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第40回 国際戦略型コロキウム

Title:Experimental survey of the KPZ universality class and its anomalous time correlation

Speaker:Kazumasa A. Takeuchi (Tokyo Tech.)

Date: 2016年3月25日(金)13:30-
Place:理学部5号館401号室
Abstract:

The Kardar-Parisi-Zhang (KPZ) universality class,   originally introduced for fluctuations of growing   interfaces
 but not restricted to, is now appreciated   as a prominent situation where many fluctuation   properties can be
 solved exactly in one dimension [1].     In this talk, I will first overview main outcomes of   these developments
, following our experimental observations   of growing interfaces in liquid-crystal turbulence [2].  
 Then I will focus on time correlation; theoretically,   time correlation still remains largely intractable,  
 but experimentally we found anomalous time correlation   characterized by (weak) ergodicity breaking [3].  

  [1] For a review, see T. Kriecherbauer and J. Krug, J. Phys. A 43, 403001 (2010); I. Corwin, Random Matrices
 Theory Appl. 1, 1130001 (2012); T. Sasamoto, Prog. Theor. Exp. Phys. 2016, 022A01. 
  [2] K. A. Takeuchi and M. Sano, Phys. Rev. Lett. 104, 230601 (2010); Sci. Rep. 1, 34 (2011); 
                                                                                                                J. Stat. Phys. 147, 853 (2012).    
 [3] K. A. Takeuchi and T. Akimoto, arXiv:1509.03082 (2015). 

第39回 国際戦略型コロキウム

Title:Molecular Dynamics Study of Structure and Spectroscopy at Liquid Interface

Speaker:Tatsuya Ishiyama (石山 達也氏) (Graduate School of Science and Engineering, University of Toyama ) Date: 2016年3月15日(火)13:00-
Place:理学部5号館401号室
Abstract:

Liquid interfaces are ubiquitous and of fundamental importance in many physicochemical phenomena,
such as atmospheric reactions on aerosol particles, cavitation bubbles, biochemical reactions, and
so forth. The interfacial region is very limited in space and has unique properties compared to the
bulk due to its heterogeneous environment. Molecular simulation is a powerful technique to elucidate
and predict physical and chemical properties of interfaces with thickness of nm order. In this talk,
we focus on the recent progresses of the simulation studies of molecular structure, vibrational
spectroscopy at the interfacial region. A key experimental technique to elucidate interfacial
molecular structure is the interface-selective vibrational sum frequency generation (VSFG)
spectroscopy. A close collaboration of VSFG studies with molecular simulation has opened an avenue
for understanding new aspects of the structures of aqueous surfaces. We introduce a basic theory of
VSFG and discuss molecular structures of aqueous surfaces depicted from VSFG spectroscopy.

第38回 国際戦略型コロキウム

Title:Anomalous diffusion processes with general waiting times

Speaker:Dr. Adrian Baule (Queen Mary, University of London, United Kingdom)

Date: 2015年12月14日(月)13:30-
Place:理学部5号館401号室
Abstract:

Many transport processes in nature exhibit anomalous  diffusive properties with nontrivial scaling of the  
mean square displacement, e.g., diffusion of cells  of biomolecules inside the cell nucleus, where typically 
 a crossover between different scaling regimes appears  over time. Here, we investigate a class of anomalous
  diffusion processes that is able to capture such  complex dynamics by virtue of a general waiting time  
distribution. We obtain a complete characterization  of such generalized anomalous processes, including 
 their functionals and multipoint structure, using  a representation in terms of a normal diffusive  process plus
 a stochastic time change. We also  discuss the problem of Galilei invariance for these  types of processes, 
which is usually broken due to  the strong correlations between the system and  environment. A new type of 
Galilei invariant  anomalous processes is introduced.   

 Ref: Andrea Cairoli and Adrian Baule,  Phys. Rev. Lett. 115, 110601 (2015)

第37回 国際戦略型コロキウム

Title:Applied statisitical mechanics for engineering: from molecular dynamics and coarse-graining
to big data analysis of fluctuation measurements and single-particle characterization

Speaker:Itsuo Hanasaki (花崎 逸雄氏) (Tokyo University of Agriculture and Technology)  

Date: 2015年12月8日(火)13:00-
Place:理学部5号館401号室
Abstract:

Ubiquity and importance of thermal fluctuation in nanotechnology is obvious from the typical spatio-temporal
scales of interest and the central limit theorem. However, its consequence is not fully recognized in the
engineering fields, and they are far from fully exploited in spite of the epoch-making advances in the statistical
mechanics in the recent decades. Applied mechanics is not merely an application of the fundamentals, but it
requires deep and sharp appreciation of both science and technology in a sensible manner: Recent trend of strong
emphasis on the “innovation” in the academia as well as industries sheds light on the essential role of the
applied mechanics that has not been fully appreciated. I would like to introduce some of my work with an emphasis
on the viewpoints of statistical mechanics and dynamical systems while they are not always explicitly manifested.
The time-series introduction of the specific topics hopefully conveys the idea of this ongoing journey for the creative
combination of science and technology.

第36回 国際戦略型コロキウム

Title:HYDRODYNAMIC COLLECTIVE EFFECTS OF ACTIVE PROTEINS IN BIOLOGICAL CELLS

Speaker:Alexander S. Mikhailov Department of Physical Chemistry, Fritz Haber Institute of the

Max Planck Society, Berlin

Date: 2015年11月30日(月)13:30-
Place:理学部5号館401号室
Abstract:

Recent in vivo experiments with optical tracking of particles in living  biological cells indicate that active forces 
strongly dominate thermal  Brownian forces in the cellular environment, impacting motion of objects  from 
nanometers to microns in scale. As we show [PNAS 112, E3639 (2015)],  such non-thermal fluctuating forces 
can arise from hydrodynamic stirring  of the cytoplasm by various protein machines, enzymes and molecular 
motors  that densely populate the cell. Independent of their specific functions,  all such macromolecules are 
repeatedly changing their conformations and  act as oscillating stochastic force dipoles. Numerical estimates
 reveal  that hydrodynamic collective effects of active proteins may account for  the experimentally observed 
dramatic diffusion enhancement in the  cytoplasm under ATP supply.

 

第35回 国際戦略型コロキウム

Title:Theory on dynamics of electrolyte solutions: Interplay between dynamics of bound pairs and ionic atmosphere
Speaker:Tsuyoshi Yamaguchi (山口 毅氏) (Nagoya University)  

Date: 2015年11月17日(火)13:00-
Place:理学部5号館401号室
Abstract:


Transport properties of electrolyte solutions, such as ionic conductivity, viscosity and ultrasonic absorption, are dynamic
quantities of both academic and industrial importance. The dynamics of electrolyte solution is characterized by the
influence of strong Coulombic interaction between ions, which makes it different from the dynamics of liquids composed
of neutral molecules.
There are two different effects of the Coulombic interaction on the dynamics of electrolyte solutions. The first one is
the ionic association, and the second one is the ionic atmosphere. The strong attraction between a cation and an anion makes
them bound to each other in weakly polar solvents, leading to the formation of a neutral molecule, called "ion pair". On the
other hand, a diffuse distribution of counter ion, called "ionic atmosphere", is formed around an ion due to the long-range
nature of the Coulombic interaction. These two effects have been treated separately in traditional theories, although they
work simultaneously in real solutions.
In this work, we developed a theory that can calculate transport coefficients from the pair distribution functions between ions
without introducing the association species a priori [1,2]. The theory can describe both the bound dynamics of ion pairs and the
collective long-range dynamics related to the ionic atmosphere.
The theory was first applied to the ultrasonic absorption [1,3]. Our theoretical calculation reproduced the bimodal relaxation
often observed in experiments. The slower mode was ascribed to the association dynamics of CIP as had been proposed by the conventional
model. On the other hand, the faster mode was assigned to the collective dynamics in our calculation.
The theory was then applied to the ionic conductivity [2,4]. The effects of the interionic interaction on ionic conductivity were divided
into the contributions of the pair distributions of ions at various interionic distances. It was demonstrated that the lifetime of
CIP must be much longer than its reorientational relaxation time in order for all the pairs of contact ions to be regarded as CIP in
conductometry. An extension of the theory to include the hydrodynamic interaction between ions was also proposed, and applied to the
ionic conductivity of the aqueous solution of NaCl [4].

