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FEBRUARY 2008 |
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Department Colloquium |
Topic: |
Volume of polytopes, operator analogues, and Arthur's trace formula |
Presenter: |
Erez Lapid, Hebrew University |
Date: |
Wednesday, February 13, 2008, Time: 4:30 p.m., Location: Fine Hall 314 |
Abstract: |
There are two ways (among many others) to compute the volume of a (convex) polytope. One using a formula of Brion and another using an argument of P. McMullen and R. Schneider. The ensuing identity suggests a non-commutative generalization which we can currently prove for Coxeter zonotopes (e.g. a permutahedron). This algebraic equality plays a role in Arthur's trace formula. This has applications to spectral asymptotics of locally symmetric spaces. No prior knowledge of these subjects is assumed. Joint work with Tobias Finis and Werner Muller. |
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Graduate Student Seminar |
Topic: |
An Outline of the h-Cobordism Theorem |
Presenter: |
Sucharit Sarkar, Princeton University |
Date: |
Thursday, February 14, 2008, Time: 12:30 p.m., Location: Fine Hall 214 |
Abstract: |
In the first half of the talk, we shall go through the definitions of manifold, cobordism, h-cobordism, Morse functions and gradient-like flows, and demonstrate many of their properties. In the second half of the talk we shall give an outline of the proof. In the process, we shall prove lemmas about commutation and cancellation of critical points, and see the Whitney trick in action. Time permitting, we shall show how the h-cobordism theorem proves the topological Poincare conjecture in high dimensions. |
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Ergodic Theory and Statistical Mechanics Seminar |
Topic: |
Quenched Central Limit Theorem for Random Toral Automorphism |
Presenter: |
Mikko Stenlund, Courant Institute, NYU |
Date: |
Thursday, February 14, 2008, Time: 2:00 p.m., Location: Fine Hall 401 |
Abstract: |
The statistical properties of the Lorentz gas with periodically positioned obstacles are well understood. The random case, obtained after each of the obstacles undergoes a small i.i.d. displacement, stands as a challenge. The latter can be studied in terms of a random sequence of hyperbolic symplectic (billiard) maps, which however is not i.i.d. due to recollisions. In fact, even the i.i.d. sequence (no recollisions) is poorly understood.
Motivated by the above, we study an i.i.d. sequence of toral automorphisms in two dimensions. We will argue that the time-N average of any observable has Gaussian fluctuations of order \sqrt{N} for almost every sequence of maps, and that the variance is independent of the sequence. Joint work with Arvind Ayyer (Rutgers) and Carlangelo Liverani (Rome 1). |
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Discrete Mathematics Seminar |
Topic: |
Ramsey numbers of sparse graphs and hypergraphs |
Presenter: |
Jakob Fox, Princeton University |
Date: |
Thursday, February 14, 2008, Time: 2:15 p.m., Location: Fine Hall 314 |
Abstract: |
The Ramsey number r(G) of a graph G is the minimum N such that every 2-coloring of the edges of the complete graph on N vertices contains a monochromatic copy of G. Determining or estimating Ramsey numbers is one of the central problem in Ramsey theory. Besides the complete graph, the next most classical topic in this area concerns the Ramsey number of sparse graphs. The study of these Ramsey numbers was initiated by Burr and Erdos in 1975, and this topic has since placed a central role in graph Ramsey theory. In this talk we will discuss recent progress in this area. Joint work with Benny Sudakov. |
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Differential Geometry Seminar ***Please note special date |
Topic: |
TBA |
Presenter: |
Luc Nguyen, Rutgers University |
Date: |
Thursday, February 14, 2008, Time: 3:00 p.m., Location: Fine 110 |
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Princeton University/IAS Joint Number Theory Seminar |
Topic: |
Prime Chains and Pratt trees |
Presenter: |
Kevin Ford, The University of Illinois at Urbana-Champaign |
Date: |
Thursday, February 14, 2008, Time: 4:30 p.m., Location: Fine Hall 214 |
Abstract: |
