ABSTRACT Spontaneous pneumomediastinum, is a little common, benign and self-limited disease, characterized by the presence of air in the mediastinum, may be idiopathic or secondary to triggers drugs, vomiting, coughing. Occurs at any age, although it tends to predominate in young males, smokers with a history of prior pulmonary pathology. His diagnosis is established before a series of signs and symptoms that characterize it; e images. We report the case of a young patient, consulting to the urgency by respiratory picture, radiologic studies, made the diagnosis, evolution was favorable, discussed aspects of this clinical entity.

RESUMEN El neumomediastino espontáneo, es una patología poco frecuente, benigna y autolimitada, se caracteriza por la presencia de aire en el mediastino, puede ser idiopática o secundaria a factores desencadenantes drogas, vómitos, accesos de tos. Se da a cualquier edad, aunque suele predominar en varones jóvenes, fumadores y con antecedentes de patología pulmonar previa. Su diagnóstico se establece ante una serie de síntomas y signos que lo caracterizan; e imágenes. Reportamos el caso de un paciente joven, que consulta a la urgencia por cuadro respiratorio, los estudios radiológicos, hicieron el diagnóstico, la evolución fue favorable, se discute los aspectos relevantes de esta entidad clínica.

O movimento da Lua tem aspectos pouco intuitivos quando observado de um referencial fixo no Sol. Existem muitas concepções errôneas sobre esse movimento, encontradas em vários textos de referência e aceitas pela maioria das pessoas como parte do senso comum. Neste trabalho nós discutimos porque as noções usuais sobre a trajetória da Lua em torno do Sol estão erradas, e apresentamos uma descrição simples da geometria da órbita lunar. As órbitas dos demais satélites planetários do sistema solar também são analisadas.

The trajectory of the Moon has a nonintuitive aspect when observed from the Sun. Misconceptions about this motion are widespread and found even in textbooks. In this work we discuss what is wrong with the common sense notions about the trajectory of the Moon around the Sun, and investigate how pervasive these notions are.We also present a simple description of the geometry of the lunar orbit as seen from the Sun and find that the trajectory of the Moon is quite exceptional among the satellites in the solar system.

In this work, we use the Casimir effect to probe the existence of one extra dimension. We begin by evaluating the Casimir pressure between two plates in a M4 × S¹ manifold, and then use an appropriate statistical analysis in order to compare the theoretical expression with a recent experimental data and set bounds for the compactification radius.

In order to popularize the so called Schwinger's method we reconsider the Feynman propagator of two non-relativistic systems: a charged particle in a uniform magnetic field and a charged harmonic oscillator in a uniform magnetic field. Instead of solving the Heisenberg equations for the position and the canonical momentum operators, R and P, we apply this method by solving the Heisenberg equations for the gauge invariant operators R and pi = P-eA, the latter being the mechanical momentum operator. In our procedure we avoid fixing the gauge from the beginning and the result thus obtained shows explicitly the gauge dependence of the Feynman propagator.

Apresentamos uma solução alternativa para o problema do pêndulo cicloidal. Trata-se de um procedimento híbrido, envolvendo algumas idéias puramente geométricas utilizadas por Huygens e conhecimentos rudimentares de cálculo diferencial e integral. Ao final, discutimos um aparente paradoxo relacionado com esse problema.

We present an alternative solution to the cycloidal pendulum problem. Our procedure is an hybrid one, since it involves some purely geometrical ideas as well as the rudiments of integral and differential calculus. At the end, we discuss an apparent paradox related to this problem.

We compute the Casimir energy for a massive scalar field constrained between two parallel planes (Dirichlet boundary conditions) in order to investigate its non-relativistic limit. Instead of employing the usual relativistic dispersion relation omega(p) = <img SRC="http:/img/fbpe/bjp/v31n1/08eq01.gif">, we use the non-relativistic one, omega(p) = p²/2m. It turns out that the Casimir energy is zero. We include the relativistic corrections perturbatively and show that at all orders the Casimir energy remains zero, since each term in the power series in 1/c² is proportional to the Riemann zeta function of a negative even integer. This puzzling result shows that, at least for the free massive scalar field, the Casimir effect is non-perturbative in the relativistic sense.

The influence of an external constant uniform magnetic field on the Casimir energy associated with a Dirac field under antiperiodic boundary condition is computed using Schwinger's method. The obtained result shows that the magnetic field enhances the fermionic Casimir energy, in oposition to the bosonic Casimir energy which is inhibited by the magnetic field.

We compute the Casimir pressure between an unusual pair of parallel plates, namely, a perfectly conducting plate (<FONT FACE="Symbol">e®¥)</font> and an infinitely permeable one (<FONT FACE="Symbol">m®¥</font>) with the generalized <FONT FACE="Symbol">z</font>-function method. The result for this problem, which has been rarely discussed in the literature, is a repulsive Casimir force. The <FONT FACE="Symbol">z</font>-function method provides a very compact and economic way of obtaining the final result.

We use the Green function method to compute the Casimir energy of a massive scalar particle. In order to evaluate the Green function we employ the image method which had been used before only for the massless case.