MEAM Seminar Series Spring 2012

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).

To be added to the MEAM Events mailing list (which sends notifications regarding all departmental seminars and events) please email us at meam-events@lists.seas.upenn.edu.


January 17

Sumita Pennathur, Assistant Professor, Department of Mechanical Engineering, University of California, Santa Barbara
"Electrokinetic characterization of micro- and nano-fluidic channels for bioanalytical applications"

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Abstract: Electrokinetic based micro- and nanofluidic technologies provide revolutionary opportunities to separate, identify and analyze biomolecular species. The coupled physics unique to nanofluidic systems allows for separations based on different analyte properties, including charge, size, conformation, hydrophobicity, and mass. Coupled with optical or electronic detection technologies, such systems allow for great opportunities the field of biomolecular analysis, providing separation, identification, and detection of biomolecules with superior speed, sensitivity, selectivity and quantitation. Key to fully harnessing the power of such systems is a thorough understanding of the influence of the electrokinetic surface properties. In this work, we will present recent results from a joint theoretical and experimental study of electrokinetic surface properties in nano- and microfluidic channels fabricated with fused silica, insulated metals, and/or polymeric material. First, we will describe techniques used to measure electrokinetic properties within experimental micro- and nanofluidic systems, including the solution displacement method of current monitoring and electrokinetic injection techniques. Furthermore, we will describe a useful model developed to find the effective zeta potential in a channel with an embedded insulated gate electrode using such techniques. Next, we will present a robust theoretical model of a fused silica channel surface consisting of three parts: (1) a chemical equilibrium model of the wall, (2) a chemical equilibrium model of the bulk electrolyte, and (3) a self-consistent Gouy--Chapman--Stern triple-layer model of the electrochemical double layer coupling between (1) and (2). We will show three separate experimental validations of this electrokinetic surface model, specifically, one using capillary filling, one with electrokinetic flow, and one using pressure driven flow, all within fused silica nanochannels. Finally, we discuss two studies in our lab towards the practical development of nanofluidic biosensors, namely, a nanoscale preconcentration method, and a unique fabrication technique to allow for the integration of electrodes in nanofluidic channels.

Biography: Pennathur began teaching at UCSB in the Mechanical Engineering department in July 2007. Her research group focuses on using fundamental fluidics knowledge at both micro- and nano -scales to create novel devices for practical applications. Major efforts include creating and developing enabling tools to identify and characterize biological substances, improving current bionalaytical devices, and designing/engineering entire systems for point-of-care usage. Prior to coming to UCSB, Pennathur did postdoctoral work at the University of Twente, and Sandia National Labortories, after a phD from Stanford and B.S./M.S. from MIT. Since arriving at UCSB, she has written over a dozen journal publications, won the DARPA Young Faculty Award, the UC Junior Regents Faculty Fellowship, and the PECASE award.

January 20 (Friday)

Doctoral Defense, 9:00 AM, 307 Levine Hall
Daniel Mellinger, Ph.D. Candidate, MEAM, University of Pennsylvania
Advisors: Dr. Vijay Kumar
" Trajectory Generation and Control for Quadrotors"

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Quadrotor helicopters are agile crafts with impressive dynamic capabilities. In this presentation I will describe the multiple quadrotor testbed used at the GRASP Lab and several projects that have been conducted in this space. I will describe a controller capable of following trajectories requiring large accelerations as well as recovering from extreme initial conditions. I will describe a few different trajectory generation methods which enable flight through narrow windows, robust perching on vertical surfaces, dynamically optimal flight through thrown hula hoops, and collision-free flight for teams of heterogeneous quadrotors. I will also describe a control method for multiple quadrotors rigidly attached to the same payload which enables cooperative transport.

January 23 (Monday)

Doctoral Defense, 9:30 AM, 315 Levine Hall
Subhrajit Bhattacharya, Ph.D. Candidate, MEAM, University of Pennsylvania

Advisors: Dr. Vijay Kumar & Dr. Maxim Likhachev
"Topological and Geometric Techniques in Graph-Search Based Robot Planning"

