19 research outputs found
Universal Multifractality in Quantum Hall Systems with Long-Range Disorder Potential
We investigate numerically the localization-delocalization transition in
quantum Hall systems with long-range disorder potential with respect to
multifractal properties. Wavefunctions at the transition energy are obtained
within the framework of the generalized Chalker--Coddington network model. We
determine the critical exponent characterizing the scaling behavior
of the local order parameter for systems with potential correlation length
up to magnetic lengths . Our results show that does not
depend on the ratio . With increasing , effects due to classical
percolation only cause an increase of the microscopic length scale, whereas the
critical behavior on larger scales remains unchanged. This proves that systems
with long-range disorder belong to the same universality class as those with
short-range disorder.Comment: 4 pages, 2 figures, postsript, uuencoded, gz-compresse
Level spacings at the metal-insulator transition in the Anderson Hamiltonians and multifractal random matrix ensembles
We consider orthogonal, unitary, and symplectic ensembles of random matrices
with (1/a)(ln x)^2 potentials, which obey spectral statistics different from
the Wigner-Dyson and are argued to have multifractal eigenstates. If the
coefficient is small, spectral correlations in the bulk are universally
governed by a translationally invariant, one-parameter generalization of the
sine kernel. We provide analytic expressions for the level spacing distribution
functions of this kernel, which are hybrids of the Wigner-Dyson and Poisson
distributions. By tuning the single parameter, our results can be excellently
fitted to the numerical data for three symmetry classes of the
three-dimensional Anderson Hamiltonians at the metal-insulator transition,
previously measured by several groups using exact diagonalization.Comment: 12 pages, 8 figures, REVTeX. Additional figure and text on the level
number variance, to appear in Phys.Rev.
Perfil de resistência antimicrobiana e produção de biofilme por Staphylococcus aureus isolados de novilhas.
On BPS preons, generalized holonomies and D=11 supergravities
We develop the BPS preon conjecture to analyze the supersymmetric solutions
of D=11 supergravity. By relating the notions of Killing spinors and BPS
preons, we develop a moving G-frame method (G=GL(32,R), SL(32,R) or Sp(32,R))
to analyze their associated generalized holonomies. As a first application we
derive here the equations determining the generalized holonomies of k/32
supersymmetric solutions and, in particular, those solving the necessary
conditions for the existence of BPS preonic (31/32) solutions of the standard
D=11 supergravity. We also show that there exist elementary preonic solutions,
i.e. solutions preserving 31 out of 32 supersymmetries in a Chern--Simons type
supergravity. We present as well a family of worldvolume actions describing the
motion of pointlike and extended BPS preons in the background of a D'Auria-Fre
type OSp(1|32)-related supergravity model. We discuss the possible implications
for M-theory.Comment: 11 pages, RevTeX Typos corrected, a short note and references adde
Solar Neutrinos and the Principle of Equivalence
We study the proposed solution of the solar neutrino problem which requires a
flavor nondiagonal coupling of neutrinos to gravity. We adopt a
phenomenological point of view and investigate the consequences of the
hypothesis that the neutrino weak interaction eigenstates are linear
combinations of the gravitational eigenstates which have slightly different
couplings to gravity, and , , corresponding to a
difference in red-shift between electron and muon neutrinos, . We perform a analysis of the latest available solar
neutrino data and obtain the allowed regions in the space of the relevant
parameters. The existing data rule out most of the parameter space which can be
probed in solar neutrino experiments, allowing only for small values of the mixing angle () and for large mixing (). Measurements of the -neutrino energy spectrum in the SNO and
Super-Kamiokande experiments will provide stronger constraints independent of
all considerations related to solar models. We show that these measurements
will be able to exclude part of the allowed region as well as to distinguish
between conventional oscillations and oscillations due to the violation of the
equivalence principle.Comment: 20 pages + 4 figures, IASSNS-AST 94/5
A social and ecological assessment of tropical land uses at multiple scales: the Sustainable amazon network
Science has a critical role to play in guiding more sustainable development trajectories. Here, we present the Sustainable Amazon Network (Rede Amazônia Sustentável, RAS): a multidisciplinary research initiative involving more than 30 partner organizations working to assess both social and ecological dimensions of land-use sustainability in eastern Brazilian Amazonia. The research approach adopted by RAS offers three advantages for addressing land-use sustainability problems: (i) the collection of synchronized and co-located ecological and socioeconomic data across broad gradients of past and present human use; (ii) a nested sampling design to aid comparison of ecological and socioeconomic conditions associated with different land uses across local, landscape and regional scales; and (iii) a strong engagement with a wide variety of actors and non-research institutions. Here, we elaborate on these key features, and identify the ways in which RAS can help in highlighting those problems in most urgent need of attention, and in guiding improvements in land-use sustainability in Amazonia and elsewhere in the tropics. We also discuss some of the practical lessons, limitations and realities faced during the development of the RAS initiative so far
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A social and ecological assessment of tropical land uses at multiple scales: the Sustainable Amazon Network
Science has a critical role to play in guiding more sustainable development trajectories. Here, we present the Sustainable Amazon Network (Rede Amazonia Sustentavel, RAS): a multidisciplinary research initiative involving more than 30 partner organizations working to assess both social and ecological dimensions of land-use sustainability in eastern Brazilian Amazonia. The research approach adopted by RAS offers three advantages for addressing land-use sustainability problems: (i) the collection of synchronized and co-located ecological and socioeconomic data across broad gradients of past and present human use; (ii) a nested sampling design to aid comparison of ecological and socioeconomic conditions associated with different land uses across local, landscape and regional scales; and (iii) a strong engagement with a wide variety of actors and non-research institutions. Here, we elaborate on these key features, and identify the ways in which RAS can help in highlighting those problems in most urgent need of attention, and in guiding improvements in land-use sustainability in Amazonia and elsewhere in the tropics. We also discuss some of the practical lessons, limitations and realities faced during the development of the RAS initiative so far.Keywords: Social–ecological systems, Tropical forests, Land use, Interdisciplinary research, Sustainability, Trade-off
Aproximando XML ao mundo Relacional Um Framework para Consultas Genéricas a Banco de Dados
TCC (graduação) - Universidade Federal de Santa Catarina. Centro Tecnológico. Curso de Ciências da Computação.Sem resumo
Aspectos epidemiológicos da mastite bovina causada por Staphylococcus aureus.
A finalidade deste trabalho foi monitorar os casos de mastite bovina e verificar a presença de Staphylococcus aureus com agente etiológicoda doença. A sua presença em diferentes sítios de localização e a relação entre o aparecimento da doença e as características ambientais foram acompanhadas