A subset $X$ in $\{0,1\}^n$ is a called an $\epsilon$-biased set if for any nonempty subset $T\subseteq [n]$ the following condition holds. Randomly choosing an element $x\in X$, the parity of its T-coordinates sum has bias at most $\epsilon$. This concept is essentially equivalent or close to expanders, pseudorandom generators and linear codes of certain parameters. For instance, viewing $X$ as a generator matrix, an $\epsilon$-biased set is equivalent to an $[|X|, n]_2$-linear code of relative distance at least $1/2-\epsilon$. For fixed $n$ and $\epsilon$, it's a challenging problem to construct smallest $\epsilon$-biased sets. In this talk we will first introduce several known constructions of $\epsilon$-bias sets with the methods from number theory and geometrical coding theory. Then we will present a construction with a conjecture, which is closely related to the subset sum problem over prime fields.

What is the probability that a random abelian variety over F_q is ordinary? Using (semi)linear algebra, we will answer an analogue of this question, and explain how our method can be used to answer similar statistical questions about p-rank and a-number. The answers are perhaps surprising, and deviate from what one might expect via naive reasoning. Using these computations and numerical evidence, we formulate several ``Cohen-Lenstra" heuristics for the structure of the p-torsion on the Jacobian of a random hyperelliptic curve over F_q. These heuristics are the "l=p " analogue of Cohen-Lenstra in the function field setting. This is joint work with Jordan Ellenberg and David Zureick-Brown.

I will discuss a general approach for constructing SRB measures for diffeomorphisms possessing chaotic attractors (i.e., attractors with nonzero Lyapunov exponents). I introduce a certain recurrence condition on the iterates of Lebesgue measure called “effective hyperbolicity” and I will show that if the asymptotic rate of effective hyperbolicity is exponential on a set of positive Lebesgue measure, then the system has an SRB measure. Along the way a new notion of hyperbolicity -- "effective hyperbolicity'' will be introduced and a new example of a chaotic attractor will be presented. This is a joint work with V. Climenhaga and D. Dolgopyat.

Mirror map is a central object in the study of mirror symmetry. They are obtained in hypergeometric series by solving Picard-Fuchs equations. In this talk, I will explain a geometric meaning of mirror maps for toric varieties in terms of counting of holomorphic discs bounded by Lagrangian submanifolds. It is motivated by the study of SYZ mirror symmetry. This is a joint work with K. Chan, N.-C. Leung and H.-H. Tseng.

The endomorphism rings of ordinary jacobians of genus two curves defined over finite
fields are orders in quartic CM fields. The conductor gap between two endomorphism rings is
defined as the largest prime number that divides the conductor of one endomorphism ring but not
the other. We call a genus two curve isolated, if its endomorphism ring has large conductor gap
(>=80 bits) with any other possible endomorphism rings. There is no known algorithm to explicitly
construct isogenies from an isolated curve to curves in other endomorphism classes. I will
explain results on criteria for a curve to be isolated, as well as the heuristic asymptotic
distribution of isolated genus two curves.