Vol. 55 No. 3 (2009): Revista Mexicana de Física.

Published: 2009-01-01

Articles

  • Two techniques for generating a secondary electromagnetic source with desired statistical properties

    A.S. Ostrovsk, M.A. Olvera-Santamaría, C. Rickenstorff-Parrao, G. Martínez-Niconoff, V. Arrizón, .
    153-0
    Abstract:
    Two alternative techniques for generating a secondary electromagnetic source with the desired degree of polarization and transverse coherence length are considered and compared. The first technique is based on the changes of coherence and polarization in propagation, while the second one makes use of the coherence and polarization modulation by a random phase screen. The dependence of the results on the employed definition of electromagnetic coherence is discussed.
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  • Analytical description of the evolution of polarized light in homogeneous retarders using Jones formalism

    C. A, ala Díaz., D. Tentori Santa Cruz, M. Avendaño Alejo
    156-0
    Abstract:
    In this work we present analytical expressions for the trajectories depicted in the complex plane by the evolution of the state of polarization of totally polarized light, as it propagates through a homogeneous retarder. For any retarder and input state of polarization of the signal, the polarization state evolves, depicting one circle on the complex plane. The radius and position of each circle depends on the orientation of the fast birefringence axis of the sample, the polarization state of the input signal and the specific anisotropy of the medium.
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  • Formación de burbujas en líquidos viscosos contenidos en conos y cilindros

    A. Ortiz, A. López-Villa, A. Medina, F.J. Higuera
    166-0
    Abstract:
    In this work we consider the problem of growth and detachment of gas bubbles in reservoirs filled with viscous liquids whose walls are very close to the gas injection orifice, in such a manner that the walls affects the bubble shape and its maximum volume of growing. Using the Stokes equations for slow viscous flow, we have studied two cases of interest: a) the case where the walls make a vertical inverted cone, and b) the case of a cylindrical wall concentric to the injection orifice. In both cases the fluid flow equations were solved numerically by using the Boundary Element Method (BEM), and the results are given in terms of the bubble shapes, their maximum volumes and other properties of interest for different values of the Bond and Capillary numbers. We present a qualitative comparison with the experimental bubbles obtained at constant gas flow rates, in the air-gliceryn and air-silicone oil systems. This comparison allows us to conclude that the numerical solutions describe very well this phenomenon. Our results also show that possibility of change of the cone angle or the cylinder radius yields an efficient method to control the shape and size of the produced bubbles.
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  • Zonas de Brillouin del grafito

    A. Velázquez-Arriaga, P. Rosendo-Francisco, J. López-Lemus
    180-0
    Abstract:
    The unit cell of a graphite crystal is analyzed by using the basic principle of the harmonic oscillator. For this purpose, we consider the atoms that conform the hexagonal unit cell, connected by small springs. The equation of motion of such cell is established in order to obtain the vibration natural frequency of the system (% \emph{w}) in terms of the wave vector (\emph{k}) and the interatomic distance. With these data the Brillouin zones are generated and the seat points in the energy contours, which are a characteristic of a periodic system, are determined. By means of a simple model, the Brillouin zones and the patterns of the energy contours have been reproduced for a graphite sheet, without losing generalities or crystal properties. This analysis was carried out in a simple way with high grade of efficiency in comparison with other more elaborated theories.
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  • Reduced order ocean model using proper orthogonal decomposition

    D.A. Salas-de-León, M.A. Monreal-Gómez, E. van-de-Ven, S. Weil, D. Salas-Monreal, .
    185-0
    Abstract:
    The proper orthogonal decomposition (POD) is shown to be an efficient model reduction technique for simulating physical processes governed by partial differential equations. In this paper, a POD reduced model of a barotropic ocean circulation for coastal region domains was made. The POD basis functions and the results from this POD model were constructed and compared with that of the original model. The main findings were: 1) the variability of the barotropic circulation obtained by the original model is well captured by a low dimensional system of order of 22, which is constructed using 15 snapshots and 7 leading POD basis functions; 2) the RMS errors for the POD model is of order 10$^{ - 4}$ and the correlations between the original results with that from the POD model of more than 0.99; 3) the CPU model time solution is reduced is five times less than the original one; and 4) it is necessary to retain modes that capture more than 99% of the energy is necessary in order to construct POD models yielding a high accuracy.
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  • Exergoeconomic performance optimization for an endoreversible regenerative gas turbine closed-cycle cogeneration plant

