*Reception to be held directly afterwards, lobby area of Mudd Hall
Presented by Professor Michael Sheetz, Ph.D., Director
Mechanobiology Institute of Singapore, National University of Singapore and
Department of Biological Sciences, Columbia University
Since repeated tissue damage correlates with increased risk of cancer, there could be a correlation between tissue regeneration and cancer in that they involve growth in adult tissues. Indeed microRNA-21 levels are upregulated in both tissue regeneration and cancer. miRNA-21 causes depletion of several proteins but particularly, tropomyosin (Tpm) 2.1 depletion blocks rigidity sensing and causes growth on soft surfaces. In over forty cancer cell lines tested, at least 75% were missing major components of the rigidity sensing complex (about 60% had low Tpm 2.1). The rigidity sensing complex (about 2 m in length) contracts matrix adhesions by ~100nm; and if the force generated is greater than ~25 pN, then adhesions are reinforced and cells can grow (Wolfenson et al., 2016. Nat Cell Bio. 18:33). However, if the surface is soft and matrix force low, then the rigidity sensor in normal cells causes apoptosis by DAPK1 activation (Qin et al., 2018 BioRxiv. 320739). Transformed cancer cells lack rigidity-sensing contractions and grow on soft surfaces. Restoration of rigidity sensing in cancer cells by normalizing cytoskeletal protein levels (most often by restoring Tpm 2.1 levels) restores rigidity-dependent growth (Yang, B. et al., 2018 BioRxiv. 221176). Surprisingly, we find that cyclic mechanical stretch of transformed cancer cells activates apoptosis through calpain-dependent apoptosis. Restoring rigidity sensing in transformed cancer cells blocked stretch-induced apoptosis and caused rigidity-dependent growth (Tijore et al., 2018 BioRxiv. 491746). Conversely, normal cells become stretch-sensitive for apoptosis after transformation by depleting rigidity sensors through Tpm2.1 kockdown or knockdown of other tumor suppressor proteins needed for rigidity sensing. Thus, it seems that stretch sensitivity is a weakness of many cancer cell lines and this is related to the transformed cell state and not to the tissue type or other factors. Depletion of the rigidity mechanosensor to allow regenerative growth can lead to sustained loss of mechanosensing that enables cancerous growth.
Professor Michael Sheetz is a cell biologist at Columbia University and a Distinguished Professor and the founding Director of the Mechanobiology Institute at the National University of Singapore. He pioneered mechanobiology and biomechanics. In 1968, Sheetz earned a bachelor’s degree at Albion College, and in 1972 received his Ph.D. at the California Institute of Technology. In 1985 he became a professor of cell biology and physiology at the Washington University in St. Louis, Missouri. Since 1990 he is the William R. Kenan, Jr. Professor of Cell Biology at Columbia University, New York. He has also been a professor at Duke University.
4:10 pm Presentation
“Turbulent Flow over Fractal Urban-Like Topography: Prognostic Roughness Model for Unresolved Generations”
Presented by XIAOWEI ZHU (Adviser: Prof. Zaki)
Urban-like topographies are composed of a wide spectrum of topographic elements, which results in a multiscale, fractal-like surface height distribution. Computational modeling of turbulent flows responding to fractal-like geometries poses unique challenges, especially when the number of self-similar generations renders a spectrum of the constituent wavelengths ﬁner than the computer mesh resolution. In the background of large-eddy simulation (LES), high-resolution multiscale topography needs to be spatially ﬁltered to obtain a resolved topography to be directly used in LES. The eﬀects of the subgrid-scale topography need to be modeled. Inspired by the self-similar nature of the topography, we modeled the effects of these truncated topographic modes based on the behaviors of the large-scale geometry. Firstly, the iterated function system (IFS) was used to construct urban-like, fractal geometries. And five fractal dimensions were used to investigate the parameterization of unresolved generations. Secondly, we quantiﬁed the momentum deficit associated with changing attributes (such as fractal dimension and generation), which enabled a posteriori deduction of roughness length parameters needed to model aerodynamic surface stress. We further showed that aerodynamic stress associated with the descendant, sub-generation elements can be parameterized, with only the first few generations resolved on the computational mesh. Finally, a logarithmic law-based roughness model was proposed for the unresolved, sub-generation topographic elements.
