Faculty of Mathematics, University of Waterloo

WebNotice Postings: 16-Jan-2017 through 22-Jan-2017

Postings for all Departments


Monday, 16 January 2017, 10:30AM -- DC 1304 true
Human-Computer Interaction Seminar -- Computer Science
Speaker: Tovi Grossman, Autodesk Research
Title: "Instrumented and Connected: Designing Next-Generation Learning Experiences"
Abstract: Abstract: The history of computing is rich with examples of how computers, among their many purposes, serve as tools which enhance our ability to learn. As these computing technologies advance, so too do the ways in which we learn.

Today, we are moving faster than ever towards Weiser’s seminal vision of technology being woven into the fabric of our everyday lives. Not only have we adopted mobile, and more recently, wearable technologies, that we depend on almost every hour of our waking lives, there is an internet, and more recently, an Internet of Things, that connects us to each other and our surrounding environments. This unique combination of instrumentation and connectivity offers an opportunity to fundamentally change the way in which we learn and share knowledge with one another.

In this talk, I will outline my research in what I define as next-generation learning experiences, which leverage instrumented and connected environments to aid in human learning and performance. I first demonstrate how instrumented and connected environments can be used to improve the way in which we learn to use complex software applications. I then discuss how wearable and IoT technologies can be similarly leveraged to aid in the learning, performance, and coordination of real-world physical tasks.

Bio: Tovi Grossman is a Distinguished Research Scientist at Autodesk Research, located in downtown Toronto. Dr. Grossman’s research is in HCI, focusing on input and interaction with new technologies. In particular, he has been exploring how emerging technologies, such as wearables, the Internet of Things, and gamification can be leveraged to enhance learning and knowledge sharing for both software applications and real-world physical tasks. This work has led to a number of technologies now in Autodesk products used by millions of users, such as Autodesk Screencast and Autodesk ToolClip™ videos. Dr. Grossman received a Ph.D. in Human-Computer Interaction from the Department of Computer Science at the University of Toronto. He has over 80 peer-reviewed journal and conference publications. Fourteen of these publications have received best paper awards and nominations at the ACM UIST and CHI conferences. He has also served as the Technical Program Co-Chair for the ACM CHI 2014 Conference, and the Program Co-Chair for the ACM UIST 2015 Conference.

Monday, 16 January 2017, 10:30AM -- DC 1304
Computer Science Seminar -- Computer Science
Speaker: Tovi Grossman, Distinguished Research Scientist, Autodesk Research
Title: "Instrumented and Connected: Designing Next-Generation Learning Experiences"
Abstract: The history of computing is rich with examples of how computers, among their many purposes, serve as tools which enhance our ability to learn. As these computing technologies advance, so too do the ways in which we learn.

Today, we are moving faster than ever towards Weiser’s seminal vision of technology being woven into the fabric of our everyday lives. Not only have we adopted mobile, and more recently, wearable technologies, that we depend on almost every hour of our waking lives, there is an internet, and more recently, an Internet of Things, that connects us to each other and our surrounding environments. This unique combination of instrumentation and connectivity offers an opportunity to fundamentally change the way in which we learn and share knowledge with one another.

In this talk, I will outline my research in what I define as next-generation learning experiences, which leverage instrumented and connected environments to aid in human learning and performance. I first demonstrate how instrumented and connected environments can be used to improve the way in which we learn to use complex software applications. I then discuss how wearable and IoT technologies can be similarly leveraged to aid in the learning, performance, and coordination of real-world physical tasks.

Bio: Tovi Grossman is a Distinguished Research Scientist at Autodesk Research, located in downtown Toronto. Dr. Grossman’s research is in HCI, focusing on input and interaction with new technologies. In particular, he has been exploring how emerging technologies, such as wearables, the Internet of Things, and gamification can be leveraged to enhance learning and knowledge sharing for both software applications and real-world physical tasks. This work has led to a number of technologies now in Autodesk products used by millions of users, such as Autodesk Screencast and Autodesk ToolClip™ videos. Dr. Grossman received a Ph.D. in Human-Computer Interaction from the Department of Computer Science at the University of Toronto. He has over 80 peer-reviewed journal and conference publications. Fourteen of these publications have received best paper awards and nominations at the ACM UIST and CHI conferences. He has also served as the Technical Program Co-Chair for the ACM CHI 2014 Conference, and the Program Co-Chair for the ACM UIST 2015 Conference.

