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D C B Whittet - One of the best experts on this subject based on the ideXlab platform.
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Oxygen depletion in the interstellar medium implications for grain models and the distribution of Elemental Oxygen
The Astrophysical Journal, 2010Co-Authors: D C B WhittetAbstract:This paper assesses the implications of a recent discovery that atomic Oxygen is being depleted from diffuse interstellar gas at a rate that cannot be accounted for by its presence in silicate and metallic oxide particles. To place this discovery in context, the uptake of Elemental O into dust is considered over a wide range of environments, from the tenuous intercloud gas and diffuse clouds sampled by the depletion observations to dense clouds where ice mantles and gaseous CO become important reservoirs of O. The distribution of O in these contrasting regions is quantified in terms of a common parameter, the mean number density of hydrogen n H. At the interface between diffuse and dense phases (just before the onset of ice-mantle growth) as much as ~160 ppm of the O abundance is unaccounted for. If this reservoir of depleted Oxygen persists to higher densities it has implications for the Oxygen budget in molecular clouds, where a shortfall of the same order is observed. Of various potential carriers, the most plausible appears to be a form of O-bearing carbonaceous matter similar to the organics found in cometary particles returned by the Stardust mission. The organic refractory model for interstellar dust is re-examined in the light of these findings, and it is concluded that further observations and laboratory work are needed to determine whether this class of material is present in quantities sufficient to account for a significant fraction of the unidentified depleted Oxygen.
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Oxygen depletion in the interstellar medium implications for grain models and the distribution of Elemental Oxygen
arXiv: Astrophysics of Galaxies, 2009Co-Authors: D C B WhittetAbstract:This paper assesses the implications of a recent discovery (Jenkins 2009) that atomic Oxygen is being depleted from diffuse interstellar gas at a rate that cannot be accounted for by its presence in silicate and metallic oxide particles. To place this discovery in context, the uptake of Elemental O into dust is considered over a wide range of environments, from the tenuous intercloud gas and diffuse clouds sampled by the depletion observations to dense clouds where ice mantles and gaseous CO become important reservoirs of O. The distribution of O in these contrasting regions is quantified in terms of a common parameter, the mean number density of hydrogen. At the interface between diffuse and dense phases (just before the onset of ice mantle growth) as much as 160 ppm of the O abundance is unaccounted for. If this reservoir of depleted Oxygen persists to higher densities it has implications for the Oxygen budget in molecular clouds, where a shortfall of the same order is observed. Of various potential carriers, the most plausible appears to be a form of O-bearing carbonaceous matter similar to the organics found in cometary particles returned by the Stardust mission. The "organic refractory" model for interstellar dust is re-examined in the light of these findings, and it is concluded that further observations and laboratory work are needed to determine whether this class of material is present in quantities sufficient to account for a significant fraction of the unidentified depleted Oxygen.
G J Melnick - One of the best experts on this subject based on the ideXlab platform.
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water o2 and ice in molecular clouds
The Astrophysical Journal, 2009Co-Authors: David J Hollenbach, M J Kaufman, Edwin A Bergin, G J MelnickAbstract:We model the temperature and chemical structure of molecular clouds as a function of depth into the cloud, assuming a cloud of constant density n illuminated by an external far-ultraviolet (FUV; 6 eV
Elemental Oxygen freezes out as water ice and the Elemental C/O abundance ratio can exceed unity, leading to complex carbon chemistry. Gas-phase H2O and O2 peak in abundance at intermediate depth into the cloud, roughly AV ~ 3-8 from the surface, the depth proportional to ln(G 0/n). Closer to the surface, molecules are photodissociated. Deeper into the cloud, molecules freeze to grain surfaces. At intermediate depths, PDRs are attenuated by dust extinction, but photodesorption prevents total freeze-out. For G 0 < 500, abundances of H2O and O2 peak at values ~10–7, producing columns ~1015 cm–2, independent of G 0 and n. The peak abundances depend primarily on the product of the photodesorption yield of water ice and the grain surface area per H nucleus. At higher values of G 0, thermal desorption of O atoms from grains slightly enhances the gas-phase H2O peak abundance and column, whereas the gas-phase O2 peak abundance rises to ~10–5 and the column to ~2 × 1016 cm–2. We present simple analytical equations for the abundances as a function of depth, which clarify the dependence on parameters. The models are applied to observations of H2O, O2, and water ice in a number of sources, including B68, NGC 2024, and ρ Oph. -
water o2 and ice in molecular clouds
