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See detailA Bayesian framework to identify random parameter fields based on the copula theorem and Gaussian fields: Application to polycrystalline materials
Rappel, Hussein UL; Wu, Ling; Noels, Ludovic et al

in Journal of Applied Mechanics (in press)

For many models of solids, we frequently assume that the material parameters do not vary in space, nor that they vary from one product realization to another. If the length scale of the application ... [more ▼]

For many models of solids, we frequently assume that the material parameters do not vary in space, nor that they vary from one product realization to another. If the length scale of the application approaches the length scale of the micro-structure however, spatially fluctuating parameter fi elds (which vary from one realization of the fi eld to another) can be incorporated to make the model capture the stochasticity of the underlying micro-structure. Randomly fluctuating parameter fields are often described as Gaussian fields. Gaussian fi elds however assume that the probability density function of a material parameter at a given location is a univariate Gaussian distribution. This entails for instance that negative parameter values can be realized, whereas most material parameters have physical bounds (e.g. the Young's modulus cannot be negative). In this contribution, randomly fluctuating parameter fi elds are therefore described using the copula theorem and Gaussian fi elds, which allow di fferent types of univariate marginal distributions to be incorporated, but with the same correlation structure as Gaussian fields. It is convenient to keep the Gaussian correlation structure, as it allows us to draw samples from Gaussian fi elds and transform them into the new random fields. The bene fit of this approach is that any type of univariate marginal distribution can be incorporated. If the selected univariate marginal distribution has bounds, unphysical material parameter values will never be realized. We then use Bayesian inference to identify the distribution parameters (which govern the random fi eld). Bayesian inference regards the parameters that are to be identi fied as random variables and requires a user-defi ned prior distribution of the parameters to which the observations are inferred. For the homogenized Young's modulus of a columnar polycrystalline material of interest in this study, the results show that with a relatively wide prior (i.e. a prior distribution without strong assumptions), a single specimen is su ciffient to accurately recover the distribution parameter values. [less ▲]

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See detailA refinement indicator for adaptive quasicontinuum approaches for structural lattices
Chen, Li UL; Berke, Peter; Massart, Thierry et al

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 ▲]

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See detailIntercorrelated random fields with bounds and the Bayesian identification of their parameters: Application to linear elastic struts and fibers
Rappel, Hussein; Girolami, Mark; Beex, Lars UL

in International Journal for Numerical Methods in Engineering (in press)

Many materials and structures consist of numerous slender struts or fibers. Due to the manufacturing processes of different types of struts and the growth processes of natural fibers, their mechanical ... [more ▼]

Many materials and structures consist of numerous slender struts or fibers. Due to the manufacturing processes of different types of struts and the growth processes of natural fibers, their mechanical response frequently fluctuates from strut to strut, as well as locally within each strut. In associated mechanical models each strut is often represented by a string of beam elements, since the use of conventional three-dimensional finite elements renders the simulations computationally inefficient. The parameter input fields of each string of beam elements are ideally such that the local fluctuations and fluctuations between individual strings of beam elements are accurately captured. The goal of this study is to capture these fluctuations in several intercorrelated bounded random fields. Two formulations to describe the intercorrelations between each random field, as well as the case without any intercorrelation, are investigated. As only a few sets of input fields are available (due to time constraints of the supposed experimental techniques), the identification of the random fields’ parameters involves substantial uncertainties. A probabilistic identification approach based on Bayes’ theorem is employed to treat the involved uncertainties. [less ▲]

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See detailNitsche’s method for two and three dimensional NURBS patch coupling
Nguyen, Vinh-Phu; Kerfriden, Pierre; Brino, Marco et al

in Computational Mechanics (in press)

We present a Nitche’s method to couple non-conforming two and three-dimensional NURBS (Non Uniform Rational B-splines) patches in the context of isogeometric analysis (IGA). We present results for linear ... [more ▼]

We present a Nitche’s method to couple non-conforming two and three-dimensional NURBS (Non Uniform Rational B-splines) patches in the context of isogeometric analysis (IGA). We present results for linear elastostatics in two and and three-dimensions. The method can deal with surface-surface or volume-volume coupling, and we show how it can be used to handle heterogeneities such as inclusions. We also present preliminary results on modal analysis. This simple coupling method has the potential to increase the applicability of NURBS-based isogeometric analysis for practical applications. [less ▲]

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See detailNetwork Identifiability from Intrinsic Noise
Goncalves, Jorge UL; Hayden, David; Yuan, Ye

in IEEE Transactions on Automatic Control (in press)

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See detailDemand and Interference Aware Adaptive Resource Management for High Throughput GEO Satellite Systems
Abdu, Tedros Salih UL; Kisseleff, Steven UL; Lagunas, Eva UL et al

in IEEE Open Journal of the Communications Society (2022)

