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Series: Dissertation Defense

The talk consists of two parts.The first part is devoted to results in Discrepancy Theory. We consider geometric discrepancy in higher dimensions (d > 2) and obtain estimates in Exponential Orlicz Spaces. We establish a series of dichotomy-type results for the discrepancy function which state that if the $L^1$ norm of the discrepancy function is too small (smaller than the conjectural bound), then the discrepancy function has to be very large in some other function space.The second part of the thesis is devoted to results in Additive Combinatorics. For a set with small doubling an order-preserving Freiman 2-isomorphism is constructed which maps the set to a dense subset of an interval. We also present several applications.

Series: Dissertation Defense

We say that a cover of surfaces S-> X has the Birman--Hilden property if the subgroup of the mapping class group of X consisting of mapping classes that have representatives that lift to S embeds in the mapping class group of S modulo the group of deck transformations. We identify one necessary condition and one sufficient condition for when a cover has this property. We give new explicit examples of irregular branched covers that do not satisfy the necessary condition as well as explicit covers that satisfy the sufficient condition. Our criteria are conditions on simple closed curves, and our proofs use the combinatorial topology of curves on surfaces.

Series: Dissertation Defense

Series: Dissertation Defense

Advisor: Dr. Matthew Baker

We study various binomial and monomial ideals related to the theory of
divisors, orientations, and matroids on graphs. We use ideas from potential
theory on graphs and from the theory of Delaunay decompositions for lattices
to describe minimal polyhedral cellular free resolutions for these ideals.
We will show that the resolutions of all these ideals are closely related
and that their Betti tables coincide. As corollaries we give conceptual
proofs of conjectures and questions posed by Postnikov and Shapiro, by
Manjunath and Sturmfels, and by Perkinson, Perlman, and Wilmes. Various
other results related in the theory of chip-firing games on graphs --
including Merino's proof of Biggs' conjecture and Baker-Shokrieh's
characterization of reduced divisors in terms of potential theory -- also
follow immediately from our general techniques and results.

Series: Dissertation Defense

Series: Dissertation Defense

Series: Dissertation Defense

Series: Dissertation Defense

Series: Dissertation Defense

Series: Dissertation Defense

This work studies two topics in sequence analysis. In the first part, we
investigate the large deviations of the shape of the random RSK Young
diagrams, associated with a random word of size n whose letters are
independently drawn from an alphabet of size m=m(n). When the letters are
drawn uniformly and when both n and m converge together to infinity, m
not growing too fast with respect to n, the large deviations of the shape
of the Young diagrams are shown to be the same as that of the spectrum of
the traceless GUE. Since the length of the top row of the Young diagrams is
the length of the longest (weakly) increasing subsequence of the random
word, the corresponding large deviations follow. When the letters are drawn
with non-uniform probability, a control of both highest probabilities will
ensure that the length of the top row of the diagrams satisfies a large
deviation principle. In either case, speeds and rate functions are
identified. To complete this first part, non-asymptotic concentration bounds
for the length of the top row of the diagrams are obtained.
In the second part, we investigate the order of the r-th, 1\le r <
+\infty, central moment of the length of the longest common subsequence of
two independent random words of size n whose letters are identically
distributed and independently drawn from a finite alphabet. When all but one
of the letters are drawn with small probabilities, which depend on the size
of the alphabet, the r-th central moment is shown to be of order
n^{r/2}. In particular, when r=2, the order of the variance is linear.