Supporting Agencies
Publication Abstracts
Romero-Gomez, P., C. K. Ho, and C. Y. Choi. 2008. Mixing at Cross Junctions in Water Distribution Systems – Part I. A Numerical Study. ASCE Journal of Water Resources Planning and Management134(3):284-294.
Abstract: The present study investigates solute mixing phenomena at various flow rates within a cross junction, which is commonly found in municipal drinking water distribution systems. Simulations using computational fluid dynamics are employed to model the solute concentrations leaving the junction when one inlet is comprised of clean water while the other inlet carries a solute at R>10,000. For a few exemplary cases, the resulting velocity vectors and contours of dimensionless concentration are presented to explain the detailed mixing mechanisms at the impinging interface. The turbulent Schmidt number (Sct), an important scaling parameter, is also evaluated. Experimental results were used to assess values of Sct for various flow conditions that accurately captured the detailed mixing processes within the junction. The present study clearly indicates that mixing at pipe cross junctions is far from “perfect.” Incomplete mixing results from bifurcating inlet flows that reflect off one another with minimal contact time. Improving the existing water quality model based on accurate mixing data and simulations is important not only to predict concentrations of chemical species such as chlorine in water distribution systems, but also to prepare for potential intentional and accidental contamination events.
Austin, R. G., B. van Bloemen Waanders, S. McKenna and C. Y. Choi. 2008. Mixing at Cross Junctions in Water Distribution Systems – Part II. An Experimental Study. ASCE Journal of Water Resources Planning and Management 134(3):295-302.
Abstract: The present experimental study focuses on the characterization of complex mixing phenomena at pipe intersections within pressurized water distribution networks. To examine the complete mixing assumption at a cross junction, a series of experiments were conducted in the turbulent regime (R>10,000). The experimental setup consists of a cross junction with various sensors, pumps, and a data acquisition system to accurately measure solute concentration. Selected experimental results are compared to computational fluid dynamics (CFD) results. In addition, the water quality model associated with a standard water distribution network simulator (EPANET) was reevaluated based on CFD and experimental data. Corrections based on experimental results are incorporated into EPANET (AZRED 1.0) for use in a case study. The study concludes that the complete mixing assumption can potentially create considerable errors in water quality modeling. Further, severe errors are likely to occur in systems with many cross type junctions due to bifurcation of the incoming flows.
Masago, Y., T. Shibata, and J. B. Rose. 2008. Bacteriophage P22 and Staphylococcus aureus Attenuation on Nonporous Fomites as Determined by Plate Assay and Quantitative PCR. Applied and Environmental Microbiology 74(18):5838-5840.
Abstract: Decay rates of bacteriophage P22 and Staphylococcus aureus on six types of common household inanimate surfaces were evaluated based on cultivation and quantitative PCR. A much higher level of inactivation was observed using the plate assay, suggesting that detection of the pathogen genome in samples from fomites does not necessarily imply a health risk to humans.
Bartrand, T. A., M. H. Weir, and C. N. Haas. 2008. Dose-Response Models for Inhalation of Bacillus anthracis Spores: Interspecies Comparisions. Risk Analysis 28(4):1115-1124.
Abstract: Because experiments with Bacillus anthracis are costly and dangerous, the scientific, public health, and engineering communities are served by thorough collation and analysis of experiments reported in the open literature. This study identifies available dose-response data from the open literature for inhalation exposure to B. anthracis and, via dose-response modeling, characterizes the response of nonhuman animal models to challenges. Two studies involving four data sets amenable to dose-response modeling were found in the literature: two data sets of response of guinea pigs to intranasal dosing with the Vollum and ATCC-6605 strains, one set of responses of rhesus monkeys to aerosol exposure to the Vollum strain, and one data set of guinea pig response to aerosol exposure to the Vollum strain. None of the data sets exhibited overdispersion and all but one were best fit by an exponential dose-response model. The beta-Poisson dose-response model provided the best fit to the remaining data set. As indicated in prior studies, the response to aerosol challenges is a strong function of aerosol diameter. For guinea pigs, the LD50 increases with aerosol size for aerosols at and above 4.5 μm. For both rhesus monkeys and guinea pigs there is about a 15-fold increase in LD50 when aerosol size is increased from 1 μm to 12 μm. Future experimental research and dose-response modeling should be performed to quantify differences in responses of subpopulations to B. anthracis and to generate data allowing development of interspecies correction factors.
Tamrakar, S.B. and C. N. Haas. 2008. Dose-Response Model for Lassa Virus. Human and Ecological Risk Assessment 14(4): 742-752.
Abstract: This article develops dose-response models for Lassa fever virus using data sets found in the open literature. Dose-response data were drawn from two studies in which guinea pigs were given subcutaneous and aerosol exposure to Lassa virus. In one study, six groups of inbred guinea pigs were inoculated subcutaneously with doses of Lassa virus and five groups of out-bred guinea pigs were similarly treated. We found that the out-bred subcutaneously exposed guinea pig did not exhibit a dose-dependent trend in response. The inbred guinea pigs data were best fit by an exponential dose-response model. In a second study, four groups of out-bred guinea pigs were exposed to doses of Lassa virus via the aerosol route. In that study, aerosol diameter was less than 4.5 μ m and both mortality and morbidity were used as endpoints. The log-probit dose-response model provided a somewhat better fit than the Beta-Poisson model for data with mortality as the endpoint, but the Beta-Poisson is considered the best fit model because it can be derived using biological considerations. Morbidity data were best fit with an exponential dose-response model.
