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See detailPublic Transport in the Era of ITS: The Role of Public Transport in Sustainable Cities and Regions
Rosello, Xavier; Langeland, Anders; Viti, Francesco UL

in Public Transport in the Era of ITS (2016)

Detailed reference viewed: 123 (5 UL)
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See detailQuadratic Surface Lyapunov Functions in Global Stability Analysis of Saturation Systems
Goncalves, Jorge UL

in Proceedings of the American Control Conference (2001)

Detailed reference viewed: 85 (0 UL)
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See detailQuadratic Surface Lyapunov Functions in the Analysis of Feedback Systems with Double Integrators and Saturations
Goncalves, Jorge UL

in Proceedings of the 10th IEEE Mediterranean Conference on Control and Automation (2002)

Many systems like servo systems, satellites, harddisks, and CD players, can be modeled as linear systems with a single integrator and a saturation. Many times, such systems are controlled with a PI ... [more ▼]

Many systems like servo systems, satellites, harddisks, and CD players, can be modeled as linear systems with a single integrator and a saturation. Many times, such systems are controlled with a PI controller resulting in a feedback interconnection with a double integrator and a saturation. In this paper, we propose a loop transformation that results in bounded operators so that classical analysis tools like mu􀀀-analysis or IQCs can be applied. In order to show boundedness of all operators, we use quadratic surface Lyapunov functions to efficiently check if a double integrator in feedback with a saturation nonlinearity has L2 􀀀-gain less than gamma > 0 􀀀. We show that for many of such systems, the L2 􀀀-gain is non-conservative in the sense that this is approximately equal to the lower bound obtained by replacing the saturation with a constant gain of . [less ▲]

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See detailQualifying and Measuring Transparency: A Medical Data System Case Study
Spagnuelo, Dayana; Bartolini, Cesare UL; Lenzini, Gabriele UL

in Computers and Security (2020)

Transparency is a data processing principle enforced by the GDPR but purposely left open to interpretation. As such, the means to adhere to it are left unspecified. Article 29 Working Party provides ... [more ▼]

Transparency is a data processing principle enforced by the GDPR but purposely left open to interpretation. As such, the means to adhere to it are left unspecified. Article 29 Working Party provides practical guidance on how to interpret transparency, however there are no defined requirements nor ways to verify the quality of the implementation of transparency. We address this problem. We discuss and define applicable metrics for transparency, propose how measurement can be conducted in an operative system, and suggest a practical way in which these metrics can be interpreted in order to increase confidence that transparency is realised in a system. [less ▲]

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See detailQuantifying partial observability in network sensor location problems
Viti, Francesco UL; Rinaldi, Marco; Corman, Francesco

Scientific Conference (2013)

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See detailQuantitative Assignment of Reaction Directionality in a Multicompartmental Human Metabolic Reconstruction
Haraldsdottir, Hulda UL; Thiele, Ines UL; Fleming, Ronan MT UL

in Biophysical Journal (2012), 102(8), 17031711

Reaction directionality is a key constraint in the modeling of genome-scale metabolic networks. We thermodynamically constrained reaction directionality in a multicompartmental genome-scale model of human ... [more ▼]

Reaction directionality is a key constraint in the modeling of genome-scale metabolic networks. We thermodynamically constrained reaction directionality in a multicompartmental genome-scale model of human metabolism, Recon 1, by calculating, in vivo, standard transformed reaction Gibbs energy as a function of compartment-specific pH, electrical potential, and ionic strength. We show that compartmental pH is an important determinant of thermodynamically determined reaction directionality. The effects of pH on transport reaction thermodynamics are only seen to their full extent when metabolites are represented as pseudoisomer groups of multiple protonated species. We accurately predict the irreversibility of 387 reactions, with detailed propagation of uncertainty in input data, and manually curate the literature to resolve conflicting directionality assignments. In at least half of all cases, a prediction of a reversible reaction directionality is due to the paucity of compartment-specific quantitative metabolomic data, with remaining cases due to uncertainty in estimation of standard reaction Gibbs energy. This study points to the pressing need for 1), quantitative metabolomic data, and 2), experimental measurement of thermochemical properties for human metabolites. [less ▲]

