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Sample records for actual photochemical efficiency

  1. on the growth and photochemical efficiency of Acropora cervicornis

    NASA Astrophysics Data System (ADS)

    Enochs, I. C.; Manzello, D. P.; Carlton, R.; Schopmeyer, S.; van Hooidonk, R.; Lirman, D.

    2014-06-01

    The effects of light and elevated pCO2 on the growth and photochemical efficiency of the critically endangered staghorn coral, Acropora cervicornis, were examined experimentally. Corals were subjected to high and low treatments of CO2 and light in a fully crossed design and monitored using 3D scanning and buoyant weight methodologies. Calcification rates, linear extension, as well as colony surface area and volume of A. cervicornis were highly dependent on light intensity. At pCO2 levels projected to occur by the end of the century from ocean acidification (OA), A. cervicornis exhibited depressed calcification, but no change in linear extension. Photochemical efficiency ( F v / F m ) was higher at low light, but unaffected by CO2. Amelioration of OA-depressed calcification under high-light treatments was not observed, and we suggest that the high-light intensity necessary to reach saturation of photosynthesis and calcification in A. cervicornis may limit the effectiveness of this potentially protective mechanism in this species. High CO2 causes depressed skeletal density, but not linear extension, illustrating that the measurement of extension by itself is inadequate to detect CO2 impacts. The skeletal integrity of A. cervicornis will be impaired by OA, which may further reduce the resilience of the already diminished populations of this endangered species.

  2. Mechanistic details for cobalt catalyzed photochemical hydrogen production in aqueous solution: Efficiencies of the photochemical and non-photochemical steps

    SciTech Connect

    Shan, Bing; Baine, Teera; Ma, Xuan Anh N.; Zhao, Xuan; Schmehl, Russell H.

    2013-04-17

    The use of sunlight to drive chemical reactions that lead to the reduction of water to produce hydrogen is a potential avenue of solar energy utilization. There are many individual steps that take place in this process. This paper reports the investigation of a particular system that involves light absorbing molecules, electron donating agents and a catalyst for water reduction to hydrogen. We evaluated the efficiency of the light induced formation of a strong electron donor, the use of this donor to reduce the catalyst and finally the efficiency of the catalyst to produce hydrogen from water. From this, the sources of loss of efficiency could be clearly identified and used in the design of better systems to produce hydrogen from water.

  3. Mechanistic details for cobalt catalyzed photochemical hydrogen production in aqueous solution: Efficiencies of the photochemical and non-photochemical steps

    DOE PAGES

    Shan, Bing; Baine, Teera; Ma, Xuan Anh N.; ...

    2013-04-17

    The use of sunlight to drive chemical reactions that lead to the reduction of water to produce hydrogen is a potential avenue of solar energy utilization. There are many individual steps that take place in this process. This paper reports the investigation of a particular system that involves light absorbing molecules, electron donating agents and a catalyst for water reduction to hydrogen. We evaluated the efficiency of the light induced formation of a strong electron donor, the use of this donor to reduce the catalyst and finally the efficiency of the catalyst to produce hydrogen from water. From this, themore » sources of loss of efficiency could be clearly identified and used in the design of better systems to produce hydrogen from water.« less

  4. [Effects of NO3- stress on photosynthetic rate, photochemical efficiency of PS II and light energy allocation in cucumber seedling leaves].

    PubMed

    Su, Xiu-Rong; Wang, Xiu-Feng; Yang, Feng-Juan; Wei, Min

    2007-07-01

    This paper studied the effects of different NO3- concentration on the photosynthetic rate, photochemical efficiency, and absorbed light energy allocation in cucumber seedling leaves. The results indicated that when the available NO3- concentration in the medium was low (14-98 mmol NO3- x L(-1)), an appropriate supplement of NO3- could enhance the capability of cucumber leaves in capturing light energy, and promote the photosynthesis. However, with further increase of NO3-, the photochemical efficiency of PS II decreased, electron transfer restrained, and net photosynthetic rate as well as the absorbed light energy used in photochemical reaction of PS II decreased. At the same time, the light energy used in antenna heat dissipation increased, while the photochemical efficiency decreased. After treated with 140 and 182 mmol NO3- x L(-1) for 6 days, the photosynthetic rate (P(n)) was decreased by 35% and 78%, respectively, maximal PS II efficiency at open centers in the absence of NPQ (F(v)/F(m)), antenna efficiency at open centers in the presence of NPQ (F(v)'/F(m)'), actual PS II efficiency (phi (PSII ) and photochemical quenching (q(P)) were lower, non-photochemical quenching (NPQ) was higher, and the deviation from full balance between PS I and PS II (beta/alpha - 1) was improved significantly, compared with the control. The fluctuant ranges of these chlorophyll fluorescence parameters were increased at higher NO3- concentration, compared with those at lower NO3- concentration. The absorbed light energy allocated to the photochemical reaction of PS II (P) was reduced by high light intensity and high NO3- concentration. Meanwhile, the proportion allocated in antenna heat dissipation (D) increased significantly. Antenna heat dissipation was the main way for excessive energy dissipation.

  5. Efficient, Mg(2+)-dependent photochemical DNA cleavage by the antitumor quinobenzoxazine (S)-A-62176.

    PubMed

    Yu, H; Kwok, Y; Hurley, L H; Kerwin, S M

    2000-08-22

    The quinobenzoxazines, a group of structural analogues of the antibacterial fluoroquinolones, are topoisomerase II inhibitors that have demonstrated promising anticancer activity in mice. It has been proposed that the quinobenzoxazines form a 2:2 drug-Mg(2+) self-assembly complex on DNA. The quinobenzoxazine (S)-A-62176 is photochemically unstable and undergoes a DNA-accelerated photochemical reaction to afford a highly fluorescent photoproduct. Here we report that the irradiation of both supercoiled DNA and DNA oligonucleotides in the presence of (S)-A-62176 results in photochemical cleavage of the DNA. The (S)-A-62176-mediated DNA photocleavage reaction requires Mg(2+). Photochemical cleavage of supercoiled DNA by (S)-A-62176 is much more efficient that the DNA photocleavage reactions of the fluoroquinolones norfloxacin, ciprofloxacin, and enoxacin. The photocleavage of supercoiled DNA by (S)-A-62176 is unaffected by the presence of SOD, catalase, or other reactive oxygen scavengers, but is inhibited by deoxygenation. The photochemical cleavage of supercoiled DNA is also inhibited by 1 mM KI. Photochemical cleavage of DNA oligonucleotides by (S)-A-62176 occurs most extensively at DNA sites bound by drug, as determined by DNase I footprinting, and especially at certain G and T residues. The nature of the DNA photoproducts, and inhibition studies, indicate that the photocleavage reaction occurs by a free radical mechanism initiated by abstraction of the 4'- and 1'-hydrogens from the DNA minor groove. These results lend further support for the proposed DNA binding model for the quinobenzoxazine 2:2 drug-Mg(2+) complex and serve to define the position of this complex on the minor groove of DNA.

  6. Intraspecific Variation in Pinus Pinaster PSII Photochemical Efficiency in Response to Winter Stress and Freezing Temperatures

    PubMed Central

    Corcuera, Leyre; Gil-Pelegrin, Eustaquio; Notivol, Eduardo

    2011-01-01

    As part of a program to select maritime pine (Pinus pinaster Ait.) genotypes for resistance to low winter temperatures, we examined variation in photosystem II activity by chlorophyll fluorescence. Populations and families within populations from contrasting climates were tested during two consecutive winters through two progeny trials, one located at a continental and xeric site and one at a mesic site with Atlantic influence. We also obtained the LT50, or the temperature that causes 50% damage, by controlled freezing and the subsequent analysis of chlorophyll fluorescence in needles and stems that were collected from populations at the continental trial site. P. pinaster showed sensitivity to winter stress at the continental site, during the colder winter. The combination of low temperatures, high solar irradiation and low precipitation caused sustained decreases in maximal photochemical efficiency (Fv/Fm), quantum yield of non-cyclic electron transport (ΦPSII) and photochemical quenching (qP). The variation in photochemical parameters was larger among families than among populations, and population differences appeared only under the harshest conditions at the continental site. As expected, the environmental effects (winter and site) on the photochemical parameters were much larger than the genotypic effects (population or family). LT50 was closely related to the minimum winter temperatures of the population's range. The dark-adapted Fv/Fm ratio discriminated clearly between interior and coastal populations. In conclusion, variations in Fv/Fm, ΦPSII, qP and non-photochemical quenching (NPQ) in response to winter stress were primarily due to the differences between the winter conditions and the sites and secondarily due to the differences among families and their interactions with the environment. Populations from continental climates showed higher frost tolerance (LT50) than coastal populations that typically experience mild winters. Therefore, LT50, as

  7. Intraspecific variation in Pinus pinaster PSII photochemical efficiency in response to winter stress and freezing temperatures.

    PubMed

    Corcuera, Leyre; Gil-Pelegrin, Eustaquio; Notivol, Eduardo

    2011-01-01

    As part of a program to select maritime pine (Pinus pinaster Ait.) genotypes for resistance to low winter temperatures, we examined variation in photosystem II activity by chlorophyll fluorescence. Populations and families within populations from contrasting climates were tested during two consecutive winters through two progeny trials, one located at a continental and xeric site and one at a mesic site with Atlantic influence. We also obtained the LT₅₀, or the temperature that causes 50% damage, by controlled freezing and the subsequent analysis of chlorophyll fluorescence in needles and stems that were collected from populations at the continental trial site.P. pinaster showed sensitivity to winter stress at the continental site, during the colder winter. The combination of low temperatures, high solar irradiation and low precipitation caused sustained decreases in maximal photochemical efficiency (F(v)/F(m)), quantum yield of non-cyclic electron transport (Φ(PSII)) and photochemical quenching (qP). The variation in photochemical parameters was larger among families than among populations, and population differences appeared only under the harshest conditions at the continental site. As expected, the environmental effects (winter and site) on the photochemical parameters were much larger than the genotypic effects (population or family). LT₅₀ was closely related to the minimum winter temperatures of the population's range. The dark-adapted F(v)/F(m) ratio discriminated clearly between interior and coastal populations.In conclusion, variations in F(v)/F(m), Φ(PSII), qP and non-photochemical quenching (NPQ) in response to winter stress were primarily due to the differences between the winter conditions and the sites and secondarily due to the differences among families and their interactions with the environment. Populations from continental climates showed higher frost tolerance (LT₅₀) than coastal populations that typically experience mild winters

  8. [PS II photochemical efficiency in flag leaf of wheat varieties and its adaptation to strong sun- light intensity on farmland of Xiangride in Qinghai Province, Northwest China].

    PubMed

    Shi, Sheng-Bo; Chen, Wen-Jie; Shi, Rui; Li, Miao; Zhang, Huai-Gang; Sun, Ya-Nan

    2014-09-01

    Taking four wheat varieties developed by Northwest Institute of Plateau Biology, Chinese Academy of Sciences, as test materials, with the measurement of content of photosynthetic pigments, leaf area, fresh and dry mass of flag leaf, the PS II photochemistry efficiency of abaxial and adaxial surface of flag leaf and its adaptation to strong solar radiation during the period of heading stage in Xiangride region were investigated with the pulse-modulated in-vivo chlorophyll fluorescence technique. The results indicated that flag leaf angle mainly grew in horizontal state in Gaoyuan 314, Gaoyuan 363 and Gaoyuan 584, and mainly in vertical state in Gaoyuan 913 because of its smaller leaf area and larger width. Photosynthetic pigments were different among the 4 varieties, and positively correlated with intrinsic PS II photochemistry efficiencies (Fv/Fm). In clear days, especially at noon, the photosynthetic photoinhibition was more serious in abaxial surface of flag leaf due to directly facing the solar radiation, but it could recover after reduction of sunlight intensity in the afternoon, which meant that no inactive damage happened in PS II reaction centers. There were significant differences of PS II actual and maximum photochemical efficiencies at the actinic light intensity (ΦPS II and Fv'/Fm') between abaxial and adaxial surface, and their relative variation trends were on the contrary. The photochemical and non-photochemical quenching coefficients (qP and NPQ) had a similar tendency in both abaxial and adaxial surfaces. Although ΦPS II and qP were lower in adaxial surface of flag leaf, the Fv'/Fm' was significantly higher, which indicated that the potential PS II capture efficiency of excited energy was higher. The results demonstrated that process of photochemical and non-photochemical quenching could effectively dissipate excited energy caused by strong solar radiation, and there were higher adaptation capacities in wheat varieties natively cultivated in

  9. Functional organization of a plant Photosystem I: evolution of a highly efficient photochemical machine.

    PubMed

    Amunts, Alexey; Nelson, Nathan

    2008-03-01

    Despite its enormous complexity, a plant Photosystem I (PSI) is arguably the most efficient nano-photochemical machine in Nature. It emerged as a homodimeric structure containing several chlorophyll molecules over 3.5 billion years ago, and has perfected its photoelectric properties ever since. The recently determined structure of plant PSI, which is at the top of the evolutionary tree of this kind of complexes, provided the first relatively high-resolution structural model of the supercomplex containing a reaction center (RC) and a peripheral antenna (LHCI) complexes. The RC is highly homologous to that of the cyanobacterial PSI and maintains the position of most transmembrane helices and chlorophylls during 1.5 years of separate evolution. The LHCI is composed of four nuclear gene products (Lhca1-Lhca4) that are unique among the chlorophyll a/b binding proteins in their pronounced long-wavelength absorbance and their assembly into dimers. In this respect, we describe structural elements, which establish the biological significance of a plant PSI and discuss structural variance from the cyanobacterial version. The present comprehensive structural analysis summarizes our current state of knowledge, providing the first glimpse at the architecture of this highly efficient photochemical machine at the atomic level.

  10. Endogenous circadian rhythms in pigment composition induce changes in photochemical efficiency in plant canopies.

    PubMed

    García-Plazaola, José Ignacio; Fernández-Marín, Beatriz; Ferrio, Juan Pedro; Alday, Josu G; Hoch, Günter; Landais, Damien; Milcu, Alexandru; Tissue, David T; Voltas, Jordi; Gessler, Arthur; Roy, Jacques; Resco de Dios, Víctor

    2017-01-18

    There is increasing evidence that the circadian clock is a significant driver of photosynthesis that becomes apparent when environmental cues are experimentally held constant. We studied whether the composition of photosynthetic pigments is under circadian regulation, and whether pigment oscillations lead to rhythmic changes in photochemical efficiency. To address these questions, canopies of bean and cotton were maintained, after an entrainment phase, under constant (light or darkness) conditions for 30-48 h. Photosynthesis and quantum yield peaked at subjective noon and non-photochemical quenching peaked at night. These oscillations were not associated to parallel changes in carbohydrate content or xanthophyll cycle activity. We observed robust oscillations of Chla/b during constant light in both species, and also under constant darkness in bean, peaking when it would have been night during the entrainment (subjective nights). These oscillations could be attributed to the synthesis and/or degradation of trimeric light-harvesting complex II (reflected by the rhythmic changes in Chla/b), with the antenna size minimal at night and maximal around subjective noon. Considering together the oscillations of pigments and photochemistry, the observed pattern of changes is counterintuitive if we assume that the plant strategy is to avoid photo-damage, but consistent with a strategy where non-stressed plants maximize photosynthesis.

  11. Isoprene improves photochemical efficiency and enhances heat dissipation in plants at physiological temperatures.

    PubMed

    Pollastri, Susanna; Tsonev, Tsonko; Loreto, Francesco

    2014-04-01

    Isoprene-emitting plants are better protected against thermal and oxidative stresses. Isoprene may strengthen membranes avoiding their denaturation and may quench reactive oxygen and nitrogen species, achieving a similar protective effect. The physiological role of isoprene in unstressed plants, up to now, is not understood. It is shown here, by monitoring the non-photochemical quenching (NPQ) of chlorophyll fluorescence of leaves with chemically or genetically altered isoprene biosynthesis, that chloroplasts of isoprene-emitting leaves dissipate less energy as heat than chloroplasts of non-emitting leaves, when exposed to physiologically high temperatures (28-37 °C) that do not impair the photosynthetic apparatus. The effect was especially remarkable at foliar temperatures between 30 °C and 35 °C, at which isoprene emission is maximized and NPQ is quenched by about 20%. Isoprene may also allow better stability of photosynthetic membranes and a more efficient electron transfer through PSII at physiological temperatures, explaining most of the NPQ reduction and the slightly higher photochemical quenching that was also observed in isoprene-emitting leaves. The possibility that isoprene emission helps in removing thermal energy at the thylakoid level is also put forward, although such an effect was calculated to be minimal. These experiments expand current evidence that isoprene is an important trait against thermal and oxidative stresses and also explains why plants invest resources in isoprene under unstressed conditions. By improving PSII efficiency and reducing the need for heat dissipation in photosynthetic membranes, isoprene emitters are best fitted to physiologically high temperatures and will have an evolutionary advantage when adapting to a warming climate.

  12. Photochemical reflectance ratio for tracking light use efficiency for sunlit leaves in two forest types

    NASA Astrophysics Data System (ADS)

    Zheng, Ting; Chen, Jing M.

    2017-01-01

    The estimation of maximum carboxylation rate (Vcmax)-a critical determinant of the terrestrial carbon simulation-over space remains a challenging task. Inverting the Vcmax through the sunlit gross primary productivity (GPP) is a possible solution if the key parameter sunlit light use efficiency (ɛsun) could be acquired through remote sensing approaches. Previous studies have shown that the reflectance centered at 531 nm (R531) is very sensitive to variations of ɛsun and the photochemical reflectance index (PRI, the normalized difference index using R531 and R570) can be used as an indicator of ɛsun at the leaf level though little is known about the PRI-ɛsun relationship at the canopy level due to the mixing of sunlit and shaded leaves. In this study, the photochemical reflectance ratio (PRR, defined as the ratio between R531 and R570) is proposed to enable the sunlit-shaded separation of the canopy reflectance observations acquired from a tower based multi-angular platform. The canopy PRR can be expressed as the algebraic sum of sunlit PRR and shaded PRR weighted by the visible portions of the sunlit canopy and the shaded canopy respectively. The visible portions from different angles were simulated using the 4-Scale model and the sunlit (/shaded) PRR was acquired through solving a set of equations describing the canopy PRR obtained from different angles. The relationships between the sunlit PRR (PRRsun) and ɛsun were studied for a white pine stand (TP39) and a sugar maple stand (HA). At both sites, significant correlations between PRRsun and ɛsun were obtained (R2 = 0.57 (TP39), 0.585 (HA), p < 0.001), showing the ability of PRRsun to track the variation of ɛsun. Nevertheless, differences existed in the expressions of the PRRsun-ɛsun relationship between TP39 and HA, a general expression could not be found. Further studies have shown that introducing the normalized difference vegetation index (NDVI) to correct PRRsun (NDVI × PRRsun) largely removed such

  13. UV-photochemical vapor generation of selenium for atomic absorption spectrometry: Optimization and 75Se radiotracer efficiency study

    NASA Astrophysics Data System (ADS)

    Rybínová, Marcela; Musil, Stanislav; Červený, Václav; Vobecký, Miloslav; Rychlovský, Petr

    2016-09-01

    Volatile selenium compounds were generated UV-photochemically in the continuous flow mode using four UV-photoreactors differing in the material of the reaction coil; Teflon tubing and quartz tubes with various inner diameters and wall thicknesses were tested. Atomic absorption spectrometry with an externally heated quartz furnace atomizer was employed as the detector. The relevant experimental generation parameters were optimized and the basic analytical characteristics were determined. Using formic acid as the photochemical agent, limits of detection achieved for selenium were in the range 46-102 ng L- 1 in dependence on the type of UV-photoreactor employed. When nitric acid was also added to the photochemical agent, the limits of detection were reduced to 27-44 ng L- 1. The repeatability did not exceed 2.4% (5 μg L- 1 Se(IV), n = 10). Experiments with 75Se radiotracer have been performed for the first time to quantify the efficiency of UV-photochemical vapor generation (UV-PVG) of selenium. The highest efficiency of 67 ± 1% was obtained for a UV-photoreactor containing a quartz reaction coil (2.0 mm i.d., 4.0 mm o.d.). The generation efficiency of 61 ± 1% was obtained for a Teflon reaction coil (1.0 mm i.d., 1.4 mm o.d.). Mapping of the radiotracer distribution in the individual parts of the apparatus did not reveal substantial transport losses of the analyte in the UV-PVG system.

  14. Accounting for the decrease of photosystem photochemical efficiency with increasing irradiance to estimate quantum yield of leaf photosynthesis.

    PubMed

    Yin, Xinyou; Belay, Daniel W; van der Putten, Peter E L; Struik, Paul C

    2014-12-01

    Maximum quantum yield for leaf CO2 assimilation under limiting light conditions (Φ CO2LL) is commonly estimated as the slope of the linear regression of net photosynthetic rate against absorbed irradiance over a range of low-irradiance conditions. Methodological errors associated with this estimation have often been attributed either to light absorptance by non-photosynthetic pigments or to some data points being beyond the linear range of the irradiance response, both causing an underestimation of Φ CO2LL. We demonstrate here that a decrease in photosystem (PS) photochemical efficiency with increasing irradiance, even at very low levels, is another source of error that causes a systematic underestimation of Φ CO2LL. A model method accounting for this error was developed, and was used to estimate Φ CO2LL from simultaneous measurements of gas exchange and chlorophyll fluorescence on leaves using various combinations of species, CO2, O2, or leaf temperature levels. The conventional linear regression method under-estimated Φ CO2LL by ca. 10-15%. Differences in the estimated Φ CO2LL among measurement conditions were generally accounted for by different levels of photorespiration as described by the Farquhar-von Caemmerer-Berry model. However, our data revealed that the temperature dependence of PSII photochemical efficiency under low light was an additional factor that should be accounted for in the model.

  15. Efficient photochemical generation of peroxycarboxylic nitric anhydrides with ultraviolet light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Rider, N. D.; Taha, Y. M.; Odame-Ankrah, C. A.; Huo, J. A.; Tokarek, T. W.; Cairns, E.; Moussa, S. G.; Liggio, J.; Osthoff, H. D.

    2015-07-01

    Photochemical sources of peroxycarboxylic nitric anhydrides (PANs) are utilized in many atmospheric measurement techniques for calibration or to deliver an internal standard. Conventionally, such sources rely on phosphor-coated low-pressure mercury (Hg) lamps to generate the UV light necessary to photo-dissociate a dialkyl ketone (usually acetone) in the presence of a calibrated amount of nitric oxide (NO) and oxygen (O2). In this manuscript, a photochemical PAN source in which the Hg lamp has been replaced by arrays of ultraviolet light-emitting diodes (UV-LEDs) is described. The output of the UV-LED source was analyzed by gas chromatography (PAN-GC) and thermal dissociation cavity ring-down spectroscopy (TD-CRDS). Using acetone, diethyl ketone (DIEK), diisopropyl ketone (DIPK), or di-n-propyl ketone (DNPK), respectively, the source produces peroxyacetic (PAN), peroxypropionic (PPN), peroxyisobutanoic (PiBN), or peroxy-n-butanoic nitric anhydride (PnBN) from NO in high yield (> 90 %). Box model simulations with a subset of the Master Chemical Mechanism (MCM) were carried out to rationalize product yields and to identify side products. The present work demonstrates that UV-LED arrays are a viable alternative to current Hg lamp setups.

  16. Explaining the variability of Photochemical Reflectance Index (PRI): deconvolution of variability related to Light Use Efficiency and Canopy attributes.

    NASA Astrophysics Data System (ADS)

    Merlier, Elodie; Hmimina, Gabriel; Dufrêne, Eric; Soudani, Kamel

    2014-05-01

    The Photochemical Reflectance Index (PRI) was designed as a proxy of the state of xanthophyll cycle which is used as a response of plants to excess of light (Gamon et al., 1990; 1992). Strong relationships between PRI and LUE were shown at leaf and canopy scales and over a wide range of species (Garbulsky et al., 2011). However, its use at canopy scale was shown to be significantly hampered by effects of confounding factors such as the PRI sensitivity to leaf pigment content (Gamon et al. 2001; Nakaji et al. 2006) and to canopy structure (Hilker et al. 2008). Several approaches aimed at correcting such effects and recent works focused on the deconvolution of LUE related and LUE unrelated PRI variability (Rahimzadeh-Bajgiran et al. 2012).In this study, the PRI variability at canopy scale is investigated over two years on three species (Fagus sylvatica, Quercus robur and Pinus sylvestris) growing under two water regimes. At daily scale, PRI variability is mainly explained by radiation conditions. As already reported at leaf scale in Hmimina et al. (2014), analysis of PRI responses to incoming photosynthetically active radiation over seasonal scale allowed to separate two sources of variability : a constitutive variability mainly related to canopy structure and leaf chlorophyll content and a facultative variability mainly related to LUE and soil moisture content. These results highlight the composite nature of PRI signal measured at canopy scale and the importance of disentangling its sources of variability in order to accurately assess ecosystem light use efficiency. Gamon JA, Field CB, Bilger W, Björkman O, Fredeen AL, Peñuelas J. 1990. Remote sensing of the xanthophyll cycle and chlorophyll fluorescence in sunflower leaves and canopies. Oecologia 85, 1-7. Gamon JA, Field CB, Fredeen A AL, Thayer S. 2001. Assessing photosynthetic downregulation in sunflower stands with an optically-based model. Photosynthesis Research 67, 113-125. Gamon JA, Peñuelas J, Field CB

  17. An efficient photochemical route to Pd nanoparticles; application to the one-step synthesis of Pd@polymer nanocomposite films

    NASA Astrophysics Data System (ADS)

    Wolak, Séverine; Vidal, Loïc; Becht, Jean-Michel; Michelin, Laure; Balan, Lavinia

    2016-08-01

    We have developed a facile, efficient, low cost and ‘green’ photochemical approach to preparing surfactant-free Pd nanoparticles and Pd-immobilized@acrylate photo-polymer films at room temperature, under air and without any additional treatment. The reaction system only includes a photo-initiator used as a generator of free radicals and a Pd(II) salt. In ethanol solution, the photochemical reduction of Pd(II) to Pd(0) generates very small metal particles with a narrow size distribution (2-4 nm). Furthermore, we have shown that the formation of Pd nanoparticles from a Pd(II) salt can be reversible thus allowing easy handling and safe storage with the possibility of generating the nanoparticles just before use. In the presence of an acrylate bifunctional monomer, Pd@polymer film was obtained through a ‘one-pot, one-step’ process resulting from a simultaneous photo-reduction of Pd(II) and photo-polymerization of acrylate units. The simultaneous generation of a 3D polymer network and of metal particles leads to a homogeneous distribution of Pd nanoparticles in the photo-polymer matrix with an average diameter of approximately 3.7 ± 1.1 nm. Such as-prepared Pd@polymer films were found to efficiently catalyze the Mizoroki-Heck reaction in the presence of only 0.9 mequiv. of supported palladium. The major interest of this arrangement is its recoverability and reusability, which makes it very attractive both from a practical and economical viewpoint. Finally, it is worth noting that this innovation offers a great advantage over concurrent methods in that it is simply generated within minutes, it is highly stable, and there is sharp monodispersity in the size of the Pd nanoparticles that can be stored for months without alteration of their physico-chemical properties and catalytic activity.

  18. Estimating Light Use Efficiency Of A Pine And Beech Forest From Leaf To Ecosystem Scale Using The Photochemical Reflectance Index

    NASA Astrophysics Data System (ADS)

    Vanikiotis, Theofilos; Markos, Nikos; Stagakis, Stavros; Tzotsos, Angelos; Sykioti, Olga; Kyparissis, Aris

    2013-12-01

    The prospect of accurately tracking photosynthetic processes using satellite observations is very important for understanding and monitoring global carbon cycle and climate change. The present study investigates the efficiency of the Photochemical Reflectance Index (PRI) in detecting light use efficiency (ɛ) in different spatial scales. The study sites concern two dense and homogenous forests in the region of Epirus (Greece), one evergreen coniferous forest dominated by Pinus nigra species and one deciduous forest dominated by Fagus sylvatica. Field and laboratory measurements of canopy structure (Leaf Area Index - LAI, needle and shoot structure characteristics), leaf pigment concentrations, leaf photosynthesis and water potential were performed throughout the growth period. These measurements were used for an accurate description of the ecophysiological characteristics of the two species and thus the parameterization of a Canopy Photosynthesis Model in order to estimate canopy photosynthesis. During the same period, leaf and canopy reflectance measurements were performed in the field to test and evaluate PRI regarding it's efficiency to track ɛ in leaf and canopy scale. In order to investigate the potential application of PRI for estimating ɛ in a broader spatial scale, satellite hyperspectral or superspectral sensors can be used. Compact High Resolution Imaging Spectrometer (CHRIS) and Moderate Resolution Imaging Spectroradiometer (MODIS) are currently available for this purpose and their performances were tested within the present study. An agreement between the fluctuations of CHRIS PRI and the field measured canopy PRI has been found, with both of them appearing to track the ɛ fluctuation efficiently. However, MODIS PRI shows no intense fluctuation and no relationship with ɛ and field measured PRI, probably due to lack of atmospheric correction and the effects of viewing and illumination geometry.

  19. Efficient photochemical water splitting by a chemically modified n-TiO2.

    PubMed

    Khan, Shahed U M; Al-Shahry, Mofareh; Ingler, William B

    2002-09-27

    Although n-type titanium dioxide (TiO2) is a promising substrate for photogeneration of hydrogen from water, most attempts at doping this material so that it absorbs light in the visible region of the solar spectrum have met with limited success. We synthesized a chemically modified n-type TiO2 by controlled combustion of Ti metal in a natural gas flame. This material, in which carbon substitutes for some of the lattice oxygen atoms, absorbs light at wavelengths below 535 nanometers and has a lower band-gap energy than rutile (2.32 versus 3.00 electron volts). At an applied potential of 0.3 volt, chemically modified n-type TiO2 performs water splitting with a total conversion efficiency of 11% and a maximum photoconversion efficiency of 8.35% when illuminated at 40 milliwatts per square centimeter. The latter value compares favorably with a maximum photoconversion efficiency of 1% for n-type TiO2 biased at 0.6 volt.

  20. Remote sensing of assimilating branch light use efficiency using the photochemical reflectance index in Haloxylon ammodendron forest

    NASA Astrophysics Data System (ADS)

    Nyongesah, Maina John; Quan, Wang; Lu, Xu

    2016-04-01

    Five healthy Haloxylon ammodendron trees were randomly selected to monitor the photochemical reflectance index (PRI) and its relation to light use efficiency (LUE) in shaded and sunlit assimilating branches. Linear regression was performed where the results revealed that LUE decreased with seasonal courses with vivid midday depression regardless of light variation within canopies. PRI and LUE decoupled in early spring when the foliage was deeply downregulated, with high correlation (R2=0.8, p<0.001) during most parts of the year. Measured and estimated LUE were highly correlated for the July to September dataset (R2=0.73, p<0.001) compared to May to June datasets (R2=0.35, p<0.001). The estimated LUE for young assimilating branches could be obtained with a high RMSE of 0.01, compared to mature branches with an RMSE of 0.003. The measured LUE values were ˜20% higher than estimated LUE during the period from May to June, and values were slightly lower at the end of the growing season. This was attributed to differences in the physiological and biochemical mechanisms controlling the seasonal dynamics of PRI. Therefore, PRI is the best estimator of LUE when age-related changes and canopy light partitioning are considered in assimilating organs. Combined use of PRI with pigments could improve the remote evaluation of LUE.

  1. Actual fusion efficiency in the lipid mixing assay - Comparison between nanodiscs and liposomes

    PubMed Central

    François-Martin, Claire; Pincet, Frédéric

    2017-01-01

    Lipid exchange occurs between membranes during fusion or active lipid transfer. These processes are necessary in vivo for the homeostasis of the cell at the level of the membranes, the organelles and the cell itself. They are also used by the cell to interact with the surrounding medium. Several assays have been developed to characterize in vitro these processes on model systems. The most common one, relying on fluorescence dequenching, measures lipid mixing between small membranes such as liposomes or nanodiscs in bulk. Usually, relative comparisons of the rate of lipid exchange are made between measurements performed in parallel. Here, we establish a quantitative standardization of this assay to avoid any bias resulting from the temperatures, the chosen fluorescent lipid fractions and from the various detergents used to normalize the measurements. We used this standardization to quantitatively compare the efficiency of SNARE-induced fusion in liposome-liposome and liposome-nanodisc configurations having similar collision frequency. We found that the initial yield of fusion is comparable in both cases, 1 per 2–3 million collisions in spite of a much larger dequenching signal with nanodiscs. Also, the long-term actual fusion rate is slightly lower with nanodiscs than in the liposome-liposome assay. PMID:28266607

  2. Actual fusion efficiency in the lipid mixing assay - Comparison between nanodiscs and liposomes

    NASA Astrophysics Data System (ADS)

    François-Martin, Claire; Pincet, Frédéric

    2017-03-01

    Lipid exchange occurs between membranes during fusion or active lipid transfer. These processes are necessary in vivo for the homeostasis of the cell at the level of the membranes, the organelles and the cell itself. They are also used by the cell to interact with the surrounding medium. Several assays have been developed to characterize in vitro these processes on model systems. The most common one, relying on fluorescence dequenching, measures lipid mixing between small membranes such as liposomes or nanodiscs in bulk. Usually, relative comparisons of the rate of lipid exchange are made between measurements performed in parallel. Here, we establish a quantitative standardization of this assay to avoid any bias resulting from the temperatures, the chosen fluorescent lipid fractions and from the various detergents used to normalize the measurements. We used this standardization to quantitatively compare the efficiency of SNARE-induced fusion in liposome-liposome and liposome-nanodisc configurations having similar collision frequency. We found that the initial yield of fusion is comparable in both cases, 1 per 2–3 million collisions in spite of a much larger dequenching signal with nanodiscs. Also, the long-term actual fusion rate is slightly lower with nanodiscs than in the liposome-liposome assay.

  3. Photochemical efficiency of adult and young leaves of the neotropical understory shrub Psychotria limonensis (Rubiaceae) in response to changes in the light environment.

    PubMed

    Avalos, Gerardo; Mulkey, Stephen S

    2004-12-01

    We explored the short-term adjustment in photochemical efficiency (Fv/Fm) in adult and young leaves of the understory neotropical shrub Psychotria limonensis Krause (Rubiaceae) in response to rapid changes in the light environment. Leaves were collected from 20 individual plants growing under sun and shade conditions on Gigante Peninsula, Barro Colorado Natural Monument (Republic of Panama), during the wet season of 1996. Leaves were distributed in four sequences of light treatments (AB leaves were expanded under sun and were transferred to shade, BA leaves experienced the opposite transfer, and the controls AA and BB leaves that were expanded and maintained under sun or shade conditions). Adult and young leaves did not differ in overall photochemical efficiency. Instead, differences were found among light environments, for which leaves transferred from shade to sun showed the lowest Fv/Fm ratios. There was no relationship between photochemical efficiency and leaf temperature. In P. limonensis, understory plants are susceptible of photoinhibition independently of the leaf ontogenetic stage. The approach utilized in this experiment allowed the rapid exploration of this capacity, and could be applied to poorly studied understory species.

  4. Light Use Efficiency and Photochemical Reflectance Index: do we have a common basis defining them? Implications for productivity estimation (Invited)

    NASA Astrophysics Data System (ADS)

    Gitelson, A. A.; Gamon, J. A.

    2013-12-01

    There are at least three commonly used definitions of photosynthetic Light Use Efficiency (LUE) based on: (a) incident radiation (LUEinc); (b) total absorbed light (LUEtotal); and (c) radiation absorbed by photosynthetically active vegetation (LUEps). Consequently, LUE values reported do not have a common basis, bringing confusion and limiting the utility of reported LUE values for comparative analyses. Not surprisingly, the value of LUE reported in literature varies by a factor of three. Similarly, the Photochemical Reflectance Index (PRI) has different operational definitions, resulting in a wide range of reported values for comparable conditions. The objectives of this paper are to investigate (a) temporal behavior of each definition of LUE; and (b) factors affecting PRI, often used as a surrogate of LUE at leaf and canopy levels. We focused on annual and winter-deciduous vegetation where total chlorophyll content is closely tied to the seasonal dynamics of GPP. In these conditions, LUEinc is closely related to total plant chlorophyll (Chl) content. LUEtotal oscillates around a constant value during the vegetative stage, depending mainly on plant physiological status, PAR composition and magnitude, while in reproductive and senescence stages it relates closely to Chl content. LUEps may vary 2- to 3-fold during the growing season with no clear seasonal pattern, and does not seem to be related to any biophysical characteristic studied; rather, it depends on the physiological status of vegetation, PAR composition and magnitude as well as air temperature and soil moisture. At the leaf level, PRI depends greatly on pigment content and composition and relates closely to the ratio of Chl to carotenoid content. At the canopy and stand levels, both total plant Chl content and green LAI are responsible for more than 95% of PRI variation, demonstrating that PRI is confounded by pigment pool sizes and canopy structure in these conditions. Importantly, the close relationship

  5. Cu/Zn superoxide dismutase and catalase activities in Pinus mugo needles growing at elevated stands in the mountains, and their photochemical efficiency of PSII.

    PubMed

    Miszalski, Zbigniew; Libik, Marta; Surówka, Ewa; Niewiadomska, Ewa

    2005-08-01

    Pinus mugo needles were sampled at different altitudes (1420, 1590 and 1920 m a.s.l.) to analyse levels of oxidative stress and changes in maximum photochemical efficiency of PSII. Polyacrylamide gel electrophoresis demonstrated that almost all superoxide dismutase activity represented Cu/Zn superoxide dismutase, and only 4-6% represents Mn superoxide dismutase. In extracts from plants sampled at 1590 and 1920 m a.s.l., lower activity of Cu/Zn superoxide dismutase was found. Comparing these data with immunoblots, it can be concluded that the differences in superoxide dismutase activity was related to protein amount. In needles from higher altitudes, a decrease in catalase activity was detected, as opposed to the protein amount, which was higher in needles from the higher stands. Considering the decrease in catalase and Cu/Zn superoxide dismutase activities in needles collected at 1590 and 1920 m a.s.l., we suggest that higher levels of oxidative stress may induce changes in photochemical efficiency of PSII.

  6. Photoperiod and temperature constraints on the relationship between the photochemical reflectance index and the light use efficiency of photosynthesis in Pinus strobus.

    PubMed

    Fréchette, Emmanuelle; Chang, Christine Yao-Yun; Ensminger, Ingo

    2016-03-01

    The photochemical reflectance index (PRI) is a proxy for the activity of the photoprotective xanthophyll cycle and photosynthetic light use efficiency (LUE) in plants. Evergreen conifers downregulate photosynthesis in autumn in response to low temperature and shorter photoperiod, and the dynamic xanthophyll cycle-mediated non-photochemical quenching (NPQ) is replaced by sustained NPQ. We hypothesized that this shift in xanthophyll cycle-dependent energy partitioning during the autumn is the cause for variations in the PRI-LUE relationship. In order to test our hypothesis, we characterized energy partitioning and pigment composition during a simulated summer-autumn transition in a conifer and assessed the effects of temperature and photoperiod on the PRI-LUE relationship. We measured gas exchange, chlorophyll fluorescence and leaf reflectance during the photosynthetic downregulation in Pinus strobus L. seedlings exposed to low temperature/short photoperiod or elevated temperature/short photoperiod conditions. Shifts in energy partitioning during simulated autumn were observed when the pools of chlorophylls decreased and pools of photoprotective carotenoids increased. On a seasonal timescale, PRI was controlled by carotenoid pool sizes rather than xanthophyll cycle dynamics. Photochemical reflectance index variation under cold autumn conditions mainly reflected long-term pigment pool adjustments associated with sustained NPQ, which impaired the PRI-LUE relationship. Exposure to warm autumn conditions prevented the induction of sustained NPQ but still impaired the PRI-LUE relationship. We therefore conclude that alternative zeaxanthin-independent NPQ mechanisms, which remain undetected by the PRI, are present under both cold and warm autumn conditions, contributing to the discrepancy in the PRI-LUE relationship during autumn.

  7. Photoperiod and temperature constraints on the relationship between the photochemical reflectance index and the light use efficiency of photosynthesis in Pinus strobus

    PubMed Central

    Fréchette, Emmanuelle; Chang, Christine Yao-Yun; Ensminger, Ingo

    2016-01-01

    The photochemical reflectance index (PRI) is a proxy for the activity of the photoprotective xanthophyll cycle and photosynthetic light use efficiency (LUE) in plants. Evergreen conifers downregulate photosynthesis in autumn in response to low temperature and shorter photoperiod, and the dynamic xanthophyll cycle-mediated non-photochemical quenching (NPQ) is replaced by sustained NPQ. We hypothesized that this shift in xanthophyll cycle-dependent energy partitioning during the autumn is the cause for variations in the PRI–LUE relationship. In order to test our hypothesis, we characterized energy partitioning and pigment composition during a simulated summer–autumn transition in a conifer and assessed the effects of temperature and photoperiod on the PRI–LUE relationship. We measured gas exchange, chlorophyll fluorescence and leaf reflectance during the photosynthetic downregulation in Pinus strobus L. seedlings exposed to low temperature/short photoperiod or elevated temperature/short photoperiod conditions. Shifts in energy partitioning during simulated autumn were observed when the pools of chlorophylls decreased and pools of photoprotective carotenoids increased. On a seasonal timescale, PRI was controlled by carotenoid pool sizes rather than xanthophyll cycle dynamics. Photochemical reflectance index variation under cold autumn conditions mainly reflected long-term pigment pool adjustments associated with sustained NPQ, which impaired the PRI–LUE relationship. Exposure to warm autumn conditions prevented the induction of sustained NPQ but still impaired the PRI–LUE relationship. We therefore conclude that alternative zeaxanthin-independent NPQ mechanisms, which remain undetected by the PRI, are present under both cold and warm autumn conditions, contributing to the discrepancy in the PRI–LUE relationship during autumn. PMID:26846980

  8. Photochemical Molecular Tailoring for Efficient Diffusion and Reorganization of Organic Nanocrystals for Ultra-Flexible Organic Semiconductor Arrays.

    PubMed

    Kang, Jingu; Kim, Jaehyun; Jo, Jeong-Wan; Heo, Jae Sang; Kim, Myung-Gil; Kim, Yong-Hoon; Kim, Jaekyun; Park, Sung Kyu

    2017-01-01

    Solution-processed organic single crystals with high carrier mobility have been actively investigated for diverse applications such as displays, sensors, and next generation electronics on a flexible platform. However, the lack of precise alignment and growth control of organic single crystals impedes the widespread adoption of organic materials in an industrial perspective. Here, a photochemical modification approach is reported tailoring the solubility and molecular diffusivity of polymeric sacrificial layer and sequential batch-type vapor annealing to implement high-performance (average saturation mobility: 8.01 cm(2) V(-1) s(-1) ) organic single-crystal thin film transistors with large channel width including multiple aligned single crystals. Additionally, the mechanical properties of the organic single crystals are systematically investigated with extreme strain conditions such as bending radius of 150 μm.

  9. Decreased photochemical efficiency of photosystem II following sunlight exposure of shade-grown leaves of avocado: because of, or in spite of, two kinetically distinct xanthophyll cycles?

    PubMed

    Jia, Husen; Förster, Britta; Chow, Wah Soon; Pogson, Barry James; Osmond, C Barry

    2013-02-01

    This study resolved correlations between changes in xanthophyll pigments and photosynthetic properties in attached and detached shade-grown avocado (Persea americana) leaves upon sun exposure. Lutein epoxide (Lx) was deepoxidized to lutein (L), increasing the total pool by ΔL over 5 h, whereas violaxanthin (V) conversion to antheraxanthin (A) and zeaxanthin (Z) ceased after 1 h. During subsequent dark or shade recovery, de novo synthesis of L and Z continued, followed by epoxidation of A and Z but not of L. Light-saturated nonphotochemical quenching (NPQ) was strongly and linearly correlated with decreasing [Lx] and increasing [L] but showed a biphasic correlation with declining [V] and increasing [A+Z] separated when V deepoxidation ceased. When considering [ΔL+Z], the monophasic linear correlation was restored. Photochemical efficiency of photosystem II (PSII) and photosystem (PSI; deduced from the delivery of electrons to PSI in saturating single-turnover flashes) showed a strong correlation in their continuous decline in sunlight and an increase in NPQ capacity. This decrease was also reflected in the initial reduction of the slope of photosynthetic electron transport versus photon flux density. Generally longer, stronger sun exposures enhanced declines in both slope and maximum photosynthetic electron transport rates as well as photochemical efficiency of PSII and PSII/PSI more severely and prevented full recovery. Interestingly, increased NPQ capacity was accompanied by slower relaxation. This was more prominent in detached leaves with closed stomata, indicating that photorespiratory recycling of CO(2) provided little photoprotection to avocado shade leaves. Sun exposure of these shade leaves initiates a continuum of photoprotection, beyond full engagement of the Lx and V cycle in the antenna, but ultimately photoinactivated PSII reaction centers.

  10. An efficient surface modification using 2-methacryloyloxyethyl phosphorylcholine to control cell attachment via photochemical reaction in a microchannel.

    PubMed

    Jang, Kihoon; Sato, Kae; Tanaka, Yo; Xu, Yan; Sato, Moritoshi; Nakajima, Takahiro; Mawatari, Kazuma; Konno, Tomohiro; Ishihara, Kazuhiko; Kitamori, Takehiko

    2010-08-07

    This report describes a direct approach for cell micropatterning in a closed glass microchannel. To control the cell adhesiveness inside the microchannel, the application of an external stimulus such as ultraviolet (UV) was indispensible. This technique focused on the use of a modified 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, which is known to be a non-biofouling compound that is a photocleavable linker (PL), to localize cells via connection to an amino-terminated silanized surface. Using UV light illumination, the MPC polymer was selectively eliminated by photochemical reaction that controlled the cell attachment inside the microchannel. For suitable cell micropatterning in a microchannel, the optimal UV illumination time and concentration for cell suspension were investigated. After selective removal of the MPC polymer through the photomask, MC-3T3 E1 cells and vascular endothelial cells (ECs) were localized only to the UV-exposed area. In addition, the stability of patterned ECs was also confirmed by culturing for 2 weeks in a microchannel under flow conditions. Furthermore, we employed two different types of cells inside the same microchannel through multiple removal of the MPC polymer. ECs and Piccells were localized in both the upper and down streams of the microchannel, respectively. When the ECs were stimulated by adenosine triphosphate (ATP), NO was secreted from the ECs and could be detected by fluorescence resonance energy transfer (FRET) in Piccells, which is a cell-based NO indicator. This technique can be a powerful tool for analyzing cell interaction research.

  11. Seasonal variation in photosystem II efficiency and photochemical reflectance index of evergreen trees and perennial grasses growing at low and high elevations in subtropical Taiwan.

    PubMed

    Weng, Jen-Hsien; Liao, Tien-Szu; Hwang, Mon-Yuan; Chung, Chi-Ch; Lin, Chung-Ping; Chu, Chung-Hei

    2006-08-01

    Three pines species, three evergreen broadleaf trees, one C(3) and two C(4) perennial grasses of subtropical Taiwan were studied to elucidate the correlation between photosystem II (PSII) efficiency and photochemical reflectance index (PRI = (R(531) - R(570))/(R(531) + R(570))). Measurements were made at two sites differing in altitude (800 and 2600 m) over several growing seasons. At high elevation, potential PSII efficiency, measured by chlorophyll fluorescence (the ratio of variable to maximal fluorescence; F(v)/F(m)) at predawn, decreased with decreasing air temperature and varied greatly among species. At the lowest air temperature (-3 degrees C) studied, variation in F(v)/F(m) among species ranged from 0.33 to 0.72. In contrast, at low elevation where air temperature was moderate, seasonal variation in F(v)/F(m) was small in all of the study species. When species, elevation and season data were pooled, despite the high variation in F(v)/F(m) among species, a good correlation between F(v)/F(m) and PRI was observed. When compared at the same value of PRI, F(v)/F(m) of evergreen trees was higher than that of perennial grasses; however, when the minimum temperature on the measurement day was below 0 degrees C, F(v)/F(m) was underestimated relative to PRI. We conclude that PRI could be used as a remote indicator of photosynthetic function when air temperature is above 0 degrees C.

  12. Catalysis of Photochemical Reactions.

    ERIC Educational Resources Information Center

    Albini, A.

    1986-01-01

    Offers a classification system of catalytic effects in photochemical reactions, contrasting characteristic properties of photochemical and thermal reactions. Discusses catalysis and sensitization, examples of catalyzed reactions of excepted states, complexing ground state substrates, and catalysis of primary photoproducts. (JM)

  13. Research opportunities in photochemical sciences

    SciTech Connect

    1996-07-01

    The workshop entitled {open_quotes}Research Opportunities in Photochemical Sciences{close_quotes} was initiated by the U.S. Department of Energy (DOE), Office of Energy Research (ER), Office of Basic Energy Sciences (BES), Division of Chemical Sciences. The National Renewable Energy Laboratory (NREL) in Golden, Colorado was requested by ER to host the workshop. It was held February 5-8, 1996 at the Estes Park Conference Center, Estes Park, CO, and attended by about 115 leading scientists and engineers from the U.S., Japan, and Europe; program managers for the DOE ER and Energy Efficiency and Renewable Energy (EERE) programs also attended. The purpose of the workshop was to bridge the communication gap between the practioneers and supporters of basic research in photochemical science and the practioneers and supporters of applied research and development in technologies related to photochemical science. For the purposes of the workshop the definition of the term {open_quotes}photochemical science{close_quotes} was broadened to include homogeneous photochemistry, heterogeneous photochemistry, photoelectrochemistry, photocatalysis, photobiology (for example, the light-driven processes of biological photosynthesis and proton pumping), artificial photosynthesis, solid state photochemistry, and solar photochemistry. The technologies under development through DOE support that are most closely related to photochemical science, as defined above, are the renewable energy technologies of photovoltaics, biofuels, hydrogen energy, carbon dioxide reduction and utilization, and photocatalysis for environmental cleanup of water and air. Individual papers were processed separately for the United states Department of Energy databases.

  14. Efficient photochemical oxidation of anisole in protic solvents: electron transfer driven by specific solvent-solute interactions.

    PubMed

    Lewandowska, Anna; Hug, Gordon L; Hörner, Gerald; Pedzinski, Tomasz; Filipiak, Piotr; Marciniak, Bronislaw

    2010-07-12

    The dynamics of the bimolecular quenching of triplet excited benzophenone by anisole was studied by nanosecond flash photolysis. We carried out a detailed study of the solvent dependence of the reaction rates and efficiencies in a number of protic and non-protic solvents. These studies were augmented by theoretical modelling and experimental investigation of solute/solvent interactions in the triplet excited and the ground state, respectively. The triplet quenching that follows Stern-Volmer kinetics in all cases is profoundly dependent on the nature of the solvent, with the highest reactivity being consistently found in protic solvents. The results in non-protic solvents are compatible with unproductive quenching via a charge-transfer state, whereas the generally fast quenching in protic solvents is accompanied by efficient formation of free-radical products. Analysis of the solvent dependence in terms of Marcus theory reveals the impact of specific solvation of benzophenone by protic solvents on the ET driving force and kinetics. Specific solvation is found to support efficient free radical ion formation in media of moderate and low polarity as well.

  15. Recovery kinetics of photochemical efficiency in winter stressed conifers: the effects of growth light environment, extent of the season and species.

    PubMed

    Verhoeven, Amy S

    2013-02-01

    Evergreens undergo reductions in maximal photochemical efficiency (F(v)/F(m)) during winter due to increases in sustained thermal energy dissipation. Upon removing winter stressed leaves to room temperature and low light, F(v)/F(m) recovers and can include both a rapid and a slow phase. The goal of this study was to determine whether the rapid component to recovery exists in winter stressed conifers at any point during the season in a seasonally extreme environment. Additional goals were to compare the effects of species, growth light environment and the extent of the winter season on recovery kinetics in conifers. Four species (sun and shade needle) were monitored during the winter of 2007/2008: eastern white pine (Pinus strobus), balsam fir (Abies balsamea), Taxus cuspidata and white spruce (Picea glauca). F(v)/F(m) was measured in the field, and then monitored indoors at room temperature and low light for 6 days. The results showed that all species showed a rapid component to recovery in early winter that disappeared later in the season in sun needles but was present in shade needles on most days monitored during winter. There were differences among species in the recovery kinetics across the season, with pine recovering the most slowly and spruce the most quickly. The results suggest an important role for the rapidly reversible form of energy dissipation in early winter, as well as important differences between species in their rate of recovery in late winter/early spring which may have implications for spring onset of photosynthesis.

  16. A highly efficient polyampholyte hydrogel sorbent based fixed-bed process for heavy metal removal in actual industrial effluent.

    PubMed

    Zhou, Guiyin; Luo, Jinming; Liu, Chengbin; Chu, Lin; Ma, Jianhong; Tang, Yanhong; Zeng, Zebing; Luo, Shenglian

    2016-02-01

    High sorption capacity, high sorption rate, and fast separation and regeneration for qualified sorbents used in removing heavy metals from wastewater are urgently needed. In this study, a polyampholyte hydrogel was well designed and prepared via a simple radical polymerization procedure. Due to the remarkable mechanical strength, the three-dimensional polyampholyte hydrogel could be fast separated, easily regenerated and highly reused. The sorption capacities were as high as 216.1 mg/g for Pb(II) and 153.8 mg/g for Cd(II) owing to the existence of the large number of active groups. The adsorption could be conducted in a wide pH range of 3-6 and the equilibrium fast reached in 30 min due to its excellent water penetration for highly accessible to metal ions. The fixed-bed column sorption results indicated that the polyampholyte hydrogel was particularly effective in removing Pb(II) and Cd(II) from actual industrial effluent to meet the regulatory requirements. The treatment volumes of actual smelting effluent using one fixed bed column were as high as 684 bed volumes (BV) (7736 mL) for Pb(II) and 200 BV (2262 mL) for Cd(II). Furthermore, the treatment volumes of actual smelting effluent using tandem three columns reached 924 BV (31,351 mL) for Pb(II) and 250 BV (8483 mL) for Cd(II), producing only 4 BV (136 mL) eluent. Compared with the traditional high density slurry (HDS) process with large amount of sludge, the proposed process would be expected to produce only a small amount of sludge. When the treatment volume was controlled below 209.3 BV (7103 mL), all metal ions in the actual industrial effluent could be effectively removed (<0.01 mg/L). This wok develops a highly practical process based on polyampholyte hydrogel sorbents for the removal of heavy metal ions from practical wastewater.

  17. Photochemical Modeling Applications

    EPA Pesticide Factsheets

    Provides access to modeling applications involving photochemical models, including modeling of ozone, particulate matter (PM), and mercury for national and regional EPA regulations such as the Clean Air Interstate Rule (CAIR) and the Clean Air Mercury Rule

  18. Is less really more: Does a prefrontal efficiency genotype actually confer better performance when working memory becomes difficult?

    PubMed

    Ihne, Jessica L; Gallagher, Natalie M; Sullivan, Marie; Callicott, Joseph H; Green, Adam E

    2016-01-01

    Perhaps the most widely studied effect to emerge from the combination of neuroimaging and human genetics is the association of the COMT-Val(108/158)Met polymorphism with prefrontal activity during working memory. COMT-Val is a putative risk factor in schizophrenia, which is characterized by disordered prefrontal function. Work in healthy populations has sought to characterize mechanisms by which the valine (Val) allele may lead to disadvantaged prefrontal cognition. Lower activity in methionine (Met) carriers has been interpreted as advantageous neural efficiency. Notably, however, studies reporting COMT effects on neural efficiency have generally not reported working memory performance effects. Those studies have employed relatively low/easy working memory loads. Higher loads are known to elicit individual differences in working memory performance that are not visible at lower loads. If COMT-Met confers greater neural efficiency when working memory is easy, a reasonable prediction is that Met carriers will be better able to cope with increasing demand for neural resources when working memory becomes difficult. To our knowledge, this prediction has thus far gone untested. Here, we tested performance on three working memory tasks. Performance on each task was measured at multiple levels of load/difficulty, including loads more demanding than those used in prior studies. We found no genotype-by-load interactions or main effects of COMT genotype on accuracy or reaction time. Indeed, even testing for performance differences at each load of each task failed to find a single significant effect of COMT genotype. Thus, even if COMT genotype has the effects on prefrontal efficiency that prior work has suggested, such effects may not directly impact high-load working memory ability. The present findings accord with previous evidence that behavioral effects of COMT are small or nonexistent and, more broadly, with a growing consensus that substantial effects on phenotype will

  19. Numerical method for the estimation of column radial heterogeneity and of the actual column efficiency from tailing peak profiles.

    PubMed

    Miyabe, Kanji; Guiochon, Georges

    2011-01-01

    It is probably impossible to prepare high-performance liquid chromatography (HPLC) columns that have a completely homogeneous packing structure. Many reports in the literature show that the radial distributions of the mobile phase flow velocity and the local column efficiency are not flat, even in columns considered as good. A degree of radial heterogeneity seems to be a common property of all HPLC columns and an important source of peak tailing, which prevents the derivation of accurate information on chromatographic behavior from a straightforward analysis of elution peak profiles. This work reports on a numerical method developed to derive from recorded peak profiles the column efficiency at the column center, the degree of column radial heterogeneity, and the polynomial function that best represents the radial distributions of the flow velocity and the column efficiency. This numerical method was applied to two concrete examples of tailing peak profiles previously described. It was demonstrated that this numerical method is effective to estimate important parameters characterizing the radial heterogeneity of chromatographic columns.

  20. Suppressing photochemical reactions with quantized light fields

    NASA Astrophysics Data System (ADS)

    Galego, Javier; Garcia-Vidal, Francisco J.; Feist, Johannes

    2016-12-01

    Photoisomerization, that is, a photochemical reaction leading to a change of molecular structure after absorption of a photon, can have detrimental effects such as leading to DNA damage under solar irradiation, or as a limiting factor for the efficiency of solar cells. Here, we show that strong coupling of organic molecules to a confined light mode can be used to strongly suppress photoisomerization, as well as other photochemical reactions, and thus convert molecules that normally show fast photodegradation into photostable forms. We find this to be especially efficient in the case of collective strong coupling, where the distribution of a single excitation over many molecules and the light mode leads to a collective protection effect that almost completely suppresses the photochemical reaction.

  1. Suppressing photochemical reactions with quantized light fields

    PubMed Central

    Galego, Javier; Garcia-Vidal, Francisco J.; Feist, Johannes

    2016-01-01

    Photoisomerization, that is, a photochemical reaction leading to a change of molecular structure after absorption of a photon, can have detrimental effects such as leading to DNA damage under solar irradiation, or as a limiting factor for the efficiency of solar cells. Here, we show that strong coupling of organic molecules to a confined light mode can be used to strongly suppress photoisomerization, as well as other photochemical reactions, and thus convert molecules that normally show fast photodegradation into photostable forms. We find this to be especially efficient in the case of collective strong coupling, where the distribution of a single excitation over many molecules and the light mode leads to a collective protection effect that almost completely suppresses the photochemical reaction. PMID:27941754

  2. Integrated adsorptive technique for efficient recovery of m-cresol and m-toluidine from actual acidic and salty wastewater.

    PubMed

    Chen, Da; Liu, Fuqiang; Zong, Lidan; Sun, Xiaowen; Zhang, Xiaopeng; Zhu, Changqing; Tao, Xuewen; Li, Aimin

    2016-07-15

    An integrated adsorptive technique combining an m-cresol adsorption unit, an acid retardation unit and an m-toluidine adsorption unit in sequence was designed to recover m-cresol and m-toluidine from highly acidic and salty m-cresol manufacturing wastewater. In the first column packed with hypercrosslinked polymeric resin (NDA-99), most m-cresol was captured through π-π and hydrogen-bonding interactions as well as the salting-out effect, while m-toluidine was not absorbed due to protonation. To separate acid from salt, an acid retardation unit was introduced successively to adsorb sulfuric acid by strong base anion exchange resin (201×7). After the acid retardation unit and mild neutralization reaction, the last column filled with NDA-99 was applied to trap neutral m-toluidine from the salty effluent. Moreover, the eluent of the acid retardation unit was utilized as the regenerant to recover m-toluidine, and the recycled high-acidity and low-salinity solution of m-toluidine was directly used to produce m-cresol as the raw material. Therefore, the proposed method not only efficiently recycled m-cresol and m-toluidine, but also reduced the consumption of alkali dramatically (saving 0.1628t/t wastewater). These findings will inspire design of integrated adsorptive techniques for treating complex organic wastewater with high efficiency and low cost.

  3. Additive and Photochemical Manufacturing of Copper

    NASA Astrophysics Data System (ADS)

    Yung, Winco K. C.; Sun, Bo; Meng, Zhengong; Huang, Junfeng; Jin, Yingdi; Choy, Hang Shan; Cai, Zhixiang; Li, Guijun; Ho, Cheuk Lam; Yang, Jinlong; Wong, Wai Yeung

    2016-12-01

    In recent years, 3D printing technologies have been extensively developed, enabling rapid prototyping from a conceptual design to an actual product. However, additive manufacturing of metals in the existing technologies is still cost-intensive and time-consuming. Herein a novel platform for low-cost additive manufacturing is introduced by simultaneously combining the laser-induced forward transfer (LIFT) method with photochemical reaction. Using acrylonitrile butadiene styrene (ABS) polymer as the sacrificial layer, sufficient ejection momentum can be generated in the LIFT method. A low-cost continuous wave (CW) laser diode at 405 nm was utilized and proved to be able to transfer the photochemically synthesized copper onto the target substrate. The wavelength-dependent photochemical behaviour in the LIFT method was verified and characterized by both theoretical and experimental studies compared to 1064 nm fiber laser. The conductivity of the synthesized copper patterns could be enhanced using post electroless plating while retaining the designed pattern shapes. Prototypes of electronic circuits were accordingly built and demonstrated for powering up LEDs. Apart from pristine PDMS materials with low surface energies, the proposed method can simultaneously perform laser-induced forward transfer and photochemical synthesis of metals, starting from their metal oxide forms, onto various target substrates such as polyimide, glass and thermoplastics.

  4. Additive and Photochemical Manufacturing of Copper

    PubMed Central

    Yung, Winco K. C.; Sun, Bo; Meng, Zhengong; Huang, Junfeng; Jin, Yingdi; Choy, Hang Shan; Cai, Zhixiang; Li, Guijun; Ho, Cheuk Lam; Yang, Jinlong; Wong, Wai Yeung

    2016-01-01

    In recent years, 3D printing technologies have been extensively developed, enabling rapid prototyping from a conceptual design to an actual product. However, additive manufacturing of metals in the existing technologies is still cost-intensive and time-consuming. Herein a novel platform for low-cost additive manufacturing is introduced by simultaneously combining the laser-induced forward transfer (LIFT) method with photochemical reaction. Using acrylonitrile butadiene styrene (ABS) polymer as the sacrificial layer, sufficient ejection momentum can be generated in the LIFT method. A low-cost continuous wave (CW) laser diode at 405 nm was utilized and proved to be able to transfer the photochemically synthesized copper onto the target substrate. The wavelength-dependent photochemical behaviour in the LIFT method was verified and characterized by both theoretical and experimental studies compared to 1064 nm fiber laser. The conductivity of the synthesized copper patterns could be enhanced using post electroless plating while retaining the designed pattern shapes. Prototypes of electronic circuits were accordingly built and demonstrated for powering up LEDs. Apart from pristine PDMS materials with low surface energies, the proposed method can simultaneously perform laser-induced forward transfer and photochemical synthesis of metals, starting from their metal oxide forms, onto various target substrates such as polyimide, glass and thermoplastics. PMID:28000733

  5. Additive and Photochemical Manufacturing of Copper.

    PubMed

    Yung, Winco K C; Sun, Bo; Meng, Zhengong; Huang, Junfeng; Jin, Yingdi; Choy, Hang Shan; Cai, Zhixiang; Li, Guijun; Ho, Cheuk Lam; Yang, Jinlong; Wong, Wai Yeung

    2016-12-21

    In recent years, 3D printing technologies have been extensively developed, enabling rapid prototyping from a conceptual design to an actual product. However, additive manufacturing of metals in the existing technologies is still cost-intensive and time-consuming. Herein a novel platform for low-cost additive manufacturing is introduced by simultaneously combining the laser-induced forward transfer (LIFT) method with photochemical reaction. Using acrylonitrile butadiene styrene (ABS) polymer as the sacrificial layer, sufficient ejection momentum can be generated in the LIFT method. A low-cost continuous wave (CW) laser diode at 405 nm was utilized and proved to be able to transfer the photochemically synthesized copper onto the target substrate. The wavelength-dependent photochemical behaviour in the LIFT method was verified and characterized by both theoretical and experimental studies compared to 1064 nm fiber laser. The conductivity of the synthesized copper patterns could be enhanced using post electroless plating while retaining the designed pattern shapes. Prototypes of electronic circuits were accordingly built and demonstrated for powering up LEDs. Apart from pristine PDMS materials with low surface energies, the proposed method can simultaneously perform laser-induced forward transfer and photochemical synthesis of metals, starting from their metal oxide forms, onto various target substrates such as polyimide, glass and thermoplastics.

  6. Photochemical tissue bonding

    DOEpatents

    Redmond, Robert W [Brookline, MA; Kochevar, Irene E [Charlestown, MA

    2012-01-10

    Photochemical tissue bonding methods include the application of a photosensitizer to a tissue and/or tissue graft, followed by irradiation with electromagnetic energy to produce a tissue seal. The methods are useful for tissue adhesion, such as in wound closure, tissue grafting, skin grafting, musculoskeletal tissue repair, ligament or tendon repair and corneal repair.

  7. [Effects of exogenous nitric oxide on highbush blueberry PSII photochemical activity and antioxidant system under high temperature stress].

    PubMed

    Wei, Hai-rong; Meng, Yan-ling; Sun, Yang; Liu, Qing-zhong

    2010-10-01

    Taking the test tube 'Duke' highbush blueberry (Vaccinium corymbosum) seedlings having been transplanted to the field for 6 months as test materials, this paper studied the effects of exogenous nitric oxide (NO) on their growth, PS II photochemical activity, and antioxidant system under high temperature stress. Applying 0.2, 0.5, and 1.0 mmol x L(-1) of exogenous sodium nitroprusside (SNP) could alleviate the decrease of maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency under light (phi PS II), photochemical quench (q(P)), and nonphotochemical quench (NPQ) caused by high temperature, and prevented the damage of high temperature on photosynthetic apparatus. Comparing with the control, treatments NO decreased the leaf membrane permeability and MDA content, increased the SOD and CAT activities significantly, and promoted proline accumulation. Appropriate concentration SNP could significantly alleviate the damage of high temperature stress on highbush blueberry seedlings, and 0.5 mmol x L(-1) of SNP had the most satisfactory effect.

  8. Methods for the photochemical utilization of solar energy

    NASA Technical Reports Server (NTRS)

    Schwerzel, R. E.

