Enhanced plastic deformation in a metallic glass induced by notches

It is shown that the compressive plasticity of a metallic glass, namely Zr_52.5Ni_14.6Al₁₀Cu_17.9Ti₅, can be improved by the introduction of two symmetrical notches. The enhanced plasticity may be ascribed to a blocking effect of the propagation of shear bands caused by large stress gradients around the notches. In contrast to ceramic specimens with similar notches, the plasticity enhancement of metallic glass induced by notches can provide a new approach to understanding its unique mechanism of deformation.     

HRTEM observation of misfit dislocations at non-faceted Al–Pb interfaces

Al–Pb samples containing 1?at.%?Pb were produced by high-energy ball milling and investigated by high-resolution transmission electron microscopy. The Pb inclusions embedded in an Al matrix exhibit a non-faceted, curved morphology. Dislocations have been found to accommodate the misfit of about 22% at the Al–Pb interfaces. Burgers circuits, drawn around these misfit dislocations, exhibit closing failures of the type a₀ /4〈211〉.     

Reversible plasticity under nanoindentation of atomically flat and stepped surfaces of fcc metals

Using atomistic simulation, the indentation of single-crystalline Cu is investigated for both an ideal and a stepped (111) surface. Both systems exhibit an intermediate regime of reversible plasticity, characterized by the formation of extended stacking faults, which heal entirely upon withdrawal of the indenter. This regime can be employed to clarify the role of pure stacking fault generation and cross-slip in plasticity. Its existence reveals that, on the atomistic scale, plastic deformation is characterized by material transport rather than by the nucleation of stacking faults. Finally, we establish a criterion–based on the total displacement of particles–to determine after which indentation depth plasticity is generated irreversibly in the material.     

Importance of crack-propagation-induced ε-martensite in strain-controlled low-cycle fatigue of high-Mn austenitic steel

We investigated the roles of deformation-induced ε-martensitic transformation on strain-controlled low-cycle fatigue (LCF) through crack-propagation analysis involving a notching technique that used a focused ion beam (FIB) setup on Fe–30Mn–4Si–2Al austenitic steel. Using the FIB notch, we separated the microstructure evolution into macroscopic cyclic deformation-induced and crack-propagation-induced microstructures. Following this, we clarified the fatigue crack-propagation-induced ε-martensitic transformation to decelerate crack propagation at a total strain range of 2%, obtaining an extraordinary LCF life of 1.1 × 10⁴ cycles.     

儿童青少年认知能力发展与脑发育

自发展认知神经科学兴起以来, 研究者就开始借助MRI等脑成像技术探讨儿童青少年认知能力发展与大脑结构发育和功能特点等之间的关系, 这为揭示行为发展与生理成熟之间的关系、儿童认知发展的神经活动规律、正常和障碍群体的独特大脑神经结构及活动特点等提供了重要启示。通过对有关儿童青少年智力、工作记忆、反应抑制等认知能力发展与大脑结构发育、大脑功能发育之间关系, 以及认知能力训练与大脑可塑性等研究的介绍, 指出发展认知神经科学的未来研究应重视采用纵向设计, 关注自然成熟和经验对正常或障碍儿童青少年认知发展与脑发育关系的交互影响, 同时从练习和训练的角度对大脑可塑性的特点进行探讨。     

Transgenic inhibition of neuronal calcineurin activity in the forebrain facilitates fear conditioning, but inhibits the extinction of contextual fear memories

It is unclear whether protein phosphatases, which counteract the actions of protein kinases, play a beneficial role in the formation and extinction of previously acquired fear memories. In this study, we investigated the role of the calcium/calmodulin dependent phosphatase 2B, also known as calcineurin (CaN) in the formation of contextual fear memory and extinction of previously acquired contextual fear. We used a temporally regulated transgenic approach, that allowed us to selectively inhibit neuronal CaN activity in the forebrain either during conditioning or only during extinction training leaving the conditioning undisturbed. Reducing CaN activity through the expression of a CaN inhibitor facilitated contextual fear conditioning, while it impaired the extinction of previously formed contextual fear memory. These findings give the first genetic evidence that neuronal CaN plays an opposite role in the formation of contextual fear memories and the extinction of previously formed contextual fear memories.     

非面孔物体倒置效应形成过程的认知神经机制

物体识别, 尤其是人造新异物体专家识别形成过程的神经机制是了解大脑可塑性的一个重要窗口。当前, 从行为学上或神经机制上探讨物体特定角度体验程度与物体专家识别形成关系的研究较少, 本项目采用事件相关电位与行为训练相结合的方法, 分别选择在社会生活中自然形成的某类物体识别专家和经人为训练形成的人造新异物体识别专家作为被试, 研究非面孔物体识别倒置效应从无到有、从小到大整个过程的脑机制。通过对倒置效应大小的操纵, 分离出专家识别状态下的ERP成分, 并分析专家识别形成过程的脑电动态变化过程, 探讨非面孔物体识别大脑可塑性变化的神经机制。在上述研究的基础上, 研究者试图提出物体特定角度体验程度与物体识别加工方式选择关系模型并完善当前物体识别整体布局加工连续量假设(configural processing continuum)理论。     

老年人加工速度的干预研究

对老年人加工速度进行干预, 旨在考察加工速度在老年期的可塑性。首先对46名60~79岁城市社区老年人实施前测, 包括两项加工速度测验(数字比较、图形匹配)、成套基本心理能力测验和老年人日常智力自我效能感问卷。然后, 干预组25名老年人接受每周一期(每期50min)共计5期的加工速度训练。训练内容为图形模式比较。所有被试在训练周期结束后接受后测, 并在后测结束4个月后接受追踪测验。结果表明, 能够通过加工速度干预显著提高老年人图形匹配测验成绩, 并对词汇流畅测验成绩有迁移作用, 但干预和迁移效果并未保持到4个月。与数字比较测验相比, 图形匹配测验能够更稳定地反映干预的效果。     

工作记忆刷新功能的可塑性

从工作记忆刷新功能的训练入手, 以不同人群为研究对象, 采用活动记忆任务, 从行为层面和认知神经层面探讨工作记忆刷新功能的可塑性。结果发现, 工作记忆刷新功能具有可塑性。具体表现为, 通过刷新功能训练, 个体在工作记忆刷新任务上的成绩提高。工作记忆刷新功能训练使得个体对刺激的识别能力增强, 对无关信息的抑制能力提高, 进而促使工作记忆中的更新能力得到提升。通过工作记忆刷新训练可以提高个体其它认知功能, 但是, 相对于认知能力稳定以及衰退的个体, 这种迁移效应在工作记忆能力发展个体中的表现更为明显。     

Brain plasticity and behavior

Although the brain was once seen as a rather static organ, it is now clear that the organization of brain circuitry is constantly changing as a function of experience. These changes are referred to as brain plasticity, and they are associated with functional changes that include phenomena such as memory, addiction, and recovery of function. Recent research has shown that brain plasticity and behavior can be influenced by a myriad of factors, including both pre- and postnatal experience, drugs, hormones, maturation, aging, diet, disease, and stress. Understanding how these factors influence brain organization and function is important not only for understanding both normal and abnormal behavior, but also for designing treatments for behavioral and psychological disorders ranging from addiction to stroke.