MEAM Seminar Series Spring 2015
For Fall 2014 Seminars, click here.
Seminars are held on Tuesday mornings, with coffee at 10:30 am in the Levine Hall Mezzanine and the seminar beginning at 10:45 am in Wu and Chen Auditorium (unless otherwise noted).
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Yanfei Gao, Associate Professor, Department of Materials Science and Engineering, University of Tennessee
"Convoluted Thermal/Spatial Statistics and Scale Effects in Nanoindentation Plasticity"
Sudden discontinuities, or called pop-ins, are often found on nanoindentation load-displacement curves for single crystals. For defect-free crystals under nano-contacts, the pop-in is a result of homogeneous dislocation nucleation, and the observed fluctuations in the pop-in load result purely from the thermally activated process. At intermediate contact sizes, such fluctuations can arise from the spatial statistics of pre-existing defects. It is found that the convolution of the above thermal and spatial effects exhibits a distinct dependence on the stressed volume size, dislocation density, and geometric factors that describe crystallography and slip anisotropy. Both homogeneous and heterogeneous mechanisms are modeled in a unified framework that predicts how the fluctuations of pop-in loads vary with respect to the above factors. Predictions agree very well with our experiments on Mo and NiAl single crystals. Our method has also been generated to develop a “mechanical probe” of the microscopic structural heterogeneities in the metallic glasses, in which a quantitative relationship between defect density and the ductile-to-brittle transition can be established.
Yanfei Gao is currently an Associate Professor and Director of Graduate Studies of the Department of Materials Science and Engineering, University of Tennessee, and a Joint Faculty in Materials Science and Technology Division, Oak Ridge National Laboratory. His research group focuses on modeling and simulation of plasticity at small length scales, thin-film growth, contact and friction, and constitutive behavior of amorphous alloys, among many others. He has been the PI on five NSF grants and co-PI on a number of other NSF and DOE projects. He has given two invited talks in the Gordon Research Conferences. He received degrees from Tsinghua University (China) and Princeton University, and performed post-doctoral research at Brown University.
Nikolaos Aravas, Professor of Computational Mechanics, Department of Mechanical Engineering University of Thessaly, Greece and Visiting Professor, Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania
"Strain-gradient elasticity: Constitutive Modeling and Numerical Techniques"
Theories with intrinsic or material length scales find applications in the modeling of size-dependent phenomena, such as the localization of plastic flow into shear bands. In gradient-type plasticity theories, length scales are introduced through the coefficients of spatial gradients of one or more internal variables. In elasticity, length scales enter the constitutive equations through the elastic strain energy function, which, in this case, depends not only on the strain tensor but also on gradients of the rotation and strain tensors.
We focus our attention on linear strain-gradient elasticity theories. The appropriate Airy stress functions and double-stress functions are identified and the appropriate boundary value problem is formulated. A reciprocity theorem is developed and the corresponding Saint-Venant principle is derived. It is shown also that several “technical theories of beams”, such as axial tension and torsion of pretwisted beams, can be viewed as special cases of a strain-gradient elasticity theory.
In such theories, when the problem is formulated in term of displacements, the governing partial differential equation is of fourth order. If traditional finite elements are used for the numerical solution of such problems, then C1 displacement continuity is required. An alternative "mixed" finite element formulation is developed, in which the displacement and displacement –gradients are used as independent unknowns and their relationship is enforced in an "integral-sense." The resulting finite elements require only C0 continuity and are simple to formulate.
An asymptotic crack-tip solution under plane strain conditions is developed, the corresponding “energy release rate” is determined in terms of the material length scale, and possible fracture criteria are discussed.
Nick Aravas was born (1957) and raised in Thessaloniki, Greece, where he studied Mechanical Engineering at the Aristotle University of Thessaloniki and graduated in 1980. He received his M.S. (1982) and Ph.D. (1984) in Theoretical and Applied Mechanics from the University of Illinois at Urbana-Champaign (UIUC). During his graduate studies he worked as a Teaching and Research Assistant, and in 1982 he received the “J. O. Smith Award for teaching excellence”, which is presented every year by the Department of Theoretical and Applied Mechanics of the UIUC to the “outstanding young teacher in Engineering Mechanics”.
In 1985, he worked as a Senior Engineer in Hibbitt, Karlsson and Sorensen, Inc., the developers of the ABAQUS general purpose finite element program. His academic career started in 1986 when he joined the Department of Mechanical Engineering and Applied Mechanics of the University of Pennsylvania (PENN), where he taught for 11 years. At PENN he held also a secondary appointment in the department of Materials Science and Engineering. His research focuses in the areas of Mechanics of Materials and Computational Mechanics. He is the author or numerous papers in scientific journals, Associate Editor of the ASME Journal of Applied Mechanics, and serves as a reviewer for many scientific journals in the areas of mechanics and materials. His work is recognized internationally and has received a large number of citations by other scientists.
