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Auswahl der wissenschaftlichen Literatur zum Thema „Nitrate particulaire“
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Zeitschriftenartikel zum Thema "Nitrate particulaire"
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Lee, L., P. J. Wooldridge, J. deGouw, et al. "Particulate organic nitrates observed in an oil and natural gas production region during wintertime." Atmospheric Chemistry and Physics Discussions 15, no. 7 (2015): 10677–708. http://dx.doi.org/10.5194/acpd-15-10677-2015.
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Abstract. Organic nitrates in both gas and condensed (aerosol) phases were measured during the Uintah Basin Winter Ozone Study from January to February in 2012. A high degree of correlation between total aerosol volume at diameters less than 500 nm and the particulate organic nitrate concentration indicates that organic nitrates are a consistent, if not dominant, fraction of fine aerosol mass. In contrast, a similar correlation with sub 2.5 μm aerosol volume is weaker. The C : N atomic ratio inferred from field measurements of PM2.5 and particulate organic nitrate is 34 : 1. Calculations constrained by the observations indicate that both condensation of gas phase nitrates and heterogeneous reactions of NO3 / N2O5 are responsible for introducing organic nitrate functionality into the aerosol and that the source molecules are alkanes. Extrapolating the results to urban aerosol suggests organic nitrate production from alkanes may be a major secondary organic aerosol source.
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Lee, L., P. J. Wooldridge, J. deGouw, et al. "Particulate organic nitrates observed in an oil and natural gas production region during wintertime." Atmospheric Chemistry and Physics 15, no. 16 (2015): 9313–25. http://dx.doi.org/10.5194/acp-15-9313-2015.
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Abstract. Organic nitrates in both gas and condensed (aerosol) phases were measured during the Uintah Basin Winter Ozone Study from January to February in 2012. A high degree of correlation between total aerosol volume at diameters less than 500 nm and the particulate organic nitrate concentration indicates that organic nitrates are a consistent, if not dominant, fraction of fine aerosol mass. In contrast, a similar correlation with sub-2.5 μm aerosol volume is weaker. The C : N atomic ratio inferred from field measurements of PM2.5 and particulate organic nitrate is 34 : 1. Calculations constrained by the observations indicate that both condensation of gas-phase nitrates and heterogeneous reactions of NO3 / N2O5 are responsible for introducing organic nitrate functionality into the aerosol and that the source molecules are alkanes. Extrapolating the results to urban aerosol suggests organic nitrate production from alkanes may be a major secondary organic aerosol source.
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Lean, D. R. S., and R. Knowles. "Nitrogen Transformations in Lake Ontario." Canadian Journal of Fisheries and Aquatic Sciences 44, no. 12 (1987): 2133–43. http://dx.doi.org/10.1139/f87-262.
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Concentrations of ammonium plus nitrite in Lake Ontario were highly correlated with ammonium regeneration from zooplankton excretion (r = 0.966), inferring that elevated nitrite concentrations result from nitrification. Nitrapyrin-sensitive dark 14C-labeled bicarbonate assays confirmed high rates of nitrification by chemoautotrophic bacteria. 15N-labeled nitrate experiments showed that nitrate, not ammonium, was the principal form of N used for total microbial protein synthesis. Size fractionation experiments also suggested that small cells were responsible for most of the ammonium uptake, while large cells used mostly nitrate. Nitrate depletion in the surface waters during summer stratification resulted from movement to particulate N, nitrite, and ammonium as well as losses in particulate N due to sedimentation. At least one third, however, was unaccounted for (i.e. 30 mg N∙m−2∙d−1) and may have been converted to protein which would move up the food chain to larger organisms (e.g. fish) not sampled during conventional water chemistry. Nitrous oxide profiles showed that nitrate losses through denitrification are unlikely to occur. Consequently, unless nitrate loading to Lake Ontario is reduced, nitrate concentrations should be expected to continue to increase.
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Jacob, Juliane, Tina Sanders, and Kirstin Dähnke. "Nitrite consumption and associated isotope changes during a river flood event." Biogeosciences 13, no. 19 (2016): 5649–59. http://dx.doi.org/10.5194/bg-13-5649-2016.
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Abstract. In oceans, estuaries, and rivers, nitrification is an important nitrate source, and stable isotopes of nitrate are often used to investigate recycling processes (e.g. remineralisation, nitrification) in the water column. Nitrification is a two-step process, where ammonia is oxidised via nitrite to nitrate. Nitrite usually does not accumulate in natural environments, which makes it difficult to study the single isotope effect of ammonia oxidation or nitrite oxidation in natural systems. However, during an exceptional flood in the Elbe River in June 2013, we found a unique co-occurrence of ammonium, nitrite, and nitrate in the water column, returning towards normal summer conditions within 1 week. Over the course of the flood, we analysed the evolution of δ15N–NH4+ and δ15N–NO2− in the Elbe River. In concert with changes in suspended particulate matter (SPM) and δ15N SPM, as well as nitrate concentration, δ15N–NO3− and δ18O–NO3−, we calculated apparent isotope effects during net nitrite and nitrate consumption. During the flood event, > 97 % of total reactive nitrogen was nitrate, which was leached from the catchment area and appeared to be subject to assimilation. Ammonium and nitrite concentrations increased to 3.4 and 4.4 µmol L−1, respectively, likely due to remineralisation, nitrification, and denitrification in the water column. δ15N–NH4+ values increased up to 12 ‰, and δ15N–NO2− ranged from −8.0 to −14.2 ‰. Based on this, we calculated an apparent isotope effect 15ε of −10.0 ± 0.1 ‰ during net nitrite consumption, as well as an isotope effect 15ε of −4.0 ± 0.1 ‰ and 18ε of −5.3 ± 0.1 ‰ during net nitrate consumption. On the basis of the observed nitrite isotope changes, we evaluated different nitrite uptake processes in a simple box model. We found that a regime of combined riparian denitrification and 22 to 36 % nitrification fits best with measured data for the nitrite concentration decrease and isotope increase.
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Karwowska, Małgorzata, and Anna Kononiuk. "Nitrates/Nitrites in Food—Risk for Nitrosative Stress and Benefits." Antioxidants 9, no. 3 (2020): 241. http://dx.doi.org/10.3390/antiox9030241.
