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第41回拠点形成コロキウム

Title: Non-Brownian behavior of polymer grafted nanoparticles studied by X-ray photon correlation spectroscopy
Speaker: Dr. Taiki Hoshino
(JST, ERATO, Takahara soft interface project)
Date: 平成25年1月23日(水) 15:30~
Place: 理学部5号館401号室
Abstract:
Although the dynamical behavior of nanoparticles in polymer matrix is different from that of the conventional Brownian motion, the details of such dynamical behavior are still unknown. Moreover, the dynamical features of polymer-grafted nanoparticles are rarely studied. In the present study, the dynamics of the polystyrene (PS)-grafted nanoparticles dispersed in PS matrix have been studied using X-ray photon correlation spectroscopy. We observed the hyperdiffusive behavior at T<1.26Tg, where Tg is the glass transition temperature of the PS matrix, while subdiffusive behavior was observed at T>1.26Tg. These behaviors are assumed to be affected by the dynamic heterogeneity of the PS matrix and the interactions between the PS brushes and the PS matrix.

第40回拠点形成コロキウム

Title: Active phase field crystal model
Speaker: Dr. Andreas Menzel
(University of Duesseldorf, Germany)
Date: 平成25年2月15日(金) 10:30~
Place: 理学部5号館401号室
Abstract:
We are interested in the formation and in the behavior of crystals that are composed of self-propelled particles. To study such materials using a field approach, we combine the phase field crystal model by Elder and Grant with the Toner-Tu theory for active media. In general, we observe collective motion of the emergent crystals above a threshold value of the active drive. Various different crystalline phases can be observed: resting hexagonal, traveling hexagonal, swinging hexagonal, traveling rhombic, traveling quadratic, resting lamellar, and traveling lamellar. Upon quenching from the fluid phase, the traveling crystals emerge through a coarse-graining process from domains of different directions of collective motion. Furthermore, we qualitatively outline the impact of additional hydrodynamic interactions.

第39回拠点形成コロキウム

Title: Field-induced self-assembly of suspended colloidal membranes
Speaker: Jure Dobnikar
(Department of Chemistry, University of Cambridge and Joˇzef Stefan Institute, Ljubljana, Slovenia)
Date: 平成24年11月29日(木) 14:00~
Place: 理学部5号館413号室
Abstract:
Superparamagnetic colloids in external time-dependent magnetic fields are a verstile tool to study the self-assembly process. We report experiments that probe self-assembly of micrometer-size colloids in both, in 2D confinement and in bulk systems. In quasi 2D confinement, the colloids interact via core-softened repulsive potentials and - in the absence of any attractive forces - clustering is observed and characterized. In 3D bulk systems, in a magic- angle precessing magnetic field, superparamagnetic spheres experience isotropic pair attraction similar to the van der Waals force between atoms. However, the complex many-body polarization interactions among them steer an ordered aggregation pathway consisting of growth of short chains, cross-linking and network formation, network coarsening, and consolidation of membrane patches — resulting in one-particle-thick, robust, and self-healing membranes. We theoretically explain the membrane stability, their elastic and self-healing properties and the observed aggregation pathway. This generic scenario can be induced in any particles of large enough susceptibility.
詳しくは、こちらへ。

第38回拠点形成コロキウム

Title: Colloidal and metallic liquids out of equilibrium : linking structure and kinetics
Speaker: Paddy Royall (Bristol University, UK)
Date: 平成24年11月14日(水) 16:00~
Place: 理学部5号館502号室 (第4講義室)
Abstract:
The liquid state is central to two great challenges of condensed matter : crystallisation and dynamical arrest. We will consider the role of local structure in both. Due to the simplicity in their interactions, colloidal model systems form an ideal complement to computer simulation in tackling these problems. However, in crystallisation, the only system for which quantitative data exists, colloidal "hard" spheres, experiment and simulation disagree wildly. Meanwhile in dynamical arrest, the role of structure is highly controversial.
We shall use a novel structural analysis to tackle both crystallisation and dynamical arrest. With a careful comparison between experiment and simulation, we find evidence to support the discrepancy in nucleation rates, and reveal new pathways in crystallisation. Applying our methods to dynamical arrest, we find a clear structural mechanism for gelation. For the glass transition, we find clear structural changes which reveal a fundamental difference between these two modes of dynamical arrest : gelation is (quasi) first-order and vitrification is continuous.

