eating and eating disorders; however, comparisons of eating behaviors under attachment versus other types of stress have yet to be explored. The present laboratory study examined the eating patterns in self-identified stress-undereaters and stress-eaters under various types of stress. More specifically, the study examined the effects of academic and attachment stress on calorie, carbohydrate and sugar consumption within these two groups. Under the guise of critiquing student films, university students viewed either one of two stress-inducing videos (academic stress or attachment stress, both designed to be emotionally arousing) or a control video (designed to be emotionally neutral), and their food intake was recorded. Results demonstrated that the video manipulations were effective in inducing stress. Differential patterns of eating were noted based on group and stress condition. Specifically, stress-undereaters ate fewer calories, carbohydrates and sugars than stress-eaters in the academic stress condition, but not in the attachment stress or control condition. Findings suggest that specific types of stressors may influence eating behaviors differently.

  9. Telomere dynamics may link stress exposure and ageing across generations.

    Science.gov (United States)

    Haussmann, Mark F; Heidinger, Britt J

    2015-11-01

    Although exposure to stressors is known to increase disease susceptibility and accelerate ageing, evidence is accumulating that these effects can span more than one generation. Stressors experienced by parents have been reported to negatively influence the longevity of their offspring and even grand offspring. The mechanisms underlying these long-term, cross-generational effects are still poorly understood, but we argue here that telomere dynamics are likely to play an important role. In this review, we begin by surveying the current connections between stress and telomere dynamics. We then lay out the evidence that exposure to stressors in the parental generation influences telomere dynamics in offspring and potentially subsequent generations. We focus on evidence in mammalian and avian studies and highlight several promising areas where our understanding is incomplete and future investigations are critically needed. Understanding the mechanisms that link stress exposure across generations requires interdisciplinary studies and is essential to both the biomedical community seeking to understand how early adversity impacts health span and evolutionary ecologists interested in how changing environmental conditions are likely to influence age-structured population dynamics.

  10. Numerical Analysis of Frictional Heat-Stress Coupled Field at Dynamic Contact

    Institute of Scientific and Technical Information of China (English)

    张一兵; 刘佐民

    2004-01-01

    A new analysis method was developed to simulate the dynamic process of a frictional heat-stress coupled field.The relationship between the frictional heat and the thermal stress was investigated for concave cylinder contact conditions.The results show that, as a nonlinear contact problem, the frictional heat at the contact areas changes with moving velocity in both value and distribution, and that the transient frictional heat at the dynamic condition has a peak within a cycle.The dynamic process of friction heat and thermal stresses affects diffusion of the frictional effects.The result can be helpful for dynamic simulation of diffusion lubrication of elements at elevated temperatures.

  11. Analysis of interlaminar stress and nonlinear dynamic response for composite laminated plates with interfacial damage

    Science.gov (United States)

    Zhu, F. H.; Fu, Y. M.

    2008-12-01

    By considering the effect of interfacial damage and using the variation principle, three-dimensional nonlinear dynamic governing equations of the laminated plates with interfacial damage are derived based on the general six-degrees-of-freedom plate theory towards the accurate stress analysis. The solutions of interlaminar stress and nonlinear dynamic response for a simply supported laminated plate with interfacial damage are obtained by using the finite difference method, and the results are validated by comparison with the solution of nonlinear finite element method. In numerical calculations, the effects of interfacial damage on the stress in the interface and the nonlinear dynamic response of laminated plates are discussed.

  12. Dynamic neural activity during stress signals resilient coping

    OpenAIRE

    Sinha, Rajita; Lacadie, Cheryl M; Constable, R. Todd; Seo, Dongju

    2016-01-01

    We live in a time of increasing terror, stress, and trauma, and yet humans show a remarkable ability to cope under high stress states. How the brain supports such active resilient coping is not well-understood. Findings showed high stress levels are accompanied by dynamic brain signals in circuits representing the stress reaction, adaptation, and behavioral control responses. In addition, a ventromedial prefrontal cortical region showed initial decreases in brain activation, but then mobilize...

  13. A Finite Element Solution for Barrel Dynamic Stress

    Institute of Scientific and Technical Information of China (English)

    ZENG Zhi-yin; NING Bian-fang; WANG Zai-sen

    2007-01-01

    With the APDL language of ANSYS finite element analysis software, the solution program for barrel dynamic stress is developed. The paper describes the pivotal problems of dynamic strength design and provides a foundation for realizing the engineering and programming of barrel dynamic strength design.

  14. Dynamic stress intensity factor KⅢ and dynamic crack propagation characteristics of anisotropic materials

    Institute of Scientific and Technical Information of China (English)

    GAO Xin; WANG Han-gong; KANG Xing-wu

    2008-01-01

    Based on the mechanics of anisotropic materials,the dynamic propagation problem of a mode Ⅲ crack in an infinite anisotropic body is investigated.Stress,strain and displacement around the crack tip are expressed as an analytical complex function,which can be represented in power series.Constant coefficients of series are determined by boundary conditions.Expressions of dynamic stress intensity factors for a mode Ⅲ crack are obtained.Components of dynamic stress,dynamic strain and dynamic displacement around the crack tip are derived.Crack propagation characteristics are represented by the mechanical properties of the anisotropic materials,i.e.,crack propagation velocity M and the parameter α.The faster the crack velocity is,the greater the maximums of stress components and dynamic displacement components around the crack tip are.In particular,the parameter α affects stress and dynamic displacement around the crack tip.

  15. Biaxial stress effects on magnetization perpendicular to the stress plane

    Energy Technology Data Exchange (ETDEWEB)

    Sablik, M.J.; Kwun, H.; Burkhardt, G.L. [Southwest Research Inst., San Antonio, TX (United States); Langman, R.A. [Univ. of Tasmania, Hobart, Tasmania (Australia)

    1995-11-01

    Effects of biaxial stress in steel on magnetization in a direction normal to the stress plane were investigated both theoretically and experimentally. The two results, which agreed qualitatively, showed that the magnetization in the normal direction generally decreased with the absolute value of the sum of the two principal stresses. The implication to nondestructive measurements of biaxial stress is discussed.

  16. Effective stress coefficient for uniaxial strain condition

    DEFF Research Database (Denmark)

    Alam, Mohammad Monzurul; Fabricius, Ida Lykke

    2012-01-01

    the reason for change in effective stress coefficient under stress. Our model suggests that change in effective stress coefficient will be higher at uniaxial stress condition than at hydrostatic condition. We derived equations from the original definition of Biot to estimate effective stress coefficient from...... one dimensional rock mechanical deformation. We further investigated the effect of boundary condition on the stress dependency of effective stress coefficient and discussed its application in reservoir study. As stress field in the reservoirs are most unlikely to be hydrostatic, effective stress...

  17. Dynamic residual stress in thermal sprayed coatings

    Institute of Scientific and Technical Information of China (English)

    Wang Zhiping; Yang Yuanyuan

    2005-01-01

    With the modified Almen method, the forming and development process of residual stress in a thermal sprayed coating has been obtained. The test results identify that the residual stress in a coating is depend on coating material properties, technique and coating thickness. The paper pays much attention to the hysteresis between the coating temperature and residual stress in the coating or between the applied stress and the strain of the coating, and confirms that the fact is resulted from the"Gas Fix" character of a thermal sprayed coating.

  18. Measuring Propellant Stress Relaxation Modulus Using Dynamic Mechanical Analyzer

    Science.gov (United States)

    2017-03-29

    P. N., Singh, P. P., and Bhattacharya, B., “Determination of Activation Energy of Relaxation Events in Composite Solid Propellants by Dynamic...Article 3. DATES COVERED (From - To) 04 August 2016 – 29 March 2017 4. TITLE AND SUBTITLE Measuring Propellant Stress Relaxation Modulus Using Dynamic...ERC 14. ABSTRACT A method for determining the stress relaxation master curve of solid rocket propellants was developed. The propellant was tested in

  19. Dynamic neural activity during stress signals resilient coping.

    Science.gov (United States)

    Sinha, Rajita; Lacadie, Cheryl M; Constable, R Todd; Seo, Dongju

    2016-08-02

    Active coping underlies a healthy stress response, but neural processes supporting such resilient coping are not well-known. Using a brief, sustained exposure paradigm contrasting highly stressful, threatening, and violent stimuli versus nonaversive neutral visual stimuli in a functional magnetic resonance imaging (fMRI) study, we show significant subjective, physiologic, and endocrine increases and temporally related dynamically distinct patterns of neural activation in brain circuits underlying the stress response. First, stress-specific sustained increases in the amygdala, striatum, hypothalamus, midbrain, right insula, and right dorsolateral prefrontal cortex (DLPFC) regions supported the stress processing and reactivity circuit. Second, dynamic neural activation during stress versus neutral runs, showing early increases followed by later reduced activation in the ventrolateral prefrontal cortex (VLPFC), dorsal anterior cingulate cortex (dACC), left DLPFC, hippocampus, and left insula, suggested a stress adaptation response network. Finally, dynamic stress-specific mobilization of the ventromedial prefrontal cortex (VmPFC), marked by initial hypoactivity followed by increased VmPFC activation, pointed to the VmPFC as a key locus of the emotional and behavioral control network. Consistent with this finding, greater neural flexibility signals in the VmPFC during stress correlated with active coping ratings whereas lower dynamic activity in the VmPFC also predicted a higher level of maladaptive coping behaviors in real life, including binge alcohol intake, emotional eating, and frequency of arguments and fights. These findings demonstrate acute functional neuroplasticity during stress, with distinct and separable brain networks that underlie critical components of the stress response, and a specific role for VmPFC neuroflexibility in stress-resilient coping.

  20. Research on Dynamic Stress Triggering at Chinese North-South Seismic Belt in Recent Years

    Science.gov (United States)

    Zhang, B.

    2012-12-01

    Seismic stress triggering refers to the influence induced by one earthquake to the nearby and remote seismic activity, including static stress triggering and dynamic stress triggering. Scientists have studied static stress triggering for a long time and have got lots of achievement. However, the researches of dynamic stress triggering were scarce. The time we actually researched on seismic dynamic stress triggering was after the Landers earthquake in 1992, USA. Due to the superiority of dynamic stress triggering in explaining remote triggering, it has been developing rapidly in recent years. China locates between the Pacific Ocean seismic zone and the Asia-Europe seismic zone, so Chinese mainland and its periphery has more strong shocks. Although Chinese seismologists study seismic dynamic stress triggering later, it is necessary to study seismic dynamic stress triggering in China. In order to explore Chinese seismic dynamic stress triggering, we take Chinese North-South seismic belt as an example in this article. With the method of calculating seismic dynamic stress, we researched the triggered situation of some strong earthquakes in Chinese North-South seismic belt: calculate stress tensor and coulomb stress in triggered area, including M8.0 earthquake of 2000 in Sumatra triggered M5.8 earthquake of Jingtai in Gansu and M6.5 earthquake of Burma, M7.9 earthquake of 2003 in border of China, Russia and Mongolia triggered M6.1 earthquake of Minle-Shandan and M5.2 earthquake of Minxian in Gansu, M8.7 earthquake of 2004 in Sumatra triggered M5.1 earthquake of Shuangbai and M5.1 earthquake of Simao in Yunnan. The results show that the dynamic stress peak value on triggered fault produced by several strong shocks all exceeds to triggering threshold value. All in all, the earthquake activity is triggered easily in the North-South seismic belt, but the earthquakes in different area have different triggering effect in the North-South seismic belt, probably influenced by the

  1. Effects of Boron Nutrition and Water Stress on Nitrogen Fixation, Seed δ 15N and δ 13C Dynamics, and Seed Composition in Soybean Cultivars Differing in Maturities

    Science.gov (United States)

    Bellaloui, Nacer; Mengistu, Alemu

    2015-01-01

    Therefore, the objective of the current research was to investigate the effects of foliar B nutrition on seed protein, oil, fatty acids, and sugars under water stress conditions. A repeated greenhouse experiment was conducted using different maturity group (MG) cultivars. Plants were well-watered with no foliar B (W − B), well-watered with foliar B (W + B), water-stressed with no foliar B (WS − B), and water-stressed with foliar B (WS + B). Foliar B was applied at rate of 0.45 kg·ha−1 and was applied twice at flowering and at seed-fill stages. The results showed that seed protein, sucrose, fructose, and glucose were higher in W + B treatment than in W − B, WS + B, and WS − B. The increase in protein in W + B resulted in lower seed oil, and the increase of oleic in WS − B or WS + B resulted in lower linolenic acid. Foliar B resulted in higher nitrogen fixation and water stress resulted in seed δ 15N and δ 13C alteration. Increased stachyose indicated possible physiological and metabolic changes in carbon and nitrogen pathways and their sources under water stress. This research is beneficial to growers for fertilizer management and seed quality and to breeders to use 15N/14N and 13C/12C ratios and stachyose to select for drought tolerance soybean. PMID:25667936

  2. Effects of Boron Nutrition and Water Stress on Nitrogen Fixation, Seed δ15N and δ13C Dynamics, and Seed Composition in Soybean Cultivars Differing in Maturities

    Directory of Open Access Journals (Sweden)

    Nacer Bellaloui

    2015-01-01

    Full Text Available Therefore, the objective of the current research was to investigate the effects of foliar B nutrition on seed protein, oil, fatty acids, and sugars under water stress conditions. A repeated greenhouse experiment was conducted using different maturity group (MG cultivars. Plants were well-watered with no foliar B (W − B, well-watered with foliar B (W + B, water-stressed with no foliar B (WS − B, and water-stressed with foliar B (WS + B. Foliar B was applied at rate of 0.45 kg·ha−1 and was applied twice at flowering and at seed-fill stages. The results showed that seed protein, sucrose, fructose, and glucose were higher in W + B treatment than in W − B, WS + B, and WS − B. The increase in protein in W + B resulted in lower seed oil, and the increase of oleic in WS − B or WS + B resulted in lower linolenic acid. Foliar B resulted in higher nitrogen fixation and water stress resulted in seed δ15N and δ13C alteration. Increased stachyose indicated possible physiological and metabolic changes in carbon and nitrogen pathways and their sources under water stress. This research is beneficial to growers for fertilizer management and seed quality and to breeders to use 15N/14N and 13C/12C ratios and stachyose to select for drought tolerance soybean.

  3. Does Salicylic Acid (SA) Improve Tolerance to Salt Stress in Plants? A Study of SA Effects On Tomato Plant Growth, Water Dynamics, Photosynthesis, and Biochemical Parameters.

    Science.gov (United States)

    Mimouni, Hajer; Wasti, Salma; Manaa, Arafet; Gharbi, Emna; Chalh, Abdellah; Vandoorne, Bertrand; Lutts, Stanley; Ben Ahmed, Hela

    2016-03-01

    Environmental stresses such as salinity directly impact crop growth, and by extension, world food supply and societal prosperity. It is estimated that over 800 million hectares of land throughout the world are salt-affected. In arid and semi-arid regions, salt concentration can be close to that in the seawater. Hence, there are intensive efforts to improve plant tolerance to salinity and other environmental stressors. Salicylic acid (SA) is an important signal molecule for modulating plant responses to stress. In the present study, we examined, on multiple plant growth related endpoints, whether SA applied through the rooting medium could mitigate the adverse effects of salinity on tomato (Solanum lycopersicum) cv. Marmande. The latter is a hitherto understudied tomato plant from the above perspective; it is a classic variety that produces the large ribbed tomatoes in the Mediterranean and consumed worldwide. We found salt stress negatively affected the growth of cv. Marmande tomato plants. However, the SA-treated plants had greater shoot and root dry mass, leaf area compared to untreated plants when exposed to salt stress. Application of SA restores photosynthetic rates and photosynthetic pigment levels under salt (NaCl) exposure. Leaf water, osmotic potential, stomatal conductance transpiration rate, and biochemical parameters were also ameliorated in SA-treated plants under saline stress conditions. Overall, these data illustrate that SA increases cv. Marmande tomato growth by improving photosynthesis, regulation and balance of osmotic potential, induction of compatible osmolyte metabolism, and alleviating membrane damage. We suggest salicylic acid might be considered as a potential growth regulator to improve tomato plant salinity stress resistance, in the current era of global climate change.

  4. METHOD FOR CALCULATION OF STRESSED STATE SUBSTANTIATED BY DYNAMIC MICROTWIN

    Directory of Open Access Journals (Sweden)

    V. V. Vlashevich

    2014-01-01

    Full Text Available Method for calculation of the stressed state in a dynamic twin has been developed on the basis of a non-thin non-coherent micro-twin model with continuous distribution of twinning dislocations at twin boundaries. In this case there is no additional generation with the help of twinning dislocation source. The model takes into account that the twin has coherent and noncoherent boundary sections. The developed model has made it possible to take into consideration a form of non-coherent sections of twinning boundaries in calculations of stressed and deformed state at dynamic twins. It has been established that localized stresses are migrating together with non-coherent sections of the twin. Normal stresses σxx change their sign in relation to direction of the twin development. Shear stresses σxy are alternating in signs in relation to an axis which is perpendicular to the direction of the twin development and which is passing through a mid-point of non-coherent twin section. Distribution of stresses σyy и σyz has similar configuration. Stresses σzx in the second and fourth quarters of XOY plane are negative and the stresses in the first and third quarters are positive. Distribution of stresses σzz practically does not differ from distribution of stresses σyy according to configuration but numerical values of stress tensor component data are different.The results have been obtained without thin twin model that permits to consider only elastic stage of the twinning process. The executed stress calculations at dynamic twin are important for forecasting at the accumulation stage of damage origination which is caused by twinning destruction and permit to improve forecasting accuracy of technical system resources on the basis of twinning materials such as alloys based on iron, copper, zinc, aluminium, titanium.

  5. Dynamic Treatment Effects.

    Science.gov (United States)

    Heckman, James J; Humphries, John Eric; Veramendi, Gregory

    2016-02-01

    This paper develops robust models for estimating and interpreting treatment effects arising from both ordered and unordered multistage decision problems. Identification is secured through instrumental variables and/or conditional independence (matching) assumptions. We decompose treatment effects into direct effects and continuation values associated with moving to the next stage of a decision problem. Using our framework, we decompose the IV estimator, showing that IV generally does not estimate economically interpretable or policy relevant parameters in prototypical dynamic discrete choice models, unless policy variables are instruments. Continuation values are an empirically important component of estimated total treatment effects of education. We use our analysis to estimate the components of what LATE estimates in a dynamic discrete choice model.

  6. Intact soft clay’s critical response to dynamic stress paths on different combinations of principal stress orientation

    Institute of Scientific and Technical Information of China (English)

    沈扬; 周建; 龚晓南; 刘汉龙

    2008-01-01

    Comprehensive tests on Hangzhou intact soft clay were performed, which were used to obtain the soils’ critical response to undrained dynamic stress paths under different combinations of principal stress orientation. The different combinations included cyclic principal stress rotation (CPSR for short), cyclic shear with abrupt change of principal stress orientation (CAPSO for short) and cyclic shear with fixed principal stress orientation (CFPSO for short). On one side, under all these stress paths, samples have obvious strain inflection points and shear bands, and the excess pore water pressure is far from the level of initial effective confining pressure at failure. Stress paths of major principal stress orientation (α) alternating from negative and positive have quite different influence on soil’s properties with those in which α is kept negative or positive. On the other side, due to the soil’s strongly initial anisotropy, samples under double-amplitudes CPSR and CAPSO (or single-amplitude CPSR and CFPSO) have similar properties on dynamic shear strength and pore water pressure development tendency when α is kept within ±45°, while have quite different properties when α oversteps ±45°.

  7. Correlation between electron-irradiation defects and applied stress in graphene: A molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Kida, Shogo; Yamamoto, Masaya; Kawata, Hiroaki; Hirai, Yoshihiko; Yasuda, Masaaki, E-mail: yasuda@pe.osakafu-u.ac.jp [Department of Physics and Electronics, Osaka Prefecture University, Sakai, Osaka 599-8531 (Japan); Tada, Kazuhiro [Department of Electrical and Control Systems Engineering, National Institute of Technology, Toyama College, Toyama 939-8630 (Japan)

    2015-09-15

    Molecular dynamics (MD) simulations are performed to study the correlation between electron irradiation defects and applied stress in graphene. The electron irradiation effect is introduced by the binary collision model in the MD simulation. By applying a tensile stress to graphene, the number of adatom-vacancy (AV) and Stone–Wales (SW) defects increase under electron irradiation, while the number of single-vacancy defects is not noticeably affected by the applied stress. Both the activation and formation energies of an AV defect and the activation energy of an SW defect decrease when a tensile stress is applied to graphene. Applying tensile stress also relaxes the compression stress associated with SW defect formation. These effects induced by the applied stress cause the increase in AV and SW defect formation under electron irradiation.

  8. Effective stress coefficient for uniaxial strain condition

    DEFF Research Database (Denmark)

    Alam, M.M.; Fabricius, I.L.

    2012-01-01

    one dimensional rock mechanical deformation. We further investigated the effect of boundary condition on the stress dependency of effective stress coefficient and discussed its application in reservoir study. As stress field in the reservoirs are most unlikely to be hydrostatic, effective stress...... determined under uniaxial strain condition will be more relevant in reservoir studies. Copyright 2012 ARMA, American Rock Mechanics Association....

  9. Effective stress coefficient for uniaxial strain condition

    DEFF Research Database (Denmark)

    Alam, Mohammad Monzurul; Fabricius, Ida Lykke

    2012-01-01

    one dimensional rock mechanical deformation. We further investigated the effect of boundary condition on the stress dependency of effective stress coefficient and discussed its application in reservoir study. As stress field in the reservoirs are most unlikely to be hydrostatic, effective stress...

  10. Till stress do us part: On the interplay between perceived stress and communication network dynamics.

    Science.gov (United States)

    Kalish, Yuval; Luria, Gil; Toker, Sharon; Westman, Mina

    2015-11-01

    This study of perceived stress and communication networks fills 2 theoretical gaps in the literature: First, drawing predominantly on conservation of resource theory and faultline theory, we demonstrate the role of stress as an "engine of action" in network evolution. Second, we extend the stress literature to the interpersonal domain by arguing that others' levels of stress influence the individual's communication network, and this, in turn, changes his or her stress level. At 3 time points, we evaluated the communication ties and perceived stress in a unique field setting comprising 115 male participants (in 6 groups) performing group-based tasks. We introduce stochastic actor-based models for the coevolution of network ties and actor attributes, statistical models that enable causal inferences to be drawn regarding the interplay between dynamic networks and individual attributes. Using these models, we find that over time, individuals experiencing higher levels of perceived stress were less likely to create new communication ties and were more likely to maintain existing ties to others. Participants also tended to communicate with similarly stressed others. Such communication network dynamics further increased individuals' levels of perceived stress over time, leading to stress-related vicious cycles. We discuss organizational implications that relate to stress and network-related interventions.

  11. Laboratory evidence for particle mobilization as a mechanism for permeability enhancement via dynamic stressing

    Science.gov (United States)

    Candela, Thibault; Brodsky, Emily E.; Marone, Chris; Elsworth, Derek

    2014-04-01

    It is well-established that seismic waves can increase the permeability in natural systems, yet the mechanism remains poorly understood. We investigate the underlying mechanics by generating well-controlled, repeatable permeability enhancement in laboratory experiments. Pore pressure oscillations, simulating dynamic stresses, were applied to intact and fractured Berea sandstone samples under confining stresses of tens of MPa. Dynamic stressing produces an immediate permeability enhancement ranging from 1 to 60%, which scales with the amplitude of the dynamic strain (7×10-7 to 7×10-6) followed by a gradual permeability recovery. We investigated the mechanism by: (1) recording deformation of samples both before and after fracturing during the experiment, (2) varying the chemistry of the water and therefore particle mobility, (3) evaluating the dependence of permeability enhancement and recovery on dynamic stress amplitude, and (4) examining micro-scale pore textures of the rock samples before and after experiments. We find that dynamic stressing does not produce permanent deformation in our samples. Water chemistry has a pronounced effect on the sensitivity to dynamic stressing, with the magnitude of permeability enhancement and the rate of permeability recovery varying with ionic strength of the pore fluid. Permeability recovery rates generally correlate with the permeability enhancement sensitivity. Microstructural observations of our samples show clearing of clay particulates from fracture surfaces during the experiment. From these four lines of evidence, we conclude that a flow-dependent mechanism associated with mobilization of fines controls both the magnitude of the permeability enhancement and the recovery rate in our experiments. We also find that permeability sensitivity to dynamic stressing increases after fracturing, which is a process that generates abundant particulate matter in situ. Our results suggest that fluid permeability in many areas of the

  12. Acoustoelastic effect in stressed heterostructures.

    Science.gov (United States)

    Osetrov, Alexander Vladimirovich; Fröhlich, Heinz-Jürgen; Koch, Reinhold; Chilla, Eduard

    2002-01-01

    Mechanical stresses influence the phase velocity of acoustic waves, known as the AE (acoustoelastic) effect. In order to calculate the AE effect of biaxially stressed layered systems, we extended the transfer matrix method for acoustic wave propagation by considering the change of the density, the influence of residual stress, and the modification of the elastic stiffness tensor by residual strain and by third-order constants. The generalized method is applied to the calculation of the angular dispersion of the AE effect for transverse bulk modes and surface acoustic waves on Ge(001). Our calculations reveal that the AE effect significantly depends on the propagation direction and can even change sign. The maximal velocity change occurs for transversally polarized waves propagating parallel to the [110] direction. For the layered Ge/Si(001) system, the AE effect is investigated for Love modes propagating in the [100] and [110] directions. The AE effect increases rapidly with increasing layer thickness and almost reaches its maximal value when the wave still penetrates into the unstressed substrate.

  13. Dynamic ADI computations of thermoelastic stresses in crystalline laser media

    Energy Technology Data Exchange (ETDEWEB)

    Gelinas, R.J.; Doss, S.K.; Carlson, N.N.

    1985-01-01

    This article considers thermoelastic effects which influence both the thermal engineering design and optical propagation in solid state high average power laser (HAPL) systems. The methods and computations described here have been developed for applications, ultimately, to crystalline slabs with arbitrary symmetry properties and with arbitrary spatial orientations between crystalline axes and slab configurations. For this, accurate numerical solutions are required simultaneously for the heat equation and Hooke's law in thier most general tensor forms. Prompted by the optical problem requirements in HAPL systems, this work utilizes implementations of Eulerian discretizations and dynamic ADI methods for solving general fourth-order elliptic partial differential equations (PDE's) which describe stress potentials in anisotropic media. These formulations can provide both steady state and transient PDE solutions. This article concludes with computed results for trigonal Al/sub 2/O/sub 3/ crystal deformations in various crystal axes/slab orientations.

  14. Analysis of Deformation in Inconel 718 When the Stress Anomaly and Dynamic Strain Aging Coexist

    Science.gov (United States)

    Follansbee, Paul S.

    2016-09-01

    Deformation in Inconel 718 in the presence of combined effects of the stress anomaly and dynamic strain aging is analyzed according to an internal state variable model formulation. The analysis relies on the availability of experimental data in regimes of behavior where both the stress anomaly and dynamic strain aging are absent. A model that introduces two internal state variables—one characterizing interactions of dislocations with solute atoms and one characterizing interaction of dislocations with precipitates—is shown to adequately describe the temperature and strain-rate dependence of the yield stress in several superalloy systems. Strain hardening is then added with a third internal state variable to enable description of the full stress-strain curve. These equations are extrapolated into regimes where the stress anomaly and dynamic strain aging are present to identify signatures of their effects and to compare to similar analyses in a variety of metal systems. Dynamic strain aging in Inconel 718 follows similar trends to those observed previously. The magnitude of the stress anomaly tracks measurements of stress vs test temperature in pure Ni3Al. Several trends in the strain-rate sensitivity of elevated temperature deformation in superalloys are identified based on limited availability of measurements over a wide range of strain rates or tests using strain-rate changes.

  15. Stresses and elastic constants of crystalline sodium, from molecular dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Schiferl, S.K.

    1985-02-01

    The stresses and the elastic constants of bcc sodium are calculated by molecular dynamics (MD) for temperatures to T = 340K. The total adiabatic potential of a system of sodium atoms is represented by pseudopotential model. The resulting expression has two terms: a large, strictly volume-dependent potential, plus a sum over ion pairs of a small, volume-dependent two-body potential. The stresses and the elastic constants are given as strain derivatives of the Helmholtz free energy. The resulting expressions involve canonical ensemble averages (and fluctuation averages) of the position and volume derivatives of the potential. An ensemble correction relates the results to MD equilibrium averages. Evaluation of the potential and its derivatives requires the calculation of integrals with infinite upper limits of integration, and integrand singularities. Methods for calculating these integrals and estimating the effects of integration errors are developed. A method is given for choosing initial conditions that relax quickly to a desired equilibrium state. Statistical methods developed earlier for MD data are extended to evaluate uncertainties in fluctuation averages, and to test for symmetry. 45 refs., 10 figs., 4 tabs.

  16. Dynamics of Traction Stress Field during Cell Division

    Science.gov (United States)

    Tanimoto, Hirokazu; Sano, Masaki

    2012-12-01

    We report a quantitative measurement of traction stress exerted by dividing eukaryotic cells. The stress field was highly dynamic and sequentially changed as follows: (1) strong and localized as two spots, (2) weak and broadly distributed, and (3) strong and localized as four spots. At the final stage of cytokinesis, the dividing cells exerted strong tensile force on the intercellular bridge. The asymmetry of the traction stress and the orientation of the division axis matched throughout the division process, suggesting the possible role of the mechanical force as a “store” of the orientational information.

  17. Effect of residual stress on peak cap stress in arteries.

    Science.gov (United States)

    Vandiver, Rebecca

    2014-10-01

    Vulnerable plaques are a subset of atherosclerotic plaques that are prone to rupture when high stresses occur in the cap. The roles of residual stress, plaque morphology, and cap stiffness on the cap stress are not completely understood. Here, arteries are modeled within the framework of nonlinear elasticity as incompressible cylindrical structures that are residually stressed through differential growth. These structures are assumed to have a nonlinear, anisotropic, hyperelastic response to stresses in the media and adventitia layers and an isotropic response in the intima and necrotic layers. The effect of differential growth on the peak stress is explored in a simple, concentric geometry and it is shown that axial differential growth decreases the peak stress in the inner layer. Furthermore, morphological risk factors are explored. The peak stress in residually stressed cylinders is not greatly affected by changing the thickness of the intima. The thickness of the necrotic layer is shown to be the most important morphological feature that affects the peak stress in a residually stressed vessel.

  18. Fluid Dynamical Consequences of Current and Stress-Energy Conservation

    Science.gov (United States)

    Scofield, Dillon; Huq, Pablo

    The dynamical consequences of fluid current conservation combined with the conservation of fluid stress-energy are used to develop the geometrodynamical theory of fluid flow (GTF). In the derivation of the GTF, we highlight the fact the continuity equation, equivalently the conservation of current density, implies the existence of the fluid dynamical vortex field. The vortex field transports part of the stress-energy; the other part of the stress-energy is transported by the fluid inertia field. Two channels of energy dissipation are determined by the GTF. One is an analog of the Joule heating found in electrodynamics. This follows from the conservation of stress-energy. The other dissipation channel arises from mechanisms leading to complex-valued constitutive parameters described in the electrodynamical analogy as due to a lossy medium. The dynamical consequences of the continuity equation, combined with the conservation of total stress-energy, then lead to a causal, covariant, theory of fluid flow, consistent with thermodynamics for all physically possible flow rates.

  19. Dynamic Investigation of Interface Stress on Below-Knee Residual Limb in a Prosthetic Socket

    Institute of Scientific and Technical Information of China (English)

    贾晓红; 张明; 王人成; 金德闻

    2004-01-01

    The dynamic effects of inertial loads on the interface stresses between a residual limb and the trans-tibial prosthetic socket were investigated. A 3-D nonlinear finite element model, based on the actual geometry of the residual limb, including internal bones and socket liner, was developed to study the mechanical interaction between the socket and the residual limb during walking. To simulate the friction/slip boundary conditions between the skin and liner, automated surface-to-surface contact was used. The results show that interface pressure and shear stress have a similar double-peaked waveform shape in the stance phase. The average difference in interface stresses between the cases with and without consideration of inertial forces is 8.4% in the stance phase and 20.1% in the swing phase. The results suggest that the dynamic effects of inertial loads on interface stress distribution during walking must be considered in prosthetic socket design.

  20. Analysis of interlaminar stress and nonlinear dynamic response for composite laminated plates with interfacial damage

    Institute of Scientific and Technical Information of China (English)

    F. H. Zhu; Y. M. Fu

    2008-01-01

    By considering the effect of interfacial damage and using the variation principle, three-dimensional nonli-near dynamic governing equations of the laminated plates with interfacial damage are derived based on the general six-degrees-of-freedom plate theory towards the accurate stress analysis. The solutions of interlaminar stress and nonlinear dynamic response for a simply supported laminated plate with interfacial damage are obtained by using the finite dif-ference method, and the results are validated by compari-son with the solution of nonlinear finite element method. In numerical calculations, the effects of interfacial damage on the stress in the interface and the nonlinear dynamic response of laminated plates are discussed.

  1. Effects of a Father-based In-Home Intervention on Perceived Stress and Family Dynamics in Parents of Children with Autism

    OpenAIRE

    Bendixen, Roxanna M.; Elder, Jennifer H.; Donaldson, Susan; Kairalla, John A.; Valcante, Greg; Ferdig, Richard E.

    2011-01-01

    Parents of children with autism report high rates of stress. Parental differences in stress are inconsistent, with most research demonstrating that mothers report higher levels of stress than fathers. This study explored parental differences pre-post an interdisciplinary in-home training program. Fathers of children with autism were taught an intervention designed to improve their child's social reciprocity and communication, and then trained the mothers. Stress through the PSI and family dyn...

  2. Effects of a Father-based In-Home Intervention on Perceived Stress and Family Dynamics in Parents of Children with Autism

    OpenAIRE

    Bendixen, Roxanna M.; Elder, Jennifer H.; Donaldson, Susan; Kairalla, John A.; Valcante, Greg; Ferdig, Richard E.

    2011-01-01

    Parents of children with autism report high rates of stress. Parental differences in stress are inconsistent, with most research demonstrating that mothers report higher levels of stress than fathers. This study explored parental differences pre-post an interdisciplinary in-home training program. Fathers of children with autism were taught an intervention designed to improve their child's social reciprocity and communication, and then trained the mothers. Stress through the PSI and family dyn...

  3. ELASTIC WAVE SCATTERING AND DYNAMIC STRESS IN COMPOSITE WITH FIBER

    Institute of Scientific and Technical Information of China (English)

    胡超; 李凤明; 黄文虎

    2003-01-01

    Based on the theory of elastic dynamics, multiple scattering of elastic waves and dynamic stress concentrations in fiber-reinforced composite were studied. The analyticalexpressions of elastic waves in different region were presented and an analytic method tosolve this problem was established. The mode coefficients of elastic waves were determinedin accordance with the continuous conditiors of displacement and stress on the boundary ofthe multi-interfaces. By making use of the addition theorem of Hankel functions, theformulations of scattered wave fields in different local coordinates were transformed intothose in one local coordinate to determine the unknown coefficients and dynamic stressconcentration factors. The influence of distance between two inclusions, material propertiesand structural size on the dynamic stress concentration factors near the interfaces wasanalyzed. It indicates in the analysis that distance between two inclusions, materialproperties and structural size has great influence on the dynamic properties of fiber-reinforced composite near the interfaces. As examples, the numerical results of dynamicstress concentration factors near the interfaces in a fiber- reinforced composite are presentedand discussed.

  4. EFFECTIVE STRESS AND STRAIN IN FINITE DEFORMATION

    Institute of Scientific and Technical Information of China (English)

    周喆; 秦伶俐; 黄文彬; 王红卫

    2004-01-01

    Whether the concept of effective stress and strain in elastic-plastic theory is still valid under the condition of finite deformation was mainly discussed. The uni-axial compression experiments in plane stress and plane strain states were chosen for study. In the two kinds of stress states, the stress- strain curve described by logarithm strain and rotated Kirchhoff stress matches the experiments data better than the curves defined by other stressstrain description.

  5. Influence of linear profile modification and loading conditions on the dynamic tooth load and stress of high contact ratio gears

    Science.gov (United States)

    Lee, Chinwai; Lin, Hsiang Hsi; Oswald, Fred B.; Townsend, Dennis P.

    1990-01-01

    A computer simulation for the dynamic response of high-contact-ratio spur gear transmissions is presented. High contact ratio gears have the potential to produce lower dynamic tooth loads and minimum root stress but they can be sensitive to tooth profile errors. The analysis presented examines various profile modifications under realistic loading conditions. The effect of these modifications on the dynamic load (force) between mating gear teeth and the dynamic root stress is presented. Since the contact stress is dependent on the dynamic load, minimizing dynamic loads will also minimize contact stresses. It is shown that the combination of profile modification and the applied load (torque) carried by a gear system has a significant influence on gear dynamics. The ideal modification at one value of applied load will not be the best solution for a different load. High-contact-ratio gears were found to require less modification than standard low-contact-ratio gears. High-contact-ratio gears are more adversely affected by excess modification than by under modification. In addition, the optimal profile modification required to minimize the dynamic load (hence the contact stress) on a gear tooth differs from the optimal modification required to minimize the dynamic root (bending) stress. Computer simulation can help find the design tradeoffs to determine the best profile modification to satisfy the conflicting constraints of minimizing both the load and root stress in gears which must operate over a range of applied loads.

  6. Dynamics of telomerase activity in response to acute psychological stress

    Science.gov (United States)

    Epel, Elissa S.; Lin, Jue; Dhabhar, Firdaus S.; Wolkowitz, Owen M.; Puterman, E; Karan, Lori; Blackburn, Elizabeth H.

    2010-01-01

    Telomerase activity plays an essential role in cel0l survival, by lengthening telomeres and promoting cell growth and longevity. It is now possible to quantify the low levels of telomerase activity in human leukocytes. Low basal telomerase activity has been related to chronic stress in people and to chronic glucocorticoid exposure in vitro. Here we test whether leukocyte telomerase activity changes under acute psychological stress. We exposed 44 elderly women, including 22 high stress dementia caregivers and 22 matched low stress controls, to a brief laboratory psychological stressor, while examining changes in telomerase activity of peripheral blood mononuclear cells (PBMC). At baseline, caregivers had lower telomerase activity levels than controls, but during stress telomerase activity increased similarly in both groups. Across the entire sample, subsequent telomerase activity increased by 18% one hour after the end of the stressor (p<0.01). The increase in telomerase activity was independent of changes in numbers or percentages of monocytes, lymphocytes, and specific T cell types, although we cannot fully rule out some potential contribution from immune cell redistribution in the change in telomerase activity. Telomerase activity increases were associated with greater cortisol increases in response to the stressor. Lastly, psychological response to the tasks (greater threat perception) was also related to greater telomerase activity increases in controls. These findings uncover novel relationships of dynamic telomerase activity with exposure to an acute stressor, and with two classic aspects of the stress response -- perceived psychological stress and neuroendocrine (cortisol) responses to the stressor. PMID:20018236

  7. Effective stress coefficient for uniaxial strain condition

    DEFF Research Database (Denmark)

    Alam, M.M.; Fabricius, I.L.

    2012-01-01

    The effective stress coefficient, introduced by Biot, is used for predicting effective stress or pore pressure in the subsurface. It is not a constant value. It is different for different types of sediment and it is stress dependent. We used a model, based on contact between the grains to describ...

  8. EFFECTS OF ROCK BEHAVIOR AND STRESS CONDITIONON FIELD STRESS DETERMINATION

    Institute of Scientific and Technical Information of China (English)

    D.H.(Steve)Zou

    1995-01-01

    Non-consistency of stress results is often observed during field measurements. In some cases, even the measurements are made at the same location in a massive rockmass, the results can vary widely. In order to solve the problem, extensive research has been carried out to study the major factors which may affect stress determination. They include the rock behaviour and the stress state. For rocks showing non-isotropic behaviour, the values of Young's modulus and Poisson ratio vary with the orientation of loading and measurement. Stress condition in the rock affects the rock behaviour. Furthermore, the loading condition on rock samples during laboratory tests is different from in the field and therefore the determined elastic constants may not represent the field condition. In general, the Young's modulus may depend on the orientation, the loading path, the stress magnitude and the stress ratio. This paper examines in detail the effects of those factors, especially for rocks showing transversely isotropic behaviour. It is found that the discrepancy of stress results from fieldts in this type of rock is mainly due to over simplification of the rock behavior and inadequate use of elastic constants of the rock during stress calculation. A case study is given, which indicates the significance of these factors and demonstrates the proper procedure for stress calculation from

  9. Stress-enhanced Gelation: A Dynamic Nonlinearity of Elasticity

    Science.gov (United States)

    Yao, Norman Y.; Broedersz, Chase P.; Depken, Martin; Becker, Daniel J.; Pollak, Martin R.; MacKintosh, Frederick C.; Weitz, David A.

    2013-01-01

    A hallmark of biopolymer networks is their sensitivity to stress, reflected by pronounced nonlinear elastic stiffening. Here, we demonstrate a distinct dynamical nonlinearity in biopolymer networks consisting of F-actin cross-linked by α-actinin-4. Applied stress delays the onset of relaxation and flow, markedly enhancing gelation and extending the regime of solid-like behavior to much lower frequencies. We show that this macroscopic network response can be accounted for at the single molecule level by the increased binding affinity of the cross-linker under load, characteristic of catch-bond-like behavior. PMID:23383843

  10. Computational Psychometrics for Modeling System Dynamics during Stressful Disasters

    Directory of Open Access Journals (Sweden)

    Pietro Cipresso

    2017-08-01

    Full Text Available Disasters can be very stressful events. However, computational models of stress require data that might be very difficult to collect during disasters. Moreover, personal experiences are not repeatable, so it is not possible to collect bottom-up information when building a coherent model. To overcome these problems, we propose the use of computational models and virtual reality integration to recreate disaster situations, while examining possible dynamics in order to understand human behavior and relative consequences. By providing realistic parameters associated with disaster situations, computational scientists can work more closely with emergency responders to improve the quality of interventions in the future.

  11. Dynamics of the Contact Stress in Granular Media

    Science.gov (United States)

    Glam, B.; Britan, A.; Ben-Dor, G.; Igra, O.; Goldenberg, A.

    2004-07-01

    Experiments were conducted in a vertical shock tube with an optically transparent single straight chain of 20-mm diameter discs made of epoxy. The dynamic time dependent fringe patterns of the stress in the contact points between the discs were registered using a Q-switched YAG laser, a transmission polariscope and CCD cameras. The main details of the experiment, the data acquisition and the computer aid processing are briefly discussed first. Thereafter the stress wave propagation and its reflection at the chain boundaries are analyzed based on the results of photo elastic experiments and their comparison with those obtained using strain gauges.

  12. Impact of an intensive dynamic exercise program on oxidative stress and on the outcome in patients with fibromyalgia

    Directory of Open Access Journals (Sweden)

    Amal F Soliman

    2016-01-01

    Conclusion Twelve weeks of intensive dynamic exercise program should be recommended to patients with FM as it was effective in decreasing the oxidative stress parameters, increasing the antioxidant parameters, and improving the clinical outcome of this disease.

  13. A stress "deafness" effect in European Portuguese.

    Science.gov (United States)

    Correia, Susana; Butler, Joseph; Vigário, Marina; Frota, Sónia

    2015-03-01

    Research on the perception of word stress suggests that speakers of languages with non-predictable or variable stress (e.g., English and Spanish) are more efficient than speakers of languages with fixed stress (e.g., French and Finnish) at distinguishing nonsense words contrasting in stress location. In addition, segmental and suprasegmental cues to word stress may also impact on the ability of speakers to perceive stress. European Portuguese (EP) is a language with variable stress and vowel reduction. Previous studies on EP have identified duration as the main cue for stress. In the present study, we investigated the perception of word stress in EP, both in nuclear (NP) and post-nuclear (PN) positions, by means of three experiments. Experiment I was an ABX discrimination task with stress and phoneme contrasts, without vowel reduction. Experiments 2 and 3 were sequence recall tasks with stress and phoneme contrasts, vowel reduction being added to the stress contrast only in experiment 3. Results showed significantly higher error rates in the stress contrast condition than in the phoneme contrast condition, when duration alone (PN), or duration and pitch accents (NP), are present in the stimuli (experiments I and 2). When vowel reduction is added, EP speakers are able to perceive stress contrasts (experiment 3). The results show that vowel reduction appears to be the most robust cue for stress in EP. In the absence of vowel quality cues, a stress "deafness" effect may emerge in a language with non-predictable stress that combines both suprasegmental and segmental information to signal word stress. These findings have implications for claims of a prosodic-based cross-linguistic perception of word stress in the absence of vowel quality, and for stress "deafness" as a consequence of a predictable stress grammar.

  14. Analysis of the dynamic stress of planar flexible-links parallel robots

    Institute of Scientific and Technical Information of China (English)

    DU Zhaocai; YU Yueqing; YANG Jianxin

    2007-01-01

    This paper presents a method for the dynamic stress analysis of planar parallel robots with flexible links and a rigid moving platform.The finite element-based dynamic model of flexible parallel robots is proposed.The relation between elastic deformations and elastic displacements of the flexible links is investigated,considering the coupling effects of elastic motion and rigid motion.The elastic deformations of links are calculated.Considering the effects of bendingshearing strain and tensile-compression strain,the dynamic stress of the links and its position are derived by using the Kineto-Elastodynamics theory and the Timoshenko beam theory.Due to the flexibility of the links,the dynamic stresses are well illustrated through numerical simulation.Compared with the results of the finite element software SAMCEF,the numerical simulation results show the good coherence and advantages of the analysis method.The dynamic stress analysis is demonstrated to have a significant impact on the analysis,design and control of flexible parallel robots.

  15. Dynamic stress concentrations in thick plates with two holes based on refined theory

    Institute of Scientific and Technical Information of China (English)

    周伟平; 胡超; 刘殿魁

    2014-01-01

    Based on complex variables and conformal mapping, the elastic wave scat-tering and dynamic stress concentrations in the plates with two holes are studied by the refined dynamic equation of plate bending. The problem to be solved is changed to a set of infinite algebraic equations by an orthogonal function expansion method. As examples, under free boundary conditions, the numerical results of the dynamic moment concen-tration factors in the plates with two circular holes are computed. The results indicate that the parameters such as the incident wave number, the thickness of plates, and the spacing between holes have great effects on the dynamic stress distributions. The results are accurate because the refined equation is derived without any engineering hypothese.

  16. Stress Effects on Multiple Memory System Interactions.

    Science.gov (United States)

    Ness, Deborah; Calabrese, Pasquale

    2016-01-01

    Extensive behavioural, pharmacological, and neurological research reports stress effects on mammalian memory processes. While stress effects on memory quantity have been known for decades, the influence of stress on multiple memory systems and their distinct contributions to the learning process have only recently been described. In this paper, after summarizing the fundamental biological aspects of stress/emotional arousal and recapitulating functionally and anatomically distinct memory systems, we review recent animal and human studies exploring the effects of stress on multiple memory systems. Apart from discussing the interaction between distinct memory systems in stressful situations, we will also outline the fundamental role of the amygdala in mediating such stress effects. Additionally, based on the methods applied in the herein discussed studies, we will discuss how memory translates into behaviour.

  17. Stress Effects on Multiple Memory System Interactions

    Directory of Open Access Journals (Sweden)

    Deborah Ness

    2016-01-01

    Full Text Available Extensive behavioural, pharmacological, and neurological research reports stress effects on mammalian memory processes. While stress effects on memory quantity have been known for decades, the influence of stress on multiple memory systems and their distinct contributions to the learning process have only recently been described. In this paper, after summarizing the fundamental biological aspects of stress/emotional arousal and recapitulating functionally and anatomically distinct memory systems, we review recent animal and human studies exploring the effects of stress on multiple memory systems. Apart from discussing the interaction between distinct memory systems in stressful situations, we will also outline the fundamental role of the amygdala in mediating such stress effects. Additionally, based on the methods applied in the herein discussed studies, we will discuss how memory translates into behaviour.

  18. The impact of zinc sulfate addition on the dynamic metabolic profiling of Saccharomyces cerevisiae subjected to long term acetic acid stress treatment and identification of key metabolites involved in the antioxidant effect of zinc.

    Science.gov (United States)

    Wan, Chun; Zhang, Mingming; Fang, Qing; Xiong, Liang; Zhao, Xinqing; Hasunuma, Tomohisa; Bai, Fengwu; Kondo, Akihiko

    2015-02-01

    The mechanisms of how zinc protects the cells against acetic acid toxicity and acts as an antioxidant are still not clear. Here we present results of the metabolic profiling of the eukaryotic model yeast species Saccharomyces cerevisiae subjected to long term high concentration acetic acid stress treatment in the presence and absence of zinc supplementation. Zinc addition decreased the release of reactive oxygen species (ROS) in the presence of chronic acetic acid stress. The dynamic changes in the accumulation of intermediates in central carbon metabolism were observed, and higher contents of intracellular alanine, valine and serine were observed by zinc supplementation. The most significant change was observed in alanine content, which is 3.51-fold of that of the control culture in cells in the stationary phase. Subsequently, it was found that 0.5 g L(-1) alanine addition resulted in faster glucose consumption in the presence of 5 g L(-1) acetic acid, and apparently decreased ROS accumulation in zinc-supplemented cells. This indicates that alanine exerted its antioxidant effect at least partially through the detoxification of acetic acid. In addition, intracellular glutathione (GSH) accumulation was enhanced by zinc addition, which is related to the protection of yeast cells from the oxidative injury caused by acetic acid. Our studies revealed for the first time that zinc modulates cellular amino acid metabolism and redox balance, especially biosynthesis of alanine and glutathione to exert its antioxidant effect.

  19. Spatio-temporal Dynamics and Mechanisms of Stress Granule Assembly.

    Directory of Open Access Journals (Sweden)

    Daisuke Ohshima

    2015-06-01

    Full Text Available Stress granules (SGs are non-membranous cytoplasmic aggregates of mRNAs and related proteins, assembled in response to environmental stresses such as heat shock, hypoxia, endoplasmic reticulum (ER stress, chemicals (e.g. arsenite, and viral infections. SGs are hypothesized as a loci of mRNA triage and/or maintenance of proper translation capacity ratio to the pool of mRNAs. In brain ischemia, hippocampal CA3 neurons, which are resilient to ischemia, assemble SGs. In contrast, CA1 neurons, which are vulnerable to ischemia, do not assemble SGs. These results suggest a critical role SG plays in regards to cell fate decisions. Thus SG assembly along with its dynamics should determine the cell fate. However, the process that exactly determines the SG assembly dynamics is largely unknown. In this paper, analyses of experimental data and computer simulations were used to approach this problem. SGs were assembled as a result of applying arsenite to HeLa cells. The number of SGs increased after a short latent period, reached a maximum, then decreased during the application of arsenite. At the same time, the size of SGs grew larger and became localized at the perinuclear region. A minimal mathematical model was constructed, and stochastic simulations were run to test the modeling. Since SGs are discrete entities as there are only several tens of them in a cell, commonly used deterministic simulations could not be employed. The stochastic simulations replicated observed dynamics of SG assembly. In addition, these stochastic simulations predicted a gamma distribution relative to the size of SGs. This same distribution was also found in our experimental data suggesting the existence of multiple fusion steps in the SG assembly. Furthermore, we found that the initial steps in the SG assembly process and microtubules were critical to the dynamics. Thus our experiments and stochastic simulations presented a possible mechanism regulating SG assembly.

  20. APPROACH FOR LAYOUT OPTIMIZATION OF TRUSS STRUCTURES WITH DISCRETE VARIABLES UNDER DYNAMIC STRESS, DISPLACEMENT AND STABILITY CONSTRAINTS

    Institute of Scientific and Technical Information of China (English)

    SHI Lian-shuan; WANG Yue-fang; SUN Huan-chun

    2006-01-01

    A mathematical model was developed for layout optimization of truss structures with discrete variables subjected to dynamic stress, dynamic displacement and dynamic stability constraints. By using the quasi-static method, the mathematical model of structure optimization under dynamic stress, dynamic displacement and dynamic stability constraints were transformed into one subjected to static stress, displacement and stability constraints. The optimization procedures include two levels, i.e., the topology optimization and the shape optimization. In each level, the comprehensive algorithm was used and the relative difference quotients of two kinds of variables were used to search the optimum solution. A comparison between the optimum results of model with stability constraints and the optimum results of model without stability constraint was given. And that shows the stability constraints have a great effect on the optimum solutions.

  1. Effect of stress on structural brain asymmetry.

    Science.gov (United States)

    Zach, Petr; Vales, Karel; Stuchlik, Ales; Cermakova, Pavla; Mrzilkova, Jana; Koutela, Antonella; Kutova, Martina

    2016-09-01

    There is a growing body of evidence that stressful events may affect the brain not only as a whole, but also in multiple laterality aspects. The present review is aimed at discussing the effect of stress and stress hormones on structural brain asymmetry. Differences and crossroads of functional and structural asymmetry are briefly mentioned throughout the document. The first part of this review summarizes major findings in the field of structural brain asymmetries in animals and humans from the evolutionary perspective. Additionally, effect of stress on animals is discussed generally. The second part then explores asymmetrical effects of stress on structural changes of principal brain areas - amygdala, hippocampus, neocortex, diencephalon, basal forebrain and basal ganglia from the point of normal lateralization, steroids, trauma and genetic factors. At the end we present hypothesis why stress appears to have asymmetrical effects on lateralized brain structures.

  2. Multimillion-atom molecular dynamics simulation of atomic level stresses in Si(111)/Si3N4(0001) nanopixels

    Science.gov (United States)

    Bachlechner, Martina E.; Omeltchenko, Andrey; Nakano, Aiichiro; Kalia, Rajiv K.; Vashishta, Priya; Ebbsjö, Ingvar; Madhukar, Anupam; Messina, Paul

    1998-04-01

    Ten million atom multiresolution molecular-dynamics simulations are performed on parallel computers to determine atomic-level stress distributions in a 54 nm nanopixel on a 0.1 μm silicon substrate. Effects of surfaces, edges, and lattice mismatch at the Si(111)/Si3N4(0001) interface on the stress distributions are investigated. Stresses are found to be highly inhomogeneous in the nanopixel. The top surface of silicon nitride has a compressive stress of +3 GPa and the stress is tensile, -1 GPa, in silicon below the interface.

  3. Shear-stress-controlled dynamics of nematic complex fluids.

    Science.gov (United States)

    Klapp, Sabine H L; Hess, Siegfried

    2010-05-01

    Based on a mesoscopic theory we investigate the nonequilibrium dynamics of a sheared nematic liquid, with the control parameter being the shear stress σ xy (rather than the usual shear rate, γ). To this end we supplement the equations of motion for the orientational order parameters by an equation for γ, which then becomes time dependent. Shearing the system from an isotropic state, the stress-controlled flow properties turn out to be essentially identical to those at fixed γ. Pronounced differences occur when the equilibrium state is nematic. Here, shearing at controlled γ yields several nonequilibrium transitions between different dynamic states, including chaotic regimes. The corresponding stress-controlled system has only one transition from a regular periodic into a stationary (shear-aligned) state. The position of this transition in the σ xy-γ plane turns out to be tunable by the delay time entering our control scheme for σ xy. Moreover, a sudden change in the control method can stabilize the chaotic states appearing at fixed γ.

  4. Distribution of Side Abutment Stress in Roadway Subjected to Dynamic Pressure and Its Engineering Application

    Directory of Open Access Journals (Sweden)

    Yao Qiangling

    2015-01-01

    Full Text Available The borehole stress-meter was employed in this study to investigate the distribution of the side abutment stress in roadway subjected to dynamic pressure. The results demonstrate that the side abutment stress of the mining roadway reaches a peak value when the distance to the gob is 8 m and the distribution curve of the side abutment stress can be divided into three zones: stress rising zone, stress stabilizing zone, and stress decreasing zone. Further numerical investigation was carried out to study the effect of the coal mass strength, coal seam depth, immediate roof strength, and thickness on the distribution of the side abutment stress. Based on the research results, we determined the reasonable position of the mining roadway and the optimal width of the barrier pillar. The engineering application demonstrates that the retention of the barrier pillar with a width of 5 m along the gob as the haulage roadway for the next panel is feasible, which delivers favorable technological and economic benefits.

  5. Experimental Study on Common and Steel Fiber Reinforced Concrete Under Dynamic Tensile Stress

    Institute of Scientific and Technical Information of China (English)

    董新龙; 陈江瑛; 高培正; 祁振林; 王永忠; 王永刚; 王礼立

    2004-01-01

    Split Hopkinson technique has been developed to test the strength of common concrete and steel fiber reinforced concrete under dynamic tensile stress. Two types of test methods are considered, the splitting tensile test and a modified spalling test in which a specimen is loaded under uniaxial stress. The result shows that the dynamic strength enhancement of concrete is remarkable by using the reinforcing fiber. But for the common concrete, the base of compressive strength seems to show little effect on the tensile strength under dynamic loading. The experimental results also show that the resistance to tensile fracture of the steel fiber reinforced concrete for C100-mix is higher than those of C40-mix.

  6. Dynamic wetting and stress singularity on contact line

    Institute of Scientific and Technical Information of China (English)

    WANG; Xiaodong; (王晓东); PENG; Xiaofeng; (彭晓峰); LEE; Duzhong; (李笃中)

    2003-01-01

    A theoretical investigation is conducted to understand the contact line movement and associated contact angle phenomena. Contact line is supposed to move on a thin precursor film, and contact line has a velocity and is subject to viscous stress on the film or geometrically on the solid surface. With the introduction of a characteristic parameter, λ′, the movement of contact line and contact angle phenomena are very well described in both physics and mathematics. The viscous shearing stress exerted by liquid on solid surface was derived, and the behavior of dynamic contact angle was recognized on rough solid surfaces. The analyses indicate that characteristic parameter λ′ is dependent upon solid wall intrinsic property and mechanical performance, and is irrelevant to liquid property. Theoretical predictions are in good agreement with available experimental data in literature.

  7. Effect of bending stresses on the dynamic magnetic properties of the amorphous Co69Fe3.7Cr3.8Si12.5B11 alloy with a near-zero magnetostriction

    Science.gov (United States)

    Kekalo, I. B.; Mogil'nikov, P. S.

    2015-07-01

    When studying the amorphous alloy Co69Fe3.7Cr3.8Si12.5B11 with a near-zero magnetostriction (|λs| ≤ 10-7), uncommon (anomalous) effects of bending stresses (of the diameter D of toroidal samples) on the hysteretic magnetic properties ( H c, μ5) measured in a dynamic regime at frequencies f of the ac magnetic field from 0.1 to 20 kHz have been revealed. At low frequencies ( f < 1 kHz), the coercive force H c of the alloy is almost independent of D. The permeability μ5 ( H = 5 mOe) is independent of D at high frequencies and depends on D at low frequencies. In samples subjected to high-temperature annealing (390°C) with subsequent water quenching, uncommon regularities are observed; the permeability μ5 increases with decreasing radius of the toroidal samples, i.e., with increasing bending stresses.

  8. Emotional effects of dynamic textures

    NARCIS (Netherlands)

    Toet, A.; Henselmans, M.; Lucassen, M.P.; Gevers, T.

