5,349 research outputs found
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
Microwave fidelity studies by varying antenna coupling
The fidelity decay in a microwave billiard is considered, where the coupling
to an attached antenna is varied. The resulting quantity, coupling fidelity, is
experimentally studied for three different terminators of the varied antenna: a
hard wall reflection, an open wall reflection, and a 50 Ohm load, corresponding
to a totally open channel. The model description in terms of an effective
Hamiltonian with a complex coupling constant is given. Quantitative agreement
is found with the theory obtained from a modified VWZ approach [Verbaarschot et
al, Phys. Rep. 129, 367 (1985)].Comment: 9 pages 5 figur
On the theory of cavities with point-like perturbations. Part I: General theory
The theoretical interpretation of measurements of "wavefunctions" and spectra
in electromagnetic cavities excited by antennas is considered. Assuming that
the characteristic wavelength of the field inside the cavity is much larger
than the radius of the antenna, we describe antennas as "point-like
perturbations". This approach strongly simplifies the problem reducing the
whole information on the antenna to four effective constants. In the framework
of this approach we overcame the divergency of series of the phenomenological
scattering theory and justify assumptions lying at the heart of "wavefunction
measurements". This selfconsistent approach allowed us to go beyond the
one-pole approximation, in particular, to treat the experiments with
degenerated states. The central idea of the approach is to introduce
``renormalized'' Green function, which contains the information on boundary
reflections and has no singularity inside the cavity.Comment: 23 pages, 6 figure
1D quantum models with correlated disorder vs. classical oscillators with coloured noise
We perform an analytical study of the correspondence between a classical
oscillator with frequency perturbed by a coloured noise and the one-dimensional
Anderson-type model with correlated diagonal disorder. It is rigorously shown
that localisation of electronic states in the quantum model corresponds to
exponential divergence of nearby trajectories of the classical random
oscillator. We discuss the relation between the localisation length for the
quantum model and the rate of energy growth for the stochastic oscillator.
Finally, we examine the problem of electron transmission through a finite
disordered barrier by considering the evolution of the classical oscillator.Comment: 23 pages, LaTeX fil
Spectral correlations in systems undergoing a transition from periodicity to disorder
We study the spectral statistics for extended yet finite quasi 1-d systems
which undergo a transition from periodicity to disorder. In particular we
compute the spectral two-point form factor, and the resulting expression
depends on the degree of disorder. It interpolates smoothly between the two
extreme limits -- the approach to Poissonian statistics in the (weakly)
disordered case, and the universal expressions derived for the periodic case.
The theoretical results agree very well with the spectral statistics obtained
numerically for chains of chaotic billiards and graphs.Comment: 16 pages, Late
Global versus local billiard level dynamics: The limits of universality
Level dynamics measurements have been performed in a Sinai microwave billiard
as a function of a single length, as well as in rectangular billiards with
randomly distributed disks as a function of the position of one disk. In the
first case the field distribution is changed globally, and velocity
distributions and autocorrelation functions are well described by universal
functions derived by Simons and Altshuler. In the second case the field
distribution is changed locally. Here another type of universal correlations is
observed. It can be derived under the assumption that chaotic wave functions
may be described by a random superposition of plane waves
Anderson localization as a parametric instability of the linear kicked oscillator
We rigorously analyse the correspondence between the one-dimensional standard
Anderson model and a related classical system, the `kicked oscillator' with
noisy frequency. We show that the Anderson localization corresponds to a
parametric instability of the oscillator, with the localization length
determined by an increment of the exponential growth of the energy. Analytical
expression for a weak disorder is obtained, which is valid both inside the
energy band and at the band edge.Comment: 7 pages, Revtex, no figures, submitted to Phys. Rev.
Anomalous Behavior Of The Complex Conductivity Of Y_{1-x}Pr_xBa_2Cu_3O_7 Observed With THz Spectroscopy
We have measured the electrodynamic properties of Y_{1-x}Pr_xBa_2Cu_3O_7
single crystal thin films as a function of temperature using coherent
THz-time-domain spectroscopy. We obtain directly the complex conductivity
, the London penetration depth , the
plasma frequency , and the quasiparticle scattering rate . We
find that drops exponentially rapidly with below the critical
temperature in {\em all} the superconducting samples, implying that this
behavior is a {\em signature} of high- superconductivity. The plasma
frequency decreases with increasing Pr content, providing evidence that Pr
depletes carriers, leaving the CuO planes {\em underdoped}. Both the
conductivity in the THz region and the dc resistivity yield evidence for the
opening of a spin gap {\em above} .Comment: 9 pages, REVTEX 3.
Willing and able: action-state orientation and the relation between procedural justice and employee cooperation
Existing justice theory explains why fair procedures motivate employees to adopt cooperative goals, but it fails to explain how employees strive towards these goals. We study self-regulatory abilities that underlie goal striving; abilities that should thus affect employees’ display of cooperative behavior in response to procedural justice. Building on action control theory, we argue that employees who display effective self-regulatory strategies (action oriented employees) display relatively strong cooperative behavioral responses to fair procedures. A multisource field study and a laboratory experiment support this prediction. A subsequent experiment addresses the process underlying this effect by explicitly showing that action orientation facilitates attainment of the cooperative goals that people adopt in response to fair procedures, thus facilitating the display of actual cooperative behavior. This goal striving approach better integrates research on the relationship between procedural justice and employee cooperation in the self-regulation and the work motivation literature. It also offers organizations a new perspective on making procedural justice effective in stimulating employee cooperation by suggesting factors that help employees reach their adopted goals
Tailoring Anderson localization by disorder correlations in 1D speckle potentials
We study Anderson localization of single particles in continuous, correlated,
one-dimensional disordered potentials. We show that tailored correlations can
completely change the energy-dependence of the localization length. By
considering two suitable models of disorder, we explicitly show that disorder
correlations can lead to a nonmonotonic behavior of the localization length
versus energy. Numerical calculations performed within the transfer-matrix
approach and analytical calculations performed within the phase formalism up to
order three show excellent agreement and demonstrate the effect. We finally
show how the nonmonotonic behavior of the localization length with energy can
be observed using expanding ultracold-atom gases
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