Events Archive

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...
Apr
01
2013
How networks drove the rapid evolution of early life: clues from the canonical genetic code
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
2013
The Dynamics and Kinematics of Swimming
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
2013
Prospects for Gravitational Wave Astronomy
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
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 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
2013
Annual Joseph Ford Commemorative Lecture: The Neuromechanics of Insect Locomotion: How Cockroaches Run Fast and Stably Without (much) Thought
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
2013
Electromagnetic Emission from Supermassive Black Hole Mergers
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
2013
Geometric Mechanics and Optimal Coordinates for Locomotion
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
2013
Magneto-optics in Carbon Nanotubes, Graphene, and Graphite
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
2013
A Discovery! The Higgs? Why it is Important and How it Was Done.
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....

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