1,290 research outputs found
No Supermassive Black Hole in M33?
We analyze optical long-slit spectroscopy of the nucleus of M33 obtained from
the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope.
Rather than the steep rise expected within the radius of influence of a
supermassive black hole, the velocity dispersion drops significantly within the
inner parsec. Dynamical modelling yields an estimated upper limit of 3000 solar
masses for the mass of a central compact object. This upper limit is however
consistent within the uncertainties with the mass predicted by the M-sigma
relation, which is between 2000 and 20,000 solar masses. We therefore can not
conclude that the presence of a massive black hole in the nucleus of M33 would
require a different formation mechanism from that of the black holes detected
in galaxies with more luminous bulges.Comment: 10 pages, 4 postscript figure
The Low End of the Supermassive Black Hole Mass Function: Constraining the Mass of a Nuclear Black Hole in NGC 205 via Stellar Kinematics
Hubble Space Telescope (HST) images and spectra of the nucleated dwarf
elliptical galaxy NGC 205 are combined with 3-integral axisymmetric dynamical
models to constrain the mass (M_BH) of a putative nuclear black hole. This is
only the second attempt, after M33, to use resolved stellar kinematics to
search for a nuclear black hole with mass below 10^6 solar masses. We are
unable to identify a best-fit value of M_BH in NGC 205; however, the data
impose a upper limit of 2.2x10^4 M_sun (1sigma confidence) and and upper limit
of 3.8x10^4 M_sun (3sigma confidence). This upper limit is consistent with the
extrapolation of the M_BH-sigma relation to the M_BH < 10^6 M_sunregime. If we
assume that NGC 205 and M33 both contain nuclear black holes, the upper limits
on M_BH in the two galaxies imply a slope of ~5.5 or greater for the M_BH-sigma
relation. We use our 3-integral models to evaluate the relaxation time (T_r)
and stellar collision time (T_coll) in NGC 205; T_r~10^8 yr or less in the
nucleus and T_coll~10^11 yr. The low value of T_r is consistent with core
collapse having already occurred, but we are unable to draw conclusions from
nuclear morphology about the presence or absence of a massive black hole.Comment: Latex emulateapj, 15 pages, 16 figures, Version accepted for
Publication in ApJ, 20 July 2005, v628. Minor changes to discussion
Supermassive Black Holes in Active Galactic Nuclei. I. The Consistency of Black Hole Masses in Quiescent and Active Galaxies
We report the first results of a program to measure accurate stellar velocity
dispersions in the bulges of the host galaxies of active galactic nuclei (AGNs)
for which accurate black hole (BH) masses have been determined via
reverberation mapping. We find good agreement between BH masses obtained from
reverberation mapping, and from the M(BH) - sigma relation as defined by
quiescent galaxies, indicating a common relationship between active and
quiescent black holes and their large-scale environments.Comment: Submitted to ApJ
DEVELOPMENT OF CORROSION-RESISTANT ALLOYS FOR USE AS CONTAINER MATERIALS FOR DECLADDING SOLUTIONS OR AS WELDING ALLOYS
Twenty-four experimental alloys were developed and evaluated as container materials or welding alloys for use with Sulfex and Niflex decladding solutions. Niflex solutions which were more corrosive than Sulfex solutions to most of the experimental alloys, produced severe localized attack on weldments made on vacuum-melted Hastelloy F with the experimental alloys. However, several of the alloys, when self-welded, were not selectively attacked. Some of these showed a substantial improvement in resistance to the decladding solutions. The most promising alloys were based on either 45 wt.% nickel--22 wt.% chromium or 50 wt.% nickel--25 wt.% chromium, with at least 6 wt.% molybdenum, and 1 wt.% titanium, 0.6 wt.% manganese, 0.4 wt. % silicon, 0.02 wt.% carbon, and the balance, iron. The alloy most resistant to both solutions contained 6 wt.% molybdenum and 1 wt.% copper in the 50 wt.% nickel--25 wt.% chromium base. Its corrosion rate of 22 mils per month in Niflex, with no selective attack, was significantly lower than the 105 mils per month recorded for Hastelloy F. Even lower rates would be expected under the less stringent conditions of actual process operation. Indications are that more resistance might be obtained by increasing the chromium and nickel contents. (auth
Explanatory multivariate modeling for disability, pain, and claims in patients with spine pain via a physical therapy direct access model of care
BACKGROUND: Direct access physical therapy (DAPT) may result in improved patient outcomes and reduced healthcare costs. Prognostic factors associated with spine-related outcomes and insurance claims with DAPT are needed.
OBJECTIVE: To identify factors that predict variations in outcomes for spine pain and insurance claims using DAPT.
METHODS: Individuals (N = 250) with spine pain were analyzed. Outcomes were classified into High, Low, or Did Not Meet
minimal clinically important difference (MCID) scores. Claims were categorized into low, medium, or high tertiles. Prognostic
variables were identified from patient information.
