# Alumni Dissertations

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### Forms of Generic Common Knowledge

Author:Evangelia AntonakosYear of Dissertation:2013Program:MathematicsAdvisor:Sergei ArtemovAbstract:In multi-agent epistemic logics, common knowledge has been a central consideration of study. A generic common knowledge (

*G.C.K.*) system is one that yields iterated knowledge*I*(φ): ‘any agent knows that any agent knows that any agent knows…φ’ for any number of iterations. Generic common knowledge yields iterated knowledge,*G.C.K.*(φ)→*I*(φ), but is not necessarily logically equivalent to it. This contrasts with the most prevalent formulation of common knowledge*C*as equivalent to iterated knowledge. A spectrum of systems may satisfy the*G.C.K.*condition, of which*C*is just one. It has been shown that in the usual epistemic scenarios,*G.C.K.*can replace conventional common knowledge and Artemov has noted that such standard sources of common knowledge as public announcements of atomic sentences generally yield*G.C.K.*rather than*C*.

In this dissertation we study mathematical properties of generic common knowledge and compare them to the traditional common knowledge notion. In particular, we contrast the modal*G.C.K.*logics of McCarthy (e.g.**M4**) and Artemov (e.g.**S4**) with_{n}^{J}*C*-systems (e.g.**S4**) and present a joint_{n}^{C}*C/G.C.K.*implicit knowledge logic**S4**as a conservative extension of both. We show that in standard epistemic scenarios in which common knowledge of certain premises is assumed, whose conclusion does not concern common knowledge (such as Muddy Children, Wise Men, Unfaithful Wives, etc.), a lighter_{n}^{CJ}*G.C.K.*can be used instead of the traditional, more complicated, common knowledge. We then present the first fully explicit*G.C.K.*system**LP**. This justification logic realizes the corresponding modal system_{n}(LP)**S4**so that_{n}^{J}*G.C.K.*, along with individual knowledge modalities, can always be made explicit.### Geometric Interpretation of the Two Dimensional Poisson Kernel And Its Applications.

Author:Sergei ArtamoshinYear of Dissertation:2011Program:MathematicsAdvisor:Jozef DodziukAbstract:Hermann Schwarz, while studying complex analysis, introduced the geometric interpretation for the Poisson kernel in 1890. We shall see here that the geometric interpretation can be useful to develop a new approach to some old classical problems as well as to obtain several new results, mostly related to hyperbolic geometry. For example, we obtain One Radius Theorem saying that any two radial eigenfunctions of a Hyperbolic Laplacian assuming the value 1 at the origin can not assume any other common value within some interval [0, p], where the length of this interval depends only on the location of the eigenvalues on the complex plane and does not depend on the distance between them.

### The Geometry of Gauss' Composition Law

Author:Yelena BaishanskiYear of Dissertation:2010Program:MathematicsAdvisor:Lucien SzpiroAbstract:Gauss' identification of a composition law for primitive integral binary quadratic forms of given discriminant D--which provides the set F

_{D<\sub> of SL2<\sub>(Z) equivalence classes of such forms with a group structure--essentially amounts to the discovery of the class group of an order in a quadratic number field. We consider quadratic extensions of the field of rational functions k(u), where k is an algebraically closed field, and seek an analogue of Gauss composition in this context. A quadratic extension of k(u) corresponds to the function field of a curve C with affine model t2<\super> = D(u) for some polynomial D = D(u) in k[u], which is of odd degree if and only if C has a smooth ramified point at infinity. Focusing on this case--the analogue of quadratic number fields with one complex place at infinity--we extend the notion of the degree of a Weil divisor on a curve to Cartier divisors on C, and find a bijection between the set of SL2<\sub>(k[u])-equivalence classes of primitive forms with coefficients in k[u] of discriminant D, and the group Pic0<\super>(C) of isomorphism classes of degree zero lines bundles on C. In parallel fashion, we reinterpret the arithmetic case using Arakelov's invention of metrics associated to the infinite places of a number field. Given an invertible R-module L for R a quadratic ring of discriminant D and fraction field K, we have for each infinite place v of K a corresponding one-dimensional C-vector space Lv<\sub>, with a positive non-degenerate hermitian metric. Using a notion of degree of an invertible metrized module--which mirrors the notion of degree used in the geometric case, yielding in both cases a "product formula" deg(f) = 0 for a principal divisor (f)--we establish for D < 0 a bijection between FD<\sub> and the compactified Picard group Picc<\sub>0<\super>(R) of isometry classes of degree zero invertible R-modules.}### Sensor Strip Cover: Maximizing Network Lifetime on an Interval

