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  • Physics  (27)
  • Atomic, Molecular and Optical Physics  (12)
  • Organic Chemistry
  • 1980-1984  (45)
  • 1965-1969
  • 1940-1944
  • 1981  (45)
  • 1
    Electronic Resource
    Electronic Resource
    Effect of water on the tautomeric equilibrium of 2-oxopyridine. A Monte Carlo simulation studyThis work was begun during one of the authors' (V.I.D.) stay in Poland in 1980. (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 20 (1981), S. 359-364 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With the empirical atom-atom potential the systems of one and three water molecules surrounding either the lactim or the lactam tautomer of 2-oxopyridine are simulated at temperatures of 198, 248, 298, and 348 K, using Monte Carlo techniques. The results show that the lactam form of the molecule is more stabilized by the water molecules than the lactim form by about 17-29 kJ/mol (4-7 kcal/mol), thus remaining in accordance with the conclusions inferred from experimental evidence.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560200732
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  • 2
    Electronic Resource
    Electronic Resource
    Small-angle x-ray scattering studies of isothermally crystallized bulk polyethylene (1981)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 19 (1981), S. 1577-1591 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A set of isothermally melt-crystallized polyethylene samples was examined using small-angle x-ray scattering (SAXS). Time and temperature of crystallization were the variable parameters used to create the set of samples. Following background subtraction, desmearing, and application of the Lorentz factor to the raw SAXS data it is possible to see many orders of reflection. This suggests that much higher degrees of order are present in isothermally melt-crystallized samples than had previously been thought possible. A combination of SAXS and DSC data indicates that there is no evidence for isothermal thickening in these samples. This study, coupled with data obtained from PE single crystals, produced information concerning the extrapolation of single-crystal data to fit bulk systems. In addition, the equilibrium melting point T0m determined is somewhat lower than previously claimed. This study also suggests that the surface energy of the mature crystals is always lower than that of the nucleated state and/or the nucleation factor Kσen increases with decreasing supercooling.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1981.180191008
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  • 3
    Electronic Resource
    Electronic Resource
    SAXS instrumental broadening and the order dependence of peak width (1981)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 19 (1981), S. 487-497 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The width at half-height of SAXS discrete diffraction peaks has been used to compute the number of polyethylene lamellae in a stack. The dependence of this width on diffraction order reflects the nature and magnitude of lattice fluctuations. Within the literature there have been conflicting reports on this order dependence and hence on the nature of the lattice fluctuations. Previous studies have neglected the effects of instrumental broadening. These present studies show that instrumental effects can account for some 40% of the observed first-order peak width and drastically change the ratio of peak widths as a function of order. These studies, carried out on isothermally grown polyethylene single-crystal mats, also demonstrate the importance of the functions chosen to represent the various broadening factors. A mat was made up consisting of randomly stacked lamella with two distinct fold periods. The scattering from this mixed mat could not be described by either of the prevailing theories.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1981.180190309
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  • 4
    Electronic Resource
    Electronic Resource
    Rates of Proton Abstraction from Conjugated Dienes in the Gas Phase (1981)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 1058-1062 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rates of proton transfer from 2, 4-hexadiene, 1, 3-cycloheptadiene, cyclopentadiene and acetone to t-butoxide have been measured in the gas phase using pulsed-ion-cyclotron-resonance spectroscopy. The rate constants are (units of 10-10 cm3 molecule-1 s-1): 2.7 ± 0.4, 3.8 ± 0.4, 6.1 ± 0.7 and 10.8 ± 1.5, respectively. These results are analyzed in terms of the properties of the encounter complex and reaction transition states. The reaction profile for t-butoxide + cyclopentadiene is modeled using RRKM theory and an estimate for the central barrier height is obtained.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19810640411
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  • 5
    Electronic Resource
    Electronic Resource
    Tasmanin, ein neues Indolalkaloid aus Aristotelia peduncularis (LABILL.) HOOK. F. 181. Mitteilung über organische Naturstoffe180. Mitt. s. [1].Teil der geplanten Dissertation von R.K., Universität Zürich. (1981)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 2555-2562 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Tasmanine, a New Indole Alkaloid from Aristotelia peduncularis (LABILL.) HOOK. F.The new indole alkaloid tasmanine (3) was isolated from Aristotelia peduncularis. Its relative configuration was elucidated on the basis of spectroscopic data (mainly NMR. spectra). It is closely related to the other known alkaloids from Aristotelia with double substitution at the indole nucleus. A biosynthetic pathway to these related natural compounds is proposed; also a biogenetic numbering system is suggested.
    Notes: No Abstract.Another representative of this group of alkaloids, aristoteline (2), was also isolated from A. peduncularis. This natural compound has previously been isolated from A. serrata and A. chilensis.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19810640811
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  • 6
    Electronic Resource
    Electronic Resource
    Simple relationship between total molecular correlation energies and LMO sizes (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 25-31 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As an alternative to the density functional approach to estimating total molecular correlation energies, the equation Ecorr=-0.06593 ∑i=1M Ri-0.3916, where Ri=〈r2〉i½ and i runs over the localized molecular orbitals was fitted to 25 STO-3G data points with a root-mean-square error of 0.025 hartree. Other more general equations were tried but no significant improvement was observed in the fit.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560190104
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  • 7
    Electronic Resource
    Electronic Resource
    Magnesium and calcium cation-ligand interactions within the pseudopotential approach. II. Cation-GABA interactionsSupported in part by the Polish Academy of Sciences within Project PAN-09.7.1 and Conacyt PNCB-1615, México. Presented in part at the Sanibel Quantum Biology Symposium (1979) held in honor of A. Pullman and B. Pullman. (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 463-475 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We performed ab initio pseudopotential and CNDO calculations on γ-aminobutyric acid (GABA) and its Ca2+ and Mg2+ clathrates. We were particularly interested in the rotational barrier existing between two extreme conformers of GABA and its modification upon metal complexing. We found that the pseudopotential method predicts a coordination of the ions to GABA and that this coordination inverts the rotational barrier observed for the isolated molecule. We also looked into the adequacy of CNDO for the study of this type of coordination and found several shortcomings in its predictions. The biological implications of these findings are discussed and a hypothesis on the role of a GABA-Ca2+ complex is presented.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560190309
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  • 8
    Electronic Resource
    Electronic Resource
    Self-Consistent APW-k · p method. I. Theory (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 681-691 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A first principles method based on an APW-k · p band structure calculation is derived in order to obtain the self-consistent eigenenergies, crystal potential, and electronic density. The simplicity and extensions of the method are discussed, including comparison with the results obtained by the use of the Chadi and Cohen special points technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560190419
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  • 9
    Electronic Resource
    Electronic Resource
    Erratum (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 719-720 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560190422
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  • 10
    Electronic Resource
    Electronic Resource
    Self-Consistent APW-k · p method. II. Application to NaCl (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 20 (1981), S. 933-949 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-consistent APW-k · p method is utilized to obtain the band structure of NaCl in the “muffin-tin” approximation. Qe have investigated the convergence of many intermediate results, e.g., crystalline potential, matrix elements of the momentum operator, and energy eigenvalues at the Γ point. The summation in reciprocal space, included in the definition of the matrix D of the theory, is performed by direct sum and also by a special points technique. For the convergence criteria used, the results converged after five iterations.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560200417
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