30,300 research outputs found
A View From the Field: Helping Community Organizations Meet Capacity Challenges
Based on monitoring and site visits, examines the capacity needs of community-based out-of-school time organizations, including a full, qualified staff, support from schools, adequate curriculum development, and fiscal management. Suggests solutions
Modeling Belief in Dynamic Systems, Part II: Revision and Update
The study of belief change has been an active area in philosophy and AI. In
recent years two special cases of belief change, belief revision and belief
update, have been studied in detail. In a companion paper (Friedman & Halpern,
1997), we introduce a new framework to model belief change. This framework
combines temporal and epistemic modalities with a notion of plausibility,
allowing us to examine the change of beliefs over time. In this paper, we show
how belief revision and belief update can be captured in our framework. This
allows us to compare the assumptions made by each method, and to better
understand the principles underlying them. In particular, it shows that Katsuno
and Mendelzon's notion of belief update (Katsuno & Mendelzon, 1991a) depends on
several strong assumptions that may limit its applicability in artificial
intelligence. Finally, our analysis allow us to identify a notion of minimal
change that underlies a broad range of belief change operations including
revision and update.Comment: See http://www.jair.org/ for other files accompanying this articl
Few-body calculations of -nuclear quasibound states
We report on precise hyperspherical-basis calculations of and quasibound states, using energy dependent interaction potentials
derived from coupled-channel models of the nucleon
resonance. The attraction generated in these models is too weak to
generate a two-body bound state. No bound-state solution was found in
our calculations in models where Re fm, with the scattering length, covering thereby the majority of
resonance models. A near-threshold bound-state
solution, with separation energy of less than 1 MeV and width of about
15 MeV, was obtained in the 2005 Green-Wycech model where Re fm. The role of handling self consistently the subthreshold
interaction is carefully studied.Comment: a second footnote added in v2, matching published versio
Why Does the Paper-Bill Spread Predict Real Economic Activity?
Evidence based on the past three decades of U.S. experience shows that the difference between the interest rates on commercial paper and Treasury bills has consistently borne a systematic relationship to subsequent fluctuations of nonfinancial economic activity. This interest rate spread typically widens in advance of recessions, and narrows again before recoveries. The relationship remains valid even after allowance for other financial variables that previous researchers have often advanced as potential business cycle predictors. This paper provides support for each of three different explanations for this predictive power of the paper?bill spread. First, changing perceptions of default risk exert a clearly recognizable influence on the spread. This influence is all the more discernable after allowance for effects associated with the changing volume of paper issuance when investors view commercial paper and Treasury bills as imperfect portfolio substitutes -- a key assumption for which the evidence introduced here provides support. Second, again under conditions of imperfect substitutability, a widening paper-bill spread is also a symptom of the contraction in bank lending due to tighter monetary policy. Third, there is also evidence of a further role for independent changes in the behavior of borrowers in the commercial paper market due to their changing cash requirements over the course of the business cycle.
Onset of -nuclear binding in a pionless EFT approach
and bound states are explored in stochastic
variational method (SVM) calculations within a pionless effective field theory
(EFT) approach at leading order. The theoretical input consists of regulated
and contact terms, and a regulated energy dependent contact
term derived from coupled-channel models of the nucleon
resonance plus a regulated contact term. A self consistency procedure
is applied to deal with the energy dependence of the subthreshold
input, resulting in a weak dependence of the calculated -nuclear binding
energies on the EFT regulator. It is found, in terms of the scattering
length , that the onset of binding \eta\,^3He requires a minimal
value of Re close to 1 fm, yielding then a few MeV binding
in \eta\,^4He. The onset of binding \eta\,^4He requires a lower value of
Re, but exceeding 0.7 fm.Comment: v4 consists of the published Physics Letters B version [31] plus
Erratum ([30], Appendix A here); main results and conclusions remain intac
Simple Pricing Schemes for the Cloud
The problem of pricing the cloud has attracted much recent attention due to
the widespread use of cloud computing and cloud services. From a theoretical
perspective, several mechanisms that provide strong efficiency or fairness
guarantees and desirable incentive properties have been designed. However,
these mechanisms often rely on a rigid model, with several parameters needing
to be precisely known in order for the guarantees to hold. In this paper, we
consider a stochastic model and show that it is possible to obtain good welfare
and revenue guarantees with simple mechanisms that do not make use of the
information on some of these parameters. In particular, we prove that a
mechanism that sets the same price per time step for jobs of any length
achieves at least 50% of the welfare and revenue obtained by a mechanism that
can set different prices for jobs of different lengths, and the ratio can be
improved if we have more specific knowledge of some parameters. Similarly, a
mechanism that sets the same price for all servers even though the servers may
receive different kinds of jobs can provide a reasonable welfare and revenue
approximation compared to a mechanism that is allowed to set different prices
for different servers.Comment: To appear in the 13th Conference on Web and Internet Economics
(WINE), 2017. A preliminary version was presented at the 12th Workshop on the
Economics of Networks, Systems and Computation (NetEcon), 201
Economic Activity and the Short-term Credit Markets: An Analysis of Prices and Quantities
macroeconomics, economic activity, short-term, credit markets, price, quantities
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