Sleep, Stress & Relaxation: Rejuvenate Body & Mind

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Nonlinear effects in thermal stress analysis of a solid propellant rocket motor

NASA Technical Reports Server (NTRS)

Francis, E. C.; Peeters, R. L.; Murch, S. A.

1976-01-01

Direct characterization procedures were used to determine the relaxation modulus as a function of time, temperature, and state of strain. Using the quasi-elastic method of linearviscoelasticity, these properties were employed in a finite element computer code to analyze a thick-walled, nonlinear viscoelastic cylinder in the state of plane strain bonded to a thin (but stiff) elastic casing and subjected to slow thermal cooling. The viscoelastic solution is then expressed as a sequence of elastic finite element solutions. The strain-dependent character of the relaxation modulus is included by replacing the single relaxation curve used in the linear viscoelastic theory by a family of relaxation functions obtained at various strain levels. These functions may be regarded as a collection of stress histories or responses to specific loads (in this case, step strains) with which the cooldown solution is made to agree by iterations on the modulus and strain level.

Inhibition of endoplasmic reticulum stress improves coronary artery function in type 2 diabetic mice.

PubMed

Choi, Soo-Kyoung; Lim, Mihwa; Yeon, Soo-In; Lee, Young-Ho

2016-06-01

What is the central question of this study? Endoplasmic reticulum (ER) stress has been reported to be involved in type 2 diabetes; however, the role of exacerbated ER stress in vascular dysfunction in type 2 diabetes remains unknown. What is the main finding and its importance? The main findings of this study are that ER stress is increased in the coronary arteries in type 2 diabetes, and inhibition of ER stress using taurine-conjugated ursodeoxycholic acid improves vascular function, which is associated with normalization of the myogenic response and endothelium-dependent relaxation. Vascular dysfunction is a major complication in type 2 diabetes. Although endoplasmic reticulum (ER) stress has been suggested to be a contributory factor in cardiovascular diseases, the relationship between ER stress and vascular dysfunction in type 2 diabetes remains unclear. Thus, in the present study, we examined whether ER stress contributes to coronary artery dysfunction and whether inhibition of ER stress ameliorates vascular function in type 2 diabetes. Type 2 diabetic mice and their control counterparts were treated with an ER stress inhibitor (taurine-conjugated ursodeoxycholic acid, 150 mg kg(-1)  day(-1) , by i.p. injection) for 2 weeks or not treated. The myogenic response and endothelium-dependent relaxation were measured in pressurized coronary arteries. In type 2 diabetic mice, blood glucose and body weight were elevated compared with control mice. The myogenic response was potentiated and endothelium-dependent relaxation impaired in coronary arteries from the type 2 diabetic mice. Interestingly, treatment with the ER stress inhibitor normalized the myogenic responses and endothelium-dependent relaxation. These data were associated with an increase in ER stress marker expression or phosphorylation (IRE1-XBP-1 and PERK-eIF2α) in type 2 diabetic mice, which were reduced by treatment with the ER stress inhibitor. Inhibition of ER stress normalizes the myogenic response and improves vascular function in type 2 diabetes. Therefore, ER stress could be a potential target for cardiovascular diseases in diabetes mellitus. © 2016 The Authors. Experimental Physiology © 2016 The Physiological Society.

Finite cohesion due to chain entanglement in polymer melts.

PubMed

Cheng, Shiwang; Lu, Yuyuan; Liu, Gengxin; Wang, Shi-Qing

2016-04-14

Three different types of experiments, quiescent stress relaxation, delayed rate-switching during stress relaxation, and elastic recovery after step strain, are carried out in this work to elucidate the existence of a finite cohesion barrier against free chain retraction in entangled polymers. Our experiments show that there is little hastened stress relaxation from step-wise shear up to γ = 0.7 and step-wise extension up to the stretching ratio λ = 1.5 at any time before or after the Rouse time. In contrast, a noticeable stress drop stemming from the built-in barrier-free chain retraction is predicted using the GLaMM model. In other words, the experiment reveals a threshold magnitude of step-wise deformation below which the stress relaxation follows identical dynamics whereas the GLaMM or Doi-Edwards model indicates a monotonic acceleration of the stress relaxation dynamics as a function of the magnitude of the step-wise deformation. Furthermore, a sudden application of startup extension during different stages of stress relaxation after a step-wise extension, i.e. the delayed rate-switching experiment, shows that the geometric condensation of entanglement strands in the cross-sectional area survives beyond the reptation time τd that is over 100 times the Rouse time τR. Our results point to the existence of a cohesion barrier that can prevent free chain retraction upon moderate deformation in well-entangled polymer melts.

Load relaxation of olivine single crystals

NASA Astrophysics Data System (ADS)

Cooper, Reid F.; Stone, Donald S.; Plookphol, Thawatchai

2016-10-01

Single crystals of ferromagnesian olivine (San Carlos, AZ, peridot; Fo88-90) have been deformed in both uniaxial creep and load relaxation under conditions of ambient pressure, T = 1500°C and pO2 = 10-10 atm; creep stresses were in the range 40 ≤ σ1 (MPa) ≤ 220. The crystals were oriented such that the applied stress was parallel to [011]c, which promotes single slip on the slowest slip system in olivine, (010)[001]. The creep rates at steady state match well the results of earlier investigators, as does the stress sensitivity (a power law exponent of n = 3.6). Dislocation microstructures, including spatial distribution of low-angle (subgrain) boundaries, additionally confirm previous investigations. Inverted primary creep (an accelerating strain rate with an increase in stress) was observed. Load relaxation, however, produced a singular response—a single hardness curve—regardless of the magnitude of creep stress or total accumulated strain preceding relaxation. The log stress versus log strain rate data from load-relaxation and creep experiments overlap to within experimental error. The load-relaxation behavior is distinctly different than that described for other crystalline solids, where the flow stress is affected strongly by work hardening such that a family of distinct hardness curves is generated, which are related by a scaling function. The response of olivine for the conditions studied, we argue, indicates flow that is rate limited by dislocation glide, reflecting specifically a high intrinsic lattice resistance (Peierls stress).

Load Relaxation of Olivine Single Crystals

NASA Astrophysics Data System (ADS)

Cooper, R. F.; Stone, D. S.; Plookphol, T.

2016-12-01

Single crystals of ferromagnesian olivine (San Carlos, AZ, peridot; Fo90-92) have been deformed in both uniaxial creep and load relaxation under conditions of ambient pressure, T = 1500ºC and pO2 = 10-10 atm; creep stresses were in the range 40 ≤ σ1 (MPa) ≤ 220. The crystals were oriented such that the applied stress was parallel to [011]c, which promotes single slip on the slowest slip system in olivine, (010)[001]. The creep rates at steady state match well the results of earlier investigators, as does the stress sensitivity (a power-law exponent of n = 3.6). Dislocation microstructures, including spatial distribution of low-angle (subgrain) boundaries, additionally confirm previous investigations. Inverted primary creep (an accelerating strain rate with an increase in stress) was observed. Load-relaxation, however, produced a singular response—a single hardness curve—regardless of the magnitude of creep stress or total accumulated strain preceding relaxation. The log-stress v. log-strain rate data from load-relaxation and creep experiments overlap to within experimental error. The load-relaxation behavior is distinctly different that that described for other crystalline solids, where the flow stress is affected strongly by work hardening such that a family of distinct hardness curves is generated, which are related by a scaling function. The response of olivine for the conditions studied, thus, indicates flow that is rate-limited by dislocation glide, reflecting specifically a high intrinsic lattice resistance (Peierls stress).

Effects of the aging temperature and stress relaxation conditions on γ‧ precipitation in Inconel X-750

NASA Astrophysics Data System (ADS)

Ha, Jeong Won; Seong, Baek Seok; Jeong, Hi Won; Choi, Yoon Suk; Kang, Namhyun

2015-02-01

Inconel X-750 is a Ni-based precipitation-hardened superalloy typically used in springs designed for high-temperature applications such as the hold-down springs in nuclear power plants. γ‧ is a major precipitate in X-750 alloys which affects the strength, creep resistance, and stress relaxation properties of the spring. In this study, a solution-treated X-750 wire coiled into a spring was used that was aged at various temperatures and submitted to stress relaxation tests with and without loading. Small angle neutron scattering was employed to quantify the size and volume fraction of γ‧ phase in the springs as a function of the aging temperature and the application of a load during stress relaxation. The volume fraction of γ‧ precipitates increased in the specimen aged at 732 °C following stress relaxation at 500 °C for 300 h. However, the mean size of the precipitates in the samples was not affected by stress relaxation. The specimen aged at the lower temperature (620 °C) contained a smaller γ‧ volume fraction and gained a smaller fraction of γ‧ during stress relaxation compared with the sample aged at the higher temperature (732 °C). The smaller increase in the γ‧ volume fraction for the sample aged at 620 °C was associated with a larger increase in the M23C6 secondary carbide content during relaxation. The Cr depletion zone around the secondary carbides raises the solubility of γ‧ thereby decreasing the volume fraction of γ‧ precipitates in Inconel X-750. In terms of stress relaxation, a larger increase in the γ‧ volume fraction was measured with loading rather than without. This is probably associated with the dislocation accumulation generated under loading that facilitate the nucleation and growth of heterogeneous γ‧ phase due to enhanced diffusion.

Kubo formulas for the shear and bulk viscosity relaxation times and the scalar field theory shear τπ calculation

NASA Astrophysics Data System (ADS)

Czajka, Alina; Jeon, Sangyong

2017-06-01

In this paper we provide a quantum field theoretical study on the shear and bulk relaxation times. First, we find Kubo formulas for the shear and the bulk relaxation times, respectively. They are found by examining response functions of the stress-energy tensor. We use general properties of correlation functions and the gravitational Ward identity to parametrize analytical structures of the Green functions describing both sound and diffusion mode. We find that the hydrodynamic limits of the real parts of the respective energy-momentum tensor correlation functions provide us with the method of computing both the shear and bulk viscosity relaxation times. Next, we calculate the shear viscosity relaxation time using the diagrammatic approach in the Keldysh basis for the massless λ ϕ4 theory. We derive a respective integral equation which enables us to compute η τπ and then we extract the shear relaxation time. The relaxation time is shown to be inversely related to the thermal width as it should be.

Internal strain analysis of ceramics using scanning laser acoustic microscopy

NASA Technical Reports Server (NTRS)

Kent, Renee M.

1993-01-01

Quantitative studies of material behavior characteristics are essential for predicting the functionality of a material under its operating conditions. A nonintrusive methodology for measuring the in situ strain of small dimeter (to 11 microns) ceramic fibers under uniaxial tensile loading and the local internal strains of ceramics and ceramic composites under flexural loading is introduced. The strain measurements and experimentally observed mechanical behavior are analyzed in terms of the microstructural development and fracture behavior of each test specimen evaluated. Measurement and analysis of Nicalon silicon carbide (SiC) fiber (15 microns diameter) indicate that the mean elastic modulus of the individual fiber is 185.3 GPa. Deviations observed in the experimentally determined elastic modulus values between specimens were attributed to microstructural variations which occur during processing. Corresponding variations in the fracture surface morphology were also observed. The observed local mechanical behavior of a lithium alumino-silicate (LAS) glass ceramic, a LAS/SiC monofilament composite, and a calcium alumino-silicate (CAS)/SiC fully reinforced composite exhibits nonlinearities and apparent hysteresis due to the subcritical mechanical loading. Local hysteresis in the LAS matrices coincided with the occurrence of multiple fracture initiation sites, localized microcracking, and secondary cracking. The observed microcracking phenomenon was attributed to stress relaxation of residual stresses developed during processing, and local interaction of the crack front with the microstructure. The relaxation strain and stress predicted on apparent mechanical hysteresis effects were defined and correlated with the magnitude of the measured fracture stress for each specimen studied. This quantitative correlation indicated a repeatable measure of the stress at which matrix microcracking occurred for stress relief of each material system. Stress relaxation occurred prior to the onset of steady state cracking conditions. The relaxation stress occurred at 18.5 percent of the fracture stress in LAS and 11.0 percent of the yield stress in CAS/SiC. The relaxation stress ratio was dependent upon the dominant fracture mode of the LAS/SiC specimens. Relaxation stress ratios greater than 0.30 were observed for specimens which fractured due to shear at the fiber matrix interface; specimens which fracture due to tensile cracking had relaxation stress ratios less than 0.30. The stress relaxation ratio appeared to be a specific characteristic of the glass ceramic material. The measured stress relaxation for LAS indicated a measure of the inherent residual stresses in the material due to processing and suggested localized toughening mechanisms for brittle material structures.

The time dependence of rock healing as a universal relaxation process, a tutorial

NASA Astrophysics Data System (ADS)

Snieder, Roel; Sens-Schönfelder, Christoph; Wu, Renjie

2017-01-01

The material properties of earth materials often change after the material has been perturbed (slow dynamics). For example, the seismic velocity of subsurface materials changes after earthquakes, and granular materials compact after being shaken. Such relaxation processes are associated by observables that change logarithmically with time. Since the logarithm diverges for short and long times, the relaxation can, strictly speaking, not have a log-time dependence. We present a self-contained description of a relaxation function that consists of a superposition of decaying exponentials that has log-time behaviour for intermediate times, but converges to zero for long times, and is finite for t = 0. The relaxation function depends on two parameters, the minimum and maximum relaxation time. These parameters can, in principle, be extracted from the observed relaxation. As an example, we present a crude model of a fracture that is closing under an external stress. Although the fracture model violates some of the assumptions on which the relaxation function is based, it follows the relaxation function well. We provide qualitative arguments that the relaxation process, just like the Gutenberg-Richter law, is applicable to a wide range of systems and has universal properties.

Exposure of natural rubber to personal lubricants--swelling and stress relaxation as potential indicators of reduced seal integrity of non-lubricated male condoms.

PubMed

Sarkar Das, Srilekha; Coburn, James C; Tack, Charles; Schwerin, Matthew R; Richardson, D Coleman

2014-07-01

Male condoms act as mechanical barriers to prevent passage of body fluids. For effective use of condoms the mechanical seal is also expected to remain intact under reasonable use conditions, including with personal lubricants. Absorption of low molecular weight lubricant components into the material of male condoms may initiate material changes leading to swelling and stress relaxation of the polymer network chains that could affect performance of the sealing function of the device. Swelling indicates both a rubber-solvent interaction and stress relaxation, the latter of which may indicate and/or result in a reduced seal pressure in the current context. Swelling and stress relaxation of natural rubber latex condoms were assessed in a laboratory model in the presence of silicone-, glycol-, and water-based lubricants. Within 15 minutes, significant swelling (≥6 %) and stress reduction (≥12 %) of condoms were observed with 2 out of 4 silicone-based lubricants tested, but neither was observed with glycol- or water-based lubricants tested. Under a given strain, reduction in stress was prominent during the swelling processes, but not after the process was complete. Lubricant induced swelling and stress relaxation may loosen the circumferential stress responsible for the mechanical seal. Swelling and stress relaxation behavior of latex condoms in the presence of personal lubricants may be useful tests to identify lubricant-rooted changes in condom-materials. For non-lubricated latex condoms, material characteristics--which are relevant to failure--may change in the presence of a few silicone-based personal lubricants. These changes may in turn induce a loss of condom seal during use, specifically at low strain conditions. Published by Elsevier Inc.

Altered functional connectivity to stressful stimuli in prenatally cocaine-exposed adolescents.

PubMed

Zakiniaeiz, Yasmin; Yip, Sarah W; Balodis, Iris M; Lacadie, Cheryl M; Scheinost, Dustin; Constable, R Todd; Mayes, Linda C; Sinha, Rajita; Potenza, Marc N

2017-11-01

Prenatal cocaine exposure (PCE) is linked to addiction and obesity vulnerability. Neural responses to stressful and appetitive cues in adolescents with PCE versus those without have been differentially linked to substance-use initiation. However, no prior studies have assessed cue-reactivity responses among PCE adolescents using a connectivity-based approach. Twenty-two PCE and 22 non-prenatally drug-exposed (NDE) age-, sex-, IQ- and BMI-matched adolescents participated in individualized guided imagery with appetitive (favorite-food), stressful and neutral-relaxing cue scripts during functional magnetic resonance imaging. Subjective favorite-food craving scores were collected before and after script exposure. A data-driven voxel-wise intrinsic connectivity distribution analysis was used to identify between-group differences and examine relationships with craving scores. A group-by-cue interaction effect identified a parietal lobe cluster where PCE versus NDE adolescents showed less connectivity during stressful and more connectivity during neutral-relaxing conditions. Follow-up seed-based connectivity analyses revealed that, among PCE adolescents, the parietal seed was positively connected to inferior parietal and sensory areas and negatively connected to corticolimbic during both stress and neutral-relaxing conditions. For NDE, greater parietal connectivity to parietal, cingulate and sensory areas and lesser parietal connectivity to medial prefrontal areas were found during stress compared to neutral-relaxing cueing. Craving scores inversely correlated with corticolimbic connectivity in PCE, but not NDE adolescents, during the favorite-food condition. Findings from this first data-driven intrinsic connectivity analysis of PCE influences on adolescent brain function indicate differences relating to PCE status and craving. These findings provide insight into the developmental impact of in utero drug exposure. Copyright © 2017 Elsevier B.V. All rights reserved.

Common and Dissociable Neural Activity After Mindfulness-Based Stress Reduction and Relaxation Response Programs.

PubMed

Sevinc, Gunes; Hölzel, Britta K; Hashmi, Javeria; Greenberg, Jonathan; McCallister, Adrienne; Treadway, Michael; Schneider, Marissa L; Dusek, Jeffery A; Carmody, James; Lazar, Sara W

2018-06-01

We investigated common and dissociable neural and psychological correlates of two widely used meditation-based stress reduction programs. Participants were randomized to the Relaxation Response (RR; n = 18; 56% female) or the Mindfulness-Based Stress Reduction (MBSR; n = 16; 56% female) programs. Both programs use a "bodyscan" meditation; however, the RR program explicitly emphasizes physical relaxation during this practice, whereas the MBSR program emphasizes mindful awareness with no explicit relaxation instructions. After the programs, neural activity during the respective meditation was investigated using functional magnetic resonance imaging. Both programs were associated with reduced stress (for RR, from 14.1 ± 6.6 to 11.3 ± 5.5 [Cohen's d = 0.50; for MBSR, from 17.7 ± 5.7 to 11.9 ± 5.0 [Cohen's d = 1.02]). Conjunction analyses revealed functional coupling between ventromedial prefrontal regions and supplementary motor areas (p < .001). The disjunction analysis indicated that the RR bodyscan was associated with stronger functional connectivity of the right inferior frontal gyrus-an important hub of intentional inhibition and control-with supplementary motor areas (p < .001, family-wise error [FWE] rate corrected). The MBSR program was uniquely associated with improvements in self-compassion and rumination, and the within-group analysis of MBSR bodyscan revealed significant functional connectivity of the right anterior insula-an important hub of sensory awareness and salience-with pregenual anterior cingulate during bodyscan meditation compared with rest (p = .03, FWE corrected). The bodyscan exercises in each program were associated with both overlapping and differential functional coupling patterns, which were consistent with each program's theoretical foundation. These results may have implications for the differential effects of these programs for the treatment of diverse conditions.

Quasi-linear viscoelastic properties of the human medial patello-femoral ligament.

PubMed

Criscenti, G; De Maria, C; Sebastiani, E; Tei, M; Placella, G; Speziali, A; Vozzi, G; Cerulli, G

2015-12-16

The evaluation of viscoelastic properties of human medial patello-femoral ligament is fundamental to understand its physiological function and contribution as stabilizer for the selection of the methods of repair and reconstruction and for the development of scaffolds with adequate mechanical properties. In this work, 12 human specimens were tested to evaluate the time- and history-dependent non linear viscoelastic properties of human medial patello-femoral ligament using the quasi-linear viscoelastic (QLV) theory formulated by Fung et al. (1972) and modified by Abramowitch and Woo (2004). The five constant of the QLV theory, used to describe the instantaneous elastic response and the reduced relaxation function on stress relaxation experiments, were successfully evaluated. It was found that the constant A was 1.21±0.96MPa and the dimensionless constant B was 26.03±4.16. The magnitude of viscous response, the constant C, was 0.11±0.02 and the initial and late relaxation time constants τ1 and τ2 were 6.32±1.76s and 903.47±504.73s respectively. The total stress relaxation was 32.7±4.7%. To validate our results, the obtained constants were used to evaluate peak stresses from a cyclic stress relaxation test on three different specimens. The theoretically predicted values fit the experimental ones demonstrating that the QLV theory could be used to evaluate the viscoelastic properties of the human medial patello-femoral ligament. Copyright © 2015 Elsevier Ltd. All rights reserved.

Glass-like stress relaxation of a permanent gelatin network as a signature of pretransitional helix-coil fluctuations

NASA Astrophysics Data System (ADS)

Caroli, Christiane; Ronsin, Olivier; Lemaître, Anaël

2018-02-01

The stress response of permanently crosslinked gelatin gels was recently observed to display glass-like features, namely, a stretched-exponential behavior terminated by an exponential decay, the characteristic time scales of which increase dramatically with decreasing temperature. This phenomenon is studied here using a model of flexible polymer gel network where relaxation proceeds via elementary monomer exchanges between helix and coil segments. The relaxation dynamics of a full network simulation is found to be nearly identical to that of a model of independent strands, which shows that for flexible polymer gels in the range of elastic moduli of interest, both strand contour length disorder and elastic couplings are irrelevant. We thus focus on the independent strand model and find it not only to explain the observed functional form of the stress relaxation curves but also to yield predictions that match very satisfactorily the experimental measurements of final relaxation time and total stress drop. The system under study thus constitutes a rare case where the origin of glass-like behavior can be unambiguously identified, namely, as the signature of the enhancement of helix content fluctuations when approaching from above the mean-field helix-coil transition of strands.

Understanding of the development of in-plane residual stress in sol-gel-derived metal oxide thin films

NASA Astrophysics Data System (ADS)

Ohno, Kentaro; Uchiyama, Hiroaki; Kozuka, Hiromitsu

2012-01-01

The in-plane residual stress in thin films greatly affects their properties and functionality as well as the substrate bending, and hence is an important factor to be controlled. In order to obtain general knowledge on the development of residual stress in sol-gel-derived oxide thin films, the in-plane residual stress was measured for yttria stabilized zirconia gel films on Si(100) wafers as a function of firing temperature by measuring the substrate curvature. The films showed a rather complex variation in residual stress, and the mechanism of the residual stress evolution was discussed, referencing the intrinsic stress and the x-ray diffraction data. At low annealing temperatures of 100-200 °C, the residual tensile stress decreased and became compressive partially due to the structural relaxation occurring during cooling. When the firing temperature was increased over 200 °C, the residual stress turned tensile, and increased with increasing annealing temperature, which was attributed to the increase in intrinsic stress due to film densification as well as to the reduced structural relaxation due to the progress of densification. The residual tensile stress slightly decreased at firing temperatures of 500-600 °C, which was attributed to the reduction in intrinsic stress due to thermally activated atomic diffusion as well as to emergence of thermal stress. At firing temperature over 600 °C, the residual tensile stress increased again, which was attributed to the increase in thermal stress generated during cooling due to the increased Young's modulus of the film. Although appearing to be complicated, the whole variation of residual stress with firing temperature could be understood in terms of film densification, structural relaxation, atomic diffusion, progress of crystallization and thermal strain. The illustration presented in the work may provide a clear insight on how the residual stress could be developed in a variety of functional sol-gel-derived, crystalline oxide thin films.

Time-dependent stress concentration and microcrack nucleation in TiAl

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoo, M.H.

1995-07-01

Localized stress evolution associated with the interaction of slip or twinning with an interface is treated by means of a superposition of the {open_quotes}internal loading{close_quotes} of a crystalline subsystem by dynamic dislocation pile-up and the stress relaxation by climb of interfacial dislocations. The peak value of a stress concentration factor depends on both the angular function that includes the effect of mode mixity and the ratio of characteristic times for stress relaxation and internal loading. The available experimental data on orientation and strain-rate dependences of interfacial fracture mode in polysynthetically twinned TiAl crystals are discussed in view of the theoreticalmore » concepts presented in this paper.« less

Quasi-dynamic Earthquake Cycle Simulation in a Viscoelastic Medium with Memory Variables

NASA Astrophysics Data System (ADS)

Hirahara, K.; Ohtani, M.; Shikakura, Y.

2011-12-01

Earthquake cycle simulations based on rate and state friction laws have successfully reproduced the observed complex earthquake cycles at subduction zones. Most of simulations have assumed elastic media. The lower crust and the upper mantle have, however, viscoelastic properties, which cause postseismic stress relaxation. Hence the slip evolution on the plate interfaces or the faults in long earthquake cycles is different from that in elastic media. Especially, the viscoelasticity plays an important role in the interactive occurrence of inland and great interplate earthquakes. In viscoelastic media, the stress is usually calculated by the temporal convolution of the slip response function matrix and the slip deficit rate vector, which needs the past history of slip rates at all cells. Even if properly truncating the convolution, it requires huge computations. This is why few simulation studies have considered viscoelastic media so far. In this study, we examine the method using memory variables or anelastic functions, which has been developed for the time-domain finite-difference calculation of seismic waves in a dissipative medium (e.g., Emmerich and Korn,1987; Moczo and Kristek, 2005). The procedure for stress calculation with memory variables is as follows. First, we approximate the time-domain slip response function calculated in a viscoelastic medium with a series of relaxation functions with coefficients and relaxation times derived from a generalized Maxell body model. Then we can define the time-domain material-independent memory variable or anelastic function for each relaxation mechanism. Each time-domain memory variable satisfies the first-order differential equation. As a result, we can calculate the stress simply by the product of the unrelaxed modulus and the slip deficit subtracted from the sum of memory variables without temporal convolution. With respect to computational cost, we can summarize as in the followings. Dividing the plate interface into N cells, in elastic media, the stress at all cells is calculated by the product of the slip response function matrix and the slip deficit vector. The computational cost is O(N**2). With H-matrices method, we can reduce this to O(N)-O(NlogN) (Ohtani et al. 2011). The memory size is also reduced from O(N**2) to O(N). In viscoelastic media, the product of the unrelaxed modulus matrix and the vector of the slip deficit subtracted from the sum of memory variables costs O(N) with H-matrices method, which is the same as in elastic ones. If we use m relaxation functions, m x N differential equations are additionally solved at a time. The increase in memory size is (4m+1) x N**2. For approximation of slip response function, we need to estimate coefficients and relaxation times for m relaxation functions non-linearly with constraints. Because it is difficult to execute the non-linear least square estimation with constraints, we consider only m=2 with satisfying constraints. Test calculations in a layered or 3-D heterogeneous viscoelastic structure show this gives the satisfactory approximation. As an example, we report a 2-D earthquake cycle simulation for the 2011 giant Tohoku earthquake in a layered viscoelastic medium.

Body mass index, metabolic factors, and striatal activation during stressful and neutral-relaxing states: an FMRI study.

PubMed

Jastreboff, Ania M; Potenza, Marc N; Lacadie, Cheryl; Hong, Kwangik A; Sherwin, Robert S; Sinha, Rajita

2011-02-01

Stress is associated with alterations in neural motivational-reward pathways in the ventral striatum (VS), hormonal/metabolic changes, and weight increases. The relationship between these different factors is not well understood. We hypothesized that body mass index (BMI) status and hormonal/metabolic factors would be associated with VS activation. We used functional magnetic resonance imaging (fMRI) to compare brain responses of overweight and obese (OW/OB: BMI ≥ 25 kg/m(2): N=27) individuals with normal weight (NW: BMI<18.5-24.9 kg/m(2): N=21) individuals during exposure to personalized stress, alcohol cue, and neutral-relaxing situations using a validated, autobiographical, script-driven, guided-imagery paradigm. Metabolic factors, including fasting plasma glucose (FPG), insulin, and leptin, were examined for their association with VS activation. Consistent with previous studies, stress and alcohol cue exposure each increased activity in cortico-limbic regions. Compared with NW individuals, OW/OB individuals showed greater VS activation in the neutral-relaxing and stress conditions. FPG was correlated with VS activation. Significant associations between VS activation and metabolic factors during stress and relaxation suggest the involvement of metabolic factors in striatal dysfunction in OW/OB individuals. This relationship may contribute to non-homeostatic feeding in obesity.

Body Mass Index, Metabolic Factors, and Striatal Activation During Stressful and Neutral-Relaxing States: An fMRI Study

PubMed Central

Jastreboff, Ania M; Potenza, Marc N; Lacadie, Cheryl; Hong, Kwangik A; Sherwin, Robert S; Sinha, Rajita

2011-01-01

Stress is associated with alterations in neural motivational-reward pathways in the ventral striatum (VS), hormonal/metabolic changes, and weight increases. The relationship between these different factors is not well understood. We hypothesized that body mass index (BMI) status and hormonal/metabolic factors would be associated with VS activation. We used functional magnetic resonance imaging (fMRI) to compare brain responses of overweight and obese (OW/OB: BMI ⩾25 kg/m2: N=27) individuals with normal weight (NW: BMI<18.5–24.9 kg/m2: N=21) individuals during exposure to personalized stress, alcohol cue, and neutral-relaxing situations using a validated, autobiographical, script-driven, guided-imagery paradigm. Metabolic factors, including fasting plasma glucose (FPG), insulin, and leptin, were examined for their association with VS activation. Consistent with previous studies, stress and alcohol cue exposure each increased activity in cortico-limbic regions. Compared with NW individuals, OW/OB individuals showed greater VS activation in the neutral-relaxing and stress conditions. FPG was correlated with VS activation. Significant associations between VS activation and metabolic factors during stress and relaxation suggest the involvement of metabolic factors in striatal dysfunction in OW/OB individuals. This relationship may contribute to non-homeostatic feeding in obesity. PMID:21048702

Preparation and properties of hybrid materials for high-rise constructions

NASA Astrophysics Data System (ADS)

Matseevich, Tatyana

2018-03-01

The theme of the research is important because it allows to use hybrid materials as finishing in the high-rise constructions. The aim of the study was the development of producing coloured hybrid materials based on liquid glass, a polyisocyanate, epoxy resin and 2.4-toluylenediisocyanate. The detailed study of the process of stress relaxation at different temperatures in the range of 20-100°C was provided. The study found that the obtained materials are subject to the simplified technology. The materials easy to turn different colors, and dyes (e.g. Sudan blue G) are the catalysts for the curing process of the polymeric precursors. The materials have improved mechanical relaxation properties, possess different color and presentable, can be easily combined with inorganic base (concrete, metal). The limit of compressive strength varies from 32 to 17.5 MPa at a temperature of 20 to 100°C. The values σ∞ are from 20.4 to 7.7 MPa within the temperature range from 20 to 100°C. The physical parameters of materials were evaluated basing on the data of stress relaxation: the initial stress σ0, which occurs at the end of the deformation to a predetermined value; quasi-equilibrium stress σ∞, which persists for a long time relaxation process. Obtained master curves provide prediction relaxation behavior for large durations of relaxation. The study obtained new results. So, the addition of epoxy resin in the composition of the precursor improves the properties of hybrid materials. By the method of IR spectroscopy identified chemical transformations in the course of obtaining the hybrid material. Evaluated mechanical performance of these materials is long-time. Applied modern physically-based memory functions, which perfectly describe the stress relaxation process.

Stress and strain relaxation in magnesium AZ31 rolled plate: In-situ neutron measurement and elastic viscoplastic polycrystal modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Huamiao; Clausen, Bjorn; Capolungo, Laurent

Continuous mechanical tests with strain holds (stress relaxation) and with stress holds (strain relaxation) are performed simultaneously with in-situ neutron measurements to analyze the mechanisms of stress and strain relaxation in Mg AZ31 rolled plate. A dislocation activity based constitutive model, accounting for internal stress statistical distributions, is proposed and implemented into an elastic viscoplastic self-consistent (EVPSC) framework to simultaneously describe both stress and strain relaxation. The model captures the experimental data in terms of macroscopic stress strain curves, evolution of stress and strain during holding, as well as evolution of the internal elastic strains. Model results indicate that themore » magnitude of the stress relaxed during strain holding is dependent on both, the magnitude of the flow stress and the spread of the resolved shear stress distribution. The magnitude of strain accumulated during stress holding is, on the other hand, dependent on the magnitude of the hardening rate and on the spread of the resolved shear stress distribution. Furthermore, the internal elastic strains are directly correlated with the stress state, and hence the stress relaxation during strain holds has a greater influence on the lattice strains than strain relaxation during stress holds.« less

Stress and strain relaxation in magnesium AZ31 rolled plate: In-situ neutron measurement and elastic viscoplastic polycrystal modeling

DOE PAGES

Wang, Huamiao; Clausen, Bjorn; Capolungo, Laurent; ...

2015-07-16

Continuous mechanical tests with strain holds (stress relaxation) and with stress holds (strain relaxation) are performed simultaneously with in-situ neutron measurements to analyze the mechanisms of stress and strain relaxation in Mg AZ31 rolled plate. A dislocation activity based constitutive model, accounting for internal stress statistical distributions, is proposed and implemented into an elastic viscoplastic self-consistent (EVPSC) framework to simultaneously describe both stress and strain relaxation. The model captures the experimental data in terms of macroscopic stress strain curves, evolution of stress and strain during holding, as well as evolution of the internal elastic strains. Model results indicate that themore » magnitude of the stress relaxed during strain holding is dependent on both, the magnitude of the flow stress and the spread of the resolved shear stress distribution. The magnitude of strain accumulated during stress holding is, on the other hand, dependent on the magnitude of the hardening rate and on the spread of the resolved shear stress distribution. Furthermore, the internal elastic strains are directly correlated with the stress state, and hence the stress relaxation during strain holds has a greater influence on the lattice strains than strain relaxation during stress holds.« less

Polymeric Materials Models in the Warrior Injury Assessment Manikin (WIAMan) Anthropomorphic Test Device (ATD) Tech Demonstrator

DTIC Science & Technology

2017-01-01

are the shear relaxation moduli and relaxation times , which make up the classical Prony series . A Prony- series expansion is a relaxation function...approximation for modeling time -dependent damping. The scalar parameters 1 and 2 control the nonlinearity of the Prony series . Under the...Velodyne that best fit the experimental stress-strain data. To do so, the Design Analysis Kit for Optimization and Terascale Applications (DAKOTA

Stress Relaxation in Tensile Deformation of 304 Stainless Steel

NASA Astrophysics Data System (ADS)

Li, Xifeng; Li, Jiaojiao; Ding, Wei; Zhao, Shuangjun; Chen, Jun

2017-02-01

Improved ductility by stress relaxation has been reported in different kinds of steels. The influence of stress relaxation and its parameters on the ductility of 304 stainless steel has not been established so far. Stress relaxation behavior during tensile tests at different strain rates is studied in 304 stainless steel. It is observed that stress relaxation can obviously increase the elongation of 304 stainless steel in all cases. The elongation improvement of interrupted tension reaches to 14.9% compared with monotonic tension at 0.05 s-1. Contradicting with the published results, stress drop during stress relaxation increases with strain at all strain rates. It is related with dislocation motion velocity variation and martensitic transformation.

Slip-deficit rate distribution along the Nankai trough, southwest Japan, with elastic lithosphere and viscoelastic asthenosphere

NASA Astrophysics Data System (ADS)

Noda, A.; Saito, T.; Fukuyama, E.

2017-12-01

In southwest Japan, great thrust earthquakes occurred on the plate interface along the Nankai trough with a recurrence time of about 100 yr. Most studies estimated slip deficits on the seismogenic zone from interseismic GNSS velocity data assuming elastic slip-response functions (e.g. Loveless and Meade, 2016; Yokota et al., 2016). The observed surface velocities, however, include effects of viscoelastic relaxation in the asthenosphere caused by slip history of seismic cycles on the plate interface. Following Noda et al. (2013, GJI), the interseismic surface velocities due to seismic cycle can be represented by the superposition of (1) completely relaxed viscoelastic response to steady slip rate over the whole plate interface, (2) completely relaxed viscoelastic response to steady slip deficit rate in the seismogenic zone, and (3) surface velocity due to viscoelastic stress relaxation after the last interplate earthquake. Subtracting calculated velocities due to steady slip (1) from velocity data observed after the postseismic stress relaxation (3) decays sufficiently, we can formulate an inverse problem of estimating slip deficit rates from the residual velocities using completely relaxed slip-response functions. In an elastic (lithosphere) - viscoelastic (asthenosphere) layered half-space, the completely relaxed responses do not depend on the viscosity of asthenosphere, but depend on the thickness of lithosphere. In this study, we investigate the effects of structure model on the estimation of slip deficit rate distribution. First, we analyze GNSS daily coordinate data (GEONET F3 Solution, GSI), and obtain surface velocity data for overlapped periods of 6 yr (1996-2002, 1999-2005, 2002-2008, 2005-2011). There is no significant temporal change in the velocity data, which suggests that postseismic stress relaxations after the 1944 Tonankai and the 1946 Nankai earthquakes decayed sufficiently. Next, we estimate slip deficit rate distribution from velocity data from 2005 to 2011 together with seafloor geodetic data (Yokota et al., 2016). There is a significant difference between the results using elastic and completely relaxed responses. While the result using elastic responses shows high slip-deficit rate zone in coastal regions, they are located trenchward if using completely relaxed responses.

Massage Therapy for Reducing Stress Hormones and Enhancing Immune Function in Breast Cancer Survivors

DTIC Science & Technology

2000-08-01

massage therapy (n=20), a relaxation therapy (n=20) or a control group (n=20). Women in the massage and relaxation therapies will receive 3 sessions a...women reveal that women in the massage therapy group showed (1) reduced anxiety, (2) improved mood, (3) increased serotonin levels and (4) increased...support for the hypotheses that massage therapy enhances mood and immune function for women with breast cancer.

Multiscale Relaxation Dynamics in Ultrathin Metallic Glass-Forming Films

NASA Astrophysics Data System (ADS)

Bi, Q. L.; Lü, Y. J.; Wang, W. H.

2018-04-01

The density layering phenomenon originating from a free surface gives rise to the layerlike dynamics and stress heterogeneity in ultrathin Cu-Zr glassy films, which facilitates the occurrence of multistep relaxations in the timescale of computer simulations. Taking advantage of this condition, we trace the relaxation decoupling and evolution with temperature simply via the intermediate scattering function. We show that the β relaxation hierarchically follows fast and slow modes in films, and there is a β -relaxation transition as the film is cooled close to the glass transition. We provide the direct observation of particle motions responsible for the β relaxation and reveal the dominant mechanism varying from the thermal activated to the cooperative jumps across the transition.

Deformation, Stress Relaxation, and Crystallization of Lithium Silicate Glass Fibers Below the Glass Transition Temperature

NASA Technical Reports Server (NTRS)

Ray, Chandra S.; Brow, Richard K.; Kim, Cheol W.; Reis, Signo T.

2004-01-01

The deformation and crystallization of Li(sub 2)O (center dot) 2SiO2 and Li(sub 2)O (center dot) 1.6SiO2 glass fibers subjected to a bending stress were measured as a function of time over the temperature range -50 to -150 C below the glass transition temperature (Tg). The glass fibers can be permanently deformed at temperatures about 100 C below T (sub)g, and they crystallize significantly at temperatures close to, but below T,, about 150 C lower than the onset temperature for crystallization for these glasses in the no-stress condition. The crystallization was found to occur only on the surface of the glass fibers with no detectable difference in the extent of crystallization in tensile and compressive stress regions. The relaxation mechanism for fiber deformation can be best described by a stretched exponential (Kohlrausch-Williams-Watt (KWW) approximation), rather than a single exponential model.The activation energy for stress relaxation, Es, for the glass fibers ranges between 175 and 195 kJ/mol, which is considerably smaller than the activation energy for viscous flow, E, (about 400 kJ/mol) near T, for these glasses at normal, stress-free condition. It is suspected that a viscosity relaxation mechanism could be responsible for permanent deformation and crystallization of the glass fibers below T,

Effects of progressive relaxation and classical music on measurements of attention, relaxation, and stress responses.

PubMed

Scheufele, P M

2000-04-01

The present experiment examined relaxation using different experimental conditions to test whether the effects of individual elements of relaxation could be measured, whether specific effects were revealed, or whether relaxation resulted from a generalized "relaxation response." Sixty-seven normal, male volunteers were exposed to a stress manipulation and then to one of two relaxation (Progressive Relaxation, Music) or control (Attention Control, Silence) conditions. Measurements of attention, relaxation, and stress responses were obtained during each phase of the experiment. All four groups exhibited similar performance on behavioral measures of attention that suggested a reduction in physiological arousal following their relaxation or control condition, as well as a decreased heart rate. Progressive Relaxation, however, resulted in the greatest effects on behavioral and self-report measures of relaxation, suggesting that cognitive cues provided by stress management techniques contribute to relaxation.

Method and apparatus for cartilage reshaping by radiofrequency heating

DOEpatents

Wong, Brian J.; Milner, Thomas E.; Sobol, Emil N.; Keefe, Michael W.

2003-07-08

A method and apparatus for reshaping cartilage using radiofrequency heating. The cartilage temperature is raised sufficiently for stress relaxation to occur in the cartilage, but low enough so that significant denaturation of the cartilage does not occur. The RF electrodes may be designed to also function as molds, preses, clamps, or mandrills to deform the cartilage tissue. Changes in various properties of the cartilage associated with stress relaxation in the cartilage may be measured in order to provide the control signal to provide effective reshaping without denaturation.

Neural correlates of stress-induced and cue-induced drug craving: influences of sex and cocaine dependence.

PubMed

Potenza, Marc N; Hong, Kwang-ik Adam; Lacadie, Cheryl M; Fulbright, Robert K; Tuit, Keri L; Sinha, Rajita

2012-04-01

Although stress and drug cue exposure each increase drug craving and contribute to relapse in cocaine dependence, no previous research has directly examined the neural correlates of stress-induced and drug cue-induced craving in cocaine-dependent women and men relative to comparison subjects. Functional MRI was used to assess responses to individualized scripts for stress, drug/alcohol cue and neutral-relaxing-imagery conditions in 30 abstinent cocaine-dependent individuals (16 women, 14 men) and 36 healthy recreational-drinking comparison subjects (18 women, 18 men). Significant three-way interactions between diagnostic group, sex, and script condition were observed in multiple brain regions including the striatum, insula, and anterior and posterior cingulate. Within women, group-by-condition interactions were observed involving these regions and were attributable to relatively increased regional activations in cocaine-dependent women during the stress and, to a lesser extent, neutral-relaxing conditions. Within men, group main effects were observed involving these same regions, with cocaine-dependent men demonstrating relatively increased activation across conditions, with the main contributions from the drug and neutral-relaxing conditions. In men and women, subjective drug-induced craving measures correlated positively with corticostriatal-limbic activations. In cocaine dependence, corticostriatal-limbic hyperactivity appears to be linked to stress cues in women, drug cues in men, and neutral-relaxing conditions in both. These findings suggest that sex should be taken into account in the selection of therapies in the treatment of addiction, particularly those targeting stress reduction.

Massage Therapy for Reducing Stress Hormones and Enhancing Immune Function in Breast Cancer Survivors

DTIC Science & Technology

2001-08-01

massage therapy (n=20), a relaxation therapy (n=20) or a control group (n=20). Women in the massage and relaxation therapies will receive 3 sessions a...women reveal for the massage therapy group 1) reduced anxiety, 2) improved mood, 3) increased serotonin and dopamine levels and 4) increased Natural

Heart rate variability is enhanced in controls but not maladaptive perfectionists during brief mindfulness meditation following stress-induction: A stratified-randomized trial.

PubMed

Azam, Muhammad Abid; Katz, Joel; Fashler, Samantha R; Changoor, Tina; Azargive, Saam; Ritvo, Paul

2015-10-01

Heart rate variability (HRV) is a vagal nerve-mediated biomarker of cardiac function used to investigate chronic illness, psychopathology, stress and, more recently, attention-regulation processes such as meditation. This study investigated HRV in relation to maladaptive perfectionism, a stress-related personality factor, and mindfulness meditation, a stress coping practice expected to elevate HRV, and thereby promote relaxation. Maladaptive perfectionists (n=21) and Controls (n=39) were exposed to a lab-based assessment in which HRV was measured during (1) a 5-minute baseline resting phase, (2) a 5-minute cognitive stress-induction phase, and (3) a post-stress phase. In the post-stress phase, participants were randomly assigned to a 10-minute audio-instructed mindfulness meditation condition or a 10-minute rest condition with audio-description of mindfulness meditation. Analyses revealed a significant elevation in HRV during meditation for Controls but not for Perfectionists. These results suggest that mindfulness meditation promotes relaxation following cognitive stress and that the perfectionist personality hinders relaxation possibly because of decreased cardiac vagal tone. The results are discussed in the context of developing psychophysiological models to advance therapeutic interventions for distressed populations. Copyright © 2015 Elsevier B.V. All rights reserved.

Poly(ADP-ribose) polymerase-1 protects from oxidative stress induced endothelial dysfunction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gebhard, Catherine; Staehli, Barbara E.; Zurich Center for Integrative Human Physiology

2011-11-04

Highlights: Black-Right-Pointing-Pointer The nuclear enzyme PARP-1 is a downstream effector of oxidative stress. Black-Right-Pointing-Pointer PARP-1 protects from oxidative stress induced endothelial dysfunction. Black-Right-Pointing-Pointer This effect is mediated through inhibition of vasoconstrictor prostanoid production. Black-Right-Pointing-Pointer Thus, PARP-1 may play a protective role as antioxidant defense mechanism. -- Abstract: Background: Generation of reactive oxygen species (ROS) is a key feature of vascular disease. Activation of the nuclear enzyme poly (adenosine diphosphate [ADP]-ribose) polymerase-1 (PARP-1) is a downstream effector of oxidative stress. Methods: PARP-1(-/-) and PARP-1(+/+) mice were injected with paraquat (PQ; 10 mg/kg i.p.) to induce intracellular oxidative stress. Aortic rings weremore » suspended in organ chambers for isometric tension recording to analyze vascular function. Results: PQ treatment markedly impaired endothelium-dependent relaxations to acetylcholine in PARP-1(-/-), but not PARP-1(+/+) mice (p < 0.0001). Maximal relaxation was 45% in PQ treated PARP-1(-/-) mice compared to 79% in PARP-1(+/+) mice. In contrast, endothelium-independent relaxations to sodium nitroprusside (SNP) were not altered. After PQ treatment, L-NAME enhanced contractions to norepinephrine by 2.0-fold in PARP-1(-/-) mice, and those to acetylcholine by 3.3-fold, respectively, as compared to PARP-1(+/+) mice. PEG-superoxide dismutase (SOD) and PEG-catalase prevented the effect of PQ on endothelium-dependent relaxations to acetylcholine in PARP-1(-/-) mice (p < 0.001 vs. PQ treated PARP-1(+/+) mice. Indomethacin restored endothelium-dependent relaxations to acetylcholine in PQ treated PARP-1(-/-) mice (p < 0.05 vs. PQ treated PARP-1(+/+). Conclusion: PARP-1 protects from acute intracellular oxidative stress induced endothelial dysfunction by inhibiting ROS induced production of vasoconstrictor prostanoids.« less

[Effects of Monochord Music on Heart Rate Variability and Self-Reports of Relaxation in Healthy Adults].

PubMed

Gäbel, Christine; Garrido, Natalia; Koenig, Julian; Hillecke, Thomas Karl; Warth, Marco

Music-based interventions are considered an effective and low-cost treatment option for stress-related symptoms. The present study aimed to examine the trajectories of the psychophysiological response in apparently healthy participants during a music-based relaxation intervention compared to a verbal relaxation exercise. 70 participants were assigned to either receptive live music (experimental group) or a prerecorded verbal relaxation exercise (control group). Self-ratings of relaxation were assessed before and after each intervention on visual analogue scales and the Relaxation Inventory (RI). The heart rate variability (HRV) was continuously recorded throughout the sessions. Statistical analysis focused on HRV parameters indicative of parasympathetic cardiovascular outflow. We found significant quadratic main effects for time on the mean R-R interval (heart rate), the high-frequency power of HRV (indicative of parasympathetic activity), and the self-ratings of relaxation in both groups. A significant group × time interaction was observed for the cognitive tension subscale of the RI. Participants in both groups showed psychophysiological changes indicative of greater relaxation over the course of the interventions. However, differences between groups were only marginal. Music might be effective in relieving stress and promoting relaxation by altering the autonomic nervous system function. Future studies need to explore the long-term outcomes of such interventions. © 2017 S. Karger GmbH, Freiburg.

Cytokines and macrophage function in humans - role of stress

NASA Technical Reports Server (NTRS)

Sonnenfeld, Gerald (Principal Investigator)

1996-01-01

We have begun this study to commence the determination of the role of mild chronic stress in the effects of space flight on macrophage/monocyte function, a component of the immune response. Medical students undergoing regular periods of stress and relaxation have been shown to be an excellent model for determining the effects of stress on immune responses. We have begun using this model using the macrophage/monocyte as model leukocyte. The monocyte/macrophage plays a central role in immunoregulation. The studies to be included in this three year project are the effects of stress on: (1) interactions of monocytes with microbes, (2) monocyte production of cytokines, (3) monocyte phagocytosis and activity, and (4) monocyte expression of cell surface antigens important in immune responses. Stress hormone levels will also be carried out to determine if there is a correlation between stress effects on immune responses and hormonal levels. Psychological testing to insure subjects are actually stressed or relaxed at the time of testing will also be carried out. The results obtained from the proposed studies should be comparable with space flight studies with whole animals and isolated cell cultures. When complete this study should allow the commencement of the establishment of the role of stress as one compartment of the induction of immune alterations by space flight.

Idiosyncratic reality claims, relaxation dispositions, and ABC relaxation theory: happiness, literal christianity, miraculous powers, metaphysics, and the paranormal.

PubMed

Smith, Jonathan C; Karmin, Aaron D

2002-12-01

This study examined idiosyncratic reality claims, that is, irrational or paranormal beliefs often claimed to enhance relaxation and happiness and reduce stress. The Smith Idiosyncratic Reality Claims Inventory and the Smith Relaxation Dispositions Inventory (which measures relaxation and stress dispositions, or enduring states of mind frequently associated with relaxation or stress) were given to 310 junior college student volunteers. Principal components factor analysis with varimax rotation identified five idiosyncratic reality claim factors: belief in Literal Christianity; Magic; Space Aliens: After Death experiences; and Miraculous Powers of Meditation, Prayer, and Belief. No factor correlated with increased relaxation dispositions Peace, Energy, or Joy, or reduced dispositional somatic stress, worry, or negative emotion on the Smith Relaxation Dispositions Inventory. It was concluded that idiosyncratic reality claims may not be associated with reported relaxation, happiness, or stress. In contrast, previous research strongly supported self-affirming beliefs with few paranormal assumptions display such an association.

Stress relaxation and mechanical properties of RL-1973 and PD-200-16 silicone resin sponge materials

NASA Technical Reports Server (NTRS)

Saylak, D.; Noel, J. S.; Ham, J. S.; Mccoy, R.

1975-01-01

Stress relaxation tests were conducted by loading specimens in double-lap shear to a preselected strain level and monitoring the decay of stress with time. The stress relaxation response characteristics were measured over a temperature range of 100 to 300 K and four strain levels. It is concluded that only a slight amount of stress relaxation was observed, and the stiffness increased approximately two orders of magnitude over the range of temperatures.

Hydrogels with tunable stress relaxation regulate stem cell fate and activity

NASA Astrophysics Data System (ADS)

Chaudhuri, Ovijit; Gu, Luo; Klumpers, Darinka; Darnell, Max; Bencherif, Sidi A.; Weaver, James C.; Huebsch, Nathaniel; Lee, Hong-Pyo; Lippens, Evi; Duda, Georg N.; Mooney, David J.

2016-03-01

Natural extracellular matrices (ECMs) are viscoelastic and exhibit stress relaxation. However, hydrogels used as synthetic ECMs for three-dimensional (3D) culture are typically elastic. Here, we report a materials approach to tune the rate of stress relaxation of hydrogels for 3D culture, independently of the hydrogel's initial elastic modulus, degradation, and cell-adhesion-ligand density. We find that cell spreading, proliferation, and osteogenic differentiation of mesenchymal stem cells (MSCs) are all enhanced in cells cultured in gels with faster relaxation. Strikingly, MSCs form a mineralized, collagen-1-rich matrix similar to bone in rapidly relaxing hydrogels with an initial elastic modulus of 17 kPa. We also show that the effects of stress relaxation are mediated by adhesion-ligand binding, actomyosin contractility and mechanical clustering of adhesion ligands. Our findings highlight stress relaxation as a key characteristic of cell-ECM interactions and as an important design parameter of biomaterials for cell culture.

[Mind-body approach in the area of preventive medicine: focusing on relaxation and meditation for stress management].

PubMed

Kang, Yunesik

2010-09-01

Emotional support and a stress management program should be simultaneously provided to clients as effective preventive services for healthy behavioral change. This study was conducted to review various relaxation and meditation intervention methods and their applicability for a preventive service program. The author of this paper tried to find various relaxation and meditation programs through a literature review and program searching and to introduce them. The 'Relaxation Response' and 'Mindfulness Based Stress Reduction (MBSR)' are the most the widely used meditative programs in mainstream medical systems. Abdominal breathing, Progressive Musclular Relaxation (PMR), Relaxative Imagery, Autogenic Training (AT) and Biofeedback are other well-known techniques for relaxation and stress management. I have developed and implemented some programs using these methods. Relaxation and meditation classes for cancer patients and a meditation based stress coping workshop are examples of this program. Relaxation and meditation seem to be good and effective methods for primary, secondary and tertiary preventive service programs. Program development and standardization and further study are needed for more and wider use of the mind-body approach in the preventive service area of medicine.

Modeling and Predicting the Stress Relaxation of Composites with Short and Randomly Oriented Fibers

PubMed Central

Obaid, Numaira; Sain, Mohini

2017-01-01

The addition of short fibers has been experimentally observed to slow the stress relaxation of viscoelastic polymers, producing a change in the relaxation time constant. Our recent study attributed this effect of fibers on stress relaxation behavior to the interfacial shear stress transfer at the fiber-matrix interface. This model explained the effect of fiber addition on stress relaxation without the need to postulate structural changes at the interface. In our previous study, we developed an analytical model for the effect of fully aligned short fibers, and the model predictions were successfully compared to finite element simulations. However, in most industrial applications of short-fiber composites, fibers are not aligned, and hence it is necessary to examine the time dependence of viscoelastic polymers containing randomly oriented short fibers. In this study, we propose an analytical model to predict the stress relaxation behavior of short-fiber composites where the fibers are randomly oriented. The model predictions were compared to results obtained from Monte Carlo finite element simulations, and good agreement between the two was observed. The analytical model provides an excellent tool to accurately predict the stress relaxation behavior of randomly oriented short-fiber composites. PMID:29053601

Time-Dependent Testing Evaluation and Modeling for Rubber Stopper Seal Performance.

PubMed

Zeng, Qingyu; Zhao, Xia

2018-01-01

Sufficient rubber stopper sealing performance throughout the entire sealed product life cycle is essential for maintaining container closure integrity in the parenteral packaging industry. However, prior publications have lacked systematic considerations for the time-dependent influence on sealing performance that results from the viscoelastic characteristics of the rubber stoppers. In this paper, we report results of an effort to study these effects by applying both compression stress relaxation testing and residual seal force testing for time-dependent experimental data collection. These experiments were followed by modeling fit calculations based on the Maxwell-Wiechert theory modified with the Kohlrausch-Williams-Watts stretched exponential function, resulting in a nonlinear, time-dependent sealing force model. By employing both testing evaluations and modeling calculations, an in-depth understanding of the time-dependent effects on rubber stopper sealing force was developed. Both testing and modeling data show good consistency, demonstrating that the sealing force decays exponentially over time and eventually levels off because of the viscoelastic nature of the rubber stoppers. The nonlinearity of stress relaxation derives from the viscoelastic characteristics of the rubber stoppers coupled with the large stopper compression deformation into restrained geometry conditions. The modeling fit with capability to handle actual testing data can be employed as a tool to calculate the compression stress relaxation and residual seal force throughout the entire sealed product life cycle. In addition to being time-dependent, stress relaxation is also experimentally shown to be temperature-dependent. The present work provides a new, integrated methodology framework and some fresh insights to the parenteral packaging industry for practically and proactively considering, designing, setting up, controlling, and managing stopper sealing performance throughout the entire sealed product life cycle. LAY ABSTRACT: Historical publications in the parenteral packaging industry have lacked systematic considerations for the time-dependent influence on the sealing performance that results from effects of viscoelastic characteristic of the rubber stoppers. This study applied compression stress relaxation testing and residual seal force testing for time-dependent experimental data collection. These experiments were followed by modeling fit calculations based on the Maxwell-Wiechert theory modified with the Kohlrausch-Williams-Watts stretched exponential function, resulting in a nonlinear, time-dependent sealing force model. Experimental and modeling data show good consistency, demonstrating that sealing force decays exponentially over time and eventually levels off. The nonlinearity of stress relaxation derives from the viscoelastic characteristics of the rubber stoppers coupled with the large stopper compression deformation into restrained geometry conditions. In addition to being time-dependent stress relaxation, it is also experimentally shown to be temperature-dependent. The present work provides a new, integrated methodology framework and some fresh insights to the industry for practically and proactively considering, designing, setting up, controlling, and managing of the stopper sealing performance throughout the entire sealed product life cycle. © PDA, Inc. 2018.

Dissipation of mechanical work and temperature rise in AS4/PEEK thermoplastic composite

NASA Technical Reports Server (NTRS)

Georgiou, I.; Sun, C. T.

1990-01-01

The dissipated mechanical work per cycle of sinusoidal stress in the thermoplastic composite material AS4/PEEK was measured as a function of stress amplitude for fixed frequency and fiber orientation. The experimental result shows that the dissipated work per cycle is proportional to the square of the stress amplitude. Using the concept of the equivalent isotropic material, it is shown that the relaxation modulus satisfies a proportionality condition. Also, the rate of temperature rise due to sinusoidal stresses has been measured as a function of stress amplitude. The result shows that the rate of temperature rise is not proportional to the square of the stress amplitude.

How Do You #relax When You're #stressed? A Content Analysis and Infodemiology Study of Stress-Related Tweets.

PubMed

Doan, Son; Ritchart, Amanda; Perry, Nicholas; Chaparro, Juan D; Conway, Mike

2017-06-13

Stress is a contributing factor to many major health problems in the United States, such as heart disease, depression, and autoimmune diseases. Relaxation is often recommended in mental health treatment as a frontline strategy to reduce stress, thereby improving health conditions. Twitter is a microblog platform that allows users to post their own personal messages (tweets), including their expressions about feelings and actions related to stress and stress management (eg, relaxing). While Twitter is increasingly used as a source of data for understanding mental health from a population perspective, the specific issue of stress-as manifested on Twitter-has not yet been the focus of any systematic study. The objective of our study was to understand how people express their feelings of stress and relaxation through Twitter messages. In addition, we aimed at investigating automated natural language processing methods to (1) classify stress versus nonstress and relaxation versus nonrelaxation tweets, and (2) identify first-hand experience-that is, who is the experiencer-in stress and relaxation tweets. We first performed a qualitative content analysis of 1326 and 781 tweets containing the keywords "stress" and "relax," respectively. We then investigated the use of machine learning algorithms-in particular naive Bayes and support vector machines-to automatically classify tweets as stress versus nonstress and relaxation versus nonrelaxation. Finally, we applied these classifiers to sample datasets drawn from 4 cities in the United States (Los Angeles, New York, San Diego, and San Francisco) obtained from Twitter's streaming application programming interface, with the goal of evaluating the extent of any correlation between our automatic classification of tweets and results from public stress surveys. Content analysis showed that the most frequent topic of stress tweets was education, followed by work and social relationships. The most frequent topic of relaxation tweets was rest & vacation, followed by nature and water. When we applied the classifiers to the cities dataset, the proportion of stress tweets in New York and San Diego was substantially higher than that in Los Angeles and San Francisco. In addition, we found that characteristic expressions of stress and relaxation varied for each city based on its geolocation. This content analysis and infodemiology study revealed that Twitter, when used in conjunction with natural language processing techniques, is a useful data source for understanding stress and stress management strategies, and can potentially supplement infrequently collected survey-based stress data. ©Son Doan, Amanda Ritchart, Nicholas Perry, Juan D Chaparro, Mike Conway. Originally published in JMIR Public Health and Surveillance (http://publichealth.jmir.org), 13.06.2017.

Model and prediction of stress relaxation of polyurethane fiber

NASA Astrophysics Data System (ADS)

You, Gexin; Wang, Chunyan; Mei, Shuqin; Yang, Bo; Zhou, Xiuwen

2018-03-01

In this study, the effect of small strain (less than 10%) on hydrogen bond (H-bond) and crystallinity of dry-spun polyurethane fiber was investigated with fourier transform infrared spectroscopy and x-ray diffractometer, respectively. The results showed that the H-bond of hard segments hardly broke and its degree of crystallinity scarcely varied below strain of 10%. The fiber stress relaxation behavior at 25 °C under small strain was researched using dynamic mechanical analyzer. The stress relaxation modulus constitutive equation was obtained by transforming the non-linear relationship between stress and time into the linear relationship between stress and strain. The stress relaxation modulus master curve at 25 °C was established in terms of short-term stress relaxation tests at elevated temperatures (35 °C, 45 °C, 65 °C and 75 °C) according to time-temperature superposition principle (TTS) to predict long-term behavior within 353 year.

Hydrogels with tunable stress relaxation regulate stem cell fate and activity

PubMed Central

Chaudhuri, Ovijit; Gu, Luo; Klumpers, Darinka; Darnell, Max; Bencherif, Sidi A.; Weaver, James C.; Huebsch, Nathaniel; Lee, Hong-pyo; Lippens, Evi; Duda, Georg N.; Mooney, David J.

2015-01-01

Natural extracellular matrices (ECMs) are viscoelastic and exhibit stress relaxation. However, hydrogels used as synthetic ECMs for three-dimensional (3D) culture are typically elastic. Here, we report a materials approach to tune the rate of stress relaxation of hydrogels for 3D culture, independently of the hydrogel’s initial elastic modulus, cell-adhesion-ligand density and degradation. We find that cell spreading, proliferation, and osteogenic differentiation of mesenchymal stem cells (MSCs) are all enhanced in cells cultured in gels with faster relaxation. Strikingly, MSCs form a mineralized, collagen-1-rich matrix similar to bone in rapidly relaxing hydrogels with an initial elastic modulus of 17 kPa. We also show that the effects of stress relaxation are mediated by adhesion-ligand binding, actomyosin contractility and mechanical clustering of adhesion ligands. Our findings highlight stress relaxation as a key characteristic of cell-ECM interactions and as an important design parameter of biomaterials for cell culture. PMID:26618884

Frequency and Wavevector Dependence of the Atomic Level Stress-Stress Correlation Function in a Model Supercooled Liquid

NASA Astrophysics Data System (ADS)

Levashov, Valentin A.; Morris, James R.; Egami, Takeshi

2012-02-01

Temporal and spatial correlations among the local atomic level shear stresses were studied for a model liquid iron by molecular dynamics simulation [PRL 106,115703]. Integration over time and space of the shear stress correlation function F(r,t) yields viscosity via Green-Kubo relation. The stress correlation function in time and space F(r,t) was Fourier transformed to study the dependence on frequency, E, and wave vector, Q. The results, F(Q,E), showed damped shear stress waves propagating in the liquid for small Q at high and low temperatures. We also observed additional diffuse feature that appears as temperature is reduced below crossover temperature of potential energy landscape at relatively low frequencies at small Q. We suggest that this additional feature might be related to dynamic heterogeneity and boson peaks. We also discuss a relation between the time-scale of the stress-stress correlation function and the alpha-relaxation time of the intermediate self-scattering function S(Q,E).

Music listening as a means of stress reduction in daily life.

PubMed

Linnemann, Alexandra; Ditzen, Beate; Strahler, Jana; Doerr, Johanna M; Nater, Urs M

2015-10-01

The relation between music listening and stress is inconsistently reported across studies, with the major part of studies being set in experimental settings. Furthermore, the psychobiological mechanisms for a potential stress-reducing effect remain unclear. We examined the potential stress-reducing effect of music listening in everyday life using both subjective and objective indicators of stress. Fifty-five healthy university students were examined in an ambulatory assessment study, both during a regular term week (five days) and during an examination week (five days). Participants rated their current music-listening behavior and perceived stress levels four times per day, and a sub-sample (n = 25) additionally provided saliva samples for the later analysis of cortisol and alpha-amylase on two consecutive days during both weeks. Results revealed that mere music listening was effective in reducing subjective stress levels (p = 0.010). The most profound effects were found when 'relaxation' was stated as the reason for music listening, with subsequent decreases in subjective stress levels (p ≤ 0.001) and lower cortisol concentrations (p ≤ 0.001). Alpha-amylase varied as a function of the arousal of the selected music, with energizing music increasing and relaxing music decreasing alpha-amylase activity (p = 0.025). These findings suggest that music listening can be considered a means of stress reduction in daily life, especially if it is listened to for the reason of relaxation. Furthermore, these results shed light on the physiological mechanisms underlying the stress-reducing effect of music, with music listening differentially affecting the physiological stress systems. Copyright © 2015 Elsevier Ltd. All rights reserved.

Stress relaxation of grouted entirely large diameter B-GFRP soil nail

NASA Astrophysics Data System (ADS)

Li, Guo-wei; Ni, Chun; Pei, Hua-fu; Ge, Wan-ming; Ng, Charles Wang Wai

2013-08-01

One of the potential solutions to steel-corrosion-related problems is the usage of fiber reinforced polymer (FRP) as a replacement of steel bars. In the past few decades, researchers have conducted a large number of experimental and theoretical studies on the behavior of small size glass fiber reinforce polymer (GFRP) bars (diameter smaller than 20 mm). However, the behavior of large size GFRP bar is still not well understood. Particularly, few studies were conducted on the stress relaxation of grouted entirely large diameter GFRP soil nail. This paper investigates the effect of stress levels on the relaxation behavior of GFRP soil nail under sustained deformation ranging from 30% to 60% of its ultimate strain. In order to study the behavior of stress relaxation, two B-GFRP soil nail element specimens were developed and instrumented with fiber Bragg grating (FBG) strain sensors which were used to measure strains along the B-GFRP bars. The test results reveal that the behavior of stress relaxation of B-GFRP soil nail element subjected to pre-stress is significantly related to the elapsed time and the initial stress of relaxation procedure. The newly proposed model for evaluating stress relaxation ratio can substantially reflect the influences of the nature of B-GFRP bar and the property of grip body. The strain on the nail body can be redistributed automatically. Modulus reduction is not the single reason for the stress degradation.

Effects of Stress and Relaxation on Central Pain Modulation in Chronic Whiplash and Fibromyalgia Patients Compared to Healthy Controls.

PubMed

Coppieters, Iris; Cagnie, Barbara; Nijs, Jo; van Oosterwijck, Jessica; Danneels, Lieven; De Pauw, Robby; Meeus, Mira

2016-03-01

Compelling evidence has demonstrated that impaired central pain modulation contributes to persistent pain in patients with chronic whiplash associated disorders (WAD) and fibromyalgia (FM). However, there is limited research concerning the influence of stress and relaxation on central pain modulation in patients with chronic WAD and FM. The present study aims to investigate the effects of acute cognitive stress and relaxation on central pain modulation in chronic WAD and FM patients compared to healthy individuals. A randomized crossover design was employed. The present study took place at the University of Brussels, the University Hospital Brussels, and the University of Antwerp. Fifty-nine participants (16 chronic WAD patients, 21 FM, 22 pain-free controls) were enrolled and subjected to various pain measurements. Temporal summation (TS) of pain and conditioned pain modulation (CPM) were evaluated. Subsequently, participants were randomly allocated to either a group that received progressive relaxation therapy or a group that performed a battery of cognitive tests (= cognitive stressor). Afterwards, all pain measurements were repeated. One week later participant groups were switched. A significant difference was found between the groups in the change in TS in response to relaxation (P = 0.008) and cognitive stress (P = 0.003). TS decreased in response to relaxation and cognitive stress in chronic WAD patients and controls. In contrast, TS increased after both interventions in FM patients. CPM efficacy decreased in all 3 groups in response to relaxation (P = 0.002) and cognitive stress (P = 0.001). The obtained results only apply for a single session of muscle relaxation therapy and cognitive stress, whereby no conclusions can be made for effects on pain perception and modulation of chronic cognitive stress and long-term relaxation therapies. A single relaxation session as well as cognitive stress may have negative acute effects on pain modulation in patients with FM, while cognitive stress and relaxation did not worsen bottom-up sensitization in chronic WAD patients and healthy persons. However, endogenous pain inhibition, assessed using a CPM paradigm, worsened in chronic WAD and FM patients, as well as in healthy people following both interventions.

How Do You #relax When You’re #stressed? A Content Analysis and Infodemiology Study of Stress-Related Tweets

PubMed Central

Ritchart, Amanda; Perry, Nicholas; Chaparro, Juan D; Conway, Mike

2017-01-01

Background Stress is a contributing factor to many major health problems in the United States, such as heart disease, depression, and autoimmune diseases. Relaxation is often recommended in mental health treatment as a frontline strategy to reduce stress, thereby improving health conditions. Twitter is a microblog platform that allows users to post their own personal messages (tweets), including their expressions about feelings and actions related to stress and stress management (eg, relaxing). While Twitter is increasingly used as a source of data for understanding mental health from a population perspective, the specific issue of stress—as manifested on Twitter—has not yet been the focus of any systematic study. Objective The objective of our study was to understand how people express their feelings of stress and relaxation through Twitter messages. In addition, we aimed at investigating automated natural language processing methods to (1) classify stress versus nonstress and relaxation versus nonrelaxation tweets, and (2) identify first-hand experience—that is, who is the experiencer—in stress and relaxation tweets. Methods We first performed a qualitative content analysis of 1326 and 781 tweets containing the keywords “stress” and “relax,” respectively. We then investigated the use of machine learning algorithms—in particular naive Bayes and support vector machines—to automatically classify tweets as stress versus nonstress and relaxation versus nonrelaxation. Finally, we applied these classifiers to sample datasets drawn from 4 cities in the United States (Los Angeles, New York, San Diego, and San Francisco) obtained from Twitter’s streaming application programming interface, with the goal of evaluating the extent of any correlation between our automatic classification of tweets and results from public stress surveys. Results Content analysis showed that the most frequent topic of stress tweets was education, followed by work and social relationships. The most frequent topic of relaxation tweets was rest & vacation, followed by nature and water. When we applied the classifiers to the cities dataset, the proportion of stress tweets in New York and San Diego was substantially higher than that in Los Angeles and San Francisco. In addition, we found that characteristic expressions of stress and relaxation varied for each city based on its geolocation. Conclusions This content analysis and infodemiology study revealed that Twitter, when used in conjunction with natural language processing techniques, is a useful data source for understanding stress and stress management strategies, and can potentially supplement infrequently collected survey-based stress data. PMID:28611016

Stress-relaxation heat treatment in FeSiBNb amorphous alloy: Thermal, microstructure, nanomechanical and magnetic texture measurements

NASA Astrophysics Data System (ADS)

Lashgari, H. R.; Cadogan, J. M.; Kong, C.; Tang, C.; Doherty, C.; Chu, D.; Li, S.

2018-06-01

In the present study, the effect of stress-relaxation treatment (Tstress-relaxation < Tglass transition) on the magnetic texture, nanomechanical properties, and variation of free-volume in FeSiBNb amorphous alloy was investigated using Mössbauer spectroscopy, nanoindentation, dynamic mechanical analysis (DMA), and positron annihilation lifetime spectroscopy (PALS) techniques. It was shown that stress-relaxation treatment slightly improved the magnetic texture by 6% at T ≪Tg due to small-scale displacement of atoms whereas the magnetic texture was deteriorated due to thermal treatment at temperatures around the glass transition point (large-scale displacement of atoms). According to nanoindentation results, the hardness (H) and reduced modulus (Er) of the amorphous ribbon increased by 15% and 13%, respectively, after stress-relaxation treatment at 716 K for 5 min. Increasing the stress-relaxation time from 5 min to 60 min at 716 K resulted in decreases in the hardness and reduced modulus which are attributed to the increase of free-volume defects (increase of τ2 lifetime measured by PALS). Transmission electron microscopy (TEM) showed the formation of extremely fine embryos of α-Fe (3-5 nm in size) after stress-relaxation treatment.

Endothelial relaxation mechanisms and nitrative stress are partly restored by Vitamin D3 therapy in a rat model of polycystic ovary syndrome.

PubMed

Masszi, Gabriella; Benko, Rita; Csibi, Noemi; Horvath, Eszter M; Tokes, Anna-Maria; Novak, Agnes; Beres, Nora Judit; Tarszabo, Robert; Buday, Anna; Repas, Csaba; Bekesi, Gabor; Patocs, Attila; Nadasy, Gyorgy L; Hamar, Peter; Benyo, Zoltan; Varbiro, Szabolcs

2013-08-06

In polycystic ovary syndrome (PCOS), metabolic and cardiovascular dysfunction is related to hyperandrogenic status and insulin resistance, however, Vitamin D3 has a beneficial effect partly due to its anti-oxidant capacity. Nitrative stress is a major factor in the development of cardiovascular dysfunction and insulin resistance in various diseases. Our aim was to determine the effects of vitamin D3 in a rat model of PCOS, particularly the pathogenic role of nitrative stress. Female Wistar rats weighing 100-140g were administered vehicle (C), dihydrotestosterone (DHT) or dihydrotestosterone plus vitamin D3 (DHT+D) (n=10 per group). On the 10th week, acetylcholine (Ach) induced relaxation ability of the isolated thoracic aorta rings was determined. In order to examine the possible role of endothelial nitric oxide synthase (eNOS) and cyclooxygenase-2 (COX-2) pathways in the impaired endothelial function, immunohistochemical labeling of aortas with anti-eNOS and anti-COX-2 antibodies was performed. Leukocyte smears, aorta and ovary tissue sections were also immunostained with anti-nitrotyrosine antibody to determine nitrative stress. Relaxation ability of aorta was reduced in group DHT, and vitamin D3 partly restored Ach induced relaxation. eNOS labeling was significantly lower in DHT rats compared to the other two groups, however COX-2 staining showed an increment. Nitrative stress showed a significant increase in response to dihydrotestosterone, while vitamin D3 treatment, in case of the ovaries, was able to reverse this effect. Nitrative stress may play a role in the pathogenesis of PCOS and in the development of the therapeutic effect of vitamin D3. Copyright © 2013 Elsevier Inc. All rights reserved.

