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  • Articles  (9,663)
  • Articles: DFG German National Licenses  (9,663)
  • Springer  (9,663)
  • American Association for the Advancement of Science (AAAS)
  • American Association of Petroleum Geologists (AAPG)
  • Emerald
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  • 2020-2022
  • 1995-1999  (9,663)
  • 1997  (9,663)
  • Physics  (8,265)
  • Geosciences  (2,359)
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  • Articles  (9,663)
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  • 2020-2022
  • 1995-1999  (9,663)
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  • 1
    Electronic Resource
    Electronic Resource
    Effect of Ca doping on the structural and superconducting properties of EuBaSrCu3O7−δ (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 645-647 
    Details
    ISSN: 1557-1947
    Keywords: EuBaSrCu3O7−δ superconductor ; Ca doping ; orthorhombicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The effect of Ca doping in EuBaSrCu3O7−δ has been investigated by X-ray diffraction, ac susceptibility, and electrical resistivity measurements. X-Ray diffraction analyses of the samples showed that up to 30 at.% Ca can be substituted for Sr in EuBaSrCu3O7−δ, which has orthorhombic symmetry. The orthorhombicity decreases with increase inx, in EuBaSr1−xCax Cu3O7−δ, the material becoming tetragonal atx=0.2. Ac susceptibility and dc electrical resistivity measurements as function of temperature from 10 to 300 K showed that the superconducting transition temperatureT c decreases monotonically from 84 to 75K as the Ca concentrationx increases from 0.0 to 0.3 The decrease inT c can be attributed to the structural change taking place in EuBaSrCu3O7 as a consequence of replacement of Sr by Ca.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471926
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  • 2
    Electronic Resource
    Electronic Resource
    New research opportunities in superconductivity IV (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 583-621 
    Details
    ISSN: 1557-1947
    Keywords: Superconductivity ; research opportunities ; state of the art
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract This report surveys the considerable progress made over the last five years—such as the marketing of superconducting quantum interference devices (SQUIDs), cellular wireless filter systems, and high current leads—and assesses needs and opportunities in the areas of fundamental science, materials development, thin film and device applications, and wire and bulk applications. It examines the challenges facing high-temperature superconductivity: from the need to understand the mechanism of high-temperature superconductivity and the unusual “normal” state to the need for new instrumentation for material characterization. Advances in thin film and bulk materials are reviewed, and obstacles impeding the commercialization of HTS materials are examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471924
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  • 3
    Electronic Resource
    Electronic Resource
    High-resolution electron microscopy and low-temperature electron diffraction studies of a Bi2212 single crystal grown by the floating zone method (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 649-655 
    Details
    ISSN: 1557-1947
    Keywords: Single crystal of Bi2Sr2CaCu2O8 ; high-resolution electron microscopy ; low-temperature electron diffraction ; lattice anomaly
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract High-resolution electron microscopy of a Bi2Sr2CaCu2O8 (Bi2212) single crystal prepared by the floating zone method shows that the single crystal is of high quality; there is no intergrowth faulting in the layered structure along thec-axis. Low-temperature selected area diffraction and convergent beam electron diffraction (CBED) studies of this high-quality single crystal show that there is no detectable change for both the point group symmetry of the basic structure and the modulated structure from room temperature to about 15 K. However, a lattice anomaly around 215 K was suggested by measuring the temperature dependence of the ratio between the cross-point distances of the HOLZ lines in high-index CBED patterns. The presence of the lattice anomaly was further confirmed by low-temperature X-ray diffraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471927
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  • 4
    Electronic Resource
    Electronic Resource
    The crystal field in rare earth based high-temperature superconductors (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 623-643 
    Details
    ISSN: 1557-1947
    Keywords: Superconductivity ; crystal field ; rare earth ; relaxation ; gap symmetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Neutron spectroscopy is a powerful tool to determine unambiguously the crystal-field (CF) potential in rare-earth (R) based high-T c superconducting materials. This technique provides detailed information on the electronic ground state of the R ions which is important to understand the thermodynamic magnetic properties as well as the observed coexistence between superconductivity and long-range magnetic ordering of the R ion sublattice at low temperatures. Moreover, the decay of the antiferromagnetic state of the parent compound as well as the evolution of the superconducting state upon doping can be directly and quantitatively monitored. It is found that the observed CF spectra separate into different local components whose spectral weights distinctly depend on the doping level, i.e., there is clear experimental evidence for cluster formation. The onset of superconductivity can be shown to result from percolation which means that the superconductivity is an inhomogeneous materials property. Since the linewidths of CF transitions directly probe the static electronic susceptibility, we discuss temperature-dependent experiments of the relaxation rate of CF excitations in both optimally doped and underdoped regimes. It is shown that there is clear evidence for the opening of an electronic gap in the normal state of underdoped superconductors. Furthermore, the relaxation behavior appears to be extremely dependent upon the energy at which the static susceptibility is being probed. The main observed features can be reproduced by considering a strongly anisotropic gap function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471925
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  • 5
    Electronic Resource
    Electronic Resource
    The effects of cobalt substitution on the thermal diffusivity of YBa2Cu3O7−δ superconductor (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 663-668 
    Details
    ISSN: 1557-1947
    Keywords: Thermal diffusivity ; acoustic plasmons ; cobalt substitution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The thermal diffusivity κ(T) of the cobalt-substituted sintered YBCO system, YBa2Cu3−x Co x O7∮δ (x=0.0, 0.1), has been measured to, investigate, effects of atomic substitution and charge carrier concentration on the thermal diffusion processes. The thermal diffusivity was measured in the temperature range 35–300 K, using the transient-plane-source technique. The results show that, belowT c , the κ(T) values of the doped (x=0.1), samples are lower than the corresponding values for the undoped (x=0.0) samples. This may be due to the difference in the free-charge carrier concentrations of the two samples. A decoupling between the conducting Cu−O planes as a result, of Co-doping in the chain sites may contribute to additional decrease in the thermal diffusivity of the doped sample. An attempt was made to explain the rise in the thermal diffusivity belowT c by adopting a recent theoretical model based on the existence of weakly damped collective electron excitations of Bose type, with acoustic dispersion relation, (acoustic plasmons) inside the superconducting gap.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471929
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  • 6
    Electronic Resource
    Electronic Resource
    Intrinsic surface depression of the order parameter under mixed (s+id)-wave pair symmetry and its effect on the critical current of high-T c SIS Josephson junctions (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 657-662 
    Details
    ISSN: 1557-1947
    Keywords: High-T c superconductors ; order parameter ; Josephson junctions ; Josephson critical current ; pair symmetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract An intrinsic gap depression at the superconductor-insulator interface due to the very short value of the coherence length in high-T c superconductors [HTS] is considered in the framework of a mixed (s+id)-wave pair symmetry for the order parameter ranging from pures to pured-wave. This gap depression acts as the main physical agent causing the relevant reduction ofI c (T)R n (T) values with respect to BCS expectations in HTS SIS Josephson junctions. Good agreement with various experimental data is obtained with both pures-wave and pured-wave symmetries of the order parameter, but with amounts of gap depression depending on the pair symmetry adopted. Regardless of the apir symmetry considered, these results prove the importance of the surface order-parameter depression in the correct interpretation of theI c (T)R n (T) data in HTS SIS junctions. In the case of a planar YBCO-based junction the use of the de Gennes condition allowed us to tentatively obtain an upper limit for the amount ofd-wave present in the gap of YBCO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471928
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  • 7
    Electronic Resource
    Electronic Resource
    An equation of state of high-temperature superconductor (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 669-672 
    Details
    ISSN: 1557-1947
    Keywords: Equation of state ; bulk modulus ; cohesive energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract In the present paper the expression of cohesive energy and the bulk modulus as a function of volume are formulated for high-T c copper oxide superconductors. The model employed consists of long-range electrostatic Coulomb interaction and short-range overlap repulsion. The short-range overlap potential is considered in the Born-Landé inverse power form. The model, parameters of the Born-Landé model are calculated from the equilibrium condition and data of bulk modulus at room temperature. The computed values of pressure derivatives of bulk modulus atP=0 and the values of bulk modulus are found to be in very close agreement with experimental values for high-T c copper oxide and their nonsuperconducting parent compounds. It is also found that the quantity ΔU/U(V o) of these compounds increases with increasing hydrostistic pressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471930
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  • 8
    Electronic Resource
    Electronic Resource
    Van hove singularity and “pseudo-gap” in HTSC (1997)
    Springer
    Journal of superconductivity and novel magnetism 10 (1997), S. 673-675 
    Details
    ISSN: 1557-1947
    Keywords: Cuprates ; van Hove singularity ; pseudo-gap
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Several experimental features in the normal state of cuprates have been interpreted using a “pseudogap”. We show that these results may be explained by the band structure of the CuO2 planes in the metallic region, which exhibits, saddle points (van Hove singularities).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02471931
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  • 9
    Electronic Resource
    Electronic Resource
    A bivariate meta-Gaussian density for use in hydrology (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 17-31 
    Details
    ISSN: 1436-3259
    Keywords: Bivariate density ; meta-Gaussian density ; normal quantile transform ; likelihood ratio dependence ; correlation coefficient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Convenient bivariate densities found in the literature are often unsuitable for modeling hydrologic variates. They either constrain the range of association between variates, or fix the form of the marginal distributions. The bivariate meta-Gaussian density is constructed by embedding the normal quantile transform of each variate into the Gaussian law. The density can represent a full range of association between variates and admits arbitrarily specified marginal distributions. Modeling and estimation can be decomposed into i) independent analyses of the marginal distributions, and ii) investigation of the dependence structure. Both statistical and judgmental estimation procedures are possible. Some comparisons to recent applications of bivariate densities in the hydrologic literature motivate and illustrate the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02428423
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  • 10
    Electronic Resource
    Electronic Resource
    Reliability analysis of hydraulic structures considering unit hydrograph uncertainty (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 33-50 
    Details
    ISSN: 1436-3259
    Keywords: Unit hydrograph ; uncertainty analysis ; linearly constrained Monte-Carlo simulation ; reliability analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Unit hydrographs (UHs), along with design rainfalls, are frequently used to determine the discharge hydrograph for design and evaluation of hydraulic structures. Due to the presence of various uncertainties in its derivation, the resulting UH is inevitably subject to uncertainty. Consequently, the performance of hydraulic structures under the design storm condition is uncertain. This paper integrates the linearly constrained Monte-Carlo simulation with the UH theory and routing techniques to evaluate the reliability of hydraulic structures. The linear constraint is considered because the water volume of each generated design direct runoff hydrograph should be equal to that of the design effective rainfall hyetograph or the water volume of each generated UH must be equal to one inch (or cm) over the watershed. For illustration, the proposed methodology is applied to evaluate the overtopping risk of a hypothetical flood detention reservoir downstream of Tong-Tou watershed in Taiwan.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02428424
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  • 11
    Electronic Resource
    Electronic Resource
    Estimation for rainfall-runoff modeled as a partially observed Markov process (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 1-16 
    Details
    ISSN: 1436-3259