Holger Flechsig 氏のセミナーは都合により中止となりました。

第37回拠点形成コロキウム

Title: Investigation of slow conformational motions in proteins using coarse-grained dynamical models
Speaker: Dr. Holger Flechsig (Fritz-Haber-Institut der Max-Planck-Gesellschaft)
Date: 平成24年11月13日(火) 13:30~
Place: 理学部5号館401号室
Abstract:
Proteins are fascinating macromolecules which are perfected by the biological evolution and exhibit an enormous functional variety. In the cells they can operate as molecular machines which cyclically change their structure to implement a certain function. These nanoscale engines can be, e.g., motors whose activity is related to force generation and intracellular transport. They can also work as channels which mediate the exchange of ions through the cellular membrane. Although today a wealth of structures of these proteins is available, important aspects of their operation are not yet explored well enough. Since internal conformational motions accompanying the operation cycles in these proteins are slow, with timescales ranging between tens of millisecond to seconds, they cannot be studied within all-atom molecular dynamics simulations. To circumvent these difficulties, coarse-grained descriptions picturing the protein as elastic networks have become increasingly popular within the last decade. Previously, we have used such approximate mechanical descriptions to investigate functional motions in motor proteins which separate duplex DNA and RNA (1,2). In this work, it became possible to follow entire functional cycles of an important viral motor protein in a structurally resolved fashion. In my talk, after introducing the concept of elastic-network modeling of protein dynamics, I will provide a review of our previous studies. After that, I will present recent results which have been obtained by us for an ion channel which is organizing the transmembrane exchange of magnesium. Here, we have probed the dynamical properties of the cytosolic channel domains and checked the response exerted on the ion-guiding pore. A possible operation mechanism as revealed by our studies will be discussed.
[1] H. Flechsig and A.S. Mikhailov (2010), Proc. Natl. Acad. Sci. USA 107, 20875-20880
[2] H. Flechsig, D. Popp, and A.S. Mikhailov (2011), PLoS ONE 6, e:21809

第36回拠点形成コロキウム

Title: Large organized surface domains self-assembled from non-polar amphiphiles
Speaker: Marie Pierre Krafft (Université de Strasbourg, France)
Date: 平成24年10月26日(金) 10:30~
Place: 理学部5号館401号室

Abstract

第35回拠点形成コロキウム

Title: Magnetic Surfactants
Speaker: Dr. Paul Brown (School of Chemistry, University of Bristol Cantock’s Close, UK)
Date: 平成24年10月10日(水) 10:30~
Place: 理学部5号館北棟第二講義室
Abstract:
Recently, a new class of surfactants have been discovered that respond to a magnetic field. These magneto-responsive surfactants are based on common cationic surfactants with metal complex anions, which, because they contain high effective concentrations of metal centres, allows their physico-chemical properties (hydrophbicity, electrical conductivity, etc) to be controlled non-invasively and reversibly by external magnetic fields. It has been shown that the controlled conjugation of these surfactants to DNA (and other biomolecules) is possible, allowing for manipulation in solution simply by switching "on" and "off" a magnetic field. Further to this it has been demonstrated that magnetic emulsions and microemulsions can be readily generated with suggested applications from environmental cleanup to targeted drug delivery. Finally, a combination of small-angle neutron scattering and SQUID magnetometry has shown that magnetic microemulsions (nanoparticle-free ferrofluids) can act as tunable nanomagnets, providing a new method to bridge the gap in our understanding of magnetic behaviour on an intermediate scale between molecular and solid-state bulk objects."

第34回拠点形成コロキウム

Title: Soft deformable self-propelled particles
Speaker: Dr. Andreas Menzel (ディユッセルドルフ大学)
Date: 平成24年9月7日(金) 10:30~
Place: 理学部5号館401号室
Abstract:
We study the behavior of self-propelled particles that deform due to steric repulsion. As will be explained, such induced deformations can lead to pairwise alignment of the velocity vectors. The collective properties of these soft deformable self-propelled particles are investigated in the presence of an additional Gaussian-core repulsion. Collective phenomena such as migrating hexagonal and rectangular crystals, reentrant fluidity, cluster crystals, and laning are found. Finally, we outline the role of orientational noise, which provides a link to the famous Vicsek approach.

第33回拠点形成コロキウム

Title: A variational principle for a complex fluid
Speaker: 深川宏樹氏(アライドエンジニアリング)
Date: 平成24年7月18日(水) 16:30~
Place: 理学部5号館413号室
Abstract:
The action of a complex fluid is given by the integral of the difference between the kinetic energy density and the internal energy density over space and time. In this variational principle, mass conservation law and constitutive equations are considered as holonomic constraints. Note that the entropy production in these dissipative fluids gives a nonholonomic constraint. The velocity field is obtained from the stationary condition of the action under these constraints. The associated Hamiltonian formulation is derived by regarding the velocity field as the input in the framework of control theory.

第32回拠点形成コロキウム

Title: Ultrafast electron diffraction using electrons accelerated by intense femtosecond laser pulses
Speaker: 阪部 周二氏(京都大学化学研究所・物理第二教室)
Date: 平成24年7月17日(火) 15:30~
Place: 理学部5号館401号室
Abstract:
The key issue to realize single-shot ultrafast electron diffraction (UED) is to develop intense short electron-pulse sources. With conventional UED instruments, an electron pulse is generated at a photocathode irradiated by a femtosecond laser pulse and accelerated by an additional external static electric field. The amount of electrons in the pulse is limited because the electron pulse expands during its flight by space-charge forces in the pulse. For the mid-energy range of around 100keV to 1MeV, corresponding to the energies of conventional transmission electron microscopy, there is no satisfactory method for generating femtosecond electron pulses. We have demonstrated femtosecond pulse compression of a laser-accelerated electron beam with energy of around 350keV. The electron pulses are generated by irradiating a tightly focused terawatt femtosecond laser pulse on a foil target, then, the pulses are compressed by using an achromatic bending magnet system. These femtosecond electron pulses have potential to produce sufficient intensity to take a single-shot diffraction pattern.

