All Seminars
| Title: Preserving Individual Privacy in Spatio-Temporal Data Analytics |
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| Defense: Dissertation |
| Speaker: Liyue Fan of Emory University |
| Contact: Liyue Fan, liyue.fan@emory.edu |
| Date: 2014-06-27 at 2:00PM |
| Venue: MSC W301 |
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| Abstract: We live in the age of big data. With an increasing number of people, devices, and sensors connected with digital networks, individual data now can be largely collected and analyzed by data mining applications for social good as well as for commercial interests. However, the data generated by individual users exhibit unique behavioral patterns and sensitive information, and therefore must be transformed prior to the release for analysis. The AOL search log release in 2006 is an example of privacy catastrophe, where the searches of an innocent citizen were quickly re-identified by a newspaper journalist. In this talk, I will present a novel framework to release continuous aggregation of private data for an important class of real-time data mining tasks, such as disease outbreak detection and web mining, to name a few. The key innovation is that the proposed framework captures the underlying dynamics of the continual aggregate statistics with time series state-space models, and simultaneously adopts filtering techniques to correct the observed, noisy data. I will show that the new framework provides a rigorous, provable privacy guarantee to individual data contributors without compromising the output analysis results. Extensive empirical studies confirm that it will enable privacy-preserving data analytical tasks in a broad range of application domains. |
| Title: Inverse Problems in Hyperspectral Imaging |
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| Defense: Dissertation |
| Speaker: Sebastian Berisha of Emory University |
| Contact: Sebastian Berisha, sberish@emory.edu |
| Date: 2014-06-20 at 11:30AM |
| Venue: W304 |
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| Abstract: In hyperpsectral imaging, multiple images of the same scene are obtained over a contiguous range of wavelengths in the electromagnetic spectrum. Hyperspectral images represent observations of a scene at many different wavelengths and most importantly associate to each pixel in the imaged scene a full spectral vector or spectral signature. However, due to the presence of spectral mixtures (at different scales) in the scene and/or low spatial resolution of the hyperspectral sensor, the acquired spectral vectors of each pixel are actually a mixture of the spectra of the various materials present in the spatial coverage area of the corresponding pixel, and they also contain additional degradations caused by atmospheric blurring.We present a numerical approach for deblurring and sparse unmixing of space objects taken by ground based telescopes. A major challenge for deblurring hyperspectral images is that of estimating the overall blurring operator, taking into account the fact that the blurring operator point spread function (PSF) can be wavelength dependent and depend on the imaging system as well as the effects of atmospheric turbulence. We formulate the PSF estimation as a nonlinear least squares problem, which is solved using a variable projection Gauss-Newton method. Our analysis shows that the Jacobian can be potentially very ill-conditioned. To deal with this ill-conditioning, we use a combination of subset selection and regularization. We then incorporate the PSF estimation scheme with a preconditioned alternating direction method of multipliers to solve the deblurring and sparse unmixing problem. Experimental results illustrate the effectiveness of the resulting numerical schemes. |
| Title: Resonance asymptotics for asymptotically hyperbolic manifolds with warped-product ends |
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| Defense: Dissertation |
| Speaker: Pascal Philipp of Emory University |
| Contact: Pascal Philipp, pphilip@emory.edu |
| Date: 2014-06-03 at 10:00AM |
| Venue: MSC W301 |
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| Abstract: We study the spectral theory of asymptotically hyperbolic manifolds with ends of warped-product type. Our main result is an upper bound on the resonance counting function, with a geometric constant expressed in terms of the respective Weyl constants for the core of the manifold and the base manifold defining the ends. As part of this analysis, we derive asymptotic expansions of the modified Bessel functions of complex order. |
| Title: Secure and Privacy-Preserving Distributed Data Release |
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| Defense: Dissertation |
| Speaker: Slawomir Goryczka of Emory University |