The scarce spectrum and power resources, the inter-beam interference, together with the high traffic demand, pose new major challenges for the next generation of Very High Throughput Satellite (VHTS ... [more ▼]

The scarce spectrum and power resources, the inter-beam interference, together with the high traffic demand, pose new major challenges for the next generation of Very High Throughput Satellite (VHTS) systems. Accordingly, future satellites are expected to employ advanced resource/interference management techniques to achieve high system spectrum efficiency and low power consumption while ensuring user demand satisfaction. This paper proposes a novel demand and interference aware adaptive resource management for geostationary (GEO) VHTS systems. For this, we formulate a multi-objective optimization problem to minimize the total transmit power consumption and system bandwidth usage while matching the offered capacity with the demand per beam. In this context, we consider resource management for a system with full-precoding, i.e. all beams are precoded; without precoding, i.e. no precoding is applied to any beam; and with partial precoding, i.e. only some beams are precoded. The nature of the problem is non-convex and we solve it by jointly using the Dinkelbach and Successive Convex Approximation (SCA) methods. The simulation results show that the proposed method outperforms the benchmark schemes. Specifically, we show that the proposed method requires low resource consumption, low computational time, and simultaneously achieves a high demand satisfaction. [less ▲]

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See detailFlexible Resource Optimization for GEO Multibeam Satellite Communication System
Abdu, Tedros Salih UL; Kisseleff, Steven UL; Lagunas, Eva UL et al

in IEEE Transactions on Wireless Communications (2021)

Conventional GEO satellite communication systems rely on a multibeam foot-print with a uniform resource allocation to provide connectivity to users. However, applying uniform resource allocation is ... [more ▼]

Conventional GEO satellite communication systems rely on a multibeam foot-print with a uniform resource allocation to provide connectivity to users. However, applying uniform resource allocation is inefficient in presence of non-uniform demand distribution. To overcome this limitation, the next generation of broadband GEO satellite systems will enable flexibility in terms of power and bandwidth assignment, enabling on-demand resource allocation. In this paper, we propose a novel satellite resource assignment design whose goal is to satisfy the beam traffic demand by making use of the minimum transmit power and utilized bandwidth. The motivation behind the proposed design is to maximize the satellite spectrum utilization by pushing the spectrum reuse to affordable limits in terms of tolerable interference. The proposed problem formulation results in a non-convex optimization structure, for which we propose an efficient tractable solution. We validate the proposed method with extensive numerical results, which demonstrate the efficiency of the proposed approach with respect to benchmark schemes. [less ▲]

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See detailPublic Covid-19 X-ray datasets and their impact on model bias - a systematic review of a significant problem
Garcia Santa Cruz, Beatriz UL; Bossa, Matias Nicolas UL; Sölter, Jan UL et al

in Medical Image Analysis (2021), 74

Computer-aided diagnosis and stratification of COVID-19 based on chest X-ray suffers from weak bias assessment and limited quality-control. Undetected bias induced by inappropriate use of datasets, and ... [more ▼]

Computer-aided diagnosis and stratification of COVID-19 based on chest X-ray suffers from weak bias assessment and limited quality-control. Undetected bias induced by inappropriate use of datasets, and improper consideration of confounders prevents the translation of prediction models into clinical practice. By adopting established tools for model evaluation to the task of evaluating datasets, this study provides a systematic appraisal of publicly available COVID-19 chest X-ray datasets, determining their potential use and evaluating potential sources of bias. Only 9 out of more than a hundred identified datasets met at least the criteria for proper assessment of the risk of bias and could be analysed in detail. Remarkably most of the datasets utilised in 201 papers published in peer-reviewed journals, are not among these 9 datasets, thus leading to models with a high risk of bias. This raises concerns about the suitability of such models for clinical use. This systematic review highlights the limited description of datasets employed for modelling and aids researchers to select the most suitable datasets for their task. [less ▲]

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See detailPublic Covid-19 X-ray datasets and their impact on model bias - a systematic review of a significant problem
Garcia Santa Cruz, Beatriz UL; Bossa, Matias Nicolas UL; Sölter, Jan UL et al

in Medical Image Analysis (2021), 74

Computer-aided diagnosis and stratification of COVID-19 based on chest X-ray suffers from weak bias assessment and limited quality-control. Undetected bias induced by inappropriate use of datasets, and ... [more ▼]