第31回拠点形成コロキウム

Title: Granular friction in a wide range of shear rates
Speaker: Takahiro Hatano (University of Tokyo)
Date: 平成24年7月12日(木) 10:30~
Place: 理学部5号館413号室
Abstract:
The rheological properties of granular matter are important for analyzing various phenomena in geosciences, such as landslides, debris flows, and crater formation. Among the rheological properties of granular matter, the shear-rate dependence of the friction coefficient determines the stability of deformation and therefore has been paid major attention. Here we report simulation and experiment that address this problem. We conduct an experiment on the frictional properties of granular matter over a wide range of shear rate that covers both the quasistatic and the inertial regimes. We show that the friction coefficient exhibits negative shear-rate dependence in the quasistatic regime, whereas the shear-rate dependence is positive in the inertial regime. The crossover shear rate is determined in terms of the competition between two physical processes, namely frictional healing and anelasticity. We also find that the result does not depend on the shape of the grains and that the behavior in the inertial regime is quantitatively the same as that in some numerical simulations.

第30回拠点形成コロキウム

Title: The shear effects on a mixture of water / organic solvent / antagonistic salt
Speaker: Koichiro Sadakane (KEK)
Date: 平成24年7月10日(火) 13:30~
Place: 理学部5号館401号室
Abstract:
Mesoscopic structures, such as lamellar, in a mixture of water, 3-methylpyridine, and antagonistic salt, NaBPh4, are discovered in our recent studies [1,2]. According to the theoretical investigations by Onuki [3], hydrophilic and hydrophobic ions tend to adsorb near the interface between water and organic solvent. These ions reduce the interfacial tension between the solvents, and mesoscopic structures are induced [3]. In order to understand the previous experimental results, it is assumed that pairs of hydrophilic (Na+) and hydrophobic ions (BPh4-) play roles of surface-active agent in a mixture of water and 3-methylpyridine. The details of ion distribution, however, have not been clarified experimentally yet in such mixtures.
In this study, the effects of shear on a mixture of water / 3-methylpyridine / NaBPh4 are investigated. Then, we found that the mixture at lamellar phase shows shear thickening as is the case with polymer gels. Furthermore, onions or fiber-like structures are also observed by means of Rheo-SALS and Rheo-SANS measurements.
[1] K. Sadakane, H. Seto, H. Endo and M. Shibayama, J. Phys. Soc. Jpn, 76, pp. 113602(1)-(3) (2007).
[2] K. Sadakane, A. Onuki, K. Nishida, S. Koizumi and H. Seto, Phys. Rev. Lett., 103, pp. 167803(1)-(4) (2009).
[3] A. Onuki, J. Chem. Phys., 128, 224704 (2008).

第29回拠点形成コロキウム

Title: Lipid membrane deformation in response to a local pH modification
Speaker: Professor Masayuki Imai (Tohoku Univ.)
Date: 平成24年7月4日(水) 16:30~
Place: 理学部5号館413号室
Abstract:
Morphology transition induced by chemical stimulus is characteristic phenomena in soft matter. Here we report the deformation of a lipid membrane in response to a local pH modification.

第28回拠点形成コロキウム

Title: Mechanical control of cell rearrangements in the development of animal forms
Speaker:  Dr. Shuji Ishihara (University of Tokyo)
Date: 平成24年6月25日(月) 13:30~
Place: 理学部5号館401号室
Abstract:
Understanding dynamics of forces that drive body deformation is one of the central questions in developmental biology. To address the question, we developed a Bayesian formulation for estimating the cell pressure and the cortical tension from the morphology of cells. By using the method in combination with experimental validations, we identified a novel mechanism of cell rearrangements in the growing Drosophila wing.

第27回拠点形成コロキウム

Title: Topological defects of nematic liquid crystal confined in complex geometry
Speaker: Takeaki Araki (Kyoto University)
Date: 平成24年6月12日(火) 13:30~
Place: 理学部5号館401号室
Abstract:
We numerically studied nematic liquid crystals flowing in a regular-shaped porous medium. With strong anchoring, the director field cannot align uniformly and topological defects are stably formed. Depending on the geometry, some of the defects are topologically locked inside the channels and the others are free from the topological locking. In a weak flow, both the locked and free defects are sustained, only showing small displacements of the positions. In an intermediate flow, the free defects move with the background flow. When the defects reach a critical displacement, they are annihilated and new ones are generated near the original positions repeatedly. In a strong flow, even the locked defects show similar repeated motions with a longer period. We also show flow can switch the orientation of the nematic phase. Owing to the topological locking, the orientation is memorized even after the flow is stopped.

第26回拠点形成コロキウム

Title: Elucidation of the role counterions on the interaction between macroions: Electrostatic interaction and beyond
Speaker: Prof. Chwen-Yang Shew (Department of Chemistry College of Staten Island, City University of New York, USA)
Date: 平成24年6月1日(金) 10:30~
Place: 理学部5号館401号室
Abstract:
Like-charge attraction remains one of the most intriguing mysteries in science, and revealing its origin is expected to generate a great impact on numerous communities including biophysics, nanomaterials and polymer sciences, etc. This phenomenon is referred to the condition when like-charge macroions induce attraction in solution. Such a concept is somewhat counterintuitive because like-charge objects are supposed to repel each other. The unique role of like-charge attraction lies in the fact that it yields a driving force to induce self-assembly processes. In biological systems, like-charge attraction is ubiquitous partly because the majority of biomolecules are macroions, for instance aggregation of actin filaments, in the form of bundles. Besides, nano-scaled polyoxometalates (polyanions) self-assemble into a much larger hollow sphere with a near uniform size while the solvent dielectric constant is decreased. Unlike other aggregation processes with infinity aggregate size, like-charge aggregates share a common feature, that is, their aggregate size becomes leveled-off at a finite size. One scenario for finite aggregate size is attributed to the survival charge of aggregates that prevents charged aggregates from growing. Through our studies by using integral equation theories and simulations, we suggest that the specific binding between counterion and macroion may play an important for like-charge attraction. Incorporating specific binding into models allows us to better understand the solution structure of short DNA segments and polyoxometalates. Furthermore, changing the specific binding affinity from macroions to their aggregates manifests a possible mechanism to account for the finite aggregate growth.

