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  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 34 (1988), S. 209-222 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A model is presented for convection and chemical reacton in porous media. An irreversible chemical reaction of arbitrary order is considered. Reactant depletion allows for basic solutions in either the kinetic or the diffusion regime. The cases of forced flow parallel to the lateral walls of the cavity and a closed system are addressed. A linear stability analysis of the basic states is performed and critical values of the thermal Rayleigh number for the onset of natural convection are determined. A dispersion relation is derived and a graphical representation of the linear stability analysis results is provided for typical values of the system parameters. Analytical predictions are verified by results obtained by numerical integration of the complete set of nonlinear partial differential equations. The effect of natural convection is discussed when the basic state is either in the kinetic or in the diffusion regime. For large gradients, associated with the diffusion regime, chemical reaction can drive free convection even for low values of the Rayleigh number. In forced flow systems, natural convection can change substantially the flow pattern of the system.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 287-292 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Multitubular reactors of the heat exchanger type are commonly used to carry out highly exothermic reactions. Two of the main goals, when designing this type of reactor, are to guarantee a safe operation and to minimize the reactor length. Therefore, these concepts are used here as criteria for comparing the performance of the three most common cooling-medium flow arrangements. The analysis of the parametric sensitivity behavior, as well as that of some related measures, indicates that, at least from the steady-state standpoint, the cocurrent arrangement should be considered the most attractive alternative.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 33 (1987), S. 819-833 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A general analysis of the reaction wave propagation in nonlinear exothermic nonadiabatic diffusion-convection-reaction systems is presented. The following topics are considered: approximation of temperature profiles based on the idea of infinitesimaly thin reaction front, estimation of maximum temperature, estimation of the conversion at the hot spot, a priori calculation of the front velocity, analysis of the self-ignition phenomena and their relation to wave propagation, and discussion of the effect of the heat loss parameter on the direction of propagation and shape of traveling waves. A comparison of the analytical work with exact numerical results reveals excellent agreement. The main objective of this paper is to provide a definite analysis of reaction wave propagation in reacting flow systems.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 2668-2682 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A bioartificial pancreas, consisting of immobilized islets encapsulated within hollow fibers, is investigated as an alternative treatment for insulin-dependent diabetes. A mathematical model is developed to determine whether this configuration of the bioartificial pancreas can yield an insulin response to a glucose challenge with the appropriate dynamics in diabetic humans. The model consists of the 2-D mass-conservation equations for glucose and insulin within the hollow fiber and capillaries. The equations contain terms for insulin-production kinetics by porcine islets and glucose-consumption kinetics. The boundary conditions account for transport resistances of the fiber membrane, the tissue surrounding the implant, and a thin film within the capillaries. The equations are coupled to a pharmacokinetic model of the circulatory system. The calculations show that an optimized design with this configuration will be feasible for human use and requires a total volume of 4.6 mL to reach the target insulin concentration in the bloodstream following a glucose challenge. The parameters and processes controlling the system performance are discussed.
    Additional Material: 13 Ill.
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  • 5
    Publication Date: 2013-11-01
    Description: The biogeochemical cycles of carbon (C), nitrogen (N) and phosphorus (P) are interlinked by primary production, respiration and decomposition in terrestrial ecosystems. It has been suggested that the C, N and P cycles could become uncoupled under rapid climate change because of the different degrees of control exerted on the supply of these elements by biological and geochemical processes. Climatic controls on biogeochemical cycles are particularly relevant in arid, semi-arid and dry sub-humid ecosystems (drylands) because their biological activity is mainly driven by water availability. The increase in aridity predicted for the twenty-first century in many drylands worldwide may therefore threaten the balance between these cycles, differentially affecting the availability of essential nutrients. Here we evaluate how aridity affects the balance between C, N and P in soils collected from 224 dryland sites from all continents except Antarctica. We find a negative effect of aridity on the concentration of soil organic C and total N, but a positive effect on the concentration of inorganic P. Aridity is negatively related to plant cover, which may favour the dominance of physical processes such as rock weathering, a major source of P to ecosystems, over biological processes that provide more C and N, such as litter decomposition. Our findings suggest that any predicted increase in aridity with climate change will probably reduce the concentrations of N and C in global drylands, but increase that of P. These changes would uncouple the C, N and P cycles in drylands and could negatively affect the provision of key services provided by these ecosystems.