126 research outputs found
Reduction of the spin-orbit potential in light drip-line nuclei
The isospin dependence of the spin-orbit interaction in light neutron rich
nuclei is investigated in the framework of relativistic mean field theory. The
magnitude of the spin-orbit potential is considerably reduced in drip line
nuclei, resulting in smaller energy splittings between spin-orbit partners. The
effect does not depend on the parametrization of the effective Lagrangian. The
results are compared with corresponding calculations in the non-relativistic
Skyrme model.Comment: 8 Pages, LateX, 4 P.S. Figures, submit. Phys. Lett.
Cooling dynamics of a dilute gas of inelastic rods: a many particle simulation
We present results of simulations for a dilute gas of inelastically colliding
particles. Collisions are modelled as a stochastic process, which on average
decreases the translational energy (cooling), but allows for fluctuations in
the transfer of energy to internal vibrations. We show that these fluctuations
are strong enough to suppress inelastic collapse. This allows us to study large
systems for long times in the truely inelastic regime. During the cooling stage
we observe complex cluster dynamics, as large clusters of particles form,
collide and merge or dissolve. Typical clusters are found to survive long
enough to establish local equilibrium within a cluster, but not among different
clusters. We extend the model to include net dissipation of energy by damping
of the internal vibrations. Inelatic collapse is avoided also in this case but
in contrast to the conservative system the translational energy decays
according to the mean field scaling law, E(t)\propto t^{-2}, for asymptotically
long times.Comment: 10 pages, 12 figures, Latex; extended discussion, accepted for
publication in Phys. Rev.
Tomograms in the Quantum-Classical transition
The quantum-classical limits for quantum tomograms are studied and compared
with the corresponding classical tomograms, using two different definitions for
the limit. One is the Planck limit where in all -dependent physical observables, and the other is the Ehrenfest limit where
while keeping constant the mean value of the energy.The Ehrenfest
limit of eigenstate tomograms for a particle in a box and a harmonic
oscillatoris shown to agree with the corresponding classical tomograms of
phase-space distributions, after a time averaging. The Planck limit of
superposition state tomograms of the harmonic oscillator demostrating the
decreasing contribution of interferences terms as .Comment: 21 page
Production and Equilibration of the Quark-Gluon Plasma with Chromoelectric Field and Minijets
Production and equilibration of quark-gluon plasma are studied within the
color flux-tube model, at the RHIC and LHC energies. Non-Abelian relativistic
transport equations for quarks, antiquarks and gluons, are solved in the
extended phase space which includes coordinates, momenta and color. Before the
chromoelectric field is formed, hard and semihard partons are produced via
minijets which provide the initial conditions necessary to solve the transport
equations. The model predicts that in spite of the vast difference between the
RHIC and LHC incident energies, once the local equilibrium is reached, the
energy densities, the number densities and the temperatures at the two machines
may not be very different from each other. The minijet input significantly
alters the evolution of the deconfined matter, unless the color field is too
strong. For the input parameters used here the equilibration time is estimated
to be fm at RHIC and fm at LHC, measured from the instant
when the two colliding nuclei have just passed through each other. The
temperature at equilibration is found to be MeV at RHIC and MeV at LHC.Comment: version to appear in Phys. Rev. C; discussion enlarged to include
comparison with other models; conclusions unchanged; 14 single-spaced pages +
8 ps figure
Large Nuclear shape transition at finite temperature in a relativistic mean field approach
The relativistic Hartree-BCS theory is applied to study the temperature
dependence of nuclear shape and pairing gap for and . For
both the nuclei, we find that as temperature increases the pairing gap vanishes
leading to phase transition from superfluid to normal phase as is observed in
nonrelativistic calculation. The deformation evolves from prolate shapes to
spherical shapes at MeV. Comparison of our results for heat
capacity with the ones obtained in the non-relativistic mean field framework
indicates that in the relativistic mean field theory the shape transition
occurs at a temperature about 0.9 MeV higher and is relatively weaker. The
effect of thermal shape fluctuations on the temperature dependence of
deformation is also studied. Relevant results for the level density parameter
are further presented.
PACS numbers: 21.10.Ma, 21.60.-n, 27.70.+qComment: ReVtex file of 17 pages, 11 ps files for figures, To be appear in
Phys. ReV.
