Zur Kenntnis cyclischer Acylale, 8. Mitt.

Zusammenfassung Cyclische Acylale substituierter Methylen-malonsäuren verhalten sich bei der Titration mit Alkali wie einprotonige Säuren. Die Ursache dieses Verhaltens ist eine sehr rasch verlaufende und durch Zugabe von Mineralsäure wieder umkehrbare Addition von OH^–-Ionen an die genannten Verbindungen. Es werden chemische und spektroskopische Beweise für die Struktur der durch die OH^–-Anlagerung entstandenen mesomeren Anionen beigebracht. Über Darstellung und Reaktionen einiger Acylale substituierter Methylen-malonsäuren wird berichtet.Cyclic acylals of substituted methylenemalonic acids can be titrated as monoprotonic acids. The reason for such a behaviour is the very rapidly proceeding addition of OH^– to these compounds, readily reversible on addition of mineral acids. Chemical and spectroscopical evidence for the structure of the mesomeric anions formed by the addition of OH^– is given. The preparation and reactions of some acylals of substituted methylenemalonic acids are reported.Mit 3 AbbildungenEinige wichtige Ergebnisse der in dieser Arbeit mitgeteilten Untersuchungen wurden bereits in einer kurzen vorläufigen Mitt. veröffentlicht. Hier sollen die dort erwähnten Befunde ergänzt und das experimentelle Material nachgetragen werden.     

Relationship between refined Griffith criterion and power laws for cracking

Rice [J. Mech. Phys. Solids 26 (1978) 61] proposes a refined Griffith criterion, at any local crack front, where G is the Irwin's energy release rate, γ is the surface free energy and is the rate of crack advance. The refined version implies that the entropy production inequality should holds locally rather than globally from the thermodynamic point of view. Within the irreversible thermodynamic framework developed by Rice [J. Mech. Phys. Solids 19 (1971) 433; Constitutive Equations in Plasticity, 1975, p. 23], it is revealed in this paper that the entropy production inequality holds for each internal variable if its rate is a homogeneous function in its conjugate force. It is further shown that widely-used power laws for crack growth are just certain homogeneous kinetic rate laws, so it is concluded that the power laws directly lead to the refined Griffith criterion.     

OH-radical induced degradation of hydroxybenzoic- and hydroxycinnamic acids and formation of aromatic products—A gamma radiolysis study

The OH-radical induced degradation of hydroxybenzoic acids (HBA), hydroxycinnamic acids (HCiA) and methoxylated derivatives, as well as of chlorogenic acid and rosmarinic acid was studied by gamma radiolysis in aerated aqueous solutions. Primary aromatic products resulting from an OH-radical attachment to the ring (hydroxylation), to the position occupied by the methoxyl group (replacement –OCH₃ by ?OH) as well as to the propenoic acid side chain of the cinnamic acids (benzaldehyde formations) were analysed by HPLC–UV and LC–ESI–MS. A comparison of the extent of these processes is given for 3,4-dihydroxybenzoic acid, vanillic acid, isovanillic acid, syringic acid, cinnamic acid, 4-hydroxycinnamic acid, caffeic acid, ferulic acid, isoferulic acid, chlorogenic acid, and rosmarinic acid. For all cinnamic acids and derivatives benzaldehydes were significant oxidation products. With the release of caffeic acid from chlorogenic acid the cleavage of a phenolic glycoside could be demonstrated. Reaction mechanisms are discussed.     

170 Mb/s multilevel transmission over 115 m standard step-index plastic optical fiber using an integrated optical receiver

An optical receiver having a high linearity is used for multilevel communication over standard step plastic optical fiber. A large-diameter photodiode with an antireflection coating optimized for red light was integrated. These features enable the used optical receiver to be a promising plastic optical fiber receiver. An error free (< 10⁻⁸) 170 Mb/s data rate over 115 m standard PMMA step-index plastic optical fiber is achieved with four-level and eight-level pulse amplitude modulation.     

Schwefelbestimmung in unlegierten St?hlen, legierten St?hlen, Roheisen und Ferrolegierungen durch Verbrennung im Sauerstoffstrom

Zusammenfassung Es wird die Ausführung eines Verfahrens zur schnellen und genauen Bestimmung des Schwefels in unlegierten Stahlen, legierten Stählen, Roheisen und auch in Ferrolegierungen durch Verbrennung im Sauerstoffstrom und anschliessende Titration beschrieben, wobei hinsichtlich Genauigkeit der Titration der gleiche Grad wie beim Entwicklungsverfahren erreicht wird.     

Zur Kenntnis cyclischer Acylale, 4. Mitt.: Über die Bildung von Cyclopropan-spiroderivaten

Ohne Zusammenfassung     

The Electron-Hole plasma in CdS between 5 K and room temperature

We investigate and analyze the time-integrated nonlinear optical behaviour of an electronhole plasma in CdS as a function of the temperature and the exciting intensity. The competition between the temperature dependences of the absorption tail and of the manyparticle effects leads with increasing temperature around 160 K to a turn-over from a red- to a blue-shift of the absorption edge under excitation. The frequency dependence of the absorption for high plasma concentrations is in good agreement with theoretical calculations.     

Zur Konstitution des Produktes aus Benzyliden-bis-acetamid und Dihydroresorcin

Zusammenfassung Das aus Benzyliden-bis-acetamid und Dihydroresorcin erhaltene Reaktionsprodukt¹ ist nicht das 2-Benzyliden-cyclohexan-1,3-dion, sondern mit dem erstmals vonD. Vorländer undO. Strauss ⁷ hergestellten 9-Phenyl-1,2,3,4,5,6,7,8-octahydroxanthen-1,8-dion identisch.the author is geb. A dametz H. Hellmann, G. Aichinger undH.-P. Wiedemann, Ann. Chem.626, 35 (1959).