***DISSERTATION DEFENSE***
Center for Statistical Sciences Seminar
Abstract: When regression models adjust for mediators on the causal path from exposure to outcome, the regression coefficient of exposure is commonly viewed as a measure of the direct exposure effect. This interpretation can be misleading, even with a randomly assigned exposure. This is because adjustment for post-exposure measurements introduces bias whenever their association with outcome is confounded by more than just the exposure. By the same token, adjustment for such confounders stays problematic when these are themselves affected by the exposure. Robins (1999) accommodated this by introducing linear structural nested direct-effect models with direct effect parameters that can be estimated using inverse probability weighting by a conditional distribution of the mediator. The resulting estimators are consistent, but inefficient and can be extremely unstable when the intermediate variable is absolutely continuous. This talk will focus on the development of direct-effect estimators which are not only more efficient, but also consistent under a less demanding model for a conditional expectation of the outcome. We find that the one estimator which avoids inverse probability weighting altogether, a sequential G-estimator, to perform best. This estimator is intuitive, computationally straightforward and, as demonstrated by simulation, competes extremely well with ordinary least squares estimators in settings where standard regression is valid. We discuss applications of the method in several public health problems. This represents joint work with Sylvie Goetgeluk and Stijn Vansteelandt.
Brown Analysis Seminar
Lefschetz Center for Dynamical Systems Seminar
Abstract: In this talk I shall present existence results for periodic boundary value problems for third-order nonlinear ordinary differential equations subjected to impulsive effects.
***DISSERTATION DEFENSE***
***DISSERTATION DEFENSE***
The Fluids, Thermal and Chemical Processes Group of Engineering and Center for Fluid Mechanics Seminar
Abstract: Soft materials are critical to the function of numerous engineering technologies that impact our lives, from consumer products and pharmaceuticals to optical devices and energy solutions. Common to all soft materials is the presence of an underlying structure, whether droplets, topological defects, or macromolecules. These materials interact readily with surfaces and with external fields such as flows, leading to unique and tunable properties. For example, colloidal particles of precise size and composition are effective vectors for targeted drug delivery. Rapid, precise alignment of liquid crystal molecules determines the quality of the LCD display on your laptop. Spreading of complex liquids on surfaces and within porous media controls the efficiency of processes from inkjet printing to carbon sequestration and oil recovery. Microfluidics has revolutionized our approach to synthesis of soft materials and our approach to characterization of the underlying physics by enabling precise fabrication at length scales that interact with the microstructure. The first part of this talk will focus on our current research in generating monodisperse emulsions with microfluidic devices. In particular, the addition of surfactant molecules leads to the observation of a tipstreaming-like phenomenon that provides a mechanism to form sub-micron droplets. Uniform droplets at this scale can form the basis for synthesis of nanoparticles for drug delivery, biomedical imaging, and other applications. The interaction of surfactant-laden interfaces with strong flows leads to highly nonlinear behavior, and this talk will describe our approach to understanding this interaction through experimentation, scaling, and analytical modeling. The second part of this talk will introduce our work to develop techniques for measuring microscale dynamics of complex liquids. For example, changing the length scale of the flow device enhances control over defect microstructures that are ubiquitous in layered liquid crystals. Precise fabrication and high speed videography enables us to probe pore-level dynamics during invasion of a fluid into a saturated porous medium. Overall, our efforts in the Micro Complex Fluids Laboratory aim to synthesize and characterize complex fluids via novel experimentation and modeling. Biography: Dr. Shelley L. Anna is an Assistant Professor of Mechanical Engineering at Carnegie Mellon University. She received her Ph.D. in 2000 from Harvard University for research on rheology of polymer solutions. Prior to joining the faculty at Carnegie Mellon University in 2003, she worked at Solutia, Inc., a major manufacturer of polymer films and coatings, and she completed a postdoctoral fellowship at Harvard University in microfluidics and complex fluids. Dr. Anna is a faculty member in the Center for Complex Fluids Engineering and a courtesy faculty in the Departments of Chemical Engineering and Physics. She has received a National Science Foundation CAREER Award and the George Tallman Ladd Research Award.
Center for Computational Molecular Biology, Department of Molecular Biology, Cell Biology and Biochemistry
Abstract: Joe W. Gray, Ph.D., is Associate Laboratory Director for Life and Environmental Sciences and Life Sciences Division Director at the Lawrence Berkeley National Laboratory (LBNL). He is also Adjunct Professor of Laboratory Medicine at the University of California, San Francisco (UCSF) and program leader for the Breast Oncology Program in the UCSF Comprehensive Cancer Center. Dr. Gray's current research program focuses on molecular analysis technology, identification of genomic aberrations that contribute to cancer pathophysiology, development of efficient strategies for enhanced marker guided cancer therapy, especially for breast and ovarian cancer and early breast cancer detection. His work is described in more than 330 publications and 50 patents. Major awards include the Radiation Research Society Research Award (1985), the E.O. Lawrence Award from the US Department of Energy (1986), Election as a Fellow of the American Association for the Advancement of Science (1996), the Curt Stern Award from the American Society for Human Genetics (2001), an Honorary Doctorate from the University of Tampere, Tampere, Finland (2005) a DOD Innovator Award (2007) and the Brinker Award (2007). Dr. Gray earned a Ph.D. in physics from Kansas State University.
Department of Mathematics Colloquium
Applied Mathematics Colloquium
Abstract: In many applications there are models for dynamics but specific parameters are unknown or not directly measurable. This suggests the need to be able to search through parameter space for specific types of dynamical behavior. Ideally, this would be done computationally in some automated manner, and then later the researcher would be able to query the results. In this talk, we discuss computational topological methods which can extract coarse, but rigorous, global descriptions of dynamics and changes with respect to parameters. Moreover, we discuss ongoing efforts to develop a method for building databases that contain useful, rapidly identifiable information about the types of dynamics computed.
Center for Fluid Mechanics Seminar
Abstract: Particle methods (smoothed particle hydrodynamics and dissipative particle dynamics), lattice Boltzmann simulation and numerical solution of the incompressible Navier-Stokes equations with interface capturing (volume-of-fluid, level-set and phase-field) have been used to simulate multiphase fluid flow and reactive transport in fractured and porous media. Particle methods are much less computationally efficient than grid-based computational fluid dynamics, but they have important advantages including rigorous mass conservation, momentum conservation and Galilean invariance. In addition, code development is relatively simple, there is no need for interface tracking/capturing, and the contact angle dynamics produced by particle models in realistic, but not necessarily correct. A variety of examples will be used to illustrate the capabilities of there models, and future research opportunities will be discussed.
Scientific Computing Seminar
Abstract: I will discuss a general approach to simulate geophysical phenomena such as mantle convection, global seismic wave propagation or ice sheet melting. Models for these types of simulations contain many uncertain parameters which can only be measured indirectly implying the need for the solution of inverse problems and uncertainty quantification. The resolution required for the forward modules used in the inverse problem themselves is just now becoming tractable with advanced numerical methods and the advent of petascale machines. As a first step to our goal we have developed a parallel dynamic h-adaptive finite element code which has been scaled up to 32,000 cores on Ranger, the new 500 Teraflops system at TACC. I will discuss the design and implementation of this finite element framework to support this large level of parallelism. Finally I will present some initial results of modeling convection.
***GRADUATE STUDENT SEMINAR***
PDE Seminar
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