The paper deals with an application of the modified Nussbaum Gain in connection with the adaptive stabilization of the process with completely (i.e. in the magnitude and sign) unknown high frequency ...gain. The original idea of the Nussbaum gain is to invert the sign of the gain of the controller periodically and to increase its gain. The stability of such schema was proved for first order systems. The proposed modification is to increase the period of the changing sign rather than the gain of the controller. The idea was applied to the adaptive stabilization of an undesired lateral motion of the balloon gondola. Laboratory experiments have shown higher damping of undesired oscillations in comparison with standard adaptive notch filter approach.
Two approaches to adaptive stabilisation of the undesired lateral motion of the balloon gondola (theadaptive notch filter and the adaptive Butterworth filter which controls the phase of undesired ...oscillations) are reviewed, demonstrated and compared by simulations and laboratory experiments. This undesired motion is caused by asymmetric loading of the gondola, and is sensed by a simple magnetic sensor due to the vertical component of the earth's magnetic field. With the adaptive Butterworth filter a technique similar to Nussbaum's controller for the global stabilisation of adaptive systems with unknown high-frequency gains is proposed and used to stabilise the closed-loop system.
Nonlinear theory of a Cherenkov free-electron laser Fares, Hesham; Mahmoud, Mohamed
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2020, Letnik:
976
Journal Article
Recenzirano
Plasma fluid and Maxwell equations are used to derive an analytical expression for the high-gain of a Cherenkov Free-Electron Laser (FEL). The evolution of the gain from the linear to the non-linear ...regime is investigated. The gain expression is then generalized to predict the linear and non-linear effects at any stage of interaction, permitting us to identify the criteria of optimal design of Cherenkov FELs. In this study, the spatial dependence of the characterizing parameters of electron beam velocity and density, such as the average value and modulation amplitude, are considered. Also, the phase shift between the bunched electrons and the radiation field is taken into account. In the linear limit, it is shown that our gain expression agrees satisfactorily with those obtained in previous studies.
The proposed research presents an analysis of MIMO system performance for two models: max- and minsemicorrelated channels. Closed form analytical expressions for finite signal-to-noise ratio (SNR) ...diversity gain which is the practically valuable indicator of MIMO system reliability were derived. The values of SNR which put the system into asymptotically full-diversity-gain and degeneration regimes are obtained for both models. The influence of such factors as signal constellation size, MIMO system geometry, one-step correlation coefficient on the SNRs are described. The results demonstrate the achievable efficiency of the system in terms of diversity and hence reliability, and under what conditions it is achieved.
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