Vol. 52 No. 1 Jan-Jun (2006): Revista Mexicana de Física E

Published: 2006-01-01

Artículos

  • Magnetic field visualisation and inductance calculation of a simple configuration surface coil at low magnetic field

    A.O. Rodríguez, R. Amador, R. Rojas, F.A. Barrios
    1-12
    Abstract:
    We propose a simple method based on the quasi-static approach to visualise the magnetic field created by a simple configuration coil using the calculation for coil inductance. Faraday's law was used to calculate the inductance value and to simulate the magnetic field produced by circular-shaped and square-shaped coils. A software tool was developed to compute the coil inductance, and display the simulated magnetic field. We compared the predicted measured values of inductance, and performed a comparison plot of area versus inductance for both coils. Three dimensional plots of simulated fields are also shown. A circular-shaped coil was built using the method reported here, and brain images were acquired. This approach proved to be useful as an aid to visualise the magnetic field generated by simple coil geometries, and, simultaneously, calculate their coil inductance values.
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  • Normal and anti-normal ordered expressions for annihilation and creation operators

    J.M. Vargas-Martínez, H. Moya-Cessa, M. Fernández Guasti
    13-16
    Abstract:
    We obtain normal and anti-normal order expressions of the number operator to the power $k$ by using the commutation relation between the annihilation and creation operators. We use those expressions to obtain general formulae for functions of the number operator in normal and anti-normal order.
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  • Some integrals involving a class of filtering functions\pmb{$^\dag$}

    E. Capelas de Oliveira
    17-20
    Abstract:
    We discuss some properties of the function $\sin \pi x / \pi x$ which is (sometimes) indicated by the symbol sinc $x$. This function is associated with problems involving filtering or interpolating functions. Several integrals are presented and a general rule is discussed.
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  • Teaching thermal wave physics with soils

    E. Marín, L.E. Jean-Baptiste, M. Hernández
    21-27
    Abstract:
    In this paper, we discuss the features of a possible student experiment related to the conduction of heat in soils excited by a natural periodically time dependent source, namely the daily periodical oscillations in the earth's temperature, which can be denoted as thermal waves. A measuring device was designed and constructed for automatic measurements of the daily time air temperature variations as well as of the daily time temperature variations, at different depths beneath the soil's surface. Measurements were performed using LM-335 solid state temperature sensors incorporated into a computer-controlled probe. The data acquisition software was developed using a programming environment LabVIEW from National Instruments. In order to obtain characteristic parameters governing the physical phenomena involved, the results of our measurements were fitted to a thermal wave like solution of the heat diffusion equation in the presence of periodical heat sources. The phase shift as well as the attenuation of the temperature waves with depth was demonstrated, as well as their dependence on soil thermal properties, in particular its thermal diffusivity.
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  • Exploring the behavior of solitons on a desktop personal computer

    S. López-Aguayo, J.P. Ochoa-Ricoux, J.C. Gutiérrez-Vega
    28-36
    Abstract:
    In recent years, there has been a growing interest in studying and applying nonlinear wave equations and their soliton solutions. In this paper we discuss at undergraduate level a simple finite--difference numerical method for solving nonlinear wave equations. This method is applied for studying the striking behavior of the optical solitons. The procedures presented can be reproduced by enthusiastic students and instructor with a minimum of programming experience. We provide a set of interesting problems that could be taken as starting point to numerically explore the solutions of nonlinear wave equations.
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  • Estrellas de neutrones

    P. Salas, M.A. Solís
    37-46
    Abstract:
    Far, far away from Earth, there are extremely dense objects in the sky from which we can only begin to learn about with the aids of modern telescopes. These objects once were bright stars which have evolved to their final destiny marked by their original mass. Massive stars go through a supernova stage and end up as the highest density objects of the Universe, called Neutron Stars, or simply as Black Holes. Here we make emphasis on neutron stars characteristics, such as flashing pulses, sudden changes in their angular velocity known as glitches, or the cooling process they all go through. We will briefly mention less known facts related to very young neutron stars with highly intense magnetic fields called ``magnetars'', or to the brightests explosions in the universe called ``gamma ray bursts'', which are probably related either to giant supernovas or to binary system collapse that involve neutron stars.
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  • Medición de la transmitancia espectral de filtros de gelatina

    M. Ibáñez-Porras, J.J. Báez-Rojas, J.A. Delgado-Atencio, J.C. Conde-Acevedo
    47-50
    Abstract:
    In this work we propose a method to estimate the spectral transmitance of gelatin filters. This method use a spectrophotometer designed to measure a spectral reflectance. We present the model and results obtained experimentally.
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  • Prueba de impacto: ensayo Charpy

