Vol. 55 No. 1 (2009): Revista Mexicana de Física.

Published: 2009-01-01

Articles

  • Transferencia energética en un modelo multicapa de tejido humano sometido a irradiación electromagnética de alta frecuencia

    Á.J. García-Collado, G.J. Molina-Cuberos, M.J. Núñez
    1-0
    Abstract:
    The way the energy is absorbed when skin surface is being exposed to an electromagnetic radiation, and the physical consequences involved, are essentially the purposes of this study. In particular, we are dealing with High Frequency radiation. When it is directed toward the surface of the skin, energy is transmitted to its inner layers causing an increase of the temperature. This process has experimentally been proved to be beneficial in many cases. Yet theoretically there is still a slightly hollow basis about it. This study pretends to deal with that subject from its origin, and allows future study doors to tap in depth this theme. Skin tissue is actually a multilayer tissue with a different tissue in each layer. Each one of them is characterized by some parameters, such as permittivity, conductivity, density and specific heat. Two kinds of skin tissues will be analysed: a fibrous and a fatty one, each of both with a different skin humidity. In this study some parameters such as the non-linear temporal evolution of tissue temperature and the redistribution of heat them will be take into account.
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  • Resolved component of the photon in heavy quark photoproduction

    E. Cuautle, I.A. Maldonado-Cervantes, G. Mora
    8-0
    Abstract:
    Heavy quarks in $\gamma-N$ interactions are produced mainly by photon-gluon fusion. Nevertheless a small contribution to the total cross section comes from processes like those appearing in heavy quarks hadroproduction through the resolved component of the photon. Here we concentrate on the resolved contributions of the photon to heavy meson photoproduction. We discuss the calculation of the cross section to $D's$ and $B's$, as well as its dependence on the fragmentation function and the center of mass energy available in the collisions.
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  • Electromechanical analysis of a piezoresistive pressure microsensor for low-pressure biomedical applications

    A.L. Herrera-Ma, B.S. Soto-Cruz, F. López-Huerta, L.A. Aguilera Cortés, .
    14-0
    Abstract:
    The electromechanical analysis of a piezoresistive pressure microsensor with a square-shaped diaphragm for low-pressure biomedical applications is presented. This analysis is developed through a novel polynomial model and a finite element method (FEM) model. A microsensor with a diaphragm 1000 $\mu $m length and with three different thicknesses (10, 15, and 20 $\mu $m) is studied. The electric response of this microsensor is obtained with a Wheatstone bridge of four p-type piezoresistors located on the diaphragm surface. The diaphragm that is 10 $\mu $m thick exhibits a maximum deflection of 3.74 $\mu $m using the polynomial model, which has a relative difference of 5.14 and 0.92% with respect to the Timoshenko model and the FEM model, respectively. The maximum sensitivity and normal stress calculated using the polynomial model are 1.64 mV/V/kPa and 102.1 MPa, respectively. The results of the polynomial model agree well with the Timoshenko model and FEM model for small deflections. In addition, the polynomial model can be easily used to predict the deflection, normal stress, electric response and sensitivity of a piezoresistive pressure microsensor with a square-shaped diaphragm under small deflections.
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  • Optimization of the diffraction efficiency in non-uniform gratings in sillenite crystals (Bi$_{12}$SiO$_{20}$ and Bi$_{12}$TiO$_{2}$) considering the variation of fringe period, optical activity and polarization angles in a strong non-linear regime

    G. González, A. Zúñiga, F. Magaña
    25-0
    Abstract:
    We included the non-uniformity of the grating and of the magnitude and phase of light modulation throughout the sample thickness to optimize the diffraction efficiency. The variation of fringe period, optical activity, birefringence, absorption of light, and polarization angle were considered. We studied strong nonlinear conditions and two crystal orientations one is with the grating vector parallel to the face [001] and the other is with the grating vector perpendicular to the same face. We included applied fields There is a complex relationship among all these parameters, and the prediction of the conditions for the optimum value of the diffraction efficiency is complicated. We report the optimal sample thickness for different situations, considering two wavelengths for reading: green (532 nm) and red (632 nm).
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  • Crystallization kinetics of a soda lime silica glass with TiO$_{2}$ addition

    S.M. de la Parra-Arciniega, A. Álvarez-Méndez, L.C. Torres-González, E.M. Sánchez
    32-0
    Abstract:
    Studies conducted into Na$_{2}$O-CaO-3SiO$_{2}$ glass composition suggest that its phase transformation occurs from the surface towards the interior of the sample. In a study carried out in 1982, it was reported that no addition of nucleating agents modified the mechanism. Taking advantage of the disposition materials synthesized by nanotechnology, in this study TiO$_{2}$ in nanometer size was used with the idea that, because of its qualities, it could modify the crystallization mechanism. The glasses obtained as well as the thermally treated samples, were evaluated by the X-ray diffraction (XRD) powder method, differential thermal analysis (DTA), and by optical microscopy and high resolution transmission electron microscopy (HRTEM). Within the range of TiO$_{2}$ concentration studied (0 -- 10 wt %), 10 wt % of TiO$_{2}$ considerably reduced the Na$_{2}$O-2CaO-3SiO$_{2}$ phase crystallization process. The crystallization mechanism was not modified and TiO$_{2}$ did not form compounds with the matrix components.
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  • Fluctuaciones aleatorias en la acción quimioterapéutica sobre tumores cancerosos

