Vol. 50 No. 2 Jul-Dec (2004): Revista Mexicana de Física E
Published:
2004-01-01
Artículos
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La densidad es una propiedad intensiva de la materia (pero su medida no)
Abstract:Measuring the density of a solid is a basic laboratory task for Introductory Physics courses that can be quite enriched by using some variety of samples. On one hand, probing the intensive character of the quantity, on the other hand ---and with more interest from the experimental methods point of view--- allowing to elucidate how the methods of measuremnets can be conditioned by the shape and nature of the samples and the measured values of the quantity.⬇️ Scroll down to see the full summary -
La aproximación LDA+U en la teoría DFT
Abstract:We discuss one of the methods currently used in the calculations of electronics, structural and magnetics properties etc, of atoms, molecules and solids that present the so called strong electron correlation (SEC). The method is based on the LDA+U approximation (Local Density Approximation + Hubbarb correction term) in the context of the density functionals (DFT), developed by Anisimov et al., in the 90's. The type of systems that present SEC are lanthanides compound (whose interest electrons are $4f)$, actinides (whose interest electrons are $5f)$, and compounds of element transition $(3d)$, in addition of some organic and carbon compounds, etc.⬇️ Scroll down to see the full summary -
Fonones en cristales con estructura de diamante
Abstract:A study of the vibrational modes of crystals with diamond structure is presented. In the study we apply the Keating's model for describing the short-range interatomic interactions and incorporating, in the simplest way, three-body interactions, associated with the deformation of the angle between two covalent bonds. Within the framework of the harmonic approximation, we obtain analytical expressions for the dispersion relations of phonons with wave vectors along three high-symmetry directions: $[001]$, $[110]$ and $[111]$. These expressions show clearly the effect of the force constants upon the phonon band structure for crystals with diamond structure. Our results are illustrated in the specific case of C.⬇️ Scroll down to see the full summary -
Ecuaciones de Schwinger-Dyson y fenómenos no perturbativos de la electrodinámica cuántica
Abstract:We present the detailed derivation of the Schwinger-Dyson Equations in Quantum Electrodynamics and we comment on the usefulness of these equations in the study of nonperturbative phenomena, like the dynamical generation of fermion masses.⬇️ Scroll down to see the full summary -
El inversor CMOS y su uso en el diseño de sistemas de mayor complejidad
Abstract:This paper presents the design of digital systems by using a basic inverter circuit, hereafter named basic cell. The purpose of this work is not only to show the usefulness of this cell to design major systems, but also to depict design considerations, as well as test hints for the characterization process of the systems under analysis. All circuits were manufactured in a CMOS technology, 1.2$\mu $m, N-well.⬇️ Scroll down to see the full summary -
Levitation in an "almost" electrostatic field
Abstract:It is well known that a charged particle cannot be in stable equilibrium in a purely electrostatic field. The situation is different in a magnetostatic field; consequently, magnetic levitation is possible while electrostatic levitation is not. In this paper, motivated by an analogy with a mechanical system, we show that the addition of a small oscillating electrical field to an otherwise electrostatic configuration leads to the stabilisation of unstable equilibrium points. Therefore, levitation becomes possible in an ``almost electrostatic'' field.⬇️ Scroll down to see the full summary -
No adiabaticidad en moléculas y el efecto Jahn-Teller
Abstract:In studying the electron properties in molecules and solids, the Born-Oppenheimer approximation is the most commonly used. Going beyond this approximation implies that the motion of the electrons and nuclei is coupled, given rise to what is known as vibronic states, manifesting with new chemical and physical properties. In this work we present a brief review of one of the most striking manifestations of vibronic coupling in molecules and clusters, the Jahn-Teller and pseudo Jahn-Teller effect. We discussed the conditions for the failure of the adiabatic approximation and the applicability of a perturbative approach to find the vibronic states. We also present the use of group theory techniques to calculate the vibronic coupling. As an example, we present a Jahn-Teller analysis for the $CuO_{6}$ cluster in regular and deformed octahedral arrays, $O_{h}$ and $D_{4h}$ symmetries respectively.⬇️ Scroll down to see the full summary -
Electrostatic, magnetostatic and electromagnetic fields for harmonically distributed sources on infinite planes
Abstract:The static uniform electric charge distribution, the stationary and time-harmonically-varying uniform electric current distributions, on infinite planes, are known to produce uniform electrostatic, uniform magnetostatic and plane wave electromagnetic fields around the respective sources, since the introductory course of electricity and magnetism. This paper presents some natural extensions of these familiar systems for harmonically distributed sources on the planes, which can be assimilated in the electromagnetic theory course.⬇️ Scroll down to see the full summary -
Electromagnetic fields from high frequency currents harmonically distributed on infinitely long circular cylinders
Abstract:High frequency currents harmonically distributed around the surface of infinitely long circular cylinders, in the directions of the generatrices and of the circles, are identified, and their associated electromagnetic fields are constructed. The latter are obtained as exact traveling wave solutions of Maxwell equations in differential and boundary condition forms. The study of these systems is appropriate for Electromagnetic Theory courses.⬇️ Scroll down to see the full summary
