Ordering dynamics of the driven lattice gas model

The evolution of a two-dimensional driven lattice-gas model is studied on an L_x X L_y lattice. Scaling arguments and extensive numerical simulations are used to show that starting from random initial configuration the model evolves via two stages: (a) an early stage in which alternating stripes of particles and vacancies are formed along the direction y of the driving field, and (b) a stripe coarsening stage, in which the number of stripes is reduced and their average width increases. The number of stripes formed at the end of the first stage is shown to be a function of L_x/L_y^\phi, with \phi ~ 0.2. Thus, depending on this parameter, the resulting state could be either single or multi striped. In the second, stripe coarsening stage, the coarsening time is found to be proportional to L_y, becoming infinitely long in the thermodynamic limit. This implies that the multi striped state is thermodynamically stable. The results put previous studies of the model in a more general framework

An instrument to guide instructors of undergraduate experimental programs: A comment on findings from physics

Degree programs usually have a series of experimental activities, ranging from practicals, investigations, projects, to field work, forming a contained program often referred to as the ‘undergraduate experimental program’. The experimental program provides students with an understanding of the processes of science, contributes to student experiences and is relevant for mapping against graduate qualities – soft skills. While extant literature points to evaluations of individual experiments (Barrie et al., 2015; Yeung, Cornish, Kable, & Sharma, 2019), evaluations of complete experimental programs are rare. To this end, we have developed the ASELL Laboratory Program Evaluation (ALPE) survey for eliciting student experiences of undergraduate experimental programs. The ALPE was administered with 9790 students in 71 programs at 10 Australian universities, in five disciplines. Based on exploratory factor analysis, two factors emerged: the first factor included ALPE items relating to how the laboratory program influenced students’ science discipline knowledge and skills; the second factor included ALPE items related to how well the course contributed to development of general capabilities, such as items about “teamwork” and “ethics”. Herzberg’s 1968 Two Factor Motivation-Hygiene theory originated in the organisational psychology sphere and has since been applied in various educational settings. The “motivation” factor refers to the elements of work that enhance a person’s satisfaction – associated with achievement and competency. The “hygiene” factor refers to the elements of work that include the provision of resources and support, such as supervision practices and procedures. In this presentation, we demonstrate how the “motivation-hygiene” theory applies to the two factors that emerged from the ALPE survey data, and how it can provide a meaningful framework for interpreting students’ perspectives of their undergraduate laboratory programs. Finally, we comment on the findings from physics within this data set – of the five disciplines included in the large study of the ALPE survey, physics is a standout with lower correlations between individual items and overall laboratory program experience. REFERENCES Barrie, S. C., Bucat, R. B., Buntine, M. A., Burke da Silva, K., Crisp, G. T., George, A. V., Jamie, I. M., Kable, S. H., Lim, K. F., Pyke, S. M., Read, J. R., Sharma M. D., and Yeung A. A (2015) Development, Evaluation and Use of a Student Experience Survey in Undergraduate Science Laboratories: The Advancing Science by Enhancing Learning in the Laboratory Student Laboratory Learning Experience Survey. International Journal of Science Education, 37(11), 1795-1814. Herzberg, F. (1968). "One More Time: How Do You Motivate Employees?". Harvard Business Review, 46(1), 53–62, OCLC 219963337. Yeung, A., S. Cornish, S. Kable, and M. Sharma. (2019). "What can instructors focus on when improving undergraduate science experiments? Supporting a cross- disciplinary approach." International Journal of Innovation in Science and Mathematics Education, 27(3), 25-40

Non-equilibrium interface equations: An application to thermo-capillary motion in binary systems

Interface equations are derived for both binary diffusive and binary fluid systems subjected to non-equilibrium conditions, starting from the coarse-grained (mesoscopic) models. The equations are used to describe thermo-capillary motion of a droplet in both purely diffusive and fluid cases, and the results are compared with numerical simulations. A mesoscopic chemical potential shift, owing to the temperature gradient, and associated mesoscopic corrections involved in droplet motion are elucidated.Comment: 12 pages; Latex, revtex, ap

Coenzyme Q10 dose-escalation study in hemodialysis patients: safety, tolerability, and effect on oxidative stress.

