345 research outputs found
Electroreduction of silicon from the NaI–KI–K2SiF6 melt for lithium-ion power sources
Silicon and silicon-based materials are increasingly used in microelectronics, metallurgy and power generation. To date the active study aimed at the development of silicon materials to be used in devices for solar energy conversion, accumulation and storage is underway. In addition, silicon is a promising anode material for lithium-ion fuel cells. In the present paper a possibility of silicon electroreduction from the NaI–KI–K2SiF6 melt in the argon atmosphere is studied. With this aim in view the electrolysis of the NaI–KI–K2SiF6 melt with glassy carbon cathode was performed under galvanostatic and potentiostatic regimes at the temperatures ranging from 650 to 750 °С. The morphology, phase and elemental analyses of the obtained silicon deposits were performed after their separation from the electrolytes by the ICP, SEM-EDX, XRD and Raman spectroscopy methods. Fiber and thread-like silicon samples of 60 to 320 nm in dimeter with admixtures concentrations (mainly oxygen) from 1.2 to 4.6 wt.% were experimentally synthesized. The obtained samples were tested as possible Si/C composite anodes for lithium-ion power sources. The discharge capacity of such power sources after 30 cycles of lithiation-delithiation ranged from 440 to 565 mAh·g–1 and the coloumbic efficiency ranged from 89 to 91%
Critical sound attenuation in a diluted Ising system
The field-theoretic description of dynamical critical effects of the
influence of disorder on acoustic anomalies near the temperature of the
second-order phase transition is considered for three-dimensional Ising-like
systems. Calculations of the sound attenuation in pure and dilute Ising-like
systems near the critical point are presented. The dynamical scaling function
for the critical attenuation coefficient is calculated. The influence of
quenched disorder on the asymptotic behaviour of the critical ultrasonic
anomalies is discussed.Comment: 12 RevTeX pages, 4 figure
Eigenvalue estimates for non-selfadjoint Dirac operators on the real line
We show that the non-embedded eigenvalues of the Dirac operator on the real
line with non-Hermitian potential lie in the disjoint union of two disks in
the right and left half plane, respectively, provided that the of
is bounded from above by the speed of light times the reduced Planck
constant. An analogous result for the Schr\"odinger operator, originally proved
by Abramov, Aslanyan and Davies, emerges in the nonrelativistic limit. For
massless Dirac operators, the condition on implies the absence of nonreal
eigenvalues. Our results are further generalized to potentials with slower
decay at infinity. As an application, we determine bounds on resonances and
embedded eigenvalues of Dirac operators with Hermitian dilation-analytic
potentials
Eigenvalue bounds for Schr\"odinger operators with a homogeneous magnetic field
We prove Lieb-Thirring inequalities for Schr\"odinger operators with a
homogeneous magnetic field in two and three space dimensions. The inequalities
bound sums of eigenvalues by a semi-classical approximation which depends on
the strength of the magnetic field, and hence quantifies the diamagnetic
behavior of the system. For a harmonic oscillator in a homogenous magnetic
field, we obtain the sharp constants in the inequalities.Comment: 12 page
Lieb-Thirring inequalities for geometrically induced bound states
We prove new inequalities of the Lieb-Thirring type on the eigenvalues of
Schr\"odinger operators in wave guides with local perturbations. The estimates
are optimal in the weak-coupling case. To illustrate their applications, we
consider, in particular, a straight strip and a straight circular tube with
either mixed boundary conditions or boundary deformations.Comment: LaTeX2e, 14 page
Avaliação dos aspectos financeiros das pequenas e médias empresas: experiência russa
The aim of this study was to assess the key financials of an array of micro-sized businesses, small and medium-sized enterprises as grouped by industry. This article deals with the assessment results of such financials as the net financial result of enterprises, the proportion of profitable and loss-making enterprises, the profitability of manufactured and sold products, the current levels of profit and loss, respectively, per profitable and loss-making enterprise. The dynamics of such financials during the period from 2010 to 2014 was presented. Accounting and statistical reporting was used as the input data. In the course of this research it was proven that during that period the profitable enterprises accounted for about 80%. However, the level of profitability did not depend on the size of an enterprise. The