Guest Seminars
Speaker: Deepak Dhingra (IIT Kanpur)
Title: Multi-Sensor Remote Sensing Investigations of the Lunar Surface
Date: March 26 (Tue) 2024, 15:00-
Place: OU Science bldg. F202 + Zoom
Abstract:
Earth's Moon is the hot spot of exploration activities today. Orbital, lander and rover missions from multiple countries (including Japan) are being sent to different parts of the Moon. We are using a variety of lunar remote sensing data (imaging, spectroscopy, topography) acquired by various missions in order to address brand new as well as outstanding problems in lunar science. I will discuss our research results on some of these scientifically fascinating and challenging problems in lunar science.
Speaker: Ishan Sharma (IIT Kanpur)
Title: Resurfacing and texturing of rubble-pile minor planets
Date: April 28 (Fri) 2023, 17:00-
Place: OU Science bldg. F202 + Zoom
Abstract:
Many asteroids, small moons and trans-Neptunian objects (TNOs) are now thought to be rubble piles, i.e. granular aggregates that are held together mainly by their self-gravity. The study of their dynamics and physics thus necessitates an investigation into the mechanics of self-gravitating and rotating granular aggregates in space. I will present some of our recent work into the processes by which the surfaces of such objects may be reshaped and textured by landslides and seismic shaking that may be induced by impact events.
Brief biography: Ishan Sharma is a Professor in the Departments of Mechanical Engineering and Space Science & Astronomy at the Indian Institute of Technology (IIT) Kanpur. He did is B. Tech. in Mechanical Engineering from IIT Kanpur (1999) and then a Ph. D. in Theoretical & Applied Mechanics from Cornell University (2004). He then spend 2 years at the Department of Applied Mathematics & Theoretical Physics (DAMTP) at Cambridge University, UK. He returned to IIT Kanpur in 2006 where he has been since. He is interested in using mechanics to understand the physical processes that drive natural systems on Earth and in space.
Speaker: Jonathan E. Kollmer (Universität Duisburg-Essen)
Title: Slow Impacts on Asteroid Surfaces
Date: April 10 (Mon) 2023, 13:00-
Place: OU Science bldg. F608 + Zoom
Abstract:
As space missions such as Hayabusa and Osiris Rex revealed, the surface structure of rubble pile asteroids is much more heterogeneously structured than expected. Some areas are covered mainly by larger boulders, while small particles form seas of pebble sized grains elsewhere. One proposed hypothesis to explain this observation is the so called Ballistic Sorting Effect (BSE) [1] which states that collisions with a surface consisting of small particles are more dissipative than impacts on areas covered by large rocks. According to this hypothesis slow impactors will therefore aggregate in places that are already covered by small particles.
To study the validity of the BSE hypothesis, we perform a drop tower experiment [2] as well as numerical DEM simulations. Our experiment is designed to recreate an asteroid environment as closely as possible, with regolith simulant in a vacuum and constant low gravity with minimal disturbance. We then collide an impactor with the regolith surface. These collisions will either result in sticking, bouncing or splashing. For the bouncing case we can measure a coefficient of restitution (COR) which appears to not follow a monotonic decrease with particle size as suggested by Shinbrot [3]. Instead the COR shows a minimum at a specific particle size. We also compare our experiment results to numerical simulations which can resolve the parameter range, especially the bed particle size and cohesion strength in more detail. We conclude that the elasticity of asteroid surfaces is governed by inter-particle cohesion [4].
[1] A. Fujiwara, J. Kawaguchi, D.K. Yeomans, M. Abe, T. Mukai, T. Okada, J. Saito, H. Yano, M. Yoshikawa, D.J. Scheeres et al., Science 312,1330 (2006)
[2] K. Joeris, L. Schönau, L. Schmidt, M. Keulen, V. De-sai, P. Born, J. Kollmer, EPJ Web of Conferences 249, 13003 (2021)
[3] T. Shinbrot, T. Sabuwala, T. Siu, M.V. Lazo,P. Chakraborty, Phys. Rev. Lett. 118 (2017)
[4] K. Joeris, L. Schönau, M. Keulen, P. Born, J. E. Kollmer, npj Microgravity 8, 36 (2022)
Speaker: Lola Gonzalez-Garcia (INM - Leibniz-Institut für Neue Materialien gGmbH)
Title: Electrofluids: conductive particle suspensions as flowing leads
Date: Oct. 5 (Wed) 2022, 13:00-
Place: OU Science bldg. F202
Astract:
Liquid metals, printed conductive structures, or composites are today the alternatives to the classical stiff electronic components for wearables and soft robots. Here, we propose a new concept: “Electrofluids”, that conduct electrons while flowing. We formulate highly concentrated suspensions of conductive particles (carbon black and silver) in solvents with different polarity and viscosity. Electrical conductivity is ensured through the 3D percolative networks of the solid fillers. The contacts between the particles are transient, so they can move in the liquid and rearrange under mechanical stress preserving the electrical conductivity of the material.We will show that the filler-matrix interaction determines the network formation and how the rheoelectrical properties of the material can be tailored. For example, the polarity of the liquid matrix, employed in the fabrication of electrofluids, has a strong impact on the network structure, determining the concentration of the solid fillers required to achieve electrical conductivity in the material (percolation threshold): 4.93 vol% and 0.41 vol% of C-black is required in PDMS and in Glycerol respectively.The shape of the particles also influences the network formation. While the employed Ag particles are spheroids of 1-3 m in diameter, C-black is made of fractal aggregates, of primary particles, with typical sizes of hundreds of nanometres. The concentration required to achieve electrical conductivity using Ag in liquid PDMS lay between 32 vol% and 35 vol%, which is almost an order of magnitude larger than that found for C-black.To understand the structure of the network formed by the particles in the different matrices, we performed rheoelectrical measurements. A clear correlation between the changes in the electrical properties and the shape of the storage and loss moduli, G’ and G’’, was observed.We also tested the electrical response to mechanical stress of electrofluids encapsulated in elastomeric tubes as previous step for their device integration. We found out the gauge factor of the material to be dependent on the volume fraction of the filler and the matrix employed. We will exploit this behaviour and discuss the use of these materials as soft conductive leads and strain sensors.
Speaker: Kerstin Nordstrom (Mount Holyoke College)
Title: How Do You Know If It Will Flow?
Date: April 22 (Fri) 2022, 15:00-
Place: OU Science bldg. F202 + Zoom
Abstract:
The flow of granular material through a silo or hopper has been studied for many years. In addition to its great practical importance in many industrial processing situations, it is also thought to be a model system for other bottleneck flows such as blood flow, crowd egress, and traffic merges. In recent times, advances in computing and high-speed imaging have allowed detailed study of these flows. We present results from a high-speed imaging study of silo flow. Specifically, we report on how metrics such as velocity fluctuations, non-affine motion, and dynamical heterogeneities change on approach to the clogging point. We do find changes in these metrics on approach to the clogging point, however we do not see evidence to suggest the clogging point is a critical point. We contrast the clogging transition with the jamming transition in light of these results. We will also briefly summarize recent extensions to this work involving obstacles and soft particles.