    A. Castellanos-Moreno, J. Argüelles-Campo, A. Corella-Madueño., S. Gutiérrez-López, R.A. Rosas-Burgos., .
    38-0
    Abstract:
    A small patch of a tumor is considered, so that lymphocytes and cancerigenic cell densities are independent of the spatial position. So, a non spatial model with random transition birth and death rates are treated through one-step processes and such that chemotherapy on the physical system is included. Van Kampen expansion is used to separate a macroscopic and a microscopic part. The first one is described through a set of two nonlinear and coupled ordinary differential equations, and the microscopic part is described by using a Fokker-Planck equation. Evolution on time of the mean fluctuations and autocorrelation functions of noise are linear non autonomous systems. The macroscopic part is studied numerically, so that two basins are found, one of fatal results and other of healthy patient. Jacobian matrix has negative eigenvalues, so that there are stable attractor points inside each basin. When a chemotherapy parameter is increased, the final macroscopic state is moved from fatal to healthy basin. While macroscopic stability is found, microscopic results are very different and this is seen by studying the asymptotic behavior of the random fluctuations. This is done by evaluating the eigenvalues of the involved matrices and it is found that random fluctuations has unbounded standard deviations, suggesting that disease could appear again.
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  • Effects of indium doping on the structural and optical properties of CdSe thin films deposited by chemical bath

    A.M. Pérez González, I.V. Arreola, C.S. Tepantlán
    51-0
    Abstract:
    Thin films of n-type CdSe have been grown on Corning glass substrate by chemical bath deposition, prepared with Sodium Seleno-Sulphate (Na$_{2}$SSeO$_{3})$, Cadmium Chloride (CdCl$_{2})$ and Indium Tri-Chloride (InCl$_{3})$, mixed in an aqueous environment. The effects of different In doping concentrations have been investigated. X-ray diffraction spectra show that at low In concentration only the CdSe lattice is present in the deposited film, whereas CdIn$_{2}$Se$_{4 }$and InSe compounds are obtained at higher In concentrations. Optical properties have been calculated from transmission spectra and photoluminescence measurements. From transmission spectra, the absorption coefficient and optical gap were obtained; photoluminescence spectra show band-band recombination from 10 K to room temperature.
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  • Optimal configuration of heat engines for maximum efficiency with generalized radiative heat transfer law

    Lingen Chen., Hanjiang Song., Fengrui Sun., Shengbing Wang.
    55-0
    Abstract:
    Optimal configuration of a class of endoreversible heat engines with generalized radiative heat transfer law $[q \propto \Delta (T^n)]$ has been determined by this paper. The optimal cycle that maximizes the efficiency of the engines with fixed input energy has been obtained using optimal-control theory, and the differential equations are solved by Taylor series expansion. It is shown that the optimal cycle for maximum efficiency has eight branches including two isothermal branches, four maximum-efficiency branches and two adiabatic branches. The interval of each branch has been obtained, as well as the solutions of the temperatures of heat reservoirs and working fluid. Numerical examples are given for the optimal configurations with $n {=} - 1$, $n {=} 1$, $n {=} 2$, $n {=} 3$ and $n {=} 4$, respectively. The results obtained are compared with each other and with those results obtained for maximum power output.
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  • Robustness of noise induced resonances

    J. Escalona, P. Parman, a.
    68-0
    Abstract:
    In order to confirm the emergence of resonances in the presence of non-stationary noise, an excitable FitzHugh-Nagumo (FN) system is subjected to stochastic forcing both in the absence and in the presence of sub-threshold signals. This non-stationarity of noise is mimicked by varying the noise sequence (seed) for each amplitude of the superimposed noise while preserving their statistical properties. Our numerical computations indicate that noise induced resonances for this non-stationarity stochastic forcing become less conclusive for complex subthreshold signals.
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  • Láser de fibra con emisión dual seleccionable usando rejillas de bragg de fibra y fibra dopada con erbio

    M. Durán-Sánchez, E.A. Kuzin, B. Ibarra-Escamilla, M. Bello-Jiménez., A. Flores-Rosas, G. Beltrán Pérez, J.L. Hernández Rebollar
    73-0
    Abstract:
    A switchable dual wavelength fiber laser is proposed and experimentally demonstrated based on fiber Bragg gratings by using a linear cavity, adjusting the overlap on the Bragg gratings and the homogeneous gain broadening of the erbium doped fiber (EDF). The single or dual lasing wavelength can be also obtained by matching the wavelength of the Bragg gratings.
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