| 1. |
- Fuselier, S. A., et al.
(författare)
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Ion chemistry in the coma of comet 67P near perihelion
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462, s. S67-S77
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Tidskriftsartikel (refereegranskat)abstract
- The coma and the comet-solar wind interaction of comet 67P/Churyumov-Gerasimenko changed dramatically from the initial Rosetta spacecraft encounter in 2014 August through perihelion in 2015 August. Just before equinox (at 1.6 au from the Sun), the solar wind signal disappeared and two regions of different cometary ion characteristics were observed. These 'outer' and 'inner' regions have cometary ion characteristics similar to outside and inside the ion pileup region observed during the Giotto approach to comet 1P/Halley. Rosetta/Double-Focusing Mass Spectrometer ion mass spectrometer observations are used here to investigate the H3O+/H2O+ ratio in the outer and inner regions at 67P/Churyumov-Gerasimenko. The H3O+/H2O+ ratio and the H3O+ signal are observed to increase in the transition from the outer to the inner region and the H3O+ signal appears to be weakly correlated with cometary ion energy. These ion composition changes are similar to the ones observed during the 1P/Halley flyby. Modelling is used to determine the importance of neutral composition and transport of neutrals and ions away from the nucleus. This modelling demonstrates that changes in the H3O+/H2O+ ratio appear to be driven largely by transport properties and only weakly by neutral composition in the coma.
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| 2. |
- Tettamanti, T., et al.
(författare)
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Robust real-time control for urban road traffic networks
- 2014
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Ingår i: IEEE Transactions on Intelligent Transportation Systems. - 1524-9050 .- 1558-0016. ; 15:1, s. 385-398
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the presented research is to elaborate a traffic-responsive optimal signal split algorithm taking uncertainty into account. The traffic control objective is to minimize the weighted link queue lengths within an urban network area. The control problem is formulated in a centralized rolling-horizon fashion in which unknown but bounded demand and queue uncertainty influences the prediction. An efficient constrained minimax optimization is suggested to obtain the green time combination, which minimizes the objective function when worst case uncertainty appears. As an illustrative example, a simulation study is carried out to demonstrate the effectiveness and computational feasibility of the robust predictive approach. By using real-world traffic data and microscopic traffic simulator, the proposed robust signal split algorithm is analyzed and compared with well-tuned fixed-time signal timing and to nominal predictive solutions under different traffic conditions.
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| 3. |
- Tettamanti, T., et al.
(författare)
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Uncertainty modeling and robust control in urban traffic
- 2011
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Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). - 2405-8963. - 9783902661937 ; 18:PART 1, s. 14910-14915
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Konferensbidrag (refereegranskat)abstract
- The paper investigates the problem of uncertainty modeling and constrained robust control of urban traffic. Linear polytopic approach is used by state-space representations to describe the uncertain network system. In order to handle model mismatches, robust and infinite horizon model predictive control (MPC) method is proposed. The control strategy is an efficient method to reduce travel time and improve homogeneous traffic flow under changing model conditions. Centralized numerical solution has been carried out as a solution of Linear Matrix Inequalities (LMI) by using semidefinite programming (SDP). Closed-loop control results were tested in simulation environment taking alternative model uncertainty levels into account.
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| 4. |
- Luspay, T., et al.
(författare)
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Constrained Freeway Traffic Control via Linear Parameter Varying Paradigms
- 2012
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Ingår i: J. Mohammadpour and C.W. Scherer (eds.), Control of linear parameter varying systems with applications, Springer. - Boston, MA : Springer US. - 9781461418320 ; 9781461418337, s. 461-482
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- A novel freeway traffic control design framework is proposed in the chapter. The derivation is based on the parameter-dependent reformulation of the second-order macroscopic freeway model. Hard physical constraints are handled implicitly, by introducing additional scheduling parameter for controller saturation measure. The ramp metering problem is then formulated as an induced L2 norm minimization, where the effects of undesired traffic phenomena are attenuated on the network throughput. The solution of the resulting problem involves convex optimization methods subjected to Linear Matrix Inequalities. A numerical example is given to validate the parameter-dependent controller and evaluate its effectiveness under various traffic situations.