Monday, 16 January 2017, 11:30AM -- MC 5403
Seminar -- Pure Mathematics
Speaker: Yoav Len, Department of Combinatorics & Optimization, University of Waterloo
Title: "Combinatorial Hodge Theory"
Abstract: Our seminar will follow the paper ``Hodge theory for combinatorial geometries" by Adiprasito--Huh--Katz. The main result is a proof of Rota's conjecture on the log concavity of the characteristic polynomial of arbitrary matroids. This generalizes the log concavity of both the chromatic polynomial of a graph and of the f-vector of a realizable matroid. In this first talk, I will introduce some of the ideas that show up in the paper such as matroids, chromatic polynomials, and Chow groups. I will explain how they fit together, and give an overview of the main results.

Monday, 16 January 2017, 1:00PM -- MC 5501
Seminar -- Applied Mathematics
Speaker: Jorma Louko, University of Nottingham
Title: "Smooth and sharp creation of a pointlike source in quantum field theory"
Abstract: We analyse the smooth and sharp creation of a pointlike source for a quantised massless scalar field in (3+1)-dimensional Minkowski spacetime, as a model for proposed breakdown of correlations at the horizon of an evaporating black hole. Implementing the creation by time-dependence of a self-adjointness parameter, we give a quantitative characterisation of the singularity in the field's energy density, and the singularity in the response of an Unruh-DeWitt detector. These singularities may be strong enough to break quantum correlations as proposed to happen in a corresponding black hole spacetime.

Monday, 16 January 2017, 2:30PM -- MC 6460 true
Seminar -- Applied Mathematics
Speaker: Dr. Lise-Marie Imbert-Gérard, Courant Institute of Mathematical Sciences | New York University
Title: "Variable coefficients and numerical methods for electromagnetic waves"
Abstract: In the first part of the talk, we will discuss a numerical method for wave propagation in inhomogeneous media. The Trefftz method relies on basis functions that are solution of the homogeneous equation. In the case of variable coefficients, basis functions are designed to solve an approximation of the homogeneous equation. The design process yields high order interpolation properties for solutions of the homogeneous equation. This introduces a consistency error, requiring a specific analysis.

In the second part of the talk, we will discuss a numerical method for elliptic partial differential equations on manifolds. In this framework the geometry of the manifold introduces variable coefficients. Fast, high order, pseudo-spectral algorithms were developed for inverting the Laplace-Beltrami operator and computing the Hodge decomposition of a tangential vector field on closed surfaces of genus one in a three dimensional space. Robust, well-conditioned solvers for the Maxwell equations will rely on these algorithms.

Tuesday, 17 January 2017, 10:00AM -- MC 6460 true
PhD Seminar -- Applied Mathematics
Speaker: Yinan Li, Dept. of Applied Mathematics
Title: "Control Synthesis for Dynamical Systems with Linear-Time Specifications"
Abstract: There is an increasing demand on control synthesis for dynamical systems with rich specifications in recent years. Examples include traffic control, motion planning, and control of power networks. Apart from conventional stabilization requirements, linear-time properties, such as safety, reachability, liveness and fairness, are more suitable for specifying the control objectives for such systems. To cope with the difficulties arising from complex system dynamics and specifications, the proposed research focuses on computer-aided control design for dynamical systems with linear-time specifications. This talk will present some ongoing research on abstraction-based and specification-guided control synthesis. The control design methods will be illustrated with examples drawn from different applications.

Tuesday, 17 January 2017, 11:00AM -- MC 5403 true
Logic Seminar Seminar -- Pure Mathematics
Speaker: Ilya Shapirovsky, .
Title: "Locally tabular modal logics"
Abstract: A logic is called locally tabular if it has only finitely many pairwise non-equivalent formulas in each of its finite-variable fragments. Algebraically, modal logics are equational theories of Boolean algebras with operators, thus a modal logic L is locally tabular iff the variety of L-algebras is locally finite, i.e., every finitely generated L-algebra is finite. Recently, it was shown that local tabularity of modal logics can be characterized in terms of partitions of relational structures of finite height. In my talk, I will formulate this semantic criterion and discuss some of its corollaries. Also, I would like to discuss some open problems on local tabularity and the finite model property of modal logics.

This talk is based on joint work with Valentin Shehtman.

