Faculty of Mathematics, University of Waterloo

WebNotice Postings: 21-Apr-2014 through 27-Apr-2014

Postings for all Departments


Monday, 21 April 2014, 1:00PM -- QNC 0101
Colloquium -- Institute for Quantum Computing
Speaker: Dr. Takashi Imai, Department of Physics and Astronomy, McMaster University, and Canadian Institute for Advanced Research
Title: "NMR as a low energy probe of condensed matter"
Abstract: NMR (Nuclear Magnetic Resonance) is a versatile probe of condensed matter, and has a broad range of applications in chemistry, medicine (MRI), oil industry, etc. NMR has become so popular outside the conventional realm of physics that the crucial role NMR has been playing in condensed matter physics is sometimes overlooked. I will explain how condensed matter physicists use NMR as a powerful low energy probe of solids, drawing examples from modern research into statistical physics, magnetism, and superconductivity.

Monday, 21 April 2014, 1:00PM -- QNC 3401
Miscellaneous -- Applied Mathematics
Speaker: Daniel Puzzuoli, Applied Mathematics, University of Waterloo
Title: "MMath Defence: Honest Approximations to Realistic Fault Models and Their Application to Efficient Simulation of Quantum Error Correction"
Abstract: Understanding the performance of realistic noisy encoded circuits is an important task for the development of large-scale practical quantum computers. Specifically, the development of proposals for quantum computation must be well informed by both the qualities of the low-level physical system of choice, and the properties of the high-level quantum error correction and fault-tolerance schemes. Gaining insight into how a particular computation will play out on a physical system is in general a difficult problem, as the classical simulation of arbitrary noisy quantum circuits is inefficient. Nevertheless, important classes of noisy circuits can be simulated efficiently. Such simulations have led to numerical estimates of threshold errors rates and resource estimates in topological codes subject to efficiently simulable error models. This thesis describes and analyzes a method that my collaborators and I have introduced for leveraging efficient simulation techniques to understand the performance of large quantum processors that are subject to errors lying outside of the efficient simulation algorithm’s applicability. The idea is to approximate an arbitrary gate error with an error from the efficiently simulable set in a way that “honestly” represents the original error’s ability to preserve or distort quantum information. After introducing and analyzing the individual gate approximation method, its utility as a means for estimating circuit performance is studied. In particular, the method is tested within the use-case for which it was originally conceived; understanding the performance of a hypothetical physical implementation of a quantum error-correction protocol. It is found that the method performs exactly as desired.

Tuesday, 22 April 2014, 11:00AM -- QNC 0101
Seminar -- Institute for Quantum Computing
Speaker: Michael Hilke, McGill University
Title: "Graphene growth and characterization for device applications"
Abstract: We will review several proof of principle applications for graphene based devices performed in our group, including in field sensors, electronics, THz spectroscopy, spintronics, nanofluidics, and even musical instruments. We will then discuss the synthesis mechanism of graphene as well as the synthesis of very large single layered graphene monocrystals with various shapes, ranging from hexagons to fractals, dubbed graphlocons. Various characterization tools will be presented including modelling, isotope engineering and low temperature scanning probe microscopy and transport, leading to interesting new insights on the fascinating properties of grapheme.

Short Bio: Michael Hilke is an associate professor in the department of physics at McGill University, where he has been a faculty member since 2001. He is currently the director of the Center for the Physics of Materials (CPM), composed of members from the faculties of Science and Engineering. His current research interests lie in quantum and low-dimensional systems, such as graphene and semiconducting heterostructures. In his Quantum Nano Electronic Lab (QNEL) the focus is on synthesis, characterization and modelling of new materials as well as device applications. Michael completed a PhD ('96) at the University of Geneva in theoretical physics on disordered systems under the supervision of Charles Enz (a former assistant of Wolfgang Pauli). He then moved to Princeton as a post-doc in the laboratory of Dan Tsui (1998 Nobel laureate) to work as an experimentalist on quantum Hall devices for five years.

Tuesday, 22 April 2014, 12:00PM -- DC 2310
Human-Computer Interaction PhD Seminar -- Computer Science
Speaker: Ben Lafreniere, PhD candidate, David R. Cheriton School of Comp. Sci., Univ. Waterloo
Title: "Investigating the Feasibility of Extracting Tool Demonstrations from In-Situ Video Content"
Abstract: Short video demonstrations are an effective way to help users learn tools and commands in complex software, but manually creating demonstrations for the hundreds (or thousands) of individual features in these programs would be impractical. In this talk, I discuss work that investigates the feasibility of identifying good tool demonstrations from within screen recordings of users performing real-world tasks.

