Vol. 56 No. 5 (2010): Revista Mexicana de Física.

Published: 2010-01-01

Articles

  • Sobre el carbón y el oxígeno en una química primordial no estándar del Big Bang

    J.C. Campos-García
    348-0
    Abstract:
    In the present paper its considered the acumulation of species basedes in primordial carbon and primordial oxygen during the dark ages. This analysis its make through the acumulative conversion aplicade to the chanels of a spacious chemical red for carbon and oxygen in a no standard model of the Big Bang. Its find that the species of major acumulation result be the species C, CH, C$^{+}$, CH$^{+}$, CH$_{2}^{+}$, O, OH, OH$^{+}$, O$^{+}$, H$_{2}O^{+}$. Moreover, its make an observational estimation in rotational lines of the CH molecule.
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  • Influence of heat- and mass-transfer coupling on the optimal performance of a non-isothermal chemical engine

    Yanhua Cai., Guozhen Su., Jincan Chen.
    356-0
    Abstract:
    The cyclic model of a non-isothermal chemical engine operated between two reservoirs with different temperatures and chemical potentials is established, in which the irreversibilities resulting from the heat and mass transfer between the working fluid and the reservoirs are taken into account. Expressions for the power output and efficiency of the engine are analytically derived and used to analyze the performance characteristics of the engine at the maximum power output. The general characteristics of the efficiency of the engine are searched in detail. The optimal criteria for some important parameters, such as the power output and efficiency, are obtained and the reasonably operating region of the engine is determined. Some interesting cases are specially discussed. The results obtained here can reveal the performance characteristics of a non-isothermal chemical engine affected by the irreversibilities of heat- and mass-transfer coupling.
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  • Formas de representación del transporte de nitrógeno atómico en el sistema Fe-N: Estudio del estado estacionario en un proceso de nitruración post-descarga

    A Fraguela., F. Castillo, J. Oseguera, .
    363-0
    Abstract:
    A moving boundary diffusion model for post-discharge nitriding is presented. This model assumes that the nitriding process does not depend on the parallel directions to the specimen surface, but only on the correspondent orthogonal direction. For a specimen of finite depth, different boundary conditions on its base are attached. Then, existence and uniqueness of the steady states of the considered models are studied. The examination of possible steady states under the assumption of certain qualitative behavior of the diffusion coefficients leads to analytic expressions for the nitrogen concentration profiles. The obtained analytic expressions, together with nitrogen concentration measurements at each phase and additional measurement of the nitrogen flux, allows to determine the diffusion coefficients as functions of the nitrogen concentration. It is therefore the object of the present work to provide a theoretically grounded method for obtaining analytic expressions of nitrogen concentration profiles and concentration-dependent diffusion coefficients. This method only uses measurements of the nitrogen concentration and the nitrogen fluxes and does not assume any ``a priori'' behavior of the layer growth.
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  • Multivariate analysis of Raman spectra applied to microbiology: Discrimination of microorganisms at the species level

    P. Mobili, A. Londero, G. De Antoni, A. Gómez-Zavaglia, C. Araujo-Andrade, H. Ávila-Donoso, R. Ivanov-Tzonchev, I. Moreno, C. Frausto-Re, es.
    378-0
    Abstract:
    In this work, multivariate methods such as: principal component analysis (PCA) and partial least square-discriminant analysis (PLS-DA), were applied for the analysis and interpretation of Raman spectra, collected from microorganisms of different species. The main objective was to develop a methodology for a rapid and free of chemical-reagents discrimination and classification of microorganism at the species level. The raw Raman spectra of microorganisms were recorded in the spectral range of 2000 to 200 cm$^{ - 1}$. However, a detailed analysis of the results obtained by means of PCA, showed that the spectral region from 1700 to 1500 cm$^{ - 1}$, provides chemical and biochemical information highly correlated with the species of the microorganisms analyzed in this study, allowing a clear discrimination among species. Also, in order to evaluate the capability of multivariate methods to develop a classification rule, PLS-DA in a leave-one-out-cross-validation method (LOOCV) was used for the calibration and validation of a classification model, as a first approach. The results obtained for this method, showed an acceptable classification among the strains under study. On the other hand, taken into account the complexity of microorganisms' communities and the experimental procedures for their identification, discrimination and classification, the non-destructive and versatility of Raman spectroscopy and the capability of the multivariate methods for the analysis of spectral data, result useful tools for the classification and discrimination of this kind of samples.
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  • Ecological performance optimization of a thermoacoustic heat engine