| Contact: Vaidy Sunderam, vss@emory.edu |
| Date: 2014-05-13 at 11:00AM |
| Venue: MSC W301 |
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| Abstract: The rapidly increasing prevalence of distributed data-driven applications has highlighted security and privacy issues in storing and processing sensitive data. Although manipulating raw data may violate privacy of their owners, different techniques of preparing and using privacy-preserving data descriptions can be still used. It remains a challenge, however, to ensure that adapted and new solutions are efficient, secure, and preserve privacy of data owners without disclosing confidentiality of data providers.\\ \\ The dissertation proposes a new notion of $m$-privacy that addresses the challenges when data providers may act as adversaries. To verify if such adversaries are capable of breaching privacy, we introduce a few different strategies and an adaptive algorithm to select and run the most efficient approach. In addition, we designed an algorithm to anonymize data, such that its results are $m$-private, i.e., knowing the results would not help any $m$ colluding parties in their attacks. All verification and anonymization algorithms have been implemented to be run in distributed environments by a trusted third party.\\ \\ For settings without a trusted third party, we introduce new secure multiparty computation protocols that implement centralized $m$-privacy verification and anonymization algorithms. For each protocol, we provedits security, analyzed its communication complexity, and evaluated its overall performance for various settings.\\ \\ The dissertation also describes a new algorithm to build differentially private histograms for records with customized privacy levels. The algorithm has two data partitioning phases (privacy-driven and data-driven). In addition, we adapted a v-optimal partitioning algorithm to be used with differential privacy, and experimentally evaluated their performance. \\ \\ Finally, the dissertation presents a new differential privacy mechanism that achieves collusion resistance in distributed environments with small overhead. We also defined an enhanced fault tolerant secure scheme (EFT), which can be used to design a variety of secure multiparty aggregation operations, and we employed it to implement our differential privacy mechanism in distributed environments. Both, the privacy mechanism and the EFT scheme have been extensively analyzed and experimentally evaluated. |
| Title: Field invariants via refinements to patching |
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| Seminar: Algebra |
| Speaker: David Harbater of UPenn |
| Contact: David Zureick-Brown, dzb@mathcs.emory.edu |
| Date: 2014-05-13 at 3:00PM |
| Venue: W306 |
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| Abstract: We consider fraction fields of complete two-dimensional domains, and obtain their u-invariant and period-index bound. This work, which is joint with Julia Hartmann and Daniel Krashen, builds on the method of patching, and introduces a new notion of refinement. Using that, we obtain local-global principles for quadratic forms and central simple algebras over the fields we consider, and also our results on numerical invariants of fields. |
| Title: The set of non-n-th powers in a number field is Diophantine |
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| Seminar: Algebra |
| Speaker: Jean-Louis Colliot-Thelene of Universite Paris-Sud |
| Contact: David Zureick-Brown, dzb@mathcs.emory.edu |
| Date: 2014-05-08 at 3:00PM |
| Venue: W306 |
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| Abstract: In a joint work with J. Van Geel, we prove: For any natural integer n, the complement of the set of n-th powers in a number field k is the image of the set of k-rational points of some k-variety X under some k-morphism from X to the affine line. For n=2, this is a result of B. Poonen (2009). His proof uses local-global theorems (CT, Coray, Sansuc, 1980) for rational points on Ch\^{a}telet surfaces. Our proof for n arbitrary combines Poonen’s method and local-global theorems (CT, Swinnerton-Dyer, Skorobogatov, 1994, 1998) for zero-cycles on higher dimensional analogues of Ch\^{a}telet surfaces. |
| Title: Log canonical and F-pure thresholds and ordinary reduction |
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| Seminar: Algebra |
| Speaker: Lance Edward Miller of University of Arkansas |
| Contact: David Zureick-Brown, dzb@mathcs.emory.edu |
| Date: 2014-05-06 at 4:00PM |
| Venue: W306 |