References
[1] T. Yamaguchi, T. Matsuoka, and S. Koda, J. Chem. Phys., 126(14), 144505 (2007).
[2] T. Yamaguchi, T. Matsuoka, and S. Koda, J. Chem. Phys., 127(6), 064508 (2007).
[3] T. Yamaguchi, T. Matsuoka, and S. Koda, J. Chem. Phys., 127(23), 234501 (2007).
[4] T. Yamaguchi, T. Matsuoka, and S. Koda, J. Chem. Phys., 130(9), 094506 (2009).

第34回 国際戦略型コロキウム

Title:Water in a Capacitor: Structure, Fluctuation, and Response
Speaker:Kyohei Takae (高江 恭平氏) (University of Tokyo) 

Date: 2015年11月13日(金)17:00-
Place:理学部5号館401号室
Abstract:


The dielectric response of condensed matter is often studied under
the assumption that the external electric field is a controllable parameter.
However, it is needed to solve the Poisson equation under an appropriate
boundary condition to obtain the macroscopic electric field, because it
depends on the polarization of the system. We construct a method of
molecular simulation for calculating the electrostatic interactions
among charged particles between parallel metallic plates [1].
By applying this method, we study structure and dynamics of water in a
capacitor [2,3]. Image interaction arising from the dielectric discontinuity
at the interface induces polarization near the surface, which decreases
the bulk electric field. Homogeneous correlation of polarization fluctuation
emerges in this geometry. Next we discuss the relationship between macroscopic
electric field and local electric field exerted on each molecule, where the
latter is considerably larger than the former. The orientation of water
dipole is almost parallel to the local electric field, and small fluctuation
is relaxed by the librational motions. We also discuss responses of water
molecules after sudden change of potential difference, where collective
reorientation is observed.

references
[1] K. Takae and A. Onuki, J. Chem. Phys. 139, 124108 (2013).
[2] K. Takae and A. Onuki, J. Phys. Chem. B 119, 9377 (2015).
[3] K. Takae and A. Onuki, J. Chem. Phys. 143, 154503 (2015).

第33回 国際戦略型コロキウム

Title: Power law statistics and nonequilibrium steady state of cold atoms
Speaker:Andreas Dechant

Date: 2015年11月2日13:30-
Place:京都大学理学部5号館401号室
Abstract:

We investigate the statistical properties of atoms in a Sisyphus cool  ing lattice. In this system, the nonlinearity
 of the friction force induces   a wealth of interesting effects. We discuss the diffusive dynamics of “free”   
atoms, with long-ranged correlations, heavy-tailed power law distributions   and superdiffusion with a tunable
 exponent. Introducing a confining field cr  eates a nonequilibrium steady state, in which the equivalence 
between energy   and probability is broken in a subtle manner. This leads to an imbalance be  tween kinetic
and potential energy, which could potentially be exploited to   improve cooling.  

第32回 国際戦略型コロキウム

Title:A new interpretation on an atmospheric phenomenon "Stratospheric Sudden Warming" in terms

of equilibrium statistical mechanics
Speaker:安田勇輝(東大理・地球惑星科学専攻)

Date: 2015年10月26日13:30-
Place:京都大学理学部5号館401号室
Abstract:

There exists the largest vortex called the polar vortex (perimeter: a half  of the equator) in the stratosphere 
(height: 10-50 km) over the polar  region in winter. The polar vortex sometimes collapses within a few days  
with an increase in temperature, which is sometimes over 50K. This  phenomenon is called Stratospheric 
Sudden Warming. We investigated the  Stratospheric Sudden Warming by using a theory of the equilibrium  
statistical mechanics. This theory predicts a structure of a large-scale  vortex field realized after strong mixing
 of vortices. We obtained a phase  diagram of the vortex field with a parameter region where metastable  
states exist, and compared it to the results of the numerical simulations  and the analyses of the 55-year
climatological dataset. It is shown that  the Stratospheric Sudden Warming can be qualitatively interpreted 
as the  relaxation towards the equilibrium from the metastable state.

第31回 国際戦略型コロキウム

Title:A case of wave-particle duality at macroscopic-scale
Speaker:Prof. Yves Couder
(Laboratoire Matière et Systèmes Complexes,Université Paris Diderot –Paris)

Date: 2015年10月23日(金)13:30-
Place:理学部5号館401号室
Abstract:

A droplet bouncing on a vertically vibrated liquid interface excites surface waves. For large forcing amplitudes, there is a symmetry breaking bifurcation by which the whole structure becomes spontaneously propagative It is thus called “a walker”. This system is characterized by an interesting information interplay. The particle generates the wave and the wave determines where the particle goes. It is more than a classical echolocation system because the waves have a specific asset: they are standing Faraday waves, partly sustained by parametric forcing, so that their interference structure contains a memory of the drop recent trajectory. Through several experiments we addressed the same question: what are the self organized modes where the discrete droplet can have a common dynamics with the continuous and spatially extended wave? Surprisingly, in spite of the classical nature of this system, several quantum-like behaviours emerge. I will specifically discuss recent experiments in which a walker, confined in a potential well, has an orbiting motion. In this situation the possible orbits exhibit both a form of quantization(1) and probabilistic behaviours(2).
(1) S. Perrard, M. Labousse, M. Miskin, E. Fort, & Y. Couder, Nature Com. 5, 3219, (2014)
(2) S. Perrard, M. Labousse, E. Fort, Y. Couder, Phys Rev Lett, 113, 104101, (2014).

