Vol. 53 No. 1 Jan-Jun (2007): Revista Mexicana de Física E
Published:
2007-01-01
Artículos
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Analyzing switched circuits to design DC-DC and DC-AC converters
Abstract:The purpose of this paper is to present an alternative analysis of switched circuit to design square wave generators (SWG). A SWG may be designed by using low-cost electronic components, which allows to the readers to understand how DC-DC and DC-AC converters based on the switched approach is an economic option to introduce network analysis concepts. Experimental results show that used techniques allow calculate the frequency range operation not only of the electronic components but also the effect of the power supply value on the generators' performance.⬇️ Scroll down to see the full summary -
Fenómeno de lentes gravitacionales en el espacio-tiempo de Janis, Newman y Winicour
Abstract:In the present work we integrate the null geodesic equations of the light cone of an arbitrary point in the Janis, Newman and Winicour space-time and we construct, in an exact way, the equations that describe the gravitational lensing phenomenon. We show that under certain conditions our exact results reduce to the thin lens equation. Furthermore, we use our exact equations to reobtain the results obtained by Virbhadra and Ellis by using their strong field limit equation\,\cite{VirbhadraIV}. That is, we show that for, $0 < q/M < \sqrt{3}$, the gravitational lensing phenomenon in the JNW solutión is qualitatively similar to that due to a Schwarzschild black hole and that for, $q/M > \sqrt{3}$, the gravitational lensing phenomenon, in these two solutions, is totally different.⬇️ Scroll down to see the full summary -
Obtención eficiente de espectros basada en un algoritmo mejorado de ventana ajustable
Abstract:The improved algorithm can produce a more accurate spectrum than the sines windows and the FFT, because reduces the spectral leakage only of signals that need it; very different situation with the sines windows and the FFT utilization. The cited algorithm is based on acquired signal fundamental frequency calculation and right adjusting of the sampling frequency by software via decimation and interpolation techniques, in order to obtain a rectangular window wide with a complete number of signal periods. For to develop the improved algorithm, first is taken the algorithm of Hidalgo, et al. (2002) like reference, which was developed in the C language, then is developed again in MATLAB6.5 language and his spectral results showed to be deficients for the polyharmonics signals case. Therefore, in the present paper, we do the procedures to solve these deficiency problems. Therefore, the new algorithm is called improved algorithm (IA), which shows, in base to several achieved tests, that is more efficiently than the reference one. Finally, the mixed signals spectrum of the IA was validated by the Dadisp software of DSP, Co., and the algorithm could be used to look for masking frequencies and signals identification with leakage spectrum.⬇️ Scroll down to see the full summary -
Estudio experimental de la viscosidad de un fluido magneto-reológico a base de magnetita mineral
Abstract:We experimentally study the viscosity of a magnetorheological (MR) fluid based on mineral magnetite and automotive oil for brakes. We use a Brookfield cone-plate rheometer to which it was adapted a solenoid that produces and controls a magnetic field parallel to the cone rotation axis. Even though the particles contain variable amounts of silica impurities and present a wide dispersion in the sizes, the system experiments important changes in the viscosity as a function of the magnetic field, shear rate and particle mean size. We study the behavior of a simplified MR damper and show some of its advantages respect to a conventional damper.⬇️ Scroll down to see the full summary -
On the potential of an infinite dielectric cylinder and a line of charge: Green's function in an elliptic coordinate approach
Abstract:A two-dimensional Laplace equation is separable in elliptic coordinates and leads to a Chebyshev-like differential equation for both angular and radial variables. In the case of the angular variable $\eta$ ($-1\leq\eta \leq1),$ the solutions are the well known first class Chebyshev polynomials. However, in the case of the radial variable $\xi$ ($1\leq\xi<\infty)$ it is necessary to construct another independent solution which, to our knowledge, has not been previously reported in the current literature nor in textbooks; this new solution can be constructed either by a Fröbenius series representation or by using the standard methods through the knowledge of the first solution (first-class Chebyshev polynomials). In any case, either must lead to the same result because of linear independence. Once we know these functions, the complete solution of a two-dimensional Laplace equation in this coordinate system can be constructed accordingly, and it could be used to study a variety of boundary-value electrostatic problems involving infinite dielectric or conducting cylinders and lines of charge of this shape, since with this information, the corresponding Green's function for the Laplace operator can also be readily obtained using the procedures outlined in standard textbooks on mathematical physics. These aspects are dealt with and discussed in the present work and some useful trends regarding applications of the results are also given in the case of an explicit example, namely, the case of a dielectric elliptic cylinder and an infinite line of charge.⬇️ Scroll down to see the full summary -
Ecuaciones de advección-difusión, telégrafo y onda advectiva como superposiciones de transporte, difusión y onda: un enfoque didáctico
Abstract:In this work we present exact solutions of the advection-diffusion and the telegraph equations. These equations are considered as combinations of the basic equations: wave, heat and transport equation. Thus, in a natural way, a third combination that we called advection-wave is introduced. Although this equation is not so popular like the other combinations, it is a simple example of didactical value that allow us to explain physical and mathematical relations for the superposition of transport and wave motion.⬇️ Scroll down to see the full summary -
Tiempo mínimo y trayectoria de movimiento
Abstract:The application of basic differential calculus to the solution of a minimum time problem is presented. Under the experimental conditions here discussed it is shown that human beings choose movement trajectories that agree with the ones calculated using the minimum time principle. These conclusions are obtained from the analysis of a group of students who must run along a swimming pool and then jump and swim through the pool to reach an object placed on the opposite side. The mathematical analysis of the problem is presented, its solution and comparison with experimental results.⬇️ Scroll down to see the full summary -