Tuesday, 22 April 2014, 2:00PM -- DC 1331
Software Engineering Research Group PhD Thesis Presentation/Defence -- Computer Science
Speaker: Olga Baysal, PhD candidate, David R. Cheriton School of Comp. Sci., Univ. Waterloo
Title: "Software Analytics to Support Development Decisions"
Abstract: Software practitioners make technical and business decisions based on the understanding they have of their software systems. This understanding is grounded in their own experiences, but can be augmented by studying various kinds of development artifacts, including source code, bug reports, version control meta-data, test cases, usage logs, etc. Unfortunately, the information contained in these artifacts is typically not organized in the way that is immediately useful to developers’ everyday decision making needs.

The thesis of this dissertation is that by employing software analytics to various development stages and activities, we can support software practitioners with better insights into their processes, systems, products, users and help them make better informed data-driven decisions. While quantitative analytics can help project managers understand the big picture, plan for the future, and monitor trends, qualitative analytics can enable developers to perform their daily tasks and activities more quickly and to help them better manage high volumes of information.

To support this thesis, we provide three different examples of employing software analytics. First, we show how analysis of real-world usage data can be used to assess user dynamic behaviour and adoption trends of a software system by revealing valuable information on how software systems are used in practice.

Second, we have created a lifecycle model that synthesizes knowledge from software development artifacts, such as reported issues, source code, discussions, community contributions, etc. Lifecycle models capture the dynamic nature of how various development artifacts change over time in an annotated graphical form that can be easily understood and communicated. We demonstrate how lifecycle models can be generated, and we present industrial case studies where we apply lifecycle models to assess the code review process of three different projects.

Third, we present a developer-centric approach to issue tracking that aims to reduce information overload and improve developers’ situational awareness. Our approach is motivated by a grounded theory study of developer interviews, which suggests that customized views of a projects repositories that are tailored to developer-specific tasks can help developers better track their progress and understand the surrounding technical context. We have created a model of the kinds of information elements that we understood to be essential for developers in completing their daily tasks, and from this model we have developed a prototype tool organized around customized dashboards.

The results of our studies show that software analytics can inform evidence-based decisions related to user adoption of a software project, code review processes, and improved developers’ awareness on their daily tasks and activities.

Tuesday, 22 April 2014, 3:30PM -- DC 1302 true
Colloquium -- Applied Mathematics
Speaker: Lydia Bourouiba, Dept of Civil and Environmental Engineering, MIT
Title: "Disease transmission through the lens of fluid fragmentation"
Remarks: Wine and cheese will follow in DC 1301
Abstract: The transmission mechanisms of most infectious diseases in fauna and flora share common features, in particular they involve multiphase flows. Pathogens are suspended in a liquid phase taking the form of films, drops, or bubbles, and can, in turn, become suspended in a gas phase. The common physical features of such processes ensure that understanding one biological system via the lens of fluid dynamics can yield insights into another. Here, the interplay between fluid fragmentation processes and pathogens will be discussed to highlight common aspects of indoor disease transmission. Fragmentation as arises in sneezes, burst of bubbles from a contaminated pool, and nosocomial disease transmission will be discussed.

Wednesday, 23 April 2014, 10:00AM -- M3 - 2134 true
Miscellaneous -- Applied Mathematics
Speaker: Yangxin He, Applied Mathematics , University of Waterloo
Title: "MMath Defence: Modelling Internal Solitary Waves and the Alternative Ostrovsky Equation"
Abstract: Internal solitary waves (ISWs) are commonly observed in the ocean, and they play important roles in many ways, such as transport of mass and various nutrients through propagation. The fluids considered in this thesis are assumed to be incompressible, inviscid, non-diffusive and to be weakly affected by the Earth's rotation. Comparisons of the evolution of an initial solitary wave predicted by a fully nonlinear model, IGW, and two weakly-nonlinear wave equations, the Ostrovsky equation and a new alternative Ostrovsky equation, are done.

