Events

## SMARTech Video Archive

Nov

10

Superconducting Josephson Junctions are one of the most active areas of research in Condensed Matter Physics today. One unique aspect of Josephson Junctions is the nonlinear relation between the phase of the wave function and the supercurrent flowing though the junction. This manifests itself in a nonlinear, pendulum-like equation for the dynamics of the phase when the junction is placed in circuit. Josephson junctions can be fabricated with adjustable parameters, measured in a straightforward fashion, and easily scaled to large network sizes. In addition, a large Josephson junction circuit measured over a long time contains dynamics...

Nov

09

Most biological processes are mediated by mediated by protein association, and often are under kinetic rather than thermodynamic control. We have developed the transient-complex theory for protein association, which presents a framework for elucidating the mechanisms of protein association and for predicting the association rates. The transient complex refers to an intermediate along the association process, in which the two associating molecules have near-native separation and relative...

Nov

08

Ion channels play vital cellular functions. How an external simulation (e.g., cross-membrane voltage, binding of a ligand, or decrease in external pH) triggers the opening of an ion channel is at the core of its functional mechanism. We have used molecular dynamics simulations and other computational techniques to develop models for the functional mechanisms of several ion channels, including a nicotinic acetylcholine receptor, an AMPA-subtype glutamate receptor, and the M2 proton channel of the influenza virus. A very useful way to validate these mechanistic models is to compare changes in residue solvent...

Nov

07

The Vlasov-Poisson and Vlasov-Maxwell equations possess various variational formulations or action principles. I will discuss a particular variational principle that is based on a Hamiltonian-Jacobi formulation of Vlasov theory, a formulation that is not widely known. I will show how this formulation can be reduced for describing the Vlasov-Poisson system. The resulting system is of Hamilton-Jacobi form, but with nonlinear global coupling to the Poisson equation. A description of phase (function)space geometry and relation to Hamilton-Jacobi PDE methods and weak KAM will be given.

H. Ye and P. J. Morrison Phys. Fluids 4B, 771 (1992). D. Pfirsch, Z. Naturforsch....

Nov

02

Oct

31

Winner of the Nobel Prize in Physics in 2007, Fert speaks about his work in spintronics.

Oct

31

*Albert Fert, Nobel Prize in Physics 2007*

*Joint colloquium between the School of Physics and MRSEC*

Spintronics exploits the influence of the electron spin orientation on electronic transport. It is mainly known for the “giant magnetoresistance” (GMR) and the large increase of the hard disc capacity obtained with read heads based on the GMR, but it has...

Oct

28

A quantum computer uses superposition states to accomplish tasks (e.g., database search and factoring of integers) more efficiently than any known classical computing strategy. In conventional registers for quantum information processing, quantum bits are associated with individual two-level quantum systems. Separate addressing and interaction with these systems permit one-bit gates, while an interaction between systems is needed

to accomplish two-bit gates.

The seminar will review recent theoretical proposals to implement quantum computing in collective excitation degrees of freedom in ensembles of

identical quantum systems. In these proposals one does not address...

Oct

26

Computational models of the Earth system lie at the heart of modern climate science. Concerns about their predictions have been illegitimately used to undercut the case that the climate is changing and this has put dynamical modelling in an awkward position. I will discuss ways that we, as a community, can contribute by highlighting some of the major outstanding questions that drive climate science, and I will outline their mathematical dimensions. I will put a particular focus on the issue of simultaneously handling the information coming from data and models, and argue that this balancing act will impact the way in...

Oct

25

At the small scale of a cell swimming in water, inertial effects are unimportant. Therefore, the motion of the fluid is governed by Stokes equations, which are linear. Nevertheless, there are many situations in which nonlinear effects are important. In this talk I will describe two such situations. The first is swimming in a viscoelastic material, which is motivated by the fact that many microorganisms move in non-Newtonian media such as mucus. I will present a simple model that shows how fading memory affects swimming speed. We will also present experimental results for a helix swimming in a viscoelastic fluid. The second situation I will consider is the...

Oct

19

Neutron stars are observed to rotate as fast as 716 Hz. Astrophysicists believe that they are spun-up by accretion of matter and angular momentum in binary star systems. However, the "r-mode" instability of rotating neutron stars, which is driven by gravitational radiation reaction, appears to prevent spin up via accretion to rotation frequencies above about 350 Hz.

Oct

13

We all know that modern science is undergoing a profound transformation as it aims to tackle the complex problems of the 21st Century. It is

becoming highly collaborative; problems as diverse as climate change, renewable energy, or the origin of gamma-ray bursts require understanding

processes that no single group or community alone has the skills to address. At the same time, after centuries of little change, compute, data, and network environments have grown by 9-12 orders of magnitude in the last few decades. Moreover, science is not only compute-intensive but is dominated now by data-intensive methods. This dramatic change in the culture and methodology of...

Oct

07

In the framework of the Fitzhugh-Nagumo kinetics and the oscillatory recovery in excitable media, we present a new type of meandering of the spiral waves, which leads to spiral break up and spatiotemporal chaos. The tip of the spiral follows an outward spiral-like trajectory and the spiral core expands in time. This type of destabilization of simple rotation is attributed to the effects of curvature and the wave-fronts interactions in the case of oscillatory damped recovery to the rest state. This model offers a new route to and caricature for cardiac fibrillation, and when we apply the feedback resonant drift method, for defibrillation all wave activity gets eliminated at the...

Oct

05

Gamma-ray bursts have been detected at photon energies up to tens of GeV, and there are reasons to believe that the sources emit at least up to TeV energies, via leptonic or/and hadronic mechanisms. I review some recent developments in the GeV photon phenomenology in the light of Fermi observations, as well as recent related theoretical work. I discuss then the expected production of gravitational waves, the possibility of accelerating cosmic rays resulting in high energy neutrinos, and recent observational constraints.