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See detailOptimal mix of funded and unfunded pension systems: The case of Luxembourg
Guigou, Jean-Daniel UL; Lovat, Bruno; Schiltz, Jang UL

in Pensions (2012), 17(4), 208-222

Financing of the Luxembourg pension system is based on a pay-as-you-go (PAYG) system and hence on an intergenerational contract. As is the case for most other European countries, this system will be ... [more ▼]

Financing of the Luxembourg pension system is based on a pay-as-you-go (PAYG) system and hence on an intergenerational contract. As is the case for most other European countries, this system will be exposed to the effects of demographic ageing over the coming decades. The aim of this article is to develop a model that allows evaluating the effi ciency of a diversifi ed pension system fi nanced partly by a PAYG scheme and partly by capitalization. The efficiency is measured by the long-term sustainability of the system. We compare the sustainability of our model with the one of a pure PAYG system. [less ▲]

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See detailOptimal mix of funded and unfunded pension systems: the case of Luxembourg
Guigou, Jean-Daniel UL; Lovat, Bruno; Schiltz, Jang UL

E-print/Working paper (2012)

Financing of the Luxembourg pension system is based on a pay-as-you-go (PAYG) system <br />and hence on an inter-generational contract. As is the case for most other European <br />countries, this system ... [more ▼]

Financing of the Luxembourg pension system is based on a pay-as-you-go (PAYG) system <br />and hence on an inter-generational contract. As is the case for most other European <br />countries, this system will be exposed to the effects of demographic ageing over the coming <br />decades. <br />The aim of this paper is to develop a model that allows to evaluate the efficiency of a <br />diversified pension system financed partly by a pay-as-you-go scheme and partly by <br />capitalisation. The efficiency is measured by the long term sustainability of the system. We <br />compare the sustainability of our model to the one of a pure pay-as-you-go system. [less ▲]

Detailed reference viewed: 89 (4 UL)
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See detailOptimal Mix of Funded and Unfunded Pension Systems: the Case of Luxembourg
Guigou, Jean-Daniel UL; Lovat, Bruno; Schiltz, Jang UL

Scientific Conference (2010, May 20)

Detailed reference viewed: 79 (0 UL)
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See detailOptimal mix of funded and unfunded pension systems: The case of Luxembourg
Schiltz, Jang UL; Guigou, Jean-Daniel UL; Lovat, Bruno

Scientific Conference (2014, June 20)

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See detailOptimal Motion Planning and Control with Safety Guarantees for Aerial Robots
Castillo López, Manuel UL

Doctoral thesis (2021)

Autonomous aerial robots are expected to revolutionize many industries, such as construction, transportation or even space exploration. However, to target an industry where different robots and humans are ... [more ▼]

Autonomous aerial robots are expected to revolutionize many industries, such as construction, transportation or even space exploration. However, to target an industry where different robots and humans are meant to share the same space our algorithms need to provide safety and efficiency guarantees. Navigating autonomously in these kind of environments poses a great challenge. We may face a significant number of obstacles, and we can only estimate where they are and where they are expected to be, but not exactly. Dealing with these uncertainties is a challenging problem in most robotics applications, including motion planning and control. During the last decade, major contributions have established the theoretical basis upon which optimal motion planning and control with safety guarantees can be achieved. However, they involve a high computational cost that scales exponentially with the number of obstacles, rendering a limited domain of robotic applications. The main contribution of this thesis provides an efficient, scalable and safe approximation to this problem, allowing its application to embedded systems with fast dynamics such as aerial robots. This thesis also includes an additional contribution that allow these methods to plan longer trajectories with a minimal computational footprint, allowing to better anticipate evasive maneuvers. These contributions have been validated mathematically, in simulation and in real-time operation on aerial robots, handling uncertain dynamic obstacles such as pedestrians. [less ▲]

Detailed reference viewed: 84 (6 UL)
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See detailOptimal multi-line bus dispatching at terminals with electric charging scheduling constraints
Rinaldi, Marco UL; Parisi, Federico; D'Ariano, Andrea et al

Scientific Conference (2018, July)

We consider the problem of optimally determining the sequence of electric and conventional internal combustion buses departing from a multi-line bus terminal, considering both service constraints ... [more ▼]

