Department Seminars & Colloquia
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In gas dynamics, Y. Sone (U of Kyoto) has used the term "ghost" effect for problems of transpirational flow of a gas. The reason for the word "ghost" is that the gas moves with constant pressure. In every day Newtonian mechanics that is analogous to saying a body initiates motion in the absence of force violating $F=ma$. So one might say a "ghost" has moved the gas. Of course there is no "ghost" only a need for better mathematical models and PDEs. This not hard to do but unlike the Kyoto group I will use PDEs instead of the Boltzmann equation of Kinetic theory.
E6-1 #1409
Discrete Math
Jang Soo Kim (KIAS)
Combinatorics of continued fractions and its application to Jacobi’s triple product identity
Log del Pezzo pairs frequently appear motivated by developments in the minimal model program. However, they are not very well understood from the viewpoint of classification. We define suitable smooth models of del Pezzo pairs, and we show that they are the same. This result with the comprehensive study of anticanonical morphisms of ruled surfaces by Sakai and Badescu reduces the problem of classification of log del Pezzo pairs to that of del Pezzo surfaces. In particular, we completely classify non-rational weak log canonical del Pezzo pairs, and we characterize when they have finitely generated Cox rings. This is a joint work with DongSeon Hwang. At the end of the talk, we will discuss a higher dimensional generalization of these results. This is a joint work in progress with DongSeon Hwang and Sung Rak Choi.
In this talk we will consider some aspects of abstract harmonic analysis on compact groups and its quantum extension, namely operator amenabilities of the L^1 algebras. Basic concepts on compact groups and quantum groups will be briefly reviewed focusing on the examples of SU(2) and its q-deformations.
For a smooth projective curve over a number field the motivic finiteness conjectures predict that SK_1 should be a torsion group. In this survey talk we motivate this conjecture, and explain some of the difficulties
that arise in an attempt to compute this group.
All possible (minimal good) resolution graphs of complex surface singularities that admit a rational homology disk smoothing (that is, a smoothing whose Milnor number is $0$) are classified by Stipsicz--Szab'o--Wahl~[J. Topol. 2008], except the well-known class of linear graphs, into three classes: (i) graphs with only one star, called ``star-shaped graphs'' (here, a emph{star} is a vertex with valency $ge 3$); (ii) non-star-shaped graphs with all stars with valencies $le 3$; or (iii) non-star-shaped graphs with all stars with valencies $le 3$ but only one star with valency $4$. Thanks to the work of Bhupal and Stipsicz~[Amer. J. Math. 2011], one has a complete list of star-shaped graphs having a rational homology disk smoothing. In contrast we prove that any non-star-shaped graphs with all stars with valencies $le 3$ cannot be the resolution graphs of complex surface singularities with a rational homology disk smoothing. Our result supports the conjecture of Wahl~[Geom. Topol. 2011] that the only complex surface singularities admitting a rational homology disk smoothing are the known weighted homogeneous examples, whose resolution graphs are linear or star-shaped. This is a joint work with Heesang Park and Andr'as I. Stipsicz.
In this talk we will present a new method of providing both conductivity and permittivity images at the MR Larmor frequency in magnetic resonance electrical property tomography (MREPT), a relatively new MR-based electrical tissue property imaging modality.