Vol. 56 No. 6 (2010): Revista Mexicana de Física.

Published: 2010-01-01

Articles

  • Phase transitions of granular disks with a magnetic dipole

    P. Coutiño, N. Ibarra-ávalos, A. Gil-Villegas
    435-0
    Abstract:
    We present a simple experiment to study phase transitions of a granular system composed of disks with a magnetic dipole. The particles are contained within a cylindrical container and are excited through alternating magnetic fields. The initial configuration of this system is a low-density isotropic phase. By increasing the density, a critical value is reached and the system starts to organize into columns. At higher densities an ordered state is obtained where structural columnar patterns are formed. The set up of the experimental device is very easy to implement, using standard high-school and undergraduate physics laboratory facilities. The experiment can be used, combined with computer simulations, to introduce the subject of phase transitions in complex materials.
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  • Effect of pressure on the electrical properties of GaSe/InSe heterocontacts

    M.O. Vorobets
    441-0
    Abstract:
    Barrier structures were produced using optical contact between the indium and gallium selenides. The effect of mechanical pressure ranging from 0 to 100 kPa on the electrical properties of the GaSe/InSe heterocontacts was investigated. The data was analyzed assuming the SIS (semiconductor -- insulator -- semiconductor) model. Using this model we were able to explain the current -- voltage dependence. It was found that the modification of heteroboundary significantly affects the electric transport.
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  • Digital in-line holographic microscopy with partially coherent light: micrometer resolution

    D. Alvarez-Palacio, J. Garcia-Sucerquia
    445-0
    Abstract:
    Using a blue light-emitting diode (LED) it is shown that lensless Digital In-line Holography Microscopy (DIHM) with spherical waves can yield micrometer resolution, even when large objects, such as the head of a fruit fly (Drosophila melanogaster), are imaged. By changing the size of the pinhole, the influence of spatial coherence of the spherical wave at the plane of the sample on the resolution is analysed. Although the achieved resolution is less than that ultimately obtained with a fully coherent laser and a numerical aperture of over 0.5, the use of a LED allows for a very compact and low cost implementation of DIHM. Experiments with micrometer-size beads support the claim of micrometer resolution.
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  • Non linear optical properties of novel amphiphilic azo-polymers bearing well defined oligo (ethylene glycol) spacers

    O.G. Morales-Saavedra, T. García, C. Caicedo, E. Rivera
    449-0
    Abstract:
    Non linear optical (NLO) properties of a new series of pnPEGMAN polymers: p2PEGMAN or Poly[(E)-2-(2-(methyl(4-((4-nitrophenyl) diazenyl)phenyl) amino)ethoxy)ethyl methacrylate], p3PEGMAN or Poly[(E)-2-(2-(2-(methyl(4-((4-nitrophenyl)diazenyl)phenyl) amino) ethoxy)ethoxy)ethyl methacrylate], p4PEGMAN or Poly[(E)-2-(4-((4-nitrophenyl)diazenyl)phenyl)-5,8,11-trioxa-2-azatridecan-13-yl me- thacrylate] and p6PEGMAN or Poly[(E)-2-(4-((4-nitrophenyl) diazenyl) phenyl) -5,8,11,14,17-pentaoxa -2- azanonadecan -19-yl methacrylate] were studied by the Z-Scan technique. These azo-polymers exhibited high $\chi ^{(3)}$ NLO-responses with excitation below the resonance absorption region of the polymers and the evaluated n$_{2}$-values are in the order of 10$^{ - 4}$ to 10$^{ - 5}$~esu, with negative sign for all the studied materials.
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  • Numerical solution of the wave equation on particular space-times using CMC slices and scri-fixing conformal compactification

    A. Cruz-Osorio, A. González-Juárez, F.S. Guzmán, F.D. Lora-Clavijo
    456-0
    Abstract:
    In this paper we present the numerical solution of the conformally invariant wave equation on top of a fixed background space-time corresponding to two different cases: i) 1+1 Minkowski space-time in Cartesian coordinates and ii) Schwarzschild space-time. In both cases we use hyperboloidal constant mean curvature slices and scri-fixing conformal compactification, and solve the wave equation on the conformal space-time. In the case of the Schwarzschild space-time we study the quasinormal mode oscillations and the late-time polynomial tail decay exponents corresponding to a mass-less scalar field. We also present general formulas to construct hyperboloidal constant mean curvature slicings of spherically symmetric, static, space-times in spherical coordinates.
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  • A mapping between Lorentz-violating and conventional electrodynamics

    Ralf Lehnert.
    469-0
    Abstract:
    The Chern--Simons-type term in the photon sector of the Lorentz- and CPT-breaking minimal Standard-Model Extension (mSME) is considered. It is argued that under certain circumstances this term can be removed from the mSME. In particular, it is demonstrated that for lightlike Lorentz violation a field redefinition exists that maps the on-shell free Chern--Simons model to conventional on-shell free electrodynamics. A compact explicit expression for an operator implementing such a mapping is constructed. This expression establishes that the field redefinition is non-local.
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  • Múltiples alturas de equilibrio en capilares cónicos

    M. Pliego, C. Fuentes, G.J. Gutiérrez, A. Medina, M.R. Aguilar
    475-0
    Abstract:
    An analysis, based on the method of extremals of the energy, to compute the equilibrium heights of a liquid that penetrates spontaneously capillaries of variable cross-section (divergent or convergent cones, with small slope angles, $\alpha $, of the generatrix) is presented. The general criterion that allows characterizing the equilibrium heights or depths, is given as a function of $\alpha $, the Bond number, $Bo$, and the contact angle,~$\theta$.
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  • Evaluación de desempeño del micropet focus 120 con los radionúclidos $^{11}$C, $^{13}$N y $^{18}$F

    F. Trejo Ballado, N. Ortega López, R. Ojeda Flores, M.A. Ávila Rodríguez
    482-0
    Abstract:
    The aim of this work is to evaluate the characteristics involved in the data acquisition and image reconstruction of a microPET Focus 120 system. Energy resolution, spatial resolution, sensitivity, count rate and image quality characteristics were evaluated using different phantoms with three conventional positron emitter radionuclides used in PET imaging ($^{11}$C, $^{13}$N and $^{18}$F). Some tests performed in this work are from the new protocol NEMA NU4 -- 2008.
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  • Láser de alta potencia y alta eficiencia bombeado por diodo

    N.A. Barboza, L.A. Ríos, R.S. Cudne, .
    489-0
    Abstract:
    We present a simple diode-pumped, cw Nd:YVO$_{4}$ laser that emits more than 7 W at 1064 nm. The mode of this laser is nearly TEM$_{00}$ ($M^{2}$=1.7) and the absorbed pump power to output power conversion efficiency is around 51%. We also present a simple technique to convert this cw laser into a Q-switched laser; using this technique we obtained 25 ns pulses at a repetition rate of over 7 KHz.
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