    Lingen Chen., Xuxian Kan., Fengrui Sun., Feng Wu., Fangzhong Guo.
    386-0
    Abstract:
    Ecological performance optimization of a generalized irreversible thermoacoustic heat engine with heat resistance, heat leakage, thermal relaxation and internal dissipation, in which heat transfer between the working fluid and heat reservoirs obeys a complex generalized heat transfer law $Q \propto \Delta (T)^n$ -where $n$ is a complex-, is investigated in this paper. Both the real part and the imaginary part of the complex heat transfer exponent change the optimal ecological function versus efficiency relationship, quantitatively. The analytical formulas about the ecological function and thermal efficiency of the thermoacoustic heat engine are derived. Furthermore, the comparative analysis of the influences of various factors on optimal performance of the generalized irreversible thermoacoustic heat engine is carried out by detailed numerical examples. The optimal zone on the performance of the thermoacoustic heat engine is obtained by numerical analysis. The results obtained herein can provide some theoretical guidelines for the design of real thermoacoustic engines.
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  • Computation of crack tip elastic stress intensity factor in mode I by in-plane electronic speckle pattern interferometry

    J. Parra-Michel, A. Martínez, J.A. Ra, as.
    394-0
    Abstract:
    In this work, a dual illumination beam system is used to obtain the stress intensity factor in modes one (mode $I)$ to mechanical elements during tension testing. The displacement field is obtained by means of electronic speckle pattern interferometry and phase stepping technique. Deformations are calculated by the Stokes differentiation method. Results are compared with a numerical simulation using a finite element analysis technique.
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  • Electrical properties of resistive switches based on Ba$_{1 -x}$Sr$_{x}$TiO$_{3}$ thin films prepared by RF co-sputtering

    A. Márquez-Herrera, E. Hernández-Rodríguez, M.P. Cruz, O. Calzadilla-Ama, a., M. Meléndez-Lira, J. Guillén-Rodríguez, M. Zapata-Torres
    401-0
    Abstract:
    In this work, we propose the use of Ba$_{1-x}$Sr$_{x}$TiO$_{3 }$(0 $ \le $ x $ \le $ 1) thin films for the construction of MIM (metal-insulator-metal) heterostructures; and their great potential for the development of non-volatile resistance memories (ReRAM) is shown. The deposition of Ba$_{1-x}$Sr$_{x}$TiO$_{3}$ thin films was done by the rf co-sputtering technique using two magnetron sputtering cathodes with BaTiO$_{3}$ and SrTiO$_{3}$ targets. The chemical composition (x parameter) in the deposited Ba$_{1-x}$Sr$_{x}$TiO$_{3}$ thin films was varied through the rf power applied to the targets. The constructed MIM heterostructures were Al/Ba$_{1 - x}$Sr$_{x}$TiO$_{3}$/nichrome. The I-V measurements of the heterostructures showed that their hysteretic characteristics change depending on the Ba/Sr ratio of the Ba$_{1-x}$Sr$_{x}$TiO$_{3}$ thin films; the Ba/Sr ratio was determined by employing the energy dispersive spectroscopy; SEM micrographs showed that Ba$_{1-x}$Sr$_{x}$TiO$_{3 }$thin films were uniform without cracks or pinholes. Additionally, the analysis of the x-ray diffraction results indicated the substitutional incorporation of Sr into the BaTiO$_{3}$ lattice and the obtainment of crystalline films for the entire range of the x values.
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  • Métrica de despolarización escalar Q(M) como criterio para identificar sistemas retardadores o desfasadores puros

    R. Espinosa-Luna, G. Atondo-Rubio, O.J. Velarde-Escobar
    406-0
    Abstract:
    The trace criterion or theorem of Gil-Bernabeu is a neccesary and sufficient condition for a Jones matrix to be derivable from a Mueller matrix associated to passive optical systems. The matrix obtained in this way is named Mueller-Jones or pure Mueller matrix. In this work, several examples are shown of physical systems, diattenuating and non-diattenuating, which fulfill the theorem of Gil-Bernabeu or equivalently take on the upper limit for the depolarization index. This means that this criterion can provide only information about the non-depolarizing character of light by systems, but it is unable to distinguish the diattenuating character associated to the systems and consequently it cannot distinguish a polarizer from a retarder. It is shown the upper limit of $Q(M)$ can be employed as a criterion to identity uniquely non-diattenuating Jones matrices; that is, systems associated to pure retarders or dephasers.
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  • Desorption influence of water on structural, electrical properties and molecular order of vanadium pentoxide xerogel films

