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  • Articles  (130)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Acta mechanica 107 (1994), S. 101-115 
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The general solution for tangential loading histories of similar bodies with circular areas of contact is outlined and applied to the tangential impact. Classical numerical methods use an interpolation function for the stress distribution on a set of points and obtain the stress distribution for given displacements by inversion of a linear equation system. Our solution avoids large systems of simultaneous equations and gives exact solutions for loading histories in form of finite, successive displacement increments. The general equations of motion for the impact are derived and applied to the case, where the normal and the tangential equations of impact are uncoupled. The Nassi-Shneiderman diagrams of the contact algorithm and the impact algorithm are presented. The solution is compared with other results from earlier publications. A tangential coefficient of restitution, which determines the behaviour of the bodies after impact, is plotted as a function of two parameters.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Zusammenfassung Die Absorptionsspektren von CeCl3·7 H2O, LaCl3·7 H2O, CeCl3·7 D2O und LaCl3·7 D2O wurden bei tiefen Temperaturen im Gebiet des 4 f→4 f Übergangs gemessen. Die Energieniveaus der Ce3+-Ionen in diesen Verbindungen wurden bestimmt. Desgleichen wurden aus den zwischen 4000 cm−1 und 50 cm−1 gemessenen Reflexionsspektren dieser Kristalle die infrarot-aktiven Phononenübergänge bestimmt. Einige der Energieniveaus der Ce3+-Ionen in den deuterierten Kristallen werden um etwa 10 Wellenzahlen gegen die des CeCl3·7 H2O verschoben. Diese Verschiebungen sind wahrscheinlich auf eine resonante Elektron-Phonon-Wechselwirkung in der einen oder anderen der beiden Verbindungen zurückzuführen.
    Abstract: Résumé Les spectres d'absorption de CeCl3·7 H2O, LaCl3·7 H2O, CeCl3·7 D2O et LaCl3·7 D2O ont été mesurés à basses températures dans la région des transitions infrarouges 4 f→4 f. Les niveaus d'énergie de l'ion Ce3+ en ces deux composés ont été dérivés. De même les transitions infrarouges des phonons ont été déterminées à partir des spectres de reflexion de ces cristaux mesurés entre 4000 cm−1 et 50 cm−1. Un certain nombre des niveaus d'énergie des ions Ce3+ est décalé d'environ 10 nombres d'ondes vers ceux du CeCl3·7 H2O. Ces décalages sont probablement dus à une interaction entre niveaus électroniques et états resonants de phonons dans l'un ou l'autre des deux composés.
    Notes: Abstract The absorption spectra of CeCl3·7 H2O, LaCl3·7 H2O, CeCl3·7 D2O and LaCl3·7 D2O have been measured at low temperatures in the region of the 4 f→4 f infrared transitions. The energy levels of the Ce3+-ion in these compounds have been derived. The infrared phonon transitions have also been determined from the reflection spectra of these crystals measured in the region between 4000 cm−1 and 50 cm−1. Some of the energy levels of the Ce3+-ions in the deuterated crystals are shifted for about 10 wavenumbers against those in CeCl3·7 H2O. These shifts are probably due to an interaction of the electronic levels with resonant phonon-states in one or the other of the two compounds.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0365-9496
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1618-2650
    Keywords: Best. von Benzo(a)pyren in Luft ; Fluorimetrie ; DC-Trennung, H2SO4-Lösung
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Summary The potentiality of the method for the determination of benzo(a)pyrene (BaP) in airborne particulates, based on the fluorescence measurements in H2SO4, was investigated. Stability of the BaP fluorescence in H2SO4, isolation of the BaP fraction by thin-layer chromatography and the effect of quenchers on the fluorescence intensity of BaP were studied and the results are discussed. The relative standard deviation of the method was determined to be 2.9 and 5.9% for BaP levels of 265 and 68 ng, respectively.
