Scielo RSS <![CDATA[Revista mexicana de física E]]> http://www.scielo.org.mx/rss.php?pid=1870-354220180002&lang=es vol. 64 num. 2 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.mx/img/en/fbpelogp.gif http://www.scielo.org.mx <![CDATA[El camino hacia la luz láser]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200100&lng=es&nrm=iso&tlng=es Resumen En este trabajo se presenta el desarrollo cronológico de la invención del láser, partiendo desde la propuesta teórica de la emisión estimulada hasta la invención del primer dispositivo láser. Se analizan los trabajos de investigación más relevantes y se discuten las dificultades que se tuvieron que afrontar e inclusive las disputas que surgieron al momento de registrar la patente del láser. También, se estudian los principios físicos que hacen posible la emisión del láser, describiendo la inversión de población en un sistema de tres niveles de energía a partir de un modelo matemático y la arquitectura que debe de tener una cavidad láser.<hr/>Abstract The present work is a review of the chronological development of the laser invention, starting from the theoretical proposal of stimulated emission to the invention of the first laser device. We present the most relevant research papers and discuss the difficulties that had to be faced, including the disputes that occurred at the time of registering the laser patent. Besides, the theoretical principles that make possible the emission of the laser are studied, describing the population inversion in a system of three levels of energy from a mathematical model and the architecture that must have a laser linear cavity. <![CDATA[El formalismo 3+1 en relatividad general y la descomposición tensorial completa]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200108&lng=es&nrm=iso&tlng=es Resumen Se presenta una breve revisión del formalismo 3 + 1 en Relatividad General, y se introducen algunas novedosas convenciones así como elementos de notación que permiten facilitar el tratamiento de las expresiones de todas las proyecciones tensoriales involucradas en este formalismo. También se obtienen expresiones 3 + 1 útiles para la manipulación de índices (contracción, simetrización, antisimetrización), productos tensoriales y derivación covariante de tensores arbitrarios.<hr/>Abstract A brief review of 3 + 1 formalism in General Relativity is presented, introducing innovative conventions and notation elements which make it easier to deal with all of the tensorial projections involved in this formalism. Also, useful 3 + 1 expressions for manipulation of indexes (contraction, symmetrization, anti-symmetrization), tensorial producs and the covariant derivative of arbitrary tensors are obtained. <![CDATA[An algebraic approach to a charged particle in a uniform magnetic field]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200127&lng=es&nrm=iso&tlng=es Abstract We study the problem of a charged particle in a uniform magnetic field with two different gauges, known as Landau and symmetric gauges. By using a similarity transformation in terms of the displacement operator we show that, for the Landau gauge, the eigenfunctions for this problem are the harmonic oscillator number coherent states. In the symmetric gauge, we calculate the SU (1,1) Perelomov number coherent states for this problem in cylindrical coordinates in a closed form. Finally, we show that these Perelomov number coherent states are related to the harmonic oscillator number coherent states by the contraction of the SU (1,1) group to the Heisenberg-Weyl group. <![CDATA[Design and construction of an apparatus to visualize incompressible fluid flow in several regimes]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200133&lng=es&nrm=iso&tlng=es Abstract In this work, the design and construction of a didactic experimental equipment to visualize the fluid flow behavior in the laminar, transition and turbulent regimes is presented; as well as the ability to measure and display the respective Reynolds number (Re) of each flow; current educational equipments have limited or null capacity in this regard. The equipment was designed taking into account the basic laws of fluids such as mass, momentum and energy conservation. The analytical calculations were numerically validated using the finite element method (FEM), for which the Ansys software was used in its Ansys® Parametric Design Language (APDL) and Workbench platforms. Solidworks tools for conceptual design and Stratasys Catalist for three dimension (3D) printing were used. Additionally, hardware was implemented for the step of measuring the flow velocity, temperature and Re calculation. The apparatus is a valuable resource in fluid flow visualization since it permits to read several fluid parameters immediately from a display. <![CDATA[Exact solutions for electromagnetic fields inside and outside a spherical surface with magnetic/electric dipole distributed sources]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200139&lng=es&nrm=iso&tlng=es Abstract Exact solutions of the Maxwell equations for the electromagnetic fields inside and outside a spherical surface, with time alternating magnetic or electric dipole source distributions, are constructed as alternatives to the respective familiar point-dipole solutions in undergraduate and graduate books. These solutions are valid