    2011-01-01

    This study explores the effects of various spatiotemporal dynamic texture characteristics on human emotions. The emotional experience of auditory (eg, music) and haptic repetitive patterns has been studied extensively. In contrast, the emotional experience of visual dynamic textures is still largely

  9. Emotional Effects of Dynamic Textures

    Directory of Open Access Journals (Sweden)

    Alexander Toet

    2011-12-01

    Full Text Available This study explores the effects of various spatiotemporal dynamic texture characteristics on human emotions. The emotional experience of auditory (eg, music and haptic repetitive patterns has been studied extensively. In contrast, the emotional experience of visual dynamic textures is still largely unknown, despite their natural ubiquity and increasing use in digital media. Participants watched a set of dynamic textures, representing either water or various different media, and self-reported their emotional experience. Motion complexity was found to have mildly relaxing and nondominant effects. In contrast, motion change complexity was found to be arousing and dominant. The speed of dynamics had arousing, dominant, and unpleasant effects. The amplitude of dynamics was also regarded as unpleasant. The regularity of the dynamics over the textures' area was found to be uninteresting, nondominant, mildly relaxing, and mildly pleasant. The spatial scale of the dynamics had an unpleasant, arousing, and dominant effect, which was larger for textures with diverse content than for water textures. For water textures, the effects of spatial contrast were arousing, dominant, interesting, and mildly unpleasant. None of these effects were observed for textures of diverse content. The current findings are relevant for the design and synthesis of affective multimedia content and for affective scene indexing and retrieval.

  10. Dynamic changes in DNA methylation of stress-associated genes (OXTR, BDNF ) after acute psychosocial stress.

    Science.gov (United States)

    Unternaehrer, E; Luers, P; Mill, J; Dempster, E; Meyer, A H; Staehli, S; Lieb, R; Hellhammer, D H; Meinlschmidt, G

    2012-08-14

    Environmentally induced epigenetic alterations are related to mental health. We investigated quantitative DNA methylation status before and after an acute psychosocial stressor in two stress-related genes: oxytocin receptor (OXTR) and brain-derived neurotrophic factor (BDNF ). The cross sectional study took place at the Division of Theoretical and Clinical Psychobiology, University of Trier, Germany and was conducted from February to August 2009. We included 83 participants aged 61-67 years. Thereof, 76 participants completed the full study procedure consisting of blood sampling before (pre-stress), 10 min after (post-stress) and 90 min after (follow-up) the Trier social stress test. We assessed quantitative DNA methylation of whole-blood cells using Sequenom EpiTYPER. Methylation status differed between sampling times in one target sequence of OXTR (POXTR (P=0.034), where it lost statistical significance when blood cell count was statistically controlled. We did not detect any time-associated differences in methylation status of the examined BDNF region. The results suggest a dynamic regulation of DNA methylation in OXTR-which may in part reflect changes in blood cell composition-but not BDNF after acute psychosocial stress. This may enhance the understanding of how psychosocial events alter DNA methylation and could provide new insights into the etiology of mental disorders.

  11. AN IMPROVED DYNAMIC SUBGRID-SCALE STRESS MODEL

    Institute of Scientific and Technical Information of China (English)

    TANG Xue-ling; QIAN Zhong-dong; WU Yu-lin; LIU Shu-hong; YANG Fan

    2004-01-01

    According to modeling principle that a model must be more accurate if including more flow information, and based on the Cauchy-Helmholtz theorem and the Smagorinsky model, a second-order dynamic model with double dynamic coefficients was proposed by applying dimension analyses. The Subgrid-Scale (SGS) stress is a function of both strain-rate tensor and rotation-rate tensor. The SIMPLEC algorithm and staggering grid system was applied to give the solution of the discretized governing equations, and for the turbulent flow through a 90° bend, the distributions of velocity and pressure were achieved. The comparison between experimental data and simulation results at a Reynolds number 40000 shows a good agreement and implies that this model is practicable and credible.

  12. Dynamic stress of impeller blade of shaft extension tubular pump device based on bidirectional fluid-structure interaction

    Energy Technology Data Exchange (ETDEWEB)

    Kan, Kan; Liu, Huiwen; Yang, Chunxia [Hohai University, Nanjing (China); Zheng, Yuan [National Engineering Research Center of Water Resources Efficient Utilization and Engineering Safety, Nanjing (China); Fu, Shifeng; Zhang, Xin [Power China Huadong Engineering Corporation, Hangzhou (China)

    2017-04-15

    Current research on the stability of tubular pumps is mainly concerned with the transient hydrodynamic characteristics. However, the structural response under the influence of fluid-structure interaction hasn't been taken fully into consideration. The instability of the structure can cause vibration and cracks, which may threaten the safety of the unit. We used bidirectional fluid-structure interaction to comprehensively analyze the dynamic stress characteristics of the impeller blades of the shaft extension tubular pump device. Furthermore, dynamic stress of impeller blade of shaft extension tubular pump device was solved under different lift conditions of 0° blade angle. Based on Reynolds-average N-S equation and SST k-ω turbulence model, numerical simulation was carried out for three-dimensional unsteady incompressible turbulent flow field of the pump device whole flow passage. Meanwhile, the finite element method was used to calculate dynamic characteristics of the blade structure. The blade dynamic stress distribution was obtained on the basis of fourth strength theory. The research results indicate that the maximum blade dynamic stress appears at the joint between root of inlet side of the blade suction surface and the axis. Considering the influence of gravity, the fluctuation of the blade dynamic stress increases initially and decreases afterwards within a rotation period. In the meantime, the dynamic stress in the middle part of inlet edge presents larger relative fluctuation amplitude. Finally, a prediction method for dynamic stress distribution of tubular pump considering fluid-structure interaction and gravity effect was proposed. This method can be used in the design stage of tubular pump to predict dynamic stress distribution of the structure under different operating conditions, improve the reliability of pump impeller and analyze the impeller fatigue life.

  13. Cost-Effective Stress Management Training.

    Science.gov (United States)

    Shea, Gordon F.

    1980-01-01

    Stress management training can be a cost effective way to improve productivity and job performance. Among many relaxation techniques, the most effective in terms of teachability, participant motivation, and profitability are self-hypnosis, progressive relaxation, and transcendental meditation. (SK)

  14. A METHOD FOR TOPOLOGICAL OPTIMIZATION OF STRUCTURES WITH DISCRETE VARIABLES UNDER DYNAMIC STRESS AND DISPLACEMENT CONSTRAINTS

    Institute of Scientific and Technical Information of China (English)

    石连栓; 孙焕纯; 冯恩民

    2001-01-01

    A method for topological optimization of structures with discrete variables subjected to dynamic stress and displacement constraints is presented. By using the quasistatic method, the structure optimization problem under dynamic stress and displacement constraints is converted into one subjected to static stress and displacement constraints. The comprehensive algorithm for topological optimization of structures with discrete variables is used to find the optimum solution.

  15. Examination of effective stress in clay rock

    Directory of Open Access Journals (Sweden)

    Chun-Liang Zhang

    2017-06-01

    Full Text Available This paper examines the effective stress in indurated clay rock theoretically and experimentally. A stress concept is derived from the analysis of the microstructure and of the pore water in the highly-indurated Callovo-Oxfordian and Opalinus clay rocks, and subsequently validated by various experiments performed on these claystones. The concept suggests that the interparticle or effective stress in a dense clay–water system is transferred through both the adsorbed interparticle pore water in narrow pores and the solid–solid contact between non-clay mineral grains. The experiments show that the adsorbed pore water in the claystones is capable of bearing deviatoric effective stresses up to the failure strength. The applied stresses are for the most part or even totally transferred by the bound pore water, i.e. the swelling pressure in the interparticle bound pore water is almost equivalent to the effective stress. This stress concept provides a reasonable view to the nature of the effective stress in argillaceous rock and forms the fundamental basis for studies of the hydro-mechanical properties and processes in clay formations.

  16. Wear particles: Influence on local stress and dynamical instabilities

    Science.gov (United States)

    Nhu, Viet-Hung; Renouf, Mathieu; Massi, Francesco; Saulot, Aurélien

    2013-06-01

    When two continuous bodies are in contact and subjected to relative motion, both particle detachment and dynamic instabilities naturally occur. To properly model such interacting phenomena, it is required to take account for the discontinuity of the interfacial layer (usually modeled with Discrete Element Model) as well as the continuity of the bodies in contact (usually modeled with Finite Element Model). For that, the present paper aims at validating experimentally the coupled FEM-DEM method. The experimental set-up aims at modeling the frictional behavior between a holed disk, tied on its exterior side and made of transparent polymer with birefringence property, and an inner rotating cylinder, made of steel. This last is statically enlarged to reach the wanted contact pressure and then animated with constant angular velocity. The birefringence property of the disk is used to dynamically visualize the evolution of stresses in the disk at both contact scale and body scale. Based on the same principle with the same boundary conditions, the numerical model coupled the modeling of a deformable disk, a pseudo-rigid cylinder and wear particles by a combination of a finite element method and a discrete element method. Parametrical study has been numerically made to study the influence of particle morphology on stress evolution in the disk. A good agreement is showed between the numerical results obtained with particles artificially introduced in the contact and the experimental results obtained with wear particles naturally produced in the contact.

  17. Ageing under Shear: Effect of Stress and Temperature Field

    Science.gov (United States)

    Shukla, Asheesh; Joshi, Yogesh M.

    2008-07-01

    In this work we studied the effect of oscillatory stress and temperature on the ageing dynamics of aqueous suspension of laponite. At the higher magnitude of stress, elastic and viscous moduli of the system underwent a sharp rise with the ageing time. The age at the onset of rise and the sharpness of the same increased with the magnitude of stress. We propose that at the beginning of ageing, the strain associated with the oscillatory stress field affects the lower modes in the relaxation time distribution. The higher modes, which are not significantly affected by the deformation field, continue to grow increasing the viscosity of the system thereby lowering the magnitude of the deformation field. Progressive decrease in the later reduces the range of relaxation modes affected by it. This dynamics eventually leads to an auto-catalytic increase in the elastic and viscous moduli. An increase in temperature accelerates the ageing process by shifting the ageing dynamics to a lower ageing time. This is due the microscopic relaxation dynamics, which causes ageing, becomes faster with increase in the temperature.

  18. Dynamic Response in Transient Stress-Field Behavior Induced by Hydraulic Fracturing

    Science.gov (United States)

    Jenkins, Andrew

    Hydraulic fracturing is a technique which is used to exploit geologic features and subsurface properties in an effort to increase production in low-permeability formations. The process of hydraulic fracturing provides a greater surface contact area between the producing formation and the wellbore and thus increases the amount of recoverable hydrocarbons from within the reservoir. The use of this stimulation technique has brought on massive applause from the industry due to its widespread success and effectiveness, however the dynamic processes that take part in the development of hydraulic fractures is a relatively new area of research with respect to the massive scale operations that are seen today. The process of hydraulic fracturing relies upon understanding and exploiting the in-situ stress distribution throughout the area of study. These in-situ stress conditions are responsible for directing fracture orientation and propagation paths throughout the period of injection. The relative magnitude of these principle stresses is key in developing a successful stimulation plan. In horizontal well plan development the interpretation of stress within the reservoir is required for determining the azimuth of the horizontal well path. These horizontal laterals are typically oriented in a manner such that the well path lies parallel to the minimum horizontal stress. This allows for vertical fractures to develop transversely to the wellbore, or normal to the least principle stress without the theoretical possibility of fractures overlapping, creating the most efficient use of the fluid energy during injection. The orientation and magnitude of these in-situ stress fields however can be dynamic, controlled by the subsequent fracture propagation and redistribution of the surrounding stresses. That is, that as the fracture propagates throughout the reservoir, the relative stress fields surrounding the fractures may see a shift and deviate from their original direction or

  19. Adverse effects of stress on microbiota

    Science.gov (United States)

    The complex communities of microorganisms that colonize the gastrointestinal tract impact the health status of an animal. The health of an animal as well as production traits are also affected by exposure to stress. The aim of present study was to evaluate the effects of dehorning stress on the gut ...

  20. Predicting the synergy of multiple stress effects

    Science.gov (United States)

    Liess, Matthias; Foit, Kaarina; Knillmann, Saskia; Schäfer, Ralf B.; Liess, Hans-Dieter

    2016-09-01

    Toxicants and other, non-chemical environmental stressors contribute to the global biodiversity crisis. Examples include the loss of bees and the reduction of aquatic biodiversity. Although non-compliance with regulations might be contributing, the widespread existence of these impacts suggests that for example the current approach of pesticide risk assessment fails to protect biodiversity when multiple stressors concurrently affect organisms. To quantify such multiple stress effects, we analysed all applicable aquatic studies and found that the presence of environmental stressors increases individual sensitivity to toxicants (pesticides, trace metals) by a factor of up to 100. To predict this dependence, we developed the “Stress Addition Model” (SAM). With the SAM, we assume that each individual has a general stress capacity towards all types of specific stress that should not be exhausted. Experimental stress levels are transferred into general stress levels of the SAM using the stress-related mortality as a common link. These general stress levels of independent stressors are additive, with the sum determining the total stress exerted on a population. With this approach, we provide a tool that quantitatively predicts the highly synergistic direct effects of independent stressor combinations.

  1. Starting with a handicap: effects of asynchronous hatching on growth rate, oxidative stress and telomere dynamics in free-living great tits.

    Science.gov (United States)

    Stier, Antoine; Massemin, Sylvie; Zahn, Sandrine; Tissier, Mathilde L; Criscuolo, François

    2015-12-01

    A trade-off between resource investment into growth rate and body self-maintenance is likely to occur, but the underlying molecular mediators of such a trade-off remain to be determined. In many altricial birds, hatching asynchrony creates a sibling competitive hierarchy within the brood, with first-hatched nestlings enjoying substantial advantages compared to last-hatched nestlings. We used this opportunity to test for a trade-off between growth and self-maintenance processes (oxidative stress, telomere erosion) in great tit nestlings, since resource availability and allocation are likely to differ between first-hatched and last-hatched nestlings. We found that despite their starting competitive handicap (i.e. being smaller/lighter before day 16), last-hatched nestlings exhibited growth rate and mass/size at fledging similar to first-hatched ones. However, last-hatched nestlings suffered more in terms of oxidative stress, and ended growth with shorter telomeres than first-hatched ones. Interestingly, growth rate was positively related to plasma antioxidant capacity and early life telomere length (i.e. at 7 days old), but among last-hatched nestlings, those exhibiting the faster body size growth were also those exhibiting the greatest telomere erosion. Last-hatched nestlings exhibited elevated levels of plasma testosterone (T), but only at day 7. T levels were positively associated with oxidative damage levels and plasma antioxidant capacity, the latter being only significant for first-hatched nestlings. Our results suggest that last-hatched nestlings present a specific trade-off between growth rate and self-maintenance processes, which is possibly driven by their need to compete with their older siblings and potentially mediated by elevated levels of T.

  2. Dynamic regulation of NMDAR function in the adult brain by the stress hormone corticosterone

    Directory of Open Access Journals (Sweden)

    Yiu Chung eTse

    2012-03-01

    Full Text Available Stress and corticosteroids dynamically modulate the expression of synaptic plasticity at glutamatergic synapses in the developed brain. Together with alpha-amino-3-hydroxy-methyl-4-isoxazole propionic acid receptors (AMPAR, N-methyl-D-aspartate receptors (NMDAR are critical mediators of synaptic function and are essential for the induction of many forms of synaptic plasticity. Regulation of NMDAR function by cortisol/corticosterone (CORT may be fundamental to the effects of stress on synaptic plasticity. Recent reports of the efficacy of NMDAR antagonists in treating certain stress-associated psychopathologies further highlight the importance of understanding the regulation of NMDAR function by CORT. Knowledge of how corticosteroids regulate NMDAR function within the adult brain is relatively sparse, perhaps due to a common belief that NMDAR function is relatively stable in the adult brain. We review recent results from our laboratory and others demonstrating dynamic regulation of NMDAR function by CORT in the adult brain. In addition, we consider the issue of how differences in the early life environment may program differential sensitivity to modulation of NMDAR function by CORT and how this may influence synaptic function during stress. Findings from these studies demonstrate that NMDAR function in the adult hippocampus remains sensitive to even brief exposures to CORT and that the capacity for modulation of NMDAR may be programmed, in part, by the early life environment. Modulation of NMDAR function may contribute to dynamic regulation of synaptic plasticity and adaptation in the face of stress, however enhanced NMDAR function may be implicated in mechanisms of stress related psychopathologies including depression.

  3. Complete Coulomb stress changes induced by the Ms7.6 earthquake in Lancang-Gengma, Yunnan and triggering of aftershocks by dynamic and static stress

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The spatiotemporal evolution patterns of complete Coulomb stress changes caused by 1988 Ms7.6 earthquake in Lancang-Gengma,Yunnan,are calculated and studied.And the triggering problems of Ms7.2 Gengma shock occurring 13 minutes after the main shock and of Ms5.0―6.9 aftershocks within 24 days after the main shock are discussed.The results show that the spatial distribution patterns of complete Coulomb stress changes of the Ms7.6 main shock are strongly asymmetric.The areas of positive dynamic and static Coulomb stress are both coincident well with the strong aftershocks' locations.The Ms7.2 Gengma shock and most of strong aftershocks are subjected to the triggering effect of dynamic and static Coulomb stresses induced by the Ms7.6 Lancang earthquake.

  4. Dynamic damage and stress-strain relations of ultra-high performance cementitious composites subjected to repeated impact

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Ultra-high performance cementitious composites (UHPCC) were prepared by replacing 60% of cement with ultra-fine industrial waste powders.The dynamic damage and compressive stress-strain relations of UHPCC were studied using split Hopkinson pressure bar (SHPB).The damage of UHPCC subjected to repeated impact was measured by the ultrasonic pulse velocity method.Results show that the dynamic damage of UHPCC increases linearly with impact times and the abilities of repeated impact resistance of UHPCC are improved with increasing fiber volume fraction.The stress waves on impact were recorded and the average stress,strain and strain rate of UHPCC were calculated based on the wave propagation theory.The effects of strain rate,fibers volume fraction and impact times on the stress-strain relations of UHPCC were studied.Results show that the peak stress and elastic modulus decrease while the strain rate and peak strain increase gradually with increasing impact times.

  5. Dynamical effects in the fusion hindrance

    Directory of Open Access Journals (Sweden)

    Abe Yasuhisa

    2011-10-01

    Full Text Available It is well known that there is a hindrance to fusion in collisions with heavy nuclei that plays a decisive role in synthesis of the super-heavy elements (SHE. The origin of the fusion hindrance is nowadays qualitatively understood but there are still quantitative ambiguities on the dynamics of the fusion mechanism and the predictions need to be assessed. In this communication, we stress the fact that dynamical effects play a crucial role in the amplitude of the reduction of the fusion probability. We found that the fast evolution of the neck degree of freedom affects the slow radial motion, i.e., the fusioning motion, through a dynamical coupling. We showed that we could do a so-called adiabatic elimination of the fast variable in the coupled equation, resulting in an effective one-dimensional equation for the radial motion with a shift of the starting point. This treatment of the dynamical coupling leads to a larger hindrance.

  6. Thermal vibration of a single-layered graphene with initial stress predicted by semiquantum molecular dynamics

    Science.gov (United States)

    Liu, Rumeng; Wang, Lifeng; Jiang, Jingnong

    2016-09-01

    Thermal vibration of a rectangular single-layered graphene sheet (RSLGS) with initial stress is investigated by a semiquantum molecular dynamics (SQMD) method on the basis of modified Langevin dynamics. The quantum effect in the thermal vibration of RSLGS is accounted by introducing a quantum thermal bath. The spectrum of the thermal vibration of RSLGSs is obtained both by SQMD and classical molecular dynamics (CMD). The RSLGS vibrates with the same frequencies via both the SQMD simulation and the CMD simulation. The root of mean squared (rms) amplitude obtained via the CMD is greater than that obtained via the SQMD. The energy in high order mode is frozen at very low temperature if quantum effect is taken into consideration. An elastic plate model with initial stress considering quantum effects is established to describe the thermal vibration of the RSLGS. The rms amplitude of RSLGS calculated by plate model with the law of energy equipartition and that obtained from the CMD coincide very well. The plate model considering the quantum effects provides accurate prediction of the rms amplitude of the RSLGS obtained from the SQMD. These results indicate that quantum effects cannot be neglected in the thermal vibration of the RSLGS at low temperature case.

  7. Order effects in dynamic semantics.

    Science.gov (United States)

    Graben, Peter Beim

    2014-01-01

    In their target article, Wang and Busemeyer (2013) discuss question order effects in terms of incompatible projectors on a Hilbert space. In a similar vein, Blutner recently presented an orthoalgebraic query language essentially relying on dynamic update semantics. Here, I shall comment on some interesting analogies between the different variants of dynamic semantics and generalized quantum theory to illustrate other kinds of order effects in human cognition, such as belief revision, the resolution of anaphors, and default reasoning that result from the crucial non-commutativity of mental operations upon the belief state of a cognitive agent.

  8. Stress

    Science.gov (United States)

    ... sudden negative change, such as losing a job, divorce, or illness Traumatic stress, which happens when you ... stress, so you can avoid more serious health effects. NIH: National Institute of Mental Health

  9. Molecular Dynamics of the Shewanella oneidensis Response to Chromate Stress

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Steven D [ORNL; Thompson, Melissa R [ORNL; Verberkmoes, Nathan C [ORNL; Chourey, Karuna [ORNL; Shah, Manesh B [ORNL; Zhou, Jizhong [ORNL; Hettich, Robert {Bob} L [ORNL; Thompson, Dorothea K [ORNL

    2006-01-01

    Temporal genomic profiling and whole-cell proteomic analyses were performed to characterize the dynamic molecular response of the metal-reducing bacterium Shewanella oneidensis MR-1 to an acute chromate shock. The complex dynamics of cellular processes demand the integration of methodologies that describe biological systems at the levels of regulation, gene and protein expression, and metabolite production. Genomic microarray analysis of the transcriptome dynamics of midexponential phase cells subjected to 1 mM potassium chromate (K2CrO4) at exposure time intervals of 5, 30, 60, and 90 min revealed 910 genes that were differentially expressed at one or more time points. Strongly induced genes included those encoding components of a TonB1 iron transport system (tonB1-exbB1-exbD1), hemin ATP-binding cassette transporters (hmuTUV), TonB-dependent receptors as well as sulfate transporters (cysP, cysW-2, and cysA-2), and enzymes involved in assimilative sulfur metabolism (cysC, cysN, cysD, cysH, cysI, and cysJ). Transcript levels for genes with annotated functions in DNA repair (lexA, recX, recA, recN, dinP, and umuD), cellular detoxification (so1756, so3585, and so3586), and two-component signal transduction systems (so2426) were also significantly upregulated (p < 0.05) in Cr(VI)-exposed cells relative to untreated cells. By contrast, genes with functions linked to energy metabolism, particularly electron transport (e.g. so0902-03-04, mtrA, omcA, and omcB), showed dramatic temporal alterations in expression with the majority exhibiting repression. Differential proteomics based on multidimensional HPLC-MS/MS was used to complement the transcriptome data, resulting in comparable induction and repression patterns for a subset of corresponding proteins. In total, expression of 2,370 proteins were confidently verified with 624 (26%) of these annotated as hypothetical or conserved hypothetical proteins. The initial response of S. oneidensis to chromate shock appears to

  10. Oxidative stress effects of thinner inhalation

    OpenAIRE

    2011-01-01

    Thinners are chemical mixtures used as industrial solvents. Humans can come into contact with thinner by occupational exposure or by intentional inhalation abuse. Thinner sniffing causes damage to the brain, kidney, liver, lung, and reproductive system. We discuss some proposed mechanism by which thinner induces damage. Recently, the induction of oxidative stress has been suggested as a possible mechanism of damage. This paper reviews the current evidence for oxidative stress effects induced ...

  11. Application of a PVDF-based stress gauge in determining dynamic stress-strain curves of concrete under impact testing

    Science.gov (United States)

    Meng, Yi; Yi, Weijian

    2011-06-01

    Polyvinylidene fluoride (PVDF) piezoelectric material has been successfully applied in many engineering fields and scientific research. However, it has rarely been used for direct measurement of concrete stresses under impact loading. In this paper, a new PVDF-based stress gauge was developed to measure concrete stresses under impact loading. Calibrated on a split Hopkinson pressure bar (SHPB) with a simple measurement circuit of resistance strain gauges, the PVDF gauge was then used to establish dynamic stress-strain curves of concrete cylinders from a series of axial impact testing on a drop-hammer test facility. Test results show that the stress curves measured by the PVDF-based stress gauges are more stable and cleaner than that of the stress curves calculated with the impact force measured from a load cell.

  12. Static and dynamic mechanics of the temporomandibular joint: plowing forces, joint load and tissue stress.

    Science.gov (United States)

    Nickel, J; Spilker, R; Iwasaki, L; Gonzalez, Y; McCall, W D; Ohrbach, R; Beatty, M W; Marx, D

    2009-08-01

    OBJECTIVES - To determine the combined effects 1) of stress-field aspect ratio and velocity and compressive strain and 2) joint load, on temporomandibular joint (TMJ) disc mechanics. SETTING AND SAMPLE POPULATION - Fifty-two subjects (30 female; 22 male) participated in the TMJ load experiments. MATERIAL AND METHODS - In the absence of human tissue, pig TMJ discs were used to determine the effects of variables 1) on surface plowing forces, and to build a biphasic finite element model (bFEM) to test the effect of human joint loads and 2) on tissue stresses. In the laboratory, discs received a 7.6 N static load via an acrylic indenter before cyclic movement. Data were recorded and analysed using anova. To determine human joint loads, Research Diagnostic Criteria calibrated investigators classified subjects based on signs of disc displacement (DD) and pain (+DD/+pain, n = 18; +DD/-pain, n = 17; -DD/-pain, n = 17). Three-dimensional geometries were produced for each subject and used in a computer model to calculate joint loads. RESULTS - The combined effects of compressive strain, and aspect ratio and velocity of stress-field translation correlated with plowing forces (R(2) = 0.85). +DD/-pain subjects produced 60% higher joint loads (ANOVA, p dynamic variables of the stress-field and subject-dependent joint load significantly affect disc mechanics.

  13. Dynamical Franz-Keldysh Effect

    DEFF Research Database (Denmark)

    Jauho, Antti-Pekka; Johnsen, Kristinn

    1996-01-01

    We introduce and analyze the properties of dynamical Franz-Keldysh effect, i.e., the change of density of states, or absorption spectra, of semiconductors under the influence of time-dependent electric fields. In the case of a harmonic time dependence, we predict the occurrence of significant fine...

  14. The effects of perceived stress, traits, mood states, and stressful daily events on salivary cortisol

    NARCIS (Netherlands)

    vanEck, M; Berkhof, H; Nicolson, N; Sulon, J

    1996-01-01

    This study examined the effects of perceived stress and related individual characteristics, mood states, and stressful daily events on salivary cortisol levels. Forty-one ''high stress'' and 46 ''low stress'' subjects were selected on the basis of Perceived Stress Scale scores from a sample of male,

  15. Effects of Curvature on Dynamics

    CERN Document Server

    Dutta, Gautam

    2010-01-01

    In this article we discuss the effect of curvature on dynamics when a physical system moves adiabatically in a curved space. These effects give a way to measure the curvature of the space intrinsically without referring to higher dimensional space. Two interesting examples, the Foucault Pendulum and the perihelion shift of planetary orbits, are presented in a simple geometric way. A paper model is presented to see the perihelion shift.

  16. Osho Dynamic Meditation’s Effect on Serum Cortisol Level

    Science.gov (United States)

    Bansal, Anuj; Mittal, Ashish

    2016-01-01

    Introduction Dynamic meditation is one of the most popular active meditation, introduced by an Indian mystic Osho in 1970. This one hour meditation consists of five stages: Deep fast chaotic breathing, catharsis, using a mantra "Hoo", silence, and dancing. A previous study observed that Osho dynamic meditation causes decrease in several psychopathological variables such as aggressive behaviour, anxiety and depression. However, it is not objectively established that the dynamic meditation has an anti-stress effect. Aim To find out the effect of Osho dynamic meditation on the serum cortisol levels (cortisol is an indicator of stress) and therefore to observe whether it has any anti-stress effect. Materials and Methods An experimental study was planned doing the dynamic meditation empty stomach in morning at 6 to 7 am every day for 21 days from 1st March 2015 to 21st March 2015 at Lucknow. Twenty healthy volunteers between 20 to 50 years (14 males and 6 females) participated in the study. Serum cortisol level was estimated from the blood samples collected in the morning one day prior (baseline) and post-meditation on the 21st day of the study. The difference between mean cortisol levels of the baseline and post-meditation groups were tested for significance by applying the paired t-test. Results Sixteen volunteers out of the 20 completed the study while four dropped out due to their health and personal reasons. The serum cortisol levels were decreased in all the 16 participants on 21st day as compared to the baseline levels and the decline in the mean cortisol level was highly significant (pstress effects. The mechanism of action could primarily be attributed to the release of repressed emotions and psychological inhibitions and traumas. Thus, dynamic meditation could be recommended for the amelioration of stress and stress related physical and mental disorders. More clinical studies should be done on dynamic meditation to prove its efficacy and become an approved

  17. A fiber-bridging model with stress gradient effects

    Science.gov (United States)

    Yi, Sun; Tao, Li

    2000-05-01

    A fiber-bridging model with stress gradient effects is proposed for unidirectional fiber-reinforced composites. The stress gradient terms are introduced by solving a micromechanical model under a non-uniform stress loading. It is shown that the stress gradient effect is significant on both the fiber-bridging stress distribution and the value of the critical load of fiber failure.

  18. The stress state of geological structure and mining dynamic disaster in Fuxin basin

    Institute of Scientific and Technical Information of China (English)

    HAN Jun; WANG Hai-bing; ZHU Guang-zong; LIU Ting-bo

    2008-01-01

    Further evidences show that most mining dynamic disasters are mainly occurred nearby NNE and near SN geological structures.In-situ stress measurement in Fuxin basin shows that the orientation of major compressed stress is near EW.At this stress field,geological structures with deferent strike have deferent stress state and displace mode.NNE and near SN geological structures are compressed to thrust and come into being high stress zone.NWW and NEE geological structures are tensile to separate and not prone to being low stress zone.NW structure is intervenient of them.So NEE and near SN structures are easy to occurre mining dynamic disasters and NWW and NEE structures is "safety" comparatively.The mining dynamic disaster is controlled by stress state of geologic structure,which is determined by its strike.

  19. Strain rate effects in stress corrosion cracking

    Energy Technology Data Exchange (ETDEWEB)

    Parkins, R.N. (Newcastle upon Tyne Univ. (UK). Dept. of Metallurgy and Engineering Materials)

    1990-03-01

    Slow strain rate testing (SSRT) was initially developed as a rapid, ad hoc laboratory method for assessing the propensity for metals an environments to promote stress corrosion cracking. It is now clear, however, that there are good theoretical reasons why strain rate, as opposed to stress per se, will often be the controlling parameter in determining whether or not cracks are nucleated and, if so, are propagated. The synergistic effects of the time dependence of corrosion-related reactions and microplastic strain provide the basis for mechanistic understanding of stress corrosion cracking in high-pressure pipelines and other structures. However, while this may be readily comprehended in the context of laboratory slow strain tests, its extension to service situations may be less apparent. Laboratory work involving realistic stressing conditions, including low-frequency cyclic loading, shows that strain or creep rates give good correlation with thresholds for cracking and with crack growth kinetics.

  20. Noise and stress effects on preschool personnel

    Directory of Open Access Journals (Sweden)

    Fredrik Sjödin

    2012-01-01

    Full Text Available The aim of the study was to analyze the presence of stress-related health problems among preschool employees and the way in which these reactions are related to noise and other work parameters. The investigation included 101 employees at 17 preschools in Umeå County, located in northern Sweden. Individual noise recordings and recordings in dining rooms and play halls were made at two departments from each preschool. The adverse effects on the employees were analyzed by use of different validated questionnaires and by saliva cortisol samples. Stress and energy output were pronounced among the employees, and about 30% of the staff experienced strong burnout syndromes. Mental recovery after work was low, indicated by remaining high levels of stress after work. The burnout symptoms were associated with reduced sleep quality and morning sleepiness. Cortisol levels supported the conclusion about pronounced daily stress levels of the preschool employees.

  1. Reconstructing a Network of Stress-Response Regulators via Dynamic System Modeling of Gene Regulation

    Directory of Open Access Journals (Sweden)

    Wei-Sheng Wu

    2008-01-01

    Full Text Available Unicellular organisms such as yeasts have evolved mechanisms to respond to environmental stresses by rapidly reorganizing the gene expression program. Although many stress-response genes in yeast have been discovered by DNA microarrays, the stress-response transcription factors (TFs that regulate these stress-response genes remain to be investigated. In this study, we use a dynamic system model of gene regulation to describe the mechanism of how TFs may control a gene’s expression. Then, based on the dynamic system model, we develop the Stress Regulator Identification Algorithm (SRIA to identify stress-response TFs for six kinds of stresses. We identified some general stress-response TFs that respond to various stresses and some specific stress-response TFs that respond to one specifi c stress. The biological significance of our findings is validated by the literature. We found that a small number of TFs is probably suffi cient to control a wide variety of expression patterns in yeast under different stresses. Two implications can be inferred from this observation. First, the response mechanisms to different stresses may have a bow-tie structure. Second, there may be regulatory cross-talks among different stress responses. In conclusion, this study proposes a network of stress-response regulators and the details of their actions.

  2. Reconstructing a network of stress-response regulators via dynamic system modeling of gene regulation.

    Science.gov (United States)

    Wu, Wei-Sheng; Li, Wen-Hsiung; Chen, Bor-Sen

    2008-02-10

    Unicellular organisms such as yeasts have evolved mechanisms to respond to environmental stresses by rapidly reorganizing the gene expression program. Although many stress-response genes in yeast have been discovered by DNA microarrays, the stress-response transcription factors (TFs) that regulate these stress-response genes remain to be investigated. In this study, we use a dynamic system model of gene regulation to describe the mechanism of how TFs may control a gene's expression. Then, based on the dynamic system model, we develop the Stress Regulator Identification Algorithm (SRIA) to identify stress-response TFs for six kinds of stresses. We identified some general stress-response TFs that respond to various stresses and some specific stress-response TFs that respond to one specific stress. The biological significance of our findings is validated by the literature. We found that a small number of TFs is probably sufficient to control a wide variety of expression patterns in yeast under different stresses. Two implications can be inferred from this observation. First, the response mechanisms to different stresses may have a bow-tie structure. Second, there may be regulatory cross-talks among different stress responses. In conclusion, this study proposes a network of stress-response regulators and the details of their actions.

  3. Fluid dynamic effects on staphylococci bacteria biofilms

    Science.gov (United States)

    Sherman, Erica; Bayles, Kenneth; Endres, Jennifer; Wei, Timothy

    2016-11-01

    Staphylococcus aureus bacteria are able to form biofilms and distinctive tower structures that facilitate their ability to tolerate treatment and to spread within the human body. The formation of towers, which break off, get carried downstream and serve to initiate biofilms in other parts of the body are of particular interest here. It is known that flow conditions play a role in the development, dispersion and propagation of biofilms in general. The influence of flow on tower formation, however, is not at all understood. This work is focused on the effect of applied shear on tower development. The hypothesis being examined is that tower structures form within a specific range of shear stresses and that there is an as yet ill defined fluid dynamic phenomenon that occurs hours before a tower forms. In this study, a range of shear stresses is examined that brackets 0.6 dynes/cm2, the nominal shear stress where towers seem most likely to form. This talk will include µPTV measurements and cell density data indicating variations in flow and biofilm evolution as a function of the applied shear. Causal relations between flow and biofilm development will be discussed.

  4. Mechanical vulnerability of lower second premolar utilising visco-elastic dynamic stress analysis.

    Science.gov (United States)

    Khani, M M; Tafazzoli-Shadpour, M; Aghajani, F; Naderi, P

    2009-10-01

    Stress analysis determines vulnerability of dental tissues to external loads. Stress values depend on loading conditions, mechanical properties and constrains of structural components. The critical stress levels lead to tissue damage. The aim of this study is to analyse dynamic stress distribution of lower second premolar due to physiological cyclic loading, and dependency of pulsatile stress characteristics to visco-elastic property of dental components by finite element modelling. Results show that visco-elastic property markedly influences stress determinants in major anatomical sites including dentin, cementum-enamel and dentin-enamel junctions. Reduction of visco-elastic parameter leads to mechanical vulnerability through elevation of stress pulse amplitude, maximum stress value; and reduction of stress phase shift as a determinant of stress wave propagation. The results may be applied in situations in which visco-elasticity is reduced such as root canal therapy and post and core restoration in which teeth are more vulnerable to fracture.

  5. Bauschinger effect in thin metal films: Discrete dislocation dynamics study

    NARCIS (Netherlands)

    Davoudi, K.M.; Nicola, L.; Vlassak, J.J.

    2014-01-01

    The effects of dislocation climb on plastic deformation during loading and unloading are studied using a two-dimensional discrete dislocation dynamics model. Simulations are performed for polycrystalline thin films passivated on both surfaces. Dislocation climb lowers the overall level of the stress

  6. Preliminary study on variation characteristics of ocean tide dynamic stress in crust and its relationship with earthquakes

    Institute of Scientific and Technical Information of China (English)

    LU Ming-yong; ZHENG Wen-heng

    2005-01-01

    The variation characteristics of dynamic stress in crustal blocks and its relationship with earthquakes are comprehensively studied by analyzing geophysical data and calculating the dynamic response of crustal blocks in North China to the tide level change of Bohai Sea and Yellow Sea using a 3D nonlinear dynamic finite element simulation. This study has noticed some new features of crustal dynamic stress: (a) High stress level appears at the place where the stress waves superpose and interference during the process of propagation, and the enhancement of dynamic shear stress is more significant as compared with that of compressive stress; (b) Variation of dynamic stress has influence on seismogenic environment and hence earthquake occurrence; (c) As viewed from the variation characteristics of crustal dynamic stress, the superimposing process of shear stress manifests the preparation process of earthquakes.

  7. A new dynamical diffraction-based technique of residual stress measurements in thin films

    CERN Document Server

    Agamalian, M; Kaiser, H; Rehm, C; Werner, S A

    2002-01-01

    The recently discovered dynamical diffraction effect 'neutron camel' was used for residual stress measurements in a thick Si (111) crystal coated with a 2000 A-thick Ni film. The observed asymmetry of the back-face rocking curve corresponds to the bending radius of propor to 19 km and the tension force applied to the Ni film is propor to 90 N/m. Relative deformation of the Si crystallographic cells in the vicinity of diffractive surfaces is vertical stroke partial deriv u sub z /partial deriv z vertical stroke approx 1.6 x 10 sup - sup 6. (orig.)

  8. Greater physiological and behavioral effects of interrupted stress pattern compared to daily restraint stress in rats.

    Directory of Open Access Journals (Sweden)

    Wei Zhang

    Full Text Available Repeated stress can trigger a range of psychiatric disorders, including anxiety. The propensity to develop abnormal behaviors after repeated stress is related to the severity, frequency and number of stressors. However, the pattern of stress exposure may contribute to the impact of stress. In addition, the anxiogenic nature of repeated stress exposure can be moderated by the degree of coping that occurs, and can be reflected in homotypic habituation to the repeated stress. However, expectations are not clear when a pattern of stress presentation is utilized that diminishes habituation. The purpose of these experiments is to test whether interrupted stress exposure decreases homotypic habituation and leads to greater effects on anxiety-like behavior in adult male rats. We found that repeated interrupted restraint stress resulted in less overall homotypic habituation compared to repeated daily restraint stress. This was demonstrated by greater production of fecal boli and greater corticosterone response to restraint. Furthermore, interrupted restraint stress resulted in a lower body weight and greater adrenal gland weight than daily restraint stress, and greater anxiety-like behavior in the elevated plus maze. Control experiments demonstrated that these effects of the interrupted pattern could not be explained by differences in the total number of stress exposures, differences in the total number of days that the stress periods encompased, nor could it be explained as a result of only the stress exposures after an interruption from stress. These experiments demonstrate that the pattern of stress exposure is a significant determinant of the effects of repeated stress, and that interrupted stress exposure that decreases habituation can have larger effects than a greater number of daily stress exposures. Differences in the pattern of stress exposure are therefore an important factor to consider when predicting the severity of the effects of repeated

  9. Couple-Stress Fluid Improves Dynamic Response of Gear-Pair System Supported by Journal Bearings

    Directory of Open Access Journals (Sweden)

    Cai-Wan Chang-Jian

    2012-01-01

    Full Text Available A systematic analysis of the dynamic behavior of a gear-bearing system with nonlinear suspension, couple-stress fluid flow effect, nonlinear oil-film force, and nonlinear gear mesh force is performed in the present study. The dynamic orbits of the system are observed using bifurcation diagrams plotted using the dimensionless rotational speed ratio as a control parameter. The onset of chaotic motion is identified from the phase diagrams, power spectra, Poincaré maps, Lyapunov exponents and fractal dimension of the gear-bearing system. The numerical results reveal that the system exhibits a diverse range of periodic, subharmonic, quasiperiodic, and chaotic behaviors. The couple-stress fluid would be a useful lubricating fluid to suppress nonlinear dynamic responses and improve the steady of the systems. The results presented in this study provide some useful insights into the design and development of a gear-bearing system for rotating machinery that operates in highly rotational speed and highly nonlinear regimes.

  10. Analysis of faults stability with dynamic phenomena in the mine based on slide criterion and in-situ stress measurement

    Institute of Scientific and Technical Information of China (English)

    SONG Wei-hua; WANG Yu-feng; WANG Xin-hua

    2008-01-01

    For the study on the relationship between the dynamic phenomena in the mining such as mine earthquakes,outburst and faults slide,firstly,double shear friction experiments of sandstone were made,and its slide criterion was suggested considering the viewing of engineering.Secondly,in order to study the stability of underground rock and zone of tectonic stress field,based on the analysis on distribution characteristic of initial rock stress measurements,the geology structural model was built and tectonic stress field was made a back-analysis by applying finite element method.The calculating results fit with the analysis result of earthquakes mechanism and the distribution characteristic of the measurements.The high stress regional centers station locates discontinuous zone of I level faults and is corresponding to underground earthquakes scene.From then it is certain that tectonic stress is the major origin and necessary condition of mine earthquakes.The instability slide of the faults is the main manifest and the mining activity is the leading factor.Beipiao fault has a dominate effect on other sub faults and tectonic stress area and is dynamical fountain of dynamic phenomena in the Beipiao Mines.

  11. Analysis of faults stability with dynamic phenomena in the mine based on slide criterion and in-situ stress measurement

    Institute of Scientific and Technical Information of China (English)

    SONG Wei-hua; WANG Yu-feng; WANG Xin-hua

    2008-01-01

    For the study on the relationshfp between the dynamic phenomena in the min-ing such as mine earthquakes, outburst and faults slide, firstly, double shear friction ex-periments of sandstone were made, and its slide criterion was suggested considering the viewing of engineering. Secondly, in order to study the stability of underground rock and zone of tectonic stress field, based on the analysis on distribution characteristic of initial rock stress measurements, the geology structural model was built and tectonic stress field was made a back-analysis by applying finite element method. The calculating results fit with the analysis result of earthquakes mechanism and the distribution characteristic of the measurements. The high stress regional centers station locates discontinuous zone of I level faults and is corresponding to underground earthquakes scene. From then it is cer-tain that tectonic stress is the major origin and necessary condition of mine earthquakes. The instability slide of the faults is the main manifest and the mining activity is the leading factor. Beipiao fault has a dominate effect on other sub faults and tectonic stress area and is dynamical fountain of dynamic phenomena in the Beipiao Mines.

  12. Stress distribution and effective stress intensity factor of a blunt crack after dislocation emission

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The stress fields induced by a dislocation and its image dislocations around a narrow elliptic void are formulated. Based on the solution, the stress distribution and effective stress intensity factor of a blunt (elliptic) crack were calculated under mode I constant loading. The results show that a dislocation-free zone (DFZ) is formed after dislocation emission. There exists a second stress peak in the DFZ except a stress peak at the blunt crack tip. With an increase in the applied stress intensity factor KIa or the friction stress τf of the material, the DFZ size and the peak stress at the crack tip decrease, but the peak stress in the DFZ and the effective stress intensity factor KIf presiding at the crack tip increase. Because of dislocation shielding effects, shielding ratio KIa/KIf increases with increasing KIa}, but it decreases with increasing τf.

  13. Stress distribution and effective stress intensity factor of a blunt crack after dislocation emission

    Institute of Scientific and Technical Information of China (English)

    钱才富; 乔利杰; 褚武扬

    2000-01-01

    The stress fields induced by a dislocation and its image dislocations around a narrow elliptic void are formulated. Based on the solution, the stress distribution and effective stress intensity factor of a blunt (elliptic) crack were calculated under mode I constant loading. The results show that a dislocation-free zone (DFZ) is formed after dislocation emission. There exists a second stress peak in the DFZ except a stress peak at the blunt crack tip. With an increase in the applied stress intensity factor Kla or the friction stress T, of the material, the DFZ size and the peak stress at the crack tip decrease, but the peak stress in the DFZ and the effective stress intensity factor Klf presiding at the crack tip increase. Because of dislocation shielding effects, shielding ratio Kla/Klf increases with increasing Kla, but it decreases with increasing Tf.

  14. Dynamics of neuroendocrine stress response: bistability, timing, and control of hypocortisolism

    Science.gov (United States)

    D'Orsogna, Maria; Chou, Tom; Kim, Lae

    The hypothalamic-pituitary-adrenal (HPA) axis is a neuroendocrine system that regulates numerous physiological processes. Disruptions in its activity are correlated with stress-related diseases such as post-traumatic stress disorder (PTSD) and major depressive disorder. We characterize ``normal'' and ``diseased'' states of the HPA axis as basins of attraction of a dynamical system describing the inhibition of peptide hormones, corticotropin-releasing hormone (CRH) and adrenocorticotropic hormone (ACTH), by circulating glucocorticoids such as cortisol (CORT). Our model includes ultradian oscillations, CRH self-upregulation of CRH release, and distinguishes two components of negative feedback by cortisol on circulating CRH levels: a slow direct suppression of CRH synthesis and a fast indirect effect on CRH release. The slow regulation mechanism mediates external stress-driven transitions between the stable states in novel, intensity, duration, and timing-dependent ways. We find that the timing of traumatic events may be an important factor in determining if and how the hallmarks of depressive disorders will manifest. Our model also suggests a mechanism whereby exposure therapy of stress disorders may act to normalize downstream dysregulation of the HPA axis.

  15. Dynamic microglial alterations underlie stress-induced depressive-like behavior and suppressed neurogenesis.

    Science.gov (United States)

    Kreisel, T; Frank, M G; Licht, T; Reshef, R; Ben-Menachem-Zidon, O; Baratta, M V; Maier, S F; Yirmiya, R

    2014-06-01

    The limited success in understanding the pathophysiology of major depression may result from excessive focus on the dysfunctioning of neurons, as compared with other types of brain cells. Therefore, we examined the role of dynamic alterations in microglia activation status in the development of chronic unpredictable stress (CUS)-induced depressive-like condition in rodents. We report that following an initial period (2-3 days) of stress-induced microglial proliferation and activation, some microglia underwent apoptosis, leading to reductions in their numbers within the hippocampus, but not in other brain regions, following 5 weeks of CUS exposure. At that time, microglia displayed reduced expression of activation markers as well as dystrophic morphology. Blockade of the initial stress-induced microglial activation by minocycline or by transgenic interleukin-1 receptor antagonist overexpression rescued the subsequent microglial apoptosis and decline, as well as the CUS-induced depressive-like behavior and suppressed neurogenesis. Similarly, the antidepressant drug imipramine blocked the initial stress-induced microglial activation as well as the CUS-induced microglial decline and depressive-like behavior. Treatment of CUS-exposed mice with either endotoxin, macrophage colony-stimulating factor or granulocyte-macrophage colony-stimulating factor, all of which stimulated hippocampal microglial proliferation, partially or completely reversed the depressive-like behavior and dramatically increased hippocampal neurogenesis, whereas treatment with imipramine or minocycline had minimal or no anti-depressive effects, respectively, in these mice. These findings provide direct causal evidence that disturbances in microglial functioning has an etiological role in chronic stress-induced depression, suggesting that microglia stimulators could serve as fast-acting anti-depressants in some forms of depressive and stress-related conditions.

  16. Dynamical effects in electron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Jianqiang Sky, E-mail: jianqiang.zhou@polytechnique.edu; Reshetnyak, Igor; Giorgetti, Christine; Sottile, Francesco; Reining, Lucia [Laboratoire des Solides Irradiés, École Polytechnique, CNRS, CEA-DSM-IRAMIS, Université Paris-Saclay, F-91128 Palaiseau (France); Kas, J. J.; Rehr, J. J. [Department of Physics, University of Washington, Seattle, Washington 98195-1560 (United States); Sponza, Lorenzo [Department of Physics, King’s College London, London WC2R 2LS (United Kingdom); Guzzo, Matteo [Institut für Physik und IRIS Adlershof, Humboldt-Universität zu Berlin, D-12489 Berlin (Germany); Gatti, Matteo [Laboratoire des Solides Irradiés, École Polytechnique, CNRS, CEA-DSM-IRAMIS, Université Paris-Saclay, F-91128 Palaiseau (France); Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP 48, F-91192 Gif-sur-Yvette (France)

    2015-11-14

    One of the big challenges of theoretical condensed-matter physics is the description, understanding, and prediction of the effects of the Coulomb interaction on materials properties. In electronic spectra, the Coulomb interaction causes a renormalization of energies and change of spectral weight. Most importantly, it can lead to new structures, often called satellites. These can be linked to the coupling of excitations, also termed dynamical effects. State-of-the-art methods in the framework of many-body perturbation theory, in particular, the widely used GW approximation, often fail to describe satellite spectra. Instead, approaches based on a picture of electron-boson coupling such as the cumulant expansion are promising for the description of plasmon satellites. In this work, we give a unified derivation of the GW approximation and the cumulant expansion for the one-body Green’s function. Using the example of bulk sodium, we compare the resulting spectral functions both in the valence and in the core region, and we discuss the dispersion of quasi-particles and satellites. We show that self-consistency is crucial to obtain meaningful results, in particular, at large binding energies. Very good agreement with experiment is obtained when the intrinsic spectral function is corrected for extrinsic and interference effects. Finally, we sketch how one can approach the problem in the case of the two-body Green’s function, and we discuss the cancellation of various dynamical effects that occur in that case.

  17. Relationship between muscle stress and intramuscular pressure during dynamic muscle contractions.

    Science.gov (United States)

    Ward, Samuel R; Davis, Jennifer; Kaufman, Kenton R; Lieber, Richard L

    2007-09-01

    Intramuscular pressure (IMP) has been used to estimate muscle stress indirectly. However, the ability of this technique to estimate muscle stress under dynamic conditions is poorly characterized. Therefore, the purpose of this study was to determine the extent to which IMP is a valid surrogate for muscle stress during dynamic contractions. IMP and muscle stress were compared under steady-state isotonic conditions and during complex dynamic length changes. During concentric contractions the shape of the IMP-velocity curve mimicked the basic shape of the force-velocity curve but with much higher variability. For eccentric contractions, a precipitous drop in IMP was observed despite increased muscle stress. The dissociation between muscle stress and IMP during dynamic contractions was partially explained by sensor movement. When the muscle was not moving, IMP explained 89% +/- 5% of the variance in muscle force. However, when transducer movement occurred the linear relationship between IMP and stress was no longer observed. These findings demonstrate the difficulty in interpreting IMP under dynamic conditions when sensor movement occurs. They also illustrate the need to control transducer movement if muscle stress is to be inferred from IMP measurements such as might be desired during clinical gait testing.

  18. Effects of simulation parameters on residual stresses for laser shock peening finite element analysis

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ju Hee [Korea Military Academy, Seoul (Korea, Republic of); Kim, Yun Jae [Korea University, Seoul (Korea, Republic of); Kim, Joung Soo [KAERI, Daejeon (Korea, Republic of)

    2013-07-15

    By using finite element analysis, we proposed an applicable finite element method of laser shock peening (LSP) and discussed various parameters, such as solution time, stability limit, dynamic yield stress, peak pressure, pressure pulse duration, laser spot size, and multiple LSP. The effects of parameters related to the finite element simulation of the LSP process on the residual stresses of 35CD4 30HRC steel alloy are discussed. Parametric sensitivity analyses were performed to establish the optimum processing variables of the LSP process. In addition, we evaluated the effects of initial residual stress, such as welding-induced residual stress field.

  19. Stress Matters: Effects of Anticipated Lexical Stress on Silent Reading

    Science.gov (United States)

    Breen, Mara; Clifton, Charles, Jr.

    2011-01-01

    This paper presents findings from two eye-tracking studies designed to investigate the role of metrical prosody in silent reading. In Experiment 1, participants read stress-alternating noun-verb or noun-adjective homographs (e.g. "PREsent", "preSENT") embedded in limericks, such that the lexical stress of the homograph, as determined by context,…

  20. Stress, strain, and structural dynamics an interactive handbook of formulas, solutions, and Matlab toolboxes

    CERN Document Server

    Yang, Bingen

    2005-01-01

    Stress, Strain, and Structural Dynamics is a comprehensive and definitive reference to statics and dynamics of solids and structures, including mechanics of materials, structural mechanics, elasticity, rigid-body dynamics, vibrations, structural dynamics, and structural controls. This text integrates the development of fundamental theories, formulas and mathematical models with user-friendly interactive computer programs, written in the powerful and popular MATLAB. This unique merger of technical referencing and interactive computing allows instant solution of a variety of engineering problems

  1. Stress effects in twisted highly birefringent fibers

    Science.gov (United States)

    Wolinski, Tomasz R.

    1994-03-01

    Hydrostatic pressure and uniaxial longitudinal strain effects in twisted highly birefringent optical fibers have been investigated from the point of the Marcuse mode-coupling theory. The problem is analyzed in terms of local normal modes of the ideal fiber and in the limit of weak twist, where large linear birefringence dominates over twist effect, and therefore twist coupling between local modes is not effective. The authors present the results of birefringence measurements in highly birefringent bow-tie fibers influenced simultaneously by hydrostatic pressure up to 100 MPa and twisting the result for highly birefringent elliptical-core fibers influenced by uniaxial longitudinal strain up to 4000 (mu) (epsilon) and twisting effect. The birefringence measurement method is based on twist-induced effects and has been successfully applied in a stress environment. The experiment was conducted with a specially designed stress generating device that makes it possible to simultaneously generate various mechanical perturbations such as hydrostatic and radial pressure, axial strain and twist, allowing study of their influence on mode propagation in optical fibers. A comparison with theoretical results as well as with pervious experimental data on stress influence on the beat length parameter in highly birefringent fibers is also provided.

  2. Dynamic changes in saliva after acute mental stress

    Science.gov (United States)

    Naumova, Ella A.; Sandulescu, Tudor; Bochnig, Clemens; Khatib, Philipp Al; Lee, Wing-Kee; Zimmer, Stefan; Arnold, Wolfgang H.

    2014-01-01

    Stress-related variations of fluoride concentration in supernatant saliva and salivary sediment, salivary cortisol, total protein and pH after acute mental stress were assessed. The hypothesis was that stress reactions have no influence on these parameters. Thirty-four male students were distributed into two groups: first received the stress exposure followed by the same protocol two weeks later but without stress exposure, second underwent the protocol without stress exposure followed by the stress exposure two weeks later. The stressor was a public speech followed by tooth brushing. Saliva was collected before, immediately after stress induction and immediately, at 10, 30 and 120 min. after tooth brushing. Cortisol concentrations, total protein, intraoral pH, and fluoride content in saliva were measured. The data were analyzed statistically. Salivary sediment was ca 4.33% by weight of whole unstimulated saliva. Fluoride bioavailability was higher in salivary sediment than in supernatant saliva. The weight and fluoride concentration was not altered during 2 hours after stress exposure. After a public speech, the salivary cortisol concentration significantly increased after 20 minutes compared to the baseline. The salivary protein concentration and pH also increased. Public speaking influences protein concentration and salivary pH but does not alter the fluoride concentration of saliva. PMID:24811301

  3. Studies on effect of stress preconditioning in restrain stress-induced behavioral alterations.

    Science.gov (United States)

    Kaur, Rajneet; Jaggi, Amteshwar Singh; Singh, Nirmal

    2010-02-01

    Stress preconditioning has been documented to confer on gastroprotective effects on stress-induced gastric ulcerations. However, the effects of prior exposure of stress preconditioning episodes on stress-induced behavioral changes have not been explored yet. Therefore the present study was designed to investigate the ameliorative effects of stress preconditioning in immobilization stress-induced behavioral alterations in rats. The rats were subjected to restrain stress by placing in restrainer (5.5 cm in diameter and 18 cm in length) for 3.5 h. Stress preconditioning was induced by subjecting the rats to two cycles of restraint and restrain-free periods of 15 min each. Furthermore, a similar type of stress preconditioning was induced using different time cycles of 30 and 45 min. The extent and severity of the stress-induced behavioral alterations were assessed using different behavioral tests such as hole-board test, social interaction test, open field test, and actophotometer. Restrain stress resulted in decrease in locomotor activity, frequency of head dips and rearing in hole board, line crossing and rearing in open field, and decreased following and increased avoidance in social interaction test. Stress preconditioning with two cycles of 15, 30 or 45 min respectively, did not attenuate stress-induced behavioral changes to any extent. It may be concluded that stress preconditioning does not seem to confer any protective effect in modulating restrain stress-induced behavioral alterations.

  4. The effect of couple-stresses on the stress concentration around a moving crack

    Directory of Open Access Journals (Sweden)

    S. Itou

    1981-01-01

    Full Text Available The problem of a uniformly propagating finite crack in an infinite medium is solved within the linearized couple-stress theory. The self-equilibrated system of pressure is applied to the crack surfaces. The problem is reduced to dual integral equations and solved by a series-expansion method. The dynamic stress-intensity factor is computed numerically.

  5. Dynamic Stresses in a Francis Turbine Runner Based on Fluid-Structure Interaction Analysis

    Institute of Scientific and Technical Information of China (English)

    XIAO Ruofu; WANG Zhengwei; LUO Yongyao

    2008-01-01

    Fatigue and cracks have occurred in many large hydraulic turbines after they were put into production.The cracks are thought to be due to dynamic stresses in the runner caused by hydraulic forces.Computational fluid dynamics(CFD)simulations that included the spiral case,stay vane,guide vane,runner vane.and draft tube were run at various operating points to analyze the pressure distribution on the runner surface and the stress characteristics in the runner due to the fluid-structure interactions(FSl).The dynamic stresses in the Francis turbine runner at the most dangerous operating point were then analyzed.The results show that the dynamic stresses caused by the hydraulic forces during off-design operating points are one of the main reasons for the fatigue and cracks in the runner blade.The results can be used to optimize the runner and to analyze other critical components in the hydraulic turbine.

  6. Influence of effective stress coefficient on mechanical failure of chalk

    DEFF Research Database (Denmark)

    Alam, Mohammad Monzurul; Fabricius, Ida Lykke; Hjuler, M.L.

    2012-01-01

    and vice versa. However, as the effective stress working on the rock decreases with increased effective stress coefficient, the reduction of elastic region will have less effect on pore collapse strength if we consider the change in the effective stress coefficient. This finding will help estimate a more...

