MEAM Seminar Series Spring 2010
Seminars are held on Thursdays at 2:00 p.m. in 337 Towne Building (220 South 33rd Street), unless otherwise noted. Click the date of each seminar to find out additional information about the speaker and topic.
Speaker: Martin I. Idiart
Area Departmental Aeronáutica, Facultad de Ingeniería
Universidad Nacional de La Plata, Argentina.
Predicting the ductile failure of metals in terms of void nucleation, growth and coalescence requires a constitutive model for viscoplastic porous media. We present a new model obtained by iterated dilute homogenization and certain theoretical constructions known as 'infinite-rank laminates.' The resulting estimates for the dissipation potential have the distinguishing feature of being realizable, and are therefore guaranteed to satisfy all pertinent bounds and convexity requirements. Moreover, the model accounts for the evolution of porosity as well as for the deformation-induced pore anisotropy. Illustrative results are presented for two-dimensional power-law materials undergoing finite deformations. It will be argued that the new estimates provide more reliable predictions for viscoplastic porous media than Gurson-type models.
Host: Pedro Ponte Castaneda
Speaker: Timothy Fisher
Professor of Mechanical Engineering, Purdue University
Spatially confined forms of carbon (e.g., carbon nanotubes, graphite) exhibit very unique physical properties at the individual element level. However, harnessing these properties in useful devices and components has often proven to be very challenging. This talk will describe an approach in which carbon nanomaterials are grown directly in array form to create structures that promise superior performance at practical engineering scales. Typically, the primary challenges in applications involve scaling of the materials through self-assembly and transport processes at heterogeneous interfaces. Approaches to circumvent these issues include the use of metallic additives, intentionally introduced defects, and graphene elements. Applications to be discussed include vertical carbon nanotube field-effect transistors, heat transfer at solid and fluid interfaces, composite materials, biosensors, and photo-thermionic electron emission.
Host: Jennifer Lukes
Howard A. Stone
"Surprises in viscous flows: from charged drops to bacteria in curved channel flows"
Speaker: Howard A. Stone
Donald R. Dixon ’69 and Elizabeth W. Dixon Professor in Mechanical and Aerospace Engineering, Princeton University
Laminar viscous flows are well understood, as evidenced by the extensive discussion in standard textbooks. In this talk I present some examples of laminar flows studied in my group where the results may seem surprising. In particular, I describe experiments of drops in an electric field where oppositely charged drops fail to coalesce if the electric field is strong enough. In addition, I describe experiments with solutions of bacteria in flows in curved microchannels. Thread-like structures of biofilm are formed and the origin for these structures is traced to three-dimensional flow features in the neighborhood of corners.
Sheri D. Sheppard
"What we have learned about educating engineers: A field report from the Carnegie Study"
Please note that this seminar is being held on a MONDAY at 2:00 pm in Wu and Chen Auditorium, Levine Hall.
Speaker: Sheri D. Sheppard
Professor of Mechanical Engineering and Co-Director, Center for Design Research Stanford University
The Carnegie Foundation for the Advancement of Teaching* has embarked on an ambitious research effort to study preparation for the professions in five fields—including law, engineering, the clergy, medicine, and social work—as well as teacher preparation. These studies are collaborations with educators and practitioners in each profession with the aim to better understand and describe the state of professional education in each field.
The Foundation’s study of engineering education aims to describe and analyze both typical and exemplary approaches to teaching and learning engineering at the outset of the new century. It addresses the major questions of what engineering education looks like and how it prepares practitioners by exploring what lies inside the “black box” of preparation for the engineering profession. These questions are addressed in ways that will assist educators, students, university leaders, and practicing engineers to prepare future engineers more effectively. The study also provides an important point of linkage to foster an exchange of insights and best practices among and between disciplinary fields, and both graduate and undergraduate programs.
The recently published Educating Engineers: Designing for the Future of the Field is the final report from the Foundation’s study of engineering. As described in the report, the study’s examination of curricular and teaching strategies yielded questions about the alignment of engineering programs with the demands of today’s professional engineering practice. While describing engineering education from within the classroom and the lab, the report offers new possibilities for teaching and learning.
As the Senior Scholar at the Foundation leading the study on engineering education, I will describe the dominate model of engineering education we observed, outline improvements to better align educational practices with the needs to today’s engineering professionals, and propose an alternate (and fairly radical) model suggested by new understanding of how people learn. Ample time will be allotted in the session for Q&A, and discussion.
