1,565 research outputs found
On a refinement of the theory of the moon's physical librations
Mathematical model for lunar librational motio
Cosmologies with Null Singularities and their Gauge Theory Duals
We investigate backgrounds of Type IIB string theory with null singularities
and their duals proposed in hep-th/0602107. The dual theory is a deformed N=4
Yang-Mills theory in 3+1 dimensions with couplings dependent on a light-like
direction. We concentrate on backgrounds which become AdS_5 x S^5 at early and
late times and where the string coupling is bounded, vanishing at the
singularity. Our main conclusion is that in these cases the dual gauge theory
is nonsingular. We show this by arguing that there exists a complete set of
gauge invariant observables in the dual gauge theory whose correlation
functions are nonsingular at all times. The two-point correlator for some
operators calculated in the gauge theory does not agree with the result from
the bulk supergravity solution. However, the bulk calculation is invalid near
the singularity where corrections to the supergravity approximation become
important. We also obtain pp-waves which are suitable Penrose limits of this
general class of solutions, and construct the Matrix Membrane theory which
describes these pp-wave backgrounds.Comment: 43 pages REVTeX and AMSLaTeX. v2: references adde
The Gamma-Ray Blazar Content of the Northern Sky
Using survey data, we have re-evaluated the correlation of flat spectrum
radio sources with EGRET sources in the Northern sky. A likelihood analysis
incorporating the radio and X-ray properties and the Gamma-ray source
localization is used to gauge the reliability of associations and to search for
counterparts of previously unidentified EGRET sources. Above |b|=10deg, where
the classification is complete, we find that 70% of the Northern EGRET sources
have counterparts similar to the bright EGRET blazars. For several of these we
identify known blazar counterparts more likely than the earlier proposed 3EG
association; for ~20 we have new identifications. Spectroscopic confirmation of
these candidates is in progress and we have found flat spectrum radio quasars
and BL Lac counterparts with redshifts as high as 4. We also find strong
evidence for a set of 28 objects with no plausible counterpart like the known
EGRET Blazars. These thus represent either a new extragalactic population or a
population of Galactic objects with a large scale height. The survey has been
extended into the plane, where we find several new blazar candidates; the bulk
of the sources are, however, Galactic. Looking ahead to the GLAST era we
predict that several of the present 3EG sources are composite and that higher
resolution data will break these into multiple Blazar IDs.Comment: 13 pages, 6 figures, submitted to Ap
Industrial-Scale Manufacture of Oleosin 30G for Use as Contrast Agent in Echocardiography
In ultrasound sonography, microbubbles are used as contrasting agents to improve the effectiveness of ultrasound imaging. Monodisperse microbubbles are required to achieve the optimal image quality. In order to achieve a uniform size distribution, microbubbles are stabilized with surfactant molecules. One such molecule is Oleosin, an amphiphilic structural protein found in vascular plant oil bodies that contains one hydrophobic and two hydrophilic sections. Controlling the functionalization of microbubbles is a comprehensive and versatile process using recombinant technology to produce a genetically engineered form of Oleosin called Oleosin 30G. With the control of a microfluidic device, uniformly-sized and resonant microbubbles can be readily produced and stored in stable conditions up to one month. Currently, Oleosin microbubbles are limited to the lab-scale; however, through development of an integrated batch bioprocessing model, the overall product yield of Oleosin 30G can be increased to 7.39 kg/year to meet needs on the industrial-scale. An Oleosin-stabilized microbubble suspension as a contrast agent is in a strong position to take a competitive share of the current market, capitalizing on needs unmet by current market leader, Definity®. Based on market dynamics and process logistics, scaled-up production of Oleosin 30G for use as a contrast agent is expected to be both a useful and profitable venture
A pp-Wave With 26 Supercharges
A pp-wave solution to 11-dimensional supergravity is given with precisely 26
supercharges. Its uniqueness and the absence of 11-dimensional pp-waves which
preserve (precisely) 28 or 30 supercharges is discussed. Compactification on a
spacelike circle gives a IIA configuration with all 26 of the supercharges. For
this compactification, D0 brane charge does not appear in the supersymmetry
algebra. Indeed, the 26 supercharge IIA background does not admit any
supersymmetric D-branes. In an appendix, a 28 supercharge IIB pp-wave is
presented along with its supersymmetry algebra.Comment: 18 pages REVTeX 4 and AMSLaTeX. v3: Equations (III.17) and (III.18)
corrected. Reference added. v4: more typos corrected and references adde
FIRI - a Far-Infrared Interferometer
Half of the energy ever emitted by stars and accreting objects comes to us in
