Vol. 63 No. 4 Jul-Aug (2017): Revista Mexicana de Física

Published: 2018-06-29

Articles

  • Electronic excitation of H$_2$, CO, and N$_2$ by positron impact

    J.L.S Lino.
    303-0
    Abstract:
    In this paper we present results for positron impact excitation of electronic states of H$_2$ (x$^1 \sum_{g}^{+} \raisebox{-.2ex}[0cm][0cm]{-} \hspace{-5pt}> $ B$^1 \sum_u^+ $, C$^1 \Pi u$), CO(X$^1 \sum_g \rightarrow $ a$^1 \Pi_g$), and, N$_2$(X$^1 \sum_g \rightarrow $ a$^1 \Pi_g$) using the scaling of plane wave Born cross sections. This method was originally proposed by Kim (Phys.Rev.A64032713(2001)) to electron scattering and adapted by Lino (Chin. J. Phys. 50 (2016) 223.) for positron scattering. Integral cross sections calculations are reported using this new method. For H$_2$ molecule our cross sections exhibit results comparable to the sophisticated theories, and experimental data. For isoelectronic molecules CO, and N$_2$ the results are compared to the ab initio Schwinger multichannel (SMC) method. For positron-CO scattering our model is very reasonable when compared with SMC method and as expected for positron-N$_2$ scattering, our results, as well as SMC method, failed to reproduce some structure observed by experimentalists. A important observation using the scaling plane wave Born for positron scattering is that the method is comparable to more sophisticated theories indicating the possibility of rapid and reliable calculations of excitation cross sections.
    ⬇️ Scroll down to see the full summary

  • Low-temperature oxidation effects on the morphological and structural properties of hexagonal Zn nanodisks

    R. López, E. Vigueras-Santiago, S. Hernández-López, P. Acuña, A. Argueta-Vega, N. Colín-Becerril, G. Villa-Sánchez, J. Rosales-Dávalos
    308-0
    Abstract:
    Ambient-atmosphere oxidation in the temperature range of 90-450$^{\circ}$C was performed over Zn films composed by well-faceted hexagonal nanodisks, which were deposited by thermal evaporation. Morphological and structural properties of oxidized Zn nanodisks were studied by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and Raman scattering measurements. It was found that Zn nanodisks keep its original shape only when they are annealed at 90 or 150$^{\circ}$C. Smooth oxidation ocurred only on the rectangular faces of Zn nandodisks heated at 150$^{\circ}$C. Thermal oxidation at 250$^{\circ}$C favored growth of ZnO nanoneedles over the surface of the Zn nanodisks. Hexagonal-shape of Zn nanodisks was transformed completely into a complex morphology composed by different shaped particles, with further increase in oxidation temperature to 450$^{\circ}$C.
    ⬇️ Scroll down to see the full summary

  • Stochastic dynamics of a Brownian motor based on morphological changes

    F. Ambía, H. Híjar
    314-0
    Abstract:
    We introduce a simplified model for a microscopic system that performs directed Brownian motion due to coordinated morphological adaptations. This system consists of two spherical particles with adaptable size, that interact through elastic and repulsive forces. We propose an algorithm to control the time dependence of the system's shape that turns it into a Brownian motor, whose stochastic dynamics is analyzed by means of a Langevin model. We restrict ourselves to the simplified case of motors with small shape asymmetries and slow morphological changes, and calculate the average speed at which they should move. We compare the theoretical predictions with the results from Brownian Dynamics simulations and find that they are in very good quantitative agreement. We carry out a comparison of the proposed rectifying algorithm with a classical one based on a ratchet potential and show that in some cases morphological adaptations could produce larger velocities. We thus propose the locomotion mechanism based on controlled structural changes as a novel alternative method from which Brownian motors could operate autonomously, i.e., requiring neither a substrate nor a ratchet field.
    ⬇️ Scroll down to see the full summary

  • Polarization properties of light scattered by a metallic cylinder

    G. López-Morales, I. Saucedo-Orozco, R. Espinosa-Luna, Q. Zhan, F. Villa-Villa
    328-0
    Abstract:
    The experimental determination of the angularly resolved Mueller matrix associated to light scattered by a metallic cylinder is reported. The angle-dependent values of depolarization index and Gil-Bernabeu theorem confirm there are not depolarization effects. To our knowledge, this is the cheapest and easiest way to generate uniform linear horizontal and vertical polarizations scattered angularly. A possible application associated to the use of plastic optical fibers acting like a polarization de-multiplexer is briefly discussed.
    ⬇️ Scroll down to see the full summary

