Vol. 50 No. 1 Jan-Jun (2004): Revista Mexicana de Física E

Published: 2004-01-01

Artículos

  • Caracterización de microondas y sus aplicaciones en el análisis estructural de cristales 2D en el laboratorio de enseñanza

    J. Nieto Pérez
    1-7
    Abstract:
    In our daily environment, manipulating TV controls, car alarms, cell telephones and even in the kitchen, we usually take advantage of infrared, ultrasonic and microwave technologies. Nevertheless university students do not always have the opportunity to study such frequencies in the teaching laboratory. In this work, we introduce microwaves to be studied experimentally just as an electromagnetic phenomenon capable to be scattered, polarized, diffracted, absorbed and so on. It is comparable to the way that visible light behaves. Recognizing the didactic power of image in teaching process, we decided to get an image of microwave diffraction patterns as they are observed for visible light and X-ray on photographic films. To get such images, measurements of intensities are made and a suitable software is used to obtain a pattern of the radiation. Difficulties in carry out proposed experiments are reported and some techniques and procedures are suggested to obtain best results on emulating X-ray diffraction and structural analysis methods used for actual crystals, we have obtained the analogous diffraction pattern from two dimensional crystalline models exposed to microwaves.
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  • Propiedades magnéticas y de transporte de sistemas nanocristalinos: conceptos básicos y aplicaciones a sistemas reales

    M. Knobel, L.M. Socolovsky, J.M. Vargas
    8-28
    Abstract:
    We give an introduction to the magnetic and transport properties of the nanocrystalline systems, starting with the study of superparamagnetism, to follow with the case of ensembles of nanosized particles. We provide some insight to the problem of interacting particles. We study the physical effects caused by the nanoparticles in the transport properties, with emphasis in the Giant Magnetoresistance effect and Giant Hall effect in real systems. Basic concepts and different techniques useful for the study of such systems are reviewed. We include a comprehensive list of references, in order to serve as a guide for interested readers. We show the scientific complexity of these technologically important systems.
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  • An experimental setup to verify stokes' law using an electronic balance

    M. Dolz, A. Casanovas, J. Delegido, M.J. Hernández
    29-32
    Abstract:
    An experimental setup has been designed to allow direct measurement of the force acting upon a sphere immersed in a moving fluid. This experiment confirms the direct proportionality between the force and each of the variables involved (sphere-fluid relative velocity, sphere radius and fluid viscosity). A simple experimental demonstration has been made of Stokes' law for spheres immersed in fluids moving, for very small Reynolds numbers, along cylindrical tubes.
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  • Cambio del estado de polarización por reflexión en un espejo elíptico

    O.G. Rodríguez-Herrera, M. Rosete-Aguilar, N.C. Bruce
    33-40
    Abstract:
    The analysis of the change in the polarization state due to reflection of light on a surface, is not always trivial. This change will depend on the properties of the material, the shape of the surface and the angle of incidence. In this paper we present an example of this kind of analysis for an elliptical mirror, showing the importance of the shape and the material of the surface.
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  • The lorentz group, a galilean approach

    D.E. Jaramillo, N. Vanegas
    41-46
    Abstract:
    We present a pedagogical approach to the Lorentz group. We start by introducing a compact notation to express the elements of the fundamental representation of the rotations group. Lorentz coordinate transformations are derived in a novel and compact form. We show how to make a Lorentz transformation on the electromagnetic fields as well. A covariant time-derivative is introduced in order to deal with non-inertial systems. Examples of the usefulness of these results such as the rotating system and the Thomas precession, are also presented.
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  • An eikonal approach for the atomic photoelectric effect on H-like atoms

    S. Otranto, G. Gasaneo, E.D. Alberdi
    47-50
    Abstract:
    Most quantum mechanics textbooks introduce the atomic photoelectric effect expressing the final continuum state in the high energy limit as a plane wave. This approximation has shown to give clear differences between gauges though. In this work, we show that an approximation based on the asymptotic limit of the exact wave function for the final state leads to better results whether form of the interaction Hamiltonian is used as the photon energy increases. This asymptotic eikonal approximation leads to the exact result in velocity gauge for increasing photon energies, evidencing the relevance of the Coulomb potential even at large distances.
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  • Mexico and the early history of magnetism*

