HREM examination of [101] screw dislocations in Ni3Al

Abstract

The dissociation of [101] screw dislocations in Ni³Al has been examined using high-resolution electron microscopy. [101] superdislocations are found to be dissociated into (a/2)[101] superpartial dislocations on the (010) cube cross-slip plane. These superpartials in turn dissociate into complex stacking faults on the (111) or (111) which are bounded by Shockley partials in agreement with theoretical predictions. The degree of antiphase boundary spreading on (010) was found to increase with deformation temperature while the superpartial core dissociations remain unchanged.     

Novel fabrication of bulk Al with gradient grain size distributions via powder metallurgy

We describe a novel approach to synthesize gradient microstructures, defined hereafter as containing a broad but continuous distribution of grain sizes. These microstructures extend the concept of a bimodal grain size distribution and the ability to design with multiple length scales. We demonstrate the proposed approach via experiments involving cryogenic ball milling of Al–4.5Mg–0.4Mn–0.05Fe and Al–50Mg powder followed by subsequent consolidation. Our results reveal that the grains in the consolidated powder present a gradient size distribution ranging from <100 nm to >3 μm. Moreover, phase composition analysis revealed a unique “interfingered” structure where the two starting phases were intermixed in a complex three-dimensional mesh. Hardness studies of this gradient microstructure show average Vickers hardness values of 200 ± 2.6, 204 ± 4.3 and 266 ± 50 for macrohardness, microhardness and nanoindentation, respectively. The standard deviation values highlight that the gradient microstructure is disordered locally, but homogenous macroscopically.     

Abnormally high residual dislocation density in pure aluminum after Al/Ti/Al laminate annealing for seven days

We report an abnormally high residual dislocation density in aluminium in an Al/Ti/Al laminate annealed at 873 K for seven days. The residual dislocation density reaches 7.5 × 10¹⁴ m^?2, higher than that in aluminum after severe plastic deformation processes such as accumulative roll bonding and high-pressure torsion. It is proposed that the high residual dislocation density may result from obstruction of the movement of TiAl₃ nanoparticles by the grain boundary and Ti atoms conglomerating at vacancies distributed in the aluminium matrix at a high temperature for a sufficient time to allow a relatively stable crystal.     

Site preference and alloying effect of Re atoms in the edge dislocation cores in Ni3Al

Using Cambridge sequential total energy package method based on the density functional theory, we investigated the site preference and alloying effect of Re atoms in the [1 0 0] (0 1 0) edge dislocation cores in Ni₃Al. Due to the introduction of a Re atom, the energetic and electronic structure of dislocation core systems have been changed a lot. The binding energy results suggest Re atom prefers Al site, especially the centre site in the centre-Al system, which can be explained by the results of Mulliken orbital population and density of states. When Re atom occupies the centre site in the centre-Al system, the DC system has the highest stability and stronger bonds formed between the Re atom and its nearest neighbouring atom due to hybridization of the Re-5d and Ni-3d orbitals.     

Temperature dependence of the stacking fault energy of glide set-dissociated dislocations in Si

Recently, it was found that the dissociation distance of glide set dislocations introduced in Si just below the melting temperature by laser shock peening (LSP) is unusually wide (Iwata et al. J. Jpn Inst. Met. Materi.,79(2015),308–314). In order to distinguish whether or not this is to be attributed to uncorrelated motions of leading and trailing Shockley partials or the intrinsic temperature dependence of the stacking fault energy (SFE), dislocations introduced by LSP were annealed at 1350 °C, which should be high enough for the uncorrelated partials to assume the equilibrium correlated configuration. It was found that this unusual widening of a dissociated dislocation introduced by LSP is attributed to uncorrelated motions of Shockley partials. Following this conclusion, the temperature dependence of the intrinsic SFE of Si was determined on correlated dissociated dislocations up to near the melting temperature. The intrinsic SFE of Si shows only negligibly small temperature dependence from 400 °C up to near the melting temperature.     

Twin-coupled domain structures in epitaxial relaxor ferroelectric Ba(Zr,Ti)O3 thin films on (001) MgO substrate

We report the twin-coupled multi-oriented domain structures in the epitaxial BZT20 (20%Zr) films grown on the (001) MgO substrate using pulsed-laser deposition. Transmission electron microscopy shows that the film consists of an epitaxial layer of pseudo-cubic perovskite structure and a nanopillar layer of multi-oriented twin domain structures near the surface. Four types of the twin domains were formed in the nanopillar layers by coherently joining their {111} with the epilayer and aligning their ?110? directions parallel to the ?110? axes of the epilayer. A non-uniform polarization switching behavior was observed due to the formation of such complex structure in the BZT20 films.     

Precipitation of an icosahedral quasicrystalline phase in Hf59Ni8Cu20Al10Ti3 metallic glass

The crystallization process of a Hf₅₉Ni₈Cu₂₀Al₁₀Ti₃     

Formation of profuse <c+a> dislocations in deformed calcium-containing magnesium alloys

We report that <c+a> pyramidal slipping could be more easily activated in textured Mg–Ca alloys with increasing Ca contents dissolved in α-Mg matrix under tensile deformation, and it is proposed that the decreased stacking fault energy plays the critical rule. In contrast, only twins and <a> basal dislocations are observed in the compressed samples. The results would provide insight into understanding of the deformation mechanism and designing more ductile Mg alloys.     