    Keywords: Nash cascade reservoir model ; rainfall-runoff ; EM algorithm ; filtering ; maximum likelihood estimation ; martingale estimating function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Abstract: Linear continuous time stochastic Nash cascade conceptual models for runoff are developed. The runoff is modeled as a simple system of linear stochastic differential equations driven by white Gaussian and marked point process noises. In the case of d reservoirs, the outputs of these reservoirs form a d dimensional vector Markov process, of which only the dth coordinate process is observed, usually at a discrete sample of time points. The dth coordinate process is not Markovian. Thus runoff is a partially observed Markov process if it is modeled using the stochastic Nash cascade model. We consider how to estimate the parameters in such models. In principle, maximum likelihood estimation for the complete process parameters can be carried out directly or through some form of the EM (estimation and maximization) algorithm or variation thereof, applied to the observed process data. In this research we consider a direct approximate likelihood approach and a filtering approach to an algorithm of EM type, as developed in Thompson and Kaseke (1994). These two methods are applied to some real life runoff data from a catchment in Wales, England. We also consider a special case of the martingale estimating function approach on the runoff model in the presence of rainfall. Finally, some simulations of the runoff process are given based on the estimated parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02428422
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  • 12
    Electronic Resource
    Electronic Resource
    Regionalization of unit hydrograph Parameters: 2. Uncertainty analysis (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 173-192 
    Details
    ISSN: 1436-3259
    Keywords: Uncertainty analysis ; unit hydrograph ; regression analysis ; probabilistic point estimation methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Hydrologic model parameters obtained from regional regression equations are subject to uncertainty. Consequently, hydrologic model outputs based on the stochastic parameters are random. This paper presents a systematic analysis of uncertainty associated with the two parameters, N and K, in Nash's IUH model from different regional regression equations. The uncertainty features associated with N and K are further incorporated to assess the uncertainty of the resulting IUH. Numerical results indicate that uncertainty of N and K from the regional regression equations are too significant to be ignored.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427914
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  • 13
    Electronic Resource
    Electronic Resource
    Regionalization of unit hydrograph parameters: 1. Comparison of regression analysis techniques (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 145-171 
    Details
    ISSN: 1436-3259
    Keywords: Hydrologic regionalization ; unit hydrograph ; regression analysis ; multivariate regression ; seemingly unrelated regression ; validation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Hydrologic regionalization is a useful tool that allows for the transfer of hydrological information from gaged sites to ungaged sites. This study developed regional regression equations that relate the two parameters in Nash's IUH model to the basin characteristics for 42 major watersheds in Taiwan. In the process of developing the regional equations, different regression procedures including the conventional univariate regression, multivariate regression, and seemingly unrelated regression were used. Multivariate regression and seeming unrelated regression were applied because there exists a rather strong correlation between the Nash's IUH parameters. Furthermore, a validation study was conducted to examine the predictability of regional equations derived by different regression procedures. The study indicates that hydrologic regionalization involving several dependent variables should consider their correlations in the process of establishing the regional equations. The consideration of such correlation will enhance the predictability of resulting regional equations as compared with the ones from the conventional univariate regression procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427913
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  • 14
    Electronic Resource
    Electronic Resource
    An analysis of the characteristics of rough bed turbulent shear stresses in an open channel (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 193-210 
    Details
    ISSN: 1436-3259
    Keywords: Turbulence ; sediment ; fluvial ; river ; bursting process ; statistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Entrainment of sediment particles from channel beds into the channel flow is influenced by the characteristics of the flow turbulence which produces stochastic shear stress fluctuations at the bed. Recent studies of the structure of turbulent flow has recognized the importance of bursting processes as important mechanisms for the transfer of momentum into the laminar boundary layer. Of these processes, the sweep event has been recognized as the most important bursting event for entrainment of sediment particles as it imposes forces in the direction of the flow resulting in movement of particles by rolling, sliding and occasionally saltating. Similarly, the ejection event has been recognized as important for sediment transport since these events maintain the sediment particles in suspension. In this study, the characteristics of bursting processes and, in particular, the sweep event were investigated in a flume with a rough bed. The instantaneous velocity fluctuations of the flow were measured in two-dimensions using a small electromagnetic velocity meter and the turbulent shear stresses were determined from these velocity fluctuations. It was found that the shear stress applied to the sediment particles on the bed resulting from sweep events depends on the magnitude of the turbulent shear stress and its probability distribution. A statistical analysis of the experimental data was undertaken and it was found necessary to apply a Box-Cox transformation to transform the data into a normally distributed sample. This enabled determination of the mean shear stress, angle of action and standard error of estimate for sweep and ejection events. These instantaneous shear stresses were found to be greater than the mean flow shear stress and for the sweep event to be approximately 40 percent greater near the channel bed. Results from this analysis suggest that the critical shear stress determined from Shield's diagram is not sufficient to predict the initiation of motion due to its use of the temporal mean shear stress. It is suggested that initiation of particle motion, but not continuous motion, can occur earlier than suggested by Shield's diagram due to the higher shear stresses imposed on the particles by the stochastic shear stresses resulting from turbulence within the flow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427915
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  • 15
    Electronic Resource
    Electronic Resource
    Parameter estimation for 2-parameter generalized pareto distribution by POME (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 211-227 
    Details
    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The principle of maximum entropy (POME) was employed to derive a new method of parameter estimation for the 2-parameter generalized Pareto (GP2) distribution. Monte Carlo simulated data were used to evaluate this method and compare it with the methods of moments (MOM), probability weighted moments (PWM), and maximum likelihood estimation (MLE). The parameter estimates yielded by POME were comparable or better within certain ranges of sample size and coefficient of variation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427916
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  • 16
    Electronic Resource
    Electronic Resource
    Evaluation of kernel density estimation methods for daily precipitation resampling (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 523-547 
    Details
    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Kernel density estimators are useful building blocks for empirical statistical modeling of precipitation and other hydroclimatic variables. Data driven estimates of the marginal probability density function of these variables (which may have discrete or continuous arguments) provide a useful basis for Monte Carlo resampling and are also useful for posing and testing hypotheses (e.g bimodality) as to the frequency distributions of the variable. In this paper, some issues related to the selection and design of univariate kernel density estimators are reviewed. Some strategies for bandwidth and kernel selection are discussed in an applied context and recommendations for parameter selection are offered. This paper complements the nonparametric wet/dry spell resampling methodology presented in Lall et al. (1996).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02428432
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  • 17
    Electronic Resource
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    Simulation of normal distributed smooth fields by Karhunen-Loéve expansion in combination with kriging (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 459-482 
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    ISSN: 1436-3259
    Keywords: Karhunen-Loéve expansion ; Empirical Orthogonal Functions ; stochastic simulation ; gaussian fields ; analytical covariance functions ; eigenfunctions ; kriging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Simulation of multigaussian stochastic fields can be made after a Karhunen-Loéve expansion of a given covariance function. This method is also called simulation by Empirical Orthogonal Functions. The simulations are made by drawing stochastic coefficients from a random generator. These numbers are multiplied with eigenfunctions and eigenvalues derived from the predefined covariance model. The number of eigenfunctions necessary to reproduce the stochastic process within a predefined variance error, turns out to be a cardinal question. Some ordinary analytical covariance functions are used to evaluate how quickly the series of eigenfunctions can be truncated. This analysis demonstrates extremely quick convergence to 99.5% of total variance for the 2nd order exponential (‘gaussian’) covariance function, while the opposite is true for the 1st order exponential covariance function. Due to these convergence characteristics, the Karhunen-Loéve method is most suitable for simulating smooth fields with ‘gaussian’ shaped covariance functions. Practical applications of Karhunen-Loéve simulations can be improved by spatial interpolation of the eigenfunctions. In this paper, we suggest interpolation by kriging and limits for reproduction of the predefined covariance functions are evaluated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02428429
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  • 18
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    Dehydrogenative polycondensation of telechelically bis(dimethylsilyl)functionalized oligo(dimethylsiloxane)s or aromatics and 1,3,3,5,5,7,7,7-octamethyltetrasiloxane (1997)
    Springer
    Polymer bulletin 38 (1997), S. 1-5 
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    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: Abstract. Telechelically bis(hydrodimethylsilyl)-functionalized oligo(dimethylsiloxane)s or aromatics were found to give polymers constituting of alternating disilylene and oligodimethylsiloxane or 4,4′-diylaromatics as repeating units by dehydrogenative coupling reaction in the presence of palladium dibenzylideneacetone complex. The same catalyst gave polysilylenes with trisiloxane pendant from 1,1-dihydro-1,3,3,5,5,7,7,7-octamethyltetrasiloxane.
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    URL: http://dx.doi.org/10.1007/s002890050011
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  • 19
    Electronic Resource
    Electronic Resource
    Synthesis of polyorganosiloxane particles (1997)
    Springer
    Polymer bulletin 38 (1997), S. 23-25 
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    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: Abstract. Hybrid particles have been synthesized from methyltriethoxysilane (MTEOS) by the sol-gel process. The particle size, size distribution, particle surface morphology conductivity and pH of the reaction solution at different reaction times were determined. Compared with tetraethyl orthosilicate (TEOS) and p-(chloromethyl)phenyl-trimethoxysilane (CMPTOS), MTEOS has a slower hydrolysis rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002890050014
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  • 20
    Electronic Resource
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    Polymerization of 4-n-alkylstyrenes with typical Ziegler-Natta and metallocene catalysts (1997)
    Springer
    Polymer bulletin 38 (1997), S. 43-48 
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    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: Abstract. Polymerization of 4-n-alkylstyrenes (alkyl side group; methyl, ethyl, propyl and buthyl) was carried out with the η-C5(CH3)5TiCl3-methylaluminoxane (MAO) and TiCl3-triethylaluminum (TEA) catalyst systems. When the η-C5(CH3)5TiCl3-MAO catalyst was used, the stereoregularity of resulting polymers markedly depended on the length of substituted alkyl groups, i.e., the catalyst gave highly syndiotactic poly(4-methylstyrene), but produced atactic polymers for the monomers with ethyl, propyl and buthyl substituents. On the other hand, all the poly(4-n-alkylstyrene)s obtained with the TiCl3-TEA catalyst were highly isotactic. As a result, a large difference was observed in the thermal properties of polymers obtained between the two catalyst systems.
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    URL: http://dx.doi.org/10.1007/s002890050017
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  • 21
    Electronic Resource
    Electronic Resource
    Enzyme-catalyzed peptide syntheses in aqueous polymer two-phase systems (1997)
    Springer
    Polymer bulletin 38 (1997), S. 49-53 
    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: Abstract. Peptide synthesis in the aqueous polymer two-phase system was examined. Water soluble polymers adopted were dextran and polyethyleneglycol (PEG). By the modification of a proteolytic enzyme, trypsin, with dextran carrying a very small number of carboxyl groups, a separation of the enzyme from its peptide product, N-benzoyl-L-arginine glycinamide, which is relatively more soluble in a PEG phase could be realized. This separation drastically reduced a so-called "mass-law" effect, and increased the yield of the reaction product. The aqueous polymer two-phase system would be useful to enhance the usefulness of biocatalysts in organic syntheses.
