Ibaraki University's
Graduate School of Science and Engineering (Science)
Department of Science (Mathematics and Informatics Course)

Associate Professor



  1. 北海道大学 大学院理学研究院 専門研究員 2008/04-2008/07
  2. 北海道大学 大学院工学系研究科 COE研究員 2008/08-2008/12
  3. 東京大学 大学院情報理工学系研究科 特任研究員 2009/01-2011/03
  4. 東北大学 大学院情報科学研究科 助教 2011/04-2015/03
  5. 茨城大学 理学部理学科 准教授 2015/04-Present

Academic background

  1. 北海道大学 理学部 物理学科 2003 Graduated
  2. 北海道大学 理学研究科 物理学専攻 Master course 2005/03 Completed
  3. 北海道大学 理学研究科 物理学専攻 Doctor later 2008/03 Completed

Academic degrees

  1. 博士(理学) 北海道大学 2008/03

Research Areas

  1. Mathematical physics/Fundamental condensed matter physics

Research keywords

  1. 統計物理
  2. 複雑ネットワーク
  3. ネットワーク科学
  4. 相転移・臨界現象
  5. パーコレーション
  6. モンテカルロシミュレーション
  7. 感染症


  1. Research paper (scientific journal) Joint Sudden spreading of infections in an epidemic model with a finite seed fraction Takehisa Hasegawa, Koji Nemoto The European Physical Journal B 91 2018/03/29 10.1140/epjb/e2018-80343-3
  2. Joint Efficiency of prompt quarantine measures on a susceptible-infected-removed model in networks Hasegawa Takehisa, Nemoto Koji Physical Review E American Physical Society (APS) 96/ 2 2017/08/11 2470-0045 10.1103/PhysRevE.96.022311 URL
  3. Joint Local cluster-size statistics in the critical phase of bond percolation on the Cayley tree Tomoaki Nogawa, Takehisa Hasegawa, Koji Nemoto Journal of Statistical Mechanics: Theory and Experiment 2016/05/11 10.1088/1742-5468/2016/05/053202
  4. Joint Outbreaks in susceptible-infected-removed epidemics with multiple seeds Hasegawa Takehisa, Nemoto Koji Physical Review E American Physical Society (APS) 93/ 3 2016/03/31 2470-0045 10.1103/PhysRevE.93.032324 URL We study a susceptible-infected-removed (SIR) model with multiple seeds on a regular random graph. Many researchers have studied the epidemic threshold of epidemic models above which a global outbreak can occur, starting from an infinitesimal fraction of seeds. However, there have been few studies of epidemic models with finite fractions of seeds. The aim of this paper is to clarify what happens in phase transitions in such cases. The SIR model in networks exhibits two percolation transitions. We derive the percolation transition points for the SIR model with multiple seeds to show that as the infection rate increases epidemic clusters generated from each seed percolate before a single seed can induce a global outbreak.
  5. Joint Advantage or disadvantage of migration in a prey-predator system Kazunori Sato, Takehisa Hasegawa, Satoru Morita, Jin Yoshimura, Kei-ichi Tainaka Far East Journal of Applied Mathematics 2015

Research presentations

  1. Oral presentation(general) 階層スモールワールドネットワーク上の確率過程におけるロバストな臨界性 日本物理学会2016年秋季大会 2016/09
  2. Oral presentation(general) 複数の感染源が引き起こす感染症の爆発的拡がり 日本物理学会2016年秋季大会 2016/09
  3. Oral presentation(general) ネットワーク上の感染症における隔離対策の効果 日本物理学会2016年秋季大会 2016/09
  4. Oral presentation(general) Outbreaks in the SIR epidemics with multiple seeds - a statistical physics approach The 2016 (26th) annual meeting of the Japanese Society for Mathematical Biology (JSMB2016) 2016/09
  5. Oral presentation(general) 複数の感染源を持つSIRモデルが起こすパーコレーション転移 日本物理学会2015年秋季大会 2015/09

Memberships of academic societies

  1. 日本数理生物学会
  2. 日本物理学会