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See detailCondition assessment of concrete structures and bridges using vibration monitoring in comparison to changes in their static properties
Bungard, Volker UL

Doctoral thesis (2010)

The thesis deals with the non-destructive condition assessment of civil engineering structures made of reinforced and prestressed concrete as well as bridges and concentrates on a comparison of static and ... [more ▼]

The thesis deals with the non-destructive condition assessment of civil engineering structures made of reinforced and prestressed concrete as well as bridges and concentrates on a comparison of static and dynamic investigation methods. The main questions discuss the sensitivity of changes in static as well as in dynamic properties during the mechanical lifetime of those types of structures under laboratory conditions, the sensitivity of these changes when testing in-situ and the dimension of undesired environmental influences on the dynamic properties. Therefore, a gradually loaded laboratory reinforced concrete beam (cp. chapter 7) and a reinforced as well as a prestressed concrete slab (cp. chapter 8) are investigated for changes in their static and dynamic parameters until reaching their ultimate loads. Furthermore, a successively damaged and stepwise loaded laboratory reinforced concrete slab and a prestressed concrete slab (cp. also chapter 8) are under investigation and also compared in changes in their static as well as in dynamic properties during their lifetimes. By means of static and dynamic tests on a successively damaged and stepwise loaded prestressed concrete bridge (cp. chapter 9) it was possible to investigate the amount of changes in static and dynamic properties for a real in-situ object. A long-term measurement of a composite bridge (cp. chapter 10) demonstrates the environmental influences on the static and dynamic properties of a system which have to be considered when conducting comparative non-destructive condition assessment techniques on real objects. All tests are calculated respectively simulated by the method of the integration of stress (cp. chapter 6) or the finite element method by using the softwares ANSYS and SOFISTIK. Furthermore, measured eigenfrequencies and modeshapes are used to adapt finite element models with the aim to improve the model or to locate and quantify damaged areas. The work is a contribution to the application of non-destructive static and dynamic condition assessment methods on civil engineering structures made of concrete in the sector of civil engineering. [less ▲]

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See detailConfined in a Fiber: Realizing Flexible Gas Sensors by Electrospinning Liquid Crystals
Reyes, Catherine UL

Doctoral thesis (2019)

Liquid crystalline phases (LCs) readily exhibit optical responsivity to small fluctuations in their immediate environment. By encapsulating LC phase forming compounds within polymer fibers through the ... [more ▼]

Liquid crystalline phases (LCs) readily exhibit optical responsivity to small fluctuations in their immediate environment. By encapsulating LC phase forming compounds within polymer fibers through the electrospinning process (a fiber spinning method known for being a fast way of forming chemically diverse non-woven mats), it is possible to create functionalized LC-polymer fiber mats that are responsive as well. As these fiber mats can be handled macroscopically, a usercan observe the responses of the mats macroscopically without the need for bulky electronics. This thesis presents several non-woven fiber mats that were coaxially electrospun to contain LC within their individual polymer fibers cores for use as novel volatile organic compound (VOC) sensors. The mats are flexible, lightweight, and shown to both macroscopically and microscopically respond to toluene gas. Such gas responsive mats may be incorporated into garments for visually alerting the wearer when they are exposed to harmful levels of VOCs for example. Additionally, the interaction and re-prioritization of several electrospinning variables (from the chemistry based to the processing based) for forming the LC-mats are also discussed. The balance of these variables determines whether a wide range of phenomena occur during fiber formation. For instance, unexpected phase separation between the polymer sheath solution and the LC core can mean the difference between forming fully dried fibrous mats and wet/meshed films. A chapter is devoted to discussing the impact that solvent miscibility with an LC can have on fiber production, including also the effect that water can have when condensed into the electrospinning coaxial jet. The fiber shapes that the polymer fiber sheaths adopt (beaded versus non-beaded), as well as the continuity of the LC core, will influence the visual app earance of the mats. These optical properties, in turn, influence the mats’ responsivity to gases and whether the responses can be macroscopically observed with or without additional polarizers. During two types of gas sensing experiments --mats exposed to gas when contained in a cell, and mats exposed to gas diffused in ambient air without containment, we see that not all fibers within a mat respond at the same time. Moreover, different segments of the fibers within the same non-woven mat also show slightly different rates of response due to variations in fiber thickness, LC content, and whether the fiber cores had variations in LC filling (i.e. LC director twists, and gaps). [less ▲]