Computer-aided diagnosis and stratification of COVID-19 based on chest X-ray suffers from weak bias assessment and limited quality-control. Undetected bias induced by inappropriate use of datasets, and improper consideration of confounders prevents the translation of prediction models into clinical practice. By adopting established tools for model evaluation to the task of evaluating datasets, this study provides a systematic appraisal of publicly available COVID-19 chest X-ray datasets, determining their potential use and evaluating potential sources of bias. Only 9 out of more than a hundred identified datasets met at least the criteria for proper assessment of the risk of bias and could be analysed in detail. Remarkably most of the datasets utilised in 201 papers published in peer-reviewed journals, are not among these 9 datasets, thus leading to models with a high risk of bias. This raises concerns about the suitability of such models for clinical use. This systematic review highlights the limited description of datasets employed for modelling and aids researchers to select the most suitable datasets for their task. [less ▲]

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See detailAnalysis of MaaS membership attributes: an agent-based approach
Cisterna, Carolina UL; Bigi, Federico UL; Tinessa, Fiore et al

in Transportation Research Procedia (2021)

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See detail1361-9209/© 2021 Elsevier Ltd. All rights reserved.Microscopic energy consumption modelling of electric buses: model development, calibration, and validation
Fiori, Chiara; Montanino, Marcello; Nielsen, Sune et al

in Transportation Research. Part D, Transport and Environment (2021)

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See detailAssessing Equity in Carsharing Systems: the case of Munich, Germany
Giorgione, Giulio; Viti, Francesco UL

in Transportation Research Procedia (2021)

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See detailAlmost global convergence to practical synchronization in the generalized Kuramoto model on networks over the n-sphere
Markdahl, Johan UL; Proverbio, Daniele UL; Mi, La et al

in Communications Physics (2021), 4

From the flashing of fireflies to autonomous robot swarms, synchronization phenomena are ubiquitous in nature and technology. They are commonly described by the Kuramoto model that, in this paper, we ... [more ▼]

From the flashing of fireflies to autonomous robot swarms, synchronization phenomena are ubiquitous in nature and technology. They are commonly described by the Kuramoto model that, in this paper, we generalise to networks over n-dimensional spheres. We show that, for almost all initial conditions, the sphere model converges to a set with small diameter if the model parameters satisfy a given bound. Moreover, for even n, a special case of the generalized model can achieve phase synchronization with nonidentical frequency parameters. These results contrast with the standard n = 1 Kuramoto model, which is multistable (i.e., has multiple equilibria), and converges to phase synchronization only if the frequency parameters are identical. Hence, this paper shows that the generalized network Kuramoto models for n ≥ 2 displays more coherent and predictable behavior than the standard n = 1 model, a desirable property both in flocks of animals and for robot control. [less ▲]

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See detailA rigged model of the breast for preoperative surgical planning
Mazier, Arnaud UL; Ribes, Sophie; Gilles, Benjamin et al

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 ▲]

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See detailCreativity in Humans, Robots, Humbots
Lubart, Todd; Esposito, Dario; Gubenko, Alla UL et al

in Creativity: Theories – Research – Applications (2021), 8(1),

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See detailA hyper-reduction method using adaptivity to cut the assembly costs of reduced order models
Hale, Jack UL; Schenone, Elisa; Baroli, Davide UL et al

in Computer Methods in Applied Mechanics and Engineering (2021), 380

At every iteration or timestep of the online phase of some reduced-order modelling schemes, large linear systems must be assembled and then projected onto a reduced order basis of small dimension. The ... [more ▼]

At every iteration or timestep of the online phase of some reduced-order modelling schemes, large linear systems must be assembled and then projected onto a reduced order basis of small dimension. The projected small linear systems are cheap to solve, but assembly and projection are now the dominant computational cost. In this paper we introduce a new hyper-reduction strategy called reduced assembly (RA) that drastically cuts these costs. RA consists of a triangulation adaptation algorithm that uses a local error indicator to con- struct a reduced assembly triangulation specially suited to the reduced order basis. Crucially, this reduced assembly triangulation has fewer cells than the original one, resulting in lower assembly and projection costs. We demonstrate the efficacy of RA on a Galerkin-POD type reduced order model (RAPOD). We show performance increases of up to five times over the baseline Galerkin-POD method on a non-linear reaction-diffusion problem solved with a semi-implicit time-stepping scheme and up to seven times for a 3D hyperelasticity problem solved with a continuation Newton-Raphson algorithm. The examples are implemented in the DOLFIN finite element solver using PETSc and SLEPc for linear algebra. Full code and data files to produce the results in this paper are provided as supplementary material. [less ▲]

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See detailThe Impact of SARS-COVID-19 Outbreak on European Cities Urban Mobility
Vitello, Piergiorgio UL; Connors, Richard UL; Viti, Francesco UL

in Frontiers in Future Transportation (2021)