Steven Schmid, Professor, Aerospace and Mechanical Engineering Department, University of Notre Dame
"Selected Topics in Orthopedic Implant Design"
This seminar will present two advances for the orthopedics industry that have been extensively investigated at the University of Notre Dame: the design of minimally invasive implants, and manufacturing options for bone ingrowth scaffolds.
Minimal invasiveness has always been a design goal for the orthopedic implant industry. However, recent advances in surgical techniques, materials and instruments have allowed innovative new designs to come to the fore, allowing a simultaneous reduction in pain, surgery complexity, and rehabilitation time and cost while preserving existing implant costs. New designs exploiting the in vivo phase change are described, with materials research progress emphasized.
Over the past ten years, a novel cellular solid, trabecular metal (TM), has been developed for use in the orthopedics industry as an ingrowth scaffold. Manufactured using chemical vapor deposition (CVD) on top of a graphite foam substrate, this material has a regular matrix of interconnecting pores, high strength, and high porosity. For some implant applications, plastic deformation through stamping is a useful manufacturing approach after CVD, but a better knowledge of the forming properties of TM is required. In this study, a forming limit diagram for TM was obtained using 1.65 mm thick sheets.
Dr. Schmid is a Full Professor in the Aerospace and Mechanical Engineering Department at the University of Notre Dame, where he conducts research in manufacturing, tribology and design, especially as related to orthopedic implants. Dr. Schmid has co-authored twenty books, has written over 90 peer-reviewed papers and over 120 conference papers and presentations. Of his textbooks, Manufacturing Engineering and Technology (with S. Kalpakjian) is the world's most popular manufacturing textbook, and is available in Spanish, Chinese, Italian, Arabic, Greek, German, and Korean editions, with Indonesian and Macedonian translations in process. Manufacturing Processes for Engineering Materials (with S. Kalpakjian), Fundamentals of Machine Elements and Fundamentals of Fluid Film Lubrication (with B. Hamrock and B. Jacobson) are selected titles of his other books. Dr. Schmid has received numerous teaching and research awards, and is a Kaneb Teaching Fellow at the University of Notre Dame. From 2012-2013, he served as the first Faculty Fellow at the Advanced Manufacturing National Program Office, where he was part of the team that developed the preliminary design of the National Network for Manufacturing Innovation.
Denis Cormier, Earl W. Brinkman Professor of Industrial and Systems Engineering, Rochester Institute of Technology
"Multifunctional 3D Printing"
3D printing is the result of 2D images that are printed on top of one another to build up thickness. Although 3D printing has existed for over 20 years, the majority of 3D printers have been designed to work with a single material. However, inkjet and Xerographic printers with three or more print heads/engines have long been used to produce 2D multi-color documents. When multiple print heads are repurposed to deposit functional nanomaterials rather than color pigments, a whole new world of possibilities emerges. Rather than printing parts that serve purely mechanical functions, multifunctional 3D printing technologies have potential to produce parts that perform mechanical, electrical, thermal, optical, and/or chemical functions. Blending multiple materials within a part is not trivial though, and a great deal of development work is needed to realize the tremendous potential of multifunctional 3D printing. This talk will introduce the audience to several multifunctional printing technologies such as Aerosol Jet printing, micro-extrusion, and pulsed photonic curing. Selected multi-material applications will then be presented. Lastly, some open research challenges associated with multifunctional 3D printing will be discussed.
Dr. Denis Cormier is the Earl W. Brinkman Professor of Industrial and Systems Engineering at the Rochester Institute of Technology. He has worked in the area of additive manufacturing (commonly known as 3D printing) for nearly 20 years. Most recently, his research has focused on multi-material functional printing processes and materials. Prior to joining RIT in 2009, he was a professor at North Carolina State University for 15 years where he founded NC State's Rapid Prototyping Lab in 1996. He is a founding member of ASTM’s F-42 additive manufacturing standards group, and he serves as Chairman of the Society of Manufacturing Engineer’s Rapid Technologies and Additive Manufacturing steering committee. He also serves on the editorial advisory boards for two journals - the Rapid Prototyping Journal, and Additive Manufacturing. Dr. Cormier is also a UPenn alum (BS in Systems Engineering, 1989).
Thursday, March 5
Mahmut Selman Sakar, Senior Research Scientist, Institute of Robotics and Intelligent Systems, ETH Zurich
1:45 pm, Levine 307
"Microrobotic Platforms in Bioengineering and Translational Medicine"
Biological systems are exquisitely sensitive to the location, dose and timing of physiologic cues and drugs. This spatiotemporal sensitivity necessitates the development of bioengineering platforms that can apply well-characterized local signals to understand fundamental principles of cellular behavior and to create novel therapeutic approaches for minimally invasive medicine. Microrobotics is a relatively young field in which materials science and microelectromechanical systems (MEMS) technology meet robotics creating the next generation complex machines operating in three-dimensional microenvironments. In this talk, I will present the design and fabrication of untethered magnetic microrobots for targeted and triggered therapy. Several examples will be demonstrated to explain how microrobotic technologies can be utilized to introduce compact and versatile bioengineering platforms. These platforms will be able to perform automated micromanipulation on biological samples with high dexterity and precision and provide critical mechanistic insight on the generation, transmission and coordination of cellular forces during development, regeneration and physiological function.
