Vol. 52 No. 3 (2006): Revista Mexicana de Física.

Published: 2006-01-01

Articles

  • Estudio teórico y numérico de la difracción en óptica electromagnética. VII. Resonancias en la transmisión por una rendija en el régimen de sublongitud de onda

    O. Mata-Mendez, J. Avendaño, F. Chavez-Rivas
    190-0
    Abstract:
    Using a rigorous theory we study the diffraction of TM-polarized plane waves by a slit of width $l$ in a screen of infinite conductivity and thickness $h$. We have determined the resonances that appear when the incident wavelength is bigger than the slit width (subwavelength regime). We analyze numerically the transmission coefficient and the normally diffracted energy as functions of the incident wavelength, the screen thickness, and the slit width. We have found that both quantities present high anomalous values (resonances) for certain incident wavelengths radiation. Also, we show numerically that there are linear relationships between the resonant amplitudes and the optogeometrical parameters of the system, as well as among the same resonant magnitudes.
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  • Reconocimiento de formas con un correlador óptico aplicado a imágenes desenfocadas: invariancia por medio de la selección y fusión de bandas

    A. Vargas, R. Figueroa, J. Campos, C. San Martín, J. Marileo
    199-0
    Abstract:
    In this work, experimental result measuring the performance of a composite filter designed to solve the optical pattern recognition problem of defocus images is presented. We apply a methodology that considers optical decomposition of the input scene in frequency bands. In each band a pattern recognition filter is applied. Finally this information is fused by means of addition or geometric mean. We analyze both the individual information, and the fusion scheme. We also present results when total spectral information of the optical pattern recognition process is taken in to account.
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  • The Gordon and Zarmi model for convective atmospheric cells under the ecological criterion applied to the planets of the solar system.

    M.A. Barranco-Jiménez, J.C. Chimal-Eguía, F. Angulo-Brown
    205-0
    Abstract:
    In the present paper we calculate the surface temperatures of the nine planets of the Solar System by means of the Gordon and Zarmi model for dealing with the Earth's wind energy as a solar-driven Carnot-like heat engine, incorporating the role of the greenhouse effect and internal irreversibilities in the performance of this heat engine model. This oversimplified Carnot-like engine corresponds very approximately to the global scale motion of wind in convective cells. Our numerical results for the surface temperatures are in good agreement with the observed temperatures reported in the literature. Our calculations were made by means of two regimes of performance of the model: the maximum power regime and the maximum ecological function regime. In particular, Venus and Earth temperatures were calculated with a new approach by using the role of the tropopauses on the convective cells.
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  • The dynamics of coupled atom and field assisted by continuous external pumping

    G. Burlak, O. Starostenko, J.A. Hern, ez.
    213-0
    Abstract:
    The dynamics of a coupled system comprising a two-level atom and cavity field assisted by a continuous external classical field (driving Jaynes-Cummings model) is studied. When the initial field is prepared in a coherent state, the dynamics strongly depends on the algebraic sum of both fields. If this sum is zero (the compensative case) in the system, only the vacuum Rabi oscillations occur. The results with dissipation and external field detuning from the cavity field are also discussed.
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  • The rotational spectra of the most asymmetric molecules

    M.T. Valdés, E. Piña
    220-0
    Abstract:
    We consider the Schrödinger equation for the rotational spectra of the most asymmetric molecules. The energy eigenfunctions are also eigenfunctions of the square of the angular momentum vector and of one component of the angular momentum in the inertial frame. We follow our point of view in which the properties of the angular momentum spectra are used to delete, without loss of generality, one constant of motion and one of the Euler's angles. Then, instead of using Euler's angles, the Schrödinger equation and the energy eigenfunctions are expressed in terms of spheroconal coordinates in which that equation may be separable. The most asymmetric case is specially analyzed. The characteristic symmetries of this problem are used to reduce the number of differential equations considered and the number of steps for a complete solution.
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  • Estudio de campos locales residuales mediante relaxometría magnética nuclear en el sistema rotante

