Conferences, Lectures, & Seminars
Events for March
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Closing the Gap on Missing Sources of Organic Aerosol in the Atmosphere
Wed, Mar 02, 2011 @ 02:00 PM - 03:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Christopher Hennigan, Carnegie Mellon University
Talk Title: Closing the Gap on Missing Sources of Organic Aerosol in the Atmosphere
Abstract: Aerosols, or particulate matter, are ubiquitous components of the atmosphere that exert important impacts on human health and global climate, though our understanding of these effects is far from clear. A better characterization of aerosol physical and chemical properties, including their sources and fate, is vital in obtaining a more accurate assessment of their contribution to climate change and in devising mitigation strategies with public health in mind. Extensive ambient measurements have demonstrated that organic compounds comprise a significant fraction of aerosol mass in many locations globally. Our knowledge of this organic aerosol (OA), however, is incomplete, as evidenced by the systematic underprediction of OA concentrations by state-of-the-art computer models. Recent research efforts have intensified to identify this âmissingâ source of OA, with many hypotheses emerging. Measurements conducted in Atlanta point to liquid water associated with aerosols as an important OA source that has not been considered previously. This mechanism involves the dissolution and subsequent reaction of soluble organic gases in the aerosol aqueous phase. It is likely different from processes occurring in cloud and fog water due to extreme concentration differences. Previous studies have ignored this possibility due to the relatively small amount of water associated with fine particles (aerosols with diameters smaller than 2.5 µm); however, our results provide strong evidence that this pathway contributes significantly to ambient OA concentrations. This mechanism is likely to be important in other locations, as well, and may represent the dominant source of OA missing from current models.
Host: Sonny Astani Dept. of Civil and Environmental Engineering
Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Erin Sigman
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Scaling of Fracture in Quasibrittle Structures
Tue, Mar 08, 2011 @ 02:00 PM - 03:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Qiang Yu, Northwestern University
Talk Title: Scaling of Fracture in Quasibrittle Structures
Abstract: Quasibrittle Materials, which include concrete, fiber composites, tough ceramics, bone and many other engineering materials, are widely used in the fields of civil engineering, aerospace engineering, mechanical engineering and bio-engineering. A salient feature of quasibrittle material is that its constituents are brittle and, due to heterogeneity, its fracture process zone is not negligible compared with the structure size. The consequence is that the structure strength (nominal stress at failure) is size dependent. Statistical studies showed that if size effect is ignored in concrete design, the failure probability may increase by orders of magnitude, e.g., from 10-6 to 10-3. Therefore, the proper scaling of quasibrittle structure strength is of great importance for structural safety and reliability.
In this study, the scaling of fracture in shear of RC beams, at reentrant corners, and in metal-composite hybrid joints is investigated theoretically, experimentally, and numerically. Dimensional analysis and asymptotic matching are exploited to identify the small- and large-size behaviors and the transition between these asymptotic trends. In contrast to notches and pre-existing cracks, the real part of the stress singularity exponent for the tip of a reentrant corner or bi-material corner is not -1/2, as required for finiteness of the energy flux into the crack. Therefore, one must take into account the fact that a cohesive crack must emanate from the corner and, for a large enough structure, must be embedded in a more remote singular stress field of the corner. The crack tip field, corner tip field and boundary influenced field are matched energetically through the strength of the singularities. By connecting the energy release and cohesive cracking of the embedded crack with the singular stress field of the corner, a general size effect law can be derived via asymptotic matching. The derived size effect laws for shear of reinforced concrete beams, for reentrant corners and for hybrid joints are validated by experiments and numerical simulations.
