Design of linear equalizers optimized for the structural similarity index.

We propose an algorithm for designing linear equalizers that maximize the structural similarity (SSIM) index between the reference and restored signals. The SSIM index has enjoyed considerable application in the evaluation of image processing algorithms. Algorithms, however, have not been designed yet to explicitly optimize for this measure. The design of such an algorithm is nontrivial due to the nonconvex nature of the distortion measure. In this paper, we reformulate the nonconvex problem as a quasi-convex optimization problem, which admits a tractable solution. We compute the optimal solution in near closed form, with complexity of the resulting algorithm comparable to complexity of the linear minimum mean squared error (MMSE) solution, independent of the number of filter taps. To demonstrate the usefulness of the proposed algorithm, it is applied to restore images that have been blurred and corrupted with additive white gaussian noise. As a special case, we consider blur-free image denoising. In each case, its performance is compared to a locally adaptive linear MSE-optimal filter. We show that the images denoised and restored using the SSIM-optimal filter have higher SSIM index, and superior perceptual quality than those restored using the MSE-optimal adaptive linear filter. Through these results, we demonstrate that a) designing image processing algorithms, and, in particular, denoising and restoration-type algorithms, can yield significant gains over existing (in particular, linear MMSE-based) algorithms by optimizing them for perceptual distortion measures, and b) these gains may be obtained without significant increase in the computational complexity of the algorithm.     

Nanoimprint lithography fabrication of waveguide-integrated optical gratings with inexpensive stamps

We demonstrate that a replica grating can be effectively used as an inexpensive stamp for nanoimprint lithography to pattern diffractive optical couplers integrated with planar optical waveguides. Imprinted grating patterns were integrated with silicon oxynitride waveguide films to be used as an evanescent wave sensor in the input grating-coupler configuration. An anti-adhesion layer using an inexpensive, two-step chemical functionalization was developed for the stamps. The stamps were able to withstand imprint temperatures ranging from 140 to 190 °C and high fidelity imprints were obtained. The groove pattern was integrated in waveguide films by etch transfer and light-coupling properties of gratings with 1.2 μm pitch were tested using a λ = 1.55 μm laser. Compared to etched silicon masters, replica optical gratings provide uniform pattern density over their entire surface with no unstructured regions, are inexpensive, and readily available for R&D use.     

Spatial firm competition in two dimensions with linear transportation costs: simulations and analytical results

Models of spatial firm competition assume that customers are distributed in space andtransportation costs are associated with their purchases of products from a small numberof firms that are also placed at definite locations. It has been long known that thecompetition equilibrium is not guaranteed to exist if the most straightforward lineartransportation costs are assumed. We show by simulations and also analytically that ifperiodic boundary conditions in a plane are assumed, the equilibrium exists for a pair offirms at any distance. When a larger number of firms is considered, we find that theirtotal equilibrium profit is inversely proportional to the square root of the number offirms. We end with a numerical investigation of the system’s behavior for a generaltransportation cost exponent.     

Simplification and analysis of a model of social interaction in voting

A recently proposed model of social interaction in voting is investigated by simplifyingit down into a version that is more analytically tractable and which allows a mathematicalanalysis to be performed. This analysis clarifies the interplay of the different elementspresent in the system – social influence, heterogeneity and noise – and leads to a betterunderstanding of its properties. The origin of a regime of bistability is identified. Theinsight gained in this way gives further intuition into the behaviour of the originalmodel.     

Precision branching ratio measurement for the superallowed beta+ emitter 62Ga and isospin-symmetry-breaking corrections in A>or=62 nuclei

A high-precision branching ratio measurement for the superallowed beta+ decay of 62Ga was performed at the Isotope Separator and Accelerator radioactive ion beam facility. Nineteen gamma rays emitted following beta+ decay of 62Ga were identified, establishing the dominant superallowed branching ratio to be (99.861+/-0.011)%. Combined with recent half-life and Q-value measurements, this branching ratio yields a superallowed ft value of 3075.6+/-1.4 s for 62Ga decay. These results demonstrate the feasibility of high-precision superallowed branching ratio measurements in the A>or=62 mass region and provide the first stringent tests of the large isospin-symmetry-breaking effects predicted for these decays.     

Aggregated colloids under flow

Summary We have recently reported on a new scaling theory of the rupture of colloid aggregates. The scaling theory is compared with a simulation study of the transient response of sheared 2d aggregates. In this paper we discuss the origins of deviations from the predicted scaling behaviour. We also report some of the steady-state configurations formed post rupture. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Up to 30 mW of broadly tunable CW green-to-orange light, based on sum-frequency mixing of Cr:forsterite and Nd:YVO4 lasers

Efficient generation of continuous-wave (CW) tunable light in the yellow region is reported. The method is based on sum-frequency mixing of a tunable Cr⁴⁺:forsterite laser with a Nd:YVO₄ laser. A periodically poled lithium niobate crystal was placed intra-cavity in a Nd:YVO₄ laser, and the Cr⁴⁺:forsterite laser was single-passed through the non-linear media. With this setup, it was possible to generate up to 3 mW of yellow light smoothly tunable from 573 to 587 nm. This is the highest output demonstrated to date for a tunable diode pumped solid-state CW laser in this wavelength region. The ways to improve the efficiency further are discussed.     

The linear noise approximation for reaction-diffusion systems on networks

Stochastic reaction-diffusion models can be analytically studied on complex networks using the linear noise approximation. This is illustrated through the use of a specific stochastic model, which displays travelling waves in its deterministic limit. The role of stochastic fluctuations is investigated and shown to drive the emergence of stochastic waves beyond the region of the instability predicted from the deterministic theory. Simulations are performed to test the theoretical results and are analyzed via a generalized Fourier transform algorithm. This transform is defined using the eigenvectors of the discrete Laplacian defined on the network. A peak in the numerical power spectrum of the fluctuations is observed in quantitative agreement with the theoretical predictions.     

An Improved Algorithm for the Multi-commodity Location Problem

Distribution systems designs commonly require the optimal location decisions of regional ware-houses or distribution centers which function as intermediate facilities between plants and customers. This paper deals with such a location problem in which the facilities can handle one of several commodities. We term this problem the multi-commodity facility location problem. A branch and bound algorithm is proposed for solving this problem. Improved bounds are developed for increasing the efficiency of the algorithm. Computational results are provided.