A sequence of primes p_1, ..., p_k is called a prime chain if p_j | (p_{j+1}-1) for each j; e.g. 3, 7, 29, 59. We will discuss problems about counting prime chains with certain properties, and about the existence of prime chains with various properties. The Pratt tree for a prime p is the tree with root node p and below p are the Pratt trees of the odd prime factors of p-1. Example: 79
................................../\
................................3 13
........................................\
........................................3
We are concerned with the normal and extremal behavior of the depth of such trees. |
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Symplectic Geometry Seminar |
Topic: |
(Conjectural) triply graded link homology groups of the Hopf link and Hilbert schemes of points on the plane |
Presenter: |
Hiraku Nakajima, Kyoto University and IAS |
Date: |
Friday, February 15, 2008, Time: 2:00 p.m., Location: Fine Hall 314 |
Abstract: |
Gukov et al. suggested triply graded link homology groups via refined BPS counting on the deformed conifold. Through large N duality they identify their Poincar\'e polynomials as refined topological vertices. I further apply the geometric engineering to interpret them as holomorphic Euler characteristics of natural vector bundles over Hilbert schemes of points on the affine plane. Then they perfectly make sense mathematically. This work is very preliminary, but I hope it could be developed further. |
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Group Actions Seminar |
Topic: |
Regularity of conjugacy for actions of large groups |
Presenter: |
Alex Gorodnik, University of Bristol/Princeton University |
Date: |
Monday, February 18, 2008, Time: 12:30 p.m., Location: Fine Hall PL |
Abstract: |
t is well know that a small perturbation of an Anosov map is topologically conjugate to the original map, but the conjugacy is not smooth in general. We prove that for actions of "large" (e.g., Zariski dense) groups topological conjugacy is smooth. This is a joint work with Hitchman and Spatzier. |
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PACM Colloquium |
Topic: |
Did the great masters 'cheat' using optics? Computer vision and graphics addresses a bold theory in art history |
Presenter: |
David G. Stork, Ricoh Innovations and Stanford University |
Date: |
Monday, February 18, 2008, Time: 4:00 p.m., Location: Fine Hall 214 |
Abstract: |
In 2001, artist David Hockney and scientist Charles Falco stunned the art world with a controversial theory that, if correct, would profoundly alter our view of the development of image making. They claimed that as early as 1420, Renaissance artists employed optical devices such as concave mirrors to project images onto their canvases, which they then traced or painted over. In this way, the theory attempts to explain the newfound heightened naturalism or "opticality" of painters such as Jan van Eyck, Robert Campin, Hans Holbein the Younger, and many others.
This talk will describe the application of rigorous computer image analysis to masterpieces adduced as evidence for this theory. It covers basic geometrical optics of image projection, the analysis of perspective, curved surface reflections, shadows, lighting and color. While there remain some loose ends, such analysis of the paintings, infra-red reflectograms, modern reenactments, internal consistency of the theory, and alternate explanations allows us to judge with high confidence the plausibility of this bold theory. You may never see Renaissance paintings the same way again (http://www.diatrope.com/stork/FAQs.html). |
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Geometry, Representation Theory, and Moduli Seminar |
Topic: |
TBA |
Presenter: |
A. Bayer, University of Utah |
Date: |
Wednesday, February 20, 2008, Time: 3:00 p.m., Location: Fine Hall 214 |
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Department Colloquium |
Topic: |
TBA |
Presenter: |
Francois Labourie, Universite de PARIS-SUD |
Date: |
Wednesday, February 20, 2008, Time: 4:30 p.m., Location: Fine Hall 314 |
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Ergodic Theory and Statistical Mechanics Seminar |
Topic: |
TBA |
Presenter: |
Konstantin Khanin, University of Toronto |
Date: |
Thursday, February 21, 2008, Time: 2:00 p.m., Location: Fine Hall 401 |
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Joint Princeton University/IAS Number Theory Seminar |
Topic: |
TBA |
Presenter: |
Mark Kisin, University of Chicago |