Host: Sonny Astani Dept. of Civil and Environmental Engineering
Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Erin Sigman
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The nanochemomechanics of geomaterials
Wed, Mar 09, 2011 @ 02:00 PM - 03:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Alberto Ortega, Massachusetts Institute of Technology
Talk Title: The nanochemomechanics of geomaterials
Abstract: Geomaterials such as rocks, soils, and concrete have emerged as crucial components in advanced engineering solutions related to enhanced oil recovery, geothermal energy, carbon sequestration, and green construction materials. These engineering challenges demand an intimate understanding of the multiscale mechanical behaviors of natural and engineered porous composites. In this presentation, a combination of experimental and theoretical microporomechanics approaches deployed at fundamental material scales is proposed as a means to decode complex mechanical responses of two geomaterials: shale, a type of clay-bearing sedimentary rock, and a high-performance cement paste. For shale, experiments involving statistical grid nanoindentation and an original application of wave dispersive spectroscopy allowed for the proper chemomechanical quantification of the in situ clay matrix response and the nature of the clay-silt grain interface. The micromechanics modeling of the clay matrix as a composite of nano-sized building blocks of clay agglomerates and nanoporosity revealed a granular and anisotropic mechanical behavior, which drives the poroelasticity of shale observed at macroscopic scales. For cement, the intrinsic solid properties of the calcium silicate hydrate (C-S-H) phase in high-performance pastes were determined by employing a similar experimental program and the micromechanics modeling tools. The improved elasticity and strength of the solid backbone compared to those of ordinary cement pastes provided valuable insight into the effects of mix design and curing on the mechanical response of the hardened materials. The nanochemomechanics of these geomaterials learned from fundamental scales can be used as instrumental information for the design and validation of upscaling models capable of predicting macroscopic engineering properties. Furthermore, the proposed geo-genome approach represents a viable framework for the mechanical modeling of other natural porous composites.
Host: Sonny Astani Dept. of Civil and Environmental Engineering
Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Erin Sigman
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Novel Methods for Hydrogeophysical Joint Inversion and Data Integration
Tue, Mar 22, 2011 @ 02:00 PM - 03:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Michael Cardiff, Boise State University
Talk Title: Novel Methods for Hydrogeophysical Joint Inversion and Data Integration
Abstract: The search for improved estimates of subsurface flow and transport parameters, and the expense and time associated with collecting hydrologic measurements, have both lead many hydrologists to consider the use of geophysical data for aquifer characterization.
Geophysical surveys, such as ground-penetrating radar (GPR), electrical tomography, and active seismic are often relatively cheap and fast to collect, when compared to hydrologic tests such as pumping tests and tracer injections. However, the key drawback of geophysical tests is that they are sensitive to geophysical parameters (e.g., electrical resistivity, seismic velocity, etc.) instead of the hydrologic parameters of interest. In this talk, I present two novel methods for the joint analysis of hydrologic and geophysical data when characterizing hydrologic systems.
In the first part of my presentation, I discuss the use of petrophysical transforms for converting geophysical parameters to hydrologic parameters. While petrophysical transforms are relatively easy to implement, the existence of non-unique petrophysical relations or multiple petrophysical relations can make the conversion to hydrologic parameters difficult. Using a Bayesian perspective, I derive a generalized maximum likelihood estimator that takes into account errors in both hydrologic and geophysical parameter estimates in order to estimate petrophysical relationships. The derived estimator is a generalization of so-called âGaussian Mixture Modelsâ, but with added flexibility. In terms of performance, the derived estimator is often capable of determining 1) The complexity of underlying petrophysical relations and 2) Whether multiple petrophysical relations are present.
The second part of my presentation discusses a novel inversion strategy for estimating boundaries between lithologic units (i.e.
facies) using either single datasets or combinations of hydrologic and geophysical data. By using a series of âlevel set functionsâ, I represent boundaries between facies that are allowed to iteratively deform and improve fit to both datasets. Both hydrologic and geophysical data are used to simultaneously drive boundary movement.
After presenting the theory and key equations, I will show performance on numerical experiments in addition to an application to a sandbox hydraulic tomography study.
Application of imaging and optimization methodologies to water resources systems is a rapidly growing and evolving field, with many opportunities for future research in both field, theoretical, and numerical methods. At the end of my talk, I will discuss some promising areas for future research in hydrogeophysical data integration and inversion, as well as other areas in which computational and optimization methods can be used to improve environmental decision making.
Host: Sonny Astani Dept. of Civil and Environmental Engineering
Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Erin Sigman
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Variable origin-destination trip matrix estimation: A maximum entropy-least squares estimator
Wed, Mar 23, 2011 @ 02:00 PM - 03:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Chi Xie, The University of Texas at Austin
Talk Title: Variable origin-destination trip matrix estimation: A maximum entropy-least squares estimator
Abstract: In transportation subnetwork-supernetwork analysis, it is well known that the origin-destination (O-D) flow table of a subnetwork is not only determined by trip generation and distribution, but also by traffic routing and diversion, due to the existence of internal-external, external-internal and external-external flows. This result indicates the variable nature of subnetwork O-D flows. This talk presents a variable O-D flow table estimation problem for subnetwork analysis. The underlying assumption is that each cell of the subnetwork O-D flow table contains an elastic demand function rather than a fixed demand rate and the demand function can properly capture traffic diversion effects under various network changes.
