Vol. 56 No. 1 (2010): Revista Mexicana de Física.

Published: 2010-01-01

Articles

  • Estimación-identificación como filtro digital integrado: descripción e implementación recursiva

    Abstract:
    The digital filter theory with identification process allows knowing internal states dynamics, with respect to a reference system, commonly considered as a black box or base system. This gives the identifier its input and output signals as essential information; so that the identifier is formed by identification actions. The actions developed by the identifier consider the transition matrix ``described by the exponential function respect to internal parameters for the unknown black box reference system'', identifying states delayed, with gain matrix ``formatted by correlation convergence error'' and the innovation process ``build by the output base system noise and the identification result.'' Unfortunately, in the black box concept the internal parameters have the same problem, which means, neither observed nor transition matrix, because it is a description function depicted exponentially. Thus, the identifier structure considers that the transition matrix is an essential problem. This paper proposes the estimator as internal parameter descriptor ``this is a technique required to describe the internal gains with respect to the black box system'' thus generating the transition matrix. With respect to the gain matrix, the identification error ``expressed by a second probability moment in recursive forms'' affects the identifier as an adaptive algorithm. This allows having a sufficient convergence rate. The filter is built with two actions: estimator and identifier, this considers the adaptive properties with respect to the gain and dynamically adjusts the identifier convergence levels, observed in simulation results.
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    J.J. Medel Juárez, M.T. Zagaceta Álvarez
    1-0

  • Estudio de las características de propagación de un plasma pulsado generado en un acelerador coaxial

    Abstract:
    The propagation and expansion of the plasma produced by a coaxial plasma gun is evaluated simultaneously using a laser beam deflection technique and a Langmuir double probe. The first method is very sensitive to the time and space dependent gradients produced by the pulsed plasma, and it is applied to measure the resulting beam deflection over a He-Ne laser beam that is placed perpendicular to the propagation axis. The system with a quadrature detector has a rise time response of 10 ns and a resolution of 2 $\mu$rad. The Langmuir double probe is used along the axis and allows us to measure the time of flight under diverse plasmas conditions. We present comparative measurements for Nitrogen and Helium background gases from 50 to 500 mTorr, in a 50 cm long and 10 cm diameter chamber.
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    R. Castell, E. Iglesias, J. Ruiz-Camacho, J. Ramírez
    9-0

  • Unfolding ray trace for plates and wedges

    Abstract:
    We present a new procedure to obtain analytic expressions for tracing rays in plates and wedges used edgewise applying the unfolding method for ray tracing, to be able to analyze the behavior of these optical components for transporting light in optical systems. The plates and wedges are useful in transforming the shape and characteristics of light beams, and also for changing the focal ratio or aperture number of these beams. The analytic expressions derived are simple to use in any application.
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    O. Cardona-Nuñez, A. Cornejo-Rodríguez, P.C. García-Flores
    14-0

  • Electronic and magnetic properties of NiPd and CoPd nanostructures

    Abstract:
    We study the dependence of the magnetic properties of NiPd and CoPd segregated nanoclusters and slabs as a function of the 3 d magnetic component concentration ($x$), the chemical order, and size. In the case of clusters we consider $3d$ cores coated by Pd atoms ($3d$/Pd) and also onion-like (Pd/$3d$/Pd) configurations. For the slabs we consider different possible segregated structures of the $3d$ and $4d$ atoms and study the evolution of the magnetic properties on these different configurations. We show that Pd coating gives rise to an enhancement of the average magnetic moment of the Ni or Co core atoms and of the Pd atoms as well. Larger values of the average magnetic moments are obtained in the onion-like structures (Pd/$3d$/Pd) than in the core/shell ($3d$/Pd) configuration. We compare with theoretical and experimental results available in the literature.
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    J. Guevara, A.M. Llois, F. Aguilera-Granja, J.M. Montejano-Carrizales
    21-0

  • Entanglement and control operations in Heisenberg 3-D interactions of two qubits

    Abstract:
    Entanglement generated by the Heisenberg model has been studied by several authors in order to understand its relation to the magnetic properties of materials, using mainly particular cases in one or two dimensions for two or more particles. In this work, the evolution of the Heisenberg model is solved for two particles including an inhomogeneous magnetic field in three dimensions, giving a detailed study of the entanglement properties derived from this interaction. Some relations between entanglement and energy or spin are verified, based on known relations for these observables. Finally, some possible quantum control operations are suggested to drive bipartite qubits with an external magnetic field, controlling their evolution into a periodical behavior. These operations become useful to preserve the system properties as well as to transfer information between two parts which can be exploited in engineering applications (e.g. quantum computation or quantum information).
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    F. Delgado
    30-0

