82,175 research outputs found
The RHIC azimuth quadrupole: "perfect liquid" or gluonic radiation?
Large elliptic flow at RHIC seems to indicate that ideal hydrodynamics
provides a good description of Au-Au collisions, at least at the maximum RHIC
energy. The medium formed has been interpreted as a nearly perfect
(low-viscosity) liquid, and connections have been made to gravitation through
string theory. Recently, claimed observations of large flow fluctuations
comparable to participant eccentricity fluctuations seem to confirm the ideal
hydro scenario. However, determination of the azimuth quadrupole with 2D
angular autocorrelations, which accurately distinguish ``flow'' (quadrupole)
from ``nonflow'' (minijets), contradicts conventional interpretations.
Centrality trends may depend only on the initial parton geometry, and methods
used to isolate flow fluctuations are sensitive instead mainly to minijet
correlations. The results presented in this paper suggest that the azimuth
quadrupole may be a manifestation of gluonic multipole radiation.Comment: 11 pages, 6 figure
Transverse Momentum Correlations in Relativistic Nuclear Collisions
From the correlation structure of transverse momentum in relativistic
nuclear collisions we observe for the first time temperature/velocity structure
resulting from low- partons. Our novel analysis technique does not invoke
an {\em a priori} jet hypothesis. autocorrelations derived from the scale
dependence of fluctuations reveal a complex parton dissipation process
in RHIC heavy ion collisions. We also observe structure which may result from
collective bulk-medium recoil in response to parton stopping.Comment: 10 pages, 10 figures, proceedings, MIT workshop on fluctuations and
correlations in relativistic nuclear collision
Don't Panic! Closed String Tachyons in ALE Spacetimes
We consider closed string tachyons localized at the fixed points of
noncompact nonsupersymmetric orbifolds. We argue that tachyon condensation
drives these orbifolds to flat space or supersymmetric ALE spaces. The decay
proceeds via an expanding shell of dilaton gradients and curvature which
interpolates between two regions of distinct angular geometry. The string
coupling remains weak throughout. For small tachyon VEVs, evidence comes from
quiver theories on D-branes probes, in which deformations by twisted couplings
smoothly connect non-supersymmetric orbifolds to supersymmetric orbifolds of
reduced order. For large tachyon VEVs, evidence comes from worldsheet RG flow
and spacetime gravity. For \IC^2/\IZ_n, we exhibit infinite sequences of
transitions producing SUSY ALE spaces via twisted closed string condensation
from non-supersymmetric ALE spaces. In a -dual description this provides a
mechanism for creating NS5-branes via {\it closed} string tachyon condensation
similar to the creation of D-branes via {\it open} string tachyon condensation.
We also apply our results to recent duality conjectures involving fluxbranes
and the type 0 string.Comment: 48 pages, harvmac big; 13 figures. v2: added references; comment on
gravity regime added to section 5.2. v3: added reference
Fracture mechanics of cellular glass
The fracture mechanics of cellular glasses (for the structural substrate of mirrored glass for solr concentrator reflecting panels) are discussed. Commercial and developmental cellular glasses were tested and analyzed using standard testing techniques and models developed from linear fracture mechanics. Two models describing the fracture behavior of these materials were developed. Slow crack growth behavior in cellular glass was found to be more complex than that encountered in dense glasses or ceramics. The crack velocity was found to be strongly dependent upon water vapor transport to the tip of the moving crack. The existence of a static fatigue limit was not conclusively established, however, it is speculated that slow crack growth behavior in Region 1 may be slower, by orders of magnitude, than that found in dense glasses
Tachyon condensation and off-shell gravity/gauge duality
We investigate quasilocal tachyon condensation by using gravity/gauge
duality. In order to cure the IR divergence due to a tachyon, we introduce two
regularization schemes: AdS space and a d=10 Schwarzschild black hole in a
cavity. These provide stable canonical ensembles and thus are good candidates
for the endpoint of tachyon condensation. Introducing the Cardy-Verlinde
formula, we establish the on-shell gravity/gauge duality. We propose that the
stringy geometry resulting from the off-shell tachyon dynamics matches onto the
off-shell AdS black hole, where "off-shell" means non-equilibrium
configuration. The instability induced by condensation of a tachyon behaves
like an off-shell black hole and evolves toward a large stable black hole. The
off-shell free energy and its derivative (-function) are used to show
the off-shell gravity/gauge duality for the process of tachyon condensation.
