Vol. 59 No. 4 (2013): Revista Mexicana de Física.

Published: 2013-01-01

Articles

  • On the mass flow rate from silos with lateral exit holes

    A. Medina, D. A, G. J, K. Kesava Rao, C. A
    287-0
    Abstract:
    The mass flow rate, $\overset{\cdot }{m}$, associated with the lateral outflow of dry, cohesionless granular material through circular orifices of diameter $D$ made in vertical walls of silos was measured experimentally in order to determine also the influence of the wall thickness of the silo, $w$. Geometrical arguments, based on the outflow happening, are given in order to have a general correlation for $\overset{\cdot }{m}$ embracing both quantities, $D$ and $w$. The angle of repose appears to be an important characterization factor in these kinds of flows.
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  • Element distribution imaging in rat kidney using a 2D rapid scan EDXRF device

    R.G. Figueroa, E. Lozano, G. Bongiovanni
    292-0
    Abstract:
    Visualization of elemental distributions of biological tissue is gaining importance in many disciplines of biological, forensic, and medical research. Furthermore, the maps of elements have wide application in archeology for the understanding of the pigments, modes of preservation and environmental context. Since major advances in relation to collimators and detectors have yielded micro scale images, the chemical mapping via synchrotron scanning micro-X-ray fluorescence spectrometry (SR-$\mu $XRF) is widely used as microanalytical techniques. However, the acquisition time is a limitation of current SR-$\mu $XRF imaging protocols, doing tedious micro analysis of samples of more than 1 cm and very difficult to study of larger samples such as animal organ, whole organisms, work of art, etc. Recently we have developed a robotic system to image the chemistry of large specimens rapidly at concentration levels of parts per million. Multiple images of distribution of elements can be obtained on surfaces of 100$\times$100 mm and a spatial resolution of up to 0.2 mm$^{2}$ per pixel, with a spectral capture time up to 1 ms per point. This system has proven to be highly efficient for the XRF mapping of elements in large biological samples, achieving comparables results to those obtained by SR-$\mu $XRF. Thus, images of As and Cu accumulation in renal cortex of arsenic-exposed rats were obtained by both methodologies. However, the new imaging system enables the XRF scanning in few minutes, whereas SR-$\mu $XRF required several hours. These and other advantages as well as the potential applications of this system, will be discussed.
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  • Element distribution imaging in rat kidney using a 2D rapid scan EDXRF device

    R.G. Figueroa, E. Lozano, G. Bongiovanni
    292-0
    Abstract:
    Visualization of elemental distributions of biological tissue is gaining importance in many disciplines of biological, forensic, and medical research. Furthermore, the maps of elements have wide application in archeology for the understanding of the pigments, modes of preservation and environmental context. Since major advances in relation to collimators and detectors have yielded micro scale images, the chemical mapping via synchrotron scanning micro-X-ray fluorescence spectrometry (SR-$\mu $XRF) is widely used as microanalytical techniques. However, the acquisition time is a limitation of current SR-$\mu $XRF imaging protocols, doing tedious micro analysis of samples of more than 1 cm and very difficult to study of larger samples such as animal organ, whole organisms, work of art, etc. Recently we have developed a robotic system to image the chemistry of large specimens rapidly at concentration levels of parts per million. Multiple images of distribution of elements can be obtained on surfaces of 100x100 mm and a spatial resolution of up to 0.2 mm$^{2}$ per pixel, with a spectral capture time up to 1 ms per point. This system has proven to be highly efficient for the XRF mapping of elements in large biological samples, achieving comparables results to those obtained by SR-$\mu $XRF. Thus, images of As and Cu accumulation in renal cortex of arsenic-exposed rats were obtained by both methodologies. However, the new imaging system enables the XRF scanning in few minutes, whereas SR-$\mu $XRF required several hours. These and other advantages as well as the potential applications of this system, will be discussed.
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  • Collinear inelastic collisions of an atom and a diatomic molecule using operator methods