第30回 国際戦略型コロキウム

Title: Aggregation Rates of Charged Colloidal Particles in a Couette Flow: Trajectory Analysis with Non-linear Poisson-Boltzmann Solution
Speaker:Takuya Sugimoto (Graduate School of Life and Environmental Sciences, University of Tsukuba) 

Date: 2015年6月16日(火)13:00-
Place:理学部5号館401号室

第29回 国際戦略型コロキウム

Title: Membrane simulation - elasticity, surface tension, and some applications
Speaker:芝 隼人

(東京大学 物性研究所)

Date: 平成27年6月2日(火)13:30~
Place: 理学部5号館401号室
Abstract:

  Based on coarse-grained simulations of membrane models, I would like to talk about the following issues.
(i) Structure formation of surfactant membrane Coarse-grained simulations have been a powerful tool for simulations of soft matter on micrometer scales. In order to address structure formation of surfactant membranes under shear flow, we employ the meshless membrane model. It realises topological changes (e.g. rupture and reconnections) of membrane surfaces and is highly coarse-grained, so that we can treat large-scale defect dynamics underlying multilamellar membranes. [1]
(ii) Membrane elasticity and residual tension Using the above coarse-grained model, I will talk about the systematic way in which we can asses the "true" value of the bending rigidity, based on the knowledge on the wavenumber dependence[2]. In addition, we would like to address "residual surface tension" problem on a stress-free membrane [3].
[1] Hayato Shiba, Hiroshi Noguchi and Gerhard Gompper, JCP 139, 014702/1-11 (2013).
[2] Hayato Shiba and Hiroshi Noguchi, PRE 84, 031926/1-13 (2011).
[3] Hayato Shiba, Hiroshi Noguchi, and Jean-Baptiste Fournier, to be submitted (2015)

第28回 国際戦略型コロキウム

Title: 過剰熱容量から見る単純分子液体のガラス転移における普遍性と特異性
Speaker:辰巳創一

(京都工芸繊維大学)

Date: 平成27年1月26日(火)13:30~
Place: 理学部5号館401号室
Abstract:

“ガラス転移は物性科学における,重要な未解決問題である.”このフレーズは品を  変え形を変え様々な形で繰り返され
ている.にもかかわらず依然としてそれがいつま  でも未解決問題として居座り続けている主要な理由に,実験的には
ガラス転移が人間  の扱える時間スケールの遥かに向こう側を本質的に含まざるを得ない,という点は見  過ごせない.
ガラス転移について提唱される様々な仮説や理論が,検証段階で実験的  に人間の持てる時間,という壁に阻まれて
しまう.こうした困難を回避するために重  要なのは,ガラス転移の向こう側にあるものを,人間がアクセス可能な実時間
スケー  ルの結果から推測することを許すようにデザインされた実験であり,それに対応した  理論の構築である.  
我々は以上のような方針のもと,ガラス形成物質につきものの分子の構造の複雑さや,  分子間相互作用の詳細を出来
る限り省くことを目指して実験系を構築した.具体的に  は,直鎖状炭化水素,プロペン,1-ブテン,1-ペンテンのような
一連の単純な分子を  不凍化し,そのガラスー過冷却液体の熱容量を測定している.この熱容量から,微視  的な解析
を通じて,液体ー過冷却液体中の分子の協調的な運動に起因する過剰熱容量  を分離することが出来るのだが,
解析の結果,この過剰熱容量は分子種の違いに関係  なく普遍的な性質を持つことを見出しており,ガラス転移温度より
も下の温度におい  て何らかの転移があることを想起させる結果となった[1].本講演では以上の実験と  その解析の
詳細について述べると共に,付随して見つかった協同的に動くと考える領  域の分子種による違いなどにも踏み込んで
議論したい.   

 [1] "Thermodynamic Study of Simple Molecular Glasses: Universal Features  in Their Heat Capacity and the
 Size of the Cooperatively Rearranging  Regions", S. Tatsumi, S. Aso, and O. Yamamuro, 
Phys. Rev. Lett., 109,  045701 (2012)  

第27回 国際戦略型コロキウム

Title: Molecular dynamics simulation of fluids in nanopores
Speaker:Toshiki Mima (美馬 俊喜氏)(The University of Tokyo) 

Date: 2015年1月20日(火)15:00
Place: 理学部5号館401号室
Abstract:
Fluids in nanopores are of importance for a wide range of industrial applications because their mass and heat transfer characteristics are different from those of the bulk fluids. The major reason of the anomalous characteristics is that the number of molecules near the solid surface is comparable with that in the bulk region. The experimental approach is still a great challenge to observe molecules near the solid surface at an atomistic scale, therefore, the molecular dynamics simulation is one of the effective scheme. In this presentation, the properties of nano-confined liquid crystal and water are mainly investigated.
There are two topics of liquid crystals confined in nano-slit. First, the self-diffusion coefficient and the rotational coefficient depending on the distance from the solid surface are investigated. The results are analyzed through the Fourier transform of the correlation function corresponding to each individual transport coefficient. Second, the system size dependence of the order parameter is discussed. The result indicates that liquid crystals in the slit with the gap of several molecules length exhibit the Kosterlitz-Thouless transition. In the talk of water in nanocylinder, the wettability and pore size dependences of saturation pressure are investigated and the validity of the Kelvin equation is examined.

第26回 国際戦略型コロキウム

Title: Bounds on Efficiency and Power of thermoelectric Heat Engines with Broken Time-Reversal Symmetry
Speaker:Kay Brandner

(University of Stuttgart)

Date: 平成27年1月19日(火)13:30~
Place: 理学部5号館401号室
Abstract:

A cornerstone result of classical thermodynamics states that the  efficiency of any heat engine operating 
between two heat baths of  temperature Tc and Th > Tc is bounded by the Carnot value eta _C = 1  – 
Tc/Th. Moreover, it is generally believed that this bound can be  reached only in the quasi-static limit, which 
is inevitably accompanied by  vanishing power output. This expectation, however, has recently been  called 
into question by G. Benenti et al. in an intriguing paper  considering thermoelectric energy conversion in the
 presence of a magnetic  field [1]. Their quite general analysis within the framework of linear  irreversible
 thermodynamics reveals that, as soon as time-reversal  symmetry is broken, Carnot efficiency at finite 
power might indeed be  achievable.   
 We scrutinize this exciting option, by investigating the simple but  paradigmatic class of multi-terminal models
. By using an original  algebraic approach, we derive a universal constraint on the Onsager  coefficients, which
 depends only on the number of terminals [2,3]. This  constraint, which ultimately follows from current 
conservation, implies a  stronger bound on the efficiency of multi-terminal thermoelectric heat  engines than
 the bare second law. It becomes, however, successively weaker  as the number of terminals is increased 
and finally disappears when this  number goes to infinity [3].   
 In a second step, we therefore investigate, whether not only efficiency  but also power can be bounded.
We present strong numerical evidence for  the existence of a an additional constraint on the Onsager 
coefficients  [5]. The new constraint implies, inter alia,that power vanishes at least  linearly when the 
maximum efficiency is approached. This result holds for  an arbitrarily large number of terminals and thus 
finally rules out the  option of Carnot efficiency at finite power for the multi-terminal set-up.  We illustrate our 
results by introducing a simple classical model using  four terminals for a thermoelectric engine based on 
the Nernst effect [4].  Within this set-up, the predicted bounds on efficiency and power can  indeed be 
saturated for large magnetic fields and small fugacity in the  thermochemical reservoirs.   

