461 research outputs found
Constraining cosmological models with cluster power spectra
Using extensive N-body simulations we estimate redshift space power spectra
of clusters of galaxies for different cosmological models (SCDM, TCDM, CHDM,
Lambda-CDM, OCDM, BSI, tau-CDM) and compare the results with observational data
for Abell-ACO clusters. Our mock samples of galaxy clusters have the same
geometry and selection functions as the observational sample which contains 417
clusters of galaxies in a double cone of galactic latitude |b| > 30 degrees up
to a depth of 240 Mpc/h.
The power spectrum has been estimated for wave numbers k in the range 0.03 <
k k_max ~ 0.05 h/Mpc the power spectrum of the Abell-ACO
clusters has a power-law shape, P(k)\propto k^n, with n ~ -1.9, while it
changes sharply to a positive slope at k < k_max. By comparison with the mock
catalogues SCDM, TCDM (n=0.9), and also OCDM with Omega_0 = 0.35 are rejected.
Better agreement with observation can be found for the Lambda-CDM model with
Omega_0 = 0.35 and h = 0.7 and the CHDM model with two degenerate neutrinos and
Omega_HDM = 0.2 as well as for a CDM model with broken scale invariance (BSI)
and the tau-CDM model. As for the peak in the Abell-ACO cluster power spectrum,
we find that it does not represent a very unusual finding within the set of
mock samples extracted from our simulations.Comment: LaTeX, 27 pages, 8 figures (EPS). Revised version (title changed,
CHDM model added, discussion expanded). Accepted by New
Achieving maximum unit Mission capability: an impact study of system availability, proficiency, cost, and OPTEMPO
MBA Professional ReportThe highest level of Unit Mission Capability is the ultimate goal of any unit commander. Members of the user community, especially unit commanders, must be aware of the factors that influence their war fighting capability. Understanding these factors and their relationships, coupled with the implementation of specific strategies, can facilitate maximizing Unit Mission Capability. This is the primary focus of this project. This report will provide aviation unit commanders and user representatives with a clear explanation and demonstration of the variables that influence a commanderb2ss ability to improve Unit Mission Capability. The tool demonstrated in this report is the Availability, Proficiency, Cost, and Operational Tempo (OPTEMPO) model for assessing and maximizing Unit Mission Capability. The user community must understand how competing funding requirements influences their ability to train and maintain a strong fighting force. Current DOD funding levels will decline in the near future. It will become more and more difficult to achieve the desired state of Unit Mission Capability. Users must implement strategic cost saving initiatives to preserve our war fighting capability. .http://archive.org/details/achievingmaximum1094510000US Army (USA) author.Approved for public release; distribution is unlimited
On The Violation Of Marshall-Peierls Sign Rule In The Frustrated Heisenberg Antiferromagnet
We present a number of arguments in favor of the suggestion that the
Marshall-Peierls sign rule survives the frustration in the square-lattice
Heisenberg antiferromagnet with frustrating next-nearest-neighbor (diagonal)
bonds ( model) for relatively large values of the parameter
. Both the spin-wave analysis and the exact-diagonalization data
concerning the weight of Marshall states support the above suggestion.Comment: 8 pages, LaTex, 2 figurs on reques
Large-scale structure formation for power spectra with broken scale invariance
We have simulated the formation of large-scale structure arising from
COBE-normalized spectra computed by convolving a primordial double-inflation
perturbation spectrum with the CDM transfer function. Due to the broken scale
invariance ('BSI') characterizing the primordial perturbation spectrum, this
model has less small-scale power than the (COBE-normalized) standard CDM model.