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In the context of impact on human health, nitrite/nitrate and related nitrogen species such as nitric oxide (NO) are a matter of increasing scientific controversy. An increase in the content of reactive nitrogen species may result in nitrosative stress—a deleterious process, which can be an important mediator of damage to cell structures, including lipids, membranes, proteins and DNA. Nitrates and nitrites are widespread in the environment and occur naturally in foods of plant origin as a part of the nitrogen cycle. Additionally, these compounds are used as additives to improve food quality and protect against microbial contamination and chemical changes. Some vegetables such as raw spinach, beets, celery and lettuce are considered to contain high concentrations of nitrates. Due to the high consumption of vegetables, they have been identified as the primary source of nitrates in the human diet. Processed meats are another source of nitrites in our diet because the meat industry uses nitrates/nitrites as additives in the meat curing process. Although the vast majority of consumed nitrates and nitrites come from natural vegetables and fruits rather than food additives, there is currently a great deal of consumer pressure for the production of meat products free of or with reduced quantities of these compounds. This is because, for years, the cancer risks of nitrates/nitrites have been considered, since they potentially convert into the nitrosamines that have carcinogenic effects. This has resulted in the development and rapid expansion of meat products processed with plant-derived nitrates as nitrite alternatives in meat products. On the other hand, recently, these two ions have been discussed as essential nutrients which allow nitric oxide production and thus help cardiovascular health. Thus, this manuscript reviews the main sources of dietary exposure to nitrates and nitrites, metabolism of nitrites/nitrates, and health concerns related to dietary nitrites/nitrates, with particular emphasis on the effect on nitrosative stress, the role of nitrites/nitrates in meat products and alternatives to these additives used in meat products.
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Yu, Kuangyou, Qiao Zhu, Ke Du, and Xiao-Feng Huang. "Characterization of nighttime formation of particulate organic nitrates based on high-resolution aerosol mass spectrometry in an urban atmosphere in China." Atmospheric Chemistry and Physics 19, no. 7 (2019): 5235–49. http://dx.doi.org/10.5194/acp-19-5235-2019.
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Abstract. Organic nitrates are important atmospheric species that significantly affect the cycling of NOx and ozone production. However, characterization of particulate organic nitrates and their sources in polluted atmosphere is a big challenge and has not been comprehensively studied in Asia. In this study, an aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed at an urban site in China from 2015 to 2016 to characterize particulate organic nitrates in total nitrates with a high time resolution. Based on the cross-validation of two different data processing methods, organic nitrates were effectively quantified to contribute a notable fraction of organic aerosol (OA), namely 9 %–21 % in spring, 11 %–25 % in summer, and 9 %–20 % in autumn, while contributing a very small fraction in winter. The good correlation between organic nitrates and fresh secondary organic aerosol (SOA) at night, as well as the diurnal trend of size distribution of organic nitrates, indicated a key role of nighttime local secondary formation of organic nitrates. Furthermore, theoretical calculations of nighttime SOA production of NO3 reactions with volatile organic compounds (VOCs) measured during the spring campaign were performed, resulting in three biogenic VOCs (α-pinene, limonene, and camphene) and one anthropogenic VOC (styrene) identified as the possible key VOC precursors to particulate organic nitrates. The comparison with similar studies in the literature implied that nighttime particulate organic nitrate formation is highly relevant to NOx levels. This study proposes that unlike the documented cases in the United States and Europe, modeling nighttime particulate organic nitrate formation in China should incorporate not only biogenic VOCs but also anthropogenic VOCs for urban air pollution, which needs the support of relevant smog chamber studies in the future.
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Parks, S. E., D. O. Huett, L. C. Campbell, and L. J. Spohr. "Nitrate and nitrite in Australian leafy vegetables." Australian Journal of Agricultural Research 59, no. 7 (2008): 632. http://dx.doi.org/10.1071/ar07198.
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A market survey of Australian leafy vegetables and a winter and spring experiment with Swiss chard were conducted to examine nitrate and nitrite levels in leaves. The relationship between growth response to nitrogen (N) supply and light level and accumulation of N in leaves was of particular interest. The survey that included 7 types of lettuce and endive (Asteraceae), 6 leafy Asian vegetables (Brassicaceae), and Swiss chard and spinach (Amaranthaceae) showed that fresh leafy vegetables available during a 6-month period on the Australian market can range in nitrate-N from 12 to 1400 mg/kg fresh weight and nitrite-N from 0 to 37.5 mg/kg. Some samples exceeded the limits for nitrate and nitrite based on international food safety standards. The response of Swiss chard to N supply and light was investigated. The accumulation of nitrate in Swiss chard was primarily influenced by increasing N supply and not by light level. Light conditions for all treatments in both the winter and spring experiments exceeded the critical level (~200 μmol/m2.s) required to increase leaf nitrate. Growth and leaf nitrate concentration were higher for spring, associated with average minimum to maximum temperatures of 18–39°C, compared with 14–28°C for winter. Treatment effects on nitrite-N in Swiss chard could not be determined because nitrite was only detected in one-third of plants. The importance of N supply in affecting nitrate accumulation in vegetables is highlighted by the Swiss chard experiments. It confirmed that nitrate accumulation occurs at optimal to supra-optimal nitrate supply, emphasising for growers the undesirable effect of excessive fertiliser use.
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González-Sánchez, Juan Miguel, Nicolas Brun, Junteng Wu, et al. "On the importance of atmospheric loss of organic nitrates by aqueous-phase ●OH oxidation." Atmospheric Chemistry and Physics 21, no. 6 (2021): 4915–37. http://dx.doi.org/10.5194/acp-21-4915-2021.
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Abstract. Organic nitrates are secondary species in the atmosphere. Their fate is related to the chemical transport of pollutants from polluted areas to more distant zones. While their gas-phase chemistry has been studied, their reactivity in condensed phases is far from being understood. However, these compounds represent an important fraction of organic matter in condensed phases. In particular, their partition to the aqueous phase may be especially important for oxidized organic nitrates for which water solubility increases with functionalization. This work has studied for the first time the aqueous-phase ⚫OH-oxidation kinetics of four alkyl nitrates (isopropyl nitrate, isobutyl nitrate, 1-pentyl nitrate, and isopentyl nitrate) and three functionalized organic nitrates (α-nitrooxyacetone, 1-nitrooxy-2-propanol, and isosorbide 5-mononitrate) by developing a novel and accurate competition kinetic method. Low reactivity was observed, with kOH ranging from 8×107 to 3.1×109 L mol−1 s−1 at 296±2 K. Using these results, a previously developed aqueous-phase structure–activity relationship (SAR) was extended, and the resulting parameters confirmed the extreme deactivating effect of the nitrate group, up to two adjacent carbon atoms. The achieved extended SAR was then used to determine the ⚫OH-oxidation rate constants of 49 organic nitrates, including hydroxy nitrates, ketonitrates, aldehyde nitrates, nitrooxy carboxylic acids, and more functionalized organic nitrates such as isoprene and terpene nitrates. Their multiphase atmospheric lifetimes towards ⚫OH oxidation were calculated using these rate constants, and they were compared to their gas-phase lifetimes. Large differences were observed, especially for polyfunctional organic nitrates: for 50 % of the proposed organic nitrates for which the ⚫OH reaction occurs mainly in the aqueous phase (more than 50 % of the overall removal), their ⚫OH-oxidation lifetimes increased by 20 % to 155 % under cloud/fog conditions (liquid water content LWC = 0.35 g m−3). In particular, for 83 % of the proposed terpene nitrates, the reactivity towards ⚫OH occurred mostly (>98 %) in the aqueous phase, while for 60 % of these terpene nitrates, their lifetimes increased by 25 % to 140 % compared to their gas-phase reactivity. We demonstrate that these effects are of importance under cloud/fog conditions but also under wet aerosol conditions, especially for the terpene nitrates. These results suggest that considering aqueous-phase ⚫OH-oxidation reactivity of biogenic nitrates is necessary to improve the predictions of their atmospheric fate.
