29,758 research outputs found
Orbit Transfer Vehicle (OTV) engine study, phase "A" extension 2
The operation of the Advanced Expander Cycle OTV engine was evaluated at high mixture ratios, and intermediate and low thrust levels to establish the impact upon the engine design and costs, and/or operating characteristics. The engine operation was analyzed at tank head and pumped idle conditions with the nozzle extension retracted. The engine performance, weight, and envelope parametrics data were expanded to include mixture ratios of 7.5 and 8.0
I give at the office: A review of workplace giving research, theory, and practice
Workplace giving is a widely used philanthropic tool. Although it may have great unmet potential, it is also facing a number of challenges, including competition from informal crowdfunding campaigns. In the face of such challenges, we take stock of the extant research to better understand the value and future of workplace giving, emphasizing employee actions and preferences in our review. Workplace giving studies can also augment knowledge about contextual giving or bounded settings for exploring basic philanthropic questions (e.g., donor control or gift elasticity). We use a three‐part conceptual framework to synthesize and discuss research on individual workplace giving in the context of broader giving behaviors. We address what researchers know, do not know, and need to know on the topic of workplace giving
The devil is in the detail: hints for practical optimisation
Finding the minimum of an objective function, such as a least squares or negative log-likelihood function, with respect to the unknown model parameters is a problem often encountered in econometrics. Consequently, students of econometrics and applied econometricians are usually well-grounded in the broad differences between the numerical procedures employed to solve these problems. Often, however, relatively little time is given to understanding the practical subtleties of implementing these schemes when faced with illbehaved problems. This paper addresses some of the details involved in practical optimisation, such as dealing with constraints on the parameters, specifying starting values, termination criteria and analytical gradients, and illustrates some of the general ideas with several instructive examples
Examining the Efficiency of the U.S. Courts of Appeals: Pathologies and Prescriptions
Until recently (e.g., Lindquist 2007), few studies have examined the factors that might affect aspects of judicial efficiency, including the time it takes a court to decide a case. In our analysis of a sample o f U.S. Courts of Appeals decisions from 1971-1996, we examine a variety of potential causes of inefficiency, or pathologies, before suggesting a series of prescriptions. 1 Both authors equally contributed to this manuscript. The authors would like to thank Reese Manceaux for his assistance in merging a variety of seemingly incompatible databases, as well as Nicole Arnold for her assistance in collecting data.judicial efficiency, Courts of Appeals, litigation
Transitions in non-conserving models of Self-Organized Criticality
We investigate a random--neighbours version of the two dimensional
non-conserving earthquake model of Olami, Feder and Christensen [Phys. Rev.
Lett. {\bf 68}, 1244 (1992)]. We show both analytically and numerically that
criticality can be expected even in the presence of dissipation. As the
critical level of conservation, , is approached, the cut--off of the
avalanche size distribution scales as . The
transition from non-SOC to SOC behaviour is controlled by the average branching
ratio of an avalanche, which can thus be regarded as an order
parameter of the system. The relevance of the results are discussed in
connection to the nearest-neighbours OFC model (in particular we analyse the
relevance of synchronization in the latter).Comment: 8 pages in latex format; 5 figures available upon reques
Groups which do not admit ghosts
A ghost in the stable module category of a group G is a map between
representations of G that is invisible to Tate cohomology. We show that the
only non-trivial finite p-groups whose stable module categories have no
non-trivial ghosts are the cyclic groups of order 2 and 3. We compare this to
the situation in the derived category of a commutative ring. We also determine
for which groups G the second power of the Jacobson radical of kG is stably
isomorphic to a suspension of k.Comment: 9 pages, improved exposition and fixed several typos, to appear in
the Proceedings of the AM
On R-duals and the duality principle in Gabor analysis
The concept of R-duals of a frame was introduced by Casazza, Kutyniok and
Lammers in 2004, with the motivation to obtain a general version of the duality
principle in Gabor analysis. For tight Gabor frames and Gabor Riesz bases the
three authors were actually able to show that the duality principle is a
special case of general results for R-duals. In this paper we introduce various
alternative R-duals, with focus on what we call R-duals of type II and III. We
show how they are related and provide characterizations of the R-duals of type
II and III. In particular, we prove that for tight frames these classes
coincide with the R-duals by Casazza et el., which is desirable in the sense
that the motivating case of tight Gabor frames already is well covered by these
R-duals. On the other hand, all the introduced types of R-duals generalize the
duality principle for larger classes of Gabor frames than just the tight frames
and the Riesz bases; in particular, the R-duals of type III cover the duality
principle for all Gabor frames
The concept of social pharmacy
The 13th International Social Pharmacy Workshop will be held in Malta in July 2004. The Social Pharmacy Workshops are international conferences for research in social and behavioural pharmacy. Meetings are held every second year and participation has grown steadily since the first Workshop was held in Helsinki, Finland, in 1980. Following the successful 2002 conference in Sydney, Australia, the 2004 meeting in Malta will be the first one held in the Mediterranean area!peer-reviewe
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