Resolution tests have been run for each of the models to confirm that the current choices of the spatial and time steps are appropriate. Then we have run three numerical simulations with varying initial wave amplitudes. The rigid-lid approximation has been used for all of the models. Stratification, flat bottom and water depth stay the same for all three simulations.

In the simulation analysis, we use the results from the IGW as the standard. Both of the two weakly nonlinear models give fairly good predictions regarding the leading wave amplitudes, shapes of the wave train and the propagation speeds. However, the weakly nonlinear models over-predict the propagation speed of the leading solitary wave and that the alternative Ostrovsky equation gives the worst prediction. The difference between the two weakly nonlinear models decreases as the initial wave amplitude decreases.

Wednesday, 23 April 2014, 10:00AM -- MC 6496 true
Comprehensive Exam -- Applied Mathematics
Speaker: Zhen Wang, Applied Mathematics , University of Waterloo
Title: "Clustering Behavior in Neural Networks with Time Delay"
Abstract: A neural network is an information processing paradigm that is inspired by the way biological nervous systems, such as the brain, process information. It is composed of a large number of highly interconnected processing elements (neurons) working in unison to solve specific problems. It is well known that oscillations occur in many neural networks models, and the properties of the oscillations depend on the characteristics of the individual neurons, how the neurons are connected to each other and the presence of time delays in the connection. Cluster state is a special state of the oscillations in which multiple subpopulations coexist and each of the cluster consists of fully phase synchronized oscillators.

In this talk, I will give a brief review of modelling of neural networks and literature in this field, then introduce the linear stability results about a system of N globally coupled oscillators. Finally, an example model for six globally coupled Morris-Lecar oscillators is presented to show how to use phase model to analyze the stability of clustering behavior.

Wednesday, 23 April 2014, 3:00PM -- MC 6496 true
Miscellaneous -- Applied Mathematics
Speaker: Tung Hoang, Applied Mathematics, University of Waterloo
Title: "PhD Comprehensive Seminar: Post-processing and superconvergence for discontinuous Galerkin solutions"
Abstract: Post-processing is used to enhance accuracy of numerical solutions of partial differential equations. Usually it is applied to the solution at the final time. Thus, it requires little computing time as compared with the cost of obtaining the numerical solution itself. For discontinuous Galerkin methods applied to hyperbolic conservation laws B-spline based post-processing increases accuracy from order k+1 to 2k+1 provided that the exact solution is smooth enough. The post-processing is based on convolution of the numerical solution with a kernel defined in terms of these B-splines. The accuracy enhancement is based on the super accuracy of DG solution in the negative Sobolev norms. Extensive numerical experiments demonstrate the efficiency of this technique. In this seminar I will give a novel analysis of post-processing technique and connect post-processing to super accuracy of DG in the wave number approximation. Finally I will propose some questions for future investigation.

Thursday, 24 April 2014, 10:00AM -- M3 - 2134 true
Miscellaneous -- Applied Mathematics
Speaker: Arman Tavakoli, Applied Mathematics , University of Waterloo
Title: "MMath Defence: H2-Optimal Sensor Location"
Abstract: Optimal sensor placement is an important problem with many applications such as placing thermostats in rooms, installing pressure sensors in chemical columns or attaching vibration detection devices to structures. Frequently, this problem is encountered while noise is present; therefore, one approach to the problem is to combine it with a control strategy designed for systems that have exogenous disturbing inputs, called H2-optimal control. In this work, the optimal sensor location and the H2-optimal control problems are explained independently and then combined into one problem called the H2-optimal sensor location.

The problem is examined for the Euler-Bernoulli equation on a one-dimensional beam and the heat equation in a two-dimensional room. Optimal sensor location is calculated numerically for both models, and multiple scenarios are considered where the location of the disturbance and the actuator are varied. The effects of different model parameters such as the weight of the state and the disturbance are investigated.

For a system that is heavily weighted by the disturbance, it is found that the optimal sensor location tends to collocate with the disturbance. A larger weight for the state variable tends to move the optimal sensor location towards the actuator.

Thursday, 24 April 2014, 10:30AM -- DC 1302
Software Architecture Group Seminar -- Computer Science
Speaker: Laura Inozemtseva, PhD candidate, David R. Cheriton School of Comp. Sci., Univ. Waterloo
Title: "Integrating Software Project Resources Using Source Code Identifiers"
Abstract: Source code identifiers such as classes, methods, and fields appear in many different contexts. For instance, a developer performing a task using the android.app.Activity class could consult various project resources including the class's source file, its API documentation, its issue tracker, mailing list discussions, code reviews, or questions on Stack Overflow.