*The Carnegie Foundation for the Advancement of Teaching focuses on the scholarship of teaching and seeks to generate discussion and promulgate sustainable, long-term changes in educational research, policy and practice. The Foundation’s programs are designed to foster deep, significant, lasting learning for all students and to improve the ability of education to develop students' understanding, skills and integrity. The study described in this talk was funded by The Carnegie Foundation for the Advancement of Teaching and The Atlantic Philanthropies.
"Manipulating motion with light: Cavity optomechanics in nanophotonic structures"
Please note that this seminar is being held on a MONDAY at 2:00 pm in room 227 of the Towne Building.
Speaker: Qiang Lin
California Institute of Technology
Optical control of mechanical motion underlies a variety of applications ranging from laser cooling to optical tweezing, playing a critical role across many multidisciplinary fields extending from atomic physics to molecular biology. In this talk, I will discuss our recent progress in enhancing the relatively weak force exerted by photons through specially designed coupled-disk nano-optomechanical structures. The dramatically enhanced optical force introduces strong nonlinear coupling between the mechanical and optical degrees of freedom of nanophotonic cavities, enabling precise engineering of the optomechanical properties and sensitive probing of the mechanical motion through the optical wave dynamics. This provides a new testbed to study fundamental physics such as quantum optomechanical dynamics at the mesoscopic scale, and also allows to realize novel optical functionalities unprecedented by conventional approaches. I will give a brief overview of the current state of optomechanical research, then will move on to discuss our work on how to use this type of force to excite regenerative mechanical oscillation, cool the mechanical thermal Brownian motion, optically modify the mechanical rigidity, and to actuate EIT-like (electromagnetically-induced transparency) coherent mixing of optomechanical excitations, as well as how to utilize these cavity-optomechanical effects for on-chip photonic signal processing such as broadband wavelength routing, fast optical switching, and other applications.
Speaker: Richard D. James
Russell J. Penrose Professor and Distinguished McKnight University Professor
University of Minnesota
The most important deformations in solid mechanics are those that represent the bending, twisting and extension of beams. The most important flows in fluid mechanics are viscometric flows. In both cases these are the motions that, when compared with the corresponding experiments, are used to measure the material constants. We give a universal molecular level interpretation of these motions. We argue that all these motions are associated at molecular level with a time-dependent invariant manifold of the equations of molecular dynamics. The presence of this manifold can be used to simplify molecular-level computations, and deliver dynamic properties in the absence of a constitutive relation. Its presence also suggests a modification of the principle of material frame-indifference, a cornerstone of nonlinear continuum mechanics. Interesting links to theories of turbulence, to the kinetic theory of gases (i.e., the Boltzmann equation), and to the dynamics of nanostructures will be discussed. Joint work with Kaushik Dayal, Traian Dumitrica and Stefan Mueller.
Host: Prashant Purohit
Speaker: Cameron Riviere
Associate Research Professor, The Robotics Institute
Carnegie Mellon University
Accuracy enhancement for micromanipulation has the potential to produce significant benefits in clinical microsurgery, cell micromanipulation, and other applications. The goal of enhancing accuracy while also minimizing cost and maximizing ease of use has led my laboratory to develop a fully handheld instrument, known as "Micron," which performs active compensation of erroneous motion such as hand tremor. The instrument estimates the undesired component of its movement, and compensates by deflecting its tip using a piezoelectrically-actuated three-degree-of-freedom parallel manipulator. Feedback sensing for control is provided by an optical tracker constructed in our laboratory. The tracker uses two position-sensitive detectors mounted near the workspace to detect three LED's on the manipulator and one on the handle, providing six-degree-of-freedom tracking with resolution of 4 microns at 2 kHz sampling. The system has been augmented with a stereo pair of cameras that view the workspace through the operating microscope, enabling vision-based control modes. Current research involves moving beyond the original application of tremor suppression to investigate the wider range of possibilities that such a system offers, including local motion scaling, position-based adaptations of virtual fixtures, and automation of tasks. The talk will describe the design and operation of Micron, and will present experimental results from a variety of control modes and application domains.
Kevin T. Turner
"Ultracompliant single-crystalline silicon substrates: Mechanics and manufacturing"
Please note that this seminar is being held on a Tuesday at 11:00 am in room 337 of the Towne Building.
