Generation of tunable Terahertz out-of-plane radiation using Josephson vortices in modulated layered superconductors

We show that a moving Josephson vortex in spatially modulated layered superconductors generates out-of-plane THz radiation. Remarkably, the magnetic and in-plane electric fields radiated are of the same order, which is very unusual for any good-conducting medium. Therefore, the out-of-plane radiation can be emitted to the vacuum without the standard impedance mismatch problem. Thus, the proposed design can be more efficient for tunable THz emitters than previous proposals, for radiation only propagating along the ab-plane.Comment: 7 pages, 1 figure. Phys. Rev. B (2005), in pres

Pre-meeting support views based on SISCO model

This report presents and compares three different approaches on the implementation of a pre-meeting support sstem. The prototypes described here were developed by three independent teams, two from Brazil and one from Chile. SISCO-Recife and SISCO-Rio are the Brazilian prototypes and USISCO is Chilean. The development of the three prototypes was based on the same SISCO discussion model. SISCO has as its main goal the enhancemnt of meetings productivity through previous discussion. The developed prototypes support asynchronous collaboration, as a preparation for a face-to-face meeting

Effect of Oscillating Landau Bandwidth on the Integer Quantum Hall Effect in a Unidirectional Lateral Superlattice

We have measured activation gaps for odd-integer quantum Hall states in a unidirectional lateral superlattice (ULSL) -- a two-dimensional electron gas (2DEG) subjected to a unidirectional periodic modulation of the electrostatic potential. By comparing the activation gaps with those simultaneously measured in the adjacent section of the same 2DEG sample without modulation, we find that the gaps are reduced in the ULSL by an amount corresponding to the width acquired by the Landau levels through the introduction of the modulation. The decrement of the activation gap varies with the magnetic field following the variation of the Landau bandwidth due to the commensurability effect. Notably, the decrement vanishes at the flat band conditions.Comment: 7 pages, 6 figures, minor revisio

Commensurability oscillations in the rf conductivity of unidirectional lateral superlattices: measurement of anisotropic conductivity by coplanar waveguide

We have measured the rf magnetoconductivity of unidirectional lateral superlattices (ULSLs) by detecting the attenuation of microwave through a coplanar waveguide placed on the surface. ULSL samples with the principal axis of the modulation perpendicular (S_perp) and parallel (S_||) to the microwave electric field are examined. For low microwave power, we observe expected anisotropic behavior of the commensurability oscillations (CO), with CO in samples S_perp and S_|| dominated by the diffusion and the collisional contributions, respectively. Amplitude modulation of the Shubnikov-de Haas oscillations is observed to be more prominent in sample S_||. The difference between the two samples is washed out with the increase of the microwave power, letting the diffusion contribution govern the CO in both samples. The failure of the intended directional selectivity in the conductivity measured with high microwave power is interpreted in terms of large-angle electron-phonon scattering.Comment: 8 pages, 5 figure

Modulation Induced Phase Transition from Fractional Quantum Hall to Stripe State at nu=5/3

We have investigated the effect of unidirectional periodic potential modulation on the fractional quantum Hall (FQH) state at filling factors nu=5/3 and 4/3. For large enough modulation amplitude, we find that the resistivity minimum at nu=5/3 gives way to a peak that grows with decreasing temperature. Density matrix renormalization group calculation reveals that phase transition from FQH state to unidirectional striped state having a period sim 4 l (with l the magnetic length) takes place at nu=1/3 (equivalent to nu=5/3 by the particle-hole symmetry) with the increase of the modulation amplitude, suggesting that the observed peak is the manifestation of the stripe phase.Comment: 4 pages, 6 figures; minor revisio

Timing and spectral studies of the transient X-ray pulsar EXO 053109-6609.2 with ASCA and Beppo-SAX

