Solving the Neoclassical Growth Model with Quasi-Geometric Discounting: A Grid-Based Euler-Equation Method

The standard neoclassical growth model with quasi-geometric discounting is shown elsewhere (Krusell, P. and Smith, A., CEPR Discussion Paper No. 2651, 2000) to have multiple solutions. As a result, value-iterative methods fail to converge. The set of equilibria is however reduced if we restrict our attention to the interior (satisfying the Euler equation) solution. We study the performance of a grid-based Euler-equation methods in the given context. We find that such a method converges to an interior solution in a wide range of parameter values, not only in the “test” model with the closed-form solution but also in more general settings, including those with uncertainty. JEL Classification: C73, D90, E21     

Study of new flow field geometries to enhance water redistribution and pressure head losses reduction within PEM fuel cell

Efficiency of fuel cell is dependent on reactant distribution, products evacuation, pressure losses and many of these factors is dependent on the design of flow field plate. With an effective design, reactant distribution, pressure drop, and water and heat management can be further improved. In this work, two new designs, as multi-serpentine set-up with additional slots and hybrid geometry, on stainless steel bipolar plates, are presented. Electrical performance, and pressure head losses are analyzed by electrochemical methods such as polarization curve and use of electrochemical noise as a diagnostic tool to further understand the impact of water management on performance. On the one hand, multi-serpentine design shows the best electrical performance with an increase of 0.2 V (66%) at 0.9 A/cm² in comparison of traditional serpentine design. On the other hand, hybrid design reveals the lowest pressure head losses, with a decrease of 2 mbar (about 50%) in comparison of traditional serpentine design, and a higher stability with time that can be useful to downsize compressor and provide lower impact on fuel cell stack durability.     

Heterogeneous Catalytic Polymerization of Ethylene in Microtubular Reactor Systems

The feasibility of using a microtubular reactor for heterogeneous polymerization of ethylene was investigated experimentally. Chemically inert polymer tubing of 800–2300 μm in inner diameter was fabricated and used as a polymerization reactor. Nonporous silica nanoparticles with a diameter of 400 nm were synthesized and used as support for the high‐activity rac‐ethylene(indenyl)₂ZrCl₂ catalyst with methylaluminoxane as cocatalyst and toluene as diluent. Large‐diameter microtubular reactors were also successfully used to conduct heterogeneous polymerization of ethylene in continuous reaction operations. High initial catalyst activity was obtained and the overall polymerization activity per volume or reactor length was quite high. No particle fragmentation occurred and the polymer particles were covered with small subgrains or nanofibrils with a diameter of 30 nm.     

Stochastic geometry of network of randomly distributed moving vehicles on a highway

Vehicular ad hoc networks (VANETs) have become an extensively studied topic in contemporary research. One of the fundamental problems that has arisen in such research is understanding the network statistical properties, such as the cluster number distribution and the cluster size distribution. In this paper, we analyze these characteristics in the case in which vehicles are located on a straight road. Assuming the Rayleigh fading model and a probabilistic model of intervehicle distance, we derive probabilistic distributions of the aforementioned connectivity characteristics, as well as distributions of the biggest cluster and the number of disconnected vehicles. All of the results are confirmed by simulations carried out for the realistic values of parameters.     

Finite Element Simulation of Thermal Residual Stresses in Joining Ceramics with Thin Metal Interlayers

Finite element analysis was used to estimate thermal residual stresses developed in silicon nitride bodies bonded by metallic interlayers. Stresses were calculated for various characteristic metals, namely, Ni, Al, and Si, assuming elastic and elastic-plastic behavior. The relative importance of the metal properties, such as thermal expansion coefficient, stiffness and ductility, has been evaluated. Two different joint geometries, butt and lap, have been used in stress calculations, and special care was taken in the mesh generation, to obtain comparable results. The yield stress of the interlayer material rather than thermal expansion mismatch is the critical factor in thermal residual tensile stress buildup inside ceramic adherents.     

Bacterial Kinetics of Sulfur Oxidizing Bacteria and Their Biodeterioration Rates of Concrete Sewer Pipe Samples

The importance of bacteria in catalyzing microbially induced concrete corrosion was evaluated. Experiments were conducted to determine the optimum pH and growth kinetics of four selected bacterial strains (Thiobacillus neapolitanus C2, Thiobacillus thioparus H1, Acidithiobacillus thiooxidans, and Acidiphilium cryptum LHET2). Combinations of these strains were inoculated into flasks containing ～ 42?g concrete blocks half-submerged in 600 mL of synthetic wastewater with hydrogen sulfide in the headspace air. Controls not inoculated with bacteria lost 0–3 mg/g concrete over 227 days; in the aqueous phase the minimum pH was 6–6.7 and 19–23 mg of calcium/g concrete was released. Systems inoculated with two species of neutrophilic sulfur oxidizing microorganisms (SOM) lost 8 mg/g concrete; in the aqueous phase the minimum pH was 4.5 and 25 mg of calcium/g concrete was released. The concrete samples incubated with neutrophilic and acidophilic SOM and an acidophilic heterotroph experienced the greatest deterioration, with a total mass loss of 13 mg/g concrete, minimum aqueous pH of 3.0, 28 mg calcium/g concrete released, and 47 mg sulfate/g concrete produced.     

Power efficient scheduling over fading channel for cross‐layer optimization

We consider the minimization of long‐term average power consumption for packet transmission between a mobile station and the base station over Nakagami‐m fading channel. Power consumption is minimized by intelligent transmission scheduling design, with the average queuing delay and joint packet loss across MAC and physical layers being confined below certain levels. The problem is formulated as an infinite horizon constrained Markov decision problem and solved by linear programming (LP) method. The primary intention of this paper is to provide a visible paradigm on using LP method to optimize the performance of mobile wireless communication systems. We elaborate the detailed mathematical solution with consistent simulation experiments and emphasize the effectiveness of adaptive transmission scheduling for cross‐layer QoS provisioning. Copyright © 2010 John Wiley & Sons, Ltd.