9,540 research outputs found
A Tidal Flare Candidate in Abell 1795
As part of our ongoing archival X-ray survey of galaxy clusters for tidal
flares, we present evidence of an X-ray transient source within 1 arcmin of the
core of Abell 1795. The extreme variability (a factor of nearly 50), luminosity
(> 2 x 10^42 erg s^{-1}), long duration (> 5 years) and supersoft X-ray
spectrum (< 0.1 keV) are characteristic signatures of a stellar tidal
disruption event according to theoretical predictions and to existing X-ray
observations, implying a massive >~10^5 M_sun black hole at the centre of that
galaxy. The large number of X-ray source counts (~700) and long temporal
baseline (~12 years with Chandra and XMM-Newton) make this one of the
best-sampled examples of any tidal flare candidate to date. The transient may
be the same EUV source originally found contaminating the diffuse ICM
observations of Bowyer et al. (1999), which would make it the only tidal flare
candidate with reported EUV observations and implies an early source luminosity
1-2 orders of magnitude greater. If the host galaxy is a cluster member then it
must be a dwarf galaxy, an order of magnitude less massive than the quiescent
galaxy Henize 2-10 which hosts a massive black hole that is difficult to
reconcile with its low mass. The unusual faintness of the host galaxy may be
explained by tidal stripping in the cluster core.Comment: Accepted by MNRAS 2013 July 23. 27 pages, 10 figure
X-ray Observations of Distant Optically Selected Cluster
We have measured fluxes or flux limits for 31 of the 79 cluster candidates in
the Palomar Distant Cluster Survey (PDCS) using archival ROSAT/PSPC pointed
observations. Our X-ray survey reaches a flux limit of erg s cm (0.4 - 2.0 keV), which corresponds to
luminosities of erg s ( = 50 km
s Mpc, = ), if we assume the PDCS estimated
redshifts. Of the 31 cluster candidates, we detect six at a signal-to-noise
greater than three. We estimate that (90% confidence
limits) of these six detections are a result of X-ray emission from objects
unrelated to the PDCS cluster candidates. The net surface density of X-ray
emitting cluster candidates in our survey, clusters
deg, agrees with that of other, X-ray selected, surveys. It is possible,
given the large error on our contamination rate, that we have not detected
X-ray emission from any of our observed PDCS cluster candidates. We find no
statistically significant difference between the X-ray luminosities of PDCS
cluster candidates and those of Abell clusters of similar optical richness.
This suggests that the PDCS contains objects at high redshift similar to the
low redshift clusters in the Abell catalogs. We show that the PDCS cluster
candidates are not bright X-ray sources, the average luminosity of the six
detected candidates is only erg s (0.4-2.0
keV). This finding is in agreement with previous X-ray studies of high
redshift, optically selected, rich clusters of galaxies.Comment: 19 pages, LaTeX with AAS Preprint Macros (v. 4), 3 embedded
postscript figures, 3 Seperate Tables using aj_pt4.sty, Accepted by the
Astronomical Journal for November 199
A Search for X-Ray Bright Distant Clusters of Galaxies
We present the results of a search for X--ray luminous distant clusters of
galaxies. We found extended X--ray emission characteristic of a cluster towards
two of our candidate clusters of galaxies. They both have a luminosity in the
ROSAT bandpass of and a redshift of ;
thus making them two of the most distant X--ray clusters ever observed.
Furthermore, we show that both clusters are optically rich and have a known
radio source associated with them. We compare our result with other recent
searches for distant X--ray luminous clusters and present a lower limit of
for the number density of such high redshift
clusters. This limit is consistent with the expected abundance of such clusters
in a standard (b=2) Cold Dark Matter Universe. Finally, our clusters provide
important high redshift targets for further study into the origin and evolution
of massive clusters of galaxies. Accepted for publication in the 10th September
1994 issue of ApJ.Comment: 20 pages Latex file + 1 postscript figure file appende
Observation of Spin Flips with a Single Trapped Proton
Radio-frequency induced spin transitions of one individual proton are
observed for the first time. The spin quantum jumps are detected via the
continuous Stern-Gerlach effect, which is used in an experiment with a single
proton stored in a cryogenic Penning trap. This is an important milestone
towards a direct high-precision measurement of the magnetic moment of the
proton and a new test of the matter-antimatter symmetry in the baryon sector
Microbial Production of 3-hydroxypropionaldehyde from Glycerol Bioconversion
3-Hydroxypropionaldehyde (3-HPA) is of high industrial interest as a new platform intermediate from bioconversion of renewable materials because it can be converted into a number of large scale commodity chemicals. In this work we studied the production of 3-HPA from bioconversion of glycerol in a two-stage process. In the first stage active biomass is produced. The active biomass is then used for the production of 3-HPA in a second stage by biotransformation with the help of semicarbazide to trap 3-HPA from the culture. First we optimized the conditions for active biomass production for the biotransformation in the second step. By using a fed-batch process with proper feeding of semicarbazide and supplementary addition of active biomass we reached a final concentration of 54 g/l 3-HPA with a yield of 97 %mol/mol. This represents the highest 3-HPA concentration and yield reported so far for the microbial production of 3-HPA from glycerol
Telluric correction in the near-infrared: Standard star or synthetic transmission?