Speaker: Kevin T. Turner
Assistant Professor, Department of Mechanical Engineering
University of Wisconsin-Madison
Reducing the thickness of single-crystalline semiconductor substrates, on which integrated circuits are fabricated, significantly increases the mechanical compliance and enables new classes of high performance flexible electronics, unique 3-D stacking strategies, and novel materials integration approaches. Here, the fabrication of and growth on ultracompliant silicon substrates with thicknesses of less than one micrometer will be discussed. First, the mechanics of microtransfer printing processes, in which a stamp is used to retrieve, transfer, and print thin semiconductor layers, will be presented. Transfer printing requires careful manipulation of interfacial adhesion in order to ensure high yield in retrieval and printing. Combined computational and experimental fracture mechanics studies have been performed to improve process performance by elucidating the underlying mechanics. Second, it will be shown that ultrathin freestanding silicon substrates provide unique opportunities to engineer the growth of strained epitaxial films. Specifically, three-dimensional SiGe islands grown on freestanding crystalline silicon sheets self-order due to strain fields induced in the compliant substrate during growth. A mechanics analysis demonstrates the driving force for this ordering and shows that it is unique to ultrathin substrates with thicknesses below 50 nm. Finally, prospects and challenges for thin crystalline silicon substrates will be highlighted.
Speaker: Yonggang Huang
Joseph Cummings Professor of Civil and Mechanical Engineering
Although buckling has historically been viewed as a mechanism for structural failure, pioneering work in the late 1990's showed that buckling can be controlled in micro and nanoscale systems to generate interesting structures with well defined geometries and dimensions in the 100 nm - 100 ?m range. These observations created renewed interest in this area which persists today, with many active research groups currently exploring basic scientific aspects as well as applications in stretchable electronics, micro and nanoelectromechanical systems, tunable phase optics, force spectroscopy in cells, biocompatible topographic matrices for cell alignment, high precision micro and nano-metrology methods, and pattern formation for micro/nano-fabrication. In these systems, controlled buckling is realized in thin films deposited, typically by vapor phase or physical transfer processes, onto prestrained elastomeric substrates. Depositing a film on this stretched substrate and then releasing the prestrain can create 'wavy' structures.
Mechanics plays a key role in this development since it provides not only the fundamental understanding of deformation and buckling mechanisms but also simple analytical solutions that are very useful to the design and fabrication. Several mechanics problems related to stretchable electronics will be discussed in this talk, including wavelength and amplitude of stretchable silicon film , controlled buckling mode , finite deformation effect , and 2D herringbone pattern . Their applications include stretchable, foldable and twistable circuits [5-6], electronic-eye camera , flexible LED display , transfer printing , flexible silicon solar microcell , and curvilinear electronics .
1. Khang et al., Science 311, pp 208-212, 2006.
2. Sun et al., Nature Nanotechnology 1, p 201, 2006
3. Jiang et al., PNAS 104, p 15607, 2007
4. Choi et al., Nano Letters 7, p 1655, 2007
5. Kim et al., Science 320, p 507, 2008
6. Kim et al., PNAS 105, p 18675, 2008 (cover article)
7. Ko et al., Nature 454, p 748, 2008 (cover article)
8. Park et al., Science 325, p 977, 2009
9. Meitl et al., Nature Materials 5, p 33, 2006
10. Yoon et al., Nature Materials 7, p 907, 2008 (cover article)
11. Rogers and Huang, PNAS 106, p 10875, 2009
Speaker: Sanjay Govindjee
Professor of Civil Engineering and Chancellor's Professor
University of California at Berkeley
Many material systems admit morphological changes under mechanical, electrical, thermal stimuli or other generalized forces. Such behaviours are broadly classified as phase transformations – the study of which goes back at least 100 years in modern thermodynamic terms. These phenomena have equally well been exploited for a long time for productive engineering purposes. Shape memory alloys and superelastic alloys are particular material systems that admit a unique subset of such morophological transformations and are for this reason very attractive for the design of novel engineering systems. One impediment, however, to effective design with such materials is the lack of a general-purpose constitutive framework suitable for use in solving boundary value problems using analysis software such as FEA programs. In the past two decades there has been an explosive interest in this issue with many new experimental results being reported along with many important new developments in modelling.