Mahmut Selman Sakar received the B.S. in Electrical and Electronics Engineering with honors from Bogazici University in 2005 and the Ph.D. in Electrical and Systems Engineering from University of Pennsylvania in 2010. During his doctoral studies, he worked on microrobotics and single cell manipulation under the supervision of Prof. George J. Pappas and Prof. Vijay Kumar. Before joining Institute of Robotics and Intelligent Systems in 2012, he worked as a postdoctoral associate with Prof. Harry Asada in the Department of Mechanical Engineering, Massachusetts Institute of Technology on the generation and optogenetic control of engineered skeletal muscle microtissues. Currently he is a senior research scientist in Prof. Bradley Nelsonís laboratory at ETH Zurich and he is working on the development of microrobotic platforms for several bioengineering applications.
Ellen Kuhl, Associate Professor of Mechanical Engineering, Bioengineering (courtesy), and Cardiothoracic Surgery (courtesy), Stanford University
"Neuromechanics of Human Brain Development"
Convolutions are a classical hallmark of most mammalian brains. Brain surface morphology is often associated with intelligence and closely correlated to neurological dysfunction. Yet, we know surprisingly little about the underlying mechanisms that drive cortical folding. To explore the evolution of brain surface morphology, we have created a neuromechanical model using the nonlinear field theories of mechanics supplemented by the continuum theory of finite growth. Continuum modeling allows us to seamlessly integrate information across the scales and correlate organ-level phenomena such as cortical folding to molecular-level processes such as axonal elongation. We show that our model can predict the formation of complex surface morphologies including symmetry breaking and secondary folding. Computational modeling naturally explains why larger mammalian brains tend to be more convoluted than smaller brains and provides a mechanistic interpretation of pathological malformations of lissencephaly and polymicrogyria. Understanding the role of mechanics during the development of the nervous system may have direct implications on the diagnostics and treatment of neurological disorders including severe retardation, epilepsy, schizophrenia, and autism.
Dr. Kuhl is an Associate Professor of Mechanical Engineering, Bioengineering (courtesy), and Cardiothoracic Surgery (courtesy). She completed her Ph.D in Civil Engineering at the University of Stuttgart, Germany, in 2000. Her professional expertise is living matter physics, the creation of theoretical and computational models to predict the acute and chronic response of living structures to environmental changes during development and disease. Her specific interest is the multiscale modeling of growth and remodeling, the study of how living matter adapts its form and function to changes in mechanical loading, and how this adaptation can be traced back to structural alterations on the cellular or molecular levels. Growth and remodeling can be induced naturally, e.g., through elevated pressure, stress, or strain, or interventionally, e.g., through prostheses, stents, tissue grafts, or stem cell injection. Combining theories of electrophysiology, photoelectrochemistry, biophysics, and continuum mechanics, Dr. Kuhl's lab has specialized in predicting the chronic loss of form and function in growing and remodeling cardiac tissue using patient-specific custom-designed finite element models.
Joint MEAM-ESE Special Seminar
Hiroyuki Fujita, Professor, Institute of Industrial Science and Director, Center for International Research on Micronano Mechatronics (CIRMM)
University of Tokyo
1:30 - 2:30 pm, Singh Center Glandt Forum
"In situ TEM Observation Using Active MEMS Devices"
My research group has investigated MEMS (micro electro mechanical system) fabrication and microactuators since 1986. Recently, we inserted and operated MEMS devices in the specimen chamber of the transmission electron microscope (TEM). We conducted the tensile and shear testing, and the heat transfer measurement of nano junctions while the junctions were in situ observed by TEM. The tensile testing of a silicon junction of a few nm in diameter showed its extraordinary large plastic deformation. The shear deformation of a silver nano junction exhibited series of sub-nm steps correlated with the crystalline spacing of the material; this is like a miniaturized version of stick-slips during frictional motion. Furthermore, the heat transfer through a short and thin, both in a few nm, silicon junction was much higher than the bulk value because of ballistic heat transfer. Also we have built a MEMS liquid cell in which the growth of a gold electrode by electroplating was observed in real time.
Hiroyuki Fujita is a Professor (1993-present) and served as the Deputy Director (2009-2012) of the Institute of Industrial Science, the University of Tokyo. He is also the Director of the Center for International Research on Micronano Mechatronics (2000-present). He received the B.S., M.S. and Ph.D. degrees from Department of Electrical Engineering of The University of Tokyo, Tokyo, Japan in 1975, 1977 and 1980, respectively. He joined IIS as an assistant professor just after earning his Ph.D. degree. Currently he stays in UC Berkeley as a Russell Severance Springer Professor.
