Vol. 54 No. 4 (2008): Revista Mexicana de Física.

Published: 2008-01-01

Articles

  • A hamiltonian control approach for the stabilization of the angular velocity of a rigid body system controlled by two torques

    C. Aguilar-Ibáñez, M.S. Suárez-Castañón, F. Guzmán-Aguilar
    265-0
    Abstract:
    We present a Hamiltonian control approach for the stabilization of a rigid body system that is controlled by two torques. The stabilization strategy consists in solving a feasible matching condition in order to derive a feedback controller which forces the closed-loop system to be globally asymptotically stable.
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  • Characterization of ALN thin films deposited by DC reactive magnetron sputtering

    M. García-Méndez, S. Morales-Rodríguez, R. Machorro, W. De La Cruz
    271-0
    Abstract:
    A set of AlN thin-films was prepared by reactive magnetron sputtering at room temperature. The purpose of this work was to study the effect of oxygen impurities on the structural and optical properties of AlN films. The structural and optical properties of the resulting films were characterized using X-ray diffraction (XRD) and spectroscopic ellipsometry, respectively. Depending on the deposition conditions, films can be hexagonal (wurtzite, P6$_{3}$m3) or cubic (zinc blende, Fm3m) in their microstructure. From the optical measurements, the ellipsometric parameters ($\psi $,$\Delta )$ and the real refractive index as a function of energy were obtained. From the ellipsometric measurements, a model of the Lorentz single-oscillator was employed to estimate the optical band gap, $E_{g}$.
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  • Laser beam quality factor (M$^{2}$) measured by distorted fresnel zone plates

    R. Cortés, R. Villagómez, V. Coello, R. López
    279-0
    Abstract:
    In this paper we present a novel method, based on diffractive optics, for measuring M$^{2}$. This novel optical arrangement consists of a lens along with a set of 1 or 2 distorted diffraction gratings and a single array detector. As a result, this system produces simultaneous images of a number of different object planes centred over the laser beam propagation axis symmetrically to the laser beam waist. This image is gathered around the image plane using a CCD camera producing, in a single image and after some image processing, an instantaneous measurement for the laser beam quality. This technique allows for the possibility of monitoring the beam quality in real time, in a continuous or pulse-to-pulse mode operation. Nowadays, high power laser machining is a standard technique in manufacturing material processing that is widely used in industry. Although these lasers are not always stable for long periods of time, which is required in this kind of process, it usually takes considerable time to diagnose them and restore them to working order. The M$^{2}$ parameter is a numerical expression for laser beam quality that can be measured in real time over a process line. However, to measure the M$^{2}$ parameter, several measurements in the neighbourhood of the laser beam waist are required.
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  • On the optimum operation conditions of an endoreversible heat engine with different heat transfer laws in the thermal couplings

    M.A. Barranco-Jiménez, N. Sánchez-Salas, F. Angulo-Brown
    284-0
    Abstract:
    Within the context of Finite-Time Thermodynamics (FTT) we study the optimum operating conditions of an endoreversible engine model. In this model we consider different heat transfer modes from the hot reservoir to the working fluid, while the mode of heat transfer from the working fluid to the cold reservoir is governed by a Newtonian heat transfer law. In our analysis we use two modes of performance, the maximum power regimen and the so-called ecological function. We calculate the optimum temperatures of the working fluid and the optimum efficiency in terms of the relevant system parameters. We show how the efficiency under a maximum ecological function is greater than the maximum efficiency under maximum power conditions.
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  • Calculation of vertical force between finite, cylindrical magnets and superconductors

    E. Várguez-Villanueva, V. Rodríguez-Zermeño, V. Sosa
    293-0
    Abstract:
    The maximum force between a permanent magnet and a superconductor in the Meissner state has been calculated. The calculation was performed assuming the superconductor to be a perfect diamagnet and neglecting the London penetration depth. The resulting force takes into account the geometric dimensions of both the magnet and the superconductor. This constitutes an important improvement for the description of the maximum force attainable in these systems. The method can be applied in cases with azimuthal symmetry.
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  • Synchronization of multi-scroll chaos generators: application to private communication

