2,052 research outputs found
Probing Gluon Saturation through Dihadron Correlations at an Electron-Ion Collider
Two-particle azimuthal angle correlations have been proposed to be one of the
most direct and sensitive probes to access the underlying gluon dynamics
involved in hard scatterings. In anticipation of an Electron-Ion Collider
(EIC), detailed studies of dihadron correlation measurements in electron-proton
and electron-ion collisions at an EIC have been performed. The impact of such
measurements on the understanding of the different gluon distribution
functions, as a clean signature for gluon saturation and to constrain
saturation models further, has been explored. It is shown that dihadron
correlation measurements will be one of the key methods to probe gluon
saturation phenomena at a future EIC.Comment: 13 pages, 13 eps figure
Cosmological Evolution of Interacting Dark Energy Models with Mass Varying Neutrinos
In this paper we consider the cosmological implications of dark energy models
with a coupled system of a dynamical scalar field (the quintessence) and the
neutrinos. By detailed numerical calculations we study the various
possibilities on the evolution and the fates of the universe in this class of
models. Our results show that due to the interaction with quintessence,
neutrinos could be dominant over the quintessence in the future universe,
however would eventually decay away.Comment: One typographical error corrected, references updated and
presentation improve
Empirical modeling of the stellar spectrum of galaxies
An empirical method of modeling the stellar spectrum of galaxies is proposed,
based on two successive applications of Principal Component Analysis (PCA). PCA
is first applied to the newly available stellar library STELIB, supplemented by
the J, H and K magnitudes taken mainly from the 2 Micron All Sky Survey
(2MASS). Next the resultant eigen-spectra are used to fit the observed spectra
of a sample of 1016 galaxies selected from the Sloan Digital Sky Survey Data
Release One (SDSS DR1). PCA is again applied, to the fitted spectra to
construct the eigen-spectra of galaxies with zero velocity dispersion. The
first 9 galactic eigen-spectra so obtained are then used to model the stellar
spectrum of the galaxies in SDSS DR1, and synchronously to estimate the stellar
velocity dispersion, the spectral type, the near-infrared SED, and the average
reddening. Extensive tests show that the spectra of different type galaxies can
be modeled quite accurately using these eigen-spectra. The method can yield
stellar velocity dispersion with accuracies better than 10%, for the spectra of
typical S/N ratios in SDSS DR1.Comment: 34 pages with 18 figures, submitted to A
Stability of Silk and Collagen Protein Materials in Space
Collagen and silk materials, in neat forms and as silica composites, were flown for 18 months on the International Space Station [Materials International Space Station Experiment (MISSE)-6] to assess the impact of space radiation on structure and function. As natural biomaterials, the impact of the space environment on films of these proteins was investigated to understand fundamental changes in structure and function related to the future utility in materials and medicine in space environments. About 15% of the film surfaces were etched by heavy ionizing particles such as atomic oxygen, the major component of the low-Earth orbit space environment. Unexpectedly, more than 80% of the silk and collagen materials were chemically crosslinked by space radiation. These findings are critical for designing next-generation biocompatible materials for contact with living systems in space environments, where the effects of heavy ionizing particles and other cosmic radiation need to be considered
Constraints on Lorentz invariance violation from gamma-ray burst GRB090510
We obtain modified dispersion relations by requiring the vanishing of
determinant of inverse of modified photon propagators in Lorentz invariance
violation (LIV) theory. Inspired by these dispersion relations, we give a more
general dispersion relation with less assumption and apply it to the recent
observed gamma-ray burst GRB090510 to extract various constraints on LIV
parameters. We find that the constraint on quantum gravity mass is slightly
larger than the Planck mass but is consistent with the other recent
observations, so the corresponding LIV coefficient has reached the
natural order () as one expects. From our analysis, the linear LIV
corrections to photon group velocity might be not excluded yet.Comment: 10 latex pages, no figures, version accepted for publication in PR
Dorsal turning of motor corticospinal axons at the pyramidal decussation requires plexin signaling
<p>Abstract</p> <p>Background</p> <p>The development of the corticospinal tract (CST) in higher vertebrates relies on a series of axon guidance decisions along its long projection pathway. Several guidance molecules are known to be involved at various decision points to regulate the projection of CST axons. However, previous analyses of the CST guidance defects in mutant mice lacking these molecules have suggested that there are other molecules involved in CST axon guidance that are yet to be identified. In this study, we investigate the role of plexin signaling in the guidance of motor CST axons <it>in vivo</it>.</p> <p>Results</p> <p>Expression pattern studies show that <it>plexin-A3</it>, <it>plexin-A4</it>, and <it>neuropilin-1 </it>are expressed in the developing cerebral cortex when the motor CST axons originating from layer V cortical neurons are guided down to the spinal cord. By analyzing mutant mice, we show that motor CST axons that turn dorsally to cross the midline at the pyramidal decussation require plexin-A3 and plexin-A4 signaling. Although other CST guidance defects are found in neuropilin-1 mutants, this dorsal turning defect is not observed in either neuropilin-1 or neuropilin-2 mutants, suggesting that the local cues that activate plexin signaling at the dorsal turning point are membrane-bound semaphorins. Further expression pattern study and mutant analysis indicate that Sema6A is one of the local cues for motor CST axon turning at the pyramidal decussation.</p> <p>Conclusion</p> <p>Dorsal turning and midline crossing at the pyramidal decussation is a crucial step to properly direct CST axons into the dorsal spinal cord. We show that the signaling of plexin-A3, plexin-A4, and Sema6A is at least partially required for dorsal turning of the CST axons, while neuropilin-1 is required for proper fasciculation of the tract at midline crossing. Together with previous reports, these results demonstrate that several guidance cues are specifically utilized to regulate the dorsal turning and midline crossing of developing CST axons.</p
Electronic structure of Fe1.04(Te0.66Se0.34)
We report the electronic structure of the iron-chalcogenide superconductor,
Fe1.04(Te0.66Se0.34), obtained with high resolution angle-resolved
photoemission spectroscopy and density functional calculations. In
photoemission measurements, various photon energies and polarizations are
exploited to study the Fermi surface topology and symmetry properties of the
bands. The measured band structure and their symmetry characters qualitatively
agree with our density function theory calculations of Fe(Te0.66Se0.34),
although the band structure is renormalized by about a factor of three. We find
that the electronic structures of this iron-chalcogenides and the
iron-pnictides have many aspects in common, however, significant differences
exist near the Gamma-point. For Fe1.04(Te0.66Se0.34), there are clearly
separated three bands with distinct even or odd symmetry that cross the Fermi
energy (EF) near the zone center, which contribute to three hole-like Fermi
surfaces. Especially, both experiments and calculations show a hole-like
elliptical Fermi surface at the zone center. Moreover, no sign of spin density
wave was observed in the electronic structure and susceptibility measurements
of this compound.Comment: 7 pages, 9 figures. submitted to PRB on November 15, 2009, and
accepted on January 6, 201
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