388 research outputs found
Integrated Assessment of Agriculture and Sustainable Development: Setting the Agenda for Science and Policy (AgSAP 2009)
Conservation of Neutral Substitution Rate and Substitutional Asymmetries in Mammalian Genes
Local variation in neutral substitution rate across mammalian genomes is governed
by several factors, including sequence context variables and structural
variables. In addition, the interplay of replication and transcription, known to
induce a strand bias in mutation rate, gives rise to variation in substitutional
strand asymmetries. Here, we address the conservation of variation in mutation
rate and substitutional strand asymmetries using primate- and rodent-specific
repeat elements located within the introns of protein-coding genes. We find
significant but weak conservation of local mutation rates between human and
mouse orthologs. Likewise, substitutional strand asymmetries are conserved
between human and mouse, where substitution rate asymmetries show a higher
degree of conservation than mutation rate. Moreover, we provide evidence that
replication and transcription are correlated to the strength of substitutional
asymmetries. The effect of transcription is particularly visible for genes with
highly conserved gene expression. In comparison with replication and
transcription, mutation rate influences the strength of substitutional
asymmetries only marginally
Heavy ion collisions with non-equilibrium Dirac-Brueckner mean fields
The influence of realistic interactions on the reaction dynamics in
intermediate energy heavy ion collisions is investigated. The mean field in
relativistic transport calculations is derived from microscopic Dirac-Brueckner
(DB) self-energies, taking non-equilibrium effects, in particular the
anisotropy of the local phase space configurations, into account. Thus this
approach goes beyond the local density approximation. A detailed analysis of
various in-plane and out-of-plane flow observables is presented for Au on Au
reactions at incident energies ranging from 250 to 800 A.MeV and the results
are compared to recent measurements of the FOPI collaboration. An overall good
agreement with in-plane flow data and a reasonable description of the
out-of-plane emission is achieved. For these results the intrinsic momentum
dependence of the non-equilibrium mean fields is important. On the other hand,
the local density approximation with the same underlying DB forces as well as a
standard non-linear version of the model are less successful in
describing the present data. This gives evidence of the applicability of self
energies derived from the DB approach to nuclear matter also far from
saturation and equilibrium.Comment: 63 pages Latex, using Elsevier style, 20 ps-figures, to appear in
Nucl. Phys.
Low Q^2 Jet Production at HERA and Virtual Photon Structure
The transition between photoproduction and deep-inelastic scattering is
investigated in jet production at the HERA ep collider, using data collected by
the H1 experiment. Measurements of the differential inclusive jet
cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the
transverse energy and the pseudorapidity of the jets in the virtual
photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3
< y < 0.6. The interpretation of the results in terms of the structure of the
virtual photon is discussed. The data are best described by QCD calculations
which include a partonic structure of the virtual photon that evolves with Q2.Comment: 20 pages, 5 Figure
Hadron Production in Diffractive Deep-Inelastic Scattering
Characteristics of hadron production in diffractive deep-inelastic
positron-proton scattering are studied using data collected in 1994 by the H1
experiment at HERA. The following distributions are measured in the
centre-of-mass frame of the photon dissociation system: the hadronic energy
flow, the Feynman-x (x_F) variable for charged particles, the squared
transverse momentum of charged particles (p_T^{*2}), and the mean p_T^{*2} as a
function of x_F. These distributions are compared with results in the gamma^* p
centre-of-mass frame from inclusive deep-inelastic scattering in the
fixed-target experiment EMC, and also with the predictions of several Monte
Carlo calculations. The data are consistent with a picture in which the
partonic structure of the diffractive exchange is dominated at low Q^2 by hard
gluons.Comment: 16 pages, 6 figures, submitted to Phys. Lett.
Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA
An investigation of the hadronic final state in diffractive and
non--diffractive deep--inelastic electron--proton scattering at HERA is
presented, where diffractive data are selected experimentally by demanding a
large gap in pseudo --rapidity around the proton remnant direction. The
transverse energy flow in the hadronic final state is evaluated using a set of
estimators which quantify topological properties. Using available Monte Carlo
QCD calculations, it is demonstrated that the final state in diffractive DIS
exhibits the features expected if the interaction is interpreted as the
scattering of an electron off a current quark with associated effects of
perturbative QCD. A model in which deep--inelastic diffraction is taken to be
the exchange of a pomeron with partonic structure is found to reproduce the
measurements well. Models for deep--inelastic scattering, in which a
sizeable diffractive contribution is present because of non--perturbative
effects in the production of the hadronic final state, reproduce the general
tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil
A Search for Selectrons and Squarks at HERA
Data from electron-proton collisions at a center-of-mass energy of 300 GeV
are used for a search for selectrons and squarks within the framework of the
minimal supersymmetric model. The decays of selectrons and squarks into the
lightest supersymmetric particle lead to final states with an electron and
hadrons accompanied by large missing energy and transverse momentum. No signal
is found and new bounds on the existence of these particles are derived. At 95%
confidence level the excluded region extends to 65 GeV for selectron and squark
masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure
Lambda Hyperons in 2 A*GeV Ni + Cu Collisions
A sample of Lambda's produced in 2 A*GeV Ni + Cu collisions has been obtained
with the EOS Time Projection Chamber at the Bevalac. Low background in the
invariant mass distribution allows for the unambiguous demonstration of Lambda
directed flow. The transverse mass spectrum at mid-rapidity has the
characteristic shoulder-arm shape of particles undergoing radial transverse
expansion. A linear dependence of Lambda multiplicity on impact parameter is
observed, from which a total Lambda + Sigma^0 production cross section of $112
+/- 24 mb is deduced. Detailed comparisons with the ARC and RVUU models are
made.Comment: Revised version accepted for publication in Phys. Lett.
Gamma-induced background in the KATRIN main spectrometer
International audienceThe KArlsruhe TRItium Neutrino (KATRIN) experiment aims to make a model-independent determination of the effective electron antineutrino mass with a sensitivity of 0.2 eV/c 2 . It investigates the kinematics of β -particles from tritium β -decay close to the endpoint of the energy spectrum. Because the KATRIN main spectrometer (MS) is located above ground, muon-induced backgrounds are of particular concern. Coincidence measurements with the MS and a scintillator-based muon detector system confirmed the model of secondary electron production by cosmic-ray muons inside the MS. Correlation measurements with the same setup showed that about 12% of secondary electrons emitted from the inner surface are induced by cosmic-ray muons, with approximately one secondary electron produced for every 17 muon crossings. However, the magnetic and electrostatic shielding of the MS is able to efficiently suppress these electrons, and we find that muons are responsible for less than 17% (90% confidence level) of the overall MS background
White Matter Lesion Progression: Genome-Wide Search for Genetic Influences
White matter lesion (WML) progression on magnetic resonance imaging (MRI) is related to cognitive decline and stroke, but its determinants besides baseline WML burden are largely unknown. Here, we estimated heritability of WML progression, and sought common genetic variants associated with WML progression in elderly participants from the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) consortium
- …