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See detailBalancing Shareability and Positive Interdependence to Support Collaborative Problem-Solving on Interactive Tabletops
Maquil, Valérie; Afkari, Hoorieh; Arend, Béatrice UL et al

in Advances in Human-Computer Interaction (2021)

To support collaboration, researchers from different fields have proposed the design principles of shareability (engaging users in shared interactions around the same content) and positive interdependence ... [more ▼]

To support collaboration, researchers from different fields have proposed the design principles of shareability (engaging users in shared interactions around the same content) and positive interdependence (distributing roles and information to make users dependent on each other). While, on its own, each principle was shown to successfully support collaboration in different contexts, these principles are also partially conflicting, and their combination creates several design challenges. This paper describes how shareability and positive interdependency were jointly implemented in an interactive tabletop-mediated environment called Orbitia, with the aim of inducing collaboration between three adult participants. We present the design details and rationale behind the proposed application. Furthermore, we describe the results of an empirical evaluation focusing on joint problem-solving efficiency, collaboration styles, participation equity, and perceived collaboration effectiveness. [less ▲]

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See detailBubble-Enriched Smoothed Finite Element Methods for Nearly-Incompressible Solids
Lee, Changkye; Natarajan, Sundararajan; Hale, Jack UL et al

in Computer Modeling in Engineering and Sciences (2021), 127(2), 411-436

This work presents a locking-free smoothed finite element method (S-FEM) for the simulation of soft matter modelled by the equations of quasi-incompressible hyperelasticity. The proposed method overcomes ... [more ▼]

This work presents a locking-free smoothed finite element method (S-FEM) for the simulation of soft matter modelled by the equations of quasi-incompressible hyperelasticity. The proposed method overcomes well-known issues of standard finite element methods (FEM) in the incompressible limit: the over-estimation of stiffness and sensitivity to severely distorted meshes. The concepts of cell-based, edge-based and node-based S-FEMs are extended in this paper to three-dimensions. Additionally, a cubic bubble function is utilized to improve accuracy and stability. For the bubble function, an additional displacement degree of freedom is added at the centroid of the element. Several numerical studies are performed demonstrating the stability and validity of the proposed approach. The obtained results are compared with standard FEM and with analytical solutions to show the effectiveness of the method. [less ▲]

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See detailFrictional interactions for non-localised beam-to-beam and beam-inside-beam contact
Magliulo, Marco; Lengiewicz, Jakub UL; Zilian, Andreas UL et al

in International Journal for Numerical Methods in Engineering (2021), 122(7), 1706-1731

This contribution presents the extensions of beam-to-beam and beam-inside-beam contact schemes of the same authors towards frictional interactions. Since the schemes are based on the beams’ true surfaces ... [more ▼]

This contribution presents the extensions of beam-to-beam and beam-inside-beam contact schemes of the same authors towards frictional interactions. Since the schemes are based on the beams’ true surfaces (instead of surfaces implicitly deduced from the beams’ centroid lines), the presented enhancements are not only able to account for frictional sliding in the beams’ axial directions, but also in the circumferential directions. Both the frictional beam-to-beam approach as well as the frictional beam-inside-beam approach are applicable to shear-deformable and shear-undeformable beams, as well as to beams with both circular and elliptical cross-sections (although the cross-sections must be rigid). A penalty formulation is used to treat unilateral and frictional contact constraints. FE implementation details are discussed, where automatic differentiation techniques are used to derive the implementations. Simulations involving large sliding displacements and large deformations are presented for both beam-to-beam and beam-inside-beam schemes. All simulation results are compared to those of the frictionless schemes. [less ▲]

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See detailTowards global flood mapping onboard low cost satellites with machine learning
Mateo‑Garcia, Gonzalo; Veitch‑Michaelis, Joshua; Smith, Lewis et al

in Scientific Reports (2021), 11(7249 (2021)),

Spaceborne Earth observation is a key technology for flood response, offering valuable information to decision makers on the ground. Very large constellations of small, nano satellites— ’CubeSats’ are a ... [more ▼]

Spaceborne Earth observation is a key technology for flood response, offering valuable information to decision makers on the ground. Very large constellations of small, nano satellites— ’CubeSats’ are a promising solution to reduce revisit time in disaster areas from days to hours. However, data transmission to ground receivers is limited by constraints on power and bandwidth of CubeSats. Onboard processing offers a solution to decrease the amount of data to transmit by reducing large sensor images to smaller data products. The ESA’s recent PhiSat-1 mission aims to facilitate the demonstration of this concept, providing the hardware capability to perform onboard processing by including a power-constrained machine learning accelerator and the software to run custom applications. This work demonstrates a flood segmentation algorithm that produces flood masks to be transmitted instead of the raw images, while running efficiently on the accelerator aboard the PhiSat-1. Our models are trained on WorldFloods: a newly compiled dataset of 119 globally verified flooding events from disaster response organizations, which we make available in a common format. We test the system on independent locations, demonstrating that it produces fast and accurate segmentation masks on the hardware accelerator, acting as a proof of concept for this approach. [less ▲]