A criterion for determining the optimum value of twist in the topological model

In previous works, in which the topological model has been applied to martensitic phase transformations, the value of twist angle ω was determined based on the habit plane-(HP) matching method, where the physical realization of the so-predicted interfacial defect networks may require reorientations of defect line directions by short-range diffusion, though no long-range diffusion was needed. In the present work, a novel criterion for determining the optimum value of twist is proposed so that the predicted interface defects are not only able to fulfil the function of fully accommodating the coherency strains arising on the terrace plane, but also capable of reaching the required position at the HP without long- or short-range diffusions. A numerical analysis for an Fe–20Ni–5Mn alloy is demonstrated based on the newly proposed criterion, and the predictions so obtained are in good agreement with the results provided by the phenomenological theory and experimental measurements.     

On the internal structure of Guinier-Preston zones in Al-3 at.% Ag

High-angle annular dark-field scanning transmission electron microscopy has been employed to study partially decomposed Al-3 at.% Ag. After solutionizing at 550°C and quenching to room temperature, samples of an Al-3 at.% Ag single crystal were aged for short times at 105, 140 and 180°C. Independent of the ageing temperature for these early stages, Guinier-Preston zones with a diameter of about 3 nm are found. Most of these zones consist of a silver-depleted core surrounded by a silver-rich shell. The shell structure is not uniformly pronounced. Irregularly shaped Guinier-Preston zones are common, but the shell structure dominates. No indication of different structures of the Guinier-Preston zones in Al-3 at.% Ag was found after short ageing at the three different temperatures. The shell model for Guinier-Preston zones in aluminium-rich Al-Ag alloys, which was previously proposed on the basis of X-ray and neutron scattering experiments, is thus appropriate to describe the structure of the Guinier-Preston zones in the early stages of the decomposition.     

The effects of type of instruction,animacy cues,and dimensionality of objects on the shape bias in 3‐ to 6‐year‐old children

Robust evidence exists for the shape bias, or children's tendency to extend novel names and categorize objects more readily on the basis of shape than on other object features. However, issues remain about the conditions that affect the shape bias and its importance as a linguistic device. In this research, we examined how type of instruction (common noun naming, proper noun naming, same kind, and goes with), animacy of objects (animate, inanimate), and dimensionality of objects (two‐dimensional, three‐dimensional) affect the shape bias in 3‐ to 6‐year‐old children. Overall, all children showed strong use of the shape bias with categorization (same kind, goes with) instructions, the former in line with the shape‐as‐cue theory. Additionally, the shape bias was quite robust in the inanimate condition, regardless of type of instruction or dimensionality of objects. However, in the animate condition, a proper noun naming instruction coupled with an animate object cue reduced the shape bias across both two‐ and three‐dimensional objects. Implications of these findings are presented.

Highlights

• This study assessed the “shape bias,” a linguistic strategy young children routinely use when confronted with the task of extending a novel name from one object to another.
• Novel name extension and categorization tasks were used in this study.
• Shape bias was affected by the type of instructions, animacy of objects, and dimensionality of objects.

     

The orientation and temperature dependences of dislocation velocity in Ni 3 Al single crystals

The average velocities of screw dislocations in Ni 3 Al single crystals have been directly measured as a function of resolved shear stress (RSS) and orientation in the temperature domain of the flow stress anomaly using the etch-pit technique. The velocity was found to be extremely sensitive to the RSS in all cases. In contrast with ordinary metals, the screw dislocation velocities in Ni 3 Al show anomalous behaviour; under a constant RSS, the velocities decrease dramatically with increasing temperature. Furthermore, the velocities and the tension-compression asymmetry of the velocities depend on the orientation of applied stress.     

The processing of rhythmic structures in music and prosody by children with developmental dyslexia and developmental language disorder

Rhythm perception seems to be crucial to language development. Many studies have shown that children with developmental dyslexia and developmental language disorder have difficulties in processing rhythmic structures. In this study, we investigated the relationships between prosody and musical processing in Italian children with typical and atypical development. The tasks aimed to reproduce linguistic prosodic structures through musical sequences, offering a direct comparison between the two domains without violating the specificities of each one. About 16 Typically Developing children, 16 children with a diagnosis of Developmental Dyslexia, and 16 with a diagnosis of developmental language disorder (age 10–13 years) participated in the experimental study. Three tasks were administered: an association task between a sentence and its humming version, a stress discrimination task (between couples of sounds reproducing the intonation of Italian trisyllabic words), and an association task between trisyllabic nonwords with different stress position and three‐notes musical sequences with different musical stress. Children with developmental language disorder perform significantly lower than Typically Developing children on the humming test. By contrast, children with developmental dyslexia are significantly slower than TD in associating nonwords with musical sequences. Accuracy and speed in the experimental tests correlate with metaphonological, language, and word reading scores. Theoretical and clinical implications are discussed within a multidimensional model of neurodevelopmental disorders including prosodic and rhythmic skills at word and sentence level.     

