2,985 research outputs found
Quality assurance in higher education - meta-evaluationof multi-stage evaluation procedures in Germany
Systematic procedures for quality assurance and improvement through evaluation have been in place in Western Europe since the mid 1980s and in Germany since the mid 1990s. As studies in Europe and beyond show that multi-stage evaluation procedures as the main quality assurance instrument for evaluation of teaching and learning in higher education institutions have proved reliable and have gained acceptance, in Germany (as well as in other countries) the evaluation of teaching and learning through internal and external evaluations has long come under the fire of criticism. Our results of the first comprehensive and representative investigation of procedures for the evaluation of teaching and learning in Germany show that former participants in the evaluations (reviewers and those reviewed) are satisfied all in all with the multi-stage procedure. They are convinced that the goals of quality assurance and improvement were achieved. Suggestions for improving the procedures target individual aspects, such as, for example, the composition of the review panel. Against this background, it makes sense to perform regular quality assessments of the procedures for quality assurance and improvemen
Perfect magnetohydrodynamics as a field theory
We propose the generally covariant action for the theory of a self-coupled
complex scalar field and electromagnetism which by virtue of constraints is
equivalent, in the regime of long wavelengths, to perfect magnetohydrodynamics
(MHD). We recover from it the Euler equation with Lorentz force, and the
thermodynamic relations for a prefect fluid. The equation of state of the
latter is related to the scalar field's self potential. We introduce 1+3
notation to elucidate the relation between MHD and field variables. In our
approach the requirement that the scalar field be single valued leads to the
quantization of a certain circulation in steps of ; this feature leads,
in the classical limit, to the conservation of that circulation. The
circulation is identical to that in Oron's generalization of Kelvin's
circulation theorem to perfect MHD; we here characterize the new conserved
helicity associated with it. We also demonstrate the existence for MHD of two
Bernoulli-like theorems for each spacetime symmetry of the flow and geometry;
one of these is pertinent to suitably defined potential flow. We exhibit the
conserved quantities explicitly in the case that two symmetries are
simultaneously present, and give examples. Also in this case we exhibit a new
conserved MHD circulation distinct from Oron's, and provide an example.Comment: RevTeX, 16 pages, no figures; clarifications added and typos
corrected; version to be published in Phys. Rev.
The grand canonical ABC model: a reflection asymmetric mean field Potts model
We investigate the phase diagram of a three-component system of particles on
a one-dimensional filled lattice, or equivalently of a one-dimensional
three-state Potts model, with reflection asymmetric mean field interactions.
The three types of particles are designated as , , and . The system is
described by a grand canonical ensemble with temperature and chemical
potentials , , and . We find that for
the system undergoes a phase transition from a
uniform density to a continuum of phases at a critical temperature . For other values of the chemical potentials the system
has a unique equilibrium state. As is the case for the canonical ensemble for
this model, the grand canonical ensemble is the stationary measure
satisfying detailed balance for a natural dynamics. We note that , where is the critical temperature for a similar transition in
the canonical ensemble at fixed equal densities .Comment: 24 pages, 3 figure
An alternative scenario for the formation of specialized protein nano-domains (cluster phases) in biomembranes
We discuss a realistic scenario, accounting for the existence of
sub-micrometric protein domains in cell membranes. At the biological level,
such membrane domains have been shown to be specialized, in order to perform a
determined biological task, in the sense that they gather one or a few protein
species out of the hundreds of different ones that a cell membrane may contain.
By analyzing the balance between mixing entropy and protein affinities, we
propose that such protein sorting in distinct domains can be explained without
appealing to pre-existing lipidic micro-phase separations, as in the lipid raft
scenario. We show that the proposed scenario is compatible with known physical
interactions between membrane proteins, even if thousands of different species
coexist.Comment: 6 pages, 2 figures, published versio
Image restoration using the chiral Potts spin-glass
We report on the image reconstruction (IR) problem by making use of the
random chiral q-state Potts model, whose Hamiltonian possesses the same gauge
invariance as the usual Ising spin glass model. We show that the pixel
representation by means of the Potts variables is suitable for the gray-scale
level image which can not be represented by the Ising model. We find that the
IR quality is highly improved by the presence of a glassy term, besides the
usual ferromagnetic term under random external fields, as very recently pointed
out by Nishimori and Wong. We give the exact solution of the infinite range
model with q=3, the three gray-scale level case. In order to check our
analytical result and the efficiency of our model, 2D Monte Carlo simulations
have been carried out on real-world pictures with three and eight gray-scale
levels.Comment: RevTex 13 pages, 10 figure
Variational method and duality in the 2D square Potts model
The ferromagnetic q-state Potts model on a square lattice is analyzed, for
q>4, through an elaborate version of the operatorial variational method. In the
variational approach proposed in the paper, the duality relations are exactly
satisfied, involving at a more fundamental level, a duality relationship
between variational parameters. Besides some exact predictions, the approach is
very effective in the numerical estimates over the whole range of temperature
and can be systematically improved.Comment: 20 pages, 5 EPS figure
Topological Landau-Ginzburg Theory for Vortices in Superfluid He
We propose a new Landau-Ginzburg theory for arbitrarily shaped vortex strings
in superfluid He. The theory contains a topological term and directly
describes vortex dynamics. We introduce gauge fields in order to remove
singularities from the Landau-Ginzburg order parameter of the superfluid, so
that two kinds of gauge symmetries appear, making the continuity equation and
conservation of the total vorticity manifest. The topological term gives rise
to the Berry phase term in the vortex mechanical actions.Comment: LATEX, 9 page
Corner Exponents in the Two-Dimensional Potts Model
The critical behavior at a corner in two-dimensional Ising and three-state
Potts models is studied numerically on the square lattice using transfer
operator techniques. The local critical exponents for the magnetization and the
energy density for various opening angles are deduced from finite-size scaling
results at the critical point for isotropic or anisotropic couplings. The
scaling dimensions compare quite well with the values expected from conformal
invariance, provided the opening angle is replaced by an effective one in
anisotropic systems.Comment: 11 pages, 2 eps-figures, uses LaTex and eps
Non-commuting coordinates, exotic particles, & anomalous anyons in the Hall effect
Our previous ``exotic'' particle, together with the more recent anomalous
anyon model (which has arbitrary gyromagnetic factor ) are reviewed. The
non-relativistic limit of the anyon generalizes the exotic particle which has
to any .When put into planar electric and magnetic fields, the Hall
effect becomes mandatory for all , when the field takes some critical
value.Comment: A new reference added. Talk given by P. Horvathy at the International
Workshop "Nonlinear Physics: Theory and Experiment. III. July'04, Gallipoli
(Lecce, Italy). To be published in Theor. Math. Phys. Latex 9 pages, no
figure
Boundary and Bulk Phase Transitions in the Two Dimensional Q > 4 State Potts Model
The surface and bulk properties of the two-dimensional Q > 4 state Potts
model in the vicinity of the first order bulk transition point have been
studied by exact calculations and by density matrix renormalization group
techniques. For the surface transition the complete analytical solution of the
problem is presented in the limit, including the critical and
tricritical exponents, magnetization profiles and scaling functions. According
to the accurate numerical results the universality class of the surface
transition is independent of the value of Q > 4. For the bulk transition we
have numerically calculated the latent heat and the magnetization discontinuity
and we have shown that the correlation lengths in the ordered and in the
disordered phases are identical at the transition point.Comment: 11 pages, RevTeX, 6 PostScript figures included. Manuscript
substantially extended, details on the analytical and numerical calculations
added. To appear in Phys. Rev.
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