KE Tableaux for Public Announcement Logic

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 ▲]

L2-gain of double integrators with saturation nonlinearity

in Proceedings of the 15th IFAC World Congress (2002)

This paper uses quadratic surface Lyapunov functions to efficiently check if a double integrator in feedback with a saturation nonlinearity has L2-gain less than gamma > 0. We show that for many of such ... [more ▼]

This paper uses quadratic surface Lyapunov functions to efficiently check if a double integrator in feedback with a saturation nonlinearity has L2-gain less than gamma > 0. We show that for many of such systems, the L2-gain is non-conservative in the sense that they are approximately equal to the low erbound obtained by replacing the saturation with a constant gain of 1. These results allow the use of classical analysis tools like mu -analysis or IQCs to analyze systems with double integrators and saturations, including servo systems like some mechanical systems, satellites, hard-disks, CD players, etc. [less ▲]

Lab Testing Beyond Usability: Challenges and Recommendations for Assessing User Experiences

in Journal of Usability Studies (2017), 12(3), 133-154

In the “third wave” of human-computer interaction (HCI), the advent of the conceptual approach of UX broadens and changes the HCI landscape. Methods approved before, mainly within the conceptual approach ... [more ▼]

In the “third wave” of human-computer interaction (HCI), the advent of the conceptual approach of UX broadens and changes the HCI landscape. Methods approved before, mainly within the conceptual approach of usability, are still widely used, and yet their adequacy for UX evaluation remains uncertain in many applications. Laboratory testing is undoubtedly the most prominent example of such a method. Hence, in this study, we investigated how the more comprehensive and emotional scope of UX can be assessed by laboratory testing. In this paper, we report on a use case study involving 70 participants. They first took part in user/laboratory tests and then were asked to evaluate their experience with the two systems (perceived UX) by filling out an AttrakDiff scale and a UX needs fulfillment questionnaire. We conducted post-test interviews to better understand participants’ experiences. We analyzed how the participants’ perceived UX depends on quantitative (e.g., task completion time, task sequence, level of familiarity with the system) and qualitative aspects (think aloud, debriefing interviews) within the laboratory context. Results indicate that the laboratory setting has a strong impact on the participants’ perceived UX, and support a discussion of the quality and limitations of laboratory evaluations regarding UX assessment. In this paper, we have identified concrete challenges and have provided solutions and tips useful for both practitioners and researchers who seek to account for the subjective, situated, and temporal nature of the UX in their assessments. [less ▲]

Large scale phase field model of fracture and cutting in soft tissues

Scientific Conference (2015, July)

The phase field method has proven to be an important tool in computational mechanics in that it is able to deal naturally with crack nucleation and branching [1]. In this contribution, we demonstrate a ... [more ▼]

The phase field method has proven to be an important tool in computational mechanics in that it is able to deal naturally with crack nucleation and branching [1]. In this contribution, we demonstrate a large scale phase field model of fracture and cutting of soft tissues undergoing non-linear deformations with a material law defined by a hyperelastic energy density functional. We will also provide some initial thoughts on the how the effect of a porous medium can be incorporated into the phase field model. We implement this work using the FEniCS project and PETSc software packages [2, 3]. [less ▲]

Lessons learnt from a corporate car-sharing system: the case of the University of Luxembourg

Scientific Conference (2017, May)

Leveraging state-of-the-art architectures by enriching training information - a case study

Speeches/Talks (2021)

Our working hypothesis is that key factors in COVID-19 imaging are the available imaging data and their label noise and confounders, rather than network architectures per se. Thus, we applied existing ... [more ▼]

