Vol. 58 No. 5 Sept-Oct (2012): Revista Mexicana de Física.

Published: 2012-01-01

Articles

  • Detection of metallic cylindrical inclusions by thermoelectric coupling

    H. Carreon, J.L. González-Carrasco
    372-377
    Abstract:
    In this paper, we present a technique that can give information on surface metallic inclusions embedded in a host material, i.e. by the magnetic sensing of local thermoelectric currents produced when a temperature gradient is established in the material. These thermoelectric currents generate flux magnetic densities that are detected by a highly sensitive magnetometer. A comparison between reported analytical results with experimental data of the magnetic field produced by thermoelectric currents around surface-breaking cylindrical tin inclusions in copper under external thermal excitation for different lift-off distances between the sensor and the surface of the specimen is presented. The diameter of the inclusions varied from 4.76 to 12.7 mm at different lift-off distance magnetometer probe and the specimen 1 to 8 mm respetively. A fairly modest 1.46$^{\circ}$C/cm temperature gradient in the specimen produced magnetic flux densities ranging from 60 to 1460 nT.
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  • Thermodynamics and structure behavior of a confined binary mixture by Reactive Monte Carlo simulations

    H. Domínguez
    378-383
    Abstract:
    Adsorption and structure of a confined binary mixture is investigated with Reactive Monte Carlo (RxMC) simulations. This method allowed us to study thermodynamics of the system at different temperatures and at different pore sizes at chemical equilibrium imposed by the reaction A $\rightleftharpoons$ B. In particular studies of equilibrium composition as a function of particle interactions between particles of the same specie and cross interactions between particles of different species were investigated. As a pore model it was used the slit-like geometry where it was observed that at very narrow pores the particle composition departed from that in the bulk. The results also showed that the creation of particles was determined not only by the strength of the particle-particle interactions but also by the wall-particle interactions. In fact, it was possible to enhance creation of a specific specie in the mixture by changing the affinity of the walls to that particular specie.
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  • Explicit classical solutions and comments on Higher-Derivative Klein-Gordon equation in (1+1)-D

    A. Cherman, L.G. Ferreira Filho, L.L. Santos Guedes, J.A. Hela, ël-Neto.
    384-390
    Abstract:
    We present a simple and general method to solve higher-power D'Alembert equation in (1+1) dimensions for a set of completely general initial conditions. Explicit solutions are written down for the cases of $\Box^{2}$ and $\Box^{3}$ and the singularity structure is manifest through the derivative terms of some of the initial-condition functions. The explicit solutions found out may be useful if one wishes to device external sources which may suppress the non-physical modes introduced by the higher derivatives.
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  • Magnetisation of red blood cells: a Brownian Dynamics Simulation

    M.E. Cano, R. Castañeda-Priego, A. Barrera, J.C. Estrada, P. Knauth, M.A. Sosa
    391-396
    Abstract:
    A model to calculate the magnetisation of deoxyhemoglobin of human blood by means of Brownian dynamics simulations is presented. We consider a system made up of dipolar magnetic spheres, which can interact but do not overlap. Particles are exposed to external magnetic fields to compute the magnetisation curve, which exhibit a Langevin-like behaviour. The magnetic susceptibility of the erythrocytes and completely deoxygenated whole blood are $\chi _p = 1.61\times 10^{ - 6}$(SI) and $\chi _{WB} = - 4.46\times 10^{ - 6}$(SI), respectively, which are in good agreement to experimental data and theoretical calculations. Moreover, we also compute the paramagnetic component of the susceptibility of erythrocytes that in our simulations normal blood from beta thalassemia major samples could be differentiated.
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  • Estudio comparativo de la degradación de celdas solares de CdTe con CdS procesado por CBD y CSVT

    R. Mendoza-Pérez, J. Aguilar Hernández, G. Contreras-Puente, J. Sastre-Hernández
    397-403
    Abstract:
    In this work we presented a comparative study of the degradation of thin films solar cells of CdS/CdTe, with the Cadmium Sulfide (CdS) deposited by Chemical Bath Deposition (CdS-CBD) and Closed Space Vapor Transport (CdS-CSVT) techniques, in both cases the Cadmium Telluride (CdTe) thin film was deposited by CSVT and both the CdS and CdTe were submitted at the same heat treatment (TT) with Cadmium Chloride (CdCl$_{2})$. In the CdS-CBD solar cells, the CdS was deposited at different relations of sulfur with respect to cadmium (S/Cd) in chemical bath; wherever the CdS-CSVT solar cells, the CdS was deposited at different times for obtained the similar thickness to CdS-CBD solar cells. The initial photovoltaic efficiency of the best CdS-CBD solar cells was 12.3% for the sample with relation S/Cd=5:1 and the initial photovoltaic efficiency of the best CdS-CSVT solar cells was 11.2% for CdS sample with the thickness of 140 nm before TT-CdCl$_{2}$. The solar cells CdS-CDB and CdS-CSVT obtained 6 years ago were characterization regularly by optical transmittance, photoluminescence, spectral quantum efficiency (QE) and current function voltage (I vs. V); the measurements shows the degradation in these photovoltaic devices submitted at exposed to the weather.
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  • Fluctuation-induced conductivity of polycrystalline Gd$_{1 - x}$Ce$_{x}$Ba$_{2}$Cu$_{3}$O$_{7 - \delta }$ superconductor

