Ferroelectric properties of liquid-crystalline SC* phases induced by optically active cyanocyclohexylcyclohexanone derivatives

Derivatives of optically active cyanocyclohexylcyclohexanone have been synthesized and used as dipolar chiral dopants to induce ferroelectric S_C* phases in an achiral host phase. The dopant molecules are the first examples in which the chiral centres are incorporated into a rigid core with transverse dipoles directly attached. The spontaneous polarization P_s and the tilt angle θ of the induced S_C* phases have been measured. P_s is strongly influenced by the relatively small changes of the molecular structure of the cyclohexanones, for example a change of the sign of P_s or a vanishing value of P_s. These effects are discussed in terms of a sterically hindered rotation of the dopant molecules around their long axes and explained by the assumption that the transverse dipole must not be necessarily parallel to P_s in the equilibrium state of rotation.     

Messung der Kettenlänge für den β-Zerfall der Spaltprodukte bei der thermischen Spaltung von U235

The various masses of fission products of U²³⁵-thermal fission were spacially separated by a helium filled magnetic mass separator. The number and energy of theβ-decays to the stable nuclides were counted and measured by a scintillation spectrometer. The time dependance of theβ-activity andβ-energy of the total of the U²³⁵ fission products was measured. The number ofβ-decays/fission was found to be (6,9±0,4)β-particles fission, the energy liberated byβ-decays (8,1±0,4) MeV/fission. A calculation of the totalβ-decay energy is given and compared with experimental data. The chainlengths ofβ-decay chains as a function of mass of the fission products were measured. Data on prompt neutron emission from fission products combined with the chainlength measurement give the mass dependance of the most probable charge of the primarily formed fission products. A recent model of asymmetric fission is shown to agree with the experimental data. The data give strong evidence that the filled nucleon shells ofZ=50 andN=50 are responsible for the asymmetric fission mechanism.     

Die Bewegung des Polarisationsvektors eines Dirac-Teilchens im makroskopischen elektromagnetischen Feld

Scattering has been observed of 70-keV electrons by Kollodium-foils containing elements of high atomic number (lead). The contents of lead are determined and the kind of distribution of lead in the foil is described. The differential cross-section as a function of the angle of scattering approximates the cross-section calculated by Sherman with lower contents of lead of the foils. Remaining deviations can be explained by screening-effects of the electron cloud.     

Irreducible subrepresentations of the conjugation representation of finitep-groups

For finitep-groupsG we study the conjugation representation γG which is defined by lettingG act on itself by conjugation. Roth conjectured that every irreducible representation ofG which is trivial on the center ofG, occurs in γG. However, this is not true in general. We construct minimal counterexamples and verify Roth's conjecture for various classes of finitep-groups, for instance those of maximal class. Dedicated to Professor George Maltese on the occasion of his 60th birthday     

Charge participation in the fragmentation of functionalized steroids

A series of steroidal model compounds specifically designed to allow maximal as well as minimal charge localization at certain functional groups was subjected to mass spectrometric analysis. The results indicate that electron deficiency at the potentially reactive site is a prequisite for any fragmentation reaction to occur to an appreciable extent. The amount of charge density required at such a site seems to vary substantially for different types of fragmentation processes.     

Two canonical wedge problems for the Helmholtz equation

Boundary-transmission problems for two-dimensional Helmholtz equations in a quadrant and its complement, respectively, are considered in a Sobolev space setting. The first problem of a quadrant with Dirichlet condition on one face and transmission condition on the other is solved in closed form for the case where all the quadrants are occupied by the same medium. Unique solvability can also be shown in the case of two different media up to exceptional cases of wave numbers, while the Fredholm property holds in general. In the second problem, transmission conditions are prescribed on both faces. Similar results are obtained in the one-medium case, but the two-media case turns out to be more complicated and the equivalent system of boundary pseudodifferential equations cannot be completely analysed by this reasoning.     

Ellen Gleditsch: Pioneer Woman in Radiochemistry

We present the life and work of the Norwegian scientist Ellen Gleditsch (1879-1968) in the early era of radioactivity. From 1907-1912, Gleditsch worked as Marie Curies assistant in the Laboratoire Curie in Paris on the alleged copper-lithium radioactive transformation and on the radiumuranium ratio, as well as studying chemistry and related subjects at the Sorbonne. Later,in 1913-1914, she worked in Bertram Boltwoods laboratory at Yale University on the half-life of radium. Gleditsch also was concerned with academic opportunities for women, and she became the president of the International Federation of University Women. As a professor, the second female professor in Norway, she initiated a research group on radioactivity at the University of Oslo.     

Rationally designed ligands for asymmetric iridium-catalyzed hydrogenation of olefins

A new class of chiral N,P-ligands for the Ir-catalyzed asymmetric hydrogenation of aryl alkenes has been developed. These new ligands proved to be highly efficient and tolerates a broad range of substrates. The enantiomeric excesses are in the range of the best ever reported. The results can be rationalized with the proposed selectivity model.