A comparison of theoretical compton profiles for aromatic and non-aromatic molecules

This paper compares Compton profiles and electronic momentum distributions derived from minimal Slater orbital basis set SCF MO wavefunctions for the molecules benzene, fulvene, trimethylene cyclopropane, dimethylene cyclobutene, pyridine and borazine. Except for borazine the total molecular Compton profiles are expected to be experimentally indistinguishable. It is concluded that momentum space properties seem to be more dependent on electronegativity than on aromaticity.     

Localized orbitals for the oxygen and nitric oxide molecules

Localized orbitals are derived for the ground states of the oxygen and nitric oxide molecules by applying localization methods separately to the orbitals containing electrons of alpha- and betaspin. Both the intrinsic energy localization and the uniform localization methods are used. The resulting localized orbitals are in good agreement with the formulae suggested by Linnett.

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Zusammenfassung Für die Grundzustände der Moleküle O₂ und NO werden lokalisierte Orbitale abgeleitet, indem die Lokalisierungsmethoden getrennt für die Orbitale mit- und-Spin angewendet werden. Dabei werden sowohl die eigentlichen Energielokalisierungsmethoden als auch die gleichförmigen Lokalisierungsmethoden benutzt. Die erhaltenen lokalisierten Orbitale stimmen gut mit den von Linnett vorgeschlagenen Formeln überein.

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Résumé Obtention d'orbitales localisées pour l'état fondamental des molécules d'oxygène et d'oxyde nitreux par localisation indépendante des orbitales de spin et des orbitales de spin. Emploi simultané de la localisation selon l'énergie intrinsèque et de la localisation uniforme. Les orbitales localisées résultantes sont en bon accord avec les formules suggérées par Linnett.

     

A static cone penetrometer for ocean sediments: T.J. Hirst, A.F. Richards and A.L. InderbitzenASTM Spec. Techn. Publ. No. STP 501, 69–80 (1972)

A static cone penetrometer for deep ocean exploration has been developed and successfully tested in soft sea floor sediments at an ocean depth in excess of 1200 m. The penetration resistance of a standard 60-deg cone is detected by appropriately insulated strain gauges whose output may be monitored remotely from the sensing unit. Initial deployment of the device was aboard the submersible Deep Quest in the San Diego Trough off the coast of southern California. Resistances as low as 7 N (1·6 lb) were measured near the surface of the sediment, generally increasing with depth. At the maximum depth of penetration of 1.1 m (restricted by the limited negative buoyancy of the submersible) tip resistance reached 80 N (18 lb). By means of a conventional bearing capacity analysis, the cone resistance was converted to in situ strength and compared to vane shear measurements taken in the immediate vicinity of the penetration tests. Reasonable agreement between vane shear and penetration strengths were obtained for an assumed bearing capacity factor N_c = 9.     

Hyperfine fields in 3d impurities in metals

The dynamic spin polarization of conduction electrons by an impurity spin is shown to provide a significant positive contribution to the impurity hyperfine field, accounting for the fact that the hyperfine field per unit impurity spin is only about half as large for impurities in metals as in insulators. The anomalously small hyperfine fields of Fe impurities in the noble metals are found to result from an orbital contribution. Quantitative analysis of this orbital contribution suggests that a strong dynamic Jahn-Teller effect is present. Similar orbital contributions can yield a strongly anisotropic hyperfine field for Fe or Cr impurities in hexagonal host metals, depending on the type of crystal-field orbital ground state.     

On the stability of CoMFA models

Abrupt, smooth, and box methods for the calculation of electrostatic and steric field values in the comparative molecular field analysis (CoMFA) 3D QSAR technique are assessed on three diverse data sets of medicinal chemistry interest. While the standard CoMFA settings are robust to small changes in the position of the lattice, superior results may sometimes be obtained by use of only one field. However, if only the electrostatic field is used, then sometimes large differences between models are apparent. This appears to be due to a lack of column dropping, and these difficulties can be remedied by use of the box method.     

Theory of E.P.R. of 3d impurities in metals

The application to the E.P.R. behaviour of dilute alloys of the generalized s-d interaction model appropriate to a 3d impurity with orbital degrees of freedom is considered. It gives rise in some cases to a large spin-lattice relaxation rate in addition to the usual cross relaxation to the conduction-electron spin. Our calculation shows why bottlenecking is effective for some 3d impurities and ineffective for others, leading to qualitative differences in the observed E.P.R. behaviour. It is emphasized that, as a result of the bottlenecking phenomenon, E.P.R. is a uniquely powerful method for determining the electronic states of 3d impurities in metals.     

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