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機能創成セミナー Seminar on Mechanical Science and Bioengineering

基礎工学研究科J棟3階 J306セミナー室
Exploring motor control mechanisms during physical human-robot interaction to improve rehabilitation outcomes
In the last decade there has been a growing interest in studying physical coupling between humans or humans and machines. Indeed, having a machine capable of understanding the intention of a movement and interactively cooperate with a human is among the frontiers of the research in robotics as well as rehabilitation. On one side, physical coupling between two subjects was shown to be an advantageous solution in many cooperative contexts. On the other, little is known about how two people mutually exchange information to exploit the coupling. The studies heretofore conducted investigated the ability of subjects to learn a novel skill and adapt their knowledge to a cooperative context that requires negotiating a common strategy while being physically coupled. The main goal of this talk is presenting how learning develops in a context where training on a novel skill occurs in pairs. The exploitation of robotic technologies to accomplish the goal will be underlined and experiments to characterize different motor control strategies will be described. Potential applications in rehabilitation will be proposed and discussed.
Jacopo Zenzeri, PhD
Head of the Motor Learning, Assistive and Rehabilitation Robotics Laboratory,
Robotics, Brain and Cognitive Sciences Department Italian Institute of Technology
世話人:野村泰伸 / 参加者:未定
基礎工学C棟4階 C棟共用セミナー室
Large Reynolds number asymptotic theories for three-dimensional hydrodynamic and magneto-hydrodynamic flows
The first half of this talk presents a brief review of the large Reynolds number asymptotic descriptions of coherent vortex structures in shear flows. In recent times Dynamical Systems Theory picture of turbulence has revealed that complicated turbulent flows are actually supported by simple Navier-Stokes solutions, known as exact coherent structures. The structures exhibit cleaner asymptotic development than turbulence, thereby providing ideal testing grounds of the asymptotic theories. The second part of the talk concerns the large Reynolds number asymptotic theory of resistive magneto-hydrodynamic equations. The new theory has emerged by considering a nice combination of the vortex-wave interaction theory by Hall and Smith (1991) and the resonant absorption theories for Alfven and cusp waves, developed in solar physics community. We will discuss when the high Reynolds number dynamos can be self-sustained based on the theory.
出口健悟 博士
School of Mathematical Sciences,
Monash University
世話人:河原 源太 / 参加者:未定
in vitro骨格筋収縮モデルの開発と医療分野における基礎研究への応用
骨格筋は、全身の40%の重量を占める大きな器官である。これまで、骨格筋を対象とした研究は「動き」を生み出すメカニズムの解明にフォーカスしたものが主流であった。しかし、骨格筋は、単に「動き」を生み出すための器官として存在しているだけではなく、「骨格筋を動かすこと(筋収縮)」が積極的に健康の維持・増進に関わっていることが明らかになってきた。運動(筋収縮)が健康に関係することは、当然のこととして考えられているが、実は運動の何が、どのようなメカニズムを通して全身性の健康維持に寄与しているかについてはほとんどわかっていない。これまで明らかにされてこなかった理由として、骨格筋が生命維持に必須の臓器とは考えられていなかったため医療分野で基礎研究として取り組む対象とされてきていなかったこと、in vitroで運動を模倣する適切なモデルがなく、運動刺激によって筋細胞内で誘導される分子レベルでの変化が検証できなかったこと、などが考えられる。しかし、最近になってQOL維持と健康寿命の延伸には骨格筋が必須の器官であることが明らかにされつつあり、医療・薬学・農学から工学にわたる様々な分野で骨格筋研究への関心が高まっている。  演者の所属するグループでは、骨格筋の収縮(運動)と健康の維持への寄与について研究しており、これまでに様々なin vitro筋収縮モデルを開発してきた。新たな筋収縮モデルの開発は、これまで明らかにされてこなかった筋収縮時の筋細胞内分子応答を検証する上で重要となる。本発表では、我々が開発した筋収縮モデルとそれを用いた応用研究のうち、特に「糖尿病」「マイオカイン」「筋萎縮」をキーワードとした研究を紹介する。
眞鍋 康子 准教授
世話人:出口 真次 / 参加者:未定
基礎工学C棟4階 C棟共用セミナー室
Effect of Distributed Surface Roughness on the Laminar-Turbulent Transition