arXiv: Astrophysics, 2008Co-Authors: David J Hollenbach, M J Kaufman, Edwin A Bergin, G J MelnickAbstract:We model the temperature and chemical structure of molecular clouds as a function of depth into the cloud, assuming a cloud of constant density n illuminated by an external FUV (6 eV < E < 13.6 eV) flux G_0 (scaling factor in multiples of the local interstellar field). Extending previous photodissociation region models, we include the freezing of species, simple grain surface chemistry, and desorption (including FUV photodesorption) of ices. We also treat the opaque cloud interior with time-dependent chemistry. Here, under certain conditions, gas phase Elemental Oxygen freezes out as water ice and the Elemental C/O abundance ratio can exceed unity, leading to complex carbon chemistry. Gas phase H2O and O2 peak in abundance at intermediate depth into the cloud, roughly A_V~3-8 from the surface, the depth proportional to ln(G_0/n). Closer to the surface, molecules are photodissociated. Deeper into the cloud, molecules freeze to grain surfaces. At intermediate depths photodissociation rates are attenuated by dust extinction, but photodesorption prevents total freezeout. For G_0 < 500, abundances of H2O and O2 peak at values ~10^(-7), producing columns ~10^(15) per cm^2, independent of G_0 and n. The peak abundances depend primarily on the product of the photodesorption yield of water ice and the grain surface area per H nucleus. At higher values of G_0, thermal desorption of O atoms from grains enhances the gas phase H2O peak abundance and column slightly, whereas the gas phase O2 peak abundance rises to ~10^(-5) and the column to ~2x10^(16) per cm^2. We present simple analytic equations for the abundances as a function of depth which clarify the dependence on parameters. The models are applied to observations of H2O, O2, and water ice in a number of sources, including B68, NGC 2024, and Rho Oph.
Rongji Li - One of the best experts on this subject based on the ideXlab platform.
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engine performance and emission characteristics of marine fish oil biodiesel produced from the discarded parts of marine fish
Fuel Processing Technology, 2009Co-Authors: Rongji LiAbstract:Biodiesel is recognized as a clean alternative fuel or as a fuel additive to reduce pollutant emissions from combustion equipment. Because cultivated land is too limited to grow seed-oil plants sufficient to produce both food and biodiesel, non-land-based oleaginous materials have been considered important sources for the production of the latter. In this study, the discarded parts of mixed marine fish species were used as the raw material to produce biodiesel. Marine fish oil was extracted from the discarded parts of mixed marine fish and refined through a series of pretreatment processes. The refined marine fish oil was then transesterified with methyl alcohol to produce biodiesel, which was used thereafter as engine fuel to investigate its engine performance and emission characteristics. The experimental results show that, compared with commercial biodiesel from waste cooking oil, marine fish-oil biodiesel has a larger gross heating value, Elemental carbon and hydrogen content, cetane index, exhaust gas temperature, brake fuel conversion efficiency, NOx and O2 emissions, and black smoke opacity and a lower Elemental Oxygen content, fuel consumption rate, brake-specific fuel consumption rate, equivalence ratio, and CO emission. Compared with ASTM No. 2D diesel, both marine fish-oil and waste cooking-oil biodiesels appear to have a lower gross heating value, cetane index, exhaust gas temperature, equivalence ratio, black smoke opacity, Elemental carbon content, and CO emission and a higher fuel consumption rate and Elemental Oxygen content.
Cascarosa E. - One of the best experts on this subject based on the ideXlab platform.
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A statistical analysis of the auto thermal fast pyrolysis of elephant grass in fluidized bed reactor based on produced charcoal
Reino Unido, 2020Co-Authors: Mesa-perez J.m., Cortez L.a.b., Marin-mesa H.r., Pelaez-samaniego M.r., Rocha J.d., Cascarosa E.Abstract:This research presents and discusses the results of product yields, higher heating value, proximate and ultimate analyses of the charcoal obtained in the Fast Pyrolysis Plant – PPR-200. It is a fast pyrolysis plant with a biomass feed capacity of 200 kg per hour, owned by Unicamp. Elephant grass with an average particle diameter of 2 mm and 12% of moisture was used as raw material. The PPR-200 facility operated under different conditions. Air was used as fluidization agent. This study tries to increase the knowledge of the PPR-200 plant operation in fast pyrolysis regimen. Experimental tests were carried out considering two independent factors: fluidization air and stoichiometric air ratio and the height of the fixed bed. In the pyrolysis process, a charcoal with a high carbon content is obtained as well as the release of Oxygen from the biomass. Experimental results showed that the favorable operating conditions for Oxygen release from elephant grass and carbon concentration in the charcoal are a fixed fluidized bed of 207 mm height and 8% of supplied air to the stoichiometric air ratio. Under these optimized conditions, the fluidized bed temperature resulted to be 650 °C on average and the yield production of charcoal in relation to the biomass fed (dry and ash free, d.a.f.) was of 14 wt.%. The charcoal produced under such conditions presented 92.4% of Elemental carbon, and 2.85% of Elemental Oxygen.651-2322329CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPSem informaçãoSem informaçã
