Spontaneous DC Current Generation in a Resistively Shunted Semiconductor Superlattice Driven by a TeraHertz Field

We study a resistively shunted semiconductor superlattice subject to a high-frequency electric field. Using a balance equation approach that incorporates the influence of the electric circuit, we determine numerically a range of amplitude and frequency of the ac field for which a dc bias and current are generated spontaneously and show that this region is likely accessible to current experiments. Our simulations reveal that the Bloch frequency corresponding to the spontaneous dc bias is approximately an integer multiple of the ac field frequency.

Late onset of huntington's disease

Twenty-five patients with late-onset Huntington's disease were studied; motor impairment appeared at age 50 years or later. The average age at onset of chorea was 57.5 years, with an average age at diagnosis of 63.1 years. Approximately 25% of persons affected by Huntington's disease exhibit late onset. A preponderance of maternal transmission was noted in late-onset Huntington's disease. The clinical features resembled those of mid-life onset Huntington's disease but progressed more slowly. Neuropathological evaluation of two cases reveal less severe neuronal atrophy than for mid-life onset disease.