Добірка наукової літератури з теми "Oxygen isotopes, atmospheric effects"
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Статті в журналах з теми "Oxygen isotopes, atmospheric effects":
1
Passey, Benjamin H. "Reconstructing Terrestrial Environments Using Stable Isotopes in Fossil Teeth and Paleosol Carbonates." Paleontological Society Papers 18 (November 2012): 167–94. http://dx.doi.org/10.1017/s1089332600002606.
Анотація:
Carbon isotopes in Neogene-age fossil teeth and paleosol carbonates are commonly interpreted in the context of past distributions of C3 and C4 vegetation. These two plant types have very different distributions in relation to climate and ecology, and provide a robust basis for reconstructing terrestrial paleoclimates and paleoenvironments during the Neogene. Carbon isotopes in pre-Neogene fossil teeth are usually interpreted in the context of changes in the δ13C value of atmospheric CO2, and variable climate-dependent carbon-isotope discrimination in C3 plants. Carbon isotopes in pre-Neogene soil carbonates can be used to estimate past levels of atmospheric CO2. Oxygen isotopes in fossil teeth and paleosol carbonates primarily are influenced by the oxygen isotopic compositions of ancient rainfall and surface waters. The oxygen isotopic composition of rainfall is has a complex, but tractable, relationship with climate, and variably relates to temperature, elevation, precipitation amount, and other factors. Mammal species that rely on moisture in dietary plant tissues to satisfy their water requirements (rather than surface drinking water) may have oxygen isotopic compositions that track aridity. Thus, oxygen isotopes of fossil mammals can place broad constraints on paleoaridity. Carbonate clumped isotope thermometry allows for reconstruction of soil temperatures at the time of pedogenic carbonate mineralization. The method is unique because it is the only thermodynamically based isotopic paleothermometer that does not require assumptions about the isotopic composition of the fluid in which the archive mineral formed. Soil temperature reflects a complex interplay of air temperature, solar radiative heating, latent heat effects, soil thermal diffusivity, and seasonal variations of these parameters. Because plants and most animals live in and/or near the soil, soil temperature is an important aspect of terrestrial (paleo)climate.
2
Michalski, G., S. K. Bhattacharya, and G. Girsch. "NO<sub>x</sub> cycle and the tropospheric ozone isotope anomaly: an experimental investigation." Atmospheric Chemistry and Physics 14, no. 10 (May 21, 2014): 4935–53. http://dx.doi.org/10.5194/acp-14-4935-2014.
Анотація:
Abstract. The oxygen isotope composition of nitrogen oxides (NOx) in the atmosphere is a useful tool for understanding the oxidation of NOx into nitric acid / nitrate in the atmosphere. A set of experiments was conducted to examine change in isotopic composition of NOx due to NOx–O2–O3 photochemical cycling. At low NOx / O2 mixing ratios, NOx became progressively and nearly equally enriched in 17O and 18O over time until it reached a steady state with Δ17O values of 39.3 ± 1.9‰ and δ18O values of 84.2 ± 4‰, relative to the isotopic composition of the initial O2 gas. As the mixing ratios were increased, the isotopic enrichments were suppressed by isotopic exchange between O atoms, O2, and NOx. A kinetic model was developed to simulate the observed data and it showed that the isotope effects occurring during O3 formation play a dominant role in controlling NOx isotopes and, in addition, secondary kinetic isotope effects or isotope exchange reactions are also important during NOx cycling. The data and model were consistent with previous studies which showed that the NO + O3 reactions occur mainly via the transfer of the terminal atoms of O3. The model predicts that under tropospheric concentrations of NOx and O3, the timescale of NOx–O3 isotopic equilibrium ranges from hours (for ppbv NOx / O2 mixing ratios) to days (for pptv mixing ratios) and yields steady state Δ17O and δ18O values of 45‰ and 117‰ respectively (relative to Vienna Standard Mean Ocean Water (VSMOW)) in both cases. Under atmospheric conditions when O3 has high concentrations, the equilibrium between NOx and O3 should occur rapidly (h) but this equilibrium cannot be reached during polar winters and/or nights if the NOx conversion to HNO3 is faster. The experimentally derived rate coefficients can be used to model the major NOx–O3 isotopologue reactions at various pressures and in isotope modeling of tropospheric nitrate.
3
Gao, Jing, You He, Valerie Masson-Delmotte, and Tandong Yao. "ENSO Effects on Annual Variations of Summer Precipitation Stable Isotopes in Lhasa, Southern Tibetan Plateau." Journal of Climate 31, no. 3 (January 19, 2018): 1173–82. http://dx.doi.org/10.1175/jcli-d-16-0868.1.
Анотація:
Abstract Although El Niño–Southern Oscillation (ENSO) influences the Indian summer monsoon, its impact on moisture transport toward the southern Tibetan Plateau (TP) remains poorly understood. Precipitation stable isotopes are useful indices for climate change in the TP. Classical interpretations of variations of precipitation stable isotopes focus on the local surface air temperature or precipitation amount. However, several of the latest studies suggested they may correlate with large-scale modes of variability, such as ENSO. This paper presents a detailed study of ENSO’s effect on annual variations of the oxygen stable isotopic composition of precipitation (δ18Op) at Lhasa in the southern TP for up to 10 years. The stable isotopic composition of water vapor from satellite data [Tropospheric Emission Spectrometer (TES)] and simulations from an isotopically enabled atmospheric general circulation model (zoomed LMDZiso) are used to explore the mechanism that leads to variations of δ18Op at Lhasa. Statistically significant correlations between δ18Op and ENSO indices [Southern Oscillation index (SOI) and Niño-3.4 sea surface temperature index (Niño-3.4)] are observed. This paper shows that ENSO’s effects on the location and intensity of convection over the Arabian Sea, the Bay of Bengal, and the tropical Indian Ocean, along moisture transport paths toward Lhasa, further impact convection from the northern Tibetan Plateau. The changing of this convection results in lower δ18Op at Lhasa in 2007, a La Niña year, and higher δ18Op in 2006, an El Niño year. The study presented here confirms that the regional upstream convection related to ENSO teleconnections plays an important role in variations of δ18Op at the interannual scale and that the more depleted oxygen stable isotopic composition of vapor (δ18Oυ) from the northwestern region of India during a La Niña year intensifies the lower δ18Op at Lhasa in a La Niña year. The study’s results have implications for the interpretation of past variations of archives with precipitation stable isotopes, such as ice cores, tree rings, lake sediments, and speleothems, in this region.
4
Nyamgerel, Yalalt, Yeongcheol Han, Minji Kim, Dongchan Koh, and Jeonghoon Lee. "Review on Applications of 17O in Hydrological Cycle." Molecules 26, no. 15 (July 24, 2021): 4468. http://dx.doi.org/10.3390/molecules26154468.
