Improving photoelectron counting and particle identification in scintillation detectors with Bayesian techniques

Many current and future dark matter and neutrino detectors are designed to measure scintillation light with a large array of photomultiplier tubes (PMTs). The energy resolution and particle identification capabilities of these detectors depend in part on the ability to accurately identify individual photoelectrons in PMT waveforms despite large variability in pulse amplitudes and pulse pileup. We describe a Bayesian technique that can identify the times of individual photoelectrons in a sampled PMT waveform without deconvolution, even when pileup is present. To demonstrate the technique, we apply it to the general problem of particle identification in single-phase liquid argon dark matter detectors. Using the output of the Bayesian photoelectron counting algorithm described in this paper, we construct several test statistics for rejection of backgrounds for dark matter searches in argon. Compared to simpler methods based on either observed charge or peak finding, the photoelectron counting technique improves both energy resolution and particle identification of low energy events in calibration data from the DEAP-1 detector and simulation of the larger MiniCLEAN dark matter detector.     

贝叶斯判别分析在中长期径流预报中的应用研究

基于贝叶斯判别分析原理,考虑径流形成的特点及物理成因,选择研究区碧流河水库1959~2011年的实测资料,且将径流分为5个级别,用相关系数模型,考虑因子的不确定性,筛选出相关性高、彼此间独立性强的10个判别因子,分别构建基于朴素贝叶斯分类器(N-Bayes)和贝叶斯判别准则(DBayes)的年径流属性级别预报模型,并利用研究区2001~2011年资料进行了试报和检验。预报结果表明:两种模型的预报结果相近,准确率均超过70%,D-Bayes的预报效果略优于N-Bayes,初步说明:贝叶斯判别分析原理在水文预报中的应用,有着较好的前景。     

基于分形先验信息的非线性反演

基于分形先验信息的非线性反演方法能综合利用测井数据和地震信息,在贝叶斯框架下,通过分形高斯噪音算法得到基于分形理论的先验信息,然后根据地震资料构建似然函数,最终利用基于快速模拟退火算法(Very Fast Simulated Annealing,VFSA)改进的粒子群优化(Particle Swarm Optimization,PSO)算法(VFSA-PSO)实现后验概率密度的抽样。与确定性反演结果相比,该方法能够有效地融合测井资料中的高频信息,提高反演结果的分辨率,并且目标函数的建立融合了确定性反演中的低频约束,从而得到宽频带的反演结果。数值模拟试验表明:基于分形先验的非线性反演结果与理论模型吻合较好,实际资料的应用效果也证明了该反演方法的有效性。     

城镇绿地树种识别的数学描述符

讨论了城镇绿地树种识别数学描述符的设计思想和方法。本着具有确切的物理意义、几何意义或植物生态 学意义以及分割阈值具有环境不变性的原则,设计了归一化阴影指数、饱和度明度相对差、相对边缘点数、相对暗 细节密度、相对骨架密度和加权平均冠径等14个分别涉及波谱、纹理和形状特征的新描述符。经过样本统计分析和 遥感图像实例测试,证明这些描述符在城镇绿地树种识别方面比经典描述符具有更好的针对性和更强的适应性。此 外,本文还讨论并测试了红色欠饱和像元补偿集的提取方法,以及基于cell分割或分类的方法。对于城镇绿地树种 分类问题,在决策树分类输入矢量中,使用本文的描述符组合误分率为5.8%,相比传统的分色亮度组合(误分率为 25.9%)有明显改进。     

Load or concentration,logged or unlogged? Addressing ten years of uncertainty in neural network suspended sediment prediction

This paper addresses current inconsistencies in methodological approaches for neural network modelling of suspended sediment. An expansion in the number of case studies being published over the last decade has yet to result in agreed guidelines on whether suspended sediment load or concentration should be modelled, and whether log‐transformation of data is either necessary or potentially beneficial. This contrasts with the well‐recognized guidelines that direct traditional sediment rating curve studies. The paper reports a comprehensive set of single‐input single‐output neural network suspended sediment modelling experiments performed on two catchments in Puerto Rico. It examines the impact of internal complexity, input variable choice and data transformation on the form, consistency and physical rationality of model outputs, the existence of localized overfitting and the usefulness of global performance metrics. Sound guidance on whether to model sediment load or concentration, and whether to model log‐transformed data is provided. Copyright © 2011 John Wiley & Sons, Ltd.     

