Speaker: Thomas Hughes, University of Texas
Topic: Isogeometric Modeling and Analysis of Fluid-structure Interaction with Particular Emphasis on Patient-specific Cardiovascular Simulation
Description: Isogeometric analysis is a recently developed methodology based on technologies that were originated in the field of computational geometry and widely used in design, graphics and animation. It includes standard finite element analysis as a special case, but offers other possibilities that are unique and powerful. It allows more precise and efficient geometric modeling, it simplifies mesh refinement, and it possesses superior approximation properties. Isogeometric analysis has been applied to numerous problems in solid and fluid mechanics. This presentation describes an isogeometric formulation for fluid-structure interaction of incompressible viscous flows and nonlinear solids. The fluid discretization derives from a residual-based variational multiscale formulation, applicable to laminar and turbulent phenomena. Both fluid and solid domains may undergo large motions, and the geometry and kinematics are fully compatible across fluid-structure interfaces. A strongly coupled, monolithic solution algorithm is adopted to preclude instabilities that often afflict weakly coupled procedures. A modeling system based on templates is developed for patient-specific cardiovascular anatomy. The procedures are applied to various patient-specific models including an abdominal aortic aneurysm, a thoracic aorta with left ventricular assist device (LVAD), a cerebral aneurysm, and a catheter based drug delivery system for coronary arteries.

Speaker: Robert M. McMeeking, University of California, Santa Barbara
Topic: The Mechanics of the Cytoskeleton and Cell Adhesions
Description: The mechanical characteristics of eukaryotic cells arise largely due to the cytoskeleton, which assembles and dissociates in response to biochemical signals. Actin protein chains form the most significant structural element in the cytoskeleton, with myosin motor proteins endowing such stress-fibres with contractility. It is notable that tensile stress seems to stabilise stress fibres against depolymerisation, so that there is an intimate coupling between the mechanics of the cytoskeleton and its biochemistry. In addition, stress-fibres interact with integrins that are the principal proteins in the adhesions transducting contractile force to the cell’s substrate or extracellular matrix. A model is presented for the processes of cytoskeleton stress-fibre formation, dissociation, contractility and their interaction with focal adhesions and mobile integrins. In the model, the polymerisation of the stress fibre network is driven by a signal that rises quickly and then decays exponentially, causing the stress-fibre formation process to be self-limited. Subsequent depolymerisation of the stress-fibers occurs spontaneously, unless it is inhibited by tension, which is generated by the constrained contractility of the actomyosin fibres. Consequently, the stress-fibre component of the cytoskeleton is most robust when it is able to generate tensile stress by contracting against an external constraint. Examples characterising the model are given, illustrating the mechanical features and behavior of eukaryotic cells. The model is able to simulate the cell’s differing behavior when attached to a stiff substrate compared to its activity on a compliant substrate. In addition, a cell’s response to a measurement protocol can be predicted with the model, such as when a bead is attached to the cell and displaced outwards by an external force, causing a reconfiguration of the cytoskeleton. Additional phenomena that are successfully simulated with use of the model include the orientation of the stress-fibres in cyclically strained cells, and their orientations when a cell is adhered to a shaped pattern of fibronectin.

10:00am-11:30am
2-3-5 Vibration and Acoustic in Biomedical Applications

Speaker: Jeffrey Fredberg, Harvard School of Public Health
Topic: A Hard Day in the Life of a Soft Cell
Description: With every beat of the heart, inflation of the lung, or peristalsis of the gut, cell types of diverse function are subjected to substantial stretch. But what physical laws govern the abilities of the cytoskeleton to deform, contract, and remodel? New data support the idea that the cytoskeleton is at once a crowded chemical space and a fragile soft material in which the effects of biochemistry, molecular crowding, and physical forces are complex and inseparable, yet conspire nonetheless to yield remarkably simple phenomenological laws. These laws appear to be universal and thus comprise a striking intersection between the worlds of cell biology and soft matter physics.

10:00am-11:30am
13-20-1 Keynote Speech by Meyya Meyyappan, NASA

Speaker: Meyya Meyyappan, NASA Ames Research Center
Topic: Nanotechnology: Practical Systems and Integration with MEMS
Description: There are strong nanotechnology research programs across the world in the fields of chemical sensors, biosensors, instrumentation, electromechanical devices, actuators, and other nanodevices. Nanoscale is not a human scale. In many cases, practical systems demand seamless integration of nano-micro-macro scaled components and processes. Examples of this using carbon nanotube based chemical and biosensors and instrumentation will be presented. Opportunities for various inorganic nanowires in several applications will also be highlighted. The author thanks all his past and present NASA Ames colleagues for their contributions to the NASA application development efforts.

Speaker: Robert Clark, Duke University
Topic: From Aircraft to Biomolecules: Crossing Disciplinary Boundaries and Dimensional Scales

1:45pm-3:15pm
13-20-2 Keynote speech by Professor Ted Belytschko

Speaker: Ted Belytschko, Northwestern University
Topic: Multiscale Computations of Fracture - When Does Flaw Tolerance Occur
Description: The prediction of the strength of materials from fundamental principles poses an interesting challenge. Since bond breaking is involved, a first principles attack on the problem requires quantum mechanical modeling at the bond breaking level. However, it has become apparent that even at the nanoscale, strength seems to be dominated by defects in the specimen. To study such defects in term so basic physics, quantum mechanics is usually necessary to model bond breaking. However, to account for bond breaking, the models must be substantially larger than can be treated by quantum mechanics with modest computational power. Therefore either coarse-graining or concurrent coupling methods must be used. Here a coupled method for quantum/molecular/continuum mechanics is described. A method for concurrent coupling quantum mechanics with molecular mechanics is summarized, as well as methods for coupling molecular mechanics with continuum mechanics. [Ref. 1]. In addition, a semiconcurrent or hierarchical method for failure analysis is described. This method is motivated by the fact that standard coarse-graining methods are not applicable to failure because at the macroscale, failure results in loss of ellipticity in static problems.[Ref 2]

The coupled method is then applied to the analysis of the strength of crystalline carbon nanotubes and nanoscale graphene sheets with defects. Both holes and slit like defects that are similar to cracks are considered. The results show that the strength in crystalline carbon diminishes rapidly with flaw size and in fact agrees quite closely with the Griffith formula when the surface energy is obtained by a quantum calculation. Computations of the strength of amorphous carbon nanostructures have also been made.[Ref 3] The environment-independent interatomic potential of Marks, which is well suited to amorphous carbon, is used for modeling amorphous carbon These manifest much less decrease in strength with increasing flaw size, indicative of a flaw tolerance.

References [1] R. Khare, S.L. Mielke, J.T. Paci, S. Zhang, R. Ballarini, G.C. Schatz, and T. Belytschko, “Coupled quantum mechanical/molecular mechanical modeling of the fracture of defective carbon nanotubes and grapheme sheets,” Physical Review B, v. 75, issue 7, article number 075412, 2007. [2]T. Belytschko, S. Loehnert, and J.-H. Song, “Multiscale aggregating discontinuities: A method for circumventing loss of material stability,” International Journal for Numerical Methods in Engineering, 73:869-894, 2007 [3] Q. Lu, N. Marks, G.C. Schatz, and T. Belytschko, “Nanoscale fracture of tetrahedral amorphous carbon by molecular dynamics: Flaw size insensitivity,” Physical Review B, v. 77, issue 1, article number 014109, 2008.

Speaker: Kemo Hanjalic, Delft University of Technology, Netherlands
Topic: Turbulence Modeling