Magnetic Fields In Astrophysical Objects

Magnetic fields are known to reside in many astrophysical objects and are now believed to be crucially important for the creation of phenomena on a wide variety of scales. However, the role of the magnetic field in the bodies that we observe has not always been clear. In certain situations, the importance of a magnetic field has been over looked on the grounds that the large-scale magnetic field was believed to be too weak to play and important role in the dynamics. In this article I discuss some of the recent developments concerning magnetic fields in stars, planets and accretion discs. I choose to emphasise some of the situations where it has been suggested that weak magnetic fields may play a more significant role than previously thought. At the end of the article I list some of the questions to be answered in the future.Comment: 11 pages, 5 figures, to appear in Phil. Trans.

Influence of frustration on a d=3 diluted antiferromagnet: FexZn1−xF2Fe_{x}Zn_{1-x}F_{2}

The influence of a frustrated bond on the magnetic properties of a d=3 uniaxial (Ising) b.c.c. diluted antiferromagnet, with emphasis in the compound $Fe_{x}Zn_{1-x}F_{2}$, is investigated by a local mean-field numerical simulation. In particular we find that the initial drop of the saturation staggered magnetization ($M_{S}$) with concentration follows a percolation-like phenomenon characterized by an exponent $\beta_{p}$. For the frustrated samples, however, this regime is followed by a second one identified by a ``long tail" effect such that $M_{S}$ is zero only at the percolation threshold. Our numerical data also confirms a spin-glass phase near this threshold.Comment: 11 pages (Latex) with 3 uuencoded postscript figure

T-duality of axial and vector dyonic integrable models

A general construction of affine Non Abelian (NA) - Toda models in terms of axial and vector gauged two loop WZNW model is discussed. They represent {\it integrable perturbations} of the conformal $\sigma$-models (with tachyons included) describing (charged) black hole type string backgrounds. We study the {\it off-critical} T-duality between certain families of axial and vector type of integrable models for the case of affine NA- Toda theories with one global U(1) symmetry. In particular we find the Lie algebraic condition defining a subclass of {\it T-selfdual} torsionless NA Toda models and their zero curvature representation.Comment: 20 pages, latex, no figures,improvments in the text of Sects.1,2 and 6;typos corrected,references added, to appear in Ann. of Physics (NY

Collapse of ρxx\rho_{xx} ringlike structures in 2DEGs under tilted magnetic fields

In the quantum Hall regime, the longitudinal resistivity $\rho_{xx}$ plotted as a density--magnetic-field ($n_{2D}-B$) diagram displays ringlike structures due to the crossings of two sets of spin split Landau levels from different subbands [e.g., Zhang \textit{et al.}, Phys. Rev. Lett. \textbf{95}, 216801 (2005)]. For tilted magnetic fields, some of these ringlike structures "shrink" as the tilt angle is increased and fully collapse at $\theta_c \approx 6^\circ$. Here we theoretically investigate the topology of these structures via a non-interacting model for the 2DEG. We account for the inter Landau-level coupling induced by the tilted magnetic field via perturbation theory. This coupling results in anti-crossings of Landau levels with parallel spins. With the new energy spectrum, we calculate the corresponding $n_{2D}-B$ diagram of the density of states (DOS) near the Fermi level. We argue that the DOS displays the same topology as $\rho_{xx}$ in the $n_{2D}-B$ diagram. For the ring with filling factor $\nu=4$, we find that the anti-crossings make it shrink for increasing tilt angles and collapse at a large enough angle. Using effective parameters to fit the $\theta = 0^\circ$ data, we find a collapsing angle $\theta_c \approx 3.6^\circ$. Despite this factor-of-two discrepancy with the experimental data, our model captures the essential mechanism underlying the ring collapse.Comment: 3 pages, 2 figures; Proceedings of the PASPS V Conference Held in August 2008 in Foz do Igua\c{c}u, Brazi

Dyonic Integrable Models

A class of non abelian affine Toda models arising from the axial gauged two-loop WZW model is presented. Their zero curvature representation is constructed in terms of a graded Kac-Moody algebra. It is shown that the discrete multivacua structure of the potential together with non abelian nature of the zero grade subalgebra allows soliton solutions with non trivial electric and topological charges. The dressing transformation is employed to explicitly construct one and two soliton solutions and their bound states in terms of the tau functions. A discussion of the classical spectra of such solutions and the time delays are given in detail.Comment: Latex 30 pages, corrected some typo

A new variety of purple tomato as a rich source of bioactive carotenoids and its potential health benefits