Predictors of posttraumatic stress in children following injury: The influence of appraisals, heart rate, and morphine use

Prospective studies of posttraumatic stress disorder (PTSD) in children that investigate simultaneously both cognitive and biological or psychophysiological predictors are rare. The present research reports on the impact of cognitive factors (trauma-related appraisals) and biological indicators (heart rate, morphine use) in predicting PTSD and depression symptoms following single-incident trauma. Children and adolescents (N = 48) were assessed within 4 weeks of an injury that led to hospital treatment and followed up 6-months later. While morphine did not predict initial PTSD severity, it was associated with lower levels of PTSD at follow-up. Reductions in PTSD symptoms (change scores) between assessments were similarly associated with morphine dosage. Trauma-related appraisals also contributed to PTSD and depression symptom severity. While slightly different patterns of results were obtained depending on whether static or change scores were examined, as a whole the study adds to a growing literature that morphine has the potential to reduce PTSD symptoms severity. Likewise the relationship between unhelpful trauma appraisals and posttrauma psychopathology was replicated.     

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     

神经颗粒素与脑老化、疾病及应激关系

神经颗粒素是一种神经元特异性、Ca2＋敏感性的鈣调蛋白（CaM）结合蛋白,是蛋白激酶C的突触后底物,与信号传导和长时程增强（LTP）有关。这是一种新发现的脑特异性蛋白质。主要分布在前脑和海马,在皮质、海马CA1-CA3区、齿状回、纹状体和杏仁核中高表达。在大脑发育的不同阶段,神经颗粒素在脑内的含量和分布区域会发生变化,其生物学作用受到国内外学者的关注。近年来国外学者开始对神经颗粒素与脑老化、疾病及应激关系进行考查。该文将着重介绍对神经颗粒素在脑老化、疾病和应激过程中所扮演的角色的研究工作及其新发现,目的是对脑与行为关系的理解及有关的脑机制的研究提供一个新的视点。     

High-pressure electrical resistivity behaviour of nanocrystalline perovskite (La,Sr)(Mn,Fe)O3

We report here the electrical resistivity of nanocrystalline perovskite-structured La–Sr manganites as a function of pressures up to 8?GPa, at room temperature. The nanocrystalline perovskite manganites were prepared by the sol–gel technique and found to have crystallite sizes of 12–18?nm. The pressure dependence of the electrical resistivity shows a first-order phase transition at 0.66(2)?GPa and a subtle phase transition between 3.5 and 3.8?GPa. The first-order transition at 0.66?GPa can be related to the transition from localized-electron to band magnetism.     

Involvement of the σ Receptor inPassive-Avoidance Learning in the Day-Old Chick during the Second Wave of Neuronal Activity

The specific σ-receptor agonist (+)-SKF 10047 and antagonist BD 1047 were used to investigate whether this receptor was involved in passive-avoidance training in the day-old chick. We found 300 μM (+)-SKF 10047 to be amnesic when injected into the lobus parolfactorius 5 h after training (p < .01). Higher or lower concentrations of (+)-SKF 10047 did not disrupt memory formation. The amnesia produced by the efficacious dose of (+)-SKF 10047 was reversed by the specific antagonist, BD 1047. It is suggested that the σ-receptor may exert its effect on passive-avoidance memory consolidation during the later stages of long-term memory formation by modulation of memory-related neurotransmission.     

压力认知评价理论在管理心理学中的应用：场景、方式与迷思

工作场所中,压力源无处不在;面对压力源,个体会如何反应？压力认知评价理论从认知评价和应对角度为这一问题提供了系统解释。在过去的40年里,该理论已成为阐释个体压力反应的主流框架。然而,由于提出时间较早,该理论没有提供各理论要素间的精确关系,这使得后续实证研究从各自研究问题出发,对该理论的应用五花八门,甚至因曲解理论观点而造成不当应用,不利于对该理论的持续应用和深入发展。在系统回顾理论观点的基础上,重点梳理了125篇以该理论作为核心理论基础的管理心理学实证研究。总体发现：在应用场景方面,压力认知评价理论可以用来解释6种压力源对员工工作态度、行为、身心健康和工作-家庭关系的影响;其应用形式可以从初级评价、次级评价和应对3个方面分别考虑;一些研究在应用该理论时存在误区。未来研究需要优化理论要素的测量方式,进一步拓展该理论的应用场景,同时丰富认知评价过程的影响因素研究。     

Stress,strain, and hardiness as predictors of adaptation in farm and ranch families

We examined the relationship between potential family vulnerability factors (stressor and strains), manifestations of maladaptation (family discord and distress), family strengths (hardiness), and measures of bonadaptation (quality of life) as reported by 188 men and women representing 100 Idaho farm and ranch families. Family strains, and stressors unique to farming and ranching, were positively associated with family discord and distress but negatively associated with hardiness and quality of life. Greater family hardiness as reported by both wives and husbands was positively correlated with their perceptions of family quality of life. The results have implications for mental health professionals and family life educators whose goal is to help farm and ranch families manage stress more effectively, increase hardiness, and enhance their overall quality of life.