Survival and coexistence for a multitype contact process

We study the ergodic theory of a multitype contact process with equal death rates and unequal birth rates on the $d$-dimensional integer lattice and regular trees. We prove that for birth rates in a certain interval there is coexistence on the tree, which by a result of Neuhauser is not possible on the lattice. We also prove a complete convergence result when the larger birth rate falls outside of this interval.Comment: Published in at http://dx.doi.org/10.1214/08-AOP422 the Annals of Probability (http://www.imstat.org/aop/) by the Institute of Mathematical Statistics (http://www.imstat.org

A Branching Process for Virus Survival

Quasispecies theory predicts that there is a critical mutation probability above which a viral population will go extinct. Above this threshold the virus loses the ability to replicate the best adapted genotype, leading to a population composed of low replicating mutants that is eventually doomed. We propose a new branching model that shows that this is not necessarily so. That is, a population composed of ever changing mutants may survive

Web Applet For Predicting Structure And Thermodynamics Of Complex Fluids

Based on a recently introduced analytical strategy [Hollingshead et al., J. Chem. Phys. 139, 161102 (2013)], we present a web applet that can quickly and semi-quantitatively estimate the equilibrium radial distribution function and related thermodynamic properties of a fluid from knowledge of its pair interaction. We describe the applet's features and present two (of many possible) examples of how it can be used to illustrate concepts of interest for introductory statistical mechanics courses: the transition from ideal gas-like behavior to correlated-liquid behavior with increasing density, and the tradeoff between dominant length scales with changing temperature in a system with ramp-shaped repulsions. The latter type of interaction qualitatively captures distinctive thermodynamic properties of liquid water, because its energetic bias toward locally open structures mimics that of water's hydrogen-bond network. (C) 2015 American Association of Physics Teachers.Chemical Engineerin

CO Line Emission and Absorption from the HL Tau Disk: Where is all the dust?

We present high-resolution infrared spectra of HL Tau, a heavily embedded young star. The spectra exhibit broad emission lines of hot CO gas as well as narrow absorption lines of cold CO gas. The column density for this cooler material (7.5+/-0.2 x 10^18 cm-2) indicates a large column of absorbing gas along the line of sight. In dense interstellar clouds, this column density of CO gas is associated with Av~52 magnitudes. However, the extinction toward this source (Av~23) suggests that there is less dust along the line of sight than inferred from the CO absorption data. We discuss three possibilities for the apparent paucity of dust along the line of sight through the flared disk: 1) the dust extinction has been underestimated due to differences in circumstellar grain properties, such as grain agglomeration; 2) the effect of scattering has been underestimated and the actual extinction is much higher; or (3) the line of sight through the disk is probing a gas-rich, dust-depleted region, possibly due to the stratification of gas and dust in a pre-planetary disk.Comment: To be published in The Astrophysical Journa

SUPPLY CHAIN INTEGRATION IN THE FOOD AND CONSUMER GOODS INDUSTRIES

The interorganizational structures necessary to implement and achieve the logistical performance improvements identified in the Efficient Consumer Response (ECR) initiative and related supply chain management concepts are difficult to develop. Firms continue to struggle to implement integrated programs and techniques, particularly with respect to changing operating structures, relationships, and mindsets to facilitate true supply chain integration. This research explores the logistical strategies and structures used by selected food and consumer goods firms to integrate their supply chains. It illustrates effective integration strategies and identifies critical success factors and barriers to successful ECR implementation. A framework is used to guide managers in developing the competencies essential to integrating the supply chain and to establishing the relationships necessary to operate in an ECR environment. The framework, entitled Supply Chain 2000, depicts supply chain value creation as achieving synchronization and coordination across four critical supply chain flows: product/service; market accommodation; information; and cash.Industrial Organization,