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    URL: http://dx.doi.org/10.1007/s002890050018
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    Effect of the crosslinking with 1,1,1-trimethylolpropane trimethacrylate on 5-fluorouracil release from poly(2-hydroxyethyl methacrylate) hydrogels (1997)
    Springer
    Polymer bulletin 38 (1997), S. 55-62 
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    ISSN: 1436-2449
    Keywords: Key words: Poly(2-hydroxyethyl methacrylate) (PHEMA) – 5-fluorouracil (5-FU) – 1,1,1-trimethylolpropane trimethacrylate (TPT) – hydrogel – controlled release – diffusion coefficient
    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: Abstract. The aim of this study is to examine the influence of crosslinking density on 5-Fluorouracil release from poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels crosslinked with 1,1,1-trimethylolpropane trimethacrylate (TPT). PHEMA hydrogels were synthesized by bulk polymerization with different proportions of TPT (1 – 10 wt%) as crosslinker agent and ammonium persulphate as initiator, enabling polymerization in the feed mixture in the presence of water. As a result, 5-FU could be trapped by including it as a sodium salt in the feed mixture of polymerization. Discs with 5-FU loads between 1 – 16 mg/disc were obtained. Swelling and 5-FU release kinetics studies were carried out in saline solution at 310 K. The diffusion studies were in accordance with Fick's second law during the initial stages, enabling the diffusion coefficients of the process to be determined. The time required for discs to reach total 5-FU release was between 35 h and 160 h and was a function of crosslinking density of the gels and 5-FU load of the discs.
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    Effect of surfactant concentration, pH, and shear rate on the rheological properties of aqueous systems of a hydrophobically modified chitosan and its unmodified analogue (1997)
    Springer
    Polymer bulletin 38 (1997), S. 71-79 
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    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: Abstract. Oscillatory shear, shear relaxation and viscosity experiments have been carried out on semidilute solutions of chitosan and on a hydrophobically modified analogue (HM-chitosan) in 1% acetic acid. This was done in the presence of various amounts of cetyltrimethylammonium bromide (CTAB) and at different pH values. All the rheological measurements on the HM-chitosan solutions revealed significant polymer-surfactant interaction and pH effects. The observed rheological effects were least pronounced at pH ≈ 4, while a strong viscoelastic response was found at pH values of 1 and 5 in HM-chitosan solutions of low surfactant concentration. At these conditions, significant shear-thinning effects were observed. In semidilute solutions of unmodified chitosan, the influence of pH, surfactant concentration and shear rate on the rheological properties was moderate or insignificant.
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    URL: http://dx.doi.org/10.1007/s002890050021
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    Electrical conductivity of polystyrene/styrene-butadiene block copolymer blends containing carbon black (1997)
    Springer
    Polymer bulletin 38 (1997), S. 95-100 
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    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: Abstract. The electrical resistivity and mechanical properties of carbon black (CB)-filled polystyrene (PS)/styrene-butadiene block copolymer (SB) blends have been studied. Good electrical performance was achieved with pure SB and PS/SB blends indicating an inhomogeneity of these materials and the heterogeneous micro-dispersion of the CB particles. The percolation threshold of the filler inside SB or PS/SB blends is around 3.6 wt%, which is lower than that expected for incompatible PS/PBD blend. The addition of small amount CB decreases the elongation at break of PS/SB blends indicating some disturbance at the interface of these compatible material.
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    Homo-, co- and terpolymerization of 1,5-hexadiene using a methylalumoxane activated mono-Cp-amido-complex (1997)
    Springer
    Polymer bulletin 38 (1997), S. 141-148 
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    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: Abstract. Homo- and copolymerizations of 1,5-hexadiene with ethene and styrene using halfsandwich metallocene catalyst Me2Si(Me4Cp)(N-tert.-butyl)TiCl2/MAO (Cp = cyclopentadienyl, Me = methyl, MAO = methylalumoxane) were investigated. According to 13C-NMR spectroscopic microstructure analysis, cyclopolymerization of 1,5-hexadiene afforded randomly distributed cis- and trans-cyclopentane rings in the homo- and copolymer backbone. 1,5-hexadiene incorporation reached 52 mol-%. The ratio of vinyl side chains to cyclopentane rings was controlled by 1,5-hexadiene concentration, where low 1,5-hexadiene concentration promoted cyclopolymerization. Copolymer glass transition temperatures increased with increasing content of cyclic units in the backbone. Styrene was used successfully as termonomer in ethene/1,5-hexadiene polymerization, resulting in a semicrystalline terpolymer with cyclic and styrenic units in the polymer backbone.
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    Synthesis and properties of polyurethanes containing phosphatidylcholine analogues in the main chains and long-chain alkyl groups in the side chains (1997)
    Springer
    Polymer bulletin 38 (1997), S. 133-140 
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    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: Abstract. New phospholipid polyurethanes containing phosphatidylcholine analogues in the main chains and octyl or oleyl groups in the side chains were synthesized by the addition polymerization of diols, bis[2-(2-hydroxyethyldimethylammonio)ethyl]2-octyl-1,3-propanediphosphate or bis[2-(2-hydroxyethyldimethylammonio)ethyl]2-oleyl-1,3-propanediphosphate, with diisocyanates such as 4,4′-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), and 2,4-tolylene diisocyanate (TDI). The new phospholipid diols and polyurethanes were characterized by their IR and 1H-NMR spectral data and elemental analysis. The new phospholipid polyurethanes exhibit common polyelectrolyte viscosity behaviours revealed by viscosity measurements. Moreover, π-A isotherms for these polyurethanes were also prepared.
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    Photoinitiated cationic ring-opening polymerization of a cyclosiloxane (1997)
    Springer
    Polymer bulletin 38 (1997), S. 165-168 
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    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: Abstract. Hexamethylcyclotrisiloxane was found to undergo photoinitiated cationic ring-opening polymerization in solution and bulk, upon exposure to UV radiation, in the presence of either sulfonium or iodonium salts or an iminosulfonate derivative. Glass transition temperatures were below − 100 °C. Molecular weights, determined by size exclusion chromatography relative to polystyrene standards, increased with photolysis lamp intensity. Use of an iodonium photoinitiator afforded poly(dimethylsiloxane) with Mn = 172,000. Polymerization of hexamethylcyclotrisiloxane was accompanied by a small increase in volume (3 – 4%).
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    An alternating copolymer for a blue light-emitting diode (1997)
    Springer
    Polymer bulletin 38 (1997), S. 169-176 
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    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: Abstract. An alternating copolymer composed of 9,9′-dihexylfluorene and N-2-ethylhexyl carbazole was synthesized to use as an emissive polymer in a light-emitting diode (LED). The copolymer is soluble in organic solvents and spin-cast to make a fine film. An LED fabricated by sandwiching the alternating copolymer between indium-tin oxide and aluminum emits a white color with the full width at half maximum of 150 nm. The electroluminescence spectrum becomes simplified to have an emission peak at 460 nm for fine blue color when the copolymer is blended with poly(vinylcarbazole) with a ratio of 1 to 4 before the use as an emissive layer. The forward bias turn-on voltage for the LED is 13, and quantum efficiency is 0.002%.
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    IR study of hydrogen bonding in novel liquid crystalline epoxy/DGEBA blends (1997)
    Springer
    Polymer bulletin 38 (1997), S. 439-445 
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    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: Abstract. The hydrogen bonding of LCE/DGEBA blend was studied using FT-IR. IR spectra of hydroxyl region and carbonyl region were investigated according to the content of LCE. IR spectra of LCE/DGEBA blend before and after curing were compared. Most hydroxyl group in DGEBA rich blends formed intermolecular or intramolecular hydrogen bonding after curing, while free hydroxyl group was present in LCE rich blends. Intramolecular hydrogen bonding was popular in DGEBA rich blends due to the conformational reason. Most carbonyl group was hydrogen bonded with hydroxyl or amine group after curing and the fraction of hydrogen bonded carbonyl was high in DGEBA rich blends.
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    A route to polysiloxanes with pendant imidazole groups Hydrosilylation of N-allylimidazole hydrochloride with methyldichlorosilane (1997)
    Springer
    Polymer bulletin 38 (1997), S. 371-378 
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    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: Abstract. Hydrosilylation of N-allylimidazole hydrochloride by methyldichlorosilane (MeCl2SiH) under mild conditions leads to a high yield of N-[γ-(methyldichlorosilyl)propyl]imidazole hydrochloride – highly reactive monomer for synthesis of imidazole modified polysiloxanes. This compound was used as the substrate for the generation of new cyclooligosiloxanes with the imidazole group attached through the trimethylene bridge to a siloxane ring. The anionic ring-opening polymerization of these cyclics permits the controlled synthesis of polysiloxanes with imidazole groups pendant to the polymer chain.
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    Novel aprotic polar polymers 1. Synthesis of aliphatic polysulfoxides (1997)
    Springer
    Polymer bulletin 38 (1997), S. 379-386 
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    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: Abstract. Aliphatic polysulfoxides having sulfoxide groups in the main chain were prepared by the selective oxidation of aliphatic polysulfides using aqueous hydrogen peroxide in chloroform. Degree of oxidation to sulfoxides was calculated from the integral ratios of methylene protons adjacent to sulfur atoms in 1H-NMR spectra. Poly(hexamethylene sulfoxide) was subjected to Swern oxidation of primary or secondary alcohols, in which 1-octanol and 6-undecanol were oxidized to give octanal and 6-undecanone, respectively, in quantitative yields.
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    Electrical conductivity in iodine-doped nonconjugated polyanilinefurfural (1997)
    Springer
    Polymer bulletin 38 (1997), S. 573-577 
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    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: Abstract. Polyanilinefurfural (PAF) has been prepared. Its chain contains aromatic and furan rings, but the backbone is nonconjugated. However, when treatment with iodine, the color of PAF turns metallic black, and PAF becomes electrically conductive. The electrical conductivity of I2-doped PAF can reach 10−3 S ⋅ cm−1 which is more than 10 orders of magnitude higher than what was observed at the pristine state. The effects of iodine content on the conductivity of PAF and the conductivity stability were investigated. FTIR spectra, U.v./vis absorption spectra, E.s.r. measurement and X.p.s. measurement of the undoped and doped PAF were studied. This paper will demonstrate that: if given appropriate substituents and dopants, significant charge transfer may be expected even for nonconjugated polymers and it may display electronic conductivity to a certain level.
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    Factor analysis in the NMR characterization of multicomponent polymers (1997)
    Springer
    Polymer bulletin 38 (1997), S. 555-562 
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    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: Abstract. Factor analysis has been found to be suitable for the analysis NMR data of polymers which contain multiple components. Two series of ethylene/propylene copolymers have been studied by this technique. In general, the number of components that can be resolved from NMR data depends on both the quality and the quantity of available experimental data.
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    The role of complex formation in the anionic polymerization of l-lactide (1997)
    Springer
    Polymer bulletin 38 (1997), S. 609-612 
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    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: Abstract. The rate lowering effect of crown ethers in the anionic polymerization of l-lactide is interpreted by the formation of activated monomer-cation complex. This interpretation is supported by molecular mechanics calculations. The formation of a 1 : 1 complex between lithium ion and l-lactide in THF was proved by 1H NMR and the formation constant was measured to be 3.8 M−1.
