Interactive Effects Of Stress Research Articles

Stress Effects on Activity of Primary Cracks Initiating at Stress Concentrator

This study has been performed to investigate the stress distribution around defects that behave as stress concentrators and fracture mechanical analysis for cracks initiating at stress concentrators. The stress distribution was analyzed using Finite Element Method and non-dimensional stress intensity factor was determined by the mean stress method. This method could be applied to determine the activity of primary crack initiated at the stress concentrator in experiment. In addition, stress interaction effects around defects and cracks were compared.

Micromechanics-based prediction of creep failure of hard rock for long-term safety of high-level radioactive waste disposal system

A high-level radioactive waste disposal project is under way in Japan. Isolation of the radioactive waste in a rock formation at great depth is considered as one of the promising disposal methods. Before proceeding with the disposal project, however, assessment of the long-term stability of rock mass surrounding waste packages is necessary. This paper presents a micromechanics-based model for predicting the creep failure of hard rock under compression. The subcritical crack growth due to stress corrosion cracking and interaction effects between cracks are considered as the main mechanisms of creep failure. An evolution problem of two interacting cracks is formulated and creep failure following tertiary creep is represented as unstable extension of the interacting cracks in the present model. The time to failure is calculated for different values of axial stress, confining pressure, and environmental conditions such as temperature and presence of water. The effects of water, temperature, and stress states on the long-term behavior are also included in the proposed model.

Rheology of non-Newtonian suspensions of fly ash: effect of concentration, yield stress and hydrodynamic interactions

Two different water-washed municipal solid waste (MSW) incinerator fly ashes were investigated. The rheological behaviour of these fly ashes in aqueous suspensions was studied using a parallel plate rheometer. Shear-thinning behaviour was observed in one sample whereas thixotropic behaviour was found in the other. Viscosity depends on both the volume fraction of solids in the suspension and on the yield stress. The data could be well correlated to a model we proposed which takes into account the volume fraction of solid and the shear rate. The comparison with various models of the literature is discussed. The hydrodynamic theory of particle movement in non-Newtonian fluids is discussed, focusing on inertia and viscous effects. Two modified Reynolds numbers involving respectively the shear rate and the yield stress, and with the shear rate and the volume fraction of solids, are proposed and discussed. The flow regime in the investigated experimental conditions is laminar and governed by hydrodynamic interactions. The results also show that inertia cannot be neglected.

Social relationships, stress and mortality

Empirically it has been demonstrated in many cases that social networks induce lower mortality rates. This article discusses various approaches to explain this phenomenon in consideration of the influence of stress. The empirical analysis refers to the complex interrelation between social networks, stress and mortality. In doing so, quantitative and qualitative aspects of social networks, different indicators of stress as well as the interaction effect of stress and social network is analyzed. Data derive from the German "MONICA Project" (MONICA=Monitoring of trends and determinants of cardiovascular diseases). The data comprise two cross-sectional surveys in 1984/85 and 1989/90 in the Augsburg area as well as a mortality follow-up in 1997/98. The study includes 7329 persons between the age of 25 and 74 years with German nationality. The empirical analyses confirm the findings that social relationships induce lower mortality rates. Yet, social relationships lead to lower mortality independent of stress and social strains.

Additive Effect of Stress and Drug Cues on Reinstatement of Ethanol Seeking: Exacerbation by History of Dependence and Role of Concurrent Activation of Corticotropin-Releasing Factor and Opioid Mechanisms

Stress and exposure to drug-related environmental stimuli have been implicated as critical factors in relapse to drug use. What has received little attention, however, is the significance of interactions between these factors for motivating drug-seeking behavior. To address this issue, a reinstatement model of relapse was used. Footshock stress and response-contingent presentation of an ethanol-associated light cue, acting as a conditioned stimulus (CS), effectively reinstated extinguished responding at a previously active, drug-paired lever in male Wistar rats. When response-contingent availability of the ethanol CS was preceded by footshock, additive effects of these stimuli on responding were observed. Both the individual and interactive effects of footshock and the CS were significantly greater in previously ethanol-dependent than in nondependent rats. Responding induced by the ethanol CS was selectively reversed by the nonselective opiate antagonist naltrexone, whereas the effects of footshock were selectively reversed by the corticotropin-releasing factor (CRF) antagonist d-Phe-CRF(12-41). However, both agents only partially reversed the enhanced drug-seeking response produced by the interactive effects of stress and the ethanol CS; full reversal required coadministration of d-Phe-CRF and naltrexone. The results document that stress and drug-related environmental stimuli interact to augment the resumption of drug seeking after extinction and suggest that this effect results from concurrent activation of opioid and CRF transmission.