Prof. Fujita is currently engaged in the investigation of micro and nano electromechanical systems fabricated by IC-compatible processes and applications to bio and nano technology. Major research projects include MEMS-in-TEM experiment for simultaneous visualization and material property measurement of nano objects, and biomolecular characterization by using MEMS tools.
He received the M. Hetenyi Award of Experimental Mechanics from the Society for Experimental Mechanics in 1986, Chevalier de l'Ordre des Palmes Academiques from Government of France in 2001, the Prize for Science and Technology in Research Category from Japanese Ministry of Education, Culture, Sports, Science and Technology, Outstanding Achievement Award from The Institute of Electrical Engineers of Japan in 2005, and the Yamazaki-Teiichi Prize from Foundation for Promotion of Material Science and Technology of Japan in 2013.
Eric Shaqfeh, Lester Levi Carter Professor and Department Chair of Chemical Engineering, Stanford University, NAE
"How the Dynamics of Vesicle and Capsule Suspensions in Flow May Affect Your Bleeding Time"
It is well known that individual vesicles or liposomes (i.e. fluid enclosed by a lipid bilayer membrane suspended in a second fluid) are characterized by a remarkable dynamics in flow. For vesicles that are “near spheres” this dynamics includes at least 5 different types of orbits in shear flow that are functions of the viscosity ratio between the inner and outer fluid as well as the Capillary number based on the bending modulus. It is therefore not surprising that a suspension of vesicles is characterized by fascinating collective behavior as well. I will discuss our recent development of a numerical code (based on Loop subdivision) which allows the Stokes flow simulation of non-dilute suspensions of vesicles and capsules at essentially any value of the reduced volume. We will then use these numerical simulations to examine a number of interesting phenomena including: 1) The stability of vesicle shapes in extensional flows, 2) The lift of a vesicle away from a wall and the resulting “Fahraeus-Lindqvist” layer for the flow of a wall-bound suspension of vesicles/capsules, and 3) Platelet margination and adsorption in the microcirculation as a function of hematocrit and its relation to bleeding time.
Eric Shaqfeh is the Lester Levi Carter Professor and Department Chair of Chemical Engineering at Stanford University. He joined Stanford’s faculty in 1990 after earning a B.S.E. summa cum laude from Princeton University (1981), and a M.S. (1982) and Ph.D. (1986) from Stanford University. In 2001 he received a dual appointment and became Professor of Mechanical Engineering. He is most recently (as of 2004) a faculty member in the Institute of Computational and Mathematical Engineering at Stanford. Shaqfeh’s current research interests include non-Newtonian fluid mechanics (especially in the area of elastic instabilities, and turbulent drag reduction), nonequilibrium polymer statistical dynamics (focusing on single molecules studies of DNA), and suspension mechanics (particularly of fiber suspensions and particles/vesicles in microfluidics). He has authored or co-authored over 170 publications and has been an Associate Editor of the Physics of Fluids since 2006. Shaqfeh has received the APS Francois N. Frenkiel Award 1989, the NSF Presidential Young Investigator Award 1990, the David and Lucile Packard Fellowship in Science and Engineering 1991, the Camile and Henry Dreyfus Teacher--Scholar Award 1994, the W.M. Keck Foundation Engineering Teaching Excellence Award 1994, the 1998 ASEE Curtis W. McGraw Award, and the 2011 Bingham Medal from the Society of Rheology. A Fellow of the American Physical Society (2001) and a member of the National Academy of Engineering (2013), he has held a number of professional lectureships, including the Merck Distinguished Lectureship, Rutgers (2003), the Corrsin Lectureship, Johns Hopkins (2003) and the Katz Lectureship, CCNY (2004). He was also the Hougen Professor of Chemical Engineering at the University of Wisconsin (2004) and the Probstein Lecturer at MIT (2011).
George Adams, College of Engineering Distinguished Professor, Department of Mechanical and Industrial Engineering, Northeastern University
"Adhesion and Pull-Off Force of an Elastic Indenter from an Elastic Half Space"
The adhesion between an elastic punch and an elastic half-space is investigated for plane and axisymmetric geometries.The pull-off force is determined for a range of material combinations. This configuration is characterized by a generalized stress intensity factor which has an order less than one-half.The critical value of this generalized stress intensity factor is related to the work of adhesion, under tensile loading, by using a cohesive zone model in an asymptotic analysis of the separation near the elastic punch corner.These results are used in conjunction with existing results in the literature for the frictionless contact between an elastic semi-infinite strip and half-space in both plane and axisymmetric configurations.It is found that the value of the pull-off force includes a dependence on the maximum stress of the cohesive zone model.As expected this dependence vanishes as the punch becomes rigid, in which case the order of the singularity approaches one-half.At the other limit, when the half-space becomes rigid, the stresses become bounded and uniform and the pull-off force depends linearly on the cohesive stress and is independent of the work of adhesion.Thus the transition from fracture-dominated adhesion to strength-dominated adhesion is demonstrated.
