Oxidation of D=3 cosets and Bonnor dualities in D≤6D\leq 6

Bonnor's map in General Relativity is duality between (dimensionally reduced) vacuum gravity and static truncation of electro-vacuum theory. It was used as a tool to generate an exact solution of electro-vacuum from some vacuum solution. It can be expected that similar dualities will be useful for solution generation in higher-dimensional theories too. Here we study such maps within a class of theories in dimensions $D\leq 6$ using oxidation of D=3 cosets and consistent truncation of the corresponding theories. Our class includes those theories whose D=3 symmetries are subgroups of $G=O(5,4)$. It contains six-dimensional minimal supergravity, five-dimensional minimal and $U(1)^3$ supergravities and a number of four-dimensional theories which attracted attention recently in the search of exact solutions. We give explicit reduction/truncation formulas relating different theories in dimensions $D=4, 5, 6$ in terms of metrics and matter fields and discuss various alternative duality chains between them.Comment: Two references added, Introduction slightly edited, mispints removed. Journal versio

Bertotti-Robinson solutions of D=5 Einstein-Maxwell-Chern-Simons-Lambda theory

We present a series of new solutions in five-dimensional Einstein-Maxwell-Chern-Simons theory with an arbitrary Chern-Simons coupling $\gamma$ and a cosmological constant $\Lambda$. For general $\gamma$ and $\Lambda$ we give various generalizations of the Bertotti-Robinson solutions supported by electric and magnetic fluxes, some of which presumably describe the near-horizon regions of black strings or black rings. Among them there is a solution which could apply to the horizon of a topological AdS black ring in gauged minimal supergravity. Others are horizonless and geodesically complete. We also construct extremal asymptotically flat multi-string solutions for $\Lambda=0$ and arbitrary $\gamma$.Comment: 17 pages, revtex

Cosmological perturbations of a perfect fluid and noncommutative variables

We describe the linear cosmological perturbations of a perfect fluid at the level of an action, providing thus an alternative to the standard approach based only on the equations of motion. This action is suited not only to perfect fluids with a barotropic equation of state, but also to those for which the pressure depends on two thermodynamical variables. By quantizing the system we find that (1) some perturbation fields exhibit a noncommutativity quite analogous to the one observed for a charged particle moving in a strong magnetic field, (2) local curvature and pressure perturbations cannot be measured simultaneously, (3) ghosts appear if the null energy condition is violated.Comment: 4 pages, uses RevTeX. Title modified, references and comments added

Simple and accurate analytical model of planar grids and high-impedance surfaces comprising metal strips or patches

This paper introduces simple analytical formulas for the grid impedance of electrically dense arrays of square patches and for the surface impedance of high-impedance surfaces based on the dense arrays of metal strips or square patches over ground planes. Emphasis is on the oblique-incidence excitation. The approach is based on the known analytical models for strip grids combined with the approximate Babinet principle for planar grids located at a dielectric interface. Analytical expressions for the surface impedance and reflection coefficient resulting from our analysis are thoroughly verified by full-wave simulations and compared with available data in open literature for particular cases. The results can be used in the design of various antennas and microwave or millimeter wave devices which use artificial impedance surfaces and artificial magnetic conductors (reflect-array antennas, tunable phase shifters, etc.), as well as for the derivation of accurate higher-order impedance boundary conditions for artificial (high-) impedance surfaces. As an example, the propagation properties of surface waves along the high-impedance surfaces are studied.Comment: 12 pages, 10 figures, submitted to IEEE Transactions on Antennas and Propagatio

Emission and its back-reaction accompanying electron motion in relativistically strong and QED-strong pulsed laser fields

The emission from an electron in the field of a relativistically strong laser pulse is analyzed. At pulse intensities of J > 2 10^22 W/cm2 the emission from counter-propagating electrons is modified by the effects of Quantum ElectroDynamics (QED), as long as the electron energy is sufficiently high: E > 1 GeV. The radiation force experienced by an electron is for the first time derived from the QED principles and its applicability range is extended towards the QED-strong fields.Comment: 14 pages, 5 figures. Submitted to Phys.Rev.