Combining walking and relaxation for stress reduction-A randomized cross-over trial in healthy adults.

PubMed

Matzer, Franziska; Nagele, Eva; Lerch, Nikolaus; Vajda, Christian; Fazekas, Christian

2018-04-01

Both physical activity and relaxation have stress-relieving potential. This study investigates their combined impact on the relaxation response while considering participants' initial stress level. In a randomized cross-over trial, 81 healthy adults completed 4 types of short-term interventions for stress reduction, each lasting for 1 hr: (1) physical activity (walking) combined with resting, (2) walking combined with balneotherapy, (3) combined resting and balneotherapy, and (4) resting only. Saliva cortisol, blood pressure, state of mood, and relaxation were measured preintervention and postintervention. Stress levels were determined by validated questionnaires. All interventions were associated with relaxation responses in the variables saliva cortisol, blood pressure, state of mood, and subjective relaxation. No significant differences were found regarding the reduction of salivary cortisol (F = 1.30; p = .281). The systolic blood pressure was reduced best when walking was combined with balneotherapy or resting (F = 7.34; p < .001). Participants with high stress levels (n = 25) felt more alert after interventions including balneotherapy, whereas they reported an increase of tiredness when walking was combined with resting (F = 3.20; p = .044). Results suggest that combining physical activity and relaxation (resting or balneotherapy) is an advantageous short-term strategy for stress reduction as systolic blood pressure is reduced best while similar levels of relaxation can be obtained. Copyright © 2017 John Wiley & Sons, Ltd.

Bend stress relaxation and tensile primary creep of a polycrystalline alpha-SiC fiber

NASA Technical Reports Server (NTRS)

Hee Man, Yun; Goldsby, Jon C.; Morscher, Gregory N.

1995-01-01

Understanding the thermomechanical behavior (creep and stress relaxation) of ceramic fibers is of both practical and basic interest. On the practical level, ceramic fibers are the reinforcement for ceramic matrix composites which are being developed for use in high temperature applications. It is important to understand and model the total creep of fibers at low strain levels where creep is predominantly in the primary stage. In addition, there are many applications where the component will only be subjected to thermal strains. Therefore, the stress relaxation of composite consituents in such circumstances will be an important factor in composite design and performance. The objective of this paper is to compare and analyze bend stress relaxation and tensile creep data for alpha-SiC fibers produced by the Carborundum Co. (Niagara Falls, NY). This fiber is of current technical interest and is similar in composition to bulk alpha-SiC which has been studied under compressive creep conditions. The temperature, time, and stress dependences will be discussed for the stress relaxation and creep results. In addition, some creep and relaxation recovery experiments were performed in order to understand the complete viscoelastic behavior, i.e. both recoverable and nonrecoverable creep components of these materials. The data will be presented in order to model the deformation behavior and compare relaxation and/or creep behavior for relatively low deformation strain conditions of practical concern. Where applicable, the tensile creep results will be compared to bend stress relaxation data.

The Application of Stress-Relaxation Test to Life Assessment of T911/T22 Weld Metal

NASA Astrophysics Data System (ADS)

Cao, Tieshan; Zhao, Jie; Cheng, Congqian; Li, Huifang

2016-03-01

A dissimilar weld metal was obtained through submerged arc welding of a T911 steel to a T22 steel, and its creep property was explored by stress-relaxation test assisted by some conventional creep tests. The creep rate information of the stress-relaxation test was compared to the minimum and the average creep rates of the conventional creep test. Log-log graph showed that the creep rate of the stress-relaxation test was in a linear relationship with the minimum creep rate of the conventional creep test. Thus, the creep rate of stress-relaxation test could be used in the Monkman-Grant relation to calculate the rupture life. The creep rate of the stress-relaxation test was similar to the average creep rate, and thereby the rupture life could be evaluated by a method of "time to rupture strain." The results also showed that rupture life which was assessed by the Monkman-Grant relation was more accurate than that obtained through the method of "time to rupture strain."

Stress relaxing hyaluronic acid-collagen hydrogels promote cell spreading, fiber remodeling, and focal adhesion formation in 3D cell culture.

PubMed

Lou, Junzhe; Stowers, Ryan; Nam, Sungmin; Xia, Yan; Chaudhuri, Ovijit

2018-02-01

The physical and architectural cues of the extracellular matrix (ECM) play a critical role in regulating important cellular functions such as spreading, migration, proliferation, and differentiation. Natural ECM is a complex viscoelastic scaffold composed of various distinct components that are often organized into a fibrillar microstructure. Hydrogels are frequently used as synthetic ECMs for 3D cell culture, but are typically elastic, due to covalent crosslinking, and non-fibrillar. Recent work has revealed the importance of stress relaxation in viscoelastic hydrogels in regulating biological processes such as spreading and differentiation, but these studies all utilize synthetic ECM hydrogels that are non-fibrillar. Key mechanotransduction events, such as focal adhesion formation, have only been observed in fibrillar networks in 3D culture to date. Here we present an interpenetrating network (IPN) hydrogel system based on HA crosslinked with dynamic covalent bonds and collagen I that captures the viscoelasticity and fibrillarity of ECM in tissues. The IPN hydrogels exhibit two distinct processes in stress relaxation, one from collagen and the other from HA crosslinking dynamics. Stress relaxation in the IPN hydrogels can be tuned by modulating HA crosslinker affinity, molecular weight of the HA, or HA concentration. Faster relaxation in the IPN hydrogels promotes cell spreading, fiber remodeling, and focal adhesion (FA) formation - behaviors often inhibited in other hydrogel-based materials in 3D culture. This study presents a new, broadly adaptable materials platform for mimicking key ECM features of viscoelasticity and fibrillarity in hydrogels for 3D cell culture and sheds light on how these mechanical and structural cues regulate cell behavior. Copyright © 2017 Elsevier Ltd. All rights reserved.

Work-related stress, inability to relax after work and risk of adult asthma: a population-based cohort study.

PubMed

Loerbroks, A; Gadinger, M C; Bosch, J A; Stürmer, T; Amelang, M

2010-10-01

There is an extensive literature linking stressful work conditions to adverse health outcomes. Notwithstanding, the relationship with asthma has not been examined, although various other measures of psychological stress have been associated with asthma. Therefore, we aimed to investigate the relation between work stress and asthma prevalence and incidence. We used data from a population-based cohort study (n = 5114 at baseline in 1992-1995 and n = 4010 at follow-up in 2002/2003). Asthma was measured by self-reports. Two scales that assessed psychologically adverse work conditions were extracted from a list of work-condition items by factor analysis (these scales were termed 'work stress' and 'inability to relax after work'). For each scale, the derived score was employed both as continuous z-score and as categorized variable in analyses. Associations with asthma were estimated by prevalence ratios (PRs) and risk ratios (RRs) using Poisson regression with a log-link function adjusting for demographics, health-related lifestyles, body mass index and family history of asthma. Analyses were restricted to those in employment (n = 3341). Work stress and inability to relax z-scores were positively associated with asthma prevalence (PR = 1.15, 95%CI = 0.97, 1.36 and PR = 1.43, 95%CI = 1.12, 1.83, respectively). Prospective analyses using z-scores showed that for each 1 standard deviation increase in work stress and inability to relax, the risk of asthma increased by approximately 40% (RR for work stress = 1.46, 95%CI = 1.06, 2.00; RR for inability to relax = 1.39, 95%CI = 1.01, 1.91). Similar patterns of associations were observed in analyses of categorized exposures. This is the first study to show a cross-sectional and longitudinal association of work stress with asthma.

Effect of molecular weight on polymer processability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karg, R.F.

1983-01-01

Differences in rheological behavior due to the polymer molecular weight and molecular weight distribution have been shown with the MPT. SBR polymers having high molecular weight fractions develop higher stress relaxation time values due to the higher degree of polymer entanglements. Tests conducted at increasing temperatures show the diminishing influence of the polymer entanglements upon stress relaxation time. EPDM polymers show stress relaxation time and head pressure behavior which correlates with mill processability. As anticipated, compounded stock of EPDM have broad molecular weight distribution has higher stress relaxation time values than EPDM compounds with narrow molecular weight distribution.

Relaxation of bending stresses and the reversibility of residual stresses in amorphous soft magnetic alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kekalo, I. B.; Mogil’nikov, P. S., E-mail: pavel-mog@mail.ru

2015-06-15

The reversibility of residual bending stresses is revealed in ribbon samples of cobalt- and iron-based amorphous alloys Co{sub 69}Fe{sub 3.7}Cr{sub 3.8}Si{sub 12.5}B{sub 11} and Fe{sub 57}Co{sub 31}Si{sub 2.9}B{sub 9.1}: the ribbons that are free of applied stresses and bent under the action of residual stresses become completely or incompletely straight upon annealing at the initial temperatures. The influence of annealing on the relaxation of bending stresses is studied. Preliminary annealing is found to sharply decrease the relaxation rate of bending stresses, and the initial stage of fast relaxation of these stresses is absent. Complete straightening of preliminarily annealed ribbons ismore » shown to occur at significantly higher temperatures than that of the initial ribbons. Incomplete straightening of the ribbons is explained by the fact that bending stresses relaxation at high annealing temperatures proceeds due to both reversible anelastic deformation and viscous flow, which is a fully irreversible process. Incomplete reversibility is also caused by irreversible processes, such as the release of excess free volume and clustering (detected by small-angle X-ray scattering). The revealed differences in the relaxation processes that occur in the cobalt- and iron-based amorphous alloys are discussed in terms of different atomic diffusion mobilities in these alloys.« less

The Relation Between Collagen Fibril Kinematics and Mechanical Properties in the Mitral Valve Anterior Leaflet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liao,J.; Yang, L.; Grashow, J.

2007-01-01

We have recently demonstrated that the mitral valve anterior leaflet (MVAL) exhibited minimal hysteresis, no strain rate sensitivity, stress relaxation but not creep (Grashow et al., 2006, Ann Biomed Eng., 34(2), pp. 315-325; Grashow et al., 2006, Ann Biomed. Eng., 34(10), pp. 1509-1518). However, the underlying structural basis for this unique quasi-elastic mechanical behavior is presently unknown. As collagen is the major structural component of the MVAL, we investigated the relation between collagen fibril kinematics (rotation and stretch) and tissue-level mechanical properties in the MVAL under biaxial loading using small angle X-ray scattering. A novel device was developed and utilizedmore » to perform simultaneous measurements of tissue level forces and strain under a planar biaxial loading state. Collagen fibril D-period strain ({epsilon}{sub D}) and the fibrillar angular distribution were measured under equibiaxial tension, creep, and stress relaxation to a peak tension of 90 N/m. Results indicated that, under equibiaxial tension, collagen fibril straining did not initiate until the end of the nonlinear region of the tissue-level stress-strain curve. At higher tissue tension levels, {epsilon}{sub D} increased linearly with increasing tension. Changes in the angular distribution of the collagen fibrils mainly occurred in the tissue toe region. Using {epsilon}{sub D}, the tangent modulus of collagen fibrils was estimated to be 95.5{+-}25.5 MPa, which was {approx}27 times higher than the tissue tensile tangent modulus of 3.58{+-}1.83 MPa. In creep tests performed at 90 N/m equibiaxial tension for 60 min, both tissue strain and D remained constant with no observable changes over the test length. In contrast, in stress relaxation tests performed for 90 min {epsilon}{sub D} was found to rapidly decrease in the first 10 min followed by a slower decay rate for the remainder of the test. Using a single exponential model, the time constant for the reduction in collagen fibril strain was 8.3 min, which was smaller than the tissue-level stress relaxation time constants of 22.0 and 16.9 min in the circumferential and radial directions, respectively. Moreover, there was no change in the fibril angular distribution under both creep and stress relaxation over the test period. Our results suggest that (1) the MVAL collagen fibrils do not exhibit intrinsic viscoelastic behavior, (2) tissue relaxation results from the removal of stress from the fibrils, possibly by a slipping mechanism modulated by noncollagenous components (e.g. proteoglycans), and (3) the lack of creep but the occurrence of stress relaxation suggests a 'load-locking' behavior under maintained loading conditions. These unique mechanical characteristics are likely necessary for normal valvular function.« less

Effects of 7-ketocholesterol on the activity of endothelial poly(ADP-ribose) polymerase and on endothelium-dependent relaxant function.

PubMed

Kiss, Levente; Chen, Min; Gero, Domokos; Módis, Katalin; Lacza, Zsombor; Szabó, Csaba

2006-12-01

Oxidative and nitrosative stress play an important role in the development of endothelial vascular dysfunction during early atherosclerosis. Oxidative stress activates the nuclear enzyme poly(ADP-ribose) polymerase (PARP) in endothelial cells. In patients with atherosclerosis the level of oxidized LDL in the plasma is elevated. In oxidized LDL various oxysterols have been identified, such as 7-ketocholesterol (7K). 7K has been shown to induce PARP activation in microglial cells. The aim of the current study was to clarify the effects of 7K on the activity of endothelial PARP and on the endothelium-dependent relaxant function of blood vessels. We treated human umbilical vein endothelial (HUVEC) cells with 2-16 microg/ml 7K as well as vascular rings harvested from BALB/c mouse thoracic aorta with 90 microg/ml 7K for 2 h. A group of mice was treated with 7K subcutaneously for 1 week (10 mg/kg/day). We also conducted in vitro and in vivo experiments using pretreatment with buthionine sulphoximine (BSO), a glutathione-lowering agent. The activity of PARP was calculated by measurement of tritiated NAD incorporation. The activity of PARP increased significantly in 7K-treated HUVEC cells. After BSO pretreatment, this increase was higher. Isolated vascular rings demonstrated no change in endothelium-dependent relaxant function after 2 h of incubation with 7K, even after BSO pretreatment. In vivo treatment with 7K for 1 week had no effect on the relaxant function. Our experimental results suggest that although 7-ketocholesterol can activate PARP enzyme in endothelial cells, it is not sufficient on its own to cause impairment in the endothelium-dependent vascular reactivity.

Fitting stress relaxation experiments with fractional Zener model to predict high frequency moduli of polymeric acoustic foams

NASA Astrophysics Data System (ADS)

Guo, Xinxin; Yan, Guqi; Benyahia, Lazhar; Sahraoui, Sohbi

2016-11-01

This paper presents a time domain method to determine viscoelastic properties of open-cell foams on a wide frequency range. This method is based on the adjustment of the stress-time relationship, obtained from relaxation tests on polymeric foams' samples under static compression, with the four fractional derivatives Zener model. The experimental relaxation function, well described by the Mittag-Leffler function, allows for straightforward prediction of the frequency-dependence of complex modulus of polyurethane foams. To show the feasibility of this approach, complex shear moduli of the same foams were measured in the frequency range between 0.1 and 16 Hz and at different temperatures between -20 °C and 20 °C. A curve was reconstructed on the reduced frequency range (0.1 Hz-1 MHz) using the time-temperature superposition principle. Very good agreement was obtained between experimental complex moduli values and the fractional Zener model predictions. The proposed time domain method may constitute an improved alternative to resonant and non-resonant techniques often used for dynamic characterization of polymers for the determination of viscoelastic moduli on a broad frequency range.

After stress comes relax(ation)

NASA Astrophysics Data System (ADS)

Isa, Lucio

2015-11-01

Viscoelastic materials take a finite time to relax and dissipate stress and this time scale is directly connected to the microstructure of the material itself. In their paper, Gomez-Solano and Bechinger (2015 New J. Phys. 17 103032) perform ‘miniaturized’ mechanical tests on a range of viscoelastic materials by dragging a micron-sized bead across them using optical tweezers. Upon switching off all the external forces, they watch the bead recoil to its original position and by tracking its motion they pinpoint the relaxation time of the material. These experiments open up a new range of possibilities to characterize stress relaxation at the microscale just by watching it.

Neural Correlates of Stress and Favorite-Food Cue Exposure in Adolescents: A Functional Magnetic Resonance Imaging Study

PubMed Central

Hommer, Rebecca E.; Seo, Dongju; Lacadie, Cheryl M.; Chaplin, Tara M.; Mayes, Linda C.; Sinha, Rajita; Potenza, Marc N.

2012-01-01

Adolescence is a critical period of neurodevelopment for stress and appetitive processing, as well as a time of increased vulnerability to stress and engagement in risky behaviors. The current study was conducted to examine brain activation patterns during stress and favorite-food-cue experiences relative to a neutral-relaxing condition in adolescents. Functional magnetic resonance imaging was employed using individualized script-driven guided imagery to compare brain responses to such experiences in 43 adolescents. Main effects of condition and gender were found, without a significant gender-by-condition interaction. Stress imagery, relative to neutral, was associated with activation in the caudate, thalamus, left hippocampus/parahippocampal gyrus, midbrain, left superior/middle temporal gyrus, and right posterior cerebellum. Appetitive imagery of favorite food was associated with caudate, thalamus, and midbrain activation compared to the neutral-relaxing condition. To understand neural correlates of anxiety and craving, subjective (self-reported) measures of stress-induced anxiety and favorite-food-cue-induced craving were correlated with brain activity during stress and appetitive food-cue conditions, respectively. High self-reported stress-induced anxiety was associated with hypoactivity in the striatum, thalamus, hippocampus and midbrain. Self-reported favorite-food-cue-induced craving was associated with blunted activity in cortical-striatal regions, including the right dorsal and ventral striatum, medial prefrontal cortex, motor cortex, and left anterior cingulate cortex. The current findings in adolescents indicate the activation of predominantly subcortical-striatal regions in the processing of stressful and appetitive experiences and link hypoactive striatal circuits to self-reported stress-induced anxiety and cue-induced favorite-food craving. PMID:22504779

Neural correlates of stress and favorite-food cue exposure in adolescents: a functional magnetic resonance imaging study.

PubMed

Hommer, Rebecca E; Seo, Dongju; Lacadie, Cheryl M; Chaplin, Tara M; Mayes, Linda C; Sinha, Rajita; Potenza, Marc N

2013-10-01

Adolescence is a critical period of neurodevelopment for stress and appetitive processing, as well as a time of increased vulnerability to stress and engagement in risky behaviors. This study was conducted to examine brain activation patterns during stress and favorite-food-cue experiences relative to a neutral-relaxing condition in adolescents. Functional magnetic resonance imaging was employed using individualized script-driven guided imagery to compare brain responses with such experiences in 43 adolescents. Main effects of condition and gender were found, without a significant gender-by-condition interaction. Stress imagery, relative to neutral, was associated with activation in the caudate, thalamus, left hippocampus/parahippocampal gyrus, midbrain, left superior/middle temporal gyrus, and right posterior cerebellum. Appetitive imagery of favorite food was associated with caudate, thalamus, and midbrain activation compared with the neutral-relaxing condition. To understand neural correlates of anxiety and craving, subjective (self-reported) measures of stress-induced anxiety and favorite-food-cue-induced craving were correlated with brain activity during stress and appetitive food-cue conditions, respectively. High self-reported stress-induced anxiety was associated with hypoactivity in the striatum, thalamus, hippocampus, and midbrain. Self-reported favorite-food-cue-induced craving was associated with blunted activity in cortical-striatal regions, including the right dorsal and ventral striatum, medial prefrontal cortex, motor cortex, and left anterior cingulate cortex. These findings in adolescents indicate the activation of predominantly subcortical-striatal regions in the processing of stressful and appetitive experiences and link hypoactive striatal circuits to self-reported stress-induced anxiety and cue-induced favorite-food craving. Copyright © 2012 Wiley Periodicals, Inc.

Time and Temperature Dependence of Viscoelastic Stress Relaxation in Gold and Gold Alloy Thin Films

NASA Astrophysics Data System (ADS)

Mongkolsuttirat, Kittisun

Radio frequency (RF) switches based on capacitive MicroElectroMechanical System (MEMS) devices have been proposed as replacements for traditional solid-state field effect transistor (FET) devices. However, one of the limitations of the existing capacitive switch designs is long-term reliability. Failure is generally attributed to electrical charging in the capacitor's dielectric layer that creates an attractive electrostatic force between a moving upper capacitor plate (a metal membrane) and the dielectric. This acts as an attractive stiction force between them that may cause the switch to stay permanently in the closed state. The force that is responsible for opening the switch is the elastic restoring force due to stress in the film membrane. If the restoring force decreases over time due to stress relaxation, the tendency for stiction failure behavior will increase. Au films have been shown to exhibit stress relaxation even at room temperature. The stress relaxation observed is a type of viscoelastic behavior that is more significant in thin metal films than in bulk materials. Metal films with a high relaxation resistance would have a lower probability of device failure due to stress relaxation. It has been shown that solid solution and oxide dispersion can strengthen a material without unacceptable decreases in electrical conductivity. In this study, the viscoelastic behavior of Au, AuV solid solution and AuV2O5 dispersion created by DC magnetron sputtering are investigated using the gas pressure bulge testing technique in the temperature range from 20 to 80°C. The effectiveness of the two strengthening approaches is compared with the pure Au in terms of relaxation modulus and 3 hour modulus decay. The time dependent relaxation curves can be fitted very well with a four-term Prony series model. From the temperature dependence of the terms of the series, activation energies have been deduced to identify the possible dominant relaxation mechanism. The measured modulus relaxation of Au films also proves that the films exhibit linear viscoelastic behavior. From this, a linear viscoelastic model is shown to fit very well to experimental steady state stress relaxation data and can predict time dependent stress for complex loading histories including the ability to predict stress-time behavior at other strain rates during loading. Two specific factors that are expected to influence the viscoelastic behavior-degree of alloying and grain size are investigated to explore the influence of V concentration in solid solution and grain size of pure Au. It is found that the normalized modulus of Au films is dependent on both concentration (C) and grain size (D) with proportionalities of C1/3 and D 2, respectively. A quantitative model of the rate-equation for dislocation glide plasticity based on Frost and Ashby is proposed and fitted well with steady state anelastic stress relaxation experimental data. The activation volume and the density of mobile dislocations is determined using repeated stress relaxation tests in order to further understand the viscoelastic relaxation mechanism. A rapid decrease of mobile dislocation density is found at the beginning of relaxation, which correlates well with a large reduction of viscoelastic modulus at the early stage of relaxation. The extracted activation volume and dislocation mobility can be ascribed to mobile dislocation loops with double kinks generated at grain boundaries, consistent with the dislocation mechanism proposed for the low activation energy measured in this study.

Stress relaxation at a gelatin hydrogel-glass interface in direct shear sliding

NASA Astrophysics Data System (ADS)

Gupta, Vinit; Singh, Arun K.

2018-01-01

In this paper, we study experimentally the stress relaxation behavior of soft solids such as gelatin hydrogels on a smooth glass surface in direct shear sliding. It is observed experimentally that irrespective of pulling velocity, the sliding block relaxes to the same level of nonzero residual stress. However, residual stress increases with increasing gelatin concentration in the hydrogels. We have also validated a friction model for strong bond formation during steady relaxation in light of the experimental observations. Our theoretical analysis establishes that population of dangling chains at the sliding interface significantly affects the relaxation process. As a result, residual stress increases with increasing gelatin concentration or decreasing mesh size of the three-dimensional structures in the hydrogels. It is also found that the transition time, at which a weak bond converts to strong bond, increases with increasing mesh size of the hydrogels. Moreover, relaxation time constant of a strong bond decreases with increasing mesh size. However, activation length of a strong bond increases with mesh size. Finally, this study signifies the role of residual strength in frictional shear sliding and it is believed that these results should be useful to understand the role of residual stress in stick-slip instability.

5 Things To Know About Relaxation Techniques for Stress

MedlinePlus

... 5 Things To Know About Relaxation Techniques for Stress Share: When you’re under stress, your body reacts by releasing hormones that produce ... vessels narrow (restricting the flow of blood). Occasional stress is a normal coping mechanism. But over the ...

Oxidative stress and successful antioxidant treatment in models of RYR1-related myopathy

PubMed Central

Arbogast, Sandrine; Hur, Junguk; Nelson, Darcee D.; McEvoy, Anna; Waugh, Trent; Marty, Isabelle; Lunardi, Joel; Brooks, Susan V.; Kuwada, John Y.; Ferreiro, Ana

2012-01-01

The skeletal muscle ryanodine receptor is an essential component of the excitation–contraction coupling apparatus. Mutations in RYR1 are associated with several congenital myopathies (termed RYR1-related myopathies) that are the most common non-dystrophic muscle diseases of childhood. Currently, no treatments exist for these disorders. Although the primary pathogenic abnormality involves defective excitation–contraction coupling, other abnormalities likely play a role in disease pathogenesis. In an effort to discover novel pathogenic mechanisms, we analysed two complementary models of RYR1-related myopathies, the relatively relaxed zebrafish and cultured myotubes from patients with RYR1-related myopathies. Expression array analysis in the zebrafish disclosed significant abnormalities in pathways associated with cellular stress. Subsequent studies focused on oxidative stress in relatively relaxed zebrafish and RYR1-related myopathy myotubes and demonstrated increased oxidant activity, the presence of oxidative stress markers, excessive production of oxidants by mitochondria and diminished survival under oxidant conditions. Exposure to the antioxidant N-acetylcysteine reduced oxidative stress and improved survival in the RYR1-related myopathies human myotubes ex vivo and led to significant restoration of aspects of muscle function in the relatively relaxed zebrafish, thereby confirming its efficacy in vivo. We conclude that oxidative stress is an important pathophysiological mechanism in RYR1-related myopathies and that N-acetylcysteine is a successful treatment modality ex vivo and in a vertebrate disease model. We propose that N-acetylcysteine represents the first potential therapeutic strategy for these debilitating muscle diseases. PMID:22418739

Breathing and Relaxation

MedlinePlus

... Programs Health Information Doctors & Departments Clinical Research & Science Education & Training Home Health Insights Stress & Relaxation Breathing and Relaxation Breathing and Relaxation Make ...

Shear-stress fluctuations and relaxation in polymer glasses

NASA Astrophysics Data System (ADS)

Kriuchevskyi, I.; Wittmer, J. P.; Meyer, H.; Benzerara, O.; Baschnagel, J.

2018-01-01

We investigate by means of molecular dynamics simulation a coarse-grained polymer glass model focusing on (quasistatic and dynamical) shear-stress fluctuations as a function of temperature T and sampling time Δ t . The linear response is characterized using (ensemble-averaged) expectation values of the contributions (time averaged for each shear plane) to the stress-fluctuation relation μsf for the shear modulus and the shear-stress relaxation modulus G (t ) . Using 100 independent configurations, we pay attention to the respective standard deviations. While the ensemble-averaged modulus μsf(T ) decreases continuously with increasing T for all Δ t sampled, its standard deviation δ μsf(T ) is nonmonotonic with a striking peak at the glass transition. The question of whether the shear modulus is continuous or has a jump singularity at the glass transition is thus ill posed. Confirming the effective time-translational invariance of our systems, the Δ t dependence of μsf and related quantities can be understood using a weighted integral over G (t ) .

Surface properties and exponential stress relaxations of mammalian meibum films.

PubMed

Eftimov, Petar; Yokoi, Norihiko; Tonchev, Vesselin; Nencheva, Yana; Georgiev, Georgi As

2017-03-01

The surface properties of meibomian secretion (MGS), the major constituent of the tear film (TF) lipid layer, are of key importance for TF stability. The interfacial properties of canine, cMGS, and feline, fMGS, meibum films were studied using a Langmuir surface balance. These species were selected because they have blinking frequency and TF stability similar to those of humans. The sample's performance during dynamic area changes was evaluated by surface pressure (π)-area (A) isocycles and the layer structure was monitored with Brewster angle microscopy. The films' dilatational rheology was probed via the stress-relaxation technique. The animal MGS showed similar behavior both between each other and with human MGS (studied previously). They form reversible, non-collapsible, multilayer thick films. The relaxations of canine, feline, and human MGS films were well described by double exponential decay reflecting the presence of two processes: (1) fast elastic process, with characteristic time τ < 10 s and (2) slow viscous process, with τ > 100 s-emphasizing the meibum layers viscoelasticity. The temperature decrease from 35 to 25 °C resulted in decreased thickness and lateral expansion of all MGS layers accompanied with increase of the π/A hysteresis and of the elastic process contribution to π relaxation transients. Thus, MGS films of mammals with similar blinking frequency and TF stability have similar surface properties and stress relaxations unaltered by the interspecies MGS compositional variations. Such knowledge may impact the selection of animal mimics of human MGS and on a better understanding of lipid classes' impact on meibum functionality.

Stress-relieving effects of short-term balneotherapy - a randomized controlled pilot study in healthy adults.

PubMed

Matzer, Franziska; Nagele, Eva; Bahadori, Babak; Dam, Karl; Fazekas, Christian

2014-01-01

Stress-relieving effects of balneotherapy compared to progressive muscle relaxation (PMR) and to resting were investigated by measuring subjective relaxation and salivary cortisol. It was also examined whether participants with a high versus low stress level would have a different relaxation response. A sample of healthy volunteers was randomized to balneotherapy, PMR, or a resting control group, each intervention lasting for 25 min. Pre- and post-intervention salivary cortisol samples were collected, and participants rated their status of relaxation on a quantitative scale. In addition, 3 questionnaires were applied to detect participants' stress level and bodily complaints. 49 healthy participants were recruited (65.3% female). In a pre-post comparison, salivary cortisol decreased (F = 23.53, p < 0.001) and subjective relaxation ratings increased (F = 132.18, p < 0.001) in all 3 groups. Study participants in the balneotherapy group rated themselves as more relaxed after the intervention as compared to the other groups (F = 5.22, p < 0.009). Participants with a high versus low stress level differed in somatic symptoms and in morning cortisol levels, but showed a similar relaxation response. Findings suggest that compared to PMR and resting, balneotherapy seems to be more beneficial with regard to subjective relaxation effects and similarly beneficial with regard to a decrease in salivary cortisol. © 2014 S. Karger GmbH, Freiburg.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fiorim, Jonaina, E-mail: nanafiorim@hotmail.com; Ribeiro Júnior, Rogério Faustino, E-mail: faustino43@oi.com.br; Azevedo, Bruna Fernades, E-mail: brunafernandes.azevedo@gmail.com

Seven day exposure to a low concentration of lead acetate increases nitric oxide bioavailability suggesting a putative role of K{sup +} channels affecting vascular reactivity. This could be an adaptive mechanism at the initial stages of toxicity from lead exposure due to oxidative stress. We evaluated whether lead alters the participation of K{sup +} channels and Na{sup +}/K{sup +}-ATPase (NKA) on vascular function. Wistar rats were treated with lead (1st dose 4 μg/100 g, subsequent doses 0.05 μg/100 g, im, 7 days) or vehicle. Lead treatment reduced the contractile response of aortic rings to phenylephrine (PHE) without changing the vasodilatormore » response to acetylcholine (ACh) or sodium nitroprusside (SNP). Furthermore, this treatment increased basal O{sub 2}{sup −} production, and apocynin (0.3 μM), superoxide dismutase (150 U/mL) and catalase (1000 U/mL) reduced the response to PHE only in the treated group. Lead also increased aortic functional NKA activity evaluated by K{sup +}-induced relaxation curves. Ouabain (100 μM) plus L-NAME (100 μM), aminoguanidine (50 μM) or tetraethylammonium (TEA, 2 mM) reduced the K{sup +}-induced relaxation only in lead-treated rats. When aortic rings were precontracted with KCl (60 mM/L) or preincubated with TEA (2 mM), 4-aminopyridine (4-AP, 5 mM), iberiotoxin (IbTX, 30 nM), apamin (0.5 μM) or charybdotoxin (0.1 μM), the ACh-induced relaxation was more reduced in the lead-treated rats. Additionally, 4-AP and IbTX reduced the relaxation elicited by SNP more in the lead-treated rats. Results suggest that lead treatment promoted NKA and K{sup +} channels activation and these effects might contribute to the preservation of aortic endothelial function against oxidative stress. -- Highlights: ► Increased free radicals production ► Increased Na{sup +}/K{sup +} ATPase activity ► Promotes activation of the K{sup +} channels and reduced vascular reactivity ► These effects preserve endothelial function against oxidative stress. ► Low concentrations constitute environmental cardiovascular risk factor.« less

Stress-Rupture and Stress-Relaxation of SiC/SiC Composites at Intermediate Temperature

NASA Technical Reports Server (NTRS)

Morscher, Gregory N.; Hurst, Janet; Levine, Stanley (Technical Monitor)

2001-01-01

Tensile static stress and static strain experiments were performed on woven Sylramic (Dow Corning, Midland, MI) and Hi-Nicalon (Nippon Carbon, Japan) fiber reinforced, BN interphase, melt-infiltrated SiC matrix composites at 815 C. Acoustic emission was used to monitor the damage accumulation during the test. The stress-rupture properties of Sylramic composites were superior to that of Hi-Nicalon Tm composites. Conversely, the applied strain levels that Hi-Nicalon composites can withstand for stress-relaxation experiments were superior to Sylramic composites; however, at a cost of poor retained strength properties for Hi-Nicalon composites. Sylramic composites exhibited much less stress-oxidation induced matrix cracking compared to Hi-Nicalon composites. This was attributed to the greater stiffness and roughness of Sylramic fibers themselves and the lack of a carbon layer between the fiber and the BN interphase for Sylramic composites, which existed in Hi-Nicalon composites. Due to the lack of stress-relief for Sylramic composites, time to failure for Sylramic composite stress-relaxation experiments was not much longer than for stress-rupture experiments when comparing the peak stress condition for stress-relaxation with the applied stress of stress-rupture.

Effect of Temper Condition on Stress Relaxation Behavior of an Aluminum Copper Lithium Alloy

NASA Astrophysics Data System (ADS)

Mishra, Sumeet; Beura, Vikrant Kumar; Singh, Amit; Yadava, Manasij; Nayan, Niraj

2018-07-01

Deformation behavior of an Al-Cu-Li alloy in different temper conditions (solutionized and T8) is investigated using stress relaxation tests. Fundamental parameters such as the apparent and physical activation volume, strain rate sensitivity, effective stress, and exhaustion rate of mobile dislocation density are determined from single and multiple relaxation tests. It was found that dislocation-dislocation interaction controls the kinetics of plastic deformation in the solutionized sample, whereas dislocation-precipitate interaction is the overriding factor in the presence of T1 precipitates. The apparent activation volume was found to be significantly lower in the presence of T1 precipitates compared with solutionized samples. Strain rate sensitivity and effective stress were found to be higher in the presence of T1 precipitates. In addition, multiple relaxation tests showed that irrespective of microstructural features (solutes, semi-coherent precipitates), the mobile dislocation density reduces during the relaxation period. Further evidence regarding reduction in mobile dislocation density is obtained from uniaxial tensile tests carried out after stress relaxation tests, where both solutionized and T8 samples show an increase in strength. Additional discussion on relaxation strain is included to provide a complete overview regarding the time-dependent deformation behavior of the Al-Cu-Li alloy in different temper conditions.

Effect of Temper Condition on Stress Relaxation Behavior of an Aluminum Copper Lithium Alloy

NASA Astrophysics Data System (ADS)

Mishra, Sumeet; Beura, Vikrant Kumar; Singh, Amit; Yadava, Manasij; Nayan, Niraj

2018-04-01

Deformation behavior of an Al-Cu-Li alloy in different temper conditions (solutionized and T8) is investigated using stress relaxation tests. Fundamental parameters such as the apparent and physical activation volume, strain rate sensitivity, effective stress, and exhaustion rate of mobile dislocation density are determined from single and multiple relaxation tests. It was found that dislocation-dislocation interaction controls the kinetics of plastic deformation in the solutionized sample, whereas dislocation-precipitate interaction is the overriding factor in the presence of T1 precipitates. The apparent activation volume was found to be significantly lower in the presence of T1 precipitates compared with solutionized samples. Strain rate sensitivity and effective stress were found to be higher in the presence of T1 precipitates. In addition, multiple relaxation tests showed that irrespective of microstructural features (solutes, semi-coherent precipitates), the mobile dislocation density reduces during the relaxation period. Further evidence regarding reduction in mobile dislocation density is obtained from uniaxial tensile tests carried out after stress relaxation tests, where both solutionized and T8 samples show an increase in strength. Additional discussion on relaxation strain is included to provide a complete overview regarding the time-dependent deformation behavior of the Al-Cu-Li alloy in different temper conditions.

N-acetylcysteine does not improve the endothelial and smooth muscle function in the human saphenous vein.

PubMed

Sharif, Muhammad Anees; Bayraktutan, Ulvi; Young, Ian Stuart; Soong, Chee Voon

2007-01-01

Oxidative stress can lead to vein graft dysfunction in the saphenous vein. This ex vivo study is aimed to compare the effects of increasing concentrations of the antioxidant N-acetylcysteine (NAC) with heparinized saline (HS) on endothelial and smooth muscle function in the human saphenous vein. Long saphenous vein segment obtained during infrainguinal bypass surgery was divided into 7 rings; 1 immersed in HS and the remaining 6 in increasing NAC concentrations (0.0025%, 0.005%, 0.01%, 0.02%, 0.03%, and 0.04%). Rings were mounted in an organ bath, and relaxant responses to acetylcholine and sodium nitroprusside were assessed through isometric tension studies. Endothelium-dependent relaxations were observed in 77 vein segments from 11 patients. No significant difference was seen in veins treated with either lower NAC concentrations (0.0025%, 0.005%, 0.01%, 0.02%, and 0.03%) or HS. However, HS-treated veins showed significantly better relaxation compared to those treated with maximum (0.04%) NAC (P < .05). Endothelium-independent relaxations were observed in 91 segments from 13 patients. No difference in relaxation was observed between veins treated with HS or any of the NAC concentrations. In conclusion, lower NAC concentrations do not offer better endothelial protection than HS, whereas the highest NAC concentration has a detrimental effect on endothelium-dependent relaxation. Moreover, NAC did not show beneficial effect on direct smooth muscle relaxation.

A wrinkling-based method for investigating glassy polymer film relaxation as a function of film thickness and temperature.

PubMed

Chung, Jun Young; Douglas, Jack F; Stafford, Christopher M

2017-10-21

We investigate the relaxation dynamics of thin polymer films at temperatures below the bulk glass transition T g by first compressing polystyrene films supported on a polydimethylsiloxane substrate to create wrinkling patterns and then observing the slow relaxation of the wrinkled films back to their final equilibrium flat state by small angle light scattering. As with recent relaxation measurements on thin glassy films reported by Fakhraai and co-workers, we find the relaxation time of our wrinkled films to be strongly dependent on film thickness below an onset thickness on the order of 100 nm. By varying the temperature between room temperature and T g (≈100 °C), we find that the relaxation time follows an Arrhenius-type temperature dependence to a good approximation at all film thicknesses investigated, where both the activation energy and the relaxation time pre-factor depend appreciably on film thickness. The wrinkling relaxation curves tend to cross at a common temperature somewhat below T g , indicating an entropy-enthalpy compensation relation between the activation free energy parameters. This compensation effect has also been observed recently in simulated supported polymer films in the high temperature Arrhenius relaxation regime rather than the glassy state. In addition, we find that the film stress relaxation function, as well as the height of the wrinkle ridges, follows a stretched exponential time dependence and the short-time effective Young's modulus derived from our modeling decreases sigmoidally with increasing temperature-both characteristic features of glassy materials. The relatively facile nature of the wrinkling-based measurements in comparison to other film relaxation measurements makes our method attractive for practical materials development, as well as fundamental studies of glass formation.

A wrinkling-based method for investigating glassy polymer film relaxation as a function of film thickness and temperature

NASA Astrophysics Data System (ADS)

Chung, Jun Young; Douglas, Jack F.; Stafford, Christopher M.

2017-10-01

We investigate the relaxation dynamics of thin polymer films at temperatures below the bulk glass transition Tg by first compressing polystyrene films supported on a polydimethylsiloxane substrate to create wrinkling patterns and then observing the slow relaxation of the wrinkled films back to their final equilibrium flat state by small angle light scattering. As with recent relaxation measurements on thin glassy films reported by Fakhraai and co-workers, we find the relaxation time of our wrinkled films to be strongly dependent on film thickness below an onset thickness on the order of 100 nm. By varying the temperature between room temperature and Tg (≈100 °C), we find that the relaxation time follows an Arrhenius-type temperature dependence to a good approximation at all film thicknesses investigated, where both the activation energy and the relaxation time pre-factor depend appreciably on film thickness. The wrinkling relaxation curves tend to cross at a common temperature somewhat below Tg, indicating an entropy-enthalpy compensation relation between the activation free energy parameters. This compensation effect has also been observed recently in simulated supported polymer films in the high temperature Arrhenius relaxation regime rather than the glassy state. In addition, we find that the film stress relaxation function, as well as the height of the wrinkle ridges, follows a stretched exponential time dependence and the short-time effective Young's modulus derived from our modeling decreases sigmoidally with increasing temperature—both characteristic features of glassy materials. The relatively facile nature of the wrinkling-based measurements in comparison to other film relaxation measurements makes our method attractive for practical materials development, as well as fundamental studies of glass formation.

Improving Health by Reducing Stress: An Experiential Activity

ERIC Educational Resources Information Center

Largo-Wight, Erin; Moore, Michele J.; Barr, Elissa M.

2011-01-01

Stress is a leading health issue among college students. Managing stress involves enhancing resources necessary to cope with life's demands. Relaxation techniques are especially critical coping strategies when stress is chronic and coping resources are overused and fatigued. Methods: This article describes a research-based relaxation technique…

Steps To Beat Stress.

ERIC Educational Resources Information Center

Shelton, Michael

1998-01-01

Explains techniques for reducing stress: diaphragmatic breathing, relaxation, progressive muscle relaxation, and meditation. Two sidebars define the fight-or-flight response and the camp administration's role in helping to lower stress through staff training and reduction of camp-wide stressors. (SAS)

Mozart versus new age music: relaxation states, stress, and ABC relaxation theory.

PubMed

Smith, Jonathan C; Joyce, Carol A

2004-01-01

Smith's (2001) Attentional Behavioral Cognitive (ABC) relaxation theory proposes that all approaches to relaxation (including music) have the potential for evoking one or more of 15 factor-analytically derived relaxation states, or "R-States" (Sleepiness, Disengagement, Rested / Refreshed, Energized, Physical Relaxation, At Ease/Peace, Joy, Mental Quiet, Childlike Innocence, Thankfulness and Love, Mystery, Awe and Wonder, Prayerfulness, Timeless/Boundless/Infinite, and Aware). The present study investigated R-States and stress symptom-patterns associated with listening to Mozart versus New Age music. Students (N = 63) were divided into three relaxation groups based on previously determined preferences. Fourteen listened to a 28-minute tape recording of Mozart's Eine Kleine Nachtmusik and 14 listened to a 28-minute tape of Steven Halpern's New Age Serenity Suite. Others (n = 35) did not want music and instead chose a set of popular recreational magazines. Participants engaged in their relaxation activity at home for three consecutive days for 28 minutes a session. Before and after each session, each person completed the Smith Relaxation States Inventory (Smith, 2001), a comprehensive questionnaire tapping 15 R-States as well as the stress states of somatic stress, worry, and negative emotion. Results revealed no differences at Session 1. At Session 2, those who listened to Mozart reported higher levels of At Ease/Peace and lower levels of Negative Emotion. Pronounced differences emerged at Session 3. Mozart listeners uniquely reported substantially higher levels of Mental Quiet, Awe and Wonder, and Mystery. Mozart listeners reported higher levels, and New Age listeners slightly elevated levels, of At Ease/Peace and Rested/Refreshed. Both Mozart and New Age listeners reported higher levels of Thankfulness and Love. In summary, those who listened to Mozart's Eine Kleine Nachtmusik reported more psychological relaxation and less stress than either those who listened to New Age music or read popular recreational magazines. Results suggest the usefulness of ABC relaxation theory in comparing the different effects of music and relaxation techniques.

A Viscoplastic Stress Relaxation Model for Predicting Variations of the Least Principal Stress With Depth in Unconventional Reservoirs

NASA Astrophysics Data System (ADS)

Zoback, M. D.; Xu, S.; Rassouli, F.; Ma, X.

2016-12-01

In this paper we extend the viscoplastic stress relaxation model of Sone and Zoback (Jour. Petrol. Sci. and Eng., 2014) for predicting variations of least principal stress with stress and its impact on the vertical propagation of hydraulic fractures. Viscoplastic stress relaxation in clay-rich (or diagenetically immature) sedimentary rocks makes the stress field more isotropic. In normal faulting and strike-slip faulting environments, this causes the least principal stress to increase making such formations likely barriers to vertical hydraulic fracture growth. In order to predict the magnitude of viscoplastic stress relaxation in different unconventional formations, we generalize a constitutive law developed from a wide range of creep experiments in our lab over the past several years and apply it to areas of stacked pay in Oklahoma and Texas. Using frac gradients were measured from minifrac and DFIT (Diagnostic Fracture Injection Test) experiments. The viscoplastic model does a good job of explaining vertical hydraulic fracture propagation, as indicated by the distribution of microseismic events recorded during stimulation.

Tocotrienol Rich Palm Oil Extract Is More Effective Than Pure Tocotrienols at Improving Endothelium-Dependent Relaxation in the Presence of Oxidative Stress

PubMed Central

Ali, Saher F.; Woodman, Owen L.

2015-01-01

Oxidative endothelial dysfunction is a critical initiator of vascular disease. Vitamin E is an effective antioxidant but attempts to use it to treat vascular disorders have been disappointing. This study investigated whether tocotrienols, the less abundant components of vitamin E compared to tocopherols, might be more effective at preserving endothelial function. Superoxide generated by hypoxanthine/xanthine oxidase or rat aorta was measured using lucigenin-enhanced chemiluminescence. The effect of α-tocopherol, α-, δ-, and γ-tocotrienols and a tocotrienol rich palm oil extract (tocomin) on levels of superoxide was assessed. Endothelial function in rat aorta was assessed in the presence of the auto-oxidant pyrogallol. Whilst all of the compounds displayed antioxidant activity, the tocotrienols were more effective when superoxide was produced by hypoxanthine/xanthine oxidase whereas tocomin and α-tocopherol were more effective in the isolated aorta. Tocomin and α-tocopherol restored endothelial function in the presence of oxidant stress but α-, δ-, and γ-tocotrienols were ineffective. The protective effect of tocomin was replicated when the tocotrienols were present with, but not without, α-tocopherol. Tocotrienol rich tocomin is more effective than α-tocopherol at reducing oxidative stress and restoring endothelium-dependent relaxation in rat aortae and although α-, δ-, and γ-tocotrienols effectively scavenged superoxide, they did not improve endothelial function. PMID:26075031

Tocotrienol Rich Palm Oil Extract Is More Effective Than Pure Tocotrienols at Improving Endothelium-Dependent Relaxation in the Presence of Oxidative Stress.

PubMed

Ali, Saher F; Woodman, Owen L

2015-01-01

Oxidative endothelial dysfunction is a critical initiator of vascular disease. Vitamin E is an effective antioxidant but attempts to use it to treat vascular disorders have been disappointing. This study investigated whether tocotrienols, the less abundant components of vitamin E compared to tocopherols, might be more effective at preserving endothelial function. Superoxide generated by hypoxanthine/xanthine oxidase or rat aorta was measured using lucigenin-enhanced chemiluminescence. The effect of α-tocopherol, α-, δ-, and γ-tocotrienols and a tocotrienol rich palm oil extract (tocomin) on levels of superoxide was assessed. Endothelial function in rat aorta was assessed in the presence of the auto-oxidant pyrogallol. Whilst all of the compounds displayed antioxidant activity, the tocotrienols were more effective when superoxide was produced by hypoxanthine/xanthine oxidase whereas tocomin and α-tocopherol were more effective in the isolated aorta. Tocomin and α-tocopherol restored endothelial function in the presence of oxidant stress but α-, δ-, and γ-tocotrienols were ineffective. The protective effect of tocomin was replicated when the tocotrienols were present with, but not without, α-tocopherol. Tocotrienol rich tocomin is more effective than α-tocopherol at reducing oxidative stress and restoring endothelium-dependent relaxation in rat aortae and although α-, δ-, and γ-tocotrienols effectively scavenged superoxide, they did not improve endothelial function.

Unified viscoelasticity: Applying discrete element models to soft tissues with two characteristic times.

PubMed

Anssari-Benam, Afshin; Bucchi, Andrea; Bader, Dan L

2015-09-18

Discrete element models have often been the primary tool in investigating and characterising the viscoelastic behaviour of soft tissues. However, studies have employed varied configurations of these models, based on the choice of the number of elements and the utilised formation, for different subject tissues. This approach has yielded a diverse array of viscoelastic models in the literature, each seemingly resulting in different descriptions of viscoelastic constitutive behaviour and/or stress-relaxation and creep functions. Moreover, most studies do not apply a single discrete element model to characterise both stress-relaxation and creep behaviours of tissues. The underlying assumption for this disparity is the implicit perception that the viscoelasticity of soft tissues cannot be described by a universal behaviour or law, resulting in the lack of a unified approach in the literature based on discrete element representations. This paper derives the constitutive equation for different viscoelastic models applicable to soft tissues with two characteristic times. It demonstrates that all possible configurations exhibit a unified and universal behaviour, captured by a single constitutive relationship between stress, strain and time as: σ+Aσ̇+Bσ¨=Pε̇+Qε¨. The ensuing stress-relaxation G(t) and creep J(t) functions are also unified and universal, derived as [Formula: see text] and J(t)=c2+(ε0-c2)e(-PQt)+σ0Pt, respectively. Application of these relationships to experimental data is illustrated for various tissues including the aortic valve, ligament and cerebral artery. The unified model presented in this paper may be applied to all tissues with two characteristic times, obviating the need for employing varied configurations of discrete element models in preliminary investigation of the viscoelastic behaviour of soft tissues. Copyright © 2015 Elsevier Ltd. All rights reserved.

Developing a Hypnotic Relaxation Intervention to Improve Body Image: A Feasibility Study.

PubMed

Cieslak, Alison; Elkins, Gary; Banerjee, Tanima; Marsack, Jessica; Hickman, Kimberly; Johnson, Alisa; Henry, Norah; Barton, Debra

2016-11-01

To determine the content, feasibility, and best outcome of a mind-body intervention involving self-directed hypnotic relaxation to target body image.
. A five-week, uncontrolled, unblinded feasibility intervention study.
. Behavioral therapy offices in Ann Arbor, Michigan, and Waco, Texas.
. 10 female breast cancer survivors and 1 breast and gynecologic cancer survivor. 
. Adult women with a history of breast and gynecologic cancer and no major psychiatric history were eligible. The intervention included four face-to-face sessions with a research therapist lasting 40-60 minutes, logged home practice, one telephone check-in call at week 5, and one intervention feedback telephone call to complete the study. Descriptive statistics and paired t-tests were used to test feasibility and content validity.
. Stress from body changes as measured by the Impact of Treatment Scale, sexual function as measured by the Female Sexual Function Index, and sexual self-image as measured by the Sexual Self-Schema Scale for women were the variables of interest.
. The intervention content was confirmed. Changes in scores from the baseline to week 5 suggested that stress from body changes decreased and sexual self-schema and function improved during the intervention. Nine of the 11 women were satisfied with the intervention, and all 11 indicated that their body image improved. 
. Hypnotic relaxation therapy shows promise for improving body image and, in doing so, improving sexual health in this population. Additional testing of this intervention is warranted.
. Hypnotic relaxation therapy is feasible to improve body image and sexual health in women diagnosed with cancer and may be an important intervention that could be offered by nurses and other behavioral therapists.

Study on the residual stress relaxation in girth-welded steel pipes under bending load using diffraction methods

DOE PAGES

Hempel, Nico; Bunn, Jeffrey R.; Nitschke-Pagel, Thomas; ...

2017-02-02

This research is dedicated to the experimental investigation of the residual stress relaxation in girth-welded pipes due to quasi-static bending loads. Ferritic-pearlitic steel pipes are welded with two passes, resulting in a characteristic residual stress state with high tensile residual stresses at the weld root. Also, four-point bending is applied to generate axial load stress causing changes in the residual stress state. These are determined both on the outer and inner surfaces of the pipes, as well as in the pipe wall, using X-ray and neutron diffraction. Focusing on the effect of tensile load stress, it is revealed that notmore » only the tensile residual stresses are reduced due to exceeding the yield stress, but also the compressive residual stresses for equilibrium reasons. Furthermore, residual stress relaxation occurs both parallel and perpendicular to the applied load stress.« less

Study on the residual stress relaxation in girth-welded steel pipes under bending load using diffraction methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hempel, Nico; Bunn, Jeffrey R.; Nitschke-Pagel, Thomas

This research is dedicated to the experimental investigation of the residual stress relaxation in girth-welded pipes due to quasi-static bending loads. Ferritic-pearlitic steel pipes are welded with two passes, resulting in a characteristic residual stress state with high tensile residual stresses at the weld root. Also, four-point bending is applied to generate axial load stress causing changes in the residual stress state. These are determined both on the outer and inner surfaces of the pipes, as well as in the pipe wall, using X-ray and neutron diffraction. Focusing on the effect of tensile load stress, it is revealed that notmore » only the tensile residual stresses are reduced due to exceeding the yield stress, but also the compressive residual stresses for equilibrium reasons. Furthermore, residual stress relaxation occurs both parallel and perpendicular to the applied load stress.« less

Ferroelectric and structural properties of stress-constrained and stress-relaxed polycrystalline BiFeO3 thin films

NASA Astrophysics Data System (ADS)

Nakashima, Seiji; Ricinschi, Dan; Park, Jung Min; Kanashima, Takeshi; Fujisawa, Hironori; Shimizu, Masaru; Okuyama, Masanori

2009-03-01

The stress influence of the structural and ferroelectric properties of polycrystalline BiFeO3 (BFO) thin films has been investigated using a membrane substrate for relaxing stress. Reciprocal space mapping (RSM) measurement has been performed to confirm the stress dependence of the crystal structure of polycrystalline BFO thin films on the Pt (200 nm)/TiO2 (50 nm)/SiO2 (600 nm)/Si (625 μm) substrate (stress-constrained BFO film) and the Pt (200 nm)/TiO2 (50 nm)/SiO2 (600 nm)/Si (15 μm) membrane substrate (stress-relaxed BFO film). The BFO thin films prepared by pulsed laser deposition were polycrystalline and mainly exhibit a texture with (001) and (110) plane orientations. From the RSM results, the crystal structure of the (001)-oriented domain changes from Pm monoclinic to Cm monoclinic or to R3c rhombohedral due to stress relaxation. Moreover, at room temperature as well as at 150 K, remanent polarization (Pr) increases and double coercive field (2Ec) decreases (in the latter case from 88 to 94 μC/cm2 and from 532 to 457 kV/cm, respectively) due to relaxing stress. The enhancement of ferroelectricity is attributed to the crystal structural deformation and/or transition and angle change between the polarization direction and film plane.

Nanorheology of Entangled Polymer Melts

DOE PAGES

Ge, Ting; Grest, Gary S.; Rubinstein, Michael

2018-02-01

In this study, we use molecular simulations to probe the local viscoelasticity of an entangled polymer melt by tracking the motion of embedded nonsticky nanoparticles (NPs). As in conventional microrheology, the generalized Stokes-Einstein relation is employed to extract an effective stress relaxation function G GSE(t) from the mean square displacement of NPs. G GSE(t) for different NP diameters d are compared with the stress relaxation function G(t) of a pure polymer melt. The deviation of G GSE(t) from G(t) reflects the incomplete coupling between NPs and the dynamic modes of the melt. For linear polymers, a plateau in G GSE(t)more » emerges as d exceeds the entanglement mesh size a and approaches the entanglement plateau in G(t) for a pure melt with increasing d. For ring polymers, as d increases towards the spanning size R of ring polymers, G GSE(t) approaches G(t) of the ring melt with no entanglement plateau.« less

Nanorheology of Entangled Polymer Melts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ge, Ting; Grest, Gary S.; Rubinstein, Michael

In this study, we use molecular simulations to probe the local viscoelasticity of an entangled polymer melt by tracking the motion of embedded nonsticky nanoparticles (NPs). As in conventional microrheology, the generalized Stokes-Einstein relation is employed to extract an effective stress relaxation function G GSE(t) from the mean square displacement of NPs. G GSE(t) for different NP diameters d are compared with the stress relaxation function G(t) of a pure polymer melt. The deviation of G GSE(t) from G(t) reflects the incomplete coupling between NPs and the dynamic modes of the melt. For linear polymers, a plateau in G GSE(t)more » emerges as d exceeds the entanglement mesh size a and approaches the entanglement plateau in G(t) for a pure melt with increasing d. For ring polymers, as d increases towards the spanning size R of ring polymers, G GSE(t) approaches G(t) of the ring melt with no entanglement plateau.« less

Relaxation training methods for nurse managers in Hong Kong: a controlled study.

PubMed

Yung, Paul M B; Fung, Man Yi; Chan, Tony M F; Lau, Bernard W K

2004-12-01

Nurse managers are under increased stress because of excessive workloads and hospitals' restructuring which is affecting their work tasks. High levels of stress could affect their mental health. Yet, few stress management training programmes are provided for this population. The purpose of this study was to apply stretch-release relaxation and cognitive relaxation training to enhance the mental health for nurse managers. A total of 65 nurse managers in Hong Kong were randomly assigned to stretch-release relaxation (n = 17), cognitive relaxation (n = 18), and a test control group (n = 35). Mental health status was assessed using the Chinese version of State-Trait Anxiety Inventory and the Chinese version of the General Health Questionnaire. Participants were assessed at the pretreatment session, the fourth posttreatment session, and at the 1-month follow-up session. The results revealed both the stretch-release and cognitive relaxation training enhanced mental health in nurse managers in Hong Kong. The application of relaxation training in enhancing mental health status for nurses and health professionals is discussed.

The efficacy of relaxation training on stress, anxiety, and pain perception in hemodialysis patients.

PubMed

Heidari Gorji, M A; Davanloo, A Abbaskhani; Heidarigorji, A M

2014-11-01

Patients on dialysis experience psychological distress, which can impact pain perception. Reduction of stress and anxiety in patients provides psychological resources to cope with their physical condition. We examined the efficacy of relaxation training on stress, anxiety, and pain perception of hemodialysis (HD) patients. eighty HD patients were randomized into two groups (intervention and control). Benson relaxation training was implemented in the intervention group for 15 min twice daily during 4 weeks. Pain perception, stress, and anxiety scale were evaluated before and after intervention. There were significant differences between pain perception, stress, and anxiety levels in case group before and after intervention (P < 0.001) and there was a correlation between pain perception with stress and anxiety. Instructing Benson's relaxation technique is accompanied by reducing pain, stress, and anxiety level of HD patients. Reducing stress and anxiety can provide calmness for the patients so that pursuing medical therapy would be accompanied with more tranquility and low pain intensity. We suggest improving and preventing the patients' psychological problems as well as other chronic disorders through applying nonpharmacological interventions.

Modelling of loading, stress relaxation and stress recovery in a shape memory polymer.

PubMed

Sweeney, J; Bonner, M; Ward, I M

2014-09-01

A multi-element constitutive model for a lactide-based shape memory polymer has been developed that represents loading to large tensile deformations, stress relaxation and stress recovery at 60, 65 and 70°C. The model consists of parallel Maxwell arms each comprising neo-Hookean and Eyring elements. Guiu-Pratt analysis of the stress relaxation curves yields Eyring parameters. When these parameters are used to define the Eyring process in a single Maxwell arm, the resulting model yields at too low a stress, but gives good predictions for longer times. Stress dip tests show a very stiff response on unloading by a small strain decrement. This would create an unrealistically high stress on loading to large strain if it were modelled by an elastic element. Instead it is modelled by an Eyring process operating via a flow rule that introduces strain hardening after yield. When this process is incorporated into a second parallel Maxwell arm, there results a model that fully represents both stress relaxation and stress dip tests at 60°C. At higher temperatures a third arm is required for valid predictions. Crown Copyright © 2014. Published by Elsevier Ltd. All rights reserved.

Behavioral Treatment of Menopausal Hot Flashes: Evaluation by Objective Methods.

ERIC Educational Resources Information Center

Germaine, Leonard M.; Freedman, Robert R.

1984-01-01

Used latency to hot flash onset under heat stress to evaluate the effects of relaxation treatment or a control procedure in 14 menopausal women. Following treatment, the latency to hot flash onset during heat stress was increased in relaxation subjects. Reported symptom frequency was significantly reduced in relaxation subjects. (BH)

Quantification of local strain distributions in nanoscale strained SiGe FinFET structures

NASA Astrophysics Data System (ADS)

Mochizuki, Shogo; Murray, Conal E.; Madan, Anita; Pinto, Teresa; Wang, Yun-Yu; Li, Juntao; Weng, Weihao; Jagannathan, Hemanth; Imai, Yasuhiko; Kimura, Shigeru; Takeuchi, Shotaro; Sakai, Akira

2017-10-01

Strain within nanoscale strained SiGe FinFET structures has been investigated using a combination of X-ray diffraction and transmission electron microscopy-based nanobeam diffraction (NBD) techniques to reveal the evolution of the stress state within the FinFETs. Reciprocal space maps collected using high-resolution X-ray diffraction exhibited distinct features corresponding to the SiGe fin width, pitch, and lattice deformation and were analyzed to quantify the state of stress within the fins. Although the majority of the SiGe fin volume exhibited a uniaxial stress state due to elastic relaxation of the transverse in-plane stress, NBD measurements confirmed a small interaction region near the SOI interface that is mechanically constrained by the underlying substrate. We have quantitatively characterized the evolution of the fin stress state from biaxial to uniaxial as a function of fin aspect ratio and Ge fraction and confirmed that the fins obey elastic deformation based on a model that depends on the relative difference between the equilibrium Si and SiGe lattice constants and relative fraction of in-plane stress transverse to the SiGe fins. Spatially resolved, nanobeam X-ray diffraction measurements conducted near the SiGe fin edge indicate the presence of additional elastic relaxation from a uniaxial stress state to a fully relaxed state at the fin edge. Mapping of the lattice deformation within 500 nm of this fin edge by NBD revealed large gradients, particularly at the top corner of the fin. The values of the volume averaged lattice deformation obtained by nanoXRD and NBD are qualitatively consistent. Furthermore, the modulation of strain at the fin edge obtained by quantitative analysis of the nanoXRD results agrees with the lattice deformation profile obtained by NBD.

Local yield stress statistics in model amorphous solids

NASA Astrophysics Data System (ADS)

Barbot, Armand; Lerbinger, Matthias; Hernandez-Garcia, Anier; García-García, Reinaldo; Falk, Michael L.; Vandembroucq, Damien; Patinet, Sylvain

2018-03-01

We develop and extend a method presented by Patinet, Vandembroucq, and Falk [Phys. Rev. Lett. 117, 045501 (2016), 10.1103/PhysRevLett.117.045501] to compute the local yield stresses at the atomic scale in model two-dimensional Lennard-Jones glasses produced via differing quench protocols. This technique allows us to sample the plastic rearrangements in a nonperturbative manner for different loading directions on a well-controlled length scale. Plastic activity upon shearing correlates strongly with the locations of low yield stresses in the quenched states. This correlation is higher in more structurally relaxed systems. The distribution of local yield stresses is also shown to strongly depend on the quench protocol: the more relaxed the glass, the higher the local plastic thresholds. Analysis of the magnitude of local plastic relaxations reveals that stress drops follow exponential distributions, justifying the hypothesis of an average characteristic amplitude often conjectured in mesoscopic or continuum models. The amplitude of the local plastic rearrangements increases on average with the yield stress, regardless of the system preparation. The local yield stress varies with the shear orientation tested and strongly correlates with the plastic rearrangement locations when the system is sheared correspondingly. It is thus argued that plastic rearrangements are the consequence of shear transformation zones encoded in the glass structure that possess weak slip planes along different orientations. Finally, we justify the length scale employed in this work and extract the yield threshold statistics as a function of the size of the probing zones. This method makes it possible to derive physically grounded models of plasticity for amorphous materials by directly revealing the relevant details of the shear transformation zones that mediate this process.

Experimental identification and mathematical modeling of viscoplastic material behavior

NASA Astrophysics Data System (ADS)

Haupt, P.; Lion, A.

1995-03-01

Uniaxial torsion and biaxial torsion-tension experiments on thin-walled tubes were carried out to investigate the viscoplastic behavior of stainless steel XCrNi18.9. A series of monotonic tests under strain and stress control shows nonlinear rate dependence and suggests the existence of equilibrium states, which are asymptotically approached during relaxation and creep processes. Strain controlled cyclic experiments display various hardening and softening phenomena that depend on strain amplitude and mean strain. All experiments indicate that the equilibrium states within the material depend on the history of the input process, whereas the history-dependence of the relaxation and creep behavior appears less significant. From the experiments the design of a constitutive model of viscoplasticity is motivated: The basic assumption is a decomposition of the total stress into an equilibrium stress and a non-equilibrium overstress: At constant strain, the overstress relaxes to zero, where the relaxation time depends on the overstress in order to account for the nonlinear rate-dependence. The equilibrium stress is assumed to be a rate independent functional of the total strain history. Classical plasticity is utilized with a kinematic hardening rule of the Armstrong-Frederick type. In order to incorporate the amplitude-dependent hardening and softening behavior, a generalized arc length representation is applied [14]. The introduction of an additional kinematic hardening variable facilitates consideration of additional hardening effects resulting from the non-radiality of the input process. Apart from the common yield and loading criterion of classical plasticity, the proposed constitutive model does not contain any further distinction of different cases. The experimental data are sufficient to identify the material parameters of the constitutive model. The results of the identification procedure demonstrate the ability of the model to represent the observed phenomena with satisfactory approximation.

Biaxial stress relaxation of semilunar heart valve leaflets during simulated collagen catabolism: Effects of collagenase concentration and equibiaxial strain state.

PubMed

Huang, Siyao; Huang, Hsiao-Ying Shadow

2015-10-01

Heart valve leaflet collagen turnover and remodeling are innate to physiological homeostasis; valvular interstitial cells routinely catabolize damaged collagen and affect repair. Moreover, evidence indicates that leaflets can adapt to altered physiological (e.g. pregnancy) and pathological (e.g. hypertension) mechanical load states, tuning collagen structure and composition to changes in pressure and flow. However, while valvular interstitial cell-secreted matrix metalloproteinases are considered the primary effectors of collagen catabolism, the mechanisms by which damaged collagen fibers are selectively degraded remain unclear. Growing evidence suggests that the collagen fiber strain state plays a key role, with the strain-dependent configuration of the collagen molecules either masking or presenting proteolytic sites, thereby protecting or accelerating collagen proteolysis. In this study, the effects of equibiaxial strain state on collagen catabolism were investigated in porcine aortic valve and pulmonary valve tissues. Bacterial collagenase (0.2 and 0.5 mg/mL) was utilized to simulate endogenous matrix metalloproteinases, and biaxial stress relaxation and biochemical collagen concentration served as functional and compositional measures of collagen catabolism, respectively. At a collagenase concentration of 0.5 mg/mL, increasing the equibiaxial strain imposed during stress relaxation (0%, 37.5%, and 50%) yielded significantly lower median collagen concentrations in the aortic valve (p = 0.0231) and pulmonary valve (p = 0.0183), suggesting that relatively large strain magnitudes may enhance collagen catabolism. Collagen concentration decreases were paralleled by trends of accelerated normalized stress relaxation rate with equibiaxial strain in aortic valve tissues. Collectively, these in vitro results indicate that biaxial strain state is capable of affecting the susceptibility of valvular collagens to catabolism, providing a basis for further investigation of how such phenomena may manifest at different strain magnitudes or in vivo. © IMechE 2015.

Investigation of stress relaxation mechanisms for ductility improvement in SS316L

NASA Astrophysics Data System (ADS)

Varma, Anand; Gokhale, Aditya; Jain, Jayant; Hariharan, Krishnaswamy; Cizek, Pavel; Barnett, Matthew

2018-01-01

Stress relaxation during plastic deformation has been reported to improve ductility and alter the mechanical properties of metallic materials. The aim of the present study is to investigate the role of various mechanisms responsible for this in stainless steel SS 316L. The fractography of the tested samples is analysed using an image analyser and the void fraction at failure is correlated with the corresponding mechanisms. The parametric studies on stress relaxation at different pre-strain and relaxation time correlate well with the fractography results supporting the proposed mechanisms. TEM investigation of dislocation structures and void characterisation further confirm the role of dislocation annihilation. Moreover, a novel indentation technique combining micro- and nano-indentation techniques is used to verify the role of stress homogenisation mechanism.

Substrate stress relaxation regulates cell spreading

NASA Astrophysics Data System (ADS)

Chaudhuri, Ovijit; Gu, Luo; Darnell, Max; Klumpers, Darinka; Bencherif, Sidi A.; Weaver, James C.; Huebsch, Nathaniel; Mooney, David J.

2015-02-01

Studies of cellular mechanotransduction have converged upon the idea that cells sense extracellular matrix (ECM) elasticity by gauging resistance to the traction forces they exert on the ECM. However, these studies typically utilize purely elastic materials as substrates, whereas physiological ECMs are viscoelastic, and exhibit stress relaxation, so that cellular traction forces exerted by cells remodel the ECM. Here we investigate the influence of ECM stress relaxation on cell behaviour through computational modelling and cellular experiments. Surprisingly, both our computational model and experiments find that spreading for cells cultured on soft substrates that exhibit stress relaxation is greater than cells spreading on elastic substrates of the same modulus, but similar to that of cells spreading on stiffer elastic substrates. These findings challenge the current view of how cells sense and respond to the ECM.

Stress Management for Special Educators: The Self-Administered Tool for Awareness and Relaxation (STAR)

ERIC Educational Resources Information Center

Williams, Krista; Poel, Elissa Wolfe

2006-01-01

The Self-Administered Tool for Awareness and Relaxation (STAR) is a stress management strategy designed to facilitate awareness of the physical, mental, emotional, and physiological effects of stress through the interconnectedness of the brain, body, and emotions. The purpose of this article is to present a stress-management model for teachers,…

Skeletal muscle tensile strain dependence: hyperviscoelastic nonlinearity

PubMed Central

Wheatley, Benjamin B; Morrow, Duane A; Odegard, Gregory M; Kaufman, Kenton R; Donahue, Tammy L Haut

2015-01-01

Introduction Computational modeling of skeletal muscle requires characterization at the tissue level. While most skeletal muscle studies focus on hyperelasticity, the goal of this study was to examine and model the nonlinear behavior of both time-independent and time-dependent properties of skeletal muscle as a function of strain. Materials and Methods Nine tibialis anterior muscles from New Zealand White rabbits were subject to five consecutive stress relaxation cycles of roughly 3% strain. Individual relaxation steps were fit with a three-term linear Prony series. Prony series coefficients and relaxation ratio were assessed for strain dependence using a general linear statistical model. A fully nonlinear constitutive model was employed to capture the strain dependence of both the viscoelastic and instantaneous components. Results Instantaneous modulus (p<0.0005) and mid-range relaxation (p<0.0005) increased significantly with strain level, while relaxation at longer time periods decreased with strain (p<0.0005). Time constants and overall relaxation ratio did not change with strain level (p>0.1). Additionally, the fully nonlinear hyperviscoelastic constitutive model provided an excellent fit to experimental data, while other models which included linear components failed to capture muscle function as accurately. Conclusions Material properties of skeletal muscle are strain-dependent at the tissue level. This strain dependence can be included in computational models of skeletal muscle performance with a fully nonlinear hyperviscoelastic model. PMID:26409235

Stress-relaxation behavior of lignocellulosic high-density polyethlene composites

Treesearch

Babak Mirzaei; Mehdi Tajvidi; Robert H. Falk; Colin Felton

2011-01-01

In this study, stress-relaxation performance of HDPE-based injection-molded composites containing four types of natural fibers (i.e., wood flour, rice hulls, newsprint, and kenaf fiber) at 25 and 50 wt% contents, and the effect of prescribed strain levels were investigated. The results indicated that incorporating more filler causes lower relaxation values and rates,...

Rate Dependency During Relaxation of Superelastic Orthodontic NiTi Alloys After Hydrogen Charging

NASA Astrophysics Data System (ADS)

Elkhal Letaief, Wissem; Hassine, Tarek; Gamaoun, Fehmi

2016-03-01

The relaxation behavior under tensile loading of a superelastic NiTi alloy was investigated after hydrogen charging with respect to aging from one to 77 days in air at room temperature. The specimens were immersed for 3 h in a 0.9 % NaCl aqueous solution and then relaxed with an imposed strain of 4.8 %—which results in half of the martensite transformation—for different strain rates of 10-4, 10-3, and 5 × 10-3 s-1. For the non-charged specimens, the relaxed stress at the beginning exhibited a temporary dependence on the strain rates and then reached the same equilibrium stress after 2.5 h. After hydrogen charging, this equilibrium stress did not vary for the as-charged specimen. Nevertheless, the greater the aging period is the greater the equilibrium stress is. This behavior can be attributed to the diffusion of hydrogen into the entire specimen, which hinders the relaxation mechanism of the martensite bands.

Stress relaxation in pre-stressed aluminum core–shell particles: X-ray diffraction study, modeling, and improved reactivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levitas, Valery I.; McCollum, Jena; Pantoya, Michelle L.