An integrated maximum entropy-least squares (ME-LS) estimator is proposed, by which O-D flows are distributed over the subnetwork so as to maximize the trip distribution entropy, while demand function parameters are estimated for achieving the least sum of squared estimation errors. While the estimator is powered by the classic convex combination algorithm, computational difficulties emerge within the algorithm implementation until partial optimality conditions and a column generation procedure are incorporated into the algorithmic framework. Numerical results from applying the integrated estimator to a couple of subnetwork examples show that a variable O-D flow table, when used as input for subnetwork flow evaluations, reflects network flow changes significantly better than its fixed counterpart.
Host: Sonny Astani Dept. of Civil and Environmental Engineering
Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Erin Sigman
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Chlorinated phenol based biocides and the opportunistic pathogen Pseudomonas aeruginosa
Mon, Mar 28, 2011 @ 02:00 PM - 03:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Sudeshna Ghosh, University of Michigan
Talk Title: Chlorinated phenol based biocides and the opportunistic pathogen Pseudomonas aeruginosa
Abstract: Increasing resistance to antimicrobials among bacteria is a growing problem. While antimicrobials are used to treat infections, their use also selects for drug resistant bacteria that elude treatment. Understanding the ecology of antibiotic resistance has been an important part of my research. Recently, I started looking at this problem from a different angle. I am asking if certain biocides, in addition to selecting for resistant bacteria, have other roles, such as increasing the infectivity of pathogens.
My presentation concerns an opportunistic pathogen, Pseudomonas aeruginosa, that infects people with lower immunity. Infections caused by P. aeruginosa are particularly hard to treat due to its large arsenal of defense mechanisms against antimicrobials. Prominent among its antibiotic resistance mechanisms is antibiotic efflux by the MexAB-OprM efflux pump, which confers resistance to a wide spectrum of antibiotics. I have found that chlorinated phenols control the expression of the MexAB-OprM efflux pump by interacting with a protein regulator of the pump. This interaction renders P. aeruginosa more resistant to antibiotics. Additionally, it raises the possibility that chlorinated phenols may influence other microbial characteristics, including virulence. Chlorinated phenol based biocides such as triclosan and chloroxylenol are commonly used as disinfectants in household cleaners, in health-care facilities and on medical devices. Is it possible that our use of these chlorinated phenol based biocides is self-defeating? This is the question that I am addressing now.
Host: Sonny Astani Dept. of Civil and Environmental Engineering
Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Erin Sigman
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Field measurements and numerical modeling of energy transport in urban areas
Wed, Mar 30, 2011 @ 02:00 PM - 03:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Speaker: Zhihua Wang, Princeton University
Talk Title: Field measurements and numerical modeling of energy transport in urban areas
Abstract: Changes of surface landuse types, resulting from rapid global urbanization and anthropogenic stressors, have significant impacts on urban environmental and engineered systems such as heat island formation and modification of the hydrological cycle and air quality. A better understanding of the transport and storage of energy in urban areas, in particular, is essential to the long term sustainability of cities. The last few decades have seen increasing efforts to characterize the energy transport in the lower urban atmosphere; one of the useful tools that have emerged is the physically-based urban canopy model (UCM). We developed an energy transport model based on the single-layer UCM used in the Weather Research and Forecasting (WRF) model. Our implementation does not require coupling to an atmospheric flow model and features several improvements in the urban surface energy exchange scheme including: (1) derivation and implementation of a spatially-analytical method that captures surface temperatures and heat storage better, (2) statistical characterization of uncertainties in the surface input parameter space using Markov-Chain Monte Carlo simulations, and (3) coupling to a hydrological model to better parameterize the water transport and evaporation from urban surfaces. Intensive field measurements are also carried out through a large wireless network of sensors deployed over the campus of Princeton University. Data collected from the sensor network are used to provide input parameters as well as to validate the proposed numerical scheme.
Host: Sonny Astani Dept. of Civil and Environmental Engineering
Location: Kaprielian Hall (KAP) - 209
Audiences: Everyone Is Invited
Contact: Erin Sigman