Vol. 50 No. 1 (2004): Revista Mexicana de Física.

Published: 2004-01-01

Articles

  • Analyse of the lateral surface generation in MOS structures

    P. Pe, kov., T. Diaz, M. Aceves
    1-0
    Abstract:
    In the measurements of the generation lifetime, using the method of Zerbst, an effective generation lifetime is measured. According to the model used, this parameter includes the real generation lifetime, surface generation velocity at the depleted lateral space charge region and the diameter of the gate. In this paper is shown that not all but part of the lateral space charge region is fully depleted during the time of measurement. A correction of the model, taking into account the contribution of surface generation velocity only on the depleted lateral space charge region to the generation process, is proposed. The influence of this correction on the generation lifetime obtained by the method of Zerbst is shown.
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  • Transferencia de cargas en los polimeros semiconductores conteniendo espiropirano. Aplicaciones al diseño de elementos ópticos biestables y la detección de imagenes infrarrojas

    J.J. Robillard, D. Luna Moreno
    6-0
    Abstract:
    This paper describes a new method for infrared to visible image conversion based on charge transfer between Langmuir Blodgett films. The method is used for the design of an infrared camera operating with purely optical conversion, without any electronic scanning and digital treatment of the image.
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  • Measurement of dynamic deformation using a superimposed grating

    B. Barrientos, M. C, wiak., W.K. Lee, P. Br, anston-Cross.
    12-0
    Abstract:
    Mechanical devices are normally used under conditions of dynamic motion. Due to resonance effects, this condition produces undesired modes of vibration, which are necessary to be measured for satisfactory design. This paper describes a method to measure the temporal development of the vibrational modes in mechanical objects subjected to external vibration, by a double exposure fringe technique. A grating placed directly on the object under study serves as a carrier frequency, which enables automatic phase calculation. This grating, which is imaged by a commercial digital camera, used in conjunction with a spatial carrier fringe method for phase evaluation, allows determining the vibration deformation. This technique is suitable for the analysis of rapid transient events since no movable parts are required in the system. The obtained range of deformation by the proposed method goes from a few tenths of micrometers to millimetres.
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  • Caracterización estructural y biointegración del substituto óseo BioOsteo$^\circledR$

    C. Mendoza-Barrera, M. Meléndez-Lira, E. García-López, C. Hernández-Flores
    19-0
    Abstract:
    The aim of this work is the characterization and evaluation of the biointegration of BioOsteo$^\circledR$ (Hig-Med) bony graft on a rat tibia model. No implant rejection or inflammatory reaction was observed during an 8 weeks period in our in vivo studies. The evolution of the osteointegration was followed employing scanning electronic microscopy (SEM), energy dispersive X-rays Spectroscopy (EDS) and X-ray diffraction (XRD). We concluded that BioOsteo$^\circledR$ based graft is a calcite-based biomaterial that works by a displacement mechanism and we suggested its use like bony graft for width bones.
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  • Radiative corrections to the weak-magnetic dipole moment of leptons in the unbroken minimal supersymmetric standard model

    Rogelio Cuevas., Jesús García., Alfonso Queijeiro.
    24-0
    Abstract:
    We compute, within the context of the Minimal Supersymetric Standard Model, the one loop radiative corrections, to the weak-magnetic dipole moment of leptons. We prove that this weak-magnetic dipole moment vanishes in the limit of exact supersymmetry, in analogy to the vanishing of the magnetic moment.
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  • Size effects on the magnetism of vanadium clusters

    E.M. Sosa-Hernández, P.G. Alvarado-Le, va., J.M. Montejano-Carrizales, F. Aguilera-Granja
    30-0
    Abstract:
    The magnetism of free vanadium clusters (V$_{N}$, $2\leq N \leq 169 $) with a bcc-like structure is studied using a d electron tight binding Hamiltonian. The spin polarized density of states is calculated self-consistently in the unrestricted Hartree-Fock approximation. We have found that the free V clusters shown different magnetic behavior depending on their size. Results for the local magnetic moments, $\mu_i$, average magnetic moment, $\bar \mu$, and the magnetic order at $T=0$ are obtained as a function of $N$. For the V$_{N}$ clusters $\bar \mu$ varies as a function of $N$ due to the interplay between the changes in coordination number and local environment; for $N \leq 4$ the ground state is ferromagnetic whereas for $N \geq 9$ the ground state is mainly antiferromagnetic in agreement with ab initio and tight binding calculations, respectively. In the case of large size clusters the local magnetic moments of most of the internal atomic shells vanish to avoid local frustrations leading the system in this way to very small magnetic moment as the cluster size increases.
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  • Convección natural en medios porosos y libres: simulación numérica

