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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Random Fine Needle Aspiration of the Breast of Women at Increased Breast Cancer Risk and Standard Risk Controls (1998)
    Oxford, UK : Blackwell Science Inc
    The @breast journal 4 (1998), S. 0 
    Details
    ISSN: 1524-4741
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The diagnosis of occult breast epithelial proliferation by random fine needle aspiration biopsy (FNAB) of the breast remains controversial. However, the detection of proliferative change using FNAB would potentially improve assessment of breast cancer risk among women entering chemoprevention trials. To assess the validity of this procedure in risk stratification for breast cancer, we performed FNAB on 70 women while they were anesthetized for a variety of general surgical procedures. The contralateral breasts of 32 women with a history of breast cancer (cases) and both breasts of 38 women at standard risk for breast cancer (controls) were subjected to random FNAB. Cytospin preparations from four pooled FNAB passes from each breast were stained by the papanicolaou technique and interpreted according to previously published criteria. Inadequate aspirates comprised 40% (28/70) of the samples. In the remaining cases, there was a statistically significant difference between the frequency of proliferative changes and atypical hyperplasia in high-risk cases versus controls (Pearson χ2= 9.98, p = 0.019). The contralateral breasts of women with sporadic breast cancer demonstrated proliferative changes at higher rates than breasts of asymptomatic control women. Similarly, in a logistic regression model, the odds of a diagnosis of breast cancer increased with the presence of proliferative changes with or without atypia [odds ratio (OR) = 3.6, p 〈 0.02]. This study suggests that FNAB may have a role in the further stratification of high-risk women and provide a suitable sample for the monitoring of surrogate end point biomarkers in chemoprevention trials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1524-4741.1998.460420.x
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  • 3
    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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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Structural and functional analysis of the single-strand origin of replication from the lactococcal plasmid pWV01 (1995)
    Springer
    Molecular genetics and genomics 249 (1995), S. 43-50 
    Details
    ISSN: 1617-4623
    Keywords: Rolling-circle plasmid ; Lagging strand synthesis ; Single-strand origin ; RNA polymerise Lactococcus lactis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The single-strand origin (SSO) of the rolling-circle (RC), broad-host-range lactococcal plasmid pWVO1 was functionally characterized. The activity of this SSO in the conversion of single-stranded DNA to double-stranded DNA was tested both in vivo and in vitro. In addition, the effect of this SSO on plasmid maintenance was determined. The functional pWVO1 SSO comprises a 250 by region, containing two inverted repeats (IRs). The activity of each IR was tested, separately and in combination, in a plasmid derivative that was otherwise completely devoid of structures that might function as SSO. One of the IRs (IR 1) showed some homology with other previously described SSOs of the SSOA type, as well as with the conversion signal of the Escherichia coli phage ΦX174. This IR was shown to have a partial, RNA polymerise-independent activity in complementary strand synthesis, both in vivo and in vitro. The second IR, which had no activity of its own, was required for full SSO activity, both in vivo and in vitro. The conversion of single-stranded DNA to the double-stranded form by the complete SSO was only partly sensitive to inhibition by rifampicin, indicating the existence of an RNA polymerase-independent pathway for this event. The results suggest that the pWVO1 SSO can be activated by two different routes: an RNA polymerise-dependent one (requiring the entire SSO), and an RNA polymerase-independent one (requiring only IR I).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00290234
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  • 6
    Electronic Resource
    Electronic Resource
    Salting-in behavior of isotropic and anisotropic aqueous hydroxypropylcellulose solutions (1997)
    Springer
    Colloid & polymer science 275 (1997), S. 284-287 
    Details
    ISSN: 1435-1536
    Keywords: Key words Salting-in ; hydroxypropylcellulose ; rheology ; chiral nematic mesophase ; liquid crystal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Salts with large polarizable ions are capable of salting-in complex aqueous polymer solutions exhibiting microstructure, thereby inducing changes in the phase behavior and properties of the solutions. In this work, the dynamic rheological properties of isotropic and mesomor-phic hydroxypropylcellulose (HPC) in aqueous media have been investigated in the presence of one such salt, guanidine thiocyanate (GuSCN). Addition of this salt to isotropic aqueous HPC solutions is found to induce an increase in the magnitude of the elastic shear modulus (G′). At HPC concentrations above the isotropic→mesophase transition, however, addition of GuSCN results in a substantial reduction in G′ due to microstructural changes in the chiral nematic HPC mesophase. This reduction in G′ indicates that the microstructure of a water-soluble polymer exhibiting supramolecular organization can be tailored through salting-in, and is likewise expected to facilitate the commercial processing of HPC at high solids concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050082
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  • 7
    Electronic Resource
    Electronic Resource
    Thermoplastic elastomer gels. II. Effects of composition and temperature on morphology and gel rheology (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2513-2523 
    Details
    ISSN: 0887-6266
    Keywords: block copolymer ; thermoplastic elastomer ; physical gel ; order-disorder transition ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Thermoplastic elastomer gels (TPEGs) composed of a poly[styrene-b-(ethylene-co-butylene)-b-styrene] triblock copolymer and a low-volatility, midblock-compatible mineral oil have been investigated here to ascertain the effects of composition on TPEG morphology, and temperature on mechanical properties. Cryofracture-replication transmission electron micrographs reveal the existence of spheroidal bumps due to copolymer micelles, as well as a network of irregularly shaped, high-aspect-ratio features. Since the density of this network decreases with increasing oil concentration, these features are attributed to copolymer grain boundaries. Micellar periodicities are discerned from small-angle X-ray scattering as a function of copolymer concentration and compared with previously reported data from related systems. Dynamic rheological tests performed up to 140°C indicate that the linear viscoelastic regime for these TPEGs decreases with both increasing copolymer concentration and temperature. A concentration-dependent thermal transition, signified by an abrupt reduction in the dynamic elastic modulus (G′), has also been identified.© 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2513-2523, 1998
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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