Vol. 55 No. 5 (2009): Revista Mexicana de Física.

Published: 2009-01-01

Articles

  • Multibody effects in intermolecular interactions and reaction pathways for catalytic processes. Part II the contributions of Sidonio Castillo

    O. Novaro, J.H. Pacheco-Sánchez, H. Luna
    332-0
    Abstract:
    We here continue the review on the work of Octavio Novaro and collaborators in the important fields of nonadditivity of intermolecular interactions and catalysis, with special interest in the work that Sidonio Castillo contributed to this effort before his demise. His early work with Polish coauthors on methane and ammonia trimers and with British coauthors on N$_{3}$, P$_{3}$, N$_{4}$ and P$_{4}$ are highlighted. Then our focus will shift mainly to his work on the activation of methane, silane and germane starting with his Ph.D. thesis under O. Novaro and ending in his last papers with the present authors which marked the end of his short but brilliant career.
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  • Effects of compositional proportions, metal-ion concentration and pH conditions into the structural characteristics of Au, Pt and AuPt nanoparticles

    R. Esparza, J.A. Ascencio, R. Pérez, G. Rosas, U. Pal
    339-0
    Abstract:
    Nanometric metallic particles of Pt, Au and Au/Pt of different nominal compositions were synthesized using a chemical reduction method with a polymer (PVP) as the protecting agent. The effects of the gold ion concentrations and also of the concentration of the reducing agent compound, on the morphology and structural characteristics of the obtained gold nanoparticles have been explored. Particles with different pH reaction mixtures have been synthesized. High resolution transmission electron microscopy (HRTEM) observations have been used in the nanoparticles characterization. Depending of the pH reaction mixtures, different nanometric sizes and consequently different atomic structural configurations of the particles are obtained. Theoretical simulations based on molecular dynamics have been used to interpret some of the experimental results and also to get an insight on macroscopic properties such as: stability and catalytic activity.
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  • Bode plots applied to microscopic interferometry

    J.M. Flores, M. C, wiak., M. Servín, L. Juárez
    347-0
    Abstract:
    We describe a technique for using Bode plots in microscopic interferometry, in particular as applied to the three Gaussian beam interferometer recently reported in the literature. The technique is used in a similar manner to its application to an electric or electronic system in finding its frequency response. The Bode response is used to deconvolve the raw data obtained directly from the interferometer to compensate for the data in frequency, making it possible to obtain more realistic profiles of the samples under test. We apply this technique to obtain profiles of the inner reflective layers of two optical types of surfaces for data storage commercially available, namely, the compact disk (CD-R) and the digital versatile disk (DVD-R). We report the experimental results of radial scans of these devices without data marks, before and after applying the transfer function of the system. The measurements are obtained by placing the devices with the polycarbonate surfaces so as to aim the probe beam of the interferometer at them, taking advantage of the vertical depth discrimination of the microscope. We show that the resulting profiles, obtained across the Polycarbonate layer, measured with this interferometer, give valuable information of the real track profiles, making the combination of the Bode plots with this interferometer a suitable tool for quality control of the surface storage devices.
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  • Reconstrucción de dosis a partir del efecto pre-dosis del cuarzo: procedimiento combinado de dosis aditiva y activación múltiple

    V. Correcher, J.M. Gomez-Ros, A. Delgado, J. Garcia-Guinea
    354-0
    Abstract:
    The pre-dose effect of the 110$^{\circ}$C thermoluminescence (TL) peak of quartz gives rise to the use of a sensitive technique to estimate of low-level doses under retrospective conditions. However, one can appreciate how aliquots of quartz, from the same mineral fraction, display different sensitivities. In this sense, we herein report on a new measurement protocol based on the aforementioned pre-dose effect. Such procedure includes additive dose (DA) and multiple activation (MA) steps and allows us to determine simultaneously (i) the sensitivity changes induced by the thermal activation and (ii) the TL dose dependence. This behaviour let us calculate the field accrued dose by interpolation thus permitting an increase of both precision and accuracy.
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  • Influencia de la inestabilidad modulacional en la generación de un espectro continuo en fibras ópticas con pulsos de nanosegundos