Further, d=10 Schwarzschild black hole in a cavity is considered for the
Hagedorn transition as a possible explanation of the tachyon condensation.Comment: 28 pages, 13 eps figures, version to appear in IJMP
Nondestructive testing of brazed rocket engine components
Report details study made of nondestructive radiographic, ultrasonic, thermographic, and leak test methods used to inspect and evaluate the quality of the various brazed joints in liquid-propellant rocket engine components and assemblies. Descriptions of some of the unique equipment and methods developed are included
Parameters for Twisted Representations
The study of Hermitian forms on a real reductive group gives rise, in the
unequal rank case, to a new class of Kazhdan-Lusztig-Vogan polynomials. These
are associated with an outer automorphism of , and are related to
representations of the extended group . These polynomials were
defined geometrically by Lusztig and Vogan in "Quasisplit Hecke Algebras and
Symmetric Spaces", Duke Math. J. 163 (2014), 983--1034. In order to use their
results to compute the polynomials, one needs to describe explicitly the
extension of representations to the extended group. This paper analyzes these
extensions, and thereby gives a complete algorithm for computing the
polynomials. This algorithm is being implemented in the Atlas of Lie Groups and
Representations software
Searching a biomedical bibliographic database from the Ukraine: the Panteleimon database
The Panteleimon database is available via the Internet and is a public access, database, capable of being searched in English, Russian and Ukrainian, covering medical, pharmaceutical, and chemical publications, published in he Ukraine and Russia from 1998. Describes the formulation of a search strategy for the Panteleimon database, for the identification of citations to randomized controlled trials (RCTs), and the comparison of the search results with records included in the Cochrane Library's Cochrane Central Register of Controlled Trials (CENTRAL) database, to evaluate how comprehensive the coverage of the CENTRAL database is for the literature of the Ukraine. The results indicated that Panteleimon is an easily accessible bibliographic database offering easy access to the Ukrainian biomedical literature. The English language retrieval functions picked up most of the reports of RCTs/CCTs (91 per cent precision but the lower recall of 55 per cent indicates the need to search using Russian and Ukrainian terms for completeness. The overall precision of 26 per cent compares favourably with a search for RCTs in EMBASE, carried out by the UK Cochrane Centre, where 70,000 reports of RCTs were identified from 300,000 records down-loaded (precision 23 per cent). (Quotes from original text
Why the xE distribution triggered by a leading particle does not measure the fragmentation function but does measure the ratio of the transverse momenta of the away-side jet to the trigger-side jet
Hard-scattering of point-like constituents (or partons) in p-p collisions was
discovered at the CERN-ISR in 1972 by measurements utilizing inclusive single
or pairs of hadrons with large transverse momentum (). It was generally
assumed, following Feynman, Field and Fox, as shown by data from the CERN-ISR
experiments, that the distribution of away side hadrons from a single
particle trigger [with ], corrected for of fragmentation would
be the same as that from a jet-trigger and follow the same fragmentation
function as observed in or DIS. PHENIX attempted to measure the
fragmentation function from the away side
distribution of charged particles triggered by a in p-p collisions at
RHIC and showed by explicit calculation that the distribution is actually
quite insensitive to the fragmentation function. Illustrations of the original
arguments and ISR results will be presented. Then the lack of sensitivity to
the fragmentation function will be explained, and an analytic formula for the
distribution given, in terms of incomplete Gamma functions, for the case
where the fragmentation function is exponential. The away-side distribution in
this formulation has the nice property that it both exhibits scaling and
is directly sensitive to the ratio of the away jet to that of
the trigger jet, , and thus can be used, for example, to measure
the relative energy loss of the two jets from a hard-scattering which escape
from the medium in A+A collisions. Comparisons of the analytical formula to
RHIC measurements will be presented, including data from STAR and PHENIX,
leading to some interesting conclusions.Comment: 6 pages, 5 figures, Proceedings of Poster Session, 19th International
Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter
2006), November 14-20, 2006, Shanghai, P. R. Chin
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