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Search-based techniques have been widely used in robot path planning for finding optimal trajectories in configuration spaces. They have the advantages of being complete, optimal (up to the metric induced by the discretization) and efficient (in low dimensional problems), and broadly applicable, even to complex environments. Continuous techniques, on the other hand, that incorporate concepts from differential and algebraic topology and geometry, have the ability to exploit specific structures in the original configuration space and can be used to solve different problems that do not lend themselves to graph-search based techniques. We propose several novel ideas and develop new methodologies that will let us bring these two separate techniques under one umbrella. Using tools from algebraic topology we define differential forms with special properties whose integral reveal topological information about the solution path allowing us to impose topological constraints on the planning problems. Metric information can be used along with search-based techniques for creating Voronoi tessellations in coverage and exploration problems. In particular, we use entropy as a metric for multi-robot exploration and coverage of unknown or partially known non-convex environments. Finally, in multi-robot constrained planning problems we exploit certain special product structure in the high dimensional configuration space that combine the advantages of graph search methods and gradient descent algorithms allowing us to develop powerful tools to solve very high-dimensional planning problems.

January 24

Pradeep Guduru, James R. Rice Associate Professor of Engineering, Division of Engineering, Brown University
"On the Role of Mechanics in the Design and Performance of Electrode Materials for Energy Storage"

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Abstract:

The increasing interest in employing alternative energy sources, especially for transportation applications, led to a large scale national effort in recent years towards developing electrochemical energy storage systems (batteries) with significantly higher energy density and cycle-life compared to the prevailing technologies. The performance of the new classes of materials being developed/considered is severely limited by the mechanical degradation that accumulates during operation, which is a main impediment that needs to be overcome.  This talk focuses on the mechanics issues in silicon, which is considered to be a promising anode material to increase the specific energy of lithium-ion batteries by as much as 30%. For accurate modeling of battery performance, cycle life and reliability, there is a need to understand the failure modes and how mechanical fields influence electrochemical response. Our experiments show that lithiated silicon is capable of undergoing large plastic deformation in constrained geometries; the ability to undergo plastic deformation underpins the failure behavior in all silicon anode architectures.  An analysis of the dependence of electric potential on the state of stress of a lithiated-silicon electrode is also presented. Based on the Larche and Cahn chemical potential for a solid solution, a thermodynamic argument is made for the existence of a stress-potential coupling in lithiated-silicon, the magnitude of which is estimated to be  ~ 60 mV/GPa. The analysis was validated by an accompanying experimental investigation that measured the coupling to be around 100 mV/GPa.  The implications of the stress-potential coupling to Li plating and safety are discussed. We also present an experimental method to measure average stress field in practical electrode microstructures during electrochemical cycling.

Bio: Pradeep Guduru received Bachelor's degree in Mechanical Engineering from Sri Venkateswara University and Master's degree in Aerospace Engineering from Indian Institute of Science. He received his PhD in Aeronautics from California Institute of Technology in 2001. Subsequently he joined the Division of Engineering at Brown University as a postdoctoral research associate and was appointed as an assistant professor of Engineering in 2002. He has been an associate professor of Engineering since 2008 and the James R. Rice Associate Professor of Engineering since 2009. Prof. Guduru’s research interests span problems in Experimental Solid Mechanics; the thrust of the current research is on problems at the interface between Solid Mechanics and Chemistry, with applications to energy technologies.

January 26 (Thursday)

10:00 AM, 337 Towne Building
Cary Pint, Research Scientist, Extreme Technologies Research Group Intel Corporation
"Nanocarbon Scaffolds for Efficient Energy Conversion and Storage"

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Abstract: One of the greatest challenges facing mankind in the next century is energy management amidst consumption of a finite and limited amount of energy resources.  Future innovation in diverse areas ranging from electronics to health is intimately tied to our ability to discover and implement cost-effective alternative energy systems that are efficient and composed of earth-abundant materials.  My talk will begin by discussing fabrication routes whereby nanocarbon materials can be assembled or chemically rendered to possess characteristics appealing to diverse energy systems.  This includes the synthesis and transfer of hierarchical self-assembled single-walled carbon nanotube materials into controllable, complex 3-D assemblies and nanofabrication routes to graft complex chemical architectures into atomically-thin transferred graphene sheets.  I will then discuss how these tunable material architectures can be utilized as bottom-up templates to build efficient energy systems.  First I will discuss routes to build fully solid-state and mechanically robust capacitive energy storage materials utilizing atomic layer deposition (ALD) on high surface-area aligned single-walled carbon nanotube templates.  I will then discuss the use of nanocarbons as efficient templates for solar-to-fuel conversion applications, where elastocapillary forces can be utilized as a nanofabrication tool for structural design of three-dimensional carbon nanofiber templates enabling photon management and efficient device performance.  Overall, my talk will demonstrate how controlled synthesis and nanofabrication techniques can be utilized as powerful tools for the design of next-generation efficient energy systems. 

