Department of Mechanical and Aerospace
Engineering
Abstracts
2003 - 2004
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479 EBU-II
Dr. Upal Ghosh
Department of Civil and Environmental
“Microscale Association of Organic Contaminants to Sediment
Particles and Implications for Environmental Risk Management”
Persistent
organic contaminants like polychlorinated biphenyls (PCBs) are widespread in
sediments and pose risks to humans and wildlife and the nation's economy
through deterioration of water quality.
The magnitude of the sediment contamination problem in the
In this research we seek to close the knowledge gap between
sediment chemistry and toxicity, and apply new insights to innovative and
practical strategies for management of contaminated sediments. We have applied microscale
measurement techniques to examine the location and association of organic
contaminants in sediments at the sub-particle scale. We have found that in the
presence of natural carbonaceous particles such as coal, coke, and charcoal in
sediments, hydrophobic contaminants accumulate in these types of particles
making the bound contaminants relatively unavailable to benthic organisms and
for transport in the water column. We show that sediment rich in black
carbonaceous particles, either naturally occurring or as an amendment, has much reduced bioavailability for organic
contaminants. We are applying this
mechanistic knowledge to assess a novel sediment management strategy. We are finding that the addition of a strong sorbent like granular activated carbon to contaminated
sediments may be a cost-effective, in-situ management strategy. The added carbon acts as a strong binding
agent for the contaminants reducing contaminant transport and bioavailability
to organisms. Such a management strategy is especially attractive for large
areas of low level contamination. This management strategy requires
mechanistic understanding of linked physical and biological processes and using
such information in conceptual and quantitative models to understand the
long-term efficacy of the in-situ stabilization process.
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479 EBU-II
Dr. Daniel M. Tartakovsky
“Flow and Transport in Highly
Heterogeneous Aquifers: Coping With Uncertainty”
Although it has long been recognized that simulations of most physical systems are fundamentally stochastic, this fact remains overlooked in most practical applications. Even essentially deterministic systems must be treated stochastically when their parameters, boundary and initial conditions, or forcing functions are under-specified by data. The method of random domain decomposition (RDD) provides a powerful tool for dealing with the kinds of spatially heterogeneous random processes that typically appear in realistic simulations of physical systems. RDD is based on a doubly stochastic model in which the problem domain is decomposed according to stochastic geometries into disjoint random fields. The stochastic decomposition is determined by variations in the parameter space based on additional (uncertain) geometric information that can be derived from new characterization techniques and also from expert knowledge. Previous work has tended to concentrate on spatially homogeneous parameterizations, or at most on heterogeneous parameter fields whose geometry is assumed known with certainty. This is almost never the case in natural systems. On the other hand, random domain decomposition allows us to estimate system states when heterogeneous parameterizations depend on realistic geometric uncertainty.
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Thursday, February 19, 2004
2:30 p.m.
479 EBU-II
Dr. Andrea Cortis
Department of Environmental Sciences and Energy Research
Weizmann Institute of Science
“Anomalous Transport in Multiple-Scale Heterogeneous
Porous Media”
The
behavior of chemical species as they are transported through heterogeneous
porous media is considered. Field and
laboratory experiments clearly indicate that this transport cannot be treated
by means of the classical Fickian-base
advection-dispersion equation. Deviation
from this behavior is labeled as “anomalous” and can be attributed to the
(multiple scale) heterogeneities of the porous matrix through which the tracer
element migrates. This anomalous
behavior can be explained and quantified in the framework of the Continuous
Time Random Walk (CTRW) theory. In this
talk, the basic concepts and mathematical developments of the CTRW are
presented, and application to laboratory and field-related experiments is
demonstrated.
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479 EBU-II
Mickaël Tanter,
Ph.D.
Laboratoire Ondes et
Paris
“New Advances in Ultrasonic Medical Imaging and Therapy”
This talk will focus on two
applications we develop in the Laboratory Waves and Acoustics,
Ultrasonic imaging or H.I.F.U. systems capabilities
are strongly dependent on the focusing quality of the ultrasonic beam. In the case of brain imaging or therapy, the
skull strongly degrades the focusing pattern quality by introducing high phase
and amplitude aberrations of the wavefront. In the past, we proposed several adaptive
focusing techniques in order to correct this degradation of the beam. For
H.I.F.U. treatments, a small acoustic hydrophone could be placed near the
target during the biopsy. Recording the Green's function relating this
hydrophone to the elements of the ultrasonic array enables to recover
information about skull aberrations. From the knowledge of this Green's
function, several adaptive focusing techniques were envisioned and studied such
as time reversal combined with amplitude compensation, inverse filtering or
phase conjugation. These minimally invasive techniques can be replaced by a
totally non invasive approach if ones can rely on information about the skull
bone structure. We proposed recently such a focusing technique based on prior
acquisition of CT scans of the skull patients. CT images are converted into
acoustic parameters and used in a full 3D finite differences simulation
allowing to compute accurately and virtually the
ultrasonic propagation through bone and so to predict and correct the
aberrations for real experiments. A 300 elements random sparse array for transcranial brain HIFU was recently built and allows for
the first time very high precision transcranial
surgery.
The second part of the talk concerns the estimation of viscoelastic properties of human soft tissues using a worldwide unique ultrafast echographic system. Indeed, current imaging technologies fail to visualize very fast transient motion occurring in human tissues due to internal (heartbeat) or external (shocks) vibrations. Nevertheless, such transient displacements are of great interest as they reveal visco-elastic properties of tissues. For this purpose, an ultrafast ultrasonic scanner producing more than 5000 frames.s-1 was developed that realizes complete movies of organs motion meanwhile a conventional scanner produces a single image. Using a breakthrough emission sequence, the acoustic radiation force produced by ultrasonic beams is remotely producing supersonic moving shear sources in soft tissues. Such virtual palpating fingers are activated to induce shear propagation in a Mach cone and reveal hard inclusion deeply in tissues.
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479 EBU-II
Dr. Scott C. James
Geohydrology Department
Sandia National Laboratories
“Modeling Colloid and Contaminant Co-Transport in
Fractured Media”
Hazardous
wastes, especially radioactive materials, are often disposed of in canisters
and buried in deep, fractured, low–permeability rock formations (e.g.,
granites, slates, salts, and clays). Primary examples include the Waste
Isolation Pilot Plant and the Geologic Repository for the Disposal of Spent Nuclear
Fuel and High–Level Radioactive Waste at
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Information: (858) 534-0113