Three-dimensional molecular dynamics simulations of void coalescence during dynamic fracture of ductile metals

Void coalescence and interaction in dynamic fracture of ductile metals have been investigated using three-dimensional strain-controlled multi-million atom molecular dynamics simulations of copper. The correlated growth of two voids during the coalescence process leading to fracture is investigated, both in terms of its onset and the ensuing dynamical interactions. Void interactions are quantified through the rate of reduction of the distance between the voids, through the correlated directional growth of the voids, and through correlated shape evolution of the voids. The critical inter-void ligament distance marking the onset of coalescence is shown to be approximately one void radius based on the quantification measurements used, independent of the initial separation distance between the voids and the strain-rate of the expansion of the system. The interaction of the voids is not reflected in the volumetric asymptotic growth rate of the voids, as demonstrated here. Finally, the practice of using a single void and periodic boundary conditions to study coalescence is examined critically and shown to produce results markedly different than the coalescence of a pair of isolated voids.Comment: Accepted for publication in Physical Review

First Principles Modeling of the Thermodynamic and Kinetic Properties of Anatase LixTiO2 and the Ti-Al Alloy System With Dilute Vacancies.

We perform a comprehensive first-principles statistical mechanical study of the thermodynamic and kinetic properties of two separate materials systems with very different applications using a collection of reliable computational methods. Anatase TiO2 can be lithiated to LixTiO2 and has thus been a candidate material for Li-ion battery electrodes for quite some time. We establish that the experimentally observed step in the voltage vs lithium composition curve between x = 0.5 and 0.6 is due to Li ordering. Furthermore, we predict that full lithiation of anatase TiO2 is thermodynamically possible at positive voltages but that there is an enormous difference in Li diffusion coefficients in the dilute and fully lithiated forms of TiO2, providing an explanation for the limited capacity in large electrode particles. We also predict that Li diffusion in the ordered phase (Li0.5TiO2) is strictly one-dimensional. The TiO2 to Li0.5TiO2 phase transition has much in common with shape memory alloys. Crystallographically, it can support strain invariant interfaces separating TiO2 and Li0.5TiO2 within the same particle. The strain invariant interfaces are parallel to the one-dimensional diffusion direction in Li0.5TiO2, which, we argue, has important consequences for the role of particle shape on achievable capacity, charge and discharge rates, and hysteresis. The titanium-aluminum alloy system has many important structural applications in the automotive and aerospace realms. Variations in alloy concentration or the degree of short or long range order affect the vacancy concentration and thereby the mobility of the constituents of the alloy. Here we develop statistical mechanical methods to predict the thermodynamic properties of vacancies within multi-component solids from first principles. We introduce a coarse graining procedure that enables the prediction of very dilute vacancy concentrations and their associated thermodynamic properties with Monte Carlo simulations. We apply this approach to a study of vacancies in HCP based Ti-Al binary alloys to explore the role of variations in both short range and long range order on the equilibrium vacancy concentration. We find a strong dependence of the equilibrium vacancy concentration on Al concentration and degree of long range order, especially at low temperature.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/110441/1/aabelak_1.pd

Effect of stress-triaxiality on void growth in dynamic fracture of metals: a molecular dynamics study

The effect of stress-triaxiality on growth of a void in a three dimensional single-crystal face-centered-cubic (FCC) lattice has been studied. Molecular dynamics (MD) simulations using an embedded-atom (EAM) potential for copper have been performed at room temperature and using strain controlling with high strain rates ranging from 10^7/sec to 10^10/sec. Strain-rates of these magnitudes can be studied experimentally, e.g. using shock waves induced by laser ablation. Void growth has been simulated in three different conditions, namely uniaxial, biaxial, and triaxial expansion. The response of the system in the three cases have been compared in terms of the void growth rate, the detailed void shape evolution, and the stress-strain behavior including the development of plastic strain. Also macroscopic observables as plastic work and porosity have been computed from the atomistic level. The stress thresholds for void growth are found to be comparable with spall strength values determined by dynamic fracture experiments. The conventional macroscopic assumption that the mean plastic strain results from the growth of the void is validated. The evolution of the system in the uniaxial case is found to exhibit four different regimes: elastic expansion; plastic yielding, when the mean stress is nearly constant, but the stress-triaxiality increases rapidly together with exponential growth of the void; saturation of the stress-triaxiality; and finally the failure.Comment: 35 figures, which are small (and blurry) due to the space limitations; submitted (with original figures) to Physical Review B. Final versio

Why don't health care frontline professionals do more for segregated Roma?:Exploring mechanisms supporting unequal care practices

