Scielo RSS <![CDATA[Revista mexicana de física]]> vol. 63 num. 4 lang. es <![CDATA[SciELO Logo]]> <![CDATA[Análisis de tensión/tamaño en compuestos ternarios AgIn<sub>5</sub>VI<sub>8</sub> (VI = S, Se, Te) mediante difracción de Rayos-x]]> En este trabajo estudiamos las propiedades microestructurales de compuestos ternarios AgIn5VI8 (VI= S, Se, Te) mediante la técnica de Difracción de Rayos-X (DRX). El ancho de línea del perfil de DRX es medido como función del ángulo de difracción. Los parámetros microestructurales, tales como, el tamaño medio de grano, microtensión y densidad de dislocaciones cristalinas, son obtenidos a partir de un análisis de Tensión/Tamaño basado en la ecuación modificada de Scherrer para perfiles Gaussianos. La distribución de las dislocaciones cristalinas corresponde a la cola de una función de Gaussiana, indicando que estas conforman arreglos aleatorios en los granos.<hr/>In this work, we have study the microestructural properties of the ternary compounds AgIn5VI8 (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. <![CDATA[Effect of the variational symmetries of the lagrangian on the propagator and associated conserved operators]]> 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.<hr/>Haciendo uso de la expresión para el propagador en términos de integrales de trayectoria, estudiamos el efecto de ciertas simetrías variacionales de una lagrangiana sobre el propagador correspondiente. Mostramos también que, considerando una transformación puntual que relaciona dos lagrangianas diferentes, se puede obtener una relación entre los propagadores correspondientes. <![CDATA[Construction and validation of a non-conventional elliptical zone plate that generates auto-images singular optical fields]]> 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. <![CDATA[Plasma diagnostics of glow discharges in mixtures of CO<sub>2</sub> with noble gases]]> This study presents the plasma diagnostics of a glow discharge produced in two different mixtures, CO2/He and CO2/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 (OES) 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 (ni) and the electronic temperature (Te), 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 × 109 and 18.70 × 109 particles/cm3. The principal bands and lines identified in the OES correspond to C O 2 +, CO2, CO+, CO, O*, O2, O 2 +, C2, He* and Ar*. <![CDATA[Y<sub>2</sub>O<sub>3</sub>:Dy<sup>3+</sup>/Li<sup>+</sup> phosphors synthesized by spray]]> Dysprosium and Lithium-activated yttrium oxide phosphor was synthesized at 1100 °C by ultrasonic spray pyrolysis (USP) using DI water as solvent and metal chlorides as precursors. The characteristic emission peaks of Dy3+ due to the transitions 4F9/2 to 6H15/2 at 483 nm, 4F9/2 to 6H13/2 at 573 nm, 4F9/2 to 6H11/2; at 667 nm and 4F9/2 to 6H9/2 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 Dy3+ _Li+ doped Y2O3 phosphors was checked by X-ray diffraction (XRD) technique. The phosphors form clusters that were found to be ∼1 μm in size, however, particles that form these clusters have sizes between 40 and 120 nm. <![CDATA[Dynamics of solitons of the nonlinear dispersion Drinfel’d-Sokolov system by ansatz method and He’s varitional principle]]> 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. <![CDATA[Formation and interaction of multiple dipoles in a periodic driving flow]]> 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.