BackgroundCoenzyme Q10 (CoQ10) supplementation improves mitochondrial coupling of respiration to oxidative phosphorylation, decreases superoxide production in endothelial cells, and may improve functional cardiac capacity in patients with congestive heart failure. There are no studies evaluating the safety, tolerability and efficacy of varying doses of CoQ10 in chronic hemodialysis patients, a population subject to increased oxidative stress.MethodsWe performed a dose escalation study to test the hypothesis that CoQ10 therapy is safe, well-tolerated, and improves biomarkers of oxidative stress in patients receiving hemodialysis therapy. Plasma concentrations of F2-isoprostanes and isofurans were measured to assess systemic oxidative stress and plasma CoQ10 concentrations were measured to determine dose, concentration and response relationships.ResultsFifteen of the 20 subjects completed the entire dose escalation sequence. Mean CoQ10 levels increased in a linear fashion from 704 ± 286 ng/mL at baseline to 4033 ± 1637 ng/mL, and plasma isofuran concentrations decreased from 141 ± 67.5 pg/mL at baseline to 72.2 ± 37.5 pg/mL at the completion of the study (P = 0.003 vs. baseline and P < 0.001 for the effect of dose escalation on isofurans). Plasma F2-isoprostane concentrations did not change during the study.ConclusionsCoQ10 supplementation at doses as high as 1800 mg per day was safe in all subjects and well-tolerated in most. Short-term daily CoQ10 supplementation decreased plasma isofuran concentrations in a dose dependent manner. CoQ10 supplementation may improve mitochondrial function and decrease oxidative stress in patients receiving hemodialysis.Trial registrationThis clinical trial was registered on clinicaltrials.gov [NCT00908297] on May 21, 2009

Coherence of Nitrogen-Vacancy Electronic Spin Ensembles in Diamond

We present an experimental and theoretical study of electronic spin decoherence in ensembles of nitrogen-vacancy (NV) color centers in bulk high-purity diamond at room temperature. Under appropriate conditions, we find ensemble NV spin coherence times (T_2) comparable to that of single NVs, with T_2 > 600 microseconds for a sample with natural abundance of 13C and paramagnetic impurity density ~10^15 cm^(-3). We also observe a sharp decrease of the coherence time with misalignment of the static magnetic field relative to the NV electronic spin axis, consistent with theoretical modeling of NV coupling to a 13C nuclear spin bath. The long coherence times and increased signal-to-noise provided by room-temperature NV ensembles will aid many applications of NV centers in precision magnetometry and quantum information.Comment: 5 pages, 3 figures; v2 minor correction

Evolution of speckle during spinodal decomposition

Time-dependent properties of the speckled intensity patterns created by scattering coherent radiation from materials undergoing spinodal decomposition are investigated by numerical integration of the Cahn-Hilliard-Cook equation. For binary systems which obey a local conservation law, the characteristic domain size is known to grow in time $\tau$ as $R = [B \tau]^n$ with n=1/3, where B is a constant. The intensities of individual speckles are found to be nonstationary, persistent time series. The two-time intensity covariance at wave vector ${\bf k}$ can be collapsed onto a scaling function $Cov(\delta t,\bar{t})$, where $\delta t = k^{1/n} B |\tau_2-\tau_1|$ and $\bar{t} = k^{1/n} B (\tau_1+\tau_2)/2$. Both analytically and numerically, the covariance is found to depend on $\delta t$ only through $\delta t/\bar{t}$ in the small-$\bar{t}$ limit and $\delta t/\bar{t} ^{1-n}$ in the large-$\bar{t}$ limit, consistent with a simple theory of moving interfaces that applies to any universality class described by a scalar order parameter. The speckle-intensity covariance is numerically demonstrated to be equal to the square of the two-time structure factor of the scattering material, for which an analytic scaling function is obtained for large $\bar{t}.$ In addition, the two-time, two-point order-parameter correlation function is found to scale as $C(r/(B^n\sqrt{\tau_1^{2n}+\tau_2^{2n}}),\tau_1/\tau_2)$, even for quite large distances $r$. The asymptotic power-law exponent for the autocorrelation function is found to be $\lambda \approx 4.47$, violating an upper bound conjectured by Fisher and Huse.Comment: RevTex: 11 pages + 12 figures, submitted to PR

