Vol. 58 No. 2 (2012): Revista Mexicana de Física.

Published: 2012-01-01

Articles

  • Cien años de la función de distribución de Jüttner para el gas relativista

    G. Chacón-Acosta
    117-126
    Abstract:
    In 2011 marks a century that Ferencz Jüttner obtained the distribution function for the relativistic gas. This distribution was involved in a controversy that lasted nearly a century and was related to the foundations of relativistic thermodynamics. In this paper it is done a brief review of what happened in the last hundred years around the relativistic Jüttner distribution. It is described part of the Jüttner's original work, the circumstances under which he obtain his distribution as well as the particular characteristics of it compared with those od the well known Maxwell-Boltzmann equilibrium distribution for the non-relativistic gas. In the final sections, there are listed the main applications of the Jüttner distribution, from the work of Chandrasekhar to the quark-gluon plasma. There are also discussed the most recent developments that suggest a solution to the controversy that was surrounded the relativistic distribution.
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  • Estimador de parámetros para sistemas de orden superior

    J.J. Medel Juárez, M.T. Zagaceta Álvarez
    127-132
    Abstract:
    This paper~presents parameter estimations considering~an observable~black box~system signal represented with high order finite differences. The model is~expressed as a~sequence of delayed observable states~conforming space state vector~to its~known associated parameters. The estimation technique is based on~pseudo-inverse~and an innovation process~associated with perturbation and an observable signal. The simulation~uses two high order~finite difference~models, second and third grades with associate parameters. In both cases the observed signal~depends~on their delayed states. Therefore, it is necessary to estimate two~and three parameters with respect to second and third order models, respectively. The estimation results allowed identifying~the observable signal with a high convergence rate in base of functional error, as~shown in~the figures. Instrumental~variable~is the technique applied to the second~probability~moment constructing~the estimator~for a~high finite difference~order system.
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  • Higher dimensional gravity and Farkas property in oriented matroid theory

    J.A. Nieto, E.A. León
    133-138
    Abstract:
    We assume gravity in a $d$-dimensional manifold $M$ and consider a splitting of the form $M=M_{p}\times M_{q}$, with $d=p+q$. The most general two-block metric associated with $M_{p}$ and $M_{q}$ is used to derive the corresponding Einstein-Hilbert action $\mathcal{S}$. We focus on the special case of two distinct conformal factors $\psi $ and $\varphi $ ($\psi $ for the metric in $M_{p}$ and $\varphi $ for the metric in $M_{q}$), and we write the action $\mathcal{S}$ in the form $\mathcal{S=S}_{p}\mathcal{+S}_{q} $, where $\mathcal{S}_{p}$ and $\mathcal{S}_{q}$ are actions associated with $M_{p}$ and $M_{q}$, respectively. We show that a simplified action is obtained precisely when $\psi =\varphi ^{-1}$. In this case, we find that under the duality transformation $\varphi \leftrightarrow \varphi ^{-1}$, the action $\mathcal{S}_{p}$ for the $M_{p}$-space or the action $\mathcal{S}% _{q}$ for the $M_{q}$-space remain invariant, but not both. This result establishes an analogy between Farkas property in oriented matroid theory and duality in general relativity. Furthermore, we argue that our approach can be used in several physical scenarios such as 2t physics and cosmology.
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  • 2D radial distribution function of silicene

    M.R. Chávez-Castillo, M.A. Rodríguez-Meza, L. Meza-Montes
    139-143
    Abstract:
    Silicene is the counterpart of graphene and its potential applications as a part of the current electronics, based in silicon, make it a very important system to study. We perform molecular dynamics simulations and analyze the structure of a two dimensional array of Si atoms by means of the radial distribution function at different temperatures and densities. As a first approach, the Lennard-Jones potential is used and two sets of parameters are tested. We find that the radial distribution function does not change with the parameters and resembles the corresponding to the (111) surface of the FCC structure. The liquid phase appears at very high temperatures, suggesting a very stable system in the solid phase.
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  • Growth and characterization of $\beta $-InN films on MgO: the key role of a $\beta $-GaN buffer layer in growing cubic InN

    H. Navarro-Contreras, M. Pérez Caro, A.G. Rodríguez, E. López-Luna, M.A. Vidal
    144-151
    Abstract:
    Cubic InN samples were grown on MgO (001) substrates by gas source molecular beam epitaxy (GSMBE). In general, we find that InN directly deposited onto the MgO substrate results in polycrystalline or columnar films of hexagonal symmetry. We find that adequate conditions to grow the cubic phase of this compound require the growth of an initial cubic GaN buffer interlayer ($\beta$-tGaN) on the MgO surface. Subsequently, the growth conditions were optimized to obtain good photoluminescence (PL) emission. The resultant InN growth is mostly cubic, with very small hexagonal inclusions, as confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies. Good crystalline quality requires that the samples to be grown under rich Indium metal flux. The cubic $\beta$-tInN/GaN/MgO samples exhibit a high signal to noise ratio for PL at low temperatures (20 K). The PL is centered at 0.75 eV and persists at room temperature.
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  • On renormalizability of a non-linear abelian gauge model

