著者

Hisashi Sanada

雑誌

2020 横浜スポーツ学術会議

巻号頁・発行日

2020-08-19

著者

成田 悠輔 矢田 紘平

出版者

人工知能学会

雑誌

2020年度 人工知能学会全国大会(第34回)

巻号頁・発行日

2020-04-01

著者

松下 祥子 管原 星弥 池田 拓未 荒木 拓真 関谷 颯人 木幡 春輝 磯部 敏宏 中島 章

雑誌

2020年第81回応用物理学会秋季学術講演会

巻号頁・発行日

2020-07-09

著者

宮本 健太郎

雑誌

第43回日本神経科学大会

巻号頁・発行日

2020-06-15

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To explore and survive in an unpredictable, volatile world with multiple alternatives available, people and other animals, such as macaque monkeys, need to estimate uncertainty before making a decision. However, the neural mechanism to enable proactive metacognitive judgements based on evaluation of uncertainties is unknown.In our first study on humans with functional neuroimaging and transcranial magnetic stimulation, we newly invented a prospective metacognitive matching task. In the task, participants were required to estimate their performance (`subjective probability') to classify the direction of ambiguous motion in random-dot kinematogram task. Then they compared this subjective probability with the probability of reward offered by the alternative external cues (`environmental probability') and chose the better probability option in prior to performing the motion classification. Activity in several frontal and parietal areas reflected both subjective and environmental probabilities during perceptual decision making. Anterior lateral prefrontal cortex (alPFC, area 47), however, tracked evidence relating to subjective probabilities both when a choice was taken and when it was rejected. Moreover, fMRI signals in alPFC modulated by subjective probability predicted prospective metacognition performance and ability. These observations suggest that alPFC plays a critical role to assess one's own cognitive skills and mental states proactively to take an optimal choice in the future.In our second study on monkeys with functional neuroimaging and targeted pharmacological intervention, we previously found that the dorsal prefrontal and frontopolar cortices confer decision confidence on experience and ignorance, respectively, during a serial-probe recognition memory task (Miyamoto et al., 2017, Science 355(6321); Miyamoto et al., 2018 Neuron 97(4)). We have newly found that the inferior parietal lobule (area PG) contributes to integrate these confidence read-outs and execute a strategically optimal decision making for post-decision wagering based on self-reflection of performance in the precedent memory task.These human and monkey studies converge to suggest that higher-order processes to proactively evaluate subjective uncertainties are implemented in primate neural networks. The neural mechanism would be essential to convert metacognition into action.

著者

船水 章大 Fred Marbach Anthony M Zador

雑誌

第43回日本神経科学大会

巻号頁・発行日

2020-06-15

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Neurons in auditory cortex encode auditory stimuli, but the precise encoding can depend strongly on task-relevant variables such as stimulus or reward expectation. This raises the question: If the cortical representation of the stimulus varies with task-relevant variables, how can areas downstream of auditory cortex decode these representations? One possibility is that decoding in downstream areas also depends on these task-relevant variables. To address this question, we developed a two-alternative choice auditory task for head-fixed mice in which we varied either reward expectation (by varying the amount of reward, in blocks of 200 trials) or stimulus expectation (by varying the probability of different stimuli). The task was based on our previous study (Marbach and Zador, bioRxiv, 2016) in which mice selected left or right spout depending on the frequency of tone stimuli (low or high). We used two-photon calcium imaging to record populations of neurons in auditory cortex while mice performed the task. We found that varying either reward or stimulus expectation changed neural representations (i.e. stimulus encoding). However, the optimal decoder was remarkably invariant to different encodings induced by different expectations. The discrepancy between the neural encoding and decoding could be that the prior encoding was independent from the sound decoding in the auditory cortex. Our results suggest that stimuli encoded by auditory cortex can be reliably read out by downstream areas, even when the encoding is modulated by task-relevant contingencies.

