5,619 research outputs found
A cell-based smoothed finite element method for kinematic limit analysis
This paper presents a new numerical procedure for kinematic limit analysis problems, which incorporates the cell-based smoothed finite element method with second-order cone programming. The application of a strain smoothing technique to the standard displacement finite element both rules out volumetric locking and also results in an efficient method that can provide accurate solutions with minimal computational effort. The non-smooth optimization problem is formulated as a problem of minimizing a sum of Euclidean norms, ensuring that the resulting optimization problem can be solved by an efficient second-order cone programming algorithm. Plane stress and plane strain problems governed by the von Mises criterion are considered, but extensions to problems with other yield criteria having a similar conic quadratic form or 3D problems can be envisaged
Driven particle in a random landscape: disorder correlator, avalanche distribution and extreme value statistics of records
We review how the renormalized force correlator Delta(u), the function
computed in the functional RG field theory, can be measured directly in
numerics and experiments on the dynamics of elastic manifolds in presence of
pinning disorder. We show how this function can be computed analytically for a
particle dragged through a 1-dimensional random-force landscape. The limit of
small velocity allows to access the critical behavior at the depinning
transition. For uncorrelated forces one finds three universality classes,
corresponding to the three extreme value statistics, Gumbel, Weibull, and
Frechet. For each class we obtain analytically the universal function Delta(u),
the corrections to the critical force, and the joint probability distribution
of avalanche sizes s and waiting times w. We find P(s)=P(w) for all three
cases. All results are checked numerically. For a Brownian force landscape,
known as the ABBM model, avalanche distributions and Delta(u) can be computed
for any velocity. For 2-dimensional disorder, we perform large-scale numerical
simulations to calculate the renormalized force correlator tensor
Delta_{ij}(u), and to extract the anisotropic scaling exponents zeta_x >
zeta_y. We also show how the Middleton theorem is violated. Our results are
relevant for the record statistics of random sequences with linear trends, as
encountered e.g. in some models of global warming. We give the joint
distribution of the time s between two successive records and their difference
in value w.Comment: 41 pages, 35 figure
Thermodynamics of Quasi-Particles
We present in this work a generalization of the solution of Gorenstein and
Yang for a consistent thermodynamics for systems with a temperature dependent
Hamiltonian. We show that there is a large class of solutions, work out three
particular ones, and discuss their physical relevance. We apply the particular
solutions for an ideal gas of quasi-gluons, and compare the calculation to
lattice and perturbative QCD results.Comment: 26 pages, 1 figure. To appear in Nuclear Physics
A thermodynamically consistent quasi-particle model without temperature-dependent infinity of the vacuum zero point energy
In this paper, an improved quasi-particle model is presented. Unlike the
previous approach of establishing quasi-particle model, we introduce a
classical background field (it is allowed to depend on the temperature) to deal
with the infinity of thermal vacuum energy which exists in previous
quasi-particle models. After taking into account the effect of this classical
background field, the partition function of quasi-particle system can be made
well-defined. Based on this and following the standard ensemble theory, we
construct a thermodynamically consistent quasi-particle model without the need
of any reformulation of statistical mechanics or thermodynamical consistency
relation. As an application of our model, we employ it to the case of (2+1)
flavor QGP at zero chemical potential and finite temperature and obtain a good
fit to the recent lattice simulation results of S. Borsanyi . A
comparison of the result of our model with early calculations using other
models is also presented. It is shown that our method is general and can be
generalized to the case where the effective mass depends not only on the
temperature but also on the chemical potential.Comment: 7 pages, 4 figure
Some Applications of Thermal Field Theory to Quark-Gluon Plasma
The lecture provides a brief introduction of thermal field theory within
imaginary time formalism, the Hard Thermal Loop perturbation theory and some of
its application to the physics of the quark-gluon plasma, possibly created in
relativistic heavy ion collisions.Comment: 17 pages, 12 figures : Lectures given in "Workshop on Hadron Physics"
during March 7-17, 2005, Puri, Indi
EXTRAPOLATED ALTERNATING ALGORITHMS FOR APPROXIMATE CANONICAL POLYADIC DECOMPOSITION
Tensor decompositions have become a central tool in machine learning to extract interpretable patterns from multiway arrays of data. However, computing the approximate Canonical Polyadic Decomposition (aCPD), one of the most important tensor decomposition model, remains a challenge. In this work, we propose several algorithms based on extrapolation that improve over existing alternating methods for aCPD. We show on several simulated and real data sets that carefully designed extrapolation can significantly improve the convergence speed hence reduce the computational time, especially in difficult scenarios
The pressure of QED from the two-loop 2PI effective action
We compute the pressure of hot quantum electrodynamics from the two-loop
truncation of the 2PI effective action. Since the 2PI resummation guarantees
gauge-fixing independence only up to the order of the truncation, our result
for the pressure presents a gauge dependent contribution of O(e^4). We
numerically characterize the credibility of this gauge-dependent calculation
and find that the uncertainty due to gauge parameter dependence is under
control for xi<1. Our calculation also suggests that the choice of Landau gauge
may minimize gauge-dependent effects.Comment: 15 latex pages with 3 figure
Orbitally excited D and B mesons in the approach of the QCD string with quarks at the ends
In this letter we discuss the masses and the splittings of 1(2S+1)P_J states
in the spectrum of D and B mesons, as they appear in the approach of the QCD
string with quarks at the ends. We find good agreement of our predictions with
those of other QCD-motivated models as well as with the lattice and
experimental data, including recent experimental results. We discuss the
ordering pattern for P levels in D- and B-mesonic spectrum.Comment: 7 pages, LaTeX2e, 2 EPS figures, added comments, to appear in
Phys.Lett.
Resummation in Hot Field Theories
There has been significant progress in our understanding of
finite-temperature field theory over the past decade. In this paper, we review
the progress in perturbative thermal field theory focusing on thermodynamic
quantities. We first discuss the breakdown of naive perturbation theory at
finite temperature and the need for an effective expansion that resums an
infinite class of diagrams in the perturbative expansion. This effective
expansion which is due to Braaten and Pisarski, can be used to systematically
calculate various static and dynamical quantities as a weak-coupling expansion
in powers of g. However, it turns that the weak-coupling expansion for
thermodynamic quantities are useless unless the coupling constant is very
small. We critically discuss various ways of reorganizing the perturbative
series for thermal field theories in order to improve its convergence. These
include screened perturbation theory (SPT), hard-thermal-loop perturbation
theory (HTLPT), the Phi-derivable approach, dimensionally reduced (DR) SPT, and
the DR Phi-derivable approach.Comment: 82 pages, 20 figures; v2 - typos corrected, references adde
- …