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See detailQuasi-dynamic traffic assignment with spatial queueing, control and blocking back
Smith, Mike; Huang, Wei; Viti, Francesco UL et al

in Transportation Research. Part B, Methodological (2019)

This paper introduces a steady-state, fixed (or inelastic) demand equilibrium model with explicit link-exit capacities, explicit bottleneck or queueing delays and explicit bounds on queue storage ... [more ▼]

This paper introduces a steady-state, fixed (or inelastic) demand equilibrium model with explicit link-exit capacities, explicit bottleneck or queueing delays and explicit bounds on queue storage capacities. The model is a quasi-dynamic model. The link model at the heart of this quasi-dynamic equilibrium model is a spatial queueing model, which takes account of the space taken up by queues both when there is no blocking back and also when there is blocking back. The paper shows that if this quasi-dynamic model is utilised then for any feasible demand there is an equilibrium solution, provided (i) queue storage capacities are large or (ii) prices are used to help impose capacity restrictions; the prices either remove queueing delays entirely or just reduce spatial queues sufficiently to ensure that blocking back does not occur at equilibrium. Similar results, but now involving the P0 control policy (introduced in Smith (1979a, 1987)) and two new variations of this policy (i.e., the spatial P0 control policy, and the biased spatial P0 control policy) are obtained. In these results, the control policies allow green-times to vary in response to prices as well as spatial queueing delays. These three policies are also tested on a small simple network. In these tests, the biased spatial version of P0 is much the best in reducing equilibrium delays (on this simple network). The paper further illustrates how the spatial queueing model works on simple networks with different merge models; it is demonstrated that equilibrium may be prevented by certain (fixed ratio) merge models. It is also shown in this case that equilibrium may be imposed on just the controlled area itself by a variety of (merge model, gating strategy) combinations. Opportunities for developing such combined gating and merging control strategies are finally discussed. [less ▲]

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See detailQuasicontinuum methods for planar beam lattices (abstract)
Beex, Lars UL; Kerfriden, Pierre; Heaney, Claire et al

Scientific Conference (2015, July)

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See detailQuizbot: Exploring Formative Feedback with Conversational Interfaces
Vijayakumar, Bharathi UL; Höhn, Sviatlana UL; Schommer, Christoph UL

in Vijayakumar, Bharathi; Höhn, Sviatlana; Schommer, Christoph (Eds.) Proceedings of the (2018)

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See detailRandomised controlled non-inferiority trial of primary care-based facilitated access to an alcohol reduction website: cost-effectiveness analysis
Hunter, Rachael; Wallace, Paul; Struzzo, Pierluigi et al

in BMJ Open (2017), 7(11),

Objectives To evaluate the 12-month costs and quality-adjusted life years (QALYs) gained to the Italian National Health Service of facilitated access to a website for hazardous drinkers compared with a ... [more ▼]

