A boundary only procedure for time-dependent diffusion equations

In the recent literature, the boundary element method (BEM) is extensively used to solve time-dependent partial differential equations. However, most of these formulations yield algorithms where one has to include all interior points in the computation process if finite difference procedures are used to approximate the temporal derivative. This obviously restricts the advantages of the BEM, which is mainly considered to be a boundary only algorithm for time-independent problems. A new algorithm is demonstrated here, which extends the boundary only nature of the method to time-dependent partial differential equations. Using this procedure, one can reduce the finite difference time integration algorithm, generated in a standard manner, to a boundary only process. The proposed method is demonstrated with considerable success for diffusion problems. Results obtained in these applications are presented comparatively with analytical and other boundary element time integration procedures. The algorithm proposed may utilize several coordinate functions in the secondary reduction phase of the formulation. A summary of such functions is described here and performances of these functions are tested and compared in three applications. It is shown that some coordinate functions perform better than others under certain conditions. Using these results, we propose a general coordinate function, which may be used with satisfactory results in all parabolic partial differential equation applications.     

Photophysical and photochemical study of laser-dye coumarin-481 and its photoproduct in solution

An ultraviolet light-induced photophysical and Photochemical changes of coumarin-481 in cyclohexane have been studied by photolysis technique at room temperature, due to its potential applications in photonics, photochemistry, and electronic spectroscopy. During the optical pumping, coumarin-481 showed photochemical changes, therefore as the concentration of coumarin-481 decreased, a photoproduct concentration increased rapidly. An absorption band of the product was observed at around 250 nm. Photoproduct emission spectra characteristics show that photoproduct molecules can also be used as a laser-dye at different emission frequency.     

Calculation of charge vibration in fission with Strutinsky shell correction

The Strutinsky shell correction method has been applied to the two spheroid model to study charge vibrations in fission. The investigation is carried out by calculating the potential energy surface with respect to three degrees of freedom: charge vibration from the uniform value and the deformations of the two fragments. The results suggest that the effect of shells at Z = 50 and N = 82 do not cause large deviations from the liquid drop model charge density around mass 132; their effect is much more pronounced in the fragment excitation energy. The results also suggest that the fragment excitation and kinetic energies for a given mass ratio are markedly charge density dependent. Some features inherent to this treatment with respect to characteristic periods of individual degrees of freedom have been discussed.     

Induced supercontinuum and steepening of an ultrafast laser pulse

The problem of the propagation of an intense ultrashort pulse in a cubic (χ³) nonlinear medium is generalized to include coupling between the primary and second harmonics signals. It is shown that the presence of a strong primary signal induces the superbroadening of the spectrum of a weak second harmonic signal and the deformation of its pulse shape.     

A Long Wavelength Excitable Fluorophore; Chloro Phenyl Imino Propenyl Aniline (CPIPA) for Selective Sensing of Hg (II)

In this study, a very sensitive and highly selective irreversible optical chemical sensor (optode) for mercury ions was described. The sensing scheme was based on the interaction of Hg (II) with a newly synthesized fluoroionophore; chloro phenyl imino propenyl aniline (CPIPA) in plasticized PVC membrane. The sensor membranes were tested for the determination of mercury ion in aqueous solutions by batch and flow-through methods. The optodes allow determination of Hg (II) in the working range of 1.0 × 10⁻⁹–1.0 × 10⁻⁵ M with a detection limit of 4.3 ppb. The sensor exhibited excellent selectivity for Hg (II) with respect to several common alkali, alkaline earth and transition metal ions. The association constant of the 1:1 complex formation for Hg (II) was found to be K_a = 1.86 × 10⁵ M⁻¹. The CPIPA exhibited high fluorescence quantum yield, long excitation and emission wavelength and high Stokes’ shift values in the solid matrix which makes it compatible with solid state optics.     

Evaluation of micro-bubble size and gas hold-up in two-phase gas-liquid columns via scattered light measurements

In this paper, potential use of an elliptically polarized light scattering (EPLS) method to monitor both bubble size and gas hold-up in a bubble-laden medium is explored. It is shown that with the use of the new EPLS system, normalized scattering matrix elements (M_ij's) measured at different side and back-scattering angles can be used to obtain the desired correlations between the bubble sizes and input flow parameters for a gas-liquid (GL) column, including gas flow rate and surfactant concentrations. The bubble size distributions were first evaluated experimentally using a digital image processing system for different gas flows and surfactant concentrations. These images showed that the bubbles were not necessarily spherical. We investigated the possibility of modeling the bubbles as effective spheres. The scattering matrix elements were calculated using the Lorenz-Mie theory and the results were compared against the experimentally determined values. It was observed that the change in the bubble size yields significant changes in M₁₁, M₃₃, M₄₄, and M₃₄ profiles. An optimum single measurement angle of θ=120^° was determined for a gas velocity range of 0.04-0.35 cm/s (). The choice of the optimum angle depends on frit pore size, column diameter, gas pressure, and surfactant concentration. These results suggest that a simplified version of the present EPLS system can effectively be used as a two-phase flow sensor to monitor bubble size and liquid hold-up in industrial systems.     

High-resolution discrete absorption spectrum of alpha-methallyl free radical in the vapor phase

The alpha-methallyl free radical is formed in the flash photolysis of 3-methylbut-1-ene, and cis-pent-2-ene in the vapor phase, and then subsequent reactions have been investigated by kinetic spectroscopy and gas-liquid chromatography. The photolysis flash was of short duration and it was possible to follow the kinetics of the radicals' decay, which occurred predominantly by bimolecular recombination. The measured rate constant for the alpha-methallyl recombination was (3.5+/-0.3) x 10(10) mol(-1) ls(-1) at 295+/-2K. The absolute extinction coefficients of the alpha-methallyl radical are calculated from the optical densities of the absorption bands. Detailed analysis of related absorption bands and lifetime measurements in the original alpha-methallyl high-resolution discrete absorption spectrum image were also carried out by image processing techniques.     

Multiplex identification of bacteria in bacterial mixtures with surface‐enhanced Raman scattering

Surface‐enhanced Raman scattering (SERS) is a technique capable of identifying each component in a mixture because of its intrinsically narrow spectral bands. In a clinical setting, the identification of bacteria from its initial culture by collecting the colonies on the culture plate significantly decreases the analysis time and the cost. The identification of bacteria from their mixtures is attempted using SERS. A simple mixing procedure of bacterial samples and concentrated colloidal suspension is proven to be mostly satisfactory for the generation of the reproducible SERS spectra that can be used for bacterial identification. The mixture of three different but related bacterial species Shigella sonnei, Proteus vulgaris, and Erwinia amylovara and three Escherichia coli strains (BFK13, BHK7, DH5 α) are used as model systems to test the feasibility of the approach. The results indicate that it is possible to identify the composition of a bacterial mixture. This approach can easily be utilized for the bacteria originating from the same source with similar growth profiles. Copyright © 2009 John Wiley & Sons, Ltd.