 参考文献: 
 [1] G. Benenti, K. Saito, and G. Casati, Phys. Rev. Lett. 106, 230602  (2011)
 [2] K. Brandner, K. Saito and U. Seifert, Phys. Rev. Lett. 110, 070603  (2013)  
 [3] K. Brandner and U. Seifert, New J. Phys. 15, 105003 (2013)  
 [4] J. Stark, K. Brandner, K. Saito and U. Seifert, Phys. Rev. Lett. 112,  140601 (2014)  
 [5] K. Brandner and U. Seifert, to appear in Phys. Rev. E (2015)

 

第25回 国際戦略型コロキウム

Title: ケルディッシュ形式・非平衡グリーン関数に関するレビュー
Speaker:伊與田 英輝

(東京大学助教)

Date: 平成26年12月15日(月)13:30~
Place: 理学部5号館401号室
Abstract:

場の量子論におけるグリーン関数に関するファインマンダイアグラムの手法は、ケルディッシュによって非平衡系へと
拡張された[1]。時間をケルディッシュ経路上の経  路時間へと拡張し経路上でのグリーン関数を考えることによって系統
的な摂動展開が  可能になった。また、グリーン関数の運動方程式を議論することにより、ボルツマン  方程式の導出が
なされた。その後も拡張されながらいくつかの系に適用され、非平衡  系における相互作用を扱う上での枠組みとしての
役割を担ってきた。    
しかし、非平衡系におけるファインマンダイアグラムの方法が提案されたとは言え、  一般の非平衡状態は分からない。
さらに、摂動計算においては非摂動項の取り方が問  題となるが、一般の非平衡系における汎用的な非摂動項が知られ
ていないため、計算  可能な系や設定が限られているのが現状である。とはいえ、近年の量子系における非 平衡の実験
技術の進歩や、理論的にも統計力学の基礎などに進歩がある中で、ケルディ ッシュ形式や非平衡グリーン関数と呼ば
れる枠組みについて見直すことには意味があ  るのではないかと思われる。    
本セミナーでは、上記の枠組みについてレビューを行う。まず、量子多体系の平衡状  態におけるグリーン関数から
はじめ、非平衡系でケルディッシュ経路が必要になる理  由をみる。非平衡系への拡張を行った後、経路時間と実時間の
関係、運動方程式と勾  配展開、ボルツマン方程式をはじめとする古典系で知られている理論との関係などの 基本的な
項目をおさえる。そしてその他の適用例などをみながら、時間が許せば量子  輸送系などにおける具体的な計算例を
紹介する。    

[1] L. V. Keldysh, Sov. Phys. JETP, 20, 1018(1965)

 

第24回 国際戦略型コロキウム

Title: Wave chemotaxis: spatial and temporal sensing in cells
Speaker:石原秀至

(明治大学)

Date: 平成26年12月8日(月)13:30~
Place: 理学部5号館401号室
Abstract:

細胞は外界からのシグナルを感知し、極性形成や走化性を示す。一般に真核生物では、  細胞の前後での濃度差から
シグナルの勾配方向を感知すると考えられているが、この  空間差検知方式では、シグナルが波でやってくる場合には、
波の前後で濃度の空間勾  配が逆転してしまうので、シグナルのやってくる向きがわからない。実際には、細胞  性粘菌
の集合期にみられるように、波で来るシグナルに対して細胞は方向を検知できる(Wave paradox)。  
我々は、MicroFluidics技術を用いて、細胞性粘菌に対してcAMP濃度の波を通過速度  や波形を変えて与え、同時に
細胞内Ras分子の応答を観察した。細胞は常に波を登れ  るわけではなく、あるシグナル通過速度領域でのみ登れる
ことを見出した。この実験  結果をLocal excitation global inhibition (LEGI) Modelを拡張する事で、細胞が  空間的
応答と時間的応答をどのように組み合わせ、波が来る方向の検出を行っている のかを説明する。また、一般論として、
細胞が周期的な波を動く事によるドップラー 効果などについても話したい。  

 A. Nakajima, S. Ishihara, D. Imoto and S. Sawai, Rectified directional  
sensing in long-range cell migration. Nature Communications 5, 5367 (2014)

 

第23回 国際戦略型コロキウム

Title: 実験室レベルでの破壊の前兆現象とそのスケール依存性
Speaker:波多野恭弘

(東京大学)

Date: 平成26年12月1日(月)13:30~
Place: 理学部5号館401号室
Abstract:

表題については二種類に大別される:統計的性質の変化および亀裂の核形成過程である。 セミナーでは地震・破壊・
摩擦についての基礎的事項を解説したのち、これら 二つについてスケール依存性を意識しつつレビューする。
我々がこれらの問題に関して最近開始した 試みも簡潔に紹介する。  

第22回 国際戦略型コロキウム

Title: Cooperative Motion and Structural Relaxation in Glass-Forming Materials
Speaker:Jack F. Douglas (National Institute of Standards and Technology)

Date: 2014年11月18日(火)10:30
Place: 理学部5号館413号室
Abstract:
Collective motion and relaxation in coarse-grained polymeric liquids are investigated by complementary molecular dynamics (MD) simulations and analytic modeling. MD simulation indicates that nanoparticle additives, which can effectively modify molecular packing, can cause significant changes in both the strength of the temperature dependence of structural relaxation time $\tau$ (as measured by the fragility of glass formation) and the spatial extent of cooperative particle motion in the form of string-like dynamic structures that spontaneously emerge at equilibrium in glass-forming liquids. Physical arguments of Adam-Gibbs (AG) relating the rate of structural relaxation to the extent (average mass) of cooperative motion in glass-forming liquids are summarized and we test whether this model can rationalize the large nanoparticle additive-induced changes in polymer melt dynamics found in our simulations where the string excitations are directly identified with the abstract cooperatively rearranging regions of AG (see figure below and Refs. 1 and 2 for discussion). This comparison leads to a remarkable reduction of all our relaxation data and provides a new means of testing the AG model. These observations are consistent with the implicit AG picture that changes in the fragility of glass-forming liquids with the addition of additives, finite size confinement, and changes of molecular structure derive from changes in the strength of the temperature dependence of the extent of cooperative molecular motion. The classical entropy theory of glass-formation, combining a thermodynamic calculation of the configurational entropy sc and the AG model of structural relaxation relating $\tau$ to sc, is considered as a complementary tool to gain analytic insights into these additive-induced effects on the temperature dependence on structural relaxation in glass-forming liquids.

第21回 国際戦略型コロキウム

Title:Analysis of electrokinetic transports of nano-confined electrolyte solutions by means of the molecular dynamics simulations
Speaker:Hiroaki Yoshida (Toyota Central R&D Labs.)

Date:2014年11月18日(火)10:30
Place: 理学部5号館413号室
Abstract:
Current interest of our group is centered on the electrokinetic phenomena caused by interaction between the electrical double layer formed near solid-liquid interface and external forces. Aiming at comprehensive understanding of the phenomena and their automotive applications, we are attempting to develop a framework of computer simulations. Among the approaches at different length scales we employ, the main topic in my talk will be a methodology for analyzing dynamics of a liquid electrolyte solution in confined geometries at a scale of nano meter, along with some numerical results. Specifically, an aqueous NaCl solution in nanochannels with negatively charged surfaces is considered, and electrokinetic flows of the solution are studied using molecular dynamics (MD) simulations. The transport coefficients that characterize the response to weak external forces, such as the electric and pressure fields, are obtained in the linear regime using a Green-Kubo approach. The non-equilibrium MD simulations with explicit external fields are also carried out, and the flow rates are directly compared. Using the numeri

第20回 国際戦略型コロキウム

Title: ないはずの所の自由度
Speaker:関本謙

(パリ第7大学/ESPCI)

Date: 平成26年10月27日(月)13:30~
Place: 理学部5号館401号室
Abstract:

標題の問題意識のもと、「熱浴を介した相互作用」および  「剛体の内部の相互作用」についてお話します。  


 第19回 国際戦略型コロキウム

Title: Dynamics of active deformable particles in flow field
Speaker:多羅間充輔

(京都大学)

Date: 平成26年10月6日(月)13:30~
Place: 理学部5号館401号室
Abstract:

Dynamics of active deformable particles is investigated theoretically by  using model equations derived from 
symmetry argument. We consider a  particle in an external flow field and introduce time-evolution equations
  for the centre-of-mass position and velocity vector variables, symmetric  tensor variables representing 
deformation, and an anti-symmetric tensor  variable characterising the rotation of the particle.  In this seminar,
 we would talk about the dynamics in the following three  situations. One is the case of a quiescent flow filed, 
where we  concentrate on the spinning motions of active deformable particles and  argue that there are 
at least two types of spinning motions. Then, a  linear shear flow is taken into consideration as simplest flow 
geometry.  Finally, the dynamics in a swirl is investigated. Since the flow profile  of a swirl is similar to that of 
a scattering geometry and possesses  therefore analogy to the classical Kepler and Rutherford problem, we
  investigate an analogous setup in the context of active particles.  