Анотація:
The triple oxygen isotopes (16O, 17O, and 18O) are very useful in hydrological and climatological studies because of their sensitivity to environmental conditions. This review presents an overview of the published literature on the potential applications of 17O in hydrological studies. Dual-inlet isotope ratio mass spectrometry and laser absorption spectroscopy have been used to measure 17O, which provides information on atmospheric conditions at the moisture source and isotopic fractionations during transport and deposition processes. The variations of δ17O from the developed global meteoric water line, with a slope of 0.528, indicate the importance of regional or local effects on the 17O distribution. In polar regions, factors such as the supersaturation effect, intrusion of stratospheric vapor, post-depositional processes (local moisture recycling through sublimation), regional circulation patterns, sea ice concentration and local meteorological conditions determine the distribution of 17O-excess. Numerous studies have used these isotopes to detect the changes in the moisture source, mixing of different water vapor, evaporative loss in dry regions, re-evaporation of rain drops during warm precipitation and convective storms in low and mid-latitude waters. Owing to the large variation of the spatial scale of hydrological processes with their extent (i.e., whether the processes are local or regional), more studies based on isotopic composition of surface and subsurface water, convective precipitation, and water vapor, are required. In particular, in situ measurements are important for accurate simulations of atmospheric hydrological cycles by isotope-enabled general circulation models.
5
Schumacher, M., R. A. Werner, H. A. J. Meijer, H. G. Jansen, W. A. Brand, H. Geilmann, and R. E. M. Neubert. "Oxygen isotopic signature of CO<sub>2</sub> from combustion processes." Atmospheric Chemistry and Physics 11, no. 4 (February 16, 2011): 1473–90. http://dx.doi.org/10.5194/acp-11-1473-2011.
Анотація:
Abstract. For a comprehensive understanding of the global carbon cycle precise knowledge of all processes is necessary. Stable isotope (13C and 18O) abundances provide information for the qualification and the quantification of the diverse source and sink processes. This study focuses on the δ18O signature of CO2 from combustion processes, which are widely present both naturally (wild fires), and human induced (fossil fuel combustion, biomass burning) in the carbon cycle. All these combustion processes use atmospheric oxygen, of which the isotopic signature is assumed to be constant with time throughout the whole atmosphere. The combustion is generally presumed to take place at high temperatures, thus minimizing isotopic fractionation. Therefore it is generally supposed that the 18O signature of the produced CO2 is equal to that of the atmospheric oxygen. This study, however, reveals that the situation is much more complicated and that important fractionation effects do occur. From laboratory studies fractionation effects on the order of up to 26%permil; became obvious in the derived CO2 from combustion of different kinds of material, a clear differentiation of about 7‰ was also found in car exhausts which were sampled directly under ambient atmospheric conditions. We investigated a wide range of materials (both different raw materials and similar materials with different inherent 18O signature), sample geometries (e.g. texture and surface-volume ratios) and combustion circumstances. We found that the main factor influencing the specific isotopic signatures of the combustion-derived CO2 and of the concomitantly released oxygen-containing side products, is the case-specific rate of combustion. This points firmly into the direction of (diffusive) transport of oxygen to the reaction zone as the cause of the isotope fractionation. The original total 18O signature of the material appeared to have little influence, however, a contribution of specific bio-chemical compounds to individual combustion products released from the involved material became obvious.
6
Zahn, A., P. Franz, C. Bechtel, J. U. Grooß, and T. Röckmann. "Modelling the budget of middle atmospheric water vapour isotopes." Atmospheric Chemistry and Physics 6, no. 8 (June 20, 2006): 2073–90. http://dx.doi.org/10.5194/acp-6-2073-2006.
Анотація:
Abstract. A one-dimensional chemistry model is applied to study the stable hydrogen (D) and stable oxygen isotope (17O, 18O) composition of water vapour in stratosphere and mesosphere. In the troposphere, this isotope composition is determined by "physical'' fractionation effects, that are phase changes (e.g. during cloud formation), diffusion processes (e.g. during evaporation from the ocean), and mixing of air masses. Due to these processes water vapour entering the stratosphere first shows isotope depletions in D/H relative to ocean water, which are ~5 times of those in 18O/16O, and secondly is mass-dependently fractionated (MDF), i.e. changes in the isotope ratio 17O/16O are ~0.52 times of those of 18O/16O. In contrast, in the stratosphere and mesosphere "chemical'' fractionation mechanisms, that are the production of HO due to the oxidation of methane, re-cycling of H2O via the HOx family, and isotope exchange reactions considerably enhance the isotope ratios in the water vapour imported from the troposphere. The model reasonably predicts overall enhancements of the stable isotope ratios in H2O by up to ~25% for D/H, ~8.5% for 17O/16O, and ~14% for 18O/16O in the mesosphere relative to the tropopause values. The 17O/16O and 18O/16O ratios in H2O are shown to be a measure of the relative fractions of HOx that receive the O atom either from the reservoirs O2 or O3. Throughout the middle atmosphere, MDF O2 is the major donator of oxygen atoms incorporated in OH and HO2 and thus in H2O. In the stratosphere the known mass-independent fractionation (MIF) signal in O3 is in a first step transferred to the NOx family and only in a second step to HOx and H2O. In contrast to CO2, O(1D) only plays a minor role in this MIF transfer. The major uncertainty in our calculation arises from poorly quantified isotope exchange reaction rate coefficients and kinetic isotope fractionation factors.
7
Schumacher, M., R. E. M. Neubert, H. A. J. Meijer, H. G. Jansen, W. A. Brand, H. Geilmann, and R. A. Werner. "Oxygen isotopic signature of CO<sub>2</sub> from combustion processes." Atmospheric Chemistry and Physics Discussions 8, no. 6 (November 5, 2008): 18993–9034. http://dx.doi.org/10.5194/acpd-8-18993-2008.
Анотація:
Abstract. For a comprehensive understanding of the global carbon cycle precise knowledge of all processes is necessary. Stable isotope (13C and 18O) abundances provide information for the qualification and the quantification of the diverse source and sink processes. This study focuses on the δ18O signature of CO2 from combustion processes, which are widely present both naturally (wild fires), and human induced (fossil fuel combustion, biomass burning) in the carbon cycle. All these combustion processes use atmospheric oxygen, of which the isotopic signature is assumed to be constant with time throughout the whole atmosphere. The combustion is generally presumed to take place at high temperatures, thus minimizing isotopic fractionation. Therefore it is generally supposed that the 18O signature of the produced CO2 is equal to that of the atmospheric oxygen. This study, however, reveals that the situation is much more complicated and that important fractionation effects do occur. From laboratory studies fractionation effects in the order of about 26‰ became obvious, a clear differentiation of about 7‰ was also found in car exhausts which were sampled directly under ambient atmospheric conditions. We investigated a wide range of materials (both different raw materials and similar materials with different inherent 18O signature), sample geometries (e.g. texture and surface-volume ratios) and combustion circumstances. We found that the main factor influencing the specific isotopic signatures of the combustion-derived CO2 and of the concomitantly released oxygen-containing side products, is the case-specific rate of combustion. This points firmly into the direction of (diffusive) transport of oxygen to the reaction zone as the cause of the isotope fractionation. The original 18O signature of the material appeared to have little or no influence.