These information sources are logically connected by the source code elements they describe, but are generally decoupled from each other. This has historically been tolerated by developers, since there was no obvious way to easily navigate between the data sources. However, it is now common for these sources to have web-based front ends that provide a standard mechanism (the browser) for viewing and interacting with the data in the resources. Augmenting these front ends with hyperlinks and search would make development easier by allowing developers to navigate between disparate sources of information about the same code element.

We propose a method of automatically linking disparate information repositories with very high precision using structural elements present in source code. We also propose a method of augmenting web-based front ends with these links to make it easier for developers to quickly gain a comprehensive view of the source code elements they are investigating. Research challenges include identifying source code tokens in the midst of natural language text and incomplete code fragments, dynamically augmenting the web views of the data repositories, and supporting novel composition of the link data to provide comprehensive views for specific source code elements.

Thursday, 24 April 2014, 1:00PM -- DC 1302 true
Software Architecture Group Master's Research Paper Presentation -- Computer Science
Speaker: Ashar Ghani, graduate student, David R. Cheriton School of Comp. Sci., Univ. Waterloo
Title: "An Empirical Study of Test Suite Reduction"
Abstract: Test suites form an integral part of automated regression testing for software projects. With time, test suites for large software projects can grow to massive sizes that take a significant amount of time to execute. This can result in delays for developers who are verifying the impact of the changes they are making to their systems. Test suite reduction approaches aim to identify a subset of a test suite that is relevant to code change being introduce to the system. In this talk we introduce a framework for test suite reduction that can be used for continuous regression testing and present the results of an empirical study to evaluate the effectiveness of several different test suite reduction techniques.

Thursday, 24 April 2014, 1:30PM -- DC 1302 true
Software Architecture Group Master's Research Paper Presentation -- Computer Science
Speaker: Ravi M. Chandra, graduate student, David R. Cheriton School of Comp. Sci., Univ. Waterloo
Title: "Continuous Partial Test Suite Execution"
Abstract: Test driven development (TDD) is a software development paradigm in which test cases are written prior to the source code. Studies reveal that TDD helps improve software quality and and developer productivity. Continuos testing (CT) is an approach in which runs tests cases are continuously executed as developers modify their system. This approach helps developers quickly identify when changes cause the test suite to fail; unfortunately, running all test cases at all times is not practical as suite execution is often too slow or expensive for background analysis. In this talk, we propose executing subsets of tests continuously by applying filters on the available test suite data to determine relevant test cases. This process of obtaining and executing the partial test suite is performed in continuos manner to offer the benefits of CT to the developer and increase the speed with which they become aware of test case failures.

Thursday, 24 April 2014, 2:30PM -- DC 1304
Cryptography, Security, and Privacy (CrySP) Group Seminar -- Computer Science
Speaker: Rajesh Krishna Balan, Associate Professor, Singapore Management Univ. and School of Information Systems
Title: "The LiveLabs Urban LifeStyle Innovation Platform : Opportunities, Challenges, and Current Results"
Abstract: A central question in mobile computing is how do you test mobile applications, that depend on real context, in real environments with real users? User studies done in lab environments are frequently insufficient to understand the real-world interactions between user context, privacy, environmental factors, application behaviour, and performance results. I will introduce LiveLabs, a 5 year project that started at the Singapore Management University in early 2012. The goal of LiveLabs is to convert four real environments, the entire Singapore Management University campus, a popular resort island, a large airport, and a popular shopping mall, into living testbeds where we instrument both the environment and the cell phones of opted-in participants (drawn from the student population and members of the public). We can then provide 3rd party companies, and researchers the opportunity to test their mobile applications and scenarios on the opted-in participants -- on their real phones in the four real environments described above. LiveLabs will provide the software necessary to collect network statistics and any necessary context information. In addition, LiveLabs will provide software and mechanisms to ensure that privacy, proper participant selection, resource management, and experimental results and data are maintained and provided on a need-to-know basis to the appropriate parties.

