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It is shown that neutral weakly bonded defects in semiconductors may give rise to scattering rates comparable in magnitude to those contributed by ionised impurities. An expression for mobility as a function of temperature is derived for this class of defects and compared with the well known Sclar (1956), and Erginsoy's (1950) formulae.

We have carried out full-scale pseudopotential calculations of the effect of zone-fol-ding on band structure, optical absorption and non-linear response function of semiconductor superlattices. To provide a complete picture of this phenomenon we chose to study GaAs-Gal-xAlxAs, Si-Si1-xGe and HgTe-CdTe superlattices which represent examples of the breakdown of the simple particle-in-a-box model because of Γ - X mixing, strain and relativistic effects, respectively.

In order to compare the extent of the elicited vasoconstrictive and vasodilative response at the microcirculatory level in essential hypertension (EH), we measured the skin blood flow by means of a laser Doppler flowmeter (LDF). Thirty-four mild-to-moderate EH patients were enrolled. Twenty-two sex- and age-matched healthy subjects were selected as a control group. The LDF measurements were carried out with the probe over the fingertip of the distal phalanx at baseline conditions (Rest flow, RF), after an ischaemic test (post-ischaemic peak flow) and during an arithmetic stress test (AT). The flow was expressed in arbitrary units. The data were processed using the Perisoft computer program. The relative flows after the ischaemic test (Rel F1) and during the AT (Rel F2) were expressed as a percentage of the previous RF values (RF1 and RF2, respectively). During the AT, the lag time was calculated (in seconds). As compared to the control subjects, RF was significantly lower in the EH group (p0.01). During the AT, the EH patients showed a statistically lower mean Rel F2 decrease compared to the control subjects (p0.01). No statistically significant difference occurred in the Rel F1 and lag time. These data suggest that the vasoconstrictive capacity of the precapillary vessels is impaired in patients with hypertension.