Large tunable photonic band gaps in nanostructured doped semiconductors

A plasmonic nanostructure conceived with periodic layers of a doped semiconductor and passive semiconductor is shown to generate spontaneously surface plasmon polaritons thanks to its periodic nature. The nanostructure is demonstrated to behave as an effective material modeled by a simple dielectric function of ionic-crystal type, and possesses a fully tunable photonic band gap, with widths exceeding 50%, in the region extending from mid-infra-red to Tera-Hertz.Comment: 6 pages, 4 figures, publishe

Teaching "Symmetry" in the Introductory Physics Curriculum

Modern physics is largely defined by fundamental symmetry principles and Noether's Theorem. Yet these are not taught, or rarely mentioned, to beginning students, thus missing an opportunity to reveal that the subject of physics is as lively and contemporary as molecular biology, and as beautiful as the arts. We prescribe a symmetry module to insert into the curriculum, of a week's length.Comment: 15 pages, 4 figure

Self-similar cosmologies in 5D: spatially flat anisotropic models

In the context of theories of Kaluza-Klein type, with a large extra dimension, we study self-similar cosmological models in 5D that are homogeneous, anisotropic and spatially flat. The "ladder" to go between the physics in 5D and 4D is provided by Campbell-Maagard's embedding theorems. We show that the 5-dimensional field equations $R_{AB} = 0$ determine the form of the similarity variable. There are three different possibilities: homothetic, conformal and "wave-like" solutions in 5D. We derive the most general homothetic and conformal solutions to the 5D field equations. They require the extra dimension to be spacelike, and are given in terms of one arbitrary function of the similarity variable and three parameters. The Riemann tensor in 5D is not zero, except in the isotropic limit, which corresponds to the case where the parameters are equal to each other. The solutions can be used as 5D embeddings for a great variety of 4D homogeneous cosmological models, with and without matter, including the Kasner universe. Since the extra dimension is spacelike, the 5D solutions are invariant under the exchange of spatial coordinates. Therefore they also embed a family of spatially {\it inhomogeneous} models in 4D. We show that these models can be interpreted as vacuum solutions in braneworld theory. Our work (I) generalizes the 5D embeddings used for the FLRW models; (II) shows that anisotropic cosmologies are, in general, curved in 5D, in contrast with FLRW models which can always be embedded in a 5D Riemann-flat (Minkowski) manifold; (III) reveals that anisotropic cosmologies can be curved and devoid of matter, both in 5D and 4D, even when the metric in 5D explicitly depends on the extra coordinate, which is quite different from the isotropic case.Comment: Typos corrected. Minor editorial changes and additions in the Introduction and Summary section

Gamma-rays from the compact colliding wind region in Cyg OB2 #5

In this contribution we model the non-thermal emission (from radio to gamma-rays) produced in the compact (and recently detected) colliding wind region in the multiple stellar system Cyg OB2 #5. We focus our study on the detectability of the produced gamma-rays.Comment: To appear in the proceedings of the 5th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma2012), held in Heidelberg, July 9-13, 201

Large tunable photonic band gaps in nanostructured doped semiconductors

A plasmonic nanostructure conceived with periodic layers of a doped semiconductor and passive semiconductor is shown to generate spontaneously surface plasmon polaritons thanks to its periodic nature. The nanostructure is demonstrated to behave as an effective material modeled by a simple dielectric function of ionic-crystal type, and possesses a fully tunable photonic band gap, with widths exceeding 50%, in the region extending from mid-infra-red to Tera-Hertz.Comment: 6 pages, 4 figures, publishe

Equivalence Between Space-Time-Matter and Brane-World Theories

We study the relationship between space-time-matter (STM) and brane theories. These two theories look very different at first sight, and have different motivation for the introduction of a large extra dimension. However, we show that they are equivalent to each other. First we demonstrate that STM predicts local and non-local high-energy corrections to general relativity in 4D, which are identical to those predicted by brane-world models. Secondly, we notice that in brane models the usual matter in 4D is a consequence of the dependence of five-dimensional metrics on the extra coordinate. If the 5D bulk metric is independent of the extra dimension, then the brane is void of matter. Thus, in brane theory matter and geometry are unified, which is exactly the paradigm proposed in STM. Consequently, these two 5D theories share the same concepts and predict the same physics. This is important not only from a theoretical point of view, but also in practice. We propose to use a combination of both methods to alleviate the difficult task of finding solutions on the brane. We show an explicit example that illustrate the feasibility of our proposal.Comment: Typos corrected, three references added. To appear in Mod. Phys. Let

Thorium-Uranium fractionation as an indicator of petrogenetic processes

A mean Th/U ratio, ~4, seems to characterize most terrestrial, lunar, and meteoritic igneous materials and major patterns of lead isotopic evolution develop principally in systems with Th/U about 3.7-4.0. Some important crustal igneous subsystems show systematic deviations from these values. Such fractionation generally is attributed to the geochemical behavior of the large lithophile actinide ions in various enriched minor phases. This probably is true in highly differentiated series with higher Th and U levels (>8 and 2 ppm). A different fractionation mechanism may be more important in some lower concentration systems. Isotope dilution mass spectrometric studies of U and Th in diverse igneous feldspar separates reveal significant U and Th partitioning into them with drastic fractionation of Th/U (values 0.2- 3.0). Alkali feldspars in granitic rocks display partition coefficients (feldspar/total rock) of about 0.005-0.02 for U and 0.001-0.004 for Th; Th/U~0.5-3.0. In plagioclase in gabbros, tonalites, and granodiorites with lower Th and U, the coefficients appear larger (U~0.1-0.4, Th~0.04-0.2) but Th/U appears lower (Th/U~0.2-2.0) than in K-feldspar. Limited data suggests some pyraxenes and other major minerals may also fractionate Th/U to lower ratios. Differences in ionic radius and uranium oxidation states may contribute to the undefined fractionation mechanism. Processes of primary differentiation (fractional crystallization, partial melting) involving gabbroic systems seem to reflect this fractionation. Oceanic tholeiites, end massive gabbroic complexes display generally low Th/U values. Their lead isotopes reflect reservoirs with more normal Th/U ratios. This suggests limits on the number of fractionation cycles, mantle mixing, and/or reservoir dimensions for primary basaltic systems. Th and U and their associated lead isotope systems can be used with lanthanide R.E.E. to assist in developmet of petrogenetic models