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See detailExplorative analysis of potential MaaS customers: An agent-based scenario
Cisterna, Carolina UL; Giorgione, Giulio UL; Viti, Francesco UL

in Transportation Research Procedia (2021)

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See detailExperimental Evaluation of a Team of Multiple Unmanned Aerial Vehicles for Cooperative Construction
Real, Fran; Castaño, Angel; Torres-Gonzalez, Arturo et al

in IEEE Access (2021)

This article presents a team of multiple Unmanned Aerial Vehicles (UAVs) to perform cooperative missions for autonomous construction. In particular, the UAVs have to build a wall made of bricks that need ... [more ▼]

This article presents a team of multiple Unmanned Aerial Vehicles (UAVs) to perform cooperative missions for autonomous construction. In particular, the UAVs have to build a wall made of bricks that need to be picked and transported from different locations. First, we propose a novel architecture for multi-robot systems operating in outdoor and unstructured environments, where robustness and reliability play a key role. Then, we describe the design of our aerial platforms and grasping mechanisms to pick, transport and place bricks. The system was particularly developed for the Mohamed Bin Zayed International Robotics Challenge (MBZIRC), where Challenge 2 consisted of building a wall cooperatively with multiple UAVs. However, our approach is more general and extensible to other multi-UAV applications involving physical interaction, like package delivery. We present not only our results in the final stage of MBZIRC, but also our simulations and field experiments throughout the previous months to the competition, where we tuned our system and assessed its performance. [less ▲]

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See detailModelling of residually stressed, extended and inflated cylinders with application to aneurysms
Font, Alejandro; Jha, Niraj Kumar; Dehghani, Hamidreza UL et al

in Mechanics Research Communications (2021), 111

The paper presents the localized bifurcation abnormal enlargement associated with certain human diseases such as abdominal aortic aneurysms (AAA), among others. The constitutive framework herewith ... [more ▼]

The paper presents the localized bifurcation abnormal enlargement associated with certain human diseases such as abdominal aortic aneurysms (AAA), among others. The constitutive framework herewith proposed is constructed relying on the modelling of non-linear elastic materials under the action of residual stresses. The suitable incorporation on the mechanical response of residual stresses in the analysis is regarded important for the formation of aneurysms in soft tissues. From a mechanical perspective, the onset of aneurysms formation can be interpreted through bifurcation conditions, whose localization is relatively sensitive to different material and geometrical parameters as it is shown here. In order to reduce the risk and interpret aneurysm formation, we perform a thorough sensitivity analysis of the effect of design parameters such as tube diameter, length, thickness and strength of the residual stress field on bifurcation of a tube under inflation and extesion. A consistent residually stressed material model is formulated in terms of invariants for a general elastic strain-energy function. The dependence of applied pressure, axial stretch and different geometrical and constitutive parameters on bulging and bending bifurcation is illustrated. The numerical procedure to analyse the bifurcation of the finite deformation boundary-value problem at hand is developed based on the modified Riks method. The proposed formulation is implemented in the general-purpose finite element code ABAQUS using user-defined material subroutines.For a given material model, bulging bifurcation is expected for sufficiently large values of the axial stretch while the onset of bifurcation is found to be the bending mode for small values of the axial stretch. This transition zone from bending bifurcation to bulging bifurcation is analyzed for the different parameters considered. [less ▲]

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See detailDyPS: Dynamic, Private and Secure GWAS
Pascoal, Túlio UL; Decouchant, Jérémie UL; Boutet, Antoine et al

in Proceedings on Privacy Enhancing Technologies (2021)

Genome-Wide Association Studies (GWAS) identify the genomic variations that are statistically associated with a particular phenotype (e.g., a disease). The confidence in GWAS results increases with the ... [more ▼]

