Comparative study of dimer vacancies and dimer-vacancy lines on Si(001) and Ge(001)

Although the clean Si(001) and Ge(001) surfaces are very similar, experiments to date have shown that dimer-vacancy (DV) defects self-organize into vacancy lines (VLs) on Si(001), but not on Ge(001). In this paper, we perform empirical-potential calculations aimed at understanding the differences between the vacancies on Si(001) and Ge(001). We identify three energetic parameters that characterize the DVs on the two surfaces: the formation energy of a single DV, the attraction between two DVs in adjacent dimer rows, and the strain sensitivity of the formation energy of DVs and VLs. At the empirical level of treatment of the atomic interactions (Tersoff potentials), all three parameters are favorable for the self-assembly of DVs on the Si(001) surface rather than on Ge(001). The most significant difference between the defects on Si(001) and on Ge(001) concerns the formation energy of single DVs, which is three times larger in the latter case. By calculating the strain-dependent formation energies of DVs and VLs, we propose that the experimental observation of self-assembly of vacancies on clean Ge(001) could be achieved by applying compressive strains of the order of 2%.Comment: 3 tables, 4 figures, to appear in Surface Scienc

Mechanisms of enhanced heterogeneous nucleation during solidification in binary Al-Mg alloys

This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2012 ElsevierThe mechanisms involved in the grain refinement of Al–Mg alloys through varying the Mg content and applying intensive melt shearing were investigated. It was found that the oxide formed in Al–Mg alloys under normal melting conditions is MgAl2O4, which displays an equiaxed and faceted morphology with {1 1 1} planes exposed as its natural surfaces. Depending on the Mg content, MgAl2O4 particles exist either as oxide films in dilute Al–Mg alloys (Mg 1 wt.%). Such MgAl2O4 particles can act as potent sites for nucleation of α-Al grains, which is evidenced by the well-defined cube-on-cube orientation relationship between MgAl2O4 and α-Al. Enhanced heterogeneous nucleation in Al–Mg alloys can be attributed to the high potency of MgAl2O4 particles with a lattice misfit of 1.4% and the increased number density of MgAl2O4 particles due to either natural dispersion by the increased Mg content or forced dispersion through intensive melt shearing. It was also found that intensive melt shearing leads to significant grain refinement of dilute Al–Mg alloys by effective dispersion of the MgAl2O4 particles entrapped in oxide films, but it has marginal effect on the grain refinement of concentrated Al–Mg alloys, where MgAl2O4 particles have been naturally dispersed into individual particles by the increased Mg content.This study is funded from the EPSRC Grant EP/H026177/1

Multicriteria VMAT optimization

Purpose: To make the planning of volumetric modulated arc therapy (VMAT) faster and to explore the tradeoffs between planning objectives and delivery efficiency. Methods: A convex multicriteria dose optimization problem is solved for an angular grid of 180 equi-spaced beams. This allows the planner to navigate the ideal dose distribution Pareto surface and select a plan of desired target coverage versus organ at risk sparing. The selected plan is then made VMAT deliverable by a fluence map merging and sequencing algorithm, which combines neighboring fluence maps based on a similarity score and then delivers the merged maps together, simplifying delivery. Successive merges are made as long as the dose distribution quality is maintained. The complete algorithm is called VMERGE. Results: VMERGE is applied to three cases: a prostate, a pancreas, and a brain. In each case, the selected Pareto-optimal plan is matched almost exactly with the VMAT merging routine, resulting in a high quality plan delivered with a single arc in less than five minutes on average. VMERGE offers significant improvements over existing VMAT algorithms. The first is the multicriteria planning aspect, which greatly speeds up planning time and allows the user to select the plan which represents the most desirable compromise between target coverage and organ at risk sparing. The second is the user-chosen epsilon-optimality guarantee of the final VMAT plan. Finally, the user can explore the tradeoff between delivery time and plan quality, which is a fundamental aspect of VMAT that cannot be easily investigated with current commercial planning systems

Molecular characterization of cathepsin B from Clonorchis sinensis excretory/secretory products and assessment of its potential for serodiagnosis of clonorchiasis

