Events Archive

Apr
22
2013
The Astrophysics of Black Hole Spin
In addition to providing vital clues as to the formation and evolution of black holes, the spin of black holes may be an important energy source in the Universe.  Over the past couple of years, tremendous progress has been made in the realm of observational measurements of spin.   I will describe these efforts with particular focus on the use of X-ray spectroscopy to probe the spin of supermassive black holes in active galactic nuclei (AGN).   I shall describe results from the Suzaku AGNSpin Survey, a Suzaku Key Project that targets five bright and well-known AGN...
Apr
18
2013
Non-equilibrium Spin Domains in Quenched Sodium Spinor Bose-Einstein Condensates
Understanding dynamics of pattern formation, following a symmetry breaking quantum phase transition is an area of active interest. Spontaneous spin domain is formed in sodium Bose-Einstein condensates that are quenched, i.e. rapidly tuned, through a quantum phase transition from polar to antiferromagnetic phases. A microwave ``dressing'' field globally shifts the energy of the mF= 0 level below the average of the mF= ±1 energy levels, inducing a dynamical instability . We use local spin measurements to quantify the spatial ordering kinetics in the vicinity...
Apr
15
2013
Was Mars Ever Habitable?
NASA has followed the water on Mars, and has now progressed further to asking: is or was this environment ever actually habitable by life as we know it?  All such life has some common physical and chemical requirements, which we can look for via orbital remote sensing and missions to the Martian surface.  Recent results from the Curiosity rover are providing a delightfully nuanced answer to this question.  The talk will discuss how we arrived at Gale crater (versus the many other interesting places on Mars), what we have been doing there, and what...
Apr
09
2013
Anticipating sudden transitions in biological populations: Cooperation, cheating, and collapse
Natural populations can suffer catastrophic collapse in response to small changes in environmental conditions, and recovery after such a collapse can be exceedingly difficult. We have used laboratory microbial ecosystems to study early warning signals of impending population collapse. Yeast cooperatively breakdown the sugar sucrose, meaning that below a critical size the population cannot sustain itself. We have demonstrated experimentally that changes in the fluctuations of the population size can serve as an early warning signal that the population is...
Apr
09
2013
Insights from insects: neural and mechanical determinants of locomotor control
Movement is a defining characteristic of animals. They have evolved a diversity of successfulmovement strategies where responsiveness to their surroundings is paramount and perturbations arethe norm. My research program seeks to understand the physiological basis of a central challenge foranimals: the generation of stable, versatile locomotion through complex environments. Locomotionarises through the interplay of multiple physiological systems acting in the context of an organism’sinteractions with it environment. A central task for animals during locomotion is acquiring, processing,transforming and acting upon information. Yet nervous systems...
Apr
08
2013
What happened before the big bang?
The standard model of cosmology suggests that the universe started with a phase of very high density, described by general relativity as a singularity. Quantum gravity attempts to resolve the singularity by a more fundamental, microscopic theory whose equations remain valid and could tell us what happened at or even before the big bang. This talk reviews one approach, loop quantum gravity, and discusses several surprising new results that shed light on the structure of quantum space-time, with implications for mathematical modeling and conceptual questions in cosmology.
Apr
04
2013
Public Lecture: Baseball and Physics: "You Can Observe a Lot by Watching"
Following Yogi Berra's advice, I will use high-speed video clips to highlight some of the interesting physics underlying the game of baseball.  The talk will focus on two broad aspects of the game:  the physics of the baseball-bat collision and the flight of the baseball through the air. I will investigate some very practical questions and show how a  physicist goes about trying to answer these question.  Some examples:  what is the "sweet spot" of a bat; how does the batter's grip affect the batted ball; why does aluminum outperform wood; how determines how far a fly travels; how much...
Apr
04
2013
The fluid dynamics of disease transmission
The mechanisms governing the transfer of pathogens between infected and non-infected members of a population are critical in shaping the outcome of an epidemic. This is true whether one considers human, animal or plant populations. Despite major efforts to investigate the large-scale population-level disease dynamics and the micro-scale pathogen-level dynamics, the fundamental mechanisms of transmission of most pathogens remain poorly understood. A critical gap in our understanding of the bridge between population-level and pathogen-level mechanisms persists. Drawing upon clinical data, fluid experiments and theoretical modeling I will discuss...
Apr
03
2013
The Dynamics of Vertical Running: Analysis and Robotic Implementation
Animals move with a level of grace, speed, and agility that, as of yet, eludes our best  attempts at robotic mimicry.  In this talk we will discuss the modeling and dynamics of rapid vertical ascension and review some recent efforts at instantiating these results into climbing robots.  
Apr
02
2013
May the force be within you: A tale of the kinesin motor
The motor protein kinesin uses adenosine triphosphate (ATP) as a fuel and walks along the microtubule filaments in the cell. They are vital for manycellular processes including intracellular transport and cell division.  Although recent progress in experiments yielded much information regardingtheir motility, a structure-based, physical mechanism by which the motor amplifies the ATP-driven small conformational change in the motor head intoa large, 8-nm stepping motion remains largely a mystery. I will discuss molecular dynamics simulations elucidating its force-generation mechanismand tests by...

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