Center for Applied Mathematical Sciences
Colloquia for the Spring 2012 Semester

Nathan Glatt-Holtz
Indiana University
Wednesday, January 11 KAP 414 3:30 PM - 4:30 PM
Local and global existence of smooth solutions for the stochastic Euler equations on a bounded domain

We prove the local existence of pathwise solutions for the stochastic Euler equa tions in a three-dimensional bounded domain, with a general nonlinear multiplica tive noise and slip boundary conditions. In the two-dimensional case, we obtain the global existence of these solutions with additive or linear-multiplicative n oise. Lastly, we show that linear multiplicative noise provides a regularizing effect in the sense that the global existence of solutions occurs with high prob ability if the initial data is sufficiently small or if the noise coefficient is sufficiently large. This is recent joint work with V. Vicol.


Paul Macklin
USC Medical School
Monday, February 6 KAP 414 3:30 PM - 4:30 PM
Patient-calibrated simulation of ductal carcinoma in situ (DCIS): a small step from the blackboard towards the bedside

Ductal carcinoma in situ (DCIS)--a type of breast cancer whose growth is confined to the duct lumen--is a significant precursor to invasive breast carcinoma. DCIS is commonly detected as a subtle pattern of calcifications in mammograms. Radiologic imaging (including mammography) is used to plan surgical resection of the tumor (lumpectomy), but multiple surgeries are often required to fully eliminate DCIS. On the other hand, pathologists use pre-surgical biopsies to stage the DCIS, assess its metastatic potential, and choose adjuvant therapies. There is currently no technique to combine these data to improve surgical and therapeutic planning. Mechanistic, patient-tailored computational models may provide such a link between multiple data types. In this talk, we focus on developing and calibrating biologically-grounded mathematical models to individual patients, encouraging (and validated!) results in quantitatively predicting clinical progression, the implications for making and quantitatively testing biological hypotheses, and the role of mathematical modeling in facilitating a deeper understanding of pathology and mammography.


Christian Borgs
Microsoft Research New England
Monday, February 13 KAP 414 3:30 PM - 4:30 PM
Everyone Wants their Fair Share: Nash Bargaining on Exchange Networks

If two people are asked to split a dollar, with one of them suggesting a split, and the other either accepting the offer, or rejecting it (in which case the dollar is taken away), most subjects reject the offer unless the split is fair, i.e., roughly 50/50. In exchange networks, where agents have to decide which neighbor they want to trade with, as well as how to split the profit realized in a trade, the notion of fair splits is more complicated, and is captured in the concept of a so-called Nash bargaining solution. But this concept is an equilibrium concept, and does not address the question whether there exist local algorithms which mimic the behavior of real players and at the same time converge fast to the Nash bargaining solution.
In this talk I review work by M. Bayati, J.T.Chayes, Y. Kanoria, A. Montanari and myself in which we give such an algorithm, and prove that it converges. One of the tools used in the paper is a beautiful fixed point theorem Brouwer wanted to prove but couldn't.


Jennifer Chayes
Microsoft Research New England
Tuesday, February 14 SSL 150 3:30 PM - 5:00 PM
Special Location
Interdisciplinarity in the Age of Networks

Everywhere we turn, we find that networks have become increasing appropriate descriptions of relevant interactions. In the high tech world, we see mobile networks, the Internet, the World Wide Web, and a variety of online social networks. In economics, we are increasingly experiencing both the positive and negative effects of a global networked economy. In epidemiology, we find disease spreading over our ever growing social networks, complicated by mutation of the disease agents. In problems of world health, distribution of limited resources, such as water resources, quickly becomes a problem of finding the optimal network for resource allocation. In biomedical research, we are beginning to understand the structure of gene regulatory networks, with the prospect of using this understanding to manage the many diseases caused by gene misregulation. In this talk, I look quite generally at some of the models we are using to describe these networks, and at some of the methods we are developing to indirectly infer network structure from measured data. In particular, I will discuss models and techniques which cut across many disciplinary boundaries.


Victor Pereyra
Stanford, Energy Resources Engineering
Monday, February 27 KAP 414 3:30 PM - 4:30 PM
Compressed fast solution of the acoustic wave equation

There are many applications in which is necessary to solve the acoustic or elastic wave equation in general media repeatedly, such as seismic imaging for seismology and energy resources exploration, optimal design and in general parametric studies such as those necessary to overcome uncertainty.
In 3D general media, even with the largest supercomputers, it is still impossible to get timely solutions for the problems listed above. We propose to use a general technique: Model Order Reduction, in order to lessen the size and cost of simulations of large dynamical systems to solve this problem.
One such approach is obtained when using he Proper Orthogonal Decomposition or Karhunen-Loeve transform, which relies on taking as a basis snapshots of one or just a few full fidelity simulations for use in a Galerkin collocatiom method.
We show (in 2D) how this approach can produce reasonably accurate solutions to problems that are perturbations of the ones used for calculating the snapshots, leading to a methodology that can be applied today to solve the above large scale time demanding problems.


