706 research outputs found
The Universe With Bulk Viscosity
Exact solutions for a model with variable , 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 .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
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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
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