29,815 research outputs found
Methods for Determining Blood Flow Through Intact Vessels of Experimental Animals Under Conditions of Gravitational Stress and in Extra-terrestrial Space Capsules Final Report, 1 Nov. 1960 - 31 Dec. 1964
Electromagnetic blood flow meter to determine blood flow through intact vessels of test animals in gravitational stress and in extraterrestrial space capsule
Electrochemical characterization of nonaqueous systems for secondary battery application
Electrochemical evaluation of electrode organic electrolyte combinations for rechargeable battery system
A low-luminosity soft state in the short period black hole X-ray binary Swift J1753.5-0127
We present results from the spectral fitting of the candidate black hole
X-ray binary Swift J1753.5-0127 in an accretion state previously unseen in this
source. We fit the 0.7-78 keV spectrum with a number of models, however the
preferred model is one of a multi-temperature disk with an inner disk
temperature keV scattered into a steep
power-law with photon index and an additional
hard power law tail (). We report on the emergence of a
strong disk-dominated component in the X-ray spectrum and we conclude that the
source has entered the soft state for the first time in its ~10 year prolonged
outburst. Using reasonable estimates for the distance to the source ( kpc)
and black hole mass (), we find the unabsorbed luminosity (0.1-100
keV) to be % of the Eddington luminosity, making this one of the
lowest luminosity soft states recorded in X-ray binaries. We also find that the
accretion disk extended towards the compact object during its transition from
hard to soft, with the inner radius estimated to be
or ~, dependent on the boundary
condition chosen, assuming the above distance and mass, a spectral hardening
factor and a binary inclination .Comment: 10 pages, 5 figures, accepted for publication in MNRA
A subarcsecond resolution near-infrared study of Seyfert and `normal' galaxies: II. Morphology
We present a detailed study of the bar fraction in the CfA sample of Seyfert
galaxies, and in a carefully selected control sample of non-active galaxies, to
investigate the relation between the presence of bars and of nuclear activity.
To avoid the problems related to bar classification in the RC3, e.g.,
subjectivity, low resolution and contamination by dust, we have developed an
objective bar classification method, which we conservatively apply to our new
sub-arcsecond resolution near-infrared imaging data set (Peletier et al. 1999).
We are able to use stringent criteria based on radial profiles of ellipticity
and major axis position angle to determine the presence of a bar and its axial
ratio. Concentrating on non-interacting galaxies in our sample for which
morphological information can be obtained, we find that Seyfert hosts are
barred more often (79% +/- 7.5%) than the non-active galaxies in our control
sample (59% +/- 9%), a result which is at the 2.5 sigma significance level. The
fraction of non-axisymmetric hosts becomes even larger when interacting
galaxies are taken into account. We discuss the implications of this result for
the fueling of central activity by large-scale bars. This paper improves on
previous work by means of imaging at higher spatial resolution and by the use
of a set of stringent criteria for bar presence, and confirms that the use of
NIR is superior to optical imaging for detection of bars in disk galaxies.Comment: Latex, 3 figures, includes aaspptwo.sty, accepted for publication in
the Astrophysical Journa
Developing a field experience for natural resource majors
Conversion from quarters to semesters allowed us to reinvent the field experience for College of Natural Resource majors. The new field experience strives to teach students the fundamental measurement skills needed for a summer job and to provide field experience and opportunities for teamwork. “Camp” operates for four weeks following spring semester, allowing students time to obtain summer jobs with university, state, and federal employers, which capitalize on students’ newly acquired field skills. The modular curriculum focuses on breadth of skills and uses technology to integrate them. Topics include map and compass, GPS, GIS, soil science, wildlife measurements, basic ecology, disturbance ecology, stream and watershed measurements, social and biophysical recreation measurements, plant identification and forest inventory methods. Students maintain journals and document their experiences using digital photography. Students spend the last four days in a self-guided resource data collection exercise that ranges from traditional timber surveys to stream assessments to recreational user surveys. Students analyze their data, and present their results to peers and CNR faculty in a PowerPoint presentation complete with ArcView maps and digital images of their study area
Events leading up to the June 2015 outburst of V404 Cyg
On 2015 June 15 the burst alert telescope (BAT) on board {\em Swift} detected
an X-ray outburst from the black hole transient V404 Cyg. We monitored V404 Cyg
for the last 10 years with the 2-m Faulkes Telescope North in three optical