RESULTS: Females were more likely to meet High MCID (odds ratio [OR] 2.84 (95% CI = 1.32, 6.11) and Low MCID (OR
2.86, 95% CI = 1.34, 6.10). Higher initial ODI/NDI scores were associated with High MCID (OR 1.04, 95% CI = 1.07, 1.22) and Low MCID (OR 0.91, 95% CI = 0.77, 1.07). Odds of a high claim were lowered by the absence of imaging (OR 0.04, 95% CI = 0.02, 0.09) and an active versus passive treatment (OR 0.38, 95% CI = 0.18, 0.80).
CONCLUSION: Females and higher initial disability predicted favorable outcomes. The novel introduction of claims into the prognostic modeling supports that active interventions and avoiding imaging may reduce claims
SDSS 0956+5128: A Broad-line Quasar with Extreme Velocity Offsets
We report on the discovery of a Type 1 quasar, SDSS 0956+5128, with a
surprising combination of extreme velocity offsets. SDSS 0956+5128 is a
broad-lined quasar exhibiting emission lines at three substantially different
redshifts: a systemic redshift of z ~ 0.714 based on narrow emission lines, a
broad MgII emission line centered 1200 km/s bluer than the systemic velocity,
at z ~ 0.707, and broad H\alpha and H\beta emission lines centered at z ~
0.690. The Balmer line peaks are 4100 km/s bluer than the systemic redshift.
There are no previously known objects with such an extreme difference between
broad MgII and broad Balmer emission. The two most promising explanations are
either an extreme disk emitter or a high-velocity black hole recoil. However,
neither explanation appears able to explain all of the observed features of
SDSS 0956+5128, so the object may provide a challenge to our general
understanding of quasar physics.Comment: ApJ, accepte
Distribution of Mycobacterium ulcerans in Buruli Ulcer Endemic and Non-Endemic Aquatic Sites in Ghana
Mycobacterium ulcerans, the causative agent of Buruli ulcer, is an emerging environmental bacterium in Australia and West Africa. The primary risk factor associated with Buruli ulcer is proximity to slow moving water. Environmental constraints for disease are shown by the absence of infection in arid regions of infected countries. A particularly mysterious aspect of Buruli ulcer is the fact that endemic and non-endemic villages may be only a few kilometers apart within the same watershed. Recent studies suggest that aquatic invertebrate species may serve as reservoirs for M. ulcerans, although transmission pathways remain unknown. Systematic studies of the distribution of M. ulcerans in the environment using standard ecological methods have not been reported. Here we present results from the first study based on random sampling of endemic and non-endemic sites. In this study PCR-based methods, along with biofilm collections, have been used to map the presence of M. ulcerans within 26 aquatic sites in Ghana. Results suggest that M. ulcerans is present in both endemic and non-endemic sites and that variable number tandem repeat (VNTR) profiling can be used to follow chains of transmission from the environment to humans. Our results suggesting that the distribution of M. ulcerans is far broader than the distribution of human disease is characteristic of environmental pathogens. These findings imply that focal demography, along with patterns of human water contact, may play a major role in transmission of Buruli ulcer
Taking the Measure of the Universe: Precision Astrometry with SIM PlanetQuest
Precision astrometry at microarcsecond accuracy has application to a wide
range of astrophysical problems. This paper is a study of the science questions
that can be addressed using an instrument that delivers parallaxes at about 4
microarcsec on targets as faint as V = 20, differential accuracy of 0.6
microarcsec on bright targets, and with flexible scheduling. The science topics
are drawn primarily from the Team Key Projects, selected in 2000, for the Space
Interferometry Mission PlanetQuest (SIM PlanetQuest). We use the capabilities
of this mission to illustrate the importance of the next level of astrometric
precision in modern astrophysics. SIM PlanetQuest is currently in the detailed
design phase, having completed all of the enabling technologies needed for the
flight instrument in 2005. It will be the first space-based long baseline
Michelson interferometer designed for precision astrometry. SIM will contribute
strongly to many astronomical fields including stellar and galactic
astrophysics, planetary systems around nearby stars, and the study of quasar
and AGN nuclei. SIM will search for planets with masses as small as an Earth
orbiting in the `habitable zone' around the nearest stars using differential
astrometry, and could discover many dozen if Earth-like planets are common. It
will be the most capable instrument for detecting planets around young stars,
thereby providing insights into how planetary systems are born and how they
evolve with time. SIM will observe significant numbers of very high- and
low-mass stars, providing stellar masses to 1%, the accuracy needed to
challenge physical models. Using precision proper motion measurements, SIM will
probe the galactic mass distribution and the formation and evolution of the
Galactic halo. (abridged)Comment: 54 pages, 28 figures, uses emulateapj. Submitted to PAS
- …