In this talk, I will broadly discuss the physics of the systems of interest from the molecular to the macroscopic scale, touching upon discrete as well as continuum issues of behaviour. A review of the major modelling approaches of the past will be presented with a discussion of their strengths and weaknesses – this will include physics-style as well as engineering-style models. Lastly a presentation will be given of the modern concept of relaxation and its promise and application to the generation of well-posed macroscopic models for phase transforming systems. Of particular interest will not only be models that can estimate stress-free transition states but those that can reliably predict stressed transition states. The talk will close with a brief discussion of open problems in the modelling of such material systems.
Mo Li, Postdoctoral Associate
"Nanomechanics meets nanophotonics: harnessing optical forces on a silicon chip"
Please note that this seminar is being held at 9:00 am in room 337 of the Towne Building.
Speaker: Mo Li
Postdoctoral Associate, Department of Electrical Engineering
Nanomechanics and nanophotonics are among the most exciting areas of nanoscience. By generating and controlling a new type of gradient optical force in integrated photonic systems, we are able to seamlessly integrate these two fields together to form the new nano-optomechanical systems (NOMS). In this talk, we first demonstrate all-optical operation of nanomechanical resonators embedded in silicon waveguide circuits using optical forces. Further we experimentally prove the theoretical prediction that this waveguide optical force is bipolar – its direction can be tuned to be attractive or repulsive by changing the relative optical phase of coupled lightwaves. Subsequently, we show exploitation of optical forces in a variety of interesting optomechanical structures, including photonic crystal and micro-disk optical resonators. Harnessing the optical forces on a silicon chip enables new paradigms of nanophotonic and nanomechanical devices, such as all-optical switching, tunable nanophotonics, radio-frequency photonics and large-scale integration of NEMS.
Speaker: Gang Bao
Professor and Robert A. Milton Chair in Biomedical Engineering
College of Engineering Distinguished Professor
Georgia Institute of Technology
The ability to detect, localize, quantify and monitor the expression and dynamics of specific RNA and proteins in living cells in real-time offers unprecedented opportunities for biological and biomechanics studies, and medical diagnostics. This requires the development of sophisticated probes to detect intracellular biomolecules with high specificity and sensitivity, and convert target recognition directly into a measurable signal. We have developed nano-probes for different applications, including molecular beacons for sensitive detection of RNA in living cells, quantum dot – fluorescent protein bioconjugates for measuring intracellular environment, and protein tagging and targeting strategies for studying protein complexes and cellular machines. In this presentation I will demonstrate the design of molecular beacons for targeting specific RNAs in living cells, and their application to detect cancer stem cells and characterize viral infection. I will illustrate the beacon design issues including target accessibility, probe-target interactions, and the background signal in long-time monitoring of mRNAs in living cells. The application of nano-probes to studies of nucleoprotein machines will also be discussed.
Udo D. Schwarz
"A focus on friction: From atomically resolved static forces to scaling laws for superlubric sliding
Speaker: Udo D. Schwarz
Associate Professor of Mechanical Engineering
Even after centuries of research, the atomic scale origins of friction are still poorly understood. Therefore, new tools and methods have been introduced in the last two or three decades that allow novel aspects and systems to be investigated. Here, we discuss results from two original approaches that we developed in recent years. In the first approach, we studied the contact area dependence of friction at the nanometer scale. Surprisingly, we find two coexisting frictional states: While some particles show finite friction increasing linearly with the interface areas, other particles assume a state of virtually frictionless sliding . Analysis suggests that this state might be due to ‘superlubricity’, a theoretically predicted state where the lattice mismatch at the interface causes a decrease of shear stress with increasing contact area that ultimately leads to vanishing friction. In the second approach, we applied a new force microscopy based imaging method to resolve normal and lateral surface forces in all three dimensions with picometer and piconewton resolution . For graphite, the lateral forces are found to be heavily concentrated in the hollow sites of the lattice, surrounded by a matrix of very small forces. It will be speculated that this astonishing localization may be a reason for graphite’s excellent lubrication properties.
 Dietzel et al., Phys. Rev. Lett. 101, 125505 (2008).
