Reduction of Phenyl-Substituted Pyridinium Methoiodides with Sodium Borohydride. Formation of Amine-Borane Complexes in Water

Reduction of phenyl-substituted pyridinium methoiodides with sodium borohydride in water afforded besides the desired tetrahydropyridines substantial amounts of amine-borane complexes. Reduction in methanol afforded tetrahydropyridines in high yield, with almost no amine-boranes formed.     

Nonlinear spectral-spatial control and localization of supercontinuum radiation

We present the first observation of spatiospectral control and localization of supercontinuum light through the nonlinear interaction of spectral components in extended periodic structures. We use an array of optical waveguides in a LiNbO3 crystal and employ the interplay between diffraction and nonlinearity to dynamically control the output spectrum of the supercontinuum radiation. This effect presents an efficient scheme for optically tunable spectral filtering of supercontinua.     

Two-dimensional state-space discrete models for hyperbolic partial differential equations

It is shown that the finite difference technique can be used to transform some important linear distributed processes described by partial differential equations into so-called Roesser discrete state-space models. Two illustrative examples of numerical solutions are given and compared with exact solutions.     

Enhanced Ratiometric pH Sensing Using SNAFL-2 on Silver Island Films: Metal-enhanced Fluorescence Sensing

We have explored the opportunities for enhanced ratiometric pH sensing using the well-known carboxy seminaphthofluorescein (SNAFL-2) and silver island films (SiFs). Our results show that the metallic surfaces can provide up to a 40-fold increase in probe fluorescence intensity as compared to nonmetallic surfaces with the same probe coverage. However, while the S/N is significantly better for pH sensing, the emission wavelength ratiometric values are similar to that obtained in solution, due to the fact that the emission of both the acidic and basic forms of the probe are enhanced to similar extents. To the best of our knowledge this is the first report of enhanced ratiometric fluorescence sensing on metallic surfaces.     

Nonlinear BLOCH-wave interaction and bragg scattering in optically induced lattices

We study, both theoretically and experimentally, the Bragg scattering of light in optically induced photonic lattices and reveal the key physical mechanisms which govern the nonlinear self-action of narrow beams under the combined effects of Bragg scattering and wave diffraction, allowing for selecting bands with different effective dispersion.     

Calcium imaging using fluorescence lifetimes and long-wavelength probes

We describe imaging of calcium concentrations using the long-wavelength Ca²⁺ indicators, Calcium Green, Orange, and Crimson. The lifetimes of these probes were measured using the frequency-domain method and were found to increase from 50% to severalfold in response to calcium. The two-dimensional images of the calcium concentration were obtained using a new apparatus for fluorescence lifetime imaging (FLIM). We also describe procedures to correct for the position-dependent frequency response of the gain-modulated image intensifier used in the FLIM apparatus. Importantly, the FLIM method does not require the probe to display shifts in the excitation or emission spectra. Using the FLIM method, calcium imaging is possible using probes which display changes in lifetime in response to calcium. Consequently, calcium imaging is possible with excitation wavelengths ranging from 488 to as long as 620 nm, where autofluorescence and/or photochemical damage is minimal. These probes are also suitable for calcium measurements of single cells using lifetime-based flow cytometry.     

An efficient algorithm for a job shop problem

We study the problem of minimizing makespan in a two-machine job shop with unit processing time operations. An efficient algorithm with respect to a succinct encoding of the problem instances is proposed. The algorithm is an improvement of earlier algorithms proposed for the problem by Brucker [1,2], Hefetz and Adiri [7], and Timkovskiy [15]. The idea behind the algorithm has the potential of extension to job shops with parallel machines.This research is supported in part by NSERC Grants A4619, OGP0105675, OGP0104900, General Motors of Canada, and the Manufacturing Research Corporation of Ontario.     

Synthesis and 1H NMR characterization of substituted 1-amino-9-imino-4-nitro-9,10-dihydr oacridines as potential antitumor agents

A convenient method for the synthesis of unsubstituted and substituted 1-amino-9-imino-4-nitro-9,10-dihydroacridines, 9 and 10 , respectively, is reported. Their ¹H nmr data are reported and discussed in order to confirm the imino tautomeric structure.     

Observation of nonlinear self-trapping in triangular photonic lattices

We experimentally study light self-trapping in triangular photonic lattices induced optically in nonlinear photorefractive crystals. We observe the formation of two-dimensional discrete and gap spatial solitons originating from the first and second bands of the linear transmission spectrum.