Author:Benjamin BaumerYear of Dissertation:2012Program:MathematicsAdvisor:Amotz Bar-NoyAbstract:Suppose that

n sensors are deployed on a one-dimensional region (a strip, or interval) that we wish to cover with a wireless sensor network. Each sensor is equipped with a finite battery, and has an adjustable sensing range, which we control. If each sensor's battery drains in inverse linear proportion to its sensing radius, which schedule will maximize the lifetime of the resulting network? We study this Sensor Strip Cover problem and several related variants. For the general Sensor Strip Cover problem, we analyze performance in both the worst-case and average-case for several algorithms, and show that the simplest algorithm, in which the sensors take turns covering the entire line, has a tight 3/2-approximation ratio. Moreover, we demonstrate a more sophisticated algorithm that achieves an expected lifetime of within 12% of the theoretical maximum against uniform random deployment of the sensors. We show that if the sensing radii can be set only once, then the resulting Set Once Strip Cover problem is NP-hard. However, if all sensors must be activated immediately, then we provide a polynomial time algorithm for the resulting Set Radius Strip Cover problem. Finally, we consider the imposition of a duty cycling restriction, which forces disjoint subsets of the sensors (called shifts) to act in concert to cover the entire interval. We provide a polynomial-time solution for the case in which each shift contains at most two sensors. For shifts of sizek , we provide worst-case and average-case analysis for the performance of several algorithms.### Normal Families and Mondromies of Holomorphic Motions

Author:Michael BeckYear of Dissertation:2012Program:MathematicsAdvisor:Yunping JiangAbstract:We explore some generalizations of results in holomorphic motions that result from Earle's infinite-dimensional generalization of Montel's Theorem. We then investigate topological obstructions to extending holomorphic motions. We finish with some miscellaneous facts.

### Points of Canonical Height Zero on Projective Varieties

Author:Anupam BhatnagarYear of Dissertation:2010Program:MathematicsAdvisor:Lucien SzpiroAbstract:Let k be an algebraically closed field of characteristic zero, C a smooth connected projective curve defined over k, K =k(C) the function field of C. Let Y be a projective K-variety, L a very ample line bundle on Y and α : Y &rarr Y a K-morphism such that α

*<\super>L = L × d . We prove that a projective integral C-scheme Y is isotrivial when it is covered by a projective integral k-scheme X= X _{0<\sub> × C, where X0<\sub> is a k-scheme. This result provides a setup for a conjecture of L. Szpiro on parametrization of points of canonical height zero of the dynamical system (Y,L, α).}### On the Arithmetic and Geometry of Quaternion Algebras: a spectral correspondence for Maass waveforms

Author:Terrence BlackmanYear of Dissertation:2011Program:MathematicsAdvisor:Stefan LemurellAbstract:Abstract ## ABSTRACT

Let be an indefinite rational division quaternion algebra with discriminant d equal to pq where p and q are primes such that p,q > 2 and let

_{pq}be a maximal order in . Further, let_{pq,p2rq2s},r,s ≥ 1 be an order of index p^{2r}q^{2s}in_{pq}with Eichler invariant equal to negative one at p and at q . Finally, let_{pq,p2rq2s}^{1}be the cocompact Fuchsian group given as the group of units of norm one in_{pq,p2rq2s}. Using the classical Selberg trace formula, we show that the positive Laplace eigenvalues, including multiplicities, for Maass forms on_{pq,p2rq2s}^{1}coincide with the Laplace spectrum for Maass newforms defined on the Hecke congruence group Γ_{0}(M) where, M, the level of the congruence group, is equal to p^{2r+1}q^{2s+1}, i.e., the discriminant of_{pq,p2rq2s}.### Late Points of Projections of Planar Symmetric Random Walks on the Lattice Torus

Author:Michael CarlisleYear of Dissertation:2012Program:MathematicsAdvisor:Jay RosenAbstract:We examine the

cover time and set oflate points of a symmetric random walk on Z2 projected onto the torus Z2 _{K}. This extends the work done for the simple random walk in [Late Points, DPRZ, 2006] to a large class of random walks. The approach uses comparisons between planar and toral hitting times and distributions on annuli, and uses only random walk methods. There are also generalizations of Green's functions, hitting times, and hitting distributions on Z2 and Z2 _{K}which are of independent interest.### Uniqueness Theorems for Some Nonlinear Parabolic Equations

Author:Yimao ChenYear of Dissertation:2012Program:MathematicsAdvisor:Leon KarpAbstract:We study the uniqueness of solutions of the Cauchy problem of two nonlinear parabolic equations in this thesis. We first study the uniqueness of the solutions of the initial value problem associated with the infinity-Laplacian operators. We prove the uniqueness of solutions of the Cauchy problem for the infinity-Laplacian heat equation in a class of functions with exponential growth. We also study the uniqueness of the solutions of the evolution associated with the minimal surface equation. We obtain a new uniqueness class of solutions of the Cauchy problem for the parabolic minimal surface equation, which is reminiscent of the classical results for the heat equation.

### Geometric Characterization and Dynamics of Holomorphic maps

Author:Tao ChenYear of Dissertation:2013Program:MathematicsAdvisor:Yunping JiangAbstract:We prove the existence of the canonical Thurston obstruction for sub-hyperbolic semi-rational branched coverings when they are obstructed. Then we geometrically characterize meromorphic maps with exactly two asymptotic values and no critical values. We finish with the proof of non-existence of the invariant line fields for a family of entire functions