6,814 research outputs found
Quantum electrodynamic calculation of the hyperfine structure of 3He
The combined fine and hyperfine structure of the states in He is
calculated within the framework of nonrelativistic quantum electrodynamics. The
calculation accounts for the effects of order and increases the
accuracy of theoretical predictions by an order of magnitude. The results
obtained are in good agreement with recent spectroscopic measurements in
He.Comment: 13 pages, spelling and grammar correcte
Square-free class sizes in products of groups
We obtain some structural properties of a factorised group , given
that the conjugacy class sizes of certain elements in are not
divisible by , for some prime . The case when is a mutually
permutable product is especially considered
First measurement of cluster temperature using the thermal Sunyaev-Zeldovich effect
We discuss a new method of finding the cluster temperatures which is
independent of distance and therefore very useful for distant clusters. The hot
gas of electrons in clusters of galaxies scatters and distorts the cosmic
microwave background radiation in a well determined way. This
Sunyaev-Zel'dovich (SZ) effect is a useful tool for extracting information
about clusters such as their peculiar radial velocity and optical depth. Here
we show how the temperature of the cluster can be inferred from the SZ effect,
in principle without use of X-ray data. We use recent millimetre observation of
Abell 2163 to determine for the first time a cluster temperature using SZ
observations only. The result T_e = 26^+34_-19 keV at 68% confidence level (at
95% c.l. we find T>1.5 keV) is in reasonable agreement with the X-ray results,
T_e =12.4^+2.8_-1.9 keV.Comment: 7 pages, 2 figure
Spectral distortion of cosmic background radiation by scattering on hot electrons. Exact calculations
The spectral distortion of the cosmic background radiation produced by the
inverse Compton scattering on hot electrons in clusters of galaxies (thermal
Sunyaev-Zeldovich effect) is calculated for arbitrary optical depth and
electron temperature. The distortion is found by a numerical solution of the
exact Boltzmann equation for the photon distribution function. In the limit of
small optical depth and low electron temperature our results confirm the
previous analyses. In the opposite limits, our method is the only one that
permits to make accurate calculations.Comment: 18 pages, 7 figures, to be published in Ap
Typical medium theory of Anderson localization: A local order parameter approach to strong disorder effects
We present a self-consistent theory of Anderson localization that yields a
simple algorithm to obtain \emph{typical local density of states} as an order
parameter, thereby reproducing the essential features of a phase-diagram of
localization-delocalization quantum phase transition in the standard lattice
models of disordered electron problem. Due to the local character of our
theory, it can easily be combined with dynamical mean-field approaches to
strongly correlated electrons, thus opening an attractive avenue for a genuine
{\em non-perturbative} treatment of the interplay of strong interactions and
strong disorder.Comment: 7 pages, 4 EPS figures, revised version to appear in Europhysics
Letter
Quasi-chemical approximation for polyatomic mixtures
The statistical thermodynamics of binary mixtures of polyatomic species was
developed on a generalization in the spirit of the lattice-gas model and the
quasi-chemical approximation (QCA). The new theoretical framework is obtained
by combining: (i) the exact analytical expression for the partition function of
non-interacting mixtures of linear -mers and -mers (species occupying
sites and sites, respectively) adsorbed in one dimension, and its extension
to higher dimensions; and (ii) a generalization of the classical QCA for
multicomponent adsorbates and multisite-occupancy adsorption. The process is
analyzed through the partial adsorption isotherms corresponding to both species
of the mixture. Comparisons with analytical data from Bragg-Williams
approximation (BWA) and Monte Carlo simulations are performed in order to test
the validity of the theoretical model. Even though a good fitting is obtained
from BWA, it is found that QCA provides a more accurate description of the
phenomenon of adsorption of interacting polyatomic mixtures.Comment: 27 pages, 8 figure
Photon Filamentation in Resonant Media with High Fresnel Numbers
The phenomenon of turbulent photon filamentation occurs in lasers and other
active optical media at high Fresnel numbers. A description of this phenomenon
is suggested. The solutions to evolution equations are presented in the form of
a bunch of filaments chaotically distributed in space and having different
radii. The probability distribution of patterns is defined characterizing the
probabilistic weight of different filaments. The most probable filament radius
and filament number are found, being in good agreement with experiment.Comment: Revtex file, 5 pages. Reference to the English edition of the journal
is give
Glassy behavior of electrons near metal-insulator transitions
The emergence of glassy behavior of electrons is investigated for systems
close to the disorder and/or interaction-driven metal-insulator transitions.
Our results indicate that Anderson localization effects strongly stabilize such
glassy behavior, while Mott localization tends to suppress it. We predict the
emergence of an intermediate metallic glassy phase separating the insulator
from the normal metal. This effect is expected to be most pronounced for
sufficiently disordered systems, in agreement with recent experimental
observations.Comment: Final version as published in Physical Review Letter
Perception questionnaire of teaching competences in Physical Education
La incorporación de las competencias en la universidad española es un elemento clave de su calidad. Sin embargo, no se dispone de instrumentos adecuados ni suficientes para su medida en el campo concreto de la formación inicial del profesorado de Educación Física. El principal objetivo de este trabajo es diseñar y validar una escala para medir la percepción de competencias docentes de este alumnado. Para su construcción y validación, se ha seguido una metodología fundamentada en la Teoría Clásica de Test incidiendo especialmente en el cálculo de la fiabilidad y de la validez de la escala. La muestra para su validación es de 1713 estudiantes y egresados (1240 estudiantes, 473 egresados), pertenecientes a 20 universidades españolas. La escala final presenta una
estructura factorial de cuatro factores principales y 22 ítems con los que se alcanza una alta fiabilidad y una adecuada validez de contenido y de constructoThe incorporation of competences in Spain is a key element of its quality. However, there are no instruments available to measure them in the specific field of Physical Education Teacher Education. The main objective of this study is to design and validate a scale to measure the perception of the teaching competences of these students. For its construction and validation, a methodology based on the Theory of the Classic Test was followed, with special emphasis on the calculation of the reliability and validity of the scale. The sample for its validation is 1713 students and graduates (1240 students, 473 graduates), belonging to 20 Spanish universities. The final scale presents a factorial structure of four main factors and 22 items with which high reliability and adequate content and construct validity are achievedEste estudio se ha llevado a cabo dentro del proyecto de I+D+i: “La competencias docentes en la formación inicial del profesorado de educación física”. Convocatoria de noviembre de 2013 del Programa Estatal de Investigación, Desarrollo e Innovación Orientada a los Retos de la Sociedad, en el marco del Plan Estatal de Investigación Científica y Técnica y de Innovación 2014-2017. Referencia: EDU 2013-42024-R. Duración: 3 años (2014-2017
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