Vol. 54 No. 1 (2008): Revista Mexicana de Física.

Published: 2008-01-01

Articles

  • Experimental study of a Q-switched ytterbium-doped double-clad fiber laser

    G. Anzueto-Sánchez, A. Martínez-Rios, I. Torres-Gómez, R. Selvas-Aguilar, J.M. Estudillo-A, ala.
    1-0
    Abstract:
    We report an experimental characterization of a Q-switched operation of an all-fiber laser using $\sim $ 30 m of a double-clad ytterbium-doped fiber spliced to a piece of single-mode un-doped holey fiber. Loss modulation in the splicing point between the active and un-doped fiber due to a substantial coupling of light into lossy cladding modes stimulates pulsed operation of the fiber laser. Pulse energy of $\sim2.5$ $\mu$J was estimated and the repetition rate was measured in the range of 4-16 KHz.
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  • Quantum bouncer with quadratic dissipation

    Gabriel González.
    5-0
    Abstract:
    The energy loss due to a quadratic velocity-dependent force on a quantum particle bouncing off a perfectly reflecting surface is obtained for a full cycle of motion. We approach this problem by means of a new, effective, phenomenological Hamiltonian which corresponds to the actual energy of the system and obtain the correction to the eigenvalues of the energy in first-order quantum perturbation theory for the case of weak dissipation.
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  • Drag reduction by microbubble injection in a channel flow

    C. del C, Y.A. Hassan, J.A. Jiménez Bernal, J.G. Barbosa Saldaña
    8-0
    Abstract:
    The injection of microbubbles within the turbulent boundary layer in a channel is investigated to elucidate the drag reduction phenomenon. Experimental data for a fully developed flow were obtained using the Particle Image Velocimetry (PIV) technique for single-and two-phase flow. Both cases are compared to examine the effects of the presence of microbubbles within the boundary layer, specifically the modification of vorticity, vortex structures, and fluctuating rate of strain, which is directly related to the energy dissipation in turbulent flows. A notorious decrease in the rate of strain as well as vorticity was observed for the two-phase flow. These results are significant and will help to reveal the physical mechanism of drag reduction by injection of microbubbles.
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  • An alternative deduction of relativistic transformations in thermodynamics

    B. López-Carrera, V. Granados, G. Ares de Parga
    15-0
    Abstract:
    In this article, we propose an alternative deduction to the Ares de Parga et al. proposal for the relativistic transformation laws in thermodynamics [J. of Phys. A: Math and Gen. 38 (2005) 2821]. A generalization of the so-called thermal work is proposed. The covariance of the theory is discussed.
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  • Effect of CaO on the microstructure and non-ohmic properties of (Co,Sb)-doped SnO$_{2}$ varistors

    J.A. Aguilar-Martínez, A. Durán-Régules, A.B. Glot, M.B. Hernández, M.I. Pech-Canul, J. Castillo-Torres
    20-0
    Abstract:
    The effect of CaO through additions of CaCO$_{3}$ on the physical characteristics, microstructure, and current-voltage properties of (Co-Sb)-doped SnO$_{2}$ varistors was investigated. SnO$_{2}$-Co$_{3}$O$_{4}$-Sb$_{2}$O$_{5}$ ceramics with additions of 0.1, 0.5 and 1 mol % CaO were sintered at 1450$^{\circ}$C under oxidizing atmosphere and characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Results show that, at low and intermediate CaO levels, density is not significantly influenced, whilst at the highest level, density decreases substantially. The nonlinear coefficient and the breakdown voltage behave similarly in one sense because both present a maximum, and because at the highest CaO level, both response variables show the lowest values. The nonlinear coefficient presents a maximum of 12.9 at 0.1 mol % CaO, while the same maximum for the breakdown voltage occurs at 0.5 mol % CaO. At 1 mol % CaO, the breakdown voltage is 288 Vcm$^{ - 1}$.
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  • On the spinodal decomposition of In$_{x}$Ga$_{1 - x}$N$_{y}$As$_{1 - y}$ and GaSb$_{x}$N$_{y}$As$_{1 - x - y}$ alloys

