1,214 research outputs found
Manual measurement of retinal bifurcation features
This paper introduces a new computerized tool for
accurate manual measurement of features of retinal bifurcation
geometry, designed for use in investigating correlations between measurement features and clinical conditions. The tool uses user-placed rectangles to measure the vessel width, and lines placed along vessel center lines to measure the angles. An
analysis is presented of measurements taken from 435 bifurcations.
These are compared with theoretical predictions based on
optimality principles presented in the literature. The new tool shows better agreement with the theoretical predictions than a simpler manual method published in the literature, but there remains a significant discrepancy between current theory and measured geometry
Robust control in the quantum domain
Recent progress in quantum physics has made it possible to perform
experiments in which individual quantum systems are monitored and manipulated
in real time. The advent of such new technical capabilities provides strong
motivation for the development of theoretical and experimental methodologies
for quantum feedback control. The availability of such methods would enable
radically new approaches to experimental physics in the quantum realm.
Likewise, the investigation of quantum feedback control will introduce crucial
new considerations to control theory, such as the uniquely quantum phenomena of
entanglement and measurement back-action. The extension of established analysis
techniques from control theory into the quantum domain may also provide new
insight into the dynamics of complex quantum systems. We anticipate that the
successful formulation of an input-output approach to the analysis and
reduction of large quantum systems could have very general applications in
non-equilibrium quantum statistical mechanics and in the nascent field of
quantum information theory.Comment: 12 pages, 1 figur
Quantum feedback control and classical control theory
We introduce and discuss the problem of quantum feedback control in the context of established formulations of classical control theory, examining conceptual analogies and essential differences. We describe the application of state-observer-based control laws, familiar in classical control theory, to quantum systems and apply our methods to the particular case of switching the state of a particle in a double-well potential
REVIEW - A reference data set for retinal vessel profiles
This paper describes REVIEW, a new retinal vessel reference dataset. This dataset includes 16 images with 193 vessel segments, demonstrating a variety of pathologies and vessel types. The vessel edges are marked by three observers using a special drawing tool. The paper also describes the algorithm used to process these segments to produce vessel profiles, against which vessel width measurement algorithms can be assessed. Recommendations are given for use of the dataset in performance assessment. REVIEW can be downloaded from http://ReviewDB.lincoln.ac.uk
Nonlinear Quantum Dynamics
The vast majority of the literature dealing with quantum dynamics is
concerned with linear evolution of the wave function or the density matrix. A
complete dynamical description requires a full understanding of the evolution
of measured quantum systems, necessary to explain actual experimental results.
The dynamics of such systems is intrinsically nonlinear even at the level of
distribution functions, both classically as well as quantum mechanically. Aside
from being physically more complete, this treatment reveals the existence of
dynamical regimes, such as chaos, that have no counterpart in the linear case.
Here, we present a short introductory review of some of these aspects, with a
few illustrative results and examples.Comment: 13 pages, 3 figures, invited talk at the NATO Advanced Workshop,
"Nonlinear Dynamics and Fundamental Interactions," (October, 2004, Tashkent
Evolution of Efimov States
The Efimov phenomenon manifests itself as an emergent discrete scaling
symmetry in the quantum three-body problem. In the unitarity limit, it leads to
an infinite tower of three-body bound states with energies forming a geometric
sequence. In this work, we study the evolution of these so-called Efimov states
using relativistic scattering theory. We identify them as poles of the
three-particle matrix and trace their trajectories in the complex energy
plane as they evolve from virtual states through bound states to resonances. We
dial the scattering parameters toward the unitarity limit and observe the
emergence of the universal scaling of energies and couplings -- a behavior
known from the non-relativistic case. Interestingly, we find that Efimov
resonances follow unusual, cyclic trajectories accumulating at the three-body
threshold and then disappear at some values of the two-body scattering length.
We propose a partial resolution to this "missing states" problem.Comment: 15 pages, 10 figures
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