References of "Scientific congresses, symposiums and conference proceedings"
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See detailCellular Automata Evolution Of Leader Election
Banda, Peter UL

in Kampis, George; Karsai, István; Szathmáry, Eörs (Eds.) Advances in Artificial Life. Darwin Meets von Neumann (2011)

The leader election problem is a crucial problem in the theory of distributed algorithms, multi-agent systems as well as in sociobiology. In this paper we investigate one-dimensional binary state cellular ... [more ▼]

The leader election problem is a crucial problem in the theory of distributed algorithms, multi-agent systems as well as in sociobiology. In this paper we investigate one-dimensional binary state cellular automata with an intention to track self-organizational mechanisms that finally enable a global leader to be elected. Since our model is anonymous and uniform we also have to deal with a problem of symmetry that in great majority of cases is broken by inhomogeneity of arbitrary initial configurations. Our approach to the problem is based on the evolution of cellular automata by genetic algorithms and the methodology of computational mechanics. The presented new solution of the leader election reaches remarkably high performance of 94 − 99%. The analysis shows a sophisticated collective computation demonstrated by so called particles and their interactions. Due to the simplicity of our model, presented approach is general and universal enough to be applicable even at the level of primitive biological or artificial societies. [less ▲]

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See detailGeneralized Information Theory based on the Theory of Hints
Pouly, Marc UL

in Liu, Weiru (Ed.) Symbolic and Quantitative Approaches to Reasoning with Uncertainty (2011)

The aggregate uncertainty is the only known functional for Dempster-Shafer theory that generalizes the Shannon and Hartley mea- sures and satis?es all classical requirements for uncertainty measures ... [more ▼]

The aggregate uncertainty is the only known functional for Dempster-Shafer theory that generalizes the Shannon and Hartley mea- sures and satis?es all classical requirements for uncertainty measures, including subadditivity. Although being posed several times in the liter- ature, it is still an open problem whether the aggregate uncertainty is unique under these properties. This paper derives an uncertainty measure based on the theory of hints and shows its equivalence to the pignistic entropy. It does not satisfy subadditivity, but the viewpoint of hints un- covers a weaker version of subadditivity. On the other hand, the pignistic entropy has some crucial advantages over the aggregate uncertainty. i.e. explicitness of the formula and sensitivity to changes in evidence. We observe that neither of the two measures captures the full uncertainty of hints and propose an extension of the pignistic entropy called hints en- tropy that satis?es all axiomatic requirements, including subadditivity, while preserving the above advantages over the aggregate uncertainty. [less ▲]

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See detailDevelopments in Mesh-Moving and Mesh-Update Schemes for Space-Time Finite Element Dicretisations of Fluid Flows
Schippke, Henning; Zilian, Andreas UL

Scientific Conference (2011)

Space-time discretisations of physical problems involving moving and deforming bodies, boundaries and interfaces have been shown to offer advantageous properties, while being methodologically uniform and ... [more ▼]

Space-time discretisations of physical problems involving moving and deforming bodies, boundaries and interfaces have been shown to offer advantageous properties, while being methodologically uniform and flexible. Well-known phenomena, which are ideally suited to be analysed by space-time methods, are fluid-structure interaction problems in general as well as fluid flows with subdomain phase boundaries or immersed moving objects. In this contribution existing mesh-moving and mesh-update techniques are comparatively discussed within the framework of finite element discretisations of the Navier-Stokes equations in space and time. The investigation is based on a SUPG/PSPG velocity-pressure formulation on the deforming space-time do- main. Developments of mesh reconnection at fluid-solid interfaces due to mesh-moving/reconnecting proce- dures for space-time discretisations of fluid flows are presented. Furthermore mesh-update/reconnecting techniques are examined occurring in engineering problems involving sliding or rotating space-time fluid meshes. The presented techniques are accompanied by numerical examples of translational fluid flow as well as fluid flow with immersed rotating fluid bodies. The quality of the approximative solution on the moving and deforming mesh as well as its conservation properties are investigated. [less ▲]

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See detailImpulse parametric sensitivity analysis
Perumal, Thanneer Malai UL; Gunawan, R.

Scientific Conference (2011)

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See detailApplication of Design Models in Mechatronic Product Development and Building Design Reflection of Researchers and Practitioners
Eisenbart, Boris UL; Blessing, Lucienne UL

in Krause, Dieter, Paetzold, Kristin (Ed.) Beiträge zum 22. DfX-Symposium (2011)

Design models are an essential means for abstract representation and visualisation of information in the design process. Comprehension of design models in interdisciplinary engineering design teams is ... [more ▼]

Design models are an essential means for abstract representation and visualisation of information in the design process. Comprehension of design models in interdisciplinary engineering design teams is often hindered by different terminology and different discipline-specific modelling approaches. This paper presents the results of an interview study conducted with practitioners and researchers from engineering design and building design. The study elaborates the different ways of collaboration and use of design models in building design as compared to engineering design, in order to derive the potentials for cross-fertilisation between both areas of product development. [less ▲]

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See detailLifetime prediction for solder joints with the extended finite element method
Menk, Alexander; Pearce, Chris J.; Lanier, Olivier et al

in Proceedings of 12th Int. Conf. on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2011 (2011)

Predicting the lifetime of solder joints undergoing thermal cycling is crucial for the electronics industry in order to guarantee a certain performance of their products in the field. Semi-empirical ... [more ▼]

Predicting the lifetime of solder joints undergoing thermal cycling is crucial for the electronics industry in order to guarantee a certain performance of their products in the field. Semi-empirical methods are often used to predict the average lifetime of the critical joints. However, to get a reliable failure probability the standard deviation must also be addressed. The deviation of the lifetime from the mean value is a consequence of the variation in microstructure found in actual joints. We therefore propose a new methodology that calculates crack growth based on microstructural features of the joint. A series of random microstructures is generated. Crack growth calculations are performed for each of these structures. The structural problem is solved numerically with the extended finite element method which allows a complete automation of the process. The mean crack length and standard deviation are calculated from the crack growth simulations and the result is compared to experimental data. [less ▲]

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See detailEstimación precisa del error en magnitudes de interés mediante técnicas de recovery con equilibrio local
Nadal, E.; Ródenas, J. J.; González-Estrada, O. A. et al

in Congress on Numerical Methods in Engineering (2011)

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See detailGeneric Solution Construction in Valuation-Based Systems
Pouly, Marc UL

in Butz, Cory; Lingras, Pawan (Eds.) Advances in Artificial Intelligence (2011)

Valuation algebras abstract a large number of formalisms for automated reasoning and enable the definition of generic inference procedures. Many of these formalisms provide some notions of solutions ... [more ▼]

Valuation algebras abstract a large number of formalisms for automated reasoning and enable the definition of generic inference procedures. Many of these formalisms provide some notions of solutions. Typical examples are satisfying assignments in constraint systems, models in logics or solutions to linear equation systems. Contrary to inference, there is no general algorithm to compute solutions in arbitrary valuation algebras. This paper states formal requirements for the presence of solutions and proposes a generic algorithm for solution construction based on the results of a previously executed inference scheme. We study the application of generic solution construction to semiring constraint systems, sparse linear systems and algebraic path problems and show that the proposed method generalizes various existing approaches for specific formalisms in the literature. [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 detailAccurate evaluation of K in XFEM using error estimation in quantities of interest based on equilibrated recovery
González-Estrada, O. A.; Ródenas, J. J.; Nadal, E. et al

in Bordas, Stéphane; Kerfriden, P (Eds.) 2nd International Conference on the Extended Finite Element Method (2011)

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See detailComparisons of design methodologies and process models across disciplines: A literature review
Gericke, Kilian UL; Blessing, Lucienne UL

in Proceedings of the 18th International Conference on Engineering Design (2011)

Challenges resulting from an environment characterised by complexity, competition on global markets, dynamics and ever-changing user wants and needs are increasing and affect all design processes ... [more ▼]

Challenges resulting from an environment characterised by complexity, competition on global markets, dynamics and ever-changing user wants and needs are increasing and affect all design processes, irrespective of whether the product or system designed is a machine, a building, software, service, etc.. These challenges require collaboration between disciplines, but current design processes of large systems, such as aircraft, essentially show separate development strands for each discipline. Research into methods is ongoing, but the original design methodologies have not been adapted accordingly. Based on a literature study this paper consolidates findings from different comparisons of design methodologies and process models across disciplines. A consensus can be found that at least on an abstract level design process models have a generic core of common stages. On a detailed level the picture is different. The extent to which design approaches appear similar depends on the perspective of the analyses. The literature study provides an overview of shortcomings of existing design methodologies which may serve as starting points for further research and development of design methodologies. [less ▲]

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See detailA boolean control network approach to pursuit evasion problems in polygonal environments
Thunberg, Johan UL; Ogren, P.; Hu, X.

in Proceedings of the 2011 IEEE International Conference on Robotics and Automation (ICRA) (2011)

In this paper, the multi pursuer version of the pursuit evasion problem in polygonal environments is addressed. This problem is NP-hard, and therefore we seek good enough, but not optimal solutions. By ... [more ▼]

In this paper, the multi pursuer version of the pursuit evasion problem in polygonal environments is addressed. This problem is NP-hard, and therefore we seek good enough, but not optimal solutions. By modeling the problem as a Boolean Control Network, we can efficiently keep track of which regions are cleared, and which are not, while the input nodes of the network are used to represent the motion of the pursuers. The environment is partitioned into a set of convex regions, where each region correspond to a set of nodes in the network. The method is implemented in ANSI C, and efficiently solves complex environments containing multiple loops and requiring so-called recontamination. The provided examples demonstrate the effectiveness of the method in terms of computational time. [less ▲]

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See detailOn the use of recovery techniques for accurate error estimation and error bounding in XFEM
Ródenas, J. J.; González-Estrada, O. A.; Fuenmayor, F. J. et al

in Bordas, Stéphane; Kerfriden, Pierre (Eds.) 2nd International Conference on the Extended Finite Element Method (2011)

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See detailDecentralised minimal-time consensus
Yuan, Y.; Stan, G.-B.; Barahona, M. et al

in The proceedings of the 2011 50th IEEE Conference on Decision and Control and European Control Conference (CDC-ECC) (2011)

This study considers the discrete-time dynamics of a network of agents that exchange information according to the nearest-neighbour protocol under which all agents are guaranteed to reach consensus ... [more ▼]

This study considers the discrete-time dynamics of a network of agents that exchange information according to the nearest-neighbour protocol under which all agents are guaranteed to reach consensus asymptotically. We present a fully decentralised algorithm that allows any agent to compute the consensus value of the whole network in finite time using only the minimal number of successive values of its own history. We show that this minimal number of steps is related to a Jordan block decomposition of the network dynamics and present an algorithm to obtain the minimal number of steps in question by checking a rank condition on a Hankel matrix of the local observations. Furthermore, we prove that the minimal number of steps is related to other algebraic and graph theoretical notions that can be directly computed from the Laplacian matrix of the graph and from the underlying graph topology. [less ▲]

