Vol. 56 No. 2 Jul-Dec (2010): Revista Mexicana de Física E
Published:
2010-01-01
Artículos
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Numerical calculation of near field scalar diffraction using angular spectrum of plane waves theory and FFT
Abstract:It is a known fact that near field diffraction or Fresnel diffraction calculations are difficult to perform exactly. It is in general necessary to make some approximations in order to obtain a more suitable form. In this work, a numerical implementation based on angular spectrum theory for near field diffraction is presented. The method uses Fast Fourier Transforms (FFT), and it turns out to be accurate and fast. In order to show the capabilities of the method, diffraction near field for a circular aperture and a spiral slit are studied. Numerical and experimental results are shown. This method could be useful to implement pc based physical optics learning.⬇️ Scroll down to see the full summary -
Un complemento al teorema de Nyquist
Abstract:The content of this article is specially designed for students that are starting their education in data acquisition and signal processing. In some scientific majors this can happen in a compulsory or an elective course or in an experimental one. We review some of the fundamental requirements for proper signal acquisition in order to reconstruct the most important characteristics of the original signal, and at the same time obtain the required resolution when transforming to frequency space. We show that the satisfaction of Nyquist criterion is not sufficient to assure adequate resolution in frequency space. Finally we suggest how to choose the parameters for the best possible acquisition.⬇️ Scroll down to see the full summary -
Some classical properties of the non-abelian Yang-Mills theories
Abstract:We present some classical properties for non-abelian Yang-Mills theories that we extract directly from the Maxwell's equations of the theory. We write the equations of motion for the $SU(3)$ Yang-Mills theory using the language of Maxwell's equations in both differential and integral forms. We show that vectorial gauge fields in this theory are non-fermionic sources for non-abelian electric and magnetic fields. These vectorial gauge fields are also responsible for the existence of magnetic monopoles. We build the continuity equation and the energy-momentum tensor for the non-abelian case.⬇️ Scroll down to see the full summary -
Unveiling the tachyon dynamics in the Carrollian limit
Abstract:We briefly study the dynamics at classical level of the Carrollian limit, with vanishing speed of light and no possible propagation of signals, for a simply effective action in a flat space with an open string tachyon as a scalar field. The canonical analysis of the theory indicates that the equation of motion is of Dirac type contrary to the non-relativistic case where the equation is of Schrodinger type. The ultimate intention is to analize the latter case with electromagnetic fluxes to find that in this case the open string tachyon cannot be interpreted as time.⬇️ Scroll down to see the full summary -
Reflexiones sobre los conceptos velocidad y rapidez de una partícula en física
Abstract:The concepts velocity and speed in diverse physics text books and articles related with the concepts mentioned are revised. Lacks in the formative content associated with the above mentioned concepts are found. One proposes the boarding of the formative content related to the concepts mentioned from the point of view of the formation of scientific concepts in physics, which we consider, will allow the Physics apprentice and related areas, on the one hand, to familiarize with basic aspects in the formation of scientific concepts, and for other one, to penetrate into the cinematic aspects of the motion.⬇️ Scroll down to see the full summary -
Umbrales de percolación exactos en redes duales
Abstract:Bond percolation threshold is calculated for lattices with hexagonal symmetry, using the transformation triangle - star and the duality of lattices. This calculation is exact and widely well - known especially for triangular and hexagonal lattices. This technique applied to Kagomé lattice in sites and bonds reproduces the percolation thresholds obtained by Scullard and Ziff. This procedure is enlarged to square lattice of bonds, being obtained the exact value of the percolation threshold. According to the simplicity of the utilized methodology, this can be applied to other plane geometries and possibly to 3D lattices.⬇️ Scroll down to see the full summary -
Conceptos básicos acerca del espín, helicidad, quiralidad y polarización de una partícula de Dirac
Abstract:The recent technological advances, based on the profound understanding of the electron´s inherent characteristics are the elements that are ready to innovate the technology of information, as well as to refine the (MRI) technique of imagery through the efect of magnetic resonance, which is crucial as a tool for diagnosis and generation of views of live tissues without invasion or harm. So, with the intention to explain the basic theoretical concepts, which are, in general, not clarified in the specialized literature and traditional textbooks, which are related with the particles in Dirac equation, we analize the quantum operators that project some of their peculiar characteristics. These operators are related with the conserved quantities in the theory and therefore with the symmetries of the system. We consider the Hamiltonian formulation to establish the conservation principle and the properties of the projectors that determine the helicity, quirality and polarization of the Dirac particles.⬇️ Scroll down to see the full summary -
Scattering matrix of elliptically polarized waves
Abstract:We analyze the scattering of elliptically polarized plane waves normally incident at the planar interface between two different materials; we consider two cases: dielectric-dielectric and dielectric-conductor interfaces. The scattering $S$ matrix in both cases is obtained using the boundary conditions and Poynting's theorem. In the dielectric-dielectric case we write $S$ using two different basis, the usual $xy$ and a rotated one. For the dielectric-conductor interface, the use of the rotated basis together with an energy balance argument leads us, in a natural way, to construct a unitary $S$ matrix after recognizing the need to introduce two equivalent parasitic channels due to dissipation in the conductor, and the transmission coefficient into these parasitic channels measures the absorption strength.⬇️ Scroll down to see the full summary -
Radiación de Hawking
Abstract:The aim of this article is to provide a general analysis of the so-called Hawking radiation in black holes from a didactic perspective, including a brief introduction to quantization in curved spacetime. Two main methods for obtaining the radiation spectrum are explained: the original one due to Hawking and the tunneling method. Also, it is shown how the second mechanism can be extended to obtain the radiation spectrum in a different kind of horizon, that associated to the Friedmann-Robertson-Walker metric. Finally, some recent objections to the derivation by the tunneling method are mentioned.⬇️ Scroll down to see the full summary -
On a tautochrone-related family of paths
Abstract:An alternative approach to the properties of the tautochrone and brachistochrone curves is used to introduce a family of curves complying with relations where the time of descent is proportional to a fractional power of the height difference. These curves are classified acording with their symmetries. Further properties of these curves are studied.⬇️ Scroll down to see the full summary -
Fuentes para la biografía del profesor de física Ladislao de la Pascua Martínez (1815-1891)
Abstract:Ladislao de la Pascua was a Teacher of Physics in Mexico City between 1838 and 1872 at the Military Academy, School of Medicine, the {\sl Preparatoria Nacional} and other schools. He wrote a text to teach Physics in 1853. He had a rich life with important activities as a physician and as a priest. There is a large amount of literature on his life, however his biographies are incomplete and some with inexact legend. In this work emphasis is given to original documents and sources of the XIX Century completed by some few sources from the XX and XXI Centuries.⬇️ Scroll down to see the full summary
