Catálogo de publicaciones - revistas

<jats:p> Shielding involves much more than just putting a conductive screen in between an emitting source and a susceptible device. Starting from Maxwell's equations, the concept of electromagnetic shielding is formally explained. The physical working mechanisms behind the two basic forms of shielding, electric field and magnetic field shielding, are given, and the link between them at higher frequencies is clarified. Several aspects, like the effect of gridding or weaving a shield, the effect of the finite size of a shield, and the penetration through the metal of a shield, are discussed based on very simple canonical shielding topologies that can be solved analytically. Although the classical paradigm to explain shielding based on the notions of skin depth and eddy current is not followed, conceptual links with this classical paradigm are explained. </jats:p>

<jats:p> We investigate the electrostatic energy of one-dimensional line charges, focusing on the energy difference between lines of different shapes. The self-energy of a strictly one-dimensional charge is infinite, but one can quantify the energy by considering geometries that approach a one-dimensional curve, for example, thin wires, thin strips, or chains of close point charges. In each model, the energy diverges logarithmically as the geometry approaches a perfect one-dimensional curve, but the energy also contains a finite term depending on the shape of the line—the “shape energy.” The difference in shape energy between a straight line and a circle is checked to be the same using a range of models. To calculate the shape energy of more complex shapes numerically, we propose a line integral where the singularity in the integrand is canceled. This integral is used to calculate the shape energy of a helix. </jats:p>

<jats:p> In recent years, more courses in electromagnetism are using the “Système International” (SI) units as opposed to Gaussian-cgs. The confusing notation used to formulate SI with origins in the early 19th century still persists in instruction. This work shows that electromagnetism may be taught relatively painlessly in the units that virtually everyone uses by employing a new presentation that makes the equations nearly as simple as those in the Heaviside–Lorentz system commonly used by theoretical physicists. Introducing a new coupling constant κ and some new notation for the fields, it is possible to dispense with ϵ<jats:sub>0</jats:sub> and μ<jats:sub>0</jats:sub> and the conceptual framework from which they come. As a result, it is possible achieve much greater clarity, while using all the same symbols and relations as in the extant literature. </jats:p>

<jats:p> We propose here a simple black-hole analog in vehicular-traffic dynamics. The corresponding causal diagram is determined by the propagation of the tail light flashes emitted by a convoy of cars on a highway. In addition to being a new black-hole analog, this illustrates how causal diagrams, so common in general relativity, may be useful in areas as unexpected as vehicular-traffic dynamics. </jats:p>

<jats:p> Although attending departmental seminars is a common requirement in graduate education, the goals of this requirement are seldom explicitly stated, and its success at achieving these goals has not been studied. We developed a model for a graded colloquium course that encourages students to reflect on the effectiveness of the presentations, since the faculty in our department stated that one of their main goals for the students was to help them learn to give high quality presentations. An informal survey of students finds that this goal was partially achieved and also suggests improvements to the assignments and topics for future study. </jats:p>

<jats:p> We present a simple experiment developed for the advanced physics instructional laboratory to calculate the Mueller matrix of a microscopic sample. The Mueller matrix is obtained from intensity-based images of the sample acquired by a polarization-sensitive microscope. The experiment requires a bright-field microscope and standard polarizing optical components such as linear polarizers and waveplates. We provide a practical procedure for implementing the apparatus, measuring the complete Mueller matrix of linear polarizers used as samples, and discuss the possibility of analyzing biological samples using our apparatus and method. Due to the simplicity of the apparatus and method, this experiment allows students to increase their knowledge about light polarization and initiate their training in optical instrumentation. </jats:p>

<jats:p> Although the longitudinal mode spacing and longitudinal mode widths of a typical laser diode can, in principle, be determined from an optical coherence tomography signal, the values presented by Poddar et al. [Am. J. Phys. 75, 569–571 (2006)] do not agree with the Fourier transform theory. Also, the mode spacing is inconsistent with the peak separation in the interference signal. Moreover, the laser cavity mirror reflectivity calculated from the laser spectrum is incorrect because it ignores the gain and the loss within the laser cavity. This Comment aims to help readers who may struggle to understand that paper or to reproduce its results. </jats:p>