Stress relaxation in aluminum micron-scale particles covered by alumina shell after pre-stressing by thermal treatment and storage was measured using X-ray diffraction with synchrotron radiation. Pre-stressing was produced by annealing Al particles at 573K followed by fast cooling. While averaged dilatational strain in Al core was negligible for untreated particles, it was measured at 4.40×10 -5 and 2.85×10 -5 after 2 and 48 days of storage. Consistently, such a treatment leads to increase in flame propagation speed for Al+CuO mixture by 37% and 25%, respectively. Analytical model for creep in alumna shell and stress relaxation in Al core-alumina shellmore » structure is developed and activation energy and pre-exponential multiplier are estimated. The effect of storage temperature and annealing temperature on the kinetics of stress relaxation was evaluated theoretically. These results provide estimates for optimizing Al reactivity with the holding time at annealing temperature and allowable time for storage of Al particles for various environmental temperatures.« less

Stress relaxation in pre-stressed aluminum core–shell particles: X-ray diffraction study, modeling, and improved reactivity

DOE PAGES

Levitas, Valery I.; McCollum, Jena; Pantoya, Michelle L.; ...

2016-05-30

Stress relaxation in aluminum micron-scale particles covered by alumina shell after pre-stressing by thermal treatment and storage was measured using X-ray diffraction with synchrotron radiation. Pre-stressing was produced by annealing Al particles at 573K followed by fast cooling. While averaged dilatational strain in Al core was negligible for untreated particles, it was measured at 4.40×10 -5 and 2.85×10 -5 after 2 and 48 days of storage. Consistently, such a treatment leads to increase in flame propagation speed for Al+CuO mixture by 37% and 25%, respectively. Analytical model for creep in alumna shell and stress relaxation in Al core-alumina shellmore » structure is developed and activation energy and pre-exponential multiplier are estimated. The effect of storage temperature and annealing temperature on the kinetics of stress relaxation was evaluated theoretically. These results provide estimates for optimizing Al reactivity with the holding time at annealing temperature and allowable time for storage of Al particles for various environmental temperatures.« less

[Psychological approaches in hypertension management].

PubMed

Abgrall-Barbry, Gaëlle; Consoli, Silla M

2006-06-01

Stress factors, especially high levels of occupational stress, are associated with hypertension. Several so-called psychological techniques have been applied to hypertension: biofeedback, relaxation techniques (Schultz' autogenic training, Jacobson's progressive relaxation), transcendental meditation, and cognitive behavioral techniques for stress management. Randomized studies show that the best results come from cognitive behavioral methods, whether or not they include relaxation techniques. Other forms of psychotherapy (such as psychoanalysis) may be useful, although their benefits for blood pressure have not been tested in controlled trials. Patients should be informed about the personal benefits they may obtain from psychological treatment. Indications are hyperreactivity to stress, high levels of occupational stress, and difficulty in tolerating or complying with antihypertensive drugs.

Decreased contraction induced by endothelium-derived contracting factor in prolonged treatment of rat renal artery with endoplasmic reticulum stress inducer.

PubMed

Ando, Makoto; Matsumoto, Takayuki; Taguchi, Kumiko; Kobayashi, Tsuneo

2018-05-04

Recent evidence suggests that endoplasmic reticulum (ER) stress is involved in the regulation of various physiological functions, including those of the vascular system. However, the relationship between ER stress and vascular function is poorly understood. The endothelial cells control the vascular tone by releasing endothelium-derived relaxing factors and contracting factors (EDCFs). We hypothesized that tunicamycin, an inducer of ER stress, modifies endothelium-dependent contraction and prostaglandins (PGs), a major class of EDCFs, induced contractions in the rat renal artery in rats. An organ-culture technique was used to purely investigate the effects of ER stress on the vascular tissue. We observed that tunicamycin treatment (20 μg/mL for 23 ± 1 h) did not affect acetylcholine (ACh)-induced relaxation and decreased EDCF-mediated contractions under nitric oxide synthase (NOS) inhibition induced by ACh, ATP, or A23187 (a calcium ionophore) in the renal arteries. Under NOS inhibition, U46619 (a thromboxane A 2 mimetic)- and beraprost (a prostacyclin analog)-induced contractions were also decreased in the renal arteries of the tunicamycin-treated group (vs. vehicle), while PGE 2 - and PGF 2α -induced contractions were similar between the groups. Tunicamycin treatment slightly enhanced the contractions induced by phenylephrine, an α 1 adrenoceptor ligand. Isotonic high-K + -induced contractions were similar between the vehicle- and tunicamycin-treated groups. Another ER stress inducer, thapsigargin (4 μmol/L for 23 ± 1 h), also caused substantial reduction of ACh-induced EDCF-mediated contraction (vs. vehicle-treated group). In the cultured renal arteries, tunicamycin and thapsigargin increased the expression of binding immunoglobulin protein (BiP), an ER stress marker. In conclusion, ER stress induction directly affects renal arterial function, especially in reducing EDCF-mediated contractions.

A-FABP and oxidative stress underlie the impairment of endothelium-dependent relaxations to serotonin and the intima-medial thickening in the porcine coronary artery with regenerated endothelium.

PubMed

Chan, Calvin K; Zhao, Yingzi; Liao, Song Yan; Zhang, Yue Lin; Lee, Mary Y K; Xu, Aimin; Tse, Hung Fat; Vanhoutte, Paul M

2013-01-16

Experiments were designed to determine the cause of the selective dysfunction of G(i) proteins, characterized by a reduced endothelium-dependent relaxation to serotonin (5-hydroxytryptamine), in coronary arteries lined with regenerated endothelial cells. Part of the endothelium of the left anterior descending coronary artery of female pigs was removed in vivo to induce regeneration. The animals were treated chronically with vehicle (control), apocynin (antioxidant), or BMS309403 (A-FABP inhibitor) for 28 days before functional examination and histological analysis of segments of coronary arteries with native or regenerated endothelium of the same hearts. Isometric tension was recorded in organ chambers and cumulative concentration-relaxation curves obtained in response to endothelium-dependent [serotonin (G(i) protein mediated activation of eNOS) and bradykinin (G(q) protein mediated activation of eNOS)] and independent [detaNONOate (cGMP-mediated), isoproterenol (cAMP-mediated)] vasodilators. The two inhibitors tested did not acutely affect relaxations of preparations with either native or regenerated endothelium. In the chronically treated groups, however, both apocynin and BMS309403 abolished the reduction in relaxation to serotonin in segments covered with regenerated endothelium and prevented the intima-medial thickening caused by endothelial regeneration, without affecting responses to bradykinin or endothelium-independent agonists (detaNONOate and isoproterenol). Thus, inhibition of either oxidative stress or A-FABP likely prevents both the selective dysfunction of G(i) protein mediated relaxation to serotonin and the neointimal thickening resulting from endothelial regeneration.

Is the time-dependent behaviour of the aortic valve intrinsically quasi-linear?

NASA Astrophysics Data System (ADS)

Anssari-Benam, Afshin

2014-05-01

The widely popular quasi-linear viscoelasticity (QLV) theory has been employed extensively in the literature for characterising the time-dependent behaviour of many biological tissues, including the aortic valve (AV). However, in contrast to other tissues, application of QLV to AV data has been met with varying success, with studies reporting discrepancies in the values of the associated quantified parameters for data collected from different timescales in experiments. Furthermore, some studies investigating the stress-relaxation phenomenon in valvular tissues have suggested discrete relaxation spectra, as an alternative to the continuous spectrum proposed by the QLV. These indications put forward a more fundamental question: Is the time-dependent behaviour of the aortic valve intrinsically quasi-linear? In other words, can the inherent characteristics of the tissue that govern its biomechanical behaviour facilitate a quasi-linear time-dependent behaviour? This paper attempts to address these questions by presenting a mathematical analysis to derive the expressions for the stress-relaxation G( t) and creep J( t) functions for the AV tissue within the QLV theory. The principal inherent characteristic of the tissue is incorporated into the QLV formulation in the form of the well-established gradual fibre recruitment model, and the corresponding expressions for G( t) and J( t) are derived. The outcomes indicate that the resulting stress-relaxation and creep functions do not appear to voluntarily follow the observed experimental trends reported in previous studies. These results highlight that the time-dependent behaviour of the AV may not be quasi-linear, and more suitable theoretical criteria and models may be required to explain the phenomenon based on tissue's microstructure, and for more accurate estimation of the associated material parameters. In general, these results may further be applicable to other planar soft tissues of the same class, i.e. with the same representation for fibre recruitment mechanism and discrete time-dependent spectra.

Functional Assessment and Treatment of Migraine Reports and School Absences in an Adolescent with Asperger's Disorder

ERIC Educational Resources Information Center

Arvans, Rebecca K.; LeBlanc, Linda A.

2009-01-01

Psychological interventions for migraines typically include biofeedback training, stress-management training, or relaxation training and are implemented without consideration of environmental variables that might maintain migraines or complaints of migraines. An adolescent with daily reports of migraines that negatively impacted school attendance…

A review of recent findings about stress-relaxation in the respiratory system tissues.

PubMed

Rubini, Alessandro; Carniel, Emanuele Luigi

2014-12-01

This article reviews the state of the art about an unclear physiological phenomenon interesting respiratory system tissues, i.e., stress-relaxation. Due to their visco-elastic properties, the tissues do not maintain constant stress under constant deformation. Rather, the stress slowly relaxes and falls to a lower value. The exact molecular basis of this complex visco-elastic behavior is not well defined, but it has been suggested that it may be generated because of the anisotropic mechanical properties of elastin and collagen fibers in the alveolar septa and their interaction phenomena, such as reciprocal sliding, also in relation to interstitial liquid movements. The effects on stress-relaxation of various biochemical and physical factors are reviewed, including the consequences of body temperature variations, respiratory system inflammations and hyperbaric oxygen exposure, endocrinal factors, circulating blood volume variations, changes in inflation volume and/or flow, changes in intra-abdominal pressure because of pneumoperitoneum or Trendelenburg position. The effects of these factors on stress-relaxation have practical consequences because, depending on visco-elastic pressure amount which is requested to inflate the respiratory system in different conditions, respiratory muscles have to produce different values of inspiratory pressure during spontaneous breathing. High inspiratory pressure values might increase the risk of respiratory failure development on mechanical basis.

A randomized controlled pilot study feasibility of a tablet-based guided audio-visual relaxation intervention for reducing stress and pain in adults with sickle cell disease.

PubMed

Ezenwa, Miriam O; Yao, Yingwei; Engeland, Christopher G; Molokie, Robert E; Wang, Zaijie Jim; Suarez, Marie L; Wilkie, Diana J

2016-06-01

To test feasibility of a guided audio-visual relaxation intervention protocol for reducing stress and pain in adults with sickle cell disease. Sickle cell pain is inadequately controlled using opioids, necessitating further intervention such as guided relaxation to reduce stress and pain. Attention-control, randomized clinical feasibility pilot study with repeated measures. Randomized to guided relaxation or control groups, all patients recruited between 2013-2014 during clinical visits, completed stress and pain measures via a Galaxy Internet-enabled Android tablet at the Baseline visit (pre/post intervention), 2-week posttest visit and also daily at home between the two visits. Experimental group patients were asked to use a guided relaxation intervention at the Baseline visit and at least once daily for 2 weeks. Control group patients engaged in a recorded sickle cell discussion at the Baseline visit. Data were analysed using linear regression with bootstrapping. At baseline, 27/28 of consented patients completed the study protocol. Group comparison showed that guided relaxation significantly reduced current stress and pain. At the 2-week posttest, 24/27 of patients completed the study, all of whom reported liking the study. Patients completed tablet-based measures on 71% of study days (69% in control group, 72% in experiment group). At the 2-week posttest, the experimental group had significantly lower composite pain index scores, but the two groups did not differ significantly on stress intensity. This study protocol appears feasible. The tablet-based guided relaxation intervention shows promise for reducing sickle cell pain and warrants a larger efficacy trial. The ClinicalTrials.gov Identifier is: NCT02501447. © 2016 John Wiley & Sons Ltd.

Internal structural changes in keratin fibres resulting from combined hair waving and stress relaxation treatments: a Raman spectroscopic investigation.

PubMed

Kuzuhara, A

2016-04-01

The objective of our research was to investigate the influence of chemical treatments (reduction, stress relaxation and oxidation) on hair keratin fibres. The structure of cross-sections at various depths of virgin white human hair resulting from permanent waving treatments with stress relaxation process was directly analysed at a molecular level using Raman spectroscopy. In particular, the three disulphide (-SS-) conformations in human hair were compared by S-S band analysis. The gauche-gauche-gauche (GGG) and gauche-gauche-trans (GGT) contents of -SS- groups remarkably decreased, while the trans-gauche-trans (TGT) content was not changed by performing the reduction process with thioglycolic acid. In addition, the high-temperature stress relaxation process after reduction accelerated the disconnection of -SS- (GGG and GGT) groups in the human hair, while the low-temperature stress relaxation process after reduction accelerated the reconnection of -SS- (GGG and GGT) groups. Moreover, the S-O band intensity at 1042 cm(-1) , assigned to cysteic acid, existing in the cuticle region and the surface of the cortex region increased, while the GGG content significantly decreased by performing the oxidation process after the reduction and the high-temperature stress relaxation processes. The author concluded that the high-temperature relaxation process after reduction accelerated the disconnection of -SS- (GGG and GGT) groups, thereby leading to the remarkable local molecular disorganization (an increase in the cysteic acid content and a decrease in the GGG content) on the cuticle and cortex cells during the oxidation process. © 2015 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

Lipid Emulsions Containing Medium Chain Triacylglycerols Blunt Bradykinin-Induced Endothelium-Dependent Relaxation in Porcine Coronary Artery Rings.

PubMed

Amissi, Said; Boisramé-Helms, Julie; Burban, Mélanie; Rashid, Sherzad K; León-González, Antonio J; Auger, Cyril; Toti, Florence; Meziani, Ferhat; Schini-Kerth, Valérie B

2017-03-01

Lipid emulsions for parenteral nutrition are used to provide calories and essential fatty acids for patients. They have been associated with hypertriglyceridemia, hypercholesterolemia, and metabolic stress, which may promote the development of endothelial dysfunction in patients. The aim of the present study was to determine whether five different industrial lipid emulsions may affect the endothelial function of coronary arteries. Porcine coronary artery rings were incubated with lipid emulsions 0.5, 1, or 2% (v/v) for 30 min before the determination of vascular reactivity in organ chambers and the level of oxidative stress using electron paramagnetic resonance. Incubation of coronary artery rings with either Lipidem ® , Medialipid ® containing long- and medium-chain triacylglycerols (LCT/MCT), or SMOFlipid ® containing LCT, MCT, omega-9, and -3, significantly reduced the bradykinin-induced endothelium-dependent relaxation, affecting both the nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) components, whereas, Intralipid ® containing LCT (soybean oil) and ClinOleic ® containing LCT (soybean and olive oil) did not have such an effect. The endothelial dysfunction induced by Lipidem ® was significantly improved by indomethacin, a cyclooxygenase (COX) inhibitor, inhibitors of oxidative stress (N-acetylcysteine, superoxide dismutase, catalase) and transition metal chelating agents (neocuproine, tetrathiomolybdate, deferoxamine and L-histidine). Lipidem ® significantly increased the arterial level of oxidative stress. The present findings indicate that lipid emulsions containing LCT/MCT induce endothelial dysfunction in coronary artery rings by blunting both NO- and EDH-mediated relaxations. The Lipidem ® -induced endothelial dysfunction is associated with increased vascular oxidative stress and the formation of COX-derived vasoconstrictor prostanoids.

Effects of patterning induced stress relaxation in strained SOI/SiGe layers and substrate

NASA Astrophysics Data System (ADS)

Hermann, P.; Hecker, M.; Renn, F.; Rölke, M.; Kolanek, K.; Rinderknecht, J.; Eng, L. M.

2011-06-01

Local stress fields in strained silicon structures important for CMOS technology are essentially related to size effects and properties of involved materials. In the present investigation, Raman spectroscopy was utilized to analyze the stress distribution within strained silicon (sSi) and silicon-germanium (SiGe) island structures. As a result of the structuring of initially unpatterned strained films, a size-dependent relaxation of the intrinsic film stresses was obtained in agreement with model calculations. This changed stress state in the features also results in the appearance of opposing stresses in the substrate underneath the islands. Even for strained island structures on top of silicon-on-insulator (SOI) wafers, corresponding stresses in the silicon substrate underneath the oxide were detected. Within structures, the stress relaxation is more pronounced for islands on SOI substrates as compared to those on bulk silicon substrates.

Giant deviation of a relaxation time from generalized Newtonian theory in discontinuous shear thickening suspensions

NASA Astrophysics Data System (ADS)

Maharjan, Rijan; Brown, Eric

2017-12-01

We investigated the transient relaxation of a discontinuous shear thickening (DST) suspension of cornstarch in water. We performed two types of relaxation experiments starting from a steady shear in a parallel-plate rheometer, followed either by stopping the top plate rotation and measuring the transient torque relaxation or by removing the torque on the plate and measuring the transient rotation of the tool. We found that at low effective weight fraction ϕeff<58.8 ±0.4 % , the suspensions exhibited a relaxation behavior consistent with a generalized Newtonian fluid in which the relaxation is determined by the steady-state relationship between shear stress and shear rate. However, for larger weight fraction 58.8 %<ϕeff<61.0 % , near the liquid-solid transition ϕc=61.0 ±0.7 % , we found relaxation behaviors qualitatively and quantitatively different from the generalized Newtonian model. The regime where the relaxation was inconsistent with the generalized Newtonian model was the same where we found positive normal stress during relaxation, and in some cases we found an oscillatory response, suggestive of a solidlike structure consisting of a system-spanning contact network of particles. This regime also corresponds to the same packing fraction range where we consistently found discontinuous shear thickening in rate-controlled, steady-state measurements. The relaxation time in this range scales with the inverse of the critical shear rate at the onset of shear thickening, which may correspond to a contact relaxation time for nearby particles in the structure to flow away from each other. In this range, the relaxation time was the same in both stress- and rate-controlled relaxation experiments, indicating the relaxation time is more intrinsic than an effective viscosity in this range and is needed in addition to the steady-state viscosity function to describe transient flows. The discrepancy between the measured relaxation times and the generalized Newtonian prediction was found to be as large as four orders of magnitude, and extrapolations diverge in the limit as ϕeff→ϕc as the generalized Newtonian prediction approaches 0. This quantitative discrepancy indicates the relaxation is not controlled by the dissipative terms in the constitutive relation. At the highest weight fractions, the relaxation time scales were measured to be on the order of ˜1 s. The fact that this time scale is resolvable by the naked eye may be important to understanding some of the dynamic phenomenon commonly observed in cornstarch and water suspensions. We also showed that using the critical shear rate γ˙c at the onset of shear thickening to characterize the effective weight fraction ϕeff can more precisely characterize material properties near the critical point ϕc, allowing us to resolve this transition so close to ϕc. This conversion to ϕeff can also be used to compare experiments done in other laboratories or under different temperature and humidity conditions on a consistent ϕeff scale at our reference temperature and humidity environment.

The calculation of viscosity of liquid n-decane and n-hexadecane by the Green-Kubo method

NASA Astrophysics Data System (ADS)

Cui, S. T.; Cummings, P. T.; Cochran, H. D.

This short commentary presents the result of long molecular dynamics simulation calculations of the shear viscosity of liquid n-decane and n-hexadecane using the Green-Kubo integration method. The relaxation time of the stress-stress correlation function is compared with those of rotation and diffusion. The rotational and diffusional relaxation times, which are easy to calculate, provide useful guides for the required simulation time in viscosity calculations. Also, the computational time required for viscosity calculations of these systems by the Green-Kubo method is compared with the time required for previous non-equilibrium molecular dynamics calculations of the same systems. The method of choice for a particular calculation is determined largely by the properties of interest, since the efficiencies of the two methods are comparable for calculation of the zero strain rate viscosity.

Stress generation and evolution in oxide heteroepitaxy

NASA Astrophysics Data System (ADS)

Fluri, Aline; Pergolesi, Daniele; Wokaun, Alexander; Lippert, Thomas

2018-03-01

Many physical properties of oxides can be changed by inducing lattice distortions in the crystal through heteroepitaxial growth of thin films. The average lattice strain can often be tuned by changing the film thickness or using suitable buffer layers between film and substrate. The exploitation of the full potential of strain engineering for sample or device fabrication rests on the understanding of the fundamental mechanisms of stress generation and evolution. For this study an optical measurement of the substrate curvature is used to monitor in situ how the stress builds up and relaxes during the growth of oxide thin films by pulsed laser deposition. The relaxation behavior is correlated with the growth mode, which is monitored simultaneously with reflection high-energy electron diffraction. The stress relaxation data is fitted and compared with theoretical models for stress evolution which were established for semiconductor epitaxy. The initial stage of the growth appears to be governed by surface stress and surface energy effects, while the subsequent stress relaxation is found to be fundamentally different between films grown on single-crystal substrates and on buffer layers. The first case can be rationalized with established theoretical models, but these models fail in the attempt to describe the growth on buffer layers. This is most probably due to the larger average density of crystalline defects in the buffer layers, which leads to a two-step stress relaxation mechanism, driven first by the nucleation and later by the migration of dislocation lines.

A fractional model with parallel fractional Maxwell elements for amorphous thermoplastics

NASA Astrophysics Data System (ADS)

Lei, Dong; Liang, Yingjie; Xiao, Rui

2018-01-01

We develop a fractional model to describe the thermomechanical behavior of amorphous thermoplastics. The fractional model is composed of two parallel fractional Maxwell elements. The first fractional Maxwell model is used to describe the glass transition, while the second component is aimed at describing the viscous flow. We further derive the analytical solutions for the stress relaxation modulus and complex modulus through Laplace transform. We then demonstrate the model is able to describe the master curves of the stress relaxation modulus, storage modulus and loss modulus, which all show two distinct transition regions. The obtained parameters show that the modulus of the two fractional Maxwell elements differs in 2-3 orders of magnitude, while the relaxation time differs in 7-9 orders of magnitude. Finally, we apply the model to describe the stress response of constant strain rate tests. The model, together with the parameters obtained from fitting the master curve of stress relaxation modulus, can accurately predict the temperature and strain rate dependent stress response.

Matrix dominated stress/strain behavior in polymeric composites: Effects of hold time, nonlinearity and rate dependency

NASA Technical Reports Server (NTRS)

Gates, Thomas S.

1992-01-01

In order to understand matrix dominated behavior in laminated polymer matrix composites, an elastic/viscoplastic constitutive model was developed and used to predict stress strain behavior of off-axis and angle-ply symmetric laminates under in-plane, tensile axial loading. The model was validated for short duration tests at elevated temperatures. Short term stress relaxation and short term creep, strain rate sensitivity, and material nonlinearity were accounted for. The testing times were extended for longer durations, and periods of creep and stress relaxation were used to investigate the ability of the model to account for long term behavior. The model generally underestimated the total change in strain and stress for both long term creep and long term relaxation respectively.

Improved method for determining the stress relaxation at the crack tip

NASA Astrophysics Data System (ADS)

Grinevich, A. V.; Erasov, V. S.; Avtaev, V. V.

2017-10-01

A technique is suggested to determine the stress relaxation at the crack tip during tests of a specimen of a new type at a constant crack opening fixed by a stay bolt. The shape and geometry of the specimen make it possible to set the load and to determine the crack closure force after long-term exposure using the force transducer of a tensile-testing machine. The stress relaxation at the crack tip is determined in a V95pchT2 alloy specimen at elevated temperatures.

Evolution of the plasma-sprayed microstructure in 7 wt% yttria-stabilized zirconia thermal barrier coatings during uniaxial stress relaxation and the concomitant changes in material properties

NASA Astrophysics Data System (ADS)

Petorak, Christopher

The understanding of failure mechanisms in plasma sprayed 7 wt% yttria stabilized zirconia (YSZ) is a key step toward optimizing thermal barrier coating (TBC) usage, design, and life prediction. The purpose of the present work is to characterize and understand the stress relaxation behavior occurring in plasma-sprayed YSZ coatings, so that the correlating magnitude of unfavorable tensile stress, which coatings experienced upon cooling, may be reduced through microstructural design. The microstructure and properties of as-sprayed coatings changes immensely during service at high temperature, and therefore the effects of long heat-treatment times, and the concomitant change within the microstructure, on the time-dependent mechanical behavior of stand-alone YSZ coatings was studied in parallel with the as-sprayed coating condition. Aside from influencing the mechanical properties, stress relaxation also affects the insulating efficiency of plasma-sprayed 7wt% YSZ coatings. Directionally dependent changes in microstructure due to stress relaxation of a uniaxially applied stress at 1200°C were observed in plasma-sprayed coatings. Small angle neutron scattering (SANS) investigation of coatings after stress relaxation displayed a 46% reduction in the specific surface area connected to the load-orientation dependent closure of void surface area perpendicular to the applied load when compared to coatings sintered in air, i.e. no applied load. These anisotropic microstructural changes were linked to the thermal properties of the coating. For example, a coating stress relaxed from 60 MPa for 5-min at 1200°C exhibited a thermal conductivity of 2.1 W/m-K. A coating that was only heat-treated for 5-min at 1200°C (i.e. no stress applied) exhibited a thermal conductivity of 1.7 W/m·K. In the current study, uniaxial stress relaxation in plasma-sprayed 7wt% YSZ coatings was determined the result of: (1) A more uniform distribution of the applied load with time, (2) A reduction in the SSA associated with void systems due to sintering, specifically the closing and healing of intralamellar cracks perpendicular to the applied stress, and (3) A compaction and closure of void systems under the applied load. These anisotropic changes in microstructure result in distinguishable changes in thermo-mechanical properties, with very minute changes to the overall bulk density.

Integrating a Relaxation Response-Based Curriculum into a Public High School in Massachusetts

ERIC Educational Resources Information Center

Foret, Megan M.; Scult, Matthew; Wilcher, Marilyn; Chudnofsky, Rana; Malloy, Laura; Hasheminejad, Nicole; Park, Elyse R.

2012-01-01

Academic and societal pressures result in U.S. high school students feeling stressed. Stress management and relaxation interventions may help students increase resiliency to stress and overall well-being. The objectives of this study were to examine the feasibility (enrollment, participation and acceptability) and potential effectiveness (changes…

Effects of Stress Relaxation Aging with Electrical Pulses on Microstructures and Properties of 2219 Aluminum Alloy

PubMed Central

Tan, Jingsheng; Zhan, Lihua; Zhang, Jiao; Yang, Zhan; Ma, Ziyao

2016-01-01

To realize the high-efficiency and high-performance manufacture of complex high-web panels, this paper introduced electric pulse current (EPC) into the stress relaxation aging forming process of 2219 aluminum alloy and systematically studied the effects of EPC, stress, and aging time upon the microstructure and properties of 2219 aluminum alloy. It is discovered that: (a) EPC greatly enhanced the mechanical properties after stress relaxation aging and reduced the sensitivity of the yield strength for the initial stress under the aging system of 165 °C/11 h; (b) compared with general aging, stress relaxation aging instead delayed the aging process of 2219 aluminum alloy and greatly increased the peak strength value; (c) EPC accelerated the aging precipitation behavior of 2219 aluminum alloy and reduced transgranular and grain-boundary energy difference, thus leading to a more diffused distribution of the transgranular precipitated phase and the absence of a significant precipitation-free zone (PFZ) and grain-boundary stable phase in the grain boundary, further improving the mechanical properties of the alloy. PMID:28773660

The effect of radiation-induced cross-linking on the relaxation of taut tie molecules during annealing of drawn LDPE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rong Jiang Yan; Yunxia Luo; Bingzheng Jiang

1993-02-05

Shrinkage, retractive stress, and infrared dichroism of the drawn low-density polyethylene (LDPE) as-drawn and irradiated by [sup 60]Co-ray have been measured under different annealing conditions. The shrinkage and the disorientation of the irradiated sample was undergone more rapidly than that of unirradiated one as the temperature was continuously increased, surpassing a certain value, and a higher degree of shrinkage and disorientation was achieved finally for the irradiated sample when the samples were annealed with free ends. For the samples heated isothermally with fixed ends, the retractive stress went through a maximum and then attenuated to a limited value, and themore » degree of such a stress attenuation for the unirradiated sample was much more than that for the irradiated sample. These results show that the taut tie molecules (TTMs) in drawn PE can relax by the pulling of chain segments out of crystal blocks that they anchored in at elevated temperatures higher than the [alpha] transition and also by the displacing of microfibrils if the samples were annealed with free ends. The cross-links produced by irradiation prohibit the former process. It was further observed that the dependence of the average extinction coefficient of the band at 2,016 cm[sup [minus]1] on that of the band at 1,894 cm[sup [minus]1] is related to irradiation and annealing conditions, which has also been explained by the relaxation of TTMs and the function of irradiation-induced cross-linking on the relaxation.« less

Mindfulness meditation training alters stress-related amygdala resting state functional connectivity: a randomized controlled trial

PubMed Central

Taren, Adrienne A.; Gianaros, Peter J.; Greco, Carol M.; Lindsay, Emily K.; Fairgrieve, April; Brown, Kirk Warren; Rosen, Rhonda K.; Ferris, Jennifer L.; Julson, Erica; Marsland, Anna L.; Bursley, James K.; Ramsburg, Jared

2015-01-01

Recent studies indicate that mindfulness meditation training interventions reduce stress and improve stress-related health outcomes, but the neural pathways for these effects are unknown. The present research evaluates whether mindfulness meditation training alters resting state functional connectivity (rsFC) of the amygdala, a region known to coordinate stress processing and physiological stress responses. We show in an initial discovery study that higher perceived stress over the past month is associated with greater bilateral amygdala-subgenual anterior cingulate cortex (sgACC) rsFC in a sample of community adults (n = 130). A follow-up, single-blind randomized controlled trial shows that a 3-day intensive mindfulness meditation training intervention (relative to a well-matched 3-day relaxation training intervention without a mindfulness component) reduced right amygdala-sgACC rsFC in a sample of stressed unemployed community adults (n = 35). Although stress may increase amygdala-sgACC rsFC, brief training in mindfulness meditation could reverse these effects. This work provides an initial indication that mindfulness meditation training promotes functional neuroplastic changes, suggesting an amygdala-sgACC pathway for stress reduction effects. PMID:26048176

Cost-Effective Stress Management Training.

ERIC Educational Resources Information Center

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)

Unexpected power-law stress relaxation of entangled ring polymers

PubMed Central

KAPNISTOS, M.; LANG, M.; PYCKHOUT-HINTZEN, W.; RICHTER, D.; CHO, D.; CHANG, T.

2016-01-01

After many years of intense research, most aspects of the motion of entangled polymers have been understood. Long linear and branched polymers have a characteristic entanglement plateau and their stress relaxes by chain reptation or branch retraction, respectively. In both mechanisms, the presence of chain ends is essential. But how do entangled polymers without ends relax their stress? Using properly purified high-molar-mass ring polymers, we demonstrate that these materials exhibit self-similar dynamics, yielding a power-law stress relaxation. However, trace amounts of linear chains at a concentration almost two decades below their overlap cause an enhanced mechanical response. An entanglement plateau is recovered at higher concentrations of linear chains. These results constitute an important step towards solving an outstanding problem of polymer science and are useful for manipulating properties of materials ranging from DNA to polycarbonate. They also provide possible directions for tuning the rheology of entangled polymers. PMID:18953345

Wall relaxation and the driving forces for cell expansive growth

NASA Technical Reports Server (NTRS)

Cosgrove, D. J.

1987-01-01

When water uptake by growing cells is prevented, the turgor pressure and the tensile stress in the cell wall are reduced by continued wall loosening. This process, termed in vivo stress relaxation, provides a new way to study the dynamics of wall loosening and to measure the wall yield threshold and the physiological wall extensibility. Stress relaxation experiments indicate that wall stress supplies the mechanical driving force for wall yielding. Cell expansion also requires water absorption. The driving force for water uptake during growth is created by wall relaxation, which lowers the water potential of the expanding cells. New techniques for measuring this driving force show that it is smaller than believed previously; in elongating stems it is only 0.3 to 0.5 bar. This means that the hydraulic resistance of the water transport pathway is small and that rate of cell expansion is controlled primarily by wall loosening and yielding.

Enhanced Stress Relaxation and Reduced Cure Stress in Thermosets with Ferrocene-Based Crosslinkers

NASA Astrophysics Data System (ADS)

Jones, Brad; Wheeler, David; Stavig, Mark; Black, Hayden; Sawyer, Patricia; Giron, Nicholas; Celina, Mathias; Alam, Todd

Organometallic sandwich compounds are characterized by facile isomerization among a variety of unique states. For example, ferrocene exhibits an extraordinarily low barrier to rotation of its cyclopentadienyl (Cp) ligands about the metal-Cp axis. We propose that this phenomenon can be exploited to enhance stress relaxation of polymers containing organometallic sandwich backbone moieties. Here, we describe the synthesis and characterization of several thermosets that employ ferrocene derivatives as crosslinkers. In particular, we compare a ferrocene diamine to several conventional diamines in the crosslinking of epoxy resin. Stress relaxation and dynamic mechanical analyses reveal that the ferrocene-based thermosets are distinguished from conventional thermosets by their capacity for physical relaxation. More importantly, these materials exhibit markedly different residual stress evolution during cure. For example, the cure stress in ferrocene-based thermosets drops precipitously with decreasing crosslink density. Our results highlight the unique role organometallic chemistry can play for stress management of thermosets and, more broadly, in manipulating their structure-property relationships. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the US Department of Energy National Nuclear Security Administration under contract DE-AC04-94AL85000.

Photomechanical Deformation of Azobenzene-Functionalized Polyimides Synthesized with Bulky Substituents (Postprint)

DTIC Science & Technology

2017-12-06

mechanical response of the azobenzene- functionalized polyimide is correlated to the rotational freedom of the polyimide chains (resulting in extensive... correlated to the rotational freedom of the polyimide chains (resulting in extensive segmental mobility) and fractional free volume (FFV > 0.1...response has been described,34 and a recent simulation study on the stress relaxation dynamics of azo-polyimides has provided insights into the correlation

Long-Term Stability of Residual Stress Improvement by Water Jet Peening Considering Working Processes.

PubMed

Hashimoto, Tadafumi; Osawa, Yusuke; Itoh, Shinsuke; Mochizuki, Masahito; Nishimoto, Kazutoshi

2013-06-01

To prevent primary water stress corrosion cracking (PWSCC), water jet peening (WJP) has been used on the welds of Ni-based alloys in pressurized water reactors (PWRs). Before WJP, the welds are machined and buffed in order to conduct a penetrant test (PT) to verify the weld qualities to access, and microstructure evolution takes place in the target area due to the severe plastic deformation. The compressive residual stresses induced by WJP might be unstable under elevated temperatures because of the high dislocation density in the compressive stress layer. Therefore, the stability of the compressive residual stresses caused by WJP was investigated during long-term operation by considering the microstructure evolution due to the working processes. The following conclusions were made: The compressive residual stresses were slightly relaxed in the surface layers of the thermally aged specimens. There were no differences in the magnitude of the relaxation based on temperature or time. The compressive residual stresses induced by WJP were confirmed to remain stable under elevated temperatures. The stress relaxation at the surface followed the Johnson-Mehl equation, which states that stress relaxation can occur due to the recovery of severe plastic strain, since the estimated activation energy agrees very well with the self-diffusion energy for Ni. By utilizing the additivity rule, it was indicated that stress relaxation due to recovery is completed during the startup process. It was proposed that the long-term stability of WJP under elevated temperatures must be assessed based on compressive stresses with respect to the yield stress. Thermal elastic-plastic creep analysis was performed to predict the effect of creep strain. After 100 yr of simulated continuous operation at 80% capacity, there was little change in the WJP compressive stresses under an actual operating temperature of 623 K. Therefore, the long-term stability of WJP during actual operation was analytically predicted.

Complex interplay between stress perturbations and viscoelastic relaxation in a two-asperity fault model

NASA Astrophysics Data System (ADS)

Lorenzano, Emanuele; Dragoni, Michele

2018-03-01

We consider a plane fault with two asperities embedded in a shear zone, subject to a uniform strain rate owing to tectonic loading. After an earthquake, the static stress field is relaxed by viscoelastic deformation in the asthenosphere. We treat the fault as a discrete dynamical system with 3 degrees of freedom: the slip deficits of the asperities and the variation of their difference due to viscoelastic deformation. The evolution of the fault is described in terms of inter-seismic intervals and slip episodes, which may involve the slip of a single asperity or both. We consider the effect of stress transfers connected to earthquakes produced by neighbouring faults. The perturbation alters the slip deficits of both asperities and the stress redistribution on the fault associated with viscoelastic relaxation. The interplay between the stress perturbation and the viscoelastic relaxation significantly complicates the evolution of the fault and its seismic activity. We show that the presence of viscoelastic relaxation prevents any simple correlation between the change of Coulomb stresses on the asperities and the anticipation or delay of their failures. As an application, we study the effects of the 1999 Hector Mine, California, earthquake on the post-seismic evolution of the fault that generated the 1992 Landers, California, earthquake, which we model as a two-mode event associated with the consecutive failure of two asperities.

Effect of misalignment on mechanical behavior of metals in creep. [computer programs

NASA Technical Reports Server (NTRS)

Wu, H. C.

1979-01-01

Application of the endochronic theory of viscoplasticity to creep, creep recovery, and stress relaxation at the small strain and short time range produced the following results: (1) The governing constitutive equations for constant-strain-rate stress-strain behavior, creep, creep recovery, and stress relaxation were derived by imposing appropriate constraints on the general constitutive equation of the endochronic theory. (2) A set of material constants was found which correlate strain-hardening, creep, creep recovery, and stress relaxation. (3) The theory predicts with reasonable accuracy the creep and creep recovery behaviors at short time. (4) The initial strain history prior to the creep stage affects the subsequent creep significantly. (5) A critical stress was established for creep recovery. A computer program, written for the misalignment problem is reported.

Effect of Applied Stress and Temperature on Residual Stresses Induced by Peening Surface Treatments in Alloy 600

NASA Astrophysics Data System (ADS)

Telang, A.; Gnäupel-Herold, T.; Gill, A.; Vasudevan, V. K.

2018-04-01

In this study, the effects of applied tensile stress and temperature on laser shock peening (LSP) and cavitation shotless peening (CSP)-induced compressive residual stresses were investigated using neutron and x-ray diffraction. Residual stresses on the surface, measured in situ, were lower than the applied stress in LSP- and CSP-treated Alloy 600 samples (2 mm thick). The residual stress averaged over the volume was similar to the applied stress. Compressive residual stresses on the surface and balancing tensile stresses in the interior relax differently due to hardening induced by LSP. Ex situ residual stress measurements, using XRD, show that residual stresses relaxed as the applied stress exceeded the yield strength of the LSP- and CSP-treated Alloy 600. Compressive residual stresses induced by CSP and LSP decreased by 15-25% in magnitude, respectively, on exposure to 250-450 °C for more than 500 h with 10-11% of relaxation occurring in the first few hours. Further, 80% of the compressive residual stresses induced by LSP and CSP treatments in Alloy 600 were retained even after long-term aging at 350 °C for 2400 h.

Acute dyskerin depletion triggers cellular senescence and renders osteosarcoma cells resistant to genotoxic stress-induced apoptosis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Ping; Mobasher, Maral E.; Alawi, Faizan, E-mail: falawi@upenn.edu

Highlights: • Dyskerin depletion triggers cellular senescence in U2OS osteosarcoma cells. • Dyskerin-depleted cells are resistant to apoptosis induced by genotoxic stress. • Chromatin relaxation sensitizes dyskerin-depleted cells to apoptosis. - Abstract: Dyskerin is a conserved, nucleolar RNA-binding protein implicated in an increasing array of fundamental cellular processes. Germline mutation in the dyskerin gene (DKC1) is the cause of X-linked dyskeratosis congenita (DC). Conversely, wild-type dyskerin is overexpressed in sporadic cancers, and high-levels may be associated with poor prognosis. It was previously reported that acute loss of dyskerin function via siRNA-mediated depletion slowed the proliferation of transformed cell lines. However,more » the mechanisms remained unclear. Using human U2OS osteosarcoma cells, we show that siRNA-mediated dyskerin depletion induced cellular senescence as evidenced by proliferative arrest, senescence-associated heterochromatinization and a senescence-associated molecular profile. Senescence can render cells resistant to apoptosis. Conversely, chromatin relaxation can reverse the repressive effects of senescence-associated heterochromatinization on apoptosis. To this end, genotoxic stress-induced apoptosis was suppressed in dyskerin-depleted cells. In contrast, agents that induce chromatin relaxation, including histone deacetylase inhibitors and the DNA intercalator chloroquine, sensitized dyskerin-depleted cells to apoptosis. Dyskerin is a core component of the telomerase complex and plays an important role in telomere homeostasis. Defective telomere maintenance resulting in premature senescence is thought to primarily underlie the pathogenesis of X-linked DC. Since U2OS cells are telomerase-negative, this leads us to conclude that loss of dyskerin function can also induce cellular senescence via mechanisms independent of telomere shortening.« less

Burnout: An Occupational Hazard.

ERIC Educational Resources Information Center

Hamann, Donald L.; Gordon, Debra G.

2000-01-01

Describes a five-step pattern of burnout and discusses various stress factors that can contribute to burnout. Explores solutions to burnout, such as keeping a balance in life, exercising, and relaxation. Includes sections on balanced breathing, imagery relaxation, and resources for stress reduction. (CMK)

Comparison of Models of Stress Relaxation in Failure Analysis for Connectors under Long-term Storage

NASA Astrophysics Data System (ADS)

Zhou, Yilin; Wan, Mengru

2018-03-01

Reliability requirements of the system equipment under long-term storage are put forward especially for the military products, so that the connectors in the equipment also need long-term storage life correspondingly. In this paper, the effects of stress relaxation of the elastic components on electrical contact of the connectors in long-term storage process were studied from the failure mechanism and degradation models. A wire spring connector was taken as an example to discuss the life prediction method for electrical contacts of the connectors based on stress relaxation degradation under long -term storage.

[Stress management in the treatment of essential arterial hypertension].

PubMed

Schwickert, M; Langhorst, J; Paul, A; Michalsen, A; Dobos, G J

2006-11-23

Between 60 and 90% of patients consult their family doctor for stress-associated complaints. Not infrequently, a considerable number of these patients already have elevated blood pressure. The positive effect on high blood pressure of relaxation techniques has been confirmed in various studies. Accordingly, stress management should now have a permanent place in effective antihypertensive treatment. Appropriate relaxation techniques include, for example, autogenic training, progressive muscle relaxation, visualization and breathing exercises, chi gong and yoga. These practices are incorporated in various lifestyle programs. They act in different ways, and can be offered to the patient in accordance with his/her individual wishes.

Leg massage therapy promotes psychological relaxation and reinforces the first-line host defense in cancer patients.

PubMed

Noto, Yuka; Kitajima, Maiko; Kudo, Mihoko; Okudera, Koichi; Hirota, Kazuyoshi

2010-12-01

Patients with cancer suffer a wide range of physical symptoms coupled with psychological stress. Moreover, cancer chemotherapy induces immunosuppression and consequently causes respiratory infections. Massage therapy has been reported to reduce symptoms in cancer patients via an increase in psychosocial relaxation and to enhance and/or improve immune function. In the present study, we determined whether leg massage could induce psychosocial relaxation and activate the first line of the host defense system. To assess effects of rest and leg massage, 15 healthy volunteers rested on a bed for 20 min on the first day, and 3 days later the subjects received a standardized massage of the legs for 20 min with nonaromatic oil. Twenty-nine cancer patients also received the same standardized massage of the legs. Anxiety/stress was assessed before and just after the rest or the massage using the State-Trait Anxiety Inventory (STAI-s) and visual analogue scale (VAS). To evaluate oral immune function, salivary chromogranin A (CgA) and secretory immunoglobulin A (sIgA) levels were measured. In healthy volunteers, rest significantly reduced VAS by 34% and increased sIgA by 61%. In contrast, leg massage significantly reduced both STAI-s and VAS by 24% and 63%, and increased both sIgA and CgA by 104% and 90%, respectively. In cancer patients, leg massage significantly decreased both STAI-s and VAS by 16% and 38%, and increased both salivary CgA and sIgA by 33% and 35%, respectively. Leg massage may promote psychosocial relaxation and reinforce a first-line host defense with an increase in secretion of antimicrobial peptides.

Elastically driven intermittent microscopic dynamics in soft solids

NASA Astrophysics Data System (ADS)

Bouzid, Mehdi; Colombo, Jader; Barbosa, Lucas Vieira; Del Gado, Emanuela

2017-06-01

Soft solids with tunable mechanical response are at the core of new material technologies, but a crucial limit for applications is their progressive aging over time, which dramatically affects their functionalities. The generally accepted paradigm is that such aging is gradual and its origin is in slower than exponential microscopic dynamics, akin to the ones in supercooled liquids or glasses. Nevertheless, time- and space-resolved measurements have provided contrasting evidence: dynamics faster than exponential, intermittency and abrupt structural changes. Here we use 3D computer simulations of a microscopic model to reveal that the timescales governing stress relaxation, respectively, through thermal fluctuations and elastic recovery are key for the aging dynamics. When thermal fluctuations are too weak, stress heterogeneities frozen-in upon solidification can still partially relax through elastically driven fluctuations. Such fluctuations are intermittent, because of strong correlations that persist over the timescale of experiments or simulations, leading to faster than exponential dynamics.

Phosphodiesterase-3 inhibitor cilostazol reverses endothelial dysfunction with ageing in rat mesenteric resistance arteries.

PubMed

Moreira, Hicla S; Lima-Leal, Geórgia A; Santos-Rocha, Juliana; Gomes-Pereira, Leonardo; Duarte, Gloria P; Xavier, Fabiano E

2018-03-05

Ageing impairs endothelial function, which is considered a hallmark of the development of cardiovascular diseases in elderly. Cilostazol, a phosphodiesterase-3 inhibitor, has antiplatelet, antithrombotic and protective effects on endothelial cells. Here, we hypothesized that cilostazol could improve endothelial function in mesenteric resistance arteries (MRA) from old rats. Using eight-week cilostazol-treated (100mg/kg/day) or untreated 72-week-old Wistar rats, we evaluate the relaxation to acetylcholine, sodium nitroprusside (SNP), forskolin and isoproterenol and the noradrenaline-induced contraction in MRA. Superoxide anion and nitric oxide (NO) was measured by dihydroethidium- and diaminofluorescein-2-emitted fluorescence, respectively. Normotensive old rats had impaired acetylcholine-induced NO- and EDHF-mediated relaxation and increased noradrenaline vasoconstriction than young rats. This age-associated endothelial dysfunction was restored by cilostazol treatment. Relaxation to SNP, forskolin or isoproterenol remained unmodified by cilostazol. Diaminofluorescein-2-emitted fluorescence was increased while dihydroethidium-emitted was decreased by cilostazol, indicating increased NO and reduced superoxide generation, respectively. Cilostazol improves endothelial function in old MRA without affecting blood pressure. This protective effect of cilostazol could be attributed to reduced oxidative stress, increased NO bioavailability and EDHF-type relaxation. Although these results are preliminary, we believe that should stimulate further interest in cilostazol as an alternative for the treatment of age-related vascular disorders. Copyright © 2018 Elsevier B.V. All rights reserved.

Postcoalescence evolution of growth stress in polycrystalline films.

PubMed

González-González, A; Polop, C; Vasco, E

2013-02-01

The growth stress generated once grains coalesce in Volmer-Weber-type thin films is investigated by time-multiscale simulations comprising complementary modules of (i) finite-element modeling to address the interactions between grains happening at atomic vibration time scales (~0.1 ps), (ii) dynamic scaling to account for the surface stress relaxation via morphology changes at surface diffusion time scales (~μs-ms), and (iii) the mesoscopic rate equation approach to simulate the bulk stress relaxation at deposition time scales (~sec-h). On the basis of addressing the main experimental evidence reported so far on the topic dealt with, the simulation results provide key findings concerning the interplay between anisotropic grain interactions at complementary space scales, deposition conditions (such as flux and mobility), and mechanisms of stress accommodation-relaxation, which underlies the origin, nature and spatial distribution, and the flux dependence of the postcoalescence growth stress.

The Relationship of Relaxation Technique, Test Anxiety, Academic Stress, and Nursing Students Intention to Stay in a Baccalaureate Degree Nursing Program

ERIC Educational Resources Information Center

Manansingh, Sherry

2017-01-01

The purpose of this study was to examine the effect of relaxation techniques among first semester Baccalaureate Degree nursing students' test anxiety and academic stress. Additionally, this study examined if there was a relationship among demographic characteristics of the respondents and test anxiety and academic stress. The pretest and posttest…

In situ stress relaxation mechanism of a superelastic NiTi shape memory alloy under hydrogen charging

NASA Astrophysics Data System (ADS)

Elkhal Letaief, Wissem; Hassine, Tarek; Gamaoun, Fehmi

2017-02-01

On account of its good biocompatibility, superelastic Ni-Ti arc wire alloys have been successfully used in orthodontic clinics. Nevertheless, delayed fracture in the oral cavity caused by hydrogen diffusion can be observed. The in situ stress relaxation susceptibility of a Ni-Ti shape memory alloy towards hydrogen embrittlement has been examined with respect to the current densities and imposed deformations. Orthodontic wires have been relaxed at different martensite volume fractions using current densities of 5, 10 and 20 A/m2 at 20 °C. The in situ relaxation stress shows that, for an imposed strain at the middle of the austenite-martensite transformation, the specimen fractures at the martensite-austenite reverse transformation. However, for an imposed strain at the beginning of the austenite-martensite plateau, the stress decreases in a similar way to the full austenite structure. Moreover, the stress plateau has been recorded at the reverse transformation for a short period. For the fully martensite structure, embrittlement occurs at a higher stress value. This behaviour is attributed to the interaction between the in situ austenite phase expansion and the diffusion of hydrogen in the different volume fractions of the martensite phase, produced at an imposed strain.

The stress relaxation of cement clinkers under high temperature

NASA Astrophysics Data System (ADS)

Wang, Xiufang; Bao, Yiwang; Liu, Xiaogen; Qiu, Yan

2015-12-01

The energy consumption of crushing is directly affected by the mechanical properties of cement materials. This research provides a theoretical proof for the mechanism of the stress relaxation of cement clinkers under high temperature. Compression stress relaxation under various high temperatures is discussed using a specially developed load cell, which can measure stress and displacement under high temperatures inside an autoclave. The cell shows that stress relaxation dramatically increases and that the remaining stress rapidly decreases with an increase in temperature. Mechanical experiments are conducted under various temperatures during the cooling process to study the changes in the grinding resistance of the cement clinker with temperature. The effects of high temperature on the load-displacement curve, compressive strength, and elastic modulus of cement clinkers are systematically studied. Results show that the hardening phenomenon of the clinker becomes apparent with a decrease in temperature and that post-peak behaviors manifest characteristics of the transformation from plasticity to brittleness. The elastic modulus and compressive strength of cement clinkers increase with a decrease in temperature. The elastic modulus increases greatly when the temperature is lower than 1000 °C. The compressive strength of clinkers increases by 73.4% when the temperature drops from 1100 to 800 °C.

Si1-yGey or Ge1-zSnz Source/Drain Stressors on Strained Si1-xGex-Channel P-Type Field-Effect Transistors: A Technology Computer-Aided Design Study

NASA Astrophysics Data System (ADS)

Eneman, Geert; De Keersgieter, An; Witters, Liesbeth; Mitard, Jerome; Vincent, Benjamin; Hikavyy, Andriy; Loo, Roger; Horiguchi, Naoto; Collaert, Nadine; Thean, Aaron

2013-04-01

The interaction between two stress techniques, strain-relaxed buffers (SRBs) and epitaxial source/drain stressors, is studied on short, Si1-xGex- and Ge-channel planar transistors. This work focuses on the longitudinal channel stress generated by these two techniques. Unlike for unstrained silicon-channel transistors, for strained channels on top of a strain-relaxed buffer a source/drain stressor without recess generates similar longitudinal channel stress than source/drain stressors with a deep recess. The least efficient stress transfer is obtained for source/drain stressors with a small recess that removes only the strained channel, not the substrate underneath. These trends are explained by a trade-off between elastic relaxation of the strained-channel during source/drain recess and the increased stress generation of thicker source/drain stressors. For Ge-channel pFETs, GeSn source/drains and Si1-xGex strain-relaxed buffers are efficient stressors for mobility enhancement. The former is more efficient for gate-last schemes than for gate-first, while the stress generated by the SRB is found to be independent of the gate-scheme.

GPER Mediates Functional Endothelial Aging in Renal Arteries.

PubMed

Meyer, Matthias R; Rosemann, Thomas; Barton, Matthias; Prossnitz, Eric R

2017-01-01

Aging is associated with impaired renal artery function, which is partly characterized by arterial stiffening and a reduced vasodilatory capacity due to excessive generation of reactive oxygen species by NADPH oxidases (Nox). The abundance and activity of Nox depends on basal activity of the heptahelical transmembrane receptor GPER; however, whether GPER contributes to age-dependent functional changes in renal arteries is unknown. This study investigated the effect of aging and Nox activity on renal artery tone in wild-type and GPER-deficient (Gper-/-) mice (4 and 24 months old). In wild-type mice, aging markedly impaired endothelium-dependent, nitric oxide (NO)-mediated relaxations to acetylcholine, which were largely preserved in renal arteries of aged Gper-/- mice. The Nox inhibitor gp91ds-tat abolished this difference by greatly enhancing relaxations in wild-type mice, while having no effect in Gper-/- mice. Contractions to angiotensin II and phenylephrine in wild-type mice were partly sensitive to gp91ds-tat but unaffected by aging. Again, deletion of GPER abolished effects of Nox inhibition on contractile responses. In conclusion, basal activity of GPER is required for the age-dependent impairment of endothelium-dependent, NO-mediated relaxation in the renal artery. Restoration of relaxation by a Nox inhibitor in aged wild-type but not Gper-/- mice strongly supports a role for Nox-derived reactive oxygen species as the underlying cause. Pharmacological blockers of GPER signaling may thus be suitable to inhibit functional endothelial aging of renal arteries by reducing Nox-derived oxidative stress and, possibly, the associated age-dependent deterioration of kidney function. © 2017 S. Karger AG, Basel.

Creep and stress relaxation induced by interface diffusion in metal matrix composites

NASA Astrophysics Data System (ADS)

Li, Yinfeng; Li, Zhonghua

2013-03-01

An analytical solution is developed to predict the creep rate induced by interface diffusion in unidirectional fiber-reinforced and particle reinforced composites. The driving force for the interface diffusion is the normal stress acting on the interface, which is obtained from rigorous Eshelby inclusion theory. The closed-form solution is an explicit function of the applied stress, volume fraction and radius of the fiber, as well as the modulus ratio between the fiber and the matrix. It is interesting that the solution is formally similar to that of Coble creep in polycrystalline materials. For the application of the present solution in the realistic composites, the scale effect is taken into account by finite element analysis based on a unit cell. Based on the solution, a closed-form solution is also given as a description of stress relaxation induced by interfacial diffusion under constant strain. In addition, the analytical solution for the interface stress presented in this study gives some insight into the relationship between the interface diffusion and interface slip. This work was supported by the financial support from the Nature Science Foundation of China (No. 10932007), the National Basic Research Program of China (No. 2010CB631003/5), and the Doctoral Program of Higher Education of China (No. 20100073110006).

Arm retraction dynamics of entangled star polymers: A forward flux sampling method study

NASA Astrophysics Data System (ADS)

Zhu, Jian; Likhtman, Alexei E.; Wang, Zuowei

2017-07-01

The study of dynamics and rheology of well-entangled branched polymers remains a challenge for computer simulations due to the exponentially growing terminal relaxation times of these polymers with increasing molecular weights. We present an efficient simulation algorithm for studying the arm retraction dynamics of entangled star polymers by combining the coarse-grained slip-spring (SS) model with the forward flux sampling (FFS) method. This algorithm is first applied to simulate symmetric star polymers in the absence of constraint release (CR). The reaction coordinate for the FFS method is determined by finding good agreement of the simulation results on the terminal relaxation times of mildly entangled stars with those obtained from direct shooting SS model simulations with the relative difference between them less than 5%. The FFS simulations are then carried out for strongly entangled stars with arm lengths up to 16 entanglements that are far beyond the accessibility of brute force simulations in the non-CR condition. Apart from the terminal relaxation times, the same method can also be applied to generate the relaxation spectra of all entanglements along the arms which are desired for the development of quantitative theories of entangled branched polymers. Furthermore, we propose a numerical route to construct the experimentally measurable relaxation correlation functions by effectively linking the data stored at each interface during the FFS runs. The obtained star arm end-to-end vector relaxation functions Φ (t ) and the stress relaxation function G(t) are found to be in reasonably good agreement with standard SS simulation results in the terminal regime. Finally, we demonstrate that this simulation method can be conveniently extended to study the arm-retraction problem in entangled star polymer melts with CR by modifying the definition of the reaction coordinate, while the computational efficiency will depend on the particular slip-spring or slip-link model employed.

Modeling the glass transition of amorphous networks for shape-memory behavior

NASA Astrophysics Data System (ADS)

Xiao, Rui; Choi, Jinwoo; Lakhera, Nishant; Yakacki, Christopher M.; Frick, Carl P.; Nguyen, Thao D.

2013-07-01

In this paper, a thermomechanical constitutive model was developed for the time-dependent behaviors of the glass transition of amorphous networks. The model used multiple discrete relaxation processes to describe the distribution of relaxation times for stress relaxation, structural relaxation, and stress-activated viscous flow. A non-equilibrium thermodynamic framework based on the fictive temperature was introduced to demonstrate the thermodynamic consistency of the constitutive theory. Experimental and theoretical methods were developed to determine the parameters describing the distribution of stress and structural relaxation times and the dependence of the relaxation times on temperature, structure, and driving stress. The model was applied to study the effects of deformation temperatures and physical aging on the shape-memory behavior of amorphous networks. The model was able to reproduce important features of the partially constrained recovery response observed in experiments. Specifically, the model demonstrated a strain-recovery overshoot for cases programmed below Tg and subjected to a constant mechanical load. This phenomenon was not observed for materials programmed above Tg. Physical aging, in which the material was annealed for an extended period of time below Tg, shifted the activation of strain recovery to higher temperatures and increased significantly the initial recovery rate. For fixed-strain recovery, the model showed a larger overshoot in the stress response for cases programmed below Tg, which was consistent with previous experimental observations. Altogether, this work demonstrates how an understanding of the time-dependent behaviors of the glass transition can be used to tailor the temperature and deformation history of the shape-memory programming process to achieve more complex shape recovery pathways, faster recovery responses, and larger activation stresses.

Finite element calculation of residual stress in dental restorative material

NASA Astrophysics Data System (ADS)

Grassia, Luigi; D'Amore, Alberto

2012-07-01

A finite element methodology for residual stresses calculation in dental restorative materials is proposed. The material under concern is a multifunctional methacrylate-based composite for dental restorations, activated by visible light. Reaction kinetics, curing shrinkage, and viscoelastic relaxation functions were required as input data on a structural finite element solver. Post cure effects were considered in order to quantify the residual stresses coming out from natural contraction with respect to those debited to the chemical shrinkage. The analysis showed for a given test case that residual stresses frozen in the dental restoration at uniform temperature of 37°C are of the same order of magnitude of the strength of the dental composite material per se.

A New Hybrid Viscoelastic Soft Tissue Model based on Meshless Method for Haptic Surgical Simulation

PubMed Central

Bao, Yidong; Wu, Dongmei; Yan, Zhiyuan; Du, Zhijiang

2013-01-01

This paper proposes a hybrid soft tissue model that consists of a multilayer structure and many spheres for surgical simulation system based on meshless. To improve accuracy of the model, tension is added to the three-parameter viscoelastic structure that connects the two spheres. By using haptic device, the three-parameter viscoelastic model (TPM) produces accurate deformationand also has better stress-strain, stress relaxation and creep properties. Stress relaxation and creep formulas have been obtained by mathematical formula derivation. Comparing with the experimental results of the real pig liver which were reported by Evren et al. and Amy et al., the curve lines of stress-strain, stress relaxation and creep of TPM are close to the experimental data of the real liver. Simulated results show that TPM has better real-time, stability and accuracy. PMID:24339837

Interdependency between mechanical parameters and afferent nerve discharge in remodeled diabetic Goto-Kakizaki rat intestine.

PubMed

Zhao, Jingbo; Yang, Jian; Liao, Donghua; Gregersen, Hans

2017-01-01

Gastrointestinal disorders are very common in diabetic patients, but the pathogenesis is still not well understood. Peripheral afferent nerves may be involved due to the complex regulation of gastrointestinal function by the enteric nervous system. We aimed to characterize the stimulus-response function of afferent fibers innervating the jejunum in the Goto-Kakizaki (GK) type 2 diabetic rat model. A key question is whether changes in afferent firing arise from remodeled tissue or from adaptive afferent processes. Seven 32-week-old male GK rats and seven age-matched normal Wistar rats were studied. Firing from mesenteric afferent nerves was recorded in excised jejunal segments of seven GK rats and seven normal Wistar rats during ramp test, stress relaxation test, and creep test. The circumferential stress-strain, spike rate increase ratio (SRIR), and single unit firing rates were calculated for evaluation of interdependency of the mechanical stimulations and the afferent nerve discharge. Elevated sensitivity to mechanical stimuli was found for diabetic nerve bundles and single unit activity ( P <0.05). The stress relaxed less in the diabetic intestinal segment ( P <0.05). Linear association between SRIR and the thickness of circumferential muscle layer was found at high stress levels as well as for SRIR and the glucose level. Altered viscoelastic properties and elevated mechanosensitivity were found in the GK rat intestine. The altered nerve signaling is related to muscle layer remodeling and glucose levels and may contribute to gastrointestinal symptoms experienced by diabetic patients.

Mechanical confinement regulates cartilage matrix formation by chondrocytes

NASA Astrophysics Data System (ADS)

Lee, Hong-Pyo; Gu, Luo; Mooney, David J.; Levenston, Marc E.; Chaudhuri, Ovijit

2017-12-01

Cartilage tissue equivalents formed from hydrogels containing chondrocytes could provide a solution for replacing damaged cartilage. Previous approaches have often utilized elastic hydrogels. However, elastic stresses may restrict cartilage matrix formation and alter the chondrocyte phenotype. Here we investigated the use of viscoelastic hydrogels, in which stresses are relaxed over time and which exhibit creep, for three-dimensional (3D) culture of chondrocytes. We found that faster relaxation promoted a striking increase in the volume of interconnected cartilage matrix formed by chondrocytes. In slower relaxing gels, restriction of cell volume expansion by elastic stresses led to increased secretion of IL-1β, which in turn drove strong up-regulation of genes associated with cartilage degradation and cell death. As no cell-adhesion ligands are presented by the hydrogels, these results reveal cell sensing of cell volume confinement as an adhesion-independent mechanism of mechanotransduction in 3D culture, and highlight stress relaxation as a key design parameter for cartilage tissue engineering.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kashiwa, Bryan Andrew; Hull, Lawrence Mark

Highlights of recent phenomenological studies of metal failure are given. Failure leading to spallation and fragmentation are typically of interest. The current ‘best model’ includes the following; a full history stress in tension; nucleation initiating dynamic relaxation; toward a tensile yield function; failure dependent on strain, strain rate, and temperature; a mean-preserving ‘macrodefect’ is introduced when failure occurs in tension; and multifield theoretical refinements

Osmotic stress and cryoinjury of koala sperm: an integrative study of the plasma membrane, chromatin stability and mitochondrial function.

PubMed

Johnston, S D; Satake, N; Zee, Y; López-Fernández, C; Holt, W V; Gosálvez, J

2012-06-01

This study investigated whether cryopreservation-induced injury to koala spermatozoa could be explained using an experimental model that mimics the structural and physiological effects of osmotic flux. DNA labelling after in situ nick translation of thawed cryopreserved spermatozoa revealed a positive correlation (r=0.573; P<0.001; n=50) between the area of relaxed chromatin in the nucleus and the degree of nucleotide labelling. While the chromatin of some spermatozoa increased more than eight times its normal size, not all sperm nuclei with relaxed chromatin showed evidence of nucleotide incorporation. Preferential staining associated with sperm DNA fragmentation (SDF) was typically located in the peri-acrosomal and peripheral regions of the sperm head and at the base of the spermatozoa where it appear to be 'hot spots' of DNA damage following cryopreservation. Results of the comparative effects of anisotonic media and cryopreservation on the integrity of koala spermatozoa revealed that injury induced by exposure to osmotic flux, essentially imitated the results found following cryopreservation. Plasma membrane integrity, chromatin relaxation and SDF appeared particularly susceptible to extreme hypotonic environments. Mitochondrial membrane potential (MMP), while susceptible to extreme hypo- and hypertonic environments, showed an ability to rebound from hypertonic stress when returned to isotonic conditions. Koala spermatozoa exposed to 64 mOsm/kg media showed an equivalent, or more severe, degree of structural and physiological injury to that of frozen-thawed spermatozoa, supporting the hypothesis that cryoinjury is principally associated with a hypo-osmotic effect. A direct comparison of SDF of thawed cryopreserved spermatozoa and those exposed to a 64 mOsm/kg excursion showed a significant correlation (r=0.878; P<0.05; n=5); however, no correlation was found when the percentage of sperm with relaxed chromatin was compared. While a cryo-induced osmotic injury model appears to explain post-thaw changes in koala SDF, the mechanisms resulting in relaxed chromatin require further study. A lack of correlation between the percentage of sperm with relaxed chromatin and SDF suggests that the timing of these pathologies are asynchronous. We propose an integrative model of cryo-induced osmotic injury that involves a combination of structural damage (rupture of membrane) and oxidative stress that first leads to the reduction of MMP and the relaxation of chromatin, which is then ultimately followed by an increase in DNA fragmentation.

The mass function and dynamical mass of young star clusters: why their initial crossing-time matters crucially

NASA Astrophysics Data System (ADS)

Parmentier, Geneviève; Baumgardt, Holger

2012-12-01

We highlight the impact of cluster-mass-dependent evolutionary rates upon the evolution of the cluster mass function during violent relaxation, that is, while clusters dynamically respond to the expulsion of their residual star-forming gas. Mass-dependent evolutionary rates arise when the mean volume density of cluster-forming regions is mass-dependent. In that case, even if the initial conditions are such that the cluster mass function at the end of violent relaxation has the same shape as the embedded-cluster mass function (i.e. infant weight-loss is mass-independent), the shape of the cluster mass function does change transiently during violent relaxation. In contrast, for cluster-forming regions of constant mean volume density, the cluster mass function shape is preserved all through violent relaxation since all clusters then evolve at the same mass-independent rate. On the scale of individual clusters, we model the evolution of the ratio of the dynamical mass to luminous mass of a cluster after gas expulsion. Specifically, we map the radial dependence of the time-scale for a star cluster to return to equilibrium. We stress that fields of view a few pc in size only, typical of compact clusters with rapid evolutionary rates, are likely to reveal cluster regions which have returned to equilibrium even if the cluster experienced a major gas expulsion episode a few Myr earlier. We provide models with the aperture and time expressed in units of the initial half-mass radius and initial crossing-time, respectively, so that our results can be applied to clusters with initial densities, sizes, and apertures different from ours.

Mindfulness meditation training alters stress-related amygdala resting state functional connectivity: a randomized controlled trial.

PubMed

Taren, Adrienne A; Gianaros, Peter J; Greco, Carol M; Lindsay, Emily K; Fairgrieve, April; Brown, Kirk Warren; Rosen, Rhonda K; Ferris, Jennifer L; Julson, Erica; Marsland, Anna L; Bursley, James K; Ramsburg, Jared; Creswell, J David

2015-12-01

Recent studies indicate that mindfulness meditation training interventions reduce stress and improve stress-related health outcomes, but the neural pathways for these effects are unknown. The present research evaluates whether mindfulness meditation training alters resting state functional connectivity (rsFC) of the amygdala, a region known to coordinate stress processing and physiological stress responses. We show in an initial discovery study that higher perceived stress over the past month is associated with greater bilateral amygdala-subgenual anterior cingulate cortex (sgACC) rsFC in a sample of community adults (n = 130). A follow-up, single-blind randomized controlled trial shows that a 3-day intensive mindfulness meditation training intervention (relative to a well-matched 3-day relaxation training intervention without a mindfulness component) reduced right amygdala-sgACC rsFC in a sample of stressed unemployed community adults (n = 35). Although stress may increase amygdala-sgACC rsFC, brief training in mindfulness meditation could reverse these effects. This work provides an initial indication that mindfulness meditation training promotes functional neuroplastic changes, suggesting an amygdala-sgACC pathway for stress reduction effects. © The Author (2015). Published by Oxford University Press. For Permissions, please email: journals.permissions@oup.com.

Strain-enhanced stress relaxation impacts nonlinear elasticity in collagen gels

PubMed Central

Nam, Sungmin; Hu, Kenneth H.; Chaudhuri, Ovijit

2016-01-01

The extracellular matrix (ECM) is a complex assembly of structural proteins that provides physical support and biochemical signaling to cells in tissues. The mechanical properties of the ECM have been found to play a key role in regulating cell behaviors such as differentiation and malignancy. Gels formed from ECM protein biopolymers such as collagen or fibrin are commonly used for 3D cell culture models of tissue. One of the most striking features of these gels is that they exhibit nonlinear elasticity, undergoing strain stiffening. However, these gels are also viscoelastic and exhibit stress relaxation, with the resistance of the gel to a deformation relaxing over time. Recent studies have suggested that cells sense and respond to both nonlinear elasticity and viscoelasticity of ECM, yet little is known about the connection between nonlinear elasticity and viscoelasticity. Here, we report that, as strain is increased, not only do biopolymer gels stiffen but they also exhibit faster stress relaxation, reducing the timescale over which elastic energy is dissipated. This effect is not universal to all biological gels and is mediated through weak cross-links. Mechanistically, computational modeling and atomic force microscopy (AFM) indicate that strain-enhanced stress relaxation of collagen gels arises from force-dependent unbinding of weak bonds between collagen fibers. The broader effect of strain-enhanced stress relaxation is to rapidly diminish strain stiffening over time. These results reveal the interplay between nonlinear elasticity and viscoelasticity in collagen gels, and highlight the complexity of the ECM mechanics that are likely sensed through cellular mechanotransduction. PMID:27140623

Behavior of stress generated in semiconductor chips with high-temperature joints: Influence of mechanical properties of joint materials

NASA Astrophysics Data System (ADS)

Ito, H.; Kuwahara, M.; Ohta, R.; Usui, M.

2018-04-01

High-temperature joint materials are indispensable to realizing next-generation power modules with high-output performance. However, crack initiation resulting from stress concentration in semiconductor chips joined with high-temperature joint materials remains a critical problem in high-temperature operation. Therefore, clarifying the quantitative influence of joint materials on the stress generated in chips is essential. This study investigates the stress behavior of chips joined by Ni-Sn solid-liquid interdiffusion (SLID), which results in a high-temperature joint material likely to generate cracks after joining or when under thermal cycling. The results are compared with those fabricated using three types of solders, Pb-10%Sn, Sn-0.7%Cu, and Sn-10%Sb (mass %), which are conventional joint materials with different melting points and mechanical properties. Using Ni-Sn SLID results in the generation of high compressive stress (500 MPa) without stress relaxation after the joining process in contrast to the case of solders in which the compressive stresses are low (<300 MPa) and decrease to still lower levels (<250 MPa). In addition, no stress relaxation occurs during thermal cycling when using Ni-Sn SLID, whereas stress relaxation is clearly observed during heating to 200 °C using solders. Different stress behaviors between Ni-Sn SLID and other joint materials are illustrated by their mechanical strength and resistance against plastic and creep deformation. These results suggest that stress relaxation in a chip is key in suppressing crack initiation in highly reliable modules during high-temperature operation.

Blue lighting accelerates post-stress relaxation: Results of a preliminary study.

PubMed

Minguillon, Jesus; Lopez-Gordo, Miguel Angel; Renedo-Criado, Diego A; Sanchez-Carrion, Maria Jose; Pelayo, Francisco

2017-01-01

Several authors have studied the influence of light on both human physiology and emotions. Blue light has been proved to reduce sleepiness by suppression of melatonin secretion and it is also present in many emotion-related studies. Most of these have a common lack of objective methodology since results and conclusions are based on subjective perception of emotions. The aim of this work was the objective assessment of the effect of blue lighting in post-stress relaxation, in comparison with white lighting, by means of bio-signals and standardized procedures. We conducted a study in which twelve healthy volunteers were stressed and then performed a relaxation session within a chromotherapy room with blue (test group) or white (control group) lighting. We conclude that the blue lighting accelerates the relaxation process after stress in comparison with conventional white lighting. The relaxation time decreased by approximately three-fold (1.1 vs. 3.5 minutes). We also observed a convergence time (3.5-5 minutes) after which the advantage of blue lighting disappeared. This supports the relationship between color of light and stress, and the observations reported in previous works. These findings could be useful in clinical and educational environments, as well as in daily-life context and emerging technologies such as neuromarketing. However, our study must be extended to draw reliable conclusions and solid scientific evidence.

Blue lighting accelerates post-stress relaxation: Results of a preliminary study

PubMed Central

Lopez-Gordo, Miguel Angel; Renedo-Criado, Diego A.; Sanchez-Carrion, Maria Jose; Pelayo, Francisco

2017-01-01

Several authors have studied the influence of light on both human physiology and emotions. Blue light has been proved to reduce sleepiness by suppression of melatonin secretion and it is also present in many emotion-related studies. Most of these have a common lack of objective methodology since results and conclusions are based on subjective perception of emotions. The aim of this work was the objective assessment of the effect of blue lighting in post-stress relaxation, in comparison with white lighting, by means of bio-signals and standardized procedures. We conducted a study in which twelve healthy volunteers were stressed and then performed a relaxation session within a chromotherapy room with blue (test group) or white (control group) lighting. We conclude that the blue lighting accelerates the relaxation process after stress in comparison with conventional white lighting. The relaxation time decreased by approximately three-fold (1.1 vs. 3.5 minutes). We also observed a convergence time (3.5–5 minutes) after which the advantage of blue lighting disappeared. This supports the relationship between color of light and stress, and the observations reported in previous works. These findings could be useful in clinical and educational environments, as well as in daily-life context and emerging technologies such as neuromarketing. However, our study must be extended to draw reliable conclusions and solid scientific evidence. PMID:29049332

Short-term impact of a stress management and health promotion program on perceived stress, parental stress, health locus of control, and cortisol levels in parents of children and adolescents with diabetes type 1: a pilot randomized controlled trial.

