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A three-dimensional, computational fluid dynamics (CFD) model of a PEM fuel cell is presented. The model consists of straight channels, porous gas diffusion layers, porous catalyst layers and a membrane. In this computational domain, most of the transport phenomena which govern the performance of the PEM fuel cell are dealt with in detail. The model solves the convective and diffusive transport of the gaseous phase in the fuel cell and allows prediction of the concentration of the species present. A special feature of the model is a method that allows detailed modelling and prediction of electrode kinetics. The transport of electrons in the gas diffusion layer and catalyst layer is accounted for, as well as the transport of protons in the membrane and catalyst layer. This provides the possibility of predicting the three-dimensional distribution of the activation overpotential in the catalyst layer. The current density dependency on the gas concentration and activation overpotential can thereby be addressed. The proposed model makes it possible to predict the effect of geometrical and material properties on the fuel cell’s performance. It is shown how the ionic conductivity and porosity of the catalyst layer affects the distribution of current density and further how this affects the polarization curve. The porosity and conductivity of the catalyst layer are some of the most difficult parameters to measure, estimate and especially control. Yet the proposed model shows how these two parameters can have significant influence on the performance of the fuel cell. The two parameters are shown to be key elements in adjusting the three-dimensional model to fit measured polarization curves. Results from the proposed model are compared to single cell measurements on a test MEA from IRD Fuel Cells.

Electric vehicle seems to go well together with the growing societal trend of becoming more self-supplying with renewable electricity produced in the household. However, aligning household electricity production and electric vehicle charging have received little attention in HCI although both areas have been pursued separately for a number of years. In this paper, we present findings from a qualitative study that explore the potential of aligning electric vehicle charging with times where renewable electricity is being produced in the household. We present an empirical qualitative study of 5 households (19 persons) that own electric vehicles and also produce their own renewable electricity. Our findings, described in five themes, reveal that aligning charging and electricity production can be a challenge and tension exist for aligning consumption such as motivation, roles, mobility patterns, and electricity producing technology. We further discuss our findings and possible directions for future HCI research in the field.

An effective controller is proposed for the 'Photovoltaic(PV) - Battery - Diesel Generator(DG)' based hybrid standalone system in this article. A bidirectional DC to DC device which can allow power in both directions is integrated among the DC-link and battery bank to maintain contact voltage by maintaining power balance in the system. Further, a bidirectional inverter is also considered between point of common coupling (PCC) and DC-link for providing supply to AC loads as well as charging the battery from diesel generator based on requirement. However, the phenomenon of partial shading condition (PSC) commonly occurring on PV modules and also generated power from PV always fluctuates according to changes in weather. To achieve a superior performance of the system, a Takagi-Sugeno Fuzzy (TSF) based controllers are implemented in proposed control schemes. The novel control schemes are implemented on a bidirectional DC to DC converter as well as three phase bidirectional inverter. However, the proper deloading process of the PV system should be incorporated into the controller of the DC to DC converter to achieve power balance during light load conditions. Balanced quality voltages (3-phase) at PCC are achieved by inverter control which forces to maintain balanced currents generated by DG during the operation of unbalanced loads. Maintaining balanced DG currents can help to reduce the oscillations on the torque of the shaft which increases the fatigue life. Further the reactive power demanded at PCC is compensated by the inverter control, hence DG need not to provide it which results can reduce the consumption of diesel. Various case studies are examined by using MATLAB to present results and Real Time Digital Simulator (RTDS) based results are also provided in this paper.

Isotretinoin is effective in the treatment of severe acne and rosacea. Both parent drug and its main metabolite 4-oxo-isotretinoin are potentially teratogenic compounds and contain a carboxylic acid moiety. In the presence of ethanol, naturally occurring as well as synthetic retinoids also containing a carboxylic acid moiety are capable of undergoing an ethyl esterification with the metabolic formation of more lipophilic compounds with a much longer terminal half-life.To determine if isotretinoin (13-cis-RA), its main metabolite 4-oxo-isotretinoin (4-oxo-13-cis-RA), and other possible metabolites in the presence or absence of ethanol are converted to their corresponding ethyl derivatives in patients with severe acne or rosacea after multiple isotretinoin dosing. In addition, pharmacokinetic parameters of the parent drug and its 4-oxo metabolite were determined.Eleven patients with severe acne or rosacea were treated with isotretinoin daily for 3 months and investigated pharmacokinetically during 24 h after 1 month of treatment and for up to 28 days after discontinuation of therapy. A possible influence of ethanol was evaluated using a simple self-administered questionnaire and by measuring serum ethanol levels during treatment. The concentrations of isotretinoin, 4-oxo-isotretinoin and possible ethylated and nonethylated metabolites were measured by reverse-phase high-performance liquid chromatography.Although seven of 11 patients had a considerable weekly alcohol intake, no endogenous synthesis of ethyl derivatives of isotretinoin, the main 4-oxo metabolite or the all-trans compounds was chromatographically detectable in any of the patients' plasma samples during the treatment period. Multiple dose pharmacokinetic data for the parent drug and its main metabolite were comparable to previous studies.The metabolism and pharmacokinetics of isotretinoin and its main metabolites are not influenced by ethanol during long-term isotretinoin treatment. After ceasing long-term isotretinoin therapy the recommended period of 1 month for using anticonceptive measures in fertile women seems adequate.

The chapter gives an introduction to the book "Environmental planning and management : tools for a sustainable development".

The paper presents a computational fluid dynamics (CFD) analysis of a 33 MW straw-fired grate boiler. Combustion on the grate plays akey-role in the analysis of these boilers and in this work a stand-alone code was used to provide inlet conditions for the CFD analysis. Modelpredictions were compared with available gas temperature and species concentration measurements showing good agreement. Combustionof biomass in grate-based boilers is often associated with high emission levels and relatively high amounts of unburnt carbon in the fly ash.Based on the CFD analysis, it is suggested that poor mixing in the furnace is a key issue leading to these problems. q 2003 Elsevier Ltd. All rights reserved. Udgivelsesdato: JUN

The potential of offshore wind energy has been commonly recognized and explored globally. Many countries have implemented and planned offshore wind farms to meet their increasing electricity demands and public environmental appeals, especially in Europe. With relatively less space limitation, an offshore wind farm could have a capacity rating to hundreds of MWs or even GWs that is large enough to compete with conventional power plants. Thus the impacts of a large offshore wind farm on power system operation and security should be thoroughly studied and understood. This paper investigates the impacts of integrating a large-scale offshore wind farm into the transmission system of a power grid through VSC-HVDC connection. The concerns are focused on steady-state voltage stability, dynamic voltage stability and transient angle stability. Simulation results based on an exemplary power system are presented and analyzed.