2,885 research outputs found
Shack-Hartmann wavefront sensing with elongated sodium laser beacons: centroiding versus matched filtering
We describe modeling and simulation results for the Thirty Meter Telescope on the degradation of sodium laser guide star Shack-Hartmann wavefront sensor measurement accuracy that will occur due to the spatial structure and temporal variations of the mesospheric sodium layer. By using a contiguous set of lidar measurements of the sodium profile, the performance of a standard centroid and of a more refined noise-optimal matched filter spot position estimation algorithm is analyzed and compared for a nominal mean signal level equal to 1000 photodetected electrons per subaperture per integration time, as a function of subaperture to laser launch telescope distance and CCD pixel readout noise. Both algorithms are compared in terms of their rms spot position estimation error due to noise, their associated wavefront error when implemented on the Thirty Meter Telescope facility adaptive optics system, their linear dynamic range, and their bias when detuned from the current sodium profile
Modeling update for the Thirty Meter Telescope laser guide star dual-conjugate adaptive optics system
This paper describes the modeling efforts undertaken in the past couple of years to derive wavefront error (WFE) performance estimates for the Narrow Field Infrared Adaptive Optics System (NFIRAOS), which is the facility laser guide star (LGS) dual-conjugate adaptive optics (AO) system for the Thirty Meter Telescope (TMT). The estimates describe the expected performance of NFIRAOS as a function of seeing on Mauna Kea, zenith angle, and galactic latitude (GL). They have been developed through a combination of integrated AO simulations, side analyses, allocations, lab and lidar experiments
Remote Sampling with Applications to General Entanglement Simulation
We show how to sample exactly discrete probability distributions whose
defining parameters are distributed among remote parties. For this purpose, von
Neumann's rejection algorithm is turned into a distributed sampling
communication protocol. We study the expected number of bits communicated among
the parties and also exhibit a trade-off between the number of rounds of the
rejection algorithm and the number of bits transmitted in the initial phase.
Finally, we apply remote sampling to the simulation of quantum entanglement in
its most general form possible, when an arbitrary number of parties share
systems of arbitrary dimensions on which they apply arbitrary measurements (not
restricted to being projective measurements). In case the dimension of the
systems and the number of possible outcomes per party is bounded by a constant,
it suffices to communicate an expected O(m^2) bits in order to simulate exactly
the outcomes that these measurements would have produced on those systems,
where m is the number of participants.Comment: 17 pages, 1 figure, 4 algorithms (protocols); Complete generalization
of previous paper arXiv:1303.5942 [cs.IT] -- Exact simulation of the GHZ
distribution -- by the same author
Morphology transition at depinning in a solvable model of interface growth in a random medium
We propose a simple, exactly solvable, model of interface growth in a random
medium that is a variant of the zero-temperature random-field Ising model on
the Cayley tree. This model is shown to have a phase diagram (critical
depinning field versus disorder strength) qualitatively similar to that
obtained numerically on the cubic lattice. We then introduce a specifically
tailored random graph that allows an exact asymptotic analysis of the height
and width of the interface. We characterize the change of morphology of the
interface as a function of the disorder strength, a change that is found to
take place at a multicritical point along the depinning-transition line.Comment: 7 pages, 6 figure
Hysteresis and avalanches in the T=0 random-field Ising model with 2-spin-flip dynamics
We study the non-equilibrium behavior of the three-dimensional Gaussian
random-field Ising model at T=0 in the presence of a uniform external field
using a 2-spin-flip dynamics. The deterministic, history-dependent evolution of
the system is compared with the one obtained with the standard 1-spin-flip
dynamics used in previous studies of the model. The change in the dynamics
yields a significant suppression of coercivity, but the distribution of
avalanches (in number and size) stays remarkably similar, except for the
largest ones that are responsible for the jump in the saturation magnetization
curve at low disorder in the thermodynamic limit. By performing a finite-size
scaling study, we find strong evidence that the change in the dynamics does not
modify the universality class of the disorder-induced phase transition.Comment: 9 pages, 10 figure
Contractor Programming
WOSInternational audienceThis paper describes a solver programming method, called "contractor programming", that copes with two issues related to constraint processing over the reals. First, continuous constraints involve an inevitable step of solver design. Existing softwares provide an insufficient answer by restricting users to choose among a list of fixed strategies. Our first contribution is to give more freedom in solver design by introducing programming concepts where only configuration parameters were previously available. Programming consists in applying operators (intersection, composition, etc.) on algorithms called "contractors" that are somehow similar to propagators. Second, many problems with real variables cannot be cast as the search for vectors simultaneously satisfying the set of constraints, but a large variety of different outputs may be demanded from a set of constraints (e.g., a paving with boxes inside and outside of the solution set). These outputs can actually be viewed as the result of different "contractors" working concurrently on the same search space, with a bisection procedure intervening in case of deadlock. Such algorithms (which are not strictly speaking solvers) will be made easy to build thanks to a new branch & prune system, called "paver". Thus, this paper gives a way to deal harmoniously with a larger set of problems while giving a fine control on the solving mechanisms. The contractor formalism and the paver system are the two contributions. The approach is motivated and justified through different cases of study. An implementation of this framework named Quimper is also presented
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