Matania Ben Artzi
Hebrew University
Monday, March 26 KAP 414 3:30 PM - 4:30 PM
The evolution of vortices in planar flows

The celebrated work of Leray (eighty years ago) settled the basic questions concerning the well-posedness of the Navier-Stokes equations in the plane (two dimensions). However, the basic premise of this work was the assumption that the initial velocity field is (at least) locally square integrable (namely, locally finite kinetic energy).
Thus, some primary fluid dynamical objects (notably point vortices) have been excluded (as they generate non square integrable velocities).
The topic of well posedness of such flows has been taken up only some twenty five years ago, and the final uniqueness result was obtained by Gallagher and Gallay five years ago.
In this talk we review the story of such flows, including basic open problems concerning the behavior of steady state solutions in bounded domains.


Edward Witten
Institute for Advanced Study
Wednesday, March 28 SAL 101 3:45 PM - 4:45 PM
Special Time & Location
Khovanov Homology And Gauge Theory

In this talk, I will sketch a new approach to Khovanov homology of knots and links based on counting the solutions of certain elliptic partial differential equations in four and five dimensions. The equations are formulated on four and five-dimensional manifolds with boundary, with a rather subtle boundary condition that encodes the knots and links. The construction is formally analogous to Floer and Donaldson theory in three and four dimensions. It was discovered using quantum field theory arguments but can be described and understood purely in terms of classical gauge theory.


Yali Amit
University of Chicago
Monday, April 9 KAP 414 3:30 PM - 4:30 PM
Object configuration models in computer vision

The goal of Computer Vision is the automatic labeling of images containing multiple objects as well as noise and clutter. Recent work has focused on two main tasks. The first is the classification among object classes in segmented images containing only one object and the second is the detection of a particular object class in a large image. Both tasks have been primarily addressed using discriminative learning.
It is not clear however how these methods can extend to deal with the recognition of multiple object classes in images containing a number of objects in a wide range of configurations.
I will present an approach which starts from simple statistical models for individual objects. With these models the important notion of invariance can be clearly formulated.
Furthermore the individual object models can be composed to define models for object configurations. Decisions are likelihood based and do not depend on pretrained decision boundaries.
The model formulation also leads to a coarse to fine strategy for efficient computation of the optimal scene annotation.
These ideas will be illustrated in several applications reading handwritten zipcodes, detecting faces, and tracking vesicles in video microscopy.


Eva Kanso
USC Aerospace and Mechanical Engineering
Monday, April 16 KAP 414 3:30 PM - 4:30 PM
Fishes and Multi-dipole Interactions

I will discuss aspects of (a) passive locomotion and stability in unsteady flows and (b) motion synchronization of m ultiple dipoles. The main theme connecting these projects, and one of the underlying motivation for this work, comes from our efforts to understand the role of fluid-structure interactions in fish locomotion and fish schooling. Throughout the talk, I w ill use a low-order modeling and computational approach and show, among other results, that fluid coupling may facilitate pass ive synchronization of multiple swimmers.

Short Bio: Eva Kanso is an associate professor and Z.A. Kaprielian fellow in Aerospace and Mechanical Engineering at the Unive rsity of Southern California (USC). Prior to joining USC in 2005, Kanso held a two-year post-doctoral position at Caltech. She received her PhD (2003) and MS (1999) in Mechanical Engineering as well as her MA (2002) in Mathematics from the University o f California at Berkeley.


Olivier Pinaud
Stanford Math Department
Monday, April 23 KAP 414 3:30 PM - 4:30 PM
Wave in random media and applications

We will review some recent results related to wave propagation in random media and applications to imaging. We'll explain how some relevant physical scales influence the nature of the inverse problem and present different adapted techniques. In particular, we will focus on a regime in which the wave strongly interacts with the medium and present some related results of asymptotics of random PDEs, possibly non-linear.
Various numerical simulations confirming the theory will be shown.

Colloquia for the Fall 2011 Semester

Milton Lopes
University of Campinas
Monday, September 12 KAP 414 3:30 PM - 4:30 PM
On the vortex-wave system

The vortex-wave system is the coupling of the two-dimensional vorticity equation with the point vortex system.
It represents the motion of sharply concentrated vorticity in a continuously varying vorticity background. In this talk we discuss some recent results on existence and uniqueness of solutions, and directions for future investigation.