Tuesday, 17 January 2017, 2:30PM -- MC 6460 true
Seminar -- Applied Mathematics
Speaker: Dr. Henry Shum, Department of Chemical & Petroleum Engineering | University of Pittsburgh
Title: "Harnessing Chemical Reactions for Novel Functionality in Microfluidic Systems"
Abstract: Chemical reactions are essential for biological processes, from the directed transport of molecules within a cell to the carefully orchestrated growth and morphological development of an organism. As we expand our experimental capabilities in nanofabrication and synthetic biology, it is becoming possible to construct artificial microscale systems that incorporate biological components or function on the same principles as their living analogues. Here, we examine two potential applications of chemical reactions in synthetic systems, namely, to generate tunable fluid flow fields in an enclosed microfluidic device and to design "artificial cells" that communicate with each other. Recent experiments demonstrated that an immobilised patch of enzyme could function as a pump, generating persistent flows in a small, fluid-filled chamber. Experimental evidence suggested that the fluid motion was due to buoyancy effects. We develop a mathematical model to describe the changes in fluid density in the chamber due to a generic chemical reaction. Unexpectedly, we find that non-trivial, time-dependent fluid flows can be generated even under the assumption that the reaction rate is constant. This raises the intriguing possibility of a new paradigm for achieving complex flow and particle transport in microfluidic devices. A network of enzymatic pumps could autonomously and dynamically regulate flow to transport cargo "intelligently". Before we can design such systems, however, we must understand the more general and fundamental problem of chemical reaction networks in spatially extended systems. Building on studies of gene regulatory network dynamics based on ordinary differential equations, we model the behaviour of colonies of artificial cells that act as localised sources of chemicals. We show that imposing an oscillatory reaction network known as the repressilator to regulate chemical production in the cells endows them with the capability to collectively gauge the population size and density of the colony, a common ability in microorganisms referred to as quorum sensing. Thus, simple physical and chemical processes can be harnessed to attain life-like, biomimetic functionality in synthetic systems.

Tuesday, 17 January 2017, 3:00PM -- MC 5403
Computability Learning Seminar -- Pure Mathematics
Speaker: Mohammad Mahmoud, Department of Pure Mathematics, University of Waterloo
Title: "Existentially Algebraic Structures"
Abstract: This week we talk about existentially algebraic structures. We will prove that every existentially algebraic structure is in fact existentially atomic. We will also try to establish a necessary and sufficient condition for a structure $\mathcal{A}=(A,<, \mbox{Adj})$ (linear order with the adjacency relation) to be existentially atomic.

Tuesday, 17 January 2017, 4:00PM -- M3 3127
Seminar -- Statistics & Actuarial Science
Speaker: Yang Chen, Harvard University
Title: "Delineating Protein Transportation Processes: Hierarchical Models for Single-Molecule Data"
Remarks: Refreshments will be provided.
Abstract: Single-molecule experiments investigate the kinetics of individual molecules and thus can substantially enhance our understandings of various organisms. Analyzing data from single-molecule experiments poses a number of challenges: (a) the inherent stochasticity of molecules is usually buried in random experimental noise; (b) single-molecule behavior can be highly volatile. For both of these reasons, replicated experiments are usually required. In order to combine information from replicated experiments while accounting for the heterogeneities among experimental replicates, we introduce a Bayesian hierarchical model on top of an experiment-level hidden Markov model, where the hidden Markov model has been widely adopted to analyze each experimental replicate individually in previous studies. We apply the proposed model to three data sets obtained from experiments aimed at unveiling mechanisms underlying protein transportation – a biological process vital for the proper functioning of cells. Our statistical results enable us to give a comprehensive picture of the protein transportation mechanism and provide a general framework for rigorous statistical analysis of experimental replicates from single-molecule experiments. Please refer to the published manuscript of this work for details, which is available at http://scholar.harvard.edu/yangchen/publications.

Wednesday, 18 January 2017, 1:00PM - ** Date Change ** - now Friday, 20 January 2017, 1:00PM
** See updated entry for additional event information **
Speaker: Dhinakaran Vinayagamurthy, David R. Cheriton School of Computer Science
Title: "Riding on Asymmetry: Efficient Attribute-based Encryption for Branching Programs"

Wednesday, 18 January 2017, 2:30PM -- MC 5417 true
Seminar -- Pure Mathematics
Speaker: Anthony McCormick, Department of Pure Mathematics, University of Waterloo
Title: "Nuclearity of Spaces of Distributions"
Abstract: We will discuss the nuclearity of various useful locally convex spaces such as the spaces of smooth functions, compactly supported smooth functions, distributions, polynomials and formal power series. The notion of a parametrix, interpreted using the formalism we develop here, will provide valuable intuition when we discuss operator product expansions and vertex algebras in later talks.

