Crystal plasticity finite element simulations of cast α-uranium

α-uranium, the stable phase of uranium up to 670◦C, has a base-centred orthorombic crystal structure. This crystal structure gives rise to elastic and thermal anisotropy, meaning α-uranium exhibits complex deformation and fracture behaviour. Understanding the relationship between the microstructure and mechanical properties is important to prevent fracture during manufacture and usage of components. The lattice of α-uranium corresponds to a distorted close-packed-hexagonal crystal structure and it exhibits twins of both the 1st and 2nd kind. Therefore, detailed examination of the behaviour of α-uranium can also contribute to the general understanding of the interaction between plasticity, twinning and fracture in hcp crystals. Plastic deformation in α-uranium can be accommodated by 4 slip systems and 3 twin systems, previously identified by McCabe et al. These deformation modes are implemented into a crystal plasticity finite element (CPFE) material model. A temperature dependent, dislocation density based law is implemented to describe the critical resolved shear stress on the different slip/twin systems. The strong anisotropic thermal expansion behaviour is taken into account to simulate the development of internal residual stresses following casting of the material. During cooling, the internal stresses in α-uranium are sufficient to induce plasticity. This effect is quantified using polycrystal simulations, in which first the temperature is decreased, then plastic relaxation takes place, followed by application of a mechanical load. The asymmetry between mechanical properties in tension and compression, due to the presence of twins, is investigated. The model is calibrated using stress strain curves and the lattice strain found from published neutron diffraction experiments carried out on textured samples at ISIS. The strength of the slip systems is found to be lower than in fine grained material, while the strength of the twin system is similar to single crystals. The CPFE method allows the heterogeneity of the strain between neighbouring grains and its influence on the evolution of the internal stress state to be investigated

Orientation-dependent indentation response of helium-implanted tungsten

A literature review of studies investigating the topography of nano-indents in ion-implanted materials reveals seemingly inconsistent observations, with report of both pile-up and sink-in. This may be due to the crystallographic orientation of the measured sample point, which is often not considered when evaluating implantation-induced changes in the deformation response. Here we explore the orientation dependence of spherical nano-indentation in pure and helium-implanted tungsten, considering grains with , and out-of-plane orientations. Atomic force microscopy (AFM) of indents in unimplanted tungsten shows little orientation dependence. However, in the implanted material a much larger, more localised pile-up is observed for grains than for and orientations. Based on the observations for grains, we hypothesise that a large initial hardening due to helium-induced defects is followed by localised defect removal and subsequent strain softening. A crystal plasticity finite element model of the indentation process, formulated based on this hypothesis, accurately reproduces the experimentally-observed orientation-dependence of indent morphology. The results suggest that the mechanism governing the interaction of helium-induced defects with glide dislocations is orientation independent. Rather, differences in pile-up morphology are due to the relative orientations of the crystal slip systems, sample surface and spherical indenter. This highlights the importance of accounting for crystallographic orientation when probing the deformation behaviour of ion-implanted materials using nano-indentation

Hardening and Strain Localisation in Helium-Ion-Implanted Tungsten

Tungsten is the main candidate material for plasma-facing armour components in future fusion reactors. In-service, fusion neutron irradiation creates lattice defects through collision cascades. Helium, injected from plasma, aggravates damage by increasing defect retention. Both can be mimicked using helium-ion-implantation. In a recent study on 3000 appm helium-implanted tungsten (W-3000He), we hypothesized helium-induced irradiation hardening, followed by softening during deformation. The hypothesis was founded on observations of large increase in hardness, substantial pile-up and slip-step formation around nano-indents and Laue diffraction measurements of localised deformation underlying indents. Here we test this hypothesis by implementing it in a crystal plasticity finite element (CPFE) formulation, simulating nano-indentation in W-3000He at 300 K. The model considers thermally-activated dislocation glide through helium-defect obstacles, whose barrier strength is derived as a function of defect concentration and morphology. Only one fitting parameter is used for the simulated helium-implanted tungsten; defect removal rate. The simulation captures the localised large pile-up remarkably well and predicts confined fields of lattice distortions and geometrically necessary dislocation underlying indents which agree quantitatively with previous Laue measurements. Strain localisation is further confirmed through high resolution electron backscatter diffraction and transmission electron microscopy measurements on cross-section lift-outs from centre of nano-indents in W-3000He