Exploring Cost Constraints on Stem Elongation in Plants Using Phenotypic Manipulation

Exploring Cost Constraints on Stem Elongation in Plants Using Phenotypic Manipulation

Qualitative Assessment of Failure in Bolted Connections: Tsai-Wu Criterion

Abstract In a companion paper, a characterization is presented of stress fields in a single-shear bolted connection subjected to tension loading. Numerous stress contours are presented that illustrate the magnitude of the parallel-to-grain compression and shear stresses, as well as the perpendicular-to-grain tension stresses. In addition, regions of potential failure in the selected specimens are identified based on a maximum stress failure criterion. The work presented in this paper represents additional efforts to identify the effect of stress interactions on the strength of the previously mentioned connections. The Tsai-Wu criterion, quantified by its failure index, is used as the tool to identify stress interactions between the aforementioned stress components. Connection geometries similar to those discussed in the companion paper [end distance/bolt diameter (e∕d)=4; and length of bolt in main member/bolt diameter (aspect ratio) (l∕d)=2,5,and7] are studied. In addition, several other geometries are discussed that illustrate the effects of changing aspect ratio and end distance. A number of significant findings are reached in this study. As is the case in the companion study, all connections with (l∕d)=2 have nearly uniform distributions of the Tsai-Wu failure index (FI) through the specimen thickness. No significant pin bending is associated with this geometry. Connections with l∕d>4 have a failure mode (interpreted from the numerical model) that includes substantial pin bending due to steel yielding, wood crushing, and localized cracking.

A potential moderating role of stress in the association of disease activity and psychological status among patients with rheumatoid arthritis.

This study investigated the role of perceived daily stress as a potential moderator in the relation between a set of predictors (disease activity, education, pain) and psychological status (anxiety, depression) of 31 patients with rheumatoid arthritis. Psychological measures served as dependent variables in hierarchical regression analyses testing for potential interaction effects of daily stress upon relationships between predictors and dependent measures. No predictors predicted directly scores on depression and anxiety; however, daily stress directly predicted scores on depression and anxiety, even after having separately controlled for each of the predictors. Increased disease activity had significantly stronger associations with increased psychological morbidity only among patients reporting high scores on daily stress, suggesting a potential moderating role for stress.

Dysfunctional attitudes and vulnerability to depressive symptoms : A 14-week longitudinal study

Beck's acute-onset model of depression proposesthat initially asymptomatic individuals with high levelsof dysfunctional attitudes (DA) will become depressedwhen stressors occur. Using a large student sample (n = 275), we conducted a 14-weeklongitudinal study aimed at testing Beck's model as anacute-onset model. Consistent with past studies (Monroe,Bromet, Connell, & Steiner, 1986; Roberts & Monroe, 1992), a DA Stress interaction did notobtain when all subjects (both symptomatic andasymptomatic) were included in the data analyses.However, when analyses were restricted to initiallyasymptomatic subjects, the predicted DA Stress interactioneffect did obtain. Specifically, under conditions ofhigh stress, initially asymptomatic subjects with highlevels of dysfunctional attitudes showed greater increases in depressive symptoms than initiallyasymptomatic subjects with low levels of dysfunctionalattitudes. Follow-up analyses revealed that this DAStress interaction was specific to females and not males. Possible reasons for the female-specificeffect are discussed. In general, these findings callattention to the fact that subject selection proceduresmay affect a researcher's ability to predict future onset of depression.

Analysis of stress distribution around defects and inclusions by F.E.M.

This study has been made to investigate the stress distribution around defects and inclusions that behave as stress concentrators. The stress distribution and interaction effects around defects and inclusions were analyzed using Finite Element Method.

