2,797 research outputs found
Photon production in relativistic nuclear collisions at SPS and RHIC energies
Chiral Lagrangians are used to compute the production rate of photons from
the hadronic phase of relativistic nuclear collisions. Special attention is
paid to the role of the pseudovector a_1 meson. Calculations that include
reactions with strange mesons, hadronic form factors and vector spectral
densities consistent with dilepton production, as well as the emission from a
quark-gluon plasma and primordial nucleon-nucleon collisions, reproduce the
photon spectra measured at the Super Proton Synchrotron (SPS). Predictions for
the Relativistic Heavy Ion Collider (RHIC) are made.Comment: Work presented at the 26th annual Montreal-Rochester-Syracuse-Toronto
conference (MRST 2004) on high energy physics, Montreal, QC, Canada, 12-14
May 2004. 8 pages, 3 figure
Catalytic reduction of dinitrogen to silylamines by earth-abundant lanthanide and group 4 complexes
Dinitrogen is a challenging molecule to reduce to useful products under ambient conditions. The range of d-block metal complexes that can catalyze dinitrogen reduction to ammonia or tris(silyl)amines under ambient conditions has increased recently but lacks electropositive metal complexes, such as those of the f-block which lack filled d-orbitals that would support classical binding modes of N2. Here, metallacyclic phenolate structures with lanthanide or group 4 cations can bind dinitrogen and catalyze its conversion to bis(silyl)amines under ambient conditions. The formation of this unusual product is controlled by metallacycle sterics. The group 4 complexes featuring small cavities are most selective for bis(silyl)amine, while the lanthanide complexes and the solvated uranium(IV) congener, with larger cavities, can also make the conventional tris(silyl)amine product. These results offer new catalytic applications for plentiful titanium and the more earth-abundant members of the lanthanides that are also less toxic than many base metals used in catalysis
Photons from Quark Gluon Plasma and Hot Hadronic Matter
The productions of real photons from quark gluon plasma and hot hadronic
matter formed after the nucleus - nucleus collisions at ultra-relativistic
energies are discussed. The effects of the spectral shift of the hadrons at
finite temperature on the production of photons are investigated. On the basis
of the present analysis it is shown that the photon spectra measured by WA98
collaboration in Pb + Pb collisions at CERN SPS energies can be explained by
both QGP as well as hadronic initial states if the spectral shift of hadrons at
finite temperature is taken into account. Several other works on the analysis
of WA98 photon data have also been briefly discussed.Comment: Latex file, six eps figures include
A Reference Database of Standardised Continuous Lumbar Intervertebral Motion Analysis for Conducting Patient-Specific Comparisons
Lumbar instability has long been thought of as the failure of lumbar vertebrae to maintain their normal patterns of displacement. However, it is unknown what these patterns consist of. Research using quantitative fluoroscopy (QF) has shown that continuous lumbar intervertebral patterns of rotational displacement can be reliably measured during standing flexion and return motion using standardised protocols and can be used to assess patients with suspected lumbar spine motion disorders. However, normative values are needed to make individualised comparisons. One hundred and thirty-one healthy asymptomatic participants were recruited and performed guided flexion and return motion by following the rotating arm of an upright motion frame. Fluoroscopic image acquisition at 15fps was performed and individual intervertebral levels from L2-3 to L5-S1 were tracked and analysed during separate outward flexion and return phases. Results were presented as proportional intervertebral motion representing these phases using continuous means and 95%CIs, followed by verification of the differences between levels using Statistical Parametric Mapping (SPM). A secondary analysis of 8 control participants matched to 8 patients with chronic, non-specific low back pain (CNSLBP) was performed for comparison. One hundred and twenty-seven asymptomatic participants’ data were analysed. Their ages ranged from 18 to 70 years (mean 38.6) with mean body mass index 23.8 kg/m2 48.8% were female. Both the flexion and return phases for each level evidenced continuous change in mean proportional motion share, with narrow confidence intervals, highly significant differences and discrete motion paths between levels as confirmed by SPM. Patients in the secondary analysis evidenced significantly less L5-S1 motion than controls (p < 0.05). A reference database of spinal displacement patterns during lumbar (L2-S1) intersegmental flexion and return motion using a standardised motion protocol using fluoroscopy is presented. Spinal displacement patterns in asymptomatic individuals were found to be distinctive and consistent for Edited by: Babak Bazrgari, University of Kentucky, United States Reviewed by: Navid Arjmand, Sharif University of Technology, Iran Ameet Krishnan Aiyangar, Swiss Federal Laboratories for Materials Science and Technology, Switzerland *Correspondence: Alan Breen [email protected] Specialty section: This article was submitted to Biomechanics, a section of the journal Frontiers in Bioengineering and Biotechnology Received: 22 July 2021 Accepted: 08 September 2021 Published: 27 September 2021 Citation: Breen A, De Carvalho D, Funabashi M, Kawchuk G, Pagé I, Wong AYL and Breen A (2021) A Reference Database of Standardised Continuous Lumbar Intervertebral Motion Analysis for Conducting Patient- Specific Comparisons. Front. Bioeng. Biotechnol. 9:745837. doi: 10.3389/fbioe.2021.745837 Frontiers in Bioengineering and Biotechnology | www.frontiersin.org 1 September 2021 | Volume 9 | Article 745837 ORIGINAL RESEARCH published: 27 September 2021 doi: 10.3389/fbioe.2021.745837 each intervertebral level, and to continuously change during bending and return. This database may be used to allow continuous intervertebral kinematics to drive dynamic models of joint and muscular forces as well as reference values against which to make patient-specific comparisons in suspected cases of lumbar spine motion disorders