8
NOON, PHILIPPA E., M. J. LENG, C. ARROWSMITH, M. G. EDWORTHY, and R. J. STRACHAN. "Seasonal observations of stable isotope variations in a valley catchment, Signy Island, South Orkney Islands." Antarctic Science 14, no. 4 (December 2002): 333–42. http://dx.doi.org/10.1017/s0954102002000159.
Анотація:
The oxygen and hydrogen isotope composition of waters in a small valley at Signy Island, South Orkney Islands, were monitored over three summers (1999 to 2001). These stable isotopes track water movement through the catchment, especially seasonal precipitation and snow melt. All samples fall close to the regional meteoric water line but factors other than air temperature cause year-to-year variability. Residence times are in the order of days thus the lake water provides an average of precipitation falling only a few days before, except in the winter when the lakes are effectively closed. Freezing of surface waters preserves the isotope signature of the underlying waters from the previous summer. In spring, meltwaters from winter snow are isotopically depleted having δ18O and δD as low as -13‰ and -100‰ (VSMOW). Ice- cover break-up in late December allows complete water column mixing. By February, the lakes are relatively enriched isotopically (δ18O -9‰) by summer precipitation. Precipitation isotopic composition at Halley Station, Brunt Ice Shelf, is similar, illustrating the broad-scale effects of the Weddell Sea cyclonic atmospheric circulation. These data form a useful reference data-set for the ground-based validation of atmospheric models and palaeoclimate reconstructions in this isolated sector of the South Atlantic Ocean.
9
Bauch, Henning A., Helmut Erlenkeuser, Pieter M. Grootes, and Jean Jouzel. "Implications of Stratigraphic and Paleoclimatic Records of the Last Interglaciation from the Nordic Seas." Quaternary Research 46, no. 3 (November 1996): 260–69. http://dx.doi.org/10.1006/qres.1996.0065.
Анотація:
Climatic reconstruction of glacial to interglacial episodes from oxygen isotopes in sediment cores from the Nordic seas is complicated by strong local meltwater contributions to the oxygen isotope changes. Combination of benthic and planktic foraminiferal isotope data with foraminiferal abundances and ice-rafted debris (IRD) allows separation of local and global effects and subdivision of the marine oxygen isotope events 6.2–5.4, which include the last interglaciation, into: (1) a meltwater phase after glacial stage 6, recorded by large amounts of IRD and low foraminiferal abundance, indicating surface water warming; (2) an IRD-free period with high deposition rates of subpolar foraminifera and other CaCO3 pelagic components, recognized here as the “full” interglaciation; and (3) a phase with the recurrence of IRD and the demise of subpolar species. Comparison of ice-core records and marine data implies that the global climate during the last full interglaciation and that during the postdeglacial Holocene were similar. The records show no significantly different variations in the proxy data. In contrast, the oxygen isotopes of planktic foraminifera and ice cores indicate significant differences during each of the deglacial transitions (Terminations I and II) that preceded these two interglaciations. These suggest that during Termination II the climatic evolution in the Nordic seas was less affected by abrupt changes in ocean–atmosphere circulation than during the last glacial to interglacial transition.
10
Lin, Mang, Xiaolin Zhang, Menghan Li, Yilun Xu, Zhisheng Zhang, Jun Tao, Binbin Su, Lanzhong Liu, Yanan Shen, and Mark H. Thiemens. "Five-S-isotope evidence of two distinct mass-independent sulfur isotope effects and implications for the modern and Archean atmospheres." Proceedings of the National Academy of Sciences 115, no. 34 (August 6, 2018): 8541–46. http://dx.doi.org/10.1073/pnas.1803420115.
Анотація:
The signature of mass-independent fractionation of quadruple sulfur stable isotopes (S-MIF) in Archean rocks, ice cores, and Martian meteorites provides a unique probe of the oxygen and sulfur cycles in the terrestrial and Martian paleoatmospheres. Its mechanistic origin, however, contains some uncertainties. Even for the modern atmosphere, the primary mechanism responsible for the S-MIF observed in nearly all tropospheric sulfates has not been identified. Here we present high-sensitivity measurements of a fifth sulfur isotope, stratospherically produced radiosulfur, along with all four stable sulfur isotopes in the same sulfate aerosols and a suite of chemical species to define sources and mechanisms on a field observational basis. The five-sulfur-isotope and multiple chemical species analysis approach provides strong evidence that S-MIF signatures in tropospheric sulfates are concomitantly affected by two distinct processes: an altitude-dependent positive 33S anomaly, likely linked to stratospheric SO2 photolysis, and a negative 36S anomaly mainly associated with combustion. Our quadruple stable sulfur isotopic measurements in varying coal samples (formed in the Carboniferous, Permian, and Triassic periods) and in SO2 emitted from combustion display normal 33S and 36S, indicating that the observed negative 36S anomalies originate from a previously unknown S-MIF mechanism during combustion (likely recombination reactions) instead of coal itself. The basic chemical physics of S-MIF in both photolytic and thermal reactions and their interplay, which were not explored together in the past, may be another ingredient for providing deeper understanding of the evolution of Earth’s atmosphere and life’s origin.
Дисертації з теми "Oxygen isotopes, atmospheric effects":
1
Soens, Bastien. "Petrographic and geochemical characterization of the micrometeorite collection from the Sør Rondane Mountains: Nature and origin of the extraterrestrial flux to Earth." Doctoral thesis, Universite Libre de Bruxelles, 2021. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/331729.
