Nonlinear design procedures for single-frequency and broad-band GaAs MESFET power amplifiers

This study is motivated by the vibrations that plague coating processes used in the manufacturing of coated sheet metal. These vibrations arise from time-dependent tension fluctuations within the sheet metal plate as well as from the eccentricity of the rollers used to transport the plate. The time-dependent tension is observed to be rather broad-band and creates multi-frequency parametric excitation. By contrast, the roller eccentricity is largely single-frequency (synchronized with the roller speed) and creates single-frequency external excitation. The plate and excitation sources are studied herein using a single-degree-of-freedom model with a cubic nonlinearity, subject to combined parametric and external excitation. In our study, we investigate the resonances that arise from the synergistic effects of multi-frequency parametric excitation and single-frequency external excitation. For the simpler case of single-frequency parametric excitation, we observe both sum and difference combination resonances in addition to principal parametric resonance. For the case of multi-frequency parametric excitation, we observe a frequency shift for the parametric resonance that derives from the cubic nonlinearity and external excitation. Moreover, the phase relationships of the external and each parametric excitation source have a significant effect on the resulting response amplitude. We use these analyses to explain the resonance mechanisms observed in experiments conducted on an example sheet metal coating process.

Download Full-text

Tubuloglomerular feedback dynamics and renal blood flow autoregulation in rats

AJP Renal Physiology ◽

10.1152/ajprenal.1991.260.1.f53 ◽

1991 ◽

Vol 260 (1) ◽

pp. F53-F68 ◽

Cited By ~ 40

Author(s):

N. H. Holstein-Rathlou ◽

A. J. Wagner ◽

D. J. Marsh

Keyword(s):

Blood Flow ◽

Arterial Pressure ◽

Renal Blood Flow ◽

Slow Component ◽

Broad Band ◽

Experimental Results ◽

Tubuloglomerular Feedback ◽

Single Frequency ◽

Vascular Control ◽

Arterial Blood

To decide whether tubuloglomerular feedback (TGF) can account for renal autoregulation, we tested predictions of a TGF simulation. Broad-band and single-frequency perturbations were applied to arterial pressure; arterial blood pressure, renal blood flow and proximal tubule pressure were measured. Data were analyzed by linear systems analysis. Broad-band forcings of arterial pressure were also applied to the model to compare experimental results with simulations. With arterial pressure as the input and tubular pressure, renal blood flow, or renal vascular resistance as outputs, the model correctly predicted gain and phase only in the low-frequency range. Experimental results revealed a second component of vascular control active at 100-150 mHz that was not predicted by the simulation. Forcings at single frequencies showed that the system behaves linearly except in the band of 33-50 mHz in which, in addition, there are autonomous oscillations in TGF. Higher amplitude forcings in this band were attenuated by autoregulatory mechanisms, but low-amplitude forcings entrained the autonomous oscillations and provoked amplified oscillations in blood flow, showing an effect of TGF on whole kidney blood flow. We conclude that two components can be detected in the dynamic regulation of renal blood flow, i.e., a slow component that represents TGF and a faster component that most likely represents an intrinsic vascular myogenic mechanism.

Download Full-text