 B. J. Albers et al., Nature Nanotechnology 4, 307 (2009).
"Transport Phenomena Associated with Inkjet Printing of Colloidal Drops for Printable Electronics Fabrication"
Speaker: Ying Sun
Assistant Professor of Mechanical Engineering and Mechanics
Printable and flexible electronics, ranging from low-cost consumer products, solar cells, and low-power lighting to highly specialized small scale sensors and healthcare devices, have become a multi-billion dollar industry impacting the energy, healthcare, entertainment, security, and military sectors. Roll-to-Roll fabrication using inkjet printing and direct laser patterning of flexible substrates is an enabling technology that will provide desired high-volume, low-cost production of flexible electronic devices. The intrinsic limits on the spatial accuracy of inkjetting devices, wetting, de-wetting, contact line pinning, interfacial instabilities, microflows within the deposited drop, and the self-assembly of particulate matter during drop evaporation all contribute to the lack of precise control of deposited electronic materials and an inability to meet resolution requirements.
This talk summarizes our combined modeling and experimental investigations on how the dynamics of specific transport processes impact the deposited microstructure of inkjet printed functional materials on flexible substrates. In contrast to previous experimental studies that have only been concerned with post-mortem analysis of the deposited structures, we integrate ultrafast confocal microscopy and micro-particle image velocimetry (m-PIV) systems to monitor in real-time particle self-assembly during the evaporation phase. Our integrated confocal m-PIV system is used to characterize the fluid transport and deposition morphology as a function of physicochemical properties of the colloidal suspension, substrate materials, surface modification methodology, surface roughness and temperature, and inkjetting parameters. A multiphase particle suspension lattice Boltzmann model has been developed to correlate with experimental observations and to provide fundamental understanding of materials behavior under process conditions, the synthetic capabilities for preparing well-defined new materials, as well as morphology analysis and development of processing tools.
Nandan Nerurkar, PhD Candidate
"Integrating theoretical and experimental methods for multi-scale tissue engineering of the annulus fibrosus of the intervertebral disc"
Please note that this seminar is being held on a Tuesday at 1:30 pm in Levine Hall, Room 307.
Due to the hierarchical organization of the intervertebral disc, successful recapitulation of its functional behavior requires replication of anatomic form and physiologic function over a wide range of length scales. In this work, we employ the technology of electrospinning for tissue engineering of the annulus fibrosus (AF) of the intervertebral disc using a multi-scale approach. Throughout, mathematical modeling is used to understand material behavior, quantify functional growth, and to guide comparison between engineered AF constructs and native tissue benchmarks. The proposed work will span from sub-lamellar investigations of cell-mediated extracellular matrix deposition to engineering of an angle-ply fiber-reinforced hydrogel composite that parallels the macroscopic structural organization of the intervertebral disc. Emphasis is placed on reconciling compositional and structural observations with their macroscopic mechanical implications and utilizing models to understand these relationships.
Spring Berman, PhD Candidate
"Abstractions, Analysis Techniques, and Synthesis of Scalable Control Strategies for Robot Swarms"
Please note that this seminar is being held on Friday, April 16 at 3:30 pm in Levine Hall, Room 307
Speaker: Spring Berman
Advisor: Vijay Kumar
Tasks that require parallelism, redundancy, and adaptation to dynamic, possibly hazardous environments can potentially be performed very efficiently and robustly by a swarm robotic system. Such a system would consist of hundreds or thousands of anonymous, resource-constrained robots that operate autonomously, with little to no direct human supervision. The massive parallelism of a swarm would allow it to perform effectively in the event of robot failures, and the simplicity of individual robots facilitates a low unit cost.
Key challenges in the development of swarm robotic systems include the accurate prediction of swarm behavior and the design of robot controllers that can be proven to produce a desired macroscopic outcome. The controllers should be scalable, meaning that they ensure system operation regardless of the swarm size. In this talk, I will present a comprehensive approach to modeling a swarm robotic system, analyzing its
performance, and synthesizing scalable stochastic control policies that cause the swarm members to collectively achieve a target objective. The control policies are decentralized, computed a priori, implementable on robots with limited sensing and communication capabilities, and have theoretical guarantees on performance. I will demonstrate the application of this approach to the design of a swarm task allocation
strategy that does not rely on inter-robot communication, a reconfigurable manufacturing system, and a multi-robot collective transport system. My approach is inspired by the self-organized behavior of natural swarms such as ant colonies, which
achieve complex tasks through the local interactions of many simple individuals.