1,184 research outputs found
Compact High-Velocity Clouds at High Resolution
Six examples of the compact, isolated high-velocity clouds catalogued by
Braun & Burton (1999) and identified with a dynamically cold ensemble of
primitive objects falling towards the barycenter of the Local Group have been
imaged with the Westerbork Synthesis Radio Telescope; an additional ten have
been imaged with the Arecibo telescope. The imaging reveals a characteristic
core/halo morphology: one or several cores of cool, relatively
high-column-density material, are embedded in an extended halo of warmer,
lower-density material. Several of the cores show kinematic gradients
consistent with rotation; these CHVCs are evidently rotationally supported and
dark-matter dominated. The imaging data allows several independent estimates of
the distances to these objects, which lie in the range 0.3 to 1.0 Mpc. The CHVC
properties resemble what might be expected from very dark dwarf irregular
galaxies.Comment: 12 pages, 7 figures, to appear in "The Chemical Evolution of the
Milky Way: Stars versus Clusters", eds. F. Matteuchi and F. Giovannelli,
Kluwer Academic Publisher
Large Scale Structure of the Universe
Galaxies are not uniformly distributed in space. On large scales the Universe
displays coherent structure, with galaxies residing in groups and clusters on
scales of ~1-3 Mpc/h, which lie at the intersections of long filaments of
galaxies that are >10 Mpc/h in length. Vast regions of relatively empty space,
known as voids, contain very few galaxies and span the volume in between these
structures. This observed large scale structure depends both on cosmological
parameters and on the formation and evolution of galaxies. Using the two-point
correlation function, one can trace the dependence of large scale structure on
galaxy properties such as luminosity, color, stellar mass, and track its
evolution with redshift. Comparison of the observed galaxy clustering
signatures with dark matter simulations allows one to model and understand the
clustering of galaxies and their formation and evolution within their parent
dark matter halos. Clustering measurements can determine the parent dark matter
halo mass of a given galaxy population, connect observed galaxy populations at
different epochs, and constrain cosmological parameters and galaxy evolution
models. This chapter describes the methods used to measure the two-point
correlation function in both redshift and real space, presents the current
results of how the clustering amplitude depends on various galaxy properties,
and discusses quantitative measurements of the structures of voids and
filaments. The interpretation of these results with current theoretical models
is also presented.Comment: Invited contribution to be published in Vol. 8 of book "Planets,
Stars, and Stellar Systems", Springer, series editor T. D. Oswalt, volume
editor W. C. Keel, v2 includes additional references, updated to match
published versio
The Real Gauge Singlet Scalar Extension of Standard Model: A Possible Candidate of Cold Dark Matter
We consider a simplest extension of Standard Model in which a real SM gauge
singlet scalar with an additional discrete symmetry is introduced to SM.
This additional scalar can be a viable candidate of cold dark matter since the
stability of is achieved by the application of symmetry on .
Considering as a possible candidate of cold dark matter we have solved
Boltzmann's equation to find the freeze out temperature and relic density of
for Higgs mass 120 GeV in the scalar mass range 5 GeV to 1 TeV. As
coupling appearing in Lagrangian depends upon the value of scalar
mass and Higgs mass , we have constrained the
parameter space by using the WMAP limit on the relic density of dark matter in
the universe and the results of recent ongoing dark matter direct search
experiments namely CDMS-II, CoGeNT, DAMA, EDELWEISS-II, XENON-10, XENON-100.
From such analysis we find two distinct mass regions (a lower and higher mass
domain) for such a dark matter candidate that satisfy both the WMAP limit and
the experimental results considered here. We have estimated the possible
differential direct detection rates and annual variation of total detection
rates for this scalar dark matter candidate for two detector materials
namely Ge, Xe. Finally we have calculated the ray flux from the
galactic centre due to annihilation of two 130 GeV scalar dark matter into two
monoenergetic rays.Comment: 21 pages, New calculations, figures and references adde
General Analysis of Antideuteron Searches for Dark Matter
Low energy cosmic ray antideuterons provide a unique low background channel
for indirect detection of dark matter. We compute the cosmic ray flux of
antideuterons from hadronic annihilations of dark matter for various Standard
Model final states and determine the mass reach of two future experiments
(AMS-02 and GAPS) designed to greatly increase the sensitivity of antideuteron
detection over current bounds. We consider generic models of scalar, fermion,
and massive vector bosons as thermal dark matter, describe their basic features
relevant to direct and indirect detection, and discuss the implications of
direct detection bounds on models of dark matter as a thermal relic. We also
consider specific dark matter candidates and assess their potential for
detection via antideuterons from their hadronic annihilation channels. Since
the dark matter mass reach of the GAPS experiment can be well above 100 GeV, we
find that antideuterons can be a good indirect detection channel for a variety
of thermal relic electroweak scale dark matter candidates, even when the rate
for direct detection is highly suppressed.Comment: 44 pages, 15 Figure
