Mathematical Modeling of Reverse Flow Oxidation Catalysts

A theoretical model and a computer simulation on methane (CH4) reduction in a simulated natural gas exhaust mixture are performed for a Reverse-Flow Oxidation Catalyst. This theoretical model is to predict the conversion of methane flowing through an oxidation catalyst with periodic reversal of flow direction. The model developed for this purpose is a transient, 1-Dimensional plug flow model with gas phase reactions and surface reactions. The derivation of the model resulted in the mole balance equation and the energy balance equation for the gas phase and the solid phase. The momentum equation for this model is neglected as it is assumed that there is no pressure drop across the catalyst. A FORTRAN code was developed to simulate the forward flow and the reverse flow of the gas species through the catalyst. This code can have a symmetrical or an asymmetrical switching according to the user. It also gives an option of running the code either in the forward direction or with periodic switching to analyze the effect of switching. With this code, the optimum switching time for the maximum conversion of methane was found. The effect of various parameters such as the length of the catalyst, the concentration of the gas species, pre-exponential term and the activation energy was also analyzed. The results show that the optimum switching frequency is 25 seconds for all space velocities for a 10 cm long catalyst with 2000 ppm of inlet methane. The increase in the conversion of methane when compared to the unidirectional flow was found to be 47% at 450oC for a gas hourly space velocity of 50,000 hr-1. It was also found that, at 450oC for a gas hourly space velocity of 50,000 hr-1, the pre-exponential factor and the length of the catalyst had negligible effect on the conversion of methane. The activation energy and the inlet concentration had a significant effect on the methane conversion which is discussed in further chapters. It was also found that symmetric switching had increased solid temperature profile and methane conversion efficiency when compared to the asymmetric switching frequency

Recursive SDN for Carrier Networks

Control planes for global carrier networks should be programmable (so that new functionality can be easily introduced) and scalable (so they can handle the numerical scale and geographic scope of these networks). Neither traditional control planes nor new SDN-based control planes meet both of these goals. In this paper, we propose a framework for recursive routing computations that combines the best of SDN (programmability) and traditional networks (scalability through hierarchy) to achieve these two desired properties. Through simulation on graphs of up to 10,000 nodes, we evaluate our design's ability to support a variety of routing and traffic engineering solutions, while incorporating a fast failure recovery mechanism

Self-Obviating Systems and their Application to Sustainability

Most research in computing and information science reinforces the premise that information and communications technology (ICT) can be productively applied even more broadly than it is at present. A recent thread of research in sustainable HCI, however, has focused on the possibility that there are many situations where less ICT, not more, may be desirable. We envision an adaptation of this premise, where the goal is not just to consciously omit or remove ICT systems, but rather to create systems explicitly designed to make themselves superfluous through their use. Such a system—one in which the successful operation of the system in the short term renders it superfluous in the long term—could be called a “self-obviating system”. We present a case study in the sustainable food domain for a context in which self-obviating systems could be useful, and a typology of self-obviating systems that could be relevant to other domains. Self-obviating systems could be an important part of a sustainable future, and could be applied more broadly in ICT design.ye

Regulatory T cells and their role in rheumatic diseases: a potential target for novel therapeutic development

Regulatory T cells have an important role in limiting immune reactions and are essential regulators of self-tolerance. Among them, CD4+CD25high regulatory T cells are the best-described subset. In this article, we summarize current knowledge on the phenotype, function, and development of CD4+CD25high regulatory T cells. We also review the literature on the role of these T cells in rheumatic diseases and discuss the potential for their use in immunotherapy