  7. Development of crankshaft dynamic stress prediction; Jitsudoji crankshaft oryoku yosoku shuho no kaihatsu

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, S.; Iwamoto, A.; Miyazawa, H.; Sato, K.; Ozaki, H. [Honda R and D Co. Ltd., Tokyo (Japan)

    1997-10-01

    In this paper, the development of the simulation model which predicts the stress of the crankshaft under running condition precisely is described. This simulation model considers about the nonlinearity of the oil film stiffness in the main bearing, the dynamic characteristic of the crankshaft system including resonance and the cylinder block stiffness. By the development of this stress analysis simulation, the stress m each part of the crankshaft during durability testing could be precisely predicted. 1 ref., 10 figs.

  8. Multimillion-atom molecular dynamics simulation of atomic level stresses in Si(111)/Si{sub 3}N{sub 4}(0001) nanopixels

    Energy Technology Data Exchange (ETDEWEB)

    Bachlechner, M.E.; Omeltchenko, A.; Nakano, A.; Kalia, R.K.; Vashishta, P. [Concurrent Computing Laboratory for Materials Simulations, Department of Physics Astronomy and Department of Computer Science, Louisiana State University, Baton Rouge, Louisiana70803-4001 (United States); Ebbsjoe, I. [Studsvik Neutron Research Laboratory, University of Uppsala, S-611 82Nykoeping (Sweden); Madhukar, A. [Department of Materials Science and Engineering, University of Southern California, Los Angeles, California90089-0241 (United States); Messina, P. [Center for Advanced Computing Research, California Institute of Technology, Pasadena, California91125 (United States)

    1998-04-01

    Ten million atom multiresolution molecular-dynamics simulations are performed on parallel computers to determine atomic-level stress distributions in a 54 nm nanopixel on a 0.1 {mu}m silicon substrate. Effects of surfaces, edges, and lattice mismatch at the Si(111)/Si{sub 3}N{sub 4}(0001) interface on the stress distributions are investigated. Stresses are found to be highly inhomogeneous in the nanopixel. The top surface of silicon nitride has a compressive stress of +3GPa and the stress is tensile, {minus}1GPa, in silicon below the interface. {copyright} {ital 1998 American Institute of Physics.}

  9. Effect of Conductor Verbalization, Dynamic Markings, Conductor Gesture, and Choir Dynamic Level on Singers' Dynamic Responses.

    Science.gov (United States)

    Skadsem, Julie A.

    1997-01-01

    Examines the effects of conductor verbalization, dynamic markings, conductor gesture, and choir dynamic level on individual singers' dynamic responses. Indicates that verbal instructions from the conductor elicited significantly stronger dynamic performance responses than did the other instructional conditions. Suggests that additional research…

  10. Stress Management Strategies for Students: The Immediate Effects of Yoga, Humor, and Reading on Stress

    Science.gov (United States)

    Rizzolo, Denise; Zipp, Genevieve Pinto; Stiskal, Doreen; Simpkins, Susan

    2009-01-01

    Background: Health science programs can be demanding and difficult for many students, leading to high levels of stress. High levels of stress can have a negative effect on students and subsequently the practicing clinician. Research suggests that yoga, humor, and reading are simple, effective methods to help reduce stress. To date no research…

  11. A FIBER-BRIDGING MODEL WITH STRESS GRADIENT EFFECTS

    Institute of Scientific and Technical Information of China (English)

    孙毅; 李涛

    2000-01-01

    Institute of Mechanics, Chinese Academy of Sciences, Beijing 100080, China)ABSTRACT: A fiber-bridging model with stress gradient effects is proposed for unidirectional fiber-reinforced composites. The stress gradient terms are introduced by solving a micromechanical model under a non-uniform stress loading. It is shown that the stress gradient effect is significant on both the fiber-bridging stress distribution and the value of the critical load of fiber failure.

  12. Dynamic topography as constraints on stress and viscosity in the mantle and lithosphere

    Science.gov (United States)

    Zhong, S.

    2015-12-01

    Mantle convection generates stress in the mantle and lithosphere. The lithosphere stress is responsible for localized deformation including seismic deformation at plate boundaries, and localized stress highs in lithosphere are also suggested to cause dynamically self-consistent generation of plate tectonics and continental lithosphere instability, as the stress exceeds a threshold or yield stress. Modeling load-induced deformation at oceanic islands (e.g., Hawaii) constrains lithospheric stress at 100-200 MPa in the plate interiors, leading to a lower limit on lithospheric yield stress (Zhong and Watts, 2013). However, convection-induced lithospheric stress is poorly understood, ranging from 500 MPa to tens of MPa as reported in mantle convection studies. The magnitude and distribution of lithospheric and mantle stress depend critically on buoyancy and viscosity, particularly the latter. Unfortunately, lithospheric and mantle viscosity is also poorly constrained. For example, the inferred lower mantle viscosity from post-glacial rebound and geoid modeling studies ranges from 1023 Pas to 1022 Pas (e.g., Mitrovica and Forte, 2004; Simons and Hager, 1996; Paulson et al., 2007). In addition to the stress, the lower mantle viscosity may also affect the time evolution of mantle structure including sinking rate of slabs and formation of the degree-2 mantle seismic structure. Therefore, it is important to develop independent constraints on mantle viscosity and convection-induced stress. In this study, I demonstrate that dynamic topography can be used to place first-order constraints on both lithospheric stress and mantle viscosity. For a given superadiabatic temperature difference across the mantle (e.g., 2500 K), a larger mantle viscosity (or a smaller Rayleigh number) leads to a larger lithospheric stress and a larger dynamic topography. To be consistent with the inferred dynamic topography, the lower mantle viscosity is constrained to be significantly smaller than 1023

  13. Stress Symptoms: Effects on Your Body and Behavior

    Science.gov (United States)

    ... heart disease, obesity and diabetes. Common effects of stress on your body Headache Muscle tension or pain ... drive Stomach upset Sleep problems Common effects of stress on your mood Anxiety Restlessness Lack of motivation ...

  14. Dynamical Stress Analysis of Tectonic Earthquakes in Nusa Tenggara and its possible relations to the Activity of Mt. Rinjani, Indonesia

    Directory of Open Access Journals (Sweden)

    Bakti Sukrisna

    2017-01-01

    Full Text Available Some strong earthquakes are associated with increasing of volcanic activity in near and also in far field. This research is to investigate the effect of the tectonic earthquakes in Nusa Tenggara Island area towards the October 25th,2015 eruption of Mt. Rinjani, Indonesia. Three earthquakes occurred before the eruptions; Mw 5 Sumba earthquake on June 10th 2015, Mw 5.8 South of Java earthaquake July 26th, 2016 and Mw 5 South of Bali on August 6th, 2015. In theory, dynamical stress transfer can be calculated by analyzing synthetic seismogram as a waveform simulation at the volcano and the change of dynamical stress can be calculated with the finitedifference numerical method. Our result indicates that the dynamic stress value is still below the threshold value that can trigger eruptions. Simulation of three earthquakes by varying the magnitude of each earthquake shows that dynamic stress changes will surpass the threshold at Mw  7.5. As all the earthquake that used in this study have magnitude smaller then the threshold, it can be concluded that the eruption of Mount Rinjani was triggered by internal factors, and very unlikely triggered by tyhe earthquake we investigated in this study.

  15. Visualization of stress propagation in dynamically compacted wetted particle beds

    Science.gov (United States)

    Marr, Bradley J.; Frost, David L.

    2017-01-01

    The high-strain-rate response of granular media has received considerable attention due to increasing interest in granular penetration. Introduction of a liquid phase into the particle bed alters the global deformation response of the system as the liquid is capable of supporting stresses. In the present study, we investigate the response of arrays of stacked glass rods, both dry and immersed in liquid, under varying drop weight-induced stress loadings. We examine the role of saturation on particle and bed deformation, using well-defined loading conditions and particle bed arrangements. Using high-speed photograph and the photoelastic nature of the glass rods, the propagation of the stress wave through the two-phase system can be visualized. The liquid phase was seen to contribute to the mean stress transfer within the system, resulting in reduced total driver displacements as well as increased bed strains at the time when particle fracturing was first observed.

  16. Osmotic and Heat Stress Effects on Segmentation

    Science.gov (United States)

    Weiss, Julian

    2016-01-01

    During vertebrate embryonic development, early skin, muscle, and bone progenitor populations organize into segments known as somites. Defects in this conserved process of segmentation lead to skeletal and muscular deformities, such as congenital scoliosis, a curvature of the spine caused by vertebral defects. Environmental stresses such as hypoxia or heat shock produce segmentation defects, and significantly increase the penetrance and severity of vertebral defects in genetically susceptible individuals. Here we show that a brief exposure to a high osmolarity solution causes reproducible segmentation defects in developing zebrafish (Danio rerio) embryos. Both osmotic shock and heat shock produce border defects in a dose-dependent manner, with an increase in both frequency and severity of defects. We also show that osmotic treatment has a delayed effect on somite development, similar to that observed in heat shocked embryos. Our results establish osmotic shock as an alternate experimental model for stress, affecting segmentation in a manner comparable to other known environmental stressors. The similar effects of these two distinct environmental stressors support a model in which a variety of cellular stresses act through a related response pathway that leads to disturbances in the segmentation process. PMID:28006008

  17. Stress vulnerability and the effects of moderate daily stress on sleep polysomnography and subjective sleepiness.

    Science.gov (United States)

    Petersen, Helena; Kecklund, Göran; D'Onofrio, Paolo; Nilsson, Jens; Åkerstedt, Torbjörn

    2013-02-01

    The purpose of this study was to investigate if and how sleep physiology is affected by naturally occurring high work stress and identify individual differences in the response of sleep to stress. Probable upcoming stress levels were estimated through weekly web questionnaire ratings. Based on the modified FIRST-scale (Ford insomnia response to stress) participants were grouped into high (n = 9) or low (n = 19) sensitivity to stress related sleep disturbances (Drake et al., 2004). Sleep was recorded in 28 teachers with polysomnography, sleep diaries and actigraphs during one high stress and one low stress condition in the participants home. EEG showed a decrease in sleep efficiency during the high stress condition. Significant interactions between group and condition were seen for REM sleep, arousals and stage transitions. The sensitive group had an increase in arousals and stage transitions during the high stress condition and a decrease in REM, whereas the opposite was seen in the resilient group. Diary ratings during the high stress condition showed higher bedtime stress and lower ratings on the awakening index (insufficient sleep and difficulties awakening). Ratings also showed lower cognitive function and preoccupation with work thoughts in the evening. KSS ratings of sleepiness increased during stress for the sensitive group. Saliva samples of cortisol showed no effect of stress. It was concluded that moderate daily stress is associated with a moderate negative effect on sleep sleep efficiency and fragmentation. A slightly stronger effect was seen in the sensitive group. © 2012 European Sleep Research Society.

  18. Growing up with stress - carbon sequestration and allocation dynamics of a broadleaf evergreen forest

    Science.gov (United States)

    Griebel, Anne; Bennett, Lauren T.; Arndt, Stefan K.

    2016-04-01

    recorded in the years with highest NEE, but NEE was not a strong seasonal driver of stem increment. Recently developed terrestrial lidar scanners (VEGNET) monitored the daily changes in canopy dynamics with a comparable temporal resolution to dendrometer and eddy covariance measurements. Growth of each canopy stratum was distinctly seasonal, and we detected contrasting responses to climatic stress along the canopy height gradient. Leaf turnover was predominantly in summer and was initiated by prolonged heat stress and isolated storm events. Leaf shedding and replacement happened concurrently, with leaves being mainly discarded from the middle stratum and replaced in the top stratum. Due to our novel multi-instrument approach and the high temporal resolution of tree to ecosystem-scale growth dynamics we were able to demonstrate that above ground carbon allocation to stem and crown pools followed separate seasonal dynamics that did not necessarily follow the same seasonality as ecosystem scale carbon sequestration. Our findings will ultimately improve our understanding of the effects of short- and long-term variability in temperature and moisture stress on carbon allocation dynamics to the above ground biomass pools for broadleaf evergreen ecosystems.

  19. Effect of material parameters on stress wave propagation during fast upsetting

    Institute of Scientific and Technical Information of China (English)

    WANG Zhong-jin; CHENG Li-dong

    2008-01-01

    Based'on a dynamic analysis method and an explicit algorithm, a dynamic explicit finite element code was developed for modeling the fast upsetting process of block under drop hammer impact, in which the hammer velocity during the deformation was calculated by energy conservation law according to the operating principle of hammer equipment. The stress wave propagation and its effect on the deformation were analyzed by the stress and strain distributions. Industrial pure lead, oxygen-free high-conductivity (OFHC) copper and 7039 aluminum alloy were chosen to investigate the effect of material parameters on the stress wave propagation. The results show that the stress wave propagates from top to bottom of block, and then reflects back when it reaches the bottom surface. After that, stress wave propagates and reflects repeatedly between the upper surface and bottom surface. The stress wave propagation has a significant effect on the deformation at the initial stage, and then becomes weak at the middle-final stage. When the ratio of elastic modulus or the slope of stress-strain curve to mass density becomes larger, the velocity of stress wave propagation increases, and the influence of stress wave on the deformation becomes small.

  20. Tunnel design considering stress release effect

    Institute of Scientific and Technical Information of China (English)

    Van-hung DAO

    2009-01-01

    In tunnel design,the determination of installation time and the stiffness of supporting structures is very important to the tunnel stability.This study used the convergence-confinement method to determine the stress and displacement of the tunnel while considering the counter-pressure curve of the ground base,the stress release effect,and the interaction between the tunnel lining and the rock surrounding the tunnel chamber.The results allowed for the determination of the installation time,distribution and strength of supporting structures.This method was applied to the intake tunnel in the Ban Ve Hydroelectric Power Plant,in Nghe An Province,Vietnam.The results show that when a suitable displacement u0 ranging from 0.0865 m to 0.0919 m occurrs,we can install supporting structures that satisfy the stability and economical requirements.

  1. Dynamic modeling of cellular response to DNA damage based on p53 stress response networks

    Institute of Scientific and Technical Information of China (English)

    Jinpeng Qi; Yongsheng Ding; Shihuang Shao

    2009-01-01

    Under acute perturbations from the outside, cells can trigger self-defensive mechanisms to fight against genome stress. To investigate the cellular response to continuous ion radiation (IR), a dynamic model for p53 stress response networks at the cellular level is proposed. The model can successfully be used to simulate the dynamic processes of double-strand breaks (DSBs) generation and their repair, switch-like ataxia telangiectasia mutated (ATM) activation, oscillations occurring in the p53-MDM2 feedback loop, as well as toxins elimination triggered by p53 stress response networks. Especially, the model can predict the plausible outcomes of cellular response under different IR dose regimes.

  2. Long-range correlations and fractal dynamics in C. elegans: Changes with aging and stress

    Science.gov (United States)

    Alves, Luiz G. A.; Winter, Peter B.; Ferreira, Leonardo N.; Brielmann, Renée M.; Morimoto, Richard I.; Amaral, Luís A. N.

    2017-08-01

    Reduced motor control is one of the most frequent features associated with aging and disease. Nonlinear and fractal analyses have proved to be useful in investigating human physiological alterations with age and disease. Similar findings have not been established for any of the model organisms typically studied by biologists, though. If the physiology of a simpler model organism displays the same characteristics, this fact would open a new research window on the control mechanisms that organisms use to regulate physiological processes during aging and stress. Here, we use a recently introduced animal-tracking technology to simultaneously follow tens of Caenorhabdits elegans for several hours and use tools from fractal physiology to quantitatively evaluate the effects of aging and temperature stress on nematode motility. Similar to human physiological signals, scaling analysis reveals long-range correlations in numerous motility variables, fractal properties in behavioral shifts, and fluctuation dynamics over a wide range of timescales. These properties change as a result of a superposition of age and stress-related adaptive mechanisms that regulate motility.

  3. THE DYNAMIC INTERCONNECTION BETWEEN MAN AND ENVIRONMENT, A FACTOR OF STRESS AND ECO STRESS

    OpenAIRE

    SIMIONESCU IRINA

    2014-01-01

    The reason for writing this paper is the omnipresence but also the impact of stress in our times. In order to explain why stress has gained an important place in modern history, we need to understand the evolution of medical science and technology, which over the last decades, have taken important steps towards establishing the biological links between stress and human behaviour but also the political and cultural contexts that have endowed with meaning and authority the scien...

  4. Stress effects on memory : An update and integration

    NARCIS (Netherlands)

    Schwabe, Lars; Joëls, Marian; Roozendaal, Benno; Wolf, Oliver T.; Oitzl, Melly S.

    2012-01-01

    It is well known that stressful experiences may affect learning and memory processes. Less clear is the exact nature of these stress effects on memory: both enhancing and impairing effects have been reported. These opposite effects may be explained if the different time courses of stress hormone, in

  5. Stress effects on memory: an update and integration

    NARCIS (Netherlands)

    Schwabe, L.; Joels, M.; Roozendaal, B.; Wolf, O.T.; Oitzl, M.S.

    2012-01-01

    It is well known that stressful experiences may affect learning and memory processes. Less clear is the exact nature of these stress effects on memory: both enhancing and impairing effects have been reported. These opposite effects may be explained if the different time courses of stress hormone, in

  6. Stress effects on memory : An update and integration

    NARCIS (Netherlands)

    Schwabe, Lars; Joëls, Marian; Roozendaal, Benno; Wolf, Oliver T.; Oitzl, Melly S.

    2012-01-01

    It is well known that stressful experiences may affect learning and memory processes. Less clear is the exact nature of these stress effects on memory: both enhancing and impairing effects have been reported. These opposite effects may be explained if the different time courses of stress hormone, in

  7. Dynamic Stress Analysis of the Leg Joints of Self-Elevating Platform

    Institute of Scientific and Technical Information of China (English)

    HUANG Zhao-yu; TANG Wen-yong; WANG Yi; WANG Wen-tao

    2011-01-01

    Since a self-elevating platform often works in water for a long time, the lattice leg is largely influenced by wave and current. The amplitude of leg joint stresses is a very important factor for the fatigue life of the platform. However, there are not many researches having been done on the mechanism and dynamic stress analysis of these leg joints. This paper focuses on the dynamic stress analysis and suppression methods of the leg joints of self-elevating platforms. Firstly, the dynamic stresses of the lattice leg joints are analyzed for a self-elevating platform by use of the 5th-order Stokes wave theory. Secondly, the axial and bending stresses are studied due to their large contributions to total stresses. And then, different joint types are considered and the leg-hull interface stiffness is analyzed for the improvement of the joint dynamic stress amplitude. Finally, some useful conclusions are drawn for the optimization design of the self-elevating platform.

  8. Multibody Dynamic Stress Simulation of Rigid-Flexible Shovel Crawler Shoes

    Directory of Open Access Journals (Sweden)

    Samuel Frimpong

    2016-06-01

    Full Text Available Electric shovels are used in surface mining operations to achieve economic production capacities. The capital investments and operating costs associated with the shovels deployed in the Athabasca oil sands formation are high due to the abrasive conditions. The shovel crawler shoes interact with sharp and abrasive sand particles, and, thus, are subjected to high transient dynamic stresses. These high stresses cause wear and tear leading to crack initiation, propagation and premature fatigue failure. The objective of this paper is to develop a model to characterize the crawler stresses and deformation for the P&H 4100C BOSS during propel and loading using rigid-flexible multi-body dynamic theory. A 3-D virtual prototype model of the rigid-flexible crawler track assembly and its interactions with oil sand formation is simulated to capture the model dynamics within multibody dynamics software MSC ADAMS. The modal and stress shapes and modal loads due to machine weight for each flexible crawler shoes are generated from finite element analysis (FEA. The modal coordinates from the simulation are combined with mode and stress shapes using modal superposition method to calculate real-time stresses and deformation of flexible crawler shoes. The results show a maximum von Mises stress value of 170 MPa occurring in the driving crawler shoe during the propel motion. This study provides a foundation for the subsequent fatigue life analysis of crawler shoes for extending crawler service life.

  9. Effect of longwall length on mechanical characteristics of surrounding rock stress shell in mining face

    Energy Technology Data Exchange (ETDEWEB)

    Guang-Xiang Xie; Lei Wang [Anhui University of Science and Technology, Huainan (China)

    2008-12-15

    The mechanical characteristics of surrounding rock stress shell in longwall mining face were studied, based on the results of in-situ measurement combined with numerical simulation, and the effect of longwall length on mechanical characteristics of surrounding rock stress shell was discovered. The results show that the mechanical characteristics of surrounding rock stress shell are influenced by the length of the face. With an increase of mining face length, the level of concentration of shell stress located in the front face and surrounding rock of roadway is amplified and the three- dimensional stress is focused in the working face. The damage lies in the head entry corner of face and the vertical displacement is reduced but horizontal displacement is enlarged. The dynamic balance of surrounding rock stress shell is improved with rational adjustment of face length. It is effective in protecting the working face and controlling strata behavior. 5 refs., 7 figs.

  10. Acute stress does not affect the impairing effect of chronic stress on memory retrieval

    Directory of Open Access Journals (Sweden)

    Jamile Ozbaki

    2016-07-01

    Full Text Available Objective(s: Due to the prevalence and pervasiveness of stress in modern life and exposure to both chronic and acute stresses, it is not clear whether prior exposure to chronic stress can influence the impairing effects of acute stress on memory retrieval. This issue was tested in this study. Materials and Methods: Adult male Wistar rats were randomly assigned to the following groups: control, acute, chronic, and chronic + acute stress groups. The rats were trained with six trials per day for 6 consecutive days in the water maze. Following training, the rats were either kept in control conditions or exposed to chronic stress in a restrainer 6 hr/day for 21 days. On day 22, a probe test was done to measure memory retention. Time spent in target and opposite areas, platform location latency, and proximity were used as indices of memory retention. To induce acute stress, 30 min before the probe test, animals received a mild footshock. Results: Stressed animals spent significantly less time in the target quadrant and more time in the opposite quadrant than control animals. Moreover, the stressed animals showed significantly increased platform location latency and proximity as compared with control animals. No significant differences were found in these measures among stress exposure groups. Finally, both chronic and acute stress significantly increased corticosterone levels. Conclusion: Our results indicate that both chronic and acute stress impair memory retrieval similarly. Additionally, the impairing effects of chronic stress on memory retrieval were not influenced by acute stress.

  11. Acute stress does not affect the impairing effect of chronic stress on memory retrieval

    Science.gov (United States)

    Ozbaki, Jamile; Goudarzi, Iran; Salmani, Mahmoud Elahdadi; Rashidy-Pour, Ali

    2016-01-01

    Objective(s): Due to the prevalence and pervasiveness of stress in modern life and exposure to both chronic and acute stresses, it is not clear whether prior exposure to chronic stress can influence the impairing effects of acute stress on memory retrieval. This issue was tested in this study. Materials and Methods: Adult male Wistar rats were randomly assigned to the following groups: control, acute, chronic, and chronic + acute stress groups. The rats were trained with six trials per day for 6 consecutive days in the water maze. Following training, the rats were either kept in control conditions or exposed to chronic stress in a restrainer 6 hr/day for 21 days. On day 22, a probe test was done to measure memory retention. Time spent in target and opposite areas, platform location latency, and proximity were used as indices of memory retention. To induce acute stress, 30 min before the probe test, animals received a mild footshock. Results: Stressed animals spent significantly less time in the target quadrant and more time in the opposite quadrant than control animals. Moreover, the stressed animals showed significantly increased platform location latency and proximity as compared with control animals. No significant differences were found in these measures among stress exposure groups. Finally, both chronic and acute stress significantly increased corticosterone levels. Conclusion: Our results indicate that both chronic and acute stress impair memory retrieval similarly. Additionally, the impairing effects of chronic stress on memory retrieval were not influenced by acute stress. PMID:27635201

  12. The effects of stress on glutamatergic transmission in the brain.

    Science.gov (United States)

    Yuan, Ti-Fei; Hou, Gonglin

    2015-01-01

    Stress leads to detrimental effects on brain functions and results in various diseases. Recent studies highlight the involvement of glutamatergic transmission in pathogenesis of depressive behaviors and fears. Acute stress generates different impacts on the excitatory transmission compared to chronic stress. Different neuromodulators and epigenetic factors also participate in the alteration of synaptic transmission and the regulation of synaptic plasticity. Restoration of the glutamatergic transmission in stress-affected brain areas therefore provides novel directions of therapeutic interventions against stress.

  13. Investigating the effect of chemical stress and resource ...

    Science.gov (United States)

    Modeling exposure and recovery of fish and wildlife populations after stressor mitigation serves as a basis for evaluating population status and remediation success. The Atlantic killifish (Fundulus heteroclitus) is an important and well-studied model organism for understanding the effects of pollutants and other stressors in estuarine and marine ecosystems. Herein, we develop a density dependent matrix population model for Atlantic killifish that analyzes both size-structure and age class-structure of the population so that we could readily incorporate output from a dynamic energy budget (DEB) model currently under development. This population modeling approach emphasizes application in conjunction with field monitoring efforts (e.g., through effects-based monitoring programs) and/or laboratory analysis to link effects due to chemical stress to adverse outcomes in whole organisms and populations. We applied the model using data for killifish exposed to dioxin-like compounds, taken from a previously published study. Specifically, the model was used to investigate population trajectories for Atlantic killifish with dietary exposures to 112, 296, and 875 pg/g of dioxin with effects on fertility and survival rates. All effects were expressed relative to control fish. Further, the population model was employed to examine age and size distributions of a population exposed to resource limitation in addition to chemical stress. For each dietary exposure concentration o

  14. Balancer effects in opinion dynamics

    CERN Document Server

    Cheon, Taksu

    2016-01-01

    We introduce a novel type of contrarian agent, the balancer, to Galam model of opinion dynamics, in order to account for the skepticism over one-sidedness and for the sense of fairness. We find that the inclusion of balancers along with floaters and inflexibles brings about a critical point on parametric plane of the dynamical system, which results in the new kind of stable final states of the opinion dynamics, that seem to capture several intriguing features found often in mature democracies.

  15. Modeling the Effects of Stress: An Approach to Training

    Science.gov (United States)

    Cuper, Taryn

    2010-01-01

    Stress is an integral element of the operational conditions experienced by combat medics. The effects of stress can compromise the performance of combat medics who must reach and treat their comrades under often threatening circumstances. Examples of these effects include tunnel vision, loss of motor control, and diminished hearing, which can result in an inability to perceive further danger, satisfactorily treat the casualty, and communicate with others. While many training programs strive to recreate this stress to aid in the experiential learning process, stress inducement may not always be feasible or desired. In addition, live simulations are not always a practical, convenient, and repeatable method of training. Instead, presenting situational training on a personal computer is proposed as an effective training platform in which the effects of stress can be addressed in a different way. We explore the cognitive and motor effects of stress, as well as the benefits of training for mitigating these effects in real life. While many training applications focus on inducing stress in order to "condition" the stress response, the author explores the possibilities of modeling stress to produce a similar effect. Can presenting modeled effects of stress help prepare or inoculate soldiers for stressful situations in which they must perform at a high level? This paper investigates feasibility of modeling stress and describes the preliminary design considerations of a combat medic training system that utilizes this method of battlefield preparation.

  16. Inoculation of drought-stressed strawberry with a mixed inoculum of two arbuscular mycorrhizal fungi: effects on population dynamics of fungal species in roots and consequential plant tolerance to water deficiency.

    Science.gov (United States)

    Boyer, Louisa Robinson; Brain, Philip; Xu, Xiang-Ming; Jeffries, Peter

    2015-04-01

    The effect of inoculation with two arbuscular mycorrhizal fungi (AMF) on growth and drought tolerance of cultivated strawberry (Fragaria × ananassa) was studied. Three treatments (a single treatment either of Funneliformis mosseae BEG25, Funneliformis geosporus BEG11 or a 50:50 mixed inoculation treatment of both species) were compared to uninoculated plants. Species-specific primers for qPCR quantification of F. geosporus and F. mosseae DNA were developed to quantify the relative abundance of each fungus in roots of strawberry under different conditions of water stress. Co-occupation of the same root by both species was shown to commonly occur, but their relative abundance varied with water stress (reduced irrigation of up to 40%). Greater root colonisation was observed microscopically under water stress, but this increased colonisation was often accompanied with decreased amounts of fungal DNA in the root. F. mosseae tended to become more abundant under water stress relative to F. geosporus. There was significant correlation in the fungal colonisation measurements from the microscopic and qPCR methods under some conditions, but the nature of this relationship varied greatly with AMF inoculum and abiotic conditions. Single-species inoculation treatments gave similar benefits to the host to the mixed inoculation treatment regardless of irrigation regime; here, amount of colonisation was of greater importance than functional diversity. The addition of AMF inocula to plants subjected to reduced irrigation restored plant growth to the same or higher values as the non-mycorrhizal, fully-watered plants. The water use efficiency of plants was greater under the regulated deficit irrigation (RDI) regime and in AMF-inoculated plants, but there were no significant differences between plants inoculated with the single or combined inoculum. This study demonstrated that the increase in plant growth was directly influenced by an increase in root colonisation by AMF when

  17. Carbon and Nitrogen dynamics in deciduous and broad leaf trees under drought stress

    Science.gov (United States)

    Joseph, Jobin; Schaub, Marcus; Arend, Matthias; Saurer, Matthias; siegwolf, Rolf; Weiler, Markus; Gessler, Arthur

    2017-04-01

    Climate change is projected to lead to an increased frequency and duration of severe drought events in future. Already within the last twenty years, however, drought stress related forest mortality has been increasing across the globe. Tree and forest die off events have multiple adverse effects on ecosystem functioning and might convert previous carbon sinks to act as carbon sources instead and can thus intensify the effect of climate change and global warming. Current predictions of forest's functioning under drought and thus forest mortality under future climatic conditions are constrained by a still incomplete picture of the trees' physiological reactions that allows some trees to survive drought periods while others succumb. Concerning the effects of drought on the carbon balance and on tree hydraulics our picture is getting more complete, but still interactions between abiotic factors and pest and diseases as well as the interaction between carbon and nutrient balances as factors affecting drought induced mortality are not well understood. Reduced carbon allocation from shoots to roots might cause a lack of energy for root nutrient uptake and to a shortage of carbon skeletons for nitrogen assimilation and thus to an impaired nutrient status of trees. To tackle these points, we have performed a drought stress experiment with six different plant species, 3 broad leaf (maple, beech and oak) and 3 deciduous (pine, fir and spruce). Potted two-year-old seedlings were kept inside a greenhouse for 5 months and 3 levels of drought stress (no stress (control), intermediate and intensive drought stress) were applied by controlling water supply. Gas exchange measurements were performed periodically to monitor photosynthesis, transpiration, stomatal conductance. At the pinnacle of drought stress, we applied isotopic pulse labelling: On the one hand we exposed trees to 13CO2 to investigate on carbon dynamics and the allocation of new assimilates within the plant. Moreover

  18. 3D Dynamic Finite Element Analysis of the Nonuniform Residual Stress in Ultrasonic Impact Treatment Process

    Science.gov (United States)

    Hu, Shengsun; Guo, Chaobo; Wang, Dongpo; Wang, Zhijiang

    2016-09-01

    The nonuniform distributions of the residual stress were simulated by a 3D finite element model to analyze the elastic-plastic dynamic ultrasonic impact treatment (UIT) process of multiple impacts on the 2024 aluminum alloy. The evolution of the stress during the impact process was discussed. The successive impacts during the UIT process improve the uniformity of the plastic deformation and decrease the maximum compressive residual stress beneath the former impact indentations. The influences of different controlled parameters, including the initial impact velocity, pin diameter, pin tip, device moving, and offset distances, on the residual stress distributions were analyzed. The influences of the controlled parameters on the residual stress distributions are apparent in the offset direction due to the different surface coverage in different directions. The influences can be used to understand the UIT process and to obtain the desired residual stress by optimizing the controlled parameters.

  19. Risk evaluation of rock burst through theory of static and dynamic stresses superposition

    Institute of Scientific and Technical Information of China (English)

    李振雷; 蔡武; 窦林名; 何江; 王桂峰; 丁言露

    2015-01-01

    Rock burst is one of the most catastrophic dynamic hazards in coal mining. A static and dynamic stresses superposition-based (SDSS-based) risk evaluation method of rock burst was proposed to pre-evaluate rock burst risk. Theoretical basis of this method is the stress criterion incurring rock burst and rock burst risk is evaluated according to the closeness degree of the total stress (due to the superposition of static stress in the coal and dynamic stress induced by tremors) with the critical stress. In addition, risk evaluation criterion of rock burst was established by defining the “Satisfaction Degree” of static stress. Furthermore, the method was used to pre-evaluate rock burst risk degree and prejudge endangered area of an insular longwall face in Nanshan Coal Mine in China. Results show that rock burst risk is moderate at advance extent of 97 m, strong at advance extent of 97−131 m, and extremely strong (i.e. inevitable to occur) when advance extent exceeds 131 m (mining is prohibited in this case). The section of two gateways whose floor abuts 15−3 coal seam is a susceptible area prone to rock burst. Evaluation results were further compared with rock bursts and tremors detected by microseismic monitoring. Comparison results indicate that evaluation results are consistent with microseismic monitoring, which proves the method’s feasibility.

  20. Theory of nonlinear elasticity, stress-induced relaxation, and dynamic yielding in dense fluids of hard nonspherical colloids.

    Science.gov (United States)

    Zhang, Rui; Schweizer, Kenneth S

    2012-04-21

    We generalize the microscopic naïve mode coupling and nonlinear Langevin equation theories of the coupled translation-rotation dynamics of dense suspensions of uniaxial colloids to treat the effect of applied stress on shear elasticity, cooperative cage escape, structural relaxation, and dynamic and static yielding. The key concept is a stress-dependent dynamic free energy surface that quantifies the center-of-mass force and torque on a moving colloid. The consequences of variable particle aspect ratio and volume fraction, and the role of plastic versus double glasses, are established in the context of dense, glass-forming suspensions of hard-core dicolloids. For low aspect ratios, the theory provides a microscopic basis for the recently observed phenomenon of double yielding as a consequence of stress-driven sequential unlocking of caging constraints via reduction of the distinct entropic barriers associated with the rotational and translational degrees of freedom. The existence, and breadth in volume fraction, of the double yielding phenomena is predicted to generally depend on both the degree of particle anisotropy and experimental probing frequency, and as a consequence typically occurs only over a window of (high) volume fractions where there is strong decoupling of rotational and translational activated relaxation. At high enough concentrations, a return to single yielding is predicted. For large aspect ratio dicolloids, rotation and translation are always strongly coupled in the activated barrier hopping event, and hence for all stresses only a single yielding process is predicted.

  1. Non-linear hydrotectonic phenomena: Part I - fluid flow in open fractures under dynamical stress loading

    Energy Technology Data Exchange (ETDEWEB)

    Archambeau, C.B. [Univ. of Colorado, Boulder, CO (United States)

    1994-01-01

    A fractured solid under stress loading (or unloading) can be viewed as behaving macroscopically as a medium with internal, hidden, degrees of freedom, wherein changes in fracture geometry (i.e. opening, closing and extension) and flow of fluid and gas within fractures will produce major changes in stresses and strains within the solid. Likewise, the flow process within fractures will be strongly coupled to deformation within the solid through boundary conditions on the fracture surfaces. The effects in the solid can, in part, be phenomenologically represented as inelastic or plastic processes in the macroscopic view. However, there are clearly phenomena associated with fracture growth and open fracture fluid flows that produce effects that can not be described using ordinary inelastic phenomenology. This is evident from the fact that a variety of energy release phenomena can occur, including seismic emissions of previously stored strain energy due to fracture growth, release of disolved gas from fluids in the fractures resulting in enhanced buoyancy and subsequent energetic flows of gas and fluids through the fracture system which can produce raid extension of old fractures and the creation of new ones. Additionally, the flows will be modulated by the opening and closing of fractures due to deformation in the solid, so that the flow process is strongly coupled to dynamical processes in the surrounding solid matrix, some of which are induced by the flow itself.

  2. Stress of dynamic loaded protection cab ROPS of truck

    Directory of Open Access Journals (Sweden)

    Ševčík Ladislav

    2017-01-01

    Full Text Available The paper describes the design geometry, calculate deformation, deformation energy and stress safety of extended hydraulically lifted ROPS frame lorry TATRA by FEM according to Australian Standard AS 2294.2-1997 Earth-moving machinery-Protective Structures, Part 2: Laboratory tests and performance requirements for roll-over protective structures and by international Standard ISO 3471: 2008 (E for the proposed design solution.

  3. Effects of work stress and home stress on autonomic nervous function in Japanese male workers.

    Science.gov (United States)

    Maeda, Eri; Iwata, Toyoto; Murata, Katsuyuki

    2015-01-01

    Autonomic imbalance is one of the important pathways through which psychological stress contributes to cardiovascular diseases/sudden death. Although previous studies have focused mainly on stress at work (work stress), the association between autonomic function and stress at home (home stress) is still poorly understood. The purpose was to clarify the effect of work/home stress on autonomic function in 1,809 Japanese male workers. We measured corrected QT (QTc) interval and QT index on the electrocardiogram along with blood pressure and heart rate. Participants provided self-reported information about the presence/absence of work/home stress and the possible confounders affecting QT indicators. Home stress was related positively to QT index (p=0.040) after adjusting for the possible confounders, though work stress did not show a significant relation to QTc interval or QT index. The odds ratio of home stress to elevated QT index (≥105) was 2.677 (95% CI, 1.050 to 6.822). Work/home stress showed no significant relation to blood pressure or heart rate. These findings suggest that autonomic imbalance, readily assessed by QT indicators, can be induced by home stress in Japanese workers. Additional research is needed to identify different types of home stress that are strongly associated with autonomic imbalance.

  4. Perceived stress and self-esteem mediate the effects of work-related stress on depression.

    Science.gov (United States)

    Lee, Jong-Sun; Joo, Eun-Jeong; Choi, Kyeong-Sook

    2013-02-01

    The aim of the present study was to investigate the impact of perceived stress and self-esteem on work-related stress and depression. Two hundred and eighty-four Korean nurses participated in the study. The participants completed four questionnaires, including the Korean short version of the occupational stress scale, the perceived stress scale, the Rosenberg self-esteem scale and the Beck depression inventory. Structural equation modelling was used to determine the relationships among work-related stress, perceived stress, self-esteem, and depression. Work-related stress was positively associated with depression. Perceived stress was inversely related to self-esteem and positively associated with work-related stress and depression, respectively. Self-esteem was negatively associated with work-related stress and depression. Structural equation modelling revealed that self-esteem and perceived stress fully mediate the relationship between work-related stress and depression. Future studies should further investigate the effect of psychological characteristics on work-related stress and symptoms of depression.

  5. Dynamic Finite Element Analysis of Impulsive Stress Waves Propagating from Distal End of Femur

    Directory of Open Access Journals (Sweden)

    Sarai,Takaaki

    2012-10-01

    Full Text Available The human femur is subjected to an impulsive load at its distal end during daily life. Femoral bone fracture caused by impact loading is common in elderly women. It is important to clarify the dynamic response of the femur and to evaluate the change in its stress state during impact loading. A 3-dimensional model of the femur was prepared in the present study, and the impulsive stress waves propagating from the distal end of the femur were analyzed by the dynamic finite element method. This model showed that the von Mises equivalent stress is large on the anterior and posterior sides of the mid-diaphysis when the impact direction is different from that of the bone axis. As for the femoral neck, the absolute value of minimum principal stress initially increases on the medial side;slightly later the maximum principal stress increases on the lateral side. In this case, the absolute value of the maximum principal stress was found to be larger than that of the minimum principal stress, and the absolute value of the principal stress decreased as the impact angle increased. Further, the femoral neck and the trochanter were shown to have a higher risk of bone fracture when the impact direction is coincident with the bone axis.

  6. The importance of temporal stress variation and dynamic disequilibrium for the initiation of plate tectonics

    Science.gov (United States)

    Stamenković, V.; Höink, T.; Lenardic, A.

    2016-06-01

    We use 1-D thermal history models and 3-D numerical experiments to study the impact of dynamic thermal disequilibrium and large temporal variations of normal and shear stresses on the initiation of plate tectonics. Previous models that explored plate tectonics initiation from a steady state, single plate mode of convection concluded that normal stresses govern the initiation of plate tectonics, which based on our 1-D model leads to plate yielding being more likely with increasing interior heat and planet mass for a depth-dependent Byerlee yield stress. Using 3-D spherical shell mantle convection models in an episodic regime allows us to explore larger temporal stress variations than can be addressed by considering plate failure from a steady state stagnant lid configuration. The episodic models show that an increase in convective mantle shear stress at the lithospheric base initiates plate failure, which leads with our 1-D model to plate yielding being less likely with increasing interior heat and planet mass. In this out-of-equilibrium and strongly time-dependent stress scenario, the onset of lithospheric overturn events cannot be explained by boundary layer thickening and normal stresses alone. Our results indicate that in order to understand the initiation of plate tectonics, one should consider the temporal variation of stresses and dynamic disequilibrium.

  7. Drought stress had a predominant effect over heat stress on three tomato cultivars subjected to combined stress.

    Science.gov (United States)

    Zhou, Rong; Yu, Xiaqing; Ottosen, Carl-Otto; Rosenqvist, Eva; Zhao, Liping; Wang, Yinlei; Yu, Wengui; Zhao, Tongmin; Wu, Zhen

    2017-01-25

    with combined stress tolerance might not be correlated with the single stress tolerance. In this study, drought stress had a predominant effect on tomato over heat stress, which explained why simultaneous application of heat and drought revealed similar physiological responses to the drought stress. These results will uncover the difference and linkage between the physiological response of tomatoes to drought, heat and combined stress and be important for the selection and breeding of tolerant tomato cultivars under single and combine stress.

  8. Spur Gears Static and Dynamic Meshing Simulation and Tooth Stress Calculation

    Directory of Open Access Journals (Sweden)

    Jammal Ali

    2015-01-01

    Full Text Available Gear meshing is a complicated process, and is subjected to the simulation process in the following paper. A flexible quasi-static and dynamic finite element analysis (FEA models were built, to calculate contact principal and shear stresses. Full sized 3D spur gears are simulated under different boundary conditions. The first model, was a quasi-static analysis, where torque was used as input; and the second model, which was transient dynamic analysis, where rotational speed was used as input. The static analysis showed high stress concentration at the tooth contact point and under the contacting surface. The dynamic analysis provided the highest stress value at the different stages of gear engagement points along the line of action. Analytical and simulation result were in agreement in general, and the use of the new simulation model was discussed.

  9. Characterisation of dynamic behaviour of alumina ceramics: evaluation of stress uniformity

    Directory of Open Access Journals (Sweden)

    Zhiyong Wang

    2015-10-01

    Full Text Available Accurate characterisation of dynamic behaviour of ceramics requires the reliable split-Hopkinson pressure bar (SHPB technique and the condition of uniaxial homogeneous specimen deformation. In this study, an experimentally validated 3D finite element model of the full scale SHPB experiment was developed to quantitatively evaluate the wave propagation in the bars and the stress distribution/evolution in the alumina specimen. Wave signals in both the SHPB experiments and the finite element model were analysed to characterise the dynamic behaviour of alumina. It was found that the equilibrium of both stresses within the specimen and forces at the specimen ends can be established in the intermediate stage of deformation. The validity of stress uniformity in the alumina specimen supports the assumption of uniaxial homogeneous specimen deformation in the SHPB and validates the characterisation of dynamic behaviour of alumina ceramics.

  10. Spatial and temporal task characteristics as stress: a test of the dynamic adaptability theory of stress, workload, and performance.

    Science.gov (United States)

    Szalma, James L; Teo, Grace W L

    2012-03-01

    The goal for this study was to test assertions of the dynamic adaptability theory of stress, which proposes two fundamental task dimensions, information rate (temporal properties of a task) and information structure (spatial properties of a task). The theory predicts adaptive stability across stress magnitudes, with progressive and precipitous changes in adaptive response manifesting first as increases in perceived workload and stress and then as performance failure. Information structure was manipulated by varying the number of displays to be monitored (1, 2, 4 or 8 displays). Information rate was manipulated by varying stimulus presentation rate (8, 12, 16, or 20 events/min). A signal detection task was used in which critical signals were pairs of digits that differed by 0 or 1. Performance accuracy declined and workload and stress increased as a function of increased task demand, with a precipitous decline in accuracy at the highest demand levels. However, the form of performance change as well as the pattern of relationships between speed and accuracy and between performance and workload/stress indicates that some aspects of the theory need revision. Implications of the results for the theory and for future research are discussed.

  11. Nonlinear cosmological consistency relations and effective matter stresses

    Energy Technology Data Exchange (ETDEWEB)

    Ballesteros, Guillermo [Museo Storico della Fisica e Centro Studi e Ricerche ' ' Enrico Fermi' ' , Piazza del Viminale 1, I-00184 Rome (Italy); Hollenstein, Lukas; Jain, Rajeev Kumar; Kunz, Martin, E-mail: guillermo.ballesteros@pd.infn.it, E-mail: lukas.hollenstein@unige.ch, E-mail: rajeev.jain@unige.ch, E-mail: martin.kunz@unige.ch [Département de Physique Théorique and Center for Astroparticle Physics, Université de Genève, Quai E. Ansermet 24, CH-1211 Genève 4 (Switzerland)

    2012-05-01

    We propose a fully nonlinear framework to construct consistency relations for testing generic cosmological scenarios using the evolution of large scale structure. It is based on the covariant approach in combination with a frame that is purely given by the metric, the normal frame. As an example, we apply this framework to the ΛCDM model, by extending the usual first order conditions on the metric potentials to second order, where the two potentials start to differ from each other. We argue that working in the normal frame is not only a practical choice but also helps with the physical interpretation of nonlinear dynamics. In this frame, effective pressures and anisotropic stresses appear at second order in perturbation theory, even for ''pressureless'' dust. We quantify their effect and compare them, for illustration, to the pressure of a generic clustering dark energy fluid and the anisotropic stress in the DGP model. Besides, we also discuss the effect of a mismatch of the potentials on the determination of galaxy bias.

  12. Expectancy of Stress-Reducing Aromatherapy Effect and Performance on a Stress-Sensitive Cognitive Task

    Directory of Open Access Journals (Sweden)

    Irina Chamine

    2015-01-01

    Full Text Available Objective. Stress-reducing therapies help maintain cognitive performance during stress. Aromatherapy is popular for stress reduction, but its effectiveness and mechanism are unclear. This study examined stress-reducing effects of aromatherapy on cognitive function using the go/no-go (GNG task performance and event related potentials (ERP components sensitive to stress. The study also assessed the importance of expectancy in aromatherapy actions. Methods. 81 adults were randomized to 3 aroma groups (active experimental, detectable, and undetectable placebo and 2 prime subgroups (prime suggesting stress-reducing aroma effects or no-prime. GNG performance, ERPs, subjective expected aroma effects, and stress ratings were assessed at baseline and poststress. Results. No specific aroma effects on stress or cognition were observed. However, regardless of experienced aroma, people receiving a prime displayed faster poststress median reaction times than those receiving no prime. A significant interaction for N200 amplitude indicated divergent ERP patterns between baseline and poststress for go and no-go stimuli depending on the prime subgroup. Furthermore, trends for beneficial prime effects were shown on poststress no-go N200/P300 latencies and N200 amplitude. Conclusion. While there were no aroma-specific effects on stress or cognition, these results highlight the role of expectancy for poststress response inhibition and attention.

  13. Effective long wavelength scalar dynamics in de Sitter

    CERN Document Server

    Moss, Ian

    2016-01-01

    We discuss the effective infrared theory governing a light scalar's long wavelength dynamics in de Sitter spacetime. We show how the separation of scales around the physical curvature radius $k/a \\sim H$ can be performed consistently with a window function and how short wavelengths can be integrated out in the Schwinger-Keldysh path integral formalism. At leading order, and for time scales $\\Delta t \\gg H^{-1}$, this results in the well-known Starobinsky stochastic evolution. Our approach allows for the computation of quantum UV corrections, generating an effective potential on which the stochastic dynamics takes place, as well as the description of dynamics on spatial and temporal scales comparable to $H^{-1}$ and above. We further elaborate on the use of a Wigner function to evaluate the non-perturbative expectation values of field correlators and the stress-energy tensor of $\\phi$ within the stochastic formalism.

  14. Parasitic Effects on Memristor Dynamics

    Science.gov (United States)

    Itoh, Makoto; Chua, Leon O.

    2016-06-01

    In this paper, we show that parasitic elements have a significant effect on the dynamics of memristor circuits. We first show that certain 2-terminal elements such as memristors, memcapacitors, and meminductors can be used as nonvolatile memories, if the principle of conservation of state variables hold by open-circuiting, or short-circuiting, their terminals. We also show that a passive memristor with a strictly-increasing constitutive relation will eventually lose its stored flux when we switch off the power if there is a parasitic capacitance across the memristor. Similarly, a memcapacitor (resp., meminductor) with a positive memcapacitance (resp., meminductance) will eventually lose their stored physical states when we switch off the power, if it is connected to a parasitic resistance. We then show that the discontinuous jump that circuit engineers assumed to occur at impasse points of memristor circuits contradicts the principles of conservation of charge and flux at the time of the discontinuous jump. A parasitic element can be used to break an impasse point, resulting in the emergence of a continuous oscillation in the circuit. We also define a distance, a diameter, and a dimension, for each circuit element in order to measure the complexity order of the parasitic elements. They can be used to find higher-order parasitic elements which can break impasse points. Furthermore, we derived a memristor-based Chua’s circuit from a three-element circuit containing a memristor by connecting two parasitic memcapacitances to break the impasse points. We finally show that a higher-order parasitic element can be used for breaking the impasse points on two-dimensional and three-dimensional constrained spaces.

  15. Handling magnetic anisotropy and magnetoimpedance effect in flexible multilayers under external stress

    Science.gov (United States)

    Agra, K.; Bohn, F.; Mori, T. J. A.; Callegari, G. L.; Dorneles, L. S.; Correa, M. A.

    2016-12-01

    We investigate the dynamic magnetic response though magnetoimpedance effect of ferromagnetic flexible NiFe/Ta and FeCuNbSiB/Ta multilayers under external stress. We explore the possibility of handling magnetic anisotropy, and consequently the magnetoimpedance effect, of magnetostrictive multilayers deposited onto flexible substrates. We quantify the sensitivity of the multilayers under external stress by calculating the ratio between impedance variations and external stress changes, and show that considerable values can be reached by tuning the magnetic field, frequency, magnetostriction constant, and external stress. The results extend possibilities of application of magnetostrictive multilayers deposited onto flexible substrates when under external stress and place them as very attractive candidates as element sensor for the development of sensitive smart touch sensors.

  16. Transient magneto-peristaltic flow of couple stress biofluids: a magneto-hydro-dynamical study on digestive transport phenomena.

    Science.gov (United States)

    Tripathi, Dharmendra; Anwar Bég, O

    2013-11-01

    Magnetic fields are increasingly being utilized in endoscopy and gastric transport control. In this regard, the present study investigates the influence of a transverse magnetic field in the transient peristaltic rheological transport. An electrically-conducting couple stress non-Newtonian model is employed to accurately simulate physiological fluids in peristaltic flow through a sinusoidally contracting channel of finite length. This model is designed for computing the intra-bolus oesophageal and intestinal pressures during the movement of food bolus in the digestive system under magneto-hydro-dynamic effects. Long wavelength and low Reynolds number approximations have been employed to reduce the governing equations from nonlinear to linear form, this being a valid approach for creeping flows which characterizes physiological dynamics. Analytical approximate solutions for axial velocity, transverse velocity, pressure gradient, local wall shear stress and volumetric flow rate are obtained for the non-dimensional conservation equations subject to appropriate boundary conditions. The effects of couple stress parameter and transverse magnetic field on the velocity profile, pressure distribution, local wall shear stress and the averaged flow rate are discussed with the aid of computational results. The comparative study of non-integral and integral number of waves propagating along the finite length channel is also presented. Magnetic field and non-Newtonian properties are found to strongly influence peristaltic transport.

  17. A Damaged Constitutive Model for Rock under Dynamic and High Stress State

    Directory of Open Access Journals (Sweden)

    Yan-Long Li

    2017-01-01

    Full Text Available The main research work of this paper focuses on the theoretical prediction of the constitutive relationship for rock, concrete, and other quasi-brittle materials under dynamic and complex stress state and the influence of dynamic mechanical behavior of rock on practical engineering problems was studied. A damaged elastoplastic model (DEPM is established for the investigation and prediction of static or dynamic mechanical behavior of rock material. The mechanical behavior (brittleness or plasticity and dynamic response (due to underground impact pressure and high-velocity impact of projectile of rock under high in situ stress were investigated via the DEPM combined with the explicit finite element method. This paper suggests the influence of the brittle or plastic mechanical behavior of rock material on deep underground rock engineering.

  18. Is Terzaghi’s effective stress a stress variable under seepage conditions?

    Institute of Scientific and Technical Information of China (English)

    雷国辉; 赵仲辉; 吴宏伟

    2015-01-01

    From the continuum mechanics perspective, an attempt was made to clarify the role of Terzaghi’s effective stress in the theoretical analysis of saturated soil subjected to seepage. The necessity of performing a coupled hydromechanical analysis to solve the seepage−deformation interaction problem was illustrated by examining the equations of static equilibrium among the effective stress, seepage force, pore-water pressure and total stress. The conceptual definition of stress variable that satisfies the principles of continuum mechanics is applied in the coupled hydromechanical analysis. It is shown that Terzaghi’s effective stress is in fact not a stress variable under seepage conditions, and the seepage force acting on the soil skeleton cannot be viewed as a body force. This offers a clue to the underlying cause of a paradox between the real Pascal’s hydrostatic state and the hydrostatic state predicted by a class of continuum hydromechanical theories.

  19. Effects of Humor on Teacher Stress, Affect, and Job Satisfaction

    Science.gov (United States)

    Shirley, Jacqueline Dena

    2013-01-01

    Teachers are at high risk for stress, negative emotion, and job dissatisfaction, which has been linked with health problems and early attrition. Humor has been found to relieve various forms of stress. However, there is a gap in the literature regarding humor effects on teacher stress and its related consequences. The purpose of this quantitative,…

  20. Effects of Humor on Teacher Stress, Affect, and Job Satisfaction

    Science.gov (United States)

    Shirley, Jacqueline Dena

    2013-01-01

    Teachers are at high risk for stress, negative emotion, and job dissatisfaction, which has been linked with health problems and early attrition. Humor has been found to relieve various forms of stress. However, there is a gap in the literature regarding humor effects on teacher stress and its related consequences. The purpose of this quantitative,…

  1. THE DYNAMIC INTERCONNECTION BETWEEN MAN AND ENVIRONMENT, A FACTOR OF STRESS AND ECO STRESS

    Directory of Open Access Journals (Sweden)

    SIMIONESCU (BARBU IRINA

    2014-05-01

    Full Text Available The reason for writing this paper is the omnipresence but also the impact of stress in our times. In order to explain why stress has gained an important place in modern history, we need to understand the evolution of medical science and technology, which over the last decades, have taken important steps towards establishing the biological links between stress and human behaviour but also the political and cultural contexts that have endowed with meaning and authority the scientific knowledge. In the same time, we must concentrate on the interaction between the individual and his social and physical environment from a holistic perspective, surpassing the interdisciplinary limits. The term ‘stress’ is used as a metaphor for disasters at a macroeconomic level, when national economies are destabilized and recently it has been associated with the idea of environmental damage. All natural disasters are environmental events, and their impact on human beings (from a psychological, physical, economic and social point of view can be seen as a major eco-stress. It’s essential to understand man`s influence on the environment in order to review the attitude of communities that, under the pretext of modernity, continue to exert destructive actions

  2. Effects of Hospital Workers' Friendship Networks on Job Stress.

    Science.gov (United States)

    Shin, Sung Yae; Lee, Sang Gyu

    2016-01-01

    This study attempted to identify the sources of job stress according to job position and investigate how friendship networks affect job stress. Questionnaires based on The Health Professions Stress Inventory (HPSI) developed by Wolfgang experienced by healthcare providers were collected from 420 nurses, doctors and radiological technologists in two general hospitals in Korea by a multistage cluster sampling method. Multiple regression analysis was used to examine the effects of friendship networks on job stress after controlling for other factors. The severity of job stress differed according to level of job demands (p = .006); radiologic technologists experienced the least stress (45.4), nurses experienced moderate stress (52.4), and doctors experienced the most stress (53.6). Those with long-term friendships characterized by strong connections reported lower levels of stress than did those with weak ties to friends among nurses (1.3, p stress experienced by nurses (8.2, p stress (9.2, p stress. The strength and density of such friendship networks were related to job stress. Life information support from their friendship network was the primary positive contributor to control of job stress.

  3. Effects of gully terrain on stress field distribution and ground pressure behavior in shallow seam mining

    Institute of Scientific and Technical Information of China (English)

    Li Jianwei; Liu Changyou; Zhao Tong

    2016-01-01

    This study proposes a novel approach to study stress field distribution and overlying ground pressure behavior in shallow seam mining in gully terrain. This approach combines numerical simulations and field tests based on the conditions of gully terrain in the Chuancao Gedan Mine. The effects of gully ter-rain on the in situ stress field of coal beds can be identified by the ratio of self-weight stress to vertical stress (g) at the location corresponding to the maximum vertical stress. Based on the function g=f(h), the effect of gully terrain on the stress field of overlying strata of the entire field can be characterized as a significantly affected area, moderately affected area, or non-affected area. Working face 6106 in the Chuancao Gedan Mine had a coal bed depth<80 m and was located in what was identified as a signifi-cantly affected area. Hence, mining may cause sliding of the gully slope and increased loading (including significant dynamic loading) on the roof strata. Field tests suggest that significant dynamic pressures were observed at the body and foot of the gully slope, and that dynamic loadings were observed upslope of the working face expansion, provided that the expanding direction of the working face is parallel to the gully.

  4. Influence of effective stress on swelling pressure of expansive soils

    Directory of Open Access Journals (Sweden)

    Baille Wiebke

    2016-01-01

    Full Text Available The volume change and shear strength behaviour of soils are controlled by the effective stress. Recent advances in unsaturated soil mechanics have shown that the effective stress as applicable to unsaturated soils is equal to the difference between the externally applied stress and the suction stress. The latter can be established based on the soil-water characteristic curve (SWCC of the soil. In the present study, the evolution of swelling pressure in compacted bentonite-sand mixtures was investigated. Comparisons were made between magnitudes of applied suction, suction stress, and swelling pressure.

  5. Shearographic System for Dynamic Analysis of Materials under Heat Stress

    Directory of Open Access Journals (Sweden)

    Nelson A. Correa-Rojas

    2013-11-01

    Full Text Available Shearography is a tool for monitoring and inspecting of structural flaws and imperfections in different types of industrial, automotive and aeronautics applications. It is based on digital correlation of two speckle patterns in two states of interest: with and without load. The technique has the special quality of being very robust against environmental disturbances. We present a shearographic system to analyze the dynamic behavior of the strain that suffers a material in response to changes in temperature throughout the thermal load process.

  6. Bias stress effect and recovery in organic field effect transistors: proton migration mechanism

    Science.gov (United States)

    Sharma, A.; Mathijssen, Simon G. J.; Kemerink, M.; de Leeuw, Dago M.; Bobbert, Peter A.

