![]() Bordas, Stéphane ![]() ![]() Presentation (2014, May 12) We present recent results aiming at affording faster and error-controlled simulations of multi scale phenomena including fracture of heterogeneous materials and cutting of biological tissue. In a second ... [more ▼] We present recent results aiming at affording faster and error-controlled simulations of multi scale phenomena including fracture of heterogeneous materials and cutting of biological tissue. In a second part, we describe methodologies to isolate the user from the burden of mesh generation and regeneration as moving boundaries evolve. Results include advances in implicit boundary finite elements, (enriched) isogeometric boundary elements and extended finite element methods for multi-crack propagation. ABOUT THE PRESENTER In 1999, Stéphane Bordas joined a joint graduate programme of the French Institute of Technology (Ecole Spéciale des Travaux Publics) and the American Northwestern University. In 2003, he graduated in Theoretical and Applied Mechanics with a PhD from Northwestern University. Between 2003 and 2006, he was at the Laboratory of Structural and Continuum Mechanics at the Swiss Federal Institute of Technology in Lausanne, Switzerland. In 2006, he became permanent lecturer at Glasgow University’s Civil Engineering Department. Stéphane joined the Computational Mechanics team at Cardiff University in September 2009, as a Professor in Computational Mechanics and directed the institute of Mechanics and Advanced Materials from October 2010 to November 2013. He is the Editor of the book series “Advances in Applied Mechanics” since July 2013. In November 2013, he joined the University of Luxembourg as a Professor in Computational Mechanics. The main axes of his research team include (1) free boundary problems and problems involving complex geometries, in particular moving boundaries and (2) ‘a posteriori’ discretisation and model error control, rationalisation of the computational expense. Stéphane’s keen interest is to actively participate in innovation, technological transfer as well as software tool generation. This has been done through a number of joint ventures with various industrial partners (Bosch GmbH, Cenaero, inuTech GmbH, Siemens-LMS, Soitec SA) and the release of open-source software. In 2012, Stéphane was awarded an ERC Starting Independent Research Grant (RealTcut), to address the need for surgical simulators with a computational mechanics angle with a focus on the multi-scale simulation of cutting of heterogeneous materials in real-time. [less ▲] Detailed reference viewed: 236 (6 UL)![]() Chen, Li ![]() in International Journal for Numerical Methods in Engineering (in press) The quasicontinuum method is a concurrent multiscale approach in which lattice models are fully resolved in small regions of interest and coarse-grained elsewhere. Since the method was originally proposed ... [more ▼] The quasicontinuum method is a concurrent multiscale approach in which lattice models are fully resolved in small regions of interest and coarse-grained elsewhere. Since the method was originally proposed to accelerate atomistic lattice simulations, its refinement criteria – that drive refining coarse-grained regions and/or increasing fully-resolved regions – are generally associated with quantities relevant to the atomistic scale. In this contribution, a new refinement indicator is presented, based on the energies of dedicated cells at coarse-grained domain surfaces. This indicator is incorporated in an adaptive scheme of a generalization of the quasicontinuum method able to consider periodic representative volume elements, like the ones employed in most computational homogenization approaches. However, this indicator can also be used for conventional quasicontinuum frameworks. Illustrative numerical examples of elastic indentation and scratch of different lattices demonstrate the capabilities of the refinement indicator and its impact on adaptive quasicontinuum simulations. [less ▲] Detailed reference viewed: 233 (24 UL)![]() Schmitz, Sandra ![]() in Onwubiko, Cyril; Rosati, Pierangelo; Rege, Aunshul (Eds.) et al Proceedings of the International Conference on Cybersecurity, Situational Awareness and Social Media (2023, March 08) Detailed reference viewed: 43 (0 UL)![]() Jones, Catherine ![]() in Kyriakidis, P; Hadjimitsis, D; Skarlatos, D (Eds.) et al Geospatial Technologies for Local and Regional Development (2019) Location-based gaming (LBG) apps present many challenges to the design process. They have very different requirements compared to games that are aspatial in nature. They take place in the wild and this ... [more ▼] Location-based gaming (LBG) apps present many challenges to the design process. They have very different requirements compared to games that are aspatial in nature. They take place in the wild and this brings unique challenges to the practicalities of their design. There is a need to balance the core game play with the spatial requirements of location-aware technologies as well as considering the overall theme and objectives of the game together with the motivations and behaviours of players. We reflect upon this balancing act and explore an approach to creative paper prototyping through the medium of board games to co-design LBG requirements. We examine two case studies of location-based games with different goals. The first case study discusses the CrossCult Pilot 4 app built to trigger reflection on historical stories through thoughtful play. Whilst the second case study uses the