    S.F. Díaz Albarrán, V.A. El, ukhin., P. Rodríguez Peralta, A.G. González Noguéz
    25-0
    Abstract:
    Spinodal decomposition ranges of GaAs-enriched $\mbox{GaSb}_x \mbox{N}_y \mbox{As}_{1 - x - y} $ and $\mbox{In}_x \mbox{Ga}_{1 - x} \mbox{N}_y \mbox{As}_{1 - y} $ quaternary alloys as the result of the transformations of the bonds, strain and coherency strain energies at the phase separation are described. The alloys are represented as strictly regular solutions. The spinodal decomposition ranges of the alloys are demonstrated up to 600$^{\circ}$C. It is shown that $\mbox{GaSb}_x \mbox{N}_y \mbox{As}_{1 - x - y} $ alloys having one mixed sublattice are more promising from the standpoint of spinodal decomposition than $\mbox{In}_x \mbox{Ga}_{1 - x} \mbox{N}_y \mbox{As}_{1 - y} $ alloys with two mixed sublattices.
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  • Deviations from the universality of slepton masses in the MSSM

    M. Gómez-Bock
    30-0
    Abstract:
    In this paper we propose an ansatz that applies to the slepton mass matrices. In our approach, these matrices contain a dominant sector that can be diagonalized exactly. We study the numerical results for the slepton mass eigenstates, looking for deviations from universality, which is usually assumed when one evaluates the production of sleptons at future colliders.
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  • Diffraction of hermite-gaussian beams by Ronchi and aperiodic rulings

    A. Ortiz-Acebedo, O. Mata-Mendez, F. Chavez-Rivas
    35-0
    Abstract:
    In this paper, the diffraction of beams by Ronchi rulings is considered. The theory of diffraction is based on the Rayleigh-Sommerfeld integral equation with Dirichlet conditions. The diffraction of Gaussian and Hermite-Gaussian beams is studied numerically. The transmitted power and the normally diffracted energy are analyzed as a function of the spot size. The diffraction patterns obtained at maximum and minimum transmitted power are also deal with. We show that the two methods to determine the Gaussian spot size with Ronchi rulings which were experimentally compared in a previous paper [Rev. Mex. Fís. 53 (2007) 133] cannot be extended to the case of Hermite-Gaussian beams. Finally, for aperiodic rulings we propose a method for obtaining the Gaussian spot size by means of the normally diffracted energy.
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  • Structural properties of Pb(Mg$_{1 / 3}$Nb$_{2 / 3}$)$_{0.90}$Ti$_{0.10}$O$_{3}$ films deposited by pulsed laser ablation on titanium nitride substrates

    A. Fundora, E. Martínez, O. Blanco, J.M. Siqueiros
    42-0
    Abstract:
    Pulsed laser ablation is used to deposit Pb(Mg$_{1 / 3}$Nb$_{2 / 3})_{0.90}$Ti$_{0.10}$O$_{3}$ (PMNT) polycrystalline thin films on TiN bottom electrodes, which in turn are prepared by DC sputtering on Si wafers. The PMNT perovskite phase formation is confirmed by x-ray diffraction analysis. The morphology of the films is analyzed by scanning electron microscopy. The nature of the ferroelectric layer-electrode interface is studied by transmission electron microscopy. The effect of the characteristics of the interface in the performance of the multilayer system is also studied. The characteristics of the TiN films, used as electrodes, are evaluated using Auger electron spectroscopy and x-ray photoelectron spectroscopy. Finally, a model for the PMNT/TiN/SiO$_{2}$/Si film system thus obtained is proposed.
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  • Hydrogen atom in a magnetic field: electromagnetic transitions of the lowest states

    J.C. López Vie, ra., H.O.~Pilón.
    49-0
    Abstract:
    A detailed study of the lowest states $1s_0, 2p_{-1},2p_0$ of the hydrogen atom placed in a magnetic field $B\in(0-4.414\times 10^{13}\,{\rm G})$ and their electromagnetic transitions ($1s_{0} \leftrightarrow 2p_{-1}$ and $ 1s_{0} \leftrightarrow 2p_{0}$) is carried out in the infinite-proton-mass (Born-Oppenheimer) approximation. The variational method is used with a physically motivated recipe to design simple trial functions applicable to the whole domain of magnetic fields. We show that the proposed functions yield very accurate results for the ionization (binding) energies. Dipole and oscillator strengths are in good agreement with results by Ruder {\em et al.}~\cite{Ruderbook}, although we observe deviations of up to $\sim 30%$ for the oscillator strength of the linearly polarized electromagnetic transition $1s_{0} \leftrightarrow 2p_{0}$ at strong magnetic fields $B\gtrsim 1000$\,a.u.
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  • Electronic structure for the series of Cu based chalcopyrites of the CuInM$_{2}^{VI}$ type

