Doctor of Philosophy

dissertationThis dissertation develops the structure theory of the category Whittaker modules for a complex semisimple Lie algebra. We establish a character theory that distinguishes isomorphism classes of Whittaker modules in the Grothendieck group of the category, then use the localization functor of Beilinson and Bernstein to realize Whittaker modules geometrically as certain twisted D-modules on the associated flag variety (so called "twisted Harish-Chandra sheaves"). The main result of this document is an algorithm for computing the multiplicities of irreducible Whittaker modules in the composition series of standard Whittaker modules, which are generalizations of Verma modules. This algorithm establishes that the multiplicities are determined by a collection of polynomials we refer to as Whittaker Kazhdan--Lusztig polynomials

Revealing the Dark Secrets of BERT

BERT-based architectures currently give state-of-the-art performance on many NLP tasks, but little is known about the exact mechanisms that contribute to its success. In the current work, we focus on the interpretation of self-attention, which is one of the fundamental underlying components of BERT. Using a subset of GLUE tasks and a set of handcrafted features-of-interest, we propose the methodology and carry out a qualitative and quantitative analysis of the information encoded by the individual BERT's heads. Our findings suggest that there is a limited set of attention patterns that are repeated across different heads, indicating the overall model overparametrization. While different heads consistently use the same attention patterns, they have varying impact on performance across different tasks. We show that manually disabling attention in certain heads leads to a performance improvement over the regular fine-tuned BERT models.Comment: Accepted to EMNLP 201

Representations of elastic fields of circular dislocation and disclination loops in terms of spherical harmonics and their application to various problems of the theory of defects

AbstractElastic fields of circular dislocation and disclination loops are represented in explicit form in terms of spherical harmonics, i.e. via series with Legendre and associated Legendre polynomials. Representations are obtained by expanding Lipschitz-Hankel integrals with two Bessel functions into Legendre series. Found representations are then applied to the solutions of elasticity boundary-value problems of the theory of defects and to the calculation of elastic fields of segmented spherical inclusions. In the framework of virtual circular dislocation–disclination loops technique, a general scheme to solving axisymmetric elasticity problems with boundary conditions specified on a sphere is given. New solutions for elastic fields of a twist disclination loop in a spherical particle and near a spherical pore are demonstrated. The easy and straightforward way for calculations of elastic fields of segmented spherical inclusion with uniaxial eigenstrain is shown

Electrically-Detected ESR in Silicon Nanostructures Inserted in Microcavities

We present the first findings of the new electrically-detected electron spin resonance technique (EDESR), which reveal the point defects in the ultra-narrow silicon quantum wells (Si-QW) confined by the superconductor delta-barriers. This technique allows the ESR identification without application of an external cavity, as well as a high frequency source and recorder, and with measuring the only response of the magnetoresistance, with internal GHz Josephson emission within frameworks of the normal-mode coupling (NMC) caused by the microcavities embedded in the Si-QW plane