Vol. 60 No. 6 Nov-Dec (2014): Revista Mexicana de Física.

Published: 2014-01-01

Articles

  • Quality control of the breast ca treatments on HDR brachytherapy with TLD-100

    F. Torres Ho, os., N. De La Espriella Vélez, A. Sánchez Caraballo
    409-0
    Abstract:
    An anthropomorphic Phantom, a female trunk, was built with a natural bone structure and experimental material coated, glycerin and water-based material called JJT to build soft tissue equivalent to the muscle of human tissue, and a polymer (styrofoam) to build the lung as critical organ to simulate the treatment of breast cancer, with high dose rate brachytherapy (HDR) and sources of Ir-192. The treatments were planned and calculated for the critical organ: Lung, and injury of 2 cm in diameter in breast with MicroSelectron HDR system and the software Plato Brachytherapy V 14.1 of the Nucletron (Netherlands) which uses the standard protocol of radiotherapy for brachytherapy treatments. The dose experimentally measured with dosimeters TLD-100 LIF: Mg; Ti, which were previously calibrated, were placed in the same positions and bodies mentioned above, with less than 5% uncertainty. The reading dosimeters was carried out in a Harshaw TLD 4500.The results obtained for calculated treatments, using the standard simulator, and the experimental with TLD-100, show a high concordance, as they are on average a $\pm$ 1.1% making process becomes in a quality control of this type of treatments.
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  • Complete solutions of the Hamilton--Jacobi equation and the envelope method

    G.F. Torres del Castillo, G.S. Ana, a González.
    414-0
    Abstract:
    It is shown that the parameters contained in any two complete solutions of the Hamilton--Jacobi equation, corresponding to a given Hamiltonian, are related by means of a time-independent canonical transformation and that, in some cases, a generating function of this transformation is given by the envelope of a family of surfaces defined by the difference of the two complete solutions. Conversely, in those cases, one of the complete solutions is given by the envelope of a family of surfaces defined by the sum of the other complete solution and the generating function of the canonical transformation. Some applications of these results to geometrical optics are also given.
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  • Monte Carlo studies of critical phenomena in mixed spin-3/2 and spin-5/2 Ising model on square lattice

    N. De La Espriella Vélez, J. Madera Yancez, M. S
    419-0
    Abstract:
    We used a Monte Carlo simulation to analize the magnetic behavior of Ising model of mixed spins $S_{i}^{A}$= $\pm 3/2, \pm 1/2$ and \linebreak $\sigma_{j}^{B}$ = $\pm 5/2, \pm 3/2, \pm 1/2$, on a square lattice. Were studied the possible critical phenomena that may emerge in the region around the multiphase point $(D/|J_{1}|=-3, J_{2}/|J_{1}|=1)$ and the dependence of the phase diagrams with the intensities of the anisotropy field of single ion ($D/|J_{1}|$) and the ferromagnetic coupling of exchange spin $S_{i}^{A}$ ($J_{2}/|J_{1}|$). The system displays first order phase transitions in a certain range of the parameters of the Hamiltonian, which depend on $D/|J_{1}|$ and $|J_{2}/|J_{1}|$. In the plane ($D/|J_{1}|, k_{B}T/|J_{1}|$), the decrease of $|D/|J_{1}||$, implies that the critical temperature, $T_{c}$, increases and the first order transition temperature, $T_{t}$, decreases. In the plane ($J_{2}/|J_{1}|, k_{B}T/|J_{1}|$), $T_{c}$ increases with the increasing of $J_{2}/|J_{1}|$, while that $T_{t}$ decreases.
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  • Micro displacement measured by the grating interferometer with rings pattern

    A. Olivares-Perez
    425-0
    Abstract:
    Micro displacements are measured with holographic gratings by using a grating interferometer of one order that detects the phase changes in the diffracted orders caused by movement of the grooves in the diffraction gratings. The period can be on the order of fractions of a micron, with high reproducibility and an error of a half period. The basic operating principle involves the superposition of order +1, with order 0. The interferometer system produces standing waves; it works by measuring the intensity variations at the center of a ring-shaped interference pattern, which indicate the phase shift introduced by displacement of the grating grooves. When these rings move to the center of the pattern or to the border, the direction of the grating displacement can be detected; the interferometer system has no moving parts, except for the diffraction grating, and is very stable and robust. This system has the ability to measure micro displacements even with damaged gratings, as long as the gratings diffract evenly.
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  • Desarrollo de una cama de pruebas experimental para sistemas IR-UWBoF-IM/DD basándose en el uso de la plataforma de simulación VPIphotonics

