Application of a three-component competitive adsorption model to evaluate and optimize granular activated carbon systems

A recently developed kinetic model for granular activated carbon (GAC) adsorbers (COMPSORB-GAC) that quantitatively describes the adsorption of trace organic contaminant in the presence of competing natural organic matter (NOM) was applied to evaluate the performance of different GAC system configurations: conventional fixed-bed adsorbers, layered upflow carbon adsorbers (LUCA), and moving-bed adsorbers (with few or many bed sections). COMPSORB-GAC separately tracks the adsorption of three components: a trace compound, a strongly competing NOM fraction that reduces trace compound equilibrium capacity, and a pore-blocking NOM fraction that reduces kinetics. Performance was simulated for various design criteria and with model parameters derived for two natural waters with significantly different NOM concentrations. For the range of simulated conditions and with baseline performance defined by a fixed-bed adsorber, LUCA generally reduced carbon usage rates (CURs) by 15-35%. A 2-section and a 16-section moving-bed reactor reduced baseline CURs by 20-30% and 45-55%, respectively. Projected CURs for the water source with a relatively high NOM concentration were 2-3 times higher for all reactor configurations and indicated that NOM preloading would cause performance deterioration in deep GAC beds, which highlights the importance of source water quality. These results show how COMPSORB-GAC can be used in a comprehensive, site-specific optimization of GAC systems to ensure robust system performance and to balance capital and operating costs.     

A Markov chain model for an optical shared-memory packet switch

This paper first presents a Markov chain that exactly models an optical shared-memory packet switch. Without loss in model accuracy, this Markov chain state size is greatly reduced to form a reduced Markov chain (RMC). A simplified construction method is given to make the RMC tractable. Throughput and probability of packet loss derived using the RMC are also presented     

Tool selection for optimal part production: a Lagrangian relaxation approach

This paper extends previous work on implementation problems associated with a flexible system that produces flat sheet-metal parts with interior holes. The paper makes four main contributions. First, we formulate the problem of selecting tooling and design standards to minimize the cost of producing parts as an optimization model. Second, we develop a projected subgradient algorithm for the Lagrangian relaxation of the problem by using the model's special structure to develop relationships between the Lagrangian multipliers. Third, we demonstrate that the algorithm produces close to optimal solutions (duality gap less than 2%) very quickly on a number of problems derived using a substantial data set obtained from a Chicago area firm. Fourth, an important variant of the traditional repair kit problem is shown to be a special case of the tool selection problem.     

Employee response to a company-sponsored program of colorectal and prostate cancer screening

Studies done in the mid-1970s documented increased risk for respiratory cancer and leukemia among employees in a chemical company manufacturing plant where chloromethyl ethers were used in production from 1948 to 1971. In the late 1980s, the company informed current and former employees about the results of follow-up studies which showed a moderation of risk of respiratory cancer and leukemia. New data showing elevated rates of mortality from colorectal, prostate, bladder, and pancreatic cancer in the population were also reported. Via mailed correspondence, the company made a no-cost program of colorectal and prostate cancer screening available to employees upon request; and information about bladder and pancreatic cancer was made available. Thirteen percent of employees in the population indicated interest in colorectal and prostate cancer screening (response). Thirty-one percent of these responders were screened (adherence). Multivariate analyses showed that education and length of employment in the plant were positively associated with response. Being white was positively associated with response for younger workers; while among older workers being male was positively associated with response. In terms of adherence, we found that older, more highly educated workers were more likely to have a screening examination. Findings indicate that employee participation in workplace-sponsored colorectal and prostate cancer screening can vary according to worker sociodemographic factors and length of employment in areas of potential exposure.