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See detailConsensus and Pursuit-Evasion in Nonlinear Multi-Agent Systems
Thunberg, Johan UL

Doctoral thesis (2014)

Within the field of multi-agent systems theory, we study the problems of consensus and pursuit-evasion. In our study of the consensus problem, we first provide some theoretical results and then consider ... [more ▼]

Within the field of multi-agent systems theory, we study the problems of consensus and pursuit-evasion. In our study of the consensus problem, we first provide some theoretical results and then consider the problem of consensus on SO(3) or attitude synchronization. In Chapter 2, for agents with states in Rm, we present two theorems along the lines of Lyapunov’s second method that, under different conditions, guarantee asymptotic state consensus in multi-agent systems where the interconnection topologies are switching. The first theorem is formulated by using the states of the agents in the multiagent system, whereas the second theorem is formulated by using the pairwise states for pairs of agents in the multi-agent system. In Chapter 3, the problem of consensus on SO(3) for a multi-agent system with directed and switching interconnection topologies is addressed. We provide two different types of kinematic control laws for a broad class of local representations of SO(3). The first control law consists of a weighted sum of pairwise differences between positions of neighboring agents, expressed as coordinates in a local representation. The structure of the control law is well known in the consensus community for being used in systems of agents in the Euclidean space, and here we show that the same type of control law can be used in the context of consensus on SO(3). In a later part of this chapter, based on the kinematic control laws, we introduce torque control laws for a system of rigid bodies in space and show that the system reaches consensus when these control laws are used. Chapter 4 addresses the problem of consensus on SO(3) for networks of uncalibrated cameras. Under the assumption that each agent uses a camera in order to measure its rotation, we prove convergence to the consensus set for two types of kinematic control laws, where only conjugate rotation matrices are available for the agents. In these conjugate rotations, the rotation matrix can be seen as distorted by the (unknown) intrinsic parameters of the camera. For the conjugate rotations we introduce distorted versions of well known local parameterizations of SO(3) and show consensus by using control laws that are similar to the ones in Chapter 3, with the difference that the distorted local representations are used instead. In Chapter 5, we study the output consensus problem for homogeneous systems of agents with linear continuous time-invariant dynamics. We derive control laws that solve the problem, while minimizing a cost functional of the control signal. Instead of considering a fixed communication topology for the system, we derive the optimal control law without any restrictions on the topology. We show that for all linear output controllable homogeneous systems, the optimal control law uses only relative information but requires the connectivity graph to be complete and in general requires measurements of the state errors. We identify cases where the optimal control law is only based on output errors. In Chapter 6, we address the multi-pursuer version of the visibility pursuit-evasion problem in polygonal environments. By discretizing the problem and applying a Mixed Integer Linear Programming (MILP) framework, we are able to address problems requiring so-called recontamination and also impose additional constraints, such as connectivity between the pursuers. The proposed MILP formulation is less conservative than solutions based on graph discretizations of the environment, but still somewhat more conservative than the original underlying problem. It is well known that MILPs, as well as multi-pursuer pursuit-evasion problems, are NP-hard. Therefore we apply an iterative Receding Horizon Control (RHC) scheme, where a number of smaller MILPs are solved over shorter planning horizons. The proposed approach is illustrated by a number of solved examples. [less ▲]

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See detailConsistent Estimation of Gibbs Energy Using Component Contributions
Noor, Elad; Haraldsdottir, Hulda UL; Milo, Ron et al

in PLoS Computational Biology (2013), 9(7), 1003098

Standard Gibbs energies of reactions are increasingly being used in metabolic modeling for applying thermodynamic constraints on reaction rates, metabolite concentrations and kinetic parameters. The ... [more ▼]

