918 research outputs found
Lattice Boltzmann modeling of dendritic growth in forced and natural convection
AbstractA two-dimensional (2D) coupled model is developed for the simulation of dendritic growth during alloy solidification in the presence of forced and natural convection. Instead of conventional continuum-based NavierâStokes (NS) solvers, the present model adopts a kinetic-based lattice Boltzmann method (LBM), which describes flow dynamics by the evolution of distribution functions of moving pseudo-particles, for the numerical computations of flow dynamics as well as thermal and solutal transport. The dendritic growth is modeled using a solutal equilibrium approach previously proposed by Zhu and Stefanescu (ZS), in which the evolution of the solid/liquid interface is driven by the difference between the local equilibrium composition and the local actual liquid composition. The local equilibrium composition is calculated from the local temperature and curvature. The local temperature and actual liquid composition, controlled by both diffusion and convection, are obtained by solving the LB equations using the lattice BhatnagarâGrossâKrook (LBGK) scheme. Detailed model validation is performed by comparing the simulations with analytical predictions, which demonstrates the quantitative capability of the proposed model. Furthermore, the convective dendritic growth features predicted by the present model are compared with those obtained from the ZhuâStefanescu and NavierâStokes (ZSâNS) model, in which the fluid flow is calculated using an NS solver. It is found that the evolution of the solid fraction of dendritic growth calculated by both models coincides well. However, the present model has the significant advantages of numerical stability and computational efficiency for the simulation of dendritic growth with melt convection
Single Spin Measurement using Single Electron Transistors to Probe Two Electron Systems
We present a method for measuring single spins embedded in a solid by probing
two electron systems with a single electron transistor (SET). Restrictions
imposed by the Pauli Principle on allowed two electron states mean that the
spin state of such systems has a profound impact on the orbital states
(positions) of the electrons, a parameter which SET's are extremely well suited
to measure. We focus on a particular system capable of being fabricated with
current technology: a Te double donor in Si adjacent to a Si/SiO2 interface and
lying directly beneath the SET island electrode, and we outline a measurement
strategy capable of resolving single electron and nuclear spins in this system.
We discuss the limitations of the measurement imposed by spin scattering
arising from fluctuations emanating from the SET and from lattice phonons. We
conclude that measurement of single spins, a necessary requirement for several
proposed quantum computer architectures, is feasible in Si using this strategy.Comment: 22 Pages, 8 Figures; revised version contains updated references and
small textual changes. Submitted to Phys. Rev.
Selection of Bread Wheat for Low Grain Cadmium Concentration at the Seedling Stage Using Hydroponics versus Molecular Markers
The excessive accumulation of Cd in harvested crops grown on high-Cd soils has increased public concerns for food safety. Due to the high consumption of bread wheat (Triticum aestivum L.) per capita, high concentrations of Cd in wheat grain can significantly affect human health. Breeding is a promising way to reduce grain Cd concentration. However, a lack of efficient selection methods impedes breeding for low grain Cd concentration in bread wheat. In this study, a recombinant inbred population segregating for grain Cd concentration was used to assess the efficacy of two selection methods for decreasing grain Cd concentration in bread wheat: a hydroponic selection method used shoot Cd concentration in 2-wk-old seedlings growing in Cd-containing medium, and a marker-based selection method using markers linked to heavy metal transporting P1B-ATPase 3 (HMA3), the gene underlying Cdu1. Both methods effectively selected low-Cd lines. The HMA3-linked marker-based selection was superior to hydroponic selection in terms of both simplicity and response to selection. The HMA3-linked markers explained 20% of the phenotypic variation in grain Cd concentration with an additive effect of 0.014 mg kgâ1. The hydroponic selection and marker-based selection may target two different and independent processes controlling grain Cd accumulation, and they had no effect on grain Zn and Fe concentrations. The ALMT1-UPS4 marker associated with Al tolerance was not associated with grain Cd concentration but increased grain Zn and Fe concentrations. The 193-bp allele of the Rht8-associated marker, GWM261, was associated with increased grain Cd concentration
R-parity violation effect on the top-quark pair production at linear colliders
We investigate in detail the effects of the R-parity lepton number violation
in the minimal supersymmetric standard model (MSSM) on the top-quark pair
production via both and collision modes at the linear
colliders. We find that with the present experimental constrained
parameters, the effect from interactions on the processes
and could be
significant and may reach -30% and several percent, respectively. Our results
show that the effects are sensitive to the c.m.s. energy and the
relevant parameters. However, they are not sensitive to squark and
slepton masses when (or ) and are almost independent on the Comment: Accepted by Phys.Rev.