    E. Báez, B. Bermúdez, A. Nicolás
    36-0
    Abstract:
    Numerical simulations are presented for natural convection in rectangular tilted cavities for a porous medium and for a homogeneous fluid as well. In both cases the mathematical modeling is based on the time dependent Boussinesq approximation which gives an incompressible fluid structure; the momentum equations are given for the Darcy ones in porous medium and for the Navier-Stokes equations in homogeneous fluid. The formulation in stream function and vorticity variables is considered. The numerical simulations are obtained with a simple numerical scheme whose effectiveness relies mainly on a fixed point iterative process to solve the elliptic nonlinear system that is obtained once a convenient second order time discretization is performed on each equation that depends explicitly in time. The iterative process leads to the solution of symmetric linear elliptic equations for which very efficient numerical solvers exist. The parameters involved in the simulations are the Rayleigh number, the aspect ratio, and the inclination angle of the cavity.
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  • Polarization rotation of electromagnetic waves by two abelian gauge fields coupled to torsion

    C. Wolf
    49-0
    Abstract:
    By considering the coupling of two abelian gauge fields to pseudoscalar torsion we demonstrate that three different rotated polarized waves result for propagation over cosmological distances in a torsion field with constant gradient. It is also demonstrated that one of the waves is twice as intense as the other two providing us with a signature to identify the above coupling.
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  • Efecto de la temperatura en las propiedades estructurales y dinámicas de Ag líquida: un estudio con dinámica molecular

    E. Urrutia Bañuelos, A. Posada Amarillas
    53-0
    Abstract:
    In this work we studied the temperature-induced changes in the structural and dynamical properties of liquid Ag using molecular dynamics (DM) computer simulation. The atomic interactions are modeled through a semiempirical potential function which incorporates n-body effects and is based on the second moments approximation of the density of states of a tight-binding Hamiltonian. The caloric curve was used to calculate the latent heat of fusion and the pair distribution function, g(r), was calculated from a set of atomic configurations collected at several time-steps. The dynamical properties are studied through the velocity autocorrelation function and the mean-square displacement. The self-diffusion coefficient and its behavior with the temperature, obtained from our simulations, shows the typical behavior of the simple liquids. Our results are compared to available experimental data.
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  • Caracterización de un amplficador de fibra óptica dopada con erbio con pulsos en función del tiempo

    J.L. Camas Anzueto, E.A. Kuzin, R. Téllez, B. Ibarra E., G. Beltrán
    60-0
    Abstract:
    In this work we show simple characterization of an EDFA. We analyze the confiability of this method, we makes the comparison with another method. We discuss the advantage of this method. The EDFA that was used in the arrangement has a 10 meters Erbium doped fiber length with a concentration of 1000~ppm.
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  • Electrical and magnetic properties of UFe$_{x}$ compounds

    E. Verdín, R. Escudero
    64-0
    Abstract:
    UFe$_{x}$ alloys with compositions from x = 1.60 to 13.20 at. % of Fe, are superconducting with maximum transition temperature, Tc = 3.59 K. X-ray diffraction analysis, shows the existence of different compositions with formula $\alpha $-U+Fe and solubility limit close to x = 1.76 $\pm $ 0.87~at. % Fe. With increasing Fe the solid solution U$_{6}$Fe phase forms and coexists with the metastable $\alpha $-U+Fe until it saturates. The annealing process to the samples accelerates the formation of U$_{6}$Fe, modifying substantially the magnetic characteristics, but without changing its superconducting transition.
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  • Familias de superficies nulas en el espacio-tiempo tridimensional de Minkowski y sus ecuaciones diferenciales asociadas

    G. Silva-Ortigoza, P. García-Godínez
    70-0
    Abstract:
    In this work we describe the procedure to obtain all the family of third order ordinary differential equations connected by a contact transformation such that in their spaces of solutions is defined a conformal three demensional Minkowski metric.
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  • Bose-Einstein condensation in real space

    J.J. Valencia, M. de Llano, M.A. Solís
    84-0
    Abstract:
    We show how Bose-Einstein condensation (BEC) occurs not only in momentum space but also in coordinate (or real) space. Analogies between the isotherms of a van der Waals classical gas of extended (or finite-diameter) identical atoms and the point (or zero-diameter) particles of an ideal BE gas allow concluding that, in contrast with the classical case, the volume per particle vanishes in the pure BE condensate phase precisely because the boson diameters are zero. Thus a BE condensate forms in real space without exhibiting a liquid branch as does the classical gas.
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  • Gauge-invariant formulation of the electromagnetic interaction in Hamiltonian mechanics

    G.F. Torres del Castillo
    88-0
    Abstract:
    Making use of the fact that for an arbitrary autonomous mechanical system any constant of motion can be used as Hamiltonian, the equations of motion of a charged particle in an electromagnetic field are written in Hamiltonian form without introducing potentials for the electromagnetic field. It is shown that the Hamiltonian and the Poisson bracket obtained here coincide with those appearing in the standard Hamiltonian formulation.
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