largest proportion of profitable enterprises was noted in such sectors as education and commerce. The net financial result per employee in micro-enterprises was significantly higher than those for medium-sized enterprises and small enterprises. The results of this study may be used to validate business development plans and programs for various regions and sectors of the Russian economy. El objetivo de este estudio fue evaluar las finanzas clave de una serie de pequeñas empresas, pequeñas y medianas empresas agrupadas por industria. Este artículo trata de los resultados de la evaluación de tales finanzas como el resultado financiero neto de las empresas, la proporción de empresas rentables y que generan pérdidas, la rentabilidad de los productos fabricados y vendidos, los niveles actuales de ganancias y pérdidas, respectivamente, por rentabilidad y pérdida empresa de creación. La dinámica de tales finanzas durante el período 2010-2014 se presentó. Los informes contables y estadísticos se usaron como datos de entrada. En el curso de esta investigación, se comprobó que durante ese período las empresas rentables representaron aproximadamente el 80%. Sin embargo, el nivel de rentabilidad no depende del tamaño de una empresa. La mayor proporción de empresas rentables se observó en sectores como la educación y el comercio. El resultado financiero neto por empleado en las microempresas fue significativamente mayor que el de las medianas y pequeñas empresas. Los resultados de este estudio pueden usarse para validar planes y programas de desarrollo comercial para diversas regiones y sectores de la economía rusa. O objetivo deste estudo foi avaliar as principais finanças de uma série de microempresas, pequenas e médias empresas agrupadas por setor. Este artigo trata dos resultados da avaliação de tais finanças como o resultado financeiro líquido das empresas, a proporção de empresas lucrativas e deficitárias, a rentabilidade dos produtos fabricados e vendidos, os níveis atuais de lucros e perdas, respectivamente, por lucro e perda empresa de fabricação. A dinâmica de tais finanças durante o período de 2010 a 2014 foi apresentada. Relatórios contábeis e estatísticos foram usados como dados de entrada. No decorrer desta pesquisa, ficou provado que, durante esse período, as empresas lucrativas representavam cerca de 80%. No entanto, o nível de lucratividade não dependia do tamanho de uma empresa. A maior proporção de empresas lucrativas foi observada em setores como educação e comércio. O resultado financeiro líquido por empregado nas microempresas foi significativamente superior ao das médias empresas e pequenas empresas. Os resultados deste estudo podem ser usados para validar planos e programas de desenvolvimento de negócios para várias regiões e setores da economia russa
Experimental study of direct photon emission in K- --> pi- pi0 gamma decay using ISTRA+ detector
The branching ratio in the charged-pion kinetic energy region of 55 to 90 MeV
for the direct photon emission in the K- --> pi- pi0 gamma decay has been
measured using in-flight decays detected with the ISTRA+ setup operating in the
25 GeV/c negative secondary beam of the U-70 PS. The value
Br(DE)=[0.37+-0.39(stat)+-0.10(syst)]*10^(-5) obtained from the analysis of 930
completely reconstructed events is consistent with the average value of two
stopped-kaon experiments, but it differs by 2.5 standard deviations from the
average value of three in-flight-kaon experiments. The result is also compared
with recent theoretical predictions.Comment: 13 pages, 8 figure
Lower order terms in Szego type limit theorems on Zoll manifolds
This is a detailed version of the paper math.FA/0212273. The main motivation
for this work was to find an explicit formula for a "Szego-regularized"
determinant of a zeroth order pseudodifferential operator (PsDO) on a Zoll
manifold. The idea of the Szego-regularization was suggested by V. Guillemin
and K. Okikiolu. They have computed the second term in a Szego type expansion
on a Zoll manifold of an arbitrary dimension. In the present work we compute
the third asymptotic term in any dimension. In the case of dimension 2, our
formula gives the above mentioned expression for the Szego-redularized
determinant of a zeroth order PsDO. The proof uses a new combinatorial
identity, which generalizes a formula due to G.A.Hunt and F.J.Dyson. This
identity is related to the distribution of the maximum of a random walk with
i.i.d. steps on the real line. The proof of this combinatorial identity
together with historical remarks and a discussion of probabilistic and
algebraic connections has been published separately.Comment: 39 pages, full version, submitte
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