Biography: Dr. Cary L. Pint is currently a Research Scientist in the Extreme Technology Research Group at Intel Labs pursuing research in the area of efficient energy devices.  Cary received his Ph.D. from Rice University in 2010 and spent one year as a postdoctoral fellow at the University of California, Berkeley before joining Intel.  Cary has authored ~ 40 publications in top journals, has over 10 patents submitted, is a coauthor on a book on carbon nanomaterials soon to be published, and has been the recipient or finalist for numerous national awards, including the APS LeRoy Apker Award, the Vanderbilt Prize, and the AVS Dorothy and Earl Hoffman Scholarship.  Recently, Cary was also named as a “Top 30 Under 30” Rising Star in Science & Innovation by Forbes Magazine for his work on energy systems.

January 31

David Erickson, Director, Integrated Nanofluidic Systems Lab, Associate Professor, Sibley School of Mechanical and Aerospace Engineering, Cornell University
"Handling the very big and very small: Optofluidics for Nanomanipulation and Energy Application"

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Abstract: At its most basic level, Optofluidics is focused on enabling or exploiting the precise control or over fluids and light at micro- and nano-scales. Over the past 5 years, these successes in this area has led to the development of many new technologies including from tunable dye lasers, more precise biosensing, and compact microscopy. In this talk I will discuss some new opportunities to which this same skill set could be applied. In particular I will focus on applications at the smallest of scales (nanomanipulation and single molecule analysis) and the largest of scales (photosynthetic fuel production). Whenever possible, the ultimate potential of entry into these new fields will be discussed as well as the challenges that must be overcome. A particular focus will be placed on how to upscale optofluidic technology (which to date has been largely chip based) to address problems in these areas (which can be global in scale).

 

Biography: Prof. David Erickson is an Associate Professor in the Sibley School of Mechanical and Aerospace Engineering at Cornell University where he directs the Integrated Micro- and Nanofluidic Systems Laboratory. Prior to joining the faculty in September 2005, Dr. Erickson was a postdoctoral scholar at the California Institute of Technology (2004-2005) and he received his Ph.D. degree from the University of Toronto in 2004. He is currently an associate editor of the Journal of Microfluidics and Nanofluidics. Research in the Erickson lab is primarily funded through grants from the NSF, NIH, AFOSR, ONR, DOE and DARPA. Prof. Erickson is the Co-Founder of Optofluidics, Inc. which is focused on commercializing single molecule instrumentatio n and traumatic injury diagnostics. In recent years, Dr. Erickson has received the DARPA-MTO Young Faculty Award (2007), the Robert ’55 and Vanne ’57 Cowie Excellence in Teaching Award (2007), the NSF CAREER Award (2009), and the Department of Energy Early Career Award (2010). In 2011 he was awarded the Presidential Early Career Award for Scientist and Engineers, PECASE, for his work with the DOE by President Obama.

February 2 (Thursday)

10:00 AM, 337 Towne Building
Zlatan Aksamija, NSF CI TraCS Fellow, Nanoelectronics Theory Group, University of Wisconsin-Madison
"Semiconductor Nanostructures for Efficient Thermo-electric Energy Conversion"

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Abstract: Thermoelectric (TE), or solid-state, refrigeration using semiconductor-based nanostructures, such as nanowires, nanoribbons, and superlattices, is an attractive approach for targeted cooling of local hotspots inside integrated circuits due to inherently no moving parts, ease of miniaturization and on-chip integration, and the nanostructures’ enhanced TE conversion efficiency. In addition, thermoelectric power generation enables the reuse of waste heat in a variety of applications, from low-power and energy-efficient designs all the way up to internal combustion engines and solar cells. Thermoelectric efficiency, measured by the figure-of-merit ZT, is dictated by the ratio of electronic power factor S2σ over the total thermal conductivity. Consequently, largest gains in TE conversion efficiency have come from the ability to reduce thermal conductivity. This is especially true in nanostructures, where small physical dimensions lead to reduced thermal transport due to the scattering of lattice waves, or phonons, with the boundaries and interfaces of the nanostructure. The design of efficient semiconductor thermocouples requires a thorough understanding of both charge and heat transport; therefore, thermoelectricity in semiconductor-based nanostructures requires that both electronic and thermal transport are treated on equal footing. Silicon-on-insulator (SOI) nano-membranes and membrane-based nanowires and ribbons show promise for application as efficient thermoelectrics, which requires both high electronic power factor and low thermal conductivity. In this talk, we present numerical simulation and modeling of both carrier and phonon transport in ultrathin silicon nanomembranes and gated nanoribbons. We show that the thermoelectric response of Si-membrane-based nanostructures can be improved by employing the anisotropy of the lattice thermal conductivity, revealed in ultrathin SOI nanostructures due to boundary scattering, or by using a gate to provide additional carrier confinement and enhance the thermoelectric power factor. Furthermore, we explore the consequences of nanostructuring on silicon/germanium and Si/SiGe alloy superlattices, and show that the drastic reduction of thermal conductivity in these structures comes from the increased interaction of lattice waves with rough interfaces and boundaries. Finally we demonstrate reduced thermal conductivity in both suspended and supported graphene nanoribbons (GNRs), which exhibit strong anisotropy due to interaction of lattice waves with line edge roughness (LER) and the competition between LER and substrate scattering. The talk will conclude with an outlook for future nanostructured thermoelectric based on nanocrystalline and nanocomposite semiconductors, and graphene.

