Proposal for a phonon laser utilizing quantum-dot spin states.

We propose a nanoscale realization of a phonon laser utilizing phonon-assisted spin flips in quantum dots to amplify sound. Owing to a long spin relaxation time, the device can be operated in a strong pumping regime, in which the population inversion is close to its maximal value allowed under Fermi statistics. In this regime, the threshold for stimulated emission is unaffected by spontaneous spin flips. Considering a nanowire with quantum dots defined along its length, we show that a further improvement arises from confining the phonons to one dimension, and thus reducing the number of phonon modes available for spontaneous emission. Our work calls for the development of nanowire-based, high-finesse phonon resonators.

Nature of tunable hole g factors in quantum dots.

We report an electric-field-induced giant modulation of the hole g factor in SiGe nanocrystals. The observed effect is ascribed to a so-far overlooked contribution to the g factor that stems from the mixing between heavy- and light-hole wave functions. We show that the relative displacement between the confined heavy- and light-hole states, occurring upon application of the electric field, alters their mixing strength leading to a strong nonmonotonic modulation of the g factor.

Observation of spin-selective tunneling in SiGe nanocrystals.

Spin-selective tunneling of holes in SiGe nanocrystals contacted by normal-metal leads is reported. The spin selectivity arises from an interplay of the orbital effect of the magnetic field with the strong spin-orbit interaction present in the valence band of the semiconductor. We demonstrate both experimentally and theoretically that spin-selective tunneling in semiconductor nanostructures can be achieved without the use of ferromagnetic contacts. The reported effect, which relies on mixing the light and heavy holes, should be observable in a broad class of quantum-dot systems formed in semiconductors with a degenerate valence band.

[Fructose content and aldolase activity in the tissues of chickens under ultraviolet irradiation]. / Vmist fruktozy i al'dolazna aktyvnist' u tkanynakh kurei za ul'trafioletovoho oprominiuvannia.

The effect of UV-irradiation was studied as applied to the content of fructose and activity of aldolase in the liver tissue and muscles of chickens and embryos obtained from eggs eight months after the chicken irradiation. It is established that the content of fructose and activity of aldolase in the tissues of 19-day embryos are approximately the same as in 40-140 day chickens. Under the effect of UV-irradiation the content of fructose in the liver increases in 140-day chickens and in embryos of the group under experiment, and it decreases in the muscular tissue of 80-day chickens. In the liver of embryos obtained from the irradiated bird the activity of aldolase lowers and in young chickens no essential difference is observed between the groups. The value of the ratio of the aldolase activity for both substrates in the liver of embryos and chickens of the group under study at the age of 40 and 140 days is somewhat higher than in the control, and in the muscular tissue it is lower (in embryos and chickens at the age of 40- and 80-days).