  • Comparison of solutions to the Thomas-Fermi equation by a direct method and variational calculus

    D. Sierra-Porta, M. Chirinos, J. Stock
    333-0
    Abstract:
    In this paper we perform a comparison between two solutions of the Thomas-Fermi equation. One of these solutions is the one recently found by Bougoffa (2014) which makes use of a direct method to solve the differential equation. The other solution found uses a variational method. The first method uses approximations of the residual conditions after assuming a trial function, inspired by the Sommerfeld solution. Our solution does not require approximations and we found that it reproduces more conveniently the corresponding numerical solution in terms of relative error.
    ⬇️ Scroll down to see the full summary

  • Global sensitivity analysis of dispersion maximum position of photonic crystal fibers with circular holes

    I. Guryev, J.A. Andrade Lucio, O. Shulika, G. Hernández Gómez, I. Sukhoivanov
    339-0
    Abstract:
    We apply global sensitivity analysis technique to investigate the dispersion characteristic maximum behavior of single-mode photonic crystal fiber regarding geometric parameters variation. There have been considered two cases with 5 and 7 parameters. Results demonstrate significant differences in tilt and even the opposite signs slopes of the dependencies when varying different parameters. This fact allows fine tuning the PCF parameters with high flexibility and efficiency. Comparing the 5 and 7-parameters scheme reveals very low differences. However, additional two parameters may be useful for precise tuning of the dispersion characteristic.
    ⬇️ Scroll down to see the full summary

  • Análisis de tensión/tamaño en compuestos ternarios AgIn$_5$VI$_8$ (VI = S, Se, Te) mediante difracción de Rayos-x

    J.R. Fermina, D.Y. Salcedo, C. Durante Rincóna, J.A. Castro
    345-0
    Abstract:
    In this work, we have study the microestructural properties of the ternary compounds AgIn$_5$VI$_8$ (VI= S, Se, Te) by X-ray diffraction technique (XRD). The linewidth of the XRD profile is measured as function of the diffraction angle. Structural parameters such as, average grain size, microstrains, and crystalline dislocation density, are obtained on the framework of a strain/size analysis based on the modified Scherrer equation for Gaussian profiles. The crystalline dislocations arrange according to a Gaussian distribution function, indicating that these dislocations are randomly distributed within the grains.
    ⬇️ Scroll down to see the full summary

  • Effect of the variational symmetries of the lagrangian on the propagator and associated conserved operators

    G.F. Torres del Castillo, R.L. Lechuga-Solís
    351-0
    Abstract:
    Making use of the expression for the propagator in terms of path integrals, we study the effect of certain variational symmetries of a Lagrangian on the corresponding propagator. We also show that by considering a point transformation that relates two different Lagrangians one can obtain a relation between the corresponding propagators.
    ⬇️ Scroll down to see the full summary

  • Construction and validation of a non-conventional elliptical zone plate that generates auto-images singular optical fields

    S.E. Balderas-Mata, J.E. Gómez-Correa, J. Medina-Márquez
    356-0
    Abstract:
    The aim of this work is to construct an optical element which has the property of having a family of curves that possesses the same evolute and common parallel. Also, the family of curves must be replicated as in a conventional zone plate, which by definition has a circular geometry. The zone plate to be generated will be called non-conventional due to the fact that it does not have circular geometry. The focalization properties of this plate are explained from the rays associated with a spherical wavefront emitted by each point of the transmittance, i.e., the parallel curves evolution by diffraction effects along the propagation axis, which replicate themselves when the constructive interference exists due to the contribution of the different rings of the plate.
    ⬇️ Scroll down to see the full summary

