61 research outputs found
Water formation at low temperatures by surface O2 hydrogenation II: the reaction network
Water is abundantly present in the Universe. It is the main component of
interstellar ice mantles and a key ingredient for life. Water in space is
mainly formed through surface reactions. Three formation routes have been
proposed in the past: hydrogenation of surface O, O2, and O3. In a previous
paper [Ioppolo et al., Astrophys. J., 2008, 686, 1474] we discussed an
unexpected non-standard zeroth-order H2O2 production behaviour in O2
hydrogenation experiments, which suggests that the proposed reaction network is
not complete, and that the reaction channels are probably more interconnected
than previously thought. In this paper we aim to derive the full reaction
scheme for O2 surface hydrogenation and to constrain the rates of the
individual reactions. This is achieved through simultaneous H-atom and O2
deposition under ultra-high vacuum conditions for astronomically relevant
temperatures. Different H/O2 ratios are used to trace different stages in the
hydrogenation network. The chemical changes in the forming ice are followed by
means of reflection absorption infrared spectroscopy (RAIRS). New reaction
paths are revealed as compared to previous experiments. Several reaction steps
prove to be much more efficient (H + O2) or less efficient (H + OH and H2 + OH)
than originally thought. These are the main conclusions of this work and the
extended network concluded here will have profound implications for models that
describe the formation of water in space.Comment: 1 page, 1 figur
Chemical kinetics in an atmospheric pressure helium plasma containing humidity
Atmospheric pressure plasmas are sources of biologically active oxygen and nitrogen species, which makes them potentially suitable for the use as biomedical devices. Here, experiments and simulations are combined to investigate the formation of the key reactive oxygen species, atomic oxygen (O) and hydroxyl radicals (OH), in a radio-frequency driven atmospheric pressure plasma jet operated in humidified helium. Vacuum ultra-violet high-resolution Fourier-transform absorption spectroscopy and ultra-violet broad-band absorption spectroscopy are used to measure absolute densities of O and OH. These densities increase with increasing H 2 O content in the feed gas, and approach saturation values at higher admixtures on the order of 3 Ă 10 14 cm â3 for OH and 3 Ă 10 13 cm â3 for O. Experimental results are used to benchmark densities obtained from zero-dimensional plasma chemical kinetics simulations, which reveal the dominant formation pathways. At low humidity content, O is formed from OH + by proton transfer to H 2 O, which also initiates the formation of large cluster ions. At higher humidity content, O is created by reactions between OH radicals, and lost by recombination with OH. OH is produced mainly from H 2 O + by proton transfer to H 2 O and by electron impact dissociation of H 2 O. It is lost by reactions with other OH molecules to form either H 2 O + O or H 2 O 2 . Formation pathways change as a function of humidity content and position in the plasma channel. The understanding of the chemical kinetics of O and OH gained in this work will help in the development of plasma tailoring strategies to optimise their densities in applications
Karikaturer og krenkelse. En postkolonial analyse av debatten om Siv Jensens indianerkostyme
I forbindelse med fremlegg av statsbudsjettet i 2017, dukket den norske finansministeren opp pÄ stortingsfest utkledt som indianer. Kostymet utlÞste en debatt om krenkelse, urfolk og ytringsfrihet. Oppgaven skal svare pÄ fÞlgende spÞrsmÄl: Hva forteller debatten om Siv Jensens indianerkostyme om den norske krenkedebatten? PÄ hvilken mÄte kan postkoloniale perspektiver benyttes for Ä belyse, (nyansere og forstÄ) norsk krenkedebatt? MÄlet med oppgaven er Ä benytte postkoloniale perspektiver for Ä nyansere debatten om Jensens indianerkostyme, og Ä understreke funnenes relevans for en stÞrre debatt om krenkelse.
Ved bruk av diskursanalyse som teoretisk og metodisk innretning, har jeg i debatten identifisert to ledende diskurser: ytringsfrihetsdiskursen og urfolksdiskursen. Analysen viser hvordan debatten og dens diskurser kan fungere som uttrykk for en overordnet, norsk debatt om krenkelse. De to sidene av debatten er uenige i helt grunnleggende prinsipper om sammenhenger mellom sprĂ„k og samfunn. Rasjonalitet, ytringsfrihet og en frykt for radikalisering, stĂ„r opp mot fĂžlelser, en betent urfolkshistorie og ujevne maktrelasjoner. Debatten springer ut av komplekse og sammensatte kontekstuelle forhold som partipolitisk kamp, medienes samfunnsrolle, integreringsdebatt, ytringsfrihet, dekolonisering, ujevne maktstrukturer og undertrykkelsesmekanismer. Postkoloniale perspektiver viser hvordan opplysning om kostymets problematiske konnotasjoner forstĂ„s som en del av det ansvaret som hviler pĂ„ oss alle i den postkoloniale tilstanden â ansvar for Ă„ ta et oppgjĂžr med de undertrykkelsesstrukturene som fremdeles gjĂžr seg gjeldende i nĂ„tiden. I en slik forstĂ„else mĂ„ ytringsfrihet handle om mer enn Ă„ bare ytre â det mĂ„ ogsĂ„ handle om Ă„ lytte
Studier av atmosfĂŠrisk nedbrytning og bidrag til drivhuseffekt til 2-fluoretanol, 2,2-difluoretanol og 2,2,2-trifluoretanol
I dette arbeidet ble det studert hvilken innvirkning 2-fluoretanol, 2,2-difluoretanol og 2,2,2-trifluoretanol har pÄ miljÞet og klimaet. Disse forbindelsene er foreslÄtt som nye erstatningsstoffer for klorfluorkarboner (KFK) og hydrogenfluorkarboner (HFK). Hovedfokuset har vÊrt Ä bestemme hvor raskt forbindelsene brytes ned i atmosfÊren og hvor mye de bidrar til drivhuseffekt. I tillegg ble det gjort kvantekjemiske berekninger av vibrasjonsfrekvenser og integrerte absorpsjonsintensiteter til forbindelsene. Det ble ogsÄ gjort en produktstudie av reaksjonen mellom 2,2,2-trifluoretanol og kloratomer.