    Guisheng Tao., Lingen Chen., Fengrui Sun.
    192-0
    Abstract:
    Finite time exergoeconomic performance of an endoreversible regenerative gas turbine closed-cycle cogeneration plant coupled to constant temperature heat reservoirs is investigated. The analytical formulae about profit rate and exergy efficiency of the cogeneration plant with the heat resistance losses in the hot-, cold- and consumer-side heat exchangers and the regenerator are deduced, respectively. By means of numerical calculations, the heat conductance allocation among the four heat exchangers and pressure ratio of the compressor are optimized by taking the maximum profit rate as the objective. The characteristic of optimal dimensionless profit rate versus corresponding exergy efficiency is investigated and the effects of design parameters on optimal performance of the cogeneration plant are also analyzed. The results show that there exist a sole group of optimal heat conductance allocations among the four heat exchangers and an optimal pressure ratio of the compressor which lead to the maximum dimensionless profit rate, and there exists an optimal consumer-side temperature which leads to double-maximum dimensionless profit rate.
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  • Manejo e interpretación polarimétrica de las matrices de Mueller

    R. Espinosa-Luna, S. Hinojosa-Ruíz, G. Atondo-Rubio
    201-0
    Abstract:
    The $Q(M)$ depolarization scalar metric and a graphical polarimetric analysis are applied to several reported Mueller matrices. A brief review of the main polarimetric concepts and the depolarizations scalar metrics is presented. It is shown the depolarization scalar metric $Q(M)$ provides consistent results with the reported scalar metrics and offers more information about the internal nature of the Mueller matrix.
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  • Finite-time thermoeconomic optimization of a non endoreversible heat engine model

    M.A. Barranco-Jiménez
    211-0
    Abstract:
    Within the context of Finite-Time Thermodynamics (FTT), we study the thermoeconomics of a simplified non-endoreversible thermal power plant model (the so-called Novikov engine). In our study, we use different heat transfer laws: the so called Newton's law of cooling, the Stefan-Boltzmann radiation law, the Dulong-Petit's law and another phenomenological heat transfer law. We use two FTT optimization criteria: the maximum power regime (MP) and the so-named modified ecological criterion for performance analysis. This last criterion leads the engine model towards a mode of performance that appreciably diminishes the engine's wasted energy. It is shown that under ecological conditions the plant dramatically reduces the amount of heat rejected to the environment, and a loss of profit is translated into a better usage of fuel such that the heat rejected towards the environment is remarkably reduced compared to that of a maximum power regime. Besides, we analyze the effect on the reduction of power output and the optimal efficiencies in terms of an internal irreversibility parameter that comes from the Clausius inequality which characterizes the degree of internal irreversibility.
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  • Trapping effects on short-range two-body interactions

    L.E.C. Rosales-Zárate, R. Jáuregui
    221-0
    Abstract:
    In contrast to conventional ideal Bose and Fermi degenerate gases, atoms in experimental ultracold gases interact among themselves and are trapped by an external potential. In this work, we consider two particles of mass $m$ trapped by a $3D$ harmonic potential of frequency $\omega$, and interacting through an isotropic short range potential of intensity $V_0$ and range $b/2 $, with $b/2 \ll \sqrt{\hbar/m\omega}$. Eigenfunctions and eigenenergies are obtained and compared with those resulting (a) from an effective contact interaction and (b) in the absence of the trapping potential. Concepts like zero-resonance and binding energy, usually introduced for problems that allow a continuum spectra, are discussed for trapped particles.
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  • Caracterización de películas luminiscentes de óxido de hafnio activadas con Eu$^{3 + }$ depositadas por la técnica de rocío pirolítico ultrasónico

    R. Chora-Corella, M. García-Hipólito, O. Álvarez-Fragoso., M.A. Álvarez-Pérez, C. Falcon., .
    226-0
    Abstract:
    By means of the ultrasonic spray pyrolysis technique, trivalent europium doped hafnium oxide films were deposited. These films are amorphous at substrate temperatures lower than 350$^{\circ}$C, for higher substrate temperatures the films are polycrystalline presenting the HfO$_{2}$ monoclinic phase. The photoluminescence spectra for these films were studied as a function of the substrate temperature and the doping concentration. Samples excited with 395 nm radiation showed photoluminescence emission bands centered at 578, 591, 598, 612, 653 and 703 nm, associated to the electronic transitions of the trivalent europium. As the substrate temperatures are increased, an increment of the photoluminescence emission intensity was detected. Also, a concentration quenching of the photoluminescence intensity was observed. In addition, the chemical compositions of the deposited coatings and the characteristics of their surface morphologies are shown. The excitation band peaked at 395 nm, makes this material an excellent candidate for applications in solid state white lamps.
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  • Sample holder for measurement at very low temperatures by electron paramagnetic resonance spectroscopy

    J. Barreto, J.L. Boldú, H. del Castillo, R. Gleason, E. Muñoz P.
    232-0
    Abstract:
    In this paper we describe the design and use of a sample holder for measurements of colour centers in elpasolite crystals irradiated at liquid nitrogen temperatures and measured at the same temperature by electron paramagnetic resonance spectroscopy.
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