for all positions, inside and outside the sphere, including the quasi-static, induction and radiation zones; the solutions inside make the difference from the point-dipole solutions; the definitions of the dynamic dipole moments must be based on the ordinary spherical Bessel functions for the solutions outside, and on the outgoing spherical Hankel functions for the solutions inside, instead of the powers of the radial coordinate as solutions of the Laplace equation valid for the static case. The solutions for the resonating cavities are associated with the nodes of the spherical Bessel function for the TE modes of the magnetic dipole source, and with the extremes of the product of the radial coordinate times the same spherical function for the TM modes of the electric dipole source; both conditions also guarantee the vanishing of the fields outside. <![CDATA[Comparative analysis of proximity potentials to describe scattering of <sup>13</sup>C projectile off <sup>12</sup>C, <sup>16</sup>O, <sup>28</sup>Si and <sup>208</sup>Pb nuclei]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200149&lng=es&nrm=iso&tlng=es Abstract In this work, we examine the elastic scattering cross sections of 13C on 12C, 16O, 28Si and 208Pb target nuclei at different incident energies. For the first time, we apply six types of proximity potentials such as Broglia and Winther 1991 (BW 91), Aage Winther (AW 95), Christensen and Winther 1976 (CW 76), Bass 1973 (Bass 73), Bass 1977 (Bass 77) and Bass 1980 (Bass 80) in order to obtain the real part of the optical potential. The imaginary part is taken as the Woods-Saxon potential. Theoretical results are compared with each other as well as the experimental data. <![CDATA[Modos electromagnéticos en esferas metálicas; plasmones en micro y nanopartículas]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200154&lng=es&nrm=iso&tlng=es Resumen Estudiamos teóricamente la excitación de plasmones de superficie en esferas metálicas. Se supone que la esfera metálica es de tipo Drude. La excitación de modos, para esferas metálicas, de igual forma que las dieléctricas, es observada como picos en la sección eficaz de esparcimiento total. Bajo condiciones de excitación, el modo se comporta como una onda que se propaga a lo largo de la circunferencia pero en la esfera, su intensidad es prominentemente confinada a la superficie. El número de modos observados depende del radio de la esfera.<hr/>Abstract The excitation of surface plasmons in metallic spheres is studied theoretically. The metallic sphere is supposed to be of the Drude type. The modes excitations for metallic spheres, like the dielectric spheres are observed as peaks in the total scattering cross section. Under excitation condition, the modes are behaved as waves that propagates along the circumference, but in the sphere, its intensity is highly confined to the surface. The number of modes observed depends on the radius of the sphere. <![CDATA[Clifford’s attempt to test his gravitation hypothesis]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200162&lng=es&nrm=iso&tlng=es Abstract Almost half a century before Einstein expounded his general theory of relativity, the English mathematician William Kingdon Clifford argued that space might not be Euclidean and proposed that matter is nothing but a small distortion in that spatial curvature. He further proposed that matter in motion is not more than the simple variation in space of this distortion. In this work, we conjecture that Clifford went further than his aforementioned proposals, as he tried to show that matter effectively curves space. For this purpose he made an unsuccessful observation on the change of the plane of polarization of the skylight during the solar eclipse of December 22, 1870 in Sicily.<hr/>Resumen Casi medio siglo antes de que Einstein expusiera su teoría general de la relatividad, el matemático inglés William Kingdon Clifford argumentó que el espacio podría no ser euclidiano y propuso que la materia no es más que una pequeña distorsión en esa curvatura espacial. Propuso además que la materia en movimiento no es más que la simple variación en el espacio de esta distorsión. En este trabajo, conjeturamos que Clifford fue más allá de dichas propuestas, pues trató de demostrar que efectivamente la materia curva el espacio. Para ello hizo una observación infructuosa sobre el cambio del plano de polarización de la luz solar durante el eclipse solar del 22 de diciembre de 1870 en Sicilia. <![CDATA[Cómo las radiaciones alteran los objetos]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200169&lng=es&nrm=iso&tlng=es Resumen Se presenta una enumeración de tópicos sobre los que se desarrolla un curso de posgrado sobre interacción de radiación con materia. Abarca los fenómenos físicos mediante los cuales las radiaciones producen modificaciones estructurales en los materiales, y algunos métodos que se emplean para estudiarlos. Comenzando con los primeros eventos binarios, se describe la secuencia de sucesos típicos de paso de radiaciones por materia con énfasis en los desplazamientos atómicos y su evolución en cascadas. Se esbozan procesos en que intervienen gran número de eventos en los que se usan métodos estadísticos como cálculos de tipo Monte Carlo y dinámica molecular. Estos desembocan en la descripción de efectos macroscópicos, conduciendo finalmente a teorías de funciones continuas.