Sequential Design for Computer Experiments with a Flexible Bayesian Additive Model

In computer experiments, a mathematical model implemented on a computer is used to represent complex physical phenomena. These models, known as computer simulators, enable experimental study of a virtual representation of the complex phenomena. Simulators can be thought of as complex functions that take many inputs and provide an output. Often these simulators are themselves expensive to compute, and may be approximated by "surrogate models" such as statistical regression models. In this paper we consider a new kind of surrogate model, a Bayesian ensemble of trees (Chipman et al. 2010), with the specific goal of learning enough about the simulator that a particular feature of the simulator can be estimated. We focus on identifying the simulator's global minimum. Utilizing the Bayesian version of the Expected Improvement criterion (Jones et al. 1998), we show that this ensemble is particularly effective when the simulator is ill-behaved, exhibiting nonstationarity or abrupt changes in the response. A number of illustrations of the approach are given, including a tidal power application.Comment: 21 page

Global existence of weak solution to the heat and moisture transport system in fibrous porous media

This paper is concerned with theoretical analysis of a heat and moisture transfer model arising from textile industries, which is described by a degenerate and strongly coupled parabolic system. We prove the global (in time) existence of weak solution by constructing an approximate solution with some standard smoothing. The proof is based on the physcial nature of gas convection, in which the heat (energy) flux in convection is determined by the mass (vapor) flux in convection.Comment: 19 page

Inter-Temporal Investment in Climate Change Adaptation and Mitigation

Currently, different dimensions of mitigation strategies have been investigated in policy analysis. However, ambitious mitigation action aiming at reducing future climate change will not prevent much climate change before mid-century. Short-term and medium-term temperature as well as associated damages cannot be avoided completely. Increasingly there appears to be recognition of the need to simultaneously implement adaptation and mitigation. However, the optimal combination between adaptation and mitigation that can best address climate change over time is still an open question. Literature base is rather small, yet very diverse and inconsistent in conclusions. In this paper, we do an exploration of the temporal optimal investment mix between adaptation and mitigation and their relative contributions to climate change damage reduction. By proposing a conceptual framework that integrates both strategies and developing a more complete integrated assessment model, the temporal investment allocation between adaptation and mitigation is identified. Results suggest that adaptation is an effective climate change damages reduction strategy and a complement to mitigation. Adaptation investment tackles the short run reduction of damages in the first 250 years while mitigation dominates from thereon.Climate Change Damages, Adaptation, Mitigation, Temporal Investment, Integrated Assessment Model, Environmental Economics and Policy, Resource /Energy Economics and Policy, Risk and Uncertainty, Q54, Q58,

Construction of 3D Biomimetic Tissue Niches for Directing Pancreatic Lineage Differentiation of Human Embryonic Stem Cells

The potential of human embryonic stem cells (hESCs) to differentiate into insulin producing beta cells offers great hope for cell-based therapy for diabetes treatment. However, in vitro pancreatic differentiation of hESCs remains challenging. In the past decade, most protocols for differentiating pancreatic cells have been focused on the use of signaling molecule cocktails on 2D substrates. Studies on embryonic development biology strongly suggest that extracellular matrix (ECM) plays a critical role on hESCs behavior. In this work, we first established a 3D collagen scaffold culture system for hESCs differentiating into definitive endoderm (DE), which is the first and most important step for coaxing hESCs into transplantable beta cells. Collagen scaffold have shown to promote the attachment, proliferation and DE differentiation of hESCs in 3D microenvironment. Furthermore, we optimized the 3D scaffold compositions by integrating various ECM proteins into collagen scaffold. Our data showed that compared to collagen with single ECM protein, collagen combined with fibronectin, laminin, and vitronectin can greatly enhance DE differentiation generating up to 93% SOX17 positive DE population. Finally, we demonstrated that mature insulin-producing cells can be achieved by differentiating hESCs in 3D biomimic scaffold made of collagen and Matrigel, combined with a modified step-wise protocol. More mature insulin-producing cells were generated with our 3D scaffold compared to traditional 2D culture. The 3D differentiated pancreatic endocrine cells were assembled into tissue-like structure and displayed greater similarities in phenotype and gene expression profile to adult human islets. These hESC-induced pancreatic cells comprised 20% insulin positive cells in 3D culture and can response to high glucose and release four-fold insulin as compared to 2D culture. Insulin-secreting granules were also observed, which confirmed the generation of insulin-producing cells in 3D scaffold