    Notes: Zusammenfassung Die Möglichkeiten der Benzo(a)pyrenbestimmung durch Fluorescenzmessung in schwefelsaurer Lösung wurden untersucht. Die Stabilität der Fluorescenz, die Isolierung der Benzo(a)pyrenfraktion durch Dünnschicht-Chromatographie sowie der Einfluß fluorescenzlöschender Substanzen wurden geprüft und die Ergebnisse diskutiert. Die relative Standardabweichung des Verfahrens beträgt 2,9 und 5,9% für Benzo(a)pyrenmengen von 265 bzw. 68 ng.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Novel Cluster Frameworks from the Reactions of the Unsaturated Clusters Fe4(CO)11(μ4-PR)2 with AlkynesThe unsaturated clusters Fe4(CO)11(μ4-PR)2 (1-3, R = Ph, p-Tol, t-Bu) react with terminal alkynes primarily by insertion of the alkyne between one phosphorus and two iron atoms. The structure analysis of Fe4(CO)11(μ4-PTol)[μ4-P(Tol)-CMeCH] and NMR studies in solution show that the insertion products exist as two isomers, which differ by the orientation of the alkyne (P—CR—CH—Fe/P—CH—CR—Fe), and whose interconversion in solution can be catalyzed by bases. Starting from 3, additionally and preferentially alkyne-containing clusters are formed with CO elimination, which contain a novel Fe4P2C2 framework that can be derived from a pentagonal bipyramid with an equatorial Fe2PC2 unit as evidenced by the structure determination of Fe4(CO)9(μ3-P-tBu)[μ4-P-(tBu)CHCMe]. The primary alkyne-insertion products are easily induced by an excess of donor ligands [CO, P(OM)3, tBuNC] or by iodine oxidation to eliminate one ironcarbonyl unit and form the clusters Fe4(CO)9(μ3-P-tBu)[μ4-P-(tBu)CHCMe] and substituted derivatives thereof. For these the structure analysis of the (PhPCHCMePPh) compound proves the PCCP sequence and a side-on coordination of the C2 unit to one iron atom. The degradation with P(OMe)3 and tBuNC produces as intermediates the substitution derivatives Fe4(CO)10L(μ4-PPh)-[μ4-P(Ph)CRCH], which also exist as two isomers with different orientation of the CR—CH unit.
    Notes: Die ungesättigten Cluster Fe4(CO)11(μ4-PR)2 (1-3, R = Ph, p-Tol, t-Bu) reagieren mit terminalen Alkinen primär unter Insertion des Alkins zwischen einem Phosphor- und zwei Eisen-Atomen. Die Strukturanalyse von Fe4(CO)11(μ4-PTol)[μ4-P(Tol)-CMeCH] und NMR-Studien in Lösung zeigen, daß die Insertionsprodukte in Form von zwei Isomeren vorliegen, die sich durch die Orientierung des Alkins (P—CR—CH—Fe/P—CH—CR—Fe) unterscheiden und deren gegenseitige Umwandlung in Lösung sich durch Basen katalysieren läßt. Aus 3 entstehen zusätzlich und bevorzugt unter CO-Abspaltung alkinhaltige Cluster mit einem neuartigen Fe4P2C2-Gerüst, das sich von einer pentagonalen Bipyramide mit äquatorialer Fe2PC2-Einheit ableiten läßt, wie die Strukturanalyse von Fe4(CO)9(μ3-P-tBu)[μ4-P-(tBu)CHCMe] belegt. Die primären Alkin-Insertionsprodukte werden durch überschüssige Donorliganden [CO, P(OM)3, tBuNC] und durch Oxidation mit Iod leicht unter Abspaltung einer Eisencarbonyl-Einheit zu den Clustern Fe3(CO)9[μ3-μ3-P(R)-CHCR′PR] bzw. substituierten Derivaten davon abgebaut. Für diese beweist die Strukturanalyse der (PhPCHCMePPh)-Verbindung die PCCP-Verknüpfung und eine Seitwärtskoordination der C2-Einheit an ein Eisen-Atom. Der Abbau verläft mit P(OM)3 und tBuNC über die Substitutionsprodukte Fe4(CO)10L(μ4—PPh)-[μ-P(Ph)CRCH], die ebenfalls in Form von zwei Isomeren mit unterschiedlicher CR—CH-Orientierung vorkommen.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    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 growth-regulating factor MDGI belongs to the fatty acid binding proteins of which the amino acid sequence is known. Starting from hydrodynamic and dichroic measurements which yield estimations about mass, diameter, thickness, and content of α and β structure of the MDGI protein, we used theoretical methods to calculate the structures and electrostatic properties of selected β-chain sequences. The hydrophobic character of possible binding sites for fatty acids is demonstrated by the molecular electrostatic potential and field of this structures. A nonstandard turn element, formed by an H-bridge between polar side chains, Lys-Leu-Gly-Val-Glu, which connects two extended β chains, was found. Bound oleic acid could be able to stabilize such turn structure, which seems to appear also at the entrance of the cavity of two other proteins. The optimization of an oleic acid-turn van der Waals complex results in an interaction energy of about -50 kJ/mol originating mainly from the dispersion term and shows the participation of the four hydrophobic side chains Phe 64, Leu 66, Val 68, and Phe 70. Of these, at least Phe 64 and Phe 70 are known as possible binding sites of fatty acids.
    Additional Material: 1 Ill.
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  • 8
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 9
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0022-2836
    Keywords: lectins ; receptor complex ; sialic acid binding
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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