 

第18回 国際戦略型コロキウム

Title: Structural relaxation is a scale-free process
Speaker:Anaël Lemaître

(Laboratoire Navier, Universit´e Paris-Est)

Date: 平成26年8月27日(水)13:30~
Place: 理学部5号館413号室
Abstract:

 We show that in deeply supercooled liquids, structural relaxation proceeds via the accumulation of Eshelby events, i.e. local rearrangements that create long-ranged and anisotropic stresses in the surrounding medium. Such events must be characterized using tensorial observables and we construct an analytical framework to probe their correlations using local stress data. By analyzing numerical simulations, we thus demonstrate that events are power-law correlated in space, with a time-dependent amplitude which peaks at the alpha relaxation time. This effect, which becomes stronger near the glass transition, results from the increasingly important role of local stress fluctuations in facilitating relaxation events. Our work thus precludes the existence of any lengthscale beyond which the relaxation process decorrelates and shows that instead relaxation arises from the scale-free accumulation of events with a tensorial signature.

 第17回 国際戦略型コロキウム

Title: ペーストのメモリー効果とその消去
Speaker:中原明生

(日本大学理工学部)

Date: 平成26年6月23日(月)13:30~
Place: 理学部5号館401号室
Abstract:

粉と水を混ぜた高濃度ペーストは塑性ゆえに揺れや流れなどの動きを記憶し、その記  憶はその後乾燥させた時に発生
する亀裂パターンの形状として視覚化される[1]。例  えば、ペーストが揺れを記憶した時は亀裂は揺れに対し垂直に伝播
し、一方、ペース  トが流れを記憶した時は亀裂は流れに対し平行に伝播する[2]。これまで、加振機に  載せて揺すって
ある方向の揺れを記憶したペーストに対しその後別の方向に揺すって  記憶を書き換え亀裂の伝播方向を変えておくこと
はできたが、いったん記憶された情  報を消去して初期化することはできなかった。  
今回、揺れや流れを記憶したペーストに対し、短時間超音波を照射することでその後  発生する乾燥亀裂の形状を等方
的でセル状なものにすることに成功した[3]。記憶に  起因する亀裂の異方性を消去できたことはペーストの記憶を消去
できたことを示唆しているので、そのメカニズムについて議論したい。  

[1] A. Nakahara and Y. Matsuo, "Imprinting Memory Into Paste and Its  Visualization as Crack Patterns in
Drying Process", J. Phys. Soc. Jpn. 74  (2005) 1362-1365.  
[2] A. Nakahara and Y. Matsuo, "Transition in the pattern of cracks  resulting from memory effects in paste", 
Phys. Rev. E, 74 (2006)  045102(R). 
[3] 中原明生、松尾洋介、伊藤丸人、米山瞭汰、「超音波照射による固液混合材料の  異方構造の消去」、
特願2014-038777、2014-2-28

第16回 国際戦略型コロキウム

Title:Pair interaction between colloidal particles in nematic liquid crystal
Speaker:Mohammad Reza Mozaffari (University of Qom, Qom, Iran )

Date: 2014年5月14日(水)15:30
Place: 理学部5号館413号室
Abstract:
Structure of colloidal particles in anisotropic solvent with long-range orientational ordering, such as nematic liquid crystals, has attracted great attention in science and technology. The nematic director is distorted from its uniform orientation in the bulk due to anchoring on the surface of the colloidal particles. These elastic distortions create topological defects around the particles and induce long and short range anisotropic interactions between the particles. Depending on the anchoring type and the colloidal geometry, the particle-defect can induce a long-range dipolar-dipolar, quadrupolar-quadrupolar and/or dipolar-quadrupolar potential. Experimentally, the colloidal interactions in nematic liquid crystals are studied using optical or magneto-optical traps. Smalyukh et al.[Phys. Rev. Lett. 95, 157801 (2005)] have measured the angular and the radial components of the force between two particles with planar anchoring in a nematic liquid crystal as a function of the interparticle separation and the angle with the bulk nematic. They showed that the particles aggregate in chains directed at nearly 30 degree with respect to the nematic direction. Lapointe et al.[Science 326, 1083 (2009)] indicated that the elastic colloidal interactions in nematic liquid crystals are sensitive to the colloids shapes. Equilibrium director field around platelet equilateral polygonal colloids exhibit dipolar symmetry if they have odd number of the edges and quadrupolar symmetry if it is is even. This is giving rise to dipolar and quadrupolar elastic colloidal interactions, respectively. Studing the degenerate planar anchoring on the spherical particles is numerically interest and hard in comparison to the normal anchoring. Here, the interaction between two spherical colloidal particles with degenerate planar anchoring in a nematic media has been studied by numerically minimizing the bulk Landau-de Gennes free energy and the surface energy by the mean of a finite element method. The results indicate that the particles form an angle 28+-2 degree with respect to the far-field nematic direction that is consistent with Smalyukh research. We have also investigated interactions between two long parallel prism particles when their long axes are perpendicular with far-field nematic direction. Using adaptive finite element method the 2D Landau-de Gennes free energy with strong planar anchoring has been minimized. In agreement with Lapointe’s results, interaction between two triangle prisms has dipolar symmetry while the square prisms show quadrupolar symmetry.

第15回 国際戦略型コロキウム

Title: ソフトマターの構造形成における流体力学的効果に関する研究
Speaker:清水 涼太郎(東京大学生産技術研究所)

Date: 2014年4月21日(月)13:30-
Place: 理学研究科5号館413号室
Abstract:
相分離過程、結晶化過程はソフトマターに広く観察されるパターン形成の基本的過程として幅広く研究されてきた。本講演では、講演者が行ったこの2つの相転移ダイナミクスに関する数値シミュレーションによる研究について紹介する。前半では2成分流体系における液滴分散型相分離の粗大化過程に関する研究について述べる。後半では剛体球コロイド分散系の結晶化過程に関する研究について述べる。 

 

第14回 国際戦略型コロキウム

Title: 光屈性の力学:成長、塑性、曲線
Speaker:和田浩史

(立命館大学理工学部准教授)

Date: 平成26年3月10日(月)13:30~
Place: 理学部5号館401号室
Abstract:

