MCMC Control Spreadsheets for Exponential Mixture Estimation

Abstract

This article presents Bayesian inference for exponential mixtures, including the choice of a noninformative prior based on a location-scale reparameterization of the mixture. Adapted control sheets are proposed for studying the convergence of the associated Gibbs sampler. They exhibit a strong lack of stability in the allocations of the observations to the different components of the mixture. The setup is extended to the case when the number of components in the mixture is unknown and a reversible jump MCMC technique is implemented. The results are illustrated on simulations and a real dataset.     

Scaling limits of random bipartite planar maps with a prescribed degree sequence

We study the asymptotic behavior of uniform random maps with a prescribed face‐degree sequence, in the bipartite case, as the number of faces tends to infinity. Under mild assumptions, we show that, properly rescaled, such maps converge in distribution toward the Brownian map in the Gromov–Hausdorff sense. This result encompasses a previous one of Le Gall for uniform random q‐angulations where q is an even integer. It applies also to random maps sampled from a Boltzmann distribution, under a second moment assumption only, conditioned to be large in either of the sense of the number of edges, vertices, or faces. The proof relies on the convergence of so‐called “discrete snakes” obtained by adding spatial positions to the nodes of uniform random plane trees with a prescribed child sequence recently studied by Broutin and Marckert. This paper can alternatively be seen as a contribution to the study of the geometry of such trees.     

Lipschitz-volume rigidity on limit spaces with Ricci curvature bounded from below

We prove a Lipschitz-Volume rigidity theorem for the non-collapsed Gromov–Hausdorff limits of manifolds with Ricci curvature bounded from below. This is a counterpart of the Lipschitz-Volume rigidity in Alexandrov geometry.     

A fast image encryption algorithm based on only blocks in cipher text

In this paper, a fast image encryption algorithm is proposed, in which the shuffling and diffusion is performed simul- taneously. The cipher-text image is divided into blocks and each block has k x k pixels, while the pixels of the plain-text are scanned one by one. Four logistic maps are used to generate the encryption key stream and the new place in the cipher image of plain image pixels, including the row and column of the block which the pixel belongs to and the place where the pixel would be placed in the block. After encrypting each pixel, the initial conditions of logistic maps would be changed ac- cording to the encrypted pixel＇s value; after encrypting each row of plain image, the initial condition would also be changed by the skew tent map. At last, it is illustrated that this algorithm has a faster speed, big key space, and better properties in withstanding differential attacks, statistical analysis, known plaintext, and chosen plaintext attacks.     

基于磁共振成像的人脑图谱构建方法研究进展

基于磁共振成像的脑图谱构建对于脑与认知科学的研究非常重要，借助脑图谱，研究者可以精确地分析比较不同的脑影像数据，然而目前尚没有比较统一的标准脑图谱.本文针对基于磁共振成像的脑图谱构建方法进行概述，首先介绍了人脑图谱构建的发展进程，阐述脑图谱构建中需解决的技术问题及其局限性；然后着重描述了构建脑图谱的基本方法；最后论述了应用脑图谱进行精确定量分析的统计学方法，包括基于体素的形态学测量分析法和基于纤维束示踪的空间统计分析法，并较深入地比较了两种方法的差异和近期研究进展.通过分析目前研究现状，本文总结了脑图谱构建研究中的主要方法及不足，并就该领域未来的研究进展进行了展望.     

具有收获和阶段结构的时滞脉冲的捕食-食饵模型

研究了食饵分布在不同斑块,捕食者具有阶段结构和收获的时滞脉冲的捕食-食饵模型.利用离散动力系统的频闪映射,得到了捕食者灭绝周期解的存在性和它的精确表达式.使用比较原理,得到了捕食者灭绝周期解全局渐近稳定的充分条件和系统的持久性.最后,用Matlab软件进行数值仿真验证了获得的结果.     

A new coupled map car-following model considering drivers’ steady desired speed

Based on the pioneering work of Konishi et al., in consideration of the influence of drivers＇ steady desired speed ef/ect on the traffic flow, we develop a new coupled map car-following model in the real world. By use of the control theory, the stability condition of our model is derived. The validity of the present theoretical scheme is verified via numerical simulation, confirming the correctness of our theoretical analysis.     

Graphs obtained from Moufang loops and regular maps

Using ideas from regular maps, we prove the existence of infinitely many non‐vertex‐transitive Cayley graphs obtained from Moufang loops. Copyright © 2011 Wiley Periodicals, Inc. J Graph Theory