A phase-field model for deformation twinning

We propose a phase-field model for modeling microstructure evolution during deformation twinning. The order parameters are proportional to the shear strains defined in terms of twin plane orientations and twinning directions. Using a face-centered cubic Al as an example, the deformation energy as a function of shear strain is obtained using first-principle calculations. The gradient energy coefficients are fitted to the twin boundary energies along the twinning planes and to the dislocation core energies along the directions that are perpendicular to the twinning planes. The elastic strain energy of a twinned structure is included using the Khachaturyan's elastic theory. We simulated the twinning process and microstructure evolution under a number of fixed deformations and predicted the twinning plane orientations and microstructures.     

General analytical solution for stress intensity factor of a hypocycloid hole with many cusps in an infinite plate

In this article, the problem for the determination of the displacement functions and the stress intensity factors (SIFs) around a boundary of a hypocycloid hole with cusps in an infinite elastic plate subject to normal and shear stresses are presented. A hole with cusps (hypocycloid) is mapped onto a unit circle and the modified complex potential is used for solving the relevant boundary value problems. An analytical solution for the SIF of a hypocycloid hole is obtained. For a special case, our results agree with others.     

Crystallization behaviour of Al-based amorphous alloy and nanocomposites by rapid quenching

The microstructure and crystallization behaviour of melt-spun Al₈₈Ni₉Ce₂Fe₁ amorphous alloy and nanophase composites have been studied by means of X-ray diffraction, transmission electron microscopy and scanning and isothermal calorimetry. The diffraction patterns from Al₈₈Ni₉Ce₂Fe₁ amorphous alloys are diffuse, indicating a basically amorphous structure but contain two rings presumed to be associated with quenched-in nuclei. In the cases of Al₈₈Ni₉Ce₂Fe₁ nanophase composites, nanoscale precipitated particles are homogeneously dispersed in an amorphous matrix, and the crystallite diameter and volume fraction are sensitive to quenching conditions. During thermal crystallization, a two-step phase transformation occurs in the amorphous alloy and nanocomposites, which is characterized by a diffusion-controlled precipitation of nanoscale Al particles and the growth of a Al₃(Ni, Fe) nanophase prior to a Al₁₁Ce₃ nanophase. This study gives insight into structure-control for obtaining nanophases dispersed in an amorphous matrix by rapid quenching.     

基于双加工理论解释下信念偏差效应的神经机制

信念偏差效应是指人们已有的知识信念对逻辑推理的影响现象.对此,双加工理论认为这是由于信念偏向系统和逻辑分析系统之间的冲突所导致的.近年来,该理论得到来自认知神经科学证据的有力支持:一方面,基于功能磁共振成像(fMRI)、近红外光谱(NIRS)以及重复性经颅磁刺激(rTMS)等技术的研究从不同角度证实右侧前额皮层与信念偏差抑制有关;另一方面,基于脑电(ERP)的研究表明,晚期正成分和晚期负成分可能参与了不同推理类型下信念偏差效应的认知加工.未来的研究可以从工作记忆、不同加工阶段、推理前提本身可信度、实验分析、实验材料生态学效度以及思维训练等方面对信念偏差效应作进一步探索.     

Covert communication in laboratories, classrooms, and the truly real world

Hundreds of research studies have demonstrated that one person's expectations for the behavior of another person can actually affect that other person's behavior. These studies implicate the operation of processes of covert communication, communication that is subtle, largely nonverbal, and ordinarily unintended. The earliest studies of these processes showed that through their expectations, laboratory researchers unwittingly affected the responses of their research participants. Later studies showed that teachers' experimentally induced expectations about their pupils affected the pupils' intellectual performance. Most recently, studies of covert communication processes have extended to diverse contexts, such as the judicial and health care systems. For example, research indicates that judges' beliefs about the guilt of trial defendants can be unwittingly communicated to juries by the judges' nonverbal behavior during jury instruction. In addition, studies of covert communication in medical contexts show that physicians' effectiveness in persuading their patients to enter into treatment can be predicted from their tone of voice in talking to or about their patients. For example, one study showed that surgeons who used a bossy tone of voice when talking to their patients were more likely to be sued by their patients than were surgeons who used a more respectful tone. In sum, then, we have learned a great deal about the importance of subtle processes of nonverbal communication, but a great deal more is yet to be learned about these processes as they occur in the relatively sheltered context of laboratories and classrooms and in the rough-and-tumble of the truly real world beyond.     

