12,309 research outputs found
Selecting land use for sand and gravel sites / project no. 3
"Project no.3, 1965-1967, University of Illinois, National Sand and Gravel Association"--Cover."This research project of the University of Illinois was sponsored by the National Sand & Gravel Association".Includes bibliographical references (p. 64-65)
Emission Line Properties of Seyfert Galaxies in the 12 Micron Sample
We present spectroscopy of emission lines for 81 Seyfert 1 and 104 Seyfert 2
galaxies in the IRAS 12m galaxy sample. We analyzed the emission-line
luminosity functions, reddening, and other gas diagnostics. The narrow-line
regions (NLR) of Sy1 and 2 galaxies do not significantly differ from each other
in most of these diagnostics. Combining the H/H ratio with a new
reddening indicator-the [SII]6720/[OII]3727 ratio, we find the average
for Sy1s and for Sy2s. The NLR of Sy1
galaxies has only marginally higher ionization than the Sy2s. Our sample
includes 22 Sy1.9s and 1.8s. In their narrow lines, these low-luminosity
Seyferts are more similar to the Sy2s than the Sy1s. We construct a BPT
diagram, and include the Sy1.8s and 1.9s. They overlap the region occupied by
the Sy2s. The C IV equivalent width correlates more strongly with [O
III]/H than with UV luminosity. The Sy1 and Sy2 luminosity functions of
[OII]3727 and [OIII]5007 are indistinguishable. Unlike the LF's of Seyfert
galaxies measured by SDSS, ours are nearly flat at low L. The larger number of
faint Sloan "AGN" is attributable to their inclusion of weakly emitting LINERs
and H II+AGN "composite" nuclei, which do not meet our classification criteria
for Seyferts. An Appendix investigates which emission line luminosities provide
the most reliable measures of the total non-stellar luminosity. The hard X-ray
or near-ultraviolet continuum luminosity can be crudely predicted from either
the [O III]5007 luminosity, or the combination of [O III]+H, or [N
II]+H lines, with a scatter of times for the Sy1s and
times for the Sy2s. The latter two hybrid (NLR+BLR) indicators have
the advantage of predicting the same HX luminosity independent of Seyfert type.Comment: 70 pages, including 15 Figures and 10 Tables. Accepted for
publication in The Astrophysical Journa
Modal survey of the space shuttle solid rocket motor using multiple input methods
The ability to accurately characterize propellant in a finite element model is a concern of engineers tasked with studying the dynamic response of the Space Shuttle Solid Rocket Motor (SRM). THe uncertainties arising from propellant characterization through specimem testing led to the decision to perform a model survey and model correlation of a single segment of the Shuttle SRM. Multiple input methods were used to excite and define case/propellant modes of both an inert segment and, later, a live propellant segment. These tests were successful at defining highly damped, flexible modes, several pairs of which occured with frequency spacing of less than two percent
Positron annihilation induced Auger electron spectroscopy
Recently, Weiss et al. have demonstrated that it is possible to excite Auger transitions by annihilating core electrons using a low energy (less than 30eV) beam of positrons. This mechanism makes possible a new electron spectroscopy, Positron annihilation induced Auger Electron Spectroscopy (PAES). The probability of exciting an Auger transition is proportional to the overlap of the positron wavefunction with atomic core levels. Since the Auger electron energy provides a signature of the atomic species making the transition, PAES makes it possible to determine the overlap of the positron wavefunction with a particular element. PAES may therefore provide a means of detecting positron-atom complexes. Measurements of PAES intensities from clean and adsorbate covered Cu surfaces are presented which indicate that approx. 5 percent of positrons injected into CU at 25eV produce core annihilations that result in Auger transitions
Improving Transit Predictions of Known Exoplanets with TERMS
Transiting planet discoveries have largely been restricted to the
short-period or low-periastron distance regimes due to the bias inherent in the
geometric transit probability. Through the refinement of planetary orbital
parameters, and hence reducing the size of transit windows, long-period planets
become feasible targets for photometric follow-up. Here we describe the TERMS
project that is monitoring these host stars at predicted transit times.Comment: 3 pages, 2 figures, to be published in ASP Conf. Proceedings:
"Detection and dynamics of transiting exoplanets" 2010, OHP, France (eds.: F.
