1,245 research outputs found
A Revised Model for the Formation of Disk Galaxies: Low Spin and Dark-Halo Expansion
We use observed rotation velocity-luminosity (VL) and size-luminosity (RL)
relations to single out a specific scenario for disk galaxy formation in the
LCDM cosmology. Our model involves four independent log-normal random
variables: dark-halo concentration c, disk spin lam_gal, disk mass fraction
m_gal, and stellar mass-to-light ratio M/L_I. A simultaneous match of the VL
and RL zero points with adiabatic contraction requires low-c halos, but this
model has V_2.2~1.8 V_vir (where V_2.2 and V_vir are the circular velocity at
2.2 disk scale lengths and the virial radius, respectively) which will be
unable to match the luminosity function (LF). Similarly models without
adiabatic contraction but standard c also predict high values of V_2.2/V_vir.
Models in which disk formation induces an expansion rather than the commonly
assumed contraction of the dark-matter halos have V_2.2~1.2 V_vir which allows
a simultaneous fit of the LF. This may result from non-spherical, clumpy gas
accretion, where dynamical friction transfers energy from the gas to the dark
matter. This model requires low lam_gal and m_gal values, contrary to naive
expectations. However, the low lam_gal is consistent with the notion that disk
galaxies predominantly survive in halos with a quiet merger history, while a
low m_gal is also indicated by galaxy-galaxy lensing. The smaller than expected
scatter in the RL relation, and the lack of correlation between the residuals
of the VL and RL relations, respectively, imply that the scatter in lam_gal and
in c need to be smaller than predicted for LCDM halos, again consistent with
the idea that disk galaxies preferentially reside in halos with a quiet merger
history.Comment: 28 pages, 16 figures, ApJ accepted, minor changes from unpublished
version, uses emulateapj.cls, high-resolution version available at
http://www.ucolick.org/~dutton/65200/hi-res-version/ms.dutton.v2_hr.p
A Topcolor Jungle Gym
We discuss an alternative to the topcolor seesaw mechanism. In our scheme,
all the light quarks carry topcolor, and there are many composite SU(2)
doublets. This makes it possible to get the observed top quark mass and
observed breaking in a way that is quite different from the
classic seesaw mechanism. We discuss a model of this kind that arises naturally
in the context of dynamically broken topcolor. There are many composite scalars
in a theory of this kind. This has important effects on the Pagels-Stokar
relation and the Higgs mass. We find GeV, lighter than in
typical topcolor models. We also show that the electroweak singlet quarks in
such a model can be lighter than the corresponding quarks in a seesaw model.Comment: 23 pages, LaTeX, uses epsf and psfi
Dorsal penile nerve block for robot-assisted radical prostatectomy catheter related pain: a randomized, double-blind, placebo-controlled trial
Purpose: Following Robotic-Assisted Radical Prostatectomy (RARP) patients routinely have penile pain and urethral discomfort secondary to an indwelling urethral catheter. Our objective was to assess the effect of dorsal penile nerve block with bupivacaine on urethral catheter-related pain after RARP. Methods: From 2012â2013, 140 patients with organ-confined prostate cancer were enrolled in an IRB approved double-blinded, randomized control trial comparing a dorsal penile nerve block of bupivacaine versus placebo after RARP performed by a single-surgeon. Patients were asked to complete questionnaires using the Wong-Bakers FACES Pain Rating scale while hospitalized and for 9Â days post-operatively, until the catheter was removed. The primary end-points were: catheter-related discomfort, abdominal (incisional) pain, and bladder spasm-related discomfort. Secondary end-points included narcotic and other analgesic usage. Results: 120 patients were randomized to placebo vs. bupivacaine dorsal penile nerve bock. The two arms (nâ=â56 bupivacaine and nâ=â60 placebo) did not differ in preoperative, perioperative, or pathological results. There was no difference in narcotic utilization between the two cohorts. Abdominal pain was slightly lower in the bupivacaine arm at 6Â hours compared to the placebo arm, but there was no difference in abdominal pain at other time points, and there were no differences in reported catheter-related discomfort or bladder spasm-associated discomfort at any of the measured time points. Conclusions: The data does not support the routine use of a dorsal penile nerve block with bupivacaine following RARP
Mass Modeling of Disk Galaxies: Constraints, Degeneracies and Adiabatic Contraction
This paper addresses available constraints on mass models fitted to rotation
curves. Mass models of disk galaxies have well-known degeneracies, that prevent
a unique mass decomposition. The most notable is due to the unknown value of
the stellar mass-to-light ratio (the disk-halo degeneracy); even with this
known, degeneracies between the halo parameters themselves may prevent an
unambiguous determination of the shape of the dark halo profile, which includes
the inner density slope of the dark matter halo. The latter is often referred
to as the ``cusp-core degeneracy''. We explore constraints on the disk and halo
parameters and apply these to four mock and six observed disk galaxies with
high resolution and extended rotation curves. Our full set of constraints
consists of mass-to-light (M/L) ratios from stellar population synthesis models
based on B-R colors, constraints on halo parameters from N-body simulations,
and constraining the halo virial velocity to be less than the maximum observed
velocity. These constraints are only partially successful in lifting the
cusp-core degeneracy. The effect of adiabatic contraction of the halo by the
disk is to steepen cores into cusps and reduce the best-fit halo concentration
and M/L values (often significantly). We also discuss the effect of disk
thickness, halo flattening, distance errors, and rotation curve error values on
mass modeling. Increasing the imposed minimum rotation curve error from
typically low, underestimated values to more realistic estimates decreases the
chi-square substantially and makes distinguishing between a cuspy or cored halo
profile even more difficult. In spite of the degeneracies and uncertainties
present, our constrained mass modeling favors sub-maximal disks (i.e., a
dominant halo) at 2.2 disk scale lengths, with Vdisk/Vtot < 0.6.Comment: 26 pages, 11 figures, minor changes to agree with published version,
uses emulateap
Imprints of Nuclear Symmetry Energy on Properties of Neutron Stars
Significant progress has been made in recent years in constraining the
density dependence of nuclear symmetry energy using terrestrial nuclear
laboratory data. Around and below the nuclear matter saturation density, the
experimental constraints start to merge in a relatively narrow region. At
supra-saturation densities, there are, however, still large uncertainties.
