Vol. 60 No. 3 May-Jun (2014): Revista Mexicana de Física.

Published: 2014-01-01

Articles

  • Determinación de la cinética de crecimiento de grano durante la solidificación de una aleación eutéctica Al-Cu

    M. Morua-Ramírez, M. Ramírez-Argaez, C. González-Rivera, A. Juárez-Hernández, M. Herrera-Trejo
    176-0
    Abstract:
    In this work a methodology is applied to describe quantitatively grain growth during solidification of a near eutectic Al-Cu alloy using cooling curves, volume grain density and solid fraction evolution data. The methodology assumes free grain growth before impingement and an exponential dependence of the grain growth rate on undercooling. Information collected is processed numerically in order to find numerical values for the pre-exponential and exponential parameters that characterize the grain growth kinetics as a function of undercooling. The evolution of solid fraction in the sample during solidification is determined by applying the Fourier (FTA) and the Newton (NTA) thermal analysis methods in order to compare their performances. The volume grain density is obtained using metallographic methods. All the obtained parameters were feed into a mechanistic model, elaborated as a part of this work, to validate the methodology. It was found a relatively good agreement between the experimental and the predicted cooling curves, which suggest that this methodology could be used to generate useful information needed to simulate eutectic solidification. NTA method is less effective than FTA method to obtain the growth parameters but its simplicity justifies its use as a first approach.
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  • A numerical calculation of the electronic specific heat for the compound \sr below its superconducting transition temperature

    P. Contreras, J. Burgos, E. Ochoa, D. Uzcategui, Rafael Almeida.
    184-0
    Abstract:
    In this work, a numerical study of the superconducting specific heat of the unconventional multiband superconductor Strontium Ruthenate, \sr, is performed. Two band gaps models are employed, and the results rendered for each of them are compared. One of the models, previously proposed by one of the authors to explain the experimental temperature behavior of the ultrasound attenuation, considers two gaps with point nodes of different magnitude on different gap surface sheets, while the other one is an isotropic and line node model, reported in the literature for describing quantitatively experimental specific heat data. The \sr superconducting density of states, DOS, is computed by employing these two models and then, a detailed numerical study of the electronic specific heat, that includes the contribution from the different Fermi sheets, is carried out. It is found that the calculated point node model specific heat temperature behavior shows an excellent agreement with the existent \sr experimental data at zero field, particularly, it is obtained that the observed specific heat jump at T$_c$ is precisely reproduced. Also, it is found that the sum of the contributions from the different bands fits quantitatively the measured specific heat data. The results in this work evidence that the \sr superconducting states are of unconventional nature, corresponding to those of a point node superconductor, and show the importance of taking into account the multiband nature of the material when calculating thermodynamic superconducting quantities.
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  • Retardo temporal en las lentes por galaxias en el contexto de Reissner - Nordstrom

    C. Mir, a., U. Molina, P. Viloria
    190-0
    Abstract:
    In this work we derive the mathematical expressions for the time delay between two images due to gravitational lensing with symmetric distributions of both: mass and electric charge from the line element in the context of Reissner - Nordstrom (RN). For this, is important to study the motion of photons that are curved around the mass distribution charged by RN metric, obtaining expressions for the deflection angle and deflection potential studying the phenomenon of so much for a lensing precise mass to mass distribution. Then applied the results, the singular sphere model isotherm (ESI), and compared with those in which only considers galaxies mass distribution. But, that this expression of the time delay is applicable to any gravitational lens model loaded too.
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  • Expanded use of a fast photography technique to characterize laser-induced plasma plumes

    M. A, T. García-Fernández, G. Diáz-Cortés, J. L, E. Rodríguez-González, C. Sánchez-Aké, A. Quintana-Nedelcos, M. Villagrán-Muniz
    195-0
    Abstract:
    Expanded use of fast photography is proposed to characterize laser ablation plasma plumes by the analysis of a set of photographs by means of appropriate mathematical algorithms. The laser ablation plasma plumes studied were generated by ablation of both a multicomponent target of the nominal composition Ni$_{50}$Mn$_{37}$Sn$_{13}$ and a highly pure Cu target (Cu) using a Q-switched Nd-YAG laser system$. $The experiments were conducted under different background argon pressures. Several photograph parameters such as intensity per unit time of exposure for a pixel, mean intensity per pixel per unit time of exposure, integrated intensity and cross correlation were studied. The intensity per unit time of exposure allowed for identification of the fast component of the triple structure of the expanding plasma into the background gas (that travels at a speed close to the one measured in vacuum). This parameter together with the use of cross correlation enabled the identification of regions of the expanded plasma plume with higher and lower similarities in their optical emission behavior. The mean intensity per pixel per unit time of exposure can be used as a measurement of the amount of light emitted by the plume as a function of time.
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  • Gravitational waves bounds in Brane-Worlds

