11,746 research outputs found
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
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,
Stress Tensor from the Trace Anomaly in Reissner-Nordstrom Spacetimes
The effective action associated with the trace anomaly provides a general
algorithm for approximating the expectation value of the stress tensor of
conformal matter fields in arbitrary curved spacetimes. In static, spherically
symmetric spacetimes, the algorithm involves solving a fourth order linear
differential equation in the radial coordinate r for the two scalar auxiliary
fields appearing in the anomaly action, and its corresponding stress tensor. By
appropriate choice of the homogeneous solutions of the auxiliary field
equations, we show that it is possible to obtain finite stress tensors on all
Reissner-Nordstrom event horizons, including the extreme Q=M case. We compare
these finite results to previous analytic approximation methods, which yield
invariably an infinite stress-energy on charged black hole horizons, as well as
with detailed numerical calculations that indicate the contrary. The
approximation scheme based on the auxiliary field effective action reproduces
all physically allowed behaviors of the quantum stress tensor, in a variety of
quantum states, for fields of any spin, in the vicinity of the entire family (0
le Q le M) of RN horizons.Comment: 43 pages, 12 figure
IC 751: a new changing-look AGN discovered by NuSTAR
We present the results of five NuSTAR observations of the type 2 active
galactic nucleus (AGN) in IC 751, three of which were performed simultaneously
with XMM-Newton or Swift/XRT. We find that the nuclear X-ray source underwent a
clear transition from a Compton-thick () to a Compton-thin () state on timescales of months, which makes
IC 751 the first changing-look AGN discovered by NuSTAR. Changes of the
line-of-sight column density at a level are also found on a
time-scale of hours ().
From the lack of spectral variability on timescales of ks we infer
that the varying absorber is located beyond the emission-weighted average
radius of the broad-line region, and could therefore be related either to the
external part of the broad-line region or a clumpy molecular torus. By adopting
a physical torus X-ray spectral model, we are able to disentangle the column
density of the non-varying absorber () from that of the varying clouds
[], and to constrain that of
the material responsible for the reprocessed X-ray radiation (). We find evidence of significant intrinsic X-ray
variability, with the flux varying by a factor of five on timescales of a few
months in the 2-10 and 10-50 keV band.Comment: Accepted for publication in ApJ, 11 pages, 6 figure
Positivity of Spin Foam Amplitudes
The amplitude for a spin foam in the Barrett-Crane model of Riemannian
quantum gravity is given as a product over its vertices, edges and faces, with
one factor of the Riemannian 10j symbols appearing for each vertex, and simpler
factors for the edges and faces. We prove that these amplitudes are always
nonnegative for closed spin foams. As a corollary, all open spin foams going
between a fixed pair of spin networks have real amplitudes of the same sign.
This means one can use the Metropolis algorithm to compute expectation values
of observables in the Riemannian Barrett-Crane model, as in statistical
mechanics, even though this theory is based on a real-time (e^{iS}) rather than
imaginary-time (e^{-S}) path integral. Our proof uses the fact that when the
Riemannian 10j symbols are nonzero, their sign is positive or negative
depending on whether the sum of the ten spins is an integer or half-integer.
For the product of 10j symbols appearing in the amplitude for a closed spin
foam, these signs cancel. We conclude with some numerical evidence suggesting
that the Lorentzian 10j symbols are always nonnegative, which would imply
similar results for the Lorentzian Barrett-Crane model.Comment: 15 pages LaTeX. v3: Final version, with updated conclusions and other
minor changes. To appear in Classical and Quantum Gravity. v4: corrects # of
samples in Lorentzian tabl
The N=2(4) string is self-dual N=4 Yang-Mills
N=2 string amplitudes, when required to have the Lorentz covariance of the
equivalent N=4 string, describe a self-dual form of N=4 super Yang-Mills in 2+2
dimensions. Spin-independent couplings and the ghost nature of SO(2,2)
spacetime make it a topological-like theory with vanishing loop corrections.Comment: 7 pg., ITP-SB-92-24 (uuencoded dvi file; otherwise same as original
On Cosmological Implication of the Trace Anomaly
We establish a connection between the trace anomaly and a thermal radiation
in the context of the standard cosmology. This is done by solving the covariant
conservation equation of the stress tensor associated with a conformally
invariant quantum scalar field. The solution corresponds to a thermal radiation
with a temperature which is given in terms of a cut-off time excluding the
spacetime regions very close to the initial singularity. We discuss the
interrelation between this result and the result obtained in a two-dimensional
schwarzschild spacetime.Comment: 8 pages, no figure
Detection-Loophole-Free Test of Quantum Nonlocality, and Applications
We present a source of entangled photons that violates a Bell inequality free
of the "fair-sampling" assumption, by over 7 standard deviations. This
violation is the first experiment with photons to close the detection loophole,
and we demonstrate enough "efficiency" overhead to eventually perform a fully
loophole-free test of local realism. The entanglement quality is verified by
maximally violating additional Bell tests, testing the upper limit of quantum
correlations. Finally, we use the source to generate secure private quantum
random numbers at rates over 4 orders of magnitude beyond previous experiments.Comment: Main text: 5 pages, 2 figures, 1 table. Supplementary Information: 7
pages, 2 figure
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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