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McKnight, G. M., C. W. Duncan, C. Leifert, and M. H. Golden. "Dietary nitrate in man: friend or foe?" British Journal of Nutrition 81, no. 5 (1999): 349–58. http://dx.doi.org/10.1017/s000711459900063x.
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Based on the premise that dietary nitrate is detrimental to human health, increasingly stringent regulations are being instituted to lower nitrate levels in food and water. Not only does this pose a financial challenge to water boards and a threat to vegetable production in Northern Europe, but also may be eliminating an important non-immune mechanism for host defence. Until recently nitrate was perceived as a purely harmful dietary component which causes infantile methaemoglobinaemia, carcinogenesis and possibly even teratogenesis. Epidemiological studies have failed to substantiate this. It has been shown that dietary nitrate undergoes enterosalivary circulation. It is recirculated in the blood, concentrated by the salivary glands, secreted in the saliva and reduced to nitrite by facultative Gram-positive anaerobes (Staphylococcus sciuriandS. intermedius) on the tongue. Salivary nitrite is swallowed into the acidic stomach where it is reduced to large quantities of NO and other oxides of N and, conceivably, also contributes to the formation of systemic S-nitrosothiols. NO and solutions of acidified nitrite, mimicking gastric conditions, have been shown to have antimicrobial activity against a wide range of organisms. In particular, acidified nitrite is bactericidal for a variety of gastrointestinal pathogens such asYersiniaandSalmonella.NO is known to have vasodilator properties and to modulate platelet function, as are S-nitrosothiols. Thus, nitrate in the diet, which determines reactive nitrogen oxide species production in the stomach (McKnightet al.1997), is emerging as an effective host defence against gastrointestinal pathogens, as a modulator of platelet activity and possibly even of gastrointestinal motility and microcirculation. Therefore dietary nitrate may have an important therapeutic role to play, not least in the immunocompromised and in refugees who are at particular risk of contracting gastroenteritides.
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Spryn, K. R., M. V. Sabadashka, and N. O. Sybirna. "Effects of agmatine and red wine concentrate, enriched with polyphenolic compounds, on L-arginine / nitrogen oxide system in the brain of rats with experimental diabetes mellitus." Studia Biologica 15, no. 2 (2021): 25–34. http://dx.doi.org/10.30970/sbi.1502.655.
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Background. Diabetes mellitus is a chronic endocrine metabolic disease with absolute or relative insufficiency of insulin, accompanied by impaired metabolism. Endogenous bioamine agmatine may become a basis of new antidiabetic drugs, as it is capable to induce the release of some peptide hormones, in particular insulin, and can regulate NO synthesis. Natural polyphenols are potential multifunctional agents that also can reduce the risk of diabetes and diabetic complications. The aim of the study was to evaluate the effect of agmatine and red wine concentrate, enriched with polyphenolic compounds, on NO-synthase activity and the content of NO stable metabolites under experimental diabetes mellitus. Materials and Methods. The experiments were conducted on white Wistar male rats. Diabetes was induced by intra-abdominal injection of streptozotocin. From the 14th day after the induction of diabetes, agmatine was injected intramuscularly or red wine concentrate, enriched with polyphenolic compounds was administrated orally to animals for 14 days. Rats were decapitated under ether anesthesia on the 28th day of the experiment. In the brain of rats, the activity of constitutive (Ca2+-dependent) and inducible (Ca2+-independent) isoforms of NO-synthase and the content of nitrite and nitrate anions were determined. Results and Discussion. The activities of constitutive and inducible isoforms of NO-synthase were increased in the brain of diabetic rats. The administration of both agmatine and red wine concentrate, enriched with polyphenolic compounds, caused the reduction of the activities of NO-synthase isoforms. In the case of diabetes, the administration of agmatine contributes to the increase of nitrite and nitrate content in brain cells compared to diabetes. The administration of red wine concentrate, enriched with polyphenolic compounds, also promotes nitrite levels but does not affect the nitrate level. Conclusion. We found that the red wine concentrate, enriched with polyphenolic compounds, has a stronger effect on the activity of Ca2+-dependent and Ca2+-independent isoforms of NO-synthase, as well as the content of nitrites and nitrates in brain of rats with experimental diabetes mellitus, compared to the effect of agmatine.
Dissertationen zum Thema "Nitrate particulaire"
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Xue, Chaoyang. "Les sources de HONO atmosphérique rural et leur impact sur la qualité de l'air régional dans la Plaine de Chine du Nord." Electronic Thesis or Diss., Orléans, 2020. http://www.theses.fr/2020ORLE3107.
