578 research outputs found
Large Wind Energy Converter: Growian 3 MW
The final report on the projected application of larger-scale wind turbine on the northern German coast is summarized. The designs of the tower, machinery housing, rotor, and rotor blades are described accompanied various construction materials are examined. Rotor blade adjustment devices auxiliary and accessory equipment are examined
The non-abelian D-brane effective action through order
Requiring the existence of certain BPS solutions to the equations of motion,
we determine the bosonic part of the non-abelian D-brane effective action
through order . We also propose an economic organizational
principle for the effective action.Comment: 12 pages, 2 figures, JHEP styl
Application of ERTS-1 imagery and underflight photography in the detection and monitoring of forest insect infections in the Sierra Nevada Mountains of California
The author has identified the following significant results. Analysis of ERTS-1 imagery with underflight aerial photo support including U-2, in the Sierra Nevada Mountains of California, indicates promising possibilities of detecting and monitoring forest insect outbreaks visually with some mechanical support utilizing the VP-8 image analyzer. Visually, it is possible at a scale of 1:1,000,000 to discriminate between large areas of damaged and undamaged forests; timbered and non-timbered areas; pasture land and cultivated fields; desert and riparian vegetation. At a scale of 1:80,000 it is possible to distinguish among three classes of tree mortality; defoliated and undefoliated areas; non-host mixed conifers; and mountain meadows, rock domes, lakes and glaciers. Machine tests showed significant differences in image densities among various bands and mortality areas
A landscape of non-supersymmetric AdS vacua on coset manifolds
We construct new families of non-supersymmetric sourceless type IIA AdS4
vacua on those coset manifolds that also admit supersymmetric solutions. We
investigate the spectrum of left-invariant modes and find that most, but not
all, of the vacua are stable under these fluctuations. Generically, there are
also no massless moduli.Comment: 20 pages, 11 figures, v2: added some clarifications, references, v3:
corrections addressing comments refere
Reformulating Supersymmetry with a Generalized Dolbeault Operator
The conditions for N=1 supersymmetry in type II supergravity have been
previously reformulated in terms of generalized complex geometry. We improve
that reformulation so as to completely eliminate the remaining explicit
dependence on the metric. Doing so involves a natural generalization of the
Dolbeault operator. As an application, we present some general arguments about
supersymmetric moduli. In particular, a subset of them are then classified by a
certain cohomology. We also argue that the Dolbeault reformulation should make
it easier to find existence theorems for the N=1 equations.Comment: 30 pages, no figures. v2: minor correction
First record of the hypoptopomatine genus Eurycheilichthys Reis & Schaefer, 1993 (Siluriformes, Loricariidae) from Argentina
The hypoptopomatine genus Eurycheilichthys was so far considered to be endemic to the South of Brazil. One of its species, E. pantherinus, was described from the upper Uruguay river basin. We inform about the finding of this species within the Garibaldi creek, headwater of the arroyo Yabotí Guazú. This is the first record for Argentina which is found in a tributary of the middle Uruguay river.Facultad de Ciencias Naturales y Muse
Supersymmetric sources, integrability and generalized-structure compactifications
In the context of supersymmetric compactifications of type II supergravity to
four dimensions, we show that orientifold sources can be compatible with a
generalized SU(3) x SU(3)-structure that is neither strictly SU(3) nor static
SU(2). We illustrate this with explicit examples, obtained by suitably
T-dualizing known solutions on the six-torus. In addition we prove the
following integrability statements, valid under certain mild assumptions: (a)
for general type II supergravity backgrounds with orientifold and/or D-brane
generalized-calibrated sources, the source-corrected Einstein and dilaton
equations of motion follow automatically from the supersymmetry equations once
the likewise source-corrected form equations of motion and Bianchi identities
are imposed; (b) in the special case of supersymmetric compactifications to
four-dimensional Minkowski space, the equations of motion of all fields,
including the NSNS three-form, follow automatically once the supersymmetry and
the Bianchi identities of the forms are imposed. Both (a) and (b) are equally
valid whether the sources are smeared or localized. As a byproduct we obtain
the calibration form for a space-filling NS5-brane.Comment: 32 pages, 1 table, v2: added references, v3: corrected mistake in
(4.1) leading to factor 2 mistake in (B.6), corrected (B.5), smaller typo
From ten to four and back again: how to generalize the geometry
We discuss the four-dimensional N=1 effective approach in the study of warped
type II flux compactifications with SU(3)x SU(3)-structure to AdS_4 or flat
Minkowski space-time. The non-trivial warping makes it natural to use a
supergravity formulation invariant under local complexified Weyl
transformations. We obtain the classical superpotential from a standard
argument involving domain walls and generalized calibrations and show how the
resulting F-flatness and D-flatness equations exactly reproduce the full
ten-dimensional supersymmetry equations. Furthermore, we consider the effect of
non-perturbative corrections to this superpotential arising from gaugino
condensation or Euclidean D-brane instantons. For the latter we derive the
supersymmetry conditions in N=1 flux vacua in full generality. We find that the
non-perturbative corrections induce a quantum deformation of the internal
generalized geometry. Smeared instantons allow to understand KKLT-like AdS
vacua from a ten-dimensional point of view. On the other hand, non-smeared
instantons in IIB warped Calabi-Yau compactifications 'destabilize' the
Calabi-Yau complex structure into a genuine generalized complex one. This
deformation gives a geometrical explanation of the non-trivial superpotential
for mobile D3-branes induced by the non-perturbative corrections.Comment: LaTeX, 47 pages, v2, references, hyperref added, v3, correcting small
inaccuracies in eqs. (2.6a) and (5.16
D-branes on AdS flux compactifications
We study D-branes in N=1 flux compactifications to AdS_4. We derive their
supersymmetry conditions and express them in terms of background generalized
calibrations. Basically because AdS has a boundary, the analysis of stability
is more subtle and qualitatively different from the usual case of Minkowski
compactifications. For instance, stable D-branes filling AdS_4 may wrap trivial
internal cycles. Our analysis gives a geometric realization of the
four-dimensional field theory approach of Freedman and collaborators.
Furthermore, the one-to-one correspondence between the supersymmetry conditions
of the background and the existence of generalized calibrations for D-branes is
clarified and extended to any supersymmetric flux background that admits a
time-like Killing vector and for which all fields are time-independent with
respect to the associated time. As explicit examples, we discuss supersymmetric
D-branes on IIA nearly Kaehler AdS_4 flux compactifications.Comment: 43 pages, 2 pictures, 1 table; v2: added references, color to figure
and corrected typo in (6.21b
A second look at N=1 supersymmetric AdS_4 vacua of type IIA supergravity
We show that a class of type IIA vacua recently found within the N=4
effective approach corresponds to compactification on Ads_4 \times S^3 \times
S^3/Z_2^3. The results obtained using the effective method completely match the
general ten-dimensional analysis for the existence of N=1 warped
compactifications on Ads_4 \times M_6. In particular, we verify that the
internal metric is nearly-Kahler and that for specific values of the parameters
the Bianchi identity of the RR 2-form is fulfilled without sources. For another
range of parameters, including the massless case, the Bianchi identity is
satisfied when D6-branes are introduced. Solving the tadpole cancellation
conditions in D=4 we are able to find examples of appropriate sets of branes.
In the second part of this paper we describe how an example with internal space
CP^3 but with non nearly-Kahler metric fits into the general analysis of flux
vacua.Comment: Latex file, 35 pages, no figures. Reference added, minor corrections
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