    H. Tototzintle-Huitle, J.A. Rodríguez, R. Baquero
    58-0
    Abstract:
    In this paper we study the electronic band structure for the series of Cu-based chalcopyrites CuInM$_{2}^{VI}$ with M$^{VI}$= S,Se,Te. We use the tight-binding method and obtain the tight-binding parameters in such a way that we fit the experimental gap value for the whole series of Cu-based chalcopyrites. Chalcopyrites can deviate from the ideal symmetry in two ways: tetragonal deformation and anionic distortion. In this paper, we calculate the ideal configuration and the effect of anionic distortion. Our calculation can be used further to obtain surface, interface and superlattice electronic band structures using the Surface Green's Function Matching Method in a straightforward way.
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  • Effects of potassium doping on the composition, structure and carbon dioxide chemisorption of Na$_{2}$ZrO$_{3}$

    A. S, oval-Díaz., H. Pfeiffer
    65-0
    Abstract:
    Solid solutions of sodium and potassium metazirconate, Na$_{2 - x}$K$_{x}$ZrO$_{3}$, were prepared by coprecipitation. Then, samples were characterized by powder X-ray diffraction, scanning electron microscopy and thermogravimetric analysis. Results show that the solubility limits of potassium in Na$_{2}$ZrO$_{3}$ is 0.2, Na$_{1.8}$K$_{0.2}$ZrO$_{3}$, and the addition of potassium produced the formation of needle-like particles. Furthermore, Na$_{2 - x}$K$_{x}$ZrO$_{3}$ solid solutions were tested as CO$_{2}$ captors. The analyses of these materials showed that, although all the solid solutions present similar behaviors, the chemisorption and diffusion kinetics were enhanced by the addition of potassium. Na$_{1.6}$K$_{0.4}$ZrO$_{3}$ seems to be the best solid solution for the CO$_{2}$ capture. The differences observed in the CO$_{2}$ sorption processes were explained by the different ionic radii of sodium and potassium and with thermodynamic data.
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  • Properties of the spectra of asymmetric molecules: matrix evaluation in bases of spherical harmonics and common generating function

    E. Le, -Koo., R. Méndez-Fragoso
    69-0
    Abstract:
    The Schrödinger equation for the rotational states of asymmetric molecules is known to be separable in spheroconal coordinates and integrable in terms of Lamé functions. However, the numerical evaluation of the latter has not been developed efficiently, thereby limiting the practical application of such solutions. In this article, the matrix evaluation of the rotational states is formulated and implemented numerically for any asymmetric molecule, using the familiar bases of spherical harmonics. The matrix of the Hamiltonian - in a frame of reference fixed in the molecule and oriented along its principal axes - is constructed in the chosen basis and shown to separate into blocks of $(\ell+1) \times (\ell+1)$ and $\ell \times \ell$, for each value of the angular momentum quantum number $\ell$. The diagonalization of the successive blocks leads to accurate values of eigenenergies and eigenvectors for all values of the asymmetry parameters. The connection between these rotational states and their Lamé function representation is also established, identifying at the same time a common generating function for spherical harmonics and spheroconal harmonics.
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  • Aspectos dinámicos del movimiento lento del dedo índice

    J.A. Peralta, P. Re, es López., R. Delgado Lezama, E. Yépez
    78-0
    Abstract:
    In this work we present the design and construction of a high precision meter for the movement of the index finger under conditions that require slow and precise movements. The apparatus uses a mechanical device coupled to an induction coil, the signals are amplified, filtered and captured by a personal computer for their further processing. The displacements, speeds and accelerations that produce the involved muscles can be known with great precision. The device was proven in a sample of 15 individuals, obtaining that the precise movements of the finger are made up of a constant force that balances the load and of small impulses producing pulses of very slow speed. This observation of pulsed movements and its quantification constitutes a novel result. The apparatus is able to detect neuro-motor pathologies. The advantages of this meter are: their low cost, their operation easiness and the precision with which the subtle movements of the index finger can be measured.
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