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  • Life and Medical Sciences  (76)
  • Cell & Developmental Biology  (59)
  • Chemical Engineering  (52)
  • cactus  (4)
  • 11
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 212 (1992), S. 257-267 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The ontogeny of various middle-ear structures was examined in 11 groups of chicks between 10 days embryonic and adult. Measurements of the tympanic membrane surface area and height, columella length, and that of the columella footplate, annular ligament, and oval window area were obtained using video micrographs and computer digitization techniques. The oval window matures first at 53 days post-hatching, whereas the columella achieves adult size at 74 days. The tympanic membrane surface area is the last middle-ear variable studied to reach adult size (79 days post-hatch). The columella increases its length from 0.63 mm (10 days embryonic) to 2.73 mm in the adult. The tympanic membrane area expands by 280% whereas the columellar footplate area increases by 11x. As a result, the pressure amplification of the middle ear due to the tympanic membrane/columellar footplate area ratio improves by over 400%. These data further contribute to our understanding of the functional development of the middle ear. © 1992 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical ecology 15 (1989), S. 663-676 
    ISSN: 1573-1561
    Keywords: Drosophila ; Diptera ; Drosophilidae ; triterpene glycosides ; cactus ; fitness components ; host-plant relationships
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The effects of pentacyclic triterpene glycosides extracted from agria and organ pipe cacti on three fitness parameters of the cactophilic fruit fly,Drosophila mojavensis were tested. Triterpene glycosides from organ pipe increased development time and reduced larval viability while those from agria produced smaller adults (reduced fecundity). In addition, the microbial communities in the organ pipe saponin media were less dense than those in the media to which agria saponins had been added. The role of cactus triterpene glycosides in the ecology of thisDrosophila species is discussed.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 1671-1674 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 1251-1265 
    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 comprehensive kinetic model developed for molecular weight calculations of ethylene axsnd α-olefin copolymerizations in the context of a terminal model accounts for multiple-type active centers of the catalyst, detailed elementary chemical reactions, and catalyst composition. The moments of copolymer chain distributions are defined considering molecular weights of comonomer units so that copolymer molecular weight averages can be directly calculated from those moments. A double Z-transformation is introduced for the derivation of differential equations of the moments. Model simulations are carried out based on ethylene and 1-butene copolymerizations in a gas-phase fluidized-bed reactor. Polydisperity of accumulated copolymer depends on catalyst composition and kinetic characteristics of the catalyst. For a catalyst with specified kinetic characteristics, the polydispersity depends on the mole fraction of each type of active center. For a catalyst with two types of active centers, the maximum polydispersity of copolymer occurs at 50 wt. % of the total copolymer if polydispersities of the copolymers generated at each active site are the same. Polydispersity of accumulated copolymer is sensitive to propagation reactions and chain transfer to hydrogen reactions. Differences in chain transfer to cocatalyst and monomers and in spontaneous deactivation rates for different types of active centers may play minor roles in controlling molecular weight development in the presence of hydrogen. This model can be used for catalyst composition design, simulation of commercial olefin copolymerization processes, and kinetic parameter estimation.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2356-2370 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Direct numerical simulations were used to study chemical selectivity in a series-parallel reaction scheme in a decaying, homogenous turbulent flow, where A, B, R, and S represent chemical species with R the principal product and S the secondary product. These simulations involve solution of the unsteady Navier-Stokes and mass conservation equations by a pseudo-spectral method in a 643 wavenumber domain. Reactants A and B were initially spatially segregated, corresponding to a nonpremixed system. The effect of turbulence Reynolds number and other physical parameters on selectivity was determined. Turbulence increases the formation of primary product R over byproduct S compared to the case of no fluid motion, as expected. It was also found that any mechanism promoting homogenization of reactants favors the formation of R, Whereas any mechanism sustaining segregation favors the formation of S.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1757-1760 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 296-297 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 1454-1464 
    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 method of determining control coefficients and pseudo-first-order kinetic parameters is presented for cell growth, substrate consumption, and product formation in a chemostat bioreactor. From the equations that relate the control coefficients to process variables, such as feed concentrations of the limiting substrate and the product of interest, a perturbation method is developed to determine control coefficients from steady-state measurements. This method combined with the transient response analysis provides a practical way for determining control coefficients and estimating kinetic properties in chemostat bioreactor systems. To determine the kinetic parameters, one measures cell mass, concentrations of the limiting substrate and the product of interest following a step change in the feed concentration until the system reaches a new steady state. The time courses of these variables are processed to obtain control coefficients, which yield the pseudo-first-order kinetic constants for cell growth, substrate consumption, and product formation. Only steady-state responses are needed in calculation, if a step change in cell concentration in the feed stream can also be introduced without significantly perturbing cell physiology. This method is useful in characterizing the kinetics of whole cell bioreactions: results from chemostat experiments can be used to design operating strategies for batch or fed-batch bioreactions. It is generally applicable to continuous-stir-tank reactors with interacting parallel reactions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 902-912 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Simple first-order closure models for covariances of concentration fluctuations, for use in modeling turbulent flow reactors, were tested by direct numerical simulations. Concentration covariances and other statistical functions were evaluated for a series parallel reaction scheme in decaying, homogeneous turbulent flow. The simulations involve solving the unsteady Navier-Stokes and mass conservation equations by a pseudo-spectral method in a 643 wavenumber domain, with initially segregated reactants, for an initial turbulence Reynolds number of 29.9. Simulation results show that covariances of concentration fluctuations normalized with respect to mean concentration values are almost constant and that the time dependence of concentration covariances can be estimated if the mean concentrations are known at any one time after the initial time. Predictions of the first-order closure models of Bourne and Toor, Brodkey and Lewalle, Li and Toor, and Dutta and Tarbell were compared to simulation results. While none of these closures are satisfactory for all the conditions tested, the Brodkey-Lewalle closure agrees best with the simulations.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 20
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 13-24 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In most industrial gas-phase polyethylene reactors, heat is removed by cooling the recycle gas stream in an external heat exchanger, where a portion of the vapor is condensed. The condensate evaporates in the reactor to absorb heat released by polymerization reactions, thereby increasing the production capacity of the unit. Nonequilibrium methods of multicomponent condensation are applied to develop a 1-D model to simulate the cooling unit of an industrial polyethylene reactor system operated in partial condensing mode. Finite difference approximations are used to convert the resulting set of differential equations to algebraic equations. A practical method of solving the equations is to combine the rapid local convergence of Newton's method with a globally convergent strategy. Correlation methods for estimating local heat-transfer coefficients in the liquid film layer are discussed. Butterworth's method for shear-stress-controlled condensate flow gives reasonable agreement between simulation results and industrial data, while Chen et al.'s method can better describe the transition process of condensate flow from laminar to turbulent flow.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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