| 1. |
- Folkesson, Anders, et al.
(författare)
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Real life testing of a hybrid PEM fuel cell bus
- 2003
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Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 118:1-2, s. 349-357
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Tidskriftsartikel (refereegranskat)abstract
- Fuel cells produce low quantities of local emissions, if any, and are therefore one of the most promising alternatives to internal combustion engines as the main power source in future vehicles. It is likely that urban buses will be among the first commercial applications for fuel cells in vehicles. This is due to the fact that urban buses are highly visible for the public, they contribute significantly to air pollution in urban areas, they have small limitations in weight and volume and fuelling is handled via a centralised infrastructure. Results and experiences from real life measurements of energy flows in a Scania Hybrid PEM Fuel Cell Concept Bus are presented in this paper. The tests consist of measurements during several standard duty cycles. The efficiency of the fuel cell system and of the complete vehicle are presented and discussed. The net efficiency of the fuel cell system was approximately 40% and the fuel consumption of the concept bus is between 42 and 48% lower compared to a standard Scania bus. Energy recovery by regenerative braking saves up 28% energy. Bus subsystems such as the pneumatic system for door opening, suspension and brakes, the hydraulic power steering, the 24 V grid, the water pump and the cooling fans consume approximately 7% of the energy in the fuel input or 17% of the net power output from the fuel cell system. The bus was built by a number of companies in a project partly financed by the European Commission's Joule programme. The comprehensive testing is partly financed by the Swedish programme "Den Grona Bilen" (The Green Car). A 50 kW(el) fuel cell system is the power source and a high voltage battery pack works as an energy buffer and power booster. The fuel, compressed hydrogen, is stored in two high-pressure stainless steel vessels mounted on the roof of the bus. The bus has a series hybrid electric driveline with wheel hub motors with a maximum power of 100 kW. Hybrid Fuel Cell Buses have a big potential, but there are still many issues to consider prior to full-scale commercialisation of the technology. These are related to durability, lifetime, costs, vehicle and system optimisation and subsystem design. A very important factor is to implement an automotive design policy in the design and construction of all components, both in the propulsion system as well as in the subsystems.
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| 2. |
- Pioro, Michal, et al.
(författare)
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On efficient max-min fair routing algorithms
- 2003
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Ingår i: Proceedings of the Eighth IEEE Symposium on Computers and Communications. ISCC 2003. - Antalya : IEEE conference proceedings. - 076951961X ; , s. 365-372
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Konferensbidrag (refereegranskat)abstract
- In the paper, we consider the problem of routing and bandwidth allocation in networks that support elastic traffic. We assume that the bandwidth demand between each source-destination (S-D) pair is specified in terms of a minimum and maximum value, and a set of flows between each S-D pair is allowed to realize these demands. (We say that a set of flows realizes the demand associated with an S-D pair, if the sum of the bandwidths allocated to these flows is greater than the minimum value assumed for the demand of that S-D pair). In this setting, we show that routing and bandwidth allocation can be formulated as an optimization problem, where network utilization is to be maximized under capacity and the widely used max-min fairness constraints. We describe three different algorithms to solve variants of this problem. The most important one, an efficient, original algorithm assuming multipath routing is studied in detail and illustrated with a numerical example
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| 3. |
- Larsdotter, Karin, et al.
(författare)
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A small scale hydroponics wastewater treatment system under Swedish conditions
- 2003
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 48:11, s. 161-167
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Tidskriftsartikel (refereegranskat)abstract
- A treatment plant using conventional biological treatment combined with hydroponics and microalgae is constructed in a greenhouse in the area of Stockholm, Sweden. The treatment plant is built for research purposes and presently treats 0.559 m(3) of domestic wastewater from the surrounding area per day. The system uses anoxic pre-denitrification followed by aerobic tanks for nitrification and plant growth. A microalgal step further reduces phosphorus, and a final sand filter polishes the water. During a three week period in July 2002 the treatment capacity of this system was evaluated with respect to removal of organic matter, phosphorus and nitrogen. 90% COD removal was obtained early in the system. Nitrification and denitrification was well established with total nitrogen reduction of 72%. Phosphorus was removed by 47% in the process. However, higher phosphorus removal values are expected as the microalgal step will be further developed. The results show that acceptable treatment can be achieved using this kind of system. Further optimisation of the system will lead to clean water as well as valuable plants to be harvested from the nutrient rich wastewater.
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| 4. |
- Torto, N., et al.