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See detailAlleviating the Mesh Burden in Computational Solid Mechanics
Bordas, Stéphane UL; Rabczuk, Timon; Ródenas, Juan-Jo et al

in Proceedings of ECT2010 (2010, December 12)

The goal of this chapter is to review recent avenues of investigation to alleviate meshing difficulties in computational mechanics and give a few exemplar applications. Keywords: meshing; enrichment ... [more ▼]

The goal of this chapter is to review recent avenues of investigation to alleviate meshing difficulties in computational mechanics and give a few exemplar applications. Keywords: meshing; enrichment; meshfree methods; extended finite element methods; isogeometric analysis; advanced remeshing techniques. [less ▲]

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See detailAn agenda for establishing the Ecological Footprint as communication instrument and indicator for sustainable development in small countries: Case study Luxembourg
Hild, Paula UL; Schmitt, Bianca; Morgane, Mey et al

Poster (2010, June)

The Ecological Footprint methodology proposed by the Global Footprint Network (GFN) seems to be not entirely appropriate for small countries with less than one million inhabitants [Ewing et al., 2008 ... [more ▼]

The Ecological Footprint methodology proposed by the Global Footprint Network (GFN) seems to be not entirely appropriate for small countries with less than one million inhabitants [Ewing et al., 2008]. This may be a reason why e.g. results for Luxembourg, a country with 470,000 inhabitants, have never been included into official country Footprint comparisons. Therefore, the methodology needs to be adapted to be used for communication purpose in Luxembourg. This contribution presents Luxembourg’s approach for illustrating the national consumption impacts to finally discuss the integration of the Ecological Footprint as an indicator for sustainable development in the national indicator system. [less ▲]

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See detailLINEAR BUCKLING ANALYSIS OF CRACKED ISOTROPIC PLATES USING THE EXTENDED FINITE ELEMENT METHOD
Baiz, PM; Natarajan, Stéphane; Kerfriden, P. et al

Scientific Conference (2010, March)

The behaviour of plate structures under compressive loads has been of great concern for engineering applications, especially in aeronautical and aerospace structures in which the demanding design of ... [more ▼]

The behaviour of plate structures under compressive loads has been of great concern for engineering applications, especially in aeronautical and aerospace structures in which the demanding design of weight critical applications usually leads to stability problems. In this paper, the linear buckling problem of cracked isotropic plates is studied using the extended finite element method (XFEM). The mixed interpolation technique of the well-established MITC4 quadrilateral finite element with 12 standard degrees of freedom per element is used. The critical buckling load and mode shapes of simply supported square plates are computed as a function of crack length. [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 detailRepresenting Structure in Linear Interconnected Dynamical Systems
Yeung, Y.; Goncalves, Jorge UL; Sandberg, H. et al

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

Interconnected dynamical systems are a pervasive component in our modern world's infrastructure. One of the fundamental steps to understanding the complex behavior and dynamics of these systems is ... [more ▼]

Interconnected dynamical systems are a pervasive component in our modern world's infrastructure. One of the fundamental steps to understanding the complex behavior and dynamics of these systems is determining how to appropriately represent their structure. In this work, we discuss different ways of representing a system's structure. We define and present, in particular, four representations of system structure-complete computational, subsystem, signal, and zero pattern structure-and discuss some of their fundamental properties. We illustrate their application with a numerical example and show how radically different representations of structure can be consistent with a single LTI input-output system. [less ▲]

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See detailOn numerical integration of discontinuous approximations in partition of unity finite elements
Natarajan, S.; Bordas, Stéphane UL; Mahapatra, D. R.

in IUTAM Bookseries (2010), 19

This contribution presents two advances in the formulation of discontinuous approximations in finite elements. The first method relies on Schwarz-Christoffel mapping for integration on arbitrary polygonal ... [more ▼]

This contribution presents two advances in the formulation of discontinuous approximations in finite elements. The first method relies on Schwarz-Christoffel mapping for integration on arbitrary polygonal domains [1]. When an element is split into two subdomains by a piecewise continuous discontinuity, each of these polygonal domains is mapped onto a unit disk on which cubature rules are utilized. This suppresses the need for the usual two-level isoparametric mapping. The second method relies on strain smoothing applied to discontinuous finite element approximations. By writing the strain field as a non-local weighted average of the compatible strain field, integration on the surface of the finite elements is transformed into boundary integration, so that the usual subdivision into integration cells is not required, an isoparametric mapping is not needed and the derivatives of the shape (enrichment) functions do not need to be computed. Results in fracture mechanics and composite materials are presented and both methods are compared in terms of accuracy and simplicity. The interested reader is referred to [1,6,13] for more details and should contact the authors to receive a version of the MATLAB codes used to obtain the results herein. © 2010 Springer Science+Business Media B.V. [less ▲]

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See detailFM Discriminator for AIS Satellite Detection
Jurado Gallardo, Maria De Los Angeles UL; Ruy, Ghislain

in Personal Satellite Services (2010)

The Automatic Identification System (AIS) is a tracking system used on ships for several decades to improve traffic monitoring and safety at sea in a short range. The modulation technique used is Gaussian ... [more ▼]

The Automatic Identification System (AIS) is a tracking system used on ships for several decades to improve traffic monitoring and safety at sea in a short range. The modulation technique used is Gaussian Minimum Shift Keying (GMSK). Recently, the idea of receiving AIS signals from space arose. This presents mainly two challenges. The first one is that received signals present a large Doppler range due to the satellite speed. The second one is the simultaneous reception of signals from ships because of the broad satellite coverage. In this paper, a novel non-coherent GMSK demodulator is proposed to handle the large Doppler shift problem based on several FM discriminators in parallel. A frame collision detection algorithm is presented but the collision problem is not addressed. In addition, computer simulated and real signals are used to study the receiver performance on an AWGN channel. [less ▲]

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See detailCognitive estimation in the ideation phase of engineering design
Adolphy, Sebastian; Gericke, Kilian UL; Blessing, Lucienne UL

Poster (2010)

Estimation in its diverse forms is assumed to be relevant for problem solving in engineering design due to the inherent deficiencies in information availability and reliability. Nevertheless aside from ... [more ▼]

Estimation in its diverse forms is assumed to be relevant for problem solving in engineering design due to the inherent deficiencies in information availability and reliability. Nevertheless aside from some exception estimation as a method is hardly mentioned in standard literature on systematic approaches to engineering design like Pahl and Beitz. As well it is rarely deliberate addressed in engineering education. Engineering designers are expected to gain estimation competence by experience. Good performance in estimation and the development of estimation competence by hat is left to chance. Estimation as a problem solving strategy covers a wide range of activities on a continuous spectrum between the extremes of random guesses and highly mathematical statistics based approaches. Our research addresses estimation activities which are solely based on cognitive performance, without using specific mathematical procedures or technological support. Our current study is an explorative, qualitative protocol analysis of two idea creation meetings addressing different problems in the early phases of a technology-driven innovation project recorded by the DTRS7 organisation. The addressed research questions are: Where, how, why and what for is estimation used in engineering design? This analysis should give further insight in the not widely delineated topic of estimation in engineering design. [less ▲]

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See detailEntwicklungsmethodik nach Pahl und Beitz und Design thinking. Vergleich und Einordnung
Gericke, Kilian UL; Beinke, Christian; Gemmer, Pascal et al

in Proceedings of 19th Symposium Design for X (2010)

Die Konstruktionsforschung strebt danach die Entwicklungspraxis zu unterstützen indem Methodiken, Methoden, Tools und Empfehlungen erarbeitet werden, welche die Arbeit der Entwickler erleichtern sollen ... [more ▼]

Die Konstruktionsforschung strebt danach die Entwicklungspraxis zu unterstützen indem Methodiken, Methoden, Tools und Empfehlungen erarbeitet werden, welche die Arbeit der Entwickler erleichtern sollen, mit dem Ziel bessere Produkte zu entwickeln. Das Umfeld der Entwicklungspraxis ist dabei gekennzeichnet durch Komplexität, Wettbewerb auf globalen Märkten, Dynamik und sich ständig ändernden Kundenwünschen und -bedürfnissen. Die daraus erwachsenden Herausforderungen nehmen fortlaufend zu und tangieren alle Entwicklungsprozesse unabhängig davon ob eine Maschine, eine Software, ein Service oder ein andere Produktform entwickelt wird. Neben den genannten Aspekten stellt auch das veränderte Konsumentenverhalten eine Herausforderung für die Produktentwicklung dar. Das Internet ermöglicht eine nie dagewesene Auswahl- und Vergleichsmöglichkeit von Produkten, wodurch wesentlich selektiver konsumiert wird und infolge dessen Produkte immer differenzierter und tärker an die Kundenwünsche und –bedürfnisse angepasst werden müssen. Abhängig von Entwicklungsgegenstand, Marktsegment, Branche und weiteren Faktoren sind die existierenden methodischen Hilfsmittel unterschiedlich gut geeignet, die Arbeit des Entwicklers zu erleichtern und die Entwicklung besserer Produkte zu unterstützen. Dies bedeutet, dass methodische Ansätze Kontext-abhängig ausgewählt bzw. adaptiert werden müssen. In jüngster Zeit hält Design Thinking, ein neuer Ansatz zur methodischen Produktentwicklung, Einzug in verschiedenste Branchen. Im nachfolgenden Artikel wird Design Thinking kurz beschrieben und exemplarisch mit dem methodischen Vorgehen nach Pahl und Beitz verglichen. Der Vergleich beinhaltet den Prozessumfang (welche Phasen des Entwicklungsprozesses werden abgebildet) und ausgewählte Kontext-Aspekte (für welche Art von Entwicklungsvorhaben ist der Ansatz anwendbar). Anhand dieser Aspekte wird diskutiert, welche wesentlichen Unterschiede zwischen den Ansätzen bestehen, wo Überschneidungen existieren und welches Potential die Kombination beider Ansätze in sich birgt. [less ▲]

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See detailFluctuations and Limitations of a Multi-Sector Economic Model with Delays
Tonita, R.; Lestas, I.; Goncalves, Jorge UL et al

in The proceedings of the 2010 American Control Conference (ACC) (2010)

A general multi-sector model of the economy is investigated. A sector's input to production, labor, evolves according to a jump Markov process. Labor jumps between sectors to balance supply and demand ... [more ▼]

A general multi-sector model of the economy is investigated. A sector's input to production, labor, evolves according to a jump Markov process. Labor jumps between sectors to balance supply and demand, where each sector differs by its productivity. The jump model captures the intrinsic noise of the micro agents on the macro level, which is represented by the random timing of labor jumps. Quantifying this noise is a central theme of this paper. An operator theoretic approach is utilized to capture the fluctuations of a linearized jump system exactly. As an illustrative example two sector and three sector economies are studied. In each case the optimal aggressiveness, gain, of a sector is determined for minimal variance. Delays are then introduced into the model. It is shown that the presence of a delay creates a limit on the minimum variance achievable and that high gain is destabilizing. For both the two and three sector models the nonlinear jump systems are simulated. It is shown that the operator theoretic approach is an appropriate method for quantifying the second moments. [less ▲]