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    Application of a statistical method to study the spherulitic growth of polymer blends (1997)
    Springer
    Polymer bulletin 38 (1997), S. 601-608 
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    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: Abstract. This paper has two objectives. Firstly, to plan experimental blends (based on PVDF, PMMA and PVA) according to a statistical method proposed by Scheffé and subsequently to apply the model to the study of the spherulitic growth of PVDF with the aim of assess its suitability. In case it proved adequate, a simple method would become for the design of new materials from the polymer under study.
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    An investigation into the synthesis of polycarbazole squaraine derivatives (1997)
    Springer
    Polymer bulletin 38 (1997), S. 493-499 
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    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: Abstract. The polycondensation of squaric acid with 1,2-(9-Ethylcarbazol-3-yl)ethene and N-ethyliminostilbene in polyphosphoric acid yielded insoluble polymers which included substituted phosphate groups on the phenyl rings. The presence of phosphorus in these polymers was identified using solid-state 31P NMR and EDAX techniques. Furthermore the phosphate groups were not ionic, hence no charge-balancing anions were present. Both polymers did not electrically conduct but exhibited dielectric breakdown values of 0.1 and 0.06 MV cm−1 respectively.
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    Comparative study on the lamellar crystal structure of high and low density polyethylenes (1997)
    Springer
    Polymer bulletin 38 (1997), S. 707-714 
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    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: Abstract. A comparative study was undertaken on well characterized HDPE and LDPE samples in order to obtain a better understanding of the morphology of the crystalline phase. Thickness of the lamellae was determined by WAXS. The melting points were calculated by empirical and Gibbs-Thomson equations, considering either folded or extended chains, and compared to DSC data. The results confirm that in HDPE the chains are folded, the segment between folds containing about 100 carbon atoms, while in LDPE, the chains are extended, with segments of about 73 carbon atoms in the crystalline core, linked to the paracrystalline layer and amorphous zones, which contain long folds and chain ends, as proposed in the 3-phase model by Vile et al.
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    The synthesis and thermotropic liquid crystalline behavior of the novel poly(aryl ether ketone)s containing chloro-side group (1997)
    Springer
    Polymer bulletin 38 (1997), S. 621-625 
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    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: Abstract. The novel poly(aryl ether ketone)s containing chloro-side group were synthesized by nucleophilic substitution reactions of 4,4′-biphenol and chlorohydroquinone with either 4,4′-difluorobenzophenone (BP/CH/DF) or 1,4-bis(p-fluorobenzoyl)benzene (BP/CH/BF) and their thermotropic liquid crystalline properties were characterized by a variety of experimental techniques. The thermotropic liquid crystalline behavior was observed in the copolymers containing 50 and 70% biphenol. Melting transition (Tm) and isotropization transition (Ti) both appeared in the DSC thermograms. A banded texture was formed after shearing the sample in the liquid crystalline state. The novel poly(aryl ether ketone)s had relatively higher glass transition temperature (Tg) in the range of 168 ∼ 200 °C and lower melting temperature (Tm) in the range of 290 ∼ 340 °C. The thermal stability (Td) was in the range of 430 ∼ 490 °C.
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    Synthesis and characterization of wholly aromatic polyamides containing pendent amino and cyano groups (1997)
    Springer
    Polymer bulletin 38 (1997), S. 635-642 
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    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: Abstract. The new pyrazole-ring containing diamine monomer with amino and cyano groups, 1,3-di-p-aminophenyl-4-cyano-5-aminopyrazole (PYA), was prepared from 4-nitrobenzoyl chloride and 4-nitrophenyl hydrazine with 4 steps. The monomer was converted to polyamides with terephthaloyl chloride and isophthaloyl chloride. The amino and cyano groups on the pyrazole-ring were not affected during polymerization. The synthesized polyamides having intrinsic viscosities of 0.92 – 1.18 dL/g were amorphous, and soluble in polar aprotic solvents and boiling acetone and THF. The polymers had high glass transition temperatures and high thermal stability. 5% weight loss temperatures in nitrogen occurred around 490 °C, but these polymers are partially degraded at 300 °C in air due to the amino group on the pyrazole-ring.
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    On-line HPLC 1H NMR coupling for the analysis of fatty alcohol ethoxylates (1997)
    Springer
    Polymer bulletin 38 (1997), S. 673-679 
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    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: Abstract. The characterisation of fatty alcohol ethoxylate based surfactants by on-line LC-NMR coupling is described. Different surfactant mixtures were separated by a mixed exclusion-adsorption method of liquid chromatography and simultaneously characterised by 1H-NMR spectroscopy. Information about the degree of oligomerisation of the ethylene oxide chain and the chemical structure of the endgroups can be obtained in a one-step experiment.
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    Synthesis and characterization of polyamides based on cubane-1,4-dicarboxylic acid (1997)
    Springer
    Polymer bulletin 38 (1997), S. 651-655 
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    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: Abstract. The direct polycondensations of cubane-1,4-dicarboxylic acid with 1,4-phenylenediamine (2 a), 4,4′-oxydianiline (2 b), 4,4′-sulfonyldianiline (2 c), and 9,9′-bis(4-aminophenyl)florene (2 d) were carried out in N-methyl-2-pyrrolidone/pyridine containing triphenylphosphite and lithium chloride at 110 °C for 9 h. Polyamide 3 a obtained from 2 a was scarcely soluble in organic solvent even during heating, and was soluble only in conc-H2SO4, whereas 3 c and 3 d derived from 2 c and 2 d, respectively, were readily soluble in N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethylsulfoxide. After treating polyamide 3 d with the rhodium complex catalyst in NMP, cubane units were quantitatively converted into cyclooctatetraenes.
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    Separation of block copolymers from parent homopolymers by means of liquid chromatography at the critical adsorption point (1997)
    Springer
    Polymer bulletin 38 (1997), S. 681-688 
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    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: Abstract. The characterization of a block copolymer consisting of blocks of tetrahydrofuran, THF, and methyl methacrylate, MMA, was attempted with the aid of liquid chromatography, LC, at the critical adsorption point, CAP. The conditions applying to the CAP at 30 °C for the homopolymers are: PTHF: eluent composition: THF : acetonitrile = 50 : 50, w/w; column: Nucleosil C18. PMMA: eluent composition: THF : n-hexane = 81.8 : 18.2, w/w; column: bare silica gel. The presence of homo PTHF and of homo PMMA in the crude block copolymer was evidenced. Moreover, chromatography at the CAP for PMMA showed that the block copolymer contains multiblock (triblock) fractions. The formation of triblock copolymer is expected when the polymerization of MMA is terminated (partially) by combination. In conclusion, LC at the CAP is a powerful tool to characterize block copolymers regarding the presence of homopolymer and multiblock (triblock) fractions.
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    New thermoplastic polyolefin elastomers from the novel Multicatalysts Reactor Granule Technology: their relevant physical-mechanical properties after crosslinking (1997)
    Springer
    Polymer bulletin 38 (1997), S. 701-705 
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    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: Abstract. A new process for the sequential copolymerization of olefins has been devised (Multicatalysts Reactor Granule Technology); it allows the synthesis of thermoplastic polyolefin elastomers having polypropylene from Ti-based catalysts and ethylene-propylene rubbers from metallocenes. Such new materials have been cured with peroxides and the relevant mechanical properties measured in comparison with those of heterophasic copolymers synthesized with traditional catalysts. It resulted that the new materials present an improved balance between strength and elasticity, especially at high temperature.
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    Synthesis of graft copolymers by ring-opening polymerization of 2-nonyl- and 2-phenyl-2-oxazoline initiated by macroinitiators containing benzylchloride functions (1997)
    Springer
    Polymer bulletin 38 (1997), S. 657-664 
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    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: Abstract. Graft copolymers with poly(2-nonyl-2-oxazoline) and poly(2-phenyl-2-oxazoline) graft arms have been synthesized using the "grafting from" method. Slightly branched statistical copolymers of isobutene and (m,p)-chloromethylstyrene, synthesized cationically, as well as linear homo-poly((m,p)-chloromethylstyrene) have been used as macroinitiators for the ring-opening polymerization of the substituted oxazolines. The graft copolymerizations were carried out in bulk and in benzonitrile solutions with and without addition of potassium iodide. The influence of the reaction conditions on the rate of polymerization and the different reactivities of 2-nonyl-2-oxazoline and 2-phenyl-2-oxazoline were discussed.
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    The effect of stereoregularity on the thermal behavior of poly(methacrylic acid)s I. Thermal analysis studies (1997)
    Springer
    Polymer bulletin 39 (1997), S. 85-91 
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    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: Abstract. The thermal degradation of a series of poly(methacrylic acid)s (PMADs) with different tacticities has been investigated under inert atmosphere. All the samples showed two main degradation stages. The first decomposition process of isotactic PMAD consisted of the formation of anhydride groups, almost quantitatively, by dehydration. In the case of PMADs with lower isotactic content, the elimination of water between neighboring carboxylic groups is less favored and the anhydridization shifts at higher temperatures where other degradation reactions may take place at the same time. The temperatures of maximum volatilization rates at the second step of decomposition increased in the order isotactic 〉 atactic 〉 syndiotactic.
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    Rheometrical behavior and equilibrium swelling in NR/BR/CEL II composites (1997)
    Springer
    Polymer bulletin 39 (1997), S. 117-124 
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    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: Abstract. Natural rubber/butadiene rubber/cellulose II blends (NR/BR/CEL II) have been obtained by coprecipitation of the rubber latex-cellulose xanthate mixtures through acidulation. The elastomer ratio NR/BR has been varied from 100/0 to 25/75 and the cellulose content from 0 to 25 phr. The cure behavior of the compositions has been investigated by a Monsanto Oscillating Disk Rheometer. The results are a function of cellulose filler, NR, and BR contents. Some compositions were also analysed by equilibrium swelling in order to investigate polymer-filler interaction. The results show that composites with higher BR contents exhibit higher elastomer-filler attachment.
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    Polymerization by phase transfer catalysis 22. Synthesis of poly(amide-carbonate)s and poly(amide-thiocarbonate)s derived from diphenols with the amide group in the side chain (1997)
    Springer
    Polymer bulletin 39 (1997), S. 9-14 
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    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: Abstract. Poly(amide-carbonate)s and poly(amide-thiocarbonate)s derived from the diphenol-amides N-(2,6-dichloro-4-nitrophenyl)-2,2-bis(hydroxyphenyl)-propylamide (I), N-(2,6-dichloro-4-nitrophenyl)-3,3-bis(hydroxyphenyl)-butylamide (II), and N-(2,6-dichloro-4-nitrophenyl)-4,4-bis(hydroxyphenyl)-pentylamide (III), and phosgene or thiophosgene, have been synthesized under phase transfer conditions using several quaternary ammonium salts as phase transfer catalysts. Benzyltriethylammonium chloride (BTEAC) was effective in practically all cases due the hydrophilicity of this catalysts.