Tamrakar, S.B. and C. N. Haas. 2008. Dose-Response Model for Burkholderia pseudomallei (melioidosis). Journal of Applied Microbiology 105(5):1361-1371.
Abstract: The objective of this study was development of a dose-response model for exposure to Burkholderia pseudomallei in different animal hosts and analysis of the results. The data sets with which the model was developed were taken from the open literature. All data sets were initially tested for a trend between dose and outcome using the Cochran-Armitage test. Only data showing a statistically significant trend were subjected to further analysis (fitting with parametric dose-response relationships). Dose-response relationships (exponential, beta-Poisson and log-probit) were fit to data using the method of maximum likelihood estimation. Dose-response analysis of BALB/c mice, C57BL/6 mice, guinea pigs and diabetic rats showed that BALB/c mice exposed intranasally (i.n.) and guinea pigs exposed intraperitoneally (i.p.) are significantly more sensitive to B. pseudomallei than C57BL/6 mice exposed i.n. and diabetic rats exposed i.p. The results confirmed the findings of a study of outbreak data that the diabetic population is more susceptible to infection with B. pseudomallei than the general population. The low dose prediction from best fit dose-response models can be used to draw guidelines for public health decision making processes, including consideration of sensitive subpopulations.
Casman, E. A. and B. Fischhoff. 2008. Risk Communication Planning for the Aftermath of a Plague Bioattack. Risk Analysis 28(5): 1327-1342.
Abstract: We create an influence diagram of how a plague bioattack could unfold and then use it to identify factors shaping infection risks in many possible scenarios. The influence diagram and associated explanations provide a compact reference that allows risk communicators to identify key messages for pre-event preparation and testing. It can also be used to answer specific questions in whatever unique situations arise, considering both the conditions of the attack and the properties of the attacked populations. The influence diagram allows a quick, visual check of the factors that must be covered when evaluating audience information needs. The documentation provides content for explaining the resultant advice. We show how these tools can help in preparing for crises and responding to them.
Weber, R. O., S. Gunawardena, and C. MacDonald. 2008. Horizontal Case Representation. In: Advances in Case-Based Reasoning: Proceedings of the European Conference on Case-Based Reasoning. Althoff, K.-D., R. Bergmann, M. Minor, and A. Hanft, eds. pp. 548-561. Springer, Berlin / Heidelberg.
Abstract: We present a new case representation that seeks to make case-based reasoning (CBR) more suited to real world applications. We propose a horizontal representation that is composed of two features, one to represent the problem and one to represent the solution. We also present a similarity metric tailored to our representation. Rather than parametrizing the distance function with weights, it requires one parameter that recommends the cardinality of values for new problems to be solved by the system. Our representation is less restrictive during case acquisition as it does not constrain how non-experts can populate cases and it requires less knowledge engineering effort than the traditional method. We compare our representation to the traditional case representation and show that it is superior when cases are incomplete. Finally, we illustrate the effectiveness of our representation in a real world application, where the demarcation between problem and solution is blurred.
Weber, R. O. and S. Gunawardena. 2008. Designing Multifunctional Knowledge Management Systems. Proceedings of the 41st Annual Hawaii International Conference on System Sciences (HICSS-41):368-377.
Abstract: Expert locators and repository-based knowledge management systems (KMS) are different architectures proposed to perform different kinds of knowledge management functions. While expert locators can recommend an expert to perform a task, repository- based KMS can share a learned strategy to solve a given problem. In this paper, we describe a framework to develop KMS that can perform multifunctional tasks, usually performed by repository-based and expert locators separately, in one single architecture. The proposed framework follows principles from knowledge engineering and from the management literature on how to prevent failure in KMS. We illustrate the proposed framework with an implementation to support a community of science.
Jones, R.M., Y. Masago, T. A. Bartrand, C. N. Haas, M. Nicas, and J. Rose. 2009. Characterizing the Risk of Infection from Mycobacterium tuberculosis in Commercial Passenger Aircraft using Quantitative Microbial Risk Assessment. Risk Analysis (In press).
Abstract: Quantitative microbial risk assessment was used to predict the likelihood and spatial organization of Mycobacterium tuberculosis (Mtb) transmission in a commercial aircraft. Passenger exposure was predicted via a multizone Markov model in four scenarios: seated or moving infectious passengers and with or without filtration of recirculated cabin air. The traditional exponential (k= 1) and a new exponential (k= 0.0218) dose-response function were used to compute infection risk. Emission variability was included by Monte Carlo simulation. Infection risks were higher nearer and aft of the source; steady state airborne concentration levels were not attained. Expected incidence was low to moderate, with the central 95% ranging from 10−6 to 10−1 per 169 passengers in the four scenarios. Emission rates used were low compared to measurements from active TB patients in wards, thus a "superspreader" emitting 44 quanta/h could produce 6.2 cases or more under these scenarios. Use of respiratory protection by the infectious source and/or susceptible passengers reduced infection incidence up to one order of magnitude.