3,047 research outputs found
On thermalization of a boost-invariant non Abelian plasma
Using a holographic method, we further investigate the relaxation towards the
hydrodynamic regime of a boost-invariant non-Abelian plasma taken
out-of-equilibrium. In the dual description, the system is driven
out-of-equilibrium by boundary sourcing, a deformation of the boundary metric,
as proposed by Chesler and Yaffe. The effects of several deformation profiles
on the bulk geometry are investigated by the analysis of the corresponding
solutions of the Einstein equations. The time of restoration of the
hydrodynamic regime is investigated: setting the effective temperature of the
system at the end of the boundary quenching to MeV, the
hydrodynamic regime is reached after a lapse of time of (1 fm/c).Comment: 24 pages, 11 figures. Improved numerical analysis, one more appendix,
two new figures. To appear in JHE
Quarkonium dissociation in a far-from-equilibrium holographic setup
The real-time dissociation of the heavy quarkonium in a strongly coupled
boost-invariant non-Abelian plasma relaxing towards equilibrium is analyzed in
a holographic framework. The effects driving the plasma out of equilibrium are
described by boundary quenching, impulsive variations of the boundary metric.
Quarkonium is represented by a classical string with endpoints kept close to
the boundary. The evolution of the string profile is computed in the
time-dependent geometry, and the dissociation time is evaluated for different
configurations with respect to the direction of the plasma expansion.
Dissociation occurs fastly for the quarkonium placed in the transverse plane.Comment: 14 pages, 8 figures. References added. Matches the published versio
Mid-Infrared Galaxy Morphology Along the Hubble Sequence
The mid-infrared emission from 18 nearby galaxies imaged with the IRAC
instrument on Spitzer Space Telescope samples the spatial distributions of the
reddening-free stellar photospheric emission and the warm dust in the ISM.
These two components provide a new framework for galaxy morphological
classification, in which the presence of spiral arms and their emission
strength relative to the starlight can be measured directly and with high
contrast. Four mid-infrared classification methods are explored, three of which
are based on quantitative global parameters (colors, bulge-to-disk ratio)
similar to those used in the past for optical studies; in this limited sample,
all correlate well with traditional B-band classification. We suggest reasons
why infrared classification may be superior to optical classification.Comment: ApJS (in press), Spitzer Space Telescope Special Issue; 13 pages,
LaTeX (or Latex, etc); Figure 1ab is large, color plate; full-resolution
plates in .pdf format available at
http://cfa-www.harvard.edu/irac/publications
Ordinary and Extraordinary Hadrons
Resonances and enhancements in meson-meson scattering can be divided into two
classes distinguished by their behavior as the number of colors N_c in QCD
becomes large: The first are ordinary mesons that become stable as N_c goes to
infinity. This class includes textbook q-bar q mesons as well as glueballs and
hybrids. The second class, extraordinary mesons, are enhancements that
disappear as N_c goes to infinity; they subside into the hadronic continuum.
This class includes indistinct and controversial objects that have been
classified as q-bar q-bar q q mesons or meson-meson molecules. Pelaez's study
of the N_c dependence of unitarized chiral dynamics illustrates both classes:
the p-wave pi-pi and K-pi resonances, the rho(770) and K*(892), behave as
ordinary mesons; the s-wave pi-pi and K-pi enhancements, the sigma(600) and
kappa(800), behave like extraordinary mesons. Ordinary mesons resemble Feshbach
resonances while extraordinary mesons look more like effects due to potentials
in meson-meson scattering channels. I build and explore toy models along these
lines. Finally I discuss some related dynamical issues affecting the
interpretation of extraordinary mesons.Comment: 18 pages, 10 figures, talk presented at the 2006 Yukawa International
Seminar: New Frontiers in QCD, Kyoto University, November 2006. This talk is
dedicated to the memory of R. H. Dalit
Possible complex annihilation and B -> K pi direct CP asymmetry
We point out that a sizable strong phase could be generated from the penguin
annihilation in the soft-collinear effective theory for B meson decays. Keeping
a small scale suppressed by O(Lambda/m_b), Lambda being a hadronic scale and
m_b the b quark mass, in the denominators of internal particle propagators
without expansion, the resultant strong phase can accommodate the data of the
B^0 -> K^-+ pi^+- direct CP asymmetry. Our study reconciles the opposite
conclusions on the real or complex penguin annihilation amplitude drawn in the
soft-collinear effective theory and in the perturbative QCD approach based on
k_T factorization theorem.Comment: 8 pages, 1 figure, added reference
Quarkonium dissociation in strongly coupled far-from-equilibrium matter: holographic description
Abstract The heavy quarkonium real-time dissociation in a strongly coupled non-Abelian matter relaxing to equilibrium is described in a holographic approach. Boundary sourcing, impulsive distortions of the boundary metric, are used to mimic effects driving the matter far-from-equilibrium. Quarkonium is represented by a string with endpoints kept close to the boundary, and its evolution in the time-dependent geometry is studied
Alignment transition in a nematic liquid crystal due to field-induced breaking of anchoring
We report on the alignment transition of a nematic liquid crystal from
initially homeotropic to quasi-planar due to field-induced anchoring breaking.
The initial homeotropic alignment is achieved by Langmuir-Blodgett monolayers.
In this geometry the anchoring strength can be evaluated by the Frederiks
transition technique. Applying an electric field above a certain threshold
provokes turbulent states denoted DSM1 and DSM2. While DSM1 does not affect the
anchoring, DSM2 breaks the coupling between the surface and the liquid crystal:
switching off the field from a DSM2 state does not immediately restore the
homeotropic alignment. Instead, we obtain a quasi-planar metastable alignment.
The cell thickness dependence for the transition is related to theComment: 7 pages, LaTeX2e article, 4 figures, 7 EPS files, added references,
accepted for publication in Europhysics Letter
Preliminary realization of an electric-powered hydraulic pump system for a waste compactor truck and a techno-economic analysis
Most industrial trucks are equipped with hydraulic systems designed for specic operations, for which the required power is supplied by the internal combustion engine (ICE). The largest share of the power consumption is required by the hydraulic system during idling operations, and, consequently, the current literature focuses on energy saving strategies for the hydraulic system rather than making the vehicle traction more efficient. This study presents the preliminary realization of an electric-powered hydraulic pump system (e-HPS) that drives the lifting of the dumpster and the garbage compaction in a waste compactor truck, rather than traditional ICE-driven hydraulic pump systems (ICE-HPSs). The different components of the e-HPS are described and the battery pack was modelled using the kinetic battery model. The end-of-life of the battery pack was determined to assess the economic feasibility of the proposed e-HPS for the truck lifespan, using numerical simulations. The aim was twofold: To provide an implementation method to retrofit the e-HPS to a conventional waste compactor truck and to assess its economic feasibility, investigating fuel savings during the use phase and the consequent reduction of CO2 emissions. Results show that the total lifespan cost saving achieved a value of 65,000. Furthermore, total CO2 emissions for the e-HPS were about 80% lower than those of the ICE-HPS, highlighting that the e-HPS can provide significant environmental benefits in an urban context
Blockade and Counterflow Supercurrent in exciton-condensate Josephson junctions
We demonstrate that perfect conversion between charged supercurrents in
superconductors and neutral supercurrents in electron-hole pair condensates is
possible via a new Andreev-like scattering mechanism. As a result, when two
superconducting circuits are coupled through a bilayer exciton condensate, the
superflow in both layers is drastically modified. Depending on the phase biases
the supercurrents can be completely blocked or exhibit perfect drag.Comment: 4 pages, 2 figure
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