the FIR waveband and has yet to be properly explored. We propose a powerful
Far-InfraRed Interferometer mission, FIRI, to carry out high-resolution imaging
spectroscopy in the FIR. This key observational capability is essential to
reveal how gas and dust evolve into stars and planets, how the first luminous
objects in the Universe ignited, how galaxies formed, and when super-massive
black holes grew. FIRI will disentangle the cosmic histories of star formation
and accretion onto black holes and will trace the assembly and evolution of
quiescent galaxies like our Milky Way. Perhaps most importantly, FIRI will
observe all stages of planetary system formation and recognise Earth-like
planets that may harbour life, via its ability to image the dust structures in
planetary systems. It will thus address directly questions fundamental to our
understanding of how the Universe has developed and evolved - the very
questions posed by ESA's Cosmic Vision.Comment: Proposal developed by a large team of astronomers from Europe, USA
and Canada and submitted to the European Space Agency as part of "Cosmic
Vision 2015-2025
Detection of Anisotropies in the Gravitational-Wave Stochastic Background
By correlating the signals from a pair of gravitational-wave detectors, one
can undertake sensitive searches for a stochastic background of gravitational
radiation. If the stochastic background is anisotropic, then this correlated
signal varies harmonically with the earth's rotation. We calculate how the
harmonics of this varying signal are related to the multipole moments which
characterize the anisotropy, and give a formula for the signal-to-noise ratio
of a given harmonic. The specific case of the two LIGO (Laser Interferometric
Gravitational Observatory) detectors, which will begin operation around the
year 2000, is analyzed in detail. We consider two possible examples of
anisotropy. If the gravitational-wave stochastic background contains a dipole
intensity anisotropy whose origin (like that of the Cosmic Background
Radiation) is motion of our local system, then that anisotropy will be
observable by the advanced LIGO detector (with 90% confidence in one year of
observation) if \Omega_{gw} > 5.3 \times 10^{-8} h_{100}^{-2}. We also study
the signal produced by stochastic sources distributed in the same way as the
luminous matter in the galactic disk, and in the same way as the galactic halo.
The anisotropy due to sources distributed as the galactic disk or as the
galactic halo will be observable by the advanced LIGO detector (with 90%
confidence in one year of observation) if \Omega_{gw} > 1.8 \times 10^{-10}
h_{100}^{-2} or \Omega_{gw} > 6.7 \times 10^{-8} h_{100}^{-2}, respectively.Comment: 25 pages, Latex with RevTeX and epsfig, now includes S/N ratio
calculations, expected response from anisotropy due to local motion & sources
in galax
General criteria for the stability of uniaxially ordered states of Incommensurate-Commensurate Systems
Reconsidering the variational procedure for uniaxial systems modeled by
continuous free energy functionals, we derive new general conditions for
thermodynamic extrema. The utility of these conditions is briefly illustrated
on the models for the classes I and II of incommensurate-commensurate systems.Comment: 5 pages, to be published in Phys. Rev. Let
Divergent trophic responses of sympatric penguin species to historic anthropogenic exploitation and recent climate change
The Southern Ocean is in an era of significant change. Historic overharvesting of marine mammals and recent climatic warming have cascading impacts on resource availability and, in turn, ecosystem structure and function. We examined trophic responses of sympatric chinstrap (Pygoscelis antarctica) and gentoo (Pygoscelis papua) penguins to nearly 100 y of shared environmental change in the Antarctic Peninsula region using compound-specific stable isotope analyses of museum specimens. A century ago, gentoo penguins fed almost exclusively on low-trophic level prey, such as krill, during the peak of historic overexploitation of marine mammals, which was hypothesized to have resulted in a krill surplus. In the last 40 y, gentoo penguin trophic position has increased a full level as krill declined in response to recent climate change, increased competition from recovering marine mammal populations, and the development of a commercial krill fishery. A shifting isotopic baseline supporting gentoo penguins suggests a concurrent increase in coastal productivity over this time. In contrast, chinstrap penguins exhibited no change in trophic position, despite variation in krill availability over the past century. The specialized foraging niche of chinstrap penguins likely renders them more sensitive to changes in krill availability, relative to gentoo penguins, as evinced by their declining population trends in the Antarctic Peninsula over the past 40 y. Over the next century, similarly divergent trophic and population responses are likely to occur among Antarctic krill predators if climate change and other anthropogenic impacts continue to favor generalist over specialist species
- …