411 research outputs found
Exceptional Points in a Microwave Billiard with Time-Reversal Invariance Violation
We report on the experimental study of an exceptional point (EP) in a
dissipative microwave billiard with induced time-reversal invariance (T)
violation. The associated two-state Hamiltonian is non-Hermitian and
non-symmetric. It is determined experimentally on a narrow grid in a parameter
plane around the EP. At the EP the size of T violation is given by the relative
phase of the eigenvector components. The eigenvectors are adiabatically
transported around the EP, whereupon they gather geometric phases and in
addition geometric amplitudes different from unity
Renormalization of the one-body off-diagonal Coulomb field in nuclei
Isospin violation effects in nuclei are investigated within a microscopic
approach which takes into account the influence of the residual strong
interaction on the Coulomb interaction. The renormalization of the off-diagonal
Coulomb field acting within a nucleus, by the residual strong interaction is
calculated analytically in a simplified RPA. From the expression for the
suppression coefficient of the isospin violating part of the Coulomb field, the
isospin violating spreading widths of isobaric analog states are derived. The
resulting reduction of the width is in agreement with the data on the isospin
symmetry restoration and with some earlier evaluations of the isospin violating
spreading widths.Comment: 11 pages, Late
Underwater microscope for measuring spatial and temporal changes in bed-sediment grain size
This paper is not subject to U.S. copyright. The definitive version was published in Sedimentary Geology 202 (2007): 402-408, doi:10.1016/j.sedgeo.2007.03.020.For more than a century, studies of sedimentology and sediment transport have measured bed-sediment grain size by collecting samples and transporting them back to the laboratory for grain-size analysis. This process is slow and expensive. Moreover, most sampling systems are not selective enough to sample only the surficial grains that interact with the flow; samples typically include sediment from at least a few centimeters beneath the bed surface. New hardware and software are available for in situ measurement of grain size. The new technology permits rapid measurement of surficial bed sediment. Here we describe several systems we have deployed by boat, by hand, and by tripod in rivers, oceans, and on beaches
The Impact of Isospin Breaking on the Distribution of Transition Probabilities
In the present paper we investigate the effect of symmetry breaking in the
statistical distributions of reduced transition amplitudes and reduced
transition probabilities. These quantities are easier to access experimentally
than the components of the eigenvectors and were measured by Adams et al. for
the electromagnetic transitions in ^{26}Al. We focus on isospin symmetry
breaking described by a matrix model where both, the Hamiltonian and the
electromagnetic operator, break the symmetry. The results show that for partial
isospin conservation, the statistical distribution of the reduced transition
probability can considerably deviate from the Porter-Thomas distribution.Comment: 16 pages, 8 figures, submitted to PR
Analyzing symmetry breaking within a chaotic quantum system via Bayesian inference
Bayesian inference is applied to the level fluctuations of two coupled
microwave billiards in order to extract the coupling strength. The coupled
resonators provide a model of a chaotic quantum system containing two coupled
symmetry classes of levels. The number variance is used to quantify the level
fluctuations as a function of the coupling and to construct the conditional
probability distribution of the data. The prior distribution of the coupling
parameter is obtained from an invariance argument on the entropy of the
posterior distribution.Comment: Example from chaotic dynamics. 8 pages, 7 figures. Submitted to PR
Waiting for the state: gender, citizenship and everyday encounters with bureaucracy in India
This article focuses on practices and meanings of time and waiting experienced by poor, low-class Dalits and Muslims in their routine encounters with the state in India. Drawing on ethnographic research from Tamil Nadu and Uttar Pradesh, it presents experiences of waiting around queuing and applying for paperwork, cards, and welfare schemes, in order to examine the role of temporal processes in the production of citizenship and citizen agency. An analysis of various forms of waiting â âon the dayâ, âto and froâ, and âchronicâ waiting â reveals how temporal processes operate as mechanisms of power and control through which state actors and other mediators produce differentiated forms of citizenship and citizens. Temporal processes and their material outcomes, we argue, are shaped by class, caste and religion, while also drawing on â and reproducing â gendered identities and inequalities. However, rather than being âpassiveâ patients of the state, we show how ordinary people draw on money, patronage networks and various performative acts in an attempt to secure their rights as citizens of India
Dynamics of open quantum systems
The coupling between the states of a system and the continuum into which it
is embedded, induces correlations that are especially large in the short time
scale. These correlations cannot be calculated by using a statistical or
perturbational approach. They are, however, involved in an approach describing
structure and reaction aspects in a unified manner. Such a model is the SMEC
(shell model embedded in the continuum). Some characteristic results obtained
from SMEC as well as some aspects of the correlations induced by the coupling
to the continuum are discussed.Comment: 16 pages, 5 figure
Quantum mechanical time-delay matrix in chaotic scattering
We calculate the probability distribution of the matrix Q = -i \hbar S^{-1}
dS/dE for a chaotic system with scattering matrix S at energy E. The
eigenvalues \tau_j of Q are the so-called proper delay times, introduced by E.
P. Wigner and F. T. Smith to describe the time-dependence of a scattering
process. The distribution of the inverse delay times turns out to be given by
the Laguerre ensemble from random-matrix theory.Comment: 4 pages, RevTeX; to appear in Phys. Rev. Let
Quantum relaxation in open chaotic systems
Using the supersymmetry technique, we analytically derive the recent result
of Casati, Maspero and Shepelyansky [cond-mat/9706103] according to which the
quantum dynamics of open chaotic systems follows the classical decay up to a
new quantum relaxation time scale . This scale is larger
than the classical escape time but still much smaller than the Heisenberg
time . For systems with orthogonal or unitary symmetry the quantum decay
is slower than the classical one while for the symplectic case there is an
intermediate regime in which the quantum decay is slightly faster.Comment: 4 pages Rev-Tex, one figure, important modifications in introduction
and conlusion, four references added or modifie
Time-resolved dynamics of electron wave packets in chaotic and regular quantum billiards with leads
We perform numerical studies of the wave packet propagation through open
quantum billiards whose classical counterparts exhibit regular and chaotic
dynamics. We show that for t less or similar to tau (tau being the Heisenberg
time), the features in the transmitted and reflected currents are directly
related to specific classical trajectories connecting the billiard leads. In
contrast, the long-time asymptotics of the wave packet dynamics is
qualitatively different for classical and quantum billiards. In particularly,
the decay of the quantum system obeys a power law that depends on the number of
decay channels, and is not sensitive to the nature of classical dynamics
(chaotic or regular).Comment: 5 pages, 4 figure
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