4月16日（火）13：30～15：00 太陽系小天体セミナー 南棟２階会議室
Apr 16 Tue Solar System Minor Body Seminar Conference Room, South Bldg.2F
4月17日（水）13：30～15：00 科学研究部コロキウム 開発棟３号館３階会議室
Apr 17 Wed Colloquium of Division of Science Conference room, Instrument Development Bldg. 3 3F
4月19日（金）13：30～15：00 太陽天体プラズマセミナー 院生セミナー室
Apr 19 Fri Solar and Space Plasma Seminar Student Seminar Room, Subaru Bldg.
4月19日（金）16：00～17：00 国立天文台談話会 大セミナー室
Apr 19 Fri NAOJ Seminar Large Seminar Room
詳細は以下をご覧下さい。
4月16日（火）
- キャンパス
- 三鷹
- セミナー名
- 太陽系小天体セミナー
- 定例・臨時の別
- 定例
- 日時
- 4月16日（火曜日）13時30分～15時
- 場所
- 南棟２階会議室
- 講演者
- 臼井文彦
- 所属
- 神戸大学 惑星科学研究センター
- 連絡先
- 名前：渡部潤一
- 備考
- テレビ会議またはスカイプによる参加も可
4月17日（水）
- Campus
- Mitaka
- Seminar
- Colloquium of Division of Science
- Regularly Scheduled/Sporadic
- Regularly Scheduled
- Date and time
- 2019 Apr 17th
- Place
- Conference room, Instrument Development Bldg. 3, 3F
- Speaker
- Fulvia Pucci
- Affiliation
- National Institute for Natural Sciences
- Title
- Flares, CMEs and explosive events: the “ideal” tearing mode and fast reconnection triggering in magnetized plasmas, from fluid to kinetic scales
- Abstract
- (optional)
Astrophysical plasmas are characterized by large Lundquist numbers, meaning that on large scales the effect of collisions is negligible, and that the magnetic field can not be dissipated because frozen-in conditions apply. Magnetic reconnection is thought to be the mechanism responsible for flares, CMEs and explosive events in astrophysical as well as in laboratory plasmas. One of the main questions is what triggers magnetic reconnection and how this mechanism capable to account for fast magnetic energy conversion to kinetic and thermal energies of particles. Previous models of reconnection failed to reproduce the fast dynamics of magnetic reconnection: either the mechanism is too slow to explain to the reconnection rate, or the plasmoid instability disrupts the sheets before they can even form. By examining current sheets with thicknesses scaling as different powers of the Lundquist number number S, in our work Pucci and Velli 2014 we showed that the growth rate of the tearing mode increases rapidly in thinning sheets, and, once the thickness reaches a scaling a/L∝S^{-1/3} the time-scale for the instability to develop becomes of the order of the Alfven time and independent of the resistivity. That means that a fast instability sets in well before Sweet-Parker type current sheets can form. In addition, such an instability produces many islands in the sheet, leading to a fast nonlinear evolution and most probably a final turbulent disruption of the sheet itself. This has fundamental implications for magnetically driven reconnection throughout the corona, and in particular for coronal heating and the triggering of coronal mass ejections (Shibata and Tanuma 2001). A similar critical aspect ratio scaling holds for general magnetic field equilibria, for example encompassing multiple current layers occurring in solar as well as laboratory plasmas contexts (Contopoulos 2007, Dalhburg and Karpen 1995, Ono et al. 1997). I will also talk about our latest work on the fractal reconnection scenario and reconnection in partial ionized plasmas, in collaboration with K. Shibata-san and Dr. A. Singh-san. Finally I will briefly introduce collisionless reconnection for planetary magnetospheres, the main observed features and my contribution to the study of energization in the earth’s magnetotail, a project carried out in collaboration with the MRX (magnetic reconnection experiment) group in Princeton. - Facilitator
- -Name：Shinsuke Takasao
- Comment
- (optional) Language, attending by Video conference system acceptable or not, and related information (IP address etc.)
4月19日（金）
- Campus
- Mitaka
- Seminar
- Solar and Space Plasma Seminar
- Regularly Scheduled/Sporadic
- Regular
- Date and time
- 19 April (Fri), 13:30-15:00
- Place
- Student Seminar Room, Subaru Bldg.
