316 research outputs found
Armazenamento de sementes de Louro-pardo (Cordia trichotoma (VELL.) ARRB. ex STEUD.).
bitstream/item/101584/1/1984-PA17-Zanon-ArmazenamentoSementes0001.pd
Noncommutative Gravity in two Dimensions
We deform two-dimensional topological gravity by making use of its gauge
theory formulation. The obtained noncommutative gravity model is shown to be
invariant under a class of transformations that reduce to standard
diffeomorphisms once the noncommutativity parameter is set to zero. Some
solutions of the deformed model, like fuzzy AdS_2, are obtained. Furthermore,
the transformation properties of the model under the Seiberg-Witten map are
studied.Comment: 20 pages, LaTeX, references and some comments adde
Superfield covariant analysis of the divergence structure of noncommutative supersymmetric QED
Commutative supersymmetric Yang-Mills is known to be renormalizable for
, while finite for . However, in the
noncommutative version of the model (NCSQED) the UV/IR mechanism gives rise
to infrared divergences which may spoil the perturbative expansion. In this
work we pursue the study of the consistency of NCSQED by working
systematically within the covariant superfield formulation. In the Landau
gauge, it has already been shown for that the gauge field
two-point function is free of harmful UV/IR infrared singularities, in the
one-loop approximation. Here we show that this result holds without
restrictions on the number of allowed supersymmetries and for any arbitrary
covariant gauge. We also investigate the divergence structure of the gauge
field three-point function in the one-loop approximation. It is first proved
that the cancellation of the leading UV/IR infrared divergences is a gauge
invariant statement. Surprisingly, we have also found that there exist
subleading harmful UV/IR infrared singularities whose cancellation only takes
place in a particular covariant gauge. Thus, we conclude that these last
mentioned singularities are in the gauge sector and, therefore, do not
jeopardize the perturbative expansion and/or the renormalization of the theory.Comment: 36 pages, 11 figures. Minor correction
Variação genética e seleção para características de crescimento em teste de progênies de Mimosa scabrella var. aspericarpa.
Estimativas de parâmetros genéticos foram obtidas para progênies de meiosirmãos de Mimosa scabrella var. aspericarpa, oriundas de talhões comerciais de duas localidades do Estado do Paraná: Bocaiúva do Sul e Campo Largo. O material genético foi instalado em Colombo-PR, no delineamento de blocos casualizados com quatro repetições e dez plantas por parcela. O experimento foi avaliado aos três anos de idade. As estimativas de herdabilidade mostraram um razoável controle genético para as características de crescimento, indicando boas possibilidades de seleção nesse material. Os progressos genéticos foram estimados por meio de três métodos de seleção, ao nível de bloco: a) seleção individual; b) seleção combinada e c) índice multi-efeitos. Os ganhos genéticos previstos para o volume cilíndrico das árvores, obtidos por seleção através do DAP, foram superiores a 52% para a população de Bocaiúva do Sul e superiores a 35% para a população de Campo Largo, independente do método utilizado. O ganho genético adicional previsto por meio do método do índice multi-efeitos foi de pequena magnitude, em termos percentuais, em relação aqueles obtidos por seleção individual e seleção combinada. Contudo, o método do índice multi-efeitos deve ser utilizado por propiciar maior acurácia e não implicar em custos adicionais ao processo seletivo. Além disso, pequenos ganhos podem ser significativos considerando-se que, normalmente, os reflorestamentos abrangem grandes áreas
w_{\infty} Algebras, Conformal Mechanics, and Black Holes
We discuss BPS solitons in gauged , D=4 supergravity. The
solitons represent extremal black holes interpolating between different vacua
of anti-de Sitter spaces. The isometry superalgebras are determined and the
motion of a superparticle in the extremal black hole background is studied and
confronted with superconformal mechanics. We show that the Virasoro symmetry of
conformal mechanics, which describes the dynamics of the superparticle near the
horizon of the extremal black hole under consideration, extends to a symmetry
under the algebra of area-preserving diffeomorphisms. We find that
a Virasoro subalgebra of can be associated to the Virasoro algebra
of the asymptotic symmetries of . In this way spacetime diffeomorphisms
of translate into diffeomorphisms in phase space: our system offers an
explicit realization of the correspondence. Using the
dimensionally reduced action, the central charge is computed. Finally, we also
present generalizations of superconformal mechanics which are invariant under
and superextensions of .Comment: Latex, 23 pages, minor errors corrected, references added; final
version to appear in Class. Quant. Gra
Non-commutative U(1) Super-Yang-Mills Theory: Perturbative Self-Energy Corrections
The quantization of the non-commutative N=1, U(1) super-Yang-Mills action is
performed in the superfield formalism. We calculate the one-loop corrections to
the self-energy of the vector superfield. Although the power-counting theorem
predicts quadratic ultraviolet and infrared divergences, there are actually
only logarithmic UV and IR divergences, which is a crucial feature of
non-commutative supersymmetric field theories.Comment: 18 pages, latex, uses feynmf package; references added, Wess-Zumino
gauge remove
A New Spin-Orbit Induced Universality Class in the Quantum Hall Regime ?
Using heuristic arguments and numerical simulations it is argued that the
critical exponent describing the localization length divergence at the
quantum Hall transition is modified in the presence of spin-orbit scattering
with short range correlations. The exponent is very close to , the
percolation correlation length exponent, the prediction of a semi-classical
argument. In addition, a region of weakly localized regime, where the
localization length is exponentially large, is conjectured.Comment: 4 two-column pages including 4 eps figure
Exact results in planar N=1 superconformal Yang-Mills theory
In the \beta-deformed N=4 supersymmetric SU(N) Yang-Mills theory we study the
class of operators O_J = Tr(\Phi_i^J \Phi_k), i\neq k and compute their exact
anomalous dimensions for N,J\to\infty. This leads to a prediction for the
masses of the corresponding states in the dual string theory sector. We test
the exact formula perturbatively up to two loops. The consistency of the
perturbative calculation with the exact result indicates that in the planar
limit the one--loop condition g^2=h\bar{h} for superconformal invariance is
indeed sufficient to insure the {\em exact} superconformal invariance of the
theory. We present a direct proof of this point in perturbation theory. The O_J
sector of this theory shares many similarities with the BMN sector of the N=4
theory in the large R--charge limit.Comment: LaTex, 14 pages, 3 figures; v2: minor corrections and one reference
adde
The Asymptotic Dynamics of two-dimensional (anti-)de Sitter Gravity
We show that the asymptotic dynamics of two-dimensional de Sitter or anti-de
Sitter Jackiw-Teitelboim (JT) gravity is described by a generalized
two-particle Calogero-Sutherland model. This correspondence is established by
formulating the JT model of (A)dS gravity in two dimensions as a topological
gauge theory, which reduces to a nonlinear 0+1-dimensional sigma model on the
boundary of (A)dS space. The appearance of cyclic coordinates allows then a
further reduction to the Calogero-Sutherland quantum mechanical model.Comment: 16 pages, LaTeX, no figures, uses JHEP.cls. v2: Some references and
comments added. v3: Minor errors correcte
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