11,888 research outputs found
Seismic and gravity investigations on the Malaspina Glacier, Alaska
Seismic reflections obtained from bedrock beneath the Malaspina Glacier along a tenâmile profile line indicate ice thicknesses ranging from 1130 to 2050 ft. The base of the ice is 700 ft below sea level near the center of the profile and shallows both northward toward the mountains and southward toward the ice margin. Good reflections were obtained with dynamite charges of about one ounce in 26âft waterâfilled shot holes but only in relatively crevasseâfree areas. Deeper reflections substantiate the inferred sedimentary nature of the subglacial rocks and show geologic structures consistent with the regional pattern. Gravity measurements along the central three miles of the seismic profile line indicate a gentle northwestâsoutheast trending subglacial topographic grain. Seismic refraction shots beyond the present margin of the glacier suggest a thickness of unconsolidated proglacial deposits in excess of 500 ft
RXTE monitoring observations of Markarian 3
We present Rossi X-ray Timing Explorer, monitoring observations of the
Seyfert 2 galaxy Markarian 3 spanning a 200 day period during which time the
source flux varied by a factor in the 4-20 keV bandpass. In broad
agreement with earlier Ginga results, the average spectrum can be represented
in terms of a simple spectral model consisting of a very hard power-law
continuum () modified below keV by a high
absorbing column ( \cunits) together with a high
equivalent width Fe-K emission feature at 6.4 keV. The abnormally flat spectral
index is probably the signature of a strong reflection component and we
consider two models incorporating such emission. In the first the reflected
signal suffers the same absorption as the intrinsic continuum, whereas in the
second the reflection is treated as an unabsorbed spectral component. In the
former case, we require a very strong reflection signal () in order to
match the data; in addition variability of both the intrinsic power-law and the
reflection component is required. The unabsorbed reflection model requires a
somewhat higher line-of-sight column density to the nuclear source ( \cunits), but in this case the reflected signal remains constant
whilst the level of the intrinsic continuum varies. The latter description is
consistent with the reflection originating from the illuminated far inner wall
of a molecular torus, the nearside of which screens our direct view of the
central continuum source.Comment: 7 pages, submitted to the MNRA
The average X-ray/gamma-ray spectrum of radio-quiet Seyfert 1s
We have obtained the average 1--500 keV spectrum of radio-quiet Seyfert 1s
using data from EXOSAT, Ginga, HEAO, and GRO/OSSE. The spectral fit to the
combined average EXOSAT and OSSE data is fully consistent with that for Ginga
and OSSE, confirming results from an earlier Ginga/OSSE sample. The average
spectrum is well-fitted by a power-law X-ray continuum with an energy spectral
index of moderately absorbed by an ionized medium and with
a Compton reflection component. A high-energy cutoff (or a break) in the the
power-law component at a few hundred keV or more is required by the data. We
also show that the corresponding average spectrum from HEAO A1 and A4 is fully
compatible with that obtained from EXOSAT, Ginga and OSSE. These results
confirm that the apparent discrepancy between the results of Ginga (with
) and the previous results of EXOSAT and HEAO (with ) is indeed due to ionized absorption and Compton reflection first
taken into account for Ginga but not for the previous missions. Also, our
results confirm that the Seyfert-1 spectra are on average cut off in gamma-rays
at energies of at least a few hundred keV, not at keV (as suggested
earlier by OSSE data alone). The average spectrum is compatible with emission
from either an optically-thin relativistic thermal plasma in a disk corona, or
with a nonthermal plasma with a power-law injection of relativistic electrons.Comment: 7 pages, 3 Postscript figures, MNRAS accepte
Vortex motion in axisymmetric piston-cylinder configurations
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76950/1/AIAA-8430-329.pd
Educational differences in cardiovascular mortality:The role of shared family factors and cardiovascular risk factors