Standard Gibbs energies of reactions are increasingly being used in metabolic modeling for applying thermodynamic constraints on reaction rates, metabolite concentrations and kinetic parameters. The increasing scope and diversity of metabolic models has led scientists to look for genome-scale solutions that can estimate the standard Gibbs energy of all the reactions in metabolism. Group contribution methods greatly increase coverage, albeit at the price of decreased precision. We present here a way to combine the estimations of group contribution with the more accurate reactant contributions by decomposing each reaction into two parts and applying one of the methods on each of them. This method gives priority to the reactant contributions over group contributions while guaranteeing that all estimations will be consistent, i.e. will not violate the first law of thermodynamics. We show that there is a significant increase in the accuracy of our estimations compared to standard group contribution. Specifically, our cross-validation results show an 80% reduction in the median absolute residual for reactions that can be derived by reactant contributions only. We provide the full framework and source code for deriving estimates of standard reaction Gibbs energy, as well as confidence intervals, and believe this will facilitate the wide use of thermodynamic data for a better understanding of metabolism. [less ▲]

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See detailConstructing IGA-suitable planar parameterization from complex CAD boundary by domain partition and global/local optimization
Xu, Gang; Li, Ming; Mourrain, Bernard et al

in Computer Methods in Applied Mechanics & Engineering (2018), 328

In this paper, we propose a general framework for constructing IGA-suitable planar B-spline parameterizations from given complex CAD boundaries. Instead of the computational domain bounded by four B ... [more ▼]

In this paper, we propose a general framework for constructing IGA-suitable planar B-spline parameterizations from given complex CAD boundaries. Instead of the computational domain bounded by four B-spline curves, planar domains with high genus and more complex boundary curves are considered. Firstly, some pre-processing operations including B´ezier extraction and subdivision are performed on each boundary curve in order to generate a high-quality planar parameterization; then a robust planar domain partition framework is proposed to construct high-quality patch-meshing results with few singularities from the discrete boundary formed by connecting the end points of the resulting boundary segments. After the topology information generation of quadrilateral decomposition, the optimal placement of interior B´ezier curves corresponding to the interior edges of the quadrangulation is constructed by a global optimization method to achieve a patch-partition with high quality. Finally, after the imposition of C1/G1-continuity constraints on the interface of neighboring Bezier patches with respect to each quad in the quadrangulation, the high-quality Bezier patch parameterization is obtained by a local optimization method to achieve uniform and orthogonal iso-parametric structures while keeping the continuity conditions between patches. The efficiency and robustness of the proposed method are demonstrated by several examples which are compared to results obtained by the skeleton-based parameterization approach. [less ▲]

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See detailA constructive conditional logic for access control: a preliminary report
Genovese, Valerio UL; Giordano, Laura; Gliozzi, Valentina et al

in ECAI 2010 (2010)

We define an Intuitionistic Conditional Logic for Access Control called CICL. The logic CICL is based on a conditional language allowing principals to be defined as arbitrary formulas and it includes few ... [more ▼]

We define an Intuitionistic Conditional Logic for Access Control called CICL. The logic CICL is based on a conditional language allowing principals to be defined as arbitrary formulas and it includes few uncontroversial axioms of access control logics. We provide an axiomatization and a Kripke model semantics for the logic CICL, and we prove that the axiomatization is sound and complete with respect to the semantics. [less ▲]

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See detailConstructive Synchronization of Networked Feedback Systems
Hamadeh, A.; Stan, G. B.; Goncalves, Jorge UL

in The proceedings of the 49th IEEE Conference on Decision and Control (CDC) (2010)

This paper is concerned with global asymptotic output synchronization in networks of identical feedback systems. Using an operator theoretic approach based on an incremental small gain theorem, the method ... [more ▼]

This paper is concerned with global asymptotic output synchronization in networks of identical feedback systems. Using an operator theoretic approach based on an incremental small gain theorem, the method reformulates the synchronization problem as one of achieving incremental stability using a coupling operator that plays the role of an incrementally stabilizing feedback. In this way, conditions on static or dynamic coupling operators that achieve output synchronization of nodes of arbitrary structure are derived. These conditions lead to a methodology for the construction of coupling architectures that ensure output synchronization of a wide range of systems. The result is illustrated for a network of biochemical oscillators. [less ▲]

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See detailContact between shear-deformable beams with elliptical cross-sections
Magliulo, Marco UL; Zilian, Andreas UL; Beex, Lars UL

in Acta Mechanica (2020), 231

Slender constituents are present in many structures and materials. In associated mechanical models, each slender constituent is often described with a beam. Contact between beams is essential to ... [more ▼]