Genome-Wide Association Studies (GWAS) identify the genomic variations that are statistically associated with a particular phenotype (e.g., a disease). The confidence in GWAS results increases with the number of genomes analyzed, which encourages federated computations where biocenters would periodically share the genomes they have sequenced. However, for economical and legal reasons, this collaboration will only happen if biocenters cannot learn each others’ data. In addition, GWAS releases should not jeopardize the privacy of the individuals whose genomes are used. We introduce DyPS, a novel framework to conduct dynamic privacy-preserving federated GWAS. DyPS leverages a Trusted Execution Environment to secure dynamic GWAS computations. Moreover, DyPS uses a scaling mechanism to speed up the releases of GWAS results according to the evolving number of genomes used in the study, even if individuals retract their participation consent. Lastly, DyPS also tolerates up to all-but-one colluding biocenters without privacy leaks. We implemented and extensively evaluated DyPS through several scenarios involving more than 6 million simulated genomes and up to 35,000 real genomes. Our evaluation shows that DyPS updates test statistics with a reasonable additional request processing delay (11% longer) compared to an approach that would update them with minimal delay but would lead to 8% of the genomes not being protected. In addition, DyPS can result in the same amount of aggregate statistics as a static release (i.e., at the end of the study), but can produce up to 2.6 times more statistics information during earlier dynamic releases. Besides, we show that DyPS can support a larger number of genomes and SNP positions without any significant performance penalty. [less ▲]

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See detailDistributed Prediction of Unsafe Reconfiguration Scenarios of Modular Robotic Programmable Matter
Piranda, Benoit; Chodkiewicz, Paweł; Holobut, Paweł et al

in IEEE Transactions on Robotics (2021), 37(6), 2226-2233

We present a distributed framework for predicting whether a planned reconfiguration step of a modular robot will mechanically overload the structure, causing it to break or lose stability under its own ... [more ▼]

We present a distributed framework for predicting whether a planned reconfiguration step of a modular robot will mechanically overload the structure, causing it to break or lose stability under its own weight. The algorithm is executed by the modular robot itself and based on a distributed iterative solution of mechanical equilibrium equations derived from a simplified model of the robot. The model treats intermodular connections as beams and assumes no-sliding contact between the modules and the ground. We also provide a procedure for simplified instability detection. The algorithm is verified in the Programmable Matter simulator VisibleSim, and in real-life experiments on the modular robotic system Blinky Blocks. © 2004-2012 IEEE. [less ▲]

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See detailGA4GH Passport standard for digital identity and access permissions
Voisin, Craig; Linden, Mikael; Dyke, Stephanie O. M. et al

in Cell Genomics (2021), 1(2),

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See detailHolo Study – Mixed Reality Framework for Industrial Engineering Education and Training
Minoufekr, Meysam UL; Plapper, Peter UL

in Trends in Technical & Scientific Research (2020), 4(5), 0131-0135

Nowadays, students struggle with understanding complex production processes and kinematics of machine tools and robots. While professors mostly have been dealing with these subjects for many years ... [more ▼]

Nowadays, students struggle with understanding complex production processes and kinematics of machine tools and robots. While professors mostly have been dealing with these subjects for many years, students have only short time to be introduced to the complex nature of these topics. Mixed Reality allows students to engage hands-on in their subjects to reach new dimensions of understanding. Making challenging topics for students accessible by creating a more visual and tactile experience. The applications for entertainment and gaming are off the charts, but the implications for augmented reality in education and science are also undoubtedly massive. The project focusses on making education as interactive as possible, which helps both, teachers and students receive a unique tool for communicating phenomena and processes that are difficult to describe verbally. As a result, a complex knowledge becomes simple, an involvement of students grows, the quality of education increases [less ▲]

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See detailA Survey of Information Entropy Metrics for Complex Networks
Omar, Yamila UL; Plapper, Peter UL

in Entropy (2020)

Information entropy metrics have been applied to a wide range of problems that were abstracted as complex networks. This growing body of research is scattered in multiple disciplines, which makes it ... [more ▼]

Information entropy metrics have been applied to a wide range of problems that were abstracted as complex networks. This growing body of research is scattered in multiple disciplines, which makes it difficult to identify available metrics and understand the context in which they are applicable. In this work, a narrative literature review of information entropy metrics for complex networks is conducted following the PRISMA guidelines. Existing entropy metrics are classified according to three different criteria: whether the metric provides a property of the graph or a graph component (such as the nodes), the chosen probability distribution, and the types of complex networks to which the metrics are applicable. Consequently, this work identifies the areas in need for further development aiming to guide future research efforts. [less ▲]

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See detailHigh-Level Modular Autopilot Solution for Fast Prototyping of Unmanned Aerial Systems
Rodriguez de Cos, Carlos; Fernandez, Manuel Jesus; Sanchez Cuevas, Pedro Jesus UL et al

in IEEE Access (2020)

A redundant fast prototyping autopilot solution for unmanned aerial systems has been developed and successfully tested outdoors. While its low-level backbone is executed in a Raspberry Pi R 3 + NAVIO2 R ... [more ▼]