    T. Wendler, J. Récamier, M. Berrondo
    296-0
    Abstract:
    We calculate transition probabilities between vibrational levels of a diatomic molecule induced by an incident atom. Our prototype model is constructed treating the relative translation of the colliding species as a classical variable. The vibrational states of the diatomic molecule are treated quantum mechanically in terms of the evolution operator without involving wave functions. The corresponding equations of motion are coupled quasi-classically. For illustration purposes we present applications to the time dependence of transition probabilities for different initial and final states as well as a canonical ensemble of initial conditions.
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  • On polarization of the fluorescence in erbium-doped fibers

    L. O, E. Hernández-Hernández, S. Stepanov
    302-0
    Abstract:
    Theoretical evaluations of polarization degree of the fluorescence excited in erbium doped fibers (EDF) dependence on the excitation light power are presented. In calculations we use the model of randomly oriented and not interacting Er$^{3 + }$ ions. Assumption of the reduced optical anisotropy of the individual ions (with the absorption/emission cross-sections described with the ellipsoids) is shown to be necessary to get a reasonable agreement with the existing experimental data. Similar values of the anisotropy parameters (0.6-0.7) are also utilized to explain the experimental data on polarization hole burning in EDF earlier.
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  • Síntesis y caracterización de la doble perovskita BaSrCoFe$_{1 - x}$Ni$_{x}$O$_{5.5}$ como cátodo para celdas SOFC

    J. Alvarado-Flores, L. Ávalos-Rodríguez, G. Viramontes-Gamboa, A. Re, es-Rojas.
    309-0
    Abstract:
    Have been synthesized via sol-gel method and characterized by X-ray diffraction (XRD), electrical conductivity and thermal expansion coefficient (TEC), new material composites BaSrCoFe$_{1 - x}$Ni$_{x}$O$_{5.5}$ (double perovskite type) with the addition of Ni in solid solution Ni$_{x}$ (x = 0.025, 0.05, 0.075, 0.1 and 0.2), as alternative cathodes for solid oxide fuel cells of intermediate temperature (SOFC-IT). XRD confirmed the formation of the tetragonal structure perovskite phase BaSrCoFe$_{1 - x}$Ni$_{x}$O$_{5.5}$, with the presence of small peaks identified in 2$\theta $ values below 30$^{\circ}$ as BaCO$_{3}$ and CoFe$_{2}$O$_{4}$. The electrical conductivity increases with temperature between 350-470$^{\circ}$C and then decreases due to the loss of oxygen in the net, which causes differences in conductivity. Semiconductor behavior was obtained in all compositions. TEC determination, showed a linear dependence inversely proportional to the concentration of Ni. Our results of electrical conductivity and TEC, lead us to the conclusion that the cathodes between 0.1 and 0.2 Ni, have the greatest possibility for application in IT-SOFC.
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  • Fabrication and investigation of large-mode-area photonic crystal fibers

    M. Vaca-Pereira, V. P, S. Calixto
    317-0
    Abstract:
    This paper describes design, fabrication and testing of all-silica large-mode-area (LMA) photonic crystal fibers (PCFs) with three full hexagonal air capillaries rings in a cladding. The design is based on $V$ (normalized frequency) and $W$ (normalized transverse attenuation constant) parameters. Capillaries and rods for a PCF preform were fabricated using this preliminary design. The designed preform was stretched into LMA PCF fibers and then some values for fabricated PCFs, such as geometric dimensions, numerical aperture and attenuation have been measured. Measured values are compared with ones preliminary calculated by using $V$ and $W$ parameters. It is shown that the obtained experimental results are very near to calculated ones.
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  • Influencia de un tratamiento térmico en el comportamiento tribológico de aceros Fe-Mn-Al

