Weekly Calendar

December 3-7, 2001

Monday Tuesday Wednesday Thursday Friday

Seminars Announcements Conferences Calendar Archive

Items for inclusion in the Weekly Calendar should be submitted via e-mail to Hilda Britt. Deadline for inclusion in the Weekly Calendar is 5 p.m. Thursdays. Speakers are encouraged to provide abstracts.

Orange & Blue Bar



MONDAY, DECEMBER 3

  
RAP ``Etale cohomology'',  159 Altgeld Hall,  10:00 a.m.
  
Marco Schlichting (Doob Postdoc, UIUC)
Proper base change theorem (cont.)

  
Communications Group Seminar,  141 CSL,  4:00 p.m.
  
Nigel Boston (Associate Professor, UIUC)
Stable polynomials from truncations and architecture-driven filter transformations
  
Abstract: Denote the transfer function of an IIR filter by B(z)/A(z). The computational complexity of the inner feedback loops can be considerably reduced by finding a ßtable" (i.e. all of whose roots lie in the unit circle) polynomial D(z) such that A(z)D(z) has its first few coefficients zero or powers of 2. Mathematically, this amounts to being given a polynomial f(z) and asked to find a stable polynomial D(z) which truncates to f(z). Russian mathematicians c. 1940 showed that this could always be done, but without addressing the question of the degree of D(z). In this talk, I give explicit methods that give complete answers for low degree f(z) and that in practice yield lower degree D(z) than previously found, resulting in reduction in hardware overhead.

  
Special Applied Math Seminar,  241 Altgeld Hall,  4:00 p.m.
  
Jay Mittenthal (Department of Cell and Structural Biology, UIUC)
How cells avoid errors: Design of molecular networks with topology for robust performance
  
Abstract: Networks of molecular processes within living cells are likely to be robust, in that their performance depends largely on their topology and is relatively insensitive to variations in dynamical parameters. Such robustness may be associated with a low probability of a false negative response, P(F-)-not responding to an appropriate input-and/or a low probability of a false positive response, P(F+)-producing output without appropriate input. These probabilities correlate with a basic aspect of topology, the number of reaction steps (N), differently for metabolic and regulatory networks. The matter-processing pathways of metabolism can not give a F+, producing output without the substrates that are their inputs. For metabolism natural selection tends to lower P(F-) by reducing N, as shown for the pentose phosphate pathway and the Krebs citric acid cycle. Regulatory networks, including those that mediate signaling and gene regulation, can give F+ and F- responses. A F+ response may stimulate inappropriate proliferation or death of the cell. Many signaling networks have more than the minimum N needed to transmit signals; the topology of the additional processes tends to reduce P(F+). To explore relations between robustness and topology we have developed new methods for finding the network topologies compatible with specified constraints.

  
VIGRE: Math 500,  243 Altgeld Hall,  4:00 p.m.
  
David Murphy (Graduate Student, UIUC)
Alternatives to Algebraic Quotients
  
Abstract: The set of closed orbits of a group's action in an algebraic variety can be given the structure of an algebraic variety, called the ``algebraic quotient.'' In the case of a reductive algebraic group's action, however, there may be a number of non-closed orbits that are not included in this orbit space. Recent alternatives, such as Chow and Hilbert quotients, provide a partial correction to this problem. These alternatives will be discussed and compared with algebraic quotients.



TUESDAY, DECEMBER 4

  
Symplectic and Contact Geometry RAP,  143 Henry Bldg,  10:00 a.m.
  
Hui Li (Graduate Student, UIUC)
Fundamental group of Hamiltonian S1 manifolds
  
Abstract: Let (M,w) be a connected, compact symplectic manifold equipped with a Hamiltonian S1 action. I use Morse theory to prove p1(M) = p1(minimum) = p1(maximum) = p1(Mred), where Mred is the symplectic quotient at any value in the image of the moment map.

  
Max Newman Topology,  345 Altgeld Hall,  11:00 a.m.
  
Tilman Bauer (M.I.T.)
p-compact groups as framed manifolds

  
RAP ``Spaces of non-positive curvature'',  243 Altgeld Hall,  11:00 a.m.
  
Ilya Kapovich (Assistant Professor, UIUC)
End-of-the-semester business
  
Abstract: We will discuss a few examples of boundaries of CAT(0) spaces and also talk about the plans for the next semester.

  
Quantum Information Science Seminar,  280 Materials Research Laboratory,  12:00 p.m.
  
Dr. David Kielpinski (MIT)
Entanglement and decoherence in a trapped-ion quantum register
Dr. Kielpinski has recently been a member of David Wineland's group at NIST (Boulder), and is currently a working in Wolfgang Ketterle at MIT.

