CURRENT
SCHEDULE

ARCHIVES

SPRING 2003

FALL 2002

SPRING 2003

Wednesday January 29, 2003

Topic: A Counterexample to a Discrete Analogue of Caratheodory Theorem
Abstract: Arbitrary convex polytope is a union of simplices that are spanned by vertices of the polytope, equivalently - arbitrary finite polyhedral cone is a union of simplicial cones that are spanned by extremal rays of the original cone. This is Caratheodory's classical theorem proved almost a century ago. Surprisingly, the proof of a discrete analogue of this fact that takes care on the lattice points inside a polytope (or cone) has remained elusive until very recently. A combination of an arithmetic study and extensive explicit computations (with powerful computers during several months!) have eventually led the author, in collaboration with W. Bruns, to an aesthetic and, to some extent, unexpected couterexample in dimension 5.

Speaker: Joseph Gubeladze, Georgian Academy of Sciences
Sponsor: Mathematics Department
Time: 5:00-6:00 pm
Place: Thornton Hall 211

Monday February 3, 2003

Topic: First Results from the KamLAND Neutrino Experiment
Speaker: Dr. Yoshi Uchida, Postdoctoral Fellow, Stanford University
Sponsor: Physics and Astronomy Colloquium
Time: 4:00 pm
Place: Thornton Hall 411

Monday February 3, 2003

Topic: Motivic homotopy theory
Abstract: Recent work of Morel and Voevodsky makes it possible to apply the basic principles of algebraic topology to algebraic geometry. In essence, we can now study the homotopy theory of algebraic varieties. Such algebraic topological tools have been used to answer some fundamental questions in algebraic geometry. I'll give a leisurely introduction to this subject for the non-specialist and describe how my own work fits into the picture.

Speaker: Dan Isakson, Notre Dame (Indiana)
Sponsor: Mathematics Department
Time: 5:00-6:00 pm
Place: Thornton Hall 211

Friday February 7, 2003

Topic: Chemical Composition of Stars with Extrasolar Planets
Abstract: In the past seven years, more than 100 extrasolar planets have been discovered by Doppler surveys. The Doppler detection of an extrasolar planet requires velocity measurements over one full orbital period. A natural consequence of this requirement is that there is a gradual harvesting of planets from the closest to the widest orbital separations. Because gas giant planets are expected to form outside of a 3 AU radius, the discovery of Jovian mass planets in eccentric orbits closer than 1 AU prompted a cascade of theories on orbital migration. Implicit in the concept of orbital migration is the expectation that not all migrating planets and planetesimals will park in stable orbits; some gas-depleted material will fall into the star and mix in the convective zone, enriching the chemical composition of the host stars.

Thus, it was intriguing when the first planet-bearing stars were found to have solar, or higher, iron abundances. The correlation between chemical composition and the presence of extrasolar planets has persisted and has become the subject of increasing debate. At issue is the question of whether the metallicity correlation is primarily an initial condition that enhances the formation of planets, or a by-product from the accretion of planets. In this talk I will present results from spectral analysis of about 500 star on the Lick and Keck planet search surveys and discuss the surprising lack of evidence for an accretion signature in this data set.

Speaker: Dr. Debra Fischer, Research Astronomer, University of California, Berkeley
Sponsor: Physics and Astronomy Colloquium
Time: 4:00 pm
Place: Thornton Hall 411

Friday February 7, 2003

Topic: Integer-point enumeration in polytopes
Abstract: We use generating functions and complex-analytic methods to count integer (``lattice'') points in polytopes with rational vertices. More precisely, we study the number of lattice points as the polytope gets dilated by an integer factor. This expression is known as the Ehrhart quasipolynomial.

Because polytopes can be described by a system of linear equalities and inequalities, they appear in a wealth of areas. We will show applications of Ehrhart quasipolynomials to number theory (Dedekind sums), combinatorics (the `coin-exchange problem' of Frobenius), and computational geometry (the Birkhoff polytope of doubly stochastic matrices).

Speaker: Matthias Beck, Binghamton University (SUNY)
Sponsor: Mathematics Department
Time: 5:00-6:00 pm
Place: Thornton Hall 211

Monday February 10, 2003

Topic: Polynomial Inequalities
Abstract: The classical Bernstein inequality states that for a trigonometric polynomial p(t), the absolute value |p'(t)| of the derivative at any point is bounded above by the degree of p times the supremum norm of p (think, e.g., of p(t)=cos(nt), deg(p)=n). Since p can be considered as a polynomial q(x,y) of two real variables restricted to the unit circle S (x=cost, y=sint), this inequality can be interpreted as an estimate on the tangential derivative of q along S. We show, using elementary linear algebra and calculus, that such types of polynomial inequalities characterize those smooth curves C in the plane which, like S, are algebraic, i.e., C is contained in {(x,y): Q(x,y)=0} for some polynomial Q.