    J.G. Gutiérrez, M. Vargas-Treviño, C. Romero-Salazar., O.A. Hernández Flores, E.A. Kuzin, B. Ibarra-Escamilla, R. Grajales-Coutiño, R. Rojas-Laguna, J.M. Estudillo-A, ala., E. Vargas-Rodríguez, F. Gutiérrez-Zainos
    359-0
    Abstract:
    In this work the influence of modulational instability on the supercontinuum generation in standard optical fibers in the anomalous dispersion regime is reported. A 30 ns pump pulse with wavelength equal to 1549 nm from a directly modulated DFB laser was used. Results show that the spectrum broadening is due to modulational instability and self frequency shift. The spectrum broadening was depending of fiber length and pump power.
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  • Hydriding and dehydriding properties of Mg$_{2}$Ni/Ni and Mg$_{2}$ Ni/Ni + 5 wt.% Cu prepared by mechanical alloying

    A.F. Palacios-Lazcano, J.G. Cabañas-Moreno, J. Bonifacio-Martínez, J.L. Iturbe-García, F. Cruz-G, arilla., H.A. Calderón
    367-0
    Abstract:
    Elemental powders of Mg, Ni and Cu are subjected to high-energy ball milling in order to produce alloys of nominal compositions Mg$_{2}$Ni and Mg$_{2}$Ni$_{0.95}$Cu$_{0.05}$. Nanocrystalline phases based on the Mg$_{2}$Ni structure are produced after 21 hours of milling. As-milled powders were hydrided for 5 min at temperatures of 373, 423 and 473 K, under hydrogen pressures of between 0.69 and 2.07 MPa. The mass loss of the hydrided powders during thermogravimetric analysis was associated with hydrogen release. Maximum amounts of H$_{2 }$ release of 2.9 and 3.1 wt.% were obtained, respectively, for the Mg$_{2}$Ni and Mg$_{2}$Ni$_{0.95}$Cu$_{0.05}$ samples hydrided at 473 K without prior activation. These are some of the most advantageous results ever reported concerning the behavior of the Mg$_{2}$Ni phase as a hydrogen storage material.
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  • Masa del fotón por medio de un condensador de placas paralelas

    M. Rodriguez
    373-0
    Abstract:
    Here it is obtained the electrical field inside of a parallel-plates capacitor derived from Proca's equations. The field consists of the electric field standard $\mathbf{E}_{\text{S}}$, and an additional field dependent of the photon mass $\mathbf{E}_{\gamma}$. This additional field together with an effect of the AB type for neutral particles with magnetic dipole moment can set an upper limit on the photon mass. The upper limit obtained by this scenario of quantum nature is $10^{-41}$g.
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  • Aplicación de un recubrimiento de TiAlN para el incremento de la resistencia al desgaste de una compuerta de paso fabricada en acero T9

    J. Montes de Oca, H.J. González, E. Solis, J. Moreno, J. Muñoz-Saldaña
    378-0
    Abstract:
    The present work reports a study to increase wear resistance of a ball passage floodgate (steel type T9) trough the application of a thick film (coating). This study have included a material and process selection, synthesis of the coating on steel plates as substrates and spherical device, assembling of the coated floodgate on the ball valves, and finally an evaluation of the valves in the process of a thermoelectric power station. Taking into account the different requirements, a TiAlN coating prepared by cathodic arc evaporation was finally retained. The crystal structure, morphology and chemical composition of the coating were evaluated by x-ray diffraction (XRD) and scanning electron microscopy equipped with an energy dispersive spectrometer (SEM-EDS). Finally, mechanical properties such as hardness and Young modulus were determined by nanoindentation.
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  • An indirect skin emissivity measurement in the infrared thermal range through reflection of a CO$_{2}$ laser beam

