7,457 research outputs found
N=2 Boundary conditions for non-linear sigma models and Landau-Ginzburg models
We study N=2 nonlinear two dimensional sigma models with boundaries and their
massive generalizations (the Landau-Ginzburg models). These models are defined
over either Kahler or bihermitian target space manifolds. We determine the most
general local N=2 superconformal boundary conditions (D-branes) for these sigma
models. In the Kahler case we reproduce the known results in a systematic
fashion including interesting results concerning the coisotropic A-type branes.
We further analyse the N=2 superconformal boundary conditions for sigma models
defined over a bihermitian manifold with torsion. We interpret the boundary
conditions in terms of different types of submanifolds of the target space. We
point out how the open sigma models correspond to new types of target space
geometry. For the massive Landau-Ginzburg models (both Kahler and bihermitian)
we discuss an important class of supersymmetric boundary conditions which
admits a nice geometrical interpretation.Comment: 48 pages, latex, references and minor comments added, the version to
appear in JHE
Weakly Z symmetric manifolds
We introduce a new kind of Riemannian manifold that includes weakly-, pseudo-
and pseudo projective- Ricci symmetric manifolds. The manifold is defined
through a generalization of the so called Z tensor; it is named "weakly Z
symmetric" and denoted by (WZS)_n. If the Z tensor is singular we give
conditions for the existence of a proper concircular vector. For non singular Z
tensor, we study the closedness property of the associated covectors and give
sufficient conditions for the existence of a proper concircular vector in the
conformally harmonic case, and the general form of the Ricci tensor. For
conformally flat (WZS)_n manifolds, we derive the local form of the metric
tensor.Comment: 13 page
Almost-stationary motions and gauge conditions in General Relativity
An almost-stationary gauge condition is proposed with a view to Numerical
Relativity applications. The time lines are defined as the integral curves of
the timelike solutions of the harmonic almost-Killing equation. This vector
equation is derived by a variational principle, by minimizing the deviations
from isometry. The corresponding almost-stationary gauge condition allows one
to put the field equations in hyperbolic form, both in the free-evolution ADM
and in the Z4 formalisms.Comment: Talk presented at the Spanish Relativity Meeting, September 6-10 2005
Revised versio
Halo models in modified gravity theories with self-accelerated expansion
We investigate the structure of halos in the sDGP (self-accelerating branch
of the Dvali-Gavadadze-Porrati braneworld gravity) model and the galileon
modified gravity model on the basis of the static and spherically symmetric
solutions of the collisionless Boltzmann equation, which reduce to the singular
isothermal sphere model and the King model in the limit of Newtonian gravity.
The common feature of these halos is that the density of a halo in the outer
region is larger (smaller) in the sDGP (galileon) model, respectively, in
comparison with Newtonian gravity. This comes from the suppression
(enhancement) of the effective gravity at large distance in the sDGP (galileon)
model, respectively. However, the difference between these modified gravity
models and Newtonian gravity only appears outside the halo due to the
Vainshtein mechanism, which makes it difficult to distinguish between them. We
also discuss the case in which the halo density profile is fixed independently
of the gravity model for comparison between our results and previous work.Comment: 15pages, 6 figures, maches the version to be published in Int. J.
Mod. Phys. D, typos correcte
T-duality for the sigma model with boundaries
We derive the most general local boundary conditions necessary for T-duality
to be compatible with superconformal invariance of the two-dimensional N=1
supersymmetric nonlinear sigma model with boundaries. To this end, we construct
a consistent gauge invariant parent action by gauging a U(1) isometry, with and
without boundary interactions. We investigate the behaviour of the boundary
conditions under T-duality, and interpret the results in terms of D-branes.Comment: 48 pages, LaTeX, v2: typos corrected, references adde
Building a multi-hop wireless sensor network for water level monitoring.
Abstract-Wireless Sensor Networks (WSN) are very useful for data acquisition in harsh environments or where the maintenance of wired infrastructure would not be viable. Despite of these advantages WSN nodes have a limited range ratio thus to collect data on long distance is necessary to construct a path with many relay nodes to reach the destination. Another limitation of these networks is that they often rely on batteries to operate, which can cause a serious limitation in the network lifetime. In this work it was developed a solution based on a Multi-hop WSN to collect data on long distance, and, also some strategies such as 'sleep schedule', 'data aggregation' and 'hub polling' were implemented to extend the WSN lifetime. This could be done by modifications at RFBee Libraries that reinforces the importance of flexibility and portability of this device
Temperature dependent photoluminescence in oxygen ion implanted and rapid thermally annealed ZnO/ZnMgO multiple quantum wells
The authors investigate the effect of oxygen implantation and rapid thermal annealing in ZnO∕ZnMgOmultiple quantum wells using photoluminescence. A blueshift in the photoluminescence is observed in the implanted samples. For a low implantation dose, a significant increase of activation energy and a slight increase of the photoluminescence efficiency are observed. This is attributed to the suppression of the point defect complexes and transformation between defect structures by implantation and subsequent rapid thermal annealing. A high dose of implantation leads to lattice damage and agglomeration of defects leading to large defect clusters, which result to an increase in nonradiative recombination.The authors gratefully acknowledge the Australian Research
Council for financial support and Swinburne University
of Technology for Strategic Initiative funding. One of
the authors X.W. acknowledges partial financial support of
the Chinese National Natural Science Foundation
10364004 and the Yunnan Natural Science Foundation
2003E0013M
Caracterização de um "blend" tropical elaborado com polpas de maracujá, acerola e taperebá.
bitstream/item/27821/1/BPD-59.pdfVersão eletrônica. 1ª impressão: 2009
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