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  • 2020-2024  (1)
  • 1990-1994  (23)
  • 1
    Digitale Medien
    Digitale Medien
    Uptake and incorporation in pteridines of externally supplied GTP in normal and pigment-deficient eyes ofDrosophila melanogaster (1992)
    Springer
    Biochemical genetics 30 (1992), S. 61-75 
    Details
    ISSN: 1573-4927
    Schlagwort(e): white gene ; Drosophila melanogaster ; eye pigment synthesis ; GTP cyclohydrolase activity ; drosopterin synthesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract Some aspects of the synthesis of drosopterins in the eyes ofDrosophila melanogaster have been studied in flies with different levels ofwhite gene expression. The activity of GTP cyclohydrolase was found to differ between wild-type and yellow-eyed mutantsin vivo but notin vitro. To elucidate the uptake of substrate, we measured the removal of labeled GTP from the incubation medium by excised pupal eyes and followed the subsequent fate of this label. It was found that GTP was dephosphorylated to guanosine extracellularly before label was taken up by the eye tissue. The uptake was much lower in yellow and white eyes than in wild-type eyes, and in the latter, a considerable part of the label was present in pteridine compounds. The strain differences in the uptake of label seem to be due to different rates of intracellular utilization of guanine derivatives in pteridine synthesis. We suggest that this is caused by a hampered transport of precursor (possibly GTP) in white andzeste eyes through the membrane of red pigment granules.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00554428
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  • 2
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    Uptake and incorporation in pteridines of externally supplied GTP in normal and pigment-deficient eyes ofDrosophila melanogaster (1992)
    Springer
    Details
    Publikationsdatum: 1992-02-01
    Print ISSN: 0006-2928
    Digitale ISSN: 1573-4927
    Thema: Biologie , Chemie und Pharmazie
    Publiziert von Springer
    Standort Signatur Erwartet Verfügbarkeit
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    AKTUELLE ARTIKEL
  • 3
    Digitale Medien
    Digitale Medien
    Effects of weathering on metal releases from an engineered deposit for alum shale leaching residues (1991)
    Springer
    Water, air & soil pollution 57-58 (1991), S. 431-440 
    Details
    ISSN: 1573-2932
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract A pile of ca 15,000 t of crushed alum shale leaching residues from uranium refining was deposited in Ranstad, Sweden, in 1972 as a part of a pilot study of various waste storage concepts. A field study has been performed in order to evaluate the efficiency of the engineered barriers (bentoniteltill or crushed limestone) for the prevention of weathering of the leaching residues and subsequent release of metal rich leachates. The concentration levels of Fe (from pyrite in the alum shale) as well as metals associated with the pyrite (e.g. Cu and Ni) indicate that the weathering of leaching residues underneath the cover has progressed to less than 4 cm in 15 yr. No breakthrough of precipitation is indicated from the composition of the percolation water coming from the deposit. Thus, the weathering rate is reduced by ca 3 orders of magnitude in comparison with leaching residues freely exposed to air and precipitation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00282906
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  • 4
    Digitale Medien
    Digitale Medien
    Evaluation of water and gas transport in layered soil covers for coal ash deposits: 2d-calculations and impact of a weak zone (1994)
    Springer
    Water, air & soil pollution 77 (1994), S. 97-114 
    Details
    ISSN: 1573-2932
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract A methodology for evaluating the efficiency of a soil cover to reduce water infiltration and gas transport has been adapted for coal ash deposits and two dimensions. A cover consisting of two layers, a tight layer and a protecting layer, is studied. Studied design parameters are primarily the slope and the quality of the tight layer. Simulations show that the slope has a minor impact, while the hydraulic conductivity of the tight layer is shown to be of major importance. The calculations indicate that the hydraulic conductivity of the tight layer should be smaller than 10−8 m s−1. However, for longer covers a lower hydraulic conductivity gives overflow indicating that a better lateral drainage must be provided for. This may be obtained by inserting a drainage layer. A negative side-effect, however, is that gas transport may increase due to the lower saturation of the cover. The impact of a high conductivity zone in the tight layer is illustrated with 3D calculations. For example, a weak zone covering 0.5% of the area with a hydraulic conductivity of 10−7 m s−1 (10−9 m s−1 for the rest of the layer) will increase the total water flow through the bottom by about 25%. The gas transport in such a heterogeneous cover will increase totally by a factor of 1.2 and locally by a factor of 5.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00483052
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    Artikel (Nationallizenzen)
    Volltext
  • 5
    Digitale Medien
    Digitale Medien
    Transport of volatile chlorinated hydrocarbons in unsaturated aggregated media (1993)
    Springer
    Water, air & soil pollution 68 (1993), S. 291-305 
    Details
    ISSN: 1573-2932
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract Transport of volatile hydrocarbons in soils is largely controlled by interactions of vapours with the liquid and solid phase. Sorption on solids of gaseous or dissolved compounds may be important. Since the contact time between a chemical and a specific sorption site can be rather short, kinetic or mass-transfer resistance effects may be relevant. An existing mathematical model describing advection and diffusion in the gas phase and diffusional transport from the gaseous phase into an intra-aggregate water phase is modified to include linear kinetic sorption on gas-solid and water-solid interfaces. The model accounts for kinetic mass transfer between all three phases in a soil. The solution of the Laplace-transformed equations is inverted numerically. We performed transient column experiments with 1,1,2-Trichloroethane, Trichloroethylene, and Tetrachloroethylene using air-dry solid and water-saturated porous glass beads. The breakthrough curves were calculated based on independently estimated parameters. The model calculations agree well with experimental data. The different transport behaviour of the three compounds in our system primarily depends on Henry's constants.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00479409