第25回拠点形成コロキウム

Title: Negative/Positive Photophoresis of cm-Sized Droplets
Speaker: Masatoshi Ichikawa (Kyoto University)
Date: 平成24年5月29日(火) 13:30~
Place: 理学部5号館401号室
Abstract:
The photon-induced motion of an oil droplet on an aqueous solution under local irradiation by a green laser is reported. The results showed that a repulsive force is generated on pure water, while an attractive force is observed with an aqueous solution containing a surfactant. The driving force is interpreted in terms of a thermal Marangoni effect. This difference in the photophoretic effect is interpreted by taking into account of the advection caused by the spatial gradient of the surface tension under local heating by a laser. A numerical model revealed that the balance of surface tension at each boundary defines the mode of advection around the droplet and causes switching in the direction of photophoresis.

第24回拠点形成コロキウム

Title: On Capillary Gravity Waves
Speaker:  Mr. Michael Benzaquen (PCT Laboratory UMR Gulliver 1083 CNRS/ESPCI, Paris, France)
Date: 平成24年5月23日(水) 13:30~
Place: 理学部五号館第四講義室(525号室)
Abstract:
Water waves are both fascinating and of great practical importance. For these reasons, they have attracted the attention of scientists and engineers for many decades. Water waves can for instance be generated by the wind blowing over the ocean, by a moving ship on a calm lake, or simply by throwing a pebble into a pond. Their propagation at the surface of water is driven by a balance between the liquid inertia and its tendency, under the action of gravity or of surface tension (or a combination of both in the case of capillary gravity waves), to return to a state of stable equilibrium. We here look into the theoretical features of the capillary gravity waves created at the waterair interface by a small external perturbation (pressure distribution) moving at constant velocity along a linear trajectory. This theoretical study was justified by a substantial experimental work on the same topic. Such experiments are notably led by Christophe Clanet at Ecole Polytechnique (France) and Victor Steinberg at Weizmann Institute (Israel). Firstly, we consider the case of a two-dimensional perturbation and assume that a depthdependent current is initially present in the fluid. Within the framework of linear wave theory, we derive a general expression of the wave resistance experienced by the perturbation as a function of the current profile in the case of an inviscid fluid. We then analyze and discuss in details the behavior of the wave resistance in the particular case of a linear current, a valid approximation for some wind generated currents.
Secondly, we focus on the three-dimensional case in which the pressure distribution is symmetrical about a point. We calculate the wave resistance experienced by the perturbation as a function of its size (compared to the capillary length). In particular, we analyze how the amplitude of the jump occurring at the minimum phase speed c depends on the size of the perturbation, including liquid density, the water-air surface tension, acceleration due to gravity). We also show how for pressure distributions broader than a few capillary lengths, thewave resistance in the particular case of pure gravity waves is progressively recovered.

第23回拠点形成コロキウム

Title: Alignment vs noise in self-propelled particles: minimal models for collective motion and their continuous descriptions
Speaker:  Dr. Hugues Chate (CEA - Saclay, France)
Date: 平成24年5月21日(月) 16:00~
Place: 理学部5号館401号室
Abstract:
Two important 1995 papers have marked the birth of collective motion studies in physics: Vicsek et al introduced what could now be described as the ``Ising model'' of this new subfield. This prompted Toner and Tu to propose a continuum theory of flocks which they showed to give rise to long-range orientational order even in two space dimensions. In this setting, the complexity of most natural instances of collective motion is reduced to the competition between local alignment and noise in interacting self-propelled particles. As I will show, this nevertheless gives rise to important and new physics. In this talk, I will give an update of our current knowledge about the Vicsek model, the Toner-Tu theory, and their relationship. I will also present the emerging picture of universality classes brought about by recent progress in the study of Vicsek-like models together with their continuous descriptions.

第22回拠点形成コロキウム

Title: Struggle toward understanding biology
Speaker:  Professor Y. Oono (University of Illinois at Urbana-Champaign)
Date: 平成24年5月14日(月) 13:30~
Place: 理学部5号館401号室
Abstract:
What can we learn from surveying the biological world as a physicist? Can we formulate general enough and still answerable/meaningful questions? A preliminary report.

第21回拠点形成コロキウム

Title: Self-assembly in complex fluids
Speaker:  Prof. Arun Yethiraj (Department of University of Wisconsin - Madison)
Date: 平成24年4月9日(月) 16:00~17:30
Place: 理学部5号館401号室
Abstract:
The self-assembly of molecules into nano-structured materials is a fascinating process because small changes in intermolecular interactions can have a large impact on the final mesoscopic structures. An interesting goal is the directed self-assembly of molecules where the chemical nature of the molecules is altered to drive the assembly into specific nanostructures. In this talk I will discuss two classes of molecules: -peptides and Gemini surfactants. In the former, some sequences assemble into long hollow cylinders, but other similar sequences do not. The latter form lyotropic liquid crystalline phases. Using computer simulation I will show that interactions between three molecules play an important role in the assembly of -peptides and electrostatic interactions play an important role in the self-assembly of Gemini surfactants. Both systems show promise for chemistry directed self-assembly.

