Apr
08
Teaser:

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
Teaser:

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
Teaser:

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
Teaser:

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
Teaser:

The motor protein kinesin uses adenosine triphosphate (ATP) as a fuel and walks along the microtubule filaments in the cell. They are vital for many
cellular processes including intracellular transport and cell division.  Although recent progress in experiments yielded much information regarding
their motility, a structure-based, physical mechanism by which the motor amplifies the ATP-driven small conformational change in the motor head into
a large, 8-nm stepping motion remains largely a mystery. I will discuss molecular dynamics simulations elucidating its force-generation mechanism
and tests by...

Apr
01
Teaser:

Relics of early life, preceding even the last universal common ancestor of all life on Earth, are present in the structure of the modern day canonical genetic code --- the map between DNA sequence and amino acids that form proteins.  The code is not random, as often assumed, but instead is now known to have certain error minimization properties.  How could such a code evolve, when it would seem that mutations to the code itself would cause the wrong proteins to be translated, thus killing the organism?  Using digital life simulations, I show how a unique and optimal genetic code can emerge over evolutionary time...

Mar
26
Teaser:

The motion of biological systems in fluids is inherently complex, even for the simplest organisms. In this talk, we develop methods to analyze locomotion of both mechanical and biological systems with the aim of rationalizing biology and informing robotic design. We begin by building a visualization framework studying an idealized swimmer, Purcell's three link swimmer, at low Reynolds number. This framework allows us to illustrate the complete dynamics of the system, efficiently design gaits for motion planning, and identify optimal gaits in terms of efficiency and speed. We extend the...

Mar
25
Teaser:

The rich astronomy of gravitational radiation is being intensively prepared using sophisticated analytic calculations, massive numerical simulations, and incredibly sensitive experimental facilities. These different approaches must work closely together if we are to use gravitational waves to understand the universe. Already, before the first direct detections of gravitational waves, we understand much more than a decade ago about the fascinating dynamical geometry of black holes and about the physics of how gravitational radiation is generated. Meanwhile the technologies...

Mar
13
Teaser:

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 aimed at the mathematical modeling and mitigation of infectious diseases, the fundamental mechanisms of pathogen spreading for most infectious diseases remain poorly understood.  I present here the results of  combined theoretical and...

Mar
11
Teaser:

I will describe several models for running insects, from an energy-conserving biped, through a muscle-actuated hexapod driven by a neural central pattern generator, to a reduced phase-oscillator model that captures the dynamics of unperturbed gaits and of impulsive perturbations. I will argue that both simple models and large simulations are necessary to understand biological systems.  The models show that piecewise-holonomic constraints due to intermittent foot contacts confer asymptotic stability on the...

Mar
07
Teaser:

I will review ideas that may be useful in identifying electromagnetic (EM) emission from supermassive black hole (SMBH) binaries. In particular, any detectable EM emission is likely to be time-variable, which should aid in its identification. I will discuss four possibilities for such variable emission: (i) roughly periodic signals due to the orbital motion prior to coalescence, (ii) a transient pre-cursor caused by the gas trapped inside the binary's orbit, and transients "after-glows" produced by (iii) post-merger gas accretion and (iv) by merger-induced shocks in a circumbinary disk. I will argue that these...

Mar
06
Teaser:

Understanding the locomotion of animals and robots can be a challenging problem, involving nonlinear dynamics and the coordination of many degrees of freedom. Geometric mechanics offers a vocabulary for discussing these dynamics in terms of lengths, areas, and curvatures. In particular, a tool called the *Lie bracket* combines these geometric concepts to describe the effects of cyclic changes in the locomotor's shape, such as the gaits used by walking or crawling systems.

In this talk, I will introduce some basic principles of geometric mechanics, and show how they...

Mar
05
Teaser:

Matter placed in a strong magnetic field provides a fascinating laboratory in which to study exotic quantum phenomena in a highly controllable manner.  This talk will summarize our recent findings of novel magnetic properties of carbon nanotubes, graphene, and graphite, probed via high-field magneto-optical spectroscopy.  A magnetic field applied parallel to a nanotube introduces an Aharonov-Bohm phase to the electronic wave function, which leads to band gap oscillations, magnetic brightening of dark excitons, and extremely large magnetic...

Mar
04
Teaser:

The ATLAS Experiment at the Large Hadron Collider with its sister experiment CMS reported a discovery last summer of a new boson which is consistent with the Standard Model Higgs boson.  The Higgs particle has been searched for decades. It is the final jewel in the Standard Model of particle physics, a crowning achievement of 20th century science that gives a powerful understanding of fundamental particles and their interactions. In the Standard Model, the Higgs is the quantum of a field that accounts for the masses of those particles.  We will describe the apparatus, the data and other searches....

Mar
04
Teaser:

The ATLAS Experiment at the Large Hadron Collider with its sister experiment CMS reported a discovery last summer of a new boson which is consistent with the Standard Model Higgs boson.  The Higgs particle has been searched for decades. It is the final jewel in the Standard Model of particle physics, a crowning achievement of 20th century science that gives a powerful understanding of fundamental particles and their interactions. In the Standard Model, the Higgs is the quantum of a field that accounts for the masses of those particles.  We will describe the apparatus, the...

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