1,384 research outputs found

    A zero dimensional model of lithium-sulfur batteries during charge and discharge

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    Lithium-sulfur cells present an attractive alternative to Li-ion batteries due to their large energy density, safety, and possible low cost. Their successful commercialisation is dependent on improving their performance, but also on acquiring sufficient understanding of the underlying mechanisms to allow for the development of predictive models for operational cells. To address the latter, we present a zero dimensional model that predicts many observed features in the behaviour of a lithium-sulfur cell during charge and discharge. The model accounts for two electrochemical reactions via the Nernst formulation, power limitations through Butler-Volmer kinetics, and precipitation/dissolution of one species, including nucleation. It is shown that the precipitation/dissolution causes the flat shape of the low voltage plateau, typical of the lithium-sulfur cell discharge. During charge, it is predicted that the dissolution can act as a bottleneck, as for large enough currents smaller amounts dissolve. This results in reduced charge capacity and an earlier onset of the high plateau reaction, such that the two plateaus merge. By including these effects, the model improves on the existing zero dimensional models, while requiring considerably fewer input parameters and computational resources. The model also predicts that, due to precipitation, the customary way of experimentally measuring the open circuit voltage from a low rate discharge might not be suitable for lithium-sulfur. This model can provide the basis for mechanistic studies, identification of dominant effects in a real cell, predictions of operational behaviour under realistic loads, and control algorithms for applications

    Organismic Supercategories: I. Proposals for a General Unified Theory of Systems- Classical, Quantum, and Complex Biological Systems.\ud \ud \ud

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    The representation of physical and complex biological systems in terms of organismic supercategories was introduced in 1968 by Baianu and Marinescu in the attached paper which was published in the Bulletin of Mathematical Biophysics, edited by Nicolas Rashevsky. The different approaches to relational biology, developed by Rashevsky, Rosen and by Baianu et al.(1968,1969,1973,1974,1987,2004)were later discussed. \ud The present paper is an attempt to outline an abstract unitary theory of systems. In the introduction some of the previous abstract representations of systems are discussed. Also a possible connection of abstract representations of systems with a general theory of measure is proposed. Then follow some necessary definitions and authors' proposals for an axiomatic theory of systems. Finally some concrete examples are analyzed in the light of the proposed theory.\ud \ud An abstract representation of biological systems from the standpoint of the theory of supercategories is presented. The relevance of such representations forG-relational biologies is suggested. In section A the basic concepts of our representation, that is class, system, supercategory and measure are introduced. Section B is concerned with the mathematical representation starting with some axioms and principles which are natural extensions of the current abstract representations in biology. Likewise, some extensions of the principle of adequate design are introduced in section C. Two theorems which present the connection between categories and supercategories are proved. Two other theorems concerning the dynamical behavior of biological and biophysical systems are derived on the basis of the previous considerations. Section D is devoted to a general study of oscillatory behavior in enzymic systems, some general quantitative relations being derived from our representation. Finally, the relevance of these results for a quantum theoretic approach to biology is discussed.\ud \ud http://www.springerlink.com/content/141l35843506596h

    THE DIVERSITY OF HETEROTROPHIC BACTERIAL MICROFLORA IN SOIL POLLUTED WITH CRUDE OIL AND DIFFERENT TREATMENTS

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    Petroleum hydrocarbon pollution is one of the main environmental problems, not only bythe important amounts released but also because of their toxicity. It is known that the mainmicroorganisms consuming petroleum hydrocarbons are bacteria. The present researchwork reports the diversity of microrganis from crude oil polluted soil been treated with anatural biodegradable product and bacterial inoculum. The bacterial inoculum was used toenrich indigenous microbes to enhance biodegradation rate. In soil excessively polluted with crude oil, bacterial population size in conditioned variant with Ecosol maximum dose (1%) presented values comparable to those of inoculated variants, demonstrating the protective and stimulation effect of soil bacteria, including those involved in the degradation of petroleum hydrocarbons exercised by organic compound applied Ecosol

    The Spin Mass of an Electron Liquid

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    We show that in order to calculate correctly the {\it spin current} carried by a quasiparticle in an electron liquid one must use an effective "spin mass" msm_s, that is larger than both the band mass, mbm_b, which determines the charge current, and the quasiparticle effective mass m‚ąóm^*, which determines the heat capacity. We present microscopic calculations of msm_s in a paramagnetic electron liquid in three and two dimensions, showing that the mass enhancement ms/mbm_s/m_b can be a very significant effect.Comment: 10 pages, 1 figur

    Finite-size Effects in a Two-Dimensional Electron Gas with Rashba Spin-Orbit Interaction

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    Within the Kubo formalism, we estimate the spin-Hall conductivity in a two-dimensional electron gas with Rashba spin-orbit interaction and study its variation as a function of disorder strength and system size. The numerical algorithm employed in the calculation is based on the direct numerical integration of the time-dependent Schrodinger equation in a spin-dependent variant of the particle source method. We find that the spin-precession length, L_s controlled by the strength of the Rashba coupling, establishes the critical lengthscale that marks the significant reduction of the spin-Hall conductivity in bulk systems. In contrast, the electron mean free path, inversely proportional to the strength of disorder, appears to have only a minor effect.Comment: 5 pages, 3 figure

    Spin-Hall Effect in A Symmetric Quantum Wells by A Random Rashba Field

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    Changes dopant ion concentrations in the sides of a symmetric quantum well are known to create a random Rashba-type spin-orbit coupling. Here we demonstrate that, as a consequence, a finite size spin-Hall effect is also present. Our numerical algorithm estimates the result of the Kubo formula for the spin-Hall conductivity, by using a tight-binding approximation of the Hamiltonian in the framework of a time-dependent Green's function formalism, well suited for very large systems.Comment: 4 pages, 4 figures in eps forma
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