We consider the problem of optimally determining the sequence of electric and conventional internal combustion buses departing from a multi-line bus terminal, considering both service constraints (schedule adherence) and energy constraints (electric bus charging status, bus recharging scheduling in capacitated facilities). The problem is formulated as a Mixed Integer Linear Program, with the objective of minimizing the total operational cost for the bus lines in question. System dynamics are captured by twenty sets of constraints, ranging from scheduling adherence to discharge-recharge dynamics. Individual operational costs at the bus level (cost of running an electric / non electric bus per km, cost of recharging) and at the trip level (penalty due to failed schedule adherence) are fully parametrised, allowing for extensive sensitivity analysis. We investigate a real-life case study based in the city of Luxembourg, where two charging stations have been installed in the central station’s bus terminal. Through the model we investigate: i) the minimum amount of electric buses necessary to perform a day’s schedule for two currently partially electrified lines, without resorting to conventional internal combustion alternatives; ii) the impact of electrifying two additional lines, specifically considering the trade-offs related to either adding new buses or new charging stations at the bus terminal. [less ▲]

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See detailOptimal Multiuser Transmit Beamforming: A Difficult Problem with a Simple Solution Structure [Lecture Notes]
Björnson, Emil; Bengtsson; Ottersten, Björn UL

in IEEE Signal Processing Magazine (2014), 31(4), 142-148

Transmit beamforming is a versatile technique for signal transmission from an array of antennas to one or multiple users [1]. In wireless communications, the goal is to increase the signal power at the ... [more ▼]

Transmit beamforming is a versatile technique for signal transmission from an array of antennas to one or multiple users [1]. In wireless communications, the goal is to increase the signal power at the intended user and reduce interference to nonintended users. A high signal power is achieved by transmitting the same data signal from all antennas but with different amplitudes and phases, such that the signal components add coherently at the user. Low interference is accomplished by making the signal components add destructively at nonintended users. This corresponds mathematically to designing beamforming vectors (that describe the amplitudes and phases) to have large inner products with the vectors describing the intended channels and small inner products with nonintended user channels. [less ▲]

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See detailOptimal Operation of Nearly Zero Energy Buildings using Mixed Integer Linear Programming
Rafii-Tabrizi, Sasan UL; Hadji-Minaglou, Jean-Régis UL; Scholzen, Frank UL et al

Scientific Conference (2019, September 10)

This paper proposes a deterministic mixed integer linear programming model for the optimal operation of an energy system providing thermal and electrical energy for a residential and commercial nearly ... [more ▼]

This paper proposes a deterministic mixed integer linear programming model for the optimal operation of an energy system providing thermal and electrical energy for a residential and commercial nearly zero energy building. The space heating and space cooling demand of the buildings is simulated using a resistive-capacitive model within a quadratic program respectively. Thermal energy for space heating, space cooling and domestic hot water is buffered in thermal energy storage systems. A dual source heat pump provides thermal energy for space heating and domestic hot water, whereas space cooling is covered by an underground ice storage. The environmental energy sources of the heat pump are ice storage or wind infrared sensitive collectors. The collectors are further used to regenerate the ice storage. Further space heating demands are covered by a combined heat and power unit, which also produces electricity. Photovoltaic panels produce electrical energy which can be stored in a battery storage system. The electrical energy system is capable of selling and buying electricity from the public power grid. A mixed integer linear programming model is developed to minimise the operation cost of the combined commercial and residential nearly zero energy building over a scheduling horizon of 24h. The developed model is tested on two typical days, which are representative for the summer and winter season. Furthermore, it is investigated how external incentives such as varying electricity prices impact the optimal scheduling of the energy system. [less ▲]

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See detailOptimal output consensus control and outlier detection
Thunberg, Johan UL; Hu, X.

in Proceedings of the 19th International Symposium on Mathematical Theory of Networks and Systems (2010)

In this paper we study the output consensus problem for systems of agents with linear continuous time invariant dynamics, and derive control laws that minimize a conical combination of the energies of the ... [more ▼]