    1978-01-01

    The paper considers the 'ground rules' which govern the efficiency of photochemical solar energy conversion and then summarizes the most promising approaches in each of three categories: photochemically assisted thermal systems for the heating and/or cooling of structures; photogalvanic systems for the production of electrical power in applications, such as photorechargeable batteries or inexpensive 'solar cells'; and photochemical formation of fuels for combustion and for use as chemical feedstocks or foods. Three concepts for the photochemical utilization of solar energy in space are found to be particularly promising: (1) photochemical trans-cis isomerization of indigold dyes for photoassisted heating or cooling, (2) the redox stabilized photoelectrolysis cell for the production of hydrogen (and/or oxygen or other useful chemicals), and (3) the liquid-junction photovoltaic cell for the production of electrical power.

  9. Photochemical isotope separation

    DOEpatents

    Robinson, C. Paul; Jensen, Reed J.; Cotter, Theodore P.; Greiner, Norman R.; Boyer, Keith

    1987-01-01

    A process for separating isotopes by selective excitation of isotopic species of a volatile compound by tuned laser light. A highly cooled gas of the volatile compound is produced in which the isotopic shift is sharpened and defined. Before substantial condensation occurs, the cooled gas is irradiated with laser light precisely tuned to a desired wavelength to selectively excite a particular isotopic species in the cooled gas. The laser light may impart sufficient energy to the excited species to cause it to undergo photochemical reaction or even to photoionize. Alternatively, a two-photon irradiation may be applied to the cooled gas to induce photochemical reaction or photoionization. The process is particularly applicable to the separation of isotopes of uranium and plutonium.

  10. Chemistry of bifunctional photoprobes. 3 -- Correlation between the efficiency of CH insertion by photolabile chelating agents and lifetimes of singlet nitrenes by flash photolysis: First example of photochemical attachment of {sup 99m}Tc-complex with human serum albumin

    SciTech Connect

    Pandurangi, R.S.; Lusiak, P.; Kuntz, R.R.; Volkert, W.A.; Rogowski, J.; Platz, M.S.

    1998-11-27

    Systematic functionalization of perfluoroaryl azides with chelating agents capable of complexing transition metals produces a new class of bifunctional photolabile chelating agents (BFPCAs). The strategy is shield the azide functionality from the electronic and steric influence of the electron-rich metal Pd through ester and amide bridges raised CH insertion efficiency to unprecedented levels (>92%) in a model solvent (cyclohexane). In contrast, perfluoroaryl azides attached to chelating agents via hydrazones show no significant CH insertion in cyclohexane upon photolysis. Measurements of the lifetimes of the singlet nitrenes derived from these agents by flash photolysis techniques correlate well with the efficiency of CH insertion by demonstrating longer lifetimes (10--50 times) for singlet nitrenes derived from azidotetrafluorinated esters and amides compared with the related hydrazones, which failed to yield significant CH insertion. A representative BFPCA 12 is chelated to diagnostic radionuclide {sup 99m}Tc and covalently attached to human serum albumin via photochemical activation extending the favorable bimolecular insertion characteristics of BFPCA to tracer level concentrations in buffer conditions. Flash photolysis experiments correlate singlet nitrene lifetimes with the efficiency of intermolecular insertion reactions. This work provides new photo-cross-linking technology, useful in radiodiagnostics and radiotherapy in nuclear medicine.

  11. Photochemical cutting of fabrics

    DOEpatents

    Piltch, Martin S.

    1994-01-01

    Apparatus for the cutting of garment patterns from one or more layers of fabric. A laser capable of producing laser light at an ultraviolet wavelength is utilized to shine light through a pattern, such as a holographic phase filter, and through a lens onto the one or more layers of fabric. The ultraviolet laser light causes rapid photochemical decomposition of the one or more layers of fabric, but only along the pattern. The balance of the fabric of the one or more layers of fabric is undamaged.

  12. Effects of alkoxy groups on arene rings of lignin β-O-4 model compounds on the efficiencies of single electron transfer-promoted photochemical and enzymatic C-C Bond Cleavage Reactions.

    PubMed

    Lim, Suk Hyun; Nahm, Keepyung; Ra, Choon Sup; Cho, Dae Won; Yoon, Ung Chan; Latham, John A; Dunaway-Mariano, Debra; Mariano, Patrick S

    2013-09-20

    To gain information about how alkoxy substitution in arene rings of β-O-4 structural units within lignin governs the efficiencies/rates of radical cation C1-C2 bond cleavage reactions, single electron transfer (SET) photochemical and lignin peroxidase-catalyzed oxidation reactions of dimeric/tetrameric model compounds have been explored. The results show that the radical cations derived from less alkoxy-substituted dimeric β-O-4 models undergo more rapid C1-C2 bond cleavage than those of more alkoxy-substituted analogues. These findings gained support from the results of DFT calculations, which demonstrate that C1-C2 bond dissociation energies of β-O-4 radical cations decrease as the degree of alkoxy substitution decreases. In SET reactions of tetrameric compounds consisting of two β-O-4 units, containing different degrees of alkoxy substitution, regioselective radical cation C-C bond cleavage was observed to occur in one case at the C1-C2 bond in the less alkoxy-substituted β-O-4 moiety. However, regioselective C1-C2 cleavage in the more alkoxy-substituted β-O-4 moiety was observed in another case, suggesting that other factors might participate in controlling this process. These observations show that lignins containing greater proportions of less rather than more alkoxylated rings as part of β-O-4 units would be more efficiently cleaved by SET mechanisms.

  13. Photochemical studies of a fluorescent chlorophyll catabolite--source of bright blue fluorescence in plant tissue and efficient sensitizer of singlet oxygen.

    PubMed

    Jockusch, Steffen; Turro, Nicholas J; Banala, Srinivas; Kräutler, Bernhard

    2014-02-01

    Fluorescent chlorophyll catabolites (FCCs) are fleeting intermediates of chlorophyll breakdown, which is seen as an enzyme controlled detoxification process of the chlorophylls in plants. However, some plants accumulate large amounts of persistent FCCs, such as in senescent leaves and in peels of yellow bananas. The photophysical properties of such a persistent FCC (Me-sFCC) were investigated in detail. FCCs absorb in the near UV spectral region and show blue fluorescence (max at 437 nm). The Me-sFCC fluorescence had a quantum yield of 0.21 (lifetime 1.6 ns). Photoexcited Me-sFCC intersystem crosses into the triplet state (quantum yield 0.6) and generates efficiently singlet oxygen (quantum yield 0.59). The efficient generation of singlet oxygen makes fluorescent chlorophyll catabolites phototoxic, but might also be useful as a (stress) signal and for defense of the plant tissue against infection by pathogens.

  14. Polyimides by photochemical cyclopolymerization

    NASA Technical Reports Server (NTRS)

    Meador, Michael A. (Inventor)

    2005-01-01

    The novel polyimides of this invention are derived from Diels-Alder cyclopolymerization of photochemically generated bisdienes with dienophiles, such as bismaleimides, trismaleimides and mixtures thereof with maleimide end-caps. Irradiation of one or more diketones produces two distinct hydroxy o-quinodimethane (photoenol) intermediates. These intermediates are trapped via Diels-Alder cycloaddition with appropriate dienophiles, e.g., bismaleimide and/or trismaleimides to give the corresponding polyimides in quantitative yields. When bismaleimides, trismaleimides or mixtures thereof with maleimide end-caps are used as the dienophile, the resulting polyimides have glass transition temperatures (Tg) as high as 300? C. Polyimide films can be prepared by ultraviolet irradiation of high solids content varnishes of the monomers in a small amount of solvent, e.g., cyclohexanone, dimethyl formamide, N-methylpyrollidone and the like. These novel polyimides are characterized as having high glass transition temperatures, good mechanical properties and improved processing in the manufacture of adhesives, electronic materials and films.

  15. Polyimides by Photochemical Cyclopolymerization

    NASA Technical Reports Server (NTRS)

    Meador, Michael A. (Inventor)

    2005-01-01

    The novel polyimides of this invention are derived from Diels-Alder cyclopolymerization of photochemically generated bisdienes with dienophiles, such as bismaleimides, trismaleimides and mixtures thereof with maleimide endcaps. Irradiation of one or more diketones produces two distinct hydroxy o-quinodimethane (photoenol) intermediates. These intermediates are trapped via Diels-Alder cycloaddition with appropriate dienophiles, e.g., bismaleimide and/or trismaleimides to give the corresponding polyimides in quantitative yields. When bismaleimides, trismaleimides or mixtures thereof with maleimide end-caps are used as the dienophile, the resulting polyimides have glass transition temperatures (Tg) as high as 300 C. Polyimide films can be prepared by ultraviolet irradiation of high solids content varnishes of the monomers in a small amount of solvent, e.g., cyclohexanone, dimethyl formamide, N-methylpyrollidone and the like. These novel polyimides are characterized as having high glass transition temperatures, good mechanical properties and improved processing in the manufacture of adhesives, electronic materials and films.

  16. Photochemically Synthesized Polyimides

    NASA Technical Reports Server (NTRS)

    Meador, Michael A.; Tyson, Daniel S.

    2008-01-01

    An alternative to the conventional approach to synthesis of polyimides involves the use of single monomers that are amenable to photopolymerization. Heretofore, the synthesis of polyimides has involved multiple-monomer formulations and heating to temperatures that often exceed 250 C. The present alternative approach enables synthesis under relatively mild conditions that can include room temperature. The main disadvantages of the conventional approach are the following: Elevated production temperatures can lead to high production costs and can impart thermal stresses to the final products. If the proportions of the multiple monomeric ingredients in a given batch are not exactly correct, the molecular weight and other physical properties of the final material could be reduced from their optimum or desired values. To be useful in the alternative approach, a monomer must have a molecular structure tailored to exploit Diels-Alder trapping of a photochemically generated ortho-quinodimethane. (In a Diels-Alder reaction, a diene combines with a dienophile to form molecules that contain six-membered rings.) In particular, a suitable monomer (see figure) contains ortho-methylbenzophenone connected to a dienophile (in this case, a maleimide) through a generic spacer group. Irradiation with ultraviolet light gives rise to a photochemical intermediate the aforementioned ortho-quinodimethane from the ortho-methylbenzophenone. This group may react with the dienophile on another such monomer molecule to produce an oligomer that, in turn may react in a stepgrowth manner to produce a polyimide. This approach offers several advantages in addition to those mentioned above: The monomer can be stored for a long time because it remains unreactive until exposed to light. Because the monomer is the only active starting ingredient, there is no need for mixing, no concern for ensuring correct proportions of monomers, and the purity of the final product material is inherently high. The use

  17. Photochemical conversion of solar energy.

    PubMed

    Balzani, Vincenzo; Credi, Alberto; Venturi, Margherita

    2008-01-01

    Energy is the most important issue of the 21st century. About 85% of our energy comes from fossil fuels, a finite resource unevenly distributed beneath the Earth's surface. Reserves of fossil fuels are progressively decreasing, and their continued use produces harmful effects such as pollution that threatens human health and greenhouse gases associated with global warming. Prompt global action to solve the energy crisis is therefore needed. To pursue such an action, we are urged to save energy and to use energy in more efficient ways, but we are also forced to find alternative energy sources, the most convenient of which is solar energy for several reasons. The sun continuously provides the Earth with a huge amount of energy, fairly distributed all over the world. Its enormous potential as a clean, abundant, and economical energy source, however, cannot be exploited unless it is converted into useful forms of energy. This Review starts with a brief description of the mechanism at the basis of the natural photosynthesis and, then, reports the results obtained so far in the field of photochemical conversion of solar energy. The "grand challenge" for chemists is to find a convenient means for artificial conversion of solar energy into fuels. If chemists succeed to create an artificial photosynthetic process, "... life and civilization will continue as long as the sun shines!", as the Italian scientist Giacomo Ciamician forecast almost one hundred years ago.

  18. Polyesters by Photochemical Cyclopolymerization

    NASA Technical Reports Server (NTRS)

    Meador, Michael A. (Inventor)

    2002-01-01

    The polyesters of this invention are derived from a Diels-Alder cyclopolymerization of a photochemically generated bisdiene with dienophiles, such as di(acrylates), tri (acrylates), di(methacrylates), tri(methacrylates) and mixtures thereof with mono(methacrylates) or mono(acrylate) end-caps. Irradiation of one or more diketones produces two distinct hydroxy o-quinodimethane (photoenol) intermediates. These intermediates are trapped via a Diels-Alder cycloaddition with appropriate dienophiles, e.g., di(acrylates) to give the corresponding in polyesters quantitative yields. When di(acrylates), tri(acrylates) and di and tri(methacrylates) or mixtures thereof with monoacrylate end-caps are used as the dienophile, the resulting polyesters have glass transition temperatures (Tg) as high as 200 C. Polyesters films can be prepared by ultraviolet irradiation of high solids content varnishes of the monomers in a small amount of solvent, e.g., cyclohexanone, dimethyl formamide, N-methylpyrollidone and the like. These polyesters, i.e. polyesters are characterized as having high glass transition temperatures, good mechanical properties and improved processing in the manufacture of composites, adhesives, electronic materials and films.

  19. Polyimides by Photochemical Cyclopolymerization

    NASA Technical Reports Server (NTRS)

    Meador, Michael A. (Inventor)

    2003-01-01

    The polyimides of this invention are derived from a Diels-Alder cyclopolymerization of a photochemically generated bisdiene with dienophiles, such as bismaleimides, trismaleimides and mixtures thereof with maleimide end-caps. Irradiation of one or more diketones produces two distinct hydroxy o-quinodimethane (photoenol) intermediates. These intermediates are trapped via a Diels-Alder cycloaddition with appropriate dienophiles, e.g., bismaleimide and/or trismaleimides to give the corresponding polyimides in quantitative yields. When bismaleimides, trismaleimides or mixtures thereof with maleimide end-caps are used as the dienophile, the resulting polyimides have glass transition temperatures (Tg) as high as 300 C. Polyimide films can be prepared by ultraviolet irradiation of high solids content varnishes of the monomers in a small amount of solvent, e.g., cyclohexanone, dimethyl formamide, N-methylpyrollidone and the like. These polyimides are characterized as having high glass transition temperatures, good mechanical properties and improved processing in the manufacture of adhesives, electronic materials and films.

  20. Plasmonic antenna effects on photochemical reactions.

    PubMed

    Gao, Shuyan; Ueno, Kosei; Misawa, Hiroaki

    2011-04-19

    Efficient solar energy conversion has been vigorously pursued since the 1970s, but its large-scale implementation hinges on the availability of high-efficiency modules. For maximum efficiency, it is important to absorb most of the incoming radiation, which necessitates both efficient photoexcitation and minimal electron-hole recombination. To date, researchers have primarily focused on the latter difficulty: finding a strategy to effectively separate photoinduced electrons and holes. Very few reports have been devoted to broadband sunlight absorption and photoexcitation. However, the currently available photovoltaic cells, such as amorphous silicon, and even single-crystal silicon and sensitized solar cells, cannot respond to the wide range of the solar spectrum. The photoelectric conversion characteristics of solar cells generally decrease in the infrared wavelength range. Thus, the fraction of the solar spectrum absorbed is relatively poor. In addition, the large mismatch between the diffraction limit of light and the absorption cross-section makes the probability of interactions between photons and cell materials quite low, which greatly limits photoexcitation efficiency. Therefore, there is a pressing need for research aimed at finding conditions that lead to highly efficient photoexcitation over a wide spectrum of sunlight, particularly in the visible to near-infrared wavelengths. As characterized in the emerging field of plasmonics, metallic nanostructures are endowed with optical antenna effects. These plasmonic antenna effects provide a promising platform for artificially sidestepping the diffraction limit of light and strongly enhancing absorption cross-sections. Moreover, they can efficiently excite photochemical reactions between photons and molecules close to an optical antenna through the local field enhancement. This technology has the potential to induce highly efficient photoexcitation between photons and molecules over a wide spectrum of sunlight

  1. Hairlike Percutaneous Photochemical Sensors

    NASA Technical Reports Server (NTRS)

    George, Thomas; Loeb, Gerald

    2004-01-01

    Instrumentation systems based on hairlike fiber-optic photochemical sensors have been proposed as minimally invasive means of detecting biochemicals associated with cancer and other diseases. The fiber-optic sensors could be mass-produced as inexpensive, disposable components. The sensory tip of a fiber-optic sensor would be injected through the patient's skin into subcutaneous tissue. A biosensing material on the sensory tip would bind or otherwise react with the biochemical(s) of interest [the analyte(s)] to produce a change in optical properties that would be measured by use of an external photonic analyzer. After use, a fiber-optic sensor could be simply removed by plucking it out with tweezers. A fiber-optic sensor according to the proposal would be of the approximate size and shape of a human hair, and its sensory tip would resemble a follicle. Once inserted into a patient's subcutaneous tissue, the sensor would even more closely resemble a hair growing from a follicle (see Figure 1). The biosensing material on the sensory tip could consist of a chemical and/or cells cultured and modified for the purpose. The biosensing material would be contained within a membrane that would cover the tip. If the membrane were not permeable by an analyte, then it would be necessary to create pores in the membrane that would be large enough to allow analyte molecules to diffuse to the biosensing material, but not so large as to allow cells (if present as part of the biosensing material) to diffuse out. The end of the fiber-optic sensor opposite the sensory tip would be inserted in a fiberoptic socket in the photonic analyzer.

  2. Photochemical investigation of sensitizers used in medicine

    NASA Astrophysics Data System (ADS)

    Kovalskaya, Natalia E.; Sokolova, Irina V.; Kuznetsova, Nina A.

    2001-08-01

    In this work we present the photophysical and photochemical investigation of the same sensititizers used in phototherapy. On an example water-soluble phthalocyanines of zinc some laws of influence of structure on the spectral characteristics and condition of dye in a solution are investigated. The quantum chemistry method of intermediate neglect of differential overlap with spectroscopic parameterization is used to study the spectroscopic- luminescent and physical characteristics of other sensitizers-psoralen, its isomers and metoxysubstitutes. Efficient intersystem conversion, which cause significant population of triplets, is observed for the examined compounds. Effects of isomerism and metoxysubstitution on the energy level diagram, photoelectron spectrum, and dipole moments are demonstrated.

  3. Gated photochemical hole burning in photoadducts of polyacenes

    NASA Technical Reports Server (NTRS)

    Iannone, Mark; Scott, Gary W.; Brinza, David; Coulter, Daniel R.

    1986-01-01

    A photoadduct of anthracene and tetracene (A-T) in a polymer matrix at 1.5 K generates an absorption spectrum which exhibits two-color, photon-gated photochemical hole burning (PHB) when irradiated with narrowband exciting light into the 0-0 band of the S1-S0 absorption. The efficiency of this PHB process is found to be enhanced by simultaneous irradiation near the maximum of the Tn-T1 absorption of A-T; hole widths of less than 0.07/cm have been observed for this photochemical cleavage of A-T.

  4. Photochemical Approaches to Complex Chemotypes: Applications in Natural Product Synthesis

    PubMed Central

    2016-01-01

    The use of photochemical transformations is a powerful strategy that allows for the formation of a high degree of molecular complexity from relatively simple building blocks in a single step. A central feature of all light-promoted transformations is the involvement of electronically excited states, generated upon absorption of photons. This produces transient reactive intermediates and significantly alters the reactivity of a chemical compound. The input of energy provided by light thus offers a means to produce strained and unique target compounds that cannot be assembled using thermal protocols. This review aims at highlighting photochemical transformations as a tool for rapidly accessing structurally and stereochemically diverse scaffolds. Synthetic designs based on photochemical transformations have the potential to afford complex polycyclic carbon skeletons with impressive efficiency, which are of high value in total synthesis. PMID:27120289

  5. Photochemical grid model implementation and application of VOC, NOx, and O3 source apportionment

    EPA Science Inventory

    For the purposes of developing optimal emissions control strategies, efficient approaches are needed to identify the major sources or groups of sources that contribute to elevated ozone (O3) concentrations. Source-based apportionment techniques implemented in photochemical grid m...

  6. Photochemical inactivation of alpha- and poxviruses.

    PubMed

    Sagripanti, Jose-Luis; Marschall, Hans-Jürgen; Voss, Lucy; Hülseweh, Birgit

    2011-01-01

    The objective of this study was to determine whether photochemical inactivation of viruses could be accomplished with high efficiency while preserving the molecular integrity of viral targets allowing subsequent diagnostic tests to be performed at a lower level of containment and cost. We studied the effect of 5-iodonaphthyl 1-azide (INA) and amotosalen (AMO, also known as S-59), which are photochemicals known to target either viral proteins or nucleic acids, respectively. We found that vaccinia virus (VACV, an orthopox virus with a DNA genome) and pixuna virus (PIXV, an alphavirus with an RNA genome) were stable when irradiated with UVA alone or when exposed to either INA or AMO in the dark. AMO followed by UVA exposure was at least 1000-fold more virucidal than INA/UVA on vaccinia and pixuna viruses treated under similar conditions. Photoinactivation with either INA or AMO at conditions that abolished viral infectivity resulted in only minimal impairment of subsequent ELISA and PCR testing. The results presented in this study should assist in developing methods to inactivate in the field environmental and forensic samples suspected of viral contamination, thus limiting the need for costly security and safety operations after an accidental or intentional viral release.

  7. Photochemical grid model implementation and application of ...

    EPA Pesticide Factsheets

    For the purposes of developing optimal emissions control strategies, efficient approaches are needed to identify the major sources or groups of sources that contribute to elevated ozone (O3) concentrations. Source-based apportionment techniques implemented in photochemical grid models track sources through the physical and chemical processes important to the formation and transport of air pollutants. Photochemical model source apportionment has been used to track source impacts of specific sources, groups of sources (sectors), sources in specific geographic areas, and stratospheric and lateral boundary inflow on O3. The implementation and application of a source apportionment technique for O3 and its precursors, nitrogen oxides (NOx) and volatile organic compounds (VOCs), for the Community Multiscale Air Quality (CMAQ) model are described here. The Integrated Source Apportionment Method (ISAM) O3 approach is a hybrid of source apportionment and source sensitivity in that O3 production is attributed to precursor sources based on O3 formation regime (e.g., for a NOx-sensitive regime, O3 is apportioned to participating NOx emissions). This implementation is illustrated by tracking multiple emissions source sectors and lateral boundary inflow. NOx, VOC, and O3 attribution to tracked sectors in the application are consistent with spatial and temporal patterns of precursor emissions. The O3 ISAM implementation is further evaluated through comparisons of apportioned am

  8. Photochemical functionalization of diamond surfaces

    NASA Astrophysics Data System (ADS)

    Nichols, Beth Marie

    Diamond surfaces are excellent substrates for potential applications in fields such as biotechnology, molecular sensing, and molecular electronics. In order to develop new diamond-based technologies, it is important to develop a fundamental understanding of diamond surface chemistry. Previous work in the Hamers group has demonstrated covalent functionalization of hydrogen-terminated diamond surfaces with molecules bearing a terminal vinyl group via a photochemical process using sub-bandgap light at 254 nm. While the reaction was shown to occur reproducibly with self-terminating monolayer surface coverage, the mechanism was never fully understood. This thesis investigates the photochemical modification of hydrogen-terminated surfaces of diamond. The results show that this reaction is a surface-mediated radical process initiated by the UV-assisted photoejection of electrons from the diamond surfaces into the liquid phase. To develop a better understanding of the photochemical mechanism, an electrical bias was applied to the diamond samples during the photochemical reaction. Applying a 1 volt potential between two diamond electrodes significantly increases the rate of functionalization of the negative electrode. Cyclic voltammetry and electrochemical impedance measurements show that the applied potential induces downward band-bending within the negative diamond film electrode. At higher voltages a Faradaic current is observed, with no further acceleration of the functionalization rate. The bias-dependent changes in rate are attributed to a field effect; the applied potential induces a downward band-bending on the negative electrode and facilitates electron ejection into the adjacent organic fluid. The ability to directly organically photopattern the surface on length scales of <25 microns has also been demonstrated using simple photomasking techniques. Techniques for the functionalization of diamond may be applied to other 'unreactive' surfaces. The activation of a

  9. Influence of humidity on photochemical ozone generation with 172nm xenon excimer lamps

    NASA Astrophysics Data System (ADS)

    Salvermoser, M. J.; Kogelschatz, U.; Murnick, D. E.

    2009-08-01

    The reaction kinetics of photochemical ozone (O{3}) generation in humid air and oxygen (O{2}) using efficient, narrow band vacuum ultra violet (VUV) 172 nm xenon excimer lamps is discussed. Trace amounts of water (H{2}O) vapor in the process gas leads to hydroxyl (OH) and hydroperoxy (HO{2}) radical formation. These radicals drive a catalytic O{3} destruction cycle limiting O{3} saturation concentration. This catalytic O{3} destruction cycle was included into a quantitative kinetic model describing photochemical O{3} production. Experimental O{3} saturation concentrations obtained with coaxial VUV driven photochemical O{3} generators compare satisfactorily with the models predictions.

  10. Photochemical [2 + 2] cycloaddition of N,N-diethylpropynylamine to C[sub 60

    SciTech Connect

    Zhang, X.; Romero, A.; Foote, C.S. )

    1993-11-17

    We report an efficient photochemical [2 + 2] cycloaddition route to a C[sub 60] adduct and its subsequent reaction to give a very high yield of a difunctional dihydrofullerene in one pot. These preliminary studies demonstrate a potentially versatile, high-yield photochemical functionalization of C[sub 60]. The moderately stable cyclobutenamine undergoes interesting chemical changes that lead to useful functionalized dihydrofullerenes that should be easily converted to a wide variety of derivatives. The mechanism of the photochemical [2 + 2] cycloaddition of C[sub 60] with electron-rich compounds is under investigation. 38 refs.

  11. Photochemical air pollution. Part I

    SciTech Connect

    Goldstein E.; Hackney, J.D.; Rokaw, S.N.

    1985-03-01

    In this paper, epidemiologic studies are reported which indicate that high photochemical oxidant exposures: do not cause mortality or serious illness; may increase the risk of asthmatic attacks in a small percentage of asthmatic patients; appear to reduce pulmonary function in smokers and nonsmokers after long-term exposure; cause acute discomfort of eye and throat, chest irritation and cough; and interfere with athletic performance. Exposure to high ambient levels of NO/sub 2/ is not associated with mortality, serious disease or respiratory dysfunction, but self-limiting symptoms of respiratory irritation or illness may develop in children. 106 references, 2 figures, 1 table.

  12. Photochemical mutagenesis: examples and toxicological relevance.

    PubMed

    Gocke, E

    2001-01-01

    Induction of DNA damage as a consequence of exposure to UV light has been established as the major cause of skin cancer. DNA molecules absorb photon energy directly for wavelengths <320 nm, and lead to well-characterized mutagenic DNA damage. Alternatively, endogenous or exogenous chemicals (sensitizers) may absorb light with the potential of subsequent energy or electron transfer, and lead indirectly to DNA damage. A few light-absorbing pharmaceuticals have long been known to cause photo(geno)toxic effects. Notably, psoralen and chlorpromazine derivatives have been established as photomutagens and the reaction mechanisms have been identified; the fluoroquinolone antibiotics have more recently been recognized as being photomutagenic. The type of DNA damage and the modulation by antioxidants indicate the involvement of reactive oxygen species (ROS), but other mechanisms are also reported for, at least, some derivatives. In routine genotoxicity studies, we observed the photomutagenic activity of a compound (Ro 19-8022) under development as an anxiolytic agent in the Ames tester strain TA102 under normal laboratory illumination conditions. Further investigations showed strong photogenotoxic activity in tests for gene mutations and chromosomal aberrations in mammalian cells. The finding led to the termination of drug development. Another example of a pharmaceutical for which photogenotoxic properties were observed during development is Ro 47-7737, a bisquinoline derivative of the antimalaria compound chloroquine. Also in this case, the photochemical reactivity contributed to the termination of the development process. The risk/benefit assessment for the described compounds has to take into account the human exposure situation, for example, the ability to avoid light exposure during treatment. Consideration of photochemical mutagenesis is specifically important for sunscreen ingredients. The active components of sunscreen lotions are efficient UV absorbers. Consequently

  13. Engineering photochemical smog through convection towers

    SciTech Connect

    Elliott, S.; Prueitt, M.L.; Bossert, J.E.; Mroz, E.J.; Krakowski, R.A.; Miller, R.L.; Jacobson, M.Z.; Turco, R.P. |

    1995-02-01

    Reverse convection towers have attracted attention as a medium for cleansing modern cities. Evaporation of an aqueous mist injected at the tower opening could generate electrical power by creating descent, and simultaneously scavenge unsightly and unhealthful particulates. The study offered here assesses the influence to tower water droplets on the photochemical component of Los Angeles type smog. The primary radical chain initiator OH is likely removed into aqueous phases well within the residence time of air in the tower, and then reacts away rapidly. Organics do not dissolve, but nighttime hydrolysis of N{sub 2}O{sub 5} depletes the nitrogen oxides. A lack of HOx would slow hydrocarbon oxidation and so also ozone production. Lowering of NOx would also alter ozone production rates, but the direction is uncertain. SO{sub 2} is available in sufficient quantities in some urban areas to react with stable oxidants, and if seawater were the source of the mist, the high pH would lead to fast sulfur oxidation kinetics. With an accommodation coefficient of 10{sup {minus}3}, however, ozone may not enter the aqueous phase efficiently. Even if ozone is destroyed or its production suppressed, photochemical recovery times are on the order of hours, so that tower processing must be centered on a narrow midday time window. The cost of building the number of structures necessary for this brief turnover could be prohibitive. The increase in humidity accompanying mist evaporation could be controlled with condensers, but might otherwise counteract visibility enhancements by recreating aqueous aerosols. Quantification of the divergent forcings convection towers must exert upon the cityscape would call for coupled three dimensional modeling of transport, microphysics, and photochemistry. 112 refs.

  14. Photochemical behaviour of phenylurea herbicides.

    PubMed

    Amine-Khodja, Amina; Boulkamh, Abdelaziz; Boule, Pierre

    2004-02-01

    The photochemical behaviour of phenylurea herbicides in aqueous solution is highly dependent on the nature and position of substituents on the ring. Most of these herbicides are methylated on the urea moiety, the other substituents are usually halogens or methoxy groups. The main reaction involving the aromatic ring of unhalogenated phenylureas excited at wavelengths shorter than 300 nm is an intramolecular rearrangement, similar to photo-Fries rearrangement, whereas with halogenated derivatives, photohydrolysis is the main transformation pathway. In the particular case of para-halogenated phenylureas, the intermediate formation of a carbene is observed. When the urea moiety is substituted with a methoxyl group, demethoxylation is a competitive reaction. N-Demethylation or oxidation of methyl groups is also observed, but with a lower yield. Photooxidation of phenylureas can also be induced by photocatalysis, iron salts or humic substances. In the absence of water, the main route for phototransformation of diuron is the oxidation or elimination of methyl groups. It is entirely possible that a photochemical intermediate could turn out to be more toxic than the initial herbicide.

  15. Photochemical N-demethylation of alkaloids.

    PubMed

    Ripper, J A; Tiekink, E R; Scammells, P J

    2001-02-26

    Certain alkaloids were observed to undergo N-demethylation processes under photochemical conditions. Tropine, acetyltropine, tropinone, and atropine were cleanly N-demethylated upon treatment with tetraphenylporphin, oxygen, and light. Dextromethorphan also underwent a N-demethylation reaction, but reacted further to afford an imine. In contrast, 14-acyloxycodeinones underwent a photochemically induced tandem N-demethylation acyl migration.

  16. Isoprene: a photochemical kinetic mechanism

    SciTech Connect

    Killus, J.P.; Whitten, G.Z.

    1984-03-01

    A computer-modeling study has produced a photochemical kinetic mechanism for the atmospheric chemistry of isoprene, a naturally occurring common constituent of the troposphere. The kinetic mechnism is ready for use in atmospheric models because the reactions described are shown to adequately reproduce the results of a series of outdoor smog chamber experiments which encompass a wide range of precursor conditions of isoprene and NO/sub x/. Isoprene is a very reactive molecule that can contribute as much as 50% of the overall reactivity of rural air even though isoprene might be only 6% of the ambient hydrocarbon level. The major intermediate products of the atmospheric oxidation of isoprene, methyl vinyl ketone, methacrolein, methylglyoxal, and formaldehyde are also highly reactive. 25 references.

  17. Tropospheric Ozone and Photochemical Smog

    NASA Astrophysics Data System (ADS)

    Sillman, S.

    2003-12-01

    The question of air quality in polluted regions represents one of the issues of geochemistry with direct implications for human well-being. Human health and well-being, along with the well-being of plants, animals, and agricultural crops, are dependent on the quality of air we breathe. Since the start of the industrial era, air quality has become a matter of major importance, especially in large cities or urbanized regions with heavy automobile traffic and industrial activity.Concern over air quality existed as far back as the 1600s. Originally, polluted air in cities resulted from the burning of wood or coal, largely as a source of heat. The industrial revolution in England saw a great increase in the use of coal in rapidly growing cities, both for industrial use and domestic heating. London suffered from devastating pollution events during the late 1800s and early 1900s, with thousands of excess deaths attributed to air pollution (Brimblecombe, 1987). With increasing use of coal, other instances also occurred in continental Europe and the USA. These events were caused by directly emitted pollutants (primary pollutants), including sulfur dioxide (SO2), carbon monoxide (CO), and particulates. They were especially acute in cities with northerly locations during fall and winter when sunlight is at a minimum. These original pollution events gave rise to the term "smog" (a combination of smoke and fog). Events of this type have become much less severe since the 1950s in Western Europe and the US, as natural gas replaced coal as the primary source of home heating, industrial smokestacks were designed to emit at higher altitudes (where dispersion is more rapid), and industries were required to install pollution control equipment.Beginning in the 1950s, a new type of pollution, photochemical smog, became a major concern. Photochemical smog consists of ozone (O3) and other closely related species ("secondary pollutants") that are produced photochemically from directly

  18. The Course of Actualization

    ERIC Educational Resources Information Center

    De Smet, Hendrik

    2012-01-01

    Actualization is traditionally seen as the process following syntactic reanalysis whereby an item's new syntactic status manifests itself in new syntactic behavior. The process is gradual in that some new uses of the reanalyzed item appear earlier or more readily than others. This article accounts for the order in which new uses appear during…

  19. Solar photochemical process engineering for production of fuels and chemicals

    NASA Technical Reports Server (NTRS)

    Biddle, J. R.; Peterson, D. B.; Fujita, T.

    1985-01-01

    The engineering costs and performance of a nominal 25,000 scmd (883,000 scfd) photochemical plant to produce dihydrogen from water were studied. Two systems were considered, one based on flat-plate collector/reactors and the other on linear parabolic troughs. Engineering subsystems were specified including the collector/reactor, support hardware, field transport piping, gas compression equipment, and balance-of-plant (BOP) items. Overall plant efficiencies of 10.3 and 11.6 percent are estimated for the flat-plate and trough systems, respectively, based on assumed solar photochemical efficiencies of 12.9 and 14.6 percent. Because of the opposing effects of concentration ratio and operating temperature on efficiency, it was concluded that reactor cooling would be necessary with the trough system. Both active and passive cooling methods were considered. Capital costs and energy costs, for both concentrating and non-concentrating systems, were determined and their sensitivity to efficiency and economic parameters were analyzed. The overall plant efficiency is the single most important factor in determining the cost of the fuel.

  20. Solar photochemical process engineering for production of fuels and chemicals

    NASA Astrophysics Data System (ADS)

    Biddle, J. R.; Peterson, D. B.; Fujita, T.

    The engineering costs and performance of a nominal 25,000 scmd (883,000 scfd) photochemical plant to produce dihydrogen from water were studied. Two systems were considered, one based on flat-plate collector/reactors and the other on linear parabolic troughs. Engineering subsystems were specified including the collector/reactor, support hardware, field transport piping, gas compression equipment, and balance-of-plant (BOP) items. Overall plant efficiencies of 10.3 and 11.6 percent are estimated for the flat-plate and trough systems, respectively, based on assumed solar photochemical efficiencies of 12.9 and 14.6 percent. Because of the opposing effects of concentration ratio and operating temperature on efficiency, it was concluded that reactor cooling would be necessary with the trough system. Both active and passive cooling methods were considered. Capital costs and energy costs, for both concentrating and non-concentrating systems, were determined and their sensitivity to efficiency and economic parameters were analyzed. The overall plant efficiency is the single most important factor in determining the cost of the fuel.

  1. Solar photochemical process engineering for production of fuels and chemicals

    NASA Astrophysics Data System (ADS)

    Biddle, J. R.; Peterson, D. B.; Fujita, T.

    1984-05-01

    The engineering costs and performance of a nominal 25,000 scmd (883,000 scfd) photochemical plant to produce dihydrogen from water were studied. Two systems were considered, one based on flat-plate collector/reactors and the other on linear parabolic troughs. Engineering subsystems were specified including the collector/reactor, support hardware, field transport piping, gas compression equipment, and balance-of-plant (BOP) items. Overall plant efficiencies of 10.3 and 11.6% are estimated for the flat-plate and trough systems, respectively, based on assumed solar photochemical efficiencies of 12.9 and 14.6%. Because of the opposing effects of concentration ratio and operating temperature on efficiency, it was concluded that reactor cooling would be necessary with the trough system. Both active and passive cooling methods were considered. Capital costs and energy costs, for both concentrating and non-concentrating systems, were determined and their sensitivity to efficiency and economic parameters were analyzed. The overall plant efficiency is the single most important factor in determining the cost of the fuel.

  2. Solar photochemical process engineering for production of fuels and chemicals

    NASA Technical Reports Server (NTRS)

    Biddle, J. R.; Peterson, D. B.; Fujita, T.

    1984-01-01

    The engineering costs and performance of a nominal 25,000 scmd (883,000 scfd) photochemical plant to produce dihydrogen from water were studied. Two systems were considered, one based on flat-plate collector/reactors and the other on linear parabolic troughs. Engineering subsystems were specified including the collector/reactor, support hardware, field transport piping, gas compression equipment, and balance-of-plant (BOP) items. Overall plant efficiencies of 10.3 and 11.6% are estimated for the flat-plate and trough systems, respectively, based on assumed solar photochemical efficiencies of 12.9 and 14.6%. Because of the opposing effects of concentration ratio and operating temperature on efficiency, it was concluded that reactor cooling would be necessary with the trough system. Both active and passive cooling methods were considered. Capital costs and energy costs, for both concentrating and non-concentrating systems, were determined and their sensitivity to efficiency and economic parameters were analyzed. The overall plant efficiency is the single most important factor in determining the cost of the fuel.

  3. Photochemical "triode" molecular signal transducer.

    PubMed

    Keirstead, Amy E; Bridgewater, James W; Terazono, Yuichi; Kodis, Gerdenis; Straight, Stephen; Liddell, Paul A; Moore, Ana L; Moore, Thomas A; Gust, Devens

    2010-05-12

    A molecular "hexad" in which five bis(phenylethynyl)anthracene (BPEA) fluorophores and a dithienylethene photochrome are organized by a central hexaphenylbenzene unit has been prepared. Singlet-singlet energy transfer among the BPEA units occurs on the 0.4 and 60 ps time scales, and when the dithienylethene is in the open form, the BPEA units fluoresce in the 515 nm region with a quantum yield near unity. When the dithienylethene is photoisomerized by UV light to the closed form, which absorbs in the 500-700 nm region, the closed isomer strongly quenches all of the excited singlet states of BPEA via energy transfer, causing the fluorescence quantum yield to drop to near zero. This photochemical behavior permits the hexad to function in a manner analogous to a triode vacuum tube or transistor. When a solution of the hexad is irradiated with steady-state light at 350 nm and with red light (>610 nm) of modulated intensity, the BPEA fluorescence excited by the 350 nm light is modulated accordingly. The fluorescence corresponds to the output of a triode tube or transistor and the modulated red light to the grid signal of the tube or gate voltage of the transistor. Frequency modulation, amplitude modulation, and phase modulation are all observed. The unusual ability to modulate intense, shorter-wavelength fluorescence with longer-wavelength light could be useful for the detection of fluorescence from probe molecules without interference from other emitters in biomolecular or nanotechnological applications.

  4. The photochemical smog pollution in Beijing

    SciTech Connect

    Xiaoyan Tang

    1996-12-31

    The photochemical smog pollution in summer time has been studied in Beijing area. The systematic field measurements associated with meteorological observation was conducted in 1986, 1987 and 1993. The spatial and temporal distribution of O{sub 3} and specific formation condition of photochemical smog, including vehicle emission sources and meteorological factors etc. in summer were studied and discussed. The prediction of O{sub 3} ambient air concentration in Beijing area in 2000, 2005 and 2010 by model simulation were also discussed.

  5. Arbuscular mycorrhizal symbiosis ameliorates the optimum quantum yield of photosystem II and reduces non-photochemical quenching in rice plants subjected to salt stress.

    PubMed

    Porcel, Rosa; Redondo-Gómez, Susana; Mateos-Naranjo, Enrique; Aroca, Ricardo; Garcia, Rosalva; Ruiz-Lozano, Juan Manuel

    2015-08-01

    Rice is the most important food crop in the world and is a primary source of food for more than half of the world population. However, salinity is considered the most common abiotic stress reducing its productivity. Soil salinity inhibits photosynthetic processes, which can induce an over-reduction of the reaction centres in photosystem II (PSII), damaging the photosynthetic machinery. The arbuscular mycorrhizal (AM) symbiosis may improve host plant tolerance to salinity, but it is not clear how the AM symbiosis affects the plant photosynthetic capacity, particularly the efficiency of PSII. This study aimed at determining the influence of the AM symbiosis on the performance of PSII in rice plants subjected to salinity. Photosynthetic activity, plant gas-exchange parameters, accumulation of photosynthetic pigments and rubisco activity and gene expression were also measured in order to analyse comprehensively the response of the photosynthetic processes to AM symbiosis and salinity. Results showed that the AM symbiosis enhanced the actual quantum yield of PSII photochemistry and reduced the quantum yield of non-photochemical quenching in rice plants subjected to salinity. AM rice plants maintained higher net photosynthetic rate, stomatal conductance and transpiration rate than nonAM plants. Thus, we propose that AM rice plants had a higher photochemical efficiency for CO2 fixation and solar energy utilization and this increases plant salt tolerance by preventing the injury to the photosystems reaction centres and by allowing a better utilization of light energy in photochemical processes. All these processes translated into higher photosynthetic and rubisco activities in AM rice plants and improved plant biomass production under salinity.

  6. Photochemical transformations of diazocarbonyl compounds: expected and novel reactions

    NASA Astrophysics Data System (ADS)

    Galkina, O. S.; Rodina, L. L.

    2016-05-01

    Photochemical reactions of diazocarbonyl compounds are well positioned in synthetic practice as an efficient method for ring contraction and homologation of carboxylic acids and as a carbene generation method. However, interpretation of the observed transformations of diazo compounds in electronically excited states is incomplete and requires a careful study of the fine mechanisms of these processes specific to different excited states of diazo compounds resorting to modern methods of investigation, including laser technology. The review is devoted to analysis of new data in the chemistry of excited states of diazocarbonyl compounds. The bibliography includes 155 references.

  7. Stratospheric Ozone: Transport, Photochemical Production and Loss

    NASA Technical Reports Server (NTRS)

    Douglass, A. R.; Kawa, S. R.; Jackman, C. H.

    2003-01-01

    Observations from various satellite instruments (e.g., Total Ozone Mapping Spectrometer (TOMS), Halogen Occultation Experiment (HALOE), Microwave Limb Sounder (MLS)) specify the latitude and seasonal variations of total ozone and ozone as a function of altitude. These seasonal variations change with latitude and altitude partly due to seasonal variation in transport and temperature, partly due to differences in the balance between photochemical production and loss processes, and partly due to differences in the relative importance of the various ozone loss processes. Comparisons of modeled seasonal ozone behavior with observations test the following: the seasonal dependence of dynamical processes where these dominate the ozone tendency; the seasonal dependence of photochemical processes in the upper stratosphere; and the seasonal change in the balance between photochemical and dynamical processes.

  8. Formation and inhibition of photochemical smog

    SciTech Connect

    Heicklen, J.

    1987-01-01

    Photochemical smog is caused by a free-radical chain mechanism which converts NO to NO/sub 2/. The NO/sub 2/ further reacts to produce ozone, nitric acid, and peracylnitrates. This chain mechanism can be inhibited by suitable free-radical scavengers. The chemistry and toxicology of one such free-radical scavenger, diethylhydroxylamine, has been studied in depth. It has been shown to be effective, safe, and practical for use in urban atmospheres to prevent photochemical smog formation. 42 references.

  9. meta-Oligoazobiphenyls – synthesis via site-selective Mills reaction and photochemical properties

    PubMed Central

    Reuter, Raphael

    2012-01-01

    Summary The investigation of multi-photochromic compounds constitutes a great challenge, not only from a synthetic point of view, but also with respect to the analysis of the photochemical properties. In this context we designed a novel strategy to access meta-oligoazobiphenyls via site-selective Mills reaction and Suzuki cross-coupling in a highly efficient iterative way. Photochemical examination of the resulting monomeric and oligomeric azo compounds revealed that the overall degree of switching was independent of the connected azo-units. However, one of the azobonds in the bis-azobiphenyl is isomerized preferentially despite the high structural similarity. PMID:23015837

  10. Photochemical Production of Oligothiophene and Polythiophene Micropatterns from 2,5-diiodothiophene on Au in UHV

    SciTech Connect

    Liu,G.; Natarajan, S.; Kim, S.

    2005-01-01

    Fabrication of oligothiophene and polythiophene micropatterns is demonstrated by photochemical reactions of 2, 5-diiodothiophene adsorbed on an Au coated Si wafer under UHV conditions. For patterning, a TEM grid is utilized as a model stencil mask. Fluorescence microscopic analysis shows that polymer microstructures with good pattern fidelity are attained over a large area. RAIRS and NEXAFS analyses indicate that the electronic and molecular structures of the produced polymer are similar to those of chemically synthesized polythiophene. The structural defects of the photochemically produced polymer are negligible. The present procedure provides a very efficient strategy for growth and patterning of conjugated polymer microstructures with high quality in one step.

  11. 40 CFR 52.1877 - Control strategy: Photochemical oxidants (hydrocarbons).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... oxidants (hydrocarbons). 52.1877 Section 52.1877 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY....1877 Control strategy: Photochemical oxidants (hydrocarbons). (a) The requirements of Subpart G of this... national standard for photochemical oxidants (hydrocarbons) in the Metropolitan Cincinnati...

  12. 40 CFR 52.1877 - Control strategy: Photochemical oxidants (hydrocarbons).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... oxidants (hydrocarbons). 52.1877 Section 52.1877 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY....1877 Control strategy: Photochemical oxidants (hydrocarbons). (a) The requirements of Subpart G of this... national standard for photochemical oxidants (hydrocarbons) in the Metropolitan Cincinnati...

  13. 40 CFR 52.1877 - Control strategy: Photochemical oxidants (hydrocarbons).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... oxidants (hydrocarbons). 52.1877 Section 52.1877 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY....1877 Control strategy: Photochemical oxidants (hydrocarbons). (a) The requirements of Subpart G of this... national standard for photochemical oxidants (hydrocarbons) in the Metropolitan Cincinnati...

  14. 40 CFR 52.1877 - Control strategy: Photochemical oxidants (hydrocarbons).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... oxidants (hydrocarbons). 52.1877 Section 52.1877 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY....1877 Control strategy: Photochemical oxidants (hydrocarbons). (a) The requirements of Subpart G of this... national standard for photochemical oxidants (hydrocarbons) in the Metropolitan Cincinnati...

  15. 40 CFR 52.1877 - Control strategy: Photochemical oxidants (hydrocarbons).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... oxidants (hydrocarbons). 52.1877 Section 52.1877 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY....1877 Control strategy: Photochemical oxidants (hydrocarbons). (a) The requirements of Subpart G of this... national standard for photochemical oxidants (hydrocarbons) in the Metropolitan Cincinnati...

  16. A Simple Parallel Photochemical Reactor for Photodecomposition Studies

    ERIC Educational Resources Information Center

    Xiaobo Chen; Halasz, Sarah M.; Giles, Eric C.; Mankus, Jessica V.; Johnson, Joseph C.; Burda, Clemens

    2006-01-01

    A simple and useful parallel photochemical reactor intended to study the photodecomposition of dyes using semiconductor photocatalysis is presented. The photochemical reactions are followed through time-dependent changes in the ground-state absorption spectra of the dyes.

  17. Solar photochemical process engineering for production of fuels and chemicals

    SciTech Connect

    Biddle, J.R.; Peterson, D.B.; Fujita, T.

    1984-05-01

    The engineering costs and performance of a nominal 25,000 scmd (883,000 scfd) photochemical plant to produce dihydrogen from water have been studied. Two systems were considered, one based on flat-plate collector/reactors and the other on linear parabolic troughs. Engineering subsystems were specified including the collector/reactor, support hardware, field transport piping, gas compression equipment, and balance-of-plant (BOP) items. Overall plant efficiencies of 10.3 and 11.6% are estimated for the flat-plate and trough systems, respectively, based on assumed solar photochemical efficiencies of 12.9 and 14.6%. Because of the opposing effects of concentration ratio and operating temperature on efficiency, it was concluded that reactor cooling would be necessary with the trough system. Both active and passive cooling methods were considered. Capital costs and energy costs, for both concentrating and non-concentrating systems, were determined and their sensitivity to efficiency and economic parameters were analyzed. Results predict energy costs in the range of $34 to $55/10/sup 6/ kJ ($36 to $59/10/sup 6/ Btu) for the flat-plate system and $94 to $141/10/sup 6/ kJ ($99 to $149/10/sup 6/ Btu) for the trough system. The overall plant efficiency is the single most important factor in determining the cost of the fuel. Therefore, solar quantum conversion processes were reviewed for the purpose of identifying processes which promise better performance and lower costs. Operating and systems options, including operation at elevated temperatures and hybrid and coupled quantum-thermal conversion processes, were also briefly examined.

  18. Photochemical Transformation of Graphene Oxide in Sunlight

    EPA Science Inventory

    Graphene oxide (GO) is a graphene derivative that is more easily manufactured in large scale and used to synthesize reduced graphene oxide (rGO) with properties analogous to graphene. In this study, we investigate the photochemical fate of GO under sunlight conditions. The resu...

  19. Enhanced aqueous photochemical reaction rates after freezing.

    PubMed

    Grannas, Amanda M; Bausch, Alexandra R; Mahanna, Kendell M

    2007-11-01

    Sunlit snow/ice is known to play an important role in the processing of atmospheric species, including photochemical production of NO(x), HONO, molecular halogens, alkyl halides, and carbonyl compounds, among others. It has been shown that a liquid-like (quasi-liquid or disordered) layer exists on the surface of pure ice and that this quasi-liquid layer is also found on the surface of ambient snow crystals and ice at temperatures similar to polar conditions. However, it is unclear what role the liquid-like fractions present in and on frozen water play in potential photochemical reactions, particularly with regard to organic substrates. Here, we report a detailed study of enhanced rates of photochemical nucleophilic substitution of p-nitroanisole (PNA) with pyridine, a well-characterized and commonly used actinometer system. Reaction rates were enhanced by a factor of up to approximately 40 when frozen at temperatures between 236 and 272 K. Reaction rates were dependent on temperature and solute concentration, both variables that control the nature of the liquid-like fraction in frozen water. The results obtained indicate that a major portion of the organic solutes is excluded to the liquid-like layer, significantly impacting the rate of the photochemical nucleophilic substitution reaction studied here. Also, the direct comparison of liquid-phase kinetics to reactions occurring in frozen water systems is drawn into question, indicating that a simple extrapolation of liquid-phase mechanisms to snow/ice may not be valid for certain reactions.

  20. HANDBOOK ON ADVANCED PHOTOCHEMICAL OXIDATION PROCESSES

    EPA Science Inventory

    This handbook summarizes commercial-scale system performance and cost data for advanced photochemical oxidation (APO) treatment of contaminated water, air, and solids. Similar information from pilot- and bench-scale evaluations of APO processes is also included to supplement the...

  1. MNEQA, an emissions model for photochemical simulations

    NASA Astrophysics Data System (ADS)

    Ortega, S.; Soler, M. R.; Alarcón, M.; Arasa, R.

    This study focuses on a new emissions model, Numerical Emissions Model for Air Quality (MNEQA), to be used in photochemical simulations and emission control strategies relating to tropospheric ozone pollutants. MNEQA processes available local information from external files and is easily adaptable to any desired spatial resolution. Top-down and bottom-up methodologies are combined to calculate emissions at the required resolution for photochemical simulations. It was used in conjunction with the MM5-CMAQ air quality modelling system and was applied to an episode of high ozone levels in June 2003. Emission results are widely analysed showing a difference of -8.8% with EMEP NOx emissions, and -18.7% with EMEP VOC emissions. Related to ozone simulations, comparative results between measurements and simulations indicated good behaviour of the model in reproducing diurnal ozone concentrations, as statistical values fall within the EPA and EU regulatory frameworks.

  2. PHOTOCHEMICAL HEATING OF DENSE MOLECULAR GAS

    SciTech Connect

    Glassgold, A. E.; Najita, J. R.

    2015-09-10

    Photochemical heating is analyzed with an emphasis on the heating generated by chemical reactions initiated by the products of photodissociation and photoionization. The immediate products are slowed down by collisions with the ambient gas and then heat the gas. In addition to this direct process, heating is also produced by the subsequent chemical reactions initiated by these products. Some of this chemical heating comes from the kinetic energy of the reaction products and the rest from collisional de-excitation of the product atoms and molecules. In considering dense gas dominated by molecular hydrogen, we find that the chemical heating is sometimes as large, if not much larger than, the direct heating. In very dense gas, the total photochemical heating approaches 10 eV per photodissociation (or photoionization), competitive with other ways of heating molecular gas.

  3. Photochemical aspects related to humic substances

    SciTech Connect

    Frimmel, F.H. )

    1994-01-01

    Dissolved humic substances (HS) show yellow color and relatively strong absorption in the UV range [a(254 nm) ca. 0.04 cm[sup [minus]1] for c(DOC) = 1 mg/L]. This is the basis for photochemical reactions in the photic zone of aquatic systems and in water treatment using IV sources. Even though understanding the mechanisms involved in the energy transfer and the resulting reactions is hampered by the poorly defined structure of HS, reliable information has been gathered on some typical aspects of their photochemistry. The luminescence of HS can be influenced and partly quenched by molecular interactions with other water constituents (e.g., heavy metals and organic micropollutants). The presence of oxygen may lead to the sensitized production of singlet oxygen (O[sub 2]), that can react specifically with substances containing diene structures or low valent sulfur. Because of the presence of these structures in HS, humic molecules will also react with the sensitized products. As a consequence, their biological, chemical, and physical properties are influenced. In addition, HS have a significant impact on the photochemical treatment of organic micropollutants in water. This has to be kept in mind when using photochemical steps for water treatment. The results from model experiments reflecting the conditions in surface water and in water treatment are given and discussed. In the presence of H[sub 2]O[sub 2], irradiation led to a transformation and partial degradation of HS. The rate of photochemical degradation of pesticides (e.g., atrazine) was decreased in the presence of HS. Fe and Mn quenched the luminescence. From this, a decrease of excited states of HS for sensitizing reactions can be deduced. The results suggest the manyfold and significant influences of HS on the photochemistry of aquatic systems. 66 refs., 9 figs., 7 tabs.

  4. Spring time photochemical air pollution in Osaka

    SciTech Connect

    Wakamatsu, Shinji; Uno, Itsushi; Ohara, Toshimasa

    1996-12-31

    High concentrations of nitrogen dioxide are frequently observed in Osaka area in spring season. To clarify this, a series of three dimensional field observation was conducted in April 1993 covering Osaka and surrounding area. Vertical and horizontal distributions of ozone, NO, NO{sub x}, SO{sub 2}, CO, aerosol species, hydrocarbon species and meteorological parameter such as temperature, uv radiation, wind speed, wind direction are measured on the ground and aloft. Covering the observational period yellow sand transportation from the continent and stratospheric ozone intrusion were also observed under the meteorological condition of moving high pressure system. During the aircraft observation of 19 to 21 April 1993 high concentration of photochemical air pollution was observed aloft over Osaka area. Maximum ozone concentration was me than 150 ppb. Vertical distribution of ozone showed uniform profile up to 2500m in day time. At Mt. Ikoma (600 m) ozone concentration had been almost constant ranging 80-100 ppb throughout the observational period. To clarify this phenomena three dimensional photochemical air pollution simulation model was applied based on the real meteorological and emission conditions. Simulated result showed photochemical reaction play an important role to form the spring time high concentrations of nitrogen dioxide in Osaka.

  5. New photochemical tools for controlling neuronal activity

    PubMed Central

    Kramer, Richard H.; Fortin, Doris L.; Trauner, Dirk

    2009-01-01

    Neurobiology has entered a new era in which optical methods are challenging electrophysiological techniques for their value in measuring and manipulating neuronal activity. This change is occurring largely because of the development of new photochemical tools, some synthesized by chemists and some provided by nature. This review is focused on the three types of photochemical tools for neuronal control that have emerged in recent years. Caged neurotransmitters, including caged glutamate, are synthetic molecules that enable highly localized activation of neurotransmitter receptors in response to light. Natural photosensitive proteins, including channelrhodopsin-2 and halorhodopsin, can be exogenously expressed in neurons and enable rapid photocontrol of action potential firing. Synthetic small-molecule photoswitches can bestow light-sensitivity on native or exogenously expressed proteins, including K+ channels and glutamate receptors, allowing photocontrol of action potential firing and synaptic events. At a rapid pace, these tools are being improved and new tools are being introduced, thanks to molecular biology and synthetic chemistry. The three families of photochemical tools have different capabilities and uses, but they all share in enabling precise and non-invasive exploration of neural function with light. PMID:19828309

  6. Photochemical Phenomenology Model for the New Millennium

    NASA Technical Reports Server (NTRS)

    Bishop, James; Evans, J. Scott

    2001-01-01

    The "Photochemical Phenomenology Model for the New Millennium" project tackles the issue of reengineering and extension of validated physics-based modeling capabilities ("legacy" computer codes) to application-oriented software for use in science and science-support activities. While the design and architecture layouts are in terms of general particle distributions involved in scattering, impact, and reactive interactions, initial Photochemical Phenomenology Modeling Tool (PPMT) implementations are aimed at construction and evaluation of photochemical transport models with rapid execution for use in remote sensing data analysis activities in distributed systems. Current focus is on the Composite Infrared Spectrometer (CIRS) data acquired during the CASSINI flyby of Jupiter. Overall, the project has stayed on the development track outlined in the Year 1 annual report and most Year 2 goals have been met. The issues that have required the most attention are: implementation of the core photochemistry algorithms; implementation of a functional Java Graphical User Interface; completion of a functional CORBA Component Model framework; and assessment of performance issues. Specific accomplishments and the difficulties encountered are summarized in this report. Work to be carried out in the next year center on: completion of testing of the initial operational implementation; its application to analysis of the CASSINI/CIRS Jovian flyby data; extension of the PPMT to incorporate additional phenomenology algorithms; and delivery of a mature operational implementation.

  7. Promoting Photochemical Water Oxidation with Metallic Band Structures.

    PubMed

    Liu, Hongfei; Moré, René; Grundmann, Henrik; Cui, Chunhua; Erni, Rolf; Patzke, Greta R

    2016-02-10

    The development of economic water oxidation catalysts is a key step toward large-scale water splitting. However, their current exploration remains empirical to a large extent. Elucidating the correlations between electronic properties and catalytic activity is crucial for deriving general and straightforward catalyst design principles. Herein, strongly correlated electronic systems with abundant and easily tunable electronic properties, namely La(1-x)Sr(x)BO3 perovskites and La(2-x)Sr(x)BO4 layered perovskites (B = Fe, Co, Ni, or Mn), were employed as model systems to identify favorable electronic structures for water oxidation. We established a direct correlation between the enhancement of catalytic activity and the insulator to metal transition through tuning the electronic properties of the target perovskite families via the La(3+)/Sr(2+) ratio. Their improved photochemical water oxidation performance was clearly linked to the increasingly metallic character. These electronic structure-activity relations provide a promising guideline for constructing efficient water oxidation catalysts.

  8. Charge transport in photochemically modified molecularly doped polymers

    NASA Astrophysics Data System (ADS)

    Stasiak, James W.; Storch, Teresa J.; Mao, Erji

    1995-08-01

    Hole mobilities in p-diethylaminobenzaldehyde diphenylhydrazone (DEH) doped polycarbonate films are determined using the time-of-flight transient photocurrent technique. Measurements of hole transport parameters are determined over a range of electric fields before and after the samples are deliberately irradiated with UV light. UV irradiation of the hole transport molecule DEH results in the creation of a photoproduct, 1-phenyl-3-(4- diethylamino-1-phenyl)-1, 3-indazole with moderately high efficiency. Once formed, this photoproduct has been shown to act as a barrier to hole conduction. We exploit this photochemical reaction to examine the hole transport properties in a molecularly doped polymer system containing DEH doped polycarbonate. We propose that the increase in concentration of the photoproduct modifies the intrinsic order of the system and provides a unique probe to distinguish between the disorder formalism of Baessler and coworkers and models which propose polaron formation.

  9. Photochemical Attenuation of Pesticides in Prairie Potholes

    NASA Astrophysics Data System (ADS)

    Zeng, T.; Arnold, W. A.

    2013-12-01

    Prairie potholes are small, shallow, glacially-derived wetlands scattered across a vast region extending from Midwestern United States into south central Canada known as the Prairie Pothole Region (PPR). They constitute one of the largest inland wetland systems on Earth and play a prominent role in sustaining the regional biodiversity and productivity. Throughout the PPR, historic and contemporary conversion of native prairie for agriculture resulted in a pronounced loss of potholes. Remaining potholes have become interspersed within a matrix of agricultural landscape and trap nonpoint source pollutants such as pesticides from adjacent farmland, which has raised concerns regarding negative impacts on the water quality of downstream water bodies. The fate and persistence of pesticides in potholes, however, remains largely unexplored. Prairie potholes are typically characterized by shallow depth (i.e., large photic zone) and high levels of dissolved organic matter (DOM), making them ideal for photochemical reactions. In this context, we collected pothole water samples from North Dakota to investigate the rates and mechanisms of sunlight-induced attenuation of pesticides. The photodegradation kinetics and pathways of sixteen pesticides in the pothole water were monitored under both simulated and natural sunlight. For most pesticides, photolysis accelerated in the pothole water relative to the buffer control, which pointed to the importance of photosensitized processes (i.e., indirect photolysis). Upon solar irradiation, a mixture of photochemically produced reactive intermediates (PPRIs), such as carbonate radical, hydroxyl radical, singlet oxygen, and triplet-excited state DOM, formed in the pothole water. The major pathways through which pesticides degraded were inferred from the relative contribution attributable to specific PPRIs via quencher experiments. Different classes of pesticides exhibited contrasting photochemical behavior, but singlet oxygen and triplet

  10. The actual goals of geoethics

    NASA Astrophysics Data System (ADS)

    Nemec, Vaclav

    2014-05-01

    The most actual goals of geoethics have been formulated as results of the International Conference on Geoethics (October 2013) held at the geoethics birth-place Pribram (Czech Republic): In the sphere of education and public enlightenment an appropriate needed minimum know how of Earth sciences should be intensively promoted together with cultivating ethical way of thinking and acting for the sustainable well-being of the society. The actual activities of the Intergovernmental Panel of Climate Changes are not sustainable with the existing knowledge of the Earth sciences (as presented in the results of the 33rd and 34th International Geological Congresses). This knowledge should be incorporated into any further work of the IPCC. In the sphere of legislation in a large international co-operation following steps are needed: - to re-formulate the term of a "false alarm" and its legal consequences, - to demand very consequently the needed evaluation of existing risks, - to solve problems of rights of individuals and minorities in cases of the optimum use of mineral resources and of the optimum protection of the local population against emergency dangers and disasters; common good (well-being) must be considered as the priority when solving ethical dilemmas. The precaution principle should be applied in any decision making process. Earth scientists presenting their expert opinions are not exempted from civil, administrative or even criminal liabilities. Details must be established by national law and jurisprudence. The well known case of the L'Aquila earthquake (2009) should serve as a serious warning because of the proven misuse of geoethics for protecting top Italian seismologists responsible and sentenced for their inadequate superficial behaviour causing lot of human victims. Another recent scandal with the Himalayan fossil fraud will be also documented. A support is needed for any effort to analyze and to disclose the problems of the deformation of the contemporary

  11. Photochemical synthesis of biomolecules under anoxic conditions

    NASA Technical Reports Server (NTRS)

    Folsome, C.; Brittain, A.; Zelko, M.

    1983-01-01

    The long-wavelength UV anoxic photosynthesis of uracil, various sugars (including deoxyribose and glycoaldehyde), amino acids, and other organic photoproducts is reported. The reactions were conducted in a mixture of water, calcium carbonate, hydrazine, and formaldehyde which were subjected to 24 hr or 72 hr radiation. Product yields were greatest when the hydrazine/formaldehyde ratio was one, and when the reactant concentrations were low. These data suggest that organic products can be formed in variety from those amounts of formaldehyde and hydazine precursors which are themselves formed under anoxic UV photochemical conditions.

  12. Studies toward the photochemical synthesis of functionalized [5]- and [6]carbohelicenes.

    PubMed

    Pearson, Morwenna S M; Carbery, David R

    2009-08-07

    An efficient route to nonsymmetrical helical menthyl esters by means of an oxidative photocyclization reaction of dissymmetric bis-stilbenes is reported. The developed route allows the introduction of functionality on rings A, E, or F, and the influence of the substituent pattern on the photochemical reaction has been examined. Diastereoselectivity is observed when a double chiral induction strategy with dimenthyl helicene esters synthesized in a 70:30 ratio of isomers is used.

  13. Photochemical Reaction In CdS Crystals For Holographic Information Recording

    NASA Astrophysics Data System (ADS)

    Sukhoverkhova, L. G.

    1985-01-01

    The change of various properties of CdS crystals due to photochemical reaction was used for reversible holographic recording. The change of CdS:Cu photosensitivity is used for holographic storage of phase gratings. It is shown that the diffraction efficiency of the grating can be controlled by the reconstructing beam intensity. The storage of the amplitude holographic gratings due to change of GLIS absorption by the illumination have been studied as well.