Vlad Vicol
University of Chicago
Monday, September 19 KAP 414 3:30 PM - 4:30 PM
Non-local Maximum Principles

Non-local maximum principles have recently been found to be very useful for proving the global regularity of smooth solutions to critical advection-diffusion equations, such as the critically diffusive SQG equation. In this talk I will discuss some recent results in which non-local maximum principles are successfully applied to equations that are "slightly super-critical", and even to equations without diffusion. This is joint work with M. Dabkowski and A. Kiselev.




Monday, September 26 KAP 414 3:30 PM - 4:30 PM
Panel discussion: "Planning your career: questions and advice"

All graduate students are encouraged to come and ask questions about planning their future careers.


Milind Tambe
Computer Science, USC
Monday, October 3 KAP 414 3:30 PM - 4:30 PM
Game Theory for Security: Lessons learned from deployed applications

Security at major locations of economic or political importance or transportation or other infrastructure is a key concern around the world, particularly given the threat of terrorism. Limited security resources prevent full security coverage at all times; instead, these limited resources must be deployed intelligently taking into account differences in priorities of targets requiring security coverage, the responses of the adversaries to the security posture and potential uncertainty over the types of adversaries faced. Game theory is well-suited to adversarial reasoning for security resource allocation and scheduling problems. Casting the problem as a Bayesian Stackelberg game, we have developed new algorithms for efficiently solving such games to provide randomized patrolling or inspection strategies: we can thus avoid predictability and address scale-up in these security scheduling problems, addressing key weaknesses of human scheduling. Our algorithms are now deployed in multiple applications. ARMOR, our first game theoretic application, has been deployed at the Los Angeles International Airport (LAX) since 2007 to randomizes checkpoints on the roadways entering the airport and canine patrol routes within the airport terminals. IRIS, our second application, is a game-theoretic scheduler for randomized deployment of the Federal Air Marshals (FAMS) requiring significant scale-up in underlying algorithms; IRIS has been in use since 2009. Similarly, a new set of algorithms are deployed in the port of Boston for a system called PROTECT for randomizing US coast guard patrolling; PROTECT is now headed to New York; and GUARDS is under evaluation for national deployment by the Transporation Security Administration (TSA). These applications are leading to real-world use-inspired research in computational game theory in scaling up to large-scale problems, handling significant adversarial uncertainty, dealing with bounded rationality of human adversaries, and other fundamental challenges. This talk will outline our algorithms, key research results and lessons learned from these applications.


Helena Nussenzvieg-Lopes
University of Campinas
Monday, October 10 KAP 414 3:30 PM - 4:30 PM
Recent progress on the evolution of vortex sheets

Vortex sheets are idealized models for flows with intense shear in a thin layer; they are ubiquitous in fluid flow. In this talk I will discuss recent progress on the modeling of the evolution of vortex sheets, exploring both an explicit point of view, which involves parametrizing the sheet and studying the ensuing Birkhoff-Rott equations, and an implicit point of view, in which vortex sheets are given as initial data for the incompressible Euler equations.


Julien Emile-Geay
Geophysics, USC
Monday, October 24 KAP 414 3:30 PM - 4:30 PM
The Mathematics of Paleoclimate Reconstructions

In 1998, a seminal study by Mann, Bradley and Hughes took advantage of climate signals embedded in an array of high-resolution paleoclimate proxy data to conclude that “Northern Hemisphere mean annual temperatures for three of the past eight years are warmer than any other year since (at least) AD 1400.” The so-called “hockey stick” reconstruction showed relatively stable temperatures for most of the millennium, until the start of the Industrial Revolution, when reconstructed temperatures began a steep rise to a level not seen in the last millennium.
Since 2001, when the third assessment report by the Intergovernmental Panel on Climate Change featured the “hockey stick” prominently, this graph has become the emblem of the debate on anthropogenic global warming. No other picture conveys how anomalous recent climate change is in the context of natural variations in temperature over the past millennium. Defended as definitive proof of global warming by many climate scientists and sympathetic members of the public, hailed as a "misguided and illegitimate investigation" by some politicians, it remains one of the most hotly debated climate studies ever published. After a questionable a congressional inquiry was conducted under the aegis of Edward Wegman (then president of the American Statistical Association), most statisticians are now convinced that the "hockey stick" is a fluke due to the overfitting of noisy data.
In this talk, I will describe the most recent statistical methods developed to reconstruct climate fields ; explain how their performance can be assessed in a realistic geophysical context ; and show that, contrary to popular belief, climate scientists are, in fact, working hand-in-hand with professional statisticians, with some promising results.