    J. Chauca, R. Doria, J.L. M
    152-159
    Abstract:
    Considering that physical processes work as a group, a whole gauge procedure becomes necessary. In a previous work, we have developed this new approach for a classical non-linear abelian gauge model. At this work, one intends to understand the corresponding quantum extension through its renormalizability. For this, one studies Feynman graphs, quantum action principle, power counting procedure, Ward identities and primitively divergent graphs. Under this renormalization procedure one computes a non-linear whole abelian gauge model.
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  • Non-stationary response of photorefractive crystal under an external sinusoidal electric field

    O. Salas-Torres, A. Zúñiga-Segundo, L.F. Magaña-Solís
    160-165
    Abstract:
    We calculated the non-stationary holographic current arising in a photorefractive crystal illuminated by a vibrating sinusoidal pattern along with an external sinusoidal electric field applied to the sample. We first solved numerically the set of nonlinear material rate differential equations to find the full overall space charged field and the mobile carrier density for a photorefractive BSO crystal. With these results we calculated the photocurrent, which is found to be in good agreement with corresponding values obtained from holographic experiments performed with similar samples.
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  • Characterization of the level fluctuations in a physical model of the steel continuous casting mold through image processing

    J.R. Mir, a-Tello., F. Sánchez-Rangel, C.A. Real-Ramírez, G. Khatchatourov, J.A. Aragón-Lezama, L.F. Ho, os-Re., es., E.A. Andrade-González, J.I. González-Trejo
    166-173
    Abstract:
    In this work is characterized the periodic behavior of the liquid level inside a scaled cold-model of the mold section of a steel continuous casting machine, which uses water as working fluid. The models are designed in order to simulate the dynamic forces acting on the molten steel inside a mold of continuous casting. The force magnitude can induce choppy flow, waves and vortex formation in the mold. The experimental model uses a closed-loop hydraulic configuration. In the mold, the inlet and the outlet water flow rates are the same. This configuration resembles a perfect control of the liquid level inside the water model. A high-speed video camera was used to get several video clips of the movement of the water level profile. Several techniques were tested in order to obtain the best lighting conditions for recording the water movement. The edge-detection technique of Sobel was used to determine the profile of the liquid level in each one of the images recorded. The analysis of the dynamic behavior of the water profile showed that the fluctuations of the liquid level inside the mold have a complex structure, which is repeated over large time periods.
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  • Calculation of the maximun number of vibrational and rotational energy states for diatomic molecules

    O. Cardona, M.G. Corona-Galindo
    174-179
    Abstract:
    A procedure for finding the maximum number of energy states for a diatomic molecule is presented. We consider the background energy of a gaseous thermodynamic system containing atoms, diatomic molecules and their ions, together with the spacing of adjacent energy states in the molecules. Using similitude and dimensional analysis techniques and defining linear energy densities of the molecular and thermodynamic systems we obtain expressions for the maximum levels that a molecule can attain. These results are relevant for the correct evaluation of the partition function.
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  • The conserved operators generated by a solution of the Schrödinger equation

    G.F. Torres del Castillo, E. Navarro Morales
    180-183
    Abstract:
    It is shown that, in a similar manner as a complete solution of the Hamilton--Jacobi equation for a system with $n$ degrees of freedom yields $2n$ constants of motion, each solution of the Schrödinger equation containing $n$ parameters leads to $2n$ operators that are constants of motion; these $2n$ operators form two sets of $n$ mutually commuting operators.
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  • Identificación de aceros por espectroscopia de rompimiento inducido por láser (LIBS) y análisis de componentes principales

    U. Contreras, M.A. Meneses-Nava, D. Torres-Armenta, J. Robles-Camacho, O. Barbosa-García
    184-191
    Abstract:
    Nowadays there exist more than 100 000 different types of steels according to their chemical and physical properties. Nevertheless there is not a unique method capable to identify or classify any sample of steel according to its class or grade. In this work it is described a method capable to identify and classify steels due to the chemical composition determination. The proposed method is based in the analysis of atomic spectra by Laser Induced Breakdown Spectroscopy (LIBS) and Principal Component Analysis (PCA). For steels from different classes it is possible to discriminate them due to their chemical composition. For steels from the same class but different grade, the information on the spectra is not sufficient for a satisfactory discrimination because of the relatively low difference in composition ($<0.5$%); however, discrimination of all analyzed samples is possible using PCA.
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