8,428 research outputs found
The Internet AS-Level Topology: Three Data Sources and One Definitive Metric
We calculate an extensive set of characteristics for Internet AS topologies
extracted from the three data sources most frequently used by the research
community: traceroutes, BGP, and WHOIS. We discover that traceroute and BGP
topologies are similar to one another but differ substantially from the WHOIS
topology. Among the widely considered metrics, we find that the joint degree
distribution appears to fundamentally characterize Internet AS topologies as
well as narrowly define values for other important metrics. We discuss the
interplay between the specifics of the three data collection mechanisms and the
resulting topology views. In particular, we show how the data collection
peculiarities explain differences in the resulting joint degree distributions
of the respective topologies. Finally, we release to the community the input
topology datasets, along with the scripts and output of our calculations. This
supplement should enable researchers to validate their models against real data
and to make more informed selection of topology data sources for their specific
needs.Comment: This paper is a revised journal version of cs.NI/050803
Tests of redshift-space distortions models in configuration space for the analysis of the BOSS final data release
Observations of redshift-space distortions in spectroscopic galaxy surveys
offer an attractive method for observing the build-up of cosmological
structure, which depends both on the expansion rate of the Universe and our
theory of gravity. In preparation for analysis of redshift-space distortions
from the Baryon Oscillation Spectroscopic Survey (BOSS) final data release we
compare a number of analytic and phenomenological `streaming' models, specified
in configuration space, to mock catalogs derived in different ways from several
N-body simulations. The galaxies in each mock catalog have properties similar
to those of the higher redshift galaxies measured by BOSS but differ in the
details of how small-scale velocities and halo occupancy are determined. We
find that all of the analytic models fit the simulations over a limited range
of scales while failing at small scales. We discuss which models are most
robust and on which scales they return reliable estimates of the rate of growth
of structure: we find that models based on some form of resummation can fit our
N-body data for BOSS-like galaxies above Mpc well enough to return
unbiased parameter estimates.Comment: 12 pages, 11 figures, matches version accepted by MNRA
Report from the Tri-Agency Cosmological Simulation Task Force
The Tri-Agency Cosmological Simulations (TACS) Task Force was formed when
Program Managers from the Department of Energy (DOE), the National Aeronautics
and Space Administration (NASA), and the National Science Foundation (NSF)
expressed an interest in receiving input into the cosmological simulations
landscape related to the upcoming DOE/NSF Vera Rubin Observatory (Rubin),
NASA/ESA's Euclid, and NASA's Wide Field Infrared Survey Telescope (WFIRST).
The Co-Chairs of TACS, Katrin Heitmann and Alina Kiessling, invited community
scientists from the USA and Europe who are each subject matter experts and are
also members of one or more of the surveys to contribute. The following report
represents the input from TACS that was delivered to the Agencies in December
2018.Comment: 36 pages, 3 figures. Delivered to NASA, NSF, and DOE in Dec 201
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