38,137 research outputs found
Estimating Dynamic Traffic Matrices by using Viable Routing Changes
Abstract: In this paper we propose a new approach for dealing with the ill-posed nature of traffic matrix estimation. We present three solution enhancers: an algorithm for deliberately changing link weights to obtain additional information that can make the underlying linear system full rank; a cyclo-stationary model to capture both long-term and short-term traffic variability, and a method for estimating the variance of origin-destination (OD) flows. We show how these three elements can be combined into a comprehensive traffic matrix estimation procedure that dramatically reduces the errors compared to existing methods. We demonstrate that our variance estimates can be used to identify the elephant OD flows, and we thus propose a variant of our algorithm that addresses the problem of estimating only the heavy flows in a traffic matrix. One of our key findings is that by focusing only on heavy flows, we can simplify the measurement and estimation procedure so as to render it more practical. Although there is a tradeoff between practicality and accuracy, we find that increasing the rank is so helpful that we can nevertheless keep the average errors consistently below the 10% carrier target error rate. We validate the effectiveness of our methodology and the intuition behind it using commercial traffic matrix data from Sprint's Tier-1 backbon
Photon spectra from quark generation by WIMPs
In this work we provide the fitting formula valid for the simulated photon
spectra from WIMP annihilation into light quark-anti quark (qq-) channels in a
wide range of WIMP masses. We illustrate our results for the cc- channel.Comment: To appear in the AIP proceedings of "Quark Confinement and Hadron
Spectrum IX" (QCHSIX), Madrid 30th August-3rd September 2010. 3 pages, 6
figure
Active cleaning technique for removing contamination from optical surfaces in space
An active cleaning technique for removing contaminants from optical surfaces in space was investigated with emphasis on the feasibility of using plasma exposure as a means of in-situ cleaning. The major work accomplished includes: (1) development of an in-situ reflectometer for use in conjunction with the contaminant film deposition/cleaning facility; (2) completion of Apollo Telescope Mount (ATM) filter treatment experiments to assess the effects of plasma exposure on the UV transmittance; (3) attempts to correlate the atomic oxygen flux with cleaning rate; (4) completion of in-situ butadien contamination/plasma cleaning/UV reflectance measurement experiments; (5) carbon cleaning experiments using various gases; (6) completion of silicone contamination/cleaning experiments; and (7) experiments conducted at low chamber pressures to determine cleaning rate distribution and contamination of surfaces adjacent to those being cleaned
Gamma-ray and neutrino fluxes from Heavy Dark Matter in the Galactic Center
We present a study of the Galactic Center region as a possible source of both
secondary gamma-ray and neutrino fluxes from annihilating dark matter. We have
studied the gamma-ray flux observed by the High Energy Stereoscopic System
(HESS) from the J1745-290 Galactic Center source. The data are well fitted as
annihilating dark matter in combination with an astrophysical background. The
analysis was performed by means of simulated gamma spectra produced by Monte
Carlo event generators packages. We analyze the differences in the spectra
obtained by the various Monte Carlo codes developed so far in particle physics.
We show that, within some uncertainty, the HESS data can be fitted as a signal
from a heavy dark matter density distribution peaked at the Galactic Center,
with a power-law for the background with a spectral index which is compatible
with the Fermi-Large Area Telescope (LAT) data from the same region. If this
kind of dark matter distribution generates the gamma-ray flux observed by HESS,
we also expect to observe a neutrino flux. We show prospective results for the
observation of secondary neutrinos with the Astronomy with a Neutrino Telescope
and Abyss environmental RESearch project (ANTARES), Ice Cube Neutrino
Observatory (Ice Cube) and the Cubic Kilometer Neutrino Telescope (KM3NeT).
Prospects solely depend on the device resolution angle when its effective area
and the minimum energy threshold are fixed.Comment: 10 pages, 6 figures, To appear on the proceedings of TAUP2013 "13th
International Conference on Topics in Astroparticle and Underground Physics
Modified spinning black holes
In the context of f(R) modified gravity theories we determine that the black
holes existence is determined by the sign of a parameter dependent of the mass,
the charge, the spin and the scalar curvature. We obtain the different
astrophysical objects derived from the presence of different horizons.
Thermodynamics for this kind of black holes is studied for negative values of
the curvature, revealing that we can distinguish between two kinds of BH: fast
and slow.Comment: 4 pages, 6 figures, Contribution to the ERE2011 Spanish Relativity
Meeting, Madrid 201
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