I will describe the broad LiveLabs vision and identify the key research challenges and opportunities. In particular, I will highlight our current insights into indoor location tracking, dynamic group and queue detection, privacy, and energy aware context sensing for mobile phones. I will also share our current status (we have gone live at our university campus) and some of the non-obvious challenges that arise from deploying these systems in real environments.

Bio: Rajesh is an associate professor at Singapore Management University's School of Information Systems. He received his Ph.D. in computer science from Carnegie Mellon University and has over 15 years of research experience in the broad area of mobile systems and software. Some of the diverse areas that he has worked on include infrastructure support for multiplayer mobile games, improvements to public transportation networks, understanding and improving the software development process in outsourced environments, and developing and testing novel retail-focused mobile applications.

Rajesh is also a director of the new LiveLabs Urban LifeStyle Innovation Platform. The goal of this platform is to allow mobile applications and services to be tested with real users on real phones in real-world environments. Currently, LiveLabs has been deployed at a university campus with further deployments at an airport, a resort island, and a large mall planned for the near future. More details about LiveLabs can be obtained at http://www.livelabs.smu.edu.sg

Thursday, 24 April 2014, 3:30PM -- MC 5046
Universal Algebra Seminar -- Pure Mathematics
Speaker: Alexander Wires, Department of Pure Mathematics University of Waterloo
Title: "“Dichotomy for Finite tournament of Mixed-type I”"
Abstract: Since irreflexive digraphs often pp-define partially reflexive digraphs, we can show they yield NP-complete CSP templates by understanding certain mixed-type cases. A tournament of mixed-type is a digraph in which distinct vertices have exactly one oriented edge between them, and loops are not prohibited. We classify tournaments of mixed-type closed under a Taylor operation, and show their polymorphism algebras generate congruence meet-semidistributive varieties. In this first talk, we start the proof of this result.

Friday, 25 April 2014, 10:00AM -- MC 6496 true
Miscellaneous -- Applied Mathematics
Speaker: John Ladan, Applied Mathematics, University of Waterloo
Title: "MMath Defence: An Analysis of Stockwell Transforms with Applications to Signal/Image Processing"
Abstract: Time-frequency analysis is a powerful tool for signal analysis and processing. The Fourier transform and wavelet transforms are used extensively as is the Short-Time Fourier Transform (or Gabor transform). In 1996 the Stockwell transform was introduced to maintain the phase of the Fourier transform, hile also providing the progressive resolution of the wavelet transform. The discrete orthonormal Stockwell transform is a more efficient, less redundant transform with the same properties.

There has been little work on mathematical properties of the Stockwell transform, particularly how it behaves under operations such as translation and modulation. Previous results do discuss a resolution of the identity, as well as some of the function spaces that may be associate with it. We extend the resolution of the identity results, and behaviour under translation, modulation, rotation, convolution and differentiation. We will also apply the Stockwell transform to various continuous functions.

The discrete orthonormal Stockwell transform is compared directly with Newland's harmonic wavelet transform, and we extend the definition to include variations, as well as develop the discrete cosine based Stockwell transform. There has been some work on image processing using the Stockwell transform and discrete orthonormal Stockwell transform. The tests were quite preliminary. We test all of these discrete transforms against current methods for image compression.

Friday, 25 April 2014, 11:30AM -- DC 2306C (AI Lab)
Artificial Intelligence Lab PhD Seminar -- Computer Science
Speaker: Alan Tsang, PhD candidate, David R. Cheriton School of Comp. Sci., Univ. Waterloo
Title: "Opinion Dynamics of Skeptical Agents"
Abstract: How does skepticism affect opinion formation in networks? In many settings, agents exhibit skepticism in the presence of people whose beliefs radically different from their own, and they are reluctant to be persuaded by such individuals. We present a model of opinion dynamics where agents are receptive toward other agents that have similar opinions, but remain skeptical of agents holding disparate opinions. We analyze how agents with extreme opinions affect the general population, using simulations on Barab\'{a}si-Albert random graphs, and modified Erd\"{o}s-R\'{e}nyi random graphs that incorporate homophily. Finally, we show that even skeptical agents are able to come to an early consensus and take coordinated action to reach a final opinion in most settings; but, agents in homophilic networks may fail to converge to a single opinion. Paradoxically, this happens when agents are \emph{least} skeptical, and are able to stabilize themselves by balancing influence from extremists from opposing camps.


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