Date: |
Thursday, February 21, 2008, Time: 4:30 p.m., Location: Fine 214 |
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Topology Seminar |
Topic: |
Deformation of a hyperbolic 4-orbifold |
Presenter: |
Peter Storm, University of Pennsylvania |
Date: |
Thursday, February 21, 2008, Time: 4:30 p.m., Location: Fine Hall 314 |
Abstract: |
It is well known that Thurston's beautiful deformation theory of hyperbolic structures is mostly useless in dimensions > 3. Steve Kerckhoff and I have been studying a new example of a hyperbolic deformation in 4 dimensions which produces an infinite number of new hyperbolic 4-orbifolds with interesting properties. The talk will attempt to motivate this work. It will be aimed at a general geometry/topology audience. |
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Symplectic Geometry Seminar |
Topic: |
Area-dependence in gauged Gromov-Witten theory |
Presenter: |
Chris Woodward, Rutgers University |
Date: |
Friday, February 22, 2008, Time: 2:00 p.m., Location: Fine Hall 314 |
Abstract: |
I will describe joint work with E. Gonzalez, in which we study the dependence of the moduli space of gauged pseudoholomorphic maps from a surface to a target X as the area form on the surface is varied. As an application, we get some version of the "abelianization" conjecture of Bertram et al relating Gromov Witten theory of symplectic quotients by a group and its maximal torus. This is part of a larger project which aims to develop functoriality of Gromov-Witten invariants of quotients, joint with Ziltener, Ma'u, and Ott. |
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Differential Geometry Seminar |
Topic: |
TBA |
Presenter: |
Ovidiu Munteanu, UC Irvine |
Date: |
Friday, February 22, 2008, Time: 3:00 p.m., Location: Fine Hall 314 |
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Operations Research and Financial Engineering Seminar |
Topic: |
Metric and kernel learning |
Presenter: |
Inderjit Dhillon, University of Texas |
Date: |
Tuesday, February 26, 2008, Time: 4:30 p.m., Location: E-219, E- Quad |
Abstract: |
See http://orfe.princeton.edu/papers/dhillon-abstract.pdf |
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Geometry, Representation Theory, and Moduli Seminar |
Topic: |
Stability conditions and Stokes factors |
Presenter: |
V. Laredo, Northeastern/IAS |
Date: |
Wednesday, February 27, 2008, Time: 3:00 p.m., Location: Fine Hall 214 |
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Department Colloquium |
Topic: |
Integral Apollonian circle packings |
Presenter: |
Jeff Lagarias, University of Michigan |
Date: |
Wednesday, February 27, 2008, Time: 4:30 p.m., Location: Fine Hall 314 |
Abstract: |
Apollonian circle packings are infinite packings of circles, constructed recursively from an initial configuration of four mutually touching circles by adding circles externally tangent to triples of such circles. Configurations of four mutually touching circles were studied by Descartes in 1643. If the initial four circles have integer curvatures, so do all the circles in the packing. If in addition the circles have rational centers so do all the circles in the packing. Why? This talk describes results in geometry, group theory and number theory arising from such packings. (This is joint work with Ron Graham, Colin Mallows, Allan Wilks, and Catherine Yau.) |
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Ergodic Theory and Statistical Mechanics Seminar |
Topic: |
Logarithm laws for horocycles |
Presenter: |
Jayadev Athreya, Princeton University |
Date: |
Thursday, February 28, 2008, Time: 2:00 p.m., Location: Fine Hall 401 |
Abstract: |
In joint work with G. Margulis, we prove a logarithm law for unipotent flows on the space of unimodular lattices in R^n. |
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Joint Princeton University/IAS Number Theory Seminar |
Topic: |
Hilbert Spaces of Entire Functions eand Automorphic L-Functions |
Presenter: |
Jeff Lagarias, University of Michigan |
Date: |
Thursday, February 28, 2008, Time: 4:30 p.m., Location: SH-101, IAS |
Abstract: |
We review the de Branges theory of Hilbert spaces of entire functions. This theory gives a canonical form for a class of operators as multiplication operator together with a generalized Fourier transform taking such an operator to a generalized differential operator. We discuss its relation to other theories of canonical forms for certain non-self adjoint operators, including "model spaces" and Lax-Phillips scattering theory. We present examples, including de Branges spaces associated to automorphic L-functions, and discuss how the Riemann hypothesis may be encoded in this framework. |