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    Interpolymer complex formation between form I helical and form II helical poly(l-proline) and poly(carboxylic acids) (1997)
    Springer
    Polymer bulletin 39 (1997), S. 45-52 
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    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: Abstract. Interpolymer complex formations between Form II helical poly(l-proline) [PLP(II)] and Form I helical poly(l-proline) [PLP(I)] and poly(carboxylic acids) such as polyacrylic acid (PAA), atatic polymethacrylic acid (at-PMAA), and syndiotatic polymethacrylic acid (st-PMAA) have been studied by FT-IR, X-ray diffraction, and light scattering measurements. It was found that the interpolymer complexes were formed via hydrogen bonding. The helical PLP(II) formed polymer complex more favorably with PAA and at-PMAA having a disordered structure than with st-PMAA having a ordered structure. In contrast, the helical PLP(I) formed polymer complex more favorably with st-PMAA than with PAA and at-PMAA. In addition, PLP(II) helix was destroyed on the complexation with PAA and at-PMAA, but the PLP(II) helix was perserved on the complexation with st-PMAA. However, the PLP(I) helix was all perserved on the complexation with poly(carboxylic acids). These findings could be explained in terms of molecular conformation of the complementary polymers associated with the complex formation.
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    Local motion of crosslinks for poly(methyl methacrylate) gels by the fluorescence depolarization method (1997)
    Springer
    Polymer bulletin 39 (1997), S. 109-116 
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    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: Abstract. Poly(methyl methacrylate) (PMMA) gels labeled at crosslinks with anthracene were prepared. Anthracene fluorescence depolarization was monitored to probe the local motion of crosslinks for PMMA gels at different equilibrium swelling states. The relaxation times and the activation energies of local motion were measured for PMMA gels at the swollen states in various solvents through fluorescence anisotropy decays. The local motion of PMMA gel at crosslinks became faster with the increase of swelling ratio. When the swelling ratios were almost the same, the mobility of crosslinks was the same irrespective of the molecular weights between crosslinks. These results indicate that the local motion of crosslinks for PMMA gel is mainly governed by the segment density of network chains in the vicinity of crosslinks.
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    Influence of the structure and composition on surface tension of aqueous solution of graft copolymers of polyacrylamide backbone and polyalkyleneoxide branches (1997)
    Springer
    Polymer bulletin 39 (1997), S. 73-78 
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    ISSN: 1436-2449
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. Polyacrylamide homopolymers and graft copolymers of poly(acrylamide-g-ethylene oxide) and poly(acrylamide-g-propylene oxide) were synthesized, characterized by SEC, FTIR and 13C-NMR and the behavior of their aqueous solutions was evaluated by surface tension measurements. By using the macromonomer technique, it is more difficult to incorporate poly(propylene oxide) branches than poly(ethylene oxide) branches. Graft copolymers of polyacrylamide and poly(propylene oxide) showed higher reduction of surface tension than poly(acrylamide-g-ethylene oxide) since they present a structure made up of hydrophilic and hydrophobic segments. Poly(acrylamide-g-propylene oxide) exhibits surfactant behavior, and the surface tension of its aqueous solution depends on the poly(propylene oxide) graft chain length and amount.
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    Transition temperature control of liquid crystalline poly(heptene sulphone)s (1997)
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    Polymer bulletin 39 (1997), S. 179-184 
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    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: Abstract. Liquid crystalline poly(heptene sulphone)s containing cholesteryl undecylenic ester and cholestanyl undecylenic ester were synthesized. The polymers displayed cholesteric mesophases during thermal transition. The clearing temperatures were from 114 to 172 °C depending on the molar ratio of mesogenic esters in the polymers.
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    Molecular dimensions of poly(ethylene isophthalate) and poly(ethylene naphthalene-2,6-dicarboxylate) (1997)
    Springer
    Polymer bulletin 39 (1997), S. 257-263 
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    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: Abstract. The rotational isomeric state (RIS) model was used to calculate the molecular dimensions of poly(ethylene isophthalate) (PEI) and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) by introducing new description for aromatic segments and by adopting the statistical weight parameters of PET. The mean square dimension ratios ((〈r2〉0/M)∞) of PEN and PEI were 0.653 and 1.167, respectively, and the entanglement molecular weight (Me) of PEI and PEN were 1850 and 1810, respectively.
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    Effects of cyclization and pendant vinyl group reactivity on the swelling behavior of polyacrylamide gels (1997)
    Springer
    Polymer bulletin 39 (1997), S. 233-239 
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    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: Abstract. A series of polyacrylamide (PAAm) gels were prepared by free-radical crosslinking copolymerization of acrylamide and N,N′-methylenebis(acrylamide) (BAAm) in water at various crosslinker (BAAm) and chain transfer agent (isopropyl alcohol, IPA) concentrations. It was shown that only 5% of the crosslinker used in the feed forms effective crosslinks in the final hydrogels. At BAAm contents as high as 3 mole%, the equilibrium swelling ratio of the gels in water is independent of the crosslinker content in the feed. This is due to the prevailing multiple crosslinking reactions during the gel formation process. At a fixed crosslinker content, the onset of gelation is shifted towards higher conversions and reaction times as the amount of IPA increases. Addition of IPA in the monomer mixture also increases the equilibrium swelling ratio of PAAm gels. It was shown that the gel crosslinking density increases on rising IPA concentration in the feed due to the increasing rate of intermolecular crosslinking reactions.
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    Highly flexible heterophasic copolymers through the novel multicatalysts reactor granule technology (1997)
    Springer
    Polymer bulletin 39 (1997), S. 241-247 
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    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: Abstract. New heterophasic copolymers with high rubber content have been synthesized by combining heterogeneous Ti-based catalysts with metallocenes. The molecular, morphological and mechanical features of these materials were evaluated: it was pointed out that the new copolymers, having more than 60 Wt.% of rubber, perform as reinforced elastomers whereas traditional ones show a more plastomeric behaviour. This suggests that new polyolefin materials can augment rather than compete with the traditional ones.
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    Ethylene-propylene copolymers by a supported Ziegler-Natta catalyst based on TiCl4/MgCl2 (1997)
    Springer
    Polymer bulletin 39 (1997), S. 133-140 
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    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: Abstract. Ethylene-propylene copolymers have been prepared by using Ziegler-Natta catalysts based on TiCl4, MgCl2, PCl3 and (n-Bu)3PO4. The catalysts TiCl4/MgCl2/PCl3 and TiCl4/MgCl2/(n-Bu)3PO4 were prepared by reacting TiCl4 with pretreated MgCl2. The support was prepared by ball milling of MgCl2 with varied amounts of PCl3 or (n-Bu)3PO4. The addition of PCl3 has remarkably increased the MgCl2 surface area in comparison with (n-Bu)3PO4. The effects of PCl3 and (n-Bu)3PO4 on ethylene homopolymerization, ethylene-propylene copolymerization and on copolymer properties were evaluated. The catalyst system containing PCl3 permitted to synthesize propylene-ethylene copolymers with up to 75% (w/w) of propylene and provided control of copolymer crystallinity. The reduction of the copolymer molecular weight distribution suggested that PCl3 acted as an internal donor, poisoning some active catalytic sites.
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    Grafting of side chain liquid crystal monomers onto polyethylene film (1997)
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    Polymer bulletin 39 (1997), S. 489-494 
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    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: Abstract. In order to obtain films of liquid crystalline polymers, a commercial polyethylene film was grafted with acryloyl chloride using γ-irradiation, and two tolane-containing alcohols were reacted with the chloride to obtain the corresponding acrylates. The morphology changes were studied by DSC, X-ray diffractometry and optical microscopy. The crystallinity of polyethylene films decreased by grafting, and mesophase with spherulites was observed over a wide temperature range.
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    Polymer-polymer interaction and modeling (1997)
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    Polymer bulletin 39 (1997), S. 519-526 
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    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: Abstract. The nature of intermolecular interaction in PVC/EVA system was investigated. Bathochromic shifts in infrared region revealed that not only EVA carbonyl but the ester group participates on interaction with PVC chain. These shifts were proportional to acetate content in the copolymer and the composition of EVA in the blend. The PVC group that effectively participates on interaction was not elucidated by infrared spectrometry, but molecular modeling of low molecular weight analogues indicated that hydrogen bonding is the most probable kind of intermolecular interaction present in this system.
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    Application of an association model to the PVC/EVA system (1997)
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    Polymer bulletin 39 (1997), S. 527-534 
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    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: Abstract. A thermodynamic association model was applied to the PVC/EVA system. In this model the enthalpy component is related quantitatively to intermolecular interaction forces. Molecular modeling was applied to obtain the parameters related with interaction forces. The phase diagrams showed lower critical solution temperature (LCST) behavior and also biphasic regions in PVC rich compositions.
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    Synthesis, characterization, and properties of an efficient and selective adsorbent to mercury(II) (1997)
    Springer
    Polymer bulletin 39 (1997), S. 445-452 
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    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: Abstract. The synthesis of a water-insoluble adsorbent resin was carried out by radical polymerization of [2-(methacryloyloxy)ethyl] trimethyl ammonium chloride by using ammonium peroxydisulfate as initiator and N,N′-methylene-bis-acrylamide (MBA) as crosslinking reagent. The adsorbent was characterized by elemental analyses, and FT-IR spectroscopy. The thermal stability was studied in the presence of Hg(II). The ability to bind Hg(II), Cd(II), Zn(II), Pb(II), Cu(II), Cr(III), and U(VI) as well as the maximum adsorption capacity, and elution of the Hg(II) from the loaded resin was studied. At pH 2 the adsorbent retained 95% of Hg(II) from an aqueous solution containing 1 g/L in Hg(II). The retention of other metal ions was lower than 15%. Sorption selectivity from the binary mixtures Hg(II)-Cd(II), Hg(II)-Zn(II), Hg(II)-Pb(II), and Hg(II)-Cr(III) was studied at the optimum sorption pH value.
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    Dendrite polymers from vinyl ether (1997)
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    Polymer bulletin 39 (1997), S. 399-406 
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    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: Abstract. 1-[(2-Vinyloxy)ethoxy]ethyl acetate (1) was prepared by the addition reaction between ethylene glycol divinyl ether and acetic acid. 1 contains both a cationically polymerizable C=C double bond and a dormant initiating moiety for cationic polymerization. It can, therefore, undergo self condensing cationic polymerization in the presence of a Lewis acid activator, such as zinc chloride. Using this procedure, a novel dendritic polymer consisting of vinyl ether was prepared and its hyperbranched molecular structure confirmed by FT-IR and 1H NMR spectra.
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    On a novel molecular microstructure based approach to the extrinsic space charges releasing in polypropylene (PP) (1997)
    Springer
    Polymer bulletin 39 (1997), S. 639-646 
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    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: Abstract. The release of the extrinsic charges produced when applying an electric stress has been studied for four polypropylene samples of distinct well controlled molecular microstructure by Thermal Stimulated Discharge Current (TSDC), with the aim of stating the correlation between the ρ relaxation (intensity and temperature) and the tacticity induced polymer microstructure, and of, demonstrating that the traps of space charges are not chain defects as usually proposed but that they relate to some normal local chain configurations. The results are discussed in the light of the space charge distributions as measured in earlier recent work.