 「種の起源」の発表後、ダーウィンは現在の植物生理学の礎となる植物運動に関する 一連の研究を行っている。このことは生物科学の文脈で議論されることが多いが、し かし立ち止まって考えてみると、植物の運動力は本質的に力学の問題である。光屈性を例にとり、植物の運動はどのように生み出されるのか、その基礎から考えおこし、 成長、粘弾性、塑性、運動の幾何学、など、植物のバイオメカニクスについて考えな がら、我々の研究室で進行中の実験と理論についてお話しする。

 

 第13回 国際戦略型コロキウム

Title: Mesoscopic Lattice Boltzmann Simulations of Soft Multiscale Materials
Speaker:Oliver Henrich

(University of Edinburgh)

Date: 平成26年3月4日(月)14:30~
Place: 理学部5号館401号室
Abstract:  

  Soft materials are unique in their ability to self-organise into mesoscopic structures that are larger than their constituting atoms and molecules, and yet much smaller than the macroscopic scale of the material. As the properties and interactions of these intermediate structures determine the macroscopic behavior of the material, soft materials have often complex kinetic behaviour and are difficult to describe consistently. The recent progress in computational modelling and high performance computing allows us now to address problems that were previously inaccessible such as the kinetic behaviour of soft multiscale materials. Our approach is based on the lattice Boltzmann method in combination with thermodynamically consistent hybrid models that involve free energy functionals [1].

 After a short introduction to the method I will present a number of large scale simulation studies. The first one will deal with the nonlinear bulk rheology of lamellar phases such as block-copolymers or smectic liquid crystals. We found two different rheological regimes, namely one at modest shear rates with an almost regular lamellar phase, and one at high shear rates featuring nucleation and proliferation of defects. The steady state is balanced by the annihilation of defects of opposite sign, leading to memory effects and history-dependent rheology. We offer a scaling analysis that relates the critical shear rate to a critical capillary number involving those variables [2].

  Another focus will be on cholesteric liquid crystals and so-called ’Blue Ph ases’, which consist of a network of defect lines in a locally cholesteric phase. I will present the first theoretical investigation of sheared Blue Ph ases in large systems. We were able to characterise various distinct rheolog ical regimes that depend on the imposed shear rate and topology of the under lying defect network in a very non-trivial way [3].

 We also found that colloid-cholesteric mixtures can give rise to a much wider range of soft-solid composites with tunable elastic an electro-optic properties than previously anticipated. These include regular crystals, glasses, percolating gels, isolated clusters, twisted rings and undulating colloidal ropes. The final structure can be tuned via the particle concentration, anchoring type and strength of the liquid crystal at the colloidal surface or boundary planes or by switching protocols in external electric fields. Many of the structures are multistable, i.e. they have the ability to retain memory of several different states under identical thermodynamic conditions, a must-have prerequisites for energy-saving electronics-free liquid crystal devices.

[1] M.R. Swift, W.R. Osborn, J.M. Yeomans, Lattice Boltzmann Simulation of Nonideal Fluids, Phys. Rev. Lett. 75, 830833 (1995).

[2] O. Henrich, K. Stratford, D. Marenduzzo, P.V. Coveney, M.E. Cates, Rheology of Lamellar Liquid Crystals in Two and Three Dimensions: A Simulation Study, Soft Matter 8, 3817-3831 (2012).

[3] O. Henrich, K. Stratford, D. Marenduzzo, P.V. Coveney, M.E. Cates, Rheology of Cubic Blue Phases, Soft Matter 9, 10243-10256 (2013).

 

 第12回 国際戦略型コロキウム

Title: Beyond duality analysis on finite dimensional spin glass: Critical polynomial in spin glasses
Speaker:大関真之

(京都大学大学院情報学研究科システム科学専攻 助教)

Date: 平成26年2月24日(月)13:30~
Place: 理学部5号館401号室
Abstract:  

 Little known are systematic theoretical approaches in finite-dimensional spin glass except for the gauge theory, which yields the concept of the Nishimori line. For the case without disorder, especially on the two-dimensional system, several sophisticated methods are available. One of the well-known method is the duality, which can lead to the exact location of the critical point. We have developed the duality for spin glasses in conjunction with the replica method in a series of our studies. However the duality analysis is not satisfiable due to some remaining ad hoc ideas.

 In the present study, we refine our method by regarding the disorder system as the collection of the inhomogenous system. By taking account into the consistency with the critical polynomial for the inhomogenous system, we find a new scheme to derive the accurate location of the critical points in spin glasses. The precision of the theory is controllable. In addition, the proposed new theory covers the duality analysis in spin glasses. We hope that the direction in the present study opens a new pave to the exact analyses in finite-dimensional spin glasses.

The present study is in collaboration with Jesper Lykke Jacobsen in ENS.

第11回 国際戦略型コロキウム

Title: 柔らかい粒子の電気泳動と静電相互作用

Speaker: 大島広行先生(東京理科大学名誉教授)

Date: 2014年2月12日(水)13:30-
Place: 理学研究科5号館525号室
Abstract:  
柔らかい粒子(soft particle)とは高分子電解質のようなsoft matterから成る表面電荷層で覆われた粒子を意味する。電解質水溶液中の柔らかい粒子が外部電場の下でどのような運動をするかという問題(電気泳動)と二つの柔らかい粒子が互いに接近したときにどのような静電的相互作用が生じるかという問題を議論する。微粒子分散系における電気泳動(電気浸透、沈降電位、流動電位を含む)および静電相互作用は界面電気現象と総称されるが(電気泳動等はとくに界面動電現象と呼ばれる)。これらの現象では、二つの因子が重要である。一つは帯電粒子周囲にできる拡散電気二重層(主として対イオンから成るイオン雲)であり、他の一つは粒子表面の電位である。とくに表面構造をもたない剛体粒子の界面動電現象は微粒子のゼータ電位( ~ 表面電位)に支配される。しかし、柔らかい粒子の場合、ゼータ電位は意味を失い、表面電荷層におけるDonnan電位が重要な役を担う。柔らかい粒子(soft particle)と剛体粒子(hard particle)は互いに大きく異なる挙動を示すが、基礎理論には共通の部分も多いので、柔らかい粒子のみでなく剛体粒子の界面電気現象についても述べる。さらに、二つの粒子が接近して互いの表面電荷層が接触する前の静電相互作用に加えて、表面電荷層の接触後の相互作用(interdigitationおよびinterpenetration)およびDonnan電位に対する離散電荷効果(discrete charge effect)についての最近の研究についても触れる。

 第10回 国際戦略型コロキウム

Title: Violation of FDT and energy dissipation rate
Speaker: Shouwen Wang

(Department of Engineering Physics, Tsinghua University)

Date: 平成26年2月3日(月)15:30~
Place: 理学部5号館401号室
Abstract:  

  I will introduce the adaptive sensory network in E.coli, which support robust adaptation by dissipating energy. In this model, energy dissipation rate is connected with the adaptation error by the work of Ganhui Lan et.al. Adaptation error has a similar role as susceptibility(response) of the system. According to Harada-Sasa equality, the violation of FDT is related to the energy dissipation rate in Langevin system. Although exact Harada-Sasa formula is not known in Markov system, which is the context of my problem, simulation indeed reveals such a correlation. Thus, Harada-Sasa might be a general formula. Correlation function and response function are calculated. Further, I will try to construct the connection between violation of FDT with energy dissipation rate in this realistic Markov network system.

