26,661 research outputs found
Implications of Being a Highly Rated Organization: Evidence from Four-Star Rated Nonprofits
This study examines a group of nonprofits rated four stars by Charity Navigator. The purpose is to determine whether this select group of charities exhibits characteristics associated with top charitable organizations, or whether the four-star rating achieved is limited to the more narrow financial metrics employed in the methodology utilized by Charity Navigator. This study finds that organizations rated four stars by Charity Navigator show a lower level of excess cash holdings, report a lower level of compensation expenses and exhibit lower sensitivity of compensation to performance. Financially, these organizations are less vulnerable than their lower rated peers. The results from this study shed light on the continuing debate of the effectiveness of rating agencies to accurately identify top performing charitable organizations
Rainbow universe
The formalism of rainbow gravity is studied in a cosmological setting. We
consider the very early universe which is radiation dominated. A novel
treatment in our paper is to look for an ``averaged'' cosmological metric
probed by radiation particles themselves. Taking their cosmological evolution
into account, we derive the modified Friedmann-Robertson-Walker(FRW) equations
which is a generalization of the solution presented by Magueijo and Smolin.
Based on this phenomenological cosmological model we argue that the spacetime
curvature has an upper bound such that the cosmological singularity is absent.
These modified equations can be treated as effective equations in the
semi-classical framework of quantum gravity and its analogy with the one
recently proposed in loop quantum cosmology is also discussed.Comment: 5 page
A new method to study the number of colors in the final-state interactions of hadrons
We match the scattering amplitudes of Chiral Perturbation
Theory with those from dispersion relations that respect analyticity and
coupled channel unitarity, as well as accurately describing experiment. Their
dependence on the number of colors () is obtained. By varying the
trajectories of the poles and residues (the couplings to ) of light
mesons, the , , and are investigated.
Our results show that the method proposed is a reliable way to study the
dependence in hadron-hadron scattering with final-state interactions.Comment: 7 pages, 3 figures, improved behaviou
Discrete gravity and and its continuum limit
Recently Gambini and Pullin proposed a new consistent discrete approach to
quantum gravity and applied it to cosmological models. One remarkable result of
this approach is that the cosmological singularity can be avoided in a general
fashion. However, whether the continuum limit of such discretized theories
exists is model dependent. In the case of massless scalar field coupled to
gravity with , the continuum limit can only be achieved by fine
tuning the recurrence constant. We regard this failure as the implication that
cosmological constant should vary with time. For this reason we replace the
massless scalar field by Chaplygin gas which may contribute an effective
cosmological constant term with the evolution of the universe. It turns out
that the continuum limit can be reached in this case indeed.Comment: 16 pages,revised version published in MPL
Chaotic behaviors of stable second-order digital filters with two’s complement arithmetic
In this paper, the behaviors of stable second-order digital filters with two’s complement arithmetic are investigated. It is found that even though the poles are inside the unit circle and the trajectory converges to a fixed point on the phase plane, that fixed point is not necessarily the origin. That fixed point is found and the set of initial conditions corresponding to such trajectories is determined. This set of initial conditions is a set of polygons inside the unit square, whereas it is an ellipse for the marginally stable case. Also, it is found that the occurrence of limit cycles and chaotic fractal pattern on the phase plane can be characterized by the periodic and aperiodic behaviors of the symbolic sequences, respectively. The fractal pattern is polygonal, whereas it is elliptical for the marginally stable case
Threshold Regression for Survival Analysis: Modeling Event Times by a Stochastic Process Reaching a Boundary
Many researchers have investigated first hitting times as models for survival
data. First hitting times arise naturally in many types of stochastic
processes, ranging from Wiener processes to Markov chains. In a survival
context, the state of the underlying process represents the strength of an item
or the health of an individual. The item fails or the individual experiences a
clinical endpoint when the process reaches an adverse threshold state for the
first time. The time scale can be calendar time or some other operational
measure of degradation or disease progression. In many applications, the
process is latent (i.e., unobservable). Threshold regression refers to
first-hitting-time models with regression structures that accommodate covariate
data. The parameters of the process, threshold state and time scale may depend
on the covariates. This paper reviews aspects of this topic and discusses
fruitful avenues for future research.Comment: Published at http://dx.doi.org/10.1214/088342306000000330 in the
Statistical Science (http://www.imstat.org/sts/) by the Institute of
Mathematical Statistics (http://www.imstat.org
and the structure observed around the threshold
We analyze the origin of the structure observed in the reaction for invariant masses close to the
antiproton-proton () threshold, commonly associated with the
resonance. Specifically, we explore the effect of a possible contribution from
the two-step process .
The calculation is performed in distorted-wave Born approximation which allows
an appropriate inclusion of the interaction in the transition
amplitude. The amplitude itself is generated from a corresponding
potential recently derived within chiral effective field theory. We are able to
reproduce the measured spectra for the reactions
and for invariant masses around the threshold. The structure seen in the spectrum emerges as
a threshold effect due to the opening of the channel.Comment: 9 pages, 5 figure
Re-examining the resonance in the reaction
The reaction is investigated
at energies close to the threshold with emphasis on the role played by the
resonance. The interaction in the final
system, constructed within chiral effective field theory and supplemented by a
pole diagram that represents a bare resonance, is taken into account
rigorously. The pole parameters of the are extracted and found to be
compatible with the ones of the resonance that have been established
in the reaction . The actual result for the
is MeV and MeV.
Predictions for the electromagnetic form factors in the timelike
region are presented.Comment: 11 pages, 3 figure
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