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  • 1
    Electronic Resource
    Electronic Resource
    A Simplified Analysis of Two-Well Tracer Tests in Stratified Aquifers (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 24 (1986), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: This paper illustrates several interesting effects of aquifer stratification on the results of two-well tracer tests by means of a simplified computer model. In the model, it is assumed that the aquifer is horizontal, confined, of constant thickness and porosity, and perfectly stratified in the vicinity of the test wells. The nonuniform advection pattern is taken into account in detail by the model, but the local hydrodynamic dispersion is completely neglected. This simplified model has been verified in part by comparisons with available analytical solutions valid for homogeneous aquifers and in part by comparisons with the results of a two-well field experiment of Pickens and Grisak (1981a) which was performed in a locally stratified aquifer. The applications of the model to several field situations with assumed values of the relevant parameters show that the concentration versus time breakthrough curve measured at the withdrawal well during a standard two-well test would be very sensitive to variations of the hydraulic conductivity in the vertical. Without the use of supplementary observation wells with isolated multilevel sampling points, the standard test would give little useful information about the hydraulic and dispersive characteristics of an aquifer. Factors such as the length of the tracer injection period, the use of recirculation and the physical size of the experiment all have a strong effect on the breakthrough curve measured at the withdrawal well, making the interpretation of field results difficult unless aquifer stratification is measured and properly taken into account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1986.tb01460.x
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  • 2
    Electronic Resource
    Electronic Resource
    Three-Dimensional Modeling of a Two-Well Tracer Test (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 30 (1992), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A three-dimensional (3-D), advection-based numerical model has been developed for simulating two-well injection withdrawal tracer tests in heterogeneous granular aquifers, and the model has been applied to perform various simulations of an actual two-well tracer test conducted previously in a confined aquifer at a field site near Mobile, Alabama. Information obtained from a series of independent field tests is used as input in the model to account for the 3-D spatial distribution of the hydraulic conductivity (K) at the test site.The numerical model is based on a simplified, Lagrangian approach in which the transport of the tracer between the injection and withdrawal wells is modeled taking into account advection only. Processes such as dispersion, sorption, and chemical or biological reactions are neglected. Despite field data limitations and various simplifying assumptions, the model predictions of the withdrawal-well concentration breakthrough and of the mean tracer arrival times at various levels of two multilevel observation wells are in good overall agreement with the corresponding field observations.The results of this study indicate that it will be possible to construct realistic, predictive models of contaminant transport in heterogeneous granular aquifers if the necessary effort is made to obtain field measurements of the 3-D spatial distribution of hydraulic conductivity. The extent and feasibility of such an effort are expected to depend on the particular contamination problem at hand. Future research should be directed toward the problems of field measurement scale selection and the development of K distributions for models from sparse data sets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1992.tb01578.x
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  • 3
    Electronic Resource
    Electronic Resource
    Hydrophilic and Hydrophobic interactions in alcohol solutions of high molecular weight poly(n-vinyl-2-pyrrolidone) (1984)
    Springer
    Colloid & polymer science 262 (1984), S. 892-895 
    Details
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Inter- and intra-molecular association in alcohol solutions of poly(n-vinyl-2-pyrrolidone) with molecular weight of 670,000 is investigated by viscometric techniques. While the limiting viscosity number, [η], of the polymer was observed to remain almost constant in methanol, ethanol and n-propanol solutions, the Huggins constant,k H showed an increase with increasing carbon content of the alcohols studied. Addition of denaturing agents, such as urea and guanidine hydrochloride, (GC) caused a decrease in both of the above values. The changes brought about in these parameters by the denaturing agents were found to be a result of the changes taking place in the hydrophilic and hydrophobic interactions among polymer, solvent and additive molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01452220
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of solvents on the crystallization of dilute poly(ethylene oxide) solutions (1982)
    Springer
    Colloid & polymer science 260 (1982), S. 647-651 
    Details
    ISSN: 1435-1536
    Keywords: Poly(ethylene oxide) ; crystallization kinetics ; solvent effects ; end surface free energy ; intramolecular association
