9,441 research outputs found
The study of comets, part 2
Flyby missions and systematic observations of comets are projected for studying comet nuclei and cometary dust tail structures
The study of comets, part 1
Papers are presented dealing with observations of comets. Topic discussed include: photometry, polarimetry, and astrometry of comets; detection of water and molecular transitions in comets; ion motions in comet tails; determination of comet brightness and luminosity; and evolution of cometary orbits. Emphasis is placed on analysis of observations of comet Kohoutek
Radiative corrections to the pressure and the one-loop polarization tensor of massless modes in SU(2) Yang-Mills thermodynamics
We compute the one-loop polarization tensor for the on-shell, massless
mode in a thermalized SU(2) Yang-Mills theory being in its deconfining phase.
Postulating that SU(2), we discuss
's effect on the low-momentum part of the black-body spectrum at
temperatures where K.
A table-top experiment is proposed to test the above postulate. As an
application, we point out a possible connection with the stability of dilute,
cold, and old innergalactic atomic hydrogen clouds. We also compute the
two-loop correction to the pressure arising from the instantaneous massless
mode in unitary-Coulomb gauge, which formerly was neglected, and present
improved estimates for subdominant corrections.Comment: 25 pages, 17 figs, v4: consequences of a modification of the
evolution equation for the effectice coupling implemented, no qualitative
change of the physic
What unites Europe and what divides it? Solidarity and the European heritage reconsidered
Despite the on-set on new divisions, there is a strong case to be made for the view that ultimately Europe is more united than divided. There is still significant continuity with the post-war project of reconstruction and peace and that this common ground that constitutes the European heritage needs to be given greater recognition. One of the defining features of European self-understanding is opposition to war
Improved Fokker-Planck Equation for Resonance Line Scattering
A new Fokker-Planck equation is developed for treating resonance line
scattering, especially relevant to the treatment of Lyman alpha in the early
universe. It is a "corrected" form of the equation of Rybicki & Dell'Antonio
that now obeys detailed balance, so that the approach to thermal equilibrium is
properly described. The new equation takes into account the energy changes due
to scattering off moving particles, the recoil term of Basko, and stimulated
scattering. One result is a surprising unification of the equation for
resonance line scattering and the Kompaneets equation. An improved energy
exchange formula due to resonance line scattering is derived. This formula is
compared to previous formulas of Madau, Meikson, & Rees (1997) and Chen &
Miralda-Escud\'e (2004).Comment: 10 pages, no figures, submitted to Ap
Monopoles and Instantons on Partially Compactified D-Branes
Motivated by the recent D-brane constructions of world-volume monopoles and
instantons, we study the supersymmetric SU(N) Yang-Mills theory on , spontaneously broken by a Wilson loop. In addition to the usual N-1
fundamental monopoles, the N-th BPS monopole appears from the Kaluza-Klein
sector. When all N monopoles are present, net magnetic charge vanishes and the
solution can be reinterpreted as a Wilson-loop instanton of unit Pontryagin
number. The instanton/multi-monopole moduli space is explicitly constructed,
and seen to be identical to a Coulomb phase moduli space of a U(1)^N gauge
theory in 2+1 dimensions related to Kronheimer's gauge theory of SU(N) type.
This extends the results by Intriligator and Seiberg to the finite couplings
that, in the infrared limit of Kronheimer's theory, the Coulomb phase
parameterizes a centered SU(N) instanton. We also elaborate on the case of
restored SU(N) symmetry.Comment: LaTex, 18pages, no figur
Practical long-distance quantum key distribution system using decoy levels
Quantum key distribution (QKD) has the potential for widespread real-world
applications. To date no secure long-distance experiment has demonstrated the
truly practical operation needed to move QKD from the laboratory to the real
world due largely to limitations in synchronization and poor detector
performance. Here we report results obtained using a fully automated, robust
QKD system based on the Bennett Brassard 1984 protocol (BB84) with low-noise
superconducting nanowire single-photon detectors (SNSPDs) and decoy levels.
Secret key is produced with unconditional security over a record 144.3 km of
optical fibre, an increase of more than a factor of five compared to the
previous record for unconditionally secure key generation in a practical QKD
system.Comment: 9 page
Calorons and localization of quark eigenvectors in lattice QCD
We analyze the localization properties for eigenvectors of the Dirac operator
in quenched lattice QCD in the vicinity of the deconfinement phase transition.
Studying the characteristic differences between the Z_3 sectors above the
critical temperature T_c, we find indications for the presence of calorons.Comment: 4 pages, 4 figure
Overcoming data scarcity of Twitter: using tweets as bootstrap with application to autism-related topic content analysis
Notwithstanding recent work which has demonstrated the potential of using
Twitter messages for content-specific data mining and analysis, the depth of
such analysis is inherently limited by the scarcity of data imposed by the 140
character tweet limit. In this paper we describe a novel approach for targeted
knowledge exploration which uses tweet content analysis as a preliminary step.
This step is used to bootstrap more sophisticated data collection from directly
related but much richer content sources. In particular we demonstrate that
valuable information can be collected by following URLs included in tweets. We
automatically extract content from the corresponding web pages and treating
each web page as a document linked to the original tweet show how a temporal
topic model based on a hierarchical Dirichlet process can be used to track the
evolution of a complex topic structure of a Twitter community. Using
autism-related tweets we demonstrate that our method is capable of capturing a
much more meaningful picture of information exchange than user-chosen hashtags.Comment: IEEE/ACM International Conference on Advances in Social Networks
Analysis and Mining, 201
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