19,523 research outputs found
Multivariate Fitting and the Error Matrix in Global Analysis of Data
When a large body of data from diverse experiments is analyzed using a
theoretical model with many parameters, the standard error matrix method and
the general tools for evaluating errors may become inadequate. We present an
iterative method that significantly improves the reliability of the error
matrix calculation. To obtain even better estimates of the uncertainties on
predictions of physical observables, we also present a Lagrange multiplier
method that explores the entire parameter space and avoids the linear
approximations assumed in conventional error propagation calculations. These
methods are illustrated by an example from the global analysis of parton
distribution functions.Comment: 13 pages, 5 figures, Latex; minor clarifications, fortran program
made available; Normalization of Hessian matrix changed to HEP standar
Resummation Effects in Vector-Boson and Higgs Associated Production
Fixed-order QCD radiative corrections to the vector-boson and Higgs
associated production channels, pp -> VH (V=W, Z), at hadron colliders are well
understood. We combine higher order perturbative QCD calculations with
soft-gluon resummation of both threshold logarithms and logarithms which are
important at low transverse momentum of the VH pair. We study the effects of
both types of logarithms on the scale dependence of the total cross section and
on various kinematic distributions. The next-to-next-to-next-to-leading
logarithmic (NNNLL) resummed total cross sections at the LHC are almost
identical to the fixed-order perturbative next-to-next-to-leading order (NNLO)
rates, indicating the excellent convergence of the perturbative QCD series.
Resummation of the VH transverse momentum (p_T) spectrum provides reliable
results for small values of p_T and suggests that implementing a jet-veto will
significantly decrease the cross sections.Comment: 25 pages, references update
Recommended from our members
Photothermal materials for efficient solar powered steam generation
Solar powered steam generation is an emerging area in the field of energy harvest and sustainable technologies. The nano-structured photothermal materials are able to harvest energy from the full solar spectrum and convert it to heat with high efficiency. Moreover, the materials and structures for heat management as well as the mass transportation are also brought to the forefront. Several groups have reported their materials and structures as solutions for high performance devices, a few creatively coupled other physical fields with solar energy to achieve even better results. This paper provides a systematic review on the recent developments in photothermal nanomaterial discovery, material selection, structural design and mass/heat management, as well as their applications in seawater desalination and fresh water production from waste water with free solar energy. It also discusses current technical challenges and likely future developments. This article will help to stimulate novel ideas and new designs for the photothermal materials, towards efficient, low cost practical solar-driven clean water production
Dissipative chaotic scattering
We show that weak dissipation, typical in realistic situations, can have a
metamorphic consequence on nonhyperbolic chaotic scattering in the sense that
the physically important particle-decay law is altered, no matter how small the
amount of dissipation. As a result, the previous conclusion about the unity of
the fractal dimension of the set of singularities in scattering functions, a
major claim about nonhyperbolic chaotic scattering, may not be observable.Comment: 4 pages, 2 figures, revte
Post-Newtonian Models of Binary Neutron Stars
Using an energy variational method, we calculate quasi-equilibrium
configurations of binary neutron stars modeled as compressible triaxial
ellipsoids obeying a polytropic equation of state. Our energy functional
includes terms both for the internal hydrodynamics of the stars and for the
external orbital motion. We add the leading post-Newtonian (PN) corrections to
the internal and gravitational energies of the stars, and adopt hybrid orbital
terms which are fully relativistic in the test-mass limit and always accurate
to PN order. The total energy functional is varied to find quasi-equilibrium
sequences for both corotating and irrotational binaries in circular orbits. We
examine how the orbital frequency at the innermost stable circular orbit
depends on the polytropic index n and the compactness parameter GM/Rc^2. We
find that, for a given GM/Rc^2, the innermost stable circular orbit along an
irrotational sequence is about 17% larger than the innermost secularly stable
circular orbit along the corotating sequence when n=0.5, and 20% larger when
n=1. We also examine the dependence of the maximum neutron star mass on the
orbital frequency and find that, if PN tidal effects can be neglected, the
maximum equilibrium mass increases as the orbital separation decreases.Comment: 53 pages, LaTex, 9 figures as 10 postscript files, accepted by Phys.
Rev. D, replaced version contains updated reference
The influence of ultrasonic surface rolling on the fatigue and wear properties of 23-8N engine valve steel
An ultrasonic surface rolling (USR) technique was employed for the first time as a method to enhance the fatigue and wear resistance of 33Cr23Ni8Mn3N (23â8N) austenitic engine valve steel. The microstructure of the modified layer on the material surface was characterised by scanning electron microscopy (SEM) coupled with electron back scatter diffraction (EBSD) and transmission electron microscope (TEM) methods. Nanoscale lamellar grains were discovered on the top surface of the treated material, and an increase of compressive residual stress and microhardness of the surface material observed. A comparative fretting wear test and a rotating bending fatigue test were performed out to verify the surface enhancement effect. Fractured and worn faces of specimens were evaluated through utilizing SEM and energyâdispersive spectroscopy (EDS). Compared to the untreated material, the coefficient of friction of USR treated material was significantly reduced, and the wear resistance was improved. The fatigue strength of a specimen treated at 25 °C was increased from 528 MPa to 730 MPa (38.3 %). At 650 °C, the fatigue strength increased from 345 MPa to 400 MPa (15.9 %). The fatigue resistance extension and wear resistance improvement of treated specimen can be attributed to a combination of beneficial compressive residual stress, work hardening, and the modified microstructure with fine-grains in the surface layer, and thus demonstrates the validity of this novel technique
Implications of Hadron Collider Observables on Parton Distribution Function Uncertainties
Standard parton distribution function sets do not have rigorously quantified
uncertainties. In recent years it has become apparent that these uncertainties
play an important role in the interpretation of hadron collider data. In this
paper, using the framework of statistical inference, we illustrate a technique
that can be used to efficiently propagate the uncertainties to new observables,
assess the compatibility of new data with an initial fit, and, in case the
compatibility is good, include the new data in the fit.Comment: 22 pages, 5 figure
Revised Relativistic Hydrodynamical Model for Neutron-Star Binaries
We report on numerical results from a revised hydrodynamic simulation of
binary neutron-star orbits near merger. We find that the correction recently
identified by Flanagan significantly reduces but does not eliminate the
neutron-star compression effect. Although results of the revised simulations
show that the compression is reduced for a given total orbital angular
momentum, the inner most stable circular orbit moves to closer separation
distances. At these closer orbits significant compression and even collapse is
still possible prior to merger for a sufficiently soft EOS. The reduced
compression in the corrected simulation is consistent with other recent studies
of rigid irrotational binaries in quasiequilibrium in which the compression
effect is observed to be small. Another significant effect of this correction
is that the derived binary orbital frequencies are now in closer agreement with
post-Newtonian expectations.Comment: Submitted to Phys. Rev.
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