  14. Non-photochemical fluorescence quenching and the diadinoxanthin cycle in a marine diatom.

    PubMed

    Olaizola, M; La Roche, J; Kolber, Z; Falkowski, P G

    1994-08-01

    The diadinoxanthin cycle (DD-cycle) in chromophyte algae involves the interconversion of two carotenoids, diadinoxanthin (DD) and diatoxanthin (DT). We investigated the kinetics of light-induced DD-cycling in the marine diatom Phaeodactylum tricornutum and its role in dissipating excess excitation energy in PS II. Within 15 min following an increase in irradiance, DT increased and was accompanied by a stoichiometric decrease in DD. This reaction was completely blocked by dithiothreitol (DTT). A second, time-dependent, increase in DT was detected ∼ 20 min after the light shift without a concomitant decrease in DD. DT accumulation from both processes was correlated with increases in non-photochemical quenching of chlorophyll fluorescence. Stern-Volmer analyses suggests that changes in non-photochemical quenching resulted from changes in thermal dissipation in the PS II antenna and in the reaction center. The increase in non-photochemical quenching was correlated with a small decrease in the effective absorption cross section of PS II. Model calculations suggest however that the changes in cross section are not sufficiently large to significantly reduce multiple excitation of the reaction center within the turnover time of steady-state photosynthetic electron transport at light saturation. In DTT poisoned cells, the change in non-photochemical quenching appears to result from energy dissipation in the reaction center and was associated with decreased photochemical efficiency. D1 protein degradation was slightly higher in samples poisoned with DTT than in control samples. These results suggest that while DD-cycling may dynamically alter the photosynthesis-irradiance response curve, it offers limited protection against photodamage of PS II reaction centers at irradiance levels sufficient to saturate steady-state photosynthesis.

  15. Photochemical aerosols in warm exoplanetary atmospheres

    NASA Astrophysics Data System (ADS)

    Imanaka, Hiroshi; Smith, Mark A.; McKay, Christopher P.; Cruikshank, Dale P.; Marley, Mark S.

    2016-10-01

    Recent transit observations of exoplanets have demonstrated the possibility of a wide prevalence of haze/cloud layers at high altitudes. Hydrocarbon photochemical haze could be the candidate for such haze particles on warm sub-Neptunes, but the lack of evidence for methane poses a puzzle for such hydrocarbon photochemical haze. The CH4/CO ratios in planetary atmospheres vary substantially from their temperature and dynamics. We have conducted a series of laboratory simulations to investigate how atmospheric compositions, specifically CH4/CO ratios, affect the haze production rates and their optical properties. The mass production rates in the H2-CH4-CO gas mixtures are rather insensitive to the CH4/CO ratios larger than at 0.3. Significant formation of solid material is observed in a H2-CO gas mixture even without CH4. The complex refractive indices of the aerosol analogue from the H2-CO gas mixture show strong absorption at the visible/near-IR wavelengths. These experimental facts imply that substantial carbonaceous aerosols may be generated in warm H2-CO-CH4 exoplanetary atmospheres, and that it might be responsible for the observed dark albedos at the visible wavelengths.

  16. Chitosan Adhesive Films for Photochemical Tissue Bonding

    NASA Astrophysics Data System (ADS)

    Lauto, Antonio; Mawad, Damia; Barton, Matthew; Piller, Sabine C.; Longo, Leonardo

    2011-08-01

    Photochemical tissue bonding (PTB) is a promising sutureless technique for tissue repair. PTB is often achieved by applying a solution of rose bengal (RB) between two tissue edges, which are irradiated by a green laser to crosslink collagen fibers with minimal heat production. In this study, RB has been incorporated in chitosan films to create a novel tissue adhesive that is laser-activated. Materials and Methods. Adhesive films, based on chitosan and containing ˜0.1wt% RB were manufactured and bonded to calf intestine by a solid state laser (wavelength = 532 nm, Fluence ˜110 J/cm2, spot size ˜5 mm). A single-column tensiometer, interfaced with a personal computer, tested the bonding strength. K-type thermocouples recorded the temperature (T) at the adhesive-tissue interface during laser irradiation. Human fibroblasts were also seeded on the adhesive and cultured for 48 hours to assess cell growth. Results and Conclusion. The RB-chitosan adhesive bonded firmly to the intestine (15±2 kPa, n = 31). The adhesion strength dropped to 0.5±0.1 kPa (n = 8) when the laser was not applied to the adhesive. The average temperature of the adhesive increased from 26 °C to 32 °C during laser exposure. Fibroblasts grew confluent on the adhesive without morphological changes. A new biocompatible chitosan adhesive has been developed that bonds photochemically to tissue with minimal temperature increase.

  17. 78 FR 11172 - Integrated Science Assessment for Ozone and Related Photochemical Oxidants

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-02-15

    ... AGENCY Integrated Science Assessment for Ozone and Related Photochemical Oxidants AGENCY: Environmental... final document titled, ``Integrated Science Assessment for Ozone and Related Photochemical Oxidants... ``Integrated Science Assessment for Ozone and Related Photochemical Oxidants'' will be made available...

  18. Solar Irradiation of Bilirubin: An Experiment in Photochemical Oxidation

    ERIC Educational Resources Information Center

    Pillay A. E.; Salih, F. M.

    2006-01-01

    An experiment in photochemical oxidation, which deals with bilirubin, a well-known light-sensitive biological compound that is pedagogically ideal for photochemical experiments at tertiary institutes, is presented. The experiment would benefit students in chemistry who eventually branch out into the health sciences or biochemistry.

  19. Cyclophane size drives the photochemical behaviour of benzophenone.

    PubMed

    Vida, Yolanda; Perez-Inestrosa, Ezequiel

    2012-11-01

    A new series of all-heterahomocalixarene-type structures was prepared. The new hetera[2(n)]metacyclophanes obtained contain a benzophenone moiety as photoactive component. Although both forms possess identical building blocks and differ only in ring size, they are markedly different in photochemical reactivity. The cyclophane size is the driving force for the photochemical behaviour of the benzophenone.

  20. Linguistic Theory and Actual Language.

    ERIC Educational Resources Information Center

    Segerdahl, Par

    1995-01-01

    Examines Noam Chomsky's (1957) discussion of "grammaticalness" and the role of linguistics in the "correct" way of speaking and writing. It is argued that the concern of linguistics with the tools of grammar has resulted in confusion, with the tools becoming mixed up with the actual language, thereby becoming the central…

  1. Characterizing the unique photochemical environment in China

    NASA Astrophysics Data System (ADS)

    Liu, Z.; Wang, Y.; Gu, D.; Zhao, C.; Huey, L. G.; Stickel, R.; Liao, J.

    2010-12-01

    Recent observational evidence suggests that the atmospheric chemical system over China could be more complex than expected, possibly as a result of the rapid increasing anthropogenic emissions. During the CAREBeijing-2007 Experiment in August of 2007, up to 14 ppbv of peroxyacetyl nitrate (PAN, CH3C(O)OONO2) and 4.5 ppbv of glyoxal (CHOCHO) were observed, among the highest levels observed in the world in recent years. Elevated nitrous acid (HNO2) (~1.0 ppbv on average) was also observed in the early afternoon despite of the moderate amount of its precursors, i.e. nitrogen oxides (NOx=NO + NO2). We employ a 1-D photochemical model (REAM) to analyze the observations. The results indicate that reactive aromatics are the dominating source of PAN (55%-75%) and glyoxal (90%), and methylglyoxal is the major precursor of peroxy acetyl radical (50%). Downward transport from boundary layer is found to contribute ~50% of the PAN observed at surface. Photolysis of HNO2 is by far the largest primary OH source (more than 50%) throughout the daytime, and yet the fast formation rate of HNO2 inferred from the observations could not be explained by current known mechanisms. Detailed photochemical analysis is conducted to understand the controlling factors for O3 formation. O3 formation chemistry is strongly affected by aromatics and HNO2. By providing a large primary OH source, HNO2 leads to ~25% enhancement of the average O3 production rate, and aromatics contribute ~40% by serving as a major source of RO2 and HO2 radicals. Due to the large abundance of reactive hydrocarbons, O3 formation is generally NOx limited, although the sensitivity is low that a 50% reduction of NOx could only result in less than 25% reduction of the O3 production rate. Future research targeting HNO2 formation mechanism and emission sources of aromatics is necessary for better understanding the unique photochemical environment in China under significant anthropogenic impacts and the regional pollution

  2. Photochemical Isomerization and Topochemical Polymerization of the Programmed Asymmetric Amphiphiles

    PubMed Central

    Kim, Dae-Yoon; Lee, Sang-A; Jung, Daseal; Jeong, Kwang-Un

    2016-01-01

    For the advancement in multi-stimuli responsive optical devices, we report the elaborate molecular engineering of the dual photo-functionalized amphiphile (abbreviated as AZ1DA) containing both a photo-isomerizable azobenzene and a photo-polymerizable diacetylene. To achieve the efficient photochemical reactions in thin solid films, the self-assembly of AZ1DA molecules into the ordered phases should be precisely controlled and efficiently utilized. First, the remote-controllable light shutter is successfully demonstrated based on the reversible trans-cis photo-isomerization of azobenzene group in the smectic A mesophase. Second, the self-organized monoclinic crystal phase allows us to validate the photo-polymerization of diacetylene moiety for the photo-patterned thin films and the thermo-responsible color switches. From the demonstrations of optically tunable thin films, it is realized that the construction of strong relationships between chemical structures, molecular packing structures and physical properties of the programmed molecules is the core research for the development of smart and multifunctional soft materials. PMID:27339163

  3. Photochemical Isomerization and Topochemical Polymerization of the Programmed Asymmetric Amphiphiles

    NASA Astrophysics Data System (ADS)

    Kim, Dae-Yoon; Lee, Sang-A.; Jung, Daseal; Jeong, Kwang-Un

    2016-06-01

    For the advancement in multi-stimuli responsive optical devices, we report the elaborate molecular engineering of the dual photo-functionalized amphiphile (abbreviated as AZ1DA) containing both a photo-isomerizable azobenzene and a photo-polymerizable diacetylene. To achieve the efficient photochemical reactions in thin solid films, the self-assembly of AZ1DA molecules into the ordered phases should be precisely controlled and efficiently utilized. First, the remote-controllable light shutter is successfully demonstrated based on the reversible trans-cis photo-isomerization of azobenzene group in the smectic A mesophase. Second, the self-organized monoclinic crystal phase allows us to validate the photo-polymerization of diacetylene moiety for the photo-patterned thin films and the thermo-responsible color switches. From the demonstrations of optically tunable thin films, it is realized that the construction of strong relationships between chemical structures, molecular packing structures and physical properties of the programmed molecules is the core research for the development of smart and multifunctional soft materials.

  4. UV-induced photochemical heterogeneity of dissolved and attached organic matter associated with cyanobacterial blooms in a eutrophic freshwater lake.

    PubMed

    Xu, Huacheng; Jiang, Helong

    2013-11-01

    Cyanobacterial blooms represent a significant ecological and human health problem worldwide. In aquatic environments, cyanobacterial blooms are actually surrounded by dissolved organic matter (DOM) and attached organic matter (AOM) that bind with algal cells. In this study, DOM and AOM fractionated from blooming cyanobacteria in a eutrophic freshwater lake (Lake Taihu, China) were irradiated with a polychromatic UV lamp, and the photochemical heterogeneity was investigated using fluorescence excitation-emission matrix (EEM)-parallel factor (PARAFAC) analysis and synchronous fluorescence (SF)-two dimensional correlation spectroscopy (2DCOS). It was shown that a 6-day UV irradiation caused more pronounced mineralization for DOM than AOM (59.7% vs. 41.9%). The EEM-PARAFAC analysis identified one tyrosine-, one humic-, and two tryptophan-like components in both DOM and AOM, and high component photodegradation rates were observed for DOM versus AOM (k > 0.554 vs. <0.519). Moreover, SF-2DCOS found that the photodegradation of organic matters followed the sequence of tyrosine-like > humic-like > tryptophan-like substances. Humic-like substances promoted the indirect photochemical reactions, and were responsible for the higher photochemical rate for DOM. The lower photodegradation of AOM benefited the integrality of cells in cyanobacterial blooms against the negative impact of UV irradiation. Therefore, the photochemical behavior of organic matter was related to the adaptation of enhanced-duration cyanobacterial blooms in aquatic environments.

  5. The photochemical role of tropospheric nitrogen oxides

    NASA Technical Reports Server (NTRS)

    Chameides, W. L.

    1978-01-01

    The role of nitrogen oxides in the tropospheric photochemical system is re-evaluated in the light of recent measurements of the rate constants for two key reactions. A model for nitrogen oxides is discussed which yields surface NO(x) (NO+NO2) levels approaching 1 ppb in NO(x) source regions but less than 0.1 ppb outside source regions. Applying the new rate coefficients implies increased radical concentrations and a more intense O3 and CO photochemistry. Even for densities of 0.1 ppb or less, NO(x) still leads to significant local O3 production and conversion of HO2 to OH. Unrealistic O3 profiles are obtained with the new rate coefficients for surface NO(x) densities of about 1 ppb, while reasonable agreement with observation is obtained with lower NO(x) densities. Feedback processes between CO, NO(x), OH, and CH4 are also discussed.

  6. Fibre-optic photochemical stroke: generating and measuring photochemical changes inside the brain

    NASA Astrophysics Data System (ADS)

    Tsiminis, G.; Klarić, T. S.; Schartner, E. P.; Warren-Smith, S. C.; Lewis, M. D.; Koblar, S. A.; Monro, T. M.

    2014-05-01

    We report here on the development of a method to induce a stroke in a specific location within a mouse brain through the use of an optical fibre. By capturing the emitted fluorescence signal generated using the same fibre it is then possible to monitor photochemical changes within the brain in real-time, potentially reducing the requirement for post-operative histology to determine if a stroke has successfully been induced within the animal.

  7. Photochemical processing of aqueous atmospheric brown carbon

    NASA Astrophysics Data System (ADS)

    Zhao, R.; Lee, A. K. Y.; Huang, L.; Li, X.; Yang, F.; Abbatt, J. P. D.

    2015-01-01

    Atmospheric Brown Carbon (BrC) is a collective term for light absorbing organic compounds in the atmosphere. While the identification of BrC and its formation mechanisms is currently a central effort in the community, little is known about the atmospheric removal processes of aerosol BrC. As a result, we report a series of laboratory studies of photochemical processing of BrC in the aqueous phase, by direct photolysis and OH oxidation. Solutions of ammonium sulfate mixed with glyoxal (GLYAS) or methylglyoxal (MGAS) are used as surrogates for a class of secondary BrC mediated by imine intermediates. Three nitrophenol species, namely 4-nitrophenol, 5-nitroguaiacol and 4-nitrocatechol, were investigated as a class of water soluble BrC originating from biomass burning. Photochemical processing induced significant changes in the absorptive properties of BrC. The imine-mediated BrC solutions exhibited rapid photo-bleaching with both direct photolysis and OH oxidation, with atmospheric half-lives of minutes to a few hours. The nitrophenol species exhibited photo-enhancement in the visible range during direct photolysis and the onset of OH oxidation, but rapid photo-bleaching was induced by further OH exposure on an atmospheric timescale of an hour or less. To illustrate atmospheric relevance of this work, we also performed direct photolysis experiments on water soluble organic carbon extracted from biofuel combustion samples and observed rapid changes in optical properties of these samples as well. Overall, these experiments indicate that atmospheric models need to incorporate representations of atmospheric processing of BrC species to accurately model their radiative impacts.

  8. Photochemical processing of aqueous atmospheric brown carbon

    NASA Astrophysics Data System (ADS)

    Zhao, R.; Lee, A. K. Y.; Huang, L.; Li, X.; Yang, F.; Abbatt, J. P. D.

    2015-06-01

    Atmospheric brown carbon (BrC) is a collective term for light absorbing organic compounds in the atmosphere. While the identification of BrC and its formation mechanisms is currently a central effort in the community, little is known about the atmospheric removal processes of aerosol BrC. As a result, we report on a series of laboratory studies of photochemical processing of BrC in the aqueous phase, by direct photolysis and OH oxidation. Solutions of ammonium sulfate mixed with glyoxal (GLYAS) or methylglyoxal (MGAS) are used as surrogates for a class of secondary BrC mediated by imine intermediates. Three nitrophenol species, namely 4-nitrophenol, 5-nitroguaiacol and 4-nitrocatechol, were investigated as a class of water-soluble BrC originating from biomass burning. Photochemical processing induced significant changes in the absorptive properties of BrC. The imine-mediated BrC solutions exhibited rapid photo-bleaching with both direct photolysis and OH oxidation, with atmospheric half-lives of minutes to a few hours. The nitrophenol species exhibited photo-enhancement in the visible range during direct photolysis and the onset of OH oxidation, but rapid photo-bleaching was induced by further OH exposure on an atmospheric timescale of an hour or less. To illustrate the atmospheric relevance of this work, we also performed direct photolysis experiments on water-soluble organic carbon extracted from biofuel combustion samples and observed rapid changes in the optical properties of these samples as well. Overall, these experiments indicate that atmospheric models need to incorporate representations of atmospheric processing of BrC species to accurately model their radiative impacts.

  9. Mars atmosphere loss and isotopic fractionation by solar-wind-induced sputtering and photochemical escape

    NASA Technical Reports Server (NTRS)

    Jakosky, B. M.; Pepin, R. O.; Johnson, R. E.; Fox, J. L.

    1993-01-01

    The effects of loss of Mars atmospheric constituents by solar-wind-induced sputtering and by photochemical escape during the last 3.8 b.y. were examined. Sputtering is capable of efficiently removing all species from the upper atmosphere, including the light noble gases; N also is removed by photochemical processes. Due to the diffusive separation by mass above the homopause, removal from the top of the atmosphere will fractionate the isotopes of each species, with the lighter mass being preferentially lost. For C and O, this allows us to determine the size of nonatmospheric reservoirs that mix with the atmosphere; these reserviors can be accounted for by exchange with CO2 adsorbed in the regolith and with H2O in the polar ice deposits. Both simple analytical models and time-dependent models of the loss of volatiles from and supply to the Martian atmosphere were constructed. Both Ar and Ne require continued replenishment from outgassing over geologic time.

  10. Photochemical model of photodynamic therapy applied to skin diseases by a topical photosensitizer

    NASA Astrophysics Data System (ADS)

    Fanjul-Vélez, F.; Salas-García, I.; Fernández-Fernández, L. A.; López-Escobar, M.; Buelta-Carrillo, L.; Ortega-Quijano, N.; Arce-Diego, J. L.

    2009-07-01

    Photodynamic Therapy (PDT) provides a non-invasive, efficient and safe treatment for skin diseases with good cosmetic results. These characteristics make this technique more advantageous than radiotherapy or chemotherapy, which present limitations in a big number of lesions, are painful in many cases and produce non-satisfactory cosmetic results. We present the clinical results obtained at present by this optical technique and a photochemical model of the PDT process applied to the skin by means of a topical photosensitizer, in order to find the optimal PDT parameters. Optical propagation inside the tissue is calculated by means of the three dimensional Beer-Lambert law, due to its facility to be integrated in the differential equations system used to model the photochemical processes involved. With this information it is possible to obtain an initial estimation about the optimal drug dose and the optical power required.

  11. Mars atmospheric loss and isotopic fractionation by solar-wind-induced sputtering and photochemical escape

    NASA Technical Reports Server (NTRS)

    Jakosky, B. M.; Pepin, R. O.; Johnson, R. E.; Fox, J. L.

    1993-01-01

    We examine the effects of loss of Mars atmospheric constituents by solar-wind-induced sputtering and by photochemical escape during the last 3.8 b.y. Sputtering is capable of efficiently removing all species from the upper atmosphere including the light noble gases; N is removed by photochemical processes as well. Due to diffusive separation (by mass) above the homopause, removal from the top of the atmosphere will fractionate the isotopes of each species with the lighter mass being preferentially lost. For C and O, this allows us to determine the size of nonatmospheric reservoirs that mix with the atmosphere; these reservoirs can be CO2 adsorbed in the regolith or H2O in the polar ice caps. We have constructed both simple analytical models and time-dependent models of the loss from and supply of volatiles to the Martian atmosphere.

  12. Cellular Delivery and Photochemical Activation of Antisense Agents through a Nucleobase Caging Strategy

    PubMed Central

    Govan, Jeane M.; Uprety, Rajendra; Thomas, Meryl; Lusic, Hrvoje; Lively, Mark O.; Deiters, Alexander

    2013-01-01

    Antisense oligonucleotides are powerful tools to regulate gene expression in cells and model organisms. However, a transfection or microinjection is needed for efficient delivery of the antisense agent. We report the conjugation of multiple HIV TAT peptides to a hairpin-protected antisense agent through a light-cleavable nucleobase caging group. This conjugation allows for the facile delivery of the antisense agent without a transfection reagent and photochemical activation offers precise control over gene expression. The developed approach is highly modular, as demonstrated by the conjugation of folic acid to the caged antisense agent. This enabled targeted cell delivery through cell-surface folate receptors followed by photochemical triggering of antisense activity. Importantly, the presented strategy delivers native oligonucleotides after light-activation, devoid of any delivery functionalities or modifications that could otherwise impair their antisense activity. PMID:23915424

  13. Photochemical weathering and contemporary volatile loss on Mars

    NASA Technical Reports Server (NTRS)

    Huguenin, R. L.

    1987-01-01

    In an earlier series of papers by the author it was proposed that photochemical weathering of Fe(2+) in magnetite and in mafic silicates may be occurring in the contemporary surface environment with a resultant loss of O2 from the atmosphere. Morris and Lauer challenged the photochemical weathering model, proposing that oxidation by radiant heating rather than UV photoelectron emission induced oxidation may have dominated in the authors experiments. Subsequent laboratory studies of photochemical weathering of magnetite described here support the authors original proposal that UV illunimation can indeed drive the oxidation of magnetite under contemporary Martian surface conditions. The negative results of the Morris and Lauer study can now be explained.

  14. How People Actually Use Thermostats

    SciTech Connect

    Meier, Alan; Aragon, Cecilia; Hurwitz, Becky; Mujumdar, Dhawal; Peffer, Therese; Perry, Daniel; Pritoni, Marco

    2010-08-15

    Residential thermostats have been a key element in controlling heating and cooling systems for over sixty years. However, today's modern programmable thermostats (PTs) are complicated and difficult for users to understand, leading to errors in operation and wasted energy. Four separate tests of usability were conducted in preparation for a larger study. These tests included personal interviews, an on-line survey, photographing actual thermostat settings, and measurements of ability to accomplish four tasks related to effective use of a PT. The interviews revealed that many occupants used the PT as an on-off switch and most demonstrated little knowledge of how to operate it. The on-line survey found that 89% of the respondents rarely or never used the PT to set a weekday or weekend program. The photographic survey (in low income homes) found that only 30% of the PTs were actually programmed. In the usability test, we found that we could quantify the difference in usability of two PTs as measured in time to accomplish tasks. Users accomplished the tasks in consistently shorter times with the touchscreen unit than with buttons. None of these studies are representative of the entire population of users but, together, they illustrate the importance of improving user interfaces in PTs.

  15. Metal hybrid nanoparticles for catalytic organic and photochemical transformations.

    PubMed

    Song, Hyunjoon

    2015-03-17

    In order to understand heterogeneous catalytic reactions, model catalysts such as a single crystalline surface have been widely studied for many decades. However, catalytic systems that actually advance the reactions are three-dimensional and commonly have multiple components including active metal nanoparticles and metal oxide supports. On the other hand, as nanochemistry has rapidly been developed and been applied to various fields, many researchers have begun to discuss the impact of nanochemistry on heterogeneous catalysis. Metal hybrid nanoparticles bearing multiple components are structurally very close to the actual catalysts, and their uniform and controllable morphology is suitable for investigating the relationship between the structure and the catalytic properties in detail. In this Account, we introduce four typical structures of metal hybrid nanoparticles that can be used to conduct catalytic organic and photochemical reactions. Metal@silica (or metal oxide) yolk-shell nanoparticles, in which metal cores exist in internal voids surrounded by thin silica (or metal oxide) shells, exhibited extremely high thermal and chemical stability due to the geometrical protection of the silica layers against the metal cores. The morphology of the metal cores and the pore density of the hollow shells were precisely adjusted to optimize the reaction activity and diffusion rates of the reactants. Metal@metal oxide core-shell nanoparticles and inverted structures, where the cores supported the shells serving an active surface, exhibited high activity with no diffusion barriers for the reactants and products. These nanostructures were used as effective catalysts for various organic and gas-phase reactions, including hydrogen transfer, Suzuki coupling, and steam methane reforming. In contrast to the yolk- and core-shell structures, an asymmetric arrangement of distinct domains generated acentric dumbbells and tipped rods. A large domain of each component added multiple

  16. Surface and Interface Control on Photochemically Initiated Immobilization

    SciTech Connect

    Liu, Li; Engelhard, Mark H.; Yan, Mingdi

    2006-11-01

    Surface and interface properties are important in controlling the yield and efficiency of the photochemically initiated immobilization. Using a silane-functionalized perfluorophenylazide (PFPA-silane) as the photoactive crosslinker, the immobilization of polymers was studied by adjusting the density of the surface azido groups. Dilution of the photolinker resulted in a gradual decrease in the density of surface azido groups as well as the thickness of the immobilized film. When a non-photoactive silane was added to PFPA-silane, the film thickness decreased more rapidly, indicating that the additive competed with PFPA-silane and effectively reduced the density of the surface azido groups. The effect of surface topography was studied by adding a non-photoactive silane with either a shorter (n-propyltrimethoxysilane (PTMS)) or a longer spacer (n-octadecyltrimethoxysilane (ODTMS)). In most cases the long chain ODTMS shielded the surface azido groups resulting in more rapid decrease in film thickness as compared to PTMS treated under the same conditions. As the density of the surface azido groups decreased, the immobilized polymer changed from smooth films to patched structures, and eventually single polymer molecules.

  17. A photochemical crosslinking technology for tissue engineering: enhancement of the physico-chemical properties of collagen-based scaffolds

    NASA Astrophysics Data System (ADS)

    Chan, Barbara P.

    2005-04-01

    Collagen gel is a natural biomaterial commonly used in tissue engineering because of its close resemblance to nature, negligible immunogenecity and excellent biocompatibility. However, unprocessed collagen gel is mechanically weak, highly water binding and vulnerable to chemical and enzymatic attacks that limits its use in tissue engineering in particular tissues for weight-bearing purposes. The current project aimed to strengthen and stabilize collagen scaffolds using a photochemical crosslinking technique. Photochemical crosslinking is rapid, efficient, non-thermal and does not involve toxic chemicals, comparing with other crosslinking methods such as glutaraldehyde and gamma irradiation. Collagen scaffolds were fabricated using rat-tail tendon collagen. An argon laser was used to process the collagen gel after equilibrating with a photosensitizing reagent. Scanning electronic microscope was used to characterize the surface and cross-sectional morphology of the membranes. Physico-chemical properties of the collagen scaffolds such as water-binding capacity, mechanical properties and thermostability were studied. Photochemical crosslinking significantly reduced the water-binding capacity, a parameter inversely proportional to the extent of crosslinking, of collagen scaffolds. Photochemical crosslinking also significantly increased the ultimate stress and tangent modulus at 90% of the rupture strain of the collagen scaffolds. Differential scanning calorimetry analysis showed a significantly higher shrinkage temperature and absence of the denaturation peak during the thermoscan comparing with the controls. This means greater thermostability in the photochemically crosslinked collagen scaffolds. This study demonstrates that the photochemical crosslinking technology is able to enhance the physicochemical propterties of collagen scaffolds by strengthening, stabilizing and controlling the swelling ratio of the collagen scaffolds so as to enable their use for tissue

  18. Characterizing photochemical transformation of aqueous nC60 under environmentally relevant conditions.

    PubMed

    Hwang, Yu Sik; Li, Qilin

    2010-04-15

    Engineered nanomaterials may undergo transformation upon interactions with various environmental factors. In this study, photochemical transformation of aqueous nC60 was investigated under UVA irradiation. nC60 underwent photochemical transformation in the presence of dissolved O2, resulting in surface oxygenation and hydroxylation as demonstrated by XPS and ATR-FTIR analyses. The reaction followed a pseudo-first order rate law with the apparent reaction rate constant of 2.2 x 10(-2) h(-1). However, the core of the nanoparticles remained intact over 21 days of irradiation. Although no mineralization or dissolution of nC60 was observed, experiments using fullerol as a reference fullerene derivative suggested likely dissolution and partial mineralization of nC60 under long-term UVA exposure. Aquatic humic acid reduced nC60 transformation kinetics presumably due to scavenging of reactive oxygen species. Results from this study imply that photochemical transformation is an important factor controlling nC60 physical and chemical properties as well as its fate and transport in the natural aqueous environment. In addition, changes in nC60 surface chemistry drastically reduced C60 extraction efficiency by toluene, suggesting that the existing analytical method for C60 may not be applicable to environmental samples.

  19. Photochemical Reaction Altered Cardiac Toxicity of Diesel Exhaust Inhalation

    EPA Science Inventory

    Rationale: Epidemiological studies have indicated an association between urban air pollution exposure and cardiovascular morbidity and mortality. The present study was designed to evaluate the cardiac effects of inhaled diesel exhaust and compared with photochemically altered d...

  20. Photochemical oxidation: A solution for the mixed waste dilemma

    SciTech Connect

    Prellberg, J.W.; Thornton, L.M.; Cheuvront, D.A.

    1995-12-31

    Numerous technologies are available to remove organic contamination from water or wastewater. A variety of techniques also exist that are used to neutralize radioactive waste. However, few technologies can satisfactorily address the treatment of mixed organic/radioactive waste without creating unacceptable secondary waste products or resulting in extremely high treatment costs. An innovative solution to the mixed waste problem is on-site photochemical oxidation. Liquid-phase photochemical oxidation has a long- standing history of successful application to the destruction of organic compounds. By using photochemical oxidation, the organic contaminants are destroyed on-site leaving the water, with radionuclides, that can be reused or disposed of as appropriate. This technology offers advantages that include zero air emissions, no solid or liquid waste formation, and relatively low treatment cost. Discussion of the photochemical process will be described, and several case histories from recent design testing, including cost analyses for the resulting full-scale installations, will be presented as examples.

  1. Method of making gold thiolate and photochemically functionalized microcantilevers

    DOEpatents

    Boiadjiev, Vassil I [Knoxville, TN; Brown, Gilbert M [Knoxville, TN; Pinnaduwage, Lal A [Knoxville, TN; Thundat, Thomas G [Knoxville, TN; Bonnesen, Peter V [Knoxville, TN; Goretzki, Gudrun [Nottingham, GB

    2009-08-25

    Highly sensitive sensor platforms for the detection of specific reagents, such as chromate, gasoline and biological species, using microcantilevers and other microelectromechanical systems (MEMS) whose surfaces have been modified with photochemically attached organic monolayers, such as self-assembled monolayers (SAM), or gold-thiol surface linkage are taught. The microcantilever sensors use photochemical hydrosilylation to modify silicon surfaces and gold-thiol chemistry to modify metallic surfaces thereby enabling individual microcantilevers in multicantilever array chips to be modified separately. Terminal vinyl substituted hydrocarbons with a variety of molecular recognition sites can be attached to the surface of silicon via the photochemical hydrosilylation process. By focusing the activating UV light sequentially on selected silicon or silicon nitride hydrogen terminated surfaces and soaking or spotting selected metallic surfaces with organic thiols, sulfides, or disulfides, the microcantilevers are functionalized. The device and photochemical method are intended to be integrated into systems for detecting specific agents including chromate groundwater contamination, gasoline, and biological species.

  2. Chemical kinetics and photochemical data for use in stratospheric modeling

    NASA Technical Reports Server (NTRS)

    Demore, W. B.; Margitan, J. J.; Molina, M. J.; Watson, R. T.; Golden, D. M.; Hampson, R. F.; Kurylo, M. J.; Howard, C. J.; Ravishankara, A. R.

    1985-01-01

    Rate constants and photochemical cross sections are presented. The primary application of the data is for modeling of the stratospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena.

  3. Effect of photochemical treatment on the biocompatibility of a commercial nonionic surfactant used in the textile industry.

    PubMed

    Arslan-Alaton, Idil; Erdinc, Elif

    2006-10-01

    The degradability of surfactants is a frequent and complex issue arising both at domestic as well as industrial treatment facilities. The present paper describes a laboratory study conducted to elucidate the photochemical and biochemical treatability of a nonionic, alkyl polyethylene ether-based surfactant formulation commonly used in the textile preparation stage. The application of H(2)O(2)/UV-C advanced photochemical oxidation appeared to be a suitable treatment alternative and 90% COD removal (COD(0) approximately 500 mg/L) could be achieved under optimized process conditions. A significant COD removal efficiency (74%) could also be reached after biodegradation (final COD=135 mg/L) of the surfactant; however, necessitated an acclimation period of at least 6 weeks for the achievement of steady-state conditions. H(2)O(2)/UV-C treatment efficiency was seriously retarded upon elevation of the initial COD to around 1000 mg/L, resulting in 46% COD and 38% TOC removal after 120 min photochemical oxidation (H(2)O(2,0)=1020 mg/L; pH(0)=9.1). The BOD(5)/COD ratio increased from 0.23 to 0.31 after the application of H(2)O(2)/UV-C revealing that photochemical pretreatment may have a positive effect on the ultimate biodegradation of the nonionic surfactant. Although the time required for activated sludge treatment to reach steady-state conditions could be reduced to 3 weeks for the photochemically pretreated surfactant formulation biochemical COD removal efficiency dramatically decreased from 74% to 39% for the nonionic surfactant being subjected to H(2)O(2)/UV-C pretreatment (ultimate COD after activated sludge treatment=265 mg/L).

  4. Photochemical transformation of graphene oxide in sunlight.

    PubMed

    Hou, Wen-Che; Chowdhury, Indranil; Goodwin, David G; Henderson, W Matthew; Fairbrother, D Howard; Bouchard, Dermont; Zepp, Richard G

    2015-03-17

    Graphene oxide (GO) is promising in scalable production and has useful properties that include semiconducting behavior, catalytic reactivity, and aqueous dispersibility. In this study, we investigated the photochemical fate of GO under environmentally relevant sunlight conditions. The results indicate that GO readily photoreacts under simulated sunlight with the potential involvement of electron-hole pair creation. GO was shown to photodisproportionate to CO2, reduced materials similar to reduced GO (rGO) that are fragmented compared to the starting material, and low molecular-weight (LMW) species. Kinetic studies show that the rate of the initially rapid photoreaction of GO is insensitive to the dissolved oxygen content. In contrast, at longer time points (>10 h), the presence of dissolved oxygen led to a greater production of CO2 than the same GO material under N2-saturated conditions. Regardless, the rGO species themselves persist after extended irradiation equivalent to 2 months in natural sunlight, even in the presence of dissolved oxygen. Overall, our findings indicate that GO phototransforms rapidly under sunlight exposure, resulting in chemically reduced and persistent photoproducts that are likely to exhibit transport and toxic properties unique from parent GO.

  5. Photochemical oxidants: state of the science.

    PubMed

    Kley, D; Kleinmann, M; Sanderman, H; Krupa, S

    1999-01-01

    Atmospheric photochemical processes resulting in the production of tropospheric ozone (O(3)) and other oxidants are described. The spatial and temporal variabilities in the occurrence of surface level oxidants and their relationships to air pollution meteorology are discussed. Models of photooxidant formation are reviewed in the context of control strategies and comparisons are provided of the air concentrations of O(3) at select geographic locations around the world. This overall oxidant (O(3)) climatology is coupled to human health and ecological effects. The discussion of the effects includes both acute and chronic responses, mechanisms of action, human epidemiological and plant population studies and briefly, efforts to establish cause-effect relationships through numerical modeling. A short synopsis is provided of the interactive effects of O(3) with other abiotic and biotic factors. The overall emphasis of the paper is on identifying the current uncertainties and gaps in our understanding of the state of the science and some suggestions as to how they may be addressed.

  6. Photochemical organonitrate formation in wet aerosols

    NASA Astrophysics Data System (ADS)

    Lim, Yong Bin; Kim, Hwajin; Kim, Jin Young; Turpin, Barbara J.

    2016-10-01

    Water is the most abundant component of atmospheric fine aerosol. However, despite rapid progress, multiphase chemistry involving wet aerosols is still poorly understood. In this work, we report results from smog chamber photooxidation of glyoxal- and OH-containing ammonium sulfate or sulfuric acid particles in the presence of NOx and O3 at high and low relative humidity. Particles were analyzed using ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). During the 3 h irradiation, OH oxidation products of glyoxal that are also produced in dilute aqueous solutions (e.g., oxalic acids and tartaric acids) were formed in both ammonium sulfate (AS) aerosols and sulfuric acid (SA) aerosols. However, the major products were organonitrogens (CHNO), organosulfates (CHOS), and organonitrogen sulfates (CHNOS). These were also the dominant products formed in the dark chamber, indicating non-radical formation. In the humid chamber (> 70 % relative humidity, RH), two main products for both AS and SA aerosols were organonitrates, which appeared at m / z- 147 and 226. They were formed in the aqueous phase via non-radical reactions of glyoxal and nitric acid, and their formation was enhanced by photochemistry because of the photochemical formation of nitric acid via reactions of peroxy radicals, NOx and OH during the irradiation.

  7. Photochemical Phenomenology Model for the New Millenium

    NASA Technical Reports Server (NTRS)

    Bishop, James; Evans, J. Scott

    2000-01-01

    This project tackles the problem of conversion of validated a priori physics-based modeling capabilities, specifically those relevant to the analysis and interpretation of planetary atmosphere observations, to application-oriented software for use in science and science-support activities. The software package under development, named the Photochemical Phenomenology Modeling Tool (PPMT), has particular focus on the atmospheric remote sensing data to be acquired by the CIRS instrument during the CASSINI Jupiter flyby and orbital tour of the Saturnian system. Overall, the project has followed the development outline given in the original proposal, and the Year 1 design and architecture goals have been met. Specific accomplishments and the difficulties encountered are summarized in this report. Most of the effort has gone into complete definition of the PPMT interfaces within the context of today's IT arena: adoption and adherence to the CORBA Component Model (CCM) has yielded a solid architecture basis, and CORBA-related issues (services, specification options, development plans, etc.) have been largely resolved. Implementation goals have been redirected somewhat so as to be more relevant to the upcoming CASSINI flyby of Jupiter, with focus now being more on data analysis and remote sensing retrieval applications.

  8. Mild Photochemical Biofunctionalization of Glass Microchannels.

    PubMed

    Carvalho, Rui Rijo; Pujari, Sidharam P; Gahtory, Digvijay; Vrouwe, Elwin X; Albada, Bauke; Zuilhof, Han

    2017-01-10

    The ability to locally modify the inside of microfluidic channels with bioactive molecules is of ever-rising relevance. In this article, we show the direct photochemical coupling of a N-hydroxysuccinimide-terminated ω-alkene onto hydrogen-terminated silicon oxide, and its subsequent functionalization with a catalytically active DNAzyme. To achieve this local attachment of a DNAzyme, we prepared hydrogen-phenyl-terminated glass (H-Φ-glass) by the reaction of glass with H-SiPhCl2. The presence of a radical-stabilizing substituent on the Si atom (i.e., phenyl) enabled the covalent modification of bare glass substrates and of the inside of glass microchannels with a functional organic monolayer that allowed direct reaction with an amine-functionalized biomolecule. In this study, we directly attached an NHS-functionalized alkene to the modified glass surface using light with a wavelength of 328 nm, as evidenced by SCA, G-ATR, XPS, SEM, AFM and fluorescence microscopy. Using these NHS-based active esters on the surface, we performed a direct localized attachment of a horseradish peroxidase (HRP)-mimicking hemin/G-quadruplex (hGQ) DNAzyme complex inside a microfluidic channel. This wall-coated hGQ DNAzyme effectively catalyzed the in-flow oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) [ABTS] in the presence of hydrogen peroxide. This proof-of-concept of mild biofunctionalization will allow the facile preparation of modified microchannels for myriad biorelevant applications.

  9. Investigation of the Photochemical Method for Uranium Isotope Separation

    DOE R&D Accomplishments Database

    Urey, H. C.

    1943-07-10

    To find a process for successful photochemical separation of isotopes several conditions have to be fulfilled. First, the different isotopes have to show some differences in the spectrum. Secondly, and equally important, this difference must be capable of being exploited in a photochemical process. Parts A and B outline the physical and chemical conditions, and the extent to which one might expect to find them fulfilled. Part C deals with the applicability of the process.

  10. Degradation of artificial sweeteners via direct and indirect photochemical reactions.

    PubMed

    Perkola, Noora; Vaalgamaa, Sanna; Jernberg, Joonas; Vähätalo, Anssi V

    2016-07-01

    We studied the direct and indirect photochemical reactivity of artificial sweeteners acesulfame, saccharin, cyclamic acid and sucralose in environm entally relevant dilute aqueous solutions. Aqueous solutions of sweeteners were irradiated with simulated solar radiation (>290 nm; 96 and 168 h) or ultraviolet radiation (UVR; up to 24 h) for assessing photochemical reactions in surface waters or in water treatment, respectively. The sweeteners were dissolved in deionised water for examination of direct photochemical reactions. Direct photochemical reactions degraded all sweeteners under UVR but only acesulfame under simulated solar radiation. Acesulfame was degraded over three orders of magnitude faster than the other sweeteners. For examining indirect photochemical reactions, the sweeteners were dissolved in surface waters with indigenous dissolved organic matter or irradiated with aqueous solutions of nitrate (1 mg N/L) and ferric iron (2.8 mg Fe/L) introduced as sensitizers. Iron enhanced the photodegradation rates but nitrate and dissolved organic matter did not. UVR transformed acesulfame into at least three products: iso-acesulfame, hydroxylated acesulfame and hydroxypropanyl sulfate. Photolytic half-life was one year for acesulfame and more than several years for the other sweeteners in surface waters under solar radiation. Our study shows that the photochemical reactivity of commonly used artificial sweeteners is variable: acesulfame may be sensitive to photodegradation in surface waters, while saccharin, cyclamic acid and sucralose degrade very slowly even under the energetic UVR commonly used in water treatment.

  11. Photochemical mechanisms of ocular photic injury (Abstract Only)

    NASA Astrophysics Data System (ADS)

    Stuck, Bruce E.; Lund, David J.; Zuclich, Joseph A.

    2000-03-01

    Mechanisms of photic injury to the eye can be categorized as photochemical, photothermal or photodistruptive. Exposure wavelength, exposure duration, ocular tissue characteristics and response criteria are key factors in the delineation of the ocular injury mechanisms. Depending on the exposure condition, one or all of the laser-tissue interaction mechanisms can be involved. Although photic injury to the eye was initially assumed to involve thermal mechanisms, more recent research has demonstrated that ocular effects can be produced by light exposure without a significant retinal temperature rise. Photochemical mechanisms are also implicated in UV photic injury to the cornea and lens. Exposure of the retina to short visible wavelengths for prolonged durations results in photochemical retinal damage with negligible localized retinal temperature elevation. For exposure conditions where photochemical mechanisms are dominate, the reciprocity of irradiance and exposure duration is apparent. The latency until observation of a photochemical lesion is often 24-48 hours whereas a thermal lesion is observed immediately or within a few hours after the exposure. Action spectra for photochemical injury to the eye are discussed in the context of ocular injury thresholds and current permissible exposure limits.

  12. The composition dependence of the photochemical reactivity of strontium barium titanate

    NASA Astrophysics Data System (ADS)

    Bhardwaj, Abhilasha

    The efficiency of particulate water photolysis catalysts is impractically low due to the recombination of intermediate species and charge carriers. The back reaction can occur easily if the oxidation and reduction sites on the surface of the catalyst are not far enough apart. It is hypothesized that it will be possible to increase the separation of the sites of the two half reactions and reduce the recombination of photogenerated charge carriers by using a ferroelectric material with permanent internal dipolar fields. This separation of the reaction sites may significantly increase the efficiency of the process. The present work compares the photochemical reactivities of ferroelectric and nonferroelectric materials (SrxBa1-xTiO 3, 0.0≤ x ≤1.0) with similar composition and structure. The reactivities are compared by measuring the color change of methylene blue dye after the aqueous dye solution reacts on the surface of ceramic sample pellets as a result of exposure to UV light. The reactivities are also compared by measuring the amount of silver that is formed when an aqueous AgNO3 solution photochemically reacts on the surface. The change in the color of the dye is measured by diffuse reflectance spectroscopy and absorbance measurements. The amount of silver is measured by atomic force microscopy. The photochemical reactivity of SrxBa1-xTiO3 shows a local maximum at the composition of the ferroelectric to non-ferroelectric transition. Also, the reactivities decrease as BaTiO3 and SrTiO3 become less pure. The dominant factors causing this trend in reactivities of SrxBa1-xTiO3 are the dielectric constant and alloy scattering. It is found that higher values of the dielectric constant increase the photochemical reactivity by enlarging the space charge region. The increase in alloy scattering in SrxBa1-xTiO 3 solid solutions as x increases from zero or decreases from 1, has adverse effect on reactivity. There are other factors such as ferroelectric polarization

  13. Photochemical internalization of bleomycin for glioma treatment

    PubMed Central

    Mathews, Marlon S.; Blickenstaff, Joseph W.; Shih, En-Chung; Zamora, Genesis; Vo, Van; Sun, Chung-Ho; Hirschberg, Henry; Madsen, Steen J.

    2012-01-01

    Abstract. We study the use of photochemical internalization (PCI) for enhancing chemotherapeutic response to malignant glioma cells in vitro. Two models are studied: monolayers consisting of F98 rat glioma cells and human glioma spheroids established from biopsy-derived glioma cells. In both cases, the cytotoxicity of aluminum phthalocyanine disulfonate (AlPcS2a)-based PCI of bleomycin was compared to AlPcS2a-photodynamic therapy (PDT) and chemotherapy alone. Monolayers and spheroids were incubated with AlPcS2a (PDT effect), bleomycin (chemotherapy effect), or AlPcS2a+bleomycin (PCI effect) and were illuminated (670 nm). Toxicity was evaluated using colony formation assays or spheroid growth kinetics. F98 cells in monolayer/spheroids were not particularly sensitive to the effects of low radiant exposure (1.5  J/cm2 @ 5  mW/cm2) AlPcS2a-PDT. Bleomycin was moderately toxic to F98 cells in monolayer at relatively low concentrations—incubation of F98 cells in 0.1  μg/ml for 4 h resulted in 80% survival, but less toxic in human glioma spheroids respectively. In both in vitro systems investigated, a significant PCI effect is seen. PCI using 1.5  J/cm2 together with 0.25  μg/ml bleomycin resulted in approximately 20% and 18% survival of F98 rat glioma cells and human glioma spheroids, respectively. These results show that AlPcS2a-mediated PCI can be used to enhance the efficacy of chemotherapeutic agents such as bleomycin in malignant gliomas. PMID:22612148

  14. Three-Dimensional Photochemical Machining with Lasers.

    DTIC Science & Technology

    1984-12-28

    laser beams was alternately blocked so we could record (a) background noise and (b) the intensity of the "probe" beam transmitted through the sample ...actually entering the intersection volume is dependent on the absorption spectrum of the sample as recorded on the CART 17DX. Equation 1 is used for...Spectral Analysis Absorption spectra were taken on a CARY 17DX recording spectro- photometer in the visible region at room temperature. The samples

  15. Integrated photochemical and biological treatment of a commercial textile surfactant: process optimization, process kinetics and COD fractionation.

    PubMed

    Arslan-Alaton, Idil; Cokgor, Emine Ubay; Koban, Baris

    2007-07-31

    The biodegradability of surfactants is a frequent and complex issue arising both at domestic as well as industrial treatment facilities. In the present experimental study, the integrated photochemical (H(2)O(2)/UV-C) and biochemical (activated sludge) treatment of a commercial grade nonionic/anionic textile surfactant formulation was investigated. Photochemical baseline experiments have shown that once the initial pH and H(2)O(2) dose were optimized, practically complete COD removal (COD(o)=500+/-30mgL(-1)) could be achieved. Once the COD was elevated to values being typical for the textile fabric preparation stage, treatment efficiency was seriously retarded provided that the photochemical treatment conditions remained constant. Moreover, a definite relationship existed between H(2)O(2) consumption and COD removal for H(2)O(2)/UV-C advanced oxidation of the textile surfactant. In the second part of the study, COD abatement was modeled for the biodegradation of untreated and photochemically pretreated textile surfactant formulation according to their COD fractions. Results have indicated that the readily biodegradable and rapidly hydrolysable COD fractions of the textile surfactant solution could be appreciably increased upon exposure to an optimum H(2)O(2) concentration (60mM; i.e. 2.1g H(2)O(2) (g COD(o))(-1)) and extended UV-C irradiation times (i.e. 90 and 120min).

  16. Photochemical production of hydrogen peroxide in size-fractionated Southern California coastal waters.

    PubMed

    Clark, Catherine D; De Bruyn, Warren J; Jones, Joshua G

    2009-06-01

    Hydrogen peroxide (H(2)O(2)) photochemical production was measured in bulk and size-fractionated surf zone and source waters (Orange County, California, USA). Post-irradiation (60 min; 300 W ozone-free xenon lamp), maximum H(2)O(2) concentrations were approximately 10000 nM (source) and approximately 1500 nM (surf zone). Average initial hydrogen peroxide production rates (HPPR) were higher in bulk source waters (11+/-7.0 nM s(-1)) than the surf zone (2.5+/-1 nM s(-1)). A linear relationship was observed between non-purgeable dissolved organic carbon and absorbance coefficient (m(-1) (300 nm)). HPPR increased with increasing absorbance coefficient for bulk and size-fractionated source waters, consistent with photochemical production from CDOM. However, HPPR varied significantly (5x) for surf zone samples with the same absorbance coefficients, even though optical properties suggested CDOM from salt marsh source waters dominates the surf zone. To compare samples with varying CDOM levels, apparent quantum yields (Phi) for H(2)O(2) photochemical production were calculated. Source waters showed no significant difference in Phi between bulk, large (>1000 Da (>1 kDa)) and small (<1 kDa) size fractions, suggesting H(2)O(2) production efficiency is homogeneously distributed across CDOM size. However, surf zone waters had significantly higher Phi than source (bulk 0.086+/-0.04 vs. 0.034+/-0.013; <1 kDa 0.183+/-0.012 vs. 0.027+/-0.018; >1 kDa 0.151+/-0.090 vs. 0.016+/-0.009), suggesting additional production from non-CDOM sources. H(2)O(2) photochemical production was significant for intertidal beach sand and senescent kelp (sunlight; approximately 42 nM h(-1) vs. approximately 5 nM h(-1)), on the order of CDOM production rates previously measured in coastal and oceanic waters. This is the first study of H(2)O(2) photochemical production in size-fractionated coastal waters showing significant production from non-CDOM sources in the surf zone.

  17. Multiresolution wavelet-based simulation of transport and photochemical reactions in the atmosphere

    NASA Astrophysics Data System (ADS)

    Heidarinasab, Amir; Dabir, Bahram; Sahimi, Muhammad

    We propose a novel approach for coarsening of computational grids that are used in the modelling of air pollution problems and climate change phenomena at large length scales. The method is based on the use of wavelet transformations. Starting with a fine-scale computational grid, the resolution of which depends on the amount of the experimental data that are available, as well as the topography of the area under study, a wavelet transformation is used to systematically coarsen the grid in those zones in which the fine details of the grid are not necessary, while preserving all the important information and the grid resolution in those regions where large-scale variations in the properties of interest occur. The coarsening can be static and fixed, based on the topography alone, or can be dynamic so as to produce a grid structure that varies with the time. We show that the computations for modelling transport and photochemical reactions (and the associated air pollution problems) with the new approach are orders of magnitude more efficient than the most efficient method currently available, and may render unnecessary use of massively parallel or vectorized computational strategies. To demonstrate the efficiency of the method, we study transport and photochemical reactions of 51 species, involving 117 nonlinear reactions, in the atmosphere of Tehran, Iran, a large urban area with severe air pollution problems.

  18. Versatile thin-film reactor for photochemical vapor generation.

    PubMed

    Zheng, Chengbin; Sturgeon, Ralph E; Brophy, Christine; Hou, Xiandeng

    2010-04-01

    A novel thin-film reactor is described and evaluated for its analytical performance with photochemical vapor generation (TF-PVG). The device, comprising both the generator and a gas-liquid separator, utilizes a vertical central quartz rod onto which the sample is pumped to yield a thin liquid film conducive to the rapid escape of generated hydrophobic species. The rod is housed within a concentric quartz tube through which a flow of argon carrier/stripping gas is passed to remove and transport the generated species to a detector, which in this study is an inductively coupled argon plasma optical emission spectrometer (ICP-OES). The concentric quartz tube is itself surrounded by a 78-turn 0.5 m long quartz coil low-pressure mercury discharge lamp operating at 20 W. The performance of this thin-film photoreactor was evaluated through comparison of analytical figures of merit for detection of a number of elements undergoing PVG in the presence of formic or acetic acid with those arising from conventional solution nebulization under optimized conditions. The TF-PVG reactor provided sensitivity enhancements, of 110-, 120-, 130-, 250-, 120-, 230-, 78-, 1.3-, 16-, and 32-fold for As, Sb, Bi, Se, Te, Hg, Ni, Co, Fe, and I, respectively, and detection limit enhancements of 110-, 140-, 170-, 270-, 200-, 300-, 160-, 2.7-, 50-, and 44-fold for these same elements. Vapor generation efficiencies ranged from 20-100% for this suite of analytes. The utility of this technique was demonstrated by the determination of Fe and Ni in Certified Reference Materials DORM-3 (fish protein) and DOLT-4 (dogfish liver tissue).

  19. Evaluation of the photochemical reflectance index in AVIRIS imagery

    NASA Technical Reports Server (NTRS)

    Gamon, John A.; Roberts, Dar A.; Green, Robert O.

    1995-01-01

    In this paper, we evaluate the potential for extracting the 'photochemical reflectance index' (PRI; previously called the 'physiological reflectance index') from AVIRIS data. This index, which is derived from narrow-band reflectance at 531 and 570 nm, has proven to be a useful indicator of photosynthetic function at the leaf and canopy scales. At the leaf level, PRI varies with photosynthetic capacity, radiation-use efficiency, and vegetation type (unpublished data). This finding is consistent with the hypothesis that vegetation types exhibiting chronically reduced photosynthesis during periods of stress (e.g. drought-tolerant evergreens) invest proportionally more in photoprotective processes than vegetation with high photosynthetic capacity (e.g. crops or deciduous perennials). Vertical transects in tropical and boreal forest canopies have indicated declines in PRI associated with downregulation of photosynthesis at the canopy tops under sunny, dry midday conditions (unpublished data). This reduced PRI in upper canopy levels provides a further basis for examining this signal with the 'view from above' afforded by aircraft overflights. Although many factors could confound interpretation of a subtle physiological signal at the landscape scale, we conducted a preliminary examination of PRI extracted from existing, AVIRIS imagery of Stanford University's Jasper Ridge Biological Preserve obtained on the June 2nd, 1992, overflight. The goal was to use the hyperspectral capabilities of AVIRIS to evaluate the potential of this index for obtaining useful physiological data at the landscape scale. The expectation based on leaf- and canopy-level studies was that regions containing vegetation of reduced photosynthetic capacity (e.g. chaparral or evergreen woodland) would exhibit lower PRI values than regions of high capacity (e.g. deciduous woodland).

  20. Actinometric measurement of solar ultraviolet and development of a weighted solar UV integral. [photochemical reaction rate determination

    NASA Technical Reports Server (NTRS)

    Gupta, A.; Coulbert, C.

    1978-01-01

    An actinometer has been developed to measure outdoor irradiance in the range 295-400 nm. Actinometric measurements of radiation are based on determination of photochemical reaction rates for reactions of known quantum efficiency. Actinometers have the advantage of providing irradiance data over surfaces of difficult accessibility; in addition, actinometrically determined irradiance data are wavelength weighted and therefore provide a useful means of assessing the degradation rates of polymers employed in solar energy systems.

  1. A flight experiment to determine GPS photochemical contamination accumulation rates

    NASA Technical Reports Server (NTRS)

    Tribble, A. C.; Haffner, J. W.

    1990-01-01

    It was recently suggested that photochemically deposited contamination, originating from volatiles outgassed by a spacecraft, may be responsible for the anomalous degradation in power seen on the GPS Block 1 vehicles. In an attempt to confirm, or deny, the photochemical deposition rates predicted, a study was undertaken to design a flight experiment to be incorporated on the GPS vehicles currently in production. The objective was to develop an inexpensive, light weight instrument package that would give information on the contamination levels within a few months of launch. Three types of apparatus were studied, Quartz Crystal Microbalances, (QCM's), modified solar cells, and calorimeters. A calorimeter was selected due primarily to its impact on the production schedule of the GPS vehicles. An analysis of the sensitivity of the final design is compared to the predicted contamination accumulation rates in order to determine how long after launch it will take the experiment to show the effects of photochemical contamination.

  2. Photochemical Processes in the Condensed Haze of Titan's Atmosphere

    NASA Astrophysics Data System (ADS)

    Gudipati, M. S.; Couturier, I.; Jacovi, R.; Lignell, A.

    2013-12-01

    Recently we have shown that condensed-phase photochemical processes continue to occur at altitudes where gas-phase photochemistry would not be significant due to extinction of higher energy short-wavelength photons and availability of only longer wavelength low-energy photons (>250 nm). Accretion of Titan's molecules into weakly bound van der Waals aggregates would trigger new channels of photochemical reaction pathways that are not available for gas-phase isolated molecules. Laboratory studies carried out at JPL and AMU will be discussed. Nature of Titan's haze aerosol particles will be extrapolated in the light of these laboratory studies. Ref: Gudipati et al., Nat. Commun. 4 (2013) 1648

  3. Approximate photochemical dynamics of azobenzene with reactive force fields

    SciTech Connect

    Li, Yan; Hartke, Bernd

    2013-12-14

    We have fitted reactive force fields of the ReaxFF type to the ground and first excited electronic states of azobenzene, using global parameter optimization by genetic algorithms. Upon coupling with a simple energy-gap transition probability model, this setup allows for completely force-field-based simulations of photochemical cis→trans- and trans→cis-isomerizations of azobenzene, with qualitatively acceptable quantum yields. This paves the way towards large-scale dynamics simulations of molecular machines, including bond breaking and formation (via the reactive force field) as well as photochemical engines (presented in this work)

  4. Electrolytic photodissociation of chemical compounds by iron oxide photochemical diodes

    DOEpatents

    Somorjai, Gabor A.; Leygraf, Christofer H.

    1985-01-01

    Chemical compounds can be dissociated by contacting the same with a p/n type semi-conductor photochemical diode having visible light as its sole source of energy. The photochemical diode consists of low cost, readily available materials, specifically polycrystalline iron oxide doped with silicon in the case of the n-type semi-conductor electrode, and polycrystalline iron oxide doped with magnesium in the case of the p-type electrode. So long as the light source has an energy greater than 2.2 electron volts, no added energy source is needed to achieve dissociation.

  5. Approximate photochemical dynamics of azobenzene with reactive force fields

    NASA Astrophysics Data System (ADS)

    Li, Yan; Hartke, Bernd

    2013-12-01

    We have fitted reactive force fields of the ReaxFF type to the ground and first excited electronic states of azobenzene, using global parameter optimization by genetic algorithms. Upon coupling with a simple energy-gap transition probability model, this setup allows for completely force-field-based simulations of photochemical cis→trans- and trans→cis-isomerizations of azobenzene, with qualitatively acceptable quantum yields. This paves the way towards large-scale dynamics simulations of molecular machines, including bond breaking and formation (via the reactive force field) as well as photochemical engines (presented in this work).

  6. Photochemical Transformation Processes in Sunlit Surface Waters

    NASA Astrophysics Data System (ADS)

    Vione, D.

    2012-12-01

    Photochemical reactions are major processes in the transformation of hardly biodegradable xenobiotics in surface waters. They are usually classified into direct photolysis and indirect or sensitised degradation. Direct photolysis requires xenobiotic compounds to absorb sunlight, and to get transformed as a consequence. Sensitised transformation involves reaction with transient species (e.g. °OH, CO3-°, 1O2 and triplet states of chromophoric dissolved organic matter, 3CDOM*), photogenerated by so-called photosensitisers (nitrate, nitrite and CDOM). CDOM is a major photosensitiser: is it on average the main source of °OH (and of CO3-° as a consequence, which is mainly produced upon oxidation by °OH of carbonate and bicarbonate) and the only important source of 1O2 and 3CDOM* [1, 2]. CDOM origin plays a key role in sensitised processes: allochthonous CDOM derived from soil runoff and rich in fulvic and humic substances is usually more photoactive than autochthonous CDOM (produced by in-water biological processes and mainly consisting of protein-like material) or of CDOM derived from atmospheric deposition. An interesting gradual evolution of CDOM origin and photochemistry can be found in mountain lakes across the treeline, which afford a gradual transition of allochthonous- autochtonous - atmopheric CDOM when passing from trees to alpine meadows to exposed rocks [3]. Another important issue is the sites of reactive species photoproduction in CDOM. While there is evidence that smaller molecular weight fractions are more photoactive, some studies have reported considerable 1O2 reactivity in CDOM hydrophobic sites and inside particles [4]. We have recently addressed the problem and found that dissolved species in standard humic acids (hydrodynamic diameter < 0.1 μm) account for the vast majority of 1O2 and triplet states photoproduction. In hydrophobic sites of particles, the formation rate of 1O2 is considerably lower than in the solution bulk [5], but the absence

  7. Photochemical Deposition of Semiconductor Thin Films and Their Application for Solar Cells and Gas Sensors

    NASA Astrophysics Data System (ADS)

    Ichimura, M.; Gunasekaran, M.; Sueyoshi, T.

    2009-06-01

    The photochemical deposition (PCD) technique was applied for solar cells and gas sensors. CdS and Cd1-xZnxS were deposited by PCD. Thiosulfate ions S2O32- act as a reductant and a sulfur source. The SnS absorption layer was deposited by three-step pulse electrochemical deposition. For the CdS/SnS structure, the best cell showed an efficiency of about 0.2%, while for the Cd1-xZnxS/SnS structure, an efficiency of up to 0.7% was obtained. For the gas sensor application, SnO2 was deposited by PCD from a solution containing SnSO4 and HNO3. To enhance the sensitivity to hydrogen, Pd was doped by the photochemical doping method. The current increased by a factor of 104 upon exposure to 5000 ppm hydrogen within 1 min at room temperature. 103 times conductivity increase was observed even for 50 ppm hydrogen.

  8. Studies in photochemical smog chemistry. 1. Atmospheric chemistry of toulene. 2. Analysis of chemical reaction mechanisms for photochemical smog

    SciTech Connect

    Leone, J.A.

    1985-01-01

    This study focuses on two related topics in the gas phase organic chemistry of importance in urban air pollution. An experimental effort aimed at developing a new explicit reaction mechanism for the atmospheric photooxidation of toluene is described. This mechanism is tested using experimental data from both indoor and outdoor smog chamber facilities. The predictions of the new reaction mechanism are found to be in good agreement with both sets of experimental data. Additional simulations performed with the new mechanism are used to investigate various mechanistic paths. A theoretical analysis of lumped chemical reaction mechanisms for photochemical smog is presented. Included is a description of a new counter species analysis technique which can be used to analyze any complex chemical reaction mechanism. When applied to mechanisms for photochemical smog, this analysis is shown capable of providing answers to previously inaccessible questions such as the relative contributions of individual organics to photochemical ozone formation.

  9. Liquid PEG Polymers Containing Antioxidants: A Versatile Platform for Studying Oxygen-Sensitive Photochemical Processes.

    PubMed

    Mongin, Cédric; Golden, Jessica H; Castellano, Felix N

    2016-09-14

    This article proposes the exploitation of widely available, inexpensive, innocuous "green" liquid polyethylene glycol (PEG) polymers containing the oxygen scavenger oleic acid (OA) as promising media for studying oxygen-sensitive photochemical processes. Here we report the successful application of this media to detailed investigations of triplet-sensitized photochemical upconversion, previously established as being readily poisoned by dissolved oxygen. Three different PEG materials were investigated with increasing molecular weight from 200 to 600 g/mol, coded as PEG-200, PEG-400, and PEG-600. These fluidic polymers facilitate an oxygen-depleted environment in comparison to commonly employed organic solvents while providing high solubility and diffusion for the dissolved chromophores. Moreover, the low oxygen permeation afforded by these PEG solvents allows them to remain deoxygenated in open containers under ambient conditions for extended time periods. OA, 9,10-dimethylanthracene (DMA), and 2,5-dimethylfuran (DMF) are shown to efficiently and quantitatively consume dissolved oxygen in the PEG environment in the presence of the photoactivated triplet sensitizer platinum(II) tetraphenyltetrabenzoporphyrin (PtTPBP). Oxygen consumption was directly correlated with systematically increasing sensitizer excited-state lifetimes that eventually reach the same plateau as achieved through extensive N2 sparging. Diffusion-controlled bimolecular triplet-triplet energy transfer quenching between PtTPBP and the acceptor/annihilator 9,10-bisphenylethynylanthracene (BPEA) was observed in all three PEG formulations investigated. Subsequent triplet-triplet annihilation, between triplet excited BPEA acceptors, achieves bright and stable upconverted singlet fluorescence from BPEA with no decrease in intensity over 20 h under ambient conditions. In the champion composition (PEG 200), the upconversion quantum efficiency reached 31% under conditions where triplet-triplet annihilation

  10. 76 FR 72919 - Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-28

    ... AGENCY Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants AGENCY..., ``Second External Review Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants... review of the national ambient air quality standards (NAAQS) for ozone. DATES: The public comment...

  11. 76 FR 17121 - Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-28

    ... AGENCY Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants AGENCY..., ``First External Review Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants... review of the national ambient air quality standards (NAAQS) for ozone. DATES: The public comment...

  12. Photochemical transformation of graphene oxide in sunlight (journal)

    EPA Science Inventory

    Graphene oxide (GO) is a graphene derivative that is more easily manufactured in large scale and used to synthesize reduced graphene oxide (rGO) with properties analogous to graphene. In this study, we investigate the photochemical fate of GO under sunlight conditions. The resu...

  13. Chemical kinetics and photochemical data for use in stratospheric modeling

    NASA Technical Reports Server (NTRS)

    Demore, W. B.; Sander, S. P.; Golden, D. M.; Hampson, R. F.; Kurylo, M. J.; Howard, C. J.; Ravishankara, A. R.; Kolb, C. E.; Molina, M. J.

    1992-01-01

    As part of a series of evaluated sets, rate constants and photochemical cross sections compiled by the NASA Panel for Data Evaluation are provided. The primary application of the data is in the modeling of stratospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena. Copies of this evaluation are available from the Jet Propulsion Laboratory.

  14. Packed bed reactor for photochemical .sup.196 Hg isotope separation

    DOEpatents

    Grossman, Mark W.; Speer, Richard

    1992-01-01

    Straight tubes and randomly oriented pieces of tubing having been employed in a photochemical mercury enrichment reactor and have been found to improve the enrichment factor (E) and utilization (U) compared to a non-packed reactor. One preferred embodiment of this system uses a moving bed (via gravity) for random packing.