Dr. George G. Adams is Professor of Mechanical Engineering at Northeastern University where he has served on the faculty for over thirty years. His areas of expertise are contact mechanics, adhesion, and tribology; MicroElectroMechanical Systems (MEMS), especially RF MEMS switches and micromirrors; and nano-mechanics (including material characterization, adhesion, and mechanical and electrical contacts). He has published about 100 refereed journal papers and has had numerous research grants and contracts with government and industry.
George received his B.S. in Mechanical Engineering from Cooper Union in 1969, and his M.S. and Ph.D. in Mechanical Engineering (Applied Mechanics) from the University of California at Berkeley in 1972 and 1975 respectively. Dr. Adams then became an Assistant Professor of Mechanical Engineering at Clarkson University in Potsdam, New York, and a Research Associate at the IBM Research Laboratory in San Jose, California, prior to joining Northeastern University. Professor Adams was co-founder and the first chair of the Contact Mechanics Technical Committee of the American Society of Mechanical Engineers (ASME). He has served as an Associate Editor of the ASME Journal of Tribology, STLE Tribology Transactions, and of Microsystems Technologies. Dr. Adams is a Fellow of the ASME and STLE, and is College of Engineering Distinguished Professor at Northeastern University.
Saverio Spagniole, Assistant Professor of Mathematics, University of Wisconsin-Madison
"Entrapment, escape, and diffusion of microswimmers in complex environments"
We will begin by addressing the hydrodynamic entrapment of a self-propelled body near a stationary spherical obstacle. Simulations of model equations show that the swimmer can be trapped by a spherical colloid larger than a critical size, that sub-critical interactions result in short residence times on the surface, and that the basin of attraction around the colloid is set by a power-law dependence on the colloid size and swimmer dipole strength. With the introduction of Brownian fluctuations, swimmers otherwise trapped in the deterministic setting can escape from the colloid at randomly distributed times. The distribution of trapping times is governed by an Ornstein-Uhlenbeck process, resulting in nearly inverse-Gaussian or exponential distributions. Analytical predictions are found to match very favorably with the numerical simulations. We also explore the billiard-like motion of such a body inside a regular polygon and in a patterned environment, and show that the dynamics can settle towards a stable periodic orbit or can be chaotic depending on the nature of the scattering dynamics. We envision applications in bioremediation, sorting techniques, and the study of motile suspensions in heterogeneous or porous environments.
Saverio Spagnolie received a Ph.D. in mathematics at the Courant Institute of Mathematical Sciences, then held postdoctoral positions in the Mechanical/Aerospace Engineering department at UCSD and in the School of Engineering at Brown University. He is currently an Assistant Professor in mathematics at the University of Wisconsin-Madison.
Na Zhang, Research Professor, The Institute of Engineering Thermophysics, Chinese Academy of Sciences; Visiting Professor, Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania
1:45 pm, Towne 337
"Perspectives on Sustainable Energy Development in China"
The vital importance of energy extends to its constraining impact on economic and social development in China. This lecture presents the current energy situation and challenges imposed on Chinese energy development, pointing out that although China achieved great progress in establishing a comprehensive energy industry to support its economy, it still faces significant problems such as a bottleneck of resources, low energy efficiency, high emissions, and lack of adequate management mechanisms.
To meet the needs of the ongoing rapid economic growth, increased living standards, and environmental protection, a sustainable development plan that requires strengthening of these sustainability pillars and coordination among them must be established. The main elements of the strategy for sustainable energy development must include energy-saving, optimization of the energy industry structure, support for industry modernization, diversified development, environmental protection, technology innovation, and international cooperation. The Chinese Government’s 12th Five-year Plan for Energy Saving and Emission Reduction (2012) specified the following targets for the energy saving and pollution reduction: between 2010 to 2015, the energy intensity (specific energy consumption per unit of GDP) must be reduced by 16%, and SO2 and NOx emissions must be reduced by 8% and 10%, respectively. The Medium- and Long-term Program for Renewable Energy Development (2007) target is to increase renewable energy use to 15% of the total energy consumption by 2020.
The lecture expounds the long-term development strategy with respect to the prioritizing of energy conservation, promotion of new and renewable energy technologies, and efficient utilization of primary energy, and also stresses the recent efforts on energy policy improvement and on technology research and development.