    C.L. Londoño-Calderón, C. Vargas-Hernández, J.F. Jurado
    411-0
    Abstract:
    Vanadium pentoxide xerogel films were grown by sol-gel method on pre-treated glass substrates, the gelation time was 14 days. The crystallinity of the films was analyzed with X-ray diffraction (XRD), identifying the composite V$_2$O$_5\cdot$nH$_2$O before, and both vanadium pentoxide xerogel and $\alpha$-V$_2$O$_5$ phases after, being subjected to thermal treatment (47, 97, 147, 204, 237, 272, 297 and 330$^{\circ}$C during 15~minutes in each isotherm). The termal treatment reduces the degree of hydrations gel ($n$) from 2.1 to 1.4, besides the secondary phase ($\alpha$-V$_2$O$_5$) has lattice parameters very similar to the precursor powder (which deviate about 0.3$ % $). The electrical conductivity presents a semiconductor behavior in agreement with small polaron model, thermally activated and irreversible. The activation energies for three consecutive cycles were studied and analyzed: a strong dependency between the degree of hidratation's gel $n$ with activation energy for high and low temperature regions was found. $\mu$-Raman Spectroscopy showed the influence of temperature in the vanadium pentoxide gel film, presenting a phase transition from crystalline-amorphous for temperatures above 272$^{\circ}$C and inferring that the water presence in the sample is responsible in some way for the crystallinity of the material.
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  • Coeficientes de difusión de fluidos de Yukawa y aplicación a fullerenos

    A. Onofre-Hernández, M. González-Melchor, J.F. Rivas-Silva
    416-0
    Abstract:
    Computer molecular dynamics simulations are performed to study dynamic properties of Yukawa fluids. The equations of motion are integrated by using the velocity Verlet algorithm. The diffusion coefficients are obtained through the mean square displacement and the velocity autocorrelation function. We applied this methodology to study the diffusion of C$_{60}$ and C$_{70}$ fullerenes, for which the attractive Yukawa potential has shown to be useful in reproducing the liquid-vapor coexistence curve.
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  • An on-chip magnetic probe based on MOSFET technology

    P.J. García-R., J. Martinez-C., E.A. Gutierrez-D.
    423-0
    Abstract:
    An original application for a magnetic field-sensitive Split-Drain MOSFET (MAGFET) used to monitor both the integrity of the electrical signal on-chip, as well as the magnetic flux density radiation on-chip is presented in this work. We introduce experimental and simulation results of a test chip that prove static and low-frequency on-chip generated magnetic fields that can be detected on-chip leading to a fluctuation in the drain current ($\Delta $I$_{DS}$) of a MAGFET device. The design of this first version of the test chip is intended for DC characterization as the pads, package and wiring do not allow going above a frequency of 300 MHz. In this particular case of a 0.5 $\mu $m CMOS technology and the used dimensions, the cutoff frequency of the test MAGFET is in the range of 500 MHz to 1 GHz depending on the bias conditions. For the static and low-frequency case used in this experimental work the capacitive coupling between the interconnect line and the gate electrode is negligible. The current in the interconnected line, that varies from 500 $\mu $A to 35 mA, generates a magnetic flux density at a rate of 100~$\mu $T/mA. When these magnetic lines cross through the channel of the MOS transistor, an electromagnetic coupling rate ($\Delta $I$_{DS}$/B) as far as 1.5 $\mu $A/mT is induced. We observed that from the 0.7, 0.5, and 0.35 $\mu $m characterized MOS technologies data, the ($\Delta $I$_{DS}$/B) rate increases with the miniaturization process of fabrication technology. This electromagnetic rate reduces as the temperature is increased from 20 to 120$^{\circ}$C. From numerical simulations we conclude that this phenomenon is attributed to the way carrier mobility and inversion channel charge interplay with the on-chip tangential and perpendicular components of the (B) field. Having an array of MAGFETs distributed on the surface of the chip would serve to monitor the EM radiation, which in turn may be used for estimation and mitigation of RF interference. These results allow establishing the basis for a future development for on-chip magnetic probe for nanometer MOS technologies.
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  • Joint optical-electrical technique for noninvasive glucose monitoring

    E. Guevara, F.J. González
    430-0
    Abstract:
    In Diabetes mellitus, self monitoring of blood glucose is crucial for effective treatment since it can help identify and prevent unwanted periods of hypo- and hyperglycemia; this monitoring procedure usually involves finger-stick testing which is painful to the patient and carries the risk of infection. Non-invasive techniques, including impedance and near infrared spectroscopy, have been developed to predict glucose concentration; however, these techniques have not reached the accuracy needed for glucose monitoring. In this work a new concept which involves the combination of two spectroscopic measurements, electrical impedance spectroscopy and near infrared spectroscopy, is developed to decrease the prediction error of single-measurement non-invasive glucose monitoring systems. Electrical impedance and near infrared spectroscopy measurements were performed under controlled temperature and humidity conditions on ten non-diabetic volunteers (age 26.1 $\pm $ 3.7 years, BMI 25.24 $\pm $ 3.67 kg/m$^{2})$. The results show that all of the values predicted by the joint optical-electrical technique were clinically acceptable and the root mean squared error of prediction, which in this study was compared to a commercial glucose meter, is lower than previously published values for near infrared spectroscopy and impedance spectroscopy done separately.
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