49,551 research outputs found
A peer-to-peer infrastructure for resilient web services
This work is funded by GR/M78403 “Supporting Internet Computation in Arbitrary Geographical Locations” and GR/R51872 “Reflective Application Framework for Distributed Architectures”, and by Nuffield Grant URB/01597/G “Peer-to-Peer Infrastructure for Autonomic Storage Architectures”This paper describes an infrastructure for the deployment and use of Web Services that are resilient to the failure of the nodes that host those services. The infrastructure presents a single interface that provides mechanisms for users to publish services and to find hosted services. The infrastructure supports the autonomic deployment of services and the brokerage of hosts on which services may be deployed. Once deployed, services are autonomically managed in a number of aspects including load balancing, availability, failure detection and recovery, and lifetime management. Services are published and deployed with associated metadata describing the service type. This same metadata may be used subsequently by interested parties to discover services. The infrastructure uses peer-to-peer (P2P) overlay technologies to abstract over the underlying network to deploy and locate instances of those services. It takes advantage of the P2P network to replicate directory services used to locate service instances (for using a service), Service Hosts (for deployment of services) and Autonomic Managers which manage the deployed services. The P2P overlay network is itself constructed using novel Web Services-based middleware and a variation of the Chord P2P protocol, which is self-managing.Postprin
Influence, originality and similarity in directed acyclic graphs
We introduce a framework for network analysis based on random walks on
directed acyclic graphs where the probability of passing through a given node
is the key ingredient. We illustrate its use in evaluating the mutual influence
of nodes and discovering seminal papers in a citation network. We further
introduce a new similarity metric and test it in a simple personalized
recommendation process. This metric's performance is comparable to that of
classical similarity metrics, thus further supporting the validity of our
framework.Comment: 6 pages, 4 figure
Investigating the source of Planck-detected AME: high resolution observations at 15 GHz
The Planck 28.5 GHz maps were searched for potential Anomalous Microwave
Emission (AME) regions on the scale of or smaller, and several
new regions of interest were selected. Ancillary data at both lower and higher
frequencies were used to construct spectral energy distributions (SEDs), which
seem to confirm an excess consistent with spinning dust models. Here we present
higher resolution observations of two of these new regions with the Arcminute
Microkelvin Imager Small Array (AMI SA) between 14 and 18 GHz to test for the
presence of a compact (10 arcmin or smaller) component. For
AME-G107.1+5.2, dominated by the {\sc Hii} region S140, we find evidence for
the characteristic rising spectrum associated with the either the spinning dust
mechanism for AME or an ultra/hyper-compact \textsc{Hii} region across the AMI
frequency band, however for AME-G173.6+2.8 we find no evidence for AME on
scales of arcmin.Comment: 13 pages, 8 figures, 4 tables. Submitted to Advances in Astronomy AME
Special Issu
Tracing the Conversion of Gas into Stars in Young Massive Cluster Progenitors
Whilst young massive clusters (YMCs; 10 M, age
100 Myr) have been identified in significant numbers, their
progenitor gas clouds have eluded detection. Recently, four extreme molecular
clouds residing within 200 pc of the Galactic centre have been identified as
having the properties thought necessary to form YMCs. Here we utilise far-IR
continuum data from the Herschel Infrared Galactic Plane Survey (HiGAL) and
millimetre spectral line data from the Millimetre Astronomy Legacy Team 90 GHz
Survey (MALT90) to determine their global physical and kinematic structure. We
derive their masses, dust temperatures and radii and use virial analysis to
conclude that they are all likely gravitationally bound -- confirming that they
are likely YMC progenitors. We then compare the density profiles of these
clouds to those of the gas and stellar components of the Sagittarius B2 Main
and North proto-clusters and the stellar distribution of the Arches YMC. We
find that even in these clouds -- the most massive and dense quiescent clouds
in the Galaxy -- the gas is not compact enough to form an Arches-like ( =
2x10 M, R = 0.4 pc) stellar distribution. Further
dynamical processes would be required to condense the resultant population,
indicating that the mass becomes more centrally concentrated as the
(proto)-cluster evolves. These results suggest that YMC formation may proceed
hierarchically rather than through monolithic collapse.Comment: 12 pages, 8 figures, 1 table. Accepted by MNRA
Risk Perceptions of Arsenic in Tap Water and Consumption of Bottled Water
The demand for bottled water has increased rapidly over the past decade, but bottled water is extremely costly compared to tap water. The convenience of bottled water surely matters to consumers, but are others factors at work? This manuscript examines whether purchases of bottled water are associated with the perceived risk of tap water. All of the past studies on bottled water consumption have used simple scale measures of perceived risk that do not correspond to risk measures used by risk analysts. We elicit a probability-based measure of risk and find that as perceived risks rise, expenditures for bottled water rise.Environmental Economics and Policy, Risk and Uncertainty, Q25, Q53, I12,
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