PubMed

Tsiouli, Eleni; Pavlopoulos, Vassilis; Alexopoulos, Evangelos C; Chrousos, George; Darviri, Christina

2014-01-01

Parents of children and adolescents with diabetes type 1 (DT1) usually experience high stress levels, as they have to cope with multiple demands in their everyday life. Different complex interventions have been implemented, which sometimes have led to opposite results. The purpose of this study was to assess stress levels in parents of children and adolescents with DT1 and to evaluate the effectiveness of a stress management program (progressive muscle relaxation combined with diaphragmatic breathing) in reducing perceived and parenting stress, increasing internal locus of control, promoting healthy lifestyle, and normalizing cortisol levels. Randomized controlled trial. A total of 44 parents were randomly assigned to the intervention group (performing relaxation for eight weeks, n = 19) and control group (n = 25). Pre-post measurements included cortisol levels, lifestyle characteristics, perceived stress, perception of health, and parenting stress. A statistically significant decrease in perceived stress (from 27.21 to 19.00, P = .001), as well as in parenting stress (from 85.79 to 73.68, P = .003), was observed in the intervention group. A statistically significant difference was found in perceived stress between the two groups after the intervention (Dmean = 6.64, P = .010). No significant difference was revealed between or within the groups in cortisol levels. Significant improvement was reported by the subjects of the intervention group in various lifestyle parameters. Relaxation techniques seem to have a positive impact on stress and on various lifestyle factors in parents of children and adolescents with DT1. Future research on long-term benefits of an intervention program comprising of various relaxation schemes is warranted. Copyright © 2014 Elsevier Inc. All rights reserved.

Spherical Indentation Testing of Poroelastic Relaxations in Thin Hydrogel Layers

DTIC Science & Technology

2012-01-01

Rd p =h : (4) The function fa ffiffiffiffiffiffi Rd p =h accounts for deviations from Hertz mechanics where the substrate stiffness influences...Similarly, the function fp ffiffiffiffiffiffi Rd p =h accounts for the deviation from Hertz load when the stress field is affected by substrate...Ghassemi, Y. S. Kim, B. R. Einsla and J. E. McGrath, Chem. Rev., 2004, 104, 4587–4612. 5 J. L. Drury and D. J. Mooney, Biomaterials, 2003, 24, 4337

The role of surface roughness on dislocation bending and stress evolution in low mobility AlGaN films during growth

NASA Astrophysics Data System (ADS)

Bardhan, Abheek; Mohan, Nagaboopathy; Chandrasekar, Hareesh; Ghosh, Priyadarshini; Sridhara Rao, D. V.; Raghavan, Srinivasan

2018-04-01

The bending and interaction of threading dislocations are essential to reduce their density for applications involving III-nitrides. Bending of dislocation lines also relaxes the compressive growth stress that is essential to prevent cracking on cooling down due to tensile thermal expansion mismatch stress while growing on Si substrates. It is shown in this work that surface roughness plays a key role in dislocation bending. Dislocations only bend and relax compressive stresses when the lines intersect a smooth surface. These films then crack. In rough films, dislocation lines which terminate at the bottom of the valleys remain straight. Compressive stresses are not relaxed and the films are relatively crack-free. The reasons for this difference are discussed in this work along with the implications on simultaneously meeting the requirements of films being smooth, crack free and having low defect density for device applications.

An Evaluation of Progressive Muscle Relaxation on Stress Related Symptoms in a Geriatric Population.

ERIC Educational Resources Information Center

De Berry, Stephen

1981-01-01

Studied the effect of progressive muscle relaxation training on a group of anxious older widows (N=10). Found training decreased the severity of stress-related disorders when compared with controls. Results indicated, with state anxiety, improvement continued during home practice after treatment. (Author/JAC)

Thermal fluctuations and elastic relaxation in the compressed exponential dynamics of colloidal gels

NASA Astrophysics Data System (ADS)

Bouzid, Mehdi; Colombo, Jader; Del Gado, Emanuela

Colloidal gels belong to the class of amorphous systems, they are disordered elastic solids that can form at very low volume fraction, via aggregation into a rich variety of networks. They exhibit a slow relaxation process in the aging regime similar to the glassy dynamics. A wide range of experiments on colloidal gels show unusual compressed exponential of the relaxation dynamical properties. We use molecular dynamics simulation to investigate how the dynamic change with the age of the system. Upon breaking and reorganization of the network structure, the system may display stretched or compressed exponential relaxation. We show that the transition between these two regimes is associated to the interplay between thermally activated rearrangements and the elastic relaxation of internal stresses. In particular, ballistic-like displacements emerge from the non local relaxation of internal stresses mediated by a series of ''micro-collapses''. When thermal fluctuations dominate, the gel restructuring involves instead more homogeneous displacements across the heterogeneous gel network, leading to a stretched exponential type of relaxation.

Static viscoelasticity of biomass polyethylene composites

NASA Astrophysics Data System (ADS)

Yang, Keyan; Cai, Hongzhen; Yi, Weiming; Zhang, Qingfa; Zhao, Kunpeng

The biomass polyethylene composites filled with poplar wood flour, rice husk, cotton stalk or corn stalk were prepared by extrusion molding. The static viscoelasticity of composites was investigated by the dynamic thermal mechanical analyzer (DMA). Through the stress-strain scanning, it is found that the linear viscoelasticity interval of composites gradually decreases as the temperature rises, and the critical stress and strain values are 0.8 MPa and 0.03% respectively. The experiment shows that as the temperature rises, the creep compliance of biomass polyethylene composites is increased; under the constant temperature, the creep compliance decreases with the increase of content of biomass and calcium carbonate. The biomass and calcium carbonate used to prepare composites as filler can improve damping vibration attenuation and reduce stress deformation of composites. The stress relaxation modulus of composites is reduced and the relaxation rate increases at the higher temperature. The biomass and calcium carbonate used to prepare composites as filler not only can reduce costs, but also can increase stress relaxation modulus and improve the size thermostability of composites. The corn stalk is a good kind of biomass raw material for composites since it can improve the creep resistance property and the stress relaxation resistance property of composites more effectively than other three kinds of biomass (poplar wood flour, rice husk and cotton stalk).

A pilot study of yogic meditation for family dementia caregivers with depressive symptoms: effects on mental health, cognition, and telomerase activity.

PubMed

Lavretsky, H; Epel, E S; Siddarth, P; Nazarian, N; Cyr, N St; Khalsa, D S; Lin, J; Blackburn, E; Irwin, M R

2013-01-01

This study examined the effects of brief daily yogic meditation on mental health, cognitive functioning, and immune cell telomerase activity in family dementia caregivers with mild depressive symptoms. Thirty-nine family dementia caregivers (mean age 60.3 years old (SD = 10.2)) were randomized to practicing Kirtan Kriya or listening to relaxation music for 12 min per day for 8 weeks. The severity of depressive symptoms, mental and cognitive functioning were assessed at baseline and follow-up. Telomerase activity in peripheral blood mononuclear cells (PMBC) was examined in peripheral PBMC pre-intervention and post-intervention. The meditation group showed significantly lower levels of depressive symptoms and greater improvement in mental health and cognitive functioning compared with the relaxation group. In the meditation group, 65.2% showed 50% improvement on the Hamilton Depression Rating scale and 52% of the participants showed 50% improvement on the Mental Health Composite Summary score of the Short Form-36 scale compared with 31.2% and 19%, respectively, in the relaxation group (p < 0.05). The meditation group showed 43% improvement in telomerase activity compared with 3.7% in the relaxation group (p = 0.05). This pilot study found that brief daily meditation practices by family dementia caregivers can lead to improved mental and cognitive functioning and lower levels of depressive symptoms. This improvement is accompanied by an increase in telomerase activity suggesting improvement in stress-induced cellular aging. These results need to be confirmed in a larger sample. Copyright © 2012 John Wiley & Sons, Ltd.

Strong size-dependent stress relaxation in electrospun polymer nanofibers

NASA Astrophysics Data System (ADS)

Wingert, Matthew C.; Jiang, Zhang; Chen, Renkun; Cai, Shengqiang

2017-01-01

Electrospun polymer nanofibers have garnered significant interest due to their strong size-dependent material properties, such as tensile moduli, strength, toughness, and glass transition temperatures. These properties are closely correlated with polymer chain dynamics. In most applications, polymers usually exhibit viscoelastic behaviors such as stress relaxation and creep, which are also determined by the motion of polymer chains. However, the size-dependent viscoelasticity has not been studied previously in polymer nanofibers. Here, we report the first experimental evidence of significant size-dependent stress relaxation in electrospun Nylon-11 nanofibers as well as size-dependent viscosity of the confined amorphous regions. In conjunction with the dramatically increasing stiffness of nano-scaled fibers, this strong relaxation enables size-tunable properties which break the traditional damping-stiffness tradeoff, qualifying electrospun nanofibers as a promising set of size-tunable materials with an unusual and highly desirable combination of simultaneously high stiffness and large mechanical energy dissipation.

Strong size-dependent stress relaxation in electrospun polymer nanofibers

DOE PAGES

Wingert, Matthew C.; Jiang, Zhang; Chen, Renkun; ...

2017-01-04

Here, electrospun polymer nanofibers have garnered significant interest due to their strong size-dependent material properties, such as tensile moduli, strength, toughness, and glass transition temperatures. These properties are closely correlated with polymer chain dynamics. In most applications, polymers usually exhibit viscoelastic behaviors such as stress relaxation and creep, which are also determined by the motion of polymer chains. However, the size-dependent viscoelasticity has not been studied previously in polymer nanofibers. Here, we report the first experimental evidence of significant size-dependent stress relaxation in electrospun Nylon-11 nanofibers as well as size-dependent viscosity of the confined amorphous regions. In conjunction with themore » dramatically increasing stiffness of nano-scaled fibers, this strong relaxation enables size-tunable properties which break the traditional damping-stiffness tradeoff, qualifying electrospun nanofibers as a promising set of size-tunable materials with an unusual and highly desirable combination of simultaneously high stiffness and large mechanical energy dissipation.« less

Relaxation therapies for asthma: a systematic review

PubMed Central

Huntley, A; White, A; Ernst, E

2002-01-01

Background: Emotional stress can either precipitate or exacerbate both acute and chronic asthma. There is a large body of literature available on the use of relaxation techniques for the treatment of asthma symptoms. The aim of this systematic review was to determine if there is any evidence for or against the clinical efficacy of such interventions. Methods: Four independent literature searches were performed on Medline, Cochrane Library, CISCOM, and Embase. Only randomised clinical trials (RCTs) were included. There were no restrictions on the language of publication. The data from trials that statistically compared the treatment group with that of the control were extracted in a standardised predefined manner and assessed critically by two independent reviewers. Results: Fifteen trials were identified, of which nine compared the treatment group with the control group appropriately. Five RCTs tested progressive muscle relaxation or mental and muscular relaxation, two of which showed significant effects of therapy. One RCT investigating hypnotherapy, one of autogenic training, and two of biofeedback techniques revealed no therapeutic effects. Overall, the methodological quality of the studies was poor. Conclusions: There is a lack of evidence for the efficacy of relaxation therapies in the management of asthma. This deficiency is due to the poor methodology of the studies as well as the inherent problems of conducting such trials. There is some evidence that muscular relaxation improves lung function of patients with asthma but no evidence for any other relaxation technique. PMID:11828041

Relaxation therapies for asthma: a systematic review.

PubMed

Huntley, A; White, A R; Ernst, E

2002-02-01

Emotional stress can either precipitate or exacerbate both acute and chronic asthma. There is a large body of literature available on the use of relaxation techniques for the treatment of asthma symptoms. The aim of this systematic review was to determine if there is any evidence for or against the clinical efficacy of such interventions. Four independent literature searches were performed on Medline, Cochrane Library, CISCOM, and Embase. Only randomised clinical trials (RCTs) were included. There were no restrictions on the language of publication. The data from trials that statistically compared the treatment group with that of the control were extracted in a standardised predefined manner and assessed critically by two independent reviewers. Fifteen trials were identified, of which nine compared the treatment group with the control group appropriately. Five RCTs tested progressive muscle relaxation or mental and muscular relaxation, two of which showed significant effects of therapy. One RCT investigating hypnotherapy, one of autogenic training, and two of biofeedback techniques revealed no therapeutic effects. Overall, the methodological quality of the studies was poor. There is a lack of evidence for the efficacy of relaxation therapies in the management of asthma. This deficiency is due to the poor methodology of the studies as well as the inherent problems of conducting such trials. There is some evidence that muscular relaxation improves lung function of patients with asthma but no evidence for any other relaxation technique.

Stress evolution following the 1999 Chi-Chi, Taiwan, earthquake: Consequences for afterslip, relaxation, aftershocks and departures from Omori decay

USGS Publications Warehouse

Chan, C.-H.; Stein, R.S.

2009-01-01

We explore how Coulomb stress transfer and viscoelastic relaxation control afterslip and aftershocks in a continental thrust fault system. The 1999 September 21 Mw = 7.6 Chi-Chi shock is typical of continental ramp-d??collement systems throughout the world, and so inferences drawn from this uniquely well-recorded event may be widely applicable. First, we find that the spatial and depth distribution of aftershocks and their focal mechanisms are consistent with the calculated Coulomb stress changes imparted by the coseismic rupture. Some 61 per cent of the M ??? 2 aftershocks and 83 per cent of the M ??? 4 aftershocks lie in regions for which the Coulomb stress increased by ???0.1 bars, and there is a 11-12 per cent gain in the percentage of aftershocks nodal planes on which the shear stress increased over the pre-Chi Chi control period. Second, we find that afterslip occurred where the calculated coseismic stress increased on the fault ramp and d??collement, subject to the condition that friction is high on the ramp and low on the d??collement. Third, viscoelastic relaxation is evident from the fit of the post-seismic GPS data on the footwall. Fourth, we find that the rate of seismicity began to increase during the post-seismic period in an annulus extending east of the main rupture. The spatial extent of the seismicity annulus resembles the calculated ???0.05-bar Coulomb stress increase caused by viscoelastic relaxation and afterslip, and we find a 9-12 per cent gain in the percentage of focal mechanisms with >0.01-bar shear stress increases imparted by the post-seismic afterslip and relaxation in comparison to the control period. Thus, we argue that post-seismic stress changes can for the first time be shown to alter the production of aftershocks, as judged by their rate, spatial distribution, and focal mechanisms. ?? Journal compilation ?? 2009 RAS.

Application of a Three-Dimensional Poroelastic BEM to Modeling the Biphasic Mechanics of Cell-Matrix Interactions in Articular Cartilage (REVISION)

PubMed Central

Haider, Mansoor A.; Guilak, Farshid

2009-01-01

Articular cartilage exhibits viscoelasticity in response to mechanical loading that is well described using biphasic or poroelastic continuum models. To date, boundary element methods (BEMs) have not been employed in modeling biphasic tissue mechanics. A three dimensional direct poroelastic BEM, formulated in the Laplace transform domain, is applied to modeling stress relaxation in cartilage. Macroscopic stress relaxation of a poroelastic cylinder in uni-axial confined compression is simulated and validated against a theoretical solution. Microscopic cell deformation due to poroelastic stress relaxation is also modeled. An extended Laplace inversion method is employed to accurately represent mechanical responses in the time domain. PMID:19851478

Application of a Three-Dimensional Poroelastic BEM to Modeling the Biphasic Mechanics of Cell-Matrix Interactions in Articular Cartilage (REVISION).

PubMed

Haider, Mansoor A; Guilak, Farshid

2007-06-15

Articular cartilage exhibits viscoelasticity in response to mechanical loading that is well described using biphasic or poroelastic continuum models. To date, boundary element methods (BEMs) have not been employed in modeling biphasic tissue mechanics. A three dimensional direct poroelastic BEM, formulated in the Laplace transform domain, is applied to modeling stress relaxation in cartilage. Macroscopic stress relaxation of a poroelastic cylinder in uni-axial confined compression is simulated and validated against a theoretical solution. Microscopic cell deformation due to poroelastic stress relaxation is also modeled. An extended Laplace inversion method is employed to accurately represent mechanical responses in the time domain.

Particulate Titanium Matrix Composites Tested--Show Promise for Space Propulsion Applications

NASA Technical Reports Server (NTRS)

Lerch, Bradley A.; Ellis, J. Rodney; Arnold. Steven M.

2004-01-01

Uniformly distributed particle-strengthened titanium matrix composites (TMCs) can be manufactured at lower cost than many types of continuous-fiber composites. The innovative manufacturing technology combines cold and hot isostatic pressing procedures to produce near-final-shape components. Material stiffness is increased up to 26-percent greater than that of components made with conventional titanium materials at no significant increase in the weight. The improved mechanical performance and low-cost manufacturing capability motivated an independent review to assess the improved properties of ceramic titanium carbide (TiC) particulate-reinforced titanium at elevated temperature. Researchers at the NASA Glenn Research Center creatively designed and executed deformation and durability tests to reveal operating regimes where these materials could lower the cost and weight of space propulsion systems. The program compares the elevated-temperature performance of titanium alloy Ti-6Al-4V matrix material to an alloy containing 10 wt% of TiC particles. Initial experiments showed that at these relatively low particle concentrations the material stiffness of the TMC was improved 20 percent over that of the plain Ti-6Al-4V alloy when tested at 427 C. The proportional limit and ultimate strength of the composite in tension are 21- and 14-percent greater than those of the plain alloy. Compression tests showed that the proportional limit is about 30 percent greater for TMC than for the plain alloy. The enhanced deformation resistance of the TMC was also evident in a series of tensile and compressive stress relaxation tests that were made. Specimens were subjected to tensile or compressive strain amplitudes of 0.75 percent for 24 hr followed by a return to zero strain imposed for 24 hr. The stress relaxation data were normalized with respect to the maximum stress for each case and plotted as a function of time in the following graph. Tensile stresses relaxed 19 percent for the TMC and 25 percent for the plain Ti-6Al-4V alloy. Compressive stresses relaxed 25 percent for the TMC and 39 percent for the plain Ti-6Al-4V alloy. The superior deformation resistance of the TMC extends to a creep rate that is 28-percent slower for the TMC when it is loaded to stress levels that are 26-percent higher than for the plain Ti-6Al-4V alloy.

Relaxation and guided imagery do not reduce stress, pain and unpleasantness for 11- to 12-year-old girls during vaccinations.

PubMed

Nilsson, Stefan; Forsner, Maria; Finnström, Berit; Mörelius, Evalotte

2015-07-01

Relaxation and guided imagery is a distraction technique known to reduce discomfort during paediatric medical procedures. We examined whether its use decreased the stress experienced by 11- to 12-year-old girls receiving the human papilloma virus vaccination, as well as the intensity and unpleasantness of any pain. A randomised crossover trial was conducted with 37 girls. During the first vaccination, each girl was randomised to receive either relaxation and guided imagery or standard care. They then received the other form of care during the second vaccination. Salivary cortisol was measured before each vaccination, and 30 minutes after it was administered. The girls reported pain intensity and pain unpleasantness before and directly after each vaccination and stress after each vaccination. On a group level, relaxation and guided imagery did not decrease cortisol levels, self-reported stress, pain intensity and pain unpleasantness. Salivary cortisol levels decreased significantly in both groups during the second vaccination. Relaxation and guided imagery did not prove beneficial during the vaccination of 11- to 12-year-old girls and is not recommended as a regular nursing intervention. However, further research is needed into effective techniques to help children who experience pain unpleasantness in connection with needle procedures. ©2015 Foundation Acta Paediatrica. Published by John Wiley & Sons Ltd.

Estimation of the viscous properties of skin and subcutaneous tissue in uniaxial stress relaxation tests.

PubMed

Wu, John Z; Cutlip, Robert G; Welcome, Daniel; Dong, Ren G

2006-01-01

Knowledge of viscoelastic properties of soft tissues is essential for the finite element modelling of the stress/strain distributions in finger-pad during vibratory loading, which is important in exploring the mechanism of hand-arm vibration syndrome. In conventional procedures, skin and subcutaneous tissue have to be separated for testing the viscoelastic properties. In this study, a novel method has been proposed to simultaneously determine the viscoelastic properties of skin and subcutaneous tissue in uniaxial stress relaxation tests. A mathematical approach has been derived to obtain the creep and relaxation characteristics of skin and subcutaneous tissue using uniaxial stress relaxation data of skin/subcutaneous composite specimens. The micro-structures of collagen fiber networks in the soft tissue, which underline the tissue mechanical characteristics, will be intact in the proposed method. Therefore, the viscoelastic properties of soft tissues obtained using the proposed method would be more physiologically relevant than those obtained using the conventional method. The proposed approach has been utilized to measure the viscoelastic properties of soft tissues of pig. The relaxation curves of pig skin and subcutaneous tissue obtained in the current study agree well with those in literature. Using the proposed approach, reliable material properties of soft tissues can be obtained in a cost- and time-efficient manner, which simultaneously improves the physiological relevance.

Cognitive Behavioral Training and Education for Spaceflight Operations

NASA Technical Reports Server (NTRS)

Moonmaw, Ronald

2011-01-01

Cognitive behavioral-training (CBT) is an evidence-based practice commonly used to help treat insomnia, and is part of NASA's countermeasure regimen for Fatigue Management. CBT addresses the life style and habits of individuals that are maladaptive to managing stress and fatigue. This includes addressing learned behavioral responses that may cause stress and lead to an increased sense of fatigue. While the initial cause of onset of fatigue in the individual may be no longer present, the perception and engrained anticipation of fatigue persist and cause an exaggerated state of tension. CBT combined with relaxation training allows the individual to unlearn the maladaptive beliefs and behaviors and replace them with routines and techniques that allow cognitive restructuring and resultant relief from stress. CBT allows for elimination in individuals of unwanted ruminating thoughts and anticipatory anxiety by, for example, training the individuals to practice stressful situations in a relaxed state. As a result of CBT, relaxation can be accomplished in many ways, such as progressive muscle relaxation, meditation and guided imagery. CBT is not therapy, but rather the synthesis of behavioral countermeasures. CBT utilizes progressive relaxation as a means of reinforcing educational and cognitive countermeasures. These countermeasures include: masking, elimination of distracting thoughts, anxiety control, split attention, cognitive restructuring and other advanced psychological techniques.

Stretching of Single Polymer Chains Using the Atomic Force Microscope

NASA Astrophysics Data System (ADS)

Ortiz, C.; van der Vegte, E. W.; van Swieten, E.; Robillard, G. T.; Hadziioannou, G.

1998-03-01

A variety of macroscopic phenomenon involve "nanoscale" polymer deformation including rubber elasticity, shear yielding, strain hardening, stress relaxation, fracture, and flow. With the advent of new and improved experimental techniques, such as the atomic force microscope (AFM), the probing of physical properties of polymers has reached finer and finer scales. The development of mixed self-assembling monolayer techniques and the chemical functionalization of AFM probe tips has allowed for mechanical experiments on single polymer chains of molecular dimensions. In our experiments, mixed monolayers are prepared in which end-functionalized, flexible polymer chains of thiol-terminated poly(methacrylic acid) are covalently bonded, isolated, and randomly distributed on gold substrates. The coils are then imaged, tethered to a gold-coated AFM tip, and stretched between the tip and the substrate in a conventional force / distance experiment. An increase in the attractive force due to entropic, elastic resistance to stretching, as well as fracture of the polymer chain is observed. The effect of chain stiffness, topological constraints, strain rate, mechanical hysteresis, and stress relaxation were investigated. Force modulation techniques were also employed in order to image the viscoelastic character of the polymer chains. Parallel work includes similar studies of biological systems such as wheat gluten proteins and polypeptides.

A Nano-indentation Identification Technique for Viscoelastic Constitutive Characteristics of Periodontal Ligaments.

PubMed

Ashrafi, H; Shariyat, M

2016-06-01

Nano-indentation has recently been employed as a powerful tool for determining the mechanical properties of biological tissues on nano and micro scales. A majority of soft biological tissues such as ligaments and tendons exhibit viscoelastic or time-dependent behaviors. The constitutive characterization of soft tissues is among very important subjects in clinical medicine and especially, biomechanics fields. Periodontal ligament plays an important role in initiating tooth movement when loads are applied to teeth with orthodontic appliances. It is also the most accessible ligament in human body as it can be directly manipulated without any surgical intervention. From a mechanical point of view, this ligament can be considered as a thin interface made by a solid phase, consisting mainly of collagen fibers, which is immersed into a so-called ground substance. However, the viscoelastic constitutive effects of biological tissues are seldom considered rigorous during Nano-indentation tests. In the present paper, a mathematical contact approach is developed to enable determining creep compliance and relaxation modulus of distinct periodontal ligaments, using constant-rate indentation and loading time histories, respectively. An adequate curve-fitting method is presented to determine these characteristics based on the Nano-indentation of rigid Berkovich tips. Generalized Voigt-Kelvin and Wiechert models are used to model constitutive equations of periodontal ligaments, in which the relaxation and creep functions are represented by series of decaying exponential functions of time. Time-dependent creep compliance and relaxation function have been obtained for tissue specimens of periodontal ligaments. To improve accuracy, relaxation and creep moduli are measured from two tests separately. Stress relaxation effects appear more rapidly than creep in the periodontal ligaments.

A Nano-indentation Identification Technique for Viscoelastic Constitutive Characteristics of Periodontal Ligaments

PubMed Central

Ashrafi, H.; Shariyat, M.

2016-01-01

Introduction Nano-indentation has recently been employed as a powerful tool for determining the mechanical properties of biological tissues on nano and micro scales. A majority of soft biological tissues such as ligaments and tendons exhibit viscoelastic or time-dependent behaviors. The constitutive characterization of soft tissues is among very important subjects in clinical medicine and especially, biomechanics fields. Periodontal ligament plays an important role in initiating tooth movement when loads are applied to teeth with orthodontic appliances. It is also the most accessible ligament in human body as it can be directly manipulated without any surgical intervention. From a mechanical point of view, this ligament can be considered as a thin interface made by a solid phase, consisting mainly of collagen fibers, which is immersed into a so-called ground substance. However, the viscoelastic constitutive effects of biological tissues are seldom considered rigorous during Nano-indentation tests. Methods In the present paper, a mathematical contact approach is developed to enable determining creep compliance and relaxation modulus of distinct periodontal ligaments, using constant–rate indentation and loading time histories, respectively. An adequate curve-fitting method is presented to determine these characteristics based on the Nano-indentation of rigid Berkovich tips. Generalized Voigt-Kelvin and Wiechert models are used to model constitutive equations of periodontal ligaments, in which the relaxation and creep functions are represented by series of decaying exponential functions of time. Results Time-dependent creep compliance and relaxation function have been obtained for tissue specimens of periodontal ligaments. Conclusion To improve accuracy, relaxation and creep moduli are measured from two tests separately. Stress relaxation effects appear more rapidly than creep in the periodontal ligaments. PMID:27672630

Strain relaxation of thick (11–22) semipolar InGaN layer for long wavelength nitride-based device

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jaehwan; Min, Daehong; Jang, Jongjin

2014-10-28

In this study, the properties of thick stress-relaxed (11–22) semipolar InGaN layers were investigated. Owing to the inclination of growth orientation, misfit dislocations (MDs) occurred at the heterointerface when the strain state of the (11–22) semipolar InGaN layers reached the critical point. We found that unlike InGaN layers based on polar and nonpolar growth orientations, the surface morphologies of the stress-relaxed (11–22) semipolar InGaN layers did not differ from each other and were similar to the morphology of the underlying GaN layer. In addition, misfit strain across the whole InGaN layer was gradually relaxed by MD formation at the heterointerface.more » To minimize the effect of surface roughness and defects in GaN layers on the InGaN layer, we conducted further investigation on a thick (11–22) semipolar InGaN layer grown on an epitaxial lateral overgrown GaN template. We found that the lateral indium composition across the whole stress-relaxed InGaN layer was almost uniform. Therefore, thick stress-relaxed (11–22) semipolar InGaN layers are suitable candidates for use as underlying layers in long-wavelength devices, as they can be used to control strain accumulation in the heterostructure active region without additional influence of surface roughness.« less

Effects of stress and relaxation on pain perception in subjects with pain-free occlusional disharmony compared with healthy controls.

PubMed

Ruscheweyh, R; Becker, T; Born, Y; Çolak-Ekici, R; Marziniak, M; Evers, S; Gerlach, A L; Wolowski, A

2015-04-01

The significance of occlusal disharmony for the development of painful temporomandibular disorder (TMD) is controversial. The ongoing biomechanical strain caused by occlusal disharmony might lead to sensitization processes in the nociceptive system. Understanding these processes might be an important step toward understanding the possible relationship between occlusal disharmony and TMD. In this study, we therefore investigated whether subjects with occlusal disharmony (n = 22) differ from healthy controls (n = 26) in their pain perception and pain modulation by stress and relaxation. Trigeminal and extratrigeminal experimental pain perception (pinprick, heat, and pressure pain) was assessed before and after stress (mental arithmetic) and relaxation (viewing of low-arousal pictures). There were no group differences in pain perception at baseline or during the stress task. Compared with controls, the occlusal disharmony group exhibited an inadequate reduction in pain perception during relaxation, which was significant for the extratrigeminal site (P < 0.01) and reached a trend for significance at the trigeminal site (P = 0.1). These results suggest that subjects with occlusal disharmony show signs of disturbed endogenous pain inhibition during relaxation. There is evidence for the presence of sensitization of the nociceptive system in subjects with occlusal disharmony. Possibly, deficient inhibition of extratrigeminal and trigeminal pain perception by relaxation might contribute to the development of TMD or other chronic pain disorders. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Internal Stress and Microstructure of Zinc Oxide Films Sputter-Deposited with Carbon Dioxide Gas

NASA Astrophysics Data System (ADS)

Toru Ashida,; Kazuhiro Kato,; Hideo Omoto,; Atsushi Takamatsu,

2010-06-01

The internal stress and microstructure of ZnO films were investigated as a function of carbon dioxide (CO2) gas flow ratio [CO2/(O2+CO2)] during sputter deposition. The internal stress of the ZnO films decreased with increasing CO2 gas flow ratio. The carbon concentration in the films deposited using CO2 gas increased by up to 4.0 at. %. Furthermore, the ZnO films deposited without CO2 gas exhibited a preferred orientation of (002); however, the C-doped ZnO films exhibited random orientations. These findings suggest that the C atoms incorporated in the ZnO crystal lattice induce this random orientation, thereby relaxing the internal stress of C-doped ZnO films.

Separating the Influence of Environment from Stress Relaxation Effects on Dwell Fatigue Crack Growth

NASA Technical Reports Server (NTRS)

Telesman, Jack; Gabb, Tim; Ghosn, Louis J.

2016-01-01

Seven different microstructural variations of LSHR were produced by controlling the cooling rate and the subsequent aging and thermal exposure heat treatments. Through cyclic fatigue crack growth testing performed both in air and vacuum, it was established that four out of the seven LSHR heat treatments evaluated, possessed similar intrinsic environmental resistance to cyclic crack growth. For these four heat treatments, it was further shown that the large differences in dwell crack growth behavior which still persisted, were related to their measured stress relaxation behavior. The apparent differences in their dwell crack growth resistance were attributed to the inability of the standard linear elastic fracture mechanics (LEFM) stress intensity parameter to account for visco-plastic behavior. Crack tip stress relaxation controls the magnitude of the remaining local tensile stresses which are directly related to the measured dwell crack growth rates. It was hypothesized that the environmentally weakened grain boundary crack tip regions fail during the dwells when their strength is exceeded by the remaining local crack tip tensile stresses. It was shown that the classical creep crack growth mechanisms such as grain boundary sliding did not contribute to crack growth, but the local visco-plastic behavior still plays a very significant role by determining the crack tip tensile stress field which controls the dwell crack growth behavior. To account for the influence of the visco-plastic behavior on the crack tip stress field, an empirical modification to the LEFM stress intensity parameter, Kmax, was developed by incorporating into the formulation the remaining stress level concept as measured by simple stress relaxation tests. The newly proposed parameter, Ksrf, did an excellent job in correlating the dwell crack growth rates for the four heat treatments which were shown to have similar intrinsic environmental cyclic fatigue crack growth resistance.

Relaxation approximation in the theory of shear turbulence

NASA Technical Reports Server (NTRS)

Rubinstein, Robert

1995-01-01

Leslie's perturbative treatment of the direct interaction approximation for shear turbulence (Modern Developments in the Theory of Turbulence, 1972) is applied to derive a time dependent model for the Reynolds stresses. The stresses are decomposed into tensor components which satisfy coupled linear relaxation equations; the present theory therefore differs from phenomenological Reynolds stress closures in which the time derivatives of the stresses are expressed in terms of the stresses themselves. The theory accounts naturally for the time dependence of the Reynolds normal stress ratios in simple shear flow. The distortion of wavenumber space by the mean shear plays a crucial role in this theory.

A Coupled Model of Stress-Driven Frictional Afterslip and Viscoelastic Relaxation Following the 2011 Tohoku-oki Earthquake

NASA Astrophysics Data System (ADS)

Fukuda, J.; Johnson, K. M.

2017-12-01

Postseismic deformation following the 2011 Mw9.0 Tohoku-oki earthquake has been captured by both on-land GNSS and seafloor GPS/Acoustic networks. Previous studies have shown that the observed postseismic displacements can be reproduced as the sum of contributions from viscoelastic relaxation of coseismic stress changes in the upper mantle and afterslip on the plate interface surrounding the coseismic rupture. In most previous studies, viscoelastic relaxation and afterslip were modeled separately and afterslip was estimated kinematically. In this study, we develop a mechanical model of postseismic deformation in which afterslip and viscoelastic relaxation are driven by coseismic stress perturbations and are mechanically coupled. We assume that afterslip is governed by a rate-strengthening friction law that is characterized with a friction parameter (a-b)*sigma, where a-b represents the rate dependence of steady-state friction and sigma is the effective normal stress. Viscoelastic relaxation of the upper mantle is modeled with a biviscous Burgers rheology that is characterized with the steady-state and transient viscosities. We calculate the evolution of afterslip and viscoelastic relaxation using stress changes computed from an assumed coseismic slip model as the initial condition. We examine the effects of the friction parameters, mantle viscosities, elastic thickness of the slab and upper plate, and coseismic slip distribution on the model prediction and explore the range of the parameters that can fit the observed postseismic displacements. We find that the vertical postseismic displacements are particularly sensitive to these parameters. Our modeling results indicate that the on-land postseismic deformation is dominated by afterslip, whereas the seafloor postseismic deformation is dominated by viscoelastic relaxation. We also examine if afterslip overlaps regions that ruptured seismically during M6.3-7.2 earthquakes between 2003 and 2010. We find that significant overlap between afterslip and the historical M6.3-7.2 coseismic rupture areas are required to fit the horizontal postseismic displacements.

Relaxation Training and Opioid Inhibition of Blood Pressure Response to Stress.

ERIC Educational Resources Information Center

McCubbin, James A.; And Others

1996-01-01

Sought to determine the role of endogenous opioid mechanisms in the circulatory effects of relaxation training. Subjects were 32 young men with mildly elevated casual arterial pressure. Assessed opioid mechanisms by examining the effects of opioid receptor blockade with naltrexone on acute cardiovascular reactivity to laboratory stress before and…

Anxiety Management Training and Relaxation as Self-Control in the Treatment of Generalized Anxiety in Medical Outpatients.

ERIC Educational Resources Information Center

Cragan, Mary K.; Deffenbacher, Jerry L.

1984-01-01

Compared Anxiety Management Training (AMT) and Relaxation as Self-Control (RSC) in reducing stress in 55 anxious medical outpatients. At posttreatment and follow-up assessments, both AMT and RSC groups reported significantly less anxiety, stress reactivity, general physiological arousal, depression, and anger than controls. (JAC)

Structural Model for Viscoelastic Properties of Pericardial Bioprosthetic Valves.

PubMed

Rassoli, Aisa; Fatouraee, Nasser; Guidoin, Robert

2018-03-30

The benefit of bioprosthetic aortic valve over mechanical valve replacements is the release of thromboembolism and digression of long-term anticoagulation treatment. The function of bioprostheses and their efficiency is known to depend on the mechanical properties of the leaflet tissue. So it is necessary to select a suitable tissue for the bioprosthesis. The purpose of the present study is to clarify the viscoelastic behavior of bovine, equine, and porcine pericardium. In this study, pericardiums were compared mechanically from the viscoelastic aspect. After fixation of the tissues in glutaraldehyde, first uniaxial tests with different extension rates in the fiber direction were performed. Then, the stress relaxation tests in the fiber direction were done on these pericardial tissues by exerting 20, 30,40, and 50% strains. After evaluation of viscoelastic linearity, the Prony series, quasilinear viscoelastic (QLV) and modified superposition theory were applied to the stress relaxation data. Finally, the parameters of these constitutive models were extracted for each pericardium tissue. All three tissues exhibited a decrease in relaxation rate with elevating strain, indicating the nonlinear viscoelastic behavior of these tissues. The three-term Prony model was selected for describing the linear viscoelasticity. Among different models, the QLV model was best able to capture the relaxation behavior of the pericardium tissues. More stiffness of porcine pericardium was observed in comparison to the two other pericardium tissues. The relaxation percentage of porcine pericardium was less than the two others. It can be concluded that porcine pericardium behaves more as an elastic and less like a viscous tissue in comparison to the bovine and equine pericardium. © 2018 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Effects of a relaxation training programme on immediate and prolonged stress responses in women with preterm labour.

PubMed

Chuang, Li-Lan; Lin, Li-Chan; Cheng, Po-Jen; Chen, Chung-Hey; Wu, Shiao-Chi; Chang, Chuan-Lin

2012-01-01

This paper is a report of an experimental study of the effects of relaxation-training programme on immediate and prolonged stress responses in women with preterm labour. Hospitalized pregnant women with preterm labour experience developmental and situational stress. However, few studies have been performed on stress management in such women. An experimental pretest and repeated post-test design was used to compare the outcomes for two groups in northern Taiwan from December 2008, to May 2010. A total of 129 women were randomly assigned to an experimental (n = 68) or control (n = 61) group. The experimental group participants were instructed to listen daily to a 13-minute relaxation programme. Measurements involved the stress visual analogue scale, finger temperatures, State Trait Anxiety Inventory, Perceived Stress Scale and Pregnancy-related Anxiety. Two-way analysis of variance and hierarchical linear modelling were used to analyse the group differences. Compared with those in the control group, participants in the experimental group showed immediate improvements in the stress visual analogue scale scores and finger temperatures. The State Trait Anxiety Inventory-State subscale score for the experimental group was significantly lower than that for the control group (P = 0·03). However, no statistically significant differences for the Perceived Stress Scale and Pregnancy-related Anxiety scores were found between the experimental group and the control group. The relaxation-training programme could improve the stress responses of women with preterm labour. © 2011 The Authors. Journal of Advanced Nursing © 2011 Blackwell Publishing Ltd.

Pragmatical access to the viscous flow of undercooled liquids

NASA Astrophysics Data System (ADS)

Buchenau, U.

2017-06-01

The paper derives a relation for the viscosity of undercooled liquids on the basis of the pragmatical model concept of Eshelby relaxations with a finite lifetime. From accurate shear relaxation data in the literature, one finds that slightly less than half of the internal stresses relax directly via single Eshelby relaxations; the larger part dissolves at the terminal lifetime, which is a combined effect of many Eshelby relaxations.

Response of turbulence subjected to a straining-relaxation-destraining cycle

NASA Astrophysics Data System (ADS)

Chen, Jun; Meneveau, Charles; Katz, Joseph

2004-11-01

The response of turbulence subjected to planar straining and de-straining is studied experimentally, and the impact of the applied distortions on the energy transfer across different length scales is quantified. The data are obtained using Planar Particle Image Velocimetry (PIV) in a water tank, in which high Reynolds number turbulence with very low mean velocity is generated by an array of spinning grids. Planar straining and de-straining mean flows are produced by pushing and pulling a rectangular piston towards, and away from, the bottom wall of the tank. The data are processed to yield the time evolution of Reynolds stresses, anisotropy tensors, turbulence kinetic energy production, and mean subgrid dissipation rate at various scales. During straining, the production rises rapidly. After the relaxation period the small-scale SGS stresses recover isotropy, but the Reynolds stresses at large scales still display significant anisotropy. When destraining is applied, a strong negative production (back-scattering) is observed, by which turbulence fluctuations return kinetic energy to the mean flow. Reversed energy transfer is also revealed in the vorticity fluctuations history. The experiment allows to disentangle in detail the causes for this global backscatter phenomenon in terms of non-equilibrium conditions of the Reynolds stresses, and to follow the trends as function of scale.

Investigation of the Use of Laser Shock Peening for Enhancing Fatigue and Stress Corrosion Cracking Resistance of Nuclear Energy Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vasudevan, Vijay K.; Jackson, John; Teysseyre, Sebastien

The objective of this project, which includes close collaboration with scientists from INL and ANL, is to investigate and demonstrate the use of advanced mechanical surface treatments like laser shock peening (LSP) and ultrasonic nanocrystal surface modification (UNSM) and establish baseline parameters for enhancing the fatigue properties and SCC resistance of nuclear materials like nickel-based alloy 600 and 304 stainless steel. The research program includes the following key elements/tasks: 1) Procurement of Alloy 600 and 304 SS, heat treatment studies; 2) LSP and UNSM processing of base metal and welds/HAZ of alloys 600 and 304; (3) measurement and mapping ofmore » surface and sub-surface residual strains/stresses and microstructural changes as a function of process parameters using novel methods; (4) determination of thermal relaxation of residual stresses (macro and micro) and microstructure evolution with time at high temperatures typical of service conditions and modeling of the kinetics of relaxation; (5) evaluation of the effects of residual stress, near surface microstructure and temperature on SCC and fatigue resistance and associated microstructural mechanisms; and (6) studies of the effects of bulk and surface grain boundary engineering on improvements in the SCC resistance and associated microstructural and cracking mechanisms« less

Game-based peripheral biofeedback for stress assessment in children.

PubMed

Pop-Jordanova, Nada; Gucev, Zoran

2010-06-01

Peripheral biofeedback is considered to be an efficient method for assessment and stress mitigation in children. The aim of the present study was to assess the levels of stress and stress mitigation in healthy school children (HSC), in children with cystic fibrosis (CF), general anxiety (GA) and attention-deficit-hyperactivity disorder (ADHD). Each investigated group (HSC, CF, GA, ADHD) consisted of 30 school-aged children from both sexes. Psychological characteristics were evaluated on Eysenck Personality Questionnaire (EPQ). The lie scale was used to determine participant honesty. Four biofeedback games using a pulls detector were applied for assessment of the stress levels as well as to evaluate ability to relax. EPQ found more psychopathological traits (P < 0.001) and less extroversion (P < 0.001) in children with GA and ADHD. In addition, high neurotic tendencies were found in children with CF (P < 0.01) and GA (P < 0.01). Unexpectedly, the lie scale was lower in ADHD children (P < 0.01) than in all other groups (HSC, CF, GA). The Magic blocks score was significantly different in relaxation levels between control and CF children (P < 0.05). Speed in the game Canal was significantly different in relaxation levels between healthy controls and all other groups, but no changes in pulls, as a relaxation measure, were found during the game. The CF group had much more commissions stemming from impulsivity (t= 5.71, P < 0.01), while the GA and ADHD children had more inattention omissions (P < 0.05). Strong negative correlation between age and pulls (r= 0.49, P= 0.003) and strong negative correlation between age and omissions (r=-0.86, P= 0.029) were found among all groups analyzed. The ability to learn stress mediation is correlated with age. All three groups of children had significantly lower relaxation levels when compared to healthy controls. Relaxation was more difficult for children with GA or ADHD, and easier for children with CF.

Dual and mixed nonsymmetric stress-based variational formulations for coupled thermoelastodynamics with second sound effect

NASA Astrophysics Data System (ADS)

Tóth, Balázs

2018-03-01

Some new dual and mixed variational formulations based on a priori nonsymmetric stresses will be developed for linearly coupled irreversible thermoelastodynamic problems associated with second sound effect according to the Lord-Shulman theory. Having introduced the entropy flux vector instead of the entropy field and defining the dissipation and the relaxation potential as the function of the entropy flux, a seven-field dual and mixed variational formulation will be derived from the complementary Biot-Hamilton-type variational principle, using the Lagrange multiplier method. The momentum-, the displacement- and the infinitesimal rotation vector, and the a priori nonsymmetric stress tensor, the temperature change, the entropy field and its flux vector are considered as the independent field variables of this formulation. In order to handle appropriately the six different groups of temporal prescriptions in the relaxed- and/or the strong form, two variational integrals will be incorporated into the seven-field functional. Then, eliminating the entropy from this formulation through the strong fulfillment of the constitutive relation for the temperature change with the use of the Legendre transformation between the enthalpy and Gibbs potential, a six-field dual and mixed action functional is obtained. As a further development, the elimination of the momentum- and the velocity vector from the six-field principle through the a priori satisfaction of the kinematic equation and the constitutive relation for the momentum vector leads to a five-field variational formulation. These principles are suitable for the transient analyses of the structures exposed to a thermal shock of short temporal domain or a large heat flux.

Elasticity measurement of nasal cartilage as a function of temperature using optical coherence elastography

NASA Astrophysics Data System (ADS)

Liu, Chih Hao; Skryabina, M. N.; Singh, Manmohan; Li, Jiasong; Wu, Chen; Sobol, E.; Larin, Kirill V.

2015-03-01

Current clinical methods of reconstruction surgery involve laser reshaping of nasal cartilage. The process of stress relaxation caused by laser heating is the primary method to achieve nasal cartilage reshaping. Based on this, a rapid, non-destructive and accurate elasticity measurement would allow for a more robust reshaping procedure. In this work, we have utilized a phase-stabilized swept source optical coherence elastography (PhSSSOCE) to quantify the Young's modulus of porcine nasal septal cartilage during the relaxation process induced by heating. The results show that PhS-SSOCE was able to monitor changes in elasticity of hyaline cartilage, and this method could potentially be applied in vivo during laser reshaping therapies.

A comparative study of the effect of stress on the cognitive parameters in women with increased body mass index before and after menopause.

PubMed

Ramesh, M B; Ammu, S; Nayanatara, A K; Vinodini, N A; Pratik, K C; Anupama, N; Bhagyalakshmi, K

2018-03-23

The increasing prevalence of overweight and obesity is a critical public health problem for women. The negative effect of stress on memory and cognitive functions has been widely explored for decades in numerous research projects using a wide range of methodology. Deterioration of memory and other brain functions is a hallmark of Alzheimer's disease. Estrogen fluctuations and withdrawal have myriad direct effects on the central nervous system that have the potential to influence cognitive functions. The present study aims to compare the effect of stress on the cognitive functions in overweight/obese women before and after menopause. A total of 142 female subjects constituting women before menopause between the ages of 18 and 44 years and women after menopause between the ages of 45 and 60 years were included in the sample. Participants were categorized into overweight/obese groups based on the body mass index. The major tool perceived stress scale was used for measuring the perception of stress. On the basis of the stress scale measurement, each group was classified into with stress and without stress. Addenbrooke's Cognitive Examination-III was used for measuring the cognitive functions. Premenopausal women with stress showed a significant (p<0.05) decrease in the cognitive parameters such as attention and orientation, fluency, language and visuospatial ability. Memory did not show any significant changes in this group. Whereas, in the postmenopausal stressed women, all the cognitive functions except fluency showed a significant (p<0.05) decrease. Stress is a significant factor on the cognitive functions of obese and overweight women before and after menopause. Practice of yoga and encouragement in activities like gardening, embroidery, games and relaxation techniques should be recommended to prevent stress. Insights into the neurobiology before and after menopause can be gained from future studies examining the effect on the hypothalamic-pituitary-adrenal axis in relation to cognition and stress.

Evolution des contraintes résiduelles dans des films minces de tungstène en fonction de l'irradiation

NASA Astrophysics Data System (ADS)

Durand, N.; Badawi, K. F.; Goudeau, P.; Naudon, A.

1994-01-01

The influence of the irradiation dose upon the residual stresses in 1 000 Å tungsten thin films has been studied by two different techniques. Results show a relaxation of the strong initial compressive stresses σ=- 4,5 GPa) in virgin samples when the irradiation dose increases. The existence of a relaxation threshold is also clearly evidenced, it indicates a strong correlation between the thin film microstructure (point defects, grain size) and the relaxation phenomenon, and consequently, the residual stresses. Nous avons étudié, par deux méthodes différentes, l'évolution des contraintes résiduelles dans des couches minces de 1 000 Å de W en fonction de la dose d'irradiation. Ces expériences mettent en évidence une relaxation des fortes contraintes de compression (σ=- 4,5 GPa) observées dans les échantillons vierges quand la dose de l'irradiation augmente. Notre étude montre par ailleurs, l'existence d'un seuil de relaxation et relie de façon indiscutable, la microstructure de la couche mince (défauts ponctuels, taille de grains) au phénomène de relaxation, donc aux contraintes elles-mêmes.

Stress and structure development in polymeric coatings

NASA Astrophysics Data System (ADS)

Vaessen, Diane Melissa

2002-09-01

The main goal of this research is to measure the stress evolution in various polymer coating systems to establish the mechanisms responsible for stress development, stress relaxation, and defect formation. Investigated systems include ultraviolet (UV)-curable coatings, dense and porous coatings from polymer solutions, and latex coatings. Coating stress was measured using a controlled environment stress apparatus based on a cantilever deflection principle. For acrylate coatings, it was found that by cycling a UV-lamp on and off, keeping the total dose constant, coating stress was lowered by 60% by decreasing the cycle period. A stress minimum was also found to exist for a given dose of radiation. The lower stress is attributed to stress relaxation and/or slower reaction during dark periods. A viscoelastic stress model of this process was formulated and predicted stress values close to those observed experimentally. During drying of cellulose acetate (CA) coatings cast in acetone, final stress increased from 10 to 45 MPa as coating thickness decreased from 60 to 10 mum. This thickness dependent coating stress for a solvent-cast polymer coating is a new finding and is attributed to (1) less shrinkage in thicker coatings due to more trapped solvent (from skinning) and (2) greater amounts of polymer stress relaxation in thicker coatings. For porous CA coatings prepared by dry-cast phase separation, final in-plane stresses ranged from 20 MPa for coatings containing small pores (˜1 mum) to 5 MPa for coatings containing small pores and macrovoids (˜200 mum). For these coatings, a small amount of stress relaxation occurs due to capillary pressure relief. A stress plateau for the macrovoid-containing coating is likely caused by stress-induced rupture of the polymer-rich phase. Measured stress in pigment-free latex coatings was much lower (˜0.3 MPa) than UV-curable and solvent-cast polymer coatings and was found to increase with increasing latex glass transition temperature. Observations from infrared spectroscopy, scanning electron microscopy, camera imaging, and indentation were also studied to correlate coating properties to measured stresses. The results obtained in this thesis will lead to strategies for material selection, process optimization, and defect elimination in polymeric coatings.

LGM-30B, Stage II Dissected Motors Test Report,

DTIC Science & Technology

1980-07-01

Relaxation Test Data (Outer Propellant) 29 Table 9, Stress Relaxation Test Data (Inner Propellant) 31 Table 10 , Cohesive Tear Energy Test Data (Outer...Outer) 45 7 Maximum Stress (Inner) 46 8Strain at Rupture (Inner) 47 9 Modulus (Inner) 48 Regression Plot, Low Rate Tensile 10 Maximum Stress (Outer...outer propellants are almost the same. H. TEAR ENERGY TEST: Data from this test period are contained in Tables 10 and 11. Sufficient valid data became

Relaxation for Children. (Revised and Expanded Edition.)

ERIC Educational Resources Information Center

Rickard, Jenny

Intended as a guide to reduce negative stress in children, this book suggests relaxation and meditation techniques to help children cope with stressful events. Part 1 provides an introduction to the format of the book. Part 2 contains summaries of the 10 sessions that make up the program. Each session has six sequential stages in which students…

Stress Management and Anxiety Reduction Through EMG Biofeedback/Relaxation Training upon Junior High School Students.

ERIC Educational Resources Information Center

Lang, Darrel

The effectiveness of electromyographic (EMG) biofeedback/relaxation training on the stress management and anxiety levels of 18 eighth-grade students was tested. Chapter I serves as an introduction and presents information on the need for the study, hypotheses, limitations, and definition of terms. Chapter II contains a review of related…

Stress Testing Recovery EMG for Evaluation of Biofeedback and Progressive Muscle Relaxation Training Effects.

ERIC Educational Resources Information Center

Sime, Wesley E.; DeGood, Douglas E.

The purpose of this investigation was to assess biofeedback (BF) and progressive muscle relaxation (PMR) and placebo-control training by means of a post-training transfer test. The subjects for the research were 30 women. Initial tests consisted of measuring the electromyographic response of the frontalis muscle of the forehead to stress. After…

Impact of relaxation training according to Yoga In Daily Life® system on perceived stress after breast cancer surgery.

PubMed

Kovačič, Tine; Kovačič, Miha

2011-03-01

The purpose of this pilot study was to gather information on the immediate and short-term effects of relaxation training according to Yoga In Daily Life(®) (YIDL) system on the psychological distress of breast cancer patients. 32 patients at the Institute for Oncology of Ljubljana were randomized to the experimental (N=16) and to the control group (N=16). Both groups received the same standard physiotherapy for 1 week, while the experimental group additionally received a group relaxation training sessions according to YIDL(®) system. At discharge the experimental group was issued with audiocassette recordings containing the similar instructions for relaxation training to be practiced individually at home (for further 3 weeks). An experimental repeated measures design was used to investigate the differences over 1 month period in stress levels, changes in mental health and psychological parameters. Measures were obtained at three time points during the study period: baseline, at 1 week, and at 4 weeks, by blinded investigators using standardized questionnaires General Health Questionnaire-12 (GHQ-12), Rotterdam Symptom Checklist (RSCL) psychological subscale, Perceived Stress Scale (PSS). Patients who received relaxation training reported feeling significantly less distressed during hospitalization and after discharge-period than did the controls that did not receive relaxation training. The results indicate that relaxation training according to Yoga in Daily Life(®) system could be useful clinical physiotherapy intervention for breast cancer patients experiencing psychological distress. Although this kind of relaxation training can be applied to clinical oncology in Slovenia, more studies need to be done. © The Author(s) 2011

Evolution of microstructure and residual stress during annealing of austenitic and ferritic steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wawszczak, R.; Baczmański, A., E-mail: Andrzej.Baczmanski@fis.agh.edu.pl; Marciszko, M.

2016-02-15

In this work the recovery and recrystallization processes occurring in ferritic and austenitic steels were studied. To determine the evolution of residual stresses during material annealing the nonlinear sin{sup 2}ψ diffraction method was used and an important relaxation of the macrostresses as well as the microstresses was found in the cold rolled samples subjected to heat treatment. Such relaxation occurs at the beginning of recovery, when any changes of microstructure cannot be detected using other experimental techniques. Stress evolution in the annealed steel samples was correlated with the progress of recovery process, which significantly depends on the value of stackingmore » fault energy. - Highlights: • X-ray diffraction was used to determine the first order and second order stresses. • Diffraction data were analyzed using scale transition elastoplastic models model. • Stress relaxation in annealed ferritic and austenitic steels was correlated with evolution of microstructure. • Influence of stacking fault energy on thermally induced processes was discussed.« less

Teaching to Relax: Development of a Program to Potentiate Stress-Results of a Feasibility Study with Medical Undergraduate Students.

PubMed

Scholz, Michael; Neumann, Carolin; Wild, Katharina; Garreis, Fabian; Hammer, Christian M; Ropohl, Axel; Paulsen, Friedrich; Burger, Pascal H M

2016-09-01

Medical students are a population at risk for the development of stress-related risk states (e.g. burnout) and manifest mental disorders (e.g. depression). Still the learning of coping mechanisms against stress is not an integral part of the medical curriculum. In a pilot study we developed an elective course for learning relaxation techniques (Relacs) which was geared to the clinical practice of autogenic training (AT) with psychiatric patients. The course focussed on an innovative and mostly communicative transfer of knowledge about AT, progressive muscle relaxation and medical hypnosis and stressed the principle of repeated and supervised exercises in small student groups alongside self-administered exercise. 42 students took part in this course and showed a very high acceptance for the topic and positive evaluation. Moreover, we found a distinct improvement of the participants' mental parameters (burnout, anxiety) and a good knowledge about the course's contents within the final exams at the end of the semester. The structure and realisation of the course is easily adaptable and very effective regarding the improvement of the students' mental health. Due to our results and the commonly known prevalence of stress-related disorders in medical students we postulate the integration of courses on relaxation strategies in the medical curriculum.

Viscoelastic Relaxation of Topographic Highs on Venus to Produce Coronae

NASA Technical Reports Server (NTRS)

Janes, Daniel M.; Squyres, Steven W.

1995-01-01

Coronae on Venus are believed to result from the gravitationally driven relaxation of topography that was originally raised by mantle diapirs. We examine this relaxation using a viscoelastic finite element code, and show that an initially plateau shaped load will evolve to the characteristic corona topography of central raised bowl, annular rim, and surrounding moat. Stresses induced by the relaxation are consistent with the development of concentric extensional fracturing common on the outer margins of corona moats. However, relaxation is not expected to produce the concentric faulting often observed on the annular rim. The relaxation timescale is shorter than the diapir cooling timescale, so loss of thermal support controls the rate at which topography is reduced. The final corona shape is supported by buoyancy and flexural stresses and will persist through geologic time. Development of lower, flatter central bowls and narrower and more pronounced annular rims and moats enhanced by thicker crusts, higher thermal gradients, and crustal thinning over the diapir.

Connexin 43 and ATP-sensitive potassium channels crosstalk: a missing link in hypoxia/ischemia stress.

PubMed

Ahmad Waza, Ajaz; Ahmad Bhat, Shabir; Ul Hussain, Mahboob; Ganai, Bashir A

2018-02-01

Connexin 43 (Cx43) is a gap junction protein expressed in various tissues and organs of vertebrates. Besides functioning as a gap junction, Cx43 also regulates diverse cellular processes like cell growth and differentiation, cell migration, cell survival, etc. Cx43 is critical for normal cardiac functioning and is therefore abundantly expressed in cardiomyocytes. On the other hand, ATP-sensitive potassium (K ATP ) channels are metabolic sensors converting metabolic changes into electrical activity. These channels are important in maintaining the neurotransmitter release, smooth muscle relaxation, cardiac action potential repolarization, normal physiology of cellular repolarization, insulin secretion and immune function. Cx43 and K ATP channels are part of the same signaling pathway, regulating cell survival during stress conditions and ischemia/hypoxia preconditioning. However, the underlying molecular mechanism for their combined role in ischemia/hypoxia preconditioning is largely unknown. The current review focuses on understanding the molecular mechanism responsible for the coordinated role of Cx43 and K ATP channel protein in protecting cardiomyocytes against ischemia/hypoxia stress.

Stress recovery and cyclic behaviour of an Fe-Mn-Si shape memory alloy after multiple thermal activation

NASA Astrophysics Data System (ADS)

Hosseini, E.; Ghafoori, E.; Leinenbach, C.; Motavalli, M.; Holdsworth, S. R.

2018-02-01

The stress recovery and cyclic deformation behaviour of Fe-17Mn-5Si-10Cr-4Ni-1(V,C) shape memory alloy (Fe-SMA) strips, which are often used for pre-stressed strengthening of structural members, were studied. The evolution of recovery stress under different constraint conditions was studied. The results showed that the magnitude of the tensile stress in the Fe-SMA member during thermal activation can have a signification effect on the final recovery stress. The higher the tensile load in the Fe-SMA (e.g., caused by dead load or thermal expansion of parent structure during heating phase), the lower the final recovery stress. Furthermore, this study investigated the cyclic behaviour of the activated SMA followed by a second thermal activation. Although the magnitude of the recovery stress decreased during the cyclic loading, the second thermal activation could retrieve a significant part of the relaxed recovery stress. This observation suggests that the relaxation of recovery stress during cyclic loading is due to a reversible phase transformation-induced deformation (i.e., forward austenite-to-martensite transformation) rather than an irreversible dislocation-induced plasticity. Retrieval of the relaxed recovery stress by the reactivation process has important practical implications as the prestressing loss in pre-stressed civil structures can be simply recovered by reheating of the Fe-SMA elements.

Functional fitness improvements after a worksite-based yoga initiative.

PubMed

Cowen, Virginia S

2010-01-01

This study explored the benefits of yoga on functional fitness, flexibility, and perceived stress. A quasi-experimental design was used to measure benefits of yoga in sample of firefighters from a major metropolitan fire department. Yoga classes were conducted on-shift, in the fire stations over the period of 6 weeks. The classes included pranayama (breathing), asana (postures), and savasana (relaxation); 108 firefighters enrolled in the study, most were physically active but had no prior experience with yoga. Baseline and post-yoga assessments were completed by 77 participants. Paired t-tests revealed significant improvements in the Functional Movement Screen, a seven item test that measures functional fitness. Improvements were also noted in trunk flexibility and perceived stress. Participants also reported favorable perceptions of yoga: feeling more focused and less musculoskeletal pain. These findings - along with the retention of the majority of the participants - indicate that participants benefited from yoga.

Thermo-mechanical treatment effects on stress relaxation and hydrogen embrittlement of cold-drawn eutectoid steels

NASA Astrophysics Data System (ADS)

Caballero, L.; Atienza, J. M.; Elices, M.

2011-12-01

The effects of the temperature and stretching levels used in the stress-relieving treatment of cold-drawn eutectoid steel wires are evaluated with the aim of improving the stress relaxation behavior and the resistance to hydrogen embrittlement. Five industrial treatments are studied, combining three temperatures (330, 400, and 460 °C) and three stretching levels (38, 50 and 64% of the rupture load). The change of the residual stress produced by the treatments is taken into consideration to account for the results. Surface residual stresses allow us to explain the time to failure in standard hydrogen embrittlement tests.

Detection of stress/anxiety state from EEG features during video watching.

PubMed

Giannakakis, Giorgos; Grigoriadis, Dimitris; Tsiknakis, Manolis

2015-01-01

This paper studies the effect of stress/anxiety states on EEG signals during video sessions. The levels of arousal and valence that are induced to each subject while watching each video are self rated. These levels are mapped in stress and relaxed states and subjects that fufill criteria of adequate anxiety/stress scale were chosen leading to a subset of 18 subjects. Then, temporal, spectral and non linear EEG features are evaluated for being able to represent accurately states under investigation. Feature selection schemes choose the most significant of them in order to provide increased discrimination ability between relaxed and anxiety/stress states.

Stress and Mood

MedlinePlus

... Relaxation Emotions & Relationships HealthyYouTXT Tools Home » Stress & Mood Stress & Mood Many people who go back to smoking ... story: Time Out Times 10 >> share What Causes Stress? Read full story: What Causes Stress? >> share The ...

Localization of Secondary Metabolites in Marine Invertebrates: Contribution of MALDI MSI for the Study of Saponins in Cuvierian Tubules of H. forskali

PubMed Central

Meriaux, Céline; Bonnel, David; Salzet, Michel; Fournier, Isabelle; Wisztorski, Maxence

2010-01-01

Background Several species of sea cucumbers of the family Holothuriidae possess a particular mechanical defense system called the Cuvierian tubules (Ct). It is also a chemical defense system as triterpene glycosides (saponins) appear to be particularly concentrated in Ct. In the present study, the precise localization of saponins in the Ct of Holothuria forskali is investigated. Classical histochemical labeling using lectin was firstly performed but did not generate any conclusive results. Thus, MALDI mass spectrometry Imaging (MALDI-MSI) was directly applied and completed by statistical multivariate tests. A comparison between the tubules of relaxed and stressed animals was realized. Results These analyses allowed the detection of three groups of ions, corresponding to the isomeric saponins of the tubules. Saponins detected at m/z 1287 and 1303 were the most abundant and were apparently localized in the connective tissue of the tubules of both relaxed and stressed individuals. Saponins at m/z 1125 and 1141 were detected in lower amount and were present in tissues of relaxed animals. Finally, saponin ions at 1433, 1449, 1463 and 1479 were observed in some Ct of stressed holothuroids in the outer part of the connective tissue. The saponin group m/z 14xx seems therefore to be stress-specific and could originate from modifications of the saponins with m/z of 11xx. Conclusions All the results taken together indicate a complex chemical defense mechanism with, for a single organ, different sets of saponins originating from different cell populations and presenting different responses to stress. The present study also reflects that MALDI-MSI is a valuable tool for chemical ecology studies in which specific chemical signalling molecules like allelochemicals or pheromones have to be tracked. This report represents one of the very first studies using these tools to provide a functional and ecological understanding of the role of natural products from marine invertebrates. PMID:21085713

Effect of saline absorption on the flexural stress relaxation behavior of epoxy/cotton composite materials for orthopedics applications

NASA Astrophysics Data System (ADS)

Kontaxis, L. C.; Pavlou, C.; Portan, D. V.; Papanicolaou, G. C.

2018-02-01

In the present study, a composite material consisting of a polymeric epoxy resin matrix, reinforced with forty layers of non-woven cotton fiber fabric was manufactured. The method used to manufacture the composite was the Resin Vacuum Infusion technique. This is a technique widely used for high-performance, defect-free, composite materials. Composites and neat polymers are subjected to stresses during their function, while at the same time being influenced by environmental conditions, such as temperature and humidity. The main goal of this study was the investigation of the degradation of composite's viscoelastic behavior, after saline absorption. At this point, it should be mentioned, that this material could be used in biomedical applications. Therefore, a sealed container full of saline was used for the immer s ion of the specimens manufactured, and was placed in a bath at 37°C (body temperature). The specimens remained there for five different immersion periods (24, 72, 144, 216, 336 hours). The viscoelastic behavior of the composite material was determined through stress relaxation under flexure conditions, and the effect of immersion time and amount of saline absorption was studied. It was observed that after 24 hours of immersion a 42% decrease in stress was observed, which in the sequence remained almost constant. The stress relaxation experimental results were predicted by using the Residua l Property Model (RPM), a model developed by Papanicolaou et al. The same model has been successfully applied in the past, to many different materials previously subjected to various types of damage, in order to predict their residual behavior. For its application, the RPM predictive model needs only two experimental points. It was found that in all cases, predictions were in good agreement with experimental findings. Furthermore, the comparison between experimental values and theoretical predictions formed the basis of useful observations and conclusions.

Ab-initio atomic level stress and role of d-orbitals in CuZr, CuZn and CuY

NASA Astrophysics Data System (ADS)

Ojha, Madhusudan; Nicholson, Don M.; Egami, Takeshi

2015-03-01

Atomic level stress offers a new tool to characterize materials within the local approximation to density functional theory (DFT). Ab-initio atomic level stresses in B2 structures of CuZr, CuZn and CuY are calculated and results are explained on the basis of d-orbital contributions to Density of States (DOS). The overlap of d-orbital DOS plays an important role in the relative magnitude of atomic level stresses in these structures. The trends in atomic level stresses that we observed in these simple B2 structures are also seen in complex structures such as liquids, glasses and solid solutions. The stresses are however modified by the different coordination and relaxed separation distances in these complex structures. We used the Locally Self-Consistent Multiple Scattering (LSMS) code and Vienna Ab-initio Simulation Package (VASP) for ab-initio calculations.

Separating the Influence of Environment from Stress Relaxation Effects on Dwell Fatigue Crack Growth in a Nickel-Base Disk Alloy

NASA Technical Reports Server (NTRS)

Telesman, J.; Gabb, T. P.; Ghosn, L. J.

2016-01-01

Both environmental embrittlement and crack tip visco-plastic stress relaxation play a significant role in determining the dwell fatigue crack growth (DFCG) resistance of nickel-based disk superalloys. In the current study performed on the Low Solvus High Refractory (LSHR) disk alloy, the influence of these two mechanisms were separated so that the effects of each could be quantified and modeled. Seven different microstructural variations of LSHR were produced by controlling the cooling rate and the subsequent aging and thermal exposure heat treatments. Through cyclic fatigue crack growth testing performed both in air and vacuum, it was established that four out of the seven LSHR heat treatments evaluated, possessed similar intrinsic environmental resistance to cyclic crack growth. For these four heat treatments, it was further shown that the large differences in dwell crack growth behavior which still persisted, were related to their measured stress relaxation behavior. The apparent differences in their dwell crack growth resistance were attributed to the inability of the standard linear elastic fracture mechanics (LEFM) stress intensity parameter to account for visco-plastic behavior. Crack tip stress relaxation controls the magnitude of the remaining local tensile stresses which are directly related to the measured dwell crack growth rates. It was hypothesized that the environmentally weakened grain boundary crack tip regions fail during the dwells when their strength is exceeded by the remaining local crack tip tensile stresses. It was shown that the classical creep crack growth mechanisms such as grain boundary sliding did not contribute to crack growth, but the local visco-plastic behavior still plays a very significant role by determining the crack tip tensile stress field which controls the dwell crack growth behavior. To account for the influence of the visco-plastic behavior on the crack tip stress field, an empirical modification to the LEFM stress intensity parameter, Kmax, was developed by incorporating into the formulation the remaining stress level concept as measured by simple stress relaxation tests. The newly proposed parameter, Ksrf, did an excellent job in correlating the dwell crack growth rates for the four heat treatments which were shown to have similar intrinsic environmental cyclic fatigue crack growth resistance.

Interpretation of Offshore Crustal Movements Following the 2011 Tohoku-Oki Earthquake by the Combined Effect of Afterslip and Viscoelastic Stress Relaxation

NASA Astrophysics Data System (ADS)

Noda, Akemi; Takahama, Tsutomu; Kawasato, Takeshi; Matsu'ura, Mitsuhiro

2018-02-01

On the 11th March 2011, a megathrust event, called the Tohoku-oki earthquake, occurred at the North American-Pacific plate interface off northeast Japan. Transient crustal movements following this earthquake were clearly observed by a dense GPS network (GEONET) on land and a sparse GPS/Acoustic positioning network on seafloor. The observed crustal movements are in accordance with ordinary expectations on land, but not on seafloor; that is, slowly decaying landward movements above the main rupture area and rapidly decaying trench-ward movements in its southern extension. To reveal the cause of such curious offshore crustal movements, we analyzed the coseismic and postseismic GPS array data on land with a sequential stepwise inversion method considering viscoelastic stress relaxation in the asthenosphere, and obtained the following results: The afterslip of the Tohoku-oki earthquake rapidly proceeds for the first 1 year on a high-angle downdip extension of the main rupture, which occurred on the low-angle offshore plate interface. The theoretical patterns of seafloor horizontal movements due to the afterslip and the viscoelastic relaxation of coseismic stress changes in the asthenosphere are essentially different both in space and time; inshore trench-ward movements and offshore landward movements for the afterslip, while overall landward movements for the viscoelastic stress relaxation. General agreement between the computed horizontal movements and the GPS/Acoustic observations demonstrates that the postseismic curious offshore crustal movements can be ascribed to the combined effect of afterslip on a high-angle downdip extension of the main rupture and viscoelastic stress relaxation in the asthenosphere.

Study on the Aging Behaviors of Rubber Materials in Tension and Compression Loads

NASA Astrophysics Data System (ADS)

Jiang, Can; Wang, Hongyu; Ma, Xiaobing

Rubber materials are widely used in aviation, aerospace, shipbuilding, automobile and other military field. However, rubber materials are easy to aging, which largely restricts its using life. In working environment, due to the combined effect of heat and oxygen, vulcanized rubber will undergo degradation and crosslinking reaction which will cause elasticity decease and permanent deformation, so mostly rubber products are used under stress state. Due to the asymmetric structure and asymmetric stress distribution, mechanical stress may cause serious damage to molecular structure; therefore, this paper is aimed to analyze the aging behavior of rubber materials under tensile and compressive loadings, through analyzing experiment data, and adopting Gauss function to describe stress relaxation coefficient, to build an aging equation containing compression ratio parameter and aging time.

Dimensionless number is central to stress relaxation and expansive growth of the cell wall.

PubMed

Ortega, Joseph K E

2017-06-07

Experiments demonstrate that both plastic and elastic deformation of the cell wall are necessary for wall stress relaxation and expansive growth of walled cells. A biophysical equation (Augmented Growth Equation) was previously shown to accurately model the experimentally observed wall stress relaxation and expansive growth rate. Here, dimensional analysis is used to obtain a dimensionless Augmented Growth Equation with dimensionless coefficients (groups of variables, or Π parameters). It is shown that a single Π parameter controls the wall stress relaxation rate. The Π parameter represents the ratio of plastic and elastic deformation rates, and provides an explicit relationship between expansive growth rate and the wall's mechanical properties. Values for Π are calculated for plant, algal, and fungal cells from previously reported experimental results. It is found that the Π values for each cell species are large and very different from each other. Expansive growth rates are calculated using the calculated Π values and are compared to those measured for plant and fungal cells during different growth conditions, after treatment with IAA, and in different developmental stages. The comparison shows good agreement and supports the claim that the Π parameter is central to expansive growth rate of walled cells.

Teacher-led relaxation response curriculum in an urban high school: impact on student behavioral health and classroom environment.

