Vol. 53 No. 2 Jul-Dec (2007): Revista Mexicana de Física E
Published:
2007-01-01
Artículos
-
Basic circuits to design switched-based DC-DC converters
Abstract:The purpose of this paper is twofold. On one hand, basics on switched circuits for designing a DC-DC converter are presented and, on the other hand, power electronics definitions associated with simple electrical networks are mentioned. In the analysis of these networks, it is necessary to take into account not only converters' non-idealities but also how to minimize power losses. Since power losses may be minimized by increasing the clock frequency of switched-based converters, experimental results of basic clock generators are presented. These generators were implemented with low-cost components.⬇️ Scroll down to see the full summary -
Ley de reflexión para espejos planos en movimiento relativista
Abstract:In this paper, we study the reflection of light on uniformly moving mirrors. The mirrors are assumed to be perfectly reflecting and oblique with respect to the direction of the movement. Analytical expressions for the angle of reflection, for the reflected frequency and for radiation pressure are given. In the particular case that the mirror moves away from the luminous ray a critical angle of incidence exists for which the reflected luminous ray is parallel to the surface of the mirror. We analyze numerically the influence or the angle of incidence, the speed and the orientation of the mirror in the reflection angle, reflected frequency and in the radiation pressure. Finally we obtain an analytic expression for the determination of the speed of the mirror in terms of parameters that can be measured experimentally.⬇️ Scroll down to see the full summary -
Exact spectrum and wave functions of the hyperbolic Scarf potential in terms of finite Romanovski polynomials
Abstract:The Schrödinger equation with the hyperbolic Scarf potential reported so far in the literature is somewhat artificially manipulated into the form of the Jacobi equation with an imaginary argument and parameters that are complex conjugate to each other. Instead we here solve the former equation anew and make the case that it reduces straightforward to a particular form of the generalized real hypergeometric equation whose solutions are referred to in the mathematics literature as the finite Romanovski polynomials, in reference to the observation that for any parameter set only a finite number of such polynomials appear to be orthogonal. This is a qualitatively new integral property that does not copy any of the features of the Jacobi polynomials. In this manner, the finite number of bound states within the hyperbolic Scarf potential is brought into correspondence with a finite system of a new class of orthogonal polynomials. This work adds a new example to the circle of the problems on the Schrödinger equation. The techniques used by us extend the teachings on the Sturm-Liouville theory of ordinary differential equations beyond their standard presentation in the textbooks on mathematical methods in physics.⬇️ Scroll down to see the full summary -
Resolviendo ecuaciones diferenciales ordinarias con Maple y Mathematica
Abstract:In this work we present solutions of ordinary differential equations by using Maple and Mathematica. The basic commands in both packages are presented throught a series of examples that show some of the advantages of using computer algebra and graphical representation in the process of teaching and learning odes.⬇️ Scroll down to see the full summary -
Laser amplification: experiment and electronic simulation
Abstract:The experimental results of a molecular nitrogen laser system based on a master oscillator and an amplifier with Blumline configurations are reported, as well as an electronic system based on a microcontroller and operational amplifiers which qualitatively reproduce the results obtained with the laser system. The usefulness of the developed electronic system and its application during university level lectures and popularization talks about lasers, photonics and quantum electronics is discussed.⬇️ Scroll down to see the full summary -
Response coefficients in thermodynamic systems (I)
Abstract:In the first undergraduate Physical Chemistry or Classical Thermodynamics courses in the Chemistry areas, the study of equations of state is usually included. The differential forms of the equations of state contain the response coefficients, which are the relations among the relevant properties of state of a particular system. The classic solution to the differential equations thus requires that the response coefficients be known, which must be experimentally obtained. A confined gas is one of the systems that can be experimentally studied in a simple manner. The response coefficient $\left( {\partial P / \partial T} \right)_V $ is important from different points of view. In this communication, the design, the experimental produce and the results for the experimental determination (in an accessible temperature range) of the response coefficient $\left( {\partial P / \partial T} \right)_V $ for atmospheric air, are presented. The value for this coefficient has been highly reproducible by students throughout the courses, no matter the types of manometers, flasks or thermal baths are used in the experiment.⬇️ Scroll down to see the full summary -
Dificultades de entendimiento en el uso de vectores en cursos introductorios de mecánica
Abstract:An understanding of the basic properties of vectors is fundamental to understand vector operations. Many students in the introductory physics courses do not develop a meaningful understanding of the vector nature of some physical quantities such as: Force, acceleration, tension and velocity. To foster a conceptual understanding of these quantities, an exploration of the cognitive problems is necessary through a traditional or a modified instruction. This investigation shows the students' difficulties detected and characterized during the teaching process of the operations of addition and subtraction of vectors in their context. The information sources are some universities in the United States and one university in Mexico.⬇️ Scroll down to see the full summary -
The elastic rod
Abstract:The form of an elastic rod in equilibrium subject to a buckling by the action of two opposite forces at its ends is explicitly calculated and drawn. The full expression for the radius of curvature in the equation of the beam is considered. It is known that the differential equation describing the form of the rod, written in terms of the arc length and the angle that forms the tangent line to the curve with the horizontal axis of coordinates, is exactly the same one finds in describing the dynamics of great amplitude oscillations of a simple pendulum. This equation is solved exactly in terms of Jacobi's elliptic functions. The solutions are drawn by using in iterated form the addition formulas of those functions. Useful relations among the physical constants of the system and the geometric parameters of the rod are also obtained.⬇️ Scroll down to see the full summary -
De la mecánica estadística a la teoría ergódica
Abstract:In this article we will briefly review some of the interactions occurred during the last hundred years, between Statistical Mechanics and Ergodic Theory. In particular, we will mention the recently proved rigorous results concerning the Boltzmann's hypothesis.⬇️ Scroll down to see the full summary -
Movimiento de rotación de un cuerpo rígido libre de torcas
Abstract:The demonstration experiment here presented illustrates how the stability of the rotational motion of a rigid body in the absence of torques depends on the relative value of the moment of inertia associated to the axis of rotation. The objective is satisfactorily gotten using a tennis racket and a box with similar values of its moments of inertia to those of the racket. The rotating body is thrown into the air and when goes down is caught by the thrower. The motion is stable when the body rotates about the principal axis corresponding to either the greatest or smallest principal moment of inertia. However, when the body rotates about the axis corresponding to the intermediate moment, the body also rotates about the axis which has associated the smallest moment of inertia.⬇️ Scroll down to see the full summary
