On the classification of random two-dimensional cellular structures

The correlation of lengths and angles in random cellular crack patterns, produced by thermal shock in commercial ceramic materials used to make tableware, is determined. The straight line describing this correlation has a slope one half of that describing the cooling-induced crack networks formed in lava flows. In order to compare the polygonal crack structures formed at slow and extremely fast cooling rates with other random cellular structures, the correlation of lengths and angles for some known cellular patterns in epidermal vegetable tissues, magnetic garnet films and soap froths are presented. It is shown that this correlation can be used to classify two-dimensional random cellular structures.     

慢性应激对大鼠行为和免疫细胞热休克蛋白70表达的影响

目的：研究慢性不确定应激对大鼠急性整体热水浴后外周血和脾脏免疫细胞热休克蛋白70（Heat shock protein 70, HSP70）表达的影响。方法：随机将大鼠分成慢性应激组和控制组（每组14只）。通过4周的慢性不确定性应激诱发实验组大鼠明显的抑郁行为,此期间控制组大鼠正常饲养。随后给予大鼠42度整体热水浴刺激,维持直肠温度41度25min。热刺激后6h,采用流式细胞仪测定大鼠外周血和脾脏免疫细胞HSP70 水平。结果：与控制组大鼠相比,慢性应激大鼠在急性热刺激后HSP70合成明显减少。控制组大鼠的所有被检测的免疫细胞热应激后HSP70合成均明显增加。相反,慢性应激大鼠仅在外周血的单核细胞和粒细胞检测到HSP70合成增加,同时升高的水平明显低于控制组大鼠。结论：慢性应激降低大鼠免疫细胞HSP70的热诱导反应,提示HSP70保护性作用减弱可能参与了慢性应激损害免疫细胞功能的生物学过程     

Stress conditioning in mice: alterations in immunity and tumor growth

The neuroendocrine and autonomic nervous systems are known regulators of brain-immune interaction. However, the functional significance of this interaction under stress is not fully understood. We investigated the effect of a stress paradigm by applying electric foot shock followed by three reminders, on behavior, immune parameters, and lymphoma tumor growth. Male C3H mice were divided into two groups: Group 1-exposed to electric foot shock followed by three reminders, and Group 2-untreated (controls). Sets of mice underwent the elevated plus maze, staircase, and hot plate tests. After foot shock, natural killer (NK) cell activity, and lymphocyte proliferation were measured. In addition, sets of mice were either vaccinated twice with B-cell lymphoma 38C-13 immunoglobulin for determination of anti-idiotype (Id) antibodies in sera, or inoculated with tumor cells and monitored for tumor development and survival time. Mice exposed to electric foot shock followed by the three reminders had higher NK cell activity, levels of anti-Id antibodies, and a higher proliferation rate of splenocytes in response to mitogens, than the control mice. The exposed mice also showed attenuated tumor growth. Thus, the stress paradigm inhibited tumor development and lead to some immune changes that were not accompanied by behavioral changes.     

A new device for the application of electrical shock

A new apparatus has been developed for the simple, safe, and effective delivery of electric shock. It delivers a single-pulse high-voltage shock of very short duration. Both voltage and current are easily measured and the applied energy can be calculated. Constant energy applications depend less upon skin contact resistance than is the case with 600-V 60-Hz shockers.     

An atomistic modelling and statistical analysis study of crack–void interaction in Aluminum

The interaction between a brittle crack and pre-existing void in front of the crack tip was studied in the realm of molecular dynamics simulations at the nanoscale in face centred cubic Al within the framework of embedded-atom method. The results provide corroborative evidence of the fact that presence of a void in front of a running crack deters further crack growth. By performing an extensive series of simulations with different void sizes and crack-void distances coupled with statistical analysis, it has been found that (1) major role of voids is to decrease the fracture stress with increasing void size, in addition to slight increase in strain at which the crack growth occurs and the consequent strain to fracture, (2) fracture stress for a constant void size follows a sinusoidal distribution by varying the crack-void distance and (3) it is the void size that is most crucial in dictating the fracture properties of the material, rather than the void placement.     