Leonid Ryzhik
Stanford University
Monday, October 31 KAP 414 3:30 PM - 4:30 PM
Waves and particles in weakly random media

Particles propagating in a weakly random medium are affected in a non-trivial way after propagation over long distance. Typically, after a sufficiently long time their trajectories converge in law to a Brownian motion or another random process, often a diffusion. It has been recently observed that when the random medium has two-point correlations that decay sufficiently slow in space, various observables become randomized on different time scales leading to a greater "temporal diversity". I will review some of the results in this direction.


Gautam Iyer
Carnegie-Mellon
Friday, November 11 KAP 245 3:30 PM - 4:30 PM
Special Location
Pressure and Incompressibility

The evolution of the velocity field of incompressible fluids is governed by the Navier-Stokes equations. The pressure term in these equations is a Lagrange multiplier used to enforce the incompressibility constraint. Unfortunately, the non-local (and non-linear) nature of the pressure causes numerous problems, both from a numerical and analytical perspective.
In order to produce efficient (and unconditionally stable) numerical schemes, Liu, Liu and Pego replaced the incompressibility constraint with an explicit formula for the pressure. While this helped the numerics, some analytical questions become much harder. I will briefly address a few resolved, and unresolved analytical issues related to these equations.


Josef Malek
Mathematical Institute, Charles University in Prague
Friday, November 18 KAP 245 3:30 PM - 4:30 PM
Special Location
On Large Data Analysis of Kolmogorov's Two Equation Model of Turbulence

Kolmogorov seems to be the first who recognized (in 1941) that a two equation model of turbulence might be appropriate to turbulent flow prediction. We present the results (joint work with M. Bulicek) concerning long-time and large-data existence of weak solution to three-dimensional flows described by this Kolmogorov's two equation model of turbulence. Similar results (joint work with M. Bulicek and R. Lewandowski) associated with one equation model of turbulence (for turbulence kinetic energy) will be presented as well. The latter result will be completed by a conjecture concerning the regularity of such a weak solution.


Yuval Peres
Microsoft
Monday, November 21 KAP 414 3:30 PM - 4:30 PM
Laplacian Growth and the Mystery of the Abelian Sandpile: a Visual Tour

We compare several growth models on the two dimensional lattice.
In some models, like internal DLA and rotor-router aggregation, the scaling limits are universal; in particular, starting from a point source yields a disk. In the abelian sandpile, particles are added at the origin and whenever a site has four particles or more, the top four particles topple, with one going to each neighbor. Despite similarities to other models, for the sandpile, the intriguing pattern that arises is not circular and depends on the particular lattice. A scaling limit exists for the sandpile, as was recently shown by Pegden and Smart, but it is not universal and still mysterious. This research has been greatly influenced by pictures of the relevant sets, which I will show in the talk. They suggest a connection to conformal mapping which has not been established yet. Talk based on joint works with Lionel Levine.


Walter Craig
McMaster University
Monday, November 28 KAP 414 3:30 PM - 4:30 PM
Lower bounds on the Navier - Stokes singular set

The well-known result of partial regularity for solutions of the Navier - Stokes equations provides an upper bound on the size of the singular set of (suitable) weak solutions. This talk will describe complementary lower bounds, both for the the singular set and the energy (L^2 norm) concentration set, in case that they are nonempty. The bounds are microlocal in nature, and are based on a novel estimate for weak solutions of the Navier - Stokes equations. These results, in part, represent joint work with A. Biryuk and M. Arnold.


Nancy Kopell
Boston University
Monday, December 5 GER Auditorium 3:30 PM - 4:30 PM
Special Location
Connecting The Dots: Propofol, Parkinson’s Disease and Brain Rhythms

Rhythms of the nervous system are produced in all cognitive states, and have been shown to be highly associated with a myriad of cognitive tasks. Thus, changes in these rhythms, however they come about, are likely to change the ability to do such tasks. This talk focuses on the beta (12-30 Hz) and alpha (9-11) rhythms, and pathological states due to anesthesia and PD; it is about three related studies, the latter two emerging from the first one. The first concerns an early stage of anesthesia, in which, paradoxically, the subject gets more excited and disoriented. With low propofol, the brain rhythms show an increase in beta oscillations, which in normal awake state is associated with brain functions including motor preparation and higher-order processing.
The second concerns the beta oscillations associated with abnormal motor control in Parkinson’s disease. The relationship between the two phenomena can be seen from the underlying physiology using modeling as well as experiments. Finally, the first story led to looking at higher doses of propofol at which consciousness is lost, and uses experimental data to get new ideas about the physiological basis for the loss of consciousness. Again, the focus on relevant physiology of the rhythms is what led, though modeling, to the new insights. Applications to other states of consciousness, such as coma, may be discussed.