    2010-08-01

    Organic field-effect transistors exhibit operational instabilities when a gate bias is applied. For a constant gate bias the threshold voltage shifts towards the applied gate bias voltage, an effect known as the bias-stress effect. We have performed a detailed experimental and theoretical study of operational instabilities in p-type transistors with silicon-dioxide gate dielectric. We propose a mechanism in which holes in the semiconductor are converted into protons in the presence of water and a reversible migration of these protons into the gate dielectric to explain the instabilities in organic transistors. We show how redistribution of charge between holes in the semiconductor and protons in the gate dielectric can consistently explain the experimental observations. Furthermore, we explain in detail the recovery of a pres-stressed transistor on applying zero gate bias. We show that recovery dynamics depends strongly on the extent of stressing. Our mechanism is consistent with the known aspects of bias-stress effect like acceleration due to humidity, constant activation energy and reversibility.

  7. Stress effects on mood, HPA axis, and autonomic response: comparison of three psychosocial stress paradigms.

    Science.gov (United States)

    Giles, Grace E; Mahoney, Caroline R; Brunyé, Tad T; Taylor, Holly A; Kanarek, Robin B

    2014-01-01

    Extensive experimental psychology research has attempted to parse the complex relationship between psychosocial stress, mood, cognitive performance, and physiological changes. To do so, it is necessary to have effective, validated methods to experimentally induce psychosocial stress. The Trier Social Stress Test (TSST) is the most commonly used method of experimentally inducing psychosocial stress, but it is resource intensive. Less resource intense psychosocial stress tasks include the Socially Evaluative Cold Pressor Task (SECPT) and a computerized mental arithmetic task (MAT). These tasks effectively produce a physiological and psychological stress response and have the benefits of requiring fewer experimenters and affording data collection from multiple participants simultaneously. The objective of this study was to compare the magnitude and duration of these three experimental psychosocial stress induction paradigms. On each of four separate days, participants completed either a control non-stressful task or one of the three experimental stressors: the TSST, SECPT, or MAT. We measured mood, working memory performance, salivary cortisol and alpha-amylase (AA), and heart rate. The TSST and SECPT exerted the most robust effects on mood and physiological measures. TSST effects were generally evident immediately post-stress as well as 10- and 20-minutes after stress cessation, whereas SECPT effects were generally limited to the duration of the stressor. The stress duration is a key determinant when planning a study that utilizes an experimental stressor, as researchers may be interested in collecting dependent measures prior to stress cessation. In this way, the TSST would allow the investigator a longer window to administer tasks of interest.

  8. Stress effects on mood, HPA axis, and autonomic response: comparison of three psychosocial stress paradigms.

    Directory of Open Access Journals (Sweden)

    Grace E Giles

    Full Text Available Extensive experimental psychology research has attempted to parse the complex relationship between psychosocial stress, mood, cognitive performance, and physiological changes. To do so, it is necessary to have effective, validated methods to experimentally induce psychosocial stress. The Trier Social Stress Test (TSST is the most commonly used method of experimentally inducing psychosocial stress, but it is resource intensive. Less resource intense psychosocial stress tasks include the Socially Evaluative Cold Pressor Task (SECPT and a computerized mental arithmetic task (MAT. These tasks effectively produce a physiological and psychological stress response and have the benefits of requiring fewer experimenters and affording data collection from multiple participants simultaneously. The objective of this study was to compare the magnitude and duration of these three experimental psychosocial stress induction paradigms. On each of four separate days, participants completed either a control non-stressful task or one of the three experimental stressors: the TSST, SECPT, or MAT. We measured mood, working memory performance, salivary cortisol and alpha-amylase (AA, and heart rate. The TSST and SECPT exerted the most robust effects on mood and physiological measures. TSST effects were generally evident immediately post-stress as well as 10- and 20-minutes after stress cessation, whereas SECPT effects were generally limited to the duration of the stressor. The stress duration is a key determinant when planning a study that utilizes an experimental stressor, as researchers may be interested in collecting dependent measures prior to stress cessation. In this way, the TSST would allow the investigator a longer window to administer tasks of interest.

  9. Static and dynamic stress analyses of the prototype high head Francis runner based on site measurement

    Science.gov (United States)

    Huang, X.; Oram, C.; Sick, M.

    2014-03-01

    More efforts are put on hydro-power to balance voltage and frequency within seconds for primary control in modern smart grids. This requires hydraulic turbines to run at off-design conditions. especially at low load or speed-no load. Besides. the tendency of increasing power output and decreasing weight of the turbine runners has also led to the high level vibration problem of the runners. especially high head Francis runners. Therefore. it is important to carry out the static and dynamic stress analyses of prototype high head Francis runners. This paper investigates the static and dynamic stresses on the prototype high head Francis runner based on site measurements and numerical simulations. The site measurements are performed with pressure transducers and strain gauges. Based on the measured results. computational fluid dynamics (CFD) simulations for the flow channel from stay vane to draft tube cone are performed. Static pressure distributions and dynamic pressure pulsations caused by rotor-stator interaction (RSI) are obtained under various operating conditions. With the CFD results. static and dynamic stresses on the runner at different operating points are calculated by means of the finite element method (FEM). The agreement between simulation and measurement is analysed with linear regression method. which indicates that the numerical result agrees well with that of measurement. Furthermore. the maximum static and dynamic stresses on the runner blade are obtained at various operating points. The relations of the maximum stresses and the power output are discussed in detail. The influences of the boundary conditions on the structural behaviour of the runner are also discussed.

  10. CONVOLUTION OF THE IMPACT THREE-DIMENSIONAL ELASTO-DYNAMICS AND DYNAMIC STRESS INTENSITY FACTOR FOR AN ELLIPTIC CRACK

    Institute of Scientific and Technical Information of China (English)

    孙竹凤; 范天佑; 吴祥法

    2002-01-01

    This paper presents a formulation for three-dimensional elastodynamics with an elliptic crack based on the Laplace and Fourier transforms and the convolution theorem. The dynamic stress intensity factor for the crack is determined by solving a Fredholm integral equation of the first kind. The results of this paper are very close to those given by the two-dimensional dual integral equation method.

  11. Bioinjection treatment: effects of post-injection residual stress on left ventricular wall stress.

    Science.gov (United States)

    Lee, Lik Chuan; Wall, Samuel T; Genet, Martin; Hinson, Andy; Guccione, Julius M

    2014-09-22

    Injection of biomaterials into diseased myocardium has been associated with decreased myofiber stress, restored left ventricular (LV) geometry and improved LV function. However, its exact mechanism(s) of action remained unclear. In this work, we present the first patient-specific computational model of biomaterial injection that accounts for the possibility of residual strain and stress introduced by this treatment. We show that the presence of residual stress can create more heterogeneous regional myofiber stress and strain fields. Our simulation results show that the treatment generates low stress and stretch areas between injection sites, and high stress and stretch areas between the injections and both the endocardium and epicardium. Globally, these local changes are translated into an increase in average myofiber stress and its standard deviation (from 6.9 ± 4.6 to 11.2 ± 48.8 kPa and 30 ± 15 to 35.1 ± 50.9 kPa at end-diastole and end-systole, respectively). We also show that the myofiber stress field is sensitive to the void-to-size ratio. For a constant void size, the myofiber stress field became less heterogeneous with decreasing injection volume. These results suggest that the residual stress and strain possibly generated by biomaterial injection treatment can have large effects on the regional myocardial stress and strain fields, which may be important in the remodeling process.

  12. Evidence for particle mobilization as a mechanism for permeability enhancement via dynamic stressing

    Science.gov (United States)

    Candela, T.; Brodsky, E. E.; Marone, C.; Elsworth, D.

    2013-12-01

    Dynamic permeability change by seismic waves is a well-established natural phenomenon yet the mechanism remains poorly understood. We investigate the mechanism by generating well-controlled repeatable permeability enhancement in a laboratory experiment. Each experiment proceeded as: (1) pore pressure oscillations, simulating dynamic stresses, were applied at one end of intact Berea sandstone samples under triaxial stresses of tens of megapascals, (2) samples were fractured within the apparatus, and (3) pore pressure oscillations resumed post-fracturing. In this way, both the fracture and porous media response to the dynamic stresses were investigated. In addition, we controled the mobility of fine particles by adjusting the pore fluid chemistry (deionized water, and brines of: NaCl 5%, NaCl 35%, CaCl2 5%). Our results are consistent with natural observations. Dynamic stressing produces an immediate permeability enhancement ranging from 1-60%, which scales with the amplitude of the dynamic strain, 7*10^-7 to 7*10^-6, followed by a progressive permeability recovery. In our experiments a flow-dependent mechanism associated with mobilization of fines appears to control both the magnitude of the permeability enhancement and the recovery rate. Both processes operate at two time scales, i.e., fast flushing/unclogging of the fines during the pore pressure oscillations and progressive clogging of the pore throats by particle migration, and were influenced by the fluid chemistry. The dynamic permeability changes were not associated with permanent deformation. We show that: 1) injection of unequilibrated fluids favors particle mobilization, and 2) transient permeability change results from the migration of fines which in turn results from dynamic stressing. Our results suggest that areas where pore fluids are in disequilibrium should be more sensitive to dynamic stressing. Interestingly, early observations of dynamic earthquake-triggering revealed preferential triggering in

  13. When does stress help or harm? The effects of stress controllability and subjective stress response on Stroop performance.

    Directory of Open Access Journals (Sweden)

    Roselinde Kaiser Henderson

    2012-06-01

    Full Text Available The ability to engage in goal-directed behavior despite exposure to stress is critical to resilience. Questions of how stress can impair or improve behavioral functioning are important in diverse settings, from athletic competitions to academic testing to clinical therapy. Previous research suggests that controllability is a key factor in the impact of stress on behavior: learning how to control stressors buffers people from the negative effects of stress on subsequent cognitively demanding tasks. In addition, research suggests that the impact of stress on cognitive functioning depends on an individual’s response to stressors: moderate responses to stress can lead to improved performance while extreme (high or low responses can lead to impaired performance. The present studies tested the hypothesis that 1 learning to behaviorally control stressors leads to improved performance on a test of general executive functioning, the color-word Stroop, and that 2 this improvement emerges specifically for people who report moderate (subjective responses to stress. Experiment 1: Stroop performance, measured before and after a stress manipulation, was compared across groups of undergraduate participants (n=109. People who learned to control a noise stressor and received accurate performance feedback demonstrated reduced Stroop interference compared with people exposed to uncontrollable noise stress and feedback indicating an exaggerated rate of failure. In the group who learned behavioral control, those who reported moderate levels of stress showed the greatest reduction in Stroop interference. In contrast, in the group exposed to uncontrollable events, self-reported stress failed to predict performance. Experiment 2: In a second sample (n=90, we specifically investigated the role of controllability by keeping the rate of failure feedback constant across groups. In the group who learned behavioral control, those who reported moderate levels of stress

  14. The Effects of Heat Stress on Job Satisfaction, Job Performance and Occupational Stress in Casting Workers

    Directory of Open Access Journals (Sweden)

    Dehghan

    2016-06-01

    Full Text Available Background Job satisfaction, job performance, job stress and heat stress affect the productivity of workers. Objectives This research aimed to study the relationship between heat stress indices with job satisfaction, job performance and job stress in casting workers. Patients and Methods This descriptive-analytical cross sectional survey was performed during summer 2013 on one hundred casting workers. Data were collected by questionnaires of occupational stress, job satisfaction and job performance. Heat stress was measured by the Wet Bulb Globe Temperature (WBGT and Heat Strain Score Index (HSSI questionnaire. The data were analyzed using correlation coefficient by the SPSS16 software. Results The results showed that job satisfaction had a negative correlation with WBGT index (R = -0.42, P < 0.001 and HSSI (R = -0.49, P < 0.001. Also, there was no statistical correlation among occupational stress and job performance with heat stress indices. Conclusions The present study showed that heat stress had a negative effect on job satisfaction; also there were no significant effects on job stress and job performance.

  15. Effect of stress on field dependence.

    Science.gov (United States)

    Sarris, V; Heineken, E; Peters, H

    1976-08-01

    60 subjects were tested in the rod-and-frame test under flicker conditions (stress). As compared to scores in a control situation (no flicker), the rod-and-frame scores were large under stress and increased monotonically during the session. Futhermore, both intra- and interindividual variability of rod-and-frame performance changed under stress conditions in a consistent manner. The general results, which clearly point to a reliable influence of stress on field dependency, are discussed within the methodological framework of Witkin's theory of perception and personality.

  16. EFFECT OF WORKPLACE STRESS ON JOB PERFORMANCE

    Directory of Open Access Journals (Sweden)

    Azman Ismail

    2015-05-01

    Full Text Available The study examines the relationship between workplace stress and job performance. A survey method was employed to gather self-administered questionnaires from executive and non-executive employees of a leading private investment bank in Peninsular Malaysia. The outcomes of SmartPLS path model analysis of the data showed two important findings: firstly, physiological stress was positively and significantly correlated with job performance. Secondly, psychological stress was positively and significantly correlated with job performance. This finding reveals that physiological and psychological stresses act as important predictors of job performance in the studied organization. The paper provides discussion, implications and conclusion.

  17. Schwinger's Dynamical Casimir Effect Bulk Energy Contribution

    CERN Document Server

    Carlson, C E; Pérez-Mercader, J; Visser, M; Carlson, C E; Carlson, Carl E.; Molina-Paris, Carmen; Perez-Mercader, Juan; Visser, Matt

    1997-01-01

    Schwinger's Dynamical Casimir Effect is one of several candidate explanations for sonoluminescence. Recently, several papers have claimed that Schwinger's estimate of the Casimir energy involved is grossly inaccurate. In this letter, we show that these calculations omit the crucial volume term. When the missing term is correctly included one finds full agreement with Schwinger's result for the Dynamical Casimir Effect. We have nothing new to say about sonoluminescence itself except to affirm that the Casimir effect is energetically adequate as a candidate explanation. Schwinger's Dynamical Casimir Effect is one of several candidate explanations for sonoluminescence. Recently, several papers have claimed that Schwinger's estimate of the Casimir energy involved is grossly inaccurate. In this letter, we show that these calculations omit the crucial volume term. When the missing term is correctly included one finds full agreement with Schwinger's result for the Dynamical Casimir Effect. We have nothing new to say...

  18. A detailed modular analysis of heat-shock protein dynamics under acute and chronic stress and its implication in anxiety disorders.

    Science.gov (United States)

    Sriram, K; Rodriguez-Fernandez, Maria; Doyle, Francis J

    2012-01-01

    Physiological and psychological stresses cause anxiety disorders such as depression and post-traumatic stress disorder (PTSD) and induce drastic changes at a molecular level in the brain. To counteract this stress, the heat-shock protein (HSP) network plays a vital role in restoring the homeostasis of the system. To study the stress-induced dynamics of heat-shock network, we analyzed three modules of the HSP90 network--namely trimerization reactions, phosphorylation-dephosphorylation reactions, and the conversion of HSP90 from an open to a closed conformation--and constructed a corresponding nonlinear differential equation model based on mass action kinetics laws. The kinetic parameters of the model were obtained through global optimization, and sensitivity analyses revealed that the most sensitive parameters are the kinase and phosphatase that drive the phosphorylation-dephosphorylation reactions. Bifurcation analysis carried out with the estimated kinetic parameters of the model with stress as bifurcation parameter revealed the occurrence of "mushroom", a type of complex dynamics in which S-shaped and Z-shaped hysteretic bistable forms are present together. We mapped the molecular events responsible for generating the mushroom dynamics under stress and interpreted the occurrence of the S-shaped hysteresis to a normal level of stress, and the Z-shaped hysteresis to the HSP90 variations under acute and chronic stress in the fear conditioned system, and further, we hypothesized that this can be extended to stress-related disorders such as depression and PTSD in humans. Finally, we studied the effect of parameter variations on the mushroom dynamics to get insight about the role of phosphorylation-dephosphorylation parameters in HSP90 network in bringing about complex dynamics such as isolas, where the stable steady states in a bistable system are isolated and separated from each other and not connected by an unstable steady state.

  19. A detailed modular analysis of heat-shock protein dynamics under acute and chronic stress and its implication in anxiety disorders.

    Directory of Open Access Journals (Sweden)

    K Sriram

    Full Text Available Physiological and psychological stresses cause anxiety disorders such as depression and post-traumatic stress disorder (PTSD and induce drastic changes at a molecular level in the brain. To counteract this stress, the heat-shock protein (HSP network plays a vital role in restoring the homeostasis of the system. To study the stress-induced dynamics of heat-shock network, we analyzed three modules of the HSP90 network--namely trimerization reactions, phosphorylation-dephosphorylation reactions, and the conversion of HSP90 from an open to a closed conformation--and constructed a corresponding nonlinear differential equation model based on mass action kinetics laws. The kinetic parameters of the model were obtained through global optimization, and sensitivity analyses revealed that the most sensitive parameters are the kinase and phosphatase that drive the phosphorylation-dephosphorylation reactions. Bifurcation analysis carried out with the estimated kinetic parameters of the model with stress as bifurcation parameter revealed the occurrence of "mushroom", a type of complex dynamics in which S-shaped and Z-shaped hysteretic bistable forms are present together. We mapped the molecular events responsible for generating the mushroom dynamics under stress and interpreted the occurrence of the S-shaped hysteresis to a normal level of stress, and the Z-shaped hysteresis to the HSP90 variations under acute and chronic stress in the fear conditioned system, and further, we hypothesized that this can be extended to stress-related disorders such as depression and PTSD in humans. Finally, we studied the effect of parameter variations on the mushroom dynamics to get insight about the role of phosphorylation-dephosphorylation parameters in HSP90 network in bringing about complex dynamics such as isolas, where the stable steady states in a bistable system are isolated and separated from each other and not connected by an unstable steady state.

  20. Disruption of multisystem responses to stress in type 2 diabetes: Investigating the dynamics of allostatic load

    Science.gov (United States)

    Steptoe, Andrew; Hackett, Ruth A.; Lazzarino, Antonio I.; Bostock, Sophie; La Marca, Roberto; Carvalho, Livia A.; Hamer, Mark

    2014-01-01

    Psychological stress-related processes are thought to contribute to the development and progression of type 2 diabetes, but the biological mechanisms involved are poorly understood. Here, we tested the notion that people with type 2 diabetes experience chronic allostatic load, manifest as dynamic disturbances in reactivity to and recovery from stress across multiple (cardiovascular, neuroendocrine, inflammatory, metabolic) biological systems, coupled with heightened experience of chronic life stress. We carried out an experimental comparison of 140 men and women aged 50–75 y with type 2 diabetes and 280 nondiabetic individuals matched on age, sex, and income. We monitored blood pressure (BP) and heart rate, salivary cortisol, plasma interleukin (IL)-6, and total cholesterol in response to standardized mental stress, and assessed salivary cortisol over the day. People with type 2 diabetes showed impaired poststress recovery in systolic and diastolic BP, heart rate and cholesterol, and blunted stress reactivity in systolic BP, cortisol, cholesterol, and IL-6. Cortisol and IL-6 concentrations were elevated, and cortisol measured over the day was higher in the type 2 diabetes group. Diabetic persons reported greater depressive and hostile symptoms and greater stress experience than did healthy controls. Type 2 diabetes is characterized by disruption of stress-related processes across multiple biological systems and increased exposure to life stress. Chronic allostatic load provides a unifying perspective with implications for etiology and patient management. PMID:25331894

  1. Static and dynamic stress heterogeneity in a multiscale model of the asthmatic airway wall.

    Science.gov (United States)

    Hiorns, J E; Jensen, O E; Brook, B S

    2016-07-01

    Airway hyperresponsiveness (AHR) is a key characteristic of asthma that remains poorly understood. Tidal breathing and deep inspiration ordinarily cause rapid relaxation of airway smooth muscle (ASM) (as demonstrated via application of length fluctuations to tissue strips) and are therefore implicated in modulation of AHR, but in some cases (such as application of transmural pressure oscillations to isolated intact airways) this mechanism fails. Here we use a multiscale biomechanical model for intact airways that incorporates strain stiffening due to collagen recruitment and dynamic force generation by ASM cells to show that the geometry of the airway, together with interplay between dynamic active and passive forces, gives rise to large stress and compliance heterogeneities across the airway wall that are absent in tissue strips. We show further that these stress heterogeneities result in auxotonic loading conditions that are currently not replicated in tissue-strip experiments; stresses in the strip are similar to hoop stress only at the outer airway wall and are under- or overestimates of stresses at the lumen. Taken together these results suggest that a previously underappreciated factor, stress heterogeneities within the airway wall and consequent ASM cellular response to this micromechanical environment, could contribute to AHR and should be explored further both theoretically and experimentally. Copyright © 2016 the American Physiological Society.

  2. Effects of Cultivation Conditions on Dynamic Changes of Stress Parameters in Strawberry%栽培条件对草莓逆境参数变化的影响

    Institute of Scientific and Technical Information of China (English)

    张庆雨; 祝春; 祝子坪; 段可; 张丽勍; 高清华

    2014-01-01

    We studied the dynamic changes of stress parameters including Catalase (CAT), Peroxidase (POD), Malondialde-hyde (MDA), and Superoxide dismutase (SOD) in the leaves of four strawberry cultivars (Benihoppe, Akihime, Sweet Charlie, Jiuxiang) in Shanghai area under the condition of Plasticulture Production System ( PPS) and Greenhouse Production System (GPS).The results showed that:(1) In PPS, the MDA content in strawberry leaves showed a sigmoid curve variation , and that in the leaves of Sweet Charlie reached a peak in middle January and maintained at a stable level later .The CAT activity in various strawberry cultivars had different variations , and that in Sweet Charlie and Akihime reached a maximum in early December , while that in Benihoppe and Jiuxiang reached a peak in middle November .The POD activity in the leaves of Jiuxiang generally displayed a continuous decrease , while that in other three cultivars revealed the changing trend of “rising -decline -steady”.The SOD ac-tivity in the leaves of Jiuxiang presented the changing trend of inverse “U”-shape, while that in other three cultivars showed a sig-moid curve variation.(2) In GPS, the dynamic accumulation of MDA in leaves was quite distinct from that in PPS .The peak of CAT activity in the leaves of Akihime and Jiuxiang appeared 3 weeks later than that in Benihoppe and Sweet Charlie .The same changing trend of POD activity was shown in different strawberry cultivars .The dynamic alteration of SOD activity was similar to that in PPS.%以红颜、章姬、甜查理和久香等4个草莓品种为材料,研究了上海地区塑料大棚和玻璃温室栽培条件下,草莓叶片中与逆境胁迫相关参数包括过氧化氢酶( CAT)、过氧化物酶( POD)、丙二醛( MDA)和超氧化物歧化酶( SOD)的变化动态。结果表明:(1)塑料大棚栽培条件下,草莓叶片中MDA含量呈现“S”型变化曲线,其中甜查理在1月中旬达到峰值并维持在

  3. Transient Permeability Enhancement via Dynamic Stressing: The Role of Shear Displacement

    Science.gov (United States)

    Madara, B.; Riviere, J.; Marone, C.; Elsworth, D.

    2016-12-01

    Reservoir productivity is reliant on the presence and quality of flow pathways. The creation or stimulation of fracture networks has the potential to improve the efficiency of energy production and recovery. Changes in stress conditions by dynamic perturbations have been shown to increase permeability of aquifer systems at both field and lab scales1,2. The primary mechanism for this increase has been identified by previous studies as a mobilization of fine particles2. Here, we describe results of a laboratory study focused on the role of dynamic stressing and flow perturbations. We used both intact and fractured Berea sandstone samples to investigate the mobilization of fines and the relation between shear displacement and fracture permeability. Intact L-shaped samples were subjected to true triaxial stress conditions on the order of 10MPa. The initially intact samples were fractured in situ and permeability evolution was recorded throughout the experiments. Flow was forced across the sample and the resulting fracture plane, by maintaining a differential fluid pressure along a line source at the fracture inlet and outlet. After fracture, we measured permeability at multiple shear displacement steps. At each stage of the experiment (intact, then fractured, and after each discrete shear displacement step), the sample was dynamically stressed through pore pressure or normal stress oscillations at 1Hz. The resulting transient permeability enhancements are compared at each stage and for multiple samples. The results of these experiments will lead to a better understanding of the relationship between dynamic stressing, shear displacement, and permeability evolution. References: 1 Elkhoury, Jean E., et al., Nature 441.7097 (2006): 1135-1138. 2 Candela, Thibault, et al., J. Geophys. Res., 120.4 (2015): 2037-2055.

  4. Nonlinear bifurcations of psychological stress negotiation: new properties of a formal dynamical model.

    Science.gov (United States)

    Levy, Lawrence R; Yao, Weiguang; McGuire, George; Vollick, Dan N; Jette, Jennifer; Shanahan, Matthew J; Hay, James M; Neufeld, Richard W J

    2012-10-01

    Dynamical systems analysis is applied to a nonlinear model of stress and coping (Neufeld, 1999). The model is composed of 6 order parameters and 11 control parameters, and integrates core constructs of the topic domain, including variants of cognitive appraisal, differential stress susceptibility, stress activation, and coping propensity. In part owing to recent advances in Competitive Modes Theory (Yao, Yu & Essex, 2002), previously intractable but substantively significant dynamical properties of the 6-dimensional model are identified. They include stable and unstable fixed-point equilibria (higher-dimensional saddle-node bifurcation), oscillatory patterns attending fixed-point de-stabilization, and chaotic behaviors. Examination of the nature of system fixed-point de-stabilization, in relation to its control parameters, unveils mechanisms of re-stabilization, and dynamic stability control. All identified dynamics emerge naturally from a system whose construction guideposts are lodged in the addressed content domain. Dynamical complexities therefore may be intrinsic to the present content domain, possibly no less so than in other disciplines where the presence of such attributes has been established.

  5. Dynamical 3-Space Gravitational Waves: Reverberation Effect

    CERN Document Server

    Cahill, Reginald T

    2012-01-01

    Gravity theory missed a key dynamical process that became apparent only when expressed in terms of a velocity field, instead of the Newtonian gravitational acceleration field. This dynamical process involves an additional self-interaction of the dynamical 3-space, and experimental data reveals that its strength is set by the fine structure constant, implying a fundamental link between gravity and quantum theory. The dynamical 3-space has been directly detected in numerous light-speed anisotropy experiments. Quantum matter has been shown to exhibit an acceleration caused by the time-dependence and inhomogeneity of the 3-space flow, giving the first derivation of gravity from a deeper theory, as a quantum wave refraction effect. EM radiation is also refracted in a similar manner. The anisotropy experiments have all shown 3-space wave/turbulence effects, with the latest revealing the fractal structure of 3-space. Here we report the prediction of a new effect, namely a reverberation effect, when the gravitational...

  6. Discussion and prediction on decreasing flow stress scale effect

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Based on crystal plasticity theory and surface layer model, relation of flow stress to billet dimension and grain size was built,and rationality of derived relation was verified with tensile tests of different size billets. With derived expressions, relation of decreasing flow stress scale effect to billet dimension, grain size as well as billet shape was discussed and predicted. The results show that flow stress is proportional to billet size; with decrease of grain size, flow stress is less influenced by billet dimension. When both cross section area and grain size are same, flow stress decrease of rectangular section billet or sheet is larger than that of circular section billet.

  7. The Role of Molecular Microtubule Motors and the Microtubule Cytoskeleton in Stress Granule Dynamics

    Directory of Open Access Journals (Sweden)

    Kristen M. Bartoli

    2011-01-01

    Full Text Available Stress granules (SGs are cytoplasmic foci that appear in cells exposed to stress-induced translational inhibition. SGs function as a triage center, where mRNAs are sorted for storage, degradation, and translation reinitiation. The underlying mechanisms of SGs dynamics are still being characterized, although many key players have been identified. The main components of SGs are stalled 48S preinitiation complexes. To date, many other proteins have also been found to localize in SGs and are hypothesized to function in SG dynamics. Most recently, the microtubule cytoskeleton and associated motor proteins have been demonstrated to function in SG dynamics. In this paper, we will discuss current literature examining the function of microtubules and the molecular microtubule motors in SG assembly, coalescence, movement, composition, organization, and disassembly.

  8. Effective Stress Management: A Model of Emotional Intelligence, Self-Leadership, and Student Stress Coping

    Science.gov (United States)

    Houghton, Jeffery D.; Wu, Jinpei; Godwin, Jeffrey L.; Neck, Christopher P.; Manz, Charles C.

    2012-01-01

    This article develops and presents a model of the relationships among emotional intelligence, self-leadership, and stress coping among management students. In short, the authors' model suggests that effective emotion regulation and self-leadership, as mediated through positive affect and self-efficacy, has the potential to facilitate stress coping…

  9. Effective Stress Management: A Model of Emotional Intelligence, Self-Leadership, and Student Stress Coping

    Science.gov (United States)

    Houghton, Jeffery D.; Wu, Jinpei; Godwin, Jeffrey L.; Neck, Christopher P.; Manz, Charles C.

    2012-01-01

    This article develops and presents a model of the relationships among emotional intelligence, self-leadership, and stress coping among management students. In short, the authors' model suggests that effective emotion regulation and self-leadership, as mediated through positive affect and self-efficacy, has the potential to facilitate stress coping…

  10. On statistical behaviour of stress drops in Portevin–Le Chatelier effect

    Indian Academy of Sciences (India)

    A Chatterjee; P Mukherjee; N Gayathri; P Barat; Arnab Barat; A Sarkar

    2011-08-01

    The Portevin–Le Chatelier (PLC) effect is a kind of plastic instability observed in many dilute alloys when deformed at certain ranges of strain rate and temperature. In this paper we present a comprehensive statistical analysis of the observed experimental data obtained during PLC effect and establish that the occurrence probability of the stress drops in the dynamical process responsible for PLC effect is Poisson in nature.

  11. Effective stress analysis method of seismic response for high tailings dam

    Institute of Scientific and Technical Information of China (English)

    LIU Hou-xiang; LI Ning; LIAO Xue; WU Cong-shi; PAN Xu-dong

    2007-01-01

    Based on the analysis method for tailings dam in upstream raising method presently used in metallurgy and nonferrous metals tailings depository in the world, an effective stress analysis method of seismic response for high tailings dam was developed according to the results of engineering geological exploration, static and dynamic test and stability analysis on Baizhishan tailing dam 113.5 m high. The law of generation, diflusion and dissipation of seismic pore water pressure during and after earthquake was investigated, and the results of tailings dam's acceleration, seismic dynamic stress and pore water pressure were obtained.The results show that the seismic stability and liquefaction resistance of high tailings dam are strengthened remarkably, and the scope and depth of liquefaction area at the top of dam are reduced greatly.The interior stress is compressive stress.the stress level of every element is less than 1.0 and the safety coefficient of every element is greater than 1.O. The safety coefficient against liquefaction of every element of tailing dam is greater than 1.5 according to the effective stress analysis of seismic response by finite element method.The calculated results prove that liquefaction is the main reason of seismic failure of high tailing dams, and the effect of seismic inertia forces on high tailing dams'stability during earthquake is secondary reason.

  12. Low-stress and high-stress singing have contrasting effects on glucocorticoid response

    Directory of Open Access Journals (Sweden)

    Daisy eFancourt

    2015-09-01

    Full Text Available Performing music in public is widely recognised as a potentially stress-inducing activity. However, despite the interest in music performance as an acute psychosocial stressor, there has been relatively little research on the effects of public performance on the endocrine system. This study examined the impact of singing in a low-stress performance situation and a high-stress live concert on levels of glucocorticoids (cortisol and cortisone in 15 professional singers. The results showed a significant decrease in both cortisol and cortisone across the low-stress condition, suggesting that singing in itself is a stress-reducing (and possibly health-promoting activity, but significant increases across the high-stress condition. This is the first study to demonstrate that singing affects glucocorticoid responses and that these responses are modulated by the conditions of performance.

  13. Thickness Effect of Pulse Shaper on Dynamic Stress Equilibrium and Dynamic Deformation Behavior in the Polycarbonate Using SHPB Technique%波形整形器厚度对SHPB实验中聚碳酸酯试件的动应力平衡和变形行为的影响

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The Split Hopkinson Pressure Bar(SHPB) technique with a special experimental apparatus can be used to obtain the material behaviors under high strain rate loading condition. Attempts to apply the Split Hopkison Pressure Bar in measurement on polymeric materials suffer from limitations on the maximum achievable strain and from high noise to signal ratios. This paper introduces a Split Hopkinson Pressure Bar technique, to overcome these limitations. The proposed method uses aluminum pressure bars to achieve a closer impedance match between the pressure bars and the specimen materials, thus providing both data having a low noise to signal ratio and a longer input pulse at higher maximum strain. In addition, a pulse shaper technique was used for increasing the rise time of the incident pulse to ensure stress equilibrium and homogeneous deformation in the specimen under dynamic compression. A pulse shaper is utilized to lengthen the rising time of the incident pulse to ensure stress equilibrium and homogeneous deformation of polycarbonate. The dynamic deformation behaviors of Polymeric material under compressive high strain rate are evaluated using the modified SHPB technique.

  14. Effects of orthostasis on endocrine responses to psychosocial stress.

    Science.gov (United States)

    Nater, Urs M; Ditzen, Beate; Strahler, Jana; Ehlert, Ulrike

    2013-12-01

    Standardized psychological procedures have been designed to induce physiological stress responses. However, the impact of standing (orthostasis) on the physiological reaction after psychological stress remains unclear. The purpose of the current analysis was to examine and quantify the relative contribution of orthostasis to the physiological stress response by comparing a "standing with stress" to a "standing without stress" condition. We investigated the effect of standing with and without stress on responses of the sympathetic-adrenomedullary (SAM) system and the hypothalamic-pituitary-adrenal (HPA) axis using a standardized psychosocial stress protocol (Trier Social Stress Test) and a non-stress condition in a repeated measures design. Subjects (N=30) were exposed to both conditions in randomized order and had to maintain a standing, upright position for 10minutes. In the "standing with stress" condition, significant increases in repeatedly assessed plasma norepinephrine (NE) and epinephrine (EP), as well as in saliva cortisol were found, while in the "standing without stress" condition, no significant changes in plasma epinephrine and saliva cortisol were observed. Calculations of the relative contribution of orthostasis to physiological stress responses revealed that 25.61% of the NE increase, 82.94% of the EP increase, and 68.91% of the cortisol increase, could be attributed to psychosocial stress adjusted for the effects of orthostasis and basal endocrine output. Although these results are indicative for a marked endocrine reaction that is caused by psychosocial stress alone, our findings show that the contribution of orthostasis must be taken into account when interpreting endocrine data collected in a psychosocial stress test.

  15. The effectiveness of stress management training program on depression, anxiety and stress of the nursing students

    Science.gov (United States)

    Yazdani, Mohsen; Rezaei, Sara; Pahlavanzadeh, Saeid

    2010-01-01

    BACKGROUND: Stress has been defined as a barrier to concentration, problem solving, decision making, and other necessary abilities for students’ learning; it also has some symptoms and illnesses in the students such as depression and anxiety. In reviewing stress and its consequences, the methods of coping with stress in the method of response to it would be more important than the nature of stress itself. Therefore, this study aimed to determine the effectiveness of stress management training program on depression, anxiety and stress rate of the nursing students. METHODS: This parallel group randomized quasi-experimental trial, was done on 68 Bs nursing students of Nursing and Midwifery School in Isfahan University of Medical Sciences from 2010 to 2011. The questionnaires of this study consisted of individual characteristics and Depression, Anxiety and Stress Scale (DASS-42). In a random fashion, The intervention group was trained with stress management training program in 8 two hours sessions, twice a week. The questionnaires were completed by both groups before, after and one month after the study. RESULTS: The results of the study indicated that there was no significant difference before the intervention in depression, anxiety and stress mean scores in the two groups. After the intervention, the mean scores of anxiety and stress in the intervention group was 5.09 (4.87) and 8.93 (6.01) and in the control group was 10 (6.45) and 13.17 (7.20), that reduction in depression mean score was significantly greater in the intervention group in the control group (p = 0.040). Furthermore, the mean scores of anxiety and stress showed a significant difference between the two groups (Anxiety p = 0.001; Stress p = 0.011); this reduction also had been remained after a month. CONCLUSIONS: According to the results of the present study, holding stress management training program workshops in different courses of the mental health department can improve mental health of the

  16. Effects of controllable vs. uncontrollable stress on circadian temperature rhythms.

    Science.gov (United States)

    Kant, G J; Bauman, R A; Pastel, R H; Myatt, C A; Closser-Gomez, E; D'Angelo, C P

    1991-03-01

    The effects of sustained stress on body temperature were investigated in rats implanted with mini-transmitters that permitted remote measurement of body temperature. Temperature was first monitored during control conditions. Following the control period, rats were either shaped to avoid/escape signalled around-the-clock intermittent footshock (controllable stress) or yoked to the controlling rats such that the controlling rat and the yoked rat received shock of the same duration, but only the controlling rat could terminate shock by pulling a ceiling chain. Under control conditions, rats demonstrated regular rhythms in body temperature which averaged 1 degree higher during the 12-h dark cycle than the light cycle. Stress disrupted the rhythm and markedly decreased the night-day difference in temperature, especially in the yoked rats in which almost no difference between light and dark cycle temperature was seen. The disruption was most marked for the first days of stress. A regular temperature rhythm was reestablished following about 5 days of stress although the stress condition continued. Leverpressing for food was also affected by the stress conditions with both stress groups leverpressing less than controls and the uncontrollable stress group pressing less than the controllable stress group. These data offer additional evidence of the increased pathophysiological effects of uncontrollable as compared to controllable stress.

  17. Analysis and numerical simulation of dynamic effect on rock under high pressure water jet

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-hong; SI Hu; WANG Dan-dan

    2008-01-01

    Based on continuum mechanics and rock dynamics, analyzed the micro-structure damage of rock and the impulsive effect under high pressure water jet and developed the dynamic model. Further, on the assumption of that rock was homogeneous and isotropic, a computational model was established based on nonlinear finite element and Arbitrary Lagrangian-Eulerian(ALE) method. The dynamic effect impacted on rock under high pressure water jet was simulated by the dynamic contact method. The propagation of stress wave in rock was numerically simulated at different impacting velocity. The results show that the propagation velocity of stress wave is proportional to the impacting velocity of high pressure water jet. The faster the impacting velocity is, the quicker the comedown of stress wave.

  18. Overcoming the effects of stress on reactor operator performance

    Energy Technology Data Exchange (ETDEWEB)

    He Xuhong; Wei Li; Zhao Bingquan [Tsinghua Univ., Nuclear Power Plant Simulation Training Center, Beijing (China)

    2003-03-01

    Reactor operators may be exposed to significant levels of stress during plant emergencies and their performance may be affected by the stress. This paper first identified the potential sources of stress in the nuclear power plant, then discussed the ways in which stress is likely to affect the reactor operators, and finally identified several training approaches for reducing or eliminating stress effects. The challenges for effective stress reducing training may seem daunting, yet the challenges are real and must be addressed. This paper reviewed researches in training design, knowledge and skill acquisition, and training transfer point to a number of strategies that can be used to address these challenges and lead to more effective training and development. (author)

  19. Analysis of domain wall dynamics based on skewness of magnetic Barkhausen noise for applied stress determination

    Science.gov (United States)

    Ding, Song; Tian, GuiYun; Dobmann, Gerd; Wang, Ping

    2017-01-01

    Skewness of Magnetic Barkhausen Noise (MBN) signal is used as a new feature for applied stress determination. After experimental studies, skewness presents its ability for measuring applied tensile stress compared with conventional feature, meanwhile, a non-linear behavior of this new feature and an independence of the excitation conditions under compressive stress are found and discussed. Effective damping during domain wall motion influencing the asymmetric shape of the MBN statistical distribution function is discussed under compressive and tensile stress variation. Domain wall (DW) energy and distance between pinning edges of the DW are considered altering the characteristic relaxation time, which is the reason for the non-linear phenomenon of skewness.

  20. Influence of effective stress coefficient on mechanical failure of chalk

    DEFF Research Database (Denmark)

    Alam, Mohammad Monzurul; Fabricius, Ida Lykke; Hjuler, M.L.

    2012-01-01

    The Effective stress coefficient is a measure of how chalk grains are connected with each other. The stiffness of chalk may decrease if the amount of contact cements between the grains decreases, which may lead to an increase of the effective stress coefficient. We performed CO2 injection in chal...

  1. Contrast-induced nephrotoxicity: possible synergistic effect of stress hyperglycemia.

    LENUS (Irish Health Repository)

    O'Donnell, David H

    2010-07-01

    Oxidative stress on the renal tubules has been implicated as a mechanism of injury in both stress hyperglycemia and contrast-induced nephrotoxicity. The purpose of this study was to determine whether the combination of these effects has a synergistic effect on accentuating renal tubular apoptosis and therefore increasing the risk of contrast-induced nephrotoxicity.

  2. Effects of shear stress on the microalgae Chaetoceros muelleri

    NARCIS (Netherlands)

    Michels, M.H.A.; Goot, van der A.J.; Norsker, N.H.; Wijffels, R.H.

    2010-01-01

    The effect of shear stress on the viability of Chaetoceros muelleri was studied using a combination of a rheometer and dedicated shearing devices. Different levels of shear stress were applied by varying the shear rates and the medium viscosities. It was possible to quantify the effect of shear

  3. STUDY REGARDING THE DYNAMICS OF AFFECTIVE MANIFESTATIONS IN MIDDLE DISTANCE AND LONG DISTANCE RUNNERS, IN DIFFERENT SITUATIONS OF MENTAL STRESS

    Directory of Open Access Journals (Sweden)

    MAREŞ GABRIEL

    2012-09-01

    Full Text Available AbstractIntroduction. High performance in track and field is constantly conditioned by the athletes' reaction to different stress factors. The analysis of mental stress on athletes in different situations has made certain specialists to say that the psychological effect of a stress agent (seen as a response of the athlete is less predictable than the physiological effect, one reason being the complex and difficult nature of objectively predicting the response provoked by the effect of the stress factor, considering the fact that high performance athletes react differently to the pressure of complex situations during training and competitions. Methodology. The research was conducted on 12 subjects with different experience in high performance track and field/athletics, and in this specific event. The subjects were given three psychological tests, within a period of six months, during three different stress situations: two tests (initial and final before two major competitions (the national championships - selection competitions, and an intermediate testing (halfway between the two competitions, when the subjects were in full training process for the second competition. During these six months the previously planned training program was followed, but with a larger emphasis (in comparison with other training periods on the psychological training of the athletes.Results. The statistical analysis of the values for the studied variables has shown the existence of significant differences only in the manifestations associated with certain psychological states of the ones we studied, during different tests. Conclusions The affective manifestations of the middle distance-long distance runners during different situations of mental stress present an oscillatory dynamics with a slightly descendant curve, showing a complexity of the psycho-affective states and reactions.

  4. Dynamic Reliability Analysis Method of Degraded Mechanical Components Based on Process Probability Density Function of Stress

    Directory of Open Access Journals (Sweden)

    Peng Gao

    2014-01-01

    Full Text Available It is necessary to develop dynamic reliability models when considering strength degradation of mechanical components. Instant probability density function (IPDF of stress and process probability density function (PPDF of stress, which are obtained via different statistical methods, are defined, respectively. In practical engineering, the probability density function (PDF for the usage of mechanical components is mostly PPDF, such as the PDF acquired via the rain flow counting method. For the convenience of application, IPDF is always approximated by PPDF when using the existing dynamic reliability models. However, it may cause errors in the reliability calculation due to the approximation of IPDF by PPDF. Therefore, dynamic reliability models directly based on PPDF of stress are developed in this paper. Furthermore, the proposed models can be used for reliability assessment in the case of small amount of stress process samples by employing the fuzzy set theory. In addition, the mechanical components in solar array of satellites are chosen as representative examples to illustrate the proposed models. The results show that errors are caused because of the approximation of IPDF by PPDF and the proposed models are accurate in the reliability computation.

  5. Effect of Thermal Stress on Cardiac Function

    OpenAIRE

    Wilson, Thad E.; Crandall, Craig G.

    2011-01-01

    Whole-body heating decreases pulmonary capillary wedge pressure and cerebral vascular conductance, and causes an inotropic shift in the Frank-Starling curve. Whole-body cooling increases pulmonary capillary wedge pressure and cerebral vascular conductance without changing systolic function. These and other data indicate factors affecting cardiac function may mechanistically contribute to syncope during heat stress and improvements in orthostatic tolerance during cold stress.

  6. Excitonic dynamical Franz-Keldysh effect

    DEFF Research Database (Denmark)

    Nordstrøm, K.B.; Johnsen, Kristinn; Allen, S.J.

    1998-01-01

    The dynamical Franz-Keldysh effect is exposed by exploring near-band-gap absorption in the presence of intense THz electric fields. It bridges the gap between the de Franz-Keldysh effect and multiphoton absorption and competes with the THz ac Stark effect in shifting the energy of the excitonic...... resonance. A theoretical model which includes the strong THz field nonperturbatively via a nonequilibrium Green functions technique is able to describe the dynamical Franz-Keldysh effect in the presence of excitonic absorption....

  7. Gravity Probe-B Spacecraft attitude control based on the dynamics of slosh wave-induced fluid stress distribution on rotating dewar container of cryogenic propellant

    Science.gov (United States)

    Hung, R. J.; Lee, C. C.; Leslie, F. W.

    1991-01-01

    The dynamical behavior of fluids, in particular the effect of surface tension on partially-filled rotating fluids, in a full-scale Gravity Probe-B Spacecraft propellant dewar tank imposed by various frequencies of gravity jitters have been investigated. Results show that fluid stress distribution exerted on the outer and inner walls of rotating dewar are closely related to the characteristics of slosh waves excited on the liquid-vapor interface in the rotating dewar tank. This can provide a set of tool for the spacecraft dynamic control leading toward the control of spacecraft unbalance caused by the uneven fluid stress distribution due to slosh wave excitations.

  8. Decay of aftershock density with distance indicates triggering by dynamic stress.

    Science.gov (United States)

    Felzer, K R; Brodsky, E E

    2006-06-01

    The majority of earthquakes are aftershocks, yet aftershock physics is not well understood. Many studies suggest that static stress changes trigger aftershocks, but recent work suggests that shaking (dynamic stresses) may also play a role. Here we measure the decay of aftershocks as a function of distance from magnitude 2-6 mainshocks in order to clarify the aftershock triggering process. We find that for short times after the mainshock, when low background seismicity rates allow for good aftershock detection, the decay is well fitted by a single inverse power law over distances of 0.2-50 km. The consistency of the trend indicates that the same triggering mechanism is working over the entire range. As static stress changes at the more distant aftershocks are negligible, this suggests that dynamic stresses may be triggering all of these aftershocks. We infer that the observed aftershock density is consistent with the probability of triggering aftershocks being nearly proportional to seismic wave amplitude. The data are not fitted well by models that combine static stress change with the evolution of frictionally locked faults.

  9. Dynamics of chloroplast proteome in salt-stressed mangrove Kandelia candel (L.) Druce.

    Science.gov (United States)

    Wang, Lingxia; Liang, Wenyu; Xing, Jianhong; Tan, Fanglin; Chen, Yiyong; Huang, Li; Cheng, Chi-Lien; Chen, Wei

    2013-11-01

    Kandelia candel is being established as a model xylophyte for ecoadaptation due to its salt tolerance. To adapt to high salinity, the photosynthesis apparatus must function efficiently under these conditions. Proteomic analysis of chloroplasts isolated from plants under different degrees of salt stress was performed to quantify the changes of individual proteins and to gain a global view of the total chloroplast protein dynamics. Among the 1030 proteins quantified (unique peptide ≥ 1), 76 showed a more than 1.5-fold change in abundance, of which 36 are involved in the light-dependent reactions and 12 in the Calvin cycle. The dynamic change of these proteins indicates that light-dependent reactions are maintained by up-regulating the levels of component proteins at both moderate and high salinity, and the Calvin cycle remained functional at moderate salinity but showed a decline at high salinity. In addition to proteins related to photosynthesis, some known abiotic-stress proteins and plastoglobuli were up-regulated in salt-stressed plants. Plastoglobuli might contribute to maintaining membrane integrity and fluidity. In conclusion, this extensive proteomic investigation on intact chloroplasts of the salt-tolerant xylophyte under salt stress provides some important novel information on adaptative mechanisms involving photosynthesis in responses to salt stress in K. candel.

  10. Stress Analysis of the Subsea Dynamic Riser BaseProcess Piping

    Institute of Scientific and Technical Information of China (English)

    Xuanze Ju; Wei Fang; Hanjun Yin; Ying Jiang

    2014-01-01

    Thesubsea dynamic riser base(SDRB)is an important piece of equipment for the floating production platform mooring system.One end is connected to the rigid pipeline, carrying a rigid pipeline thermal expansion load and the other end is connected to a flexible riser, carrying the dynamic load of the flexible riser, so its function is a transition connection between the flexible riser and the rigid pipeline which fixes the flexible riser on the seabed. On the other hand , as a typical subsea product, the design will satisfythe requirements of the standards for subsea products. By studying the stress analysisphilosophy of the topside piping and subsea pipeline, a physical model and procedure for piping stress analysis of the SDRB have been established.The conditions of the adverse design load have been considered, and a combination of the static load from the rigid pipeline and the dynamic load flexibility has also been optimized. And a comparative analysis between the AMSE, DNV and API standards for piping stress with the checking rules has been done.Because theSDRB belongs to the subsea pipeline terminal product, the use of DNV standards to check its process piping stress is recommended. Finally, the process piping stress of the SDRB has been calculated, and the results show that the jacket pipe and the carrier pipe stress of the SDRB process piping satisfy the DNV standards as a whole.The bulkhead cannot be accurately simulated by the AutoPIPE software which uses the FEA software ANSYS inthe detailed analysis, but the checking results will still meet the requirements of the DNV standards.

  11. Investigation of the dynamic mechanical behavior of polyetheretherketone (PEEK) in the high stress tensile regime

    Science.gov (United States)

    Berer, M.; Major, Z.; Pinter, G.; Constantinescu, D. M.; Marsavina, L.

    2014-11-01

    Due to its outstanding mechanical performance both in static and dynamic loading and its resistance up to very high temperatures, Polyetheretherketone (PEEK) has attracted many practical applications. The loaded contact state for the application of PEEK rolls as bearing elements was recently analyzed by the corresponding author. High irreversible deformations on the mantle side were caused by the rolling contact and thus the rolling performance is supposed to be strongly affected by the dynamic mechanical properties of this irreversibly deformed material. Tensile fatigue tests at various stress levels up to the thermally dominated fatigue regime were conducted in order to get information regarding the dynamic mechanical material behavior at high stress regimes. Two types of PEEK (annealed and untreated) were investigated and two load ratios, R, were used (0.1 and 0.5). During the fatigue tests extensometer strain, load and surface temperature were recorded and a quantitative hysteresis loop analysis with calculated secant modulus and dynamic modulus was performed. Furthermore, the concept of isocyclic stress-strain diagrams was applied to enlarge and confirm the results obtained from the hysteresis loop analysis. A sharp transition between thermally dominated and mechanically dominated fatigue regimes was found for both PEEK types (annealed and untreated) and for both load ratios. Moreover, the annealed PEEK was stiffer in the tensile fatigue tests than the untreated material. Both examined PEEK types showed distinct hardening throughout the fatigue tests which made them "more elastic" (higher stiffness and less damping).

  12. Stretching the Stress Boundary: Linking Air Pollution Health Effects to a Neurohormonal Stress Response

    Science.gov (United States)

    Inhaled pollutants produce effects in virtually all organ systems in our body and have been linked to chronic diseases including hypertension, atherosclerosis, Alzheimer’s and diabetes. A neurohormonal stress response (referred here as a systemic response produced by activ...

  13. Stretching the Stress Boundary: Linking Air Pollution Health Effects to a Neurohormonal Stress Response

    Science.gov (United States)

    Inhaled pollutants produce effects in virtually all organ systems in our body and have been linked to chronic diseases including hypertension, atherosclerosis, Alzheimer’s and diabetes. A neurohormonal stress response (referred here as a systemic response produced by activ...

  14. Stress and Memory: Behavioral Effects and Neurobiological Mechanisms

    Directory of Open Access Journals (Sweden)

    Carmen Sandi

    2007-01-01

    Full Text Available Stress is a potent modulator of learning and memory processes. Although there have been a few attempts in the literature to explain the diversity of effects (including facilitating, impairing, and lack of effects described for the impact of stress on memory function according to single classification criterion, they have proved insufficient to explain the whole complexity of effects. Here, we review the literature in the field of stress and memory interactions according to five selected classifying factors (source of stress, stressor duration, stressor intensity, stressor timing with regard to memory phase, and learning type in an attempt to develop an integrative model to understand how stress affects memory function. Summarizing on those conditions in which there was enough information, we conclude that high stress levels, whether intrinsic (triggered by the cognitive challenge or extrinsic (induced by conditions completely unrelated to the cognitive task, tend to facilitate Pavlovian conditioning (in a linear-asymptotic manner, while being deleterious for spatial/explicit information processing (which with regard to intrinsic stress levels follows an inverted U-shape effect. Moreover, after reviewing the literature, we conclude that all selected factors are essential to develop an integrative model that defines the outcome of stress effects in memory processes. In parallel, we provide a brief review of the main neurobiological mechanisms proposed to account for the different effects of stress in memory function. Glucocorticoids were found as a common mediating mechanism for both the facilitating and impairing actions of stress in different memory processes and phases. Among the brain regions implicated, the hippocampus, amygdala, and prefrontal cortex were highlighted as critical for the mediation of stress effects.

  15. [STRESS AND INFARCT LIMITING EFFECTS OF EARLY HYPOXIC PRECONDITIONING].

    Science.gov (United States)

    Lishmanov, Yu B; Maslov, L N; Sementsov, A S; Naryzhnaya, N V; Tsibulnikov, S Yu

    2015-09-01

    It was established that early hypoxic preconditioning is an adaptive state different from eustress and distress. Hypoxic preconditioning has the cross effects, increasing the tolerance of the heart to ischemia-reperfusion and providing antiulcerogenic effect during immobilization stress.

  16. Mechanical fatigue of polysilicon: Effects of mean stress and stress amplitude

    Energy Technology Data Exchange (ETDEWEB)

    Kahn, H. [Department of Materials Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106 7204 (United States)]. E-mail: harold.kahn@case.edu; Chen, L. [Department of Civil Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106 7201 (United States); Ballarini, R. [Department of Civil Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106 7201 (United States); Heuer, A.H. [Department of Materials Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106 7204 (United States)

    2006-02-15

    Polycrystalline silicon (polysilicon) fatigue specimens with micrometer-sized dimensions were fabricated and subjected to cyclic loading using an integrated electrostatic actuator. The fatigue effects were determined by comparing the single edge-notched beam monotonic bend strength measured after cyclic loading to the monotonic strength of 'virgin' specimens that had received no cycling. Both strengthening and weakening were observed, depending on the levels of mean stress and fatigue stress amplitude during the cyclic loading. Monotonic loading with similar sub-critical stress levels had no effect. The physical mechanisms responsible for this behavior are discussed, and a model based on grain boundary plasticity is presented for the strengthening behavior.

  17. Morphologic effects of the stress response in fish.

    Science.gov (United States)

    Harper, Claudia; Wolf, Jeffrey C

    2009-01-01

    Fish and other aquatic animals are subject to a broad variety of stressors because their homeostatic mechanisms are highly dependent on prevailing conditions in their immediate surroundings. Yet few studies have addressed stress as a potential confounding factor for bioassays that use fish as test subjects. Common stressors encountered by captive fish include physical and mental trauma associated with capture, transport, handling, and crowding; malnutrition; variations in water temperature, oxygen, and salinity; and peripheral effects of contaminant exposure or infectious disease. Some stress responses are detectable through gross or microscopic examination of various organs or tissues; as reported in the literature, stress responses are most consistently observed in the gills, liver, skin, and components of the urogenital tract. In addition to presenting examples of various stressors and corresponding morphologic effects, this review highlights certain challenges of evaluating stress in fish: (1) stress is an amorphous term that does not have a consistently applied definition; (2) procedures used to determine or measure stress can be inherently stressful; (3) interactions between stressors and stress responses are highly complex; and (4) morphologically, stress responses are often difficult to distinguish from tissue damage or compensatory adaptations induced specifically by the stressor. Further investigations are necessary to more precisely define the role of stress in the interpretation of fish research results.

  18. Dynamical memory effects in correlated quantum channels

    Science.gov (United States)

    Addis, Carole; Karpat, Göktuǧ; Macchiavello, Chiara; Maniscalco, Sabrina

    2016-09-01

    Memory effects play a fundamental role in the study of the dynamics of open quantum systems. There exist two conceptually distinct notions of memory discussed for quantum channels in the literature. In quantum information theory quantum channels with memory are characterized by the existence of correlations between successive applications of the channel on a sequence of quantum systems. In open quantum systems theory memory effects arise dynamically during the time evolution of quantum systems and define non-Markovian dynamics. Here we relate and combine these two different concepts of memory. In particular, we study the interplay between correlations between multiple uses of quantum channels and non-Markovianity as nondivisibility of the t -parametrized family of channels defining the dynamical map.

  19. Dynamical 3-Space Gravitational Waves: Reverberation Effects

    Directory of Open Access Journals (Sweden)

    Cahill R. T.

    2013-04-01

    Full Text Available Gravity theory missed a key dynamical process that became ap parent only when ex- pressed in terms of a velocity field, instead of the Newtonian gravitational acceleration field. This dynamical process involves an additional self-i nteraction of the dynam- ical 3-space, and experimental data reveals that its streng th is set by the fine struc- ture constant, implying a fundamental link between gravity and quantum theory. The dynamical 3-space has been directly detected in numerous li ght-speed anisotropy ex- periments. Quantum matter has been shown to exhibit an accel eration caused by the time-dependence and inhomogeneity of the 3-space flow, givi ng the first derivation of gravity from a deeper theory, as a quantum wave refraction effect. EM radiation is also refracted in a similar manner. The anisotropy experiments have all shown 3-space wave / turbulence effects, with the latest revealing the fractal structure of 3-s pace. Here we report the prediction of a new effect, namely a reverberation effect, when the gravi- tational waves propagate in the 3-space inflow of a large mass . This effect arises from the non-linear dynamics of 3-space. These reverberations c ould offer an explanation for the Shnoll effect, in which cosmological factors influence stochastic pro cesses, such as radioactive decay rates.

  20. Dynamic effects of diabatization in distillation columns

    DEFF Research Database (Denmark)

    Bisgaard, Thomas; Huusom, Jakob Kjøbsted; Abildskov, Jens

    2013-01-01

    The dynamic effects of diabatization in distillation columns are investigated in simulation emphasizing the heat-integrated distillation column (HIDiC). A generic, dynamic, first-principle model has been formulated, which is flexible enough to describe various diabatic distillation configurations....... Dynamic Relative Gain Array and Singular Value Analysis have been applied in a comparative study of a conventional distillation column and a HIDiC. The study showed increased input-output coupling due to diabatization. Feasible SISO control structures for the HIDiC were also found and control...

  1. The effects of stress on nuclear power plant operational decision making and training approaches to reduce stress effects

    Energy Technology Data Exchange (ETDEWEB)

    Mumaw, R.J.

    1994-08-01

    Operational personnel may be exposed to significant levels of stress during unexpected changes in plant state an plant emergencies. The decision making that identifies operational actions, which is strongly determined by procedures, may be affected by stress, and performance may be impaired. ER report analyzes potential effects of stress in nuclear power plant (NPP) settings, especially in the context of severe accident management (SAM). First, potential sources of stress in the NPP setting are identified. This analysis is followed by a review of the ways in which stress is likely to affect performance, with an emphasis on performance of cognitive skills that are linked to operational decision making. Finally, potential training approaches for reducing or eliminating stress effects are identified. Several training approaches have the potential to eliminate or mitigate stress effects on cognitive skill performance. First, the use of simulated events for training can reduce the novelty and uncertainty that can lead to stress and performance impairments. Second, training to make cognitive processing more efficient and less reliant on attention and memory resources can offset the reductions in these resources that occur under stressful conditions. Third, training that targets crew communications skills can reduce the likelihood that communications will fail under stress.