Ductile fracture mechanism in fine-grained magnesium alloy

The ductile fracture mechanism in a fine-grained magnesium alloy has been investigated by transmission electron microscopy-focused ion beam techniques. In coarse-grained or conventional magnesium alloys, twins form at the very beginning of the deformation process, and crack propagation occurs through the twin boundaries. However, in the alloy used in this study, subgrain structures were found instead of twins at the crack tip. Nanoscale twins formed subsequently owing to large stress in the crack propagation route. The fine-grained alloys showed high fracture toughness resulting from resistance to the twins at the beginning of the deformation.     

Gastric secretion as a function of acute and chronic stress in the gastric fistula rat.

In Experiment 1 rats exposed to signaled and unsignaled grid shock secreted more gastric acid after shock stress (chronic stress) for 8 days compared to the first 12 hr. of shock stress (acute stress). However, Experiment 2 indicated that the higher gastric acid values under chronic stress were not significantly greater than prestress baseline values. The results are interpreted to reflect an inhibition of gastric acid secretion as a function of acute stress. During chronic stress this inhibition is followed by a habituation of gastric secretory processes which is observed as a return of secretion volume to baseline levels.     

Response Speed and Accuracy During Anticipatory Stress

Response speed and accuracy of 48 general aviation pilots were determined under condition of anticipatory physical threat stress (APTS). Variables included unpleasantness of the event (electrical shock), proximity of the event, and relationship of Ss’ performance to the occurrence of the event. The data support inclusion of these variables in Wherry’s model of APTS. Ss who believed they could avoid the shock by an adequate performance were able to maintain or improve that performance while the performance of Ss who perceived the shock as inevitable was deteriorating. Two possible modifications of the APTS model were discussed: (1) weighting APTS determiners according to their effectiveness in generating anticipatory stress, (2) recognizing the interaction of the APTS variables with S’s personality structure.     

A new high-pressure phase transition in a zirconium-niobium alloy

It is reported for the first time that a g M y transformation can be induced in a g -stabilized zirconium alloy subjected to shock pressure. The y phase formed in the g matrix has been found to have a plate shape akin to martensitic plates. The lattice correspondence between the g and y structures has been found to be the same as that produced by thermal treatment. The formation of the plate-shaped y phase is explained in terms of a mechanism involving shear on <112> planes of the bcc lattice and the mechanical instability of the g phase.     

Effects of instructions and biofeedback on EEG-alpha production and the effects of EEG-alpha biofeedback training for controlling arousal in a subsequent stressful situation

In Phase One, 44 subjects participated in a 2 (instructions to increase alpha, no instructions to increase alpha) × 2 (alpha biofeedback, no alpha biofeedback) factorial experiment. Results indicated that increases in alpha production were due to instructions to increase alpha and that biofeedback had no effect on alpha production. In Phase Two, the 44 subjects from Phase One were exposed to a threat of shock whereas 11 additional subjects in a control condition were not. The design employed in Phase Two was a 2 (previous instructions and stress, no previous instructions and stress) × 2 (previous biofeedback and stress, no previous biofeedback and stress) plus 1 (no previous instructions/no previous biofeedback, no stress). Results indicated that the threat of shock was effective in increasing arousal (as measured by heart rate and skin resistance) but previous EEG-alpha biofeedback training was not effective in helping subjects decrease arousal while in the stressful situation. The results indicate that it is the instructions (and related information concerning alpha) rather than the biofeedback that is critical in alpha biofeedback training and that this training does not appear to have utility for controlling arousal under stress.     