    L. Ipaz, W. Aperador, A. Esguerra-Arce
    322-0
    Abstract:
    In this paper, we evaluate the wear resistance of two types of alloys fermanal (AF1 and AF2) with and without thermal treatment (TT) and compared with ASTM A240 stainless steel (AI) through the testing pin-on-disk. The tribological tests were carried out using a alumina pin diameter of 6 mm, a normal load of 10 N and 300 m of travel, the test speed was 120 rpm and were evaluated at two temperatures: room temperature and 300$^{\circ}$C. It was observed that fermanal alloys with high content of manganese (AF2) have the highest wear resistance at room temperature and at high temperatures is resistant the AI, followed by fermanal AF1. Through Scanning electron microscopy is found micro-plowing, adhesion and oxidation as the dominant wear mechanisms.
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  • The lumped heat capacity method applied to target heating

    J. Rickards
    328-0
    Abstract:
    The temperature of metal samples was measured while they were bombarded by the beam from the a particle accelerator. The evolution of the temperature with time can be explained using the lumped heat capacity method of heat transfer. A strong dependence on the type of mounting was found.
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  • SnO$_{2}$:F thin films deposited by RF magnetron sputtering: effect of the SnF$_{2}$ amount in the target on the physical properties

    F. de Moure-Flores, A. Guillén-Cervantes, K.E. Nieto-Zepeda, J.G. Quiñones-Galván, A. Hernández-Hernández, M. de la L, M. Meléndez-Lira
    335-0
    Abstract:
    SnO$_{2}$:F thin films were prepared by RF magnetron sputtering onto glass substrates using SnF$_{2}$ as fluorine source. The films were deposited under a mixed argon/hydrogen atmosphere at a substrate temperature of 500$^{\circ}$C. The X-ray diffraction shows that polycrystalline films were grown with a phases mixture of SnO$_{2}$ and SnO. The optical transmittance is between 80 and 90%. The physical properties of the films suggest that SnO$_{2}$ thin films grown with small SnF$_{2}$ content in the target can be considered as candidates for transparent electrodes.
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  • Dose distribution calculation for in-vivo X-ray fluorescence scanning

    R.G. Figueroa, E. Lozano, M. Valente
    339-0
    Abstract:
    In-vivo X-ray fluorescence constitutes a useful and accurate technique, worldwide established for constituent elementary distribution assessment. Actually, concentration distributions of arbitrary user-selected elements can be achieved along sample surface with the aim of identifying and simultaneously quantifying every constituent element. The method is based on the use of a collimated X-ray beam reaching the sample. However, one common drawback for considering the application of this technique for routine clinical examinations was the lack of information about associated dose delivery. This work presents a complete study of the dose distribution resulting from an in-vivo X-ray fluorescence scanning for quantifying biohazard materials on human hands. Absorbed dose has been estimated by means of dosimetric models specifically developed to this aim. In addition, complete dose distributions have been obtained by means of full radiation transport calculations in based on stochastic Monte Carlo techniques. A dedicated subroutine has been developed using the PENELOPE 2008 main code also integrated with dedicated programs -MatLab supported- for 3D dose distribution visualization. The obtained results show very good agreement between approximate analytical models and full descriptions by means of Monte Carlo simulations.
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  • Catodoluminiscencia en películas de óxido de hafnio activadas con europio y terbio, depositadas por la técnica de RPU

    R. Carbajal-Valdez, J. Guzmán-Mendoza, M. García-Hipólito, O. Álvarez-Fragoso, M. A, C. Falcon, .
    343-0
    Abstract:
    By means of the ultrasonic spray pyrolysis technique, trivalent terbium and europium doped hafnium oxide coatings were synthesized. These coatings are non-crystalline at substrate temperatures lower than 350$^{\circ}$C; for higher substrate temperatures the films are polycrystalline presenting the HfO$_{2}$ monoclinic phase. The cathodoluminescence spectra for these films were studied as a function of the substrate temperature and the doping concentration. Samples excited with electron beam showed visible emission bands, associated to the electronic transitions of the trivalent europium and terbium ions. As the substrate temperatures are increased, an increment of the cathodoluminescence emission intensity was detected. In addition, a concentration quenching of the cathodoluminescence intensity was observed. Also, the chemical compositions of the deposited coatings and the characteristics of their surface morphologies are shown.
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  • SL(2,R)-geometric phase space and (2+2)-dimensions

