Modeling Rice Plant-Mediated Methane Emission

Late-season methane (CH₄) emissions from flooded ricefields appear to be fueled by root exudation and death and to be transmitted to the atmosphere largely through the plant. We present a general transport-reaction model which accommodates these phenomena, together with a simplified ("cartoon") version intended to reproduce the salient features of most plant-dominated CH₄-emitting systems. Our cartoon model is capable of reproducing measured concentration profiles and fluxes. Sensitivity annalysis suggests that cultivars with high specific root transmissivity may, other things being equal, reduce rather than enhance net emission. Simulations assuming exponential growth of the root system followed by Gaussian die-back resemble measured flux trajectories and also point to great variability in the fraction of CH₄ oxidized before it reaches the atmosphere. Air entry on drainage reduces simulated CH₄ fluxes and the fractions of those fluxes mediated by plants. It also increases the fraction of CH₄ oxidized.     

Mathematical model for warehouse design and product allocation

The two primary functions of a warehouse include (1) temporary storage and protection of goods and (2) providing value added services such as fulfilment of individual customer orders, packaging of goods, after sales services, repairs, testing, inspection and assembly. To perform the above functions, the warehouse is divided into several functional areas such as reserve storage area, forward (order collation) area and cross-docking. The paper presents a mathematical model and a heuristic algorithm that jointly determine product allocation to the functional areas in the warehouse as well as the size of each area using data readily available to a warehouse manager.     

Resin screening for the removal of pyridine-derivatives from waste-water by solvent impregnated resin technology

The selective removal of pyridine derivatives by solvent impregnated resins has been studied. A solvent impregnated resin consists of a macro-porous particle that is impregnated with a solvent. This technology allows the use liquid–liquid extraction in fixed-bed operation, and prevents problems like entrainment and irreversible emulsification. 4-Cyanopyridine was chosen as model pyridine derivative, and 4-nonylphenol was used as solvent. The aim of this study was to select the most suitable resin for this application. While in the literature there are mainly two types of resins used, MPP and Amberlite XAD type, a comparative study has not yet been conducted. In this study, a series of resins were impregnated with the solvent and applied in sorption experiments to study on the effect of the resin properties on the capacity, selectivity and mass-transfer rates of the solvent impregnated resins. It was found that the capacity could be estimated accurately with the previously developed liquid–liquid extraction equilibrium model. Additionally, the selectivity was determined by the solvent properties, and hardly affected by the resin matrix. The mass-transfer rates were primarily determined the by particle diameter, whereas the effect of the porosity is small. On the basis of the results it was established that Amberlite XAD4 had the best combination of capacity, mass-transfer rate, mechanical strength, selectivity and pressure drop over a fixed-bed column and was therefore chosen for a more detailed study. The results showed that the breakthrough curve is broad due to mass-transfer limitations. The loading cycle of the column could be described with great accuracy using the mathematical model developed in this study. Regeneration of the column could be performed efficiently with a pH-swing using hydrochloric acid at a pH of 1. The fixed bed column was percolated with 7000 bed volumes of aqueous solutions varying in composition. No reduction in the capacity was observed which demonstrated that the SIR consisting of Amberlite XAD4 and 4-nonylphenol is highly stable.     

Infrared Spectra Simulation of Substituted Benzene Derivatives on the Basis of a 3D Structure Representation

The identification of chemical compounds from their infrared spectra faces new challenges from novel experimental techniques such as combinatorial chemistry. To rapidly provide estimates for the infrared spectra of candidate structures, an empirical approach to the modeling of the relationships between the 3D structure of a molecule and its infrared spectrum has been developed. This method is based on a novel 3D structure representation and a powerful modeling technique, a counterpropagation neural network. A dataset of 871 mono-, di-, and trisubstitued benzene derivatives is analyzed with this approach.     

Synthesis of polyether-based block copolymers based on poly(propylene oxide) and terephthalates

Poly(propylene oxide) (PPO) is a low reactive telechelic polyether and the synthesis of high molecular weight poly(propylene oxide)-based block copolymers was studied. The poly(propylene oxide) used was end capped with 20 wt % ethylene oxide and had a molecular weight of 2300 g/mol (ultra-low monol PEO-b-PPO-b-PEO). The type of terephthalic acid based precursors was varied: terephthalic acid, dimethyl terephthalate, diphenyl terephthalate, di(trifluoro ethyl) terephthalate, di(p-nitrophenyl) terephthalate) and terephthalic acid chloride. High molecular weight poly(propylene oxide) based segmented block copolymers were obtained with diphenyl terephthalate (inherent viscosity: 1.6 dl/g).The synthesis of polyether(ester-amide)s comprising PPO and isophthalamide-based segments was also studied by varying the polymerization temperature and time. High molecular weight poly(propylene oxide) block copolymers could be obtained if the reaction was carried out for 2 h at 250 °C under vacuum. Higher temperatures (280 °C) and longer times result in lower inherent viscosities, probably due to degradation of the polyether.     

Polyurethane elastomers with amide chain extenders of uniform length

Toluene diisocyanate based polyurethanes with amide extenders were synthesized poly(propylene oxide) with a number average molecular weight of 2000 and endcapped with toluene diisocyanate was used as the polyether segment. The chain extenders were based on poly(hexamethylene terephthalamide): hexamethylene diamine, bisamine-diamide and bisamine-tetra-amide. The linear poly(ether bisurethane-bisurea-amide)s (PUA) were colorless transparent thermoplastic elastomers with a high molecular weight. The polymers were analyzed by IR and DSC, the morphology studied by TEM, the mechanical properties studied by DMTA and the tensile, the elastic properties by compression and tensile set and thermal stability by melt rheology.The phase separation with these amide extenders was by crystallization. Increasing the length of the amide chain extender increased the modulus and the melting temperature of the PUA without changing the good low temperature properties. Also the elastic properties improved with amide segment length. The fracture stress increases with amide extender length. At 200 °C, the melt stability of the PUA with the bisamine-diamide chain extender was good.     

Degrees of terminal cooperativeness and the efficiency of the barge handling process

We study the effect of different degrees of cooperativeness on the efficiency of the barge handling process. The barge handling process is about the alignment of barge and terminal operations in a port. The efficiency of this alignment process depends on the cooperation of different players and especially terminal operators. In an earlier study we developed a Multi-Agent system assuming that terminals are fully cooperative, i.e., they provide insight in their occupation and make reliable appointments. In practice, terminals might decide to be less cooperative. We consider three degrees of cooperativeness: low, partly, and full cooperativeness. Experimental results indicate that there are two reasonable alternatives: full and low cooperativeness. In the lowly cooperative case, the lack of cooperativeness of terminals is compensated by cooperation among barge operators. We provide an extensive discussion on both alternatives. Our results provide useful insights for barge and terminal operators in the options they have to improve the barge handling process.     

Look-ahead strategies for dynamic pickup and delivery problems

In this paper we consider a dynamic full truckload pickup and delivery problem with time-windows. Jobs arrive over time and are offered in a second-price auction. Individual vehicles bid on these jobs and maintain a schedule of the jobs they have won. We propose a pricing and scheduling strategy based on dynamic programming where not only the direct costs of a job insertion are taken into account, but also the impact on future opportunities. Simulation is used to evaluate the benefits of pricing opportunities compared to simple pricing strategies in various market settings. Numerical results show that the proposed approach provides high quality solutions, in terms of profits, capacity utilization, and delivery reliability.