  
Analytic and Elementary Number Theory,  243 Altgeld Hall,  1:00 p.m.
``No meeting; see the Erdos video presentation at 4 pm''.
Geometry/Topology group meeting

  
Logic Seminar,  241 Altgeld Hall,  1:00 p.m.
  
Carl Jockusch (Professor, UIUC)
Ramsey's Theorem and the Arithmetical Hierarchy
  
Abstract: Let [X]n denote the set of all n-element subsets of the set X . A form of Ramsey's Theorem asserts that for any infinite set X and any function f from [X]n to {0,1} there is an infinite subset Y of X which is ``homogeneous'' in the sense that f is constant on [Y]n. Effective versions of this result concern the case where X is the set of all natural numbers and the function f is computable. I will discuss where Y can be chosen to lie in the arithmetical hierarchy, with emphasis on the strong form where the infinite homogeneous set Y must be independent of the computable function f , modulo finite sets. This is recent joint work with Tamara Lakins and answers some questions we raised (for the case n > 2) and also (blush) refutes a previously published result of ours (for the case n = 2). These results shed some light on the extent to which the proof of Ramsey's Theorem can be made effective.

  
Geometric Potpourri Seminar,  243 Altgeld Hall,  2:00 p.m.
  
John Sullivan (Associate Professor, UIUC)
Ropelength Criticality, the Tight Clasp, and the Distance between Circles
  
Abstract: The ropelength of a curve is its length divided by its thickness, the radius of the largest embedded normal tube. We will consider a balancing condition for a curve to be tight, that is, a critical point for ropelength. Surprisingly, the tips of a tight simple clasp (between two parallel planes) are not semicircles. We will also consider the related problem of finding the distance between two skew circles in space.

  
RAP on Geometric Representation Theory,  345 Altgeld Hall,  2:30 p.m.
  
William Haboush, (Professor, UIUC)
Chapter 2 of Chriss and Ginzburg (cont.)

  
Graph Theory and Combinatorics,  241 Altgeld Hall,  3:00 p.m.
  
Rong Luo (West Virginia University)
Nowhere-zero 4-flows and simultaneous edge-colorings
  
Abstract: It is proved that every bipartite graphic sequence with minimum degree at least 2 has a realization that admits a nowhere-zero 4-flow. This result implies a conjecture originally proposed by Keedwell in 1993 and reproposed by Cameron in 1999 about simultaneous edge-colorings and critical partial Latin squares. This is joint work with Wenan Zang and Cunquan Zhang.

  
Study Seminar on Harmonic Analysis,  347 Altgeld Hall,  3:00 p.m.
  
Dr. Jorge Rivera-Noriega (Doob Postdoc, UIUC)
Harmonic analysis in locally flat domains, cont.
  
Abstract: We are studying the paper of C. Kenig and T. Toro on harmonic analysis in locally flat domains

  
Erdos video presentation,  245 Altgeld Hall,  4:00 p.m.
  
Abstract: This is an encore presentation of a documentary on Paul Erdos that was first shown during the summer. With over 1500 papers, Erdos is the most prolific mathematician of all time, and is perhaps most famous for the problems he posed which stimulated legions of mathematicians. Erdos passed away in 1996 at the age of 83, while attending a mathematical meeting. He was a frequent visitor to this department, and many faculty and staff know him personally and have fond memories of his visits. Erdos received an honorary doctorate from the University of Illinois for having contributed to more existing fields than any other living mathematician. The video shown will be an award winning documentary on Erdos, produced by George Csicsery, and titled ``N is a number: a portrait of Paul Erdos. The story of a wandering mathematician obsessed with unsolved problems.''

WEDNESDAY, DECEMBER 5

  
RAP ``Etale cohomology'',  159 Altgeld Hall,  10:00 a.m.
  
Marco Schlichting (Doob Postdoc, UIUC)
Proper base change theorem (cont.)

  
RAP on Quantum Cohomology,  160 English Bldg,  3:00 p.m.
  
Yong Fu (Graduate Student, UIUC)
Chapter 9 of the paper by Fulton and Pandheripande

  
Nonstandard Analysis Seminar,  243 Altgeld Hall,  4:00 p.m.
  
Peter Loeb (Professor, UIUC)
The Best way to differentiate measures and the connection with a fundamental operator in analysis, II
  
Abstract: The first talk uses no nonstandard analysis. It deals with measure differentiation, and is background for what comes later. We show that there is an optimal way to differentiate measures when given a consistent choice of where zero limits must occur. The appropriate differentiation basis is formed following a pattern similar to an optimal approach system for producing boundary limits in potential theory. Applications include the existence of Lebesgue points, approximate continuity, and liftings for the space of bounded measurable functions.
This is joint work with J. Bliedtner.