Анотація:
The Antarctic continent has traditionally been a successful searching ground for meteoritic material due to its cold and dry climate. Meteorites, and their microscopic analogues micrometeorites, were originally sampled from Antarctic ice and snow. Recently, however, a large collection of micrometeorites was discovered in sedimentary traps and moraine deposits from the Transantarctic Mountains, where extraterrestrial dust particles have accumulated for a prolonged time span (ca. 3–4 Ma). Micrometeorites (or ‘cosmic dust’) show unique chemical and isotopic signatures, which originate from a large and diverse amount of asteroidal and cometary bodies within the Solar System. In addition, they document major events such as the origin and evolution of the Solar System, and provide insight into the source region of their precursor bodies. These sedimentary deposits consequently represent a valuable archive that documents the flux of extraterrestrial material to Earth and ancient meteoritic events over Antarctica.Yet, much of this information is lost during the atmospheric entry stage, where cosmic dust is subjected to frictional heating and is partially or completely molten down. This may significantly alter the original physicochemical and isotopic properties of extraterrestrial dust particles. A thorough understanding of these physicochemical processes is thus required to reconstruct the atmospheric entry of cosmic dust (but also larger objects) and interpret their chemical and isotopic data. During the course of this PhD research, multiple sedimentary deposits from the Sør Rondane Mountains (Dronning Maud Land, East Antarctica) were petrographically examined and chemically-isotopically characterized using state-of-the-art instruments. Furthermore, various experiments and numerical models were constructed to replicate the atmospheric entry stage of both small- and large-sized meteoritic material. This study has demonstrated that the Sør Rondane Mountains sedimentary deposits contain a rich and pristine variety of extraterrestrial- and impact-related materials, including micrometeorites, microtektites and meteoritic condensation spherules. Statistical analysis suggests that the Sør Rondane Mountains micrometeorite collection is representative of the contemporary flux of cosmic dust to Earth. Extraterrestrial material is subjected to a complex interplay of redox and volatilization processes during atmospheric entry heating, which allow to explain the chemical trends observed in cosmic dust. Isotopic studies also suggest that at least a minor fraction of the micrometeorite population has sampled new, unknown types of asteroidal and/or cometary bodies. Microtektites and meteoritic condensation spherules have been linked to major meteoritic events on Earth ca. 790 ka and ca. 430 ka ago, respectively, and underline the importance of the Earth’s atmosphere during their formation. The results of this PhD research emphasize the scientific value of Antarctic sedimentary deposits and provide more insight into the processes taking place during the atmospheric entry of extraterrestrial material.Le continent antarctique a traditionnellement été un terrain de recherche fructueux pour le matériel extraterrestre en raison de son climat froid et sec. Les météorites et leurs analogues microscopiques, les micrométéorites, ont été à l'origine échantillonnés dans la glace et la neige de l'Antarctique. Plus récemment, une grande collection de micrométéorites a été découverte dans des pièges sédimentaires et des dépôts de moraine des montagnes transantarctiques, où des particules de poussière extraterrestres se sont accumulées pendant une période prolongée (environ 3-4 Ma). Les micrométéorites (ou « poussière cosmique ») présentent des signatures chimiques et isotopiques uniques, qui proviennent d'une quantité importante et diversifiée de corps astéroïdes et cométaires au sein du système solaire. En outre, elles documentent des événements majeurs tels que l'origine et l'évolution du système solaire et donnent un aperçu de la région source de leurs corps parents. Ces dépôts sédimentaires représentent par conséquent une archive précieuse qui documente le flux de matière extraterrestre vers la Terre et les événements météoritiques anciens au-dessus de l'Antarctique.Pourtant, une grande partie de cette information est perdue au cours de l'étape d'entrée dans l'atmosphère, où la poussière cosmique est soumise à un chauffage par friction et est partiellement ou complètement fondue. Cela peut altérer considérablement les propriétés physico-chimiques et isotopiques d'origine des particules de poussière extraterrestres. Une compréhension approfondie de ces processus physico-chimiques est donc nécessaire pour reconstituer l'entrée atmosphérique des poussières cosmiques (mais aussi des objets plus gros) et interpréter leurs données chimiques et isotopiques. Au cours de cette recherche de doctorat, plusieurs dépôts sédimentaires des montagnes Sør Rondane (Dronning Maud Land, Antarctique de l'Est) ont été examinés pétrographiquement et caractérisés chimiquement et isotopiquement. En outre, diverses expériences et modèles numériques ont été construits pour reproduire l'étape d'entrée dans l'atmosphère de matériaux météoritiques de petite et de grande taille.Cette étude a démontré que les dépôts sédimentaires des montagnes Sør Rondane contiennent une variété riche et peu altérée de matériaux extraterrestres et de cratères d’impacts, notamment des micrométéorites, des microtektites et des sphérules de condensation météoritique. L'analyse statistique suggère que la collection de micrométéorites des montagnes Sør Rondane est représentative du flux contemporain de poussière cosmique vers la Terre. La matière extraterrestre est soumise à une interaction complexe de processus d'oxydo-réduction et de volatilisation lors de l'entrée dans l'atmosphère, ce qui permet d'expliquer les tendances chimiques observées dans la poussière cosmique. Des études isotopiques suggèrent également qu'au moins une fraction mineure de la population de micrométéorites a échantillonné de nouveaux types inconnus d’astéroïdes et/ou de comètes. Les microtektites et les sphérules de condensation météoritiques ont été liées à des événements météoritiques majeurs sur Terre il y a ~790 ka et ~430 ka, respectivement, et soulignent l'importance de l'atmosphère terrestre lors de leur formation. Les résultats de cette recherche doctorale soulignent la valeur scientifique des dépôts sédimentaires de l'Antarctique et donnent un meilleur aperçu des processus qui se déroulent lors de l'entrée dans l'atmosphère de matière extraterrestre
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
2
Missell, Christine Ann. "Thermoregulatory adaptations of Acrocanthosaurus atokensis - evidence from oxygen isotopes." NCSU, 2004. http://www.lib.ncsu.edu/theses/available/etd-12312003-115912/.
Анотація:
Isotopic analyses of bone phosphate oxygen from a modern alligator, ostrich, and elephant have provided a means for examining diagenesis and thermoregulatory strategy within the dinosaur Acrocanthosaurus atokensis. The Acrocanthosaurus specimen is assumed to retain an original isotopic signature, based on a lack of linear correlation between δ18Ophosphate and structural δ18Ocarbonate, equal standard deviations between δ18Ophosphate values for spongy and compact bone, and a significant difference between δ18Ophosphate and cement δ18Ocarbonate. Interbone and intrabone temperature variation patterns suggest that Acrocanthosaurus followed a homeothermic pattern of heat distribution (i.e. maintenance of a 4°C temperature range). Comparison with the modern animals yields a closer resemblance to the ostrich and elephant versus the alligator, thereby suggesting Acrocanthosaurus was endothermic. The Acrocanthosaurus sacral spines and palatal bones show evidence of use as heat shedding structures and the braincase yields a significantly higher calculated temperature than the body.
3
Warrington, Anita Glasgow. "Stable isotopes of carbon and oxygen in the shells of terrestrial molluscs." Thesis, University of Liverpool, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316976.
4
Dejwakh, Navid Rene. "Using 15N, 18O, and 17O to Determine Nitrate Sources and Removal Processes from Groundwater, Tucson, Arizona." Thesis, The University of Arizona, 2008. http://hdl.handle.net/10150/193327.
Анотація:
Nitrate is a common groundwater contaminant. Due to adverse health effects, waters above the Maximum Contaminant Level (MCL) of 10 mg NO3-N/L or 0.71 mmols/L, are banned from domestic consumption by the EPA. Studies have measured elevated nitrate concentrations in arid land soils and groundwater around the world. These elevated concentrations could be detrimental to the environment and to human health. Thus, it is important to consider the different sources and processes affecting nitrate concentrations Here, a novel triple isotope system approach was employed, coupling δ17O with δ18O and δ15N of nitrate to determine the sources (atmospheric, terrestrial, fertilizer, wastewater) and removal processes influencing nitrate concentrations in the Tucson basin groundwater system. Results show low groundwater nitrate concentrations (0.2 mmols/L) where wastewater was not a predominant source of water, versus high concentrations (1 mmols/L) above the MCL in groundwaters where wastewater was the dominant water source. Furthermore, groundwater up to 1.6 Km away from the wastewater stream was contaminated with effluent recharge waters. In addition, denitrification was inferred from δ18O and δ15N data with this inference reinforced by δ17O data and δ15N enrichments up to 26. Finally, low atmospheric nitrate was measured in groundwater, representing up to 6% of total nitrate. The triple isotope approach studied here is ideal for determining the proportion of atmospheric nitrate versus other terrestrial nitrate sources and the significance of nitrate removal processes.
