In this brief, we introduce a "bandwidth-on-demand" variable-gain control (VGC) strategy that allows for a varying bandwidth of the feedback controller. The proposed VGC can achieve improved performance given time-varying, reference-dependent performance requirements compared with linear time-invariant (LTI) control suffering from design tradeoffs between low-frequency tracking performance and sensitivity to higher-frequency disturbances. The VGC consists of frequency-domain loop-shaped linear filters and a variable-gain element, which depends on reference information. We present easy-to-use controller design guidelines and data-based frequency-domain conditions to verify stability and convergence of the closed-loop system. Moreover, the ability of the ``bandwidth-on-demand'' controller to outperform LTI controllers is emphasized through experiments on an industrial nanopositioning motion stage.

Saturn has an intense and broad eastward equatorial jet with a complex three-dimensional structure mixed with time variability. The equatorial region experiences strong seasonal insolation variations enhanced by ring shadowing, and three of the six known giant planetary-scale storms have developed in it. These factors make Saturn’s equator a natural laboratory to test models of jets in giant planets. Here we report on a bright equatorial atmospheric feature imaged in 2015 that moved steadily at a high speed of 450 ms 1 not measured since 1980–1981 with other equatorial clouds moving within an ample range of velocities. Radiative transfer models show that these motions occur at three altitude levels within the upper haze and clouds. We find that the peak of the jet (latitudes 10 N to 10 S) suffers intense vertical shears reaching þ2.5 ms 1 km 1, two orders of magnitude higher than meridional shears, and temporal variability above 1 bar altitude level.