  2. Post-training reward partially restores chronic stress induced effects in mice.

    Directory of Open Access Journals (Sweden)

    Sergiu Dalm

    Full Text Available Reduced responsiveness to positive stimuli is a core symptom of depression, known as anhedonia. In the present study, we assessed the expression of anhedonia in our chronic stress mouse model using a subset of read-out parameters. In line with this, we investigated in how far chronic stress would affect the facilitating effect of post-training self-administration of sugar, as we previously observed in naïve mice. Male C57BL/6J mice were repeatedly and at unpredictable times exposed to rats (no physical contact over the course of two weeks. Following novelty exploration, (non- spatial learning and memory processes with and without post-training sugar acting as reinforcer, emotionality, reward sensitivity and corticosterone levels were determined. We found that (1 the effects of chronic stress persisted beyond the period of the actual rat exposure. (2 Post-training self-administration of sugar as reinforcer improved spatial performance in naïve mice, whereas (3 in stressed mice sugar partially "normalized" the impaired performance to the level of controls without sugar. Chronic stress (4 increased behavioral inhibition in response to novelty; (5 induced dynamic changes in the pattern of circadian corticosterone secretion during the first week after rat stress and (6 increased the intake of sucrose and water. (7 Chronic stress and sugar consumed during spatial training facilitated the memory for the location of the sucrose bottle weeks later. Concluding, our chronic stress paradigm induces the expression of anhedonia in mice, at different levels of behavior. The behavioral inhibition appears to be long lasting in stressed mice. Interestingly, sugar consumed in close context with spatial learning partially rescued the stress-induced emotional and cognitive impairments. This suggests that reward can ameliorate part of the negative consequences of chronic stress on memory.

  3. Polymer Prize Talk: Segmental Dynamics in Polymers : From Cold Melts to Aging and Stressed Glasses

    Science.gov (United States)

    Schweizer, Kenneth

    2008-03-01

    Polymers are excellent glass formers. In the cold molten state they exhibit chemically-specific and strongly non-Arrenhius segmental relaxation which sets the time scale for the generic chain scale dynamics. In the amorphous solid or plastic state the temperature dependence of the alpha relaxation time changes, physical aging emerges, and a rich mechanical response occurs characterized by the dynamic yielding, strain softening and strain hardening processes. We have developed a statistical mechanical theory of activated segmental relaxation in cold melts by combining and extending methods of mode coupling, dynamic density functional and activated hopping theories. The approach is built on the concept of a confining nonequilibrium free energy which quantifies local dynamical constraints and the barrier hopping process. The localizing consequences of interchain caging forces are quantified by the amplitude of nanometer scale density fluctuations (compressibility) and backbone stiffness. Predictions for the kinetic glass and dynamic crossover temperatures, dynamic fragility, and thermal dependence of the segmental relaxation time are consistent with experiments. The theory has been generalized to treat alpha relaxation, physical aging, and nonlinear mechanical properties in the glass. The structural component of density fluctuations become (partially) frozen resulting in a crossover to Arrenhius relaxation. Physical aging is modeled based on a kinetic equation for collective density fluctuations. At intermediate time scales the relaxation time (shear modulus) grows as a power law (logarithmic) function of aging time with a temperature dependent exponent. Applied stress weakens dynamical constraints thereby accelerating relaxation and softening the elastic modulus. A constitutive equation has been constructed from which the temperature dependent dynamic yielding and mechanical response under constant strain rate, constant stress (creep), and other modes of deformation

  4. Effect of Surface Topography on Stress Concentration Factor

    Institute of Scientific and Technical Information of China (English)

    CHENG Zhengkun; LIAO Ridong

    2015-01-01

    Neuber rule and Arola-Ramulu model are widely used to predict the stress concentration factor of rough specimens. However, the height parameters and effective valley radius used in these two models depend strongly on the resolution of the roughness-measuring instruments and are easily introduce measuring errors. Besides, it is difficult to find a suitable parameter to characterize surface topography to quantitatively describe its effect on stress concentration factor. In order to overcome these disadvantages, profile moments are carried out to characterize surface topography, surface topography is simulated by superposing series of cosine components, the stress concentration factors of different micro cosine-shaped surface topographies are investigated by finite element analysis. In terms of micro cosine-shaped surface topography, an equation using the second profile moment to estimate the stress concentration factor is proposed, predictions for the stress concentration factor using the proposed expression are within 10% error compared with the results of finite element analysis, which are more accurate than other models. Moreover, the proposed equation is applied to the real surface topography machined by turning. Predictions for the stress concentration factor using the proposed expression are within 10% of the maximum stress concentration factors and about 5% of the effective stress concentration factors estimated from the finite element analysis for three levels of turning surface topographies under different simulated scales. The proposed model is feasible in predicting the stress concentration factors of real machined surface topographies.

  5. Dynamics of Mount Somma-Vesuvius edifice: from stress field inversion to analogue and numerical modelling

    Science.gov (United States)

    De Matteo, Ada; Massa, Bruno; D'Auria, Luca; Castaldo, Raffaele

    2017-04-01

    Geological processes are generally very complex and too slow to be directly observed in their completeness; modelling procedures overcome this limit. The state of stress in the upper lithosphere is the main responsible for driving geodynamical processes; in order to retrieve the active stress field in a rock volume, stress inversion techniques can be applied on both seismological and structural datasets. This approach has been successfully applied to active tectonics as well as volcanic areas. In this context the best approach in managing heterogeneous datasets in volcanic environments consists in the analysis of spatial variations of the stress field by applying robust techniques of inversion. The study of volcanic seismicity is an efficient tool to retrieve spatial and temporal pattern of the pre-, syn- and inter-eruptive stress field: magma migration as well as dynamics of magma chamber and hydrothermal system are directly connected to the volcanic seismicity. Additionally, analysis of the temporal variations of stress field pattern in volcanoes could be a useful monitoring tool. Recently the stress field acting on several active volcanoes has been investigated by using stress inversion techniques on seismological datasets (Massa et al., 2016). The Bayesian Right Trihedra Method (BRTM; D'Auria and Massa, 2015) is able to successfully manage heterogeneous datasets allowing the identification of regional fields locally overcame by the stress field due to volcano specific dynamics. In particular, the analysis of seismicity and stress field inversion at the Somma-Vesuvius highlighted the presence of two superposed volumes characterized by different behaviour and stress field pattern: a top volume dominated by an extensional stress field, in accordance with a gravitational spreading-style of deformation, and a bottom volume related to a regional extensional stress field. In addition, in order to evaluate the dynamics of deformation, both analogue and numerical

  6. Effects of Hospital Workers' Friendship Networks on Job Stress.

    Directory of Open Access Journals (Sweden)

    Sung Yae Shin

    Full Text Available This study attempted to identify the sources of job stress according to job position and investigate how friendship networks affect job stress.Questionnaires based on The Health Professions Stress Inventory (HPSI developed by Wolfgang experienced by healthcare providers were collected from 420 nurses, doctors and radiological technologists in two general hospitals in Korea by a multistage cluster sampling method. Multiple regression analysis was used to examine the effects of friendship networks on job stress after controlling for other factors.The severity of job stress differed according to level of job demands (p = .006; radiologic technologists experienced the least stress (45.4, nurses experienced moderate stress (52.4, and doctors experienced the most stress (53.6. Those with long-term friendships characterized by strong connections reported lower levels of stress than did those with weak ties to friends among nurses (1.3, p < .05 and radiological technologists (11.4, p < .01. The degree of cohesion among friends had a positive impact on the level of job stress experienced by nurses (8.2, p < .001 and radiological technologists (14.6, p < .1. Doctors who participated in workplace alumni meetings scored higher than those who did not. However, those who participated in alumni meetings outside the workplace showed the opposite tendency, scoring 9.4 (p < .05 lower than those who did not. The resources from their friendship network include both information and instrumental support. As most radiological technologists were male, their instrumental support positively affected their job stress (9.2, p < .05. Life information support was the primary positive contributor to control of nurses' (4.1, p < .05, radiological technologists' (8.0, p < .05 job stress.The strength and density of such friendship networks were related to job stress. Life information support from their friendship network was the primary positive contributor to control of job

  7. Structure and stress in Cu/Au and Fe/Au systems: A molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Zientarski, Tomasz, E-mail: martom@dyzio.umcs.lublin.pl [Department for the Modelling of Physico-Chemical Processes, Maria Curie-Skłodowska University, ul. Gliniana 33, 20-614 Lublin (Poland); Chocyk, Dariusz [Department of Applied Physics, Lublin University of Technology, ul. Nadbystrzycka 38, 20-618 Lublin (Poland)

    2014-07-01

    Growth of Fe and Cu thin films on Au substrate and stress evolution were modeled using molecular dynamics simulation. The interactions in the system are described by embedded atom method. The kinematical theory of scattering is performed to identify the structure obtained from simulations. The gold layers undergo reconstruction before deposition. The deposited copper atoms do not disturb the atoms in the reconstructed gold layer, but the deposited iron atoms cause the disappearance of the reconstructed gold surfaces. In both systems Cu/Au and Fe/Au, in the early stage of growth one observes compressive stress. Next, Cu/Au systems have the compressive stress, while in the case of Fe/Au the tensile stress is observed. In the Fe/Au system, the body-centered cubic lattice of Fe changes its orientation relative to the Au layer. In the Fe/Au system we observed a larger diffusion of Au atoms than in Cu/Au systems. - Highlights: • The kinematical theory of scattering is performed to identify the structure. • The correlation between the stress and the deformation is observed. • The relaxation of the stress depends on the orientation of layers. • The lattice of Fe changes its orientation relative to the Au layer in the Fe/Au system. • The Cu layer continues the lattice of Au in the Cu/Au system.

  8. STUDY ON DYNAMIC STRESS INTENSITY FACTORS OF DISK WITH A RADIAL EDGE CRACK SUBJECTED TO EXTERNAL IMPULSIVE PRESSURE

    Institute of Scientific and Technical Information of China (English)

    Chen Aijun

    2007-01-01

    A dynamic weight function method is presented for dynamic stress intensity factors of circular disk with a radial edge crack under external impulsive pressure. The dynamic stresses in a circular disk are solved under abrupt step external pressure using the eigenfunction method.The solution consists of a quasi-static solution satisfying inhomogeneous boundary conditions and a dynamic solution satisfying homogeneous boundary conditions. By making use of FourierBessel series expansion, the history and distribution of dynamic stresses in the circular disk are derived. Furthermore, the equation for stress intensity factors under uniform pressure is used as the reference case, the weight function equation for the circular disk containing an edge crack is worked out, and the dynamic stress intensity factor equation for the circular disk containing a radial edge crack can be given. The results indicate that the stress intensity factors under sudden step external pressure vary periodically with time, and the ratio of the maximum value of dynamic stress intensity factors to the corresponding static value is about 2.0.

  9. Effect of Dynamic Meditation on Mental Health.

    Science.gov (United States)

    Iqbal, Naved; Singh, Archana; Aleem, Sheema

    2016-02-01

    Although traditional meditation has been found to be effective in improving physical and mental health of subjects, there was a paucity of research of the effect of active or dynamic meditation on these variables. Therefore, the present study was aimed at studying the effect of dynamic meditation on mental health of the subjects. Total sample of the present study comprised 60 subjects, 30 each in experimental and control group. Subjects in experimental group were given 21-day training in dynamic meditation. Mental health of the experimental and control group subjects was measured in pre- and post-condition with the help of Mental Health Inventory developed by Jagadish and Srivastava (Mental Health inventory, Manovaigyanik Parikshan Sansthan, Varanasi, 1983). Obtained data were analyzed with the help of ANCOVA. In post-condition, experimental group scored better than control group on integration of personality, autonomy and environmental mastery. Effect sizes of dynamic meditation on these dimensions of mental health were large. However, experimental group and control group did not differ significantly on positive self-evaluation, perception of reality and group-oriented attitude dimensions of mental health in post-condition. Overall, dynamic meditation training was effective in improving mental health of the subjects.

  10. Nuclear Dynamics with Effective Field Theories

    CERN Document Server

    Epelbaum, Evgeny

    2013-01-01

    These are the proceedings of the international workshop on "Nuclear Dynamics with Effective Field Theories" held at Ruhr-Universitaet Bochum, Germany from July 1 to 3, 2013. The workshop focused on effective field theories of low-energy QCD, chiral perturbation theory for nuclear forces as well as few- and many-body physics. Included are a short contribution per talk.

  11. Dynamical Analysis of DTNN with Impulsive Effect

    Directory of Open Access Journals (Sweden)

    Chao Chen

    2009-01-01

    Full Text Available We present dynamical analysis of discrete-time delayed neural networks with impulsive effect. Under impulsive effect, we derive some new criteria for the invariance and attractivity of discrete-time neural networks by using decomposition approach and delay difference inequalities. Our results improve or extend the existing ones.

  12. Evaluation of static and dynamic contact stresses in simulated granular particles using strain gages

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Y.; Shukla, A. (Univ. of Rhode Island, Kingston (United States))

    1993-01-01

    The application of strain gages for the determination of static and dynamic contact loads in granular particles is demonstrated. For experimental convenience, the granular particles are simulated by circular disks fabricated from Homalite-100, a brittle polyester material. Stress field equations in the vicinity of the contact points are carefully evaluated to optimize the relative position of strain gages. The results obtained from strain gages were compared with those obtained using the optical technique of photoelasticity for both static and dynamic problems. Finally, as an example, strain gages are used to study wave propagation in a single chain assembly of disks.

  13. Dying piece by piece: carbohydrate dynamics in aspen seedlings under severe carbon stress and starvation

    Science.gov (United States)

    Wiley, Erin; Chow, Pak; Landhäusser, Simon

    2016-04-01

    Carbon stress and starvation remain poorly understood in trees, despite their potential role in mortality from a variety of agents. To explore the effects of carbon stress on nonstructural carbohydrate (NSC) dynamics and recovery potential and to examine the process of starvation, we grew aspen seedlings under one of three levels of shade: 40% (light shade), 8% (medium shade), and 4% (dark shade) of full sunlight. We then exposed seedlings to 24 hours darkness at either 20° or 28° C until trees had died. Periodically, seedlings were harvested for NSC analysis and to measure stem and root respiration. In addition, some seedlings were moved back into the light to determine if recovery was possible at certain points during starvation. Specifically, we sought to address the following questions: 1) Do NSC concentrations or mass influence tree survival under carbon stress? 2) At what carbohydrate levels do trees fail to recover and starve? 3) Does temperature affect the NSC level at which trees starve? Increasing shade reduced growth, but surprisingly did not reduce NSC levels, except in a portion of deep shade seedlings that experienced dieback. Once in darkness, leaves died first, with final NSC levels ranging from ~4% (Medium shade, 28 degrees) to 7.5% (Light shade). Stem death generally occurred gradually down the stem. Stem tissues retained ~1-2% NSC when dead. Recovery was still possible when only the upper half of the stem had died; at this point, seedlings had relatively high root NSC levels in their remaining roots (7-10%), with 1-3% starch. No trees recovered after the whole stem had died, at which point, some trees root systems were completely dead. However, most retained substantial amounts of live roots, averaging 5-6% NSC, with 0.25-1.5% starch. Despite the initially similar NSC concentrations, light shade seedlings took longer to reach half stem and whole stem death than seedlings from medium and dark shade. Longer survival times were associated with

  14. Effective stress law for the permeability of a limestone

    CERN Document Server

    Ghabezloo, Siavash; Guédon, Sylvine; Martineau, François

    2008-01-01

    The effective stress law for the permeability of a limestone is studied experimentally by performing constant head permeability tests in a triaxial cell with different conditions of confining pressure and pore pressure. Test results have shown that a pore pressure increase and a confining pressure decrease both result in an increase of the permeability, and that the effect of the pore pressure change on the variation of the permeability is more important than the effect of a change of the confining pressure. A power law is proposed for the variation of the permeability with the effective stress. The permeability effective stress coefficient increases linearly with the differential pressure and is greater than one as soon the differential pressure exceeds few bars. The test results are well reproduced using the proposed permeability-effective stress law. A conceptual pore-shell model based on a detailed observation of the microstructure of the studied limestone is proposed. This model is able to explain the ex...

  15. Fluid epitaxialization effect on velocity dependence of dynamic contact angle in molecular scale.

    Science.gov (United States)

    Ito, Takahiro; Hirata, Yosuke; Kukita, Yutaka

    2010-02-07

    Molecular dynamics simulations were used to investigate the effect of epitaxial ordering of the fluid molecules on the microscopic dynamic contact angle. The simulations were performed in a Couette-flow-like geometry where two immiscible fluids were confined between two parallel walls moving in opposite directions. The extent of ordering was varied by changing the number density of the wall particles. As the ordering becomes more evident, the change in the dynamic contact angle tends to be more sensitive to the increase in the relative velocity of the contact line to the wall. Stress components around the contact line is evaluated in order to examine the stress balance among the hydrodynamic stresses (viscous stress and pressure), the deviation of Young's stress from the static equilibrium condition, and the fluid-wall shear stress induced by the relative motion between them. It is shown that the magnitude of the shear stress on the fluid-wall surface is the primary contribution to the sensitivity of the dynamic contact angle and that the sensitivity is intensified by the fluid ordering near the wall surface.

  16. Prenatal stress and its effect on infant development

    NARCIS (Netherlands)

    Huizink, A.C.

    2000-01-01

    In this dissertation the effect of prenatal maternal stress on infant development and behavior is discussed. In a prospective longitudinal study of 170 nulliparous women, data was gatheren on the maternal stress level three times during pregnancy by means of questionnaires and endocrinologic

  17. Effect of Huzikang-duannaibao on piglets' ablactation stress

    Institute of Scientific and Technical Information of China (English)

    Zhou Shenglin; Jiang Zhengyun

    2003-01-01

    Piglets' alactation-stress with diarrhea as a main symptom is a serious problem in pig farming. The experiment indicates that the complex premix additive Huzikang-duannaibao can be used to control ablactation-stress syndromes and its effects are better than that of the common antibiotic ligomycin.

  18. Investigation of topographical effects on rupture dynamics and ground motions

    Science.gov (United States)

    Huang, H.; Chen, X.; Zhang, Z.

    2016-12-01

    Using the curved grid finite-difference method (CG-FDM), we model spontaneous dynamic rupture on vertical strike-slip faults with irregular free surfaces to investigate the effect of topography on near-source ground motion. Four groups of simulations, in which the epicentral distances from the topographical perturbations of the nucleation patch were varied, are modeled in this work. The simulated results show that the presence of irregular topography along the fault trace may increase the ground motion. Whether the irregular topography exhibits higher ground motion overall depends on the irregular topography's ability to prevent the sub-Rayleigh-to-supershear transition. When irregular topography prevents this transition, sub-Rayleigh rupture produces stronger ground motions than those of the sub-Rayleigh-to-supershear transition, although the moment magnitudes does not differ substantially between the two cases. To thoroughly understand the effects of irregular topography on near-source ground motion, we also model spontaneous dynamic rupture on a planar fault in full-space and half-space with varying initial shear stresses, and the corresponding modeling results indicate that the effect of initial shear stress on near-source ground motion is strong. These results may have implications for ground-motion prediction in future earthquakes involving geometrically complex faults.

  19. Calculation of Cauchy stress tensor in molecular dynamics system with a generalized Irving-Kirkwood formulism

    CERN Document Server

    Yang, Jerry Zhijian

    2014-01-01

    Irving and Kirkwood formulism (IK formulism) provides a way to compute continuum mechanics quantities at certain location in terms of molecular variables. To make the approach more practical in computer simulation, Hardy proposed to use a spacial kernel function that couples continuum quantities with atomistic information. To reduce irrational fluctuations, Murdoch proposed to use a temporal kernel function to smooth the physical quantities obtained in Hardy's approach. In this paper, we generalize the original IK formulism to systematically incorporate both spacial and temporal average. The Cauchy stress tensor is derived in this generalized IK formulism (g-IK formulism). Analysis is given to illuminate the connection and difference between g-IK formulism and traditional temporal post-process approach. The relationship between Cauchy stress and first Piola-Kirchhoff stress is restudied in the framework of g-IK formulism. Numerical experiments using molecular dynamics are conducted to examine the analysis res...

  20. Prediction of shear stress-related hemolysis in centrifugal blood pumps by computational fluid dynamics

    Institute of Scientific and Technical Information of China (English)

    WANG Fangqun; LI Lan; FENG Zhigang; QIAN Kunxi

    2005-01-01

    A quantitative evaluation of shear stress-related hemolysis in centrifugal blood pumps with different impeller designs has been investigated. Computational fluid dynamics (CFD) is applied to track the shear stress history of the streamlines of red cells. The power law model of the relations among the hemolysis, shear stress and exposure time is used to evaluate the hemolysis in the pumps.Hemolysis tests are also conducted to verify the estimations. Both the estimations and experimentally measured hemolysis levels show that the hemolysis in the streamlined impeller pump developed by the authors is lower than the pump with straight-vane under the same boundary conditions. The approach is proved to be acceptable and practical to predict hemolysis levels of blood pumps.

  1. Dynamic behavior of nano-voids in magnesium under hydrostatic tensile stress

    Science.gov (United States)

    Ponga, Mauricio; Ramabathiran, Amuthan A.; Bhattacharya, Kaushik; Ortiz, Michael

    2016-08-01

    We investigate the mechanisms responsible for nano-void growth in single crystal magnesium under dynamic hydrostatic tensile stress. A key conclusion derived from our study is that there is no secondary strain hardening near the nano-void. This behavior, which is in remarkable contrast to face-centered cubic and body-centered cubic materials, greatly limits the peak stress and explains the relatively lower spall strength of magnesium. The lack of secondary strain hardening is due to the fact that pyramidal dislocations do not interact with basal or prismatic dislocations. Our analysis also shows that for loads applied at moderate strain rates (\\overset{\\centerdot}{ɛ} ≤slant {{10}6} s-1) the peak stress, dislocation velocity and temperature distribution converge asymptotically. However at very high strain rates (\\overset{\\centerdot}{ɛ} ≥slant {{10}8} s-1), there is a sharp transition in these quantities.

  2. Defects in mitochondrial dynamics and metabolomic signatures of evolving energetic stress in mouse models of familial Alzheimer's disease.

    Directory of Open Access Journals (Sweden)

    Eugenia Trushina

    Full Text Available BACKGROUND: The identification of early mechanisms underlying Alzheimer's Disease (AD and associated biomarkers could advance development of new therapies and improve monitoring and predicting of AD progression. Mitochondrial dysfunction has been suggested to underlie AD pathophysiology, however, no comprehensive study exists that evaluates the effect of different familial AD (FAD mutations on mitochondrial function, dynamics, and brain energetics. METHODS AND FINDINGS: We characterized early mitochondrial dysfunction and metabolomic signatures of energetic stress in three commonly used transgenic mouse models of FAD. Assessment of mitochondrial motility, distribution, dynamics, morphology, and metabolomic profiling revealed the specific effect of each FAD mutation on the development of mitochondrial stress and dysfunction. Inhibition of mitochondrial trafficking was characteristic for embryonic neurons from mice expressing mutant human presenilin 1, PS1(M146L and the double mutation of human amyloid precursor protein APP(Tg2576 and PS1(M146L contributing to the increased susceptibility of neurons to excitotoxic cell death. Significant changes in mitochondrial morphology were detected in APP and APP/PS1 mice. All three FAD models demonstrated a loss of the integrity of synaptic mitochondria and energy production. Metabolomic profiling revealed mutation-specific changes in the levels of metabolites reflecting altered energy metabolism and mitochondrial dysfunction in brains of FAD mice. Metabolic biomarkers adequately reflected gender differences similar to that reported for AD patients and correlated well with the biomarkers currently used for diagnosis in humans. CONCLUSIONS: Mutation-specific alterations in mitochondrial dynamics, morphology and function in FAD mice occurred prior to the onset of memory and neurological phenotype and before the formation of amyloid deposits. Metabolomic signatures of mitochondrial stress and altered energy

  3. No effects of psychosocial stress on intertemporal choice.

    Directory of Open Access Journals (Sweden)

    Johannes Haushofer

    Full Text Available Intertemporal choices - involving decisions which trade off instant and delayed outcomes - are often made under stress. It remains unknown, however, whether and how stress affects intertemporal choice. We subjected 142 healthy male subjects to a laboratory stress or control protocol, and asked them to make a series of intertemporal choices either directly after stress, or 20 minutes later (resulting in four experimental groups. Based on theory and evidence from behavioral economics and cellular neuroscience, we predicted a bidirectional effect of stress on intertemporal choice, with increases in impatience or present bias immediately after stress, but decreases in present bias or impatience when subjects are tested 20 minutes later. However, our results show no effects of stress on intertemporal choice at either time point, and individual differences in stress reactivity (changes in stress hormone levels over time are not related to individual differences in intertemporal choice. Together, we did not find support for the hypothesis that psychosocial laboratory stressors affect intertemporal choice.

  4. Effects of Stress and MDMA on Hippocampal Gene Expression

    Directory of Open Access Journals (Sweden)

    Georg F. Weber

    2014-01-01

    Full Text Available MDMA (3,4-methylenedioxymethamphetamine is a substituted amphetamine and popular drug of abuse. Its mood-enhancing short-term effects may prompt its consumption under stress. Clinical studies indicate that MDMA treatment may mitigate the symptoms of stress disorders such as posttraumatic stress syndrome (PTSD. On the other hand, repeated administration of MDMA results in persistent deficits in markers of serotonergic (5-HT nerve terminals that have been viewed as indicative of 5-HT neurotoxicity. Exposure to chronic stress has been shown to augment MDMA-induced 5-HT neurotoxicity. Here, we examine the transcriptional responses in the hippocampus to MDMA treatment of control rats and rats exposed to chronic stress. MDMA altered the expression of genes that regulate unfolded protein binding, protein folding, calmodulin-dependent protein kinase activity, and neuropeptide signaling. In stressed rats, the gene expression profile in response to MDMA was altered to affect sensory processing and responses to tissue damage in nerve sheaths. Subsequent treatment with MDMA also markedly altered the genetic responses to stress such that the stress-induced downregulation of genes related to the circadian rhythm was reversed. The data support the view that MDMA-induced transcriptional responses accompany the persistent effects of this drug on neuronal structure/function. In addition, MDMA treatment alters the stress-induced transcriptional signature.

  5. Effect of Rotor Diameter on the Thermal Stresses of a Turbine Rotor Model

    Science.gov (United States)

    Dávalos, J. O.; García, J. C.; Urquiza, G.; Castro-Gómez, L. L.; Rodríguez, J. A.; De Santiago, O.

    2016-04-01

    Thermal stresses in a simplified steam turbine rotor model during a cold startup are analyzed using finite element analysis (FEA). In order to validate the numerical model, an experimental array is developed in which a hollow cylinder is heated with hot air in the external surface. At the thick wall of the cylinder, temperature distribution is measured in real time, while at the same time an algorithm computes thermal stresses. Additional computational fluid dynamics (CFD) calculations are made to obtain magnitudes of velocity and pressure in order to compute convective heat transfer coefficient. The experimental results show good agreement with the FEA computations. To evaluate the effect of rotor diameter size, FEA computations with variation in external and internal diameters are performed. Results show that thermal stresses are proportional to rotor diameter size. Also, zones of higher stress concentration are found in the external and internal surfaces of the rotor.

  6. Effect of texture and grain size on the residual stress of nanocrystalline thin films

    Science.gov (United States)

    Cao, Lei; Sengupta, Arkaprabha; Pantuso, Daniel; Koslowski, Marisol

    2017-10-01

    Residual stresses develop in thin film interconnects mainly as a result of deposition conditions and multiple thermal loading cycles during the manufacturing flow. Understanding the relation between the distribution of residual stress and the interconnect microstructure is of key importance to manage the nucleation and growth of defects that can lead to failure under reliability testing and use conditions. Dislocation dynamics simulations are performed in nanocrystalline copper subjected to cyclic loading to quantify the distribution of residual stresses as a function of grain misorientation and grain size distribution. The outcomes of this work help to evaluate the effect of microstructure in thin films failure by identifying potential voiding sites. Furthermore, the simulations show how dislocation structures are influenced by texture and grain size distribution that affect the residual stress. For example, when dislocation loops reach the opposite grain boundary during loading, these dislocations remain locked during unloading.

  7. [Stress prevention programs--strategies, techniques, effectiveness. Part II. Organizational activities to prevent stress at work].

    Science.gov (United States)

    Małgorzata, W; Merecz, Dorota; Drabek, Marcin

    2010-01-01

    This is the second part of the publication on approaches to occupational stress prevention and a state of the art in different European countries. In this part, stress prevention within an organization is described and discussed. Although there is no one way of tackling stress at work, some recommendations can be formulated to increase the effectiveness of such interventions. The effective stress reducing programs should be aimed both at changes in the organization itself and empowerment of employees' coping with stress resources. It is also important to take the advantage of wide spectrum of methods and techniques (e.g., work redesign, participation, team work, cognitive behavioral methods, relaxation, etc.) remembering that one size does not fit all. The intervention should be carefully planned and adopted to the various branches, an individual organization or department and should be preceded by the identification of stress risks and risk groups. To have the stress prevention program successfully introduced one should also consider factors which may influence (positively or negatively) the process of program implementation.

  8. NEGATIVE EFFECT OF METALLOID STRESS ON WHEAT

    Directory of Open Access Journals (Sweden)

    Marína Maglovski

    2015-02-01

    Full Text Available Arsenic (As belongs to heavy metals and its accumulation in plants, besides damaging the organism itself, represents a potential health risk to animal and human consumers. Therefore, contamination of soils and waters with this compound is a serious environmental problem. In this work we focused on investigating a negative impact of As on selected parameters of growth of wheat plants (Triticum aestivum L. cv. Genoveva grown in hydropony. In the stage of first assimilation leaves we applied a solution of heavy metal (1 mg.kg-1 As3+ on wheat plants. For plants grown under hydropony conditions we observed different plant parameters such as length, weight, amount of fresh and dry biomass. Further we analyzed accumulation of hydrogen peroxide and products membrane lipid peroxidation as indicators of oxidative stress. In addition to these we also measured the content of photosynthetic pigments, maximal quantum yield and proline in plant tissue. Our data indicate reduction of the biomass of shoots forthcoming as a result of exposure of stressed plants to As. Decline of biomass accumulation was accompanied by increase of hydrogen peroxide in plant tissue. In contrast, level of lipid peroxidation was suppressed in stressed shoots. Contents of photosynthetic pigments soundly decreased. Interestingly, fluorescence (Fp=Fm in stressed wheat shoots increased. Similarly in tested shoots the content of proline was increased. The results indicate that the applied dose of As has a negative impact on the growth and photosynthetic performance of stressed plants. A better understanding of the mechanisms responsible for As resistance and toxicity in plants requires further investigation.

  9. The Role of Musculoskeletal Dynamics and Neuromuscular Control in Stress Development in Bone

    Science.gov (United States)

    DeWoody, Yssa

    1996-01-01

    The role of forces produced by the musculotendon units in the stress development of the long bones during gait has not been fully analyzed. It is well known that the musculotendons act as actuators producing the joint torques which drive the body. Although the joint torques required to perform certain motor tasks can be recovered through a kinematic analysis, it remains a difficult problem to determine the actual forces produced by each muscle that resulted in these torques. As a consequence, few studies have focused on the role of individual muscles in the development of stress in the bone. This study takes a control theoretic approach to the problem. A seven-link, eight degrees of freedom model of the body is controlled by various muscle groups on each leg to simulate gait. The simulations incorporate Hill-type models of muscles with activation and contraction dynamics controlled through neural inputs. This direct approach allows one to know the exact muscle forces exerted by each musculotendon throughout the gait cycle as well the joint torques and reaction forces at the ankle and knee. Stress and strain computed by finite element analysis on skeletal members will be related to these derived loading conditions. Thus the role of musculoskeletal dynamics and neuromuscular control in the stress development of the tibia during gait can be analyzed.

  10. Solid Dynamic Models for Analysis of Stress and Strain in Human Hearts

    Directory of Open Access Journals (Sweden)

    Qiu Guan

    2012-01-01

    Full Text Available This paper proposes a solid model based on four-dimensional trivariate B-spline for strain and stress analysis of ventricular myocardium. With a series of processing steps in the four-dimensional medical images, the feature points of ventricular inner and outer wall are obtained. A B-spline surface is then used to build the dynamic deformation model of the myocardial walls. With such a surface model, a hexahedron control mesh can be constructed by sweeping the cloud data, and the ventricular solid model is built by fitting the trivariate B-spline parameters. Based on these models, a method of isogeometric analysis can be applied to calculate the stress and strain continuously distributed in the ventricle. The model is represented smoothly in the cylindrical coordinate system and is easy to measure myocardium dynamics for finding abnormal motion. Experiments are carried out for comparing the stress and strain distribution. It is found that the solid model can determine ventricular dynamics which can well reflect the deformation distribution in the heart and imply early clues of cardiac diseases.

  11. The Dynamics of DNA Methylation in Maize Roots under Pb Stress

    Directory of Open Access Journals (Sweden)

    Haiping Ding

    2014-12-01

    Full Text Available Plants adapt to adverse conditions through a series of physiological, cellular, and molecular processes, culminating in stress tolerance. However, little is known about the associated regulatory mechanisms at the epigenetic level in maize under lead (Pb stress. Therefore, in this study, we aimed to compare DNA methylation profiles during the dynamic development of maize roots following Pb treatment to identify candidate genes involved in the response to Pb stress. Methylated DNA immunoprecipitation-sequencing (MeDIP-seq was used to investigate the genome-wide DNA methylation patterns in maize roots under normal condition (A1 and 3 mM Pb(NO32 stress for 12 h (K2, 24 h (K3 and 48 h (K4. The results showed that the average methylation density was the highest in CpG islands (CGIs, followed by the intergenic regions. Within the gene body, the methylation density of the introns was higher than those of the UTRs and exons. In total, 3857 methylated genes were found in 4 tested samples, including 1805 differentially methylated genes for K2 versus A1, 1508 for K3 versus A1, and 1660 for K4 versus A1. Further analysis showed that 140 genes exhibited altered DNA methylation in all three comparisons, including some well-known stress-responsive transcription factors and proteins, such as MYB, AP2/ERF, bZIP, serine-threonine/tyrosine-proteins, pentatricopeptide repeat proteins, RING zinc finger proteins, F-box proteins, leucine-rich repeat proteins and tetratricopeptide repeat proteins. This study revealed the genome-scale DNA methylation patterns of maize roots in response to Pb exposure and identified candidate genes that potentially regulate root dynamic development under Pb stress at the methylation level.

  12. Orogenic delamination - dynamics, effects, and geological expression

    Science.gov (United States)

    Ueda, Kosuke; Gerya, Taras

    2010-05-01

    Unbundling of continental lithosphere and removal of its mantle portion have been described by two mutually rather exclusive models, convective thinning and integral delamination. Either disburdens the remaining lithosphere, weakens the remainder, and causes uplift and extension. Increased heat flux is likely to promote high-degree crustal melting, and has been viewed as a source for voluminous granitic intrusions in late or collapsing orogenic settings. Collapse may be driven by any of gravitational potential differences from orogen to foreland, by stress inversion in the unburdened domain, or by suction of a retreating trench. In this study, we investigate prerequisites, mechanism, and development paths for orogeny-related mantle lithosphere removal. Our experiments numerically reproduce delamination which self-consistently results from the dynamics of a decoupling collision zone. In particular, it succeeds without a seed facilitating initial separation of layers. External shortening of a continent - ocean - continent assembly, such as to initiate oceanic subduction, is lifted before the whole oceanic part is consumed, leaving slab pull to govern further convergence. Once buoyant continental crust enters, the collision zone locks, and convergence diminishes. Under favourable conditions, delamination then initiates close to the edge of the mantle wedge and at deep crustal levels. While it initially separates upper crust from lower crust according to the weakness minimum in the lithospheric strength profile, the lower crust is eventually also delaminated from the subducting lithospheric mantle, owing to buoyancy differences. The level of delamination within the lithosphere seems thus first rheology-controlled, then density-controlled. Subduction-coupled delamination is contingent on retreat and decoupling of the subducting slab, which in turn is dependent on effective rheological weakening of the plate contact. Weakening is a function of shear-heating and hereby of

  13. Effects of oxidative and thermal stresses on stress granule formation in human induced pluripotent stem cells.

    Science.gov (United States)

    Palangi, Freshteh; Samuel, Samson M; Thompson, I Richard; Triggle, Chris R; Emara, Mohamed M

    2017-01-01

    Stress Granules (SGs) are dynamic ribonucleoprotein aggregates, which have been observed in cells subjected to environmental stresses, such as oxidative stress and heat shock (HS). Although pluripotent stem cells (PSCs) are highly sensitive to oxidative stress, the role of SGs in regulating PSC self-renewal and differentiation has not been fully elucidated. Here we found that sodium arsenite (SA) and HS, but not hydrogen peroxide (H2O2), induce SG formation in human induced (hi) PSCs. Particularly, we found that these granules contain the well-known SG proteins (G3BP, TIAR, eIF4E, eIF4A, eIF3B, eIF4G, and PABP), were found in juxtaposition to processing bodies (PBs), and were disassembled after the removal of the stress. Moreover, we showed that SA and HS, but not H2O2, promote eIF2α phosphorylation in hiPSCs forming SGs. Analysis of pluripotent protein expression showed that HS significantly reduced all tested markers (OCT4, SOX2, NANOG, KLF4, L1TD1, and LIN28A), while SA selectively reduced the expression levels of NANOG and L1TD1. Finally, in addition to LIN28A and L1TD1, we identified DPPA5 (pluripotent protein marker) as a novel component of SGs. Collectively, these results provide new insights into the molecular cues of hiPSCs responses to environmental insults.

  14. Dynamic Dilution Effects in Polymeric Networks

    DEFF Research Database (Denmark)

    Skov, Anne Ladegaard; Sommer-Larsen, Peter; Hassager, Ole

    2006-01-01

    processes, namely the reptation of linear species within the network and the arm withdrawal process of star arms in the sol fraction and of dangling single-chain ends attached to the network. The relaxation spectra are influenced by the stoichiometry to a large extent due to dynamic dilution effects caused...... by the change in the amount of dangling arms and solubles with stoichiometry. The star arm relaxation is suppressed by washing out the sol fraction which is seen as a clear example of the dynamic dilution effect arising from the small amount of non-reactive PDMS....

  15. Cellular effects of swim stress in the dorsal raphe nucleus.

    Science.gov (United States)

    Kirby, Lynn G; Pan, Yu-Zhen; Freeman-Daniels, Emily; Rani, Shobha; Nunan, John D; Akanwa, Adaure; Beck, Sheryl G

    2007-07-01

    Swim stress regulates forebrain 5-hydroxytryptamine (5-HT) release in a complex manner and its effects are initiated in the serotonergic dorsal raphe nucleus (DRN). The purpose of this study was to examine the effects of swim stress on the physiology of DRN neurons in conjunction with 5-HT immunohistochemistry. Basic membrane properties, 5-HT(1A) and 5-HT(1B) receptor-mediated responses and glutamatergic excitatory postsynaptic currents (EPSCs) were measured using whole-cell patch clamp techniques. Rats were forced to swim for 15min and 24h later DRN brain slices were prepared for electrophysiology. Swim stress altered the resting membrane potential, input resistance and action potential duration of DRN neurons in a neurochemical-specific manner. Swim stress selectively elevated glutamate EPSC frequency in 5-HT DRN neurons. Swim stress non-selectively reduced EPSC amplitude in all DRN cells. Swim stress elevated the 5-HT(1B) receptor-mediated inhibition of glutamatergic synaptic activity that selectively targeted 5-HT cells. Non-5-HT DRN neurons appeared to be particularly responsive to the effects of a milder handling stress. Handling elevated EPSC frequency, reduced EPSC decay time and enhanced a 5-HT(1B) receptor-mediated inhibition of mEPSC frequency selectively in non-5-HT DRN cells. These results indicate that swim stress has both direct, i.e., changes in membrane characteristics, and indirect effects, i.e., via glutamatergic afferents, on DRN neurons. These results also indicate that there are distinct local glutamatergic afferents to neurochemically specific populations of DRN neurons, and furthermore that these distinct afferents are differentially regulated by swim stress. These cellular changes may contribute to the complex effects of swim stress on 5-HT neurotransmission and/or the behavioral changes underlying the forced swimming test model of depression.

  16. Effects of the Basal Boundary on Debris-flow Dynamics

    Science.gov (United States)

    Iverson, R. M.; Logan, M.; Lahusen, R. G.; Berti, M.

    2006-12-01

    Data aggregated from 37 large-scale experiments reveal some counterintuitive effects of bed roughness on debris-flow dynamics. In each experiment 10 m3 of water-saturated sand and gravel, mixed with 1 to 12% silt and clay by dry weight, was abruptly released from a gate at the head of a 2-m wide, 1.2-m deep, 82.5-m long rectangular flume inclined 31° throughout most of its length and adjoined to a gently sloping, planar runout surface at its toe. The flume's basal boundary consisted of either a smooth, planar concrete surface or a concrete surface roughened with a grid of conical bumps. Tilt-table tests with dry debris-flow sediment showed that this roughness imparted a basal friction angle of 38°, comparable to the sediment's internal friction angle of 38-42°, whereas the smooth-bed friction angle was 28°. About 20 electronic sensors installed in the flume yielded data on flow speeds and depths as well as basal stresses and pore pressures. Behavior observed in all experiments included development of steep, unsaturated, coarse-grained debris-flow snouts and tapering, liquefied, fine-grained tails. Flows on the rough bed were typically about 50% thicker and 20% slower than flows on the smooth bed, although the rough bed caused snout steepening that enabled flow fronts to move faster than expected, given the increased bed friction. Moreover, flows on rough beds ran out further than flows on smooth beds owing to enhanced grain-size segregation and lateral levee formation. With the rough bed, measured basal stresses and pore pressures differed little from values expected from static gravitational loading of partially liquefied debris. With the smooth bed, however, measured basal stresses and pore pressures were nearly twice as large as expected values. This anomaly resulted from flow disturbance at the upstream lips of steel plates in which sensors were mounted. The lips produced barely visible ripples in otherwise smooth flow surfaces, yet sufficed to generate

  17. Effects of heat stress on day-old broiler chicks.

    Science.gov (United States)

    Ernst, R A; Weathers, W W; Smith, J

    1984-09-01

    Short-term heat stress can occur when chicks are transported from the hatchery to growing facilities. Two experiments were conducted to determine the possible effects of short-term heat stress on growth and feed conversion of broiler (Hubbard X Hubbard) chicks. The heat stress was accomplished by placing chicks in Jamesway 252 incubators at dry bulb temperatures ranging from 40 to 45 C for variable times. Growth, feed consumption, and mortality were measured for 16 days following the heat stress. Short sublethal heat stress significantly reduced growth rate to 16 days in these experiments without any effect on feed conversion ratio. The results indicate that the hatchery industry should avoid overheating chicks even for periods as short as 1 hr.

  18. Residual stresses and their effects in composite laminates

    Science.gov (United States)

    Hahn, H. T.; Hwang, D. G.

    1983-01-01

    Residual stresses in composite laminates are caused by the anisotropy in expansional properties of constituent unidirectional plies. The effect of these residual stresses on dimensional stability is studied through the warping of unsymmetric (0 sub 4/90 sub 4)sub T graphite/epoxy laminates while their effect on ply failure is analyzed for (0/90)sub 2s Kevlar 49/epoxy laminate. The classical laminated plate theory is used to predict the warping of small and large panels. The change of warping does not indicate a noticeable stress relaxation at 75 C while it is very sensitive to moisture content and hence to environment. A prolonged gellation at the initial cure temperature reduces residual stresses while postcure does not. The matrix/interface cracking in dry (0/90)sub 2s Kevlar 49/epoxy laminate is shown to be the result of the residual stress exceeding the transverse strength.

  19. Differential effects of stress and glucocorticoids on adult neurogenesis.

    Science.gov (United States)

    Schoenfeld, Timothy J; Gould, Elizabeth

    2013-01-01

    Stress is known to inhibit neuronal growth in the hippocampus. In addition to reducing the size and complexity of the dendritic tree, stress and elevated glucocorticoid levels are known to inhibit adult neurogenesis. Despite the negative effects of stress hormones on progenitor cell proliferation in the hippocampus, some experiences which produce robust increases in glucocorticoid levels actually promote neuronal growth. These experiences, including running, mating, enriched environment living, and intracranial self-stimulation, all share in common a strong hedonic component. Taken together, the findings suggest that rewarding experiences buffer progenitor cells in the dentate gyrus from the negative effects of elevated stress hormones. This chapter considers the evidence that stress and glucocorticoids inhibit neuronal growth along with the paradoxical findings of enhanced neuronal growth under rewarding conditions with a view toward understanding the underlying biological mechanisms.

  20. Dobutamine stress echocardiography for assessing the role of dynamic intraventricular obstruction in left ventricular ballooning syndrome

    Directory of Open Access Journals (Sweden)

    Repetto Alessandra

    2010-04-01

    Full Text Available Abstract Background Dynamic intraventricular obstruction has been observed in patients with left ventricular ballooning syndrome (LVBS and has been hypothesized as a possible mechanism of the syndrome. The aim of this study was to assess the prevalence and significance of dynamic intraventricular obstruction in patients with LVBS. Methods and Results Dobutamine stress echocardiography was carried out in 22 patients with LVBS (82% apical, all women, aged 68 ± 9 years. At baseline 1 patient had a > 30 mmHg LV gradient; during stress a LV gradient > 30 mm Hg developed in 6/21 patients (28% and was caused by systolic anterior motion of the mitral valve in the 3 patients with severe gradient (mean 116 ± 29 mmHg, who developed mitral regurgitation and impaired apical wall motion and by obstruction at mid-ventricular level in the other 3 with a moderate gradient (mean 46 ± 16 mmHg. Compared with patients without obstruction those with obstruction had a greater mean septal thickness (11.6 ± .6 vs 9.8. ± 3, p Conclusion Spontaneous or dobutamine-induced dynamic LV obstruction is documented in 32% of patients with LVBS, is correlated with the presence of septal hypertrophy and may play a role in the development of LVBS in this subset of patients. In those without septal hypertrophy a dynamic obstruction is rarely induced with dobutamine and is unlikely to be a major pathogenetic factor of the syndrome.

  1. Dynamical effects of overparametrization in nonlinear models

    Science.gov (United States)

    Aguirre, Luis Antonio; Billings, S. A.

    1995-01-01

    This paper is concemed with dynamical reconstruction for nonlinear systems. The effects of the driving function and of the complexity of a given representation on the bifurcation patter are investigated. It is shown that the use of different driving functions to excite the system may yield models with different bifurcation patterns. The complexity of the reconstructions considered is quantified by the embedding dimension and the number of estimated parameters. In this respect it appears that models which reproduce the original bifurcation behaviour are of limited complexity and that excessively complex models tend to induce ghost bifurcations and spurious dynamical regimes. Moreover, some results suggest that the effects of overparametrization on the global dynamical behaviour of a nonlinear model may be more deleterious than the presence of moderate noise levels. In order to precisely quantify the complexity of the reconstructions, global polynomials are used although the results are believed to apply to a much wider class of representations including neural networks.

  2. Effective dynamics of a classical point charges

    CERN Document Server

    Polonyi, Janos

    2013-01-01

    The effective Lagrangian of a point charge is derived by eliminating the electromagnetic field within the framework of the classical closed time path formalism. The short distance singularity of the electromagnetic field is regulated by an UV cutoff. The Abraham-Lorentz force is recovered and its similarity to anomalies is underlined. The full cutoff-dependent linearized equation of motion is obtained, no runaway trajectories are found but the effective dynamics shows acausality if the cutoff is beyond the classical charge radius. The strength of the radiation reaction force displays a pole in its cutoff-dependence in a manner reminiscent of the Landau-pole of perturbative QED. Similarity between the dynamical breakdown of the time reversal invariance and dynamical symmetry breaking is pointed out.

  3. Memory effects in nanoparticle dynamics and transport

    Science.gov (United States)

    Sanghi, Tarun; Bhadauria, Ravi; Aluru, N. R.

    2016-10-01

    In this work, we use the generalized Langevin equation (GLE) to characterize and understand memory effects in nanoparticle dynamics and transport. Using the GLE formulation, we compute the memory function and investigate its scaling with the mass, shape, and size of the nanoparticle. It is observed that changing the mass of the nanoparticle leads to a rescaling of the memory function with the reduced mass of the system. Further, we show that for different mass nanoparticles it is the initial value of the memory function and not its relaxation time that determines the "memory" or "memoryless" dynamics. The size and the shape of the nanoparticle are found to influence both the functional-form and the initial value of the memory function. For a fixed mass nanoparticle, increasing its size enhances the memory effects. Using GLE simulations we also investigate and highlight the role of memory in nanoparticle dynamics and transport.

  4. Chaos in effective classical and quantum dynamics

    CERN Document Server

    Casetti, L; Modugno, M; Casetti, Lapo; Gatto, Raoul; Modugno, Michele

    1998-01-01

    We investigate the dynamics of classical and quantum N-component phi^4 oscillators in presence of an external field. In the large N limit the effective dynamics is described by two-degree-of-freedom classical Hamiltonian systems. In the classical model we observe chaotic orbits for any value of the external field, while in the quantum case chaos is strongly suppressed. A simple explanation of this behaviour is found in the change in the structure of the orbits induced by quantum corrections. Consistently with Heisenberg's principle, quantum fluctuations are forced away from zero, removing in the effective quantum dynamics a hyperbolic fixed point that is a major source of chaos in the classical model.

  5. Effects of stress on human mating preferences: stressed individuals prefer dissimilar mates

    Science.gov (United States)

    Lass-Hennemann, Johanna; Deuter, Christian E.; Kuehl, Linn K.; Schulz, André; Blumenthal, Terry D.; Schachinger, Hartmut

    2010-01-01

    Although humans usually prefer mates that resemble themselves, mating preferences can vary with context. Stress has been shown to alter mating preferences in animals, but the effects of stress on human mating preferences are unknown. Here, we investigated whether stress alters men's preference for self-resembling mates. Participants first underwent a cold-pressor test (stress induction) or a control procedure. Then, participants viewed either neutral pictures or pictures of erotic female nudes whose facial characteristics were computer-modified to resemble either the participant or another participant, or were not modified, while startle eyeblink responses were elicited by noise probes. Erotic pictures were rated as being pleasant, and reduced startle magnitude compared with neutral pictures. In the control group, startle magnitude was smaller during foreground presentation of photographs of self-resembling female nudes compared with other-resembling female nudes and non-manipulated female nudes, indicating a higher approach motivation to self-resembling mates. In the stress group, startle magnitude was larger during foreground presentation of self-resembling female nudes compared with other-resembling female nudes and non-manipulated female nudes, indicating a higher approach motivation to dissimilar mates. Our findings show that stress affects human mating preferences: unstressed individuals showed the expected preference for similar mates, but stressed individuals seem to prefer dissimilar mates. PMID:20219732

  6. Resistance to early-life stress in mice: effects of genetic background and stress duration

    Directory of Open Access Journals (Sweden)

    Helene M. Savignac

    2011-04-01

    Full Text Available Early-life stress can induce marked behavioural and physiological impairments in adulthood including cognitive deficits, depression, anxiety and gastrointestinal dysfunction. Although robust rat models of early-life stress exist there are few established effective paradigms in the mouse. Genetic background and protocol parameters used are two critical variables in such model development.Thus we investigated the impact of two different early-life stress protocols in two commonly used inbred mouse strains. C57BL/6 and innately anxious BALB/c male mice were maternally deprived 3 hrs daily, either from postnatal day 1 to 14 (Protocol 1 or 6 to 10 (Protocol 2. Animals were assessed in adulthood for cognitive performance (spontaneous alternation behaviour test, anxiety (open field, light/dark box and elevated plus maze tests and depression-related behaviours (forced swim test in addition to stress-sensitive physiological changes. Overall, the results showed that early-life stressed mice from both strains displayed good cognitive ability and no elevations in anxiety. However, paradoxical changes occurred in C57BL/6 mice as the longer protocol (protocol 1 decreased anxiety in the light-dark box and increased exploration in the elevated plus maze. In BALB/c mice there were also limited effects of maternal separation with both separation protocols inducing reductions in stress-induced defecation and protocol 1 reducing the colon length. These data suggest that, independent of stress duration, mice from both strains were on the whole resilient to the maladaptive effects of early-life stress. Thus maternal-separation models of brain-gut axis dysfunction should rely on either different stressor protocols or other strains of mice.

  7. Perceived effectiveness of critical incident stress debriefing by Australian nurses

    National Research Council Canada - National Science Library

    O'Connor, J; Jeavons, S

    2003-01-01

    This paper examines the perceived effectiveness of stress debriefing by a sample of 129 Australian hospital nurses and the relationship of their perceptions to demographic variables such as qualifications and work area...

  8. Effect of drought stress induced by polyethylene glycol (PEG) on ...

    African Journals Online (AJOL)

    Effect of drought stress induced by polyethylene glycol (PEG) on germination indices in corn ( Zea mays L.) hybrids. ... African Journal of Biotechnology ... and success in this stage is dependent on moisture content of soil at time of planting.

  9. Using Estimations of Entropy to Optimize Complex Human Dynamic Networks under Stress

    Science.gov (United States)

    2013-12-30

    blood components , during various physically and mentally stressful exercises, we will be able to determine the factors that drive overall team success and assemble more effective teams using these factors. Sixteen WVU Air Force ROTC participants were selected, divided into four different teams of four individuals, their biological responses were monitored (some in real-time and some prior to and immediately following) in response to stressful teamwork exercises (mock hostage rescue). Individuals were outfitted with EEG, heart rate, breathing rate, estimated core

  10. Abnormal enhancement of interface trap generation under dynamic oxide field stress at MHz region

    OpenAIRE

    Zhu, Shiyang; Nakajima, Anri

    2005-01-01

    By stressing metal-oxide-semiconductor field-effect transistors with ultrathin silicon dioxide or oxynitride gate dielectrics under square wave form voltage at the MHz region, an abnormal enhancement of interface trap generation in the midchannel region has been observed at some special frequencies. A hypothesis, including self-accelerating interface trap generation originated from the positive feedback of a charge pumping current to be contributed by the stress-induced near-interface oxide t...

  11. Stretching the stress boundary: Linking air pollution health effects to a neurohormonal stress response.

    Science.gov (United States)

    Kodavanti, Urmila P

    2016-12-01

    Inhaled pollutants produce effects in virtually all organ systems in our body and have been linked to chronic diseases including hypertension, atherosclerosis, Alzheimer's and diabetes. A neurohormonal stress response (referred to here as a systemic response produced by activation of the sympathetic nervous system and hypothalamus-pituitary-adrenal (HPA)-axis) has been implicated in a variety of psychological and physical stresses, which involves immune and metabolic homeostatic mechanisms affecting all organs in the body. In this review, we provide new evidence for the involvement of this well-characterized neurohormonal stress response in mediating systemic and pulmonary effects of a prototypic air pollutant - ozone. A plethora of systemic metabolic and immune effects are induced in animals exposed to inhaled pollutants, which could result from increased circulating stress hormones. The release of adrenal-derived stress hormones in response to ozone exposure not only mediates systemic immune and metabolic responses, but by doing so, also modulates pulmonary injury and inflammation. With recurring pollutant exposures, these effects can contribute to multi-organ chronic conditions associated with air pollution. This review will cover, 1) the potential mechanisms by which air pollutants can initiate the relay of signals from respiratory tract to brain through trigeminal and vagus nerves, and activate stress responsive regions including hypothalamus; and 2) the contribution of sympathetic and HPA-axis activation in mediating systemic homeostatic metabolic and immune effects of ozone in various organs. The potential contribution of chronic environmental stress in cardiovascular, neurological, reproductive and metabolic diseases, and the knowledge gaps are also discussed. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

  12. Effects of heat stress on baroreflex function in humans

    Science.gov (United States)

    Crandall, Craig G.; Cui, Jian; Wilson, Thad E.

    2003-01-01

    INTRODUCTION: Heat stress significantly reduces orthostatic tolerance in humans. The mechanism(s) causing this response remain unknown. The purpose of this review article is to present data pertaining to the hypothesis that reduced orthostatic tolerance in heat stressed individuals is a result of heat stress induced alterations in baroflex function. METHODS: In both normothermic and heat stressed conditions baroreflex responsiveness was assessed via pharmacological and non-pharmacological methods. In addition, the effects of heat stress on post-synaptic vasoconstrictor responsiveness were assessed. RESULTS: Generally, whole body heating did not alter baroreflex sensitivity defined as the gain of the linear portion of the baroreflex curve around the operating point. However, whole body heating shifted the baroreflex curve to the prevailing (i.e. elevated) heart rate and muscle sympathetic nerve activity. Finally, the heat stress impaired vasoconstrictor responses to exogenous administration of adrenergic agonists. CONCLUSION: Current data do not support the hypothesis that reduced orthostatic tolerance associated with heat stress in humans is due to impaired baroreflex responsiveness. This phenomenon may be partially due to the effects of heat stress on reducing vasoconstrictor responsiveness.

  13. Effects of Cadmium Stress on the Quality of Rice Seeds

    Institute of Scientific and Technical Information of China (English)

    Juan; CHEN; Hui; FANG; Ying; ZHANG; Yuanyuan; FAN

    2013-01-01

    Germination and hydroponic experiments are performed on rice seeds growing in soils treated with Cd stress,with rice seeds of the same variety that is not treated with Cd stress as a control,to study the effects of Cd stress on quality of rice seeds.The results have shown that:(1)Cd stress reduces the thousand grain weight of rice seeds,and higher Cd content means lower thousand grain weight;(2)The germination vigor and germination percentage of rice seeds under Cd stress as well as theirα-amylase activity andβ-amylase activity are all lower than those of the control.They decreases as the Cd stress increases;(3)For rice seeds under Cd stress,the height,fresh and dry weight of seedlings,as well as the chlorophyll content,photosynthetic rate and content of soluble protein of their leaves are all lower than those of the control.This indicates that Cd stress has certain effects on the germination and growth of the rice seeds.

  14. Effects of Consolidation Stress State on Normally Consolidated Clay

    DEFF Research Database (Denmark)

    Lade, Poul V.

    2000-01-01

    and on isotropically consolidated, cubical specimens, both tested in triaxial compression and extension, clearly showed the influence of the undisturbed fabric as well as the effect of the initial consolidation stress states. While the K0-consolidated specimens appeared to retain their original fabric and exhibit......The effect of consolidation stress state on the stress-strain and strength characteristics has been studied from experiments on undisturbed block samples of a natural, normally consolidated clay known as San Francisco Bay Mud. The results of experiments on K0-consolidated, hollow cylinder specimens...

  15. Cohesive stresses and size effect in quasi-brittle materials

    Indian Academy of Sciences (India)

    V E Saouma; D Natekar

    2002-08-01

    A novel approach to the derivation of Ba$\\breve{z}$ant’s size effect law is presented. Contrarily to the original Lagrangian derivation which hinged on energetic consideration, a Newtonian approach based on local stress intensity factors is presented. Through this approach, it is shown that Ba$\\breve{z}$ant’s size effect law is the first (and dominant) term in a series expansion for the nominal stress. Furthermore, analytical expressions for are derived for selected specimen geometries.