Dr. Zhang is a research professor at the Institute of Engineering Thermophysics at the Chinese Academy of Sciences (CAS), and an elected deputy to the local people’s congress, Beijing, China. Zhang earned her bachelor’s degree in Thermal Energy Engineering at Tsinghua University, Beijing, in 1991 and Ph.D. in Engineering Thermophysics at the Chinese Academy of Sciences in 1999. From 2002 to 2003, she worked as a visiting scholar in the Department of Mechanical Engineering and Applied Mechanics at the University of Pennsylvania, Philadelphia.
Her major research efforts include gas turbines and combined cycles, cogeneration systems, coal-fired power systems, CO2 capture from power plants, power generation with liquefied natural gas cold exergy, solar thermal power generation and distributed energy systems. She has authored or co-authored more than 80 archival technical publications, is an associate editor of Energy–the International Journal, and is the Executive Editor of the Journal of Engineering Thermophysics (in Chinese).
Her honors include the CAS President Fellowship Award (1996), the National Electric Power Company Science and Technology Progress Award (1999), the National Electric Power Science and Technology of China Award (2002), the Zhonghua Wu Outstanding Young Scientist Award (2008) and the Chinese National Natural Science Award (2009). She, along with Dr. Noam Lior, received a Best Paper Award from the ASME Advanced Energy Systems Division in 2004, and an ASME Society Award - the Edward F. Obert Award for thermodynamics in 2010.
Jinzhou Yuan, Ph.D Candidate, University of Pennsylvania
Advisor: Haim H. Bau
1:00 pm, Towne 227
"Understanding and Manipulating the Locomotion of Undulatory Microswimmers"
"Microswimmer" encompasses a wide range of self-propelling microscopic entities, including flagellated bacteria, small nematodes, microalgae, sperm, and synthetic motile particles. They are of interest to scientists from diverse disciplines, including biologists fascinated with the molecular machinery driving the motility of microswimmers, physicists intrigued by the counter-intuitive propulsion mechanisms adopted by microswimmers, and engineers enthusiastic about harnessing microswimmers for various applications. An essential part of all of these endeavors centers on understanding and being able to control the locomotion of microswimmers. Combining theoretical analysis, numerical modeling, and microfluidic techniques, my dissertation focuses on studying the locomotion of undulatory microswimmers; their interactions with surfaces, fluid flow, and with each other; and developing new methods/devices to manipulate their locomotion. The small free-living nematode Caenorhabditis (C.) elegans is used as the model microswimmer throughout my work.
In the first half of my talk, I investigate, experimentally and theoretically, the swimming dynamics of undulatory microswimmers near surfaces and in channel flow, as well as their collective behavior. I discovered that 1) when swimming in close proximity, undulatory microswimmers synchronize their gait by direct collisions among the swimmers; 2) independent of their touch sensation ability, undulatory microswimmers accumulate near and swim along surfaces as the result of a compromise between surface-induced hydrodynamic attraction and steric repulsion; 3) undulatory microswimmers exhibit positive rheotaxis (upstream swimming behavior) near solid surfaces induced by the combination of a hydrodynamic surface attraction effect and the fluid velocity gradient near solid surfaces. These findings help explain certain intriguing behaviors of undulatory microswimmers, highlight the diverse roles of hydrodynamic forces in microswimmers' life cycles, and lay the foundation of designing novel microswimmer manipulation methods for various applications.
In the second half of my talk, I present the design, fabrication, characterization, and applications of several devices/methods for dynamic trapping, motility measurement, motility-based sorting, and directing the motion of microswimmers. The motility-based sorting device was used in a large-scale forward genetic screen project and successfully selected C. elegans mutants exhibiting abnormal sleep behavior in a high-throughput manner. Subsequent genomic sequencing and analysis led to the identification of a new gene regulating sleep-like quiescence in C. elegans. Using the motility measurement device, I studied the effect of aging on C. elegans and found that the motility of C. elegans declined slowly during the first 8 days of adulthood followed by a sharp decline in their 9th day of adulthood. Using the dynamic trapping device, I studied the effect of confinement on the swimming gait of C. elegans and found that the swimming gait is affected only by steric effects. Finally, I devised a 3-D printed microratchet to direct the motion of microswimmers and achieved a high directing efficiency. These new devices/methods enable studies that are otherwise impossible or impractical with conventional methods.
Sean Anderson, Ph.D Candidate, University of Pennsylvania
Advisor: Haim H. Bau
2:00 pm, DLRB 4N30
"Carbon Nanopipettes for Advanced Cellular Probing and Microinjection"
Carbon nanopipettes (CNPs) consist of a pulled-quartz micropipette with a thin layer of amorphous carbon deposited along its entire interior surface via chemical vapor deposition. The micropipette maintains a continuous fluidic pathway from its nanoscopic tip to its distal macroscopic end, while the insulated carbon film provides an electrical path to the tip that can be used as a working electrode. The quartz at the tip of the CNP can be chemically etched to expose a desired length of a carbon pipe to control its size and characteristics. The tips can vary in diameter from tens to hundreds of nanometers. CNPs are inexpensive, batch-fabricated, and can be made hollow or solid. They can be used as nanoelectrodes, nanoinjectors, or both simultaneously, with improved durability and biocompatibility compared with glass micropipettes.
