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  • 1
    Electronic Resource
    Electronic Resource
    Buildup of epoxycycloaliphatic amine networks. Kinetics, vitrification, and gelation (1990)
    s.l. : American Chemical Society
    Macromolecules 23 (1990), S. 725-731 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00205a006
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  • 2
    Electronic Resource
    Electronic Resource
    On the existence of positive solutions of semilinear elliptic equations with Dirichlet boundary conditions (1994)
    Springer
    Mathematische Annalen 298 (1994), S. 543-556 
    Details
    ISSN: 1432-1807
    Keywords: 35J65 ; 60J65 ; 53C21
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01459750
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  • 3
    Electronic Resource
    Electronic Resource
    Protein dynamics studied by NMR (1993)
    Springer
    European biophysics journal 21 (1993), S. 393-401 
    Details
    ISSN: 1432-1017
    Keywords: NMR ; β-sheets ; α-helices ; dynamics ; protein-actions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The results of NMR studies using several nuclei indicate that proteins have considerable internal mobility. The most obvious is the mobility of side-chains. This mobility is general on the exterior surfaces but extends internally in a differential way. The functional value of surface mobility concerns both on and off rates of ligand binding (e.g. metal ions and parts of substrates) and protein/protein interactions. The mobility, which indicates that recognition is more in the hand-in-glove class than in the lock-in-key class, makes for a modified view of the specificity of protein interactions. Thus, fast on/off systems cannot be as selective as slower systems. Segmental mobility of proteins is considered in the context of protein secondary structure. The least mobile segments are the β-sheet and the tight β-turn. Mobility is always possible for, but not within, rod-like helices and in loose turns. Many examples are given and the importance of mobility in molecular machines is described. Finally, examples are given of virtually random-coil proteins, segments, and linker regions between domains and the functional value of such extremely dynamic regions of proteins is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00185866
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  • 4
    Electronic Resource
    Electronic Resource
    Structure of adsorbates on alkali halides (theory). I. HBr on LiF(001) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 978-996 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a first computation of the geometry of HBr adsorbed on a LiF(001) substrate. The interaction energy of 200 HBr molecules with periodic boundary conditions was determined with respect to adsorbate–substrate and adsorbate–adsorbate electrostatic interaction (point charges in HBr simulated its dipole and multipoles) as well as a short-range "core'' potential (comprising dispersion forces and repulsive overlap). The monolayer heat of adsorption at T=100 K according to this model was 0. 27 eV, which was also the experimental value [E. B. D. Bourdon, et al., J. Chem. Phys. (submitted)]. The major contribution to this energy came from electrostatic binding. The preferred HBr location at all surface coverages (0.25, 0.50, and 1.0 ML) in the temperature range T=70–130 K was with Br over Li+ and H almost eclipsing one of the four neighboring F−. In this configuration, Br–H is tilted down by 23 ° from the crystal plane in an arrangement resembling a Br–H– –F− hydrogen bond. This computed geometry agrees well with recent experimental findings for HBr/LiF(001) using polarized infrared spectroscopy [P. M. Blass et al.; J. Chem. Phys. (submitted)], and is also in qualitative accord with the observed angular distribution of fast H from the photolysis of HBr adsorbed on LiF(001). At the separations dictated by the LiF(001) lattice, the net adsorbate–adsorbate interaction is attractive, leading to a tentative prediction of island formation at lower coverages under equilibrium conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459937
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  • 5
    Electronic Resource
    Electronic Resource
    Simazine Concentrations in a Stream Draining an Agricultural Catchment (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Water and environment journal 5 (1991), S. 0 
    Details
    ISSN: 1747-6593
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: This paper reports the concentrations of the herbicide simazine which were found in a stream draining a small agricultural catchment as a result of normal agricultural practice. The study, part of the National Rivers Authority Research and Development programme, shows that peaks in the concentration of simazine occurred very soon after rainfall events. It goes on to show that although the mass of simazine transported from the catchment during each rainfall event is small as a percentage of that applied (less than 1%), the concentrations observed are far from insignificant. It is suggested that monitoring programmes need to be designed to cover such pesticide pulses generated as the result of rainfall events occurring at times of peak application. Also, more realistic environmental-quality standards need to be developed and applied where the EC drinking water Directive is inappropriate, and to reflect the intermittent nature of the problem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1747-6593.1991.tb00591.x
