1,094 research outputs found
Quantum pumping: The charge transported due to a translation of a scatterer
The amount of charge which is pushed by a moving scatterer is ,
where is the displacement of the scatterer. The question is what is .
Does it depend on the transmission of the scatterer? Does the answer
depend on whether the system is open (with leads attached to reservoirs) or
closed? In the latter case: what are the implications of having ``quantum
chaos" and/or coupling to to the environment? The answers to these questions
illuminate some fundamental aspects of the theory of quantum pumping. For the
analysis we take a network (graph) as a model system, and use the Kubo formula
approach.Comment: 4 pages, 2 figures, minor changes, to be published in PRE (Rapid
Spin-Boson Hamiltonian and Optical Absorption of Molecular Dimers
An analysis of the eigenstates of a symmetry-broken spin-boson Hamiltonian is
performed by computing Bloch and Husimi projections. The eigenstate analysis is
combined with the calculation of absorption bands of asymmetric dimer
configurations constituted by monomers with nonidentical excitation energies
and optical transition matrix elements. Absorption bands with regular and
irregular fine structures are obtained and related to the transition from the
coexistence to a mixing of adiabatic branches in the spectrum. It is shown that
correlations between spin states allow for an interpolation between absorption
bands for different optical asymmetries.Comment: 15 pages, revTeX, 8 figures, accepted for publication in Phys. Rev.
Trace identities and their semiclassical implications
The compatibility of the semiclassical quantization of area-preserving maps
with some exact identities which follow from the unitarity of the quantum
evolution operator is discussed. The quantum identities involve relations
between traces of powers of the evolution operator. For classically {\it
integrable} maps, the semiclassical approximation is shown to be compatible
with the trace identities. This is done by the identification of stationary
phase manifolds which give the main contributions to the result. The same
technique is not applicable for {\it chaotic} maps, and the compatibility of
the semiclassical theory in this case remains unsettled. The compatibility of
the semiclassical quantization with the trace identities demonstrates the
crucial importance of non-diagonal contributions.Comment: LaTeX - IOP styl
Application of Two-Phase Regression to Geotechnical Data
2000 Mathematics Subject Classification: 62F10, 62J05, 62P30A method for estimating a transition parameter in two-phase regression
is described. The two phases are fitted and simultaneously the transition
point is estimated. Practical application of the method is demonstrated on
the data for determining soil hydraulic properties.Partly supported by projects FOR 444, Deutsche Forschungsgemeinschaft, Germany, MM1301/2003, National Science Fund, Bulgaria, and PRO-ENBIS: GTC1-2001-43031
Can One Hear the Shape of a Graph?
We show that the spectrum of the Schrodinger operator on a finite, metric
graph determines uniquely the connectivity matrix and the bond lengths,
provided that the lengths are non-commensurate and the connectivity is simple
(no parallel bonds between vertices and no loops connecting a vertex to
itself). That is, one can hear the shape of the graph! We also consider a
related inversion problem: A compact graph can be converted into a scattering
system by attaching to its vertices leads to infinity. We show that the
scattering phase determines uniquely the compact part of the graph, under
similar conditions as above.Comment: 9 pages, 1 figur
Shot noise from action correlations
We consider universal shot noise in ballistic chaotic cavities from a
semiclassical point of view and show that it is due to action correlations
within certain groups of classical trajectories. Using quantum graphs as a
model system we sum these trajectories analytically and find agreement with
random-matrix theory. Unlike all action correlations which have been considered
before, the correlations relevant for shot noise involve four trajectories and
do not depend on the presence of any symmetry.Comment: 4 pages, 2 figures (a mistake in version 1 has been corrected
Scars on quantum networks ignore the Lyapunov exponent
We show that enhanced wavefunction localization due to the presence of short
unstable orbits and strong scarring can rely on completely different
mechanisms. Specifically we find that in quantum networks the shortest and most
stable orbits do not support visible scars, although they are responsible for
enhanced localization in the majority of the eigenstates. Scarring orbits are
selected by a criterion which does not involve the classical Lyapunov exponent.
We obtain predictions for the energies of visible scars and the distributions
of scarring strengths and inverse participation ratios.Comment: 5 pages, 2 figure
Spectral Statistics in Chaotic Systems with Two Identical Connected Cells
Chaotic systems that decompose into two cells connected only by a narrow
channel exhibit characteristic deviations of their quantum spectral statistics
from the canonical random-matrix ensembles. The equilibration between the cells
introduces an additional classical time scale that is manifest also in the
spectral form factor. If the two cells are related by a spatial symmetry, the
spectrum shows doublets, reflected in the form factor as a positive peak around
the Heisenberg time. We combine a semiclassical analysis with an independent
random-matrix approach to the doublet splittings to obtain the form factor on
all time (energy) scales. Its only free parameter is the characteristic time of
exchange between the cells in units of the Heisenberg time.Comment: 37 pages, 15 figures, changed content, additional autho
Self-directed passive-aggressive behaviour as an essential component of depression: findings from two cross-sectional observational studies
Background: The self-control model of depression suggests depressive symptoms to derive from distorted self-monitoring, dysfunctional self-evaluation and reduced self-reward as well as increased self-punishment. Building on this
model a relationship between self-directed passive-aggressive behaviour, that is, harmful inactivity, and depression
has been assumed. This association has been supported by a recent study in an inpatient sample. However, it remains
unclear if patients with depressive disorders report more self-directed passive-aggressive behaviour than patients
without depressive disorders and if self-directed passive aggression mediates the associations between distorted selfmonitoring and dysfunctional self-evaluation with depressive symptoms.
Methods: Study 1 compared self-directed passive-aggressive behaviour levels between 220 psychotherapy outpatients with (n=140; 67.9% female; Mage=40.0) and without (n=80; 65.0% female; Mage=36.2) depressive disorders.
Diagnoses were made based on the Structured Clinical Interview for DSM-IV. Study 2 examined self-directed passiveaggressive behaviour as a mediator of the relationship between distorted self-monitoring and dysfunctional selfevaluation and self-reported depressive symptoms in 200 undergraduate Psychology students.
Results: Compared to outpatients without depressive disorders, outpatients with depressive disorder reported
signifcantly more self-directed passive aggression (d=0.51). Furthermore, Study 2 verifed self-directed passiveaggressive behaviour as a partial mediator of the relationship between dysfunctional attitudes (abcs=.22, 95%-CI: .14,
.31), attributional style (abcs=.20, 95%-CI: .13, .27), ruminative response style (abcs=.15, 95%-CI: .09, .21) and depressive symptoms.
Conclusion: Self-directed passive-aggressive behaviour partially mediates the association between distorted selfmonitoring and dysfunctional self-evaluation with depressive symptoms. Future longitudinal studies need to examine
a potential causal relationship that would form a base to include interventions targeting self-directed passive-aggressive behaviour in prevention and treatment of depression.
Trial registration: Both studies were preregistered at the German Clinical Trials Register (DRKS00014005 and
DRKS00019020)
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