PubMed

Wilson, H Kent; Scult, Matthew; Wilcher, Marilyn; Chudnofsky, Rana; Malloy, Laura; Drewel, Emily; Riklin, Eric; Saul, Southey; Fricchione, Gregory L; Benson, Herbert; Denninger, John W

2015-01-01

Recent data suggest that severe stress during the adolescent period is becoming a problem of epidemic proportions. Elicitation of the relaxation response (RR) has been shown to be effective in treating anxiety, reducing stress, and increasing positive health behaviors. The research team's objective was to assess the impact of an RR-based curriculum, led by teachers, on the psychological status and health management behaviors of high-school students and to determine whether a train-the-trainer model would be feasible in a high-school setting. The research team designed a pilot study. The setting was a Horace Mann charter school within Boston's public school system. Participants were teachers and students at the charter school. The team taught teachers a curriculum that included (1) relaxation strategies, such as breathing and imagery; (2) psychoeducation regarding mind-body pathways; and (3) positive psychology. Teachers implemented this curriculum with students. The research team assessed changes in student outcomes (eg, stress, anxiety, and stress management behaviors) using preintervention/postintervention surveys, including the Perceived Stress Scale (PSS), the State-Trait Anxiety Inventory-Form Y (STAI-Y), the stress management subscale of the Health-promoting Lifestyle Profile II (HPLP-II), the Rosenberg Self-Esteem Scale (RSES), the Locus of Control (LOC) questionnaire, and the Life Orientation Test-Revised (LOTR). Classroom observations using the Classroom Assessment Scoring System (CLASS)-Secondary were also completed to assess changes in classroom environment. Using a Bonferroni correction (P < .007), the study found that students experienced a significant reduction (P < .001) in measures of state-level anxiety on the STAI from pre- to postintervention. The study also found an increase in the use of stress management behaviors at that point. Using a Bonferroni correction (P < .007), the study found that students had significantly less perceived stress (P < .001), less state anxiety (P < .001) and trait anxiety (P < . 001), and increased use of positive stress management behaviors (P < .004) at the follow-up assessment in the fall of the following year. Using a Bonferroni correction (P < .002), the study found a significant increase in overall classroom productivity (eg, increased time spent on activities and instruction from pre- to postintervention). This study showed that teachers can lead an RR curriculum with fidelity and suggests that such a curriculum has positive benefits on student emotional and behavioral health and on classroom functioning.

Time Out from Tension: Teaching Young Children How To Relax. Teaching Strategies.

ERIC Educational Resources Information Center

Scully, Patricia

2003-01-01

Discusses how using relaxation and stress reduction activities with individual preschool and elementary school-age children during difficult periods can help them regain control, and how integrating relaxation techniques into everyday activities helps to establish positive behavior patterns to support healthy living. Presents breathing activities…

Relaxation Theory for Rural Youth. Research Bulletin No. 46.

ERIC Educational Resources Information Center

Matthews, Doris B.

This document synthesizes research findings to formulate a theory to guide relaxation training in educational settings, particularly rural schools. Young people experience many intense life events that require coping skills or relaxation. Family-related stress factors include instability in the home, lack of a support system, conflicting values,…

Fractional calculus model of articular cartilage based on experimental stress-relaxation

NASA Astrophysics Data System (ADS)

Smyth, P. A.; Green, I.

2015-05-01

Articular cartilage is a unique substance that protects joints from damage and wear. Many decades of research have led to detailed biphasic and triphasic models for the intricate structure and behavior of cartilage. However, the models contain many assumptions on boundary conditions, permeability, viscosity, model size, loading, etc., that complicate the description of cartilage. For impact studies or biomimetic applications, cartilage can be studied phenomenologically to reduce modeling complexity. This work reports experimental results on the stress-relaxation of equine articular cartilage in unconfined loading. The response is described by a fractional calculus viscoelastic model, which gives storage and loss moduli as functions of frequency, rendering multiple advantages: (1) the fractional calculus model is robust, meaning that fewer constants are needed to accurately capture a wide spectrum of viscoelastic behavior compared to other viscoelastic models (e.g., Prony series), (2) in the special case where the fractional derivative is 1/2, it is shown that there is a straightforward time-domain representation, (3) the eigenvalue problem is simplified in subsequent dynamic studies, and (4) cartilage stress-relaxation can be described with as few as three constants, giving an advantage for large-scale dynamic studies that account for joint motion or impact. Moreover, the resulting storage and loss moduli can quantify healthy, damaged, or cultured cartilage, as well as artificial joints. The proposed characterization is suited for high-level analysis of multiphase materials, where the separate contribution of each phase is not desired. Potential uses of this analysis include biomimetic dampers and bearings, or artificial joints where the effective stiffness and damping are fundamental parameters.

Characterization of bovine cartilage by fiber Bragg grating-based stress relaxation measurements

NASA Astrophysics Data System (ADS)

Baier, V.; Marchi, G.; Foehr, P.; Burgkart, R.; Roths, J.

2017-04-01

A fiber-based device for testing mechanical properties of cartilage is presented within this study. The measurement principle is based on stepwise indentation into the tissue and observing of corresponding relaxation of the stress. The indenter tip is constituted of a cleaved optical fiber that includes a fiber Bragg grating which is used as the force sensor. Stress relaxation measurements at 25 different positions on a healthy bovine cartilage sample were performed to assess the behavior of healthy cartilage. For each indentation step a good agreement was found with a viscoelastic model that included two time constants. The model parameters showed low variability and a clear dependence with indentation depth. The parameters can be used as reference values for discriminating healthy and degenerated cartilage.

Time-Dependent Behaviors of Granite: Loading-Rate Dependence, Creep, and Relaxation

NASA Astrophysics Data System (ADS)

Hashiba, K.; Fukui, K.

2016-07-01

To assess the long-term stability of underground structures, it is important to understand the time-dependent behaviors of rocks, such as their loading-rate dependence, creep, and relaxation. However, there have been fewer studies on crystalline rocks than on tuff, mudstone, and rock salt, because the high strength of crystalline rocks makes the detection of their time-dependent behaviors much more difficult. Moreover, studies on the relaxation, temporal change of stress and strain (TCSS) conditions, and relations between various time-dependent behaviors are scarce for not only granites, but also other rocks. In this study, previous reports on the time-dependent behaviors of granites were reviewed and various laboratory tests were conducted using Toki granite. These tests included an alternating-loading-rate test, creep test, relaxation test, and TCSS test. The results showed that the degree of time dependence of Toki granite is similar to other granites, and that the TCSS resembles the stress-relaxation curve and creep-strain curve. A viscoelastic constitutive model, proposed in a previous study, was modified to investigate the relations between the time-dependent behaviors in the pre- and post-peak regions. The modified model reproduced the stress-strain curve, creep, relaxation, and the results of the TCSS test. Based on a comparison of the results of the laboratory tests and numerical simulations, close relations between the time-dependent behaviors were revealed quantitatively.

A coupled creep plasticity model for residual stress relaxation of a shot-peened nickel-based superalloy

NASA Astrophysics Data System (ADS)

Buchanan, Dennis J.; John, Reji; Brockman, Robert A.; Rosenberger, Andrew H.

2010-01-01

Shot peening is a commonly used surface treatment process that imparts compressive residual stresses into the surface of metal components. Compressive residual stresses retard initiation and growth of fatigue cracks. During component loading history, shot-peened residual stresses may change due to thermal exposure, creep, and cyclic loading. In these instances, taking full credit for compressive residual stresses would result in a nonconservative life prediction. This article describes a methodical approach for characterizing and modeling residual stress relaxation under elevated temperature loading, near and above the monotonic yield strength of INI 00. The model incorporates the dominant creep deformation mechanism, coupling between the creep and plasticity models, and effects of prior plastic strain to simulate surface treatment deformation.

Dynamics of Lithium Polymer Electrolytes using X-ray Photon Correlation Spectroscopy and Rheology

NASA Astrophysics Data System (ADS)

Oparaji, Onyekachi; Narayanan, Suresh; Sandy, Alec; Hallinan, Daniel, Jr.

Polymer electrolytes are promising materials for high energy density rechargeable batteries. Battery fade can be caused by structural evolution in the battery electrode and loss of electrode/electrolyte adhesion during cycling. Both of these effects are dependent on polymer mechanical properties. In addition, cycling rate is dictated by the ion mobility of the polymer electrolyte. Lithium ion mobility is expected to be strongly coupled to polymer dynamics. Therefore, we investigate polymer dynamics as a function of salt concentration using X-ray Photon Correlation Spectroscopy (XPCS) and rheology. We report the influence of lithium salt concentration on the structural relaxation time (XPCS) and stress relaxation time (rheology) of high molecular weight poly(styrene - ethylene oxide) block copolymer membranes.

Evaluation of Surface Residual Stresses in Friction Stir Welds Due to Laser and Shot Peening

NASA Technical Reports Server (NTRS)

Hatamleh, Omar; Rivero, Iris V.; Lyons, Jed

2007-01-01

The effects of laser, and shot peening on the residual stresses in Friction Stir Welds (FSW) has been investigated. The surface residual stresses were measured at five different locations across the weld in order to produce an adequate residual stress profile. The residual stresses before and after sectioning the coupon from the welded plate were also measured, and the effect of coupon size on the residual stress relaxation was determined and characterized. Measurements indicate that residual stresses were not uniform along the welded plate, and large variation in stress magnitude could be exhibited at various locations along the FSW plate. Sectioning resulted in significant residual stress relaxation in the longitudinal direction attributed to the large change in dimensions in this direction. Overall, Laser and shot peening resulted in a significant reduction in tensile residual stresses at the surface of the specimens.

Occupational stress, relaxation therapies, exercise and biofeedback.

PubMed

Stein, Franklin

2001-01-01

Occupational stress is a widespread occurrence in the United States. It is a contributing factor to absenteeism, disease, injury and lowered productivity. In general stress management programs in the work place that include relaxation therapies, exercise, and biofeedback have been shown to reduce the physiological symptoms such as hypertension, and increase job satisfaction and job performance. Strategies to implement a successful stress management program include incorporating the coping activities into one's daily schedule, monitoring one's symptoms and stressors, and being realistic in setting up a schedule that is relevant and attainable. A short form of meditation, daily exercise program and the use of heart rate or thermal biofeedback can be helpful to a worker experiencing occupational stress.

Creep behaviour and creep mechanisms of normal and healing ligaments

NASA Astrophysics Data System (ADS)

Thornton, Gail Marilyn

Patients with knee ligament injuries often undergo ligament reconstructions to restore joint stability and, potentially, abate osteoarthritis. Careful literature review suggests that in 10% to 40% of these patients the graft tissue "stretches out". Some graft elongation is likely due to creep (increased elongation of tissue under repeated or sustained load). Quantifying creep behaviour and identifying creep mechanisms in both normal and healing ligaments is important for finding clinically relevant means to prevent creep. Ligament creep was accurately predicted using a novel yet simple structural model that incorporated both collagen fibre recruitment and fibre creep. Using the inverse stress relaxation function to model fibre creep in conjunction with fibre recruitment produced a superior prediction of ligament creep than that obtained from the inverse stress relaxation function alone. This implied mechanistic role of fibre recruitment during creep was supported using a new approach to quantify crimp patterns at stresses in the toe region (increasing stiffness) and linear region (constant stiffness) of the stress-strain curve. Ligament creep was relatively insensitive to increases in stress in the toe region; however, creep strain increased significantly when tested at the linear region stress. Concomitantly, fibre recruitment was evident at the toe region stresses; however, recruitment was limited at the linear region stress. Elevating the water content of normal ligament using phosphate buffered saline increased the creep response. Therefore, both water content and fibre recruitment are important mechanistic factors involved in creep of normal ligaments. Ligament scars had inferior creep behaviour compared to normal ligaments even after 14 weeks. In addition to inferior collagen properties affecting fibre recruitment and increased water content, increased glycosaminoglycan content and flaws in scar tissue were implicated as potential mechanisms of scar creep. Similarly, ligament autografts had persistently abnormal creep behaviour and creep recovery after 2 years likely due to infiltration by scar tissue. Short-term immobilization of autografts had long-term detrimental consequences perhaps due to re-injury of the graft at remobilization. Treatments that restore normal properties to these mechanistic factors in order to control creep would improve joint healing by restoring joint kinematics and maintaining normal joint loading.

Performance of bolted closure joint elastomers under cask aging conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verst, C.; Sindelar, R.; Skidmore, E.

The bolted closure joint of a bare spent fuel cask is susceptible to age-related degradation and potential loss of confinement function under long-term storage conditions. Elastomeric seals, a component of the joint typically used to facilitate leak testing of the primary seal that includes the metallic seal and bolting, is susceptible to degradation over time by several mechanisms, principally via thermo-oxidation, stress-relaxation, and radiolytic degradation under time and temperature condition. Irradiation and thermal exposure testing and evaluation of an ethylene-propylene diene monomer (EPDM) elastomeric seal material similar to that used in the CASTOR® V/21 cask for a matrix of temperaturemore » and radiation exposure conditions relevant to the cask extended storage conditions, and development of semiempirical predictive models for loss of sealing force is in progress. A special insert was developed to allow Compressive Stress Relaxation (CSR) measurements before and after the irradiation and/or thermal exposure without unloading the elastomer. A condition of the loss of sealing force for the onset of leakage was suggested. The experimentation and modeling being performed could enable acquisition of extensive coupled aging data as well as an estimation of the timeframe when loss of sealing function under aging (temperature/radiation) conditions may occur.« less

Poroelastic finite difference modeling of seismic attenuation and dispersion due to mesoscopic-scale heterogeneity

NASA Astrophysics Data System (ADS)

Masson, Y. J.; Pride, S. R.

2007-03-01

Seismic attenuation and dispersion are numerically determined for computer-generated porous materials that contain arbitrary amounts of mesoscopic-scale heterogeneity in the porous continuum properties. The local equations used to determine the poroelastic response within such materials are those of Biot (1962). Upon applying a step change in stress to samples containing mesoscopic-scale heterogeneity, the poroelastic response is determined using finite difference modeling, and the average strain throughout the sample computed, along with the effective complex and frequency-dependent elastic moduli of the sample. The ratio of the imaginary and real parts of these moduli determines the attenuation as a function of frequency associated with the modes of applied stress (pure compression and pure shear). By having a wide range of heterogeneity present, there exists a wide range of relaxation frequencies in the response with the result that the curves of attenuation as a function of frequency are broader than in existing analytical theories based on a single relaxation frequency. Analytical explanations are given for the various high-frequency and low-frequency asymptotic behavior observed in the numerical simulations. It is also shown that the overall level of attenuation of a given sample is proportional to the square of the incompressibility contrasts locally present.

The interaction of fatigue cracks with a residual stress field using thermoelastic stress analysis and synchrotron X-ray diffraction experiments

PubMed Central

Amjad, Khurram; Asquith, David; Sebastian, Christopher M.; Wang, Wei-Chung

2017-01-01

This article presents an experimental study on the fatigue behaviour of cracks emanating from cold-expanded holes utilizing thermoelastic stress analysis (TSA) and synchrotron X-ray diffraction (SXRD) techniques with the aim of resolving the long-standing ambiguity in the literature regarding potential relaxation, or modification, of beneficial compressive residual stresses as a result of fatigue crack propagation. The crack growth rates are found to be substantially lower as the crack tip moved through the residual stress zone induced by cold expansion. The TSA results demonstrated that the crack tip plastic zones were reduced in size by the presence of the residual compressive stresses induced by cold expansion. The crack tip plastic zones were found to be insignificant in size in comparison to the residual stress zone resulting from cold expansion, which implied that they were unlikely to have had a notable impact on the surrounding residual stresses induced by cold expansion. The residual stress distributions measured along the direction of crack growth, using SXRD, showed no signs of any significant stress relaxation or redistribution, which validates the conclusions drawn from the TSA data. Fractographic analysis qualitatively confirmed the influence on crack initiation of the residual stresses induced by the cold expansion. It was found that the application of single compressive overload caused a relaxation, or reduction in the residual stresses, which has wider implications for improving the fatigue life. PMID:29291095

The effects of equal caloric high fat and western diet on metabolic syndrome, oxidative stress and vascular endothelial function in mice.

PubMed

Heinonen, I; Rinne, P; Ruohonen, S T; Ruohonen, S; Ahotupa, M; Savontaus, E

2014-07-01

Nutrition contributes to increased adiposity, but it remains to be determined whether high fat rather than Western diet exacerbates the development of obesity and other characteristics of metabolic syndrome and vascular function. We studied the effects of high fat (45% kcal) diet (HFD) and equal caloric Western diet (WD) high in fat, sucrose and cholesterol for 8 weeks in male C57B1/6N mice. Mice fed with HFD and WD showed substantially higher body adiposity (body fat %) compared with control mice receiving low fat (10%) diet (LFD). However, total body weight was higher only in HFD mice compared with other groups. The amount of liver triglycerides, cholesterol and oxidative damage was higher in WD mice compared with mice on LFD. There were no significant differences in fasting blood glucose or serum insulin, serum or muscle triglycerides, glucose tolerance or systolic blood pressure between the groups, but serum free fatty acids were increased in HFD mice compared with LFD. Increased levels of tissue and serum diene conjugation as a marker of oxidative stress were evident especially in WD mice. The endothelium-dependent relaxations were significantly impaired in the small mesenteric arteries of HFD mice, but not in the aorta. Maximal relaxations correlated negatively with body adiposity in WD but not in HFD mice. The major finding in the present study is that without changing body weight, Western diet induces marked whole-body oxidative stress and elevates body adiposity, which associates with the endothelial function of resistance arteries. © 2014 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.

A comparison the effects of reflexology and relaxation on the psychological symptoms in women with multiple sclerosis

PubMed Central

Soheili, Mozhgan; Nazari, Fatemeh; Shaygannejad, Vahid; Valiani, Mahboobeh

2017-01-01

Background: Multiple sclerosis (MS) occurs with a variety of physical and psychological symptoms, yet there is not a conclusive cure for this disease. Complementary medicine is a current treatment which seems is effective in relieving symptoms of patients with MS. Therefore, this study is aimed to determine and compare the effects of reflexology and relaxation on anxiety, stress, and depression in women with MS. Subjects and Methods: This study is a randomized clinical trial that is done on 75 women with MS referred to MS Clinic of Kashani Hospital. After simple non random sampling, participants were randomly assigned by minimization method to three groups: reflexology, relaxation and control (25 patients in each group). In the experimental groups were performed reflexology and relaxation interventions within 4 weeks, twice a week for 40 min and the control group were received only routine treatment as directed by a doctor. Data were collected through depression anxiety and stress scale questionnaire, before, immediately after and 2 months after interventions in all three groups. Chi-square, Kruskal–Wallis, repeated measures analysis of variance and one-way analysis of variance and least significant difference post hoc test via SPSS version 18 were used to analyze the data (P < 0.05) was considered as significant level. Results: The results showed a significant reduction in the severity of anxiety, stress and depression during the different times in the reflexology and relaxation groups as compared with the control group (P < 0.05). Conclusion: The results showed that reflexology and relaxation in relieving anxiety, stress and depression are effective in women with MS. Hence, these two methods, as effective techniques, can be recommended. PMID:28546976

A comparison the effects of reflexology and relaxation on the psychological symptoms in women with multiple sclerosis.

PubMed

Soheili, Mozhgan; Nazari, Fatemeh; Shaygannejad, Vahid; Valiani, Mahboobeh

2017-01-01

Multiple sclerosis (MS) occurs with a variety of physical and psychological symptoms, yet there is not a conclusive cure for this disease. Complementary medicine is a current treatment which seems is effective in relieving symptoms of patients with MS. Therefore, this study is aimed to determine and compare the effects of reflexology and relaxation on anxiety, stress, and depression in women with MS. This study is a randomized clinical trial that is done on 75 women with MS referred to MS Clinic of Kashani Hospital. After simple non random sampling, participants were randomly assigned by minimization method to three groups: reflexology, relaxation and control (25 patients in each group). In the experimental groups were performed reflexology and relaxation interventions within 4 weeks, twice a week for 40 min and the control group were received only routine treatment as directed by a doctor. Data were collected through depression anxiety and stress scale questionnaire, before, immediately after and 2 months after interventions in all three groups. Chi-square, Kruskal-Wallis, repeated measures analysis of variance and one-way analysis of variance and least significant difference post hoc test via SPSS version 18 were used to analyze the data ( P < 0.05) was considered as significant level. The results showed a significant reduction in the severity of anxiety, stress and depression during the different times in the reflexology and relaxation groups as compared with the control group ( P < 0.05). The results showed that reflexology and relaxation in relieving anxiety, stress and depression are effective in women with MS. Hence, these two methods, as effective techniques, can be recommended.

Misfit stress relaxation in composite core-shell nanowires with parallelepiped cores using rectangular prismatic dislocation loops

NASA Astrophysics Data System (ADS)

Krasnitckii, S. A.; Kolomoetc, D. R.; Smirnov, A. M.; Gutkin, M. Yu

2018-03-01

The misfit stress relaxation via generation of rectangular prismatic dislocation loops at the interface in core-shell nanowires is considered. The core has the shape of a long parallelepiped of a square cross-section. The energy change caused by loop generation in such nanowires is calculated. Critical conditions for the onset of such loops are calculated and analyzed.

Searching for Affective and Cognitive Restoration: Examining the Restorative Effects of Casual Video Game Play.

PubMed

Rupp, Michael A; Sweetman, Richard; Sosa, Alejandra E; Smither, Janan A; McConnell, Daniel S

2017-11-01

We investigated the effects of a passive break, relaxation activity, and casual video game on affect, stress, engagement, and cognitive performance. Reducing stress and improving cognitive performance is critical across many domains. Previous studies investigated taking a break, relaxation techniques, or playing a game; however, these methods have not been compared within a single experiment. Participants completed a baseline affective and cognitive assessment (ACA), which included the Positive and Negative Affect Schedule, shortened version of the Dundee Stress State Questionnaire, and backward digit-span. Next, participants completed a vigilance task, followed by another ACA. Participants were then assigned at random to complete a break or relaxation activity or play a casual video game, followed by a final ACA. Participants who played the casual video game exhibited greater engagement and affective restoration than the relaxation condition. The break condition slightly decreased affect and prevented cognitive restoration. Playing a casual video game even briefly can restore individuals' affective abilities, making it a suitable activity to restore mood in response to stress. However, future research is needed to find activities capable of cognitive restoration. Many activities in life require sustained cognitive demand, which are stressful and decrease performance, especially for workers in performance-critical domains. Our research suggests some leisure activities are better than others for restoring fatigued affective processes.

Snack and Relax®: A Strategy to Address Nurses' Professional Quality of Life.

PubMed

Markwell, Perpetua; Polivka, Barbara J; Morris, Katrina; Ryan, Carol; Taylor, Annetra

2016-03-01

Snack and Relax® (S&R), a program providing healthy snacks and holistic relaxation modalities to hospital employees, was evaluated for immediate impact. A cross-sectional survey was then conducted to assess the professional quality of life (ProQOL) in registered nurses (RNs); compare S&R participants/nonparticipants on compassion satisfaction (CS), burnout, and secondary traumatic stress (STS); and identify situations in which RNs experienced compassion fatigue or burnout and the strategies used to address these situations. Pre- and post vital signs and self-reported stress were obtained from S&R attendees (N = 210). RNs completed the ProQOL Scale measuring CS, burnout, and STS (N = 158). Significant decreases in self-reported stress, respirations, and heart rate were found immediately after S&R. Low CS was noted in 28.5% of participants, 25.3% had high burnout, and 23.4% had high STS. S&R participants and nonparticipants did not differ on any of the ProQOL scales. Situations in which participants experienced compassion fatigue/burnout were categorized as patient-related, work-related, and personal/family-related. Strategies to address these situations were holistic and stress reducing. Providing holistic interventions such as S&R for nurses in the workplace may alleviate immediate feelings of stress and provide a moment of relaxation in the workday. © The Author(s) 2015.

Relaxation Response Induces Temporal Transcriptome Changes in Energy Metabolism, Insulin Secretion and Inflammatory Pathways

PubMed Central

Joseph, Marie G.; Denninger, John W.; Fricchione, Gregory L.; Benson, Herbert; Libermann, Towia A.

2013-01-01

The relaxation response (RR) is the counterpart of the stress response. Millennia-old practices evoking the RR include meditation, yoga and repetitive prayer. Although RR elicitation is an effective therapeutic intervention that counteracts the adverse clinical effects of stress in disorders including hypertension, anxiety, insomnia and aging, the underlying molecular mechanisms that explain these clinical benefits remain undetermined. To assess rapid time-dependent (temporal) genomic changes during one session of RR practice among healthy practitioners with years of RR practice and also in novices before and after 8 weeks of RR training, we measured the transcriptome in peripheral blood prior to, immediately after, and 15 minutes after listening to an RR-eliciting or a health education CD. Both short-term and long-term practitioners evoked significant temporal gene expression changes with greater significance in the latter as compared to novices. RR practice enhanced expression of genes associated with energy metabolism, mitochondrial function, insulin secretion and telomere maintenance, and reduced expression of genes linked to inflammatory response and stress-related pathways. Interactive network analyses of RR-affected pathways identified mitochondrial ATP synthase and insulin (INS) as top upregulated critical molecules (focus hubs) and NF-κB pathway genes as top downregulated focus hubs. Our results for the first time indicate that RR elicitation, particularly after long-term practice, may evoke its downstream health benefits by improving mitochondrial energy production and utilization and thus promoting mitochondrial resiliency through upregulation of ATPase and insulin function. Mitochondrial resiliency might also be promoted by RR-induced downregulation of NF-κB-associated upstream and downstream targets that mitigates stress. PMID:23650531

A Reynolds stress model for near-wall turbulence

NASA Technical Reports Server (NTRS)

Durbin, P. A.

1993-01-01

The paper formulates a tensorially consistent near-wall second-order closure model. Redistributive terms in the Reynolds stress equations are modeled by an elliptic relaxation equation in order to represent strongly nonhomogeneous effects produced by the presence of walls; this replaces the quasi-homogeneous algebraic models that are usually employed, and avoids the need for ad hoc damping functions. The model is solved for channel flow and boundary layers with zero and adverse pressure gradients. Good predictions of Reynolds stress components, mean flow, skin friction, and displacement thickness are obtained in various comparisons to experimental and direct numerical simulation data. The model is also applied to a boundary layer flowing along a wall with a 90-deg, constant-radius, convex bend.

Analysis of the tensile stress-strain behavior of elastomers at constant strain rates. I - Criteria for separability of the time and strain effects

NASA Technical Reports Server (NTRS)

Hong, S. D.; Fedors, R. F.; Schwarzl, F.; Moacanin, J.; Landel, R. F.

1981-01-01

A theoretical analysis of the tensile stress-strain relation of elastomers at constant strain rate is presented which shows that the time and the stress effect are separable if the experimental time scale coincides with a segment of the relaxation modulus that can be described by a single power law. It is also shown that time-strain separability is valid if the strain function is linearly proportional to the Cauchy strain, and that when time-strain separability holds, two strain-dependent quantities can be obtained experimentally. In the case where time and strain effect are not separable, superposition can be achieved only by using temperature and strain-dependent shift factors.

A fast quadrature-based numerical method for the continuous spectrum biphasic poroviscoelastic model of articular cartilage.

PubMed

Stuebner, Michael; Haider, Mansoor A

2010-06-18

A new and efficient method for numerical solution of the continuous spectrum biphasic poroviscoelastic (BPVE) model of articular cartilage is presented. Development of the method is based on a composite Gauss-Legendre quadrature approximation of the continuous spectrum relaxation function that leads to an exponential series representation. The separability property of the exponential terms in the series is exploited to develop a numerical scheme that can be reduced to an update rule requiring retention of the strain history at only the previous time step. The cost of the resulting temporal discretization scheme is O(N) for N time steps. Application and calibration of the method is illustrated in the context of a finite difference solution of the one-dimensional confined compression BPVE stress-relaxation problem. Accuracy of the numerical method is demonstrated by comparison to a theoretical Laplace transform solution for a range of viscoelastic relaxation times that are representative of articular cartilage. Copyright (c) 2010 Elsevier Ltd. All rights reserved.

Elliptic Relaxation of a Tensor Representation for the Redistribution Terms in a Reynolds Stress Turbulence Model

NASA Technical Reports Server (NTRS)

Carlson, J. R.; Gatski, T. B.

2002-01-01

A formulation to include the effects of wall proximity in a second-moment closure model that utilizes a tensor representation for the redistribution terms in the Reynolds stress equations is presented. The wall-proximity effects are modeled through an elliptic relaxation process of the tensor expansion coefficients that properly accounts for both correlation length and time scales as the wall is approached. Direct numerical simulation data and Reynolds stress solutions using a full differential approach are compared for the case of fully developed channel flow.

Mechanism of laser-induced stress relaxation in cartilage

NASA Astrophysics Data System (ADS)

Sobol, Emil N.; Sviridov, Alexander P.; Omelchenko, Alexander I.; Bagratashvili, Victor N.; Bagratashvili, Nodar V.; Popov, Vladimir K.

1997-06-01

The paper presents theoretical and experimental results allowing to discuss and understand the mechanism of stress relaxation and reshaping of cartilage under laser radiation. A carbon dioxide and a Holmium laser was used for treatment of rabbits and human cartilage. We measured temperature, stress, amplitude of oscillation by free and forced vibration, internal friction, and light scattering in the course of laser irradiation. Using experimental data and theoretical modeling of heat and mass transfer in cartilaginous tissue we estimated the values of transformation heat, diffusion coefficients and energy activation for water movement.

The neurological basis of occupation.

PubMed

Gutman, Sharon A; Schindler, Victoria P

2007-01-01

The purpose of the present paper was to survey the literature about the neurological basis of human activity and its relationship to occupation and health. Activities related to neurological function were organized into three categories: those that activate the brain's reward system; those that promote the relaxation response; and those that preserve cognitive function into old age. The results from the literature review correlating neurological evidence and activities showed that purposeful and meaningful activities could counter the effects of stress-related diseases and reduce the risk for dementia. Specifically, it was found that music, drawing, meditation, reading, arts and crafts, and home repairs, for example, can stimulate the neurogical system and enhance health and well-being, Prospective research studies are needed to examine the effects of purposeful activities on reducing stress and slowing the rate of cognitive decline.

Psychological Treatment

MedlinePlus

... Print Jump to Topic Psychological Treatments Understanding Stress Cognitive Behavioral Therapy Relaxation Techniques for IBS The cause of irritable ... used to treat IBS include psychotherapy (dynamic and cognitive-behavioral therapy ), relaxation ... and biofeedback therapy . Psychological treatments ...

Relaxation techniques for stress

MedlinePlus

... of your body. These sensors measure your skin temperature, brain waves, breathing, and muscle activity. You can ... more about any of these techniques through local classes, books, videos, or online. Alternative Names Relaxation response ...

Fundamental studies of stress distributions and stress relaxation in oxide scales on high temperature alloys. [Final progress report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shores, D.A.; Stout, J.H.; Gerberich, W.W.

1993-06-01

This report summarizes a three-year study of stresses arising in the oxide scale and underlying metal during high temperature oxidation and of scale cracking. In-situ XRD was developed to measure strains during oxidation over 1000{degrees}C on pure metals. Acoustic emission was used to observe scale fracture during isothermal oxidation and cooling, and statistical analysis was used to infer mechanical aspects of cracking. A microscratch technique was used to measure the fracture toughness of scale/metal interface. A theoretical model was evaluated for the development and relaxation of stresses in scale and metal substrate during oxidation.

Estimation of limit strains in disk-type flywheels made of a compliant elastomeric matrix composite undergoing radial creep

NASA Astrophysics Data System (ADS)

Portnov, G. G.; Bakis, Ch. E.

2000-01-01

Fiber reinforced elastomeric matrix composites (EMCs) offer several potential advantages for construction of rotors for flywheel energy storage systems. One potential advantage, for safety considerations, is the existence of maximum stresses near the outside radius of thick circumferentially wound EMC disks, which could lead to a desirable self-arresting failure mode at ultimate speeds. Certain unidirectionally reinforced EMCs, however, have been noted to creep readily under the influence of stress transverse to the fibers. In this paper, stress redistribution in a spinning thick disk made of a circumferentially filament wound EMC material on a small rigid hub has been analyzed with the assumption of total radial stress relaxation due to radial creep. It is shown that, following complete relaxation, the circumferential strains and stresses are maximized at the outside radius of the disk. Importantly, the radial tensile strains are three times greater than the circumferential strains at any given radius. Therefore, a unidirectional EMC material system that can safely endure transverse tensile creep strains of at least three times the elastic longitudinal strain capacity of the same material is likely to maintain the theoretically safe failure mode despite complete radial stress relaxation.

Time and temperature dependent modulus of pyrrone and polyimide moldings

NASA Technical Reports Server (NTRS)

Lander, L. L.

1972-01-01

A method is presented by which the modulus obtained from a stress relaxation test can be used to estimate the modulus which would be obtained from a sonic vibration test. The method was applied to stress relaxation, sonic vibration, and high speed stress-strain data which was obtained on a flexible epoxy. The modulus as measured by the three test methods was identical for identical test times, and a change of test temperature was equivalent to a shift in the logarithmic time scale. An estimate was then made of the dynamic modulus of moldings of two Pyrrones and two polyimides, using stress relaxation data and the method of analysis which was developed for the epoxy. Over the common temperature range (350 to 500 K) in which data from both types of tests were available, the estimated dynamic modulus value differed by only a few percent from the measured value. As a result, it is concluded that, over the 500 to 700 K temperature range, the estimated dynamic modulus values are accurate.

Time-Dependent Mechanical Response of APbX 3 (A = Cs, CH 3NH 3; X = I, Br) Single Crystals [The Dynamic Mechanical Properties of Lead-Halide Perovskite Single Crystals are Independent of A-site Cation Chemistry

DOE PAGES

Reyes-Martinez, Marcos A.; Abdelhady, Ahmed L.; Saidaminov, Makhsud I.; ...

2017-05-02

The ease of processing hybrid organic–inorganic perovskite (HOIPs) films, belonging to a material class with composition ABX 3, from solution and at mild temperatures promises their use in deformable technologies, including flexible photovoltaic devices, sensors, and displays. To successfully apply these materials in deformable devices, knowledge of their mechanical response to dynamic strain is necessary. The authors elucidate the time- and rate-dependent mechanical properties of HOIPs and an inorganic perovskite (IP) single crystal by measuring nanoindentation creep and stress relaxation. The observation of pop-in events and slip bands on the surface of the indented crystals demonstrate dislocation-mediated plastic deformation. Themore » magnitudes of creep and relaxation of both HOIPs and IPs are similar, negating prior hypothesis that the presence of organic A-site cations alters the mechanical response of these materials. Moreover, these samples exhibit a pronounced increase in creep, and stress relaxation as a function of indentation rate whose magnitudes reflect differences in the rates of nucleation and propagation of dislocations within the crystal structures of HOIPs and IP. In conclusion, this contribution provides understanding that is critical for designing perovskite devices capable of withstanding mechanical deformations.« less

In situ stress observation in oxide films and how tensile stress influences oxygen ion conduction

PubMed Central

Fluri, Aline; Pergolesi, Daniele; Roddatis, Vladimir; Wokaun, Alexander; Lippert, Thomas

2016-01-01

Many properties of materials can be changed by varying the interatomic distances in the crystal lattice by applying stress. Ideal model systems for investigations are heteroepitaxial thin films where lattice distortions can be induced by the crystallographic mismatch with the substrate. Here we describe an in situ simultaneous diagnostic of growth mode and stress during pulsed laser deposition of oxide thin films. The stress state and evolution up to the relaxation onset are monitored during the growth of oxygen ion conducting Ce0.85Sm0.15O2-δ thin films via optical wafer curvature measurements. Increasing tensile stress lowers the activation energy for charge transport and a thorough characterization of stress and morphology allows quantifying this effect using samples with the conductive properties of single crystals. The combined in situ application of optical deflectometry and electron diffraction provides an invaluable tool for strain engineering in Materials Science to fabricate novel devices with intriguing functionalities. PMID:26912416

Three-dimensional wave field modeling by a collocated-grid finite-difference method in the anelastic model with surface topography

NASA Astrophysics Data System (ADS)

Wang, N.; Li, J.; Borisov, D.; Gharti, H. N.; Shen, Y.; Zhang, W.; Savage, B. K.

2016-12-01

We incorporate 3D anelastic attenuation into the collocated-grid finite-difference method on curvilinear grids (Zhang et al., 2012), using the rheological model of the generalized Maxwell body (Emmerich and Korn, 1987; Moczo and Kristek, 2005; Käser et al., 2007). We follow a conventional procedure to calculate the anelastic coefficients (Emmerich and Korn, 1987) determined by the Q(ω)-law, with a modification in the choice of frequency band and thus the relaxation frequencies that equidistantly cover the logarithmic frequency range. We show that such an optimization of anelastic coefficients is more accurate when using a fixed number of relaxation mechanisms to fit the frequency independent Q-factors. We use curvilinear grids to represent the surface topography. The velocity-stress form of the 3D isotropic anelastic wave equation is solved with a collocated-grid finite-difference method. Compared with the elastic case, we need to solve additional material-independent anelastic functions (Kristek and Moczo, 2003) for the mechanisms at each relaxation frequency. Based on the stress-strain relation, we calculate the spatial partial derivatives of the anelastic functions indirectly thereby saving computational storage and improving computational efficiency. The complex-frequency-shifted perfectly matched layer (CFS-PML) is used for the absorbing boundary condition based on the auxiliary difference equation (Zhang and Shen, 2010). The traction image method (Zhang and Chen, 2006) is employed for the free-surface boundary condition. We perform several numerical experiments including homogeneous full-space models and layered half-space models, considering both flat and 3D Gaussian-shape hill surfaces. The results match very well with those of the spectral-element method (Komatitisch and Tromp, 2002; Savage et al., 2010), verifying the simulations by our method in the anelastic model with surface topography.

Environmental design, work, and well being: managing occupational stress through changes in the workplace environment.

PubMed

Heerwagen, J H; Heubach, J G; Montgomery, J; Weimer, W C

1995-09-01

The physical environment can be an important contributor to occupational stress. Factors that contribute to stress and other negative outcomes include: lack of control over the environment, distractions from coworkers, lack of privacy, noise, crowding, and environmental deprivations (such as lack of windows and aesthetic impoverishment). The design of "salutogenic" environments requires not only the elimination of negative stress inducing features, but also the addition of environmental enhancements, including such factors as increased personal control, contact with nature and daylight, aesthetically pleasing spaces, and spaces for relaxation alone or with others. Salutogenic environments also take into consideration positive psychosocial "fit," as well as functional fit between people and environments. At the heart of the current interest in the work environment are two major concerns: organizational productivity and employee well being.

New Variational Formulations of Hybrid Stress Elements

NASA Technical Reports Server (NTRS)

Pian, T. H. H.; Sumihara, K.; Kang, D.

1984-01-01

In the variational formulations of finite elements by the Hu-Washizu and Hellinger-Reissner principles the stress equilibrium condition is maintained by the inclusion of internal displacements which function as the Lagrange multipliers for the constraints. These versions permit the use of natural coordinates and the relaxation of the equilibrium conditions and render considerable improvements in the assumed stress hybrid elements. These include the derivation of invariant hybrid elements which possess the ideal qualities such as minimum sensitivity to geometric distortions, minimum number of independent stress parameters, rank sufficient, and ability to represent constant strain states and bending moments. Another application is the formulation of semiLoof thin shell elements which can yield excellent results for many severe test cases because the rigid body nodes, the momentless membrane strains, and the inextensional bending modes are all represented.

Using Dielectric Relaxation Spectroscopy to Characterize the Glass Transition Time of Polydextrose.

PubMed

Buehler, Martin G; Kindle, Michael L; Carter, Brady P

2015-06-01

Dielectric relaxation spectroscopy was used to characterize the glass transition time, tg , of polydextrose, where the glass transition temperature, Tg , and water activity, aw (relative humidity), were held constant during polydextrose relaxation. The tg was determined from a shift in the peak frequency of the imaginary capacitance spectrum with time. It was found that when the peak frequency reaches 30 mHz, polydextrose undergoes glass transition. Glass transition time, tg , is the time for polydextrose to undergo glass transition at a specific Tg and aw . Results lead to a modified state diagram, where Tg is depressed with increasing aw . This curve forms a boundary: (a) below the boundary, polydextrose does not undergo glass transition and (b) above the boundary, polydextrose rapidly undergoes glass transition. As the boundary curve is specified by a tg value, it can assist in the selection of storage conditions. An important point on the boundary curve is at aw = 0, where Tg0 = 115 °C. The methodology can also be used to calculate the stress-relaxation viscosity of polydextrose as a function of Tg and aw , which is important when characterizing the flow properties of polydextrose initially in powder form. © 2015 Institute of Food Technologists®

Intensification of the Process of Flame Combustion of a Pulverized Coal Fuel

NASA Astrophysics Data System (ADS)

Popov, V. I.

2017-11-01

Consideration is given to a method of mechanoactivation intensification of the flame combustion of a pulverized coal fuel through the formation of a stressed state for the microstructure of its particles; the method is based on the use of the regularities of their external (diffusion) and internal (relaxation) kinetics. A study has been made of mechanoactivation nonequilibrium processes that occur in fuel particles during the induced relaxation of their stressed state with a resumed mobility of the microstructure of the particles and intensify diffusion-controlled chemical reactions in them under the assumption that the time of these reactions is much shorter than the times of mechanical action on a particle and of stress relaxation in it. The influence of the diffusion and relaxation factors on the burnup time of a fuel particle and on the flame distance has been analyzed. Ranges of variation in the parameters of flame combustion have been singled out in which the flame distance is determined by the mechanisms of combustion of the fuel and of mixing of combustion products.

The development and validation of a numerical integration method for non-linear viscoelastic modeling

PubMed Central

Ramo, Nicole L.; Puttlitz, Christian M.

2018-01-01

Compelling evidence that many biological soft tissues display both strain- and time-dependent behavior has led to the development of fully non-linear viscoelastic modeling techniques to represent the tissue’s mechanical response under dynamic conditions. Since the current stress state of a viscoelastic material is dependent on all previous loading events, numerical analyses are complicated by the requirement of computing and storing the stress at each step throughout the load history. This requirement quickly becomes computationally expensive, and in some cases intractable, for finite element models. Therefore, we have developed a strain-dependent numerical integration approach for capturing non-linear viscoelasticity that enables calculation of the current stress from a strain-dependent history state variable stored from the preceding time step only, which improves both fitting efficiency and computational tractability. This methodology was validated based on its ability to recover non-linear viscoelastic coefficients from simulated stress-relaxation (six strain levels) and dynamic cyclic (three frequencies) experimental stress-strain data. The model successfully fit each data set with average errors in recovered coefficients of 0.3% for stress-relaxation fits and 0.1% for cyclic. The results support the use of the presented methodology to develop linear or non-linear viscoelastic models from stress-relaxation or cyclic experimental data of biological soft tissues. PMID:29293558

Noise and Stress in Primary and Secondary School Children: Noise Reduction and Increased Concentration Ability through a Short but Regular Exercise and Relaxation Program

ERIC Educational Resources Information Center

Norlander, Torsten; Moas, Leif; Archer, Trevor

2005-01-01

The present study examined whether a short but regularly used program of relaxation, applied to Primary and Secondary school children, could (a) reduce noise levels (in decibels), (b) reduce pupils' experienced stress levels, and (c) increase the pupils' ability to concentrate, as measured by teachers' estimates. Noise levels in 5 classrooms (84…

β-distribution for Reynolds stress and turbulent heat flux in relaxation turbulent boundary layer of compression ramp

NASA Astrophysics Data System (ADS)

Hu, YanChao; Bi, WeiTao; Li, ShiYao; She, ZhenSu

2017-12-01

A challenge in the study of turbulent boundary layers (TBLs) is to understand the non-equilibrium relaxation process after sep-aration and reattachment due to shock-wave/boundary-layer interaction. The classical boundary layer theory cannot deal with the strong adverse pressure gradient, and hence, the computational modeling of this process remains inaccurate. Here, we report the direct numerical simulation results of the relaxation TBL behind a compression ramp, which reveal the presence of intense large-scale eddies, with significantly enhanced Reynolds stress and turbulent heat flux. A crucial finding is that the wall-normal profiles of the excess Reynolds stress and turbulent heat flux obey a β-distribution, which is a product of two power laws with respect to the wall-normal distances from the wall and from the boundary layer edge. In addition, the streamwise decays of the excess Reynolds stress and turbulent heat flux also exhibit power laws with respect to the streamwise distance from the corner of the compression ramp. These results suggest that the relaxation TBL obeys the dilation symmetry, which is a specific form of self-organization in this complex non-equilibrium flow. The β-distribution yields important hints for the development of a turbulence model.

Using 20-million-year-old amber to test the super-Arrhenius behaviour of glass-forming systems.

PubMed

Zhao, Jing; Simon, Sindee L; McKenna, Gregory B

2013-01-01

Fossil amber offers the opportunity to investigate the dynamics of glass-forming materials far below the nominal glass transition temperature. This is important in the context of classical theory, as well as some new theories that challenge the idea of an 'ideal' glass transition. Here we report results from calorimetric and stress relaxation experiments using a 20-million-year-old Dominican amber. By performing the stress relaxation experiments in a step-wise fashion, we measured the relaxation time at each temperature and, above the fictive temperature of this 20-million-year-old glass, this is an upper bound to the equilibrium relaxation time. The results deviate dramatically from the expectation of classical theory and are consistent with some modern ideas, in which the diverging timescale signature of complex fluids disappears below the glass transition temperature.

Oxidation stress evolution and relaxation of oxide film/metal substrate system

NASA Astrophysics Data System (ADS)

Dong, Xuelin; Feng, Xue; Hwang, Keh-Chih

2012-07-01

Stresses in the oxide film/metal substrate system are crucial to the reliability of the system at high temperature. Two models for predicting the stress evolution during isothermal oxidation are proposed. The deformation of the system is depicted by the curvature for single surface oxidation. The creep strain of the oxide and metal, and the lateral growth strain of the oxide are considered. The proposed models are compared with the experimental results in literature, which demonstrates that the elastic model only considering for elastic strain gives an overestimated stress in magnitude, but the creep model is consistent with the experimental data and captures the stress relaxation phenomenon during oxidation. The effects of the parameter for the lateral growth strain rate are also analyzed.

Dynamics of Bottlebrush Networks

NASA Astrophysics Data System (ADS)

Cao, Zhen; Daniel, William; Vatankhah-Varnosfaderani, Mohammad; Sheiko, Sergei; Dobrynin, Andrey

The deformation dynamics of bottlebrush networks in a melt state is studied using a combination of theoretical, computational, and experimental techniques. Three main molecular relaxation processes are identified in these systems: (i) relaxation of the side chains, (ii) relaxation of the bottlebrush backbones on length scales shorter than the bottlebrush Kuhn length (bK) , and (iii) relaxation of the bottlebrush network strands between cross-links. The relaxation of side chains having a degree of polymerization (DP), nsc, dominates the network dynamics on the time scales τ0 < t <=τsc , where τ0 and τsc τ0 (nsc + 1)2 are the characteristic relaxation times of monomeric units and side chains, respectively. In this time interval, the shear modulus at small deformations decays with time as G0BB (t) t - 1 / 2. On time scales t >τsc, bottlebrush elastomers behave as networks of filaments with a shear modulus G0BB (t) (nsc + 1)- 1 / 4t - 1 / 2 . Finally, the response of the bottlebrush networks becomes time independent at times scales longer than the Rouse time of the bottlebrush network strands. In this time interval, the network shear modulus depends on the network molecular parameters as G0BB (t) (nsc + 1)-1N-1 . Analysis of the simulation data shows that the stress evolution in the bottlebrush networks during constant strain-rate deformation can be described by a universal function. NSF DMR-1409710, DMR-1407645, DMR-1624569, DMR-1436201.

Micromachined sensor for stress measurement and micromechanical study of free-standing thin films for MEMS applications

NASA Astrophysics Data System (ADS)

Zhang, Ping

Microelectromechanical systems (MEMS) have a wide range of applications. In the field of wireless and microwave technology, considerable attention has been given to the development and integration of MEMS-based RF (radio frequency) components. An RF MEMS switch requires low insertion loss, high isolation, and low actuation voltage - electrical aspects that have been extensively studied. The mechanical requirements of the switch, such as low sensitivity to built-in stress and high reliability, greatly depend on the micromechanical properties of the switch materials, and have not been thoroughly explored. RF MEMS switches are typically in the form of a free-standing thin film structure. Large stress gradients and across-wafer stress variations developed during fabrication severely degrade their electrical performance. A micromachined stress measurement sensor has been developed that can potentially be employed for in-situ monitoring of stress evolution and stress variation. The sensors were micromachined using five masks on two wafer levels, each measuring 5x3x1 mm. They function by means of an electron tunneling mechanism, where a 2x2 mm silicon nitride membrane elastically deflects under an applied deflection voltage via an external feedback circuitry. For the current design, the sensors are capable of measuring tensile stresses up to the GPa range under deflection voltages of 50--100 V. Sensor functionality was studied by finite element modeling and a theoretical analysis of square membrane deflection. While the mechanical properties of thin films on substrates have been extensively studied, studies of free-standing thin films have been limited due to the practical difficulties in sample handling and testing. Free-standing Al and Al-Ti thin films specimens have been successfully fabricated and microtensile and stress relaxation tests have been performed using a custom-designed micromechanical testing apparatus. A dedicated TEM (transmission electron microscopy) sample preparation technique allows the investigation of the microstructures of these thin films both before and after mechanical testing to correlate the microstructural findings with the mechanical behavior. Major studies include grain boundary strengthening in pure Al, plastic deformation in pure Al by inhomogeneous deformation and localized grain thinning, solid solution and precipitate strengthening in Al-Ti alloys, and stress relaxation of Al and Al-Ti.

The role of frictional stress in misfit dislocation generation

NASA Technical Reports Server (NTRS)

Jesser, William A.

1992-01-01

An evaluation is undertaken of the implications of the friction and frictionless models of misfit dislocation generation in view of: (1) experimental measurements of the critical thickness above which misfit dislocation generation occurs; and (2) the amount of strain relaxation that occurs as a function of layer thickness, time, and temperature. Some of the frictional force terms that were expected to exhibit a strong temperature dependence are shown to be independent of temperature.

High Temperature Uniaxial Compression and Stress-Relaxation Behavior of India-Specific RAFM Steel

NASA Astrophysics Data System (ADS)

Shah, Naimish S.; Sunil, Saurav; Sarkar, Apu

2018-07-01

India-specific reduced activity ferritic martensitic steel (INRAFM), a modified 9Cr-1Mo grade, has been developed by India as its own structural material for fabrication of the Indian Test Blanket Module (TBM) to be installed in the International Thermonuclear Energy Reactor (ITER). The extensive study on mechanical and physical properties of this material has been currently going on for appraisal of this material before being put to use in the ITER. High temperature compression, stress-relaxation, and strain-rate change behavior of the INRAFM steel have been investigated. The optical microscopic and scanning electron microscopic characterizations were carried out to observe the microstructural changes that occur during uniaxial compressive deformation test. Comparable true plastic stress values at 300 °C and 500 °C and a high drop in true plastic stress at 600 °C were observed during the compression test. Stress-relaxation behaviors were investigated at 500 °C, 550 °C, and 600 °C at a strain rate of 10-3 s-1. The creep properties of the steel at different temperatures were predicted from the stress-relaxation test. The Norton's stress exponent ( n) was found to decrease with the increasing temperature. Using Bird-Mukherjee-Dorn relationship, the temperature-compensated normalized strain rate vs stress was plotted. The stress exponent ( n) value of 10.05 was obtained from the normalized plot. The increasing nature of the strain rate sensitivity ( m) with the test temperature was found from strain-rate change test. The low plastic stability with m 0.06 was observed at 600 °C. The activation volume ( V *) values were obtained in the range of 100 to 300 b3. By comparing the experimental values with the literature, the rate-controlling mechanisms at the thermally activated region of high temperature were found to be the nonconservative movement of jogged screw dislocations and thermal breaking of attractive junctions.

High Temperature Uniaxial Compression and Stress-Relaxation Behavior of India-Specific RAFM Steel

NASA Astrophysics Data System (ADS)

Shah, Naimish S.; Sunil, Saurav; Sarkar, Apu

2018-05-01

India-specific reduced activity ferritic martensitic steel (INRAFM), a modified 9Cr-1Mo grade, has been developed by India as its own structural material for fabrication of the Indian Test Blanket Module (TBM) to be installed in the International Thermonuclear Energy Reactor (ITER). The extensive study on mechanical and physical properties of this material has been currently going on for appraisal of this material before being put to use in the ITER. High temperature compression, stress-relaxation, and strain-rate change behavior of the INRAFM steel have been investigated. The optical microscopic and scanning electron microscopic characterizations were carried out to observe the microstructural changes that occur during uniaxial compressive deformation test. Comparable true plastic stress values at 300 °C and 500 °C and a high drop in true plastic stress at 600 °C were observed during the compression test. Stress-relaxation behaviors were investigated at 500 °C, 550 °C, and 600 °C at a strain rate of 10-3 s-1. The creep properties of the steel at different temperatures were predicted from the stress-relaxation test. The Norton's stress exponent (n) was found to decrease with the increasing temperature. Using Bird-Mukherjee-Dorn relationship, the temperature-compensated normalized strain rate vs stress was plotted. The stress exponent (n) value of 10.05 was obtained from the normalized plot. The increasing nature of the strain rate sensitivity (m) with the test temperature was found from strain-rate change test. The low plastic stability with m 0.06 was observed at 600 °C. The activation volume (V *) values were obtained in the range of 100 to 300 b3. By comparing the experimental values with the literature, the rate-controlling mechanisms at the thermally activated region of high temperature were found to be the nonconservative movement of jogged screw dislocations and thermal breaking of attractive junctions.

Effects of adrenal sensitivity, stress- and cue-induced craving, and anxiety on subsequent alcohol relapse and treatment outcomes.

PubMed

Sinha, Rajita; Fox, Helen C; Hong, Kwang-Ik Adam; Hansen, Julie; Tuit, Keri; Kreek, Mary Jeanne

2011-09-01

Alcoholism is a chronic, relapsing illness in which stress and alcohol cues contribute significantly to relapse risk. Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, increased anxiety, and high alcohol craving have been documented during early alcohol recovery, but their influence on relapse risk has not been well studied. To investigate these responses in treatment-engaged, 1-month-abstinent, recovering alcohol-dependent patients relative to matched controls (study 1) and to assess whether HPA axis function, anxiety, and craving responses are predictive of subsequent alcohol relapse and treatment outcome (study 2). Experimental exposure to stress, alcohol cues, and neutral, relaxing context to provoke alcohol craving, anxiety, and HPA axis responses (corticotropin and cortisol levels and cortisol to corticotropin ratio) and a prospective 90-day follow-up outcome design to assess alcohol relapse and aftercare treatment outcomes. Inpatient treatment in a community mental health center and hospital-based research unit. Treatment-engaged alcohol-dependent individuals and healthy controls. Time to alcohol relapse and to heavy drinking relapse. Significant HPA axis dysregulation, marked by higher basal corticotropin level and lack of stress- and cue-induced corticotropin and cortisol responses, higher anxiety, and greater stress- and cue-induced alcohol craving, was seen in the alcohol-dependent patients vs the control group. Stress- and cue-induced anxiety and stress-induced alcohol craving were associated with fewer days in aftercare alcohol treatment. High provoked alcohol craving to both stress and to cues and greater neutral, relaxed-state cortisol to corticotropin ratio (adrenal sensitivity) were each predictive of shorter time to alcohol relapse. These results identify a significant effect of high adrenal sensitivity, anxiety, and increased stress- and cue-induced alcohol craving on subsequent alcohol relapse and treatment outcomes. Findings suggest that new treatments that decrease adrenal sensitivity, stress- and cue-induced alcohol craving, and anxiety could be beneficial in improving alcohol relapse outcomes.

The relationships between residual stress relaxation and texture development in AZ31 Mg alloys via the vibratory stress relief technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jia-Siang, E-mail: andy304312003@yahoo.com.tw; Hsieh, Chih-Chun, E-mail: jeromehsieh@gmail.com; Lai, Hsuan-Han, E-mail: g099066020@mail.nchu.edu.tw

2015-01-15

A systematic study of residual stress relaxation and the texture evolution of cold-rolled AZ31 Mg alloys using the vibratory stress relief technique with a simple cantilever beam vibration system was performed using a high-resolution X-ray diffractometer and a portable X-ray residual stress analyzer. The effects of vibrational stress excitation on the surface residual stress distribution and on the texture of pole figures (0002) occurring during the vibratory stress relief were examined. Compared with the effects corresponding to the same alloy under non-vibration condition, it can be observed that the uniform surface residual stress distribution and relaxation of the compressive residualmore » stress in the stress concentration zone were observed rather than all of the residual stresses being eliminated. Furthermore, with an increase in the vibrational aging time, the compressive residual stress, texture density, and (0002) preferred orientation increased first and then decreased. It should be underlined that the vibratory stress relief process for the vibrational aging time of more than 10 min is able to weaken the strong basal textures of AZ31 Mg alloys, which is valuable for enhancement of their formability and is responsible for an almost perfect 3D-Debye–Scherrer ring. - Highlights: • 3D-Debye ring about VSR technique is not discussed in the existing literature. • A newly developed VSR method is suitable for small or thin workpieces. • The cosα method accurately and effectively determines the residual stresses. • The VSR technique is valuable for enhancement of their formability. • The texture and preferred orientation change with the vibrational aging time.« less

Effect of water content on specific heat capacity of porcine septum cartilage

NASA Astrophysics Data System (ADS)

Chae, Yongseok; Lavernia, Enrique J.; Wong, Brian J.

2002-06-01

The effect of water content on specific heat capacity was examined using temperature modulated Differential Scanning Calorimetry (TMDSC). This research was motivated in part by the development laser cartilage reshaping operations, which use photothermal heating to accelerate stress relaxation and shape change. Deposition of thermal energy leads to mechanical stress relaxation and redistribution of cartilage internal stresses, which may lead to a permanent shape change. The specific heat of cartilage specimens (dia: 3 mm and thickness 1-2 mm) was measured using a heating rate of 2 degree(s)C/min for conventional DSC and 2 degree(s)C/min with an amplitude 0.38-0.45 degree(s)C and a period 60-100 sec for TMDSC. The amount of water in cartilaginous tissue was determined using thermogravimetry analysis (TGA) under ambient conditions. In order to correlate changes in heat flow with alterations in cartilage mechanical behavior, dynamic mechanical temperature analysis (DMTA) was used to estimate the specific transition temperatures where stress relaxation occurs. With decreasing water content, we identified a phase transition that shifted to a higher temperature after 35-45% water content was measured. The phase transition energy increased from 0.12 J/g to 1.68 J/g after a 45% weight loss. This study is a preliminary investigation focused on understanding the mechanism of the stress relaxation of cartilage during heating. The energy requirement of such a transition estimated using TMDSC and temperature range, where cartilage shape changes likely occur, was estimated.

Acoustic and Seismic Dispersion in Complex Fluids and Solids

NASA Astrophysics Data System (ADS)

Goddard, Joe

2017-04-01

The first part of the present paper is the continuation of a previous work [3] on the effects of higher spatial gradients and temporal relaxation on stress and heat flux in complex fluids. In particular, the general linear theory is applied to acoustic dispersion, extending a simpler model proposed by Davis and Brenner [2]. The theory is applied to a linearized version of the Chapman-Enskog fluid [1] valid to terms of Burnett order and including Maxwell-Cataneo relaxation of stress and heat flux on relaxation time scales τ. For this model, the dispersion relation k(ω) giving spatial wave number k as function of temporal frequency ω is a cubic in k2, in contrast to the quadratic in k2 given by the classical model and the recently proposed modification [2]. The cubic terms are shown to be important only for ωτ = O(1) where Maxwell-Cataneo relaxation is also important. As a second part of the present work, it is shown how the above model can also be applied to isotropic solids, where both shear and pressure waves are important. Finally, consideration is given to hyperstress in micro- polar continua, including both graded and micro-morphic varieties. [1]S. Chapman and T. Cowling. The mathematical theory of non-uniform gases. Cambridge University Press, [Cambridge, UK], 1960. [2]A. M.J. Davis and H. Brenner. Thermal and viscous effects on sound waves: revised classical theory. J. Acoust. Soc. Am., 132(5):2963-9, 2012. [3] J.D. Goddard. On material velocities and non-locality in the thermo-mechanics of continua. Int. J. Eng. Sci., 48(11):1279-88, 2010.

Mitochondrial Cyclophilin D in Vascular Oxidative Stress and Hypertension.

PubMed

Itani, Hana A; Dikalova, Anna E; McMaster, William G; Nazarewicz, Rafal R; Bikineyeva, Alfiya T; Harrison, David G; Dikalov, Sergey I

2016-06-01

Vascular superoxide (O˙2 (-)) and inflammation contribute to hypertension. The mitochondria are an important source of O˙2 (-); however, the regulation of mitochondrial O˙2 (-) and the antihypertensive potential of targeting the mitochondria remain poorly defined. Angiotensin II and inflammatory cytokines, such as interleukin 17A and tumor necrosis factor-α (TNFα) significantly contribute to hypertension. We hypothesized that angiotensin II and cytokines co-operatively induce cyclophilin D (CypD)-dependent mitochondrial O˙2 (-) production in hypertension. We tested whether CypD inhibition attenuates endothelial oxidative stress and reduces hypertension. CypD depletion in CypD(-/-) mice prevents overproduction of mitochondrial O˙2 (-) in angiotensin II-infused mice, attenuates hypertension by 20 mm Hg, and improves vascular relaxation compared with wild-type C57Bl/6J mice. Treatment of hypertensive mice with the specific CypD inhibitor Sanglifehrin A reduces blood pressure by 28 mm Hg, inhibits production of mitochondrial O˙2 (-) by 40%, and improves vascular relaxation. Angiotensin II-induced hypertension was associated with CypD redox activation by S-glutathionylation, and expression of the mitochondria-targeted H2O2 scavenger, catalase, abolished CypD S-glutathionylation, prevented stimulation mitochondrial O˙2 (-), and attenuated hypertension. The functional role of cytokine-angiotensin II interplay was confirmed by co-operative stimulation of mitochondrial O˙2 (-) by 3-fold in cultured endothelial cells and impairment of aortic relaxation incubated with combination of angiotensin II, interleukin 17A, and tumor necrosis factor-α which was prevented by CypD depletion or expression of mitochondria-targeted SOD2 and catalase. These data support a novel role of CypD in hypertension and demonstrate that targeting CypD decreases mitochondrial O˙2 (-), improves vascular relaxation, and reduces hypertension. © 2016 American Heart Association, Inc.

Interdependency between mechanical parameters and afferent nerve discharge in remodeled diabetic Goto-Kakizaki rat intestine

PubMed Central

Zhao, Jingbo; Yang, Jian; Liao, Donghua; Gregersen, Hans

2017-01-01

Background Gastrointestinal disorders are very common in diabetic patients, but the pathogenesis is still not well understood. Peripheral afferent nerves may be involved due to the complex regulation of gastrointestinal function by the enteric nervous system. Objective We aimed to characterize the stimulus–response function of afferent fibers innervating the jejunum in the Goto-Kakizaki (GK) type 2 diabetic rat model. A key question is whether changes in afferent firing arise from remodeled tissue or from adaptive afferent processes. Design Seven 32-week-old male GK rats and seven age-matched normal Wistar rats were studied. Firing from mesenteric afferent nerves was recorded in excised jejunal segments of seven GK rats and seven normal Wistar rats during ramp test, stress relaxation test, and creep test. The circumferential stress–strain, spike rate increase ratio (SRIR), and single unit firing rates were calculated for evaluation of interdependency of the mechanical stimulations and the afferent nerve discharge. Results Elevated sensitivity to mechanical stimuli was found for diabetic nerve bundles and single unit activity (P<0.05). The stress relaxed less in the diabetic intestinal segment (P<0.05). Linear association between SRIR and the thickness of circumferential muscle layer was found at high stress levels as well as for SRIR and the glucose level. Conclusion Altered viscoelastic properties and elevated mechanosensitivity were found in the GK rat intestine. The altered nerve signaling is related to muscle layer remodeling and glucose levels and may contribute to gastrointestinal symptoms experienced by diabetic patients. PMID:29238211

A Qualitative Analysis of Stress and Relaxation Themes Contributing to Burnout in First-Year Psychiatry and Medicine Residents.

PubMed

Benson, Nicole M; Chaukos, Deanna; Vestal, Heather; Chad-Friedman, Emma F; Denninger, John W; Borba, Christina P C

2018-05-14

Qualitative research on trainee well-being can add nuance to the understanding of propagators of burnout, and the role for interventions aimed at supporting well-being. This qualitative study was conducted to identify (i) situations and environments that cause stress for trainees, (ii) stress-reducing activities that trainees utilize, and (iii) whether trainees who report distress (high burnout and depression scores) describe different stressors and relaxation factors than those who do not. The study was conducted with a convenience sample of first-year medicine and psychiatry residents at a large urban teaching hospital. Participants were asked to complete electronic stress and relaxation diaries daily for 1 week. Diary entries were coded for recurrent themes. Participants were screened for burnout and depression. Codes were compared by subgroup based on baseline burnout and depression status to elucidate if specific themes emerged in these subgroups. Study sample included 51 interns. Sixteen (16/50, 32%) screened positive for burnout and three (3/50, 14%) had a positive depression screen. The most common stressors related to aspects of the learning environment, compounded by feeling under-equipped, overwhelmed, or out of time. The majority of relaxation activities involved social connection, food, other comforts, and occurred outside of the hospital environment. This study reveals that interns (regardless of burnout or depression screen) identify stressors that derive primarily from organizational, interpersonal, and cultural experiences of the learning environment; whereas relaxation themes are diversely represented across realms (home, leisure, social, health), though emphasize activities that occur outside of the work place.

The Extensional Rheology of Non-Newtonian Materials

NASA Technical Reports Server (NTRS)

Spiegelberg, Stephen H.; McKinley, Gareth H.

1996-01-01

The evolution of the transient extensional stresses in dilute and semi-dilute viscoelastic polymer solutions are measured with a filament stretching rheometer of a design similar to that first introduced by Sridhar, et al. The solutions are polystyrene-based (PS) Boger fluids that are stretched at constant strain rates ranging from 0.6 less than or equal to epsilon(0) less than or equal to 4s(exp -1) and to Hencky strains of epsilon greater than 4. The test fluids all strain harden and Trouton ratios exceeding 1000 are obtained at high strains. The experimental data strain hardens at lower strain levels than predicted by bead-spring FENE models. In addition to measuring the transient tensile stress growth, we also monitor the decay of the tensile viscoelastic stress difference in the fluid column following cessation of uniaxial elongation as a function of the total imposed Hencky strain and the strain rate. The extensional stresses initially decay very rapidly upon cessation of uniaxial elongation followed by a slower viscoelastic relaxation, and deviate significantly from FENE relaxation predictions. The relaxation at long times t is greater than or equal to 5 s, is compromised by gravitational draining leading to non-uniform filament profiles. For the most elastic fluids, partial decohension of the fluid filament from the endplates of the rheometer is observed in tests conducted at high strain rates. This elastic instability is initiated near the rigid endplate fixtures of the device and it results in the progressive breakup of the fluid column into individual threads or 'fibrils' with a regular azimuthal spacing. These fibrils elongate and bifurcate as the fluid sample is elongated further. Flow visualization experiments using a modified stretching device show that the instability develops as a consequence of an axisymmetry-breaking meniscus instability in the nonhomogeneous region of highly deformed fluid near the rigid endplate.

Development of constitutive models for cyclic plasticity and creep behavior of super alloys at high temperature

NASA Technical Reports Server (NTRS)

Haisler, W. E.

1983-01-01

An uncoupled constitutive model for predicting the transient response of thermal and rate dependent, inelastic material behavior was developed. The uncoupled model assumes that there is a temperature below which the total strain consists essentially of elastic and rate insensitive inelastic strains only. Above this temperature, the rate dependent inelastic strain (creep) dominates. The rate insensitive inelastic strain component is modelled in an incremental form with a yield function, blow rule and hardening law. Revisions to the hardening rule permit the model to predict temperature-dependent kinematic-isotropic hardening behavior, cyclic saturation, asymmetric stress-strain response upon stress reversal, and variable Bauschinger effect. The rate dependent inelastic strain component is modelled using a rate equation in terms of back stress, drag stress and exponent n as functions of temperature and strain. A sequence of hysteresis loops and relaxation tests are utilized to define the rate dependent inelastic strain rate. Evaluation of the model has been performed by comparison with experiments involving various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy X.

Towards functionalization of graphene: in situ study of the nucleation of copper-phtalocyanine on graphene

NASA Astrophysics Data System (ADS)

Schwarz, Daniel; Henneke, Caroline; Kumpf, Christian

2016-02-01

Molecular films present an elegant way for the uniform functionalization or doping of graphene. Here, we present an in situ study on the initial growth of copper phthalocyanine (CuPc) on epitaxial graphene on Ir(111). We followed the growth up to a closed monolayer with low energy electron microscopy and selected area electron diffraction (μLEED). The molecules coexist on graphene in a disordered phase without long-range order and an ordered crystalline phase. The local topography of the graphene substrate plays an important role in the nucleation process of the crystalline phase. Graphene flakes on Ir(111) feature regions that are under more tensile stress than others. We observe that the CuPc molecules form ordered domains initially on those graphene regions that are closest to the fully relaxed lattice. We attribute this effect to a stronger influence of the underlying Ir(111) substrate for molecules adsorbed on those relaxed regions.

Differentiable McCormick relaxations

DOE PAGES

Khan, Kamil A.; Watson, Harry A. J.; Barton, Paul I.

2016-05-27

McCormick's classical relaxation technique constructs closed-form convex and concave relaxations of compositions of simple intrinsic functions. These relaxations have several properties which make them useful for lower bounding problems in global optimization: they can be evaluated automatically, accurately, and computationally inexpensively, and they converge rapidly to the relaxed function as the underlying domain is reduced in size. They may also be adapted to yield relaxations of certain implicit functions and differential equation solutions. However, McCormick's relaxations may be nonsmooth, and this nonsmoothness can create theoretical and computational obstacles when relaxations are to be deployed. This article presents a continuously differentiablemore » variant of McCormick's original relaxations in the multivariate McCormick framework of Tsoukalas and Mitsos. Gradients of the new differentiable relaxations may be computed efficiently using the standard forward or reverse modes of automatic differentiation. Furthermore, extensions to differentiable relaxations of implicit functions and solutions of parametric ordinary differential equations are discussed. A C++ implementation based on the library MC++ is described and applied to a case study in nonsmooth nonconvex optimization.« less

Tic Frequency Decreases during Short-term Psychosocial Stress - An Experimental Study on Children with Tic Disorders.

PubMed

Buse, Judith; Enghardt, Stephanie; Kirschbaum, Clemens; Ehrlich, Stefan; Roessner, Veit

2016-01-01

It has been suggested that psychosocial stress influences situational fluctuations of tic frequency. However, evidence from experimental studies is lacking. The current study investigated the effects of the Trier Social Stress Test (TSST-C) on tic frequency in 31 children and adolescents with tic disorders. A relaxation and a concentration situation served as control conditions. Patients were asked either to suppress their tics or to "tic freely." Physiological measures of stress were measured throughout the experiment. The TSST-C elicited a clear stress response with elevated levels of saliva cortisol, increased heart rate, and a larger number of skin conductance responses. During relaxation and concentration, the instruction to suppress tics reduced the number of tics, whereas during stress, the number of tics was low, regardless of the given instruction. Our study suggests that the stress might result in a situational decrease of tic frequency.

Tic Frequency Decreases during Short-term Psychosocial Stress – An Experimental Study on Children with Tic Disorders

PubMed Central

Buse, Judith; Enghardt, Stephanie; Kirschbaum, Clemens; Ehrlich, Stefan; Roessner, Veit

2016-01-01

It has been suggested that psychosocial stress influences situational fluctuations of tic frequency. However, evidence from experimental studies is lacking. The current study investigated the effects of the Trier Social Stress Test (TSST-C) on tic frequency in 31 children and adolescents with tic disorders. A relaxation and a concentration situation served as control conditions. Patients were asked either to suppress their tics or to “tic freely.” Physiological measures of stress were measured throughout the experiment. The TSST-C elicited a clear stress response with elevated levels of saliva cortisol, increased heart rate, and a larger number of skin conductance responses. During relaxation and concentration, the instruction to suppress tics reduced the number of tics, whereas during stress, the number of tics was low, regardless of the given instruction. Our study suggests that the stress might result in a situational decrease of tic frequency. PMID:27242554

Theoretical calculations of oxygen relaxation in YBa2Cu3O6+x ceramics

NASA Astrophysics Data System (ADS)

Mi, Y.; Schaller, R.; Sathish, S.; Benoit, W.

1991-12-01

A two-dimensional theoretical model of stress-induced point-defect relaxation in a layered structure is presented, with a detailed discussion of the special case of YBa2Cu3O6+x. The experimental results of oxygen relaxation in YBa2Cu3O6+x can be explained qualitatively by this model.

Extended MHD modeling of tearing-driven magnetic relaxation

NASA Astrophysics Data System (ADS)

Sauppe, J. P.; Sovinec, C. R.

2017-05-01

Discrete relaxation events in reversed-field pinch relevant configurations are investigated numerically with nonlinear extended magnetohydrodynamic (MHD) modeling, including the Hall term in Ohm's law and first-order ion finite Larmor radius effects. Results show variability among relaxation events, where the Hall dynamo effect may help or impede the MHD dynamo effect in relaxing the parallel current density profile. The competitive behavior arises from multi-helicity conditions where the dominant magnetic fluctuation is relatively small. The resulting changes in parallel current density and parallel flow are aligned in the core, consistent with experimental observations. The analysis of simulation results also confirms that the force density from fluctuation-induced Reynolds stress arises subsequent to the drive from the fluctuation-induced Lorentz force density. Transport of the momentum density is found to be dominated by the fluctuation-induced Maxwell stress over most of the cross section with viscous and gyroviscous contributions being large in the edge region. The findings resolve a discrepancy with respect to the relative orientation of current density and flow relaxation, which had not been realized or investigated in King et al. [Phys. Plasmas 19, 055905 (2012)], where only the magnitude of flow relaxation is actually consistent with experimental results.