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La pollution de l'air est toujours un problème environnemental qui doit être résolu de toute urgence dans la Plaine de Chine du Nord (PCN). Dans le but d'explorer la formation de l’acide nitreux (HONO) et son impact sur la qualité de l'air régional dans la PCN, le développement et l'évaluation systématique d'instruments pour mesurer la concentration de HONO atmosphérique et son flux d'émission du sol ont été réalisés. Sur la base de mesures sur le terrain, un modèle 3D de chimie-transport (le système communautaire de modélisation de la qualité de l'air à plusieurs échelles : CMAQ, de l’EPA) et un modèle de boîte (0D) de mécanisme chimique (Master Chemical Mechanism : MCM) ont été utilisés pour explorer le bilan de HONO et son impact sur la pollution atmosphérique régionale, par exemple la pollution estivale à l'ozone (O3) et la pollution par la brume hivernale. Nous avons constaté que le sol agricole était une source importante de HONO avec un impact significatif sur la pollution régionale à l'ozone en été. Un nouveau mécanisme d'émission de HONO du sol lié à la nitrification a été proposé. HONO joue également un rôle important dans la capacité oxydante de l’atmosphère et la détérioration de la qualité de l'air régional en hiver<br>Air pollution is still an environmental problem that urgently needs to be solved in the North China Plain (NCP). With the aim to explore nitrous acid (HONO) formation and its impact on regional air quality in the NCP, the development and systematic assessment of instruments to measure atmospheric HONO concentration and soil HONO emission flux were realized. Based on field measurements, a 3D chemistry-transport model (the Community Multiscale Air Quality Modeling System, CMAQ) and a box (0D) model (Master Chemical Mechanism, MCM) were used to explore the HONO budget and its impact on regional air pollution, e.g., summer ozone (O3) pollution and winter haze pollution. We found that agricultural soil was an important HONO source with a significant impact on regional O3 pollution in the summertime. A new soil HONO emission mechanism related to nitrification was proposed. HONO also plays an important role in atmospheric oxidizing capacity and deteriorating regional air quality in the wintertime
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Roig, Rodelas Roger. "Chemical characterization, sources and origins of secondary inorganic aerosols measured at a suburban site in Northern France." Thesis, Lille 1, 2018. http://www.theses.fr/2018LIL1R017/document.
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Les particules fines troposphériques de diamètre aérodynamique inférieur à 2,5 µm (PM2.5) peuvent impacter la santé et les écosystèmes. Les aérosols inorganiques secondaires (AIS) et organiques (AO) contribuent fortement aux PM2.5. Pour comprendre leur formation et leur origine, une campagne d’1 an (août 2015 - juillet 2016) de mesures horaires de gaz précurseurs inorganiques et d’ions hydrosolubles particulaires a été menée sur un site urbain du nord de la France avec un MARGA 1S, complétées par les concentrations massiques en PM2.5, carbone suie, oxydes d’azote et éléments traces. Des niveaux élevés de nitrate d’ammonium (NA) ont été observés la nuit au printemps et de sulfate d’ammonium la journée en été. L’étude de la contribution des sources par le modèle PMF (Positive Matrix Factorization) a permis d’identifier 8 facteurs sources: 3 régionaux (riche en sulfates, riche en nitrates et marin) pour 73 à 78%, et 5 locaux (trafic, combustion de biomasse, fond industriel métallurgique, industrie locale et poussières minérales) (22-27%). De plus, un HR-ToF-AMS (spectromètre de masse à aérosols) et un SMPS (granulomètre) ont été utilisés lors d’une campagne intensive en hiver, afin de mieux documenter l’AO et la formation de nouvelles particules, respectivement. L’application du PMF aux spectres de masses d’AO a permis d’identifier 5 facteurs liés au trafic (15%), à la cuisson (11%), à la combustion de biomasse (25%), et à une oxydation plus ou moins forte de la matière organique (33% et 16%). Plusieurs événements nocturnes de formation de nouvelles particules impliquant les AIS, notamment du NA, ont été observés<br>Tropospheric fine particles with aerodynamic diameters less than 2.5 µm (PM2.5) may impact health, climate and ecosystems. Secondary inorganic (SIA) and organic aerosols (OA) contribute largely to PM2.5. To understand their formation and origin, a 1-year campaign (August 2015 to July 2016) of inorganic precursor gases and PM2.5 water-soluble ions was performed at an hourly resolution at a suburban site in northern France using a MARGA 1S, complemented by mass concentrations of PM2.5, Black Carbon, nitrogen oxides and trace elements. The highest levels of ammonium nitrate (AN) and sulfate were observed at night in spring and during daytime in summer, respectively. A source apportionment study performed by positive matrix factorization (PMF) determined 8 source factors, 3 having a regional origin (sulfate-rich, nitrate-rich, marine) contributing to PM2.5 mass for 73-78%; and 5 a local one (road traffic, biomass combustion, metal industry background, local industry and dust) (22-27%). In addition, a HR-ToF-AMS (aerosol mass spectrometer) and a SMPS (particle sizer) were deployed during an intensive winter campaign, to gain further insight on OA composition and new particle formation, respectively. The application of PMF to the AMS OA mass spectra allowed identifying 5 source factors: hydrocarbon-like (15%), cooking-like (11%), oxidized biomass burning (25%), less- and more-oxidized oxygenated factors (16% and 33%, respectively). Combining the SMPS size distribution with the chemical speciation of the aerosols and precursor gases allowed the identification of nocturnal new particle formation (NPF) events associated to the formation of SIA, in particular AN
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Evans, Melissa Cheryl Foster. "Characterization and Formation of Particulate Nitrate in a Coastal Area." [Tampa, Fla.] : University of South Florida, 2003. http://purl.fcla.edu/fcla/etd/SFE0000142.
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Whelan, Michael John. "Numerical modelling of small catchment nitrogen dynamics with particular reference to the Slapton Wood catchment, South Devon." Thesis, University of Leeds, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343483.
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Lai, Ka Wun. "Particulate nitrate in PM1 and PM2.5 at a suburban site in Hong Kong." Thesis, University of Macau, 2018. http://umaclib3.umac.mo/record=b3868748.
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Turan, Servet. "Microstructural characterisation of silicon nitride-silicon carbide particulate composites." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627653.
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Andriamandroso, Daniel. "Sur une nouvelle famille de matériaux particulaires pour l'enregistrement magnétique dérivée du nitrure FeN." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb375955281.
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Andriamandroso, Jean Harry Daniel. "Sur une nouvelle famille de matériaux particulaires pour l'enregistrement magnétique dérivée du nitrure Fe4N." Bordeaux 1, 1986. http://www.theses.fr/1986BOR10580.
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De nouveaux materiaux ferromagnetiques derives du nitrure de fer fe::(4)n ont ete prepares. La substitution partielle de l'azote par du carbone leur confere une meilleure resistance a l'oxydation. La morphologie des pigments magnetiques est induite par celle des precurseurs. Etude de la modification de la taille du fer par l'etain. Etude generale de l'influence de substituants tels que ru, os, ir sur l'anisotropie magnetocristalline
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Klein, Robert. "Propriétés de composites céramiques particulaires électroconducteurs, élaborés par compression isostatique à chaud." Limoges, 2004. http://aurore.unilim.fr/theses/nxfile/default/87d1df87-738c-4644-865a-5aa25c91abfd/blobholder:0/2004LIMO0009.pdf.