  15. Quantitative photochemical formation of [Ru(tpy)(bpy)H]+.

    PubMed

    Matsubara, Yasuo; Konno, Hideo; Kobayashi, Atsuo; Ishitani, Osamu

    2009-11-02

    Quantitative photochemical production of [Ru(tpy)(bpy)H](+) (Ru-H(+)) was achieved by irradiation of [Ru(tpy)(bpy)(DMF)](2+) (Ru-DMF(2+); DMF = N,N-dimethylformamide) in a tetrahydrofuran (THF) solution containing excess triethylamine (NEt(3)). The mechanism of the Ru-H(+) formation was investigated in detail. A photochemical ligand substitution reaction of Ru-DMF(2+) in THF proceeded to give [Ru(tpy)(bpy)(THF)](2+) (Ru-THF(2+)) with a quantum yield of (7.6 +/- 0.7) x 10(-2). In the presence of NEt(3), a similar photochemical ligand substitution reaction also proceeded quickly, but the products were an equilibrium mixture of Ru-THF(2+) and [Ru(tpy)(bpy)(NEt(3))](2+) (Ru-NEt(3)(2+)) with a considerable amount of Ru-H(+) even in the first stage of the photochemical reaction. The equilibrium constant between Ru-THF(2+) and Ru-NEt(3)(2+) was determined as 6.9 +/- 2.1. Irradiation to Ru-NEt(3)(2+) gave Ru-H(+) with a quantum yield of (9.1 +/- 0.5) x 10(-3). An important intermediate, Ru-NEt(3)(2+), was isolated, and its properties were investigated in detail.

  16. PHOTOCHEMICAL TRANSFORMATIONS OF DISSOLVED ORGANIC MATTER IN A BLACKWATER RIVER

    EPA Science Inventory

    We examined photochemical alterations of dissolved organic matter (DOM) from the Satilla River, a high DOC (10-40 mg/liter) blackwater river of southeast Georgia. Water samples were filtered to remove most organisms, placed in quartz tubes, and incubated under natural sunlight a...

  17. A Simple Photochemical Experiment for the Advanced Laboratory.

    ERIC Educational Resources Information Center

    Rosenfeld, Stuart M.

    1986-01-01

    Describes an experiment to provide students with: (1) an introduction to photochemical techniques and theory; (2) an experience with semimicro techniques; (3) an application of carbon-14 nuclear magnetic resonance; and (4) a laboratory with some qualities of a genuine experiment. These criteria are met in the photooxidation of 9,…

  18. Photochemical Copper Coating on 3D Printed Thermoplastics.

    PubMed

    Yung, Winco K C; Sun, Bo; Huang, Junfeng; Jin, Yingdi; Meng, Zhengong; Choy, Hang Shan; Cai, Zhixiang; Li, Guijun; Ho, Cheuk Lam; Yang, Jinlong; Wong, Wai Yeung

    2016-08-09

    3D printing using thermoplastics has become very popular in recent years, however, it is challenging to provide a metal coating on 3D objects without using specialized and expensive tools. Herein, a novel acrylic paint containing malachite for coating on 3D printed objects is introduced, which can be transformed to copper via one-step laser treatment. The malachite containing pigment can be used as a commercial acrylic paint, which can be brushed onto 3D printed objects. The material properties and photochemical transformation processes have been comprehensively studied. The underlying physics of the photochemical synthesis of copper was characterized using density functional theory calculations. After laser treatment, the surface coating of the 3D printed objects was transformed to copper, which was experimentally characterized by XRD. 3D printed prototypes, including model of the Statue of Liberty covered with a copper surface coating and a robotic hand with copper interconnections, are demonstrated using this painting method. This composite material can provide a novel solution for coating metals on 3D printed objects. The photochemical reduction analysis indicates that the copper rust in malachite form can be remotely and photo-chemically reduced to pure copper with sufficient photon energy.

  19. Chemical kinetic and photochemical data for use in stratospheric modelling

    NASA Technical Reports Server (NTRS)

    Demore, W. B.; Stief, L. J.; Kaufman, F.; Golden, D. M.; Hampton, R. F.; Kurylo, M. J.; Margitan, J. J.; Molina, M. J.; Watson, R. T.

    1979-01-01

    An evaluated set of rate constants and photochemical cross sections were compiled for use in modelling stratospheric processes. The data are primarily relevant to the ozone layer, and its possible perturbation by anthropogenic activities. The evaluation is current to, approximately, January, 1979.

  20. Electrochemical and photochemical treatment of aqueous waste streams

    SciTech Connect

    Farmer, J.C.; Pekala, R.W.; Wang, F.T.; Fix, D.V.; Volpe, A.M.; Dietrich, D.D.; Siegel, W.H.; Carley, J.F.

    1996-03-01

    Carbon aerogel electrodes have been used to remove NH{sub 4}ClO{sub 4} and heavy metals from aqueous waste streams. Photochemical oixdation with H{sub 2}O{sub 2} has been used to destroy organic contamination and is proposed as a means of avoiding the fouling of carbon aerogel electrodes.

  1. Complex Equilibria Changing in Photochemical Reaction: Computerized Evaluation and Simulation.

    ERIC Educational Resources Information Center

    Horvath, Otto; Papp, Sandor

    1988-01-01

    States that if photochemical reactions can be followed spectrophotometrically, reactivities can be estimated by evaluating data from only one curve. Studies such a system using computerized evaluation and simulation. Uses chlorocuprate(II) complexes in acetonitrile solutions for the model systems. (MVL)

  2. Photochemical Copper Coating on 3D Printed Thermoplastics

    PubMed Central

    Yung, Winco K. C.; Sun, Bo; Huang, Junfeng; Jin, Yingdi; Meng, Zhengong; Choy, Hang Shan; Cai, Zhixiang; Li, Guijun; Ho, Cheuk Lam; Yang, Jinlong; Wong, Wai Yeung

    2016-01-01

    3D printing using thermoplastics has become very popular in recent years, however, it is challenging to provide a metal coating on 3D objects without using specialized and expensive tools. Herein, a novel acrylic paint containing malachite for coating on 3D printed objects is introduced, which can be transformed to copper via one-step laser treatment. The malachite containing pigment can be used as a commercial acrylic paint, which can be brushed onto 3D printed objects. The material properties and photochemical transformation processes have been comprehensively studied. The underlying physics of the photochemical synthesis of copper was characterized using density functional theory calculations. After laser treatment, the surface coating of the 3D printed objects was transformed to copper, which was experimentally characterized by XRD. 3D printed prototypes, including model of the Statue of Liberty covered with a copper surface coating and a robotic hand with copper interconnections, are demonstrated using this painting method. This composite material can provide a novel solution for coating metals on 3D printed objects. The photochemical reduction analysis indicates that the copper rust in malachite form can be remotely and photo-chemically reduced to pure copper with sufficient photon energy. PMID:27501761

  3. Photochemical Copper Coating on 3D Printed Thermoplastics

    NASA Astrophysics Data System (ADS)

    Yung, Winco K. C.; Sun, Bo; Huang, Junfeng; Jin, Yingdi; Meng, Zhengong; Choy, Hang Shan; Cai, Zhixiang; Li, Guijun; Ho, Cheuk Lam; Yang, Jinlong; Wong, Wai Yeung

    2016-08-01

    3D printing using thermoplastics has become very popular in recent years, however, it is challenging to provide a metal coating on 3D objects without using specialized and expensive tools. Herein, a novel acrylic paint containing malachite for coating on 3D printed objects is introduced, which can be transformed to copper via one-step laser treatment. The malachite containing pigment can be used as a commercial acrylic paint, which can be brushed onto 3D printed objects. The material properties and photochemical transformation processes have been comprehensively studied. The underlying physics of the photochemical synthesis of copper was characterized using density functional theory calculations. After laser treatment, the surface coating of the 3D printed objects was transformed to copper, which was experimentally characterized by XRD. 3D printed prototypes, including model of the Statue of Liberty covered with a copper surface coating and a robotic hand with copper interconnections, are demonstrated using this painting method. This composite material can provide a novel solution for coating metals on 3D printed objects. The photochemical reduction analysis indicates that the copper rust in malachite form can be remotely and photo-chemically reduced to pure copper with sufficient photon energy.

  4. AIR QUALITY CRITERIA FOR OZONE AND RELATED PHOTOCHEMICAL OXIDANTS

    EPA Science Inventory

    The Clean Air Act requires periodic (5-year) update revision of criteria and National Ambient Air Quality Standards (NAAQS) for Ozone. The previous revision of the criteria contained in the Air Quality Criteria Document (AQCD) for Ozone and Related Photochemical Oxidants was co...

  5. 40 CFR 52.269 - Control strategy and regulations: Photochemical oxidants (hydrocarbons) and carbon monoxide.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ...: Photochemical oxidants (hydrocarbons) and carbon monoxide. 52.269 Section 52.269 Protection of Environment... PLANS California § 52.269 Control strategy and regulations: Photochemical oxidants (hydrocarbons) and... provide for attainment and maintenance of the national standards for photochemical oxidants...

  6. 40 CFR 52.269 - Control strategy and regulations: Photochemical oxidants (hydrocarbons) and carbon monoxide.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...: Photochemical oxidants (hydrocarbons) and carbon monoxide. 52.269 Section 52.269 Protection of Environment... PLANS California § 52.269 Control strategy and regulations: Photochemical oxidants (hydrocarbons) and... provide for attainment and maintenance of the national standards for photochemical oxidants...

  7. 40 CFR 52.269 - Control strategy and regulations: Photochemical oxidants (hydrocarbons) and carbon monoxide.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...: Photochemical oxidants (hydrocarbons) and carbon monoxide. 52.269 Section 52.269 Protection of Environment... PLANS California § 52.269 Control strategy and regulations: Photochemical oxidants (hydrocarbons) and... provide for attainment and maintenance of the national standards for photochemical oxidants...

  8. 40 CFR 52.269 - Control strategy and regulations: Photochemical oxidants (hydrocarbons) and carbon monoxide.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...: Photochemical oxidants (hydrocarbons) and carbon monoxide. 52.269 Section 52.269 Protection of Environment... PLANS California § 52.269 Control strategy and regulations: Photochemical oxidants (hydrocarbons) and... provide for attainment and maintenance of the national standards for photochemical oxidants...

  9. 40 CFR 52.269 - Control strategy and regulations: Photochemical oxidants (hydrocarbons) and carbon monoxide.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...: Photochemical oxidants (hydrocarbons) and carbon monoxide. 52.269 Section 52.269 Protection of Environment... PLANS California § 52.269 Control strategy and regulations: Photochemical oxidants (hydrocarbons) and... provide for attainment and maintenance of the national standards for photochemical oxidants...

  10. Binding of carbon dioxide to metal macrocycles: Toward a mechanistic understanding of electrochemical and photochemical carbon dioxide reduction

    SciTech Connect

    Fujita, E.

    1993-01-01

    Efforts were made to find effective catalysts for photochemical and electrochemical reduction of CO[sub 2]. We are studying the factors controlling excited-state lifetimes, electron-transfer rates to mediators/catalysts, properties of reduced mediators, binding of small molecules to reduced mediators, and reactivity of the mediators to yield the desired products. This document describes some of the results of binding on CO[sub 2] to metal macrocycles. The electrocatalytic activity of cobalt macrocycle complexes in reduction of CO[sub 2] in CO[sub 2]-saturated water at the Hg electrode is being studied. We are ready to study the mechanism and kinetics of the photochemical CO[sub 2] reduction in order to design more efficient photo-energy conversion systems. 19 refs.

  11. Binding of carbon dioxide to metal macrocycles: Toward a mechanistic understanding of electrochemical and photochemical carbon dioxide reduction

    SciTech Connect

    Fujita, E.

    1993-07-01

    Efforts were made to find effective catalysts for photochemical and electrochemical reduction of CO{sub 2}. We are studying the factors controlling excited-state lifetimes, electron-transfer rates to mediators/catalysts, properties of reduced mediators, binding of small molecules to reduced mediators, and reactivity of the mediators to yield the desired products. This document describes some of the results of binding on CO{sub 2} to metal macrocycles. The electrocatalytic activity of cobalt macrocycle complexes in reduction of CO{sub 2} in CO{sub 2}-saturated water at the Hg electrode is being studied. We are ready to study the mechanism and kinetics of the photochemical CO{sub 2} reduction in order to design more efficient photo-energy conversion systems. 19 refs.

  12. A review of iron and cobalt porphyrins, phthalocyanines, and related complexes for electrochemical and photochemical reduction of carbon dioxide

    SciTech Connect

    Manbeck, Gerald F.; Fujita, Etsuko

    2015-03-30

    This review summarizes research on the electrochemical and photochemical reduction of CO₂ using a variety of iron and cobalt porphyrins, phthalocyanines, and related complexes. Metalloporphyrins and metallophthalocyanines are visible light absorbers with extremely large extinction coefficients. However, yields of photochemically-generated active catalysts for CO₂ reduction are typically low owing to the requirement of a second photoinduced electron. This requirement is not relevant to the case of electrochemical CO₂ reduction. Recent progress on efficient and stable electrochemical systems includes the use of FeTPP catalysts that have prepositioned phenyl OH groups in their second coordination spheres. This has led to remarkable progress in carrying out coupled proton-electron transfer reactions for CO₂ reduction. Such ground-breaking research has to be continued in order to produce renewable fuels in an economically feasible manner.

  13. A review of iron and cobalt porphyrins, phthalocyanines, and related complexes for electrochemical and photochemical reduction of carbon dioxide

    DOE PAGES

    Manbeck, Gerald F.; Fujita, Etsuko

    2015-03-30

    This review summarizes research on the electrochemical and photochemical reduction of CO₂ using a variety of iron and cobalt porphyrins, phthalocyanines, and related complexes. Metalloporphyrins and metallophthalocyanines are visible light absorbers with extremely large extinction coefficients. However, yields of photochemically-generated active catalysts for CO₂ reduction are typically low owing to the requirement of a second photoinduced electron. This requirement is not relevant to the case of electrochemical CO₂ reduction. Recent progress on efficient and stable electrochemical systems includes the use of FeTPP catalysts that have prepositioned phenyl OH groups in their second coordination spheres. This has led to remarkable progressmore » in carrying out coupled proton-electron transfer reactions for CO₂ reduction. Such ground-breaking research has to be continued in order to produce renewable fuels in an economically feasible manner.« less

  14. Effects of crystal orientation and ferroelastic domain structure on the photochemical reactivity of BiVO4 and related compounds

    NASA Astrophysics Data System (ADS)

    Munprom, Ratiporn

    Bismuth vanadate, BiVO4, has been recognized for its high efficiency as a photoanode for water splitting. However, its performance is limited by photogenerated electron--hole recombination. Thus, researchers have attempted to modify BiVO4 to improve its performance. One strategy to improve charge separation is to utilize an internal field arising from surface termination differences. Previous studies concentrated on polygonal single crystals of BiVO4, providing limited information about the orientation-reactivity relationship. The current research focuses on polycrystalline BiVO4, which makes it possible to study the photochemical reactivity of all possible orientations and determine the complete orientation dependence of the photochemical reactivity of BiVO4. (Abstract shortened by UMI.).

  15. Increased biomass productivity in green algae by tuning non-photochemical quenching.

    PubMed

    Berteotti, Silvia; Ballottari, Matteo; Bassi, Roberto

    2016-02-18

    Photosynthetic microalgae have a high potential for the production of biofuels and highly valued metabolites. However, their current industrial exploitation is limited by a productivity in photobioreactors that is low compared to potential productivity. The high cell density and pigment content of the surface layers of photosynthetic microalgae result in absorption of excess photons and energy dissipation through non-photochemical quenching (NPQ). NPQ prevents photoinhibition, but its activation reduces the efficiency of photosynthetic energy conversion. In Chlamydomonas reinhardtii, NPQ is catalyzed by protein subunits encoded by three lhcsr (light harvesting complex stress related) genes. Here, we show that heat dissipation and biomass productivity depends on LHCSR protein accumulation. Indeed, algal strains lacking two lhcsr genes can grow in a wide range of light growth conditions without suffering from photoinhibition and are more productive than wild-type. Thus, the down-regulation of NPQ appears to be a suitable strategy for improving light use efficiency for biomass and biofuel production in microalgae.

  16. Aquatic photochemical kinetics of benzotriazole and structurally related compounds.

    PubMed

    Janssen, Elisabeth M L; Marron, Emily; McNeill, Kristopher

    2015-05-01

    Benzotriazole corrosion inhibitors are not completely removed during wastewater treatment and are frequently detected in surface waters. Here, the photochemical kinetics of benzotriazoles and structurally related compounds were assessed for natural aqueous environments. The direct photochemical half-lives during exposure to simulated sunlight ranged from 1.3 to 1.8 days for benzotriazole and its derivatives (4-methyl-, 5-methyl-, 4-hydroxy-substituted benzotriazoles). Benzotriazole is more resistant to direct photodegradation than indazole (0.28 days) and indole (0.09 days), while benzimidazole showed no significant decay. Hydroxyl radicals (1.6 × 10(-16) M) and singlet oxygen (2.5 × 10(-13) M) are formed during simulated sunlight exposure in the presence of dissolved organic matter (13 mgC L(-1)). All tested compounds reacted rapidly with hydroxyl radicals near the diffusion-controlled limit (8.3 to 12 × 10(9) M(-1) s(-1)). Only 4-hydroxybenzotriazole and indole showed significant reactivity towards singlet oxygen and their photochemical half-lives in the presence of organic matter were shorter (0.1 days for both) than for benzotriazole and its methylated derivatives (1.4-1.5 days). The photochemical half-lives determined here are relatively long and support the persistence of benzotriazoles in the environment. At the same time, these results suggest that photochemical transformation can be supplementary to microbial degradation. While the presented study focused on environmental photodegradation kinetics, the relevance of transformation products remains to be investigated.

  17. Photochemical degradation of a brominated flame retardant (tetrabromobisphenol A) in ice under field and laboratory conditions

    NASA Astrophysics Data System (ADS)

    Waligroski, G.; Grannas, A. M.

    2013-12-01

    Studies of brominated flame retardants have raised awareness of their potential environmental impact as toxic compounds. Because these compounds are now globally distributed, including in the Polar Regions, it is important to assess their potential fate in the environment. It has been shown that active photochemistry occurs in sunlit snow and ice, but there is little information regarding potential photochemical degradation of brominated flame retardants in snow and ice. The purpose of this research is to investigate the direct and indirect photochemical transformation pathways of a widely used brominated flame retardant, tetrabromobisphenol A (TBBPA). We have conducted field-based experiments in Barrow, Alaska to investigate the potential photochemical degradation of TBBPA in snow and ice under environmentally-relevant conditions. Field-based results show that TBBPA is efficiently degraded under direct photolysis conditions in frozen aqueous samples under natural Barrow sunlight. In aqueous solution the light absorption properties of TBBPA are pH dependent. Therefore, the photodegradation of TBBPA in snow and ice will be highly pH dependent. Reactions that are pH dependent may be affected by the nature of the liquid-like layers in snow/ice as well as the presence of other solutes that may indirectly affect the local pH experienced by TBBPA in snow and ice samples. In order to establish how the effective pH of liquid-like regions in ice might impact the degradation of TBBPA, various salts (sodium chloride, sodium fluoride, sodium bromide, ammonium chloride, ammonium acetate and ammonium sulfate) were added to aqueous solutions of TBBPA. Upon freezing, these different salts will induce pH differences in the liquid-like regions of the sample due to a phenomenon known as the freezing potential. Observed reactivity differences upon addition of these salts will be evaluated and discussed. Additionally, the presence of natural dissolved organic matter (DOM), an effective

  18. Mars atmospheric loss and isotopic fractionation by solar-wind-induced sputtering and photochemical escape

    NASA Technical Reports Server (NTRS)

    Jakosky, Bruce M.; Pepin, Robert O.; Johnson, Robert E.; Fox, J. L.

    1994-01-01

    We examine the effects of the loss of Mars atmospheric constituents by solar-wind-induced sputtering and by photochemical escape during the past 3.8 billion years. Sputtering is capable of efficiently removing species from the upper atmosphere, including the light noble gases; nitrogen and oxygen are removed by photochemical processes as well. Due to diffusive separation (by mass) above the homopause, removal from the top of the atmosphere will fractionate the isotopes of each species, with the lighter mass being preferentially lost. For carbon and oxygen, this allows us to determine the size of nonatmospheric reservoirs which mix with the atmosphere; these reservoirs can be CO2 adsorbed in the regolith and H2O in the polar ice caps. We have constructed both simple analytical models and time-dependent models of the loss of volatiles from and supply to the martian atmosphere. Both argon and neon require continued replenishment from outgassing over geologic time. For argon, sputtering loss explains the fractionation of (Ar-36)/(Ar-38) without requiring a distinct epoch of hydrodynamic escape (although fractionation of Xe isotopes still requires very early hydrodynamic loss). For neon, the current (Ne-22)/(Ne-20) ratio represents a balance between loss to space and continued resupply from the interior; the similarity of the ratio to the terrestrial value is coincidental. For nitrogen, the loss by both sputtering and photochemical escape would produce a fractionation of (N-15)/(N-14) larger than observed; an early, thicker carbon dioxide atmosphere could mitigate the nitrogen loss and produce the observed fractionation, as could continued outgassing of juvenile nitorgen. Based on the isotopic constraints, the total amount of carbon dioxide lost over geologic time is probably on the order of tens of millibars rather than a substantial fraction of a bar. The total loss from solar-wind-induced sputtering and photochemical escape, therefore, does not seem able to explain

  19. Fuel from water: the photochemical generation of hydrogen from water.

    PubMed

    Han, Zhiji; Eisenberg, Richard

    2014-08-19

    Hydrogen has been labeled the fuel of the future since it contains no carbon, has the highest specific enthalpy of combustion of any chemical fuel, yields only water upon complete oxidation, and is not limited by Carnot considerations in the amount of work obtained when used in a fuel cell. To be used on the scale needed for sustainable growth on a global scale, hydrogen must be produced by the light-driven splitting of water into its elements, as opposed to reforming of methane, as is currently done. The photochemical generation of H2, which is the reductive side of the water splitting reaction, is the focus of this Account, particularly with regard to work done in the senior author's laboratory over the last 5 years. Despite seminal work done more than 30 years ago and the extensive research conducted since then on all aspects of the process, no viable system has been developed for the efficient and robust photogeneration of H2 from water using only earth abundant elements. For the photogeneration of H2 from water, a system must contain a light absorber, a catalyst, and a source of electrons. In this Account, the discovery and study of new Co and Ni catalysts are described that suggest H2 forms via a heterocoupling mechanism from a metal-hydride and a ligand-bound proton. Several complexes with redox active dithiolene ligands are newly recognized to be effective in promoting the reaction. A major new development in the work described is the use of water-soluble CdSe quantum dots (QDs) as light absorbers for H2 generation in water. Both activity and robustness of the most successful systems are impressive with turnover numbers (TONs) approaching 10(6), activity maintained over 15 days, and a quantum yield for H2 of 36% with 520 nm light. The water solubilizing capping agent for the first system examined was dihydrolipoic acid (DHLA) anion, and the catalyst was determined to be a DHLA complex of Ni(II) formed in situ. Dissociation of DHLA from the QD surface proved

  20. A metal-organic cage incorporating multiple light harvesting and catalytic centres for photochemical hydrogen production

    PubMed Central

    Chen, Sha; Li, Kang; Zhao, Fang; Zhang, Lei; Pan, Mei; Fan, Yan-Zhong; Guo, Jing; Shi, Jianying; Su, Cheng-Yong

    2016-01-01

    Photocatalytic water splitting is a natural but challenging chemical way of harnessing renewable solar power to generate clean hydrogen energy. Here we report a potential hydrogen-evolving photochemical molecular device based on a self-assembled ruthenium–palladium heterometallic coordination cage, incorporating multiple photo- and catalytic metal centres. The photophysical properties are investigated by absorption/emission spectroscopy, electrochemical measurements and preliminary DFT calculations and the stepwise electron transfer processes from ruthenium-photocentres to catalytic palladium-centres is probed by ultrafast transient absorption spectroscopy. The photocatalytic hydrogen production assessments reveal an initial reaction rate of 380 μmol h−1 and a turnover number of 635 after 48 h. The efficient hydrogen production may derive from the directional electron transfers through multiple channels owing to proper organization of the photo- and catalytic multi-units within the octahedral cage, which may open a new door to design photochemical molecular devices with well-organized metallosupramolecules for homogenous photocatalytic applications. PMID:27827376

  1. A metal-organic cage incorporating multiple light harvesting and catalytic centres for photochemical hydrogen production

    NASA Astrophysics Data System (ADS)

    Chen, Sha; Li, Kang; Zhao, Fang; Zhang, Lei; Pan, Mei; Fan, Yan-Zhong; Guo, Jing; Shi, Jianying; Su, Cheng-Yong

    2016-11-01

    Photocatalytic water splitting is a natural but challenging chemical way of harnessing renewable solar power to generate clean hydrogen energy. Here we report a potential hydrogen-evolving photochemical molecular device based on a self-assembled ruthenium-palladium heterometallic coordination cage, incorporating multiple photo- and catalytic metal centres. The photophysical properties are investigated by absorption/emission spectroscopy, electrochemical measurements and preliminary DFT calculations and the stepwise electron transfer processes from ruthenium-photocentres to catalytic palladium-centres is probed by ultrafast transient absorption spectroscopy. The photocatalytic hydrogen production assessments reveal an initial reaction rate of 380 μmol h-1 and a turnover number of 635 after 48 h. The efficient hydrogen production may derive from the directional electron transfers through multiple channels owing to proper organization of the photo- and catalytic multi-units within the octahedral cage, which may open a new door to design photochemical molecular devices with well-organized metallosupramolecules for homogenous photocatalytic applications.

  2. Solar Photochemical Synthesis: From the Beginnings of Organic Photochemistry to the Solar Manufacturing of Commodity Chemicals.

    PubMed

    Oelgemöller, Michael

    2016-09-14

    Natural sunlight offers a cost-efficient and sustainable energy source for photochemical reactions. In contrast to the lengthy and small-scale "flask in the sun" procedures of the past, modern solar concentrator systems nowadays significantly shorten reaction times and enable technical-scale operations. After a brief historical introduction, this review presents the most important solar reactor types and their successful application in preparative solar syntheses. The examples demonstrate that solar manufacturing of fine chemicals is technically feasible and environmentally sustainable. After over 100 years, Ciamician's prophetic vision of "the photochemistry of the future" as a clean and green manufacturing methodology has yet to be realized. At the same time, his warning "for nature is not in a hurry but mankind is" is still valid today. It is hoped that this review will lead to a renewed interest in this truly enlightening technology, that it will stimulate photochemists and photochemical engineers to "go back to the roots onto the roofs" and that it will ultimately result in industrial applications in the foreseeable future.

  3. Mars atmospheric loss and isotopic fractionation by pick-up-ion sputtering and photochemical escape

    NASA Technical Reports Server (NTRS)

    Jakosky, B. M.; Pepin, R. O.; Johnson, R. E.; Fox, J. L.

    1994-01-01

    We examine the effects of loss of constituents of the Martian atmosphere due to sputtering by solar-wind pick-up ions and photochemical escape during the last 3.8 billion years. Sputtering is capable of efficiently removing species from the upper atmosphere to space, including the light noble gases; nitrogen and oxygen are removed by both sputtering ad photochemical processes. Due to diffusive separation (by mass) above the homopause, removal from the top of the atmosphere will fractionate the isotopes of each species, with the lighter isotope being preferentially lost. This allows current measurements of the isotopic ratios to be used as a measure of the atmospheric evolution as integrated over geologic time. For carbon and oxygen, isotopic fractionation is buffered by exchange of atmospheric species with non-atmospheric reservoirs of CO2 and H2O. This allows us to determine the size of the non-atmospheric reservoirs which are capable of mixing with the atmosphere; these reservoirs can be CO2 absorbed in the regolith and/or H2O in the polar ice caps. Such an exchangeable reservoir is required in order to keep the fractionation of the atmospheric gases as low as is observed.

  4. Photochemical electron transfer reactions of tirapazamine.

    PubMed

    Poole, James S; Hadad, Christopher M; Platz, Matthew S; Fredin, Zachary P; Pickard, Laura; Guerrero, Elisa Levya; Kessler, Margarita; Chowdhury, Goutam; Kotandeniya, Delshanee; Gates, Kent S

    2002-04-01

    The absorption and fluorescence spectra of 3-aminobenzo-1,2,4-triazine di-N-oxide (tirapazamine) have been recorded and exhibit a dependence on solvent that correlates with the Dimroth ET30 parameter. Time-dependent density functional theory calculations reveal that the transition of tirapazamine in the visible region is pi-->pi* in nature. The fluorescence lifetime is 98+/-2 ps in water. The fluorescence quantum yield is approximately 0.002 in water. The fluorescence of tirapazamine is efficiently quenched by electron donors via an electron-transfer process. Linear Stern-Volmer fluorescence quenching plots are observed with sodium azide, potassium thiocyanate, guanosine monophosphate and tryptophan (Trp) methyl ester hydrochloride. Guanosine monophosphate, tyrosine (Tyr) methyl ester hydrochloride and Trp methyl ester hydrochloride appear to quench the fluorescence at a rate greater than diffusion control implying that these substrates complex with tirapazamine in its ground state. This complexation was detected by absorption spectroscopy.

  5. Composition/bandgap selective dry photochemical etching of semiconductor materials

    DOEpatents

    Ashby, C.I.H.; Dishman, J.L.

    1985-10-11

    Disclosed is a method of selectively photochemically dry etching a first semiconductor material of a given composition and direct bandgap Eg/sub 1/ in the presence of a second semiconductor material of a different composition and direct bandgap Eg/sub 2/, wherein Eg/sub 2/ > Eg/sub 1/, said second semiconductor material substantially not being etched during said method. The method comprises subjecting both materials to the same photon flux and to the same gaseous etchant under conditions where said etchant would be ineffective for chemical etching of either material were the photons not present, said photons being of an energy greater than Eg/sub 1/ but less than Eg/sub 2/, whereby said first semiconductor material is photochemically etched and said second material is substantially not etched.

  6. Composition/bandgap selective dry photochemical etching of semiconductor materials

    DOEpatents

    Ashby, Carol I. H.; Dishman, James L.

    1987-01-01

    A method of selectively photochemically dry etching a first semiconductor material of a given composition and direct bandgap Eg.sub.1 in the presence of a second semiconductor material of a different composition and direct bandgap Eg.sub.2, wherein Eg.sub.2 >Eg.sub.1, said second semiconductor material substantially not being etched during said method, comprises subjecting both materials to the same photon flux and to the same gaseous etchant under conditions where said etchant would be ineffective for chemical etching of either material were the photons not present, said photons being of an energy greater than Eg.sub.1 but less than Eg.sub.2, whereby said first semiconductor material is photochemically etched and said second material is substantially not etched.

  7. Photochemical mechanisms of light-triggered release from nanocarriers

    PubMed Central

    Fomina, Nadezda; Sankaranarayanan, Jagadis; Almutairi, Adah

    2012-01-01

    Over the last three decades, a handful of photochemical mechanisms have been applied to a large number of nanoscale assemblies that encapsulate a payload to afford spatio-temporal and remote control over activity of the encapsulated payload. Many of these systems are designed with an eye towards biomedical applications, as spatio-temporal and remote control of bioactivity would advance research and clinical practice. This review covers five underlying photochemical mechanisms that govern the activity of the majority of photoresponsive nanocarriers: 1. photo driven isomerization and oxidation, 2. surface plasmon absorption and photothermal effects, 3. photo driven hydrophobicity changes, 4. photo driven polymer backbone fragmentation and 5. photo driven de-crosslinking. The ways in which these mechanisms have been incorporated into nanocarriers and how they affect release is detailed, as well as the advantages and disadvantages of each system. PMID:22386560

  8. Unravelling Photochemical Relationships Among Natural Products from Aplysia dactylomela

    PubMed Central

    2016-01-01

    Aplydactone (1) is a brominated ladderane sesquiterpenoid that was isolated from the sea hare Aplysia dactylomela together with the chamigranes dactylone (2) and 10-epi-dactylone (3). Given the habitat of A. dactylomela, it seems likely that 1 is formed from 2 through a photochemical [2 + 2] cycloaddition. Here, we disclose a concise synthesis of 1, 2, and 3 that was guided by excited state theory and relied on several highly stereoselective transformations. Our experiments and calculations confirm the photochemical origin of 1 and explain why it is formed as the sole isomer. Irradiation of 3 with long wavelength UV light resulted in a [2 + 2] cycloaddition that proceeded with opposite regioselectivity. On the basis of this finding, it seems likely that the resulting regioisomer, termed “8-epi-isoaplydactone”, could also be found in A. dactylomela. PMID:28149951

  9. Intrinsic response of polymer liquid crystals in photochemical phase transition

    SciTech Connect

    Ikeda, Tomiki; Sasaki, Takeo; Kim, Haengboo )

    1991-01-24

    Time-resolved measurements were performed on the photochemically induced isothermal phase transition of polymer liquid crystals (PLC) with mesogenic side chains of phenyl benzoate (PAPB3) and cyanobiphenyl (PACB3) under conditions wherein the photochemical reaction of the doped photoresponsive molecule (4-butyl-4-{prime}-methoxyazobenzene, BMAB) was completed within {approximately} 10 ns, and the subsequent phase transition of the matrix PLC from nematic (N) to isotropic (I) state was followed by time-resolved measurements of the birefringence of the system. Formation of a sufficient amount of the cis isomer of BMAB with a single pulse of a laser lowered the N-I phase transition temperature of the mixture, inducing the N-I phase transition of PLCs isothermally in a time range of {approximately} 200 ms. This time range is comparable to that of low molecular weight liquid crystals, indicating that suppression in mobility of mesogens in PLCs does not affect significantly the thermodynamically controlled process.

  10. Thermal and photochemical crosslinking of hyperbranched polyphenylene with organic azides.

    PubMed

    Pötzsch, Robert; Voit, Brigitte

    2012-04-23

    Here, we report on the first example of crosslinking (CL) hyperbranched polyphenylene (hb-PPh) with a small molecule crosslinker 1,3,5-tris(azidomethyl)benzene (TAMB). It was successfully shown that CL of the hb-PPh/TAMB (9:1) film is possible either thermally or photochemically making use of fundamentally different reaction mechanisms. Starting from a model reaction to prove the feasibility of the thermal CL reaction, we went on to check both the thermal and the photochemical crosslinkability of micrometer thick films. IR spectroscopy was furthermore used to confirm the CL process. Finally, the thin film morphology of the films before and after CL was investigated by AFM, revealing that the surface morphology was unaffected by the CL processes.

  11. Air Quality Criteria for Ozone and Related Photochemical ...

    EPA Pesticide Factsheets

    In February 2006, EPA released the final document, Air Quality Criteria for Ozone and Other Photochemical Oxidants. Tropospheric or surface-level ozone (O3) is one of six major air pollutants regulated by National Ambient Air Quality Standards (NAAQS) under the U.S. Clean Air Act. As mandated by the Clean Air Act, the U.S. Environmental Protection Agency (EPA) must periodically review the scientific bases (or criteria) for the various NAAQS by assessing newly available scientific information on a given criteria air pollutant. This document, Air Quality Criteria for Ozone and Other Photochemical Oxidants, is an updated revision of the 1996 Ozone Air Quality Criteria Document (O3 AQCD) that provided scientific bases for the current O3 NAAQS set in 1997. The Clean Air Act mandates periodic review of the National Ambient Air Quality Standards (NAAQS) for six common air pollutants, also referred to as criteria pollutants, including ozone.

  12. Contributions of biogenic and anthropogenic hydrocarbons to photochemical smog formation

    SciTech Connect

    Paulson, S.E.

    1991-01-01

    Photochemical oxidation of biogenic (Isoprene) and anthropogenic (1-octene) hydrocarbons are examined. Experiments studied the individual daylight reactions of both isoprene and 1-octene, including those of OH, O{sub 3}, O({sup 3}P), and NO{sub 2}. The O{sub 3} reactions are found to produce significant quantities of OH, O({sup 3}P), and carbonyl yields that total about 100%. Isomerization is found to be an important channel for both isoprene and 1-octene. O({sup 3}P) reactions are found to have relatively minor decomposition pathways, resulting instead in epoxide formation. Results from both the smog chamber experiments and computer kinetic modeling were then used to develop photochemical oxidation mechanisms for each hydrocarbon. Aerosol formed by isoprene and another biogenic, {beta}-pinene, are characterized.

  13. Venus ionosphere: photochemical and thermal diffusion control of ion composition.

    PubMed

    Bauer, S J; Donahue, T M; Hartle, R E; Taylor, H A

    1979-07-06

    The major photochemical sources and sinks for ten of the ions measured by the ion mass spectrometer on the Pioneer Venus bus and orbiter spacecraft that are consistent with the neutral gas composition measured on the same spacecraft have been identified. The neutral gas temperature (Tn) as a function of solar zenith angle (chi) derived from measured ion distributions in photochemical equilibrium is given by Tn (K) = 323 cos(1/5)chi. Above 200 kilometers, the altitude behavior of ions is generally controlled by plasma diffusion, with important modifications for minor ions due to thermal diffusion resulting from the observed gradients of plasma temperatures. The dayside equilibrium distributions of ions are sometimes perturbed by plasma convection, while lateral transport of ions from the dayside seems to be a major source of the nightside ionosphere.

  14. Enhanced transfection of brain tumor suppressor genes by photochemical internalization

    NASA Astrophysics Data System (ADS)

    Chou, Chih H.; Sun, Chung-Ho; Zhou, Yi-Hong; Madsen, Steen J.; Hirschberg, Henry

    2011-03-01

    One of many limitations for cancer gene therapy is the inability of the therapeutic gene to transfect a sufficient number of tumor cells. Photochemical internalization (PCI) is a photodynamic therapy-based approach for improving the delivery of macromolecules and genes into the cell cytosol. The utility of PCI for the delivery of a tumor suppressor gene (PAX-6) was investigated in monolayers and spheroids consisting of F98 rat glioma cells.

  15. Explicit photochemical mechanism for atmospheric oxidation of n-butane

    SciTech Connect

    Wen, L.

    1992-01-01

    Alkanes, being an important component of atmosphere, serve as precursors to ozone formation in urban and rural air masses. An explicit photochemical oxidation mechanism for n-butane, which is the major hydrocarbon component of automobile exhaust, is created in this work. The yields of organic nitrates from n-butane, n-pentane, and methyl ethyl ketone photooxidations were studied in Teflon bag and smog chamber experiments. Comparing with the expression currently using the most atmospheric model studies, the total butyl nitrates yield obtained in this work is about 36% lower, and the ratio of primary to secondary butyl nitrates is slightly higher. It is shown in this work that the yields of hydroxyl and carbonyl butyl nitrates are very low, and can be ignored in the explicit photochemical mechanisms. The explicit photochemical oxidation mechanism for methyl ethyl ketone (MEK) was created first because it is the major product from photooxidation of n-butane. The explicit photochemical oxidation mechanism for n-butane, created later, draws on the MEK mechanism. The mechanisms were tested by comparing model predictions with experimental observations from smog chamber experiments. The comparisons were conducted for species which had experimental observation data, such as O[sub 3], NO, and NO[sub 2], n-butane, MEK, organic nitrates, and aldehydes species. The sixteen smog chamber experiments, used in model simulations, were conducted during 1978 to 1992. The mechanisms are mainly based on the available kinetic data in literature and the experimental result in this work. The rate constants for some reactions in the mechanisms were adjusted to make a better fit with the experimental observations. These reactions were: reaction of OH and n-butane to form secondary butyl peroxy radical, decomposition of secondary butoxy radical, and reaction of OH and MEK.

  16. Photochemical manipulation of colloidal structures in liquid-crystal colloids

    NASA Astrophysics Data System (ADS)

    Yamamoto, T.; Tabe, Y.; Yokoyama, H.

    2007-05-01

    We investigated photochemical manipulation of physical properties and colloidal structures in liquid-crystal (LC) colloids containing azobenzene compounds. In a LC suspension where polymeric particles were dispersed in a host LC, we achieved photochemical control of light-scattering properties of the suspension. In a nematic phase, when the suspension was sandwiched with two glass plates, the film became opaque. This would be attributable to an appearance of both multidomain structures of LC alignment and mismatches of refractive indices between the materials. The opaque state turned into a transparent one when a nematic-to-isotropic phase transition was induced by the trans-to-cis photoisomerization of the azo-dye. This will result from a disappearance of both the multidomain structures and the refractive-index mismatches in the isotropic phase. The transparent film went back into the initial opaque film when the nematic phase was obtained by the cis-to-trans photoisomerization. In a LC emulsion in which glycerol or water droplets were dispersed in liquid crystals, we examined photochemical change of defect structures and inter-droplet distances by the photochemical manner. At the initial state, Saturn ring and hedgehog defects were formed around the droplets. For the glycerol droplets, we observed structural transformations between Saturn ring and boojums on irradiation with ultra-violet and visible light. For the water droplets, the inter-droplet distances varied by changing defect size on the irradiation. These phenomena would result from modulation of anchoring conditions of the droplets by the photoisomerization of the azo-dyes.

  17. Molecular-beam Studies of Primary Photochemical Processes

    DOE R&D Accomplishments Database

    Lee, Y. T.

    1982-12-01

    Application of the method of molecular-beam photofragmentation translational spectroscopy to the investigation of primary photochemical processes of polyatomic molecules is described. Examples will be given to illustrate how information concerning the energetics, dynamics, and mechanism of dissociation processes can be obtained from the precise measurements of angular and velocity distributions of products in an experiment in which a well-defined beam of molecules is crossed with a laser.

  18. Apertureless cantilever-free pen arrays for scanning photochemical printing.

    PubMed

    Zhou, Yu; Xie, Zhuang; Brown, Keith A; Park, Daniel J; Zhou, Xiaozhu; Chen, Peng-Cheng; Hirtz, Michael; Lin, Qing-Yuan; Dravid, Vinayak P; Schatz, George C; Zheng, Zijian; Mirkin, Chad A

    2015-02-25

    A novel, apertureless, cantilever-free pen array can be used for dual scanning photochemical and molecular printing. Serial writing with light is enabled by combining self-focusing pyramidal pens with an opaque backing between pens. The elastomeric pens also afford force-tuned illumination and simultaneous delivery of materials and optical energy. These attributes make the technique a promising candidate for maskless high-resolution photopatterning and combinatorial chemistry.

  19. Improving Joint Function Using Photochemical Hydrogels for Articular Surface Repair

    DTIC Science & Technology

    2012-10-01

    to collagenase digestion over uncrosslinked gels, but had little effect on changing the bulk modulus (stiffness) of the gels. Adding a secondary...step had a negative effect on cartilage formation by encapsulated cells. Testing in year one of the PEG thiol ene gels showed changes in the shear...Noncrosslinked fibrin (without cells) has a high bulk modulus (>2100 Pa) and photochemical crosslinking has little additional effect on the modulus. On the

  20. The photochemical properties of fluoroaluminum phthalocyanine.

    PubMed

    Rosenthal, I; Shafirovich, V Y; Geacintov, N E; Ben-Hur, E; Horowitz, B

    1994-09-01

    Fluoride is known to inhibit the photodynamic activity of aluminium phthalocyanine in a variety of biological systems. In order to gain insight into this phenomenon, the effect of fluoride on the photophysical properties of free and albumin-bound chloroaluminum phthalocyanine sulfonate (AlPcSn) were studied. The association constant of NaF with AlPcSn in aqueous solution was measured as 500 +/- 20 M-1. This binding affects the photophysical properties of the dye: the absorption bands in the visible range are blue-shifted by 6-8 nm, and this effect is mirrored in the fluorescence emission spectrum. Human serum albumin significantly quenched the dye fluorescence independent of the presence of fluoride ion. The transient absorption spectrum of the excited dye triplet is unchanged by NaF, but the quantum yield for its generation is increased by 50%, with no decrease in its lifetime. Formation of fluoroaluminum phthalocyanine complexes was also observed in tetrabutylammonium fluoride-assisted solutions in wet acetonitrile. The fluoro-AlPcSn complex is a better photosensitizer for generation of singlet oxygen than the original dye-hydroxyl ion complex, as confirmed using the imidazole-N,N-dimethyl-4-nitrosoaniline method. On the other hand, the fluoro-AlPcSn complex exhibits an intense inhibitory effect on photohemolysis of red blood cells (RBC) even after the cells are washed to remove free dye and fluoride prior to irradiation, indicating that once the dye is attached to the cellular site, the fluoride ligand is no longer prone to displacement (by hydroxyl ion, for example). Nonetheless, it is clear from the spectroscopic data that the new fluoro complex is an efficient sensitizer for photooxidation.(ABSTRACT TRUNCATED AT 250 WORDS)

  1. The photochemical stability of carbonates on Mars.

    PubMed

    Quinn, Richard; Zent, Aaron P; McKay, Christopher P

    2006-08-01

    Carbonates, predominately MgCO3, have been spectroscopically identified at a level of 2-5% in martian dust. However, in spite of this observation, and a large number of climate studies that suggest 1 to several bars of CO2 should be sequestered in carbonate rocks, no outcrop-scale exposures of carbonate have been detected anywhere on Mars to date. To address one hypothesis for this long-standing puzzle, the effect of ultraviolet (UV) light on the stability of calcium carbonate in a simulated martian atmosphere was experimentally investigated. Using 13C-labeled calcite, we found no experimental evidence of the UV photodecomposition of calcium carbonate in a simulated martian atmosphere. Extrapolating the lower limit of detection of our experimental system to an upper limit of carbonate decomposition on Mars yields a quantum efficiency of 3.5 x 10(-8) molecules/photon over the wavelength interval of 190-390 nm and a maximum UV photodecomposition rate of 1.2 x 10(-13) kg m(-2) s(-1) from a calcite surface. The maximum loss of bulk calcite due to this process would be 2.5 nm year(-1) (Mars year). However, calcite is expected to be thermodynamically stable on the surface of Mars, and potential UV photodecomposition reaction mechanisms indicate that, though calcium carbonate may decompose under vacuum, it would be stable in a CO2 atmosphere. Given the expected stability of carbonate on Mars and our inability to detect carbonate decomposition, we conclude that it is unlikely that the apparent absence of extensive carbonate deposits on the martian surface is due to UV photodecomposition in the current environment.

  2. Development of a photochemical source for the production and calibration of acyl peroxynitrate compounds

    NASA Astrophysics Data System (ADS)

    Veres, P. R.; Roberts, J. M.

    2015-02-01

    A dynamic system for the calibration of acyl peroxynitrate compounds (APNs) has been developed in the laboratory to reduce the difficulty, required time, and stability of laboratory produced standards for difficult to synthesize APN species. In this work we present a photochemical source for the generation of APN standards: acetyl peroxynitrate (PAN), propionyl peroxynitrate (PPN), acryloyl peroxynitrate (APAN), methacryloyl peroxynitrate (MPAN) and crotonyl peroxynitrate (CPAN). APNs are generated via photolysis of a mixture of acyl chloride (RC(O)Cl) and ketone (RC(=O)R) precursor compounds in the presence of O2 and NO2. Subsequent separation by a prep-scale gas chromatograph and detection with a total NOy instrument serves to quantify the output of the APN source. Validation of the APN products was performed using iodide ion chemical ionization mass spectroscopy (I- CIMS). This method of standard production is an efficient and accurate technique for the calibration of instrumentation used to measure PAN, PPN, APAN, MPAN, and CPAN.

  3. Photochemically induced gene silencing using small interfering RNA molecules in combination with lipid carriers.

    PubMed

    Bøe, S; Longva, A S; Hovig, E

    2007-01-01

    Novel strategies for efficient delivery of small interfering RNA (siRNA) molecules with a potential for targeting are required for development of RNA interference (RNAi) therapeutics. Here, we present a strategy that is based on delivery of siRNA molecules through the endocytic pathway, in order to develop a method for site-specific gene silencing. To achieve this, we combined the use of cationic lipids and photochemical internalization (PCI). Using the human S100A4 gene as a model system, we obtained potent gene silencing in four tested human cancer cell lines following PCI induction when using the cationic lipid jetSI-ENDO. Gene silencing was shown at both the RNA and protein levels, with no observed PCI toxicity when using the jetSI reagent and an optimized PCI protocol. This novel induction method opens for in vivo site-specific delivery of siRNA molecules toward a sequence of interest.

  4. Ultrasound and photochemical procedures for nanocatalysts preparation: application in photocatalytic biomass valorization.

    PubMed

    Colmenares, Juan Carlos

    2013-07-01

    Nano-photocatalysis is becoming increasingly important due to its multiple applications and multidisciplinary aspects. Applications such as water/air purification, solar energy storage, chemicals production and optoelectronics are some of the most promising. In recent years, the development of novel environmental friendly and cost efficient methods for materials preparation that could replace the old ones is on demand. Unconventional and "soft" techniques such as sonication and photochemistry offer huge possibilities for the synthesis of a broad spectrum of nanostructured materials (e.g., nano-photocatalysts). In the present study, I focus on ultrasound and photochemical procedures for the preparation of nanostructured photocatalysts (e.g., supported metals, metal oxides) and their application in food organic wastes valorization.

  5. Photochemical/Microchannel Plasma Reactors Driven By High Power Vacuum Ultraviolet Lamps

    NASA Astrophysics Data System (ADS)

    Shin, Chul; Park, Sung-Jin; Eden, Gary

    2016-09-01

    Experiments are being conducted in which molecular dissociation or other chemical reactions in microchannel plasmas are accelerated by the introduction of vacuum ultraviolet photons. Initial emphasis is being placed on recently-developed Xe2 lamps that are efficient sources of 172 nm (h ν 7.2 eV) photons. Thin, flat lamps, fabricated from fused silica and having microcavity arrays internal to the lamp, have been developed by the University of Illinois and Eden Park Illumination and produce intensities above 200 mW/cm2. Integrating such lamps into a microcavity plasma reactor yields a hybrid photochemical/plasma system in which product yield and power consumption can be optimized. The selectivity of photodissociation in generating radicals and atomic fragments offers new synergies in plasma processing. Data concerning CO2 dissociation in arrays of microchannel plasmas, and the modification of this process by external 172 nm radiation, will be presented.

  6. Dosimetry Determines the Initial OH Radical Concentration in Fast Photochemical Oxidation of Proteins (FPOP)

    NASA Astrophysics Data System (ADS)

    Niu, Ben; Zhang, Hao; Giblin, Daryl; Rempel, Don L.; Gross, Michael L.

    2015-05-01

    Fast photochemical oxidation of proteins (FPOP) employs laser photolysis of hydrogen peroxide to give OH radicals that label amino acid side-chains of proteins on the microsecond time scale. A method for quantitation of hydroxyl radicals after laser photolysis is of importance to FPOP because it establishes a means to adjust the yield of •OH, offers the opportunity of tunable modifications, and provides a basis for kinetic measurements. The initial concentration of OH radicals has yet to be measured experimentally. We report here an approach using isotope dilution gas chromatography/mass spectrometry (GC/MS) to determine quantitatively the initial •OH concentration (we found ~0.95 mM from 15 mM H2O2) from laser photolysis and to investigate the quenching efficiencies for various •OH scavengers.

  7. Enhancing the efficacy of cytotoxic agents for cancer therapy using photochemical internalisation.

    PubMed

    Martinez de Pinillos Bayona, Alejandra; Moore, Caroline M; Loizidou, Marilena; MacRobert, Alexander J; Woodhams, Josephine H

    2016-03-01

    Photochemical internalisation (PCI) is a technique for improving cellular delivery of certain bioactive agents which are prone to sequestration within endolysosomes. There is a wide range of agents suitable for PCI-based delivery including toxins, oligonucleotides, genes and immunoconjugates which demonstrates the versatility of this technique. The basic mechanism of PCI involves triggering release of the agent from endolysosomes within the target cells using a photosensitiser which is selectively retained with the endolysosomal membranes. Excitation of the photosensitiser by visible light leads to disruption of the membranes via photooxidative damage thereby releasing the agent into the cytosol. This treatment enables the drugs to reach their intended subcellular target more efficiently and improves their efficacy. In this review we summarise the applications of this technique with the main emphasis placed on cancer chemotherapy.

  8. Mechanistic insights into chemical and photochemical transformations of bismuth vanadate photoanodes

    NASA Astrophysics Data System (ADS)

    Toma, Francesca M.; Cooper, Jason K.; Kunzelmann, Viktoria; McDowell, Matthew T.; Yu, Jie; Larson, David M.; Borys, Nicholas J.; Abelyan, Christine; Beeman, Jeffrey W.; Yu, Kin Man; Yang, Jinhui; Chen, Le; Shaner, Matthew R.; Spurgeon, Joshua; Houle, Frances A.; Persson, Kristin A.; Sharp, Ian D.

    2016-07-01

    Artificial photosynthesis relies on the availability of semiconductors that are chemically stable and can efficiently capture solar energy. Although metal oxide semiconductors have been investigated for their promise to resist oxidative attack, materials in this class can suffer from chemical and photochemical instability. Here we present a methodology for evaluating corrosion mechanisms and apply it to bismuth vanadate, a state-of-the-art photoanode. Analysis of changing morphology and composition under solar water splitting conditions reveals chemical instabilities that are not predicted from thermodynamic considerations of stable solid oxide phases, as represented by the Pourbaix diagram for the system. Computational modelling indicates that photoexcited charge carriers accumulated at the surface destabilize the lattice, and that self-passivation by formation of a chemically stable surface phase is kinetically hindered. Although chemical stability of metal oxides cannot be assumed, insight into corrosion mechanisms aids development of protection strategies and discovery of semiconductors with improved stability.

  9. Mechanistic insights into chemical and photochemical transformations of bismuth vanadate photoanodes

    PubMed Central

    Toma, Francesca M.; Cooper, Jason K.; Kunzelmann, Viktoria; McDowell, Matthew T.; Yu, Jie; Larson, David M.; Borys, Nicholas J.; Abelyan, Christine; Beeman, Jeffrey W.; Yu, Kin Man; Yang, Jinhui; Chen, Le; Shaner, Matthew R.; Spurgeon, Joshua; Houle, Frances A.; Persson, Kristin A.; Sharp, Ian D.

    2016-01-01

    Artificial photosynthesis relies on the availability of semiconductors that are chemically stable and can efficiently capture solar energy. Although metal oxide semiconductors have been investigated for their promise to resist oxidative attack, materials in this class can suffer from chemical and photochemical instability. Here we present a methodology for evaluating corrosion mechanisms and apply it to bismuth vanadate, a state-of-the-art photoanode. Analysis of changing morphology and composition under solar water splitting conditions reveals chemical instabilities that are not predicted from thermodynamic considerations of stable solid oxide phases, as represented by the Pourbaix diagram for the system. Computational modelling indicates that photoexcited charge carriers accumulated at the surface destabilize the lattice, and that self-passivation by formation of a chemically stable surface phase is kinetically hindered. Although chemical stability of metal oxides cannot be assumed, insight into corrosion mechanisms aids development of protection strategies and discovery of semiconductors with improved stability. PMID:27377305

  10. The use of the solar energy in photochemical and photocatalytic processes

    NASA Astrophysics Data System (ADS)

    Kuburovic, Natasha D.; Valent, Vladimir J.; Todorovic, Marija S.

    2003-06-01

    The increasing use of the Earth's natural resources has generated increasing disposal of waste products and contamination of the environment. Many of these products are organic chemicals. Characteristic examples of waste products in the atmosphere, hydrosphere and soil are insecticides, herbicides and pesticides used to protect crops, accidental leakages and spills, and the continual discharge of waste by products in effluent streams from petrochemical and essential industries. To purify these contaminated atmospheres, hydrosphere and soil a procedure and process has been developing with minimal specific consumption energy from a renewable energy source. This paper will provide a survey and analysis of the parameters, thermal efficiency and conversion energy in the use of solar energy in the photochemical and photocatalytic degradation processes of organic effluents. As a consequence of the use of solar energy in the degradation of these effluents, a conceptual solution of a technical-technological and photocatalytic process is given for effluents which are located in watercourses and soil in Yugoslavia.

  11. Mechanistic insights into chemical and photochemical transformations of bismuth vanadate photoanodes.

    PubMed

    Toma, Francesca M; Cooper, Jason K; Kunzelmann, Viktoria; McDowell, Matthew T; Yu, Jie; Larson, David M; Borys, Nicholas J; Abelyan, Christine; Beeman, Jeffrey W; Yu, Kin Man; Yang, Jinhui; Chen, Le; Shaner, Matthew R; Spurgeon, Joshua; Houle, Frances A; Persson, Kristin A; Sharp, Ian D

    2016-07-05

    Artificial photosynthesis relies on the availability of semiconductors that are chemically stable and can efficiently capture solar energy. Although metal oxide semiconductors have been investigated for their promise to resist oxidative attack, materials in this class can suffer from chemical and photochemical instability. Here we present a methodology for evaluating corrosion mechanisms and apply it to bismuth vanadate, a state-of-the-art photoanode. Analysis of changing morphology and composition under solar water splitting conditions reveals chemical instabilities that are not predicted from thermodynamic considerations of stable solid oxide phases, as represented by the Pourbaix diagram for the system. Computational modelling indicates that photoexcited charge carriers accumulated at the surface destabilize the lattice, and that self-passivation by formation of a chemically stable surface phase is kinetically hindered. Although chemical stability of metal oxides cannot be assumed, insight into corrosion mechanisms aids development of protection strategies and discovery of semiconductors with improved stability.

  12. Enhancing the efficacy of cytotoxic agents for cancer therapy using photochemical internalisation

    PubMed Central

    Moore, Caroline M.; Loizidou, Marilena; MacRobert, Alexander J.; Woodhams, Josephine H.

    2016-01-01

    Photochemical internalisation (PCI) is a technique for improving cellular delivery of certain bioactive agents which are prone to sequestration within endolysosomes. There is a wide range of agents suitable for PCI‐based delivery including toxins, oligonucleotides, genes and immunoconjugates which demonstrates the versatility of this technique. The basic mechanism of PCI involves triggering release of the agent from endolysosomes within the target cells using a photosensitiser which is selectively retained with the endolysosomal membranes. Excitation of the photosensitiser by visible light leads to disruption of the membranes via photooxidative damage thereby releasing the agent into the cytosol. This treatment enables the drugs to reach their intended subcellular target more efficiently and improves their efficacy. In this review we summarise the applications of this technique with the main emphasis placed on cancer chemotherapy. PMID:25758607

  13. Photophysical and photochemical processes in 3D self-assembled gels as confined microenvironments.

    PubMed

    Pérez-Ruiz, Raúl; Díaz Díaz, David

    2015-07-14

    Numerous challenging transformations take place in nature with high efficiency within confined and compartmented environments. This has inspired scientists to develop spatially micro- and nanoreactors by 'bottom-up' approaches in order to improve different processes in comparison to solution, in terms of kinetics, selectivity or processability. In this respect, investigation of photophysical and photochemical processes in soft gel materials has recently emerged as a new and promising research field oriented towards expanding their applications in important areas such as photovoltaics, photocatalysis and phototherapy. Herein, we summarize the few examples dealing with intragel photo-induced physical and chemical processes involving embedded reactants that do not participate in the assembly of the gel network.

  14. Synthesis, Photophysical and Photochemical Properties of a Set of Silicon Phthalocyanines Bearing Anti-Inflammatory Groups.

    PubMed

    Şahin, Belgin; Topal, Sevinc Zehra; Atilla, Devrim

    2017-01-01

    In this study, a series of novel silicon (IV) phthalocyanines conjugated axially with anti-inflammatory (sulindac) and triethylene glycol groups has been synthesized. Different synthetic strategies were attempted to obtain the targeted molecules in high yield. The compounds were fully characterized by using different analyses techniques. Our objectives were to generate a system with sulindac group which enhances the singlet oxygen generation and exhibits anti-cancer effect. Therefore, photophysical and photochemical properties of these compounds were investigated in different solvents. The substituent effect on fluorescence quantum yield and singlet oxygen generation was evaluated for efficiency in photodynamic therapy (PDT) as photosensitizer. The molecules exhibited no aggregation tendency, solubility in common organic solvents, high singlet oxygen quantum yield and high photostability in DMSO so these favourable properties make them good candidates as photosensitizer for PDT. In addition, their stabilities were investigated in DMSO, THF, acetonitrile and DMF.

  15. O2-dependent electron flow, membrane energization and the mechanism of non-photochemical quenching of chlorophyll fluorescence.

    PubMed

    Schreiber, U; Neubauer, C

    1990-09-01

    Recent progress in chlorophyll fluorescence research is reviewed, with emphasis on separation of photochemical and non-photochemical quenching coefficients (qP and qN) by the 'saturation pulse method'. This is part of an introductory talk at the Wageningen Meeting on 'The use of chlorophyll fluorescence and other non-invasive techniques in plant stress physiology'. The sequence of events is investigated which leads to down-regulation of PS II quantum yield in vivo, expressed in formation of qN. The role of O2-dependent electron flow for ΔpH- and qN-formation is emphasized. Previous conclusions on the rate of 'pseudocyclic' transport are re-evaluated in view of high ascorbate peroxidase activity observed in intact chloroplasts. It is proposed that the combined Mehler-Peroxidase reaction is responsible for most of the qN developed when CO2-assimilation is limited. Dithiothreitol is shown to inhibit part of qN-formation as well as peroxidase-induced electron flow. As to the actual mechanism of non-photochemical quenching, it is demonstrated that quenching is favored by treatments which slow down reactions at the PS II donor side. The same treatments are shown to stimulate charge recombination, as measured via 50 μs luminescence. It is suggested that also in vivo internal thylakoid acidification leads to stimulation of charge recombination, although on a more rapid time scale. A unifying model is proposed, incorporating reaction center and antenna quenching, with primary control of ΔpH at the PS II reaction center, involving radical pair spin transition and charge recombination to the triplet state in a first quenching step. In a second step, triplet excitation is trapped by zeaxanthin (if present) which in its triplet excited state causes additional quenching of singlet excited chlorophyll.

  16. Iron in non-hydroxyl radical mediated photochemical processes for dye degradation: Catalyst or inhibitor?

    PubMed

    Wu, Bingdang; Zhang, Shujuan; Li, Xuchun; Liu, Xitong; Pan, Bingcai

    2015-07-01

    The acetylacetone (AA) mediated photochemical process has been proven as an efficient approach for decoloration. For azo dyes, the UV/AA process was several to more than ten times more efficient than the UV/H2O2 process. Iron is one of the most common elements on the earth. It is well known that iron can improve the UV/H2O2 process through thermal Fenton and photo-Fenton reactions. What will be the role of iron in the UV/AA process? Could iron-AA complexes act as photocatalysts in environmental remediation? To answer these questions, the photo-degradation of an azo dye, Acid Orange 7 (AO7), was conducted under the variant combinations of AA with iron species in both ionic (Fe2+, Fe3+) and complex (Fe(AA)3) forms. The pseudo-first-order decoloration rate constants of AO7 in these photochemical processes followed such an order: UV/Fe(II)/AA

  17. Studies leading to the development of a single-electron transfer (SET) photochemical strategy for syntheses of macrocyclic polyethers, polythioethers, and polyamides.

    PubMed

    Cho, Dae Won; Yoon, Ung Chan; Mariano, Patrick S

    2011-03-15

    Organic photochemists began to recognize in the 1970s that a new mechanistic pathway involving excited-state single-electron transfer (SET) could be used to drive unique photochemical reactions. Arnold's seminal studies demonstrated that SET photochemical reactions proceed by way of ion radical intermediates, the properties of which govern the nature of the ensuing reaction pathways. Thus, in contrast to classical photochemical reactions, SET-promoted excited-state processes are controlled by the nature and rates of secondary reactions of intermediate ion radicals. In this Account, we discuss our work in harnessing SET pathways for photochemical synthesis, focusing on the successful production of macrocyclic polyethers, polythioethers, and polyamides. One major thrust of our studies in SET photochemistry has been to develop new, efficient reactions that can be used for the preparation of important natural and non-natural substances. Our efforts with α-silyl donor-tethered phthalimides and naphthalimides have led to the discovery of efficient photochemical processes in which excited-state SET is followed by regioselective formation of carbon-centered radicals. The radical formation takes place through nucleophile-assisted desilylation of intermediate α-silyl-substituted ether-, thioether-, amine-, and amide-centered cation radicals. Early laser flash photolysis studies demonstrated that the rates of methanol- and water-promoted bimolecular desilylations of cation radicals (derived from α-silyl electron donors) exceeded the rates of other cation radical α-fragmentation processes, such as α-deprotonation. In addition, mechanistic analyses of a variety of SET-promoted photocyclization reactions of α-silyl polydonor-linked phthalimides and naphthalimides showed that the chemical and quantum efficiencies of the processes are highly dependent on the lengths and types of the chains connecting the imide acceptor and α-silyl electron donor centers. We also observed

  18. On the in vivo photochemical rate parameters for PDT reactive oxygen species modeling

    NASA Astrophysics Data System (ADS)

    Kim, Michele M.; Ghogare, Ashwini A.; Greer, Alexander; Zhu, Timothy C.

    2017-03-01

    Photosensitizer photochemical parameters are crucial data in accurate dosimetry for photodynamic therapy (PDT) based on photochemical modeling. Progress has been made in the last few decades in determining the photochemical properties of commonly used photosensitizers (PS), but mostly in solution or in vitro. Recent developments allow for the estimation of some of these photochemical parameters in vivo. This review will cover the currently available in vivo photochemical properties of photosensitizers as well as the techniques for measuring those parameters. Furthermore, photochemical parameters that are independent of environmental factors or are universal for different photosensitizers will be examined. Most photosensitizers discussed in this review are of the type II (singlet oxygen) photooxidation category, although type I photosensitizers that involve other reactive oxygen species (ROS) will be discussed as well. The compilation of these parameters will be essential for ROS modeling of PDT.

  19. [Effects of plastic film mulching and rain harvesting modes on chlorophyll fluorescence characteristics, yield and water use efficiency of dryland maize].

    PubMed

    Li, Shang-Zhong; Fan, Ting-Lu; Wang, Yong; Zhao, Gang; Wang, Lei; Tang, Xiao-Ming; Dang, Yi; Zhao, Hui

    2014-02-01

    The differences on chlorophyll fluorescence parameters, yield and water use efficiency of dryland maize were compared among full plastic film mulching on double ridges and planting in catchment furrows (FFDRF), half plastic film mulching on double ridges and planting in catchment furrows (HFDRF), plastic film mulching on ridge and planting in film-side (FS), and flat planting with no plastic film mulching (NM) under field conditions in dry highland of Loess Plateau in 2007-2012. The results showed that fluorescence yield (Fo), the maximum fluorescence yield (Fm), light-adapted fluorescence yield when PS II reaction centers were totally open (F), light-adapted fluorescence yield when PS II reaction centers closed (Fm'), the maximal photochemical efficiency of PS II (Fv/Fm), the actual photochemical efficiency of PS II in the light (Phi PS II), the relative electron transport rate (ETR), photochemical quenching (qP) and non-photochemical quenching (qN) in maize leaves of FFDRF were higher than that of control (NM), and the value of 1-qP was lower than that of control, at 13:00, chlorophyll fluorescence parameters values of FFDRF was significantly higher than control, which were increased by 5.3%, 56.8%, 10.7%, 36.3%, 23.6%, 56.7%, 64.4%, 45.5%, 23.6% and -55.6%, respectively, compared with the control. Yield and water use efficiency of FFDRF were the highest in every year no matter dry year, normal year, humid year and hail disaster year. Average yield and water use efficiency of FFDRF were 12,650 kg x hm(-2) and 40.4 kg x mm(-1) x hm(-2) during 2007-2012, increased by 57.8% and 61.6% compared with the control, respectively, and also significantly higher compared with HFDRF and PS. Therefore, it was concluded that FFDRF had significantly increased the efficiency of light energy conversion and improved the production capacity of dryland maize.