Speaker: Dr. Norman Levenberg, University of Auckland and Indiana University
Sponsor: Mathematics Department
Time: 5:00-6:00 pm
Place: Thornton Hall 211

Tuesday February 11, 2003

Topic: River Incision into Bedrock: Linking Tectonics, Climate and Topography

Speaker: Dr. Leonard Sklar, U.C. Berkeley, Department of Earth and Planetary Science
Candidate for the faculty position in engineering geology/surficial processes
Sponsor: Geosciences Department
Time: 1:00-2:00 pm
Place: Thornton Hall 604

Wednesday February 12, 2003

Topic: Spatial Statistics for Modeling Phytoplankton Levels
Abstract: Phytoplankton are important elements of lake and ocean ecosystems: they are the base of aquatic and oceanic food chains and may affect global climate through fixation of atmospheric carbon by photosynthesis. Statistical challenges associated with modeling phytoplankton biomass include calibration of indirect measurements, covariance model specification for anisotropic processes, combining different measurement methods, and computational limitations associated with large data sets. We present potential solutions to these problems that though developed with an eye to understanding phytoplankton dynamics are general enough to be relevant to many spatial and environmental problems.

Speaker: Dr. Norman Levenberg, University of Auckland and Indiana University
Sponsor: Mathematics Department
Time: 5:00-6:00 pm
Place: Thornton Hall 211

Wednesday February 12, 2003

Topic: Image Understanding & Web Security
Abstract: Internet services offered for human use are suffering abuse by programs ('bots, spiders, scrapers, spammers, etc). We mount a defense against such attacks with CAPTCHAs, `completely automatic public Turing tests to tell computers and humans apart;' these are special cases of `human interactive proofs' (HIPs), a class of security protocols allowing people easily to identify themselves over networks as members of given groups. I will review the five years of evolution of HIP R&D, highlights of the first NSF HIP workshop, and applications of HIPs now in use and on the horizon. One of the best ways to construct a CAPTCHA is to exploit the gap in ability between humans and machines in attempting to read images of text. I will describe two such reading-based CAPTCHAs, developed in collaborations between PARC and UC Berkeley:

PessimalPrint, motivated by studies of physics-based image degradations, uses images synthesized pseudo-randomly over certain ranges of words, typefaces, and image quality; and BaffleText, motivated by the psychophysics of human reading, uses image-masking degradations that seem to require Gestalt perception skills.

Both CAPTCHAs have been validated by experiments on human subjects and commercial OCR machines, and both have successfully resisted attack (so far) by advanced computer-vision techniques. I'll offer proposals for an image understanding research agenda to advance further the state of the art of web security.

[Joint work with Richard Fateman, Allison Coates, Kris Popat, Monica Chew, Tom Breuel, & Mark Luk.]

Speaker: Henry Baird, Palo Alto Research Center
Sponsor: PERNET Colloquium
Time: 5:30 pm
Place: Thornton Hall 331

Thursday February 13, 2003

Topic: GIS Applications to Earthquake-induced Landsliding

Speaker: Bijan Khazai, U.C. Berkeley Department of Civil and Environmental Engineering
Candidate for the faculty position in engineering geology/surficial processes
Sponsor: Geosciences Department
Time: 1:00-2:00 pm
Place: Thornton Hall 604

Thursday February 13, 2003

Topic: Molecular Mechanisms Coordinating Cell Growth and Cell Division

Speaker: Dr. Doug Kellogg, Assistant Professor, Molecular, Cellular, & Developmental Biology, UC Santa Cruz
Sponsor: Biology 871 Colloquium
Time: 4 to 5:15pm
Place: SCI 101

Friday February 14, 2003

Topic: Pre-Main-Sequence Dynamical Evolution
Abstract: The general outline of the evolutionary stages through which tenuous interstellar gas and dust passes in the process of forming an isolated, Sun-like star has been developed from both observations and theory over the past two decades. Nevertheless, much remains to be learned, with one outstanding mystery being the process of formation of binary or multiple stars. Current research results aimed at this problem will be presented and discussed.

Speaker: Dr. Mary Barsony, Visiting Research Scientist, Jet Propulsion Lab
Staff Scientist, Space Science Institute (Boulder, CO)
Sponsor: Physics and Astronomy Colloquium
Time: 4:00 pm
Place: Thornton Hall 411

Friday February 14, 2003

Topic: From Banach's Theorem to Rice's Formula
Abstract: The classical result of Banach states that variation of a function can be read from the number of its level crossings. In celebrated Rice's formula, the statistical average of the number of level crossings by a stochastic process in an interval is related to the mean value of the derivative of the process. We present the connection between these two results and provide with a generalized Rice formula for random fields. Using this generalization we derive some statistical properties of random sea waves.

Speaker: Krzysztof Podgorski, Indiana University. - Purdue University, Indianapolis
Sponsor: Mathematics Department
Time: 5:00-6:00 pm
Place: Thornton Hall 211

Thursday February 20, 2003

Topic: What are the Consequences of Aneuploidy? Tools for Measuring Phenotype and Manipulating the Genome in Yeast

Speaker: Dr. Kirk Anders, Department of Genetics, Stanford University
Sponsor: Biology 871 Colloquium
Time: 4:10 PM
Place: SCI 101