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  • Articles  (1,060)
  • Chemistry  (1,012)
  • Mice  (48)
  • ASTROPHYSICS
  • STRUCTURAL MECHANICS
  • 1990-1994  (644)
  • 1975-1979  (416)
  • 1990  (644)
  • 1979  (416)
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  • 1990-1994  (644)
  • 1975-1979  (416)
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  • 1
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A study has been made of the structure and properties of alternating equimolar and random copolymers of vinylcyclohexanne and α-methylvinylcyclohexane with acrylonitrile using infrared and 1H-NMR spectroscopy methods, as well as x-ray diffraction and differential thermal analyses. The spectral methods allowed an estimation of the composition and distribution of comonomer units in the copolymer macrochains. The thermal stability of alternating copolymers was found to be higher than that of polyacrylonitrile. Alternating and random copolymers are amorphous products with various dimensions of crystallites. Information on the molecular motion intensity and temperatures of structural transitions in copolymer macrochains was obtained by the spin-probe technique.
    Additional Material: 5 Ill.
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  • 2
    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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  • 3
    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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  • 4
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 1990-12-21
    Description: A major mechanism for generating tolerance in developing T cells is the intrathymic clonal deletion of T cells that have receptors for those self antigens that are presented on hematopoietic cells. The mechanisms of tolerance induction to antigens not expressed in the thymus remain unclear. Tolerance to self antigens can be generated extrathymically through the induction of clonal nonresponsiveness in T cells with self-reactive receptors. A second mechanism of extrathymic tolerance was identified: clonal elimination of mature T cells with self-reactive receptors that had previously displayed functional reactivity.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Jones, L A -- Chin, L T -- Longo, D L -- Kruisbeek, A M -- New York, N.Y. -- Science. 1990 Dec 21;250(4988):1726-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Biological Response Modifiers Program, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2125368" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Antibodies, Monoclonal/immunology ; Antigens, CD4/analysis ; Antigens, CD8 ; Antigens, Differentiation, T-Lymphocyte/analysis ; Clone Cells ; *Immune Tolerance ; Kinetics ; *Lymphocyte Depletion ; Mice ; Mice, Inbred DBA ; Mice, Inbred Strains ; Spleen/immunology ; T-Lymphocytes/cytology/*immunology ; Thymus Gland/immunology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 5
    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.
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  • 6
    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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  • 7
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Measurements of translational diffusion coefficients by quasielastic laser light scattering, sedimentation coefficients, and intrinsic viscosities at zero shear of proteoglycan subunit fraction A1-D1-D1 isolated from bovine nasal septa are reported. Molecular weights and hydrodynamic dimensions are compared with those expected on the basis of structural models previously proposed. Comparison of the concentration dependence of the diffusion coefficient in the presence of NaCl and GdnHCl leads to the conclusion that significant self-association behaviour of subunit occurs in the absence of GdnHCl. In the absence of added salt, anomalous nonlinear concentration dependence of Dt estimated from wide-angle light-scattering experiments is observed. In addition, Dt apparently becomes angle dependent. These results are interpreted in terms of the perturbation of normal translational diffusion of the monomer by strong repulsive intermolecular interactions due to the combined effects of long-range electrostatic forces and macromolecular congestion at higher concentrations. By carrying out experiments at small scattering angles, it is possible to determine Dt0 for proteoglycan subunit in the absence of supporting electrolyte. Titration of a dilute solution of subunit with hyaluronic acid results in a sigmoidal behaviour of the Stokes radius, indicating the formation of complexes of higher molecular weight results from the noncovalent association of proteoglycan subunits with hyaluronate. Observation of Dt appears to provide a useful method for studying the proteoglycan subunit-hyaluronate interactions.
    Additional Material: 14 Ill.
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  • 8
    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.
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  • 9
    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.
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  • 10
    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).
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