768 research outputs found
Gravitational Radiation from Preheating with Many Fields
Parametric resonances provide a mechanism by which particles can be created
just after inflation. Thus far, attention has focused on a single or many
inflaton fields coupled to a single scalar field. However, generically we
expect the inflaton to couple to many other relativistic degrees of freedom
present in the early universe. Using simulations in an expanding
Friedmann-Lema\^itre-Robertson-Walker spacetime, in this paper we show how
preheating is affected by the addition of multiple fields coupled to the
inflaton. We focus our attention on gravitational wave production--an important
potential observational signature of the preheating stage. We find that
preheating and its gravitational wave signature is robust to the coupling of
the inflaton to more matter fields.Comment: 7 pages, 8 figures, v2 submission version, thank you for comments
Scalar Synchrotron Radiation in the Schwarzschild-anti-de Sitter Geometry
We present a complete relativistic analysis for the scalar radiation emitted
by a particle in circular orbit around a Schwarzschild-anti-de Sitter black
hole. If the black hole is large, then the radiation is concentrated in narrow
angles- high multipolar distribution- i.e., the radiation is synchrotronic.
However, small black holes exhibit a totally different behavior: in the small
black hole regime, the radiation is concentrated in low multipoles. There is a
transition mass at , where is the AdS radius. This behavior is
new, it is not present in asymptotically flat spacetimes.Comment: 13 pages, 6 figures, published version. References adde
The imposition of Cauchy data to the Teukolsky equation I: The nonrotating case
Gravitational perturbations about a Kerr black hole in the Newman-Penrose
formalism are concisely described by the Teukolsky equation. New numerical
methods for studying the evolution of such perturbations require not only the
construction of appropriate initial data to describe the collision of two
orbiting black holes, but also to know how such new data must be imposed into
the Teukolsky equation. In this paper we show how Cauchy data can be
incorporated explicitly into the Teukolsky equation for non-rotating black
holes. The Teukolsky function and its first time derivative
can be written in terms of only the 3-geometry and the
extrinsic curvature in a gauge invariant way. Taking a Laplace transform of the
Teukolsky equation incorporates initial data as a source term. We show that for
astrophysical data the straightforward Green function method leads to divergent
integrals that can be regularized like for the case of a source generated by a
particle coming from infinity.Comment: 9 pages, REVTEX. Misprints corrected in formulas (2.4)-(2.7). Final
version to appear in PR
A novel compartment, the 'subqpical stem' of the aerial hyphae, is the location of a sigN-dependent, developmentally distinct transcription in Streptomyces coelicolor.
Streptomyces coelicolor has nine SigB-like RNA polymerase sigma factors, several of them implicated in morphological differentiation and/or responses to different stresses. One of the nine, SigN, is the focus of this article. A constructed sigN null mutant was delayed in development and exhibited a bald phenotype when grown on minimal medium containing glucose as carbon source. One of two distinct sigN promoters, sigNP1, was active only during growth on solid medium, when its activation coincided with aerial hyphae formation. Transcription from sigNP1 was readily detected in several whi mutants (interrupted in morphogenesis of aerial mycelium into spores), but was absent from all bld mutants tested, suggesting that sigNP1 activity was restricted to the aerial hyphae. It also depended on sigN, thus sigN was autoregulated. Mutational and transcription studies revealed no functional significance to the location of sigN next to sigF, encoding another SigB-like sigma factor. We identified another potential SigN target, nepA, encoding a putative small secreted protein. Transcription of nepA originated from a single, aerial hyphae-specific and sigN-dependent promoter. While in vitro run-off transcription using purified SigN on the Bacillus subtilis ctc promoter confirmed that SigN is an RNA polymerase sigma factor, SigN failed to initiate transcription from sigNP1 and from the nepA promoter in vitro. Additional in vivo data indicated that further nepA upstream sequences, which are likely to bind a potential activator, are required for successful transcription. Using a nepAâegfp transcriptional fusion we located nepA transcription to a novel compartment, the âsubapical stemâ of the aerial hyphae. We suggest that this newly recognized compartment defines an interface between the aerial and vegetative parts of the Streptomyces colony and might also be involved in communication between these two compartments
Cornerstones of Sampling of Operator Theory
This paper reviews some results on the identifiability of classes of
operators whose Kohn-Nirenberg symbols are band-limited (called band-limited
operators), which we refer to as sampling of operators. We trace the motivation
and history of the subject back to the original work of the third-named author
in the late 1950s and early 1960s, and to the innovations in spread-spectrum
communications that preceded that work. We give a brief overview of the NOMAC
(Noise Modulation and Correlation) and Rake receivers, which were early
implementations of spread-spectrum multi-path wireless communication systems.
We examine in detail the original proof of the third-named author
characterizing identifiability of channels in terms of the maximum time and
Doppler spread of the channel, and do the same for the subsequent
generalization of that work by Bello.