Earthquake sequence simulations of a fault in a viscoelastic material with a spectral boundary integral equation method: The effect of interseismic stress relaxation on a behavior of a rate-weakening patch

NASA Astrophysics Data System (ADS)

Miyake, Y.; Noda, H.

2017-12-01

Earthquake sequences involve many processes in a wide range of time scales, from quasistatic loading to dynamic rupture. At a depth of brittle-plastic transitional and deeper, rock behaves as a viscous fluid in a long timescale, but as an elastic material in a short timescale. Viscoelastic stress relaxation may be important in the interseismic periods at the depth, near the deeper limit of the seismogenic layer or the region of slow slip events (SSEs) [Namiki et al., 2014 and references therein]. In the present study, we implemented the viscoelastic effect (Maxwell material) in fully-dynamic earthquake sequence simulations using a spectral boundary integral equation method (SBIEM) [e.g., Lapusta et al., 2000]. SBIEM is efficient in calculation of convolutional terms for dynamic stress transfer, and the problem size is limited by the amount of memory available. Linear viscoelasticity could be implemented by convolution of slip rate history and Green's function, but this method requires additional memory and thus not suitable for the implementation to the present code. Instead, we integrated the evolution of "effective slip" distribution, which gives static stress distribution when convolved with static elastic Green's function. This method works only for simple viscoelastic property distributions, but such models are suitable for numerical experiments aiming basic understanding of the system behavior because of the virtue of SBIEM, the ability of fine on-fault spatial resolution and efficient computation utilizing the fast Fourier transformation. In the present study, we examined the effect of viscoelasticity on earthquake sequences of a fault with a rate-weakening patch. A series of simulations with various relaxation time tc revealed that as decreasing tc, recurrence intervals of earthquakes increases and seismicity ultimately disappears. As long as studied, this transition to aseismic behavior is NOT associated with SSEs. In a case where the rate-weakening patch produces a series of SSEs in an elastic medium, viscoelasticity causes smaller amplitude of the SSEs or steady-state sliding, consistently with a linear stability analysis. With increasing depth, properties of both the medium and the frictional surface change. Since the former does not promote SSEs, the latter may be the key to generation of SSEs.

Effectiveness of progressive muscle relaxation therapy as a worksite health promotion program in the automobile assembly line

PubMed Central

SUNDRAM, Bala Murali; DAHLUI, Maznah; CHINNA, Karuthan

2015-01-01

The aim of this study was to examine the effectiveness of Progressive Muscle Relaxation (PMR) as part of a Worksite Health Promotion Program on self-perceived stress, anxiety and depression among male automotive assembly-line workers through a quasi-experimental trial. Two assembly plants were chosen with one receiving PMR therapy and the other Pamphlets. Intention-to-treat analysis was conducted to test the effectiveness of the relaxation therapy. Stress, Depression and Anxiety levels were measured using the shortened DASS-21 questionnaire. Data were analyzed using Chi-square, Independent sample t test and Repeated-measures analysis of variance to test the significance of the effects of intervention (time * group) for the measures of Stress, Depression and Anxiety. Significant favourable intervention effects on stress were found in the PMR group (Effect size=0.6) as compared to the Pamphlet group (Effect size=0.2). There was a significant group *time interaction effect (p<0.001) on Stress levels. Depression and Anxiety levels were minimal at baseline in both the groups with mild or no reduction in levels. The improvement in stress levels showed the potential of PMR therapy as a coping strategy at the workplace. Further research in this field is necessary to examine the beneficial effects of coping strategies in the workplace. PMID:26726829

Effectiveness of progressive muscle relaxation therapy as a worksite health promotion program in the automobile assembly line.

PubMed

Sundram, Bala Murali; Dahlui, Maznah; Chinna, Karuthan

2016-06-10

The aim of this study was to examine the effectiveness of Progressive Muscle Relaxation (PMR) as part of a Worksite Health Promotion Program on self-perceived stress, anxiety and depression among male automotive assembly-line workers through a quasi-experimental trial. Two assembly plants were chosen with one receiving PMR therapy and the other Pamphlets. Intention-to-treat analysis was conducted to test the effectiveness of the relaxation therapy. Stress, Depression and Anxiety levels were measured using the shortened DASS-21 questionnaire. Data were analyzed using Chi-square, Independent sample t test and Repeated-measures analysis of variance to test the significance of the effects of intervention (time * group) for the measures of Stress, Depression and Anxiety. Significant favourable intervention effects on stress were found in the PMR group (Effect size=0.6) as compared to the Pamphlet group (Effect size=0.2). There was a significant group *time interaction effect (p<0.001) on Stress levels. Depression and Anxiety levels were minimal at baseline in both the groups with mild or no reduction in levels. The improvement in stress levels showed the potential of PMR therapy as a coping strategy at the workplace. Further research in this field is necessary to examine the beneficial effects of coping strategies in the workplace.

Sensitivity of polycrystal plasticity to slip system kinematic hardening laws for Al 7075-T6

DOE PAGES

Hennessey, Conor; Castelluccio, Gustavo M.; McDowell, David L.

2017-02-01

The prediction of formation and early growth of microstructurally small fatigue cracks requires use of constitutive models that accurately estimate local states of stress, strain, and cyclic plastic strain. However, few research efforts have attempted to systematically consider the sensitivity of overall cyclic stress-strain hysteresis and higher order mean stress relaxation and plastic strain ratcheting responses introduced by the slip system back-stress formulation in crystal plasticity, even for face centered cubic (FCC) crystal systems. This paper explores the performance of two slip system level kinematic hardening models using a finite element crystal plasticity implementation as a User Material Subroutine (UMAT)more » within ABAQUS, with fully implicit numerical integration. The two kinematic hardening formulations aim to reproduce the cyclic deformation of polycrystalline Al 7075-T6 in terms of both macroscopic cyclic stress-strain hysteresis loop shape, as well as ratcheting and mean stress relaxation under strain- or stress-controlled loading with mean strain or stress, respectively. The first formulation is an Armstrong-Frederick type hardening-dynamic recovery law for evolution of the back stress. This approach is capable of reproducing observed deformation under completely reversed uniaxial loading conditions, but overpredicts the rate of cyclic ratcheting and associated mean stress relaxation. The second formulation corresponds to a multiple back stress Ohno-Wang type hardening law with nonlinear dynamic recovery. The adoption of this back stress evolution law greatly improves the capability to model experimental results for polycrystalline specimens subjected to cycling with mean stress or strain. As a result, the relation of such nonlinear dynamic recovery effects are related to slip system interactions with dislocation substructures.« less

Sensitivity of polycrystal plasticity to slip system kinematic hardening laws for Al 7075-T6

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hennessey, Conor; Castelluccio, Gustavo M.; McDowell, David L.

The prediction of formation and early growth of microstructurally small fatigue cracks requires use of constitutive models that accurately estimate local states of stress, strain, and cyclic plastic strain. However, few research efforts have attempted to systematically consider the sensitivity of overall cyclic stress-strain hysteresis and higher order mean stress relaxation and plastic strain ratcheting responses introduced by the slip system back-stress formulation in crystal plasticity, even for face centered cubic (FCC) crystal systems. This paper explores the performance of two slip system level kinematic hardening models using a finite element crystal plasticity implementation as a User Material Subroutine (UMAT)more » within ABAQUS, with fully implicit numerical integration. The two kinematic hardening formulations aim to reproduce the cyclic deformation of polycrystalline Al 7075-T6 in terms of both macroscopic cyclic stress-strain hysteresis loop shape, as well as ratcheting and mean stress relaxation under strain- or stress-controlled loading with mean strain or stress, respectively. The first formulation is an Armstrong-Frederick type hardening-dynamic recovery law for evolution of the back stress. This approach is capable of reproducing observed deformation under completely reversed uniaxial loading conditions, but overpredicts the rate of cyclic ratcheting and associated mean stress relaxation. The second formulation corresponds to a multiple back stress Ohno-Wang type hardening law with nonlinear dynamic recovery. The adoption of this back stress evolution law greatly improves the capability to model experimental results for polycrystalline specimens subjected to cycling with mean stress or strain. As a result, the relation of such nonlinear dynamic recovery effects are related to slip system interactions with dislocation substructures.« less

Short-term adaptation and chronic cardiac remodelling to high altitude in lowlander natives and Himalayan Sherpa.

PubMed

Stembridge, Mike; Ainslie, Philip N; Shave, Rob

2015-11-01

What is the topic of this review? At high altitude, the cardiovascular system must adapt in order to meet the metabolic demand for oxygen. This review summarizes recent findings relating to short-term and life-long cardiac adaptation to high altitude in the context of exercise capacity. What advances does it highlight? Both Sherpa and lowlanders exhibit smaller left ventricular volumes at high altitude; however, myocardial relaxation, as evidenced by diastolic untwist, is reduced only in Sherpa, indicating that short-term hypoxia does not impair diastolic relaxation. Potential remodelling of systolic function, as evidenced by lower left ventricular systolic twist in Sherpa, may facilitate the requisite sea-level mechanical reserve required during exercise, although this remains to be confirmed. Both short-term and life-long high-altitude exposure challenge the cardiovascular system to meet the metabolic demand for O2 in a hypoxic environment. As the demand for O2 delivery increases during exercise, the circulatory component of oxygen transport is placed under additional stress. Acute adaptation and chronic remodelling of cardiac structure and function may occur to facilitate O2 delivery in lowlanders during sojourn to high altitude and in permanent highland residents. However, our understanding of cardiac structural and functional adaption in Sherpa remains confined to a higher maximal heart rate, lower pulmonary vascular resistance and no differences in resting cardiac output. Ventricular form and function are intrinsically linked through the left ventricular (LV) mechanics that facilitate efficient ejection, minimize myofibre stress during contraction and aid diastolic recoil. Recent examination of LV mechanics has allowed detailed insight into fundamental cardiac adaptation in high-altitude Sherpa. In this symposium report, we review recent advances in our understanding of LV function in both lowlanders and Sherpa at rest and discuss the potential consequences for exercise capacity. Collectively, data indicate chronic structural ventricular adaptation, with adult Sherpa having smaller absolute and relative LV size. Consistent with structural remodelling, cardiac mechanics also differ in Sherpa when compared with lowlanders at high altitude. These differences are characterized by a reduction in resting systolic deformation and slower diastolic untwisting, a surrogate of relaxation. These changes may reflect a functional cardiac adaptation that affords Sherpa the same mechanical reserve seen in lowlanders at sea level, which is absent when they ascend to high altitude. © 2014 The Authors. Experimental Physiology © 2014 The Physiological Society.

Short-Term Coping Techniques for Managing Stress.

ERIC Educational Resources Information Center

Grasha, Anthony F.

1987-01-01

A number of brief, focused self-help interventions designed to help faculty manage stress more effectively are described such as being assertive, setting priorities, and using quick relaxation techniques. Related causes of stress are cited. (MSE)

Stress evolution of GaN/AlN heterostructure grown on 6H-SiC substrate by plasma assisted molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Agrawal, M.; Ravikiran, L.; Dharmarasu, N.; Radhakrishnan, K.; Karthikeyan, G. S.; Zheng, Y.

2017-01-01

The stress evolution of GaN/AlN heterostructure grown on 6H-SiC substrate by plasma assisted molecular beam epitaxy (PA-MBE) has been studied. AlN nucleation layer and GaN layer were grown as a function of III/V ratio. GaN/AlN structure is found to form buried cracks when AlN is grown in the intermediate growth regime(III/V˜1)and GaN is grown under N-rich growth regime (III/V<1). The III/V ratio determines the growth mode of the layers that influences the lattice mismatch at the GaN/AlN interface. The lattice mismatch induced interfacial stress at the GaN/AlN interface relaxes by the formation of buried cracks in the structure. Additionally, the stress also relaxes by misorienting the AlN resulting in two misorientations with different tilts. Crack-free layers were obtained when AlN and GaN were grown in the N-rich growth regime (III/V<1) and metal rich growth regime (III/V≥1), respectively. AlGaN/GaN high electron mobility transistor (HEMT) heterostructure was demonstrated on 2-inch SiC that showed good two dimensional electron gas (2DEG) properties with a sheet resistance of 480 Ω/sq, mobility of 1280 cm2/V.s and sheet carrier density of 1×1013 cm-2.

Dynamics of carbon dioxide concentrations in the air and its effect on the cognitive ability of school students

NASA Astrophysics Data System (ADS)

Sidorin, D. I.

2015-12-01

The carbon dioxide (CO2) production intensity by a secondary school student is studied using a nondispersive infrared CO2 logger for different conditions: relaxation, mental stress, and physical stress. CO2 production measured for mental stress is 24% higher than that for relaxation, while CO2 production for physical stress is more than 2.5 times higher than relaxation levels. Dynamics of CO2 concentration in the classroom air is measured for a typical school building. It is shown that even when the classroom is ventilated between classes, CO2 concentration exceeds 2100 parts per million (ppm), which is significantly higher than the recommended limits defined in developed countries. The ability of seventh-grade school students to perform tasks requiring mental concentration is tested under different CO2 concentration conditions (below 1000 ppm and above 2000 ppm). Five-letter word anagrams are used as test tasks. Statistical analysis of the test results revealed a significant reduction in the number of provided correct answers and an increase in the number of errors when CO2 levels exceeded 2000 ppm.

Impact of stress relaxation in GaAsSb cladding layers on quantum dot creation in InAs/GaAsSb structures grown on GaAs (001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bremner, S. P.; Ban, K.-Y.; Faleev, N. N.

2013-09-14

We describe InAs quantum dot creation in InAs/GaAsSb barrier structures grown on GaAs (001) wafers by molecular beam epitaxy. The structures consist of 20-nm-thick GaAsSb barrier layers with Sb content of 8%, 13%, 15%, 16%, and 37% enclosing 2 monolayers of self-assembled InAs quantum dots. Transmission electron microscopy and X-ray diffraction results indicate the onset of relaxation of the GaAsSb layers at around 15% Sb content with intersected 60° dislocation semi-loops, and edge segments created within the volume of the epitaxial structures. 38% relaxation of initial elastic stress is seen for 37% Sb content, accompanied by the creation of amore » dense net of dislocations. The degradation of In surface migration by these dislocation trenches is so severe that quantum dot formation is completely suppressed. The results highlight the importance of understanding defect formation during stress relaxation for quantum dot structures particularly those with larger numbers of InAs quantum-dot layers, such as those proposed for realizing an intermediate band material.« less

Analysis of Cantilever-Beam Bending Stress Relaxation Properties of Thin Wood Composites

Treesearch

John F. Hunt; Houjiang Zhang; Yan Huang

2015-01-01

An equivalent strain method was used to analyze and determine material relaxation properties for specimens from particleboard, high density fiberboard, and medium density fiberboard. Cantilever beams were clamped and then deflected to 11 m and held for either 2 h or 3 h, while the load to maintain that deflection was measured vs. time. Plots of load relaxation for each...

Wall relaxation in growing stems: comparison of four species and assessment of measurement techniques

NASA Technical Reports Server (NTRS)

Cosgrove, D. J.

1987-01-01

This study was carried out to develop improved methods for measuring in-vivo stress relaxation of growing tissues and to compare relaxation in the stems of four different species. When water uptake by growing tissue is prevented, in-vivo stress relaxation occurs because continued wall loosening reduces wall stress and cell turgor pressure. With this procedure one may measure the yield threshold for growth (Y), the turgor pressure in excess of the yield threshold (P-Y), and the physiological wall extensibility (phi). Three relaxation techniques proved useful: "turgor-relaxation", "balance-pressure" and "pressure-block". In the turgor-relaxation method, water is withheld from growing tissue and the reduction in turgor is measured directly with the pressure probe. This technique gives absolute values for P and Y, but requires tissue excision. In the balance-pressure technique, the excised growing region is sealed in a pressure chamber, and the subsequent reduction in water potential is measured as the applied pressure needed to return xylem sap to the cut surface. This method is simple, but only measures (P-Y), not the individual values of P and Y. In the pressure-block technique, the growing tissue is sealed into a pressure chamber, growth is monitored continuously, and just sufficient pressure is applied to the chamber to block growth. The method gives high-resolution kinetics of relaxation and does not require tissue excision, but only measures (P-Y). The three methods gave similar results when applied to the growing stems of pea (Pisum sativum L.), cucumber (Cucumis sativus L.), soybean (Glycine max (L.) Merr.) and zucchini (Curcubita pepo L.) seedlings. Values for (P-Y) averaged between 1.4 and 2.7 bar, depending on species. Yield thresholds averaged between 1.3 and 3.0 bar. Compared with the other methods, relaxation by pressure-block was faster and exhibited dynamic changes in wall-yielding properties. The two pressure-chamber methods were also used to measure the internal water-potential gradient (between the xylem and the epidermis) which drives water uptake for growth. For the four species it was small, between 0.3 and 0.6 bar, and so did not limit growth substantially.

Synoptic forcing of wind relaxations at Pt. Conception, California

NASA Astrophysics Data System (ADS)

Fewings, Melanie R.; Washburn, Libe; Dorman, Clive E.; Gotschalk, Christopher; Lombardo, Kelly

2016-08-01

Over the California Current upwelling system in summer, the prevailing upwelling-favorable winds episodically weaken (relax) or reverse direction for a few days. Near Pt. Conception, California, the wind usually does not reverse, but wind relaxation allows poleward oceanic coastal flow with ecological consequences. To determine the offshore extent and synoptic forcing of these wind relaxations, we formed composite averages of wind stress from the QuikSCAT satellite and atmospheric pressure from the North American Regional Reanalysis (NARR) using 67 wind relaxations during summer 2000-2009. Wind relaxations at Pt. Conception are the third stage of an event sequence that repeatedly affects the west coast of North America in summer. First, 5-7 days before the wind weakens near Pt. Conception, the wind weakens or reverses off Oregon and northern California. Second, the upwelling-favorable wind intensifies along central California. Third, the wind relaxes at Pt. Conception, and the area of weakened winds extends poleward to northern California over 3-5 days. The NARR underestimates the wind stress within ˜200 km of coastal capes by a factor of 2. Wind relaxations at Pt. Conception are caused by offshore extension of the desert heat low. This synoptic forcing is related to event cycles that cause wind reversal as in Halliwell and Allen (1987) and Mass and Bond (1996), but includes weaker events. The wind relaxations extend ˜600 km offshore, similarly to the California-scale hydraulic expansion fan shaping the prevailing winds, and ˜1000 km alongshore, limited by an opposing pressure gradient force at Cape Mendocino.

Stress and Quality of Life in Cancer Patients: Medical and Psychological Intervention.

PubMed

Barre, Prasad Vijay; Padmaja, Gadiraju; Rana, Suvashisa; Tiamongla

2018-01-01

Cancer pervades many dimensions of an individual's life - demanding a holistic treatment approach. However, studies with combined medical and psychological interventions (MPIs) are sparse. High-level stress and poor quality of life (QoL) can hinder patients' prognosis. The study thus aimed to analyze the impact of combined medical and psychological (psychoeducation, relaxation technique-guided imagery, and cognitive therapy) interventions on stress and QoL of cancer patients - head and neck, breast, and lung cancers. The study was conducted in cancer hospitals employing one-group pretest-posttest-preexperimental design. Descriptive statistics, paired t -test, Cohen's d, and bar graphs were used to analyze the data. Findings showed high impact of the combined MPIs in reducing both the overall stress as well as the various components of the stress scale-fear, psychosomatic complaints, information deficit, and everyday life restrictions. Significant changes were also seen in QoL and its domains - global health status, besides functional and symptom scales. Results showed a significant improvement in physical, role and emotional functioning scale, while decrement in fatigue, pain, insomnia, appetite loss, diarrhea, and constipation of symptoms scales. It can be concluded that combined MPI has a positive impact - decreasing stress and improving QoL in cancer patients, which can further enhance their prognosis.

Good Counsel on Curbing Counselors' Stress.

ERIC Educational Resources Information Center

Bucci, Frank A.

1994-01-01

Presents results from survey of 610 College Placement Council members to determine causes of career counselor stress. Offers 13 suggestions for relieving stress: learn to relax, resist perfectionism, learn to laugh, listen to soft music, try stress inoculation, practice desensitization, get organized, physical exercise, healthy lifestyles, get…

Effect of thermal exposure on the residual stress relaxation in a hardened cylindrical sample under creep conditions

NASA Astrophysics Data System (ADS)

Radchenko, V. P.; Saushkin, M. N.; Tsvetkov, V. V.

2016-05-01

This paper describes the effect of thermal exposure (high-temperature exposure) ( T = 675°C) on the residual creep stress relaxation in a surface hardened solid cylindrical sample made of ZhS6UVI alloy. The analysis is carried out with the use of experimental data for residual stresses after micro-shot peening and exposures to temperatures equal to T = 675°C during 50, 150, and 300 h. The paper presents the technique for solving the boundary-value creep problem for the hardened cylindrical sample with the initial stress-strain state under the condition of thermal exposure. The uniaxial experimental creep curves obtained under constant stresses of 500, 530, 570, and 600 MPa are used to construct the models describing the primary and secondary stages of creep. The calculated and experimental data for the longitudinal (axial) tensor components of residual stresses are compared, and their satisfactory agreement is determined.

Prior Heat Stress Effects Fatigue Recovery of the Elbow Flexor Muscles

PubMed Central

Iguchi, Masaki; Shields, Richard K.

2011-01-01

Introduction Long-lasting alterations in hormones, neurotransmitters and stress proteins after hyperthermia may be responsible for the impairment in motor performance during muscle fatigue. Methods Subjects (n = 25) performed a maximal intermittent fatigue task of elbow flexion after sitting in either 73 or 26 deg C to examine the effects of prior heat stress on fatigue mechanisms. Results The heat stress increased the tympanic and rectal temperatures by 2.3 and 0.82 deg C, respectively, but there was full recovery prior to the fatigue task. While prior heat stress had no effects on fatigue-related changes in volitional torque, EMG activity, torque relaxation rate, MEP size and SP duration, prior heat stress acutely increased the pre-fatigue relaxation rate and chronically prevented long-duration fatigue (p < 0.05). Discussion These findings indicate that prior passive heat stress alone does not alter voluntary activation during fatigue, but prior heat stress and exercise produce longer-term protection against long-duration fatigue. PMID:21674526

Probing cytoskeletal pre-stress and nuclear mechanics in endothelial cells with spatiotemporally controlled (de-)adhesion kinetics on micropatterned substrates

PubMed Central

Versaevel, Marie; Riaz, Maryam; Corne, Tobias; Grevesse, Thomas; Lantoine, Joséphine; Mohammed, Danahe; Bruyère, Céline; Alaimo, Laura; De Vos, Winnok H.; Gabriele, Sylvain

2017-01-01

ABSTRACT The mechanical properties of living cells reflect their propensity to migrate and respond to external forces. Both cellular and nuclear stiffnesses are strongly influenced by the rigidity of the extracellular matrix (ECM) through reorganization of the cyto- and nucleoskeletal protein connections. Changes in this architectural continuum affect cell mechanics and underlie many pathological conditions. In this context, an accurate and combined quantification of the mechanical properties of both cells and nuclei can contribute to a better understanding of cellular (dys-)function. To address this challenge, we have established a robust method for probing cellular and nuclear deformation during spreading and detachment from micropatterned substrates. We show that (de-)adhesion kinetics of endothelial cells are modulated by substrate stiffness and rely on the actomyosin network. We combined this approach with measurements of cell stiffness by magnetic tweezers to show that relaxation dynamics can be considered as a reliable parameter of cellular pre-stress in adherent cells. During the adhesion stage, large cellular and nuclear deformations occur over a long time span (>60 min). Conversely, nuclear deformation and condensed chromatin are relaxed in a few seconds after detachment. Finally, our results show that accumulation of farnesylated prelamin leads to modifications of the nuclear viscoelastic properties, as reflected by increased nuclear relaxation times. Our method offers an original and non-intrusive way of simultaneously gauging cellular and nuclear mechanics, which can be extended to high-throughput screens of pathological conditions and potential countermeasures. PMID:27111836

Probing cytoskeletal pre-stress and nuclear mechanics in endothelial cells with spatiotemporally controlled (de-)adhesion kinetics on micropatterned substrates.

PubMed

Versaevel, Marie; Riaz, Maryam; Corne, Tobias; Grevesse, Thomas; Lantoine, Joséphine; Mohammed, Danahe; Bruyère, Céline; Alaimo, Laura; De Vos, Winnok H; Gabriele, Sylvain

2017-01-02

The mechanical properties of living cells reflect their propensity to migrate and respond to external forces. Both cellular and nuclear stiffnesses are strongly influenced by the rigidity of the extracellular matrix (ECM) through reorganization of the cyto- and nucleoskeletal protein connections. Changes in this architectural continuum affect cell mechanics and underlie many pathological conditions. In this context, an accurate and combined quantification of the mechanical properties of both cells and nuclei can contribute to a better understanding of cellular (dys-)function. To address this challenge, we have established a robust method for probing cellular and nuclear deformation during spreading and detachment from micropatterned substrates. We show that (de-)adhesion kinetics of endothelial cells are modulated by substrate stiffness and rely on the actomyosin network. We combined this approach with measurements of cell stiffness by magnetic tweezers to show that relaxation dynamics can be considered as a reliable parameter of cellular pre-stress in adherent cells. During the adhesion stage, large cellular and nuclear deformations occur over a long time span (>60 min). Conversely, nuclear deformation and condensed chromatin are relaxed in a few seconds after detachment. Finally, our results show that accumulation of farnesylated prelamin leads to modifications of the nuclear viscoelastic properties, as reflected by increased nuclear relaxation times. Our method offers an original and non-intrusive way of simultaneously gauging cellular and nuclear mechanics, which can be extended to high-throughput screens of pathological conditions and potential countermeasures.

Interfaces in polymer nanocomposites – An NMR study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Böhme, Ute; Scheler, Ulrich, E-mail: scheler@ipfdd.de

Nuclear Magnetic Resonance (NMR) is applied for the investigation of polymer nanocomposites. Solid-state NMR is applied to study the modification steps to compatibilize layered double hydroxides with non-polar polymers. {sup 1}H relaxation NMR gives insight on the polymer dynamics over a wide range of correlation times. For the polymer chain dynamics the transverse relaxation time T{sub 2} is most suited. In this presentation we report on two applications of T{sub 2} measurements under external mechanical stress. In a low-field system relaxation NMR studies are performed in-situ under uniaxial stress. High-temperature experiments in a Couette cell permit the investigation of themore » polymer dynamics in the melt under shear flow.« less

Temperature and voltage stress dependent dielectric relaxation process of the doped Ba0.67Sr0.33TiO3 ceramics

NASA Astrophysics Data System (ADS)

Yan, Shiguang; Mao, Chaoliang; Wang, Genshui; Yao, Chunhua; Cao, Fei; Dong, Xianlin

2013-09-01

The current decay characteristic in the time domain is studied in Y3+ and Mn2+ modified Ba0.67Sr0.33TiO3 ceramics under different temperatures (25 °C-213 °C) and voltage stresses (0 V-800 V). The decay of the current is correlated with the overlapping of the relaxation process and leakage current. With respect to the inherent remarkable dielectric nonlinearity, a simple method through curve fitting is derived to differentiate these two currents. Two mechanisms of the relaxation process are proposed: a distribution of the potential barriers mode around room temperature and an electron injection mode at the elevated temperature of 110 °C.

The stress-reducing effect of music listening varies depending on the social context.

PubMed

Linnemann, Alexandra; Strahler, Jana; Nater, Urs M

2016-10-01

Given that music listening often occurs in a social context, and given that social support can be associated with a stress-reducing effect, it was tested whether the mere presence of others while listening to music enhances the stress-reducing effect of listening to music. A total of 53 participants responded to questions on stress, presence of others, and music listening five times per day (30min after awakening, 1100h, 1400h, 1800h, 2100h) for seven consecutive days. After each assessment, participants were asked to collect a saliva sample for the later analysis of salivary cortisol (as a marker for the hypothalamic-pituitary-adrenal axis) and salivary alpha-amylase (as a marker for the autonomic nervous system). Hierarchical linear modeling revealed that music listening per se was not associated with a stress-reducing effect. However, listening to music in the presence of others led to decreased subjective stress levels, attenuated secretion of salivary cortisol, and higher activity of salivary alpha-amylase. When listening to music alone, music that was listened to for the reason of relaxation predicted lower subjective stress. The stress-reducing effect of music listening in daily life varies depending on the presence of others. Music listening in the presence of others enhanced the stress-reducing effect of music listening independently of reasons for music listening. Solitary music listening was stress-reducing when relaxation was stated as the reason for music listening. Thus, in daily life, music listening can be used for stress reduction purposes, with the greatest success when it occurs in the presence of others or when it is deliberately listened to for the reason of relaxation. Copyright © 2016 Elsevier Ltd. All rights reserved.

Finite element simulation and analysis of local stress concentration in polymers with a nonlinear viscoelastic constitutive model

NASA Astrophysics Data System (ADS)

Chea, Limdara O.

Given a nonlinear viscoelastic (NLVE) constitutive model for a polymer, this numerical study aims at simulating local stress concentrations in a boundary value problem with a corner stress singularity. A rectangular sample of Polyvinyl Acetate (PVAc)-like cross-linked polymer clamped by two metallic rigid grips and subjected to a compression and tension load is numerically simulated. A modified version of the finite element code FEAP, that incorporated a NLVE model based on the free volume theory, was used. First, the program was validated by comparing numerical and analytical results. Two simple mechanical tests (a uniaxial and a simple shear test) were performed on a Standard Linear Solid material model, using a linear viscoelastic (LVE) constitutive model. The LVE model was obtained by setting the proportionality coefficient [...] to zero in the free volume theory equations. Second, the LVE model was used on the corner singularity boundary value problem for three material models with different bulk relaxation functions K(t). The time-dependent stress field distribution was investigated using two sets of plots: the stress distribution contour plots and the stress time curves. Third, using the NLVE constitutive model, compression and tension cases were compared using the stress results (normal stress [...] and shear stress [...]). These two cases assessed the effect of the creep retardation-creep acceleration phenomena. The shift between the beginning of the relaxation moduli was shown to play an important role. This parameter affects strongly the fluctuation pattern of the stress curves. For two different shift values, in one case, the stress response presents a 'double peak' and 'stress inversion' characteristic whereas, in the other case, it presents a 'single peak' and no 'inversion'. Another important factor was the material's compressibility. In the case of a nearly-incompressible material, the LVE and NLVE models yielded identical results; thus, the simpler LVE model is preferable. However, in the case of sufficient volume dilatation (or contraction), the NLVE model predicted correct characteristic responses, whereas LVE results were erroneous. This proves the necessity of using the NLVE model over the LVE model.

[Essential hypertension and stress. When do yoga, psychotherapy and autogenic training help?].

PubMed

Herrmann, J M

2002-05-09

Psychosocial factors play an important role in the development and course of essential hypertension, although "stress" can account for only 10% of blood pressure variance. A variety of psychotherapeutic interventions, such as relaxation techniques (autogenic training or progressive muscular relaxation), behavioral therapy or biofeedback techniques, can lower elevated blood pressure by an average of 10 mmHg (systolic) and 5 mmHg (diastolic). As a "secondary effect", such measures may also prompt the hypertensive to adopt a more health-conscious lifestyle.

[Free from stress by autogenic therapy. Relaxation technique yielding peace of mind and self-insight].

PubMed

Broms, C

1999-02-10

The utilisation of self-regulatory capacity is one of the purposes of autogenic therapy, a method consisting of exercises focused on the limbs, lungs, heart, diaphragm and head. The physiological response is muscle relaxation, increased peripheral blood flow, lower heart rate and blood pressure, slower and deeper breathing, and reduced oxygen consumption. Autogenic training is applicable in most pathological conditions associated with stress, and can be used preventively or as a complement to conventional treatment.

Changes in shear-wave splitting before volcanic eruptions

NASA Astrophysics Data System (ADS)

Liu, Sha; Crampin, Stuart

2015-04-01

We have shown that observations of shear-wave splitting (SWS) monitor stress-accumulation and stress-relaxation before earthquakes which allows the time, magnitude, and in some circumstances fault-plane of impending earthquakes to be stress-forecast. (We call this procedure stress-forecasting rather than predicting or forecasting to emphasise the different formalism.) We have stress-forecast these parameters successfully three-days before a 1988 M5 earthquake in SW Iceland, and identified characteristic anomalies retrospectively before ~16 other earthquakes in Iceland and elsewhere. SWS monitors microcrack geometry and shows that microcracks are so closely spaced that they verge on fracturing and earthquakes. Phenomena verging on failure in this way are critical-systems with 'butterfly wings' sensitivity. Such critical-systems are very common. The Earth is an archetypal complex heterogeneous interactive phenomenon and must be expected to be a critical-system. We claim this critical system as a New Geophysics of a critically-microcracked rock mass. Such critical systems impose a range of fundamentally-new properties on conventional sub-critical physics/geophysics, one of which is universality. Consequently it is expected that we observe similar stress-accumulation and stress-relaxation before volcanic eruptions to those before earthquakes. There are three eruptions where appropriate changes in SWS have been observed similar to those observed before earthquakes. These are: the 1996 Gjálp fissure eruption, Vatnajökull, Iceland; a 2001 flank eruption on Mount Etna, Sicily (reported by Francesca Bianco, INGV, Naples); and the 2010 Eyjafjajökull ash-cloud eruption, SW Iceland. These will be presented in the same normalised format as is used before earthquakes. The 1996 Gjálp eruption showed a 2½-month stress-accumulation, and a ~1-year stress-relaxation (attributed to the North Atlantic Ridge adjusting to the magma injection beneath the Vatnajökull Ice Cap). The 2001 flank eruption of Etna showed stress-accumulation and stress-relaxation typical of a small earthquake. However, the changes in SWS before the 2010 Eyjafjajökull Eruption, SW Iceland, showed the most distinctive correlations with earthquakes, as it was only ~90km-west of the 1988 M5 in SW Iceland, which was successfully stress-forecast. The behaviour of SWS before the M5 earthquake and the Eyjafjajökull flank (ash-cloud) eruption is almost identical both showing linear stress-accumulation increases, and linear stress-relaxation decreases to the earthquake and the onset of the flank eruption, respectively. There are comparable slopes and durations. We consider this strong confirmation of the universality property of the New Geophysics of a critically-microcracked Earth. Papers referring to these developments can be found in geos.ed.ac.uk/home/scrampin/opinion. Also see abstracts in EGU2015 Sessions: Crampin & Gao (SM1.1), Gao & Crampin (SM3.1), and Crampin & Gao (GD.1).

Nanoindentation data analysis of loading curve performed on DLC thin films: Effect of residual stress on the elasto-plastic properties

NASA Astrophysics Data System (ADS)

Ouchabane, M.; Dublanche-Tixier, Ch.; Dergham, D.

2017-11-01

The present work is a contribution to the understanding of the mechanical behavior of DLC thin films through nanoindentation tests. DLC films of different thicknesses deposited by the PECVD process on a silicon substrate contain high residual compressive stresses when they are very thin and the stresses become relatively low and more relaxed as the film thickens. These different levels of residual stress influence the values of hardness (H) and Young's modulus (E) obtained when probing the film-substrate system by nanoindentation. It is observed that the DLC layers exhibit different mechanical behaviors even when they are deposited under the same conditions. It is proposed that the compressive stress induces structural modifications resulting in modifying the elasto-plastic properties of each thin film-substrate system. Data analysis of the loading curve can provide information on the elasto-plastic properties of DLC thin films, particularly the stiffness (S) and Er2/H, as a function of residual compressive stresses. The structural changes induced by residual stresses were probed by using Raman spectroscopy and correlated to the mechanical properties.

Relaxation spectra of binary blends: Extension of the Doi-Edwards theory

NASA Astrophysics Data System (ADS)

Tchesnokov, M. A.; Molenaar, J.; Slot, J. J. M.; Stepanyan, R.

2007-10-01

A molecular model is presented which allows the calculation of the stress relaxation function G for binary blends consisting of two monodisperse samples with arbitrary molecular weights. It extends the Doi-Edwards reptation theory (Doi M. and Edwards S. F., The Theory of Polymer Dynamics (Oxford Press, New York) 1986) to highly polydisperse melts by including constraint release (CR) and thermal fluctuations (CLF), yet making use of the same input parameters. The model reveals an explicit nonlinear dependence of CR frequency in the blend on the blend's molecular weight distribution (MWD). It provides an alternative way to quantify polydisperse systems compared to the widely used "double-reptation" theories. The results of the present model are in a good agreement with the experimental data given in Rubinstein M. and Colby R. H., J. Chem. Phys., 89 (1988) 5291.

Meditation as an Intervention in Stress Reactivity

ERIC Educational Resources Information Center

Goleman, Daniel J.; Schwartz, Gary E.

1976-01-01

Meditation and relaxation were compared for ability to reduce stress reactions in a laboratory threat situation. Meditation can produce a psychophysiological configuration in stress situations opposite to that seen in stress-related syndromes. Research is indicated on clinical applications and on the process whereby meditation state effects may…

Helping Young Children Manage Stress.

ERIC Educational Resources Information Center

Texas Child Care, 2002

2002-01-01

Describes the common symptoms of stress exhibited by young children including: (1) social or behavioral; (2) physical; (3) emotional; (4) cognitive; and (5) language. Addresses causes of stress, which typically represent change, fear, or loss in children. Offers strategies for easing children's stress including muscle relaxation, deep breathing,…

Tips for Chronic Pain

MedlinePlus

... Don’t let stress compound your pain. • Stress is the result of the way you react to the world, and heightened stress equals heightened pain. Learn relaxation techniques or seek help in reducing your stress level. Get enough sleep. • Practice good sleep habits and get adequate sleep on a ...

Stress Can Be a Friend: Approaches to Producing Good Stresses That Reduce and Control Bad Stresses.

ERIC Educational Resources Information Center

Demery, Marie

Individuals can produce good stresses that will inhibit or eliminate the bad stresses of anxiety, depression, resentment, and hopelessness. This can be accomplished as individuals learn to include in their lifestyles these nine approaches: self-talk, commitment, self-control, challenge, interpersonal relations, time management, relaxation,…

Isothermal enthalpy relaxation of glassy 1,2,6-hexanetriol

NASA Astrophysics Data System (ADS)

Fransson, Å.; Bäckström, G.

The isothermal enthalpy relaxation of glassy 1,2,6-hexanetriol has been measured at six temperatures. The relaxation time and the distribution parameters extracted from fits of the Williams-Watts relaxation function are compared with parameters obtained by other techniques and on other substances. A detailed comparison of the Williams-Watts and the Davidson-Cole relaxation functions is presented.

Find the Calm, Avoid the Storm: Relaxation Techniques.

ERIC Educational Resources Information Center

Texas Child Care, 1995

1995-01-01

Provides classroom techniques to help children develop the skill to pull back from turmoil or stress, evaluate their emotional states, redirect their energy, and find peace in their minds. Activities described include relaxation and breathing games, as well as calming physical activities. (HTH)

The Effect of Tungsten and Niobium on the Stress Relaxation Rates of Disk Alloy CH98

NASA Technical Reports Server (NTRS)

Gayda, John

2003-01-01

Gas turbine engines for future subsonic transports will probably have higher pressure ratios which will require nickel-base superalloy disks with 1300 to 1400 F temperature capability. Several advanced disk alloys are being developed to fill this need. One of these, CH98, is a promising candidate for gas turbine engines and is being studied in NASA s Advanced Subsonic Technology (AST) program. For large disks, residual stresses generated during quenching from solution heat treatment are often reduced by a stabilization heat treatment, in which the disk is heated to 1500 to 1600 F for several hours followed by a static air cool. The reduction in residual stress levels lessens distortion during machining of disks. However, previous work on CH98 has indicated that stabilization treatments decrease creep capability. Additions of the refractory elements tungsten and niobium improve tensile and creep properties after stabilization, while maintaining good crack growth resistance at elevated temperatures. As the additions of refractory elements increase creep capability, they might also effect stress relaxation rates and therefore the reduction in residual stress levels obtained for a given stabilization treatment. To answer this question, the stress relaxation rates of CH98 with and without tungsten and niobium additions are compared in this paper for temperatures and times generally employed in stabilization treatments on modern disk alloys.

On the state of stress in the near-surface of the earth's crust

USGS Publications Warehouse

Savage, W.Z.; Swolfs, H.S.; Amadei, B.

1992-01-01

Five models for near-surface crustal stresses induced by gravity and horizontal deformation and the influence of rock property contrasts, rock strength, and stress relaxation on these stresses are presented. Three of the models-the lateral constraint model, the model for crustal stresses caused by horizontal deformation, and the model for the effects of anisotropy-are linearly elastic. The other two models assume that crustal rocks are brittle or viscoelastic in order to account for the effects of rock strength and time on near-surface stresses. It is shown that the lateral constraint model is simply a special case of the combined gravity-and deformation-induced stress field when horizontal strains vanish and that the inclusion of the effect of rock anisotropy in the solution for crustal stresses caused by gravity and horizontal deformation broadens the range for predicted stresses. It is also shown that when stress levels in the crust reach the limits of brittle rock strength, these stresses become independent of strain rates and that stress relaxation in ductile crustal rocks subject to constant horizontal strain rates causes horizontal stresses to become independent of time in the long term. ?? 1992 Birkha??user Verlag.

Fluid shear stress as a regulator of gene expression in vascular cells: possible correlations with diabetic abnormalities

NASA Technical Reports Server (NTRS)

Papadaki, M.; Eskin, S. G.; Ruef, J.; Runge, M. S.; McIntire, L. V.

1999-01-01

Diabetes mellitus is associated with increased frequency, severity and more rapid progression of cardiovascular diseases. Metabolic perturbations from hyperglycemia result in disturbed endothelium-dependent relaxation, activation of coagulation pathways, depressed fibrinolysis, and other abnormalities in vascular homeostasis. Atherosclerosis is localized mainly at areas of geometric irregularity at which blood vessels branch, curve and change diameter, and where blood is subjected to sudden changes in velocity and/or direction of flow. Shear stress resulting from blood flow is a well known modulator of vascular cell function. This paper presents what is currently known regarding the molecular mechanisms responsible for signal transduction and gene regulation in vascular cells exposed to shear stress. Considering the importance of the hemodynamic environment of vascular cells might be vital to increasing our understanding of diabetes.

Rate Dependence in Force Networks of Sheared Granular Materials

NASA Astrophysics Data System (ADS)

Hartley, Robert; Behringer, Robert P.

2003-03-01

We describe experiments that explore rate dependence in force networks of dense granular materials undergoing slow deformation by shear and by compression. The experiments were carried out using 2D photoelastic particles so that it was possible to visualize forces at the grain scale. Shear experiments were carried out in a Couette geometry with a rate Ω. Compression experiments were carried out by repetitive compaction via a piston in a rigid chamber at comparable rates to the shear experiments. Under shearing the mean stress/force grew logarithmically with Ω for at least four decades. For compression, no dependence of the mean stress on rate was observed. In related measurements, we observed relaxation of stress in static samples that had been sheared and where the shearing was abruptly stopped. Relaxation of the force network occured over time scales of days. No relaxation of the force network was observable for uniformly compressed static samples. These results are of particular interest because they provide insight into creep and failure in granular materials.

Adsorption of phospholipids at oil/water interfaces during emulsification is controlled by stress relaxation and diffusion.

PubMed

Hildebrandt, Ellen; Nirschl, Hermann; Kok, Robbert Jan; Leneweit, Gero

2018-05-16

Adsorption of phosphatidylcholines at oil/water interfaces strongly deviates from spread monolayers at air/water surfaces. Understanding its nature and consequences could vastly improve applications in medical nanoemulsions and biotechnologies. Adsorption kinetics at interfaces of water with different oil phases were measured by profile analysis tensiometry. Adsorption kinetics for 2 different phospholipids, DPPC and POPC, as well as 2 organic phases, squalene and squalane, show that formation of interfacial monolayers is initially dominated by stress-relaxation in the first minutes. Diffusion only gradually contributes to a decrease in interfacial tension at later stages of time and higher film pressures. The results can be applied for the optimization of emulsification protocols using mechanical treatments. Emulsions using phospholipids with unsaturated fatty acids are dominated much more strongly by stress-relaxation and cover interfaces very fast compared to those with saturated fatty acids. In contrast, phospholipid layers consisting of saturated fatty acids converge faster towards the equilibrium than those with unsaturated fatty acids.

High Load Ratio Fatigue Strength and Mean Stress Evolution of Quenched and Tempered 42CrMo4 Steel

NASA Astrophysics Data System (ADS)

Bertini, Leonardo; Le Bone, Luca; Santus, Ciro; Chiesi, Francesco; Tognarelli, Leonardo

2017-08-01

The fatigue strength at a high number of cycles with initial elastic-plastic behavior was experimentally investigated on quenched and tempered 42CrMo4 steel. Fatigue tests on unnotched specimens were performed both under load and strain controls, by imposing various levels of amplitude and with several high load ratios. Different ratcheting and relaxation trends, with significant effects on fatigue, are observed and discussed, and then reported in the Haigh diagram, highlighting a clear correlation with the Smith-Watson-Topper model. High load ratio tests were also conducted on notched specimens with C (blunt) and V (sharp) geometries. A Chaboche model with three parameter couples was proposed by fitting plain specimen cyclic and relaxation tests, and then finite element analyses were performed to simulate the notched specimen test results. A significant stress relaxation at the notch root became clearly evident by reporting the numerical results in the Haigh diagram, thus explaining the low mean stress sensitivity of the notched specimens.

Effect of organo-clay on the dielectric relaxation response of silicone rubber

NASA Astrophysics Data System (ADS)

Gharavi, N.; Razzaghi-Kashani, M.; Golshan-Ebrahimi, N.

2010-02-01

Dielectric elastomers are light weight, low-cost, highly deformable and fast response smart materials capable of converting electrical energy into mechanical work or vice versa. Silicone rubber is a well-known dielectric elastomer which is used as actuator, and in order to enhance the efficiency of this smart material, compounding of silicone rubber with various fillers can be carried out. The effect of organically modified montmorillonite (OMMT) nano-clay on improvement of dielectric properties, actuation stress and its relaxation response was considered in this study. OMMT was dispersed in room temperature vulcanized (RTV) silicone rubber, and a composite film was cast. Using an in-house actuation set-up, it was shown that the actuation stress for a given electric field intensity is higher for composites than that for pristine silicone rubber. Also, the time-dependent actuation response of the samples was evaluated, and it was shown that the characteristic relaxation time of the actuation stress for composites is less than for the pristine rubber as a result of OMMT addition.

Anxiety

MedlinePlus

... in Healthy Young Adults (07/19/11) Transcendental Meditation Helps Young Adults Cope With Stress (12/14/ ... Clinical Digest: Stress and Relaxation Techniques Clinical Digest: Meditation for Health Scientific Literature Systematic Reviews/Reviews/Meta- ...

Stress management versus lifestyle modification on systolic hypertension and medication elimination: a randomized trial.

PubMed

Dusek, Jeffery A; Hibberd, Patricia L; Buczynski, Beverly; Chang, Bei-Hung; Dusek, Kathryn C; Johnston, Jennifer M; Wohlhueter, Ann L; Benson, Herbert; Zusman, Randall M

2008-03-01

Isolated systolic hypertension is common in the elderly, but decreasing systolic blood pressure (SBP) without lowering diastolic blood pressure (DBP) remains a therapeutic challenge. Although stress management training, in particular eliciting the relaxation response, reduces essential hypertension its efficacy in treating isolated systolic hypertension has not been evaluated. We conducted a double-blind, randomized trial comparing 8 weeks of stress management, specifically relaxation response training (61 patients), versus lifestyle modification (control, 61 patients). Inclusion criteria were >or=55 years, SBP 140-159 mm Hg, DBP <90 mm Hg, and at least two antihypertensive medications. The primary outcome measure was change in SBP after 8 weeks. Patients who achieved SBP <140 mm Hg and >or=5 mm Hg reduction in SBP were eligible for 8 additional weeks of training with supervised medication elimination. SBP decreased 9.4 (standard deviation [SD] 11.4) and 8.8 (SD 13.0) mm Hg in relaxation response and control groups, respectively (both ps <0.0001) without group difference (p=0.75). DBP decreased 1.5 (SD 6.2) and 2.4 (SD 6.9) mm Hg (p=0.05 and 0.01, respectively) without group difference (p=0.48). Forty-four (44) in the relaxation response group and 36 in the control group were eligible for supervised antihypertensive medication elimination. After controlling for differences in characteristics at the start of medication elimination, patients in the relaxation response group were more likely to successfully eliminate an antihypertensive medication (odds ratio 4.3, 95% confidence interval 1.2-15.9, p=0.03). Although both groups had similar reductions in SBP, significantly more participants in the relaxation response group eliminated an antihypertensive medication while maintaining adequate blood pressure control.

Biophysically defined and cytocompatible covalently adaptable networks as viscoelastic 3D cell culture systems.

PubMed

McKinnon, Daniel D; Domaille, Dylan W; Cha, Jennifer N; Anseth, Kristi S

2014-02-12

Presented here is a cytocompatible covalently adaptable hydrogel uniquely capable of mimicking the complex biophysical properties of native tissue and enabling natural cell functions without matrix degradation. Demonstrated is both the ability to control elastic modulus and stress relaxation time constants by more than an order of magnitude while predicting these values based on fundamental theoretical understanding and the simulation of muscle tissue and the encapsulation of myoblasts. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Prenatal cocaine exposure, illicit-substance use and stress and craving processes during adolescence.

PubMed

Yip, Sarah W; Lacadie, Cheryl M; Sinha, Rajita; Mayes, Linda C; Potenza, Marc N

2016-01-01

Prenatal cocaine exposure (PCE) is associated with increased rates of illicit-substance use during adolescence. In addition, both PCE and illicit-substance use are associated with alterations in cortico-striato-limbic neurocircuitry, development of which is ongoing throughout adolescence. However, the relationship between illicit-substance use, PCE and functional neural responses has not previously been assessed concurrently. Sixty-eight adolescents were recruited from an ongoing longitudinal study of childhood and adolescent development. All participants had been followed since birth. Functional magnetic resonance imaging (fMRI) data were acquired during presentation of personalized stressful, favorite-food and neutral/relaxing imagery scripts and compared between 46 PCE and 22 non-prenatally-drug-exposed (NDE) adolescents with and without lifetime illicit-substance use initiation. Data were analyzed using multi-level ANOVAs (pFWE<.05). There was a significant three-way interaction between illicit-substance use, PCE status and cue condition on neural responses within primarily cortical brain regions, including regions of the left and right insula. Among PCE versus NDE adolescents, illicit-substance use was associated with decreased subcortical and increased cortical activity during the favorite-food condition, whereas the opposite pattern of activation was observed during the neutral/relaxing condition. Among PCE versus NDE adolescents, illicit-substance use during stress processing was associated with decreased activity in cortical and subcortical regions including amygdala, hippocampus and prefrontal cortex. Neural activity within cortico-striato-limbic regions was significantly negatively associated with subjective ratings of anxiety and craving among illicit-substance users, but not among non-users. These findings suggest different neural substrates of experimentation with illicit drugs between adolescents with and without in utero cocaine exposure. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Tensile properties of the human glenoid labrum

PubMed Central

Smith, C D; Masouros, S D; Hill, A M; Wallace, A L; Amis, A A; Bull, A M J

2008-01-01

Human fresh-frozen cadaveric glenoid labrae from 16 donors were harvested and ten of these had no gross degeneration. These ten were divided into eight equal circumferential sections. Each section was cut to produce test-samples from the core layer with a cross-section of 1 × 1 mm. Tensile testing was performed within a controlled environment unit at 37 ± 1 °C and 100% relative humidity. Each test-sample was precycled to a quasi-static state to alleviate the effects of deep-freezing, prior to final testing. The tangent modulus was calculated for each test-sample before and after a 5-min period of stress relaxation and at yield. The mean elastic modulus and yield stress of the glenoid labrum were 22.8 ± 11.4 and 2.5 ± 2.1 MPa, respectively. The anterosuperior portion had a lower elastic modulus and lower yield stress than the inferior portion (both P < 0.02). The pre-stress relaxation tangent modulus was significantly lower than the post-stress relaxation tangent modulus for all portions of the labrum. The glenoid labrum has similar tensile material properties to articular cartilage. Its elastic modulus varies around its circumference. This suggests that the labrum may encounter different forces at different positions. PMID:18031481

Time-Temperature Dependent Response of Filament Wound Composites for Flywheel Rotors

NASA Technical Reports Server (NTRS)

Thesken, John C.; Bowman, Cheryl L.; Arnold, Steven M.; Thompson, Richard C.

2004-01-01

Flywheel energy storage offers an attractive alternative to battery systems used in space applications such as the International Space Station. Rotor designs capable of high specific energies benefit from the load carrying capacity of hoop wound carbon fibers but their long-term durability may be limited by time-temperature dependent radial deformations. This was investigated for the carbon/epoxy rotor material, IM7/8552. Coupon specimens were sectioned from filament wound panels. These were tested in compression and tension at room temperature (RT), 95 and 135 C for strain rates from 5x10(exp -6) per second to 5x10(exp -3) per second. Time, temperature and load sign dependent effects were significant transverse to the fiber. At -0.5 percent strain for 72 hr, compressive stresses relaxed 16.4 percent at 135 C and 13 percent at 95 C. Tensile stresses relaxed only 7 percent in 72 hr at 135 C for 0.5 percent strain. Using linear hereditary material response and Boltzmann s principle of superposition to describe this behavior is problematic if not intractable. Micromechanics analysis including the effects of processing residual stresses is needed to resolve the paradoxes. Uniaxial compressive stress relaxation data may be used to bound the loss of radial pre-load stresses in flywheel rotors.

Wrinkle-free design of thin membrane structures using stress-based topology optimization

NASA Astrophysics Data System (ADS)

Luo, Yangjun; Xing, Jian; Niu, Yanzhuang; Li, Ming; Kang, Zhan

2017-05-01

Thin membrane structures would experience wrinkling due to local buckling deformation when compressive stresses are induced in some regions. Using the stress criterion for membranes in wrinkled and taut states, this paper proposed a new stress-based topology optimization methodology to seek the optimal wrinkle-free design of macro-scale thin membrane structures under stretching. Based on the continuum model and linearly elastic assumption in the taut state, the optimization problem is defined as to maximize the structural stiffness under membrane area and principal stress constraints. In order to make the problem computationally tractable, the stress constraints are reformulated into equivalent ones and relaxed by a cosine-type relaxation scheme. The reformulated optimization problem is solved by a standard gradient-based algorithm with the adjoint-variable sensitivity analysis. Several examples with post-bulking simulations and experimental tests are given to demonstrate the effectiveness of the proposed optimization model for eliminating stress-related wrinkles in the novel design of thin membrane structures.

A Stress Management Classroom Tool for Teachers of Children with BD.

ERIC Educational Resources Information Center

Jackson, James T.; Owens, James L.

1999-01-01

This article discusses how stress may affect the lives of children with behavior disorders, provides educators with a model for introducing stress management techniques, and closes with strategies for managing stress in the classroom, including listening to relaxing music, manipulating the environment, and providing a morning physical education…

Teaching Relaxation Skills in Physical Education

ERIC Educational Resources Information Center

Courtney, Anita

2005-01-01

"Stressed out" has become a way of life for many Americans. For children, stress comes from a variety of situations such as bullying, divorce, high stakes testing, and peer pressure. Because many children are not exposed to stress management techniques, stressful situations often result in unhealthy coping mechanisms such as overeating, "acting…

Effects of Stress Inoculation Training on Anxiety, Stress, and Academic Performance among Adolescents.

ERIC Educational Resources Information Center

Kiselica, Mark S.; And Others

1994-01-01

Examined effectiveness of preventive stress inoculation program for adolescents (n=48) that consisted of progressive muscle relaxation, cognitive restructuring, and assertiveness training. Compared with control subjects, trainees showed significantly greater improvements on self-report measures of trait anxiety and stress-related symptoms at…

Impact of substrate on structure and electrical properties in lead-based ferroelectric thin films

NASA Astrophysics Data System (ADS)

Valanoor, Nagarajan Venkatasubramanian

Current trends in semiconductor technology demand that ferroelectric materials be used in thin film form, rather than bulk, for integration and scaling purposes. An inevitable consequence of integration is substrate induced constraint and stress. Sources of this stress are the lattice and thermal mismatch between film and substrate, structural phase transformation which leads to spontaneous strains, and dislocation cores at the film substrate interface. In addition to classical stress relaxation mechanisms all highly tetragonal ferroelectrics relax internal stress via formation of polydomain (90° domains and not 180° domains) structures below the phase transformation, which brings about a change in the microstructure of the film. Hence it is possible to control the resultant microstructure by controlling the degree of polydomain relaxation. Obviously this affects the electrical and electro-mechanical properties and in turn the device performance. The goal of this research is to study this structure-property relationship of ferroelectric thin films where in the structure has been systematically modified by changing the substrate-induced effect. To investigate the effect of the substrate, epitaxial films of PbZr 0.2Ti0.8O3 were grown by pulsed laser deposition (PLD). Epitaxial films reduce the complexities introduced grain boundaries and multiple domain orientations. By systematically changing the thickness the spontaneous strain or c/a ratio can be varied. As a consequence polydomain formation varies as a function of film thickness. Thus this is an effective yet simple method to fully understand the impact of stress on structure-property inter-relationships. The theoretical background for these experiments is first laid out by a thermodynamic analysis of the polydomain formation. It leads to the construction of a domain stability map and indicates a presence of a critical thickness for polydomain formation. This is followed by an investigation of the impact of polydomain formation on quasi-static and dynamic polarization switching. To correlate the material microstructure to switching, an activation field, alpha, is introduced. It is shown theoretically that alpha ∝ (c/a-1)3.5 and a good experimental fit can be obtained. However it is observed that polydomain formation does not impact the electromechanical and dielectric response significantly. It is shown experimentally and theoretically that stress-induced polarization varies only by 10%. Therefore to study the impact of in plane stresses induced by substrate on piezoelectric and dielectric response we chose a "soft" relaxor ferroelectric (RFE) wherein the Curie temperature is close to room temperature. In this case even a small application of stress can change the properties significantly. The relaxor composition chosen was PbMg1/3Nb 2/3O3(90%)-PbTiO3(10%). By systematically changing the substrate and the thickness, stresses in the film the electromechanical constants is varied. High-resolution electron microscopy revealed a distinct change in the microstructure as a function of thickness, and a probable answer as to why thin films show inferior properties compared to bulk materials is proposed. The last part of this thesis focuses on the effect of micro stresses. Two examples are demonstrated where the mechanical forces of interaction between the film and substrate are manipulated on a very local scale. We show that by inducing stresses at local regions one can induce polydomains in film thinner than previously calculated critical thickness, while by removing constraint at local regions we can enhance the d33 co-efficient to values higher than those shown by bulk ceramics.

Structural relaxation in the hydrogen-bonding liquids N-methylacetamide and water studied by optical Kerr effect spectroscopy.

PubMed

Turton, David A; Wynne, Klaas

2008-04-21

Structural relaxation in the peptide model N-methylacetamide (NMA) is studied experimentally by ultrafast optical Kerr effect spectroscopy over the normal-liquid temperature range and compared to the relaxation measured in water at room temperature. It is seen that in both hydrogen-bonding liquids, beta relaxation is present, and in each case, it is found that this can be described by the Cole-Cole function. For NMA in this temperature range, the alpha and beta relaxations are each found to have an Arrhenius temperature dependence with indistinguishable activation energies. It is known that the variations on the Debye function, including the Cole-Cole function, are unphysical, and we introduce two general modifications: One allows for the initial rise of the function, determined by the librational frequencies, and the second allows the function to be terminated in the alpha relaxation.

Exponential decline of aftershocks of the M7.9 1868 great Kau earthquake, Hawaii, through the 20th century

USGS Publications Warehouse

Klein, F.W.; Wright, Tim

2008-01-01

The remarkable catalog of Hawaiian earthquakes going back to the 1820s is based on missionary diaries, newspaper accounts, and instrumental records and spans the great M7.9 Kau earthquake of April 1868 and its aftershock sequence. The earthquake record since 1868 defines a smooth curve complete to M5.2 of the declining rate into the 21st century, after five short volcanic swarms are removed. A single aftershock curve fits the earthquake record, even with numerous M6 and 7 main shocks and eruptions. The timing of some moderate earthquakes may be controlled by magmatic stresses, but their overall long-term rate reflects one of aftershocks of the Kau earthquake. The 1868 earthquake is, therefore, the largest and most controlling stress event in the 19th and 20th centuries. We fit both the modified Omori (power law) and stretched exponential (SE) functions to the earthquakes. We found that the modified Omori law is a good fit to the M ??? 5.2 earthquake rate for the first 10 years or so and the more rapidly declining SE function fits better thereafter, as supported by three statistical tests. The switch to exponential decay suggests that a possible change in aftershock physics may occur from rate and state fault friction, with no change in the stress rate, to viscoelastic stress relaxation. The 61-year exponential decay constant is at the upper end of the range of geodetic relaxation times seen after other global earthquakes. Modeling deformation in Hawaii is beyond the scope of this paper, but a simple interpretation of the decay suggests an effective viscosity of 1019 to 1020 Pa s pertains in the volcanic spreading of Hawaii's flanks. The rapid decline in earthquake rate poses questions for seismic hazard estimates in an area that is cited as one of the most hazardous in the United States.

Oxidative stress augments secretion of endothelium-derived relaxing peptides, C-type natriuretic peptide and adrenomedullin.

PubMed

Chun, T H; Itoh, H; Saito, T; Yamahara, K; Doi, K; Mori, Y; Ogawa, Y; Yamashita, J; Tanaka, T; Inoue, M; Masatsugu, K; Sawada, N; Fukunaga, Y; Nakao, K

2000-05-01

Excess oxidative stress is one of the major metabolic abnormalities on vascular walls in hypertension and atherosclerosis. In order to further elucidate the endothelial function under oxidative stress, the effect of hydrogen peroxide (H2O2) on expression of two novel endothelium-derived vasorelaxing peptides, C-type natriuretic peptide (CNP) and adrenomedullin (AM) from bovine carotid artery endothelial cells (BCAECs) was examined. BCAECs were treated with H2O2 (0.1-1.0 mmol/ l) and/or an antioxidant, N-acetylcysteine (NAC) (5-10 mmol/l), and incubated for 48 h. The concentrations of CNP and AM were measured with the specific radioimmuno assays that we originally developed. CNP and AM mRNA expressions were also examined by reverse transcription-polymerase chain reaction (RT-PCR). Treatment of BCAECs with 0.5 and 1 mmol/l H2O2 induced 9-and 10-fold increases of CNP concentration in the media. Addition of 10 mmol/l NAC significantly suppressed the effect of H2O2 by 52%. RT-PCR analysis showed that CNP mRNA expression in BCAECs was also rapidly augmented within 1 h with H2O2 (1 mmol/l) treatment, and reached a peak at 3 h to show a 10-fold increase. AM secretion from BCAECs also increased to two-fold with exposure to 0.5 mmol/l H2O2, accompanied with the augmented level of AM mRNA. NAC 10 mmol/l completely suppressed the effect of H2O2 on AM secretion. In this study, it has been demonstrated that H2O2 augments endothelial secretion of the two endothelium-derived relaxing peptides, CNP and AM. Our findings suggest the increased secretion of CNP and AM from endothelium under oxidative stress may function to compensate the impaired nitric oxide-dependent vasorelaxation in hypertension and atherosclerosis.

Landscape-scale soil moisture heterogeneity and its influence on surface fluxes at the Jornada LTER site: Evaluating a new model parameterization for subgrid-scale soil moisture variability

NASA Astrophysics Data System (ADS)

Baker, I. T.; Prihodko, L.; Vivoni, E. R.; Denning, A. S.

2017-12-01

Arid and semiarid regions represent a large fraction of global land, with attendant importance of surface energy and trace gas flux to global totals. These regions are characterized by strong seasonality, especially in precipitation, that defines the level of ecosystem stress. Individual plants have been observed to respond non-linearly to increasing soil moisture stress, where plant function is generally maintained as soils dry down to a threshold at which rapid closure of stomates occurs. Incorporating this nonlinear mechanism into landscape-scale models can result in unrealistic binary "on-off" behavior that is especially problematic in arid landscapes. Subsequently, models have `relaxed' their simulation of soil moisture stress on evapotranspiration (ET). Unfortunately, these relaxations are not physically based, but are imposed upon model physics as a means to force a more realistic response. Previously, we have introduced a new method to represent soil moisture regulation of ET, whereby the landscape is partitioned into `BINS' of soil moisture wetness, each associated with a fractional area of the landscape or grid cell. A physically- and observationally-based nonlinear soil moisture stress function is applied, but when convolved with the relative area distribution represented by wetness BINS the system has the emergent property of `smoothing' the landscape-scale response without the need for non-physical impositions on model physics. In this research we confront BINS simulations of Bowen ratio, soil moisture variability and trace gas flux with soil moisture and eddy covariance observations taken at the Jornada LTER dryland site in southern New Mexico. We calculate the mean annual wetting cycle and associated variability about the mean state and evaluate model performance against this variability and time series of land surface fluxes from the highly instrumented Tromble Weir watershed. The BINS simulations capture the relatively rapid reaction to wetting events and more prolonged response to drying cycles, as opposed to binary behavior in the control.

The effects of music relaxation and muscle relaxation techniques on sleep quality and emotional measures among individuals with posttraumatic stress disorder

PubMed Central

Blanaru, Monica; Bloch, Boaz; Vadas, Limor; Arnon, Zahi; Ziv, Naomi; Kremer, Ilana; Haimov, Iris

2012-01-01

Posttraumatic stress disorder (PTSD), an anxiety disorder with lifetime prevalence of 7.8%, is characterized by symptoms that develop following exposure to traumatic life events and that cause an immediate experience of intense fear, helplessness or horror. PTSD is marked by recurrent nightmares typified by the recall of intrusive experiences and by extended disturbance throughout sleep. Individuals with PTSD respond poorly to drug treatments for insomnia. The disadvantages of drug treatment for insomnia underline the importance of non-pharmacological alternatives. Thus, the present study had three aims: first, to compare the efficiency of two relaxation techniques (muscular relaxation and progressive music relaxation) in alleviating insomnia among individuals with PTSD using both objective and subjective measures of sleep quality; second, to examine whether these two techniques have different effects on psychological indicators of PTSD, such as depression and anxiety; and finally, to examine how initial PTSD symptom severity and baseline emotional measures are related to the efficiency of these two relaxation methods. Thirteen PTSD patients with no other major psychiatric or neurological disorders participated in the study. The study comprised one seven-day running-in, no-treatment period, followed by two seven-day experimental periods. The treatments constituted either music relaxation or muscle relaxation techniques at desired bedtime. These treatments were randomly assigned. During each of these three experimental periods, subjects' sleep was continuously monitored with a wrist actigraph (Ambulatory Monitoring, Inc.), and subjects were asked to fill out several questionnaires concerned with a wide spectrum of issues, such as sleep, depression, and anxiety. Analyses revealed a significant increase in objective and subjective sleep efficiency and a significant reduction in depression level following music relaxation. Moreover, following music relaxation, a highly significant negative correlation was found between improvement in objective sleep efficiency and reduction in depression scale. The study's findings provide evidence that music relaxation at bedtime can be used as treatment for insomnia among individuals with PTSD. PMID:25478114

Stability of (Fe-Tm-B) amorphous alloys: relaxation and crystallization phenomena

NASA Astrophysics Data System (ADS)

Zemčík, T.

1994-12-01

Fe-Tm-B base (TM=transition metal) amorphous alloys (metallic glasses) are thermodynamically metastable. This limits their use as otherwise favourable materials, e.g. magnetically soft, corrosion resistant and mechanically firm. By analogy of the mechanical strain-stress dependence, at a certain degree of thermal activation the amorphous structure reaches its limiting state where it changes its character and physical properties. Relaxation and early crystallization processes in amorphous alloys, starting already around 100°C, are reviewed involving subsequently stress relief, free volume shrinking, topological and chemical ordering, pre-crystallization phenomena up to partial (primary) crystallization. Two diametrically different examples are demonstrated from among the soft magnetic materials: relaxation and early crystallization processes in the Fe-Co-B metallic glasses and controlled crystallization of amorphous ribbons yielding rather modern nanocrystalline “Finemet” alloys where late relaxation and pre-crystallization phenomena overlap when forming extremely dispersive and fine-grained nanocrystals-in-amorphous-sauce structure. Mössbauer spectroscopy seems to be unique for magnetic and phase analysis of such complicated systems.

Using a Mobile Application in the Treatment of Dysregulated Anger Among Veterans.

PubMed

Mackintosh, Margaret-Anne; Niehaus, James; Taft, Casey T; Marx, Brian P; Grubbs, Kathleen; Morland, Leslie A

2017-11-01

Anger is a symptom of post-traumatic stress disorder (PTSD) associated with a range of clinical and functional impairments, and may be especially prevalent among veterans with PTSD. Effective anger management therapies exist but may be undermined by poor engagement or lack of treatment availability. Finding ways to engage veterans in anger management therapy or to improve access can be helpful in improving clinical outcomes. This randomized controlled trial compared anger management treatment (AMT) with AMT augmented by a mobile application (app) system, Remote Exercises for Learning Anger and Excitation Management (RELAX). Participants were 58 veterans enrolled in 12 sessions of either AMT alone or AMT with the RELAX system (AMT + RELAX). The RELAX system includes the RELAX app, a wearable heart rate monitor, a remote server, and a web-based therapist interface. RELAX allows the user to practice skills, monitor symptoms, and record physiological data. The server collects data on app use. A web-based interface allows the therapist to access data on between-session practice, and skills use. Measures administered at baseline, post-treatment, and 3-and 6-month follow-up include state and trait anger, dimensions of anger, PTSD, depression, interpersonal functioning, and satisfaction. We used multilevel modeling to account for the nesting of time points within participants and participants within treatment groups. Predictors were Treatment Condition (AMT + RELAX and AMT), Linear Time (baseline, post-treatment, 3-and 6-month follow-up), and Quadratic Time and Treatment Condition × Linear Time interaction. All analyses were conducted using SPSS 21 (Armonk, New York). Approval was obtained from the institutional review board. Across groups, the treatment dropout rate was 13.8%; of those who remained in treatment, 90% received an adequate dose of treatment (10 or more sessions). There were no significant differences between groups on attendance or treatment completion. Participants in both treatments demonstrated statistically significant and clinically meaningful reductions in anger severity and significant post-treatment reductions in PTSD. Veterans did not report significant changes in depression or interpersonal functioning. Veterans in the AMT + RELAX group reported spending significantly less time on homework assignments, and they rated the AMT + RELAX app as helpful and easy to use, with these ratings improving over time. Findings suggest that AMT + RELAX was beneficial in reducing anger symptoms and promoting efficient use of the between-session practice; however, AMT + RELAX did not outperform AMT. This study is an important contribution as it is one of the first randomized controlled trials to study the efficacy of a technology-enhanced, evidence-based psychotherapy for anger management. Findings are limited because of small sample size and modifications to the technology during the trial. However, the results highlight the possible benefits of mobile app-supported treatment, including increasing the accessibility of treatment, lowering therapist workload, reducing costs of treatment, reducing practice time, and enabling new activities and types of treatments. This study presents preliminary evidence that mobile apps can be a valuable addition to treatment for patients with anger difficulties. Future research should evaluate how much therapist involvement is needed to support anger management. Reprint & Copyright © 2017 Association of Military Surgeons of the U.S.

Bending moment evaluation of a long specimen using a radial speckle pattern interferometer in combination with relaxation methods

NASA Astrophysics Data System (ADS)

Pacheco, Anderson; Fontana, Filipe; Viotti, Matias R.; Veiga, Celso L. N.; Lothhammer, Lívia R.; Albertazzi G., Armando, Jr.

2015-08-01

The authors developed an achromatic speckle pattern interferometer able to measure in-plane displacements in polar coordinates. It has been used to measure combined stresses resulting from the superposition of mechanical loading and residual stresses. Relaxation methods have been applied to produce on the surface of the specimen a displacement field that can be used to determine the amount of combined stresses. Two relaxation methods are explored in this work: blind hole-drilling and indentation. The first one results from a blind hole drilled with a high-speed drilling unit in the area of interest. The measured displacement data is fitted in an appropriate model to quantify the stress level using an indirect approach based on a set of finite element coefficients. The second approach uses indentation, where a hard spherical tip is firmly pressed against the surface to be measured with a predetermined indentation load. A plastic flow occurs around the indentation mark producing a radial in-plane displacement field that is related to the amount of combined stresses. Also in this case, displacements are measured by the radial interferometer and used to determine the stresses by least square fitting it to a displacement field determined by calibration. Both approaches are used to quantify the amount of bending stresses and moment in eight sections of a 12 m long 200 mm diameter steel pipe submitted to a known transverse loading. Reference values of bending stresses are also determined by strain gauges. The comparison between the four results is discussed in the paper.