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See detailOn the structure of a new superhard hexagonal carbon phase
Zhang, Bin; Liang, Yongcheng; Guo, Zaoyang et al

in AIP Conference Proceedings (2010), 1233(PART 1), 489-493

Molecular dynamics simulations show that graphite will transform into a superhard phase under cold compression. Recent experiments show that there is a sp 3-rich hexagonal carbon polymorph (a 0=2.496 Å, c ... [more ▼]

Molecular dynamics simulations show that graphite will transform into a superhard phase under cold compression. Recent experiments show that there is a sp 3-rich hexagonal carbon polymorph (a 0=2.496 Å, c 0=4.123Å) with a bulk modulus of 447 GPa and average density about 3.6g/cm 3, restricted to the space group of P-62c (No. 190), but the detailed atomic structure was not obtained [Wang et al., P. Natl. Acad. Sci. 101(38), 13699]. Here we set carbon atoms occupying P-62c 4f Wyckoff positions of P-62c, and calculate the total energy of the different structures changing the internal parameter z by first-principles calculations using geometry optimisation algorithm in CASTEP code, which shows that the stable structures in energy (at local minimum points) are hexagonal carbon (z=1/4) and hexagonal diamond (z=1/16). The calculated mechanical properties and lattice parameters of the structure P-62c 4f (z=1/4) are in good agreement with those of the new hexagonal carbon proposed by Wang et al., which indicates that the atomic structure is a possible candidate. © 2010 American Institute of Physics. [less ▲]

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See detailINFLUENCE OF PISTON DISPLACEMENT ON THE SCAVENGING AND SWIRLING FLOW IN TWO-STROKE DIESEL ENGINES
Obeidat, Anas UL; Haider, Sajjad; Ingvorsen, K.M. et al

in 23rd Nordic Seminar on Computational Mechanics NSCM-23 (2010)

Detailed reference viewed: 76 (3 UL)
See detailA Logic of Privacy
Barker, Steve; Genovese, Valerio UL

in Data and Applications Security and Privacy XXIV (2010)

We consider the problem of developing an abstract meta-model of access control in terms of which policies for protecting a principal’s private information may be specified. Our concern is with developing ... [more ▼]

We consider the problem of developing an abstract meta-model of access control in terms of which policies for protecting a principal’s private information may be specified. Our concern is with developing the formal foundations of our conceptual model. For both the specific access control models and privacy policies, which may be defined in terms of the meta-model, we adopt a combining approach: we combine access control concepts to form the meta-model and we use a fibred logic for the formal foundations. Our approach enables data subjects to specify flexibly what access controls they wish to apply on their personal data and it provides a formal foundation for policies that are defined in terms of the meta-model. [less ▲]

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See detailRobust dynamical network reconstruction
Yuan, Y.; Stan, G. B.; Warnick, S. et al

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

Motivated by biological applications, this paper addresses the problem of network reconstruction from data. Previous work has shown necessary and sufficient conditions for network reconstruction of noise ... [more ▼]

Motivated by biological applications, this paper addresses the problem of network reconstruction from data. Previous work has shown necessary and sufficient conditions for network reconstruction of noise-free LTI systems. This paper assumes that the conditions for network reconstruction have been met but here we additionally take into account noise and unmodelled dynamics (including nonlinearities). Algorithms are therefore proposed to reconstruct dynamical (Boolean) network structure from time-series (steady-state) data respectively in presence of noise and nonlinearities. In order to identify the network structure that generated the data, we compute the smallest distances between the measured data and the data that would have been generated by particular Boolean structures. Information criteria and optimisation technique balancing such distance and model complexity are introduced to search for the true structure. We conclude with biologically-inspired network reconstruction examples which include noise and nonlinearities. [less ▲]

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See detailAn iterative Mixed Integer Linear Programming Approach to pursuit evasion problems in polygonal environments
Thunberg, Johan UL; Ögren, P.

in Proceedings of the 2010 IEEE International Conference on Robotics and Automation (ICRA) (2010)

In this paper, we address the multi pursuer version of the pursuit evasion problem in polygonal environments. It is well known that this problem is NP-hard, and therefore we seek efficient, but not ... [more ▼]

In this paper, we address the multi pursuer version of the pursuit evasion problem in polygonal environments. It is well known that this problem is NP-hard, and therefore we seek efficient, but not optimal, solutions by relaxing the problem and applying the tools of Mixed Integer Linear Programming (MILP) and Receding Horizon Control (RHC). Approaches using MILP and RHC are known to produce efficient algorithms in other path planning domains, such as obstacle avoidance. Here we show how the MILP formalism can be used in a pursuit evasion setting to capture the motion of the pursuers as well as the partitioning of the pursuit search region into a cleared and a contaminated part. RHC is furthermore a well known way of balancing performance and computation requirements by iteratively solving path planning problems over a receding planning horizon, and adapt the length of that horizon to the computational resources available. The proposed approach is implemented in Matlab/Cplex and illustrated by a number of solved examples. [less ▲]

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See detailAn element nodal force-based large increment method for elastoplasticity
Long, Danbin; Guo, Zaoyang; Liu, Xila et al

in AIP Conference Proceedings (2010), 1233(PART 1), 1401-1405

This paper presents a new method for establishing the basic equations in the novel force-based large increment method (LIM) for continuum elastoplastic problems. In LIM, unlike traditional displacement ... [more ▼]

This paper presents a new method for establishing the basic equations in the novel force-based large increment method (LIM) for continuum elastoplastic problems. In LIM, unlike traditional displacement methods, the (generalised) elemental force variables are adopted as system unknowns. The equilibrium equations can then be obtained directly at every nodal degree of freedom without physical equations (i.e., constitutive equations) involved. The generalised inverse of the non-square system of equations is employed to obtain the set of solutions of the non-square matrix equations directly. A conjugate gradient procedure is then used to find the correct solution from this set of solutions by optimising the compatibility of the solution based on the fact that the correct solution should also satisfy the constitutive equations and the compatibility equations. In this paper, the generalised elemental force variables are defined based on the element nodal forces. The LIM framework is therefore successfully applied to elements based on this definition. The efficiency and accuracy of the LIM are illustrated with a few benchmark problems and the results are compared with the analytical solution and the conventional displacement-based finite element method. [less ▲]

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See detailRobust dynamical network structure reconstruction
Yuan, Y.; Stan, G. B.; Warnick, S. et al

Scientific Conference (2010)

Motivated by biological applications, this paper addresses the problem of network reconstruction from data. Previous work has shown necessary and sufficient conditions for network reconstruction of noise ... [more ▼]

Motivated by biological applications, this paper addresses the problem of network reconstruction from data. Previous work has shown necessary and sufficient conditions for network reconstruction of noise-free LTI systems. This paper assumes that the conditions for network reconstruction have been met but here we additionally take into account noise and unmodelled dynamics (including nonlinearities). Algorithms are therefore proposed to reconstruct dynamical (Boolean) network structure from time-series (steady-state) data respectively in presence of noise and nonlinearities. In order to identify the network structure that generated the data, we compute the smallest distances between the measured data and the data that would have been generated by particular Boolean structures. Information criteria and optimisation technique balancing such distance and model complexity are introduced to search for the true structure. We conclude with biologically-inspired network reconstruction examples which include noise and nonlinearities. [less ▲]

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See detailVicinity Resource Cartography for Delay-Tolerant Networks: a Holistic Perspective
Sandulescu, Gabriel UL; Schaffer, Peter UL; Nadjm-Tehrani, Simin UL

in 2010 IFIP W IRELESS D AYS (2010)

In this paper we propose a distributed algorithm allowing nodes in delay-tolerant networks to construct vicinity resource maps based on past encounters. Our algorithm estimates the availability of the ... [more ▼]

In this paper we propose a distributed algorithm allowing nodes in delay-tolerant networks to construct vicinity resource maps based on past encounters. Our algorithm estimates the availability of the following resources: energy, buffer space, and bandwidth. We then show how a store-carry-forward scheme may benefit from having access to these resource estimates. While knowledge about resources available in the vicinity allows nodes to implement meaningful custodian election strategies, an evaluation of available bandwidth and contact time allows them to carry out adaptive queue management strategies. Thus, such strategies can be approached from a holistic perspective based on the availability of the three resources under consideration in node proximity.We validate our model separately in time-varying and space-varying environments. In addition to synthetic mobility models (random waypoint) we validate our resource estimation in a disaster area mobility model (using Bonn motion traces). We show that by using this information a routing protocol may dramatically improve its delivery rate and energy overhead while keeping delivery latency almost constant. [less ▲]

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See detailMinimal-time network reconstruction for DTLTI systems
Yuan, Y.; Goncalves, Jorge UL

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

This paper considers the problem of obtaining in minimal time the “dynamical network structure” (DNS) from partial state observations of a discrete-time linear time-invariant system. From the DNS, we can ... [more ▼]

This paper considers the problem of obtaining in minimal time the “dynamical network structure” (DNS) from partial state observations of a discrete-time linear time-invariant system. From the DNS, we can not only obtain the network structure of the system at the measurement level, but also estimate the minimal number of hidden states which are not observed directly. First, we discuss when reconstruction of the DNS is and is not possible. Then, we give an algorithm to find the minimal number of successive outputs to find the DNS. Finally, we discuss extensions of the results to non-linear and noisy systems. These results can be directly applied to the decentralised network control problem of multi-agent systems to find network connections of the observed agents. [less ▲]

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See detailMinimal-time uncertain output final value of unknown DT-LTI systems with application to the decentralised network consensus problem
Yuan, Y.; Stan, G. B. V.; Shi, L. et al

Scientific Conference (2010)

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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 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 detailRobust Traffic Anomaly Detection with Principal Component Pursuit
Abdelkefi, Atef; Jiang, Yuming; Wang, Wei UL et al

in Proceedings of the ACM CoNEXT Student Workshop (2010)

Principal component analysis (PCA) is a statistical technique that has been used for data analysis and dimensionality reduction. It was introduced as a network traffic anomaly detection technique firstly ... [more ▼]

Principal component analysis (PCA) is a statistical technique that has been used for data analysis and dimensionality reduction. It was introduced as a network traffic anomaly detection technique firstly in [1]. Since then, a lot of research attention has been received, which results in an extensive analysis and several extensions. In [2], the sensitivity of PCA to its tuning parameters, such as the dimension of the low-rank subspace and the detection threshold, on traffic anomaly detection was indicated. However, no explanation on the underlying reasons of the problem was given in [2]. In [3], further investigation on the PCA sensitivity was conducted and it was found that the PCA sensitivity comes from the inability of PCA to detect temporal correlations. Based on this finding, an extension of PCA to Kalman-Loeve expansion (KLE) was proposed in [3]. While KLE shows slight improvement, it still exhibits similar sensitivity issue since a new tuning parameter called temporal correlation range was introduced. Recently, in [4], additional effort was paid to illustrate the PCA-poisoning problem. To underline this problem, an evading strategy called Boiled-Frog was proposed which adds a high fraction of outliers to the traffic. To defend against this, the authors employed a more robust version of PCA called PCA-GRID. While PCA-GRID shows performance improvement regarding the robustness to the outliers, it experiences a high sensitivity to the threshold estimate and the k-dimensional subspace that maximizes the dispersion of the data. The purpose of this work is to consider another technique to address the PCA poisoning problems to provide robust traffic anomaly detection: The Principal Component Pursuit. [less ▲]

