Easier access to X-ray microtomography (lCT) facilities has provided much new insight from high-resolution imaging for various problems in porous media research. Pore space analysis with respect to functional properties usually requires segmentation of the intensity data into different classes. Image segmentation is a nontrivial problem that may have a profound impact on all subsequent image analyses. This review deals with two issues that are neglected in most of the recent studies on image segmentation: (i) focus on multiclass segmentation and (ii) detailed descriptions as to why a specific method may fail together with strategies for preventing the failure by applying suitable image enhancement prior to segmentation. In this way, the presented algorithms become very robust and are less prone to operator bias. Three different test images are examined: a synthetic image with ground-truth information, a synchrotron image of precision beads with three different fluids residing in the pore space, and a lCT image of a soil sample containing macropores, rocks, organic matter, and the soil matrix. Image blur is identified as the major cause for poor segmentation results. Other impairments of the raw data like noise, ring artifacts, and intensity variation can be removed with current image enhancement methods. Bayesian Markov random field segmentation, watershed segmentation, and converging active contours are well suited for multiclass segmentation, yet with different success to correct for partial volume effects and conserve small image features simultaneously.

Despite their growing popularity, worksite health-promotion programs have generally been characterized as having low participation rates, high attrition rates, and modest outcomes. This investigation identified the predictors of participation, attrition, and outcome of worksite smoking-cessation program. Subjects were regular cigarette smokers recruited from two worksites. Of 66 eligible smokers in the two worksites, 44 (67%) agreed to participate in the program. Fifty-five percent (24 of 44) of these completed the program. Of those completing the program, 29% had quit smoking by posttest and 17% were abstinent at the 6-month follow-up. Results indicated that a different set of variables predicted participation, attrition, and outcome. The significant predictors of smokers who participated were the length of cessation in previous abstinence attempts, the number of years they smoked, and the belief regarding personal vulnerability in contracting a smoking-related disease. Levels of pretest carbon monoxide along with attitudes regarding the adoption of smoking restrictions in the worksite predicted attrition. Posttest cessation was related to nicotine levels of cigarette brand smoked at pretest and pretest beliefs regarding postcessation weight gain. Abstinence at the 6-month follow-up was predicted by the number of co-workers who smoked and pretest concerns related to postcessation weight gain. The results are discussed in terms of future evaluation and intervention efforts.

The purpose of this investigation was to evaluate carefully smoking-related knowledge and beliefs and their relationships to smoking status in a large, heterogeneous sample of smokers and nonsmokers in two settings: (a) a large, biracial southern city and (b) a small midwestern community. Participants were 611 (198 male, 413 female) adult respondents to a random-dialing telephone survey in Fargo, North Dakota (n = 200), and Memphis, Tennessee (n = 411). Each participant was given the Smoking Attitudes Survey, which assesses generalized health beliefs as well as health-related problems associated with smoking. Participants' knowledge of smoking-associated diseases (e.g., lung cancer) and of diseases not associated with smoking (e.g., kidney stones) was assessed. Stepwise regression analysis of composite knowledge scores revealed four independent predictors of the health consequences of smoking: education, race, smoking status, and income. Smokers, compared to nonsmokers, reported less knowledge related to the health consequences of smoking, were more likely to be male, were less concerned with the health consequences of smoking, and were more concerned about the health consequences of cholesterol. The best predictor of smokers who had never attempted cessation was their greater concern over weight control when compared to smokers with a history of smoking cessation attempts. The results are discussed in terms of smoking prevention and intervention efforts.