The particle-mesh code (with cells and particles) includes a
model for thermodynamic evolution of baryons in addition to the usual
gravitational dynamics of dark matter. It provides an estimate of the local gas
temperature. In particular, our galaxy-finding procedure seeks peaks in the
distribution of gas that has cooled. It exploits the fact that ``cold"
particles trace visible matter better than average and thus provides a natural
biasing mechanism. The basic picture of large-scale structure formation in the
BSI model is the familiar hierarchical clustering scenario. We obtain particle
in cell statistics, the galaxy correlation function, the cluster abundance and
the cluster-cluster correlation function and statistics for large and small
scale velocity fields. We also report here on a semi-quantitative study of the
distribution of gas in different temperature ranges. Based on confrontation
with observations and comparison with standard CDM, we conclude that the BSI
scenario could represent a promising modification of the CDM picture capable of
describing many details of large-scale structure formation.Comment: 15 pages, Latex using mn.sty, uuencoded compressed ps-file with 15
figures by anonymous ftp to ftp://ftp.aip.de/incoming/mueller/bsi.u
Bilingual, digital, audio-visual training modules improve technical knowledge of feedlot and dairy workers
Two studies were conducted to determine the effectiveness of digital multimedia modules as training tools for animal care workers. Employees at a commercial feedlot (n = 17) and a commercial dairy (n = 10) were asked to independently complete a 10-question quiz prior to and following viewing of training modules. Module topics in the feedlot were proper handling of non-ambulatory animals and humane methods of euthanasia; modules were administered to the workers, as a group, in either English (n = 7) or Spanish (N = 10), depending on previously indicated worker preference. Modules addressing dairy cattle health practices and dairy cattle handling were presented to the dairy care workers who had a preference for learning in either English (n = 7) or Spanish (n = 3). For feedlot workers, post-test scores were improved by 28% after viewing the modules compared to pre-test scores (74% vs. 58%; P 0.30) between language, topic, and between-test variation, indicating that the modules were equally effective at information delivery to both audiences in both languages. For the dairy workers, test scores improved by 27% from pre-viewing to post-viewing (73% vs. 92%; P < 0.01); there was an interaction between the effect of module and language preference (P < 0.01) indicating that although scores increased for both of the topic areas for the English-speaking workers, only the score for the animal health topic increased for the Spanish-speaking workers. Regardless of nationality, level of formal education, topic, or preferred language, digital media are effective at improving knowledge transfer to animal care professionals
Minkowski Functionals of Abell/ACO Clusters
We determine the Minkowski functionals for a sample of Abell/ACO clusters,
401 with measured and 16 with estimated redshifts. The four Minkowski
functionals (including the void probability function and the mean genus)
deliver a global description of the spatial distribution of clusters on scales
from to 60\hMpc with a clear geometric interpretation. Comparisons with
mock catalogues of N--body simulations using different variants of the CDM
model demonstrate the discriminative power of the description. The standard CDM
model and the model with tilted perturbation spectrum cannot generate the
Minkowski functionals of the cluster data, while a model with a cosmological
constant and a model with breaking of the scale invariance of perturbations
(BSI) yield compatible results.Comment: 10 pages, 13 Postscript figures, uses epsf.sty and mn.sty (included),
submitted to MNRA
Quantum Heisenberg Antiferromagnet: Improved Spin-Wave Theories Versus Exact-Diagonalization Data
We reconsider the results cocerning the extreme-quantum
square-lattice Heisenberg antiferromagnet with frustrating diagonal couplings
( model) drawn from a comparison with exact-diagonalization data. A
combined approach using also some intrinsic features of the self-consistent
spin-wave theory leads to the conclusion that the theory strongly overestimates
the stabilizing role of quantum flutcuations in respect to the N\'{e}el phase
in the extreme-quantum case . On the other hand, the analysis implies
that the N\'{e}el phase remains stable at least up to the limit which is pretty larger than some previous estimates. In addition, it is
argued that the spin-wave ansatz predicts the existence of a finite range
( in the linear spin-wave theory) where the Marshall-Peierls
sigh rule survives the frustrations.Comment: 13 pages, LaTex, 7 figures on reques
Band gap bowing of binary alloys: Experimental results compared to theoretical tight-binding supercell calculations for CdZnSe
Compound semiconductor alloys of the type ABC find widespread applications as
their electronic bulk band gap varies continuously with x, and therefore a
tayloring of the energy gap is possible by variation of the concentration. We
model the electronic properties of such semiconductor alloys by a multiband
tight-binding model on a finite ensemble of supercells and determine the band
gap of the alloy. This treatment allows for an intrinsic reproduction of band
bowing effects as a function of the concentration x and is exact in the
alloy-induced disorder. In the present paper, we concentrate on bulk CdZnSe as
a well-defined model system and give a careful analysis on the proper choice of
the basis set and supercell size, as well as on the necessary number of
realizations. The results are compared to experimental results obtained from
ellipsometric measurements of CdZnSe layers prepared by molecular beam epitaxy
(MBE) and photoluminescence (PL) measurements on catalytically grown CdZnSe
nanowires reported in the literature.Comment: 7 pages, 6 figure
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