    M. Murer, Y. Aparecido Opata, J.F.H. Le, ro Monteiro., S. Aparecida da Silva, P. Rodrigues Júnior, A.R. Jurelo
    404-410
    Abstract:
    This paper reports on measurements of the resistive transition in polycrystalline Gd$_{1 - x}$Ce$_{x}$Ba$_{2}$Cu$_{3}$O$_{7 - \delta }$ samples ($x = 0.000$, 0.025 and 0.050). The samples were produced by a standard solid state reaction method and in two different thermal routes. The microstructure was analyzed by X-ray diffraction. The samples were considered homogeneous since no extra peaks due to impurity phase were observed. To identify power-law divergences in conductivity, the results were analyzed in terms of the temperature derivative of the resistivity and the logarithmic temperature derivative of the conductivity ($d\ln \left( {\Delta \sigma } \right) / dT$). From the results, the occurrence of a two-stage transition besides the pairing transition splitting for sample with $x = 0.050$ was observed. Such splitting was associated with Ce doping and related with the occurrence of a phase separation. In the normal phase, Gaussian and critical fluctuations conductivity regimes were identified. On approaching the zero resistance state, our results showed a power-law behavior that corresponds to a phase transition from a paracoherent to a coherent state of the granular array.
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  • Raman and structural studies on the high-temperature regime of the KH$_2$PO$_4$-NH$_4$H$_2$PO$_4$ system

    J.F. Jurado, C. Vargas-Hernández, R.A. Vargas
    411-416
    Abstract:
    We have studied the high-temperature phase transition (HTPT) of crystalline potassium and ammonium dehydrogen phosphates and solid solutions of them with composition (1-$x$)KH$_2$PO$_4+x$NH$_4$H$_2$PO$_4$ (KADPx, for $x$ =0.0, 0.1, 0.2, 0.3, 0.4, 0.6 and 1.0), by means of X-ray diffraction analysis at room temperature and in situ Raman spectroscopy as function of temperature. Analysis of the Raman spectra made it possible to monitor the temperature dependence of vibrational bands associated to structural changes taking place during a proposed partial dehydration reaction that starts to take place at a characteristic temperature T$_p$ and tends to increase above it. This assignment is supported using characteristic vibrational bands of phosphates and polyphosphates (produced as a consequence of the partial dehydration reaction of the crystals above T$_p$). The presence of the polyphosphate vibrational bands assigned to the stretch vibration of its PO$_{2}$ species (at about 1120 \cm for pure KDP) accompanied by a broad band assigned to P-O-P backbone vibrations (at about 713 \cm for pure KDP) [14] become evident at temperature higher than T$_p$ depending on the composition of KADPx.
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  • The effect of grain refinement on the mechanical properties of a micro alloyed steel

    M.A. Suarez, O. Alvarez, M. A, R. Herrera, C. Zorrilla, S. Valdez, J. A
    417-421
    Abstract:
    High strength low alloy steel was produced by electric arc furnace, vacuum degassing, ladle treatment and continuous casting route. The steel was hot rolled by applying a schedule to simulate industrial control of hot rolling procedure for the production of plates as closely as possible in laboratory level, in order to investigate the effect of applying different strain rates onto hot rolling procedure in the range of temperatures between 1250 to 900$^{\circ}$C. After the hot rolling procedure, the plate was spray cooled at a cooling rate of 5$^{\circ}$C/s to a temperature of 650$^{\circ}$C and then cooled to room temperature. The results showed a grain refinement as a function of the strain rate increases from 1 to 8 s$^{ - 1}$ and as a consequence an increase in mechanical properties of: yield strength and ultimate tensile strength; and keeping almost constant the ductility.
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  • Vibrometer based on a self-mixing effect interferometer

    L. Martí-López, R. González-Peña, R.A. Martínez-Celorio, E.E. Ramírez-Miquet
    422-427
    Abstract:
    We outline the basic principles of the self-mixing effect and present the design and construction of an interferometer based on this phenomenon. It differs from the previously reported in the literature by the use of two photodetectors, located at different arms of the interferometer. This feature allows widening the arsenal of strategies for the digital processing of the signal. The interferometer is used as vibrometer for the characterization of professional loudspeakers. Experimental results are presented as an illustration.
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  • Diabatic quantum gates

    P.J. Salas Peralta
    428-437
    Abstract:
    At present, several models for quantum computation have been proposed. Adiabatic quantum computation scheme particularly offers this possibility and is based on a slow enough time evolution of the system, where no transitions take place. In this work, a new strategy for quantum computation is provided from the opposite point of view. The objective is to control the non-adiabatic transitions between some states in order to produce the desired exit states after the evolution. The model is introduced by means of an analogy between the adiabatic quantum computation and an inelastic atomic collision. By means of a simple two-state model, several quantum gates are reproduced, concluding the possibility of diabatic universal fault-tolerant quantum computation. Going a step further, a new quantum diabatic computation model is glimpsed, where a carefully chosen Hamiltonian could carry out a non-adiabatic transition between the initial and the sought final state.
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  • A density oscillator model

    A. Hubard, C. Málaga, H. Arce, H. González
    438-444
    Abstract:
    We present a model equation describing the behavior of a density oscillator and a set of experiments to test the model. The system consists of a cup containing salty water with an orifice in its base, partially submerged in an outer vessel filled with fresh water. Such a setup produces an oscillatory flow of water through the orifice. The density oscillator is an oscillatory system that shares common features with more complex systems with a stable limit cycle. Although a Rayleigh equation has been used as a model equation for these systems, we propose a different approach based on the integration of the hydrodynamic equations on a streamline. The model reproduces the experimental oscillation and predicts the period as a function of the physical parameters. Phase resetting curves observed in experiments under external biphasic excitation can be reproduced by the model.
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