Composite grain size sensitive and grain size insensitive creep of bischofite, carnallite and mixed bischofite-carnallite-halite salt rock

NASA Astrophysics Data System (ADS)

Muhammad, Nawaz; de Bresser, Hans; Peach, Colin; Spiers, Chris

2016-04-01

Deformation experiments have been conducted on rock samples of the valuable magnesium and potassium salts bischofite and carnallite, and on mixed bischofite-carnallite-halite rocks. The samples have been machined from a natural core from the northern part of the Netherlands. Main aim was to produce constitutive flow laws that can be applied at the in situ conditions that hold in the undissolved wall rock of caverns resulting from solution mining. The experiments were triaxial compression tests carried out at true in situ conditions of 70° C temperature and 40 MPa confining pressure. A typical experiment consisted of a few steps at constant strain rate, in the range 10-5 to 10-8 s-1, interrupted by periods of stress relaxation. During the constant strain rate part of the test, the sample was deformed until a steady (or near steady) state of stress was reached. This usually required about 2-4% of shortening. Then the piston was arrested and the stress on the sample was allowed to relax until the diminishing force on the sample reached the limits of the load cell resolution, usually at a strain rate in the order of 10-9 s-1. The duration of each relaxation step was a few days. Carnallite was found to be 4-5 times stronger than bischofite. The bischofite-carnallite-halite mixtures, at their turn, were stronger than carnallite, and hence substantially stronger than pure bischofite. For bischofite as well as carnallite, we observed that during stress relaxation, the stress exponent nof a conventional power law changed from ˜5 at strain rate 10-5 s-1 to ˜1 at 10-9 s-1. The absolute strength of both materials remained higher if relaxation started at a higher stress, i.e. at a faster strain rate. We interpret this as indicating a difference in microstructure at the initiation of the relaxation, notably a smaller grain size related to dynamical recrystallization during the constant strain rate step. The data thus suggest that there is a gradual change in deformation mechanism with decreasing strain rate for both bischofite and carnallite, from grain size insensitive (GSI) dislocation creep at the higher strain rates to grain size sensitive (GSS, i.e. pressure solution) creep at slow strain rate. We can speculate about the composite GSI-GSS nature of the constitutive laws describing the creep of the salt materials.

Simulating the Formation of Lunar Floor-Fracture Craters Using Elastoviscoplastic Relaxation

NASA Technical Reports Server (NTRS)

Dombard, A. J.; Gillis, J. J.

1999-01-01

Lunar floor-fracture craters formed during the height of mare basalt emplacement. Due to a general temporal and spatial relation with the maria, these craters, numbering some 200, may be diagnostic of the thermal structure of the crust during this time. As the name suggests, these craters exhibit brittle failure, generally limited to the central floor region. That, and a shallower depth than fresh lunar craters, has led to two main theories as to their formation: laccolith emplacement under the crater and viscous relaxation. The implications of each model for the state of the Moon's crust during this time are quite different, so the viability of each model must be checked. Laccolith emplacement has been treated elsewhere. However, previous attempts to study the relaxation of the craters have assumed only a uniform, Newtonian viscous response of the near surface to the topographic driving forces, and simply postulated that the fractures resulted from tensile stresses associated with floor uplift. Here, we use a more sophisticated rheological model that includes not only non-Newtonian viscous behavior (i.e., the viscosity is stress-dependent), but also incorporates elastic behavior and a plastic component to the rheology to directly simulate the formation of the floor fractures. The results of our simulations show that while elastoviscoplastic relaxation is potentially viable for larger floor-fracture craters, it is not viable for craters with diameters < or = 60 km, the size of the majority of floor-fracture craters. We employ the finite element method, a numerical technique well suited for boundary-value problems, via the commercially available MARC software package. To test the viability of topographic relaxation, our goal is to prepare the simulations as to maximize the amount of relaxation. We take advantage of the natural axisymmetry of craters, simulating one radial plane. Initial shapes are based on data for fresh craters from Pike. To simplify implementation, a fourth order polynomial is used for the basin, while a third order inverse function is used for the rim. This form closely approximates the long-wavelength behavior of complex craters, while ignoring higher-frequency topography, save the rim. This approximation is appropriate because crater relaxation is strongly controlled by long-wavelength topography. Loading is accomplished assuming a uniform gravity field (1.62 m/s-square) and a uniform density of 2900 kg/cubic m. The initial stress state is set to be hydrostatic, with an additional pressure term to account for any overlying topography. This additional pressure term is tapered exponentially with depth. While the simulations quickly settle on a preferred stress state, and while the final solution is fairly insensitive to the choice of the e-folding depth of the taper, selecting an e-folding depth close to the diameter of the crater sets the initial stress state near the preferred state. We assume a diuranally averaged surface temperature of -20 C, and allow temperature to increase with depth at a rate of 50 K//km. Assuming a thermal conductivity of 2 W/in/K, this gradient translates to a heat flow of 100mW/square m, an extremely high value for the Moon. Temperature, of course, will not increase without bound. To maximize relaxation, we allow our temperature profile to increase linearly until it reaches the solidus (assumed to be 1200C) at a depth of 24.4 km, at which point it is kept constant. The presence of melt will drop the bulk viscosity; however, we have no rheological control for partial melts. Therefore, we make no attempt to simulate this situation. Elastoviscoplastic rheological model. In general, geologic materials can behave in three main ways: elastically, viscously (via solid-state creep), and brittly (plasticity is a continuum approach to simulate this phenomenon). We combine these three deformation mechanisms in an extended Maxwell solid, where the total strain can be broken down into a simple summation of the elastic, creep, and plastic strains. In relaxation phenomena in general, the system takes advantage of any means possible to eliminate deviatoric stresses by relaxing away the topography. Previous analyses have only modeled the viscous response. Comparatively, the elastic response in our model can augment the relaxation, to a point. This effect decreases as the elastic response becomes stiffer; indeed, in the limit of infinite elastic Young's modulus (and with no plasticity), the solution converges on the purely viscous solution. Igneous rocks common to the lunar near-surface have Young's modulii in the range of 10-100 GPa. To maximize relaxation, we use a Young's modulus of 10 GPa. (There is negligible sensitivity to the other elastic modulus, the Poisson's ratio; we use 0.25.) For the viscous response, we use a flow law for steady-state creep in thoroughly dried Columbia diabase, because the high plagioclase (about 70 vol%) and orthopyroxene (about 17 vol%) content is similar to the composition of the lunar highland crust as described by remote sensing and sample studies: noritic anorthosite. This flow law is highly non-Newtonian, i.e., the viscosity is highly stress dependent. That, and the variability with temperature, stands in strong contrast to previous examinations of lunar floor-fracture crater relaxation. To model discrete, brittle faulting, we assume "Byerlee's rule," a standard geodynamical technique. We implement this "rule" with an-angle of internal friction of about 40 deg, and a higher-than-normal cohesion of about 3.2 MPa (to approximate the breaking of unfractured rock). The actual behavior of geologic materials is more complex than in our rheological model, so the uncertainties in the plasticity do not represent the state-of-the-art error. Additional information is contained in the original.

A Viscoelastic earthquake simulator with application to the San Francisco Bay region

USGS Publications Warehouse

Pollitz, Fred F.

2009-01-01

Earthquake simulation on synthetic fault networks carries great potential for characterizing the statistical patterns of earthquake occurrence. I present an earthquake simulator based on elastic dislocation theory. It accounts for the effects of interseismic tectonic loading, static stress steps at the time of earthquakes, and postearthquake stress readjustment through viscoelastic relaxation of the lower crust and mantle. Earthquake rupture initiation and termination are determined with a Coulomb failure stress criterion and the static cascade model. The simulator is applied to interacting multifault systems: one, a synthetic two-fault network, and the other, a fault network representative of the San Francisco Bay region. The faults are discretized both along strike and along dip and can accommodate both strike slip and dip slip. Stress and seismicity functions are evaluated over 30,000 yr trial time periods, resulting in a detailed statistical characterization of the fault systems. Seismicity functions such as the coefficient of variation and a- and b-values exhibit systematic patterns with respect to simple model parameters. This suggests that reliable estimation of the controlling parameters of an earthquake simulator is a prerequisite to the interpretation of its output in terms of seismic hazard.

Long-Term Stress Management.

ERIC Educational Resources Information Center

Noel, James L.

1987-01-01

Techniques enabling faculty to decrease stress to more reasonable and productive levels are discussed, including management of chemical stressors, physical activities, relaxation, coping strategies for disappointment, emotional support, assertiveness, and time management. (MSE)

A simplified method for elastic-plastic-creep structural analysis

NASA Technical Reports Server (NTRS)

Kaufman, A.

1984-01-01

A simplified inelastic analysis computer program (ANSYPM) was developed for predicting the stress-strain history at the critical location of a thermomechanically cycled structure from an elastic solution. The program uses an iterative and incremental procedure to estimate the plastic strains from the material stress-strain properties and a plasticity hardening model. Creep effects are calculated on the basis of stress relaxation at constant strain, creep at constant stress or a combination of stress relaxation and creep accumulation. The simplified method was exercised on a number of problems involving uniaxial and multiaxial loading, isothermal and nonisothermal conditions, dwell times at various points in the cycles, different materials and kinematic hardening. Good agreement was found between these analytical results and nonlinear finite element solutions for these problems. The simplified analysis program used less than 1 percent of the CPU time required for a nonlinear finite element analysis.

A simplified method for elastic-plastic-creep structural analysis

NASA Technical Reports Server (NTRS)

Kaufman, A.

1985-01-01

A simplified inelastic analysis computer program (ANSYPM) was developed for predicting the stress-strain history at the critical location of a thermomechanically cycled structure from an elastic solution. The program uses an iterative and incremental procedure to estimate the plastic strains from the material stress-strain properties and a plasticity hardening model. Creep effects are calculated on the basis of stress relaxation at constant strain, creep at constant stress or a combination of stress relaxation and creep accumulation. The simplified method was exercised on a number of problems involving uniaxial and multiaxial loading, isothermal and nonisothermal conditions, dwell times at various points in the cycles, different materials and kinematic hardening. Good agreement was found between these analytical results and nonlinear finite element solutions for these problems. The simplified analysis program used less than 1 percent of the CPU time required for a nonlinear finite element analysis.

Cognitive-behavioral therapy and hypnotic relaxation to treat sleep problems in an adolescent with diabetes.

PubMed

Perfect, Michelle M; Elkins, Gary R

2010-11-01

Inadequate sleep among adolescents frequently contributes to obesity and reduced academic performance, along with symptoms of anxiety, depression, fatigue, and attention deficits. The etiological bases of sleep quality has been associated with both stress and sleep habits. These problems tend to be especially important for adolescents with diabetes as the effects of poor sleep complicate health outcomes. This case example concerns a 14-year-old adolescent girl with a history of type I diabetes and stress-related sleep difficulties. Treatment included cognitive-behavioral methods and hypnotic relaxation therapy. Results of this case example and other controlled research suggest that hypnotic relaxation therapy is well accepted, results in good compliance, and serves as a useful adjunctive to cognitive-behavioral intervention for sleep problems. © 2010 Wiley Periodicals, Inc.

Computational Fluid Dynamic Solutions of Optimized Heat Shields Designed for Earth Entry

DTIC Science & Technology

2010-01-01

domain ρ = Density (kg/m3) σ = Stefan Boltzmann constant τ = Shear stress tensor τT−V = T-V relaxation time τe−V = e-V relaxation time xi φ = Sweep angle...Vehicle DES = Differential evolutionary Scheme DOR = Design Optimization Tools DPLR = Data Parallel Line Relaxation GSLR = Gauss- Seidel Line... Stefan - Boltzmann constant. This model provides accurate heating predictions, especially for the non-ablating heat-shields explored in this work. Various

Stress management using UMTS cellular phones: a controlled trial.

PubMed

Riva, Giuseppe; Preziosa, Alessandra; Grassi, Alessandra; Villani, Daniela

2006-01-01

One of the best strategies for dealing with stress is learning how to relax. However, relaxing is difficult to achieve in typical real world situations. For this study, we developed a specific protocol based on mobile narratives - multimedia narratives experienced on UMTS/3G phones - to help workers in reducing commuting stress. In a controlled trial 33 commuters were randomly divided between three conditions: Mobile narratives (MN); New age music and videos (NA); no treatment (CT). In two consecutive days the MN and NA samples experienced during their commute trip 2 x 2 6-minute multimedia experiences on a Motorola A925 3G phone provided by the "TRE" Italian UMTS carrier: the MN sample experienced a mobile narrative based on the exploration of a desert beach; the NA sample experienced a commercial new age video with similar visual contents. The trials showed the efficacy of mobile narratives in reducing the level of stress experienced during a commute trip. No effects were found in the other groups. These results suggest that 3G mobile handsets may be used as relaxation tool if backed by a specific therapeutic protocol and meaningful narratives.

[Relaxation treatments and biofeedback for anxiety and somatic stress-related disorders].

PubMed

Biondi, Massimo; Valentini, Martina

2014-01-01

Relaxation techniques (TR) and biofeedback (BFB) are widely used in psychiatric and psychological practice for the treatment for anxiety and stress-related disorders. An examination of studies focusing on the correlates of psychophysiology of relaxation and biofeedback has been done, in addiction to controlled therapeutic studies that describes clinical aspects, efficacy and limits. There are different TR and BFB procedures, but they have the same goal and same physiological modifications, resulting in stress and anxiety reduction. There is a proven action to musculoskeletal, neuroendocrine and autonomic nervous system, showing similar results. Very few data on immune changes are available. Meta-Analysis show superior efficacy to no treatment or placebo in anxiety disorders, tension headache, bruxism, temporomandibular pain syndrome, rehabilitation and prevention of ischemic heart disease. Moderate efficacy is shown for chronic low back pain, cancer-related pain, rheumatoid arthritis and gastrointestinal disorders; data for essential hypertension are controversial. Variability of techniques, procedures, sampling problems, non-systematic make definitive conclusions difficult. TR and BFB are often used in combination with cognitive-behavioral and educational techniques. The association of the active relaxation technique facilitates generalization and self-control during stress situation and outside the training session. TR and BFB are effective for anxiety and somatic stress-related disorders, associated with coping and quality of life improvement and affordable costs; they are minimally invasive but needing an active participation in the treatment process. Some limits are responders' prediction, continuity of practice and limited effectiveness for depression disorders. Finally, it is shown that they are real psychosomatic therapies that are able to produce somatic peripheral changes (neuroendocrine, neurovegetative and muscular systems) generated by the mind and secondary to the involvement of central neurotransmitter circuits.

Alleviating Stress for Women Administrators.

ERIC Educational Resources Information Center

Ten Elshof, Annette; Tomlinson, Elaine

1981-01-01

Describes a workshop designed to help women administrators assess individual stress levels. Stress can be alleviated through exercise, support groups or networking, sleep and diet, relaxation, guided fantasy, and planned activity. The long-term implications include preventing illness and making women more effective within the administrative…

Precipitation behavior in a nitride-strengthened martensitic heat resistant steel during hot deformation.

PubMed

Zhang, Wenfeng; Su, Qingyong; Xu, Mi; Yan, Wei

2015-09-01

The stress relaxation curves for three different hot deformation processes in the temperature range of 750-1000 °C were studied to develop an understanding of the precipitation behavior in a nitride-strengthened martensitic heat resistant steel (Zhang et al., Mater. Sci. Eng. A, 2015) [1]. This data article provides supporting data and detailed information on how to accurately analysis the stress relaxation data. The statistical analysis of the stress peak curves, including the number of peaks, the intensity of the peaks and the integral value of the pumps, was carried out. Meanwhile, the XRD energy spectrum data was also calculated in terms of lattice distortion.

Precipitation behavior in a nitride-strengthened martensitic heat resistant steel during hot deformation

PubMed Central

Zhang, Wenfeng; Su, Qingyong; Xu, Mi; Yan, Wei

2015-01-01

The stress relaxation curves for three different hot deformation processes in the temperature range of 750–1000 °C were studied to develop an understanding of the precipitation behavior in a nitride-strengthened martensitic heat resistant steel (Zhang et al., Mater. Sci. Eng. A, 2015) [1]. This data article provides supporting data and detailed information on how to accurately analysis the stress relaxation data. The statistical analysis of the stress peak curves, including the number of peaks, the intensity of the peaks and the integral value of the pumps, was carried out. Meanwhile, the XRD energy spectrum data was also calculated in terms of lattice distortion. PMID:26306310

Surface mechanical property and residual stress of peened nickel-aluminum bronze determined by in-situ X-ray diffraction

NASA Astrophysics Data System (ADS)

Wang, Chengxi; Jiang, Chuanhai; Zhao, Yuantao; Chen, Ming; Ji, Vincent

2017-10-01

As one of the most important surface strengthening method, shot peening is widely used to improve the fatigue and stress corrosion crack resistance of components by introducing the refined microstructure and compressive residual stress in the surface layer. However, the mechanical properties of this thin layer are different from the base metal and are difficult to be characterized by conventional techniques. In this work, a micro uniaxial tensile tester equipped with in-situ X-ray stress analyzer was employed to make it achievable on a nickel-aluminum bronze with shot peening treatment. According to the equivalent stress-strain relationship based on Von Mises stress criterion, the Young's modulus and yield strength of the peened layer were calculated. The results showed that the Young's modulus was the same as the bulk material, and the yield strength corresponding to the permanent plastic strain of 0.2% was increased by 21% after SP. But the fractographic analysis showed that the fracture feature of the surface layer was likely to transform from the dimple to the cleavage, indicating the improved strength might be attained at the expense of ductility. The monotonic and cyclic loading were also performed via the same combined set-up. In addition, the specific relaxation behavior of compressive residual stress was quantified by linear logarithm relationship between residual stress and cycle numbers. It was found that the compressive residual stress mainly relaxed in the first few cycles, and then reached steady state with further cycles. The relaxation rate and the stable value were chiefly depended on the stress amplitude and number of cycles. The retained residual stress kept in compressive under all given applied stress levels, suggesting that the shot peening could introduce a more stable surface layer of compressive residual stress other than the elevated strength of nickel-aluminum bronze alloy.

Origin of MeV ion irradiation-induced stress changes in SiO2

NASA Astrophysics Data System (ADS)

Brongersma, M. L.; Snoeks, E.; van Dillen, T.; Polman, A.

2000-07-01

The 4 MeV Xe ion irradiation of a thin thermally grown SiO2 film on a Si substrate leads to four different effects in which each manifests itself by a characteristic change in the mechanical stress state of the film: densification, ascribed to a beam-induced structural change in the silica network; stress relaxation by radiation-enhanced plastic flow; anisotropic expansion and stress generation; and transient stress relaxation ascribed to the annealing of point defects. Using sensitive wafer-curvature measurements, in situ measurements of the in-plane mechanical stress were made during and after ion irradiation at various temperatures in the range from 95 to 575 K, in order to study the magnitude of these effects, the mechanism behind them, as well as their interplay. It is found that the structural transformation leads to a state with an equilibrium density that is 1.7%-3.2% higher than the initial state, depending on the irradiation temperature. Due to the constraint imposed by the substrate, this transformation causes a tensile in-plane stress in the oxide film. This stress is relaxed by plastic flow, leading to densification of the film. The anisotropic strain-generation rate decreases linearly with temperature from (2.5±0.4)×10-17cm2/ion at 95 K to (-0.9±0.7)×10-17 cm2/ion at 575 K. The spectrum of irradiation-induced point defects, measured from the stress change after the ion beam was switched off, peaks below 0.23 eV and extends up to 0.80 eV. All four irradiation-induced effects can be described using a thermal spike model.

Mechanical characterization of stomach tissue under uniaxial tensile action.

PubMed

Jia, Z G; Li, W; Zhou, Z R

2015-02-26

In this article, the tensile properties of gastric wall were investigated by using biomechanical test and theoretical analysis. The samples of porcine stomach strips from smaller and greater curvature of the stomach were cut in longitudinal and circumferential direction, respectively. The loading-unloading, stress relaxation, strain creep, tensile fracture tests were performed at mucosa-submucosa, serosa-muscle and intact layer, respectively. Results showed that the biomechanical properties of the porcine stomach depended on the layers, orientations and locations of the gastric wall and presented typical viscoelastic, nonlinear and anisotropic mechanical properties. During loading-unloading test, the stress of serosa-muscle layer in the longitudinal direction was 15-20% more than that in the circumferential direction at 12% stretch ratio, while it could reach about 40% for the intact layer and 50% for the mucosa-submucosa layer. The results of stress relaxation and strain creep showed that the variation degree was obviously faster in the circumferential direction than that in the longitudinal direction, and the ultimate residual values were also different for the different layers, orientations and locations. In the process of fracture test, the serosa-muscle layer fractured firstly followed by the mucosa-submucosa layer when the intact layer was tested, the longitudinal strips firstly began to fracture and the required stress value was about twice as much as that in the circumferential strips. The anisotropy and heterogeneity of mechanical characterization of the porcine stomach were related to its complicated geometry, structure and functions. The results would help us to understand the biomechanics of soft organ tissue. Copyright © 2015 Elsevier Ltd. All rights reserved.

Postseismic deformation following the 2015 Mw 7.8 Gorkha earthquake and the distribution of brittle and ductile crustal processes beneath Nepal

NASA Astrophysics Data System (ADS)

Moore, J. D. P.; Barbot, S.; Peng, D.; Yu, H.; Qiu, Q.; Wang, T.; Masuti, S.; Dauwels, J.; Lindsey, E. O.; Tang, C. H.; Feng, L.; Wei, S.; Hsu, Y. J.; Nanjundiah, P.; Lambert, V.; Antoine, S.

2017-12-01

Studies of geodetic data across the earthquake cycle indicate that a wide range of mechanisms contribute to cycles of stress buildup and relaxation. Both on-fault rate and state friction and off-fault rheologies can contribute to the observed deformation; in particular, during the postseismic transient phase of the earthquake cycle. We present a novel approach to simulate on-fault and off-fault deformation simultaneously using analytical Green's functions for distributed deformation at depth [Barbot, Moore and Lambert., 2017] and surface tractions, within an integral framework [Lambert & Barbot, 2016]. This allows us to jointly explore dynamic frictional properties on the fault, and the plastic properties of the bulk rocks (including grain size and water distribution) in the lower crust with low computational cost, whilst taking into account contributions from topography and a surface approximation for gravity. These displacement and stress Green's functions can be used for both forward and inverse modelling of distributed shear, where the calculated strain-rates can be converted to effective viscosities. Here, we draw insight from the postseismic geodetic observations following the 2015 Mw 7.8 Gorkha earthquake. We forward model afterslip using rate and state friction on the megathrust geometry with the two ramp-décollement system presented by Hubbard et al., (2016) and viscoelastic relaxation using recent experimentally derived flow laws with transient rheology and the thermal structure from Cattin et al. (2001). Multivariate posterior probability density functions for model parameters are generated by incorporating the forward model evaluation and comparison to geodetic observations into a Gaussian copula framework. In particular, we find that no afterslip occurred on the up-dip portion of the fault beneath Kathmandu. A combination of viscoelastic relaxation and down-dip afterslip is required to fit the data, taking into account the bi-directional coupling between the two processes. Finally, the inclusion of topographic corrections can modify the modelled deformation field by around 10%. The postseismic deformation brings new insights into the distribution of brittle and ductile crustal processes beneath Nepal, with serious implications for future seismic hazard at Kathmandu.

Osmoregulation in Methanogens (and Other Interesting Organisms)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roberts, Mary Fedarko

2014-12-03

Our research has been aimed at (i) identifying, (ii) determining mode of regulation, and (iii) understanding how different classes of compatible solutes (also termed osmolytes) affect macromolecular stability in response to osmotic and thermal stress. For solutes we have identified (e.g., di-inositol-1,1’-phosphate (DIP)), we used NMR to elucidate biosynthetic pathways and then cloned suspected enzymes in the pathway to explore how they are regulated. Compatible solutes are thought to protect proteins from thermal and osmotic stresses by being excluded from the surface, allowing critical water molecules to interact with the protein. This implies there are no specific binding interactions betweenmore » osmolytes and proteins. However, we and others have often observed very specific solute effects for proteins that suggest a more direct interaction between solute and protein is likely can occur. Measuring such a weak interaction is extremely difficult. We have developed a solution NMR method, high-resolution field cycling relaxometry, that can measure spin-lattice relaxation rates as a function of magnetic field from 11.7 (the field of a 500 MHz spectrometer) to 0.003 T. The methodology is ideal for nuclei in small molecules with moderately long relaxation times at high fields – phosphate groups (31P), enriched carbonyls (13C), or methyl groups (1H). The protein of interest is spin-labeled to introduce a large dipole on it that will dominate the relaxation of nuclei on any small molecules that bind transiently. The key is to measure relaxation below 1-2 T (and extract nuclei-spin label distances in the bound complex) where the small molecule relaxation will be dominated by dipolar mechanisms with a correlation time indicative of the large protein complex. Our explorations of an inositol monophosphatase (the last step in DIP generation) localized four discrete binding sides for the thermoprotectant α-glutamate. This is a novel approach, and while the work did not fully explain how this solute protected the IMPase from thermal denaturation, it did showcase a new and exciting method to monitor weak binding in biological systems.« less

Imposition of physical parameters in dissipative particle dynamics

NASA Astrophysics Data System (ADS)

Mai-Duy, N.; Phan-Thien, N.; Tran-Cong, T.

2017-12-01

In the mesoscale simulations by the dissipative particle dynamics (DPD), the motion of a fluid is modelled by a set of particles interacting in a pairwise manner, and it has been shown to be governed by the Navier-Stokes equation, with its physical properties, such as viscosity, Schmidt number, isothermal compressibility, relaxation and inertia time scales, in fact its whole rheology resulted from the choice of the DPD model parameters. In this work, we will explore the response of a DPD fluid with respect to its parameter space, where the model input parameters can be chosen in advance so that (i) the ratio between the relaxation and inertia time scales is fixed; (ii) the isothermal compressibility of water at room temperature is enforced; and (iii) the viscosity and Schmidt number can be specified as inputs. These impositions are possible with some extra degrees of freedom in the weighting functions for the conservative and dissipative forces. Numerical experiments show an improvement in the solution quality over conventional DPD parameters/weighting functions, particularly for the number density distribution and computed stresses.

The effect of relaxation therapy on autonomic functioning, symptoms and daily functioning, in patients with chronic fatigue syndrome or fibromyalgia: a systematic review.

PubMed

Meeus, Mira; Nijs, Jo; Vanderheiden, Tanja; Baert, Isabel; Descheemaeker, Filip; Struyf, Filip

2015-03-01

To establish the effects of relaxation therapy on autonomic function, pain, fatigue and daily functioning in patients with chronic fatigue syndrome or fibromyalgia. A systematic literature study was performed. Using specific keywords related to fibromyalgia or chronic fatigue syndrome and relaxation therapy, the electronic databases PubMed and Web of Science were searched. Included articles were assessed for their risk of bias and relevant information regarding relaxation was extracted. The review was conducted and reported according to the PRISMA-statement. Thirteen randomized clinical trials of sufficient quality were included, resulting in a total of 650 fibromyalgia patients (11 studies) and 88 chronic fatigue syndrome patients (3 studies). None of the studies reported effects on autonomic function. Six studies reported the effect of guided imagery on pain and daily functioning in fibromyalgia. The acute effect of a single session of guided imagery was studied in two studies and seems beneficial for pain relief. For other relaxation techniques (eg. muscle relaxation, autogenic training) no conclusive evidence was found for the effect on pain and functioning in fibromyalgia patients comparison to multimodal treatment programs. For fatigue a multimodal approach seemed better than relaxation, as shown in the sole three studies on chronic fatigue syndrome patients. There is moderate evidence for the acute effect of guided imagery on pain, although the content of the visualization is a matter of debate. Other relaxation formats and the effects on functionality and autonomic function require further study. © The Author(s) 2014.

Mechanistic link between erectile dysfunction and systemic endothelial dysfunction in type 2 diabetic rats

PubMed Central

Musicki, Biljana; Hannan, Johanna L.; Lagoda, Gwen; Bivalacqua, Trinity J.; Burnett, Arthur L.

2016-01-01

Men with type 2 diabetes mellitus (T2DM) and erectile dysfunction (ED) have greater risk of cardiovascular events than T2DM men without ED, suggesting ED as a predictor of cardiovascular events in diabetic men. However, molecular mechanisms underlying endothelial dysfunction in the diabetic penis explaining these clinical observations are not known. We evaluated whether the temporal relationship between ED and endothelial dysfunction in the systemic vasculature in T2DM involves earlier redox imbalance and endothelial nitric oxidase synthase (eNOS) dysfunction in the penis than in the systemic vasculature, such as the carotid artery. Rats were rendered T2DM by high-fat diet for 2 weeks, followed by an injection with low-dose streptozotocin. After 3 weeks, erectile function (intracavernosal pressure) was measured and penes and carotid arteries were collected for molecular analyses of eNOS uncoupling, protein S-glutathionylation, oxidative stress (4-hydroxy-2-nonenal, 4-HNE), protein expression of NADPH oxidase subunit gp91phox, endothelium-dependent vasodilation in the carotid artery, and non-andrenergic, non-cholinergic (NANC) mediated cavernosal relaxation. Erectile response to electrical stimulation of the cavernous nerve and NANC mediated cavernosal relaxation were decreased (p<0.05), while relaxation of the carotid artery to acetylcholine was not impaired in T2DM rats. eNOS monomerization, protein expressions of 4-HNE and gp91phox, and protein S-glutathionylation, were increased (p<0.05) in the penis, but not in the carotid artery, of T2DM compared to nondiabetic rats. In conclusion, redox imbalance, increased oxidative stress by NADPH oxidase, and eNOS uncoupling, occur early in T2DM in the penis, but not in the carotid artery. These molecular changes contribute to T2DM ED, while vascular function in the systemic vasculature remains preserved. PMID:27153512

Elliptic Relaxation of a Tensor Representation of the Pressure-Strain and Dissipation Rate

NASA Technical Reports Server (NTRS)

Carlson, John R.; Gatski, Thomas B.

2002-01-01

A formulation to include the effects of wall-proximity in a second moment closure model is presented that utilizes a tensor representation for the redistribution term in the Reynolds stress equations. The wall-proximity effects are modeled through an elliptic relaxation process of the tensor expansion coefficients that properly accounts for both correlation length and time scales as the wall is approached. DNS data and Reynolds stress solutions using a full differential approach at channel Reynolds number of 590 are compared to the new model.

Tensorial analysis of Eshelby stresses in 3D supercooled liquids

NASA Astrophysics Data System (ADS)

Lemaître, Anaël

2015-10-01

It was recently proposed that the local rearrangements governing relaxation in supercooled liquids impress on the liquid medium long-ranged (Eshelby) stress fluctuations that accumulate over time. From this viewpoint, events must be characterized by elastic dipoles, which are second order tensors, and Eshelby fields are expected to show up in stress and stress increment correlations, which are fourth order tensor fields. We construct here an analytical framework that permits analyzing such tensorial correlations in isotropic media in view of accessing Eshelby fields. Two spherical bases are introduced, which correspond to Cartesian and spherical coordinates for tensors. We show how they can be used to decompose stress correlations and thus test such properties as isotropy and power-law scalings. Eshelby fields and the predicted stress correlations in an infinite medium are shown to belong to an algebra that can conveniently be described using the spherical tensor bases. Using this formalism, we demonstrate that the inherent stress field of 3D supercooled liquids is power law correlated and carries the signature of Eshelby fields, thus supporting the idea that relaxation events give rise to Eshelby stresses that accumulate over time.

The first experimental confirmation of the fractional kinetics containing the complex-power-law exponents: Dielectric measurements of polymerization reactions

NASA Astrophysics Data System (ADS)

Nigmatullin, R. R.; Arbuzov, A. A.; Salehli, F.; Giz, A.; Bayrak, I.; Catalgil-Giz, H.

2007-01-01

For the first time we achieved incontestable evidence that the real process of dielectric relaxation during the polymerization reaction of polyvinylpyrrolidone (PVP) is described in terms of the fractional kinetic equations containing complex-power-law exponents. The possibility of the existence of the fractional kinetics containing non-integer complex-power-law exponents follows from the general theory of dielectric relaxation that has been suggested recently by one of the authors (R.R.N). Based on the physical/geometrical meaning of the fractional integral with complex exponents there is a possibility to develop a general theory of dielectric relaxation based on the self-similar (fractal) character of the reduced (averaged) microprocesses that take place in the mesoscale region. This theory contains some essential predictions related to existence of the non-integer power-law kinetics and the results of this paper can be considered as the first confirmation of existence of the kinetic phenomena that are described by fractional derivatives with complex-power-law exponents. We want to stress here that with the help of a new complex fitting function for the complex permittivity it becomes possible to describe the whole process for real and imaginary parts simultaneously throughout the admissible frequency range (30 Hz-13 MHz). The fitting parameters obtained for the complex permittivity function for three temperatures (70, 90 and 110 °C) confirm in general the picture of reaction that was known qualitatively before. They also reveal some new features, which improve the interpretation of the whole polymerization process. We hope that these first results obtained in the paper will serve as a good stimulus for other researches to find the traces of the existence of new fractional kinetics in other relaxation processes unrelated to the dielectric relaxation. These results should lead to the reconsideration and generalization of irreversibility and kinetic phenomena that can take place for many linear non-equilibrium systems.

Personal Approaches to Stress Reduction: A Workshop.

ERIC Educational Resources Information Center

Remer, Rory

1984-01-01

Seven topic areas which may be variously combined to comprise a workshop in personal stress reduction are outlined. They include definitions and types of stress, life style planning, nutrition, exercise, networking/social support system, relaxation and other trophotropic interventions, and communication skills. Suggestions are included for…

Self-Management Procedures for Coping with Stress

ERIC Educational Resources Information Center

Vattano, Anthony J.

1978-01-01

Relaxation training, systematic desensitization, and meditation are effective self-management procedures for coping with stress and anxiety. This article describes research on stress and anxiety that led to development of these techniques, as well as current applications, and implications for social work education and practice. (Author)

Raman Study of Uncoated and P-bn/sic-coated Hi-nicalon Reinforced Celsian Matrix Composites. Part 2; Residual Stress in the Fibers

NASA Technical Reports Server (NTRS)

Gouadec, Gwenael; Colomban, Philippe; Bansal, Narottam P.

2000-01-01

Band shifts on Raman spectra were used to assess, at a microscopic scale, the residual strain existing in Hi-Nicalon fibers reinforcing celsian matrix composites. Uncoated as well as p-BN/SiC- and p-B(Si)N/SiC-coated Hi-Nicalon fibers were used as the reinforcements. We unambiguously conclude that the fibers are in a state of compressive residual stress. Quantitative determination of the residual stress was made possible by taking into account the heating induced by laser probing and by using a reference line, of fixed wavenumber. We found fiber compressive residual stress values between 110 and 960 MPa depending on the fiber/matrix coating in the composite. A stress relaxation-like phenomenon was observed at the surface of p-BN/SiC-coated Hi-Nicalon fibers whereas the uncoated or p-B(Si)N/SiC-coated Hi-Nicalon fibers did not show any stress relaxation in the Celsian matrix composites.

Mesoscopic Simulations of Crosslinked Polymer Networks

NASA Astrophysics Data System (ADS)

Megariotis, Grigorios; Vogiatzis, Georgios G.; Schneider, Ludwig; Müller, Marcus; Theodorou, Doros N.

2016-08-01

A new methodology and the corresponding C++ code for mesoscopic simulations of elastomers are presented. The test system, crosslinked ds-1’4-polyisoprene’ is simulated with a Brownian Dynamics/kinetic Monte Carlo algorithm as a dense liquid of soft, coarse-grained beads, each representing 5-10 Kuhn segments. From the thermodynamic point of view, the system is described by a Helmholtz free-energy containing contributions from entropic springs between successive beads along a chain, slip-springs representing entanglements between beads on different chains, and non-bonded interactions. The methodology is employed for the calculation of the stress relaxation function from simulations of several microseconds at equilibrium, as well as for the prediction of stress-strain curves of crosslinked polymer networks under deformation.

Anger Management Program Participants Gain Behavioral Changes in Interpersonal Relationships

ERIC Educational Resources Information Center

Pish, Suzanne; Clark-Jones, Teresa; Eschbach, Cheryl; Tiret, Holly

2016-01-01

RELAX: Alternatives to Anger is an educational anger management program that helps adults understand and manage anger, develop communication skills, manage stress, and make positive behavioral changes in their interpersonal relationships. A sample of 1,168 evaluation surveys were collected from RELAX: Alternatives to Anger participants over 3…

Efficacy of Abbreviated Progressive Muscle Relaxation Training: A Quantitative Review of Behavioral Medicine Research.

ERIC Educational Resources Information Center

Carlson, Charles R.; Hoyle, Rick H.

1993-01-01

Conducted quantitative review of research in which abbreviated progressive muscle relaxation training (APRT) was used as intervention for psychophysiological and stress-related disorders. Calculated strength of association between APRT and outcome measures for 29 experiments published after 1980. APRT was most strongly associated with improvement…

The poro-viscoelastic properties of trabecular bone: a micro computed tomography-based finite element study.

PubMed

Sandino, Clara; McErlain, David D; Schipilow, John; Boyd, Steven K

2015-04-01

Bone is a porous structure with a solid phase that contains hydroxyapatite and collagen. Due to its composition, bone is often represented either as a poroelastic or as a viscoelastic material; however, the poro-viscoelastic formulation that allows integrating the effect of both the fluid flow and the collagen on the mechanical response of the tissue, has not been applied yet. The objective of this study was to develop a micro computed tomography (µCT)-based finite element (FE) model of trabecular bone that includes both the poroelastic and the viscoelastic nature of the tissue. Cubes of trabecular bone (N=25) from human distal tibia were scanned with µCT and stress relaxation experiments were conducted. The µCT images were the basis for sample specific FE models, and the stress relaxation experiments were simulated applying a poro-viscoelastic formulation. The model considers two scales of the tissue: the intertrabecular pore and the lacunar-canalicular pore scales. Independent viscoelastic and poroelastic models were also developed to determine their contribution to the poro-viscoelastic model. All the experiments exhibited a similar relaxation trend. The average reaction force before relaxation was 9.28 × 10(2)N (SD ± 5.11 × 10(2)N), and after relaxation was 4.69 × 10(2)N (SD ± 2.88 × 10(2)N). The slope of the regression line between the force before and after relaxation was 1.92 (R(2)=0.96). The poro-viscoelastic models captured 49% of the variability of the experimental data before relaxation and 33% after relaxation. The relaxation predicted with viscoelastic models was similar to the poro-viscoelastic ones; however, the poroelastic formulation underestimated the reaction force before relaxation. These data suggest that the contribution of viscoelasticity (fluid flow-independent mechanism) to the mechanical response of the tissue is significantly greater than the contribution of the poroelasticity (fluid flow-dependent mechanism). Copyright © 2015 Elsevier Ltd. All rights reserved.

Improvement of emotional healthcare system with stress detection from ECG signal.

PubMed

Tivatansakul, S; Ohkura, M

2015-01-01

Our emotional healthcare system is designed to cope with users' negative emotions in daily life. To make the system more intelligent, we integrated emotion recognition by facial expression to provide appropriate services based on user's current emotional state. Our emotion recognition by facial expression has confusion issue to recognize some positive, neutral and negative emotions that make the emotional healthcare system provide a relaxation service even though users don't have negative emotions. Therefore, to increase the effectiveness of the system to provide the relaxation service, we integrate stress detection from ECG signal. The stress detection might be able to address the confusion issue of emotion recognition by facial expression to provide the service. Indeed, our results show that integration of stress detection increases the effectiveness and efficiency of the emotional healthcare system to provide services.

Bread dough rheology: Computing with a damage function model

NASA Astrophysics Data System (ADS)

Tanner, Roger I.; Qi, Fuzhong; Dai, Shaocong

2015-01-01

We describe an improved damage function model for bread dough rheology. The model has relatively few parameters, all of which can easily be found from simple experiments. Small deformations in the linear region are described by a gel-like power-law memory function. A set of large non-reversing deformations - stress relaxation after a step of shear, steady shearing and elongation beginning from rest, and biaxial stretching, is used to test the model. With the introduction of a revised strain measure which includes a Mooney-Rivlin term, all of these motions can be well described by the damage function described in previous papers. For reversing step strains, larger amplitude oscillatory shearing and recoil reasonable predictions have been found. The numerical methods used are discussed and we give some examples.

Strain Modulations as a Mechanism to Reduce Stress Relaxation in Laryngeal Tissues

PubMed Central

Hunter, Eric J.; Siegmund, Thomas; Chan, Roger W.

2014-01-01

Vocal fold tissues in animal and human species undergo deformation processes at several types of loading rates: a slow strain involved in vocal fold posturing (on the order of 1 Hz or so), cyclic and faster posturing often found in speech tasks or vocal embellishment (1–10 Hz), and shear strain associated with vocal fold vibration during phonation (100 Hz and higher). Relevant to these deformation patterns are the viscous properties of laryngeal tissues, which exhibit non-linear stress relaxation and recovery. In the current study, a large strain time-dependent constitutive model of human vocal fold tissue is used to investigate effects of phonatory posturing cyclic strain in the range of 1 Hz to 10 Hz. Tissue data for two subjects are considered and used to contrast the potential effects of age. Results suggest that modulation frequency and extent (amplitude), as well as the amount of vocal fold overall strain, all affect the change in stress relaxation with modulation added. Generally, the vocal fold cover reduces the rate of relaxation while the opposite is true for the vocal ligament. Further, higher modulation frequencies appear to reduce the rate of relaxation, primarily affecting the ligament. The potential benefits of cyclic strain, often found in vibrato (around 5 Hz modulation) and intonational inflection, are discussed in terms of vocal effort and vocal pitch maintenance. Additionally, elderly tissue appears to not exhibit these benefits to modulation. The exacerbating effect such modulations may have on certain voice disorders, such as muscle tension dysphonia, are explored. PMID:24614616

Strain modulations as a mechanism to reduce stress relaxation in laryngeal tissues.

PubMed

Hunter, Eric J; Siegmund, Thomas; Chan, Roger W

2014-01-01

Vocal fold tissues in animal and human species undergo deformation processes at several types of loading rates: a slow strain involved in vocal fold posturing (on the order of 1 Hz or so), cyclic and faster posturing often found in speech tasks or vocal embellishment (1-10 Hz), and shear strain associated with vocal fold vibration during phonation (100 Hz and higher). Relevant to these deformation patterns are the viscous properties of laryngeal tissues, which exhibit non-linear stress relaxation and recovery. In the current study, a large strain time-dependent constitutive model of human vocal fold tissue is used to investigate effects of phonatory posturing cyclic strain in the range of 1 Hz to 10 Hz. Tissue data for two subjects are considered and used to contrast the potential effects of age. Results suggest that modulation frequency and extent (amplitude), as well as the amount of vocal fold overall strain, all affect the change in stress relaxation with modulation added. Generally, the vocal fold cover reduces the rate of relaxation while the opposite is true for the vocal ligament. Further, higher modulation frequencies appear to reduce the rate of relaxation, primarily affecting the ligament. The potential benefits of cyclic strain, often found in vibrato (around 5 Hz modulation) and intonational inflection, are discussed in terms of vocal effort and vocal pitch maintenance. Additionally, elderly tissue appears to not exhibit these benefits to modulation. The exacerbating effect such modulations may have on certain voice disorders, such as muscle tension dysphonia, are explored.

A Mixed-Methods Pilot Study of Mindfulness-Based Stress Reduction for HIV-Associated Chronic Pain.

PubMed

George, Mary Catherine; Wongmek, Arada; Kaku, Michelle; Nmashie, Alexandra; Robinson-Papp, Jessica

2017-01-01

Treatment guidelines for chronic pain recommend nonpharmacologic modalities as part of a comprehensive management plan. Chronic pain is common among people living with HIV/AIDS, but there is little data to guide the choice of nonpharmacologic therapies in this complex population. We performed a mixed-methods feasibility study of Mindfulness-Based Stress Reduction (MBSR) versus health education control with 32 inner city, HIV-infected participants. Outcome measures included: the Brief Pain Inventory, Perceived Stress Scale, HIV Symptoms Index, autonomic function testing, and audiotaped focus groups. Post-intervention, participants reported modest improvements in pain measures and perceived stress, but no effect of group assignment was observed. At 3-month follow-up, 79% of MBSR participants were still practicing, and pain intensity was improved, whereas in the control group pain intensity had worsened. Qualitative analysis revealed a strong sense of community in both groups, but only MBSR was perceived as useful for relaxation and pain relief.

Stress: The Special Educator's Perspective.

ERIC Educational Resources Information Center

Raschke, Donna; And Others

1988-01-01

The article describes approaches special education teachers can take to reduce stress including diet and exercise, relaxation techniques, use of social support systems, goal setting, time management, and networking. A survey of special education teachers found the use of humor the most common strategy for coping with stress. (DB)

Special Teacher Stress: Its Product and Prevention. Special Report.

ERIC Educational Resources Information Center

Bradfield, Robert H.; Fones, Donald M.

1985-01-01

Findings from a study involving 60 special education teachers examine characteristics of 20 Ss who scored highest and 20 who scored lowest on both job stress and life stress measures. Teachers are urged to begin relaxation training, exercise, emphasize positive attitudes, and maintain adequate diets. (CL)

Goal-orientated cognitive rehabilitation for dementias associated with Parkinson's disease-A pilot randomised controlled trial.

PubMed

Hindle, John V; Watermeyer, Tamlyn J; Roberts, Julie; Brand, Andrew; Hoare, Zoe; Martyr, Anthony; Clare, Linda

2018-05-01

To examine the appropriateness and feasibility of cognitive rehabilitation for people with dementias associated with Parkinson's in a pilot randomised controlled study. This was a single-blind pilot randomised controlled trial of goal-oriented cognitive rehabilitation for dementias associated with Parkinson's. After goal setting, participants were randomised to cognitive rehabilitation (n = 10), relaxation therapy (n = 10), or treatment-as-usual (n = 9). Primary outcomes were ratings of goal attainment and satisfaction with goal attainment. Secondary outcomes included quality of life, mood, cognition, health status, everyday functioning, and carers' ratings of goal attainment and their own quality of life and stress levels. Assessments were at 2 and 6 months following randomisation. At 2 months, cognitive rehabilitation was superior to treatment-as-usual and relaxation therapy for the primary outcomes of self-rated goal attainment (d = 1.63 and d = 1.82, respectively) and self-rated satisfaction with goal attainment (d = 2.04 and d = 1.84). At 6 months, cognitive rehabilitation remained superior to treatment-as-usual (d = 1.36) and relaxation therapy (d = 1.77) for self-rated goal attainment. Cognitive rehabilitation was superior to treatment as usual and/or relaxation therapy in a number of secondary outcomes at 2 months (mood, self-efficacy, social domain of quality of life, carers' ratings of participants' goal attainment) and at 6 months (delayed recall, health status, quality of life, carer ratings of participants' goal attainment). Carers receiving cognitive rehabilitation reported better quality of life, health status, and lower stress than those allocated to treatment-as-usual. Cognitive rehabilitation is feasible and potentially effective for dementias associated with Parkinson's disease. Copyright © 2018 John Wiley & Sons, Ltd.

Precession relaxation of viscoelastic oblate rotators

NASA Astrophysics Data System (ADS)

Frouard, Julien; Efroimsky, Michael

2018-01-01

Perturbations of all sorts destabilize the rotation of a small body and leave it in a non-principal spin state. In such a state, the body experiences alternating stresses generated by the inertial forces. This yields nutation relaxation, i.e. evolution of the spin towards the principal rotation about the maximal-inertia axis. Knowledge of the time-scales needed to damp the nutation is crucial in studies of small bodies' dynamics. In the literature hitherto, nutation relaxation has always been described with aid of an empirical quality factor Q introduced to parametrize the energy dissipation rate. Among the drawbacks of this approach was its inability to describe the dependence of the relaxation rate upon the current nutation angle. This inability stemmed from our lack of knowledge of the quality factor's dependence on the forcing frequency. In this article, we derive our description of nutation damping directly from the rheological law obeyed by the material. This renders us the nutation damping rate as a function of the current nutation angle, as well as of the shape and the rheological parameters of the body. In contradistinction from the approach based on an empirical Q factor, our development gives a zero damping rate in the spherical-shape limit. Our method is generic and applicable to any shape and to any linear rheological law. However, to simplify the developments, here we consider a dynamically oblate rotator with a Maxwell rheology.

Macro-mesoscopic Fracture and Strength Character of Pre-cracked Granite Under Stress Relaxation Condition

NASA Astrophysics Data System (ADS)

Liu, Junfeng; Yang, Haiqing; Xiao, Yang; Zhou, Xiaoping

2018-05-01

The fracture characters are important index to study the strength and deformation behavior of rock mass in rock engineering. In order to investigate the influencing mechanism of loading conditions on the strength and macro-mesoscopic fracture character of rock material, pre-cracked granite specimens are prepared to conduct a series of uniaxial compression experiments. For parts of the experiments, stress relaxation tests of different durations are also conducted during the uniaxial loading process. Furthermore, the stereomicroscope is adopted to observe the microstructure of the crack surfaces of the specimens. The experimental results indicate that the crack surfaces show several typical fracture characters in accordance with loading conditions. In detail, some cleavage fracture can be observed under conventional uniaxial compression and the fractured surface is relatively rough, whereas as stress relaxation tests are attached, relative slip trace appears between the crack faces and some shear fracture starts to come into being. Besides, the crack faces tend to become smoother and typical terrace structures can be observed in local areas. Combining the macroscopic failure pattern of the specimens, it can be deduced that the duration time for the stress relaxation test contributes to the improvement of the elastic-plastic strain range as well as the axial peak strength for the studied material. Moreover, the derived conclusion is also consistent with the experimental and analytical solution for the pre-peak stage of the rock material. The present work may provide some primary understanding about the strength character and fracture mechanism of hard rock under different engineering environments.

Examining the effectiveness of psychological strategies on physiologic markers: evidence-based suggestions for holistic care of the athlete.

PubMed

Dawson, Michelle A; Hamson-Utley, Jennifer Jordan; Hansen, Rodney; Olpin, Michael

2014-01-01

Current holistic rehabilitation blends both physical and psychological techniques. However, validation of the usefulness of psychological strategies is limited in the literature. To quantify the effects of psychological strategies on both physiologic (salivary cortisol) and subjective assessments of stress. Randomized controlled clinical trial. Laboratory. A total of 97 college-aged students (age = 20.65 ± 4.38 years), most with little to no experience with psychological strategies. A 15-minute script via an iPod led the participant through visual imagery (cognitive relaxation) or deep breathing exercises (somatic relaxation) cues. The control group listened to 15 minutes of ambient nature sounds. Two samples (pretest, posttest) of salivary cortisol were analyzed using an enzyme immunoassay kit; the average was used for statistical analysis. Descriptive statistics and correlations were conducted to examine group differences in time of day, salivary cortisol, sex, Stress-O-Meter values, and Perceived Stress Scale scores. Salivary cortisol levels were lower in the treatment group than the control group (F2,97 = 15.62, P < .001). Females had higher scores on both the pretest Stress-O-Meter (5.15 ± 1.796) and the Perceived Stress Scale (18.31 ± 5.833) than males (4.25 ± 1.741 and 15.272 ± 5.390, respectively). Both cognitive and somatic relaxation strategies reduced cortisol levels. Participants who received verbal guidance achieved a larger cortisol reduction. However, the change in cortisol level was uncorrelated with the change in report of acute stress; females reported higher levels of stress. Clinical implications include attention to sex when assessing stress and providing coping skills during the rehabilitation process.

Fracturing and Transformation Into Veins Beneath the Crustal Scale Brittle Ductile Transition - a Record of Co-seismic Loading and Post-seismic Relaxation

NASA Astrophysics Data System (ADS)

Nüchter, J. A.; Stöckhert, B.

2005-12-01

Metamorphic rocks approaching the crustal scale brittle-ductile transition (BDT) during exhumation are expected to become increasingly affected by short term stress fluctuations related to seismic activity in the overlying seismogenic layer (schizosphere), while still residing in a long-term viscous environment (plastosphere). The structural and microstructural record of quartz veins in low grade - high pressure metamorphic rocks from southern Evia, Greece, yields insight into the processes and conditions just beneath the long-term BDT at temperatures of about 300 to 350°C, which switches between brittle failure and viscous flow as a function of imposed stress or strain rate. The following features are characteristic: (1) The veins have formed from tensile fractures, with a typical length on the order of 10-1 to 101 m; (2) The veins are discordant with respect to foliation and all pre-existing structures, with a uniform orientation over more than 500 km2; (3) The veins show a low aspect ratio of about 10 to 100 and an irregular or characteristic flame shape, which requires distributed ductile deformation of the host rock; (4) Fabrics of the sealing vein quartz indicate that - at a time - the veins were wide open cavities; (5) The sealing quartz crystals reveal a broad spectrum of microstructural features indicative of crystal plastic deformation at high stress and temperatures of about 300 to 350°C. These features indicate that opening and sealing of the fractures commenced immediately after brittle failure, controlled by ductile deformation of the host rock. Vein-parallel shortening was generally less than about 2%. Crystals formed early during sealing were plastically deformed upon progressive deformation and opening of the vein. The structural and microstructural record is interpreted as follows: Brittle failure is proposed to be a consequence of short term co-seismic loading. Subsequent opening of the fracture and sealing to become a vein is interpreted to reflect the slower (but still very short term on geological time scales) deformation during post-seismic stress relaxation, with precipitation of minerals from the pore fluid percolating into the evolving cavity. The record provides insight into earthquake-related damage in the uppermost plastosphere and the transient crustal properties during post-seismic creep and stress relaxation.

Composite Ceramic Superconducting Wires for Electric Motor Applications

DTIC Science & Technology

1989-04-28

anneal, reaching a zero stress condition. One must consider the kinetics of stress relaxation to estimate the retained residual stress. Also, upon cooling...temperature residual stress. Starting from zero stress after intercalation, thermomechanical stress builds up from around 300’C or so, depending upon...silicon diode thermometer. The sample filament is electroded in a four-point geometry using either silver epoxy over sputteredd silver pads or fired-on

On the effects of thermal history on the development and relaxation of thermo-mechanical stress in cryopreservation

NASA Astrophysics Data System (ADS)

Eisenberg, David P.; Steif, Paul S.; Rabin, Yoed

2014-11-01

This study investigates the effects of the thermal protocol on the development and relaxation of thermo-mechanical stress in cryopreservation by means of glass formation, also known as vitrification. The cryopreserved medium is modeled as a homogeneous viscoelastic domain, constrained within either a stiff cylindrical container or a highly compliant bag. Annealing effects during the cooling phase of the cryopreservation protocol are analyzed. Results demonstrate that an intermediate temperature-hold period can significantly reduce the maximum tensile stress, thereby decreasing the potential for structural damage. It is also demonstrated that annealing at temperatures close to glass transition significantly weakens the dependency of thermo-mechanical stress on the cooling rate. Furthermore, a slower initial rewarming rate after cryogenic storage may drastically reduce the maximum tensile stress in the material, which supports previous experimental observations on the likelihood of fracture at this stage. This study discusses the dependency of the various stress components on the storage temperature. Finally, it is demonstrated that the stiffness of the container wall can affect the location of maximum stress, with implications on the development of cryopreservation protocols.

Dislocation mechanisms in stressed crystals with surface effects

NASA Astrophysics Data System (ADS)

Wu, Chi-Chin; Crone, Joshua; Munday, Lynn; Discrete Dislocation Dynamics Team

2014-03-01

Understanding dislocation properties in stressed crystals is the key for important processes in materials science, including the strengthening of metals and the stress relaxation during the growth of hetero-epitaxial structures. Despite existing experimental approaches and theories, many dislocation mechanisms with surface effects still remain elusive in experiments. Even though discrete dislocation dynamics (DDD) simulations are commonly employed to study dislocations, few demonstrate sufficient computational capabilities for massive dislocations with the combined effects of surfaces and stresses. Utilizing the Army's newly developed FED3 code, a DDD computation code coupled with finite elements, this work presents several dislocation mechanisms near different types of surfaces in finite domains. Our simulation models include dislocations in a bended metallic cantilever beam, near voids in stressed metals, as well as threading and misfit dislocations in as-grown semiconductor epitaxial layers and their quantitative inter-correlations to stress relaxation and surface instability. Our studies provide not only detailed physics of individual dislocation mechanisms, but also important collective dislocation properties such as dislocation densities and strain-stress profiles and their interactions with surfaces.

Stress changes along the Sunda trench following the 26 December 2004 Sumatra-Andaman and 28 March 2005 Nias earthquakes

USGS Publications Warehouse

Pollitz, F.F.; Banerjee, P.; Burgmann, R.; Hashimoto, M.; Choosakul, N.

2006-01-01

The 26 December 2004 Mw = 9.2 and 28 March 2005 Mw = 8.7 earthquakes on the Sumatra megathrust altered the state of stress over a large region surrounding the earthquakes. We evaluate the stress changes associated with coseismic and postseismic deformation following these two large events, focusing on postseismic deformation that is driven by viscoelastic relaxation of a low-viscosity asthenosphere. Under Coulomb failure stress (CFS) theory, the December 2004 event increased CFS on the future hypocentral zone of the March 2005 event by about 0.25 bar, with little or no contribution from viscous relaxation. Coseismic stresses around the rupture zones of the 1797 and 1833 Sunda trench events are negligible, but postseismic stress perturbations since December 2004 are predicted to result in CFS increases of 0.1 to 0.2 bar around these rupture zones between 2 and 8 years after the December 2004 event. These are considerable stress perturbations given that the 1797 and 1833 rupture zones are likely approaching the end of a complete seismic cycle. Copyright 2006 by the American Geophysical Union.

Branching, Superdiffusion and Stress Relaxation in Surfactant Micelles

NASA Astrophysics Data System (ADS)

Sureshkumar, R.; Dhakal, S.; Syracuse University Team

2016-11-01

We investigate the mechanism of branch formation and its effects on the dynamics and rheology of a model cationic micellar fluid using molecular dynamics (MD) simulations. Branched structures are formed upon increasing counter ion density. A sharp decrease in the solution viscosity with increasing salinity has long been attributed to the sliding motion of micellar branches along the main chain. Simulations not only provide firm evidence of branch sliding in real time, but also show enhanced diffusion of surfactants by virtue of such motion. Insights into the mechanism of stress relaxation associated with branch sliding will be discussed. Specifically, an externally imposed stress damps out more quickly in a branched system compared to that in an unbranched one. NSF Grants 1049489, 1049454.

The relaxation response: reducing stress and improving cognition in healthy aging adults.

PubMed

Galvin, Jennifer A; Benson, Herbert; Deckro, Gloria R; Fricchione, Gregory L; Dusek, Jeffery A

2006-08-01

Aging adults are vulnerable to the effects of a negative emotional state. The relaxation response (RR) is a mind-body intervention that counteracts the harmful effects of stress. Previous studies with relaxation techniques have shown the non-pharmacological benefit of reducing stress and improving the memory of healthy older adults. Our pilot study evaluated whether a RR training program would decrease anxiety levels, improve attention, declarative memory performance and/or decrease salivary cortisol levels in healthy older adults. Fifteen adults participated and were randomly assigned to a RR training or control groups. Mean age was 71.3 years and mean education level was 17.9 years. Reaction time on a simple attention/psychomotor task was significantly improved (p<0.0025) with RR training, whereas there was no significant improvement on complex tasks of attention, verbal, or visual declarative memory tests. Self-reported state anxiety levels showed a marginally significant reduction (p<0.066). All subjects' salivary cortisol levels were within low-normal range and did not significantly change. Our 5-week program in highly educated, mobile, healthy, aging adults significantly improved performance on a simple attention task.

Ultrasonic influence on evolution of disordered dislocation structures

NASA Astrophysics Data System (ADS)

Bachurin, D. V.; Murzaev, R. T.; Nazarov, A. A.

2017-12-01

Evolution of disordered dislocation structures under ultrasonic influence is studied in a model two-dimensional grain within the discrete-dislocation approach. Non-equilibrium grain boundary state is mimicked by a mesodefect located at the corners of the grain, stress field of which is described by that of a wedge junction disclination quadrupole. Significant rearrangement related to gliding of lattice dislocations towards the grain boundaries is found, which results in a noticeable reduction of internal stress fields and cancel of disclination quadrupole. The process of dislocation structure evolution passes through two stages: rapid and slow. The main dislocation rearrangement occurs during the first stage. Reduction of internal stress fields is associated with the number of dislocations entered into the grain boundaries. The change of misorientation angle due to lattice dislocations absorbed by the grain boundaries is evaluated. Amplitude of ultrasonic treatment significantly influences the relaxation of dislocation structure. Preliminary elastic relaxation of dislocation structure does not affect substantially the results of the following ultrasonic treatment. Substantial grain size dependence of relaxation of disordered dislocation systems is found. Simulation results are consistent with experimental data.

Postseismic viscoelastic surface deformation and stress. Part 1: Theoretical considerations, displacement and strain calculations

NASA Technical Reports Server (NTRS)

Cohen, S. C.

1979-01-01

A model of viscoelastic deformations associated with earthquakes is presented. A strike-slip fault is represented by a rectangular dislocation in a viscoelastic layer (lithosphere) lying over a viscoelastic half-space (asthenosphere). Deformations occur on three time scales. The initial response is governed by the instantaneous elastic properties of the earth. A slower response is associated with viscoelastic relaxation of the lithosphere and a yet slower response is due to viscoelastic relaxation of the asthenosphere. The major conceptual contribution is the inclusion of lithospheric viscoelastic properties into a dislocation model of earthquake related deformations and stresses. Numerical calculations using typical fault parameters reveal that the postseismic displacements and strains are small compared to the coseismic ones near the fault, but become significant further away. Moreover, the directional sense of the deformations attributable to the elastic response, the lithospheric viscoelastic softening, and the asthenospheric viscoelastic flow may differ and depend on location and model details. The results and theoretical arguments suggest that the stress changes accompanying lithospheric relaxation may also be in a different sense than and be larger than the strain changes.

Transient Postseismic Relaxation With Burger's Body Viscoelasticity

NASA Astrophysics Data System (ADS)

Hetland, E. A.; Hager, B. H.; O'Connell, R. J.

2002-12-01

Typical models used to investigate postseismic deformation are composed of an elastic layer over a Maxwell viscoelastic region. Geodetic observations made after a number of large earthquakes show a rapid exponential decay in postseismic velocity immediately after the rupture, followed by a more slowly decaying (or constant) velocity at a later time. Models of a Maxwell viscoelastic interior predict a single exponential postseismic velocity relaxation. To account for observed rapid, short-term relaxation decay, surprisingly low viscosities in the lower-crust or upper-mantle have been proposed. To model the difference in short and long time decay rates, the Maxwell element is sometimes modified to have a non-linear rheology, which results in a lower effective viscosity immediately after the rupture, evolving to a higher effective viscosity as the co-seismic stresses relax. Incorporation of models of after-slip in the lower crust on a down-dip extension of the fault have also had some success at modeling the above observations. When real rocks are subjected to a sudden change in stress or strain, e.g., that caused by an earthquake, they exhibit a transient response. The transient deformation is typically accommodated by grain boundary sliding and the longer-time deformation is accommodated by motion of dislocations. Both a short-term transient response and long-term steady creep are exhibited by a Burger's body, a Maxwell element (a spring in series with a viscous dash-pot) in series with a Voigt element (a spring in parallel with a viscous dash-pot). Typically the (transient) viscosity of the Voigt element is 10 - 100 times less than the (steady) viscosity of the Maxwell element. Thus, with a Burger's body, stress relaxation is a superposition of two exponential decays. For a model composed of an elastic layer over a viscoelastic region, the coseismic changes in stress (and strain) depend only on the elastic moduli, and are independent of the description of the viscous component of the rheology. In a Burger's body model of viscoelasticity, if the viscosity of the Voigt element is much less than that of the Maxwell element, the initial relaxation time is given by the decay time τ = η {Voigt}}/G{ {Maxwell}. Whereas, for a Maxwell rheology, the initial relaxation time is given by τ = η {Maxwell}}/G{ {Maxwell}. For both models, the initial spatial distribution of stresses is the same, which results in identical initial spatial distribution of velocities. Thus it is easy to mistake the transient response of a Burger's body for that of a Maxwell rheology with unrealistically low viscosity. Only later in the seismic cycle do the spatial patterns of velocity differ for the two rheologies.

Strategies for Coping with Stress and Chronic Pain.

ERIC Educational Resources Information Center

Meyer, Genevieve Rogge

This guide presents strategies used in Pain Management and Stress Reduction workshops for helping the elderly cope with stress and chronic pain. Client evaluations of the workshops are given along with an analysis of the clients' presenting problems. Coping strategies described include: the relaxation response, imagery, daily logs, journal…

Stress Management Techniques for Young Children.

ERIC Educational Resources Information Center

Piper, Francesca M.

The director of a not-for-profit nursery school adapted the adult stress management techniques of exercise and relaxation for use with 3- to 5-year-old children. Specifically, children were taught visualization techniques and yoga exercises involving deep breathing. The goal of the practicum was to rechannel children's negative stress-related…

Ni exposure impacts the pool of free Fe and modifies DNA supercoiling via metal-induced oxidative stress in Escherichia coli K-12.

PubMed

Gault, Manon; Effantin, Géraldine; Rodrigue, Agnès

2016-08-01

The biology of nickel has been widely studied in mammals because of its carcinogenic properties, whereas few studies have been performed in microorganisms. In the present work, changes accompanying stress caused by nickel were evaluated at the cellular level using RNA-Seq in Escherichia coli K-12. Interestingly, a very large number of genes were found to be deregulated by Ni stress. Iron and oxidative stress homeostasis maintenance were among the most highly enriched functional categories, and genes involved in periplasmic copper efflux were among the most highly upregulated. These results suggest that the deregulation of Fe and Cu homeostatic genes is caused by a release of free Cu and Fe ions in the cell which in turn activate the Cu and Fe homeostatic systems. The content of Cu was not significantly affected upon the addition of Ni to the growth medium, nor were the Cus and CopA Cu-efflux systems important for the survival of bacteria under Ni stress In contrast the addition of Ni slightly decreased the amount of cellular Fe and activated the transcription of Fur regulated genes in a Fur-dependent manner. Cu or Fe imbalance together with oxidative stress might affect the structure of DNA. Further experiments revealed that Ni alters the state of DNA folding by causing a relaxed conformation, a phenomenon that is reversible by addition of the antioxidant Tiron or the Fe chelator Dip. The Tiron-reversible DNA relaxation was also observed for Fe and to a lesser extent with Cu but not with Co. DNA supercoiling is well recognized as an integral aspect of gene regulation. Moreover our results show that Ni modifies the expression of several nucleoid-associated proteins (NAPs), important agents of DNA topology and global gene regulation. This is the first report describing the impact of metal-induced oxidative on global regulatory networks. Copyright © 2016 Elsevier Inc. All rights reserved.

Estimation of stress relaxation time for normal and abnormal breast phantoms using optical technique

NASA Astrophysics Data System (ADS)

Udayakumar, K.; Sujatha, N.

2015-03-01

Many of the early occurring micro-anomalies in breast may transform into a deadliest cancer tumor in future. Probability of curing early occurring abnormalities in breast is more if rightly identified. Even in mammogram, considered as a golden standard technique for breast imaging, it is hard to pick up early occurring changes in the breast tissue due to the difference in mechanical behavior of the normal and abnormal tissue when subjected to compression prior to x-ray or laser exposure. In this paper, an attempt has been made to estimate the stress relaxation time of normal and abnormal breast mimicking phantom using laser speckle image correlation. Phantoms mimicking normal breast is prepared and subjected to precise mechanical compression. The phantom is illuminated by a Helium Neon laser and by using a CCD camera, a sequence of strained phantom speckle images are captured and correlated by the image mean intensity value at specific time intervals. From the relation between mean intensity versus time, tissue stress relaxation time is quantified. Experiments were repeated for phantoms with increased stiffness mimicking abnormal tissue for similar ranges of applied loading. Results shows that phantom with more stiffness representing abnormal tissue shows uniform relaxation for varying load of the selected range, whereas phantom with less stiffness representing normal tissue shows irregular behavior for varying loadings in the given range.

The effect of strain and age on the mechanical properties of rat Achilles tendons

PubMed Central

Vafek, Emily C.; Plate, Johannes F.; Friedman, Eric; Mannava, Sandeep; Scott, Aaron T.; Danelson, Kerry A.

2017-01-01

Summary Background Achilles tendon (AT) ruptures are common in the middle age population; however, the pathophysiology and influence of age on AT ruptures is not fully understood. This study evaluates the effect and interactions between, strain and age on the in vitro biomechanical properties of ATs. Methods Bilateral ATs were harvested from 17 young (8 months) and 14 middle-aged (24 months) rats and underwent stress-relaxation using Fung’s quasilinear viscoelastic (QLV) modeling and load-to-failure testing. Results The initial viscoelastic response (parameter B) in middle-age animals was dependent on the amount of strain applied to the tendon and was significantly increased in middle-aged animals at higher strain. Higher strain in older animals led to a prolonged relaxation time (parameter tau 2). There was a trend toward an increased magnitude of the relaxation response (parameter C) at higher strain in the middle-aged animals. Middle-aged animals had a significantly lower mean stress at ultimate failure (p=0.01), while Young’s modulus was similar in both groups (p=0.46). Conclusions The passive biomechanical properties of the rat AT change with age and the influence stress-relaxation response of the AT, thereby possibly predisposing the AT of older animals to fail at lower loads compared to younger animals. Level of evidence Not applicable, this is a basic science study. PMID:29387650

Cardiac Dysfunction in HIV-1 Transgenic Mouse: Role of Stress and BAG3.

PubMed

Cheung, Joseph Y; Gordon, Jennifer; Wang, JuFang; Song, Jianliang; Zhang, Xue-Qian; Tilley, Douglas G; Gao, Erhe; Koch, Walter J; Rabinowitz, Joseph; Klotman, Paul E; Khalili, Kamel; Feldman, Arthur M

2015-08-01

Since highly active antiretroviral therapy improved long-term survival of acquired immunodeficiency syndrome (AIDS) patients, AIDS cardiomyopathy has become an increasingly relevant clinical problem. We used human immunodeficiency virus (HIV)-1 transgenic (Tg26) mouse to explore molecular mechanisms of AIDS cardiomyopathy. Tg26 mice had significantly lower left ventricular (LV) mass and smaller end-diastolic and end-systolic LV volumes. Under basal conditions, cardiac contractility and relaxation and single myocyte contraction dynamics were not different between wild-type (WT) and Tg26 mice. Ten days after open heart surgery, contractility and relaxation remained significantly depressed in Tg26 hearts, suggesting that Tg26 mice did not tolerate surgical stress well. To simulate heart failure in which expression of Bcl2-associated athanogene 3 (BAG3) is reduced, we down-regulated BAG3 by small hairpin ribonucleic acid in WT and Tg26 hearts. BAG3 down-regulation significantly reduced contractility in Tg26 hearts. BAG3 overexpression rescued contractile abnormalities in myocytes expressing the HIV-1 protein Tat. We conclude: (i) Tg26 mice exhibit normal contractile function at baseline; (ii) Tg26 mice do not tolerate surgical stress well; (iii) BAG3 down-regulation exacerbated cardiac dysfunction in Tg26 mice; (iv) BAG3 overexpression rescued contractile abnormalities in myocytes expressing HIV-1 protein Tat; and (v) BAG3 may occupy a role in pathogenesis of AIDS cardiomyopathy. © 2015 Wiley Periodicals, Inc.

Exercise Protects against PCB-Induced Inflammation and Associated Cardiovascular Risk Factors

PubMed Central

Murphy, Margaret O.; Petriello, Michael C.; Han, Sung Gu; Sunkara, Manjula; Morris, Andrew J; Esser, Karyn; Hennig, Bernhard

2015-01-01

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants that contribute to the initiation of cardiovascular disease. Exercise has been shown to reduce the risk of cardiovascular disease; however, whether exercise can modulate PCB-induced vascular endothelial dysfunction and associated cardiovascular risk factors is unknown. We examined the effects of exercise on coplanar PCB- induced cardiovascular risk factors including oxidative stress, inflammation, impaired glucose tolerance, hypercholesteremia, and endothelium-dependent relaxation. Male ApoE−/− mice were divided into sedentary and exercise groups (voluntary wheel running) over a 12 week period. Half of each group was exposed to vehicle or PCB 77 at weeks 1, 2, 9, and 10. For ex vivo studies, male C57BL/6 mice exercised via voluntary wheel training for 5 weeks and then were administered with vehicle or PCB 77 24 hours before vascular reactivity studies were performed. Exposure to coplanar PCB increased risk factors associated with cardiovascular disease, including oxidative stress and systemic inflammation, glucose intolerance, and hypercholesteremia. The 12 week exercise intervention significantly reduced these pro-atherogenic parameters. Exercise also upregulated antioxidant enzymes including phase II detoxification enzymes. Sedentary animals exposed to PCB 77 exhibited endothelial dysfunction as demonstrated by significant impairment of endothelium-dependent relaxation, which was prevented by exercise. Lifestyle modifications such as aerobic exercise could be utilized as a therapeutic approach for the prevention of adverse cardiovascular health effects induced by environmental pollutants such as PCBs. Keywords: exercise, polychlorinated biphenyl, endothelial function, antioxidant response, cardiovascular disease, inflammation, oxidative stress PMID:25586614

The Effects of Relaxation and Cognitive Expectancy on Attraction in a Social Interaction.

ERIC Educational Resources Information Center

Wilson, Midge

One approach to searching for determinants of interpersonal attraction involves the altering and studying of physiological arousal, psychological stress, and moods. On the basis of the reinforcement-affect model of attraction, it was hypothesized that the positive feelings obtained from undergoing relaxation exercises could serve to enhance…

Does Moderate Level of Alcohol Consumption Produce a Relaxation Effect?

ERIC Educational Resources Information Center

Chen, William; Lockhart, Judy O.

Although many individuals use alcohol to cope with stress (their behavior being based on the belief that alcohol can produce a relaxation effect), research has reported conflicting results on the effects of alcohol on tension reduction. A study was conducted to examine the psychophysiological effects of moderate levels of alcohol consumption under…

The Effect of a Self-Monitored Relaxation Breathing Exercise on Male Adolescent Aggressive Behavior

ERIC Educational Resources Information Center

Gaines, Trudi; Barry, Leasha M.

