Ultraviolet light

About: Ultraviolet light is a research topic. Over the lifetime, 49494 publications have been published within this topic receiving 843151 citations.

Development of silica/vanadia/titania catalysts for removal of elemental mercury from coal-combustion flue gas.

Abstract: SiO2/V2O5/TiO2 catalysts were synthesized for removing elemental mercury (Hg0) from simulated coal-combustion flue gas. Experiments were carried out in fixed-bed reactors using both pellet and powder catalysts. In contrast to the SiO2-TiO2 composites developed in previous studies, the V2O5 based catalysts do not need ultraviolet light activation and have higher Hg0 oxidation efficiencies. For Hg0 removal by SiO2-V2O5 catalysts, the optimal V2O5 loading was found between 5 and 8%, which may correspond to a maximum coverage of polymeric vanadates on the catalyst surface. Hg0 oxidation follows an Eley-Rideal mechanism where HCI, NO, and NO2 are first adsorbed on the V2O5 active sites and then react with gas-phase Hg0. HCI, NO, and NO2 promote Hg oxidation, while SO2 has an insignificant effect and water vapor inhibits Hgo oxidation. The SiO2-TiO2-V2O5 catalysts exhibit greater Hg0 oxidation efficiencies than SiO2-V2O5, may be because the V-O-Ti bonds are more active than the V-O-Si bonds. This superior oxidation capability is advantageous to power plants equipped with wet-scrubbers where oxidized Hg can be easily captured. The findings in this work revealed the importance of optimizing the composition and microstructures of SCR (selective catalytic reduction) catalysts for Hg0 oxidation in coal-combustion flue gas.

Sealants Revisted: An Update of the Effectiveness of Pit-and-Fissure Sealants

Abstract: The first sealant clinical trials used cyanoacrylate-based materials. These were replaced by dimethacrylate-based products which were marketed. A major difference between marketed sealants is their method of polymerization. First-generation sealants were initiated by ultraviolet light, second-generation sealants are autopolymerized, and third-generation sealants use visible light. Over time, clinical retention was found to be greater for second generation as compared with first-generation sealants. Five to 7 years after initial application the pits and fissures of approximately one third of teeth treated with first-generation sealants were fully protected as compared with two thirds of the teeth treated with second-generation sealants. First-generation, ultraviolet light initiated, sealants are no longer marketed. Clinical reports indicate that retention is similar for second- and third-generation systems, but longer clinical evaluations are necessary. A recent innovation is the addition of fluoride to sealants. Fluoride release to the saliva from a fluoride sealant system is rapid, but clinical studies are needed to determine if the fluoride addition improves caries inhibition.

Neurofibrillary tangles in Niemann—Pick disease type C

Abstract: Post-mortem neuropathological examination of five cases of Niemann-Pick disease type C revealed neurofibrillary tangles in many parts of the brain. Tangles were a consistent finding in the hippocampus, hypothalamus, substantia innominata, midbrain pons and medulla. Other regions of the brain in which tangles were present included neocortex, basal ganglia, thalamus, cerebellar cortex in one case, and dentate nucleus in another. The tangles were argyrophilic, fluoresced under ultraviolet light when stained with thioflavin S, and reacted strongly with antibody to tau protein. Some of the tangles could be immunostained for ubiquitin. Electron microscopy, performed in one of the cases, showed the tangles to consist of paired helical filaments ultrastructurally identical to those of Alzheimer's disease. The distribution of the tangles in the central nervous system as a whole and also within many individual neurons corresponded fairly closely with that of the abnormal storage material. Both the tangles and the storage material extended into, and distended, the proximal parts of many dendrites and axons. No A4/beta protein, either in the form of plaques or in the walls of blood vessels, was detected in any of the cases. Our findings suggest that neurofibrillary tangles are a common feature of Niemann-Pick disease type C and that their formation may be a reaction to the abnormal storage material.