  • Plasma diagnostics of glow discharges in mixtures of CO$_{2}$ with noble gases

    P.G. Reyes, A. Gómez, J. Vergara, H. Martínez, C. Torres
    363-0
    Abstract:
    This study presents the plasma diagnostics of a glow discharge produced in two different mixtures, CO$_{2}$/He and CO$_{2} $/Ar, at a constant pressure of 1.5 Torr. The experiment was conducted to determine the carbon dioxide decomposition in the plasma by using the optical emission spectroscopy $\left(OES\right)$ method through identifying lines and emission bands in the spectra. In addition, an electrical characterization of the mixture plasma was made by the determination of ion density $(n_{i})$ and the electronic temperature $(T_{e})$, estimated through a double Langmuir probe. The electronic temperature for the mixture plasma was in the range of 2.07-5.37 eV, and the ion density between $2.15\times 10^{9}$ and $18.70\times 10^{9}$ particles/cm$^{3}$. The principal bands and lines identified in the OES correspond to CO$_{2}^{+}$, CO$_{2}$, CO$^{+}$, CO, O*, O$_{2}$, O$_{2}^{+}$, C$_{2}$, He* and Ar*.
    ⬇️ Scroll down to see the full summary

  • Y$_2$O$_3$:D{y}$^{3+}$/L{i}$^{+}$ phosphors synthesized by spray

    R. Balderas-Xicohténcatl, S. Carmona-Tellez, C. Falcony
    372-0
    Abstract:
    Dysprosium and Lithium-activated yttrium oxide phosphor was synthesized at 1100 $^\circ$C by ultrasonic spray pyrolysis (USP) using DI water as solvent and metal chlorides as precursors. The characteristic emission peaks of Dy$^{3+}$ due to the transitions $^4$F$_{9/2}$ to $^6$H$_{15/2}$ at 483 nm, $^4$F$_{9/2}$ to $^6$H$_{13/2}$ at 573 nm, $^4$F$_{9/2}$ to $^6$H$_{11/2}$; at 667 nm and $^4$F$_{9/2}$ to $^6$H$_{9/2}$ at 766 nm were observed. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) measurements were carried out to understand surface morphological features and the particle size of the phosphor. The uniformity of phase of Dy$^{3+}$ $_-$Li$^+$ doped Y$_2$O$_3$ phosphors was checked by X-ray diffraction (XRD) technique. The phosphors form clusters that were found to be $\sim 1$ $\mu$m in size, however, particles that form these clusters have sizes between 40 and 120~nm.
    ⬇️ Scroll down to see the full summary

  • Dynamics of solitons of the nonlinear dispersion Drinfel'd-Sokolov system by ansatz method and He's varitional principle

    F. Tchier, L. Ragoub, D. Baleanu, M. Inc
    378-0
    Abstract:
    In this article, the exact-special solutions of the nonlinear dispersion Drinfel'd-Sokolov (shortly $D(m,n)$) system are analyzed. We use the ansatz approach and the He's variational principle for the mentioned equation. The general formulae for the compactons, solitary patterns, solitons and periodic solutions are acquired. These types of solutions are useful and attractive for clarifying some types of nonlinear physical phenomena. These two methods will be used to carry out the integration.
    ⬇️ Scroll down to see the full summary

  • Formation and interaction of multiple dipoles in a periodic driving flow

    G. Ruiz-Chavarría, E.J. López-Sánchez
    386-0
    Abstract:
    We present herein the results of a numerical simulation of a periodic flow which take place in a channel and an open domain. To investigate this flow we solve the fluid dynamics equations in the vorticity-stream function formulation by using a pseudospectral method based on Chebyshev polynomials. According to these numerical simulations, a pair of counter-rotating vortices (known as a dipole) forms during each period. The lifetime of these vortices can exceed the driving period, which allows multiple dipoles to coexist. The attention is focused on the interaction of vortices. A possible outcome is that dipoles created in consecutive periods coalesce. Another outcome is the formation of vorticity spots in front of the emerging dipole which reduce the dipole speed. On the other hand, it is observed that a fraction of the vorticity created into the channel cannot incorporate to the vortices, leading to the formation of a vorticity band between the channel mouth and the dipole. Based on this fact an analytical model is proposed to describe the properties of dipoles emerging from the channel; the results of this model are consistent with numerical data. The parameters governing the development of this flow are the Strouhal number, whose value determines the intensity of the dipole interaction, and the Reynolds number, whose growth leads to the emergence of instabilities and to the breaking of the flow symmetries.
    ⬇️ Scroll down to see the full summary