    M. A
    205-0
    Abstract:
    This paper is dedicated to investigate an astrophysical method to obtain the new dynamics generated by extra dimensions as well as bounds for the brane tension. Using the modified Einstein equations in the brane with a vanishing non-local effects, we study the contributions of the modified radiated power by gravitational waves and the stellar period modified by branes in a binary system composed by two neutron stars. Finally we propose two lower energy bounds, using these astrophysical methods.
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  • Adherence and electrochemical behavior of calcium titanate coatings onto 304 stainless steel substrate

    J. Esguerra-Arce, Y. Aguilar, W. Aperador, N. Alba de Sánchez, G. Bolaños Pantoja, C. Rincón
    210-0
    Abstract:
    Calcium titanate has been proposed as a coating for biomedical applications but it has not been reported characterization of adhesion failure mechanisms or electrochemical properties in time. In this work have been studied these properties of a calcium titanate coating growth onto AISI 304 steel deposited by r.f. magnetron sputtering. It was found that the coating has a critical adhesive load of 6.53 $\pm$ 0.14 N. With respect to its electrochemical properties potentiodynamic polarization curves show that the calcium titanate coating provides protection to AISI 304 steel. However, EIS indicates that even though metal dissolution occur through the pores in the coating, this leads to the precipitation of salts that block pores; this precipitates layer acts like an additional barrier to the metal dissolution in the system.
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  • Optical characterization of amber of Chiapas

    G. López-Morales, R. Espinosa-Luna, C. Frausto-Re, es.
    217-0
    Abstract:
    We show the refractive index value is a vulnerable test to discriminate true amber from false amber. In this sense, the fluorescence spectral signal is also a vulnerable test if the illuminating source has a broad spectral emission. We present results that allow us to conclude the Raman spectroscopy is a reliable test to distinguish amber of Chiapas from amber of the Baltic regions, and from false amber. We suggest the inclusion of the Raman spectroscopy to the Official Mexican Norm, NOM-152-SCFI-2003, to authenticate the amber of Chiapas.
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  • An approximation of tribological behavior of Ti$_{1 - x}$Al$_{x}$N coatings against animal bone in ringer's solution

    A. Esguerra-Arce, N. A, C. Ama, a., L. Ipaz, N. Alba de Sánchez, Y. Aguilar
    222-0
    Abstract:
    Due to their excellent properties, Ti-Al-N coatings have become attractive for biomedical applications. In this paper, friction and wear properties of Ti$_{1 - x}$Al$_{x}$N films having various aluminum contents, $x$, have been studied. Adhesion was measured by the scratch test technique; friction was carried out by a pin-on-disk tribometer using an animal bone-pin as counterpart and Ringer's solution as simulated body fluid; and wear mechanisms were identified by SEM and EDS. It was found that the coating with $x$ = 0.41 exhibited the highest COF, conserves its integrity as a coating, and causes the lowest wear on the bone in Ringer's solution.
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  • Growth of metal micro and/or nanoparticles utilizing arc-discharge immersed in liquid

    B. Rebollo-Plata, M. P, G. Gallardo-Gómez, N. Ortega-Mir, a., C. F, G. Daniel-Pérez, B. Zenteno-Mateo, D. Hernández-Cruz, S. Jiménez-S, oval.
    227-0
    Abstract:
    In this paper, we present results on the metal microcrystals and nanoparticles of Al, Cu and Al-Cu composite growth by arc-discharge with the system immersed in distilled water, under different conditions and varying the current from 50 to 150 A with constant voltage (27 V). These structures are characterized using X-ray diffraction, scanning electron microscopy, Raman spectroscopy and Uv-Vis spectroscopy. Our results demonstrate that metal micro and nanostructures can be prepared at low cost with high quality.
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  • Structural changes in ZrO$_{x}$N$_{y}$/ZrO$_{2}$ coatings deposited through spray pyrolisis-nitriding