Short Biography: Zlatan Aksamija received his B.S. in Computer Engineering in 2003, and his M.S. and Ph.D. in Electrical Engineering (with Computational Science and Engineering option) in 2005 and 2009, respectively, all from the University of Illinois at Urbana/Champaign. His dissertation work entitled "Thermal effects in semiconductor materials and devices" was supported by a DOE Computational Science Graduate Fellowship (2005-2009). Zlatan was ranked as an "Outstanding TA" by his students in the Fall of 2004. He was awarded an Outstanding Paper award at the EIT'07 conference and a Greg Stillman Memorial semiconductor graduate research award in 2008. From 2009 to 2011, Zlatan was a Computing Innovation Postdoctoral Fellow in the ECE.

February 6 (Monday)

10:00 am, 337 Towne Building

Mona Zebarjadi, Postdoctoral Associate, Massachusetts Institute of Technology
"Thermoelectric transport in nanostructures"

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Abstract: Thermoelectrics can directly convert heat into electricity and therefore have applications in waste heat recovery. These solid-state devices can also be integrated directly on chips and actively cool down hot spots of high-speed devices.  In this talk, I will discuss modeling of electron and phonon transport inside thermoelectric legs to identify fundamental length scales such as carrier mean free path and momentum and energy relaxation lengths. Knowing the fundamental length scales, we can design nanostructured materials with enhanced thermoelectric figure of merit (Z=sS2/k). I will discuss strategies to reduce the thermal conductivity via introducing interfaces and rattling atoms to scatter phonons, to increase the electrical conductivity by means of modulation doping and to improve the Seebeck coefficient by energy filtering and introducing sharp features in the density of states. In each strategy the challenge is to improve one property without deteriorating the other properties. We have fabricated and characterized bulk samples as well as superlattices, which were designed based on different strategies. The obtained experimental results are in agreement with theoretical predictions but there is still a lot of room for improvement in terms of materials designing. Finally, I will address the issue of heat management. By using a Monte Carlo algorithm, we have identified the energy relaxation length and the location of Peltier cooling/heating at heterointerfaces. We have also explored the nonlinearity of heat current when the applied electric field is strong and electrons are out of equilibrium with phonons. The nonlinearity of thermoelectric transport coefficients could be used to enhance the device performance significantly especially at low temperatures.

Bio: Mona Zebarjadi is a joint postdoctoral associate with Prof. Gang Chen (ME) and Prof. Mildred Dresselhaus (EE and Physics) in the Mechanical Engineering Department of the Massachusetts Institute of Technology were she is working on materials design and magnetotransport. She has defended her Ph.D. at the University of California, Santa Cruz in November of 2009. She was working in the quantum electronics group supervised by Prof. Ali Shakouri on characterization and simulation of transport properties in thermoelectric materials. Her research interests are in electron, phonon and photon transport modeling, materials and device design, fabrication and characterization for energy conversion systems such as thermoelectrics, solar cells, and diffusion cells and heat management in high power electronics and optoelectronic devices.

