Reentrant quantum Hall effect in bilayer system at high filling factors

We report on the measurements of the quantum Hall effect states in double quantum well structures at the filling factors v = 4N + 1 and 4N + 3, where N is the Landau index number, in the presence of the in-plane magnetic field. The quantum Hall states at these filling factors vanish and reappear several times. Repeated reentrance of the transport gap occurs due to the periodic vanishing of the tunneling amplitude in the presence of the in-plane field. When the gap vanishes, the transport becomes anisotropic. The anisotropy persist at half-odd filling factors, when bilayer quantum Hall states are recovered with increase of the tilt angle. (C) 2007 Elsevier B.V. All rights reserved.

Effect of Ti-C and Cr Additions on Magnetic Properties of Nanocrystalline (Pr,Nd)-Fe-B Alloys

The addition of both Ti-C and Cr as grain refiners in Nd-Fe-B nanocomposites substantially increases the coercive field Hc. This motived our investigation of the effect of Ti-C and Cr on Pr-Fe-B nanocomposites. Melt-spun ribbons of composition (Pr(9.5)Fe(84.5)B(6))(0.97-x)Cr(x)(TiC)(0.03)(x = 0; 0.25; 0.5; 0.75; 1) and (Nd(9.5)Fe(84.5)B(6))(0.97-x)Cr(x)(TiC)(0.03)(x = 0.5 and 1) were produced for study. For a Pr nanocomposite with 1% Cr, Hc = 12.5 kOe. However, the energy product was limited to 13.6 MGOe by the remanence value. Rietveld analysis of X-ray spectra showed the ribbons to consist of predominantly hard (similar to 70 wt%) R(2)Fe(14)B, the soft phase being (similar to 30 wt%) alpha-Fe. Mossbauer measurements at 300 K are consistent with a reduced hyperfine field for the hard magnetic phase due to the Cr addition. Analysis of transmission electron microscopy images showed the Pr nanocomposite with 1% Cr to have an increased average grain size.

Coherent and semiclassical states in a magnetic field in the presence of the Aharonov-Bohm solenoid

A new approach to constructing coherent states (CS) and semiclassical states (SS) in a magnetic-solenoid field is proposed. The main idea is based on the fact that the AB solenoid breaks the translational symmetry in the xy-plane; this has a topological effect such that there appear two types of trajectories which embrace and do not embrace the solenoid. Due to this fact, one has to construct two different kinds of CS/SS which correspond to such trajectories in the semiclassical limit. Following this idea, we construct CS in two steps, first the instantaneous CS (ICS) and then the time-dependent CS/SS as an evolution of the ICS. The construction is realized for nonrelativistic and relativistic spinning particles both in (2 + 1) and (3 + 1) dimensions and gives a non-trivial example of SS/CS for systems with a nonquadratic Hamiltonian. It is stressed that CS depending on their parameters (quantum numbers) describe both pure quantum and semiclassical states. An analysis is represented that classifies parameters of the CS in such respect. Such a classification is used for the semiclassical decompositions of various physical quantities.

The effect of the negative coupling parameter on the spectrum of a trapped Bose gas

The interest in attractive Bose-Einstein Condensates arises due to the chemical instabilities generate when the number of trapped atoms is above a critical number. In this case, recombination process promotes the collapse of the cloud. This behavior is normally geometry dependent. Within the context of the mean field approximation, the system is described by the Gross-Pitaevskii equation. We have considered the attractive Bose-Einstein condensate, confined in a nonspherical trap, investigating numerically and analytically the solutions, using controlled perturbation and self-similar approximation methods. This approximation is valid in all interval of the negative coupling parameter allowing interpolation between weak-coupling and strong-coupling limits. When using the self-similar approximation methods, accurate analytical formulas were derived. These obtained expressions are discussed for several different traps and may contribute to the understanding of experimental observations.