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L'élaboration de matériaux composites particulaires à base de nitrure de silicium Si3N4-TiN, Si3N4-TiB2, Si3N4-HfB2, a été réalisée par compression isostatique à chaud (CIC ou HIP), avec de faibles quantités d'ajouts (Y2O 3, Al2O3 ), afin d'obtenir des matériaux denses. Grâce à la présence de la seconde phase qui leur confère une bonne conductivité électrique, les composites sont usinables par électroérosion (EDM). Leur caractérisation est effectuée par analyses DRX, MEB et MET et leurs propriétés mécaniques (dureté, ténacité, résistance à la rupture à température ambiante et élevée) ainsi que leurs modules élastiques sont analysés. L'étude de la résistance à l'oxydation de ces composites sous flux dynamique d'oxygène pur (900-1400ʿC) montre le meilleur comportement du matériau Si3N4-HfB2. Un matériau multicouche a pu être élaboré après étude de la mouillabilité et de la réactivité d'une brasure Ag-Cu-Ti<br>The aim of this work was the elaboration and the characterization of electroconductive silicon nitride based ceramic composites Si3N4-TiN, Si3N4-TiB2 and Si3N4-HfB2, elaborated by Hot Isostatic Pressing (HIPing). A small amount of sintering aids (Y2O3, Al2O3) led to good densification and their high electrical conductivity authorized electrodischarge machining (EDM). The characterization of the materials was done by XRD, SEM and TEM analysis. Their mechanical properties (microhardness, fracture toughness, flexural strength at low and high temperatures) and the elastic moduli were analyzed. The oxidation resistance, studied under dynamic conditions in pure oxygen, between 900 and 1400ʿC, showed the better behavior of the Si3N4-HfB2 material. A multi-layered material was elaborated after the study of the wettability and reactivity with an Ag-Cu-Ti braze
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Stephens, Clifford. "Analysis of the thermal conductivity of epoxy and reaction bonded silicon nitride matrix particulate composites." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/11239.
Der volle Inhalt der QuelleBücher zum Thema "Nitrate particulaire"
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Peake, Eric. Nitric acid, peroxyacetyl nitrate (PAN), and particulate nitrate in the atmosphere of the City of Edmonton. Research Management Division, Alberta Environment, 1985.
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Peake, Eric. Nitric acid, peroxyacetyl nitrate (PAN), and particulate nitrate in the atmosphere of the City of Edmonton. Research Management Division, Alberta Environment, 1985.
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Liles, K. J. Mechanical and physical properties of particulate composites in the system titanium nitride-alumina-aluminum nitride. Dept. of the Interior, 1989.
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Liles, K. J. Mechanical and physical properties of particulate composites in the system titanium nitride-alumina-aluminum nitride. U.S. Dept. of the Interior, Bureau of Mines, 1989.
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Bliznakovska, Blagica. Analysis methods and techniques for hard thin layer-coatings characterization: In particular on titanium nitride. Forschungszentrum Jülich, 1993.
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Harrison, Mark. Cardiovascular system. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780198765875.003.0039.
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This chapter describes the pharmacology of the cardiovascular system as it applies to Emergency Medicine, and in particular the Primary FRCEM examination. The chapter outlines the key details of cardiac glycosides, diuretics, antiarrhythmics, beta-adrenoceptor blockers, hypertension and heart failure, nitrates and antianginal drugs, sympathomimetics, anticholinergics, anticoagulants, antiplatelet drugs, fibrinolytics, and lipid-regulating drugs. This chapter is laid out exactly following the RCEM syllabus, to allow easy reference and consolidation of learning.
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Rosenman, Kenneth D. Cardiovascular Disorders. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780190662677.003.0029.
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This chapter describes cardiovascular disorders related to occupational and environmental exposures. Sections of the chapter address cardiovascular disease due to carbon monoxide, nitrates, particulate air pollution, and psychosocial factors. The chapter also addresses shift work and sedentary work. A section describes arrhythmias due to various specific chemical exposures. Another section describes hypertension related to lead, excessive noise, and other factors. Finally, a section addresses peripheral vascular disease and Raynaud disease. Cardiovascular disorders are very common and recognition of how occupational and environmental exposures contribute to the occurrence and exacerbation of cardiovascular disorders is important in their prevention, diagnosis, and management.
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Randall, Michael S. Processing, characterization and modelling of borosilicate glass matrix-particulate silicon nitride composites, containing controlled additions of porosity, for use in high speed electronic packaging. 1993.
Den vollen Inhalt der Quelle findenBuchteile zum Thema "Nitrate particulaire"
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Andrievski, R. A. "Particulate Nanostructured Silicon Nitride and Titanium Nitride." In ACS Symposium Series. American Chemical Society, 1996. http://dx.doi.org/10.1021/bk-1996-0622.ch020.
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Kim, N. K., Y. P. Kim, and C. H. Kang. "Major Factors Affecting the Ambient Particulate Nitrate Level at Gosan, Korea." In Nucleation and Atmospheric Aerosols. Springer Netherlands, 2007. http://dx.doi.org/10.1007/978-1-4020-6475-3_124.
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Bosch-Roig, Pilar, and Patricia Sanmartín. "Bioremoval of Graffiti in the Context of Current Biocleaning Research." In Microorganisms in the Deterioration and Preservation of Cultural Heritage. Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-69411-1_8.
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AbstractSome microorganisms can be used as bioremediation agents, in biocleaning treatments, to remove undesired sulphates, nitrates and organic matter from cultural heritage surfaces. Graffiti materials (mainly spray paints) are now included in the list of materials that can be biocleaned, with studies on this topic being initiated just over 5 years ago. Research on the bioremoval of graffiti is continuing and on a promising track. This chapter reports a critical analysis of studies of the bioremoval of graffiti carried out in recent years, which are compared with similar studies of the removal of salts (mainly nitrates and sulphates) and organic matter conducted in the last thirty years. Likewise, the present challenges and ways of overcoming them are addressed towards developing a complete protocol for the use of bioremediation to remove graffiti, with particular emphasis on the use of the method for cleaning facades and buildings.
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Rajkumar, K., and M. Selvaraj. "Study of Hexagonal Boron Nitride Particulate as Vibration Behaviour Modifier of Alternate Stacked Glass–Natural Fibre Polymer Composite Laminate." In Lecture Notes in Mechanical Engineering. Springer Singapore, 2020. http://dx.doi.org/10.1007/978-981-15-4745-4_40.
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Cecinato, A., E. Brancaleoni, C. Di Palo, R. Draisci, and P. Ciccioli. "Detection of Nitrated and Oxygenated Polyaromatic Hydrocarbons (PAH) in Suspended Particulate Matter Sampled in Urban Areas and their Relation with Anthropogenic Emission and Photochemical Smog Formation." In Physico-Chemical Behaviour of Atmospheric Pollutants. Springer Netherlands, 1987. http://dx.doi.org/10.1007/978-94-009-3841-0_7.