<p>Abstract</p> <p>Background</p> <p>Cathepsin cysteine proteases play multiple roles in the life cycle of parasites such as food uptake, immune invasion and pathogenesis, making them valuable targets for diagnostic assays, vaccines and drugs. The purpose of this study was to identify a cathepsin B of <it>Clonorchis sinensis </it>(<it>Cs</it>CB) and to investigate its diagnostic value for human helminthiases.</p> <p>Results</p> <p>The predicted amino acid sequence of the cathepsin B of <it>C. sinensis </it>shared 63%, 52%, 50% identity with that of <it>Schistosoma japonicum</it>, <it>Homo sapiens </it>and <it>Fasciola hepatica</it>, respectively. Sequence encoding proenzyme of <it>Cs</it>CB was overexpressed in <it>Escherichia coli</it>. Reverse transcription PCR experiments revealed that <it>Cs</it>CB transcribed in both adult worm and metacercaria of <it>C. sinensis</it>. <it>Cs</it>CB was identified as a <it>C. sinensis </it>excretory/secretory product by immunoblot assay, which was consistent with immunohistochemical localization showing that <it>Cs</it>CB was especially expressed in the intestine of <it>C. sinensis </it>adults. Both ELISA and western blotting analysis showed recombinant <it>Cs</it>CB could react with human sera from clonorchiasis and other helminthiases.</p> <p>Conclusions</p> <p>Our findings revealed that secreted CsCB may play an important role in the biology of C. sinensis and could be a diagnostic candidate for helminthiases.</p

Artificial radionuclides in neon flying squid from the northwestern Pacific in 2011 following the Fukushima accident

In order to better understand the impact of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident on a commercial marine species, neon flying squid (Ommastrephes bartramii) samples obtained from the northwestern Pacific in November 2011 were analyzed for a range of artificial and natural radionuclides (Cs-134, Cs-137, Ag-110m, U-238, Ra-226, and K-40). Short-lived radionuclides Cs-134 and Ag-110m released from the FDNPP accident were found in the samples, with an extremely high water-to-organism concentration ratio for Ag-110m ( &gt; 2.9×104). While accident-derived radionuclides were present, their associated dose rates for the squid were far lower than the relevant benchmark of 10&thinsp;µGy&thinsp;h−1. For human consumers ingesting these squid, the dose contribution from natural radionuclides, including Po-210, was far greater ( &gt; 99.9&thinsp;%) than that of Fukushima-accident radionuclides ( &lt; 0.1&thinsp;%). The whole-body to tissue and whole-body to gut concentration ratios were calculated and reported, providing a simple method to estimate the whole-body concentration in environmental monitoring programs, and filling a data gap for concentration ratios in cephalopods. Our results help fill data gaps in uptake of nuclear power plant radionuclides in the commercially important Cephalopoda class and add to scarce data on open-ocean nekton in the northwestern Pacific shortly after the Fukushima accident.</p

Ventricular divergence correlates with epicardial wavebreaks and predicts ventricular arrhythmia in isolated rabbit hearts during therapeutic hypothermia

INTRODUCTION: High beat-to-beat morphological variation (divergence) on the ventricular electrogram during programmed ventricular stimulation (PVS) is associated with increased risk of ventricular fibrillation (VF), with unclear mechanisms. We hypothesized that ventricular divergence is associated with epicardial wavebreaks during PVS, and that it predicts VF occurrence. METHOD AND RESULTS: Langendorff-perfused rabbit hearts (n = 10) underwent 30-min therapeutic hypothermia (TH, 30°C), followed by a 20-min treatment with rotigaptide (300 nM), a gap junction modifier. VF inducibility was tested using burst ventricular pacing at the shortest pacing cycle length achieving 1:1 ventricular capture. Pseudo-ECG (p-ECG) and epicardial activation maps were simultaneously recorded for divergence and wavebreaks analysis, respectively. A total of 112 optical and p-ECG recordings (62 at TH, 50 at TH treated with rotigaptide) were analyzed. Adding rotigaptide reduced ventricular divergence, from 0.13±0.10 at TH to 0.09±0.07 (p = 0.018). Similarly, rotigaptide reduced the number of epicardial wavebreaks, from 0.59±0.73 at TH to 0.30±0.49 (p = 0.036). VF inducibility decreased, from 48±31% at TH to 22±32% after rotigaptide infusion (p = 0.032). Linear regression models showed that ventricular divergence correlated with epicardial wavebreaks during TH (p<0.001). CONCLUSION: Ventricular divergence correlated with, and might be predictive of epicardial wavebreaks during PVS at TH. Rotigaptide decreased both the ventricular divergence and epicardial wavebreaks, and reduced the probability of pacing-induced VF during TH