An investigation of the loss of ductility in hydrogen charged beta-Ti alloys

The high strength, low density, and good corrosion resistance of Ti-based alloys make them candidate materials for a number of applications in the aerospace industry. A major limitation in the use of these alloys in the advanced hypersonic flight vehicle program is their susceptibility to hydrogen embrittlement. This study focuses on the hydrogen sensitivity of TIMETAL 21S beta-Ti alloy. The material received was in the form of grip-ends of failed tensile test samples which had been exposed to different charging conditions (combinations of hydrogen pressure and temperature). The samples received, the charging conditions, and their fracture mode are discussed. It can be seen that the fracture behavior changes from ductile to brittle with increasing hydrogen content, but the transition in behavior occurs for a small increase in hydrogen concentration. The aim of this program was to assess the microstructural differences between the ductile and brittle alloys to ascertain the embrittlement mechanism. A range of tools which included x-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used

Dislocation Grain Boundary Interactions in Irradiated Metals

The behavior of dislocations in unirradiated and ion-irradiated austenitic stainless steels has been observed directly by performing straining experiments in-situ in the transmission electron microscope. This has enabled direct observation of how dislocations interact with each other, with the irradiation produced obstacles and with grain boundaries. These experiments have provided insight as to the mechanisms by which dislocations annihilate the irradiation produced defects to form a channel as well as determination of the conditions that control slip transfer across a grain boundary and how it is impacted by the presence of the irradiation produced defects

Dislocation Grain Boundary Interactions in Irradiated Metals

The behavior of dislocations in unirradiated and ion-irradiated austenitic stainless steels has been observed directly by performing straining experiments in-situ in the transmission electron microscope. This has enabled direct observation of how dislocations interact with each other, with the irradiation produced obstacles and with grain boundaries. These experiments have provided insight as to the mechanisms by which dislocations annihilate the irradiation produced defects to form a channel as well as determination of the conditions that control slip transfer across a grain boundary and how it is impacted by the presence of the irradiation produced defects

European colonization, not Polynesian arrival, impacted population size and genetic diversity in the critically endangered New Zealand Kākāpō.

Island endemic species are often vulnerable to decline and extinction following human settlement, and the genetic study of historical museum specimens can be useful in understanding these processes. The kākāpō (Strigops habroptilus) is a critically endangered New Zealand parrot that was formerly widespread and abundant. It is well established that both Polynesian and European colonization of New Zealand impacted the native avifauna, but the timeframe and severity of impacts have differed depending on species. Here, we investigated the relative importance of the 2 waves of human settlement on kākāpō decline, using microsatellites and mitochondrial DNA (mtDNA) to characterize recent kākāpō genetic and demographic history. We analyzed samples from 49 contemporary individuals and 54 museum specimens dating from 1884 to 1985. Genetic diversity decreased significantly between historical and contemporary kākāpō, with a decline in mean number of microsatellite alleles from 6.15 to 3.08 and in number of mtDNA haplotypes from 17 to 3. Modeling of demographic history indicated a recent population bottleneck linked to the period of European colonization (approximately 5 generations ago) but did not support a major decline linked to Polynesian settlement. Effective population size estimates were also larger for historical than contemporary kākāpō. Our findings inform contemporary kākāpō management by indicating the timeframe and possible cause of the bottleneck, which has implications for the management of extant genetic diversity. We demonstrate the broader utility of a historical perspective in understanding causes of decline and managing extinction risk in contemporary endangered species

Dislocation-Radiation Obstacle Interactions: Developing Improved Mechanical Property Constitutive Models

Radiation damage to structural and cladding materials, including austenitic stainless steels, ferritic steels, and zirconium alloys, in nuclear reactor environments results in significant mechanical property degradation, including yield strength increases, severe ductility losses and flow localization, which impacts reliability and performance. Generation IV and advanced fuel cycle concepts under consideration will require the development of advanced structural materials, which will operate in increasingly hostile environments. The development of predictive models is required to assess the performance and response of materials in extreme Gen IV reactor operating conditions (temperature, stress, and pressure), to decrease the time to rapidly assess the properties of new materials and insert them into technological applications (Gen IV and Advanced Fuel Cycle Operations)