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The crystallization kinetics of a poly(ethylene oxide) sample with molecular weight of 20 000 was studied in dilute solutions ofn-propanol,n-butanol andn-pentanol by dilatometric methods. The value of the Avrami exponent was observed to change with crystallization temperature in poorer solvents. The temperature coefficient of overall rate was analyzed according to the theory developed for polymer-diluent mixtures. Statistical analysis of data pertinent to overall rate temperature coefficient showed that the end surface free energyσ en changes with the thermodynamic quality of the solvent. This is considered to be attributed to the loss in flexibility of polymer chains due to the intramolecular association displayed by poly(ethylene oxide) in its solutions of poor solvents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01414650
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  • 5
    Electronic Resource
    Electronic Resource
    Thermal degradation of poly(ethyl methacrylate) and its copolymer with poly(ethyl acrylate) (1997)
    Springer
    Journal of thermal analysis and calorimetry 48 (1997), S. 783-789 
    Details
    ISSN: 1572-8943
    Keywords: poly(ethyl acrylate) ; poly(ethyl methacrylate) ; thermal degradation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The thermal degradation behaviour of poly(ethyl methacrylate) homopolymers and poly(ethyl methacrylate) and poly(ethyl acrylate) copolymers synthesized by using the benzoyl peroxide-di-methyl aniline redox pair at different temperatures (18–35
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01997183
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of γ-rays on the crystallization behaviour of lower poly(ethylene glycol) fractions (1979)
    Springer
    Colloid & polymer science 257 (1979), S. 23-26 
    Details
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Zusammenfassung Die Kristallisationsisothermen von drei γ-bestrahlten niedrig-molekularen Polyäthylenglykolfraktionen wurden dilatometrisch bestimmt. Die untersuchten Proben hatten ein zahlenmäßig durchschnittliches Molekulargewicht von 1500, 4000 und 35000. Die Kristallisationskinetik wurde mittels einer Avrami-Analyse untersucht und dern-Wert für nicht bestrahlte Proben als 2 ermittelt. Durch Bestrahlung ändern sich die Neigungen der Isothermenab einem, Kristallisasationsgrad von etwa 30 Prozent abrupt, und der Wert von n wird gleich eins. Dieses Verhalten wird durch einen diffusionskontrollierten Wachstumsmechanismus erklärt.
    Notes: Summary Crystallization isotherms of three- γ-irradiated low molecular weight poly(ethylene glycol), PEG, fractions were determined dilatometrically. Samples investigated had number average molecular weights of 1500, 4000 and 35000. Crystallization kinetics were analyzed according to theAvrami formalism, then value being 2 for unirradiated samples. With irradiation, the slopes of isotherms changed abruptly at about 30% crystallinity, after this crystallinity then value became equal to 1. This behaviour is explained by the diffusion control of the growth mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01539012
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  • 7
    Electronic Resource
    Electronic Resource
    Spectrophotometric behavior of polyvinylpyrrolidone in aqueous and nonaqueous media (I) (1990)
    Springer
    Colloid & polymer science 268 (1990), S. 337-344 
    Details
    ISSN: 1435-1536
    Keywords: Polyvinylpyrrolidonesolutions ; spectrophotometricbehavior ; UV-spectra ; solventeffects ; salteffect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Electronic spectral behavior of polyvinylpyrrolidone solutions in various media has been determined by UV-VIS spectrophotometry. A theoretical approach has been developed to explain the experimentally observed concentration dependent spectral behavior of polyvinyl pyrrolidone in aqueous and nonaqueous solvents. Increase in the concentration of the polymer or the addition of guanidine salts caused bathochromic shift. A similar concentration effect has been observed in nonaqueous media in the absence of guanidine salts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01411677
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  • 8
    Electronic Resource
    Electronic Resource
    Investigation of complex formation between poly(N-vinyl imidazole) and various metal ions using the molar ratio method (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 570-573 
    Details
    ISSN: 1435-1536
    Keywords: Key words Poly(N-vinyl imidazole) ; Complexation ; Molar ratio method ; UV spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The complex formation of poly(N-vinyl imidazole) (PVIm) with various metal ions was studied. UV-vis spectroscopy was employed to study the interaction of PVIm and metal ions in aqueous solution. Formation constants of PVIm-metal complexes were calculated by applying a “mole ratio” method. The stoichiometric ratios between polymer and metal ions were found to be␣4. The stability constants for the complexes of PVIm with bivalent transition metal ions were in agreement with the Irving-William series. The biggest formation constant was found for the PVIm-Cu2+ complex system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050426
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  • 9
    Electronic Resource
    Electronic Resource
    Effects ofγ-rays on poly(alkyl methacrylate)s (1979)
    Springer
    Colloid & polymer science 257 (1979), S. 990-991 
    Details
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01520728
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  • 10
    Electronic Resource
    Electronic Resource
    Thermal stability of poly(pyrrole) (1987)
    Springer
    Journal of materials science 6 (1987), S. 1013-1015 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01729116
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