Multi-symptom asthma is closely related to nasal blockage, rhinorrhea and symptoms of chronic rhinosinusitis-evidence from the West Sweden Asthma Study
Efficacy of a 7-day course of furazolidone, levofloxacin, and lansoprazole after failed Helicobacter pylori eradication
<p>Abstract</p> <p>Background</p> <p>Increasing resistance to clarithromycin and nitroimidazole is the main cause of failure in the <it>Helicobacter pylori </it>eradication. The ideal retreatment regimen remains unclear, especially in developing countries, where the infection presents high prevalence and resistance to antibiotics. The study aimed at determining the efficacy, compliance and adverse effects of a regimen that included furazolidone, levofloxacin and lansoprazole in patients with persistent <it>Helicobacter pylori </it>infection, who had failed to respond to at least one prior eradication treatment regimen.</p> <p>Methods</p> <p>This study included 48 patients with peptic ulcer disease. <it>Helicobacter pylori </it>infection was confirmed by a rapid urease test and histological examination of samples obtained from the antrum and corpus during endoscopy. The eradication therapy consisted of a 7-day twice daily oral administration of lansoprazole 30 mg, furazolidone 200 mg and levofloxacin 250 mg. Therapeutic success was confirmed by a negative rapid urease test, histological examination and 14C- urea breath test, performed 12 weeks after treatment completion. The Chi-square method was used for comparisons among eradication rates, previous treatments and previous furazolidone use.</p> <p>Results</p> <p>Only one of the 48 patients failed to take all medications, which was due to adverse effects (vomiting). Per-protocol and intention-to-treat eradication rates were 89% (95% CI- 89%–99%) and 88% (88–92%), respectively. Mild and moderate adverse effects were reported by 41 patients (85%). For patients with one previous treatment failure, the eradication rate was 100%. Compared to furazolidone-naïve patients, eradication rates were lower in those who had failed prior furazolidone-containing regimen(s) (74% vs. 100%, p = 0.002).</p> <p>Conclusion</p> <p>An empiric salvage-regimen including levofloxacin, furazolidone and lansoprazole is very effective in the eradication of <it>Helicobacter pylori</it>, particularly in patients that have failed one prior eradication therapy.</p
The Hubble Constant
I review the current state of determinations of the Hubble constant, which
gives the length scale of the Universe by relating the expansion velocity of
objects to their distance. There are two broad categories of measurements. The
first uses individual astrophysical objects which have some property that
allows their intrinsic luminosity or size to be determined, or allows the
determination of their distance by geometric means. The second category
comprises the use of all-sky cosmic microwave background, or correlations
between large samples of galaxies, to determine information about the geometry
of the Universe and hence the Hubble constant, typically in a combination with
other cosmological parameters. Many, but not all, object-based measurements
give values of around 72-74km/s/Mpc , with typical errors of 2-3km/s/Mpc.
This is in mild discrepancy with CMB-based measurements, in particular those
from the Planck satellite, which give values of 67-68km/s/Mpc and typical
errors of 1-2km/s/Mpc. The size of the remaining systematics indicate that
accuracy rather than precision is the remaining problem in a good determination
of the Hubble constant. Whether a discrepancy exists, and whether new physics
is needed to resolve it, depends on details of the systematics of the
object-based methods, and also on the assumptions about other cosmological
parameters and which datasets are combined in the case of the all-sky methods.Comment: Extensively revised and updated since the 2007 version: accepted by
Living Reviews in Relativity as a major (2014) update of LRR 10, 4, 200
The stellar halo of the Galaxy
Stellar halos may hold some of the best preserved fossils of the formation
history of galaxies. They are a natural product of the merging processes that
probably take place during the assembly of a galaxy, and hence may well be the
most ubiquitous component of galaxies, independently of their Hubble type. This
review focuses on our current understanding of the spatial structure, the
kinematics and chemistry of halo stars in the Milky Way. In recent years, we
have experienced a change in paradigm thanks to the discovery of large amounts
of substructure, especially in the outer halo. I discuss the implications of
the currently available observational constraints and fold them into several
possible formation scenarios. Unraveling the formation of the Galactic halo
will be possible in the near future through a combination of large wide field
photometric and spectroscopic surveys, and especially in the era of Gaia.Comment: 46 pages, 16 figures. References updated and some minor changes.
Full-resolution version available at
http://www.astro.rug.nl/~ahelmi/stellar-halo-review.pd
Bayes Factors for Mixed Models: a Discussion
van Doorn et al. (2021) outlined various questions that arise when conducting Bayesian model comparison for mixed effects models. Seven response articles offered their own perspective on the preferred setup for mixed model comparison, on the most appropriate specification of prior distributions, and on the desirability of default recommendations. This article presents a round-table discussion that aims to clarify outstanding issues, explore common ground, and outline practical considerations for any researcher wishing to conduct a Bayesian mixed effects model comparison
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