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  • 6
    Digitale Medien
    Digitale Medien
    Semibatch reaction crystallization of benzoic acid (1992)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 328-342 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: An experimental study of a semibatch reaction crystallization is presented. Dilute hydrochloric acid is fed to a stirred solution of sodium benzoate to crystallize benzoic acid. The weight mean size of the product crystals increases with increasing stirring rate, reaches a maximum, and then decreases again. Larger crystals may be produced if the reactant feed point is positioned close to the outlet stream of the impeller. At equal power input the influence of stirrer type is negligible. Decreasing reactant concentrations or feed rate increases the crystal size significantly. Experimental results are explained qualitatively focusing on nucleation and growth conditions and on feed point mixing. The feed point micromixing brings reactants together to generate supersaturation and allow for nucleation. Continued mixing, however, may partially dilute supersaturation before nucleation takes place or may restrict nuclei growth, thus promoting more efficient Ostwald ripening in the bulk. This may result in high bulk supersaturations which in turn hampers the dilution effects.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690380303
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  • 7
    Digitale Medien
    Digitale Medien
    Growth and dissolution of succinic acid crystals in a batch stirred crystallizer (1990)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 36 (1990), S. 665-676 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Growth and dissolution of succinic acid crystals have been studied in an isothermal stirred tank crystallizer. Seeded desupersaturation and deundersaturation experiments have been performed. Parameters of a desired growth rate equation are estimated by fitting the supersaturation balance equation directly to the supersaturation measurements. The procedure is based on nonlinear optimization techniques. Thus, uncertainties in the traditional approximation of the concentration vs. time curve are circumvented. The growth process for succinic acid crystals in an aqueous solution is found to be controlled by a significant resistance in both the volume diffusion step and in the surface integration step. An implicit equation is given to accurately represent the crystal growth rate as a function of the supersaturation. When extrapolating outside the range of experiments, this equation is shown to predict growth rates that are significantly different from those predicted by a corresponding power law expression. The dissolution rate exhibits a nonlinear dependence on undersaturation which is interpreted as changes in the crystal shape. Initial dissolution rate coefficients are in good agreement with volume diffusion coefficients obtained from growth experiments.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690360504
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    Artikel (Nationallizenzen)
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  • 8
    Digitale Medien
    Digitale Medien
    Modeling of growth rate dispersion in batch cooling crystallization (1992)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 1853-1863 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The influence of growth rate dispersion on the product-size distribution of batch cooling crystallization is investigated by computer simulations. The model accounts for primary and magma density-dependent secondary nucleation, and growth rate dispersion of the constant crystal growth type. The model is solved by a combination of the method of characteristics and moment analysis, by which the entire product-size distribution is recovered. The study includes three different growth rate activity distributions, and the influence of the corresponding coefficient of variation is analyzed for unseeded and seeded processes. The results show that the effect of growth rate dispersion on the crystal-size distribution may be significant even at moderate dispersion. At high dispersion, even the actual shape of the growth rate activity distribution may become important.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690381202
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  • 9
    Digitale Medien
    Digitale Medien
    Estimation of crystallization kinetics from batch cooling experiments (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 799-812 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A direct optimization method to estimate nucleation and crystal growth rate parameters from seeded batch cooling crystallization experiments is evaluated. The experimental information applied comprises the concentration of the solution and the temperature as functions of time and the final product size distribution. Parameters in kinetic equations are determined by nonlinear optimization of a dynamic model of the experiment, by which intermediate approximations of experimental data are avoided. The optimization objective function includes both solution concentration data and product size distribution data. Kinetics are estimated for succinic acid crystallizing in aqueous solutions. Results from several different cooling crystallizations are simultaneously supplied into one single optimization to determine seven parameters.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690400507
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  • 10
    Digitale Medien
    Digitale Medien
    Nucleation and growth of succinic acid in a batch cooling crystallizer (1991)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 1293-1304 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A method to evaluate nucleation and crystal growth rates from batch cooling crystallization experiments is presented. Solute concentration and suspension temperature are recorded during the experiment and the product crystal size distribution is analyzed. The crystal growth and nucleation rates at any instant are calculated by solving the population balance equation using the method of characteristics, together with the mass balance equation. Based on a set of different cooling crystallization experiments, kinetics for succinic acid are determined. Applying these kinetics in process simulation allows for a reasonably accurate prediction of the product weight mean size.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690370903
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