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    Regioselective introduction of β-galactoside branches into chitosan and chitin (1997)
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    Polymer bulletin 39 (1997), S. 543-549 
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    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: Abstract. β-d-Galactoside branches have been introduced into chitosan and chitin regioselectively through a series of controlled modification reactions based on N-phthaloyl-chitosan. The glycosylation reaction between a chitosan derivative having a reactive group only at C-6 and an orthoester of d-galactose proceeded efficiently to give a protected product with a degree of substitution up to about 0.5. Deprotection gave a branched chitosan, and the subsequent N-acetylation afforded a branched chitin. Unlike chitosan and chitin, the resulting nonnatural branched polysaccharides were characterized by high affinity for solvents and readily soluble in neutral water. Furthermore, branched chitin was easily degraded by lysozyme.
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    Effective catalysts for polymerization of cyclohexene oxide: Preparation of novel Martin-type pentacoordinate silicates (1997)
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    Polymer bulletin 39 (1997), S. 573-579 
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    Notes: Abstract. The novel dialkylanilinium salts of pentacoordinate Martin-type silicates were prepared. They were found to be air stable catalysts for polymerization of cyclohexene oxide. The preparation of those silicates bearing a bulky substituent such as mesityl group was not successful.
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    Molecular packing of poly(azomethine)s having flexible (n-alkyloxy)methyl side chains in films (1997)
    Springer
    Polymer bulletin 39 (1997), S. 701-705 
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    Notes: Abstract. The molecular packing of poly(azomethine)s having (n-alkyloxy)methyl side chains in films was studied by wide-angle X-ray scattering. Solution-cast films on silicon wafer and melt-sheared films show the same type of molecular packing, i.e. the main chain layers are aligned parallel to the film surface but the main chains are macroscopically isotropic in the film surface plane. In the melt-sheared films, the shear does not orient the main chains but the main chain layers, which can be easily understood by their geometric shapes.
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    Characteristics of permeation and separation of dimethyl acrylamidemethyl methacrylate random and graft copolymer membranes for a benzene/cyclohexane mixture (1997)
    Springer
    Polymer bulletin 39 (1997), S. 733-740 
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. When a benzene/cyclohexane mixture was permeated through poly(dimethyl acrylamide-random-methyl methacrylate) (DMAA-r-MMA) and poly(dimethyl acrylamide)-graft-poly(methyl methacrylate) (DMAA-g-MMA) membranes by pervaporation, the benzene-permselectivity of the DMAA-r-MMA membrane changed from the diffusivity selectivity to the solubility selectivity with increasing DMAA content but DMAA-g-MMA membranes with a high DMAA content had the higher apparent diffusivity selectivity than the apparent solubility selectivity. Furthermore, the apparent solubility selectivity for a benzene/cyclohexane mixture between the DMAA-r-MMA membrane and the DMAA-g-MMA membrane with a high DMAA content was remarkably different. These results were attributed to the difference of structure between the copolymers.
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    Oriented overgrowth of vapour deposited tin on highly oriented PTFE substrates (1997)
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    Polymer bulletin 39 (1997), S. 761-765 
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    ISSN: 1436-2449
    Keywords: metal/polymer interface – friction transfer – ultra-thin films
    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: Abstract. The vapour deposition of tin on highly uniaxially oriented PTFE causes an oriented overgrowth of tin islands. The origin of this orientation is not clear. Classic epitaxy as well as graphoepitaxy seems to be an explanation for the occurring orientation. The appearance of this orientation was observed in a temperature range from −80 °C to 90 °C. An orientation by crystallization from the melt could not be achieved so far. In this short communication, a metal/polymer system is introduced which offers new possibilities to investigate the origin of oriented overgrowth.
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    Polymerization of methyl and phenyl oxazoline initiated with carboxylic acid chlorides (1997)
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    Polymer bulletin 38 (1997), S. 7-13 
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    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: Abstract. Methyl and phenyl oxazoline were polymerized using carboxylic acid chlorides as initiators. The first step of the reaction was shown to consist in a fast reaction of the carboxylic acid chloride with the oxazoline. Resulting product, which was isolated and identified, act as the proper initiator of the polymerization of the oxazoline, which proceeds via covalent or, when chloride counter ion is replaced with iodide or triflate, ionic active species. Apparent rate constants of the chain growth were determined. When methacryloyl chloride is used as initiator macromonomers are obtained, which were copolymerized with styrene. Macromolecular carboxylic acid chlorides initiate the polymerization of oxazolines, yielding graft polymers.
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    Photodegradation of chain halogenated polystyrene: Poly(c-chloro and c-bromostyrene)s (1997)
    Springer
    Polymer bulletin 38 (1997), S. 191-196 
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    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: Abstract. The photodegradation of films of poly chain-chlorostyrene (PCCS) and poly chain-bromostyrene (PCBS) achieved by exposure to 254-nm radiation under dynamic vacuum was studied. The minor gaseous products obtained were hydrogen halides and monomer. The polymers were investigated by ir, gel permeation chromatography, and microanalysis. Both polymers undergo main chain scission. The ir spectra of the degraded polymers indicate the presence of unsaturated species. An initial α-carbon-halogen bond fission is required to account for the present reaction products. Possible mechanism of the various photoreactions are discussed.
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    URL: http://dx.doi.org/10.1007/s002890050037
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    Compatibilization of low-density polyethylene/polystyrene blends by segmented EB(PS-block-EB)n block copolymers (1997)
    Springer
    Polymer bulletin 38 (1997), S. 203-210 
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    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: Abstract. Hydrogenated segmented poly[butadiene-block-(styrene-block-butadiene)n] block copolymers, which were developed by use of a polymeric iniferter technique, were tested on their compatibilizing effectiveness for (10/90) LDPE/PS blends. They were found to be effective compatibilizers for this mixture, already giving a pronounced improvement in both tensile strength and strain of the blend at block copolymer concentrations of one percent. A concentration of five weight percent of segmented block copolymer provided a tenfold improvement in blend toughness. The effectiveness of the segmented block copolymers was found be dependent on the block copolymer composition. Block copolymer compositions of close to 50 : 50 EB : PS gave the best results.
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    Dynamic mechanical behaviour of random copolymers of a LC-methacrylate and octyl methacrylate (1997)
    Springer
    Polymer bulletin 38 (1997), S. 219-226 
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    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: Abstract. The dynamic mechanical behaviour of random copolymers of LC monomer-1-(hexyloxycarbonyl)ethyl 4-[4-(methacryloyloxy)benzoyloxy]benzoate (HB) and octyl methacrylate (OMA) was studied in the main transition and flow regions. Even though the aliphatic end groups of the side chain of HB and OMA are roughly the same, the T g temperature of poly(HB) is ∼ 80 K higher than that of poly(OMA); this fact is due to the presence of the stiff phenyl benzoate mesogenic group in the side chain of HB. With increasing content of OMA in the copolymer the superimposed curves of the storage G′ p and loss G′′ p moduli at a constant temperature shift towards shorter frequencies. It has been shown that this shift is mainly due to an increase of the free volume in the copolymers with increasing content of OMA. While HB monomer shows liquid crystalline (LC) properties, its polymer (poly(HB)) and random copolymers with OMA show only isotropic thermal behaviour because no flexible spacer is present in the side chain of HB which would decouple the main chain and mesogenic group motions. This means that neither the homopolymer of HB, nor its copolymers with a flexible comonomer retain the LC properties of the starting LC monomer, HB.
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    A new approach to anisotropic conductive networks A liquid-crystalline side-chain polymer containing a thienyl moiety at the extremity of its side chain (1997)
    Springer
    Polymer bulletin 38 (1997), S. 551-554 
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    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: Abstract. A liquid-crystalline bifunctional monomer with two different reactive moieties was prepared by esterification of 4-(6-(acryloyloxy)hexyloxy)benzoic acid and 4-[11-(3-thienyl)undecyloxy]-4′-hydroxybiphenyl. A mesogenic side-chain polyacrylate containing a thienyl moiety at the extremity of its side chain was obtained by radical polymerization of the monomer. The subsequent reaction of the thienyl moiety with FeCl3 leads to the formation of an anisotropic network with a poly(thiophene) unit.
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    Asymmetric polymerization of N-triphenylmethylmaleimide with chiral anionic initiators (1997)
    Springer
    Polymer bulletin 38 (1997), S. 509-514 
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    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: Abstract. Asymmetric polymerization of N-triphenylmethylmaleimide (TrMI) is performed with chiral anionic initiators in tetrahydrofuran and toluene at − 78 and 0 °C to obtain optically active polymer. It is found that the (S)-(+)-1-(2-pyrrolidinylmethyl) pyrrolidinelithium [Li-(+)-PMP] and lithium (−)-menthoxide are effective for the asymmetric polymerization of N-triphenylmethylmaleimide in THF. The polymers obtained are characterized by circular dichroism (CD). It is inferred that the propagation reaction of polymerization of TrMI with Li-(+)-PMP is dominated by ion pair mechanism and meanwhile free ion mechanism cannot be ignored based on GPC analysis.
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    Synthesis and characterization of some polyazomethine conducting polymers and oligomers (1997)
    Springer
    Polymer bulletin 39 (1997), S. 1-7 
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    ISSN: 1436-2449
    Keywords: Key words: polyazomethines – oligomers – conducting polymers – synthesis – characterization
    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: Abstract. Polyazomethine polymers were prepared from the polycondensation of terephthaldehyde with different diamines, namely, benzidine, 2,3-diaminopyridine, 1,4-diaminoanthraquinone and 3,5-diamino-1,2,4-triazole. The electrical conductivities of the polymers were studied with doping with H2SO4 and 5% I2 together with the undoped polymers. The crystallinity and morphology of the polymers were studied using XRD and scanning electron microscopy. A comparative study of the electrical conductivities of oligomers of polyazomethines and those of their corresponding polymers was performed.
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    Syntheses and radical ring-opening polymerizations of 1,1-bis(hydroxymethyl)-2-vinylcyclopropane and 1,1-bis(methoxymethyl)-2-vinylcyclopropane (1997)
    Springer
    Polymer bulletin 39 (1997), S. 141-148 
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    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: Abstract. Syntheses and radical ring-opening polymerization of 1,1-bis(hydroxymethyl)-2-vinylcyclopropane (1 a) and 1,1-bis(methoxymethyl)-2-vinylcyclopropane (1 b) were examined. Novel polymers bearing hydroxyl and methyl ether moieties in the side chains as well as olefinic moieties in the main chain were obtained. The main structure of the polymers, obtained by radical polymerization, originated from the cleavage of the cyclopropane ring near the hydroxymethyl or methoxymethyl groups. The difference in the two-center energies and bond orders of the C−C bonds of the cyclopropane ring well explained the selectivity in the direction of the cleavage. The number-average molecular weights (Mˇ n) of poly(1 a) and poly(1 b) were 94 200 and 11 200 in the polymerization in bulk at 60 °C, respectively. The intermolecular hydrogen bonding of 1 a might increase the radical polymerizability. The oxygen permeability of poly(1a) was 6.19 mL ⋅ 20 mm ⋅ m−2 ⋅ day−1 ⋅ atm−1 at 35 °C, demonstrating that poly(1 a) could be a good oxygen barrier material.