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Columbia-Courant-Princeton Algebraic Geometry Seminar |
Topic: |
TBA |
Presenter: |
Mikhail Kapranov, Yale University
Kiran Kedlaya, MIT
James McKernan, MIT |
Date: |
Friday, February 29, 2008, Time: TBA, Location: Columbia University |
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Differential Geometry Seminar |
Topic: |
TBA |
Presenter: |
Aaron Naber, Princeton University |
Date: |
Friday, February 29, 2008, Time: 3:00 p.m., Location: Fine Hall 314 |
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MARCH 2008 |
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Group Actions Seminar |
Topic: |
TBA |
Presenter: |
Amir Mohammadi, Yale University |
Date: |
Monday, March 3, 2008, Time: 12:30 p.m., Location: Fine Hall PL |
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Analysis Seminar |
Topic: |
TBA |
Presenter: |
Sigmund Selberg, Norwegian University of Science and Technology |
Date: |
Monday, March 3, 2008, Time: 4:00 p.m., Location: Fine Hall 110 |
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PACM Colloquium |
Topic: |
TBA |
Presenter: |
Brendan Frey, Electrical & Computer Engineering, University of Toronto |
Date: |
Monday, March 3, 2008, Time: 4:00 p.m., Location: Fine Hall 214 |
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Algebraic Geometry Seminar |
Topic: |
TBA |
Presenter: |
Klaus Hulek, Leibniz Universität Hannover |
Date: |
Tuesday, March 4, 2008, Time: 4:30 p.m., Location: Fine Hall 322 |
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Department Colloquium |
Topic: |
TBA |
Presenter: |
Natasa Sesum, Columbia University |
Date: |
Wednesday, March 5, 2008, Time: 4:30 p.m., Location: Fine Hall 314 |
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Topology Seminar |
Topic: |
Real Projective Structures and Non-standard analysis |
Presenter: |
Daryl Cooper, UCSB |
Date: |
Thursday, March 6, 2008, Time: 4:30 p.m., Location: Fine Hall 314 |
Abstract: |
We investigate the analog of the Thurston boundary of Teichmuller space in the context of convex real projective structures on closed manifolds. In particular we give a new interpretation of measured laminations in terms of non-standard hyperbolic structures over the hyper-reals. |
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Symplectic Geometry Seminar |
Topic: |
TBA |
Presenter: |
Tom Mark, University of Virginia |
Date: |
Friday, March 7, 2008, Time: 2:00 p.m., Location: Fine Hall 314 |
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Analysis Seminar |
Topic: |
TBA |
Presenter: |
Scott Sheffield, Courant Institute |
Date: |
Monday, March 10, 2008, Time: 4:00 p.m., Location: Fine Hall 110 |
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PACM Colloquium |
Topic: |
Branched Polymers |
Presenter: |
Peter Winkler, Mathematics, Dartmouth College |
Date: |
Monday, March 10, 2008, Time: 4:00 p.m., Location: Fine Hall 214 |
Abstract: |
A branched polymer is a finite, connected set of non-overlapping unit balls in space. The powerful "dimension reduction" theorem of Brydges and Imbrie permits computation of the volume of the space of branched polymers of size N in dimensions 2 or 3. We will show how these and some related computations can be done using elementary calculus and combinatorics. New results include methods for random generation, asymptotic diameter in 3-space, and a combinatorial proof of the notorious "random flight" problem of Rayleigh and Spitzer. Joint work with Rick Kenyon (Brown). |
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Algebraic Geometry Seminar |
Topic: |
TBA |
Presenter: |
Gavril Farkas, Humboldt Universität zu Berlin |
Date: |
Tuesday, March 11, 2008, Time: 4:30 p.m., Location: Fine Hall 322 |
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Geometry, Representation Theory, and Moduli Seminar |
Topic: |
TBA |
Presenter: |
Y. Soibelman, Kansas State University |
Date: |
Wednesday, March 12, 2008, Time: 3:00 p.m., Location: Fine Hall 214 |
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Department Colloquium |
Topic: |
TBA |
Presenter: |