 

 第9回 国際戦略型コロキウム

Title: Information thermodynamics on causal networks
Speaker: 伊藤創祐
(東京大学 大学院 理学研究科 佐野研究室)
Date: 平成26年2月3日(月)13:30~
Place: 理学部5号館401号室
Abstract:  

 In recent years, relations between information theory and nonequilibrium statical physics has been intensively investigated. According to the recent study of the second law for small systems, the second law seems to be violated in the presence of the feedback control by Maxwell's demon. For such case, the second law has been generalized as the equation including the mutual information that is exchanged between the system and controller [1]. Although such a relation is applicable to a simple "feedback control" system, the general theory has been elusive for more complex cases such as "autonomous interacting systems" and "time-delayed feedback control".

 Here, we study a system that is involved in a complex information flow induced by multiple other systems [2]. Characterizing the interaction of multiple systems by causal networks, i.e., Bayesian networks, we obtain a novel generalization of the second law for subsystem. Our result implies that the entropy production in a single system in the presence of multiple other systems is generally bounded by the information flow between these systems.

[1] T. Sagawa and M. Ueda, Phys. Rev. Lett. 104, 090602 (2010).

[2] S. Ito and T. Sagawa, Phys. Rev. Lett. 111, 180603 (2013).

 

 第8回 国際戦略型コロキウム

Title: Typical behavior of the linear programming method for combinatorial optimization problems:

From a statistical-mechanical perspective
Speaker: 高邉 賢史
(東京大学 総合文化研究科 福島研究室)
Date: 平成26年1月22日(水)15:30~
Place: 理学部5号館413号室
Abstract:  

  A linear programming problem (LP) is a popular class of optimization problem s. It can be solved in 
polynomial time of the number N of variables while ot  her combinatorial optimization problems usually 
belong to a class of NP-hard  . We study typical behavior of the LP as a relaxation problem of the minimum  
 vertex cover problem which is a type of the integer programming problem (IP  ). To deal with the LP and IP 
by statistical mechanics, a lattice-gas model  on the Erdos-Renyi random graphs including both problems
 as specific limits  in a model parameter is analyzed by a replica method. It is found that the L  P optimal 
solution is equal to that of the IP up to the highest order of N b  elow the critical average degree c*=e=2.71... 
as N→∞. The critical thresho  ld for LP=IP is beyond a mathematical result, c=1, predicted by a mathematic  
al theorems for correspondence up to O(N). The threshold also coincides with   the replica-symmetry-breaking
 threshold of the IP. I would like to explain  details of our study and related topics.

 

 第7回 国際戦略型コロキウム

Title: 配向自由度を有する粒子系のガラス転移
Speaker: 高江 恭平
(京都大学 相転移動力学グループPD)
Date: 平成25年12月16日(月)13:30~
Place: 理学部5号館401号室
Abstract:  
 通常、液体は凝固点以下に冷却することで結晶化する。しかし、結晶化を阻害しつつ液体を冷却していくと、結晶化が
起こらないまま、ついには運動が凍結することがある。これをガラス転移と呼び、ガラス転移点近傍における遅いダイナ
ミクスなどに興味が持たれている。数値シミュレーションでガラス転移を研究する際、サイズの異なる2種類の球を混ぜ
ることで結晶化を阻害することが多いが、分子性液体では、分子は球ではなく、向きをもつ。我々はこのような、配向の
自由度を有する粒子の典型例 として、わずかに異方性をもつ楕円体を考え、配向自由度を持たない球との混合系に
ついて、分子動力学シミュレーションを行った。ガラス転移についての簡単な導入ののち、以下の2点について報告する。
  1.楕円体と球とが同等のサイズであるとき、結晶秩序を持つが、配向秩序が消失し  たまま運動が凍結する、配向ガラ
ス形成を発見した [1]。このときの微視的な構造、 粒子回転のスローダイナミクス、および特異な外場応答について解説
する。
  2.球が楕円体と大きく異なるサイズのとき、結晶秩序と配向秩序がともに消失した  まま凍結することを見出した [2]。
両者の結合した遅い緩和や、結晶欠陥と配向欠陥の関係について解説する。 
   [1] K. Takae and A. Onuki, arXiv:1310.5106.  
   [2] K. Takae and A. Onuki, Phys. Rev. E 88, 042317.

 第6回 国際戦略型コロキウム

Title: Loop Calculus for Non-Binary Alphabets using Concepts of Information Geometry
Speaker: 森 立平
(東京工業大学 情報理工学研究科 渡辺研究室 博士研究員)
Date: 平成25年12月2日(月)13:30~
Place: 理学部5号館401号室
Abstract:  
 ベーテ近似は統計物理の分野で考案された分配関数の近似手法である。最近、二元の グラフィカルモデルについて
真の分配関数とそのベーテ近似との間に成り立つ等式がChertkovと Chernyak によって発見された。その等式はルー
プ計算(loop calculus)  と呼ばれ、ベーテ近似の誤差がループ構造に対応する重みの和として表現される。本講演では
ループ計算とその導出によるベーテ近似の特徴付け、また多元のグラフィカ  ルモデルへの一般化を扱う。

 第5回 国際戦略型コロキウム

Title: スピングラスのゼロ点と量子クエンチダイナミクス
Speaker: 小渕智之
(東京工業大学 樺島研究室 助教)
Date: 平成25年11月25日(月)13:30~
Place: 理学部5号館401号室
Abstract:
 分配関数のゼロ点を求める問題は、統計物理の中でも比較的マニアックな問題と受け 止められがちである。しかし
近年、量子ダイナミクスにおける波動関数間のオーバー ラップ(Fidelity)が、複素パラメータを持った分配関数に形式
的に類似することが 知られるようになり、量子ダイナミクスの特異性を求める一方法として脚光を浴びつ つ有る [1,2]。
特に量子クエンチと呼ばれる、量子性を制御するパラメータを突然大  きく変化させた場合の解析は、古典的な分配関数
の評価とほぼ並列であり、量子多体  ダイナミクスを理解・制御するための第一歩として重要とかんがえられる。    
 ところで一方、スピングラスのようなランダム系におけるゼロ点は解析の困難さから、  長らくその性質が知られてこな
かったが、ごく近年になって、平均場系におけるゼロ  点の一般的解析法が開発・整備された [3,4,5,6]。この方法は量子
クエンチダイナミ クスの解析にも直接応用することができ、量子ランダム系のダイナミクスを一般的に理解する方法論
ともなりうる。    
 本講演では、上記の方法に基づいた、いくつかのスピングラスモデルの量子クエンチ  ダイナミクスにおける解析結果
を紹介する[7,8]。いくつか特徴的な結果として、
  ・解析したほぼ全てのモデルに対して、ある特徴的な時間t_cにてFidelityに特異性 が現れ、t>t_cではカオティックな
振る舞い(時間に対してFidelityが激しく振動する)が見られる。
  ・このFidelityが振動する”相”にレプリカ対称性の破れは起こっていない。
  ・2次元イジングスピングラスには平衡転移は無いがFidelityに特異性は出る。  
などの結果が得られている。ただ残念なことに、これらの結果の物理的な意義は今の ところはっきりしていない。特に、
Fidelityにおける特異性が、ローカルな物理量に  て観測できる例が見つかっていないのが大きな問題である。
Fidelity自体を物理量だ と強弁出来ないわけでもないのだが、いかんせん巨大な系では、"Fidelity=所望の波 動関数
に収束する確率"が指数関数的に小さくなるため、実際にそれを観測するには 指数関数的にたくさんの実験をしなくては
いけないため事実上不可能である。講演で はぜひこれらの問題点について議論させていただきたい。   
 References:  
[1] M. Heyl et. al.: Phys. Rev. Lett. 110, 135704 (2013) 
[2] C. Karrasch and D. Schuricht: Phys. Rev. B 87, 195104 (2013)  
[3] Y. Matsuda et. al: J. Phys. A: Math. Theor. 43 (2010) 285002  
[4] K. Takahashi: J. Phys. A: Math. Theor. 44 (2011) 235001
[5] T. Obuchi and K. Takahashi: J. Phys. A: Math. Theor. 45 (2012) 125003
[6] 小渕 智之: YSM-SPIP2012会議録
  http://www-adsys.sys.i.kyoto-u.ac.jp/mohzeki/YSMSPIP/Proc2012/poster.pdf
[7] K. Takahashi and T. Obuchi: arXiv:1309.0076 
[8] T. Obuchi and K. Takahashi: Phys. Rev. E 86 (2012) 051125

