Cyclotron resonance in lead —I: Tipping effect of magnetic field

The cyclotron resonances in lead in field tipped geometry have been observed for large tipping angles up to 40° from the sample surfaces of the (111) and (100) planes. In addition to the resonance of the orbit ζ on a cylindrical arm of the electron Fermi surface, two new series of resonances, ζ^A and ζ^B have been found, of which the clotron masses are very close to that of ζ but which differ slightly in tipping angle dependence. The mass of ζ^A is dependent on microwave frequency, so that ζ^A is attributed to the Doppler-shifted cyclotron resonance of a non-stationary orbit near, ζ, whose location is discussed in relation to the Fermi surface model of Van Dyke. In field geometry normal to the (100) surface, two series of resonances have been observed, which are characterized as the extinction of even numbered harmonic resonances. This effect arises from the skipping orbit which has a trajectory topologically similar to a baseball seam in real space. One of these series is attributed to the orbit v around the junction of four electron arms.     

Frequency dependence of dielectric crystalline dispersion in oxidized polyethylene

Summary Observed results of the frequency dependence of the dielectric crystalline dispersion in oxidized polyethylene are shown at various temperatures. The value ofɛ(0)—ɛ (∞) increases with the increase of the amount of the carbonyl groups and also the degree of crystallinity. The shape of the absorption curve is nearly the same for various temperatures and also for various samples, including a single-crystallites one. It is also noticeable that the absorption curve has a nearly symmetric shape when it is plotted against the logarithm of frequency. The estimated value of activation enthalpy lies between 24 and 29 Kcal/mol, and the value for a single-crystallites sample is smaller than that for a melt-grown sample. All the experimental results can be explained quantitatively by using a modified theory of our general theory for the dielectric crystalline dispersion. The modification was necessary because the inserted carbonyl groups made the properties of the dielectric crystalline dispersion in oxidized polyethylene to be different from that in other pure polymers. The agreement between the theory and the observed data seems to be satisfactory, except the shape of the absorption curve. The theoretical curve is slightly narrower than the observed shape because of, presumably, too idealized calculations in the present paper.

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Zusammenfassung Die beobachteten Ergebnisse für die Frequenzabh?ngigkeit der Dielektrizit?tskonstante im Kristallinen für oxydierte Poly?thylene werden für verschiedene Temperaturen gezeigt. Die Werte vonɛ(0) —ɛ(∞) steigen mit wachsendem Anteil an Carbonylgruppen und auch mit dem Kristallmit?tsgrad. Die Form der Absorptionskurve ist nahezu für verschiedene Temperaturen und auch für verschiedene Proben dieselbe, einschlie?lich für Einkristallite. Es ist auch bemerkenswert, da? die Absorptionskurve eine beinahe symmetrische Form besitzt, wenn man sie gegen den Logarithmus der Frequenz auftr?gt. Der gesch?tzte Wert der Aktivierungs-Enthalpie liegt zwischen 24 und 29 kcal/mol, und der Wert für die Probe aus Einkristallen ist kleiner als für die aus der Schmelze kristallisierten. Alle experimentellen Ergebnisse k?nnen quantitativ erkl?rt werden unter Benutzung einer modifizierten Theorie aus unserer allgemeinen, für die dielektrische kristalline Dispersion aufgestellten Theorie. Die Modifikation ist notwendig, weil die Zahl der Carbonylgruppen zu klein ist, um die allgemeine Theorie anzuwenden. Die übereinstimmung zwischen Theorie und Experiment scheint zufriedenstellend, au?er hinsichtlich der Gestalt der Absorptionskurve. Die theoretische Kurve ist etwas schmaler als die beobachtete, vermutlich weil die Errechnungen im vorliegenden Fall zu sehr idealisiert sind.

     

Stresses in heterogeneous plates

Conclusion The numerical solution described in the preceding section shows that the heterogeneity of a plate affects seriously the strain distribution but not so much the stress distribution (although this need not be true in general). This conclusion which cannot be immediately introduced from the known knowledge of elasticity, tends to support the assumption made by Müller and Macherauch.Electronic computers allow to find numerical solutions of complicated differential equations. But direct application of an electronic computer to the evaluation of a problem such as treated here is not possible, since the boundary conditions are not prescribed concretely.The solution obtained in this paper also applies to more complicated problems, such as the problems of heterogeneous plates containing holes or notches, because it represents the solution at points distant from the holes or notches. Using this solution, one can prescribe the boundary conditions for those problems concretely, hence numerical solutions can be obtained by the use of an electronic computer.A grant-in-aid for scientific research was given for this study by the Educational Department of Japan.     

C 78 IPR fullerenes: Computed B3LYP/6-31G*//HF/3-21G temperature-dependent relative concentrations

The five isolated-pentagon-rule (IPR) satisfying isomers of C₇₈, labeled 1-5, or according to symmetry as D₃, C_2v, C' _2v , D_3h, and D' _3h , are computed. The cage geometries are optimized at the ab initio HF level with the standard 3-21G basis set (HF/3-21G). The separation energetics is then computed using the B3LYP density-functional treatment in the standard 6-31G* basis set (B3LYP/6-31G*//HF/3-21G). Harmonic vibrational frequencies are calculated by the SAM1 semiempirical method. The computed energies, structural and vibrational data are employed in the construction of isomeric partition functions and evaluation of the relative Gibbs free energies. The results are converted into relative concentrations for a wide temperature interval. The C' _2v structure is the most populated throughout while the D_3h species is negligible at all temperatures. The agreement between theory and experiment is reasonable, though some aspects are still to be clarified. Received 28 November 2000     

Asymmetric Total Synthesis of Indole Alkaloids Containing an Indoline Spiroaminal Framework

The total synthesis of the indole alkaloids, neoxaline, oxaline and meleagrin A, all containing a unique indoline spiroaminal framework, was accomplished through the stereoselective introduction of a reverse prenyl group to the congested benzylic carbon of furoindoline, a two‐pot transformation of indoline (containing three nitrogen atoms at appropriate positions) to the featured indoline spiroaminal framework, and elimination of carbonate assisted by the adjacent imidazole moiety to construct the (E)‐dehydrohistidine. The absolute stereochemistry of neoxaline was elucidated through our total synthesis. In addition, we evaluated the bioactivity, especially the anti‐infectious properties, of neoxaline and oxaline, and of some synthetic intermediates.