Vol. 63 No. 1 Jan-Jun (2017): Revista Mexicana de Física E
Published:
2017-01-01
Artículos
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Anomaly of non-locality and entanglement in teaching quantum information
Abstract:Non-locality and quantum entanglement constitute two special features of quantum systems of enormous relevance in quantum information theory (QIT). Historically regarded as identical or equivalent for many years, they constitute different concepts. We want to stress in the present contribution such difference which actually may guide the instructor to cover the most essential topics of QIT in any section of some introductory course. We shall address the simplest possible case of that of two qubits. The material may be of interest to instructors teaching high-undergraduate quantum mechanics, as well as students.⬇️ Scroll down to see the full summary -
Approximate frequencies of the pendulum for large angles
Abstract:By approximating the cosine function to a polynomial, analytical approximations of pendulum trajectories are developed for initial angles close to $\pi $. The periods are deduced and they are compared with other techniques recently developed for the same purpose. Our results practically match with the exact solutions. A process that allows to understand the difficulties of dealing with nonlinear equations, of using the minimization of the standard deviation and the importance played by energy conservation is done.⬇️ Scroll down to see the full summary -
Implementation details of a variational method to solve the time independent Schrödinger equation
Abstract:The time independent Schrödinger equation is a differential equation of great interest in computational physics. In many cases, it is impossible to reach an analytical solution for it, due to the potential function complexity, therefore numerical methods play an important role in its solution for practical cases. By means of numerical methods it is possible to solve the stationary Schrödinger equation for arbitrary potentials, allowing the study of interesting potentials that exhibit fascinating phenomena. Some of these potentials are the Kronig-Penney and pseudo-Coulomb potential functions, or more single like barrier potential function. Nevertheless, in many cases, the implementation of the sequence of steps needed to solve the differential equation is not straightforward. In this work we present and explain a sequence of steps to solving the time independent Schrödinger equation by means of the variational method, and apply it to solve non-periodic potential functions, like the harmonic oscillator potential well and rectangular potential barrier, and periodic potential functions like the Kronig-Penney and pseudo-Coulomb. Our main purpose is for this work to be an introduction to the computational quantum mechanics field.⬇️ Scroll down to see the full summary -
Determinación de presiones parciales: el caso de H$_2$O(v) en aire
Abstract:In introductory Classical Thermodynamics courses, the Equations of State topic is necessarily revised, and the one or more components PVT systems, are the selected examples in almost all the cases. For multicomponent systems, the understanding of the concept of component partial pressure is required. Although the revision in classroom is feasible, the experimental study is difficult; for example, selective pressure sensors are required for the specific measurement of manometric pressures, which are far from being common in teaching undergraduate laboratories. This difficulty can be avoided if certain gaseous fluid mixtures are chosen, as atmospheric air, and the study is focused on the behavior of H$_2$O(v) contained in the air. In fact, this is what is called Psychrometry. In this communication, the psychrometric basis, the experimental development and the results concerning the H$_2$O(v) partial pressure in a local atmospheric air determination, are presented. As a complement, the air temperature value (dew point) at which the H$_2$O(v) becomes a saturated vapor (isobaric process), is obtained.⬇️ Scroll down to see the full summary -
Pseudospectral vs finite differences methods in Numerical Relativity
Abstract:Inspired by the recent discovery of Gravitational Waves (GWs) by the LIGO array, we consider necessary to strengthen the formation of our students in Numerical Relativity (NR) in México. A key issue in the future GW astronomy is the efficiency at solving inverse problems, this means, reconstructing the physical parameters of the GW source. In the case of the Binary Black Holes (BBH) inspirals, we find the appropriate example where NR has shown its usefulness, because the waveforms predicted by NR simulations in BBH collisions are used to filter the data in the interferometer runs. The size of a catalog of such numerically generated waveforms is therefore of great importance because the more waveforms it has the easier is to reconstruct the intrinsic parameters of the BBH system. In this way, the purpose of this educative paper is to show the comparison, in terms of performance and accuracy, of the two different numerical methods used to build the catalogs, applied to the evolution of a training problem, namely the evolution of a single black hole. We present a comparison between a pseudospectral and a finite differences method in the solution of numerical general relativity equations. The system we choose to test the performance and accuracy is a spherically symmetric black hole in Eddington-Finkelstein coordinates. For the evolution we use the Einstein-Christoffel formulation of General Relativity. We compare accuracy in the violation of the Hamiltonian constraint and CPU time, both in terms of the spectral and finite differences resolution.⬇️ Scroll down to see the full summary -
