Z-contrast imaging of the arrangement of Cu in precipitates in 6XXX-series aluminium alloys

High-resolution annular dark field imaging has been used to study small precipitates in the Al matrix of 6XXX-series aluminium alloys. Cu-containing columns in precipitates were imaged by atomic number contrast along a 〈100〉 matrix direction. At an under-aged condition, large, lath-shaped particles of the Cu-containing Q′-phase were observed at grain boundaries. At over-aged conditions, Q′ was the main matrix phase. In both cases the laths showed an Al {150} habit plane. A precursor phase was found, with different arrangement of Cu-rich columns from that of the Q′-phase and sharing Al {100} habit planes. Precipitates containing elements of both the Q′-phase and the precursor were found to be common. Annular dark field imaging can differentiate directly between phases. The method complements and aids interpretation of conventional high-resolution TEM images and nano beam diffraction observations. The results obtained contribute to an improved understanding of the crystallography of the precursor and details of the structural transformation taking place during the precipitation process.     

Neutron and X-ray diffraction studies and cohesive interface model of the fatigue crack deformation behavior

The crack-tip deformation behavior during a single overload, fatigue test of ferritic stainless steel, and Ni-based HAYNES 230 superalloy is studied at different structural levels using (1) neutron-diffraction, from which both the elastic-lattice strain and volume-averaged total dislocation densities are obtained, (2) polychromatic X-ray microdiffraction to probe the geometrically necessary dislocations and boundaries distribution, and (3) an irreversible and hysteretic cohesive interface model which has been implemented into a finite element framework to simulate the stress/strain evolution near the fatigue crack tip. Neutron strain measurements and finite element simulations are in qualitative agreement on the macroscopic length scale. Large plastic deformation induced by the overload and the resulting compressive residual strains are observed in front of the crack tip after the overload, and are the principal reason for the fatigue-crack-growth retardation. Strong strain gradients surrounding the crack propagation result in the formation of a high density of geometrically necessary dislocations near the fractured surface and cause local lattice rotations on the submicron level.     

Compositions of different phases appearing during devitrification of Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass

The devitrification process of Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5 metallic glass during annealing in the supercooled liquid region has been studied by conventional, high-resolution and analytical transmission electron microscopy (TEM). Two kinds of particle appear during devitrification: quasicrystals and crystalline precipitates. Nanoanalysis with energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy reveal that quasicrystals are Be free, while the crystallites have the ZrBe₂ hexagonal structure. These experiments confirm the key role of Be during devitrification. They also indicate that quasicrystals can form in the system Zr–Ti–Cu–Ni (without Be), as further evidenced by direct synthesis and an in situ neutron diffraction investigation, according to the chemical composition deduced from the TEM analysis.     

An anxiety-induced bias in the perception of a bistable point-light walker

Human sensitivity for social cues is exquisite, as illustrated by the ease with which simplified point-light movements invoke social and emotional responses. Compared to faces, these biological motion stimuli only recently started to be used to explore questions regarding social cognition and anxiety. We presented human point-light walkers that could be perceived as facing towards or facing away from the observer, and tested whether participants with high social anxiety would perceive these bistable stimuli differently, because this type of stimuli has particular relevance for them. The results showed that observers with high social anxiety tended to see walkers as facing away more frequently than those with low social anxiety. This may mean that high socially anxious observers are biased towards the more positive perceptual alternative because they are motivated to protect themselves against threatening social experiences, but we also explore alternative explanations. The findings are in line with the evidence for a positivity bias in perception, also called wishful seeing, but in contrast with the attentional negativity bias often found in social anxiety. We discuss reasons for this divergence and possible limitations of the current study.     

Collective contributions to career efficacy in adolescents: A cross-cultural study

This study extended the concept of collective efficacy to supplement the variable of career self-efficacy to predict vocational exploration and commitment among adolescents. We developed a Collective Contributions to Career Efficacy Scale (CCCE) to measure adolescents' perceived contributions from parents, teachers, and peers on their career-related matters. A total of 1175 high school students from Hong Kong, Shanghai and Michigan participated in the study by completing the CCCE, the Career Decision Self-Efficacy Scale (CDSE-SF), and the Vocational Exploration and Commitment Subscale (VEC). Using multi-sample Structural Equation Modeling, we found that the effect of CCCE on VEC was mediated by CDSE. Although we found cultural differences in the overall level of the vocational measures among the Hong Kong, Shanghai, and American students, the mediation model was confirmed in all three groups of students.     

Social comparison influences on disciplinary panels: a brief qualitative study in Kenyan secondary schools

This study investigated the influences of social comparisons on group polarization in decision making among members of selected Kenyan secondary school disciplinary panels. Ten participants from 10 selected secondary school disciplinary panels were involved. Semi-structured interviews were used to collect qualitative data on the experiences of the participants regarding the influences of social comparisons on their decision-making behaviours during participation in their schools’ disciplinary hearing meetings. The results revealed that in the dynamic interactions among disciplinary panel members during disciplinary hearing meetings, the panel members engaged in social comparisons among themselves, leading to their shifts in decision-making behaviours in favour of consensus in group decisions or group polarization in decision making.     

Children's Loss of Agency under Extreme Adversity

This study explores the notion of children's agency in situations of extreme adversity. The child participants (n=117) live in the midst of the HIV/AIDS pandemic; extreme poverty; and systemic educational malfunction. Four focus group interviews were conducted with the children to explore their experiences of potential barriers to education. The findings indicated that contextual factors had a profoundly negative impact on the children, with their agentive capacity being severely compromised through their exposure to multiple, complex layers of risk. There was very little evidence to suggest that children retain any sense of their own agency in such adversity. This has implications for their resilience and for the development of policy and intervention strategies that may meet these children's needs.