25,105 research outputs found
A body-bound navigation system. Analysis and design of a capsule landing system and surface vehicle control system for Mars exploration
Large angle gyro sensing system for body mount on unmanned Mars surface vehicl
Bilateral and Community Enforcement in a Networked Market with Simple Strategies
We present a model of repeated games in large buyer-seller networks in the presence of reputation networks via which buyers share information about past transactions. The model allows us to characterize cooperation networks - networks in which each seller cooperates (by providing high quality goods) with every buyer that is connected to her. To this end, we provide conditions under which: [1] the incentives of a seller s to cooperate depend only on her beliefs with respect to her local neighborhood - a subnetwork that includes seller s and is of a size that is independent of the size of the entire network; and [2] the incentives of a seller s to cooperate can be calculated as if the network was a random tree with seller s at its root. Our characterization sheds light on the welfare costs of relying only on repeated interactions for sustaining cooperation, and on how to mitigate such costs.Networks, moral hazard, graph theory, repeated games
Efficient Implementation of a Synchronous Parallel Push-Relabel Algorithm
Motivated by the observation that FIFO-based push-relabel algorithms are able
to outperform highest label-based variants on modern, large maximum flow
problem instances, we introduce an efficient implementation of the algorithm
that uses coarse-grained parallelism to avoid the problems of existing parallel
approaches. We demonstrate good relative and absolute speedups of our algorithm
on a set of large graph instances taken from real-world applications. On a
modern 40-core machine, our parallel implementation outperforms existing
sequential implementations by up to a factor of 12 and other parallel
implementations by factors of up to 3
What is the excess risk of infertility in women after genital chlamydia infection? A systematic review of the evidence
Methods: Twelve databases were searched, limited to peer-reviewed literature published from January 1970 to September 2007. Conference abstracts and reference lists from reviews published since 2000 and from key articles were hand-searched. Studies were selected for review if they met the following criteria: (1) the study population comprised women of child-bearing age (defined as 15–45 years) and incorporated a comparison group of women documented as "chlamydia negative"; (2) the study outcomes included either infertility or successful pregnancy; and (3) the study design was one of the following: cohort, randomised controlled trial, "before and after" study, screening trial and systematic review. Studies were excluded if they described genital infections that either did not include Chlamydia trachomatis or described genital chlamydial co-infection, in which no data were available for C trachomatis infection alone.
Results: 3349 studies were identified by the search. One study satisfied the inclusion criteria, a longitudinal investigation measuring pregnancy rates in adolescent women with and without current chlamydial infection at baseline. That study reported no significant difference in subsequent pregnancy rates; however, it had serious methodological limitations, which restricted its conclusions.
Conclusions: This systematic review demonstrates the absence of valid evidence on the attributable risk of post-infective tubal factor infertility after genital chlamydial infection. The findings contribute empirical data to the growing debate surrounding previous assumptions about the natural history of chlamydial infection in women
Completeness of Wilson loop functionals on the moduli space of and -connections
The structure of the moduli spaces \M := \A/\G of (all, not just flat)
and connections on a n-manifold is analysed. For any
topology on the corresponding spaces \A of all connections which satisfies
the weak requirement of compatibility with the affine structure of \A, the
moduli space \M is shown to be non-Hausdorff. It is then shown that the
Wilson loop functionals --i.e., the traces of holonomies of connections around
closed loops-- are complete in the sense that they suffice to separate all
separable points of \M. The methods are general enough to allow the
underlying n-manifold to be topologically non-trivial and for connections to be
defined on non-trivial bundles. The results have implications for canonical
quantum general relativity in 4 and 3 dimensions.Comment: Plain TeX, 7 pages, SU-GP-93/4-
Weak Gravitational Flexion
Flexion is the significant third-order weak gravitational lensing effect
responsible for the weakly skewed and arc-like appearance of lensed galaxies.
Here we demonstrate how flexion measurements can be used to measure galaxy halo
density profiles and large-scale structure on non-linear scales, via
galaxy-galaxy lensing, dark matter mapping and cosmic flexion correlation
functions. We describe the origin of gravitational flexion, and discuss its
four components, two of which are first described here. We also introduce an
efficient complex formalism for all orders of lensing distortion. We proceed to
examine the flexion predictions for galaxy-galaxy lensing, examining isothermal
sphere and Navarro, Frenk & White (NFW) profiles and both circularly symmetric
and elliptical cases. We show that in combination with shear we can precisely
measure galaxy masses and NFW halo concentrations. We also show how flexion
measurements can be used to reconstruct mass maps in 2-D projection on the sky,
and in 3-D in combination with redshift data. Finally, we examine the
predictions for cosmic flexion, including convergence-flexion
cross-correlations, and find that the signal is an effective probe of structure
on non-linear scales.Comment: 17 pages, including 12 figures, submitted to MNRA
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