Lattice points in stretched model domains of finite type in Rd\mathbb{R}^d

We study an optimal stretching problem for certain convex domain in $\mathbb{R}^d$ ($d\geq 3$) whose boundary has points of vanishing Gaussian curvature. We prove that the optimal domain which contains the most positive (or least nonnegative) lattice points is asymptotically balanced. This type of problem has its origin in the "eigenvalue optimization among rectangles" problem in spectral geometry. Our proof relies on two-term bounds for lattice counting for general convex domains in $\mathbb{R}^d$ and an explicit estimate of the Fourier transform of the characteristic function associated with the specific domain under consideration.Comment: 13 page

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

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,

Photoconductivity of Single-crystalline Selenium Nanotubes

Photoconductivity of single-crystalline selenium nanotubes (SCSNT) under a range of illumination intensities of a 633nm laser is carried out with a novel two terminal device arrangement at room temperature. It's found that SCSNT forms Schottky barriers with the W and Au contacts, and the barrier height is a function of the light intensities. In low illumination regime below 1.46x10E-4 muWmum-2, the Au-Se-W hybrid structure exhibits sharp switch on/off behavior, and the turn-on voltages decrease with increasing illuminating intensities. In the high illumination regime above 7x10E-4 muWmum-2, the device exhibits ohmic conductance with a photoconductivity as high as 0.59Ohmcm-1, significantly higher that reported values for carbon and GaN nanotubes. This finding suggests that SCSNT is potentially a good photo-sensor material as well we a very effective solar cell material.Comment: 12pages including 5 figures, submitted to Nanotechnolog