The time dependence of the surface potential of an insulating materialis theoretically investigated in the case of simultaneous surface and volume ohmicconduction. When the material presents a constant surface conductivity, the first partof the decrease with time of the surface potential is strongly influenced by theinitial distribution of charges and cannot be used to determine the surfaceconductivity. On the other hand, at rather long times after the surface has beencharged, the potential of the surface follows an exponential variation with time, the expression of the corresponding time constant is given in different cases. This modelis found in good agreement with experiments performed with photo-oxidized epoxy resinsplaced in a humid atmosphere.

Calorimetric studies have been made in glassy Se80−x Te20Sbx where 0 ≤x ≤ 15 with a view to calculate the crystallization kinetic parameters. Multi scantechnique has been used to calculate the activation energy of crystallizationΔE and the order parameter (n). The results indicate that ΔE ishighly composition dependent in these glasses. A discontinuity in ΔE is observedat 10% of Sb which is explained in terms of mechanically optimised structure at aparticular average co-ordination number.

In this work, we study the non–Gaussian dynamic of the magnetic field linesof a plasma confined in a toroidal configuration. We have used the Fourier pathstechnique in order to calculate the kurtosis of the magnetic field lines. We have alsocalculate numerically this quantity. The magnetic field lines are described by thestandard mapping. A comparison between our analytical and numerical calculations hasbeen done.

The true and apparent temperature of samples during the deposition of III-V layers by molecular beam epitaxy changes as a result of the variation in spectral emissivityϵ with layer thickness. Taking into account the infrared optical propertiesof these materials, we modelized the variations of the true sample temperature and theapparent temperature (as determined by pyrometric measurement) during the growth. Welimited our study to deposits involving at least one absorbing material (at thepyrometer wavelength), for example GaSb, InAs or InSb. We showed that our simple modelcan agree reasonably with experiments in the 400−500 °C temperature range.