17,172 research outputs found
Can Effects of Dark Matter be Explained by the Turbulent Flow of Spacetime?
For the past forty years the search for dark matter has been one of the
primary foci of astrophysics, although there has yet to be any direct evidence
for its existence (Porter et al. 2011). Indirect evidence for the existence of
dark matter is largely rooted in the rotational speeds of stars within their
host galaxies, where, instead of having a ~ r^1/2 radial dependence, stars
appear to have orbital speeds independent of their distance from the galactic
center, which led to proposed existence of dark matter (Porter et al. 2011;
Peebles 1993). We propose an alternate explanation for the observed stellar
motions within galaxies, combining the standard treatment of a fluid-like
spacetime with the possibility of a "bulk flow" of mass through the Universe.
The differential "flow" of spacetime could generate vorticies capable of
providing the "perceived" rotational speeds in excess of those predicted by
Newtonian mechanics. Although a more detailed analysis of our theory is
forthcoming, we find a crude "order of magnitude" calculation can explain this
phenomena. We also find that this can be used to explain the graviational
lensing observed around globular clusters like "Bullet Cluster".Comment: 5 pages, Accepted for publication in Journal of Modern Physics:
Gravitation and Cosmology (Sept. 2012
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Assessing the performance of the Asian/Pacific islander identification algorithm to infer Hmong ethnicity from electronic health records in California.
OBJECTIVE:This study assesses the performance of the North American Association of Central Cancer Registries Asian/Pacific Islander Identification Algorithm (NAPIIA) to infer Hmong ethnicity. DESIGN AND SETTING:Analyses of electronic health records (EHRs) from 1 January 2011 to 1 October 2015. The NAPIIA was applied to the EHR data, and self-reported Hmong ethnicity from a questionnaire was used as the gold standard. Sensitivity, specificity, positive (PPV) and negative predictive values (NPVs) were calculated comparing the source data ethnicity inferred by the algorithm with the self-reported ethnicity from the questionnaire. PARTICIPANTS:EHRs indicating Hmong, Chinese, Vietnamese and Korean ethnicity who met the original study inclusion criteria were analysed. RESULTS:The NAPIIA had a sensitivity of 78%, a specificity of 99.9%, a PPV of 96% and an NPV of 99%. The prevalence of Hmong population in the sample was 3.9%. CONCLUSION:The high sensitivity of the NAPIIA indicates its effectiveness in detecting Hmong ethnicity. The applicability of the NAPIIA to a multitude of Asian subgroups can advance Asian health disparity research by enabling researchers to disaggregate Asian data and unmask health challenges of different Asian subgroups
Spectra: Robust Estimation of Distribution Functions in Networks
Distributed aggregation allows the derivation of a given global aggregate
property from many individual local values in nodes of an interconnected
network system. Simple aggregates such as minima/maxima, counts, sums and
averages have been thoroughly studied in the past and are important tools for
distributed algorithms and network coordination. Nonetheless, this kind of
aggregates may not be comprehensive enough to characterize biased data
distributions or when in presence of outliers, making the case for richer
estimates of the values on the network. This work presents Spectra, a
distributed algorithm for the estimation of distribution functions over large
scale networks. The estimate is available at all nodes and the technique
depicts important properties, namely: robust when exposed to high levels of
message loss, fast convergence speed and fine precision in the estimate. It can
also dynamically cope with changes of the sampled local property, not requiring
algorithm restarts, and is highly resilient to node churn. The proposed
approach is experimentally evaluated and contrasted to a competing state of the
art distribution aggregation technique.Comment: Full version of the paper published at 12th IFIP International
Conference on Distributed Applications and Interoperable Systems (DAIS),
Stockholm (Sweden), June 201
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