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  • Polymer and Materials Science  (276)
  • ASTROPHYSICS  (177)
  • Analytical Chemistry and Spectroscopy  (107)
  • EARTH RESOURCES AND REMOTE SENSING
  • SPACE SCIENCES
  • 1990-1994  (589)
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  • 1990  (589)
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  • 1990-1994  (589)
  • 1975-1979
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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 4 (1990), S. 9-12 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Discrimination effects in secondary electron multipliers due to the differences in kinetic energy with which ions of different masses strike the dynode surface are investigated. The threshold energy at which ions of a particular mass can be detected is discussed. The efficiencies of such multipliers when used with cluster ions such as H+(H2O)N (where Cat+ represents an alkali-metal cation) are investigated and discussed, in terms of both the ‘kinetic’ and ‘potential’ emission coefficients.
    Additional Material: 7 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 4 (1990), S. 13-15 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The characteristics of the detection of ions of the alkali metals and of cluster ions of the type (H2O)NMH+ (where M is an amino acid) are markedly different from those for the detection of protonated saccharose ions. The latter are shown to produce a signal from a secondary electron multiplier detector at a lower ion energy than the threshold energy for the former ions. An explanation is proposed in terms of the charge localization.
    Additional Material: 2 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 87-91 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simple relationship between frequency shifts to be expected in molecular vibrational spectra upon isotopic substitution and component values of eigenvectors is displayed. Application of this expression to the problem of force constant refinement is discussed in terms of a refinement algorithm developed some years ago to overcome particular problems associated with large molecular systems. Calculations of expected isotopic shifts have been calculated and are tabulated here for experimental reference.
    Additional Material: 1 Tab.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 174 (1990), S. 189-203 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Zur Sicherung von Produktqualität und Qualitätskonstanz bei der Polymerherstellung ist eine genaue Kenntnis des Polymerisationsprozesses notwendig. Für die Suspensionspolymerisation von Ethylen mit hochaktiven Ziegler-Katalysator/Cokatalysator-Systemen wurde ein Prozeß-Modell entwickelt. Dieses Modell gibt an, welcher Satz von Prozeßparametern innerhalb bestimmter Grenzen konstant gehalten werden muß, um die Produktdaten in den vorgegebenen Abnahmegrenzen zu halten. Die Konsequenzen für eine Produktionsanlage werden diskutiert.
    Notes: Saving product quality and quality consistency in polymer production needs a detailed knowledge of the polymerization process. A process model for the slurry polymerization of ethylene with high mileage Ziegler-catalyst/cocatalyst systems has been developed. This model teaches which set of process parameters must be kept constant together with their acceptable deviations to keep product data within the required frame. The consequences for a technical production plant are also discussed.
    Additional Material: 6 Ill.
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  • 5
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oscillatory and steady shear rheological properties of concentrated solutions of proteoglycan subunit (PGS) and aggregate (PGA) from bovine articular cartilage have been studied using a Rheometrics fluids spectrometer. At comparable concentrations in the physiological range tan δ increases from 0.5 to 1.0 for PGA as the oscillation frequency (ω) increases from 10-1 to 102 rads / s, compared to a decrease from 40 to 5 for PGS. Thus PGA solutions exhibit predominantly elastic response whereas those of PGS exhibit primarily viscous behavior. PGA solutions show pronounced shear-thinning behavior at all shear rates (γ) in the range 10-2 〈 γ (s-1) 〈 10 2, whereas PGS solutions exhibit predominantly Newtonian flow. For PGA, the small-strain complex viscosity η* (ω) is substantially smaller than the steady-flow viscosity η (γ) at comparable values of ω and γ. These observations indicate that the presence of proteoglycan aggregates leads to formation of a transient or weak-gel network. Since aggregation leads to a large increase in molecular hydrodynamic volume and hence in the relaxation times for macromolecular rotation, it appears that role of aggregate formation is to shift the linear viscoelastic response from the terminal viscous flow into the plateau elastomeric regime of relaxational behavior. Normal or pathological changes that produce a decrease in aggregation will result in a loss of elastomeric behavior of the proteoglycan matrix.
    Additional Material: 5 Ill.
