19,171 research outputs found
Analysis of ancient sediments and extra-terrestrial materials Semiannual report, 1 Jun. - 30 Nov. 1966
Isolation and identification of organic components of meteorites, and ancient sediment
Nature and changes in organic matter in organic sediments
A series of isoprenoid compounds were isolated from a heat treated marine sediment (from Tanner Basin) which were not present in the original sediment. Among the compounds identified were: phytol, dihydrophytol, C-18-isoprenoid ketone, phytanic and pristanic acids, C-19- and C-10-monoolefines, and the alkanes pristane and phytane. The significance and possible routes leading to these compounds is discussed
The Isotopic Abundance and Content of Sulfur in Meteorites
Isotopic abundance and content of sulfur in stony and iron meteorite
Thermal alteration of organic matter in recent marine sediments. 1: Pigments
Sediment from Tanner Basin, the outer continental shelf off Southern California, was analyzed for photosynthetic pigments and their derivatives, namely carotenes and chlorins. Samples of the sediment were also exposed to raised temperatures (65, 100, 150 C) for various periods of time (1 week, 1 month, 2 months). Analysis of the heat-treated sediment revealed the presence of alpha-ionene and 2,6-dimethylnapthalene, thermal degradation products of Betacarotente. Chlorins were converted to nickel porphyrins of both DPEP and etio series. Possible mechanisms of these transformations are presented
Eigenstate Structure in Graphs and Disordered Lattices
We study wave function structure for quantum graphs in the chaotic and
disordered regime, using measures such as the wave function intensity
distribution and the inverse participation ratio. The result is much less
ergodicity than expected from random matrix theory, even though the spectral
statistics are in agreement with random matrix predictions. Instead, analytical
calculations based on short-time semiclassical behavior correctly describe the
eigenstate structure.Comment: 4 pages, including 2 figure
On Toroidal Horizons in Binary Black Hole Inspirals
We examine the structure of the event horizon for numerical simulations of
two black holes that begin in a quasicircular orbit, inspiral, and finally
merge. We find that the spatial cross section of the merged event horizon has
spherical topology (to the limit of our resolution), despite the expectation
that generic binary black hole mergers in the absence of symmetries should
result in an event horizon that briefly has a toroidal cross section. Using
insight gained from our numerical simulations, we investigate how the choice of
time slicing affects both the spatial cross section of the event horizon and
the locus of points at which generators of the event horizon cross. To ensure
the robustness of our conclusions, our results are checked at multiple
numerical resolutions. 3D visualization data for these resolutions are
available for public access online. We find that the structure of the horizon
generators in our simulations is consistent with expectations, and the lack of
toroidal horizons in our simulations is due to our choice of time slicing.Comment: Submitted to Phys. Rev.
Comments on Redox potentials by equilibration, by W. G. Breck
Breck (1972) has proposed a new approach for determining the redox level (Eh) in aerated natural waters and has described an electrode arrangement which, supposedly, is capable of accurately measuring Eh in such waters
New Limits on Radio Emission from X-ray Dim Isolated Neutron Stars
We have carried out a search for radio emission at 820 MHz from six X-ray dim
isolated neutron stars with the Robert C. Byrd Green Bank Radio Telescope. No
transient or pulsed emission was found using fast folding, fast Fourier
transform, and single-pulse searches. The corresponding flux limits are about
0.01 mJy for pulsed emission, depending on the integration time for the
particular source and assuming a duty cycle of 2%, and 20 mJy for single
dispersed pulses. These are the most sensitive limits to date on radio emission
from X-ray dim isolated neutron stars. There is no evidence for isolated radio
pulses, as seen in a class of neutron stars known as rotating radio transients.
Our results imply that either the radio luminosities of these objects are lower
than those of any known radio pulsars, or they could simply be long-period
nearby radio pulsars with high magnetic fields beaming away from the Earth. To
test the latter possibility, we would need around 40 similar sources to provide
a 1 sigma probability of at least one of them beaming toward us. We also give a
detailed description of our implementation of the Fast Folding Algorithm.Comment: 16 pages, 8 figures, 3 tables, accepted to Ap
Vibrational properties of phonons in random binary alloys: An augmented space recursive technique in the k-representation
We present here an augmented space recursive technique in the
k-representation which include diagonal, off-diagonal and the environmental
disorder explicitly : an analytic, translationally invariant, multiple
scattering theory for phonons in random binary alloys.We propose the augmented
space recursion (ASR) as a computationally fast and accurate technique which
will incorporate configuration fluctuations over a large local environment. We
apply the formalism to , Ni_{88}Cr_12} and
alloys which is not a random choice. Numerical results on spectral functions,
coherent structure factors, dispersion curves and disordered induced FWHM's are
presented. Finally the results are compared with the recent itinerant coherent
potential approximation (ICPA) and also with experiments.Comment: 20 pages, LaTeX, 23 figure
Dispersion interactions from a local polarizability model
A local approximation for dynamic polarizability leads to a nonlocal
functional for the long-range dispersion interaction energy via an
imaginary-frequency integral. We analyze several local polarizability
approximations and argue that the form underlying the construction of our
recent van der Waals functional [O. A. Vydrov and T. Van Voorhis, Phys. Rev.
Lett. 103, 063004 (2009)] is particularly well physically justified. Using this
improved formula, we compute dynamic dipole polarizabilities and van der Waals
C_6 coefficients for a set of atoms and molecules. Good agreement with the
benchmark values is obtained in most cases
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