8,623 research outputs found
A study of a NLO matrix element generator for Wgamma and matching scheme for NLO events and PYTHIA parton shower
We compare a NLO W gamma matrix element generator with the leading order
calculation in Pythia . A matching scheme between a next-to-leading order W
gamma matrix element generator by Baur et. al. and the Pythia parton shower is
presented. The NLO package produces W gamma+0 jet and W gamma+1jet final states
in the hard scattering and the objective is to consistently match these to the
initial state radiation from Pythia parton shower. The proposed methodology
preserves both the rate of the hard scattering process as well as various
kinematic distributions of experimental interest.Comment: 16 pages, 12 figures, 2 tables, 8 references, an abbreviated version
to appear in the proceedings of Physics at TeV Colliders, Les Houches 8-26
June 200
On the imaginary parts and infrared divergences of two-loop vector boson self-energies in thermal QCD
We calculate the imaginary part of the retarded two-loop self-energy of a
static vector boson in a plasma of quarks and gluons of temperature T, using
the imaginary time formalism. We recombine various cuts of the self-energy to
generate physical processes. We demonstrate how cuts containing loops may be
reinterpreted in terms of interference between Order tree diagrams and
the Born term along with spectators from the medium. We apply our results to
the rate of dilepton production in the limit of dilepton invariant mass E>>T.
We find that all infrared and collinear singularities cancel in the final
result obtained in this limit.Comment: references added, typos corrected, slightly abridged, version
accepted for publication in Phys. Rev.
Linkage mapping of quantitative trait loci in humans: an overview
In this article, we provide an overview of the different statistical procedures that have been developed for linkage mapping of quantitative trait loci. We outline the model assumptions, the data requirements and the underlying tests for linkage for the different methods
Study of electron spin dynamics in grain aligned LaCoPO: an itinerant ferromagnet
139La NMR study was performed in grain aligned (c|| H0) sample of LaCoPO and
polycrystalline LaFePO. Knight shift is isotropic and temperature independent
in LaFePO. It is strongly temperature dependent and anisotropic in LaCoPO. The
spin-lattice relaxation rate in LaCoPO clearly reveals the existence of 3D spin
fluctuations both in the paramagnetic and ferromagnetic state over and above
the dominant 2D spin fluctuations in the paramagnetic state, observed earlier
from 31P NMR measurements in the same oriented sample. The spin fluctuation
parameters in LaCoPO determined from 139La NMR relaxation and magnetization
data, using the self consistent renormalization (SCR) theory, are in close
agreement and follow the universal Rhodes-Wohlfarth curve.Comment: Accepted in PR
Effect of DNA Groove Binder Distamycin A upon Chromatin Structure
BACKGROUND: Distamycin A is a prototype minor groove binder, which binds to B-form DNA, preferentially at A/T rich sites. Extensive work in the past few decades has characterized the binding at the level of double stranded DNA. However, effect of the same on physiological DNA, i.e. DNA complexed in chromatin, has not been well studied. Here we elucidate from a structural perspective, the interaction of distamycin with soluble chromatin, isolated from Sprague-Dawley rat. METHODOLOGY/PRINCIPAL FINDINGS: Chromatin is a hierarchical assemblage of DNA and protein. Therefore, in order to characterize the interaction of the same with distamycin, we have classified the system into various levels, according to the requirements of the method adopted, and the information to be obtained. Isothermal titration calorimetry has been employed to characterize the binding at the levels of chromatin, chromatosome and chromosomal DNA. Thermodynamic parameters obtained thereof, identify enthalpy as the driving force for the association, with comparable binding affinity and free energy for chromatin and chromosomal DNA. Reaction enthalpies at different temperatures were utilized to evaluate the change in specific heat capacity (ΔCp), which, in turn, indicated a possible binding associated structural change. Ligand induced structural alterations have been monitored by two complementary methods--dynamic light scattering, and transmission electron microscopy. They indicate compaction of chromatin. Using transmission electron microscopy, we have visualized the effect of distamycin upon chromatin architecture at di- and trinucleosome levels. Our results elucidate the simultaneous involvement of linker bending and internucleosomal angle contraction in compaction process induced by distamycin. CONCLUSIONS/SIGNIFICANCE: We summarize here, for the first time, the thermodynamic parameters for the interaction of distamycin with soluble chromatin, and elucidate its effect on chromatin architecture. The study provides insight into a ligand induced compaction phenomenon, and suggests new mechanisms of chromatin architectural alteration
Comparing Single-Objective Optimization Protocols for Calibrating the Birds Nest Aquifer Model—A Problem Having Multiple Local Optima
To best represent reality, simulation models of environmental and health-related systems might be very nonlinear. Model calibration ideally identifies globally optimal sets of parameters to use for subsequent prediction. For a nonlinear system having multiple local optima, calibration can be tedious. For such a system, we contrast calibration results from PEST, a commonly used automated parameter estimation program versus several meta-heuristic global optimizers available as external packages for the Python computer language—the Gray Wolf Optimization (GWO) algorithm; the DYCORS optimizer framework with a Radial Basis Function surrogate simulator (DRB); and particle swarm optimization (PSO). We ran each optimizer 15 times, with nearly 10,000 MODFLOW simulations per run for the global optimizers, to calibrate a steady-state, groundwater flow simulation model of the complex Birds Nest aquifer, a three-layer system having 8 horizontal hydraulic conductivity zones and 25 head observation locations. In calibrating the eight hydraulic conductivity values, GWO averaged the best root mean squared error (RMSE) between observed and simulated heads—20 percent better (lower) than the next lowest optimizer, DRB. The best PEST run matched the best GWO RMSE, but both the average PEST RMSE and the range of PEST RMSE results were an order of magnitude larger than any of the global optimizers
Hard and soft probe - medium interactions in a 3D hydro+micro approach at RHIC
We utilize a 3D hybrid hydro+micro model for a comprehensive and consistent
description of soft and hard particle production in ultra-relativistic
heavy-ion collisions at RHIC. In the soft sector we focus on the dynamics of
(multi-)strange baryons, where a clear strangeness dependence of their
collision rates and freeze-out is observed. In the hard sector we study the
radiative energy loss of hard partons in a soft medium in the multiple soft
scattering approximation. While the nuclear suppression factor does
not reflect the high quality of the medium description (except in a reduced
systematic uncertainty in extracting the quenching power of the medium), the
hydrodynamical model also allows to study different centralities and in
particular the angular variation of with respect to the reaction
plane, allowing for a controlled variation of the in-medium path-length.Comment: 5 pages, 4 figures, Quark Matter 2006 proceedings, to appear in
Journal of Physics
- …