Objectives To evaluate the 12-month costs and quality-adjusted life years (QALYs) gained to the Italian National Health Service of facilitated access to a website for hazardous drinkers compared with a standard face-to-face brief intervention (BI). Design Randomised 1:1 non-inferiority trial. Setting Practices of 58 general practitioners (GPs) in Italy. Participants Of 9080 patients (>18 years old) approached to take part in the trial, 4529 (49·9%) logged on to the website and 3841 (84.8%) undertook online screening for hazardous drinking. 822 (21.4%) screened positive and 763 (19.9%) were recruited to the trial. Interventions Patients were randomised to receive either a face-to-face BI or access via a brochure from their GP to an alcohol reduction website (facilitated access). Primary and secondary outcome measures The primary outcome is the cost per QALY gained of facilitated access compared with face-to-face. A secondary analysis includes total costs and benefits per 100 patients, including number of hazardous drinkers prevented at 12 months. Results The average time required for the face-to-face BI was 8 min (95% CI 7.5 min to 8.6 min). Given the maximum time taken for facilitated access of 5 min, face-to-face is an additional 3 min: equivalent to having time for another GP appointment for every three patients referred to the website. Complete case analysis adjusting for baseline the difference in QALYs for facilitated access is 0.002 QALYs per patient (95% CI −0.007 to 0.011). Conclusions Facilitated access to a website to reduce hazardous drinking costs less than a face-to-face BI given by a GP with no worse outcomes. The lower cost of facilitated access, particularly in regards to investment of time, may facilitate the increase in provision of BIs for hazardous drinking. Trial registration number NCT01638338;Post-results. [less ▲]

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See detailRationalised computational time in fracture simulation: adaptive model reduction and domain decomposition
Goury, Olivier; Kerfriden, Pierre; Margetts, Lee et al

Scientific Conference (2011, June)

Detailed reference viewed: 79 (1 UL)
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See detailRe-Interpretation of Conceptualisation - A Contribution to the Advance of Design Theory
Bender, Bernd; Blessing, Lucienne UL

in Lindemann, Udo (Ed.) Human Behaviour in Design. Individuals, Teams, Tools (2003)

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See detailReachability analysis of continuous time piecewise linear systems
Hamadeh, A. O.; Goncalves, Jorge UL

in Proceedings of the 44th IEEE Conference on Decision and Control and European Control Conference (2005)

This paper presents a new approach to the reachability problem for a class of hybrid systems called Piecewise Linear Systems (PLS). The principal tool used is the impact map between switching surfaces ... [more ▼]

This paper presents a new approach to the reachability problem for a class of hybrid systems called Piecewise Linear Systems (PLS). The principal tool used is the impact map between switching surfaces. The method consists of specifying a ellipsoidal set on the initial switching surface and finding upper- and lower-bound estimates of the possible reach sets using tools such as the S-procedure to set up linear matrix inequalities, of which numerical solutions are then computed. [less ▲]

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See detailReachability analysis of continuous-time piecewise affine systems
Hamadeh, A. O.; Goncalves, Jorge UL

in Automatica (2008), 44(12), 3189-3194

This paper proposes an algorithm for the characterization of reachable sets of states for continuous-time piecewise affine systems. Given a model of the system and a bounded set of possible initial states ... [more ▼]

This paper proposes an algorithm for the characterization of reachable sets of states for continuous-time piecewise affine systems. Given a model of the system and a bounded set of possible initial states, the algorithm employs an LMI approach to compute both upper and lower bounds on reachable regions. Rather than performing computations in the state-space, this method uses impact maps to find the reachable sets on the switching surfaces of the system. This tool can then be used to deduce safety and performance results about the system. [less ▲]

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See detailReal Time Holding Control for Multiline Networks
Laskaris, Georgios UL; Cats, Oded; Jenelius, Erik et al

Poster (2020, January 12)

We introduce a rule based multiline holding criterion for regularity in branch and trunk networks accounting for all passenger groups. On the shared transit corridor, we consider synchronization at the ... [more ▼]

We introduce a rule based multiline holding criterion for regularity in branch and trunk networks accounting for all passenger groups. On the shared transit corridor, we consider synchronization at the merging or the diverging stop. The decision between holding for regularity or synchronization is taken by comparing the expected passenger cost of each control action. The proposed criterion is tested through simulation in a synthetic double fork network with different shares of transferring passengers, control schemes for regularity and synchronization. The results show that multiline control outperforms the state of the art schemes at the network level, stemming from benefits occurring at the first part of the route and the shared transit corridor and a 3.5% more stable joint headway compared to the other schemes. Additionally, it is advised to perform the synchronization at the diverging stop, as it proves to result in a more stable transferring time equal to the joint frequency of the corridor while reducing the transfer time variability up to -42.7%. [less ▲]