In this paper we study the output consensus problem for systems of agents with linear continuous time invariant dynamics, and derive control laws that minimize a conical combination of the energies of the agents control signals, while only using local information. We show that the optimal control requires the connectivity graph to be complete and in general requires measurements of the state errors. We identify the cases where the optimal control is only based on output errors, and show that in the infinite time horizon case, the optimal control can always be expressed as a dynamic control that is only based on the output errors. We also give a Lemma for the position of the equilibrium point for a large class of agent dynamics. As a second part of this paper we consider the problem of outlier detection, in which an agent wants to deduce if an other agent is using the consensus controller, or if it is an outlier that uses a different controller. We introduce the outlier detection equation. [less ▲]

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See detailOptimal output consensus control for systems of agents with continuous linear dynamics
Thunberg, Johan UL; Hu, X.

in Proceedings of 18th IFAC World Congress (2011)

In this paper we study the output consensus problem for systems of agents with linear continuous, time invariant dynamics. We derive control laws with minimal energy that solves the problem, while using ... [more ▼]

In this paper we study the output consensus problem for systems of agents with linear continuous, time invariant dynamics. We derive control laws with minimal energy that solves the problem, while using only relative information. Instead of considering a fixed communication topology for the agents, and derive the optimal control for that topology, we derive the optimal control law for any communication topology between the agents. We show that the optimal control uses only relative information but requires the connectivity graph to be complete and in general requires measurements of the state errors. We identify the cases where the optimal control is only based on output errors, and show that in the infinite time horizon case, the optimal controller can always be expressed as a dynamic controller that is only based on the output errors. Regarding the theoretic contributions of this paper, the control laws are derived using methods from linear vector space optimization and are given in closed form. To the authors knowledge these methods have not been used within this context before. [less ▲]

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See detailOptimal output consensus for linear systems: a topology free approach
Thunberg, Johan UL; Hu, Xiaoming

in Automatica (2016), 68

In this paper, for any homogeneous system of agents with linear continuous time dynamics, we formulate an optimal control problem. In this problem a convex cost functional of the control signals of the ... [more ▼]

In this paper, for any homogeneous system of agents with linear continuous time dynamics, we formulate an optimal control problem. In this problem a convex cost functional of the control signals of the agents shall be minimized, while the outputs of the agents shall coincide at some given finite time. This is an instance of the rendezvous or finite time consensus problem. We solve this problem without any constraints on the communication topology and provide a solution as an explicit feedback control law for the case when the dynamics of the agents is output controllable. It turns out that the communication graph topology induced by the solution is complete. Based on this solution for the finite time consensus problem, we provide a solution to the case of infinite time horizon. Furthermore, we investigate under what circumstances it is possible to express the controller as a feedback control law of the output instead of the states. [less ▲]

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See detailOptimal positioning of surveillance UGVs
Nilsson, U.; Ögren, P.; Thunberg, Johan UL

in Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems (2008)

Unmanned ground vehicles (UGVs) equipped with surveillance cameras present a flexible complement to the numerous stationary sensors being used in security applications today. However, to take full ... [more ▼]

Unmanned ground vehicles (UGVs) equipped with surveillance cameras present a flexible complement to the numerous stationary sensors being used in security applications today. However, to take full advantage of the flexibility and speed offered by a group of UGV platforms, a fast way to compute desired camera locations that cover or surround a set of buildings e.g., in response to an alarm, is needed. In this paper we focus on two problems. The first is how to create a line-of-sight perimeter around a given set of buildings with a minimal number of UGVs. The second problem is how to find UGV positions such that a given set of walls are covered by the cameras while taking constraints in terms of zoom, range, resolution and field of view into account. For the first problem we propose a polynomial time algorithm and for the second problem we extend our previous work to include zoom cameras and furthermore provide a theoretical analysis of the approach itself. A number of examples are presented to illustrate the two algorithms. [less ▲]

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See detailOptimal power and efficiency of odd engines
Fodor, Etienne UL; Souslov2, Anton

in Physical Review. E (2021)

Odd materials feature antisymmetric response to perturbations. This anomalous property can stem from the nonequilibrium activity of their components, which is sustained by an external energy supply. These ... [more ▼]

Odd materials feature antisymmetric response to perturbations. This anomalous property can stem from the nonequilibrium activity of their components, which is sustained by an external energy supply. These materials open the door to designing innovative engines which extract work by applying cyclic deformations, without any equivalent in equilibrium. Here, we reveal that the efficiency of such energy conversion, from local activity to macroscopic work, can be arbitrarily close to unity when the cycles of deformation are properly designed. We illustrate these principles in some canonical viscoelastic materials, which leads us to identify strategies for optimizing power and efficiency according to material properties and to delineate guidelines for the design of more complex odd engines. [less ▲]