    Josefina Perlo., Esteban Anoardo.
    230-0
    Abstract:
    We present advances on the study of a nuclear magnetic resonance technique in the rotating frame. The method, based on the spin-lock experiment, allows to get information on the residual local fields in molecular organized materials. The magnetization after a certain lock-time is studied as a function of the radio-frequency field atenuation. The obtained dispersion curve, within a frequency interval ranging from a few kHz to about 50 kHz, contains information about the residual local field along the external magnetic field. The interpretation of the results is consistent and comparable with those obtained by other methods.
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  • Estimación de la temperatura de suelo desde datos satelitales AVHRR-NOAA aplicando algoritmos de split window

    J.C. Parra, J.A. Sobrino, P.S. Acevedo, L.J. Morales
    238-0
    Abstract:
    Four algorithms based on the technique of split-window, to estimate the land surface temperature starting from the data provided by the sensor Advanced Very High Resolution radiometer (AVHRR), on board the series of satellites of the National Oceanic and Atmospheric Administration (NOAA), are carried out. These algorithms consider corrections for atmospheric characteristics and emissivity of the different surfaces of the land. Fourteen images AVHRR-NOAA corresponding to the months of October of 2003, and January of 2004 were used. Simultaneously, measurements of soil temperature in the Carillanca hydro-meteorological station were collected in the Region of La Araucanía, Chile (38$^\circ$41' S; 72$^\circ$25' W). Of all the used algorithms, the best results correspond to the model proposed by Sobrino and Raussoni (2000), with a media and standard deviation corresponding to the difference among the temperature of floor measure in situ and the estimated for this algorithm, of -0.06 and 2.11K, respectively.
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  • Randomly rough rectangular-groove surfaces with predetermined backscatter intensities

    N.C. Bruce
    246-0
    Abstract:
    The backscattered intensity of the scattered light in rectangular-grooved surfaces is used as a design parameter for randomly rough surfaces. A modified Kirchhoff method and the integral equation method are used to calculate the scattered light distribution for these designed surfaces. The results of the two calculation methods are found to show good agreement, with the Kirchhoff method slightly overestimating the double scattered intensity, perhaps due to the limitations of the geometrical shadow functions used in this method. These results show that the backscattered intensity can be controlled in this type of surface.
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  • Zeolitas Na-A4 como anfitrión de nanopartículas de PbS

    M. Flores-Acosta, R. Pérez-Salas, R. Aceves-Torres, H. Arizpe-Chávez, M. Sotelo-Lerma, R. Ramírez-Bon
    255-0
    Abstract:
    In this work we report the optical and structural properties of composite materials based on the semiconductor PbS enclosed in type A zeolite. The composite materials were obtained by chemical reaction in several steps of the zeolite in alkaline aqueous solutions containing de Pb$^{2 + }$ and S$^{2 - }$ions successively. Three samples were prepared at temperatures of 40, 50 and 60$^\circ$C during the chemical reaction with S$^{2 - }$ions. The obtained materials were studied by x-ray diffraction, scanning and transmission electron microscopy, diffuse reflectance spectroscopy and photoluminescence. The experimental results show the formation of spherical-shaped PbS particles with nanometric size and cubic crystalline structure embedded in the zeolite matrix. The absorption spectra of the samples display a well defined absorption band at about 300 nm due to the PbS nanoparticles in the zeolite matrix. In addition, an absorption peak appears in the absorption spectra at about 400 nm assigned to exciton transitions.
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  • Propiedades ópticas de películas delgadas de CdSe obtenidas por rocío pirolítico

    A.M. Pérez González, C. Santiago Tepantlán, F. Renero Carrillo
    263-0
    Abstract:
    In this paper the optical properties of CdSe thin films obtained by spray pyrolisis are presented. The films are prepared by Sodium Selenosulphate (Na$_{2}$SSeO$_{3})$ and Cadmium Chloride (CdC$_{l2})$ mixing in aqueous environment. Optical parameters of the films (refractive index, absorption coefficient and optical bangap) were calculated from transmittance spectra. The obtained values of the optical bangap are compared with the result obtained by other deposition methods.
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  • A limit-cycle solver for nonautonomous dynamical systems

