19,225 research outputs found
The Age of the Universe and the Cosmological Constant Determined from Cosmic Microwave Background Anisotropy Measurements
If Omega_tot = 1 and structure formed from adiabatic initial conditions then
the age of the Universe, as constrained by measurements of the cosmic microwave
background (CMB), is t_0=14.0 +/- 0.5 Gyr. The uncertainty is surprisingly
small given that CMB data alone constrain neither h nor Omega_Lambda
significantly. It is due to the tight (and accidental) correlation, in these
models, of the age with the angle subtended by the sound horizon on the
last--scattering surface and thus with the well-determined acoustic peak
locations. If we assume either the HST Key Project result h = 0.72 \pm .08 or
simply that h > 0.55, we find Omega_Lambda > 0.4 at 95% confidence--another
argument for dark energy, independent of supernovae observations. Our analysis
is greatly simplified by the Monte Carlo Markov chain approach to Bayesian
inference combined with a fast method for calculating angular power spectra.Comment: 5 pages, including 2 figures and one table final published versio
Comment on "Formation of primordial black holes by cosmic strings"
We show that in a pioneering paper by Polnarev and Zembowicz, some
conclusions concerning the characteristics of the Turok-strings are generally
not correct. In addition we show that the probability of string collapse given
there, is off by a large prefactor (~1000).Comment: 5 pages, LaTeX and 1 figure, postscript. To appear in PR
MCMC Exploration of Supermassive Black Hole Binary Inspirals
The Laser Interferometer Space Antenna will be able to detect the inspiral
and merger of Super Massive Black Hole Binaries (SMBHBs) anywhere in the
Universe. Standard matched filtering techniques can be used to detect and
characterize these systems. Markov Chain Monte Carlo (MCMC) methods are ideally
suited to this and other LISA data analysis problems as they are able to
efficiently handle models with large dimensions. Here we compare the posterior
parameter distributions derived by an MCMC algorithm with the distributions
predicted by the Fisher information matrix. We find excellent agreement for the
extrinsic parameters, while the Fisher matrix slightly overestimates errors in
the intrinsic parameters.Comment: Submitted to CQG as a GWDAW-10 Conference Proceedings, 9 pages, 5
figures, Published Versio
Evolution of magnetic states in frustrated diamond lattice antiferromagnetic Co(Al1-xCox)2O4 spinels
Using neutron powder diffraction and Monte-Carlo simulations we show that a
spin-liquid regime emerges at $all compositions in the diamond-lattice
antiferromagnets Co(Al1-xCox)2O4. This spin-liquid regime induced by
frustration due to the second-neighbour exchange coupling J2, is gradually
superseded by antiferromagnetic collinear long-range order (k=0) at low
temperatures. Upon substitution of Al3+ by Co3+ in the octahedral B-site the
temperature range occupied by the spin-liquid regime narrows and TN increases.
To explain the experimental observations we considered magnetic anisotropy D or
third-neighbour exchange coupling J3 as degeneracy-breaking perturbations. We
conclude that Co(Al1-xCox)2O4 is below the theoretical critical point
J2/J1=1/8, and that magnetic anisotropy assists in selecting a collinear
long-range ordered ground state, which becomes more stable with increasing x
due to a higher efficiency of O-Co3+-O as an interaction path compared to
O-Al3+-O
A study of quantum decoherence in a system with Kolmogorov-Arnol'd-Moser tori
We present an experimental and numerical study of the effects of decoherence
on a quantum system whose classical analogue has Kolmogorov-Arnol'd-Moser (KAM)
tori in its phase space. Atoms are prepared in a caesium magneto-optical trap
at temperatures and densities which necessitate a quantum description. This
real quantum system is coupled to the environment via spontaneous emission. The
degree of coupling is varied and the effects of this coupling on the quantum
coherence of the system are studied. When the classical diffusion through a
partially broken torus is < hbar, diffusion of quantum particles is inhibited.
We find that increasing decoherence via spontaneous emission increases the
transport of quantum particles through the boundary.Comment: 19 pages including 6 figure
Cosmic String Loops Collapsing to Black Holes
We reexamine the question of collapse of Turok's two-parameter family of cosmic strings. We first give a few simple explicit examples showing that previously obtained results in the literature cannot generally be correct in the complete two-dimensional parameter-space. We then perform a classification of the strings according to the specific time(s) the minimal string size is reached during one period. Finally we obtain an exact analytical expression for the probability of collapse to black holes for the Turok strings. Our result has the same general behavior as previously obtained in the literature but we find, in addition, a numerical prefactor that changes the result by approximately a factor 2000
Southwestern Minnesota Farm Business Management Association 2008 Annual Report
Average net farm income was 242,267 in 2007 (Figure 1). 2008 ended a steady trend of increasing year-to-year incomes for these farms from 2001 to 2007. Crop farms, with historically high corn and soybean prices, remained very profitable. However, specialized hog farms, which had been very profitable for the past four years, experienced substantial losses. Highlights of association financial results for 2008: Median net farm income was 449,997 while the least profitable lost 115,999. The average debt-to-asset ratio improved slightly to 39%, down from 40% (Figure 4). ⢠Corn yields were up but soybean yields were down. Corn averaged 172 bushels per acre compared to 162 in 2007. Soybeans yields decreased to 44 bushels from 49 in 2007 (Figure 5). ⢠Both corn and soybean prices received increased by over 50% to 10.83 for soybeans. ⢠The cost to raise an acre of corn (with land rent) increased by 23% while soybean costs increased by 21%. The cost to produce a bushel of corn on cash rented land increased from 2.90 in 2008, while soybean costs per bushel increased from 7.21. ⢠The average specialized hog operation (those with 70% of sales from hogs or pigs) lost over 1,000,000, were the least profitable based on rate of return on assets. This group earned an average ROA of 7% compared to 14% for farms that grossed between 1,000,000. ⢠With exceptionally high feed prices, no hog or beef enterprise, with the exception of contract growing of hogs (where the contractor provided the feed) covered even direct costs of production. The report provides additional information on profitability, liquidity, and solvency as well as other whole-farm information and detailed information on crop and livestock enterprises. Also reported are whole-farm financial condition and performance by county, sales size class, type of farm, debt-to-asset ratio, and age of operator.Agricultural Finance, Farm Management,
Surfaces Meeting Porous Sets in Positive Measure
Let n>2 and X be a Banach space of dimension strictly greater than n. We show
there exists a directionally porous set P in X for which the set of C^1
surfaces of dimension n meeting P in positive measure is not meager. If X is
separable this leads to a decomposition of X into a countable union of
directionally porous sets and a set which is null on residually many C^1
surfaces of dimension n. This is of interest in the study of certain classes of
null sets used to investigate differentiability of Lipschitz functions on
Banach spaces
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