Learning associated increase in heat shock cognate 70 mRNA and protein expression

The Morris water maze is a task widely used to investigate cellular and molecular changes associated with spatial learning and memory. This task has both spatial and aversive (swimming related stress) components. It is possible that stress may influence cellular modifications observed after learning the Morris water maze spatial task. Heat shock proteins, also known as stress proteins, are up-regulated in response to thermal stress, trauma, or environmental insults. In the rat hippocampus, psychophysiological stress increases the levels of heat shock protein 70 (HSC70). In this study, we investigated whether the expression of the hsc70 gene is modulated in the hippocampus during learning of the Morris water maze task. Five groups of rats were trained in the Morris water maze task for varying amounts of time (either 1, 2, 3, 4, or 5 days). Training consisted of 10 trials/day in which the animals were given 60s to find a submerged platform. Rats were sacrificed 24h after their last training trial. Results showed a significant increase in hsc70 mRNA and protein levels in the hippocampal formation after two and three days of training, respectively. The increase in mRNA and protein was associated with learning but not stress because the increase was not observed in the yoked control animals. These findings suggest that cellular and molecular changes can occur independent of stress. Moreover, the results are the first to implicate hsc70 expression in spatial learning.     

An integrative model of stress management groups for women

This article proposes an integrative model for stress management groups for women, representing a biopsychosocial point of view and drawing on theories of psychodynamic group psychotherapy, self-psychology, female development, and stress management. The basis of the model is an eight week traditional stress management group. The novel aspects of this integrative model are that it aims to increase the power of stress management groups for women by providing an articulated frame, attending to group process, promoting curiosity regarding resistance to behavior changes, encouraging the elaboration of affect, and giving importance to the role of relationships in each member's quest for self care and healthy entitlement.     

Medical Research: A Midcentury Survey

This article proposes an integrative model for stress management groups for women, representing a biopsychosocial point of view and drawing on theories of psychodynamic group psychotherapy, self-psychology, female development, and stress management. The basis of the model is an eight week traditional stress management group. The novel aspects of this integrative model are that it aims to increase the power of stress management groups for women by providing an articulated frame, attending to group process, promoting curiosity regarding resistance to behavior changes, encouraging the elaboration of affect, and giving importance to the role of relationships in each member's quest for self care and healthy entitlement.     

Blocking and unblocking of conditioned analgesia

Two experiments with rat subjects assessed the blocking phenomenon using inhibition of responding to painful thermal stimulation as an index of conditioned analgesia established through conditioned stimulus (CS)-shock pairings. In Experiment 1, a group of rats receiving the standard blocking procedure ($\text{A+}\text{AB+}$) showed shorter response latencies during a hot plate test of pain sensitivity in the presence of the added CS than groups of rats receiving various blocking control procedures. Experiment 2 replicated the blocking outcome of Experiment 1 and also demonstrated that the addition of a second shock unconditioned stimulus (US) during the compound conditioning phase attenuated the blocking effect; i.e., unblocking was observed. However, the deletion of a second shock US during compound conditioning in a group that had received two shocks on each trial in the first phase of the experiment failed to result in unblocking. These data extend the associative account of conditioned analgesia to situations involving stimulus selection and the implications for the analysis of aversive learning are discussed.     

Exposure to a stressor produces a long lasting enhancement of fear learning in rats

In contextual fear conditioning, footshock is given in a context, and re-exposure to this context elicits the conditional defensive response of freezing, a reliable behavioral index of conditional fear. Normally, the amount of contextual freezing is directly proportional to the number of shocks an animal receives in the context. However, pre-exposure to a stressor can produce an enhancement in conditional freezing. Pre-exposure to repeated footshock in one context produces an enhancement of conditional freezing to cues associated with a single shock in a second distinct context. This model of stress-enhanced fear learning (SEFL) can be utilized to study how stress affects learning of future aversive events. The experiments in this paper characterize the magnitude and longevity of SEFL. In the first experiment, the number of footshocks given during the pre-exposure session was varied and conditional fear to the single shock was assessed. Pre-exposure to 1 shock did not produce an enhancement in fear learning in the second context, but pre-exposure to 4 or 15 shocks did. The time-course of the enhancement was examined in the next two experiments. These experiments show that SEFL persists for at least 3 months.     

