Ab initio study of Heusler alloys Co2XY (X = Cr,Mn, Fe; Y = Al,Ga) under high pressure

The structural, electronic, and magnetic properties of ferromagnetic Heusler alloys Co₂XY (X?=?Cr, Mn, Fe; Y?=?Al, Ga) have been investigated by means of the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation for the exchange and correlation potential. The main focus of this study is to elaborate the changes brought about in the electronic and the magnetic properties by applied pressure. The calculated total spin magnetic moments of all the compounds are found to be in good agreement with experiments. Out of these compounds, Co₂CrAl is found to be perfectly half-metallic (HM) and the other compounds are found to be nearly HM. Thus the HM to metal transition was observed at 75?GPa pressure for Co₂CrAl and the nearly half-metal to half-metal transition was observed at 40?GPa and 18?GPa for Co₂CrGa and Co₂MnAl, respectively, while no transition is observed in other compounds under investigation. It can be clearly seen that pressure affects the minority spin states rather than the majority states, leading to a slight reconstruction of the minority spin states with a shift in the Fermi level driving the above-mentioned transition.     

Control of Gait Initiation

The initiation of gait from a standing posture by 6 subjects, who took controlled-length steps, was analyzed. Using an inverted-pendulum model, we found that the duration of gait initiation was independent of gait velocity. This finding suggests that subjects' biomechanical constants are the determining factors for initiating movement. Both the instantaneous velocity of the center of gravity at the end of the first step (resulting in the propulsive forces measured on the ground) and the steady-state velocity (resulting in the step length and frequency) varied with step length, whereas step frequency did not. But step frequency and progression velocity were linked, for step frequency always increased in parallel with increased progression velocity. We interpret the correlation between velocity and frequency variations to be a peripheral expression of the posturodynamic control of the step parameters by the progression forces.     

Differential hemodynamic effects during the provision of active and passive support in the laboratory

Objective: Recent research has pointed to the cardiovascular benefits of providing social support to others in times of stress; however, little is known about what factors influence such benefits.

Design and measures: In a between-groups design, we investigated the possible interaction between intimacy (friend vs. stranger) and support type (active vs. passive) in determining the cardiovascular responses of support providers. Eighty participants had their blood pressure and heart rate monitored while providing either active or passive social support to a friend or a stranger who completed a stress task.

Results: Although there was no interaction effect, a significant main effect showed that those who provided passive support showed larger decreases relative to those in the active support condition. There was no effect of intimacy. Further, these effects withstood adjustment for a number of potential confounds (e.g. sex and body mass index).

Conclusion: It appears that the greatest physiological benefit for social support providers may come from providing passive, rather than active support, regardless of whether the support receiver is a friend or a stranger.     

Aging effect on detectability,criticality and urgency under various auditory conditions

The objective of the study was to investigate the relationship between different components of an auditory warning signal and determine elderly driver’s detection, criticality and urgency perceptions under varied auditory warning conditions. A laboratory study was conducted involving 28 younger and 28 older adults. A pure-tone audiogram was administered for quantification of the participant’s hearing level (in dBHL) prior to the test protocols. Audiogram was conducted in a sound isolated booth. The main experiment investigated the effects of frequency, temporal characteristics, aging, and noise on detectability, caution and perceived urgent levels. Method of adjustment was used by the subjects to adjust the sound pressure level (dBA) till they detected, or felt caution or urgent. Overall, the results indicated that elderly had higher sound pressure threshold than younger individuals in all the sessions (i.e., detectability, caution and urgency). Elderly were found to have higher hearing thresholds especially at 4000 Hz. Higher frequencies were also seen to require less sound pressure thresholds to convey feeling of caution and urgency. Sound pressure threshold to convey the feeling of urgency was the lowest for 2000 Hz and 4000 Hz with 1000 Hz requiring the highest threshold intensity. In conclusion, current study findings suggest frequency, temporal and spectral components to influence a person’s criterion. We would recommend the use of complex tones (multi-components) having high frequency around 2000 Hz for detection, warning and urgent conditions.     

Neuroimaging of mental imagery: An introduction

Adaptive mechanisms to protect cognitive performance under stressors through compensation in energy investment have previously received much research attention. However, stressors have also often been found to substantially reduce both performance and investment. The mechanisms underlying this dual negative effect are still unclear. This study tested the hypothesis that stressors can immediately hamper performance, which in turn reduces energy investment in later phases. In an experiment (N=103), we compared control and stressor conditions (noise or time pressure), investigating the effects of stressors on performance and information-sampling investment (as behavioural measure of energy investment) in two phases of a judgement task. The results showed an instant negative effect of stressors on performance and a delayed negative effect on information-sampling investment. Furthermore, impaired initial performance predicted the decline in investment over time. Finally, the effects of stressors on investment decline were partially mediated through initial performance level. The present findings contribute to theories aiming to explain the relationship between hampered performance and motivational losses.     