PL spectroscopy of Fermi electrons in regime of the quantum Hall effect

The influence of the interlayer coupling on formation of the quantized Hall phase at the filling factor v = 2 was studied in the multilayer GaAs/AlGaAs heterostructures The disorder broaden Gaussian photoluminescence line due to the localized electrons was found in the quantized Hall phase of the isolated multi-quantum well structure On the other hand. the quantized Hall phase of the weakly-coupled multilayers emitted an asymmetrical line similar to that one observed in the metallic electron systems. We demonstrated that the observed asymmetry indicates a formation of the Fermi Surface in the quantized Hall phase of the multilayer electron system due to the interlayer peicolation. A sharp decrease of the single-particle scattering time associated with the extended states oil the Fermi surface was observed at the filling factor v = 2. (C) 2009 Elsevier B.V All rights reserved

Number of particle creation and decoherence in the nonideal dynamical Casimir effect at finite temperature

In this work we investigate the dynamical Casimir effect in a nonideal cavity by deriving an effective Hamiltonian. We first compute a general expression for the average number of particle creation, applicable for any law of motion of the cavity boundary, under the only restriction of small velocities. We also compute a general expression for the linear entropy of an arbitrary state prepared in a selected mode, also applicable for any law of motion of a slow moving boundary. As an application of our results we have analyzed both the average number of particle creation and linear entropy within a particular oscillatory motion of the cavity boundary. On the basis of these expressions we develop a comprehensive analysis of the resonances in the number of particle creation in the nonideal dynamical Casimir effect. We also demonstrate the occurrence of resonances in the loss of purity of the initial state and estimate the decoherence times associated with these resonances. Since our results were obtained in the framework of the perturbation theory, they are restricted, under resonant conditions, to a short-time approximation. (C) 2009 Elsevier Inc. All rights reserved.

The Sphene-Centered Ocellar Texture: An Effect of Grain-Supported Flow and Melt Migration in a Hyperdense Magma Mush

The sphene-centered ocellar texture consists of leucocratic ocelli with sphene (titanite) crystals at the center, enclosed in a biotite-rich matrix. This texture has been recognized worldwide in hybrid intermediate rocks. On the basis of structural, petrological, and geochronological data from selected outcrops of the Variscan Ribadelago pluton (NW Iberian Massif), we propose that the ocelli were formed by migration and accumulation of a residual melt through a plagioclase- and biotite-dominated crystalline framework. At the late stage of crystallization, the magma acted as a hyperdense suspension and reacted to the pressure gradient caused by the regional stress field, entering the domain of grain-supported flow. Microstructures reveal that aligned crystal domains arose in the crystal framework from the shearing and compaction of the crystal mush and behaved as magmatic microshears. Relative displacement of adjacent crystal clusters along these microshears corresponded to the onset of Reynolds dilatancy that generated an expansion of the crystal mush, involving melt migration and pore aperture. The mineralogy of the ocelli, dominated by andesine and sphene, represents the composition of the migrating melt. The chemistry of this late, Ti-rich melt stems from the incongruent melting of biotite. Magmatic sphene from the ocelli yields a U-Pb age of 317 +/- 1 Ma, which represents the final crystallization of the hybridized magmatic system. Moreover, this texture offers an opportunity to better understand the rheological behavior of highly crystallized magmas.

Pseudomonas aeruginosa PA14 cupD transcription is activated by the RcsB response regulator, but repressed by its putative cognate sensor RcsC

The opportunistic pathogen Pseudomonas aeruginosa PA14 possesses four fimbrial cup clusters, which may confer the ability to adapt to different environments. cupD lies in the pathogenicity island PAPI-1 next to genes coding for a putative phosphorelay system composed of the hybrid histidine kinase RcsC and the response regulator RcsB. The main focus of this work was the regulation of cupD at the mRNA level. It was found that the HN-S-like protein MvaT does not exert a strong influence on cupD transcript levels, as it does for cupA. cupD transcription is higher in cultures grown at 28 degrees C, which agrees with a cupD mutant presenting attenuated virulence only in a plant model, but not in a mouse model of infection. Whereas an rcsC in-frame deletion mutant presented higher levels of cupD mRNA, rcsB deletion had the opposite effect. Accordingly, overexpression of RcsB increased the levels of cupD transcription, and promoted biofilm formation and the appearance of fimbriae. A single transcription start site was determined for cupD and transcription from this site was induced by RcsB. A motif similar to the enterobacterial RcsB/RcsA-binding site was detected adjacent to the -35 region, suggesting that this could be the RcsB-binding site. Comparison of P. aeruginosa and Escherichia coli Rcs may provide insights into how similar systems can be used by different bacteria to control gene expression and to adapt to various environmental conditions.