    A. E, A. Arvizu, S. Villarreal-Re, es., C. Lepers, J. Santos-Aguilar, D. H
    435-0
    Abstract:
    In this work we describe the design of an Impulse-Radio Ultra-Wide band over Fiber (IR-UWBoF) system implemented on the\linebreak VPItransmissionMaker$^{\textrm{TM}}$ simulation software. This IR-UWBoF system uses the simple and low cost intensity external modulation with direct detection (IM/DD) technique to transmit IR-UWB signals at 1 Gbps of data rate through a standard single mode optical fiber (SSMF) link. We validate our proposal by means of a comparative analysis between the Power Spectral Density (PSD) of IR-UWB signals generated by simulation and the PSDs of signals obtained by an experimental IR-UWBoF IM/DD system. The maximum bandwidth of the proposed system is 10 GHz, which it is determined by the frequency response of the electro-optic modulator and the electric devices used. The analysis of results show that the simulated IR-UWBoF system can be used as an experimental testbed to analyze and to evaluate IR-UWB transmissions through optical fiber links in a fast and accurate manner.
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  • Polarimetric parameters associated to commercial optical fibers

    O. J, K. M, R. Espinosa-Luna, G. Atondo-Rubio, I. Torres-Gómez
    443-0
    Abstract:
    The most important polarimetric parameters are determined for six different types of commercially available optical fibers, at 1550 nm of transmission wavelength. The diattenuation, polarizance, retardance, polarization dependent loss (PDL), among other conventional polarimetric parameters, are determined from the Mueller matrix associated to 1m length of each fiber studied here. An improvement to the data analysis method, reported recently by our group, is presented. Results obtained show the fibers can be used not only as static elements, but also as versatile optical devices, depending on the incident polarization state employed.
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  • Interdigitated capacitance sensors in the mm scale with sub-femtoFarad resolution suitable for monitoring processes in liquid films

    A. Guadarrama-Santana, A. García-Valenzuela, F. Pérez-Jiménez, L. Polo-Parada
    451-0
    Abstract:
    We propose and analyze a high resolution capacitive sensor appropriate for monitoring physical or chemical processes in liquid films. The proposed sensor is based on a planar interdigitated capacitor with planar electrodes of dimensions in the milimeter scale. The electric field between electrodes extend above the plane of the electrodes up to a few milimeters and thus permits placing a dielectric container with a liquid film on top and still be sensitive to changes in the liquid film. First, we present numerical calculations of the capacitance of an interdigitated sensor as a function of the thickness and dielectric constant of a film placed on top of it using a finite element method. Then, we describe a suitable electronic system to sense with very high-resolution capacitance variations of the sensor by measuring the phase lag and amplitude change of a sinusoidal current signal passing through it. This is accomplished by subtracting a stable sinusoidal current of the same frequency going through a reference device. Initially the system is balanced by adjusting the reference current to cancel out the net output current. In this way, we compensate parasitic capacitances due to electronics, wiring and system hardware as well. When the capacitance of the sensor element varies the system gets unbalanced and a net current appears. The resulting current is measured with a locking-amplifier. To illustrate the sensitivity and resolution achieved by the sensing system, we present results of monitoring the capacitance of the sensor during the evaporation of liquid solvent films and discuss the time-evolution of the registered signals. The floor noise throughout the measurements was in the order of 50 atto-Farads while the signal varied in the range of several femto-Farads.
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  • DFT study of interaction between a hydrogen molecule and AgY-zeolite

    I. P, J. H, I. Echevarria-Chan, A. Bravo-Ortega
    460-0
    Abstract:
    The cationic exchange of H by Ag in a HY-{\em zeolite} is carried out to study the adsorption of a hydrogen molecule in an AgY-zeolite, which is achieved by means of a BOMD simulation. The chosen zeolite model is representative of adsorbent materials when a cation {\em Ag} forms part of surface fragments, and they are considered in this interaction. This study provides a criterion to establish the electronic property of cation promoting a relevant characteristic that must have an adsorbent material. The energy values on this interaction are analyzed to determine an evaluation of the hydrogen adsorption using a AgY{\em -zeolite} ring and fragments of 3 tetrahedral sites. The AgY{\em -zeolite} ring represents a cavity that exhibits diffusivity after an adsorption process. This study was developed in the density functional theory level with {\em DZVP} function bases.
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  • Diagrama de fase sitio-enlace en dímeros

    W. Lebrecht, M. I, J. F
    466-0
    Abstract:
    This paper presents an approximate analytical calculation to characterize the percolation in a system where coexist bonds and sites dimers. A dimer is the simplest representation of individuals who are bound to nearest neighbors. Percolation functions represented by polynomials, obtained by numerical listing of a cell of size $N=L_x \times L_y$ for sites and bonds dimers are calculated. In the thermodynamic limit, the percolation threshold for site dimer (bond dimer) is $0.562$ ($0.486$) on a square lattice, values that are in line with their counterparts obtained by numerical simulations. To determine the site-bond phase diagram of dimers on a square lattice, the OR and AND operations associated to the functions of a finite percolation cell are used and performed well with similar results in numerical simulations shown in the literature.
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