    G. I, J. J, a., M. Bethencourt, G. Cifredo, G. Blanco
    233-0
    Abstract:
    Thin films of zirconium oxynitride were deposited on stainless steel 316L and characterized through ultrasonic spray pyrolysis-nitriding (UPS-N). Initially, thin films of ZrO$_{2}$ are deposited using ultrasonic spray pyrolysis, and later ZrO$_{2 }$ films were nitrided in a NH$_{3}$ atmosphere. We analyzed the effect of some variables, such as substrate temperature, flow ratio, and time of the production of coatings and their influence on the structure of the films. The characterization was carried out using X-ray diffraction (XRD) spectroscopy, X-ray photoelectron (XPS), and scanning electron microscopy (SEM). Films that were grown using the UPS method exhibited a tetragonal zirconia polycrystalline structure with preferential orientation in plane (101). These films, after being nitrided in an atmosphere of anhydrous ammonia at 1023 K, go through two processes: a phase transition from tetragonal to monoclinic, and later the formation of zirconium oxynitride rhombohedral ZrO$_{x}$N$_{y}$.
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  • Brownian motion of a colloidal particle immersed in a polymeric solution near a rigid wall

    B. L, M. D
    243-0
    Abstract:
    By using three-dimensional digital video microscopy (DVM-3D), we study the displacement of a Brownian particle immersed in a polymeric solution located near a rigid wall. The technique takes advantage of the diffraction pattern generated by a fluorescent particle that is found below the focal plane of an optical microscope. The particle is then tracked from the analysis of a sequence of digitized images to reconstruct its trajectory, which provides relevant information about the properties of the system. In a first stage, we obtain the mean square displacement (MSD) of a spherical probe dissolved in a viscoelastic solution. This MSD is then used to determine the elastic and viscous moduli of the suspension. Such measurements are consistent with bulk measurements performed by means of two techniques, namely, diffusing wave spectroscopy and mechanical rheology. Near the rigid wall, the motion of the probe particle can be split in two directions, i.e., parallel and perpendicular to the surface. For short times (but still in the Brownian regime), such motion can be characterized by means of two distance dependent friction coefficients. We observe deviations of the measured friction coefficients in comparison with the Newtonian behavior.
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  • Dependence of the mechanical and electrical properties on the acid content in PVA+H$_{3}$PO$_{2}$+H$_2$O membranes

    M. E, J.E. Castillo, F. Bedo, a., J. E, R. A
    249-0
    Abstract:
    In this paper we report elastic modulus and ionic conductivity measurements in proton-exchange membranes based on poly (vinyl alcohol) (PVA), as a function of the acid (H$_{3}$PO$_{2}$) concentration and temperature. Tensile stress-strain test (nominal stress) was performed at low rate deformation, with acid concentration between 0.0 to 3.0 given in P/OH ratios. Results show that the elastic modulus, the elastoplastic modulus and the yield stress decrease as acid concentration increases. Ionic conductivity was obtained using the impedance spectroscopy technique on samples with the same acid concentrations, which shows an improvement in ionic conductivity of PVA+H$_{3}$PO$_{2}$+H$_2$O within the range 10$^{-3}$ - 10$^{-1}$ S cm$^{-1}$ as the acid concentration increases. The results obtained by comparing mechanical and electric properties, show that they are both directly linked to the acid content and water activity, thus these properties can be engineered to meet the appropriate conditions for an efficient fuel cell operation.
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  • Interaction of light with gravitational waves

    S. Hac, an.
    253-0
    Abstract:
    The physical properties of electromagnetic waves in the presence of a gravitational plane wave are analyzed. Formulas for the Stokes parameters describing the polarization of light are obtained in closed form. The particular case of a constant amplitude gravitational wave is worked out explicitly and it is shown that it produces a linear polarization of light.
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  • Modeling surface processes and kinetics of compound layer formation during plasma nitriding of pure iron

    F. León Cázares, A. Jiménez Ceniceros, J. Oseguera Peña, F. Castillo Aranguren
    257-0
    Abstract:
    Different approaches have been developed concerning growth description of the compact nitride layers, especially those produced by ammonia. Nitriding by plasma uses a glow discharge technology to introduce nitrogen to the surface which in turn diffuses itself into the material. During this process, the ion bombardment causes sputtering of the specimen surface. This paper presents a mathematical model of compound layer formation during plasma nitriding of pure iron. The model takes into account the erosion effect at the plasma-solid interface due to sputtering. This erosion effect is computer simulated and adjusted in order to consider its contribution to the study of layer growth kinetics. The model is presented as a moving boundary diffusion problem, which considers the observed qualitative behavior of the process.
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