We report timing and spectral properties of the transient Be X-ray pulsar EXO 053109--6609.2 studied using observations made with the ASCA and BeppoSAX observatories. Though there must have been at least one spin-down episode of the pulsar since its discovery, the new pulse period measurements show a monotonic spin-up trend since 1996. The pulse profile is found to have marginal energy dependence. There is also evidence for strong luminosity dependence of the pulse profile, a single peaked profile at low luminosity that changes to a double peaked profile at high luminosity. This suggests a change in the accretion pattern at certain luminosity level. The X-ray spectrum is found to consist of a simple power-law with photon index in the range of 0.4--0.8. At high intensity level the spectrum also shows presence of weak iron emission line.Comment: 12 pages, 8 figures, Accepted for publication in Ap

Efficient and highly selective boron-doped carbon materials-catalyzed reduction of nitroarenes

Exploring the potential catalytic applications of boron-doped carbon materials is a fascinating challenge. Here we describe that boron-doped onion-like carbon and carbon nanotubes as metal-free catalysts exhibit excellent catalytic activity and stability in nitroarene reduction under a stoichiometric amount of reductant

Avaliação da inoculação de fungos micorrízicos arbusculares sobre a incidência da fusariose da pimenta-do-reino.

A fusariose (Fusarlum solani f. sp. piperis) da pimenta-do-reino (Piper nigrum) é a doença mais devastadora à cultura na região amazônica. As medidas de controle preconizadas são dispendiosas e não apresentam controle adequado da doença, sendo necessário estudos de novos métodos de controle. Objetiva-se avaliar a possibilidade de reduzir a incidência da fusariose, através da inoculação com fungos micorrízicos arbusculares (FMAs). Foi realizado um experimento com plântulas de pimenta-do-reino, cv. Guajarina, em casa de plástico. Utilizaram-se quatro espécies de FMA: Scutellospora sp., S_ heterogama, S. gilmorei e Entropliospora colombiana. A pré-inoculação foi feita pela deposição de solo-inóculo em contato direto com as raízes das plântulas, na fase cotiledônea, em copos de 500 mJ, contendo solo fumigado. Após três meses e meio, as plântulas foram transferidas para vasos de plásticos de quatro quilos, contendo mistura de solo fumigado e inóculo de F. solani f. sp. piperis na proporção de 0,2% (v/v). Durante o transplantio, foi feita urna reinoculação de FMA, colocando solo-inoculo das mesmas espécies no fundo do vaso de plástico. A incidência da doença foi avaliada quatro meses após o transplantio. A incidência da fusariose foi de 5%,10%,15%,35% e 85% para os tratamentos de S. gilmorei, E. colombiana, S. heterogama, Scutellospora sp. e a testemunha, respectivamente. A inoculação com FMA reduziu de 50 a 80% a incidência da doença, em relação à testemunha, sendo que S. gilmorei apresentou o maior potencial para redução da doença (80%), maior produção de matéria seca das plantas sobreviventes (11,7 g por planta) e maior percentagem do comprimento das raízes colonizadas pelo FMA (55,18%). Pelos resultados obtidos, há perspectiva de se incorporar o uso de FMA num programa de controle da fusariose de pimenta-do-reino

Excitonic Correlations in the Intermetallic Fe2VAl

The intermetallic compound Fe2VAl looks non-metallic in transport and strongly metallic in thermodynamic and photoemission data. It has in its band structure a highly differentiated set of valence and conduction bands leading to a semimetallic system with a very low density of carriers. The pseudogap itself is due to interaction of Al states with the d orbitals of Fe and V, but the resulting carriers have little Al character. The effects of generalized gradient corrections to the local density band structure as well spin-orbit coupling are shown to be significant, reducing the carrier density by a factor of three. Doping of this nonmagnetic compound by 0.5 electrons per cell in a virtual crystal fashion results in a moment of 0.5 bohr magnetons and destroys the pseudogap. We assess the tendencies toward formation of an excitonic condensate and toward an excitonic Wigner crystal, and find both to be unlikely. We propose a model is which the observed properties result from excitonic correlations arising from two interpenetrating lattices of distinctive electrons (e_g on V) and holes (t_2g on Fe) of low density (one carrier of each sign per 350 formula units).Comment: 8 2-column pages, 8 postscript figure