7,758 research outputs found
B-Physics at the Tevatron (Proceedings of PASCOS2010)
We report on recent B-Physics results from the Tevatron. The topics covered
include measurement of the polarization amplitudes in ,
the search for rare flavor-changing neutral-current decays, CP violation in
and semileptonic decays, and a new measurement
of the like-sign asymmetry in dimuon events.Comment: 6 pages, proceedings paper, 16th International Symposium on
Particles, Strings, and Cosmology, Valencia, Spain, July 19 - 23, 201
Non linear particle acceleration at non-relativistic shock waves in the presence of self-generated turbulence
Particle acceleration at astrophysical shocks may be very efficient if
magnetic scattering is self-generated by the same particles. This nonlinear
process adds to the nonlinear modification of the shock due to the dynamical
reaction of the accelerated particles on the shock. Building on a previous
general solution of the problem of particle acceleration with arbitrary
diffusion coefficients (Amato & Blasi, 2005), we present here the first
semi-analytical calculation of particle acceleration with both effects taken
into account at the same time: charged particles are accelerated in the
background of Alfven waves that they generate due to the streaming instability,
and modify the dynamics of the plasma in the shock vicinity.Comment: submitted to MNRA
Leveraging Regime Change as an Opportunity to Reimagine, Reset, and Demonstrate Results in Honors
Regime changes in higher education can be a source of disruption and lead to a potential derailment of honors programs. This paper describes one honors program’s agility and effective negotiation through a rapid succession of upper administrative change, suggesting that when seen as opportunities these changes invite honors practitioners to re-envision, reset, and reevaluate programmatic set points for admissions, student learning, and curricular innovation
The Optical - Infrared Colors of CORALS QSOs: Searching for Dust Reddening Associated With High Redshift Damped Lyman Alpha Systems
The presence of dust in quasar absorbers, such as damped Lyman alpha (DLA)
systems, may cause the background QSO to appear reddened. We investigate the
extent of this potential reddening by comparing the optical-to-infrared (IR)
colors of QSOs with and without intervening absorbers. Our QSO sample is based
on the Complete Optical and Radio Absorption Line System (CORALS) survey of
Ellison et al (2001). We have obtained near-simultaneous B and K band
magnitudes for subset of the CORALS sample and supplemented our observations
with further measurements published in the literature. To account for
redshift-related color changes, the B-K colors are normalized using the Sloan
Digital Sky Survey (SDSS) QSO composite. The mean normalized B-K color of the
DLA sub-sample is +0.12, whereas the mean for the no-DLA sample is -0.10; both
distributions have RMS scatters ~0.5. Neither a student's T-test nor a KS test
indicate that there is any significant difference between the two color
distributions. Based on simulations which redden the colors of QSOs with
intervening DLAs, we determine a reddening limit which corresponds to E(B-V) <
0.04 (SMC-like extinction) at 99% confidence (3 sigma), assuming that E(B-V) is
the same for all DLAs. Finally, we do not find any general correlation between
absorber properties (such as [Fe/Zn] or neutral hydrogen column density) and
B-K color. One of these two QSOs shows evidence for strong associated
absorption from X-ray observations, an alternative explanation for its very red
color. We conclude that the presence of intervening galaxies causes a minimal
reddening of the background QSO.Comment: Accepted for publication in A
Reconstitution of recombinant human replication factor C (RFC) and identification of an RFC subcomplex possessing DNA-dependent ATPase activity
Replication factor C (RFC) is a five-subunit protein complex required for coordinate leading and lagging strand DNA synthesis during S phase and DNA repair in eukaryotic cells. It functions to load the proliferating cell nuclear antigen (PCNA), a processivity factor for polymerases delta and epsilon, onto primed DNA templates. This process, which is ATP-dependent, is carried out by 1) recognition of the primer terminus by RFC () binding to and disruption of the PCNA trimer, and then 3) topologically linking the PCNA to the DNA. In this report, we describe the purification and properties of recombinant human RFC expressed in Sf9 cells from baculovirus expression vectors. Like native RFC derived from 293 cells, recombinant RFC was found to support SV40 DNA synthesis and polymerase delta DNA synthesis in vitro and to possess an ATPase activity that was highly stimulated by DNA and further augmented by PCNA. Assembly of RFC was observed to involve distinct subunit interactions in which both the 36- and 38-kDa subunits interacted with the 37-kDa subunit, and the 40-kDa subunit interacted with the 36-kDa subunit-37-kDa subunit subcomplex. The 140-kDa subunit was found to require interactions primarily with the 38- and 40-kDa subunits for incorporation into the complex. In addition, a stable subcomplex lacking the 140-kDa subunit, although defective for DNA replication, was found to possess DNA-dependent ATPase activity that was not responsive to the addition of PCNA
A Sub-Damped Ly Absorber with Unusual Abundances: Evidence of Gas Recycling in a Low-Redshift Galaxy Group
Using Hubble Space Telescope/Space Telescope Imaging Spectrograph G140M
spectroscopy, we investigate an absorption-line system at =0.07489 in the
spectrum of the quasi-stellar object PG 1543+489 (=0.401). The
sightline passes within kpc of an edge-on disk galaxy at a
similar redshift, but the galaxy belongs to a group with four other galaxies
within kpc. We detect H I [log (H I/) = 19.120.04]
as well as N I, Mg II, Si II, and Si III, from which we measure a gas-phase
abundance of [N/H] = . Photoionization models indicate that the
nitrogen-to-silicon relative abundance is solar, yet magnesium is underabundant
by a factor of 2. We also report spatially resolved emission-line
spectroscopy of the nearby galaxy, and we extract its rotation curve. The
galaxy's metallicity is higher than [N/H] in the absorber,
and interestingly, the absorber velocities suggest that the gas at 66
kpc is corotating with the galaxy's stellar disk, possibly with an inflow
component. These characteristics could indicate that this sub-damped Ly
absorber system arises in a "cold-accretion" flow. However, the absorber
abundance patterns are peculiar. We hypothesize that the gas was ejected from
its galaxy of origin (or perhaps is a result of tidal debris from interactions
between the group galaxies) with a solar nitrogen abundance, but that
subsequently mixed with (and was diluted by) gas in the circumgalactic medium
(CGM) or group. If the gas is bound to the nearby galaxy, this system may be an
example of the gas "recycling" predicted by theoretical galaxy simulations. Our
hypothesis is testable with future observations.Comment: 16 pages (in print): The Astrophysical Journal, vol 872, 12
Some properties of synchrotron radio and inverse-Compton gamma-ray images of supernova remnants
The synchrotron radio maps of supernova remnants (SNRs) in uniform
interstellar medium and interstellar magnetic field (ISMF) are analyzed,
allowing different `sensitivity' of injection efficiency to the shock
obliquity. The very-high energy gamma-ray maps due to inverse Compton process
are also synthesized. The properties of images in these different wavelength
bands are compared, with particular emphasis on the location of the bright
limbs in bilateral SNRs. Recent H.E.S.S. observations of SN 1006 show that the
radio and IC gamma-ray limbs coincide, and we found that this may happen if: i)
injection is isotropic but the variation of the maximum energy of electrons is
rather quick to compensate for differences in magnetic field; ii) obliquity
dependence of injection (either quasi-parallel or quasi-perpendicular) and the
electron maximum energy is strong enough to dominate magnetic field variation.
