Study of heterogeneous nucleation of eutectic Si in high-purity Al-Si alloys with Sr addition

The official published version can be accessed from the link below - Copyright @ 2010 The Minerals, Metals & Materials Society and ASM InternationalAl-5 wt pct Si master-alloys with controlled Sr and/or P addition/s were produced using super purity Al 99.99 wt pct and Si 99.999 wt pct materials in an arc melter. The master-alloy was melt-spun resulting in the production of thin ribbons. The Al matrix of the ribbons contained entrained Al-Si eutectic droplets that were subsequently investigated. Differential scanning calorimetry, thermodynamic calculations, and transmission electron microscopy techniques were employed to examine the effect of the Sr and P additions on eutectic undercoolings and nucleation phenomenon. Results indicate that, unlike P, Sr does not promote nucleation. Increasing Sr additions depressed the eutectic nucleation temperature. This may be a result of the formation of a Sr phase that could consume or detrimentally affect potent AlP nucleation sites.This work is financially supported by the Higher Education Commission of Pakistan and managerially supported from the OAD

Probing R-parity violating models of neutrino mass at the Tevatron via top Squark decays

We have estimated the limiting branching ratio of the R-parity violating (RPV) decay of the lighter top squark, \tilde t_1 \ar l^+ d ($l=e$ or $\mu$ and d is a down type quark of any flavor), as a function of top squark mass(\MST) for an observable signal in the di-lepton plus di-jet channel at the Tevatron RUN-II experiment with 2 fb$^{-1}$ luminosity. Our simulations indicate that the lepton number violating nature of the underlying decay dynamics can be confirmed via the reconstruction of \MST. The above decay is interesting in the context of RPV models of neutrino mass where the RPV couplings ($\lambda'_{i3j}$) driving the above decay are constrained to be small (\lsim 10^{-3} - 10^{-4} ). If $\tilde t_1$ is the next lightest super particle - a theoretically well motivated scenario - then the RPV decay can naturally compete with the R-parity conserving (RPC) modes which also have suppressed widths. The model independent limiting BR can delineate the parameter space in specific supersymmetric models, where the dominating RPV decay is observable and predict the minimum magnitude of the RPV coupling that will be sensitive to Run-II data. We have found it to be in the same ballpark value required by models of neutrino mass, for a wide range of \MST. A comprehensive future strategy for linking top squark decays with models of neutrino mass is sketched.Comment: 28 pages, 14 Figure

The Structure of a Rigorously Conserved RNA Element within the SARS Virus Genome

We have solved the three-dimensional crystal structure of the stem-loop II motif (s2m) RNA element of the SARS virus genome to 2.7-Å resolution. SARS and related coronaviruses and astroviruses all possess a motif at the 3′ end of their RNA genomes, called the s2m, whose pathogenic importance is inferred from its rigorous sequence conservation in an otherwise rapidly mutable RNA genome. We find that this extreme conservation is clearly explained by the requirement to form a highly structured RNA whose unique tertiary structure includes a sharp 90° kink of the helix axis and several novel longer-range tertiary interactions. The tertiary base interactions create a tunnel that runs perpendicular to the main helical axis whose interior is negatively charged and binds two magnesium ions. These unusual features likely form interaction surfaces with conserved host cell components or other reactive sites required for virus function. Based on its conservation in viral pathogen genomes and its absence in the human genome, we suggest that these unusual structural features in the s2m RNA element are attractive targets for the design of anti-viral therapeutic agents. Structural genomics has sought to deduce protein function based on three-dimensional homology. Here we have extended this approach to RNA by proposing potential functions for a rigorously conserved set of RNA tertiary structural interactions that occur within the SARS RNA genome itself. Based on tertiary structural comparisons, we propose the s2m RNA binds one or more proteins possessing an oligomer-binding-like fold, and we suggest a possible mechanism for SARS viral RNA hijacking of host protein synthesis, both based upon observed s2m RNA macromolecular mimicry of a relevant ribosomal RNA fold

An aggravated trajectory of depression and anxiety co-morbid with hepatitis C: : A 21 to 62 month follow-up study in 61 South Australian outpatients

