Traversal time in periodically loaded waveguides

We derive general expressions for the transmission coefficient and the traversal time in waveguides periodically loaded with dielectric slabs. We apply the results to resonant tunneling between two regions below cut-off, with exponentially decaying modes. At the resonant frequencies, we found a relationship between the traversal time and the lifetime. We also study the photonic band gap in a periodic quarter wavelength structure. As in several experiments, we found superluminal velocities.     

Vinyllithiums from butyl-vinyl tellurides and bis-vinyl tellurides

Butyl vinyl tellurides and bis-vinyl tellurides furnish vinyllithiums with retention of configuration in good yields upon treatment with n-butyllithium at −78°C.     

Lifetimes of excited levels of Kr I and Kr II

The lifetimes of eight levels belonging to the 6p configuration of KrI and thirteen levels belonging to different configurations of KrII have been measured. The levels were excited by short electron pulses of appropriate energy and the lifetimes determined by a delayed coincidence method using single photon counting techniques. All measurements were carried out at different gas pressures. The measured lifetimes of the KrII levels are compared with other experimental results obtained by a different method (beam-foil spectroscopy) and with calculations made in the intermediate coupling scheme.     

A study of π andK production in proton-uranium and oxygen-uranium interactions at 22 GeV/A using decay muons

The like-sign dimuons copiously recorded in the NA 38 experiment both inp-U and O?U reactions at 200 GeV/nucleon are interpreted as resulting from decays of π andK mesons in comparable proportions. The ++/?? ratio is large (?1.7) and ascribed to theK ⁺ being more copiously produced than theK ^?. Both the average transverse momentum and the ++/?? ratio are comparable forp-U and O?U reactions, and both increase only slightly with the transverse energyE _T .     

Hard-sphere fluid-to-solid transition and the virial expansion

An exhaustive Padé approximant study of the Mayer virial series expansion is carried out for the classical hard-sphere system. As one increases the order of the different approximants a clear tendency is seen to reproduce both the random close packing divergence of the fluid branch as well as its instability (towards the crystalline phase) at the spinodal point.     

Nonlinear dielectric effect in carbon tetrachloride solutions of iodobenzene

The results of measurements of Δ/E² as a function of concentration for CCl₄ solutions of iodobenzene are given and compared with earlier results for CCl₄ solutions of fluoro-, chloro- and bromo-benzene. Terms contributing to the molar saturation constant for pure halogeno-derivatives of benzene have been calculated, using Kielich's theory. The change of sign of Δ/E² for bromo- and iodo-benzene is explained.     

Field dependence of uniform magnon energies in lamellar CoCl2 and CoBr2 by AFMR experiments

AFMR experiments in the frequency range 77<v<600 GHz and in the magnetic field range 0<H<75 kG on antiferromagnetic CoCl₂ and CoBr₂ single crystals at 4.2 K are reported. The waves propagate along the c axis of the crystals and the steady magnetic field is in the plane of the layers, which is also the easy plane of the spins.The influence of a rotation of the field in the easy magnetization plane is investigated, showing the existence of antiferromagnetic domains.The results of the field dependence of uniform magnon energies are reported in detail for the two compounds CoCl₂ and CoBr₂. In CoBr₂, the two magnon modes at zero field are non degenerate, their frequencies are v₁(0) = 60 GHzandv₂(0) = 675 GHz, and the field required for saturation is H_s⊥ = 74.2 kG.     

Autour des algèbres de Bernstein

Sans résuméTravail subventionné par Dirección de Investigación, Universidad de La Frontera, Temuco. Chile et CONICYT.