  20. Realizing actual feedback control of complex network

    NASA Astrophysics Data System (ADS)

    Tu, Chengyi; Cheng, Yuhua

    2014-06-01

    In this paper, we present the concept of feedbackability and how to identify the Minimum Feedbackability Set of an arbitrary complex directed network. Furthermore, we design an estimator and a feedback controller accessing one MFS to realize actual feedback control, i.e. control the system to our desired state according to the estimated system internal state from the output of estimator. Last but not least, we perform numerical simulations of a small linear time-invariant dynamics network and a real simple food network to verify the theoretical results. The framework presented here could make an arbitrary complex directed network realize actual feedback control and deepen our understanding of complex systems.

  1. Pluto's Photochemical Haze and Comparison to that of Titan

    NASA Astrophysics Data System (ADS)

    Yung, Yuk; Gao, Peter; Fan, Siteng; Wong, Michael; Kammer, Joshua A.; Summers, Michael; Gladstone, Randy; Young, Leslie

    2016-10-01

    The New Horizons flyby of Pluto confirmed the existence of hazes in its atmosphere. The observations suggest that the haze particles are fractal aggregates, analogous to the photochemical hazes on Titan. Therefore, studying the Pluto hazes can shed light on the similarities and differences between the Pluto and Titan atmospheres. We model the haze distributions of both worlds using the Community Aerosol and Radiation Model for Atmospheres assuming that the distribution is shaped by transport and aggregation of particles originating from photochemistry. The results of our models are compared to solar occultation observations taken by New Horizons for Pluto, and Cassini for Titan. For Pluto, satisfactory agreement with observations is obtained when the aggregate monomer size is 10 nm and the downward mass flux of photochemical products is equal to the column-integrated methane destruction rate. The effective particle radius is ~0.1-0.2 μm near Pluto's surface, consistent with forward scattering measurements. We also consider the effect of condensation of HCN, C2H2, C2H4, and C2H6 on the haze particles, which may play an important effect in shaping their altitude and size distributions. An alternative spherical particle case requires a downward mass flux 2-3 times larger, and resulted in particles 4 times smaller near the surface. For Titan, satisfactory agreement with data is found with comparatively smaller monomers and a downward mass flux of photochemical products much less than Titan's column-integrated methane destruction rate, though degeneracy between these two parameters may affect our results.

  2. Photochemical and photoelectrochemical quenching of chlorophyll fluorescence in photosystem II.

    PubMed

    Vredenberg, Wim; Durchan, Milan; Prásil, Ondrej

    2009-12-01

    This paper deals with kinetics and properties of variable fluorescence in leaves and thylakoids upon excitation with low intensity multi-turnover actinic light pulses corresponding with an excitation rate of about 10 Hz. These show a relatively small and amply documented rise in the sub-s time range towards the plateau level F(pl) followed by a delayed and S-shaped rise towards a steady state level F(m) which is between three and four fold the initial dark fluorescence level F(o). Properties of this retarded slow rise are i) rate of dark recovery is (1-6 s)(-1), ii) suppression by low concentration of protonophores, iii) responsiveness to complementary single turnover flash excitation with transient amplitude towards a level F(m) which is between five and six fold the initial dark fluorescence level F(o) and iv) in harmony with and quantitatively interpretable in terms of a release of photoelectrochemical quenching controlled by the trans-thylakoid proton pump powered by the light-driven Q cycle. Data show evidence for a sizeable fluorescence increase upon release of (photo) electrochemical quenching, defined as qPE. Release of qPE occurs independent of photochemical quenching defined here as qPP even under conditions at which qPP = 1. The term photochemical quenching, hitherto symbolized by qP, will require a new definition, because it incorporates in its present form a sizeable photoelectrochemical component. The same is likely to be true for definition and use of qN as an indicator of non photochemical quenching.

  3. Do Photochemical Hazes Cloud the Atmosphere of 51 Eri b?

    NASA Astrophysics Data System (ADS)

    Marley, Mark; Zahnle, Kevin; Moses, Julianne; Morley, Caroline

    2015-12-01

    The first young giant planet to be discovered by the Gemini Planet Imager was the ~ 2MJ planet 51 Eri b. This ~20 Myr old young Jupiter is the first directly imaged planet to show unmistakable methane in H band. To constrain the planet’s mass, atmospheric temperature, and composition, the GPI J and H band spectra as well as some limited photometric points were compared to the predictions of substellar atmosphere models. The best fitting models reported in the discovery paper (Macintosh et al. 2015) relied upon a combination of clear and cloudy atmospheric columns to reproduce the data. In the atmosphere of an object as cool as 700 K the global silicate and iron clouds would be expected to be found well below the photosphere, although strong vertical mixing in the low gravity atmosphere is a possibility. Instead, clouds of Na2S, as have been detected in brown dwarf atmospheres, are a likely source of particle opacity. As a third explanation we have explored whether atmospheric photochemistry, driven by the UV flux from the primary star, may yield hazes that also influence the observed spectrum of the planet. To explore this possibility we have modeled the atmospheric photochemistry of 51 Eri b using two state-of-the-art photochemical models, both capable of predicting yields of complex hydrocarbons under various atmospheric conditions. We also have explored whether photochemical products can alter the equilibrium temperature profile of the atmosphere. In our presentation we will summarize the modeling approach employed to characterize 51 Eri b, explaining constraints on the planet’s effective temperature, gravity, and atmospheric composition and also present results of our studies of atmospheric photochemistry. We will discuss whether photochemical hazes could indeed be responsible for the particulate opacity that apparently sculpts the spectrum of the planet.

  4. Photochemical Production of Alkyl Nitrates in the Tropical Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Dahl, E. E.; Yvon-Lewis, S. A.; Saltzman, E. S.

    2005-12-01

    Alkyl nitrates are important to the tropospheric NOx/ozone cycle because they represent a significant fraction of the reactive nitrogen (NOy). Previous work has shown that there is an oceanic source of alkyl nitrates. A photochemical mechanism for the formation of alkyl nitrates in seawater has been proposed. This mechanism involves the reaction of ROO and NO, where ROO is an alkyl peroxy radical. ROO and NO radicals in seawater are derived from the photolysis of DOM and nitrite, respectively. In this study, the photochemical production of low molecular weight alkyl nitrates (C1-C3) was observed in shipboard incubation experiments in the tropical Pacific during the PHASE 1 cruise. Seawater samples from several regions, including high and low-chlorophyll areas, were collected and incubated. Alkyl nitrate production rates as high as 2 nM/hour were observed. The production rate of alkyl nitrates was clearly dependent upon the initial concentration of nitrite, most likely as the source for NO radicals. While the magnitude of production varied between sample locations, the ratios of the production rates of the various alkyl nitrates remained relatively constant. The observed production ratios of methyl, ethyl, isopropyl, and n-propyl nitrate were 5.9:1.0:0.1:0.2. These ratios presumably reflect the speciation of peroxy radicals formed in seawater, and the yield of alkyl nitrates from the ROO+NO reaction. The observed production rate ratios are similar to the concentration ratios of alkyl nitrates observed in ambient seawater and the overlying atmosphere during the study. A comparison of the measured production rates and the observed concentrations, suggests that photochemically produced alkyl nitrates are a major source of atmospheric alkyl nitrates in the surface ocean and marine atmosphere.

  5. Resin–Dentin Bonding Interface After Photochemical Surface Treatment

    PubMed Central

    Sano, Kazunobu; Ichinose, Shizuko; Araki, Kouji

    2015-01-01

    Abstract Objective The aim of this study is to elucidate the structure of the resin–dentin interface formed by photochemical dentin treatment using an argon fluoride (ArF) excimer laser. Background data The ArF excimer laser processes material by photochemical reaction without generating heat, while also providing surface conditioning that enhances material adhesion. In the case of bonding between resin and dentin, we demonstrated in a previous study that laser etching using an ArF excimer laser produced bonding strength comparable to that of the traditional bonding process; however, conditions of the bonding interface have not been fully investigated. Methods A dentin surface was irradiated in air with an ArF excimer laser followed by bonding treatment. Cross sections were observed under light microscope, transmission electron microscope (TEM), and scanning electron microscope, then analyzed using an energy dispersive X-ray spectroscope (EDS): EDS line profiles of the elements C, O, Si, Cl, P, and Ca at the resin–dentin interface were obtained. Results The density of C in resin decreased as it approached the interface, reaching its lowest level within the dentin at a depth of 2 μm from the resin–dentin interface on EDS. There was no hybrid layer observed at the interface on TEM. Therefore, it was suggested that the resin monomer infiltrated into the microspaces produced on the dentin surface by laser abrasion. Conclusions The monomer infiltration without hybrid layer is thought to be the adhesion mechanism after laser etching. Therefore, the photochemical processes at the bonding interface achieved using the ArF excimer laser has great potential to be developed into a new bonding system in dentistry. PMID:25555032

  6. Resonantly enhanced selective photochemical etching of GaN

    NASA Astrophysics Data System (ADS)

    Trichas, E.; Kayambaki, M.; Iliopoulos, E.; Pelekanos, N. T.; Savvidis, P. G.

    2009-04-01

    Wavelength dependent photochemical etching of GaN films reveals a strong resonant enhancement of the photocurrent at the GaN gap, in close agreement with the excitonic absorption profile of GaN. The corresponding etching rate of GaN strongly correlates with the measured photocurrent. No photocurrent, nor etching is observed for AlGaN films under same excitation conditions. The method could pave the way to the development of truly selective etching of GaN on AlGaN for the fabrication of nitride based optoelectronic devices.

  7. The transport of photochemical pollutants to the background troposphere

    NASA Technical Reports Server (NTRS)

    Bazzell, C. C.; Peters, L. K.

    1981-01-01

    The considered investigation is concerned with the phenomena occurring as a chemically reacting plume, with specific initial concentrations of NO, NO2, O3, and hydrocarbons, emerges from an urban area and is advected to the background troposphere. A better understanding of the global NOx and hydrocarbon budgets can be realized by determining the fractions of NOx and hydrocarbons that are transported to distances far enough to be considered background. The investigation makes use of a 56-step, lumped kinetic mechanism for photochemical smog, which includes current information on pertinent chemical reactions and rate constants for the reactions.

  8. The Role of Intersection Space Segments in Photochemical Reactions

    SciTech Connect

    Castano, Obis; Sancho, Unai; Garavelli, Marco; Olivucci, Massimo; Frutos, Luis Manuel

    2007-12-26

    We analyze here the role of the intersection space in the photochemistry of some organic compounds and how the topological properties of this space affect the mechanism of the photochemical reaction. This mechanism is related to the accessibility of different reaction paths in the relaxation in the ground state once the system reaches the intersection space (i.e. a conical intersection). It is proved that sometimes, even in the photochemistry of small organic molecules, the complete analysis of the intersection space is necessary for the correct computational prediction of the chemical mechanism and the formed photoproducts underlying the photoinduced reaction.

  9. Laser machining of special designed photopolymers-photochemical ablation mechanism

    SciTech Connect

    Lippert, T.; Dickinson, J.T.; Langford, S.C.; Furutani, H.; Fukumura, H.; Masuhara, H.; Kunz, T.; Wokaun, A.

    1997-08-01

    Photopolymers based on the triazeno chromophore group (-N=N-N{lt}) have been developed. The absorption properties can be tailored for a specific irradiation wavelength. The photochemical exothermic decomposition yields high energetic gaseous products which are not contaminating the surface. The polymer can be structured with high resolution. No debris has been found around the etched corners. Maximum ablation rates of about 3 micrometer/pulse were achieved due to the dynamic absorption behavior (bleaching during the pulse). No physical or chemical modifications of the polymer surface could be detected after irradiation at the tailored absorption wavelength, whereas irradiation at different wavelengths resulted in modified (physical and chemical) surfaces.

  10. Screen Printed μ-ELECTRODES for Photochemical Applications

    NASA Astrophysics Data System (ADS)

    Della Seta, L.; Marino, S.; Masci, A.; Pilloton, R.

    2000-12-01

    A new device, based on screen printed electrodes, was realised allowing low manufacturing costs and rapid analyses with PSII or with other biological (algae) or photochemical catalysts. The μ-electrode was cut from a PVC sheet, on whose two sides graphite and silver pastes were deposited by screen printing techniques. The biosensor was placed in a flow cell obtained by carving a light emitting diode (LED). Details on the layout of the electrode and the flow-through μ-cell are described together with preliminary results obtained by detecting H2O2, K4Fe(CN)6, Glucose and PSII activity.

  11. Photochemical production of formaldehyde in earth's primitive atmosphere

    NASA Technical Reports Server (NTRS)

    Pinto, J. P.; Gladstone, G. R.; Yung, Y. L.

    1980-01-01

    Formaldehyde could have been produced by photochemical reactions in the earth's primitive atmosphere, at a time when it consisted mainly of molecular nitrogen, water vapor, carbon dioxide, and trace amounts of molecular hydrogen and carbon monoxide. Removal of formaldehyde from the atmosphere by precipitation can provide a source of organic carbon to the oceans at the rate of 100 billion moles per year. Subsequent reactions of formaldehyde in primeval aquatic environments would have implications for the abiotic synthesis of complex organic molecules and the origin of life.

  12. Chlorophyll-quinone photochemical electron transfer in liposomes

    SciTech Connect

    Hurley, J.K.; Castelli, F.; Tollin, G.

    1981-09-01

    A study is described which involves the reduction of electron acceptors (quinones) by photoexcited chlorophyll (Chl). The experimental samples consisted of Chl a (from spinach) incorporated into phosphatidylcholine (either synthetic or from hen egg yolks) liposomes suspended in 10 mM phosphate buffer (pH 7.0). The quinones were either present during liposome formation or added later, depending on their water solubility. The measurement technique employed was laser flash photolysis. Results have provided considerable insight into the ways in which membranes may modify the photochemical properties of Chl by allowing molecular compartmentalization and by permitting cooperative interactions.

  13. Children's Rights and Self-Actualization Theory.

    ERIC Educational Resources Information Center

    Farmer, Rod

    1982-01-01

    Educators need to seriously reflect upon the concept of children's rights. Though the idea of children's rights has been debated numerous times, the idea remains vague and shapeless; however, Maslow's theory of self-actualization can provide the children's rights idea with a needed theoretical framework. (Author)

  14. Group Counseling for Self-Actualization.

    ERIC Educational Resources Information Center

    Streich, William H.; Keeler, Douglas J.

    Self-concept, creativity, growth orientation, an integrated value system, and receptiveness to new experiences are considered to be crucial variables to the self-actualization process. A regular, year-long group counseling program was conducted with 85 randomly selected gifted secondary students in the Farmington, Connecticut Public Schools. A…

  15. Culture Studies and Self-Actualization Theory.

    ERIC Educational Resources Information Center

    Farmer, Rod

    1983-01-01

    True citizenship education is impossible unless students develop the habit of intelligently evaluating cultures. Abraham Maslow's theory of self-actualization, a theory of innate human needs and of human motivation, is a nonethnocentric tool which can be used by teachers and students to help them understand other cultures. (SR)

  16. Humanistic Education and Self-Actualization Theory.

    ERIC Educational Resources Information Center

    Farmer, Rod

    1984-01-01

    Stresses the need for theoretical justification for the development of humanistic education programs in today's schools. Explores Abraham Maslow's hierarchy of needs and theory of self-actualization. Argues that Maslow's theory may be the best available for educators concerned with educating the whole child. (JHZ)

  17. Developing Human Resources through Actualizing Human Potential

    ERIC Educational Resources Information Center

    Clarken, Rodney H.

    2012-01-01

    The key to human resource development is in actualizing individual and collective thinking, feeling and choosing potentials related to our minds, hearts and wills respectively. These capacities and faculties must be balanced and regulated according to the standards of truth, love and justice for individual, community and institutional development,…

  18. 50 CFR 253.16 - Actual cost.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 50 Wildlife and Fisheries 9 2011-10-01 2011-10-01 false Actual cost. 253.16 Section 253.16 Wildlife and Fisheries NATIONAL MARINE FISHERIES SERVICE, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE AID TO FISHERIES FISHERIES ASSISTANCE PROGRAMS Fisheries Finance Program §...

  19. Estimating hydroxyl radical photochemical formation rates in natural waters during long-term laboratory irradiation experiments.

    PubMed

    Sun, Luni; Chen, Hongmei; Abdulla, Hussain A; Mopper, Kenneth

    2014-04-01

    In this study it was observed that, during long-term irradiations (>1 day) of natural waters, the methods for measuring hydroxyl radical (˙OH) formation rates based upon sequentially determined cumulative concentrations of photoproducts from probes significantly underestimate actual ˙OH formation rates. Performing a correction using the photodegradation rates of the probe products improves the ˙OH estimation for short term irradiations (<1 day), but not long term irradiations. Only the 'instantaneous' formation rates, which were obtained by adding probes to aliquots at each time point and irradiating these sub-samples for a short time (≤2 h), were found appropriate for accurately estimating ˙OH photochemical formation rates during long-term laboratory irradiation experiments. Our results also showed that in iron- and dissolved organic matter (DOM)-rich water samples, ˙OH appears to be mainly produced from the Fenton reaction initially, but subsequently from other sources possibly from DOM photoreactions. Pathways of ˙OH formation in long-term irradiations in relation to H2O2 and iron concentrations are discussed.

  20. Whiteheadian Actual Entitities and String Theory

    NASA Astrophysics Data System (ADS)

    Bracken, Joseph A.

    2012-06-01

    In the philosophy of Alfred North Whitehead, the ultimate units of reality are actual entities, momentary self-constituting subjects of experience which are too small to be sensibly perceived. Their combination into "societies" with a "common element of form" produces the organisms and inanimate things of ordinary sense experience. According to the proponents of string theory, tiny vibrating strings are the ultimate constituents of physical reality which in harmonious combination yield perceptible entities at the macroscopic level of physical reality. Given that the number of Whiteheadian actual entities and of individual strings within string theory are beyond reckoning at any given moment, could they be two ways to describe the same non-verifiable foundational reality? For example, if one could establish that the "superject" or objective pattern of self- constitution of an actual entity vibrates at a specific frequency, its affinity with the individual strings of string theory would be striking. Likewise, if one were to claim that the size and complexity of Whiteheadian 'societies" require different space-time parameters for the dynamic interrelationship of constituent actual entities, would that at least partially account for the assumption of 10 or even 26 instead of just 3 dimensions within string theory? The overall conclusion of this article is that, if a suitably revised understanding of Whiteheadian metaphysics were seen as compatible with the philosophical implications of string theory, their combination into a single world view would strengthen the plausibility of both schemes taken separately. Key words: actual entities, subject/superjects, vibrating strings, structured fields of activity, multi-dimensional physical reality.

  1. Photochemical vapor generation of lead for inductively coupled plasma mass spectrometric detection

    NASA Astrophysics Data System (ADS)

    Duan, Hualing; Zhang, Ningning; Gong, Zhenbin; Li, Weifeng; Hang, Wei

    2016-06-01

    Photochemical vapor generation (PCVG) of lead was successfully achieved with a simplified and convenient system, in which only low molecular weight organic acid and a high-efficiency photochemical reactor were needed. The reactor was used to generate lead volatile species when a solution of lead containing a small amount of low molecular weight organic acid was pumped through. Several factors, including the concentration of acetic acid, the concentration of hydrochloride acid, and the irradiation time of UV light were optimized. Under the optimal conditions, including the addition of 0.90% (v/v) acetic acid and 0.03% (v/v) hydrochloride acid, and irradiation time of 28 s, intense and repeatable signal of lead volatile species was successfully obtained and identified with inductively coupled plasma mass spectrometry (ICPMS). In addition, the effects from inorganic anions and transition metal ions, including Cl-, NO3-, SO42 -, Cu2 +, Fe3 +, Co2 + and Ni2 +, were investigated, which suggests that their suppression to the PCVG of lead was in the order of Cl- < SO42 - < NO3- for anions and Ni2 +, Co2 + < Fe3 + < Cu2 + for transition metal ions. Under optimized conditions, relative standard derivation (RSD) of 4.4% was achieved from replicate measurements (n = 5) of a standard solution of 0.1 μg L- 1 lead. And, the limit of quantitation (LOQ, 10σ) of 0.012 μg L- 1 lead was obtained using this method and the method blank could be easily controlled down to 0.023 μg L- 1. To validate applicability of this method, it was also employed for the determination of lead in tap water, rain water and lake water.

  2. The influence of photochemical fractionation on the evolution of the nitrogen isotope ratios - detailed analysis of current photochemical loss rates

    NASA Astrophysics Data System (ADS)

    Mandt, K. E.; Waite, J. H., Jr.; Westlake, J.; Magee, B.; Liang, M. C.; Bell, J.

    2012-04-01

    Tracking the evolution of molecular nitrogen over geologic time scales requires an understanding of the loss rates of both isotopologues (14N2 and 14N15N) as a function of time (e.g. Mandt et al., 2009). The relative loss rates, if different, “fractionate” the isotopes so that the ratios change as a function of time, and rate at which the ratio changes due to a loss process is determined by the “fractionation factor.” Photochemistry is known to fractionate the nitrogen isotopes in Titan’s atmosphere by preferentially removing the heavy isotope from the molecular nitrogen inventory and increasing the ratio (heavy/light) in one of the primary photochemical products, HCN. This fractionation occurs due to a selective shielding during photodissociation where the photons that dissociate 14N15N penetrate deeper into the atmosphere (Liang et al., 2007) than the photons that dissociate 14N14N. Two methods can be used to determine the photochemical fractionation factor, f. The first approach for calculating f is based on the isotopic ratios of the photochemical source and product, as measured by the Huygens Gas Chromatograph Mass Spectrometer (GCMS) (Niemann et al., 2010) and the Cassini Infrared Spectrometer (CIRS) (Vinatier et al., 2007), respectively. The second method uses the loss rates and the ratio of the source and requires detailed photochemical modeling to ensure that the loss rates are calculated accurately. We compare these two methods for calculating the photochemical fractionation factor for N2 by using measurements of the isotopic ratios of N2 and HCN combined with an updated coupled ion-neutral-thermal model (De la Haye et al., 2008). We find that accurate magnetospheric electron fluxes and a rotating model that accounts for diurnal variations are essential for accurate calculations of the HCN densities and for determination of the fractionation factor through photochemical modeling. References: De La Haye, V., J. H. Waite, Jr., T. E. Cravens, I. P

  3. Photochemical Synthesis of Shape-Controlled Nanostructured Gold on Zinc Oxide Nanorods as Photocatalytically Renewable Sensors.

    PubMed

    Xu, Jia-Quan; Duo, Huan-Huan; Zhang, Yu-Ge; Zhang, Xin-Wei; Fang, Wei; Liu, Yan-Ling; Shen, Ai-Guo; Hu, Ji-Ming; Huang, Wei-Hua

    2016-04-05

    Biosensors always suffer from passivation that prevents their reutilization. To address this issue, photocatalytically renewable sensors composed of semiconductor photocatalysts and sensing materials have emerged recently. In this work, we developed a robust and versatile method to construct different kinds of renewable biosensors consisting of ZnO nanorods and nanostructured Au. Via a facile and efficient photochemical reduction, various nanostructured Au was obtained successfully on ZnO nanorods. As-prepared sensors concurrently possess excellent sensing capability and desirable photocatalytic cleaning performance. Experimental results demonstrate that dendritic Au/ZnO composite has the strongest surface-enhanced Raman scattering (SERS) enhancement, and dense Au nanoparticles (NPs)/ZnO composite has the highest electrochemical activity, which was successfully used for electrochemical detection of NO release from cells. Furthermore, both of the SERS and electrochemical sensors can be regenerated efficiently for renewable applications via photodegrading adsorbed probe molecules and biomolecules. Our strategy provides an efficient and versatile method to construct various kinds of highly sensitive renewable sensors and might expand the application of the photocatalytically renewable sensor in the biosensing area.

  4. Morphological transformations of silver nanoparticles in seedless photochemical synthesis

    NASA Astrophysics Data System (ADS)

    Lu, Ya; Zhang, Congyun; Hao, Rui; Zhang, Dongjie; Fu, Yizheng; Moeendarbari, Sina; Pickering, Christopher S.; Hao, Yaowu; Liu, Yaqing

    2016-05-01

    Photochemical synthesis is an easily controlled and reliable method for the fabrication of silver (Ag) nanoparticles with various morphologies. In this work, we have systematically investigated the seedless photochemical synthesis of anisotropic Ag nanoparticles with and without PVP as surface capping agent. The time evolution of anisotropic Ag nanoparticles during the synthesis process are studied using UV-visible spectra, optical images and transmission electron microscopy. The results show that the light irradiation precisely controls the start and termination of the reaction, and the presence or absence of PVP greatly affects the morphology evolution of anisotropic Ag nanoparticles. With PVP as the surface capping agent, Ag nanoparticles grow into decahedra or prism by the deposition of Ag atoms on {111} or {110} facets through epitaxial growth. However, a different morphology evolution could happen when Ag nanoparticle is synthesized without PVP as surface capping agent. In this case, Ag nanoparticles can fuse into the decahedrons through an edge-selective particle fusion mechanism, which involves attachment, rotation and realignment of Ag nanoparticles. This process was evidenced with HRTEM images at the different stages of the transformation from Ag colloid to decahedra nanoparticles. Oriented attachment and Ostwald ripening also play important role in the transformation process.

  5. Cancer treatment by photothermal, photochemical, and photobiological interactions

    NASA Astrophysics Data System (ADS)

    Chen, Wei R.; Korbelik, Mladen; Liu, Hong; Nordquist, Robert E.

    2005-01-01

    Laser tissue interactions hold great promise in cancer treatment. Photothermal interaction aims at the direct cell destruction through the increase of local tissue temperature, while photochemical interaction aims at the cell destruction using free radicals produced through the activation of photosensitizers in the target tissue. Photobiological interaction can target the immune host system to induce long-term control. Photothermal and photochemical interactions can be significantly enhanced by photobiological interaction through the use of immunoadjuvants. In our experiments, three different immunoadjuvants, complete Freund"s adjuvant (CF), incomplete Freund"s adjuvant (IF), and c-parvum (CP), were used in the treatment of metastatic mammary tumors in conjunction with photothermal interaction. In addition, a specific adjuvant, Glycated chitosan (GC), has been used in combination with photodynamic therapy (PDT) in the treatment of mouse tumors. In the treatment of rat tumors, CF, IF and CP raised the cure-rates from 0% to 18%, 7% and 9%, respectively. In comparison, GC resulted in a 29% long-term survival. In the treatment of EMT6 mammary sarcoma in mice, GC of 0.5% and 1.5% concentrations increased the cure rates of Photofrin-based PDT treatment from 38% to 63% and 75%, respectively. In the treatment of Line 1 lung adenocarcinoma in mice, a 1.67% GC solution enabled a non-curative mTHPC-based PDT to cure a 37% of the tumor bearing mice.

  6. Photochemical oxidation of phenanthrene sorbed on silica gel

    SciTech Connect

    Barbas, J.T.; Sigman, M.E.; Dabestani, R.

    1996-05-01

    There have been relatively few detailed studies of PAH photochemical degradation mechanisms and products at solid/air interfaces under controlled conditions. Results from mechanistic studies on particulate simulants are important in understanding the fates of PAH sorbed on similar materials in natural settings. In this study, the photolysis of phenanthrene (PH) on silica gel, in the presence of air, has been carefully examined. Once sorbed onto the silica surface, PH is not observed to repartition into the gas phase, even under vacuum, and dark reactions of PH are not observed at the silica/air interface. Photolysis (254 nm) of PH leads to the formation of 2,2`-biformylbiphenyl (1), 9,10-phenanthrenequinone (2), cis-9,10-dihydrodihydroxyphenanthrene (3), benzocoumarin (4), 2,2`-biphenyldicarboxylic acid (5), 2-formyl-2`-biphenylcarboxylic acid (6), 2-formylbiphenyl (7), 1,2-naphthalenedicarboxylic acid (8), and phthalic acid (9). These products account for 85-90% of the reacted PH. The photoproducts are independent of excitation wavelength (254 and 350 nm), and the reaction proceeds entirely through an initial step involving the addition of singlet molecular oxygen to the ground state of phenanthrene with subsequent thermal and/or photochemical reactions of the initially formed product. 20 refs., 3 figs., 1 tab.

  7. The influence of aerosols on photochemical smog in Mexico City

    NASA Astrophysics Data System (ADS)

    Castro, T.; Madronich, S.; Rivale, S.; Muhlia, A.; Mar, B.

    Aerosols in the Mexico City atmosphere can have a non-negligible effect on the ultraviolet radiation field and hence on the formation of photochemical smog. We used estimates of aerosol optical depths from sun photometer observations in a detailed radiative transfer model, to calculate photolysis rate coefficients ( JNO 2) for the key reaction NO 2+ hν→NO+O ( λ<430 nm). The calculated values are in good agreement with previously published measurements of JNO 2 at two sites in Mexico City: Palacio de Minerı´a (19°25'59″N, 99°07'58″W, 2233 masl), and IMP (19°28'48″N, 99°11'07″W, 2277 masl) and in Tres Marias, a town near Mexico City (19°03'N, 99°14'W, 2810 masl). In particular, the model reproduces very well the contrast between the two urban sites and the evidently much cleaner Tres Marias site. For the measurement days, reductions in surface JNO 2 by 10-30% could be attributed to the presence of aerosols, with considerable uncertainty due largely to lack of detailed data on aerosol optical properties at ultraviolet wavelengths (esp. the single scattering albedo). The potential impact of such large reductions in photolysis rates on surface ozone concentrations is illustrated with a simple zero-dimensional photochemical model.

  8. Photochemical trajectory modelling studies of the 1987 Antarctic spring vortex

    NASA Technical Reports Server (NTRS)

    Austin, J.; Jones, R. L.; Mckenna, D. S.

    1988-01-01

    Simulations of Antarctic ozone photochemistry performed using a photochemical model integrated along air parcel trajectories are described. This type of model has a major advantage at high latitudes of being able to simulate correctly the complex interaction between photolysis and temperature fields, which, because of the polar night cannot be represented accurately in a zonally averaged framework. Isentropic air parcel trajectories were computed using Meteorological Office global model analyses and forecast fields from positions along the ER-2 flight paths during the Airborne Antarctic Ozone Experiment in Austral Spring 1987. A photochemical model is integrated along these trajectories using the aircraft observations to initialize constituent concentrations. The model includes additional reactions of the ClO dimer and also bromine reactions, which are thought to play a significant role in Antarctica. The model also includes heterogeneous reactions which are invoked when the air parcel passes through a polar stratospheric cloud (PSC). The existence of a PSC is determined throughout the course of the model integration from the parcel temperature and the saturated vapour pressure of water over an assumed H2O/HNO3 mixture. The air parcel temperature is used to determine the saturated vapor pressure of HNO3 over the same mixture. Mixing ratios which exceed saturation result in condensation of the excess in the model and hence lead to a reduction of the amount of gas phase NO2 available for chemical reaction.

  9. Upper limits of possible photochemical hazes on Pluto

    SciTech Connect

    Stansberry, J.A.; Lunine, J.I.; Tomasko, M.G. )

    1989-11-01

    Elliot et al. (1989) invoked a haze layer near the surface of Pluto to explain certain features of a stellar occultation by that planet in June, 1988. The primary requirements for this haze layer were that it achieve unity tangential optical depth at a radius of 1174 km and be essentially transparent above 1189 km. The authors explore here the possibility that aerosols generated through methane photolysis could be responsible for such a haze layer. A comprehensive model of aerosol production, particle growth, sedimentation and condensation is applied to the atmosphere of Pluto using pressures, temperatures and composition derived from the stellar occultation and other data. They test two atmosphere models proposed in the literature, one from Elliot et al. (1989), and one from Hubbard et al. (1989), as well as a range of optical properties for the particles. In order to produce a haze with unity tangential optical depth at 1174 km, they had to use an aerosol mass production rate equal to twice the total methane dissociation rate due to solar UV expected for Pluto and assume that the particles produced were 10 times more absorbing than those in other hazes in the outer solar system. The possibility of condensation in the atmosphere was considered but did not result in distinctly different haze optical depths. If a photochemical haze on Pluto was responsible for the occultation lightcurve measured by Elliot et al., operation of a photochemical system different from those on Titan, Uranus or Neptune is indicated.

  10. Global emissions and models of photochemically active compounds

    SciTech Connect

    Penner, J.E.; Atherton, C.S.; Graedel, T.E.

    1993-05-20

    Anthropogenic emissions from industrial activity, fossil fuel combustion, and biomass burning are now known to be large enough (relative to natural sources) to perturb the chemistry of vast regions of the troposphere. A goal of the IGAC Global Emissions Inventory Activity (GEIA) is to provide authoritative and reliable emissions inventories on a 1{degree} {times} 1{degree} grid. When combined with atmospheric photochemical models, these high quality emissions inventories may be used to predict the concentrations of major photochemical products. Comparison of model results with measurements of pertinent species allows us to understand whether there are major shortcomings in our understanding of tropospheric photochemistry, the budgets and transport of trace species, and their effects in the atmosphere. Through this activity, we are building the capability to make confident predictions of the future consequences of anthropogenic emissions. This paper compares IGAC recommended emissions inventories for reactive nitrogen and sulfur dioxide to those that have been in use previously. We also present results from the three-dimensional LLNL atmospheric chemistry model that show how emissions of anthropogenic nitrogen oxides might potentially affect tropospheric ozone and OH concentrations and how emissions of anthropogenic sulfur increase sulfate aerosol loadings.

  11. Measurement of VOC reactivities using a photochemical flow reactor

    SciTech Connect

    Hurley, M.D.; Chang, T.Y.; Japar, S.M.; Wallington, T.J.

    1998-07-01

    A commercial ambient air monitoring instrument, the Airtrak 2000, has been modified for use as a photochemical flow reactor and used to measure the absolute and incremental reactivity of 18 single test VOCs and the incremental reactivity of six multicomponent VOC mixtures. A flow technique is a useful supplement to traditional static chamber experiments. The static chamber technique involves periodic sampling of an irradiated mixture in a photochemical chamber. Under these conditions, the irradiated mixture is always in transition. Using a flow system, a steady-state condition is established within the flow reactor that is representative, in this case, of the early stages of the smog forming process in the atmosphere. The measurement technique also allows changes in the background chamber reactivity to be monitored and taken into account. The incremental reactivity of 13 of the 18 test compounds measured is compared with previously reported results from a static chamber experiment, and the two data sets are generally in good agreement. The additivity of reactivity was tested by measuring the incremental reactivity of six multicomponent mixtures, the components being compounds measured individually in this study. The measured reactivity of a mixture was compared to that calculated from the sum of the measured reactivity of the mixture`s individual components. The results show that reactivity is additive for the concentration range studied.

  12. Primary targets in photochemical inactivation of cells in culture

    NASA Astrophysics Data System (ADS)

    Berg, Kristian; Jones, Stuart G.; Prydz, Kristian; Moan, Johan

    1995-01-01

    The mechanisms of photoinactivation of NHIK 3025 cells in culture sensitized by tetrasulfonated phenylporphines (TPPS4) are described). Ultracentrifugation studies on postnuclear supernatants indicated that the intracellular distribution of TPPS4 resembles that of (beta) -N-acetyl-D-glucosaminidase ((beta) -AGA), a lysosomal marker enzyme, and that the cytosolic content of TPPS4 is below the detection limit of the ultracentrifugation method. Upon light exposure more than 90% of TPPS4 was lost from the lysosomal fractions, due to lysosomal rupture. The content of TPPS4 in the postnuclear supernatants was reduced by 30 - 40% upon exposure to light. This is most likely due to binding of TPPS4 to the nuclei, which were removed from the cell extracts before ultracentrifugation, after photochemical treatment. The unpolymerized form of tubulin seems to be an important target for the photochemical inactivation of NHIK 3025 cells. Since TPPS4 is mainly localized in lysosomes it was assumed that a dose of light disrupting a substantial number of lysosomes followed by microtubule depolymerization by nocodazole would enhance the sensitivity of the cells to photoinactivation. This was confirmed by using a colony-forming assay. The increased phototoxic effect exerted by such a treatment regime could be explained by an enhanced sensitivity of tubulin to light. Another cytosolic constituent, lactate dehydrogenase, was not photoinactivated by TPPS4 and light.

  13. Dual-Templated Cobalt Oxide for Photochemical Water Oxidation.

    PubMed

    Deng, Xiaohui; Bongard, Hans-Josef; Chan, Candace K; Tüysüz, Harun

    2016-02-19

    Mesoporous Co3 O4 was prepared using a dual templating approach whereby mesopores inside SiO2 nanospheres, as well as the void spaces between the nanospheres, were used as templates. The effect of calcination temperature on the crystallinity, morphology, and textural parameters of the Co3 O4 replica was investigated. The catalytic activity of Co3 O4 for photochemical water oxidation in a [Ru(bpy)3 ](2+) [S2 O8 ](2-) system was evaluated. The Co3 O4 replica calcined at the lowest temperature (150 °C) exhibited the best performance as a result of the unique nanostructure and high surface area arising from the dual templating. The performance of Co3 O4 with highest surface area was further examined in electrochemical water oxidation. Superior activity over high temperature counterpart and decent stability was observed. Furthermore, CoO with identical morphology was prepared from Co3 O4 using an ethanol reduction method and a higher turnover-frequency number for photochemical water oxidation was obtained.

  14. Photochemical and Nonphotochemical Transformations of Cysteine with Dissolved Organic Matter.

    PubMed

    Chu, Chiheng; Erickson, Paul R; Lundeen, Rachel A; Stamatelatos, Dimitrios; Alaimo, Peter J; Latch, Douglas E; McNeill, Kristopher

    2016-06-21

    Cysteine (Cys) plays numerous key roles in the biogeochemistry of natural waters. Despite its importance, a full assessment of Cys abiotic transformation kinetics, products and pathways under environmental conditions has not been conducted. This study is a mechanistic evaluation of the photochemical and nonphotochemical (dark) transformations of Cys in solutions containing chromophoric dissolved organic matter (CDOM). The results show that Cys underwent abiotic transformations under both dark and irradiated conditions. Under dark conditions, the transformation rates of Cys were moderate and were highly pH- and temperature-dependent. Under UVA or natural sunlight irradiations, Cys transformation rates were enhanced by up to two orders of magnitude compared to rates under dark conditions. Product analysis indicated cystine and cysteine sulfinic acid were the major photooxidation products. In addition, this study provides an assessment of the contributions of singlet oxygen, hydroxyl radical, hydrogen peroxide, and triplet dissolved organic matter to the CDOM-sensitized photochemical oxidation of Cys. The results suggest that another unknown pathway was dominant in the CDOM-sensitized photodegradation of Cys, which will require further study to identify.

  15. The Actual Apollo 13 Prime Crew

    NASA Technical Reports Server (NTRS)

    1970-01-01

    The actual Apollo 13 lunar landing mission prime crew from left to right are: Commander, James A. Lovell Jr., Command Module pilot, John L. Swigert Jr.and Lunar Module pilot, Fred W. Haise Jr. The original Command Module pilot for this mission was Thomas 'Ken' Mattingly Jr. but due to exposure to German measles he was replaced by his backup, Command Module pilot, John L. 'Jack' Swigert Jr.

  16. Orientation of nucleosomes and linker DNA in calf thymus chromatin determined by photochemical dichroism

    NASA Astrophysics Data System (ADS)

    Mitra, Sekhar; Sen, Dipankar; Crothers, Donald M.

    1984-03-01

    The dichroism for photochemical attachment of a psoralen derivative to Mg2+ -stabilized chromatin fibres is used to deduce the orientation of nucleosomal disks and linker DNA in the 30-nm fibre. The new technique of photochemical electric dichroism should have general applicability to problems of nucleic acid organization in cellular subunits and viruses.

  17. Highly selective defect-mediated photochemical CO2 conversion over fluorite ceria under ambient conditions.

    PubMed

    Jiang, Dong; Wang, Wenzhong; Gao, Erping; Sun, Songmei; Zhang, Ling

    2014-02-25

    A highly selective defect-mediated photochemical CO2 conversion to CO over defective CeO2 nanorods under ambient conditions (CO2 400 ppm) is presented. The local strain and surface oxygen vacancies embedded in the defect-rich CeO2 are suggested to play a decisive role in mediating the photochemical CO2 conversion.

  18. 76 FR 60820 - Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-30

    ... AGENCY Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants AGENCY... titled, ``Second External Review Draft Integrated Science Assessment for Ozone and Related Photochemical... ambient air quality standards (NAAQS) for ozone. EPA is releasing this draft document to seek review...

  19. 77 FR 36534 - Third External Review Draft Integrated Science Assessment for Ozone and Related Photochemical...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-06-19

    ... AGENCY Third External Review Draft Integrated Science Assessment for Ozone and Related Photochemical... External Review Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants'' (EPA/600... Standards (NAAQS) for ozone. EPA is releasing this draft document to seek review by the Clean Air...

  20. Studies in photochemical smog chemistry. I. Atmospheric chemistry of toluene. II. Analysis of chemical reaction mechanisms for photochemical smog

    SciTech Connect

    Leone, J.A.

    1985-01-01

    This study focuses on two related topics in the gas phase organic chemistry of importance in urban air pollution. Part I describes an experimental and modeling effort aimed at developing a new explicit reaction mechanism for the atmospheric photooxidation of toluene. This mechanism is tested using experimental data from both indoor and outdoor smog chamber facilities. The predictions of the new reaction mechanism are found to be in good agreement with both sets of experimental data. Additional simulations performed with the new mechanism are used to investigate various mechanistic paths, and to gain insight into areas where the understanding is not complete. The outdoor experimental facility, which was built to provide the second set of experimental data, consists of a 65 cubic meter teflon smog chamber together with full instrumentation capable of measuring ozone, nitrogen dioxide, nitric oxide, peroxyacetyl nitrate (PAN), carbon monoxide, relative humidity, temperature, aerosol size distributions, and of course toluene and its photooxidation products. In Part II, a theoretical analysis of lumped chemical reaction mechanisms for photochemical smog is presented. Included is a description of a new counter species analysis technique which can be used to analyze any complex chemical reaction mechanism. Finally, a new lumped mechanism for photochemical smog is developed and tested against experimental data from two smog chamber facilities. Advantages of this mechanism relative to the existing lumped mechanisms are discussed.

  1. Photochemical etching during ultraviolet photolytic deposition of metal films on semiconductor surfaces

    NASA Astrophysics Data System (ADS)

    Kowalczyk, Steven P.; Miller, D. L.

    1986-01-01

    UV photochemical deposition of Sn films on GaAs (001) surfaces from a variety of tin-containing compounds (tetramethyltin, tetrabutyltin, dibutyltin dibromide, stannic chloride, hexamethylditin, dibutyltin sulfide, and iodotrimethyltin) was studied. X-ray photoelectron spectroscopy showed that during the initial stages of deposition from the halogenated compounds, the GaAs surface was photochemically etched, most likely by a halogen radical species. The photochemical etching resulted in an arsenic deficient surface which was particularly dramatic for the case of SnCl4. These results have important implications for the choice of sources for photochemical deposition when the metal-semiconductor interface is important and for photochemical etching if stoichiometric surfaces are required.

  2. Photochemical free radical production rates in the eastern Caribbean

    NASA Astrophysics Data System (ADS)

    Dister, Brian; Zafiriou, Oliver C.

    1993-02-01

    Potential photochemical production rates of total (NO-scavengeable) free radicals were surveyed underway (> 900 points) in the eastern Caribbean and Orinoco delta in spring and fall 1988. These data document seasonal trends and large-scale (˜ 10-1000 km) variability in the pools of sunlight-generated reactive transients, which probably mediate a major portion of marine photoredox transformations. Radical production potential was detectable in all waters and was reasonably quantifiable at rates above 0.25 nmol L-1 min-1 sun-1. Radical production rates varied from ˜ 0.1-0.5 nmol L-1 min-1 of full-sun illumination in "blue water" to > 60 nmol L-1 min-1 in some estuarine waters in the high-flow season. Qualitatively, spatiotemporal potential rate distributions strikingly resembled that of "chlorophyll" (a riverine-influence tracer of uncertain specificity) in 1979-1981 CZCS images of the region [Müller-Karger et al., 1988] at all scales. Basin-scale occurrence of greatly enhanced rates in fall compared to spring is attributed to terrestrial chromophore inputs, primarily from the Orinoco River, any contributions from Amazon water and nutrient-stimulus effects could not be resolved. A major part of the functionally photoreactive colored organic matter (COM) involved in radical formation clearly mixes without massive loss out into high-salinity waters, although humic acids may flocculate in estuaries. A similar conclusion applies over smaller scales for COM as measured optically [Blough et al., this issue]. Furthermore, optical absorption and radical production rates were positively correlated in the estuarine region in fall. These cruises demonstrated that photochemical techniques are now adequate to treat terrestrial photochemical chromophore inputs as an estuarine mixing problem on a large scale, though the ancillary data base does not currently support such an analysis in this region. Eastern Caribbean waters are not markedly more reactive at comparable salinities

  3. Evidence for dissolved organic matter as the primary source and sink of photochemically produced hydroxyl radical in arctic surface waters.

    PubMed

    Page, Sarah E; Logan, J Robert; Cory, Rose M; McNeill, Kristopher

    2014-04-01

    Hydroxyl radical (˙OH) is an indiscriminate oxidant that reacts at near-diffusion-controlled rates with organic carbon. Thus, while ˙OH is expected to be an important oxidant of dissolved organic matter (DOM) and other recalcitrant compounds, the role of ˙OH in the oxidation of these compounds in aquatic ecosystems is not well known due to the poorly constrained sources and sinks of ˙OH, especially in pristine (unpolluted) natural waters. We measured the rates of ˙OH formation and quenching across a range of surface waters in the Arctic varying in concentrations of expected sources and sinks of ˙OH. Photochemical formation of ˙OH was observed in all waters tested, with rates of formation ranging from 2.6 ± 0.6 to 900 ± 100 × 10(-12) M s(-1). Steady-state concentrations ranged from 2 ± 1 to 290 ± 60 × 10(-17) M, and overlapped with previously reported values in surface waters. While iron-mediated photo-Fenton reactions likely contributed to the observed ˙OH production, several lines of evidence suggest that DOM was the primary source and sink of photochemically produced ˙OH in pristine arctic surface waters. DOM from first-order or headwater streams was more efficient in producing ˙OH than what has previously been reported for DOM, and ˙OH formation decreased with increasing residence time of DOM in sunlit surface waters. Despite the ubiquitous formation of ˙OH in arctic surface waters observed in this study, photochemical ˙OH formation was estimated to contribute ≤4% to the observed photo-oxidation of DOM; however, key uncertainties in this estimate must be addressed before ruling out the role of ˙OH in the oxidation of DOM in these waters.

  4. Flexible metal-oxide devices made by room-temperature photochemical activation of sol-gel films.

    PubMed

    Kim, Yong-Hoon; Heo, Jae-Sang; Kim, Tae-Hyeong; Park, Sungjun; Yoon, Myung-Han; Kim, Jiwan; Oh, Min Suk; Yi, Gi-Ra; Noh, Yong-Young; Park, Sung Kyu

    2012-09-06

    Amorphous metal-oxide semiconductors have emerged as potential replacements for organic and silicon materials in thin-film electronics. The high carrier mobility in the amorphous state, and excellent large-area uniformity, have extended their applications to active-matrix electronics, including displays, sensor arrays and X-ray detectors. Moreover, their solution processability and optical transparency have opened new horizons for low-cost printable and transparent electronics on plastic substrates. But metal-oxide formation by the sol-gel route requires an annealing step at relatively high temperature, which has prevented the incorporation of these materials with the polymer substrates used in high-performance flexible electronics. Here we report a general method for forming high-performance and operationally stable metal-oxide semiconductors at room temperature, by deep-ultraviolet photochemical activation of sol-gel films. Deep-ultraviolet irradiation induces efficient condensation and densification of oxide semiconducting films by photochemical activation at low temperature. This photochemical activation is applicable to numerous metal-oxide semiconductors, and the performance (in terms of transistor mobility and operational stability) of thin-film transistors fabricated by this route compares favourably with that of thin-film transistors based on thermally annealed materials. The field-effect mobilities of the photo-activated metal-oxide semiconductors are as high as 14 and 7 cm(2) V(-1) s(-1) (with an Al(2)O(3) gate insulator) on glass and polymer substrates, respectively; and seven-stage ring oscillators fabricated on polymer substrates operate with an oscillation frequency of more than 340 kHz, corresponding to a propagation delay of less than 210 nanoseconds per stage.

  5. Disentangling the photochemical salinity tolerance in Aster tripolium L.: connecting biophysical traits with changes in fatty acid composition.

    PubMed

    Duarte, B; Cabrita, M T; Gameiro, C; Matos, A R; Godinho, R; Marques, J C; Caçador, I

    2017-03-01

    A profound analysis of A. tripolium photochemical traits under salinity exposure is lacking in the literature, with very few references focusing on its fatty acid profile role in photophysiology. To address this, the deep photochemical processes were evaluated by Pulse Amplitude Modulated (PAM) Fluorometry coupled with a discrimination of its leaf fatty acid profile. Plants exposed to 125-250 mm NaCl showed higher photochemical light harvesting efficiencies and lower energy dissipation rates. under higher NaCl exposure, there is evident damage of the oxygen evolving complexes (OECs). On the other hand, Reaction Centre (RC) closure net rate and density increased, improving the energy fluxes entering the PS II, in spite of the high amounts of energy dissipated and the loss of PS II antennae connectivity. Energy dissipation was mainly achieved through the auroxanthin pathway. Total fatty acid content displayed a similar trend, being also higher under 125-250 mm NaCl with high levels of omega-3 and omega-6 fatty acids. The increase in oleic acid and palmitic acid allows the maintenance of the good functioning of the PS II. Also relevant was the high concentration of chloroplastic C16:1t in the individuals subjected to 125-250 mm NaCl, related with a higher electron transport activity and with the organization of the Light Harvesting Complexes (LHC) and thus reducing the activation of energy dissipation mechanisms. All these new insights shed some light not only on the photophysiology of this potential cash-crop, but also highlight its important saline agriculture applications of this species as forage and potential source of essential fatty acids.

  6. Increased biomass productivity in green algae by tuning non-photochemical quenching

    PubMed Central

    Berteotti, Silvia; Ballottari, Matteo; Bassi, Roberto

    2016-01-01

    Photosynthetic microalgae have a high potential for the production of biofuels and highly valued metabolites. However, their current industrial exploitation is limited by a productivity in photobioreactors that is low compared to potential productivity. The high cell density and pigment content of the surface layers of photosynthetic microalgae result in absorption of excess photons and energy dissipation through non-photochemical quenching (NPQ). NPQ prevents photoinhibition, but its activation reduces the efficiency of photosynthetic energy conversion. In Chlamydomonas reinhardtii, NPQ is catalyzed by protein subunits encoded by three lhcsr (light harvesting complex stress related) genes. Here, we show that heat dissipation and biomass productivity depends on LHCSR protein accumulation. Indeed, algal strains lacking two lhcsr genes can grow in a wide range of light growth conditions without suffering from photoinhibition and are more productive than wild-type. Thus, the down-regulation of NPQ appears to be a suitable strategy for improving light use efficiency for biomass and biofuel production in microalgae. PMID:26888481

  7. Photochemical charges separation and photoelectric properties of flexible solar cells with two types of heterostructures

    SciTech Connect

    Liu, Xiangyang E-mail: yzgu@henu.edu.cn; Wang, Shun; Zheng, Haiwu; Cheng, Xiuying; Gu, Yuzong E-mail: yzgu@henu.edu.cn

    2015-12-14

    Photochemical charges generation, separation, and transport at nanocrystal interfaces are central to energy conversion for solar cells. Here, Zn{sub 2}SnO{sub 4} nanowires/Cu{sub 4}Bi{sub 4}S{sub 9} (ZTO/CBS), ZTO nanowires/CBS-reduced graphene oxide (ZTO/CBS-RGO), and bulk heterojunction (BHJ) solar cells were measured. The signals of steady state and electric field-induced surface photovoltage indicate that RGO with high electron mobility can evidently improve the photovoltaic response. Besides, ZTO/CBS and ZTO/CBS-RGO cells exhibit the excellent performance and the highest efficiencies of 1.2% and 2.8%, respectively. The internal relations of photoelectric properties to some factors, such as film thickness, direct paths, RGO conductive network, energy level matching, etc., were discussed in detail. Qualitative and quantitative analyses further verified the comprehensive effect of RGO and other factors. Importantly, the fine bendable characteristic of BHJ solar cells with excellent efficiency and facile, scalable production gives the as-made flexible solar cells device potential for practical application in future.

  8. Photochemical internalization-mediated nonviral gene transfection: polyamine core-shell nanoparticles as gene carrier

    NASA Astrophysics Data System (ADS)

    Zamora, Genesis; Wang, Frederick; Sun, Chung-Ho; Trinidad, Anthony; Kwon, Young Jik; Cho, Soo Kyung; Berg, Kristian; Madsen, Steen J.; Hirschberg, Henry

    2014-10-01

    The overall objective of the research was to investigate the utility of photochemical internalization (PCI) for the enhanced nonviral transfection of genes into glioma cells. The PCI-mediated introduction of the tumor suppressor gene phosphatase and tensin homolog (PTEN) or the cytosine deaminase (CD) pro-drug activating gene into U87 or U251 glioma cell monolayers and multicell tumor spheroids were evaluated. In the study reported here, polyamine-DNA gene polyplexes were encapsulated in a nanoparticle (NP) with an acid degradable polyketal outer shell. These NP synthetically mimic the roles of viral capsid and envelope, which transport and release the gene, respectively. The effects of PCI-mediated suppressor and suicide genes transfection efficiency employing either "naked" polyplex cores alone or as NP-shelled cores were compared. PCI was performed with the photosensitizer AlPcS2a and λ=670-nm laser irradiance. The results clearly demonstrated that the PCI can enhance the delivery of both the PTEN or CD genes in human glioma cell monolayers and multicell tumor spheroids. The transfection efficiency, as measured by cell survival and inhibition of spheroid growth, was found to be significantly greater at suboptimal light and DNA levels for shelled NPs compared with polyamine-DNA polyplexes alone.

  9. Photochemical charges separation and photoelectric properties of flexible solar cells with two types of heterostructures

    NASA Astrophysics Data System (ADS)

    Liu, Xiangyang; Wang, Shun; Zheng, Haiwu; Cheng, Xiuying; Gu, Yuzong

    2015-12-01

    Photochemical charges generation, separation, and transport at nanocrystal interfaces are central to energy conversion for solar cells. Here, Zn2SnO4 nanowires/Cu4Bi4S9 (ZTO/CBS), ZTO nanowires/CBS-reduced graphene oxide (ZTO/CBS-RGO), and bulk heterojunction (BHJ) solar cells were measured. The signals of steady state and electric field-induced surface photovoltage indicate that RGO with high electron mobility can evidently improve the photovoltaic response. Besides, ZTO/CBS and ZTO/CBS-RGO cells exhibit the excellent performance and the highest efficiencies of 1.2% and 2.8%, respectively. The internal relations of photoelectric properties to some factors, such as film thickness, direct paths, RGO conductive network, energy level matching, etc., were discussed in detail. Qualitative and quantitative analyses further verified the comprehensive effect of RGO and other factors. Importantly, the fine bendable characteristic of BHJ solar cells with excellent efficiency and facile, scalable production gives the as-made flexible solar cells device potential for practical application in future.

  10. Detection of bromine by ICP-oa-ToF-MS following photochemical vapor generation.

    PubMed

    Sturgeon, Ralph E

    2015-03-03

    A unique flow-through photochemical reactor is utilized for the generation of volatile methyl bromide from aqueous solutions of bromide and bromate ions in a medium of 2% acetic acid containing 3000 μg/mL NH4Cl. The volatile product is transported to a thin-film gas-liquid phase separator and directed to an inductively coupled plasma (ICP) tine-of-flight mass spectrometer for detection and quantitation using either of the (79)Br or (81)Br isotopes. Utilizing a sample flow rate of 3.3 mL/min and a 13 s irradiation time, a detection limit of 0.14 ng/mL is achieved, yielding a 17-fold enhancement over conventional solution nebulization. The estimated generation efficiency of 95% provides for a significant increase in analyte transport efficiency to the ICP. Precision of replicate measurement is 2.5% (RSD) at 20 ng/mL. The methodology was validated by successful determination of bromine in reference materials, including IRMM (BCR-611) low level bromide in groundwater, NIST SRM 1568b Rice Flour, and SRM 1632 bituminous coal.

  11. Explosive Percolation Transition is Actually Continuous

    NASA Astrophysics Data System (ADS)

    da Costa, R. A.; Dorogovtsev, S. N.; Goltsev, A. V.; Mendes, J. F. F.

    2010-12-01

    Recently a discontinuous percolation transition was reported in a new “explosive percolation” problem for irreversible systems [D. Achlioptas, R. M. D’Souza, and J. Spencer, Science 323, 1453 (2009)SCIEAS0036-807510.1126/science.1167782] in striking contrast to ordinary percolation. We consider a representative model which shows that the explosive percolation transition is actually a continuous, second order phase transition though with a uniquely small critical exponent of the percolation cluster size. We describe the unusual scaling properties of this transition and find its critical exponents and dimensions.

  12. Neoadjuvant Treatment in Rectal Cancer: Actual Status

    PubMed Central

    Garajová, Ingrid; Di Girolamo, Stefania; de Rosa, Francesco; Corbelli, Jody; Agostini, Valentina; Biasco, Guido; Brandi, Giovanni

    2011-01-01

    Neoadjuvant (preoperative) concomitant chemoradiotherapy (CRT) has become a standard treatment of locally advanced rectal adenocarcinomas. The clinical stages II (cT3-4, N0, M0) and III (cT1-4, N+, M0) according to International Union Against Cancer (IUCC) are concerned. It can reduce tumor volume and subsequently lead to an increase in complete resections (R0 resections), shows less toxicity, and improves local control rate. The aim of this review is to summarize actual approaches, main problems, and discrepancies in the treatment of locally advanced rectal adenocarcinomas. PMID:22295206

  13. Air resistance measurements on actual airplane parts

    NASA Technical Reports Server (NTRS)

    Weiselsberger, C

    1923-01-01

    For the calculation of the parasite resistance of an airplane, a knowledge of the resistance of the individual structural and accessory parts is necessary. The most reliable basis for this is given by tests with actual airplane parts at airspeeds which occur in practice. The data given here relate to the landing gear of a Siemanms-Schuckert DI airplane; the landing gear of a 'Luftfahrzeug-Gesellschaft' airplane (type Roland Dlla); landing gear of a 'Flugzeugbau Friedrichshafen' G airplane; a machine gun, and the exhaust manifold of a 269 HP engine.

  14. Photochemical aerosols on Titan and the giant planets

    NASA Astrophysics Data System (ADS)

    West, R.

    2015-10-01

    Our ideas about the nature of photochemical aerosols on Titan and the giant planets is evolving thanks to new data coming in from the Cassini spacecraft, ground-based and space-based telescopes, and theory and modeling. Aerosol formation begins at altitudes around 1000 km on Titan and around 800 km above the 1-bar pressure level in the polar thermospheres of Jupiter and Saturn where auroral energy is available to form ions and radicals. We have evidence that hydrocarbon chemistry is important in aerosol formation for all of these bodies and we believe that hydrazine on Jupiter and phosphine on Saturn may lead to aerosol production. Aeroso ls have a fractal aggregate structure on Titan and in the polar regions of Jupiter and Saturn. Their vertical and horizontal distributions reflect a balance between local production and horizontal and vertical transport governed by eddies and jets. They are important for radiative energy balance in ways that have only recently come to light.

  15. An Unprecedented Photochemical Reaction for Anthracene-Containing Derivatives.

    PubMed

    Zhao, Jiang-Lin; Jiang, Xue-Kai; Wu, Chong; Wang, Chuan-Zeng; Zeng, Xi; Redshaw, Carl; Yamato, Takehiko

    2016-10-18

    A series of anthracene-containing derivatives have been synthesised and characterised. The photochemical behaviour of these derivatives have been investigated by (1) H NMR spectroscopy. An unprecedented photolysis reaction for anthracene-containing derivatives was observed in the case of anthracenes directly armed with a -CH2 O-R group upon UV irradiation. The photolysis reaction process has been demonstrated to occur in three steps. Firstly, the anthracene-containing derivatives are converted into the corresponding endoperoxide intermediate upon UV irradiation in the presence of air; then, the endoperoxide intermediate is decomposed to the corresponding starting compound and 9-anthraldehyde; finally, 9-anthraldehyde is further oxidised to anthraquinone. Additionally, the photolysis reaction of anthracene-containing derivatives is significantly promoted in the presence of a thiacalix[4]arene platform.

  16. Photochemical and thermal evolution of interstellar/precometary ice analogs

    NASA Technical Reports Server (NTRS)

    Allamandola, L. J.; Sandford, S. A.; Valero, G. J.

    1988-01-01

    The photochemical and thermal evolution of H2O-, CH3OH-, NH3-, and CO-containing ices whose relative proportions in mixture are consistent with those of interstellar ice are presently studied experimentally. The UV photolysis of these ice analogs invariably generates H2CO, CO2, CO, CH4, and HCO, largely through the photofragmentation of CH3OH. CO and CH4 leave the samples as warmup proceeds to 100 K; most of the parent ice molecules are found to have sublimed upon the reaching of 200 K, with only a mixture of more refractory substances remaining. A residue of CH2 groups remains even after warmup to 300 K.

  17. NMR Studies on the Aqueous Phase Photochemical Degradation of TNT

    SciTech Connect

    Thorn, Kevin A.; Cox, Larry G.

    2008-04-06

    Aqueous phase photochemical degradation of 2,4,6-trinitrotoluene (TNT) is an important pathway in several environments, including washout lagoon soils, impact craters from partially detonated munitions that fill with rain or groundwater, and shallow marine environments containing unexploded munitions that have corroded. Knowledge of the degradation products is necessary for compliance issues on military firing ranges and formerly used defense sites. Previous laboratory studies have indicated that UV irradiation of aqueous TNT solutions results in a multicomponent product mixture, including polymerization compounds, that has been only partially resolved by mass spectrometric analyses. This study illustrates how a combination of solid and liquid state 1H, 13C, and 15N NMR spectroscopy, including two dimensional analyses, provides complementary information on the total product mixture from aqueous photolysis of TNT, and the effect of reaction conditions. Among the degradation products detected were amine, amide, azoxy, azo, and carboxylic acid compounds.

  18. Evaluated kinetic and photochemical data for atmospheric chemistry

    NASA Technical Reports Server (NTRS)

    Baulch, D. L.; Cox, R. A.; Hampson, R. F., Jr.; Kerr, J. A.; Troe, J.; Watson, R. T.

    1980-01-01

    This paper contains a critical evaluation of the kinetics and photochemistry of gas phase chemical reactions of neutral species involved in middle atmosphere chemistry (10-55 km altitude). Data sheets have been prepared for 148 thermal and photochemical reactions, containing summaries of the available experimental data with notes giving details of the experimental procedures. For each reaction a preferred value of the rate coefficient at 298 K is given together with a temperature dependency where possible. The selection of the preferred value is discussed, and estimates of the accuracies of the rate coefficients and temperature coefficients have been made for each reaction. The data sheets are intended to provide the basic physical chemical data needed as input for calculations which model atmospheric chemistry. A table summarizing the preferred rate data is provided, together with an appendix listing the available data on enthalpies of formation of the reactant and product species.

  19. The distribution of ammonia and its photochemical products on Jupiter

    NASA Technical Reports Server (NTRS)

    Atreya, S. K.; Donahue, T. M.; Kuhn, W. R.

    1977-01-01

    Altitude profiles of ammonia and its photochemical products are generated in the light of measurements of the Jovian temperature structure, eddy transport coefficient, improved chemical scheme, and rate constants. Realistic limits are placed on the concentration of hydrazine which may participate in the recycling of ammonia on Jupiter. The maximum hydrazine-ice production rate is calculated to be about 1.3 mg/sq m per Jovian day. The distribution of nitrogen gas is presented with and without supersaturation of hydrazine. The nitrogen mixing ratio near the ammonia cloud top is estimated to be in the range between 10 to the -9th and 10 to the -11th power. An appreciable latitudinal variation in the ammonia concentration is expected.

  20. Photochemically-assisted electrochemical degradation of landfill leachate.

    PubMed

    Tauchert, Elias; Schneider, Silvana; de Morais, Josmaria Lopes; Peralta-Zamora, Patricio

    2006-08-01

    In this work, the treatment of landfill leachates by a photoelectrochemical procedure is reported. When applied to untreated leachates the photochemical system was significantly hindered on account of the characteristic dark coloration of the samples. At this condition the degradation process was essentially electrochemical permitting typical color and COD removal of about 50% and 20%, respectively. When a previous chemical precipitation process was applied aiming the elimination of colored species (mainly humic substances) the decolorization and COD removal was extended to 90% and 60%, respectively. Considering the extremely complex character of the leachates and its usual resistance to conventional degradation processes the result reported here attest the high potentiality of photoelectrochemical processes to remediation of recalcitrant residues.

  1. Photochemical energy conversion: from molecular dyads to solar cells.

    PubMed

    Durrant, James R; Haque, Saif A; Palomares, Emilio

    2006-08-21

    Photochemical approaches to solar energy conversion are currently making rapid progress, increasing not only academic but also commercial interest in molecular-based photovoltaic solar cells. This progress has been achieved not only by increased understanding of the physics and physical chemistry of device function but also through advances in chemical and materials synthesis and processing, which now allows the design and fabrication of increasingly sophisticated device structures organised on the nanometer length scale. In this feature article, we review some progress in this field, focusing in particular upon the electron-transfer dynamics which underlie the function of dye-sensitised, nanocrystalline solar cells. The article starts by building upon the parallels between the function of such devices and the function of simple donor/acceptor molecular systems in solution. We then go on to discuss the optimisation of device function, and in particular the use of self-assembly-based strategies to control interfacial electron-transfer kinetics.

  2. An overview of photochemical smog studies in Australian cities

    SciTech Connect

    Physick, W.L.