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  • 6
    Electronic Resource
    Electronic Resource
    The Translocation of Some Herbicides between Soil and Water in a Small Catchment (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Water and environment journal 6 (1992), S. 0 
    Details
    ISSN: 1747-6593
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: This paper presents data on the distribution of four herbicides within an agricultural catchment. In the case of mecoprop, 2,4-dichlorophenoxyacetic acid and simazine, these data include concentrations in the soil, field drains and the stream, before and after applications of the herbicides following good agricultural practice. The concentrations of these herbicides in the soil were found to follow published degradation rates, and their concentrations in the stream and drains were elevated following rainfall with peak concentrations from 0.12 μg/1 to 68.0 μg/1. Atrazine was found at relatively high concentrations (peak 122 μg/1) when it had not been applied to any of the fields draining to the sampling point.The data will be used to test models that may be used as one of a number of tools for the screening of new pesticides prior to their registration. One approach using the Mackay's fugacity model is outlined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1747-6593.1992.tb00779.x
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  • 7
    Electronic Resource
    Electronic Resource
    Gelation in the cyclotrimerization of dicyanates considering substitution effects (1992)
    Springer
    Polymer bulletin 28 (1992), S. 219-225 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The cyclotrimerization of dicyanates to form polycyanurate networks has been analyzed using a pure kinetic model and a combined kinetic-recursive procedure. In both cases substitution effects were considered, i.e. the reactivity of OCN groups pertainning to clusters was assumed lower than the corresponding reactivity of the monomer groups. The gel conversion varied from 1/2 (no substitutions effects) to 2/3 (infinite substitution effects). The evolution of trimer concentration along the reaction constitutes a direct experimental evidence to decide whether the polymerization follows or not an ideal course, described by the mean-field theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00299659
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  • 8
    Electronic Resource
    Electronic Resource
    Molecular-mass distributions resulting from the homopolymerization of monoepoxides initiated by tertiary amines (1992)
    Springer
    Polymer bulletin 28 (1992), S. 459-465 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary A reaction scheme based on propagation and intramolecular chain transfer steps is proposed for the anionic homopolymerization of epoxides initiated by tertiary amines. Chain transfer regenerates a living chain and gives a dead chain with terminal vinilydene unsaturations and hydroxy groups. The possibility of generating phenols or substituted phenols is also considered. Molecular-mass distributions were predicted as a function of conversion by both kinetic and Monte Carlo methods. Predictions were compared with experimental results reported in the literature. The evolution of the number-average degree of polymerization could be reasonably predicted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00297340
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  • 9
    Electronic Resource
    Electronic Resource
    Macro- and microgelation in the homopolymerization of diepoxides initiated by tertiary amines (1991)
    Springer
    Polymer bulletin 27 (1991), S. 9-15 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The homopolymerization of an epoxy resin based on diglycidylether of bisphenol A (DGEBA), initiated by benzyldimethylamine (BDMA), was analyzed in the 80°C–140°C temperature range. An heterogeneous network characterized by regions of different glass transition temperature, was obtained. Microgels appeared early in the polymerization while an increase in the reactivity of the second epoxy group of a DGEBA molecule after reaction of the first one, was inferred from size exclusion chromatograms (SEC), obtained at different overall conversions. Both experimental findings were qualitatively explained through an intramolecular chain transfer step that regenerates the initiator in the proximity of pendant epoxy groups. The increase in the polymerization temperature produced an increase in the macroscopic gel conversion and a decrease in the glass transition temperature of regions of high crosslink density. This was ascribed to the increase in the ratio of intramolecular chain transfer over propagation rates, leading to shorter primary chains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00296318
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  • 10
    Electronic Resource
    Electronic Resource
    Gadolinium and friends (1990)
    [s.l.] : Nature Publishing Group
    Nature 344 (1990), S. 595-595 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THIS book has a somewhat strange title. If one thinks of a book on the biochemistry of an element, copper for example, then there lies behind this title the presumption that copper has a biological function. The lanthanide ions have no known biological function. It is a further remarkable fact that ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/344595a0
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