3,863 research outputs found
Extracting New Physics from the CMB
We review how initial state effects generically yield an oscillatory
component in the primordial power spectrum of inflationary density
perturbations. These oscillatory corrections parametrize unknown new physics at
a scale and are potentially observable if the ratio is
sufficiently large. We clarify to what extent present and future CMB data
analysis can distinguish between the different proposals for initial state
corrections.Comment: Invited talk by B. Greene at the XXII Texas Symposium on Relativistic
Astrophysics, Stanford University, 13-17 December 2004, (TSRA04-0001), 8
pages, LaTeX, some references added, added paragraph at the end of section 2
and an extra note added after the conclusions regarding modifications to the
large k power spectra deduced from galaxy survey
Observing the Geometry of Warped Compactification via Cosmic Inflation
Using DBI inflation as an example, we demonstrate that the detailed geometry
of warped compactification can leave an imprint on the cosmic microwave
background (CMB). We compute CMB observables for DBI inflation in a generic
class of warped throats and find that the results (such as the sign of the tilt
of the scalar perturbations and its running) depend sensitively on the precise
shape of the warp factor. In particular, we analyze the warped deformed
conifold and find that the results can differ from those of other warped
geometries, even when these geometries approximate well the exact metric of the
warped deformed conifold.Comment: 4 pages, 3 figures. v2: References and clarifications adde
Studies of new media radiation induced laser
Various lasants were investigated especially, 2-iodohepafluoropropane (i-C3F7I) for the direct solar pumped lasers. Optical pumping of iodine laser was achieved using a small flashlamp. Using i-C3F7I as a laser gain medium, threshold inversion density, small signal gain, and laser performance at the elevated temperature were measured. The experimental results and analysis are presented. The iodine laser kinetics of the C3F7I and IBr system were numerically simulated. The concept of a direct solar-pumped laser amplifier using (i-C3F7I) as the laser material was evaluated and several kinetic coefficients for i-C3F7I laser system were reexamined. The results are discussed
A blog mining framework
Blogs have become increasingly popular, and new blogs are generated every day. Many of the contents are useful for applications in various domains, such as business, politics, research, social work, and linguistics. However, automatically collecting and analyzing blogs isn't straightforward due to the large size and dynamic nature of the blogosphere. In this article, the authors propose a framework for blog mining that includes spiders, parsers, analyzers, and visualizers. They present several examples of blog mining applications based on their framework. © 2006 IEEE.published_or_final_versio
Meiotic Silencing by Unpaired DNA
AbstractThe silencing of gene expression by segments of DNA present in excess of the normal number is called cosuppression in plants and quelling in fungi. We describe a related process, meiotic silencing by unpaired DNA (MSUD). DNA unpaired in meiosis causes silencing of all DNA homologous to it, including genes that are themselves paired. A semidominant Neurospora mutant, Sad-1, fails to perform MSUD. Sad-1 suppresses the sexual phenotypes of many ascus-dominant mutants. MSUD may provide insights into the function of genes necessary for meiosis, including genes for which ablation in vegetative life would be lethal. It may also contribute to reproductive isolation of species within the genus Neurospora. The wild-type allele, sad-1+, encodes a putative RNA-directed RNA polymerase
3-D Model of Broadband Emission from Supernova Remnants Undergoing Non-linear Diffusive Shock Acceleration
We present a 3-dimensional model of supernova remnants (SNRs) where the
hydrodynamical evolution of the remnant is modeled consistently with nonlinear
diffusive shock acceleration occuring at the outer blast wave. The model
includes particle escape and diffusion outside of the forward shock, and
particle interactions with arbitrary distributions of external ambient
material, such as molecular clouds. We include synchrotron emission and
cooling, bremsstrahlung radiation, neutral pion production, inverse-Compton
(IC), and Coulomb energy-loss. Boardband spectra have been calculated for
typical parameters including dense regions of gas external to a 1000 year old
SNR. In this paper, we describe the details of our model but do not attempt a
detailed fit to any specific remnant. We also do not include magnetic field
amplification (MFA), even though this effect may be important in some young