第20回拠点形成コロキウム

Title: Adsorption on colloids and flocculation
Speaker:  Daniel Beysens (CEA and ESPCI, Paris, France)
Date: 平成24年4月23日(月) 16:00~
Place: 理学部5号館401号室
Abstract:
Colloidal particles suspended in a binary liquid mixture display many interesting features. For instance, a preferential adsorption occurs, which is more important on the side of the coexistence curve poor in the adsorbed component. Adsorption increases with the proximity of the mixture to the coexistence curve. An aggregation phenomenon, which is reversible with respect to temperature, is observed in the high adsorption regime close to the bulk coexistence. A robust set of observations, involving different colloids and liquid mixtures, are discussed. The above findings are assessed in the light of current theoretical understanding of wetting phenomena. In addition, the recent advances in the dynamics of aggregation of colloids, and the inverse process, fragmentation, are presented.

第19回拠点形成コロキウム

Title: Collective motion of binary self-propelled particle mixtures
Speaker:  Dr. Andreas Menzel (Heinrich-Heine University Düsseldorf, Germany)
Date: 平成24年2月15日(水) 17:00~
Place: 理学部5号館413号室
Abstract:
We study the onset of collective motion in a mixture of two species of self-propelled particles in the spirit of a Vicsek model (particles are pointlike and have constant magnitude of velocity). Velocity vectors within each particle species tend to orient into the same direction, whereas different alignment rules and strengths of alignment for particles of different species were investigated. Starting point of our approach are two-dimensional particle-based Langevin equations, from which Fokker-Planck and macroscopic continuum equations were derived and analyzed. Our results include copied and inverted spatial density profiles for the two species in certain density regimes and for certain coupling strengths.

第18回拠点形成コロキウム

Title: Collapse transition of a single multiblock copolymer in the selective solvent
Speaker:  Prof. Wenbing Hu
Department of Polymer Science and Engineering, State Key Laboratory of
Coordination Chemistry, School of Chemistry and Chemical Engineering,
Nanjing University, Nanjing 210093, China
Date: 平成24年1月30日(月) 16:00~
Place: 理学部5号館401号室
Abstract:
In this talk, i will present our Wang-Landau Monte Carlo simulations of a single multiblock copolymer performing collapse transition in the selective solvent. The results showed that, 1) each insoluble block first undergoes an intra-block collapse transition over the theta point, yielding a “peal-necklace” structure without sacrificing coil sizes; 2) the inter-block collapse transition then occurs at temperatures below the theta point, leading to an apparent decrease of coil sizes; 3) all the collapsed blocks gradually merge into one large globule surrounded with a corona of soluble loops, namely, a flower-like micelle. The inter-block collapse transition suspended below the theta point will be discussed.

第17回拠点形成コロキウム

Title: リン脂質部位を有する電場・光応答性リオトロピック液晶
Speaker:  蟹江澄志氏(東北大 多元物質科学研究所)
Date: 平成24年2月6日(月) 15:45~
Place: 理学部5号館401号室
Abstract:
脂質二分子膜は,膜タンパクの保持・イオン輸送・光合成など,機能材料設計の立場から観て実に魅力的な機能を有する. こうした機能は,脂質二分子膜中に存在する少量の機能性分子に由来しており,二分子膜の主成分であるリン脂質は単に機能性分子固定用の土台としての役割を担っている. そこで本研究では,外場によりアクティブな組織構造変化・ダイナミックな応答性を示す人工リン脂質を創製し,リン脂質自身に機能性を付与することを目的とした. 具体的には,サーモトロピック液晶性分子にホスファチジルコリン部位を導入することで人工リン脂質を合成し,その液晶相構造解析,電場・光応答性評価を行った.本講演では,その詳細について紹介する.

第16回拠点形成コロキウム

Title: Polyelectrolyte complexes cosisting of macromolecules with varied stiffness and different affinity to solvent
Speaker: Prof. Valentina V. Vasilevskaya (Russian Academy of Sciences, Moscow, Russia)
Date: 平成24年1月18日(水) 15:00~16:00
Place: 京都大学理学部5号館北館第二講義室
Abstract:
We study interpolymer complexes formed by oppositely charged macroions having equal total charge and study influence of different factors on the structure of such complexes. We consider the interpolymer polyelectrolyte complexes consisting of macromolecules having different affinity to solvent and different density of ionic groups along the chain. It was proposed that complexes of such macromolecules have a core-shell structure. The inner part of complex contains monomer units of both macromolecules, while exterior part consists exclusively of monomer units of hydrophilic macromolecules. With such complex organisation, the external charged hydrophilic shell effectively protects the complex from precipitation and fusion with other complex assemblies. Increasing salt concentration causes changes in the structure of complex particles. The interpolymer complexes preserve their structure and size till some a critical salt concentration , at which the complex rises sharply to a larger dimension. From this concentration, the macroions forming the interpolymer complex start to swell and fully separate at a salt concentration . After separation, the macroions coexist in solutions and with further increase of salt concentration reduce their sizes according to the screening of polyion charges by salt ions. We analyze structure of polyelectrolyte complexes consisting of two identica l but oppositely charged macroions with varying chain stiffness. It was show n that two complex structures could arise depending on stiffness of constitu ent chains. Stiff chains are organized into “ladder” structure: chains are situated parallel to each other and monomeric units are involved into ionic pairs according to their position in the chain. Flexible chains form globul ar “scrambled egg” structure with disordered position of monomer units. Co nformational transition between two structures proceeds as a phase transition.

