Influence of surroundings on photorefractive effect in lithium niobate crystals

In the paper results of the investigation of the influence of electric properties of the environment surrounding LiNbO₃ crystals on photorefractive effect induced in these crystals by Gaussian Ar⁺ laser beam with various intensities are presented. We show spatial and temporal dependences of changes of the refractive index obtained experimentally in LiNbO₃: Fe and LiNbO₃: Fe:Mn samples surrounded by media with different electric conductivities and different permittivities (water, air, water solution of CaCl₂). The space and time dependences of the refractive index changes induced by the Ar⁺ laser beam are observed by means of the Mach–Zehnder interferometer using light from HeNe laser. The experimentally obtained results are in a good agreement with those following from numerical calculations using the manifold mirroring method. The agreement between calculated and experimental results indicates that the polarization charge at the photorefractive crystal/surrounding medium boundary significantly influences the photorefractive process in the crystal. The experimentally observed slow spontaneous decrease of the refractive index change in a sample placed into a slightly conducting medium (air) after switching off the beam also indicates that the polarization charge in the sample's surroundings affects the photorefraction.     

Isosteres of Natural Phosphates. Methylene and Hydroxyrnethylene Analogues of Tyrosine O-Phosphate

Abstract

The ability of phosphonic acid analogues isosteric with natural phosphate esters to Serve as inhibitors of enzymatic phosphate hydrolysis has been documented in a wide variety of systems.¹ The use of such an analogue in place of the natural phosphate ester provides a functionality which the enzyme may not be able to distinguish from the natural ester, but which is incapable of being hydrolyzed. In some instances the use of hydroxymethylene analogues has resulted in a greater degree of recognition, and resultant inhibition of hydrolytic activity, than the simple methylene analogues.² On this basis, the methylene and hydroxymethylene analogues of tyrosine O-phosphate appear to be reasonable candidates to Serve as inhibitors for phosphoprotein phosphatases and alkaline phosphatase, and as probes for biological mechanisms.     

An Anthracene-Based Metal-Organic Framework for Selective Photo-Reduction of Carbon Dioxide to Formic Acid Coupled with Water Oxidation

A Zr-based metal-organic framework has been synthesized and employed as a catalyst for photochemical carbon dioxide reduction coupled with water oxidation. The catalyst shows significant carbon dioxide reduction property with concomitant water oxidation. The catalyst has broad visible light as well as UV light absorption property, which is further confirmed from electronic absorption spectroscopy. Formic acid was the only reduced product from carbon dioxide with a turn-over frequency (TOF) of 0.69 h⁻¹ in addition to oxygen, which was produced with a TOF of 0.54 h⁻¹. No external photosensitizer is used and the ligand itself acts as the light harvester. The efficient and selective photochemical carbon dioxide reduction to formic acid with concomitant water oxidation using Zr-based MOF as catalyst is thus demonstrated here.     

Determination of boron and hydrogen in materials for multicrystalline solar cell production with prompt gamma activation analysis

Journal of Radioanalytical and Nuclear Chemistry - For the optimization of the manufacturing process of multicrystalline silicon (mc-Si) for solar cells in order to reduce energy consumption and...     

New examples of Beauville surfaces

We find new mixed and unmixed Beauville structures for groups constructed as 2-quotients, i.e. quotients of 2-power order, of the fundamental group of a certain simplicial complex.