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Delgado-Baquerizo, Manuel -- Maestre, Fernando T -- Gallardo, Antonio -- Bowker, Matthew A -- Wallenstein, Matthew D -- Quero, Jose Luis -- Ochoa, Victoria -- Gozalo, Beatriz -- Garcia-Gomez, Miguel -- Soliveres, Santiago -- Garcia-Palacios, Pablo -- Berdugo, Miguel -- Valencia, Enrique -- Escolar, Cristina -- Arredondo, Tulio -- Barraza-Zepeda, Claudia -- Bran, Donaldo -- Carreira, Jose Antonio -- Chaieb, Mohamed -- Conceicao, Abel A -- Derak, Mchich -- Eldridge, David J -- Escudero, Adrian -- Espinosa, Carlos I -- Gaitan, Juan -- Gatica, M Gabriel -- Gomez-Gonzalez, Susana -- Guzman, Elizabeth -- Gutierrez, Julio R -- Florentino, Adriana -- Hepper, Estela -- Hernandez, Rosa M -- Huber-Sannwald, Elisabeth -- Jankju, Mohammad -- Liu, Jushan -- Mau, Rebecca L -- Miriti, Maria -- Monerris, Jorge -- Naseri, Kamal -- Noumi, Zouhaier -- Polo, Vicente -- Prina, Anibal -- Pucheta, Eduardo -- Ramirez, Elizabeth -- Ramirez-Collantes, David A -- Romao, Roberto -- Tighe, Matthew -- Torres, Duilio -- Torres-Diaz, Cristian -- Ungar, Eugene D -- Val, James -- Wamiti, Wanyoike -- Wang, Deli -- Zaady, Eli -- England -- Nature. 2013 Oct 31;502(7473):672-6. doi: 10.1038/nature12670.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] Departamento de Sistemas Fisicos, Quimicos y Naturales, Universidad Pablo de Olavide, Carretera de Utrera, kilometro 1, 41013 Sevilla, Spain [2] Area de Biodiversidad y Conservacion, Departamento de Biologia y Geologia, Escuela Superior de Ciencias Experimentales y Tecnologia, Universidad Rey Juan Carlos, Calle Tulipan Sin Numero, 28933 Mostoles, Spain.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24172979" target="_blank"〉PubMed〈/a〉
    Keywords: Aluminum Silicates/analysis ; Biomass ; Carbon/analysis/metabolism ; Carbon Cycle ; Climate Change ; *Desert Climate ; *Desiccation ; *Ecosystem ; *Geography ; Models, Theoretical ; Nitrogen/analysis/metabolism ; Nitrogen Cycle ; Phosphoric Monoester Hydrolases/analysis/metabolism ; Phosphorus/analysis/metabolism ; Plants/metabolism ; Soil/*chemistry
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 6
    Publication Date: 2012-01-17
    Description: Experiments suggest that biodiversity enhances the ability of ecosystems to maintain multiple functions, such as carbon storage, productivity, and the buildup of nutrient pools (multifunctionality). However, the relationship between biodiversity and multifunctionality has never been assessed globally in natural ecosystems. We report here on a global empirical study relating plant species richness and abiotic factors to multifunctionality in drylands, which collectively cover 41% of Earth's land surface and support over 38% of the human population. Multifunctionality was positively and significantly related to species richness. The best-fitting models accounted for over 55% of the variation in multifunctionality and always included species richness as a predictor variable. Our results suggest that the preservation of plant biodiversity is crucial to buffer negative effects of climate change and desertification in drylands.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3558739/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3558739/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Maestre, Fernando T -- Quero, Jose L -- Gotelli, Nicholas J -- Escudero, Adrian -- Ochoa, Victoria -- Delgado-Baquerizo, Manuel -- Garcia-Gomez, Miguel -- Bowker, Matthew A -- Soliveres, Santiago -- Escolar, Cristina -- Garcia-Palacios, Pablo -- Berdugo, Miguel -- Valencia, Enrique -- Gozalo, Beatriz -- Gallardo, Antonio -- Aguilera, Lorgio -- Arredondo, Tulio -- Blones, Julio -- Boeken, Bertrand -- Bran, Donaldo -- Conceicao, Abel A -- Cabrera, Omar -- Chaieb, Mohamed -- Derak, McHich -- Eldridge, David J -- Espinosa, Carlos I -- Florentino, Adriana -- Gaitan, Juan -- Gatica, M Gabriel -- Ghiloufi, Wahida -- Gomez-Gonzalez, Susana -- Gutierrez, Julio R -- Hernandez, Rosa M -- Huang, Xuewen -- Huber-Sannwald, Elisabeth -- Jankju, Mohammad -- Miriti, Maria -- Monerris, Jorge -- Mau, Rebecca L -- Morici, Ernesto -- Naseri, Kamal -- Ospina, Abelardo -- Polo, Vicente -- Prina, Anibal -- Pucheta, Eduardo -- Ramirez-Collantes, David A -- Romao, Roberto -- Tighe, Matthew -- Torres-Diaz, Cristian -- Val, James -- Veiga, Jose P -- Wang, Deli -- Zaady, Eli -- 242658/European Research Council/International -- New York, N.Y. -- Science. 2012 Jan 13;335(6065):214-8. doi: 10.1126/science.1215442.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Area de Biodiversidad y Conservacion, Departamento de Biologia y Geologia, Escuela Superior de Ciencias Experimentales y Tecnologia, Universidad Rey Juan Carlos, Calle Tulipan Sin Numero, 28933 Mostoles, Spain. fernando.maestre@urjc.es〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22246775" target="_blank"〉PubMed〈/a〉
    Keywords: *Biodiversity ; *Climate ; Climate Change ; Conservation of Natural Resources ; *Ecosystem ; Geography ; Geological Phenomena ; Models, Statistical ; *Plants ; Regression Analysis ; Temperature
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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