1,749 research outputs found
Comparing cosmic web classifiers using information theory
We introduce a decision scheme for optimally choosing a classifier, which
segments the cosmic web into different structure types (voids, sheets,
filaments, and clusters). Our framework, based on information theory, accounts
for the design aims of different classes of possible applications: (i)
parameter inference, (ii) model selection, and (iii) prediction of new
observations. As an illustration, we use cosmographic maps of web-types in the
Sloan Digital Sky Survey to assess the relative performance of the classifiers
T-web, DIVA and ORIGAMI for: (i) analyzing the morphology of the cosmic web,
(ii) discriminating dark energy models, and (iii) predicting galaxy colors. Our
study substantiates a data-supported connection between cosmic web analysis and
information theory, and paves the path towards principled design of analysis
procedures for the next generation of galaxy surveys. We have made the cosmic
web maps, galaxy catalog, and analysis scripts used in this work publicly
available.Comment: 20 pages, 8 figures, 6 tables. Matches JCAP published version. Public
data available from the first author's website (currently
http://icg.port.ac.uk/~leclercq/
Exploring heterogeneity of unreliable machines for p2p backup
P2P architecture is a viable option for enterprise backup. In contrast to
dedicated backup servers, nowadays a standard solution, making backups directly
on organization's workstations should be cheaper (as existing hardware is
used), more efficient (as there is no single bottleneck server) and more
reliable (as the machines are geographically dispersed).
We present the architecture of a p2p backup system that uses pairwise
replication contracts between a data owner and a replicator. In contrast to
standard p2p storage systems using directly a DHT, the contracts allow our
system to optimize replicas' placement depending on a specific optimization
strategy, and so to take advantage of the heterogeneity of the machines and the
network. Such optimization is particularly appealing in the context of backup:
replicas can be geographically dispersed, the load sent over the network can be
minimized, or the optimization goal can be to minimize the backup/restore time.
However, managing the contracts, keeping them consistent and adjusting them in
response to dynamically changing environment is challenging.
We built a scientific prototype and ran the experiments on 150 workstations
in the university's computer laboratories and, separately, on 50 PlanetLab
nodes. We found out that the main factor affecting the quality of the system is
the availability of the machines. Yet, our main conclusion is that it is
possible to build an efficient and reliable backup system on highly unreliable
machines (our computers had just 13% average availability)
10261 Abstracts Collection -- Algorithm Engineering
From June 27 to July 2, the Dagstuhl Seminar 10261 ``Algorithm Engineering \u27\u27 was held in Schloss Dagstuhl~--~Leibniz Center for Informatics.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
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