SummarySynchrotron-based x-ray computed microtomography contributes high-resolution, three-dimensional observations to investigations of multiphase fluid transport in porous media. Pore-scale observations are valuable to the development and validation of new theory, as well as numerical models. Computed microtomography has been used previously to measure fluid content and interfacial areas in systems containing two fluids (air-water, oil-water) and to a limited extent to measure fluid content and entrapped fluid morphology in systems containing three fluids (air-oil-water). This study addresses challenges that arise when imaging three-phase flow in spreading systems. The first challenge is related to wettability alteration. Observations reported herein suggest that the wettability of solid surfaces changed over the course of a three-fluid phase flow experiment, a phenomenon that has not been observed in similar, previously conducted two-fluid phase experiments. Follow-up experiments showed that wettability alteration is significant when oil-solid contact is combined with x-ray exposure, and is not reversed with a conventional cleaning procedure. The second challenge arises in segmenting three-phase images, and thereby obtaining data from which various measures can be quantified with sufficient accuracy. Partial volume effects and blur often cause the grey-scale values of different fluids to overlap and appropriate steps must be taken to avoid ambiguity at phase boundaries. A comparison of images collected at standard resolution (10.6 microns voxel -1 ) to those collected at a higher resolution (5.3 microns voxel -1 ) showed that saturation measurements are within 5% of each other, but interfacial areas for three-phase systems may be underestimated at standard resolution by as much as 25%.

Beaches often receive fecal contamination from more than one source. Human sources include untreated sewage as well as treated wastewater effluent, and animal sources include wildlife such as gulls. Different contamination sources are expected to pose different health risks to swimmers. Genetic microbial source tracking (MST) markers can be used to detect bacteria that are associated with different animal sources, but the health risks associated with a mixture of MST markers are unknown. This study presents a method for predicting these health risks, using human- and gull-associated markers as an example. Quantitative Microbial Risk Assessment (QMRA) is conducted with MST markers as indicators. We find that risks associated with exposure to a specific concentration of a human-associated MST marker (HF) are greater if the HF source is untreated sewage rather than treated wastewater effluent. We also provide a risk-based threshold of HF from untreated sewage at a beach, to stay below a predicted illness risk of 3 per 100 swimmers, that is a function of gull-associated MST marker (CAT) concentration.

A sensitive and specific marker of gull fecal contamination, Catellicoccus (CAT), has been used to conduct microbial source tracking in surface waters throughout the world, yet there are no guidelines for interpreting measured concentrations. Here, we use quantitative microbial risk assessment to evaluate CAT concentrations within a risk-based framework and develop a threshold at which the U.S. Environmental Protection Agency illness benchmark (∼3 illnesses/100 swimmers) is exceeded. We modeled illness risk from exposure to different concentrations of CAT in bathing waters using a Monte Carlo approach that considered densities of CAT and infectious zoonotic pathogens Salmonella and Campylobacter in gull feces, volume of water ingested during bathing, and dose–response relationships. We measured CAT densities in 37 fresh gull fecal droppings from six California beaches. Log10 densities ranged from 4.6 to 9.8 log10 copies CAT/g of wet feces. When the level of CAT exceeds 4 × 106 copies/100 mL of water, the median predicted illness exceeds 3 illnesses/100 swimmers.

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Recirculating seawater is an important component of submarine groundwater discharge, yet its role in transporting microbial contaminants from beach sand to coastal water is unknown. This study investigated the extent to which recirculating seawater carries fecal indicators, Enterococcus and bird-associated Catellicoccus, through the beach subsurface. Laboratory experiments and numerical modeling were performed to characterize the transport of fecal indicators suspended in seawater through medium-grained beach sand under transient and saturated flow conditions. Enterococcus was measured both by culture (cENT) and DNA assay (tENT), and Catellicoccus (CAT) by DNA assay. There were differences between transport of tENT and CAT compared to cENT through laboratory columns containing beach sands. Under transient flow conditions, first-order attachment rate coefficients (k) of DNA markers were greater (∼10 h) than k of cENT (∼1 h), although under saturated conditions k values were similar (∼1 h). First-order detachment rate coefficients, k, of DNA markers were greater (∼1 h) than k of cENT (∼0.1h) under both types of flow conditions. Incorporating the rate coefficients into field-scale subsurface transport simulations showed that, in this sand type, the contribution of recirculating seawater to surf zone contamination is likely to be minimal unless bird feces are deposited close to the land-sea interface.