Synthesis, crystal structure, and nonlinear optical properties of Li6CuB4O10: a congruently melting compound with isolated [CuB4O10]6- units

Single crystals of Li(6)CuB(4)O(10) have been synthesized, and its crystal structure has been determined. Li(6)CuB(4)O(10) crystallizes in the non-centrosymmetric triclinic space group P1 (No. 1). The structure consists of isolated [CuB(4)O(10)](6)(-) polyanions that are bridged by six LiO(4) tetrahedra. Li(6)CuB(4)O(10) is a congruently melting compound. It produces SHG intensity similar to that produced by KH(2)PO(4) and is phase-matchable.     

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The preparation of 5-(2-bromoethyl)-2-iminooxazolidines via the von braun cyanogen bromide reaction

The reaction of certain 1-alkyl-3-pyrrolidinols with cyanogen bromide in ether solution produced 3-alkyl-5-(2-bromoethyl)-2-iminooxazolidines. 5-(2-Bromoethyl)-2-ethyl-2-imino-5-phenyloxazolidine was tested for and found devoid of anorectic activity.     

Polyaromatic ether-sulfone-ketones with fluorosubstituted p-cyclophane units as crosslinking sites

Polyaromatic either-sulfone-ketones containing fluoro-substituted p-cyclophane units were prepared from isophthaloyl chloride, terephthaloyl chloride, diphenyl ether, diphenoxydiphenyl sulfone, and a small amount of 1,1,2,2,9,9,10,10-octafluoro-[2,2]-p-cyclophane (type A) or pseudo-p-1,12,2,9,9,10,10-octafluoro-[2,2]-p-cyclophane bis-acid chloride (type B) by Friedel-Crafts-type polymerization. The p-cyclophane units were incorporated as crosslinking sites. Crosslinking was achieved by curing polymers at 300–350°C for several days. The polymers obtained, containing 1–10 wt % fluoro-substituted p-cyclophane units, were moderately soluble in dichloromethane, DMF, and sulfuric acid with inherent viscosities between 0.4 and 0.6. Laminates on glass fiber were made with excellent thermal stability.     

Polyaromatic ether-ketones from o,o′-disubstituted diphenyl ethers

Polyaromatic ether-ketone resins with potentially open structures which are possibly useful as membranes were prepared from diphenyl ethers with alkyl substitutions in the ortho positions and isophthaloyl or terephthaloyl chloride by Friedel–Craft-type polymerization. These polymers are soluble in such solvents as DMF, DMA, and CHCl₃, and can be cast into colorless transparent films.     

A new approach to variable selection in least squares problems

The title Lasso has been suggested by Tibshirani (1996) as acolourful name for a technique of variable selection which requiresthe minimization of a sum of squares subject to an l₁ bound on the solution. This forces zero components in the minimizingsolution for small values of . Thus this bound can functionas a selection parameter. This paper makes two contributionsto computational problems associated with implementing the Lasso:(1) a compact descent method for solving the constrained problemfor a particular value of is formulated, and (2) a homotopymethod, in which the constraint bound becomes the homotopyparameter, is developed to completely describe the possibleselection regimes. Both algorithms have a finite terminationproperty. It is suggested that modified Gram-Schmidt orthogonalizationapplied to an augmented design matrix provides an effectivebasis for implementing the algorithms.     

1H and 31P NMR spectra of substituted methylphosphonic acids with indirect determination of 31P shifts

Proton and phosphorus magnetic resonance spectra of substituted methylphosphonic acids have been determined as a function of pH. A method has been developed for measuring the ³¹P shift indirectly by optimal heteronuclear decoupling of the ¹H spectra of samples and standards. Control experiments have demonstrated the broad applicability of this technique to the characterization of low milligram samples of N-phosphonomethylglycine and potential metabolites.