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| 5. |
- Luspay, T., et al.
(författare)
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Freeway ramp metering: an LPV set theoretical analysis
- 2011
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Ingår i: American Control Conference. - 0743-1619. - 9781457700804 ; , s. 733-738
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Konferensbidrag (refereegranskat)abstract
- The paper contributes to the set theoretic analysis of freeway traffic flow control by ramp metering.From the generic and discrete time non-linear second-order macroscopic dynamics of freeway, first, an equivalent, quasi Linear Parameter Varying (LPV) representation is derived by steady-state centering and factorization. Second, a polytopic LPV model form is obtained from the quasi reformulation of the non-linear problem statement. The latter polytopic LPV form is then used for the computation and analysis of distur- bance invariant sets. This framework is able to characterize constrained sets of states which can be reached by pure ramp metering control input signal respectively becomes invariant under the effect of other measured and unmeasured inputs.The application of disturbance invariant set theory clearly quantifies the set of states being invariant under the polytopic LPV dynamics and other physical constraints regardless to the open- and closed-loop nature of the system.The proposed idea is fully based on the analysis of the (transformed) non-linear macroscopic system and aims at filling the gap between the traffic modelling and quantitative freeway ramp metering.
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| 6. |
- Luspay, T., et al.
(författare)
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Ramp metering for flow maximisation and emission reduction – a set-based multi-objective design approach
- 2017
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Ingår i: Transportation Research Procedia. - : Elsevier BV. - 2352-1465 .- 2352-1457. ; 27, s. 937-944
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Konferensbidrag (refereegranskat)abstract
- A set-theoretical approach is presented for a multi-objective control design of the local ramp metering problem. Two control objectives are specified: first, the optimization of traffic performance, by the minimization of total time spent.Second, the emission factor of CO2 is minimized. The optimal state for traffic emission however lies in the unstable domain of the system. To resolve this inconsistency, the control problem is formalized in a set-theoretical context. For this purpose, the nonlinear METANET model is rewritten in a shifted coordinate frame in a parameter-varying, polytopic representation. Bounds on state-, input- and disturbance variables are expressed by convex polytopes. These sets are then used for the design of an interpolated H∞ controller that is capable of improving traffic conditions according to the prescribed multi-objective criteria.
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| 7. |
- Luspay, T., et al.
(författare)
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Set-based multi-objective control of metered ramps at ring road junctions
- 2020
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Ingår i: Transportmetrica A: Transport Science. - : Informa UK Limited. - 2324-9943 .- 2324-9935. ; 16:2, s. 337-357
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Tidskriftsartikel (refereegranskat)abstract
- A set-theoretical approach is presented for a multi-objective control design of the local ramp metering problem. Two control objectives are specified: first, the optimization of traffic performance, by the minimization of total time spent. Second, the emission factor of CO2 needs to be minimized. The optimal state for traffic emission however lies in the unstable domain of the dynamic system. To dissolve this inconsistency, the control problem is formalized for the multi-objective optimization problem by using set-theoretical methods. For this purpose, the non-linear model METANET is rewritten in a shifted coordinate frame with a parameter-varying, polytopic representation. Bounds on state-, input- and disturbance variables are expressed by convex polytopes. These sets are then used for the design of an interpolated Hinf controller that is capable of improving traffic conditions according to the prescribed multi-objective criteria
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| 8. |
- Luspay, T., et al.
(författare)
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Set-theoretic analysis of the isolated ramp metering problem
- 2016
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Ingår i: International Journal of Robust and Nonlinear Control. - : Wiley. - 1099-1239 .- 1049-8923. ; 26:6, s. 1246-1266
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of ramp metering, as an effective freeway traffic control solution, is focused in the paper. Thestudied traffic control problem is discussed in a set-theoretic context in order to quantitatively characterize its effectiveness. The notions of maximal robust controlled invariant set, as well as t-step robust controllable set are defined and used for analyzing the ramp metering problem independently of the control policy applied. Algorithms are developed to compute these sets, with special attention to their practical interpretations.Numerical examples with graphical representation of the proposed methodology are given to examine localramp metering and conclude implications to control strategies.
