23,479 research outputs found
Nucleon excited states on the lattice
We study the pion-nucleon system in s-wave in the framework of lattice QCD in
order to gain new information on the nucleon excited states. We perform
simulations for mass degenerate light quarks at a pion mass of 266
MeV. The results show that including the two-particle states drastically
changes the energy levels. The variational analysis and the distillation
approach play an important role in the extraction of the energy levels. The
phase shift analysis allows to extract information on the resonance nature of
the observed states.Comment: 6 pages, 2 figures, talk presented at Excited QCD 2013, Bjelasnica
Mountain, Sarajev
Effects of electron coupling to intra- and inter-molecular vibrational modes on the transport properties of single crystal organic semiconductors
Electron coupling to intra- and inter-molecular vibrational modes is
investigated in models appropriate to single crystal organic semiconductors,
such as oligoacenes. Focus is on spectral and transport properties of these
systems beyond perturbative approaches. The interplay between different
couplings strongly affects the temperature band renormalization that is the
result of a subtle equilibrium between opposite tendencies: band narrowing due
to interaction with local modes, band widening due to electron coupling to non
local modes. The model provides an accurate description of the mobility as
function of temperature: indeed, it has the correct order of magnitude, at low
temperatures, it scales as a power-law with the exponent
larger than unity, and, at high temperatures, shows an hopping behavior with a
small activation energy.Comment: 3 Figures, Submitte
Photon-Photon Collisions with SuperChic
The SuperChic Monte Carlo generator provides a common platform for
QCD-mediated, photoproduction and photon-induced Central Exclusive Production
(CEP), with a fully differential treatment of soft survival effects. In these
proceedings we summarise the processes generated, before discussing in more
detail those due to photon-photon collisions, paying special attention to the
correct treatment of the survival factor. We briefly consider the
light-by-light scattering process as an example, before discussing planned
extensions and refinements for the generator.Comment: 6 pages, 2 figures. Submitted to proceedings of the PHOTON 2017
conferenc
Coherent-feedback quantum control with a dynamic compensator
I present an experimental realization of a coherent-feedback control system
that was recently proposed for testing basic principles of linear quantum
stochastic control theory [M. R. James, H. I. Nurdin and I. R. Petersen, to
appear in IEEE Transactions on Automatic Control (2008),
arXiv:quant-ph/0703150v2]. For a dynamical plant consisting of an optical
ring-resonator, I demonstrate ~ 7 dB broadband disturbance rejection of
injected laser signals via all-optical feedback with a tailored dynamic
compensator. Comparison of the results with a transfer function model pinpoints
critical parameters that determine the coherent-feedback control system's
performance.Comment: 4 pages, 4 EPS figure
Effect of phospholipids and bile acids on cholesterol nucleation time and vesicular/micellar cholesterol in gallbladder bile of patients with cholesterol stones
Supersaturation and rapid nucleation of cholesterol in bile are of key importance in the pathogenesis of cholesterol gallstones. While the effects of bile acids and phospholipids on cholesterol saturation of bile have been extensively studied, their influence on the cholesterol nucleation time has not been compared. We, therefore, investigated whether increases of bile acid or phospholipid concentrations in bile by in vitro supplementation affect the cholesterol nucleation time. Bile samples were obtained at surgery from patients with cholesterol gallstones. Prior to the nucleation assay the bile samples were divided into 0.5-ml aliquots and supplemented with 1.25, 2.5, 5.0, and 10.0 mumol/ml of different phosphatidylcholines (PC-dimyristoyl, PC- dipalmitoyl, PC-distearoyl, and extracted biliary PCs) or with 5.0, 10.0, and 20.0 mumol/ml of bile acids (glycine or taurine conjugates of cholic acid, deoxycholic acid, or chenodeoxycholic acid). The increase of phosphatidylcholine or bile acid concentration decreased the mean cholesterol saturation index to a similar extent (PC: 0.1-0.3; BA: 0.1- 0.2). Supplementations of bile with increasing amounts of synthetic or biliary PCs caused a marked prolongation of the nucleation time in bile from 1.5 +/- 0.2 up to > or = 21 days or 2.5 +/- 0.7 up to > or = 21 days. Concurrently, biliary cholesterol was shifted from vesicles to mixed micelles and the cholesterol/phospholipid ratio of the remaining vesicles was progressively lowered. In contrast, the addition of bile acids to gallbladder bile did not affect the cholesterol nucleation time (2.2 +/- 0.3 days), the percentage of vesicular cholesterol, or the cholesterol/phospholipid ratio of vesicles and micelles
Towards a quantum field theory of primitive string fields
We denote generating functions of massless even higher spin fields "primitive
string fields" (PSF's). In an introduction we present the necessary definitions
and derive propagators and currents of these PDF's on flat space. Their
off-shell cubic interaction can be derived after all off-shell cubic
interactions of triplets of higher spin fields have become known [2],[3]. Then
we discuss four-point functions of any quartet of PSF's. In subsequent sections
we exploit the fact that higher spin field theories in are
determined by AdS/CFT correspondence from universality classes of critical
systems in dimensional flat spaces. The O(N) invariant sectors of the O(N)
vector models for play for us the role of "standard
models", for varying , they contain e.g. the Ising model for N=1 and the
spherical model for . A formula for the masses squared that break
gauge symmetry for these O(N) classes is presented for d = 3. For the PSF on
space it is shown that it can be derived by lifting the PSF on flat space
by a simple kernel which contains the sum over all spins. Finally we use an
algorithm to derive all symmetric tensor higher spin fields. They arise from
monomials of scalar fields by derivation and selection of conformal
(quasiprimary) fields. Typically one monomial produces a multiplet of spin
conformal higher spin fields for all , they are distinguished by
their anomalous dimensions (in ) or by their mass (in ). We sum
over these multiplets and the spins to obtain "string type fields", one for
each such monomial.Comment: 16 pages,Late
Energy-gap dynamics of superconducting NbN thin films studied by time-resolved terahertz spectroscopy
Using time-domain Terahertz spectroscopy we performed direct studies of the
photoinduced suppression and recovery of the superconducting gap in a
conventional BCS superconductor NbN. Both processes are found to be strongly
temperature and excitation density dependent. The analysis of the data with the
established phenomenological Rothwarf-Taylor model enabled us to determine the
bare quasiparticle recombination rate, the Cooper pair-breaking rate and the
electron-phonon coupling constant, \lambda = 1.1 +/- 0.1, which is in excellent
agreement with theoretical estimates.Comment: 4 pages, 4 figures; final version, accepted for publication in Phys.
Rev. Let
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