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See detailNumerical integration over arbitrary surfaces in partition of unity finite elements
Natarajan, Sundararajan; dal Pont, Stefano; Hung, Nguyen-Xuan et al

Scientific Conference (2009, September)

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See detailThe smoothed extended finite element method for strong discontinuities
Natarajan, S.; Bordas, Stéphane UL; Rabczuk, Timon

Scientific Conference (2009, June)

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See detailA novel numerical integration technique over arbitrary polygons
Natarajan, Sundararajan; Mahapatra, D Roy; Bordas, Stéphane UL et al

Scientific Conference (2009, April)

In this paper, a new numerical integration technique [1] on arbitrary polygons is presented. The polygonal do- main is mapped conformally to the unit disk using Schwarz-Christoffel mapping [2] and a ... [more ▼]

In this paper, a new numerical integration technique [1] on arbitrary polygons is presented. The polygonal do- main is mapped conformally to the unit disk using Schwarz-Christoffel mapping [2] and a midpoint quadrature rule defined on the unit circle is used. This method eliminates the need for a two level isoparametric mapping usuall required [3]. Moreover the positivity of the Jacobian is guaranteed. We present numerical results for a few benchmark problems in the context of polygonal finite elements that show the effectiveness of the method. [less ▲]

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See detailAPPLICATION OF EXTENDED ELEMENT-FREE GALERKIN METHOD TO MULTIPLE FLAWS UNDER BRITTLE FRACTURE CONDITIONS
RABCZUK, T.; BEZENSEK, B.; Bordas, Stéphane UL

in PROCEEDINGS OF THE ASME PRESSURE VESSELS AND PIPING CONFERENCE - 2008, VOL 6, PT A AND B (2009)

The extended element-free Galerkin (XEFG) method incorporates cracks through partition of unity enrichment of the standard basis functions. Discontinuous functions are added to capture the jump through ... [more ▼]

The extended element-free Galerkin (XEFG) method incorporates cracks through partition of unity enrichment of the standard basis functions. Discontinuous functions are added to capture the jump through the crack faces and near-front enrichment is added to capture the asymptotic behaviour in the vicinity of the crack fronts. Depending on the material behaviour, these functions can be of various type. The method can treat initiation, growth and coalescence of cracks seamlessly in both linear elastic and non-linear settings. The method is a powerful tool for modelling and studying crack paths, which are a central feature in the assessment of multiple flaws.The method is applied to the problem of multiple non-aligned flaws in a ferritic plate under cleavage failure. Fracture paths from two nonaligned notches in a plate are modelled. Based on the observations of crack paths the critical flaw alignment distance is established for nonaligned through-wall flaws. [less ▲]

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See detailGene expression data analysis using spatiotemporal blind source separation
Sainlez, Matthieu UL; Absil, Pierre-Antoine; Teschendorff, Andrew E.

in Verleysen, Michel (Ed.) ESANN'2009 proceedings, European Symposium on Artificial Neural Networks - Advances in Computational Intelligence and Learning. (2009)

We propose a “time-biased” and a “space-biased” method for spatiotemporal independent component analysis (ICA). The methods rely on computing an orthogonal approximate joint diagonalizer of a collection ... [more ▼]

We propose a “time-biased” and a “space-biased” method for spatiotemporal independent component analysis (ICA). The methods rely on computing an orthogonal approximate joint diagonalizer of a collection of covariance-like matrices. In the time-biased version, the time signatures of the ICA modes are imposed to be white, whereas the space-biased version imposes the same condition on the space signatures. We apply the two methods to the analysis of gene expression data, where the genes play the role of the space and the cell samples stand for the time. This study is a step towards addressing a question first raised by Liebermeister, on whether ICA methods for gene expression analysis should impose independence across genes or across cell samples. Our preliminary experiment indicates that both approaches have value, and that exploring the continuum between these two extremes can provide useful information about the interactions between genes and their impact on the phenotype. [less ▲]

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See detailA Comparison of Network Reconstruction Methods for Chemical Reaction Networks
Ward, C.; Yeung, E.; Brown, T. et al

in The proceedings of the Third International Conference on Foundations of Systems Biology in Engineering (FOSBE 2009) (2009)

Chemical reaction networks model biological interactions that regulate the functional properties of a cell; these networks characterize the chemical pathways that result in a particular phenotype. One ... [more ▼]

Chemical reaction networks model biological interactions that regulate the functional properties of a cell; these networks characterize the chemical pathways that result in a particular phenotype. One goal of systems biology is to understand the structure of these networks given concentration measurements of various species in the system. Previous work has shown that this network reconstruction problem is fundamentally impossible, even for simplified linear models, unless a particular experiment design is followed. Nevertheless, reconstruction algorithms have been developed that attempt to approximate a solution using sparsity or similar heuristics. This work compares, in silico, the results of three of these methods in situations where the necessary experiment design has been followed, and it illustrates the degradation of each method as increasing noise levels are added to the data. [less ▲]

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See detailNetwork Structure Preserving Model Reduction: Results of a Simulation Study
Yeung, E.; Goncalves, Jorge UL; Sandberg, H. et al

in The proceedings of the Third International Conference on Foundations of Systems Biology in Engineering (FOSBE 2009) (2009)

Reconstructed models of biochemical networks often reflect the high level of complexity inherent in the biological system being modeled. The difficulties of predicting gene expression and analyzing the ... [more ▼]

Reconstructed models of biochemical networks often reflect the high level of complexity inherent in the biological system being modeled. The difficulties of predicting gene expression and analyzing the effects of individual perturbations at a system-wide resolution are exacerbated by model complexity. This paper extends a state projection method for structure preserving model reduction to a particular model class of reconstructed networks known as dynamical structure functions. In contrast to traditional approaches where a priori knowledge of partitions on unmeasured species is required, dynamical structure functions require a weaker notion of system structure, specifying only the causal relationship between measured chemical species of the system. The resulting technique, like similar approaches, does not provide theoretical performance guarantees, so an extensive computational study is conducted, and it is observed to work fairly well in practice. Moreover, sufficient conditions, characterizing edge loss resulting from the reduction process, are presented. [less ▲]

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See detailMinimal dynamical structure realisations with application to network reconstruction from data
Yuan, Y.; Stan, G. B. V.; Warnick, S. et al

in The proceedings of the Joint 48th IEEE Conference on Decision and Control and 28th Chinese Control Conference (2009)

Network reconstruction, i.e., obtaining network structure from data, is a central theme in systems biology, economics, and engineering. Previous work introduced dynamical structure functions as a tool for ... [more ▼]

Network reconstruction, i.e., obtaining network structure from data, is a central theme in systems biology, economics, and engineering. Previous work introduced dynamical structure functions as a tool for posing and solving the problem of network reconstruction between measured states. While recovering the network structure between hidden states is not possible since they are not measured, in many situations it is important to estimate the number of hidden states in order to understand the complexity of the network under investigation and help identify potential targets for measurements. Estimating the number of hidden states is also crucial to obtain the simplest state-space model that captures the network structure and is coherent with the measured data. This paper characterises minimal order state-space realisations that are consistent with a given dynamical structure function by exploring properties of dynamical structure functions and developing algorithms to explicitly obtain a minimal reconstruction. [less ▲]

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See detailDecentralized final value theorem for discrete-time LTI systems with application to minimal time distributed consensus
Yuan, Y.; Stan, G. B. V.; Shi, L. et al

in The proceedings of the Joint 48th IEEE Conference on Decision and Control and 28th Chinese Control Conference (2009)

In this study, we consider an unknown discrete-time, linear time-invariant, autonomous system and characterise, the minimal number of discrete-time steps necessary to compute the asymptotic final value of ... [more ▼]

In this study, we consider an unknown discrete-time, linear time-invariant, autonomous system and characterise, the minimal number of discrete-time steps necessary to compute the asymptotic final value of a state. The results presented in this paper have a direct link with the celebrated final value theorem. We apply these results to the design of an algorithm for minimal-time distributed consensus and illustrate the results on an example. [less ▲]

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See detailRisk/Cost Valuation of Fixed Price IT Outsourcing in a Portfolio Context
Fridgen, Gilbert UL; Müller, Hanna-Vera

in 30th International Conference on Information Systems (ICIS) (2009)

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See detailThe Dynamics of Heat Shock Response Induced by Ultr asound Therapeutic Treatment
Mizera, Andrzej UL; Gambin, Barbara

in Awrejcewicz, J.; Kaźmierczak, M.; Mrozowski, J. (Eds.) et al 10th Conference on Dynamical Systems – Theory and Applications, DSTA-2009 (2009)

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See detailUntersuchungen der instationären Strömungstopologie im Nachlauf einer Seehundvibrisse.
Witte, Matthias; Michael, Mark UL; Brede, Martin et al

in Delgado, A.; Rauh, A.; Lienhart, H. (Eds.) et al Proceedings der 17.GALA-Fachtagung “Lasermethoden in der Strömungsmesstechnik“ (2009)

Die Vibrissen von Seehunden zeichnen sich durch eine komplizierte dreidimensionale Struk- turierung aus. Sie versetzen den Seehund in die Lage, hydrodynamische Nachlaufspuren von Beutefischen zu ... [more ▼]

Die Vibrissen von Seehunden zeichnen sich durch eine komplizierte dreidimensionale Struk- turierung aus. Sie versetzen den Seehund in die Lage, hydrodynamische Nachlaufspuren von Beutefischen zu detektieren. Mit Hilfe von Stereo- μ Piv Messungen an Seehundvibrissen konnte die stationäre Strömungstopologie des Vibrissennachlaufes ermittelt werden. Zum besseren Verständnis der Funktion der Vibrissenstrukturierung ist es notwendig, die instatio- näre Strömungstopologie zu kennen. Durch räumlich und zeitlich hochauflösende numeri- sche Verfahren konnte die instationäre Strömungstopologie im Nachlauf einer Seehund- vibrisse ermittelt werden. [less ▲]

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See detailComputational heuristics for simplifying a biological model
Petre, Ion; Mizera, Andrzej UL; Back, Ralph-Johan

in Lecture Notes in Computer Science (2009), 5635

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See detailThe emergence of leapfrogging in an urban growth model combining an economic approach and cellular automata
Frankhauser, Pierre; Caruso, Geoffrey UL; Peeters, Dominique et al

Scientific Conference (2009)

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See detailNetwork structure preserving model reduction with weak a priori structural information
Yeung, E.; Goncalves, Jorge UL; Sandberg, H. et al

in The proceedings of the Joint 48th IEEE Conference on Decision and Control and 28th Chinese Control Conference (2009)

This paper extends a state projection method for structure preserving model reduction to situations where only a weaker notion of system structure is available. This weaker notion of structure ... [more ▼]

