| 1. |
- Johansson, Björn, et al.
(författare)
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Distributed Model Predictive Consensus
- 2006
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Ingår i: Proceedings of the 17th International Symposium on Mathematical Theory of Networks and Systems. ; , s. 2438-2444
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Konferensbidrag (refereegranskat)abstract
- In this paper we consider the problem of designing a distributed control strategy such that a linear combination of the states of a number of vehicles coincide at a given time. The vehicles are described by linear difference equations and are subject to convex input constraints. It is demonstrated how primal decomposition techniques and incremental subgradient methods allow us to find a solution in which each vehicle performs individual planning of its trajectory and exchanges critical information with neighbors only. We explore various communication, computation, and control structures, and demonstrate the performance of the algorithms by numerical examples.
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| 2. |
- Johansson, Björn, et al.
(författare)
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On decentralized negotiation of optimal consensus
- 2008
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 44:4, s. 1175-1179
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Tidskriftsartikel (refereegranskat)abstract
- A consensus problem consists of finding a distributed control strategy that brings the state or output of a group of agents to a common value, a consensus point. In this paper, we propose a negotiation algorithm that computes an optimal consensus point for agents modeled as linear control systems subject to convex input constraints and linear state constraints. By primal decomposition and incremental subgradient methods, it is shown that the algorithm can be implemented such that each agent exchanges only a small amount of information per iteration with its neighbors.
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| 3. |
- Johansson, Björn, et al.
(författare)
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Subgradient methods and consensus algorithms for solving convex optimization problems
- 2008
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Ingår i: Decision and Control, 2008. CDC 2008. 47th IEEE Conference on. - : IEEE. - 9781424431236 ; , s. 4185-4190
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Konferensbidrag (refereegranskat)abstract
- In this paper we propose a subgradient method for solving coupled optimization problems in a distributed way given restrictions on the communication topology. The iterative procedure maintains local variables at each node and relies on local subgradient updates in combination with a consensus process. The local subgradient steps are applied simultaneously as opposed to the standard sequential or cyclic procedure. We study convergence properties of the proposed scheme using results from consensus theory and approximate subgradient methods. The framework is illustrated on an optimal distributed finite-time rendezvous problem.
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| 4. |
- Aksyutina, Yu, et al.
(författare)
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Lithium isotopes beyond the drip line
- 2008
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693. ; 666:5, s. 430-434
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Tidskriftsartikel (refereegranskat)abstract
- The unbound isotopes 10Li, 12Li and 13Li have been observed after nucleon-knockout reactions at relativistic energies with 11Li and 14Be beams impinging on a liquid hydrogen target. The channels , and were analysed in the ALADIN-LAND setup at GSI. The 10Li data confirm earlier findings, while the 12Li and 13Li nuclei were observed for the first time. The relative-energy spectrum shows that the ground state of 12Li can be described as a virtual s-state with a scattering length of -13.7(1.6) fm. A broad energy spectrum was found for the channel. Based on the assumption that the relative-energy spectrum is dominated by a correlated background presumably stemming from initial correlations in the 14Be ground-state, evidence for a 13Li resonance at 1.47(31) MeV above the threshold with a width around 2 MeV has been found.
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| 5. |
- Aksyutina, Yuliya, 1983, et al.
(författare)
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Properties of the 7He ground state from 8He neutron knockout
- 2009
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693. ; 679:3, s. 191-196
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Tidskriftsartikel (refereegranskat)abstract
- The unbound nucleus 7He, produced in neutron-knockout reactions with a 240 MeV/u 8He beam in a liquid-hydrogen target, has been studied in an experiment at the ALADIN-LAND setup at GSI. From an R-matrix analysis the resonance parameters for 7He as well as the spectroscopic factor for the 6He(0+) + n configuration in its ground-state have been obtained. The spectroscopic factor is 0.61 confirming that 7He is not a pure single-particle state. An analysis of 5He data from neutron-knockout reactions of 6He in a carbon target reveals the presence of an s-wave component at low energies in the α+n relative energy spectrum. A possible low-lying exited state in 7He observed in neutron knockout data from 8He in a carbon target and tentatively interpreted as a Iπ=1/2− state, could not be observed in the present experiment. Possible explanations of the shape difference between the 7He resonance obtained in the two knockout reactions are discussed in terms of target-dependence or different reaction mechanisms at relativistic energies.