It has been recognized since the pioneering experiments of Reynolds in 1883 that surface roughness plays a significant role in the dynamics of shear layers. This is a classical problem in fluid dynamics but, nevertheless, its resolution is still lacking. Most of the efforts have been focused on experimental approaches that have resulted in a number of correlations but have failed to uncover the mechanisms responsible for the flow response. Theoretical analyses have also failed to provide a consistent explanation of the flow dynamics. As there are an uncountable number of possible geometrical roughness forms, the problem formulation represents a logical contradiction as it might not be possible to find a general answer to a problem that has an uncountable number of variations. The recent progress towards the theoretical resolution of this apparent contradiction will be discussed and recent results dealing with the problem of distributed surface roughness will be presented. The progress has hinged on the development of the immersed boundary conditions method and the reduced geometry concept. It will be shown that it is possible to propose a rational definition of a hydraulically smooth surface by invoking flow bifurcations associated with the presence of roughness. Successful resolution of roughness problems gives access to the design of surface roughness for passive flow control where drag reduction can be achieved either directly, through re-arrangement of the form of the flow that results in the reduction of the shear stress, or indirectly, through delay of the laminar-turbulent transition.
Prof. J. M. Floryan
Department of Mechanical and Materials Engineering
The University of Western Ontario
世話人:河原 源太 / 参加者:未定
基礎工学C棟4階 C棟共用セミナー室
Signature of Large-scale Motions on Turbulent/non-turbulent Interface in Boundary Layers
In transitional and turbulent boundary layers, an interface separates the non-turbulent and turbulent regions of the flow. In the transition zone, this interface surrounds localized patches of turbulence that are formed sporadically and spread to consume the surrounding laminar flow. In the turbulent regime, the interface marks the free-stream edge of the boundary layer and separates the vortical near-wall motion from the outer potential flow. Using direct numerical simulations, we examine characteristics of this turbulent/non-turbulent (T/NT) interface. In the case of transition we relate its formation, or the inception of turbulence patches, to the streaky structures known as Klebanoff distortions. In the fully turbulent boundary layer, statistical evidence is presented that the interface is locally modulated by the large-scale velocity perturbations in both the streamwise and spanwise directions. The modulation is different when the coherent structure is high- versus low-speed motion: high-speed structures lead to a wedge-shaped deformation of the T/NT interface, which causes an anti-correlation between the angles of the interface and the internal shear layer. On the other hand, low-speed structures are correlated with crests in the interface. Finally, the sudden changes in turbulence statistics across the interface are in line with the changes in the population of low-speed structures, which consist of slower mean streamwise velocity and stronger turbulence than the high-speed counterparts.
Tamer A. Zaki, Associate Professor
Department of Mechanical Engineering
Johns Hopkins University
世話人:河原 源太/ 参加者:未定
基礎工学研究棟 大講義室(B棟3階の1番奥)
Mechanobiology of Collective Cell Migration in Health and Disease
Cells migrating in sheets or large cohorts tend to behave very differently from cells migrating individually. Such distinctive behavior of cells migrating in a collective manner underlies several important biological processes such as wound closure, maintenance of intestinal epithelium, developmental processes and even cancer metastasis. As such, they can also provide important insights towards better tissue repair and regenerative medicine. Here, we characterized the kinematic behavior of epithelial cell cohorts migrating under well defined geometrical constraints. We also studied collective cell migration over areas without cell adherent proteins to examine the formation of epithelial bridges so as to better wound closure mechanisms. Finally, we examined the collective migration of benign, non-invasive malignant and highly-invasive malignant cancer cells so as to better understand metastatic induced migration.