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Lodge, James P. "Determination of Nitrate in Atmospheric Particulate Matter (Brucine Method)." In Methods of Air Sampling and Analysis. Routledge, 2017. http://dx.doi.org/10.1201/9780203747407-68.
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Troczynski, T. B., D. Ghosh, and S. Das Gupta. "Mechanical properties of silicon nitride particulate composites." In Processing of Ceramic and Metal Matrix Composites. Elsevier, 1989. http://dx.doi.org/10.1016/b978-0-08-037298-3.50039-6.
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Davenport, A. "Clinical investigation of renal disease." In Oxford Textbook of Medicine. Oxford University Press, 2010. http://dx.doi.org/10.1093/med/9780199204854.003.2104_update_006.
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An accurate history and careful examination will determine the sequence and spectrum of clinical investigations required to make a diagnosis or decide on prognosis or treatment. Midstream urine (MSU) sample—this standard investigation requires consideration of: (1) macroscopic appearance—this may be suggestive of a diagnosis, e.g. frothy urine suggests heavy proteinuria; (2) stick testing—including for pH (<5.3 in an early-morning specimen makes a renal acidification defect unlikely), glycosuria, specific gravity (should be >1.024 in an early-morning or concentrated sample), nitrite (>90% of common urinary pathogens produce nitrite) and leucocyte esterase; and (3) microscopy—for cellular elements (in particular red cells, with the presence of dysmorphic red cells detected by experienced observers indicative of glomerular bleeding), casts (cellular casts indicate renal inflammation), and crystals....
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Lelieveld, Jos. "Air Pollution and Climate." In The Physical Geography of the Mediterranean. Oxford University Press, 2009. http://dx.doi.org/10.1093/oso/9780199268030.003.0038.
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It has long been known that atmospheric pollutants can be hazardous to human health and ecosystems. This includes effects from episodic peak levels as well as the long-term exposure to relatively moderate concentration enhancements. Environmental issues related to air pollution include acidification, mostly by the strong acids from sulphur and nitrogen oxides, eutrophication by the deposition of reactive nitrogen compounds, the reduction of air quality by photo-oxidants and particulate matter, and the radiative forcing of climate by increasing greenhouse gases and by aerosol particles. Many air pollutants are photochemically formed within the atmosphere from emissions by traffic, energy generation, industry, the burning of wastes, and forest fires. The Mediterranean basin in summer is largely cloudfree, and the relatively intense solar radiation promotes the photochemical formation of ozone (O3) and peroxyacetyl nitrate (PAN); O3 being health hazardous at levels in excess of about 100 μg/m3. Ozone is formed in the lower atmosphere as a by-product in the oxidation of reactive carbon compounds such as carbon monoxide (CO) and non-methane volatile organic compounds (NMVOC), catalysed by nitrogen oxides (NOx ≡ NO + NO2). In summer, notably the period from June to August, transport pathways of air pollution near the earth’s surface are typically dominated by northerly winds, carrying photo-oxidants and aerosol particles from Europe into the Mediterranean basin. Aerosol particles with a diameter of less than ∼10 μm (PM10) can have adverse health effects at a concentration of about 30 μg/m3 or higher. The fine mode particles (<2 μm diameter) are mostly composed of sulphates, nitrates, and particulate organic matter, whereas the coarse mode particles (≥2 μm) often contain substantial amounts of sea salt, Saharan dust (Chapter 14), and other mineral components. The aerosols can form widespread hazes that scatter and absorb solar radiation, thus reducing downward energy transfer and surface heating. Increased aerosol scattering causes a negative radiative forcing of climate (cooling tendency), to be weighted against the positive radiative forcing (warming tendency) by increasing greenhouse gases such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), halocarbons, and tropospheric ozone (IPCC 2001).
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Lanza, Gaetano Antonio, and Antonio De Vita. "Chronic stable angina." In The ESC Handbook on Cardiovascular Pharmacotherapy, edited by Alexander Niessner, Sven Wassmann, and Udo Sechtem. Oxford University Press, 2019. http://dx.doi.org/10.1093/med/9780198759935.003.0006.
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Treatment of patients with chronic stable angina has two main objectives: to improve clinical outcome and to reduce angina symptoms. Prognosis is mainly improved by a reduction in cardiovascular risk factor burden, which may be achieved by appropriate lifestyle changes and, for some risk factors (e.g. hypercholesterolaemia, hypertension, diabetes), appropriate pharmacological therapy (including, in particular, statins and renin–angiotensin–aldosterone system inhibitors) and use of antithrombotic agents. Symptoms can be improved by a variable combination of traditional (beta-blockers, calcium channel blockers, nitrates) and novel (e.g. ivabradine, ranolazine) anti-ischaemic drugs, which may act through reduction in myocardial oxygen consumption and/or improvement of myocardial perfusion.
Konferenzberichte zum Thema "Nitrate particulaire"
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Bradshaw, Robert W., Joseph G. Cordaro, and Nathan P. Siegel. "Molten Nitrate Salt Development for Thermal Energy Storage in Parabolic Trough Solar Power Systems." In ASME 2009 3rd International Conference on Energy Sustainability collocated with the Heat Transfer and InterPACK09 Conferences. ASMEDC, 2009. http://dx.doi.org/10.1115/es2009-90140.
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Multi-component molten salts have been formulated recently that may enhance thermal energy storage for parabolic trough solar power plants. This paper presents further developments regarding molten salt mixtures consisting of common alkali nitrates and either alkaline earth nitrates or alkali nitrite salts that have advantageous properties for applications as heat transfer fluids in parabolic trough systems. We report results for formulations of inorganic molten salt mixtures that display freeze-onset temperatures below 100°C. In addition to phasechange behavior, several properties of these molten salts that significantly affect their suitability as thermal energy storage fluids were evaluated, including chemical stability and viscosity. The nitrate-based molten salts have demonstrated chemical stability in the presence of air up to 500°C. The capability to operate at temperatures up to 500°C may allow an increase in maximum temperature operating capability vs. organic fluids in existing trough systems and will enable increased power cycle efficiency. Experimental measurements of viscosity were performed from near the freeze-onset temperature to about 200°C. Viscosities can exceed 100 cP near the freezing temperature but are 4 to 5 cP in the anticipated operating temperature range. Experimental measurements of density, thermal conductivity and heat capacity are in progress and will be reported at the meeting. Corrosion tests were conducted for several thousand hours at 500°C with stainless steels and at 350°C for carbon and chromium-molybdenum steels. Examination of the specimens demonstrated good compatibility of these materials with the molten nitrate salt mixtures. Laboratory studies were conducted to identify mixtures of nitrate and nitrite (NO2−) salts as additional candidates for a low-melting heat transfer fluid. Mixtures in which the cations were potassium, sodium and lithium, in various proportions, demonstrated freezing points as low as 70°C for a particular nitrate/nitrite anion composition. Development has emphasized mixtures that minimize lithium content in order to reduce the cost as the lithium salt is the most expensive constituent. Work is in progress to explore the phase diagram of the 1:1 mol ratio of nitrate/nitrite and to evaluate physical properties such as viscosity, density and thermal conductivity. Results to date indicate that the viscosity of these mixtures is considerably less than nitrate-only melts, which necessarily contain calcium cations to suppress freezing to similarly low temperatures.
