A spectral algorithm for envelope reduction of sparse matrices

The problem of reordering a sparse symmetric matrix to reduce its envelope size is considered. A new spectral algorithm for computing an envelope-reducing reordering is obtained by associating a Laplacian matrix with the given matrix and then sorting the components of a specified eigenvector of the Laplacian. This Laplacian eigenvector solves a continuous relaxation of a discrete problem related to envelope minimization called the minimum 2-sum problem. The permutation vector computed by the spectral algorithm is a closest permutation vector to the specified Laplacian eigenvector. Numerical results show that the new reording algorithm usually computes smaller envelope sizes than those obtained from the current standards such as the Gibbs—Poole—Stockmeyer (GPS) algorithm or the reverse Cuthill—McKee (RCM) algorithm in SPARSPAK, in some cases reducing the envelope by more than a factor of two.     

The synthesis and structural analysis of the new high nuclearity platinum-ruthenium cluster complex Pt2Ru8(CO)18(μ3−EtC2Et)2(μ4−EtC2Et) containing three alkyne ligands

Abstarct The ten metal cluster complex Pt₂Ru₈(CO)₂₃(µ₃–H)₂, 1 was found to react with EtC₂Et to form a new ten metal tris-alkyne complex Pt₂Ru₈(CO)₁₈(µ₃–EtC₂Et)₂ (µ₄–EtC₂Et),2 in 35% yield. Complex 2 was characterized by IR,¹H NMR , and single crystalx-ray diffraction analyses. The cluster can be viewed as a dodecahedron of eight metal atoms capped with two ruthenium carbonyl groups, two triply bridging EtC₂Et ligands and one quadruply bridging EtC₂Et ligand. Application of the standard electron counting procedures indicate that this is an unusual complex in which the 18 electron rule applies and the polyhedral skeletal electron pair theory does not. Crystal Data for 2 2.0.5 CH₂CI₂: space group = P2₁,a = 12.759(2) A,b=18.438(2)Å,c = 20.197(3) Å, = 91.59(1)°, Z. = 4, 6394 reflections,R = 0.037.     

Sodium-lead alloy in the decomposition of organic samples for the detection of heteroelements

The decomposition of organic samples using open-tube fusion with sodium-lead alloy was demonstrated to be safe, complete, and controlled, in most cases. The detection of heteroelements in the fusion mixture of common organic samples was successful with samples of 10 to 20 mg. Detection of chlorine and nitrogen by classical methods in “difficult” compounds was secured, and the detection of fluorine in the fusion mixture of fluorocompounds extended the use of the alloy into this area. The use of the pyrazolone color reaction in the detection of nitrogen allowed the detection of more minute amounts of nitrogen than was previously detected using Prussian blue formation. The detection limits for heteroelements in organic samples were in the low microgram region. The application of sodium-lead alloy in quantitative work was briefly studied and will be considered in greater detail in the future.     

An investigation into the determination of stability constants of metal complexes by convolution-deconvolution cyclic voltammetry

A technique is described for calculating stability constants of metal-ligand complexes from convolution-deconvolution voltammetry. Semi-integration of the cyclic voltammetric currents with respect to time allows calculation of E(1 2 ) values in a manner comparable to the use in polarography of the Heyrovsky-Ilkovic equation. The technique described also allows determination of the ratio of the diffusion coefficients of the free and complexed metal ions and provides a second check of the stoichiometry. A reliable route to the metal-complex stability constants by the equations of Lingane and DeFord and Hume is therefore obtained. Advantages of this technique compared with the use of polarography, differential pulse polarography and pH titrations are discussed, with the complexes formed by cadmium with glycine, alanine, valine and aspartic acid as examples.     

Deprotonated diindolylmethanes as dianionic analogues of scorpionate bis(pyrazolyl)borate ligands: synthesis and structural characterization of representative titanocene and zirconocene complexes

Deprotonation of di(3-methylindol-2-yl)phenylmethane (L₂H₂) or with two equivalents of ⁿBuLi, followed by reactions with Cp₂TiCl₂ or Cp₂ZrCl₂ yielded complexes . Compounds 1-4 were characterized by NMR spectroscopy, and compounds 1, 3, and 4 were further analyzed by X-ray crystallography and elemental analysis. The molecular structures of 1, 3, and 4 illustrate that chelating di(3-methylindol-2-yl)methanes have a structural relationship to coordinated bis(pyrazolyl)borates.     

First-principles modeling of dopants in C29 and C29H24 nanodiamonds

Presented here is our continuing first-principles density functional theory study of the structural stability of a select group of dopants in diamond nanocrystals. On the basis of the work of others concerning dopants in diamond and endohedral atoms in fullerenes, the dopants selected for use here are oxygen, aluminum, silicon, phosphorus, and sulfur. These atoms were included substitutionally in the center of a 29-carbon-atom nanodiamond crystal, and each structure was relaxed using the Vienna Ab Initio Simulation Package. We describe the bonding and structure of the relaxed doped nanocrystals via examination of the electron charge density and point group symmetry. In combination with our previously reported results, it is anticipated that these results will assist in providing a better understanding of the mechanical stability of doped nanodiamonds for use in diamond nanodevices.     

Substitutional nitrogen in nanodiamond and bucky-diamond particles

The inclusion of dopants (such as nitrogen) in diamond nanoparticles is expected to be important for use in future nanodevices, such as qubits for quantum computing. Although most commercial diamond nanoparticles contain a small fraction of nitrogen, it is still unclear whether it is located within the core or at the surface of the nanoparticle. Presented here are density functional tight binding simulations examining the configuration, potential energy surface, and electronic charge of substitutional nitrogen in nanodiamond and bucky-diamond particles. The results predict that nitrogen is likely to be positioned at the surface of both hydrogenated nanodiamond and (dehydrogenated) bucky-diamond, and that the coordination of the dopants within the particles is dependent upon the surface structure.     

Effect of surfactants on carbon monoxide fermentations byButyribacterium methylotrophicum

Butyribacterium methylotrophicum has been grown on carbon monoxide as its carbon and energy source in the presence of various surfactants that are capable of forming microbubble dispersions for the screening of surfactants for use in microbubble-sparged synthesis gas fermentations. In the range of 0–3 times the critical micelle concentration, the presence of Tween surfactants was not significantly inhibitory to growth, final cell density, and fermentation stoichiometry, although some of the Brij surfactants caused significant inhibition. As the batch fermentations entered the stationary phase both the pH and the ratio of acetate to butyrate decreased.