    Y.Ortega.
    51-57
    Abstract:
    In this paper some interesting results of Charpy impact tests are presented. The increase in the impact velocity, the present of a sharp notch and the ductile-to-brittle transition with decreasing temperature have been treated in a didactic way, by analyzing the fracture behaviour of several metals and polymers.
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  • Aplicación del método de diferencias finitas en el dominio del tiempo a la simulacion del campo electromagnetico usando Matlab

    M.A. Lopez-Esquer, J. Gaspar-Armenta, J. Manzanares-Martinez
    58-64
    Abstract:
    In this paper we describe an application of the Finite Difference Time Domain (FDTD) method to simulate the propagation of the electromagnetic field in a homogeneous medium. The strategy of this method is to formulate the differential Maxwell equations in space and time finite differences in order to write a computational code. This work tries to motivate the undergraduate students to the numerical simulation of the electromagnetic wave propagation. We propose an interactive matlab code that with easy modifications is able to simulate different physical situations.
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  • Revisando la ecuación de van der Waals

    B. Bonilla, J.N. Herrera
    65-77
    Abstract:
    From the results of the classic statistical mechanics we can deduce, over a formal way, the van der Waals (vdW) equation, using like model interaction potential an square well, also we show that the perturbation theory can be used to deduce the same result, but with a variant, the potential model used is proportional to an interaction $1/r^s$, where $s>3$, and $r$ is the relative distance. With this, one demonstrates that formally the vdW equation is one first correction to the ideal gas equation. We obtain all the van der Waals`s thermodynamic properties and the coexistence curve. We used to construct the vdW coexistence curve by different methods, by a graphical method, a numerical and an analytical one.
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  • Safety of UV radiation for autofluorescence diagnosis of skin cancer

    J.A. Delgado, I. Quesada, L.M. Montaño, L. Anasagasti
    78-83
    Abstract:
    It has been demonstrated that ex-vivo human skin autofluorescence is different for healthy and diseased tissue. In order to use these results for in vivo clinical applications, it is necessary to guarantee safe levels of UV radiation during skin scanning of patients and protect the eyes from scattered UV radiation coming from the skin surface. One of the goals of this work is to extend maximum limits of exposure to ultraviolet radiation in the spectral region between 315 and 400 nm. We also analyze irradiation levels of typical commercial ultraviolet LEDs and semiconductor lasers for application on skin cancer demarcation. Experimental measurements were not carried out in this paper.
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  • Maxwell equations in Lorentz covariant integral form

    E. Ley Koo
    84-89
    Abstract:
    Most textbooks of electromagnetism give comparable weights to the presentation of Maxwell equations in their integral and differential forms. The same books, when dealing with the Lorentz covariance of the Maxwell equations, limit themselves to the discussion of their differential forms, and make no reference to their integral forms. Such a gap in the didactic literature is bridged in this paper by explicitly constructing the latter via the integration of the former, for the source-dependent and source-independent cases, over a four-vector and a rank-3 tensor hypersurfaces, respectively.
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  • Electrostatic and magnetostatic fields for Bessel-Fourier distributed sources on infinite planes

    M.A. Rosales, E. Ley-Koo
    90-94
    Abstract:
    The fields produced by Bessel-Fourier distributions of static electric charges on an infinite plane are constructed by integrating the differential equations for the electrostatic potential and the electric intensity field, subject to the boundary conditions at the source plane. Similarly, the fields produced by Bessel-Fourier distributions of stationary electric currents on an infinite plane are constructed via the integration of the differential equations for the potential and the magnetic induction field, subject to the corresponding boundary conditions.
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  • Trabajos más citados de físicos de México

    Luis Gottdiener.
    95-103
    Abstract:
    We have tried to locate the works of physicists of Mexico that have had a substantial impact on science. The criterion for selecting them is that they should have received 100 or more citations registered in the Science Citation Index. We found 63 such works between 1959 and 2000: 54 articles, 8 books and 1 chapter in book. We discuss these results, as regards authors and participating institutions, and as a function of time.
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  • Un texto mexicano de física del siglo XVIII

    M.A. Moreno Corral
    104-110
    Abstract:
    This work introduces one of the first mexican textbooks dealing with physics issues emerging from the Scientific Revolution that took place in the 16th and 17th Centuries. There, concepts of the newtonian mechanics are discussed extensively, particularly Dynamics. Besides, we point out here that the textbook deals with contemporany ideas about electricity being generated in the world. Its author, Ignacio Fernandez del Rincon was one of the first persons in Mexico that carried on experiments with electrostatic machines, with the formel intention to establish a theory about electrical phenomena. He should be considered pioneer of experimental physics in our country.
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