著者

矢部 優 今西 和俊 西田 究

雑誌

JpGU-AGU Joint Meeting 2020

巻号頁・発行日

2020-07-04

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In order to deal with COVID-19 pandemic, social activities have been reduced around the world. Tokyo metropolitan area is no exception, where more than 30 million people live. Self-restraint was requested in various situations by local and Japanese governments, which drastically changed our life. Working from home or layoff was introduced in many companies. Shopping malls were closed. The movement of people was reduced, and economic activities stagnated.A part of noise observed by seismometers is due to human activities including transportations and machine vibrations. It is well known that seismic noise level in the daytime is higher than in the nighttime. The social activity reduction for COVID-19 is expected to decrease seismic noise in a different way from regular pattern, which would provide us a good opportunity to improve our understanding of seismic noise. Better understanding of seismic noise may also provide us a new way to monitor human activities using seismic observations. This study investigated continuous record of seismic stations in Metropolitan Seismic Observation network (MeSO-net) maintained by National Research Institute for Earth Science and Disaster Resilience (NIED). Seismic stations of MeSO-net are settled at the bottom of shallow borehole (~20 m) in the Tokyo metropolitan area. We measured hourly seismic noise level and compared its temporal changes with a timeline of COVID-19 in Tokyo metropolitan area.We observe two types of seismic noise reduction associated with different causes in MeSO-net stations. The first one is often observed in frequency bands higher than 20 Hz. This seismic noise reduction started at the beginning of March 2020. This timing corresponds to when Japanese government closed schools. As many MeSO-net stations are settled in school property, human activities there are considered to influence seismic records of MeSO-net stations strongly in a high frequency band. The second seismic noise reduction is often observed in lower frequency band between 1-20 Hz. This seismic noise reduction started on April 13th 2020. This timing corresponds to the first beginning of week after the Japanese government declared a state of emergency in Tokyo metropolitan area on April 8th 2020. Seismic noise reduction in lower frequency band is expected to be related with stagnated economic activities, such as decreasing transportations and closing buildings or factories.

著者

八代 昌樹 田口 晃 千原 鋭思 宮澤 克彰 山田 有純

雑誌

JpGU-AGU Joint Meeting 2020

巻号頁・発行日

2020-07-04

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このプロジェクトはハーバード大学教授の石井水晶先生が日本の高校生に協力を求めたものである。同大学で開発されたDegitSeisソフトフェアを用い、アナログ地震計記録をデジタル化するという作業だ。これによってデジタル化された地震計記録は、地震学や自然科学の研究に寄与され、様々な場面での利用が期待される。私たちは今後の研究や社会に役立てばと思い、このプロジェクトに参加した。

著者

Shino Suzuki

雑誌

JpGU-AGU Joint Meeting 2020

巻号頁・発行日

2020-03-13

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Almost all the microbial ecosystems on present-day Earth are supported by photosynthesis including the subsurface biosphere. Organic carbons from the photosynthesis have been accumurated and delivered into the deep subsurface ecosystem. Oxygen and oxidative compounds also have distributed everywhere on the Earth through the water and contributed to creating chemical gradients that can support microbial energy metabolisms. Therefore, opportunities are rare to address microbial ecosystems that are isolated from the effects of photosynthesis, but those are canceled in several settings, one of which includes a serpentinized ecosystem.Serpentinization is a process whereby water interacts with reduced mantle rock called peridotite to produce a new suite of minerals (e.g., serpentine), a highly alkaline fluid, and hydrogen. The hydrogen and carbon dioxide present in the system are thought to react under the highly reducing and alkaline conditions, leading to the formation of methane and hydrocarbons and the concomitant production of carbon monoxide, formate, formaldehyde and methanol. Given that the reduced compounds delivered from the water-rock reaction can support microbial energy metabolisms, such serpentinization systems have been viewed as potential habitats for early life or the other planetary bodies. Studies of serpentinizing environments to date have shown that these ecosystems host extremely low-abundance microbial communities, which is presumably attributed to the multiple extremes: 1) the highly-alkaline condition of the fluid; 2) the extremely low concentrations of oxidants (electron acceptors); and, 3) the low levels of and nutrients (available carbon and phosphate). The Cedars located in northern California is one of the active terrestrial serpentinization sites. While there are about a hundred of springs in The Cedars area with a variety of differences in geochemistry (Figure 1), spring waters discharged from The Cedars generally have extremely high pH (11-12), very low Eh (−900 mV - −550 mV) values and are rich in Ca2+ (~1 mM), hydrogen and methane gas, and contain low levels of dissolved organic carbon, total inorganic carbon, ammonium, phosphate and electron acceptors (oxygen, nitrate, sulfate)Here I present a diversity of unusual metabolisms and life strategies seen in the early Earth or other planetary bodies’ analogue sites, those of which have been identified through the studies of geochemistry, microbial cultivation, genome centric metagenomics of The Cedars microbial communities. Furthermore, I discuss the constraints and driving forces lying in the deep subsurface serpentinized settings to make a living.

