Vol. 58 No. 1 Jan-Jun (2012): Revista Mexicana de Física E
Published:
2012-01-01
Artículos
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Experimental and simulated exploration of structural deflections and acoustic waves of guitar top plates
Abstract:The focus of this paper is to describe complex theoretical concepts about vibration and acoustics, considering experimental and computational tools. Some modal behaviors of a structure were explained. First, an experiment was designed to naked eye visualization of mode shapes in a thin film. Later, simulated deflections of a guitar top plate model were explored. This exploration was done through original scientific visualization software. Moreover, the developed computational tool was essential illustrating behaviors that used to be hard to visualize: acoustic waves. Sound radiation data were calculated from the vibration of the top plate model. These data were sliced to detect acoustic wavefronts and directivity patterns. Experimental and computational procedures developed in this work were useful illustrating vibroacoustic behaviors. Mode shapes and natural frequencies in the thin film experiment were clearly detected. Scientific visualization software showed ability to display vibroacoustic information in high density, with much semantic substance and time savings. The experiment can be easily implemented in a classroom, and the software can be used to explore other kind of data in standard Visualization Tool Kit format.⬇️ Scroll down to see the full summary -
Enhancing the process of teaching and learning physics via \emph{dynamic problem solving strategies}: a proposal
Abstract:The large number of published articles in physics journals under the title ``Comments on $\cdots$'' and ``Reply to $\cdots$'' is indicative that the conceptual understanding of physical phenomena is very elusive and hard to grasp even to experts, but it has not stopped the development of Physics. In fact, from the history of the development of Physics one quickly becomes aware that, regardless of the state of conceptual understanding, without quantitative reasoning Physics would have not reached the state of development it has today. Correspondingly, quantitative reasoning and problem solving skills are a desirable outcome from the process of teaching and learning of physics. Thus, supported on results from published research, we will show evidence that a well structured problem solving strategy taught as a dynamical process offers a feasible way for students to learn physics quantitatively and conceptually, while helping them to reach the state of an \emph{Adaptive Expert} highly skillful on innovation and efficiency, a desired outcome from the perspective of a \emph{Preparation for Future Learning} approach of the process of teaching and learning Physics effectively.⬇️ Scroll down to see the full summary -
Desarrollo de un sistema para medir tiempos en experimentos de movimiento rectilíneo
Abstract:It was developed a system to measure times using photo gates and a computer's sound card on rectilinear motion experiments. The movement sensors were connected to the computer through a XOR logic gate array, the signal from the sensors was fed to the computer's sound card input line. MATLAB was used to acquire and processing data and a specialized add-on software activated the hardware to read the signals produced by the photo gates. The system developed can be built with low cost items and it was tested with two different setup to evaluate and compare theoretical versus experimental data resulting in good agreement.⬇️ Scroll down to see the full summary -
Partícula confinada en una cavidad esferoidal prolata. Algunos efectos de la pérdida de simetría esférica.
Abstract:The problem being studied is that of a particle moving unimpeded that is confined within a spheroidal box. Using the software Mathematica the spheroidal functions are plotted for six physical states. The energy levels below 8.5 rydbergs are calculated when the inverse of the excentricity $\xi o $ is taken to be $\xi o=3$ and $\xi o=30$. A comparison is drawn between the energy spectrum of a particle confined within a spherical box of the same volume, and it is found that every level of this system is split in $% l+1 $ levels when its spherical symmetry is shifted to a prolate symmetry. The matrix elements for dipolar interaction are studied and it is shown that the light that is either emitted or absorbed is circularly polarized. The electric dipole moment is calculated for the ground state and for three further excited states. Einstein's $A_{ij}$ coeficients are calculated for six allowed transitions. The simplicity of the computer work being done allows us to suggest that this material is didactically useful to understand key aspects of what happens within a quantum system in the event that its symmetry is modified. Activities are suggested that could be performed by undergraduate students.⬇️ Scroll down to see the full summary -
El fenómeno de la caída de los cuerpos
Abstract:In this paper a history on the analysis made about the bodies fall phenomenon is presented, since the first studies realized by Aristotle until the free fall law by Galileo. Also are considerate the criticism made by specialists to the explanations given by the Greek philosopher and the theories that were proposed by them as alternatives at Aristotelians ones. The works made by medieval scholars and Galileo's predecessors about this phenomenon also are presented. The influence of Arquimedes on the Galileo's work is emphasized. The fundamental notions of space, time and movement that underlying in the respective theories are analyzed. Finally, the image of Galileo Galilei leaving fall heavy bodies from the top of Incline Tower and his connotation in the development of scientific ideas are presented, although that strictly speaking such image to be a myth.⬇️ Scroll down to see the full summary -
