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  • 1
    Electronic Resource
    Electronic Resource
    Theory and simulation of the swelling of polymer gels (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 404-418 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A combined discontinuous molecular dynamics and Monte Carlo simulation technique is used to study the swelling of athermal, continuous-space, near-perfect, trifunctional polymer networks containing hard chains of lengths 20 and 35 immersed in an athermal hard-sphere solvent. The swelling simulations are conducted under conditions of constant pressure and chemical potential. A simple, analytical theory for gel swelling is presented in which the gel free energy is calculated as the sum of an elastic, affine-type term, and a liquidlike mixing term that is based on the generalized-Flory dimer equation of state. The theory shows good agreement with our simulation results for the gel properties at swelling equilibrium. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481806
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  • 2
    Electronic Resource
    Electronic Resource
    Pressure–volume properties of endlinked hard-chain polymer networks (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7556-7573 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Equilibrium molecular dynamics simulations are used to obtain the pressure and configurational chain properties of near-perfect, off-lattice, trifunctional hard-chain networks of chain lengths 20, 35, 50, and 100, and of tetrafunctional hard-chain networks of chain lengths 20, 35, and 50 over a range of packing fractions. Our simulation results show that the variation of network pressure with density is similar to that of uncrosslinked chain systems of the same chain length, except at low densities where the network pressure shows a negative region, as first observed by Escobedo and de Pablo. We present a theoretical treatment leading to an analytical expression for the network pressure as the sum of liquid-like and elastic contributions. The liquid-like contribution is obtained by extending the generalized Flory-dimer theory to networks, and the elastic contribution is obtained by treating the network as a set of interpenetrated dendrimers and using an ideal chain-spring analogy to calculate the free energy. The theoretical predictions for network pressure are in good agreement with simulation data. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478659
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  • 3
    Electronic Resource
    Electronic Resource
    Structure-activity relationships in the dodecapeptide .alpha. factor of Saccharomyces cerevisiae (1983)
    s.l. : American Chemical Society
    Biochemistry 22 (1983), S. 1298-1304 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00274a047
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  • 4
    Electronic Resource
    Electronic Resource
    Nuclear magnetic resonance studies of diamagnetic metal-diethylenetriaminepentaacetate complexes (1979)
    s.l. : American Chemical Society
    Inorganic chemistry 18 (1979), S. 1330-1332 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic50195a033
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  • 5
    Electronic Resource
    Electronic Resource
    Electrokinetic studies on ion-exchange membranes. 5. Streaming potentials (1977)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 81 (1977), S. 2114-2118 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100537a015
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular phylogeny of Gossypium species by DNA fingerprinting (2000)
    Springer
    Theoretical and applied genetics 101 (2000), S. 931-938 
    Details
    ISSN: 1432-2242
    Keywords: Key words Gossypium species ; RAPD ; Phylogeny ; Cluster ; Diversity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Total genomic DNA from 31 available Gossypium species, three subspecies and one interspecific hybrid, were analysed to evaluate genetic diversity by RAPD, using 45 random decamer primers. A total of 579 amplified bands were observed, with 12.9 bands per primer, of which 99.8% were polymorphic. OPJ-17 produced the maximum number of fragments while the minimum number of fragments was produced with primer OPA-08. Cluster analysis by the unweighted paired group method of arithmetic means (UPGMA) showed six main clusters. Cluster ’A’ consisted of two species and one subspecies of the A-genome, with a 0.78–0.92 Nei’s similarity range. Cluster B, composed of all available tetraploid species and one interspecific hybrid, showed the same sister cluster. Nei’s similarity ranged from 0.69 to 0.84. The B-genome formed the UPGMA sister cluster to the E-genome species. Cluster ’C’ consisted of five Gossypium species of which three belong to the B-genome, with Nei’s similarity values of 0.81 to 0.86. Although there was considerable disagreement at lower infra-generic ranks, particularly among the D- genome (diploid New World species) and C-genome (diploid Australian species) species. The sole F-genome species Gossypium longicalyx was resolved as a sister group to the D-genome species. Gossypium herbaceum and G. herbaceum Africanum showed the maximum Nei’s similarity (0.93). Minimum similarity (0.29) was observed between Gossypium trilobum and Gossypium nelsonii. The average similarity among all studied species was 50%. The analysis revealed that the interspecific genetic relationship of several species is related to their centre of origin. As expected, most of the species have a wide genetic base range. The results also revealed the genetic relationships of the species Gossypium hirsutum to standard cultivated Gossypium barbadense, G. herbaceum and Gossypium arboreum. These results correspond well with previous reported results. The level of variation detected in closely related genotypes by RAPD analysis indicates that it may be a more efficient marker than morphological marker, isozyme and RFLP technology for the construction of genetic linkage maps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001220051564
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  • 7
    Electronic Resource
    Electronic Resource
    Improved diffusion methods for determination of inorganic nitrogen in soil extracts and water (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 413-420 
    Details
    ISSN: 1432-0789
