20,123 research outputs found
Mesoscopic dynamical differences from quantum state preparation in a Bose-Hubbard trimer
Conventional wisdom is that quantum effects will tend to disappear as the
number of quanta in a system increases, and the evolution of a system will
become closer to that described by mean field classical equations. In this
letter we combine newly developed experimental techniques to propose and
analyse an experiment using a Bose-Hubbard trimer where the opposite is the
case. We find that differences in the preparation of a centrally evacuated
trimer can lead to readily observable differences in the subsequent dynamics
which increase with system size. Importantly, these differences can be detected
by the simple measurements of atomic number.Comment: 5 pages, 4 figures, theor
Delta Self-Consistent Field as a method to obtain potential energy surfaces of excited molecules on surfaces
We present a modification of the SCF method of calculating energies
of excited states, in order to make it applicable to resonance calculations of
molecules adsorbed on metal surfaces, where the molecular orbitals are highly
hybridized. The SCF approximation is a density functional method
closely resembling standard density functional theory (DFT), the only
difference being that in SCF one or more electrons are placed in higher
lying Kohn-Sham orbitals, instead of placing all electrons in the lowest
possible orbitals as one does when calculating the ground state energy within
standard DFT. We extend the SCF method by allowing excited electrons to
occupy orbitals which are linear combinations of Kohn-Sham orbitals. With this
extra freedom it is possible to place charge locally on adsorbed molecules in
the calculations, such that resonance energies can be estimated. The method is
applied to N, CO and NO adsorbed on different metallic surfaces and
compared to ordinary SCF without our modification, spatially
constrained DFT and inverse-photoemission spectroscopy (IPES) measurements.
This comparison shows that the modified SCF method gives results in
close agreement with experiment, significantly closer than the comparable
methods. For N adsorbed on ruthenium (0001) we map out a 2-dimensional part
of the potential energy surfaces in the ground state and the 2-resonance.
Finally we compare the SCF approach on gas-phase N and CO, to
higher accuracy methods. Excitation energies are approximated with accuracy
close to that of time-dependent density functional theory, and we see very good
agreement in the minimum shift of the potential energy surfaces in the excited
state compared to the ground state.Comment: 11 pages, 7 figure
Plasma Magnetohydrodynamics and Energy Conversion
Contains reports on five research projects.National Science Foundation (Grant G-24073)Aeronautical Accessories Laboratory, Wright-Patterson Air Force Base, Ohio (Contract AF33(616)-7624
vbyCaHbeta CCD Photometry of Clusters. VI. The Metal-Deficient Open Cluster NGC 2420
CCD photometry on the intermediate-band vbyCaHbeta system is presented for
the metal-deficient open cluster, NGC 2420. Restricting the data to probable
single members of the cluster using the CMD and the photometric indices alone
generates a sample of 106 stars at the cluster turnoff. The average E(b-y) =
0.03 +/- 0.003 (s.e.m.) or E(B-V) = 0.050 +/- 0.004 (s.e.m.), where the errors
refer to internal errors alone. With this reddening, [Fe/H] is derived from
both m1 and hk, using b-y and Hbeta as the temperature index. The agreement
among the four approaches is reasonable, leading to a final weighted average of
[Fe/H] = -0.37 +/- 0.05 (s.e.m.) for the cluster, on a scale where the Hyades
has [Fe/H] = +0.12. When combined with the abundances from DDO photometry and
from recalibrated low-resolution spectroscopy, the mean metallicity becomes
[Fe/H] = -0.32 +/- 0.03. It is also demonstrated that the average cluster
abundances based upon either DDO data or low-resolution spectroscopy are
consistently reliable to 0.05 dex or better, contrary to published attempts to
establish an open cluster metallicity scale using simplistic offset corrections
among different surveys.Comment: scheduled for Jan. 2006 AJ; 33 pages, latex, includes 7 figures and 2
table
Are All Static Black Hole Solutions Spherically Symmetric?
