9,425 research outputs found
An Institutional Approach to Donor Control: From Dyadic Ties to a FieldāLevel Analysis
Literature on the nonprofit sector focuses on charities and their interactions with clients or governmental agencies; donors are studied less often. Studies on philanthropy do examine donors but tend to focus on microlevel factors to explain their behavior. This study, in contrast, draws on institutional theory to show that macrolevel factors affect donor behavior. It also extends the institutional framework by examining the fieldālevel configurations in which donors and fundraisers are embedded. Employing the case of workplace charity, this new model highlights how the composition of the organizational field structures fundraisers and donors alike, shaping fundraisersā strategies of solicitation and, therefore, the extent of donor control.This research was supported by grants from the Aspen Instituteās Nonprofit Sector Research Fund and the National Science Foundation. I thank Susan Eckstein, Julian Go, Heather MacIndoe, Susan Ostrander, audiences in the departments of sociology at Boston University, Emory University, Ohio State University, University of Arizona, and the University of Chicago, various participants in the University of Chicago Graduate School of Business Organizations and Markets Workshop and the MITāSloan School of Management Organization Studies Group Seminar Series, and AJS reviewers for helpful comments on earlier versions. Direct correspondence to Emily Barman, Deparment of Sociology, Boston University, 96 Cummington Street, Boston, Massachusetts 02115
Book Review: Unequal Partnerships: Beyond the Rhetoric of Philanthropic Collaboration. By Ira Silver
Identification of Absorption Features in an Extrasolar Planet Atmosphere
Water absorption is identified in the atmosphere of HD209458b by comparing
models for the planet's transmitted spectrum to recent, multi-wavelength,
eclipse-depth measurements (from 0.3 to 1 microns) published by Knutson et al.
(2007). A cloud-free model which includes solar abundances, rainout of
condensates, and photoionization of sodium and potassium is in good agreement
with the entire set of eclipse-depth measurements from the ultraviolet to
near-infrared. Constraints are placed on condensate removal by gravitational
settling, the bulk metallicity, and the redistribution of absorbed stellar
flux. Comparisons are also made to the Charbonneau et al. (2002) sodium
measurements.Comment: Accepted for publication in ApJL., in emulate ApJ forma
On the Presence of Water and Global Circulation in the Transiting Planet HD 189733b
Detailed models are compared to recent infrared observations of the nearby
extrasolar planet, HD 189733b. It is demonstrated that atmospheric water is
present and that the planet's day side has a non-isothermal structure down to
gas pressures of ~ 0.1 bars. Furthermore, model spectra with different amounts
of CO are compared to the observations and an atmosphere absent of CO is
excluded at roughly 2-sigma. Constraining the CO concentration beyond that is
unfortunately not possible with the current Spitzer photometry. However,
radically enhanced (or depleted) metal abundances are unlikely and the basic
composition of this planet is probably similar to that of its host star. When
combined with Spitzer observations, a recent ground-based upper limit for the
K-band day side flux allows one to estimate the day-to-night energy
redistribution efficiency to be ~ 43%.Comment: accepted (2008 Feb. 5), ApJ Letter
All-Optical Excitation and Detection of Picosecond Dynamics of Ordered Arrays of Nanomagnets with Varying Areal Density
We have demonstrated optical excitation and detection of collective
precessional dynamics in arrays of coupled Ni80Fe20 (permalloy) nanoelements
with systematically varying areal density by an all-optical time-resolved Kerr
microscope. We have applied this technique to precisely determine three
different collective regimes in these arrays. At very high areal density, a
single uniform collective mode is observed where the edge modes of the
constituent elements are suppressed. At intermediate areal densities, three
nonuniform collective modes appear and at very low areal density, we observe
noncollective dynamics and only the centre and edge modes of the constituent
elements appear.Comment: 12 pages, 4 figure
The Edgeworth Conjecture with Small Coalitions and Approximate Equilibria in Large Economies
We revisit the connection between bargaining and equilibrium in exchange
economies, and study its algorithmic implications. We consider bargaining
outcomes to be allocations that cannot be blocked (i.e., profitably re-traded)
by coalitions of small size and show that these allocations must be approximate
Walrasian equilibria. Our results imply that deciding whether an allocation is
approximately Walrasian can be done in polynomial time, even in economies for
which finding an equilibrium is known to be computationally hard.Comment: 26 page
Finding Any Nontrivial Coarse Correlated Equilibrium Is Hard
One of the most appealing aspects of the (coarse) correlated equilibrium
concept is that natural dynamics quickly arrive at approximations of such
equilibria, even in games with many players. In addition, there exist
polynomial-time algorithms that compute exact (coarse) correlated equilibria.
In light of these results, a natural question is how good are the (coarse)
correlated equilibria that can arise from any efficient algorithm or dynamics.
In this paper we address this question, and establish strong negative
results. In particular, we show that in multiplayer games that have a succinct
representation, it is NP-hard to compute any coarse correlated equilibrium (or
approximate coarse correlated equilibrium) with welfare strictly better than
the worst possible. The focus on succinct games ensures that the underlying
complexity question is interesting; many multiplayer games of interest are in
fact succinct. Our results imply that, while one can efficiently compute a
coarse correlated equilibrium, one cannot provide any nontrivial welfare
guarantee for the resulting equilibrium, unless P=NP. We show that analogous
hardness results hold for correlated equilibria, and persist under the
egalitarian objective or Pareto optimality.
To complement the hardness results, we develop an algorithmic framework that
identifies settings in which we can efficiently compute an approximate
correlated equilibrium with near-optimal welfare. We use this framework to
develop an efficient algorithm for computing an approximate correlated
equilibrium with near-optimal welfare in aggregative games.Comment: 21 page
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