Hydrogenation of fatty acid methyl esters to fatty alcohols at supercritical conditions

Extremely rapid hydrogenation of fatty acid methyl esters (FAME) to fatty alcohols (FOH) occurs when the reaction is conducted in a substantially homogeneous supercritical phase, using propane as a solvent, over a solid catalyst. At these conditions, the limitations of hydrogen transport are eliminated. At temperatures above 240°C, complete conversion of the starting material was reached at residence times of 2 to 3 s, which is several orders of magnitude shorter than reported in the literature. Furthermore, formation of by-products, i.e., hydrocarbons, could be prevented by choosing the right process settings. Hydrogen concentration turned out to be the key parameter for achieving the above two goals. As a result of the supercritical conditions, we could control the hydrogen concentration at the catalyst surface independently of the other process parameters. When methylated rapeseed oil was used as a substrate, the hydrogenation catalyst was deactivated rapidly. However, by using methylated sunflower oil, a catalyst life similar to that obtained in industrial processes was achieved. Our results showed that the hydrogenation of FAME to FOH at supercritical conditions is a much more efficient method than any other published process.     

Evidence for a two-component external marking pheromone system in an aphid hyperparasitoid

The megaspilidDendrocerus carpenteri (Curtis) is a solitary ectohyperparasitoid of aphid primary parasitoids. It avoids superparasitism, but the avoidance rate depends on the amount of time elapsed after the first oviposition. In addition, females discriminate in a time-dependent manner between hosts parasitized by themselves and hosts parasitized by conspecifics. They recognize parasitized hosts by means of two externally perceivable chemical markers that are deposited on the mummy shell. One of the markers is highly active, short-lived, not passable through gas chromatography (GC), and freezing sensitive; the other is moderately active, persistent, GC-passable and freezing tolerant. Using two markers is believed to be advantageous for the hyperparasitoid female, as their ratio provides information on mark age and on the producer of the mark (the female herself or a conspecific female).     

Cable properties of dendrites in hippocampal neurons of the rat mapped by a voltage-sensitive dye

Dendrites of pyramidal neurons from embryonic rat hippocampus are investigated in culture using a voltage-sensitive fluorescent dye. The electrical response to somatic stimulation is observed as a time-resolved map with a resolution of 0.9 microm at a time constant of 0.4 ms without signal averaging. The data are interpreted in terms of a tapering cable with Hodgkin-Huxley parametrization. The spread of short hyperpolarizing transients is damped by capacitive shunting. The invasion of an action potential is boosted by voltage-gated conductances of a low density. No irregularity is observed at a bifurcation. The passive cable parameters of internal resistance and membrane resistance at resting voltage are Ri = 300 omega cm and Rm = 40 (k)omega cm2 respectively, at a maximum sodium conductance of approximately 4.4 mS/cm2. The electrotonic length constant and the dynamic length constant at 1 kHz are 580 and 90 microm respectively. These results are compatible with electrophysiological data of dendrites in slices of adult hippocampus and with optical data of narrow processes of leech neurons in culture. The functional implications of boosting an action potential by voltage-gated channels of low density are considered.     

Ultrastructural alterations of nonciliated cells after nitrosamine treatment and their significance for pulmonary carcinogenesis

Syrian golden hamsters received multiple subcutaneous injections of N-diethylnitrosamine (DEN) or N-dibutylnitrosamine (DBN). Ultrastructural examination of the sequential alterations of bronchial epithelia was performed. Starting from the third to fourth treatment, the formation of lamellated inclusion bodies (LBs) was observed in nonciliated cells of segmental bronchi and peripheral bronchioles. These organelles closely resembled those LBs normally found in alveolar epithelial cells Type 2, which are a characteristic feature of alveolar cell carcinomas.     

Friction properties of sputtered dichalcogenide layers

Only those dichalcogenides of group IV B, V B and VI B metals belonging to the P6₃/mmc and P ml crystallographic groups are considered as solid lubricants. Yet sputtering, which leads to highly turbostratically disordered structures, has emerged as the ‘best’ method of preparation of self-lubricating layers. WS₂, MoS₂, MoSe₂, MoTe₂, NbS₂ and TaSe₂ have been investigated. Using similar deposition parameters, only MoS₂, MoSe₂ and NbSe₂ are consistently good lubricants. Tungsten disulphide proved incompatible with high speed steel and brass substrates. The difference in morphology, substrate compatibility and chemical stability allows for the design of self-lubricating dichalcogenide layers for individual applications