After summarizing the latest experimental constraints on the density dependence
of nuclear symmetry energy, we highlight a few recent studies examining
imprints of nuclear symmetry energy on the binding energy, energy release
during hadron-quark phase transitions as well as the -mode frequency and
damping time of gravitational wave emission of neutron stars.Comment: 10 pages. Invited talk given in the Nuclear Astrophysics session of
INPC2010, July 4-9, 2010, Vancouver, Canada; Journal of Physics: Conference
Series (2011
The Impact of Feedback on Disk Galaxy Scaling Relations
We use a disk galaxy evolution model to investigate the impact of mass
outflows (a.k.a. feedback) on disk galaxy scaling relations. Our model follows
the accretion, cooling, star formation and ejection of baryonic mass inside
growing dark matter haloes, with cosmologically motivated specific angular
momentum distributions. Models without feedback produce disks that are too
small and rotate too fast. Feedback reduces the baryonic masses of galaxies,
resulting in larger disks with lower rotation velocities. Models with feedback
can reproduce the zero points of the scaling relations between rotation
velocity, stellar mass and disk size, but only in the absence of adiabatic
contraction. Our feedback mechanism is maximally efficient in expelling mass,
but our successful models require 25% of the SN energy, or 100% of the SN
momentum, to drive the outflows. It remains to be seen whether such high
efficiencies are realistic or not. Our energy and momentum driven wind models
result in different slopes of various scaling relations, such as size - stellar
mass, stellar mass - halo mass, and metallicity - stellar mass. Observations
favor the energy driven wind at stellar masses below Mstar = 10^{10.5} Msun,
but the momentum driven wind model at high masses. The ratio between the
specific angular momentum of the baryons to that of the halo, (j_gal/m_gal), is
not unity in our models. Yet this is the standard assumption in models of disk
galaxy formation. Feedback preferentially ejects low angular momentum material
because star formation is more efficient at smaller galactic radii. This
results in (j_gal/m_gal) increasing with decreasing halo mass. This effect
helps to resolve the discrepancy between the high spin parameters observed for
dwarf galaxies with the low spin parameters predicted from LCDM. [Abridged]Comment: 27 pages, 16 figures, accepted to MNRAS, two new figure
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
Respiratory Virus Surveillance Among Children with Acute Respiratory Illnesses - New Vaccine Surveillance Network, United States, 2016-2021
The New Vaccine Surveillance Network (NVSN) is a prospective, active, population-based surveillance platform that enrolls children with acute respiratory illnesses (ARIs) at seven pediatric medical centers. ARIs are caused by respiratory viruses including influenza virus, respiratory syncytial virus (RSV), human metapneumovirus (HMPV), human parainfluenza viruses (HPIVs), and most recently SARS-CoV-2 (the virus that causes COVID-19), which result in morbidity among infants and young children (1-6). NVSN estimates the incidence of pathogen-specific pediatric ARIs and collects clinical data (e.g., underlying medical conditions and vaccination status) to assess risk factors for severe disease and calculate influenza and COVID-19 vaccine effectiveness. Current NVSN inpatient (i.e., hospital) surveillance began in 2015, expanded to emergency departments (EDs) in 2016, and to outpatient clinics in 2018. This report describes demographic characteristics of enrolled children who received care in these settings, and yearly circulation of influenza, RSV, HMPV, HPIV1-3, adenovirus, human rhinovirus and enterovirus (RV/EV),* and SARS-CoV-2 during December 2016-August 2021. Among 90,085 eligible infants, children, and adolescents (children) aged \u3c18 \u3eyear
A Pre-mRNAâAssociating Factor Links Endogenous siRNAs to Chromatin Regulation
In plants and fungi, small RNAs silence gene expression in the nucleus by establishing repressive chromatin states. The role of endogenous small RNAs in metazoan nuclei is largely unknown. Here we show that endogenous small interfering RNAs (endo-siRNAs) direct Histone H3 Lysine 9 methylation (H3K9me) in Caenorhabditis elegans. In addition, we report the identification and characterization of nuclear RNAi defective (nrde)-1 and nrde-4. Endo-siRNAâdriven H3K9me requires the nuclear RNAi pathway including the Argonaute (Ago) NRDE-3, the conserved nuclear RNAi factor NRDE-2, as well as NRDE-1 and NRDE-4. Small RNAs direct NRDE-1 to associate with the pre-mRNA and chromatin of genes, which have been targeted by RNAi. NRDE-3 and NRDE-2 are required for the association of NRDE-1 with pre-mRNA and chromatin. NRDE-4 is required for NRDE-1/chromatin association, but not NRDE-1/pre-mRNA association. These data establish that NRDE-1 is a novel pre-mRNA and chromatin-associating factor that links small RNAs to H3K9 methylation. In addition, these results demonstrate that endo-siRNAs direct chromatin modifications via the Nrde pathway in C. elegans
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