5,442 research outputs found
Effect of resonance decays on hadron elliptic flows
The influence of resonance decays on the elliptic flows of stable hadrons is
studied in the quark coalescence model. Although difference between the
elliptic flow of pions from resonance decays, except the rho meson, and that of
directly produced pions is appreciable, those for other stable hadrons are
small. Since there are more pions from the decays of rho mesons than from other
resonances, including resonance decays can only account partially the deviation
of final pion elliptic flow from the observed scaling of hadron elliptic flows,
i.e., the hadron elliptic flow per quark is the same at same transverse
momentum per quark. The remaining deviation can be explained by including the
effect due to the quark momentum distribution inside hadrons.Comment: 13 pages and 5 figures, version pubblished in PRC, updated references
and figure
Prospects for strangeness measurement in ALICE
The study of strangeness production at LHC will bring significant information
on the bulk chemical properties, its dynamics and the hadronisation mechanisms
involved at these energies. The ALICE experiment will measure strange particles
from topology (secondary vertices) and from resonance decays over a wide range
in transverse momentum and shed light on this new QCD regime. These motivations
will be presented as well as the identification performance of ALICE for
strange hadrons.Comment: 12 pages, 11 figures Proceedings of the Workshop on Relativistic
Nuclear Physics (WRNP) 2007, Kiev, Ukraine Conference Info:
http://wrnp2007.bitp.kiev.ua/ Submitted to "Physics of Atomic Nuclei
Particle correlations at RHIC from parton coalescence dynamics -- first results
A new dynamical approach that combines covariant parton transport theory with
hadronization channels via parton coalescence and fragmentation is applied to
Au+Au at RHIC. Basic consequences of the simple coalescence formulas, such as
elliptic flow scaling and enhanced proton/pion ratio, turn out to be rather
sensitive to the spacetime aspects of coalescence dynamics.Comment: Contribution to Quark Matter 2004 (January 11-17, 2004, Oakland, CA).
4 pages, 2 EPS figs, IOP style fil
Recombination Models
We review the current status of recombination and coalescence models that
have been successfully applied to describe hadronization in heavy ion
collisions at RHIC energies. Basic concepts as well as actual implementations
of the idea are discussed. We try to evaluate where we stand in our
understanding at the moment and what remains to be done in the future.Comment: Plenary Talk at Quark Matter 2004, submitted to J. Phys. G, 8 pages,
3 figure
Genome-wide signatures of population bottlenecks and diversifying selection in European wolves
Genomic resources developed for domesticated species provide powerful tools for studying the evolutionary history of their wild relatives. Here we use 61K single-nucleotide polymorphisms (SNPs) evenly spaced throughout the canine nuclear genome to analyse evolutionary relationships among the three largest European populations of grey wolves in comparison with other populations worldwide, and investigate genome-wide effects of demographic bottlenecks and signatures of selection. European wolves have a discontinuous range, with large and connected populations in Eastern Europe and relatively smaller, isolated populations in Italy and the Iberian Peninsula. Our results suggest a continuous decline in wolf numbers in Europe since the Late Pleistocene, and long-term isolation and bottlenecks in the Italian and Iberian populations following their divergence from the Eastern European population. The Italian and Iberian populations have low genetic variability and high linkage disequilibrium, but relatively few autozygous segments across the genome. This last characteristic clearly distinguishes them from populations that underwent recent drastic demographic declines or founder events, and implies long-term bottlenecks in these two populations. Although genetic drift due to spatial isolation and bottlenecks seems to be a major evolutionary force diversifying the European populations, we detected 35 loci that are putatively under diversifying selection. Two of these loci flank the canine platelet-derived growth factor gene, which affects bone growth and may influence differences in body size between wolf populations. This study demonstrates the power of population genomics for identifying genetic signals of demographic bottlenecks and detecting signatures of directional selection in bottlenecked populations, despite their low background variability.Heredity advance online publication, 18 December 2013; doi:10.1038/hdy.2013.122
Magnetic moment non-conservation in magnetohydrodynamic turbulence models
The fundamental assumptions of the adiabatic theory do not apply in presence
of sharp field gradients as well as in presence of well developed
magnetohydrodynamic turbulence. For this reason in such conditions the magnetic
moment is no longer expected to be constant. This can influence particle
acceleration and have considerable implications in many astrophysical problems.
Starting with the resonant interaction between ions and a single parallel
propagating electromagnetic wave, we derive expressions for the magnetic moment
trapping width (defined as the half peak-to-peak difference in the
particle magnetic moment) and the bounce frequency . We perform
test-particle simulations to investigate magnetic moment behavior when
resonances overlapping occurs and during the interaction of a ring-beam
particle distribution with a broad-band slab spectrum.
We find that magnetic moment dynamics is strictly related to pitch angle
for a low level of magnetic fluctuation, , where is the constant and uniform background magnetic field.
Stochasticity arises for intermediate fluctuation values and its effect on
pitch angle is the isotropization of the distribution function .