Habitat selection under the risk of infectious disease

ABSTRACT Question: How does the risk of infectious disease transmission affect individual habitat selection decisions and the resulting spatial distributions of populations? Mathematical method: We use a differential equation model to describe disease dynamics in two habitats coupled by natal dispersal and use an evolutionary game theoretical approach to calculate the evolutionarily stable strategy for habitat choice. Key assumptions: Natal dispersal by offspring with ideal knowledge of habitats. Habitats differ only in resource quality. Fecundity is proportional to intake rate, which decreases with density. We assume density-dependent disease transmission, with infection reducing fecundity or lifespan. Disease may be present in both habitats or the high-quality habitat only. Conclusions: In the absence of disease, our model predicts input matching (i.e. the distribution of individuals matches the distribution of resource inputs). The negative fitness consequences of infection can result in undermatching (underuse of the high-quality habitat compared with input matching), but stable overmatching (overuse of the high-quality habitat) is never predicted. Increasing the risk of transmission increases the degree of observed undermatching when only the high-quality habitat is infected but reduces undermatching when both habitats present a risk of disease. Increasing the cost of infection by reducing fecundity reduces use of the high-quality habitat (undermatching) in both cases. Increasing the cost of infection by increasing mortality rates also reduces the use of the high-quality habitat when both habitats are infected; if only the high-quality habitat is infected, undermatching may initially increase with mortality but eventually decreases

A response to “Likelihood ratio as weight of evidence: a closer look” by Lund and Iyer

Recently, Lund and Iyer (L&I) raised an argument regarding the use of likelihood ratios in court. In our view, their argument is based on a lack of understanding of the paradigm. L&I argue that the decision maker should not accept the expert’s likelihood ratio without further consideration. This is agreed by all parties. In normal practice, there is often considerable and proper exploration in court of the basis for any probabilistic statement. We conclude that L&I argue against a practice that does not exist and which no one advocates. Further we conclude that the most informative summary of evidential weight is the likelihood ratio. We state that this is the summary that should be presented to a court in every scientific assessment of evidential weight with supporting information about how it was constructed and on what it was based

Epidemiology of epidermolysis bullosa in the antipodes: The Australasian epidermolysis bullosa registry with a focus on Herlitz junctional epidermolysis bullosa

To present epidemiologic and clinical data from the Australasian Epidermolysis Bullosa (EB) Registry, the first orphan disease registry in Australia. Design: Observational study (cross-sectional and longitudinal). Setting: Australian private dermatology practice, inpatient ward, and outpatient clinic. Patients: Systematic case finding of patients with EB simplex, junctional EB (JEB), and dystrophic EB and data collection were performed throughout Australia and New Zealand from January 1, 2006, through December 31, 2008. Patients were consecutively enrolled in the study after clinical assessment and laboratory diagnosis. Medical records were retrospectively examined, and physicians involved in EB care were contacted to obtain patient history. A Herlitz JEB case series was prepared from registry data. Main Outcome Measures: Demographics and prognosis of patients with Herlitz JEB. Results: A total of 259 patients were enrolled in the study: 139 with EBS, 91 with dystrophic EB, 28 with JEB, and 1 with Kindler syndrome. Most enrollees were Australian citizens (n=243), with an Australian prevalence rate of 10.3 cases per million. The age range in the registry was birth to 99 years, with a mean and median age of 24.1 and 18.0 years, respectively. Ages were similar in patients with EBS and dominant dystrophic EB but were markedly lower in patients with JEB. Patients with Herlitz JEB (n=10) had the highest morbidity and mortality rates, with a mean age at death of 6.8 months. Sepsis, failure to thrive, and tracheolaryngeal complications were the leading causes of death. Conclusions: The Australasian EB registry is the first registry in Australia and New Zealand to provide original data on age, sex, ethnicity, and geographical and disease subtype distribution. The Australasian Herlitz JEB cohort witnessed a high infant mortality rate and poor prognosis overall