<hr/>Abstract An outline of topics that constitute a graduate course on interaction of radiation with matter is presented. The list covers the physical events that produce structural changes in materials, and some of the techniques used to study them. Starting with the initial binary event, a sequence of typical processes that take place as radiation passes through matter is described, with emphasis on atomic displacements and the evolution of cascades. Procedures that involve large numbers of events and use statistical methods, like Monte Carlo and molecular dynamics, are sketched, leading to the description of macroscopic effects, and eventually continuum theories. <![CDATA[Algoritmo cuántico de Deutsch y Jozsa en GAMA]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200181&lng=es&nrm=iso&tlng=es Resumen Una propiedad importante de la computación cuántica es su paralelismo implícito, que permite procesar un número exponencial de transformaciones básicas mediante un número lineal de qubits en un sistema cuántico. El algoritmo de Deutsch y Jozsa ilustra la reducción, proporcionada por el cómputo cuántico, en la complejidad del procesamiento. Presentamos aquí la implementación y la ejecución del algoritmo cuántico de Deutsch y Jozsa en GAMA, herramienta que hemos desarrollado para la simulación y monitorización de algoritmos cuánticos. La simulación permite explorar los detalles de sus componentes mediante el módulo de depuración de GAMA que permite mostrar las diferentes configuraciones que cada componente puede asumir.<hr/>Abstract An important feature of quantum computing is its inherent paralellism, allowing to process an exponential number of basic transforms with just a linear number of qubits. The Deutsch-Jozsa algorithm exemplifies the computational complexity reduction. This work reports the implementation and execution of the Deutsch-Josza quantum algoritm in GAMA, a programming language for quantum computing simulation developed by ourselves. Through this simulation, it is possible to explore all the components involved by tracing all the different configurations that each component may take. <![CDATA[Límites de las dimensiones extras considerando las leyes termodinámicas de la radiación de cuerpo negro]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200190&lng=es&nrm=iso&tlng=es Resumen En este trabajo se analizara el problema de radiación de cuerpo negro en un escenario efectivo en cuatro dimensiones proveniente de un campo de norma libre en cinco dimensiones, donde la quinta dimensión esta compactificada a un círculo. El punto de partida es la descomposición de Kaluza-Klein de la acción del campo de norma en 5 dimensiones en dos sectores en cuatro dimensiones: el primer sector contiene un campo de norma sin masa, mientras el segundo sector produce un conjunto infinito de campo de norma con masa. Ambos sectores contribuyen a la ley de Stefan-Boltzmann. Contrastando los datos experimentales con los obtenidos teóricamente se obtiene una cota para el parámetro asociado al escenario.<hr/>Abstract In this paper we will analyze the problem of blackbody radiation in an effective 4D scenario that arises from the 5D free gauge field, where the fifth dimension is compactified to a circle. The starting point is the Kaluza-Klein decomposition of the 5D gauge field action into two sectors in four dimensions: the first sector contains a massless gauge field, while the second sector yields an infinite set of massive gauge fields. Both sectors contribute to Stefan-Boltzmann’s law. By contrasting the experimental data with those obtained theoretically, a bound is obtained for the parameter associated with the scenario. <![CDATA[Principles of operation of a passively mode-locked fiber ring laser and 3D mapping of ultra-short pulses]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200195&lng=es&nrm=iso&tlng=es Abstract In this article, we study the operation and basic elements in a passively mode-locked fiber ring laser (PML-FRL), emphasizing the saturable absorber (SA) effect seen as a nonlinear filter in transmission, which is produced by the non-linear polarization rotation (NPR) and a linear polarizer. Besides, we employ a technique of 3D mapping measurements for characterizing ultra-short pulse dynamics. <![CDATA[Duality symmetries behind solutions of the classical simple pendulum]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200205&lng=es&nrm=iso&tlng=es Abstract Describing the motion of the classical simple pendulum is one of the aims in every undergraduate classical mechanics course. Its analytical solutions are given in terms of elliptic functions, which are doubly periodic functions in the complex plane. The independent variable of the solutions is time and it can be considered either as a real variable or as a purely imaginary one, which introduces a rich symmetry structure in the space of solutions. When solutions are written in terms of the Jacobi elliptic functions this symmetry is codified in the functional form of its modulus, and is described mathematically by the six dimensional coset group Γ/Γ(2) where Γ is the modular group and Γ(2) is its congruence subgroup of second level. A discussion of the physical consequences that this symmetry has on the motions of the simple pendulum is presented in this contribution