On distribution of well-rounded lattices in the plane

Speaker: 

Professor Lenny Fukshansky

Institution: 

Claremont College

Time: 

Tuesday, March 2, 2010 - 2:00pm

Location: 

RH 306

A lattice of rank N is called well-rounded (abbreviated WR) if its minimal vectors span R^N. WR lattices are extremely important for discrete optimization problems. In this
talk, I will discuss the distribution of WR lattices in R^2, specifically concentrating
on WR sublattices of Z^2. Studying the structure of the set C of similarity classes of
these lattices, I will show that elements of C are in bijective correspondence with
certain ideals in Gaussian integers, and will construct an explicit parametrization of
lattices in each such similarity class by elements in the corresponding ideal. I will
then use this parameterization to investigate some basic analytic properties of zeta
function of WR sublattices of Z^2.

Skolem's Paradox: The Universe is Countable

Speaker: 

May Mei

Institution: 

UC Irvine

Time: 

Wednesday, February 3, 2010 - 5:00pm

Location: 

RH 440R

We will informally discuss a seemingly paradoxical consequence of the Lwenheim-Skolem theorem: if ZFC is consistent, there is a countable model of set theory. We will reexamine our intuitive notion of uncountablity and reach a mathematically satisfying resolution.

Pizza and soda will be served!

READINESS ASSESSMENT AND COURSE PLACEMENT THROUGH INTRODUCTORY CALCULUS

Speaker: 

Professor Alison Ahlgren

Institution: 

UIUC

Time: 

Tuesday, February 9, 2010 - 4:00pm

Location: 

RH 306

Theory of knowledge and learning spaces is used to assess readiness and de-
termine course placement for mathematics students at or below introductory calculus at
the University of Illinois. Readiness assessment is determined by the articially intelligent
system ALEKS. The ALEKS-based mechanism used at the University of Illinois eectively
reduces overplacement and is more eective than the previously used ACT-based mech-
anism. Signicant enrollment distribution changes occured as a result of the mechanism
implementation. ALEKS assessments provide more specic skill information than the ACT.
Correlations of ALEKS subscores with student maturity and performance meets explecta-
tions in many cases, and revels interesting characteristics of the student population in other
(systematic weakness in exponentials and logarithms). ALEKS revels skill bimodality in the
population not captured by the previous placement mechanism.
The data shows that preparation, as measured by ALEKS, correlates positively with
course performance, and more strongly than the ACT in general. The trending indicates
that while a student may pass a course with a lower percentage of prerequisite concepts
known, students receiving grades of A or B generally show greater preparedness. Longi-
tudinal comparison of students taking Precalculus shows that ALEKS assessments are an
eective measure of knowledge increase. Calculus students with weaker skills can be brought
to the skill level of their peers, as measured by ALEKS, by taking a preparatory course.
Interestingly, the data provided by ALEKS provides a measure of course eectiveness when
students preformance is aggregated and tracked longitudinally. The data is also used to
measure course eectiveness and visualize the aggregate skills of student populations.

Square-summable variations and absolutely continuous spectrum

Speaker: 

Yoram Last

Institution: 

Hebrew University

Time: 

Tuesday, February 2, 2010 - 2:00pm

Location: 

RH 440R

The talk will discuss Jacobi matrices with periodic right
limits and corresponding square-summable variations. In particular, it will illuminate the optimality of a recent theorem of Kaluzhny-Shamis by showing that a recent conjecture of BreuerLastSimon is wrong.

Some elliptic curves with large rank over $\bar{F_q}(t)$

Speaker: 

Tommy Occhipinti

Institution: 

University of Arizona

Time: 

Tuesday, February 2, 2010 - 2:00pm

Location: 

RH 306

It is a fascinating result of Ulmer that the elliptic curve y^2=x^4+x^3+t^d attains arbitrarily large rank over $\bar{F_q}(t)$ as d varies over the positive integers. In this talk we will provide some new examples of this phenomenon and provide an overview of previous work in this area, particularly that of Ulmer and Berger.

On conservative Newhouse phenomena

Speaker: 

Anton Gorodetski

Institution: 

UC Irvine

Time: 

Friday, January 29, 2010 - 2:00pm

Location: 

RH 340P

What kind of dynamical phenomena appear after a homoclinic bifurcation of an area preserving diffeomorphism? First we will remind some known results (mostly by P.Duarte) on conservative Newhouse phenomena and properties of the standard map, and then explain how those results can be improved to get a better understanding of the conservative Newhouse phenomena. In particular, we will show that stochastic sea of the standard map has full Hausdorff dimension for sufficiently large topologically generic parameters (a well-known open conjecture claims that it has positive measure).

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