Унификация критериев и балльно-рейтинговых систем оценки компетенций студентов лечебного и стоматологического факультетов по дисциплине "Анатомия человека"

СТУДЕНТЫОБРАЗОВАНИЕ СТОМАТОЛОГИЧЕСКОЕОБРАЗОВАНИЕ МЕДИЦИНСКОЕАНАТОМИ

CFD Modeling: Different Kinetic Approaches for Internal Reforming Reactions in an Anode-Supported SOFC

Fuel cells are electrochemical devices that convert chemical energy into electricity. Solid oxide fuel cells (SOFCs) are a particularly interesting type because they can reform hydrocarbon fuels directly within the cell, which are possible thanks to their high operating temperature. The purpose of this study is to develop an anode-supported SOFC theoretical model, to enhance the understanding of the internal reforming reactions and their effects on the transport processes. A CFD approach, based on the finite element method, is implemented to unravel the interaction between internal reforming reactions, momentum, heat and mass transport. The three different steam reforming reaction rates applied were developed and correlated to experimental studies found in the literature. An equilibrium rate equation is implemented for the water-gas shift reaction. The result showed that the reaction rates are very fast and differ quite a lot in the size. The pre-exponential values, in relation to the partial pressures, and the activation energy was affected the reaction rate. It was shown that the anode structure and catalytic composition have a major impact on the reforming reaction rate and on the cell performance. The large difference between the different activation energies and pre-exponential values found in the literature reveals that several parameters probably have significant influence on the reaction rate. As the experiments with the same chemical compositions can be conducted on a cell or only a reformer, it is important to reflect over the effect this has on the kinetic model. To fully understand the effect of the parameters connected to the internal reforming reaction, micro scale modeling is needed

Modeling Analysis of Different Renewable Fuels in an Anode Supported SOFC

Background. It is expected that fuel cells will play a significant role in a future sustainable energy system, due to their high energy efficiency and possibility to use renewable fuels. Fuels, such as biogas, can be produced locally close to the customers. The improvement for fuel cells during the last years has been fast, but the technology is still in the early phases of development, however the potential is enormous. Method of approach. A CFD approach (COMSOL Multiphysics) is employed to investigate effects of different fuels such as biogas, pre-reformed methanol, ethanol and natural gas. The effects of fuel inlet composition and temperature are studied in terms of temperature distribution, molar fraction distribution and reforming reaction rates within a singe cell for an intermediate temperature solid oxide fuel cell (IT-SOFC). The developed model is based on the governing equations of heat-, mass- and momentum transport, which are solved together with global reforming reaction kinetics. Results. The result shows that the heat generation within the cell depends mainly on the initial fuel composition and the inlet temperature. This means that the choice of internal- or external reforming has a significant effect on the operating performance. Conclusions. The anode structure and catalytic characteristic have a major impact on the reforming reaction rates and also on the cell performance. It is concluded that biogas, methanol and ethanol are suitable fuels in a SOFC system, while more complex fuels need to be externally reformed

Comparison of Humidified Hydrogen and Partly Pre-Reformed Natural Gas as Fuel for Solid Oxide Fuel Cells applying Computational Fluid Dynamics

A three-dimensional computational fluid dynamics (CFD) approach based on the finite element method (FEM) is used to investigate a solid oxide fuel cell (SOFC). Governing equations for heat, gas-phase species, electron, ion and momentum transport are implemented and coupled to kinetics describing electrochemical as well as internal reforming reactions. The model cell design is based on a cell from Ningbo Institute of Material Technology and Engineering in China and the electrochemical area-to-volume ratios are based on experimental work performed at Kyushu University in Japan. A parameter study is performed focusing on the inlet fuel composition, where humidified hydrogen, 30 % pre-reformed natural gas (as defined by IEA) and 50 % pre-reformed natural gas (as defined by Kyushu University) are compared. It is found that when 30 % pre-reformed natural gas is supplied as fuel the air mass flow rate is halved, compared to the case with humidified hydrogen, keeping the inlet and outlet temperatures constant. The current density is decreased but the fuel utilization is kept at 80 %. It is found that the cathode support layer has a significant oxygen gas-phase resistance in the direction normal to the cathode/electrolyte interface (at positions under the interconnect ribs), as well as an electron resistance inside the cathode (at positions under the air channel) in the same direction. The methane steam reforming reaction is shown, both according to the experiments and to the models, to proceed along the main flow direction throughout the cell

Short-Term Antibiotic Treatment Has Differing Long-Term Impacts on the Human Throat and Gut Microbiome

Antibiotic administration is the standard treatment for the bacterium Helicobacter pylori, the main causative agent of peptic ulcer disease and gastric cancer. However, the long-term consequences of this treatment on the human indigenous microbiota are relatively unexplored. Here we studied short- and long-term effects of clarithromycin and metronidazole treatment, a commonly used therapy regimen against H. pylori, on the indigenous microbiota in the throat and in the lower intestine. The bacterial compositions in samples collected over a four-year period were monitored by analyzing the 16S rRNA gene using 454-based pyrosequencing and terminal-restriction fragment length polymorphism (T-RFLP). While the microbial communities of untreated control subjects were relatively stable over time, dramatic shifts were observed one week after antibiotic treatment with reduced bacterial diversity in all treated subjects in both locations. While the microbiota of the different subjects responded uniquely to the antibiotic treatment some general trends could be observed; such as a dramatic decline in Actinobacteria in both throat and feces immediately after treatment. Although the diversity of the microbiota subsequently recovered to resemble the pre treatment states, the microbiota remained perturbed in some cases for up to four years post treatment. In addition, four years after treatment high levels of the macrolide resistance gene erm(B) were found, indicating that antibiotic resistance, once selected for, can persist for longer periods of time than previously recognized. This highlights the importance of a restrictive antibiotic usage in order to prevent subsequent treatment failure and potential spread of antibiotic resistance