Context. The atmospheric absorption of the Earth is an important limiting
factor for ground-based spectroscopic observations and the near-infrared and
infrared regions are the most affected. Several software packages that produce
a synthetic atmospheric transmission spectrum have been developed to correct
for the telluric absorption; these are Molecfit, TelFit, and TAPAS. Aims. Our
goal is to compare the correction achieved using these three telluric
correction packages and the division by a telluric standard star. We want to
evaluate the best method to correct near-infrared high-resolution spectra as
well as the limitations of each software package and methodology. Methods. We
applied the telluric correction methods to CRIRES archival data taken in the J
and K bands. We explored how the achieved correction level varies depending on
the atmospheric T-P profile used in the modelling, the depth of the atmospheric
lines, and the molecules creating the absorption. Results. We found that the
Molecfit and TelFit corrections lead to smaller residuals for the water lines.
The standard star method corrects best the oxygen lines. The Molecfit package
and the standard star method corrections result in global offsets always below
0.5% for all lines; the offset is similar with TelFit and TAPAS for the H2O
lines and around 1% for the O2 lines. All methods and software packages result
in a scatter between 3% and 7% inside the telluric lines. The use of a tailored
atmospheric profile for the observatory leads to a scatter two times smaller,
and the correction level improves with lower values of precipitable water
vapour. Conclusions. The synthetic transmission methods lead to an improved
correction compared to the standard star method for the water lines in the J
band with no loss of telescope time, but the oxygen lines were better corrected
by the standard star method.Comment: 18 pages, 13 figures, Accepted to A&
Uncertainties on Clusters of Galaxies Distances
We investigate in this paper the error on the cluster redshift estimate as a
function of: (1) the number of galaxy structures along the line of sight; (2)
the morphology of the clusters (regular/substructures); (3) the nature of the
observed galaxies (cD/normal galaxies); (4) the number of observed galaxies;
and (5) the distance of the clusters. We find that if we use cD galaxies we
have errors of less than 2% (at the 1- level) for the cluster distances
except when the clusters are very complex. In those cases when we use five
redshift measurements along the cluster lines of sight to compute the mean
redshift, the mean redshift estimate error is less than 5% for the clusters
closer than z=0.30. The same error of 5% for clusters in z=[0.30;0.60] requires
about 12 redshifts measurements.Comment: 6 pages, 1 table, 3 figures, accepted in A&
Economic Benefits of the Recycling Industry in Missouri
The recycling, remanufacturing, and reuse industry (RRR) plays an important role in Missouri by reducing the use of raw natural resources and by reducing energy consumption. Recycling activities also provide important economic benefits beyond environmental benefits. The Missouri Recycling Economic Information Study (MOREIS), funded by the EnvironmentalImprovement and Energy Resources Authority
(EIERA), was conducted to determine the extent of economic benefits of recycling for Missourians. A survey was conducted of potential recycling, remanufacturing, and reuse firms in the state. The surveydata along with data from the North American
Industry Classification System (NAICS) were used to estimate the direct economic impact of the industry in Missouri. Secondary impacts were then calculated from the direct economic impact. The study examined four business sectors, recycling collection, recycling processing, recycling manufacturing, and reuse and remanufacturing. The four business sectors are subdivided into 26 business categories.
Data gathered from a mail survey were used in
11 business categories, a calculation based on industry data for 2 categories, and existing data were drawn from the NAICS for the remaining 13 categories. The approach used here permits comparison with the
United States Recycling Economic Information Study (USREIS) and other state studies that were based upon the methodology used in USREIS. Three levels of economic impact were used. Data are presented according to the direct effects (actual business employees, sales, and payroll), indirect effects (the effect of purchasing products and services from other business in order to produce a product), and induced effects (wages paid to employees in the direct and supporting industries that are available for employees to purchase goods and services). The induced effect is the total effect the industry has on the region
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