3,135 research outputs found
Reduced Phase Space Quantization and Dirac Observables
In her recent work, Dittrich generalized Rovelli's idea of partial
observables to construct Dirac observables for constrained systems to the
general case of an arbitrary first class constraint algebra with structure
functions rather than structure constants. Here we use this framework and
propose a new way for how to implement explicitly a reduced phase space
quantization of a given system, at least in principle, without the need to
compute the gauge equivalence classes. The degree of practicality of this
programme depends on the choice of the partial observables involved. The
(multi-fingered) time evolution was shown to correspond to an automorphism on
the set of Dirac observables so generated and interesting representations of
the latter will be those for which a suitable preferred subgroup is realized
unitarily. We sketch how such a programme might look like for General
Relativity. We also observe that the ideas by Dittrich can be used in order to
generate constraints equivalent to those of the Hamiltonian constraints for
General Relativity such that they are spatially diffeomorphism invariant. This
has the important consequence that one can now quantize the new Hamiltonian
constraints on the partially reduced Hilbert space of spatially diffeomorphism
invariant states, just as for the recently proposed Master constraint
programme.Comment: 18 pages, no figure
Bimetal sensor averages temperature of nonuniform profile
Instrument that measures an average temperature across a nonuniform temperature profile under steady-state conditions has been developed. The principle of operation is an application of the expansion of a solid material caused by a change in temperature
Experimental study of flow distribution with circumferential manifolds
Water flow test results on fluid flow distribution and pressure loss in curved manifolds with tangential or radial entry are reported. Manifolds were studied both as inlet and outlet manifolds. Manifolds can be used for boilers and/or heat exchangers for advanced space electric power plants
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
Tunneling And The Onset Of Chaos In A Driven Bistable System
We study the interplay between coherent transport by tunneling and diffusive
transport through classically chaotic phase-space regions, as it is reflected
in the Floquet spectrum of the periodically driven quartic double well. The
tunnel splittings in the semiclassical regime are determined with high
numerical accuracy, and the association of the corresponding doublet states to
either chaotic or regular regions of the classical phase space is quantified in
terms of the overlap of the Husimi distribution with the chaotic layer along
the separatrix. We find a strong correlation between both quantities. They show
an increase by orders of magnitude as chaotic diffusion between the wells
starts to dominate the classical dynamics. We discuss semiclassical
explanations for this correlation.Comment: 17 pages in REVTeX preprint format. A version with encapsulated
Postscript figures included (via epsf) and GIF-images of wave functions are
available from the Gopher server aix.rz.uni-augsburg (port 300) in directory
U Augsburg/Inst.f.Physik/Lst.f.Theo.PhysI/Tunneling an
A perturbative approach to Dirac observables and their space-time algebra
We introduce a general approximation scheme in order to calculate gauge
invariant observables in the canonical formulation of general relativity. Using
this scheme we will show how the observables and the dynamics of field theories
on a fixed background or equivalently the observables of the linearized theory
can be understood as an approximation to the observables in full general
relativity. Gauge invariant corrections can be calculated up to an arbitrary
high order and we will explicitly calculate the first non--trivial correction.
Furthermore we will make a first investigation into the Poisson algebra between
observables corresponding to fields at different space--time points and
consider the locality properties of the observables.Comment: 23 page
Testing the Master Constraint Programme for Loop Quantum Gravity II. Finite Dimensional Systems
This is the second paper in our series of five in which we test the Master
Constraint Programme for solving the Hamiltonian constraint in Loop Quantum
Gravity. In this work we begin with the simplest examples: Finite dimensional
models with a finite number of first or second class constraints, Abelean or
non -- Abelean, with or without structure functions.Comment: 23 pages, no figure
Minimalistic approach of a complex and flexible teaching laboratory for photovoltaic energy conversion experience from courses at the Kasetsart University in Bangkok and at GPEsolar Technical University Berlin
A complex of more than ten laboratory tasks was developed complementary to lectures and seminars for teaching of principles of solar cells and their applications. The laboratory covers topics of basic characteristics, materials and types of solar cells as well as of characterization methods and applications in solar energy conversion and can be extended to research aspects. Students with different background can independently discover a certain aspect in the field of photovoltaic energy conversion within four hours. Tasks can be easily applied at universities in developed and developing countries and most of them can be reproduced at low cost. The mobile laboratory can be setup in a short time and is well suitable for changing places of teaching. The vision to implement related laboratory tasks into experimental interdisciplinary teaching centers for renewable energy at universities has been draw
Quantum Spin Dynamics VIII. The Master Constraint
Recently the Master Constraint Programme (MCP) for Loop Quantum Gravity (LQG)
was launched which replaces the infinite number of Hamiltonian constraints by a
single Master constraint. The MCP is designed to overcome the complications
associated with the non -- Lie -- algebra structure of the Dirac algebra of
Hamiltonian constraints and was successfully tested in various field theory
models. For the case of 3+1 gravity itself, so far only a positive quadratic
form for the Master Constraint Operator was derived. In this paper we close
this gap and prove that the quadratic form is closable and thus stems from a
unique self -- adjoint Master Constraint Operator. The proof rests on a simple
feature of the general pattern according to which Hamiltonian constraints in
LQG are constructed and thus extends to arbitrary matter coupling and holds for
any metric signature. With this result the existence of a physical Hilbert
space for LQG is established by standard spectral analysis.Comment: 19p, no figure
(Broken) Gauge Symmetries and Constraints in Regge Calculus
We will examine the issue of diffeomorphism symmetry in simplicial models of
(quantum) gravity, in particular for Regge calculus. We find that for a
solution with curvature there do not exist exact gauge symmetries on the
discrete level. Furthermore we derive a canonical formulation that exactly
matches the dynamics and hence symmetries of the covariant picture. In this
canonical formulation broken symmetries lead to the replacements of constraints
by so--called pseudo constraints. These considerations should be taken into
account in attempts to connect spin foam models, based on the Regge action,
with canonical loop quantum gravity, which aims at implementing proper
constraints. We will argue that the long standing problem of finding a
consistent constraint algebra for discretized gravity theories is equivalent to
the problem of finding an action with exact diffeomorphism symmetries. Finally
we will analyze different limits in which the pseudo constraints might turn
into proper constraints. This could be helpful to infer alternative
discretization schemes in which the symmetries are not broken.Comment: 32 pages, 15 figure
- …