City Conquerer app designed and played in Suzhou, China with a view to exploring notions of territoriality. The paper considers how spatial, social and interaction metaphors are used to simulate location-based games in a board game and discusses the lessons learned when transforming the paper game into a digital prototype. It forms part of a thinking by doing approach. By comparing the board games to the technical counterparts, we consider how effective are the features and activities implemented in the technology prototypes. We propose a set of 11 design constraints that developers must be mindful of when transitioning from paper to digital prototypes. [less ▲] Detailed reference viewed: 197 (4 UL)![]() Beine, Michel ![]() ![]() ![]() in Salah, Albert Ali; Pentland, Alex; Lepri, Bruno (Eds.) et al Guide to Mobile Data Analytics in Refugee Scenarios: The 'Data for Refugees Challenge' Study (2019) Our research report employs the D4R data and combines it with several <br />other sources to study one of the multiple aspects of integration of refugees, namely <br />the mobility of refugees across ... [more ▼] Our research report employs the D4R data and combines it with several <br />other sources to study one of the multiple aspects of integration of refugees, namely <br />the mobility of refugees across provinces in Turkey. In particular, we employ a <br />standard gravity model to empirically estimate a series of determinants of refugee <br />movements. These include the standard determinants such as province characteristics, <br />distances across provinces, levels of income, network effects as well as some <br />refugee-specific determinants such as the presence of refugee camps and the intensity <br />of phone call interaction among refugees. Importantly, we explore the effect <br />of certain categories of news events, notably protests, violence, and asylum grants. <br />Considering news as an indicator of policy implemented at the provincial level, we <br />gain a better understanding as to how policy can facilitate refugee mobility and thus <br />enhance integration. To benchmark our findings, we estimate the same model for the <br />mobility of individuals with a non-refugee status. [less ▲] Detailed reference viewed: 106 (4 UL)![]() Goncalves, Jorge ![]() in IEEE Transactions on Automatic Control (2005), 50(11), 1877-1882 Oscillations appear in numerous applications from biology to technology.However, besides local results, rigorous stability and robustness analysis of oscillations are rarely done due to their intrinsic ... [more ▼] Oscillations appear in numerous applications from biology to technology.However, besides local results, rigorous stability and robustness analysis of oscillations are rarely done due to their intrinsic nonlinear behavior. Poincarémaps associated with the system cannot typically be found explicitly and stability is estimated using extensive simulations and experiments. This paper gives conditions in the form of linear matrix inequalities (LMIs) that guarantee asymptotic stability in a reasonably large region around a limit cycle for a class of systems known as piecewise linear systems (PLS). Such conditions, based on recent results on impact maps and surface Lyapunov functions (SuLF), allow a systematic and efficient analysis of oscillations of PLS or arbitrarily close approximations of nonlinear systems by PLS. The methodology applies to any locally stable limit cycle of a PLS, regardless of the dimension and the number of switching surfaces of the system, and is illustrated with a biological application: a fourth-order neural oscillator, also used in many robotics applications such as juggling and locomotion. [less ▲] Detailed reference viewed: 152 (1 UL)![]() Goncalves, Jorge ![]() 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 ▲] Detailed reference viewed: 104 (0 UL)![]() ; Viti, Francesco ![]() Scientific Conference (2021, June) Detailed reference viewed: 35 (4 UL)![]() ; ; Jones, Catherine ![]() in Liapis, Antonios; Kyburz, Penny; Volz, Vanessa (Eds.) et al Proceedings of DG '20: International Conference on the Foundations of Digital Games (2020, September 15) Detailed reference viewed: 42 (2 UL)![]() Bulle, Raphaël ![]() ![]() in Applied Mathematics Letters (2020), 107 We provide a new argument proving the reliability of the Bank-Weiser estimator for Lagrange piecewise linear finite elements in both dimension two and three. The extension to dimension three constitutes ... [more ▼] We provide a new argument proving the reliability of the Bank-Weiser estimator for Lagrange piecewise linear finite elements in both dimension two and three. The extension to dimension three constitutes the main novelty of our study. In addition, we present a numerical comparison of the Bank-Weiser and residual estimators for a three-dimensional test case. [less ▲] Detailed reference viewed: 174 (41 UL)![]() ; Viti, Francesco ![]() in Transportation Research. Part C : Emerging Technologies (2016) Detailed reference viewed: 127 (2 UL)![]() ; Goncalves, Jorge ![]() 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 ▲] Detailed reference viewed: 96 (0 UL)![]() Nurunnabi, Abdul Awal Md ![]() ![]() in Resampling methods for a reliable validation set in deep learning based point cloud classification (2022, June) A validation data set plays a pivotal role in tweaking a machine learning model trained in a supervised manner. Many existing algorithms select a part of available data by using random sampling to produce ... [more ▼] A validation data set plays a pivotal