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

Toward sustainable environmental quality : priority research questions for Europe

The United Nations' Sustainable Development Goals have been established to end poverty, protect the planet, and ensure prosperity for all. Delivery of the Sustainable Development Goals will require a healthy and productive environment. An understanding of the impacts of chemicals which can negatively impact environmental health is therefore essential to the delivery of the Sustainable Development Goals. However, current research on and regulation of chemicals in the environment tend to take a simplistic view and do not account for the complexity of the real world, which inhibits the way we manage chemicals. There is therefore an urgent need for a step change in the way we study and communicate the impacts and control of chemicals in the natural environment. To do this requires the major research questions to be identified so that resources are focused on questions that really matter. We present the findings of a horizon-scanning exercise to identify research priorities of the European environmental science community around chemicals in the environment. Using the key questions approach, we identified 22 questions of priority. These questions covered overarching questions about which chemicals we should be most concerned about and where, impacts of global megatrends, protection goals, and sustainability of chemicals; the development and parameterization of assessment and management frameworks; and mechanisms to maximize the impact of the research. The research questions identified provide a first-step in the path forward for the research, regulatory, and business communities to better assess and manage chemicals in the natural environment. Environ Toxicol Chem 2018;9999:1-15

Serum magnesium and calcium levels in relation to ischemic stroke : Mendelian randomization study

ObjectiveTo determine whether serum magnesium and calcium concentrations are causally associated with ischemic stroke or any of its subtypes using the mendelian randomization approach.MethodsAnalyses were conducted using summary statistics data for 13 single-nucleotide polymorphisms robustly associated with serum magnesium (n = 6) or serum calcium (n = 7) concentrations. The corresponding data for ischemic stroke were obtained from the MEGASTROKE consortium (34,217 cases and 404,630 noncases).ResultsIn standard mendelian randomization analysis, the odds ratios for each 0.1 mmol/L (about 1 SD) increase in genetically predicted serum magnesium concentrations were 0.78 (95% confidence interval [CI] 0.69-0.89; p = 1.3 7 10-4) for all ischemic stroke, 0.63 (95% CI 0.50-0.80; p = 1.6 7 10-4) for cardioembolic stroke, and 0.60 (95% CI 0.44-0.82; p = 0.001) for large artery stroke; there was no association with small vessel stroke (odds ratio 0.90, 95% CI 0.67-1.20; p = 0.46). Only the association with cardioembolic stroke was robust in sensitivity analyses. There was no association of genetically predicted serum calcium concentrations with all ischemic stroke (per 0.5 mg/dL [about 1 SD] increase in serum calcium: odds ratio 1.03, 95% CI 0.88-1.21) or with any subtype.ConclusionsThis study found that genetically higher serum magnesium concentrations are associated with a reduced risk of cardioembolic stroke but found no significant association of genetically higher serum calcium concentrations with any ischemic stroke subtype

Innovations in major system reconfiguration in England: a study of the effectiveness, acceptability and processes of implementation of two models of stroke care

BACKGROUND: Significant changes in provision of clinical care within the English National Health Service (NHS) have been discussed in recent years, with proposals to concentrate specialist services in fewer centres. Stroke is a major public health issue, accounting for over 10% of deaths in England and Wales, and much disability among survivors. Variations have been highlighted in stroke care, with many patients not receiving evidence-based care. To address these concerns, stroke services in London and Greater Manchester were reorganised, although different models were implemented. This study will analyse processes involved in making significant changes to stroke care services over a short time period, and the factors influencing these processes. We will examine whether the changes have delivered improvements in quality of care and patient outcomes; and, in light of this, whether the significant extra financial investment represented good value for money. METHODS/DESIGN: This study brings together quantitative data on ‘what works and at what cost?’ with qualitative data on ‘understanding implementation and sustainability’ to understand major system change in two large conurbations in England. Data on processes of care and their outcomes (e.g. morbidity, mortality, and cost) will be analysed to evidence services’ performance before and after reconfiguration. The evaluation draws on theories related to the dissemination and sustainability of innovations and the ‘social matrix’ underlying processes of innovation. We will conduct a series of case studies based on stakeholder interviews and documentary analysis. These will identify drivers for change, how the reconfigurations were governed, developed, and implemented, and how they influenced service quality. DISCUSSION: The research faces challenges due to: the different timings of the reconfigurations; the retrospective nature of the evaluation; and the current organisational turbulence in the English NHS. However, these issues reflect the realities of major systems change and its evaluation. The methods applied in the study have been selected to account for and learn from these complexities, and will provide useful lessons for future reconfigurations, both in stroke care and other specialties

Exonic STK11 deletions are not a rare cause of Peutz-Jeghers syndrome

Background: Peutz-Jeghers syndrome (PJS) is a rare, autosomal dominant cancer predisposition syndrome characterised by oro-facial pigmentation and hamartomatous polyposis of the gastrointestinal tract. A causal germline mutation in STK11 can be identified in 30% to 80% of PJS patients.Methods: Here we report the comprehensive mutational analysis of STK11 in 38 PJS probands applying conventional PCR based mutation detection methods and the recently introduced MLPA (multiplex ligation dependent probe amplification) technique developed for the identification of exonic deletions/duplications.Results: Nineteen of 38 probands (50%) had detectable point mutations or small scale deletions/insertions and six probands (16%) had genomic deletions encompassing one or more STK11 exons.Conclusions: These findings demonstrate that exonic STK11 deletions are a common cause of PJS and provide a strong rationale for conducting a primary screen for such mutations in patients.Abbreviations: MLPA, multiplex ligation dependent probe amplification; PJS, Peutz-Jeghers syndrom

The mechanisms of curve squeal

Existing curve squeal theory is often contradicted by field observations such as the generation of squeal from the outer wheel (including wheel flange contact), squeal occurring at various wheel natural frequencies, coupled rail vibrations when squealing wheels pass, and the obvious influence of trackform on squeal occurrence and severity. This paper discusses the deficiencies of existing theory and explores an alternative mechanism based on the concept of mode coupling instability which shows a better match with field observations from some sites