February 7

John Hart, Assistant Professor, Mechanical Engineering, University of Michigan
"Manufacturing of 3D Carbon Nanotube Surfaces"

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Abstract: It is widely known that carbon nanotubes (CNTs) have outstanding properties in several categories, which can enable new materials and devices having novel multifunctional performance. However, precise control of the formation and hierarchical organization of CNTs remains a manufacturing challenge. I will present our research toward the use of vertically aligned CNT “forests” as a platform for 3D microfabrication and surface engineering. Low-density CNT forest microstructures grown by chemical vapor deposition are manipulated by “capillary forming”, wherein a solvent is condensed onto the substrate and infiltrates each microstructure by self-directed capillary rise. By understanding the relationship between shrinkage of the vapor-liquid-solid interface and the resultant heterogeneous strain distribution within the CNT forest, we have engineered shape transformations that create robust freeform microstructures and complex multi-directional textures. These 3D CNT surfaces can be implemented as, for example, nanocomposite master templates for replica molding of polymer microstructures, and mechanosensitive transducers driven by chemically-selective swelling of hydrogels. In a parallel effort, we have used spatially- and temporally resolved X-ray scattering to investigate the dynamics of CNT forest growth and to identify functional requirements for a continuous process. These insights are reflected in the design of a machine for roll-to-roll CNT forest growth on flexible substrates. I will close with a brief perspective on needs for scalable nanomanufacturing technologies that bridge the gap between lithography-based fabrication and bulk materials processing.

Bio: John Hart is Assistant Professor of Mechanical Engineering and Art & Design at the University of Michigan in Ann Arbor, Michigan. At Michigan, John directs the Mechanosynthesis Group, and teaches undergraduate and graduate courses in design, manufacturing, nanotechnology, and research methods. John has Ph.D. (2006) and S.M. (2002) degrees from the Massachusetts Institute of Technology, and a B.S.E. (2000) degree from the University of Michigan, all in Mechanical Engineering. Since joining Michigan in 2007, John’s research in nanostructured materials and manufacturing has been recognized by the DARPA Young Faculty Award (2008), two R&D100 Awards (2008, 2009), the ASME Pi Tau Sigma Gold Medal (2009), the SME Outstanding Young Manufacturing Engineer Award (2010), the AFOSR Young Investigator Program Award (2011), and the NSF CAREER Award (2012).

February 9 (Thursday)

10:00 am, 337 Towne Building

Igor Bargatin, Engineering Research Associate, Department of Electrical Engineering Stanford University
" Hard-boiled Electrons: Using Thermionic Emission for Solar Electricity Generation "

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Abstract: We are building MEMS-based prototypes of new types of heat-to-electricity and solar-to-electricity energy converters. The first type of the device converts very high-temperature heat (>1000 C) to electricity using evaporation of electrons from solid surfaces (thermionic effect). The second type of the device simultaneously transforms solar light and heat into electricity and is based on the recently demonstrated effect of photon-enhanced thermionic emission (PETE). Both types of converters may be used to dramatically improve the efficiency of future solar thermal power plants. I will describe the principle of operation, initial experiments, and maximum theoretical efficiency of both types of these MEMS devices.

Bio: Dr. Igor Bargatin is currently a research associate in the group of Prof. Roger T. Howe (Department of Electrical Engineering, Stanford University). A native of western Siberia, he received an undergraduate degree in theoretical physics from Moscow State University in 2000. Subsequently, Dr. Bargatin was a graduate student in the group of Prof. Michael L. Roukes at Caltech, where he became an experimentalist and studied sensor applications of high-frequency nanomechanical resonators, graduating with a Ph.D. in Physics and a minor in EE. In the summer of 2008, he was a visiting scientist at CEA/LETI in Grenoble, France, working on the development of new types of gas sensors.

February 21

Nicholas Boechler, Postdoctoral Associate, Department of Mechanical Engineering, Massachusetts Institute of Technology
"Granular Crystals: Controlling Mechanical Energy with Nonlinearity and Discreteness"

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Abstract: The presence of structural discreteness and periodicity is known to affect many types of wave propagation, including that of sound and other mechanical waves. A fundamental property of many of the periodic structures designed for this purpose is the presence of complete band gaps in their dispersion relation, where waves with frequencies in the band gap cannot propagate through the structure. However, like the concept of a band gap, the functionality of these periodic structures has historically been based on concepts from linear dynamics. Nonlinear systems can offer increased flexibility over linear systems, including new ways to localize energy, convert energy between frequencies, and tune the response of the system. Granular crystals are a type of nonlinear periodic structure composed of arrays of elastic particles that interact nonlinearly via Hertzian contact. In this work, we studied the dynamic response of one-dimensional granular crystals composed of compressed macroscopic elastic spheres. Several fundamental physical phenomena were experimentally demonstrated in the weakly nonlinear dynamical regime of granular crystals, including tunable frequency band gaps, discrete breathers, nonlinear localized defect modes, and bifurcations to quasiperiodic and chaotic states. We also explored how these phenomena can be utilized to create novel devices for tunable vibration filtering, energy harvesting and conversion, and tunable acoustic rectification. Furthermore, as many of the concepts studied here are scalable and are applicable to other nonlinear periodic systems, we envision that they will enable the design of advanced photonic, thermal, and acoustic materials and devices.

