List of Events
Wednesday, October 14, 2015
Joint IGERT/Condensed Matter Seminar
Second law and the eightfold structure of relativistic fluid dynamics
Host: Kabir Ramola
Wednesday, October 28, 2015
Itamar Procaccia, Weizmann Institute
What determines force chains in granular media?
Host: Bulbul Chakraborty
Wednesday, December 9, 2015
Arunima Ray (Brandeis)
Concordance classes of knots and satellite operations
Abstract: A knot is an embedded circle in 3-dimensional space R^3. It is said to be slice if it is the intersection of an embedded 2-dimensional sphere in R^4 with R^3 considered as a subset of R^4. We can use this notion to define an equivalence relation on knots called concordance, under which the set of knots forms a well-behaved mathematical structure called an abelian group. The group of knot concordance classes plays an important role in the study of 4-dimensional manifolds. In this talk, we will give an overview of knot concordance and describe my work in understanding the action of certain 'satellite operations' on the knot concordance group. Finally we will describe how satellite operations might illuminate a fractal structure in the knot concordance group.
Wednesday, January 27, 2016
Naziru Awal (Brandeis)
Piecewise Linear Model of the BZ reaction
Wednesday, February 10, 2016
Ruoran Zhang, Northeastern University (Note: Quantitative Biology Lunch also held at this time).
Contact Chern-Simons Theory and Legendrian Knots
Abstract: Chern-Simons theory is a 3-dimensional topological quantum field theory developed by Edward Witten. Bar-Natan studied the perturbative Chern-Simons theory and deduced new integral formula for known invariant of knots(). In 2005, Chris Beasley and Edward Witten() developed a theory called contact Chern-Simons theory which combines contact geometry with Chern-Simons theory. This theory is especially suitable for the study of Legendrian knots due to certain symmetry of its action functional.n this talk, I will first introduce the motivation of contact Chern-Simons theory and some basic concepts in contact geometry. Additionally, I will explain why Legendrian knots are related to contact Chern-Simons theory. Then, I will introduce new self-linking invariants of Legendrian knots. These invariants arise from the perturbative expansion of the contact Chern-Simons theory, and they are conjectured to agree with known finite-type invariants derived from the usual Chern-Simons gauge theory. I proved this conjecture at first non-trivial order, in which case the self-linking invariant is a linear combination of the Thurston-Bennequin invariant and the rotation number of the knot(). In physics, the self-linking invariants describe terms in the Feynman diagram expansion of the Wilson loop expectation value in contact Chern-Simons theory. At the end, I will show a cancellation of certain Feynman diagrams of the expansion of the Wilson loop expectation value. This result is a check of the finiteness of contact Chern-Simons theory. This is a joint work with Chris Beasley and Brendan McLellan.
Wednesday, March 2, 2016
Carl Merrigan, Brandeis University
Role of the Initial Force Configuration for Unjamming Grains in a Hopper
Abstract: The abrupt arrest of particles falling through a narrow outlet resembles a phase transition from a fluid to a solid. This transition is referred to as “clogging” or more broadly as “jamming.” For small spheres falling from a quasi-2D hopper, jamming occurs through the formation of an arch. It has been shown that the probability of arch formation depends on the ratio of the outlet width to grain size. Further, experiments have established that the arch formation times follow an exponential distribution, so there is a single characteristic time scale associated with this process. In contrast, recent experiments have found that arch breaking times follow a power law distribution. Consequently, the arch breaking process does not exhibit any characteristic time scale. In order to understand the origin of this power law behavior, we have carried out simulations in LAMMPS of grains in 2D hopper subject to vertical vibrations. I have focused on analyzing the evolution of the force network caused by the vibrations. In this talk, I will first present our findings for the unjamming time distributions for a large set of runs. I will then discuss what we know so far about the evolution of the force network during the vibrations. Finally, I will set out a possible model for relating the initial force configuration to the resulting unjamming time by thinking of unjamming as a kind of “first passage process.”
Tuesday, March 8, 2016 (Abelson 229 at 1pm)
Aditi Mitra (NYU)
Abstract: The non-equilibrium dynamics of isolated quantum systems following a "quench" of some parameter of the Hamiltonian raises many fundamental questions, that can now even be probed in experiments. I will first give an overview of the topic and the status of experiments. I will then show how quantum quenches in the vicinity of a critical point can lead to universal out of equilibrium dynamics with new critical exponents that are not related to thermodynamic critical exponents. I will also highlight what quantum information measures such as entanglement entropy and entanglement spectrum reveal about a system which is out of equilibrium following a quantum quench, applying them both to systems near critical points, as well as to systems with topological order.
Wednesday, March 23, 2016
Melanie Mitchell, Portland State
Using Analogy to Recognize Visual Situations
Abstract: Enabling computers to recognize abstract visual situations remains a hard open problems in artificial intelligence. No machine vision system comes close to matching human ability at identifying the contents of images or visual scenes, or at recognizing abstract similarity between different scenes, even though such abilities pervade human cognition. In this talk I will describe my research on getting computers to flexibly recognize visual situations by integrating lower-level vision algorithms with an agent-based model of higher-level concepts and analogy-making.
Bio: Melanie Mitchell is Professor of Computer Science at Portland State University, and External Professor and Member of the Science Board at the Santa Fe Institute. She received a Ph.D. in Computer Science from the University of Michigan. Her dissertation, in collaboration with her advisor Douglas Hofstadter, was the development of Copycat, a computer program that makes analogies. She is the author or editor of five books and numerous scholarly papers in the fields of artificial intelligence, cognitive science, and complex systems. Her most recent book, Complexity: A Guided Tour (Oxford, 2009), won the 2010 Phi Beta Kappa Science Book Award. It was also named by Amazon.com as one of the ten best science books of 2009, and was longlisted for the Royal Society's 2010 book prize. Melanie directs the Santa Fe Institute's Complexity Explorer project, which offers online courses and other educational resources related to the field of complex systems.
Wednesday, April 13, 2016
Jörn Callies (MIT)
Macroturbulence in the ocean
Abstract: The ocean plays a key role in regulating the earth system's response to arge fraction of the emitted carbon and the vast majority of the excess energy trapped on the planet. The rate of warming of the atmosphere therefore crucially depends on how the ocean circulation transports heat and carbon anomalies into its interior. To understand the earth system's response to carbon emissions, it is thus crucial to understand the ocean circulation. An important component of the ocean circulation are energetic transient eddies, which are similar to atmospheric weather systems but only 100 km in scale. Smaller-scale features, 1–100 km in scale, are believed to be particularly important for vertical exchanges in the upper ocean Together, these flows are known as the macroturbulence of the ocean. In this presentation, I will discuss the dynamics of oceanic macroturbulence, exploring what instability processes energize it and how we can understand aspects of the fully nonlinear, turbulent dynamics.
Wednesday, April 27, 2016
No IGERT seminar (due to Passover and Spring Recess).
Wednesday, May 11, 2016 (location: Gzang 124)
Edward Fredkin (Carnegie Mellon University)
On Cellular Automata and Physics
Abstract: Until very recently it was thought that a discrete space-time-slate Cellular Automaton model of physics, based on a cartesian lattice, could not model physical processes with continuous symmetries. We will discuss the role of QM spin and Noether's Theorem in new discrete, cartesian space-time-state models that include the apparently continuous symmetries of Physics.