role in tweaking a machine learning model trained in a supervised manner. Many existing algorithms select a part of available data by using random sampling to produce a validation set. However, this approach can be prone to overfitting. One should follow careful data splitting to have reliable training and validation sets that can produce a generalized model with a good performance for the unseen (test) data. Data splitting based on resampling techniques involves repeatedly drawing samples from the available data. Hence, resampling methods can give better generalization power to a model, because they can produce and use many training and/or validation sets. These techniques are computationally expensive, but with increasingly available high-performance computing facilities, one can exploit them. Though a multitude of resampling methods exist, investigation of their influence on the generality of deep learning (DL) algorithms is limited due to its non-linear black-box nature. This paper contributes by: (1) investigating the generalization capability of the four most popular resampling methods: k-fold cross-validation (k-CV), repeated k-CV (Rk-CV), Monte Carlo CV (MC-CV) and bootstrap for creating training and validation data sets used for developing, training and validating DL based point cloud classifiers (e.g., PointNet; Qi et al., 2017a), (2) justifying Mean Square Error (MSE) as a statistically consistent estimator, and (3) exploring the use of MSE as a reliable performance metric for supervised DL. Experiments in this paper are performed on both synthetic and real-world aerial laser scanning (ALS) point clouds. [less ▲] Detailed reference viewed: 43 (2 UL)![]() ; ; et al in Blue-Green System (2020), 2(1) Our modern cities are resource sinks designed on the current linear economic model which recovers very little of the original input. As the current model is not sustainable, a viable solution is to ... [more ▼] Our modern cities are resource sinks designed on the current linear economic model which recovers very little of the original input. As the current model is not sustainable, a viable solution is to recover and reuse parts of the input. In this context, resource recovery using nature-based solutions (NBS) is gaining popularity worldwide. In this specific review, we focus on NBS as technologies that bring nature into cities and those that are derived from nature, using (micro)organisms as principal agents, provided they enable resource recovery. The findings presented in this work are based on an extensive literature review, as well as on original results of recent innovation projects across Europe. The case studies were collected by participants of the COST Action Circular City, which includes a portfolio of more than 92 projects. The present review article focuses on urban wastewater, industrial wastewater, municipal solid waste and gaseous effluents, the recoverable products (e.g., nutrients, nanoparticles, energy), as well as the implications of source-separation and circularity by design. The analysis also includes assessment of the maturity of different technologies (technology readiness level) and the barriers that need to be overcome to accelerate the transition to resilient, self-sustainable cities of the future. [less ▲] Detailed reference viewed: 96 (3 UL)![]() ; Zilian, Andreas ![]() in International Journal for Numerical Methods in Engineering (2011), 86(6), 667-687 This contribution discusses extended physical interface models for fluid-structure interaction problems and investigates their phenomenological effects on the behavior of coupled systems by numerical ... [more ▼] This contribution discusses extended physical interface models for fluid-structure interaction problems and investigates their phenomenological effects on the behavior of coupled systems by numerical simulation. Besides the various types of friction at the fluid-structure interface the most interesting phenomena are related to effects due to additional interface stiffness and damping. The paper introduces extended models at the fluid-structure interface on the basis of rheological devices (Hooke, Newton, Kelvin, Maxwell, Zener). The interface is decomposed into a Lagrangian layer for the solid-like part and an Eulerian layer for the fluid-like part. The mechanical model for fluid-structure interaction is based on the equations of rigid body dynamics for the structural part and the incompressible Navier-Stokes equations for viscous flow. The resulting weighted residual form uses the interface velocity and interface tractions in both layers in addition to the field variables for fluid and structure. The weak formulation of the whole coupled system is discretized using space-time finite elements with a discontinuous Galerkin method for time-integration leading to a monolithic algebraic system. The deforming fluid domain is taken into account by deformable space-time finite elements and a pseudo-structure approach for mesh motion. The sensitivity of coupled systems to modification of the interface model and its parameters is investigated by numerical simulation of flow induced vibrations of a spring supported fluid-immersed cylinder. It is shown that the presented rheological interface model allows to influence flow-induced vibrations. © 2010 John Wiley & Sons, Ltd. [less ▲] Detailed reference viewed: 119 (0 UL)![]() ![]() ; ; 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 ▲] Detailed reference viewed: 90 (0 UL)![]() Mazier, Arnaud ![]() in Journal of Biomechanics (2021), 128 In breast