bands (V, R, and i). We found that, one week prior to this outburst, the
optical flux was 0.1--0.3 mag brighter than the quiescent orbital modulation,
implying an optical precursor to the X-ray outburst. There is also a hint of a
gradual optical decay (years) followed by a rise lasting two months prior to
the outburst. We fortuitously obtained an optical spectrum of V404 Cyg 13 hours
before the BAT trigger. This too was brighter () than
quiescence, and showed spectral lines typical of an accretion disk, with
characteristic absorption features of the donor being much weaker. No He II
emission was detected, which would have been expected had the X-ray flux been
substantially brightening. This, combined with the presence of intense
H emission, about 7 times the quiescent level, suggests that the disk
entered the hot, outburst state before the X-ray outburst began. We propose
that the outburst is produced by a viscous-thermal instability triggered close
to the inner edge of a truncated disk. An X-ray delay of a week is consistent
with the time needed to refill the inner region and hence move the inner edge
of the disk inwards, allowing matter to reach the central BH, finally turning
on the X-ray emission.Comment: Accepted by ApJ Letter, 7 pages, 5 figure
An Improved Semi-Analytical Spherical Collapse Model for Non-linear Density Evolution
We derive a semi-analytical extension of the spherical collapse model of
structure formation that takes account of the effects of deviations from
spherical symmetry and shell crossing which are important in the non-linear
regime. Our model is designed so that it predicts a relation between the
peculiar velocity and density contrast that agrees with the results of N-body
simulations in the region where such a comparison can sensibly be made. Prior
to turnaround, when the unmodified spherical collapse model is expect to be a
good approximation, the predictions of the two models coincide almost exactly.
The effects of a late time dominating dark energy component are also taken into
account. The improved spherical collapse model is a useful tool when one
requires a good approximation not just to the evolution of the density contrast
but also its trajectory. Moreover, the analytical fitting formulae presented is
simple enough to be used anywhere where the standard spherical collapse might
be used but with the advantage that it includes a realistic model of the
effects of virialisation.Comment: 6 pages, 3 figures. Matches the version in print at Astrophys.
The constrained modified KP hierarchy and the generalized Miura transformations
In this letter, we consider the second Hamiltonian structure of the
constrained modified KP hierarchy. After mapping the Lax operator to a pure
differential operator the second structure becomes the sum of the second and
the third Gelfand-Dickey brackets defined by this differential operator. We
simplify this Hamiltonian structure by factorizing the Lax operator into linear
terms.Comment: 8 pages, latex, no figure
Infrared Study of Fullerene Planetary Nebulae
We present a study of 16 PNe where fullerenes have been detected in their
Spitzer spectra. This large sample of objects offers an unique opportunity to
test conditions of fullerene formation and survival under different metallicity
environments as we are analyzing five sources in our own Galaxy, four in the
LMC, and seven in the SMC. Among the 16 PNe under study, we present the first
detection of C60 (possibly also C70) fullerenes in the PN M 1-60 as well as of
the unusual 6.6, 9.8, and 20 um features (possible planar C24) in the PN K
3-54. Although selection effects in the original samples of PNe observed with
Spitzer may play a potentially significant role in the statistics, we find that
the detection rate of fullerenes in C-rich PNe increases with decreasing
metallicity (5% in the Galaxy, 20% in the LMC, and 44% in the SMC). CLOUDY
photoionization modeling matches the observed IR fluxes with central stars that
display a rather narrow range in effective temperature (30,000-45,000 K),
suggesting a common evolutionary status of the objects and similar fullerene
formation conditions. The observed C60 intensity ratios in the Galactic sources
confirm our previous finding in the MCs that the fullerene emission is not
excited by the UV radiation from the central star. CLOUDY models also show that
line- and wind-blanketed model atmospheres can explain many of the observed
[NeIII]/[NeII] ratios by photoionization suggesting that possibly the UV
radiation from the central star, and not shocks, are triggering the
decomposition of the circumstellar dust grains. With the data at hand, we
suggest that the most likely explanation for the formation of fullerenes and
graphene precursors in PNe is that these molecular species are built from the
photo-chemical processing of a carbonaceous compound with a mixture of aromatic
and aliphatic structures similar to that of HAC dust.Comment: Accepted for publication in ApJ (43 pages, 11 figures, and 4 tables).
Small changes to fit the proof-corrected article to be published in Ap
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