| 1. |
- Bengtsson, J., et al.
(författare)
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Quantum Szilard Engine with Attractively Interacting Bosons
- 2018
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Ingår i: Physical Review Letters. - 0031-9007. ; 120:10
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Tidskriftsartikel (refereegranskat)abstract
- We show that a quantum Szilard engine containing many bosons with attractive interactions enhances the conversion between information and work. Using an ab initio approach to the full quantum-mechanical many-body problem, we find that the average work output increases significantly for a larger number of bosons. The highest overshoot occurs at a finite temperature, demonstrating how thermal and quantum effects conspire to enhance the conversion between information and work. The predicted effects occur over a broad range of interaction strengths and temperatures.
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| 2. |
- Diedrichs, Ben, et al.
(författare)
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Crosswind stability of high-speed train on a high embankment
- 2007
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Ingår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit. - 0954-4097 .- 2041-3017. ; 221:2, s. 205-225
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Tidskriftsartikel (refereegranskat)abstract
- This work presents aerodynamic results of crosswind stability obtained numerically and experimentally for the leading control unit (class 808) of Deutsche Bahn AG's high-speed train Inter-CityExpress 2. The train model is on top of a 6 m high embankment in accordance with the proposed European code for interoperable trains, the so-called technical specifications for interoperability. The purpose of the study is to convey the predictive accuracy that typical steady-state computational fluid dynamics-Reynolds average Navier-Stokes methods (industry standard) return and to contribute to the understanding of the aerodynamics for the current application. Attention is drawn to the aerodynamics around the train and embankment when subjected to a steady block profile crosswind of 30 degrees yaw angle on the basis of the onset velocity far upstream the embankment. The Re (Reynolds number) of the embankment cases is 4.6 x 10(6). Calculated results are obtained with the commercial code STAR-CD, with exclusively hexahedral meshes with a total cell count of 13.5 x 10(6). Results are obtained when the train stands on the windward and leeward tracks on top of the embankment. These results are first compared with a flat ground case from a previous study. Then experimental data are obtained in a high-pressure wind tunnel with a model scale of 1:100. Re effects are compensated by raising the ambient pressure by a factor of 60, which increases the air density and thus the Re by a similar factor. Calculated results are in fair agreement with the experiments, where both the calculations and the experiments predict the leeward case to be the more critical one. In addition, the related consequences on the mechanical behaviour, i.e. the stability of the car, are briefly addressed by means of a quasi-static mechanical analysis. The results of the present study indicate that the 6 m high embankment concerning the current train reduces the permissible crosswind speed with approximately 20 per cent.
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| 3. |
- Diedrichs, Ben, et al.
(författare)
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Quasistatic modelling of wheel-rail reaction due to crosswind effects for various types of high-speed rolling stock
- 2004
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Ingår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit. - : SAGE Publications. - 0954-4097 .- 2041-3017. ; 218:2, s. 133-148
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Tidskriftsartikel (refereegranskat)abstract
- This work describes a quasi-static tool developed to assess the performance swiftly of crosswind stability for three types of rolling stock with conventional, semi-trailer and Jacobs bogie running gear configurations. The prediction accuracy of the results returned by the tool for the quasistatic assumption is fair in comparison with results of more advanced multibody simulation software that is commercially available. The codes, which are based on steady equilibrium equations for the wheels and axles, bogie frames and vehicle body/bodies, handle arbitrarily canted embankments and circular curves. To a large extent the accuracy hinges on the bodies' lateral displacements relative to the contact points between the wheels and rails; therefore proper modelling of the suspension systems and bump stops are found to be important. Examples are given of the limitations associated with the quasi-static approach, studying the following: (a) the combined wind and track scenario in Deutsche Bahn AG's guideline, (b) the effects of typical track irregularities for high-speed transportation as a function of train speed and (c) the effects of oscillating crosswind. It has also been found relevant to demonstrate some of the large differences regarding provisions regulating crosswind safety. To this extent the present results are compared with those derived with the British Group Standard and also with results presented in the guideline of Deutsche Balm AG. In addition, examples are given of the differences found of the permissible crosswind speed using calculated (with CFD-RANS) and experimentally obtained aerodynamic loads.
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