Determination of the isotope distribution in partially deuterated compounds by NMR difference spectroscopy

The position and the isotope distribution within labelled compounds can be determined by NMR by analysing the difference spectrum, and its integral, of the labelled and the corresponding parent compound. The method is applied to m-terphenyl and it 4–4″-dideutero derivative.     

The magnetic-non magnetic transition of cerium impurities in lanthanum-thorium based alloys

A simple theoretical model which assumes a linear increase with thorium concentration for the cerium 4? level with respect to the Fermi level can explain both the decrease $\text{ΔT}{}_{\mathrm{c}}\text{c}$ of the superconducting temperature and the logarithmic slope $\text{d}\text{ρ}\text{c}\text{dln}\text{T}$ of the Kondo resistivity in LaTh based alloys with cerium impurities. The model yields two different maxima for |$\text{d}\text{ρ}\text{c}\text{dln}\text{T}$| and $\text{ΔT}{}_{\mathrm{c}}\text{c}$, the second one of which occurs when the resistivity minimum disappears, in very good agreement with experimental data.     

The hydrogenation of styrenes by hydridocobalt tetracarbonyl

The rates of hydrogenation of several styrene derivatives by stoichiometric hydridocobalt tetracarbonyl [HCo(CO)₄] were measured and compared. The relative rates are discussed in terms of conjugative and steric effects on the geminate radical pair mechanism. An improved method for determining HCo(CO)₄ concentration is described.     

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Determination of the orbital moment and crystal-field splitting in LaTiO3

Utilizing a sum rule in a spin-resolved photoelectron spectroscopic experiment with circularly polarized light, we show that the orbital moment in LaTiO3 is strongly reduced from its ionic value, both below and above the Ne el temperature. Using Ti L2,3 x-ray absorption spectroscopy as a local probe, we found that the crystal-field splitting in the t2g subshell is about 0.12-0.30 eV. This large splitting does not facilitate the formation of an orbital liquid.     

Band-structure modulation in carbon nanotube T junctions

We show that the band structure of metallic carbon nanotubes can be dramatically altered by the local electrostatic field. This is realized by coupling chemically functionalized nanotubes to form T junctions. The bar of the T is the conducting channel and the leg of the T is used for local gating. Transport measurements reveal that an energy gap develops upon application of a local electric field in both devices with or without linker molecules at the junction. We propose that the mechanism of the band gap modulation in the T junctions without linker molecules is the field effect, with the linker molecules introducing additional electromechanical and chemical effects.     

Four-fermion production at $\gamma\gamma$ colliders: 1. Lowest-order predictions and anomalous couplings

We have constructed a Monte Carlo generator (the corresponding FORTRAN code can be obtained from the authors upon request) for lowest-order predictions for the processes and in the standard model and extensions thereof by an effective coupling as well as anomalous triple and quartic gauge-boson couplings. Polarization is fully supported, and a realistic photon beam spectrum can be taken into account. For the processes all helicity amplitudes are explicitly given in a compact form. The presented numerical results contain, in particular, a survey of cross sections for representative final states and their comparison to results obtained with the program package Whizard/Madgraph. The impact of a realistic beam spectrum on cross sections and distributions is illustrated. Moreover, the size of various contributions to cross sections, such as from weak charged- or neutral-current, or from strong interactions, is analyzed. Particular attention is paid to W-pair production channels where we investigate the impact of background diagrams, possible definitions of the W-pair signal, and the issue of gauge-invariance violation caused by finite gauge-boson widths. Finally, the effects of triple and quartic anomalous gauge-boson couplings on cross sections as well as the possibility to constrain these anomalous couplings at future colliders are discussed.Received: 19 May 2004, Published online: 16 July 2004