We have developed an impedimetric AC technique for detecting cellular and nuclear penetration during microinjection and cellular probing with CNPs. The technique has submicron spatial and millisecond temporal resolution. Signal magnitude can be used to discern between penetration into the cytoplasm and nucleus. Using the CNPs as nanoelectrodes we find a monotonic dependence of the signal on the penetration depth into the cytoplasm. The behavior of this system is well-predicted by an equivalent circuit model, and could be used to provide electrical feedback during single-cell microinjection, nanosampling, or electrochemical studies. Using solid CNP electrodes (CNPEs), we have also characterized CNPs for use in fast-scan cyclic voltametry to measure neurotransmitter concentrations in the brain of Drosophilia melanogaster (fruit fly). CNPEs are sharper and smaller than commonly used carbon-fiber microelectrodes (CFMEs), allowing them to penetrate the tough glial sheath of the fly brain and perform more localized measurements than previously possible. CNPEs are also easier to batch-fabricate and have better dimensional control than CFMEs.
As a target biological application of microinjection, we are using injection of fluorescently labeled transfer RNA (tRNA) to monitor subcellular tRNA dynamics in real time. We have developed a simple model to capture trafficking dynamics, and fit our model to experimental data for the measurement of nuclear/cytoplasmic trafficking kinetics of tRNA during nutrient deprivation of MEF cells. This data confirms that cells have mechanisms for the regulation of tRNA transport, and suggests that we can use our microinjection technique to perform quantitative studies of tRNA trafficking.
In order to facilitate microinjection studies such as these, we have developed an adaptable Matlab-based semi-automated injection system. We have incorporated our electrical feedback signal to report cell penetration and trigger injection, with the goal of improving success rates and throughput of microinjection, while minimizing difficulty and user error.
Xin Z. Liu, Ph.D Candidate, University of Pennsylvania
Advisor: Robert W. Carpick
2:00 pm, Towne 227
"Mechanisms Controlling Friction and Adhesion at the Atomic Length-Scale"
A gap in our understanding of the fundamental mechanisms governing nanoscale adhesion and friction exists, resulting in ongoing challenges as technologically-relevant devices are miniaturized. As one key example, there is much excitement about a new generation of devices based on graphene. While recent studies have shown that graphene has promising friction-reducing properties, even at thicknesses of one atomic layer, the mechanisms controlling friction and adhesion for graphene-covered substrates are not yet well understood. In the first part of the talk, I will discuss our recent work on the frictional properties of fluorinated graphene studied by atomic force microscopy (AFM). Friction on fluorinated graphene increases substantially with increasing degree of fluorination. As evidenced by molecular dynamics (MD) simulations, performed through collaboration with Shenoy group at Penn, this strong dependence is attributed to the fact that attachment of fluorine atoms to graphene scaffold greatly enhances the corrugation of the interfacial potential energy, thus the local energy barrier for sliding is significantly increased. These observations provide new insights into the atomic-scale effects of functionalization on frictional properties of graphene. In addition, they suggest a potential approach to sensitively probe the local chemistry and structure of functionalized graphene.
I will then present our newest results on the speed dependence of atomic friction between AFM tips and atomically-flat gold surfaces. There is evidence from experiments, simulations, and theory indicating that friction can be significantly affected by the sliding speed, in accordance with the Prandtl-Tomlinson model with thermal activation (termed the "PTT model"). However, full understanding of this phenomenon is hindered since atomic-scale friction experiments have not yet achieved sliding speeds comparable to those in atomistic simulations. Here, we have slowed down MD simulation scanning speeds (through collaboration with Martini group at U.C. Merced), and obtained higher experimental scanning speeds by improving the AFM apparatus, while resolving stick-slip behavior in both. Other parameters, namely environment (vacuum), materials (a SiO2 tip on a gold sample), contact area, temperature, normal and lateral stiffness, and load were also matched as closely as possible. For the first time, both experiments and simulations are performed at overlapping scanning speeds. Using the PTT model to compare and contrast experiment and simulation data, we have made the first experimental observation of the saturation of the friction force above a critical scanning speed, as predicted by the PTT model. However, friction in experiments is larger than in simulations. PTT energetic parameters for the two are comparable, with minor differences attributable to the contact area's influence on the barrier to slip. Recognizing that the attempt frequency may be determined by thermal vibrations of the larger AFM tip mass or instrument noise fully resolves the discrepancy. Thus, atomic stick-slip friction is well described by the PTT model if sources of slip-assisting energy are accounted for.
