A computational model of the bottlenose dolphin sonar: Feature-extracting method
A process of echo‐image formation in bottlenose dolphin perception was investigated in our experiments, in which animals were trained to differentiate passive actual echoes recorded beforehand purposely, as well as echo‐like simulated impulses. The results suggest that dolphin, processing echoes within critical interval of time (∼0.2 ms), utilizes the string of three independent, hierarchically organized features (echoes subjective characteristics) being defined by different scales of spectral density oscillation, and energy. Herewith, dolphin is capable to assess features average value over a series of echoes. Distinguishing stimuli, dolphin estimates successively features values from senior to minor, terminating the process at the feature, which contains detectable differences in compared stimuli (the distinctive feature). A procedure of subsequent identification of the reference stimulus can be described by the following decision rule: If the dolphin utilizes some feature as the distinctive one, then i...
Detection of complex echoes in noise by an echolocating dolphin.
Dolphins echolocate with short broadband acoustic signals that have good time resolution properties. Received echoes are often complex, with many resolvable highlights or components caused by reflection of the incident signal from external and internal boundaries of a target and from different propagational modes within a target. A series of experiments was performed to investigate how dolphins perceive complex echoes. Echoes were produced by a microprocessor-controlled electronic target simulator that captured each emitted click and retransmitted the signal back to the animal after an appropriate time delay. The use of this "phantom" target allowed for precise control of the number of highlights, the time separation between highlights, and the relative amplitudes of highlights in the simulated echoes. An echolocating dolphin was trained to perform a target detection task in the presence of masking noise using these phantom echoes. The properties of simulated echoes were systematically varied, and corresponding shifts in the dolphin's detection threshold were observed, allowing for inferences of how the dolphin perceived echoes. The dolphin performed like an energy detector with an integration time of approximately 264 microseconds.
Quasisteady high-confinement reversed shear plasma with large bootstrap current fraction under full noninductive current drive condition in JT-60U.
A quasisteady reversed shear plasma with a large bootstrap current fraction ( approximately 80%) has been obtained for the first time in the JT-60U tokamak. The shrinkage of reversed shear region was suppressed by the bootstrap current peaked at the internal transport barrier (ITB) layer and the ITBs at a large radius were sustained, which, by combination with an H-mode edge pedestal, resulted in a high confinement or 2.2 times the H-mode scaling for 6 times energy confinement time or 2.7 s. Furthermore, a full noninductive current drive was obtained by the bootstrap current and the beam driven current.