Perfect Fluid Theory and its Extensions
We review the canonical theory for perfect fluids, in Eulerian and Lagrangian
formulations. The theory is related to a description of extended structures in
higher dimensions. Internal symmetry and supersymmetry degrees of freedom are
incorporated. Additional miscellaneous subjects that are covered include
physical topics concerning quantization, as well as mathematical issues of
volume preserving diffeomorphisms and representations of Chern-Simons terms (=
vortex or magnetic helicity).Comment: 3 figure
Photon Production in Hot and Dense Strongly Interacting Matter
This text is meant as an introduction to the theoretical physics of photon
emission in hot and dense strongly interacting matter, the principal
application being relativistic nuclear collisions. We shall cover some of the
results and techniques appropriate for studies at SPS, RHIC, and LHC energiesComment: 35 pages, accepted for publication, Landolt-Boernstein Volume 1-23
From colored glass condensate to gluon plasma: equilibration in high energy heavy ion collisions
The initial distribution of gluons at the very early times after a high
energy heavy ion collision is described by the bulk scale of gluon
saturation in the nuclear wavefunction. The subsequent evolution of the system
towards kinetic equilibrium is described by a non-linear Landau equation for
the single particle distributions \cite{Mueller1,Mueller2}. In this paper, we
solve this equation numerically for the idealized initial conditions proposed
by Mueller, and study the evolution of the system to equilibrium. We discuss
the sensitivity of our results on the dynamical screening of collinear
divergences. In a particular model of dynamical screening, the convergence to
the hydrodynamic limit is seen to be rapid relative to hydrodynamic time
scales. The equilibration time, the initial temperature, and the chemical
potential are shown to have a strong functional dependence on the initial gluon
saturation scale .Comment: 34 pages, 10 figure
Dynamical Viscosity of Nucleating Bubbles
We study the viscosity corrections to the growth rate of nucleating bubbles
in a first order phase transition in scalar field theory. We obtain the
non-equilibrium equation of motion of the coordinate that describes small
departures from the critical bubble and extract the growth rate consistently in
weak coupling and in the thin wall limit. Viscosity effects arise from the
interaction of this coordinate with the stable quantum and thermal fluctuations
around a critical bubble. In the case of 1+1 dimensions we provide an estimate
for the growth rate that depends on the details of the free energy functional.
In 3+1 dimensions we recognize robust features that are a direct consequence of
the thin wall approximation and give the leading viscosity corrections.These
are long-wavelength hydrodynamic fluctuations that describe surface waves,
quasi-Goldstone modes which are related to ripples on interfaces in phase
ordered Ising-like systems. We discuss the applicability of our results to
describe the growth rate of hadron bubbles in a quark-hadron first order
transition.Comment: 40 pages, 4 figures, revtex, minor changes, to be published in Phys.
Rev.
Dynamical Renormalization Group Approach to Quantum Kinetics in Scalar and Gauge Theories
We derive quantum kinetic equations from a quantum field theory implementing
a diagrammatic perturbative expansion improved by a resummation via the
dynamical renormalization group. The method begins by obtaining the equation of
motion of the distribution function in perturbation theory. The solution of
this equation of motion reveals secular terms that grow in time, the dynamical
renormalization group resums these secular terms in real time and leads
directly to the quantum kinetic equation. We used this method to study the
relaxation in a cool gas of pions and sigma mesons in the O(4) chiral linear
sigma model. We obtain in relaxation time approximation the pion and sigma
meson relaxation rates. We also find that in large momentum limit emission and
absorption of massless pions result in threshold infrared divergence in sigma
meson relaxation rate and lead to a crossover behavior in relaxation. We then
study the relaxation of charged quasiparticles in scalar electrodynamics
(SQED). While longitudinal, Debye screened photons lead to purely exponential
relaxation, transverse photons, only dynamically screened by Landau damping
lead to anomalous relaxation, thus leading to a crossover between two different
relaxational regimes. We emphasize that infrared divergent damping rates are
indicative of non-exponential relaxation and the dynamical renormalization
group reveals the correct relaxation directly in real time. Finally we also
show that this method provides a natural framework to interpret and resolve the
issue of pinch singularities out of equilibrium and establish a direct
correspondence between pinch singularities and secular terms. We argue that
this method is particularly well suited to study quantum kinetics and transport
in gauge theories.Comment: RevTeX, 40 pages, 4 eps figures, published versio
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