Sobre el único ejemplar latinoamericano de la primera edición de De revolutionibus orbium caelestium de Copérnico, en Guadalajara, Jalisco, México
Abstract:The ``Juan José Arreola'' Jalisco's Public Library at the Universidad de Guadalajara treasures the only surviving first edition copy (1543) in Latin America of Nicholas Copernicus`s De revolutionibus orbium c{\aelestium}. The present work gives some preliminary details related to the mentioned copy.⬇️ Scroll down to see the full summary -
Materia oscura escalar compleja (parte I): la versión hidrodinámica
Abstract:In this work we use the Euler hydrodynamic equations of fluids to study a model of galactic halos minimally coupled to a complex scalar field, which in the Newtonian limit they become the Schrödinger-Poisson system. Applying a Madelung transformation, this system of equations takes the form of hydrodynamics equations, where there are a self-interacting potential and a kind of quantum potential that depends non-linearly on the density of the fluid. In this theoretical framework we analyze the Jeans' instability, which is useful for finding the scale length of perturbations of the scalar field that will form structures. In other words, perturbations of the scalar field with lengths less than this threshold length, can not lead to the formation of galactic structures.⬇️ Scroll down to see the full summary -
Teaching the mathematics of quantum entanglement using elementary mathematical tools
Abstract:We address the problem of teaching the mathematics of entanglement using only elementary linear algebra. For this goal, we first discuss tensor products using only matrix multiplication and with this we discuss entanglement for pure bipartite systems of arbitrary dimensions. We show how to assess entanglement using only Gaussian methods, i.e. the row reduced echelon form of the familiar Gauss-Jordan algorithm for solving systems of linear equations. In this way we can present entanglement avoiding the difficulties of tensor products and without the Schmidt decomposition. Some elementary examples are provided together with MATLAB scripts. A Gaussian algorithm for the factorization of unentangled states is given.⬇️ Scroll down to see the full summary -
Fabricación de biosensores piezoeléctricos para la lectura de interacciones antígeno-anticuerpo
Abstract:In recent years, quartz crystal microbalances (QCM) have aroused great interest in the scientific and industrial communities due to their potential applications in areas such as medicine, quality control, chemistry, and the pharmaceutical industry. They are part of a rapid monitoring technique, and also have a low cost, high reproducibility, and low detection limits of the substance of interest. The following research addresses the main steps for biosensors with fibrinogen (1.5 mg/ml) or bovine serum albumin (1.5 mg/ml) monolayers anchored to the gold electrode of quartz crystals fabrication, which are used for detecting the protein/protein interaction in the saturated solution of anti-fibrinogen and anti-bovine serum albumin (1.5 mg/ml). Gold electrodes were prepared by a sputtering technique using a high purity gold target to grow thin films onto the surfaces of quartz crystals until they presented a fundamental frequency of 20 MHz. The morphology, roughness, thickness, and crystallography were characterized using scanning electron microscopy, atomic force microscopy, profilometry, and X-ray diffraction, respectively. The amino-functionalization of the gold electrodes and fibrinogen and bovine serum albumin sensitive films manufacture were performed by using molecular self-assembly. Through experimental data, the Sauerbrey model obtained the adsorbed surface concentration of protein after protein/protein interaction. The protein surface coverage of fibrinogen/anti-fibrinogen and albumin/anti-albumin interactions were 3.20 $\mu $g/cm$^{2}$ and 2.02 $\mu $g/cm$^{2}$, respectively. On the other hand, the cases of low homology, which were present in the fibrinogen/albumin and albumin/anti-fibrinogen interactions, showed values of 0.37 $\mu $g/cm$^{2}$ and 0.08 $\mu $g/cm$^{2}$, respectively.⬇️ Scroll down to see the full summary -
Increasing the attractiveness of school physics: the effects of two different designs of physics learning
Abstract:In this research we have used a specially prepared survey in order to assess the relative efficiency of two different designs of students' learning activities, called Reading, Presenting, and Questioning (RPQ) and Experimenting and Discussion (ED), both with objective to improve students' attitudes towards the attractiveness of school physics. The data of a one-semester-long high-school project indicate that RPQ group (91 students) achived an improvement of +4% in attitudes while the ED group (85 students) got an improvement of +23% as measured by the survey designed specifically for this study. Our results suggest that the ED method is a good model for a significant improvement of students' attitudes towards the attractiveness of school physics, both for girls and boys who study high school physics.⬇️ Scroll down to see the full summary