Artur Avila, IMPA and Clay Math. Inst. |
Date: |
Wednesday, March 12, 2008, Time: 4:30 p.m., Location: Fine Hall 314 |
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Symplectic Geometry Seminar |
Topic: |
TBA |
Presenter: |
Denis Auroux, MIT |
Date: |
Friday, March 14, 2008, Time: 2:00 p.m., Location: Fine Hall 314 |
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Special Analysis Seminar ***Please note special time |
Topic: |
The abstract concept of Duality and some related facts (part of a joint project with Shiri Artstein-Avidan) |
Presenter: |
Vitali Milman, Tel Aviv University |
Date: |
Monday, March 24, 2008, Time: 2:30 p.m., Location: Fine Hall 110 |
Abstract: |
We discuss in the talk an unexpected observation that very minimal basic properties essentially uniquely define some classical transforms which traditionally are defined in a concrete and quite involved form. We start with a characterization of a very basic concept in Convexity: Duality and the Legendre transform. We show that the Legendre transform is, up to linear terms, the only involution on the class of convex lower semi-continious functions in R^n which reverses the (partial) order of functions. This leads to a different understanding of the concept of duality, which we call an ``abstract duality concept'', and which we then apply also to many other well known settings. It is also true that any involutive transform (on this class) which exchanges summation with inf-convolution, is, up to linear terms, the Legendre transform. The classical Fourier transform may be also defined (essentially) uniquely by the condition of exchanging convolution with product together the form of the square of the transform (the last fact is a joint work also with Semyon Alesker). |
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Analysis Seminar |
Topic: |
TBA |
Presenter: |
Gilbert Weinstein, University of Alabama at Birmingham |
Date: |
Monday, March 24, 2008, Time: 4:00 p.m., Location: Fine Hall 110 |
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PACM Colloquium |
Topic: |
A worldwide web of images |
Presenter: |
Blaise Aguera y Arcas, Microsoft Live Labs |
Date: |
Monday, March 24, 2008, Time: 4:00 p.m., Location: Fine Hall 214 |
Abstract: |
In this talk we'll explore the emerging potential of computer vision to transform the way we think about the interconnectedness of digital imagery and the Web, and how these relate to our physical environment. We'll begin with an introduction to the foundations of "3D computer vision", a bag of tricks which has been developing steadily for three decades, combining classical photogrammetry with machine vision. We'll then dive specifically into Photosynth, based on a combination of the Photo Tourism project (a collaboration between Microsoft Research and the University of Washington) and Seadragon, a multiresolution networked platform allowing one to play with arbitrarily many arbitrary large visual objects using only constant-time and constant-bandwidth operations. The aim of Photosynth is to allow meaningful 3D navigation within real-world environments reconstructed entirely from the photos. Interesting social dimensions are added to this application when one considers that the source photos can be mined from the existing Web, aggregated from user communities, and actively contributed to and interconnected. We'll end with some preliminary findings about the latent graph structure of Internet photography, and a glimpse of where we're heading next. |
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Algebraic Geometry Seminar |
Topic: |
TBA |
Presenter: |
Izzet Coskun, University of Illinois at Chicago |
Date: |
Tuesday, March 25, 2008, Time: 4:30 p.m., Location: Fine Hall 322 |
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PACM Colloquium |
Topic: |
TBA |
Presenter: |
Joyce McLaughlin, Mathematical Sciences, Rensselaer Polytechnic Institute |
Date: |
Monday, March 31, 2008, Time: 4:00 p.m., Location: Fine Hall 214 |
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APRIL 2008 |
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Algebraic Geometry Seminar |
Topic: |
Real singular Del Pezzo surfaces and rationally connected threefolds |
Presenter: |
Frédéric Mangolte, Université de Savoie |
Date: |
Tuesday, April 1, 2008, Time: 4:30 p.m., Location: Fine Hall 322 |
Abstract: |
