# Upcoming seminars

 Upcoming Seminars Mon10/05/2015(tomorrow)4:00pm Seminar: CombinatoricsExtremal problems on diameter-critical graphsJie Ma, University of Science and Technology of ChinaContact: Dwight Duffus, dwight@mathcs.emory.eduVenue: Mathematics and Science Center, Room W301Download printable flyer (PDF, 44.8 kB)Hide abstractA graph is called diameter-$k$-critical if its diameter is $k$, and the removal of any edge strictly increases the diameter. In this talk, we will present several results related to a conjecture often attributed to Murty and Simon, regarding the maximum number of edges that any diameter-$k$-critical graph can have. In particular, we disprove a longstanding conjecture of Caccetta and H\"aggkvist (that in every diameter-2-critical graph, the average edge-degree is at most the number of vertices), which promised to completely solve the extremal problem for diameter-2-critical graphs. On the other hand, we prove that the same claim holds for all higher diameters, and is asymptotically tight, resolving the average edge-degree question in all cases except diameter-2. We also apply our techniques to prove several bounds for the original extremal question, including the correct asymptotic bound for diameter-$k$-critical graphs, and an upper bound of $(\frac{1}{6} + o(1))n^2$ for the number of edges in a diameter-3-critical graph. This is a joint work with Po-Shen Loh. Tue10/06/2015(in 2 days)4:00pm Seminar: AlgebraNorms of Roots of TrinomialsTimo de Wolff, Texas A&MContact: Vicki Powers, vicki@mathcs.emory.eduVenue: Mathematics and Science Center, Room W304Download printable flyer (PDF, 97.5 kB)Hide abstractThe behavior of norms of roots of univariate trinomials with respect to the choice of coefficients is a classical late 19th and early 20th century problem. In 1908, P. Bohl characterized the parameter space, but only in an algebraic way. By using amoeba theory we uncover a beautiful geometric and topological structure in the corresponding parameter space. More precisely, we show that norms of roots of trinomials are geometrically characterized by hypo-epitrochoids and its parameter space is topologically characterized by torus knots. Fri10/09/2015(in 5 days)1:00pm Seminar: Scientific ComputingImage Registration using Large Deformations Diffeomorphic Metric Mapping (LDDMM)Thomas Polzin, University of Luebeck, GermanyContact: Lars Ruthotto, lruthotto@emory.eduVenue: Mathematics and Science Center, Room W302Download printable flyer (PDF, 47.3 kB)Hide abstractImage registration is a key task in image analysis. Its applications range from fusing multimodal data over object tracking to motion modeling, e.g. for the respiratory system. In the latter example large motions occur and inside the lungs no foldings of tissue are to be expected. Hence it is appropriate to model the movement as a diffeomorphic nonlinear trans- formation. As requirements like diffeomorphic transformations and the capability of capturing large motions are often necessary in image registration the ”Large Deformations Diffeomorphic Metric Mapping (LDDMM)” approach is very useful. The theoretical foundations for LDDMM were laid in the late 1990s and the beginning of the 2000s by Grenander, Christensen, Miller, Trouve, Younes and others. In 2005 Beg et al. [1] provided a practical algorithm to solve the LDDMM image registration problem. LDDMM is related to optical flow. In [2] optical flow problems were solved using an optimal control approach. Following a similar approach in 2009 the LDDMM model was used for image registration from an optimal control perspective in [3]. In the talk I will give an introduction to LDDMM following loosely [3] and start with the matching of scalars, which results in a tool for linear regression. In this example, the two different concepts of relaxation and shooting are illustrated. In the relaxation approach the optimization is performed regarding the complete temporal velocity field. However, in the shooting approach the optimization is only over the initial condition, i.e., slope and possibly y-intercept