The Universe With Bulk Viscosity

Exact solutions for a model with variable $G$, $\Lambda$ and bulk viscosity are obtained. Inflationary solutions with constant (de Sitter-type) and variable energy density are found. An expanding anisotropic universe is found to isotropize during its course of expansion but a static universe is not. The gravitational constant is found to increase with time and the cosmological constant decreases with time as $\Lambda \propto t^{-2}$.Comment: 7 LateX pages, no figure

Effect of Strategic Human Resource Management Practices on Organizational Commitment

The research investigates the association between strategic human resource management techniques across many dimensions (Training, Performance appraisal, Selection, and compensation) and organizational commitment at the Middle East Food Trading Company in the Kingdom of Bahrain. The study selected and employed a descriptive quantitative research approach to fulfill the study goals via the use of a survey questionnaire designed for data collecting. The target sample consisted of personnel from the Middle East Food Trading Company in the Kingdom of Bahrain, with a total of 105 participants in this research. The findings revealed that strategic human resource management techniques (Training, Selection, and Compensation) had a statistically significant association with organizational commitment at the level of significance (0.05%). The data also revealed that the association between performance appraisal and organizational commitment was insignificant. The research proposed that the Middle East Food Trading Company combine and implement numerous training activities at all levels in respect to the varied practices of strategic human resources

Integrated Structure and Semantics for Reo Connectors and Petri Nets

In this paper, we present an integrated structural and behavioral model of Reo connectors and Petri nets, allowing a direct comparison of the two concurrency models. For this purpose, we introduce a notion of connectors which consist of a number of interconnected, user-defined primitives with fixed behavior. While the structure of connectors resembles hypergraphs, their semantics is given in terms of so-called port automata. We define both models in a categorical setting where composition operations can be elegantly defined and integrated. Specifically, we formalize structural gluings of connectors as pushouts, and joins of port automata as pullbacks. We then define a semantical functor from the connector to the port automata category which preserves this composition. We further show how to encode Reo connectors and Petri nets into this model and indicate applications to dynamic reconfigurations modeled using double pushout graph transformation

Quantitative analysis of reo- based service coordination

Quality of Service analysis of composed software systems is an active research area, with the goal of evaluating and improving performance and resource allocation in serviceoriented applications, namely, in the glue code –coordination layer– of such systems. Stochastic Reo offers constructs for service coordination and allows the specification of stochastic values for channels. But its state-of-the-art semantic models fail in several (important) ways. In this paper, we will see how Interactive Markov chains (IMC), proposed as astochastic compositional model of concurrency, can be effectively used to serve as a compositional semantic model for Stochastic Reo. Treating IMC as a direct semantic model, gives rise to more faithful models and has obvious efficiency advantages. Moreover, tool support that exists for IMC is made available, without significant effort, to verify and reason about the coordination layer modelled as Reo connectors.(undefined

Generalized phantom energy

We examine cosmological models with generalized phantom energy (GPE). Generalized phantom energy satisfies the supernegative equation of state, but its evolution with the scale factor is generally independent, i.e. not determined by its equation of state. The requirement of general covariance makes the gravitational constant time-dependent. It is found that a large class of distinct GPE models with different evolution of generalized phantom energy density and gravitational constant, but the same equation of state of GPE have the same evolution of the scale factor of the universe in the distant future. The time dependence of the equation of state parameter determines whether the universe will end in a de Sitter-like phase or diverge in finite time with the accompanying "Big Rip" effect on the bound structures.Comment: v1: 9 pages. v2: version to appear in Phys. Lett.

Coordination via Interaction Constraints I: Local Logic

Wegner describes coordination as constrained interaction. We take this approach literally and define a coordination model based on interaction constraints and partial, iterative and interactive constraint satisfaction. Our model captures behaviour described in terms of synchronisation and data flow constraints, plus various modes of interaction with the outside world provided by external constraint symbols, on-the-fly constraint generation, and coordination variables. Underlying our approach is an engine performing (partial) constraint satisfaction of the sets of constraints. Our model extends previous work on three counts: firstly, a more advanced notion of external interaction is offered; secondly, our approach enables local satisfaction of constraints with appropriate partial solutions, avoiding global synchronisation over the entire constraints set; and, as a consequence, constraint satisfaction can finally occur concurrently, and multiple parts of a set of constraints can be solved and interact with the outside world in an asynchronous manner, unless synchronisation is required by the constraints. This paper describes the underlying logic, which enables a notion of local solution, and relates this logic to the more global approach of our previous work based on classical logic

Fluorinated perovskite as magnetic spin-polarised semiconductor

Much work has been done on cation substitution of manganese perovskites, but less on anion substitution. Recently there have been reports on fluorination of these compounds, generally leading to double perovskite structures. This work explores the effect of fluorine substitution on the magnetic and electrical properties of the perovskite cubic strontium manganite using first principles DFT calculations. Results on fluorine-doped strontium manganite with one or two fluoride ions surrounding each iron are presented. The ground state of Sr2Mn2O5F is found to be a small band gap spin-biased semiconductor. This is the first proposal that a fluorinated manganite could be a ferromagnetic spin-polarised semiconductor