Our working hypothesis is that key factors in COVID-19 imaging are the available imaging data and their label noise and confounders, rather than network architectures per se. Thus, we applied existing state-of-the-art convolution neural network frameworks based on the U-Net architecture, namely nnU-Net [3], and focused on leveraging the available training data. We did not apply any pre-training nor modi ed the network architecture. First, we enriched training information by generating two additional labels for lung and body area. Lung labels were created with a public available lung segmentation network and weak body labels were generated by thresholding. Subsequently, we trained three di erent multi-class networks: 2-label (original background and lesion labels), 3-label (additional lung label) and 4-label (additional lung and body label). The 3-label obtained the best single network performance in internal cross-validation (Dice-Score 0.756) and on the leaderboard (Dice- Score 0.755, Haussdor 95-Score 57.5). To improve robustness, we created a weighted ensemble of all three models, with calibrated weights to optimise the ranking in Dice-Score. This ensemble achieved a slight performance gain in internal cross-validation (Dice-Score 0.760). On the validation set leaderboard, it improved our Dice-Score to 0.768 and Haussdor 95- Score to 54.8. It ranked 3rd in phase I according to mean Dice-Score. Adding unlabelled data from the public TCIA dataset in a student-teacher manner signi cantly improved our internal validation score (Dice-Score of 0.770). However, we noticed partial overlap between our additional training data (although not human-labelled) and  nal test data and therefore submitted the ensemble without additional data, to yield realistic assessments. [less ▲]

Lifetime prediction for solder joints with the extended finite element method

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 ▲]

LINEAR BUCKLING ANALYSIS OF CRACKED ISOTROPIC PLATES USING THE EXTENDED FINITE ELEMENT METHOD

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 ▲]

Linear identification of nonlinear systems: A lifting technique based on the Koopman operator

in Proceedings of the 55th IEEE Conference on Decision and Control (2016, December)

We exploit the key idea that nonlinear system identification is equivalent to linear identification of the socalled Koopman operator. Instead of considering nonlinear system identification in the state ... [more ▼]

We exploit the key idea that nonlinear system identification is equivalent to linear identification of the socalled Koopman operator. Instead of considering nonlinear system identification in the state space, we obtain a novel linear identification technique by recasting the problem in the infinite-dimensional space of observables. This technique can be described in two main steps. In the first step, similar to a component of the Extended Dynamic Mode Decomposition algorithm, the data are lifted to the infinite-dimensional space and used for linear identification of the Koopman operator. In the second step, the obtained Koopman operator is “projected back” to the finite-dimensional state space, and identified to the nonlinear vector field through a linear least squares problem. The proposed technique is efficient to recover (polynomial) vector fields of different classes of systems, including unstable, chaotic, and open systems. In addition, it is robust to noise, well-suited to model low sampling rate datasets, and able to infer network topology and dynamics. [less ▲]

Linear smoothed extended finite element method

E-print/Working paper (n.d.)

The extended finite element method (XFEM) was introduced in 1999 to treat problems involving discontinuities with no or minimal remeshing through appropriate enrichment functions. This enables elements to ... [more ▼]

The extended finite element method (XFEM) was introduced in 1999 to treat problems involving discontinuities with no or minimal remeshing through appropriate enrichment functions. This enables elements to be split by a discontinuity, strong or weak and hence requires the integration of discontinuous functions or functions with discontinuous derivatives over elementary volumes. Moreover, in the case of open surfaces and singularities, special, usually non-polynomial functions must also be integrated.A variety of approaches have been proposed to facilitate these special types of numerical integration, which have been shown to have a large impact on the accuracy and convergence of the numerical solution. The smoothed extended finite element method (SmXFEM) [1], for example, makes numerical integration elegant and simple by transforming volume integrals into surface integrals. However, it was reported in [1, 2] that the strain smoothing is inaccurate when non-polynomial functions are in the basis. This is due to the constant smoothing function used over the smoothing domains which destroys the effect of the singularity. In this paper, we investigate the benefits of a recently developed Linear smoothing procedure [3] which provides better approximation to higher order polynomial fields in the basis. Some benchmark problems in the context of linear elastic fracture mechanics (LEFM) are solved to compare the standard XFEM, the constant-smoothed XFEM (Sm-XFEM) and the linear-smoothed XFEM (LSm-XFEM). We observe that the convergence rates of all three methods are the same. The stress intensity factors (SIFs) computed through the proposed LSm-XFEM are however more accurate than that obtained through Sm-XFEM. To conclude, compared to the conventional XFEM, the same order of accuracy is achieved at a relatively low computational effort. [less ▲]