  16. Quantum coherence in the dynamical Casimir effect

    Science.gov (United States)

    Samos-Sáenz de Buruaga, D. N.; Sabín, Carlos

    2017-02-01

    We propose to use quantum coherence as the ultimate proof of the quantum nature of the radiation that appears by means of the dynamical Casimir effect in experiments with superconducting microwave waveguides. We show that, unlike previously considered measurements such as entanglement and discord, quantum coherence does not require a threshold value of the external pump amplitude and is highly robust to thermal noise.

  17. Effects of mechanical-bending and process-induced stresses on metal effective work function

    Science.gov (United States)

    Yang, Xiaodong; Chu, Min; Huang, Anping; Thompson, Scott

    2013-01-01

    Effective work function (EWF) change is investigated under both externally-applied mechanical stresses and process-induced stresses. Four-point wafer bending and ring bending techniques are used to generate uniaxial and biaxial mechanical stresses, respectively. For the process-induced stresses, bowing technique and charge pumping method are used for stress characterization and interface state measurement. It was found that higher stress presents in devices with thinner metal gate, regardless the thermal treatment cycle. EWF decreases under both tensile and compressive stress was observed due to the increase of defect activation energy lowering induced donor-like interface states.

  18. Effects of drought stress on annual dynamic changing pattern of the terpene lactones content in Ginkgo biloba leaves%干旱胁迫对银杏叶萜内酯年动态变化的影响

    Institute of Scientific and Technical Information of China (English)

    朱灿灿; 曹福亮; 王贵斌; 耿国民

    2011-01-01

    The effects of drought stress on terpene lactones contents of Ginkgo biloba grown in pots at 4 soil moisture levels under greenhouse conditions were investigated. The results showed that there were significant effects on the contents of bi-lobalide BB, ginkgolide GC, CA, CB and total terpene lactones in different growing seasons. With the development of season, terpene lactones contents were increased first and then decline at the subsequent. Moderate drought conditions can contribute to the synthesis of terpene lactones. The terpene lactones contents in mild and moderate drought conditions significantly increased if compared with the terpene lactones contents in appropriate water condition. Concerning the leaf yield, terpene lactones contents as well as the relationship between quantity and time of leaf collection, we suggested that the highest economic yield per single plant could be obtained by controlling soil water content at mild level ( relative water content ,55% -60% ) and harvesting leaves in June to October.%以2年生盆栽实生苗为研究材料,通过人工模拟干旱胁迫环境,探索4水平干旱胁迫(土壤含水量分别为田间持水量的75% ~ 80%、55% ~ 60%、40% ~45%和30%~35%)对银杏叶萜内酯类物质季节变化的影响.结果表明:干旱胁迫下,生长季节不同,银杏叶内白果内酯BB、银杏内酯GC、GA、GB及总萜内酯含量变化具有显著差异,随着生长季节的变化银杏叶萜内酯类物质含量变化呈“先升高后降低”的趋势.适度干旱条件下可以促进银杏萜内酯类物质的合成,尤其轻度和中度干旱条件下,萜内酯含量比适宜水分条件下明显增多.考虑到叶产量、叶萜内酯美物质含量以及采叶与采时的关系等,在实际生产中可以考虑在植物生长初期,给予银杏苗正常的水分供应以获得最大的生物产量,在6-10月份叶片发育完全后适当进行轻度干旱处理(土壤水分含量

  19. Kinetics of interstitial defects in α-Fe: The effect from uniaxial stress

    Science.gov (United States)

    Kang, Changwoo; Wang, Qingyu; Shao, Lin

    2017-03-01

    Understanding defect kinetics in a stress field is important for multiscale modeling of materials degradation of nuclear materials. By means of molecular dynamics and molecular statics simulations, we calculate formation and migration energies of self-interstitial atoms (SIA) and SIA clusters (up to size of 5 interstitials) in alpha Fe and identify their stable configurations under uniaxial tensile strains. By applying uniaxial stress along [111], oriented single SIA defects become more stable than oriented SIA, which is opposite to stress-free condition. Diffusion of single SIA defects under [111] tensile stress is facilitated along [111] direction and the diffusion becomes one dimensional (1D). For SIA clusters, their diffusion under zero stress has gradual transition from three dimensional (3D) for small clusters to one dimensional (1D) for large clusters. Under the tensile stress along [111], the 3D to 1D transition is accelerated. For large SIA clusters, the stress effect is quickly saturated with less diffusivity enhancement in comparison with small SIA clusters.

  20. A variational approach to the growth dynamics of pre-stressed actin filament networks

    Science.gov (United States)

    John, Karin; Stöter, Thomas; Misbah, Chaouqi

    2016-09-01

    In order to model the growth dynamics of elastic bodies with residual stresses a thermodynamically consistent approach is needed such that the cross-coupling between growth and mechanics can be correctly described. In the present work we apply a variational principle to the formulation of the interfacial growth dynamics of dendritic actin filament networks growing from biomimetic beads, an experimentally well studied system, where the buildup of residual stresses governs the network growth. We first introduce the material model for the network via a strain energy density for an isotropic weakly nonlinear elastic material and then derive consistently from this model the dynamic equations for the interfaces, i.e. for a polymerizing internal interface in contact with the bead and a depolymerizing external interface directed towards the solvent. We show that (i) this approach automatically preserves thermodynamic symmetry-properties, which is not the case for the often cited ‘rubber-band-model’ (Sekimoto et al 2004 Eur. Phys. J. E 13 247-59, Plastino et al 2004 Eur. Biophys. J. 33 310-20) and (ii) leads to a robust morphological instability of the treadmilling network interfaces. The nature of the instability depends on the interplay of the two dynamic interfaces. Depending on the biochemical conditions the network envelope evolves into a comet-like shape (i.e. the actin envelope thins out at one side and thickens on the opposite side of the bead) via a varicose instability or it breaks the symmetry via higher order zigzag modes. We conclude that morphological instabilities due to mechano-chemical coupling mechanisms and the presences of mechancial pre-stresses can play a major role in locally organizing the cytoskeleton of living cells.

  1. Expression dynamics of HSP70 during chronic heat stress in Tharparkar cattle

    Science.gov (United States)

    Bharati, Jaya; Dangi, S. S.; Chouhan, V. S.; Mishra, S. R.; Bharti, M. K.; Verma, V.; Shankar, O.; Yadav, V. P.; Das, K.; Paul, A.; Bag, S.; Maurya, V. P.; Singh, G.; Kumar, P.; Sarkar, M.

    2016-12-01

    Six male Tharparkar cattle aged 2-3 years were selected for the study. The animals were acclimatized in the psychrometric chamber at thermoneutral zone (TNZ) for 15 days and then exposed to 42 °C temperature up to 23 days followed by 12 days of recovery period. Physiological responses were estimated, and peripheral blood mononuclear cells (PBMCs) were isolated at TNZ on day 1, day 5, and day 12; after 6 h of heat stress exposure on day 16 to day 20, day 25, day 30, day 32, day 34, day 36, and day 38; and a recovery period on day 45 and day 50. The PBMCs were cultured to study the effect of thermal challenge on HSP70 messenger RNA (mRNA) expression pattern at different temperature-time combinations. The mRNA and protein expression of HSP70 in PBMCs along with serum extracellular HSP70 (eHSP70) was increased (P heat stress challenge treatment as compared to control in cultured PBMCs. HSP70 expression was found to be higher (P heat exposure (corresponds to chronic heat stress) as compared to the first 5 days of heat stress (corresponds to short-term heat stress) and control period at TNZ. The present findings indicate that HSP70 is possibly involved in heat stress adaptive response in Tharparkar cattle and the biphasic expression pattern may be providing a second window of protection during chronic heat stress.

  2. Dynamical magnetic effects in photoexcited ferromagnetic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Chovan, J. [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, P. O. Box 1527, 711 10 Heraklion (Greece); Kavousanaki, E.G. [Department of Physics, University of Crete, P. O. Box 2208, 710 03 Heraklion (Greece); Perakis, I.E. [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, P. O. Box 1527, 711 10 Heraklion (Greece); Department of Physics, University of Crete, P. O. Box 2208, 710 03 Heraklion (Greece)

    2006-08-15

    We develop a theory of photoinduced dynamical magnetic effects in III-Mn-V ferromagnetic semiconductors valid in presence of strong carrier spin relaxation and dephasing. We treat relaxation by using the Lindblad semigroup method and calculate the nonlinear response numerically. We predict Mn-spin relaxation and precession towards the direction determined by nonlinear optical polarization. These effects occur during the pulse. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Effect of uniaxial stress on substitutional Ni in ZnO

    Science.gov (United States)

    Lavrov, E. V.; Herklotz, F.; Kutin, Y. S.

    2013-04-01

    The influence of uniaxial stress on the electronic T13(F)→T23(F) transitions of Ni (d8) in ZnO at 4216, 4240, and 4247 cm-1 is studied. It is shown that the split pattern and polarized properties of IR absorption lines are consistent with a dynamic Jahn-Teller effect in the T23(F) state of the defect.

  4. Effect of hydrogen on stress corrosion cracking of copper

    Institute of Scientific and Technical Information of China (English)

    Li-jie QIAO

    2008-01-01

    The effects of hydrogen on electrochemical behavior and susceptibility of stress corrosion cracking (SCC) of pure copper were studied. SCC susceptibility of pure copper in a 1 M NaNO2 solution was increased by pre-charged hydrogen. The effect of hydrogen on the sus-ceptibility is more obvious in the low stress region due to the longer fracture time, which resulted in a longer time for more hydrogen to diffuse toward the crack tip. Synergistic effects of hydrogen and stress on corrosion and SCC pro-cesses were discussed. The results showed that an inter-action between stress and hydrogen at the crack tip could increase the anodic dissolution rate remarkably.

  5. Stat5 signaling specifies basal versus stress erythropoietic responses through distinct binary and graded dynamic modalities.

    Directory of Open Access Journals (Sweden)

    Ermelinda Porpiglia

    2012-08-01

    Full Text Available Erythropoietin (Epo-induced Stat5 phosphorylation (p-Stat5 is essential for both basal erythropoiesis and for its acceleration during hypoxic stress. A key challenge lies in understanding how Stat5 signaling elicits distinct functions during basal and stress erythropoiesis. Here we asked whether these distinct functions might be specified by the dynamic behavior of the Stat5 signal. We used flow cytometry to analyze Stat5 phosphorylation dynamics in primary erythropoietic tissue in vivo and in vitro, identifying two signaling modalities. In later (basophilic erythroblasts, Epo stimulation triggers a low intensity but decisive, binary (digital p-Stat5 signal. In early erythroblasts the binary signal is superseded by a high-intensity graded (analog p-Stat5 response. We elucidated the biological functions of binary and graded Stat5 signaling using the EpoR-HM mice, which express a "knocked-in" EpoR mutant lacking cytoplasmic phosphotyrosines. Strikingly, EpoR-HM mice are restricted to the binary signaling mode, which rescues these mice from fatal perinatal anemia by promoting binary survival decisions in erythroblasts. However, the absence of the graded p-Stat5 response in the EpoR-HM mice prevents them from accelerating red cell production in response to stress, including a failure to upregulate the transferrin receptor, which we show is a novel stress target. We found that Stat5 protein levels decline with erythroblast differentiation, governing the transition from high-intensity graded signaling in early erythroblasts to low-intensity binary signaling in later erythroblasts. Thus, using exogenous Stat5, we converted later erythroblasts into high-intensity graded signal transducers capable of eliciting a downstream stress response. Unlike the Stat5 protein, EpoR expression in erythroblasts does not limit the Stat5 signaling response, a non-Michaelian paradigm with therapeutic implications in myeloproliferative disease. Our findings show how the

  6. Dynamic of bioelectric activity back hypothalamus changes in conditions of pyroxan application on the background of stress-reaction developmen

    Directory of Open Access Journals (Sweden)

    T. G. Chaus

    2005-04-01

    Full Text Available The dynamic of changes of capacity of electroencephalogram’s rhythms back hypothalamus at animals of control group and group in stress conditions in parallel with rats who on a background of stress development accepted pyroxan is analyzed. The submitted results have shown influence of a pharmacological preparation pyroxan on bioelectric activity of back hypothalamus in stress conditions that restoration of electric activity under action of this preparation was more shown at 3 weeks of its application.

  7. 低切应力对动脉重构与内皮黏附分子表达的动态变化%Dynamic effects of low shear stress on arterial remodeling and expression of endothelial cell adhesion molecules

    Institute of Scientific and Technical Information of China (English)

    刘莹; 宾建平; 吴爵非; 李美瑜; 宾建国; 伍巍兰; 肖云彬; 廖旺军

    2011-01-01

    Objective To investigate the changes of vascular structure and expression of adhesion molecules in endothelial cell at different time points under low shear stress. Methods Thirty mice were equally randomized into four test groups(stenosis for 1,7,14 and 28 day groups) who underwent surgery of stenosis with an arterial silver clamp applied on abdominal aorta to create disfurbed flow, and one sham operation group without stenosis. The parameters of hemodynamics were measured by color Doppler flow imaging. The wall shear stress was calculated by Poiseiulle hydrodynamics formula. Pathological and immunohistochemical examinations were performed to analyze the morphological changes and the expression of endothelial P-selectin and VCAM-1 in abdominal aorta. Results Low shear stress was demonstrated at upstream of stenosis. Compared with the sham group, with the increase in observation time, the changes of both wall thickness and the ratio of wall thickness to inner diameter were gradually increased at the area of low shear stress (P < 0.05). The up-regulated expression of endothelial P-selectin was seen from 1 to 28 days at the area of low shear stress,the peak was on day 7 and after that the up-regulation attenuated (P < 0.05). The up-regulation of VCAM-1 was not noted until day 7 (P < 0.05) ,and the plateau was reached on day 14. Conclusion Vascular remodeling can occur in a relatively short time after exposure to low shear stress. The low shear stress may play significant initial roles in the pathological process of atherosclerosis resulting from endothelial inflammation.%目的 探讨低切应力作用下不同时间点小鼠腹主动脉形态学重构及内皮黏附分子表达的变化.方法 选择昆明小白鼠30只随机分为狭窄1、7、14、28 d组和假手术组,每组6只.用动脉银夹建立腹主动脉局部狭窄模型,彩色超声检测狭窄近心端血流动力学参数,计算切应力值;血管标本行HE染色和内皮P选择

  8. Salinity effects on the dynamics and patterns of desiccation cracks

    Science.gov (United States)

    Shokri, N.; Zhou, P.

    2012-12-01

    Cracking arising from desiccation is a ubiquitous phenomenon encountered in various industrial and geo-environmental applications including drying of clayey soil, cement, ceramics, gels, and many more colloidal suspensions. Presence of cracks in muddy sediments modifies the characteristics of the medium such as pore structure, porosity, and permeability which in turn influence various flow and transport processes. Thus it remains a topic of great interest in many disciplines to describe the dynamics of desiccation cracking under various boundary conditions. To this end, we conducted a comprehensive study to investigate effects of NaCl concentrations on cracking dynamics and patterns during desiccation of Bentonite. Mixtures of Bentonite and NaCl solutions were prepared with NaCl concentration varying from 2 to 10 percent in 0.5 percent increment (totally 17 configurations). The slurry was placed in a Petri dish mounted on a digital balance to record the evaporation dynamics. The atmospheric conditions were kept constant using an environmental chamber. An automatic camera was used to record the dynamics of macro-cracks (mm scale) at the surface of desiccating clay each minute. The obtained results illustrate the significant effects of salt concentration on the initiation, propagation, morphology and general dynamics of macro-cracks. We found that higher salt concentrations results in larger macro cracks' lengths attributed to the effects of NaCl on compressing the electric double layer of particles at increasing electrolyte concentrations which reduce considerably the repulsive forces among the particles and causing instability of the slurry and flocculation of the colloidal particles. Rheological measurements by means of a stress controlled rheometer revealed that the yield stress of the slurry decreases as NaCl concentration increases which may indicate aggregation of larger units in the slurry as a result of flocculation causing larger cracks' lengths due to

  9. Mobilization of colloidal particles by low-frequency dynamic stress stimulation

    Energy Technology Data Exchange (ETDEWEB)

    Beckham, Richard Edward [Los Alamos National Laboratory; Amr, Abdel - Fattah I [Los Alamos National Laboratory; Peter, Roberts M [Los Alamos National Laboratory; Reem, Ibrahim [Los Alamos National Laboratory; Tarimala, Sowmitri [Los Alamos National Laboratory

    2009-01-01

    Naturally occurring seismic events and artificially generated low-frequency (1 to 500 Hertz) elastic waves have been observed to alter the production rates of oil and water wells, sometimes increasing and sometimes decreasing production, and to influence the turbidity of surface and well water. The decreases in production are of particular concern - especially when artificially generated elastic waves are applied as a method for enhanced oil recovery. The exact conditions that result in a decrease in production remain unknown. While the underlying environment is certainly complex, the observed increase in water well turbidity after natural seismic events suggests the existence of a mechanism that can affect both the subsurface flow paths and mobilization of in-situ colloidal particles. This paper explores the macroscopic and microscopic effects of low-frequency dynamic stress stimulations on the release of colloidal particles from an analog core representing an infinitesimal section along the propagation paths of an elastic wave. Experiments on a column packed with 1-mm borosilicate beads and loaded with polystyrene microspheres demonstrate that axial mechanical stress oscillations enhance the mobilization of captured microspheres. Increasing the amplitude of the oscillations increases the number of microspheres released and can also result in cyclical spikes in effluent microsphere concentration during stimulation. Under a prolonged period of stimulation, the cyclical effluent spikes coincided with fluctuations in the column pressure data, and continue at a diminished level after stimulation. This behavior can be attributed to rearrangements of the beads in the column, resulting in possible changes to the void space and/or tortuosity of the packing. Optical microscopy observations of the beads during low frequency oscillations reveal that individual beads rotate, thereby rubbing against each other and scraping away portions of the adsorbed microspheres. These

  10. Effect of yoga on academic performance in relation to stress

    Directory of Open Access Journals (Sweden)

    Kauts Amit

    2009-01-01

    Full Text Available Background: Academic performance is concerned with the quantity and quality of learning attained in a subject or group of subjects after a long period of instruction. Excessive stress hampers students′ performance. Improvement in academic performance and alertness has been reported in several yogic studies. Aims and Objectives: The main objective of the study was to assess the effect of yoga on academic performance in relation to stress. Materials and Methods: The study started with 800 adolescent students; 159 high-stress students and 142 low-stress students were selected on the basis of scores obtained through Stress Battery. Experimental group and control group were given pre test in three subjects, i.e., Mathematics, Science, and Social Studies. A yoga module consisting of yoga asanas, pranayama, meditation, and a value orientation program was administered on experimental group for 7 weeks. The experimental and control groups were post-tested for their performance on the three subjects mentioned above. Results: The results show that the students, who practiced yoga performed better in academics. The study further shows that low-stress students performed better than high-stress students, meaning thereby that stress affects the students′ performance.

  11. The effects of yoga on anxiety and stress.

    Science.gov (United States)

    Li, Amber W; Goldsmith, Carroll-Ann W

    2012-03-01

    Stress and anxiety have been implicated as contributors to many chronic diseases and to decreased quality of life, even with pharmacologic treatment. Efforts are underway to find non-pharmacologic therapies to relieve stress and anxiety, and yoga is one option for which results are promising. The focus of this review is on the results of human trials assessing the role of yoga in improving the signs and symptoms of stress and anxiety. Of 35 trials addressing the effects of yoga on anxiety and stress, 25 noted a significant decrease in stress and/or anxiety symptoms when a yoga regimen was implemented; however, many of the studies were also hindered by limitations, such as small study populations, lack of randomization, and lack of a control group. Fourteen of the 35 studies reported biochemical and physiological markers of stress and anxiety, but yielded inconsistent support of yoga for relief of stress and anxiety. Evaluation of the current primary literature is suggestive of benefits of yoga in relieving stress and anxiety, but further investigation into this relationship using large, well-defined populations, adequate controls, randomization and long duration should be explored before recommending yoga as a treatment option.

  12. Dynamic effective connectivity of inter-areal brain circuits.

    Directory of Open Access Journals (Sweden)

    Demian Battaglia

    Full Text Available Anatomic connections between brain areas affect information flow between neuronal circuits and the synchronization of neuronal activity. However, such structural connectivity does not coincide with effective connectivity (or, more precisely, causal connectivity, related to the elusive question "Which areas cause the present activity of which others?". Effective connectivity is directed and depends flexibly on contexts and tasks. Here we show that dynamic effective connectivity can emerge from transitions in the collective organization of coherent neural activity. Integrating simulation and semi-analytic approaches, we study mesoscale network motifs of interacting cortical areas, modeled as large random networks of spiking neurons or as simple rate units. Through a causal analysis of time-series of model neural activity, we show that different dynamical states generated by a same structural connectivity motif correspond to distinct effective connectivity motifs. Such effective motifs can display a dominant directionality, due to spontaneous symmetry breaking and effective entrainment between local brain rhythms, although all connections in the considered structural motifs are reciprocal. We show then that transitions between effective connectivity configurations (like, for instance, reversal in the direction of inter-areal interactions can be triggered reliably by brief perturbation inputs, properly timed with respect to an ongoing local oscillation, without the need for plastic synaptic changes. Finally, we analyze how the information encoded in spiking patterns of a local neuronal population is propagated across a fixed structural connectivity motif, demonstrating that changes in the active effective connectivity regulate both the efficiency and the directionality of information transfer. Previous studies stressed the role played by coherent oscillations in establishing efficient communication between distant areas. Going beyond these early

  13. Dynamic Effective Connectivity of Inter-Areal Brain Circuits

    Science.gov (United States)

    Battaglia, Demian; Witt, Annette; Wolf, Fred; Geisel, Theo

    2012-01-01

    Anatomic connections between brain areas affect information flow between neuronal circuits and the synchronization of neuronal activity. However, such structural connectivity does not coincide with effective connectivity (or, more precisely, causal connectivity), related to the elusive question “Which areas cause the present activity of which others?”. Effective connectivity is directed and depends flexibly on contexts and tasks. Here we show that dynamic effective connectivity can emerge from transitions in the collective organization of coherent neural activity. Integrating simulation and semi-analytic approaches, we study mesoscale network motifs of interacting cortical areas, modeled as large random networks of spiking neurons or as simple rate units. Through a causal analysis of time-series of model neural activity, we show that different dynamical states generated by a same structural connectivity motif correspond to distinct effective connectivity motifs. Such effective motifs can display a dominant directionality, due to spontaneous symmetry breaking and effective entrainment between local brain rhythms, although all connections in the considered structural motifs are reciprocal. We show then that transitions between effective connectivity configurations (like, for instance, reversal in the direction of inter-areal interactions) can be triggered reliably by brief perturbation inputs, properly timed with respect to an ongoing local oscillation, without the need for plastic synaptic changes. Finally, we analyze how the information encoded in spiking patterns of a local neuronal population is propagated across a fixed structural connectivity motif, demonstrating that changes in the active effective connectivity regulate both the efficiency and the directionality of information transfer. Previous studies stressed the role played by coherent oscillations in establishing efficient communication between distant areas. Going beyond these early proposals, we

  14. Shear stress and flow dynamics of the femoral vein among obese patients who qualify for bariatric surgery.

    Science.gov (United States)

    Wiewiora, Maciej; Piecuch, Jerzy; Glűck, Marek; Slowinska-Lozynska, Ludmila; Sosada, Krystyn

    2013-01-01

    The aim of this study was to evaluate the effects of obesity on wall shear stress and its relationship to erythrocyte aggregation. We studied 35 morbidly obese patients who were qualified for bariatric surgery. The control group consisted of 20 non-obese people. Blood rheological measurements were performed using the Laser-assisted Optical Rotational Cell Analyzer (Mechatronics, the Netherlands) and a cone-plate viscometer (Brookfield DV-II). The venous flow dynamics were assessed using a duplex ultrasound. The shear rate was estimated from the measured blood flow velocity and the diameter of the femoral vein. Venous wall shear stress was calculated from the whole blood viscosity and the shear rate. The shear rate (P < 0.005) and the venous wall shear stress (P < 0.05) were significantly lower in obese patients compared with the controls. The aggregation index (P < 0.001), syllectogram amplitude - AMP (P < 0.05) and Tslow (P < 0.001) were significantly higher in the obese patients; the aggregation half-time (P < 0.001) and Tfast (P < 0.001) were decreased compared with the control group. Multivariate regression analyses found waist circumference (β -0.31, P < 0.05), thigh circumference (β 0.33, P < 0.05) and Tslow (β -0.47, P < 0.005) to be variables that independently influenced the shear rate. Nevertheless, the AMP (β 0.34, P < 0.05) and Tslow (β -0.47, P < 0.01) were independent predictors that influenced the wall shear stress. This study indicates that there is a relationship between wall shear stress in the femoral vein and the rheological impairment of the RBC among obese patients, but further studies are necessary to confirm this suggestion.

  15. Combined heart rate variability and dynamic measures for quantitatively characterizing the cardiac stress status during cycling exercise.

    Science.gov (United States)

    Chen, Szi-Wen; Liaw, Jiunn-Woei; Chang, Ya-Ju; Chuang, Li-Ling; Chien, Chun-Tse

    2015-08-01

    In this study, we aimed to seek for different ways of measuring cardiac stress in terms of heart rate variability (HRV) and heart rate (HR) dynamics, and to develop a novel index that can effectively summarize the information reflected by these measures to continuously and quantitatively characterize the cardiac stress status during physical exercise. Standard deviation, spectral measure of HRV as well as a nonlinear detrended fluctuation analysis (DFA) based fractal-like behavior measure of HR dynamics were all evaluated on the RR time series derived from windowed electrocardiogram (ECG) data for the subjects undergoing cycling exercise. We recruited eleven young healthy subjects in our tests. Each subject was asked to maintain a fixed speed under a constant load during the pedaling test. We obtained the running estimates of the standard deviation of the normal-to-normal interval (SDNN), the high-fidelity power spectral density (PSD) of HRV, and the DFA scaling exponent α, respectively. A trend analysis and a multivariate linear regression analysis of these measures were then performed. Numerical experimental results produced by our analyses showed that a decrease in both SDNN and α was seen during the cycling exercise, while there was no significant correlation between the standard lower frequency to higher frequency (LF-to-HF) spectral power ratio of HRV and the exercise intensity. In addition, while the SDNN and α were both negatively correlated with the Borg rating of perceived exertion (RPE) scale value, it seemed that the LF-to-HF power ratio might not have substantial impact on the Borg value, suggesting that the SDNN and α may be further used as features to detect the cardiac stress status during the physical exercise. We further approached this detection problem by applying a linear discriminant analysis (LDA) to both feature candidates for the task of cardiac stress stratification. As a result, a time-varying parameter, referred to as the cardiac

  16. COMT Diplotype Amplifies Effect of Stress on Risk of Temporomandibular Pain.

    Science.gov (United States)

    Slade, G D; Sanders, A E; Ohrbach, R; Bair, E; Maixner, W; Greenspan, J D; Fillingim, R B; Smith, S; Diatchenko, L

    2015-09-01

    When measured once, psychological stress predicts development of painful temporomandibular disorder (TMD). However, a single measurement fails to characterize the dynamic nature of stress over time. Moreover, effects of stress on pain likely vary according to biological susceptibility. We hypothesized that temporal escalation in stress exacerbates risk for TMD, and the effect is amplified by allelic variants in a gene, catechol-O-methyltransferase (COMT), regulating catechol neurotransmitter catabolism. We used data from the Orofacial Pain: Prospective Evaluation and Risk Assessment prospective cohort study of 2,707 community-dwelling adults with no lifetime history of TMD on enrollment. At baseline and quarterly periods thereafter, the Perceived Stress Scale (PSS) measured psychological stress. Genotyped DNA from blood samples determined COMT diplotypes. During follow-up of 0.25 to 5.2 y, 248 adults developed examiner-verified incident TMD. PSS scores at baseline were 20% greater (P developed incident TMD compared with TMD-free controls. Baseline PSS scores increased by 9% (P = 0.003) during follow-up in cases but remained stable in controls. This stress escalation was limited to incident cases with COMT diplotypes coding for low-activity COMT, signifying impaired catabolism of catecholamines. Cox regression models confirmed significant effects on TMD hazard of both baseline PSS (P < 0.001), modeled as a time-constant covariate, and change in PSS (P < 0.001), modeled as a time-varying covariate. Furthermore, a significant (P = 0.04) interaction of COMT diplotype and time-varying stress showed that a postbaseline increase of 1.0 standard deviation in PSS more than doubled risk of TMD incidence in subjects with low-activity COMT diplotypes (hazard ratio = 2.35; 95% confidence limits: 1.66, 3.32), an effect not found in subjects with high-activity COMT diplotypes (hazard ratio = 1.42; 95% confidence limits: 0.96, 2.09). Findings provide novel insights into dynamic

  17. Effects of heat current on magnetization dynamics

    Science.gov (United States)

    Vetro, Francesco Antonio; Brechet, Sylvain; Ansermet, Jean-Philippe

    The work is aimed at investigating the interplay between spin dynamics and heat currents in single-crystal Yttrium Iron Garnet (YIG). The irreversible thermodynamics for a continuous medium predicts that a thermal gradient, in the presence of magnetization waves, produces a magnetic induction field, thus a magnetic analog of the well-known Seebeck effect. Time-resolved transmission measurements revealed a change in the attenuation of magnetization waves propagating along the thermal gradient when the gradient is reversed. This magnetic damping change can be accounted for by the Magnetic Seebeck effect. In order to characterize this effect further, we have conducted studies on magnetization dynamic in YIG single crystal samples placed in various geometrical configurations, e.g. with YIG disks in which magnetic vortices might be present. Various magnetic resonance schemes were used, e.g. local probes and cavities.

  18. Phase-dependent dynamics of the lac promoter under nutrient stress.

    Science.gov (United States)

    Viswanathan, Anisha; Anufrieva, Olga; Sala, Adrien; Yli-Harja, Olli; Kandhavelu, Meenakshisundaram

    2016-01-01

    To survive, a bacterial population must sense nutrient availability and adjust its growth phase accordingly. Few studies have quantitatively analyzed the single-cell behavior of stress and growth phase-related transcriptional changes in Escherichia coli. To investigate the dynamic changes in transcription during different growth phases and starvation, we analyzed the single-cell transcriptional dynamics of the E. coli lac promoter. Cells were grown under different starvation conditions, including glucose, magnesium, phosphate and thiamine limitations, and transcription dynamics was quantified using a single RNA detection method at different phases. Differences in gene expression over conditions and phases indicate that stochasticity in transcription dynamics is directly connected to cell phase and availability of nutrients. Except for glucose, the pattern of transcription dynamics under all starvation conditions appears to be similar. Transcriptional bursts were more prominent in lag and stationary phase cells starved for energy sources. Identical behavior was observed in exponential phase cells starved for phosphate and thiamine. Noise measurements under all nutrient exhaustion conditions indicate that intrinsic noise is higher than extrinsic noise. Our results, obtained in a relA1 mutational background, which led to suboptimal production of ppGpp, suggest that the single-cell transcriptional changes we observed were largely ppGpp-independent. Taken together, we propose that, under different starvation conditions, cells are able to decrease the trend in cell-to-cell variability in transcription as a common means of adaptation.

  19. Sex, social status and physiological stress in primates: the importance of social and glucocorticoid dynamics.

    Science.gov (United States)

    Cavigelli, Sonia A; Caruso, Michael J

    2015-05-26

    Social status has been associated with health consequences, although the mechanisms by which status affects health are relatively unknown. At the physiological level, many studies have investigated the potential relationship between social behaviour/rank and physiological stress, with a particular focus on glucocorticoid (GC) production. GCs are of interest because of their experimentally established influence on health-related processes such as metabolism and immune function. Studies in a variety of species, in both naturalistic and laboratory settings, have led to complex outcomes. This paper reviews findings from primates and rodents and proposes a psychologically and physiologically relevant framework in which to study the relationship between social status and GC function. We (i) compare status-specific GC production between male and female primates, (ii) review the functional significance of different temporal patterns of GC production, (iii) propose ways to assess these temporal dynamics, and (iv) present novel hypotheses about the relationship between social status and GC temporal dynamics, and potential fitness and health implications. To understand whether GC production mediates social status-related fitness disparities, we must consider social contest conditions and the temporal dynamics of GC production. This framework will provide greater insights into the relationship between social status, physiological stress and health.

  20. The effect of music on the human stress response.

    Directory of Open Access Journals (Sweden)

    Myriam V Thoma

    Full Text Available BACKGROUND: Music listening has been suggested to beneficially impact health via stress-reducing effects. However, the existing literature presents itself with a limited number of investigations and with discrepancies in reported findings that may result from methodological shortcomings (e.g. small sample size, no valid stressor. It was the aim of the current study to address this gap in knowledge and overcome previous shortcomings by thoroughly examining music effects across endocrine, autonomic, cognitive, and emotional domains of the human stress response. METHODS: Sixty healthy female volunteers (mean age = 25 years were exposed to a standardized psychosocial stress test after having been randomly assigned to one of three different conditions prior to the stress test: 1 relaxing music ('Miserere', Allegri (RM, 2 sound of rippling water (SW, and 3 rest without acoustic stimulation (R. Salivary cortisol and salivary alpha-amylase (sAA, heart rate (HR, respiratory sinus arrhythmia (RSA, subjective stress perception and anxiety were repeatedly assessed in all subjects. We hypothesized that listening to RM prior to the stress test, compared to SW or R would result in a decreased stress response across all measured parameters. RESULTS: The three conditions significantly differed regarding cortisol response (p = 0.025 to the stressor, with highest concentrations in the RM and lowest in the SW condition. After the stressor, sAA (p=0.026 baseline values were reached considerably faster in the RM group than in the R group. HR and psychological measures did not significantly differ between groups. CONCLUSION: Our findings indicate that music listening impacted the psychobiological stress system. Listening to music prior to a standardized stressor predominantly affected the autonomic nervous system (in terms of a faster recovery, and to a lesser degree the endocrine and psychological stress response. These findings may help better understanding the

  1. The Effect of Music on the Human Stress Response

    Science.gov (United States)

    Thoma, Myriam V.; La Marca, Roberto; Brönnimann, Rebecca; Finkel, Linda; Ehlert, Ulrike; Nater, Urs M.

    2013-01-01

    Background Music listening has been suggested to beneficially impact health via stress-reducing effects. However, the existing literature presents itself with a limited number of investigations and with discrepancies in reported findings that may result from methodological shortcomings (e.g. small sample size, no valid stressor). It was the aim of the current study to address this gap in knowledge and overcome previous shortcomings by thoroughly examining music effects across endocrine, autonomic, cognitive, and emotional domains of the human stress response. Methods Sixty healthy female volunteers (mean age = 25 years) were exposed to a standardized psychosocial stress test after having been randomly assigned to one of three different conditions prior to the stress test: 1) relaxing music (‘Miserere’, Allegri) (RM), 2) sound of rippling water (SW), and 3) rest without acoustic stimulation (R). Salivary cortisol and salivary alpha-amylase (sAA), heart rate (HR), respiratory sinus arrhythmia (RSA), subjective stress perception and anxiety were repeatedly assessed in all subjects. We hypothesized that listening to RM prior to the stress test, compared to SW or R would result in a decreased stress response across all measured parameters. Results The three conditions significantly differed regarding cortisol response (p = 0.025) to the stressor, with highest concentrations in the RM and lowest in the SW condition. After the stressor, sAA (p=0.026) baseline values were reached considerably faster in the RM group than in the R group. HR and psychological measures did not significantly differ between groups. Conclusion Our findings indicate that music listening impacted the psychobiological stress system. Listening to music prior to a standardized stressor predominantly affected the autonomic nervous system (in terms of a faster recovery), and to a lesser degree the endocrine and psychological stress response. These findings may help better understanding the

  2. The effect of music on the human stress response.

    Science.gov (United States)

    Thoma, Myriam V; La Marca, Roberto; Brönnimann, Rebecca; Finkel, Linda; Ehlert, Ulrike; Nater, Urs M

    2013-01-01

    Music listening has been suggested to beneficially impact health via stress-reducing effects. However, the existing literature presents itself with a limited number of investigations and with discrepancies in reported findings that may result from methodological shortcomings (e.g. small sample size, no valid stressor). It was the aim of the current study to address this gap in knowledge and overcome previous shortcomings by thoroughly examining music effects across endocrine, autonomic, cognitive, and emotional domains of the human stress response. Sixty healthy female volunteers (mean age = 25 years) were exposed to a standardized psychosocial stress test after having been randomly assigned to one of three different conditions prior to the stress test: 1) relaxing music ('Miserere', Allegri) (RM), 2) sound of rippling water (SW), and 3) rest without acoustic stimulation (R). Salivary cortisol and salivary alpha-amylase (sAA), heart rate (HR), respiratory sinus arrhythmia (RSA), subjective stress perception and anxiety were repeatedly assessed in all subjects. We hypothesized that listening to RM prior to the stress test, compared to SW or R would result in a decreased stress response across all measured parameters. The three conditions significantly differed regarding cortisol response (p = 0.025) to the stressor, with highest concentrations in the RM and lowest in the SW condition. After the stressor, sAA (p=0.026) baseline values were reached considerably faster in the RM group than in the R group. HR and psychological measures did not significantly differ between groups. Our findings indicate that music listening impacted the psychobiological stress system. Listening to music prior to a standardized stressor predominantly affected the autonomic nervous system (in terms of a faster recovery), and to a lesser degree the endocrine and psychological stress response. These findings may help better understanding the beneficial effects of music on the human body.

  3. Effect of ground stress on hydraulic fracturing of methane well

    Institute of Scientific and Technical Information of China (English)

    DU Chun-zhi; MAO Xian-biao; MIAO Xie-xing; WANG Peng

    2008-01-01

    Most of the coal reservoirs in China are of low-permeability, so hydraulic fracturing is widely used to improve the permeability in the extraction of gas by ground drilling. The ground stress around the well was analyzed by using theory of elasticity. The pressure when the well fractured is formulated and the effect of ground stress on pressure is discussed. The effect of ground-stress-differences on hydraulic fracturing was analyzed by using the numerical software RFPA2D-Flow in reference to the tectonic stress in Jincheng coal area. The results show that: 1) the position where initial fracture appears is random and fracture branches emerge when the fractures expand if ground stresses in any two directions within a horizontal plane are equal; 2) otherwise, the fractures expand in general along the direction of maximum ground stress and the critical pressure decreases with increasing ground-stress-differences and 3) the preferred well-disposition pattern is diamond shaped. The preferred well spacing is 250 m×300 m. This study can provide a reference for the design of wells.

  4. Molecular Dynamics Study for Channel Size Dependence of Shear Stress Between Droplet and Wall.

    Science.gov (United States)

    Fukushima, Akinori; Mima, Toshiki; Kinefuchi, Ikuya; Tokumasu, Takashi

    2015-04-01

    In this study, the channel size dependence of the shear stress between water droplets and solid walls in nm-order channel was analyzed. We considered a several different-sized and highly hydrophobic channel whose macroscopic contact angle was about 150 degrees. We have evaluated the shear stress and the normal pressure by molecular dynamics simulation. Analyzing shear stress and normal pressure based on the macroscopic model, we have discussed the difference between the macroscopic model based on hydrodynamics and the microscopic model. As a result, in the high hydrophobic case, it became clear that the shear stress depends on the channel size due to the large Laplace pressure. Furthermore, in the case that the channel size was less than 50 A, the normal pressure by the molecular simulation didn't agree with the expected value from the Young-Laplace equation. From this study it was clear that molecular simulation is needed when the channel size is less than 40 A.

  5. Environmental Stress and Pathogen Dynamics in the Blue Crab Callinectes sapidus

    Science.gov (United States)

    Sullivan, T. J.; Neigel, J.; Gelpi, C. G.

    2016-02-01

    The blue crab Callinectes sapidus is an ecologically and economically valuable species along the Gulf of Mexico and Atlantic coasts of North America. Throughout its range, the blue crab encounters a diverse array of parasitic and pathogenic microorganisms that have episodic and occasionally severe impacts on population numbers and viability. This makes understanding factors that influence pathogen dynamics, such as host stress, an important priority. To explore the role of environmental stress on the susceptibility of blue crabs to pathogens we screened individuals collected during the summers of 2014 and 2015 for a number of infectious agents. We sampled three life stages (megalopae, juvenile, and adult) from multiple marsh and offshore locations in Louisiana. Duration of stressful environmental conditions at each location was quantified from hourly recordings provided by the Louisiana Coastwide Reference Monitoring System. Pathogenic microorganisms were detected in crabs from multiple locations and multiple years. Some of the variability in prevalence of infection can be explained by exposure to stressful extremes of temperature and salinity during summer months.

  6. Microfilament Dynamics is Required for Root Growth under Alkaline Stress in Arabidopsis

    Institute of Scientific and Technical Information of China (English)

    Yue Zhou; Zijun Yang; Guangqin Guo; Yan Guo

    2010-01-01

    The microfilament (MF) cytoskeleton has crucial functions in plant development. Recent studies have revealed the function of MFs in diverse stress response. Alkaline stress is harmful to plant growth;however, it remains unclear whether the MFs play a role in alkaline stress. In the present study, we find that blocking MF assembly with latrunculin B (Lat B) leads to inhibition of plant root growth, and stabilization of MFs with phalloidin does not significantly affect plant root growth under normal conditions. In high external pH conditions, MF de-polymerization is induced and that associates with the reduction of root growth; phalloidin treatment partially rescues this reduction. Moreover, Lat B treatment further decreases the survival rate of seedlings growing in high external pH conditions. However, a high external pH (8.0) does not affect MF stability in vitro. Taken together, our results suggest that alkaline stress may trigger a signal that leads the dynamics of MFs and in turn regulates root growth.

  7. Per capita interactions and stress tolerance drive stress-induced changes in biodiversity effects on ecosystem functions.

    Science.gov (United States)

    Baert, Jan M; Janssen, Colin R; Sabbe, Koen; De Laender, Frederik

    2016-08-18

    Environmental stress changes the relationship between biodiversity and ecosystem functions, but the underlying mechanisms are poorly understood. Because species interactions shape biodiversity-ecosystem functioning relationships, changes in per capita interactions under stress (as predicted by the stress gradient hypothesis) can be an important driver of stress-induced changes in these relationships. To test this hypothesis, we measure productivity in microalgae communities along a diversity and herbicide gradient. On the basis of additive partitioning and a mechanistic community model, we demonstrate that changes in per capita interactions do not explain effects of herbicide stress on the biodiversity-productivity relationship. Instead, assuming that the per capita interactions remain unaffected by stress, causing species densities to only change through differences in stress tolerance, suffices to predict the stress-induced changes in the biodiversity-productivity relationship and community composition. We discuss how our findings set the stage for developing theory on how environmental stress changes biodiversity effects on ecosystem functions.

  8. Effect of Stress on Transformer Insulation

    Directory of Open Access Journals (Sweden)

    Kapil Gandhi

    2012-06-01

    Full Text Available Power transformers use Kraft paper as insulation in the electrical windings present in the core, which is immersed in oil. In service, the temperature of the windings of core will go to 750C to 850C. If the transformer is over loaded, then the temperature can exceed upto 100°C causing the cellulose chains in the paper to cleave at an accelerated rate, which results in the degradation of mechanical strength and performance of the insulation. The Degree of Polymerization (DP will also decrease. If proper action will not take, this can lead to failure of the transformer and disruption to electricity supply and large economic losses to the operating utility. Transformer condition should be maintained because of its importance to electricity network. The life of transformer depends on the life of the oil impregnated paper insulation system to greater extent. Degradation of the cellulose insulation is an irreversible process. After thermal degradation of the paper winding, Furfuraldehyde (FFA is the chemical compound, which is released into the oil from paper. The concentration of FFA has been directly related to the condition of the paper insulation. In the present paper an experimental investigation has been made to evaluate the degradation of transformer oil contaminated by nano-particles of pine wood under accelerated thermal and electrical stress and results are correlated with breakdown strength, density & interfacial tension of the pure oil. The contaminated oil samples are tested at electric stress of 2.0 kV, 3.0 kV, 4.0 kV & 5.0 kV for 24, 48, 72 & 96 hours simultaneously.

  9. Effect of stress on semen quality in semen donors.

    Science.gov (United States)

    Poland, M L; Giblin, P T; Ager, J W; Moghissi, K S

    1986-01-01

    Fifty-three donors with good semen quality were studied monthly for sperm count and motility over 9 to 22 months. Medical students (n = 31) in freshman and sophomore years subjected to the stress of twice-yearly examinations were compared with nonstudents (n = 22) not exposed to common stressful periods. Sperm count and quality (count X motility) for the student group were significantly elevated during examination months versus nonexamination months. Controls demonstrated no differences over these months. Differences between individuals, donor selection factors, and the effects of variable degrees of stress on sperm transport may have contributed to this finding.

  10. Effective evolution equations from quantum dynamics

    CERN Document Server

    Benedikter, Niels; Schlein, Benjamin

    2016-01-01

    These notes investigate the time evolution of quantum systems, and in particular the rigorous derivation of effective equations approximating the many-body Schrödinger dynamics in certain physically interesting regimes. The focus is primarily on the derivation of time-dependent effective theories (non-equilibrium question) approximating many-body quantum dynamics. The book is divided into seven sections, the first of which briefly reviews the main properties of many-body quantum systems and their time evolution. Section 2 introduces the mean-field regime for bosonic systems and explains how the many-body dynamics can be approximated in this limit using the Hartree equation. Section 3 presents a method, based on the use of coherent states, for rigorously proving the convergence towards the Hartree dynamics, while the fluctuations around the Hartree equation are considered in Section 4. Section 5 focuses on a discussion of a more subtle regime, in which the many-body evolution can be approximated by means of t...

  11. Temporal dynamics of the response to Al stress in Eucalyptus grandis × Eucalyptus camaldulensis

    Directory of Open Access Journals (Sweden)

    Berenice K. de Alcântara

    2015-06-01

    Full Text Available Lipid peroxidation and root elongation of Eucalyptus grandis × Eucalyptus camaldulensis were studied under stress conditions in response to aluminum (Al, a metal known to limit agricultural productivity in acidic soils primarily due to reduced root elongation. In Brazil, the Grancam 1277 hybrid (E. grandis × E. camaldulensis has been planted in the "Cerrado", a region of the country with a wide occurrence of acidic soils. The present study demonstrated that the hybrid exhibited root growth reduction and increased levels of lipid peroxidation after 24h of treatment with 100 µM of Al, which was followed by a reduction in lipid peroxidation levels and the recovery of root elongation after 48h of Al exposure, suggesting a rapid response to the early stressful conditions induced by Al. The understanding of the temporal dynamics of Al tolerance may be useful for selecting more tolerant genotypes and for identifying genes of interest for applications in bioengineering.

  12. A time to be stressed? Time perspectives and cortisol dynamics among healthy adults

    Science.gov (United States)

    Olivera-Figueroa, Lening A.; Juster, Robert-Paul; Morin-Major, Julie Katia; Marin, Marie-France; Lupien, Sonia J.

    2015-01-01

    Perceptions of past, present, and future events may be related to stress pathophysiology. We assessed whether Time Perspective (TP) is associated with cortisol dynamics among healthy adults (N = 61, Ages = 18–35, M = 22.9, SD = 4.1) exposed to the Trier Social Stress Test (TSST). TP was measured according to two profiles: maladaptive Deviation from Balanced TP (DBTP) and adaptive Deviation from Negative TP (DNTP). Eight salivary cortisol samples were analyzed using area under the curve with respect to ground (AUCg) and to increase (AUCi). Statistic analyses involved partial correlations controlling for depressive symptoms. Results for both sexes showed that higher DBTP scores were associated with lower cortisol AUCg scores, while higher DNTP scores were associated with higher cortisol AUCg scores. These novel findings suggest that maladaptive TP profiles influence hypocortisolism, whereas adaptive TP profiles influence hypercortisolism. Thus, TP profiles may impact conditions characterized by altered cortisol concentrations. PMID:26362588

  13. Dynamic Stresses in the LHC TCDS Diluter from 7 TeV Beam Loading

    CERN Document Server

    Goddard, B; Presland, A; Weterings, W

    2006-01-01

    In the event of an unsynchronised beam abort, the MSD extraction septum of the LHC beam dumping system is protected from damage by the TCDS diluter. The simultaneous constraints of obtaining sufficient beam dilution while ensuring the survival of the TCDS make the design difficult, with high thermally induced dynamic stresses occurring in the material needed to attenuate the particle showers induced by the primary beam impact. In this paper, full 3D simulations are described where the worst-case beam loading has been used to generate the local temperature rise and to follow the resulting time evolution of the mechanical stresses. The results and the accompanying design changes for the TCDS, to provide an adequate performance margin, are detailed.

  14. Dynamical effects in fusion with exotic nuclei

    Science.gov (United States)

    Vo-Phuoc, K.; Simenel, C.; Simpson, E. C.

    2016-08-01

    Background: Reactions with stable beams have demonstrated strong interplay between nuclear structure and fusion. Exotic beam facilities open new perspectives to understand the impact of neutron skin, large isospin, and weak binding energies on fusion. Microscopic theories of fusion are required to guide future experiments. Purpose: To investigate new effects of exotic structures and dynamics in near-barrier fusion with exotic nuclei. Method: Microscopic approaches based on the Hartree-Fock (HF) mean-field theory are used for studying fusion barriers in -54Ca40+116Sn reactions for even isotopes. Bare potential barriers are obtained assuming frozen HF ground-state densities. Dynamical effects on the barrier are accounted for in time-dependent Hartree-Fock (TDHF) calculations of the collisions. Vibrational couplings are studied in the coupled-channel framework and near-barrier nucleon transfer is investigated with TDHF calculations. Results: The development of a neutron skin in exotic calcium isotopes strongly lowers the bare potential barrier. However, this static effect is not apparent when dynamical effects are included. On the contrary, a fusion hindrance is observed in TDHF calculations with the most neutron-rich calcium isotopes which cannot be explained by vibrational couplings. Transfer reactions are also important in these systems due to charge equilibration processes. Conclusions: Despite its impact on the bare potential, the neutron skin is not seen as playing an important role in the fusion dynamics. However, the charge transfer with exotic projectiles could lead to an increase of the Coulomb repulsion between the fragments, suppressing fusion. The effects of transfer and dissipative mechanisms on fusion with exotic nuclei deserve further studies.

  15. Effect of yoga on academic performance in relation to stress

    OpenAIRE

    Kauts Amit; Sharma Neelam

    2009-01-01

    Background: Academic performance is concerned with the quantity and quality of learning attained in a subject or group of subjects after a long period of instruction. Excessive stress hampers students′ performance. Improvement in academic performance and alertness has been reported in several yogic studies. Aims and Objectives: The main objective of the study was to assess the effect of yoga on academic performance in relation to stress. Materials and Methods: The study started ...

  16. Effects of external stress on defect complexes in semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Tessema, Genene [Department of Physics, Addis Ababa University, PO Box 1176, Addis Ababa (Ethiopia); Helmholtz-Institut fuer Strahlen und Kernphysik, Nussalle 14-16, 53115 Bonn (Germany)

    2007-07-04

    Crystal field gradients that exist at lattice sites in solids depend on the symmetry of charge distribution around atomic sites. The charge symmetry could be broken either by the presence of impurity complexes in the host matrix or by external stress on the samples, which leads to an observable magnitude of electric field gradients (EFGs). The perturbed {gamma}-{gamma} angular correlation (PAC) method is employed here to investigate the effect of uniaxial stress on {sup 111}Cd sites in crystalline doped semiconductors.

  17. Molecular dynamics simulations of thermal effects in nanometric cutting process

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Understanding the basic action of how material removing in nanoscale is a critical issue of producing well-formed components.In order to clarify thermal effects on material removal at atomic level,molecular dynamics(MD)simulations of nanometric cutting of mono-crystalline copper are performed with Morse,EAM and Tersoff potential.The effects of cutting speed on temperature distribution are investigated.The simulation results demonstrate that the temperature distribution shows a roughly concentric shape around shear zone and a steep temperature gradient lies in diamond tool,a relative high temperature is located in shear zone and machined surface,but the highest temperature is found in chip.At a high cutting speed mode,the atoms in shear zone with high temperature implies a large stress is built up in a local region.

  18. Stress

    Science.gov (United States)

    ... diabetes. Shopdiabetes.org: Your Stress-Free System for Family Dinners! - 2017-03-book-oclock-scramble.html Shopdiabetes.org Your Stress-Free System for Family Dinners! A year of delicious meals to help prevent ...

  19. The Effects of Stress on Physical Activity and Exercise

    Science.gov (United States)

    Stults-Kolehmainen, Matthew A.; Sinha, Rajita

    2013-01-01

    Background Psychological stress and physical activity (PA) are believed to be reciprocally related; however, most research examining the relationship between these constructs is devoted to the study of exercise and/or PA as an instrument to mitigate distress. Objective The aim of this paper was to review the literature investigating the influence of stress on indicators of PA and exercise. Methods A systematic search of Web of Science, Pub-Med, and SPORTDiscus was employed to find all relevant studies focusing on human participants. Search terms included “stress”, “exercise”, and “physical activity”. A rating scale (0–9) modified for this study was utilized to assess the quality of all studies with multiple time points. Results The literature search found 168 studies that examined the influence of stress on PA. Studies varied widely in their theoretical orientation and included perceived stress, distress, life events, job strain, role strain, and work–family conflict but not lifetime cumulative adversity. To more clearly address the question, prospective studies (n = 55) were considered for further review, the majority of which indicated that psychological stress predicts less PA (behavioral inhibition) and/or exercise or more sedentary behavior (76.4 %). Both objective (i.e., life events) and subjective (i.e., distress) measures of stress related to reduced PA. Prospective studies investigating the effects of objective markers of stress nearly all agreed (six of seven studies) that stress has a negative effect on PA. This was true for research examining (a) PA at periods of objectively varying levels of stress (i.e., final examinations vs. a control time point) and (b) chronically stressed populations (e.g., caregivers, parents of children with a cancer diagnosis) that were less likely to be active than controls over time. Studies examining older adults (>50 years), cohorts with both men and women, and larger sample sizes (n > 100) were more likely

  20. The effects of stress on singing voice accuracy.

    Science.gov (United States)

    Larrouy-Maestri, Pauline; Morsomme, Dominique

    2014-01-01

    The quality of a music performance can be lessened or enhanced if the performer experiences stressful conditions. In addition, the quality of a sung performance requires control of the fundamental frequency of the voice, which is particularly sensitive to stress. The present study aimed to clarify the effects of stress on singing voice accuracy. Thirty-one music students were recorded in a stressful condition (ie, a music examination) and a nonstressful condition. Two groups were defined according to the challenge level of the music examination (first and second music levels). Measurements were made by self-reported state anxiety (CSAI-2R questionnaire) and by observing heart rate activity (electrocardiogram) during each performance. In addition, the vocal accuracy of the sung performances was objectively analyzed. As expected, state anxiety and heart rate were significantly higher on the day of the music examination than in the nonstressful condition for all the music students. However, the effect of stress was positive for the first-year students but negative for the second-year students, for whom the music examination was particularly challenging. In addition, highly significant correlations were found between the intensity of cognitive symptoms and the vocal accuracy criteria. This study highlights the contrasting effects of stress on singing voice accuracy but also the need to consider the challenge level and perception of the symptoms in experimental and pedagogical settings. Copyright © 2014 The Voice Foundation. Published by Mosby, Inc. All rights reserved.

  1. Stress effects on memory: an update and integration.

    Science.gov (United States)

    Schwabe, Lars; Joëls, Marian; Roozendaal, Benno; Wolf, Oliver T; Oitzl, Melly S

    2012-08-01

    It is well known that stressful experiences may affect learning and memory processes. Less clear is the exact nature of these stress effects on memory: both enhancing and impairing effects have been reported. These opposite effects may be explained if the different time courses of stress hormone, in particular catecholamine and glucocorticoid, actions are taken into account. Integrating two popular models, we argue here that rapid catecholamine and non-genomic glucocorticoid actions interact in the basolateral amygdala to shift the organism into a 'memory formation mode' that facilitates the consolidation of stressful experiences into long-term memory. The undisturbed consolidation of these experiences is then promoted by genomic glucocorticoid actions that induce a 'memory storage mode', which suppresses competing cognitive processes and thus reduces interference by unrelated material. Highlighting some current trends in the field, we further argue that stress affects learning and memory processes beyond the basolateral amygdala and hippocampus and that stress may pre-program subsequent memory performance when it is experienced during critical periods of brain development.

  2. Effects of Simulation on Nursing Student Stress: An Integrative Review.

    Science.gov (United States)

    Cantrell, Melody L; Meyer, Susan L; Mosack, Victoria

    2017-03-01

    The effects of stress on nursing students' health and learning is important to educators. The purpose of this review was to critically integrate the literature related to the stress that nursing students experience regarding high-fidelity simulation (HFS). Literature from multiple search engines and databases was systematically searched. Keywords and Boolean combinations included nursing students, simulation, stress, anxiety, and self-efficacy. Qualitative or quantitative studies published in English between 2010 and 2015 and studies including the effects of simulation on nursing student anxiety and stress were included. Seventeen studies were chosen. Overall, students reported either moderate or high stress associated with simulation, but they rated the HFS experience as a valuable learning tool. This review demonstrated student acceptance of simulation as a learning strategy. However, more high-quality studies are needed to investigate techniques that can be implemented to decrease the negative effects of simulation stress on nursing students. [J Nurs Educ. 2017;56(3):139-144.]. Copyright 2017, SLACK Incorporated.

  3. Mechanical behavior and stress effects in hard superconductors: a review

    Energy Technology Data Exchange (ETDEWEB)

    Koch, C. C.; Easton, D. S.

    1977-11-01

    The mechanical properties of type II superconducting materials are reviewed as well as the effect of stress on the superconducting properties of these materials. The bcc alloys niobium-titanium and niobium-zirconium exhibit good strength and extensive ductility at room temperature. Mechanical tests on these alloys at 4.2/sup 0/K revealed serrated stress-strain curves, nonlinear elastic effects and reduced ductility. The nonlinear behavior is probably due to twinning and detwinning or a reversible stress-induced martensitic transformation. The brittle A-15 compound superconductors, such as Nb/sub 3/Sn and V/sub 3/Ga, exhibit unusual elastic properties and structural instabilities at cryogenic temperatures. Multifilamentary composites consisting of superconducting filaments in a normal metal matrix are generally used for superconducting devices. The mechanical properties of alloy and compound composites, tapes, as well as composites of niobium carbonitride chemically vapor deposited on high strength carbon fibers are presented. Hysteretic stress-strain behavior in the metal matrix composites produces significant heat generation, an effect which may lead to degradation in the performance of high field magnets. Measurements of the critical current density, J/sub c/, under stress in a magnetic field are reported. Modest stress-reversible degradation in J/sub c/ was observed in niobium-titanium composites, while more serious degradation was found in Nb/sub 3/Sn samples. The importance of mechanical behavior to device performance is discussed.

  4. Investigation of Effect of Slab Opening Location to the Shear Stress

    Directory of Open Access Journals (Sweden)

    Burak Yön

    2010-01-01

    Full Text Available In this study, it is investigated the effect of slab opening location in reinforced concrete building to the structural behavior. For investigation of slab irregularity, three multi storey irregular structures that have different slab opening locations in structure plans and one regular structure are designed. Linear dynamic analyses are performed for the structure models using Time History Analysis method. 13 March 1992 Erzincan Earthquake acceleration records are used for these analyses. It is assumed that slabs of selected structures are modeled as elastic diaphragm. SAP2000 Structural Analysis Program is used in the analyses. Values of slab that near space shear stress obtained from dynamic analyses of selected structures are comparatively evaluated. According to analyses results, it is determined that location of slab opening of structures reasonably both affects the behavior of structures and occurs great slab shear stress.