5
Webb, Mathew Douglas. "Carbon, chloride, and oxygen isotopes as tracers of interbasin groundwater flow at La Selva Biological Station, Costa Rica." NCSU, 2007. http://www.lib.ncsu.edu/theses/available/etd-03262007-111350/.
Анотація:
Groundwater and surface water samples were taken at 14 locations at a lowland rainforest site (La Selva Biological Station) in Costa Rica for the analysis of DIC, DOC, 14C, 13C, 36Cl, 18O, and other geochemical parameters. The data are consistent with the mixing of two endmember groundwaters. One is a local water having low Cl concentrations (<0.07 mM), low DIC (<3.0 mM), high 14C (>100 pmc), δ13C between -22? and -26?, and highly variable 36Cl/Cl ratios. This chemistry is consistent with locally recharged shallow groundwaters having short residence times in which the DIC originates from plant root respiration and atmospheric deposition is the only source of Cl. The other endmember is bedrock groundwater, representing interbasin groundwater flow (IGF) into La Selva and having relatively high Cl concentration (>0.9 mM), high DIC (about 14 mM), low 14C (<8 pmc), high δ13C (-3? to -5?), and a low and more consistent 36Cl/Cl ratio. This chemistry is consistent with the expectations for bedrock groundwater recharged on the flanks of Volcan Barva to the north of La Selva, with a majority of the DIC and Cl derived from magmatic degassing and dissolution of the volcanic rocks that make up the aquifer. A 14C age of 750 ? 4650 years before present was estimated for the bedrock groundwater endmember using NETPATH geochemical mass-balance modeling software, suggesting an average linear velocity of 3-20 m/yr for this groundwater; the actual age is probably closer to the upper limit, and velocity closer to the lower limit. The results of this study are consistent with prior work using major ion, 18O, and physical hydrologic data, suggesting that the conclusions about IGF and groundwater mixing at this site are correct. Also, new DIC data for bedrock groundwater and previous hydrologic data on bedrock groundwater inputs to the Arboleda watershed at La Selva suggest that IGF of bedrock groundwater is responsible for a large inorganic carbon flux into lowland watersheds (about 740 grams of carbon per m2 of watershed each year for the Arboleda).
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Valdez, Adelia Christina. "Analysis of Atmospheric Effects Due to Atmospheric Oxygen on a Wideband Digital Signal in the 60 Ghz Band." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/35234.
Анотація:
As lower microwave frequency bands become saturated with users, there is a motivation for the research of applications that utilize higher frequencies, especially the 60 GHz band. This band is plagued with high atmospheric absorption due to atmospheric oxygen, but has a lot of bandwidth, which makes it desirable for multi-media applications. Recently, research of wideband digital links within the 60 GHz band gained the interest of the wireless communication industry when the FCC announced that a license is not required for a wideband digital signal in this band.
Previous research on 60 GHz signals focused on how much attenuation due to atmospheric oxygen exists in the link. But a look at the physical properties of atmospheric oxygen reveals both the reason why atmospheric oxygen absorbs electromagnetic waves and how pressure affects atmospheric oxygen. Atmospheric oxygen resonates at 60 GHz due to transitions between its three closely spaced rotational states. These transitions, combined with the magnetic dipole moment of atmospheric oxygen, cause attenuation and phase dispersion in electromagnetic waves.
At lower pressures, the individual resonance lines of atmospheric oxygen appear in the attenuation and the phase dispersion plots. As pressure increases, the resonance lines broaden and contribute to neighboring resonant lines. The effect of attenuation and phase dispersion in a wideband signal becomes greater at lower atmospheric pressures, which results in signal distortion. The signal distortion leads to more bit errors and results in the presence of inter-symbol interference (ISI) in the received signal.
This thesis aims to analyze the effects of atmospheric oxygen on a wideband digital link, especially at lower pressures and higher data rates. In order to simulate the effects of atmospheric oxygen in the atmosphere, an empirical atmospheric model was used, which characterizes the behavior of oxygen under various atmospheric pressures. A wideband communication system was simulated with the absorption and dispersion due to atmospheric oxygen represented as a transfer function and placed in the link part of the system. Eye diagrams were used to view the impact of the atmospheric oxygen attenuation and phase dispersion in the signal. Also bit error rate plots were computed in order to determine the extra margin needed.Master of Science
7
Adiatma, Yoseph Datu. "Did early land plants produce a step-change in atmospheric oxygen centered on the Late Ordovician Sandbian Age ~458 Ma?" The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546386257035643.
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Mercer, A. P. "The effects of atmospheric humidity and oxygen on the wear of metals by fine abrasives." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356659.
9
Wilson, Jessica Norman. "Stable Isotopes and Trace Elements in Tooth Enamel Bioapatite: Effects of Diagenesis and Pretreatment on Primary Paleoecological Information." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4965.
Анотація:
The geochemical analysis of bioapatite in vertebrate skeletal tissues is an important tool used to obtain ecological information from fossil animals. An important consideration when conducting stable isotope and trace element analyses is obtaining biogenic information that has been unaffected by diagenetic processes.
A two-step pretreatment procedure is commonly used remove diagenetically altered material by removing organic material, via an oxidation reaction with H2O2 or NaOCl, and secondary carbonate, via dissolution in dilute acetic acid, from bioapatite. While much work has been done to determine the efficacy of the pretreatment process, little research has been conducted to determine the potential effects of this process on the oxygen isotope composition of enamel bioapatite. A comparison between δ18O values of fossil enamel treated with 18O-depleted (δ18O = -10.0 / V-SMOW) and 18O-enriched solutions (δ18O = +16.4 / V-SMOW). On average, samples treated with 18O-enriched solutions had δ18O values at least 0.4 / V-PDB more positive than samples treated with 18O-depleted solutions. These results suggest that the isotopic composition of solutions used in the pretreatment process can significantly affect the δ18O values of fossil enamel prior to isotopic analysis.
Diagenetic alteration can potentially be assessed using the linear relationship between δ18O values of the carbonate and phosphate components of bioapatite, as any deviation from a slope of 1 suggests alteration. Comparing the relationship between δ18Op and δ18Oc for fossil mammals from the Hadar Formation suggests that this method is successful at identifying samples that are significantly different from the remaining samples due to diagenetic alteration. The relationship between δ18Oc and δ18Op for the majority of sampled fossils from the Hadar Formation has a slope very close to 1 with an average offset, and apparent fractionation factor, between δ18Oc and δ18Op consistent with modern mammals. Therefore, it is likely that many of the fossil mammals sampled from the Hadar Formation retain in vivo δ18O values relating to the δ18O value of the water they consumed.
The reliability of paleodietary reconstructions using trace element ratios (notably Sr/Ca and Ba/Ca) is strongly dependent on the preservation of biogenic trace element concentrations. Although most trace element ratio research relies on bone bioapatite, enamel has a better preservation potential and may successfully preserve biogenic trace element relationships. An analysis of Sr/Ca, Ba/Ca, and Zn/Ca ratios indicates that, despite rare earth element concentrations greater than the 1ppm observed in modern enamel, mammals from the Hadar and Busidima formations potentially reflect feeding strategies observed in modern counterparts, i.e. grazers have higher Sr/Ca and Ba/Ca ratios than browsers and omnivores
10
Howard, Evan M. (Evan Michael). "Ecosystem metabolism in salt marsh tidal creeks and ponds : applying triple oxygen isotopes and other gas tracers to novel environments." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/109021.