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| 6. |
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| 7. |
- Bexell, Ulf, et al.
(författare)
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Bonding of vegetable oils to mercapto silane treated metal surfaces : Surface engineering on the nano scale
- 2006
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:2, s. 838-841
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Tidskriftsartikel (refereegranskat)abstract
- In this paper the bonding of thin vegetable oil films on mercapto silane treated aluminium surfaces has been studied. The silane molecules are attached to the surface by metal-oxygen-silicon bonds. The coupling between the unsaturated bonds of the vegetable oil and the thiol functionalised surface was obtained through a photoinduced thiol-ene reaction. The surfaces were characterised by X-ray photoelectron spectroscopy (XPS). Vegetable oil contains both saturated and unsaturated carbon chains. For the reactions investigated in this study it is the unsaturated carbon chains that can react by a thiol-ene reaction and the results indicate that it is possible to attach a vegetable oil to a metal surface pre-treated with a thiol functionalised silane.
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| 8. |
- Djurfeldt, Mikael, 1967-, et al.
(författare)
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Brain-scale simulation of the neocortex on the IBM Blue Gene/L supercomputer
- 2008
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Ingår i: IBM Journal of Research and Development. - : IBM. - 0018-8646 .- 2151-8556. ; 52:1-2, s. 31-41
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Tidskriftsartikel (refereegranskat)abstract
- Biologically detailed large-scale models of the brain can now be simulated thanks to increasingly powerful massively parallel supercomputers. We present an overview, for the general technical reader, of a neuronal network model of layers II/III of the neocortex built with biophysical model neurons. These simulations, carried out on an IBM Blue Gene/Le supercomputer, comprise up to 22 million neurons and 11 billion synapses, which makes them the largest simulations of this type ever performed. Such model sizes correspond to the cortex of a small mammal. The SPLIT library, used for these simulations, runs on single-processor as well as massively parallel machines. Performance measurements show good scaling behavior on the Blue Gene/L supercomputer up to 8,192 processors. Several key phenomena seen in the living brain appear as emergent phenomena in the simulations. We discuss the role of this kind of model in neuroscience and note that full-scale models may be necessary to preserve natural dynamics. We also discuss the need for software tools for the specification of models as well as for analysis and visualization of output data. Combining models that range from abstract connectionist type to biophysically detailed will help us unravel the basic principles underlying neocortical function.
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| 9. |
- Evander, Mikael, et al.
(författare)
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Acoustic trapping of cells in a microfluidic format
- 2005
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Ingår i: Proceedings of µTAS 2005 Conference. ; 1, s. 515-517
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Konferensbidrag (refereegranskat)abstract
- This paper presents, for the first time, non-contact acoustic trapping of cells in a microfluidic format. The employed acoustic force maintains the cells in the center of a fluidic channel while allowing for perfusion of e.g. nutrients or drugs as well as optical monitoring of the cells. Neural stem cells have been acoustically trapped and tested for viability after 15 minutes of ultrasonic radiation. It is also shown that it is possible to grow yeast cells suspended in an acoustic standing wave while perfusing with cell media.
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| 10. |
- Evander, Mikael, et al.
(författare)
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Acoustic Trapping: System Design, Optimization and Applications
- 2006
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Ingår i: Proceedings of the sixth Micro Structure Workshop. ; 1, s. 33-33
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Konferensbidrag (refereegranskat)abstract
- Manipulation, separation and trapping of particles and cells are very important tools in today's bioanalytical and medical field. The acoustic no-contact trapping method presented at earlier MSW 2004 provides a flexible platform for performing cell and particle assays in a perfusion-based microsystem. To further develop the system microfabricated glass channels are now used, resulting in shorter fabrication times and a very inert channel material. The fluidic design has been revised to minimise the risks of leaking and hydrodynamic focusing has been incorporated to ensure a high trapping efficiency. A change of piezoelectric materials has resulted in less thermal losses in the material, higher reproducibility and shorter manufacturing time. The trapping force was estimated by calculating the fluid force exerted on a single particle levitated in the standing wave as a reference. The temperature increase due to the losses in the transducer was measured using a fluorescent dye, indicating a maximum temperature increase of 10 degrees Celsius. Live cells have been trapped and shown to be viable while still suspended in the standing wave, thus making it possible to do on-line studies on, for example, drug response of cell populations.
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