Performance of the first prototype of the CALICE scintillator strip electromagnetic calorimeter
A first prototype of a scintillator strip-based electromagnetic calorimeter
was built, consisting of 26 layers of tungsten absorber plates interleaved with
planes of 45x10x3 mm3 plastic scintillator strips. Data were collected using a
positron test beam at DESY with momenta between 1 and 6 GeV/c. The prototype's
performance is presented in terms of the linearity and resolution of the energy
measurement. These results represent an important milestone in the development
of highly granular calorimeters using scintillator strip technology. This
technology is being developed for a future linear collider experiment, aiming
at the precise measurement of jet energies using particle flow techniques
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
Biogeography in the air: fungal diversity over land and oceans
Biogenic aerosols are relevant for the Earth system, climate, and public health on local, regional, and global scales. Up to now, however, little is known about the diversity and biogeography of airborne microorganisms. We present the first DNA-based analysis of airborne fungi on global scales, showing pronounced geographic patterns and boundaries. In particular we find that the ratio of species richness between Basidiomycota and Ascomycota is much higher in continental air than in marine air. This may be an important difference between the 'blue ocean' and 'green ocean' regimes in the formation of clouds and precipitation, for which fungal spores can act as nuclei. Our findings also suggest that air flow patterns and the global atmospheric circulation are important for the understanding of global changes in biodiversity.Max Planck Society (MPG)Max Planck Society (MPG)LEC Geocycles in MainzLEC Geocycles in Mainzstate Rheinland-Pfalz [596]state RheinlandPfalzGerman Research Foundation [DE1161/2-1, PO1013/5-1, FOR 1525 INUIT]German Research Foundatio
Unity in defence: honeybee workers exhibit conserved molecular responses to diverse pathogens
This is the final version of the article. Available from the publisher via the DOI in this record.Background: Organisms typically face infection by diverse pathogens, and hosts are thought to have developed specific responses to each type of pathogen they encounter. The advent of transcriptomics now makes it possible to test this hypothesis and compare host gene expression responses to multiple pathogens at a genome-wide scale. Here, we performed a meta-analysis of multiple published and new transcriptomes using a newly developed bioinformatics approach that filters genes based on their expression profile across datasets. Thereby, we identified common and unique molecular responses of a model host species, the honey bee (Apis mellifera), to its major pathogens and parasites: the Microsporidia Nosema apis and Nosema ceranae, RNA viruses, and the ectoparasitic mite Varroa destructor, which transmits viruses.
Results:
We identified a common suite of genes and conserved molecular pathways that respond to all investigated pathogens, a result that suggests a commonality in response mechanisms to diverse pathogens. We found that genes differentially expressed after infection exhibit a higher evolutionary rate than non-differentially expressed genes. Using our new bioinformatics approach, we unveiled additional pathogen-specific responses of honey bees; we found that apoptosis appeared to be an important response following microsporidian infection, while genes from the immune signalling pathways, Toll and Imd, were differentially expressed after Varroa/virus infection. Finally, we applied our bioinformatics approach and generated a gene co-expression network to identify highly connected (hub) genes that may represent important mediators and regulators of anti-pathogen responses.
Conclusions:
Our meta-analysis generated a comprehensive overview of the host metabolic and other biological processes that mediate interactions between insects and their pathogens. We identified key host genes and pathways that respond to phylogenetically diverse pathogens, representing an important source for future functional studies as well as offering new routes to identify or generate pathogen resilient honey bee stocks. The statistical and bioinformatics approaches that were developed for this study are broadly applicable to synthesize information across transcriptomic datasets. These approaches will likely have utility in addressing a variety of biological questions.This article is a joint effort of the working group TRANSBEE and an
outcome of two workshops kindly supported by sDiv, the Synthesis
Centre for Biodiversity Sciences within the German Centre for Integrative
Biodiversity Research (iDiv) Halle-Jena-Leipzig, funded by the German Science
Foundation (FZT 118). New datasets were performed thanks to the Insect
Pollinators Initiative (IPI grant BB/I000100/1 and BB/I000151/1), with participation
of the UK-USA exchange funded by the BBSRC BB/I025220/1 (datasets #4,
11 and 14). The IPI is funded jointly by the Biotechnology and Biological
Sciences Research Council, the Department for Environment, Food and Rural
Affairs, the Natural Environment Research Council, the Scottish Government
and the Wellcome Trust, under the Living with Environmental Change
Partnershi
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