Invited Lecturers

Plenary Lecturers

• Dr. Tetsuro Tsuji, Graduate School of Informatics, Kyoto University, Japan

Tetsuro Tsuji received his Ph.D. degree from the Department of Mechanical Engineering and Science at Kyoto University, Japan, in 2013. After obtaining his Ph.D., he became an Assistant Professor at the Graduate School of Engineering Science, Osaka University. In 2019, he was appointed Assistant Professor at the Graduate School of Informatics, Kyoto University. Since 2021, he has been an Associate Professor in the same department.

His current research areas include molecular fluid dynamics, rarefied gas dynamics, and microfluidics. From the beginning of his career, he has worked on numerical analysis and theoretical modeling of non-equilibrium gaseous systems. More recently, he has also focused on microfluidic and optofluidic experiments. In particular, thermally induced microflows and microparticle motion, as well as their interconnection, are among the main topics of his recent publications.

 Title of the Plenary Lecture: Thermally-induced flows in microfluidic systems: from optothermal fluidic experiments to non-equilibrium gaseous modeling

In this talk, some recent experimental and theoretical studies on thermally-induced microflows will be introduced. In the experimental part, we focus on thermophoresis, namely, a microparticle motion along a temperature gradient in fluids. Using an optothermal microfluidic system combined with optical trapping, thermally-induced flows around microparticles are detected, and the connection between the thermally-induced flows and the thermophoresis is discussed [1]. Optothermal microfluidic systems are found to be effective, feasible, and convenient experimental setup to investigate thermal microflows, and thus a semianalytical model has been developed recently [2]. In the modeling part, a kinetic model on thermally-induced non-equilibrium gas flows will be introduced. The model is shown to reproduce the sign reversal of the thermal slip coefficients according to gas-surface interaction, regardless of its simplicity [3]. These outcomes on thermally-induced microflows are expected to contribute to the development of novel microfluidic functions such as separation and concentration.
[1]    T. Tsuji, S. Mei, and S. Taguchi, “Thermo-osmotic slip flows around a thermophoretic microparticle characterized by optical trapping of tracers,” Physical Review Applied 20, 054061 (2023)
[2]    T. Tsuji, S. Saito, and S. Taguchi, “Semianalytical model of optothermal fluidics in a confinement,” Physical Review Fluids 9, 124202 (2024)
[3]    T. Tsuji, K. Takita, and S. Taguchi, in preparation

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Dr. Benjamin Schafer, John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, and Rarefied Technologies, Albuquerque, NM, USA

Ben Schafer is the CEO and Co-Founder of Rarefied Technologies and an Associate Researcher at the Harvard University John A. Paulson School of Engineering and Applied Sciences. Rarefied Technologies is a startup based in Albuquerque, New Mexico, USA, dedicated to developing photophoretic levitation for near-space flight.

Ben's research focuses on innovative designs for photophoretically flying structures, the experimental fabrication and testing of flying devices, and the application of this technology to address challenges in climate science, atmospheric sensing, and telecommunications. He is a Breakthrough Energy Fellow and was recognized in Forbes 30 Under 30 as a leader in climate-focused technology. He received his Ph.D. in Applied Physics from Harvard University in 2024.

 Title of the Plenary Lecture: Photophoretic levitation: from aerosols to aircraft

Photophoresis, or light-driven motion, of aerosols in Earth’s upper atmosphere has been studied since the 1960s. When sunlight warms an aerosol particle surrounded by rarefied gas, an asymmetry in the temperature or accommodation coefficient on the aerosol’s surface creates a photophoretic force on the aerosol, allowing it to levitate. With recent advancements in nanofabrication, could we build engineered devices that are bigger than aerosols, yet lightweight enough to fly on their own? Using aerosols as a starting point, I will discuss advancements in the field of photophoretic levitation, which include holographic displays, particle traps, and macroscopic platforms for near-space flight. The promise of photophoretic aircraft for atmospheric sensing, telecommunications, and Martian exploration has spurred new research into ultra-lightweight 2D materials that generate photophoretic gas flows.

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