Photoreactive Langmuir–Blodgett–Kuhn multilayer assemblies from functionalized liquid-crystalline side chain polymers,I. Homopolymers containing azobenzene chromophores

Stable monomolecular layers of a liquid-crystalline homopolymer bearing azobenzene chromophores in the mesogenic side groups could be prepared at the water–air interface by slow compression at room temperature. From the area per monomer unit of A₀≈0.25 nm² a structural model with tightly packed azobenzene groups oriented nearly parallel to the surface normal was deduced. After transfer to a solid support in a Y-type mode the obtained Langmuir–Blodgett–Kuhn (LBK) multilayer assemblies of varying thicknesses (from a double layer to a thick film of d = 238 nm, capable of guiding optical modes) were prepared and analyzed by X-ray reflection and optical evanescent wave techniques. A monolayer thickness of d₀ = 2.52 nm, as well as the anisotropic index of refraction of these layers, could thus be evaluated. Photo-isomerization by UV-irradiation (at λ = (360±30)nm) was examined by UV-VIS absorption spectroscopy. X-ray reflectivity data of samples illuminated for 30 min showed a complete loss of the layered structure of the LBK samples. As a result strongly light-scattering films were obtained. Surface plasmon microscopy was used to demonstrate the usefulness of this photo-induced order–disorder transition for optical information storage.     

Analysis of the hollow cathode emitted electron beams in a radialmultichannel pseudospark

A radial multichannel pseudospark switch seems advantageous for switching currents exceeding 100 kA. A single common hollow cathode guarantees the same trigger conditions for all channels. The electron beams emitted out of the hollow cathode of this switch are analyzed by means of Faraday-cups by varying the circuit as well as the trigger parameters. In addition to the cup measurements, the discharge is observed using a CCD camera. It is found that each channel of the switch must receive a respective beam, before the resistance of the switch turns low, if the discharge current is to run through that channel. In addition, most of the varied parameters do not influence the electron beam     

Greensche tensoren und asymptotische gesetze der elektromagnetischen hohlraumschwingungen

Ohne Zusammenfassung     

Monsterwellen aus Licht

Seit Jahrhunderten berichten Seefahrer von gigantischen Wellen, die scheinbar aus dem Nichts und ohne Vorwarnung auftauchen. Erst Mitte der 1990er‐Jahre hat sich die Erkenntnis durchgesetzt, dass es sie wirklich gibt und sie für eine größere Zahl katastrophaler Schiffsunglücke verantwortlich waren. In Experimenten an der University of California in Los Angeles haben wir vor kurzem überraschenderweise in Lichtleitfasern Monsterwellen aus Licht nachgewiesen. Ursache hierfür ist eine Nichtlinearität der Faser.     

Mechanismus der elektronenstossinduzierten Äathylenabspaltung aus dem Ion [C9H11]+ aus 2,5-Dimethylbenzylbromid

By the investigation of ¹³C-labelled dimethylbenzylbromide, it has been shown that the [M – Br]⁺ ion isomerises to a dimethyltrophylium cation.     

Methylthiomethylierung von Phenolen mit Dimethylsulfoxid-Essigsäureanhydrid

Zusammenfassung Versuche zur milden Oxydation alkohol. Gruppen in Ligninen führten zu einer Untersuchung der Reaktionen von ausgewählten Methoxyphenolen (Guajacol, Kreosol, 6-Methylguajacol, Vanillin, o-Vanillin, Pyrogallol-1,3-dimethyläther, 6-Hydroxymethyl-kreosol) mit Dimethylsulfoxid-Essigsäureanhydrid-Gemischen. Diese Untersuchungen führten zu ähnlichen Resultaten, wie sie kürzlich für Umsetzungen von hauptsächlich Alkylphenolen mit Dimethylsulfoxid-Dicyclohexylcarbodiimid-Phosphorsäure vonBurdon undMoffatt ^5–7 berichtet wurden. Neben orthomethylthiomethylierten Produkten konnten in einigen Fällen als Nebenprodukte Methylthiomethyläther, bei 2,6-disubstituierten Phenolen auch meta- und para-methylthiomethylierte Produkte erhalten werden. Ortho-formyl- bzw.-Hydroxymethylgruppen wurden zum Teil durch Methylthiomethylgruppen ersetzt. Pyrogallol-1,3-dimethyläther lieferte nennenswerte Mengen an Cörulignon.

---

Investigations on the mild oxidation of alcoholic groups in lignins led to studies on the reactions of selected methoxy-phenols (guaiacol, creosol, 6-methylguaiacol, vanillin, o-vanillin, pyrogallol-1.3-dimethylether, 6-hydroxymethylcreosol) with dimethylsulfoxide-acetic anhydride mixtures. The results obtained resemble those reported byBurdon andMoffatt ^5–7 who investigated the reaction of alkylphenols with dimethylsulfoxide-dicyclohexylcarbodiimide-phosphoric acid. Besides orthothiomethoxymethylated products thiomethoxymethyl ethers could be obtained in minor amounts. 2.6-Di-substituted phenols yielded meta- and para-thiomethoxymethylated products. Orthoformyl- and-hydroxymethyl-groups, resp., were substituted by thiomethoxymethyl groups. Pyrogallol-1,3-dimethylether yielded substantial amounts of coerulignone.

---

---

Herrn Prof. Dr.J. W. Breitenbach zum 60. Geburtstag gewidmet.     

A Simultaneous Enumeration Approach to the Traveling Salesman Problem

The solution procedure proposed in this paper uses certain principles of analog computers. The idea of using analog rather than digital computers to solve mathematical programming problems is not new—various methods have been proposed to solve linear programming, network flows, as well as shortest path problems (Dennis, 1959; Stern, 1965). These problems can be more efficiently solved with digital computers. To find a solution to the traveling salesman problem as well as other integer programming problems is difficult with existing hardware, especially if the number of variables is large. The question thus arises whether different hardware configurations make it possible to solve integer problems more efficiently. One such configuration is proposed below for the traveling salesman problem.