and it is argued they have similar properties to the ones termed as duality symmetries in other areas of physics, such as field theory and string theory. Thus by studying deeper a very familiar mechanical system, it is possible to get an insight to more abstract physical and mathematical concepts. In particular a single solution of pure imaginary time for all allowed values of the total mechanical energy is given and obtained as the S-dual of a single solution of real time, where S stands for the S generator of the modular group. <![CDATA[Revisiting viscosity from macroscopic to nanoscale regimes]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200222&lng=es&nrm=iso&tlng=es Abstract The response of a fluid to deformation by shear stress is known as shear viscosity. This concept arises from a macroscopic view and was first introduced by Sir Isaac Newton. Nonetheless, a fluid is a series of moving molecules that are constrained by the shape of the container. Such a view begs the treatment of viscosity from a microscopic or molecular view, a task undertaken by both Einstein and Smoluchowski independently. Here we revisit the concept of viscosity and experimentally verify that the viscosity at a molecular level, which describes the drag force, is the same as the macroscopic shear viscosity; hence, bridging different length- and time-scales. For capturing the shear stress response of a fluid, we use classical rheometry; at a molecular level we use probe diffusion to determine the local viscosity from the translational and rotational motions. In these cases, we use Fluorescence Correlation Spectroscopy and Time Resolved Fluorescence, respectively. By increasing the osmolyte (Glucose-D) concentration, we change the viscosity and find that these methods provide a unified view of viscosity, bridging the gap between the macroscopic and nanoscale regimes. Moreover, Glucose’s viscosity follows a scaling factor more commonly associated to solutions of branched polymer because the probe dimensions are comparable to the dimensions of the osmolyte that exerts the drag. <![CDATA[Cohetes hidráulicos con videos en cámara lenta]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200232&lng=es&nrm=iso&tlng=es Resumen En este artículo se determina la velocidad y aceleración de un conjunto de cuatro cohetes hidráulicos, empleando el método de mínimos cuadrados y el método de Euler. Los datos de posición y tiempo se obtienen a partir del análisis de videos en cámara lenta (slow motion) del lanzamiento de los cohetes, procesados con el software analizador de videos “Tracker”. Este experimento se propone como una herramienta pedagógica para la exploración por parte de estudiantes de ciencia e ingeniería de conceptos básicos de cinemática y dinámica en sistemas con masa y aceleración variables.<hr/>Abstract In this paper, the velocity and acceleration of four water rockets is determined, using the least squares method and the Euler’s method. The position and time data are obtained from the analysis of slow-motion videos of the launch of the rockets, processed with the video analyzer software “Tracker”. This experiment is proposed as a pedagogical tool for the exploration by students of high school and first semester of sciencie and engineering of basic concepts of kinematics and dynamics in systems with variable mass and acceleration. <![CDATA[A didactic prototype to estimate the electric power produced by an angular motion]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-35422018000200241&lng=es&nrm=iso&tlng=es Abstract This paper describes the design and implementation of an experimental system that estimates the electric power that can be produced by the angular motion showing the fundamental principles of mechanical-into-electrical energy conversion, which are the operation main basis of electromechanical devices such as wind turbines. Some theoretical concepts related with curricular subjects such as Electric mchenary, Physics, Renewable Energies, Power Electronics and Microcontrollers, were verified by Science students that participated in this project achievement. The main aim of this work is to show a simplified system development for didactic applications that can be mounted at indoor conditions and can be constructed from a set of basic and cheap electrical components.<hr/>Resumen Este trabajo describe el diseño y la implementación de un sistema experimental de tipo didáctico que puede estimar cuanta potencia eléctrica se produce por un movimiento angular, mostrando así, los principios fundamentales de la conversión de energía mecánica en eléctrica los cuales son básicos para el análisis de la operación de dispositivos electromecánicos como lo son los aerogeneradores. En este trabajo se muestran algunos principios básicos relacionados con las asignaturas de Máquinas Eléctricas, Física, Energías Renovables, Electrónica de Potencia y Microcontroladores. Durante el desarrollo de este trabajo, estos principios fueron verificados por estudiantes de licenciatura quienes participaron en el desarrollo y caracterización de este prototipo. El objetivo principal de este artículo es el de mostrar el desarrollo de un sistema simplificado para aplicaciones didácticas que puede ser implementado en condiciones controladas de laboratorio y puede construirse a partir de elementos sencillos y económicos.