The occurrence of chaotic instability of oscillations at the output of a single-stage amplifier on a powerful bipolar microwave transistor when a biharmonic signal is amplified is considered. It has been established that at a high level of the input signal at the output of the amplifier, the signal contains a significant chaotic component. Cases were experimentally studied when the frequency distance between the partial frequency components of a biharmonic signal is close to the gain band and when it is much smaller than this band. It has been established that in the first case, the chaos in oscillations is associated with the emergence of a sequence of trains of a forced oscillatory process with arbitrary initial phases and durations. In the second case, the appearance of a chaotic pedestal is associated with the chaos in the passive underexcited mode of the nonlinear circuit formed by the capacitance of the p-n junction and the input matching circuits of the amplifier stage.

Strong motion records from full-scale structures provide the ultimate evidence of how real structures, in situ, respond to earthquakes. The most effective method for visualizing the recorded response is by animation. This paper presents a novel method for visualization of the motion of a building that is densely instrumented with triaxial accelerometers and rotational seismometers. The method is based on one- and two-dimensional biharmonic spline interpolation of the motion between multiple sensors on a floor or along the building height. It is demonstrated on a 50-story skyscraper uniquely instrumented with multiple triaxial accelerometers per floor, approximately at every five floors above ground and at two basement levels, and two borehole arrays measuring the motion of the soil very near the building foundation. The animations provide valuable insight into the three-dimensional structural response, including wave propagation through the structure and the interplay between translations and rotations, which will be useful for testing existing and developing new methods for structural health monitoring of buildings and for the further development of building design codes. Animations of selected earthquakes can be found on YouTube at @TPYC-seismic.