Light conversion studies

Finally, a promising trend in the study of the photoelectrochemical behavior of objects, whose nature is close to that of semiconductors, is related to photobiology, in particular to processes of light conversion in natural photosynthesizing objects. Certain elementary stages of photosynthesis, particularly photoelectrochemical ones, can, apparently, be simulated in some cases within the framework of the concepts of photoelectrochemistry of semiconductors. 

The equilibrium ortho-para conversion studies of Rosenbaum and Hogness originally appeared inconsistent with the work of Bodenstein since the equilibration of the nuclear spins took place much more rapidly than the Bodenstein rates. Sullivan has re-interpreted the conversion data in the light of parallel molecular and free radical mechanisms and shown it to be equivalent to the results of his experiments which were run far from chemical equilibrium. 

A We also have a new light source with interesting characteristics. It s only about 20 microns in size and produces light pulses as short as 10 picoseconds, with a repetition rate of hundreds of millions per second. The beam is incredibly stable. It doesn t need power because it uses a radionuclide, a self-contained energy source, and some form of light-conversion medium to change beta or alpha pulses into showers of photons. We use this to study ultrafast events, such as the rapid kinetic features of various chemical and physical processes. 

Many problems occur in Se-speciation analysis, owing e.g. to risks of adsorption on container walls, instability of species or contamination, insufficient separation efficiency of the chromatographic techniques, problems of conversion yield of selenite to selenate etc. Prior to conducting an interlaboratory project on this topic, it was hence decided to assess the stability of selenite and selenate according to various factors (effects of container materials, additives, temperature and light). The study focused on tests of effects of physicochemical parameters on solutions stored in polyethylene and PTFE containers. Container volumes were 100 and 500 mL for polyethylene and 500 and 1000 mL for PTFE. Stock and initial working solutions were prepared in 1 and 5 L polyethylene containers previously cleaned with nitric acid (at pH 2) and rinsed with Milli-Q water. The stock solutions were prepared with sodium selenite and sodium selenate (purity >98%). 

According to O Donnell et al. [130], the emulsion polymerization of vinyl acetate follows the Smith-Ewart theory of emulsion polymerization [131] because the rate of polymerization is independent of the total amount of monomer present, the rate is a function of the 0.6th power of the emulsifer concentration, and the rate of emulsion polymerization is a function of the 0.7th power of the initiator concentration instead of the expected 0.4th power. In this work poly(vinyl alcohol), 88% hydrolyzed with a medium molecular weight (i.e., Du Font s Elvanol 52-22), was used as the only externally added emulsifier. Light-scattering studies indicated that this emulsifier formed no aggregates in the aqueous solution. These latter observations may, however, have been made at room temperature and not at the reaction temperature [1]. The conversion versus time curve was essentially linear up to 80% conversion. 

The objectives of this study were 1) to examine the possibility that photoinhibitory reduction of photosynthetic CO2 assimilation occurs in over-wintering annual crops and 2) to examine whether photoinhibitory depression of photosynthesis at low temperatures in Z. mays and B. napus crops corresponds to significant depression of light conversion efficiency, and hence production, at the whole crop level. 

We have summarized below recent results concerning spectroscopic / flow reactor investigations of hydrocarbons partial and total oxidation on different transition metal oxide catalysts. The aim of this study is to have more information on the mechanisms of the catalytic activity of transition metal oxides, to better establish selective and total oxidation ways at the catalyst surface, and to search for partial oxidation products from light alkane conversion. 

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