Recent results on classification of real algebraic threefolds will be described. Let W -> X be a real smooth projective threefold fibred by rational curves. J. Kollár proved that if the set of real points W(R) is orientable, then a connected component N of W(R) is essentially either a Seifert fibred manifold or a connected sum of lens spaces. We proved sharp estimates on the number and the multiplicities of the Seifert fibres and on the number and the torsions of the lens spaces whenever X is a geometrically rational surface. These results answer in the affirmative three questions of Kollár. They are derived from a careful study of real singular Del Pezzo surfaces with only Du Val singularities. This is joint work with F. Catanese. |
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Discrete Mathematics Seminar |
Topic: |
TBA |
Presenter: |
János Pach, NYU and Courant Institute |
Date: |
Thursday, April 3, 2008, Time: 2:15 p.m., Location: Fine Hall 314 |
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PACM Colloquium |
Topic: |
Water Information Networks & Efficiency in Irrigation Systems |
Presenter: |
Iven Mareels, Electrical & Electronic Engineering, The University of Melbourne |
Date: |
Monday, April 7, 2008, Time: 4:00 p.m., Location: Fine Hall 214 |
Abstract: |
The world's sustainable water supply is heavily used (it is estimated that annually 65% of the available water resources are extracted), and with very poor efficiency (typically less than half the water taken from the environment serves the objective for which it was intended). The UNESCO World Water reports 2003/2005 identify management as one of the main issues to be addressed in order to avoid a water catastrophe. Australia is in a particularly critical situation, where management has to deal with significant climate change effects.
In this lecture we outline a sensor networks and systems engineering approach to underpin the management of an entire water catchment basin. The technology exists to construct a sensor network to monitor at a global scale the water resource and manage in closed loop the resource through the distribution infrastructure using the data derived from the sensor network. The control objective is to deliver water on demand with maximal overall efficiency. Such technology would provide the necessary data to implement a sustainable water policy in an adaptive way, where economic, environmental and social issues are properly taken into account.
We review the results from a number of substantial pilot projects in Victoria and New South Whales Australia in which, where Rubicon Systems Australia Pty. Ltd., who commercialise the technology, have realized significant gains in water efficiency in irrigation distribution. We show how this experience may lead to substantial gains in water management overall, and leads to better on farm practices, building further water savings. At present the state government of Victoria is backing this technoly with a 1 billion dollar investment to create significant water savings across the state. We discuss aspects of modeling of water dynamics followed by the control aspects enabled in the present and envisaged hardware upgrades. |
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Geometry, Representation Theory, and Moduli Seminar |
Topic: |
TBA |
Presenter: |
B. Kim, KIAS |
Date: |
Wednesday, April 9, 2008, Time: 3:00 p.m., Location: Fine Hall 214 |
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Department Colloquium |
Topic: |
TBA |
Presenter: |
Marc Levine, Northeastern University |
Date: |
Wednesday, April 9, 2008, Time: 4:30 p.m., Location: Fine Hall 314 |
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Symplectic Geometry Seminar |
Topic: |
TBA |
Presenter: |
Yong-Geun Oh,University of Wisconsin |
Date: |
Friday, April 11, 2008, Time: 2:00 p.m., Location: Fine Hall 314 |
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PACM Colloquium |
Topic: |
Airplane boarding and space-time geometry |
Presenter: |
Eitan Bachmat, Computer Science, Ben-Gurion University and Brandeis University |
Date: |
Monday, April 14, 2008, Time: 4:00 p.m., Location: Fine Hall 214 |
Abstract: |
