104 research outputs found
The quasar Q0957+561: Lensed CO emission from a disk at z~1.4?
In recent years large efforts have been made to detect molecular gas towards
high redshifted objects. Up to now the literature reports on only two cases of
CO-detection in quasars at a redshift between 1 and 2 - Q0957+561, a
gravitationally lensed system at z=1.41 (Planesas et al. 1999), and HR10 at
z=1.44 (Andreani et al. 2000). According to Planesas et al. (1999), 12CO(2-1)
emission was detected towards both the lensed images of Q0957+561 with the IRAM
Plateau de Bure Interferometer (PdBI). In contrast to the optical spectra of
the two images which support the idea that they are images of one and the same
object, the CO-spectra were surprisingly different: the southern image (named
CO-B) shows a single blueshifted line whereas a double-peaked line profile with
a blue- and a redshifted part appears towards the northern image (CO-A). Based
on the observations and on simulations with a gravitational lens program, we
are tempted to argue that the line profile traces the presence of molecular gas
of a disk in the host galaxy around the quasar. We have now new observations
with the PdBI providing the necessary sensitivity to corroborate our disk
model.Comment: 4 pages, 1 figure, to appear in "Proceedings of the 4th
Cologne-Bonn-Zermatt-Symposium", ed. S. Pfalzner, C. Kramer, C. Straubmeier,
and A. Heithausen (Springer Verlag
Weak and Strong Lensing Statistics
After a brief introduction to gravitational lensing theory, a rough overview
of the types of gravitational lensing statistics that have been performed so
far will be given. I shall then concentrate on recent results of galaxy-galaxy
lensing, which indicate that galactic halos extend much further than can be
probed via rotation of stars and gas.Comment: 10 pages, 2 figures, talk given at the ISSI-Workshop "Matter in the
Universe", 19-23 March 2001 Bern (Switzerland
Survey of H-alpha emission from thirty nearby dwarf galaxies
Measurements of the H-alpha flux from 30 neighboring dwarf galaxies are
presented. After correction for absorption, these fluxes are used to estimate
the star formation rate (SFR). The SFR for 18 of the galaxies according to the
H-alpha emission are compared with estimates of the SFR from FUV magnitudes
obtained with the GALEX telescope. These are in good agreement over the range
log[SFR] = [-3,0]M sun/yr.Comment: 18 pages, 10 figures, 3 table
A contemporaneous infrared flash from a long gamma-ray burst: an echo from the central engine
The explosion that results in a cosmic gamma-ray burst (GRB) is thought to
produce emission from two physical processes -- the activity of the central
engine gives rise to the high-energy emission of the burst through internal
shocking and the subsequent interaction of the flow with the external
environment produces long-wavelength afterglow. While afterglow observations
continue to refine our understanding of GRB progenitors and relativistic
shocks, gamma-ray observations alone have not yielded a clear picture of the
origin of the prompt emission nor details of the central engine. Only one
concurrent visible-light transient has been found and was associated with
emission from an external shock. Here we report the discovery of infrared (IR)
emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of
GRB 041219a. Our robotic telescope acquired 21 images during the active phase
of the burst, yielding the earliest multi-colour observations of any
long-wavelength emission associated with a GRB. Analysis of an initial IR pulse
suggests an origin consistent with internal shocks. This opens a new
possibility to study the central engine of GRBs with ground-based observations
at long wavelengths.Comment: Accepted to Nature on March 1, 2005. 9 pages, 4 figures, nature12.cls
and nature1.cls files included. This paper is under press embargo until print
publicatio
In vivo and in vitro tracking of erosion in biodegradable materials using non-invasive fluorescence imaging
Author Manuscript 2012 March 1.The design of erodible biomaterials relies on the ability to program the in vivo retention time, which necessitates real-time monitoring of erosion. However, in vivo performance cannot always be predicted by traditional determination of in vitro erosion[superscript 1, 2] , and standard methods sacrifice samples or animals[superscript 3], preventing sequential measures of the same specimen. We harnessed non-invasive fluorescence imaging to sequentially follow in vivo material-mass loss to model the degradation of materials hydrolytically (PEG:dextran hydrogel) and enzymatically (collagen). Hydrogel erosion rates in vivo and in vitro correlated, enabling the prediction of in vivo erosion of new material formulations from in vitro data. Collagen in vivo erosion was used to infer physiologic in vitro conditions that mimic erosive in vivo environments. This approach enables rapid in vitro screening of materials, and can be extended to simultaneously determine drug release and material erosion from a drug-eluting scaffold, or cell viability and material fate in tissue-engineering formulations.National Institutes of Health (U.S.) (GM/HL 49039)National Institutes of Health (U.S.) (UL1 RR 025758
The Cosmological Constant
This is a review of the physics and cosmology of the cosmological constant.