- Speaker
- Fulvia Pucci
- Affiliation
- NINS/Princeton
- Title
- Flares, CMEs and explosive events: the “ideal” tearing mode as a fast reconnection triggering mechanism in magnetized plasmas and following nonlinear evolution
- Abstract
-
Magnetic reconnection is thought to be responsible for flares, CMEs and explosive events in astrophysical as well as in laboratory plasmas. One of the main questions in reconnection research concerns how this mechanism may account for fast magnetic energy conversion to kinetic and thermal energies. By examining current sheets with thicknesses scaling as different powers of the magnetic Reynolds number S, in our work Pucci and Velli 2014 we showed that the growth rate of the tearing mode increases rapidly in thinning sheets and, once the thickness reaches a scaling a/L= S^(-1/3) the time-scale for the instability to develop becomes of the order of the Alfven time and independent on the resistivity. That means that a fast instability sets in well before Sweet-Parker type current sheets can form.
In addition, such an instability produces many islands in the sheet, leading to a fast nonlinear evolution and most probably a turbulent disruption of the sheet itself. This has fundamental implications for magnetically driven reconnection throughout the corona, and in particular for coronal heating and the triggering of coronal mass ejections (Shibata and Tanuma 2001).
A similar critical aspect ratio scaling holds for general magnetic field equilibria, for example encompassing multiple current layers occurring in solar as well as laboratory plasmas contexts (Contopoulos 2007, Dalhburg and Karpen 1995, Ono et al. 1997).
I will also present our recent work in collaboration with A. Singh and K.
Shibata on partial ionized plasmas with application to the solar atmosphere. - Facilitator
- -Name：Masahito Kubo
- Comment
4月19日（金）
- Campus
- Mitaka
- Seminar
- NAOJ seminar
- Regularly Scheduled/Sporadic
- Scheduled
- Date and time
- Fri 19 Apr 16:00～17:00
- Place
- Large Seminar Room
- Speaker
- 成島 哲也
- Affiliation
- 分子科学研究所 メゾスコピック計測研究センター
- Title
- 「ホモキラリティの起源としての星間塵ナノ微粒子の可能性 」
“Another pathway to induce homochirality via a twisted optical near-field on interstellar dust nanoparticles” - Abstract
-
地球上の生命体は，単一のキラリティ（掌性）をもった分子により構成される（アミノ酸は左手系，糖は右手系）。
実験室でこれらの分子を合成すると，左と右の分子が，それぞれ等しく得られるにもかかわらず，生命体は一方の
キラリティをもつ分子だけを利用している。このホモキラリティの起源を説明するアイデアがこれまで多数提唱
されているが，地球外に起因するものとしては，主に，中性子星などからの円偏光紫外線や超新星爆発時の大線量
β線(偏極した電子線)による不斉光分解反応（片方のキラル分子のみの分解反応）が検討されている。また，これらの
分子を含む惑星大気や星間物質のモデルとして，ガス状や原子レベルで平らな固体表面上での分子が考えられている。
しかし，ガス状の分子は密度が低く，また，宇宙のどこを見ても原子レベルで平らな表面など存在しないだろう。
本講演では，星間塵の表面をホモキラリティを発生する舞台として考える。この星間塵をナノスケールの微粒子と
して捉え，そのナノ微粒子の表面近傍に発生する近接場光（局在光電場）が，場合によっては，星間塵表面上に吸着
した有機物質の効率的な光不斉反応を誘起し得ることを，我々のナノスケール顕微分光法の結果に基づき議論する[1]。
例えば，微粒子がキラルな形状を有する場合（例，文字S型）は，その周辺に強くねじれた近接場光を生じ，これが
ナノスケールのキラルな円偏光光源として作用する。また，対称な形状を有する微粒子（例，長方形型）においても，
微粒子内部の局所領域においては，キラルなナノ円偏光が生じる。本講演で示すアイデアが，ホモキラリティの起源
として現実的に検討可能なものか，天文学，宇宙物理学の専門家から，さまざまな意見を伺えることを期待する。[1] T. Narushima et al., Phys. Chem. Chem. Phys., 15, 13805 (2013), J. Phys. Chem. C, 117, 23964 (2013), ACS Photon., 1, 732 (2014), Chirality, 28, 540 (2016), H. Okamoto et al., Phys. Chem. Chem. Phys., 17, 6192 (2015).
S. Hashiyada et al., J. Phys. Chem. C, 118, 22229 (2014), ACS Photon., 5, 1486 (2018), ACS Photon., 6, 677 (2019). - Facilitator
- -Name：Narukage, Noriyuki