RATIONALE: Unequal provision of health care contributes to the poor health status of segregated Roma in Central and Eastern Europe. Studies on the drivers and mechanisms behind this are lacking. OBJECTIVE: We explored what kinds of substandard practices health care frontline professionals engage in regarding segregated Roma and what mechanisms support such practices during the professionals' careers in care services. METHODS: Over a three-month period at five different locations in Slovakia we interviewed and observed 43 frontline professionals serving segregated Roma. Next, through qualitative content analysis we identified in the data three themes regarding kinds of substandard practices and 22 themes regarding supporting mechanisms. We organized these themes into an explanatory framework, drawing on psychological models of discrimination and intergroup contact. RESULTS: The frontline staff's substandard practices mostly involved substandard communication and commitment to care, but also some overt ethnic discrimination. These practices were supported by five mechanisms: the staff's negative experiences with people labelled "problematic Roma patients"; the staff's negative attitudes regarding segregated Roma; adverse organizational aspects; adverse residential-segregation aspects; and poor state governance regarding racism. In the course of their careers, many professionals first felt obliged and diligent regarding segregated Roma patients, then failing, unequipped and abandoned, and ultimately frustrated and resigned regarding the equal standard of care towards the group. CONCLUSIONS: Health care frontline staff's practices towards segregated Roma are frequently substandard. The psychological processes underlying this substandard care are supported by specific personal, organizational and governance features. These mechanisms cause many frontline professionals gradually to become cynical regarding segregated Roma over the course of their careers. Health care staff should be supported with skills and tools for effectively handling their own and others' racism, the culturebound and structural vulnerabilities of patients as well as related professional expectations regarding equity

How Well Do Health-Mediation Programs Address the Determinants of the Poor Health Status of Roma? A Longitudinal Case Study

In Central and Eastern Europe (CEE), health-mediation programs (HMPs) have become central policy instruments targeting health inequities between segregated Roma and general populations. Social determinants of health (SDH) represent the root causes behind health inequities. We therefore evaluated how an HMP based in Slovakia addressed known SDH in its agenda and its everyday implementation. To produce descriptive data on the HMP's agenda and everyday implementation we observed and consulted 70 program participants across organizational levels and 30 program recipients over the long-term. We used a World Health Organization framework on SDH to direct data acquisition and consequent data content analysis, to structure the reporting of results, and to evaluate the program's merits. In its agenda, the HMP did not address most known SDH, except for healthcare access and health-related behaviours. In the HMP's everyday implementation, healthcare access facilitation activities were well received, performed as set out and effective. The opposite was true for most educational activities targeting health-related behaviours. The HMP fieldworkers were proactive and sometimes effective at addressing most other SDH domains beyond the HMP agenda, especially material conditions and psychosocial factors, but also selected local structural aspects. The HMP leaders supported such deliberate engagement only informally, considering the program inappropriate by definition and too unstable institutionally to handle such extensions. Reports indicate that the situation in other CEE HMPs is similar. To increase the HMPs' impact on SDH, their theories and procedures should be adapted according to the programs' more promising actual practice regarding SDH

Genes responsive to rapamycin and serum deprivation are clustered on chromosomes and undergo re-organization within local chromatin environments.

Supplementary materials are available at University of Toronto: https://tspace.library.utoronto.ca/handle/1807/9982

ABCD : Update of the 2009 guidelines on prevention and management of feline infectious diseases

In this article, the ABCD guidelines published in the JFMS Special Issue of July 2009 (Volume 11, Issue 7, pages 527-620) are updated by including previously unavailable and novel information. For a better picture, the reader is advised to consult that issue before focusing on the novel features

Influenza virus infections in cats

In the past, cats were considered resistant to influenza. Today, we know that they are susceptible to some influenza A viruses (IAVs) originating in other species. Usually, the outcome is only subclinical infection or a mild fever. However, outbreaks of feline disease caused by canine H3N2 IAV with fever, tachypnoea, sneezing, coughing, dyspnoea and lethargy are occasionally noted in shelters. In one such outbreak, the morbidity rate was 100% and the mortality rate was 40%. Recently, avian H7N2 IAV infection occurred in cats in some shelters in the USA, inducing mostly mild respiratory disease. Furthermore, cats are susceptible to experimental infection with the human H3N2 IAV that caused the pandemic in 1968. Several studies indicated that cats worldwide could be infected by H1N1 IAV during the subsequent human pandemic in 2009. In one shelter, severe cases with fatalities were noted. Finally, the highly pathogenic avian H5N1 IAV can induce a severe, fatal disease in cats, and can spread via cat-to-cat contact. In this review, the Advisory Board on Cat Diseases (ABCD), a scientifically independent board of experts in feline medicine from 11 European countries, summarises current data regarding the aetiology, epidemiology, pathogenesis, clinical picture, diagnostics, and control of feline IAV infections, as well as the zoonotic risks