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Residual Impurities (residual + impurity)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Origin of asymmetric splitting of a neutral exciton in a single semiconductor quantum dot

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2006
I. Suemune
Abstract It is well-recognized that exciton-state energy splitting makes it difficult to generate entangled photon pairs (EPP) from a single quantum dot (QD). It will be shown that the splitting of the exciton states originates from not only QD anisotropy but also ionization of residual impurities. This result shows that the growth of highly pure barrier layers will be necessary for the generation of EPP. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Excitons in AgI,oxide particle composites: AgI,SrTiO3

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2006
Fumito Fujishiro
Abstract We fabricated (x)AgI,(1,x)SrTiO3 fine particle composites over a wide composition range of 0,100 mol% AgI. It is found that the dispersion of SrTiO3 fine particles enhances the ionic conductivity and (0.6)AgI,(0.4)SrTiO3 has the highest ionic conductivity (1.68 × 10,4 S/cm which is two hundreds times in comparison with that of pristine AgI), for the first time. In order to clarify such ionic conductivity enhanced by dispersing SrTiO3 fine particles into AgI, the photoluminescence measurements were carried out at different temperatures between 10 K and room temperature under different photoexcitation intensities, together with the structural and morphological studies (X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray fluorescence spectroscopy). The spectra consist of free exciton luminescence band and several broad luminescence bands due to the excitons trapped at crystal defects and residual impurities. The free exciton luminescence band almost disappears at x = 0.6, which may suggest the existence of considerable number of non-radiative traps (crystal defects) at the AgI/SrTiO3 particle interfaces. Such crystal defects may act as ionic pathways. The structural and morphological studies confirm the randomly-stacked ,AgI/,AgI heterostructures at the AgI/SrTiO3 particle interfaces. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effects of impurities on membrane-protein crystallization in different systems

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2009
Christopher A. Kors
When starting a protein-crystallization project, scientists are faced with several unknowns. Amongst them are these questions: (i) is the purity of the starting material sufficient? and (ii) which type of crystallization experiment is the most promising to conduct? The difficulty in purifying active membrane-protein samples for crystallization trials and the high costs associated with producing such samples require an extremely pragmatic approach. Additionally, practical guidelines are needed to increase the efficiency of membrane-protein crystallization. In order to address these conundrums, the effects of commonly encountered impurities on various membrane-protein crystallization regimes have been investigated and it was found that the lipidic cubic phase (LCP) based crystallization methodology is more robust than crystallization in detergent environments using vapor diffusion or microbatch approaches in its ability to tolerate contamination in the forms of protein, lipid or other general membrane components. LCP-based crystallizations produced crystals of the photosynthetic reaction center (RC) of Rhodobacter sphaeroides from samples with substantial levels of residual impurities. Crystals were obtained with protein contamination levels of up to 50% and the addition of lipid material and membrane fragments to pure samples of RC had little effect on the number or on the quality of crystals obtained in LCP-based crystallization screens. If generally applicable, this tolerance for impurities may avoid the need for samples of ultrahigh purity when undertaking initial crystallization screening trials to determine preliminary crystallization conditions that can be optimized for a given target protein. [source]

Renewable resources , green biorefinery: separation of valuable substances from fluid,fractions by means of membrane technology

BIOFUELS, BIOPRODUCTS AND BIOREFINING, Issue 1 2009
Senad Novalin
Abstract The aim of this study is to emphasize the potential of membrane technologies and the specific performance-limiting borders of pressure-driven (microfiltration, ultrafiltration, nanofiltration, reverse ssmosis) as well as electro-membrane (electrodialysis, electrodialysis using bipolar membranes) techniques for the separation of valuable substances from silage press-juice obtained in green biorefineries. Depending on the product, nanofiltration can be considered a partially fractionating technique with great future potential. Electrodialysis turns out to be a suitable separation technique for removing huge amounts of salt and isolating individual valuable substances. However, residual impurities must be taken into account for subsequent separation steps. In any case, further separation processes (e.g. chromatography) must be integrated in future green biorefinery production plants. © 2008 Society of Chemical Industry and John Wiley & Sons, Ltd [source]