报告题目：Adaptive stratified sampling design in two-phase studi…

报 告 人：张洪

时 间：2025年5月16日（周五）上午10：00-11：00

地 点：国交二号楼315会议室

简 介：Causal inference using observational data often suffers from numerous confounding effects, with greatly distorted average causal effect (ACE) estimates if the confounders are ignored. Information on some confounders, such as genetic biomarkers and medical imaging, is prohibitively expensive to obtain in practice. Two-phase studies are resource-efficient solutions to this problem. In such studies, outcome, treatment, and inexpensive confounders are measured for a large number of subjects in the first phase; costly confounder measurements are then collected for a limited number of subjects in the second phase. An efficient statistical design is essential in controlling the cost arising in the second phase. In this paper, we propose an adaptive stratified sampling design (AdaStrat), which minimizes the variance of the ACE estimator with a given second-phase sample size. AdaStrat begins with gathering costly confounder measures for randomly selected pilot data, which are used to develop...

报告题目：An Age-structured Syphilis Model

报 告 人：阮士贵

时 间：2025年5月7日（周三） 下午：16:00-17:00

地 点：国交2号楼201会议室

简 介：Syphilis is a highly contagious bacterial disease with different stages which results in substantial morbidity and mortality worldwide. In particular, it has been resurging among all age groups in both developed and developing countries in the last a few years after the COVID-19 pandemic. Since sexual contact is the main transmission mode, age structure of the host is crucial for the spread of syphilis. In this talk, we introduce an age-structured epidemic model with four infection stages (primary, secondary, latent, and tertiary) to study the transmission dynamics of syphilis. First we establish the well-posedness of the initial–boundary value problem and derive an explicit expression of the basic reproduction number. Then we study global stability of the disease-free steady state and the uniqueness and local stability of the endemic steady state. Next we consider the optimal control of the age-structured model and calibrate the reported data in China by using a demographic model ...

报告题目：Ricci Curvature and the Fundamental Group

报 告 人：黄显涛

时 间：2025年5月6日（周二）下午16:00-17:00

地 点：国交2号楼315会议室

简 介：In this talk, I will review the research on the fundamental groups on noncompact manifolds with nonnegative Ricci curvature. And then I will introduce a recent joint work with Hongzhi Huang which says that if M is a 4-dimensional open manifold with nonnegative Ricci curvature, and its universal cover has Euclidean volume growth, then the fundamental group of M is finitely generated and contains an abelian subgroup whose index is bounded by a universal contant