Temperature rise in shear bands in a simulated metallic glass

Temperature rise ($\Delta T$) associated with shear-banding of metallic glasses is of great importance for their performance. However, experimental measurement of $\Delta T$ is difficult due to temporal and spatial localization of shear bands and, as a result, our understanding of the mechanism of $\Delta T$ is limited. Here, based on molecular dynamics simulations we observe a spectrum of $\Delta T$, which depends on both sample size and strain rate, in the shear bands of CuZr metallic glass under tension. More importantly, we find that the maximum sliding velocity of the shear bands correlates linearly with the corresponding $\Delta T$, ranging from $\sim$25 K up to near the melting point for the samples studied. Taking heat diffusion into account, we expect $\Delta T$ to be lower than 25 K for the lower end of sliding velocity. At high temperature, shear band bifurcation and/or multiplication can occur as a negative feedback mechanism that prevents temperature rising well above the melting point

Epitaxial oxide spintronic structures: ferromagnets and semiconductors

The aim of the work presented in this thesis is to fabricate an epitaxial magnetic tunnel transistor (MTT) consisting of a Niobium doped SrTiO3 collector, a La0.67Sr0.33MnO3 base, a SrTiO3 tunnel barrier and a Co emitter. The motivation is that this device is sensitive to the spin dependent scattering of hot electrons in a half-metallic ferromagnet. Further we anticipate that the high crystalline quality of the base will result in a large hot electron transmission

Atomistic origin of stress overshoots and serrations in a CuZr metallic glass

In this work we use molecular dynamics simulations to study the stress overshoots of metallic glass Cu$_{50}$Zr$_{50}$ in three scenarios (unloading-reloading, slide-stop-slide, and stress serrations) that are associated with shear band relaxation. We found that, after the elastic recovery effect is factored out, atomic volume in the shear band barely changes during compressive relaxation but decreases during tensile relaxation, while local fivefold symmetry increases consistently for both cases. We propose that the atomistic mechanism for the related stress overshoots is due to the relaxation of structural symmetry, instead of free volume, in the shear band. Upon unloading, a propagating shear band continues for some time before arrested, which results in a stress undershoot and could contribute to material fatigue under cyclic elastic loads. We did not directly observe stress serrations via molecular dynamics simulations due to the very high simulated strain rates. While athermal quasistatic simulations produce serrated flow stress, we note that such serrations result from global avalanches of shear events rather than the relaxation of the shear band

Moderation of Enterprise Social Networks – A Literature Review from a Corporate Perspective

The implementation of internal social collaboration technologies confronts corporations with new challenges. Former unidirectional information flows become multidirectional and user-content driven networks. Prior research describes the successful implementation as a challenging management task with employees’ usage at the center of attention. Consequently, corporations need to select a moderation style to encourage the usage. The degree of corporate engagement might have repercussions on the contribution behavior. We conduct a structured literature review to identify pre-existing IS contributions to the moderation phenomenon in social media tools, which help to explain on how to moderate these communication platforms in the enterprise context. We reviewed over 150 articles on the subject and assessed 31 articles in depth on the degree of corporate engagement and user content encouragement. We analyze the identified literature for gaps in understanding the phenomenon and provide a first assessment of three different moderation approaches and give implication for future research

Mental ill-health among health and social care professionals: an analysis using administrative data

Objective Health and Social Care (HSC) workers are at high risk of job-related stress, burnout and mental ill-health. This study examines differences in self-reported mental health and psychotropic medication uptake across HSC occupational groups. Method Northern Ireland (NI) data linkage study of people working in the Health and Care sector, aged between twenty and sixty-four years, enumerated at the 2011 Northern Ireland Census and living in private households, and their uptake of prescribed psychotropic medications during 2011-2012 (using data derived from routine electronically captured information on prescriptions issued within the NHS and linked at an individual level using a NI-specific Health and Care key identifier). Comparing HSC workers with all those professionals not involved in HSC occupations, we used multinomial logistic regression to examine (a) self-reported chronic mental illness and (b) uptake of psychotropic medication by occupational groups adjusting for age, sex and socio-demographic circumstance. Results When compared against other professionals highest risks for mental health problems (associated with psychotropic prescription uptake) were associated with nursing/midwifery (OR = 1.25: 95{%}CI = 1.17-1.33; OR = 1.84: 1.58-2.15 for females and males respectively), welfare (OR = 1.34: 1.21-1.48; OR = 1.71: 1.44-2.03) and formal caregiving roles (OR = 1.42: 1.31-1.53; OR = 1.70: 1.50-1.91), again for females/males respectively). These higher risk professions record notable increases in psychotropic medication use. Conclusion Working in the Health and Social Care sector, irrespective of gender, may be more stressful than other jobs. Additionally, self-reported mental ill-health and psychotropic medication treatment both appear to be associated with social class inequity

A Biogeochemical Comparison of Fossil (Carboniferous) and Modern Crustose Red Algae

The nature of the contribution of the various types of algae to sedimentary organic matter continues to be a topic of research interest. Crustose red algae have however received less attention than other types. The fossil calcareous red algae (Rhodophyta) analyzed in this study are two relatively unrecrystallized specimens of Parachaetetes (Family Solenoporacea) from the lower part of the Ste. Genevieve Formation (Carboniferous, Visean) in Union County, Illinois, USA. They occurred in the patch reef phase of a small carbonate mudmound-patchreef. The three modern specimens (collected and identified by F. Collier) are the crustose algae Lithothamnion, Clathromorphum and Phymatolithon, (Family Corallinacea, Subfamily Melobesoidea), from a rocky intertidal area near Cape May, Massachusetts, USA. The pyrolyzates of the three (dried, unextracted) modern algal specimens exhibited strong similarities, including a predominance of alkylbenzenes, phenols and indoles. Polysaccharide pyrolysis products are also important, as would be expected. The minor dipeptides detected indicate the presence of proteins. A variety of simpler nitrogen compounds, including pyrroles and benzonitriles may be derived from proteins or from more resistant macromolecular structures. The long-chain alkylnitrile is also noteworthy. The fossil specimens of Parachaetetes (pyrolyzed at 610°C after HCl digestion to remove carbonates and thermodesorption at 310° for 20 sec. to remove bitumen) yielded relatively abundant monoaromatic hydrocarbons and phenols. While their distributions are different, the importance of monoaromatic and phenolic compounds in both the Carboniferous and modern specimens demonstrates a significant similarity. The fossil specimen\u27s pyrolyzate also contains a variety of minor nitrogen compounds, some of which are also found in the modern samples and all of which are unusual in the pyrolyzates of such ancient (ca. 340 Ma) organic matter. The C16 and C18 alkylnitriles are relatively important, but normal hydrocarbons are not, except for the C15 and C17 n-alkanes. Coincidentally, the C17 n-alkane is the only significant normal hydrocarbon in the modern sample. In this study we have found significant chemical similarities between the pyrolyzates of specimens of modern and fossil coralline red algae. The encrustation of the organic matter of Parachaetetes by calcite greatly enhanced its preservation, in spite of the specimens\u27 great geologic age