Reactions of methylniobium(V) and methyltantalum(V) chlorides with ketones

The chlorides Me_xMCl_5-x, M = Nb, Ta, x = 1, 2, 3 react with carbodiimides RNCNR (R = isopropyl, cyclohexyl, p-tolyl) to give products of the types MCl₄[NR-C(Me)=NR], MeMCl₃[NR-C(Me)=NR], MCl₃[NR-C(Me)=NR]₂, Me₂MCl₂[NR-C(Me)=NR], MeMCl₂[NR-C(Me)=NR]₂, which cóntain bidentate acetamidine groups arising from insertion of the carbodiimide into the metal-carbon bond. The products have been characterised by elemental analysis IR and proton NMR spectra.     

Wrap-around partitioning for block bidiagonal linear systems

A stable vector algorithm for the solution of block diagonallinear systems is obtained by a permutation of the unknownscalled wrap-around partitioning combined with standard QR factorization.Wrap-around partitioning uses blocking and selects the unknownsin the blocks in turns. After a suitable orthogonal eliminationstep one ends up with a reduced system which is again blockbidiagonal and so wrap-around partitioning can be applied again.Using a simple model for vectorization overhead it is shownthat small block sizes give best performance. The minimal blocksize 2, which corresponds to cyclic reduction, is suboptimaldue to memory bank conflicts.     

Overlayer screening of transition metal surfaces: p(1 × 1) H on W{100}

The self-consistent calculation of the electronic levels for a dense ordered overlayer of hydrogen on tungsten {100} suggests that the hydrogen screens the tungsten from the vacuum. The outermost tungsten layer resembles bulk tungsten in contrast to the strongly perturbed surface layer of clean tungsten. The hydrogen-induced levels — those that depend on the hydrogen-tungsten layer spacing — are well described by a tight-binding hydrogen band interacting with the nearest tungsten atoms.     

Absolute Intensities of the 10-µm Bands of (16)O(3)

Two hundred ninety experimental absolute intensities of nu(1) and nu(3) transitions of ozone have been measured, with good accuracy (<2%). They are used to derive the transition-moment parameters for these bands. The agreement between our observed and calculated line intensities is satisfactory. This work shows that the intensities of these two bands are on average 4% smaller than those used in the literature. In addition, 20 intensities of the nu(2) + nu(3) - nu(2) band confirm this value. Also, 42 line intensities of the 2nu(1)-nu(3) band are reported. Copyright 2001 Academic Press.     

Synthetic methodology for the preparation of N-hydroxysulfamides

A convenient synthesis of a variety of substituted N-hydroxysulfamides from chlorosulfonyl isocyanate is reported. Alkyl groups can be introduced selectively on the N-Boc nitrogen of key intermediates 1a or 1b using the Mitsunobu reaction with alcohols. Subsequently the nitrogen carrying the silyloxy group can be alkylated under traditional conditions. Deprotection to the desired N-hydroxysulfamide can be achieved in high yields. Using this method, a number of structurally diverse N-hydroxysulfamides have been prepared. The usefulness of this methodology has further been demonstrated by the synthesis of more complex targets such as bis-hydroxysulfamide 5, and cyclic hydroxysulfamides 7 and 8.     

Identification of material properties of orthotropic elastic cylinders immersed in fluid using vibroacoustic techniques

A numerical study is presented to show the potential for using vibroacoustic-based experiments to identify elastic material properties of orthotropic cylindrical vessels immersed in fluids. Sensitivity analyses and a simulated inverse problem are shown to quantify the potential for material characterization through the use of acoustic emissions. For comparison purposes, the analyses are also shown with the normal component of the velocity at the surface of the cylinder as the measured response in place of the acoustic pressure. The simulated experiment consisted of an orthotropic cylinder immersed in water with an impact force applied to the surface of the cylinder. The material parameters of the cylinder considered in the analyses were the circumferential and longitudinal elastic moduli, and the in-plane shear modulus. The velocity response is shown to provide sufficient information for characterizing all three moduli from a single experiment. Alternatively, the acoustic pressure response is shown to provide sufficient information for characterizing only the two elastic moduli from a single experiment. The analyses show that the acoustic pressure response does not have sufficient sensitivity to the in-plane shear modulus for characterization purposes.     

First experiments on the Australian Synchrotron Imaging and Medical beamline,including investigations of the effective source size in respect of X‐ray imaging

The Imaging and Medical beamline at the Australian Synchrotron achieved `first light' in December 2008. Here, the first experiments performed on the beamline are reported, which involved both X‐ray imaging and tomography studies for a range of samples. The use of a plastic‐edge phantom for quantitative measurements of contrast and resolution proved to be very instructive and helped to confirm certain parameter values such as the effective horizontal source size, detector resolution and average X‐ray energy for the polychromatic beam.