| 氏名： 後藤
指導教員名： 古川 亮 准教授
発表題目（英語）： Collective behaviors in active matter systems : the role of hydrodynamic interactions
要旨（英語）： Active matter contains self propelling agents which can take up energy from their surroundings and turn it into mechanical work. Such systems are intrinsically out of equilibrium; the activity produces novel interactions (of purely dynamic origin) and thus results in diverse collective behaviors which are quite different from those observed in "passive" matter systems. Among a variety of active matter systems, micro-organisms are ubiquitous ones. Because most of micro-organisms live and swim in a fluid environment, hydrodynamic interactions (HIs) and their dynamic coupling to activity should be crucial to understand the properties of micro-organisms. However, due to difficulties arising from the long-range nature of HIs and the resultant many-body effects, we are still far from a thorough understanding of the role of HIs in cooperative phenomena of active suspensions. In order to tackle this problem and shed new light on the active matter physics, we are planning to study the rheology of model micro-organisms. In this talk, as well as presenting an overview of the active matter physics, I will briefly explain our research approach.
| 氏名： 秋葉
指導教員名： 石渡 晋太郎 准教授
発表題目（英語）： Transport properties of magnetic polar semiconductor
要旨（英語）： Non-centrosymmetric materials has been studied recently due to its interesting physical properties. The key point of these materials is Spin-Orbit Interaction (SOI) which connects electronic states with crystal symmetry. In particular, Rashba Effect are attracting widespread interest because of its applicability to spintronics and exotic superconductivity.
Expecting the presence of novel transport properties induced by Rashba Effect and localized magnetic moments, we have systhesized a magnetic polar semiconductor single crystal. It has non-centrosymmetric space group and localized moment. To investigate novel transport properties, we have measured the magnetic dependence of electrical resistivity (R-H) and Seebeck Coefficient (S-H). It was found that the magnetic polar semiconductor showed large positive magnetoresistance and magnetoseebeck effect which could not been explained by ordinary positive magnetoresistance induced by Lorentz force. We attribute the large positive magnetic properties to the magnetic dependence of effective mass which could be explained by s-d interaction and Rashba Effect.
| 氏名： 青木
指導教員名： 田中 肇 教授
発表題目（英語）： Energy dissipation of pseudo two-dimensional driven granular matter.
要旨（英語）： Granular matter such as grains of sand, wheat flour and other powders is familiar with our daily lives. It is many body system of dissipation and its physical treatment is difficult. Thus much is unknown about self-organization. 2D systems are usually thought as simpler systems than 3D one because there is no z-axis, but granular character of 2D systems (2D melting, KTHNY theory and so on) makes it difficult to understand interesting behavior of 2D granular systems. For instance, in the systems of 3D (2D) rigid bodies which have only repulsive interaction, phase transition depending on volume fraction was found (Alder transition). While regular transitions are occurred by attractive force and thermal motion of particulars, in rigid body system phase transition is occurred without attractive force. Alder transition of 2D rigid body systems is not considered as normal order-disorder transition because Mermin and Wagner proved that long-range positional order can’t exist in the 2D systems which have only short-range interaction (Mermin-Wagner theorem). With these theorem, many researchers have payed attention to the mechanism of Alder transition and some theorems have been made but the exact cause has not been resolved.
In this talk, I will introduce fundamental natures related to 2D rigid systems and report my experimental progress and future plans of pseudo 2D driven granular matter.
| 氏名： 浅井
指導教員名： 酒井 啓司 教授
発表題目（英語）： Improvement of droplet-oscillation-in-flight surface tension (DOF ST) meter
要旨（英語）： We developed the method for measuring time dependence of liquid surface tension in the time scale ranging from 0.1 ms to 10 ms. Oscillation of droplets was used to figure out surface tension value. Chain of droplets emitted by inkjet nozzle is disturbed as time passes. Improvement of the way to observe and analyze the oscillation of the droplets enabled to measure surface tension from the disturbed droplets. We measured dynamic surface tension of silicone oil and surfactant aqueous solution. In the presentation, I will show you method and data of DOF ST meter.
| 氏名： 青柳
指導教員名： 小林 洋平 准教授
発表題目（英語）： Pulse-by-pulse Scattered Light Imaging of Femtosecond Laser Processing
要旨（英語）： When pulsed laser light irradiates a material, a small part near its surface is removed. This phenomenon, named “ablation”, enables to process a material with a pulsed laser for various purposes. Especially, the processing using a femtosecond laser pulse draws considerable attention owing to its precise and high-quality machining ability.
A problem of pulsed laser processing is that the way of optimizing many parameters of a processing machine is inefficient. While currently these parameters are determined ad hoc in each purpose, it is desirable to distinguish a likely range of them in advance on the basis of fundamental research. In pulsed laser processing, during many laser pulses irradiate a material, different pulses lead to different result due to change of material’s physical properties. However, fundamental research focus mainly on the case that initial pulses irradiate a non-processed material. Therefore, it is impossible to predict a final result to the extent practical by fundamental research.
To solve this problem, it is necessary to understand how each pulse ablates a material and transforms its surface. Thus we aim to reveal a pulse-by-pulse change of material’s surface by imaging scattered light from a processed area with the high-speed camera. In this presentation, I introduce how the pattern of scattered light evolves while a silicon plate is irradiated by the Ti:Sapphire laser. Then, it will be shown that a new index obtained from images and ablation volume are correlative. In addition to this, the dispersion of the number of pulses which cause initial ablation and the transformation of material’s surface by initial several ablations will be discussed.