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Takao, Yasumasa, Tsuyoshi Asai, Yasuhiro Shimada, Kiyotaka Shuzenji, and Takeshi Tachibana. "Development of Particulate Unit Operations and Morphology Property Relations of Particulate Products." In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-41195.
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Some particulate unit operations (apparatus engineering) are developed to control the particle morphology. The innovative aspect of this operation is the correspondence between the necessary material properties and their apparatus optimization. Spherical powders of aluminum oxynitride and aluminum nitride are directly prepared by flame synthesis (in spite of the fact that oxygen serves as an indispensable reactant). Non-oxide powders are commonly non-spherical with a size below the submicrometer scale. The major limiting factors in their synthesis are free energy, reaction temperature, and reaction rate. The innovative aspect of this flame synthesis technology assisted by DC arc plasma concerns the reducing gas composition beyond 1500 K. A chemical equilibrium calculation indicates that the plasma heating compensates the lack of reaction temperature under a low oxygen condition. This burner realizes a high-speed reaction with the help of reactive species in the arcs. We also report the multilayer-coated cosmetic powders with regard to material application, and the powder bed shear force evaluation equipment with regard to apparatus optimization.
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Nakamura, Mayuko, Atsuto Ohashi, Yoichi Niki, Akiko Masuda, and Chiori Takahashi. "Effects of Injection Pressure on Emission and Components of Particulate Matter From Marine Diesel Engine." In ASME 2018 Internal Combustion Engine Division Fall Technical Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/icef2018-9644.
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Reduction of particulate matter (PM) is important issues even for shipping industry since PM harms the environment and human health. In order to reduce PM from marine diesel engines, we focused on components forming PM, elemental carbon (EC), organic carbon (OC), sulfate, and “others” (nitrate, bound water associated with sulfate, metal, ash and hydrogen associated with OC), and investigated the reduction effect of each component by changing fuel injection pressure of a four-stroke marine diesel engine at the two engine load points of 25% and 50%. At 50% load, the PM emissions decreased with increasing the fuel injection pressure, the reduction in the PM emissions which reflected the decrease in EC. At 25% load, the PM emissions did not decrease simply with the injection pressure since OC, sulfate, “others” components in addition to EC contributed to the injection pressure dependence of PM. The results suggest that behaviors of each component of PM should be grasped to achieve the appropriate reduction method of PM.
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Lukachko, Stephen P., Ian A. Waitz, Richard C. Miake-Lye, and Robert C. Brown. "Engine Design and Operational Impacts on Particulate Matter Precursor Emissions." In ASME Turbo Expo 2005: Power for Land, Sea, and Air. ASMEDC, 2005. http://dx.doi.org/10.1115/gt2005-69112.
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Aircraft emissions of trace sulfur and nitrogen oxides contribute to the generation of fine volatile particulate matter (PM). Resultant changes to ambient PM concentrations and radiative properties of the atmosphere may be important sources of aviation-related environmental impacts. This paper addresses engine design and operational impacts on aerosol precursor emissions of SOx and NOy species. Volatile PM formed from these species in the environment surrounding an aircraft is dependent on intra-engine oxidation processes occurring both within and downstream of the combustor. This study examines the complex response of trace chemistry to the temporal and spatial evolution of temperature and pressure along this entire intra-engine path, after combustion through the aft combustor, turbine, and exhaust nozzle. Low-order and higher fidelity tools are applied to model the interaction of chemical and fluid mechanical processes, identify important parameters, and assess uncertainties. The analysis suggests intra-engine processing is inefficient. For engine types in-service in the large commercial aviation fleet, mean conversion efficiency (ε) is estimated to be 2.8% to 6.5% for sulfate precursors and 0.3% to 5.7% for nitrate precursors at the engine exit plane. These ranges reflect technological differences within the fleet, the variation in oxidative activity with operating mode, and modeling uncertainty stemming from variance in rate parameters and initial conditions. Assuming sulfur-derived volatile PM is most likely, these results suggest emission indices of 0.06–0.13 g/kg-fuel assuming particles nucleated as 2H2SO4·H2O for a fuel sulfur content of 500 ppm.
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Tekale, S. U., A. B. Tekale, N. S. Kanhe, et al. "Nano-particulate Aluminium Nitride∕Al: An Efficient and Versatile Heterogeneous Catalyst for the Synthesis of Biginelli Scaffolds." In INTERNATIONAL CONFERENCE ON ADVANCES IN CONDENSED AND NANO MATERIALS (ICACNM-2011). AIP, 2011. http://dx.doi.org/10.1063/1.3653716.
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Cai, F., Xiao Huang, Q. Yang, and Doug Nagy. "Tribological Behaviours of Titanium Nitride and Chromium Nitride Based PVD Coating Systems." In ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/gt2012-68107.
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This study investigates the effects of the deposition process and coating composition on microstructural and tribological properties of TiN and CrN based coating systems. Coatings were produced using various PVD based processes — electron beam (EB), cathodic arc (CA) and plasma enhanced magnetron sputtering (PEMS). All coated samples were evaluated for their composition, microstructure and surface morphology. Coating mechanical properties such as hardness, Young’s modulus and coefficient of friction were also studied and related to their microstructures, wear and erosion resistances. It was found that hardness (H), Young’s modulus (E) and coefficient of friction had impact on both wear and erosion rates. In particular, the H3/E2 ratio was inversely proportional to the specific wear rate. For erosion behaviour, higher H3/E2 ratios relate to lower erosion rates at low impingement angles; whereas higher H3/E2 ratios relate to higher erosion rates at high impingement angles.
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Boren, Richard M., Charles F. Hammel, and Mark R. Bleckinger. "Multi-Pollution Removal System Using Oxides of Manganese." In ASME 2004 Power Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/power2004-52081.