Bouchy, R.F. D{\i}az, C. Moutou
Self-similar correlation function in brain resting-state fMRI
Adaptive behavior, cognition and emotion are the result of a bewildering
variety of brain spatiotemporal activity patterns. An important problem in
neuroscience is to understand the mechanism by which the human brain's 100
billion neurons and 100 trillion synapses manage to produce this large
repertoire of cortical configurations in a flexible manner. In addition, it is
recognized that temporal correlations across such configurations cannot be
arbitrary, but they need to meet two conflicting demands: while diverse
cortical areas should remain functionally segregated from each other, they must
still perform as a collective, i.e., they are functionally integrated. Here, we
investigate these large-scale dynamical properties by inspecting the character
of the spatiotemporal correlations of brain resting-state activity. In physical
systems, these correlations in space and time are captured by measuring the
correlation coefficient between a signal recorded at two different points in
space at two different times. We show that this two-point correlation function
extracted from resting-state fMRI data exhibits self-similarity in space and
time. In space, self-similarity is revealed by considering three successive
spatial coarse-graining steps while in time it is revealed by the 1/f frequency
behavior of the power spectrum. The uncovered dynamical self-similarity implies
that the brain is spontaneously at a continuously changing (in space and time)
intermediate state between two extremes, one of excessive cortical integration
and the other of complete segregation. This dynamical property may be seen as
an important marker of brain well-being both in health and disease.Comment: 14 pages 13 figures; published online before print September 2
Transcriptional Correlates of Proximal-Distal Identify and Regeneration Timing in Axolotl Limbs
Cells within salamander limbs retain memories that inform the correct replacement of amputated tissues at different positions along the length of the arm, with proximal and distal amputations completing regeneration at similar times. We investigated the possibility that positional memory is associated with variation in transcript abundances along the proximal-distal limb axis. Transcripts were deeply sampled from Ambystoma mexicanum limbs at the time they were administered fore arm vs upper arm amputations, and at 19 post-amputation time points. After amputation and prior to regenerative outgrowth, genes typically expressed by differentiated muscle cells declined more rapidly in upper arms while cell cycle transcripts were expressed more highly. These and other expression patterns suggest upper arms undergo more robust tissue remodeling and cell proliferation responses after amputation, and thus provide an explanation for why the overall time to complete regeneration is similar for proximal and distal amputations. Additionally, we identified candidate positional memory genes that were expressed differently between fore and upper arms that encode a surprising number of epithelial proteins and a variety of cell surface, cell adhesion, and extracellular matrix molecules. Also, genes were discovered that exhibited different, bivariate patterns of gene expression between fore and upper arms, implicating dynamic transcriptional regulation for the first time in limb regeneration. Finally, 43 genes expressed differently between fore and upper arm samples showed similar transcriptional patterns during retinoic acid-induced reprogramming of fore arm blastema cells into upper arm cells. Our study provides new insights about the basis of positional information in regenerating axolotl limbs
Thermodynamic large fluctuations from uniformized dynamics
Large fluctuations have received considerable attention as they encode
information on the fine-scale dynamics. Large deviation relations known as
fluctuation theorems also capture crucial nonequilibrium thermodynamical
properties. Here we report that, using the technique of uniformization, the
thermodynamic large deviation functions of continuous-time Markov processes can
be obtained from Markov chains evolving in discrete time. This formulation
offers new theoretical and numerical approaches to explore large deviation