This paper extends a state projection method for structure preserving model reduction to situations where only a weaker notion of system structure is available. This weaker notion of structure, identifying the causal relationship between manifest variables of the system, is especially relevant is settings such as systems biology, where a clear partition of state variables into distinct subsystems may be unknown, or not even exist. The resulting technique, like similar approaches, does not provide theoretical performance guarantees, so an extensive computational study is conducted, and it is observed to work fairly well in practice. Moreover, conditions characterizing structurally minimal realizations and sufficient conditions characterizing edge loss resulting from the reduction process, are presented. [less ▲]

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See detailMeasure and Failure Cost Analysis: Selecting Risk Treatment Strategies
Gericke, Kilian UL; Klimentew, Lars; Blessing, Lucienne UL

in Proceedings of the 17th International Conference on Engineering Design (2009)

Project Risk Management is used to prevent projects to fail. Despite its proven use, barriers still exist that hinder implementation and use by inexperienced persons. One barrier is the additional effort ... [more ▼]

Project Risk Management is used to prevent projects to fail. Despite its proven use, barriers still exist that hinder implementation and use by inexperienced persons. One barrier is the additional effort required by the process of Project Risk Management itself. An additional barrier is the lack of systematic support of important steps like the selection of an appropriate risk treatment strategy. The decision which strategy to select is a challenging task due to the uncertain character of the addressed issue. The trade-off of the perceived additional efforts caused by a method must be addressed by an enhancement of the cost-benefit ratio of the applied methods and implemented risk treatment measures. Decision making using the proposed Measure and Failure Cost Analysis (MFCA) method enables the Risk Manager to compare the arising costs of different risk treatment strategies caused by an occurring risk and risk treatment measures. It is based on a de-escalation principle which analyzes the course of the impact of an event. The method compares the reaction rate of different strategies and proposes the favorite one. [less ▲]

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See detailAnalysis and Visualisation of Project Structure using Linkography: Focussing Project Risk Management
Gericke, Kilian UL; Kleinod, Björn; Blessing, Lucienne UL

in Proceedings of the ASME 2009 International Design Engineering Technical Conferences & 21st International Conference on Design Theory and Methodology IDETC/DTM 2009 (2009)

Product development projects are difficult to plan due to complexity, dynamics, lack of transparency and polytely. Risk Management is often used to cope with this situation. Linkography is adapted with ... [more ▼]

Product development projects are difficult to plan due to complexity, dynamics, lack of transparency and polytely. Risk Management is often used to cope with this situation. Linkography is adapted with the aim to ease the effort of the Risk Management process. Linkography is used to focus all Risk Management activities on those work packages which might affect the project the most in the case of failing the expected outcome. The criticality of a work package is defined by the number of links to other work packages, its duration and its costs. By applying Linkography as a Risk Management method, a prioritized list of work packages can be generated which pass consecutively through the usual Risk Management process. Unlike other methods, Linkography supports the user in a visual manner. Hence, Linkography can easily be used for communication with unskilled stakeholders. [less ▲]

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See detailEstimation and its Role in Engineering Design - An Introduction
Adolphy, Sebastian; Gericke, Kilian UL; Blessing, Lucienne UL

in Proceedings of the 17th International Conference on Engineering Design (2009)

Estimation is assumed to be a relevant method for problem solving in product development due to the deficiencies in information availability and certainty, as well because of short resources. Nevertheless ... [more ▼]

Estimation is assumed to be a relevant method for problem solving in product development due to the deficiencies in information availability and certainty, as well because of short resources. Nevertheless estimation as a method is hardly mentioned in literature on product development nor is it part of engineering education. As a consequence good performance in estimation and the development of estimation competence is left to chance, i.e. expected to be built up through experience. We believe that estimation can be supported and taught. Hence estimation competence can be developed purposive and more quickly. The aims of the research introduced in this paper are to understand relevance and functioning of estimation in engineering design, and to develop support for engineering practice and education based on this understanding. This paper focuses on demonstrating the topics’ relevance by addressing the following questions: •Why is estimation important for engineering design? •What is the state of the art in understanding estimation in general? •What is the state of the art of estimation as a method in engineering design? On the basis of this initial investigation we propose our research framework. After goal, approach and scope of our research, the main research questions on estimation in engineering design we wish to answer are formulated, and the research methods we are using. Furthermore first results on characteristics of estimation in engineering design identified by tests, as well as video and protocol analysis are summarized. At least an outlook on the prospect research is given. [less ▲]

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See detailWhite Manipulation in Judgment Aggregation
Grossi, Davide; Pigozzi, Gabriella UL; Slavkovik, Marija UL

Scientific Conference (2009)

Distributive systems consisting of autonomous and intelligent components need to be able to reason and make decisions based on the information these components share. Judgment aggregation investigates how ... [more ▼]

Distributive systems consisting of autonomous and intelligent components need to be able to reason and make decisions based on the information these components share. Judgment aggregation investigates how individual judgments on logically connected propositions can be aggregated into a collective judgment on the same propositions. It is the case that seemingly reasonable aggregation procedures may force the group to hold an inconsistent judgment set. What happens when the agents realize that the group outcome will be inconsistent? We claim that, in order to avoid an untenable collective outcome, individuals may prefer to declare a non-truthful, less preferred judgment set. Thus, the prospect of an individual trying to manipulate the social outcome by submitting an insincere judgment set is turned from being an undesirable to a “virtuous” (or white) manipulation. We define white manipulation and present the initial study of it as a coordinated action of the whole group. [less ▲]

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See detailAdaptive-gain Extended Kalman Filter: Extension to the Continuous-discrete Case
Boizot, Nicolas UL; Busvelle, Eric; Gauthier, Jean-Paul

Scientific Conference (2009)

In the present article we propose a nonlinear observer that merges the behaviors 1) of an extended Kalman filter, mainly designed to smooth off noise , and 2) of high-gain observers devoted to handle ... [more ▼]

In the present article we propose a nonlinear observer that merges the behaviors 1) of an extended Kalman filter, mainly designed to smooth off noise , and 2) of high-gain observers devoted to handle large perturbations in the state estimation. We specifically aim at continuous-discrete systems. The strategy consists in letting the high-gain self adapt according to the innovation. We define innovation computed over a time window and justify its usage via an important lemma. We prove the general convergence of the resulting observer. [less ▲]

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See detailLocal vs. Global Search Strategies in Evolutionary GRID-based Conformational Sampling & Docking
Horvath, Dragos; Brillet, Lorraine; Roy, Sylvaine et al

in 2009 IEEE CONGRESS ON EVOLUTIONARY COMPUTATION, VOLS 1-5 (2009)

Conformational sampling, the computational prediction of the experimental geometries of small proteins (folding) or of protein-ligand complexes (docking), is often cited as one of the most challenging ... [more ▼]

Conformational sampling, the computational prediction of the experimental geometries of small proteins (folding) or of protein-ligand complexes (docking), is often cited as one of the most challenging multimodal optimization problems. Due to the extreme ruggedness of the energy landscape as a function of geometry, sampling heuristics must rely on an appropriate trade-off between global and local searching efforts. A previously reported "planetary strategy", a generalization of the classical island model used to deploy a hybrid genetic algorithm on computer grids, has shown a good ability to quickly discover low-energy geometries of small proteins and sugars, and sometimes even pinpoint their native structures - although not reproducibly. The procedure focused on broad exploration and used a tabu strategy to avoid revisiting the neighborhood of known solutions, at the risk of "burying" important minima in overhastily set tabu areas. The strategy reported here, termed "divide-and-conquer planetary model" couples this global search procedure to a local search tool. Grid nodes are now shared between global and local exploration tasks. The phase space is cut into "cells" corresponding to a specified sampling width for each of the N degrees of freedom. Global search locates cells containing low-energy geometries. Local searches pinpoint even deeper minima within a cell. Sampling width controls the important trade-off between the number of cells and the local search effort needed to reproducibly sample each cell. The probability to submit a cell to local search depends on the energy of the most stable geometry found within. Local searches are allotted limited resources and are not expected to converge. However, as long as they manage to discover some deeper local minima, the explored cell remains eligible for further local search, now relying on the improved energy level to enhance chances to be picked again. This competition prevents the system to waste too much effort in fruitless local searches. Eventually, after a limited number of local searches, a cell will be "closed" and used - first as "seed", later as tabu zone - to bias future global searches. Technical details and some folding and docking results will be discussed. [less ▲]

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See detailInfluence of the microstructure on the stress state of solder joints dusing thermal cycling
Menk, A.; Bordas, Stéphane UL

in Proceedings of 10th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2009 (2009)

The lifetime of a solder joint is mainly determined by its creep behaviour. Creep arises from the stresses inside the solder joints as a consequence of the thermomechanical mismatch of the board and the ... [more ▼]

The lifetime of a solder joint is mainly determined by its creep behaviour. Creep arises from the stresses inside the solder joints as a consequence of the thermomechanical mismatch of the board and the substrate. The stress state is heavily influenced by the anisotropy of tin. To understand the damage process in solder joints, the influence of the anisotropic microstructure must be understood. In this paper the influence of different grain sizes, shapes and orientations on the stress state is evaluated, based on numerical experiments. [less ▲]

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See detailBMS revisited
Aucher, Guillaume UL

in Proceedings of the 12th Conference on Theoretical Aspects of Rationality and Knowledge (2009)

The insight of the BMS logical framework (proposed by Baltag, Moss and Solecki) is to represent how an event is perceived by several agents very similarly to the way one represents how a static situation ... [more ▼]

The insight of the BMS logical framework (proposed by Baltag, Moss and Solecki) is to represent how an event is perceived by several agents very similarly to the way one represents how a static situation is perceived by them: by means of a Kripke model. There are however some differences between the definitions of an epistemic model (representing the static situation) and an event model. In this paper we restore the symmetry. The resulting logical framework allows, unlike any other one, to express statements about ongoing events and to model the fact that our perception of events (and not only of the static situation) can also be updated due to other events. We axiomatize it and prove its decidability. Finally, we show that it embeds the BMS one if we add common belief operators. [less ▲]

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See detailHeterogeneous agent models in economics: a study of heterogeneous productivity of sectors
Tonita, R. J.; Goncalves, Jorge UL; Vinnicombe, G.

in Proceedings of the 2008 American Control Conference (2008)

Macroeconomic modeling is undergoing a change from the ground up. Previously models based on fully rational representative agents were constructed to give macroeconomics soli microeconomic foundations ... [more ▼]

Macroeconomic modeling is undergoing a change from the ground up. Previously models based on fully rational representative agents were constructed to give macroeconomics soli microeconomic foundations. However the representative agent models have been shown to be inconsistent with empirical evidence and a new method of approach has emerged, one based on heterogeneity of agents. Recently heterogenous models have been used to simulate expected outcomes but due to their complexity little analytic work has been done. In this paper a basic model of the macro economy, with heterogeneous sectors differentiated by productivity, and driven by a jump Markov process, is investigated and steady state solutions for a sector’s output variance are discovered. We adjust the model to include a gain term, to represent a sector’s reaction to its error signal, excess demand, and then linearize the transition rates and apply the fluctuation dissipation theorem to solve the model. [less ▲]

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See detailDetecting User Mode Linux Honeypots is fine ... but it's better to crash them.
Wagener, Gerard UL; Raynal, Frédéric; Dulaunoy, Alexandre et al

Scientific Conference (2008)