Effects of Pentachlorophenol and Biotic Interactions on Soil Fauna and Decomposition in Humus Soil

In a laboratory experiment, effects of chemical stress (pentachlorophenol, PCP, at concentrations of 0, 50, and 500 mg/kg) and biotic interactions (nematodes in the presence or absence of collembolas and enchytraeids) on the community structure of soil animals and decomposition processes were studied. PCP was strongly adsorbed to humus that contained 65% organic matter. Numbers of fungal-feeding nematodes decreased significantly at the highest PCP concentration, while no effects were found in bacterial feeders. There were differences in the numbers of nematodes between different animal combinations, but at the highest PCP concentration, collembolas and enchytraeids had no effect on them. Numbers of collembola Willemia anophtalma were lowered at the highest PCP concentration, although PCP was not acutely toxic at this concentration. The highest PCP concentration was acutely toxic to enchytraeids, and for an unknown reason all of them died in the main experiment. Both ATP content of the soil and soil respiration were reduced at the highest PCP concentration, while no differences were found between animal treatments. Amounts of NH 4N and PO 4P in the soil increased with increasing PCP concentration. It was concluded that in the presence of simple animal communities, harmful chemicals like PCP regulate the community structure of soil animals as web as decomposition and nutrient mobilization.

Effects of dietary energy intake by gilts and heat stress from days 3 to 24 or 30 after mating on embryo survival and nitrogen and energy balance

Bred gilts were used in two experiments (n = 140) to study the interaction and main effects of dietary energy intake and heat stress on embryo survival and nitrogen (N) and energy balance from d 3 to slaughter on d 30 (Exp. 1) or d 24 (Exp. 2) after mating. In both experiments, the ME treatments were 5.4 or 8.1 Mcal of ME/(gilt.d). Temperatures were either a constant thermoneutral of 23 +/- 1 degrees C or a heat stress regimen, making four treatments in a 2 x 2 factorial arrangement. Gilts were allotted directly to one of the treatments on d 3 after mating. In Exp. 1, the 24-h cyclic heat stress regimen consisted of an increase from 25 degrees C at 0800 to 34 degrees C at 1400, 34 degrees C from 1400 to 1700, then a decline to 25 degrees C at 2000, with 25 degrees C until 0800. In Exp. 2, heat stress was constant at 33 +/- 1 degrees C. No energy x temperature treatment interactions occurred (P > .2 to .8) for the variables measured in Exp. 1 and 2. Heat stress reduced (P < .05 or .01) diet and ME intake/day, ME retained/day, and ME/GE compared with the thermoneutral controls in Exp. 1 and 2. Heat stress reduced (P < .05) N digestibility in Exp. 1 and reduced (P < .01) N retained/day and N retention/N intake in Exp. 2. Rectal temperature and respiration rate were increased (P < .01) by heat stress in Exp. 1 and 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of life stress on immunological reactivity to mild psychological stress.

This study investigated the effects of self-reported life stress and locus of control on reactivity of several immune parameters to a mild and short-lasting interpersonal stressor. Subjects were 86 male teachers aged 24 to 55 years. Immune reactivity was defined as changes in numbers of monocytes. T-lymphocytes and subsets, HLA-DR+ cells, and NK cells as well as changes in (in vitro) proliferative responses of peripheral blood lymphocytes to the antigens PHA and PWM. Multiple regression analysis was used to study the interaction effects of life stress and locus of control by experimental condition on immune reactivity. Life stress, but not locus of control, influences reactivity of the immunological parameters to the stressor. In particular, high numbers of daily hassles were associated with stressor-induced decreases in numbers of T cells and NK cells in peripheral blood. On the other hand, numbers of HLA-DR+ cells in high life stress scorers decreased only slightly during the stressor, whereas they increased in the control condition. The findings suggest that accumulated life stress is related to reactivity of immunological parameters to subsequent experimental stress. Possible physiological explanations and implications of these effects are discussed.

Nonlinear Response of Unidirectional Boron/Aluminum

Experimental results obtained for unidirectional boron/aluminum subjected to combined loading using off-axis tension, compression and Iosipescu shear specimens are correlated with a nonlinear micromechanics model. It is illustrated that the nonlinear response in the principal material directions is markedly influenced by the different load ing modes and different ratios of the applied stress components. The observed nonlinear response under pure and combined loading is discussed in terms of initial yielding, subse quent hardening, stress-interaction effects and unloading-reloading characteristics. The micromechanics model is based on the concept of a repeating unit cell representative of the composite-at-large and employs the unified theory of Bodner and Partom to model the inelastic response of the matrix. It is shown that the employed micromechanics model is sufficiently general to predict the observed nonlinear response of unidirectional boron/ aluminum with good accuracy.

Self-esteem and stress as factors in abuse of children.