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Pending legislation suggests there will be a need for increased removal of NOx, SO2, Hg (Mercury) and PM 2.5 from coal-fired power plants. Current commercial technologies only handle one of these pollutants so several different technologies must be combined to remove all of these pollutants. The Pahlman™ Process developed by Enviroscrub Technologies removes NOx, SO2 and Hg in one step. The Pahlman™ Process is a sorbent-based technology, which utilizes a proprietary Oxides of Manganese compound to remove SO2, NOx and Hg. The sorbent is spray-dried into the exhaust duct downstream of the current particulate control device. Spray drying is used to control the particle size (40 micron mean) and increases the surface area of the particle (∼300 m2 /gram). The sorbent is collected in a fabric filter baghouse, which serves two purposes: (1) it captures the entrained sorbent and (2) provides additional residence time for gas-solid contact between the sorbent and the target pollutants. The loaded sorbent is removed from the baghouse and routed to regeneration. Sorbent regeneration occurs in an aqueous solution under temperature and pressure while the solution is maintained in the proper pH and Eh ranges. The reacted manganese is oxidized back to its starting state and sulfate and nitrate byproduct compounds are produced. The insoluble oxides of manganese are then filtered out of the solution and returned to the spray-dryer for re-use. The soluble sulfate and nitrate compounds are separated and the nitrate by-products are sold as fertilizer. The sulfates are further processed and re-used in the regeneration process with excess sulfate by-products sold as fertilizer or used to produce sulfuric acid. Testing over the last three years has resulted in consistent SO2 removal of over 99% and NOx removal of greater than 95%. Testing performed in June 2003 at DTE Energy’s River Rouge Power Station Unit#3 in Detroit, Michigan showed removal rates of >99% for SO2, >98% for NOx and 97% for oxidized Mercury (Hg2+). Mercury testing was performed by the Energy and Environmental Research Center (EERC) and paid for by DTE Energy and the DOE. Testing performed in December 2003 through January 2004 at Minnesota Power’s Boswell Energy Center Unit#4 in Cohasset, Minnesota showed removal rates of >98% for SO2, >94% for NOx and 99.2% for elemental (Hg0) and 94% for total Mercury (HgT).
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Al-Thani, Jassem A., Connor Izumi, Oguz Yigiterhan, et al. "Ocean Acidification and Carbonate System Geochemistry in the Arabian Gulf." In Qatar University Annual Research Forum & Exhibition. Qatar University Press, 2020. http://dx.doi.org/10.29117/quarfe.2020.0030.
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Alkalinity (Alk) and (dissolved inorganic carbon) DIC were measured on high resolution seawater samples, collected on November 2018 and May 2019 at seven stations in the Exclusive Economic Zone (EEZ) of Qatar. Calculated surface PCO2 averaged 472 matm in 2018 and 447 matm in 2019. Thus, the Arabian Gulf is degassing CO2 at present and will not take up atmospheric CO2 until 2042. Ocean acidification is not yet an issue in the EEZ of Qatar. The elevated PCO2 values are due to CaCO3 formation. Normalized NAlk and NDIC were calculated to remove the impact of increasing salinity. NAlk and NDIC decrease corresponding to a CaCO3/OrgC removal ratio of 2/1. We calculated the nitrate corrected and salinity normalized tracer, Alk*. Values of Alk* were negative, and the change in Alk* relative to Hormuz (DAlk*) indicated that there has been an average decrease of Alk* of -130 mmol kg-1. This decrease is due to CaCO3 formation but previous studies found no evidence for coccolithophorids. One obvious possibility is that Alk removal is due to CaCO3 formation in coral reefs. However, recent study of the composition of particulate matter found that the average particulate Ca concentration was 3.6%, and was easily acid soluble (Yigiterhan et al., 2018). These results suggest that a significant amount of particulate CaCO3 is present in the water column. One hypothesis is that the particulate Ca comes from carbonate rich atmospheric dust. Using Al as a tracer for dust and the average Ca/Al ratio in Qatari dust can only explain about 3% of the particulate Ca. An alternative hypothesis is that particulate CaCO3 may form in the water column due to abiological CaCO3 formation, as proposed recently for the Red Sea (Wurgaft et al., 2016). Precipitation of CaCO3 may be induced by the large inputs of nucleation sites in the form of atmospheric dust.
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Chinnakurli Suryanarayana, Ramesh, Saleem Khan, Praveennath G. Koppad, and Zulfiqar Khan. "Tribological Behaviour of Hot Extruded Al6061-Si3N4 Composite." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-64459.
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Silicon nitride (Si3N4) possesses excellent hot hardness, wear resistance coupled with good corrosion resistance. Further, it possesses high anti friction properties making it an ideal reinforcement in developing high quality light weight, metal matrix composites for tribological applications. Silicon nitride has been successfully dispersed in aluminum alloy matrices. Their tribological properties with the beneficial effect of silicon nitride in enhancing the wear resistance of metal matrix composite have been reported by several researchers. Most of the researchers have focused on development of silicon nitride reinforced aluminum composite by powder metallurgy and casting route. However, meager information is available as regards the secondary processing of these composites in particular hot extrusion. Several researchers have reported an improved tribological behaviour in composites after extrusion. Hot extrusion of light weight metal matrix composites is very challenging. In the light of the above, this paper discusses the tribological behaviour of hot extruded Al6061 aluminum composites, which were initially developed by stir casting technique. Nickel coated silicon nitride particles were dispersed in Al6061 alloy using stir casting process. The cast composites were extruded at an extrusion ratio of 1:10 adopting a temperature of 550°C. The hot extruded composite (6Wt% Si3N4) and the matrix alloy were subjected to metallographic studies, microhardness and friction and wear tests using a pin on disc machine. Friction and wear test were carried out at loads ranging from 10 to 60 N at a sliding velocity of 0.314m/s. The worn surfaces and wear debris analysis have been carried out to understand the mechanism of wear in the developed hot extruded composites. The developed hot extruded composites exhibited lower coefficient of friction and wear rates when compared with matrix alloy.
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Taha, Jaime, T. N. Narayanan, P. M. Ajayan, Jose E. Contreras, and Josue Rodriguez. "Enhanced Dielectric Performance of Nano Boron Nitride Impregnated Cellulosic Insulations." In ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-50114.
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The application of nanodielectric materials in high voltage power transmission systems has received particular attention. This investigation shows a comparison of the AC dielectric behavior of insulating paper impregnated with conventional mineral oil and dielectric nanofluids. The AC breakdown voltages of various systems were measured according to ASTM D149 to determine the effect of using nanofluids as dielectric media. The observed results indicate that addition of insulating nanoparticles to conventional transformer oil exhibits substantially higher AC breakdown voltage than that of pure mineral oil impregnated paper.