A Geometric Variational Approach to Bayesian Inference

We propose a novel Riemannian geometric framework for variational inference in Bayesian models based on the nonparametric Fisher-Rao metric on the manifold of probability density functions. Under the square-root density representation, the manifold can be identified with the positive orthant of the unit hypersphere in L2, and the Fisher-Rao metric reduces to the standard L2 metric. Exploiting such a Riemannian structure, we formulate the task of approximating the posterior distribution as a variational problem on the hypersphere based on the alpha-divergence. This provides a tighter lower bound on the marginal distribution when compared to, and a corresponding upper bound unavailable with, approaches based on the Kullback-Leibler divergence. We propose a novel gradient-based algorithm for the variational problem based on Frechet derivative operators motivated by the geometry of the Hilbert sphere, and examine its properties. Through simulations and real-data applications, we demonstrate the utility of the proposed geometric framework and algorithm on several Bayesian models

Fast Domain Growth through Density-Dependent Diffusion in a Driven Lattice Gas

We study electromigration in a driven diffusive lattice gas (DDLG) whose continuous Monte Carlo dynamics generate higher particle mobility in areas with lower particle density. At low vacancy concentrations and low temperatures, vacancy domains tend to be faceted: the external driving force causes large domains to move much more quickly than small ones, producing exponential domain growth. At higher vacancy concentrations and temperatures, even small domains have rough boundaries: velocity differences between domains are smaller, and modest simulation times produce an average domain length scale which roughly follows $L \sim t^{\zeta}$, where $\zeta$ varies from near .55 at 50% filling to near .75 at 70% filling. This growth is faster than the $t^{1/3}$ behavior of a standard conserved order parameter Ising model. Some runs may be approaching a scaling regime. At low fields and early times, fast growth is delayed until the characteristic domain size reaches a crossover length which follows $L_{cross} \propto E^{-\beta}$. Rough numerical estimates give $\beta= >.37$ and simple theoretical arguments give $\beta= 1/3$. Our conclusion that small driving forces can significantly enhance coarsening may be relevant to the YB$_2$Cu$_3$O$_{7- \delta}$ electromigration experiments of Moeckly {\it et al.}(Appl. Phys. Let., {\bf 64}, 1427 (1994)).Comment: 18 pages, RevTex3.

Observing two dark accelerators around the Galactic Centre with Fermi Large Area Telescope

We report the results from a detailed $\gamma-$ray investigation in the field of two "dark accelerators", HESS J1745-303 and HESS J1741-302, with $6.9$ years of data obtained by the Fermi Large Area Telescope. For HESS J1745-303, we found that its MeV-GeV emission is mainly originated from the "Region A" of the TeV feature. Its $\gamma-$ray spectrum can be modeled with a single power-law with a photon index of $\Gamma\sim2.5$ from few hundreds MeV to TeV. Moreover, an elongated feature, which extends from "Region A" toward northwest for $\sim1.3^{\circ}$, is discovered for the first time. The orientation of this feature is similar to that of a large scale atomic/molecular gas distribution. For HESS J1741-302, our analysis does not yield any MeV-GeV counterpart for this unidentified TeV source. On the other hand, we have detected a new point source, Fermi J1740.1-3013, serendipitously. Its spectrum is apparently curved which resembles that of a $\gamma-$ray pulsar. This makes it possibly associated with PSR B1737-20 or PSR J1739-3023.Comment: 11 pages, 7 figures, 2 tables, accepted for publication in MNRA