A geomagnetic record over the last 3.5 million years from deep-tow magnetic anomaly profiles across the Central Indian Ridge

International audienceHigh-resolution records of the geomagnetic field intensity over the last 4 Myr provided by paleomagnetic analyses of marine sediments have shown the occurrence of short-lived low field intensity features associated with excursions or short polarity intervals. In order to evaluate the ability of marine magnetic anomalies to record the same geomagnetic events, we have collected six deep-tow (-500 m above the seafloor) and several sea surface magnetic anomaly profiles from the Central Indian Ridge across the Brunhes, Matuyama, and Gauss chrons (i.e., from the ridge axis to anomaly 2A). After removal of topography, latitude, and azimuth effects, we converted distances into time sequences using well-dated polarity reversal anomalies as tie points. We calculated the average signal to test the robustness of the short-wavelength anomalies. The resulting stacked profile is very similar to stacked sea surface and downward continued profiles from the Central Indian Ridge, the East Pacific Rise, and the Pacific-Antarctic Ridge. Our results suggest that in addition to polarity reversals, to previously suggested geomagnetic events (subchrons or excursions) within the Brunhes and Matuyama chrons. A new small-scale magnetic anomaly, likely generated by several closely spaced geomagnetic field intensity variations represent the major contributor to the detailed shape of recent marine magnetic anomalies in investigated areas. We observe a dense succession of microanomalies that are correlated excursions (Ontong Java 1 and 2, and Gilsa), is found after the Olduvai chron. The near-bottom results support the existence of three geo-magnetic features between the Gauss-Matuyama boundary and Olduvai. They also suggest three geomagnetic events during the C2A. I n subchron within the Gauss chron. This study emphasizes the potential of deep-tow magnetic surveys in detecting fluctuations in geo-magnetic field intensity and, in particular, short-lived excursions, a poorly constrained part of the geomagnetic field temporal variation spectrum

R/V HAKUHO MARU Cruise Report KH-22-2

調査海域: トカラ列島, 沖縄トラフ / Area: Tokara Isrands, Okinawa Trough ; 期間: 2022年1月29日～2022年2月5日 / Operation Period: January 29, 2022～February 5, 202

Ubiquitous Speech Processing

In the ubiquitous (pervasive) computing era, it is expected that everybody will access information services anytime anywhere, and these services are expected to augment various human intelligent activities. Speech recognition technology can play an important role in this era by providing: (a) conversational systems for accessing information services and (b) systems for transcribing, understanding and summarizing ubiquitous speech documents such as meetings, lectures, presentations and voicemails. In the former systems, robust conversation using wireless handheld/hands-free devices in the real mobile computing environment will be crucial and as will multimodal speech recognition technology. To create the latter systems, the ability to understand and summarize speech documents is one of the key requirements. This paper presents technological perspectives and introduces several research activities being conducted from these standpoints in our research group