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See detailOptimal Priority Assignment for Real-Time Systems: A Coevolution-Based Approach
Lee, Jaekwon UL; Shin, Seung Yeob UL; Nejati, Shiva et al

in Empirical Software Engineering (2022), 27

In real-time systems, priorities assigned to real-time tasks determine the order of task executions, by relying on an underlying task scheduling policy. Assigning optimal priority values to tasks is ... [more ▼]

In real-time systems, priorities assigned to real-time tasks determine the order of task executions, by relying on an underlying task scheduling policy. Assigning optimal priority values to tasks is critical to allow the tasks to complete their executions while maximizing safety margins from their specified deadlines. This enables real-time systems to tolerate unexpected overheads in task executions and still meet their deadlines. In practice, priority assignments result from an interactive process between the development and testing teams. In this article, we propose an automated method that aims to identify the best possible priority assignments in real-time systems, accounting for multiple objectives regarding safety margins and engineering constraints. Our approach is based on a multi-objective, competitive coevolutionary algorithm mimicking the interactive priority assignment process between the development and testing teams. We evaluate our approach by applying it to six industrial systems from different domains and several synthetic systems. The results indicate that our approach significantly outperforms both our baselines, i.e., random search and sequential search, and solutions defined by practitioners. Our approach scales to complex industrial systems as an offline analysis method that attempts to find near-optimal solutions within acceptable time, i.e., less than 16 hours. [less ▲]

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See detailOptimal Randomized Partial Checking for Decryption Mix Nets
Haines, Thomas; Mueller, Johannes UL

in Information Security and Privacy - 26th Australasian Conference, ACISP 2021, Virtual Event, December 1-3, 2021, Proceedings (2021)

Detailed reference viewed: 41 (0 UL)
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See detailOptimal rank-based inference for spherical location
Ley, Christophe; Swan, Yvik UL; Thiam, Baba et al

in Statistica Sinica (2013), 23

Detailed reference viewed: 41 (0 UL)
See detailOptimal rates, Fourth Moment Theorems and non-linear functionals of Brownian local times
Campese, Simon UL

Doctoral thesis (2014)

The present dissertation provides contributions to three distinct topics of modern stochastic analysis, namely: (a) optimal rates of convergence in multidimensional central limit theorems (CLTs) on a ... [more ▼]

The present dissertation provides contributions to three distinct topics of modern stochastic analysis, namely: (a) optimal rates of convergence in multidimensional central limit theorems (CLTs) on a Gaussian space, (b) Fourth Moment Theorems (and associated multidimensional generalisations) in the framework of the chaos of a Markov generator and (c) CLTs for non-linear functionals of Brownian local times. [less ▲]

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See detailOptimal Relay Selection Strategy for Joint Data and Energy Transfer in Wireless Systems
Gautam, Sumit UL; Lagunas, Eva UL; Chatzinotas, Symeon UL et al

Presentation (2018, April 17)

We study a problem of relay selection in a two-hop amplify-and-forward (AF) enabled relaying network for facilitating simultaneous Wireless Transmission of Information and Energy (Wi-TIE) to a destination ... [more ▼]

We study a problem of relay selection in a two-hop amplify-and-forward (AF) enabled relaying network for facilitating simultaneous Wireless Transmission of Information and Energy (Wi-TIE) to a destination able to perform both information processing and energy harvesting concurrently. Considering the time switching (TS) and power splitting (PS) based Wi-TIE schemes, we formulate an optimization problem to maximize the overall user data rate while ensuring a minimum harvested power. In this context, we obtain suitable closed form solution and demonstrate through simulation results the Rate-Energy (R-E) trade-off in two different scenarios: (i) with only the relay assisted link, and (ii) with the direct link together with the relay assisted link. [less ▲]

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See detailOptimal Resource Allocation for NOMA-Enabled Cache Replacement and Content Delivery
Lei, Lei UL; Vu, Thang Xuan UL; Xiang, Lin UL et al

in IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (IEEE PIMRC 2019) (2019, September)

Detailed reference viewed: 131 (12 UL)