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    Radical polymerization of (trimethylsilylethynyl)styrene and thermal properties of polystyrene with ethynyl group (1997)
    Springer
    Polymer bulletin 39 (1997), S. 173-178 
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    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: Abstract. The radical polymerizations of 2-, 3-, and 4-(trimethylsilylethynyl)styrenes (1 a – c) and copolymerizations of 1 a – c (M1) with styrene (M2) have been studied. Copolymerization parameters were determined as r1 = 1.22 and r2 = 0.54 for 1 a, 1 = 1.10 and r2 = 0.90 for 1 b, and r1 = 1.42 and r2 = 0.38 for 1 c. The deprotection of the trimethylsilyl groups in poly[(trimethylsilylethynyl)styrene] (2 a – c) and poly[(trimethylsilylethynyl)styrene-co-styrene] (4 a – c) using (C4H9)4NF smoothly proceeded to yield poly(ethynylstyrene) (3 a – c) and poly(ethynylstyrene-co-styrene) (5 a – c), respectively, which underwent curing reactions at elevated temperature to form crosslinking polystyrenes.
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    Surface activity of water soluble amphiphilic chitin derivatives (1997)
    Springer
    Polymer bulletin 39 (1997), S. 209-215 
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    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: Abstract. Chitin was derivatized to extend its applications in the field of water soluble systems. It was first carboxymethylated and then alkylated. Two technics were used for that purpose: ionic surfactants playing the role of counterions form an electrostatic complex, and covalent derivatization. The difference between covalent alkylation and dynamic association (SPEC) is discussed in relation with the length of the alkyl chain and the density of alkylation.
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    Study of siloxane-modified epoxy resin using thermally stimulated current(II) (1997)
    Springer
    Polymer bulletin 39 (1997), S. 193-199 
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    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: Abstract. Thermally stimulated current (TSC) and relaxation map analysis (RMA) was used to characterize the low temperature relaxation of epoxy resin modified with siloxane oligomers. In aminopropyl-terminated siloxane oligomer (ATSO) the β-relaxation of epoxy resin and the glass transition temperature of siloxane oligomer were folded regardless of the concentration of diphenyl. The β-relaxation of epoxy resin and the glass transition temperature of oxiranylmethoxy-terminated siloxane oligomer (OTSO) were folded and shifted to higher temperature as the concentration of diphenyl in siloxane oligomer increased. In the systems containing of diphenyl in siloxane oligomer a new relaxation peak due to the space charge was observed in the range of − 80 °C to − 50 °C and − 30 °C to 5 °C. As the concentration of diphenyl increased the compensation temperature (Tc) and the degree-of-disorder (DOD) were increased while the compensation time, τ c was decreased.
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    Microwave assisted polymerisation of phenylacetylenes (1997)
    Springer
    Polymer bulletin 39 (1997), S. 333-337 
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    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. Methathesis Polymerisation of phenylacetylenes using in situ generated (arene)M(CO)3 complexes under unconventional microwave energy condition was achieved successfully. The reaction time was reduced to 1 hour in contrast to refluxing conditions of 24 hours.
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    Transition metal complex induced morphology change in an ABC-triblock copolymer (1997)
    Springer
    Polymer bulletin 39 (1997), S. 361-368 
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    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 short 1,2-polybutadiene center block of the ternary polystyrene-block-polybutadiene-block-poly(methyl methacrylate) S45B6M49 225-triblock copolymer (subscripts indicating the weight fractions and the superscript indicating the total molecular weight in kg/mol) has been selectively modified by complexation with metal complexes of two different transition metals, namely Pd and Fe. These modifications cause significant variations in the microphase morphology. The original ls-morphology (spheres at lamellar interphase) belonging to the lamellar class changes via a cocontinuous morphology in the case of the Pd-complex to a morphology belonging to the cylindrical class for the Fe-complex.
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    Kinetics of formation of polyurethane/polymethylmethacrylate grafted semi-interpenetrating polymer networks based on the functional prepolymers (1997)
    Springer
    Polymer bulletin 39 (1997), S. 339-346 
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    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 kinetics of formation of the polyurethane network by crosslinking the polyurethane prepolymer in polyurethane/polymethacrylate grafted semi-interpenetrating networks (semi-IPN) was monitored by Fourier transform infrared spectroscopy, and the kinetic parameters were thus determined. It was found that carboxylic groups in the hard segments of the Pu component substantially decrease the reaction rate and increase the activation energy. Tertiary amine groups in the PM component catalyse the crosslinking reaction. The PM component acts as a diluent in the mixture of PU and PM reducing the reaction rate and increasing the activation energy of the corsslinking reaction. At temperatures below the Tg of the PM component, the reaction of formation of IPN becomes diffusion controlled.
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    Synthesis of polystyrene/silica gel polymer hybrids by in-situ polymerization method (1997)
    Springer
    Polymer bulletin 39 (1997), S. 303-310 
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    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. Homogeneous polystyrene and silica gel polymer hybrids were prepared by in-situ radical polymerization method. Styrene monomer was introduced into a sol-gel reaction mixture of tetramethoxysilane (TMOS) and the polymerization was initiated by Azobisisobutyronitrile (AIBN), while sol-gel reaction of TMOS proceeded to form a silica gel. The homogeneity of the hybrids was found to be dependent on the amount of the acid catalyst. The homogeneity was confirmed quantitatively by measuring porosity of charred hybrids with nitrogen porosimetry method. It was found that polystyrene was dispersed at a nano-meter level in the silica gel matrix.
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    Synthesis of novel organoboron polymers by haloboration polymerization of bisallene compounds and their reactions (1997)
    Springer
    Polymer bulletin 39 (1997), S. 295-302 
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    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. Novel organoboron polymers were prepared by haloboration polymerization of bisallene compounds. The polymers obtained have allylborane halide units in their main chain and can be expected as a novel type of reactive polymers. For example, the polymer prepared by haloboration polymerization between tribromoborane (1) and 1,2,10,11-dodecatetraene (2 b) was subjected to chain transformation reaction (dichloromethyl methyl ether rearrangement) to give the corresponding polyalcohol or polyketone. Haloboration-phenylboration polymerization of aliphatic bisallenes by using diphenylbromoborane also gave the corresponding polymers.
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    Anionic polymerization of vinylsilanes VII. Effects of N,N,N',N'-tetramethylethylenediamine on the polymerization of tetravinylsilane (1997)
    Springer
    Polymer bulletin 39 (1997), S. 287-293 
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    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 anionic polymerization of tetravinylsilane (TeVS) was carried out in the presence and absence of N,N,N',N'-tetramethylethylenediamine (TMEDA). Without TMEDA, the polymerization proceeded extremely slowly and the polymer yield was still low even after an extended polymerization time. When TMEDA was added to the system, the polymerization was remarkably accelerated and gelation was suppressed. Such polymerization behavior of TeVS is closely similar to that of methyltrivinylsilane under similar conditions. The effects of TMEDA are explained by its coordination to the propagating end that increases the selectivity in the reaction of the propagating end with vinyl groups.
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    Investigation of adhesive performances by scanning force microscopy (1997)
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    Polymer bulletin 39 (1997), S. 613-620 
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    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: Abstract. In this work an original investigation of the polymer adhesive properties by scanning force microscopy (SFM) is proposed. Polyethylene terephthalate (PET)/ethylene vinylacetate copolymers (EVA) assemblies have been separated using a peel test. SFM (tapping mode) is used to study the adhesive surface (EVA) after the mechanical separation. The topographic analysis allows to determine the average roughness due to the polymer surface deformation. A tentative correlation between the surface deformation and the adherence force is proposed. The result show that the polymer which possess the higher adhesive strength presents the greater surface deformation, measured on the SFM image. A relatively good correlation between the evolution of the adherence force and the variation of the surface topography analysed by SFM is highlighted in this original work.
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    Conductive polyaniline/poly(vinylphosphonic acid) blends (1997)
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    Polymer bulletin 39 (1997), S. 627-632 
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    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: Abstract. In-situ polymerization of aniline in poly(vinylphosphonic acid) (PVPA) resulted in conductive polyaniline/PVPA blends with conductivities in the order of 10−2 S/cm. The blends were characterized by FTIR and UV-vis spectroscopy. Thermogravimetric analysis showed that the blends have good thermal stability.
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    Poly(allylammonium acrylate) as a drug-releasing matrix I. Release of drugs mixed and sintered with the polyelectrolyte complex (1997)
    Springer
    Polymer bulletin 39 (1997), S. 707-714 
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    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: Abstract. A poly(allylammonium acrylate) complex was tested for drug release in aqueous solution. Sintered tablets of the polyelectrolyte complex, mixed respectively with human serum albumin, vitamin B12, 5-fluorouracil and tetracycline, were made and dipped into Dulbecco's PBS (pH 7.3). The release kinetics, followed spectrophotometrically, is poorly reproducible and very different for the different drugs. An explanation of such behaviours is proposed, based on the chemical structures of the drugs and of the polyelectrolyte complex, as well as on two concurrent processes: the drug extraction and the saturation by the buffer of the poorly uniform drug-complex mechanical mixtures.
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    Synthesis of fullerene-containing poly(alkyl methacrylate)s with narrow polydispersities (1997)
    Springer
    Polymer bulletin 39 (1997), S. 661-667 
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    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: Abstract. Copolymers of allyl methacrylate with methyl methacrylate or n-butyl methacrylate were synthesized by group transfer polymerization. The pendant allyl groups of the copolymers were then hydrobrominated, followed by reaction with sodium azide. Fullerene was incorporated via an addition reaction of fullerene with azide group. The resulting fullerene-containing poly(alkyl methacrylate)s have fairly narrow polydispersities.
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    Chowdhury and Stedinger's approximate confidence intervals for design floods for a single site (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 51-63 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A basic problem in hydrology is computing confidence levels for the value of the T-year flood when it is obtained from a Log Pearson III distribution in terms of estimated mean, estimated standard deviation, and estimated skew. In an important paper Chowdhury and Stedinger [1991] suggest a possible formula for approximate confidence levels, involving two functions previously used by Stedinger [1983] and a third function, λ, for which asymptotic estimates are given. This formula is tested [Chowdhury and Stedinger, 1991] by means of simulations, but these simulations assume a distribution for the sample skew which is not, for a single site, the distribution which the sample skew is forced to have by the basic hypothesis which underlies all of the analysis, namely that the maximum discharges have a Log Pearson III distribution. Here we test these approximate formulas for the case of data from a single site by means of simulations in which the sample skew has the distribution which arises when sampling from a Log Pearson III distribution. The formulas are found to be accurate for zero skew but increasingly inaccurate for larger common values of skew. Work in progress indicates that a better choice of λ can improve the accuracy of the formula.
