Shot Noise Intensity Research Articles

Sub shot-noise intensity fluctuations in a four-wave mixing oscillator

In this paper, a quantum analysis of the intensity fluctuations is given for above-threshold four-wave mixing oscillation in an atomic system. The conditions for optimum noise suppression below the shot-noise level are discussed. In our calculations, the effects of spontaneous emission and Doppler braodening are included. A comparison is made with the recent experimental results of L.M. Vallet, M. Pinard and G. Grynberg, Europhys. Lett. 11 (1990) 739.

A point rainfall model based on a three-state continuous Markov occurrence process

A four-parameter three-state Markov process model for rainfall occurrence at a point is described. The model gives rise to rainfall events which consist of clusters of showers in a similar fashion to existing Poisson cluster process models, but has a more direct physical interpretation since showers do not overlap in time. Parameters may be estimated by maximum likelihood from observed runs of wet and dry hours. Runs of dry hours follow a mixed geometric distribution which is verified using hourly occurrence data for Spokane in mid-winter. The sequential occurrence structure permits a two-parameter autocorrelated exponential (shot noise) intensity process to be associated with the occurrence process which in turn permits the model to match rainfall intensity and occurrence statistics for Denver in mid-summer better than an existing five-parameter rectangular pulse Poisson cluster process model. The occurrence model can be directly related to a simpler two-state model for applications at coarser time scales. Daily statistics for the corresponding two-state model are shown to be consistent with daily statistics for the three-state model. The occurrence model can also be extended to include additional weather states of hydrological significance, such as periods of nonprecipitating cloud.

Noise-current generated by carrier-mediated ion transport at non-equilibrium

The measured spectral intensity Sj(f) of noise-current generated by carrier-mediated ion transport on bilayer membranes agrees under equilibrium and nonequilibrium conditions with the theoretically predicted behavior. It is shown that the shot noise intensity due to this ion transport mechanism yields a frequency independent level of Sj(f) at higher frequencies. The intensity of the shot noise contribution decreases with increasing voltage. Both experimentally and theoretically it could be shown that at nonequilibrium the Nyquist-theorem can no longer be applied for a description of the spectral intensity. Especially, the low frequency tail of Sj(f) is not proportional to the mean macroscopic steady state conductance. The transition of Sj(f) between the low and high frequency limit occurs in a frequency range which is related to the relaxation time constants of the transport system. In contrary to voltage jump current relaxation experiments where two relaxation times are predicted the theory predicts for the noise analysis a third relaxation time constant of a non-zero contribution to Sj(f). Besides the measurement of Sj(f) the corresponding autocorrelation function was determined. Comparison of both methods of noise analysis shows that for the carrier-mediated ion transport the determination of the autocorrelation function is the less appropriate approach due to principal methodical difficulties.