Slender constituents are present in many structures and materials. In associated mechanical models, each slender constituent is often described with a beam. Contact between beams is essential to incorporate in mechanical models, but associated contact frameworks are only demonstrated to work for beams with circular cross-sections. Only two studies have shown the ability to treat contact between beams with elliptical cross-sections, but those frameworks are limited to point-wise contact, which narrows their applicability. This contribution presents initial results of a framework for shear-deformable beams with elliptical cross-sections if contact occurs along a line or at an area (instead of at a point). This is achieved by integrating a penalty potential over one of the beams’ surfaces. Simo-Reissner Geometrically Exact Beam (GEB) elements are employed to discretise each beam. As the surface of an assembly of such beam elements is discontinuous, a smoothed surface is introduced to formulate the contact kinematics. This enables the treatment of contact for large sliding displacements and substantial deformations. [less ▲]

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See detailContinuous Glucose Monitoring: Using CGM to Guide Insulin Therapy Virtual Trials Results
Mombaerts, Laurent UL; Thomas, Felicity; Signal, Matthew et al

in IFAC-PapersOnLine (2015)

Continuous glucose monitoring (CGM) devices can measure blood glucose levels through interstitial measurements almost continuously (1-5min sampling period). However, they are not as accurate as glucose ... [more ▼]

Continuous glucose monitoring (CGM) devices can measure blood glucose levels through interstitial measurements almost continuously (1-5min sampling period). However, they are not as accurate as glucose readings from blood measurements. The relation between tissue and blood glucose is dynamic and the sensor signal can degrade over time. In addition, CGM readings contains high frequency noise and can drift between measurements. However, maintaining continuous glucose monitoring has the potential to improve the level of glycemic control achieved and reduce nurse workload. For this purpose, a simple model was designed and tested to see the effect of inherent CGM error on the insulin therapy protocol, STAR (Stochastic TARgeted). An error model was generated from 9 patients that had one Guardian Real-Time CGM device (Medtronic Minimed, Northridge, CA, USA) inserted into their abdomen as part of an observation trial assesing the accuracy of CGM measurements compared to a blood gas analyser and glucometer readings. A resulting error model was then used to simulate the outcomes if the STAR protocol was guided by CGM values on 183 virtual patients. CGM alarms for hyper- and hypo-glycaemic region were included to improve patient safety acting as 'guardrails'. The STAR CGM protocol gave good performance and reduced workload by ~50%, reducing the number of measurements per day per patient from 13 to 7. The number of hypoglycaemic events increased compared to the current STAR from 0.03% <2.2mmol/L to 0.32%. However, in comparison to other published protocols it is still a very low level of hypoglycaemia and less than clinically acceptable value of 5% <4.0mmol/L. More importantly this study shows great promise for the future of CGM and their use in clinic. With the a newer generation of sensors, specifically designed for the ICU, promising less noise and drift suggesting that a reduced nurse workload without compromising safety or performance is with in reach. [less ▲]

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See detailA Contribution to Cyber-Physical Systems Security: an Event-based Attack-tolerant Control Approach
Bezzaoucha, Souad UL; Voos, Holger UL

in Proceedings of 10th IFAC Symposium on Fault Detection, Supervision and Safety for Technical Processes, SAFEPROCESS 2018 (2018, August 29)

In the present paper, a model-based fault/attack tolerant scheme is proposed to deal with cyber-threats on Cyber Physicals Systems. A common scheme based on observers is designed and a state feedback ... [more ▼]

In the present paper, a model-based fault/attack tolerant scheme is proposed to deal with cyber-threats on Cyber Physicals Systems. A common scheme based on observers is designed and a state feedback control based on an event-triggered framework is given with control synthesis and condition on the switching time. An event-based implementation is proposed in order to achieve novel security strategy. Observer and controller gains are deduced by solving su cient Bilinear Matrix Inequality (BMI) condition. Simulation results on a real-time laboratory three tank system are given to show the attack-tolerant control ability despite data deception attacks on both actuators and sensors. [less ▲]

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See detailA contribution to Cyber-Security of Networked Control Systems: an Event-based Control Approach
Bezzaoucha, Souad UL; Voos, Holger UL; Darouach, Mohamed

in Proceedings of 2017 3rd International Conference on Event-Based Control, Communication and Signal Processing (EBCCSP 2017) (2017, May)