surgical practice, drawing is part of the preoperative planning procedure and is essential for a successful operation. In this study, we design a pipeline to assist surgeons with patient ... [more ▼] In breast surgical practice, drawing is part of the preoperative planning procedure and is essential for a successful operation. In this study, we design a pipeline to assist surgeons with patient-specific breast surgical drawings. We use a deformable torso model containing the surgical patterns to match any breast surface scan. To be compatible with surgical timing, we build an articulated model through a skinning process coupled with shape deformers to enhance a fast registration process. On one hand, the scalable bones of the skinning account for pose and morphological variations of the patients. On the other hand, pre-designed artistic blendshapes create a linear space for guaranteeing anatomical variations. Then, we apply meaningful constraints to the model to find a trade-off between precision and speed. The experiments were conducted on 7 patients, in 2 different poses (prone and supine) with a breast size ranging from 36A and 42C (US/UK bra sizing). The acquisitions were obtained using the depth camera Structure Sensor, and the breast scans were acquired in less than 1 minute. The result is a registration method converging within a few seconds (3 maximum), reaching a Mean Absolute Error of 2.3 mm for mesh registration and 8.0 mm for breast anatomical landmarks. Compared to the existing literature, our model can be personalized and does not require any database. Finally, our registered model can be used to transfer surgical reference patterns onto any patient in any position. [less ▲] Detailed reference viewed: 132 (14 UL)![]() Sajadi Alamdari, Seyed Amin ![]() ![]() in The 20th World Congress of the International Federation of Automatic Control, IFAC 2017 World Congress, Toulouse, France, 9-14 July 2017 (2017, July 11) Stochastic nonlinear model predictive control has been developed to systematically find an optimal decision with the aim of performance improvement in dynamical systems that involve uncertainties. However ... [more ▼] Stochastic nonlinear model predictive control has been developed to systematically find an optimal decision with the aim of performance improvement in dynamical systems that involve uncertainties. However, most of the current methods are risk-neutral for safety-critical systems and depend on computationally expensive algorithms. This paper investigates on the risk-averse optimal stochastic nonlinear control subject to real-time safety-critical systems. In order to achieve a computationally tractable design and integrate knowledge about the uncertainties, bounded trajectories generated to quantify the uncertainties. The proposed controller considers these scenarios in a risk-sensitive manner. A certainty equivalent nonlinear model predictive control based on minimum principle is reformulated to optimise nominal cost and expected value of future recourse actions. The capability of proposed method in terms of states regulations, constraints fulfilment, and real-time implementation is demonstrated for a semi-autonomous ecological advanced driver assistance system specified for battery electric vehicles. This system plans for a safe and energy-efficient cruising velocity profile autonomously. [less ▲] Detailed reference viewed: 191 (8 UL)![]() Fridgen, Gilbert ![]() in 30th International Conference on Information Systems (ICIS) (2009) Detailed reference viewed: 33 (0 UL)![]() Backes, Dietmar ![]() in The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences (2020, August 12), XLIII-B2-2020 Article Metrics Related articles(1017), 1024 An efficient alternative to labour-intensive terrestrial and costly airborne surveys is the use of small, inexpensive Unmanned Aerial Vehicles (UAVs) or Remotely Piloted Aerial Systems (RPAS). These low ... [more ▼] An efficient alternative to labour-intensive terrestrial and costly airborne surveys is the use of small, inexpensive Unmanned Aerial Vehicles (UAVs) or Remotely Piloted Aerial Systems (RPAS). These low-altitude remote sensing platforms, commonly known as drones, can carry lightweight optical and LiDAR sensors. Even though UAV systems still have limited endurance, they can provide a flexible and relatively inexpensive monitoring solution for a limited area of interest. This study investigated the applicability of monitoring the morphology of a frequently changing glacial stream using high-resolution topographic surface models derived from low-altitude UAV-based photogrammetry and LiDAR. An understanding of river-channel morphology and its response to anthropogenic and natural disturbances is imperative for effective watershed management and conservation. We focus on the data acquisition, processing workflow and highlight identified challenges and shortcomings. Additionally, we demonstrate how LiDAR data acquisition simulations can help decide which laser scanning approach to use and help optimise data collection to ensure full coverage with desired level of detail. Lastly, we showcase a case study of 3D surface change analysis in an alpine stream environment with UAV-based photogrammetry. The datasets used in this study were collected as part of the ISPRS Summer School of Alpine Research, which will continue to add new data layers on a biyearly basis. This growing data repository is freely available for research. [less ▲] Detailed reference viewed: 175 (19 UL) |
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