Energy optimization in human walking
Presented by Professor Max Donelan
Biomedical Physiology & Kinesiology, Simon Fraser University
Perhaps the most general principle underlying human movement is that people prefer to move in ways that minimize their energetic cost. Although aspects of this preference are likely established over evolutionary and developmental timescales, we recently discovered that the nervous system can continuously optimize cost in real-time. Here I will present our new research focused on uncovering the mechanisms underlying the initiation of this optimization, as well as its process. Our collective findings indicate that energetic cost is not just an outcome of movement, but also plays a central role in continuously shaping it. I will also briefly touch on two other aspects of my research program – bionic energy harvesting and the scaling of control.
Max Donelan is a Professor of Biomedical Physiology & Kinesiology at Simon Fraser University in Vancouver, British Columbia. He received his Ph.D. in Integrative Biology from Berkeley in 2001 under the mentorship of Dr. Rodger Kram and Dr. Art Kuo. He completed his postdoctoral work in Neuroscience at the University of Alberta under the mentorship of Dr. Keir Pearson. Max has held Career Investigator awards from the Michael Smith Foundation for Health Research and the Canadian Institutes of Health Research. In addition to his fundamental research program, he has spun-out companies to commercialize his energy harvesting and wearable technology inventions, and is a scientific advisor to Nike Inc. Max is currently a visiting professor in Bioengineering at Stanford.
In His Own Words: I study how people and other animals move, and then apply what I find to help our society. I mostly study walking in people, and mostly pretty fundamental things about the back-and-forth relationship between how we walk and the energy we require to do so. But I also like to study big and small animals, and how their size affects how they control their movements. This comparative work has led me to study kangaroo tails, crocodile gallops, and elephant nerves, to name a few. In the course of my research, I have invented exoskeletons that harvest electrical energy from our movements, devices that stabilize people as they walk, and an iPhone app that controls people’s running pace with music. Others have used my work to develop new ways of rehabilitating people’s gait, and new ways of controlling their walking robots.
Shock wave focusing to achieve high energy concentration
Presented by Professor Veronica Eliasson
Structural Engineering, University of California San Diego
A shock wave is a thin discontinuous region over which fluid properties abruptly change from one state to another. Shock wave focusing occurs frequently both in nature and in a variety of man-made applications. It takes place when a shock wave propagates through a non-uniform or moving media, reflects from curved surfaces or through reflections with other shock waves. Extreme conditions created at the focal region – resulting in very high pressures and temperatures – can be either beneficial as in the case of shock wave lithotripsy or inertial confinement fusion or detrimental as in the case of superbooms (a type of sonic boom). As the shock wave emerges from the focal region, after the shock focusing event, the shape of the shock is often fundamentally altered. Therefore, a deeper understanding of the shock focusing process, and how to control it, is critical to fully understand its consequences and how to best enhance or mitigate it as needed depending on the application at hand. In this talk I will introduce our newest experimental setup that has the capability to produce multiple simultaneous shock waves in two or three dimensions with a turn around time between consecutive experiments that is under two minutes. Ultra-high-speed photography coupled with schlieren techniques are used to probe the shock dynamic events, and in particular, the transition from regular to irregular reflections.
Veronica Eliasson received her Ph.D. in Mechanics at the Royal Institute of Technology, Stockholm, Sweden, in 2007. After a postdoctoral appointment at Graduate Aerospace Laboratories, California Institute of Technology, she became a faculty member at University of Southern California in 2009. In 2016 Dr. Eliasson moved from USC to the Structural Engineering Department at University of California, San Diego. Dr. Eliasson’s research interests are in the area of experimental mechanics and include shock wave dynamics, high strain rate impacts and fracture mechanics.
Aeronautics at Bio-Scales
Presented by Professor Geoffrey Spedding
University of Southern California
Aeronautics is a mature and powerful engineering discipline, and great success has been achieved in predicting flows and designing aircraft configurations at large scales, where the effects of viscosity can be modeled as minor modifications to basically inviscid dynamics. That is not the case at smaller scales, those of the new generation of drones, and of smaller birds and bats. Here the competing inertial and viscous terms in the governing equations lead to a delicate balance in solutions that have extreme sensitivity to variations in boundary and initial conditions. In this talk we will show how, in a Reynolds number regime that is only now becoming of practical interest, nominally simple problems do not necessarily have simple solutions, and how seemingly modest computational and experimental goals remain elusive. Nevertheless, with a little persistence, one can perhaps exploit these flow sensitivities for efficient and novel control strategies.
