Wave forms of BEN (Broadband Electrostatic Noise) in the geomagnetic tail were first detected by the Wave Form Capture receiver on the GEOTAIL spacecraft. The results show that most of the BEN in the plasma sheet boundary layer (PSBL) are not continuous broadband noise but are composed of a series of solitary pulses having a special form which we term “Electrostatic Solitary Waves (ESW)”. A nonlinear BGK potential model is proposed as the generation mechanism for the ESW based upon a simple particle simulation which considers the highly nonlinear evolution of the electron beam instability. The wave forms produced by this simulation are very similar to those observed by GEOTAIL and suggest that the nonlinear dynamics of the electron beam play an essential role in the generation of ESW.
[1] We perform an electromagnetic full particle simulation to study the generation mechanism of VLF whistler-mode chorus emissions in the equatorial region of the magnetosphere. Parabolic variation of the static magnetic field is assumed as a model for the dipole magnetic field in the vicinity of the equator. We have cold thermal electrons and relatively low anisotropic hot electrons as plasma particles. In the initial phase, the amplitude growth of the incoherent whistler-mode waves is determined by the linear growth rate. When the wave amplitude reaches a certain level, it begins to grow more rapidly with a series of rising tone emissions consisting of coherent phase structures in the vicinity of the magnetic equator, and their wave packets propagate away form the magnetic equator. The frequency sweep rates of the excited rising tone elements decrease gradually. We find a distinct threshold for such a nonlinear wave growth generating the rising chorus-like elements. The relation between the wave amplitude and the frequency sweep rate of each element found in the simulation fully supports the nonlinear wave growth theory of chorus emissions.
Compared with the knowledge of maternal care, much less is known about the factors required for paternal parental care. Here we report that new sires of laboratory mice, though not spontaneously parental, can be induced to show maternal-like parental care (pup retrieval) using signals from dams separated from their pups. During this interaction, the maternal mates emit 38-kHz ultrasonic vocalizations to their male partners, which are equivalent to vocalizations that occur following pheromone stimulation. Without these signals or in the absence of maternal mates, the sires do not retrieve their pups within 5 min. These results show that, in mice, the maternal parent communicates to the paternal parent to encourage pup care. This new paradigm may be useful in the analysis of the parental brain during paternal care induced by interactive communication.
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