Copyright and Commerce: The DMCA, Trusted Systems, and the Stabilization of Distribution

The Digital Millennium Copyright Act has been criticized for granting too much power to copyright holders, offering them new technological controls that may harm the public interest. But, by considering this exclusively as a copyright issue, we overlook how the DMCA anticipates a technological and commercial infrastructure for regulating not only copying, but every facet of the purchase and use of cultural goods. In upholding the law in Universal v. Reimerdes, the courts not only stabilized these market-friendly arrangements in cultural distribution; they extended these arrangements into realms as diverse as encryption research and journalism, with consequences for the very production of knowledge

Night of the Witch: Alternative Spirituality, Identity and Media

This thesis works to understand the relationships witches and conjurors have with the film and television depictions of them. Employing the method of film critique, I argue that the witch stands as a cultural symbol in the US of women and femmes with power, and that their stories serve as lessons to these populations about what it means to be an acceptable woman or femme, while simultaneously creating and perpetuating stereotypes of magic practitioners. Then, using the combination of hashtag ethnography, in-person and video interviewing and internet surveys, I argue that #witchblr and #witchesofcolor, as well as the space of an interview with another practitioner, serves as a counterspace where the counternarratives against oppression, of resistance, and of personal identity work can take place. I connect the language practitioners use to describe themselves and witches and conjurors in film and television to the embracing and distancing marginalized communities engage in when crafting their identities around stereotyped notions of their group, and argue for the need for a simpler, softer, more diverse witchcraft in United States film and television

Body mass index change in adulthood and lung and upper aerodigestive tract cancers

Body mass index (BMI) has been inversely associated with lung and upper aerodigestive tract (UADT) cancers. However, only a few studies have assessed BMI change in adulthood in relation to cancer. To understand the relationship between BMI change and these cancers in both men and women, we analyzed data from a population-based case-control study conducted in Los Angeles County. Adulthood BMI change was measured as the proportional change in BMI between age 21 and 1 year before interview or diagnosis. Five categories of BMI change were included, and individuals with no more than a 5% loss or gain were defined as having a stable BMI (reference group). Adjusted odds ratios (ORs) and their 95% confidence intervals (CIs) were estimated using logistic regression models. Potential confounders included age, gender, ethnicity, education, tobacco smoking and energy intake. For UADT cancers, we also adjusted for alcohol drinking status and frequency. A BMI gain of 25% or higher in adulthood was inversely associated with lung cancer (OR 0.53, 95% CI 0.33-0.84) and UADT cancers (OR 0.44, 95% CI 0.27-0.71). In subgroup analyses, a BMI gain of ≥25% was inversely associated with lung and UADT cancers among current and former smokers, as well as among current and former alcohol drinkers. The inverse association persisted among moderate and heavy smokers (≥20 pack-years). The observed inverse associations between adulthood BMI gain and lung and UADT cancers indicate a potential role for body weight-related biological pathways in the development of lung and UADT cancers

Delayed differentiation in embryonic stem cells and mesodermal progenitors in the absence of CtBP2

