ABSTRACT
We report on the observation of terahertz (THz) radiation induced band-to-band impact ionization in HgTe quantum well (QW) structures of critical thickness, which are characterized by a nearly linear energy dispersion. The THz electric field drives the carriers initializing electron-hole pair generation. The carrier multiplication is observed for photon energies less than the energy gap under the condition that the product of the radiation angular frequency ω and momentum relaxation time τ l larger than unity. In this case, the charge carriers acquire high energies solely because of collisions in the presence of a high-frequency electric field. The developed microscopic theory shows that the probability of the light-induced impact ionization is proportional to exp ( - E 0 2 / E 2 ) , with the radiation electric field amplitude E and the characteristic field parameter E 0. As observed in experiment, it exhibits a strong frequency dependence for ω τ â« 1 characterized by the characteristic field E 0 linearly increasing with the radiation frequency ω.
ABSTRACT
The antimicrobiol activity of 6-[D(--)-alpha-aminophenylacetamido]-penicillanic acid-(pivaloyloxymethyl)-ester (privampicillin) was tested in comparison to ampicillin during the acute ascending pyelonephritis of the rat caused by E. coli. Two groups of rats were treated with different drug concentrations; group I:3 times 70 mg/kg/day pivampicillin and 3 times 50 mg/kg/day ampicillin, group II: 3 times 70 mg/kg/day pivampicillin and 3 times 150 mg/kg/day ampicillin; controls were inoculated three times daily with 1.0 ml physiological saline. A higher activity of pivampicillin was found in the first group as proved by bacterial counting in the left and the right renal parenchyma as well as in the urine. In the second group the efficacy of ampicillin was increased.