第15回拠点形成コロキウム

Title: Nonequilibrium Thermodynamics of Information Processing
Speaker: Dr. Takahiro Sagawa (Yukawa Institute)
Date: 平成24年1月25日(水) 17:30~
Place: 理学部5号館413号室
Abstract:
In this seminar, I'd like to talk about our results on the foundation of the relationship between thermodynamics and information. Theoretically, I will focus on a generalized the second law of thermodynamics for information processing processes such as feedback control, measurement, and information erasure. I'd also like to talk about our recent experiment, which has realized the Szilard-type Maxwell's demon.

第14回拠点形成コロキウム

Title: Collective behavior of bistable units with global and asymmetric local interactions
Speaker: Prof. Yoshihiro Yamazaki (Waseda Univ.)
Date: 平成24年1月16日(月) 13:30~
Place: 理学部5号館401号室
Abstract:
We have proposed a dynamical model showing the collective dynamics of bistable units with global and asymmetric local couplings. The essence of this dynamics is competition between regulation of ratio of the two unit states by the global coupling and directional transition from one state to the other states by the asymmetric local coupling.
[ref] Y. Yamazaki, Prog. Theor. Phys. 125, 641-652 (2011).

第13回拠点形成コロキウム

Title: 密度ゆらぎによってコロイド表面間に誘起される長距離斥力相互作用
Speaker: 小山岳人氏 (独立行政法人海洋研究開発機構)
Date: 平成23年12月20日(火) 14:00~
Place: 理学部5号館401号室
Abstract:
超臨界状態の流体の特徴として、臨界点とそこから延びる「密度ゆらぎの尾根線」の近傍における密度ゆらぎの発現が挙げられる。 この様な流体に粒子を分散させた場合には、密度ゆらぎによって粒子表面間力が影響を受けることが知られている。 その代表例として同種粒子間に引力を誘起する臨界カシミア力がある。また密度ゆらぎの存在下では、粒子表面近傍とバルク中で媒質の密度分布が異なる可能性も考えられる。 そのような媒質分布の不均一性は、表面近傍の局所的な媒体物性(比誘電率、屈折率)に影響し、粒子表面間力に影響を与えると予想される。  我々は、高温・高圧光学顕微鏡を用いたその場観察実験によって、超臨界流体中に分散したシリカ表面間に、10 μmにもおよぶ超長距離の斥力相互作用が現れることを見出した。 これらの相互作用は、ゆらぎの尾根線近傍でのみ見られることから媒体の密度ゆらぎが超長距離斥力の発現に重要な役割を果たしていると考えられる。 当日は、この現象の詳細と斥力の本質と発現のメカニズムについて述べる。

第12回拠点形成コロキウム

Title: The Secret Life of Water: E = H2O
Speaker: Prof. Gerald H. Pollack (Department of University of Washington, Seattle)
Date: 2011年10月14日(金)15:00~16:00
Place: 5号館413号室 物1コロキウム
Abstract:
School children learn that water has three phases: solid, liquid and vapor. But we have recently uncovered what appears to be a fourth phase. This phase occurs next to water-loving (hydrophilic) surfaces. It is surprisingly extensive, projecting out from the surface by up to millions of molecular layers. Of particular significance is the observation that this fourth phase is charged; and, the water just beyond is oppositely charged, creating a battery that can produce current. We found that light recharges this battery. Thus, water can receive and process electromagnetic energy drawn from the environment — much like plants. The absorbed light energy can then be exploited for performing work, including electrical and mechanical work. Recent experiments confirm the reality of such energy conversion. The energy-conversion framework implied above seems rich with implication. Not only does it provide an understanding of how water processes solar and other energies, but also it may provide a foundation for simpler understanding natural phenomena ranging from weather and green energy all the way to biological issues such as the origin of life, transport, and osmosis. The lecture will present evidence for the presence of this novel phase of water, and will consider the potentially broad implications of this phase for physics, chemistry and biology, as well as some practical applications for engineering.

第11回拠点形成コロキウム

Title: イオン液体の表面・界面化学の巨視と微視
Speaker: 大内 幸雄氏(名古屋大学理学研究科)
Date: 2011年10月26日(水)16:00~
Place: 5号館413号室 物1コロキウム
Abstract:
イオン液体は有機カチオンとアニオンからなる化合物群であり、構造化学的には塩であるにもかかわらず常温で液体相を示す。 反応・抽出・電気化学・環境・バイオ・エネルギーなどの諸分野で活発な応用研究が進められる一方、イオン液体の特異な物性に関して、構造とダイナミックスの観点から、その本質を明らかにするための努力が続けられている。 本講演では、イオン液体の巨視的な物性として表面・界面張力を念頭におき、微視的な描像を非線形振動分光(IV-SFG)及び準安定励起原子電子分光(MAES)、古典MDに求め、イオン液体の特徴の一端を明らかにすることを目的とする。

