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UV Wavelengths (uv + wavelength)
Selected AbstractsPhotocatalytic oxidation of methanol using silica-titania composites in a packed-bed reactorENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 4 2006Jennifer M. Stokke Abstract The processing of forest products into pulp, paper, paperboard, and other wood products results in the generation of volatile organic compounds (VOCs) and hazardous air pollutants (HAPs). This work focused on the development of a photocatalytic packed-bed reactor for the oxidation of methanol, which is the primary constituent in high volume low concentration gases emitted from pulp and paper mills. Bench-scale studies using an annular reactor packed with silica-titania composite (STC) pellets were conducted to maximize methanol removal and minimize the formation of byproducts, such as formaldehyde. Parameters such as STC pore size (ca. 40, 120, and 260 Å) and UV wavelength (UVA and UVC) were varied. In the dark, the STC pellets removed methanol via adsorption and had a finite adsorption capacity dependent on the surface area of the composite. When irradiated with UV light, the STC pellets adsorbed and oxidized methanol simultaneously. At the bench-scale, 40 Å STC pellets irradiated with UVC light achieved the greatest methanol removal (ca. 90%) with minimal byproduct formation (i.e., effluent formaldehyde concentration was <1 ppmv). Based on these results, a 40 acfm pilot reactor was fabricated and achieved methanol removal rates up to 66% ± 7% with <1 ppmv formaldehyde production at steady state. © 2006 American Institute of Chemical Engineers Environ Prog, 2006 [source] Kinetics of the gas-phase reactions of cyclo-CF2CFXCHXCHX , (X = H, F, Cl) with OH radicals at 253,328 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2009L. Chen Rate constants were determined for the reactions of OH radicals with halogenated cyclobutanes cyclo-CF2CF2CHFCH2(k1), trans -cyclo-CF2CF2CHClCHF(k2), cyclo-CF2CFClCH2CH2(k3), trans -cyclo-CF2CFClCHClCH2(k4), and cis -cyclo-CF2CFClCHClCH2(k5) by using a relative rate method. OH radicals were prepared by photolysis of ozone at a UV wavelength (254 nm) in 200 Torr of a sample reference H2OO3O2He gas mixture in an 11.5-dm3 temperature-controlled reaction chamber. Rate constants of k1 = (5.52 ± 1.32) × 10,13 exp[,(1050 ± 70)/T], k2 = (3.37 ± 0.88) × 10,13 exp[,(850 ± 80)/T], k3 = (9.54 ± 4.34) × 10,13 exp[,(1000 ± 140)/T], k4 = (5.47 ± 0.90) × 10,13 exp[,(720 ± 50)/T], and k5 = (5.21 ± 0.88) × 10,13 exp[,(630 ± 50)/T] cm3 molecule,1 s,1 were obtained at 253,328 K. The errors reported are ± 2 standard deviations, and represent precision only. Potential systematic errors associated with uncertainties in the reference rate constants could add an additional 10%,15% uncertainty to the uncertainty of k1,k5. The reactivity trends of these OH radical reactions were analyzed by using a collision theory,based kinetic equation. The rate constants k1,k5 as well as those of related halogenated cyclobutane analogues were found to be strongly correlated with their CH bond dissociation enthalpies. We consider the dominant tropospheric loss process for the halogenated cyclobutanes studied here to be by reaction with the OH radicals, and atmospheric lifetimes of 3.2, 2.5, 1.5, 0.9, and 0.7 years are calculated for cyclo-CF2CF2CHFCH2, trans -cyclo-CF2CF2CHClCHF, cyclo-CF2CFClCH2CH2, trans -cyclo-CF2CFClCHClCH2, and cis -cyclo-CF2CFClCHClCH2, respectively, by scaling from the lifetime of CH3CCl3. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 532,542, 2009 [source] Afterglow and thermally stimulated luminescence induced by UV radiation in CVD diamondPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2007M. Barboza-Flores Abstract Afterglow (AG) and thermoluminescence (TL) of CVD diamond UV-irradiated with wavelength of 200,260 nm at room temperature are reported. The AG curves monotonously decrease with time and are fitted well by the hyperbolic law. The decay times depends on UV wavelength and decreases with the AG intensity increasing. The TL glow curves exhibit two pronounced TL peaks with maxima at about 350 K and 513 K with unstructured signal between them and are fitted well by four TL peaks. The first, 350 K peak with the activation energy of 0.59 eV was supposed to be second kinetics order. The higher temperature peaks at 402 K, 445 K and 513 K with the activation energies of 0.46 eV, 0.49 eV and 0.68 eV, respectively were assumed to be first kinetics order. The comparison of the AG decay times with the kinetics parameters of the 350 K TL peak proved that AG is caused by thermal emptying of the traps responsible for the 350 K peak. The behaviour of AG and 350 K TL peak was described by the model, in which shallow traps, recombination centers and deep thermally disconnected traps are taken into account. The AG and TL creation spectra are practically the same and consists of a broad band, which exponentially increases from 260 nm, reaches a maximum at 240 nm and then begins decreasing. The creation spectra of the AG and TL peaks are the same and closely related with the fundamental absorption of UV light near indirect band gap of diamond. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Comparison between laser-induced nucleation of ZnS and CdS nanocrystals directly into polymer matricesPOLYMER COMPOSITES, Issue 6 2010Athanassia Athanassiou The nucleation of two kinds of crystalline nanoparticles, zinc sulfide (ZnS), and cadmium sulfide (CdS), is achieved directly into specific sites of polymer matrices after their irradiation with UV laser pulses. The starting samples consist of polymers doped with precursors of Zn or Cd thiolate that are proved to decompose after the absorption of UV light, resulting into the nanoparticles formation. The growth of the crystalline nanostructures is followed throughout the irradiation of the samples with successive incident pulses, by different methods, such as transmission electron microscopy, atomic force microscopy, confocal microscopy, and X-ray diffraction. Special attention is paid to the difference of the formation pathways of the two kinds of nanoparticles studied, because the Cd thiolate precursor exhibits much higher absorption efficiency than the Zn thiolate one, at the applied UV wavelength. Indeed, CdS nanoparticles become evident after the very first incident UV pulses, whereas the formation of ZnS nanocrystals requires rather prolonged irradiation, always through a macroscopically nondestructive procedure for the polymer matrix. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers [source] Preen waxes do not protect carotenoid plumage from bleaching by sunlightIBIS, Issue 2 2008ADRIAN SURMACKI The plumage coloration of wild birds often changes during the breeding season. One of the possible reasons for this is that sunlight, and particularly ultraviolet (UV) wavelengths, degrades the pigments responsible for plumage coloration. It has been suggested that birds may apply preen wax to feathers to protect feathers from bleaching. This hypothesis is tested by exposing carotenoid-based breast feathers of Great Tits to ambient light, light filtered to exclude UV and darkness. Preen waxes were experimentally removed from feather samples and the effect of light on coloration of treatment and control feathers compared. Ambient light had an effect on feather colour but preen wax did not. Feathers exposed to sun gradually became less saturated and hues shifted towards shorter wavelengths. This was not apparent in control feathers kept in darkness. Feathers exposed to full-spectra sunlight faded more than those that were kept in light with UV wavelengths removed. There was a decrease in brightness of feathers in both experimental and control groups, which was assumed to be an effect of dirt accumulation. This experiment confirmed earlier suspicions regarding the detrimental effects of UV irradiation on carotenoid-based coloration of avian feathers but failed to show any protective function of preen waxes. The possible consequences of these mechanisms of colour change for birds with regard to mating strategies are discussed. [source] Kinetics for the gas-phase reactions of OH radicals with the hydrofluoroethers CH2FCF2OCHF2, CHF2CF2OCH2CF3, CF3CHFCF2OCH2CF3, and CF3CHFCF2OCH2CF2CHF2 at 268,308 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2003L. Chen Rate constants were determined for the reactions of OH radicals with the hydrofluoroethers (HFEs) CH2FCF2OCHF2(k1), CHF2CF2OCH2CF3 (k2), CF3CHFCF2OCH2CF3(k3), and CF3CHFCF2OCH2CF2CHF2(k4) by using a relative rate method. OH radicals were prepared by photolysis of ozone at UV wavelengths (>260 nm) in 100 Torr of a HFE,reference,H2O,O3,O2,He gas mixture in a 1-m3 temperature-controlled chamber. By using CH4, CH3CCl3, CHF2Cl, and CF3CF2CF2OCH3 as the reference compounds, reaction rate constants of OH radicals of k1 = (1.68) × 10,12 exp[(,1710 ± 140)/T], k2 = (1.36) × 10,12 exp[(,1470 ± 90)/T], k3 = (1.67) × 10,12 exp[(,1560 ± 140)/T], and k4 = (2.39) × 10,12 exp[(,1560 ± 110)/T] cm3 molecule,1 s,1 were obtained at 268,308 K. The errors reported are ± 2 SD, and represent precision only. We estimate that the potential systematic errors associated with uncertainties in the reference rate constants add a further 10% uncertainty to the values of k1,k4. The results are discussed in relation to the predictions of Atkinson's structure,activity relationship model. The dominant tropospheric loss process for the HFEs studied here is considered to be by the reaction with the OH radicals, with atmospheric lifetimes of 11.5, 5.9, 6.7, and 4.7 years calculated for CH2FCF2OCHF2, CHF2CF2OCH2CF3, CF3CHFCF2OCH2CF3, and CF3CHFCF2OCH2CF2CHF2, respectively, by scaling from the lifetime of CH3CCl3. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 239,245, 2003 [source] A review of the background, operating parameters and applications of microemulsion liquid chromatography (MELC)JOURNAL OF SEPARATION SCIENCE, JSS, Issue 15 2005A. Marsh Abstract Microemulsions are dispersions of nanometre-sized droplets of an immiscible liquid within another liquid. Droplet formation is facilitated by the addition of surfactants and often also cosurfactants. Microemulsions are classified as either oil-in-water (O/W) (oil droplets such as octane dispersed throughout aqueous buffer) or water-in-oil (W/O) (aqueous droplets in oil such as hexane). Both microemulsion types have been used as mobile phases for separation in microemulsion HPLC (MELC). There has been a recent increase of interest in this area with new applications and developments such as gradient elution and optimisation of methods using experimental design. O/W microemulsions have been employed as eluents for RP-HPLC while W/O microemulsions have been used for normal phase chromatography. Separations can have superior speed and efficiency to conventional HPLC modes while offering a unique selectivity with excellent resolution. The capability for quantitative and stability-indicating analysis has also been demonstrated. Specific advantages include the ability to operate at low UV wavelengths and elimination of the need for an equilibration rinse between gradients. Operational issues associated with the use of MELC have been identified including the need to add salt to the gradient eluent, relatively high back-pressures and increased need for equipment cleaning compared to conventional RP eluent. This report details the different microemulsion types and compositions used and their reported applications. The use of gradient and isocratic elution is described. The effects on separations of varying operating parameters such as temperature, oil type and concentration, surfactant type and concentration, sample solvent, column type, and organic solvent addition will be discussed and illustrated. [source] UV laser ablation and plasma treatment of wooden surfaces , a comparing investigationLASER PHYSICS LETTERS, Issue 8 2006N. Mertens Abstract Using UV short-wavelength laser irradiation, the layer of mechanically damaged cells on wooden surfaces can be removed. Four excimer lasers (157 nm, 193 nm, 248 nm, 308 nm) were used to compare the ablation of wooden surfaces by different UV wavelengths. The ablation depth was measured by using optical microscopy. LV-SEM was applied to determine the appearance and quality of the laser ablation. In addition to the ablation process the laser can be used also to influence the surface energy. As the same effect can be achieved by plasma treatment of wooden surfaces, both methods were compared. The comparison was made by means of the water droplet test. The plasma treatment was carried out at atmospheric pressure as a dielectric barrier discharge. Two types of wood were determined: beech and thermowood beech. Thermowood is a heat treated lumber product especially made for outdoor applications. It was examined, whether the thermal treatment of wood influences the characteristic changes of the laser ablation and the plasma treatment. With the researched wavelengths, homogeneous ablation is possible. The absorption time can be reduced both with laser ablation and plasma treatment, whereas plasma treatment causes a stronger effect. A combined treatment improves the effect additionally. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] An Improved Algorithm for Satellite-derived UV Radiation,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2003Sigrid Wuttke ABSTRACT The improved algorithm surface irradiance derived from a range of satellite-based sensors (SIDES) is presented in this article. It calculates various types of surface UV intensities, such as biologically weighted or unweighted UV spectra, integrated doses or irradiance at specific wavelengths, using data from satellite instruments. These surface UV data are mainly useful for environmental impact or process studies where high accuracy or a high temporal resolution is required. In contrast to several previous studies, SIDES has been validated with spectral measurements. By this method an averaging of positive or negative deviations over the complete wavelength range is avoided. This is especially important for UV wavelengths around 300 nm where biological effectiveness is highest. The results of SIDES deviate less than 7% from ground-based observations for wavelengths between 295 and 400 nm. In contrast, the corresponding deviations of the joint research center algorithm escalate for shorter wavelengths, reaching 35% at 295 nm. This large deviation is due to an inaccurate interpolation procedure that has been detected by spectral analysis. Thus, spectral validation is demonstrated to be an appropriate tool to detect weaknesses in such an algorithm and provides information