A redundant fast prototyping autopilot solution for unmanned aerial systems has been developed and successfully tested outdoors. While its low-level backbone is executed in a Raspberry Pi R 3 + NAVIO2 R with a backup autopilot, the computational power of an Intel R NUC mini-computer is employed to implement complex functionalities directly in Simulink R , thus including in-flight debugging, tuning and monitoring. Altogether, the presented tool provides a flexible and user-friendly high-level environment with enhanced computational capabilities, which drastically reduces the prototyping timespans of complex algorithms -between 50% and 75%, according to our long and proven experience in aerial robotics-, while preventing incidents thanks to its redundant design with a human-in-the-loop pilot on the reliable PX4. Three typical outdoor cases are carried out for validation in real-life scenarios, all mounted in a DJI © F550 platform. Full integration results and telemetry for more than 50 hours of outdoor flight tests are provided. [less ▲]

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See detailGigaSOM.jl: High-performance clustering and visualization of huge cytometry datasets
Kratochvil, Miroslav UL; Hunewald, Oliver; Heirendt, Laurent UL et al

in GigaScience (2020), 9(11),

Background: The amount of data generated in large clinical and phenotyping studies that use single-cell cytometry is constantly growing. Recent technological advances allow the easy generation of data ... [more ▼]

Background: The amount of data generated in large clinical and phenotyping studies that use single-cell cytometry is constantly growing. Recent technological advances allow the easy generation of data with hundreds of millions of single-cell data points with >40 parameters, originating from thousands of individual samples. The analysis of that amount of high-dimensional data becomes demanding in both hardware and software of high-performance computational resources. Current software tools often do not scale to the datasets of such size; users are thus forced to downsample the data to bearable sizes, in turn losing accuracy and ability to detect many underlying complex phenomena. Results: We present GigaSOM.jl, a fast and scalable implementation of clustering and dimensionality reduction for flow and mass cytometry data. The implementation of GigaSOM.jl in the high-level and high-performance programming language Julia makes it accessible to the scientific community and allows for efficient handling and processing of datasets with billions of data points using distributed computing infrastructures. We describe the design of GigaSOM.jl, measure its performance and horizontal scaling capability, and showcase the functionality on a large dataset from a recent study. Conclusions: GigaSOM.jl facilitates the use of commonly available high-performance computing resources to process the largest available datasets within minutes, while producing results of the same quality as the current state-of-art software. Measurements indicate that the performance scales to much larger datasets. The example use on the data from a massive mouse phenotyping effort confirms the applicability of GigaSOM.jl to huge-scale studies. [less ▲]

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See detailAssessing the robustness of decentralized gathering: a multi‐agent approach on micro‐biological systems
Proverbio, Daniele UL; Gallo, Luca; Passalacqua, Barbara et al

in Swarm Intelligence (2020), 14

Adopting a multi-agent systems paradigm, we developed, tested and exploited a computational testbed that simulates gathering features of the social amoeba Dictyostelium discoideum. It features a tailored ... [more ▼]

Adopting a multi-agent systems paradigm, we developed, tested and exploited a computational testbed that simulates gathering features of the social amoeba Dictyostelium discoideum. It features a tailored design and implementation to manage discrete simulations with autonomous agents on a microscopic scale, thus focusing on their social behavior and mutual interactions. Hence, we could assess the behavioral conditions under which decentralized gathering could occur. We investigated the dependence of the model dynamics on the main physical variables, namely density and number of amoebas, gaining indications that the process strongly depends on both. This result integrates previous researches, where density is identified as the sole relevant variable. We determined a high-density and high-numerosity region where assuming a scale-free behavior is safe. We also estimated the systematic uncertainties arising from a number of amoebas off the scale-free region, when coping with limited computational resources. Finally, we probed the robustness of the simulated gathering process against both extrinsic and intrinsic noise sources. [less ▲]

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See detailA Big Data Demand Estimation Model for Urban Congested Networks
Cantelmo, Guido; Viti, Francesco UL

in Transport and Telecommunication (2020)

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See detailFinite deformations govern the anisotropic shear-induced area reduction of soft elastic contacts
Lengiewicz, Jakub UL; de Souza, Mariana; Lahmar, Mohamed A. et al

in Journal of the Mechanics and Physics of Solids (2020), 143

Solid contacts involving soft materials are important in mechanical engineering or biomechanics. Experimentally, such contacts have been shown to shrink significantly under shear, an effect which is ... [more ▼]

Solid contacts involving soft materials are important in mechanical engineering or biomechanics. Experimentally, such contacts have been shown to shrink significantly under shear, an effect which is usually explained using adhesion models. Here we show that quantitative agreement with recent high-load experiments can be obtained, with no adjustable parameter, using a non-adhesive model, provided that finite deformations are taken into account. Analysis of the model uncovers the basic mechanisms underlying anisotropic shear-induced area reduction, local contact lifting being the dominant one. We confirm experimentally the relevance of all those mechanisms, by tracking the shear-induced evolution of tracers inserted close to the surface of a smooth elastomer sphere in contact with a smooth glass plate. Our results suggest that finite deformations are an alternative to adhesion, when interpreting a variety of sheared contact experiments involving soft materials. [less ▲]

