Topic
Ultraviolet light
About: Ultraviolet light is a research topic. Over the lifetime, 49494 publications have been published within this topic receiving 843151 citations.
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TL;DR: It is shown that ultraviolet absorption by steady-state amounts of high-altitude organic solids produced from methane photolysis may have shielded ammonia sufficiently that ammonia resupply rates were able to maintain surface temperatures above freezing.
Abstract: Atmospheric mixing ratios of approximately 10(-5 +/- 1) for ammonia on the early Earth would have been sufficient, through the resulting greenhouse warming, to counteract the temperature effects of the faint early sun. One argument against such model atmospheres has been the short time scale for ammonia photodissociation by solar ultraviolet light. Here it is shown that ultraviolet absorption by steady-state amounts of high-altitude organic solids produced from methane photolysis may have shielded ammonia sufficiently that ammonia resupply rates were able to maintain surface temperatures above freezing.
354 citations
TL;DR: The photocatalytic activity of doped nanocrystalline titanium dioxide with mixed anatase/rutile phases exceeds that of commercial TiO2 photocatalyst Degussa P-25 for water splitting into H2 and O2 under ultraviolet light as discussed by the authors.
Abstract: Bromine and chlorine co-doped nanocrystalline titanium dioxide are synthesized by a hydrothermal method using titanium chloride in a mixed hydrobromic acid−ethanol system. TiO2 with anatase, mixed anatase/rutile, rutile, mixed rutile/brookite, mixed anatase/rutile/brookite, and rutile phases are obtained, in that order, by increasing the acidity through addition of HBr. Br- and Cl- co-doping causes the absorption edge of TiO2 to shift to a lower energy region. The photocatalytic activity of doped TiO2 with mixed anatase/rutile phases exceeds that of commercial TiO2 photocatalyst Degussa P-25 for water splitting into H2 and O2 under ultraviolet light.
353 citations
TL;DR: The attractive fuel-free propulsion performance, fast movement triggering response, low light energy requirement, and precise motion control of the TiO2-Au Janus photocatalytic micromotor hold considerable promise for diverse practical applications.
Abstract: A highly efficient light-driven photocatalytic TiO2–Au Janus micromotor with wireless steering and velocity control is described. Unlike chemically propelled micromotors which commonly require the addition of surfactants or toxic chemical fuels, the fuel-free Janus micromotor (diameter ∼1.0 μm) can be powered in pure water under an extremely low ultraviolet light intensity (2.5 × 10–3 W/cm2), and with 40 × 10–3 W/cm2, they can reach a high speed of 25 body length/s, which is comparable to common Pt-based chemically induced self-electrophoretic Janus micromotors. The photocatalytic propulsion can be switched on and off by incident light modulation. In addition, the speed of the photocatalytic TiO2–Au Janus micromotor can be accelerated by increasing the light intensity or by adding low concentrations of chemical fuel H2O2 (i.e., 0.1%). The attractive fuel-free propulsion performance, fast movement triggering response, low light energy requirement, and precise motion control of the TiO2–Au Janus photocataly...
353 citations
TL;DR: Evidence is provided that human keratinocytes produce POMC-derived peptides such as alpha MSH and ACTH, which have been recognized as potent immunomodulatory mediators and may have a major impact on the skin immune system.
Abstract: Proopiomelanocortin (POMC), the precursor for melanotropic, corticotropic, and opioid peptides such as alpha-melanocyte-stimulating hormone (alpha MSH), ACTH, and other related peptides, was originally identified as a product of the pituitary gland. However, recent evidence shows that POMC products can also be produced by nonpituitary tissues. Because keratinocytes, the major constituent of the epidermis exhibit the capacity to release a variety of proinflammatory and immunomodulatory mediators, the present study was performed to investigate whether human keratinocytes are able to produce POMC-derived peptides. Supernatants of human normal keratinocytes and an epidermal carcinoma cell line (A431) contained significant levels of immunoreactive alpha MSH and ACTH. Upon immuneprecipitation and size-exclusion chromatography, keratinocyte-derived alpha MSH exhibited a molecular mass of approximately 1 kD and was biologically active as demonstrated in a tyrosinase bioassay. Northern blot analysis revealed the expression of POMC-specific transcripts (1.3 kb) in both normal keratinocytes and A431 cells. The production of alpha MSH and ACTH could be significantly upregulated both at the protein and mRNA level upon treatment with phorbol myristate acetate, ultraviolet light, or interleukin 1. These data provide first evidence that human keratinocytes produce POMC-derived peptides such as alpha MSH and ACTH. Because POMC-derived peptides recently have been recognized as potent immunomodulatory mediators, their presence in the epidermis may have a major impact on the skin immune system.
352 citations
TL;DR: Predicted and measured UV filter concentrations were compared in a regional mass balance study for two Swiss lakes, confirming the presence of the compounds in surface waters and indicating a certain potential for bioaccumulation.
352 citations