In vivo Antidiabetic and Antioxidant Potential of Stephania hernandifolia in Streptozotocin-Induced-Diabetic Rats
Stephania hernandifolia (Menispermaceae) is a medicinal plant, used by herbalists for treating various diseases, one of which is diabetes mellitus, in Darjeeling. However, its antidiabetic activity has not been scientifically investigated so far. The aim of this study, therefore, is to investigate the antidiabetic and antioxidant potential of the powdered corm of Stephania hernandifolia. This was tested in normal and Streptozotocin (STZ)-induced diabetic rats, using oral administration of ethanol and an aqueous extract (400 mg/kg body weight) of Stephania hernandifolia corm. After the oral administration of water and ethanol extracts at doses of 400 mg/kg body weight, blood glucose levels were monitored at specific intervals and it was found that they were significant lowered. Glibenclamide was used as a standard drug at a dose of 0.25 mg/kg. The experimental data revealed that both extracts has significant antihyperglycemic and antioxidant activity in Streptozotocin-induced rats compared to the standard drug. The antioxidant activity in vitro was measured by means of the 1, 1-diphenyl-2-picrylhydrazyl (DPPH) and Superoxide-free radical scavenging assay. Ascorbic acid, a natural antioxidant, was used as a control. The extracts of ethanol and aqueous were strongly scavenged DPPH radicals, with IC50 being 265.33 and 217.90 Âľg/ml, respectively. Although the extracts of ethanol and aqueous were moderately scavenged, the superoxide radical were with IC50 values of 526.87 and 440.89 Âľg/ml. The study revealed that the ethanolic extract exhibited more significant antidiabetic and antioxidant activity then the aqueous extract
Metal enrichment processes
There are many processes that can transport gas from the galaxies to their
environment and enrich the environment in this way with metals. These metal
enrichment processes have a large influence on the evolution of both the
galaxies and their environment. Various processes can contribute to the gas
transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy
interactions and others. We review their observational evidence, corresponding
simulations, their efficiencies, and their time scales as far as they are known
to date. It seems that all processes can contribute to the enrichment. There is
not a single process that always dominates the enrichment, because the
efficiencies of the processes vary strongly with galaxy and environmental
properties.Comment: 18 pages, 8 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 17; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Magnetic relaxation and dipole-coupling-induced magnetization in nanostructured thin films during growth: A cluster Monte Carlo study
For growing inhomogeneous thin films with an island nanostructure similar as
observed in experiment, we determine the nonequilibrium and equilibrium
remanent magnetization. The single-island magnetic anisotropy, the dipole
coupling, and the exchange interaction between magnetic islands are taken into
account within a micromagnetic model. A cluster Monte Carlo method is developed
which includes coherent magnetization changes of connected islands. This causes
a fast relaxation towards equilibrium for irregularly connected systems. We
analyse the transition from dipole coupled islands at low coverages to a
strongly connected ferromagnetic film at high coverages during film growth. For
coverages below the percolation threshold, the dipole interaction induces a
collective magnetic order with ordering temperatures of 1 - 10 K for the
assumed model parameters. Anisotropy causes blocking temperatures of 10 - 100 K
and thus pronounced nonequilibrium effects. The dipole coupling leads to a
somewhat slower magnetic relaxation.Comment: 13 pages, 6 figures, revised manuscrip
The energy dependence of angular correlations inferred from mean- fluctuation scale dependence in heavy ion collisions at the SPS and RHIC
We present the first study of the energy dependence of angular
correlations inferred from event-wise mean transverse momentum
fluctuations in heavy ion collisions. We compare our large-acceptance
measurements at CM energies $\sqrt{s_{NN}} =$ 19.6, 62.4, 130 and 200 GeV to
SPS measurements at 12.3 and 17.3 GeV. $p_t$ angular correlation structure
suggests that the principal source of $p_t$ correlations and fluctuations is
minijets (minimum-bias parton fragments). We observe a dramatic increase in
correlations and fluctuations from SPS to RHIC energies, increasing linearly
with $\ln \sqrt{s_{NN}}$ from the onset of observable jet-related
fluctuations near 10 GeV.Comment: 10 pages, 4 figure
Clinical predictors of 3- and 6-month outcome for mild traumatic brain injury patients with a negative head CT scan in the emergency department: A TRACK-TBI pilot study
Aconsiderable subset of mild traumatic brain injury (mTBI) patients fail to return to baseline functional status at or beyond 3 months postinjury. Identifying at-risk patients for poor outcome in the emergency department (ED) may improve surveillance strategies and referral to care. Subjects with mTBI (Glasgow Coma Scale 13â15) and negative ED initial head CT < 24 h of injury, completing 3- or 6-month functional outcome (Glasgow Outcome Scale-Extended; GOSE), were extracted from the prospective, multicenter Transforming Research and Clinical Knowledge in Traumatic Brain Injury (TRACK-TBI) Pilot study. Outcomes were dichotomized to full recovery (GOSE = 8) vs functional deficits (GOSE < 8). Univariate predictors with p < 0.10 were considered for multivariable regression. Adjusted odds ratios (AOR) were reported for outcome predictors. Significance was assessed at p < 0.05. Subjects who completed GOSE at 3- and 6-month were 211 (GOSE < 8: 60%) and 185 (GOSE < 8: 65%). Risk factors for 6-month GOSE < 8 included less education (AOR = 0.85 per-year increase, 95% CI: (0.74â0.98)), prior psychiatric history (AOR = 3.75 (1.73â8.12)), Asian/minority race (American Indian/Alaskan/Hawaiian/Pacific Islander) (AOR = 23.99 (2.93â196.84)), and Hispanic ethnicity (AOR = 3.48 (1.29â9.37)). Risk factors for 3-month GOSE < 8 were similar with the addition of injury by assault predicting poorer outcome (AOR = 3.53 (1.17â10.63)). In mTBI patients seen in urban trauma center EDs with negative CT, education, injury by assault, Asian/minority race, and prior psychiatric history emerged as risk factors for prolonged disability
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fbâ1 of protonâproton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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