Hydrogen incorporation in diamond: the vacancy-hydrogen complex

We report the identification of the vacancy-hydrogen complex in single crystal diamond synthesized by chemical vapor deposition. The S=1 defect is observed by electron paramagnetic resonance in the negative charge state. The hydrogen atom is bonded to one of the carbon atoms neighboring the vacancy. Unlike the analogous defect in silicon, no symmetry lowering reconstruction occurs between the three remaining carbon dangling orbitals. The very small measured hydrogen hyperfine interaction is explained by dipolar coupling between the hydrogen and the unpaired electron probability density delocalized on the three equivalent carbon neighbors.     

Hydrogen incorporation in diamond: the nitrogen-vacancy-hydrogen complex

We report the identification of the nitrogen-vacancy-hydrogen complex in a freestanding nitrogen-doped isotopically engineered single crystal diamond synthesized by chemical vapor deposition. The hydrogen atom is located in the vacancy of a nearest-neighbor nitrogen-vacancy defect and appears to be bonded to the nitrogen atom maintaining the trigonal symmetry of the center. The defect is observed by electron paramagnetic resonance in the negative charge state in samples containing a suitable electron donor (e.g., substitutional nitrogen N(0)(S)).     

The heat of fusion of poly(ethylene terephthalate)

By use of the Clapeyron equation for the dependence of the melting point on pressure, the heat of fusion was found to be 32.5 cal/g, in good agreement with values determined by other methods. An equation for the dependence of the melting point on the degree of polymerization gave a heat of fusion of 27.6 cal/g when applied to hydroxyl-terminated oligomers. This simple relation applied all the way down to the smallest member of the series, di(hydroxy ethyl) terephthalate.     

Cubic irreducible graphs for the projective plane

A characterization of all cubic finite graphs that do not embed in the real projective plane P is given in the sense that Kuratowski characterized all non-planar finite graphs. Specifically it is shown that there exist exactly 6 cubic irreducible graphs for P.     

Methods for studying transmembrane peptides in bicelles: consequences of hydrophobic mismatch and peptide sequence

We have shown that bicelles prepared from dilauryl phosphatidylcholine (DLPC) and dipalmitoyl phosphatidylcholine (DPPC) align in a magnetic field under conditions similar to the more common dimyristoyl phosphatidylcholine (DMPC) bicelles. In addition, a model transmembrane peptide, P16, with a hydrophobic stretch of 24 A, and specific alanine-d(3) labels, was incorporated into all of the different bicelles. The long-chain phospholipid (DLPC, DMPC, or DPPC) remained unperturbed upon incorporation of the peptide while the quadrupolar splitting of the short-chain phospholipid along the bicelle rim increased by varying degrees in the different bicelle systems. The change in quadrupolar splitting of the short-chain phospholipids was attributed to changes in either fluidity of the planar region of the bicelle or differences in overall lipid packing. When the hydrophobic stretch of the bilayer was 22.8 (DMPC) or 26.3 A (DPPC), the peptide tilt was found to be transmembrane (33-35 degrees with respect to the bicelle normal). When the hydrophobic stretch of the bilayer was 19.5 A (DLPC), the peptide quadrupolar splittings suggested a loss of transmembrane orientation. When tryptophan was incorporated in the middle of the transmembrane region, the transmembrane orientation was also lost.     

Regioselective palladium-catalyzed arylation of 2-furaldehyde

An efficient regioselective method for the direct arylation of 2-furaldehyde to provide a range of pi-diverse 5-aryl-2-formylfuran derivatives is described. The method employs functionalized aryl halides and a catalytic amount of palladium(II) chloride under relatively mild conditions.     

General Purpose Heuristics for Integer Programming—Part II

In spite of the many special purpose heuristics for specific classes of integer programming (IP) problems, there are few developments that focus on general purpose integer programming heuristics. This stems partly from the perception that general purpose methods are likely to be less effective than specialized procedures for specific problems, and partly from the perception that there is no unifying theoretical basis for creating general purpose heuristics. Still, there is a general acknowledgment that methods which are not limited to solving IP problems on a class by class basis, but which apply to a broader range of problems, have significant value. We provide a theoretical framework and associated explicit proposals for generating general purpose IP heuristics. Our development, makes use of cutting plane derivations that also give a natural basis for marrying heuristics with exact branch and cut methods for integer programming problems.     

Improved sensitivity of the iodine pentoxide method for the estimation of carbon monoxide

Summary A simple method of improving the sensitivity of the iodometric estimation of carbon monoxide is described. Iodine vapour is trapped on dry silica gel granules instead of in potassium iodide solution as in the conventional methods. Titration of the adsorbed iodine can be conducted in a medium of optimum iodide and starch concentration, the colour change due to adding one microlitre aliquots of N/560 sodium thiosulphate, being detectable. The new technique is particularly suitable for the estimation of less than 10 p. p. m. of carbon monoxide in gas samples of about 300 ml volume, and is also useful as a rapid means of checking the apparatus blank at all times.

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Zusammenfassung Die Empfindlichkeit der jodometrischen Kohlenmonoxydbestimmung läßt sich in einfacher Weise verbessern, indem man die Joddämpfe statt wie üblich in eine Kaliumjodidlösung über trockenes Silikagel leitet. Die Titration des adsorbierten Jods kann dann bei optimaler Konzentration an Jodid und Stärke ausgeführt werden und ist infolge des auf ± 1 l 1/560^–n Thiosulfatlösung scharf erkennbaren Umschlagpunktes genau durchführbar. Das neue Verfahren ist besonders für die Bestimmung von weniger als 0,01 Vol.-% Kohlenoxyd in Gasproben von etwa 300 ml geeignet. Außerdem läßt sich damit jederzeit der Blindwert der Apparatur rasch ermitteln.

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Résumé On décrit une méthode simple pour améliorer la sensibilité du dosage iodométrique de l'oxyde de carbone. La vapeur d'iode est captée sur des grains de silicagel sec à la place de la solution d'iodure de potassium comme dans les méthodes classiques. Le titrage de l'iode adsorbé peut être conduit dans un milieu de concentration optimale en iode et amidon, le changement de coloration dû à l'addition d'aliquotes de thiosulfate de sodium N/560 étant décelable. La nouvelle technique est particulièrement convenable pour le dosage de moins de 10 p. p. m. d'oxyde de carbone dans les échantillons de volume 300 ml environ et se montre utile également comme moyen rapide de contrôle à tout moment de l'essai à blanc.