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See detailDynamical structure analysis of sparsity and minimality heuristics for reconstruction of biochemical networks
Howes, R.; Eccleston, L. J.; Goncalves, Jorge UL et al

in The proceedings of the 47th IEEE Conference on Decision and Control (2008)

Network reconstruction, i.e. obtaining network structure from input-output information, is a central theme in systems biology. A variety of approaches aim to obtaining structural information from ... [more ▼]

Network reconstruction, i.e. obtaining network structure from input-output information, is a central theme in systems biology. A variety of approaches aim to obtaining structural information from available data. Previous work has introduced dynamical structure functions as a tool for posing and solving the network reconstruction problem. Even for linear time invariant systems, reconstruction requires specific additional information not generated in the typical system identification process. This paper demonstrates that such extra information can be obtained through a limited sequence of system identification experiments on structurally modified systems, analogous to gene silencing and overexpression experiments. In the absence of such extra information, we discuss whether combined assumptions of network sparsity and minimality contribute to the recovery of the network dynamical structure. We provide sufficient conditions for a transfer function to have a completely decoupled minimal realization, and demonstrate that every transfer function is arbitrarily close to one that admits a perfectly decoupled minimal realization. This indicates that the assumptions of sparsity and minimality alone do not lend insight into the network structure. [less ▲]

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See detailRobust synchronization in networks of cyclic feedback systems
Hamadeh, A. O.; Goncalves, Jorge UL; Stan, G. B. V.

in The proceedings of the 47th IEEE Conference on Decision and Control (2008)

This paper presents a result on the robust synchronization of outputs of statically interconnected non-identical cyclic feedback systems that are used to model, among other processes, gene expression. The ... [more ▼]

This paper presents a result on the robust synchronization of outputs of statically interconnected non-identical cyclic feedback systems that are used to model, among other processes, gene expression. The result uses incremental versions of the small gain theorem and dissipativity theory to arrive at an upper bound on the norm of the synchronization error between corresponding states, giving a measure of the degree of convergence of the solutions. This error bound is shown to be a function of the difference between the parameters of the interconnected systems, and disappears in the case where the systems are identical, thus retrieving an earlier synchronization result. [less ▲]

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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 detailGlobal asymptotic stability of the limit cycle in piecewise linear versions of the Goodwin oscillator
Salinas Varela, A. A.; Stan, G. B. V.; Goncalves, Jorge UL

in Proceedings of the 17th IFAC World Congress (2008)

Conditions in the form of linear matrix inequalities (LMIs) are used in this paper to guarantee the global asymptotic stability of a limit cycle oscillation for a class of piecewise linear (PWL) systems ... [more ▼]

Conditions in the form of linear matrix inequalities (LMIs) are used in this paper to guarantee the global asymptotic stability of a limit cycle oscillation for a class of piecewise linear (PWL) systems defined as the feedback interconnection of a saturation controller with a single input, single output (SISO) linear time-invariant (LTI) system. The proposed methodology extends previous results on impact maps and surface Lyapunov functions to the case when the sets of expected switching times are arbitrarily large. The results are illustrated on a PWL version of the Goodwin oscillator. [less ▲]

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See detailWhat do we accept after an announcement?
de Boer, Mathijs UL; Herzig, Andreas; de Lima, Tiago et al

Scientific Conference (2008)

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See detailBatch control of the master equation: a linear programming approach
Goncalves, Jorge UL; Martins, N.

Scientific Conference (2008)

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See detailNumerische Untersuchungen der instationären Strömungstopologie im Nachlauf einer Seehundvibrisse
Witte, Matthias; Michael, Mark UL; Brede, Martin et al

in Ruck, B.; Leder, A.; Dopheide, D. (Eds.) Proceedings der 16.GALA-Fachtagung “Lasermethoden in der Strömungsmesstechnik“ (2008)

Im Rahmen des Schwerpunktprogramms 1207 „Strömungen in Natur und Technik“ wird die Umströmung einer Seehundvibrisse untersucht. Die Vibrissen von Seehunden zeichnen sich durch eine komplizierte ... [more ▼]

Im Rahmen des Schwerpunktprogramms 1207 „Strömungen in Natur und Technik“ wird die Umströmung einer Seehundvibrisse untersucht. Die Vibrissen von Seehunden zeichnen sich durch eine komplizierte dreidimensionale Strukturmodellierung aus. Sie versetzen den See- hund in die Lage, Nachlaufspuren von Beutefischen zu detektieren. Mit Hilfe Stereo- μ Piv Messungen an Seehundvibrissen konnte die stationäre Strömungstopologie des Vibrissen- nachlaufes ermittelt werden. Zum besseren Verständnis der Funktion der Strukturierung der Vibrisse ist es notwendig, die instationäre Strömungstopologie zu kennen. Durch räumlich und zeitlich hochauflösende numerische Verfahren soll die instationäre Strömungstopologie im Nachlauf einer Seehundvibrisse ermittelt werden. [less ▲]

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See detailTimeWarp: Interactive Time Travel with a Mobile Mixed Reality Game
Herbst, Iris; Braun, Anne-Kathrine; McCall, Roderick UL et al

in In the Proceedings of MobileHCI 2008, Amsterdam, Netherlands (2008)

Mobile location-aware applications have become quite popular across a range of new areas such as pervasive games and mobile edutainment applications. However it is only recently, that approaches have been ... [more ▼]

Mobile location-aware applications have become quite popular across a range of new areas such as pervasive games and mobile edutainment applications. However it is only recently, that approaches have been presented which combine gaming and education with mobile Augmented Reality systems. However they typically lack a close crossmedia integration of the surroundings, and often annotate or extend the environment rather than modifying and altering it. In this paper we present a mobile outdoor mixed reality game for exploring the history of a city in the spatial and the temporal dimension. We introduce the design and concept of the game and present a universal mechanism to define and setup multi-modal user interfaces for the game challenges. Finally we discuss the results of the user tests. [less ▲]

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See detailAn Improved Fast Correlation Attack on Stream Ciphers
Zhang, Bin UL; Feng, Dengguo

in Selected Areas in Cryptography (2008)

At Crypto’2000, Johansson and Jönsson proposed a fast correlation attack on stream ciphers based on the Goldreich-Rubinfeld-Sudan algorithm. In this paper we show that a combination of their approach with ... [more ▼]

At Crypto’2000, Johansson and Jönsson proposed a fast correlation attack on stream ciphers based on the Goldreich-Rubinfeld-Sudan algorithm. In this paper we show that a combination of their approach with techniques for substituting keystream and evaluating parity-checks gives us the most efficient fast correlation attack known so far. An application of the new algorithm results in the first-known near-practical key recovery attack on the shrinking generator with the parameters suggested by Krawczyk in 1994, which was verified in the 40-bit data LFSR case for which the only previously known efficient attacks were distinguishing attacks. [less ▲]

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See detailComparison of recently developed recovery type discretization error estimators for the extended finite element method
Ródenas, J. J.; Duflot, Marc; Bordas, Stéphane UL et al

in Schrefler, B A; Perego, U (Eds.) 8th World Congress on Computational Mechanics (WCCM8). 5th.European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2008) (2008)

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See detailThe smoothed extended finite element method
Natarajan, S.; Bordas, Stéphane UL; Minh, Q. D. et al

in Proceedings of the 6th International Conference on Engineering Computational Technology (2008)

This paper shows how the strain smoothing technique recently proposed by G.R.Liu [1] coined as smoothed finite element method (SFEM) can be coupled to partition of unity methods, namely extended finite ... [more ▼]

This paper shows how the strain smoothing technique recently proposed by G.R.Liu [1] coined as smoothed finite element method (SFEM) can be coupled to partition of unity methods, namely extended finite element method (XFEM) [2] to give birth to the smoothed extended finite element method (SmXFEM), which shares properties both with the SFEM and the XFEM. The proposed method suppresses the need to compute and integrate the derivatives of shape functions (which are singular at the tip in linear elastic fracture mechanics). Additionally, integration is performed along the boundary of the finite elements or smoothing cells and no isoparametric mapping is required, which allows elements of arbitrary shape. We present numerical results for cracks in linear elastic fracture mechanics problems. The method is verified on several examples and comparisons are made to the conventional XFEM. © 2008 Civil-Comp Press. [less ▲]

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See detailRobustness analysis of cellular systems for in silico drug discovery
Perumal, Thanneer Malai UL; Wu, Y.; Gunawan, R.

Scientific Conference (2008)

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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 detailBlock Backstepping, NDI and Related Cascade Designs for Efficient Development of Nonlinear Flight Control Laws
Thunberg, Johan UL; Robinson, J.W.C.

in Proceedings of the AIAA Guidance, Navigation and Control Conference and Exhibit 2008 (2008)

A common feature of many aircraft configurations is that the actuation mainly effects the moments, and thereby the angular accelerations, whereas the desired normal acceleration is achieved by adjusting ... [more ▼]

A common feature of many aircraft configurations is that the actuation mainly effects the moments, and thereby the angular accelerations, whereas the desired normal acceleration is achieved by adjusting the location of the velocity vector in body coordinates. Thus, the main desired effects of the actuators appear after one integration, and if the actuators have dynamics the effect of the primary control variable occurs after more than one integration. This inherent cascade structure of many aircraft control problems is exploited in e.g. nonlinear dynamic inversion via time scale separation (NDI-TSS) to yield a powerful nonlinear design method. In the present work we present a family of multivariable (three axis) nonlinear cascade design techniques for flight control law design which includes block backstepping and NDI-TSS as special cases and we show that this family can offer a large design flexibility and excellent performance as well as short design cycles. We show stability for the family of techniques and illustrate the theory using simulations based on the ADMIRE model which is a realistic nonlinear model of an agile fighter with delta-canard configuration. [less ▲]

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See detailKE Tableaux for Public Announcement Logic
de Boer, Mathijs UL

Scientific Conference (2007, September 06)

Public announcement logic (PAL) is a simple dynamic epistemic logic extending reasoning about knowledge of agents with a modal operator for simultaneous and transparent knowledge updates. This logic is no ... [more ▼]

Public announcement logic (PAL) is a simple dynamic epistemic logic extending reasoning about knowledge of agents with a modal operator for simultaneous and transparent knowledge updates. This logic is no more expressive than epistemic logic (EL) without updates, but exhibits compact representation of a number of complex epistemic situations. A labeled tableau proof system to reason with these updates directly is presented here. This system can analyse and present well-known epistemic puzzles like `muddy children' and `three wise men'. Using the KE tableau system as a basis, the modal and propositional characteristics of epistemic updates can be separated. [less ▲]

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See detailMathematical Modelling of Flux Decline due to Concentration Polarisation and Cake Layer Formation in Crossflow Filtration Systems
Hale, Jack UL; Li, Qilin; Harris, Alison et al

Scientific Conference (2007, May)

Crossflow membrane filtration is an effective way of removing both colloidal and dissolved organic matter from contaminated water supplies. Two phenomena domimate solute flux in crossflow systems ... [more ▼]

