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Flavodiiron nitric oxide reductases (FNORs), found in many pathogenic bacteria, are able to detoxify NO by reducing it to N2O. In this way, FNORs equip these pathogens with immunity to NO, which is a central immune defense agent in humans. Hence, FNORs are thought to promote infection of the human body, leading to chronic diseases. Despite this importance of FNORs for bacterial pathogenesis, the mechanism of NO reduction by these enzymes is not well understood. Here we present the synthesis and spectroscopic characterization of the diiron dinitrosyl model complex [Fe2(BPMP)(OPr)(NO)2](BPh4)2. The crystal structure of this complex shows two end-on-coordinated {FeNO}(7) units that, based on spectroscopic and electrochemical results, are only weakly electronically coupled. Importantly, reduction of this complex by two electrons leads to the clean formation of N2O in quantitative yield. This complex therefore represents the first example of a functional model system for FNORs. The results provide key mechanistic insight into the mechanism of FNORs and, in particular, represent strong support for the proposed "super-reduced" mechanism for these enzymes.

Wax deposition in subsea pipelines is a problem of enormous economic consequences. The carbon number distribution (CND) is an important characteristic of the deposit because it significantly affects the yield stress of wax deposit , which is important in the design of the remediation technique of pigging. In this study, the recent theories for wax thermodynamic modeling are coupled with heat and mass transport modeling to identify the critical factors that determine the carbon number distribution of wax deposits. It is found that the deposit carbon number distribution is closely related to the diffusion of different n-alkane components and their respective concentration driving forces. The impact of molecular diffusion of the multiple components on the evolution of deposit carbon number distribution is quantified by evaluating of the mass driving force for each n-paraffin component. In addition, the effects of operating conditions on the deposit carbon number distribution are investigated by modeling and are validated by series of flow-loop experiments.

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Wax removal by pigging is costly in sub-sea oil production. Cost-effective scheduling of pigging can be achieved based on the deposition rate predicted by wax deposition models. Conventional wax deposition models predict wax deposition rates on the basis of Newtonian fluid mechanics. Such an approach can become invalid for highly waxy crude oils with non-Newtonian rheology. In this investigation, different simulation techniques, including large eddy simulation, Reynolds-averaged Naiver–Stokes equations, and the law of the wall, were applied to model non-Newtonian pipe flow. It was discovered that the law of the wall method is the best method to calculate the velocity profile, shear stress and the turbulent momentum diffusivity in turbulent non-Newtonian pipe flow of waxy oil. An enhanced wax deposition model considering the non-Newtonian characteristics of waxy oil using the law of the wall method was developed and applied to predict wax deposition rates in a field-scale pipeline.

Rainfall-runoff models play an important role in urban water resource management. The storm water management model (SWMM) developed by the US Environmental Protection Agency (EPA) is a widely used dynamic rainfall-runoff model for analyzing quantity and quality problems associated with urban drainage systems. In an ideal situation, the SWMM model would be designed and analyzed using a collection of catchment modeling systems. Traditionally, catchment discretization for rainfall-runoff modeling is performed manually on watershed maps, a time-consuming job with less-than-accurate results. An alternative approach to catchment discretization based on geographic information system (GIS) is proposed in this paper. The automatic discretization approach was successfully applied to rainfall-runoff modeling in Macau using a SWMM model. The results showed that the proposed approach outperformed the conventional catchmentdiscretization method in terms of producing meaningful parameters and avoiding most of the tedious preliminary tasks.

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While diffusion as the major mechanism for wax deposition has been investigated in past decades, wax gelation has mostly been studied in quiescent conditions and is considered to be less significant than diffusion in flow conditions. In this study, gelation has been observed as a major mechanism for the formation of wax deposits in oil/water stratified flow. The experiments are carried out in a state-of-the-art flow loop using a North Sea gas condensate and formation water. The flow map study using reflex camera and X-ray tomography reveals that most of the completely stratified flows occur at low total flow rates of oil and water, which correspond to low shear stresses at the wall. It was found that the carbon number distributions of the wax deposits formed in this region have very low fractions of heavy components and are very close to the distribution of the deposit that is only formed by gelation. It was further revealed that the deposit thickness increases with increasing degree of gelation, which corresponds to decreasing shear stress of the fluids at the wall. This finding is consistent with previous studies from single-phase experiments where lower oil velocities are found to result in much higher deposit thicknesses and low wax fractions in the deposits.