Atomic geometry and energetics of carbon nanotube necking

Molecular mechanics simulations were performed to probe the incipient plastic deformation in carbon nanotubes (CNTs), which involves nucleation of Stone–Wales (SW) defects and spiral glide of 5/7 dislocation dipoles that lead to quantized necking through a stepwise reduction in tube diameter. Quantification of the strain-dependent energetics of dislocation glide reveals that such dislocation motions are energetically favoured at high tensile strain. Pre-existing dislocations critically affect subsequent nucleation and separation of SW defects, as manifested by the competing deformation modes of symmetric versus asymmetric necking. The results provide a quantitative basis for the dislocation dynamics simulations of superplastically deformed CNTs.     

Electron microscopy of grain boundaries: An application to RE-Fe-B (RE = Pr or Nd) magnetic materials

Abstract

To study the grain boundaries of the technologically important RE_13.75Fe_80.25B₆ (RE = Pr or Nd) permanent magnets, we developed a new method using small-angle dark-field imaging based on inner-potential differences at the grain boundaries, combined with high-resolution electron microscopy and nanoscale chemical analysis. In both the Pr- and Nd-based melt-quenched die-upset magnets we consistently observed a very thin Fe-rich amorphized intergranular phase at the boundaries, and this finding may have an impact on our understanding of the coercivity mechanism of these materials. Although the value of the method was demonstrated for transition metal-rare earth intermetallics, it may also be applied to grain-boundary studies in other materials.     

Two different types of shear-deformation behaviour in Au–Cu multilayers

Localised shear deformation of a material is usually identified as a particular feature of deformation inhomogeneity. Here, we show two different types of shear deformation-behaviour that occurred in Au–Cu multilayers subjected to microindentation load, namely, a cooperative-layer-buckling-induced shear banding in a nanoscale multilayer and a direct localised shearing across a layer interface along a shear plane in a submicron-scale multilayer. Theoretical analysis indicates that the formation of the two different types of shear deformation in the multilayers depends on a competition between the dislocation-pile-up-induced stress concentration at the layer interface and the barrier strength of the layer interface for glissile dislocation transmission.     

Amorphization of TiNi induced by high-pressure torsion

Using high-resolution electron microscopy, we investigated the initial stages of high-pressure-torsion-induced crystalline-to-amorphous transformation of TiNi. It is found that the deformation-induced amorphization initiated from dislocation core regions in the interior of grains and from grain boundaries. It is believed that both the energy stored in the dislocations and the energy stored in the grain boundaries contribute significantly to driving the crystalline-to-amorphous transformation.     

Study of γ/γ′ interfacial width in a nickel-based superalloy by scanning transmission electron microscopy

The γ/γ′ interfaces are thought to play an important role in determining the mechanical properties in single-crystal nickel-based superalloys. In this article, interfacial width in DD6, one second-generation single-crystal superalloy containing 2 wt% Re, has been studied by means of scanning transmission electron microscopy. From an atomic resolution high angle annular dark field image, both compositional interfaces and order–disorder interfaces are studied, and it is first found that the interfacial width of chemical composition is same with that between the ordered and disordered phases.     

Interfacial strengthening of β phase in a fully lamellar structure of TiAl alloy containing W

The strengthening of the β phase in two fully lamellar structures with different lamellar spacing of a Ti–48?at.%?Al–2?W?at.% alloy during creep deformation has been investigated. It was found that the β phase precipitates during aging treatments only within regions of α₂ lamellae following their dissolution. The strengthening of the β phase is more effective in the coarser lamellar structure, because the wider β precipitation zones, which replace the prior coarser α₂ lamellae, hinders dislocation motion stronger than the narrower ones.     

Unconsciously learning task-irrelevant perceptual sequences

We demonstrated unconscious learning of task-irrelevant perceptual regularities in a Serial Reaction Time (SRT) task in both visual and auditory domains. Participants were required to respond to different letters (‘F’ or ‘J’, experiment 1) or syllables (‘can’ or ‘you’, experiment 2) which occurred in random order. Unbeknownst to participants, the color (red, green, blue or yellow) of the two letters or the tone (1–4) of the syllables varied according to certain rules. Reaction times indicated that people indeed learnt both the color and tonal regularities indicating that task-irrelevant sequence structure can be learned perceptually. In a subsequent prediction test of knowledge of the color or tonal cues using subjective measures, we showed that people could acquire task irrelevant knowledge unconsciously.     

情绪、性别和方案数量对危机决策的影响

本研究采用实验和问卷相结合的方法,探讨了愤怒和恐惧情绪及不同的方案数量对危机决策的影响,并分析了该效应的性别差异。研究结果表明:(1)恐惧情绪下被试的危机决策时间显著长于其在愤怒情绪下的危机决策时间,且情绪和性别变量在危机决策时间上存在显著的交互作用;(2)女性在恐惧情绪下的危机决策时间显著长于其在愤怒情绪下的危机决策时间,且显著地长于男性的危机决策时间。同时,男性对其危机决策的满意程度显著高于女性,且情绪变量和性别变量在危机决策自信程度指标上存在显著的交互作用;(3)随着方案数量的增加,尤其当方案数量为4时,被试的危机决策时间较其他两种情况显著增长。该研究结果可为各类突发性危机事件的管理与决策提供依据。     

不同刺激重复量对反应抑制后效应的影响

旨在探讨不同刺激重复量对反应抑制后效应的影响。在不同刺激重复量条件下,让被试完成停止信号任务。结果发现,从总体来看,刺激重复量因素上的主效应显著,重复类型因素上主效应不显著;信号抑制条件下不同刺激重复量后无信号试次反应时与总的无信号试次反应时差异不显著;信号反应条件下不同刺激重复量后无信号试次反应时与总的无信号试次反应时差异显著。本研究表明不同刺激重复量条件下的反应抑制后效应是认知控制的执行加工而非自动化的记忆提取。     

Factors Associated With Adverse Mental Health Outcomes in Locally Recruited Aid Workers Assisting Iraqi Refugees in Jordan

Nongovernmental organizations (NGOs) serve Iraqis living in Jordan as “guests.” In 2008, 258 Jordanian humanitarian staff and Iraqi volunteers working for NGOs completed a needs assessment survey. Work characteristics, stressors, and support variables were evaluated regarding their influence on depression, anxiety, post-traumatic stress disorder (PTSD), and burnout through multivariate logistic regressions. There was a significant difference in depression, anxiety, and burnout across nationality. Traumatic exposure increased the risk for anxiety, depression, and PTSD. Working longer in the humanitarian sector was associated with less risk of anxiety and depression, and lower social support was a risk for anxiety. Managers were at higher risk for burnout, and low team cohesion was a risk for burnout. Implications for aid organizations are discussed.