23,135 research outputs found
Observations of Uranus' satellites: Bibliography and literature search
A literature search has yielded more than 10,000 observations of the satellites of Uranus made from 1787 to 1985. The type (photographic, micrometer) and the number of observations are tabulated in 5 year increments and a complete bibliography is provided
CD -24_17504 revisited: a new comprehensive element abundance analysis
With [Fe/H] ~ -3.3, CD -24_17504 is a canonical metal-poor main sequence
turn-off star. Though it has appeared in numerous literature studies, the most
comprehensive abundance analysis for the star based on high resolution, high
signal-to-noise spectra is nearly 15 years old. We present a new detailed
abundance analysis for 21 elements based on combined archival Keck-HIRES and
VLT-UVES spectra of the star that is higher in both spectral resolution and
signal-to-noise than previous data. Our results for many elements are very
similar to those of an earlier comprehensive study of the star, but we present
for the first time a carbon abundance from the CH G-band feature as well as
improved upper limits for neutron-capture species such as Y, Ba and Eu. In
particular, we find that CD -24_17504 has [Fe/H] = -3.41, [C/Fe] = +1.10,
[Sr/H] = -4.68 and [Ba/H] <= -4.46, making it a carbon enhanced metal-poor star
with neutron-capture element abundances among the lowest measured in Milky Way
halo stars.Comment: Accepted to ApJ. 24 pages, 13 figures, 7 table
Destroying black holes with test bodies
If a black hole can accrete a body whose spin or charge would send the black
hole parameters over the extremal limit, then a naked singularity would
presumably form, in violation of the cosmic censorship conjecture. We review
some previous results on testing cosmic censorship in this way using the test
body approximation, focusing mostly on the case of neutral black holes. Under
certain conditions a black hole can indeed be over-spun or over-charged in this
approximation, hence radiative and self-force effects must be taken into
account to further test cosmic censorship.Comment: Contribution to the proceedings of the First Mediterranean Conference
on Classical and Quantum Gravity (talk given by T. P. S.). Summarizes the
results of Phys. Rev. Lett. 103, 141101 (2009), arXiv:0907.4146 [gr-qc] and
considers further example
Gravitational Thermodynamics of Causal Diamonds in (A)dS
The static patch of de Sitter spacetime and the Rindler wedge of Minkowski
spacetime are causal diamonds admitting a true Killing field, and they behave
as thermodynamic equilibrium states under gravitational perturbations. We
explore the extension of this gravitational thermodynamics to all causal
diamonds in maximally symmetric spacetimes. Although such diamonds generally
admit only a conformal Killing vector, that seems in all respects to be
sufficient. We establish a Smarr formula for such diamonds and a "first law"
for variations to nearby solutions. The latter relates the variations of the
bounding area, spatial volume of the maximal slice, cosmological constant, and
matter Hamiltonian. The total Hamiltonian is the generator of evolution along
the conformal Killing vector that preserves the diamond. To interpret the first
law as a thermodynamic relation, it appears necessary to attribute a negative
temperature to the diamond, as has been previously suggested for the special
case of the static patch of de Sitter spacetime. With quantum corrections
included, for small diamonds we recover the "entanglement equilibrium" result
that the generalized entropy is stationary at the maximally symmetric vacuum at
fixed volume, and we reformulate this as the stationarity of free conformal
energy with the volume not fixed.Comment: v3: 64 pages, 6 appendices, 8 figures; matches published versio
Development of thermionic converters Quarterly progress report
Design and fabrication of high efficiency, low power thermionic converters - graph
Counting the ions surrounding nucleic acids.
Nucleic acids are strongly negatively charged, and thus electrostatic interactions-screened by ions in solution-play an important role in governing their ability to fold and participate in biomolecular interactions. The negative charge creates a region, known as the ion atmosphere, in which cation and anion concentrations are perturbed from their bulk values. Ion counting experiments quantify the ion atmosphere by measuring the preferential ion interaction coefficient: the net total number of excess ions above, or below, the number expected due to the bulk concentration. The results of such studies provide important constraints on theories, which typically predict the full three-dimensional distribution of the screening cloud. This article reviews the state of nucleic acid ion counting measurements and critically analyzes their ability to test both analytical and simulation-based models
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