Анотація:
Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2017.Cataloged from PDF version of thesis. Page 216 blank.
Includes bibliographical references (pages 179-215).
Salt marshes are physically, chemically, and biologically dynamic environments found globally at temperate latitudes. Tidal creeks and marshtop ponds may expand at the expense of productive grass-covered marsh platform. It is therefore important to understand the present magnitude and drivers of production and respiration in these submerged environments in order to evaluate the future role of salt marshes as a carbon sink. This thesis describes new methods to apply the triple oxygen isotope tracer of photosynthetic production in a salt marsh. Additionally, noble gases are applied to constrain air-water exchange processes which affect metabolism tracers. These stable, natural abundance tracers complement traditional techniques for measuring metabolism. In particular, they highlight the potential importance of daytime oxygen sinks besides aerobic respiration, such as rising bubbles. In tidal creeks, increasing nutrients may increase both production and respiration, without any apparent change in the net metabolism. In ponds, daytime production and respiration are also tightly coupled, but there is high background respiration regardless of changes in daytime production. Both tidal creeks and ponds have higher respiration rates and lower production rates than the marsh platform, suggesting that expansion of these submerged environments could limit the ability of salt marshes to sequester carbon.
by Evan M. Howard.
Ph. D.
Частини книг з теми "Oxygen isotopes, atmospheric effects":
1
Heller, H., M. Könen, A. Overlack, and K. D. Schuster. "Fractionation Effects of Oxygen Isotopes Within Interstitial Lung Disease." In Advances in Experimental Medicine and Biology, 373–78. Boston, MA: Springer US, 1996. http://dx.doi.org/10.1007/978-1-4613-0333-6_49.
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Schuster, K. D., H. Heller, and M. Könen. "Investigation of The Human Oxygen Transport System During Conditions of Rest and Increased Oxygen Consumption By Means of Fractionation Effects of Oxygen Isotopes." In Advances in Experimental Medicine and Biology, 747–53. Boston, MA: Springer US, 1994. http://dx.doi.org/10.1007/978-1-4615-2468-7_98.
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Klok, C. Jaco, Alexander Kaiser, John J. Socha, Wah-Keat Lee, and Jon F. Harrison. "Multigenerational Effects of Rearing Atmospheric Oxygen Level on the Tracheal Dimensions and Diffusing Capacities of Pupal and Adult Drosophila melanogaster." In Advances in Experimental Medicine and Biology, 285–300. Boston, MA: Springer US, 2016. http://dx.doi.org/10.1007/978-1-4899-7678-9_20.
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Farquhar, Graham D., and Jon Lloyd. "Carbon and Oxygen Isotope Effects in the Exchange of Carbon Dioxide between Terrestrial Plants and the Atmosphere." In Stable Isotopes and Plant Carbon-water Relations, 47–70. Elsevier, 1993. http://dx.doi.org/10.1016/b978-0-08-091801-3.50011-8.
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Criss, Robert E. "Isotope Hydrology." In Principles of Stable Isotope Distribution. Oxford University Press, 1999. http://dx.doi.org/10.1093/oso/9780195117752.003.0005.
Анотація:
No substance exemplifies the principles of isotope distribution better than water. Water is practically ubiquitous at the Earth’s surface, where it undergoes phase transitions, interacts with minerals and the atmosphere, and participates in complex metabolic processes essential to life. The isotopes of hydrogen and oxygen undergo large fractionations during these processes, providing a multiple isotopic tracer record of diverse phenomena. In the hydrologic cycle, hydrogen and oxygen isotope ratios provide conservative tracers, uniquely intrinsic to the water molecule, that elucidate the origin, phase transitions, and transport of H2O. In particular, the isotope data associated with these processes are amenable to theoretical modeling using the laws of physical chemistry. The characteristics of the principal reservoirs of natural waters on Earth are provided in the following sections. The distinct characters of these different reservoirs are very clearly shown on graphs where the δD values are plotted against those of δ18O. The oceans constitute 97.25% of the hydrosphere, cover 70% of the Earth’s surface to a mean depth of 3.8 km, and have an enormous total volume of 1.37 × 109 km3. This large reservoir has strikingly uniform isotopic concentrations, with almost all samples having δ18O = 0 ± 1 and δD = 0 ± 5 per mil relative to SMOW (Craig and Gordon, 1965). Values outside these ranges are almost invariably confined to surface waters that have salinities that differ from the normal value of 3.5 wt. %. These varations are generally attributable to evaporation, formation of sea ice, or addition of meteoric precipitation that may occur by direct rainfall, by river inflow, or by melting of icebergs. The latter effect was clearly documented by Epstein and Mayeda (1953) in the surface waters of the North Atlantic, where the isotopic variations were strongly correlated with variations in salinity. In detail, the deep waters of different ocean basins have distinct values of δ18O and salinity. Thus, the δ18O values of deep waters from the North Atlantic (ca. +0.05‰), Pacific (-0.15‰), and Antarctic (-0.40‰) oceans are distinct, and careful measurements can be used to infer details of oceanic circulation patterns (Craig and Gordon, 1965).
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Flanagan, Lawrence B. "Oxygen isotope effects during CO2 exchange: from leaf to ecosystem processes." In Stable Isotopes, 185–201. Garland Science, 2020. http://dx.doi.org/10.1201/9781003076865-12.
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Dawson, Todd E., Roman C. Pausch, and Hester M. Parker. "The role of hydrogen and oxygen stable isotopes in understanding water movement along the soil-plant-atmospheric continuum." In Stable Isotopes, 169–83. Garland Science, 2020. http://dx.doi.org/10.1201/9781003076865-11.
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Heimann, Martin. "The Cycle of Atmospheric Molecular Oxygen and Its Isotopes." In Global Biogeochemical Cycles in the Climate System, 235–44. Elsevier, 2001. http://dx.doi.org/10.1016/b978-012631260-7/50020-0.
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Akash, Navneet, B. S. Bhandari, and Kamal Bijlwan. "Effects of Atmospheric Pollutants on Biodiversity." In Global Perspectives on Air Pollution Prevention and Control System Design, 142–73. IGI Global, 2019. http://dx.doi.org/10.4018/978-1-5225-7289-3.ch006.
Анотація:
Biodiversity is severely affected by the various anthropogenic activities. Humans depend on natural resources for survival. The resources include food, clean drinking water, timber for construction, fibers for clothing, natural gas, and coal for industries. The biggest threat to the atmosphere is pollutants caused by different human activities. The earth atmosphere is a layer of gases that surrounds the planet and allows us to breathe and live. The atmosphere is made up of Nitrogen, Oxygen, and others types of gases. This mixture of gases is known as air. Air pollution results from a variety of pollutants like NO2, SO2, CO, CFCs, and Ozone. Carbon dioxide, which is a greenhouse gas, warms the earth. This chapter will explore the effects of atmospheric pollutants on biodiversity due to various types of adulterants in the atmosphere and its effects on the survival of earth. Additionally, it will sketch various tools that can reduce these harmful activities.