Bio: Dr. Nicholas Boechler received his Bachelor of Science degree in Aerospace Engineering from the Georgia Institute of Technology in 2007, where he published a thesis on direct conversion for space solar power and was awarded a NASA Institute for Advanced Concepts student fellowship. In 2008, he received his Master of Science degree in Aerospace Engineering from the California Institute of Technology. In 2011, he completed his Ph.D. in Aeronautics at the California Institute of Technology, where his advisor was Prof. Chiara Daraio. During his graduate research, Dr. Boechler studied granular crystals and experimentally demonstrated new phenomena including tunable acoustic band gaps, nonlinear localized modes, and tunable acoustic rectification. His research resulted in two provisional patents and multiple conference and journal publications, including a recent publication in Nature Materials. He is currently a Postdoctoral Associate, working with Prof. Nicholas Fang in the Department of Mechanical Engineering at the Massachusetts Institute of Technology, where he is studying nonlinear nanoscale periodic structures, hierarchical blast wave armors, and acoustic metamaterials.   


February 24
(Friday)

2:00 PM, Wu and Chen Auditorium, Levine Hall
JOINT AMCS/MEAM SEMINAR

Alan Needleman, Professor of Materials Science and Engineering, University of North Texas; Florence Pirce Grant University Professor Emeritus, Brown University
"Porosity Evolution in Ni-based Single Crystals under Creep Loading Conditions"

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Abstract: Single crystal Ni-based superalloys were introduced in the early 1980s and since then have been widely used in turbine aerofoils in jet engines. The desire for weight reduction and the use of advanced metal cooling schemes tends to drive designs toward thinner airfoil walls. Creep tests on Ni-based superalloy specimens have shown greater creep strain rates and/or reduced creep rupture times for thinner specimens than is predicted by current theories. This is termed the thickness debit effect. To investigate the mechanism of the thickness debit effect, isothermal, constant nominal stress creep tests were performed on uncoated PWA1484 Ni-based single crystal superalloy sheet specimens of thicknesses 3.18mm and 0.51mm under two test conditions: 760 deg. C/758MPa and 982 deg. C/248MPa. The specimens contained initial micro-voids formed during the solidification and homogenization processes. The experiments showed that porosity evolution could play a significant role in the thickness debit effect. This motivated basic mechanics studies of porosity evolution in single crystals subject to creep loading. The evolution of porosity was studied for various values of stress triaxiality and various values of the Lode parameter. These studies will be summarized in this talk with particular attention given to the evolution of the void shape and the implication of shape changes for the near-void stress fields. Implications for the thickness debit effect will be discussed.

March 20

Douglas Jerolmack, Assistant Professor, Department of Earth and Environmental Science, University of Pennsylvania
"The science of scenery: how dynamics at the fluid-granular interface creates landscapes"

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The landscape on which we live is principally granular, and has been shaped over eons by transport of sediment by water and wind. Sand ripples, desert dunes, barrier islands, river channels and deltas are patterns that have evolved through complex feedbacks among fluid flow, sediment transport and erosion and deposition. Predicting the dynamics of the sediment-fluid interface is of paramount importance for managing human development, but is difficult because these problems involve both turbulent fluid flows and heterogeneous sediment - and the boundary conditions are often unknown. Here I discuss progress by our research team in problems at several scales: anomalous diffusion of pebbles moving in a stream; coarsening dynamics in the growth of river dunes; channel network formation on river deltas; and the interaction of atmospheric boundary layer flows with surface roughness in a desert dune field. I will show how laboratory experiments and simplified analytical models, that neglect many of the complications of natural systems, nonetheless quantitatively capture the evolution of "natural" landscape patterns. I will highlight the importance of stick-slip dynamics, hysteresis, disorder, and aging/memory; and will outline opportunities for advancing our understanding of geophysical transport through by incorporating insights from solid/fluid mechanics and granular physics.

