Events Archive

Dec
10
2012
Ultra-High Energy Cosmic Rays from Blazars
Blazar astronomy is rapidly progressing thanks in large part to the successes of the Fermi Gamma-ray Space Telescope and the ground-based gamma-ray telescopes. More than 1000 active galaxies have been detected at GeV energies, and nearly 50 at Very-High Energies (VHE,  > 100 GeV). We can now explore multiwavelength and multi-messenger connections in unprecedented detail, and derive the astroparticle implications of those results. In this presentation, leptonic and hadronic spectral modeling of blazars is reviewed with the intent of identifying ultra-high energy cosmic rays (UHECRs) in  the spectral energy...
Dec
10
2012
Numerical solutions to the optimal stabilization Hamilton-Jacobi PDE in control theory
PLEASE NOTE: This is a WEBINAR A problem of practical interest in control theory is to stabilize a nonlinear dynamical system through the action of a feedback control.  The stabilization problem can be embedded as an optimal control problem leading one to solve a Hamilton-Jacobi (HJ) PDE.  The associated HJ equation is a first order nonlinear singular PDE and, under suitable conditions, can be solved locally using power series methods.  In this talk, I will present a numerical method that extends the domain of...
Dec
10
2012
A New Physiological Boundary Condition for Hemodynamics
PLEASE NOTE: This is a WEBINAR Accurate modeling of blood flow provides insights into arterial stent design, surgical planning, and analysis of stroke risk. Unfortunately, fully detailed modeling of the cardiovascular system is computationally impossible due to the enormous number of blood vessels in the body.  Instead, a common technique is to choose a small subset of arteries to model in detail while accounting for the "un-modeled" parts of the cardiovascular system through boundary conditions.  A popular tactic for deriving such a boundary condition is to...
Dec
06
2012
The Co-Evolution of Galaxies and Black Holes: A Local Perspective
I will summarize our current understanding on the relation between the evolution of black holes and galaxies in the local universe. I will show that the growth of supermassive black holes as traced by optically luminous active galactic nuclei is strongly linked to the on-going formation of stars in the bulge component of galaxies. It is likely that this co-evolution is driven by the accretion and radial transport of cold gas, but major mergers of galaxies are not the primary mechanism for doing this. I will show that the fuel source for the black hole growth may be mass loss from intermediate mass stars and that the black hole growth may be limited in part by feedback from supernovae...
Dec
04
2012
Electromechanical Pumping in the Embryonic Tubular Heart
Recent advancements in computational fluid dynamics have enabled researchers to efficiently explore problems that involve moving elastic boundaries immersed in fluids for problems such as cardiac fluid dynamics, fish swimming, and the movement of bacteria. These...
Dec
04
2012
Hamiltonian reductions in plasma physics
Given the complexity of the dynamics of a plasma, reductions are needed. The Hamiltonian framework offers various ways to carry out such reductions. I will introduce some of these methods by considering in particular the example of gyrokinetics, which is a kinetic model for plasmas in a strong magnetic field.
Dec
03
2012
How Astrophysical Black Holes Shine
The defining feature of a black hole is its event horizon through which nothing can escape outward, not even light.  And yet black holes are responsible for the brightest sources that we observe in the universe, from gamma-ray bursts to quasars. Their enormous luminosity arises from the release of gravitational binding energy outside the horizon as material falls inward.  These black hole accretion flows exhibit extraordinary behavior, including outbursts, state transitions, and quasi-periodic variability, most of which continue to defy understanding but which must be related to the magnetohydrodynamic turbulence and radioactive thermodynamics that...
Nov
28
2012
Bubble instabilities in constricted geometries
PLEASE NOTE: This is a WEBINAR The displacement of a liquid by an air bubble is a generic two-phase flow that underpins applications as diverse as microfluidics, thin-film coating, enhanced oil recovery, and biomechanics of the lungs. I will present two intriguing examples of such flows where, firstly, oscillations in the shape of propagating bubbles are induced by a simple change in tube geometry, and secondly, flexible vessel boundaries that enable streamwise variations of the channel depth...
Nov
27
2012
Conformational dynamics that allow repair proteins to detect DNA mismatches
The DNA mismatch repair system is critical for accurate DNA replication.  This system is highly conserved across organisms ranging from bacteria to humans reflecting the importance of minimizing genomic defects during cell division. The mismatch repair protein MutS has been identified the key factor that detects base-base mismatches and insertion-deletion mismatches in double stranded DNA and signals for their repair.  Despite intense study, a temporally resolved understanding of the molecular details of the MutS:DNA interactions during mismatch repair initiation has been difficult to...
Nov
27
2012
Collective interactions in Metamaterials and Cold Atomic Gases: Manipulating Light in Ensembles of Electromagnetic Emitters
In this seminar, we will discuss how interactions between discrete electromagnetic (EM) emitters lead to a cooperative response of a metamaterial or cold atomic gas to an incident field.  We will examine a number of ways the cooperative response can be engineered and exploited. The interactions responsible arise from repeated scattering of the field between its discrete constituent elements. Our focus will be on metamaterials, which are composed of subwavelength circuit elements - or meta-atoms - whose electric and magnetic multipole interactions are governed by their design.  We also...

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