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991.
Haolan Lu Cavan S. Reilly Sudipto Banerjee Bradley P. Carlin 《Environmental and Ecological Statistics》2007,14(4):433-452
Recently, public health professionals and other geostatistical researchers have shown increasing interest in boundary analysis, the detection or testing of zones or boundaries that reveal sharp changes in the values of spatially oriented variables.
For areal data (i.e., data which consist only of sums or averages over geopolitical regions), Lu and Carlin (Geogr Anal 37: 265–285,
2005) suggested a fully model-based framework for areal wombling using Bayesian hierarchical models with posterior summaries
computed using Markov chain Monte Carlo (MCMC) methods, and showed the approach to have advantages over existing non-stochastic
alternatives. In this paper, we develop Bayesian areal boundary analysis methods that estimate the spatial neighborhood structure
using the value of the process in each region and other variables that indicate how similar two regions are. Boundaries may then be determined by the posterior distribution
of either this estimated neighborhood structure or the regional mean response differences themselves. Our methods do require
several assumptions (including an appropriate prior distribution, a normal spatial random effect distribution, and a Bernoulli
distribution for a set of spatial weights), but also deliver more in terms of full posterior inference for the boundary segments
(e.g., direct probability statements regarding the probability that a particular border segment is part of the boundary).
We illustrate three different remedies for the computing difficulties encountered in implementing our method. We use simulation
to compare among existing purely algorithmic approaches, the Lu and Carlin (2005) method, and our new adjacency modeling methods.
We also illustrate more practical modeling issues (e.g., covariate selection) in the context of a breast cancer late detection
data set collected at the county level in the state of Minnesota. 相似文献
992.
Risk-Based Viable Population Monitoring 总被引:3,自引:0,他引:3
Abstract: We describe risk-based viable population monitoring, in which the monitoring indicator is a yearly prediction of the probability that, within a given timeframe, the population abundance will decline below a prespecified level. Common abundance-based monitoring strategies usually have low power to detect declines in threatened and endangered species and are largely reactive to declines. Comparisons of the population's estimated risk of decline over time will help determine status in a more defensible manner than current monitoring methods. Monitoring risk is a more proactive approach; critical changes in the population's status are more likely to be demonstrated before a devastating decline than with abundance-based monitoring methods. In this framework, recovery is defined not as a single evaluation of long-term viability but as maintaining low risk of decline for the next several generations. Effects of errors in risk prediction techniques are mitigated through shorter prediction intervals, setting threshold abundances near current abundance, and explicitly incorporating uncertainty in risk estimates. Viable population monitoring also intrinsically adjusts monitoring effort relative to the population's true status and exhibits considerable robustness to model misspecification. We present simulations showing that risk predictions made with a simple exponential growth model can be effective monitoring indicators for population dynamics ranging from random walk to density dependence with stable, decreasing, or increasing equilibrium. In analyses of time-series data for five species, risk-based monitoring warned of future declines and demonstrated secure status more effectively than statistical tests for trend. 相似文献
993.
阐述炼油厂污水处理场污泥的组成、性质及污泥脱水的实际情况,在原工艺处理流程的基础上采取增加污泥储存罐、污泥调理系统、污泥输送系统等设施,并进行一系列的技术改造,使得污泥脱水系统能够正常平稳运行,减少污泥对环境的污染.取得了一定的经济效益和社会效益。 相似文献
994.
995.
流动注射催化光度分析法的研究进展 总被引:3,自引:0,他引:3
综述了近年来流动注射催化光度分析法的研究进展,包括环境水样中金属离子、阴离子、有机物等污染物的测定,展望了流动注射催化光度分析法未来的研究方向和发展前景。 相似文献
996.
强化A2/O工艺反硝化除磷性能的运行控制策略 总被引:10,自引:2,他引:10
以啤酒废水为研究对象,重点考察了如何强化A2/O工艺反硝化除磷性能,从而提高营养物去除效果、并实现节能的目的.试验中建立了3种运行控制策略:(1)根据缺氧区末端出水硝酸盐的浓度控制内循环回流量;(2)调节厌氧/缺氧/好氧区体积比以减少厌氧区出水剩余COD对缺氧磷吸收的影响;(3)向缺氧区引入旁流并调节旁流比.试验结果表明,当缺氧区末端出水硝酸盐浓度控制在1~3 mg·L-1时,不仅可强化反硝化除磷效果,而且可以节省内循环所需能耗;厌氧/缺氧/好氧区最佳体积比为1/1/2;旁流的引入可以提高低C/N比条件下TN的去除,最优旁流比为0.32. 相似文献
997.
998.
文章应用的 Preismann 隐式差分格式,具有计算精度高,稳定性条件限制少,可为后续的河网水质模型提供完整的水力参数等特点。用这一隐式差分格式对圣维南方程组进行数值离散,采用双扫除法(追赶法)可推导出不同边界条件下的各种追赶方程。模型的计算结果与实测值的拟合程度较高。最后,通过计算结果分析了浦东开发区河网流场的基本特点,指出了该地区水环境容量较小的水动力学方面的原因,提出了改善水环境容量的方法。 相似文献
999.
1000.
Blood flow across the atrioventricular valves and outflow tracts was measured in 55 normal fetuses and 32 fetuses with haemoglobin (Hb) Bart's disease between 18 and 26 weeks of gestation. The mean velocities remained unchanged in both normal and affected fetuses over the gestations studied. The volume flow across both atrioventricular valves and outflow tracts increased as the gestation advanced in both normal and affected fetuses, but was significantly higher in affected than in normal fetuses. The same magnitude of increased flow was found in both hydropic and non-hydropic fetuses with Hb Bart's disease. These findings suggest that fetuses with severe and long-standing anaemia have a remarkable cardiac compensatory mechanism for the maintenance of tissue oxygenation. In response to anaemia and circulatory loading, the cardiac chambers and outflow tracts enlarge proportionately up to twice the normal values. Because of this response and the operation of the Frank-Starling mechanism, the heart is able to maintain a normal mean velocity of propulsion and the net output is increased to two to three times that in normal fetuses. Hydropic changes in these anaemic fetuses appear unrelated to cardiac failure as cardiac failure is not observed at the time that hydropic changes develop. 相似文献