Hastighetskonstanter for OH- og Cl-reaksjoner i gassfase med de nevnte forbindelsene, ble bestemt ut fra relative mÄlinger og Fourier-transform infrarÞd deteksjon. Hastighetskonstanten for OH-reaksjonen med 2,2,2-trifluoretanol ble ogsÄ bestemt ved hjelp av absolutte mÄlinger. De atmosfÊriske levetidene til forbindelsene ble bereknet ut fra hastighetskonstantene for OH-reaksjonene, og er 14 dager, 45 dager og 164 dager for henholdsvis 2-fluoretanol, 2,2-difluoretanol og 2,2,2-trifluoretanol.
En generell reaksjonsmekanisme for den atmosfÊriske oksidasjonen av forbindelsene i gassfase er foreslÄtt. Imidlertid bÞr det utfÞres kvantitative produktstudier av reaksjonene med OH-radikaler eller kloratomer, samt mÄlinger av absolutte absorpsjonstverrsnitt til CH2FCHO, CHF2CHO og CF3CHO i det ultrafiolette omrÄdet.
Absolutte integrerte absorpsjonsintensiteter til de fluorerte etanolene ble bestemt i bÞlgetallomrÄdet 4000-70 cm-1. Globale oppvarmingspotensialer (GWP) ble bereknet ut fra levetidene og de integrerte absorpsjonsintensitetene til forbindelsene. Det ble funnet at deres bidrag til drivhuseffekt er neglisjerbart sammenlikna med KFK-11.
Sett i lys av levetidene og GWP-verdiene, vil 2-fluoretanol, 2,2-difluoretanol og 2,2,2-trifluoretanol pÄvirke miljÞet og klimaet i langt mindre grad enn hva KFK-er og HFK-er gjÞr. Imidlertid har 2,2,2-trifluoretanol lang nok levetid til at den kan tas opp i vÊskefase der den oksideres til trifluoreddiksyre
Nel mistero dell'universo: viaggio ai confini del tempo e dello spazio alla ricerca dell'infinito
Trace determination of primary nerve agent degradation products in aqueous soil extracts by on-line solid phase extraction-liquid chromatography-mass spectrometry using ZrO2 for enrichment
A method for determination of the primary nerve agent degradation products ethyl-, isopropyl-, isobutyl-, cyclohexyl- and pinacolyl methylphosphonic acid in aqueous soil extracts has been developed utilizing on-line solid phase extraction-liquid chromatography and mass spectrometry (SPEâLCâMS). Four different stationary phases (ZrO2, TiO2, polymeric mixed mode anion exchange and porous graphitic carbon) were investigated for their suitability as SPE materials in the on-line SPEâLCâMS setup. Zirconium dioxide was chosen due to its high affinity for the alkyl methylphosphonic acids (AMPAs), and its compatibility with LCâMS. Aqueous soil extracts were acidified with 0.1% acetic acid and aliquots of 300 ÎŒL were injected on a 2 mm Ă 10 mm ZrO2 column. Separation of the analytes was performed on a reversed phase column with acetonitrile/water gradient and 15 mM ammonium acetate. Method validation was performed with the analytes added to an aqueous extract of a loam soil, and the AMPAs could be determined at concentrations as low as 0.05â0.5 ÎŒg Lâ1. The method was linear (R2 > 0.995) from the limit of quantification (LOQ) to 100 Ă LOQ, and the within assay repeatability was below 10% and 5% relative standard deviation at LOQ and 50 Ă LOQ, respectively. The developed method was employed for determination of the AMPAs which had been added to the aqueous extracts of five different soil types from cultivated and uncultivated areas. The obtained recoveries showed that the analytes could be determined at the sensitivities achieved in the method validation in four of the extracts. For the first time, we have demonstrated a method capable of detecting primary nerve agent degradation products at sub ppb levels in the aqueous extracts of various soils. The method requires no sample preparation after soil extraction other than pH adjustment of the aqueous extract
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