    C. Villaseñor-Mora, F.J. Sanchez-Marin, S. Calixto-Carrera
    387-0
    Abstract:
    An indirect procedure to measure human skin emissivity is proposed. This procedure uses a 10.6 $\mu $m CO$_{2}$ laser, to project a controlled energy on the skin, and a power meter to measure the projected, reflected, emitted and background energies. To eliminate the effects of background radiation, two power measurements are taken: one of the skin and background emission and another that includes the skin emission itself, the background radiation, as well as the reflection of the laser beam by the skin. Those two measurements are subtracted to obtain the reflected energy and, with this, the corresponding reflectivity of the skin. With such subtraction, background and other sources of noise are eliminated, and using the Kirchhoff law the emissivity is calculated. The emissivity values obtained with this procedure were corroborated using a theoretical blackbody. Both methods give practically the same values, which validates our procedure. In addition, our values are in accordance with those previously reported by other researchers, but our procedure is simpler, faster and innocuous. An additional contribution of this work is the analysis of the way the skin reflects the infrared radiation, in the mid range. It was found that the reflection of the skin is more specular than Lambertian, for the wavelength that was used in this work.
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  • Estudio de la cristalización de Cu$_{2}$O y su caracterización por difracción de rayos X, espectroscópica Raman y fotoluminiscencia

    H. Solache-Carranco, G. Juárez-Díaz, J. Martínez-Juárez., R. Peña-Sierra
    393-0
    Abstract:
    The growth of polycrystalline cuprous oxide (Cu$_{2}$O) foils with great single-crystalline areas by the secondary crystallization method from polycrystalline copper in dry air atmosphere is reported. The method comprises two stages; in the first one polycrystalline copper foils were converted in cuprous oxide at 1020$^{\circ}$C by some hours depending of their thickness, in the second stage the growth of great crystalline areas are promoted by annealing the Cu$_{2}$O foils at temperatures near to 1100$^{\circ}$C by extended periods. The growth kinetics of the crystallites was studied; X-ray diffraction (XRD), Raman spectroscopy scattering and photoluminescence (PL) measurements were done as a function of the crystallization conditions. The XRD and Raman scattering measurements reveal the existence of pure Cu$_{2}$O phase. The PL spectra taken from 10 to 180K define the main paths of the radiative recombination processes. Besides of the excitonic transition X$^{o}$ at 610 nm, three strong bands at 720, 810 and 920 nm associated with relaxed excitons at oxygen and copper vacancies, respectively was detected. The relative intensity of the PL transitions of excitons at vacancies change according to the duration of the crystallization process.
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  • Optimal configuration of a finite mass reservoir isothermal chemical engine for maximum work output with linear mass transfer law

    Shaojun Xia., Lingen Chen., Fengrui Sun.
    399-0
    Abstract:
    An isothermal endoreversible chemical engine operating between a finite high-chemical- potential reservoir and an infinite low-chemical-potential reservoir in which the mass transfer between the working fluid and the mass reservoirs obeys the linear mass-transfer law [$g \propto \Delta \mu $], is put forward in this paper. Optimal control theory is applied to determine the optimal cycle configuration corresponding to the maximum work output for the fixed total cycle time. The optimal cycle configuration is an isothermal endoreversible chemical engine cycle in which the chemical potential (concentration) of the key component in the finite high-chemical- potential mass reservoir and that in the working fluid change nonlinearly with time. The difference in chemical potentials (ratio of the concentrations) between the key component in the finite mass reservoir and the working fluid is a constant, and the chemical potential (concentration) of the key component in the working fluid at the low chemical potential side is also a constant. A numerical example is provided, and the effects of the concentration changes in the key component in the finite high-chemical-potential reservoir on the optimal configuration of the chemical engine are analyzed. The obtained results are compared with those obtained for an endoreversible heat engine operating between a finite heat source and an infinite heat sink with Newton's heat transfer law [$q \propto \Delta T$] in the heat transfer processes. The object studied in this paper is general, and the results could provide some guidelines for the optimal design and operation of real chemical engines.
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