The static black hole solutions to the Einstein-Maxwell equations are all
spherically symmetric, as are many of the recently discovered black hole
solutions in theories of gravity coupled to other forms of matter. However,
counterexamples demonstrating that static black holes need not be spherically
symmetric exist in theories, such as the standard electroweak model, with
electrically charged massive vector fields. In such theories, a magnetically
charged Reissner-Nordstrom solution with sufficiently small horizon radius is
unstable against the development of a nonzero vector field outside the horizon.
General arguments show that, for generic values of the magnetic charge, this
field cannot be spherically symmetric. Explicit construction of the solution
shows that it in fact has no rotational symmetry at all.Comment: 6 pages, plain TeX. Submitted to GRF Essay Competitio
Safety Of \u3ci\u3eBrucella Abortus\u3c/i\u3e Strain Rb51 In Black Bears
In two studies conducted from October 1999 to March 2000 and December 2000 to April 2001, adult black bears (Ursus americanus) were orally inoculated with 1.4â3.1X1010 colony-forming units (CFU) of Brucella abortus strain RB51 (SRB51, n=12) or 2 ml of 0.15 M NaCl solution (saline, n=11). We did not detect a difference (P\u3e0.05) in antibody titers to SRB51 in serum obtained before vaccination, at 8 wk after vaccination, or at necropsy at 21 or 23 wk after vaccination between SRB51-vaccinated and nonvaccinated bears. The SRB51 vaccine strain was recovered from tissues obtained at necropsy from one of six SRB51-vaccinated bears in study 1, but none of the six SRB51-vaccinated bears in study 2. Vaccination of black bears with SRB51 did not appear to influence (P\u3e0.05) reproductive performance
Gamma-Ray Burst Sequences in Hardness Ratio-Peak Energy Plane
The narrowness of the distribution of the peak energy of
spectrum of gamma-ray bursts (GRBs) and the unification of GRB population are
great puzzles yet to be solved. We investigate the two puzzles based on the
global spectral behaviors of different GRB population in the
plane (HR the spectral hardness ratio) with BATSE and HETE-2 observations. It
is found that long GRBs and XRFs observed by HETE-2 seem to follow the same
sequence in the plane, with the XRFs at the low end of this
sequence. The long and short GRBs observed by BATSE follow significantly
different sequences in the plane, with most of the short GRBs
having a larger hardness ratio than the long GRBs at a given .
These results indicate that the global spectral behaviors of the long GRB
sample and the XRF sample are similar, while that of short GRBs is different.
The short GRBs seem to be a unique subclass of GRBs, and they are not the
higher energy extension of the long GRBs (abridged).Comment: 9 pages, 3 figure
Spectroscopic Observations of Optically Selected Clusters of Galaxies from the Palomar Distant Cluster Survey
We have conducted a redshift survey of sixteen cluster candidates from the
Palomar Distant Cluster Survey (PDCS) to determine both the density of PDCS
clusters and the accuracy of the estimated redshifts presented in the PDCS
catalog (Postman et. al. 1996). We find that the matched-filter redshift
estimate presented in the PDCS has an error sigma_z = 0.06 in the redshift
range 0.1 < z < 0.35 based on eight cluster candidates with three or more
concordant galaxy redshifts.
We measure the low redshift (0.1 < z < 0.35) space density of PDCS clusters
to be 31.3^{+30.5}_{-17.1} * E-06 h^3 Mpc^-3 (68% confidence limits for a
Poisson distribution) for Richness Class 1 systems. We find a tentative space
density of 10.4^{+23.4}_{-8.4}* E-06 h^3 Mpc^-3 for Richness Class 2 clusters.
These densities compare favorably with those found for the whole of the PDCS
and support the finding that the space density of clusters in the PDCS is a
factor of ~5 above that of clusters in the Abell catalog (Abell 1958; Abell,
Corwin, and Olowin 1989). These new space density measurements were derived as
independently as possible from the original PDCS analysis and therefore,
demonstrate the robustness of the original work. Based on our survey, we
conclude that the PDCS matched-filter algorithm is successful in detecting real
clusters and in estimating their true redshifts in the redshift range we
surveyed.Comment: 23 pages with 4 figures and 3 seperate tables. To be published in the
November Issue of the Astronomical Journa
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