33,249 research outputs found
Point interactions in acoustics: one dimensional models
A one dimensional system made up of a compressible fluid and several
mechanical oscillators, coupled to the acoustic field in the fluid, is analyzed
for different settings of the oscillators array. The dynamical models are
formulated in terms of singular perturbations of the decoupled dynamics of the
acoustic field and the mechanical oscillators. Detailed spectral properties of
the generators of the dynamics are given for each model we consider. In the
case of a periodic array of mechanical oscillators it is shown that the energy
spectrum presents a band structure.Comment: revised version, 30 pages, 2 figure
Quantum singularities in (2+1) dimensional matter coupled black hole spacetimes
Quantum singularities considered in the 3D BTZ spacetime by Pitelli and
Letelier (Phys. Rev. D77: 124030, 2008) is extended to charged BTZ and 3D
Einstein-Maxwell-dilaton gravity spacetimes. The occurence of naked
singularities in the Einstein-Maxwell extension of the BTZ spacetime both in
linear and non-linear electrodynamics as well as in the
Einstein-Maxwell-dilaton gravity spacetimes are analysed with the quantum test
fields obeying the Klein-Gordon and Dirac equations. We show that with the
inclusion of the matter fields; the conical geometry near r=0 is removed and
restricted classes of solutions are admitted for the Klein-Gordon and Dirac
equations. Hence, the classical central singularity at r=0 turns out to be
quantum mechanically singular for quantum particles obeying Klein-Gordon
equation but nonsingular for fermions obeying Dirac equation. Explicit
calculations reveal that the occurrence of the timelike naked singularities in
the considered spacetimes do not violate the cosmic censorship hypothesis as
far as the Dirac fields are concerned. The role of horizons that clothes the
singularity in the black hole cases is replaced by repulsive potential barrier
against the propagation of Dirac fields.Comment: 13 pages, 1 figure. Final version, to appear in PR
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The 3D version of the finite element program FESTER
In this report, a detailed description of the 3-D version finite element pro-gram FESTER is given. This includes: 1. A brief introduction to the package FESTER; 2. Preparing an input data file for the 3D version of FESTER; 3. Principal stress and stress invariant analyses; 4. 2D joint element (surface contact) characterisation and its mathematical formulation; 5. Formulations of the 3D stress-strain analyses for both isotropic and anisotropic materials, plane of weakness and cracking criteria; 6. 3D brick elements, infinity elements and their corresponding shape and mapping functions; 7. Large-displacement formulations; 8. Modifications to the subroutines INVAR, JNTB, TMAT, MOD2 etc; 9. Numerical examples; and 10. Conclusions
Spectral resolution of the Liouvillian of the Lindblad master equation for a harmonic oscillator
A Lindblad master equation for a harmonic oscillator, which describes the
dynamics of an open system, is formally solved. The solution yields the
spectral resolution of the Liouvillian, that is, all eigenvalues and
eigenprojections are obtained. This spectral resolution is discussed in depth
in the context of the biorthogonal system and the rigged Hilbert space, and the
contribution of each eigenprojection to expectation values of physical
quantities is revealed. We also construct the ladder operators of the
Liouvillian, which clarify the structure of the spectral resolution.Comment: 22pages, no figure; title changed, minor corrections, references
added; minor correction
Scaling limits of integrable quantum field theories
Short distance scaling limits of a class of integrable models on
two-dimensional Minkowski space are considered in the algebraic framework of
quantum field theory. Making use of the wedge-local quantum fields generating
these models, it is shown that massless scaling limit theories exist, and
decompose into (twisted) tensor products of chiral, translation-dilation
covariant field theories. On the subspace which is generated from the vacuum by
the observables localized in finite light ray intervals, this symmetry can be
extended to the M\"obius group. The structure of the interval-localized
algebras in the chiral models is discussed in two explicit examples.Comment: Revised version: erased typos, improved formulations, and corrections
of Lemma 4.8/Prop. 4.9. As published in RMP. 43 pages, 1 figur
Birman-Schwinger and the number of Andreev states in BCS superconductors
The number of bound states due to inhomogeneities in a BCS superconductor is
usually established either by variational means or via exact solutions of
particularly simple, symmetric perturbations. Here we propose estimating the
number of sub-gap states using the Birman-Schwinger principle. We show how to
obtain upper bounds on the number of sub-gap states for small normal regions
and derive a suitable Cwikel-Lieb-Rozenblum inequality. We also estimate the
number of such states for large normal regions using high dimensional
generalizations of the Szego theorem. The method works equally well for local
inhomogeneities of the order parameter and for external potentials.Comment: Final version to appear in Phys Rev
Preliminary catalog of pictures taken on the lunar surface during the Apollo 16 mission
A catalog of all pictures taken from the lunar module or the lunar surface during the Apollo 16 lunar stay is presented. The tabulations are arranged for the following specific uses: (1) given the number of a particular frame, find its location in the sequence of lunar surface activity, the station from which it was taken and the subject matter of the picture; (2) given a particular location or activity within the sequence of lunar surface activity, find the pictures taken at that time and their subject matter; and (3) given a sample number from the voice transcript listed, find the designation assigned to the same sample by the lunar receiving laboratory
Positive cosmological constant in loop quantum cosmology
The k=0 Friedmann Lemaitre Robertson Walker model with a positive
cosmological constant and a massless scalar field is analyzed in detail. If one
uses the scalar field as relational time, new features arise already in the
Hamiltonian framework of classical general relativity: In a finite interval of
relational time, the universe expands out to infinite proper time and zero
matter density. In the deparameterized quantum theory, the true Hamiltonian now
fails to be essentially self-adjoint both in the Wheeler DeWitt (WDW) approach
and in LQC. Irrespective of the choice of the self-adjoint extension, the big
bang singularity persists in the WDW theory while it is resolved and replaced
by a big bounce in loop quantum cosmology (LQC). Furthermore, the quantum
evolution is surprisingly insensitive to the choice of the self-adjoint
extension. This may be a special case of an yet to be discovered general
property of a certain class of symmetric operators that fail to be essentially
self-adjoint.Comment: 36 pages, 6 figures, RevTex
Novel black hole bound states and entropy
We solve for the spectrum of the Laplacian as a Hamiltonian on
and in . A
self-adjointness analysis with and as
the boundary for the two cases shows that a general class of boundary
conditions for which the Hamiltonian operator is essentially self-adjoint are
of the mixed (Robin) type. With this class of boundary conditions we obtain
"bound state" solutions for the Schroedinger equation. Interestingly, these
solutions are all localized near the boundary. We further show that the number
of bound states is finite and is in fact proportional to the perimeter or area
of the removed \emph{disc} or \emph{ball}. We then argue that similar
considerations should hold for static black hole backgrounds with the horizon
treated as the boundary.Comment: 13 pages, 3 figures, approximate formula for energy spectrum added at
the end of section 2.1 along with additional minor changes to comply with the
version accepted in PR
Unboundedness of adjacency matrices of locally finite graphs
Given a locally finite simple graph so that its degree is not bounded, every
self-adjoint realization of the adjacency matrix is unbounded from above. In
this note we give an optimal condition to ensure it is also unbounded from
below. We also consider the case of weighted graphs. We discuss the question of
self-adjoint extensions and prove an optimal criterium.Comment: Typos corrected. Examples added. Cute drawings. Simplification of the
main condition. Case of the weight tending to zero more discussed
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