The Chemistry of Stable Carbenes. Part 2. Benzoin-type condensations of formaldehyde catalyzed by stable carbenes

Stable carbenes derived from thiazole, 1H-imidazole, and 4H-1,2,4-triazole are efficient catalysts for benzointype condensations of formaldehyde. Catalysts derived from N-substituted thiazolium salts trimerize formaldehyde to dihydroxyacetone ( II ). Catalysts based on 1,4-disubstituted 4H-1,2,4-triazol-1-ium salts give glycolaldehyde ( I ) as the main product and no II , whereas N,N′-disubstituted 1H-imidazol-3-ium salts yield mixtures of both products. The isolation of several intermediates in the catalytic cycle provide a better insight into the reaction mechanism.     

Subplane covered affine planes

Projective or affine planes that are covered by subplanes in a prescribed manner are studied and classified. This provides a generalization of the concept of regular spread.This research begun while the second author was a C.N.R. visiting professor in Italy during May–June 1994.     

Enzymatic hydrolysis of prochiral cis-1,4-diacyl-2-cyc-lopentenediols: preparation of (1S,4R)-and (1R,4S)-4-hydroxy-2-cyclopentenylderivatives,versatile building blocks for cyclopentanoid natural products.

The enzymatic hydrolysis of prochiral diesters 1 was studied in presence of seven enzymatic systems, resulting in the enantioselective preparation of both enantiomeric series of chiral building blocks 2 - 4 and $\text{ent}$- 2 - 4 on a preparative scale.     

Ranks of zero patterns and sign patterns

Let F be a field with at least three elements. Zero patterns P such that all matrices over F with pattern P have the same rank are characterized. Similar results are proven for sign patterns. These results are applied to answering two open questions on conditions for formal nonsingularity of a pattern P, as well as to proving a sufficient condition on P such that all matrices over F with pattern P have the same height characteristic.     

Magnetic measurement of transport AC losses in Bi-2223/Ag tapes

Magnetic nature of the losses in superconducting wire carrying AC current implies that it should be possible to determine these losses in a contactless way. Ribbon-like samples are quite favorable for such an experiment, because a notable portion of magnetic flux related to losses ‘escapes' the sample volume and can be detected by an appropriate pick-up coil. In this case, a model describing the AC current penetration into the tape, based, e.g., on the critical state model, allows one to derive the losses from the pick-up coil signal. Because this signal is proportional to the number of coil turns, extension of the accessible range of measured voltages (and losses) can be achieved. We demonstrate the data obtained on a 1 cm long portion of a low-loss multifilamentary tape carrying AC current with frequency 35 Hz. The pick-up coil technique allowed us to reach loss level more than one order below the experimental limit for direct measurements.     

On the direct determination of metals in lubricating oils by ICP

New equipment and procedures are evaluated for the direct analysis of metals in lubricating oils without the need for sample pretreatment or dilution. A modified Babington principle nebulizer equipped with a sample heater is shown to be capable of producing aerosols from undiluted oils, which are suitable for introduction into an inductively coupled plasma atomic emission spectrophotometer. Heating the samples immediately prior to nebulization greatly increases the output of aerosol and reduces output variations in emission intensity due to differences in oil manufacture and viscosity. The type of organometallic complex used in the preparation of standards is shown to be unimportant if the plasma observation region is properly chosen. Performance of a conventional plasma geometry and an inverted torch geometry on analysis of field collected oil samples is presented.     

Optical and magneto-optical properties of YIG and FeBO3

A survey of characteristic optical and magneto-optical properties of the representative ferrite materials yttrium iron garnet (YIG) and iron borate is presented. The interaction of light with collective magnetic excitations, leading to pronounced magnetooptical phenomena, is discussed. Typical examples for the strong influence of foreign atoms on optical and magneto-optical properties of YIG are also given.     

Über die Finslerräume mitS ijkl =0

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