  • Intergranular properties of uniaxially pressed YBa$_2$Cu$_3$O$_{7-\delta}$ ceramic samples

    Abstract:
    We performed measurements of electrical resistivity as a function of temperature, $\rho(T)$, in polycrystalline samples of YBa$_2$Cu$_3$O$_{7-\delta}$ (Y-123) subjected to different uniaxial compacting pressures. We observed by using X-ray diffractometry that samples have a very similar composition. Most of the identified peaks are related to the superconducting Y-123 phase. Also, from the X-ray diffraction patterns performed, in powder and pellet samples, we estimated the Lotgering factor along the $(00l)$ direction, $F_{(00l)}$. The results indicate that $F_{(00l)}$ increases from 0.13 to 0.16. From electrical resistivity measurements as a function of temperature, we were able to separate contributions arising from both the grain misalignment and microstructural defects. We found appreciable degradation in the normal-state transport properties of samples with an increase in uniaxial compacting pressure. It seems that this type of behavior is associated with an increase in the influence of microstructural defects at the intergranular level. The experimental results are analyzed in the framework of a current conduction model of granular samples.
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    I. García-Fornaris, E. Govea-Alcaide, P. Muné, R.F. Jardim
    40-0

  • Quasinormal frequencies of the Dirac field in the massless topological black hole

    Abstract:
    Motivated by the recent computations of the quasinormal frequencies of higher dimensional black holes, we exactly calculate the quasinormal frequencies of the Dirac field, propagating in $D$-dimensional ($D \geq 4$) massless topological black hole. From the exact values of the quasinormal frequencies for the fermion and boson fields we discuss whether the recently proposed bound on the relaxation time of a perturbed thermodynamical system is satisfied in the $D$-dimensional massless topological black hole. Also we study the consequences of these results.
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    A. López-Ortega
    44-0

  • Estimación de parámetros usando la deconvolución y la pseudoinversa: descripción e implementación recursiva

    Abstract:
    En este trabajo se presenta un estimador de parámetros recursivo con base al modelo matricial de deconvolución como proceso de filtrado, con el cual es posible conocer la dinámica interna del modelo tipo caja negra con respuesta lineal, y con evolución invariante en el tiempo. La extensión del proceso de convolución a un periodo de tiempo conformado por un grupo de intervalos en los cuales el sistema no cambia de contexto, permite hacer una aproximación al producto matricial con base en el cual el sistema real, dadas sus entradas y salidas dentro de ese periodo de tiempo, será visto como un sistema multivariable al no cambiar de contexto y al mantener sus condiciones de invarianza, de manera que es necesario el uso de la pseudoinversa en la estimación, ya que se observan problemas de inversión y de singularidad en su desarrollo. De igual forma, las medidas de dispersión respecto a una referencia, considerando la traza tanto de la matriz de referencia como de su estimada, permiten describir al error cuadrático medio, decibeles y Bode, todos desarrollados de manera recursiva, estableciendo un enlace con sus estados inmediatos anteriores para el consumo de la menor cantidad de recursos computacionales. Se realiza una descripción de las condiciones de estabilidad a cubrir por el estimador tomado en cuenta los criterios de Lyapunov. De manera ilustrativa, se presentó una simulación utilizando MatLab$^{\mbox{\textregistered }}$ [7], en la que las formas extendidas dentro de un intervalo de tiempo son vistas como matrices no cuadradas, permaneciendo el sistema invariante respecto a un vector de entrada, y se tiene como resultado un proceso de estimación recursivo. Se concluyó que en el proceso de deconvolución, la estimación extendida es una herramienta para sistemas no cuadrados con evolución invariante en el tiempo.
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    J.J. Medel Juárez, C.V. García Mendoza
    54-0

  • Estudio mediante dinámica molecular de la estructura tridimensional del $\kappa $-carragenano en diferentes solventes

    Abstract:
    The $\kappa $-carrageenan is an ionic polysaccharide extracted from marine red algae constituted by the copolymeric repetitive units of $\alpha $-(1-3) D-galactose 4 - sulfate and $\beta $-(1-4) 3,6-anhydro-D-galactose. The knowledge of the molecular bases that determine the three-dimensional conformation of this polysaccharide is fundamental to understand the interactions leading to gel formation, as well as the regulation of its industrial properties. As with other biopolymers, even though its primary structure is well-known, the secondary structure is still a matter of debate. This work present and discuss the results of Molecular Dynamics (MD) simulations of a decamer of the repeating disaccharide unit constituting the $\kappa $-carrageenan. The simulations were run using the GROMACS MD package, with the solute immersed in molecular solvent, either DMSO or water, and using Na+ atoms as counterions. The dynamics of the central glycosidic angles are presented, as well as the pattern of possible intramolecular and solvent mediated H-bonds and some characteristics interatomic distances. These results are in good agreement with the available experimental data, as well as those of previous molecular mechanics and dynamics.
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    C. Fernández Gauna, M. Villegas, S. Guidugli, C. Esteban, S. Paoletti, S. Pantano, J. Benegas
    61-0

