Waveguides induced by screening-photovoltaic solitons in biased photorefractive-photovoltaic crystals

We investigate theoretically waveguides induced by screening-photovoltaic solitons in biased photorefractive-photovoltaic crystals. We show that the number of guided modes in a waveguide induced by a bright screening-photovoltaic soliton increases monotonically with the increasing intensity ratio of the soliton, which is the ratio between the peak intensity of the soliton and the dark irradiance. On the other hand, waveguides induced by dark screening-photovoltaic solitons are always single mode for all intensity ratios and the confined energy near the centre of a dark screening-photovoltaic soliton increases monotonically with the increasing intensity ratio. When the bulk photovoltaic effect is neglectable, these waveguides are those induced by screening solitons. When the external field is absent, these waveguides predict those induced by photovoltaic solitons.

A colorimetric assay for screening microcystin class compounds in aquatic systems

Secondary metabolites produced by water-blooming cyanobacteria in eutrophic waters include some potent hepatotoxins, These compounds also have tumour-promoting properties, attributable to their inhibition and activation of protein phosphatases and kinases respectively. The inhibitory effect of these toxins on protein phosphatases have been employed in a commonly used radiometric assay, involving the use of a P-32-labeled substrate, for the detection and quantitation of these compounds. This paper investigates and describes a colorimetric method in which the activity of protein phosphatase 2A is determined by measuring the rate of colour production from the release of yellow p-nitrophenol using p-nitrophenyl phosphate as the substrate. Results of this study suggest that the colorimetric protein phosphatase inhibition assay is a simple, inexpensive tool for screening substances that may have tumour-promoting characteristics in aquatic systems. The detection limit of the colorimetric method is comparable to the radiometric assay. (C) 1998 Elsevier Science Ltd. All rights reserved.

EFFECTIVE CAVITY LENGTH IN VERTICAL-CAVITY SURFACE-EMITTING LASER

Effective cavity length method is introduced to vertical cavity surface emitting laser for characterizing some properties, including reflectivity FWHM, mode wavelength and threshold gain. Some experiment results are demonstrated, showing the agreement of theoretical analysis with experiment.