Ultraviolet light

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

The thymine-thymine pyrimidine-pyrimidone(6-4) ultraviolet light photoproduct is highly mutagenic and specifically induces 3' thymine-to-cytosine transitions in Escherichia coli.

Abstract: We have constructed single-stranded, M13-based vectors that contain a specifically located thymine-thymine pyrimidine-pyrimidone(6-4) UV photoproduct and have used these to estimate the frequency and accuracy of DNA replication past this adduct in uvrA6 cells of Escherichia coli. Both the normal and the Dewar valence photoisomer of the (6-4) adduct were studied. In the absence of SOS induction, vectors carrying the photoproducts were rarely replicated; relative to the lesion-free control, 1.9% of vectors carrying the normal (6-4) isomer produced plaques, and with the Dewar valence isomer the proportion was 0.4%. In SOS-induced cells, these frequencies rose to 22.1% and 12.3%, respectively. The error frequency of replication past the normal isomer in SOS-induced cells was high; in a random sample of 185 progeny phage analyzed, 169 (91%) contained mutations, all of which were targeted. Equally striking, a high proportion of the mutations (158/169; 93%) were of only one type, namely 3' T----C transitions. Both the error frequency and the specificity were much reduced with the Dewar valence isomer; overall, 74/140 (53%) of the phage analyzed were mutant, and of these only 34 (46%) entailed the 3' T----C transition. We speculate that the high error frequency and specificity arise from the formation of a stable T-G base pair, involving hydrogen bonds at O-2 and N-3 in the pyrimidone ring. Potential hydrogen bonds at these sites are coplanar in the normal but not in the Dewar isomer, perhaps explaining the reduced specificity of mutagenesis with the latter adduct.

Repair of ultraviolet light damage in a variety of human fibroblast cell strains.

Abstract: Postreplication repair of DNA damage after ultraviolet light irradiation has been examined in a wide variety of human fibroblast strains. The donors were patients with xeroderma pigmentosum (XP) of different complementation groups or other hereditary disorders with indications of radiosensitivity, or with light sensitivity or multiple cancers. The defect in postreplication repair previously found in XP variants (excision-proficient XP's) has now been observed in a total of five XP variants and a less severe defect in postreplication repair has been found in excision-defective XP's in Complementation Groups A, B, C, and D. Complementation Group E and all other cell strains studied showed a response that was not significantly different from that of cells from normal donors. Excision repair was also measured in some of these cell strains and was found to be defective only in XP cells. Ultraviolet cell survival characteristics have been obtained for may of the cell strains. The most sensitive were cells from the excision-deficient XP's and from a sun-sensitive child (11961); the latter had no measurable defect in either excision or postreplication repair. The rest of the survival curves lay in a band limited by normal cell strains on the one hand and the slightly more sensitive excision-proficient XP variant XP30RO. Only in the case of the variants XP30RO and XP7TA were we able to demonstrate any influence of caffeine on cell survival.

Y 3Al5 O 12 : Ce0.05 Phosphor Coatings on Gallium Nitride for White Light Emitting Diodes

Abstract: White light was obtained by mixing blue light from the emission of a gallium nitride (GaN) chip and yellow light from the fluorescence of a Y 3 Al 5 O 12 :Ce 0.05 yellow phosphor. A uniform coating and an optimized thickness of yellow phosphor layer on a GaN chip were necessary for achieving an efficient white light emitting diode. The phosphor particles were coated on a GaN chip or indium tin oxide by several methods including the slurry method, the settling method, and electrophoretic deposition (EPD). The properties of the phosphor layers prepared by these methods were examined using scanning electron microscope and photoluminescence. The chromaticity of white light was dependent upon the thickness of the phosphor layer. The properties of the phosphor layer prepared by EPD such as packing density, thickness, and uniformity could be more easily controlled than those by the slurry and settling methods. Further high packing density of the EPD could compensate for the typical thick phosphor layer, allowing the thin layer to be fabricated. To overcome the weak adhesion strength of phosphor particles by the EPD, an aqueous solution including poly(vinyl alcohol) + ammonium dichromate was coated on the phosphor layer and cured by exposure to ultraviolet light.

Method of fabricating Bragg gratings using a silica glass phase grating mask and mask used by same

Abstract: An index grating is imprinted in the core of an optical fiber using a specially designed silica glass phase grating mask The phase mask is held in close proximity to the optical fiber Laser irradiation of the phase mask with ultraviolet light at normal incidence imprints (photoinduces) into the optical fiber core the interference pattern created by the phase mask