    Keywords: Key words Ammonium analysis ; 15N ; Nitrate ; Nitrite ; Inorganic N ; Soil extract diffusion method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Diffusion methods previously developed for inorganic-N analysis of soil extracts were modified to improve reliability, increase the dynamic range, extend the scope of applications, and simplify the processing of samples for N-isotope analysis. In these methods, the soil extract is treated with MgO, or MgO plus Devarda‘s alloy, in a 473-ml (1-pint) wide-mouth Mason jar to convert NH4 +-N, NO3 –-N, and/or NO2 –-N to NH3-N. The NH3 thereby liberated is collected in H3BO3-indicator solution in a Petri dish suspended from the Mason-jar lid and determined quantitatively by acidimetric titration. With the modifications described, analyses can be performed on 10- to 100-ml samples of water, 0.5MK2SO4, 1MKCl, 2MKCl, or 4MKCl, at temperatures between 20 and 30°C. Recovery from 10 or 20ml was quantitative in 18–80h with up to 4mgN; recovery from 50 or 100ml was quantitative in 3–13 days with up to 2mgN. Removal of H3BO3 for N-isotope analysis by the Rittenberg process was effected using methanol. Mason-jar diffusion methods are much simpler and more convenient than conventional steam distillations. Comparative studies showed that quantitative determinations are more accurate and precise by diffusion than by distillation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050266
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  • 8
    Electronic Resource
    Electronic Resource
    Nitrogen fertilizers promote denitrification (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 211-220 
    Details
    ISSN: 1432-0789
    Keywords: Key words Denitrification ; Fertilizer efficiency ; 15N ; Labelled dinitrogen ; Nitrification ; Nitrous oxide ; Urea ; Waterlogged soil ; Water-soluble organic carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A laboratory study was conducted to compare the effects of different N fertilizers on emission of N2 and N2O during denitrification of NO3 – in waterlogged soil. Field-moist samples of Drummer silty clay loam soil (fine-silty, mixed, mesic Typic Haplaquoll) were incubated under aerobic conditions for 0, 2, 4, 7, 14, 21, or 42 days with or without addition of unlabelled (NH4)2SO4, urea, NH4H2PO4, (NH4)2HPO4, NH4NO3 (200 or 1000 mg N kg–1 soil), or liquid anhydrous NH3 (1000 mg N kg–1 soil). The incubated soil samples were then treated with 15N-labelled KNO3 (250 mg N kg–1 soil, 73.7 atom% 15N), and incubation was carried out under waterlogged conditions for 5 days, followed by collection of atmospheric samples for 15N analyses to determine labelled N2 and N2O. Compared to samples incubated without addition of unlabelled N, all of the fertilizers promoted denitrification of 15NO3 –. Emission of labelled N2 and N2O decreased in the order: Anhydrous NH3〉urea〈$〉\gg〈$〉 (NH4)2HPO4〉(NH4)2SO4≃NH4NO3≃NH4H2PO4. The highest emissions observed with anhydrous NH3 or urea coincided with the presence of NO2 –, and 15N analyses indicated that these emissions originated from NO2 – rather than NO3 –. Emissions of labelled N2 and N2O were significantly correlated with fertilizer effects on soil pH and water-soluble organic C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050233
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  • 9
    Electronic Resource
    Electronic Resource
    Foam rheology: Relation between extensional and shear deformations in high gas fraction foams (1987)
    Springer
    Rheologica acta 26 (1987), S. 78-84 
    Details
    ISSN: 1435-1528
    Keywords: Foam ; emulsion ; extensional deformation ; shear deformation ; hexagonal cell model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract A two-dimensional hexagonal foam cell model is used to derive analytic expressions for the bulk stress tensor and foam microstructure for any small homogeneous deformation. We show that calculations done for deformations where the principal axes of stress and strain coincide, such as in extension, are sufficient to provide all information about shear deformation. The stresses and foam structure for any given strain and initial cell orientation in shear bears a unique relation to a different strain and orientation in extension. Such a mapping is obtained using the assumption that the principal axes of strain and stress corotate with each other. This in turn implies that high gas fraction foams follow the Lodge-Meissner relation, i.e. the ratio of the normal-stress difference to the shear stress equals the shear strain. The spatially periodic structure of foam along with the fact that the cell centers move affinely with the bulk, makes the above assumption a justifiable one.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01332686
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  • 10
    Electronic Resource
    Electronic Resource
    Comparison of the rheology of polymer melts in shear, and biaxial and uniaxial extensions (1987)
    Springer
    Rheologica acta 26 (1987), S. 144-151 
    Details
    ISSN: 1435-1528
    Keywords: Extensional deformation ; polymer melt
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The experimental properties of different polymer melts, polystyrene, high density polyethylene and low density polyethylene are compared for the first time in three different deformations: step shear, step biaxial extension and steady uniaxial extension. Properties of three other melts are also studied in step biaxial and shear experiments. For our comparative purposes some data of Laun and Winter from the literature are used, as well as new data reported here. In all the step strain experiments, the stresses can be factored into a time dependent relaxation modulus and a strain dependent damping function. The data are interpreted using a differential constitutive equation of Larson which satisfies this time-strain separability and has a single parameter that describes the strain softening character of the material. Results show that differences in the properties of the melts are most pronounced in uniaxial extension and least in biaxial extension. All melts follow the Doi-Edwards prediction relatively closely in biaxial extension. In uniaxial extension, the branched material shows a strong strain hardening effect although its shear and biaxial properties are similar to the other melts. The constitutive model gives a reasonably good fit to the data in all three deformations for unbranched materials for the same value of the adjustable parameter; the model, however, fails for the branched low density polyethylene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01331972
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