BACKGROUND: This study aimed to explore the course of depression and anxiety in chronic hepatitis C patients. METHODS:   Data were combined from two studies: (1) Hospital Anxiety and Depression Scale (HADS) scores in 395 consecutive Australian outpatients from 2006 to 2010 formed the baseline measurement; and (2) Depression Anxiety Stress Scales (DASS) scores in a survey of a sub-sample of these patients in 2011 formed the follow-up measurement. After converting DASS to HADS scores, changes in symptom scores and rates of case-ness (≥8), and predictors of follow-up symptoms were assessed. RESULTS:   Follow-up data were available for 61 patients (70.5% male) whose age ranged from 24.5 to 74.6 years (M=45.6). The time to follow-up ranged from 20.7 to 61.9 months (M=43.8). Baseline rates of depression (32.8%) and anxiety (44.3%) increased to 62.3% and 67.2%, respectively. These findings were confirmed, independent of the conversion, by comparing baseline HADS and follow-up DASS scores with British community norms. Baseline anxiety and younger age predicted depression, while baseline anxiety, high school non-completion, and single relationship status predicted anxiety. CONCLUSION:  This study demonstrated a worsening trajectory of depression and anxiety. Further controlled and prospective research in a larger sample is required to confirm these findings

Subcortical volumes across the lifespan: data from 18,605 healthy individuals aged 3-90 years

Age has a major effect on brain volume. However, the normative studies available are constrained by small sample sizes, restricted age coverage and significant methodological variability. These limitations introduce inconsistencies and may obscure or distort the lifespan trajectories of brain morphometry. In response, we capitalized on the resources of the Enhancing Neuroimaging Genetics through Meta-Analysis (ENIGMA) Consortium to examine age-related trajectories inferred from cross-sectional measures of the ventricles, the basal ganglia (caudate, putamen, pallidum, and nucleus accumbens), the thalamus, hippocampus and amygdala using magnetic resonance imaging data obtained from 18,605 individuals aged 3-90 years. All subcortical structure volumes were at their maximum value early in life. The volume of the basal ganglia showed a monotonic negative association with age thereafter; there was no significant association between age and the volumes of the thalamus, amygdala and the hippocampus (with some degree of decline in thalamus) until the sixth decade of life after which they also showed a steep negative association with age. The lateral ventricles showed continuous enlargement throughout the lifespan. Age was positively associated with inter-individual variability in the hippocampus and amygdala and the lateral ventricles. These results were robust to potential confounders and could be used to examine the functional significance of deviations from typical age-related morphometric patterns.Education and Child Studie

Total Syntheses of Durgamone, Nakorone and Abudinol B via Biomimetic Oxa- and Carbacyclizations

The first biomimetic total syntheses of ent-nakorone, ent-durgamone, and ent-abudinol B were accomplished by combining features of tandem polyepoxide cyclization with biomimetic polyene cyclization. The present biomimetic synthesis route offers efficient access to these marine natural products. In addition, the synthesis of the tetrasubstituted alkene of ent-abudinol B demonstrates the application of palladium-catalyzed cross-coupling of two different polycyclic ketones via the corresponding vinyl triflates, followed by partial hydrogenation of the resulting conjugated diene. Copyright © 2007 American Chemical Society

Biomimetic Syntheses from Squalene-Like Precursors: Synthesis of Ent- Abudinol B, and Reassessment of the Structure of Muzitone

We achieved the stereoselective syntheses of two different structural patterns corresponding to the enantiomers of the marine natural products abudinol B and muzitone, by developing two-directional tandem biomimetic cyclizations of polyepoxides of squalene analogues in which one alkene was functionalized as an enolsilane. In the course of this work, we demonstrated that the structure of muzitone was misassigned. © 2010 American Chemical Society

Study of heterogeneous nucleation of eutectic Si in high-purity Al-Si alloys with Sr addition

The official published version can be accessed from the link below - Copyright @ 2010 The Minerals, Metals & Materials Society and ASM InternationalAl-5 wt pct Si master-alloys with controlled Sr and/or P addition/s were produced using super purity Al 99.99 wt pct and Si 99.999 wt pct materials in an arc melter. The master-alloy was melt-spun resulting in the production of thin ribbons. The Al matrix of the ribbons contained entrained Al-Si eutectic droplets that were subsequently investigated. Differential scanning calorimetry, thermodynamic calculations, and transmission electron microscopy techniques were employed to examine the effect of the Sr and P additions on eutectic undercoolings and nucleation phenomenon. Results indicate that, unlike P, Sr does not promote nucleation. Increasing Sr additions depressed the eutectic nucleation temperature. This may be a result of the formation of a Sr phase that could consume or detrimentally affect potent AlP nucleation sites.This work is financially supported by the Higher Education Commission of Pakistan and managerially supported from the OAD