ATD: Stochastic algorithms for countering chemical and biological threats

拟议工作的设想是利用涉及生物/化学攻击的具体领域的经验，并制定尽可能广泛的算法，以应对此类威胁。这些将以随机建模为基础，以描述污染位置和扩散的（确定性和随机性）特征，并据此开发检测威胁的算法。将检查标准参数模型的适用性，沿着开发适合具体情况的适当时空随机场。这与目前使用高斯场来模拟污染监管研究中的趋势和波动的方法类似，只需要很少的具体假设，但允许应用一般方法，如中心极限和极值理论。研究的出发点是PI在协助EPA科学家和工程师开发统计设计方面的经验，以确保在面临预算限制的情况下对建筑物中的炭疽完全去污的信心，这是基于非常简单的假设，例如炭疽沉积物位置的统计独立性。 更好的和更具成本效益的统计结论可能会导致从拟议的模型-放松独立性假设。 受污染建筑物的清除通常通过二氧化氯熏蒸来实现，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，气体可以到达污染物可能存在的所有区域。这种清理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个月内估计就需要1.3亿美元，而9/11事件后的早期事件总共需要10亿美元）。此外，尽管人们对熏蒸达到彻底清除的期望很高，但仍对残留炭疽表面进行了系统的取样，以进行确认。鉴于取样和实验室分析的费用很高，而且要合理地完全覆盖所需的样本数量很多，这不可能是详尽无遗的。因此，（使用简单的统计假设）确定了所需的取样范围，以确保如果所有样品都是阴性的，则有很高的置信度，即整个关注区域完全没有污染物。这似乎是一个合理的办法，可以充分保证成功清除，因为即使有一个样本对炭疽呈阳性反应，整个熏蒸过程也必须重复。目前确定必要取样以达到给定清除置信度的程序是在简单假设下制定的。关于这一主题的未来工作将使用更现实的统计假设的随机建模，预计将导致算法，这是更准确和成本效益。 上述建筑物净化的情况被描述为更复杂的调查的起点，例如检测在HVAC系统中主动引入的污染物的存在，以在整个建筑物中循环-这是一个在文献中已经受到一些先前关注的主题。初步活动的一个相关领域涉及区分炭疽等有毒物质和无害粉末，目前正在与环境保护局研究人员合作开发新的统计方法（例如小波）。此外，这种“国土范例”所涉及的问题在探测战场威胁（如隐藏的简易爆炸装置）时以各种形式出现，伴随着信号探测的问题-这是本赠款项下考虑的主题。最后，预计这些方法将有有用的“非恐怖主义”应用，例如防止流行病的传播和防止带有炭疽的动物产品如肉和兽皮的进口风险。

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.