Large-xF spin asymmetry inπ0 production by 200-GeV polarized protons

The spin asymmetryA _N for inclusive ⁰ production by 200-GeV transversely-polarized protons on a liquid hydrogen target has been measured at Fermilab over a wide range ofx _F, with 0.5p _T<2 gev/c.=">x _F>0.3, the asymmetry rises with increasingx _F and reaches a value ofA _N=0.15±0.03 in the region 0.6x _F<0.8. this=" result=" provides=" new=" input=" regarding=" the=" question=" of=" the=" internal=" spin=" structure=" of=" transversely-polarized=">This work was performed at the Fermi National Accelerator Laboratory, which is operated by University Research Associates, Inc., under contract DE-AC02-76CH03000 with the U.S. Department of Energy. Work supported in part by the U.S. Department of Energy, Division of High Energy Physics, Contracts W-31-109-ENG-38, W-7405-ENG-36, DE-AC02-76ER02289, DE-AS05-76ER05096     

Investigation of the spark erosion process in spark-source mass spectrometry with an electron microprobe

The spark erosion process in the ion source of the spark-source mass spectrometer is investigated by examining particles generated from aluminium and zinc alloys in an automated electron probe microanalyzer. For the element with the lowest melting point, selective evaporation was observed. Cross-sections of the sparked surface were examined. The thickness of the molten layer was found to be of the order of a few micrometers; the layer is locally homogeneous in chemical composition.     

A comparison between secondary-ion mass-spectrometry and spark-source mass-spectrometry for the quantitative analysis of steel wire

A comparison has been made between the results of the matrix-ion species ratio (MISR) method for quantification of secondary-ion mass-spectrometry data and spark-source mass-spectrometry analysis using photoplate detection for analysis of the steel basis of AlZn coated wire products. For SIMS quantification a suitable set of sensitivity factors, corrected for the actual surface sampling condition, was used. The results of both methods compare well. The SIMS results were, for most elements, within 25% of the concentration determined by SSMS. This could indicate that reasonably accurate results can be obtained by using the matrix-ion species ratio method for SIMS.     

Synthesis and properties of polyoxyarylenesiloxanes

High molecular weight polymers containing oligosiloxanes in the backbone were made by the reaction of aromatic diols with α,ω-diaminosiloxane homologs. The glass transition temperatures dropped by 30–40°C in a homologous series with each siloxane added. The thermal stability also suffered when increasing the number of siloxane groups. The polymers all displayed high % char measurements and one polymer (disiloxane) tested had a V₀ rating by UL-94 testing. The trisiloxane-containing polymer had a high percent elongation at break (>300%). All the polymers tested were fairly susceptible to hydrolysis. © 1994 John Wiley & Sons, Inc.     

Progress toward the total synthesis of bafilomycin A(1): stereoselective synthesis of the C15-C25 subunit by additions of nonracemic allenylzinc reagents to aldehydes

[reaction: see text] A highly stereoselective synthesis of the C15-C25 subunit (2) of bafilomycin A(1) (1) has been accomplished by a route utilizing additions of chiral nonracemic allenylzinc reagents to aldehydes.     

Total synthesis of bafilomycin V(1): a methanolysis product of the macrolide bafilomycin C(2)

A synthesis of bafilomycin V(1), a methanolysis product of the macrolide natural product bafilomycin C(2), is described. The route utilizes chiral nonracemic allenylzinc reagents, prepared in situ from propargylic mesylates, to access key segments of this methyl ester. The acetylenic moieties of the derived homopropargylic alcohol adducts play an important role in further elaboration of these subunits. Final assemblage of the 25-carbon chain, containing 12 stereocenters, an alpha-methoxy Z,E 1,3-dienic ester, and an additional E,E 1,3-diene, was achieved through Stille coupling of an acetylene-derived vinyl stannane and vinyl iodide of approximate equal complexity. Attempted cyclization of several C15 hydroxy acid derivatives to the 16-membered lactone bafilomycin A(1), a potent inhibitor of vacuolar ATPases, could not be achieved.