An NMR study of cis-2-butene partially oriented in a nematic phase

The NMR spectrum of cis-2-butene partially oriented in a nematic phase has been analysed, and information about the geometry and the indirect spin-spin coupling constants has been obtained. Assuming the barrier of rotation of the methyl groups and other geometrical information from microwave studies, we obtained = 126 ± 2° and = 116.8 ± 0·6°. The angle that the CH₃ rotation axis makes with the double bond was calculated to be 127·5 ± 0.4°; this value is closely linked with the assumed value of = 109°28′.     

Diffractive production of dijets at HERA

We investigate the production of a quark-antiquark pair in diffractive photon-proton scattering, approximating soft pomeron exchange by the exchange of two nonperturbative gluons. In deep inelastic scattering at HERA, events with two jets and the scattered proton in the final state are predicted to be observable, with an important contribution from charm production. For photoproduction of light quark jets with high transverse momentum we find that both exchanged gluons must have a large invariant mass, so that the cross section is very small, whereas for charm quarks it is quite appreciable. From our calculation we also extract the quark structure function of the pomeron for the scaling variablez no too close to 0 or 1, finding a strong flavour dependence and a behaviour somewhat harder thanz(1?z) for light quarks.     

A simple method for determining anisotropies of diamagnetic susceptibilities of liquid crystals: use of 1H NMR spectroscopy

In mixtures of oriented liquid crystals with opposite signs of diamagnetic susceptibility anisotropies, the point of macroscopic zero anisotropy can be detected by ¹H NMR from the degree of order of a dissolved molecule. On the basis of additivity and of the liquid-crystal molar concentrations relative anisotropies can be determined.     

Anomalous three gauge boson couplings in e+e− → W+W− and “optimal” strategies for their measurement

We discuss how to measure anomalousWWZ- andWWγ-couplings with minimal statistical error using integrated observables, without having to assume that the anomalous couplings are small. We propose a parametrisation of these couplings which is well suited for the extraction of both single and many parameters, and which leads to a very simple form of the integrated cross section, from which additional information on the couplings can be obtained.     

Open charm production in diffractive ep collisions

The cross section for the diffractive reactionγ + p → cc + p with a real or virtual photon is calculated in the nonperturbative two-gluon exchange model of Landshoff and Nachtmann. Numerical predictions are given for cross sections and spectra at typical HERA values of c.m. energy and photon virtuality. The contribution of charm to the diffractive structure function is evaluated and found to be rather small in the model, and the ratio between the production rates for bb and cc is tiny.     

Über die Eigenschaften des Xp-Teils von AnBXp-Kernresonanzspektren

The subspectral breakdown of the X-part in A_nBX_p-spectra is derived and the general properties of the subspectra are discussed. The nature of the asymmetry of X_p-spectra for n > 1 is explained and conditions for its disappearance are given. The degeneration of the X_p-part into deceptively simple spectra is described and degeneration conditions are derived. The determination of relative signs of coupling constants is discussed.     

Das Protonenresonanzspektrum von orientiertem Furan in nematisch-kristallinflüssiger Lösung

The proton spectrum of furan oriented in the nematic phase of anisoleazophenyl-n-capronate has been analysed. The ratios of the various interproton distances as well as the orientation parameters and the signs of the indirect coupling constants for furan are determined.