ATD: Stochastic algorithms for countering chemical and biological threats

拟议工作的愿景是利用涉及生物/化学攻击的特定领域的经验，并开发尽可能广泛的算法来对付这种威胁。这些将基于随机建模，以描述污染位置和扩散的(确定性和随机性)特征，由此可以开发检测威胁的算法。将检查标准参数模型的适用性，并根据具体情况开发适当的时空随机场。这类似于目前使用高斯场对污染法规研究中的趋势和波动进行建模的方法，需要很少的具体假设，但允许应用中央极限和极值理论等一般方法。起点将是PI在协助环境保护局科学家和工程师制定统计设计方面的先前经验，以确保在面临预算限制的情况下对彻底清除建筑物中的炭疽菌污染的信心，这是基于非常简单的假设，如炭疽菌沉淀物位置的统计独立性。拟议的模型可能会产生更好、更具成本效益的统计结论--放松独立性假设。受污染建筑物的清理通常是通过二氧化氯熏蒸来实现的，这是一个非常有效的过程，因为在适当的压力和应用时间下，气体可以到达可能产生污染物的所有区域。这种清关所需的成本和时间可能相当惊人(例如，仅布伦特伍德邮政设施在26个月期间的估计费用为1.3亿美元，而9/11事件早期事件的总金额为10亿美元)。此外，尽管人们对熏蒸可实现完全清除抱有很高的期望，但仍对表面进行了系统的炭疽残留物采样，以供确认。鉴于抽样和实验室分析的高成本，以及合理完整的复盖范围所需的样本数量，这不可能是详尽的。因此，(使用简单的统计假设)确定所需的抽样范围，以确保如果所有样本都是阴性的，则有非常高的置信度，即整个关注区域完全没有污染。这似乎是为成功清除提供充分保证的合理方法，因为即使一个样本的炭疽测试呈阳性，整个熏蒸也必须重复进行。目前用于确定实现给定净空置信度所需采样的例行程序是在简单的假设下开发的。未来在这个主题上的工作将使用随机建模中更现实的统计假设，这些假设有望导致更准确和更具成本效益的算法。上述建筑物净化案例被描述为更复杂的调查的起点，例如检测在暖通空调系统中积极引入的污染物的存在，以便在建筑物内循环--这一主题在以前的文献中已经得到了一些关注。最初活动的一个相关领域涉及炭疽等有毒物质和无害粉末之间的区别，已经在与环境保护局的研究人员合作开发新的统计方法(例如，小波)。此外，在探测战场威胁(如隐藏的简易爆炸装置)时，这种“国土范例”中涉及的问题以各种形式出现，并伴随着信号探测的问题--这是本拨款项下考虑的主题。最后，预计这些方法将具有有用的“非恐怖主义”应用，如流行病的传播和含有炭疽的动物产品(如肉类和兽皮)的进口风险。

The vision for the proposed work is to capitalize on experience in specific areas involving biological / chemical attacks and to develop as wide-ranging algorithms as possible for countermeasures to such threats. These will be based on stochastic modeling to describe (deterministic and random) features of contamination location and spread from which algorithms to detect threats may be developed. Standard parametric models will be examined for applicability, along with development of appropriate space-time random fields tailored to the specific situation. This is similar in approach to current use of Gaussian fields to model trends and fluctuations in pollution regulation studies, requiring few specific assumptions, but allowing application of general methods such as Central Limit and Extreme Value Theory. The starting point will be the PI's prior experience in assisting EPA scientists and engineers with the development of statistical designs for assuring confidence in complete decontamination of anthrax from buildings in the face of budgetary limitations which was based on very simple assumptions such as statistical independence of positions of anthrax deposits. Better and more cost effective statistical conclusions are likely to result from the proposed models - relaxing the independence assumptions. Clearance of contaminated buildings is typically achieved by Chlorine Dioxide fumigation - a highly effective process since the gas under appropriate pressure and duration of application can be expected to reach all areas where contaminant may be lodged. The cost of and time required for such clearance can be quite staggering (e.g. estimates of $130 million for just the Brentwood postal facility over a 26 month period, and $1 billion in all for the total of the early post 9/11 incidents). Additionally, in spite of a high expectation that fumigation achieves total clearance, systematic sampling of surfaces for residual anthrax is done for confirmation. This cannot be exhaustive in view of the high cost of sampling and laboratory analysis and the sheer number of samples required for reasonably complete coverage. Hence, determinations are made (using simple statistical assumptions) of the extent of sampling required to ensure that if all samples turn out to be negative, there is specified very high confidence that the entire area of concern is entirely contaminant free. This seems a reasonable approach to give adequate added assurance of successful clearance since if even one sample tested positive for anthrax, entire fumigation would have to be repeated. Current routines for determining necessary sampling to achieve a given clearance confidence have been developed under simple assumptions. The future work on this topic will use the more realistic statistical assumptions of stochastic modeling which are expected to lead to algorithms, which are both more accurate and cost efficient. The above case of building decontamination is described as a starting point for much more complex investigations such as detection of the presence of contaminants being actively introduced in an HVAC system for circulation throughout a building - a topic which has received some previous attention in the literature. A related area of initial activity concerns the discrimination between toxic substances such as anthrax and harmless powders for which novel statistical (for example, wavelet) methods are already being developed in collaboration with EPA researchers. Further, the issues involved in such "Homeland examples" arise in various forms in the detection of battlefield threats (such as hidden IED's) with attendant problems of signal detection - subjects for consideration under this grant. Finally, the methods are expected to have useful "non-terrorism" applications such as to the spread of pandemics and risks of importation of anthrax bearing animal products such as meat and hides.