April 28 - NO SEMINAR: RESCHEDULED FOR FALL
Ron Schoff, Senior Program Manager for Technology Innovation, Electric Power Research Institute
"Power System Transformation in an Era of Increasing Distributed Generarion, Dynamic Power Delivery, and Interactive Use of Electricity"
The electric power industry is changing at a pace that is unprecedented in its history. The inherently intermittent nature of variable generation (wind and solar), which is growing at a faster rate than any other form of generation, poses challenges for reliable power system operation. Consumers in large numbers are installing photovoltaic panels, as well as purchasing plug-in electric vehicles, smart appliances, and equipment that enables them to better manage their electricity use. Recent severe weather events, a high-profile physical attack on a west coast substation, and other high-impact, low frequency events, are forcing utilities to enhance their resiliancy. The Internet of Things and predicted explosive propagation of connectivity across consumer devices and power system devices will also drive change, while helping to address some of these challenges. EPRI's R&D portfolio is evolving to enable and support the needed revolutionary power system transformation that must take place to address these challenges. This seminar will summarize changes in the power system and EPRI's plan for working closely with stakeholders to develop innovative solutions to develop and Integrated Grid.
Ronald Schoff is the Senior manager of the Techonogy Innovation (TI) program at the Electric Power Research Institute (EPRI).
His responsibiilties include managing the five core components of the TI Program: Thought Leadership, Innovation Scouting, Strategic Programs, Breakthrough Technologies, and the Polaris Initiative. The program's cross-cutting research, development, and demonstration (RD&D) projects portfolio scouts, influences, and builds on early-stage work across the global science and technology communities to capture innovations for application-oriented development and demonstration by EPRI.
Before joining TI, Schoff worked in EPRI's CoalFleet for Tomorrow(tm) program, managing evaluations of advanced power generation technologies, including coal gassification combined cycle (IGCC), ultrasupercritical pulverized coal (USCPC), natural gas-fired combined cycles (NGCC), and power cycles incorporating carbon dioxide capture and sequestration (CCS). In addition, Schoff has been active in developing long-range technology roadmaps.
Prior to joining EPRI, Schoff worked as an engineer for Parsons Corporation's Research and Development Group in Pittsburgh, where he focused on thermodynamic power plant performance and capital cost estimation of advanced fossil power plants and a variety of other conventional and novel processes.
Schoff holds a Bachelor of Science degree in chemical engineering from the University of Pittsburgh and a Master of Science degree in chemical engineering from Villanova University. He is a senior member of the American Institute of Chemical Engineers and a registered engineer-in-training. He has published numerous papers and given talks at various technical conferences worldwide.
Nicholas M. Schneider, Ph.D Candidate, University of Pennsylvania
Advisor: Haim H. Bau
1:00 pm, Moore 216
"Liquid Cell Electron Microscopy with the Nanoaquarium: Radiation and Electrochemistry"
The advent of the electron microscope has fostered major advances in a broad spectrum of disciplines. The required vacuum environment of standard electron microscopy, however, precludes imaging of systems containing high vapor pressure liquids. The recent development of liquid cells like the Penn nanoaquarium overcomes this limitation, enabling imaging of temporally evolving processes in liquids with nanoscale resolution at video frame rates. I used Liquid Cell Electron Microscopy to investigate the morphological evolution of the electrode-electrolyte interface during electroplating, the onset of diffusive instabilities in electrodeposits, beam-mediated nucleation, growth, and dissolution of metallic nanoparticles, the nucleation and growth of nanobubbles, and the fundamentals of the electron-water interactions (Radiation Chemistry). The control of interfacial morphology in electrochemical processes is essential for applications ranging from nanomanufacturing to battery technologies.
Critical questions still remain in understanding the transition between various growth regimes, particularly the onset of diffusion-limited growth. I present quantitative observations at previously unexplored length and time scales that clarify the evolution of the metal-electrolyte interface during deposition. The interface evolution during initial stages of galvanostatic Cu deposition on Pt from an acidic electrolyte is consistent with kinetic roughening theory, while at later times the behavior is consistent with diffusion limited growth physics. To control morphology, we demonstrate rapid pulse plating without entering the diffusion-limited regime, and study the effects of the inorganic additive Pb on the growth habit. The irradiating electrons used for imaging, however, affect the chemistry of the suspending medium. The electron beam's interaction with the water solvent produces molecular and radical products such as hydrogen, oxygen, and hydrated (solvated) electrons.
A detailed understanding of the interactions between the electrons and the irradiated medium is necessary to correctly interpret experiments, minimize artifacts, and take advantage of the irradiation as a tool. We predict the composition of water subjected to electron irradiation under conditions relevant to liquid cell electron microscopy. We interpret experimental data, such as beam-induced colloid aggregation and observations of crystallization and etching of metallic particles as functions of dose rate. Our predictive model is useful for designing experiments that minimize unwanted solution chemistry effects, extend liquid cell microscopy to new applications, take advantage of beam effects for nanomanufacturing such as the patterning of nanostructures, and properly interpreting experimental observations.