    R.G. Campos, G.O. Arciniega
    267-0
    Abstract:
    A numerical technique for finding the limit cycles of nonautonomous dynamical systems is presented. This technique uses a matrix representation of the time derivative obtained through the trigonometric interpolation of periodic functions. This differentiation matrix yields exact values for the derivative of a trigonometric polynomial at uniformly spaced points selected as nodes and can therefore be used as the main ingredient of a numerical method for solving nonlinear dynamical systems. We use this technique to obtain some limit cycles and bifurcation points of a sinusoidally driven pendulum and the steady-state response of an electric circuit.
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  • A petal resonator volume coil for MR neuroimaging

    A.O. Rodríguez, S.S. Hidalgo, R. Rojas, F.A. Barrios
    272-0
    Abstract:
    A variant of the petal resonator (PERES) coil was developed for magnetic resonance neuroimaging applications. It is formed by eight \mbox{2 cm-radius} petal coils around a central circular-shaped coil with a total radius of 10 cm. As dictated by the theory proposed by Mansfield in 1988, the small coil centers were separated by three times the petal coil radius to avoid mutual inductance between them. The present configuration can easily accommodate a head shape and can be placed nearer the subject to be imaged than other volume coils. Enhancement factor maps were computed to study the coil design performance based on the PERES coil foundations. Coil uniformity was theoretically investigated using the quasi-static approach for various petal coil radii. An 8-petal band coil was built, and in vivo and in vitro experiments were conducted on a clinical MR imager together with standard imaging sequences. Brain images of a healthy volunteer are reported to show the utility of the coil.
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  • Desarrollo de un nanomaterial base TiFe, como electrodo para baterías recargables tipo NiMH, obtenido por aleado mecánico de alta energía

    I. López-Báez, F.J. Espinoza-Beltrán, G. Barreiro-Rodríguez
    278-0
    Abstract:
    In this work the development of electrodes type A-B (A: Ti; B: Fe, Co, Ni) is presented starting from nanostructured alloys for rechargeable batteries also secondary calls. The purpose of the employment of a metallic alloy in form of nanometric powder like electrode is that its great surface allows making more efficient the electrochemical processes. The methodology that is used for the development of these materials consists in: to use the high energy mechanic alloying, because it is very practical and we can obtain a grain size of nanometric order in relatively short times; to examine their physiochemical characteristic (morphology, composition); to determine the Hydrogen absorption/desorption behavior; and to evaluate their yield characteristics like hydride electrodes in an electrolytic cell.
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  • Comunicador experimental privado basado en encriptamiento caótico

    R. Nuñez
    285-0
    Abstract:
    An Encrypted Information Experimental Communicator (EIEC) is presented. It's realization is based on two Lorenz explicit synchronized circuits. All the chaotic dynamics of the circuits were studied and analysed using DSP techniques. Regarding to our real/time application, -on bidirectional audio communications field-, the optimum conclusion was to make the synchronization and the hidden information communication by the medium chaotic dynamic variable and by the most dissimilar chaotic dynamic variables, respectively. Through the complete characterization of the bidirectional channels, we got the minimum characteristics (i.e., waveform and spectrum magnitude) of the private information that it must have just for to make a confidential and robust communication. The EIEC prototype, still doing well for academics and research purposes.
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  • High signal-to-noise ratio wedges for oblique incidence in ultrasonic testing

    M. Le, -Koo., S. Salazar-Cruz
    295-0
    Abstract:
    It is experimentally shown that ultrasonic transmission through a column of couplant, with a thin film, at the end, produces greater amplitudes than through a piece of acrylic with the same length. This suggests the use of a wedge that could yield a greater signal-to-noise ratio than that of commercial wedges involved in oblique incidence ultrasonic inspection. The suggestion has been pursued, and the effects: on a weld are presented.
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