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  • Springer  (7)
  • 1985-1989  (3)
  • 1975-1979  (1)
  • 1970-1974  (3)
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  • 1
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The paper presents a qualitative analysis of the following systems ofn differential equations: $$\dot x_i = x_i x_j - x_i \sum\nolimits_r^n { = 1} x_r x_s {\mathbf{ }}(j = i - 1 + n\delta _{i1} {\mathbf{ }}and{\mathbf{ }}s = r - 1 + n\delta _{r1} )$$ , which show cyclic symmetry. These dynamical systems are of particular interest in the theory of selforganization and biological evolution as well as for application to other fields.
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  • 2
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Hydrate der Ionen Li+, Na+, Be2+, F− und Cl− mit den Koordinationszahlen 1, 2, 4, 6 und 8 sowie bis zu drei Hydrathüllen wurden mit Hilfe des CNDO/2-Verfahren berechnet. Die Stärke der Wasserstoffbrücken in den äußeren Sphären wird durch die Ladungsübertragung vom Zentralion zu den Liganden stark beeinflußt. Bei F− unterscheidet sich die mittlere Bindungsenergie in der dritten Sphäre kaum mehr vom reinen Wasser; bei Li+ reicht der Einfluß um eine Wasserhülle weiter. Für beide Ionen wird 6 als günstigste Koordinationszahl erhalten.
    Abstract: Résumé Calcul par la méthode CNDO/2 des hydrates des ions Li+, Na+, Be2+, F− et Cl−, à nombres de coordinence 1, 2, 4, 6 et 8, avec jusqu'à trois couches de molécules d'eau. La force de la liaison hydrogène dans les couches externes est largement déterminée par le transfert de charge à partir de l'ion central vers les ligands. Dans la troisième couche d'hydratation de l'ion F− l'énergie de liaison moeyenne est presque la meme que dans les essaims d'eau pure. Dans le cas de Li+ l'influence de l'ion atteint une couche supplémentaire. Pour ces deux ions le nombre de coordinence 6 s'avère le plus favorable.
    Notes: Abstract Hydrates of the ions Li+, Na+, Be2+, F− and Cl− with coordination numbers 1, 2, 4, 6 and 8 and up to three shells of water molecules were calculated with the CNDO/2 method. The strength of the hydrogen bond in the outer shells is determined largely by the charge transfer from the central ion to the ligands. In the third hydration shell of the F− ion the average binding energy is almost the same as in pure water clusters. In the case of Li+ the influence of the ion reaches one shell further. For both ions the coordination number 6 is the most favourable one.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 76 (1989), S. 211-212 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Experimental mechanics 28 (1988), S. 402-408 
    ISSN: 1741-2765
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Currently, there are a number of flow diagnostic tools available for the evaluation of fluid dynamic systems. In spite of its great potential, holographic velocimetry is one technique which has not been widely used. It does, however, have great potential in this area due to its inherent three-dimensionality. As demonstrated in this study of fully developed turbulent flow in a pipe, full three-dimensional mapping can be achieved at any instant in a flow cycle. Comparisons of holographic results with analytical predictions and laser-Doppler-anemometry (LDA) measurements demonstrate the accuracy of the technique as well as some of its advantages and disadvantages relative to LDA. Although relatively poor spatial resolution is obtained, the fact that holographic velocimetry is both an instantaneous and full volume measuring tool makes it useful for a range of complex and high-speed flow-measurement applications.
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  • 5
    ISSN: 1432-1017
    Keywords: Relaxation kinetics ; ultrasound absorption ; temperature jump ; proton transfer ; vitamin B 6
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract UV-visible and 13C NMR measurements described in the literature and our 31P NMR measurements support the following mechanism of proton transfer reactions in aqueous solutions of pyridoxamine phosphate: Only the tautomeric equilibrium between neutral form, A N, and zwitterion, A Z, which is analogous to the tautomeric equilibrium of 3-hydroxypyridine in aqueous solution, is important, and that equilibrium does not change upon the dissociation of the second phosphate proton. With these simplifying assumption, we have simulated the relaxation spectrum of the proton transfer reactions of pyridoxamine phosphate in water using parameters from analogous reactions and compared it with our ultrasound and temperature jump measurements. We have found that the relaxation process measured by the temperature jump experiment is mainly caused by the overall reaction A N=A Z (or A N - =A Z - ) and the ultrasound absorption at the isoelectric point between pK2 and pK3 is mainly caused by the overall reaction $$A^{\text{ + }} + {\text{x}} A_N^ - + \left( {1 - {\text{x}}} \right)A_Z^ - = {\text{y}}A_N + \left( {2 - {\text{y}}} \right)A_Z , 0 \leqq {\text{x}} \leqq {\text{1,}} {\text{0}} \leqq {\text{y}} \leqq 2$$ .
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  • 6
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Umsetzungen von Isobutylidenmeldrumsäure bzw. von 3-Methyl-2-äthoxycarbonylbutyliden-1-meldrumsäure mit Diazoessigester folgen Geschwindigkietsgesetzen 2. Ordnung. Aus der Temperaturabhängigkeit der Reaktionsgeschwindigkeitskonstanten errechnen sich Aktivierungsparameter, die jenen der 1,3-dipolaren Cycloaddition entsprechen. Diese Werte ändern sich nur wenig bei Übergang zu Lösungsmitteln unterschiedlicher Polarität. Die Ergebnisse lassen auf thermisch labile 1-Pyrazoline als Zwischenprodukte schließen, die dann zu den bekannten, stickstoffreien, stabilen Reaktionsprodukten zerfallen.
    Notes: Abstract The reaction of either isobutylidenmeldrum acid or 3-methyl-2-ethoxycarbonylbutyliden-1-Meldrum acid with ethyl diazoacetate exhibits second order kinetics. The values of the activation parameters, calculated from the temperature dependence of the rate constants, correspond to those obtained from 1,3 dipolar cyclo-addition reactions. These values are altered only slightly when the polarity of the solvent is changed. These results suggest that the reaction proceeds via a thermally labile 1-pyrazoline which then decomposes to give nitrogen and the observed products.
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  • 7
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Energien und Dipolmomente mehrerer Konformationen von 2,2-Dimethyl-1,3-dioxan-4,6-dion (Meldrumsäure) wurden mit Hilfe der semiempirischenLCAO-MO-SCF-Methode vonPople berechnet. Die Ergebnisse werden mit den experimentellen Dipolmomenten einiger Derivate von 1,3-Dioxan-4,6-dion verglichen. Die Unterschiede zwischen den experimentellen Dipolmomenten dieser Verbindungen können durch Annahme unterschiedlicher Konformerengleichgewichte erklärt werden. Die berechnete Protonenaffinität desMeldrumsäureanions läßt sich in eine Reihe von Aciditäten verschiedenartiger Säuren in Übereinstimmung mit den experimentellen Werten einordnen.
    Notes: Abstract The total energies and dipole moments of some conformations of 2.2-dimethyl-1,3-dioxane-4,6-dione (Meldrum's acid) were calculated withPople's semiempiricalLCAO-MO-SCF-procedure (CNDO). The results are compared with the experimental dipole moments of 2.2-dimethyl-1.3-dioxane-4.6-dione and its alkyl derivatives. The unusual high differences in the experimental dipole moments of this series of compounds are explained by the assumption of different conformational equilibria. The proton affinity ofMeldrum's acid anion fits well into a series of calculated proton affinities of otherBrønsted acids.
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