Ripplonic Lamb Shift for Electrons on Liquid Helium.

We study the shift of the energy levels of electrons on a helium surface due to the coupling to the quantum field of surface vibrations. As in quantum electrodynamics, the coupling is known, and it is known to lead to an ultraviolet divergence of the level shifts. We show that there are diverging terms of different nature and use the Bethe-type approach to show that they cancel each other, to leading order.

Resonant correlation-induced optical bistability in an electron system on liquid helium.

We show that electrons on liquid helium display intrinsic bistability of resonant intersubband absorption. The bistability occurs for comparatively weak microwave power. The underlying giant nonlinearity of the many-electron response results from the interplay of the strong short-range electron correlations, the long relaxation time, and the multisubband character of the electron energy spectrum.

Microwave saturation of the Rydberg States of electrons on helium.

We present measurements of the resonant microwave excitation of Rydberg energy levels for surface-state electrons on superfluid helium. The temperature-dependent contribution to the linewidth gamma(T) agrees with theoretical predictions and is very small below 700 mK, in the ripplon scattering regime. Absorption saturation and power broadening were observed as the fraction of electrons in the first excited state was increased to 0.

Observation of dynamical ordering in a confined Wigner crystal.

We present measurements of the conduction of nondegenerate free electrons along a low-dimensional channel at low temperatures, using surface-state electrons on liquid helium in novel microelectronic devices. Above 1 K, the electrons form an ideal classical Drude conductor. Below 1 K, Coulomb interactions produce electronic spatial order, leading to strong non-Ohmic effects and negative differential conductivity.

Descriptive epidemiology of night sweats upon admission to a university hospital.

Between March 1 and Sept 1, 1980, we interviewed a 25% random sample of patients admitted to medicine, surgery, and obstetric, and gynecology services to determine the frequency and descriptive characteristics of night sweats (NS). Seventy-two (41%) of 174 patients interviewed reported NS within three months before admission. Obstetric patients reported NS significantly more often than nonobstetric patients (60% vs 33%, P less than .