23,843 research outputs found
Controlling the path of discretized light in waveguide lattices
A general method for flexible control of the path of discretized light beams
in homogeneous waveguide lattices, based on longitudinal modulation of the
coupling constant, is theoretically proposed. As compared to beam steering and
refraction achievable in graded-index waveguide arrays, the proposed approach
enables to synthesize rather arbitrary target paths
Markovian feedback to control continuous variable entanglement
We present a model to realize quantum feedback control of continuous variable
entanglement. It consists of two interacting bosonic modes subject to amplitude
damping and achieving entangled Gaussian steady state. The possibility to
greatly improve the degree of entanglement by means of Markovian (direct)
feedback is then shown.Comment: 4 pages Revtex, new figures, added comment
Suitable weak solutions to the 3D Navier-Stokes equations are constructed with the Voigt Approximation
In this paper we consider the Navier-Stokes equations supplemented with
either the Dirichlet or vorticity-based Navier boundary conditions. We prove
that weak solutions obtained as limits of solutions to the Navier-Stokes-Voigt
model satisfy the local energy inequality. Moreover, in the periodic setting we
prove that if the parameters are chosen in an appropriate way, then we can
construct suitable weak solutions trough a Fourier-Galerkin finite-dimensional
approximation in the space variables
A PDE-constrained optimization formulation for discrete fracture network flows
We investigate a new numerical approach for the computation of the 3D flow in a discrete fracture network that does not require a conforming discretization of partial differential equations on complex 3D systems of planar fractures. The discretization within each fracture is performed independently of the discretization of the other fractures and of their intersections. Independent meshing process within each fracture is a very important issue for practical large scale simulations making easier mesh generation. Some numerical simulations are given to show the viability of the method. The resulting approach can be naturally parallelized for dealing with systems with a huge number of fractures
Minimal qudit code for a qubit in the phase-damping channel
Using the stabilizer formalism we construct the minimal code into a
D-dimensional Hilbert space (qudit) to protect a qubit against phase damping.
The effectiveness of this code is then studied by means of input-output
fidelity.Comment: 9 pages, 3 figures. REVTe
Nonlinear predictive control of autonomous soaring UAVs using 3DOF models
We design a nonlinear model predictive control (NMPC) system for a soaring UAV in order to harvest the energy from the atmospheric updrafts. Our control framework combines an online estimation with a heuristic search method to obtain the UAV optimal trajectory. To allow for real-time computation of the control commands we solve the optimal control problem using a 3 degrees-of-freedom (DOF) model but apply the inputs to a more realistic 6DOF model. Hence, we design a 3DOF-6DOF model interaction strategy. Simulations show how the control system succeeds in energy extraction in a challenging dynamic atmospheric environment while satisfying its real-time contraints
Optimal Galaxy Shape Measurements for Weak Lensing Applications Using the Hubble Space Telescope Advanced Camera for Surveys
We present three-epoch multiband (, , )
measurements of galaxy shapes using the ``polar shapelet'' or
Laguerre-expansions method with the Hubble Space Telescope () Advanced
Camera for Surveys (ACS) data, obtained as part of the {\it Great Observatories
Origin Deep Survey} (GOODS). We take advantage of the unique features of the
GOODS/ACS Fields to test the reliability of this relatively new method of
galaxy shape measurement for weak lensing analysis and to quantify the impact
of the ACS Point Spread Function (PSF) on /ACS data. We estimate the bias
introduced by the sharp PSF of the ACS on shape measurement. We show that the
bias in the tangential shear due to galaxy-galaxy lensing can be safely
neglected provided only well-resolved galaxies are used, while it would be
comparable to the signal level (1--3%) for cosmic shear measurements. These
results should of be general utility in planning and analyzing weak lensing
measurements with /ACS data.Comment: 12 pages, 3 figures. Accepted for ApJ
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