Unstable geodesics and topological field theory

A topological field theory is used to study the cohomology of mapping space. The cohomology is identified with the BRST cohomology realizing the physical Hilbert space and the coboundary operator given by the calculations of tunneling between the perturbative vacua. Our method is illustrated by a simple example.Comment: 28 pages, OCU-15

Building Secure and Anonymous Communication Channel: Formal Model and its Prototype Implementation

Various techniques need to be combined to realize anonymously authenticated communication. Cryptographic tools enable anonymous user authentication while anonymous communication protocols hide users' IP addresses from service providers. One simple approach for realizing anonymously authenticated communication is their simple combination, but this gives rise to another issue; how to build a secure channel. The current public key infrastructure cannot be used since the user's public key identifies the user. To cope with this issue, we propose a protocol that uses identity-based encryption for packet encryption without sacrificing anonymity, and group signature for anonymous user authentication. Communications in the protocol take place through proxy entities that conceal users' IP addresses from service providers. The underlying group signature is customized to meet our objective and improve its efficiency. We also introduce a proof-of-concept implementation to demonstrate the protocol's feasibility. We compare its performance to SSL communication and demonstrate its practicality, and conclude that the protocol realizes secure, anonymous, and authenticated communication between users and service providers with practical performance.Comment: This is a preprint version of our paper presented in SAC'14, March 24-28, 2014, Gyeongju, Korea. ACMSAC 201

Generation of Alfven Waves by Magnetic Reconnection

In this paper, results of 2.5-dimensional magnetohydrodynamical simulations are reported for the magnetic reconnection of non-perfectly antiparallel magnetic fields. The magnetic field has a component perpendicular to the computational plane, that is, guide field. The angle theta between magnetic field lines in two half regions is a key parameter in our simulations whereas the initial distribution of the plasma is assumed to be simple; density and pressure are uniform except for the current sheet region. Alfven waves are generated at the reconnection point and propagate along the reconnected field line. The energy fluxes of the Alfven waves and magneto-acoustic waves (slow mode and fast mode) generated by the magnetic reconnection are measured. Each flux shows the similar time evolution independent of theta. The percentage of the energies (time integral of energy fluxes) carried by the Alfven waves and magneto-acoustic waves to the released magnetic energy are calculated. The Alfven waves carry 38.9%, 36.0%, and 29.5% of the released magnetic energy at the maximum (theta=80^\circ) in the case of beta=0.1, 1, and 20 respectively, where beta is the plasma beta (the ratio of gas pressure to magnetic pressure). The magneto-acoustic waves carry 16.2% (theta=70^\circ), 25.9% (theta=60^\circ), and 75.0% (theta=180^\circ) of the energy at the maximum. Implications of these results for solar coronal heating and acceleration of high-speed solar wind are discussed.Comment: Accepted for publication in PASJ. 24 pages, 11 figure

Preparation of Standing Tree Volume Tables for Japanese Cypress in Shinshu University Forest in Tera

手良演習林のヒノキ立木材積表として現在使用されている林野庁計画課編の「長野地方ヒノキ・サワラ・ヒバ・コウヤマキ立木材積表」は,その適合度がかならずしも高くないので,手良演習林のヒノキに対する立木材積表の調製を試みた。本報告では一変数材積表と二変数材積表とを調製したが,その材積式は次のようである。log v=-3.487727+2.213185 log d (16) log v=-4.368886+1.676339 log d+1.303679 log h (23) v:材積(m3), d:胸高直径(cm), h:積高(m) 材積表は表3ならびに表4に示してある。これら両表の推計学的検討の結果は,次のように要約できる。1 両表とも手良演習林のヒノキに対しては適合度が高い 2 推定値の持つ誤差は,一変数材積表の方が二変数材積表よりも大きいから,単木材積の推定に際しては,二変数材積表の方が好ましい 3 しかし林分材積の場合のように,多数の林木材積の和を求めるような時には,外業上の有利さから,むしろ一変数材積表がすすめられるなお本報告での立木材積表は,142本の胸高直径10cm～30cm,樹高7m～21mという割合狭い範囲の資料を用いて調製されたものであるから,なお今後に修正することが必要であろう。Article信州大学農学部演習林報告 6: 29-43(1969)departmental bulletin pape

Data Science in an Agent-Based Simulation World

In data science education, the importance of learning to solve real-world problems has been argued. However, there are two issues with this approach: (1) it is very costly to prepare multiple real-world problems (using real data) according to the learning objectives, and (2) the learner must suddenly tackle complex real-world problems immediately after learning from a textbook using ideal data. To solve these issues, this paper proposes data science teaching material that uses agent-based simulation (ABS). The proposed teaching material consists of an ABS model and an ABS story. To solve issue 1, the scenario of the problem can be changed according to the learning objectives by setting the appropriate parameters of the ABS model. To solve issue 2, the difficulty level of the tasks can be adjusted by changing the description in the ABS story. We show that, by using this teaching material, the learner can simulate the typical tasks performed by a data scientist in a step-by-step manner (causal inference, data understanding, hypothesis building, data collection, data wrangling, data analysis, and hypothesis testing). The teaching material described in this paper focuses on causal inference as the learning objectives and infectious diseases as the model theme for ABS, but ABS is used as a model to reproduce many types of social phenomena, and its range of expression is extremely wide. Therefore, we expect that the proposed teaching material will inspire the construction of teaching material for various objectives in data science education.Comment: 9 pages, 10 figure