  5. Effective dynamics of strongly dissipative Rydberg gases

    CERN Document Server

    Marcuzzi, M; Olmos, B; Lesanovsky, I

    2014-01-01

    We investigate the evolution of interacting Rydberg gases in the limit of strong noise and dissipation. Starting from a description in terms of a Markovian quantum master equation we derive effective equations of motion that govern the dynamics on a "coarse-grained" timescale where fast dissipative degrees of freedom have been adiabatically eliminated. Specifically, we consider two scenarios which are of relevance for current theoretical and experimental studies --- Rydberg atoms in a two-level (spin) approximation subject to strong dephasing noise as well as Rydberg atoms under so-called electromagnetically induced transparency (EIT) conditions and fast radiative decay. In the former case we find that the effective dynamics is described by classical rate equations up to second order in an appropriate perturbative expansion. This drastically reduces the computational complexity of numerical simulations in comparison to the full quantum master equation. When accounting for the fourth order correction in this e...

  6. Some Dynamical Effects of the Cosmological Constant

    Science.gov (United States)

    Axenides, M.; Floratos, E. G.; Perivolaropoulos, L.

    Newton's law gets modified in the presence of a cosmological constant by a small repulsive term (antigravity) that is proportional to the distance. Assuming a value of the cosmological constant consistent with the recent SnIa data (Λ~=10-52 m-2), we investigate the significance of this term on various astrophysical scales. We find that on galactic scales or smaller (less than a few tens of kpc), the dynamical effects of the vacuum energy are negligible by several orders of magnitude. On scales of 1 Mpc or larger however we find that the vacuum energy can significantly affect the dynamics. For example we show that the velocity data in the local group of galaxies correspond to galactic masses increased by 35% in the presence of vacuum energy. The effect is even more important on larger low density systems like clusters of galaxies or superclusters.

  7. Dynamical effects in fusion with exotic nuclei

    CERN Document Server

    Vo-Phuoc, K; Simpson, E C

    2016-01-01

    [Background] Reactions with stable beams have demonstrated a strong interplay between nuclear structure and fusion. Exotic beam facilities open new perspectives to understand the impact of neutron skin, large isospin, and weak binding energies on fusion. Microscopic theories of fusion are required to guide future experiments. [Purpose] To investigate new effects of exotic structures and dynamics in near-barrier fusion with exotic nuclei. [Method] Microscopic approaches based on the Hartree-Fock (HF) mean-field theory are used for studying fusion barriers in $^{40-54}$Ca+$^{116}$Sn reactions for even isotopes. Bare potential barriers are obtained assuming frozen HF ground-state densities. Dynamical effects on the barrier are accounted for in time-dependent Hartree-Fock (TDHF) calculations of the collisions. Vibrational couplings are studied in the coupled-channel framework and near-barrier nucleon transfer is investigated with TDHF calculations. [Results] The development of a neutron skin in exotic calcium iso...

  8. Numerical simulation of dynamic Coulomb stress changes induced by M6.5 earthquake in Wuding, Yunnan and its relationship with aftershocks

    Institute of Scientific and Technical Information of China (English)

    HU Xiong-lin; WU Xiao-ping; YANG Run-hai; FU Hong; HU Jia-fu; HUANG Yong

    2008-01-01

    Based on the discrete wavenumber method, we calculate the fields of dynamic Coulomb rupture stress changes and static stress changes caused by M6.5 earthquake in Wuding, and study their relationship with the subsequent aftershocks. The results show that the spatial distribution patterns of the positive region of dynamic stress peak value and static stress peak value are similarly asymmetric, which are basically identical with distribution features of aftershock. The dynamic stress peak value and the static stress in the positive region are more than 0.1 MPa and 0.01 MPa of the triggering threshold, respectively, which indicates that the dynamic and static stresses are helpful for the occurrence of aftershock. This suggests that both influences of dynamic and static stresses should be con-sidered other than only either of them when studying aftershock triggering in near field.

  9. Effective "Gluon" Dynamics in a Stochastic Vacuum

    CERN Document Server

    Magpantay, J A

    2002-01-01

    Using the new scalar and vector degrees of freedom derived from the non-linear gauge condition (grad-dot-D)(grad-dot-A)=0, we show that the effective dynamics of the vector fields (identified as ``gluons'') in the stochastic vacuum defined by the scalars result in the vector fields acquiring a mass. We also find the vector fields losing their self-interactions.

  10. Effective Dynamics of Disordered Quantum Systems

    Science.gov (United States)

    Kropf, Chahan M.; Gneiting, Clemens; Buchleitner, Andreas

    2016-07-01

    We derive general evolution equations describing the ensemble-average quantum dynamics generated by disordered Hamiltonians. The disorder average affects the coherence of the evolution and can be accounted for by suitably tailored effective coupling agents and associated rates that encode the specific statistical properties of the Hamiltonian's eigenvectors and eigenvalues, respectively. Spectral disorder and isotropically disordered eigenvector distributions are considered as paradigmatic test cases.

  11. Aspects of effective dynamics for nonequilibrium systems

    OpenAIRE

    Thomas, Simi

    2013-01-01

    In this work we present a few general and some specific aspects of effective dynamics of macroscopic observables, obtained through the study of some models. The purpose of statistical physics is to build connections between microscopic variables (which are enormous in number and usually fast in ``speed'') and the macroscopic variables (usually fewer and slower compared to the microscopic variables). Much can be inferred about the microscopic state of a system from the nature of a well defined...

  12. Spelling-stress regularity effects are intact in developmental dyslexia.

    Science.gov (United States)

    Mundy, Ian R; Carroll, Julia M

    2013-01-01

    The current experiment investigated conflicting predictions regarding the effects of spelling-stress regularity on the lexical decision performance of skilled adult readers and adults with developmental dyslexia. In both reading groups, lexical decision responses were significantly faster and significantly more accurate when the orthographic structure of a word ending was a reliable as opposed to an unreliable predictor of lexical stress assignment. Furthermore, the magnitude of this spelling-stress regularity effect was found to be equivalent across reading groups. These findings are consistent with intact phoneme-level regularity effects also observed in dyslexia. The paper discusses how findings of intact spelling-sound regularity effects at both prosodic and phonemic levels, as well as other similar results, can be reconciled with the obvious difficulties that people with dyslexia experience in other domains of phonological processing.

  13. Effects of chronic stress on sleep in rats.

    Science.gov (United States)

    Kant, G J; Pastel, R H; Bauman, R A; Meininger, G R; Maughan, K R; Robinson, T N; Wright, W L; Covington, P S

    1995-02-01

    The present study was conducted to determine the effects of chronic stress on sleep using a rodent paradigm of around-the-clock signalled intermittent foot shock in which some rats can pull a chain to avoid/escape shock while another group of rats is yoked to the first group. We measured sleep using telemetry; four-channel EEG was collected 24 h/day in rats during 2 prestress days; days 1, 2, 3, 7, and 14 during chronic stress; and 3 poststress days. States of REM sleep, non-REM (NREM) sleep, and waking were scored for each 15-s period of the EEG recordings. During the prestress period, rats slept (REM plus NREM) 55% of available time during the light hours and 34% of the dark hours with the remainder represented by waking. On the first day of stress, total sleep and, especially REM sleep, decreased markedly. By the second day of stress, only REM sleep in the controllable stress group (but not the uncontrollable stress group) was still significantly decreased compared to prestress levels, and REM sleep returned to baseline levels by day 7 of stress. The recovery of sleep quantity was accomplished by increased sleep during the dark hours, resulting in a long-lasting disruption of normal circadian sleep patterning.

  14. Effective stress law for anisotropic double porous media

    Institute of Scientific and Technical Information of China (English)

    ZHAO Ying; CHEN Mian; ZHANG Guangqing

    2004-01-01

    An effective stress law is derived analytically to describe the effect of pore (fracture pore and matrix-block pore) fluid pressure on the linearly elastic response of anisotropic saturated dual-porous rocks, which exhibit anisotropy. For general anisotropy the difference between the effective stress and the applied stress is not hydrostatic simply multiplied by Biot coefficient. The effective stress law involves four constants for transversely isotropic response; these constants can be expressed in terms of the moduli of the single porous material, double porous material and of the solid material. These expressions are simplified considerably when the anisotropy is structural rather than intrinsic, i.e. in the case of an isotropic solid material with an anisotropic pore structure. In this case the effective stress law involves grain bulk modulus, four moduli and two compliances of the porous material for transverse isotropy. The law reduces, in the case of isotropic response, to that suggested by Li Shuiquan (2001). And reduction to the single-porosity (derived analytically by Carroll (1979)) is presented to demonstrate the conceptual consistency of the proposed law.

  15. [Effects of drought stress on photosynthesis capability of Spiraea fritschiana and Spiraea bunmalba 'Goldmound'].

    Science.gov (United States)

    Liu, Hui-Min; Che, Yan-Shuang; Che, Dai-Di; Yan, Yong-Qing; Wu, Feng-Zhi

    2010-08-01

    In this paper, Spiraea fritschiana and Spiraea bunmalba 'Goldmound' were treated with mild, moderate, and severe drought to study the dynamic changes of their photosynthesis capability, and two-dimensional electrophoresis and mass spectrometry were adopted to analyze and identify the differences in the protein expression of the two species before and after the treatments, and the physiological mechanisms inducing the changes of the photosynthesis capability. Drought treatments had significant effects on the photosynthesis capability of the two species. Under drought stress, the maximum photosynthetic rate, light compensation point, and light saturation point decreased gradually, suggesting that the responses of the two species to drought stress were progressive. The two species presented stronger recovery capability after the mild and moderate stresses, but weaker recovery capability after severe stress. After the inducement of drought stress, the weaker drought-resistant S. bunmalba 'Goldmound' had six protein spots lost, eleven new protein spots appeared, thirteen protein spots up-regulation expression, and four protein spots down-regulation expression. All of the proteins were low molecular weight acidic proteins, of which, there were three kinds of different proteins that had been induced expression by drought and were the oxygen-enhanced protein factor 1 and 2 and the degradation fragments of large subunit 1,5-ribulose bisphosphate carboxylase/oxygenase. The drought- resistant difference of the two Spiraea species was related to the changes of their photosynthesis capability during drought stress.

  16. The impact of stress on tumor growth: peripheral CRF mediates tumor-promoting effects of stress

    Directory of Open Access Journals (Sweden)

    Stathopoulos Efstathios N

    2010-09-01

    effect. Moreover, antalarmin suppressed neoangiogenesis in 4T1 tumors in vivo. Conclusion This is the first report demonstrating that peripheral CRF, at least in part, mediates the tumor-promoting effects of stress and implicates CRF in SMAD2 and β-catenin expression.

  17. Cross-talk between lipid and protein carbonylation in a dynamic cardiomyocyte model of mild nitroxidative stress

    Directory of Open Access Journals (Sweden)

    Eva Griesser

    2017-04-01

    Full Text Available Reactive oxygen and nitrogen species (ROS/RNS play an important role in the regulation of cardiac function. Increase in ROS/RNS concentration results in lipid and protein oxidation and is often associated with onset and/or progression of many cardiovascular disorders. However, interplay between lipid and protein modifications has not been simultaneously studied in detail so far. Biomolecule carbonylation is one of the most common biomarkers of oxidative stress. Using a dynamic model of nitroxidative stress we demonstrated rapid changes in biomolecule carbonylation in rat cardiomyocytes. Levels of carbonylated species increased as early as 15 min upon treatment with the peroxynitrite donor, 3-morpholinosydnonimine (SIN-1, and decreased to values close to control after 16 h. Total (lipids+proteins vs. protein-specific carbonylation showed different dynamics, with a significant increase in protein-bound carbonyls at later time points. Treatment with SIN-1 in combination with inhibitors of proteasomal and autophagy/lysosomal degradation pathways allowed confirmation of a significant role of the proteasome in the degradation of carbonylated proteins, whereas lipid carbonylation increased in the presence of autophagy/lysosomal inhibitors. Electrophilic aldehydes and ketones formed by lipid peroxidation were identified and relatively quantified using LC-MS/MS. Molecular identity of reactive species was used for data-driven analysis of their protein targets. Combination of different enrichment strategies with LC-MS/MS analysis allowed identification of more than 167 unique proteins with 332 sites modified by electrophilic lipid peroxidation products. Gene ontology analysis of modified proteins demonstrated enrichment of several functional categories including proteins involved in cytoskeleton, extracellular matrix, ion channels and their regulation. Using calcium mobilization assays, the effect of nitroxidative stress on the activity of several ion

  18. Stress and Incongruity Theory: Effects of Crowding,

    Science.gov (United States)

    1981-01-01

    Nogami, G. Y. Crowding: Effects of group size, room size or density. Journal of Applied Social Psychology , 1976, 6, 105-125. Osgood, C. E. and...perceived control and behavioral effects. Journal of Applied Social Psychology , 1974, 4, 171-186. -43- Sommer, R. Personal space: The behavioral

  19. Antidepressant and anti-stress effects of curcumin inmice

    Institute of Scientific and Technical Information of China (English)

    YingXU; Bao-shanKU; Hai-yanYAO; Yong-heZHANG; Xue-junLI

    2004-01-01

    Curcumin (diferuloylmethane), a yellow colouring agent contained in the rhizome of Curcuma Longa (turmeric), has a wide array of pharmacological and biological activities, such as antioxidant, anti-inflammatory, immunomodulating and anticarcinogenic effects. In this study, curcumin was examined for the antidepressant and anti-stress effects in forced swimming,

  20. Protracted effects of chronic stress on serotonin dependent thermoregulation

    Science.gov (United States)

    Natarajan, Reka; Northrop, Nicole A.; Yamamoto, Bryan K.

    2016-01-01

    Chronic stress is known to affect serotonin (5HT) neurotransmission in the brain and to alter body temperature. Body temperature is controlled in part, by the medial preoptic area of the hypothalamus (mPOA). To investigate the effect of chronic stress on 5HT and how it affects body temperature regulation, we examined whether exposure to a chronic unpredictable stress paradigm (CUS) produces long-term alterations in thermoregulatory function of the mPOA through decreased 5HT neurotransmission. Adult male Sprague-Dawley rats underwent 21 days of CUS. Four days after last stress exposure, basal body temperature in the home cage and body temperature in a cold room maintained at 10°C were recorded. CUS rats had significantly higher subcutaneous basal body temperature at 13:00 h compared to unstressed (NoStress) rats. Whereas the NoStress rats were able to significantly elevate body temperature from basal levels at 30 and 60 min of exposure to the cold room, the CUS rats showed a hypothermic response to the cold. Treatment during CUS with metyrapone, a corticosterone synthesis inhibitor, blocked stress-induced decrease in body temperature in response to the cold challenge. CUS also decreased 5HT transporter protein immunoreactivity in the mPOA and 5HT2A/C agonist injection into the mPOA after CUS exposure caused stressed rats to exhibit a sensitized hyperthermic response to cold. These results indicate that CUS induced changes to the 5HTergic system alters mPOA function in thermoregulation. These findings help explain mechanisms underlying chronic stress induced disorders such as chronic fatigue syndrome wherein long lasting thermoregulatory deficits are observed. PMID:26414686

  1. Protracted effects of chronic stress on serotonin-dependent thermoregulation.

    Science.gov (United States)

    Natarajan, Reka; Northrop, Nicole A; Yamamoto, Bryan K

    2015-01-01

    Chronic stress is known to affect serotonin (5HT) neurotransmission in the brain and to alter body temperature. The body temperature is controlled in part, by the medial preoptic area (mPOA) of the hypothalamus. To investigate the effect of chronic stress on 5HT and how it affects body temperature regulation, we examined whether exposure to a chronic unpredictable stress (CUS) paradigm produces long-term alterations in thermoregulatory function of the mPOA through decreased 5HT neurotransmission. Adult male Sprague-Dawley rats underwent 21 d of CUS. Four days after the last stress exposure, basal body temperature in the home cage and body temperature in a cold room maintained at 10 °C were recorded. The CUS rats had significantly higher subcutaneous basal body temperature at 13:00 h compared to unstressed (NoStress) rats. Whereas the NoStress rats were able to significantly elevate body temperature from basal levels at 30 and 60 min of exposure to the cold room, the CUS rats showed a hypothermic response to the cold. Treatment during CUS with metyrapone, a corticosterone synthesis inhibitor, blocked stress-induced decrease in body temperature in response to the cold challenge. CUS also decreased 5HT transporter protein immunoreactivity in the mPOA and 5HT2A/C agonist injection into the mPOA after CUS exposure caused stressed rats to exhibit a sensitized hyperthermic response to cold. These results indicate that the CUS induced changes to the 5HTergic system alter mPOA function in thermoregulation. These findings help us to explain the mechanisms underlying chronic stress-induced disorders such as chronic fatigue syndrome wherein long lasting thermoregulatory deficits are observed.

  2. Heat Stress on Poultry: Metabolism, Effects and Efforts to Overcome

    Directory of Open Access Journals (Sweden)

    Mohammad Hasil Tamzil

    2014-06-01

    Full Text Available Poultry industries in the tropics are challenged by high ambient temperatures and humidities which cause poultry suffer from heat stress. Heat stress contributes to the instability of certain compounds, such as enzymes. Consequently the enzymes function reduces. Affecting the physiological and hormonal conditions of the poultry. In such condition, the body will attempt to restore homeostasis to the state before it happened. When physiological failed to meet the condition, the body will use the genetic pathway by activating Heat Shock Protein (HSP genes to protect proteins which are sensitive to high temperatures. Heat stress in poultry triggers the emergence of various diseases and affects the growth of poultry and egg production. These negative effects on poultry can be minimized by selecting the type of chickens which are tolerant to high ambient temperature, modifying microclimates of cages and adding anti-stress compounds through feed and or drink.

  3. Performance enhancement in uniaxially tensile stressed GeSn n-channel fin tunneling field-effect transistor: Impact of stress direction

    Science.gov (United States)

    Wang, Hongjuan; Han, Genquan; Jiang, Xiangwei; Liu, Yan; Zhang, Chunfu; Zhang, Jincheng; Hao, Yue

    2017-04-01

    In this work, the boosting effect on the performance of GeSn n-channel fin tunneling FET (nFinTFET) enabled by uniaxial tensile stress is investigated theoretically. As the fin rotates within the (001) plane, the uniaxial tensile stress is always along its direction. The electrical characteristics of tensile-stressed GeSn nFinTFETs with point and line tunneling modes are computed utilizing the technology computer aided design (TCAD) simulator in which the dynamic nonlocal band-to-band tunneling (BTBT) algorithm is employed. In comparison with the relaxed devices, tensile-stressed GeSn nFinTFETs achieve a substantial enhancement in band-to-band tunneling generation rate (G BTBT) and on-state current I ON owing to the reduced bandgap E G induced by the tensile stress. Performance improvement of GeSn nFinTFETs induced by tensile stress demonstrates a strong dependence on channel direction and tunneling modes. Under the same magnitude of stress, line-nFinTFETs obtain a more pronounced I ON enhancement over the transistors with point tunneling mode.

  4. Stress effects on coarticulation in English and Greek

    Science.gov (United States)

    Koenig, Laura; Okalidou, Areti

    2003-04-01

    The effects of stress on production variability and V-to-V coarticulation were compared in American English and Greek, two languages which differ in vowel inventory size and in the magnitude of V-to-V coarticulation (Okalidou and Koenig, 1999). Six speakers, one male and two females from each language, were recorded producing nonsense VCV utterances in a carrier phrase, with randomly alternating stress. The Greek stimuli included all five vowels of the language; the English stimuli included the closest counterparts of the Greek vowels. The medial plosive consonants alternated between the bilabial and alveolar place of articulation, yielding different degrees of coarticulatory resistance (Recasens, 1985, 1989). Plosives were chosen to have similar VOT values across languages in order to minimize duration effects. A comparison of stressed versus unstressed vowel areas reveals significant differences across languages. Specific vowel effects and language effects are also noted with respect to changes in production variability under the stressed versus unstressed conditions. The magnitude of V-to-V influences as a function of stress and position is discussed in terms of the above crosslinguistic comparison in order to obtain further insight on the coarticulatory behavior of languages which differ in the size of vowel inventory (Manuel and Krakow, 1984).

  5. Stress Effects on Stop Bursts in Five Languages

    Directory of Open Access Journals (Sweden)

    Marija Tabain

    2016-11-01

    Full Text Available This study examines the effects of stress on the stop burst in five languages differing in number of places of articulation, as reflected in burst duration, spectral centre of gravity, and ­spectral standard deviation. The languages studied are English (three places of articulation /p t k/, the Indonesian language Makasar (four places /p t c k/, and the Central Australian languages ­Pitjantjatjara, Warlpiri (both five places /p t ʈ c k/, and Arrernte (six places /p t̪ t ʈ c k/. We find that languages differ in how they manifest stress on the consonant, with Makasar not ­showing any effect of stress at all, and Warlpiri showing an effect on burst duration, but not on the ­spectral measures. For the other languages, the velar /k/ has a “darker” quality (i.e., lower spectral centre of gravity, and/or a less diffuse spectrum (i.e., lower standard deviation under stress; while the alveolar /t/ has a “lighter” quality under stress. In addition, the dental /t̪/ has a more diffuse spectrum under stress. We suggest that this involves enhancement of the features [grave] and [diffuse] under stress, with velars being [+grave] and [–diffuse], alveolars being [–grave], and dentals being [+diffuse]. We discuss the various possible spectral effects of enhancement of these features. Finally, in the languages with five or six places of articulation, the stop burst is longer only for the palatal /c/ and the velar /k/, which have intrinsically long burst durations, and not for the anterior coronals /t̪ t ʈ/, which have intrinsically short burst durations. We suggest that in these systems, [burst duration] is a feature that separates these two groups of consonants.

  6. Effectiveness of stress management training on stress reduction in pregnant women

    Directory of Open Access Journals (Sweden)

    Mahboobeh Shirazi

    2016-10-01

    .1 for moderated level stress (P= 0.001 and 40.1 to 16.6 for high level of stress (P= 0.0001 respectively. Conclusion: First trimester of pregnancy is a crucial stage of fetal growth and development. Based on our findings, stress management training in this period has beneficial effects on stress reduction and enhances maternal health status.

  7. Fostering assumption-based stress-test thinking in managing groundwater systems: learning to avoid failures due to basic dynamics

    Science.gov (United States)

    Guillaume, Joseph H. A.; El Sawah, Sondoss

    2014-06-01

    Sustainable groundwater resource management can only be achieved if planning processes address the basic dynamics of the groundwater system. Conceptual and distributed groundwater models do not necessarily translate into an understanding of how a plan might operate in reality. Prompted by Australian experiences, `iterative closed-question modelling' has been used to develop a process of iterative dialogue about management options, objectives and knowledge. Simple hypothetical models of basic system dynamics that satisfy agreed assumptions are used to stress-test the ability of a proposed management plan to achieve desired future conditions. Participants learn from models in which a plan succeeds and fails, updating their assumptions, expectations or plan. Their new understanding is tested against further hypothetical models. The models act as intellectual devices that confront users with new scenarios to discuss. This theoretical approach is illustrated using simple one and two-cell groundwater models that convey basic notions of capture and spatial impacts of pumping. Simple extensions can address uncertain climate, managed-aquifer recharge and alternate water sources. Having learnt to address the dynamics captured by these models, participants may be better placed to address local conditions and develop more effective arrangements to achieve management outcomes.

  8. Angiogenin enhances cell migration by regulating stress fiber assembly and focal adhesion dynamics.

    Directory of Open Access Journals (Sweden)

    Saisai Wei

    Full Text Available Angiogenin (ANG acts on both vascular endothelial cells and cancer cells, but the underlying mechanism remains elusive. In this study, we carried out a co-immunoprecipitation assay in HeLa cells and identified 14 potential ANG-interacting proteins. Among these proteins, β-actin, α-actinin 4, and non-muscle myosin heavy chain 9 are stress fiber components and involved in cytoskeleton organization and movement, which prompted us to investigate the mechanism of action of ANG in cell migration. Upon confirmation of the interactions between ANG and the three proteins, further studies revealed that ANG co-localized with β-actin and α-actinin 4 at the leading edge of migrating cells. Down-regulation of ANG resulted in fewer but thicker stress fibers with less dynamics, which was associated with the enlargements of focal adhesions. The focal adhesion kinase activity and cell migration capacity were significantly decreased in ANG-deficient cells. Taken together, our data demonstrated that the existence of ANG in the cytoplasm optimizes stress fiber assembly and focal adhesion formation to accommodate cell migration. The finding that ANG promoted cancer cell migration might provide new clues for tumor metastasis research.

  9. The effect of occupational stress, psychological stress and burnout on employee performance: Evidence from banking industry

    Directory of Open Access Journals (Sweden)

    Shahram Hashemnia

    2014-09-01

    Full Text Available This paper presents an empirical investigation on the effects of occupational stress, psychological stress as well as job burnout on women’s employee performance in city of Karaj, Iran. The proposed study designs a questionnaire in Likert scale and distributes it among all female employees who worked for Bank Maskan in this city. In our survey, employee performance consists of three parts of interpersonal performance, job performance as well as organizational performance. Cronbach alpha has been used to verify the overall questionnaire, all components were within acceptable levels, and the implementation of Kolmogorov-Smirnov test has indicated that the data were not normally distributed. Using Spearman correlation ratio as well as regression techniques, the study has determined that while psychological stress influenced significantly on all three components of employee performance including interpersonal performance, job performance as well as organizational performance, the effect on job performance was greater than the other components. In addition, occupational stress only influences on organizational as well as interpersonal performance. Finally, employee burnout has no impact on any components of employee performance.

  10. Neuroprotective effects of sildenafil against oxidative stress and memory dysfunction in mice exposed to noise stress.

    Science.gov (United States)

    Sikandaner, Hu Erxidan; Park, So Young; Kim, Min Jung; Park, Shi Nae; Yang, Dong Won

    2017-02-15

    Noise exposure has been well characterized as an environmental stressor, and is known to have auditory and non-auditory effects. Phosphodiesterase 5 (PDE5) inhibitors affect memory and hippocampus plasticity through various signaling cascades which are regulated by cGMP. In this study, we investigated the effects of sildenafil on memory deficiency, neuroprotection and oxidative stress in mice caused by chronic noise exposure. Mice were exposed to noise for 4h every day up to 14days at 110dB SPL of noise level. Sildenafil (15mg/kg) was orally administered 30min before noise exposure for 14days. Behavioral assessments were performed using novel object recognition (NOR) test and radial arm maze (RAM) test. Higher levels of memory dysfunction and oxidative stress were observed in noise alone-induced mice compared to control group. Interestingly, sildenafil administration increased memory performance, decreased oxidative stress, and increased neuroprotection in the hippocampus region of noise alone-induced mice likely through affecting memory related pathways such as cGMP/PKG/CREB and p25/CDK5, and induction of free radical scavengers such as SOD1, SOD2, SOD3, Prdx5, and catalase in the brain of stressed mice.

  11. Antioxidant Effects of Some Drugs on Immobilization Stress Combined with Cold Restraint Stress

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    Svetlana Trivic

    2009-11-01

    Full Text Available The aim of this work was to investigate the effect on antioxidant potential of some commonly used drugs (morphine, tramadol, bromocriptine, haloperidol and azithromycin on immobilization stress (IS combined with cold restraint stress (CRS in the rat. After the drug treatment the animals were kept immobilized in the cold chamber at 4±0.3ºC for 3 hours and then decapitaed and the livers were extracted. The following parameters were determined in the liver homogenate: content of reduced glutathione, activities of catalase, xanthine oxidase, glutathione reductase, glutathione peroxidase, peroxidase, and lipid peroxidation intensity. A battery of biochemical assays was used and the resulting data were statistically analyzed. Combined stress exhibited a prooxidative action (increased catalase activity, lowered content of reduced glutathione. Significantly enhanced catalase activity that was observed in all groups compared to the control indicates that the primary reactive oxygen species (ROS metabolite is hydrogen peroxide, which decomposes very rapidly (very high catalase activity, thus hindering formation of OH radicals as the most toxic ROS. None of the tested drugs showed a protective effect on combined IS and CRS. The intensity of lipid peroxidation did not change either in the combined stress or under additional influence of the drugs. Probably, under our experimental conditions, the time was not sufficiently long to observe damage of lipid membrane by ROS.

  12. Investigation of temperature effect on stress of flexspline

    Institute of Scientific and Technical Information of China (English)

    项青; 尹征南

    2014-01-01

    The effect of temperature loading on the stress of a flexspline is investigated. Based on the geometric and mechanical characteristics of the harmonic gear flexspline, a circular thin shell model is presented in this paper. The theoretical solution for the flexspline under different displacement loads and different temperature fields is derived. Meanwhile, an impact factor formula, which reflects the effect of the temperatures of the inner and outer surfaces of the flexspline on the stress of the flexspline, is presented. Finally, numerical calculations by the finite element method (FEM) are adopted to verify the corresponding conclusions.

  13. Effect of mindfulness-based stress reduction on sleep quality

    DEFF Research Database (Denmark)

    Andersen, Signe; Würtzen, Hanne; Steding-Jessen, Marianne;

    2013-01-01

    The prevalence of sleep disturbance is high among cancer patients, and the sleep problems tend to last for years after the end of treatment. As part of a large randomized controlled clinical trial (the MICA trial, NCT00990977) of the effect of mindfulness-based stress reduction (MBSR) on psycholo......The prevalence of sleep disturbance is high among cancer patients, and the sleep problems tend to last for years after the end of treatment. As part of a large randomized controlled clinical trial (the MICA trial, NCT00990977) of the effect of mindfulness-based stress reduction (MBSR...

  14. Effects of lifetime stress exposure on mental and physical health in young adulthood: How stress degrades and forgiveness protects health.

    Science.gov (United States)

    Toussaint, Loren; Shields, Grant S; Dorn, Gabriel; Slavich, George M

    2016-06-01

    To examine risk and resilience factors that affect health, lifetime stress exposure histories, dispositional forgiveness levels, and mental and physical health were assessed in 148 young adults. Greater lifetime stress severity and lower levels of forgiveness each uniquely predicted worse mental and physical health. Analyses also revealed a graded Stress × Forgiveness interaction effect, wherein associations between stress and mental health were weaker for persons exhibiting more forgiveness. These data are the first to elucidate the interactive effects of cumulative stress severity and forgiveness on health, and suggest that developing a more forgiving coping style may help minimize stress-related disorders.

  15. Effective temperature dynamics of shear bands in metallic glasses

    Science.gov (United States)

    Daub, Eric G.; Klaumünzer, David; Löffler, Jörg F.

    2014-12-01

    We study the plastic deformation of bulk metallic glasses with shear transformation zone (STZ) theory, a physical model for plasticity in amorphous systems, and compare it with experimental data. In STZ theory, plastic deformation occurs when localized regions rearrange due to applied stress and the density of these regions is determined by a dynamically evolving effective disorder temperature. We compare the predictions of STZ theory to experiments that explore the low-temperature deformation of Zr-based bulk metallic glasses via shear bands at various thermal temperatures and strain rates. By following the evolution of effective temperature with time, strain rate, and temperature through a series of approximate and numerical solutions to the STZ equations, we successfully model a suite of experimentally observed phenomena, including shear-band aging as apparent from slide-hold-slide tests, a temperature-dependent steady-state flow stress, and a strain-rate- and temperature-dependent transition from stick-slip (serrated flow) to steady-sliding (nonserrated flow). We find that STZ theory quantitatively matches the observed experimental data and provides a framework for relating the experimentally measured energy scales to different types of atomic rearrangements.

  16. Stress memory effect in viscoelastic stagnant lid convection

    Science.gov (United States)

    Patočka, V.; Čadek, O.; Tackley, P. J.; Čížková, H.

    2017-06-01

    Present thermochemical convection models of planetary evolution often assume a purely viscous or viscoplastic rheology. Ignoring elasticity in the cold, outer boundary layer is, however, questionable since elastic effects may play an important role there and affect surface topography as well as the stress distribution within the stiff cold lithosphere. Here we present a modelling study focused on the combined effects of Maxwell viscoelastic rheology and a free surface in the stagnant lid planetary convection. We implemented viscoelastic rheology in the StagYY code using a tracer-based stress advection scheme that suppresses subgrid oscillations. We apply this code to perform thermal convection models of the cooling planetary mantles and we demonstrate that while the global characteristics of the mantle flow do not change significantly when including viscoelasticity, the stress state of the cold lithosphere may be substantially different. Transient cooling of an initially thin upper thermal boundary layer results in a complex layered stress structure due to the memory effects of viscoelastic rheology. The stress state of the lid may thus contain a record of the planetary thermal evolution.

  17. Effect of Particle Size on Shear Stress of Magnetorheological Fluids

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    Chiranjit Sarkar

    2015-05-01

    Full Text Available Magnetorheological fluids (MRF, known for their variable shear stress contain magnetisable micrometer-sized particles (few micrometer to 200 micrometers in a nonmagnetic carrier liquid. To avoid settling of particles, smaller sized (3-10 micrometers particles are preferred, while larger sized particles can be used in MR brakes, MR clutches, etc. as mechanical stirring action in those mechanisms does not allow particles to settle down. Ideally larger sized particles provide higher shear stress compared to smaller sized particles. However there is need to explore the effect of particle sizes on the shear stress. In the current paper, a comparison of different particle sizes on MR effect has been presented. Particle size distributions of iron particles were measured using HORIBA Laser Scattering Particle Size Distribution Analyser. The particle size distribution, mean sizes and standard deviations have been presented. The nature of particle shapes has been observed using scanning electron microscopy. To explore the effect of particle sizes, nine MR fluids containing small, large and mixed sized carbonyl iron particles have been synthesized. Three concentrations (9%, 18% and 36% by volume for each size of particles have been used. The shear stresses of those MRF samples have been measured using ANTON PAAR MCR-102 Rheometer. With increase in volume fraction of iron particles, the MR fluids synthesized using “mixed sized particles” show better shear stress compared to the MR fluids containing “smaller sized spherical shaped particles” and “larger sized flaked shaped particles” at higher shear rate.

  18. Study of stress, self-esteem and depression in medical students and effect of music on perceived stress.

    Science.gov (United States)

    Baste, Vrushali S; Gadkari, Jayashree V

    2014-01-01

    Medical students are exposed to many stressors and if stress is perceived negatively or becomes excessive can affect academic performance and health adversely. The objective of this study was to assess stress, predominant stressor and effect of music on perceived stress. 90 undergraduate students were selected randomly. A written questionnaire about personal information, stressful factors, ways to cope up stress, Rosenberg self-esteem scale (Rosenberg, 1965) and 'Quick Inventory of Depressive Symptomatology' self-rated 16 (QIDS-SR-16) was given.45.6% Students had mild stress, 7.7% students had moderate stress and 1.1% students had severe stress. Academic factors were the predominant cause of stress in most students, followed by physical, social and emotional. On Rosenberg self-esteem scale (Rosenberg, 1965) 85.6% students had high self-esteem and on QIDS-SR16 50% students had depression. Effect of music on perceived stress was statistically significant. Medical curriculum is associated with increased stress in students. Music can be used as simple, inexpensive and effective therapy for stress.

  19. Dynamic triggering

    Science.gov (United States)

    Hill, David P.; Prejean, Stephanie; Schubert, Gerald

    2015-01-01

    Dynamic stresses propagating as seismic waves from large earthquakes trigger a spectrum of responses at global distances. In addition to locally triggered earthquakes in a variety of tectonic environments, dynamic stresses trigger tectonic (nonvolcanic) tremor in the brittle–plastic transition zone along major plate-boundary faults, activity changes in hydrothermal and volcanic systems, and, in hydrologic domains, changes in spring discharge, water well levels, soil liquefaction, and the eruption of mud volcanoes. Surface waves with periods of 15–200 s are the most effective triggering agents; body-wave trigger is less frequent. Triggering dynamic stresses can be < 1 kPa.

  20. Inactivation model equations and their associated parameter values obtained under static acid stress conditions cannot be used directly for predicting inactivation under dynamic conditions.

    Science.gov (United States)

    Janssen, M; Verhulst, A; Valdramidis, V; Devlieghere, F; Van Impe, J F; Geeraerd, A H

    2008-11-30

    Organic acids (e.g., lactic acid, acetic acid and citric acid) are popular preservatives. In this study, the Listeria innocua inactivation is investigated under dynamic conditions of pH and undissociated lactic acid ([LaH]). A combined primary (Weibull-type) and secondary model developed for the L. innocua inactivation under static conditions [Janssen, M., Geeraerd, A.H., Cappuyns, A., Garcia-Gonzalez, L., Schockaert, G., Van Houteghem, N., Vereecken, K.M., Debevere, J., Devlieghere, F., Van Impe, J.F., 2007. Individual and combined effects of pH and lactic acid concentration on L. innocua inactivation: development of a predictive model and assessment of experimental variability. Applied and Environmental Microbiology 73(5), 1601-1611] was applied to predict the microbial inactivation under dynamic conditions. Because of its non-autonomous character, two approaches were proposed for the application of the Weibull-type model to dynamic conditions. The results quantitatively indicated that the L. innocua cell population was able to develop an induced acid stress resistance under dynamic conditions of pH and [LaH]. From a modeling point of view, it needs to be stressed that (i) inactivation model equations and associated parameter values, derived under static conditions, may not be suitable for use as such under dynamic conditions, and (ii) non-autonomous dynamic models reveal additional technical intricacies in comparison with autonomous models.

  1. Evaluation of Flow-Induced Dynamic Stress and Vibration of Volute Casing for a Large-Scale Double-Suction Centrifugal Pump

    Directory of Open Access Journals (Sweden)

    Fu-Jun Wang

    2013-01-01

    Full Text Available The transient analysis was carried out to investigate the dynamic stress and vibration of volute casing for a large double-suction centrifugal pump by using the transient fluid-structure interaction theory. The flow pulsations at flow rate ranging from 60% to 100% of the nominal flow rate (Qd were taken as the boundary conditions for FEM analysis of the pump volute casing structure. The results revealed that, for all operating conditions, the maximum stress located at the volute tongue region, whereas the maximum vibration displacement happened close to the shaft hole region. It was also found that the blade passing frequency and its harmonics were dominant in the variations of dynamic stress and vibration displacement. The amplitude of the dominant frequency for the maximum stress detected at 0.6 Qd was 1.14 times that at Qd, lower than the related difference observed for pressure fluctuations (3.23 times. This study provides an effective method to quantify the flow-induced structural dynamic characteristics for a large-scale double-suction pump. It can be used to direct the hydraulic and structural design and stable operation, as well as fatigue life prediction for large-scale pumps.

  2. Effects of progressive muscle relaxation on postmenopausal stress

    Directory of Open Access Journals (Sweden)

    Arunima Chaudhuri

    2015-01-01

    Full Text Available Background: Menopause increases stress level among females and this may be a contributing factor in developing metabolic syndrome. Objectives: The objective of this study is to study the effects of progressive muscle relaxation on cardiorespiratory efficiency and autonomic functions in over weight and obese working stressed postmenopausal females. Materials and Methods: A total of 30 postmenopausal overweight or obese (body mass index [BMI]: 24.97 ± 1.28 females belonging to the age group 50-55 years were included. Stress level in the subjects was assessed according to the presumptive life event stress scale. The perceived stress scale (PSS of Sheldon Cohen was used for measuring the perception of stress. Fasting blood samples were collected to exclude diabetic subjects and analyze lipid profile. BMI and waist/hip ratio were calculated. Resting pulse rate and blood pressure, respiratory rate were measured. VO 2 max, physical fitness index, breath holding time and 40 mm endurance test time were calculated for estimation of cardiopulmonary efficiency. Autonomic function tests were carried. Subjects were given progressive muscle relaxation training for 3 months and all parameters were reevaluated. Data was analyzed using SPSS version 16 (SPSS Inc., Chicago, USA. Results: PSS in pre-training session was 26.16 ± 1.7 and in post-training session was 14.33 ± 2.01 and the difference was statistically significant. There was a significant decrease in pulse rate, blood pressure, BMI, waist/hip ratio, cholesterol, low-density lipoprotein following preventive medicine residency training. Results of autonomic function tests and cardiopulmonary efficiency test improved significantly following relaxation training. Conclusions: Increased stress levels may increase BMI and waist/hip ratio, dyslipidemia and lead to autonomic dysfunctions and increase incidence of cardiovascular disease in postmenopausal females. Lifestyle modification with relaxation exercises

  3. Stress and its effects on horses reproduction

    OpenAIRE

    Amal M. AboEl-Maaty

    2011-01-01

    A total of 90 mares and horses were subjected to blood sampling for determining the effect of management (farm), reproductive condition, sex, age, breed and month of the year during breeding on circulating levels of cortisol and sex hormones. Blood samples were collected from December to the following June from four farms. Blood sera underwent testosterone, estradiol, progesterone and cortisol assaying using ELISA kits. Cortisol levels were significantly low in lactating mares during their fo...

  4. Effects of Temperature and Strain Rate on Dynamic Properties of Concrete

    Institute of Scientific and Technical Information of China (English)

    JIA Bin; TAO Junlin; LI Zhengliang; WANG Ruheng; ZHANG Yu

    2008-01-01

    To study the dynamic properties of the concrete subjected to impulsive loading,stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB).Effects of temperature and strain rate on the dynamic yield strength and constitutive relation of the concrete were analyzed.The dynamic mechanical properties of the reinforced concrete are subjected to high strain rates when it is at a relatively low temperature.But with temperature increasing,the temperature softening effect makes the strength of the concrete weaken and the impact toughness of the concrete is saliently relative to strain rate effect.So,strain rate effect,strain hardening and temperature softening work together on the dynamic mechanical capability of concrete and the relation between them is relatively corn plex.

  5. FOXO3a regulates BNIP3 and modulates mitochondrial calcium, dynamics, and function in cardiac stress.

    Science.gov (United States)

    Chaanine, Antoine H; Kohlbrenner, Erik; Gamb, Scott I; Guenzel, Adam J; Klaus, Katherine; Fayyaz, Ahmed U; Nair, K Sreekumaran; Hajjar, Roger J; Redfield, Margaret M

    2016-12-01

    The forkhead box O3a (FOXO3a) transcription factor has been shown to regulate glucose metabolism, muscle atrophy, and cell death in postmitotic cells. Its role in regulation of mitochondrial and myocardial function is not well studied. Based on previous work, we hypothesized that FOXO3a, through BCL2/adenovirus E1B 19-kDa protein-interacting protein 3 (BNIP3), modulates mitochondrial morphology and function in heart failure (HF). We modulated the FOXO3a-BNIP3 pathway in normal and phenylephrine (PE)-stressed adult cardiomyocytes (ACM) in vitro and developed a cardiotropic adeno-associated virus serotype 9 encoding dominant-negative FOXO3a (AAV9.dn-FX3a) for gene delivery in a rat model of HF with preserved ejection fraction (HFpEF). We found that FOXO3a upregulates BNIP3 expression in normal and PE-stressed ACM, with subsequent increases in mitochondrial Ca(2+), leading to decreased mitochondrial membrane potential, mitochondrial fragmentation, and apoptosis. Whereas dn-FX3a attenuated the increase in BNIP3 expression and its consequences in PE-stressed ACM, AAV9.dn-FX3a delivery in an experimental model of HFpEF decreased BNIP3 expression, reversed adverse left ventricular remodeling, and improved left ventricular systolic and, particularly, diastolic function, with improvements in mitochondrial structure and function. Moreover, AAV9.dn-FX3a restored phospholamban phosphorylation at S16 and enhanced dynamin-related protein 1 phosphorylation at S637. Furthermore, FOXO3a upregulates maladaptive genes involved in mitochondrial apoptosis, autophagy, and cardiac atrophy. We conclude that FOXO3a activation in cardiac stress is maladaptive, in that it modulates Ca(2+) cycling, Ca(2+) homeostasis, and mitochondrial dynamics and function. Our results suggest an important role of FOXO3a in HF, making it an attractive potential therapeutic target. Copyright © 2016 the American Physiological Society.

  6. Effect of meditation on neurophysiological changes in stress mediated depression.

    Science.gov (United States)

    Kasala, Eshvendar Reddy; Bodduluru, Lakshmi Narendra; Maneti, Yogeshwar; Thipparaboina, Rajesh

    2014-02-01

    Meditation is a complex mental practice involving changes in sensory perception, cognition, hormonal and autonomic activity. It is widely used in psychological and medical practices for stress management as well as stress mediated mental disorders like depression. A growing body of literature has shown that meditation has profound effects on numerous physiological systems that are involved in the pathophysiology of major depressive disorder (MDD). Although meditation-based interventions have been associated with improvement in depressive symptoms and prevention of relapse, the physiological mechanisms underlying the therapeutic effects of meditation are not clearly defined and even paradoxical. This paper reviews many of the physiological abnormalities found in cytokine & stress mediated depression and the reversal of these anomalies by different meditation techniques.

  7. The effect of oxidative stress during exercise in the horse.

    Science.gov (United States)

    Williams, C A

    2016-10-01

    Oxidative stress is an imbalance of the oxidant-to-antioxidant ratio in the body. Increases in oxidative stress and changes in antioxidant status have been shown during endurance and intense exercise and eventing competition in horses. Antioxidants include vitamins, minerals, enzymes, and proteins that must be synthesized in the body or obtained from the diet. Therefore, exercise level and diet are both factors that play a role in influencing the oxidative stress and antioxidant status of the equine athlete. Along with exercise intensity and duration, diet, age, and training program can also affect oxidative stress in the horse. Several studies using exogenous supplementation of vitamin E, vitamin C, and alpha-lipoic acid have shown positive results in decreasing the effects of exercise (endurance and intense exercise)-induced oxidative stress and increasing the antioxidant status based on the markers and antioxidants measured, whereas other studies using superoxide dismutase showed little effects on the exercise horse. The "free radical theory of aging" states that long-term effects of the degenerative changes associated with aging may induce oxidative stress. However, in old horses (22 ± 2 yr), lipid peroxidation levels and blood antioxidant concentrations were similar to those found in younger but mature (12 ± 2 yr) horses both at rest and during exercise. Other studies found that yearlings (18 ± 2.4 mo) that are novel to forced exercise had less lipid peroxidation and greater antioxidant status than mature mares (13 ± 2.1 yr) prior to exercise training. Exercise training reduced oxidative stress markers and improved antioxidant status in mares, whereas few effects were seen in yearlings. This indicates that youth provided more defense against oxidative stress due to exercise than the exercise training program. Other studies during competition (endurance, jumping, eventing, and racing) have investigated the influence on oxidative stress with varying results

  8. Framing Effects: Dynamics and Task Domains

    Science.gov (United States)

    Wang

    1996-11-01

    The author examines the mechanisms and dynamics of framing effects in risky choices across three distinct task domains (i.e., life-death, public property, and personal money). The choice outcomes of the problems presented in each of the three task domains had a binary structure of a sure thing vs a gamble of equal expected value; the outcomes differed in their framing conditions and the expected values, raging from 6000, 600, 60, to 6, numerically. It was hypothesized that subjects would become more risk seeking, if the sure outcome was below their aspiration level (the minimum requirement). As predicted, more subjects preferred the gamble when facing the life-death choice problems than facing the counterpart problems presented in the other two task domains. Subjects' risk preference varied categorically along the group size dimension in the life-death domain but changed more linearly over the expected value dimension in the monetary domain. Framing effects were observed in 7 of 13 pairs of problems, showing a positive frame-risk aversion and negative frame-risk seeking relationship. In addition, two types of framing effects were theoretically defined and empirically identified. A bidirectional framing effect involves a reversal in risk preference, and occurs when a decision maker's risk preference is ambiguous or weak. Four bidirectional effects were observed; in each case a majority of subjects preferred the sure outcome under a positive frame but the gamble under a negative frame. In contrast, a unidirectional framing effect refers to a preference shift due to the framing of choice outcomes: A majority of subjects preferred one choice outcome (either the sure thing or the gamble) under both framing conditions, with positive frame augmented the preference for the sure thing and negative frame augmented the preference for the gamble. These findings revealed some dynamic regularities of framing effects and posed implications for developing predictive and testable

  9. Optimization Design of Structures Subjected to Transient Loads Using First and Second Derivatives of Dynamic Displacement and Stress

    Directory of Open Access Journals (Sweden)

    Qimao Liu

    2012-01-01

    Full Text Available This paper developed an effective optimization method, i.e., gradient-Hessian matrix-based method or second order method, of frame structures subjected to the transient loads. An algorithm of first and second derivatives of dynamic displacement and stress with respect to design variables is formulated based on the Newmark method. The inequality time-dependent constraint problem is converted into a sequence of appropriately formed time-independent unconstrained problems using the integral interior point penalty function method. The gradient and Hessian matrixes of the integral interior point penalty functions are also computed. Then the Marquardt's method is employed to solve unconstrained problems. The numerical results show that the optimal design method proposed in this paper can obtain the local optimum design of frame structures and sometimes is more efficient than the augmented Lagrange multiplier method.

  10. New insights into the tonoplast architecture of plant vacuoles and vacuolar dynamics during osmotic stress

    Directory of Open Access Journals (Sweden)

    Marty Francis

    2005-08-01

    Full Text Available Abstract Background The vegetative plant vacuole occupies >90% of the volume in mature plant cells. Vacuoles play fundamental roles in adjusting cellular homeostasis and allowing cell growth. The composition of the vacuole and the regulation of its volume depend on the coordinated activities of the transporters and channels localized in the membrane (named tonoplast surrounding the vacuole. While the tonoplast protein complexes are well studied, the tonoplast itself is less well described. To extend our knowledge of how the vacuole folds inside the plant cell, we present three-dimensional reconstructions of vacuoles from tobacco suspension cells expressing the tonoplast aquaporin fusion gene BobTIP26-1::gfp. Results 3-D reconstruction of the cell vacuole made possible an accurate analysis of large spanning folds of the vacuolar membrane under both normal and stressed conditions, and suggested interactions between surrounding plastids. Dynamic, high resolution 3-D pictures of the vacuole in tobacco suspension cells monitored under different growth conditions provide additional details about vacuolar architecture. The GFP-decorated vacuole is a single continuous compartment transected by tubular-like transvacuolar strands and large membrane surfaces. Cell culture under osmotic stress led to a complex vacuolar network with an increased tonoplast surface area. In-depth 3-D realistic inspections showed that the unity of the vacuole is maintained during acclimation to osmotic stress. Vacuolar unity exhibited during stress adaptation, coupled with the intimate associations of vacuoles with other organelles, suggests a physiological role for the vacuole in metabolism, and communication between the vacuole and organelles, respectively, in plant cells. Desiccation stress ensuing from PEG treatment generates "double" membrane structures closely linked to the tonoplast within the vacuole. These membrane structures may serve as membrane reservoirs for

  11. Effects of hemin and thermal stress exposure on JWA expression

    Institute of Scientific and Technical Information of China (English)

    ZHAO Ming; CHEN Rui; LI Aiping; ZHOU Jianwei

    2007-01-01

    To investigate the expression of JWA after hemin and (or) thermal stress exposure,we treated K562 (chronic myelogenous leukemia cells) cells with different doses of hemin and thermal stress using different exposure times.The expression of JWA protein was determined by Western blot analysis.Reverse transcription-polymerase chain reaction was carried out to determine JWA mRNA expression.JWA promoter transcription activity analysis was performed by chloramphenicol acetyl transferase-enzyme linked immunosorbent assay (CAT-ELISA).The expression of JWA protein was significantly increased by up to (3.23 +0.57) folds compared to the control in K562 cells after hemin treatment (50 μM for one week),and a similar pattern was observed in the cells after treatment with thermal stress (42℃) for 2 hours [increased by (8.00+ 1.73) folds].The expression of JWA mRNA was also significantly elevated by up to (1.37 + 0.06)folds in K562 cells treated with hemin (30 μM for 48 hours),and a similar regulatory pattern [increased by (1.87±0.13)folds] was observed with thermal stress exposure (42℃) for 30 minutes.However,a combined antagonistic effect was observed in the treatment of K562 cells with hemin (30 μM,48 h) followed by thermal stress (42℃,30 min).CAT-ELISA further confirmed that either hemin or thermal stress treatment could up-regulate JWA transcription activity,however,the effects could be counteracted partly by treatment with a combination of both.Hemin and thermal stress might regulate JWA expression via distinct intracellular signal transduction pathways.

  12. Re-conceptualizing stress: Shifting views on the consequences of stress and its effects on stress reactivity

    Science.gov (United States)

    Liu, Jenny J. W.

    2017-01-01

    Background The consequences of stress are typically regarded from a deficit-oriented approach, conceptualizing stress to be entirely negative in its outcomes. This approach is unbalanced, and may further hinder individuals from engaging in adaptive coping. In the current study, we explored whether negative views and beliefs regarding stress interacted with a stress framing manipulation (positive, neutral and negative) on measures of stress reactivity for both psychosocial and physiological stressors. Method Ninety participants were randomized into one of three framing conditions that conceptualized the experience of stress in balanced, unbalanced-negative or unbalanced-positive ways. After watching a video on stress, participants underwent a psychosocial (Trier Social Stress Test), or a physiological (CO2 challenge) method of stress-induction. Subjective and objective markers of stress were assessed. Results Most of the sampled population regarded stress as negative prior to framing. Further, subjective and objective reactivity were greater to the TSST compared to the CO2 challenge. Additionally, significant cubic trends were observed in the interactions of stress framing and stress-induction methodologies on heart rate and blood pressure. Balanced framing conditions in the TSST group had a significantly larger decrease in heart rate and diastolic blood pressure following stress compared to the positive and negative framing conditions. Conclusion Findings confirmed a deficit-orientation of stress within the sampled population. In addition, results highlighted the relative efficacy of the TSST compared to CO2 as a method of stress provocation. Finally, individuals in framing conditions that posited stress outcomes in unbalanced manners responded to stressors less efficiently. This suggests that unbalanced framing of stress may have set forth unrealistic expectations regarding stress that later hindered individuals from adaptive responses to stress. Potential

  13. Dynamic stall and 3D effects

    Energy Technology Data Exchange (ETDEWEB)

    Bjoerck, A.; Thor, S.E. [Aeronautical Research Inst. of Sweden, Bromma (Sweden)

    1996-12-01

    The JOULE II project `Dynamic stall and 3D effects` started in January 1994 and was completed in September 1995. The objective of the project has been to increase the understanding of the three-dimensional and unsteady aerodynamics of stall controlled HAWT`s. The objectives have also been to develop `engineering models` suitable for inclusion into aero-elastic codes. The project included the participation of 13 parties within Europe. This paper describes an overview of the work carried out within the project and key results. 3 refs, 4 figs

  14. Ultrastrong optomechanics incorporating the dynamical Casimir effect

    Science.gov (United States)

    Nation, P. D.; Suh, J.; Blencowe, M. P.

    2016-02-01

    We propose a superconducting circuit comprising a dc superconducting quantum interference device with a mechanically compliant arm embedded in a coplanar microwave cavity that realizes an optomechanical system with a degenerate or nondegenerate parametric interaction generated via the dynamical Casimir effect. For experimentally feasible parameters, this setup is capable of reaching the single-photon ultrastrong-coupling regime while simultaneously possessing a parametric coupling strength approaching the renormalized cavity frequency. This opens up the possibility of observing the interplay between these two fundamental nonlinearities at the single-photon level.

  15. Thermodynamic Cross-Effects from Dynamical Systems

    CERN Document Server

    Matyas, L; Vollmer, J; Matyas, Laszlo; Tel, Tamas; Vollmer, Jurgen

    1999-01-01

    We give a thermodynamically consistent description of simultaneous heat and particle transport, as well as of the associated cross-effects, in the framework of a chaotic dynamical system, a generalized multibaker map. Besides the density, a second field with appropriate source terms is included in order to mimic, after coarse graining, a spatial temperature distribution and its time evolution. A new expression is derived for the irreversible entropy production in a steady state, as the average of the growth rate of the relative density, a unique combination of the two fields.

  16. MULTIPLE SCATTERING AND DYNAMIC STRESS ANALYSIS OF ELASTIC WAVES IN A FIBER-REINFORCED COMPOSITE WITH INTERFACES

    Institute of Scientific and Technical Information of China (English)

    李凤明; 胡超; 徐敏强; 黄文虎

    2003-01-01

    Based on the theory of elastic dynamics,multiple scattering of elastic waves and dynamic stress concentrations in fiber-reinforced composite are studied.The analytical expressions of elastic waves in different regions are presented.The mode coefficients of elastic waves are determined in accordance with the continuous conditions of displacement and stress on the boundary of the multiinterfaces.By using the addition theorem of Hankel functions,the formula of scattered wave fields in different local coordinates are transformed into those in one local coordinate to determine the unknown coefficients and dynamic stress concentration factors (DSCFs).The influences of the distance between two inclusions,material properties and structural size on the DSCFs near the interfaces are analyzed.As examples,the numerical results of DSCFs near the interfaces for two kinds of fiber-reinforced composites are presented and discussed.

  17. High-Speed Imaging Reveals Opposing Effects of Chronic Stress and Antidepressants on Neuronal Activity Propagation through the Hippocampal Trisynaptic Circuit

    OpenAIRE

    Jens eStepan; Florian eHladky; Andrés eUribe; Florian eHolsboer; Schmidt, Mathias V.; Matthias eEder

    2015-01-01

    Antidepressants (ADs) are used as first-line treatment for most stress-related psychiatric disorders. The alterations in brain circuit dynamics that can arise from stress exposure and underlie therapeutic actions of ADs remain, however, poorly understood. Here, enabled by a recently developed voltage-sensitive dye imaging assay in mouse brain slices, we examined the impact of chronic stress and concentration-dependent effects of eight clinically used ADs (belonging to different chemical/funct...

  18. The effects of school systems, teacher internal characteristics, and students on vocational teacher stress

    OpenAIRE

    Adams, Elaine

    1996-01-01

    Job stress is a multidimensional phenomenon. The researcher sought to examine variables that cause vocational teachers to experience stress in their teaching occupations and to evaluate the effects of these related stressors. This research evaluated the relationships between school systems and vocational teacher stress, teacher internal characteristics and vocational teacher stress, and students and vocational teacher stress. It also analyzed vocational teacher stre...

  19. Simulation of bending stress variation in long buried thick-walled pipes under the earth’s movement using combined linear dynamics and beam theories

    Directory of Open Access Journals (Sweden)

    Salau Tajudeen A.O.

    2014-01-01

    Full Text Available This study reported a simulation approach to the understanding of the interactions between a buried pipe and the soil system by computing the bending stress variation of harmonically-excited buried pipes. The established principles of linear dynamics theory and simple beam theory were utilised in the analysis of the problem of buried pipe bending stress accumulation and its dynamics. With regards to the parameters that influence the bending stress variations, the most important are the isolation factor, uniform external load, and the corresponding limiting conditions. The simulated mathematical expressions, containing static and dynamic parameters of the buried pipe and earth, were coded in Fortran programming language and applied in the simulation experiment. The results obtained showed that harmonically-excited buried thick-walled pipe became stable and effective when the ratio of the natural frequency of vibration to the forced frequency is greater than 2.0, whenever the damped factor is used as the control parameter for the maximum bending stress. The mirror image of the stress variation produces variation in the location of the maximum bending stress in quantitative terms. The acceptable pipe materials for the simulated cases must have yield strength in bending greater than or equal to 13.95 MPa. The results obtained in this work fill a gap in the literature and will be useful to pipeline engineers and designers, as well as to environmental scientists in initialising and controlling environmental issues and policy formulation concerning the influence of buried pipe on the soil and water in the environment.