Carotenoid-rich fractions (CRF) from pulp and peel of a new variety of purple tomato were investigated in comparison to a Red Cherry variety regarding carotenoids characterization, antioxidant capacity, and inhibition of proliferation of four tumor cell lines. CRF from peel of Purple tomato contains lutein, lycopene, and β-carotene up to 6, 1.5, and 2.5 times more than that of Red Cherry and it exhibited the highest antioxidant activity at 400 μg/mL, reaching 82% and 97% in DPPH and ABTS þ assays, respectively. Besides that, the Purple peel showed the highest scavenging lipoperoxides capacity as well as displayed the highest ferric reducing antioxidant power compared to the other CRF. In turn, the Red Cherry pulp CRF showed the highest antiproliferative activity against four tumor cell lines (MCF-7, NCI-H460, HeLa, and HepG2) at non-toxic concentrations. High concentration of neurosporene, and lycopene in Red Cherry pulp CRF show to be related to the good antiproliferative activity found on it. Therefore, this new variety of nutrient-rich purple tomato could be explored as well as the commercial variety Red Cherry, since both are good sources of dietary carotenoids with health-promoting properties.This work was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) [grant number 2014/11150-6]; and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) [grant numbers 306722/2012-7, 307040/2014-3, and 150015/2018-6) from Brazil; and Fundação para a Ciência e a Tecnologia (FCT) for CIMO [grant numbers Pest OE/AGR/UI0690/2014; SFRH/BPD/68344/2010] from Portugal.info:eu-repo/semantics/publishedVersio

Mudanças espaço temporal da disponibilidade de serviços ecossistêmicos em uma microbacia hidrográfica do nordeste brasileiro. Spatial and temporal changes of the ecosystem services availability in a microwatershed in Northeast Brazil.

A mudança no uso e ocupação da terra altera a dinâmica de ecossistemas e afeta a provisão de serviços ecossistêmicos, que são a base para a manutenção da vida e do bem-estar físico, mental e espiritual humano. Nesse contexto, o estabelecimento humano em países em desenvolvimento ocorreu, de modo geral, de forma desordenada e sem planejamento, ocasionando deterioração ambiental. No nordeste brasileiro, onde o recurso hídrico é escasso, as aglomerações humanas tendem a ocorrer próximas à rede hídrica, elevando a pressão antrópica sobre esse recurso. Este trabalho analisa as alterações na provisão de serviços ecossistêmicos na Microbacia Hidrográfica Riacho das Piabas, Paraíba, Brasil, associadas a mudanças do uso e ocupação da terra entre os anos de 1989, 2007 e 2014. Mudanças no uso e ocupação da terra foram identificadas e quantificadas por meio de técnicas de sensoriamento remoto e sistema de informação geográfica. Os serviços ecossistêmicos foram analisados por meio de média de valor monetário estimado de serviço ecossistêmico (VSE) disponível na literatura, utilizando o método de transferência de benefício. Em 1989, o valor total de serviço ecossistêmico foi estimado em US$7,18 milhões, reduzindo para US$ 3,73 milhões em 2007 e US$ 2,72 milhões em 2014. Houve aumento de 115% de área construída entre 1989 e 2014, resultando em redução de serviços ecossistêmicos de 62% entre os anos de 1989 e 2014. O declínio do VSE reflete o impacto negativo do processo de urbanização na manutenção de serviços ecossistêmicos, sobretudo os ofertados pela vegetação. A categoria vegetação arbórea foi a mais valiosa para a área de estudo, disponibilizando maior número de funções ecossistêmicas com alto VSE. Entretanto, foi a categoria que mais perdeu área ao longo dos anos. Portanto, é fundamental planejar, criar e manter áreas verdes para minorar os impactos do processo de urbanização na provisão de serviços ecossistêmicos

Predição De Classes De Solo Por Mineração De Dados Em área Da Bacia Sedimentar Do São Francisco

The objective of this work was to evaluate different strategies for the prediction of soil class distribution on digital soil maps of areas without reference data, in the sedimentary basin of San Francisco, in the north of the state of Minas Gerais, Brazil. The strategies included: Taxonomic generalization, training by field observations, training set expansion, and the use of different data mining algorithms. Four matrices were developed, differentiated by the volume of data for machine learning and by soil taxonomic levels to be predicted. The performance of the machine learning algorithms-Random Forest, J48, and MLP-, associated with discretization, class balancing, variable selection, and expansion of the training set was evaluated. Class balancing, variable discretization by equal frequencies, and the Random Forest algorithm showed the best performances. The representativeness extension of field observations, that assumes a larger training area, brought no predictive gain. Soil taxonomic generalization to the suborder level reduces the fragmentation of mapped polygons and improves the accuracy of digital soil maps. When generated by training on in situ soil observations at the mapping area, digital soil maps are as accurate as those trained on preexistent maps.5191396140