All Seminars

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Title: Human-centered Data Science for Crisis Informatics
Seminar: Computer Science
Speaker: Marina Kogan of University of Colorado
Contact: Li Xiong, lxiong@emory.edu
Date: 2017-03-23 at 4:00PM
Venue: W201
Abstract:
Disasters arising from natural hazards are associated with the disruption of existing social structures, but they also result in the creation of new social ties by those affected as they problem-solve alone and together. With social media now being a site for some of this interaction, there is much to learn about the nature of those changing social structures, including how and why they shift. However, the study of this social arena is challenging, because the high-tempo, high-volume convergent nature of crisis events produces vast amounts of social media data, necessitating the use of the data science methods. On the other hand, to glean meaningful insight from the crisis-related social media activity, it is necessary to use methods that account for the complex social context of the user activity, including qualitative analysis.\\ \\In this talk Kogan will show how Human-Centered Data Science provides methodological approaches that both harness the power of computation methods and account for the highly situated nature of social media activity in disaster. Utilizing these methodological approaches, she will show how disaster-related coordination and distributed problem solving take shape on two social media platforms: Twitter and OpenStreetMap.
Title: Congruence of Galois representations
Seminar: Algebra
Speaker: Sujatha Ramdorai of University of British Columbia
Contact: David Zureick-Brown, dzb@mathcs.emory.edu
Date: 2017-03-21 at 4:00PM
Venue: W306
Abstract:
We consider Galois representations whose residual representations are isomorphic and study what this implies for invariants associated to such representations.
Title: Extremal Problems for Graphs and Hypergraphs
Defense: Dissertation
Speaker: Bill Kay of Emory University
Contact: Bill Kay, w.w.kay@emory.edu
Date: 2017-03-21 at 4:00PM
Venue: W301
Abstract:
We discuss a pair of papers in extremal combinatorics. One establishes asymptotically the chromatic number of the so-called type graphs, and the other investigates a certain property of oriented hypergraphs (Property O).
Title: Designing Abstract Meaning Representations
Seminar: Computer Science
Speaker: Martha Palmer of University of Colorado
Contact: Jinho Choi, choi@mathcs.emory.edu
Date: 2017-03-17 at 3:00PM
Venue: W301
Abstract:
Title: A Method for Landscape Exploration in Global Optimization.
Seminar: N/A
Speaker: Manuela Manetta of Emory University
Contact: Bree Ettinger, bettinger@mathcs.emory.edu
Date: 2017-03-16 at 1:00PM
Venue: W303
Abstract:
Finding global minima for a general smooth objective function is a fundamental yet challenging problem arising in applied mathematics. Nevertheless, the most reliable techniques to converge to a minimum are local (gradient descent and Newton's method), and remain trapped in the basins of attraction of the minima found, which could be either local or global. Even in optimization courses, the students are often left with questions, such as, "how do we know that we found the global minimum? How do we know that we have visited the interesting regions of configuration space?" The purpose of this talk is to present methods and ideas that could help the students formulate answers to the questions above. In particular, I will present a new descent technique and a way to explore the landscape of the objective function, with no pretense that this is the answer to the problem, but with the hope of engaging the students. Interested students can begin to take small steps in the right direction toward the development of their own methods.
Title: Curvature through Cubes
Seminar: N/A
Speaker: Michael Carr of Emory University
Contact: Bree Ettinger, bettinger@mathcs.emory.edu
Date: 2017-03-15 at 4:00PM
Venue: W303
Abstract:
Everyone knows the shortest distance between two points in Euclidean space is a straight line, but what about in more exotic spaces? Mathematicians have been studying paths on curved spaces for as long as we have known we lived on one. More recently the work of Gromov showed that notions of curvature can be extended to spaces that seem to have no curves at all: complexes made from ordinary cubes glued together. We will look at applications of these spaces from robotics to chemistry to recent advances in topology.