  20. Effect of road transport stress on Erthrocyte Osmotic Fragility (EOF ...

    African Journals Online (AJOL)

    olayemitoyin

    was conducted with the aim of investigating the effect of two and half hours of road ... concentration, glucose concentration and erythrocyte osmotic fragility using standard methods. ... that road transportation was stressful to the subjects and measurement of erythrocyte ... The study was conducted in the laboratory of Human.

  1. Problem solving moderates the effects of life event stress and chronic stress on suicidal behaviors in adolescence.

    Science.gov (United States)

    Grover, Kelly E; Green, Kelly L; Pettit, Jeremy W; Monteith, Lindsey L; Garza, Monica J; Venta, Amanda

    2009-12-01

    The present study examined the unique and interactive effects of stress and problem-solving skills on suicidal behaviors among 102 inpatient adolescents. As expected, life event stress and chronic stress each significantly predicted suicidal ideation and suicide attempt. Problem solving significantly predicted suicidal ideation, but not suicide attempt. Problem solving moderated the associations between life event stress and suicidal behaviors, as well as between chronic stress and suicidal ideation, but not chronic stress and suicide attempt. At high levels of stress, adolescents with poor problem-solving skills experienced elevated suicidal ideation and were at greater risk of making a nonfatal suicide attempt. The interactive effects decreased to non-significance after controlling for depressive symptoms and hopelessness. Clinical implications are discussed.

  2. Better executive function under stress mitigates the effects of recent life stress exposure on health in young adults.

    Science.gov (United States)

    Shields, Grant S; Moons, Wesley G; Slavich, George M

    2017-01-01

    Executive function is a neuropsychological construct that enables controlled cognitive processing, which has been hypothesized to enhance individuals' resilience to stress. However, little empirical work has directly examined how executive function under different conditions mitigates the negative effects of stress exposure on health. To address this issue, we recruited 110 healthy young adults and assessed their recent life stress exposure, executive function in either a stressful or non-stressful context, and current health complaints. Based on existing research, we hypothesized that individuals exhibiting better executive function following a laboratory-based stressor (but not a control task) would demonstrate weaker associations between recent stress exposure and health because they perceived recent life stressors as being less severe. Consistent with this hypothesis, better executive function during acute stress, but not in the absence of stress, was associated with an attenuated link between participants' recent life stress exposure and their current health complaints. Moreover, this attenuating effect was mediated by lesser perceptions of stressor severity. Based on these data, we conclude that better executive function under stress is associated with fewer health complaints and that these effects may occur by reducing individuals' perceptions of stressor severity. The data thus suggest the possibility of reducing stress-related health problems by enhancing executive function.

  3. Better executive function under stress mitigates the effects of recent life stress exposure on health in young adults

    Science.gov (United States)

    Shields, Grant S.; Moons, Wesley G.; Slavich, George M.

    2017-01-01

    Executive function is a neuropsychological construct that enables controlled cognitive processing, which has been hypothesized to enhance individuals’ resilience to stress. However, little empirical work has directly examined how executive function under different conditions mitigates the negative effects of stress exposure on health. To address this issue, we recruited 110 healthy young adults and assessed their recent life stress exposure, executive function in either a stressful or non-stressful context, and current health complaints. Based on existing research, we hypothesized that individuals exhibiting better executive function following a laboratory-based stressor (but not a control task) would demonstrate weaker associations between recent stress exposure and health because they perceived recent life stressors as being less severe. Consistent with this hypothesis, better executive function during acute stress, but not in the absence of stress, was associated with an attenuated link between participants’ recent life stress exposure and their current health complaints. Moreover, this attenuating effect was mediated by lesser perceptions of stressor severity. Based on these data, we conclude that better executive function under stress is associated with fewer health complaints and that these effects may occur by reducing individuals’ perceptions of stressor severity. The data thus suggest the possibility of reducing stress-related health problems by enhancing executive function. PMID:28114849

  4. Effect of intermediate principal stress on strength of soft rock under complex stress states

    Institute of Scientific and Technical Information of China (English)

    马宗源; 廖红建; 党发宁

    2014-01-01

    A series of numerical simulations of conventional and true triaxial tests for soft rock materials using the three-dimensional finite difference code FLAC3D were presented. A hexahedral element and a strain hardening/softening constitutive model based on the unified strength theory (UST) were used to simulate both the consolidated-undrained (CU) triaxial and the consolidated-drained (CD) true triaxial tests. Based on the results of the true triaxial tests simulation, the effect of the intermediate principal stress on the strength of soft rock was investigated. Finally, an example of an axial compression test for a hard rock pillar with a soft rock interlayer was analyzed using the two-dimensional finite difference code FLAC. The CD true triaxial test simulations for diatomaceous soft rock suggest the peak and residual strengths increase by 30%when the effect of the intermediate principal stress is taken into account. The axial compression for a rock pillar indicated the peak and residual strengths increase six-fold when the soft rock interlayer approached the vertical and the effect of the intermediate principal stress is taken into account.

  5. Effect of signal modulating noise in bistable stochastic dynamical systems

    Institute of Scientific and Technical Information of China (English)

    肖方红; 闫桂荣; 张新武

    2003-01-01

    The effect of signal modulating noise in bistable stochastic dynamical systems is studied.The concept of instan taneous steady state is proposed for bistable dynamical systems.By making a dynamical analysis of bistable stochastic systems,we find that global and local effect of signal modulating noise as well as stochastic resonance can occur in bistable dynamical systems on which both a weak sinusoidal signal and noise are forced.The effect is demonstrated by numerical simulation.

  6. Food stress causes sex-specific maternal effects in mites.

    Science.gov (United States)

    Walzer, Andreas; Schausberger, Peter

    2015-08-01

    Life history theory predicts that females should produce few large eggs under food stress and many small eggs when food is abundant. We tested this prediction in three female-biased size-dimorphic predatory mites feeding on herbivorous spider mite prey: Phytoseiulus persimilis, a specialized spider mite predator; Neoseiulus californicus, a generalist preferring spider mites; Amblyseius andersoni, a broad diet generalist. Irrespective of predator species and offspring sex, most females laid only one small egg under severe food stress. Irrespective of predator species, the number of female but not male eggs decreased with increasing maternal food stress. This sex-specific effect was probably due to the higher production costs of large female than small male eggs. The complexity of the response to the varying availability of spider mite prey correlated with the predators' degree of adaptation to this prey. Most A. andersoni females did not oviposit under severe food stress, whereas N. californicus and P. persimilis did oviposit. Under moderate food stress, only P. persimilis increased its investment per offspring, at the expense of egg number, and produced few large female eggs. When prey was abundant, P. persimilis decreased the female egg sizes at the expense of increased egg numbers, resulting in a sex-specific egg size/number trade-off. Maternal effects manifested only in N. californicus and P. persimilis. Small egg size correlated with the body size of daughters but not sons. Overall, our study provides a key example of sex-specific maternal effects, i.e. food stress during egg production more strongly affects the sex of the large than the small offspring.

  7. Effects of extracellular fiber architecture on cell membrane shear stress in a 3D fibrous matrix.

    Science.gov (United States)

    Pedersen, John A; Boschetti, Federica; Swartz, Melody A

    2007-01-01

    Interstitial fluid flow has been shown to affect the organization and behavior of cells in 3D environments in vivo and in vitro, yet the forces driving such responses are not clear. Due to the complex architecture of the extracellular matrix (ECM) and the difficulty of measuring fluid flow near cells embedded in it, the levels of shear stress experienced by cells in this environment are typically estimated using bulk-averaged matrix parameters such as hydraulic permeability. While this is useful for estimating average stresses, it cannot yield insight into how local matrix fiber architecture-which is cell-controlled in the immediate pericellular environment-affects the local stresses imposed on the cell surface. To address this, we used computational fluid dynamics to study flow through an idealized mesh constructed of a cubic lattice of fibers simulating a typical in vitro collagen gel. We found that, in such high porosity matrices, the fibers strongly affect the flow fields near the cell, with peak shear stresses up to five times higher than those predicted by the Brinkman equation. We also found that minor remodeling of the fibers near the cell surface had major effects on the shear stress profile on the cell. These findings demonstrate the importance of fiber architecture to the fluid forces on a cell embedded in a 3D matrix, and also show how small modifications in the local ECM can lead to large changes in the mechanical environment of the cell.

  8. Stress and its effects on horses reproduction

    Directory of Open Access Journals (Sweden)

    Amal M. AboEl-Maaty

    2011-11-01

    Full Text Available A total of 90 mares and horses were subjected to blood sampling for determining the effect of management (farm, reproductive condition, sex, age, breed and month of the year during breeding on circulating levels of cortisol and sex hormones. Blood samples were collected from December to the following June from four farms. Blood sera underwent testosterone, estradiol, progesterone and cortisol assaying using ELISA kits. Cortisol levels were significantly low in lactating mares during their foal heat but significantly high levels were recorded in both repeat breeder mares and horses used for racing. High and significant testosterone and estradiol levels were recorded in both stallions used for breeding especially after semen collection and early pregnant mares. Similar testosterone levels were recorded in both early pregnant mares and racing horses but high levels were recorded in stallions. Estradiol was high in both early pregnant and mares with endometritis but the highest levels were observed in stallions. Horses held in private farms had high cortisol levels compared to those of governmental farms. In contrast to mares, horses had low cortisol and high estradiol levels. Cortisol levels were high from April to June (Spring and early summer compared to its levels from December to March (Winter. Arab horses had low cortisol compared to native and imported foreign breeds. In conclusion, environmental condition, exercise, breed, management and the purpose of raising horses all are affecting its cortisol levels.

  9. Stress in Irish dentists: developing effective coping strategies.

    LENUS (Irish Health Repository)

    Rogers, Cathryn

    2012-02-01

    Recent research has highlighted the need to recognise occupation-specific risk factors contributing to stress and burnout. As health professionals, it is important for dentists to recognise the symptoms and the effects of stress on physical, psychological and professional well being. This article reviews the relevant scientific evidence, and provides practical cognitive psychological measures to guide improved well-being for dentists. Any stigma-related factors need to be acknowledged and addressed for the wellbeing of dentists and their patients, and the dental profession is well placed to provide leadership on this issue. Peer support is central to meeting this challenge.

  10. Effect of Upper Mantle Heterogeneities on Lithosphere Stresses and Topography

    Science.gov (United States)

    Osei Tutu, A.; Steinberger, B.; Rogozhina, I.; Sobolev, S. V.

    2016-12-01

    The orientation and magnitude of lithosphere stresses give us knowledge about most of the processes within the Earth that are not easy to observe. It has been established (Steinberger, Schmeling, and Marquart 2001) that large contribution of the forces producing lithosphere stresses have their source origination from the buoyancies of both the upper and lower mantle acting beneath the lithosphere. The contribution of the crustal thickness to the stresses has been estimated to be less than 10% (Steinberger et al. 2001) in most region and increases in areas with high gravitational potential energy like the Himalayas. In most of these studies, the effect of the crust was determined separately by computing the gravitational potential energy from the crust (Ghosh et al. 2013) and applied as correction. (Artyushkov 1973) showed that the inhomogeneous nature of the crust contribute to the stresses observed as against using constant lithosphere thickness in most studies, due to the complexities for implementing a variable lithosphere. We seek extend the approach of Ghosh et al. (2013) by coupling the Crust 1.0 (Laske et al. 2013) to a varaible lithosphere thickness in our numerical method. Using a 3D global lithosphere-asthenosphere model (Popov and Sobolev 2008) with visco-elasto-plastic rheology, coupled at 300 km depth to a mantle modeled with a spectral technique (Hager and O'Connell, 1981), we compute lithosphere stresses and topography. we compare our model with observations; the World Stress Map, Global Strain Rate Map and the observed topgraphy. We use S40RTS seismic tomography below 300 km depth, with radial viscosity distribution (Steinberger et al 2006). To account for all the heterogeneities in the upper mantle (300 km) we used different 3D temperatures models setups. The first model is the thermal lithosphere model (Artemieva and Mooney, 2001) in continental regions and assumes half-space cooling of sea floor with age (Müller et al. 2008) for oceans. For the

  11. Effects of Telecoupling on Global Vegetation Dynamics

    Science.gov (United States)

    Viña, A.; Liu, J.

    2016-12-01

    With the ever increasing trend in telecoupling processes, such as international trade, all countries around the world are becoming more interdependent. However, the effects of this growing interdependence on vegetation (e.g., shifts in the geographic extent and distribution) remain unknown even though vegetation dynamics are crucially important for food production, carbon sequestration, provision of other ecosystem services, and biodiversity conservation. In this study we evaluate the effects of international trade on the spatio-temporal trajectories of vegetation at national and global scales, using vegetation index imagery collected over more than three decades by the Advanced Very High Resolution Radiometer (AVHRR) satellite sensor series together with concurrent national and international data on international trade (and its associated movement of people, goods, services and information). The spatio-temporal trajectories of vegetation are obtained using the scale of fluctuation technique, which is based on the decomposition of the AVHRR image time series to obtain information on its spatial dependence structure over time. Similar to the correlation length, the scale of fluctuation corresponds to the range over which fluctuations in the vegetation index are spatially correlated. Results indicate that global vegetation has changed drastically over the last three decades. These changes are not uniform across space, with hotspots in active trading countries. This study not only has direct implications for understanding global vegetation dynamics, but also sheds important insights on the complexity of human-nature interactions across telecoupled systems.

  12. Bottleneck effects on the bidirectional crowd dynamics

    Science.gov (United States)

    Yang, Xiao-Xia; Dong, Hai-Rong; Yao, Xiu-Ming; Sun, Xu-Bin

    2016-12-01

    The bottleneck effect on bidirectional crowd dynamics is of great theoretical and practical significance, especially for the designing of corridors in public places, such as subway stations or airports. Based on the famous social force model, this paper investigates the bottleneck effects on the free flow dynamics and breakdown phenomenon under different scenarios, in which different corridor shapes and inflow ratios are considered simultaneously. Numerical simulation finds an interesting self-organization phenomenon in the bidirectional flow, a typical characteristic of such a phenomenon is called lane formation, and the existence of which is independent of the corridor’s shape and inflow rate. However, the pattern of the lane formed by pedestrian flow is related to the corridor’s shape, and the free flow efficiency has close relationship with the inflow rate. Specifically, breakdown phenomenon occurs when inflows from both sides of the corridor are large enough, which mostly originates from the bottleneck and then gradually spreads to the other regions. Simulation results further indicate that the leaving efficiency becomes low as breakdown occurs, and the degree of congestion is proportional to the magnitude of inflow. The findings presented in this paper match well with some of our daily observations, hence it is possible to use them to provide us with theoretical suggestions in design of infrastructures. Project supported jointly by the National Natural Science Foundation of China (Grant Nos. 61322307 and 2016YJS023).

  13. The dynamical Casimir effect generates entanglement

    Science.gov (United States)

    Felicetti, Simone; Sanz, Mikel; Lamata, Lucas; Romero, Guillermo; Johansson, Göran; Delsing, Per; Solano, Enrique

    2014-03-01

    The existence of vacuum fluctuations, i.e., the presence of virtual particles in empty space, represents one of the most distinctive results of quantum mechanics. It is also known, under the name of dynamical Casimir effect, that fast-oscillating boundary conditions can generate real excitations out of the vacuum fluctuations. Long-awaited, the first experimental demonstration of this phenomenon has been realized only recently, in the framework of superconducting circuits [C. M. Wilson et al. Nature 479, 376-379 (2011)]. In this contribution, we will discuss novel theoretical results, showing that the dynamical Casimir effect can be exploited to generate bipartite and multipartite entanglement among qubits. We will also present a superconducting circuit design which can feasibly implement the model considered with current technology. Our scheme is composed of a SQUID device side-coupled to two transmission line resonators, each one interacting with a superconducting qubit. Such proposal can be straightforwardly generalized to the multipartite case, and it can be scaled up to build strongly correlated cavity lattices for quantum simulation and quantum computation. The authors acknowledge support from Spanish MINECO FIS2012-36673-C03-02; UPV/EHU UFI 11/55;Basque Government IT472-10; SOLID, CCQED, PROMISCE and SCALEQIT EU projects.

  14. Dynamical Casimir effect for surface plasmon polaritons

    Energy Technology Data Exchange (ETDEWEB)

    Hizhnyakov, V.; Loot, A., E-mail: ardi.loot@ut.ee; Azizabadi, S.Ch.

    2015-02-20

    The emission of photon pairs by a metal–dielectric interface placed between the mirrors of the resonator and excited by a plane wave is considered. The excitation causes oscillations in time of the optical length of surface plasmon polaritons in the interface. This leads to the dynamical Casimir effect – the generation of pairs of surface plasmon polariton quanta, which transfer to photons outside the interface. In the case of a properly chosen interface, the yield of two-photon emission may exceed that of the usual spontaneous parametric down-conversion. - Highlights: • The theory of dynamical Casimir effect (DCE) in the metal–dielectric interface excited by a monochromatic wave is proposed. • It is shown that the field enhancement associated with surface plasmon polaritons strongly enhances the yield of the DCE. • The numerical calculations of the enhancement factor are made. • The scheme of experimental setup to observe the DCE in the metal–dielectric interface is proposed. • Additional methods to enhance the DCE in the metal–dielectric interface are discussed.

  15. The Effect of De-Stress Training Program on the Stress of Mothers With Slow Paced Children

    Directory of Open Access Journals (Sweden)

    Charmforoush Jalali

    2016-05-01

    Full Text Available Background Handicap is a critical factor with significant effects on family. Stress is the main result of such effects on parents. As a classical procedure, mothers have the major caregiving role to the child; therefore, they experience more stress than other members. Then, development program for stress management is essential. Objectives The current study aimed to develop and assess a de-stress training program on decreasing the stress of mothers with mentally retarded children. Materials and Methods The current study was a semi-experimental research with Follow-up. Study subjects included 20 mothers with slow paced children connected to a non-governmental organization (NGO of show paced children in Tehran, Iran. Mothers were randomly divided into experimental and control groups (10 cases in each group. All mothers responded to the parental stress scale used to measure mothers’ stress. Experimental group received de-stress training program for 13 sessions. Post-test was administered in session fourteenth and after one month the results were followed-up. Data were analyzed by univariate analysis of covariance (P < 0.01. Results Data presented a significant difference between the control and experiment groups. Also, results did not show a significant difference between the post-test and follow up. It means that the effect of training was persistent. Conclusions De-stress training program significantly decreased the stress of mothers with show paced children, and the training effect was persistent.

  16. [Effects of organic manure on wheat growth under lead stress].

    Science.gov (United States)

    Qiao, Sha-sha; Zhang, Yong-qing; Yang, Li-wen; Pei, Hong-bin; Sun, Hong-shuai

    2011-04-01

    A pot experiment was conducted to study the effects of organic manure on the wheat growth under different levels of lead stress. With increasing lead stress level, whether fertilization or not, the plant height, shoot dry mass, adventitious root number, root total length, root dry mass, root activity, root total and active absorbing area, and root SOD and POD activities decreased, and root MDA content presented an increasing trend. The decrement of the above-mentioned parameters differed with fertilization treatments. Applying organic manure mitigated the impact of lead stress on wheat growth to some extent, delayed the senescence of wheat roots, and promoted root development and growth, ultimately leading to the increase of wheat yield and the decrease of lead content in grain.

  17. The effect of acute and chronic stress on growth.

    Science.gov (United States)

    Sävendahl, Lars

    2012-10-23

    Impaired bone growth is observed in many children exposed to stress, but whether the underlying cause is psychological or secondary to a variety of chronic disorders is unclear. The growth plate is specifically targeted by stress through many different mechanisms, including increased serum concentrations of proinflammatory cytokines and cortisol, as well as impaired actions of the growth hormone (GH)-insulin-like growth factor-1 (IGF-1) axis. Both glucocorticoids, such as cortisol, and proinflammatory cytokines adversely affect several aspects of chondrogenesis in the growth plate, and these effects can be ameliorated by raising local IGF-1 concentrations. However, this intervention does not completely normalize growth. In children with stress related to chronic inflammation, the cornerstone of improving stress-impaired growth remains the judicious use of glucocorticoids while ensuring effective control of the disease process. Specific immunomodulatory therapy that targets the actions of tumor necrosis factor-α (TNFα) is at least partially effective at rescuing linear growth in many children with juvenile idiopathic arthritis (JIA). Patients who do not respond to anti-TNF treatment may be candidates for therapeutic agents that target other proinflammatory cytokines and for GH intervention. Although GH treatment rescues linear growth in some patients with JIA, it is unknown whether GH can rescue growth in those patients who do not respond to anticytokine therapy. Further experimental and clinical studies are needed to explore these and other new potential treatment strategies that could improve bone growth in patients who do not respond to conventional therapy.

  18. The Effect of Oxidative Stress and Antioxidants on Men Fertility

    Directory of Open Access Journals (Sweden)

    Abolfazl Akbari

    2013-07-01

    Full Text Available Background: Various factors affects men fertility and oxidative stress as an important factor which affects fertility has recently got great concern. Oxidative stress refers to conditions of imbalance between productions of reactive oxygen species (ROS and antioxidant defense mechanism. Reactive species of oxygen, free radicals and peroxide are produced in the cell when metabolism of oxygen is incomplete in the mitochondrial respiratory chain.Materials and Methods: In this review we will consider effect of oxidative stress on male fertility and the principal antioxidant defences.Results: Factors such as hypoxia, cytokines, growth factors, chemotherapy, radio frequency waves and UV radiation can increase ROS production. Oxidative stress as one of the strongest physiological factors can lead to damage of sperm and reduction of seminal plasma quality and thereby cause infertility in men. Enzymatic and non-enzymatic defences inhibit oxidant attack. The enzymatic defense include: superoxide dismutases, glutathione peroxidases, and catalase. The non-enzymatic defences include ascorbate (vitamin C and a-tocopherol (vitamin E, beta carotene, and albumin, which neutralize free radicals. Conclusion: Oxidative stress affects male fertility through induction of lipid peroxidation, inactivation of proteins, impair of sperm motility and DNA damage.

  19. Effect of thermal stresses on the mechanism of tooth pain.

    Science.gov (United States)

    Oskui, Iman Z; Ashtiani, Mohammed N; Hashemi, Ata; Jafarzadeh, Hamid

    2014-11-01

    Daily hot and cold thermal loadings on teeth may result in structural deformation, mechanical stress, and pain signaling. The aim of this study was to compare the adverse effects of hot and cold beverages on an intact tooth and, then, to provide physical evidence to support the hydrodynamic theory of tooth pain sensation mechanism. Three-dimensional finite element analysis was performed on a premolar model subjected to hot and cold thermal loadings. Elapsed times for heat diffusion and stress detection at the pulp-dentin junction were calculated as measures of the pain sensation. Extreme tensile stress within the enamel resulted in damage in cold loadings. Also, extreme values of stress at the pulpal wall occurred 21.6 seconds earlier than extreme temperatures in hot and cold loadings. The intact tooth was remarkably vulnerable to cold loading. Earlier changes in mechanical stress rather than temperature at the pulp-dentin junction indicate that the dental pain caused by hot or cold beverages may be based on the hydrodynamic theory. Copyright © 2014 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  20. Investigating The Effect Of Job Stress On Performance Of Employees

    Directory of Open Access Journals (Sweden)

    Oyungerel Altangerel

    2015-02-01

    Full Text Available Abstract This study is conducted to investigate the effect of job stress on job performance. A random sampling technique is used to collect primary data of 120 employees of four telecommunication companies of Mongolia i.e. Mobicom Unitel Skytel and G-mobile. A well-structured questionnaire is utilized to collect relevant data descriptive and logistic analysis is used to estimate and describe the findings of results. It is found that work overload is major reason of stress among employees and majority of employees reduce their productivity and loss of interest in job due to stress. As for concern health issue eyes strain dizziness and disorder in sleep are due to job stress. According to results of logit model parameters of education experience and salary per month are statistically significant and have positive impact on employees performance but age family size no relaxation time giving to employees during working hours and work overload are statistically significant and have negative impact on employees job performance. For suggestions companies should increase salaries of employees and give reward to employees those have work overload. Workload of employees should reduce by proper work redesign and efficient management by proper allocation of job. It is also found that stress also becomes reason of several illnesses and majority of employees dont have medical facilities first aid at working place therefore it is suggested that companies should also provide medical facilities first aid for employees at work place.

  1. Split Node and Stress Glut Methods for Dynamic Rupture Simulations in Finite Elements.

    Science.gov (United States)

    Ramirez-Guzman, L.; Bielak, J.

    2008-12-01

    I present two numerical techniques to solve the Dynamic problem. I revisit and modify the Split Node approach and introduce a Stress Glut type Method. Both algorithms are implemented using a iso/sub- parametric FEM solver. In the first case, I discuss the formulation and perform an analysis of convergence for different orders of approximation for the acoustic case. I describe the algorithm of the second methodology as well as the assumptions made. The key to the new technique is to have an accurate representation of the traction. Thus, I devote part of the discussion to analyze the tractions for a simple example. The sensitivity of the method is tested by comparing against Split Node solutions.

  2. The Effects of Weather Sensitivity on Stressed Personnel

    Science.gov (United States)

    1981-06-01

    AD P002928 THE EFFECTS OF WEATHER SENSITIVITY ON STRESSED PERSONNEL DR, CHARLES WALLACH Decisions and Designs, Inc. 8400 Westpark Drive McLean, VA...meteorologist on his staff. But weather effects are transitory and seldom comform to the order of battle, although it might be useful to keep them in mind...is only one of many in- stances--in the Spring of 1978 I was invited to make ion mpasurements in the Defense Nuclear Agency office suite occupied by

  3. Coarse-graining scheme for simulating uniaxial stress-strain response of glassy polymers through molecular dynamics.

    Science.gov (United States)

    Majumder, Manoj K; S, Ramkumar; Mahajan, Dhiraj K; Basu, Sumit

    2010-01-01

    Simulation of the deformation of polymers below their glass transition through molecular dynamics provides an useful route to correlate their molecular architecture to deformation behavior. However, present computational capabilities severely restrict the time and length scales that can be simulated when detailed models of these macromolecules are used. Coarse-graining techniques for macromolecular structures intend to make bigger and longer simulations possible by grouping atoms into superatoms and devising ways of determining reasonable force fields for the superatoms in a manner that retains essential macromolecular features relevant to the process under study but jettisons unnecessary details. In this work we systematically develop a coarse-graining scheme aimed at simulating uniaxial stress-strain behavior of polymers below their glass transition. The scheme involves a two step process of obtaining the coarse grained force field parameters above glass transition. This seems to be enough to obtain "faithful" stress-strain responses after quenching to below the glass transition temperature. We apply the scheme developed to a commercially important polymer polystyrene, derive its complete force field parameters and thus demonstrate the effectiveness of the technique.

  4. Spin-0 to Spin-1/2 Deterministic Dynamics: From Relativistic Quantum Potential to Quantum Stress Tensor

    CERN Document Server

    Bartley, David L

    2016-01-01

    The Bohm/de Broglie theory of deterministic non-relativistic quantum mechanics is broadened to accommodate the free-particle Dirac equation. As with the spin-0 theory, an effective particle rest-mass scalar field in the presence of the spin-1/2 pilot wave is allowed, together with the assumption that the convective current component describes ensemble dynamics. Non-positive excursions of the ensemble density for extreme cases of positive-energy solutions of the Dirac equation are interpreted in terms of virtual-like pair creation and annihilation beneath the Compton wavelength. A specific second-rank tensor is defined in terms of the Dirac spinors for generalizing from simply a quantum potential to a stress tensor required to account for the force of pilot wave on particle. A simple dependence of the stress tensor on a two-component spin pseudovector field is determined. Consistency is found with an earlier non-relativistic theory of objects with spin.

  5. Microsecond molecular dynamics simulations of intrinsically disordered proteins involved in the oxidative stress response.

    Directory of Open Access Journals (Sweden)

    Elio A Cino

    Full Text Available Intrinsically disordered proteins (IDPs are abundant in cells and have central roles in protein-protein interaction networks. Interactions between the IDP Prothymosin alpha (ProTα and the Neh2 domain of Nuclear factor erythroid 2-related factor 2 (Nrf2, with a common binding partner, Kelch-like ECH-associated protein 1(Keap1, are essential for regulating cellular response to oxidative stress. Misregulation of this pathway can lead to neurodegenerative diseases, premature aging and cancer. In order to understand the mechanisms these two disordered proteins employ to bind to Keap1, we performed extensive 0.5-1.0 microsecond atomistic molecular dynamics (MD simulations and isothermal titration calorimetry experiments to investigate the structure/dynamics of free-state ProTα and Neh2 and their thermodynamics of bindings. The results show that in their free states, both ProTα and Neh2 have propensities to form bound-state-like β-turn structures but to different extents. We also found that, for both proteins, residues outside the Keap1-binding motifs may play important roles in stabilizing the bound-state-like structures. Based on our findings, we propose that the binding of disordered ProTα and Neh2 to Keap1 occurs synergistically via preformed structural elements (PSEs and coupled folding and binding, with a heavy bias towards PSEs, particularly for Neh2. Our results provide insights into the molecular mechanisms Neh2 and ProTα bind to Keap1, information that is useful for developing therapeutics to enhance the oxidative stress response.

  6. Transcriptional dynamics of immune, growth and stress related genes in skeletal muscle of the fine flounder (Paralichthys adpersus) during different nutritional statuses.

    Science.gov (United States)

    Valenzuela, Cristián A; Escobar, Daniela; Perez, Lorena; Zuloaga, Rodrigo; Estrada, Juan Manuel; Mercado, Luis; Valdés, Juan Antonio; Molina, Alfredo

    2015-11-01

    The effects of stress on immune activity and growth in early vertebrates have not been studied in detail. The present study used fine flounder (Paralichthys adspersus) skeletal muscle as a model to evaluate molecules involved in the stress response, including the glucocorticoid receptors, foxo1/3, and the target genes of these. Additionally, immune markers (il-1β and tnfα) and effector molecules of atrophy (bnip3, caspase-3, and lc3) were assessed. These molecules were analyzed during periods of long-term fasting and refeeding. During fasting, gene expression related to the stress response and atrophy increased; whereas immune markers were down-regulated. During refeeding, atrophy- and stress-related gene expression significantly decreased. In contrast, immune markers were up-regulated. These results provide novel insight on the control of growth in the skeletal muscle of a non-mammalian species under a stressful condition, suggesting that growth, stress, and immune activity in muscle are closely related and coordinated by orchestrated transcriptional dynamics.

  7. CROSS-EFFECTS OF ADAPTATION TO STRESS SITUATIONS

    Directory of Open Access Journals (Sweden)

    Alexey Viktorovich MESHCHERYAKOV

    2015-01-01

    Full Text Available To counteract the stress it is necessary to study its effect on the internal condition of the body. The level of achievements in various sports and employments is determined by the exhaust motor programs that are improved in the process of trainings, ensuring the achievement of high results and reducing the mental and energy losses. Adaptation to short-term impacts of the stressor naturally leads to increased physiological capacity of the sympathetic-adrenal regulation. The recruitment of this regulatory system is an essential and absolute link of adaptation to the effects of environmental factors. It can be affirmed that adaptation to extreme situations increases the resistance not only to separate factors but to all factors affecting the body. Thus, adaptation has a positive cross-effect. We believe it is important to assess the possible impacts of the elaborated methodology on the development of the vestibular apparatus that includes cross-effects of adaptation to stress situations on the readiness of athletes. The article presents conclusions about the possibilities to improve the coordination abilities of athletes through targeted effect on their special preparedness by the original methods which intensify the effects of adaptation to stress situations. The changes were assessed based on the data obtained using a stabilometric platform. 

  8. A three-dimensional computational fluid dynamics model of shear stress distribution during neotissue growth in a perfusion bioreactor.

    Science.gov (United States)

    Guyot, Y; Luyten, F P; Schrooten, J; Papantoniou, I; Geris, L

    2015-12-01

    Bone tissue engineering strategies use flow through perfusion bioreactors to apply mechanical stimuli to cells seeded on porous scaffolds. Cells grow on the scaffold surface but also by bridging the scaffold pores leading a fully filled scaffold following the scaffold's geometric characteristics. Current computational fluid dynamic approaches for tissue engineering bioreactor systems have been mostly carried out for empty scaffolds. The effect of 3D cell growth and extracellular matrix formation (termed in this study as neotissue growth), on its surrounding fluid flow field is a challenge yet to be tackled. In this work a combined approach was followed linking curvature driven cell growth to fluid dynamics modeling. The level-set method (LSM) was employed to capture neotissue growth driven by curvature, while the Stokes and Darcy equations, combined in the Brinkman equation, provided information regarding the distribution of the shear stress profile at the neotissue/medium interface and within the neotissue itself during growth. The neotissue was assumed to be micro-porous allowing flow through its structure while at the same time allowing the simulation of complete scaffold filling without numerical convergence issues. The results show a significant difference in the amplitude of shear stress for cells located within the micro-porous neo-tissue or at the neotissue/medium interface, demonstrating the importance of taking along the neotissue in the calculation of the mechanical stimulation of cells during culture.The presented computational framework is used on different scaffold pore geometries demonstrating its potential to be used a design as tool for scaffold architecture taking into account the growing neotissue. Biotechnol. Bioeng. 2015;112: 2591-2600. © 2015 Wiley Periodicals, Inc.

  9. Stress during pregnancy alters temporal and spatial dynamics of the maternal and offspring microbiome in a sex-specific manner

    Science.gov (United States)

    Jašarević, Eldin; Howard, Christopher D.; Misic, Ana M.; Beiting, Daniel P.; Bale, Tracy L.

    2017-01-01

    The microbiome is a regulator of host immunity, metabolism, neurodevelopment, and behavior. During early life, bacterial communities within maternal gut and vaginal compartments can have an impact on directing these processes. Maternal stress experience during pregnancy may impact offspring development by altering the temporal and spatial dynamics of the maternal microbiome during pregnancy. To examine the hypothesis that maternal stress disrupts gut and vaginal microbial dynamics during critical prenatal and postnatal windows, we used high-resolution 16S rRNA marker gene sequencing to examine outcomes in our mouse model of early prenatal stress. Consistent with predictions, maternal fecal communities shift across pregnancy, a process that is disrupted by stress. Vaginal bacterial community structure and composition exhibit lasting disruption following stress exposure. Comparison of maternal and offspring microbiota revealed that similarities in bacterial community composition was predicted by a complex interaction between maternal body niche and offspring age and sex. Importantly, early prenatal stress influenced offspring bacterial community assembly in a temporal and sex-specific manner. Taken together, our results demonstrate that early prenatal stress may influence offspring development through converging modifications to gut microbial composition during pregnancy and transmission of dysbiotic vaginal microbiome at birth. PMID:28266645

  10. Dynamic and shear stress rheological properties of guar galactomannans and its hydrolyzed derivatives.

    Science.gov (United States)

    Hussain, Majid; Bakalis, Serafim; Gouseti, Ourania; Zahoor, Tahir; Anjum, Faqir Muhammad; Shahid, Muhammad

    2015-01-01

    Guar galactomannan from seed of Cyamopsis tetragonolobus was hydrolyzed using acid (HCl), base [Ba(OH)2] and enzyme (mannanase) method to obtain depolymerized substances with possible functional applications as soluble dietary fiber. Rheological behavior of crude, purified, and depolymerized guar gum solutions was studied at 25 °C, using shear stress and dynamic oscillatory measurements, performed with controlled stress rheometer Bohlin CVO (Malvern Instruments) fitted with cone-and-plate geometry. The various guar gums solutions with different viscosities exhibited shear-thinning behavior at high shear rate and Newtonian behavior at low shear rate. At low shear rate, sigma crude guar gum (SCGG), crude guar gum (CGG), acid hydrolyzed guar gum (AHGG) and enzyme hydrolyzed guar gum (EHGG) exhibited viscosities of 18.59, 1.346, 0.149 and 0.022 Pas, respectively. Oscillatory experiments (G", G') of gums solutions showed typical behavior of weak viscoelastic gel. All investigated guar gums were further used for glucose bio-accessibility using a novel in vitro small intestinal model (SIM). All gums solutions resulted in 20% reduction in simulated glucose absorption, indicating a non-significant functionality difference between various guar gums. So, it can be concluded that hydrolyzed guar gums without disturbing their rheological and physiological behavior would be useful for incorporation in various food products as soluble dietary fiber.

  11. Dynamically regulated sumoylation of HDAC2 controls p53 deacetylation and restricts apoptosis following genotoxic stress

    Institute of Scientific and Technical Information of China (English)

    André Brandl; Tobias Wagner; Katharina M. Uhlig; Shirley K. Knauer; Roland H. Stauber; Frauke Melchior; Günter Schneider; Thorsten Heinzel; Oliver H. Kr(a)mer

    2012-01-01

    Histone deacetylase 2 (HDAC2) is relevant for homeostasis and plays a critical role in gastrointestinal cancers.Here,we report that post-translational modification of endogenous HDAC2 with small ubiquitin-related modifier 1 (SUMO1) is a new regulatory switch for the tumor suppressor p53.Sumoylation of HDAC2 at lysine 462 allows binding of HDAC2 to p53.Moreover,sumoylated HDAC2 is a previously not recognized biologically relevant site-specific deacetylase for p53.Deacetylation of p53 at lysine 320 by sumoylated HDAC2 blocks recruitment of p53 into promoter-associated complexes and p53-dependent expression of genes for cell cycle control and apoptosis.Thereby,catalytically active sumoylated HDAC2 restricts p53 functions and attenuates DNA damage-induced apoptosis.Genotoxic stress evokes desumoylation of HDAC2,enabling p53-dependent gene expression,Our data show a new molecular mechanism involving a dynamically controlled HDAC2-sumoylation/p53-acetylation switch that regulates cell fate decisions following genotoxic stress.

  12. Memory function after stress : the effects of acute stress and cortisol on memory and the inhibition of emotional distraction

    NARCIS (Netherlands)

    Oei, Nicole Yü Lan

    2010-01-01

    The present thesis contains five experimental studies into the effects of stress on memory I healthy males. Hydrocortisone (and propranolol) administration or the induction of social stress are used to heighten cortisol levels, and consequently to study its effects on working memory performance and

  13. Memory function after stress : the effects of acute stress and cortisol on memory and the inhibition of emotional distraction

    NARCIS (Netherlands)

    Oei, Nicole Yü Lan

    2010-01-01

    The present thesis contains five experimental studies into the effects of stress on memory I healthy males. Hydrocortisone (and propranolol) administration or the induction of social stress are used to heighten cortisol levels, and consequently to study its effects on working memory performance and

  14. Stress

    DEFF Research Database (Denmark)

    Keller, Hanne Dauer

    2015-01-01

    Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb.......Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb....

  15. Stress

    DEFF Research Database (Denmark)

    Keller, Hanne Dauer

    2015-01-01

    Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb.......Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb....

  16. The Relevance of the Dynamic Stall Effect for Transient

    DEFF Research Database (Denmark)

    Jauch, Clemens; Sørensen, Poul; Bak-Jensen, Birgitte

    2005-01-01

    This article describes a methodology to quantify the influence of dynamic stall on transient fault operations of active-stall turbines. The model of the dynamic stall effect is introduced briefly. The behaviour of the dynamic stall model during a transient fault operation is described...... mathematically, and from this its effect quantified. Two quantities are chosen to describe the influence of the dynamic stall effect: one is active power and the other is time delay. Subsequently a transient fault scenario is simulated with and without the dynamic stall effect and the differences discussed. From...... this comparison, the conclusion is drawn that the dynamic stall effect has some influence on the post-fault behaviour of the wind turbine, and it is hence suggested that the dynamic stall effect is considered if an active-stall wind turbine is to be modelled realistically....

  17. Amygdala-Hippocampal Connectivity Changes During Acute Psychosocial Stress: Joint Effect of Early Life Stress and Oxytocin.

    Science.gov (United States)

    Fan, Yan; Pestke, Karin; Feeser, Melanie; Aust, Sabine; Pruessner, Jens C; Böker, Heinz; Bajbouj, Malek; Grimm, Simone

    2015-11-01

    Previous evidence shows that acute stress changes both amygdala activity and its connectivity with a distributed brain network. Early life stress (ELS), especially emotional abuse (EA), is associated with altered reactivity to psychosocial stress in adulthood and moderates or even reverses the stress-attenuating effect of oxytocin (OXT). The neural underpinnings of the interaction between ELS and OXT remain unclear, though. Therefore, we here investigate the joint effect of ELS and OXT on transient changes in amygdala-centered functional connectivity induced by acute psychosocial stress, using a double-blind, randomized, placebo-controlled, within-subject crossover design. Psychophysiological interaction analysis in the placebo session revealed stress-induced increases in functional connectivity between amygdala and medial prefrontal cortex, posterior cingulate cortex, putamen, caudate and thalamus. Regression analysis showed that EA was positively associated with stress-induced changes in connectivity between amygdala and hippocampus. Moreover, hierarchical linear regression showed that this positive association between EA and stress-induced amygdala-hippocampal connectivity was moderated after the administration of intranasal OXT. Amygdala-hippocampal connectivity in the OXT session correlated negatively with cortisol stress responses. Our findings suggest that altered amygdala-hippocampal functional connectivity during psychosocial stress may have a crucial role in the altered sensitivity to OXT effects in individuals who have experienced EA in their childhood.

  18. [The role of individual stress resistance in realization of immobilization and zoosocial stress effects on pulmonary surfactant system].

    Science.gov (United States)

    Vasil'eva, N N; Bryndina, I G

    2012-07-01

    The aim of the present study was to investigate the effect of chronic exposure to immobilization and psychosocial stress on surface activity, biochemical composition of pulmonary surfactant and lung fluid balance of rats with different stress-resistance. It is shown that both types of stress lead to elevation of lysophospholipids level and decrease of surface-active properties of pulmonary surfactant, more prominent in stress-vulnerable rats. Blood supply was decreased and extravascular fluid was increased under the psychosocial stress only in stress-vulnerable animals, in all rest cases the blood supply was increased and the content of extravascular fluid was not changed. Surfactant alteration was coupled on the level of 11-OCS in the blood and amount of fluid in the lungs. The obtained results indicate that different degree of impairment in the pulmonary surfactant system during immobilization and psychosocial conflicts depends on different resistance to emotional stress.

  19. Inverse strain rate effect on cyclic stress response in annealed Zircaloy-2

    Energy Technology Data Exchange (ETDEWEB)

    Sudhakar Rao, G.; Verma, Preeti [Center of Advanced Study, Department of Metallurgical Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India); Chakravartty, J.K. [Mechanical Metallurgy Group, Bhabha Atomic Research Center, Trombay 400 085, Mumbai (India); Nudurupati, Saibaba [Nuclear Fuel Complex, Hyderabad 500 062 (India); Mahobia, G.S.; Santhi Srinivas, N.C. [Center of Advanced Study, Department of Metallurgical Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India); Singh, Vakil, E-mail: vsingh.met@itbhu.ac.in [Center of Advanced Study, Department of Metallurgical Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India)

    2015-02-15

    Low cycle fatigue behavior of annealed Zircaloy-2 was investigated at 300 and 400 °C at different strain amplitudes and strain rates of 10{sup −2}, 10{sup −3}, and 10{sup −4} s{sup −1}. Cyclic stress response showed initial hardening with decreasing rate of hardening, followed by linear cyclic hardening and finally secondary hardening with increasing rate of hardening for low strain amplitudes at both the temperatures. The rate as well the degree of linear hardening and secondary hardening decreased with decrease in strain rate at 300 °C, however, there was inverse effect of strain rate on cyclic stress response at 400 °C and cyclic stress was increased with decrease in strain rate. The fatigue life decreased with decrease in strain rate at both the temperatures. The occurrence of linear cyclic hardening, inverse effect of strain rate on cyclic stress response and deterioration in fatigue life with decrease in strain rate may be attributed to dynamic strain aging phenomena resulting from enhanced interaction of dislocations with solutes. Fracture surfaces revealed distinct striations, secondary cracking, and oxidation with decrease in strain rate. Deformation substructure showed parallel dislocation lines and dislocation band structure at 300 °C. Persistent slip band wall structure and development of fine Corduroy structure was observed at 400 °C.

  20. Experimental study of the stress effect on attenuation of normally incident P-wave through coal

    Science.gov (United States)

    Feng, Junjun; Wang, Enyuan; Chen, Liang; Li, Xuelong; Xu, Zhaoyong; Li, Guoai

    2016-09-01

    The purpose of this study is to experimentally investigate the stress effect on normally incident P-wave attenuation through coal specimens. Laboratory tests were carried out using a Split Hopkinson pressure bar (SHPB) system, and a modified method was proposed to determine the quality factor (Q) of P-waves through coal specimens. Larger quality factor denotes less energy attenuated during P-wave propagating through coal. Experimental results indicate that the quality factor and stress (σ) within coal specimens are positively correlated. The P-wave propagation through coal specimens causes crack closure at the beginning of the coal fracture process in SHPB tests, an innovative model was thus proposed to describe the relationship between the crack closure length and the dynamic stress induced by P-wave. Finally, the stress effect on P-wave attenuation through coal was quantitatively represented by a power function Q = a(c-bσ)- 6, and the material constants a, b, and c were determined as 1.227, 1.314, and 0.005, respectively. The results obtained in this study would be helpful for engineers to estimate seismic energy attenuation and coal mass instability in coal mines.

  1. Stress-mediated Allee effects can cause the sudden collapse of honey bee colonies.

    Science.gov (United States)

    Booton, Ross D; Iwasa, Yoh; Marshall, James A R; Childs, Dylan Z

    2017-05-07

    The recent rapid decline in global honey bee populations could have significant implications for ecological systems, economics and food security. No single cause of honey bee collapse has yet to be identified, although pesticides, mites and other pathogens have all been shown to have a sublethal effect. We present a model of a functioning bee hive and introduce external stress to investigate the impact on the regulatory processes of recruitment to the forager class, social inhibition and the laying rate of the queen. The model predicts that constant density-dependent stress acting through an Allee effect on the hive can result in sudden catastrophic switches in dynamical behaviour and the eventual collapse of the hive. The model proposes that around a critical point the hive undergoes a saddle-node bifurcation, and that a small increase in model parameters can have irreversible consequences for the entire hive. We predict that increased stress levels can be counteracted by a higher laying rate of the queen, lower levels of forager recruitment or lower levels of natural mortality of foragers, and that increasing social inhibition can not maintain the colony under high levels of stress. We lay the theoretical foundation for sudden honey bee collapse in order to facilitate further experimental and theoretical consideration. Copyright © 2017 Elsevier Ltd. All rights reserved.

  2. Macro design effects on stress distribution around implants: A photoelastic stress analysis

    Directory of Open Access Journals (Sweden)

    Serhat Emre Ozkir

    2012-01-01

    Conclusion: As there were observable differences between the implant types, straight placed cylindrical implants showed better stress distribution characteristics, while inclined tapering implants had better stress distribution characteristics.

  3. The effect of stress state on zirconium hydride reorientation

    Science.gov (United States)

    Cinbiz, Mahmut Nedim

    Prior to storage in a dry-cask facility, spent nuclear fuel must undergo a vacuum drying cycle during which the spent fuel rods are heated up to elevated temperatures of ≤ 400°C to remove moisture the canisters within the cask. As temperature increases during heating, some of the hydride particles within the cladding dissolve while the internal gas pressure in fuel rods increases generating multi-axial hoop and axial stresses in the closed-end thin-walled cladding tubes. As cool-down starts, the hydrogen in solid solution precipitates as hydride platelets, and if the multiaxial stresses are sufficiently large, the precipitating hydrides reorient from their initial circumferential orientation to radial orientation. Radial hydrides can severely embrittle the spent nuclear fuel cladding at low temperature in response to hoop stress loading. Because the cladding can experience a range of stress states during the thermo-mechanical treatment induced during vacuum drying, this study has investigated the effect of stress state on the process of hydride reorientation during controlled thermo-mechanical treatments utilizing the combination of in situ X-ray diffraction and novel mechanical testing analyzed by the combination of metallography and finite element analysis. The study used cold worked and stress relieved Zircaloy-4 sheet containing approx. 180 wt. ppm hydrogen as its material basis. The failure behavior of this material containing radial hydrides was also studied over a range of temperatures. Finally, samples from reactor-irradiated cladding tubes were examined by X-ray diffraction using synchrotron radiation. To reveal the stress state effect on hydride reorientation, the critical threshold stress to reorient hydrides was determined by designing novel mechanical test samples which produce a range of stress states from uniaxial to "near-equibiaxial" tension when a load is applied. The threshold stress was determined after thermo-mechanical treatments by

  4. Static Versus Dynamic Stretching Effect on Agility Performance

    OpenAIRE

    Troumbley, Patrick

    2010-01-01

    The purpose of this study was to compare effects of static and dynamic stretching on explosive agility movements, and to examine the effect of the interaction of dynamic and static stretching prior to explosive agility movements. Fourteen men and 10 women performed the different warm-up protocols, including no warm-up (NWU), static stretching (SS), dynamic stretching (DS), and dynamic stretching with static stretching (DS+SS). The T-Drill was used to assess agility. The results indicated n...

  5. Manufacturing Error Effects on Mechanical Properties and Dynamic Characteristics of Rotor Parts under High Acceleration

    Science.gov (United States)

    Jia, Mei-Hui; Wang, Cheng-Lin; Ren, Bin

    2017-07-01

    Stress, strain and vibration characteristics of rotor parts should be changed significantly under high acceleration, manufacturing error is one of the most important reason. However, current research on this problem has not been carried out. A rotor with an acceleration of 150,000 g is considered as the objective, the effects of manufacturing errors on rotor mechanical properties and dynamic characteristics are executed by the selection of the key affecting factors. Through the force balance equation of the rotor infinitesimal unit establishment, a theoretical model of stress calculation based on slice method is proposed and established, a formula for the rotor stress at any point derives. A finite element model (FEM) of rotor with holes is established with manufacturing errors. The changes of the stresses and strains of a rotor in parallelism and symmetry errors are analyzed, which verify the validity of the theoretical model. The pre-stressing modal analysis is performed based on the aforementioned static analysis. The key dynamic characteristics are analyzed. The results demonstrated that, as the parallelism and symmetry errors increase, the equivalent stresses and strains of the rotor slowly increase linearly, the highest growth rate does not exceed 4%, the maximum change rate of natural frequency is 0.1%. The rotor vibration mode is not significantly affected. The FEM construction method of the rotor with manufacturing errors can be utilized for the quantitative research on rotor characteristics, which will assist in the active control of rotor component reliability under high acceleration.

  6. Particle shape effects on the stress response of granular packings.

    Science.gov (United States)

    Athanassiadis, Athanasios G; Miskin, Marc Z; Kaplan, Paul; Rodenberg, Nicholas; Lee, Seung Hwan; Merritt, Jason; Brown, Eric; Amend, John; Lipson, Hod; Jaeger, Heinrich M

    2014-01-01

    We present measurements of the stress response of packings formed from a wide range of particle shapes. Besides spheres these include convex shapes such as the Platonic solids, truncated tetrahedra, and triangular bipyramids, as well as more complex, non-convex geometries such as hexapods with various arm lengths, dolos, and tetrahedral frames. All particles were 3D-printed in hard resin. Well-defined initial packing states were established through preconditioning by cyclic loading under given confinement pressure. Starting from such initial states, stress-strain relationships for axial compression were obtained at four different confining pressures for each particle type. While confining pressure has the largest overall effect on the mechanical response, we find that particle shape controls the details of the stress-strain curves and can be used to tune packing stiffness and yielding. By correlating the experimentally measured values for the effective Young's modulus under compression, yield stress and energy loss during cyclic loading, we identify trends among the various shapes that allow for designing a packing's aggregate behavior.

  7. History effect on the Reynolds stress in turbulent swirling flow

    Science.gov (United States)

    Hamba, Fujihiro

    2017-02-01

    The eddy-viscosity model for turbulence has some difficulty in predicting rotating and swirling flows. Turbulent swirling flow in a straight pipe is a typical example. A rapidly rotating core in the pipe decays too quickly in results obtained from the standard k-ɛ model. The eddy viscosity needs to be reduced to predict the velocity profiles well; the mechanism of the decrease in the eddy viscosity has not been clarified yet. In this work, the eddy-viscosity model was investigated using a temporally nonlocal expression for the Reynolds stress that represents the history effect. A simple transport equation for the Reynolds stress was integrated along a mean-flow pathline to obtain a temporally nonlocal model for the Reynolds stress. The nonlocal model was applied to simple swirling flows for which the time integral can be further calculated to investigate the history effect. It was shown that the history effect associated with the rotating motion gives rise to a small factor in the expression for the eddy viscosity. In order to confirm the history effect, the present model and the linear eddy-viscosity model were used to simulate a swirling pipe flow. The velocity profiles obtained from the present model agree well with experimental results; the reduced eddy viscosity can account for the slow decay of the swirling motion in the core region. The anisotropic nature of the eddy viscosity was also discussed in relation to the small factor caused by the history effect.

  8. Effects of Stress on Students' Physical and Mental Health and Academic Success

    Science.gov (United States)

    Shankar, Nilani L.; Park, Crystal L.

    2016-01-01

    Stress affects students in multiple ways. This article provides a conceptual overview of the direct (e.g., psychoneuroimmunological, endocrine) and indirect (health behavior) pathways through which stress affects physical health, the psychological effects of stress on mental health, and the cognitive effects of stress (e.g., attention,…

  9. Effects of Stress on Students' Physical and Mental Health and Academic Success

    Science.gov (United States)

    Shankar, Nilani L.; Park, Crystal L.

    2016-01-01

    Stress affects students in multiple ways. This article provides a conceptual overview of the direct (e.g., psychoneuroimmunological, endocrine) and indirect (health behavior) pathways through which stress affects physical health, the psychological effects of stress on mental health, and the cognitive effects of stress (e.g., attention,…

  10. Effects of liquid properties on the dynamics of under-liquid laser-induced shock process

    Science.gov (United States)

    Nguyen, Thao Thi Phuong; Tanabe, Rie; Ito, Yoshiro

    2016-09-01

    We compared the shock processes induced when focusing a single laser pulse (1064 nm, FWHM = 13 ns) onto the surface of epoxy resin blocks immersed in glycerol, water, liquid paraffin, and silicone oils. A custom-designed time-resolved photoelasticity imaging technique was applied to observe the strength of stress wave induced inside the solid target and the propagation of shock waves in the liquid with time resolution of nanoseconds. We demonstrated that the shock impedance of the liquid caused a noticeable effect on the strength of laser-induced stress wave: Ablation in the liquid with a higher shock impedance resulted in a stronger stress. By using glycerol instead of water as the confining medium, the pulse energy required to induce a certain level of stress was reduced by about 20 %. The dynamical behaviors of the main shock wave and the reflected wave in inverted V-shape in each liquid are also discussed in details.

  11. On the Effect of Extratropical Wind Stress Forcing on Pacific Subtropical Cells and Tropical Climate

    Science.gov (United States)

    Graffino, Giorgio; Farneti, Riccardo; Kucharski, Fred

    2017-04-01

    The influence of extratropical atmospheric dynamics on the tropical ocean state is a classical example of ocean-atmosphere teleconnection. One way to influence tropical climate is through oceanic SubTropical Cells (STCs), shallow overturning circulation structures connecting the Equatorial Ocean with the subtropical regions. STC are responsible for large mass and energy transports, and their influence on tropical climate, and consequently on the global climate, is fundamental both on the mean and its variability. These circulation structures are present in all basins across the Tropics (Pacific, Atlantic, and Indian Ocean), with different properties and strengths due to the features of each basin. We focus here on the effect of off-equatorial winds on the Pacific STCs, which are the largest and have been previously studied for their potential role in driving low-frequency Pacific variability. Using the Modular Ocean Model version 5 (MOM5), we force the ocean surface with idealized wind stress and wind stress curl anomaly patterns, in order to highlight the influence of subtropical and extratropical forcing on STCs dynamics, and, eventually, on some aspects of Pacific tropical climate. Results have been compared with a control simulation, in which a climatological forcing has been applied at the ocean surface. Our simulations show an increased (reduced) meridional water transport for positive (negative) wind stress anomalies in the Subtropics; the structure of the thermocline at the Equator is modified as well, where cold (warm) anomalies appear. Those signatures result from anomalous values of Equatorial UnderCurrent (EUC), which is partly fed by the STCs. Meridional ocean heat transport is influenced too, showing larger (weaker) values for stronger (weaker) subtropical wind stress. Anomalous circulations are further analyzed for the interior and western boundary transports, and scalings are derived linking subtropical wind stress, STC transports and tropical

  12. Vortex dynamics and wall shear stress behaviour associated with an elliptic jet impinging upon a flat plate

    Science.gov (United States)

    Long, J.; New, T. H.

    2016-07-01

    Vortical structures and dynamics of a Re h = 2100 elliptic jet impinging upon a flat plate were studied at H/ d h = 1, 2 and 4 jet-to-plate separation distances. Flow investigations were conducted along both its major and minor planes using laser-induced fluorescence and digital particle image velocimetry techniques. Results show that the impingement process along the major plane largely consists of primary jet ring-vortex and wall-separated secondary vortex formations, where they subsequently separate from the flat plate at smaller H/ d h = 1 and 2 separation distances. Key vortex formation locations occur closer to the impingement point as the separation distance increases. Interestingly, braid vortices and rib structures begin to take part in the impingement process at H/ d h = 4 and wave instabilities dominate the flow field. In contrast, significantly more coherent primary and secondary vortices with physically larger vortex core sizes and higher vortex strengths are observed along the minor plane, with no signs of braid vortices and rib structures. Lastly, influences of these different flow dynamics on the major and minor plane instantaneous and mean skin friction coefficient levels are investigated to shed light on the effects of separation distance on the wall shear stress distributions.

  13. Decay of aftershock density with distance does not indicate triggering by dynamic stress.

    Science.gov (United States)

    Richards-Dinger, Keith; Stein, Ross S; Toda, Shinji

    2010-09-30

    Resolving whether static or dynamic stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard. Felzer and Brodsky examined the distance distribution of earthquakes occurring in the first five minutes after 2 ≤ M aftershocks showed a uniform power-law decay with slope -1.35 out to 50 km from the mainshocks. From this they argued that the distance decay could be explained only by dynamic triggering. Here we propose an alternative explanation for the decay, and subject their hypothesis to a series of tests, none of which it passes. At distances more than 300 m from the 2 ≤ M aftershocks, is absent at distances exceeding 10 km from the mainshocks. Finally, the distance decay is found among aftershocks that occur before the arrival of the seismic wave front from the mainshock, which violates causality. We argue that Felzer and Brodsky implicitly assume that the first of two independent aftershocks along a fault rupture triggers the second, and that the first of two shocks in a creep- or intrusion-driven swarm triggers the second, when this need not be the case.

  14. Decay of aftershock density with distance does not indicate triggering by dynamic stress

    Science.gov (United States)

    Richards-Dinger, K.; Stein, R.S.; Toda, S.

    2010-01-01

    Resolving whether static or dynamic stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard. Felzer and Brodsky examined the distance distribution of earthquakes occurring in the first five minutes after 2 ≤ M  M  M ≥ 2 aftershocks showed a uniform power-law decay with slope −1.35 out to 50 km from the mainshocks. From this they argued that the distance decay could be explained only by dynamic