    1996-12-31

    The problem of photochemical smog is being addressed by authorities in the five major cities of Australia. Detrimental levels of smog are exceeded occasionally in the larger cities of Sydney and Melbourne, while the geographic features and meteorology of Brisbane, Perth and Adelaide suggest potentially unacceptable levels as those cities continue to grow. Motor vehicles are the dominant source of precursor emissions for smog and this is reflected in the comparison by Ahmet and van Dijk (1994) of hourly-averaged ozone exceedences for Australia`s major cities, i.e., the number of exceedences is roughly proportional to the population. Although statistics such as these can be strongly influenced by the distribution of monitors within a network, the relatively low exceedence threshold (0.08 ppm) probably ensures that the results are a realistic indicator of the relative extent of the problem in each city.

  3. Applying green chemistry to the photochemical route to artemisinin

    NASA Astrophysics Data System (ADS)

    Amara, Zacharias; Bellamy, Jessica F. B.; Horvath, Raphael; Miller, Samuel J.; Beeby, Andrew; Burgard, Andreas; Rossen, Kai; Poliakoff, Martyn; George, Michael W.

    2015-06-01

    Artemisinin is an important antimalarial drug, but, at present, the environmental and economic costs of its semi-synthetic production are relatively high. Most of these costs lie in the final chemical steps, which follow a complex acid- and photo-catalysed route with oxygenation by both singlet and triplet oxygen. We demonstrate that applying the principles of green chemistry can lead to innovative strategies that avoid many of the problems in current photochemical processes. The first strategy combines the use of liquid CO2 as solvent and a dual-function solid acid/photocatalyst. The second strategy is an ambient-temperature reaction in aqueous mixtures of organic solvents, where the only inputs are dihydroartemisinic acid, O2 and light, and the output is pure, crystalline artemisinin. Everything else—solvents, photocatalyst and aqueous acid—can be recycled. Some aspects developed here through green chemistry are likely to have wider application in photochemistry and other reactions.

  4. Applying green chemistry to the photochemical route to artemisinin.

    PubMed

    Amara, Zacharias; Bellamy, Jessica F B; Horvath, Raphael; Miller, Samuel J; Beeby, Andrew; Burgard, Andreas; Rossen, Kai; Poliakoff, Martyn; George, Michael W

    2015-06-01

    Artemisinin is an important antimalarial drug, but, at present, the environmental and economic costs of its semi-synthetic production are relatively high. Most of these costs lie in the final chemical steps, which follow a complex acid- and photo-catalysed route with oxygenation by both singlet and triplet oxygen. We demonstrate that applying the principles of green chemistry can lead to innovative strategies that avoid many of the problems in current photochemical processes. The first strategy combines the use of liquid CO2 as solvent and a dual-function solid acid/photocatalyst. The second strategy is an ambient-temperature reaction in aqueous mixtures of organic solvents, where the only inputs are dihydroartemisinic acid, O2 and light, and the output is pure, crystalline artemisinin. Everything else-solvents, photocatalyst and aqueous acid-can be recycled. Some aspects developed here through green chemistry are likely to have wider application in photochemistry and other reactions.

  5. Photochemical oxidation of persistent cyanide-related compounds

    NASA Astrophysics Data System (ADS)

    Budaev, S. L.; Batoeva, A. A.; Khandarkhaeva, M. S.; Aseev, D. G.

    2017-03-01

    Kinetic regularities of the photolysis of thiocyanate solutions using of mono- and polychromatic UV radiation sources with different spectral ranges are studied. Comparative experiments aimed at investigating the role of photochemical action during the oxidation of thiocyanates with persulfates and additional catalytic activation with iron(III) ions are performed. The rate of conversion and the initial rate of thiocyanate oxidation are found to change in the order UV < UV/S2O 8 2- < S2O 8 2- /Fe3+ < UV/S2O 8 2- /Fe3+. A synergistic effect is detected when using the combined catalytic method for the destruction of thiocyanates by the UV/S2O 8 2- /Fe3+ oxidation system. This effect is due to the formation of reactive oxygen species, as a result of both the decomposition of persulfate and the reduction of inactive Fe3+ intermediates into Fe3+.

  6. Photochemical hole burning of ionic porphins and the deuterated analogues

    NASA Astrophysics Data System (ADS)

    Sakoda, Kazuaki; Maeda, Masayuki

    1994-01-01

    The quantum yields of photochemical hole burning (PHB) of three ionic porphins and their deuterated analogues doped in poly(vinylalcohol) and poly(sodium 4-styrenesulfonate) were estimated. The deuterated compounds, whose two hydrogen atoms at the nitrogen sites in the porphin ring were exchanged with deuterium atoms, were synthesized by reacting the non-deuterated compounds with heavy water. The quantum yield of the deuterated porphin was 18 to 45 times smaller than that of the non-deuterated compound. Besides, the hole area did not decrease at least up to about 60 K. These two facts definitely show that the main mechanism of PHB in this system is not a photophysical process, but the tautomerization of the porphin ring.

  7. Photochemical energy conversion by membrane-bound photoredox systems

    SciTech Connect

    Tollin, G.

    1992-03-01

    Most of our effort during the past grant period has been directed towards investigating electron transfer processes involving redox proteins at lipid bilayer/aqueous interfaces. This theme, as was noted in our previous three year renewal proposal, is consistent with our goal of developing biomimetic solar energy conversion systems which utilize the unique properties of biological electron transfer molecules. Thus, small redox proteins such as cytochrome c, plastocyanin and ferredoxin function is biological photosynthesis as mediators of electron flow between the photochemical systems localized in the membrane, and more complex soluble or membrane-bound redox proteins which are designed to carry out specific biological tasks such as transbilayer proton gradient formation, dinitrogen fixation, ATP synthesis, dihydrogen synthesis, generation of strong reductants, etc. In these studies, we have utilized two principal experimental techniques, laser flash photolysis and cyclic voltammetry, both of which permit direct measurements of electron transfer processes.

  8. Statistical analysis of a global photochemical model of the atmosphere

    NASA Astrophysics Data System (ADS)

    Frol'Kis, V. A.; Karol', I. L.; Kiselev, A. A.; Ozolin, Yu. E.; Zubov, V. A.

    2007-08-01

    This is a study of the sensitivity of model results (atmospheric content of main gas constituents and radiative characteristics of the atmosphere) to errors in emissions of a number of atmospheric gaseous pollutants. Groups of the model variables most dependent on these errors are selected. Two variants of emissions are considered: one without their evolution and the other with their variation according to the IPCC scenario. The estimates are made on the basis of standard statistical methods for the results obtained with the detailed onedimensional radiative—photochemical model of the Main Geophysical Observatory (MGO). Some approaches to such estimations with models of higher complexity and to the solution of the inverse problem (i.e., the estimation of the necessary accuracy of external model parameters for obtaining the given accuracy of model results) are outlined.

  9. Simulations of photochemical smog formation in complex urban areas

    NASA Astrophysics Data System (ADS)

    Muilwijk, C.; Schrijvers, P. J. C.; Wuerz, S.; Kenjereš, S.

    2016-12-01

    In the present study we numerically investigated the dispersion of photochemical reactive pollutants in complex urban areas by applying an integrated Computational Fluid Dynamics (CFD) and Computational Reaction Dynamics (CRD) approach. To model chemical reactions involved in smog generation, the Generic Reaction Set (GRS) approach is used. The GRS model was selected since it does not require detailed modeling of a large set of reactive components. Smog formation is modeled first in the case of an intensive traffic emission, subjected to low to moderate wind conditions in an idealized two-dimensional street canyon with a building aspect ratio (height/width) of one. It is found that Reactive Organic Components (ROC) play an important role in the chemistry of smog formation. In contrast to the NOx/O3 photochemical steady state model that predicts a depletion of the (ground level) ozone, the GRS model predicts generation of ozone. Secondly, the effect of direct sunlight and shadow within the street canyon on the chemical reaction dynamics is investigated for three characteristic solar angles (morning, midday and afternoon). Large differences of up to one order of magnitude are found in the ozone production for different solar angles. As a proof of concept for real urban areas, the integrated CFD/CRD approach is applied for a real scale (1 × 1 km2) complex urban area (a district of the city of Rotterdam, The Netherlands) with high traffic emissions. The predicted pollutant concentration levels give realistic values that correspond to moderate to heavy smog. It is concluded that the integrated CFD/CRD method with the GRS model of chemical reactions is both accurate and numerically robust, and can be used for modeling of smog formation in complex urban areas.

  10. Photochemical versus Thermal Synthesis of Cobalt Oxyhydroxide Nanocrystals

    SciTech Connect

    Alvarado, Samuel R.; Guo, Yijun; Ruberu, T. Purnima A.; Bakac, Andreja; Vela, Javier

    2012-04-18

    Photochemical methods facilitate the generation, isolation, and study of metastable nanomaterials having unusual size, composition, and morphology. These harder-to-isolate and highly reactive phases, inaccessible using conventional high-temperature pyrolysis, are likely to possess enhanced and unprecedented chemical, electromagnetic, and catalytic properties. We report a fast, low-temperature and scalable photochemical route to synthesize very small (3 nm) monodisperse cobalt oxyhydroxide (Co(O)OH) nanocrystals. This method uses readily and commercially available pentaamminechlorocobalt(III) chloride, [Co(NH3)5Cl]Cl2, under acidic or neutral pH and proceeds under either near-UV (350 nm) or Vis (575 nm) illumination. Control experiments showed that the reaction proceeds at competent rates only in the presence of light, does not involve a free radical mechanism, is insensitive to O2, and proceeds in two steps: (1) Aquation of [Co(NH3)5Cl]2+ to yield [Co(NH3)5(H2O)]3+, followed by (2) slow photoinduced release of NH3 from the aqua complex. This reaction is slow enough for Co(O)OH to form but fast enough so that nanocrystals are small (ca. 3 nm). The alternative dark thermal reaction proceeds much more slowly and produces much larger (250 nm) polydisperse Co(O)OH aggregates. UV–Vis absorption measurements and ab initio calculations yield a Co(O)OH band gap of 1.7 eV. Fast thermal annealing of Co(O)OH nanocrystals leads to Co3O4 nanocrystals with overall retention of nanoparticle size and morphology. Thermogravimetric analysis shows that oxyhydroxide to mixed-oxide phase transition occurs at significantly lower temperatures (up to ΔT = 64 °C) for small nanocrystals compared with the bulk.

  11. Metal-polypyridyl catalysts for electro- and photochemical reduction of water to hydrogen.

    PubMed

    Zee, David Z; Chantarojsiri, Teera; Long, Jeffrey R; Chang, Christopher J

    2015-07-21

    Climate change, rising global energy demand, and energy security concerns motivate research into alternative, sustainable energy sources. In principle, solar energy can meet the world's energy needs, but the intermittent nature of solar illumination means that it is temporally and spatially separated from its consumption. Developing systems that promote solar-to-fuel conversion, such as via reduction of protons to hydrogen, could bridge this production-consumption gap, but this effort requires invention of catalysts that are cheap, robust, and efficient and that use earth-abundant elements. In this context, catalysts that utilize water as both an earth-abundant, environmentally benign substrate and a solvent for proton reduction are highly desirable. This Account summarizes our studies of molecular metal-polypyridyl catalysts for electrochemical and photochemical reduction of protons to hydrogen. Inspired by concept transfer from biological and materials catalysts, these scaffolds are remarkably resistant to decomposition in water, with fast and selective electrocatalytic and photocatalytic conversions that are sustainable for several days. Their modular nature offers a broad range of opportunities for tuning reactivity by molecular design, including altering ancillary ligand electronics, denticity, and/or incorporating redox-active elements. Our first-generation complex, [(PY4)Co(CH3CN)2](2+), catalyzes the reduction of protons from a strong organic acid to hydrogen in 50% water. Subsequent investigations with the pentapyridyl ligand PY5Me2 furnished molybdenum and cobalt complexes capable of catalyzing the reduction of water in fully aqueous electrolyte with 100% Faradaic efficiency. Of particular note, the complex [(PY5Me2)MoO](2+) possesses extremely high activity and durability in neutral water, with turnover frequencies at least 8500 mol of H2 per mole of catalyst per hour and turnover numbers over 600 000 mol of H2 per mole of catalyst over 3 days at an

  12. 7 CFR 1437.101 - Actual production history.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 10 2010-01-01 2010-01-01 false Actual production history. 1437.101 Section 1437.101... Determining Yield Coverage Using Actual Production History § 1437.101 Actual production history. Actual production history (APH) is the unit's record of crop yield by crop year for the APH base period. The...

  13. 7 CFR 1437.101 - Actual production history.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 7 Agriculture 10 2012-01-01 2012-01-01 false Actual production history. 1437.101 Section 1437.101... Determining Yield Coverage Using Actual Production History § 1437.101 Actual production history. Actual production history (APH) is the unit's record of crop yield by crop year for the APH base period. The...

  14. 7 CFR 1437.101 - Actual production history.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 7 Agriculture 10 2011-01-01 2011-01-01 false Actual production history. 1437.101 Section 1437.101... Determining Yield Coverage Using Actual Production History § 1437.101 Actual production history. Actual production history (APH) is the unit's record of crop yield by crop year for the APH base period. The...

  15. 7 CFR 1437.101 - Actual production history.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 7 Agriculture 10 2014-01-01 2014-01-01 false Actual production history. 1437.101 Section 1437.101... Determining Yield Coverage Using Actual Production History § 1437.101 Actual production history. Actual production history (APH) is the unit's record of crop yield by crop year for the APH base period. The...

  16. 7 CFR 1437.101 - Actual production history.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 7 Agriculture 10 2013-01-01 2013-01-01 false Actual production history. 1437.101 Section 1437.101... Determining Yield Coverage Using Actual Production History § 1437.101 Actual production history. Actual production history (APH) is the unit's record of crop yield by crop year for the APH base period. The...

  17. Growth of endothelial cells on different concentrations of Gly-Arg-Gly-Asp photochemically grafted in polyethylene glycol modified polyurethane.

    PubMed

    Lin, Y S; Wang, S S; Chung, T W; Wang, Y H; Chiou, S H; Hsu, J J; Chou, N K; Hsieh, K H; Chu, S H

    2001-08-01

    To improve endothelial cell adhesion and growth on the surface of polyethylene glycol modified polyurethane (PU-PEG), cell adhesive peptide Gly-Arg-Gly-Asp (GRGD) was photochemically grafted to the surface. The surface grafted GRGD-N-Succinimidyl-6-[4'-azido-2'-nitrophenylamino]hexanoate (SANPAH) on a PU-PEG surface was performed by adsorption and subsequent ultraviolet irradiation. Fourier transform infrared spectra (FTIR) and electron spectroscopy for chemical analysis (ESCA) confirmed the GRGD grafted to form a PU-PEG-GRGD surface. The composition fraction of nitrogen calculated from ESCA analysis for the PU-PEG-GRGD surface was well correlated with the concentration of GRGD to be immobilized. Human umbilical vein endothelial cells (ECs) were well adhered and growing on the PU-PEG-GRGD surface. Moreover, the viability of ECs growing on PU-PEG-GRGD surfaces, analyzed by MTT test, was also well correlated with the GRGD concentrations immobilized on the surface. With photochemical techniques, we could manipulate different contents of GRGD to form multiple regions of PU-PEG-GRGD surface that could enhance the growth of ECs on the surface, and the enhancement efficiency was well correlated with GRGD contents.

  18. Photochemical solution processing of films of metastable phases for flexible devices: the β-Bi2O3 polymorph.

    PubMed

    Pérez-Mezcua, Dulce; Bretos, Iñigo; Jiménez, Ricardo; Ricote, Jesús; Jiménez-Rioboó, Rafael J; da Silva, Cosmelina Gonçalves; Chateigner, Daniel; Fuentes-Cobas, Luis; Sirera, Rafael; Calzada, M Lourdes

    2016-12-20

    The potential of UV-light for the photochemical synthesis and stabilization of non-equilibrium crystalline phases in thin films is demonstrated for the β-Bi2O3 polymorph. The pure β-Bi2O3 phase is thermodynamically stable at high temperature (450-667 °C), which limits its applications in devices. Here, a tailored UV-absorbing bismuth(III)-N-methyldiethanolamine complex is selected as an ideal precursor for this phase, in order to induce under UV-light the formation of a -Bi-O-Bi- continuous network in the deposited layers and the further conversion into the β-Bi2O3 polymorph at a temperature as low as 250 °C. The stabilization of the β-Bi2O3 films is confirmed by their conductivity behavior and a thorough characterization of their crystal structure. This is also supported by their remarkable photocatalytic activity. Besides, this processing method has allowed us for the first time the preparation of β-Bi2O3 films on flexible plastic substrates, which opens new opportunities for using these materials in potential applications not available until now (e.g., flexible photocatalytic reactors, self-cleaning surfaces or wearable antimicrobial fabrics). Therefore, photochemical solution deposition (PCSD) demonstrates to be not only an efficient approach for the low temperature processing of oxide films, but also an excellent alternative for the stabilization of metastable phases.

  19. Photochemical and antioxidant responses in the leaves of Xerophyta viscosa Baker and Digitaria sanguinalis L. under water deficit.

    PubMed

    Ekmekci, Yasemin; Bohms, Andreas; Thomson, Jennifer A; Mundree, Sagadevan G

    2005-01-01

    In this study, photochemical and antioxidant responses of the monocotyledonous resurrection plant Xerophyta viscosa Baker and the crab grass Digitaria sanguinalis L. under water deficit were investigated as a function of time. Water deficit was imposed by withholding irrigation for 21 d. Gas exchange and chlorophyll a fluorescence analyses indicated that the dehydration treatment caused photoinhibition in both species. The reduction in the photosynthesis rate in both species during water deficit probably contributed to the decline in the photochemical efficiency of PSII and electron transport rate. However, the stomatal conductance of both species did not change during treatment whereas the intercellular CO2 pressure increased after 10 d of water deficit treatment. These observations could be related to nonstomatal limitations. The increasing net transpiration rate of both species may have contributed to leaf cooling because of water limitations. Prolonged water deficit resulted in photosynthetic pigment chlorophyll (a + b) and carotenoids content loss in only D. sanguinalis. Both species especially D. sanguinalis had increased the level of anthocyanin after 15 d of treatment, possibly to prevent the damaging effect of photooxidation. The total SOD activity of D. sanguinalis was significantly different from X. viscosa during the treatment. The total peroxidase activity in D. sanguinalis was significantly higher than in X. viscosa. X. viscosa acclimated to water deficit with no ultimate apparent oxidative damage due to endogenous protective mechanisms of resurrection. In case of D. sanguinalis, water deficit induced considerable stress and possibly caused some oxidative damage, despite the upregulation of protection mechanisms.

  20. Photochemical solution processing of films of metastable phases for flexible devices: the β-Bi2O3 polymorph

    NASA Astrophysics Data System (ADS)

    Pérez-Mezcua, Dulce; Bretos, Iñigo; Jiménez, Ricardo; Ricote, Jesús; Jiménez-Rioboó, Rafael J.; da Silva, Cosmelina Gonçalves; Chateigner, Daniel; Fuentes-Cobas, Luis; Sirera, Rafael; Calzada, M. Lourdes

    2016-12-01

    The potential of UV-light for the photochemical synthesis and stabilization of non-equilibrium crystalline phases in thin films is demonstrated for the β-Bi2O3 polymorph. The pure β-Bi2O3 phase is thermodynamically stable at high temperature (450–667 °C), which limits its applications in devices. Here, a tailored UV-absorbing bismuth(III)-N-methyldiethanolamine complex is selected as an ideal precursor for this phase, in order to induce under UV-light the formation of a –Bi–O–Bi– continuous network in the deposited layers and the further conversion into the β-Bi2O3 polymorph at a temperature as low as 250 °C. The stabilization of the β-Bi2O3 films is confirmed by their conductivity behavior and a thorough characterization of their crystal structure. This is also supported by their remarkable photocatalytic activity. Besides, this processing method has allowed us for the first time the preparation of β-Bi2O3 films on flexible plastic substrates, which opens new opportunities for using these materials in potential applications not available until now (e.g., flexible photocatalytic reactors, self-cleaning surfaces or wearable antimicrobial fabrics). Therefore, photochemical solution deposition (PCSD) demonstrates to be not only an efficient approach for the low temperature processing of oxide films, but also an excellent alternative for the stabilization of metastable phases.

  1. Photochemical solution processing of films of metastable phases for flexible devices: the β-Bi2O3 polymorph

    PubMed Central

    Pérez-Mezcua, Dulce; Bretos, Iñigo; Jiménez, Ricardo; Ricote, Jesús; Jiménez-Rioboó, Rafael J.; da Silva, Cosmelina Gonçalves; Chateigner, Daniel; Fuentes-Cobas, Luis; Sirera, Rafael; Calzada, M. Lourdes

    2016-01-01

    The potential of UV-light for the photochemical synthesis and stabilization of non-equilibrium crystalline phases in thin films is demonstrated for the β-Bi2O3 polymorph. The pure β-Bi2O3 phase is thermodynamically stable at high temperature (450–667 °C), which limits its applications in devices. Here, a tailored UV-absorbing bismuth(III)-N-methyldiethanolamine complex is selected as an ideal precursor for this phase, in order to induce under UV-light the formation of a –Bi–O–Bi– continuous network in the deposited layers and the further conversion into the β-Bi2O3 polymorph at a temperature as low as 250 °C. The stabilization of the β-Bi2O3 films is confirmed by their conductivity behavior and a thorough characterization of their crystal structure. This is also supported by their remarkable photocatalytic activity. Besides, this processing method has allowed us for the first time the preparation of β-Bi2O3 films on flexible plastic substrates, which opens new opportunities for using these materials in potential applications not available until now (e.g., flexible photocatalytic reactors, self-cleaning surfaces or wearable antimicrobial fabrics). Therefore, photochemical solution deposition (PCSD) demonstrates to be not only an efficient approach for the low temperature processing of oxide films, but also an excellent alternative for the stabilization of metastable phases. PMID:27996042

  2. The actual status of Astronomy in Moldova

    NASA Astrophysics Data System (ADS)

    Gaina, A.

    The astronomical research in the Republic of Moldova after Nicolae Donitch (Donici)(1874-1956(?)) were renewed in 1957, when a satellites observations station was open in Chisinau. Fotometric observations and rotations of first Soviet artificial satellites were investigated under a program SPIN put in action by the Academy of Sciences of former Socialist Countries. The works were conducted by Assoc. prof. Dr. V. Grigorevskij, which conducted also research in variable stars. Later, at the beginning of 60-th, an astronomical Observatory at the Chisinau State University named after Lenin (actually: the State University of Moldova), placed in Lozovo-Ciuciuleni villages was open, which were coordinated by Odessa State University (Prof. V.P. Tsesevich) and the Astrosovet of the USSR. Two main groups worked in this area: first conducted by V. Grigorevskij (till 1971) and second conducted by L.I. Shakun (till 1988), both graduated from Odessa State University. Besides this research areas another astronomical observations were made: Comets observations, astroclimate and atmospheric optics in collaboration with the Institute of the Atmospheric optics of the Siberian branch of the USSR (V. Chernobai, I. Nacu, C. Usov and A.F. Poiata). Comets observations were also made since 1988 by D. I. Gorodetskij which came to Chisinau from Alma-Ata and collaborated with Ukrainean astronomers conducted by K.I. Churyumov. Another part of space research was made at the State University of Tiraspol since the beggining of 70-th by a group of teaching staff of the Tiraspol State Pedagogical University: M.D. Polanuer, V.S. Sholokhov. No a collaboration between Moldovan astronomers and Transdniestrian ones actually exist due to War in Transdniestria in 1992. An important area of research concerned the Radiophysics of the Ionosphere, which was conducted in Beltsy at the Beltsy State Pedagogical Institute by a group of teaching staff of the University since the beginning of 70-th: N. D. Filip, E

  3. Photochemical welding of silica optical components to silicone rubber by F2 laser

    NASA Astrophysics Data System (ADS)

    Okoshi, M.; Li, J.; Herman, P. R.; Inoue, N.

    2007-04-01

    Photochemical welding of fused silica glass to silicone rubber has been demonstrated by 157-nm F2 laser-induced photochemical modification of the silicone surface in contact with the glass. Fused-silica coverslips (150 m thick), silica optical fibres (125 µm diameter), and 2.9- µm diameter microspheres were successfully welded onto 2-mm-thick silicone rubber by irradiating the silicone surface through the partially transparent glasses. Sufficient photochemical conversion for strong welding was provided by multiple exposures of tens to thousands of pulses in a narrow optimized fluence window near ~6-mJ/cm2 per pulse.

  4. Catalytic combustion of actual low and medium heating value gases

    NASA Technical Reports Server (NTRS)

    Bulzan, D. L.

    1982-01-01

    Catalytic combustion of both low and medium heating value gases using actual coal derived gases obtained from operating gasifiers was demonstrated. A fixed bed gasifier with a complete product gas cleanup system was operated in an air blown mode to produce low heating value gas. A fluidized bed gasifier with a water quench product gas cleanup system was operated in both an air enriched and an oxygen blown mode to produce low and medium, heating value gas. Noble metal catalytic reactors were evaluated in 12 cm flow diameter test rigs on both low and medium heating value gases. Combustion efficiencies greater than 99.5% were obtained with all coal derived gaseous fuels. The NOx emissions ranged from 0.2 to 4 g NO2 kg fuel.

  5. Precursors for chemical and photochemical vapor deposition of copper metal

    NASA Astrophysics Data System (ADS)

    James, Alicia Marie

    The colorless square-planar cluster [CuN(SiMe3)2] 4, which contains four Cu(I) ions with four bridging amide groups, was studied as a precursor for chemical and photochemical vapor deposition of Cu metal. The cluster phosphoresces in CH2Cl2 solution and in the solid state at room temperature. Its electronic spectrum in CH 2Cl2 consists of two intense bands which are assigned to symmetry-allowed 3d → 4p transitions; the phosphorescence is also likely to be metal-centered. Solid [CuN(SiMe3)2]4 luminesces with approximately the same spectrum as that of the CH2Cl2 solutions. At 77 K, the solid-state luminescence red-shifts slightly. The emission lifetime in glassy Et2O solution is 690 mus. [CuN(SiMe3) 2]4 deposits Cu metal via chemical vapor deposition under H2 carrier gas at substrate temperatures of 145--200°C. Deposition also occurs photochemically beginning at 136--138°C under near-UV irradiation. The preparation of monomeric derivatives of [CuN(SiMe3) 2]4 was attempted by using neutral donor ligands L (e.g. LnCuN(SiMe3)2; L = CO, PR3, CN-t-Bu; n = 1--3). The target compounds were expected to be more volatile than the copper cluster and still maintain photosensitivity. CuCl and [Cu(CH 3CN)4]PF6 were used as starting materials. Even in the presence of L, [CuN(SiMe3)2] 4 is a major product in reactions using CuCl and NaN(SiCH3) 2- [Cu(CH3CN)4]PF6 was a promising route for the monomeric Cu(I) complexes because of ready dissociation of its acetonitrile ligands. However, the characterization of these complexes was unsuccessful. Other Cu(I) amide clusters have been prepared; they may also be suitable for chemical and photochemical vapor deposition of Cu. [CuNEt2] 4, [CuN(i-Pr)2]4, and [CuN(t-Bu)(SiMe 3)]4 are phosphorescent though they are very air sensitive. They should be more volatile and produce Cu metal films more readily than [CuN(SiMe3)2]4 Cu(hfac)2 is a versatile Lewis acid, forming adducts with a variety of bases. The bases that were used were ethylene

  6. Spectroscopic and photochemical characterization of a deep ocean proteorhodopsin.

    PubMed

    Wang, Wei-Wu; Sineshchekov, Oleg A; Spudich, Elena N; Spudich, John L

    2003-09-05

    A second group of proteorhodopsin-encoding genes (blue-absorbing proteorhodopsin, BPR) differing by 20-30% in predicted primary structure from the first-discovered green-absorbing (GPR) group has been detected in picoplankton from Hawaiian deep sea water. Here we compare BPR and GPR absorption spectra, photochemical reactions, and proton transport activity. The photochemical reaction cycle of Hawaiian deep ocean BPR in cells is 10-fold slower than that of GPR with very low accumulation of a deprotonated Schiff base intermediate in cells and exhibits mechanistic differences, some of which are due to its glutamine residue rather than leucine at position 105. In contrast to GPR and other characterized microbial rhodopsins, spectral titrations of BPR indicate that a second titratable group, in addition to the retinylidene Schiff base counterion Asp-97, modulates the absorption spectrum near neutral pH. Mutant analysis confirms that Asp-97 and Glu-108 are proton acceptor and proton donor, respectively, in retinylidene Schiff base proton transfer reactions during the BPR photocycle as previously shown for GPR, but BPR contains an alternative acceptor evident in its D97N mutant, possibly the same as the second titratable group modulating the absorption spectrum. BPR, similar to GPR, carries out outward light-driven proton transport in Escherichia coli vesicles but with a reduced translocation rate attributable to its slower photocycle. In energized E. coli cells at physiological pH, the net effect of BPR photocycling is to generate proton currents dominated by a triggered proton influx, rather than efflux as observed with GPR-containing cells. Reversal of the proton current with the K+-ionophore valinomycin supports that the influx is because of voltage-gated channels in the E. coli cell membrane. These observations demonstrate diversity in photochemistry and mechanism among proteorhodopsins. Calculations of photon fluence rates at different ocean depths show that the

  7. Potential Biosignatures in Super-Earth Atmospheres II. Photochemical Responses

    PubMed Central

    Gebauer, S.; Godolt, M.; Palczynski, K.; Rauer, H.; Stock, J.; von Paris, P.; Lehmann, R.; Selsis, F.

    2013-01-01

    Abstract Spectral characterization of super-Earth atmospheres for planets orbiting in the habitable zone of M dwarf stars is a key focus in exoplanet science. A central challenge is to understand and predict the expected spectral signals of atmospheric biosignatures (species associated with life). Our work applies a global-mean radiative-convective-photochemical column model assuming a planet with an Earth-like biomass and planetary development. We investigated planets with gravities of 1g and 3g and a surface pressure of 1 bar around central stars with spectral classes from M0 to M7. The spectral signals of the calculated planetary scenarios have been presented by in an earlier work by Rauer and colleagues. The main motivation of the present work is to perform a deeper analysis of the chemical processes in the planetary atmospheres. We apply a diagnostic tool, the Pathway Analysis Program, to shed light on the photochemical pathways that form and destroy biosignature species. Ozone is a potential biosignature for complex life. An important result of our analysis is a shift in the ozone photochemistry from mainly Chapman production (which dominates in Earth's stratosphere) to smog-dominated ozone production for planets in the habitable zone of cooler (M5–M7)-class dwarf stars. This result is associated with a lower energy flux in the UVB wavelength range from the central star, hence slower planetary atmospheric photolysis of molecular oxygen, which slows the Chapman ozone production. This is important for future atmospheric characterization missions because it provides an indication of different chemical environments that can lead to very different responses of ozone, for example, cosmic rays. Nitrous oxide, a biosignature for simple bacterial life, is favored for low stratospheric UV conditions, that is, on planets orbiting cooler stars. Transport of this species from its surface source to the stratosphere where it is destroyed can also be a key process

  8. Potential biosignatures in super-Earth atmospheres II. Photochemical responses.

    PubMed

    Grenfell, J L; Gebauer, S; Godolt, M; Palczynski, K; Rauer, H; Stock, J; von Paris, P; Lehmann, R; Selsis, F

    2013-05-01

    Spectral characterization of super-Earth atmospheres for planets orbiting in the habitable zone of M dwarf stars is a key focus in exoplanet science. A central challenge is to understand and predict the expected spectral signals of atmospheric biosignatures (species associated with life). Our work applies a global-mean radiative-convective-photochemical column model assuming a planet with an Earth-like biomass and planetary development. We investigated planets with gravities of 1g and 3g and a surface pressure of 1 bar around central stars with spectral classes from M0 to M7. The spectral signals of the calculated planetary scenarios have been presented by in an earlier work by Rauer and colleagues. The main motivation of the present work is to perform a deeper analysis of the chemical processes in the planetary atmospheres. We apply a diagnostic tool, the Pathway Analysis Program, to shed light on the photochemical pathways that form and destroy biosignature species. Ozone is a potential biosignature for complex life. An important result of our analysis is a shift in the ozone photochemistry from mainly Chapman production (which dominates in Earth's stratosphere) to smog-dominated ozone production for planets in the habitable zone of cooler (M5-M7)-class dwarf stars. This result is associated with a lower energy flux in the UVB wavelength range from the central star, hence slower planetary atmospheric photolysis of molecular oxygen, which slows the Chapman ozone production. This is important for future atmospheric characterization missions because it provides an indication of different chemical environments that can lead to very different responses of ozone, for example, cosmic rays. Nitrous oxide, a biosignature for simple bacterial life, is favored for low stratospheric UV conditions, that is, on planets orbiting cooler stars. Transport of this species from its surface source to the stratosphere where it is destroyed can also be a key process. Comparing 1g with

  9. Tracking Actual Usage: The Attention Metadata Approach

    ERIC Educational Resources Information Center

    Wolpers, Martin; Najjar, Jehad; Verbert, Katrien; Duval, Erik

    2007-01-01

    The information overload in learning and teaching scenarios is a main hindering factor for efficient and effective learning. New methods are needed to help teachers and students in dealing with the vast amount of available information and learning material. Our approach aims to utilize contextualized attention metadata to capture behavioural…

  10. Development of a photochemical source for the production and calibration of acyl peroxynitrate compounds

    NASA Astrophysics Data System (ADS)

    Veres, P. R.; Roberts, J. M.

    2015-05-01

    A dynamic system for the calibration of acyl peroxynitrate compounds (APNs) has been developed in the laboratory to reduce the difficulty, required time, and instability of laboratory-produced standards for difficult-to-synthesize APN species. In this work we present a photochemical source for the generation of APN standards: acetyl peroxynitrate (PAN), propionyl peroxynitrate (PPN), acryloyl peroxynitrate (APAN), methacryloyl peroxynitrate (MPAN), and crotonyl peroxynitrate (CPAN). APNs are generated via photolysis of a mixture of acyl chloride (RC(O)Cl) and ketone (RC(=O)R) precursor compounds in the presence of O2 and NO2. Subsequent separation by a prep-scale gas chromatograph and detection with a total NOy instrument serve to quantify the output of the APN source. Validation of the APN products was performed using iodide ion chemical ionization mass spectroscopy (I- CIMS). This method of standard production is an efficient and accurate technique for the calibration of instrumentation used to measure PAN, PPN, APAN, MPAN, and CPAN.

  11. Metal-free photochemical silylations and transfer hydrogenations of benzenoid hydrocarbons and graphene

    PubMed Central

    Papadakis, Raffaello; Li, Hu; Bergman, Joakim; Lundstedt, Anna; Jorner, Kjell; Ayub, Rabia; Haldar, Soumyajyoti; Jahn, Burkhard O.; Denisova, Aleksandra; Zietz, Burkhard; Lindh, Roland; Sanyal, Biplab; Grennberg, Helena; Leifer, Klaus; Ottosson, Henrik

    2016-01-01

    The first hydrogenation step of benzene, which is endergonic in the electronic ground state (S0), becomes exergonic in the first triplet state (T1). This is in line with Baird's rule, which tells that benzene is antiaromatic and destabilized in its T1 state and also in its first singlet excited state (S1), opposite to S0, where it is aromatic and remarkably unreactive. Here we utilized this feature to show that benzene and several polycyclic aromatic hydrocarbons (PAHs) to various extents undergo metal-free photochemical (hydro)silylations and transfer-hydrogenations at mild conditions, with the highest yield for naphthalene (photosilylation: 21%). Quantum chemical computations reveal that T1-state benzene is excellent at H-atom abstraction, while cyclooctatetraene, aromatic in the T1 and S1 states according to Baird's rule, is unreactive. Remarkably, also CVD-graphene on SiO2 is efficiently transfer-photohydrogenated using formic acid/water mixtures together with white light or solar irradiation under metal-free conditions. PMID:27708336

  12. Determination of total mercury in biological tissue by isotope dilution ICPMS after UV photochemical vapor generation.

    PubMed

    Liu, Rui; Xu, Mo; Shi, Zeming; Zhang, Jiayun; Gao, Ying; Yang, Lu

    2013-12-15

    A method is developed for the determination of trace mercury in biological samples using photo chemical vapor generation (PVG) and isotope dilution inductively coupled plasma mass spectrometry (ID ICPMS) detection. Biological tissues were solubilized in formic acid. Subsequently, the sample solutions were exposed to an ultraviolet (UV) source for the reduction of mercury into vapor species prior to ICPMS measurements. The formic acid served not only as a tissue solubilizer in the sample preparation procedure, but also as a photochemical reductant for mercury in the PVG process. The problem arising from the opaque formic acid digested solution was efficiently solved by using ID method. The optimum conditions for sample treatment and PVG were investigated. A limit of detection (LOD) of 0.5 pg g(-1), based on an external calibration, provided 350-fold improvement over that obtained by utilizing conventional pneumatic nebulization sample introduction. Method validation was demonstrated by the determination of total mercury in several biological tissue certified reference materials (CRMs). The results were in good agreement with the certified values.

  13. Metal-free photochemical silylations and transfer hydrogenations of benzenoid hydrocarbons and graphene.

    PubMed

    Papadakis, Raffaello; Li, Hu; Bergman, Joakim; Lundstedt, Anna; Jorner, Kjell; Ayub, Rabia; Haldar, Soumyajyoti; Jahn, Burkhard O; Denisova, Aleksandra; Zietz, Burkhard; Lindh, Roland; Sanyal, Biplab; Grennberg, Helena; Leifer, Klaus; Ottosson, Henrik

    2016-10-06

    The first hydrogenation step of benzene, which is endergonic in the electronic ground state (S0), becomes exergonic in the first triplet state (T1). This is in line with Baird's rule, which tells that benzene is antiaromatic and destabilized in its T1 state and also in its first singlet excited state (S1), opposite to S0, where it is aromatic and remarkably unreactive. Here we utilized this feature to show that benzene and several polycyclic aromatic hydrocarbons (PAHs) to various extents undergo metal-free photochemical (hydro)silylations and transfer-hydrogenations at mild conditions, with the highest yield for naphthalene (photosilylation: 21%). Quantum chemical computations reveal that T1-state benzene is excellent at H-atom abstraction, while cyclooctatetraene, aromatic in the T1 and S1 states according to Baird's rule, is unreactive. Remarkably, also CVD-graphene on SiO2 is efficiently transfer-photohydrogenated using formic acid/water mixtures together with white light or solar irradiation under metal-free conditions.

  14. Photochemical cycling of iron mediated by dicarboxylates: special effect of malonate.

    PubMed

    Wang, Zhaohui; Chen, Xi; Ji, Hongwei; Ma, Wanhong; Chen, Chuncheng; Zhao, Jincai

    2010-01-01

    Photochemical redox cycling of iron coupled with oxidation of malonate (Mal) ligand has been investigated under conditions that are representative of atmospheric waters. Malonate exhibited significantly different characteristics from oxalate and other dicarboxylates (or monocarboxylates). Both strong chelating ability with Fe(III) and strong molar absorptivities, but much low efficiency of Fe(II) formation (Phi(Fe(II)) = 0.0022 +/- 0.0009, 300-366 nm) were observed for Fe(III)-Mal complexes (FMCs). Fe(III) speciation calculation indicated that Mal is capable of mediating the proportion between two photoactive species of Fe(III)-OH complexes and FMCs by changing the Mal concentration. Spin-trapping electron spin resonance (ESR) experiments proved the formation of both the (.)CH(2)COOH and (.)OH radicals at lower total Mal concentration ([Mal](T)), but only (.)CH(2)COOH at higher concentrations of malonate, providing strong evidence for competition between malonate and OH(-) and subsequent different photoreaction pathways. Once FMCs dominate the Fe(III) speciation, both photoproduction and photocatalyzed oxidation of Fe(II) will be greatly decelerated. There exists an induction period for both formation and decay of Fe(II) until Fe(III)(OH)(2+) species become the prevailing Fe(III) forms over FMCs as Mal ligand is depleted. A quenching mechanism of Mal in the Fe(II) photoproduction is proposed. The present study is meaningful to advance our understanding of iron cycling in acidified carbon-rich atmospheric waters.

  15. The photochemical reflectance index provides an optical indicator of spring photosynthetic activation in evergreen conifers.

    PubMed

    Wong, Christopher Y S; Gamon, John A

    2015-04-01

    In evergreens, the seasonal down-regulation and reactivation of photosynthesis is largely invisible and difficult to assess with remote sensing. This invisible phenology may be changing as a result of climate change. To better understand the mechanism and timing of these hidden physiological transitions, we explored several assays and optical indicators of spring photosynthetic activation in conifers exposed to a boreal climate. The photochemical reflectance index (PRI), chlorophyll fluorescence, and leaf pigments for evergreen conifer seedlings were monitored over 1 yr of a boreal climate with the addition of gas exchange during the spring. PRI, electron transport rate, pigment levels, light-use efficiency and photosynthesis all exhibited striking seasonal changes, with varying kinetics and strengths of correlation, which were used to evaluate the mechanisms and timing of spring activation. PRI and pigment pools were closely timed with photosynthetic reactivation measured by gas exchange. The PRI provided a clear optical indicator of spring photosynthetic activation that was detectable at leaf and stand scales in conifers. We propose that PRI might provide a useful metric of effective growing season length amenable to remote sensing and could improve remote-sensing-driven models of carbon uptake in evergreen ecosystems.

  16. Metal-free photochemical silylations and transfer hydrogenations of benzenoid hydrocarbons and graphene

    NASA Astrophysics Data System (ADS)

    Papadakis, Raffaello; Li, Hu; Bergman, Joakim; Lundstedt, Anna; Jorner, Kjell; Ayub, Rabia; Haldar, Soumyajyoti; Jahn, Burkhard O.; Denisova, Aleksandra; Zietz, Burkhard; Lindh, Roland; Sanyal, Biplab; Grennberg, Helena; Leifer, Klaus; Ottosson, Henrik

    2016-10-01

    The first hydrogenation step of benzene, which is endergonic in the electronic ground state (S0), becomes exergonic in the first triplet state (T1). This is in line with Baird's rule, which tells that benzene is antiaromatic and destabilized in its T1 state and also in its first singlet excited state (S1), opposite to S0, where it is aromatic and remarkably unreactive. Here we utilized this feature to show that benzene and several polycyclic aromatic hydrocarbons (PAHs) to various extents undergo metal-free photochemical (hydro)silylations and transfer-hydrogenations at mild conditions, with the highest yield for naphthalene (photosilylation: 21%). Quantum chemical computations reveal that T1-state benzene is excellent at H-atom abstraction, while cyclooctatetraene, aromatic in the T1 and S1 states according to Baird's rule, is unreactive. Remarkably, also CVD-graphene on SiO2 is efficiently transfer-photohydrogenated using formic acid/water mixtures together with white light or solar irradiation under metal-free conditions.

  17. Photochemical and photocatalytic evaluation of 1D titanate/TiO2 based nanomaterials

    NASA Astrophysics Data System (ADS)

    Conceição, D. S.; Ferreira, D. P.; Graça, C. A. L.; Júlio, M. F.; Ilharco, L. M.; Velosa, A. C.; Santos, P. F.; Vieira Ferreira, L. F.

    2017-01-01

    One-dimensional (1D) titanate based nanomaterials were synthesized following an alkaline hydrothermal approach of commercial TiO2 nanopowder. The morphological features of all materials were monitored by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and also Brunauer-Emmett-Teller (BET) technique. In addition the photochemical behaviour of these nanostructured materials were evaluated with the use of laser induced luminescence (LIL), ground-state diffuse reflectance (GSDR), and laser-flash photolysis in diffuse reflectance mode (DRLFP). The mixed titanate/TiO2 nanowires presented the least intense fluorescence spectra, suggesting the presence of surficial defects that can extend the lifetime of the excited charge carriers. A fluorescent 'rhodamine-like' dye was adsorbed onto different materials and examined via photoexcitation in the visible range to study the self-photosensitization mechanism. The presence of the radical cation of the dye and the degradation kinetics, when compared with a neutral substrate-cellulose, provided significant evidences regarding the photoactivity of the different materials. Regarding all the materials under study, the nanowires exhibited a strong photocatalytic efficiency, for the adsorbed fluorescent probe. The photocatalytic mechanism was also considered by studying the photodegradation capability of the titanate based materials in the presence of an herbicide, Amicarbazone, after ultraviolet (UVA) photoexcitation.

  18. Caustic-Side Solvent Extraction: Prediction of Cesium Extraction for Actual Wastes and Actual Waste Simulants

    SciTech Connect

    Delmau, L.H.; Haverlock, T.J.; Sloop, F.V., Jr.; Moyer, B.A.

    2003-02-01

    This report presents the work that followed the CSSX model development completed in FY2002. The developed cesium and potassium extraction model was based on extraction data obtained from simple aqueous media. It was tested to ensure the validity of the prediction for the cesium extraction from actual waste. Compositions of the actual tank waste were obtained from the Savannah River Site personnel and were used to prepare defined simulants and to predict cesium distribution ratios using the model. It was therefore possible to compare the cesium distribution ratios obtained from the actual waste, the simulant, and the predicted values. It was determined that the predicted values agree with the measured values for the simulants. Predicted values also agreed, with three exceptions, with measured values for the tank wastes. Discrepancies were attributed in part to the uncertainty in the cation/anion balance in the actual waste composition, but likely more so to the uncertainty in the potassium concentration in the waste, given the demonstrated large competing effect of this metal on cesium extraction. It was demonstrated that the upper limit for the potassium concentration in the feed ought to not exceed 0.05 M in order to maintain suitable cesium distribution ratios.

  19. Investigation of the Coupled Effects of Molecular Weight and Charge-Transfer Interactions on the Optical and Photochemical Properties of Dissolved Organic Matter.

    PubMed

    McKay, Garrett; Couch, Kylie D; Mezyk, Stephen P; Rosario-Ortiz, Fernando L

    2016-08-02

    We studied the formation of photochemically produced reactive intermediates (RI) from dissolved organic matter (DOM). Specifically, we focused on the effects of variable molecular weight and chemical reduction on the optical properties of DOM (absorbance and fluorescence) and the formation of singlet oxygen ((1)O2), DOM triplet excited states ((3)DOM*), and the hydroxyl radical ((•)OH). The data are largely evaluated in terms of a charge-transfer (CT) model, but deficiencies in the model to explain the data are pointed out when evident. A total of two sets of samples were studied that were subjected to different treatments; the first set included secondary-treated wastewaters and a wastewater-impacted stream, and the second was a DOM isolate. Treatments included size fractionation and chemical reduction using sodium borohydride. Taken as a whole, the results demonstrate that decreasing molecular weight and borohydride reduction work in opposition regarding quantum efficiencies for (1)O2 and (3)DOM* production but in concert for fluorescence and (•)OH production. The optical and photochemical data provide evidence for a limited role of CT interactions occurring in lower-molecular-weight DOM molecules. In addition, the data suggest that the observed optical and photochemical properties of DOM are a result of multiple populations of chromophores and that their relative contribution is changed by molecular-weight fractionation and borohydride reduction.

  20. Tree size and light availability increase photochemical instead of non-photochemical capacities of Nothofagus nitida trees growing in an evergreen temperate rain forest.

    PubMed

    Coopman, Rafael E; Briceño, Verónica F; Corcuera, Luis J; Reyes-Díaz, Marjorie; Alvarez, Daniela; Sáez, Katherine; García-Plazaola, José I; Alberdi, Miren; Bravo, León A

    2011-10-01

    Nothofagus nitida (Phil.) Krasser (Nothofagaceae) regenerates under the canopy in microsites protected from high light. Nonetheless, it is common to find older saplings in clear areas and adults as emergent trees of the Chilean evergreen forest. We hypothesized that this shade to sun transition in N. nitida is supported by an increase in photochemical and non-photochemical energy dissipation capacities of both photosystems in parallel with the increase in plant size and light availability. To dissect the relative contribution of light environment and plant developmental stage to these physiological responses, the photosynthetic performance of both photosystems was studied from the morpho-anatomical to the biochemical level in current-year leaves of N. nitida plants of different heights (ranging from 0.1 to 7 m) growing under contrasting light environments (integrated quantum flux (IQF) 5-40 mol m(-2). Tree height (TH) and light environment (IQF) independently increased the saturated electron transport rates of both photosystems, as well as leaf and palisade thickness, but non-photochemical energy flux, photoinhibition susceptibility, state transition capacity, and the contents of D1 and PsbS proteins were not affected by IQF and TH. Spongy mesophyll thickness and palisade cell diameter decreased with IQF and TH. A(max), light compensation and saturation points, Rubisco and nitrogen content (area basis) only increased with light environment (IQF), whereas dark respiration (R(d)) decreased slightly and relative chlorophyll content was higher in taller trees. Overall, the independent effects of more illuminated environment and tree height mainly increased the photochemical instead of the non-photochemical energy flux. Regardless of the photochemical increase with TH, carbon assimilation only significantly improved with higher IQF. Therefore it seems that mainly acclimation to the light environment supports the phenotypic transition of N. nitida from shade to

  1. Examining ruthenium chromophores for the photochemical reduction of CO2 to methanol

    NASA Astrophysics Data System (ADS)

    Boston, David J.

    Our consumption of energy for transportation and electricity has been growing as quickly as our population. As this demand for energy increases we increase our production of carbon dioxide by the burning of fossil fuels to try and meet this increasing demand. A sustainable method to convert carbon dioxide (CO2) to a viable liquid fuel is one potential way in which both the increasing energy demand and increasing CO2 concentration issues can both be helped. Currently such methods being investigated include thermal, electrochemical, and photochemical processes. Because thermal conversion is not an ideal situation because of the requirement of strong reducing agents or extreme conditions such as steam reformation reactions, we need to find better alternatives such as electrochemical and photochemical methods. Both electrochemical and photochemical methods have the ability to be sustainable, however, the vast majority of these systems are limited to producing CO and/or formic acid, with only a few performing deeper reduction to products such formaldehyde, methanol and methane. All of the systems capable of reducing CO2 past two electrons involve either a heterogeneous catalyst (e.g. TiO2) or an electrode. In recent times Bocarsly and coworkers have shown that pyridine was capable of reducing CO2 to methanol through a sequential process of proton and electron transfers. This process seems to start with the formation of a CO2-pyridine adduct in solution that is reduced one more time to form formate/formic acid. The next reduction is a slow process and allows for a buildup of formate in solution leading to a higher formate concentration in solution. The subsequent reductions seem to occur very rapidly and form methanol at good efficiencies. Theoretical work done recently has argued for the necessity of the Pt, Pd, or GaP surface in the electrochemistry. Carter and coworkers have claimed that the surface of the electrode is a necessary part of the catalysis with the

  2. A Photochemical Reactor for the Study of Kinetics and Adsorption Phenomena

    ERIC Educational Resources Information Center

    Poce-Fatou, J. A.; Gil, M. L. A.; Alcantara, R.; Botella, C.; Martin, J.

    2004-01-01

    The interaction between light and matter is examined with the help of a photochemical experiment. This experiment is useful for the investigation of heterogeneous catalysis, semiconductor properties and adsorption phenomena.

  3. Electronic-carrier-controlled photochemical etching process in semiconductor device fabrication

    DOEpatents

    Ashby, C.I.H.; Myers, D.R.; Vook, F.L.

    1988-06-16

    An electronic-carrier-controlled photochemical etching process for carrying out patterning and selective removing of material in semiconductor device fabrication includes the steps of selective ion implanting, photochemical dry etching, and thermal annealing, in that order. In the selective ion implanting step, regions of the semiconductor material in a desired pattern are damaged and the remainder of the regions of the material not implanted are left undamaged. The rate of recombination of electrons and holes is increased in the damaged regions of the pattern compared to undamaged regions. In the photochemical dry etching step which follows ion implanting step, the material in the undamaged regions of the semiconductor are removed substantially faster than in the damaged regions representing the pattern, leaving the ion-implanted, damaged regions as raised surface structures on the semiconductor material. After completion of photochemical dry etching step, the thermal annealing step is used to restore the electrical conductivity of the damaged regions of the semiconductor material.

  4. Electronic-carrier-controlled photochemical etching process in semiconductor device fabrication

    DOEpatents

    Ashby, Carol I. H.; Myers, David R.; Vook, Frederick L.

    1989-01-01

    An electronic-carrier-controlled photochemical etching process for carrying out patterning and selective removing of material in semiconductor device fabrication includes the steps of selective ion implanting, photochemical dry etching, and thermal annealing, in that order. In the selective ion implanting step, regions of the semiconductor material in a desired pattern are damaged and the remainder of the regions of the material not implanted are left undamaged. The rate of recombination of electrons and holes is increased in the damaged regions of the pattern compared to undamaged regions. In the photochemical dry etching step which follows ion implanting step, the material in the undamaged regions of the semiconductor are removed substantially faster than in the damaged regions representing the pattern, leaving the ion-implanted, damaged regions as raised surface structures on the semiconductor material. After completion of photochemical dry etching step, the thermal annealing step is used to restore the electrical conductivity of the damaged regions of the semiconductor material.

  5. APPLICATION OF BAYESIAN MONTE CARLO ANALYSIS TO A LAGRANGIAN PHOTOCHEMICAL AIR QUALITY MODEL. (R824792)

    EPA Science Inventory

    Uncertainties in ozone concentrations predicted with a Lagrangian photochemical air quality model have been estimated using Bayesian Monte Carlo (BMC) analysis. Bayesian Monte Carlo analysis provides a means of combining subjective "prior" uncertainty estimates developed ...

  6. Chemical kinetics and photochemical data for use in stratospheric modeling: Evaluation number 5

    NASA Technical Reports Server (NTRS)

    Demore, W. B.

    1982-01-01

    Sets of rate constants and photochemical cross sections compiled which were evaluated. The primary application of the data is in the modeling of stratospheric processes on the ozone layer and its possible perturbation by anthropogenic and natural phenomena are emphasized.

  7. Axi-symmetrical flow reactor for [sup 196]Hg photochemical enrichment

    DOEpatents

    Grossman, M.W.

    1991-04-30

    The present invention is directed to an improved photochemical reactor useful for the isotopic enrichment of a predetermined isotope of mercury, especially, [sup 196]Hg. Specifically, two axi-symmetrical flow reactors were constructed according to the teachings of the present invention. These reactors improve the mixing of the reactants during the photochemical enrichment process, affording higher yields of the desired [sup 196]Hg product. Measurements of the variation of yield (Y) and enrichment factor (E) along the flow axis of these reactors indicates very substantial improvement in process uniformity compared to previously used photochemical reactor systems. In one preferred embodiment of the present invention, the photoreactor system was built such that the reactor chamber was removable from the system without disturbing the location of either the photochemical lamp or the filter employed therewith. 10 figures.

  8. Axi-symmetrical flow reactor for .sup.196 Hg photochemical enrichment

    DOEpatents

    Grossman, Mark W.

    1991-01-01

    The present invention is directed to an improved photochemical reactor useful for the isotopic enrichment of a predetermined isotope of mercury, especially, .sup.196 Hg. Specifically, two axi-symmetrical flow reactors were constructed according to the teachings of the present invention. These reactors improve the mixing of the reactants during the photochemical enrichment process, affording higher yields of the desired .sup.196 Hg product. Measurements of the variation of yield (Y) and enrichment factor (E) along the flow axis of these reactors indicates very substantial improvement in process uniformity compared to previously used photochemical reactor systems. In one preferred embodiment of the present invention, the photoreactor system was built such that the reactor chamber was removable from the system without disturbing the location of either the photochemical lamp or the filter employed therewith.

  9. Chemical kinetics and photochemical data for use in stratospheric modeling. Evaluation number 6

    NASA Technical Reports Server (NTRS)

    Demore, W. B.; Molina, M. J.; Watson, R. T.; Golden, D. M.; Hampson, R. F.; Kurylo, M. J.; Howard, C. J.; Ravishankara, A. R.

    1983-01-01

    Evaluated sets of rate constants and photochemical cross sections are presented. The primary application of the data is in the modeling of stratospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena.

  10. Inhalation of Photochemically Altered Urban Mixtures Depresses Cardiac Function in Mice

    EPA Science Inventory

    Rationale: Epidemiological studies have indicated an association between urban air pollution exposure and cardiovascular morbidity and mortality. The present study was designed to evaluate the cardiac effects of inhaled photochemical products in urban mixtures in a murine model. ...

  11. On-line method of determining utilization factor in Hg-196 photochemical separation process

    DOEpatents

    Grossman, Mark W.; Moskowitz, Philip E.

    1992-01-01

    The present invention is directed to a method for determining the utilization factor [U] in a photochemical mercury enrichment process (.sup.196 Hg) by measuring relative .sup.196 Hg densities using absorption spectroscopy.

  12. Carrier-lifetime-controlled selective etching process for semiconductors using photochemical etching

    DOEpatents

    Ashby, Carol I. H.; Myers, David R.

    1992-01-01

    The minority carrier lifetime is significantly much shorter in semiconductor materials with very high impurity concentrations than it is in semiconductor materials with lower impurity concentration levels. This phenomenon of reduced minority carrier lifetime in semiconductor materials having high impurity concentration is utilized to advantage for permitting highly selective semiconductor material etching to be achieved using a carrier-driven photochemical etching reaction. Various means may be employed for increasing the local impurity concentration level in specific near-surface regions of a semiconductor prior to subjecting the semiconductor material to a carrier-driven photochemical etching reaction. The regions having the localized increased impurity concentration form a self-aligned mask inhibiting photochemical etching at such localized regions while the adjacent regions not having increased impurity concentrations are selectively photochemically etched. Liquid- or gas-phase etching may be performed.

  13. Photochemical Synthesis of Silver Nanodecahedrons and Related Nanostructures for Plasmonic Field Enhancement Applications

    NASA Astrophysics Data System (ADS)

    Lu, Haifei

    Noble-metal nanocrystals have received considerable attention in recent years for their size and shape dependent localized surface Plasmon resonances (LSPR). Various applications based on colloidal nanoparticles, such as surface enhanced Raman scattering (SERS), surface enhanced fluorescence (SEF), plasmonic sensing, photothermal therapy etc., have been broadly explored in the field of biomedicine, because of their extremely large optical scattering and absorption cross sections, as well as giant electric field enhancement on their surface. However, despite its high chemical stability, gold exhibits quite large losses and electric field enhancement is comparatively weaker than silver. Silver nanoparticles synthesized by the traditional technique only cover an LSPR ranged from 420~500 nm. On the other hand, the range of 500~660 nm, which is covered by several easily available commercial laser lines, very limited colloidal silver nanostructures with controllable size and shape have been reported, and realization of tuning the resonance to longer wavelengths is very important for the practical applications. In this thesis, a systematic study on photochemical synthesis of silver nanodecahedrons (NDs) and related nanostructures, and their plasmonic field enhancements are presented. First, the roles of chemicals and the light source during the formation of silver nanoparticles have been studied. We have also developed a preparation route for the production size-controlled silver nanodecahedrons (LSPR range 420 ~ 660 nm) in high purity. Indeed our experiments indicate that both the chemicals and the light sources can affect the shape and purity of final products. Adjusting the molar ratio between sodium citrate and silver nitrate can help to control the crystal structure following rapid reduction from sodium borohydride. Light from a blue LED (465 nm) can efficiently transform the polyvinylpyrrolidone stabilized small silver nanoparticles into silver NDs through photo

  14. Atmospheric photochemical degradation of 1,4-unsaturated dicarbonyls

    SciTech Connect

    Liu, X.; Jeffries, H.E.; Sexton, K.G.

    1999-12-01

    To better understand fates of aromatics hydrocarbon species in the atmosphere, the authors have investigated the transformation chemistry of butenedial (CHOCH{double{underscore}bond}CHCHO), 4-oxo-2-pentenal (CH{sub 3}COCH{double{underscore}bond}CHCHO), and 3-hexene-2, 5-dione (CH{sub 3}COCH{double{underscore}bond}CHCOCH{sub 3}). These 1,4-unsaturated dicarbonyls are known to be products of aromatic photochemical oxidation. Both hydroxyl radical (OH) and ozone (O{sub 3}) initiated smog chamber experiments under atmospheric conditions were conducted in the University of North Carolina outdoor smog chamber. Carbonyl intermediates and products were measured using the O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine derivatization method followed by gas chromatography/ion trap mass spectrometry analysis. Carbonyl products detected and identified by comparison with standards in the OH-initiated photooxidation of butenedial include formaldehyde, acrolein, glycolaldehyde, glyoxal, and malonaldehyde (CHOCH{sub 2}CHO). For 4-oxo-2-pentenal, the carbonyl products were formaldehyde, methyl vinyl ketone, glycolaldehyde, hydroxyacetone, glyoxal, methylglyoxal, and malonaldehyde. for 3-hexene-2,5-dione the products were formaldehyde, acetaldehyde, acetone, hydroxyacetone, and methylglyoxal. Carbonyl products detected in the P{sub 3}-initiated experiments with cyclohexane as the OH scavenger were formaldehyde and glyoxal in butenedial; formaldehyde, glyoxal, methyl-glyoxal, and malonaldehyde in 4-oxo-2-pentenal; and formaldehyde and methylglyoxal in 3-hexene-2,5-dione.

  15. Photochemical Studies of Chemistry in the Outer Solar System

    NASA Technical Reports Server (NTRS)

    Yung, Yuk L.

    2003-01-01

    The goal of the proposed science investigation is to gain a quantitative understanding of chemical processes and their coupling with atmospheric dynamics in the reducing atmospheres of the outer solar system, with a particular focus on Infrared Space Observatory (ISO) observations and future experiments such as the Cassini Mission to Saturn and Titan. The proposed work is divided into two related tasks. We have carried out a systematic comparison between atmospheric models for every giant planet and Titan, which employ a consistent set of photochemical reactions. Combined with recent observations of hydrocarbon species by ISO, this can provide the most rigorous test of our current understanding of the photochemistry of hydrocarbon in the outer solar system. The emphasis will be on the methyl radical (CH3), first detected by IS0 in the atmospheres of Saturn and Neptune (Bezard et al. 1998). CH3 is one of the most important radicals in the hydrocarbon photochemistry because it is the primary product of methane photolysis and plays an essential role in forming C2H6, the most abundant and stable C2 species. A fundamental understanding of the distribution of CH3 provides unique insights into the chemistry of hydrocarbons as well as comparative planetology.

  16. Photochemical degradation of Corexit components in ocean water.

    PubMed

    Glover, Caitlin M; Mezyk, Stephen P; Linden, Karl G; Rosario-Ortiz, Fernando L

    2014-09-01

    Due to the large quantities of dispersants used during the Deepwater Horizon spill in 2010, there were immediate concerns with regards to the fate and transport of the mixture in ocean waters. Direct and sensitized photolysis experiments were carried out for two compounds chosen as surrogates for the Corexit mixture (9500 and 9527) that were applied to surface waters during the oil spill in the Gulf of Mexico. The results showed that direct photolysis did not contribute significantly to the overall degradation (max ∼30%), therefore the focus shifted to sensitized photolysis, specifically the degradation stemming from the reaction rate with hydroxyl radical (HO). The direct photochemical degradation rates for two of the compounds, dioctyl sulfosuccinate (DOSS) and dipropylene glycol butyl ether (DGBE) were measured as 4.29×10(-6)s(-1) and 5.95×10(-6)s(-1), respectively; whereas the overall degradation rate in ocean water was 1.56×10(-5)s(-1) and 2.23×10(-5)s(-1). The formation rates and apparent quantum yields for HO formation were determined for six ocean water samples. The values ranged from 1.81×10(-5) near shore to 0.061×10(-5) for the open ocean. These degradation rates suggest the possibility for photolysis to play a role in the overall fate of Corexit.

  17. Spectroscopic and photochemical properties of open-chain carotenoids.

    SciTech Connect

    Frank, H. A.; Josue, J. S.; Bautista, J. A.; van der Hoef, I.; Jansen, F. J.; Lugtenburg, J.; Wiederrecht, G.; Christensen, R. L.; Chemistry; Univ. of Connecticut; Leiden Univ.; Bowdoin College

    2002-02-28

    The spectroscopic properties of open-chain, all-trans-C{sub 30} carotenoids having seven, eight and nine {pi}-electron conjugated carbon-carbon double bonds were studied using steady-state absorption, fluorescence, fluorescence excitation and time-resolved absorption spectroscopy. These diapocarotenes were purified by high performance liquid chromatography (HPLC) prior to the spectroscopic experiments. The fluorescence data show a systematic crossover from dominant S{sub 1} {yields} S{sub 0} (2{sup 1}Ag{yields} 1{sup 1}Ag) emission to dominant S{sub 2} {yields} S{sub 0} (1{sup 1}Bu {yields} 1{sup 1}Ag) with increasing extent of conjugation. The low temperatures facilitated the determination of the spectral origins of the S{sub 1} {yields} S{sub 0} (2{sup 1}Ag {yields} 1{sup 1}Ag) emissions, which were assigned by Gaussian deconvolution of the experimental line shapes. The lifetimes of the S{sub 1} states of the molecules were measured by transient absorption spectroscopy and were found to decrease as the conjugated chain length increases. The energy gap law for radiationless transitions is used to correlate the S{sub 1} energies with the dynamics. These molecules provide a systematic series for understanding the structural features that control the photochemical properties of open-chain, diapocarotenoids. The implications of these results on the roles of carotenoids in photosynthetic organisms are discussed.

  18. Spectrofluorimetric determination of tetrabenazine after photochemical derivatization in basic medium

    NASA Astrophysics Data System (ADS)

    Osório, Ana C. P.; da Cunha, Alessandra L. M. C.; Khan, Sarzamin; Ponciano, Cássia R.; Aucélio, Ricardo Q.

    Photochemical derivatization is proposed for the spectrofluorimetric determination of tetrabenazine (TBZ). A central composite design was used to adjust experimental conditions (60 min of UV in a 0.45 mol L-1 NaOH solution) enabling the improvement of the analyte signal-to-blank ratio of one order of magnitude, when compared to the TBZ original fluorescence. Limit of quantification was 4.7 × 10-8 mol L-1 but the detection power can be improved at least 10 times using solid phase extraction that also allows the separation of the analyte from matrix components, enabling the analysis of biologic fluids. Linear range covered at least three orders of magnitude. The combined uncertainty of the determination (at a 5 × 10-6 mol L-1) was 16%. Recoveries of TBZ in the analyses of a pharmaceutical formulation were in agreement with the ones obtained using a HPLC method. Recovery in saliva (5 × 10-7 mol L-1 of TBZ) was 90 ± 3% (n = 3). The procedure minimizes the use of toxic chemical derivatization reagents and the generation of hazardous waste.

  19. Photochemical-dynamical models of externally FUV irradiated protoplanetary discs

    NASA Astrophysics Data System (ADS)

    Haworth, Thomas J.; Boubert, Douglas; Facchini, Stefano; Bisbas, Thomas G.; Clarke, Cathie J.

