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DTSTART;TZID=America/New_York:20180404T163000
DTEND;TZID=America/New_York:20180404T163000
DTSTAMP:20240515T174223Z
CREATED:20240213T064751Z
LAST-MODIFIED:20240515T174223Z
UID:10002129-1522859400-1522859400@cmsa.fas.harvard.edu
SUMMARY:Black Holes and Naked Singularities
DESCRIPTION:Speaker: Ramesh Narayan\, Department of Astronomy\, Harvard University \nTitle: Black Holes and Naked Singularities \nAbstract: Black Hole solutions in General Relativity contain Event Horizons and Singularities. Astrophysicists have discovered two populations of black hole candidates in the Universe: stellar-mass objects with masses in the range 5 to 30 solar masses\, and supermassive objects with masses in the range million to several billion solar masses. There is considerable evidence that these objects have Event Horizons. It thus appears that astronomical black hole candidates are true Black Holes. Direct evidence for Singularities is much harder to obtain since\, at least in the case of Black Holes\, the Singularities are hidden inside the Event Horizon. However\, General Relativity also permits Naked Singularities which are visible to external observers. Toy Naked Singularity models have been constructed\, and some observational features of accretion flows in these spacetimes have been worked out.
URL:https://cmsa.fas.harvard.edu/event/4-4-2018-colloquium/
LOCATION:CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-Colloquium-040418-e1522340269661.png
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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180411T163000
DTEND;TZID=America/New_York:20180411T173000
DTSTAMP:20240515T144439Z
CREATED:20240213T065052Z
LAST-MODIFIED:20240515T144439Z
UID:10002134-1523464200-1523467800@cmsa.fas.harvard.edu
SUMMARY:Graph Structure in Polynomial Systems: Chordal Networks
DESCRIPTION:Speaker: Pablo Parillo (MIT) \nTitle: Graph Structure in Polynomial Systems: Chordal Networks \nAbstract: The sparsity structure of a system of polynomial equations or an optimization problem can be naturally described by a graph summarizing the interactions among the decision variables. It is natural to wonder whether the structure of this graph might help in computational algebraic geometry tasks (e.g.\, in solving the system). In this lecture we will provide a gentle introduction to this area\, focused on the key notions of chordality and treewidth\, which are of great importance in related areas such as numerical linear algebra\, database theory\, constraint satisfaction\, and graphical models. In particular\, we will discuss “chordal networks”\, a novel representation of structured polynomial systems that provides a computationally convenient decomposition of a polynomial ideal into simpler (triangular) polynomial sets\, while maintaining its underlying graphical structure. As we will illustrate through examples from different application domains\, algorithms based on chordal networks can significantly outperform existing techniques. Based on joint work with Diego Cifuentes (MIT).
URL:https://cmsa.fas.harvard.edu/event/4-11-2018-colloquium/
LOCATION:CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/2018_04_10_09_58_15-e1523369654177.png
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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180413T163000
DTEND;TZID=America/New_York:20180413T173000
DTSTAMP:20240514T185400Z
CREATED:20240213T065558Z
LAST-MODIFIED:20240514T185400Z
UID:10002143-1523637000-1523640600@cmsa.fas.harvard.edu
SUMMARY:On the fibration structure of known Calabi-Yau threefolds
DESCRIPTION:Speaker: Washington Tayor (MIT) \nTitle: On the fibration structure of known Calabi-Yau threefolds \nAbstract: In recent years\, there is increasing evidence from a variety of directions\, including the physics of F-theory and new generalized CICY constructions\, that a large fraction of known Calabi-Yau manifolds have a genus one or elliptic fibration. In this talk I will describe recent work with Yu-Chien Huang on a systematic analysis of the fibration structure of known toric hypersurface Calabi-Yau threefolds. Among other results\, this analysis shows that every known Calabi-Yau threefold with either Hodge number exceeding 150 is genus one or elliptically fibered\, and suggests that the fraction of Calabi-Yau threefolds that are not genus one or elliptically fibered decreases roughly exponentially with h_{11}. I will also make some comments on the connection with the structure of triple intersection numbers in Calabi-Yau threefolds.
URL:https://cmsa.fas.harvard.edu/event/4-18-2018-colloquium/
LOCATION:CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:Colloquium
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/2018_04_13_11_01_32-e1523633302205.png
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