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| 9. |
- Mandt, K. E., et al.
(författare)
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RPC observation of the development and evolution of plasma interaction boundaries at 67P/Churyumov-Gerasimenko
- 2016
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462, s. S9-S22
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Tidskriftsartikel (refereegranskat)abstract
- One of the primary objectives of the Rosetta Plasma Consortium, a suite of five plasma instruments on-board the Rosetta spacecraft, is to observe the formation and evolution of plasma interaction regions at the comet 67P/Churyumov-Gerasimenko (67P/CG). Observations made between 2015 April and 2016 February show that solar wind-cometary plasma interaction boundaries and regions formed around 2015 mid-April and lasted through early 2016 January. At least two regions were observed, separated by an ion-neutral collisionopause boundary. The inner region was located on the nucleus side of the boundary and was characterized by low-energy water-group ions, reduced magnetic field pileup and enhanced electron densities. The outer region was located outside of the boundary and was characterized by reduced electron densities, water-group ions that are accelerated to energies above 100 eV and enhanced magnetic field pileup compared to the inner region. The boundary discussed here is outside of the diamagnetic cavity and shows characteristics similar to observations made on-board the Giotto spacecraft in the ion pileup region at 1P/Halley. We find that the boundary is likely to be related to ion-neutral collisions and that its location is influenced by variability in the neutral density and the solar wind dynamic pressure.
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| 10. |
- Luspay, T., et al.
(författare)
-
Linear Parameter Varying Identification of Freeway Traffic Models
- 2011
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Ingår i: IEEE Transactions on Control Systems Technology. - 1063-6536 .- 1558-0865. ; 19:1, s. 31-45
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with linear parameter varying (LPV) modeling and identification of a generic, second-order freeway traffic flow model. A non-conventional technique is proposed to transform the nonlinear freeway traffic flow model into a parameter-dependent form. The resulting exact LPV model is equivalent to the original nonlinear dynamics. Simplification of the nonlinear model gives rise to the introduction of an approximate LPV description. The application of parameter varying identification approaches are made possible by the transformation. Closed-loop predictor-based subspace identification for LPV systems (PBSID LPV) is applied to estimate the affine parameter matrices of the LPV freeway models developed. If the model structure of the original plant is assumed to be known, this paper shows a solution how to estimate LPV model parameters based on the identified model. Parameter-dependent models are identified and validated using real detector measurement data in order to emphasize the applicability of the kernel PBSID LPV methodology. Comparison with traditional nonlinear parametric identification, generally used in traffic identification, is also provided.
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| 11. |
- Luspay, T., et al.
(författare)
-
Mean-square optimal control of Linear Parameter Varying systems
- 2013
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Ingår i: American Control Conference. - 0743-1619. - 9781479901777 ; , s. 6084 - 6089
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Konferensbidrag (refereegranskat)abstract
- The problem of designing parameter-dependent output feedback controllers by using inaccurate knowledge of the scheduling parameter is addressed in the paper. Discrete time Linear Parameter Varying (LPV) systems are considered with external scheduling variables corrupted by measurement noise. The paper investigates the optimal control of such LPV class in the quadratic mean-square sense. The solution of the controller design problem is obtained as a standard optimization problem subject to Linear Matrix Inequality (LMI) constraints. A comparative simulation example is given to illustrate the proposed methodology and underline the importance of embedding stochastic information in the LPV control design procedure.
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| 12. |
- Luspay, T., et al.
(författare)
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Parameter-dependent modeling of freeway traffic flow
- 2010
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Ingår i: Transportation Research, Part C: Emerging Technologies. - : Elsevier BV. - 0968-090X. ; 18:4, s. 471-488
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Tidskriftsartikel (refereegranskat)abstract
- In the paper a novel non-linear modeling formalism is suggested for freeway traffic flow. A second-order macroscopic model has been transformed into a Linear Parameter Varying (LPV) model. The paper proposes two LPV descriptions for traffic modeling: the first one covers completely the non-linear macroscopic dynamics, while the second one is an approximate description. Real test field topology and measurement data are used for validating the proposed modeling methodology. Simulation examples are given to compare real detector measurements, non-linear and the parameter-dependent responses.
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