Wednesday, August 9, 2023

2023-08-11 / 15:00 ~ 17:00

by ()

Ecosystems are complex systems of various physical, biological, and chemical processes. Since ecosystem dynamics are composed of a mixture of different levels of stochasticity and nonlinearity, handling these data is a challenge for existing methods of time series–based causal inferences. Here, we show that, by harnessing contemporary machine learning approaches, the concept of Granger causality can be effectively extended to the analysis of complex ecosystem time series and bridge the gap between dynamical and statistical approaches. The central idea is to use an ensemble of fast and highly predictive artificial neural networks to select a minimal set of variables that maximizes the prediction of a given variable. It enables decomposition of the relationship among variables through quantifying the contribution of an individual variable to the overall predictive performance. We show how our approach, EcohNet, can improve interaction network inference for a mesocosm experiment and simulated ecosystems. The application of the method to a long-term lake monitoring dataset yielded interpretable results on the drivers causing cyanobacteria blooms, which is a serious threat to ecological integrity and ecosystem services. Since performance of EcohNet is enhanced by its predictive capabilities, it also provides an optimized forecasting of overall components in ecosystems. EcohNet could be used to analyze complex and hybrid multivariate time series in many scientific areas not limited to ecosystems.

2023-08-10 / 11:00 ~ 12:30

SAARC 세미나 - SAARC 세미나:

by ()

In this lecture series, I will discuss rigidity in the long time dynamics of some evolution equation. The specific equation to be paid attention to is the self-dual Chern-Simons-Schrödinger equation (CSS) within equivariant symmetry. (CSS) is a gauged 2D cubic nonlinear Schrödinger equation that has pseudoconformal invariance and solitons. However, two distinguished features of (CSS), the self-duality and non-locality, make the long time dynamics of (CSS) surprisingly rigid. For instance, (i) any finite energy spatially decaying solutions to (CSS) decompose into at most one modulated soliton and a radiation. Moreover, (ii) in the high equivariance case (i.e., the equivariance index ≥ 1), any smooth finite-time blow-up solutions even have a universal blow-up speed, namely, the pseudoconformal one. We will explore this rigid dynamics using modulation analysis, combined with the self-duality and non-locality of the problem, in detail.

2023-08-09 / 11:00 ~ 12:30

SAARC 세미나 - SAARC 세미나:

by ()

2023-08-09 / 16:30 ~ 17:30

IBS-KAIST 세미나 - 이산수학: Intersection patterns of convex sets

by Amzi Jeffs(Carnegie Mellon University)

How can one arrange a collection of convex sets in d-dimensional Euclidean space? This guiding question is fundamental in discrete geometry, and can be made concrete in a variety of ways, for example the study of hyperplane arrangements, embeddability of simplicial complexes, Helly-type theorems, and more. This talk will focus on the classical topic of d-representable complexes and its more recent generalization to convex codes. We will show how these frameworks differ, share some novel Helly-type results, and offer several tantalizing open questions.

Events for the 취소된 행사 포함