Einige kritische Bemerkungen zur Theorie der Adsorption

Ohne Zusammenfassung(Aus dem Rudolph Spreckels Physiological Laboratory der University of California.)Aus dem Englischen übersetzt von W. Neumann     

Aspects of stereocontrol in the L-Selectride reduction of 4-acyl-1,3-dioxolane derivatives

The application of L-Selectride, either alone or in combination with ZnCl₂, to aryl ketones 1, 8 and 11 resulted in highly anti-stereoselective reduction. In contrast, lactols 22 and 23 gave a moderate syn-preference using L-Selectride alone and a high syn-preference in the presence of ZnCl₂. Uniquely, high anti- stereoselectivity was observed in the reduction of o-anisyl lactol 37 with L-Selectride alone, which was switched to a high syn-preference when ZnCl₂ was present.     

Circular logic: nonribosomal peptide-like macrocyclization with a ribosomal peptide catalyst

A protease from ribosomal peptide biosynthesis macrocyclizes diverse substrates, including those resembling nonribosomal peptide and hybrid polyketide-peptide products. The proposed mechanism is analogous to thioesterase-catalyzed chemistry, but the substrates are amide bonds rather than thioesters.     

A sensitive, rapid ferricyanide-mediated toxicity bioassay developed using Escherichia coli

A need for rapid toxicity techniques has seen recent research into developing new microbiological assays and characterising their toxicity responses using a range of substances. A microbiological bioassay that determines changes in ferricyanide-mediated respiration for toxicity measurement (FM-TOX) shows particular promise. The development and optimisation of an improved FM-TOX method, incorporating novel features, is described using Escherichia coli as the biocatalyst. Omission of an exogenous carbon source, used in previously described FM-TOX assays, substantially improves the assay sensitivity. In addition, the development of a two-step procedure (toxicant exposure followed by determination of microbial respiratory activity) was found to enhance the inhibition of E. coli by 3,5-dichlorophenol and four other toxicants, compared to single-step procedures. Other assay parameters, such as the ferricyanide concentration, exposure times and optical density of the biocatalyst were also optimised, sometimes based on practical aspects. Toxicity tests were carried out using the adopted technique on both organic and inorganic toxicants, with classic sigmoid-shaped dose-response curves observed, as well as some non-standard responses. IC₅₀ data is presented for a number of common toxicants. The optimised assay provides a good foundation for further toxicity testing using E. coli, as well as the potential for expanding the technique to utilise other bacteria with complementary toxicity responses, thereby allowing use of the assay in a range of applications.     

Radiological characterization of neutron-activated metal wastes from nuclear power stations

Three different methods for determining the long-lived radionuclide contents of highly neutron activated metal wastes are being compared and assessed using samples of pressurized-water reactor (PWR) and boiling-water reactor (BWR) spent fuel disassembly hardware and control rods. These methods include: 1) empirical analyses involving sampling and laboratory measurements; 2) direct assay techniques; 3) calculation methods. These techniques are discussed and the results of the comparisons made to date are presented. The agreement between empirical versus calculational methods for the disassembly hardware was generally within 10% to 50%, and rarely exceeded a factor of 2.5, especially near the fueled region of the reactor core. However, large discrepancies between the measured versus calculated concentrations were observed for⁵⁹Ni and⁶³Ni at the end fittings of the fuel assembly hardware, where the calculations underestimated the concentrations by factors varying from about 8 to 28. The calculation errors are believed to be due to inadequate cross section data for the nickel isotopes.Pacific Northwest Laboratory is operated for the U. S. Department of Energy by Battelle Memorial Institute under Contract DE-AC06-76RLO 1830.     

Measurement of the charging of individual dust grains in a plasma

An experiment is described for investigating the charging of dust grains in a plasma. The apparatus is a double plasma device into which single dust grains are dropped from the top. The dust charge is detected and measured by a sensitive electrometer attached to a Faraday cup on the bottom. Experiments with electrons from the emissive filaments but without plasma indicate that the grains charge to approximately the filament potential for filament bias voltages smaller in absolute value than -70 V. The charge is of order 10⁶ electrons for SiC grains 30-150 μm in diameter. At higher bias voltage the charge is reduced due to secondary emission. The charge on grains increases with grain size and is nearly independent of the filament emission current. With plasma in the device, the grains charge both positively and negatively     

Torsion in Boundary Coinvariants and K -Theory for Affine Buildings

Let (G, I, N, S) be an affine topological Tits system, and let Γ be a torsion-free cocompact lattice in G. This article studies the coinvariants H ₀(Γ; C(Ω,Z)), where Ω is the Furstenberg boundary of G. It is shown that the class [1] of the identity function in H ₀(Γ; C(Ω, Z)) has finite order, with explicit bounds for the order. A similar statement applies to the K ₀ group of the boundary crossed product C ^*-algebra C(Ω)Γ. If the Tits system has type ? ₂, exact computations are given, both for the crossed product algebra and for the reduced group C ^*-algebra.