Uniforme Hjelmslev-Ebenen und modulare Verbände

Ohne ZusammenfassungDiese Arbeit entstand während eines Aufenthaltes des Verfassers an der McMaster Universität in Hamilton, Ontario, Kanada.     

Einschiebungsreaktion von kohlendioxid in disilylierte phosphane

“Phosphacarbamicesters” are formed by insertion reaction of carbon dioxide into the disilylated phosphanes 1a-c under mild conditions.     

Über die Darstellung von m-Hydroxyphenylsulfonsäuren und m-Hydroxythiophenolen

Zusammenfassung Durch die Einwirkung von SO₃ ² bzw. HSO₃ werden Chinolacetate unter Abspaltung derAcO-Gruppe in m-Hydroxybenzol-sulfonsäuren übergeführt bzw. zum entsprechenden Phenol (BP oderP) reduziert. Mechanismen werden für beide Reaktionsweisen angegeben. Das Ausbeuteverhältnis Additions-/Reduktionsprodukt wird diskutiert. Die Sulfonsäuren werden in ihre Chloride übergeführt und diese zu den m-Hydroxythiophenolen reduziert.

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Wessely's quinol acetates react with SO₃ ² or HSO₃ in two ways: addition in meta-position to the carbonyl group as well as reduction; in both cases an acetoxyl group is removed and phenols (BP orP) are the final reaction products. Mechanisms for both ways are proposed and the addition/reduction ratio is discussed. The meta-hydroxysulfonic acids obtained were converted into their chlorides and subsequently reduced to give the corresponding m-hydroxythiophenols.

     

Influence of different extraction parameters on a solid-phase dynamic extraction for the gas chromatographic determination of d-limonene degradation products by using a fractional factorial design

Through the application of a solid-phase dynamic extraction (SPDE) method for the determination of volatile substances, different parameters may influence the extraction and desorption process and are, therefore, vital for the determination of the extracted substances via gas chromatography (GC). In this study, the influence of extraction und desorption parameters of an SPDE-GC method for the determination of the d-limonene degradation products, namely, alpha-terpineol, (-)-carveol, and (S)-carvone, in an aqueous model system was evaluated using a factorial fractional design. The aim was to reduce the number of factors that should be considered for the optimization of an SPDE procedure for different applications. It could be shown that the extraction efficiency of alpha-terpineol, (-)-carveol, and (S)-carvone is significantly influenced by the extraction parameters incubation temperature, number of extraction strokes, and amount of added NaCl. All 3 parameters have a positive effect on the extraction and determination of the examined d-limonene degradation products. Due to the identification of significant factors on the basis of an experimental design, the results of this study can be very useful for further development of SPDE methods for different applications.     

Continuous-wave room-temperature operation of a 2.8 μm GaSb-based semiconductor disk laser

We demonstrate an optically pumped semiconductor disk laser based on the (AlGaIn)(AsSb) material system, which operates at an emission wavelength of 2.8 μm. Up to 120 mW of output power were obtained in cw operation and more than 500 mW in pulsed mode. The performance of the present laser is discussed in comparison to shorter-wavelength semiconductor disk lasers based on the same materials system.     

A structural study of the retinal photoreceptor, plexiform and ganglion cell layers following exposure to UV-B and UV-C radiation in the albino rat

Over the last two decades, ultraviolet radiation levels (UV), reaching the Earth's surface, have been increasing at a rate of 1.5% per each 1% loss of the ozone layer. Moreover, artificial UV-sources have also proliferated and contributed to the rising UV-stress that many organisms have to face. To assess how the vertebrate retina responds to an exposure of short wavelength UV, we focused our attention on the rat retina, observing photoreceptor (containing outer and inner segments of rods and cones), inner plexiform, and ganglion cell layers by light and transmission electron microscopy using conventional and cytochemical techniques. We analyzed how cells of the layers in question responded to a 30 min exposure to UV-C and UV-B radiation with doses of 7200 and 590 J/cm², respectively. The results show that there are significant changes in the nuclei and cytoplasmic organelles of the exposed retinae when compared with those of the unexposed controls. The changes include an increase in heterochromatin, distension of rough endoplasmic reticulum, mitochondrial disruptions, and increases in the number of myelin bodies. The recorded morphological changes, especially those of the ganglion cells, are suggestive of apoptotic processes and show that the exposure of vertebrate retina to wavelengths ranging from 254 to 312 nm can produce alterations that are likely to impact negatively on the retina's proper functioning.