闽北强对流天气的短时监测及判别方法研究

利用2005-2009年的闽北冰雹、大风、短时强降水过程所对应的闪电资料产品,分析了闪电资料在各类不同性质的天气过程中的表现特点;用2008年10月至2010年4月的大气电场资料对不同类型天气的表现特点进行了分析,得出一些有益的结论。这些分析可加强业务人员对闪电资料产品和大气电场资料的认识,对今后闪电资料和大气电场资料在预报业务中的应用具有一定参考意义。研究发现利用闪电定位资料和大气电场资料对闽北强对流天气进行短时监测和判别预报具有定性明确、客观化程度较高等优点,在业务实践中有较高的应用价值。     

应用卫星、雷达资料的强对流天气预报预警系统

利用2005—2008年3—9月亮温（TBB）资料,采用逐步判别分析法建立强对流天气预报方程,判别监测区域内某一云团未来可能产生区域性强对流天气、局地性强对流天气、无强对流天气;同时采用指标叠加法判定某云团有无强对流天气。在统计福建省多年冰雹、雷雨大风的雷达回波参数的基础上,确定大冰雹、冰雹、雷雨大风强对流天气的雷达参数（强度、风暴顶高度、垂直液态水含量、回波顶高等）阈值,并根据当天的0℃、-20℃高度与风暴顶的高度差,将CINRAD雷达产品中输出的风暴逐个进行筛选,对系统判定可能出现大冰雹、冰雹、雷雨大风的强风暴输出其未来1h内将影响区域信息。     

同生还是后生?——热液矿床成因研究中争论的焦点问题

秦岭地区钠长角砾岩型矿床、广西大厂锡多金属矿床、广东长坑金银矿床和广东大沟谷金矿床的成因长期存在着同生还是后生的争议.研究表明,这些矿床中的钠长石岩、硅质岩、重晶石岩、电气石岩不是热水沉积成因,而是后期流体结晶和热液交代形成,矿床不存在热水喷流同生沉积成矿作用.矿床成因研究应从多个方面综合考虑,野外宏观地质特征是基础,...     

Estimating Synaphobranchus kaupii densities: Contribution of fish behaviour to differences between bait experiments and visual strip transects

Kaup's arrowtooth eel Synaphobranchus kaupii is a small-bodied fish and an abundant inhabitant of the European continental slope. To estimate its local density video information using the remotely operated vehicle (ROV) Victor 6000 were collected at three locations in the Bay of Biscay slope. Two methods for estimating local densities were tested: strip transect counts and bait experiments. For bait experiments three behaviour types were observed in about equal proportions for individuals arriving near the seafloor: moving up the current towards the ROV, moving across the current and drifting with the current. Visible attraction towards the bait was the highest for individuals swimming against the current (80%) and about equally low for the other two types (around 30%); it did not depend on current speed nor temperature. Three main innovations were introduced for estimating population densities from bait experiments: (i) inclusion of an additional behaviour category—that of passively drifting individuals, (ii) inclusion of reaction behaviour for actively swimming individuals and (iii) a hierarchical Bayesian estimation framework. The results indicated that about half of individuals were foraging actively of which less than one third reacted on encountering the bait plume and the other half were drifting with the current. Taking account of drifting individuals and the reaction probability made density estimates from bait experiments and strip transects more similar.     

Latitudinal and altitudinal patterns of the endemic cacti from the Atacama desert to Mediterranean Chile

In this study we describe the biogeographic patterns of the endemic cacti from the Atacama Desert to the Mediterranean area of Chile. Our goals were: (1) to identify areas of high endemism, (2) to test Rapoport’s rule, (3) to test the geometric constraints hypothesis, (4) to explore temperature and precipitation as explanatory variables of species richness. We used a list of 72 species of cacti, ranging from 18° to 36° S and from 0 to 4500 m.a.s.l. A Bayesian analysis of Endemicity (BAE) was used to evaluate hierarchical relationships of endemism between different latitudinal bands. Rapoport’s rule was evaluated by examining the relationships between latitudinal/altitudinal mid-point, latitudinal/altitudinal range extent and species richness. The geometric constraints hypothesis was tested by examining the existence of mid-domain effect. The BAE indicated two areas of endemism: (1) the northern area between 18° S and 26° S, and (2) the southern area between 27° S and 36° S. The shape of the latitudinal gradient is non-linear, supporting the geometric constraints hypothesis. Altitudinal patterns, however, support Rapoport’s rule; a peak of endemism was found at low altitudes. The explanatory variables were elevation, minimum temperature of the coldest month, mean temperature of wettest quarter and annual precipitation.