    L. Gámez-Guzmán, C. Cruz-Hernández, R.M. López-Gutiérrez, E.E. García-Guerrero
    299-0
    Abstract:
    In this paper, the synchronization problem of coupled 2D-grid scroll attractor families in master-slave configuration is studied numerically. In particular, we consider, for synchronization purposes, the chaos generator model of 3$\times $3-scroll grid attractors by appealing to Generalized Hamiltonian forms and observer design from nonlinear control theory. A potential application to the transmission of encrypted information is also given.
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  • Azimuthal signal variations in the engineering array of the Pierre Auger Observatory

    K.S. Caballero-Mora, L. Nellen, J.F. Valdés-Galicia
    306-0
    Abstract:
    We study the azimuthal variation of the signal in selected tanks in the engineering array of the Pierre Auger Observatory. We fit a parametrization to the observed variations. We also note that the observation of the signal variations can be used to detect mistakes in the wireing from the PMTs to the control board.
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  • DFT normal modes of vibration of the Au$_{20}$ cluster

    B. Molina, J.R. Soto, A. Calles
    314-0
    Abstract:
    The vibrational spectrum of the tetrahedral Au$_{20}$ cluster was calculated using density functional theory (DFT) with two different approximations: the hybrid-B3LYP and GGA-BP86. The normal modes of vibration obtained were classified according to the irreducible representations of the T$_d$ group. The calculated vibrational frequencies were tabulated to be compared with experimental data when they became available.
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  • Stationary oscillations in a damped wave equation from isospectral Bessel functions

    N. Barbosa-Cendejas, M.A. Re, es.
    319-0
    Abstract:
    Using the isospectral partners of the Bessel functions derived by Reyes et al. \cite{marco}, we find, on one hand, that these functions show non-typical supersymmetric (SUSY) behavior and, on the other, that the isospectral partner of the classical wave equation is equivalent to that of a damped system whose oscillations do not vanish in time, but show a non-harmonic shape.
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  • Design of a 1-V 90-nm CMOS adaptive LNA for multi-standard wireless receivers

    E.C. Becerra-Álvarez, F. S, oval-Ibarra., J.M. de la Rosa
    322-0
    Abstract:
    This paper presents the design of a reconfigurable Low-Noise Amplifier (LNA) for the next generation of wireless hand-held devices. The circuit, based on a lumped-approach design and implemented in a 90nm standard RF CMOS technology, consists of a two-stage topology that combines inductive-source degeneration with MOS-varactor based tuning networks and programmable bias currents, in order to adapt its performance to different standard specifications with reduced number of inductors and minimum power dissipation. As an application, the LNA is designed to cope with the requirements of GSM (PCS1900), WCDMA, Bluetooth and WLAN (IEEE 802.11b-g). Simulation results, including technology parasitics, demonstrate correct operation of the LNA for these standards, featuring NF$<$1.77dB, S$_{21}>$16dB, S$_{11}<$-5.5dB, S$_{22}<$-5.5 dB and IIP3$>$-3.3 dBm over the 1.85-2.48 GHz band, with an adaptive power consumption between 25.3 mW and 53.3mW. The layout of the LNA occupies an area of 1.18$\times $1.18 $\mu $m$^{2}$.
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  • Controlled Lagrangian approach to the stabilization of the inverted pendulum system

    C. Aguilar-Ibañez, O. Octavio Gutierrez F., H. Sossa A.
    329-0
    Abstract:
    A controlled Lagrangian approach is presented for the stabilization of an inverted pendulum mounted on a cart. The stabilization strategy consists in forcing the closed-loop system to behave as an Euler-Lagrange system, with a fixed inertia matrix. For carrying it out, it is necessary to adequately shape the potential and kinetic energies of the closed-loop system. The idea behind this procedure is to make an energy-balance between the overall energy of the pendulum system and the dissipation energy produced by the action of the control force. The resulting closed-loop system is locally asymptotically stable about its unstable equilibrium point with a very large attraction domain.
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