58,036 research outputs found
A Framework for Analyzing Nonprofit Governance and Accountability Policies and Strategies
This paper presents a framework for analyzing the sprawling topic of nonprofit governance and accountability. It distinguishes various accountability-generating mechanisms and actors, including the unit-level governing board; government policies aimed at shaping the behavior of governing boards; and a broader, natural demand for accountability, generated by an organizations many stakeholders. The aims of these accountability mechanisms and actors also vary, and include the prevention of theft and fraud; the efficient use of resources; the choice of socially valuable goals; and the effective performance of an organization in service of those goals.This publication is Hauser Center Working Paper No. 33.3. Hauser Working Paper Series Nos. 33.1-33.9 were prepared as background papers for the Nonprofit Governance and Accountability Symposium October 3-4, 2006
Landau-Pomeranchuk-Migdal resummation for dilepton production
We consider the thermal emission rate of dileptons from a QCD plasma in the
small invariant mass (Q^2 \sim \gs^2 T^2) but large energy (q^0 \gsim T)
range. We derive an integral equation which resums multiple scatterings to
include the LPM effect; it is valid at leading order in the coupling. Then we
recast it as a differential equation and show a simple algorithm for its
solution. We present results for dilepton rates at phenomenologically
interesting energies and invariant masses.Comment: 19 pages, 7 postscript figures, test program available at
http://www-spht.cea.fr/articles/T02/150/libLPM
Logarithmic terms in entanglement entropies of 2D quantum critical points and Shannon entropies of spin chains
Universal logarithmic terms in the entanglement entropy appear at quantum
critical points (QCPs) in one dimension (1D) and have been predicted in 2D at
QCPs described by 2D conformal field theories. The entanglement entropy in a
strip geometry at such QCPs can be obtained via the "Shannon entropy" of a 1D
spin chain with open boundary conditions. The Shannon entropy of the XXZ chain
is found to have a logarithmic term that implies, for the QCP of the
square-lattice quantum dimer model, a logarithm with universal coefficient . However, the logarithm in the Shannon entropy of the transverse-field
Ising model, which corresponds to entanglement in the 2D Ising conformal QCP,
is found to have a singular dependence on replica or R\'enyi index resulting
from flows to different boundary conditions at the entanglement cut.Comment: 4 pages and 4 page appendix, 4 figure
Optimal Estimation of Several Linear Parameters in the Presence of Lorentzian Thermal Noise
In a previous article we developed an approach to the optimal (minimum
variance, unbiased) statistical estimation technique for the equilibrium
displacement of a damped, harmonic oscillator in the presence of thermal noise.
Here, we expand that work to include the optimal estimation of several linear
parameters from a continuous time series. We show that working in the basis of
the thermal driving force both simplifies the calculations and provides
additional insight to why various approximate (not optimal) estimation
techniques perform as they do. To illustrate this point, we compare the
variance in the optimal estimator that we derive for thermal noise with those
of two approximate methods which, like the optimal estimator, suppress the
contribution to the variance that would come from the irrelevant, resonant
motion of the oscillator. We discuss how these methods fare when the dominant
noise process is either white displacement noise or noise with power spectral
density that is inversely proportional to the frequency ( noise). We also
construct, in the basis of the driving force, an estimator that performs well
for a mixture of white noise and thermal noise. To find the optimal
multi-parameter estimators for thermal noise, we derive and illustrate a
generalization of traditional matrix methods for parameter estimation that can
accommodate continuous data. We discuss how this approach may help refine the
design of experiments as they allow an exact, quantitative comparison of the
precision of estimated parameters under various data acquisition and data
analysis strategies.Comment: 16 pages, 10 figures. Accepted for publication in Classical and
Quantum Gravit
Nonlinear Evolution of the Genus Statistics with Zel'dovich Approximation
Evolution of genus density is calculated from Gaussian initial conditions
using Zel'dovich approximation. A new approach is introduced which formulates
the desired quantity in a rotationally invariant manner. It is shown that
normalized genus density does not depend on the initial spectral shape but is a
function of the fluctuation amplitude only.Comment: 21 pages, 6 Postscript figures, LaTe
Optical control and entanglement of atomic Schroedinger fields
We develop a fully quantized model of a Bose-Einstein condensate driven by a
far off-resonant pump laser which interacts with a single mode of an optical
ring cavity. In the linear regime, the cavity mode exhibits spontaneous
exponential gain correlated with the appearance of two atomic field side-modes.
These side-modes and the cavity field are generated in a highly entangled
state, characterized by thermal intensity fluctuations in the individual modes,
but with two-mode correlation functions which violate certain classical
inequalities. By injecting an initial coherent field into the optical cavity
one can significantly decrease the intensity fluctuations at the expense of
reducing the correlations, thus allowing for optical control over the quantum
statistical properties of matter waves.Comment: 4 page
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