第10回拠点形成コロキウム

Title: 結晶系における回転対称性破れの解析手法およびポロジカル欠陥ダイナミクス
Speaker: 小林未知数氏 (東京大学)
Date: 2011年10月24日(月)14:00~
Place: 理学部5号館 401号室
Abstract:
流体から結晶への相転移は、系の並進対称性および回転対称性の破れを伴う相転移であり、またこれらの対称性の破れに伴ってそれぞれdislocation, disclinationと呼ばれるトポロジカル欠陥が現れる。 系の並進対称性およびdislocationを特徴づける量として最もよく知られているのはバーガースベクトルであるが、本セミナーでは全く異なる量として系の回転対称性およびdisclinationを特徴づける量として、Qベクトルと呼ばれる複素ベクトルを紹介する。 この量は粒子系シミュレーションにおいて結晶系を分類するために用いられてきた量であるが、それだけではなく結晶の方位およびその空間依存性や、disclinationの空間配置やダイナミクスをも記述できる量であることが分かってきた。 セミナーでは、このQベクトルとその数学的取り扱いを詳細に説明し、具体的な応用例として、Qベクトルの有効模型を用いて記述されるdisclinationダイナミクスを紹介する。

第9回拠点形成コロキウム

Title: アクティブ流体系における同期現象
Speaker: 内田 就也氏 (東北大学)
Date: 2011年10月17日(月)13:30~
Place: 理学部5号館 401号室
Abstract:
多くの単細胞生物は鞭毛や繊毛の集団運動を利用して泳動を制御している。 これらの集団運動には流体力学相互作用が重要な役割を果たしていると思われるがその機構は Taylor の先駆的研究から60年が経つ今日なおよく理解されていない。 われわれはそのミニマルモデルとして、粘性流体中で駆動されて一定軌道上を回転する剛体球のダイナミクスを解析した。 駆動力が周期的に変動する場合や剛体球自身が駆動要素を持つ場合について、2体系が同期する条件や、多体系の集団運動のパターン(らせん波、平面波など)を明らかにした。 セミナーではこれらの結果と繊毛のメタクロナル波や鞭毛カーペットなどの実験系との対応を議論するとともに、長距離相互作用を持つ振動子系としての一般的性質にも触れたい。

第8回拠点形成コロキウム

Title: Chemical control of droplet motion
Speaker: 伴 貴彦 氏 (大阪大学大学院 基礎工学研究科 物質創成専攻 化学工学領域)
Date: 2011年10月12日(水) 16:30~
Place: 理学部5号館 413号室
Abstract:
We present three kinds of self-propelled droplets. First type of droplet motion is induced by the change in surface energy of a substrate due to chemical dewetting phenomena. The droplet exhibits two kinds of spontaneous motion: translational motion or oscillatory change in contact angle. The motion depends on kind of anionic surfactant. Second one is triggered by the change in interfacial energy in a liquid-liquid interface due to Marangoni effect. When an oil droplet containing surfactant is formed in buffer solution, the droplet shows random walk or periodic pore formation. The motion depends on pH of buffer solution and size of the droplet. Third one is to use the interfacial energy generated under phase separation, i.e. Korteweg force. The droplet behavior depends on the composition of the continuous phase: for higher concentrations of the continuous phase than the equilibrium value, the droplet moves unidirectionally even in a homogeneous concentration field with a constant radius, whereas for lower concentrations, the droplet shrinks or deforms like a biological cell with moving. We will discuss mechanism of the droplet behavior in comparison to theoretical study proposed by the other researchers.

The 7th colloquium

Title: Theoretical studies of the spectra of spin echo small angle neutron scattering: Structure of simple fluids
Speaker:Prof. Chwen-Yang Shew (Department of Chemistry College of Staten Island, City University of New York Staten Island)
Date: 2011年9月30日(金) 15:00~16:30
Place: 理学部5号館 413号室
Abstract:
It has been a great challenge to characterize aggregates and large particles with small angle neutron scattering because scattering signals needed to unveil their structures appear at very small angles that require high resolution instruments to resolve scattering spectra. Such an instrumental setup indeed causes tremendous signal losses and forbids accurate measurements. To this end, a novel spin-echo small angle neutron scattering method (SESANS) based on polarized neutrons has been developed, from which the spatial correlation between molecules in real space can be obtained. The method provides a new means for characterization of aggregates or other large particles. However, interpretation of SESANS data remains difficult due to its intrinsic mathematical complexities. In this talk, I will briefly introduce our new algorithm for calculation of theoretical SESANS spectra by using computer simulations. This algorithm is applicable to different particle geometries and interaction potentials, and is rigorously tested with integral equation theory via hard-sphere liquid model. Our simulations also show that the characteristic feature of SESANS spectra can be exploited to discern attractive and repulsive interaction between particles. Furthermore, I will discuss about our recent model studies to elucidate the effect of particle interactions on the spectral features of SESANS

第6回 拠点形成コロキウム

Title: Macroscopic behavior of active systems with a dynamic preferred direction
Speaker: Professor Helmut R. Brand (Theoretical Physics III, University Bayreuth, Germany)
Date: 2011年9月27日(火)14:00~
Place: 理学部5号館 401号室
Abstract:
We present the derivation of macroscopic equations for active systems with a dynamic preferred direction, which can be either axial or polar. Such an approach is expected to be applicable and important for biological systems, which have preferred directions only dynamically, but not permanently or in a static configuration. For an axial preferred direction we introduce the time derivative of the local preferred direction as a new variable and discuss its macroscopic consequences including new cross-coupling terms. We investigate the coupling to a gel for which one has the strain tensor and relative rotations between the new variable and the network as additional macroscopic variables. For the case of a dynamic polar preferred direction the additional macroscopic variables transforms like a velocity under parity and time reversal. This approach is expected to be useful for a number of biological systems including, for example, the formation of dynamic macroscopic patterns shown by certain bacteria such as Proteus mirabilis.