Retention of a Time Pressure Heuristic in a Target Identification Task

S. Rice and D. Keller (2009) previously reported that participants who were put under time pressure tended to comply more with a diagnostic aid than participants who were not put under time pressure. The present study investigates whether or not learning the benefits of this time pressure heuristic carries over to a second session. Seventy-two New Mexico State University students performed a simulated target-detection task, assisted by a 95% reliable diagnostic aid. Participants were exposed to the following conditions, which were composed of two sessions: speeded–speeded, unspeeded–speeded, speeded–unspeeded, or unspeeded–unspeeded. Results showed that participants who completed the speeded condition for Session 1 performed just as well in the 2nd session regardless of whether or not they were put under time pressure. Participants found that complying with the aid was beneficial to overall performance and continued to comply in a 2nd session even when allowed more time to overrule the aid.     

A Note on Motor Learning Without Post-Response Knowledge of Results

The authors studied the adjustment of the 2 distinct known expressions of gait velocity, the velocity of the center of gravity (CG) and the velocity of the center of foot pressure (CP) at the end of the 1st step in 2 experimental situations: natural gait initiation (the control situation, CS) and heel-off gait initiation (the test situation, TS). Gait was initiated by 7 healthy participants, from an erect spontaneous posture in the CS and from a posture with heels raised in the TS, on a force platform at 3 self-selected speed conditions. Biomechanical data from the force platform were collected in both experimental situations, and the authors used a particular gait analysis based on the differential method of Y. Brenière (2003) in order to approach velocity modulation by means of step length and frequency. Results showed that CG and CP velocities were adjusted differently during heel-off gait initiation than during natural gait initiation. CP velocity, as compared with CG velocity, was overestimated in TS. Results also established the relevance of the expression of step velocity by means of step length and frequency: The central nervous system, taking into account the specific postural constraints of each experimental situation, uses a reference value and a regulating parameter to modulate step velocity. Moreover, the contributions of 1st step length and frequency to the expression of step velocity in TS and CS were different. Thus, a specific locomotor behavior corresponds to a given experimental situation that is characterized by its own initial biomechanical constraints.     

Spatial and Temporal Adaptations That Accompany Increasing Catching Performance During Learning

During stance, head extension increases postural sway, possibly due to interference with sensory feedback. The sit-to-stand movement is potentially destabilizing due to the development of momentum as the trunk flexes forward and the body transitions to a smaller base of support. It is unclear what role head orientation plays in the postural and movement characteristics of the sit-to-stand transition. The authors assessed how moving from sitting to standing with head-on-trunk extension compared with moving with the head neutral or flexed, or with moving with the head facing forward in space (which would involve head-on-trunk extension, but not head-in-space extension) in healthy, young participants. Head-on-trunk extension increased center of pressure variability, but decreased movement velocities, movement duration, and trunk flexion compared with flexed and neutral head-on-trunk orientations. Similarities in movement characteristics between head-on-trunk extension and the forward head-in-space orientation suggest that stabilizing the head in space does not fully counteract the postural and movement changes due to head-on-trunk extension. Findings suggest that proprioceptive feedback from the neck muscles contributes to the regulation of posture and movement, and therefore should not be overlooked in research on the role of sensory feedback in postural control.     

动态颅内压监测技术的进展

动态颅内压（ICP）监测是重危颅脑疾病病人脑功能的监测技术之一,对颅高压病人的临床诊断、指导治疗和判断预后都有着重要的意义。多种颅内压监测方法被使用于临床。本文综述近年来颅内压监测方法的进展,着重介绍创伤性和非创伤性颅内压监测法,比较其优缺点,评价其临床价值及发展方向。     

员工强制性组织公民行为的多层次形成机制

组织公民行为一直被视为员工“心甘情愿”而为之, 然而随着被加班、被捐款等“被”现象的不断出现, 越来越多的研究证实强制性组织公民行为(即被迫无奈的组织公民行为)在组织中同样普遍存在, 而且会导致劳资关系紧张, 威胁企业内部和谐等, 但相关研究较为匮乏。本研究以员工的强制性组织公民行为为研究对象, 聚焦于对其形成机制的研究。具体地, 使用特质激活、强制说服和自我决定等理论, 分别从指向员工个体、领导和组织三个层次的影响因素揭示员工强制性组织公民行为的形成机制, 建立员工强制性组织公民行为多层次形成机制的概念模型。研究结果实践上有利于本土企业构建和谐的劳资关系并实施更加人性化的管理, 理论上有望为组织公民行为领域贡献新的知识, 在一定程度上推动组织公民行为理论在中国的研究与应用。