The origins of quantum drama and the critical view of Paul Ehrenfest
Abstract:In this paper we address the quantum drama that emerged from tensions around the different paradigms of physical explanation that had been developed throughout the nineteenth century. We will draw special attention to the relevance that, in order to understand this revolution in physics, have the scientific dimensions that go beyond its experimental and logical aspects, namely the important role played by the imagination, the use of mental experiments, the use of simple models, analogies, metaphors, etc. The criticism and contribution of Paul Ehrenfest on the quantum hypothesis, which he was interested in, unlike other physicists, from the very beginning, is a very valuable resource for studying the origins and these facets of quantum theory. In his writings on the subject, Ehrenfest strives to clarify the validity of the analogies and methodologies used and cares about the nature of the hypothesis, assumptions and conditions used, giving his thoughts a character of epistemological interest. We will show in what way the success attained by physics in these times of conceptual struggle, probably depended on the existence of a balance between the conservative attitude of some scientists and the more open nature of others, and between imagination and creativity of certain physicists and the skeptical and critical character of others.⬇️ Scroll down to see the full summary -
Quantum-mechanical aspects of magnetic resonance imaging
Abstract:The Magnetic Resonance Imaging (MRI) is a non-invasive technique which uses the physical phenomenon of nuclear magnetic resonance to obtain structural and compositional information about human body regions. In this imaging study we use the radio-frequency and a powerful static magnetic field, which aligns the magnetization of hydrogen nuclei. Nowadays there are many types of clinical equipment that conduct MRI studies, which have intensities of magnetic fields from 0.2T to 7.0T. Moreover, liquid helium is required for the superconducting coil. This paper presents an analysis of the magnetic resonance phenomenon; by doing a review of the quantum-mechanical aspects as the spin and Zeeman effect.⬇️ Scroll down to see the full summary -
Relatividad general; su presencia temprana en México
Abstract:One of the most important theories in Modern Physics is certainly that of General Relativity, developed by Albert Einstein for several years and presented in its final form in 1916. A century after its appearence and because of the recently in importance it has taken Cosmology's spectacular applications, it is relevant to know when and by whom it was presented and discussed in our country for the first time and what was the depth in which it was explained. This paper deals with it, comments the first book written and publish in General Relativity in Mexico.⬇️ Scroll down to see the full summary -
On the accuracy of the Debye shielding model
Abstract:The expression for the Debye shielding in plasma physics is usually derived under the assumptions that the plasma particles are weakly coupled, so that their total kinetic energy is much greater than their electrostatic interaction energy, and that the velocity distributions of the plasma species are Maxwellian. The first assumption also establishes that the number of particles within a sphere with a Debye radius, known as the plasma parameter $N_D$, should be significantly greater than 1, and determines the difference between weakly and strongly coupled plasmas. Under such assumptions, Poisson's equation can be linearized, and a simple analytic expression is obtained for the electrostatic potential. However, textbooks rarely discuss the accuracy of this approximation. In this work we compare the linearized solution with a more precise numerical (or ``exact'') solution, and show that the linearization, which underestimates the ``exact'' solution, is reasonably good even for $N_D \sim 40$. We give quantitative criteria to set the limit of the approximation when the number of particles is very small, or the distance to the test charge too short.⬇️ Scroll down to see the full summary -
Investigación en enseñanza de la física experimental en el siglo XXI
Abstract:The aims of physics education have evolved alongside the society in which we live, to be able to adapt to the rapid pace of change imposed by the application of scientific discoveries in the industry. We could define the quality of physics' teaching as its ability to learn how to reason. This approach covers both teaching competency-based and is student-centered. Each topic should be an excuse to teach how deduce it or induce it. The teacher decides if he/she deduces it or induces it from a demonstration or from experimental data. Experiments allows us to appreciate the ability of reasoning of the students, since they need to combine all they know in conducting the experiment. To evaluate the learning of a topic, we need to write questions to test the required reasoning, that it is not easy. PISA succeeds for students 15 years old, the challenge is to do it with our students.⬇️ Scroll down to see the full summary -
Analizando ondas estacionarias en tubos abiertos y cerrados con el uso de smartphone
Abstract:This project proposes the analysis of the phenomenon of standing waves in open and closed tubes used to this, two smartphones and mini bluetooth speaker. Applications waveform generator and spectrum analyzer developed under the Android operating system used. The results of harmonic number $n$ frequency plotted, obtaining a good correlation of data, calculating the slopes of straight lines, resulting in the speed of sound in air of 336.64 m/s 340.4 m/s for open and closed tubes respectively.⬇️ Scroll down to see the full summary