  
Special Seminar,  241 Altgeld Hall,  4:00 p.m.
  
Mike Mandell (Univ. of Chicago)
Algebraic Models for Homotopy Theory

  
Information Protection Seminar,  114 Coordinated Science Lab,  4:30 p.m.
  
Matt Wolak (Graduate Student, UIUC)
Power Analysis Attacks
  
Abstract: Power analysis attacks attempt to gain more information about private key data by careful observation of the power used by the cryptographic device. Power analysis is known as a ``side channel'' attack, as it uses information which is not a part of the communications of the protocol. These attacks may be used against naive implementations of algorithms which are themselves secure.


THURSDAY, DECEMBER 6

  
Math - Physics (BCDE) Lunch Seminar,  6-110 Engineering Science Bldg,  12:05 p.m.
See listing Friday at 11:30 a.m.

  
Analytic and Elementary Number Theory,  243 Altgeld Hall,  1:00 p.m.
No meeting today

  
Group Theory,  347 Altgeld Hall,  1:00 p.m.
  
Peter Brinkmann (Doob Postdoc)
Morse theory on cell complexes (cont.)
  
Abstract: I will discuss Morse theory on affine cell complexes as introduced by Bestvina and Brady, as well as applications to finiteness properties of groups

  
Algebraic Number Theory,  241 Altgeld Hall,  2:00 p.m.
  
Professor Scott Ahlgren (Assistant Professor, UIUC)
Modular forms and partitions
  
Abstract: Eighty years ago, Ramanujan conjectured and proved some striking congruences for the ordinary partition function p(n). I will describe joint work with K. Ono in which we prove that such congruences are much more widespread than was previously known. Our results rely on tools from the theory of modular forms (and in particular the work of Deligne, Serre, and Shimura).

  
Knot Theory RAP,  345 Altgeld Hall,  2:00 p.m.
Organizational meeting & Video presentation: ``Not Knot'' by Charlier Gunn

  
RAP on Research Problems in Coloring Theory and Extremal Combinatorics,  241 Altgeld Hall,  3:00 p.m.
Research Problems in Combinatorics

  
Mathematics Colloquium,  245 Altgeld Hall,  4:00 p.m.
  
Ping Xu (Penn State University)
Symplectic realizations of Poisson manifolds
  
Abstract: Poisson manifolds appear as general phase spaces in classical mechanics. A Poisson manifold is called symplectic, or non-degenerate if locally it has coordinates (qi, pi) satisfying the standard canonical relation qi, pj= dij, etc. in Hamiltonian mechanics. The idea of realizing a Poisson bracket by non-degenerate or symplectic structure can be traced back to S. Lie in the 19th century. The existence of symplectic realizations for arbitrary Poisson manifolds was proved independently by Karasev and Weinstein in late 80's. In this talk, I will discuss some recent development around this topic. In particular, I will explain a theorem by Mackenzie and myself about the integration of Lie bialgebroids. Our theorem not only gave a new proof for the Karasev and Weinstein's theorem as a consequence, but also solved some mystery surrounding their theorem about an additional structure of the so called symplectic groupoids. Such a structure of symplectic groupoids is also related to Kontsevich *-products as recently shown by Cattaneo and Felder.
Refreshments at 3:15 p.m. in Room 321 Altgeld Hall


FRIDAY, DECEMBER 7

  
RAP ``Etale cohomology'',  159 Altgeld Hall,  10:00 a.m.
TBA

  
Math - Physics (BCDE) Lunch Seminar,  358 Loomis,  11:30 a.m.
  
John McGreevy (Stanford)
Linear Sigma Models for Open Strings, with Applications
  
Abstract: I will couple two-dimensional N = (2,2) gauge theories to boundary matter in order to make them flow to worldsheet CFTs for open strings. In particular, I will focus on models for strings ending on BPS D-branes on even-dimensional cycles of Calabi-Yau threefolds. This framework provides an effective way of thinking about the role of the derived category of coherent sheaves in D-brane physics. Applications include a study of degenerations and singularities of the CFT, monodromy in closed string moduli space, local models for marginal stability behavior, and a possible matrix definition of these backgrounds.

  
Model Theory Seminar,  141 Altgeld Hall,  4:00 p.m.
  
Wai Yan Pong (Doob Postdoc, UIUC)
Euler Characteristics and Grothendieck Rings for first order structures, II
  
Abstract: We will survey a paper by Krajicek and Scanlon in which they show that K0 of the field of complex numbers contains as subring the ring of polynomials over the integers with continuum many variables.

File translated from TEX by TTH, version 2.01.
On 30 Nov 2001, 13:31.