Abstract: Neutron star mergers are among the most violent events in the Universe. Gravitational wave, electromagnetic, and neutrino signals from these mergers encode important aspects of the physics and astrophysics of neutron stars, which cannot be inferred from terrestrial laboratory experiments. For example, on the nature of the short-range interaction between nucleons, which is imprinted in the neutron star equation of state. However, harnessing these imminent detections will only be possible by combining the observational data with reliable theoretical predictions. The formers, in turn, rely on the availability of high-precision simulations. In this talk, I will review the current state-of-the art in the modeling of neutron star mergers and discuss future challenges and possibilities in this field.
"Satellite observations of interactions between atmospheric convection and surface Winds"
Abstract: Satellite scatterometers measure surface winds over the global oceans, but these observations have historically been limited by rain-related errors. We have recently developed techniques to circumvent these rain-related errors, allowing for direct observational study of convection-wind coupling over the ocean.
We use these corrected wind data to detect cool downdrafts from mesoscale convective systems (MCSs) for the first time. These wind observations are validated against surface buoys and satellite observations of cloud-top temperature.
Building on this study, we utilize satellite wind and rainfall observations to examine coupling between the land-sea breeze and the diurnal cycle of rainfall in the Bay of Bengal. Observations show co-propagation of surface convergence and rainfall anomalies from the eastern coast of India into the bay; surface convergence leads the rainfall anomalies by several hours, implying that the land breeze forces the diurnal cycle of convection over the bay.
Abstract: ccording to Alzheimer’s Association, Alzheimer Disease(AD) is the 6th leading cause of death in the United States that cannot be prevented or cured. A person suffering from AD shows different symptoms of memory loss to language disability (In later stage). To help millions of people and advance in the research of AD, Alzheimer’s Therapeutic Research Institute (ATRI) is an institute committed to advancing the development of new treatments for AD through innovation in clinical trials.
Software development, nowadays has become a vital factor in all research fields and I would like to introduce how it plays its role in Alzheimer’s Research. ATRI has been responsible in organizing more than 50 clinical trials and the Informatics team actively develops and maintains a secure data capture system to record and analyze the data received from trials. Being a software developer at ATRI, I would also like to share my experiences of different concepts and best programming practices that I have learnt.
"A ROM-HPC framework with analysis for stochastic wave propagation models"
Abstract: We consider a class of wave propagation models with aleatoric and epistemic uncertainties. Using mathematical analysis-based, shape-independent, a priori parameter estimates, we develop offline/online strategies to compute statistical moments of a key quantity of interest in such models. We present an efficient reduced order model (ROM) and high performance computing (HPC) framework with analysis for quantifying aleatoric and epistemic uncertainties in the propagation of waves through a stochastic media comprising a large number of three dimensional particles. Simulation even for a single deterministic three dimensional configuration is inherently difficult because of the large number of particles. The aleatoric uncertainty in the model leads to a larger dimensional system involving three spatial variables and additional stochastic variables. Accounting for epistemic uncertainty in key parameters of the input probability distributions leads to prohibitive computational complexity. Our hybrid ROM and HPC framework can be used in conjunction with any computational method to simulate a single particle deterministic wave propagation model.
March 29, 2017
"New Bernstein-Bezier bases for the finite element exact sequence on tetrahedra"
Abstract: We present a set of new Bernstein-Bezier bases, with a local exact sequence property, for the finite element exact sequence on tetrahedra.
March 6, 2017
University Of North Carolina At Charlotte
"Consistent coupling of nonlocal diffusion"
Abstract: Nonlocal models have been developed and received lot of attention in recent years to model systems with important scientific and engineering applications. While it is established that the nonlocal formulations can often provide more accurate descriptions of the systems, the nonlocality also increases the computational cost compared to conventional models based on PDEs. The goal is to combine the accuracy of nonlocal models with the computational and modeling efficiency of local PDEs.
In this talk, I will introduce a new self-adjoint, consistent, and stable coupling strategy for nonlocal diffusion models, inspired by the quasinonlocal atomistic-to-continuum method for crystalline solids. The proposed coupling model is coercive with respect to the energy norms induced by the nonlocal diffusion kernels as well as the L2 norm, and it satisfies the maximum principle. A finite difference approximation is used to discretize the coupled system, which inherits the property from the continuous formulation. Furthermore, we design a numerical example which shows the discrepancy between the fully nonlocal and fully local diffusions, whereas the result of the coupled diffusion agrees with that of the fully nonlocal diffusion.
"Exploiting Low-Dimensional Structures for Sensing and Control of Fluids via Data-Driven Reduced-Order Modeling"
Abstract: Many applications in engineering and the sciences generate large-amounts of data to describe physical systems, e.g., via high-dimensional approximation or experimental measurements. Fortunately, the underlying dynamics of a complex system is often of much lower dimension than the data volume suggests. Thus, much progress has been made in deriving reduced-order models from system equations to enable (or speed up) engineering tasks such as control and optimization. Data-driven reduced-order modeling complements these intrusive, equation-based methods, and offers new pathways to work with real system data.
In this talk, I will discuss recent work on indoor airflow sensing through reduced-order models and the compressed sensing method to detect flow phenomena. We use simulated data to derive a low-dimensional basis for the fluid system via dynamic mode decomposition (DMD). We then extend the basis to account for time series of measurements, making the sensing method more robust. Results based-on a two dimensional Boussinesq equation are presented.
Building on this work, I will discuss recent results on control of parameter varying systems, where the physical parameters are uncertain and unknown. In this setting, we learn reduced-order models from system data that can then be used for reduced-order feedback control. The derived data-driven controllers successfully stabilize the considered convection-diffusion equation
"Wave breaking and modulational instability in full-dispersion shallow water models"
Abstract: In the 1960s, Benjamin and Feir, and Whitham, discovered that a Stokes wave would be unstable to long wavelength perturbations, provided that (the carrier wave number) x (the undisturbed water depth) > 1.363.... In the 1990s, Bridges and Mielke studied the corresponding spectral instability in a rigorous manner. But it leaves some important issues open, such as the spectrum away from the origin. The governing equations of the water wave problem are complicated. One may resort to simple approximate models to gain insights. \n I will begin by Whitham's shallow water equation and wave breaking conjecture, and move to modulational instability, the effects of surface tension and constant vorticity, turbulent bores, and I will indicate where numerical investigation may help for further understanding. I will discuss wave breaking and modulational instability in other related equations. I will say a few words about higher order corrections, extension to bidirectional propagation and two-dimensional surfaces, if time permits. This is based on the joint works with Jared Bronski (Illinois), Mat Johnson (Kansas), Ashish Pandey (Illinois), and Leeds Tao (UC Riverside).