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Bethke, Craig M. "Stable Isotopes." In Geochemical Reaction Modeling. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195094756.003.0019.
Анотація:
Stable isotopes serve as naturally occurring tracers that can provide much information about how chemical reactions proceed in nature, such as which reactants are consumed and at what temperatures reactions occur. The stable isotopes of several of the lighter elements are sufficiently abundant and fractionate strongly enough to be of special usefulness. Foremost in importance are hydrogen, carbon, oxygen, and sulfur. The strong conceptual link between stable isotopes and chemical reaction makes it possible to integrate isotope fractionation into reaction modeling, allowing us to predict not only the mineralogical and chemical consequences of a reaction process, but also the isotopic compositions of the reaction products. By tracing the distribution of isotopes in our calculations, we can better test our reaction models against observation and perhaps better understand how isotopes fractionate in nature. Bowers and Taylor (1985) were the first to incorporate isotope fractionation into a reaction model. They used a modified version of EQ3/EQ6 (Wolery, 1979) to study the convection of hydrothermal fluids through the oceanic crust, along midocean ridges. Their calculation method is based on evaluating mass balance equations, as described in this chapter. As originally derived, however, the mass balance model has an important (and well acknowledged) limitation: implicit in its formulation is the assumption that fluid and minerals in the modeled system remain in isotopic equilibrium over the reaction path. This assumption is equivalent to assuming that isotope exchange between fluid and minerals occurs rapidly enough to maintain equilibrium compositions. We know, however, that isotope exchange in nature tends to be a slow process, especially at low temperature (e.g., O’Neil, 1987). This knowledge comes from experimental study (e.g., Cole and Ohmoto, 1986) as well as from the simple observation that, unless they have reacted together, groundwaters and minerals are seldom observed to be in isotopic equilibrium with each other. In fact, if exchange were a rapid process, it would be very difficult to interpret the origin of geologic materials from their isotopic compositions: the information would literally diffuse away. Lee and Bethke (1996) presented an alternative technique, also based on mass balance equations, in which the reaction modeler can segregate minerals from isotopic exchange. By segregating the minerals, the model traces the effects of the isotope fractionation that would result from dissolution and precipitation reactions alone.
Тези доповідей конференцій з теми "Oxygen isotopes, atmospheric effects":
1
Nickel, Hubertus, Willem J. Quadakkers, and Lorenz Singheiser. "Determination of Corrosion Layers and Protective Coatings on Steels and Alloys Used in Simulated Service Environment of Modern Power Plants." In ASME/JSME 2004 Pressure Vessels and Piping Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/pvp2004-2249.
Анотація:
The development of modern power generation systems with higher thermal efficiency requires the use of constructional materials of higher strength and improved resistance to the aggressive service atmospheres. In this paper the following examples are discussed: 1) The oxidation behavior of 9% Cr steels in simulated combustion gases: The effects of O2 and H2O content on the oxidation behavior of 9% Cr steels in the temperature range 600–800°C showed that in dry oxygen a protective scale was formed with an oxidation rate controlled by diffusion. In contrast, that in the presence of water vapor, after an incubation period, the scale became non-protective as a result of a change in the oxidation mechanism. 2) The development of NiCrAlY alloys for corrosion resistant coatings and thermal barrier coatings of gas turbine components: The increase of component surface temperature in modern gas turbines leads to an enhanced oxidation attack of the blade coating. Considerable efforts have been made in the improvement of the temperature properties of MCrAlY coatings by the additions of minor elements like yttrium, silicon and titanium. The experimental results show the positive, but different influence of the oxidation behavior of the MCrAlY coatings by the addition of these minor elements. 3) The development of light-weight intermetallics of TiAl-basis: TiAl-based intermetallics are promising materials for future turbine components because of the combination of high temperature strength and low density. These alloys, however, possess poor oxidation resistance at temperatures above 700°C. The experimental results showed that the oxidation behavior of TiAl-based intermetallics can be strongly improved by minor additions of 1–2 at.-% silver. 4) The oxide dispersion strengthened (ODS) alloys provide excellent creep resistance up to much higher temperatures than can be achieved with conventional wrought or cast alloys in combination with suitable high temperature oxidation/corrosion resistance. The growth mechanisms of protective chromia and alumina scales were examined by a two-stage oxidation method with 18O tracer. The distribution of the oxygen isotopes in the oxide scale was determined by SIMS and SNMS. The results show the positive influence of a Y2O3 dispersion on the oxidation resistance of the ODS alloys and its effect on growth mechanisms.
2
Liu, Xue, Yang Liu, Tao Li, Guohui Li, and Lixiang Jiang. "Prediction Effects of Low Earth Orbit Space Environments on Atomic Oxygen Undercutting." In 3rd AIAA Atmospheric Space Environments Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2011. http://dx.doi.org/10.2514/6.2011-3825.
3
Wang, Shouguo. "Oxygen Effects on a He/O2 Plasma Jet at Atmospheric Pressure." In IEEE Conference Record - Abstracts. 2005 IEEE International Conference on Plasma Science. IEEE, 2005. http://dx.doi.org/10.1109/plasma.2005.359072.
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Korshunov, A. "EXPERIMENTAL STUDY OF FOAMED EMULSION COMBUSTION: EFFECTS OF OXYGEN, DICHLOROETHANE, AND GLYCEROL CONCENTRATIONS." In 8TH INTERNATIONAL SYMPOSIUM ON NONEQUILIBRIUM PROCESSES, PLASMA, COMBUSTION, AND ATMOSPHERIC PHENOMENA. TORUS PRESS, 2020. http://dx.doi.org/10.30826/nepcap2018-2-10.
5
Boselli, M., V. Colombo, E. Ghedini, M. Gherardi, R. Laurita, F. Rotundo, P. Sanibondi, A. Stancampiano, M. Minelli, and M. G. De Angelis. "Comparing the effects of different atmospheric pressure non-equilibrium plasma sources on polylactide oxygen permeability." In 2012 IEEE 39th International Conference on Plasma Sciences (ICOPS). IEEE, 2012. http://dx.doi.org/10.1109/plasma.2012.6383893.
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Hashida, Toshiyuki, Yohei Takeyama, and Kazuhisa Sato. "The Effects of Oxygen Vacancy Concentration on the Mechanical Properties of Zirconia and Ceria-Based Electrolytes for SOFCs." In ASME 2009 7th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2009. http://dx.doi.org/10.1115/fuelcell2009-85241.