In the latter case, the obliquity dependence of the injection and the maximum
energy should not be opposite. We argue that the position of the limbs alone
and even their coincidence in radio, X-rays and gamma-rays, as it is discovered
by H.E.S.S. in SN 1006, cannot be conclusive about the dependence of the
electron injection efficiency, the compression/amplification of ISMF and the
electron maximum energy on the obliquity angle.Comment: Accepted for publication in MNRA
Intervening Metal Systems in GRB and QSO sight-lines: The Mgii and Civ Question
Prochter et al. 2006 recently found that the number density of strong
intervening 0.5<z<2 MgII absorbers detected in gamma-ray burst (GRB) afterglow
spectra is nearly 4 times larger than in QSO spectra. We have conducted a
similar study using CIV absorbers. Our CIV sample, consisting of a total of 20
systems, is drawn from 3 high resolution and high to moderate S/N VLT/UVES
spectra of 3 long-duration GRB afterglows, covering the redshift interval 1.6<
z<3.1. The column density distribution and number density of this sample do not
show any statistical difference with the same quantities measured in QSO
spectra. We discuss several possibilities for the discrepancy between CIV and
MgII absorbers and conclude that a higher dust extinction in the MgII QSO
samples studied up to now would give the most straightforward solution.
However, this effect is only important for the strong MgII absorbers.
Regardless of the reasons for this discrepancy, this result confirms once more
that GRBs can be used to detect a side of the universe that was unknown before,
not necessarily connected with GRBs themselves, providing an alternative and
fundamental investigative tool of the cosmic evolution of the universe.Comment: 21 pages, 4 figures, ApJ accepted, Revised after Referee Repor
The host galaxies of strong CaII QSO absorption systems at z<0.5
We present new imaging and spectroscopic observations of the fields of five
QSOs with very strong intervening CaII absorption systems at redshifts z<0.5
selected from the Sloan Digital Sky Survey. Recent studies of these very rare
absorbers indicate that they may be related to damped Lyman alpha systems
(DLAs). In all five cases we identify a galaxy at the redshift of the CaII
system with impact parameters up to ~24 kpc. In four out of five cases the
galaxies are luminous (L ~L*), metal-rich (Z ~Zsun), massive (velocity
dispersion, sigma ~100 km/s) spirals. Their star formation rates, deduced from
Halpha emission, are high, in the range SFR = 0.3 - 30 Msun/yr. In our
analysis, we paid particular attention to correcting the observed emission line
fluxes for stellar absorption and dust extinction. We show that these effects
are important for a correct SFR estimate; their neglect in previous low-z
studies of DLA-selected galaxies has probably led to an underestimate of the
star formation activity in at least some DLA hosts. We discuss possible links
between CaII-selected galaxies and DLAs and outline future observations which
will help clarify the relationship between these different classes of QSO
absorbers.Comment: Accepted for publication in MNRAS, 14 pages, 9 figures. Version with
full resolution images available at
http://www.ast.cam.ac.uk/~bjz/papers/Zych_etal_2007a.pd
Galactic Cosmic Rays from Supernova Remnants: II Shock Acceleration of Gas and Dust
This is the second paper (the first was astro-ph/9704267) of a series
analysing the Galactic Cosmic Ray (GCR) composition and origin. In this we
present a quantitative model of GCR origin and acceleration based on the
acceleration of a mixture of interstellar and/or circumstellar gas and dust by
supernova remnant blast waves. We present results from a nonlinear shock model
which includes (i) the direct acceleration of interstellar gas-phase ions, (ii)
a simplified model for the direct acceleration of weakly charged dust grains to
energies of order 100keV/amu simultaneously with the gas ions, (iii) frictional
energy losses of the grains colliding with the gas, (iv) sputtering of ions of
refractory elements from the accelerated grains and (v) the further shock
acceleration of the sputtered ions to cosmic ray energies. The calculated GCR
composition and spectra are in good agreement with observations.Comment: to appear in ApJ, 51 pages, LaTeX with AAS macros, 9 postscript
figures, also available from ftp://wonka.physics.ncsu.edu/pub/elliso
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