Wednesday, 18 January 2017, 4:00PM -- M3 3127
Seminar -- Statistics & Actuarial Science
Speaker: Shengchao Zhuang, University of Waterloo
Title: "Some Advances in Optimal Insurance Design"
Remarks: Refreshments will be provided.
Abstract: In this presentation, I will discuss two formulations of the optimal insurance problems. The first studies an optimal insurance design by maximizing the classical expected utility preference of an insured final wealth. Our formulation is novel, as we introduce the additional constraints imposed by an insurer on the upper limits of the first two moments of coverage. These constraints could restrict insurers' risk exposure. We derive the optimal insurance policy explicitly, and find that it heavily depends on the values of the upper limits. Finally, the effects of the insured's initial wealth on the demand for insurance are studied in detail. In the second formulation, I will discuss an optimal insurance design where an individual's preference is of the rank-dependent expected utility (RDU) type. Unlike the existing model which suffers from a problem of moral hazard for paying more compensation for a smaller loss, our formulation alleviates this issue by exogenously imposing the constraint that both the indemnity function and the insured's retention function be increasing with respect to the loss. Finally, we characterize the optimal solutions under general RDU criterion.

Thursday, 19 January 2017, 12:30PM -- MC 5479
Seminar -- Pure Mathematics
Speaker: Nickolas Rollick, Department of Pure Mathematics, University of Waterloo
Title: "Staying connected"
Abstract: Coming back from our long break, we will begin with a highlight reel of the topics covered last term. Afterwards, we continue our study of affine schemes as topological spaces by focusing on three important topological properties that crop up in the study of schemes: connectedness, irreducibility, and (quasi)compactness. In the process, we will get a healthy dose of examples, non-examples, and relationships between these notions in the context of affine schemes. To wrap up, we introduce the notion of closed points of a topological space and characterize the closed points of an affine scheme.

Thursday, 19 January 2017, 1:30PM -- M3 3103
Number Theory Seminar Seminar -- Pure Mathematics
Speaker: Asif Zaman, University of Toronto
Title: "A variant of Brun-Titchmarsh for the Chebotarev density theorem"
Abstract: The classical Brun-Titchmarsh theorem provides an upper bound for the number of primes in an arithmetic progression in a far wider range than that afforded by the Prime Number Theorem for arithmetic progressions. The Chebotarev density theorem, on the other hand, has few alternatives to adequately estimate the number of prime ideals with a prescribed splitting behaviour in a Galois extension of number fields. Unfortunately, these alternatives are not sufficiently robust for many interesting applications. We will discuss the existing literature and report on a new field-uniform generalization of Brun-Titchmarsh associated to the Chebotarev density theorem. This result has consequences for counting primes represented by certain binary quadratic forms and refining unconditional bounds towards the Lang-Trotter conjectures for elliptic curves.

This talk is based on joint work with Jesse Thorner.

Thursday, 19 January 2017, 1:30PM -- MC 5413
Seminar -- Pure Mathematics
Speaker: Anthony McCormick, Department of Pure Mathematics, University of Waterloo
Title: "Solvable Algebraic Groups"
Abstract: After finishing our examples from last time, we will discuss some of the structure theory of solvable algebraic groups. This will be a useful stepping-stone towards the theory of reductive and semisimple algebraic groups, which we will study next.

Thursday, 19 January 2017, 2:30PM -- MC 6460
Seminar -- Applied Mathematics
Speaker: Dr. Yoonsang Lee, Courant Institute of Mathematical Sciences | New York University
Title: "Multiscale methods for filtering turbulent systems"
Abstract: Data assimilation or filtering of nonlinear dynamical systems combines numerical models and observational data to provide the best statistical estimates of the systems. Ensemble-based methods have proved to be indispensable filtering tools in atmosphere and ocean systems that are typically high dimensional turbulent systems. In operational applications, due to the limited computing power in solving the high dimensional systems, it is desirable to use cheap and robust reduced-order forecast models to increase the number of ensemble for accuracy and reliability. This talk describes a multiscale data assimilation framework to incorporate reduced-order multiscale forecast methods for filtering high dimensional complex systems. A reduced-order model for two-layer quasi-geostrophic equations, which uses stochastic modeling for unresolved scales, will be discussed and applied for filtering to capture important features of geophysical flows such as zonal jets. If time permits, a generalization of the ensemble-based methods, multiscale clustered particle filters, will be discussed, which can capture strongly non-Gaussian statistics using relatively few particles.