It is hard to think of a process that is more boring than boarding an airplane. In the hope of relieving, or at least shortening, some of the pain, airlines have devised various boarding strategies such as back-to-front, window to aisle, boarding by zones or even unassigned seating. In the talk we will try to overturn the negative image that airplane boarding has and will try to portray it as a very exciting process which is modeled via space-time (a.k.a Lorentzian) geometry with a touch of random matrix theory. Using the model we will try to figure out what are the better strategies. If time permits, we will use insights from the airplane borading process to suggest an interpretation for Einstein's law of motion in which god plays the ultimate dice game. The talk is entirely self contained. Partly based on joint works with D. Berend, L. Sapir, S. Skiena, M. Elkin and V. Khachaturov. |
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Algebraic Geometry Seminar |
Topic: |
TBA |
Presenter: |
Rajesh Kulkarni, Michigan State University |
Date: |
Tuesday, April 15, 2008, Time: 4:30 p.m., Location: Fine Hall 322 |
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Symplectic Geometry Seminar |
Topic: |
TBA |
Presenter: |
Sergio Lukic, Rutgers University |
Date: |
Friday, April 18, 2008, Time: 2:00 p.m., Location: Fine Hall 314 |
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Group Actions Seminar |
Topic: |
TBA |
Presenter: |
Francois Maucourant, Rennes 1 University |
Date: |
Monday, April 21, 2008, Time: 12:30 p.m., Location: Fine Hall PL |
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Analysis Seminar |
Topic: |
TBA |
Presenter: |
Joachim Krieger, University of Pennsylvania |
Date: |
Monday, April 21, 2008, Time: 4:00 p.m., Location: Fine Hall 110 |
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Algebraic Geometry Seminar |
Topic: |
TBA |
Presenter: |
Robert Lazarsfeld, University of Michigan |
Date: |
Tuesday, April 22, 2008, Time: 4:30 p.m., Location: Fine Hall 322 |
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Geometry, Representation Theory, and Moduli Seminar |
Topic: |
TBA |
Presenter: |
P. Johnson, University of Michigan |
Date: |
Wednesday, April 23, 2008, Time: 3:00 p.m., Location: Fine Hall 214 |
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PACM Colloquium |
Topic: |
Active and Semi-Supervised Learning Theory |
Presenter: |
Rob Nowak, Electrical and Computer Engineering, University of Wisconsin-Madison |
Date: |
Monday, April 28, 2008, Time: 4:00 p.m., Location: Fine Hall 214 |
Abstract: |
Science is arguably the pinnacle of human intellectual achievement, yet the scientific discovery process itself remains an art. Human intuition and experience is still the driving force of the high-level discovery process: we determine which hypotheses and theories to entertain, which experiments to conduct, how data should be interpreted, when hypotheses should be abandoned, and so on. Meanwhile machines are limited to low-level tasks such as gathering and processing data. A grand challenge for scientific discovery in the 21st century is to devise machines that directly participate in the high-level discovery process. Towards this grand challenge, we must formally characterize the limits of machine learning. Statistical learning theory is usually based on supervised training, wherein a learning algorithm is presented with a finite set of i.i.d. labeled training examples. However, modern experimental methods often generate incredibly large numbers of unlabeled data for very little expense, while the task of labeling data is often painstaking and costly. Machine learning methods must leverage the abundance of unlabeled data in scientific problem domains. Active learning (AL) and semi-supervised learing (SSL) are two well known approaches to exploit unlabeled data. In both paradigms one has access to a large pool of unlabeled examples, and only a few labeled examples are provided or selected. AL is a sequential feedback process. Unlabeled examples that are predicted to have very informative labels, based on previously gathered labeled and unlabeled data, are selected for labeling. In SSL, labeled examples are randomly provided, without regard to potential informativeness. Today, little is known about theoretical limits of AL and SSL performance. Sparsity and complexity of the underlying data-generating distributions appear to play a central role in the performance of AL and SSL, and this talk will discuss some of the known theoretical results.
This work is joint with Rui Castro, Aarti Singh and Jerry Zhu. |
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