6,721 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
Large-N expansion based on the Hubbard operator path integral representation and its application to the t-J model II. The case for finite
We have introduced a new perturbative approach for model where
Hubbard operators are treated as fundamental objects. Using our vertices and
propagators we have developed a controllable large-N expansion to calculate
different correlation functions. We have investigated charge density-density
response and the phase diagram of the model. The charge correlations functions
are not very sensitive to the value of and they show collective peaks (or
zero sound) which are more pronounced when they are well separated (in energy)
from the particle-hole continuum. For a given a Fermi liquid state is found
to be stable for doping larger than a critical doping .
decreases with decreasing . For the physical region of the
parameters and, for , the system enters in an incommensurate
flux or DDW phase. The inclusion of the nearest-neighbors Coulomb repulsion
leads to a CDW phase when is larger than a critical value . The
dependence of with and is shown. We have compared the
results with other ones in the literature.Comment: 10 pages, 8 figures, to appear in Phys. Rev.
Test-particle acceleration in a hierarchical three-dimensional turbulence model
The acceleration of charged particles is relevant to the solar corona over a
broad range of scales and energies. High-energy particles are usually detected
in concomitance with large energy release events like solar eruptions and
flares, nevertheless acceleration can occur at smaller scales, characterized by
dynamical activity near current sheets. To gain insight into the complex
scenario of coronal charged particle acceleration, we investigate the
properties of acceleration with a test-particle approach using
three-dimensional magnetohydrodynamic (MHD) models. These are obtained from
direct solutions of the reduced MHD equations, well suited for a plasma
embedded in a strong axial magnetic field, relevant to the inner heliosphere. A
multi-box, multi-scale technique is used to solve the equations of motion for
protons. This method allows us to resolve an extended range of scales present
in the system, namely from the ion inertial scale of the order of a meter up to
macroscopic scales of the order of km (th of the outer scale of
the system). This new technique is useful to identify the mechanisms that,
acting at different scales, are responsible for acceleration to high energies
of a small fraction of the particles in the coronal plasma. We report results
that describe acceleration at different stages over a broad range of time,
length and energy scales.Comment: 12 pages, 8 figures, ApJ (in press
Recommended from our members
Self-immolative linkers in polymeric delivery systems
There has been significant interest in the methodologies of controlled release for a diverse range of applications spanning drug delivery, biological and chemical sensors, and diagnostics. The advancement in novel substrate-polymer coupling moieties has led to the discovery of self-immolative linkers. This new class of linker has gained popularity in recent years in polymeric release technology as a result of stable bond formation between protecting and leaving groups, which becomes labile upon activation, leading to the rapid disassembly of the parent polymer. This ability has prompted numerous studies into the design and development of self-immolative linkers and the kinetics surrounding their disassembly. This review details the main concepts that underpin self-immolative linker technologies that feature in polymeric or dendritic conjugate systems and outlines the chemistries of amplified self-immolative elimination
Electroweak 2 -> 2 amplitudes for electron-positron annihilation at TeV energies
The non-radiative scattering amplitudes for electron-positron annihilation
into quark and lepton pairs in the TeV energy range are calculated in the
double-logarithmic approximation. The expressions for the amplitudes are
obtained using infrared evolution equations with different cut-offs for virtual
photons and for W and Z bosons, and compared with previous results obtained
with an universal cut-off.Comment: Revtex4, 17 pages, 7 figures. Some minor changes made, more refs
adde
One-electron self energies and spectral functions for the t-J model in the large-N limit
Using a recently developed perturbative approach, which considers Hubbard
operators as fundamental excitations, we have performed electronic self-energy
and spectral function calculations for the model on the square lattice.
We have found that the spectral functions along the Fermi surface are
isotropic, even close to the critical doping where the -density wave phase
takes place. Fermi liquid behavior with scattering rate and a
finite quasiparticle weight was obtained. decreases with decreasing
doping taking low values for low doping. Results are compared with other ones,
analytical and numerical like slave-boson and Lanczos diagonalization finding
agreement. We discuss our results in the light of recent experiments in
cuprates.Comment: 10 pages, 9 figures, accepted for publication in Phys. Rev.
Application of density dependent parametrization models to asymmetric nuclear matter
Density dependent parametrization models of the nucleon-meson effective
couplings, including the isovector scalar \delta-field, are applied to
asymmetric nuclear matter. The nuclear equation of state and the neutron star
properties are studied in an effective Lagrangian density approach, using the
relativistic mean field hadron theory. It is known that the introduction of a
\delta-meson in the constant coupling scheme leads to an increase of the
symmetry energy at high density and so to larger neutron star masses, in a pure
nucleon-lepton scheme. We use here a more microscopic density dependent model
of the nucleon-meson couplings to study the properties of neutron star matter
and to re-examine the \delta-field effects in asymmetric nuclear matter. Our
calculations show that, due to the increase of the effective \delta coupling at
high density, with density dependent couplings the neutron star masses in fact
can be even reduced.Comment: 5 pages, 4 figure
Effect of symmetry energy on two-nucleon correlation functions in heavy-ion collisions induced by neutron-rich nuclei
Using an isospin-dependent transport model, we study the effects of nuclear
symmetry energy on two-nucleon correlation functions in heavy ion collisions
induced by neutron-rich nuclei. We find that the density dependence of the
nuclear symmetry energy affects significantly the nucleon emission times in
these collisions, leading to larger values of two-nucleon correlation functions
for a symmetry energy that has a stronger density dependence. Two-nucleon
correlation functions are thus useful tools for extracting information about
the nuclear symmetry energy from heavy ion collisions.Comment: Revised version, to appear in Phys. Rev. Let
Magnetic Reconnection and Intermittent Turbulence in the Solar Wind
A statistical relationship between magnetic reconnection, current sheets and
intermittent turbulence in the solar wind is reported for the first time using
in-situ measurements from the Wind spacecraft at 1 AU. We identify
intermittency as non-Gaussian fluctuations in increments of the magnetic field
vector, , that are spatially and temporally non-uniform. The
reconnection events and current sheets are found to be concentrated in
intervals of intermittent turbulence, identified using the partial variance of
increments method: within the most non-Gaussian 1% of fluctuations in
, we find 87%-92% of reconnection exhausts and 9% of current
sheets. Also, the likelihood that an identified current sheet will also
correspond to a reconnection exhaust increases dramatically as the least
intermittent fluctuations are removed from the dataset. Hence, the turbulent
solar wind contains a hierarchy of intermittent magnetic field structures that
are increasingly linked to current sheets, which in turn are progressively more
likely to correspond to sites of magnetic reconnection. These results could
have far reaching implications for laboratory and astrophysical plasmas where
turbulence and magnetic reconnection are ubiquitous.Comment: 5 pages, 3 figures, submitted to Physical Review Letter
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
- …