第5回 拠点形成コロキウム

Title: いまさら拡散泳動
Speaker: 和田 浩史氏 (京都大学基礎物理学研究所)
Date: 2011年8月9日(火)13:30~
Place: 理学部5号館 401号室
Abstract:
溶液中に溶質の勾配があると、その溶液と接する固体壁近傍には勾配に比例した流れが生じる(浸透流)。 固体がコロイド球のように溶液中に分散している場合にはこの流れはコロイドの泳動を引き起こす。 この現象は拡散泳動(diffusiophoresis)として古くから知られており、Derjaguinや Andersonによって理論的基礎付けが行われた。 近年ではmicrofluidicsなどへの応用も盛んである。 セミナーではAndersonの 1989年の論文にもとづいて拡散泳動の基本的事柄をレビューする。 もとの理論は希薄溶液に関するものであるが、その議論の道筋をよく見直してみると、溶質の濃度が高い場合にも拡張できる可能性に気づく。 このこと自体はほんのささやかな+αに過ぎないが、セミナーではそのあたりの議論を通じて泳動現象全般に関する双方の理解を深めることを目指したい。

第4回 拠点形成コロキウム

Title: 非線形性の困難を越える試みについて
Speaker: 蔵本 由紀教授 (京都大学数理解析研究所)
Date: 2011年7月1日(金)10:30~
Place: 理学部5号館 401号室
Abstract:
非線形システムは常に数学的困難を伴っている。 しかし、散逸系における非線形現象に関して言えば、この困難に対処するために人々が案出した一般的処方は、少なくとも基本的な考え方においては驚くほど単純である。 非本質的な技法の発展による外見上の華やかさや複雑さによってこの事実が見えにくくなっているだけである。 本セミナーでは、関連分野の歴史を振り返りながら、私的経験も織り交ぜつつ、この事実を明らかにしたい。 特に、非線形振動子系の理論に焦点を当て、この「驚くほど単純な」アイディアが及ぶ射程がどれほどのものであるかを考察したい。

第3回 拠点形成コロキウム

Title: Glassy behaviors in kinetically constrained models
Speaker: 太田 洋輝氏 (京都大学基礎物理学研究所)
Date: 2011年6月28日(火)13:30~
Place: 理学部5号館 401号室
Abstract:
I talk about glassy behaviors such as nonergodic transitions in kinetically constrained models (KCMs), which are candidates of the systems exhibiting the universality of jamming transitions in athermal systems. First, I review previous studies that KCMs on finite dimensional lattices have been proved to exhibit nonergodic transitions, of which universality is determined by the critical natures of a conventional directed percolation. Next, I introduce a KCM on the square lattice which also shows a nonergodic transition. A notable point is that the universality class is different from that of previous models. Finally, I discuss its relevance to jamming transitions in athermal systems.

第2回 拠点形成コロキウム

Title: 新規蛍光イメージング法による単一高分子鎖の構造とダイナミクスの評価
Speaker:青木裕之氏(学際融合教育研究推進センター)
Date: 2011年6月7日(火)午後2時
Place: 理学部5号館 401号室
Abstract:
高分子材料のマクロな物性を理解する上で、鎖一本のレベルでの形態と運動を直接観察することが可能になれば多くの情報を与えるものと考えられる。 しかしながら従来の顕微鏡法では単一高分子鎖レベルの構造と運動を直接的に追跡することは困難であった。 本講演では、単一高分子鎖の直接計測を実現にするための、超解像技術をはじめとする新しい蛍光顕微鏡法について紹介し、これを応用した高分子のダイナミクスの評価について述べる。

第1回 拠点形成コロキウム

Title: Rigidity-matching of cell-substrate interaction acts resonantly leading to enhancement of the stability of cardiac conduction system
Speaker: Dr. Marcel Horning
Date: 16:30, May 18, 2011 (Wed)
Place: Room 415, Physics Building, Kyoto University
Abstract:
The biomechanical interactions between cells and extracellular environments dynamically modulate the physiological tissue behavior in living body such as seen in the tissue maintenance and remodeling. Substrate-induced modulation of synchronized beating in cultured cardiomyocyte tissue was systematically characterized on elasticity-tunable substrates to elucidate the effect of biomechanical-coupling. We have discovered that myocardial conduction is resonantly enhanced when the rigidity of the cell culture environment matches cell membrane rigidity well. Both, stability of spontaneous target wave activity and calcium instabilities in high frequency-paced tissue were independently shown to be enhanced with a marked peak when cell substrate and cell membrane show rigidities of 11kPa. Rigidity- matching in cell-substrate interactions is reported to critically affect the behavior of synchronized beat in cardiomyocyte-ensembles, implying the essential manner of biomechanical-coupling of in-vivo tissue as a dynamical systems.