A statistical model of cleavage fracture in structural steels with power-law distribution of microcrack size

Based on the well-accepted physical understanding that cleavage fracture of structural steels is preceded by plastic deformation, a critical flaw in the Beremin model and its modifications is proposed, and a new statistical model with the power-law distribution of microcracks is obtained to describe the cumulative probability of cleavage fracture. A set of cleavage fracture toughness data of a nuclear pressure vessel steel is used to highlight the difference between the new model and the Beremin model.     

Proximal and Distal Defense: A New Perspective on Unconscious Motivation

Death-related thoughts produce different effects on thought and behavior when they are in current focal attention and when they are on the fringes of consciousness. When such thoughts are conscious, people attempt to either remove them from consciousness or push death into the distant future by distorting their beliefs to logically imply that they have many remaining years to live. When such thoughts are highly accessible but outside current focal attention, people increase efforts to view themselves as persons of value living in a meaningful universe. In this way, awareness of the inevitability of death produces diverse effects on human thought and behavior that bear little obvious resemblance to the problem of death.     

错认总比错过好——面孔视错觉的发生机制及其应用

面孔视错觉现象表现为个体从其他事物中感知到并不存在的面孔。面孔视错觉要素已广泛应用于艺术、广告及商品中,起到吸引注意、促进消费的作用。同时,先前的研究通过采用各种范式,发现患者在面孔视错觉的产生上同常人的差异,以及视错觉与视幻觉之间的联系。根据视觉加工通路的不同,相关范式可分为视错觉监测范式,以及视错觉辨认范式。前者侧重于基于提取的类面孔特征所做出的快速预测,后者侧重于主观期望引导个体对物体特征的提取,两者最终均会影响到后续的认知判断。日后研究可从面孔视错觉的发生机制出发,结合自上而下和自下而上两种加工通路,为面孔视错觉产生机制提供理论依据,并拓宽该要素在临床诊断及商业广告领域上的应用。     

Afraid of one afraid of all: When threat associations spread across face-types

Fear can be acquired for objects not inherently associated with threat (e.g. birds), and this threat may generalize from prototypical to peripheral category members (e.g. crows vs. penguins). When categorizing people, pervasive stereotypes link Black men to assumed violence and criminality. Faces with Afrocentric features (prototypical) are more often associated with threat and criminality than non-Afrocentric (peripheral) faces regardless of whether the individual is Black or White. In this study, using a priming paradigm, threat associations related to negative racial stereotypes were tested as a vehicle for spreading fear across face-type categories. Results showed more negative than positive judgments for White face targets but only when the prime was primarily non-Afrocentric (i.e. Eurocentric). Black face targets were judged more negatively than positively regardless of prime. This suggests some cognitive processes related to threat generalizations of objects extend to complex social categories.     

Influencing surface plastic flow in metals using common chemical media

We demonstrate a unique mechanochemical effect – change in surface plastic flow by action of chemical media such as inks and glues – in large-strain deformation of metals. Unlike other well-known phenomena such as stress corrosion cracking and liquid metal embrittlement, the effect is not catastrophic and is largely material independent. High-speed in situ imaging shows that the media influence the flow by effecting a local ductile-to-brittle transition – from unsteady, large-amplitude, plastic folding, to repeated fracture and segmentation – with large decrease in deformation forces. The benign nature of the media offers opportunities for enhancing performance of metal cutting and deformation processes.