    2016-12-01

    There is growing theoretical and observational evidence that protoplanetary disc evolution may be significantly affected by the canonical levels of far-ultraviolet (FUV) radiation found in a star-forming environment, leading to substantial stripping of material from the disc outer edge even in the absence of nearby massive stars. In this paper, we perform the first full radiation hydrodynamic simulations of the flow from the outer rim of protoplanetary discs externally irradiated by such intermediate strength FUV fields, including direct modelling of the photon-dominated region which is required to accurately compute the thermal properties. We find excellent agreement between our models and the semi-analytic models of Facchini et al. (2016) for the profile of the flow itself, as well as the mass-loss rate and location of their `critical radius'. This both validates their results (which differed significantly from prior semi-analytic estimates) and our new numerical method, the latter of which can now be applied to elements of the problem that the semi-analytic approaches are incapable of modelling. We also obtain the composition of the flow, but given the simple geometry of our models we can only hint at some diagnostics for future observations of externally irradiated discs at this stage. We also discuss the potential for these models as benchmarks for future photochemical-dynamical codes.

  20. Photochemically and Thermally Cross-Linkable Polyconjugated Systems

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This project focused on the synthesis and characterization of water soluble and/or water-borne electrically conducting polymer systems that could be cross-linked thermally or photochemically. The development of these materials was carried out so that they could be applied as metal and fabric coatings. Polyaniline and polypyrrole were the polymers under investigation. The main impediment preventing commercial development of these polymers is their inherent insolubility. Methods employed to enhance polymer solubility were monomer or polymer modifications. Some post-polymerization modifications were attempted to derivatize the parent polymers, These involved attachment of suitable pendant groups that would enhance polar solvent solubility. The pendant groups of these derivatized polymers were then further reacted to cross-link, rendering the polymer insoluble. The other modifications involved polymerization of monomers in the presence of polyelectrolytic polymers. The acid functionalities of the electrolyte served as a template/dopant for monomer alignment/complexation before polymerization, resulting in a water-borne composite or complex.

  1. Photochemical pollution at two southern California smog receptor sites

    SciTech Connect

    Grosjean, D.; Williams, E.L. II. )

    1992-06-01

    A one-year survey of air quality has been carried out at two southern California inland locations, Perris and Palm Springs to evaluate transport of photochemical smog from the Los Angeles area and to assess population exposure to toxic air pollutants in the Coachella Valley and eastern Riverside County. Air pollutants measured included formaldehyde, acetaldehyde, nitric acid, and peroxyacetyl nitrate (PAN). Acetic acid was also measured as part of the time-integrated method employed to measure PAN. In addition, intensive studies were carried out at both locations and included measurements of aldehydes, nitric acid, PAN, peroxypropionyl nitrate (PPN), methylchloroform and tetrachloroethylene. Maximum concentrations of HCHO, CH{sub 3}CHO, HNO{sub 3}, PAN, PPN, CH{sub 3}COOH and C{sub 2}Cl{sub 4} were 26, 21, 4.5, 7.6, 0.42, 6.6 and 0.29 ppb in Palm Springs and 15, 30, 6.3, 9.1, 0.73, 7.8 and 0.43 ppb in Perris. Pollutant concentrations measured in Palm Springs and Perris are compared to those measured in the Los Angeles area, and are discussed in terms of formation and removal during transport.

  2. van Hove Singularity Enhanced Photochemical Reactivity of Twisted Bilayer Graphene.

    PubMed

    Liao, Lei; Wang, Huan; Peng, Han; Yin, Jianbo; Koh, Ai Leen; Chen, Yulin; Xie, Qin; Peng, Hailin; Liu, Zhongfan

    2015-08-12

    Twisted bilayer graphene (tBLG) exhibits van Hove singularities (VHSs) in the density of states that can be tuned by changing the twist angle (θ), sparking various novel physical phenomena. Much effort has been devoted to investigate the θ-dependent physical properties of tBLG. Yet, the chemical properties of tBLG with VHSs, especially the chemical reactivity, remain unexplored. Here we report the first systematic study on the chemistry of tBLG through the photochemical reaction between graphene and benzoyl peroxide. Twisted bilayer graphene exhibits θ-dependent reactivity, and remarkably enhanced reactivity is obtained when the energy of incident laser matches with the energy interval of the VHSs of tBLG. This work provides an insight on the chemistry of tBLG, and the successful enhancement of chemical reactivity derived from VHS is highly beneficial for the controllable chemical modification of tBLG as well as the development of tBLG based devices.

  3. Isotopic ratio of nitrogen on Titan: Photochemical interpretation

    NASA Astrophysics Data System (ADS)

    Krasnopolsky, Vladimir A.

    2016-12-01

    Nitrogen isotope fractionation in predissociation of N2 (Liang et al., 2007) is combined with production of N(4S), N(2D), and N+ in dissociation and dissociative ionization by the solar EUV photons, photoelectrons, magnetospheric electrons and protons, and cosmic rays from the photochemical model. The calculated 14N/15N ratio in nitriles is 57, in excellent agreement with the observed ratio in HCN. Loss of nitrogen in condensation and polymerization of nitriles is 392 g cm-2 Byr-1 with nitrogen isotope fractionation factor of 2.8. Loss of nitrogen by sputtering is 57 g cm-2 Byr-1 (De La Haye et al., 2007) with fractionation factor of 0.73 (Mandt et al., 2014). If the current loss was constant throughout the age of the Solar System, then the initial 14N/15N ratio on Titan is 129, similar to 127±32 for ammonia in comets (Rousselot et al., 2014). However, the solar EUV and wind were stronger from the young Sun, and this tends to further reduce the initial 14N/15N ratio. Nevertheless uncertainties of the problem and of the ratio in comets support the idea that nitrogen on Titan appeared as ammonia ice with 14N/15N similar to that in comets.

  4. Methane on Mars: Thermodynamic Equilibrium and Photochemical Calculations

    NASA Technical Reports Server (NTRS)

    Levine, J. S.; Summers, M. E.; Ewell, M.

    2010-01-01

    The detection of methane (CH4) in the atmosphere of Mars by Mars Express and Earth-based spectroscopy is very surprising, very puzzling, and very intriguing. On Earth, about 90% of atmospheric ozone is produced by living systems. A major question concerning methane on Mars is its origin - biological or geological. Thermodynamic equilibrium calculations indicated that methane cannot be produced by atmospheric chemical/photochemical reactions. Thermodynamic equilibrium calculations for three gases, methane, ammonia (NH3) and nitrous oxide (N2O) in the Earth s atmosphere are summarized in Table 1. The calculations indicate that these three gases should not exist in the Earth s atmosphere. Yet they do, with methane, ammonia and nitrous oxide enhanced 139, 50 and 12 orders of magnitude above their calculated thermodynamic equilibrium concentration due to the impact of life! Thermodynamic equilibrium calculations have been performed for the same three gases in the atmosphere of Mars based on the assumed composition of the Mars atmosphere shown in Table 2. The calculated thermodynamic equilibrium concentrations of the same three gases in the atmosphere of Mars is shown in Table 3. Clearly, based on thermodynamic equilibrium calculations, methane should not be present in the atmosphere of Mars, but it is in concentrations approaching 30 ppbv from three distinct regions on Mars.

  5. Photochemical ozone budget during the BIBLE A and B campaigns

    NASA Astrophysics Data System (ADS)

    Ko, Malcolm; Hu, Wenjie; RodríGuez, José M.; Kondo, Yutaka; Koike, Makoto; Kita, Kazuyuki; Kawakami, Shuji; Blake, Donald; Liu, Shaw; Ogawa, Toshihiro

    2002-02-01

    Using the measured concentrations of NO, O3, H2O, CO, CH4, and NMHCs along the flight tracks, a photochemical box model is used to calculate the concentrations of the Ox radicals, the HOx radicals, and the nitrogen species at the sampling points. The calculations make use of the measurements from radiometers to scale clear sky photolysis rates to account for cloud cover and ground albedo at the sampling time/point. The concentrations of the nitrogen species in each of the sampled air parcels are computed assuming they are in instantaneous equilibrium with the measured NO and O3. The diurnally varying species concentrations are next calculated using the box model and used to estimate the diurnally averaged production and removal rates of ozone for the sampled air parcels. Clear sky photolysis rates are used in the diurnal calculations. The campaign also provided measured concentration of NOy. The observed NO/NOy ratio is usually larger than the model calculated equilibrium value. There are several possible explanations. It could be a result of recent injection of NO into the air parcel, recent removal of HNO3 from the parcel, recent rapid transport of an air parcel from another location, or a combination of all processes. Our analyses suggest that the local production rate of O3 can be used as another indicator of recent NO injection. However, more direct studies using air trajectory analyses and other collaborative evidences are needed to ascertain the roles played by individual process.

  6. Photochemical ozone budget during the BIBLE A and B campaigns

    NASA Astrophysics Data System (ADS)

    Ko, Malcolm; Hu, Wenjie; Rodríguez, José M.; Kondo, Yutaka; Koike, Makoto; Kita, Kazuyuki; Kawakami, Shuji; Blake, Donald; Liu, Shaw; Ogawa, Toshihiro

    2003-02-01

    Using the measured concentrations of NO, O3, H2O, CO, CH4, and NMHCs along the flight tracks, a photochemical box model is used to calculate the concentrations of the Ox radicals, the HOx radicals, and the nitrogen species at the sampling points. The calculations make use of the measurements from radiometers to scale clear sky photolysis rates to account for cloud cover and ground albedo at the sampling time/point. The concentrations of the nitrogen species in each of the sampled air parcels are computed assuming they are in instantaneous equilibrium with the measured NO and O3. The diurnally varying species concentrations are next calculated using the box model and used to estimate the diurnally averaged production and removal rates of ozone for the sampled air parcels. Clear sky photolysis rates are used in the diurnal calculations. The campaign also provided measured concentration of NOy. The observed NO/NOy ratio is usually larger than the model calculated equilibrium value. There are several possible explanations. It could be a result of recent injection of NO into the air parcel, recent removal of HNO3 from the parcel, recent rapid transport of an air parcel from another location, or a combination of all processes. Our analyses suggest that the local production rate of O3 can be used as another indicator of recent NO injection. However, more direct studies using air trajectory analyses and other collaborative evidences are needed to ascertain the roles played by individual process.

  7. Laser photochemical lead isotopes separation for harmless nuclear power engineering

    NASA Astrophysics Data System (ADS)

    Bokhan, P. A.; Fateev, N. V.; Kim, V. A.; Zakrevsky, D. E.

    2016-09-01

    The collisional quenching of the metastable 3 P 1,2 and 1 D 2 lead atoms is studied experimentally in the gas flow of the lead atoms, reagent-molecules and a carrier gas Ar. The experimental parameters were similar to the conditions that are required in the operation of the experimental setup for photochemical isotope separation. Excited atoms are generated under electron impact conditions created by a gas glow discharge through the mixture of gases and monitored photoelectrically by attenuation of atomic resonance radiation from hollow cathode 208Pb lamp. The decay of the excited atoms has been studied in the presence various molecules and total cross section data are reported. The flow tube measurements has allowed to separate the physical and chemical quenching channels and measure the rates of the chemical reaction excited lead with N2O, CH2Cl2, SF6 and CuBr molecules. These results are discussed in the prospects of the obtaining isotopically modified lead as a promising coolant in the reactors on the fast-neutron.

  8. Transport and photochemical modeling. Studies of atmospheric species

    NASA Technical Reports Server (NTRS)

    Natarajan, M.

    1987-01-01

    A program of research studies related to the photochemistry, radiative transfer, and dynamics of the stratosphere is described. Investigations were conducted in two broad areas: (1) studies of the stratospheric processes and their response to external perturbations, and (2) analysis of satellite measurements in conjunction with theoretical models. Contemporary one dimensional photochemical, radiative-convective model was used to assess the impact of perturbations such as solar flux variability, increases in atmospheric carbon dioxide, chlorofluoromethanes and other greenhouse gases. Data from satellite experiments such as LIMS and SBUV, were used along with theoretical models to develop a climatology of trace species in the stratosphere. The consistency of contemporary ozone photochemistry was examined in the light of LIMS data. Research work also includes analysis of stratospheric nitrogen dioxide distributions from different satellite experiments, investigation of the wintertime latitudinal gradients in NO2, estimation of the stratospheric odd nitrogen level and its variability, and studies related to the changes in ozone in the Antarctic, and mid latitude Southern Hemisphere.

  9. Photochemical Microscale Electrophoresis Allows Fast Quantification of Biomolecule Binding.

    PubMed

    Möller, Friederike M; Kieß, Michael; Braun, Dieter

    2016-04-27

    Intricate spatiotemporal patterns emerge when chemical reactions couple to physical transport. We induce electrophoretic transport by a confined photochemical reaction and use it to infer the binding strength of a second, biomolecular binding reaction under physiological conditions. To this end, we use the photoactive compound 2-nitrobenzaldehyde, which releases a proton upon 375 nm irradiation. The charged photoproducts locally perturb electroneutrality due to differential diffusion, giving rise to an electric potential Φ in the 100 μV range on the micrometer scale. Electrophoresis of biomolecules in this field is counterbalanced by back-diffusion within seconds. The biomolecule concentration is measured by fluorescence and settles proportionally to exp(-μ/D Φ). Typically, binding alters either the diffusion coefficient D or the electrophoretic mobility μ. Hence, the local biomolecule fluorescence directly reflects the binding state. A fit to the law of mass action reveals the dissociation constant of the binding reaction. We apply this approach to quantify the binding of the aptamer TBA15 to its protein target human-α-thrombin and to probe the hybridization of DNA. Dissociation constants in the nanomolar regime were determined and match both results in literature and in control experiments using microscale thermophoresis. As our approach is all-optical, isothermal and requires only nanoliter volumes at nanomolar concentrations, it will allow for the fast screening of biomolecule binding in low volume multiwell formats.

  10. Photochemical effects in the lens from near infrared radiation?

    NASA Astrophysics Data System (ADS)

    Söderberg, Per G.; Al-Saqry, Riyadh; Schulmeister, Karl; Gallichanin, Konstantin; Kronschläger, Martin; Yu, Zhaohua

    2009-02-01

    Conclusion: The current data are consistent with a potential photochemical effect of in vivo exposure of the crystalline lens to near infrared radiation since the onset of cataract after in just above threshold dose was at least 18 hrs delayed after the exposure. Materials and methods: The eyes of 6 weeks old Sprague-Dawley rats were exposed unilaterally in vivo to 1090 nm, 6.2 W quasi-top hat spatial distribution with a 3 mm spot on the anterior lens surface within the dilated pupil. First, four exposure time groups of rats were exposed to increasing exposure times. At 24 hrs after exposure, the difference of light scattering between the lenses from the same animal was measured. Then, based on the first experiment, four post-exposure time groups were exposed unilaterally in vivo to 8 s of 1090 nm, 6.2 W quasi-top hat spatial distribution with a 3 mm spot on the anterior lens surface within the dilated pupil. After, the intended post-exposure time, the difference of light scattering between the lenses from the same animal was measured. Results: A 3 mm spot of 6.2 W induces light scattering in the lens with exposures of at least 8 s. Further, after 8 s of 6.2 W within a 3 mm spot on the lens surface, the light scattering increase in the lens was delayed at least 18 hrs after the exposure.

  11. Highly sensitive and simple SERS substrate based on photochemically generated carbon nanotubes-gold nanorods hybrids.

    PubMed

    Caires, A J; Vaz, R P; Fantini, C; Ladeira, L O

    2015-10-01

    We report a simple and easy formation of hybrids between multi-wall carbon nanotubes and gold nanorods by one-pot in situ photochemical synthesis. Measurements of surface-enhanced Raman scattering (SERS) through the effect "coffee ring" in visible and near infrared (NIR) show high sensitivity with detection of nanomolar concentrations of aromatic dyes. The formation of nanocomposites between carbon nanotubes and gold nanorods without chemical binders simplifies the preparation. Photochemical synthesis is an advance over the techniques previously published.

  12. Seasonal Photochemical Transformations of Nitrogen Species in a Forest Stream and Lake

    PubMed Central

    Porcal, Petr; Kopáček, Jiří; Tomková, Iva

    2014-01-01

    The photochemical release of inorganic nitrogen from dissolved organic matter is an important source of bio-available nitrogen (N) in N-limited aquatic ecosystems. We conducted photochemical experiments and used mathematical models based on pseudo-first-order reaction kinetics to quantify the photochemical transformations of individual N species and their seasonal effects on N cycling in a mountain forest stream and lake (Plešné Lake, Czech Republic). Results from laboratory experiments on photochemical changes in N speciation were compared to measured lake N budgets. Concentrations of organic nitrogen (Norg; 40–58 µmol L−1) decreased from 3 to 26% during 48-hour laboratory irradiation (an equivalent of 4–5 days of natural solar insolation) due to photochemical mineralization to ammonium (NH4+) and other N forms (Nx; possibly N oxides and N2). In addition to Norg mineralization, Nx also originated from photochemical nitrate (NO3−) reduction. Laboratory exposure of a first-order forest stream water samples showed a high amount of seasonality, with the maximum rates of Norg mineralization and NH4+ production in winter and spring, and the maximum NO3− reduction occurring in summer. These photochemical changes could have an ecologically significant effect on NH4+ concentrations in streams (doubling their terrestrial fluxes from soils) and on concentrations of dissolved Norg in the lake. In contrast, photochemical reactions reduced NO3− fluxes by a negligible (<1%) amount and had a negligible effect on the aquatic cycle of this N form. PMID:25551441

  13. The carbon-bond mechanism: a condensed kinetic mechanism for photochemical smog

    SciTech Connect

    Whitten, G.Z.; Hog, H.; Killus, J.P.

    1980-06-01

    Efforts to develop a model that can simulate photochemical smog with kinetic mechanisms are discussed. The carbon-bond mechanism is a set of generalized reactions that can be used to model photochemical oxidant formation. The theoretical framework of carbon-bond mechanism is outlined. Chemical variables that are incorporated into the carbon-bond mechanism model are described. Further work that is needed on the carbon-bond mechanism model is considered. (1 diagram, 13 graphs, 30 references, 2 tables)

  14. Airborne, In Situ and Laboratory Measurements of the Optical and Photochemical Properties of Surface Marine Waters

    DTIC Science & Technology

    2016-06-07

    Airborne, In Situ And Laboratory Measurements Of The Optical And Photochemical Properties Of Surface Marine Waters Neil V. Blough Department of...matter (CDOM) in marine and estuarine waters , 2) to determine the impact of CDOM on the aquatic light field and remotely-sensed optical signals, 3) to...October 1999 was performed to examine the optical and photochemical properties of waters in the Middle Atlantic Bight and in the Delaware and Chesapeake

  15. Kinetic and photochemical data for atmospheric chemistry reactions of the nitrogen oxides

    NASA Technical Reports Server (NTRS)

    Hampson, R. F., Jr.

    1980-01-01

    Data sheets for thermal and photochemical reactions of importance in the atmospheric chemistry of the nitrogen oxides are presented. For each reaction the available experimental data are summarized and critically evaluated, and a preferred value of the rate coefficient is given. The selection of the preferred value is discussed and an estimate of its accuracy is given. For the photochemical process, the data are summarized, and preferred for the photoabsorption cross section and primary quantum yields are given.

  16. Photochemical reactions of aromatic compounds and the concept of the photon as a traceless reagent.

    PubMed

    Hoffmann, Norbert

    2012-11-01

    Electronic excitation significantly changes the reactivity of chemical compounds. Compared to ground state reactions, photochemical reactions considerably enlarge the application spectrum of a particular functional group in organic synthesis. Multistep syntheses may be simplified and perspectives for target oriented synthesis (TOS) and diversity oriented synthesis (DOS) are developed. New compound families become available or may be obtained more easily. In contrast to common chemical reagents, photons don't generate side products resulting from the transformation of a chemical reagent. Therefore, they are considered as a traceless reagent. Consequently, photochemical reactions play a central role in the methodology of sustainable chemistry. This aspect has been recognized since the beginning of the 20th century. As with many other photochemical transformations, photochemical reactions of aromatic, benzene-like compounds illustrate well the advantages in this context. Photochemical cycloadditions of aromatic compounds have been investigated for a long time. Currently, they are applied in various fields of organic synthesis. They are also studied in supramolecular structures. The phenomena of reactivity and stereoselectivity are investigated. During recent years, photochemical electron transfer mediated reactions are particularly focused. Such transformations have likewise been performed with aromatic compounds. Reactivity and selectivity as well as application to organic synthesis are studied.

  17. Consequences of Predicted or Actual Asteroid Impacts

    NASA Astrophysics Data System (ADS)

    Chapman, C. R.

    2003-12-01

    Earth impact by an asteroid could have enormous physical and environmental consequences. Impactors larger than 2 km diameter could be so destructive as to threaten civilization. Since such events greatly exceed any other natural or man-made catastrophe, much extrapolation is necessary just to understand environmental implications (e.g. sudden global cooling, tsunami magnitude, toxic effects). Responses of vital elements of the ecosystem (e.g. agriculture) and of human society to such an impact are conjectural. For instance, response to the Blackout of 2003 was restrained, but response to 9/11 terrorism was arguably exaggerated and dysfunctional; would society be fragile or robust in the face of global catastrophe? Even small impacts, or predictions of impacts (accurate or faulty), could generate disproportionate responses, especially if news media reports are hyped or inaccurate or if responsible entities (e.g. military organizations in regions of conflict) are inadequately aware of the phenomenology of small impacts. Asteroid impact is the one geophysical hazard of high potential consequence with which we, fortunately, have essentially no historical experience. It is thus important that decision makers familiarize themselves with the hazard and that society (perhaps using a formal procedure, like a National Academy of Sciences study) evaluate the priority of addressing the hazard by (a) further telescopic searches for dangerous but still-undiscovered asteroids and (b) development of mitigation strategies (including deflection of an oncoming asteroid and on- Earth civil defense). I exemplify these issues by discussing several representative cases that span the range of parameters. Many of the specific physical consequences of impact involve effects like those of other geophysical disasters (flood, fire, earthquake, etc.), but the psychological and sociological aspects of predicted and actual impacts are distinctive. Standard economic cost/benefit analyses may not

  18. Diels-Alder Trapping of Photochemically Generated Dienes with Acrylic Esters: A Novel Approach to Photocured Polymer Film Development

    NASA Technical Reports Server (NTRS)

    Ilhan, Faysal; Tyson, Daniel S.; Smith, Deedee; Meador, Mary Ann; Meador, Michael A.

    2004-01-01

    Diels-Alder cycloadditions have often been utilized in polymer synthesis as an alternative to condensation reactions. In our earlier efforts, we developed a new method for the preparation of linear aromatic polyimides, which employs o-quionodimethanes (o-QDMs), generated by a well-known photochemical reaction: the photoenolization of o-methylphenyl ketones. Photolysis of o-methylbenzophenone 1 produces hydroxy-o-quino- diemthane 2, which can be trapped with dienophiles, such as dimethyl acetylenedicarboxylate, to efficiently yield the corresponding cycloadduct (Scheme 1). Here we extend this approach to a novel photocuring process for development of polymer films. We synthesized a series of molecules with multi o-mehtylphenyl ketone functionalities. We further investigated these molecules as photoreactive monomers to obtain polyester films through Diels-Alder cycloadditions.

  19. Photochemical cleavage of individual stereoisomers of coumarin-5-fluorouracil crossdimers via single- and two-photon-absorption

    NASA Astrophysics Data System (ADS)

    Behrendt, Philipp J.; Kim, Hee-Cheol; Hampp, Norbert

    2013-11-01

    Coumarin-5-fluorouracil crossdimers were photochemically synthesized. Three different isomers were isolated and their photo-cycloreversion, induced by single- and two-photon-absorption, was studied. The single-photon absorption quantum yields strongly correlate with the dipole moments and the absorption behavior of the stereoisomers. Between the stereoisomers a maximal factor of 6.5 in cyclobutane cleavage efficiency is observed. The two-photon-absorption cross-sections were determined for all three stereoisomers. A good correlation between the single and two-photon-absorption cross-sections was found. The isomer with the highest light sensitivity is the syn-head-to-head isomer. For most applications, isomer pure preparations seem advisable as the required light intensities may be reduced significantly.

  20. Photochemical changes and oxidative damage in the aquatic macrophyte Cymodocea nodosa exposed to paraquat-induced oxidative stress.

    PubMed

    Moustakas, Michael; Malea, Paraskevi; Zafeirakoglou, Aristi; Sperdouli, Ilektra

    2016-01-01

    The non-selective herbicide paraquat (Pq) is being extensively used for broad-spectrum weed control. Through water runoff and due to its high water solubility it contaminates aquatic environments. Thus, the present study was carried out to investigate the photochemical changes and oxidative damage in the aquatic macrophyte Cymodocea nodosa to short- (2h) and long-term (24h) exposure to 2, 20, 200 and 1000μM paraquat (Pq) toxicity by using chlorophyll fluorescence imaging and H2O2 real-time imaging. The effective quantum yield of PSII (ΦPSII) show a tendency to increase at 2μM Pq after 2h exposure, and increased significantly at 20 and 200μM Pq. Τhe maximum oxidative effect on C. nodosa leaves was observed 2h after exposure to 200μM Pq concentration when the highest increases of ΦPSII due to high electron transport rate (ETR) resulted in a significant increase of H2O2 production due to the lowest non-photochemical quenching (NPQ) that was not efficient to serve as a protective mechanism, resulting in photooxidation. Prolonged exposure (24h) to 200μM Pq resulted in a decreased ΦPSII not due to an increase of the photoprotective mechanism NPQ, but due to high quantum yield of non-regulated energy loss in PSII (ΦNO), resulting to the lowest fraction of open PSII reaction centers (qp). This decreased ΦPSII has resulted to less Pq radicals to be formed, with a consequence of a small increase of H2O2 production compared to control C. nodosa leaves, but substantial lower than that of 2h exposure to 200μM Pq. Exposure of C. nodosa leaves to 1000μM Pq toxicity had lower effects on the efficiency of photochemical reactions of photosynthesis under both short- (2h) and long-term (24h) exposure than 200μM Pq. This was evident by an almost unchanged ΦPSII and qp, that remained unchanged even at a longer exposure time (48h), compared to control C. nodosa leaves. Thus, the response of C. nodosa leaves to Pq toxicity fits the "Threshold for Tolerance Model", with a

  1. Aluminosilicates as controlled molecular environments for selective photochemical and catalytic reactions

    SciTech Connect

    Carrado, K.A.

    1986-01-01

    This dissertation concerns research that involves photochemical, catalytic and spectroscopic studies of clays, pillared clays and zeolites. Incorporation of uranyl ions into hectorite, montmorillonite, bentonite and vermiculite clays was monitored by XRD and luminescence methods. Excitation and emission characteristics were studied in order to understand the behavior of uranyl ions in clays after various thermal treatments. Luminescence lifetime measurements elucidated the number of uranyl sites. Uranyl-exchanged clays were found to absorb light at lower energies (445-455nm) than analogous uranyl-exchanged zeolites (425nm). Each uranyl-exchanged clay was tested as a catalyst for the photoassisted oxidation of isopropyl alcohol. Energy transfer (ET) between uranyl and Eu(III) ions in different zeolite framework systems was examined. The efficiency of ET (eta/sub t/) was found to be affected by the type of framework present. Pillared bentonites were examined in the hydrocracking of decane. A catalytically and spectroscopically active dopant ion, Cr(III), was introduced into the clays in both pillared and unpillared forms depending upon synthetic conditions. EPR and DRS were employed to monitor the environment of Cr(III) for determination of its location - whether in the micropore structure or associated with alumina pillars. Catalytic behavior based upon this variability of location was examined. Incorporation of Cr(III) ions into an alumina pillar was found to increase the stability and activity with respect to an alumina PILC catalyst. The results of these studies suggest that selective, efficient catalysts can be designed around inorganic ions in aluminosilicate supports.

  2. [Effects of high temperature on leaf photosynthetic characteristics and photosystem II photochemical activity of kernel-used apricot].

    PubMed

    Du, Guo-dong; Lü, De-guo; Zhao, Ling; Wang, Su-su; Cai, Qian

    2011-03-01

    In order to explore the photosynthetic adaption mechanisms of kernel-used apricot under high temperature stress, gas exchange technique and chlorophyll fluorescence transient technique (JIP-test) were adopted to study the leaf photosynthetic characteristics and photosystem II (PS II) photochemical activity of 4 year-old 'Chaoren' (Armeniaca vulgaris x sibirica) growing on Horqin sandy land at 25 degrees C, 30 degrees C, 40 degrees C, and 50 degrees C. Within a definite temperature range, and as the temperature increased, the 'Chaoren' could enhance its leaf photosynthetic pigments content and ratio to maintain the light absorption, transfer, and conversion, and thereby, to ensure the function of photosynthetic apparatus. However, when the temperature exceeded the physiological adjustment threshold of leaves, the chlorophyll began to be decomposed, net photosynthetic rate (Pn) declined obviously, and intercellular CO2 concentration (Ci) increased, indicating that the decline in photosynthesis was limited by mesophyll factor. At 40 degrees C, the density of PS II reaction centers per excited cross-section (RC/CS0) dropped distinctly; and at 50 degrees C, the K phase (Wk) and J phase (Vj) in the O-J-I-P chlorophyll fluorescence transients increased distinctly, indicating that high temperature damaged the oxygen-evolving complex (OEC), donor sides, and PS II reaction centers. In addition, the minimum chlorophyll fluorescence (F0) at 50 degrees C increased significantly by 1.26 times, compared with the control, and the maximum photochemical efficiency (Fv/Fm) and performance index (PI(ABS)) reduced to 37.9% and 10.3% of the control, respectively. High temperature injured the function of the donor and acceptor sides in the PS II of photosynthetic apparatus, leading to the decrease of photosynthetic efficiency, and being one of the main mechanisms for the damage of photosynthetic apparatus in kernel-used apricot leaves under high temperature stress.

  3. THERMOCHEMICAL AND PHOTOCHEMICAL KINETICS IN COOLER HYDROGEN-DOMINATED EXTRASOLAR PLANETS: A METHANE-POOR GJ436b?

    SciTech Connect

    Line, Michael R.; Yung, Yuk L.; Vasisht, Gautam; Chen, Pin; Angerhausen, D. E-mail: gv@s383.jpl.nasa.gov

    2011-09-01

    We introduce a thermochemical kinetics and photochemical model. We use high-temperature bidirectional reaction rates for important H, C, O, and N reactions (most importantly for CH{sub 4} to CO interconversion), allowing us to attain thermochemical equilibrium, deep in an atmosphere, purely kinetically. This allows the chemical modeling of an entire atmosphere, from deep-atmosphere thermochemical equilibrium to the photochemically dominated regime. We use our model to explore the atmospheric chemistry of cooler (T{sub eff} < 10{sup 3} K) extrasolar giant planets. In particular, we choose to model the nearby hot-Neptune GJ436b, the only planet in this temperature regime for which spectroscopic measurements and estimates of chemical abundances now exist. Recent Spitzer measurements with retrieval have shown that methane is driven strongly out of equilibrium and is deeply depleted on the day side of GJ436b, whereas quenched carbon monoxide is abundant. This is surprising because GJ436b is cooler than many of the heavily irradiated hot Jovians and thermally favorable for CH{sub 4}, and thus requires an efficient mechanism for destroying it. We include realistic estimates of ultraviolet flux from the parent dM star GJ436, to bound the direct photolysis and photosensitized depletion of CH{sub 4}. While our models indicate fairly rich disequilibrium conditions are likely in cooler exoplanets over a range of planetary metallicities, we are unable to generate the conditions for substantial CH{sub 4} destruction. One possibility is an anomalous source of abundant H atoms between 0.01 and 1 bars (which attack CH{sub 4}), but we cannot as yet identify an efficient means to produce these hot atoms.

  4. Photochemical internalization for the treatment of malignant gliomas

    NASA Astrophysics Data System (ADS)

    Madsen, Steen J.; Kharkhuu, Khishigzaya; Berg, Kristian; Hirschberg, Henry

    2007-02-01

    Photochemical internalization (PCI) is a technique to improve the utilization of macromolecules (e.g. chemotherapeutic agents) in cancer therapy in a site-specific manner. The concept is based on the use of specially designed photosensitizers which localize preferentially in the membranes of endocytic vesicles. Upon exposure to light the photosensitizers induce the formation of reactive oxygen species such as singlet molecular oxygen. The photooxidation of the endocytic membranes leads to the release of the contents of the vesicles into the cytosol. In this way, macromolecules encapsulated by the vesicles will reach the cytosol and exert their biological activity instead of being degraded by lysosomal hydrolases. The utility of PCI for the treatment of malignant gliomas was investigated in vitro using an F98 rat glioma cell line. The cytotoxicity of 5-aminolevulinic acid (ALA) based PCI of bleomycin was compared to: (1) ALA-PDT, and (2) bleomycin. In all cases, monolayers were incubated in ALA, bleomycin, or ALA + bleomycin for 4 hours and were subsequently exposed to 635 nm light. Toxicity was evaluated using colony formation assays. F98 rat glioma cells in monolayer were found to be susceptible to the effects of both ALA-PDT and bleomycin. ALA-PDT was found to be particularly effective when light was delivered at a low irradiance of 5 mW cm -2. In this case, a radiant exposure of 20 J cm -2 resulted in only 4% survival. Bleomycin was found to be toxic at relatively low concentrations, incubation of F98 cells in 10 μg ml -1 for 4 hours resulted in 1% survival. The PCI effect was found to be negligible for the parameters investigated in the F98 cell line suggesting that: (1) the incubation time was sub-optimal and/or (2) ALA was inappropriate for this application.

  5. Photochemical formation of hydroxyl radical from effluent organic matter.

    PubMed

    Dong, Mei Mei; Rosario-Ortiz, Fernando L

    2012-04-03

    The photochemical formation of hydroxyl radical (HO•) from effluent organic matter (EfOM) was evaluated using three bulk wastewater samples collected at different treatment facilities under simulated sunlight. For the samples studied, the formation rates of HO•(R(HO•)) were obtained from the formation rate of phenol following the hydroxylation of benzene. The values of R(HO•) ranged from 2.3 to 3.8 × 10(-10) M s(-1) for the samples studied. The formation rate of HO• from nitrate photolysis (R(NO3)(HO•)) was determined to be 3.0 × 10(-7) M(HO)• M(NO3)(-1) s(-1). The HO• production rate from EfOM (R(EfOM)(HO•)) ranged from 0.76 to 1.3 × 10(-10) M s(-1). For the wastewater samples studied, R(EfOM)(HO•) varied from 1.5 to 2.4 × 10(-7) M(HO)• M(C)(-1) (s-1) on molarcarbon basis, which was close to HO• production from nitrate photolysis. The apparent quantum yield for the formation of HO• from nitrate (Φ(NO3-HO•)(a)) was determined as 0.010 ± 0.001 for the wavelength range 290-400 nm in ultrapure water. The apparent quantum yield for HO• formation in EfOM (Φ(EfOM-HO•)(a)) ranged from 6.1 to 9.8 × 10(-5), compared to 2.99 to 4.56 × 10(-5) for organic matter (OM) isolates. The results indicate that wastewater effluents could produce significant concentrations of HO•, as shown by potential higher nitrate levels and relatively higher quantum yields of HO• formation from EfOM.

  6. Photochemical Thrombosis Of Retinal And Choroidal Vessels Using Rose Bengal

    NASA Astrophysics Data System (ADS)

    Lewis, Mary Lou; Winward, Kirk; Watson, Brant D.; Hernandez, Eleut

    1989-09-01

    Rose bengal is an effective photosensitizing agent which interacts with argon green light to induce photochemical thrombosis of irradiated vessels. We used focal, low energy irradiation to occlude retinal and choroidal vessels in both albino and pigmented rabbits. Immediately after intravenous injection of rose bengal at concentrations of 10 and 20 mg/kg, irradiation was performed via a slit lamp-delivered argon green laser (514.5 nm) with the aid of fundus contact lens. In 11 eyes, arteries were treated with 50-100 interrupted bursts of 75u spot size at 0.2 sec and 40-100 mW (9

  7. External Validity of Contingent Valuation: Comparing Hypothetical and Actual Payments.

    PubMed

    Ryan, Mandy; Mentzakis, Emmanouil; Jareinpituk, Suthi; Cairns, John

    2016-10-09

    Whilst contingent valuation is increasingly used in economics to value benefits, questions remain concerning its external validity that is do hypothetical responses match actual responses? We present results from the first within sample field test. Whilst Hypothetical No is always an Actual No, Hypothetical Yes exceed Actual Yes responses. A constant rate of response reversals across bids/prices could suggest theoretically consistent option value responses. Certainty calibrations (verbal and numerical response scales) minimise hypothetical-actual discrepancies offering a useful solution. Helping respondents resolve uncertainty may reduce the discrepancy between hypothetical and actual payments and thus lead to more accurate policy recommendations. Copyright © 2016 John Wiley & Sons, Ltd.

  8. Actual and perceived sleep: associations with daytime functioning among postpartum women.

    PubMed

    Insana, Salvatore P; Stacom, Elizabeth E; Montgomery-Downs, Hawley E

    2011-02-01

    Sleep and wake have a homeostatic relation that influences most aspects of physiology and waking behavior. Sleep disturbance has a detrimental effect on sleepiness and psychomotor vigilance. The purpose of this study was to identify which actual or perceived sleep characteristics accounted for the most variance in daytime functioning among postpartum mothers. Seventy first-time postpartum mothers' actual sleep (actigraphically estimated: total sleep time, number of wake bouts, length of nocturnal wake, and sleep efficiency) and perceived sleep (self-reported: number of awakenings, wake time, and sleep quality) were measured along with their daytime functioning (Stanford Sleepiness Scale [SSS], Epworth Sleepiness Scale [ESS], Visual Analogue of Fatigue Scale [VAFS], and morning Psychomotor Vigilance Test [PVT]). Data were repeatedly collected from the same sample during postpartum weeks 2, 7, and 13. Four stepwise linear regressions were calculated for each postpartum week to examine which objective and/or subjective variable(s) accounted for the most variance in daytime functioning. The SSS and VAFS were both most consistently associated with perceived sleep quality. The ESS was most consistently associated with actual total sleep time. PVT performance was most consistently associated with estimates of actual and perceived sleep efficiency. Actual and perceived sleep profiles were differentially associated with specific daytime functions. These results from postpartum mothers may indicate that populations who experience specific forms of sleep disturbance (e.g. fragmentation and/or deprivation) may also experience specific daytime conditions.

  9. Actual questions raised by nanoparticle radiosensitization

    NASA Astrophysics Data System (ADS)

    Brun, Emilie; Sicard-Roselli, Cécile

    2016-11-01

    Radiosensitization by metallic nanoparticles (NP) has been explored for more than a decade with promising results in vitro and in cellulo reported in a vast number of publications. Yet, few clinical trials are on-going. This could be related to the lack of selectivity of NP leading to massive quantities to be injected to observe an effect but also to the higher degree of complexity than first thought leading to an absence of consensus probably caused by the lack of standardization in pre-clinical studies. Given the wide panel of NP used, in terms of core nature, size, coating, not to mention of cell lines and irradiation modalities, cross-comparison of data is not a walk in the park. But only a thorough examination could help identifying the key parameters and the possible mechanisms involved. This step is crucial as it should provide guidance for designing the most efficient combination NP/radiation and rationally establishing clinical protocols. In this review, we will combine and confront cellular radiosensitization results with in vitro and numerical experiments in order to give the more recent vision of this complex phenomenon. We decided to address a few hot topics such as the influence of the incident radiation energy, the localization of NP or the so-called ;biological; effect. We will highlight that among the barriers to break down, some are not restricted to the ;nano; community: an incontestable support could be offered by the ;radiation; community in the broadest sense.

  10. Synthesis, Photochemical and Photoinduced Antibacterial Activity Studies of meso-Tetra(pyren-1-yl)porphyrin and its Ni, Cu and Zn Complexes

    PubMed Central

    Zoltan, Tamara; Vargas, Franklin; Rivas, Carlos; López, Verónica; Perez, Jhackelym; Biasutto, Antonio

    2010-01-01

    The synthesis of the meso-tetra(pyren-1-yl)porphyrin (1) was successfully accomplished by means of the pyrrole condensation with pyrene-1-carb-aldehyde in acidic media. Its metallization was carried out in an almost quantitative yield to obtain the corresponding complexes of Ni(II) (2), Cu(II) (3) and Zn (4). Their photophysical properties such as fluorescence quantum yield and energy transfer to oxygen for an efficient generation of singlet oxygen were determined. Their photophysical and photochemical properties were compared with those of other similar porphyrin derivatives such as tetraphenylporphyrin and tetranaphthylporphyrin. Photochemical studies on their effectiveness as photosensitizer were carried out by means of the photoinduced oxidation of aromatic alcohols like α-naphthol to naphthoquinone. The antibacterial photoactivity assay for compounds 1–4 was testeted against Escherichia coli (ATCC 8739) and its proliferation and viability were measured by chemiluminescence. An efficient inactivation of E. coli was observed. This was more efficient for compounds 2 and 3, following the direct relationship to high generation of singlet oxygen by these compounds. PMID:21179316

  11. Binding, aggregation and photochemical properties of methylene blue in mitochondrial suspensions.

    PubMed

    Gabrielli, Dino; Belisle, Eduardo; Severino, Divinomar; Kowaltowski, Alicia J; Baptista, Mauricio S

    2004-03-01

    Methylene Blue (MB) has well-established photochemical properties and has been used in a variety of photochemical applications including photodynamic therapy. Despite the fact that most of MB's cytotoxic effects in cells are attributed to mitochondrial damage, the interactions of this dye with mitochondria and the consequent effects on photochemical properties have not yet been fully determined. We monitored MB binding, aggregation and its ability to release singlet oxygen (1O2) on irradiation when interacting with mitochondrial suspensions. MB actively binds to mitochondria and enters the matrix in a manner stimulated by the mitochondrial proton potential and by the increase in mitochondrial concentrations. The greater accumulation of MB in mitochondria with elevated proton potentials or those treated with high concentrations of MB results in the formation of MB dimers, previously shown to be less effective generators of 1O2. Accumulation of MB within mitochondria with high membrane potentials also results in the reduction of MB to the photochemically inactive leuco-MB. Indeed, irradiation of mitochondria with high proton potentials in the presence of MB results in the generation of approximately half the quantity of 1O2 compared with 1O2 generated in mitochondria with low proton potentials. These differences in photochemical properties should influence the cytotoxic effects of photodynamic treatment in the presence of MB.

  12. Trends in photochemical smog in the Cape Peninsula and the implications for health.

    PubMed

    Bailie, R S; Ehrlich, R I; Truluck, T F

    1994-11-01

    There has been growing public concern over reports of increasing air pollution in the Cape Peninsula. Attention has been focused on the 'brown haze' and on photochemical smog. Because of deficiencies in the monitoring equipment, information on trends in photochemical smog levels over the past decade is limited. Trends in oxides of nitrogen, one of the main precursors of photochemical smog, and therefore an indicator of the potential for its formation, were examined for the period 1984-1993. Meaningful data for determining trends were available from only a single site. Increases in mean monthly levels, peak hourly levels and the number of times guidelines were exceeded were demonstrated. Given the dynamics of formation of photochemical smog and the particular role of motor vehicles, it is argued that the trends measured at this site are probably an underestimate of the trends in other parts of the Cape Town metropolitan area. Some of the precursors of photochemical smog, notably nitrogen dioxide, and some of its components, notably ozone, have been shown to be detrimental to respiratory health at levels close to, or below, current recommended guidelines. A continuing increase in these pollutants will therefore result in more respiratory illness, particularly among susceptible groups. This calls for an upgrading of monitoring of air pollution in Cape Town and for appropriate steps to prevent its further increase.

  13. Zebrafish model of photochemical thrombosis for translational research and thrombolytic screening in vivo.

    PubMed

    Lee, I-Ju; Yang, Yi-Cyun; Hsu, Jia-Wen; Chang, Wei-Tien; Chuang, Yung-Jen; Liau, Ian

    2017-04-01

    Acute thromboembolic diseases remain the major global cause of death or disability. Although an array of thrombolytic and antithrombotic drugs has been approved to treat or prevent thromboembolic diseases, many more drugs that target specific clotting mechanisms are under development. Here a novel zebrafish model of photochemical thrombosis is reported and its prospective application for the screening and preclinical testing of thrombolytic agents in vivo is demonstrated. Through photochemical excitation, a thrombus was induced to form at a selected section of the dorsal aorta of larval zebrafish, which had been injected with photosensitizers. Such photochemical thrombosis can be consistently controlled to occlude partially or completely the targeted blood vessel. Detailed mechanistic tests indicate that the zebrafish model of photochemical thrombosis exhibits essential features of classical coagulation and a thrombolytic pathway. For demonstration, tissue plasminogen activator (tPA), a clinically feasible thrombolytic agent, was shown to effectively dissolve photochemically induced blood clots. In light of the numerous unique advantages of zebrafish as a model organism, our approach is expected to benefit not only the development of novel thrombolytic and antithrombotic strategies but also the fundamental or translational research targeting hereditary thrombotic or coagulation disorders.

  14. Indirect photochemical transformations of acyclovir and penciclovir in aquatic environments increase ecological risk.

    PubMed

    An, Jibin; Li, Guiying; An, Taicheng; Nie, Xiangping

    2016-03-01

    Acyclovir and penciclovir, 2 antiviral drugs, are increasingly detected in aquatic environments. The present study explores the natural photochemical transformation mechanisms and fate of these drugs, examining direct and indirect photochemical transformation under simulated sunlight irradiation. The 2 antiviral drugs are photostable under certain conditions but significantly degrade in the presence of chromophoric dissolved organic matter (DOM). The degradation rate associated with the drugs' indirect photochemical transformation scaled with chromophoric DOM concentration. Quenchers and sensitizers were used to identify indirect photochemical transformation mechanism. Results suggested that both pharmaceuticals could be transformed by reacting with (1)O2, (•)OH, and excited chromophoric DOM. The (1)O2 played an important role in indirect photochemical transformation. Furthermore, the reaction kinetics between their substructural molecules, guanine, isocytosine, and imidazole, with different reactive oxygen species were evaluated to determine which substrate functionalities were most susceptible to singlet oxygenation. Imidazole was identified as the reaction site for (1)O2, and preliminary (1)O2 oxidation mechanisms were further evaluated based on liquid chromatographic-tandem mass spectrometric results. Finally, aquatic ecotoxicity assessment of phototransformed solutions revealed that the degradation of acyclovir and penciclovir may not ultimately diminish environmental risk because of either formation of more toxic intermediates than parent pharmaceuticals or some synergistic effects existing between the intermediates.

  15. Air quality criteria for ozone and other photochemical oxidants. External Review Draft No. 2. Volume 5

    SciTech Connect

    Horstman, D.H.; Horvath, S.M.; Raub, J.A.

    1985-11-01

    Scientific information is presented and evaluated relative to the health and welfare effects associated with exposure to ozone and other photochemical oxidants. Although not intended as a complete and detailed literature review, the document covers pertinent literature through early 1985. Data on health and welfare effects are emphasized, but additional information is provided for understanding the nature of the oxidant pollution problem and for evaluating the reliability of effects data as well as their relevance to potential exposures to ozone and other oxidants at concentrations occurring in ambient air. Information is presented on the following exposure-related topics: nature, source, measurement, and concentrations of precursors to ozone and other photochemical oxidants; formation of ozone and other photochemical oxidants and their transport once formed; properties, chemistry, and measurement of ozone and other photochemical oxidants; and concentrations of ozone and other photochemical oxidants typically found in ambient air. Chapters on health and welfare effects address the toxicological effects of ozone and other oxidants; effects observed in controlled human exposures; effects observed in field and epidemiological studies; effects on vegetation seen in field and controlled exposures; effects on natural and agroecosystems; and effects on nonbiological materials observed in field and chamber studies.

  16. Isotope fractionation of mercury during its photochemical reduction by low-molecular-weight organic compounds.

    PubMed

    Zheng, Wang; Hintelmann, Holger

    2010-04-01

    Photochemical reduction of Hg(II) by various low-molecular-weight organic compounds (LMWOC) was investigated to evaluate the effect of specific functional groups that are typically encountered in natural dissolved organic matters (DOM) on the photoreactivity and isotope fractionation of Hg. LMWOC with reduced sulfur functional groups (e.g., cysteine, glutathione) resulted in slower photochemical reduction of Hg(II) than those without reduced sulfur groups (e.g., serine, oxalic acid). Reduction rate constants were specifically determined for two contrasting LMWOC: dl-serine (0.640 h(-1)) and l-cysteine (0.047 h(-1)). Different mass independent isotope effects of Hg were induced by the two types of LMWOC. S-containing ligands specifically enriched magnetic isotopes ((199)Hg and (201)Hg) in the product (Hg(0)) while sulfurless ligands enriched (199)Hg and (201)Hg in the reactant (Hg(II)), suggesting that opposite magnetic isotope effects were produced by different types of ligands. The nuclear field shift effect was also observed in the photochemical reduction by serine. These isotope effects are related to specific functional groups and reduction mechanisms, and may be used to distinguish between primary and secondary photochemical reduction mechanisms of Hg(II) and to explain isotope fractionation during the photochemical reduction of Hg(II) by natural DOM, which provides mixed bonding conditions.

  17. Assessment of diphenylcyclopropenone for photochemically induced mutagenicity in the Ames assay

    SciTech Connect

    Wilkerson, M.G.; Connor, T.H.; Henkin, J.; Wilkin, J.K.; Matney, T.S.

    1987-10-01

    The photochemical conversion of diphenylcyclopropenone to diphenylacetylene has recently been reported. Diphenylcyclopropenone is used in the treatment of alopecia areata and is nonmutagenic in a limited Ames assay. We examined diphenylcyclopropenone and diphenylacetylene, as well as synthetic precursors of diphenylcyclopropenone--dibenzylketone and alpha,alpha'-dibromodibenzylketone--for mutagenicity against TA100, TA98, TA102, UTH8413, and UTH8414. All compounds were nonmutagenic except alpha,alpha'-dibromodibenzylketone, which was a potent mutagen in TA100 with and without S-9 activation. The effect of photochemical activation of diphenylcyclopropenone in the presence of bacteria demonstrated mutagenicity in UTH8413 (two times background) at 10 micrograms/plate with S-9 microsomal activation. 8-Methoxypsoralen produces a mutagenic response in TA102 at 0.1 microgram/plate with 60 seconds of exposure to 350 nm light. In vitro photochemically activated Ames assay with S-9 microsomal fraction may enhance the trapping of short-lived photochemically produced high-energy mutagenic intermediates. This technique offers exciting opportunities to trap high-energy intermediates that may play an important role in mutagenesis. This method can be applied to a variety of topically applied dermatologic agents, potentially subjected to photochemical changes in normal use.

  18. 43 CFR 418.35 - Efficiencies.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... Distribution System Efficiency table (§ 418.13 (a)(4)). The efficiency of the Project will vary with the amount... irrigation season based on actual measured amounts. The application of any adjustments to Lahontan...

  19. 43 CFR 418.35 - Efficiencies.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Distribution System Efficiency table (§ 418.13 (a)(4)). The efficiency of the Project will vary with the amount... irrigation season based on actual measured amounts. The application of any adjustments to Lahontan...

  20. 43 CFR 418.35 - Efficiencies.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Distribution System Efficiency table (§ 418.13 (a)(4)). The efficiency of the Project will vary with the amount... irrigation season based on actual measured amounts. The application of any adjustments to Lahontan...

  1. Discovery of photochemical damage mechanisms using in vitro and in silico models

    NASA Astrophysics Data System (ADS)

    Fink, Pamela K.; Denton, Michael L.; Castellanos, Cherry C.; Tijerina, Amanda J.; Schuster, Kurt J.; Oliver, Jeffrey W.

    2013-02-01

    A computer-based model has been built that simulates the response of the retinal pigmented epithelial (RPE) cell to laser exposure in the photochemical (non-thermal) damage exposure range (>= 100 s exposures). The modeling approach used is knowledge-based, modular, and hierarchical, allowing the explicit modeling of the cascades of intracellular events in response to laser application. Thus, the model can be used to both analyze existing in vitro data sets, as well as efficiently direct sampling strategies for future in vitro and in vivo studies. This model has been validated using laboratory data from several studies reported in the literature using blue light (413 nm and 458 nm) lasers with 100 s, 200 s, and 3600 s exposure durations. The model was able to predict the in vitro ED50 response curve from these studies, as well as the results for which we have no in vitro data (extrapolated based on irradiance reciprocity), within 1-6% for the shorter duration exposures. Based on exploration of this computer model using lethal vs. non-lethal laser exposure scenarios, the RPE cell's oxidative stress response differs quantitatively very little with respect to typical oxidative stress sources such as superoxide and hydrogen peroxide. However, in the lethal exposure scenarios the model points to a potential tipping point in the oxidative stress response of the mitochondrial-based cellular energetics. Further studies are underway to explore issues related to the levels of ATP/ADP and GSH/GSSG that are predicted by the model in these lethal vs. non-lethal exposure scenarios.

  2. Management of Spent Organic Ion-Exchange Resins by Photochemical Oxidation

    SciTech Connect

    Srinivas, C.; Sugilal, S.; Wattal, P. K.

    2003-02-26

    Management of spent ion-exchange resin waste arising from nuclear reactor operations by traditional practice of encapsulation in cement is associated with problems such as swelling and disintegration. Complete oxidation (mineralization) is an attractive alternative option. This paper reports the development of photochemical mineralization process for organic ion-exchange resins of poly (styrene-divinyl benzene) type with sulfonic acid and quaternary ammonium functional groups. It is a two-step process consisting of dissolution (conversion of solid resin into water-soluble reaction products) and photo-Fenton mineralization of the dissolved resin. Cation and anion resin dissolution was effected by reaction of the resin with H2O2 at 50-60 C in the presence of ferrous/copper sulphate catalyst. Direct dissolution of mixed resin was not efficient. However, the cation resin portion in the mixed resin could be selectively dissolved without affecting the anion portion. The solid anion resin after separation from the cation resin solution could be dissolved. About 0.5 liters of 50% H2O2 was required for dissolution of one kg of wet resin. The reaction time was 4-5 hours. Dissolution experiments were conducted on up to 8 liters of wet resin. The second step, viz., photo-Fenton mineralization of the dissolved resin was effected at ambient temperature(25-35 C). Kinetic results of laboratory scale experiments in immersion type photo-reactor and pilot scale experiments in tubular flow photo-reactor were presented. These results clearly demonstrated the photo-Fenton mineralization of dissolved resin at ambient temperature with stoichiometric quantity of H2O2 as against 70-200% excess H2O2 requirement in chemical mineralization experiments under Fenton oxidation conditions at 90-95 C. Based on these studies, a treatment scheme was developed and presented in this paper.

  3. Selective disruption of the blood-brain barrier by photochemical internalization

    NASA Astrophysics Data System (ADS)

    Hirschberg, Henry; Zhang, Michelle J.; Gach, Michael H.; Uzal, Francisco A.; Chighvinadze, David; Madsen, Steen J.

    2009-02-01

    Introduction: Failure to eradicate infiltrating glioma cells using conventional treatment regimens results in tumor recurrence and is responsible for the dismal prognosis of patients with glioblastoma multiforme (GBM). This is due to the fact that these migratory cells are protected by the blood-brain barrier (BBB) which prevents the delivery of most anti-cancer agents. We have evaluated the ability of photochemical internalization (PCI) to selectively disrupt the BBB in rats. This will permit access of anti-cancer drugs to effectively target the infiltrating tumor cells, and potentially improve the treatment effectiveness for malignant gliomas. Materials and Methods: PCI treatment, coupling a macromolecule therapy of Clostridium perfringens (Cl p) epsilon prototoxin with AlPcS2a-PDT, was performed on non-tumor bearing inbred Fisher rats. T1-weighted post-contrast magnetic resonance imaging (MRI) scans were used to evaluate the extent of BBB disruption which can be inferred from the volume contrast enhancement. Results: The synergistic effect of PCI to disrupt the BBB was observed at a fluence level of 1 J with an intraperitoneal injection of Cl p prototoxin. At the fluence level of 2.5J, the extent of BBB opening induced by PCI was similar to the result of PDT suggesting no synergistic effect evoked under these conditions. Conclusion: PCI was found to be highly effective and efficient for inducing selective and localized disruption of the BBB. The extent of BBB opening peaked on day 3 and the BBB was completed restored by day 18 post treatment.

  4. UVA-induced cyclobutane pyrimidine dimers in DNA: a direct photochemical mechanism?

    PubMed

    Mouret, Stéphane; Philippe, Coralie; Gracia-Chantegrel, Jocelyne; Banyasz, Akos; Karpati, Szilvia; Markovitsi, Dimitra; Douki, Thierry

    2010-04-07

    The carcinogenic action of UVA radiation is commonly attributed to DNA oxidation mediated by endogenous photosensitisers. Yet, it was recently shown that cyclobutane pyrimidine dimers (CPD), well known for their involvement in UVB genotoxicity, are produced in larger yield than oxidative lesions in UVA-irradiated cells and skin. In the present work, we gathered mechanistic information on this photoreaction by comparing formation of all possible bipyrimidine photoproducts upon UVA irradiation of cells, purified genomic DNA and dA(20):dT(20) oligonucleotide duplex. We observed that the distribution of photoproducts, characterized by the sole formation of CPD and the absence of (6-4) photoproducts was similar in the three types of samples. The CPD involving two thymines represented 90% of the amount of photoproducts. Moreover, the yields of formation of the DNA lesions were similar in cells and isolated DNA. In addition, the effect of the wavelength of the incident photons was found to be the same in isolated DNA and cells. This set of data shows that UVA-induced cyclobutane pyrimidine dimers are formed via a direct photochemical mechanism, without mediation of a cellular photosensitiser. This is possible because the double-stranded structure increases the capacity of DNA bases to absorb UVA photons, as evidenced in the case of the oligomer dA(20):dT(20). These results emphasize the need to consider UVA in the carcinogenic effects of sunlight. An efficient photoprotection is needed that can only be complete by completely blocking incident photons, rather than by systemic approaches such as antioxidant supplementation.

  5. Testing the early Mars H2-CO2 greenhouse hypothesis with a 1-D photochemical model

    NASA Astrophysics Data System (ADS)

    Batalha, Natasha; Domagal-Goldman, Shawn D.; Ramirez, Ramses; Kasting, James F.

    2015-09-01

    A recent study by Ramirez et al. (Ramirez, R.M. et al. [2014]. Nat. Geosci. 7(1), 59-63. http://www.nature.com/doifinder/10.1038/ngeo2000 (accessed 16.09.14)) demonstrated that an atmosphere with 1.3-4 bar of CO2 and H2O, in addition to 5-20% H2, could have raised the mean annual and global surface temperature of early Mars above the freezing point of water. Such warm temperatures appear necessary to generate the rainfall (or snowfall) amounts required to carve the ancient martian valleys. Here, we use our best estimates for early martian outgassing rates, along with a 1-D photochemical model, to assess the conversion efficiency of CO, CH4, and H2S to CO2, SO2, and H2. Our outgassing estimates assume that Mars was actively recycling volatiles between its crust and interior, as Earth does today. H2 production from serpentinization and deposition of banded iron-formations is also considered. Under these assumptions, maintaining an H2 concentration of ˜1-2% by volume is achievable, but reaching 5% H2 requires additional H2 sources or a slowing of the hydrogen escape rate below the diffusion limit. If the early martian atmosphere was indeed H2-rich, we might be able to see evidence of this in the rock record. The hypothesis proposed here is consistent with new data from the Curiosity Rover, which show evidence for a long-lived lake in Gale Crater near Mt. Sharp. It is also consistent with measured oxygen fugacities of martian meteorites, which show evidence for progressive mantle oxidation over time.

  6. Does free-air carbon dioxide enrichment affect photochemical energy use by evergreen trees in different seasons? A chlorophyll fluorescence study of mature loblolly pine

    SciTech Connect

    Hymus, G.J.; Ellsworth, D.S.; Baker, N.R.; Long, S.P.

    1999-08-01

    Previous studies of the effects of growth at elevated CO{sup 2} on energy partitioning in the photosynthetic apparatus have produced conflicting results. The hypothesis was developed and tested that elevated CO{sub 2} increases photochemical energy use when there is a high demand for assimilates and decreases usage when demand is low. Modulated chlorophyll a fluorescence and leaf gas exchange were measured on needles at the tope of a mature, 12-m loblolly pine (Pinus taeda L.l) forest. Trees were exposed to ambient CO{sub 2} or ambient plus 20 Pa CO{sub 2} using free-air CO{sub 2} enrichment. During April and August, periods of shoot growth, light-saturated photo-synthesis and linear electron transport were increased by elevated CO{sub 2}. In November, when growth had ceased but temperatures were still moderate, CO{sub 2} treatment had no significant effect on linear electron transport. In February, when low temperatures were likely to inhibit translocation, CO{sub 2} treatment caused a significant decrease in linear electron transport. This coincided with a slower recovery of the maximum photosystem II efficiency on transfer of needles to the shade, indicating that growth in elevated CO{sub 2} induced a more persistent photoinhibition. Both the summer increase and the winter decrease in linear electron transport in elevated CO{sub 2} resulted from a change in photochemical quenching, not in the efficiency of energy transfer within the photosystem II antenna. There was no evidence of any effect of CO{sub 2} on photochemical energy sinks other than carbon metabolism. Their results suggest that elevated CO{sub 2} may increase the effects of winter stress on evergreen foliage.

  7. Gauging triple stores with actual biological data

    PubMed Central

    2012-01-01

    Background Semantic Web technologies have been developed to overcome the limitations of the current Web and conventional data integration solutions. The Semantic Web is expected to link all the data present on the Internet instead of linking just documents. One of the foundations of the Semantic Web technologies is the knowledge representation language Resource Description Framework (RDF). Knowledge expressed in RDF is typically stored in so-called triple stores (also known as RDF stores), from which it can be retrieved with SPARQL, a language designed for querying RDF-based models. The Semantic Web technologies should allow federated queries over multiple triple stores. In this paper we compare the efficiency of a set of biologically relevant queries as applied to a number of different triple store implementations. Results Previously we developed a library of queries to guide the use of our knowledge base Cell Cycle Ontology implemented as a triple store. We have now compared the performance of these queries on five non-commercial triple stores: OpenLink Virtuoso (Open-Source Edition), Jena SDB, Jena TDB, SwiftOWLIM and 4Store. We examined three performance aspects: the data uploading time, the query execution time and the scalability. The queries we had chosen addressed diverse ontological or biological questions, and we found that individual store performance was quite query-specific. We identified three groups of queries displaying similar behaviour across the different stores: 1) relatively short response time queries, 2) moderate response time queries and 3) relatively long response time queries. SwiftOWLIM proved to be a winner in the first group, 4Store in the second one and Virtuoso in the third one. Conclusions Our analysis showed that some queries behaved idiosyncratically, in a triple store specific manner, mainly with SwiftOWLIM and 4Store. Virtuoso, as expected, displayed a very balanced performance - its load time and its response time for all the

  8. Exogenous Melatonin Mitigates Photoinhibition by Accelerating Non-photochemical Quenching in Tomato Seedlings Exposed to Moderate Light during Chilling.

    PubMed

    Ding, Fei; Wang, Meiling; Liu, Bin; Zhang, Shuoxin

    2017-01-01

    Melatonin plays an important role in tolerance to multiple stresses in plants. Recent studies have shown that melatonin relieves photoinhibition in plants under cold stress; however, the mechanisms are not fully understood. Non-photochemical quenching (NPQ) is a key process thermally dissipating excess light energy that plants employ as a protective mechanism to prevent the over reduction of photosystem II. Here, we report the effects of exogenous melatonin on NPQ and mitigation of photoinhibition in tomato seedlings exposed to moderate light during chilling. In response to moderate light during chilling, the maximum quantum yield (Fv/Fm) and the effective photochemical efficiency (F'v/F'm) of PSII were both substantially reduced, showing severe photoinhibition in tomato seedlings, whereas exogenous application of melatonin effectively alleviated the photoinhibition. Further experiment showed that melatonin accelerated the induction of NPQ in response to moderate light and maintained higher level of NPQ upon longer exposure to light during chilling. Consistent with the increased NPQ was the elevated de-epoxidation state of xanthophyll pigments in melatonin-pretreated seedlings exposed to light during chilling. Enzyme activity assay showed that violaxanthin de-epoxidase (VDE), which catalyzes the de-epoxidation reaction in the xanthophyll cycle, was activated by light and the activity was further enhanced by application of melatonin. Further analysis revealed that melatonin induced the expression of VDE gene in tomato seedlings under moderate light and chilling conditions. Ascorbic acid is an essential cofactor of VDE and the level of it was found to be increased in melatonin-pretreated seedlings. Feeding tomato seedlings with dithiothreitol, an inhibitor of VDE, blocked the effects of melatonin on the de-epoxidation state of xanthophyll pigments and the induction of NPQ. Collectively, these results suggest that exogenous melatonin mitigates photoinhibition by

  9. Exogenous Melatonin Mitigates Photoinhibition by Accelerating Non-photochemical Quenching in Tomato Seedlings Exposed to Moderate Light during Chilling

    PubMed Central

    Ding, Fei; Wang, Meiling; Liu, Bin; Zhang, Shuoxin

    2017-01-01

    Melatonin plays an important role in tolerance to multiple stresses in plants. Recent studies have shown that melatonin relieves photoinhibition in plants under cold stress; however, the mechanisms are not fully understood. Non-photochemical quenching (NPQ) is a key process thermally dissipating excess light energy that plants employ as a protective mechanism to prevent the over reduction of photosystem II. Here, we report the effects of exogenous melatonin on NPQ and mitigation of photoinhibition in tomato seedlings exposed to moderate light during chilling. In response to moderate light during chilling, the maximum quantum yield (Fv/Fm) and the effective photochemical efficiency (F′v/F′m) of PSII were both substantially reduced, showing severe photoinhibition in tomato seedlings, whereas exogenous application of melatonin effectively alleviated the photoinhibition. Further experiment showed that melatonin accelerated the induction of NPQ in response to moderate light and maintained higher level of NPQ upon longer exposure to light during chilling. Consistent with the increased NPQ was the elevated de-epoxidation state of xanthophyll pigments in melatonin-pretreated seedlings exposed to light during chilling. Enzyme activity assay showed that violaxanthin de-epoxidase (VDE), which catalyzes the de-epoxidation reaction in the xanthophyll cycle, was activated by light and the activity was further enhanced by application of melatonin. Further analysis revealed that melatonin induced the expression of VDE gene in tomato seedlings under moderate light and chilling conditions. Ascorbic acid is an essential cofactor of VDE and the level of it was found to be increased in melatonin-pretreated seedlings. Feeding tomato seedlings with dithiothreitol, an inhibitor of VDE, blocked the effects of melatonin on the de-epoxidation state of xanthophyll pigments and the induction of NPQ. Collectively, these results suggest that exogenous melatonin mitigates photoinhibition by

  10. Photochemical modification of polymeric materials and the polarization of light in ionomeric guest/host systems

    NASA Astrophysics Data System (ADS)

    Pan, Bo

    Photochemical methods were introduced to develop important extrusion processes, through which polymers can either be functionalized or modified by altering molecular weight characteristics. Therefore, poly(methyl methacrylate) (PMMA) incorporated with a small amount of light-reactive functional groups was synthesized. These functional groups can be activated by UV irradiation in a post extrusion process to produce high molecular weight polymer and/or crosslinked polymer. Environmental stress cracking resistance of these polymers was examined and correlated to damping using dynamic mechanic analysis. To improve industrial reactive extrusion process of preparing maleic anhydride grafted polypropylene (MAR-g-PP), photografting was proposed and studied. Using benzophenone (BP) as the initiator, grafting efficiency was significantly improved compared to peroxide initiated grafting. Moreover, nearly constant conversion of maleic anhydride was observed in photografting. The high efficiency of benzophenone initiated photografting was attributed to the formation of the excited triplet state maleic anhydride. A rate constant of 6.0*109 M-1*sec-1 for the quenching of triplet state BP with MAH was obtained using laser photolysis spectroscopy. In a comparison, the hydrogen abstraction process from polypropylene by the triplet state BP molecules has a rate constant of 4.1*105 M-1*sec-1. In solution grafting with the use of benzene as the solvent, a facile triplet state energy transfer process may also occur leading to the formation of the excited triplet state MAH. Spectroscopic methods involving light were also used for the study of the guest-host interactions in polymer systems. The use of ionomers as the matrix for the oriented guest/host systems, cationic dye systems in particular, was shown to enhance polarization efficiency as well as dye uptake as comparing to conventional polymers, such as poly(vinyl alcohol). It was found that the dye molecules in carboxylated EVOH

  11. Condensation heat transfer of actual flue gas on horizontal tubes

    SciTech Connect

    Osakabe, Masahiro; Itoh, Tugue; Yagi, Kiyoyuki

    1999-07-01

    In order to improve the boiler efficiency, latent heat recovery from an exhaust flue gas is a very important concept. Condensation heat transfer on horizontal stainless steel tubes was investigated experimentally using an actual flue gas from a natural gas boiler. The experiment was conducted at different air ratios and steam mass concentrations of the flue gas, and in a wide range of tube wall temperature. The condensation pattern was similar to the dropwise condensation near the dew point. As the wall temperature was decreased, the wall region covered with a thin liquid film increased. The heat and mass transfer behavior were well predicted with the simple analogy correlation in the high wall temperature region. But in the low wall temperature region, the total heat transfer rate was higher than that predicted by the simple analogy correlation. At a high steam mass concentration artificially generated with steam injection, the total heat transfer rate was higher than that predicted by the simple analogy correlation. The analogy correlation using the modified Sherwood number taking account of the mass absorption effect was proposed. The modified correlation gave a good prediction of the heat flux at the high steam mass concentration.

