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Research Highlights |
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Robert W. Carpick |
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| Rob conducts his research at the intersection of mechanics, materials, and physics. He is an expert in experimental nanomechanics and nanotribology (friction, adhesion, and wear). His lab has developed novel advanced scanning probe microsopy tools, used to investigate the fundamental nature of materials in contact. Rob has done seminal work on nanoscale characterization of friction for many important materials, including ultra-thin organic films, solid single crystal and thin film surfaces, and polymeric materials. |
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| An atomic force microscope cantilever fabricated out of nanocrystalline diamond has a nano-scale probe tip that is far more wear-resistant than silicon and silicon nitride. This was produced in collaboration with Advanced Diamond Technologies and U. Wisconsin-Madison through a National Science Foundation STTR program. |
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Simulations of deformable biological membranes and vesicles
Dr. George Biros: His team is developing fast integral equation methods for the simulation of the dynamics of deformable vesicles in viscous flows. Deformable vesicles are models of biological capsules and cells; vesicle simulation tools will lead to a better understanding of biological particulate flows. Using potential theory, they can derive a system of integro-differential equations for the motion of the vesicles, which is driven by hydrodynamic forces and elastic forces due to tension and bending. The team has developed a semi-implicit scheme that circumvents stability constraints of existing schemes and has nearly optimal algorithmic complexity. The figures below represent flow streamlines due to elastic relaxation for the cases of one and three vesicles immersed in a stationary fluid.
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2D simulations of the dynamics of four vesicles interacting with a shear flow; the blue lines are flow streamlines and the red lines represent the vesicle boundaries.
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Rod theories for DNA and biopolymers
Dr. Prashant Purohit: Coarse-grained mechanics models for macromolecular complexes are beginning to see wide-spread use to further our understanding of biological systems. Rod theories for polymers and shell theory for biological membranes are two examples of such models that have been used to describe diverse behavior of cellular components such as DNA, actin, microtubules, cell membranes etc. We have used rod theory for DNA to describe and predict important events in the life cycle of certain bacterial viruses and have shown that simple physical models are sufficient to explain several features in the DNA packaging and ejection processes in viruses. Our current research is focused on understanding how the mechanics of DNA is crucial in the regulaton of genes through protein mediated cooperative interactions between distant sites on the genome. |
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Schematic of a bacterial virus ejecting its DNA into a solution of polyethyleneglycol(PEG) molecules. The concentration of PEG can be altered to change the osmotic pressure and hence control the amount of DNA ejected from the virus. |
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Schematic of the DNA loop formed by the lambda repressor. Such loops are implicated in the regulation of genes in bacteria such as E.Coli. The energetics of loop formation is critical in determining the probability that the gene is switched on or off. |
More on Dr. Prashant Purohit
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Fluidic manipulation in carbon nanotubes
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Dr. Jennifer Lukes: Nanofluidic control of minute quantities
of liquid has tremendous implications for biotechnology and
biochemical analysis, with a wide array of potential applications
including drug discovery, targeted deposition of optical probes,
and manipulation of entrained particles and macromolecules.
Although considerable progress has been made recently in the
ability to pump and experimentally observe fluids at the nanoscale,
much is still not understood about transport in nanochannels,
where noncontinuum behavior such as pulsatile fluidic transport,
dramatically increased effective viscosity, and 'stick-slip'
flow emerge. The objective of this project is to obtain a
fundamental understanding of the influence of external fields
on the transport of confined fluids. Specifically, atomistic
molecular dynamics simulations (Fig. 1) are being used to
model the transport of polarizable and charged fluids through
carbon nanotubes as a function of concentration, temperature,
surface charge, and electric field. This work will provide
information useful for the design of innovative new mechanisms
for nanoscale pumping and control.
Funding: Nano-Bio Interface Center
More on Dr.
Jennifer Lukes |
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An
atomic scale model of fluid flow
in carbon nanotubes. |
PDE-constrained Optimization
| Dr. George Biros: PDE-constrained optimization is a frontier
problem in computational science and engineering. All PDE-constrained
problems share the difficulty that PDE solution is just a subproblem
associated with optimization. Thus, the optimization problem
is often significantly more difficult to solve than the simulation
problem. We are particularly interested in large-scale problems
that require parallel computing to make them tractable. |
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The figure illustrates an example of a PDE-constrained
optimal control problem. The constraints are the steady incompressible
Navier-Stokes equations, modeling a viscous flow around a cylinder.
The objective is to minimize the energy dissipation. The controls
are injection points (velocity Dirichlet boundary conditions)
on the downstream portion of the cylinder surface. The left
image depicts an uncontrolled flow. The right image depicts
the optimally-controlled flow. Injecting fluid entirely eliminates
recirculation in the wake of the cylinder, thus minimizing dissipation.
The optimization problem was solved on 256 processors on a Cray
T3E-900 at the Pittsburgh Supercomputing Center.
More on Dr. George Biros |
Human Augmentation for Control of Smart Vehicles: Application
to Rehabilitation
Dr. Kumar's group is developing an intelligent system that augments
human skills in navigation tasks achieving performance that is far
beyond manual control. Our SmartChair
allows the user could interact with and control the system by touching
many virtual displays that are projected over the lap tray (or armrest
or any convenient surface). Information about the environment, including
features and landmarks behind th user, can be accessed at several
different levels (raw imagery, panoramic images, a two-dimensional
overhead map, or a three-dimensional reconstruction of the wheelchair
in the current environment). There are two main thrusts to this
project. First, we are also developing a vision-based human-computer
interface based on a tightly coupled virtual display projector and
a camera monitoring system, that can be easily configured and adapted
to different working environments. A second contribution of the
proposed work is a set of software and hardware tools for human
augmented control of computer controlled intelligent machines. The
main research issues center on the algorithms and software necessary
for human computer interaction at different levels of resolution
and representation, and for computer mediated control of the wheelchair.
More on the SmartChair.
Micro and Nano Fluidics
One of the goals of Dr. Bau's research on Micro
and Nano fluidics is to develop the science and technological
base needed for the effective use of micro and nano-fluidic systems.
To this end, his group is studying complex flow phenomena involving
single phase and particle-laden (i.e., beads, cells, and macromolecules)
flows driven by pressure, electric, and magnetic fields, and by
surface tension.
More on Microfluidics
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