3,677 research outputs found
Commutation Relations for Unitary Operators
Let be a unitary operator defined on some infinite-dimensional complex
Hilbert space . Under some suitable regularity assumptions, it is
known that a local positive commutation relation between and an auxiliary
self-adjoint operator defined on allows to prove that the
spectrum of has no singular continuous spectrum and a finite point
spectrum, at least locally. We show that these conclusions still hold under
weak regularity hypotheses and without any gap condition. As an application, we
study the spectral properties of the Floquet operator associated to some
perturbations of the quantum harmonic oscillator under resonant AC-Stark
potential
Commutation Relations for Unitary Operators III
Let be a unitary operator defined on some infinite-dimensional complex
Hilbert space . Under some suitable regularity assumptions, it is
known that a local positive commutation relation between and an auxiliary
self-adjoint operator defined on allows to prove that the
spectrum of has no singular continuous spectrum and a finite point
spectrum, at least locally. We prove that under stronger regularity hypotheses,
the local regularity properties of the spectral measure of are improved,
leading to a better control of the decay of the correlation functions. As shown
in the applications, these results may be applied to the study of periodic
time-dependent quantum systems, classical dynamical systems and spectral
problems related to the theory of orthogonal polynomials on the unit circle
Frequency and voltage partitioning in presence of renewable energy resources for power system (example: North Chile power network)
This paper investigates techniques for frequency and voltage partitioning of power network based on the
graph-theory. These methods divide the power system into distinguished regions to avoid the spread of disturbances
and to minimize the interaction between these regions for frequency and voltage control of power system. In case
of required active and reactive power for improving the performance of the power system, control can be performed
regionally instead of a centralized controller. In this paper, renewable energy sources are connected to the power
network to verify the effect of these sources on the power systems partitioning and performance. The number of
regions is found based on the frequency sensitivity for frequency partitioning and bus voltage for voltage partitioning to disturbances being applied to loads in each region. The methodology is applied to the north part of Chile power
network. The results show the performance and ability of graph frequency and voltage partitioning algorithm to divide
large scale power systems to smaller regions for applying decentralized controllers.Peer ReviewedPostprint (published version
Electron-phonon coupling in 122 Fe pnictides analyzed by femtosecond time-resolved photoemission
Based on results from femtosecond time-resolved photoemission, we compare
three different methods for determination of the electron-phonon coupling
constant {\lambda} in Eu and Ba-based 122 FeAs compounds. We find good
agreement between all three methods, which reveal a small {\lambda} < 0.2. This
makes simple electron-phonon mediated superconductivity unlikely in these
compounds.Comment: 11 pages, 3 figure
Angular dependence of magnetic properties in Ni nanowire arrays
The angular dependence of the remanence and coercivity of Ni nanowire arrays
produced inside the pores of anodic alumina membranes has been studied. By
comparing our analytical calculations with our measurements, we conclude that
the magnetization reversal in this array is driven by means of the nucleation
and propagation of a transverse wall. A simple model based on an adapted
Stoner-Wohlfarth model is used to explain the angular dependence of the
coercivity
Light-cone quantization of two dimensional field theory in the path integral approach
A quantization condition due to the boundary conditions and the
compatification of the light cone space-time coordinate is identified at
the level of the classical equations for the right-handed fermionic field in
two dimensions. A detailed analysis of the implications of the implementation
of this quantization condition at the quantum level is presented. In the case
of the Thirring model one has selection rules on the excitations as a function
of the coupling and in the case of the Schwinger model a double integer
structure of the vacuum is derived in the light-cone frame. Two different
quantized chiral Schwinger models are found, one of them without a
-vacuum structure. A generalization of the quantization condition to
theories with several fermionic fields and to higher dimensions is presented.Comment: revtex, 14 p
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