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  • 6
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three crystalline polymorphs of the helical decapeptide, Boc-Aib-Ala-Leu-Ala-Leu-Aib-Leu-Ala-Leu-Aib-OMe, have been obtained. Antiparallel helix aggregation is observed in crystals grown from methanol (A), while completely parallel packing is observed in crystals from isopropanol (B) or an ethylene glycol-ethanol mixture (C). Crystals B and C are very similar in molecular conformation and packing. The packing motifs in crystals A and B consist of rows of parallel molecules, with an almost identical arrangement in both crystals. In crystal A, adjacent rows assemble with helix axes pointed in oppsite directions, whereas in crystal B all rows assemble with helix axes pointed in the same direction. Electrostatic interactions between helix dipoles do not appear to be a major determinant of packing modes. The structures also do not provide a ready rationalization of packing preferences in terms of side-chain interactions or solvation. The α-helix of the peptide in crystal A has seven 5 → 1 hydrogen bonds; the helix in crystal B is a mixed 310/α-helix. The crystal parameters are as follows. Crystal A: C51H92N10O13·CH3OH, space group P21 with a = 10.498(1) Å, b = 18.189(3) Å, c = 16.475(3) Å, β = 99.28(1)°, Z = 2, R = 9.6% for 1860 data. Crystal B: C51H92N10O13·C3H7OH, space group P21 with a = 10.534(1) Å, b = 28.571(4) Å, c = 11.055(2) Å, β = 95.74(1)°, Z = 2, R = 6.5% for 3251 data. Crystal C: C51H92N10O13·C2H5OH, space group P21, with a = 10.450(1) Å, b = 28.442(5) Å, c = 11.020(2) Å, β = 95.44(1)°, Z = 2, R = 14.8% (isotropic) for 1948 data.
    Additional Material: 7 Ill.
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  • 7
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The isomeric decapeptides Boc-Aib-Ala-Leu-Ala-Aib-Aib-Leu-Ala-Leu-Aib-OMe (II) and Boc-Aib-Ala-Aib-Ala-Leu-Ala-Leu-Aib-Leu-Aib-OMe (III), are predominantly a-helical with little effect on the conformation with interchange of Aib/Ala residues or Aib/Leu residues. The packing motif of helices in crystal II is antiparallel, whereas the helices pack in a skewed fashion in crystal III, with a 40° angle between neighboring helix axes. Crystal III contains a water molecule in a hydrophobic hole that forms hydrogen bonds with two carbonyl oxygens that also participate in 5 → 1 type hydrogen bonds. Values for helical torsional angles φ and ψ assume a much wider range than anticipated. Crystal II: C49H88N10O13, space group P21 with a = 16.625(2) Å, b = 9.811(5) Å, c = 18.412(3) Å, β = 99.79(1)°, Z = 2, R = 5.7% for 4338 data with |F0 | 〉 3σ(F). Crystal III: C49H88N10O13. 1/2H2O, space group P21, with a = 11.072(2) Å, b = 34.663(5) Å, c = 16.446(3) Å, β = 107.85(1) °, Z = 4, R = 8.3% for 6087 data with |F0| 〉 3σ(F).
    Additional Material: 8 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 901-919 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The indirect solvent-induced effect on the free energy of binding of biopolymers is examined within the framework of classical statistical mechanics. We focus specifically on the role of the solute-solvent hydrogen bonding. In particular, we have estimated the first order solvent effedt on the indirect interaction between two biopolymers. We find that the solvent-induced interactios between two hydrophilic groups through water-bridged hydrogen bonds could significantly enhance the binding free energy. Some preliminary estimates indicate that this effect is significant and perhaps could be crucial in molecular recognition processes. Furthermore, we have calculated, from crystal structure data, the distance distribution between all the oxygens and nitrogens on the surface of some proteins that do not belong to the binding domain. In most cases we found an enhanced peak in the range of 4-5 Å, which is where we expect to find strong solvent-induced interactions.
    Additional Material: 8 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 191 (1990), S. 2615-2630 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The emulsion polymerization of butadiene was investigated with sodium dodecyl sulfate as emulsifier, and the results were compared with those obtained with the industrial-grade emulsifier Dresinate 214. Limited coagulation was observed in both cases, caused by the high ionic strength of the aqueous phase. Sodium dodecyl sulfate was found to be a better stabilizer than Dresinate 214. The average rate per particle in interval II (corresponding to the linear portion of the conversion vs. time curve) depends strongly on particle size, but not on recipe parameters used to vary the final particle diameter, such as the type and amount of emulsifier and ionic strength. The dependence of particle number per volume of water N on initiator ([I]) and emulsifier concentration ([E]) is usually expressed as the exponent in the empirical relationship N ∼ [I]x · [E]y. Promoting coagulation by increasing the ionic strength decreases x towards zero, while y increases sharply. Increasing [I] at constant [E] and constant ionic strength induces limited coagulation, presumably because the rate of emulsifier adsorption becomes insufficient.
    Additional Material: 10 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 3499-3511 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several models of monomers, homopolymers, and copolymers containing a photosensitizer group, 4-nitro-1-naphthyl-carbamoyl (NNC), have been synthesized. Synthetic methods are described, in addition to two routes for copolymers preparation. First, the radical copolymerization between monomers with the photosensitizer group built-in and comercial monomers such as styrene and methyl acrylate and, second, polymer modification by nucleophilic reaction between carbonyl group polymer supported and nitro-naphthyl amine. All products were characterized and one of the resulting soluble polymeric photosensitizer and its model compound, were tested as triplet energy donors against trans- stilbene and their Stern-Volmer constants were determined. Results show that the sensitizer efficiency is closer to that of the well known benzophenone sensitizer and higher than that of the acetophenone, while the sensitizer efficiency disminished when the chromophore is bonded to the polymer.
    Additional Material: 3 Ill.
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