    R. Flores, J. A, J. Tellez, E. A, E. R
    352-0
    Abstract:
    We propose an alternative geometric mathematical structure for arbitrary phase space. The main guide in our approach is the hidden SL(2,R)-symmetry which acts on the phase space changing coordinates by momenta and % vice versa. We show that the SL(2,R)-symmetry is implicit in any symplectic structure. We also prove that in any sensible physical theory based on the SL(2,R)-symmetry the signature of the flat target ``spacetime'' must be associated with either one-time and one-space or at least two-time and two-space coordinates. We discuss the consequences as well as possible applications of our approach on different physical scenarios.
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  • Celda lógica en un sistema bidimensional

    I. Campos-Cantón, R. E, a-Ponce., R.O. Lozo, a-Ponce.
    359-0
    Abstract:
    This paper is about the implementation of binary logic cells, based on the idea of using state space in a two-dimensional linear system with different real eigenvalues. The proposed circuit is made up of resistors, capacitors and comparators. This cell is capable of generating the logic functions OR and AND.
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  • Tribological performance evidence on ternary and quaternary nitride coatings applied for industrial steel

    J. C, W. Aperador, Y. Aguilar
    364-0
    Abstract:
    A diagnostic of mechanical and tribological behavior in ternary Ti-C-N and quaternary Ti-Nb-C-N films deposited onto Si~(100) and 4140 steel substrates by r.f. magnetron sputtering processvarying negative bias voltage from 0 to -100~V,was done in this work. Growth parameters as power density, Ar/N$_{2}$ flow rate, and substrate temperature were keptconstant at the moment of the deposition. Introduction of Nb in the ternary Ti-C-N film was evaluated by X-ray diffraction (XRD) analysis.Quantitative elemental concentration depth profile by glow discharge optical emission spectroscopy (GDOES) and the morphology via scanning electron microscopy (SEM) were observed for the layers before the tests. Mechanical and tribological properties for both coatings were obtained by mean of nanoindentation measurements throughload versus displacement method, and scratch test using the critical load criterion, respectively. The failure modes from scratch test were observed via optical microscopy. XRD results show as the amount of Nb is increased into the quaternary phase, the preferred orientation change in the film due to the modification in the strain and lattice parameter (Caicedo et al., 2007). EDX results from previous work show the TiCN and TiNbCN layers were stoichiometric (Caicedo et al., 2007). Nanoindentation results reaching the elastic-plastic behavior of the Ti{}C{}N and Ti{}C{}N films with inclusion of Nb (Ti{}Nb{}C{}N), indicate not only the hardness and elastic modulus but also the critical load for the adhesive failure increase when increasing r.f negative bias voltage. An improvement of hardness and critical load around 60% and 28% for Ti{}C{}N as well as 26% and 31%for Ti{}Nb{}C{}N, respectively, was associated to an increasing in the r.f negative bias voltage from 0 to~-100 V.
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  • Bismuth coatings deposited by the pulsed dc sputtering technique

    M.F. Ortiz J.J, a., J.E. Alfonso
    374-0
    Abstract:
    In this work we present the results obtained from the deposition of nano-structured bismuth coatings through DC pulsed unbalanced magnetron sputtering. The coatings were grown on two substrates: silicon and AISI steel 316 L. The microstructure of the Bi coatings grown on silicon and the corrosion resistance of the Bi coatings grown on AISI steel were evaluated. The microstructure was evaluated by X-ray diffraction (XRD) and the corrosion resistance was characterized by means of polarization potentiodynamic and electrochemical impedance spectroscopy. Finally the morphology of the coatings was evaluated through scanning electronic microscopy (SEM). The XRD analysis indicates that the coatings are polycrystalline; the corrosion resistance tests indicate that the films with better corrosion resistance were deposited at 40 kHz. SEM micrographs show that the coatings are grown as granular form.
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