35,838 research outputs found
Quantum noise and mixedness of a pumped dissipative non-linear oscillator
Evolutions of quantum noise, characterized by quadrature squeezing parameter
and Fano factor, and of mixedness, quantified by quantum von Neumann and linear
entropies, of a pumped dissipative non-linear oscillator are studied. The model
can describe a signal mode interacting with a thermal reservoir in a
parametrically pumped cavity with a Kerr non-linearity. It is discussed that
the initial pure states, including coherent states, Fock states, and finite
superpositions of coherent states evolve into the same steady mixed state as
verified by the quantum relative entropy and the Bures metric. It is shown
analytically and verified numerically that the steady state can be well
approximated by a nonclassical Gaussian state exhibiting quadrature squeezing
and sub-Poissonian statistics for the cold thermal reservoir. A rapid increase
is found in the mixedness, especially for the initial Fock states and
superpositions of coherent states, during a very short time interval, and then
for longer evolution times a decrease in the mixedness to the same, for all the
initial states, and relatively low value of the nonclassical Gaussian state.Comment: 10 pages, 12 figure
Singular projective varieties and quantization
By the quantization condition compact quantizable Kaehler manifolds can be
embedded into projective space. In this way they become projective varieties.
The quantum Hilbert space of the Berezin-Toeplitz quantization (and of the
geometric quantization) is the projective coordinate ring of the embedded
manifold. This allows for generalization to the case of singular varieties. The
set-up is explained in the first part of the contribution. The second part of
the contribution is of tutorial nature. Necessary notions, concepts, and
results of algebraic geometry appearing in this approach to quantization are
explained. In particular, the notions of projective varieties, embeddings,
singularities, and quotients appearing in geometric invariant theory are
recalled.Comment: 21 pages, 3 figure
Entanglement generation in continuously coupled parametric generators
We investigate a compact source of entanglement. This device is composed of a
pair of linearly coupled nonlinear waveguides operating by means of degenerate
parametric downconversion. For the vacuum state at the input the generalized
squeeze variance and logarithmic negativity are used to quantify the amount of
nonclassicality and entanglement of output beams. Squeezing and entanglement
generation for various dynamical regimes of the device are discussed.Comment: 6 pages, 7 figure
Effective Hamiltonians in quantum optics: a systematic approach
We discuss a general and systematic method for obtaining effective
Hamiltonians that describe different nonlinear optical processes. The method
exploits the existence of a nonlinear deformation of the usual su(2) algebra
that arises as the dynamical symmetry of the original model. When some physical
parameter, dictated by the process under consideration, becomes small, we
immediately get a diagonal effective Hamiltonian that correctly represents the
dynamics for arbitrary states and long times. We extend the technique to su(3)
and su(N), finding the corresponding effective Hamiltonians when some resonance
conditions are fulfilled.Comment: 13 Pages, no figures, submitted for publicatio
Actuation of Micro-Optomechanical Systems Via Cavity-Enhanced Optical Dipole Forces
We demonstrate a new type of optomechanical system employing a movable,
micron-scale waveguide evanescently-coupled to a high-Q optical microresonator.
