Swarm parameters of electrons have been calculated for fluorine by a Monte Carlo simulation and the Boltzmann equation method for the first time. Values of these parameters have been obtained for ratios of the electric field to the gas number density E/N from 100 to 3000 Td (E/p0 =35∼1000 V/cm Torr). Available experimental and theoretical cross sections were used for the calculations.

The importance of the attachment cross-section for F- formation for the effective ionisation coefficients in SF6 is discussed. The values of the dissociative attachment cross-section qa for F- formation for electron energies from 2 to 15 eV are very small compared with the values of qa for SF6 - formation at low electron energies. However, the effect of the values of qa for F- formation on the effective ionization coefficients is very great. Calculations were carried out by a two-term Boltzmann equation analysis. It is pointed out that the measured grand total electron-SF6 cross-sections were inconsistent with the sum of elastic and inelastic cross-sections used by many workers.

We describe the asymptotic boundary of the general homogeneous plane wave spacetime, using a construction of the 'points at infinity' from the causal structure of the spacetime as introduced by Geroch, Kronheimer and Penrose. We show that this construction agrees with the conformal boundary obtained by Berenstein and Nastase for the maximally supersymmetric ten-dimensional plane wave. We see in detail how the possibility of going beyond (or around) infinity arises from the structure of light cones. We also discuss the extension of the construction to time-dependent plane wave solutions, focusing on the examples obtained from the Penrose limit of Dp-branes.

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A secondary electron yield from a polycrystalline Al surface was measured under Ar þ bombardment. The yield of negatively charged particles ðÞ was measured as a function of steady state oxygen coverage of target surfaces during Ar þ bombardment. Projectile energy was changed from 20 to 80 keV. The absolute value of effective oxygen coverage of a target surface was determined in situ by means of an optical spectroscopic technique in which light intensities emitted by sputtered excited atoms from the target was measured as a function of current densities of the projectile. Absolute yield of secondary electrons at zero oxygen coverage, ð0Þ, was obtained by measuring yield variation as a function of .