This is a transient regime during which magnetic moment distribution
exhibits a characteristic one-sided long tail and starts to be influenced by
the onset of spatial parallel diffusion, i.e., the variance
grows linearly in time as in normal diffusion. With strong fluctuations
isotropizes completely, spatial diffusion sets in and
behavior is closely related to the sampling of the varying magnetic field
associated with that spatial diffusion.Comment: 13 pages, 10 figures, submitted to PR
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A 3D printed drug delivery implant formed from a dynamic supramolecular polyurethane formulation
Using a novel molecular design approach, we have prepared a thermo-responsive supramolecular polyurethane as a matrix material for use in drug eluting implants. The dynamic supramolecular polyurethane (SPU) is able to self-assemble through hydrogen bonding and π-π stacking interactions, resulting in an addressable polymer network with a relatively low processing temperature. The mechanical properties of the SPU demonstrated the material was self-supporting, stiff, yet flexible thus making it suitable for hot-melt extrusion processing, inclusive of related 3D printing approaches. Cell-based toxicity assays revealed the SPU to be non-toxic and therefore a viable candidate as a biocompatible polymer for implant applications. To this end, the SPU was formulated with paracetamol (16 %w/w) and 4 wt% or 8 wt% poly(ethylene glycol) (PEG) as an excipient and hot melt extruded at 100 °C to afford a 3D printed prototype implant to explore the extended drug release required for an implant and the potential manipulation of the release profile. Furthermore, rheological, infra-red spectroscopy, powder X-ray diffraction and scanning electron microscopy studies revealed the chemical and physical properties and compatibility of the formulation components. Successful release of paracetamol was achieved from in vitro dissolution studies and it was predicted that the drug would be released over a period of up to 8.5 months with hydrophilic PEG being able to influence the release rate. This extended release time is consistent with applications of this novel dynamic polymer as a drug eluting implant matrix
Phenomenology of single spin asymmetries in p(transv. polarized)-p -> pion + X
A phenomenological description of single transverse spin effects in
hadron-hadron inclusive processes is proposed, assuming a generalized
factorization scheme and pQCD hard interactions. The transverse momentum, k_T,
of the quarks inside the hadrons and of the hadrons relatively to the
fragmenting quark, is taken into account in distribution and fragmentation
functions, and leads to possible non zero single spin asymmetries. The role of
k_T and spin dependent quark fragmentations -- the so-called Collins effect --
is investigated in details in p(transv. polarized)-p -> pion + X processes: it
is shown how the experimental data could be described, obtaining an explicit
expression for the spin asymmetry of a polarized fragmenting quark, on which
some comments are made. Predictions for other processes, possible further
applications and experimental tests are discussed.Comment: 20+1 pages, LaTeX, 6 eps figures, uses epsfig.sty. Version v2: Some
sentences rephrased and comments added throughout the paper; one reference
added; no changes in results and figures. Final version to be published in
Phys. Rev.
Jet quenching in relativistic heavy ion collisions
Parton propagation in dense nuclear matter results in elastic, inelastic and
coherent multiple soft scattering with the in-medium color charges. Such
scattering leads to calculable modifications of the hadron production cross
section that is evaluated in the framework of the perturbative QCD
factorization approach. Final state medium-induced gluon bremsstrahlung is
arguably the most efficient way of suppressing large transverse momentum
particle production in nucleus-nucleus collisions. The observed hadronic
attenuation, known as jet quenching, can be related to the properties of the
medium, such as density and temperature, and carries valuable information about
the early stages of heavy ion reactions. Non-Abelian energy loss in the
quark-gluon plasma can be studied in much greater detail through the
modification of the two particle back-to-back correlations. Perturbative
calculations give good description of the redistribution of the lost energy in
lower transverse momentum particles and predict significant increase of the
correlation width of away-side di-hadrons. In contrast, energy loss in cold
nuclear matter was found to be small but for large values of Feynman-x is
expected to complement the dynamical higher twist shadowing in experimentally
observable forward rapidity hadron suppression.Comment: Invited plenary talk at the V-th international conference on the
physics and astrophysics of the quark-gluon plasma. 8 pages, 4 figure
Heavy-Quark Diffusion, Flow and Recombination at RHIC
We discuss recent developments in assessing heavy-quark interaction in the
Quark-Gluon Plasma (QGP). While induced gluon radiation is expected to be the
main energy-loss mechanism for fast-moving quarks, we focus on elastic
scattering which prevails toward lower energies, evaluating both perturbative
(gluon-exchange) and nonperturbative (resonance formation) interactions in the
QGP. The latter are treated within an effective model for D- and B-meson
resonances above T_c as motivated by current QCD lattice calculations.
Pertinent diffusion and drag constants, following from a Fokker-Planck
equation, are implemented into an expanding fireball model for Au-Au collisions
at RHIC using relativistic Langevin simulations. Heavy quarks are hadronized in
a combined fragmentation and coalescence framework, and resulting
electron-decay spectra are compared to recent RHIC data. A reasonable
description of both nuclear suppression factors and elliptic flow up to momenta
of ~5 GeV supports the notion of a strongly interacting QGP created at RHIC.
Consequences and further tests of the proposed resonance interactions are
discussed.Comment: 8 pages, 14 figures, contribution to the proceedings for the
"International Conference on Strangeness in Quark Matter 2006
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