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| Abstract: The F-pure threshold of a variety in characteristic p > 0 is a rational number which measure of its singularities near the origin. It is intimately connected to birrational invariants of complex varieties such as the log canonical threshold through reduction mod p. The agreement of these two invariants is also deeply connected to ordinary (in the sense of Bloch-Kato) reduction as can already been seen clearly in the case of elliptic curves. This talk introduces these thresholds and their connections and explores a special cases where agreement can be shown purely in using algebraic methods. |
| Title: On Stabilization of Classical Groups |
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| Seminar: Algebra |
| Speaker: Rabeya Basu of IISER, Pune |
| Contact: David Zureick-Brown, dzb@mathcs.emory.edu |
| Date: 2014-05-02 at 3:00PM |
| Venue: W304 |
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| Abstract: The $K_1$ stabilization of general linear groups is one of the problem related to Serre's problem on projective modules. It was first studied by Bass---Milnor---Serre during mid-sixties. They showed that the surjective bound is d+1, where d is the Krull dimension of the base ring, and conjectured that the injective bound is d+2. Shortly after that it was proved by L.N. Vaserstein. Later we see analog results for other classical groups in the work of A. Suslin, V. Kopeiko, Vaserstien, A. Bak, G. Tang, V. Petrov, W. vander Kallen et al. including the recent break through work by J.Fasel, R.A. Rao and R.G. Swan. In this talk we shall discuss results on injective stabilization for a big class of classical grou |
| Title: Transversality defect of two lagrangians and ternary index. Application: Formulas of (non) additivity of signatures and of linking forms |
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| Seminar: Algebra |
| Speaker: Jean Barge of Ecole polytechnique |
| Contact: David Zureick-Brown, dzb@mathcs.emory.edu |
| Date: 2014-04-29 at 4:00PM |
| Venue: W302 |
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| Abstract: (This is a common work with Jean Lannes) To a pair of lagrangians in a symplectic space, we associate a symetric bilinear form well defined up to the addition of non-degenerate forms and which is itself non-degenerate if and only if the two lagrangians are transversal. To a triple of lagrangians, we associate a ternary index which is a raffinement of the Leray-Kashiwara index and which generalizes for any (commutative) ring the index defined by Wall for fields. We will explain how these two invariants can be used to compute signatures and linking forms of manifolds obtained by gluing. |
| Title: Online Social Dynamics and Wellbeing |
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| Seminar: Computer Science |
| Speaker: Munmun De Choudhury of Georgia Institute of Technology |
| Contact: Eugene Agichtein, eugene@mathcs.emory.edu |
| Date: 2014-04-25 at 3:00PM |
| Venue: MSC W301 |
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| Abstract: Social networks, Facebook and Twitter are continually creating rich repositories of information relating to our activities, emotion and linguistic expression. By leveraging such trails of data and developing machine learning models, we can not only elucidate core aspects of human behavior, but can begin to solve a vista of problems relating to our health behaviors, which have traditionally been challenging. In this talk I will discuss the harnessing of social media in reasoning about behavioral health concerns experienced by populations around major disruptions in life. In a first study, I will present analyses and computational models that make automated inferences about the status and dynamics of postpartum depression in new mothers via postings made on Twitter and Facebook. In a second study, we will examine the affective responses in Twitter experienced by communities in Mexico embroiled in protracted armed conflict and how they might indicate desensitization to violence. Broadly, I will discuss how this new line of research bears potential in informing the design of early-warning systems and interventions to help individuals and policymakers be more proactive about health and wellbeing.\\ \\ Bio:\\ \\ Munmun De Choudhury is currently an assistant professor at the School of Interactive Computing, Georgia Tech. Munmun’s research interests are in computational social science, with a specific focus on reasoning about our health behaviors from social digital footprints. She has been a recipient of the Grace Hopper Scholarship, recognized with an IBM Emergent Leaders in Multimedia award, and recipient of ACM SIGCHI 2014 best paper award and ACM SIGCHI honorable mention awards in 2012 and 2013. Earlier, Munmun was a postdoctoral researcher at Microsoft Research, a research fellow at Rutgers, and obtained a PhD in Computer Science from Arizona State University in 2011. |