remnants. In this first presentation of the model we don't attempt a detailed
fit to any specific remnant. Our aim is to develop a flexible platform, which
can be generalized to include effects such as MFA, and which can be easily
adapted to various SNR environments, including Type Ia SNRs, which explode in a
constant density medium, and Type II SNRs, which explode in a pre-supernova
wind. When applied to a specific SNR, our model will predict cosmic-ray spectra
and multi-wavelength morphology in projected images for instruments with
varying spatial and spectral resolutions. We show examples of these spectra and
images and emphasize the importance of measurements in the hard X-ray, GeV, and
TeV gamma-ray bands for investigating key ingredients in the acceleration
mechanism, and for deducing whether or not TeV emission is produced by IC from
electrons or neutral pions from protons.Comment: 12 pages, 9 figures, accepted by Apj, 24 June 200
Top Quarks as a Window to String Resonances
We study the discovery potential of string resonances decaying to
final state at the LHC. We point out that top quark pair production is a
promising and an advantageous channel for studying such resonances, due to
their low Standard Model background and unique kinematics. We study the
invariant mass distribution and angular dependence of the top pair production
cross section via exchanges of string resonances. The mass ratios of these
resonances and the unusual angular distribution may help identify their
fundamental properties and distinguish them from other new physics. We find
that string resonances for a string scale below 4 TeV can be detected via the
channel, either from reconstructing the semi-leptonic
decay or recent techniques in identifying highly boosted tops.Comment: 22 pages, 6 figure
Collisionally Activated Dissociation and Electron Capture Dissociation Provide Complementary Structural Information for Branched Permethylated Oligosaccharides
Doubly charged sodiated and permethylated linear malto-oligosaccharides ({Glc}6-{Glc}9), branched N-linked glycans (high-mannose type GlcNAc2Man5-9, and complex asialo- and disialylated-biantennary glycans) were analyzed by tandem mass spectrometry using collisionally-activated dissociation (CAD) and âhotâ electron capture dissociation (ECD) available in a custom-built ESI FTICR mass spectrometer. For linear permethylated malto-oligosaccharides, both CAD and âhotâ ECD produced glycosidic cleavages (B, Y, C, and Z ions), cross-ring cleavages (A- and X-type), and internal cleavages (B/Y and C/Y type) to provide sequence and linkage information. For the branched N-linked glycans, CAD and âhotâ ECD provided complementary structural information. CAD generated abundant B and Y fragment ions by glycosidic cleavages, whereas âhotâ ECD produced dominant C and Z ions. A-type cross-ring cleavages were present in CAD spectra. Complementary A- and X-type cross-ring fragmentation pairs were generated by âhotâ ECD, and these delineated the branching patterns and linkage positions. For example, 0, 4An and 3, 5An ions defined the linkage position of the major branch as the 6-position of the central core mannose residue. The internal fragments observed in CAD were more numerous and abundant than in âhotâ ECD spectra. Since the triply charged (sodiated) molecular ion of the permethylated disialylated-biantennary N-linked glycan has relatively high abundance, it was isolated and fragmented in a âhotâ ECD experiment and extensive fragment ions (glycosidic and complementary pairs of cross-ring cleavages) were generated to fully confirm the sequence, branching, and linkage assignments for this glycan
No CPT Violation from Tilted Brane in Neutral Meson--Antimeson Systems
Tilted brane in theories with large compact extra dimensions leads to
spontaneous symmetry breaking of the Lorentz and rotational invariance in four
dimensions, as shown by Dvali and Shifman. In this brief report, we point out
that the mentioned Lorentz symmetry breaking, although leading to the
CPT--violating interaction terms, cannot lead to the CPT violation in the
experimentally interesting -- and analogous systems.Comment: 5 pages, RevTe
Three-Family Supersymmetric Standard-like Models from Intersecting Brane Worlds
We construct the first three family N=1 supersymmetric string model with
Standard Model gauge group SU(3)_C x SU(2)_L x U(1)_Y from an orientifold of
type IIA theory on T^6/(Z_2 x Z_2) and D6-branes intersecting at angles. In
addition to the minimal supersymmetric Standard Model particles, the model
contains right-handed neutrinos, a chiral (but anomaly-free) set of exotic
multiplets, and extra vector-like multiplets. We discuss some phenomenological
features of this model.Comment: 4 pages, minor typos correcte
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