The effect of hydrophobic and hydrophilic fumed silica on the rheology of magnetorheological suspensions

We investigate magnetorheological fluids (MRFs) prepared with carbonyl iron powder and different types of hydrophobic and hydrophilic fumed silica. The rheological properties of the MRF suspensions were investigated with and without an applied magnetic field. The MRF samples prepared with hydrophobic silicas presented a more pronounced thixotropic effect and a higher recovery rate than those prepared with hydrophilic silicas. The application of a magnetic field to all the MRFs samples investigated leads to an increase in the viscosity and the thixotropic effect. MRF prepared with hydrophobic silicas presented smaller values of the viscosity than those prepared with hydrophilic silicas. At low applied magnetic fields, the type of the silica used to prepare the MRF leads to noticeable differences in the shear stress. However, these differences disappear at high magnetic fields. The results obtained showed that MRF samples prepared with the hydrophobic silica with the biggest particle diameter presented better characteristics for magnetorheological fluids, with higher values of yield stress, recovery rate, and elastic modulus. (C) 2009 The Society of Rheology. [DOI: 10.1122/1.3086870]

The electrochemical effect of acid functionalisation of carbon nanotubes to be used in sensors development

The electrochemical behaviour of multi-walled carbon nanotubes was compared with that of glassy carbon, and the differences were investigated by cyclic voltammetry and electrochemical impedance spectroscopy before and after acid pre-treatment. The electrochemical techniques showed that acid functionalisation significantly improves the electrocatalytic properties of carbon nanotubes. These electrocatalytic properties enhance the analytical signal, shift the oxidation peak potential to a less positive value, and the charge-transfers rate increase of both dopamine and K(4)[Fe(CN)(6)]. The functionalisation step and the resulting appearance of edge planes covered with different chemical groups were confirmed by FTIR measurements. Carbon nanotubes after acid pre-treatment are a potentially powerful analytical tool for sensor development. (C) 2010 Elsevier B.V. All rights reserved.

Al-based anodic oxide films structure observation using field emission gun scanning electron microscopy

In the present work, the anodic oxide films of Al, Al-Cu 4.5% and Al-Si 6.5% alloys are formed using direct and pulse current. In the case of Al-Cu and Al-Si alloys, the electrolyte used contains sulfuric acid and oxalic acid, meanwhile for Al the electrolyte contains sulfuric acid only. Al-Cu alloy was submitted to a heat treatment in order to decrease the effect of inter metallic phase theta upon the anodic film structure. Fractured samples were observed using a field emission gun scanning electron microscope JSM-6330F at (LME)/Brazilian Synchrotron Light Laboratory (LNLS), Campinas, SP, Brazil. The oxide film images enable evaluation of the pore size and form with a resolution similar to the transmission electron microscope (TEM) resolution. It is also observed that the anodizing process using pulse current produces an irregular structure of pore walls, and by direct cur-rent it is produced a rectilinear pore wall. (c) 2005 Elsevier B.V. All rights reserved.

Glyphosate has low toxicity to citrus plants growing in the field

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effects of plant densities and management of purple nutsedge on sugarcane yield and effect of growth stages and main way of herbicides contact and absorption on the control of tubers

Field experiments carried out with Cyperus rotundus L. at low (58-246), medium (318773), and high (675-1198 shoots/m(2)) densities showed sugarcane yield reductions of 13.5, 29.3, and 45.2%, respectively in relation to the control. In the second field experiment, the integration of a mechanic method with two sequences of plowing and disking operations in the dry season, and complementary applications of trifloxysulfuron-sodium + ametrine and sulfentrazone (rainy season) was studied. Average of the chain connected to original shoot showed 92, 95, and 65% of reduction with trifloxysulfuron-sodium + ametrine and surfactant, at the application stages early, preflowering, and full flowering, respectively.

Effect of diameter of the cotton squares in the development of boll weevil

O objetivo deste trabalho foi estudar o efeito do diâmetro dos botões florais de algodoeiro na massa corporal de adultos do bicudo-do-algodoeiro, Anthonomus grandis Boheman (Coleoptera: Curculionidae). O experimento foi realizado em condições de campo e laboratório, em Jaboticabal (SP), Brasil. Foram realizadas seis amostragens, coletando-se ao acaso dez plantas nas cultivares Coodetec 405 e Fibermax 986, avaliando-se o número e o diâmetro de botões florais. Os botões florais com orifícios de oviposição foram individualizados em frascos e observados diariamente para a visualização da emergência dos adultos. Botões florais com maiores diâmetros proporcionam maior massa corporal de adultos de A. grandis recém-emergidos nas duas cultivares.

Effect of sequence of insemination after simultaneous thawing of multiple semen straws on conception rate to timed AI in suckled multiparous Nelore cows

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)