Coarsening dynamics of ternary amphiphilic fluids and the self-assembly of the gyroid and sponge mesophases: lattice-Boltzmann simulations

By means of a three-dimensional amphiphilic lattice-Boltzmann model with short-range interactions for the description of ternary amphiphilic fluids, we study how the phase separation kinetics of a symmetric binary immiscible fluid is altered by the presence of the amphiphilic species. We find that a gradual increase in amphiphile concentration slows down domain growth, initially from algebraic, to logarithmic temporal dependence, and, at higher concentrations, from logarithmic to stretched-exponential form. In growth-arrested stretched-exponential regimes, at late times we observe the self-assembly of sponge mesophases and gyroid liquid crystalline cubic mesophases, hence confirming that (a) amphiphile-amphiphile interactions need not be long-ranged in order for periodically modulated structures to arise in a dynamics of competing interactions, and (b) a chemically-specific model of the amphiphile is not required for the self-assembly of cubic mesophases, contradicting claims in the literature. We also observe a structural order-disorder transition between sponge and gyroid phases driven by amphiphile concentration alone or, independently, by the amphiphile-amphiphile and the amphiphile-binary fluid coupling parameters. For the growth-arrested mesophases, we also observe temporal oscillations in the structure function at all length scales; most of the wavenumbers show slow decay, and long-term stationarity or growth for the others. We ascribe this behaviour to a combination of complex amphiphile dynamics leading to Marangoni flows.Comment: 16 pages, 13 figures. Accepted for publication in Phys. Rev. E. (Replaced for the latest version, in press.) Higher-quality figures can be sent upon reques

A new class of highly efficient exact stochastic simulation algorithms for chemical reaction networks

We introduce an alternative formulation of the exact stochastic simulation algorithm (SSA) for sampling trajectories of the chemical master equation for a well-stirred system of coupled chemical reactions. Our formulation is based on factored-out, partial reaction propensities. This novel exact SSA, called the partial propensity direct method (PDM), is highly efficient and has a computational cost that scales at most linearly with the number of chemical species, irrespective of the degree of coupling of the reaction network. In addition, we propose a sorting variant, SPDM, which is especially efficient for multiscale reaction networks.Comment: 23 pages, 3 figures, 4 tables; accepted by J. Chem. Phy

Turnover Intent Among Middle School Teachers

The purpose of the study was to examine the relations among mentoring, adaptation, satisfaction, commitment, and turnover intention. Two-hundred fifty two middle school teachers from ten Midwestern U.S. schools were surveyed. Hierarchical regression results demonstrated that positive mentoring experiences, successful adaptation, and greater commitment reduced the likelihood of turnover intent

Stress response and structural transitions in sheared gyroidal and lamellar amphiphilic mesophases: lattice-Boltzmann simulations

We report on the stress response of gyroidal and lamellar amphiphilic mesophases to steady shear simulated using a bottom-up lattice-Boltzmann model for amphiphilic fluids and sliding periodic (Lees-Edwards) boundary conditions. We study the gyroid per se (above the sponge-gyroid transition, of high crystallinity) and the molten gyroid (within such a transition, of shorter-range order). We find that both mesophases exhibit shear-thinning, more pronounced and at lower strain rates for the molten gyroid. At late times after the onset of shear, the skeleton of the crystalline gyroid becomes a structure of interconnected irregular tubes and toroidal rings, mostly oriented along the velocity ramp imposed by the shear, in contradistinction with free-energy Langevin-diffusion studies which yield a much simpler structure of disentangled tubes. We also compare the shear stress and deformation of lamellar mesophases with and without amphiphile when subjected to the same shear flow applied normal to the lamellae. We find that the presence of amphiphile allows (a) the shear stress at late times to be higher than in the case without amphiphile, and (b) the formation of rich patterns on the sheared interface, characterised by alternating regions of high and low curvature.Comment: 15 pages, 10 figures, Physical Review E, in pres

Severe Withdrawal Syndrome Possibly Associated With Cessation of a Midazolam and Fentanyl Infusion

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90212/1/j.1875-9114.1995.tb02877.x.pd

Steering in computational science: mesoscale modelling and simulation

This paper outlines the benefits of computational steering for high performance computing applications. Lattice-Boltzmann mesoscale fluid simulations of binary and ternary amphiphilic fluids in two and three dimensions are used to illustrate the substantial improvements which computational steering offers in terms of resource efficiency and time to discover new physics. We discuss details of our current steering implementations and describe their future outlook with the advent of computational grids.Comment: 40 pages, 11 figures. Accepted for publication in Contemporary Physic

Genetic analysis of Theileria orientalis population in cattle following a theileriosis outbreak in Victoria, Australia