Crossflow membrane filtration is an effective way of removing both colloidal and dissolved organic matter from contaminated water supplies. Two phenomena domimate solute flux in crossflow systems; concentration polarization and cake layer formation. Many innovative mathematical models for predicting both flux decline and quasi-steady state flux have been produced in the literature. However, limited regime applicability and conflicting physical predictions have made choosing optimal performance parameters in design a challenging process. An overview of the current field of models was undertaken, including an assessment of mathematical assumptions, numerical computation workload and number and complexity of system constants. A new model incorporating viscosity dependence on concentration is developed for the concentration polarization regime. Preliminary results will also be presented from a Monte Carlo based molecular dynamics simulation of volume packing fraction in the cake layer regime. The novel aspects of these models will be compared with existing models and the experimental results of our collaborators. Laboratory ultrafiltration tests were undertaken using varying concentrations of Dextran. An outline of future model directions and refinements will be presented. [less ▲]

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See detailDynamical structure functions for the reverse engineering of LTI networks
Goncalves, Jorge UL; Howes, R.; Warnick, S.

in Proceedings of the 46th IEEE Conference on Decision and Control (2007)

This research explores the role and representation of network structure for LTI systems with partial state observations. We demonstrate that input-output representations, i.e. transfer functions, contain ... [more ▼]

This research explores the role and representation of network structure for LTI systems with partial state observations. We demonstrate that input-output representations, i.e. transfer functions, contain no internal structural information of the system. We further show that neither the additional knowledge of system order nor minimality of the true realization is generally sufficient to characterize network structure. We then introduce dynamical structure functions as an alternative, graphical-model based representation of LTI systems that contain both dynamical and structural information of the system. The main result uses dynamical structure to precisely characterize the additional information required to obtain network structure from the transfer function of the system. [less ▲]

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See detailMechanical failure in microstructural heterogeneous materials
Bordas, Stéphane UL; Hoppe, R. H. W.; Petrova, S. I.

in Lecture Notes in Computer Science (2007), 4310 LNCS

Various heterogeneous materials with multiple scales and multiple phases in the microstructure have been produced in the recent years. We consider a mechanical failure due to the initiation and ... [more ▼]

Various heterogeneous materials with multiple scales and multiple phases in the microstructure have been produced in the recent years. We consider a mechanical failure due to the initiation and propagation of cracks in places of high pore density in the microstructures. A multi-scale method based on the asymptotic homogenization theory together with the mesh superposition method (s-version of FEM) is presented for modeling of cracks. The homogenization approach is used on the global domain excluding the vicinity of the crack where the periodicity of the microstructures is lost and this approach fails. The multiple scale method relies on efficient combination of both macroscopic and microscopic models. The mesh superposition method uses two independent (global and local) finite element meshes and the concept of superposing the local mesh onto the global continuous mesh in such a way that both meshes not necessarily coincide. The homogenized material model is considered on the global mesh while the crack is analyzed in the local domain (patch) which allows to have an arbitrary geometry with respect to the underlying global finite elements. Numerical experiments for biomorphic cellular ceramics with porous microstructures produced from natural wood are presented. [less ▲]

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See detailDealing with requirements: Influences on Idea Generation in the Early Stages of Product Development
Gericke, Kilian UL; Schmidt-Kretschmer, Michael; Blessing, Lucienne UL

in Proceedings of DTRS7: Design Meeting Protocols (2007)

This paper aims at identifying factors which influence the number of ideas generated during a brainstorming meeting as part of an industrial mechanical engineering design project. A framework for ... [more ▼]

This paper aims at identifying factors which influence the number of ideas generated during a brainstorming meeting as part of an industrial mechanical engineering design project. A framework for describing groups of influencing factors and their relationships is used. As a result of an explorative, comparative protocol analysis of two design meetings the influence of some factors is described e.g. the formulation of the design task description and the sequence of the process steps. [less ▲]

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See detailMathematical models of circadian Ca2+ oscillations
Neil, D.; Goncalves, Jorge UL; Webb, A.R.

in Proceedings of the eighth International Conference on Systems Biology (2007)

In the model plant Arabidopsis thaliana, the concentration of cytosolic-free Ca2+ ([Ca2+]cyt) oscillates with a circadian rhythm. We are investigating the regulation and role of these oscillations both ... [more ▼]

In the model plant Arabidopsis thaliana, the concentration of cytosolic-free Ca2+ ([Ca2+]cyt) oscillates with a circadian rhythm. We are investigating the regulation and role of these oscillations both experimentally and mathematically. Through systems identification, we have developed simple mathematical models from a single experiment measuring [Ca2+]cyt and the promoter activity of CIRCADIAN CLOCK ASSOCIATED 1 (CCA1). Through validation with 4 contrasting datasets, including a clock-arrhythmic transgenic line (CCA1 overexpressor), we demonstrate the necessity for a light input pathway to regulate basal [Ca2+]cyt levels. [less ▲]

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See detailThree-dimensional non-linear fracture mechanics by enriched meshfree methods without asymptotic enrichment
Bordas, Stéphane UL; Zi, G.; Rabczuk, T.

in Proceedings of the IUTAM Symposium on Discretization Methods for Evolving Discontinuities (2007)

This paper presents a three-dimensional, extrinsically enriched meshfree method for initiation, growth and coalescence of an arbitrary number of cracks in non-linear solids including large deformations ... [more ▼]

This paper presents a three-dimensional, extrinsically enriched meshfree method for initiation, growth and coalescence of an arbitrary number of cracks in non-linear solids including large deformations, for statics and dynamics. The novelty of the methodology fashioned in this work is that only an extrinsic discontinuous enrichment and no near-tip/asymptotic enrichment is required. Instead, a Lagrange multiplier field is added along the crack front to close the crack along the front. This decreases the computational cost and removes difficulties involved with a branch enrichment. Numerical examples treated include the pull-out of a reinforcement bar from a concrete block, and a Taylor bar impact with very large deformation and fragmentation. The results are compared to experimental results, and other simulations from the literature, which shows the robustness and accuracy of the method. © 2007 Springer. [less ▲]

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See detailMöglichkeiten und Grenzen generischer Ansätze als Beitrag zur Steigerung der Robustheit von Produktentwicklungsprojekten
Gericke, Kilian UL; Schmidt-Kretschmer, Michael; Blessing, Lucienne UL

in Proceedings of 18th Symposium Design for X (2007)

Zur Darstellung des theoretischen Rahmens dieser Arbeit werden ein Modell zur Visualisierung der Vernetzung von Einflussfaktoren auf den Projekterfolg aus den Domänen Projekt-Management, Produkt und ... [more ▼]

Zur Darstellung des theoretischen Rahmens dieser Arbeit werden ein Modell zur Visualisierung der Vernetzung von Einflussfaktoren auf den Projekterfolg aus den Domänen Projekt-Management, Produkt und Stakeholder und ein Verbesserungsprozess zur Steigerung der Robustheit von Produktentwicklungsprojekten vorgestellt. Vor diesem Hintergrund werden die Grenzen aber auch die Möglichkeiten generischer Lösungsansätze diskutiert. Anhand einer Fallstudie wird untersucht welche Barrieren die Durchführung des Verbesserungsprozesses und somit auch die Anwendung der Lösungsansätze in der Praxis erschweren. Die Analysen zeigen, dass die Kenntnis der Ursachen von Problemen, die zu Planungsabweichungen in Produktenwicklungsprojekten führen, und eine entsprechende Anpassung der Handlungsempfehlungen Voraussetzungen zur Implementierung daraus abgeleiteter Maßnahmen sind. Die domänenübergreifende Betrachtung möglicher Einflussfaktoren gemäß dem Konzept der Robustheit führt während der Ursachenanalyse zu einem fundierten Verständnis der Problemlage und ermöglicht eine bessere Anpassung der Lösungsansätze. Aus den theoretischen Vorüberlegungen und den Ergebnissen der Fallstudie werden Anforderungen an die Weiterentwicklung des Ansatzes zur Steigerung der Robustheit von Produktentwicklungsprojekten abgeleitet, der die Anwender unterstützen soll, den Transfer empirischer Erkenntnisse und Handlungsempfehlungen auf individuelle Problemstellungen zu vollziehen. [less ▲]

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See detailOn L2 error bounds between systems
Salinas, A.; Papachristodoulou, A.; Goncalves, Jorge UL

Scientific Conference (2006)

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See detailAnalyse prozessbezogener Einflussfaktoren zur Steigerung der Robustheit von Produktenwicklungsprojekten
Gericke, Kilian UL; Blessing, Lucienne UL

in Proceedings of 17th Symposium Design for X (2006)

Auf Basis des Konzeptes der Robustheit von Produktentwicklungsprojekten werden Effekte dargelegt, die zu Planungsabweichungen führen. Das Konzept wird durch eine Diskussion der Erfolgskriterien von ... [more ▼]

Auf Basis des Konzeptes der Robustheit von Produktentwicklungsprojekten werden Effekte dargelegt, die zu Planungsabweichungen führen. Das Konzept wird durch eine Diskussion der Erfolgskriterien von Projekten und möglichen Ansatzpunkten zur Steigerung der Robustheit umrissen. Als Ergebnis einer Literaturstudie wurden Problemschwerpunkte hinsichtlich der Ursachen von Planungsabweichungen und deren Erscheinungsformen identifiziert. Auf Grundlage dieser Studien lassen sich jedoch keine Ansätze zur Steigerung der Robustheit von Produktentwicklungsprojekten ableiten. Die Betrachtung der Studien bildet den Ausgangspunkt für eigene Untersuchungen, die zu einem besseren Verständnis der Ursachen von Planungsabweichungen in Produktentwicklungsprojekten und zur Ableitung von Handlungsempfehlungen führen sollen. [less ▲]

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See detailClinical data based optimal STI strategies for HIV: a reinforcement learning approach
Ernst, D.; Stan, G.B.; Goncalves, Jorge UL et al

in Proceedings of the IEEE Conference on Decision and Control (2006)

This paper addresses the problem of computing optimal structured treatment interruption strategies for HIV infected patients. We show that reinforcement learning may be useful to extract such strategies ... [more ▼]

This paper addresses the problem of computing optimal structured treatment interruption strategies for HIV infected patients. We show that reinforcement learning may be useful to extract such strategies directly from clinical data, without the need of an accurate mathematical model of HIV infection dynamics. To support our claims, we report simulation results obtained by running a recently proposed batch-mode reinforcement learning algorithm, known as fitted Q iteration, on numerically generated data. [less ▲]

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See detailRhythmic regulation of Ca2+ signalling networks
Gardner, M.; Hotta, C.; Hubbard, K. et al

Scientific Conference (2006)

The circadian clock is the internal timekeeper of plants. This clock regulates most aspects of plant physiology providing considerable competitive advantage. We are investigating the role for oscillations ... [more ▼]