Geoffrey Spedding received his Ph.D. in 1981 from the University of Bristol, England. He began work as a Research Associate in the Department of Aerospace Engineering at the University of Southern California in the same year, where he worked on models of insect wings and models of atmospheres and oceans. He became a full Professor in 2005, and Chair of the Aerospace and Mechanical Engineering Department in 2010. His current research has three themes: (i) Geophysical Fluids: particularly the evolution of turbulence in oceans and atmospheres, and its relation to the persistence of wakes of islands and underwater vehicles; (ii) Advanced imagining and data analysis including accurate particle imagining velocimetry (PIV) techniques and novel 2D wavelet transforms and interpolation routines for scattered data; (iii) Aerodynamics of small flying devices, especially those where birds and bats coexist in engineering design space. In 2010 he was elected Fellow of the American Physical Society. In 2013 he was awarded the Chaire Joliot at ESPCI, Paris.
Harnessing thermal expansion in architected metamaterials
Presented by Professor Damiano Pasini
Mechanical Engineering, McGill University
For technology called to function under harsh temperature swings, e.g. satellite antennas, thermal expansion can be an enemy to fight against. But for others, e.g. deployable systems, thermal expansion can be an ally. In this seminar, I will contribute to address challenges currently existing on both fronts: i) how to meet strict requirements of thermal expansion in ultralightweight stiff materials, ii) how to engage temperature in morphable materials that deploy in situ under extreme conditions. The approach that I will follow draws from concepts of mechanics, geometry, materials, and structural optimization, through a combination of theory, computation and mechanical testing for performance validation.
Damiano Pasini is the Louis Scholar of the Faculty of Engineering at McGill University and Professor of Mechanical Engineering. His research interests lie in solid mechanics, advanced materials and structural optimization with current focus on mechanical metamaterials. He is fully engaged in understanding their mechanics, introducing reliable predictive models, and using them to engineer, build and test architected materials with optimally tuned functional properties that are of practical use in aerospace and other disciplines.
Shock wave focusing to achieve high energy concentration
Presented by Professor Alexander Smits
Mechanical and Aerospace Engineering, Princeton University
Biology offers a rich source of inspiration for the design of novel propulsors with the potential to overcome and surpass the performance of traditional propulsors for the next generation of underwater vehicles. To-date, however, we have not achieved the deeper understanding of the biological systems required to engineer propulsors with the high speed and efficiency of animals like sailfish, tuna, or dolphins. What is the underlying physics of the fluid-structure interaction of bio-propulsors that results in the superior performance observed in nature? Moreover, how do we replicate this performance in the next generation of man-made propulsors? Can we push beyond the limits of biology? By studying the performance of simple heaving and pitching foils, we have identified the basic scaling that describes the thrust, power and efficiency, under continuous as well as burst-coast actuation. These scaling relationships allow us to identify the natural limits on simple bio-inspired propulsors, and suggest that further improvements in performance will require adaptive flexibility and optimized profiles.
Dr. Smits is the Eugene Higgins Professor of Mechanical and Aerospace Engineering at Princeton. His research interests are centered on fundamental, experimental research in turbulence and fluid mechanics. In 2004, Dr. Smits received the Fluid Dynamics Award of the American Institute of Aeronautics and Astronautics (AIAA). In 2007, he received the Fluids Engineering Award from the American Society of Mechanical Engineers (ASME), the Pendray Aerospace Literature Award from the AIAA, and the President’s Award for Distinguished Teaching from Princeton University. In 2014, he received the Aerodynamic Measurement Technology Award from the AIAA. He is a Fellow of the American Physical Society, the American Institute of Aeronautics and Astronautics, the American Society of Mechanical Engineers, the American Academy for the Advancement of Science, the Australasian Fluid Mechanics Society, and he is a Member of the National Academy of Engineering. He is currently the Editor-in-Chief of the AIAA Journal.