  • Bonding of water to copper atom at an almost random interaction

    Abstract:
    The results of a density functional theory (DFT) study of the bonding between water and an ionized copper atom are presented through an all-electron calculation. The $C_{1},C_{2v}$ and $C_{s}$ approaches of the metal atom toward the oxygen atom on $H_{2}O$ are investigated. The analysis shows the geometric dependency of the copper-water bonding energy in the form of approaching this metal to the water molecule. Bonding exists only in the conical region perpendicular to the plane of the water molecule with vertex in the oxygen atom. Our results suggest experimental possibilities such as copper transport in water, or preventing the copper from attaching onto the water molecule by orienting it by means of external electric fields to the directions less favorable to the reaction.
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    A.N. Morales-Duarte, J.H. Pacheco-Sánchez
    69-0

  • Medidor de distancias con referencia interferometrica

    Abstract:
    An instrument for measuring distances is described. Its functioning is based in a lateral shearing interferometer and the observation of the collimation of a laser beam. Two interference patterns of straight fringes are used to measure the distance and only when the fringes are parallels the measurement is considered. Results obtained and related with resolution and uncertainty of measurement of the instrument are presented.
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    A. Jaramillo-Núñez, M. Pérez-Meza
    74-0

  • Reduction of splice loss between dissimilar fibers by tapering and fattening

    Abstract:
    A method for reducing splice loss between dissimilar optical fibers is presented. The fibers are first spliced by using a standard fusion splicing procedure, and then the fiber with the greater core is tapered before the splice point, while the fiber with the smaller core is fattened. By using this technique we have consistently obtained splice loss values of 0.13 dB between a DS/SMF and an SMF28 fiber, and 0.09 dB between a 980HP fiber and an SMF28 fiber.
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    A. Martínez-Rios, I. Torres-Gómez, D. Monzon-Hern, ez., O. Barbosa-Garcia, V.M. Duran-Ramirez
    80-0

  • Calentador de sustratos compacto y de bajo costo para tratamiento térmico in situ de películas delgadas depositadas por rf-sputtering

    Abstract:
    In this work we present the design, construction and the evaluation of a low cost substrate heater for working at high vacuum. Its use concentrates in providing in-situ annealing during the growth of thin films under conditions of controlled pressure and corrosive atmosphere. The heater was constructed mainly of stainless steel, ceramic and a resistance of khantal-Al. The body of the heater is cooled using a system of fins and cooling liquid which is isolated completely of the vacuum chamber. The design of the heater also incorporates a rotation system that allows that the substrate turns during the process of growth providing uniformity to the film. Temperature of the substrate is recorded by a type " K" thermocouple which feeds back a temperature controller that provides a modulated voltage to the heating resistance. In order to evaluate the functionality of the heating system, this was mounted in a rf-sputtering equipment and thin films of BaTiO$_{3}$ were grown under different substrate temperatures in an off-axis geometry. The heating system is able to provide an uniform temperature to the substrate as well as to operate by long periods of times.
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    A. Márquez-Herrera, E. Hernández-Rodríguez, M.P. Cruz-Jáuregui, M. Zapata-Torres, A. Zapata-Navarro
    85-0

  • Proceso de grabado seco de silicio monocristalino para aplicaciones en guías de onda coplanares

    Abstract:
    In this work, the anisotropic etching and the use of silicon rich oxide (SRO) are studied in order to improve the waveguide coplanar (CPW). Experimental results of dry etching of mono-crystalline silicon for application in CPW's using RIE/ICP reactor are presented. The contribution of the physical as much chemical components of dry etching is observed. The reactive gases that are used are Sulfur hexafluoride (SF$_{6}$) mixed with oxygen (O$_{2}$). For etching the silicon masks of photo-resist and silicon oxide (SiO2) are used, this last one is obtained by atmospheric pressure chemical vapor deposition (APCVD). Speed of etching from 2.8 to 3.4 $\mu $m/min are obtained when using SiO$_{2}$ as mask.
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    R. Leal-Romero, I.E. Zaldivar-Huerta, J.A. Re, noso-Hernández., C. Re, es-Betanzo., M.C. Ma, a-Sánchez., M. Aceves-Mijares
    92-0