The effectiveness of attentional diversion and situation redefinition for reducing stress due to a nonambiguous Threat

After receiving a sample shock, subjects in a Threat Condition were told that they would receive additional painful shocks while subjects in a Nonthreat Condition were not threatened with additional shocks. Subjects in an Attentional Diversion Condition were then instructed to read and think about an amusing story, subjects in a Situation Redefinition Condition were instructed to write down reasons why they should not be afraid in this situation, and subjects in a Control Condition were not given any instructions for coping with stress. (Coping Conditions were factorially crossed with Threat Conditions and 192 subjects were employed.) Physiological measures (pulse rate, finger pulse volume, skin resistance) indicated that unlike the results of previous research, attentional diversion was effective in reducing stress but situation redefinition was not. Discussion was focused on the parameters which determine whether or not a coping strategy will be effective.     

Stress-corrosion cracking in YBa2Cu3O7−x ceramic superconductor

Abstract

Thin-foil transmission electron microscopy specimens of orthorhombic YBa²Cu³O^7?x subjected to residual elastic strains have shown slow crack growth in an atmosphere with low moisture content. Microcracks, initiated by amorphization at the strained edges, propagate alternately along (110) twin boundaries and (001) stacking faults, where strain energy is accumulated locally. The formation of carbon-rich amorphous layers along the strained lattice planes, followed by residual stress-assisted crack propagation, resembles stress-corrosion cracking in this ceramic superconductor.     

Analytic model for the line tension of a bowing dislocation segment

The resistance of a dislocation to bowing under stress governs the strength of the gamut of metallic material systems. This resistance is commonly referred to as the dislocation line tension (Γ) and is employed ubiquitously within continuum scale models of metal plasticity. Despite its significance, a unifying model for the line tension of a bowing dislocation segment, which has been analytically derived and independently reproduces simulation results, remains lacking. Here, we report a model for Γ of a curved, semicircular bowing dislocation segment. Upon applying our model to the operative stress of a Frank–Read dislocation source, we predict a prelogarithmic scaling of the Frank–Read source strength in agreement with existing simulation results. Moreover, in the limit of infinitesimal bowout we predict a prelogarithmic line tension factor which also agrees with theoretical analyses. Our model provides insight into the evolution of an arbitrarily oriented, stressed dislocation segment without resorting to numerical methods.     

Neutron and X-ray diffraction studies and cohesive interface model of the fatigue crack deformation behavior

The crack-tip deformation behavior during a single overload, fatigue test of ferritic stainless steel, and Ni-based HAYNES 230 superalloy is studied at different structural levels using (1) neutron-diffraction, from which both the elastic-lattice strain and volume-averaged total dislocation densities are obtained, (2) polychromatic X-ray microdiffraction to probe the geometrically necessary dislocations and boundaries distribution, and (3) an irreversible and hysteretic cohesive interface model which has been implemented into a finite element framework to simulate the stress/strain evolution near the fatigue crack tip. Neutron strain measurements and finite element simulations are in qualitative agreement on the macroscopic length scale. Large plastic deformation induced by the overload and the resulting compressive residual strains are observed in front of the crack tip after the overload, and are the principal reason for the fatigue-crack-growth retardation. Strong strain gradients surrounding the crack propagation result in the formation of a high density of geometrically necessary dislocations near the fractured surface and cause local lattice rotations on the submicron level.     

The influence of various types of control on psychophysiological stress reactions

The influence of personal control on reactions to shock was found to differ not only as a function of the type of control, but also as a function of the combination of control conditions. For example, behavioral control in the presence of information (cognitive control) reduced stress, whereas behavioral control in the absence of information augmented stress. These results are discussed with regard to the appropriateness of two different models, a “substitutive” versus an “interactive” model, for understanding the effects of personal control.