Aims: To explore the confounding effects of early family factors shared by siblings and cardiovascular risk factors in midlife on the educational differences in mortality from cardiovascular disease (CVD). Methods: Data from national and regional health surveys in Norway (1974â2003) were linked with data from the Norwegian Family Based Life Course Study, the National Educational Registry and the Cause of Death Registry. The study population consisted of participants with at least one full sibling among the health survey participants ( n=271,310). Data were available on CVD risk factors, including weight, height, blood pressure, total cholesterol and smoking. Results: The hazards ratio (HR) of CVD mortality was 3.44 (95% confidence interval (CI) 2.98â3.96) in the lowest educational group relative to the highest. The HRs were little altered in the within-sibship analyses. Adjusted for risk factors, the HR for CVD mortality in the cohort analyses was 2.05 (CI 1.77â2.37) in the lowest educational group relative to the highest. The respective HR in the within-sibship analyses was 2.46 (CI 1.48â2.24). Conclusions: Using a sibling design, we did not find that the association between education and CVD mortality was confounded by early life factors shared by siblings, but it was explained to a large extent by CVD risk factors. These results suggest that reducing levels of CVD risk factors could have the greatest effect on mortality in less well-educated people. </jats:p
Metaâanalysis of laparoscopic transcystic versus transcholedochal common bile duct exploration for choledocholithiasis
Peer reviewedPublisher PD
Evidence for Orbital Motion of Material Close to the Central Black Hole of Mrk 766
Time-resolved X-ray spectroscopy has been obtained for the narrow line
Seyfert galaxy Mrk766 from XMM-Newton observations. We present analysis in the
energy-time plane of EPIC pn data in the 4-8 keV band with energy resolution
R~50. A component of Fe Ka emission detected in the maps shows a variation of
photon energy with time that appears both to be statistically significant and
to be consistent with sinusoidal variation. We investigate the interpretation
that there exists a component of line emission from matter in a Keplerian orbit
around a supermassive black hole. The orbit has a period ~165 ks and a
line-of-sight velocity ~13,500 km/s. This yields a lower limit for the central
mass of M > 4.9x10^5 solar masses within a radius of 3.6 x 10^13 cm (2.4 A.U.).
The orbit parameters are consistent with higher black hole masses, but the lack
of any substantial gravitational redshift of the orbit implies an upper limit
to the black hole mass of 4.5x10^7 solar masses.Comment: 20 pages, 6 figures (some colour). Accepted for publication in A&A.
Only minor changes since V1 (including reordering of Figs 1a & b
Predictors of subgroups based on maximum drinks per occasion over six years for 833 adolescents and young adults in COGA.
ObjectiveA person's pattern of heavier drinking often changes over time, especially during the early drinking years, and reflects complex relationships among a wide range of characteristics. Optimal understanding of the predictors of drinking during times of change might come from studies of trajectories of alcohol intake rather than cross-sectional evaluations.MethodThe patterns of maximum drinks per occasion were evaluated every 2 years between the average ages of 18 and 24 years for 833 subjects from the Collaborative Study on the Genetics of Alcoholism. Latent class growth analysis identified latent classes for the trajectories of maximum drinks, and then logistic regression analyses highlighted variables that best predicted class membership.ResultsFour latent classes were found, including Class 1 (69%), with about 5 maximum drinks per occasion across time; Class 2 (15%), with about 9 drinks at baseline that increased to 18 across time; Class 3 (10%), who began with a maximum of 18 drinks per occasion but decreased to 9 over time; and Class 4 (6%), with a maximum of about 22 drinks across time. The most consistent predictors of higher drinking classes were female sex, a low baseline level of response to alcohol, externalizing characteristics, prior alcohol and tobacco use, and heavier drinking peers.ConclusionsFour trajectory classes were observed and were best predicted by a combination of items that reflected demography, substance use, level of response and externalizing phenotypes, and baseline environment and attitudes
Seismic and gravity investigations on the Malaspina Glacier, Alaska
Seismic reflections obtained from bedrock beneath the Malaspina Glacier along a tenâmile profile line indicate ice thicknesses ranging from 1130 to 2050 ft. The base of the ice is 700 ft below sea level near the center of the profile and shallows both northward toward the mountains and southward toward the ice margin. Good reflections were obtained with dynamite charges of about one ounce in 26âft waterâfilled shot holes but only in relatively crevasseâfree areas. Deeper reflections substantiate the inferred sedimentary nature of the subglacial rocks and show geologic structures consistent with the regional pattern. Gravity measurements along the central three miles of the seismic profile line indicate a gentle northwestâsoutheast trending subglacial topographic grain. Seismic refraction shots beyond the present margin of the glacier suggest a thickness of unconsolidated proglacial deposits in excess of 500 ft
Novel Superconducting Tunneling Structures
Contains a description of one research project.Joint Services Electronics Program Contract DAAL03-89-C-000
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