1. Saw et al., Topological defects in epithelia govern cell death and extrusion, Nature, 2017.
2. Vedula et al., Mechanics of epithelial closure over non-adherent environments, Nature Communications, 2015.
3. Vedula et al., Epithelial bridges maintain tissue integrity during collective cell migration, Nature Materials, 2014.
4. Vedula et al., Emerging modes of collective cell migration induced by geometrical constraints, PNAS, 2012.
Chwee Teck (C.T.) Lim PhD, Provost's Chair Professor
Department of Biomedical Engineering and Mechanobiology Institute
National University of Singapore
世話人:出口 真次/ 参加者:未定
遠山 祐典, Assistant Professor
Mechanobiology Institute, National University of Singapore, Singapore
Department of Biological Sciences, National University of Singapore, Singapore
Temasek Lifesciences Laboratory, Singapore
世話人:出口 真次/ 参加者:未定
基礎工学J棟1階 J棟共用セミナー室
数理・データ科学の融合による高信頼性・高汎用性な最適化問題 ~流れ場の形状最適化問題を題材として~
本講演では,流れの安定性を制御する形状最適化問題を題材として,数理・データ科学で開発・発展・深化してきた数理モデルを制約関数に持つ最適化問題を構築する.具体的には,Proper Orthogonal Decomposition (POD)の固有値問題と非定常Navier-Stokes問題を制約関数,その固有値の総和を目的関数と定義する.2次元のキャビティー流れを用いて目的関数の最小化問題を解き,線形安定性解析を行ったところ,最適領域の方が初期領域よりも臨界レイノルズ数が大きくなることを数値的に確認した.
中澤 嵩 准教授
世話人:河原 源太/ 参加者:未定
基礎工学研究科A棟 A145講義室
Atomistic Aspects of Nanoscale Fracture
Nanoscale metallic objects like nanowires, thin films, or nanoparticles are usually nearly void of dislocations and can consequently sustain large stresses. Cracks or crack nuclei in nanoscale objects are furthermore inherently small. Their propagation is therefore controlled by the stress to break the atomic bonds at the crack tip rather than by the release of elastically stored energy. At the high applied stresses required to propagate such short cracks, effects like tension-shear coupling can no longer be neglected. Crack tip plasticity in dislocation-starved nano objects furthermore becomes dislocation nucleation controlled and individual crack-microstructure interactions have a more pronounced effect on the fracture behavior than in bulk materials. Cracks in nano objects and nanoscale cracks in general are also typically characterized by small radii of curvature. All these aspects can only be studied to a certain extend with the conventional continuum mechanics approaches and many require explicit atomistic modeling.
Here we present the results of recent atomistic simulations of cracks in five different simulation setups of various sizes. Using EAM-type potentials for various bcc metals we studied the influence of crack length, crack front curvature and boundary conditions on crack tip plasticity. For small cracks, crack tip plasticity was facilitated by the presence of T-stresses and tension-shear coupling. Fully-3D simulations of penny-shaped cracks revealed an increased tendency for crack tip plasticity compared to straight cracks due to the availability of more slip systems and the resulting dislocation ? crack interactions. Simulations of cracks interacting with individual pre-existing lattice dislocations showed stimulated dislocation nucleation and new crack tip blunting mechanisms. The results are discussed in the context of fracture of nanoscale objects as well as crack nuclei in bulk metals.
Prof. Erik Bitzek
Department of Materials Science and Engineering, Friedrich-Alexander-Universitat Erlangen-Nurnberg
世話人:尾方 成信 / 参加者:未定
基礎工学研究科A棟 A145講義室
Mechanics of disordered materials:
(Unrelated) cases of oxide glasses and fibrous entanglements
In this talk, I will address two aspects of mechanical behavior in disordered solids at very different length scales. First, I will present an atomic-scale study of the mechanics of oxide glasses with a special emphasis on how the mechanical energy is dissipated at high frequencies, in the THz regime of the so-called Boson peak. In particular, I will show that in this regime, energy dissipation can be expressed analytically allowing to analyze on an atom basis the source of energy dissipation. On a rather unrelated topic, I will move to the macroscopic scale to discuss the unusual mechanics of a particular type of fibrous material, called single-wire entangled material, because it is made of a single, self-entangled fiber. I will compare experiments and discrete element method calculation to highlight the remarkable mechanical properties of this architected entanglement, in particular concerning its very large deformability and its Poisson’s function, which is beyond the usual bounds.
Prof. David Rodney
Institut Lumiere Matiere, University of Lyon, France
世話人:尾方 成信 / 参加者:未定