March 22 (Thursday)

Tedori-Callinan Lecture, 1:30 PM, Wu and Chen Auditorium
Subra Suresh, Director, National Science Foundation
"Nanoscience as a Pathway to Innovation in Engineering and Biology"
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March 27

Michael Graham, Harvey D. Spangler Professor, Department of Chemical and Biological Engineering, University of Wisconsin-Madison
"Segregation phenomena in flowing suspensions of deformable particles: toward an understanding of cell and particle dynamics in blood flow"

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Abstract: Blood is a suspension of particles of various shapes, sizes and mechanical properties and the distribution of these particles during blood flow is important in many contexts. Red blood cells (RBCs) tend to migrate toward the center of a blood vessel, leaving a so-called cell-free layer at the vessel wall, while white blood cells (WBCs) and platelets are preferentially found near the walls, a phenomenon called margination. This phenomenon is critical for the physiological responses of inflammation and hemostasis. Potential beneficial effects on hemodynamics arise from addition of high molecular weight long-chain polymer molecules known as drag-reducing additives (DRAs) to blood; one effect of these additives is the reduction of the cell-free-layer thickness. Additionally, the segregation properties of WBCs, platelets, and RBCs can be employed for their separation or detection in microfluidic devices. Finally, drug delivery particles in the bloodstream will also undergo segregation phenomena – the influence of these phenomena on the efficacy of such particles is unknown. This talk describes efforts to gain a systematic understanding of flow-induced segregation phenomena in blood and other complex mixtures, using a combination of theory and direct simulations of flowing suspensions. Two specific issues are addressed here: (1) the effect of DRAs on the formation of the cell-free layer and (2) the origin of the margination phenomenon and its dependence on the relative properties of the different types of suspended particles in a mixture. In the case of polymer additives, the experimentally observed thinning of the cell-free layer is reproduced in the simulations and the mechanism underlying it is described.  The study of margination reveals that this phenomenon is largely determined by the nature of pair collisions between different types of particles during flow. Having in hand an understanding of the mechanisms underlying these phenomena now allows more rational approaches to development of quantitative models of them and processes that exploit them. This knowledge will also lead to a better understanding of the consequences of these phenomena in physiology and medicine.

Bio: Michael D. Graham is the Harvey D. Spangler Professor of Chemical and Biological Engineering at the University of Wisconsin-Madison, and also holds appointments in the departments of Mechanical Engineering and Engineering Physics. He received his B.S. in Chemical Engineering from the University of Dayton in 1986 and his PhD. from Cornell University in 1992. After postdoctoral appointments at the University of Houston and Princeton University, he joined the Chemical Engineering faculty at the University of Wisconsin-Madison in 1994. He chaired the department from 2006 to 2009. Among Mike's awards are a Best Student Paper Award from the Environmental Division of AIChE in 1986, a CAREER Award from NSF in 1995 and the François Frenkiel Award for Fluid Mechanics from the American Physical Society Division of Fluid Dynamics in 2004. He was elected a Fellow of the American Physical Society in 2011 and received a Kellett Mid-Career Award from UW-Madison in 2012. He is a member of the editorial board of the Journal of Non-Newtonian Fluid Mechanics and is an Associate Editor of the Journal of Fluid Mechanics.

April 3

Arvind Raman, Professor of Mechanical Engineering, College of Engineering, Purdue University
" Probing the mechanobiology of cells and viruses at small forces and lengthscales using multi-harmonic Atomic Force Microscopy methods"

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Abstract: Mechanobiology refers to the fundamental study of how cells and viruses, and macromolecules sense and respond to external forces. Recent work in this area has highlighted the important role of local mechanical properties in ellular processes such as morphogenesis, mechano-transduction, focal adhesion, motility, metastasis, and drug/antibiotics delivery as well as the connection between mechanical properties and the function of viruses. Exploring mechanobiology also requires the development of new tools with high sensitivity and resolution. In this talk I will discuss the role of the Atomic Force Microscope (AFM) as an indispensable tool to probe mechanobiology at -100 pN forces and at sub-10nm resolution. Following a review of key advances that are being made in the use of AFM for biological applications, I will demonstrate that a deep understanding of the mechanics of the AFM enables the creation of new modes of AFM operation that offer deep insight into the mechanobiology of live cells and viruses.