(författare)
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In situ poly(ethylene imine) coating of hollow fiber membranes used for microdialysis sampling
- 2004
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Ingår i: Pure and Applied Chemistry. - : Walter de Gruyter GmbH. - 0033-4545 .- 1365-3075. ; 76:4, s. 879-888
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Tidskriftsartikel (refereegranskat)abstract
- A method for the in situ modification of hollow fiber membranes used as sampling units for microdialysis probes is presented. The method consists of adsorption-coating, high-molecular-weight poly(ethylene imine), PEI, onto membranes, already fitted on microdialysis probes. Modification of membranes was designed to specifically explore the so-called Andrade effects and thus enhance the interaction of membranes with enzyme. The performances of polysulfone, polyethersulfone, and polyamide membranes modified with PEI-enzyrne complex were evaluated based on the membrane extraction fraction for maltose and maltotriose and membrane morphology as examined by scanning electron microscopy. Of the membranes tested, the PEI-enzyme complex least affected the performance of the polysulfone membranes. Conversion of maltoheptaose to maltotriose and maltose was increased reproducibly (within a 5 % relative standard deviation) by 50 % for modified membranes compared to the native hollow fiber membranes. The results demonstrate the potential to effectively modify membranes already fitted on a microdialysis probe. Such a procedure can be modified and employed to either promote or reduce membrane-protein interaction for hollow fibers used as microdialysis sampling units or other similar membrane applications.
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| 5. |
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| 6. |
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| 7. |
- Johansson, Björn, et al.
(författare)
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Untripped SUV rollover detection and prevention
- 2004
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Ingår i: 2004 43RD IEEE CONFERENCE ON DECISION AND CONTROL (CDC), VOLS 1-5. - 0780386825 ; , s. 5461-5466
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Konferensbidrag (refereegranskat)abstract
- Untripped Sport Utility Vehicle rollovers are dangerous and possibly lethal accidents. A new kinetic energy based measure, that indicates an imminent wheel lift-off, is introduced. This measure is used by a gain scheduled linear quadratic (LQ) controller to prevent wheel lift-off. The LQ controller outputs the desired changes of the forces acting on the chassis. These force changes acre mapped to braking and traction system commands by a control allocator. A new allocation strategy based on convex optimization is proposed. The controller is capable of preventing wheel lift-off in the simulated test cases.
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| 8. |
- Lee, S. -K, et al.
(författare)
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Reduction of the barrier height and enhancement of tunneling current of titanium contacts using embedded Au nano-particles on 4H and 6H silicon carbide
- 2002
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 389-393:2, s. 937-940
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the electrical characteristics of Ti Schottky contacts with embedded Au nano-particles on various types of epilayers of SiC (4H- and 6H-SiC). From our current-voltage (I-V) and capacitance-voltage (C-V) measurements, we observed that Ti Schottky contacts with embedded Au nano-particles had 0.19 eV (n-4H-SiC) and 0.15 eV (n-6H-SiC) lower barrier height than those of particle free Ti Schottky contacts. In order to understand this reduction of the Schottky barrier height (SBH) for Ti Schottky contacts with embedded Au nano-particles, it has been proposed that SBH lowering is caused by an enhanced electric field due to the small size of the Au nano-particles and the large SBH difference. We have also tested these contacts on highly doped n-and p-type SiC material to study ohmic contacts using linear TLM measurements.
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| 9. |
- Malicsko, Gabor, et al.
(författare)
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Link capacity dimensioning and path optimization for networks supporting elastic services
- 2002
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Ingår i: IEEE ICC Proceedings. - New York : IEEE. - 0780374002 ; , s. 2304-2311, s. 2304-2311
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Konferensbidrag (refereegranskat)abstract
- We consider the problem of link capacity dimensioning and routing optimization in networks that support elastic flows and maintain proportional fairness among these flows. We assume that each demand between the origin-destination (O-D) pairs is associated with a minimum and a maximum bandwidth requirement and that a certain allocated bandwidth to a user demand (which must be between these minimum and maximum values) generates revenue for the network operator. On the other hand, the operator is incurred a capacity dependent cost for each link in the network. We then formulate the problem of bandwidth allocation, routing optimization and link capacity dimensioning as an optimization problem where the operator's objective is to maximize profit (under the fairness constraint). We propose computationally efficient algorithms to solve some important variants of this problem.
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| 10. |
- Moroianu, Dragos, et al.
(författare)
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LES of the flow and particle ingestion into an air intake of a jet engine running on the ground
- 2004
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Ingår i: Proc. ASME Turbo Expo. - : ASMEDC. ; 2, s. 209-217
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Konferensbidrag (refereegranskat)abstract
- The flow field generated by the flow into a jet engine air-intake, with near ground effects, is considered. The axial inflow in the neighborhood of the ground generates a system of unsteady vortices. Some of these vortices extend from the air-intake towards the ground. Some of these vortices are strong enough to dislocate and even lift small objects from the ground up to the air-intake. The dynamics of the vortex system makes it difficult to study the problem by standard numerical and experimental methods. The dynamics of the vortices can be captured by using Large Eddy Simulations (LES), which is used here to enhance the understanding of the dynamics of the flow field. The computed flow field is used also to assess the ingestion of particles into the air-intake. It is shown that particles of several mm sizes can be ingested into the jet engine. This in turn may result in enhanced erosion of the compressor blades. The results of the computations in terms of mean velocity field have been compared to experimental data. These results are in good agreement with the experiments.
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