   第4回 国際戦略型コロキウム

Title:1.量子開放系における注目系と熱浴の間の自然な相関 2.非相加的な準平衡状態を持つ短距離相互作用模型
Speaker: 森 貴司
(東京大学宮下研究室 助教)
Date: 平成25年11月18日(月)13:30~
Place: 理学部5号館401号室
Abstract:

1.

 小さな注目系と巨大な環境系(熱浴)が弱く相互作用し合う系における注目系の量  子ダイナミクスの問題は古くから
研究されてきた[1]。射影演算子法を用いることで、  注目系の縮約密度行列の一般化量子マスター方程式が導かれる。
 これは一般には非Ma  rkov的なダイナミクスを与える。いま、注目系と熱浴の間の相互作用が非常に弱いと きには、
注目系の緩和時間のスケールと熱浴の特徴的な時間スケールの間に分離が起  きる。もし緩和時間のスケールでダイ
ナミクスを観察すると、いわゆるBorn-Markov  近似が正当化され、縮約密度行列の時間発展はMarkov的なRedfield
方程式で記述され る。この極限はvan Hove極限と呼ばれるが、現実にはvan Hove極限からのずれがあり、  そのずれ
による補正を考える必要がある。   
 今回のセミナーでは、量子マスター方程式の上記のような一般的な性質についてレ ビューした後、van Hove極限の
ずれによる補正に関する最近の研究[2]を紹介する。  特に、注目系と熱浴を含めた全系の状態のうち、「自然な相関」を
持った状態と呼ばれる特別な状態が存在することを示す。「自然な相関」を持った状態を初期条件とし て準備すると、
van Hove極限からのずれがあったとしても、注目系はMarkov的なRedf  ield方程式で非常によく近似される。
  [1] H. P. Breuer and F. Petruccione, “The theory of open quantum systems”  [2] T. Mori, arXiv:1310.5453

2.

 相加性は統計力学から熱力学を再現するために重要な性質の一つである。短距離相 互作用系においては通常相加
性は満たされ、その結果ミクロカノニカル分布とカノニ  カル分布の等価性のような基本的な結果が得られる[1]。相加性を
満たさない典型的な例として長距離相互作用系がよく調べられている[2]。  
 最近の研究[3]で、非相加性が出現する別の可能性を提示した。すなわち、複数の時  間スケールが十分に分離してい
るときに現れる準平衡状態(速い時間スケールのモー ドは平衡化しているが、遅い時間スケールのモードによる緩和過
程は始まっていない ような状態)において、非相加性を示す短距離相互作用模型が存在することを指摘し た。この模型
は結晶格子の弾性的運動の自由度と、各格子点上の分子の内部状態の自  由度からなる模型である。非相加性の結果
、中間的な時間スケールで現れる準平衡状  態においてアンサンブルの等価性の破れを見ることができる。また、結晶格
子の自由 度を消去して分子の内部状態の間の有効相互作用を数値的に調べ、異なる分子の内部自由度間にスクリー
ニングのない長距離相互作用が働くことを見出した。この結果は、 真の平衡状態にはない短距離模型を理解する上で
長距離相互作用系の平衡統計力学の知見が有効になる例を与えるものであり、セミナーでは以上の研究結果を詳しく
紹介する。
[1] D. Ruelle, “Statistical Mechanics” 
[2] A. Campa, T. Dauxois, and S. Ruffo, Phys. Rep. 480, 57 (2009)  
[3] T. Mori, Phys. Rev. Lett. 111, 020601 (2013)

 第3回 国際戦略型コロキウム

Title: Topological superstructure in nematic liquid crystal colloids 
Speaker: AMiha Ravnik (Faculty of Mathematics and Physics, University of Ljubliana, Centre of Excellence 
NAMASTE, Slovenia)
 Date: 2013年11月15日(月)16:00
 Place:   理学部5号館401号室
 Abstract: 
  Liquid crystal colloids show a variety of interesting mechanisms -including self-assembly, activity, and 
material flow- that can be used to creat complex optical and photonic structures. Here, I will present our 
recent modeling work, in full collaboratoin with partner experiments, on the control of nematic colloids as 
a topological soft matter. First, I will show three-dimensional colloidal crystals tat can be assembled using 
the analogy between elastic and electric dipolts. Next, I will generalize the assembly to entangled nematic 
colloids, where delocalized disclinations bind and form multi-particle states, with the prime examples being 
microscopic knots and links of disclinations. Made-to-order assembly of microscopic knots and their statistics
 on regular particle arrays will be demonstrated, commenting also on the self-linking number as an important
 topological invariant. Finally, the assembly of a Penrose P1 tiling will be presented, using nematic colloidal 
pentagonal platelets as a route for introducing quasicrstalline symmetry into a soft material, where nematic 
bost allows for tessellation at multiple hierarchcal length scales, i.e. sizes of the platelets, which is a work in
 the direction of fractal tiling as photonic materials.

 第2回 国際戦略型コロキウム

Title:Reconstruction of active blebbing motion from amoeba extract
Speaker: Masatoshi Ichikawa
(Department of Physics, Kyoto University)
Date: 平成25年6月27日(木) 16:30~
Place: 理学部5号館413号室
Abstract:
Amoeboid locomotion is one of the typical modes of biological cell migration. We developed a model system in which an actomyosin fraction moves like an amoeba through blebbing motion. Actomyosin cortex of this amoeba model contracts to make a thrust pressure for the blebbing. We will discuss of this motion based on the experimental observations and measurements.
Ref. Y. Nishigami, et al., PLOS ONE (in press).
※講演は日本語で行われます。

 第1回 国際戦略型コロキウム

Title:OxDNA: a coarse-grained model for simulations of DNA
Speaker: Dr. Flavio Romano
(Department of Chemistry, University of Oxford, UK)
Date: 平成25年4月22日(月) 13:30~
Place: 理学部5号館413号室
Abstract:
In this talk I will discuss a coarse-grained DNA model which has been developed in my group at Oxford. The model is parametrized to reproduce the thermodynamics of single- and double-stranded DNA in solution with a high salt content, where it is most useful for nanotechnology.
The performances of the model will be discussed, as well as applications to prediction of binding rated, hybridization kinetics, assembly of large structures such as DNA origami and DNA systems with topological frustration.