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    Stochastic analysis of multiphase flow in porous media: II. Nummerical simulations (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 94-94 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
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    Structure in fluctuations of large-scale soil moisture climate due to external random forcing and internal feedbacks (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 95-114 
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    ISSN: 1436-3259
    Keywords: Soil moisture ; time scale ; non-Gaussian ; colored-noise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Large-scale fields of soil moisture are forced by atmospheric precipitation and radiative forcing. When these forcing factors are themselves influenced by surface and soil moisture processes, the result is a nonlinear land-atmosphere system with inherent feedback mechanisms that may strongly modulate variability in climate. Given such feedbacks, simple randomness in the forcing factors may be manifested as a complex statistical signature in the surface hydrology. In this paper, we investigate the impacts of non-Gaussian and colored-noise on the probability distribution of soil moisture resulting from the statistical-dynamical land-atmosphere interaction model of Rodriguez-Iturbe et al. (1991). Persistence of hydroclimatologic anomalies as characterized by the correlation time scale of soil moisture is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427910
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    Rain-fall modeling: An Application of Bayesian forecasting (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 115-127 
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    ISSN: 1436-3259
    Keywords: Rainfall-runoff modeling ; transfer response ; dynamic non-linear models ; normal and gamma observational distribution ; predictive performance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The rainfall-runoff modeling is very useful for forecasting purposes. A good methodology for forecasting the future stream flow is a key requirement for designers and operators of water resources systems. A compromise between conceptual and classical time series modeling is applied to model the relationship between rainfall and runoff. The dynamic nonlinear model is composed of a probability distribution describing the observation, a link function relating its mean to the so called state parameters and a system of equations defining the evolution of these parameters. Its Bayesian nature permits to take into account subjective information, making forward intervention, defining monitoring schemes and introducing smoothing facilities. An application using the data of Fartura river's basin is reported. The assessment of the prior distribution is discussed and the predictive performance of the linear and the non-linear models is reported.
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    URL: http://dx.doi.org/10.1007/BF02427911
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  • 92
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    The role of moisture fluctuations in unsaturated transport (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 129-143 
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    ISSN: 1436-3259
    Keywords: Stochastic analysis ; perturbation methods ; unsaturated transport ; heterogeneous porous media
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Within the framework of stochastic theory and the spectral perturbation techniques, three-dimensional dispersion in partially saturated soils with a finite correlation scale of log-hydraulic conductivity is analyzed. The effects of spatial variability of the moisture distribution parameter on the asymptotic spreading behavior of a unsaturated solute plume are assessed. This is accomplished by comparing two asymptotic macrodispersivities and two variance of solute concentration, obtained for a constant moisture content and spatially varied moisture, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427912
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    Multivariate nonparametric resampling scheme for generation of daily weather variables (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 65-93 
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    ISSN: 1436-3259
    Keywords: Nonparametric ; Monte Carlo ; precipitation ; weather
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A nonparametric resampling technique for generating daily weather variables at a site is presented. The method samples the original data with replacement while smoothing the empirical conditional distribution function. The technique can be thought of as a smoothed conditional Bootstrap and is equivalent to simulation from a kernel density estimate of the multivariate conditional probability density function. This improves on the classical Bootstrap technique by generating values that have not occurred exactly in the original sample and by alleviating the reproduction of fine spurious details in the data. Precipitation is generated from the nonparametric wet/dry spell model as described in Lall et al. [1995]. A vector of other variables (solar radiation, maximum temperature, minimum temperature, average dew point temperature, and average wind speed) is then simulated by conditioning on the vector of these variables on the preceding day and the precipitation amount on the day of interest. An application of the resampling scheme with 30 years of daily weather data at Salt Lake City, Utah, USA, is provided.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02428426
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    A mean behavior model of aerobic biodegradation in heterogeneous formation (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 255-266 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract It has been observed that the field biodegradation rates for soluble hydrocarbon plumes are significantly smaller than the aerobic rates observed in the laboratory. It is believed that this difference is related to the fact that in the field oxygen and hydrocarbon must be mixed before the biodegradation reaction can occur, and that the effective degradation rate is controlled by the actual, not mean, concentrations of oxygen and hydrocarbon. In this work, we present a conceptual model of oxygen-mixing limited biodegradation, which indicates that the effective degradation rate should depend on the cross correlation between the oxygen and hydrocarbon concentration fluctuations. This is followed by a development of a rigorous, field-scale model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427918
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    On the problem of model validation for predictive exposure assessments (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 229-254 
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    ISSN: 1436-3259
    Keywords: Model validation ; analysis of uncertainty ; model verification ; quality assurance ; system identification ; model calibration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The development and use of models for predicting exposures are increasingly common and are essential for many risk assessments of the United States Environmental Protection Agency (EPA). Exposure assessments conducted by the EPA to assist regulatory or policy decisions are often challenged to demonstrate their “scientific validity”. Model validation has thus inevitably become a major concern of both EPA officials and the regulated community, sufficiently so that the EPA's Risk Assessment Forum is considering guidance for model validation. The present paper seeks to codify the issues and extensive foregoing discussion of validation with special reference to the development and use of models for predicting the impact of novel chemicals on the environment. Its preparation has been part of the process in formulating a White Paper for the EPA's Risk Assessment Forum. Its subject matter has been drawn from a variety of fields, including ecosystem analysis, surface water quality management, the contamination of groundwaters from high-level nuclear waste, and the control of air quality. The philosophical and conceptual bases of model validation are reviewed, from which it is apparent that validation should be understood as a task of product (or tool) design, for which some form of protocol for quality assurance will ultimately be needed. The commonly used procedures and methods of model validation are also reviewed, including the analysis of uncertainty. Following a survey of past attempts at resolving the issue of model validation, we close by introducing the notion of a model having maximum relevance to the performance of a specific task, such as, for example, a predictive exposure assessment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427917
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    A stochastic model of low flows (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 303-321 
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    ISSN: 1436-3259
    Keywords: Simulation ; hydrograph rise and recession ; rainfall process ; probability distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A model is developed for annual low flow hydrographs. Its two primary components reflect the fact that hydrologic processes during streamflow rise (function of water input) and recession (function of basin storage) are different. Durations of periods of rise (wet intervals) and recession (dry intervals) are modelled by discrete probability distributions — negative binomial for dry intervals and negative binomial or modified logarithmic series for wet intervals depending on goodness of fit. During wet intervals, the total inflow is modelled by the lognormal distribution and daily amounts are allocated according to a pattern-averaged model. During dry intervals, the flow recedes according to a deterministic-stochastic recession model. The model was applied to three Canadian basins with drainage area ranging from 2210 to 22000 km2 to generate 50 realizations of low flow hydrographs. The resulting two standard-error confidence band for the simulated probability distribution of annual minimum 7-day flows enclosed the probability distribution estimated from the observed record. A sensitivity analysis for the three basins revealed that in addition to the recession submodel, the most important submodel is that describing seasonality. The state of the basin at the beginning of the low flow period is of marginal importance and the daily distribution of input is unimportant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427921
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    Stochastic analysis of spatiotemporal solute content measurements using a regression model (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 267-295 
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    ISSN: 1436-3259
    Keywords: Space/time processes ; stochastic analysis ; regression model ; solute contents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A regression model is used to study spatiotemporal distributions of solute content ion concentration data (calcium, chloride and nitrate), which provide important water contamination indicators. The model consists of three random and one deterministic components. The random space/time component is assumed to be homogeneous/stationary and to have a separable covariance. The purely spatial and the purely temporal random components are assumed to have homogenous and stationary increments, respectively. The deterministic component represents the space/time mean function. Inferences of the random components involve maximum likelihood and semi-parametric methods under some restrictions on the data configuration. Computational advantages and modelling limitations of the assumptions underlying the regression model are discussed. The regression model leads to simplifications in the space/time kriging and cokriging systems used to obtain space/time estimates at unobservable locations/instants. The application of the regression model in the study of the solute content ions was done at a global scale that covers the entire region of interest. The variability analysis focuses on the calculation of the spatial direct and cross-variograms and the evaluation of correlations between the three solute content ions. The space/time kriging system is developed in terms of the space direct and cross-variograms, and allows the separate estimation of the regression model components. Maps of these components are then obtained for each one of the three ions. Using the estimates of the purely spatial component, spatial dependencies between the ions are studied. Physical causes and consequences of the space/time variability are discussed, and comparisons are made with previous analyses of the solute content dataset.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427919
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    A test sensitive to extreme hidden periodicities (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 323-330 
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    ISSN: 1436-3259
    Keywords: Kolmogorov-Smirnov test ; identification of periodic component ; goodness-of-fit test for white noise ; periodogram ; residuals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A modified version of the widely used Kolmogorov-Smirnov (K-S) test of null hypothesis is constructed, that a given time series is Gaussian white noise, against the alternative hypothesis that the time series contains an added or multiplicative deterministic-periodic component of unspecified frequency. The usual KS test is treated as a special case. The proposed test is more powerful than the ordinary K-S test in detecting extreme (low or high) hidden periodicities. Computational procedure necessary for implementation are also given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427922
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    Solutions to the stochastic transport problem of O(σ V N ) for conservative solutes (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 297-302 
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    ISSN: 1436-3259
    Keywords: Perturbation ; conservative chemical ; velocity variance ; eulerian
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A recursive perturbation solution to the eulerian transport problem for a conservative solute in a random conductivity field is reported. The stochastic concentration is given to arbitrary order inσ ν, the variance of fluctuating velocity. The result gives the stochastic concentration as a perturbation to the deterministic concentration for constant mean flow. The closed form solution is easy to implement numerically via FFT.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427920
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  • 100
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    Analytical solutions for the coefficient of variation of the volume-averaged solute concentration in heterogeneous aquifers (1997)
    Springer
    Stochastic environmental research and risk assessment 11 (1997), S. 331-348 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Under the assumption that local solute dispersion is negligible, a new general formula (in the form of a convolution integral) is found for the arbitrary k-point ensemble moment of the local concentration of a solute convected in arbitrary m spatial dimensions with general sure initial conditions. From this general formula new closed-form solutions in m=2 spatial dimensions are derived for 2-point ensemble moments of the local solute concentration for the impulse (Dirac delta) and Gaussian initial conditions. When integrated over an averaging window, these solutions lead to new closed-form expressions for the first two ensemble moments of thevolume-averaged solute concentration and to the corresponding concentration coefficients of variation (CV). Also, for the impulse (Dirac delta) solute concentration initial condition, the second ensemble moment of thesolute point concentration in two spatial dimensions and the corresponding CV are demonstrated to be unbound. For impulse initial conditions the CVs for volume-averaged concentrations axe compared with each other for a tracer from the Borden aquifer experiment. The point-concentration CV is unacceptably large in the whole domain, implying that the ensemble mean concentration is inappropriate for predicting the actual concentration values. The volume-averaged concentration CV decreases significantly with an increasing averaging volume. Since local dispersion is neglected, the new solutions should be interpreted as upper limits for the yet to be derived solutions that account for local dispersion; and so should the presented CVs for Borden tracers. The new analytical solutions may be used to test the accuracy of Monte Carlo simulations or other numerical algorithms that deal with the stochastic solute transport. They may also be used to determine the size of the averaging volume needed to make a quasi-sure statement about the solute mass contained in it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02427923
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