11,987 research outputs found
Four-Loop Decoupling Relations for the Strong Coupling
We compute the matching relation for the strong coupling constant within the
framework of QCD up to four-loop order. This allows a consistent five-loop
running (once the function is available to this order) taking into
account threshold effects. As a side product we obtain the effective coupling
of a Higgs boson to gluons with five-loop accuracy.Comment: 11 page
Understanding Confinement From Deconfinement
We use effective magnetic SU(N) pure gauge theory with cutoff M and fixed
gauge coupling g_m to calculate non-perturbative magnetic properties of the
deconfined phase of SU(N) Yang-Mills theory. We obtain the response to an
external closed loop of electric current by reinterpreting and regulating the
calculation of the one loop effective potential in Yang-Mills theory. This
effective potential gives rise to a color magnetic charge density, the
counterpart in the deconfined phase of color magnetic currents introduced in
effective dual superconductor theories of the confined phase via magnetically
charged Higgs fields. The resulting spatial Wilson loop has area law behavior.
Using values of M and g_m determined in the confined phase, we find SU(3)
spatial string tensions compatible with lattice simulations in the temperature
interval 1.5T_c < T < 2.5T_c. Use of the effective theory to analyze
experiments on heavy ion collisions will provide applications and further tests
of these ideas.Comment: 18 pages, 5 figures, v2: fixed archive title (only
Ground states versus low-temperature equilibria in random field Ising chains
We discuss with the aid of random walk arguments and exact numerical
computations the magnetization properties of one-dimensional random field
chains. The ground state structure is explained in terms of absorbing and
non-absorbing random walk excursions. At low temperatures, the magnetization
profiles follow those of the ground states except at regions where a local
random field fluctuation makes thermal excitations feasible. This follows also
from the non-absorbing random walks, and implies that the magnetization length
scale is a product of these two scales. It is not simply given by the
Imry-Ma-like ground state domain size nor by the scale of the thermal
excitations.Comment: 7 pages LaTeX, 8 eps-figures include
The warm circumstellar envelope and wind of the G9 IIb star HR 6902
IUE observations of the eclipsing binary system HR 6902 obtained at various
epochs spread over four years indicate the presence of warm circumstellar
material enveloping the G9 IIb primary. The spectra show Si IV and C IV
absorption up to a distance of 3.3 giant radii (R_g}. Line ratio diagnostics
yields an electron temperature of ~ 78000 K which appears to be constant over
the observed height range.
Applying a least square fit absorption line analysis we derive column
densities as a function of height. We find that the inner envelope (< 3 R_g) of
the bright giant is consistent with a hydrostatic density distribution. The
derived line broadening velocity of ~ 70 kms^{-1} is sufficient to provide
turbulent pressure support for the required scale height. However, an improved
agreement with observations over the whole height regime including the emission
line region is obtained with an outflow model. We demonstrate that the common
beta power-law as well as a P \propto rho wind yield appropriate fit models.
Adopting a continuous mass outflow we obtain a mass-loss rate of M_loss= (0.8 -
3.4)*10^{-11} M_{sun}yr^{-1} depending on the particular wind model.Comment: 11 pages, 8 figures, submitted to Astronomy Astrophysics main Journa
Numerical simulation of inductive heating processes
For product optimization regarding weight reduction, material properties have
to be adapted efficiently. To achieve this, new compositions of materials can be created
or the manufacturing process can be changed in a way that heterogeneous distributions
of material properties are enabled. An example for such an improved process chain is
the production of thermo-mechanically graded structures like shafts. The manufacturing
method mainly consists of three stages. The first one is characterized by a local temperature
increase of the workpiece due to inductive heating. In the second phase the workpiece
is deformed and simultaneously cooled throughout the contact with the forming die. In
the last step, however, a high pressured air stream is applied, leading to a partial cooling
of the workpiece.
The inductive heating step is controlled by an alternating current inducing a high frequency
magnetic field, which causes a temperature increase due to the resulting eddy
currents. To analyse this process, the coupling between the electric and the magnetic
field is described by the fully coupled Maxwell equations. Moreover the heat conduction
equation is considered to describe thermal effects. To solve this multifield the
equations are in the first step decoupled using an additional time differentiation. In the
second step an axisymmetric case is considered, motivated by the fact that the inductive
heating process of a cylindrical shaft is analysed. Afterwards the resulting equations are
spatially discretized by the Galerkin finite element method. The temporal discretization
is carried out via the Newmark method so that afterwards the electrical source
distribution can be achieved. As a consequence the temperature evolution is determined
in a postprocessing step
Chasing electric flux in hot QCD
In this talk, I present the status of attempts to analyze the behavior of the
so-called spatial 't Hooft loop, which can be taken as an order parameter for
the deconfinement phase transition in pure SU(N) gauge theory. While lattice
data show a strikingly universal scaling of extracted k-string tensions for
various values of k and N, the analytic approach to these observables might
need some refinement.Comment: 4 pages; to appear in the Proceedings of SEWM08, Amsterdam, the
Netherlands, August 26-29, 200
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