The circadian clock is the internal timekeeper of plants. This clock regulates most aspects of plant physiology providing considerable competitive advantage. We are investigating the role for oscillations in the cytosolic free Ca2+ concentration ([Ca2+]cyt) in the circadian control of cellular physiology. We have previously demonstrated that circadian oscillations of [Ca2+]cyt encode photoperiodic information but the precise role of circadian [Ca2+]cyt oscillations remain obscure. We have been taking a systems wide approach to determine the origin and function of circadian oscillations of [Ca2+]cyt. Using pharmacology, bioinformatics and biochemical tools we have new evidence that oscillations of [Ca2+]cyt are generated by the small signalling intermediate, cADPR. Positioning the oscillations of [Ca2+]cyt with respect to the molecular oscillator using reverse genetics indicates that [Ca2+]cyt is an output of the clock. Using a whole genome transcriptional profile we have identified over 1800 circadian-regulated transcripts, many of which encode for Ca2+ signalling elements. The function of circadian-regulated transcripts encoding signalling components is being investigated by reverse genetic screens with automated imaging. Using our extensive data sets describing the circadian regulation of [Ca2+]cyt in different backgrounds and conditions we have constructed a mathematical model. This is being validated using mutant analysis and refined by introducing complexity to the model. Our data and models suggest that [Ca2+]cyt acts an output of the clock that regulates diverse aspects of physiology and has the potential to form a feedback loop with the molecular components of the oscillator. [less ▲]

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See detailAnalysis of biochemical networks using linear programming
Simeonidis, Vangelis UL; Dartnell, Lewis; Bogle, I. David L. et al

in Proceedings of the 7th World Congress of Chemical Engineering on CD-ROM (2005, December)

The application of mathematical programming methodologies to biochemical systems is demonstrated with the presentation of a linear programming (LP) algorithm for calculating minimal pathway distances in ... [more ▼]

The application of mathematical programming methodologies to biochemical systems is demonstrated with the presentation of a linear programming (LP) algorithm for calculating minimal pathway distances in biochemical networks. Minimal pathway distances are identified as the smallest number of steps separating two nodes in the network. Two case studies are examined: 1) the minimal distances for Escherichia coli Small Molecule Metabolism (SMM) enzymes are calculated and their correlations with genome distance and enzyme function are considered; 2) a study of the p53 cell cycle and apoptosis control network is performed in order to assess the survivability of the network to both random node failures and a directed assault, by studying the modification of the network’s diameter for successive protein knockouts. The results verify the applicability of the algorithm to problems of biochemical nature. [less ▲]

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See detailTradeoffs in networks with positive and negative feedback
Goncalves, Jorge UL; Yi, T.; Doyle, J.

Scientific Conference (2005)

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See detailApplication of robust model validation using SOSTOOLS to the study of G-Protein signalling in yeast
Yi, T.; Fazel, M.; Liu, X. et al

Scientific Conference (2005)

Two major methodological challenges in modeling biological systems are model (in)validation and parameter estimation. The traditional approach is to fit the model parameters to data. An alternative ... [more ▼]

Two major methodological challenges in modeling biological systems are model (in)validation and parameter estimation. The traditional approach is to fit the model parameters to data. An alternative approach pioneered by Packard, Frenklach, Seiler and colleagues (Frenklach et al., 2002) defines the range of parameter values that is consistent with the data while taking into account parametric and data uncertainty. If an invalidation certificate is found, the feasible parameter space is proved empty; otherwise, attempts to describe the feasible parameter space are carried out. We refer to this methodology as Robust Model Validation (RMV). Here we perform RMV using sum of squares (SOS) programs implemented by the MATLAB toolbox SOSTOOLS (Prajna et al., 2002). The principal advantage of SOS over conventional semidefinite programming (SDP) techniques such as the Sprocedure is the possibility of using higher-order multipliers to obtain tighter parameter bounds. We applied SOSTOOLS to a simple model of the yeast heterotrimeric G-protein cycle. We were able to invalidate the model based on real experimental data. Furthermore, using synthetic data that did not invalidate the model, we explored different techniques for representing the feasible parameter space. [less ▲]

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See detailHow companies learn from design flaws: results from an empirical study of the german manufacturing industry
Gries, Bruno; Gericke, Kilian UL; Blessing, Lucienne UL

in Proceedings of the 15th International Conference on Engineering Design (2005)

Design flaws often become apparent at a time when the product is already in use and its development process, which in many cases includes extensive testing of parts, components and prototypes, is ... [more ▼]

Design flaws often become apparent at a time when the product is already in use and its development process, which in many cases includes extensive testing of parts, components and prototypes, is considered complete. Such flaws may reach from poor ergonomics to the total failure of the product. Often, especially when user safety is at risk, design flaws are so severe that companies are forced to announce a product callback. Petroski suggests that many (if not most) products, which we are familiar with today, have a long history of previously flawed designs [3]. This implies that designers did indeed learn from design flaws in both senses of the word “learn”: discovering the flaw and utilizing the knowledge gained about it to find a solution. As far as discovering a design flaw is concerned, it can be assumed that the feedback from those who interact with the physical products in practice – the individuals who maintain, repair, recycle but essentially use the products – plays an important role. In their previous work, the authors pointed out hat this feedback information could not only be vital for identifying potential product hazards but helps designers to review the effects of their design measures and therefore to improve their products from generation to generation [4]. In order to obtain a better understanding of how designers learn from design flaws, a mail survey was conducted that aimed at investigating company-, process- and product-related factors of this phenomenon and to answer (among others) the following research questions: • To what extent are design flaws of a company’s (or a competitor’s) product a driving force in the development of new products? • How do the designers of a company become aware of design flaws of their products? • How successful are companies in correcting design flaws? • How do successful and unsuccessful companies differ in terms of size, activity profile of their designers and characteristics of their products? • What are possible factors that influence the success in correcting a design fault? [less ▲]

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See detailEine adaptive Produktentwicklungsmethodik als Beitrag zur Prozessgestaltung in der Produktentwicklung
Meißner, Moritz; Gericke, Kilian UL; Gries, Bruno et al

in Proceedings of 16th Symposium Design for X (2005)

In den letzen Jahrzehnten ist eine Vielzahl von Modellen zur methodischen Unterstützung des Produktentwicklungsprozesses (PEP) entstanden. Diese präskriptiven Modelle beinhalten oft den impliziten ... [more ▼]

In den letzen Jahrzehnten ist eine Vielzahl von Modellen zur methodischen Unterstützung des Produktentwicklungsprozesses (PEP) entstanden. Diese präskriptiven Modelle beinhalten oft den impliziten Anspruch, in jeder Branche und auf die Entwicklung jeder Art von Produkten anwendbar zu sein. Um dem gerecht zu werden, beschreiben die Modelle den PEP auf einem relativ abstrakten Niveau. Eine Anpassung an den Kontext der Produktentwicklung erfolgt in der Regel nicht. Existierende Ansätze ermöglichen eine Analyse des Kontexts aus verschiedenen Blickwinkeln, bieten jedoch keine konkreten Vorschläge, wie diese Analyse in den Prozess der Produktentwicklung einfließen kann. Welche Auswirkungen ausgewählte Kontextfaktoren auf tatsächliche PEP haben, geht aus einer schriftlichen Befragung von 1000 deutschen Unternehmen des produzierenden Gewerbes hervor. Es werden die Grundlagen einer Vorgehensweise beschrieben, welche basierend auf dem Kontext der Produktentwicklung die Gestaltung effektiver, effizienter, transparenter und methodisch unterstützter Produktentwicklungsprozesse ermöglichen soll. [less ▲]

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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 detailStudent's Perception of a Semantic Search Engine
Reichert, Monique UL; Linckels, Serge UL; Meinel, Christoph

Scientific Conference (2005)

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See detailA Method for Designing Virtual Places
McCall, Roderick UL; O'Neill, Shaleph; Benyon, David et al

Scientific Conference (2004)

This paper discusses our experiences of using a range of methods and techniques to measure the sense of place in real and virtual environments. The paper presents a discussion on presence and how this is ... [more ▼]

This paper discusses our experiences of using a range of methods and techniques to measure the sense of place in real and virtual environments. The paper presents a discussion on presence and how this is linked directly with our sense of place. From here we discuss the development of ‘The Place Probe’ a bundle of measurement techniques that allows for the direct comparison of real and virtual scenes. We show how the data gathered from the probe can be used to inform the design of virtual places. The whole approach is predicated on the premise that by understanding place we can improve our sense of presence in virtual environments. [less ▲]

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See detailFinding surface Lyapunov functions through sum-of-squares Programming
Spanos, D.; Goncalves, Jorge UL

in Proceedings of the American Control Conference 2004 (2004)

This work presents a sum-of-squares method to construct polynomial surface Lyapunov functions (SuLF) of arbitrary order for the impact maps of limit cycles in piecewise linear systems (PLS). This work ... [more ▼]

This work presents a sum-of-squares method to construct polynomial surface Lyapunov functions (SuLF) of arbitrary order for the impact maps of limit cycles in piecewise linear systems (PLS). This work extends previous results on stability analysis of such limit cycles, which utilized quadratic SuLFs. This paper also discusses an initial study of hierarchical jump linear systems where the switching is driven by feedback of low-level dynamical system states and a Markovian process. [less ▲]

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See detailA Mixed Similarity Measure for Data with Numeric, Symbolic and Ordinal Attributes
Nguyen, Ngoc Binh; Than, Van Cuong; Nguyen, Thanh-Phuong UL et al

in The proceeding of Japan-Vietnam Joint Workshop on Active Mining (Artificial Intelligence I) (2004)

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See detailGlobal Asymptotic Stability of Oscillations with Sliding Modes
Goncalves, Jorge UL

in Proceedings of the 15th IFAC World Congress (2003)

This paper explores a new methodology based on quadratic surface Lyapunov functions to globally analyze oscillations with sliding modes in relay feedback systems (RFS). The method consists in efficiently ... [more ▼]

This paper explores a new methodology based on quadratic surface Lyapunov functions to globally analyze oscillations with sliding modes in relay feedback systems (RFS). The method consists in efficiently construct quadratic Lyapunov functions on switching surfaces that can be used to show that impact maps, i.e., maps from one switch to the next, are contracting. This, in turn, shows that the system is globally stable. Several classes of piecewise linear systems (PLS) were previously successfully analyzed with this methodology. In this paper, we consider PLS whose trajectories switch between subsystems of different dimensions. We present and discuss distinct relaxations leading to sufficient conditions of different conservatism and computationally complexity. The results in this paper open the door to the analysis of other, more complex classes of PLS. [less ▲]

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See detailRegions of Stability for Limit Cycles of Piecewise Linear Systems
Goncalves, Jorge UL

in Proceedings of the 42th IEEE Conference on Decision and Control (2003)

This paper starts by presenting local stability conditions for limit cycles of piecewise linear systems (PLS), based on analyzing the linear part of Poincare maps. Local stability guarantees the existence ... [more ▼]

This paper starts by presenting local stability conditions for limit cycles of piecewise linear systems (PLS), based on analyzing the linear part of Poincare maps. Local stability guarantees the existence of an asymptotically stable neighborhood around the limit cycle. However, tools to characterize such neighborhood do not exist. This work gives conditions in the form of LMIs that guarantee asymptotic stability of PLS in a reasonably large region around a limit cycle, based on recent results on impact maps and surface Lyapunov functions (SuLF). These are exemplified with a biological application: a 4th-order neural oscillator, also used in many robotics applications like, for example, juggling and locomotion. [less ▲]

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