Title: Bias and Uncertainty in Information Visualization
Type: Computer Science
Speaker: Michael Correll of University of Washington
Contact: TBA
Date: 2017-03-13 at 4:00PM
Venue: W303
Abstract:
We often turn to data to help us make sense of an uncertain world. However, the uncertainty in our data is often esoteric, complex, or counter-intuitive. It can be challenging to present this uncertainty, especially to audiences without backgrounds in statistics. Charts, graphs, and other visualizations of data address this issue by making people into visual statisticians: we can estimate statistical properties through visual inspection. However, just as statistical measures can be subject to bias, visualizations can also introduce bias. In this talk, I show how designers can intervene to create new visualizations that correct these biases, and improve the judgments of visual statisticians. From this perspective of designing for de-biasing, I focus on two common visualizations: error bars and thematic maps. I present visual alternatives for error bars that avoid within-the-bar bias while also promoting statistically grounded comparisons between means. I also present Surprise Maps, a technique for thematic maps that relies on Bayesian reasoning to highlight interesting regions that might otherwise be hidden in traditional maps. I conclude with a discussion of remaining challenges for visual de-biasing, and how we might use visualizations to encourage better, data-driven decision-making.
Title: The Distribution Of The Number Of Prime Factors With Restrictions - Variations Of The Classical Theme
Seminar: Algebra
Speaker: Krishna Alladi of University of Florida
Contact: David Zureick-Brown, dzb@mathcs.emory.edu
Date: 2017-02-28 at 4:00PM
Venue: W306
Abstract:
The study of $\nu(n)$ the number of prime factors of $n$ began with Hardy and Ramanujan in 1917 who showed that $\nu(n)$ has normal order $log\,log\,n$ regardless of whether the prime factors are counted singly or with multiplicity. Their ingenious proof of this utilized uniform upper bounds for $N_k(x)$, the number of integers up to $x$ with $\nu(n)=k$. Two major results followed a few decades later - the Erd\"os-Kac theorem on the distribution more generally of additive functions, and the Sathe-Selberg theorems on the asymptotic behavior of $N_k(x)$ as $k$ varies with $x$ - a significant improvement of Landau's asymptotic estimate for $N_k(x)$ for fixed $k$. We shall consider the distribution of the number of prime factors by imposing certain restrictions - such as (i) requiring all prime factors of $n$ to be \$
Title: Bounded colorings of graphs and hypergraphs
Seminar: Combinatorics
Speaker: Jan Volec of McGill University
Contact: Dwight Duffus, dwight@mathcs.emory.edu
Date: 2017-02-27 at 4:00PM
Venue: W303
Abstract:
A conjecture of Bollobas and Erdos from 1976 states that any coloring of edges of an n-vertex complete graph such that at each vertex no color appears more than (n/2)-times contains a properly-colored Hamilton cycle. This problem was motivation for the following more general question: Let c be a coloring of E(K_n) where at each vertex, no color appear more than k-times. What properly colored subgraphs does c necessarily contain? In this talk, we will be interested in spanning subgraphs of K_n that have bounded maximum degree or the total number of cherries, i.e., the paths on three vertices. We will also mention similar questions for hypergraphs, as well as analogous problems concerned with rainbow subgraphs in edge colorings of K_n, where the total number of appearances for each color is bounded. One of our main results confirms the following conjecture of Shearer from 1979: If G is an n-vertex graph with O(n) cherries and c is a coloring of E(K_n) such that at each vertex every color appears only constantly many times, then c contains a properly colored copy of G. The talk is based on a joint work with Nina Kamcev and Benny Sudakov.
Title: Uncertainty Quantification and Numerical Analysis: Interactions and Synergies
Seminar: Numerical Analysis and Scientific Computing
Speaker: Daniela Calvetti of Case Western Reserve University
Contact: James Nagy, nagy@mathcs.emory.edu
Date: 2017-02-24 at 1:00PM
Venue: W301
Abstract:
The computational costs of uncertainty quantification can be challenging, in particular when the problems are large or real time solutions are needed. Numerical methods appropriately modified can turn into powerful and efficient tools for uncertainty quantification. Conversely, state-of-the-art numerical algorithms reinterpreted from the perspective of uncertainty quantification can becomes much more powerful. This presentation will highlight the natural connections between numerical analysis and uncertainty quantification and illustrate the advantages of re-framing classical numerical analysis in a probabilistic setting.