19,934 research outputs found
Differential Astrometry of Sub-arcsecond Scale Binaries at the Palomar Testbed Interferometer
We have used the Palomar Testbed Interferometer to perform very high
precision differential astrometry on the 0.25 arcsecond separation binary star
HD 171779. In 70 minutes of observation we achieve a measurement uncertainty of
approximately 9 micro-arcseconds in one axis, consistent with theoretical
expectations. Night-to-night repeatability over four nights is at the level of
16 micro-arcseconds. This method of very-narrow-angle astrometry may be
extremely useful for searching for planets with masses as small as 0.5 Jupiter
Masses around a previously neglected class of stars -- so-called ``speckle
binaries.'' It will also provide measurements of stellar parameters such as
masses and distances, useful for constraining stellar models at the 10^-3
level.Comment: 19 pages including 6 figures. Submitted to ApJ. Typos corrected,
several parts reworded for clarificatio
Electronic structure and magnetism in two-dimensional hexagonal 5d transition metal carbides, Tan+1Cn (n=1,2,3)
Density functional calculations are used to investigate the electronic
structure of two-dimensional 5d tantalum carbides with honeycomb-like lattice
structures. We focus on changes in the low-energy bands near the Fermi level
with dimensionality. We find that the Ta 5d states dominate, but the extended
nature of the wavefunctions makes them weakly correlated. The carbide sheets
are prone to long range magnetic order. We evaluate the stability of these
states to enhanced electron--electron interactions through a Hubbard U
correction. Lastly, we find spin orbit interactions strongly renormalize the
band structure for n=2, but play a minor role in n=1 and 3.Comment: 4 pages, 4 figure
Dry matter yields and quality of organic lupin/cereal mixtures for wholecrop forage
In view of climate change predictions and the general desirability of increasing the amount of home grown protein, a case exists for the investigation of lupins and lupin/cereal bicrop combinations as wholecrop forage on organic farms. A replicated randomised block trial is described which took place at the Royal Agricultural College, Cirencester, in 2005. This involved spring sown blue, white and yellow lupins, millet, wheat and triticale and lupin/cereal bi-crops. Data for dry matter yields for wholecrop silage, crude protein, MAD fi bre content and estimated ME, are presented for a single harvest. It is concluded that white lupins and white lupin bi-crops with spring wheat or triticale offer the best prospects for a viable wholecrop forage crop in an organic situation
Space Station Spartan study
The required extension, enhancement, and upgrading of the present Spartan concept are described to conduct operations from the space station using the station's unique facilities and operational features. The space station Spartan (3S), the free flyer will be deployed from and returned to the space station and will conduct scientific missions of much longer duration than possible with the current Spartan. The potential benefits of a space station Spartan are enumerated. The objectives of the study are: (1) to develop a credible concept for a space station Spartan; and (2) to determine the associated requirements and interfaces with the space station to help ensure that the 3S can be properly accommodated
The Complexity of Computing the Size of an Interval
Given a p-order A over a universe of strings (i.e., a transitive, reflexive,
antisymmetric relation such that if (x, y) is an element of A then |x| is
polynomially bounded by |y|), an interval size function of A returns, for each
string x in the universe, the number of strings in the interval between strings
b(x) and t(x) (with respect to A), where b(x) and t(x) are functions that are
polynomial-time computable in the length of x.
By choosing sets of interval size functions based on feasibility requirements
for their underlying p-orders, we obtain new characterizations of complexity
classes. We prove that the set of all interval size functions whose underlying
p-orders are polynomial-time decidable is exactly #P. We show that the interval
size functions for orders with polynomial-time adjacency checks are closely
related to the class FPSPACE(poly). Indeed, FPSPACE(poly) is exactly the class
of all nonnegative functions that are an interval size function minus a
polynomial-time computable function.
We study two important functions in relation to interval size functions. The
function #DIV maps each natural number n to the number of nontrivial divisors
of n. We show that #DIV is an interval size function of a polynomial-time
decidable partial p-order with polynomial-time adjacency checks. The function
#MONSAT maps each monotone boolean formula F to the number of satisfying
assignments of F. We show that #MONSAT is an interval size function of a
polynomial-time decidable total p-order with polynomial-time adjacency checks.
Finally, we explore the related notion of cluster computation.Comment: This revision fixes a problem in the proof of Theorem 9.
cis-6-Methoxycarbonyl-2,10-dioxa-1-phosphabicyclo[4.4.0]decane 1-Oxide
The crystal structure of the title compound, C9H1505P, is described. The molecule consists of two cis-fused six-membered rings, both in the chair conformation.
The z=0.0912 and z=0.2212 Damped Lyman Alpha Galaxies Along the Sight-Line Toward the Quasar OI 363
New optical and infrared observations along the sight-line toward the quasar
OI 363 (0738+313) are presented and discussed. Excluding systems which lack
confirming UV spectroscopic observations of the actual Lyman alpha line, this
sight-line presently contains the two lowest-redshift classical damped Lyman
alpha (DLA) quasar absorption line systems known (i.e. with N(HI) \ge 2 x
10^{20} atoms cm^{-2}), one at z(abs)=0.0912 and the other at z(abs)=0.2212.
The z=0.09 DLA galaxy appears to be an extended low surface brightness galaxy
which is easily visible only in infrared images and shows rich morphological
structure. Subtraction of the quasar nuclear and host light yields L_K \approx
0.08L_K* at z=0.09. The impact parameter between the galaxy and quasar
sight-line is very small, b<3.6 kpc (<2 arcsec), which makes measurements
difficult. The z=0.22 DLA galaxy is an early-type dwarf with a K-band
luminosity of L_K \approx 0.1L_K* at impact parameter b=20 kpc. In general,
these results serve to support mounting evidence that DLA galaxies are drawn
from a wide variety of gas-rich galaxy types. (Abridged)Comment: 27 pages, 6 figures, 2 in color. Submitted to Ap
Symmetry and Surface Symmetry Energies in Finite Nuclei
A study of properties of the symmetry energy of nuclei is presented based on
density functional theory. Calculations for finite nuclei are given so that the
study includes isospin dependent surface symmetry considerations as well as
isospin independent surface effects. Calculations are done at both zero and
non-zero temperature. It is shown that the surface symmetry energy term is the
most sensitive to the temperature while the bulk energy term is the least
sensitive. It is also shown that the temperature dependence terms are
insensitive to the force used and even more insensitive to the existence of
neutron skin. Results for a symmetry energy with both volume and surface terms
are compared with a symmetry energy with only volume terms along the line of
stability. Differences of several MeV are shown over a good fraction of
the total mass range in . Also given are calculations for the bulk, surface
and Coulomb terms.Comment: 11 pages, 2 figures, Added a new tabl
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