Анотація:
In this paper, we discuss the effects of different oxygen partial pressures on the deformation property and fracture characteristics of representative constituent materials for solid oxide fuel cells (SOFCs). The elastic modulus and fracture strength of 8 mol% yittria stabilized zirconia (8YSZ) and 10 mol% gadolinia doped ceria (10GDC) treated under different oxygen partial pressures were evaluated using the small-punch testing method in this study. The specimens of 8YSZ and 10GDC prepared by a sintering process were treated at 800 °C under an oxygen partial pressure in the range of 0.21 to 10−22 atm for 1 hour. The treated specimens were then fast cooled down to a room temperature, and their mechanical properties were measured under an atmospheric pressure condition by using the small-punch testing method. The experimental results revealed that both the elastic modulus and fracture strength of the 10GDC decreased drastically when the oxygen partial pressure of the treatment was less than 10−15 atm, whereas no significant variation in both the mechanical properties was observed for the 8YSZ. The elastic modulus and fracture strength of 10GDC for the treatment under 10−22 atm was reduced down to 10–20% of those treated under the atmospheric pressure. SEM observations revealed that the fracture surface of the 10GDC specimens was changed from transgranular mode to intergranular mode when the oxygen partial pressure was reduced, whereas the fracture surface of the 8YSZ specimens was transgranular regardless of the different oxygen partial pressures.
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Kitazawa, Daisuke, and Michio Kumagai. "Numerical Study on the Effects of Water Surface Shield and Oxygen Injection on Water Quality in Lake Biwa." In ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2008. http://dx.doi.org/10.1115/omae2008-57669.
Анотація:
Numerical simulation was carried out by means of a three-dimensional hydrostatic and ecosystem coupled model in order to predict the effects of water surface shield and oxygen injection on the water quality in Lake Biwa. Recent observations show the degradation of water quality particularly around the water bottom in Lake Biwa. One of the possible reasons of the degradation is the depletion in the vertical mixing of waters due to climate change. The meteorological observations at Hikone show that the atmospheric temperature has increased by 1°C in the recent 20 years. If the vertical mixing of waters is weakened, the waters with rich oxygen are not supplied enough around the water bottom during winter seasons, and the concentration of dissolved oxygen is hardly recovered to the saturated level. The depletion in the vertical mixing of waters has been increasingly worried since Intergovernmental Panel on Climate Change (2007) reported that the globally mean atmospheric temperature will increase by a few °C in a century. In order to cope with such problems, the present study proposes a feasible system to inject the oxygen produced by the electrolysis of water. In the proposed system, water surface is shielded by a floating platform, which blocks off the penetration of solar radiation through the water surface and generates the density-driven current due to the horizontal difference in water temperature. In addition, solar cell modules are installed on the floating platform to produce oxygen by means of the electrolysis of water. The produced oxygen is then released from the electrodes installed around the water bottom. As a result of numerical simulation using the three-dimensional hydrostatic and ecosystem coupled model, the effect of water surface shield was negligible since the surface area of the floating platform was quite smaller than that of Lake Biwa. The effect of oxygen injection was remarkable and localized in summer than in winter. The concentration of dissolved oxygen was then expected to increase by more than 0.2mg/l within 15m from the bottom surface in summer, in the cases when 730,000m3 of oxygen was injected in an year. The effect of seasonal change in the production of oxygen was negligible since little difference was found in the concentration of dissolved oxygen. As future studies, the nested grid system should be utilized to predict precisely the diffusion of oxygen both in the vicinity of the electrode and in the whole Lake Biwa.
8
Wicksall, Donald M., and Ajay K. Agrawal. "Effects of Fuel Composition on Flammability Limit of a Lean Premixed Combustor." In ASME Turbo Expo 2001: Power for Land, Sea, and Air. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/2001-gt-0007.
Анотація:
Fuel flexibility is desired in advanced power generating gas turbines operating in the lean premixed combustion mode. In this study, experiments were performed in a lean premixed, swirl-stabilized combustor operated at atmospheric pressure to quantify how adding liquid petroleum gas (LPG), hydrogen, oxygen, nitrogen, and carbon dioxide to natural gas (NG) affected the flame stability. The flame extinction characteristics were obtained for NG fuel mixtures with up to 40% by volume of the indicated gases. The combustion air was supplied at room temperature and the fuel-air mixture was fully premixed before reaching the combustor. The total fuel-air flow rate was varied by a factor of two to achieve a range of aerodynamic conditions. Results demonstrate that additions of hydrogen and oxygen to NG extended the stable operating range of the combustor. Addition of LPG to NG had a slightly adverse effect while the non-reactive species in the NG did not affect the lean flammability limit.
9
Liu, Ting, Lili Zheng, Guanzhong Zhang, and Hui Zhang. "Effects of Solid Shield and Shroud on Plasma Jet Flame in APS Process." In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-37766.
Анотація:
Gas entrainment occurs in atmospheric plasma spray (APS) after plasma jet flows into the cold surroundings, resulting in rapid decaying of speed and unwanted oxidation. Installing a solid shield or inserting a gas shroud at the end of the nozzle may be helpful to reduce air entrainment. Effects of solid shield and inert gas shroud on plasma jet are investigated numerically. It is found that solid shield and gas shroud will expand high temperature field of plasma jet in both axial and radial direction, consequently, enabling a thorough reaction of oxygen content for virtually oxygen free plasma jet. The mass fraction of the O2 gas in the plasma flow outside the shield decreases with the increase of the inert gas velocity, which maintains nearly zero in the solid shield. Inert gas velocity and its injection angle turn out to be important factors to offset the negative effects of solid shield on the main flow. It is demonstrated that the flow field is less affected when the inert gas is axially injected with the inlet velocity of 150m/s. Ar is more appropriate than N2 as an inert gas, which is mainly attributed to its physical properties.
10
Wang, Wei, Hui Zhang, Rui Yang, Qiuju Ma, Xiaodong Liu, Cong Li, and Zhenxiang Tao. "Controlling Effect of Oxygen Concentration on Fire Behavior in Low Air Pressure Cargo Compartment." In ASME 2017 Heat Transfer Summer Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/ht2017-5065.
Анотація:
Cargo compartment fire has become the major security threat for cruising aircraft, the depressurization measurement could effectively suppress the cargo compartment fire through the reduction of the air pressure and oxygen concentration. The objective of this work is to study fire behavior characteristics in half confined chamber and high altitude laboratory at identical low atmospheric pressure, and explore the controlling effects of air exhaust condition, oxygen concentration. N-heptane pool fire experiments were conducted separately in Langfang low pressure chamber (altitude 50m) and Kangding airport laboratory (altitude 4290m) at 60 kPa air pressure, both assembled ISO-9705, but their gas supplying condition is different. Mass burning rate, gas composition, flame temperature, and radiant heat flux had been measured as the principal characteristic parameters for analysis. This paper reveals the variation characteristics of the fire behavior under different oxygen concentration but identical low atmospheric pressure. The gas composition of the chamber is controlled by the liquid fire and air intake quantity, the oxygen concentration of the chamber decreases with decreasing gas intake quantity. The mass burning rate increases and the mass burning time decreases with the increase of the oxygen concentration. The higher air intake quantity or the higher oxygen concentration could increase cargo compartment fire radiation intensity, and exacerbate the fire further propagation. However, under the low oxygen concentration condition, the liquid fire still have a higher flame temperature above a certain height. The depressurization measurement could increase the flame height and flame temperature may be caused the cabin fire-resistant liners layer is easier to burn through. The more reasonable adjustment of the cargo compartment air exhaust quantity and air pressure is very meaningful for the comprehensive fire suppression of cruising commercial airplanes.