Green's Dyadic Approach of the Self-Stress on a Dielectric-Diamagnetic Cylinder with Non-Uniform Speed of Light

We present a Green's dyadic formulation to calculate the Casimir energy for a dielectric-diamagnetic cylinder with the speed of light differing on the inside and outside. Although the result is in general divergent, special cases are meaningful. It is pointed out how the self-stress on a purely dielectric cylinder vanishes through second order in the deviation of the permittivity from its vacuum value, in agreement with the result calculated from the sum of van der Waals forces.Comment: 8 pages, submitted to proceedings of QFEXT0

Electromagnetic Non-contact Gears: Prelude

We calculate the lateral Lifshitz force between corrugated dielectric slabs of finite thickness. Taking the thickness of the plates to infinity leads us to the lateral Lifshitz force between corrugated dielectric surfaces of infinite extent. Taking the dielectric constant to infinity leads us to the conductor limit which has been evaluated earlier in the literature.Comment: 7 pages, 2 figures, Contribution to Proceedings of 9th Conference on Quantum Field Theory Under the Influence of External Conditions (QFEXT09), Norman, OK, September 21-25, 200

Surface Divergences and Boundary Energies in the Casimir Effect

Although Casimir, or quantum vacuum, forces between distinct bodies, or self-stresses of individual bodies, have been calculated by a variety of different methods since 1948, they have always been plagued by divergences. Some of these divergences are associated with the volume, and so may be more or less unambiguously removed, while other divergences are associated with the surface. The interpretation of these has been quite controversial. Particularly mysterious is the contradiction between finite total self-energies and surface divergences in the local energy density. In this paper we clarify the role of surface divergences.Comment: 8 pages, 1 figure, submitted to proceedings of QFEXT0

Local Casimir Energies for a Thin Spherical Shell

The local Casimir energy density for a massless scalar field associated with step-function potentials in a 3+1 dimensional spherical geometry is considered. The potential is chosen to be zero except in a shell of thickness $\delta$, where it has height $h$, with the constraint $h\delta=1$. In the limit of zero thickness, an ideal $\delta$-function shell is recovered. The behavior of the energy density as the surface of the shell is approached is studied in both the strong and weak coupling regimes. The former case corresponds to the well-known Dirichlet shell limit. New results, which shed light on the nature of surface divergences and on the energy contained within the shell, are obtained in the weak coupling limit, and for a shell of finite thickness. In the case of zero thickness, the energy has a contribution not only from the local energy density, but from an energy term residing entirely on the surface. It is shown that the latter coincides with the integrated local energy density within the shell. We also study the dependence of local and global quantities on the conformal parameter. In particular new insight is provided on the reason for the divergence in the global Casimir energy in third order in the coupling.Comment: 16 pages, revtex 4, no figures. Major additions, clarifications, and corections, references adde

Evolución de la composición florística post-fuego en un carrascal de Navarra (N de España)

Se presentan los resultados de cuatro años de estudio sobre la evolución de la composición florística de un carrascal mediterráneo sometido a fuegos controlados en Navarra (N de España). Los muéstreos se han llevado a cabo en ocho cuadrados permanentes de 1 m- de superficie, cada uno sometido a distinto tratamiento: distinto tipo de fuego, distinta situación en la parcela y adición o no de suelo no quemado. Se analizan la estrategia de regeneración de las especies que aparecen después de los fuegos y la influencia de los tratamientos en la regeneración de la flora. La evolución de la composición florística sigue un modelo general: las especies empiezan a aparecer progresivamente, su número crece hasta obtener un máximo entre el año y los cuatro años después de los fuegos, a partir del cual disminuye. Las especies que aparecen son las mismas que había previamente, es decir, se da un proceso de autosucesión. ABSTRACT.- This paper presents results about floristic composition dynamics during four years after controlled fires in a mediterranean pin-oak wood in Navarra (N Spain). The samples have been taken from eight permanent 1 m- plots subjected to different treatments: different fire type, different situation on the field, and with or without not fired soil addition. The regeneration strategies of the species and the influence of the different treatments on the flora are analysed. The floristic composition dynamics follows a general model: the species began to appear progressively. The number of species grows gradually to reach a maximum between one and three years after the fire. Later, the number of species diminishes. Post fire species are those that existed before the fire, that is to say, there is an autosuccession process

Evolución de la riqueza florística después de incendios controlados en un robledal de Navarra (España).

Se presentan los resultados relativos a la evolución de la riqueza florística de un robledal atlántico de Queráis robur L. obtenidos durante tres años de estudio en los que ha comenzado la recuperación después de sufrir fuegos controlados. Los muéstreos se han llevado a cabo en ocho cuadrados permanentes de 1 m2, cada uno sometido a distinto tratamiento: distinto tipo de fuego, distinta topografía y adición o no de suelo no quemado. La riqueza florística aumenta progresivamente a lo largo del tiempo después de la perturbación, hasta alcanzar un máximo durante el tercer año, a partir del cual ésta tiende a disminuir. El proceso de autosucesión queda corroborado también para este ecosistema: aparecen las mismas especies que había antes del incendio pero con diferentes abundancias. La regeneración de la vegetación es más rápida tras el fuego rápido, en zonas inferiores y en cuadrados con adición de suelo no quemado

Casimir interaction between plane and spherical metallic surfaces

We give an exact series expansion of the Casimir force between plane and spherical metallic surfaces in the non trivial situation where the sphere radius $R$, the plane-sphere distance $L$ and the plasma wavelength $\lambda_\P$ have arbitrary relative values. We then present numerical evaluation of this expansion for not too small values of $L/R$. For metallic nanospheres where $R, L$ and $\lambda_\P$ have comparable values, we interpret our results in terms of a correlation between the effects of geometry beyond the proximity force approximation (PFA) and of finite reflectivity due to material properties. We also discuss the interest of our results for the current Casimir experiments performed with spheres of large radius $R\gg L$.Comment: 4 pages, new presentation (highlighting the novelty of the results) and added references. To appear in Physical Review Letter