Spiegelung am parabolischen Zylinder

Ohne ZusammenfassungMit 5 Abbildungen     

Demonstration of a HeNe/CH4-based optical molecular clock

We implement a simple optical clock based on the F2(2) [P(7), v3] optical transition in methane. A single femtosecond laser's frequency comb undergoes difference frequency generation to provide an IR comb at 3.39 microm with a null carrier-envelope offset. This IR comb provides a phase-coherent link between the 88-THz optical reference and the rf repetition rate. Comparison of the repetition rate signal with a second femtosecond comb stabilized to molecular iodine shows an instability of 1.2 x 10(-13) at 1 s, limited by microwave detection of the repetition rates. The single-sideband phase noise of the microwave signal, normalized to a carrier frequency of 1 GHz, is below -93 dBc/Hz at 1-Hz offset.     

Osmotic force-controlled microrheometry of entangled actin networks

In studying a magnetic bead's creep response to force pulses in an entangled actin network we have found a novel regime where the bead motion obeys a power law x(t) approximately t(1/2) over two decades in time. It is flanked by a short-time regime with x(t) approximately t(3/4) and a viscous with x(t)approximately t. In the intermediate regime the creep compliance depends on the actin concentration c as c(-beta) with beta approximately 1.1 +/- 0.3. We explain this behavior in terms of osmotic restoring force generated by the piling up of filaments in front of the moving bead. A model based on this concept predicts intermediate x(t) approximately t(1/2) and long-time regimes x(t) approximately t in which the compliance varies as c(-4/3), in agreement with experiment.     

Measurement of cis and trans isomers of vitamin K1 in rat tissues by liquid chromatography with a C30 column

The purpose of this study was to validate a method for measuring vitamin K isomers in rat tissues by liquid chromatography (LC) with fluorescence detection after simple solvent extraction. This method uses separation on a C30 column, followed by zinc reduction and fluorescence measurement (243 nm, excitation; 430 nm, emission) to detect and quantitate vitamin K isomers. We were able to separate cis- and trans-vitamin K1 in methylene chloride extracts of homogenized rat livers and in hexane extracts of rat plasma. Tissue extracts were evaporated and rediluted with tetrahydrofuran-methanol (1 + 1) or methanol before being injected under isocratic conditions onto the LC column. Liver tissue of Fischer 344 rats fed a vitamin K1-containing diet ad libitum contained approximately 20 and 60 ng/g cis- and trans-vitamin K1, respectively. Mean recoveries of vitamin K1 isomers from spiked liver were 92 +/- 11% for cis-vitamin K1 and 106 +/- 5% for trans-vitamin K1. We recovered 96 +/- 8% of trans-vitamin K1 added at 1, 3, and 6 ng/mL to plasma (containing an endogenous level of 4 ng/g) from the same rats; we recovered 112 +/- 5% when trans-vitamin K1 was added to human serum (National Institute of Standards and Technology Standard Reference Material 968C). This direct method shows significant potential for the selective measurement of vitamin K1 isomers in tissues.     

Adhesion promotion of Cu on C by Cr intermediate layers investigated by the SIMS method

Copper-carbon composites are candidate materials for heat sinks for high speed/high-performance electronic components. They combine high thermal conductivity with low density and a tailorable coefficient of thermal expansion (CTE). Because of the low wettability of carbon by copper, a thin layer of chromium can be deposited to promote both the adhesion and the thermal contact of copper with the carbon fibers. Therefore, in a first step layers of Cr and Cu were deposited by magnetron sputtering on plane vitreous carbon substrates (Sigradur G), which serve as a model for carbon fibers. From pull-off-adhesion measurements an interlayer thickness of Cr in the range of 2-10 nm was found to provide the optimal adhesion for 1 micro m thick copper overlayers. To model the later serial fabrication of the composite that involves a hot pressing step following the deposition, the C/Cr/Cu samples were heat treated at 800 degrees C under vacuum for 1 h. Adhesion on the heat-treated samples was superior in comparison to the untreated ones. To obtain information about the adhesion mechanism secondary ion mass spectrometry (SIMS) investigations were done on the depth distribution of the main elements copper, chromium, and carbon. Two samples, one as deposited and one subjected to heat treatment after deposition, were compared in this investigation. We found that heat treatment mainly modifies the distribution of Cr in the C/Cr/Cu system.     

Über Dienketene aus o-Chinolacetaten

On Dien-Ketenes from o-Quinol-Acetates A detailed picture of the photochemistry of o-quinol-acetates is presented. (RS)-6-Acetoxy-6-methyl-, (RS)-6-acetoxy-2,6-dimethyl-, (RS)-6-acetoxy-5,6-dimethyl-, (RS)-6-acetoxy-2,4,6-trimethyl-, (RS)-6-acetoxy-2,3,4,6-tetramethyl-, and (RS)-6-acetoxy-2,3,4,5,6-pentamethyl-2,4-cyclohexadien-1-ones serve as representative educts. There are two separate main photochemical routes conveniently designated as ¹(π*, n) or ³(π*, π) tracks. The latter may also be attained by sensitization and leads to phenols. The former, by α-cleavage furnishes dienketens as indispensable phototransients. Photolysis of dien-ketens follows one or more of three reaction channels, each of which yields a particular type of photoproduct: heat-induced monocyclization affords 2,4-cyclohexadien-1-ones, heat-induced bicyclization stereoselectively furnishes bicyclo[3.1.0]hex-3-en-2-ones, and multi-step addition of protic nucleophiles stereoselectively gives 1,4-, 1,6- and/or 1,2-adducts. By X-ray analysis or NOE studies, the structure of isolated photoproducts is established. Conventional spectroscopy at low or flash spectroscopy at normal temperature yield information on the formation and decay of kinetically unstable intermediates. Photoproduct composition depends on the pattern of substitution of the educts, on the solvents, and on the nucleophiles that might be present. Substituents primarily exert an influence upon the population of the various conformers of the dien-keten. Solvents affect the rate of the divers reaction paths competing for the phototransient. Nucleophiles play more than a trivial role when adducts are formed. With the detailed view of a dien-keten's role on hand, the photoproduct from a given o-quinol-acetate or more general from a linear conjugated cyclohexadienone is now predictable.     

Über die Bildung eines neuen,stark fluoreszierenden Heterocyclus bei der versuchten Quarterinisierung von Chinolin

When quinoline is treated with ethyl bromoacetate in ethanol at a molar ratio of 1.5:1, a highly fluorescent pyrrolodiquinolinium ion (2a) is formed along with quarternized quinoline (1a). The structure of2a has been established by infrared, proton magnetic resonance and mass spectroscopy as well as by its characteristic ultraviolet absorption spectrum.

Herrn Prof. Dr.K. Schlögl, Universität Wien, zur Vollendung des 60. Lebensjahres mit besten Wünschen gewidmet.     

Verzweigungsordnungen,Differenten und Ganzheitsbasen bei Radikalerweiterungen II

Ohne Zusammenfassung