4,053 research outputs found
Resolving Conflicts Between Farmers and Creditors: An Analysis of the Farmer-Creditor Mediation Process
Also PCMA Working Paper #26.http://deepblue.lib.umich.edu/bitstream/2027.42/51202/1/435.pd
On optimum Hamiltonians for state transformations
For a prescribed pair of quantum states |psi_I> and |psi_F> we establish an
elementary derivation of the optimum Hamiltonian, under constraints on its
eigenvalues, that generates the unitary transformation |psi_I> --> |psi_F> in
the shortest duration. The derivation is geometric in character and does not
rely on variational calculus.Comment: 5 page
High Multiplicity Searches at the LHC Using Jet Masses
This article introduces a new class of searches for physics beyond the
Standard Model that improves the sensitivity to signals with high jet
multiplicity. The proposed searches gain access to high multiplicity signals by
reclustering events into large-radius, or "fat," jets and by requiring that
each event has multiple massive jets. This technique is applied to
supersymmetric scenarios in which gluinos are pair-produced and then
subsequently decay to final states with either moderate quantities of missing
energy or final states without missing energy. In each of these scenarios, the
use of jet mass improves the estimated reach in gluino mass by 20 % to 50 %
over current LHC searches.Comment: 9 pages, 6 figures; v3 corrects a few small typo
The Parkes quarter-Jansky flat-spectrum sample 3. Space density and evolution of QSOs
We analyze the Parkes quarter-Jansky flat-spectrum sample of QSOs in terms of
space density, including the redshift distribution, the radio luminosity
function, and the evidence for a redshift cutoff. With regard to the luminosity
function, we note the strong evolution in space density from the present day to
epochs corresponding to redshifts ~ 1. We draw attention to a selection effect
due to spread in spectral shape that may have misled other investigators to
consider the apparent similarities in shape of luminosity functions in
different redshift shells as evidence for luminosity evolution. To examine the
evolution at redshifts beyond 3, we develop a model-independent method based on
the V_max test using each object to predict expectation densities beyond z=3.
With this we show that a diminution in space density at z > 3 is present at a
significance level >4 sigma. We identify a severe bias in such determinations
from using flux-density measurements at epochs significantly later than that of
the finding survey. The form of the diminution is estimated, and is shown to be
very similar to that found for QSOs selected in X-ray and optical wavebands.
The diminution is also compared with the current estimates of star-formation
evolution, with less conclusive results. In summary we suggest that the
reionization epoch is little influenced by powerful flat-spectrum QSOs, and
that dust obscuration does not play a major role in our view of the QSO
population selected at radio, optical or X-ray wavelengths.Comment: 18 pages, 11 figures, accepted 18 Dec 2004, Astron. & Astrophys. The
accepted version is expanded to include an analysis of the form of the
decline in radio-QSO space density at high redshifts. This is compared with
the forms of epoch dependence derived for optically-selected QSOs, for
X-ray-selected QSOs, and for star formation rat
PG 1700+518 Revisited: Adaptive Optics Imaging and a Revised Starburst Age for the Companion
We present the results of adaptive-optics imaging of the z=0.2923 QSO PG
1700+518 in the J and H bands. The extension to the north of the QSO is clearly
seen to be a discrete companion with a well-defined tidal tail, rather than a
feature associated with the host galaxy of PG 1700+518 itself. On the other
hand, an extension to the southwest of the QSO (seen best in deeper, but
lower-resolution, optical images) does likely comprise tidal material from the
host galaxy. The SED derived from images in J, H, and two non-standard optical
bands indicates the presence of dust intermixed with the stellar component. We
use our previously reported Keck spectrum of the companion, the SED found from
the imaging data, and updated spectral-synthesis models to constrain the
stellar populations in the companion and to redetermine the age of the
starburst. While our best-fit age of 0.085 Gyr is nearly the same as our
earlier determination, the fit of the new models is considerably better. This
age is found to be remarkably robust with respect to different assumptions
about the nature of the older stellar component and the effects of dust.Comment: 11 pages; includes two eps figures. Latex (AASTEX). Two additional
figures in gif format. Postscript version including all figs. (424 kb) can be
obtained from http://www.ifa.hawaii.edu/~canaguby/preprints.html To appear in
ApJ. Letter
An alternative to the conventional micro-canonical ensemble
Usual approach to the foundations of quantum statistical physics is based on
conventional micro-canonical ensemble as a starting point for deriving
Boltzmann-Gibbs (BG) equilibrium. It leaves, however, a number of conceptual
and practical questions unanswered. Here we discuss these questions, thereby
motivating the study of a natural alternative known as Quantum Micro-Canonical
(QMC) ensemble. We present a detailed numerical study of the properties of the
QMC ensemble for finite quantum systems revealing a good agreement with the
existing analytical results for large quantum systems. We also propose the way
to introduce analytical corrections accounting for finite-size effects. With
the above corrections, the agreement between the analytical and the numerical
results becomes very accurate. The QMC ensemble leads to an unconventional kind
of equilibrium, which may be realizable after strong perturbations in small
isolated quantum systems having large number of levels. We demonstrate that the
variance of energy fluctuations can be used to discriminate the QMC equilibrium
from the BG equilibrium. We further suggest that the reason, why BG equilibrium
commonly occurs in nature rather than the QMC-type equilibrium, has something
to do with the notion of quantum collapse.Comment: 25 pages, 6 figure
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