Dissertação de Mestrado Integrado em Medicina VeterináriaBovine theileriosis is a tick-borne disease caused by one or more haemoprotozoan parasites of the genus Theileria. In the past, Theileria infection in cattle in Australia was largely asymptomatic and recognized to be associated with Theileria buffeli. However, in the recent years, outbreaks of theileriosis have occurred in beef and dairy cattle in subtropical climatic regions (New South Wales) of Australia. There is also one published report of a recent theileriosis outbreak on a beef farm near Seymour in the south-eastern state of Victoria. In order to gain an improved insight into the genetic composition of Theileria populations following this outbreak, we undertook herein an integrated PCR-coupled mutation scanning-sequencing-phylogenetic analysis of sequence variation in part of the major piroplasm surface protein (MPSP) gene within and among samples from cattle involved in the outbreak. Theileria DNA was detected in 89.4% of 94 cattle on the Seymour farm; the genetic analysis showed that the ikeda and chitose genotypes representing the Theileria orientalis complex were detected in 75% and 4.8% of 84 infected cattle, respectively, and that mixed populations of these two genotypes were found in 20.2% of infected cattle. Given unpublished reports of a significant increase in the number of outbreaks in Victoria, future investigations should focus sharply on elucidating the epidemiology of Theileria to subvert the economic impact on the cattle industry in this state. Although used here to explore genetic variation within the T. orientalis complex in Australia, a mutation scanning-based approach has broad applicability to other species of Theileria in other countries.RESUMO - ANÁLISE GENÉTICA DE POPULAÇÕES DE THEILERIA ORIENTALIS, EM BOVINOS, APÓS UM SURTO DE THEILERIOSE EM VITORIA, AUSTRÁLIA - A teileriose é uma doença transmitida por carraças e causada por hemoprotozoários pertencentes a uma ou mais espécies do género Theileria. Historicamente, a infecção de gado na Austrália, com este parasita, é considerada assintomática e associada especificamente à espécie Theileria buffeli. Contudo, nos últimos anos, surtos de teileriose têm ocorrido tanto em explorações de carne como de leite em regiões de clima subtropical da Austrália (Nova Gales do Sul). Recentemente foi publicado um relatório, correspondente a um surto de teileriose perto de Seymour, Victoria, um estado a sudeste do país. A fim de obter uma melhor compreensão sobre a composição genética das populações de Theileria envolvidas neste surto, foi levado a cabo um sistema de análise integrada de PCR - análise de mutações – sequenciação– filogenia, das variações existentes na sequência de parte do gene codificador da principal proteína de superfície do piroplasma (major piroplasm surface protein – MPSP), dentro e entre diferentes amostras provenientes de animais residentes na exploração envolvida no surto. O ADN do parasita foi detectado em 89,4% de 94 bovinos testados, na exploração de Seymour e a subsequente análise genética mostrou que os genótipos Ikeda e Chitose, representativos do complexo formado por diferentes estirpes pertencentes à espécie Theileria orientalis, foram detectados em 75% e 4,8% de 84 animais infectados, respectivamente, e que populações mistas compostas por ambos os genótipos foram detectadas em 20,2% desses mesmos animais. Dado que, relatórios não publicados apontam para um aumento significativo do número de surtos de teileriose em Victoria, futuras investigações deverão centrar-se fortemente na elucidação da epidemiologia deste parasita, a fim de avaliar o impacto económico que este poderá ter sobre a indústria bovina neste Estado. Ademais, apesar de usados neste estudo para explorar a variação genética das populações de T. orientalis na Austrália, uma abordagem baseada na análise de mutações tem ampla aplicabilidade para outras espécies de Theileria presentes em outros países

Three-dimensional lattice-Boltzmann simulations of critical spinodal decomposition in binary immiscible fluids

We use a modified Shan-Chen, noiseless lattice-BGK model for binary immiscible, incompressible, athermal fluids in three dimensions to simulate the coarsening of domains following a deep quench below the spinodal point from a symmetric and homogeneous mixture into a two-phase configuration. We find the average domain size growing with time as $t^\gamma$, where $\gamma$ increases in the range $0.545 < \gamma < 0.717$, consistent with a crossover between diffusive $t^{1/3}$ and hydrodynamic viscous, $t^{1.0}$, behaviour. We find good collapse onto a single scaling function, yet the domain growth exponents differ from others' works' for similar values of the unique characteristic length and time that can be constructed out of the fluid's parameters. This rebuts claims of universality for the dynamical scaling hypothesis. At early times, we also find a crossover from $q^2$ to $q^4$ in the scaled structure function, which disappears when the dynamical scaling reasonably improves at later times. This excludes noise as the cause for a $q^2$ behaviour, as proposed by others. We also observe exponential temporal growth of the structure function during the initial stages of the dynamics and for wavenumbers less than a threshold value.Comment: 45 pages, 18 figures. Accepted for publication in Physical Review

Cooperative Virus-Virus Interactions: An Evolutionary Perspective

Despite extensive evidence of virus-virus interactions, not much is known about their biological significance. Importantly, virus-virus interactions could have evolved as a form of cooperation or simply be a by-product of other processes. Here, we review anddiscuss different types of virus-virus interactions from the point of view of social evolution, which provides a well-establishedframework for interpreting thefitness costs and benefits of such traits. We also classify interactions according to theirmechanisms of action and speculate on their evolutionary implications. As in any other biological system, the evolutionarystability of viral cooperation critically requires cheaters to be excluded from cooperative interactions. We discuss how cheaterviruses exploit cooperative traits and how viral populations are able to counteract this maladaptive process