Signature Characters for A_2 and B_2

The signatures of the inner product matrices on a Lie algebra's highest weight representation are encoded in the representation's signature character. We show that the signature characters of a finite-dimensional Lie algebra's highest weight representations obey simple difference equations that have a unique solution once appropriate boundary conditions are imposed. We use these results to derive the signature characters of all $A_2$ and $B_2$ highest weight representations. Our results extend, and explain, signature patterns analogous to those observed by Friedan, Qiu and Shenker in the Virasoro algebra's representation theory.Comment: 22 p

Robust, frequency-stable and accurate mid-IR laser spectrometer based on frequency comb metrology of quantum cascade lasers up-converted in orientation-patterned GaAs

We demonstrate a robust and simple method for measurement, stabilization and tuning of the frequency of cw mid-infrared (MIR) lasers, in particular of quantum cascade lasers. The proof of principle is performed with a quantum cascade laser at 5.4 \mu m, which is upconverted to 1.2 \mu m by sum-frequency generation in orientation-patterned GaAs with the output of a standard high-power cw 1.5 \mu m fiber laser. Both the 1.2 \mu m and the 1.5 \mu m waves are measured by a standard Er:fiber frequency comb. Frequency measurement at the 100 kHz-level, stabilization to sub-10 kHz level, controlled frequency tuning and long-term stability are demonstrated

Modalités de la compétition larvaire intraspécifique chez Bruchus affinis (Coleoptera, Bruchidae) dans les graines de Lathyrus sylvestris (Leguminosae, Fabaceae)

Summary. — In spring, a high concentration of Bruchus affinis eggs laid on the first appearing pods of Lathyrus sylvestris is responsible for an important intraspecific larval competition during the colonization of growing ovules. A single adult emerges from the seed, even if the seed has been infested by several larvae. We studied the patterns of this competition. Growth and development of B. affinis larvae are concommitent with the ones of infested ovules, and two main characteristics can be pointed out : a first larval ecdysis after the colonization of a growing ovule and a larval tendency to settle down in the center of cotyledons. Larval competition is closely related to a noticeable territorial behaviour of the larvae. Meetings of larvae moving towards the centre turn them in a situation of agression. When a larva casually meets another one from the side or the rear, it can hurt it with its mouth parts and kill it. Nevertheless, a larva which is already in the center of a wider gallery shows a greater mobility and kills more easily an approaching larva. The bigger (or older) larva is not necessarily the «winner» of the competition even if it is generally favoured by its central position and greater mobility.Résumé. — Au printemps, la forte concentration des pontes de Bruchus affinis sur les premières gousses formées de Lathyrus sylvestris est à l'origine d'une importante compétition larvaire intra-spécifique au moment de la colonisation des ovules en croissance. Un seul adulte émerge de la graine même si celle-ci a été colonisée par plusieurs larves. L'analyse des modalités de cette compétition est abordée. La croissance et le développement des larves de B. affinis sont concomitants de ceux des ovules colonisés et deux caractéristiques se dégagent : première mue larvaire après occupation d'un ovule en croissance et tendance larvaire à occuper le centre des cotylédons. La compétition larvaire est en relation étroite avec un comportement territorial très marqué de la larve. Les rencontres fortuites par recoupement des galeries larvaires lors de la progression vers le centre mettent les larves en situation de compétition. Lorsque'une larve en rejoint fortuitement une autre sur le côté ou par derrière, elle peut la blesser avec ses pièces buccales et l'éliminer. Mais une larve, déjà au centre dans une galerie plus large, a une mobilité plus grande et élimine plus facilement toute autre larve tentant de la rejoindre. La larve la plus grosse (ou la plus âgée) n'est pas nécessairement le «vainqueur» de la compétition, bien qu'elle soit en général plus favorisée par sa position au centre et sa meilleure mobilité.N'diaye Saliou, Fabres Gérard, Labeyrie Vincent. Modalités de la compétition larvaire intraspécifique chez Bruchus affinis (Coleoptera, Bruchidae) dans les graines de Lathyrus sylvestris (Leguminosae, Fabaceae). In: Bulletin de la Société entomologique de France, volume 97 (2), juin 1992. pp. 135-144