6,567 research outputs found
A "Cellular Neuronal" Approach to Optimization Problems
The Hopfield-Tank (1985) recurrent neural network architecture for the
Traveling Salesman Problem is generalized to a fully interconnected "cellular"
neural network of regular oscillators. Tours are defined by synchronization
patterns, allowing the simultaneous representation of all cyclic permutations
of a given tour. The network converges to local optima some of which correspond
to shortest-distance tours, as can be shown analytically in a stationary phase
approximation. Simulated annealing is required for global optimization, but the
stochastic element might be replaced by chaotic intermittency in a further
generalization of the architecture to a network of chaotic oscillators.Comment: -2nd revised version submitted to Chaos (original version submitted
6/07
CAD of Stacked Patch Antennas Through Multipurpose Admittance Matrices From FEM and Neural Networks
In this work, a novel computer-aided design methodology for probe-fed, cavity-backed, stacked microstrip patch antennas is proposed. The methodology incorporates the rigor of a numerical technique, such as finite element methods, which, in turn, makes use of a newly developed procedure (multipurpose admittance matrices) to carry out a full-wave analysis in a given structure in spite of certain physical shapes and dimensions not yet being established. With the aid of this technique, we form a training set for a neural network, whose output is the desired response of the antenna according to the value of design parameters. Last, taking advantage of this neural network, we perform a global optimization through a genetic algorithm or simulated annealing to obtain a final design. The proposed methodology is validated through a real design whose numerical results are compared with measurements with good agreement
Experimental observation of superscattering
Superscattering, induced by degenerate resonances, breaks the fundamental
single-channel limit of scattering cross section of subwavelength structures;
in principle, an arbitrarily large total cross section can be achieved via
superscattering. It thus provides a unique way to strengthen the light-matter
interaction at the subwavelength scale, and has many potential applications in
sensing, energy harvesting, bio-imaging (such as magnetic resonance imaging),
communication and optoelectronics. However, the experimental demonstration of
superscattering remains an open challenge due to its vulnerability to
structural imperfections and intrinsic material losses. Here we report the
first experimental evidence for superscattering, by demonstrating the
superscattering simultaneously in two different frequency regimes through both
the far-field and near-field measurements. The underlying mechanism for the
observed superscattering is the degenerate resonances of confined surface
waves, by utilizing a subwavelength metasurface-based multilayer structure. Our
work paves the way towards practical applications based on superscattering
Quantum annealing for the number partitioning problem using a tunable spin glass of ions
Exploiting quantum properties to outperform classical ways of
information-processing is an outstanding goal of modern physics. A promising
route is quantum simulation, which aims at implementing relevant and
computationally hard problems in controllable quantum systems. Here we
demonstrate that in a trapped ion setup, with present day technology, it is
possible to realize a spin model of the Mattis type that exhibits spin glass
phases. Remarkably, our method produces the glassy behavior without the need
for any disorder potential, just by controlling the detuning of the spin-phonon
coupling. Applying a transverse field, the system can be used to benchmark
quantum annealing strategies which aim at reaching the ground state of the spin
glass starting from the paramagnetic phase. In the vicinity of a phonon
resonance, the problem maps onto number partitioning, and instances which are
difficult to address classically can be implemented.Comment: accepted version (11 pages, 7 figures
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