Focusing on recent developments, I present a pedagogical overview of cosmology
in the presence of a cosmological constant, observational constraints on its
magnitude, and the physics of a small (and potentially nonzero) vacuum energy.Comment: 50 pages. Submitted to Living Reviews in Relativity
(http://www.livingreviews.org/), December 199
Cluster Lenses
Clusters of galaxies are the most recently assembled, massive, bound
structures in the Universe. As predicted by General Relativity, given their
masses, clusters strongly deform space-time in their vicinity. Clusters act as
some of the most powerful gravitational lenses in the Universe. Light rays
traversing through clusters from distant sources are hence deflected, and the
resulting images of these distant objects therefore appear distorted and
magnified. Lensing by clusters occurs in two regimes, each with unique
observational signatures. The strong lensing regime is characterized by effects
readily seen by eye, namely, the production of giant arcs, multiple-images, and
arclets. The weak lensing regime is characterized by small deformations in the
shapes of background galaxies only detectable statistically. Cluster lenses
have been exploited successfully to address several important current questions
in cosmology: (i) the study of the lens(es) - understanding cluster mass
distributions and issues pertaining to cluster formation and evolution, as well
as constraining the nature of dark matter; (ii) the study of the lensed objects
- probing the properties of the background lensed galaxy population - which is
statistically at higher redshifts and of lower intrinsic luminosity thus
enabling the probing of galaxy formation at the earliest times right up to the
Dark Ages; and (iii) the study of the geometry of the Universe - as the
strength of lensing depends on the ratios of angular diameter distances between
the lens, source and observer, lens deflections are sensitive to the value of
cosmological parameters and offer a powerful geometric tool to probe Dark
Energy. In this review, we present the basics of cluster lensing and provide a
current status report of the field.Comment: About 120 pages - Published in Open Access at:
http://www.springerlink.com/content/j183018170485723/ . arXiv admin note:
text overlap with arXiv:astro-ph/0504478 and arXiv:1003.3674 by other author
Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis
BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London
Elliptic flow of charged particles in Pb-Pb collisions at 2.76 TeV
We report the first measurement of charged particle elliptic flow in Pb-Pb
collisions at 2.76 TeV with the ALICE detector at the CERN Large Hadron
Collider. The measurement is performed in the central pseudorapidity region
(||<0.8) and transverse momentum range 0.2< < 5.0 GeV/. The
elliptic flow signal v, measured using the 4-particle correlation method,
averaged over transverse momentum and pseudorapidity is 0.087 0.002
(stat) 0.004 (syst) in the 40-50% centrality class. The differential
elliptic flow v reaches a maximum of 0.2 near = 3
GeV/. Compared to RHIC Au-Au collisions at 200 GeV, the elliptic flow
increases by about 30%. Some hydrodynamic model predictions which include
viscous corrections are in agreement with the observed increase.Comment: 10 pages, 4 captioned figures, published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/389
Gravitational Lensing in Astronomy
Deflection of light by gravity was predicted by General Relativity and
observationaly confirmed in 1919. In the following decades various aspects of
the gravitational lens effect were explored theoretically, among them the
possibility of multiple or ring-like images of background sources, the use of
lensing as a gravitational telescope on very faint and distant objects, and the
possibility to determine Hubble's constant with lensing. Only relatively
recently gravitational lensing became an observational science after the
discovery of the first doubly imaged quasar in 1979. Today lensing is a booming
part of astrophysics.
In addition to multiply-imaged quasars, a number of other aspects of lensing
have been discovered since, e.g. giant luminous arcs, quasar microlensing,
Einstein rings, galactic microlensing events, arclets, or weak gravitational
lensing. By now literally hundreds of individual gravitational lens phenomena
are known.
Although still in its childhood, lensing has established itself as a very
useful astrophysical tool with some remarkable successes. It has contributed
significant new results in areas as different as the cosmological distance
scale, the large scale matter distribution in the universe, mass and mass
distribution of galaxy clusters, physics of quasars, dark matter in galaxy
halos, or galaxy structure.Comment: Review article for "Living Reviews in Relativity", see
http://www.livingreviews.org . 41 pages, latex, 22 figures (partly in GIF
format due to size constraints). High quality postscript files can be
obtained electronically at http://www.aip.de:8080/~jkw/review_figures.htm
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