On Two-Pair Two-Way Relay Channel with an Intermittently Available Relay

When multiple users share the same resource for physical layer cooperation such as relay terminals in their vicinities, this shared resource may not be always available for every user, and it is critical for transmitting terminals to know whether other users have access to that common resource in order to better utilize it. Failing to learn this critical piece of information may cause severe issues in the design of such cooperative systems. In this paper, we address this problem by investigating a two-pair two-way relay channel with an intermittently available relay. In the model, each pair of users need to exchange their messages within their own pair via the shared relay. The shared relay, however, is only intermittently available for the users to access. The accessing activities of different pairs of users are governed by independent Bernoulli random processes. Our main contribution is the characterization of the capacity region to within a bounded gap in a symmetric setting, for both delayed and instantaneous state information at transmitters. An interesting observation is that the bottleneck for information flow is the quality of state information (delayed or instantaneous) available at the relay, not those at the end users. To the best of our knowledge, our work is the first result regarding how the shared intermittent relay should cooperate with multiple pairs of users in such a two-way cooperative network.Comment: extended version of ISIT 2015 pape

Use of Impaired Waters in Power Plant Cooling Tower System:Review of Regulations and Feasibility Analysis

In 2000, the freshwater withdrawn for industrial use in the U.S., including mining, industrial process usage, power generation, etc., has reached 45% of the total daily freshwater withdrawal of 346 billion gallons. Among these industries, thermoelectric generation is the largest freshwater user with a withdrawal of 136 BGD. Fierce competition for this valuable resource will force difficult decisions to be made about allocation priorities and water availability for electric power production. Studies have shown that impaired waters can be used as alternative water sources for certain applications, including makeup water in electric power plant cooling systems. Among all possible impaired waters that could potentially be used in power production, secondary treated municipal wastewater is the most common and widespread source. Review of regulations that govern water reuse revealed that there are no federal regulations specifically addressing water reuse and that a number of states have implemented their own regulations. Several states were investigated for specific regulations and/or guidelines related to water reuse in power plant cooling water systems.The geospatial analysis performed in this study was designed to evaluate the feasibility of using treated municipal wastewater for cooling in power industry. By utilizing the geoprocessing tools of a geographic information system (GIS), this study evaluated if the water demand of a particular facility can be satisfied by nearby Publicly Owned Treatment Works (POTWs). Datasets of 110 power plants proposed for development and 11785 POTWs were evaluated as part of this feasibility analysis. Estimated cooling water needs for the proposed power plants were compared with the total wastewater flowrates discharged by nearby POTWs. Data analysis revealed that 81% of the proposed power plants would have sufficient cooling water supply from POTWs within a 10 mile radius, while 97% of the proposed power plants would be able to meet their cooling water needs from POTWs located within 25 miles from these plants. On average, 1.15 POTWs were needed to completely satisfy the cooling water demand for each of these power plants. In other words, one fairly large POTW within a reasonable distance from each power plant could meet most of its cooling water needs.Dataset of 407 existing coal fired power plants was also evaluated using the same process. All of the existing power plants were assumed to be renovated to wet recirculating cooling systems regardless of their original design. Results indicate 49.4% of the existing power plants would have sufficient cooling water supply from POTWs within a 10 miles radius; 75.9% of the existing power plants would have sufficient cooling water supply from POTWs within a 25 miles radius. For those power plants which have sufficient water supply, an average number of 1.46 POTWs are required to satisfy the cooling water demand.The tools developed in this study can be used to evaluate a number of scenarios for alternative cooling water supply needed for energy generation in the future. It is clear that the reclaimed municipal wastewater can and will likely play a more prominent role in this critical industrial sector

USE OF CHLORINE, CHLORAMINE, OR CHLORINE DIOXIDE TO CONTROL BIOLOGICAL GROWTH IN POWER PLANT RECIRCULATING COOLING SYSTEMS USING TREATED MUNICIPAL WASTEWATER

Cooling water deficiency due to limited freshwater sources posed an obstacle of expending current thermoelectric power generation in the U.S. and has led the power industry to seek an alternative water resource to meet its cooling water requirement. Of all the potential alternatives, secondary treated municipal wastewater is prominent because of its vast allocation and abundant quantity. However, the impaired water quality and unique environment make the cooling tower management more challenging. Therefore, prudent water quality management with chemicals is required to prevent corrosion, scaling, and biological growth in the cooling systems. This study focused on the understanding of the kinetic, effectiveness, and dosage requirement of chlorine-based biocides (chlorine, chloramine and chlorine dioxide) in the recirculating cooling systems using treated municipal wastewater as makeup. Laboratory-scale studies and pilot-scale cooling systems were used to evaluate the biological growth under realistic conditions associated with full-scale cooling systems. Results of 30-day field tests indicated that the pilot-scale cooling towers developed in this study are reliable for evaluating different chemical regimes by maintaining steady cooling performance under various operating conditions. Direct use of secondary treated effluent for cooling water is a feasible option when using monochloramine as major biocide. The low oxidizing ability of monochloramine resulted in a high residence time and high penetrating ability, and thus provided better biocidal effectiveness against planktonic and sessile heterotrophic bacteria and Legionella in recirculating cooling systems. A minimum monochloramine residual above 3 mg/L in the recirculating cooling water is needed for proper biological growth control with this impaired water. Biological growth potential is comparable in secondary treated effluent subjected to different tertiary treatment (i.e., nitrification, sand filtration, activated carbon adsorption) regardless of total organic carbon concentration in the wastewater. The performance of monochloramine was optimized when the secondary treated effluent was subjected to nitrification and sand filtration. The key findings of this study indicate that biological growth can be controlled in cooling systems using treated municipal effluents as makeup. The biocide regime demonstrated in this study offers a useful guideline to meet biological growth control criteria in recirculating cooling systems

A variational iteration method for solving Troesch’s problem

AbstractTroesch’s problem is an inherently unstable two-point boundary value problem. A new and efficient algorithm based on the variational iteration method and variable transformation is proposed to solve Troesch’s problem. The underlying idea of the method is to convert the hyperbolic-type nonlinearity in the problem into polynomial-type nonlinearities by variable transformation, and the variational iteration method is then directly used to solve this transformed problem. Only the second-order iterative solution is required to provide a highly accurate analytical solution as compared with those obtained by other analytical and numerical methods