Effect of nanosize BaZrO3 inclusions on vortex parameters in YBaCuO

We report on the field dependence of the microwave complex resistivity data in YBa$_2$Cu$_3$O$_{7-x}$/BaZrO$_3$ films grown by PLD at various BaZrO$_3$ content. The data, analyzed within a recently developed general framework for the mixed-state microwave response of superconductors, yield the field dependence of the fluxon parameters such as the vortex viscosity and the pinning constant. We find that pinning undergoes a change of regime when the BaZrO$_3$ content in the target increases from 2.5 mol.% to 5 mol.%. Simultaneously, the vortex viscosity becomes an increasing function of the applied magnetic field. We propose a scenario in which flux lines are pinned as bundles, and a crossover from dilute point pins to dense c-axis correlated defects takes place between 2.5 and 5 mol.% in the BZO concentration. Our data are inconsistent with vortices occupying mainly the BaZrO$_3$ sites at low fields, and suggest instead that vortices occupy both BaZrO$_3$ sites and interstitials in the YBa$_2$Cu$_3$O$_{7-x}$ matrix, even at low fields.Comment: Presented at EUCAS 2009, to be published in J. Phys.:Conf. Serie

Anisotropy and directional pinning in YBaCuO with BaZrO3 nanorods

Measurements of anisotropic transport properties (dc and high-frequency regime) of driven vortex matter in YBa$_2$Cu$_3$O$_{7-x}$ with elongated strong-pinning sites (c-axis aligned, self-assembled BaZrO$_3$ nanorods) are used to demonstrate that the effective-mass angular scaling takes place only in intrinsic physical quantities (flux-flow resistivity), and not in pinning-related Labusch parameter and critical currents. Comparison of the dynamics at different time scales shows evidence for a transition of the vortex matter toward a Mott phase, driven by the presence of nanorods. The strong pinning in dc arises partially from a dynamic effect.Comment: 4 pages, 4 figures. Accepted for publication on Applied Physics Letters. With respect to v1: changed title, slightly shortene

Slow down of a globally neutral relativistic e−e+e^-e^+ beam shearing the vacuum

The microphysics of relativistic collisionless sheared flows is investigated in a configuration consisting of a globally neutral, relativistic $e^-e^+$ beam streaming through a hollow plasma/dielectric channel. We show through multidimensional PIC simulations that this scenario excites the Mushroom instability (MI), a transverse shear instability on the electron-scale, when there is no overlap (no contact) between the $e^-e^+$ beam and the walls of the hollow plasma channel. The onset of the MI leads to the conversion of the beam's kinetic energy into magnetic (and electric) field energy, effectively slowing down a globally neutral body in the absence of contact. The collisionless shear physics explored in this configuration may operate in astrophysical environments, particularly in highly relativistic and supersonic settings where macroscopic shear processes are stable

Reply to "Comment on 'Quantization of FRW spacetimes in the presence of a cosmological constant and radiation'"

The Comment by Amore {\it et al.} [gr-qc/0611029] contains a valid criticism of the numerical precision of the results reported in a recent paper of ours [Phys. Rev. D {\bf 73}, 044022 (2006)], as well as fresh ideas on how to characterize a quantum cosmological singularity. However, we argue that, contrary to what is suggested in the Comment, the quantum cosmological models we studied show hardly any sign of singular behavior.Comment: 4 pages, accepted by Physical Review

Selection of indicator species of the tembotrione sorption in soils with different attributes

Studies on herbicide behavior in soils may be performed using biological and chemical methods. The efficiency of the biological method depends on the indicator species sensitivity to low herbicide concentrations in the soil solution. Among the herbicides commonly used in Brazil for corn cultivation, tembotrione stands out. In the last agricultural seasons, the intoxication of some crops when cultivated in succession to corn has been reported, which may be attributed to tembotrione recommendations without the knowledge of their interactions with colloids of tropical soils. In this research, we selected an indicator plant species of tembotrione residues in the soil after sorting 12 species. The sorption of this herbicide was estimated in two Oxisols (Latossolo Amarelo and Latossolo Vermelho-Amarelo, Brazilian Soil Classification) and in a Histosol (Organossolo, Brazilian Soil Classification) with different attributes. Initially, after sorting the 12 plant species, the two most efficient in detecting tembotrione in the soil were selected. In the second stage, the most sensitive species was selected. In the third stage, tembotrione sorption was assessed in the three soils by using the selected species. Among the 12 species, Beta vulgaris and Brassica oleracea var. capitata were the most efficient in detecting tembotrione at low concentrations in the soil, being B. vulgaris (beet) the most sensitive. Thus, due to its ease of cultivation, high sensitivity, and fast initial growth, beet can be used as an indicator species of tembotrione presence in the soil solution. The sorption of this herbicide was higher in the Histosol and it is directly related to the organic matter content.Estudos sobre o comportamento de herbicidas no solo podem ser realizados utilizando métodos biológicos e químicos. A condição para o método biológico ser eficiente depende da sensibilidade da espécie indicadora às baixas concentrações do herbicida na solução do solo. Entre os herbicidas comumente usados no Brasil para a cultura do milho, destaca-se o tembotrione; nas últimas safras, tem-se relatado intoxicação de algumas culturas quando cultivadas em sucessão a esta cultura. Esse fato pode ser atribuído a recomendações do tembotrione sem o conhecimento de suas interações com os coloides dos solos tropicais. Nesta pesquisa, selecionou-se uma espécie vegetal indicadora de resíduos do tembotrione no solo, após a triagem de 12 espécies. Estimou-se em seguida a sorção desse herbicida em Latossolo Amarelo, Organossolo e Latossolo Vermelho-Amarelo com diferentes atributos. Inicialmente, após a triagem das 12 espécies vegetais, selecionaram-se as duas mais eficientes em detectar o tembotrione no solo. Na segunda etapa, foi selecionada a espécie mais sensível. Na terceira, foi avaliada a sorção do tembotrione nos três solos utilizando a espécie selecionada. Das 12 espécies avaliadas, Beta vulgaris e Brassica oleracea var. capitata foram as mais eficientes em detectar o tembotrione em baixas concentrações no solo, sendo B. vulgaris (beterraba) a mais sensível. Conclui-se que a beterraba, pela sua facilidade de cultivo, alta sensibilidade e rápido crescimento inicial, pode ser usada como espécie indicadora da presença do tembotrione na solução do solo. A sorção desse herbicida foi maior no Organossolo e está diretamente relacionada ao teor de matéria orgânica