essential for improvement. [source] Comparison of broadband UVB, narrowband UVB, broadband UVA and UVA1 on activation of apoptotic pathways in human peripheral blood mononuclear cellsPHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 1 2007Chanisada Tuchinda Background/purpose: Ultraviolet (UV) radiation is an important therapy for immune-mediated cutaneous diseases. Activation of early apoptotic pathways may play a role in the clinical effectiveness. Different UV wavelengths have different efficacy for various diseases, but it remains unclear whether the ability to induce apoptosis differs with respect to the wavelength, and whether they induce apoptosis through the same mechanism. The aim of this study is to analyze the effects of different UV wavelengths that are used clinically on normal human peripheral blood mononuclear cells (PBMCs). Methods: PBMCs were treated with UV-light sources broadband UVB, narrowband UVB, broadband UVA and UVA1. Initiation of apoptosis was assessed by flow cytometry by staining,treated cells for activated caspases. Immunoblots were performed to measure for cleaved caspase-3, -8, -9, cytochrome c, Bcl 2-interacting domain and poly-(ADP ribose) polymerase cleavage. Results: We demonstrate that all the UV radiation sources induced caspase activation in a dose-and time-dependent manner. Components of both the extrinsic and intrinsic pathways of apoptosis were activated by all of the UV wavelengths tested, but differed in the level of energy needed for activation. Conclusion: The greater effectiveness of UVB on initiation of apoptotic pathway suggests that apoptosis may play a role in the clinical efficacy of UVB-responsive inflammatory cutaneous diseases. [source] 019 The COLIPA Standard for solar simulators failed to standardize sunscreen SPFSPHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 2 2002R.M. Sayre The COLIPA Standard for solar simulators was developed to insure that SPF tested in different laboratories was not different because of the solar simulator used. Indeed for products with lower SPFs 2-10, the solar simulator standard reasonably assures similar SPFs when tested in different laboratories. For products with SPFs greater than 15, the SPF for the same product could be tested at 15 in one laboratory but as an SPF 100 in another. Differences in SPF due to solar simulator filtration will occur only for sunscreen products that exhibit absorption like cut-off filters. Products which generally absorb all UV wavelengths equally will not exhibit differences in SPF due to solar simulator filtration. In addition because of different amounts of UVA allowed within the COLIPA standard, the actual response for a given exposure may in one laboratory produce persistent pigment darkening and in another a simple sunburn. Ways to correct this flaw will be examined. [source] Ultraviolet reflectance and cryptic sexual dichromatism in the ocellated lizard, Lacerta (Timon) lepida (Squamata: Lacertidae)BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2009ENRIQUE FONT Ultraviolet (UV) colorations have garnered extensive theoretical and empirical treatment in recent years, although the majority of studies have concerned themselves with avian taxa. However, many lizards have acute visual systems with retinal photoreceptors that are sensitive to UV wavelengths, and also display UV-reflecting colour patches. In the present study, we used UV photography and full-spectrum reflectance spectrophotometry to describe intra- and intersexual colour variation in adult ocellated lizards Lacerta (Timon) lepida and to obtain evidence of UV-based ornamentation. We also investigated whether any colour traits correlate with morphological traits potentially related to individual quality. The results obtained show that the prominent eyespots and blue outer ventral scales (OVS) that ocellated lizards have on their flanks reflect strongly in the UV range and are best described as UV/blue in coloration. The eyespots of males are larger and cover a larger surface area than those of females. However, these differences can be entirely accounted for by sex differences in body size, with males being generally larger than females. We also found differences in the shape of reflectance curves from males and females, with the eyespots and blue OVS of males being more UV-shifted than those of females. Other body regions have extremely low UV reflectance and are not sexually dichromatic. Eyespot size and the total surface area covered by eyespots increases with body size in males but not in females, suggesting that they may be signalling an intrinsic individual characteristic such as body size or male fighting ability. We also discuss the alternative and non-exclusive hypothesis that eyespots may function in lizards of both sexes as protective markings against predators. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 766,780. [source] | ||||||||||||||||