Animaciones en Matlab y maple de ecuaciones diferenciales parciales de la física-matemática
Abstract:In this work we present some exact solutions of time dependent partial differential equations (pdes); these solutions have the general form $u(x,t)$, with $x\in \mathcal{ R}^n$, $n=1,2,3$. The plots of the solutions at different times allow us to create animations of the solutions. We show in a general framework how to make animations in Maple and Matlab. These animations can be used as a didactic tool in order to introduce some physical phenomena such as: wave propagation, superposition, transmission from one medium to another, diffusion, etc. They can also be used to motive the students to the study of partial differential equations and its applications. A representative subset of differential equations of mathematical physics was chosen that includes: the transport equation, wave equation, heat equation and equations of Klein Gordon, Korteweg de Vries, and Maxwell. We briefly present some of the analytical methods for the solutions of pdes: scaling, characteristics and separation of variables. Finally exact solutions can be very useful for code testing in numerical implementations.⬇️ Scroll down to see the full summary -
Oscilaciones, armonía y simpatía
Abstract:In this work we present a didactic introduction to the synchronization and enrailing of dynamical systems. This phenomenon is widely encountered in physics, biology, engineering and social phenomena. It is also the basis of phenomena such as the synchronization of clocks, rhythmic processes in physiology, lasers and many others that involve a slight coupling that produces an adjustment of rhythms. Our presentation takes into account that a better understanding of the synchronization phenomenon is achieved through an adequately oriented review of the fundamentals of the basic oscillatory phenomena.⬇️ Scroll down to see the full summary -
The exactly solvable self-gravitating fermion cluster in two dimensions
Abstract:The mathematical model of a two-dimensional self-gravitating cluster formed by degenerate fermions, is solved analytically. The fermions interact with each other through a logarithmic potential. The radius of this system is shown to be constant, not depending on the total number of fermions that constitute the cluster.⬇️ Scroll down to see the full summary -
La relación entre las derivadas con respecto al tiempo de integrales de volumen, de superficie y de línea y la derivada material
Abstract:Without using the mathematical formalism of differential forms and Lie derivatives, the derivatives with respect to the time of volume, surface and line integrals are calculated by using vectorial analysis.⬇️ Scroll down to see the full summary -
An introduction to quantum interferometry: Young's experiment with fock and coherent states
Abstract:Quantum interferometry uses the quantum properties of light to surpass the Rayleigh diffraction limit inherent in classical interferometry. We have used Fock and coherent states, which describe the electromagnetic input field, a multi-photon counting apparatus, and an operator-based approach to a multi-slit Young's experiment to present the principles behind quantum interferometry. Our calculations show interference fringes that depend on the wavelength of the source $ \lambda$, the number of slits in the Young's screen---both characteristics present in the classical scheme---, and the number of photons $m$, that the measurement apparatus detects. The latter dependence generates an effective de Broglie wavelength, $\lambda/m$, a phenomenon that can only be observed by taking advantage of the quantum properties of light.⬇️ Scroll down to see the full summary -
The nonlinear pendulum: formulas for the large amplitude period
Abstract:A simple and precise formula for the period of a nonlinear pendulum is obtained using the Linear Delta Expansion, a powerful non--perturbative technique which has been applied in the past to problems in different areas of physics. Our result is based on a systematic approach which allows us to obtain a new series for the elliptic integrals, in terms of which the exact solution of our problem is cast. A further improvement of the LDE result is then obtained by using Padé approximants. Finally we make a comparison with other approximations in the literature for the period of the pendulum, valid either at small or at large angles.⬇️ Scroll down to see the full summary -
Continuous groups of transformations and time-dependent invariants
Abstract:In this paper we present a very simple derivation of the constants of motion for dynamical systems, which requires only an elementary knowledge of the theory of continuous groups. In addition, through the infinitesimal Lorenz transformations group, we obtain a clear interpretation of the invariant for the harmonic oscillator.⬇️ Scroll down to see the full summary -
Propagation of the information in a one-way quantum computer
Abstract:Both linear momentum and Poynting vector associated with the propagation of information in a one-way quantum computer are studied. It is found that, within the so-called Mean Field Theory (MFT) approximation the total energy, the linear momentum and the Poynting vector associated with the propagation of information are invariant under arbitrary rotations of logical qubits. This means that propagation of the quantum information stored in the entangled state does not depend on the choice of the quantum gates. Due that the involved cluster of neighboring particles is large enough, last property satisfies the scalability test. As a consequence, quantum information in the one-way computer is read, written and processed independently of this choice, which suggests a simple hardware for it. When an external magnetic field is switched on, the invariance under arbitrary rotations of the logic qubits of these quantities is lost, that is, the field induces a preferential direction of propagation of the information which at the same time is optimized while more intense be the field.⬇️ Scroll down to see the full summary -
Péndulo de longitud variable: experimentos
Abstract:The evolution of a pendulum with variable length is experimentally reported. The orthogonal functions invariant is shown to reproduce, under the appropriate conditions, the well known abrupt and adiabatic limits. Experimental results in these regimes are shown together with intermediate cases not previously reported. This article is dedicated to Don Juan de Oyarzábal in memorial of his extraordinary classical mechanics lectures at UAM-Iztapaplapa during 1975.⬇️ Scroll down to see the full summary