Thursday, 19 January 2017, 3:00PM -- Math & Computer, Room 6486
Seminar -- Combinatorics and Optimization
Speaker: Krystal Guo, University of Waterloo
Title: "Symbolic Dynamics for Graph Theorists"
Abstract: We introduce some basic concepts in symbolic dynamics, using graph theoretic language, and discuss some open problems.

Thursday, 19 January 2017, 4:00PM -- M3 3127
Seminar -- Statistics & Actuarial Science
Speaker: Jon Steingrimsson, Johns Hopkins University
Title: "Doubly Robust Survival Trees and Forests"
Remarks: Refreshments will be provided.
Abstract: Survival trees use recursive partitioning to separate patients into distinct risk groups when some observations are right-censored. Survival forests average multiple survival trees creating more flexible prediction models. In the absence of censoring, the corresponding algorithms rely heavily on the choice of loss function used in the decision making process. Motivated by semiparametric efficiency theory, we replace the loss function used in the absence of censoring by doubly robust loss functions. We derive properties of these loss functions and show how the doubly robust survival trees and forest algorithms can be implemented using a certain form of response transformation. Furthermore, we discuss practical issues related to the implementation of the algorithms. The performance of the resulting survival trees and forests is evaluated through simulation studies and analyzing data on death from myocardial infraction.

Friday, 20 January 2017, 1:00PM -- DC 2585 true
Cryptography, Security, and Privacy (CrySP) Group PhD Seminar -- Computer Science
Speaker: Dhinakaran Vinayagamurthy, David R. Cheriton School of Computer Science
Title: "Riding on Asymmetry: Efficient Attribute-based Encryption for Branching Programs"
Abstract: Attribute-Based Encryption (ABE) provides efficient and simple mechanism for data sharing supporting fine-grained access control. In an ABE scheme, a ciphertext encrypting a message m is associated with a public attribute vector x, and a secret key sk_P is associated with a predicate P. The decryption succeeds and returns m if and only if P(x) = 1. In addition to access control, ABE is also used as a critical component in advanced cryptographic constructions of succinct functional encryption, reusable garbled circuits, token-based obfuscation and more. In this talk, I will describe our work on constructing a new ABE scheme with short secret keys and from a mild security assumption for the predicate family of branching programs. In particular, in our construction the size of the secret key for a branching program P is |P| + poly(\lambda), where \lambda is the security parameter. And, our construction is secure assuming the standard Learning With Errors (LWE) problem with approximation factors n^{\omega(1)}. Previous constructions relied on n^{O(log n)} approximation factors of LWE (resulting in less efficient parameters instantiation) or had large secret keys of size |P| × poly(\lambda).

Friday, 20 January 2017, 2:30PM -- MC 5413
Geometry & Topology Seminar Seminar -- Pure Mathematics
Speaker: Ali Aleyasin, Universite du Quebec a Montreal
Title: "The Calabi problem on edge-cone manifolds"
Abstract: Let M be a Kahler manifold and V a complex hypersurface in it. A Kahler edge-cone metric along V is one with conical singularity along a complex hypersurface, that is, a metric which asymptotically resembles a cone metric on \mathbb{R}^2 in the directions normal to the hypersurface, and is smooth in the tangential directions. The study of problems around such singularities has received attention thanks to their role in understanding the relation between K-stability and the existence of Kahler-Einstein metrics on Fano manifolds. In this talk, we shall present some observations which help us derive new a priori estimates for the Calabi problem on such manifolds, still using classical methods. Further, we show new regularity results for canonical metrics of edge-cone type.

Friday, 20 January 2017, 3:30PM -- MC 5417
Analysis Seminar Seminar -- Pure Mathematics
Speaker: Boyu Li, Department of Pure Mathematics, University of Waterloo
Title: "Regular Dilation on Graph Products of $\mathbb{N}$"
Abstract: We extend the definition of a regular dilation to graph products of $\mathbb{N}$ which is an important class of quasi-lattice ordered semigroups. Two important results in dilation theory are unified under our result: namely, Brehmer's regular dilation on $\mathbb{N}^k$ and the Frazho-Bunce-Popescu's dilation of row contractions. We further show that a representation of a graph product has an isometric Nica-covariant dilation if and only if it is *-regular. This is related to Popescu's property (P) when the underlying graph is a complete multipartite graph.


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