6,524 research outputs found
Smooth geometries with four charges in four dimensions
A class of axially symmetric, rotating four-dimensional geometries carrying
D1, D5, KK monopole and momentum charges is constructed. The geometries are
found to be free of horizons and singulaties, and are candidates to be the
gravity duals of microstates of the (0,4) CFT. These geometries are constructed
by performing singularity analysis on a suitably chosen class of solutions of
six-dimensional minimal supergravity written over a Gibbons-Hawking base
metric. The properties of the solutions raise some interesting questions
regarding the CFT.Comment: 1+32 pages, LaTeX, v2: references added, typographical errors
correcte
Oxygen dynamics in choanosomal sponge explants
Oxygen microprofiles were measured over the boundary layer and into the tissue of 10-day-old cultivated tissue fragments (explants of 2â4 cm3) from the choanosome of the cold-water sponge Geodia barretti with oxygen-sensitive Clark-type microelectrodes. At this time of cultivation, the surface tissue and the aquiferous system of the explants is regenerating, which makes oxygen and nutrient supply by pumping activity impossible. Oxygen profiles showed a parabolic shape, indicating oxygen flux over a diffusive boundary layer and into the tissue. Oxygen was always depleted only 1 mm below the sponge surface, leaving the major part of the explants anoxic. Diffusive oxygen flux into the explant was calculated from three oxygen profiles using Fick's first law of diffusion and revealed 9 ÎŒmol O2 cmâ3 dayâ1, which is in the lower range of in situ oxygen consumption of whole sponges. The ability of G. barretti to handle continuous tissue anoxia enables choanosomal explants to survive the critical first weeks of cultivation without a functional aquiferous system, when oxygen is supplied to the sponge explant by molecular diffusion over its surface
Towards a Notion of Distributed Time for Petri Nets
We set the ground for research on a timed extension of Petri nets where time parameters are associated with tokens and arcs carry constraints that qualify the age of tokens required for enabling. The novelty is that, rather than a single global clock, we use a set of unrelated clocks --- possibly one per place --- allowing a local timing as well as distributed time synchronisation. We give a formal definition of the model and investigate properties of local versus global timing, including decidability issues and notions of processes of the respective models
A Survey of Proper Motion Stars. XVII. A Deficiency of Binary Stars on Retrograde Galactic Orbits and the Possibility that omega Centauri is Related to the Effect
We find a deficiency of binary stars moving on strongly retrograde Galactic
orbits. No binary deficiencies are seen for U or W velocities, however. From
theoretical analyses, we rule out preferential disruption of pre-existing
binary stars due to encounters with massive perturbers. We also rule out
globular clusters as the source of the effect since prograde motions are more
likely to create such an effect. We search for star streams and find one
possible candidate, but it is not on a retrograde orbit and probably represents
the remains of a cluster that has passed too near the Galactic center. Based on
a very small number of stars, we find that about the right fraction of stars on
retrograde Galactic orbits share some chemical similarities to the cluster
omega Cen, suggesting that its parent galaxy could be the explanation.Comment: To appear in the Astronomical Journal (March 2005 issue
D1-D5 on ALE Space
We construct a two-dimensional N=(0,4) quiver gauge theory on D1-brane
probing D5-branes on ALE space, and study its IR behavior. This can be thought
of as a gauged linear sigma model for the NS5-branes on ALE space.Comment: 17 pages, 1 figure, lanlmac; v2: reference adde
Microscopic Description of Black Rings in AdS/CFT
We discuss some aspects of the recently discovered BPS black ring solutions
in terms of the AdS/CFT correspondence. In the type IIB frame in which the
black ring carries the charges of the D1-D5-P system, we propose a microscopic
description of the rings in the orbifold CFT governing this system. In our
proposal, the CFT effectively splits into two parts: one part captures the
supertube-like properties of the ring, and the other captures the entropy. We
can also understand the black ring entropy by relating the geometry near the
ring to BPS black holes in four dimensions, although this latter approach does
not directly lead to an identification of black rings in terms of the D1-D5-P
CFT.Comment: 18 pages, harvmac. v2 - minor typo
The impact of pleurodesis in malignant effusion on respiratory function
AbstractPleurodesis of malignant pleural effusion provides for a substantially better quality of life compared to onging exudation with the need for repeated evacuation of fluid. Successful pleurodesis leads to permanent cessation of fluid production as a result of the formation of fibrous adhesion between the lung and costal pleura which in theory, however, might restrict lung mobility. In patients with poor lung function, or with need for bilateral pleurodesis, the apprehension of further impairment of lung function often arises. The aim of this study was to evaluate the effects of pleurodesis on lung function. Therefore 10 patients with malignant pleurisy with very limited tumour were investigated. They were without radiological signs of tumour infiltration in the lung parenchyma, without visible tumour growth in the pleural space during thoracoscopy and had undergone a successful one-sided pleurodesis. Respiratory function tests were performed at different times, 1â102 months after pleurodesis. The assessment consisted of: static and dynamic spirometry, exercise testing with blood gas determination and radiospirometry.Spirometric values were slightly low, but in general within the reference limits. Blood gas determination showed no signs of alveolar hypoventilation. Radiospirometry showed a slight attenuation of activity in the treated lung but similar turnover of gas of the treated vs. the untreated side. The study showed that pleurodesis in malignant pleurisy has only minor impact on respiratory function
Bubble generation in a twisted and bent DNA-like model
The DNA molecule is modeled by a parabola embedded chain with long-range
interactions between twisted base pair dipoles. A mechanism for bubble
generation is presented and investigated in two different configurations. Using
random normally distributed initial conditions to simulate thermal
fluctuations, a relationship between bubble generation, twist and curvature is
established. An analytical approach supports the numerical results.Comment: 7 pages, 8 figures. Accepted for Phys. Rev. E (in press
The Holographic Universe
We present a holographic description of four-dimensional single-scalar
inflationary universes in terms of a three-dimensional quantum field theory.
The holographic description correctly reproduces standard inflationary
predictions in their regime of applicability. In the opposite case, wherein
gravity is strongly coupled at early times, we propose a holographic
description in terms of perturbative QFT and present models capable of
satisfying the current observational constraints while exhibiting a
phenomenology distinct from standard inflation. This provides a qualitatively
new method for generating a nearly scale-invariant spectrum of primordial
cosmological perturbations.Comment: 20 pages, 5 figs; extended version of arXiv:0907.5542 including
background material and detailed derivations. To appear in Proceedings of 1st
Mediterranean Conference on Classical and Quantum Gravit
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