著者

内出 崇彦

雑誌

JpGU-AGU Joint Meeting 2020

巻号頁・発行日

2020-03-13

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Focal mechanism is one of earthquake source parameters that characterizes the fault geometry and the slip direction, which also implies the seismogenic stress field. In many areas in the world, focal mechanisms are routinely estimated only for earthquakes larger than a certain magnitude, such as M 3 in local cases. For better estimation of the crustal stress field, we desire a much richer focal mechanism catalog. The focal mechanism determination requires us to pick P-wave first-motion polarity, which is usually done manually and therefore time-consuming.In this study, we construct a neural network model, whose input is three-dimensional seismogram and output is the P-wave first-motion polarity. We adopt a simple convolution network as done by prior studies (Ross et al., 2018; Hara et al., 2019). We used NIED Hi-net seismograms with P-wave arrival times in the JMA Unified Earthquake catalog. The seismograms were highpass-filtered at 1 Hz to and clipped at a certain level. By flipping the vertical component and rotating horizontal components, we augmented the data. We also prepared models with three, four, and five convolution layers followed by two fully connected layers. The clipping level, the number of the data augmentation, and the number of convolution layers are chosen according to their performance to a test dataset. ~ 280 k of seismograms are used for the training.Finally, we applied the trained model to ~180 M of seismograms from ~110 k of inland microearthquakes with depths smaller than 20 km in Japan. We succeeded in determining the focal mechanisms of more than 99 % of the earthquakes.

著者

武村 俊介 奥脇 亮 久保田 達矢 汐見 勝彦 木村 武志 野田 朱美

雑誌

JpGU-AGU Joint Meeting 2020

巻号頁・発行日

2020-03-13

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Due to complex three-dimensional (3D) heterogeneous structures, conventional one-dimensional (1D) analysis techniques using onshore seismograms can yield incorrect estimation of earthquake source parameters, especially dip angles and centroid depths of offshore earthquakes. Indeed, detail analysis of 2016 southeast off the Kii Peninsula earthquake revealed that observed seismic and tsunami record could be explained by low-angle thrust faulting on the plate boundary (e.g., Kubota et al., 2018; Takemura et al., 2018; Wallace et al., 2016) but regional 1D moment tensor analysis showed high-angle reverse faulting mechanism.Combining long-term onshore seismic observations and numerical simulations of seismic wave propagation in a 3D model, we conducted centroid moment tensor (CMT) inversions of earthquakes along the Nankai Trough. Green’s functions for CMT inversions of moderate earthquakes were evaluated via OpenSWPC (Maeda et al., 2017) using the Japan Integrated Velocity Structure Model (Koketsu et al., 2012). We re-analyzed moderate (Mw 4.3-6.5) earthquakes listed in the F-net catalog (Fukuyama et al., 1998; Kubo et al., 2002) that occurred from April 2004 to August 2019. By introducing the 3D structures of the low-velocity accretionary prism and the Philippine Sea Plate, our CMT inversion method provided better constraints of dip angles and centroid depths for offshore earthquakes. These two parameters are important for evaluating earthquake types in subduction zones.Our 3D CMT catalog of offshore earthquakes and published slow earthquake catalogs (e.g., Kano et al., 2018) along the Nankai Trough depicted spatial distributions of slip behaviors on the plate boundary. The regular and slow interplate earthquakes were separately distributed, with these distributions reflecting the heterogeneous distribution of effective strengths on the plate boundary. By comparing the spatial distribution of seismic slip on the plate boundary with the slip-deficit rate distribution (Noda et al., 2018), regions with strong coupling were identified.Acknowledgments We used F-net waveform data and the F-net MT catalog (https://doi.org/10.17598/NIED.0005). Our CMT catalog and CMT results of assumed source grids for each earthquake are available from https://doi.org/10.5281/zenodo.3661116. The FDM simulations of seismic wave propagation were conducted on the computer system of the Earthquake and Volcano Information Center at the Earthquake Research Institute, the University of Tokyo. This study was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Numbers 17K14382 and 19H04626.

