6,148 research outputs found
Low-Mass X-Ray Binaries, Millisecond Radio Pulsars, and the Cosmic Star Formation Rate
We report on the implications of the peak in the cosmic star-formation rate
(SFR) at redshift z ~ 1.5 for the resulting population of low-mass X-ray
binaries(LMXB) and for that of their descendants, the millisecond radio pulsars
(MRP). Since the evolutionary timescales of LMXBs, their progenitors, and their
descendants are thought be significant fractions of the time-interval between
the SFR peak and the present epoch, there is a lag in the turn-on of the LMXB
population, with the peak activity occurring at z ~ 0.5 - 1.0. The peak in the
MRP population is delayed further, occurring at z < 0.5. We show that the
discrepancy between the birthrate of LMXBs and MRPs, found under the assumption
of a stead-state SFR, can be resolved for the population as a whole when the
effects of a time-variable SFR are included. A discrepancy may persist for
LMXBs with short orbital periods, although a detailed population synthesis will
be required to confirm this. Further, since the integrated X-ray luminosity
distribution of normal galaxies is dominated by X-ray binaries, it should show
strong luminosity evolution with redshift. In addition to an enhancement near
the peak (z ~ 1.5) of the SFR due to the prompt turn-on of the relatively
short-lived massive X-ray binaries and young supernova remnants, we predict a
second enhancement by a factor ~10 at a redshift between ~ 0.5 and ~ 1 due to
the delayed turn-on of the LMXB population. Deep X-ray observations of galaxies
out to z ~ 1 by AXAF will be able to observe this enhancement, and, by
determining its shape as a function of redshift, will provide an important new
method for constraining evolutionary models of X-ray binaries.Comment: 13 pages, including 1 figure. Accepted for publication in ApJ Letter
EuroSpine Task Force on Research: support for spine researchers
In recognition of the value of research to the practice of spine care, Federico Balagué and Ferran Pellisé, at the time President and Secretary for EuroSpine, asked Margareta Nordin to set up a Task Force on Research (TFR) for EuroSpine during summer 2011. The concept was to stimulate and facilitate a research community within the society, through two main functions: (1) distribution of EuroSpine funds to researchers; (2) develop and deliver research training/education courses. What has the EuroSpine TFR accomplished since its inception
The Next Generation Virgo Cluster Survey (NGVS). XVIII. Measurement and Calibration of Surface Brightness Fluctuation Distances for Bright Galaxies in Virgo (and Beyond)
We describe a program to measure surface brightness fluctuation (SBF)
distances to galaxies observed in the Next Generation Virgo Cluster Survey
(NGVS), a photometric imaging survey covering of the Virgo cluster
in the bandpasses with the Canada-France Hawaii Telescope. We
describe the selection of the sample galaxies, the procedures for measuring the
apparent -band SBF magnitude , and the calibration of the absolute
as a function of observed stellar population properties. The
multi-band NGVS data set provides multiple options for calibrating the SBF
distances, and we explore various calibrations involving individual color
indices as well as combinations of two different colors. Within the color range
of the present sample, the two-color calibrations do not significantly improve
the scatter with respect to wide-baseline, single-color calibrations involving
. We adopt the calibration as reference for the present
galaxy sample, with an observed scatter of 0.11 mag. For a few cases that lack
good photometry, we use an alternative relation based on a combination
of and colors, with only a slightly larger observed scatter of
0.12 mag. The agreement of our measurements with the best existing distance
estimates provides confidence that our measurements are accurate. We present a
preliminary catalog of distances for 89 galaxies brighter than
mag within the survey footprint, including members of the background M and W
Clouds at roughly twice the distance of the main body of the Virgo cluster. The
extension of the present work to fainter and bluer galaxies is in progress.Comment: ApJ accepte
Photoassociative spectroscopy at long range in ultracold strontium
We report photoassociative spectroscopy of Sr in a magneto-optical
trap operating on the intercombination line at 689 nm.
Photoassociative transitions are driven with a laser red-detuned by 600-2400
MHz from the atomic resonance at 461 nm. Photoassociation
takes place at extremely large internuclear separation, and the
photoassociative spectrum is strongly affected by relativistic retardation. A
fit of the transition frequencies determines the atomic lifetime
( ns) and resolves a discrepancy between experiment and
recent theoretical calculations.Comment: 4 pages, 4 figures, submitte
The Ontology Lookup Service: more data and better tools for controlled vocabulary queries
The Ontology Lookup Service (OLS) (http://www.ebi.ac.uk/ols) provides interactive and programmatic interfaces to query, browse and navigate an ever increasing number of biomedical ontologies and controlled vocabularies. The volume of data available for querying has more than quadrupled since it went into production and OLS functionality has been integrated into several high-usage databases and data entry tools. Improvements have been made to both OLS query interfaces, based on user feedback and requirements, to improve usability and service interoperability and provide novel ways to perform queries
Design and Construction of Compaction Grouting for Foundation Soil Improvements
This paper presents the design and construction of compaction grouting work completed for a tank replacement project in Portland, Oregon. The project site is located along the west bank of the Willamette River. The subsurface soils at the project site were determined to be highly susceptible to soil liquefaction and lateral spreading under a design earthquake event per the building code. Compaction grouting was designed and constructed to strengthen the foundation soils supporting the new steel tank that is 115 feet in diameter and 40 feet in height. The design of the compaction grouting was completed using the design guidelines outlined in ASCE/G-I Standard 53-10. Detailed quality assurance/quality control processes were implemented during grouting operations to account for the variability in soil conditions being grouted. Real time monitoring was also completed to evaluate the ground movement induced by the grouting process and its impact to adjacent structures and critical utilities. Pre- and post-grouting CPTs were completed to verify that the intended ground densification was achieved. A hydrostatic test was also completed with the tank filled with water. The tank foundation settlement under the hydrostatic test was found to range between ¼ to ¾ inches and met the acceptance criteria per API-650 and API-653 Standards
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