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Series: Analysis Seminar

Series: Research Horizons Seminar

Series: PDE Seminar

TBA

Series: Geometry Topology Seminar

Monday, October 15, 2018 - 13:55 ,
Location: Skiles 005 ,
Prof. Yun Jing ,
NCSU ,
Organizer: Molei Tao

In recent years, metamaterials have drawn a great deal of attention in the scientific community due to their unusual properties and useful applications. Metamaterials are artificial materials made of subwavelength microstructures. They are well known to exhibit exotic properties and could manipulate wave propagation in a way that is impossible by using nature materials.In this talk, I will present our recent works on membrane-type acoustic metamaterials (AMMs). First, I will talk about how to achieve near-zero density/index AMMs using membranes. We numerically show that such an AMM can be utilized to achieve angular filtering and manipulate wave-fronts. Next, I will talk about the design of an acoustic complimentary metamaterial (CMM). Such a CMM can be used to acoustically cancel out aberrating layers so that sound transmission can be greatly enhanced. This material could find usage in transcranial ultrasound beam focusing and non-destructive testing through metal layers. I will then talk about our recent work on using membrane-type AMMs for low frequency noise reduction. We integrated membranes with honeycomb structures to design simultaneously lightweight, strong, and sound-proof AMMs. Experimental results will be shown to demonstrate the effectiveness of such an AMM. Finally, I will talk about how to achieve a broad-band hyperbolic AMM using membranes.

Monday, October 15, 2018 - 13:00 ,
Location: Skiles 006 ,
Lev Tovstopyat-Nelip ,
Boston College ,
Organizer: John Etnyre

Series: Other Talks

Thanks are due to our colleague, Vladimir Koltchinskii, for arranging this visit. Please write to Vladimir if you would like to meet with Professor Gabor Lugosi during his visit, or for additional information.

In these lectures we discuss some statistical problems with an interesting combinatorial structure behind. We start by reviewing the "hidden clique" problem, a simple prototypical example with a surprisingly rich structure. We also discuss various "combinatorial" testing problems and their connections to high-dimensional random geometric graphs. Time permitting, we study the problem of estimating the mean of a random variable.

Series: Combinatorics Seminar

Spectral algorithms, such as principal component analysis and spectral
clustering, typically require careful data transformations to be
effective: upon observing a matrix A, one may look at the spectrum of
ψ(A) for a properly chosen ψ. We propose a simple and generic
construction for sparse graphs based on graph powering. It is shown
that graph powering regularizes the graph and decontaminates its
spectrum in the following sense: (i) If the graph is drawn from the
sparse Erd˝os-R´enyi ensemble, which has no spectral gap, it is shown
that graph powering produces a “maximal” spectral gap, with the latter
justified by establishing an Alon-Boppana result for powered graphs;
(ii) If the graph is drawn from the sparse SBM, graph powering is
shown to achieve the fundamental limit for weak recovery.
(Joint work with E. Abbe, E. Boix, C. Sandon.)

Series: ACO Student Seminar

Series: Stochastics Seminar