著者

奥田 花也 片山 郁夫 佐久間 博 河合 研志

雑誌

JpGU-AGU Joint Meeting 2020

巻号頁・発行日

2020-03-13

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Brucite (水酸化マグネシウム)は蛇紋岩の主構成鉱物の一つであり、超苦鉄質岩の水和反応によって形成される。これまでbruciteは粒径が非常に小さく天然環境で観察されにくいことから注目されてこなかったが、近年の研究では含水下マントルウェッジにおいてantigoriteと安定に共存し(Kawahara et al., 2016)、さらにマントルウェッジでの長期スロースリップがbruciteの形成に伴う高有効法線応力によって説明される可能性も示唆されている(Mizukami et al., 2014)。さらに、bruciteの存在はマントルウェッジ中の岩石の摩擦の安定性を変える可能性がある。このようにbruciteは水和した超苦鉄質岩帯における地震活動に影響する可能性があるが、bruciteの摩擦特性はこれまであまり調べられていなかった。本研究では一連の摩擦実験によりbruciteの基礎的な摩擦特性を報告する。摩擦実験は粒径70 nmの合成試薬を用いて広島大学の二軸摩擦試験機により行った。大気乾燥下と含水条件下の両方で、様々な垂直応力下(10, 20, 40, 60 MPa)で実験を行った。最大の剪断変位は20 mmであり、実験初期の剪断速度は3 μm/secとした。33 μm/secでのvelocity step testを数回行い、それぞれのstepから速度状態依存摩擦構成則(RSF)を用いて定量的に摩擦の不安定性を解析した。乾燥下において、定常状態の摩擦係数はおよそ0.40であり、不安定滑り(velocity-weakeningまたはstick-slip)が全ての垂直応力で観察された。剪断変位が2 mm程度において摩擦係数に明瞭なピークが観察され、このピークの摩擦係数は垂直応力に反比例した。含水下においては、ピークの摩擦係数は乾燥下と同様垂直応力に反比例したが、摩擦係数自体は乾燥下の場合より低かった。垂直応力が10と20 MPaの場合はvelocity-weakeningが観察されたが、40と60 MPaの高い垂直応力の場合はvelocity-strengtheningに変化した。こう垂直応力での安定滑りは100 MPaの垂直応力での先行研究と調和的である(Moore & Lockner, 2007)。RSF則のaとbの値は乾燥下の場合の方が含水下の場合より小さく、臨界すべり距離dcも乾燥下の場合の方が含水下の場合より短かった。Antigoriteはbruciteよりも高い摩擦係数を示すため、bruciteの不安定な摩擦挙動は含水した超苦鉄質岩帯において地震を引き起こす可能性がある。なお本研究では温度依存性については調べていない。発表では、実験したガウジの微細構造観察を通して摩擦特性のメカニズムについて考察を行い、実験結果と先行研究でのモデルから天然の超苦鉄質岩帯における地震活動について議論する予定である。

著者

舟木 類佳 永田 祐介 末永 幸平 森 信介

出版者

人工知能学会

雑誌

2020年度 人工知能学会全国大会(第34回)

巻号頁・発行日

2020-04-01

著者

山田 悠右 藤田 綜一郎 柴田 知秀 小林 隼人 田口 拓明 奥村 学

出版者

人工知能学会

雑誌

2020年度 人工知能学会全国大会(第34回)

巻号頁・発行日

2020-04-01

著者

赤間 怜奈 横井 祥 鈴木 潤 乾 健太郎

出版者

人工知能学会

雑誌

2020年度 人工知能学会全国大会(第34回)

巻号頁・発行日

2020-04-01

著者

大道 博文 目良 和也 黒澤 義明 竹澤 寿幸

出版者

人工知能学会

雑誌

2020年度 人工知能学会全国大会(第34回)

巻号頁・発行日

2020-04-01

著者

大峠 和基 大谷 まゆ

出版者

人工知能学会

雑誌

2020年度 人工知能学会全国大会(第34回)

巻号頁・発行日

2020-04-01

著者

迫田 真太郎 大渡 勝己 田中 一樹 甲野 佑

出版者

人工知能学会

雑誌

2020年度 人工知能学会全国大会(第34回)

巻号頁・発行日

2020-04-01

著者

古賀 政純

出版者

人工知能学会

雑誌

2020年度 人工知能学会全国大会(第34回)

巻号頁・発行日

2020-04-01

著者

大槻 恭士 今田 佑生也

出版者

人工知能学会

雑誌

2020年度 人工知能学会全国大会(第34回)

巻号頁・発行日

2020-04-01

著者

植田 一博

出版者

人工知能学会

雑誌

2020年度 人工知能学会全国大会(第34回)

巻号頁・発行日

2020-04-01