117,002 research outputs found
A Magnetic Monopole in Pure SU(2) Gauge Theory
The magnetic monopole in euclidean pure SU(2) gauge theory is investigated
using a background field method on the lattice.
With Monte Carlo methods we study the mass of the monopole in the full
quantum theory.
The monopole background under the quantum fluctuations is induced by imposing
fixed monopole boundary conditions on the walls of a finite lattice volume.
By varying the gauge coupling it is possible to study monopoles with scales
from the hadronic scale up to high energies.
The results for the monopole mass are consistent with a conjecture we made
previously in a realization of the dual superconductor hypothesis of
confinement.Comment: 33 pages uufiles-compressed PostScript including (all) 12 figures,
preprint numbers ITFA-93-19 (Amsterdam), OUTP-93-21P (Oxford), DFTUZ/93/23
(Zaragoza
Supersymmetric Chern-Simons-matter theory and phase transitions
We study supersymmetric Chern-Simons with
fundamental and antifundamental chiral multiplets of mass in the
complete parameter space spanned by , where denotes
the coupling constant. In particular, we analyze the matrix model description
of its partition function, both at finite using the method of orthogonal
polynomials together with Mordell integrals and, at large with fixed ,
using the theory of Toeplitz determinants. We show for the massless case that
there is an explicit realization of the Giveon-Kutasov duality. For finite ,
with , three regimes that exactly correspond to the known three large
phases of theory are identified and characterized.Comment: 28 pages, v3: Minor modification to match published versio
Numerical approximation of phase field based shape and topology optimization for fluids
We consider the problem of finding optimal shapes of fluid domains. The fluid
obeys the Navier--Stokes equations. Inside a holdall container we use a phase
field approach using diffuse interfaces to describe the domain of free flow. We
formulate a corresponding optimization problem where flow outside the fluid
domain is penalized. The resulting formulation of the shape optimization
problem is shown to be well-posed, hence there exists a minimizer, and first
order optimality conditions are derived.
For the numerical realization we introduce a mass conserving gradient flow
and obtain a Cahn--Hilliard type system, which is integrated numerically using
the finite element method. An adaptive concept using reliable, residual based
error estimation is exploited for the resolution of the spatial mesh.
The overall concept is numerically investigated and comparison values are
provided
A stochastic-dynamic model for global atmospheric mass field statistics
A model that yields the spatial correlation structure of atmospheric mass field forecast errors was developed. The model is governed by the potential vorticity equation forced by random noise. Expansion in spherical harmonics and correlation function was computed analytically using the expansion coefficients. The finite difference equivalent was solved using a fast Poisson solver and the correlation function was computed using stratified sampling of the individual realization of F(omega) and hence of phi(omega). A higher order equation for gamma was derived and solved directly in finite differences by two successive applications of the fast Poisson solver. The methods were compared for accuracy and efficiency and the third method was chosen as clearly superior. The results agree well with the latitude dependence of observed atmospheric correlation data. The value of the parameter c sub o which gives the best fit to the data is close to the value expected from dynamical considerations
Naturally ventilated geothermal foundation modeling
AbstractThis work is concerning the modeling of a heat and mass transfer within a new kind of Canadian well, a geothermal foundation, and its coupling with a solar chimney. The foundation model is based on a 3D finite volume method. A long term simulation is necessary, aiming to precisely understand the behaviour of this combined system. Since this model requires high computational resources, we propose to use a domain decomposition technique and the balanced realization reduction method to speed up computational time. The studied case shows this system seems to be relevant to supply cold air to buildings during summer
A Yee-like finite-element scheme for Maxwell's equations on unstructured grids
A novel finite element scheme is studied for solving the time-dependent
Maxwell's equations on unstructured grids efficiently. Similar to the
traditional Yee scheme, the method has one degree of freedom for most edges and
a sparse inverse mass matrix. This allows for an efficient realization by
explicit time-stepping without solving linear systems. The method is
constructed by algebraic reduction of another underlying finite element scheme
which involves two degrees of freedom for every edge. Mass-lumping and
additional modifications are used in the construction of this method to allow
for the mentioned algebraic reduction in the presence of source terms and lossy
media later on. A full error analysis of the underlying method is developed
which by construction also carries over to the reduced scheme and allows to
prove convergence rates for the latter. The efficiency and accuracy of both
methods are illustrated by numerical tests. The proposed schemes and their
analysis can be extended to structured grids and in special cases the reduced
method turns out to be algebraically equivalent to the Yee scheme. The analysis
of this paper highlights possible difficulties in extensions of the Yee scheme
to non-orthogonal or unstructured grids, discontinuous material parameters, and
non-smooth source terms, and also offers potential remedies
Analysis of electromagnetic and thermoelectric processes in the Acheson furnace
Представлены теоретические исследования и моделирование электромагнитных и термоэлектрических процессов на основе численной реализации методом конечных элементов обобщенной 3D модели графитации постоянным и переменным током, отображающей особенности электромагнитных, электротепловых и тепломассообменных процессов в печи Ачесона, ее керне и боковых шинных пакетах печной петли.The theoretical research and modeling of electromagnetic and thermoelectric processes by numerical finite element method realization of the generalized three-dimensional models of DC and AC graphitization are proposed. The features of electromagnetic, electrothermal and heat-mass transfer processes in the Acheson furnace, core and side busbar packages of furnace loops are taken into account
Appropriate SCF basis sets for orbital studies of galaxies and a `quantum-mechanical' method to compute them
We address the question of an appropriate choice of basis functions for the
self-consistent field (SCF) method of simulation of the N-body problem. Our
criterion is based on a comparison of the orbits found in N-body realizations
of analytical potential-density models of triaxial galaxies, in which the
potential is fitted by the SCF method using a variety of basis sets, with those
of the original models. Our tests refer to maximally triaxial Dehnen
gamma-models for values of in the range 0<=gamma<=1. When an N-body
realization of a model is fitted by the SCF method, the choice of radial basis
functions affects significantly the way the potential, forces, or derivatives
of the forces are reproduced, especially in the central regions of the system.
We find that this results in serious discrepancies in the relative amounts of
chaotic versus regular orbits, or in the distributions of the Lyapunov
characteristic exponents, as found by different basis sets. Numerical tests
include the Clutton-Brock and the Hernquist-Ostriker (HO) basis sets, as well
as a family of numerical basis sets which are `close' to the HO basis set. The
family of numerical basis sets is parametrized in terms of a quantity
which appears in the kernel functions of the Sturm-Liouville (SL)
equation defining each basis set. The HO basis set is the member
of the family. We demonstrate that grid solutions of the SL equation yielding
numerical basis sets introduce large errors in the variational equations of
motion. We propose a quantum-mechanical method of solution of the SL equation
which overcomes these errors. We finally give criteria for a choice of optimal
value of and calculate the latter as a function of the value of
gamma.Comment: 22 pages, 13 figures, Accepted in MNRA
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