The mathematical limitations inherent in the proofs of Bello and the third
author are removed by using mathematical tools unavailable at the time. We
survey more recent advances in sampling of operators and discuss the
implications of the use of periodically-weighted delta-trains as identifiers
for operator classes that satisfy Bello's criterion for identifiability,
leading to new insights into the theory of finite-dimensional Gabor systems. We
present novel results on operator sampling in higher dimensions, and review
implications and generalizations of the results to stochastic operators, MIMO
systems, and operators with unknown spreading domains
A connection between stress and development in the multicelular prokaryote Streptomyces coelicolor
Morphological changes leading to aerial mycelium formation and sporulation in the mycelial bacterium Streptomyces coelicolor rely on establishing distinct patterns of gene expression in separate regions of the colony. sH was identified previously as one of three paralogous sigma factors associated with stress responses in S. coelicolor. Here, we show that sigH and the upstream gene prsH (encoding a putative antisigma factor of sH) form an operon transcribed from two developmentally regulated promoters, sigHp1 and sigHp2. While sigHp1 activity is confined to the early phase of growth, transcription of sigHp2 is dramatically induced at the time of aerial hyphae formation. Localization of sigHp2 activity using a transcriptional fusion to the green fluorescent protein reporter gene (sigHp2âegfp) showed that sigHp2 transcription is spatially restricted to sporulating aerial hyphae in wild-type S. coelicolor. However, analysis of mutants unable to form aerial hyphae (bld mutants) showed that sigHp2 transcription and sH protein levels are dramatically upregulated in a bldD mutant, and that the sigHp2âegfp fusion was expressed ectopically in the substrate mycelium in the bldD background. Finally, a protein possessing sigHp2 promoter-binding activity was purified to homogeneity from crude mycelial extracts of S. coelicolor and shown to be BldD. The BldD binding site in the sigHp2 promoter was defined by DNase I footprinting. These data show that expression of sH is subject to temporal and spatial regulation during colony development, that this tissue-specific regulation is mediated directly by the developmental transcription factor BldD and suggest that stress and developmental programmes may be intimately connected in Streptomyces morphogenesis
Merkel cell polyomavirus large T antigen disrupts lysosome clustering by translocating human Vam6p from the cytoplasm to the nucleus
Merkel cell polyomavirus (MCV) has been recently described as the cause for most human Merkel cell carcinomas. MCV is similar to simian virus 40 (SV40) and encodes a nuclear large T (LT) oncoprotein that is usually mutated to eliminate viral replication among tumor-derived MCV. We identified the hVam6p cytoplasmic protein involved in lysosomal processing as a novel interactor with MCV LT but not SV40 LT. hVam6p binds through its clathrin heavy chain homology domain to a unique region of MCV LT adjacent to the retinoblastoma binding site. MCV LT translocates hVam6p to the nucleus, sequestering it from involvement in lysosomal trafficking. A naturally occurring, tumor-derived mutant LT (MCV350) lacking a nuclear localization signal binds hVam6p but fails to inhibit hVam6p-induced lysosomal clustering. MCV has evolved a novel mechanism to target hVam6p that may contribute to viral uncoating or egress through lysosomal processing during virus replication
T violation and the unidirectionality of time
An increasing number of experiments at the Belle, BNL, CERN, DA{\Phi}NE and
SLAC accelerators are confirming the violation of time reversal invariance (T).
The violation signifies a fundamental asymmetry between the past and future and
calls for a major shift in the way we think about time. Here we show that
processes which violate T symmetry induce destructive interference between
different paths that the universe can take through time. The interference
eliminates all paths except for two that represent continuously forwards and
continuously backwards time evolution. Evidence from the accelerator
experiments indicates which path the universe is effectively following. This
work may provide fresh insight into the long-standing problem of modeling the
dynamics of T violation processes. It suggests that T violation has previously
unknown, large-scale physical effects and that these effects underlie the
origin of the unidirectionality of time. It may have implications for the
Wheeler-DeWitt equation of canonical quantum gravity. Finally it provides a
view of the quantum nature of time itself.Comment: 24 pages, 5 figures. Final version accepted for publishing in
Foundations of Physics. The final publication is available at
http://www.springerlink.com/content/y3h4174jw2w78322
Displaying the Heterogeneity of the SN 2002cx-like Subclass of Type Ia Supernovae with Observations of the Pan-STARRS-1 Discovered SN2009ku
SN2009ku, discovered by Pan-STARRS-1, is a Type Ia supernova (SNIa), and a
member of the distinct SN2002cx-like class of SNeIa. Its light curves are
similar to the prototypical SN2002cx, but are slightly broader and have a later
rise to maximum in g. SN2009ku is brighter (~0.6 mag) than other SN2002cx-like
objects, peaking at M_V = -18.4 mag - which is still significantly fainter than
typical SNeIa. SN2009ku, which had an ejecta velocity of ~2000 kms^-1 at 18
days after maximum brightness is spectroscopically most similar to SN2008ha,
which also had extremely low-velocity ejecta. However, SN2008ha had an
exceedingly low luminosity, peaking at M_V = -14.2 mag, ~4 mag fainter than
SN2009ku. The contrast of high luminosity and low ejecta velocity for SN2009ku
is contrary to an emerging trend seen for the SN2002cx class. SN2009ku is a
counter-example of a previously held belief that the class was more homogeneous
than typical SNeIa, indicating that the class has a diverse progenitor
population and/or complicated explosion physics. As the first example of a
member of this class of objects from the new generation of transient surveys,
SN2009ku is an indication of the potential for these surveys to find rare and
interesting objects.Comment: 7 pages, 3 figure
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