A comparison of stress and self-esteem as made between a group of 23 couples in treatment who had abused their children and 23 control couples who were matched for age, race, sex, education, and occupation. Stress was measured by the Recent Life Changes Questionnaire. Self-esteem was measured by a synthesis of 38 items selected by mental health professionals from the Clarke Parent/Child Relations Questionnaire and the Self-description and Mate Description Form. Analysis of variance showed that couples who had abused their children had significantly greater stress than control couples. However, there was no significant difference between the groups on the measure of self-esteem. There was also no interaction effect of stress with self-esteem on abuse. While it seems well established that stress is a major contributor in child abuse, the interaction of stress with personality factors of parents who abuse their children remains uncertain.

Base-rates, cut-points and interaction effects: the problem with dichotomized continuous variables.

On the background of the recent discussion about the appropriateness of linear difference and ratio models for testing interaction effects of social support and stress, it is argued that interaction effects are basically unstable when dichotomized continuous variables are analysed. A data set with known interrelationships of the continuous variables 'stress', 'social support', and 'depression' was simulated and analysed in tabular format. It is shown that the choice of cut-points for the independent variables crucially determines the size and presence of interaction effects in ratio analysis models.

Interactive effects of stress and photoperiod history on gonadal condition in male Syrian hamsters.

A study of the effects of melatonin injections given to male Syrian hamsters (Mesocricetus auratus) late in the light phase in a 14L:10D photoperiod included control, oil-injected hamsters that had been transferred from a 16L:8D photoperiod. Many oil-injected hamsters underwent gonadal regression under these conditions. A literature review indicated that endocrine effects of 'control' injections are fairly common but that they might depend on previous photoperiodic history. A second study found that hamsters born and raised in 16L:8D had larger testes at 150 days of age than those raised in 14L:10D. Transfer from 16L:8D to 14L:10D caused some unhandled hamsters to show gonadal regression while transfer to 14L:10D combined with daily oil injections caused most hamsters to undergo gonadal regression. Injections in animals maintained in 14L:10D throughout the study did not cause gonadal regression. These results indicate that stress effects can confound interpretation of drug treatments that require daily injections. They also demonstrate that the endocrine system of male Syrian hamsters distinguishes two photoperiods that are longer than the critical daylength (12.5 h). The effects of shortening daylengths may be potentiated by environmental stressors; together these may trigger gonadal regression at variable annual phases in anticipation of the critical daylength.

Stress-Moderating Effects

Using multiple regression, the main and interactive effects of stress, social support, locus of control, and gender on psychological adjustment were investigated. In order to understand the complex interactions found, the adjustment effects of stress and social support were examined within four subgroups: internal and external men and women college students. Both social support and adjustment were assessed with multiple measures. Stress was more strongly related to levels of adjustment for women than for men. The relationships between social support and adjustment varied depending on which social support measure was used, which adjustment measure was used, as well as the locus of control orientation and gender of the subject. External men were the least able to use social support to aid adjustment. In contrast to previous investigations, there were no two-way stress X locus of control interactions. The importance of investigating the interactions of stress-moderating variables in specific subgroups is discussed.

Stress and Substance Interaction Effects on Risk Factors and Reactivity

Stress and Substance Interaction Effects on Risk Factors and Reactivity

Studies of enzyme polymorphism in the Kamuela population of Drosophila mercatorum. III. Effects of variation at the alpha GPD locus and subflight stress on the energy charge and glycolytic intermediate concentrations.

We have employed a "level crossing" strategy to study the primary effects of an enzyme polymorphism in Drosophila mercatorum. This strategy consists of following genetic differences across intervening phenotypes to possible fitness effects. In this paper, we report the steady state concentrations of the glycolytic intermediates and the adenylates (intervening phenotypes) in two genotypes (alpha GPD-F, alpha GPD-S) at two stress levels (rest, subflight). We did not detect a genotype or a genotype by stress interaction effect on glycolytic intermediate or adenylate concentrations despite the ability of the experimental design to detect a 20 to 50% difference from the mean of a control. The flux of glycolysis is adequate to maintain the energy charge in both strains under the stress levels considered. If there is a fitness difference between these alpha GPD variants, it is unlikely to be a result of modifications of glycolysis. Subflight stress, however, resulted in an increase in metabolic flux. The observed pattern of intermediate concentration differences is consistent with the modulation of glycolysis by the ratio of the ATP and AMP concentrations acting on phosphofructokinase activity.