2008-01-01

This study sought to contribute to the identification of effective interventions in the area of male adolescent aggressive behavior. Existing research includes both group- and single-case studies implementing treatments which typically include an anger-management component and its attendant relaxation and stress-reduction techniques. The design of…

Collection Development: Relaxation & Meditation, September 1, 2010

ERIC Educational Resources Information Center

Lettus, Dodi

2010-01-01

One of the first books to document the relationship between stress and physical and emotional health was "The Relaxation Response" by Herbert Benson, M.D., with Miriam Z. Klipper. Originally published in 1975, the book grew out of Benson's observations as a cardiologist and his research as a fellow at Harvard Medical School. Benson's study of…

[Justifying measures to correct functional state of operators varying in personal anxiety].

PubMed

2012-01-01

Workers of operating and dispatching occupations are exposed to high nervous and emotional exertion that result in increased personal anxiety, working stress and overstrain. That requires physiologically justified correction of hazardous psycho-physiologic states via various prophylactic measures (stay in schungite room, autogenous training, central electric analgesia, electric acupuncture). Attempted relaxation sessions in schungite room revealed in highly anxious individuals an increased velocity of visual signals perception, of attention concentration and shifting. Autogenous training sessions improve memory and have significant hypotensive effect in highly anxious individuals.

Onset of Plasticity via Relaxation Analysis (OPRA)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pandey, Amit; Wheeler, Robert; Shyam, Amit

In crystalline metals and alloys, plasticity occurs due to the movement of mobile dislocations and the yield stress for engineering applications is traditionally quantified based on strain. The onset of irreversible plasticity or “yielding” is generally identified by a deviation from linearity in the stress-strain plot or by some standard convention such as 0.2 % offset strain relative to the “linear elastic response”. In the present work, we introduce a new methodology for the determination of the true yield point based on stress relaxation. We show experimentally that this determination is self-consistent in nature and, as such, provides an objectivemore » observation of the very onset of plastic flow. Lastly, our designation for yielding is no longer related to the shape of the stress-strain curve but instead reflects the earliest signature of the activation of concerted irreversible dislocation motion in a test specimen under increasing load.« less

Stress and coping in Singaporean nurses: a literature review.

PubMed

Lim, Joanne; Bogossian, Fiona; Ahern, Kathy

2010-06-01

Stress is ubiquitous in the nursing profession and is also prevalent in Asian countries, particularly the "four tigers of Asia": Singapore, Hong Kong, Taiwan, and South Korea. Based on the theoretical framework of Lazarus and Folkman (1984), the present review of the nursing literature aims to identify sources and effects of stress in Singaporean nurses and the coping strategies they use. Nurses reported major stressors including shortage of staff, high work demands and conflict at work. Common coping strategies included problem orientation, social support and relaxation techniques. Several studies reported nurses' intent to leave the profession. Recommendations to minimize the impact of stress include in-service programs to facilitate a problem-solving approach to resolving work-related issues such as conflict. Relaxation therapy and debriefing sessions may also help in reducing negative effects of work stressors. Finally, nurses' emotional coping can be enhanced by strengthening sources of social support, particularly from family.

[Options for stress management in obesity treatment].

PubMed

Czeglédi, Edit

2016-02-14

Overeating and physical inactivity are of great importance in the etiology of obesity. Psychological factors are often found in the background of life style. Chronic stress can contribute to physical inactivity and behaviors that hinder the keeping of a diet (e.g., irregular eating pattern, emotional eating). Results of randomized controlled trials show that relaxation can reduce emotional eating, improve cognitive restraint, and thereby reduce weight. However, stress management is more than relaxation. It consists of adaptive emotion-focused and problem-focused coping strategies and skills to improve relationships. Deflection skills may help in replacing emotional eating with other behaviors. Cognitive restructuring, saying no, and problem solving help to prevent or manage conflicts and difficulties otherwise would result in overeating due to distress. Developing stress management skills may result in greater compliance with the treatment. The techniques presented in the study can be easily applied by general practitioners or specialists, and provide tools for optimizing obesity treatment.

Service Lifetime Estimation of EPDM Rubber Based on Accelerated Aging Tests

NASA Astrophysics Data System (ADS)

Liu, Jie; Li, Xiangbo; Xu, Likun; He, Tao

2017-04-01

Service lifetime of ethylene propylene diene monomer (EPDM) rubber at room temperature (25 °C) was estimated based on accelerated aging tests. The study followed sealing stress loss on compressed cylinder samples by compression stress relaxation methods. The results showed that the cylinder samples of EPDM can quickly reach the physical relaxation equilibrium by using the over-compression method. The non-Arrhenius behavior occurred at the lowest aging temperature. A significant linear relationship was observed between compression set values and normalized stress decay results, and the relationship was not related to the ambient temperature of aging. It was estimated that the sealing stress loss in view of practical application would occur after around 86.8 years at 25 °C. The estimations at 25 °C based on the non-Arrhenius behavior were in agreement with compression set data from storage aging tests in natural environment.

Onset of Plasticity via Relaxation Analysis (OPRA)

DOE PAGES

Pandey, Amit; Wheeler, Robert; Shyam, Amit; ...

2016-03-17

In crystalline metals and alloys, plasticity occurs due to the movement of mobile dislocations and the yield stress for engineering applications is traditionally quantified based on strain. The onset of irreversible plasticity or “yielding” is generally identified by a deviation from linearity in the stress-strain plot or by some standard convention such as 0.2 % offset strain relative to the “linear elastic response”. In the present work, we introduce a new methodology for the determination of the true yield point based on stress relaxation. We show experimentally that this determination is self-consistent in nature and, as such, provides an objectivemore » observation of the very onset of plastic flow. Lastly, our designation for yielding is no longer related to the shape of the stress-strain curve but instead reflects the earliest signature of the activation of concerted irreversible dislocation motion in a test specimen under increasing load.« less

Role of sulphur atoms on stress relaxation and crack propagation in monolayer MoS2

NASA Astrophysics Data System (ADS)

Wang, Baoming; Islam, Zahabul; Zhang, Kehao; Wang, Ke; Robinson, Joshua; Haque, Aman

2017-09-01

We present in-situ transmission electron microscopy of crack propagation in a freestanding monolayer MoS2 and molecular dynamic analysis of the underlying mechanisms. Chemical vapor deposited monolayer MoS2 was transferred from sapphire substrate using interfacial etching for defect and contamination minimization. Atomic resolution imaging shows crack tip atoms sustaining 14.5% strain before bond breaking, while the stress field decays at unprecedented rate of 2.15 GPa Å-1. Crack propagation is seen mostly in the zig-zag direction in both model and experiment, suggesting that the mechanics of fracture is not brittle. Our computational model captures the mechanics of the experimental observations on crack propagation in MoS2. While molybdenum atoms carry most of the mechanical load, we show that the sliding motion of weakly bonded sulphur atoms mediate crack tip stress relaxation, which helps the tip sustain very high, localized stress levels.

Effect of geometric size on mechanical properties of dielectric elastomers based on an improved visco-hyperelastic film model

NASA Astrophysics Data System (ADS)

Chang, Mengzhou; Wang, Zhenqing; Tong, Liyong; Liang, Wenyan

2017-03-01

Dielectric polymers show complex mechanical behaviors with different boundary conditions, geometry size and pre-stress. A viscoelastic model suitable for inhomogeneous deformation is presented integrating the Kelvin-Voigt model in a new form in this work. For different types of uniaxial tensile test loading along the length direction of sample, single-step-relaxation tests, loading-unloading tests and tensile-creep-relaxation tests the improved model provides a quite favorable comparison with the experiment results. Moreover, The mechanical properties of test sample with several length-width ratios under different boundary conditions are also invested. The influences of the different boundary conditions are calculated with a stress applied on the boundary point and the result show that the fixed boundary will increase the stress compare with homogeneous deformation. In modeling the effect of pre-stress in the shear test, three pre-stressed mode are discussed. The model validation on the general mechanical behavior shows excellent predictive capability.

An Investigation of Stress Dependent Atomic Oxygen Erosion of Black Kapton Observed on MISSE 6

NASA Astrophysics Data System (ADS)

Miller, Sharon K. R.; Banks, Bruce A.; Sechkar, Edward

Black Kapton XC polyimide was flown as part of the Polymer Film Tensile Experiment (PFTE) on Materials International Space Station Experiment 6 (MISSE 6). The purpose of the experiment was to expose a variety of polymer films, typical of those used for thermal control blankets or supporting membranes on Earth orbiting spacecraft, to the low Earth orbital (LEO) environment under both relaxed and tension conditions. Black Kapton XC under tensile stress experienced a higher erosion rate during exposure in LEO than the same material that was flown in a relaxed condition. Testing conducted to determine the magnitude of the stress and erosion dependence using a ground-based thermal energy atomic oxygen plasma showed a slight dependence of erosion yield on stress for Kapton HN and Black Kapton XC, but not to the extent observed on MISSE 6. More testing is needed to isolate the factors present in LEO that cause stress dependent erosion.

An Investigation of Stress Dependent Atomic Oxygen Erosion of Black Kapton Observed on MISSE 6

NASA Technical Reports Server (NTRS)

Miller, Sharon K. R.; Banks, Bruce A.; Sechkar, Edward

2012-01-01

Black Kapton XC polyimide was flown as part of the Polymer Film Tensile Experiment (PFTE) on Materials International Space Station Experiment 6 (MISSE 6). The purpose of the experiment was to expose a variety of polymer films, typical of those used for thermal control blankets or supporting membranes on Earth orbiting spacecraft, to the low Earth orbital (LEO) environment under both relaxed and tension conditions. Black Kapton XC under tensile stress experienced a higher erosion rate during exposure in LEO than the same material that was flown in a relaxed condition. Testing conducted to determine the magnitude of the stress and erosion dependence using a ground-based thermal energy atomic oxygen plasma showed a slight dependence of erosion yield on stress for Kapton HN and Black Kapton XC, but not to the extent observed on MISSE 6. More testing is needed to isolate the factors present in LEO that cause stress dependent erosion.

Chloride channel function is linked to epithelium-dependent airway relaxation.

PubMed

Fortner, C N; Lorenz, J N; Paul, R J

2001-02-01

We previously reported that substance P (SP) and ATP evoke transient, epithelium-dependent relaxation of mouse tracheal smooth muscle. Since both SP and ATP are known to evoke transepithelial Cl- secretion across epithelial monolayers, we tested the hypothesis that epithelium-dependent relaxation of mouse trachea depends on Cl- channel function. In perfused mouse tracheas, the responses to SP and ATP were both inhibited by the Cl- channel inhibitors diphenylamine-2-carboxylate and 5-nitro-2-(3-phenylpropylamino)benzoate. Relaxation to ATP or SP was unaffected by 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS), and relaxation to SP was unaffected by either DIDS or DNDS. Replacing Cl- in the buffer solutions with the impermeable anion gluconate on both sides of the trachea inhibited relaxation to SP or ATP. In contrast, increasing the gradient for Cl- secretion using Cl- free medium only in the tracheal lumen enhanced the relaxation to SP or ATP. We conclude that Cl- channel function is linked to receptor-mediated, epithelium-dependent relaxation. The finding that relaxation to SP was not blocked by DIDS suggested the involvement of a DIDS-insensitive Cl- channel, potentially the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel. To test this hypothesis, we evaluated tracheas from CFTR-deficient mice and found that the peak relaxation to SP or ATP was not significantly different from those responses in wild-type littermates. This suggests that a DIDS-insensitive Cl- channel other than CFTR is active in the SP response. This work introduces a possible role for Cl- pathways in the modulation of airway smooth muscle function and may have implications for fundamental studies of airway function as well as therapeutic approaches to pulmonary disease.

Role of internal motions and molecular geometry on the NMR relaxation of hydrocarbons

NASA Astrophysics Data System (ADS)

Singer, P. M.; Asthagiri, D.; Chen, Z.; Valiya Parambathu, A.; Hirasaki, G. J.; Chapman, W. G.

2018-04-01

The role of internal motions and molecular geometry on 1H NMR relaxation rates in liquid-state hydrocarbons is investigated using MD (molecular dynamics) simulations of the autocorrelation functions for intramolecular and intermolecular 1H-1H dipole-dipole interactions. The effects of molecular geometry and internal motions on the functional form of the autocorrelation functions are studied by comparing symmetric molecules such as neopentane and benzene to corresponding straight-chain alkanes n-pentane and n-hexane, respectively. Comparison of rigid versus flexible molecules shows that internal motions cause the intramolecular and intermolecular correlation-times to get significantly shorter, and the corresponding relaxation rates to get significantly smaller, especially for longer-chain n-alkanes. Site-by-site simulations of 1H's across the chains indicate significant variations in correlation times and relaxation rates across the molecule, and comparison with measurements reveals insights into cross-relaxation effects. Furthermore, the simulations reveal new insights into the relative strength of intramolecular versus intermolecular relaxation as a function of internal motions, as a function of molecular geometry, and on a site-by-site basis across the chain.

Employee occupational stress in banking.

PubMed

Michailidis, Maria; Georgiou, Yiota

2005-01-01

Occupational stress literature emphasizes the importance of assessment and management of work related stress. The recognition of the harmful physical and psychological effects of stress on both individuals and organizations is widely studied in many parts of the world. However, in other regions such research is only at the introductory stages. The present study examines occupational stress of employees in the banking sector. A sample of 60 bank employees at different organizational levels and educational backgrounds was used. Data collection utilized the Occupational Stress Indicator (OSI). Results of data analysis provided evidence that employees' educational levels affect the degree of stress they experience in various ways. Bank employees cannot afford the time to relax and "wind down" when they are faced with work variety, discrimination, favoritism, delegation and conflicting tasks. The study also shows the degree to which some employees tend to bring work-related problems home (and take family problems to work) depends on their educational background, the strength of the employees' family support, and the amount of time available for them to relax. Finally, the drinking habits (alcohol) of the employees were found to play a significant role in determining the levels of occupational stress.

More is less: Learning but not relaxing buffers deviance under job stressors.

PubMed

Zhang, Chen; Mayer, David M; Hwang, Eunbit

2018-02-01

Workplace deviance harms the well-being of an organization and its members. Unfortunately, theory and prior research suggest that deviance is associated with job stressors, which are endemic to work organizations and often cannot be easily eliminated. To address this conundrum, we explore actions individuals can take at work that serve as buffering conditions for the positive relationship between job stressors and deviant behavior. Drawing upon conservation of resources theory, we examine a resource-building activity (i.e., learning something new at work) and a demand-shielding activity (i.e., taking time for relaxation at work) as potential boundary conditions. In 2 studies with employee samples using complementary designs, we find support for the buffering role of learning but not for relaxation. When employees learn new things at work, the relationship between hindrance stressors and deviance is weaker; as is the indirect relationship mediated by negative emotions. Taking time for relaxation at work did not show a moderating role in either study. Therefore, although relaxation is a response that individuals might be inclined to turn to for counteracting work stress, our findings suggest that, when it comes to addressing negative emotions and deviance in stressful work environments, building positive resources by learning something new at work could be more useful. In that way, doing more (i.e., learning, and not relaxing) is associated with less (deviance) in the face of job stressors. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wingert, Matthew C.; Jiang, Zhang; Chen, Renkun

Here, electrospun polymer nanofibers have garnered significant interest due to their strong size-dependent material properties, such as tensile moduli, strength, toughness, and glass transition temperatures. These properties are closely correlated with polymer chain dynamics. In most applications, polymers usually exhibit viscoelastic behaviors such as stress relaxation and creep, which are also determined by the motion of polymer chains. However, the size-dependent viscoelasticity has not been studied previously in polymer nanofibers. Here, we report the first experimental evidence of significant size-dependent stress relaxation in electrospun Nylon-11 nanofibers as well as size-dependent viscosity of the confined amorphous regions. In conjunction with themore » dramatically increasing stiffness of nano-scaled fibers, this strong relaxation enables size-tunable properties which break the traditional damping-stiffness tradeoff, qualifying electrospun nanofibers as a promising set of size-tunable materials with an unusual and highly desirable combination of simultaneously high stiffness and large mechanical energy dissipation.« less

Nonlinear response and avalanche behavior in metallic glasses

NASA Astrophysics Data System (ADS)

Riechers, B.; Samwer, K.

2017-08-01

The response to different stress amplitudes at temperatures below the glass transition temperature is analyzed by mechanical oscillatory excitation of Pd40Ni40P20 metallic glass samples in single cantilever bending geometry. While low amplitude oscillatory excitations are commonly used in mechanical spectroscopy to probe the relaxation spectrum, in this work the response to comparably high amplitudes is investigated. The strain response of the material is well below the critical yield stress even for highest stress amplitudes, implying the expectation of a linear relation between stress and strain according to Hooke's Law. However, a deviation from the linear behavior is evident, which is analyzed in terms of temperature dependence and influence of the applied stress amplitude by two different approaches of evaluation. The nonlinear approach is based on a nonlinear expansion of the stress-strain-relation, assuming an intrinsic nonlinear character of the shear or elastic modulus. The degree of nonlinearity is extracted by a period-by-period Fourier-analysis and connected to nonlinear coefficients, describing the intensity of nonlinearity at the fundamental and higher harmonic frequencies. The characteristic timescale to adapt to a significant change in stress amplitude in terms of a recovery timescale to a steady state value is connected to the structural relaxation time of the material, suggesting a connection between the observed nonlinearity and primary relaxation processes. The second approach of evaluation is termed the incremental analysis and relates the observed response behavior to avalanches, which occur due to the activation and correlation of local microstructural rearrangements. These rearrangements are connected with shear transformation zones and correspond to localized plastic events, which are superimposed on the linear response behavior of the material.

Clinical trial to assess the effect of physical exercise on endothelial function and insulin resistance in pregnant women

PubMed Central

2009-01-01

Background Preeclampsia (PE) is a common maternal disease that complicates 5 to 10% of pregnancies and remains as the major cause of maternal and neonatal mortality. Cost-effective interventions aimed at preventing the development of preeclampsia are urgently needed. However, the pathogenesis of PE is not well known. Multiple mechanisms such as oxidative stress, endothelial dysfunction and insulin resistance may contribute to its development. Regular aerobic exercise recovers endothelial function; improves insulin resistance and decreases oxidative stress. Therefore the purpose of this clinical trial is to determine the effect of regular aerobic exercise on endothelial function, on insulin resistance and on pregnancy outcome. Methods and design 64 pregnant women will be included in a blind, randomized clinical trial, and parallel assignment. The exercise group will do regular aerobic physical exercise: walking (10 minutes), aerobic exercise (30 minutes), stretching (10 minutes) and relaxation exercise (10 minutes) in three sessions per week. Control group will do the activities of daily living (bathing, dressing, eating, and walking) without counselling from a physical therapist. Trial registration NCT00741312. PMID:19919718

Time dependent turbulence modeling and analytical theories of turbulence

NASA Technical Reports Server (NTRS)

Rubinstein, R.

1993-01-01

By simplifying the direct interaction approximation (DIA) for turbulent shear flow, time dependent formulas are derived for the Reynolds stresses which can be included in two equation models. The Green's function is treated phenomenologically, however, following Smith and Yakhot, we insist on the short and long time limits required by DIA. For small strain rates, perturbative evaluation of the correlation function yields a time dependent theory which includes normal stress effects in simple shear flows. From this standpoint, the phenomenological Launder-Reece-Rodi model is obtained by replacing the Green's function by its long time limit. Eddy damping corrections to short time behavior initiate too quickly in this model; in contrast, the present theory exhibits strong suppression of eddy damping at short times. A time dependent theory for large strain rates is proposed in which large scales are governed by rapid distortion theory while small scales are governed by Kolmogorov inertial range dynamics. At short times and large strain rates, the theory closely matches rapid distortion theory, but at long times it relaxes to an eddy damping model.

Lattice-level observation of the elastic-to-plastic relaxation process with subnanosecond resolution in shock-compressed Ta using time-resolved in situ Laue diffraction

DOE PAGES

Wehrenberg, C. E.; Comley, A. J.; Barton, N. R.; ...

2015-09-29

We report direct lattice level measurements of plastic relaxation kinetics through time-resolved, in-situ Laue diffraction of shock-compressed single-crystal [001] Ta at pressures of 27-210 GPa. For a 50 GPa shock, a range of shear strains is observed extending up to the uniaxial limit for early data points (<0.6 ns) and the average shear strain relaxes to a near steady state over ~1 ns. For 80 and 125 GPa shocks, the measured shear strains are fully relaxed already at 200 ps, consistent with rapid relaxation associated with the predicted threshold for homogeneous nucleation of dislocations occurring at shock pressure ~65 GPa.more » The relaxation rate and shear stresses are used to estimate the dislocation density and these quantities are compared to the Livermore Multiscale Strength model as well as various molecular dynamics simulations.« less

Oral intake of γ-aminobutyric acid affects mood and activities of central nervous system during stressed condition induced by mental tasks.

PubMed

Yoto, A; Murao, S; Motoki, M; Yokoyama, Y; Horie, N; Takeshima, K; Masuda, K; Kim, M; Yokogoshi, H

2012-09-01

γ-Aminobutyric acid (GABA) is a kind of amino acid contained in green tea leaves and other foods. Several reports have shown that GABA might affect brain protein synthesis, improve many brain functions such as memory and study capability, lower the blood pressure of spontaneously hypertensive rats, and may also have a relaxation effect in humans. However, the evidence for its mood-improving function is still not sufficient. In this study, we investigated how the oral intake of GABA influences human adults psychologically and physiologically under a condition of mental stress. Sixty-three adults (28 males, 35 females) participated in a randomized, single blind, placebo-controlled, crossover-designed study over two experiment days. Capsules containing 100 mg of GABA or dextrin as a placebo were used as test samples. The results showed that EEG activities including alpha band and beta band brain waves decreased depending on the mental stress task loads, and the condition of 30 min after GABA intake diminished this decrease compared with the placebo condition. That is to say, GABA might have alleviated the stress induced by the mental tasks. This effect also corresponded with the results of the POMS scores.

An analytical approach to the rise velocity of periodic bubble trains in non-Newtonian fluids.

PubMed

Frank, X; Li, H Z; Funfschilling, D

2005-01-01

The present study aims at providing insight into the acceleration mechanism of a bubble chain rising in shear-thinning viscoelastic fluids. The experimental investigation by the Particle Image Velocimetry (PIV), birefringence visualisation and rheological simulation shows that two aspects are central to bubble interactions in such media: the stress creation by the passage of bubbles, and their relaxation due to the fluid's memory forming an evanescent corridor of reduced viscosity. Interactions between bubbles were taken into account mainly through a linear superposition of the stress evolution behind each bubble. An analytical approach together with the rheological consideration was developed to compute the rise velocity of a bubble chain in function of the injection period and bubble volume. The model predictions compare satisfactorily with the experimental investigation.

Relax for Success: An Educator's Guide to Stress Management. [With CD-ROM].

ERIC Educational Resources Information Center

Glanz, Jeffrey

This book is designed as a practical, concise, easy-to-read guide for relieving stress. It is written specifically for educators, with examples and anecdotes that relate to professional educators' experiences. It assumes a holistic approach to stress relief that incorporates thought, verbal and action strategies and techniques. The harm that…

Stuttering Behavior and Physiological Stress Profiles: A Preliminary Investigation of School-Aged Children

ERIC Educational Resources Information Center

Ortega, Aishah Y.

2009-01-01

The impact of observable increases in stress during moments of stuttering has long been an interesting area of research. Although stuttering type, severity, and associated behaviors may vary widely among individuals, it is not uncommon to find stress management, relaxation, and desensitization incorporated into the therapeutic remediation of…

Keeping Fit: Stress Relievers

ERIC Educational Resources Information Center

Crupi, Jeffrey

2005-01-01

With all the extra demands that are placed on teachers during the months of May and June, the end of the year can be an extremely stressful time. This article describes several tips for diminishing the effects of end of year stress. The following relaxation tips are described: (1) Neck and Upper Shoulder Stretch; (2) Superman Stretch; (3) Doorway…

Positive technology: a free mobile platform for the self-management of psychological stress.

PubMed

Gaggioli, Andrea; Cipresso, Pietro; Serino, Silvia; Campanaro, Danilo Marco; Pallavicini, Federica; Wiederhold, Brenda K; Riva, Giuseppe

2014-01-01

We describe the main features and preliminary evaluation of Positive Technology, a free mobile platform for the self-management of psychological stress (http://positiveapp.info/). The mobile platform features three main components: (i) guided relaxation, which provides the user with the opportunity of browsing a gallery of relaxation music and video-narrative resources for reducing stress; (ii) 3D biofeedback, which helps the user learning to control his/her responses, by visualizing variations of heart rate in an engaging 3D environment; (iii) stress tracking, by the recording of heart rate and self-reports. We evaluated the Positive Technology app in an online trial involving 32 participants, out of which 7 used the application in combination with the wrist sensor. Overall, feedback from users was satisfactory and the analysis of data collected online indicated the capability of the app for reducing perceived stress levels. A future goal is to improve the usability of the application and include more advanced stress monitoring features, based on the analysis of heart rate variability indexes.

Stress reduction programs in patients with elevated blood pressure: a systematic review and meta-analysis.

PubMed

Rainforth, Maxwell V; Schneider, Robert H; Nidich, Sanford I; Gaylord-King, Carolyn; Salerno, John W; Anderson, James W

2007-12-01

Substantial evidence indicates that psychosocial stress contributes to hypertension and cardiovascular disease (CVD). Previous meta-analyses of stress reduction and high blood pressure (BP) were outdated and/or methodologically limited. Therefore, we conducted an updated systematic review of the published literature and identified 107 studies on stress reduction and BP. Seventeen trials with 23 treatment comparisons and 960 participants with elevated BP met criteria for well-designed randomized controlled trials and were replicated within intervention categories. Meta-analysis was used to calculate BP changes for biofeedback, -0.8/-2.0 mm Hg (P = NS); relaxation-assisted biofeedback, +4.3/+2.4 mm Hg (P = NS); progressive muscle relaxation, -1.9/-1.4 mm Hg (P = NS); stress management training, -2.3/-1.3 mm (P = NS); and the Transcendental Meditation program, -5.0/-2.8 mm Hg (P = 0.002/0.02). Available evidence indicates that among stress reduction approaches, the Transcendental Meditation program is associated with significant reductions in BP. Related data suggest improvements in other CVD risk factors and clinical outcomes.

Stress Reduction Programs in Patients with Elevated Blood Pressure: A Systematic Review and Meta-analysis

PubMed Central

Rainforth, Maxwell V.; Schneider, Robert H.; Nidich, Sanford I.; Gaylord-King, Carolyn; Salerno, John W.; Anderson, James W.

2007-01-01

Substantial evidence indicates that psychosocial stress contributes to hypertension and cardiovascular disease (CVD). Previous meta-analyses of stress reduction and high blood pressure (BP) were outdated and/or methodologically limited. Therefore, we conducted an updated systematic review of the published literature and identified 107 studies on stress reduction and BP. Seventeen trials with 23 treatment comparisons and 960 participants with elevated BP met criteria for well-designed randomized controlled trials and were replicated within intervention categories. Meta-analysis was used to calculate BP changes for biofeedback, −0.8/−2.0 mm Hg (P = NS); relaxation-assisted biofeedback, +4.3/+2.4 mm Hg (P = NS); progressive muscle relaxation, −1.9/−1.4 mm Hg (P = NS); stress management training, −2.3/−1.3 mm (P = NS); and the Transcendental Meditation program, −5.0/−2.8 mm Hg (P = 0.002/0.02). Available evidence indicates that among stress reduction approaches, the Transcendental Meditation program is associated with significant reductions in BP. Related data suggest improvements in other CVD risk factors and clinical outcomes. PMID:18350109

The Effect of Relaxation Interventions on Cortisol Levels in HIV-Sero-Positive Women

PubMed Central

Jones, Deborah; Owens, Mary; Kumar, Mahendra; Cook, Ryan; Weiss, Stephen M.

2016-01-01

Purpose Activation of the hypothalamic–pituitary–adrenal axis, assessed in terms of cortisol levels, may enhance the ability of HIV to infect lymphocytes and downregulate the immune system, accelerating disease progression. This study sought to determine the effects of relaxation techniques on cortisol levels in HIV-sero-positive women. Methods Women (n = 150) were randomized to a group cognitive–behavioral stress management (CBSM) condition or an individual information condition and underwent 3 types of relaxation training (progressive muscle relaxation, imagery, and autogenic training). Cortisol levels were obtained pre- and postrelaxation. Results Guided imagery was effective in reducing cortisol in the group condition (t = 3.90, P < .001), and muscle relaxation reduced cortisol in the individual condition (t = 3.11, P = .012). Among participants in the group condition attending all sessions, the magnitude of pre- to postsession reduction became greater over time. Conclusions Results suggest that specific relaxation techniques may be partially responsible for cortisol decreases associated with relaxation and CBSM. PMID:23715264

Investigation of Strain-Relaxation Characteristics of Nitrides Grown on Si(110) by Metalorganic Chemical Vapor Deposition Using X-ray Diffraction

NASA Astrophysics Data System (ADS)

Jiang, Quanzhong; Lewins, Christopher J.; Allsopp, Duncan W. E.; Bowen, Chris R.; Wang, Wang N.

2013-08-01

This paper describes the effect of an interfacial biaxial stress field on the dislocation formation dynamics during epitaxial growth of nitrides on Si(110). The anisotropic mismatch stress between a 2-fold symmetry Si(110) atomic plane and the AlN basal plane of 6-fold symmetry may be relaxed through the creation of additional characteristic dislocations, as proposed by Ruiz-Zepeda et al. with Burgers vectors: b= 1/2[bar 2110] and b= [1bar 210], +/-60° from [11bar 20]. The dislocations generated under such a biaxial stress field appear annihilating more efficiently with increasing thickness, leading to high-quality nitride epilayers on Si(110) for improved quantum efficiency of InGaN/GaN quantum wells.

Fractography of the interlaminar fracture of carbon-fibre epoxy composites

NASA Technical Reports Server (NTRS)

Bascom, W. D.; Boll, D. J.; Fuller, B.; Phillips, P. J.

1985-01-01

The failed surfaces of interlaminar fracture (mode I) specimens of AS4/3501-6 were examined using scanning electron microscopy. The principal fracture features were fiber pull-out (bundles and single fibers), hackle markings, and regions of smooth resin fracture. Considerable (30 to 50 percent) relaxation of the deformed resin occurred when the specimens were heated above the matrix glass transition temperature. This relaxation was taken as evidence of extensive shear yielding of the resin during the fracture process. Some of the fractography features are discussed in terms of transverse tensile stresses and peeling stresses acting on the fibers. In some instances these localized stresses focus failure close to the resin-fiber interface, which can be mistakenly interpreted as interfacial failure and low fiber-resin adhesion.

Immediate and long-term effects of meditation on acute stress reactivity, cognitive functions, and intelligence.

PubMed

Singh, Yogesh; Sharma, Ratna; Talwar, Anjana

2012-01-01

With the current globalization of the world's economy and demands for enhanced performance, stress is present universally. Life's stressful events and daily stresses cause both deleterious and cumulative effects on the human body. The practice of meditation might offer a way to relieve that stress. The research team intended to study the effects of meditation on stress-induced changes in physiological parameters, cognitive functions, intelligence, and emotional quotients. The research team conducted the study in two phases, with a month between them. Each participant served as his own control, and the first phase served as the control for the second phase. In phase 1, the research team studied the effects of a stressor (10 minutes playing a computer game) on participants' stress levels. In phase 2, the research team examined the effects of meditation on stress levels. The research team conducted the study in a lab setting at the All India Institute of Medical Sciences (AIIMS), New Delhi, India. The participants were 34 healthy, male volunteers who were students. To study the effects of long-term meditation on stress levels, intelligence, emotional quotients, and cognitive functions participants meditated daily for 1 month, between phases 1 and 2. To study the immediate effects of meditation on stress levels, participants meditated for 15 minutes after playing a computer game to induce stress. The research team measured galvanic skin response (GSR), heart rate (HR), and salivary cortisol and administered tests for the intelligence and emotional quotients (IQ and EQ), acute and perceived stress (AS and PS), and cognitive functions (ie, the Sternberg memory test [short-term memory] and the Stroop test [cognitive flexibility]). Using a pre-post study design, the team performed this testing (1) prior to the start of the study (baseline); (2) in phase 1, after induced stress; (3) in part 1 of phase 2, after 1 month of daily meditation, and (4) in part 2 of phase 2, after induced stress, both before and after 15 minutes of meditation. Induced stress from the computer game resulted in a significant increase in physiological markers of stress such as GSR and HR. In the short term, meditation was associated with a physiological relaxation response (significant decrease in GSR) and an improvement in scores on the Stroop test of reaction times. In the long-term, meditation brought significant improvements in IQ and scores for cognitive functions, whereas participants' stress levels (GSR and AS) decreased. EQ, salivary cortisol, and HR showed no significant changes. The practice of meditation reduced psychological stress responses and improved cognitive functions, and the effects were pronounced with practice of meditation for a longer duration (1 month).

Two-photon excitation laser scanning microscopy of porcine nasal septal cartilage following Nd:YAG laser-mediated stress relaxation

NASA Astrophysics Data System (ADS)

Kim, Charlton C.; Wallace, Vincent P.; Rasouli, Alexandre; Coleno, Mariah L.; Dao, Xavier; Tromberg, Bruce J.; Wong, Brian J.

2000-05-01

Laser irradiation of hyaline cartilage result in stable shape changes due to temperature dependent stress relaxation. In this study, we determined the structural changes in chondrocytes within porcine nasal septal cartilage tissue over a 4-day period using a two-photon laser scanning microscope (TPM) following Nd:YAG laser irradiation (lambda equals 1.32 micrometer) using parameters that result in mechanical stress relaxation (6.0 W, 5.4 mm spot diameter). TPM excitation (780 nm) result in induction of fluorescence from endogenous agents such as NADH, NADPH, and flavoproteins in the 400 - 500 nm spectral region. During laser irradiation diffuse reflectance (from a probe HeNe laser, (lambda) equals 632.8 nm), surface temperature, and stress relaxation were measured dynamically. Each specimen received one, two, or three sequential laser exposures (average irradiation times of 5, 6, and 8 seconds). The cartilage reached a peak surface temperature of about 70 degrees Celsius during irradiation. Cartilage denatured in 50% EtOH (20 minutes) was used as a positive control. TPM was performed using a mode-locked 780 nm Titanium:Sapphire (Ti:Al203) beam with a, 63X, 1.2 N.A. water immersion objective (working distance of 200 mm) to detect the fluorescence emission from the chondrocytes. Images of chondrocytes were obtained at depths up to 150 microns (lateral resolution equals 35 micrometer X 35 micrometer). Images were obtained immediately following laser exposure, and also after 4 days in culture. In both cases, the irradiated and non-irradiated specimens do not show any discernible difference in general shape or auto fluorescence. In contrast, positive controls (immersed in 50% ethanol), show markedly increased fluorescence relative to both the native and irradiated specimens, in the cytoplasmic region.

Applying Hypnosis to Treat Problems in School-Age Children: Reviewing Science and Debunking Myths

ERIC Educational Resources Information Center

Perfect, Michelle M.; McClung, Ashley A.; Bressette, Keri A.

2013-01-01

Clinical hypnosis, defined as a "therapeutic technique in which clinicians make suggestions to individuals who have undergone a procedure designed to relax them and focus their minds" (American Psychological Association, n.d.), is a relaxation-based tool that has uses in the treatment of anxiety, pain, and a range of stress-related…

Uses and Abuses of Progressive Relaxation and Biofeedback in Treating Effects of Stress: The Cognitive vs. Psychophysiological vs. Behavioral Distinction.

ERIC Educational Resources Information Center

Lehrer, Paul M.

Experimental, clinical, and personal observations give some support to the notions that: (1) intensive live training with anxious subjects is required in order to demonstrate that perspective relaxation has physiological effects; (2) physiological, cognitive, and behavioral symptoms of anxiety are separable and may respond differentially to…

The feasibility of a group stress management Liver SMART intervention for patients with end-stage liver disease: A pilot study.

PubMed

Jutagir, Devika R; Saracino, Rebecca M; Cunningham, Amy; Foran-Tuller, Kelly A; Driscoll, Mary A; Sledge, William H; Emre, Sukru H; Fehon, Dwain C

2018-06-04

Structured, empirically supported psychological interventions are lacking for patients who require organ transplantation. This stage IA psychotherapy development project developed and tested the feasibility, acceptability, tolerability, and preliminary efficacy of an 8-week group cognitive behavioral stress management intervention adapted for patients with end-stage liver disease awaiting liver transplantation. Twenty-nine English-speaking United Network for Organ Sharing-registered patients with end-stage liver disease from a single transplantation center enrolled in 8-week, group cognitive-behavioral liver stress management and relaxation training intervention adapted for patients with end-stage liver disease. Patients completed pre- and postintervention surveys that included the Beck Depression Inventory II and the Beck Anxiety Inventory. Feasibility, acceptability, tolerability, and preliminary efficacy were assessed.ResultAttendance rate was 69.40%. The intervention was rated as "good" to "excellent" by 100% of participants who completed the postintervention survey in teaching them new skills to relax and to cope with stress, and by 94.12% of participants in helping them feel supported while waiting for a liver transplant. No adverse events were recorded over the course of treatment. Attrition was 13.79%. Anxious and depressive symptoms were not statistically different after the intervention.Significance of resultsThe liver stress management and relaxation training intervention is feasible, acceptable, and tolerable to end-stage liver disease patients within a transplant clinic setting. Anxious and depressive symptoms remained stable postintervention. Randomized controlled trials are needed to study the intervention's effectiveness in this population.

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

NASA Astrophysics Data System (ADS)

Zhang, Rui; Schweizer, Kenneth S.

2012-04-01

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.

The effect of autogenic training on salivary immunoglobulin A in surgical patients with breast cancer: a randomized pilot trial.

PubMed

Minowa, Chika; Koitabashi, Kikuyo

2014-11-01

Psychological stress among breast cancer patients can inhibit immune function and contribute to disease progression. We investigated the effects of autogenic training (AT), a relaxation method for reducing stress, on salivary immunoglobulin A (sIgA) in breast cancer surgery patients. Thirty patients scheduled to undergo breast cancer surgery were randomly assigned to an AT or control group (usual care). Patients in the AT group underwent training for 7 days after surgery. Salivary IgA and heart rate variability were assessed on the day before surgery, and on the third and seventh postoperative days. Levels of sIgA were significantly higher on the seventh postoperative day in the AT group (n = 7) compared to the control group (n = 7) (p = 0.049). These findings suggest that AT may improve immune function in breast surgery patients. Copyright © 2014 Elsevier Ltd. All rights reserved.

Specific Hardening Function Definition and Characterization of a Multimechanism Generalized Potential-based Viscoelastoplasticity Model

NASA Technical Reports Server (NTRS)

Arnold, S. M.; Saleeb, A. F.

2003-01-01

Given the previous complete-potential structure framework together with the notion of strain- and stress-partitioning in terms of separate contributions of several submechanisms (viscoelastic and viscoplastic) to the thermodynamic functions (stored energy and dissipation) a detailed viscoelastoplastic multimechanism characterization of a specific hardening functional form of the model is presented and discussed. TIMETAL 21S is the material of choice as a comprehensive test matrix, including creep, relaxation, constant strain-rate tension tests, etc. are available at various temperatures. Discussion of these correlations tests, together with comparisons to several other experimental results, are given to assess the performance and predictive capabilities of the present model particularly with regard to the notion of hardening saturation as well as the interaction of multiplicity of dissipative (reversible/irreversible) mechanisms.

History Dependence of the Microstructure on Time-Dependent Deformation During In-Situ Cooling of a Nickel-Based Single-Crystal Superalloy

NASA Astrophysics Data System (ADS)

Panwisawas, Chinnapat; D'Souza, Neil; Collins, David M.; Bhowmik, Ayan; Roebuck, Bryan

2018-05-01

Time-dependent plastic deformation through stress relaxation and creep deformation during in-situ cooling of the as-cast single-crystal superalloy CMSX-4® has been studied via neutron diffraction, transmission electron microscopy, electro-thermal miniature testing, and analytical modeling across two temperature regimes. Between 1000 °C and 900 °C, stress relaxation prevails and gives rise to softening as evidenced by a decreased dislocation density and the presence of long segment stacking faults in γ phase. Lattice strains decrease in both the γ matrix and γ' precipitate phases. A constitutive viscoplastic law derived from in-situ isothermal relaxation test under-estimates the equivalent plastic strain in the prediction of the stress and strain evolution during cooling in this case. It is thereby shown that the history dependence of the microstructure needs to be taken into account while deriving a constitutive law and which becomes even more relevant at high temperatures approaching the solvus. Higher temperature cooling experiments have also been carried out between 1300 °C and 1150 °C to measure the evolution of stress and plastic strain close to the γ' solvus temperature. In-situ cooling of samples using ETMT shows that creep dominates during high-temperature deformation between 1300 °C and 1220 °C, but below a threshold temperature, typically 1220 °C work hardening begins to prevail from increasing γ' fraction and resulting in a rapid increase in stress. The history dependence of prior accumulated deformation is also confirmed in the flow stress measurements using a single sample while cooling. The saturation stresses in the flow stress experiments show very good agreement with the stresses measured in the cooling experiments when viscoplastic deformation is dominant. This study demonstrates that experimentation during high-temperature deformation as well as the history dependence of the microstructure during cooling plays a key role in deriving an accurate viscoplastic constitutive law for the thermo-mechanical process during cooling from solidification.

Mechanical response of transient telechelic networks with many-part stickers

NASA Astrophysics Data System (ADS)

Sing, Michelle K.; Ramírez, Jorge; Olsen, Bradley D.

2017-11-01

A central question in soft matter is understanding how several individual, weak bonds act together to produce collective interactions. Here, gel-forming telechelic polymers with multiple stickers at each chain end are studied through Brownian dynamics simulations to understand how collective interaction of the bonds affects mechanical response of the gels. These polymers are modeled as finitely extensible dumbbells using an explicit tau-leap algorithm and the binding energy of these associations was kept constant regardless of the number of stickers. The addition of multiple bonds to the associating ends of telechelic polymers increases or decreases the network relaxation time depending on the relative kinetics of association but increases both shear stress and extensional viscosity. The relationship between the rate of association and the Rouse time of dangling chains results in two different regimes for the equilibrium stress relaxation of associating physical networks. In case I, a dissociated dangling chain is able to fully relax before re-associating to the network, resulting in two characteristic relaxation times and a non-monotonic terminal relaxation time with increasing number of bonds per polymer endgroup. In case II, the dissociated dangling chain is only able to relax a fraction of the way before it re-attaches to the network, and increasing the number of bonds per endgroup monotonically increases the terminal relaxation time. In flow, increasing the number of stickers increases the steady-state shear and extensional viscosities even though the overall bond kinetics and equilibrium constant remain unchanged. Increased dissipation in the simulations is primarily due to higher average chain extension with increasing bond number. These results indicate that toughness and dissipation in physically associating networks can both be increased by breaking single, strong bonds into smaller components.

The Secret Life of Collagen: Temporal Changes in Nanoscale Fibrillar Pre-Strain and Molecular Organization during Physiological Loading of Cartilage.

PubMed

Inamdar, Sheetal R; Knight, David P; Terrill, Nicholas J; Karunaratne, Angelo; Cacho-Nerin, Fernando; Knight, Martin M; Gupta, Himadri S

2017-10-24

Articular cartilage is a natural biomaterial whose structure at the micro- and nanoscale is critical for healthy joint function and where degeneration is associated with widespread disorders such as osteoarthritis. At the nanoscale, cartilage mechanical functionality is dependent on the collagen fibrils and hydrated proteoglycans that form the extracellular matrix. The dynamic response of these ultrastructural building blocks at the nanoscale, however, remains unclear. Here we measure time-resolved changes in collagen fibril strain, using small-angle X-ray diffraction during compression of bovine and human cartilage explants. We demonstrate the existence of a collagen fibril tensile pre-strain, estimated from the D-period at approximately 1-2%, due to osmotic swelling pressure from the proteoglycan. We reveal a rapid reduction and recovery of this pre-strain which occurs during stress relaxation, approximately 60 s after the onset of peak load. Furthermore, we show that this reduction in pre-strain is linked to disordering in the intrafibrillar molecular packing, alongside changes in the axial overlapping of tropocollagen molecules within the fibril. Tissue degradation in the form of selective proteoglycan removal disrupts both the collagen fibril pre-strain and the transient response during stress relaxation. This study bridges a fundamental gap in the knowledge describing time-dependent changes in collagen pre-strain and molecular organization that occur during physiological loading of articular cartilage. The ultrastructural details of this transient response are likely to transform our understanding of the role of collagen fibril nanomechanics in the biomechanics of cartilage and other hydrated soft tissues.

An Experimental Evaluation of Stress-Management Training for the Airborne Soldier

DTIC Science & Technology

1980-06-01

skill takes considerable time and involves the learning of respiration control techniques and exercises to relax both the skeletal and smooth muscle...NUMBER 7. AUTHORia) 8. CONTRACT OR GRANT NUMBER(.) William P. Burke 9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASK US Army...block number) Jumpmaster training Performance under stress Stress-management training Stress reaction Respiration -control Heart rate response Deep

The contributions of cardiac myosin binding protein C and troponin I phosphorylation to β‐adrenergic enhancement of in vivo cardiac function

PubMed Central

Gresham, Kenneth S.

2016-01-01

Key points β‐adrenergic stimulation increases cardiac myosin binding protein C (MyBP‐C) and troponin I phosphorylation to accelerate pressure development and relaxation in vivo, although their relative contributions remain unknown.Using a novel mouse model lacking protein kinase A‐phosphorylatable troponin I (TnI) and MyBP‐C, we examined in vivo haemodynamic function before and after infusion of the β‐agonist dobutamine.Mice expressing phospho‐ablated MyBP‐C displayed cardiac hypertrophy and prevented full acceleration of pressure development and relaxation in response to dobutamine, whereas expression of phosphor‐ablated TnI alone had little effect on the acceleration of contractile function in response to dobutamine.Our data demonstrate that MyBP‐C phosphorylation is the principal mediator of the contractile response to increased β‐agonist stimulation in vivo.These results help us understand why MyBP‐C dephosphorylation in the failing heart contributes to contractile dysfunction and decreased adrenergic reserve in response to acute stress. Abstract β‐adrenergic stimulation plays a critical role in accelerating ventricular contraction and speeding relaxation to match cardiac output to changing circulatory demands. Two key myofilaments proteins, troponin I (TnI) and myosin binding protein‐C (MyBP‐C), are phosphorylated following β‐adrenergic stimulation; however, their relative contributions to the enhancement of in vivo cardiac contractility are unknown. To examine the roles of TnI and MyBP‐C phosphorylation in β‐adrenergic‐mediated enhancement of cardiac function, transgenic (TG) mice expressing non‐phosphorylatable TnI protein kinase A (PKA) residues (i.e. serine to alanine substitution at Ser23/24; TnIPKA−) were bred with mice expressing non‐phosphorylatable MyBP‐C PKA residues (i.e. serine to alanine substitution at Ser273, Ser282 and Ser302; MyBPCPKA−) to generate a novel mouse model expressing non‐phosphorylatable PKA residues in TnI and MyBP‐C (DBLPKA−). MyBP‐C dephosphorylation produced cardiac hypertrophy and increased wall thickness in MyBPCPKA− and DBLPKA− mice, and in vivo echocardiography and pressure–volume catheterization studies revealed impaired systolic function and prolonged diastolic relaxation compared to wild‐type and TnIPKA– mice. Infusion of the β‐agonist dobutamine resulted in accelerated rates of pressure development and relaxation in all mice; however, MyBPCPKA− and DBLPKA− mice displayed a blunted contractile response compared to wild‐type and TnIPKA– mice. Furthermore, unanaesthesized MyBPCPKA− and DBLPKA− mice displayed depressed maximum systolic pressure in response to dobutamine as measured using implantable telemetry devices. Taken together, our data show that MyBP‐C phosphorylation is a critical modulator of the in vivo acceleration of pressure development and relaxation as a result of enhanced β‐adrenergic stimulation, and reduced MyBP‐C phosphorylation may underlie depressed adrenergic reserve in heart failure. PMID:26635197

Incremental viscosity by non-equilibrium molecular dynamics and the Eyring model

NASA Astrophysics Data System (ADS)

Heyes, D. M.; Dini, D.; Smith, E. R.

2018-05-01

The viscoelastic behavior of sheared fluids is calculated by Non-Equilibrium Molecular Dynamics (NEMD) simulation, and complementary analytic solutions of a time-dependent extension of Eyring's model (EM) for shear thinning are derived. It is argued that an "incremental viscosity," ηi, or IV which is the derivative of the steady state stress with respect to the shear rate is a better measure of the physical state of the system than the conventional definition of the shear rate dependent viscosity (i.e., the shear stress divided by the strain rate). The stress relaxation function, Ci(t), associated with ηi is consistent with Boltzmann's superposition principle and is computed by NEMD and the EM. The IV of the Eyring model is shown to be a special case of the Carreau formula for shear thinning. An analytic solution for the transient time correlation function for the EM is derived. An extension of the EM to allow for significant local shear stress fluctuations on a molecular level, represented by a gaussian distribution, is shown to have the same analytic form as the original EM but with the EM stress replaced by its time and spatial average. Even at high shear rates and on small scales, the probability distribution function is almost gaussian (apart from in the wings) with the peak shifted by the shear. The Eyring formula approximately satisfies the Fluctuation Theorem, which may in part explain its success in representing the shear thinning curves of a wide range of different types of chemical systems.

Cellular interactions and biomechanical properties of a unique vascular-derived scaffold for periodontal tissue regeneration.

PubMed

Goktas, Selda; Pierre, Nicolas; Abe, Koki; Dmytryk, John; McFetridge, Peter S

2010-03-01

These investigations describe the development of a novel ex vivo three-dimensional scaffold derived from the human umbilical vein (HUV), and its potential as a regenerative matrix for tissue regeneration. Unique properties associated with the vascular wall have shown potential to function as a surgical barrier for guided tissue regeneration, particularly with the regeneration of periodontal tissues. HUV was isolated from umbilical cords using a semiautomated machining technology, decellularized using 1% sodium dodecyl sulfate, and then opened longitudinally to form tissue sheets. Uniaxial tensile testing, stress relaxation, and suture retention tests were performed on the acellular matrix to evaluate the HUV's biomechanical properties, followed by an evaluation of cellular interactions by seeding human gingival fibroblasts to assess adhesion, metabolic function, and proliferation on the scaffold. The scaffold's biomechanical properties were shown to display anisotropic behavior, which is attributed to the ex vivo material's composite structure. Detailed results indicated that the ultimate tensile strength of the longitudinal strips was significantly higher than that of the circumferential strips (p < 0.001). The HUV also exhibited significantly higher stress relaxation response in the longitudinal direction than in the circumferential orientation (p < 0.05). The ablumenal and lumenal surfaces of the material were also shown to differentially influence cell proliferation and metabolic activity, with both cellular functions significantly increased on the ablumenal surface (p < 0.05). Human gingival fibroblast migration into the scaffold was also influenced by the organization of extracellular matrix components, where the lumenal surface inhibits cell migration, acting as a barrier, while the ablumenal surface, which is proposed to interface with the wound site, promotes cellular invasion. These results show the HUV bioscaffold to be a promising naturally derived surgical barrier that may function well as a resorbable guided tissue regeneration membrane as well as in other clinical applications.

Effects of cyclooxygenase inhibition on cardiovascular function in a hypercholesterolemic swine model of chronic ischemia

PubMed Central

Chu, Louis M.; Robich, Michael P.; Bianchi, Cesario; Feng, Jun; Liu, Yuhong; Xu, Shu-Hua; Burgess, Thomas

2012-01-01

The cardiovascular effects of cyclooxygenase (COX) inhibition remain controversial, especially in the setting of cardiovascular comorbidities. We examined the effects of nonselective and selective COX inhibition on cardiovascular function in a hypercholesterolemic swine model of chronic ischemia. Twenty-four intact male Yorkshire swine underwent left circumflex ameroid constrictor placement and were subsequently given either no drug (HCC; n = 8), a nonselective COX inhibitor (440 mg/day naproxen; HCNS; n = 8), or a selective COX-2 inhibitor (200 mg/day celecoxib; HCCX; n = 8). After 7 wk, myocardial functional was measured and myocardium from the nonischemic ventricle and ischemic area-at-risk (AAR) were analyzed. Regional function as measured by segmental shortening was improved in the AAR of HCCX compared with HCC. There was no significant difference in perfusion to the nonischemic ventricle between groups, but myocardial perfusion in the AAR was significantly improved in the HCCX group compared with controls at rest and during pacing. Endothelium-dependent microvessel relaxation was diminished by ischemia in HCC animals, but both naproxen and celecoxib improved vessel relaxation in the AAR compared with controls, and also decreased the vasoconstrictive response to serotonin. Thromboxane levels in the AAR were decreased in both HCNS and HCCX compared with HCC, whereas prostacyclin levels were decreased only in HCNS, corresponding to a decrease in prostacyclin synthase expression. Chronic ischemia increased apoptosis in Troponin T negative cells and intramyocardial fibrosis, both of which were reduced by celecoxib administration in the AAR. Capillary density was decreased in both the HCNS and HCCX groups. Protein oxidative stress was decreased in both HCNS and HCCX, whereas lipid oxidative stress was decreased only in the HCCX group. Thus nonselective and especially selective COX inhibition may have beneficial myocardial effects in the setting of hypercholesterolemia and chronic ischemia. Whether these effects modulate cardiovascular risk in patients taking these drugs remains to be seen, but evidence to date suggests that they do not. PMID:22037194

Effects of cyclooxygenase inhibition on cardiovascular function in a hypercholesterolemic swine model of chronic ischemia.

PubMed

Chu, Louis M; Robich, Michael P; Bianchi, Cesario; Feng, Jun; Liu, Yuhong; Xu, Shu-Hua; Burgess, Thomas; Sellke, Frank W

2012-01-01

The cardiovascular effects of cyclooxygenase (COX) inhibition remain controversial, especially in the setting of cardiovascular comorbidities. We examined the effects of nonselective and selective COX inhibition on cardiovascular function in a hypercholesterolemic swine model of chronic ischemia. Twenty-four intact male Yorkshire swine underwent left circumflex ameroid constrictor placement and were subsequently given either no drug (HCC; n = 8), a nonselective COX inhibitor (440 mg/day naproxen; HCNS; n = 8), or a selective COX-2 inhibitor (200 mg/day celecoxib; HCCX; n = 8). After 7 wk, myocardial functional was measured and myocardium from the nonischemic ventricle and ischemic area-at-risk (AAR) were analyzed. Regional function as measured by segmental shortening was improved in the AAR of HCCX compared with HCC. There was no significant difference in perfusion to the nonischemic ventricle between groups, but myocardial perfusion in the AAR was significantly improved in the HCCX group compared with controls at rest and during pacing. Endothelium-dependent microvessel relaxation was diminished by ischemia in HCC animals, but both naproxen and celecoxib improved vessel relaxation in the AAR compared with controls, and also decreased the vasoconstrictive response to serotonin. Thromboxane levels in the AAR were decreased in both HCNS and HCCX compared with HCC, whereas prostacyclin levels were decreased only in HCNS, corresponding to a decrease in prostacyclin synthase expression. Chronic ischemia increased apoptosis in Troponin T negative cells and intramyocardial fibrosis, both of which were reduced by celecoxib administration in the AAR. Capillary density was decreased in both the HCNS and HCCX groups. Protein oxidative stress was decreased in both HCNS and HCCX, whereas lipid oxidative stress was decreased only in the HCCX group. Thus nonselective and especially selective COX inhibition may have beneficial myocardial effects in the setting of hypercholesterolemia and chronic ischemia. Whether these effects modulate cardiovascular risk in patients taking these drugs remains to be seen, but evidence to date suggests that they do not.

Cole-Davidson dynamics of simple chain models.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dotson, Taylor C.; McCoy, John Dwane; Adolf, Douglas Brian

2008-10-01

Rotational relaxation functions of the end-to-end vector of short, freely jointed and freely rotating chains were determined from molecular dynamics simulations. The associated response functions were obtained from the one-sided Fourier transform of the relaxation functions. The Cole-Davidson function was used to fit the response functions with extensive use being made of Cole-Cole plots in the fitting procedure. For the systems studied, the Cole-Davidson function provided remarkably accurate fits [as compared to the transform of the Kohlrausch-Williams-Watts (KWW) function]. The only appreciable deviations from the simulation results were in the high frequency limit and were due to ballistic or freemore » rotation effects. The accuracy of the Cole-Davidson function appears to be the result of the transition in the time domain from stretched exponential behavior at intermediate time to single exponential behavior at long time. Such a transition can be explained in terms of a distribution of relaxation times with a well-defined longest relaxation time. Since the Cole-Davidson distribution has a sharp cutoff in relaxation time (while the KWW function does not), it makes sense that the Cole-Davidson would provide a better frequency-domain description of the associated response function than the KWW function does.« less

Involvement of bilitranslocase and beta-glucuronidase in the vascular protection by hydroxytyrosol and its glucuronide metabolites in oxidative stress conditions.

PubMed

Peyrol, Julien; Meyer, Grégory; Obert, Philippe; Dangles, Olivier; Pechère, Laurent; Amiot, Marie-Josèphe; Riva, Catherine

2018-01-01

Olive oil vascular benefits have been attributed to hydroxytyrosol (HT). However, HT biological actions are still debated because it is extensively metabolized into glucuronides (GCs). The aim of this study was to test HT and GC vasculoprotective effects and the underlying mechanisms using aorta rings from 8-week-old male Wistar rats. In the absence of oxidative stress, incubation with 100 μM HT or GC for 5 min did not exert any vasorelaxing effect and did not influence the vascular function. Conversely, in condition of oxidative stress [upon incubation with 500 μM tert-butylhydroperoxide (t-BHP) for 30 min], preincubation with HT or GC improved acetylcholine-induced vasorelaxation compared with untreated samples (no t-BHP). This protective effect was lost for GC, but not for HT, when a washing step (15 min) was introduced between preincubation with HT or GC and t-BHP addition, suggesting that only HT enters the cells. In agreement, bilitranslocase inhibition with 100 μM phenylmethanesulfonyl fluoride for 20 min reduced significantly HT, but not GC, effect on the vascular function upon stress induction. Moreover, GC protective effect (improvement of endothelium-dependent relaxation in response to acetylcholine) in oxidative stress conditions was reduced by preincubation of aorta rings with 300 μM D-saccharolactone to inhibit β-glucuronidase, which can deconjugate polyphenols. Finally, only HT was detected by high-pressure liquid chromatography in aorta rings incubated with GC and t-BHP. These results suggest that, in conditions of oxidative stress, GC can be deconjugated into HT that is transported through the cell membrane by bilitranslocase to protect vascular function. Copyright © 2017 Elsevier Inc. All rights reserved.

Effects of the natural flavonoid delphinidin on diabetic microangiopathy.

PubMed

Bertuglia, S; Malandrino, S; Colantuoni, A

1995-04-01

The purpose of the present study was to investigate the effects of the flavonoid delphinidin chloride (CAS 528-53-0, IdB 1056) on diabetic microangiopathy. Hamsters were injected with alloxan and cheek pouch microcirculation was observed by a fluorescent microscopy technique 90 days from alloxan. The increase in permeability, the number of adhering leukocytes to venular vessel wall and vasodilatory responses to acetylcholine (Ach) and sodium nitroprusside (SNP) were measured. In diabetic group microvascular permeability and the number of sticking leukocytes to the venular endothelium were increased. Vasoconstriction by Ach was observed while the vasodilation by SNP was significantly attenuated in diabetic animals. These results are consistent for a decreased relaxation and suggest also an impairment in the smooth muscle cell function in diabetic arterioles. IdB 1056 exhibited an inhibitory effect on increased microvascular permeability and on leukocytes adhering to the venular vessels. Indeed, the treatment with IdB 1056 in diabetic hamsters pretreated or not with indometacin, a cyclooxygenase inhibitor, restored the relaxant responses to Ach and SNP. In conclusion, the effects of IdB 1056 observed in vivo at the microcirculatory level prevent the injury to endothelial cell function associated with diabetes and/or oxidative stress.

Viscoelastic relaxations of high alcohols and alkanes: Effects of heterogeneous structure and translation-orientation coupling

NASA Astrophysics Data System (ADS)

Yamaguchi, Tsuyoshi

2017-03-01

The frequency-dependent shear viscosity of high alcohols and linear alkanes, including 1-butanol, 1-octanol, 1-dodecanol, n-hexane, n-decane, and n-tetradecane, was calculated using molecular dynamics simulation. The relaxation of all the liquids was bimodal. The correlation functions of the collective orientation were also evaluated. The analysis of these functions showed that the slower relaxation mode of alkanes is assigned to the translation-orientation coupling, while that of high alcohols is not. The X-ray structure factors of all the alcohols showed prepeaks, as have been reported in the literature, and the intermediate scattering functions were calculated at the prepeak. Comparing the intermediate scattering function with the frequency-dependent shear viscosity based on the mode-coupling theory, it was demonstrated that the slower viscoelastic relaxation of the alcohols is assigned to the relaxation of the heterogeneous structure described by the prepeak.

The Interplay of Preference, Familiarity and Psychophysical Properties in Defining Relaxation Music.

PubMed

Tan, Xueli; Yowler, Charles J; Super, Dennis M; Fratianne, Richard B

2012-01-01

The stress response has been well documented in past music therapy literature. However, hypometabolism, or the relaxation response, has received much less attention. Music therapists have long utilized various music-assisted relaxation techniques with both live and recorded music to elicit such a response. The ongoing proliferations of relaxation music through commercial media and the dire lack of evidence to support such claims warrant attention from healthcare professionals and music therapists. The purpose of these 3 studies was to investigate the correlational relationships between 12 psychophysical properties of music, preference, familiarity, and degree of perceived relaxation in music. Fourteen music therapists recommended and analyzed 30 selections of relaxation music. A group of 80 healthy adults then rated their familiarity, preference, and degree of perceived relaxation in the music. The analysis provided a detailed description of the intrinsic properties in music that were perceived to be relaxing by listeners. These properties included tempo, mode, harmonic, rhythmic, instrumental, and melodic complexities, timbre, vocalization/lyrics, pitch range, dynamic variations, and contour. In addition, music preference was highly correlated with listeners' perception of relaxation in music for both music therapists and healthy adults. The correlation between familiarity and degree of relaxation reached significance in the healthy adult group. Results from this study provided an in-depth operational definition of the intrinsic parameters in relaxation music and also highlighted the importance of preference and familiarity in eliciting the relaxation response.

Cooling rate and stress relaxation in silica melts and glasses via microsecond molecular dyanmics

DOE PAGES

Lane, J. Matthew D.

2015-07-22

We have conducted extremely long molecular dynamics simulations of glasses to microsecond times, which close the gap between experimental and atomistic simulation time scales by two to three orders of magnitude. The static, thermal, and structural properties of silica glass are reported for glass cooling rates down to 5×10 9 K/s and viscoelastic response in silica melts and glasses are studied over nine decades of time. We finally present results from relaxation of hydrostatic compressive stress in silica and show that time-temperature superposition holds in these systems for temperatures from 3500 to 1000 K.

Viscoelastic properties of addition-cured polyimides used in high temperature polymer matrix composites

NASA Technical Reports Server (NTRS)

Roberts, Gary D.; Malarik, Diane C.; Robaidek, Jerrold O.

1991-01-01

The viscoelastic properties of an addition-cured polyimide, PMR-15, were evaluated through dynamic mechanical and stress relaxation testing. Below the glass transition temperature, the dynamic mechanical properties of the composites are strongly affected by the absorbed moisture in the resin. At temperature 20 C and more above the glass transition temperature, the storage modulus increases continuously with time, indicating that additional crosslinking is occurring in the resin. For resin moisture contents less than 2 percent, stress relaxation curves measured at different temperatures can be superimposed using horizontal shifts along the log(time) axis with only small shifts along the vertical axis.

Enhancing elastic stress relaxation in SiGe/Si heterostructures by Si pillar necking

NASA Astrophysics Data System (ADS)

Isa, F.; Salvalaglio, M.; Arroyo Rojas Dasilva, Y.; Jung, A.; Isella, G.; Erni, R.; Timotijevic, B.; Niedermann, P.; Gröning, P.; Montalenti, F.; von Känel, H.

2016-10-01

We demonstrate that the elastic stress relaxation mechanism in micrometre-sized, highly mismatched heterostructures may be enhanced by employing patterned substrates in the form of necked pillars, resulting in a significant reduction of the dislocation density. Compositionally graded Si1-xGex crystals were grown by low energy plasma enhanced chemical vapour deposition, resulting in tens of micrometres tall, three-dimensional heterostructures. The patterned Si(001) substrates consist of micrometre-sized Si pillars either with the vertical {110} or isotropically under-etched sidewalls resulting in narrow necks. The structural properties of these heterostructures were investigated by defect etching and transmission electron microscopy. We show that the dislocation density, and hence the competition between elastic and plastic stress relaxation, is highly influenced by the shape of the substrate necks and their proximity to the mismatched epitaxial material. The SiGe dislocation density increases monotonically with the crystal width but is significantly reduced by the substrate under-etching. The drop in dislocation density is interpreted as a direct effect of the enhanced compliance of the under-etched Si pillars, as confirmed by the three-dimensional finite element method simulations of the elastic energy distribution.

The effects of heat treatment on selected properties of a conventional and a resin-modified glass ionomer cement.

PubMed

Rafeek, Reisha N

2008-05-01

This study investigated the effects of application of heat alone and heat & pressure on the compressive strength and modulus, the stress relaxation characteristics and the fluoride release of a conventional and a resin-modified glass ionomer cement. Cylindrical specimens were made from both materials and divided into 3 groups. One group was heat treated in an oven at 120 degrees C for 20 min, another group was subjected to heat & pressure at 120 degrees C for 20 min at 6-bar pressure. The third group acted as a control. The compressive strength and modulus, stress relaxation and fluoride release were tested over 56 days. The results of this investigation indicate that heat treatment had no significant effect on the conventional GIC used but significantly affected the resin modified GIC by increasing both the compressive strength and modulus and reducing the stress relaxation characteristics and the fluoride release. The use of GIC to produce inlay or onlay restorations that adhere to tooth tissue and release fluoride would be highly desirable. The results of this study indicate that it is possible to improve the strength of RMGIC with heat to a limited extent, but fluoride release may decrease.

Dynamical heterogeneities and mechanical non-linearities: Modeling the onset of plasticity in polymer in the glass transition.

PubMed

Masurel, R J; Gelineau, P; Lequeux, F; Cantournet, S; Montes, H

2017-12-27

In this paper we focus on the role of dynamical heterogeneities on the non-linear response of polymers in the glass transition domain. We start from a simple coarse-grained model that assumes a random distribution of the initial local relaxation times and that quantitatively describes the linear viscoelasticity of a polymer in the glass transition regime. We extend this model to non-linear mechanics assuming a local Eyring stress dependence of the relaxation times. Implementing the model in a finite element mechanics code, we derive the mechanical properties and the local mechanical fields at the beginning of the non-linear regime. The model predicts a narrowing of distribution of relaxation times and the storage of a part of the mechanical energy --internal stress-- transferred to the material during stretching in this temperature range. We show that the stress field is not spatially correlated under and after loading and follows a Gaussian distribution. In addition the strain field exhibits shear bands, but the strain distribution is narrow. Hence, most of the mechanical quantities can be calculated analytically, in a very good approximation, with the simple assumption that the strain rate is constant.

Stress relaxation study of fillers for directly compressed tablets

PubMed Central

Rehula, M.; Adamek, R.; Spacek, V.

2012-01-01

It is possible to assess viscoelastic properties of materials by means of the stress relaxation test. This method records the decrease in pressing power in a tablet at its constant height. The cited method was used to evaluate the time-dependent deformation for six various materials: microcrystalline cellulose, cellulose powder, hydroxypropyl methylcellulose, mannitol, lactose monohydrate, and hydrogen phosphate monohydrate. The decrease in pressing powering of a tablet during a 180 s period was described mathematically by the parameters of three exponential equations, where the whole course of the stress relaxation is divided into three individual processes (instant elastic deformation, retarded elastic deformation and permanent plastic deformation). Three values of the moduli of plasticity and elasticity were calculated for each compound. The values of elastic parameters ATi have a strong relationship with bulk density. The plastic parameters PTi represent particle tendency to form bonds. The values of plasticity in the third process PT3 ranged from 400 to 600 MPas. Mannitol had higher plasticity and lactose monohydrate on the contrary reduced plasticity. A linear relation exists between AT3 and PT3 for the third process. No similar interpretation of moduli calculated on the basis of three exponential equations has been realized yet. PMID:24850972

Coseismic and Postseismic Deformation Following the 2011 Mw 9.0 Tohoku Earthquake and its Mw 7.9 Aftershock: Searching for Fault-localized Relaxation of Coseismic Stress Increments

NASA Astrophysics Data System (ADS)

Wang, F.; Bevis, M. G.; Blewitt, G.; Gomez, D.

2017-12-01

We study the postseismic transient displacements following the 2011 Mw 9.0 Tohoku earthquake using the Nevada Geodetic Laboratory's daily and 5-minute interval PPP solutions for 1,272 continuous GPS stations in Japan, with particular emphasis on the early transient displacements of these stations. One significant complication is the Mw 7.9 aftershock that occurred just 29.3 minutes after the main shock, since the coseismic (and postseismic) displacements driven by the aftershock are superimposed on the postseismic transients driven by the main shock. We address the question of whether or not the stresses induced by the Mw 9.0 main shock were relaxed by any major faults within Japan. The notion is that significant stress relaxation which is localized on a fault system should be manifested in the spatial pattern of the postseismic transient displacement field in the vicinity of that system. This would provide a basis for distinguishing between faults that engage in stick-slip behavior and those that creep instead. The distinction is important in that it has implications for the seismic risk associated with upper plate faulting. We will make the case that we do detect localized fault creeping in response to the coseismic stress field produced by the Mw 9 event.

Effect of Microstructure on Time Dependent Fatigue Crack Growth Behavior In a P/M Turbine Disk Alloy

NASA Technical Reports Server (NTRS)

Telesman, Ignacy J.; Gabb, T. P.; Bonacuse, P.; Gayda, J.

2008-01-01

A study was conducted to determine the processes which govern hold time crack growth behavior in the LSHR disk P/M superalloy. Nineteen different heat treatments of this alloy were evaluated by systematically controlling the cooling rate from the supersolvus solutioning step and applying various single and double step aging treatments. The resulting hold time crack growth rates varied by more than two orders of magnitude. It was shown that the associated stress relaxation behavior for these heat treatments was closely correlated with the crack growth behavior. As stress relaxation increased, the hold time crack growth resistance was also increased. The size of the tertiary gamma' in the general microstructure was found to be the key microstructural variable controlling both the hold time crack growth behavior and stress relaxation. No relationship between the presence of grain boundary M23C6 carbides and hold time crack growth was identified which further brings into question the importance of the grain boundary phases in determining hold time crack growth behavior. The linear elastic fracture mechanics parameter, Kmax, is unable to account for visco-plastic redistribution of the crack tip stress field during hold times and thus is inadequate for correlating time dependent crack growth data. A novel methodology was developed which captures the intrinsic crack driving force and was able to collapse hold time crack growth data onto a single curve.

Transient postseismic mantle relaxation following 2004 Sumatra earthquake: implications of seismic vulnerability in the Andaman-Nicobar region

NASA Astrophysics Data System (ADS)

Reddy, C. D.; Prajapati, S. K.; Sunil, P. S.; Arora, S. K.

2012-02-01

Throughout the world, the tsunami generation potential of some large under-sea earthquakes significantly contributes to regional seismic hazard, which gives rise to significant risk in the near-shore provinces where human settlements are in sizeable population, often referred to as coastal seismic risk. In this context, we show from the pertinent GPS data that the transient stresses generated by the viscoelastic relaxation process taking place in the mantle is capable of rupturing major faults by stress transfer from the mantle through the lower crust including triggering additional rupture on the other major faults. We also infer that postseismic relaxation at relatively large depths can push some of the fault segments to reactivation causing failure sequences. As an illustration to these effects, we consider in detail the earthquake sequence comprising six events, starting from the main event of Mw = 7.5, on 10 August 2009 and tapering off to a small earthquake of Mw = 4.5 on 2 February 2011 over a period of eighteen months in the intensely seismic Andaman Islands between India and Myanmar. The persisting transient stresses, spatio-temporal seismic pattern, modeled Coulomb stress changes, and the southward migration of earthquake activity has increased the probability of moderate earthquakes recurring in the northern Andaman region, particularly closer to or somewhat south of Diglipur.

On the Prony series representation of stretched exponential relaxation

NASA Astrophysics Data System (ADS)

Mauro, John C.; Mauro, Yihong Z.

2018-09-01

Stretched exponential relaxation is a ubiquitous feature of homogeneous glasses. The stretched exponential decay function can be derived from the diffusion-trap model, which predicts certain critical values of the fractional stretching exponent, β. In practical implementations of glass relaxation models, it is computationally convenient to represent the stretched exponential function as a Prony series of simple exponentials. Here, we perform a comprehensive mathematical analysis of the Prony series approximation of the stretched exponential relaxation, including optimized coefficients for certain critical values of β. The fitting quality of the Prony series is analyzed as a function of the number of terms in the series. With a sufficient number of terms, the Prony series can accurately capture the time evolution of the stretched exponential function, including its "fat tail" at long times. However, it is unable to capture the divergence of the first-derivative of the stretched exponential function in the limit of zero time. We also present a frequency-domain analysis of the Prony series representation of the stretched exponential function and discuss its physical implications for the modeling of glass relaxation behavior.

21 CFR 310.519 - Drug products marketed as over-the-counter (OTC) daytime sedatives.

Code of Federal Regulations, 2014 CFR

2014-04-01

... irritability that ruins your day,” “helps you relax,” “restlessness,” “when you're under occasional stress . . . helps you work relaxed.” Based on evidence presently available, there are no ingredients that can be... is labeled, represented, or promoted as an OTC daytime sedative (or any similar or related indication...