Vol. 59 No. 1 Jan-Jun (2013): Revista Mexicana de Física E
Published:
2013-01-01
Artículos
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Fourier description of lock-in
Abstract:In this study, a new interpretation about the operation of a traditional lock-in and dual lock-in is presented from the viewpoint of Fourier analysis. Once the mathematical principles under which these devices operate are understood, we could take full advantage of the magnitude and phase of the Fourier coefficients to measure the physical variables, as shown in the final example of this study. Also, a comparison between signal-to-noise ratio (SNR) of a square reference lock-in and a pure sinusoid lock-in is also presented.⬇️ Scroll down to see the full summary -
Alternative method to calculate the magnetic field of permanent magnets with azimuthal symmetry
Abstract:The magnetic field of a permanent magnet is calculated analytically for different geometries. The cases of a sphere, cone, cylinder, ring and rectangular prism are studied. The calculation on the axis of symmetry is presented in every case. For magnets with cylindrical symmetry, we propose an approach based on an expansion in Legendre polynomials to obtain the field at points off the axis. The case of a cylinder magnet was analyzed with this method by calculating the force between two magnets of this shape. Experimental results are presented too, showing a nice agreement with theory.⬇️ Scroll down to see the full summary -
Interface para esqueletizado y suavizado de interferogramas
Abstract:It is developed a GUI (graphical user interface) in order to provide a fast and easy to use computational tool, which performs smoothing and/or skeletonizing of interferometric images. The code used in the interface is based in smoothing algorithms for interferograms, where the intensity distribution along rows or columns of the image is fitted by means of least squares and using Bessel functions of the first kind as basis functions, allowing the suppression of high frequency noise components. Additionally, the dilation method is used using a Strehl structural element in order to perform skeletonizing of the interferograms.⬇️ Scroll down to see the full summary -
Spatial location in 360$^{\circ}$ of reference points over an object by using stereo vision
Abstract:Stereo Vision is a powerful tool used to get a 360$^{\circ}$ scan of an object in order to obtain topography details or getting the spatial position of a given set of points of interest. However, the required computational time could be slow to perform real-time measurements. In this work we present an alternative approach based on Hering's coordinate system and the use of high reflective markers, used as reference points to track an object movement. The advantage of using these markers is that their detection is faster than a full scene correlation since it is performed by matching the position of the centroids of each marker without using any pixel-by-pixel analysis.⬇️ Scroll down to see the full summary -
Exact solution of the 1D riemann problem in Newtonian and relativistic hydrodynamics
Abstract:Some of the most interesting scenarios that can be studied in astrophysics, contain fluids and plasma moving under the influence of strong gravitational fields. To study these problems it is required to implement numerical algorithms robust enough to deal with the equations describing such scenarios, which usually involve hydrodynamical shocks. It is traditional that the first problem a student willing to develop research in this area is to numerically solve the one dimensional Riemann problem, both Newtonian and relativistic. Even a more basic requirement is the construction of the exact solution to this problem in order to verify that the numerical implementations are correct. We describe in this paper the construction of the exact solution and a detailed procedure of its implementation.⬇️ Scroll down to see the full summary -
A handy exact solution for flow due to a stretching boundary with partial slip
Abstract:In this article we provide an exact solution to the nonlinear differential equation that describes the behaviour of a flow due to a stretching flat boundary due to partial slip. For this, we take as a guide the search for an asymptotic solution of the aforementioned equation.⬇️ Scroll down to see the full summary -
Variational approximation for wave propagation in continuum and discrete media
Abstract:We develop a variational approximation for wave propagation in continuum and discrete media based on the modulation of wave profiles described by appropriate trial functions. We illustrate the method by considering an application to the theory of dislocation of materials. We first consider the continuum approximation of the model and reproduce the exact traveling known solution. We then consider the fully discrete non integrable model and obtain an approximate solution based on trial functions with functional form similar to the exact solution of the continuum. The description of this discrete approximate solution is in terms of a discrete nonlinear dispersion relation between the wave parameters. In this last situation we compare the numerical and variational solutions at the stationary case. We thus illustrate the usage of a variational asymptotic approximation to study nonlinear problems and we contrast the differences and difficulties between continuum and discrete problems.⬇️ Scroll down to see the full summary -
Probing students' critical thinking processes by presenting ill-defined physics problems
Abstract:Students' reflections on the meaningfulness of physics problem statements and solutions were investigated. The sample consisted of 276 Croatian high school/university students. The students, being at the different learning levels, were all familiar with the physical concepts concerned. Students' critical thinking processes were explored based on their responses to two open-ended ill-defined problems. Further, the teachers' ability to predict the typical students' approach to problem solving was investigated. For this purpose, 48 teachers were administered the closed-ended questionnaire composed of the empirically obtained students' responses to the two ill-defined problems. The results show that ill-defined problems have the potential of eliciting a whole diversity of deep-rooted students' ideas regarding the meaningfulness of problem statements and solutions. Further, the results indicate that the level of students' critical thinking is low regardless of their educational level and curriculum. It seems that traditional teaching does not sufficiently develop critical thinking. The teachers correctly judge the students' ability to consider the meaningfulness of the solution but they significantly overestimate their criticism towards the problem statement. We believe this kind of problems could facilitate the teachers' efforts directed at systematically developing the students' critical thinking processes. Consequently, students' coping with ill-defined problems could help them to improve their real-life competencies, as well as to develop the habit of taking a critical attitude towards the statements and solutions of physics problems.⬇️ Scroll down to see the full summary -
El primer texto formal de óptica de México
Abstract:We present information on the optical books used in Mexico from the colonial period to the middle 20th Century, and discuss the first mexican text of that discipline, that was written by professor Pedro Carrasco Garrorena. We rebound the modern focus of this book in that time. Is analyzed the contribution of this book in the formation process of the first mexican students of Physics.⬇️ Scroll down to see the full summary
