Electron-spin beat susceptibility of excitons in semiconductor quantum wells

Recent time-resolved differential transmission and Faraday rotation measurements of long-lived electron spin coherence in quantum wells displayed intriguing parametric dependencies. For their understanding we formulate a microscopic theory of the optical response of a gas of optically incoherent excitons whose constituent electrons retain spin coherence, under a weak magnetic field applied in the quantum well's plane. We define a spin beat susceptibility and evaluate it in linear order of the exciton density. Our results explain the many-body physics underlying the basic features observed in the experimental measurements

Preparation of crosslinked 1,2,4-oxadiazole polymer

New crosslinked 1,2,4-oxadiazole elastomers were prepared by thermally condensing a monomer having the formula H2N(HON)C-R-Q, wherein Q is a triazine ring-forming group such as nitrile or amidine or a mixture of such group with amidoxime, or a mixture of said monomer with R C(NOH)NH2 sub 2 with R in these formulas standing for a bivalent organic radical. In the monomer charge, the overall proportions of amidoxime groups to triazine ring-forming groups varies depending on the extent of crosslinking desired in the final polymer

Cooperative emission of a pulse train in an optically thick scattering medium

An optically thick cold atomic cloud emits a coherent flash of light in the forward direction when the phase of an incident probe field is abruptly changed. Because of cooperativity, the duration of this phenomena can be much shorter than the excited lifetime of a single atom. Repeating periodically the abrupt phase jump, we generate a train of pulses with short repetition time, high intensity contrast and high efficiency. In this regime, the emission is fully governed by cooperativity even if the cloud is dilute.Comment: 5 pages, 3 figure

Relations between the SNO and the Super Kamiokande solar neutrino rates

By comparing the neutrino spectra measured by SNO and Super Kamiokande, we obtain inequalities between the ratios of observed rate to SSM rate for the two experiments. These inequalities apply to a possibly energy-dependent reduction of the SSM flux and to the case of neutrino oscillations. We use them to examine the relationship between the two experiments expected for the MSW and ``Just-So" oscillation scenarios.Comment: 8 pages + 3 figures, REVTeX, uuencoded file created on a VMS syste

On a stochastic control method for weakly coupled linear systems

The stochastic control of two weakly coupled linear systems with different controllers is considered. Each controller only makes measurements about his own system; no information about the other system is assumed to be available. Based on the noisy measurements, the controllers are to generate independently suitable control policies which minimize a quadratic cost functional. To account for the effects of weak coupling directly, an approximate model, which involves replacing the influence of one system on the other by a white noise process is proposed. Simple suboptimal control problem for calculating the covariances of these noises is solved using the matrix minimum principle. The overall system performance based on this scheme is analyzed as a function of the degree of intersystem coupling

Volatility and Agent Adaptability in a Self-Organizing Market

We present results for the so-called `bar-attendance' model of market behavior: $p$ adaptive agents, each possessing $n$ prediction rules chosen randomly from a pool, attempt to attend a bar whose cut-off is $s$. The global attendance time-series has a mean near, but not equal to, $s$. The variance, or `volatility', can show a minimum with increasing adaptability of the individual agents.Comment: 8 pages, 3 figs. [email protected], [email protected]