    A.P. Guimar˜aes
    51-53
    Abstract:
    The phenomenon of magnetism has been known by mankind for more than three thousand years. This fact is documented in references to the naturally occurring magnetic mineral magnetite (the iron oxide Fe$_3$O$_4$) in clay tablets in ancient Mesopotamia, as early as the second millennium BC. Less known, however, is the possible evidence for the knowledge of the magnetic properties of rocks by the peoples of pre-Columbian America. In fact, archaeologists have found in Olmec sites in Mexico many objects made of iron ore that may reveal an early acquaintance with magnetism. The Olmecs constituted the first complex culture that appeared in the Americas, before 1000 BC, in the east coast of Mexico. Among these objects, there has been found a polished bar that is magnetic, dating from 1400-1000 BC, which has led to speculations that it may have been part of a magnetic compass, one thousand years before the first Chinese compasses were made.
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  • Classical wave equation scalar normal modes and Green functions for confocal hyperboloidal electrodes

    N. Aquino, E. Castaño, E. Ley-Koo, S.E. Ulloa
    54-60
    Abstract:
    The scalar normal modes and Green functions for the classical wave equation subject to Dirichlet and Neumann boundary conditions on confocal hyperboloidal surfaces, which model the shapes of the electrodes in a scanning tunneling microscope or a conductor-insulator-conductor junction, are explicitly constructed. These modes and functions are of interest as possible starting points for the study of the Casimir effect between the electrodes of such devices.
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  • Quantum transport properties of one dimensional barriers: a simple approach to calculate transfer matrices

    M. Rodríguez-Achach, R. Huerta-Quintanilla
    61-64
    Abstract:
    We present a simple method for calculating the transfer matrix of a one dimensional system consisting of a number of rectangular barriers of arbitrary shape. We also make use of the Cayley-Hamilton theorem and the spectral theory of finite complex matrices to calculate high powers of matrices in a simple way, obtaining analytic expressions that are easily evaluated. We give an example of the transmission coefficient and conduction bands for a complex-basis superlattice. The method provides an intuitive approach to the construction for the transfer matrix.
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  • Comparative kinetics of the snowball respect to other dynamical objects

    R.A. Diaz, D.L. Gonzalez, F. Marin, R. Martinez
    65-73
    Abstract:
    We examine the kinetics of a snowball that is gaining mass while is rolling downhill. This dynamical system combines rotational motion with effects involving the variation of mass. In order to understand the consequences of both effects we compare its behavior with the one of some objects in which they are absent, so we compare the snowball with a ball with no mass variation and with a skier with no mass variation nor rotational motion. Environmental conditions are also included. We conclude that the comparative velocity of the snowball respect to the other objects is particularly sensitive to the hill profile and also depend on some retardation factors such as the friction, the drag force, the rotation, and the increment of mass (inertia). We emphasize that the increase of inertia could surprisingly diminish the retardation effect owing to the drag force. Additionally, when an exponential trajectory is assumed, the maximum velocity for the snowball can be reached at an intermediate step of the trip.
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  • La physica speculatio, primer libro de física escrito y publicado en el continente americano

    M.A. Moreno Corral
    74-80
    Abstract:
    In 1557, a text written by Friar Alonso de la Veracruz was printed in the capital of New Spain. This work dealt specifically with physics and was written for the sole purpose of teaching that field at the Real Universidad de México. This work was to become the first physics textbook published in America. Here, we discuss its content and its value, comparing it with what was taught in physics in the principal european universities at that time. In particular, we show that not only did de la Veracruz' text introduce the principal theoretical concepts of geocentric astronomy so common at that time but also presents implicitly, but clearly, the ideas of the novel heliocentric model of the solar system, a remarkable fact, since this scientific book of the colonial Mexico appeared only 14 years after the first edition of De Revolutionibus Orbium Coelestium by Nicholas Copernicus in Europe.
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