In the present paper, a networked control system under both cyber and physical attacks is considered. An adapted formulation of the problem under physical attacks, data deception and false data injection ... [more ▼]

In the present paper, a networked control system under both cyber and physical attacks is considered. An adapted formulation of the problem under physical attacks, data deception and false data injection attacks, is used for controller synthesis. Based on the classical fault tolerant detection (FTD) tools, a residual generator for attack/fault detection based on observers is proposed. An event-triggered and Bilinear Matrix Inequality (BMI) implementation is proposed in order to achieve novel and better security strategy. The purpose in using this implementation would be to reduce (limit) the total number of transmissions to only instances when the networked control system (NCS) needs attention. It is important to note that the main contribution of this paper is to establish the adequate event-triggered and BMI-based methodology so that the particular structure of the mixed attacked/faulty structure can be re-formulated within the classical FTD paradigm. Experimental results are given to illustrate the developed approach efficiency on a pilot three-tank system. The plant model is presented and the proposed control design is applied to the system. [less ▲]

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See detailControl Theory and Systems Biology
Goncalves, Jorge UL; Warnick, S.

in Iglesias, P. A.; Ingalls, B. P. (Eds.) Dynamical structure Functions in Network Reconstruction (2009)

Presenting a control-theoretic treatment of stoichiometric systems, ... local parametric sensitivity analysis, the two approaches yield identical results. ...

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See detailControl theory methods for macro models with stochastic micro foundations
Tonita, R. J.; Goncalves, Jorge UL; Lestas, I. C. et al

Scientific Conference (2008)

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See detailControllability of transportation networks
Rinaldi, Marco UL

in Transportation Research. Part B, Methodological (2018), 118

Network-wide traffic control policies determine the optimal values for the different kinds of controllers equipped on a transportation network, with the objective of reducing de- lays and congestion ... [more ▼]

Network-wide traffic control policies determine the optimal values for the different kinds of controllers equipped on a transportation network, with the objective of reducing de- lays and congestion, improving safety and reaching a target Level of Service. While models and algorithms for these problems have been extensively studied in literature, little at- tention has been devoted to investigating whether/how different locations, kinds (pricing controllers, traffic lights, ...) and amounts of controllers in a network affect the overall performance of network-wide schemes. In this work, we adapt the control-theoretical approach of controllability of complex networks to the specific instance of transportation networks, considering both propaga- tion/spillback dynamics and users’ behavior in terms of route choice. Thanks to the newly developed methodology, we then provide exact solutions to the Full Controllability Pric- ing Controller Location Problem for transportation networks. Comparing different pricing controller location policies through two artificial test cases, we empirically demonstrate how indeed the amount and kind of controllers in a network strongly affect the level of performance reachable by network-wide control policies, specifically in terms of Total Cost minimization. [less ▲]

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See detailControllability of transportation networks
Rinaldi, Marco UL; Viti, Francesco UL

Scientific Conference (2018, September)

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See detailConventional EO Satellites vs. CubeSats; FDL - AI flood detection onboard a Nano Satellite
Backes, Dietmar UL; Schumann, Guy; Teferle, Felix Norman UL

Scientific Conference (2019, December 11)

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See detailCoping with turn-taking:Investigating breakdowns in human-robot interaction from a Conversation Analysis (CA) perspective
Arend, Béatrice UL; Sunnen, Patrick UL

in Proceedings: The 8th International Conference on Society and Information Technologies (2017, March)

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See detailThe CORONA Business in Modern Cities
Vitello, Piergiorgio UL; Capponi, Andrea UL; Klopp, Pol et al

Poster (2020, November)

As a response to the global outbreak of the SARS-COVID-19 pandemic, authorities have enforced a number of measures including social distancing, travel restrictions that lead to the “temporary” closure of ... [more ▼]

As a response to the global outbreak of the SARS-COVID-19 pandemic, authorities have enforced a number of measures including social distancing, travel restrictions that lead to the “temporary” closure of activities stemming from public services, schools, industry to local businesses. In this poster we draw the attention to the impact of such measures on urban environments and activities. For this, we use crowdsensed information available from datasets like Google Popular Times and Apple Maps to shed light on the changes undergone during the outbreak and the recovery [less ▲]

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