Micron-scale displacements of the waveguide are observed for
milliwatt(mW)-level optical input powers. Measurement of the spatial variation
of the force on the waveguide indicates that it arises from a cavity-enhanced
optical dipole force due to the stored optical field of the resonator. This
force is used to realize an all-optical tunable filter operating with sub-mW
control power. A theoretical model of the system shows the maximum achievable
force to be independent of the intrinsic Q of the optical resonator and to
scale inversely with the cavity mode volume, suggesting that such forces may
become even more effective as devices approach the nanoscale.Comment: 4 pages, 5 figures. High resolution version available at
(http://copilot.caltech.edu/publications/CEODF_hires.pdf). For associated
movie, see (http://copilot.caltech.edu/research/optical_forces/index.htm
Reverse mathematics, well-quasi-orders, and Noetherian spaces
A quasi-order Q induces two natural quasi-orders on P(Q) P(Q) , but if Q is a well-quasi-order, then these quasi-orders need not necessarily be well-quasi-orders. Nevertheless, Goubault-Larrecq (Proceedings of the 22nd Annual IEEE Symposium 4 on Logic in Computer Science (LICS’07), pp. 453–462, 2007) showed that moving from a well-quasi-order Q to the quasi-orders on P(Q) P(Q) preserves well-quasi-orderedness in a topological sense. Specifically, Goubault-Larrecq proved that the upper topologies of the induced quasi-orders on P(Q) P(Q) are Noetherian, which means that they contain no infinite strictly descending sequences of closed sets. We analyze various theorems of the form “if Q is a well-quasi-order then a certain topology on (a subset of) P(Q) P(Q) is Noetherian” in the style of reverse mathematics, proving that these theorems are equivalent to ACA0 over RCA0. To state these theorems in RCA0 we introduce a new framework for dealing with second-countable topological spaces
Smolyak's algorithm: A powerful black box for the acceleration of scientific computations
We provide a general discussion of Smolyak's algorithm for the acceleration
of scientific computations. The algorithm first appeared in Smolyak's work on
multidimensional integration and interpolation. Since then, it has been
generalized in multiple directions and has been associated with the keywords:
sparse grids, hyperbolic cross approximation, combination technique, and
multilevel methods. Variants of Smolyak's algorithm have been employed in the
computation of high-dimensional integrals in finance, chemistry, and physics,
in the numerical solution of partial and stochastic differential equations, and
in uncertainty quantification. Motivated by this broad and ever-increasing
range of applications, we describe a general framework that summarizes
fundamental results and assumptions in a concise application-independent
manner
Systematic review of methodologies used to assess mastectomy flap viability
BACKGROUND
Accurate prediction of mastectomy skin flap viability is vital as necrosis causes significant morbidity, potentially compromising results and delaying oncological management. Traditionally assessed by clinical judgement, a more objective evaluation can be provided using intraoperative imaging modalities. This systematic review aimed to compare all intraoperative techniques for assessment of mastectomy flap viability.
METHODS
A systematic literature review was performed using MEDLINE and Embase databases. Primary outcomes reported included specificity, sensitivity and predictive values of each test, and mean rates of mastectomy flap necrosis and reoperation. Secondary outcomes included cost analysis.
RESULTS
Some 18 studies were included. Designs were prospective cohort study (8), retrospective case series (4), prospective case series (3), retrospective case–control study (1), prospective pilot trial (1) and cost analysis study (1). The studies compared indocyanine green angiography (ICGA) (16 studies) and fluorescein dye angiography (FA) (3 studies) with clinical judgement. Sensitivity and specificity were highest for ICGA (5 studies) ranging from 38 to 100 and 68 to 91 per cent respectively. Both methods overpredicted necrosis. Mean rates of flap necrosis and reoperation decreased with ICGA (7·9 and 5·5 per cent respectively) and FA (3 and 0 per cent) compared with clinical judgement (19·4 and 12·9 per cent). Two studies were designed to define numerical parameters corresponding to perfusion using intraoperative techniques. Two studies performed a cost analysis for ICGA; one claimed a cost benefit and the other advocated its use in high‐risk patients only.
CONCLUSION
ICGA and FA are potentially useful tools for mastectomy flap assessment. However, the predictive accuracy is subject to the specific settings and model of equipment used. Current recommendations support their use in high‐risk patients
First experimental results of very high accuracy centroiding measurements for the neat astrometric mission
NEAT is an astrometric mission proposed to ESA with the objectives of
detecting Earth-like exoplanets in the habitable zone of nearby solar-type
stars. NEAT requires the capability to measure stellar centroids at the
precision of 5e-6 pixel. Current state-of-the-art methods for centroid
estimation have reached a precision of about 2e-5 pixel at two times Nyquist
sampling, this was shown at the JPL by the VESTA experiment. A metrology system
was used to calibrate intra and inter pixel quantum efficiency variations in
order to correct pixelation errors. The European part of the NEAT consortium is
building a testbed in vacuum in order to achieve 5e-6 pixel precision for the
centroid estimation. The goal is to provide a proof of concept for the
precision requirement of the NEAT spacecraft. In this paper we present the
metrology and the pseudo stellar sources sub-systems, we present a performance
model and an error budget of the experiment and we report the present status of
the demonstration. Finally we also present our first results: the experiment
had its first light in July 2013 and a first set of data was taken in air. The
analysis of this first set of data showed that we can already measure the pixel
positions with an accuracy of about 1e-4 pixel.Comment: SPIE conference proceeding
Normal hindfoot alignment assessed by weight bearing CT : presence of a constitutional valgus?
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