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See detailA real time hybrid controller for regulating bus operations and reducing stops at signals
Laskaris, Georgios UL; Seredynski, Marcin; Viti, Francesco UL

Scientific Conference (2019, June)

We propose a hybrid controller which consists of holding and a Driver Advisory System (DAS). It combines the objectives of seeking the regularization of operation and the reduction of stop and go actions ... [more ▼]

We propose a hybrid controller which consists of holding and a Driver Advisory System (DAS). It combines the objectives of seeking the regularization of operation and the reduction of stop and go actions at signalized intersections. A simple headway based holding criterion is applied at stops to define the time needed to maintain even spaced headways between buses and additionally a speed recommendation is given to traverse during green indication at the downstream signalized intersection. The controller is tested using simulation for a bus line of the city of Luxembourg, Luxembourg and compared to a benchmark scenario, the single application of bus holding, two advisory systems and different levels of transit signal priority. Results show that there are additional benefits compared to traditional holding in terms of regularity while similar performance to strong transit signal priority is achieved in terms of time spent at traffic lights. [less ▲]

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See detailReal time multiline holding control for networks with shared transit corridor
Laskaris, Georgios UL; Cats, Oded; Jenelius, Erik et al

Scientific Conference (2018, September 05)

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See detailReal-time Error Control for Surgical Simulation
Phuoc Bui, Huu; Tomar, Satyendra; Courtecuisse, Hadrien et al

in IEEE Transactions on Biomedical Engineering (2017)

To present the first real-time a posteriori error-driven adaptive finite element approach for realtime simulation and to demonstrate the method on a needle insertion problem. Methods: We use corotational ... [more ▼]

To present the first real-time a posteriori error-driven adaptive finite element approach for realtime simulation and to demonstrate the method on a needle insertion problem. Methods: We use corotational elasticity and a frictional needle/tissue interaction model. The problem is solved using finite elements within SOFA. The refinement strategy relies upon a hexahedron-based finite element method, combined with a posteriori error estimation driven local h-refinement, for simulating soft tissue deformation. Results: We control the local and global error level in the mechanical fields (e.g. displacement or stresses) during the simulation. We show the convergence of the algorithm on academic examples, and demonstrate its practical usability on a percutaneous procedure involving needle insertion in a liver. For the latter case, we compare the force displacement curves obtained from the proposed adaptive algorithm with that obtained from a uniform refinement approach. Conclusions: Error control guarantees that a tolerable error level is not exceeded during the simulations. Local mesh refinement accelerates simulations. Significance: Our work provides a first step to discriminate between discretization error and modeling error by providing a robust quantification of discretization error during simulations. [less ▲]

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See detailReal-time error controlled adaptive mesh refinement in surgical simulation: Application to needle insertion simulation
Bui, Huu Phuoc; Tomar, Satyendra UL; Courtecuisse, Hadrien et al

in IEEE Transactions on Biomedical Engineering (n.d.)

This paper presents the first real-time discretisation-error-driven adaptive finite element approach for corotational elasticity problems involving strain localisation. We propose a hexahedron-based ... [more ▼]

This paper presents the first real-time discretisation-error-driven adaptive finite element approach for corotational elasticity problems involving strain localisation. We propose a hexahedron-based finite element method combined with local oct-tree $h$-refinement, driven by a posteriori error estimation, for simulating soft tissue deformation. This enables to control the local error and global error level in the mechanical fields during the simulation. The local error level is used to refine the mesh only where it is needed, while maintaining a coarser mesh elsewhere. We investigate the convergence of the algorithm on academic examples, and demonstrate its practical usability on a percutaneous procedure involving needle insertion in a liver. For the latter case, we compare the force displacement curves obtained from the proposed adaptive algorithm with that obtained from a uniform refinement approach. [less ▲]

Detailed reference viewed: 540 (63 UL)