Bio: Arvind Raman is a Professor of Mechanical Engineering at Purdue. Raman joined Purdue as an Assistant Professor in 2000. Earlier he was a postdoctoral scholar at the Technical University Darmstadt, Germany and he received his PhD (1999) from the University of California, Berkeley, an MSME (1993) from Purdue, and a B. Tech (1991) from the Indian Institute of Technology Delhi. He has held visiting professor appointments at the Universidad Autonoma de Madrid, Spain, and the University of Oxford (Wadham College), UK. He has published extensively in his areas of specialization in applied nonlinear dynamics, fluid-structure interactions, Atomic Force Microscopy and Micro and nanosystems. A key contribution has been the use of cloud-computing based cyber-infrastructure to help make advanced simulations accessible for the larger Scanning Probe Microscopy community. The Virtual Environment for Dynamic AFM (VEDA) developed by his group has more than thousand users worldwide and is widely used in classes at many institutions. He has received numerous awards for his research including the Gustus Larson award for outstanding achievement from the ASME, the NSF CAREER award, the Keeley fellowship from Oxford, and the College of Engineering Young Researcher award. Raman co-leads the Colombia-Purdue Institute for Advanced Scientific Research and is also involved in several global engagement activities on behalf of the College of Engineering.

April 17

Michael Shelley, Lilian and George Lyttle Professor of Applied Mathematics; Professor of Mathematics and Neural Science; Co-Director, Applied Mathematical Laboratory, Department of Mathematics, Courant Institute of Mathematical Science, New York University
"Biological Flows and Mechanics"

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Abstract:  The mechanics of fluids and structures can be extremely useful  in explaining biological phenomena. While bird flight and fish swimming are two well-known examples, and I will discuss instances where the role of mechanics seems not so obvious but turns out to be central and even surprising. These include the collective dynamics of swimming bacteria; observations and modeling of a simple undulating organism -- the nematode C. elegans -- negotiating a fluid-filled space full of obstacles; and the dynamics of the pronuclear complex in C. elegans embryo as it achieves proper position and orientation within the cell so that early development can successfully proceed.

Bio: Michael Shelley is the Lilian & George Lyttle Professor of Applied Mathematics  at NYU and is Co-Director and co-founder of NYU’s Applied Mathematics Lab. He earned his Ph.D. in Applied Math from Arizona and was a postdoctoral fellow in Applied and Computational Math at Princeton.  His honors include a Presidential Young Investigator award, the APS Francois Frenkiel Prize, the SIAM Julian Cole Lectureship and fellowship in APS and SIAM.

April 24

Michael McAlpine, Assistant Professor, Department of Mechanical Aerospace Engineering,
Princeton University
"Biointerfaced Nanodevices"

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Abstract: The development of a method for interfacing high performance devices with flexible, stretchable, and biocompatible materials could yield breakthroughs in implantable or wearable systems. Yet, most high quality materials are hard or rigid in nature, and the crystallization of these materials generally requires high temperatures for maximally efficient performance. These properties render the corresponding devices incompatible with temperature-sensitive soft materials such as plastic, rubber, and tissue. Nanotechnology provides a route for overcoming these dichotomies, by altering the mechanics of materials while simultaneously improving their performance. In this talk, I will focus on two vital areas for interfacing nanodevices with soft materials: 1) biomimetic sensors for threat and disease detection, and 2) electromechanical sensing and energy harvesting. Our general approach in both cases involves the following key steps: first, materials selection, to identify a high performance material suitable for the application in mind; second, nanomaterials synthesis or fabrication; third, fundamental studies of the effect of scaling on nanomaterial properties; fourth, integration into high performance devices; and finally, interfacing these materials with soft substrates. The enhanced performance of nanomaterials coupled with bioplatforms may enable exciting avenues in fundamental research and novel applications, including on-body threat detection and energy harvesting.

Bio: Michael McAlpine began his appointment as Assistant Professor of Mechanical Engineering at Princeton in 2008 and is an associated faculty member with the Princeton Department of Chemistry and the Princeton Institute for the Science and Technology of Materials (PRISM). He received a B.S. in Chemistry with honors from Brown University in 2000 and a Ph.D. in Chemistry from Harvard University in 2006. His research has focused on nanotechnology-enabled approaches to hybridize high performance inorganic materials with flexible organics, for fundamental investigations in the biomedical and energy sciences. His work has been published in journals such as Nature and featured in major media outlets including Time Magazine. He has given talks at several universities and conferences, most notably to the JASONs Defense Advisory Group. He has received a number of awards, most prominently a TR35 Young Innovator Award, an Air Force Young Investigator Award, an Intelligence Community Young Investigator Award, a DuPont Young Investigator Award, and an American Asthma Foundation Early Excellence Award.