of the line. I will then discuss how to extend these ideas to the problem of image matching and how to discretize the optimization problem using consistent Runge-Kutta methods for the transport equation and its adjoint. References [1] Mirza Faisal Beg, Michael I. Miller, Alain Trouve, and Laurent Younes. Computing large deformation metric mappings via geodesic flows of diffeomorphisms. International Journal of Computer Vision, 61(2):139–157, 2005. [2] Alfio Borzi, Kazufumi Ito, and Karl Kunisch. Optimal Control Formulation for Determining Optical Flow. SIAM Journal on Scientific Computing, 24(3):818–847, 2003. [3] Gabriel L. Hart, Christopher Zach, and Marc Niethammer. An optimal control approach for deformable registration. 2009 IEEE Computer Society Conference on Computer Vision and Pattern Recognition Workshops, 2(1), 2009. Fri10/16/2015(in 12 days)3:00pm Seminar: Computer SciencePrivacy-Preserving Query Processing over Encrypted Data in CloudYousef Elmehdwi, Missouri ST UniversityContact: Vaidy Sunderam, vss@mathcs.emory.eduVenue: Mathematics and Science Center, Room W303Download printable flyer (PDF, 37.6 kB)Hide abstractThe query processing of relational data has been studied extensively throughout the past decade. A number of theoretical and practical solutions to query processing have been proposed under various scenarios. With the recent popularity of cloud computing, data owners now have the opportunity to outsource not only their data, but also the data management tasks to the cloud. Because of data security and personal privacy concerns, sensitive data (e.g. medical records) should be encrypted before being outsourced to a cloud, and the cloud should perform query processing tasks on the encrypted data only. In this talk, I will present our current research on the development of secure distributed protocols to facilitate query processing over encrypted data hosted in the cloud. I will also explore possible future research directions. Tue10/20/2015(in 16 days)4:00pm Seminar: AlgebraRational points of rationally connected varieties over number fields, an overview (part 1)Olivier Wittenberg, École normale supérieureContact: David Zureick-Brown, dzb@mathcs.emory.eduVenue: Mathematics and Science Center, Room W304Download printable flyer (PDF, 35.5 kB)Hide abstractThis will be a short course (3 lectures) aimed at graduate students. Wed10/21/2015(in 17 days)4:00pm Seminar: AlgebraRational points of rationally connected varieties over number fields, an overview (part 2)Olivier Wittenberg, École normale supérieureContact: David Zureick-Brown, dzb@mathcs.emory.eduVenue: Mathematics and Science Center, Room W301Download printable flyer (PDF, 35.5 kB)Hide abstractThis will be a short course (3 lectures) aimed at graduate students. Thu10/22/2015(in 18 days)4:00pm Seminar: AlgebraRational points of rationally connected varieties over number fields, an overview (part 3)Olivier Wittenberg, École normale supérieureContact: David Zureick-Brown, dzb@mathcs.emory.eduVenue: Mathematics and Science Center, Room W304Download printable flyer (PDF, 35.6 kB)Hide abstractThis will be a short course (3 lectures) aimed at graduate students. Fri10/23/2015(in 19 days)9:00am Seminar: AlgebraThe Georgia Algebraic Geometry SymposiumMiscellaneous, MiscellaneousContact: David Zureick-Brown, dzb@mathcs.emory.eduVenue: Mathematics and Science Center, Room W201Download printable flyer (PDF, 39.6 kB)Hide abstractThe Georgia Algebraic Geometry Symposium is a conference series, jointly organized by the University of Georgia, Emory University and Georgia Tech. The conference will begin Friday afternoon and end Sunday, afternoons. \\ See gags.torsor.org for more information. \\ Confirmed speakers: \\ Valery Alexeev (University of Georgia)\\ Brian Conrad (Stanford University)\\ Brian Lehman (Boston College)\\ Max Lieblich (University of Washington)\\ Alexander Merkurjev (UCLA)\\ Alena Pirutka (École Polytechnique)\\ Aaron Pixton (Harvard University)\\ Tony Várilly-Alvarado (Rice University)\\ Olivier Wittenberg (CNRS - École Normale Superieure)\\