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A Statistical Analysis Of The Auto Thermal Fast Pyrolysis Of Elephant Grass In Fluidized Bed Reactor Based On Produced Charcoal
2015Co-Authors: Mesa-perez J.m., Cortez L.a.b., Marin-mesa H.r., Pelaez-samaniego M.r., Rocha J.d., Cascarosa E.Abstract:This research presents and discusses the results of product yields, higher heating value, proximate and ultimate analyses of the charcoal obtained in the Fast Pyrolysis Plant - PPR-200. It is a fast pyrolysis plant with a biomass feed capacity of 200 kg per hour, owned by Unicamp. Elephant grass with an average particle diameter of 2 mm and 12% of moisture was used as raw material. The PPR-200 facility operated under different conditions. Air was used as fluidization agent. This study tries to increase the knowledge of the PPR-200 plant operation in fast pyrolysis regimen. Experimental tests were carried out considering two independent factors: fluidization air and stoichiometric air ratio and the height of the fixed bed. In the pyrolysis process, a charcoal with a high carbon content is obtained as well as the release of Oxygen from the biomass. Experimental results showed that the favorable operating conditions for Oxygen release from elephant grass and carbon concentration in the charcoal are a fixed fluidized bed of 207 mm height and 8% of supplied air to the stoichiometric air ratio. Under these optimized conditions, the fluidized bed temperature resulted to be 650 C on average and the yield production of charcoal in relation to the biomass fed (dry and ash free, d.a.f.) was of 14 wt.%. The charcoal produced under such conditions presented 92.4% of Elemental carbon, and 2.85% of Elemental Oxygen. © 2014 Elsevier Ltd. All rights reserved.6501/02/15322329Bridgwater, A.V., (2002) Fast Pyrolysis of Biomass: A Handbook. [S.l.], 2. , Aston University, Bio-energy Research Group UKMesa-Pérez, J.M., (2004) Experiments in A Biomass Fast Pyrolysis Plant Using Fluidized Bed: Criteria for Its Optimization, , (PhD thesis) Faculty of Agriculture, Universidade Estadual de Campinas, UNICAMP (in Portuguese)Mesa-Pérez, J.M., Cortez, L.A.B., Rocha, J.D., Olivares-Gomez, E., Characteristics of fine char from elephant grass fast pyrolysis in fluidized bed in different operation conditions (2004) Proceedings of the 5th Energy in Rural Area Meeting, , AGRENER Campinas, SP, Brazil (in Portuguese)Mesa-Perez, J.M., Cortez, L.A.B., Rocha, J.D., Brossard-Perez, L.E., Olivares-Gomez, E., Unidimensional heat transfer analysis of elephant grass and sugar cane bagasse slow pyrolysis in a fixed bed reactor (2005) Fuel Processing Technology, 86 (5), pp. 565-575. , DOI 10.1016/j.fuproc.2004.05.014, PII S0378382004001262Bonelli, P.R., Della Roca, P.A., Cerrella, G.E., Cukierman, A.L., (2008) Comparative Study on Char Properties and Pyrolysis Kinetics of Different Lignocellulosic Wastes, , 10.1002/9780470694954.ch90Guerrero, M., Ruiz, M.P., Alzueta, M.U., Bilbao, R., Millera, A., Pyrolysis of eucalyptus at different heating rates: Studies of char characterization and oxidative reactivity (2005) J. Anal. Appl. Pyrolysis, 74, pp. 307-314Minkova, V., Marinov, S.P., Zanzi, R., Bjornbom, E., Budinova, T., Stefanova, M., Lakov, L., Thermochemical treatment of biomass in a flow of steam or in a mixture of steam and carbon dioxide (2000) Fuel processing technology, 62 (1), pp. 45-52. , DOI 10.1016/S0378-3820(99)00065-XAntonelli, L., Improvement of pyrolytic products bio-oil and bio-carbon/emulsion and slurries (1989) Energy from Biomass - 4, Proceedings of the Third E.C. Contractors Meeting, pp. 531-535. , G. Grassi, D. Pirrwitz, H. Zibetta, Elsevier Applied Science LondonGarca-Perez, M., Chaala, A., Roy, C., Co-pyrolysis of sugarcane bagasse with petroleum residue. Part II. Product yields and properties (2002) Fuel, 81 (7), pp. 893-907. , DOI 10.1016/S0016-2361(01)00215-0, PII S0016236101002150Zabaniotou, A.A., Karabelas, A.J., The Evritania (Greece) demonstration plant of biomass pyrolysis (1999) Biomass and Bioenergy, 16 (6), pp. 431-445. , DOI 10.1016/S0961-9534(99)00004-5, PII S0961953499000045Barros, N.B., Scarminio, I.S., Bruns, R.E., (2001) How to Make Experiments: Research and Development in Science and Industry, , second ed. Editora da Unicamp Campinas (in Portuguese)Mesa-Pérez, J.M., Brossard, L.E., Guerreiro, J.R., Henry, E., Estrategia de utilización del Diseño de Experimentos (1998) Tecnol. Quím., 18 (2)Brossard, L.E., Cortez, L.A.B., Mesa-Pérez, J.M., The strategy of empirical research and optimization process (2001) Pesqui. Operacional, 21 (1), pp. 89-105Teplitskiy, Y.S., Similarity of transport processes in fluidized beds (1999) International Journal of Heat and Mass Transfer, 42 (20), pp. 3887-3899. , DOI 10.1016/S0017-9310(99)00044-7, PII S0017931099000447Zanzi, R., Sjostrom, K., Bjornbom, E., Rapid pyrolysis of agricultural residues at high temperature (2002) Biomass and Bioenergy, 23 (5), pp. 357-366. , DOI 10.1016/S0961-9534(02)00061-2, PII S0961953402000612Mohammad, N.I., Ramlan, Z., Farid, N.A., Pyrolytic oil from fluidised bed pyrolysis of oil palm shell and its characterization (1999) Renew. Energy, 17, pp. 73-7
M J Kaufman - One of the best experts on this subject based on the ideXlab platform.