Mammalian embryonic stem cells (ESCs) are characterized by an ability to self-renew and give rise to each of the three germ layers. ESCs are a pluripotential source of numerous primitive progenitors and committed lineages and can make stoichiometric decisions leading to either asymmetric or symmetric cell division. Several genes have been identified as essential for maintenance of self-renewal, but few non-lineage specific genes have been identified as essential for differentiation. We selected the chromatin factor Ctbp2 from microarray data for its enriched expression in stem cells, in comparison to committed progenitors. RNA interference (RNAi) was used to knockdown gene expression in mouse ESCs and the potential for transduced cells to self-renew and differentiate was assessed in ESC and mesodermal assays. Here, we demonstrate an important role for Ctbp2 in stem cell maintenance and regulation of differentiation using an in vitro system. The knockdown of Ctbp2 increases the prevalence of ESCs in culture, delays differentiation induced by LIF withdrawal, and introduces developmental changes in mesodermal differentiation. A model is presented for the importance of Ctbp2 in maintaining a balance in decisions to self-renewal and differentiate

Magnesium Intake and Depression in U.S. Adults

Research has focused extensively on the negative health effects of inadequate Mg intake, but the extent of the problem of deficiency deserves further exploration. The notion that U.S. adults consume an inadequate amount of magnesium, leading to increased risk for chronic diseases such as depression, is plausible. National Health and Nutrition Examination Surveys (NHANES), which are large, cross-sectional, population-based data sets that assess the health and nutritional status of U.S. adults and children, indicate over half the adult population does not consume adequate amounts of magnesium based on the estimated average requirement (EAR) established by the Institute of Medicine. Using 2007 to 2010 NHANES data we found 54% of adults do not meet the EAR, confirming results from earlier surveys. As a result of this finding, a review exploring the factors impacting magnesium consumption over time and the adequacy of current intake in U.S. adults was conducted. Changes in agricultural processes that reduce magnesium levels in crops combined with the increasing consumption of processed foods containing little to no magnesium have led to a decrease in mean daily intake by 200-300 mg per day over the past century. However, population-based studies show a steady and consistent recovery in magnesium intake in U.S. adults over the past several decades. A simple, rapid, accurate test for whole body Mg status is lacking and, although population-based studies have limitations, continued monitoring of Mg consumption is essential to determine whether this positive trend continues. In the meantime, since the health consequences of inadequate magnesium are well established, there are no reported cases of hypermagnesemia from food alone, and magnesium is found in healthy foods adults should consume more often, there are few reasons not to encourage increased magnesium intake. Cross-sectional and prospective trials in other countries report an association between magnesium intake and symptoms of depression. Depression is a chronic disease affecting a significant portion of the U.S. population. Magnesium plays a role in many of the pathways involved in the pathophysiology of depression and is found in several enzymes, hormones, and neurotransmitters. Depression and magnesium are both associated with systemic inflammation. Current treatment options for depression are limited by efficacy, cost, availability, side effects, and acceptability to patients. As a result of the need for additional treatment options, interest in the role of magnesium in modulating depressive symptoms has grown. We used the NHANES 2007-2010 data to examine this relationship in U.S. adults and found a significant association between very low magnesium intake and symptoms of depression (RR=1.16; 95% confidence interval (CI) 1.06, 1.30; P=0.03). Whether inadequate magnesium leads to increased risk for depression or depression results in poor dietary intake is not known. To test whether supplementation with over-the-counter magnesium chloride improves symptoms of depression, an open-label, blocked, randomized, cross-over trial was carried out in outpatient primary care clinics on 126 adults (mean age 52; 38% male) diagnosed with, and currently experiencing, mild-to-moderate symptoms. Consumption of magnesium chloride tablets for 6 weeks resulted in a clinically significant net improvement in depression (Patient Health Questionnaire-9) scores of -6.0 points (95% CI -7.9, -4.2; P\u3c0.001) and net improvement in anxiety (Generalized Anxiety Disorders-7) scores of -4.5 points (95% CI -6.6, -2.4; P\u3c0.001). Effects were observed regardless of age, gender, baseline magnesium levels, baseline severity of depression, or use of antidepressant treatments. It worked quickly, was well tolerated, and is much safer and less expensive than conventional treatments with medication. Magnesium supplements are effective for mild-to-moderate depression and are an additional treatment option for patients suffering from depression