  12. Photochemical reduction of CO{sub 2} to fuels and chemicals

    SciTech Connect

    DuBois, D.; Eisenberg, R.; Fujita, E.

    1996-09-01

    Photochemical reduction of CO{sub 2} represents a potentially useful approach to developing a sustainable source of carbon-based chemicals, fuels, and materials. In this report the present status of photochemical CO{sub 2} reduction is assessed, areas that need to be better understood for advancement are identified, and approaches to overcoming barriers are suggested. Because of the interdisciplinary nature of this field, assessments of three closely interrelated areas are given including integrated photochemical systems for catalytic CO{sub 2} reduction, thermal catalytic CO{sub 2} reactions, and electrochemical CO{sub 2} reduction. The report concludes with a summary and assessment of potential impacts of this area on chemical and energy technologies.

  13. Site-emerging technologies: Laser induced photochemical oxidative destruction of toxic organics in leachates and groundwaters

    SciTech Connect

    Not Available

    1992-12-01

    The technology described in the report has been developed under the Emerging Technology Program of the Superfund Innovative Technology Evaluation (SITE) Program to photochemically oxidize organic compounds in wastewater by applying ultraviolet radiation using an excimer laser. The energy supplied by the laser is sufficient to stimulate photochemical reactions between the organics and hydrogen peroxide employed as a chemical oxidant, causing photooxidation and/or phototransformation of the toxic species to carbon dioxide, water and the corresponding halogenated acid. The photochemical reaction is capable of producing the complete destruction of low to moderate concentrations of toxic organics in water. Optimum conditions for the complete destruction of several different classes of compounds were developed and demonstrated in the laboratory.

  14. Photochemical reactivity of polyenes: from dienes to rhodopsin, from microseconds to femtoseconds.

    PubMed

    Liu, Robert S H; Hammond, George S

    2003-08-01

    In reviewing the photochemistry of polyenes (from dienes and trienes to the visual retinyl chromophore), we categorize condensed-phase photochemical reactivity of molecules into two groups: those from thermally equilibrated excited species and those from unequilibrated excited species. Classical theories on radiationless transitions are useful for rationalizing the reactivity of molecules belonging to the first set only. The second group includes many of the exciting ultrafast photochemical reactions reported recently for polyenes (including dienes and trienes), in some cases with rates faster than vibrational relaxation. Much of the excited singlet-state reactions of polyenes, including the Hula-twist mechanism of photoisomerization, have been integrated with concepts introduced in other ultrafast spectroscopic/photochemical studies. Taking into consideration the special environment of the retinyl chromophore in rhodopsin, we propose a new mechanism for the phototrigger that accounts for its unusually fast rate of isomerization.

  15. Effect of chemical kinetics uncertainties on calculated constituents in a tropospheric photochemical model

    NASA Technical Reports Server (NTRS)

    Thompson, Anne M.; Stewart, Richard W.

    1991-01-01

    Random photochemical reaction rates are employed in a 1D photochemical model to examine uncertainties in tropospheric concentrations and thereby determine critical kinetic processes and significant correlations. Monte Carlo computations are used to simulate different chemical environments and their related imprecisions. The most critical processes are the primary photodissociation of O3 (which initiates ozone destruction) and NO2 (which initiates ozone formation), and the OH/methane reaction is significant. Several correlations and anticorrelations between species are discussed, and the ozone/transient OH correlation is examined in detail. One important result of the modeling is that estimates of global OH are generally about 25 percent uncertain, limiting the precision of photochemical models. Techniques for reducing the imprecision are discussed which emphasize the use of species and radical species measurements.

  16. Construction of a multipurpose photochemical reactor with on-line spectrophotometric detection.

    PubMed

    Ditrói, Tamás; Kalmár, József; Pino-Chamorro, Jose Angel; Erdei, Zsolt; Lente, Gábor; Fábián, István

    2016-04-01

    A versatile photoreactor was built for studying homogeneous and heterogeneous photochemical reactions using fiber-optic devices. The reactor was designed to allow simultaneous photochemical initiation and online spectrophotometric monitoring of the reaction using independently controlled excitation and detection lamps. The system consists of a CCD spectrophotometer, a thermostated sample holder, two light sources, and standard 1.00 × 1.00 cm (or possibly smaller) fluorescence cuvettes, all coupled with fiber optic cables. The device can be used as a photoreactor, a diode-array spectrophotometer and also as a spectrofluorimeter. The reactor can be used in flow-through operation modes. Performance tests of the instrument are reported here with a number of known photochemical systems.

  17. Chemical Actinometry: Using o-Nitrobenzaldehyde to Measure Lamp Intensity in Photochemical Experiments

    NASA Astrophysics Data System (ADS)

    Willett, Kristine L.; Hites, Ronald A.

    2000-07-01

    A simple actinometry experiment that could be used in graduate or undergraduate laboratory courses is described. The photochemical reaction of o-nitrobenzaldehyde (NBA) irradiated with a medium-pressure mercury vapor lamp is used to calculate the intensity of light over the wavelength range of 300-410 nm. The reactant disappearance rate can be quantitated by gas chromatography or by gas chromatographic mass spectrometry. The calculations necessary to convert the kinetic measurements to intensity are discussed. This experiment provides an easy way to determine the intensity of different light sources over a specific wavelength range, information that could be necessary in studying various environmentally relevant photochemical reactions.

  18. Photochemical oxidant transport - Mesoscale lake breeze and synoptic-scale aspects

    NASA Technical Reports Server (NTRS)

    Lyons, W. A.; Cole, H. S.

    1976-01-01

    Data from routine ozone monitoring in southeastern Wisconsin and limited monitoring of the Milwaukee area by the Environmental Protection Agency are examined. Hourly averages as high as 30 pphm have been recorded in southeastern Wisconsin, and high readings have been reported in rural regions throughout the state. The observations indicate that photochemical oxidants and their nitrogen oxide and reactive hydrocarbon precursers advect from Chicago and northern Indiana into southeastern Wisconsin. There is evidence that synoptic-scale transport of photochemical oxidants occurs, allowing the pollution of entire anticyclones. These results cast doubt on the validity of the Air Quality Control Regions established by amendment to the Clean Air Act of 1970.

  19. Enantioselective Organocatalytic Diels–Alder Trapping of Photochemically Generated Hydroxy‐o‐Quinodimethanes

    PubMed Central

    Dell'Amico, Luca; Vega‐Peñaloza, Alberto; Cuadros, Sara

    2016-01-01

    Abstract The photoenolization/Diels–Alder strategy offers straightforward access to synthetically valuable benzannulated carbocyclic products. This historical light‐triggered process has never before succumbed to efforts to develop an enantioselective catalytic approach. Herein, we demonstrate how asymmetric organocatalysis provides simple yet effective catalytic tools to intercept photochemically generated hydroxy‐o‐quinodimethanes with high stereoselectivity. We used a chiral organic catalyst, derived from natural cinchona alkaloids, to activate maleimides toward highly stereoselective Diels–Alder reactions. An unconventional mechanism of stereocontrol is operative, wherein the organocatalyst is actively involved in both the photochemical pathway, by leveraging the formation of the reactive photoenol, and the stereoselectivity‐defining event. PMID:26797768

  20. The impact of aerosols on solar ultraviolet radiation an photochemical smog

    SciTech Connect

    Dickerson, R.R.; Kondragunta, S.; Stenchikov, G.

    1997-10-31

    Photochemical smog, or ground-level ozone, has been the most recalcitrant of air pollution problems, but reductions in emissions of sulfur and hydrocarbons may yield unanticipated benefits in air quality. While sulfate and some organic aerosol particles scatter solar radiation back into space and can cool Earth`s surface, they also change the actinic flux of ultraviolet (UV) radiation. Observations and numerical models show that UV-scattering particles in the boundary layer accelerate photochemical reactions and smog production, but UV-absorbing aerosols such as mineral dust and soot inhibit smog production. Results could have major implications for the control of air pollution. 19 refs., 4 figs.

  1. The impact of aerosols on solar ultraviolet radiation and photochemical smog.

    PubMed

    Dickerson, R R; Kondragunta, S; Stenchikov, G; Civerolo, K L; Doddridge, B G; Holben, B N

    1997-10-31

    Photochemical smog, or ground-level ozone, has been the most recalcitrant of air pollution problems, but reductions in emissions of sulfur and hydrocarbons may yield unanticipated benefits in air quality. While sulfate and some organic aerosol particles scatter solar radiation back into space and can cool Earth's surface, they also change the actinic flux of ultraviolet (UV) radiation. Observations and numerical models show that UV-scattering particles in the boundary layer accelerate photochemical reactions and smog production, but UV-absorbing aerosols such as mineral dust and soot inhibit smog production. Results could have major implications for the control of air pollution.

  2. Comparison of measured ozone in southeastern Virginia with computer predictions from a photochemical model

    NASA Technical Reports Server (NTRS)

    Wakelyn, N. T.; Gregory, G. L.

    1980-01-01

    Data for one day of the 1977 southeastern Virginia urban plume study are compared with computer predictions from a traveling air parcel model using a contemporary photochemical mechanism with a minimal description of nonmethane hydrocarbon (NMHC) constitution and chemistry. With measured initial NOx and O3 concentrations and a current separate estimate of urban source loading input to the model, and for a variation of initial NMHC over a reasonable range, an ozone increase over the day is predicted from the photochemical simulation which is consistent with the flight path averaged airborne data.

  3. A Universal Protocol for Photochemical Covalent Immobilization of Intact Carbohydrates for the Preparation of Carbohydrate Microarrays

    PubMed Central

    Wang, Huibin; Zhang, Yiming; Yuan, Xun; Chen, Yi; Yan, Mingdi

    2010-01-01

    A universal photochemical method has been established for the immobilization of intact carbohydrates and their analogues, and for the fabrication of carbohydrate microarrays. The method features the use of perfluorophenyl azide (PFPA)-modified substrates and the photochemical reaction of surface azido groups with printed carbohydrates. Various aldoses, ketoses, non-reducing sugars such as alditols and their derivatives can be directly arrayed on the PFPA-modified chips. The lectin-recognition ability of arrayed mannose, glucose and their oligo- and polysaccharides were confirmed using surface plasmon resonance imaging and laser-induced fluorescence imaging. PMID:21138274

  4. Utilization of UARS Data in Validation of Photochemical and Dynamical Mechanisms in Stratospheric Models

    NASA Technical Reports Server (NTRS)

    Ko, Malcolm K. W.; Rodriquez, Jose M.; Hu, Wenjie; Danilin, Michael Y.; Shia, Run-Li

    1998-01-01

    The proposed work utilized Upper Atmosphere Research Satellite (UARS) measurements of short-lived and long-lived species, in conjunction with existing photochemical "box" models, trajectory models, and two-dimensional global models, to elucidate outstanding questions in our understanding of photochemical and dynamical mechanisms in the stratosphere. Particular emphasis was given to arriving at the best possible understanding of the chemical and dynamical contribution to the stratospheric ozone budget. Such understanding will increase confidence in the simulations carried out by assessment models.

  5. Utilization of UARS Data in Validation of Photochemical and Dynamical Mechanisms in Stratospheric Models

    NASA Technical Reports Server (NTRS)

    Ko, M. K. W.; Rodriquez, J. M.; Hu, W.; Danilin, M. Y.; Shia, R.-L.

    1998-01-01

    The proposed work utilized Upper Atmosphere Research Satellite (UARS) measurements of short-lived and long-lived species, in conjunction with existing photochemical "box" models, trajectory models, and two-dimensional global models, to elucidate outstanding questions in our understanding of photochemical and dynamical mechanisms in the stratosphere. Particular emphasis was given to arriving at the best possible understanding of the chemical and dynamical contributions to the stratospheric ozone budget. Such understanding will increase confidence in the simulations carried out by assessment models.

  6. Photochemical Transformation Processes in Sunlit Surface Waters (Invited)

    NASA Astrophysics Data System (ADS)

    Vione, D.

    2013-12-01

    Photochemical reactions are major processes in the transformation of hardly biodegradable xenobiotics in surface waters. They are usually classified into direct photolysis and indirect or sensitised degradation. Direct photolysis requires xenobiotic compounds to absorb sunlight, and to get transformed as a consequence. Sensitised transformation involves reaction with transient species (e.g. °OH, CO3-°, 1O2 and triplet states of chromophoric dissolved organic matter, 3CDOM*), photogenerated by so-called photosensitisers (nitrate, nitrite and CDOM). CDOM is a major photosensitiser: is it on average the main source of °OH (and of CO3-° as a consequence, which is mainly produced upon oxidation by °OH of carbonate and bicarbonate) and the only important source of 1O2 and 3CDOM* [1, 2]. CDOM origin plays a key role in sensitised processes: allochthonous CDOM derived from soil runoff and rich in fulvic and humic substances is usually more photoactive than autochthonous CDOM (produced by in-water biological processes and mainly consisting of protein-like material) or of CDOM derived from atmospheric deposition. An interesting gradual evolution of CDOM origin and photochemistry can be found in mountain lakes across the treeline, which afford a gradual transition of allochthonous- autochtonous - atmopheric CDOM when passing from trees to alpine meadows to exposed rocks [3]. Another important issue is the sites of reactive species photoproduction in CDOM. While there is evidence that smaller molecular weight fractions are more photoactive, some studies have reported considerable 1O2 reactivity in CDOM hydrophobic sites and inside particles [4]. We have recently addressed the problem and found that dissolved species in standard humic acids (hydrodynamic diameter < 0.1 μm) account for the vast majority of 1O2 and triplet states photoproduction. In hydrophobic sites of particles, the formation rate of 1O2 is considerably lower than in the solution bulk [5], but the absence

  7. Photochemical Control of Organic Carbon Availability to Coastal Microbial Communities

    NASA Astrophysics Data System (ADS)

    Miller, W. L.; Reader, H. E.; Powers, L. C.

    2010-12-01

    using a three-stage filtration process to remove larger detritus and biological particles before collecting the bacterial population on a 0.2um filter, for re-suspension in a small volume of filter-sterilized seawater. To ensure eventual carbon limitation in microbial incubations, the samples were spiked with inorganic nitrogen and phosphorus. Oxygen measurements were made as a proxy for community carbon uptake with an Ocean Optics FOXY-R fluorescence probe. Post irradiation, 15 samples were immediately sacrificed to take t=0 oxygen measurements, and the remainder were incubated in the dark for 10-12 days. Seasonal biolabile carbon photoproduction values ranged from -1.8E-2 to 9.2E-2 mol C produced/mol photons absorbed. To compare seasonal and spatial variations over this large data set, irradiations were set at a photon dose of 3.2 mol photons/m^2. Progressive photon dose experiments shows that irradiation length strongly influences the total biolabile product as assayed with microbial measurements. A conceptual model is presented to explain this dependence on photon dose. This varying dependence on photon dose is different from other photochemical products such as CO, and further complicates attempts to quantify the effect of photochemistry on the bioavailability of carbon in marine environments.

  8. Photochemical Dimerization of Dibenzylideneacetone: A Convenient Exercise in [2+2] Cycloaddition Using Chemical Ionization Mass Spectrometry

    ERIC Educational Resources Information Center

    Rao, G. Nageswara; Janardhana, Chelli; Ramanathan, V.; Rajesh, T.; Kumar, P. Harish

    2006-01-01

    Chemical reactions induced by light have been utilized for synthesizing highly strained, thermodynamically unstable compounds, which are inaccessible through non-photochemical methods. Photochemical cycloaddition reactions, especially those leading to the formation of four-membered rings, constitute a convenient route to compounds that are…

  9. Self-Actualization and the Effective Social Studies Teacher.

    ERIC Educational Resources Information Center

    Farmer, Rodney B.

    1980-01-01

    Discusses a study undertaken to investigate the relationship between social studies teachers' degrees of self-actualization and their teacher effectiveness. Investigates validity of using Maslow's theory of self-actualization as a way of identifying the effective social studies teacher personality. (Author/DB)

  10. Self-Actualization Effects Of A Marathon Growth Group

    ERIC Educational Resources Information Center

    Jones, Dorothy S.; Medvene, Arnold M.

    1975-01-01

    This study examined the effects of a marathon group experience on university student's level of self-actualization two days and six weeks after the experience. Gains in self-actualization as a result of marathon group participation depended upon an individual's level of ego strength upon entering the group. (Author)

  11. Self-actualization: Its Use and Misuse in Teacher Education.

    ERIC Educational Resources Information Center

    Ivie, Stanley D.

    1982-01-01

    The writings of Abraham Maslow are analyzed to determine the meaning of the psychological term "self-actualization." After pointing out that self-actualization is a rare quality and that it has little to do with formal education, the author concludes that the concept has little practical relevance for teacher education. (PP)

  12. The Self-Actualization of Polk Community College Students.

    ERIC Educational Resources Information Center

    Pearsall, Howard E.; Thompson, Paul V., Jr.

    This article investigates the concept of self-actualization introduced by Abraham Maslow (1954). A summary of Maslow's Needs Hierarchy, along with a description of the characteristics of the self-actualized person, is presented. An analysis of humanistic education reveals it has much to offer as a means of promoting the principles of…

  13. 26 CFR 1.953-2 - Actual United States risks.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 26 Internal Revenue 10 2010-04-01 2010-04-01 false Actual United States risks. 1.953-2 Section 1... (CONTINUED) INCOME TAXES Controlled Foreign Corporations § 1.953-2 Actual United States risks. (a) In general. For purposes of paragraph (a) of § 1.953-1, the term “United States risks” means risks described...

  14. 26 CFR 1.953-2 - Actual United States risks.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 26 Internal Revenue 10 2011-04-01 2011-04-01 false Actual United States risks. 1.953-2 Section 1... (CONTINUED) INCOME TAXES (CONTINUED) Controlled Foreign Corporations § 1.953-2 Actual United States risks. (a) In general. For purposes of paragraph (a) of § 1.953-1, the term “United States risks” means...

  15. 26 CFR 1.953-2 - Actual United States risks.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 26 Internal Revenue 10 2014-04-01 2013-04-01 true Actual United States risks. 1.953-2 Section 1... (CONTINUED) INCOME TAXES (CONTINUED) Controlled Foreign Corporations § 1.953-2 Actual United States risks. (a) In general. For purposes of paragraph (a) of § 1.953-1, the term “United States risks” means...

  16. 26 CFR 1.953-2 - Actual United States risks.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 26 Internal Revenue 10 2013-04-01 2013-04-01 false Actual United States risks. 1.953-2 Section 1... (CONTINUED) INCOME TAXES (CONTINUED) Controlled Foreign Corporations § 1.953-2 Actual United States risks. (a) In general. For purposes of paragraph (a) of § 1.953-1, the term “United States risks” means...

  17. 26 CFR 1.953-2 - Actual United States risks.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 26 Internal Revenue 10 2012-04-01 2012-04-01 false Actual United States risks. 1.953-2 Section 1... (CONTINUED) INCOME TAXES (CONTINUED) Controlled Foreign Corporations § 1.953-2 Actual United States risks. (a) In general. For purposes of paragraph (a) of § 1.953-1, the term “United States risks” means...

  18. Facebook as a Library Tool: Perceived vs. Actual Use

    ERIC Educational Resources Information Center

    Jacobson, Terra B.

    2011-01-01

    As Facebook has come to dominate the social networking site arena, more libraries have created their own library pages on Facebook to create library awareness and to function as a marketing tool. This paper examines reported versus actual use of Facebook in libraries to identify discrepancies between intended goals and actual use. The results of a…

  19. School Guidance Counselors' Perceptions of Actual and Preferred Job Duties

    ERIC Educational Resources Information Center

    Edwards, John Dexter

    2010-01-01

    The purpose of this study was to provide process data for school counselors, administrators, and the public, regarding school counselors' actual roles within the guidance counselor preferred job duties and actual job duties. In addition, factors including National Certification or no National Certification, years of counseling experience, and…

  20. Transformer Efficiency Assessment - Okinawa, Japan

    SciTech Connect

    Thomas L. Baldwin; Robert J. Turk; Kurt S. Myers; Jake P. Gentle; Jason W. Bush

    2012-05-01

    The US Army Engineering & Support Center, Huntsville (USAESCH), and the US Marine Corps Base (MCB), Okinawa, Japan retained Idaho National Laboratory (INL) to conduct a Transformer Efficiency Assessment of “key” transformers located at multiple military bases in Okinawa, Japan. The purpose of this assessment is to support the Marine Corps Base, Okinawa in evaluating medium voltage distribution transformers for potential efficiency upgrades. The original scope of work included the MCB providing actual transformer nameplate data, manufacturer’s factory test sheets, electrical system data (kWh), demand data (kWd), power factor data, and electricity cost data. Unfortunately, the MCB’s actual data is not available and therefore making it necessary to de-scope the original assessment. Note: Any similar nameplate data, photos of similar transformer nameplates, and basic electrical details from one-line drawings (provided by MCB) are not a replacement for actual load loss test data. It is recommended that load measurements are performed on the high and low sides of transformers to better quantify actual load losses, demand data, and power factor data. We also recommend that actual data, when available, be inserted by MCB Okinawa where assumptions have been made and then the LCC analysis updated. This report covers a generalized assessment of modern U.S. transformers in a three level efficiency category, Low-Level efficiency, Medium-Level efficiency, and High-Level efficiency.

  1. Transformer Efficiency Assessment - Okinawa, Japan

    SciTech Connect

    Thomas L. Baldwin; Robert J. Turk; Kurt S. Myers; Jake P. Gentle; Jason W. Bush

    2012-08-01

    The US Army Engineering & Support Center, Huntsville (USAESCH), and the US Marine Corps Base (MCB), Okinawa, Japan retained Idaho National Laboratory (INL) to conduct a Transformer Efficiency Assessment of “key” transformers located at multiple military bases in Okinawa, Japan. The purpose of this assessment is to support the Marine Corps Base, Okinawa in evaluating medium voltage distribution transformers for potential efficiency upgrades. The original scope of work included the MCB providing actual transformer nameplate data, manufacturer’s factory test sheets, electrical system data (kWh), demand data (kWd), power factor data, and electricity cost data. Unfortunately, the MCB’s actual data is not available and therefore making it necessary to de-scope the original assessment. Note: Any similar nameplate data, photos of similar transformer nameplates, and basic electrical details from one-line drawings (provided by MCB) are not a replacement for actual load loss test data. It is recommended that load measurements are performed on the high and low sides of transformers to better quantify actual load losses, demand data, and power factor data. We also recommend that actual data, when available, be inserted by MCB Okinawa where assumptions have been made and then the LCC analysis updated. This report covers a generalized assessment of modern U.S. transformers in a three level efficiency category, Low-Level efficiency, Medium-Level efficiency, and High-Level efficiency.

  2. Oxidative capacity and radical chemistry in the polluted atmosphere of Hong Kong and Pearl River Delta region: analysis of a severe photochemical smog episode

    NASA Astrophysics Data System (ADS)

    Xue, Likun; Gu, Rongrong; Wang, Tao; Wang, Xinfeng; Saunders, Sandra; Blake, Donald; Louie, Peter K. K.; Luk, Connie W. Y.; Simpson, Isobel; Xu, Zheng; Wang, Zhe; Gao, Yuan; Lee, Shuncheng; Mellouki, Abdelwahid; Wang, Wenxing

    2016-08-01

    We analyze a photochemical smog episode to understand the oxidative capacity and radical chemistry of the polluted atmosphere in Hong Kong and the Pearl River Delta (PRD) region. A photochemical box model based on the Master Chemical Mechanism (MCM v3.2) is constrained by an intensive set of field observations to elucidate the budgets of ROx (ROx = OH+HO2+RO2) and NO3 radicals. Highly abundant radical precursors (i.e. O3, HONO and carbonyls), nitrogen oxides (NOx) and volatile organic compounds (VOCs) facilitate strong production and efficient recycling of ROx radicals. The OH reactivity is dominated by oxygenated VOCs (OVOCs), followed by aromatics, alkenes and alkanes. Photolysis of OVOCs (except for formaldehyde) is the dominant primary source of ROx with average daytime contributions of 34-47 %. HONO photolysis is the largest contributor to OH and the second-most significant source (19-22 %) of ROx. Other considerable ROx sources include O3 photolysis (11-20 %), formaldehyde photolysis (10-16 %), and ozonolysis reactions of unsaturated VOCs (3.9-6.2 %). In one case when solar irradiation was attenuated, possibly by the high aerosol loadings, NO3 became an important oxidant and the NO3-initiated VOC oxidation presented another significant ROx source (6.2 %) even during daytime. This study suggests the possible impacts of daytime NO3 chemistry in the polluted atmospheres under conditions with the co-existence of abundant O3, NO2, VOCs and aerosols, and also provides new insights into the radical chemistry that essentially drives the formation of photochemical smog in the high-NOx environment of Hong Kong and the PRD region.

  3. Source apportionment of VOCs and the contribution to photochemical ozone formation during summer in the typical industrial area in the Yangtze River Delta, China

    NASA Astrophysics Data System (ADS)

    Shao, Ping; An, Junlin; Xin, Jinyuan; Wu, Fangkun; Wang, Junxiu; Ji, Dongsheng; Wang, Yuesi

    2016-07-01

    Volatile organic compounds (VOCs) were continuously observated in a northern suburb of Nanjing, a typical industrial area in the Yangtze River Delta, in a summer observation period from 15th May to 31st August 2013. The average concentration of total VOCs was (34.40 ± 25.20) ppbv, including alkanes (14.98 ± 12.72) ppbv, alkenes (7.35 ± 5.93) ppbv, aromatics (9.06 ± 6.64) ppbv and alkynes (3.02 ± 2.01) ppbv, respectively. Source apportionment via Positive Matrix Factorization was conducted, and six major sources of VOCs were identified. The industry-related sources, including industrial emissions and industrial solvent usage, occupied the highest proportion, accounting for about 51.26% of the VOCs. Vehicular emissions occupied the second highest proportion, accounting for about 34.08%. The rest accounted for about 14.66%, including vegetation emission and liquefied petroleum gas/natural gas usage. Contributions of VOCs to photochemical O3 formation were evaluated by the application of a detailed chemical mechanism model (NCAR MM). Alkenes were the dominant contributors to the O3 photochemical production, followed by aromatics and alkanes. Alkynes had a very small impact on photochemical O3 formation. Based on the outcomes of the source apportionment, a sensitivity analysis of relative O3 reduction efficiency (RORE), under different source removal regimes such as using the reduction of VOCs from 10% to 100% as input, was conducted. The RORE was the highest (~ 20%-40%) when the VOCs from solvent-related sources decreased by 40%. The highest RORE values for vegetation emissions, industrial emissions, vehicle exhaust, and LPG/NG usage were presented in the scenarios of 50%, 80%, 40% and 40%, respectively.

  4. Spectroscopic and Photochemical Properties of Water-Soluble Fullerenol

    EPA Science Inventory

    Fullerenol, a hydroxylated form of C60-fullerene, is of potential environmental and biological significance due to its buckyball structure, hydroxyl groups and high water solubility. Although fullerenol is known to be an efficient triplet photosensitizer, little is known about it...

  5. Effects of water chemistry on decolorization in three photochemical processes: Pro and cons of the UV/AA process.

    PubMed

    Wu, Bingdang; Yin, Ran; Zhang, Guoyang; Yu, Chao; Zhang, Shujuan

    2016-11-15

    The poor selectivity of hydroxyl radicals is a major restriction in the practical application of the UV/H2O2 process for dyeing wastewater treatment. As an alternative, the target-selective UV/acetylacetone (AA) process was found highly efficient for dye decolorization. For the proper selection and application of the two photochemical processes, the effects of water matrices, including common inorganic anions (Cl(-), SO4(2-), NO3(-), HCO3(-)), natural organic matter, metal cations (Mg(2+), Mn(2+), Cu(2+), Fe(3+), Cr(3+)), and temperature, on the photo-degradation of an azo dye, Acid Orange 7 (AO7), were systematically investigated. The experimental results demonstrate that the UV/AA process was more sensitive to inner filter effect. NO3(-), Cu(2+), and Fe(3+) were all detrimental to the UV/AA process, whereas at certain concentrations they were beneficial to the UV/H2O2 process. However, even with severe inhibitory effects, the decolorization efficiency of the UV/AA process was still several times higher than that of the UV/H2O2 process. The results are helpful for us to better understand the mechanisms behind the UV/AA process and may shed light on the application of UV-based advanced oxidation processes for wastewater treatment.

  6. Stepwise Two-Photon-Gated Photochemical Reaction in Photochromic [2.2]Paracyclophane-Bridged Bis(imidazole dimer).

    PubMed

    Mutoh, Katsuya; Nakagawa, Yuki; Sakamoto, Akira; Kobayashi, Yoichi; Abe, Jiro

    2015-05-06

    Stepwise two-photon processes not only have great potential for efficient light harvesting but also can provide valuable insights into novel photochemical sciences. Here we have designed a [2.2]paracyclophane-bridged bis(imidazole dimer), a molecule that is composed of two photochromic units and absorbs two photons in a stepwise manner. The absorption of the first photon leads to the formation of a short-lived biradical species (half-life = 88 ms at 298 K), while the absorption of the additional photon by the biradical species triggers a subsequent photochromic reaction to afford a long-lived quinoid species. The short-lived biradical species and the long-lived quinoid species display significantly different absorption spectra and rates of the thermal back-reaction. The stepwise two-photon excitation process in this photochromic system can be initiated even by incoherent continuous-wave light irradiation, indicating that this two-photon reaction is highly efficient. Our molecule based on the bridged bis(imidazole dimer) unit should be a good candidate for multiphoton-gated optical materials.

  7. PHOTOCHEMICAL MINERALIZATION OF DISSOLVED ORGANIC NITROGEN TO AMMONIUM IN THE BALTIC SEA

    EPA Science Inventory

    Solar radiation-induced photochemistry can be considered as a new source of nutrients when photochemical reactions release bioavailable nitrogen from biologically non-reactive dissolved organic nitrogen (DON). Pretreatments of Baltic Sea waters in the dark indicated that >72% of ...

  8. Integrated Science Assessment (ISA) of Ozone and Related Photochemical Oxidants (Final Report, Feb 2013)

    EPA Science Inventory

    EPA announced the availability of the final report, Integrated Science Assessment of Ozone and Related Photochemical Oxidants. This document represents a concise synthesis and evaluation of the most policy-relevant science and will ultimately provide the scientific bases f...

  9. Integrated Science Assessment (ISA) of Ozone and Related Photochemical Oxidants (First External Review Draft, Feb 2011)

    EPA Science Inventory

    EPA announced that the First External Review Draft of the Integrated Science Assessment for Ozone and Related Photochemical Oxidants has been made available for independent peer review and public review. This draft document represents a concise synthesis and evaluation of ...

  10. Integrated Science Assessment (ISA) of Ozone and Related Photochemical Oxidants (Third External Review Draft, Jun 2012)

    EPA Science Inventory

    EPA has released the Integrated Science Assessment of Ozone and Related Photochemical Oxidants (Third External Review Draft) for independent peer review and public review. This draft document represents a concise synthesis and evaluation of the most policy-relevant science...

  11. Integrated Science Assessment (ISA) of Ozone and Related Photochemical Oxidants (Second External Review Draft, Sep 2011)

    EPA Science Inventory

    EPA has released the Integrated Science Assessment of Ozone and Related Photochemical Oxidants (Second External Review Draft) for independent peer review and public review. This draft document represents a concise synthesis and evaluation of the most policy-relevant scienc...

  12. Air Quality Criteria for Ozone and Related Photochemical Oxidants (Second External Review Draft)

    EPA Science Inventory

    This second external review draft of the Air Quality Criteria for Ozone and Related Photochemical Oxidants, Volumes I-III (Ozone Criteria Document) is being released for public comment and for review by EPA's Clean Air Scientific Advisory Committee (CASAC) r...

  13. Functional, photochemically active, and chemically asymmetric membranes by interfacial polymerization of derivatized multifunctional prepolymers

    DOEpatents

    Lonsdale, Harold K.; Wamser, Carl C.

    1990-01-01

    The preparation of a novel class of thin film membranes by interfacial polymerization is disclosed, said membranes incorporating as part of their polymeric structure the functionality of monomeric or oligomeric precursors. Specific embodiments include porphyrin and phthalocyanine derivatives that are photochemically or electrochemically active, as well as chemically asymmetric membranes.

  14. Functional, photochemically active, and chemically asymmetric membranes by interfacial polymerization of derivatized multifunctional prepolymers

    DOEpatents

    Lonsdale, H.K.; Wamser, C.C.

    1990-04-17

    The preparation of a novel class of thin film membranes by interfacial polymerization is disclosed, said membranes incorporating as part of their polymeric structure the functionality of monomeric or oligomeric precursors. Specific embodiments include porphyrin and phthalocyanine derivatives that are photochemically or electrochemically active, as well as chemically asymmetric membranes.

  15. Functional, photochemically active, and chemically asymmetric membranes by interfacial polymerization of derivatized multifunctional prepolymers

    DOEpatents

    Lonsdale, Harold K.; Wamser, Carl C.

    1988-01-01

    The preparation of a novel class of thin film membranes by interfacial polymerization is disclosed, said membanes incorporating as part of their polymeric structure the functionality of monomeric or oligomeric precursors. Specific embodiments include porphyrin and phthalocyanime derivatives that are photochemically or electrochemically active, as well as chemically asymmetric membranes.

  16. A Framework for Evaluating Regional-Scale Numerical Photochemical Modeling Systems

    EPA Science Inventory

    This paper discusses the need for critically evaluating regional-scale (~ 200-2000 km) three dimensional numerical photochemical air quality modeling systems to establish a model's credibility in simulating the spatio-temporal features embedded in the observations. Because of li...

  17. Integrated Science Assessment of Ozone and Related Photochemical Oxidants (Second External Review Draft)

    EPA Science Inventory

    EPA has released the Integrated Science Assessment of Ozone and Related Photochemical Oxidants (Second External Review Draft) for independent peer review and public review. This draft document represents a concise synthesis and evaluation of the most policy-relevant scienc...

  18. Integrated Science Assessment of Ozone and Related Photochemical Oxidants (Third External Review Draft)

    EPA Science Inventory

    EPA has released the Integrated Science Assessment of Ozone and Related Photochemical Oxidants (Third External Review Draft) for independent peer review and public review. This draft document represents a concise synthesis and evaluation of the most policy-relevant science...

  19. Air Quality Criteria for Ozone and Related Photochemical Oxidants (Final Report, 2006)

    EPA Science Inventory

    In February 2006, EPA released the final document, Air Quality Criteria for Ozone and Other Photochemical Oxidants. Tropospheric or surface-level ozone (O3) is one of six major air pollutants regulated by National Ambient Air Quality Standards (NAAQS) under the U.S...

  20. The Photochemical Synthesis, Kinetics, and Reactions of Nitrosomethane Dimer: A Physical-Organic Experiment.

    ERIC Educational Resources Information Center

    Kozubek, H.; And Others

    1982-01-01

    Provides background information procedures, and results for the photochemical synthesis and reactions of nitrosomethane dimer. The experiments described have shown a high degree of reliability with student use and are suggested to illustrate some problems of physical and organic photochemistry. (Author/JN)

  1. Has the Performance of Regional-Scale Photochemical Modelling Systems Changed over the Past Decade?

    EPA Science Inventory

    This study analyzed summertime ozone concentrations that have been simulated by various regional-scale photochemical modelling systems over the Eastern U.S. as part of more than ten independent studies. Results indicate that there has been a reduction of root mean square errors ...

  2. A single exposure to photochemical smog causes airway irritation and cardiac dysrhythmia in mice

    EPA Science Inventory

    The data presented here shows that a single exposure to photochemical smog causes airway irritation and cardiac dysrhythmia in mice. Smog, which is a complex mixture of particulate matter and gaseous irritants (ozone, sulfur dioxide, reactive aldehydes), as well as components whi...

  3. Air Quality Criteria for Ozone and Related Photochemical Oxidants (First External Review Draft)

    EPA Science Inventory

    This first external review draft of the Air Quality Criteria for Ozone and Related Photochemical Oxidants (Ozone Criteria Document) is being released in January 2005 for public comment and for review by EPA's Clean A...

  4. 2013 Final Report: Integrated Science Assessment of Ozone and Related Photochemical Oxidants

    EPA Science Inventory

    EPA announced the availability of the Integrated Science Assessment of Ozone and Related Photochemical Oxidants (Final Report). This document represents a concise synthesis and evaluation of the most policy-relevant science and will ultimately provide the scientific bases ...

  5. Synthesis of Nitrogen Heterocycles via Photochemical Ring Opening of Pyridazine N-Oxides.

    PubMed

    Portillo, Maribel; Maxwell, Michael A; Frederich, James H

    2016-10-07

    A photochemical method for the direct synthesis of 1H-pyrazoles from pyridazine N-oxides was developed. This chemistry features a regioselective approach to nonsymmetrically substituted pyridazine N-oxides. Herein, we highlight the first strategic use of photoinduced ring-opening reactions of 1,2-diazine N-oxides for the preparative synthesis of nitrogen heterocycles.

  6. Chemical Kinetics and Photochemical Data for Use in Stratospheric Modeling. Evaluation No. 12

    NASA Technical Reports Server (NTRS)

    DeMore, W. B.; Sander, S. P.; Golden, D. M.; Hampson, R. F.; Kurylo, M. J.; Howard, C. J.; Ravishankara, A. R.; Kolb, C. E.; Molina, M. J.

    1997-01-01

    This is the twelfth in a series of evaluated sets of rate constants and photochemical cross sections compiled by the NASA Panel for Data Evaluation. The primary application of the data is in the modeling of stratospheric processes, with special emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena.

  7. Synergistic photocatalytic hydrogen evolution over oxide nanosheets combined with photochemically inert additives.

    PubMed

    Nakato, Teruyuki; Fujita, Takako; Mouri, Emiko

    2015-02-28

    Photocatalytic hydrogen evolution over semiconducting niobate nanosheets is synergistically improved by coexisting photochemically inactive additives of clay particles and sodium chloride without precise nanoscopic structural regulation. In addition, the Pt cocatalyst loaded on the clay particles works better than that photodeposited on the photocatalytic nanosheets.

  8. Photochemical Upconversion: A Physical or Inorganic Chemistry Experiment for Undergraduates Using a Conventional Fluorimeter

    ERIC Educational Resources Information Center

    Wilke, Bryn M.; Castellano, Felix N.

    2013-01-01

    Photochemical upconversion is a regenerative process that transforms lower-energy photons into higher-energy light through two sequential bimolecular reactions, triplet sensitization of an appropriate acceptor followed by singlet fluorescence producing triplet-triplet annihilation derived from two energized acceptors. This laboratory directly…

  9. Hg speciation by differential photochemical vapor generation at UV-B and UV-C wavelengths

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Mercury speciation was accomplished by differential photochemical reduction at two UV wavelengths; the resulting Hg(O) vapor was quantified by atomic fluorescence spectrometry. After microwave digestion and centrifugation, analyte solutions were mixed with 20% (v/v) formic acid in a reactor coil, an...

  10. 76 FR 10893 - Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-28

    ... AGENCY Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants AGENCY... review draft of a document titled, ``First External Review Draft Integrated Science Assessment for Ozone... review of the national ambient air quality standards (NAAQS) for ozone. EPA is releasing this...

  11. 40 CFR 52.2426 - Photochemical Assessment Monitoring Stations (PAMS) Program.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... Photochemical Assessment Monitoring Stations (PAMS) Program as a state implementation plan (SIP) revision, as... Stations (PAMS) Program on September 11, 1995 and made it part of the Virginia SIP. As with all components of the SIP, Virginia must implement the program as submitted and approved by EPA....

  12. 40 CFR 52.430 - Photochemical Assessment Monitoring Stations (PAMS) Program.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... Photochemical Assessment Monitoring Stations (PAMS) Program as a state implementation plan (SIP) revision, as... Stations (PAMS) Program on September 11, 1995 and made it part of the Delaware SIP. As with all components of the SIP, Delaware must implement the program as submitted and approved by EPA....

  13. 40 CFR 52.2426 - Photochemical Assessment Monitoring Stations (PAMS) Program.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... Photochemical Assessment Monitoring Stations (PAMS) Program as a state implementation plan (SIP) revision, as... Stations (PAMS) Program on September 11, 1995 and made it part of the Virginia SIP. As with all components of the SIP, Virginia must implement the program as submitted and approved by EPA....

  14. 40 CFR 52.2426 - Photochemical Assessment Monitoring Stations (PAMS) Program.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Photochemical Assessment Monitoring Stations (PAMS) Program as a state implementation plan (SIP) revision, as... Stations (PAMS) Program on September 11, 1995 and made it part of the Virginia SIP. As with all components of the SIP, Virginia must implement the program as submitted and approved by EPA....

  15. 40 CFR 52.430 - Photochemical Assessment Monitoring Stations (PAMS) Program.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... Photochemical Assessment Monitoring Stations (PAMS) Program as a state implementation plan (SIP) revision, as... Stations (PAMS) Program on September 11, 1995 and made it part of the Delaware SIP. As with all components of the SIP, Delaware must implement the program as submitted and approved by EPA....

  16. 40 CFR 52.2426 - Photochemical Assessment Monitoring Stations (PAMS) Program.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... Photochemical Assessment Monitoring Stations (PAMS) Program as a state implementation plan (SIP) revision, as... Stations (PAMS) Program on September 11, 1995 and made it part of the Virginia SIP. As with all components of the SIP, Virginia must implement the program as submitted and approved by EPA....

  17. 40 CFR 52.2426 - Photochemical Assessment Monitoring Stations (PAMS) Program.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... Photochemical Assessment Monitoring Stations (PAMS) Program as a state implementation plan (SIP) revision, as... Stations (PAMS) Program on September 11, 1995 and made it part of the Virginia SIP. As with all components of the SIP, Virginia must implement the program as submitted and approved by EPA....

  18. 40 CFR 52.430 - Photochemical Assessment Monitoring Stations (PAMS) Program.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... Photochemical Assessment Monitoring Stations (PAMS) Program as a state implementation plan (SIP) revision, as... Stations (PAMS) Program on September 11, 1995 and made it part of the Delaware SIP. As with all components of the SIP, Delaware must implement the program as submitted and approved by EPA....

  19. 40 CFR 52.430 - Photochemical Assessment Monitoring Stations (PAMS) Program.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... Photochemical Assessment Monitoring Stations (PAMS) Program as a state implementation plan (SIP) revision, as... Stations (PAMS) Program on September 11, 1995 and made it part of the Delaware SIP. As with all components of the SIP, Delaware must implement the program as submitted and approved by EPA....

  20. 40 CFR 52.430 - Photochemical Assessment Monitoring Stations (PAMS) Program.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... Photochemical Assessment Monitoring Stations (PAMS) Program as a state implementation plan (SIP) revision, as... Stations (PAMS) Program on September 11, 1995 and made it part of the Delaware SIP. As with all components of the SIP, Delaware must implement the program as submitted and approved by EPA....

  1. Integrated Science Assessment of Ozone and Related Photochemical Oxidants (First External Review Draft)

    EPA Science Inventory

    EPA announced that the First External Review Draft of the Integrated Science Assessment for Ozone and Related Photochemical Oxidants has been made available for independent peer review and public review. This draft document represents a concise synthesis and evaluation of ...

  2. PHOTOCHEMICAL PRODUCTS IN URBAN MIXTURES ENHANCE INFLAMMATORY RESPONSES IN LUNG CELLS

    EPA Science Inventory

    Complex urban air mixtures that realistically mimic urban smog can be generated for investigating adverse health effects. "Smog chambers" have been used for over 30 yr to conduct experiments for developing and testing photochemical models that predict ambient ozone (O(3)) concent...

  3. High-temperature photochemical destruction of toxic organic wastes using concentrated solar radiation

    SciTech Connect

    Dellinger, B.; Graham, J.L.; Berman, J.M.; Taylor, P.H.

    1994-05-01

    Application of concentrated solar energy has been proposed to be a viable waste disposal option. Specifically, this concept of solar induced high-temperature photochemistry is based on the synergistic contribution of concentrated infrared (IR) radiation, which acts as an intense heating source, and near ultraviolet and visible (UV-VIS) radiation, which can induce destructive photochemical processes. Some significant advances have been made in the theoretical framework of high-temperature photochemical processes (Section 2) and development of experimental techniques for their study (Section 3). Basic thermal/photolytic studies have addressed the effect of temperature on the photochemical destruction of pure compounds (Section 4). Detailed studies of the destruction of reaction by-products have been conducted on selected waste molecules (Section 5). Some very limited results are available on the destruction of mixtures (Section 6). Fundamental spectroscopic studies have been recently initiated (Section 7). The results to date have been used to conduct some relatively simple scale-up studies of the solar detoxification process. More recent work has focused on destruction of compounds that do not directly absorb solar radiation. Research efforts have focused on homogeneous as well as heterogeneous methods of initiating destructive reaction pathways (Section 9). Although many conclusions at this point must be considered tentative due to lack of basic research, a clearer picture of the overall process is emerging (Section 10). However, much research remains to be performed and most follow several veins, including photochemical, spectroscopic, combustion kinetic, and engineering scale-up (Section 11).

  4. SMOG CHAMBERS: A TOOL TO EXAMINE EFFECTS OF PHOTOCHEMICALLY AGED AIR POLLUTANTS ON BIOLOGICAL SYSTEMS

    EPA Science Inventory

    Irradiative exposure chambers or 'Smog chambers' have been used at the University of North Carolina for over 30 years to study photochemically active mixtures of volatile organic compounds and their transformation products (a significant sub-set of Hazardous Air Pollutants, HAPs)...

  5. Diagnostic Evaluation of Ozone Production and Horizontal Transport in a Regional Photochemical Air Quality Modeling System

    EPA Science Inventory

    A diagnostic model evaluation effort has been performed to focus on photochemical ozone formation and the horizontal transport process since they strongly impact the temporal evolution and spatial distribution of ozone (O3) within the lower troposphere. Results from th...

  6. 2013 Final Report: Integrated Science Assessment of Ozone and Related Photochemical Oxidants

    EPA Science Inventory

    Cover of the Integrated Science Assessment (ISA) for Ozone and Related <span class=Photochemical Oxidants" vspace = "5" hspace="5" align="right" border="1" /> EPA is announcing the availability of the <...

  7. The photochemical reflectance index from directional cornfield reflectances: Observations and simulations

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The two-layer Markov chain Analytical Canopy Reflectance Model (ACRM) was linked with in situ hyperspectral leaf optical properties to simulate the Photochemical Reflectance Index (PRI) for a corn crop canopy at three different growth stages. This is an extended study after a successful demonstratio...

  8. Actual 10-Year Survivors Following Resection of Adrenocortical Carcinoma

    PubMed Central

    Tran, Thuy B.; Postlewait, Lauren M.; Maithel, Shishir K.; Prescott, Jason D.; Wang, Tracy S.; Glenn, Jason; Phay, John E.; Keplinger, Kara; Fields, Ryan C.; Jin, Linda X.; Weber, Sharon M.; Salem, Ahmed; Sicklick, Jason K.; Gad, Shady; Yopp, Adam C.; Mansour, John C.; Duh, Quan-Yang; Seiser, Natalie; Solorzano, Carmen C.; Kiernan, Colleen M.; Votanopoulos, Konstantinos I.; Levine, Edward A.; Hatzaras, Ioannis; Shenoy, Rivfka; Pawlik, Timothy M.; Norton, Jeffrey A.; Poultsides, George A.

    2017-01-01

    Background Adrenocortical carcinoma (ACC) is a rare and aggressive malignancy with limited therapeutic options beyond surgical resection. The characteristics of actual long-term survivors following surgical resection for ACC have not been previously reported. Method Patients who underwent resection for ACC at one of 13 academic institutions participating in the US Adrenocortical Carcinoma Group from 1993 to 2014 were analyzed. Patients were stratified into four groups: early mortality (died within 2 years), late mortality (died within 2–5 years), actual 5-year survivor (survived at least 5 years), and actual 10-year survivor (survived at least 10 years). Patients with less than 5 years of follow-up were excluded. Results Among the 180 patients available for analysis, there were 49 actual 5-year survivors (27%) and 12 actual 10-year survivors (7%). Patients who experienced early mortality had higher rates of cortisol-secreting tumors, nodal metastasis, synchronous distant metastasis, and R1 or R2 resections (all P < 0.05). The need for multi-visceral resection, perioperative blood transfusion, and adjuvant therapy correlated with early mortality. However, nodal involvement, distant metastasis, and R1 resection did not preclude patients from becoming actual 10-year survivors. Ten of twelve actual 10-year survivors were women, and of the seven 10-year survivors who experienced disease recurrence, five had undergone repeat surgery to resect the recurrence. Conclusion Surgery for ACC can offer a 1 in 4 chance of actual 5-year survival and a 1 in 15 chance of actual 10-year survival. Long-term survival was often achieved with repeat resection for local or distant recurrence, further underscoring the important role of surgery in managing patients with ACC. PMID:27633419

  9. Effect of photochemical ageing on the ice nucleation properties of diesel and wood burning particles

    NASA Astrophysics Data System (ADS)

    Chou, C.; Kanji, Z. A.; Stetzer, O.; Tritscher, T.; Chirico, R.; Heringa, M. F.; Weingartner, E.; Prévôt, A. S. H.; Baltensperger, U.; Lohmann, U.

    2013-01-01

    A measurement campaign (IMBALANCE) conducted in 2009 was aimed at characterizing the physical and chemical properties of freshly emitted and photochemically aged combustion particles emitted from a log wood burner and diesel vehicles: a EURO3 Opel Astra with a diesel oxidation catalyst (DOC) but no particle filter and a EURO2 Volkswagen Transporter TDI Syncro without emission aftertreatment. Ice nucleation experiments in the deposition and condensation freezing modes were conducted with the Portable Ice Nucleation Chamber (PINC) at three nominal temperatures, -30 °C, -35 °C and -40 °C. Freshly emitted diesel particles showed ice formation only at -40 °C in the deposition mode at 137% relative humidity with respect to ice (RHi) and 92% relative humidity with respect to water (RHw), and photochemical ageing did not play a role in modifying their ice nucleation behaviour. Only one diesel experiment where α-pinene was added for the ageing process, showed an ice nucleation enhancement at -35 °C. Wood burning particles also act as ice nuclei (IN) at -40 °C in the deposition mode at the same conditions as for diesel particles and photochemical ageing also did not alter the ice formation properties of the wood burning particles. Unlike diesel particles, wood burning particles form ice via condensation freezing at -35 °C whereas no ice nucleation was observed at -30 °C. Photochemical ageing did not affect the ice nucleation ability of the diesel and wood burning particles at the three different temperatures investigated but a broader range of temperatures below -40 °C need to be investigated in order to draw an overall conclusion on the effect of photochemical ageing on deposition/condensation ice nucleation across the entire temperature range relevant to cold clouds.

  10. Effect of photochemical aging on the ice nucleation properties of diesel and wood burning particles

    NASA Astrophysics Data System (ADS)

    Chou, C.; Stetzer, O.; Tritscher, T.; Chirico, R.; Heringa, M. F.; Kanji, Z. A.; Weingartner, E.; Prévôt, A. S. H.; Baltensperger, U.; Lohmann, U.

    2012-06-01

    A measurement campaign (IMBALANCE) was conducted in 2009 and aimed at characterizing the physical and chemical properties of freshly emitted and photochemically aged combustion particles emitted from a log wood burner and diesel vehicles: a EURO3 Opel Astra with a diesel oxidation catalyst (DOC) but no particle filter and a EURO2 Volkswagen Transporter TDI Syncro with no emission after-treatment. Ice nucleation experiments in the deposition and condensation freezing modes were conducted with the Portable Ice Nucleation Chamber (PINC) at three nominal temperatures, -30 °C, -35 °C and -40 °C. Freshly emitted diesel particles showed ice formation only at -40 °C in the deposition mode at 137% relative humidity with respect to ice (RHi) and 92% relative humidity with respect to water (RHw), and photochemical aging did not play a role in modifying their ice nucleation behavior. Only one diesel experiment where α-pinene was added, showed an ice nucleation enhancement after the aging at -35 °C. Wood burning particles also act as ice nuclei (IN) at -40 °C in the deposition mode at the same conditions as for diesel particles and photochemical aging did also not alter the ice formation properties of the wood burning particles. Unlike diesel particles, wood burning particles form ice via condensation freezing at -35 °C with no ice nucleation observed at -30 °C for wood burning particles. Photochemical aging did not affect the ice nucleation ability of the diesel and wood burning particles at the three different temperatures investigated but a broader range of temperatures below -30 °C need to be investigated in order to draw an overall conclusion on the effect of photochemical aging on deposition/condensation ice nucleation across the entire temperature range relevant to cold clouds.

  11. Experimental investigation of panel radiator heat output enhancement for efficient thermal use under actual operating conditions

    NASA Astrophysics Data System (ADS)

    Calisir, Tamer; Baskaya, Senol; Onur Yazar, Hakan; Yucedag, Sinan

    2015-05-01

    In this study the heat output of a panel-convector-convector-panel radiator (PCCP) under controlled laboratory conditions under Turkish household and especially Ankara conditions was investigated experimentally. In this sense, investigations were performed for different heating water mass flow rates, water inlet temperatures and radiator inlet and outlet connection positions, which are most commonly used in Turkey. An experimental setup was built for this purpose in a test room where temperature was controlled and held constant during the experiments. Inlet and outlet water temperatures and mass flow rates were measured and heat output of the radiator was calculated. Infrared thermal camera visualizations of the steel panel radiator front surface were also performed.

  12. Photochemical Internalization of Bleomycin Before External-Beam Radiotherapy Improves Locoregional Control in a Human Sarcoma Model

    SciTech Connect

    Norum, Ole-Jacob; Bruland, Oyvind Sverre; Gorunova, Ludmila; Berg, Kristian

    2009-11-01

    Purpose: The aim of this study was to explore the tumor growth response of the combination photochemical internalization and external-beam radiotherapy. Photochemical internalization is a technology to improve the utilization of therapeutic macromolecules in cancer therapy by photochemical release of endocytosed macromolecules into the cytosol. Methods and Materials: A human sarcoma xenograft TAX-1 was inoculated subcutaneously into nude mice. The photosensitizer AlPcS{sub 2a} and bleomycin were intraperitoneally administrated 48 h and 30 min, respectively, before diode laser light exposure at 670 nm (20 J/cm{sup 2}). Thirty minutes or 7 days after photochemical treatment, the animals were subjected to 4 Gy of ionizing radiation. Results: Using photochemical internalization of bleomycin as an adjunct to ionizing radiation increased the time to progression for the tumors from 17 to 33 days as compared with that observed with photodynamic therapy combined with ionizing radiation as well as for radiochemotherapy with bleomycin. The side effects observed when photochemical internalization of bleomycin was given shortly before ionizing radiation were eliminated by separating the treatment modalities in time. Conclusion: Photochemical internalization of bleomycin combined with ionizing radiation increased the time to progression and showed minimal toxicity and may therefore reduce the total radiation dose necessary to obtain local tumor control while avoiding long-term sequelae from radiotherapy.

  13. Electrodermal responses to implied versus actual violence on television.

    PubMed

    Kalamas, A D; Gruber, M L

    1998-01-01

    The electrodermal response (EDR) of children watching a violent show was measured. Particular attention was paid to the type of violence (actual or implied) that prompted an EDR. In addition, the impact of the auditory component (sounds associated with violence) of the show was evaluated. Implied violent stimuli, such as the villain's face, elicited the strongest EDR. The elements that elicited the weakest responses were the actual violent stimuli, such as stabbing. The background noise and voices of the sound track enhanced the total number of EDRs. The results suggest that implied violence may elicit more fear (as measured by EDRs) than actual violence does and that sounds alone contribute significantly to the emotional response to television violence. One should not, therefore, categorically assume that a show with mostly actual violence evokes less fear than one with mostly implied violence.

  14. 40. Photocopy of plan of the Castillo c. 1779 (Actual ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    40. Photocopy of plan of the Castillo c. 1779 (Actual Negative 4'x5') STAR PLAN, COURTYARD FACADE PROFILE AND DEFENSIVE LINKS - Castillo de San Marcos, 1 Castillo Drive, Saint Augustine, St. Johns County, FL

  15. Photochemical, electrochemical, and photoelectrochemical water oxidation catalyzed by water-soluble mononuclear ruthenium complexes.

    PubMed

    Li, Ting-Ting; Zhao, Wei-Liang; Chen, Yong; Li, Fu-Min; Wang, Chuan-Jun; Tian, Yong-Hua; Fu, Wen-Fu

    2014-10-20

    Two mononuclear ruthenium complexes [Ru(H2tcbp)(isoq)2] (1) and [Ru(H2tcbp)(pic)2] (2) (H4tcbp=4,4',6,6'-tetracarboxy-2,2'-bipyridine, isoq=isoquinoline, pic=4-picoline) are synthesized and fully characterized. Two spare carboxyl groups on the 4,4'-positions are introduced to enhance the solubility of 1 and 2 in water and to simultaneously allow them to tether to the electrode surface by an ester linkage. The photochemical, electrochemical, and photoelectrochemical water oxidation performance of 1 in neutral aqueous solution is investigated. Under electrochemical conditions, water oxidation is conducted on the deposited indium-tin-oxide anode, and a turnover number higher than 15,000 per water oxidation catalyst (WOC) 1 is obtained during 10 h of electrolysis under 1.42 V vs. NHE, corresponding to a turnover frequency of 0.41 s(-1). The low overpotential (0.17 V) of electrochemical water oxidation for 1 in the homogeneous solution enables water oxidation under visible light by using [Ru(bpy)3](2+) (P1) (bpy=2,2'-bipyridine) or [Ru(bpy)2(4,4'-(COOEt)2-bpy)](2+) (P2) as a photosensitizer. In a three-component system containing 1 or 2 as a light-driven WOC, P1 or P2 as a photosensitizer, and Na2S2O8 or [CoCl(NH3)5]Cl2 as a sacrificial electron acceptor, a high turnover frequency of 0.81 s(-1) and a turnover number of up to 600 for 1 under different catalytic conditions are achieved. In a photoelectrochemical system, the WOC 1 and photosensitizer are immobilized together on the photoanode. The electrons efficiently transfer from the WOC to the photogenerated oxidizing photosensitizer, and a high photocurrent density of 85 μA cm(-2) is obtained by applying 0.3 V bias vs. NHE.

  16. Photochemical Properties of Mesophyll and Bundle Sheath Chloroplasts of Maize 1

    PubMed Central

    Bazzaz, Maarib Bakri; Govindjee

    1973-01-01

    Several photochemical and spectral properties of maize (Zea mays) bundle sheath and mesophyll chloroplasts are reported that provide a better understanding of the photosynthetic apparatus of C4 plants. The difference absorption spectrum at 298 K and the fluorescence excitation and emission spectra of chlorophyll at 298 K and 77 K provide new information on the different forms of chlorophyll a in bundle sheath and mesophyll chloroplasts: the former contain, relative to short wavelength chlorophyll a forms, more long wavelength chlorophyll a form (e.g. chlorophyll a 693 and chlorophyll a 705) and less chlorophyll b than the latter. The degree of polarization of chlorophyll a fluorescence is 6% in bundle sheath and 4% in mesophyll chloroplasts. This result is consistent with the presence of relatively high amounts of oriented long wavelength forms of chlorophyll a in bundle sheath compared to mesophyll chloroplasts. The relative yield of variable, with respect to constant, chorophyll a fluorescence in mesophyll chloroplasts is more than twice that in bundle sheath chloroplast. Furthermore, the relative yield of total chlorophyll a fluorescence is 40% lower in bundle sheath compared to that in mesophyll chloroplasts. This is in agreement with the presence of the higher ratio of the weakly fluorescent pigment system I to pigment system II in bundle sheath than in mesophyll chloroplast. The efficiency of energy transfer from chlorophyll b and carotenoids to chlorophyll a are calculated to be 100 and 50%, respectively, in both types of chloroplasts. Fluorescence quenching of atebrin, reflecting high energy state of chloroplasts, is 10 times higher in mesophyll chloroplasts than in bundle sheath chloroplasts during noncyclic electron flow but is equal during cyclic flow. The entire electron transport chain is shown to be present in both types of chloroplasts, as inferred from the antagonistic effect of red (650 nm) and far red (710 nm) lights on the absorbance changes at

  17. Photochemical Reflectance Index (PRI) and remote sensing of plant CO2 uptake

    NASA Astrophysics Data System (ADS)

    Penuelas, J.; Garbulsky, M. F.; Filella, I.

    2011-12-01

    An accurate continuous quantification of the role of terrestrial ecosystems as carbon sinks everywhere constitutes a key issue in the face of ongoing environmental disturbance and climate change. The emerging consistency of the relationship between Photochemical Reflectance Index (PRI) and light use efficiency at the leaf, canopy and ecosystem scales offers promising prospects for continuous global monitoring of plant primary productivity from space. We will present and discuss this consistency. This reflectance index is based on the short term reversible xanthophyll pigment changes accompanying plant stress. It also behaves as an index of the chlorophyll:carotenoid ratios and therefore of the photosynthetic activities associated with their changes with leaf development, aging or stress at longer term. At the leaf and canopy levels, the PRI has been extensively found adequate to estimate LUE and thus photosynthetic performance, i.e. gross primary productivity, and its use has been extended increasingly in the last few years both in natural and semi-natural vegetation and in crops. The results of these studies confirm an exponential relationship between LUE and PRI over a wide range of species and conditions, hence suggesting that the overall photosynthetic system is often sufficiently regulated to maintain consistent relationships between the pigment, morphological and physiological changes linked to PRI and the changes in CO2 fixation. In a further step forward, with the availability of the MODIS sensor on TERRA and AQUA satellites, PRI is now increasingly used also at the ecosystem scale. The results of our study comparing PRI data from MODIS and CO2 exchange data from eddy covariance towers show that there may even be a common exponential relationship for all of forests. The emerging consistency of the relationship between PRI, LUE and ecosystem CO2 uptake increasingly found in these studies suggests a surprising degree of "functional convergence" of biochemical

  18. Actuarial and actual analysis of surgical results: empirical validation.

    PubMed

    Grunkemeier, G L; Anderson, R P; Starr, A

    2001-06-01

    This report validates the use of the Kaplan-Meier (actuarial) method of computing survival curves by comparing 12-year estimates published in 1978 with current assessments. It also contrasts cumulative incidence curves, referred to as "actual" analysis in the cardiac-related literature with Kaplan-Meier curves for thromboembolism and demonstrates that with the former estimate the percentage of events that will actually occur.

  19. Photochemical dehydrogenation of ethanol in dilute aqueous solution

    NASA Astrophysics Data System (ADS)

    Handman, J.; Harriman, A.; Porter, G.

    1984-02-01

    The cyclic photodissociation of water has not yet been achieved in a homogeneous solution using visible light. The replacement of the sacrificial electron donor with such waste materials as sulfide is suggested as a method for improving homogeneous systems. Attention is given to the efficient photogeneration of H2 by means of a system that employs a low grade fermentation product, aqueous ethanol, as electron donor. The photoproduction of H2 is coupled to the oxidation of the ethanol by means of NADH/alcohol dehydrogenase as a relay.

  20. Pigment-acceptor-catalyst triads for photochemical hydrogen evolution.

    PubMed

    Kitamoto, Kyoji; Sakai, Ken

    2014-04-25

    In order to solve the problems of global warming and shortage of fossil fuels, researchers have been endeavoring to achieve artificial photosynthesis: splitting water into H2 and O2 under solar light illumination. Our group has recently invented a unique system that drives photoinduced water reduction through "Z-scheme" photosynthetic pathways. Nevertheless, that system still suffered from a low turnover number (TON) of the photocatalytic cycle (TON=4.1). We have now found and describe herein a new methodology to make significant improvements in the TON, up to around TON=14-27. For the new model systems reported herein, the quantum efficiency of the second photoinduced step in the Z-scheme photosynthesis is dramatically improved by introducing multiviologen tethers to temporarily collect the high-energy electron generated in the first photoinduced step. These are unique examples of "pigment-acceptor-catalyst triads", which demonstrate a new effective type of artificial photosynthesis.