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water o2 and ice in molecular clouds
The Astrophysical Journal, 2009Co-Authors: David J Hollenbach, M J Kaufman, Edwin A Bergin, G J MelnickAbstract:We model the temperature and chemical structure of molecular clouds as a function of depth into the cloud, assuming a cloud of constant density n illuminated by an external far-ultraviolet (FUV; 6 eV
Elemental Oxygen freezes out as water ice and the Elemental C/O abundance ratio can exceed unity, leading to complex carbon chemistry. Gas-phase H2O and O2 peak in abundance at intermediate depth into the cloud, roughly AV ~ 3-8 from the surface, the depth proportional to ln(G 0/n). Closer to the surface, molecules are photodissociated. Deeper into the cloud, molecules freeze to grain surfaces. At intermediate depths, PDRs are attenuated by dust extinction, but photodesorption prevents total freeze-out. For G 0 < 500, abundances of H2O and O2 peak at values ~10–7, producing columns ~1015 cm–2, independent of G 0 and n. The peak abundances depend primarily on the product of the photodesorption yield of water ice and the grain surface area per H nucleus. At higher values of G 0, thermal desorption of O atoms from grains slightly enhances the gas-phase H2O peak abundance and column, whereas the gas-phase O2 peak abundance rises to ~10–5 and the column to ~2 × 1016 cm–2. We present simple analytical equations for the abundances as a function of depth, which clarify the dependence on parameters. The models are applied to observations of H2O, O2, and water ice in a number of sources, including B68, NGC 2024, and ρ Oph. -
water o2 and ice in molecular clouds
arXiv: Astrophysics, 2008Co-Authors: David J Hollenbach, M J Kaufman, Edwin A Bergin, G J MelnickAbstract:We model the temperature and chemical structure of molecular clouds as a function of depth into the cloud, assuming a cloud of constant density n illuminated by an external FUV (6 eV < E < 13.6 eV) flux G_0 (scaling factor in multiples of the local interstellar field). Extending previous photodissociation region models, we include the freezing of species, simple grain surface chemistry, and desorption (including FUV photodesorption) of ices. We also treat the opaque cloud interior with time-dependent chemistry. Here, under certain conditions, gas phase Elemental Oxygen freezes out as water ice and the Elemental C/O abundance ratio can exceed unity, leading to complex carbon chemistry. Gas phase H2O and O2 peak in abundance at intermediate depth into the cloud, roughly A_V~3-8 from the surface, the depth proportional to ln(G_0/n). Closer to the surface, molecules are photodissociated. Deeper into the cloud, molecules freeze to grain surfaces. At intermediate depths photodissociation rates are attenuated by dust extinction, but photodesorption prevents total freezeout. For G_0 < 500, abundances of H2O and O2 peak at values ~10^(-7), producing columns ~10^(15) per cm^2, independent of G_0 and n. The peak abundances depend primarily on the product of the photodesorption yield of water ice and the grain surface area per H nucleus. At higher values of G_0, thermal desorption of O atoms from grains enhances the gas phase H2O peak abundance and column slightly, whereas the gas phase O2 peak abundance rises to ~10^(-5) and the column to ~2x10^(16) per cm^2. We present simple analytic equations for the abundances as a function of depth which clarify the dependence on parameters. The models are applied to observations of H2O, O2, and water ice in a number of sources, including B68, NGC 2024, and Rho Oph.