Light Collimation and Focussing by a Thin Flat Metallic Slab

We present experimental and theoretical work showing that a flat metallic slab can collimate and focus light impinging on the slab from a punctual source. The effect is optimised when the radiation is around the bulk, not at the surface, plasma frequency. And the smaller the imaginary part of the permittivity is, the better the collimation. Experiments for Ag in the visible as well as calculations are presented. We also discuss the interesting case of the Aluminium whose imaginary part of the permittivity is very small at the plasma frequency in UV radiation. Generalization to other materials and radiations are also discussed.Comment: 6 pages, 3 figures. To be published on Optics Lette

Gauge invariant investigation of the nature of Confinement

We observe a strong correlation between the decrease in the number of action density peaks in SU(2) Yang-Mills configurations with cooling and that of the string tension. The nature and distribution of these peaks is investigated. The relationship with monopole currents after the abelian projection is also considered.Comment: uuencoded and Z-compressed file of the Postcript version of our contribution to LATTICE 95. 4 pages of text and 4 figure

Red-giant stars in eccentric binaries

The unparalleled photometric data obtained by NASA’s Kepler Space Telescope has led to improved understanding of red-giant stars and binary stars. We discuss the characterization of known eccentric system, containing a solar-like oscillating red-giant primary component. We also report several new binary systems that are candidates for hosting an oscillating companion. A powerful approach to study binary stars is to combine asteroseimic techniques with light curve fitting. Seismology allows us to deduce the properties of red giants. In addition, by modeling the ellipsoidal modulations we can constrain the parameters of the binary system. An valuable independent source are ground-bases, high-resolution spectrographs

On the transmission of light through a single rectangular hole

In this Letter we show that a single rectangular hole exhibits transmission resonances that appear near the cutoff wavelength of the hole waveguide. For light polarized with the electric field pointing along the short axis, it is shown that the normalized-to-area transmittance at resonance is proportional to the ratio between the long and short sides, and to the dielectric constant inside the hole. Importantly, this resonant transmission process is accompanied by a huge enhancement of the electric field at both entrance and exit interfaces of the hole. These findings open the possibility of using rectangular holes for spectroscopic purposes or for exploring non-linear effects.Comment: Submitted to PRL on Feb. 9th, 200

Diverse Sources of Social Support and Cognitive Functioning by Race, Ethnicity, and Nativity

This study examines the relationship between social support profiles and cognitive functioning by race, ethnicity and nativity in older adults using cross-sectional data drawn from the Health and Retirement Study (2010 and 2012). We employed a hierarchical clustering routine to generate nine support profiles that differentiated three sources of support: children, wider family relationships and friendships. Cognitive functioning was measured as the score on the Telephone Interview for Cognitive Status (TICS-m), a 27 point scale of cognitive function. Our approach explicitly acknowledges the ambivalence and multidimensionality of close relationships and the resources embedded within them. Descriptive analyses revealed significant differences in access to support across demographic groups. White respondents are over-represented in profiles that are characterized by support from friends, and under-represented in family support profiles. The reverse is found among Foreign-born Hispanic respondents who are over-represented in the profiles characterized by high family support and under-represented in those with high friend support. Native-born Hispanic respondents and Black respondents have less clear support patterns, although both are more likely to receive support from family and children compared to friends. Findings from the Poisson regression suggest that the relationship between familial support and cognitive decline is stronger among Hispanic respondents, particularly those who are foreign born. These findings are supported even with the inclusion of other relationship quality indicators including negative support and frequency of contact

Entropy in Spin Foam Models: The Statistical Calculation

Recently an idea for computing the entropy of black holes in the spin foam formalism has been introduced. Particularly complete calculations for the three dimensional euclidean BTZ black hole were done. The whole calculation is based on observables living at the horizon of the black hole universe. Departing from this idea of observables living at the horizon, we now go further and compute the entropy of BTZ black hole in the spirit of statistical mechanics. We compare both calculations and show that they are very interrelated and equally valid. This latter behaviour is certainly due to the importance of the observables.Comment: 11 pages, 1 figur

Virtues and Flaws of the Pauli Potential

Quantum simulations of complex fermionic systems suffer from a variety of challenging problems. In an effort to circumvent these challenges, simpler ``semi-classical'' approaches have been used to mimic fermionic correlations through a fictitious ``Pauli potential''. In this contribution we examine two issues. First, we address some of the inherent difficulties in a widely used version of the Pauli potential. Second, we refine such a potential in a manner consistent with the most basic properties of a cold Fermi gas, such as its momentum distribution and its two-body correlation function.Comment: 16 pages, 6 figure

Spin order in the one-dimensional Kondo and Hund lattices

We study numerically the one-dimensional Kondo and Hund lattices consisting of localized spins interacting antiferro or ferromagnetically with the itinerant electrons, respectively. Using the Density Matrix Renormalization Group we find, for both models and in the small coupling regime, the existence of new magnetic phases where the local spins order forming ferromagnetic islands coupled antiferromagnetically. Furthermore, by increasing the interaction parameter $|J|$ we find that this order evolves toward the ferromagnetic regime through a spiral-like phase with longer characteristic wave lengths. These results shed new light on the zero temperature magnetic phase diagram for these models.Comment: PRL, to appea