properties. In particular, the time evolution of autonomous and non-autonomous
processes can be expressed in terms of a single Poisson rate. In this way the
uniformization procedure leads to a simple and efficient way to simulate
stochastic trajectories that reproduce the exact fluxes statistics. We
illustrate the formalism for the current fluctuations in a stochastic pump
model
The diverse hot gas content and dynamics of optically similar low-mass elliptical galaxies
The presence of hot X-ray emitting gas is ubiquitous in massive early-type
galaxies. However, much less is known about the content and physical status of
the hot X-ray gas in low-mass ellipticals. In the present paper we study the
X-ray gas content of four low-mass elliptical galaxies using archival Chandra
X-ray observations. The sample galaxies, NGC821, NGC3379, NGC4278, and NGC4697,
have approximately identical K-band luminosities, and hence stellar masses, yet
their X-ray appearance is strikingly different. We conclude that the unresolved
emission in NGC821 and NGC3379 is built up from a multitude of faint compact
objects, such as coronally active binaries and cataclysmic variables. Despite
the non-detection of X-ray gas, these galaxies may host low density, and hence
low luminosity, X-ray gas components, which undergo a Type Ia supernova (SN Ia)
driven outflow. We detect hot X-ray gas with a temperature of kT ~ 0.35 keV in
NGC4278, the component of which has a steeper surface brightness distribution
than the stellar light. Within the central 50 arcsec (~3.9 kpc) the estimated
gas mass is ~3 x 10^7 M_sun, implying a gas mass fraction of ~0.06%. We
demonstrate that the X-ray gas exhibits a bipolar morphology in the
northeast-southwest direction, indicating that it may be outflowing from the
galaxy. The mass and energy budget of the outflow can be maintained by evolved
stars and SNe Ia, respectively. The X-ray gas in NGC4697 has an average
temperature of kT ~ 0.3 keV, and a significantly broader distribution than the
stellar light. The total gas mass within 90 arcsec (~5.1 kpc) is ~2.1 x 10^8
M_sun, hence the gas mass fraction is ~0.4%. Based on the distribution and
physical parameters of the X-ray gas, we conclude that it is most likely in
hydrostatic equilibrium, although a subsonic outflow may be present.Comment: 14 pages, 8 figures, 3 tables, accepted for publication in Ap
A Near-Solar Metallicity, Nitrogen-Deficient Lyman Limit Absorber Associated with two S0 Galaxies
From UV spectra of the bright quasar PHL 1811 recorded by FUSE and the E140M
configuration on STIS, we have determined the abundances of various atomic
species in a Lyman limit system at z = 0.0809 with log N(H I) = 17.98.
Considerably more hydrogen may be in ionized form, since the abundances of C
II, Si II, S II and Fe II are very large compared to that of O I, when compared
to their respective solar abundance ratios. Our determination [O/H] = -0.19 in
the H I-bearing gas indicates that the chemical enrichment of the gas is
unusually high for an extragalactic QSO absorption system. However, this same
material has an unusually low abundance of nitrogen, [N/O] < -0.59, indicating
that there may not have been enough time during this enrichment for secondary
nitrogen to arise from low and intermediate mass stars. In an earlier
investigation we found two galaxies at nearly the same redshift as this
absorption system and displaced by 34 and 87 kpc from the line of sight. An
r-band image recorded by the ACS on HST indicates these are S0 galaxies. One or
both of these galaxies may be the source of the gas, which might have been
expelled in a fast wind, by tidal stripping, or by ram-pressure stripping.
Subtraction of the ACS point-spread function from the image of the QSO reveals
the presence of a face-on spiral galaxy under the glare of the quasar; although
it is possible that this galaxy may be responsible for the Lyman limit
absorption, the exact alignment of the QSO with the center of the galaxy
suggests that the spiral is the quasar host.Comment: 74 pages, 14 figures; to be published in the Astrophysical Journal
(Part 1) May 1, 2005 issue. A version of the paper with figures of better
quality may be found at http://www.astro.princeton.edu/~ebj/PHL1811_paper.ps
(postscript) or http://www.astro.princeton.edu/~ebj/PHL1811_paper.pdf (pdf
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