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See detailMixed-fleet single-terminal bus scheduling problem: Modelling, solution scheme and potential applications
Rinaldi, Marco UL; Picarelli, Erika UL; D'Ariano, Andrea et al

in Omega: the International Journal of Management Science (2020), 96

Reducing pollutant emissions and promoting sustainable mobility solutions, including Public Transport (PT), are increasingly becoming key objectives for policymakers worldwide. In this work we develop an ... [more ▼]

Reducing pollutant emissions and promoting sustainable mobility solutions, including Public Transport (PT), are increasingly becoming key objectives for policymakers worldwide. In this work we develop an optimal vehicle scheduling approach for next generation PT systems, considering the instance of mixed electric / hybrid fleet. Our objective is that of investigating to what extent electrification, coupled with optimal fleet management, can yield operational cost savings for PT operators. We propose a Mixed In- teger Linear Program (MILP) to address the problem of optimal scheduling of a mixed fleet of electric and hybrid / non-electric buses, coupled with an ad-hoc decomposition scheme aimed at enhancing the scalability of the proposed MILP. Two case studies arising from the PT network of the city of Luxem- bourg are employed in order to validate the model; sensitivity analysis to fleet design parameters is performed, specifically in terms of fleet size and fleet composition. Conclusions point to the fact that careful modelling and handling of mixed-fleet conditions are necessary to achieve operational savings, and that marginal savings gradually reduce as more conventional buses are replaced by their electric counterparts. We believe the methodology proposed may be a key part of advanced decision support systems for policymakers and operators that are dealing with the on-going transition from conventional bus fleets towards greener transport solutions. [less ▲]

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See detailPoroelastic model parameter identification using artificial neural networks: on the effects of heterogeneous porosity and solid matrix Poisson ratio
Dehghani, Hamidreza UL; Zilian, Andreas UL

in Computational Mechanics (2020), 66

Predictive analysis of poroelastic materials typically require expensive and time-consuming multiscale and multiphysics approaches, which demand either several simplifications or costly experimental tests ... [more ▼]

Predictive analysis of poroelastic materials typically require expensive and time-consuming multiscale and multiphysics approaches, which demand either several simplifications or costly experimental tests for model parameter identification. This problem motivates us to develop a more efficient approach to address complex problems with an acceptable computational cost. In particular, we employ artificial neural network (ANN) for reliable and fast computation of poroelastic model parameters. Based on the strong-form governing equations for the poroelastic problem derived from asymptotic homogenisation, the weighted residuals formulation of the cell problem is obtained. Approximate solution of the resulting linear variational boundary value problem is achieved by means of the finite element method. The advantages and downsides of macroscale properties identification via asymptotic homogenisation and the application of ANN to overcome parameter characterisation challenges caused by the costly solution of cell problems are presented. Numerical examples, in this study, include spatially dependent porosity and solid matrix Poisson ratio for a generic model problem, application in tumour modelling, and utilisation in soil mechanics context which demonstrate the feasibility of the presented framework. [less ▲]

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See detailInvestigating the Relationship between Controller Locations and Dynamic Traffic Control in Generic Transportation Networks
Rinaldi, Marco UL; Viti, Francesco UL

in Transportation Research Record: Journal of the Transportation Research Board (2020), 2674(5), 172-182

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See detailMultiscale Integration of High-Resolution Spaceborne and Drone-Based Imagery for a High-Accuracy Digital Elevation Model Over Tristan da Cunha
Backes, Dietmar UL; Teferle, Felix Norman UL

in Frontiers in Earth Science (2020)

Very high-resolution (VHR) optical Earth observation (EO) satellites as well as low-altitude and easy-to-use unmanned aerial systems (UAS/drones) provide ever-improving data sources for the generation of ... [more ▼]

Very high-resolution (VHR) optical Earth observation (EO) satellites as well as low-altitude and easy-to-use unmanned aerial systems (UAS/drones) provide ever-improving data sources for the generation of detailed 3-dimensional (3D) data using digital photogrammetric methods with dense image matching. Today both data sources represent cost-effective alternatives to dedicated airborne sensors, especially for remote regions. The latest generation of EO satellites can collect VHR imagery up to 0.30 m ground sample distance (GSD) of even the most remote location from different viewing angles many times per year. Consequently, well-chosen scenes from growing image archives enable the generation of high-resolution digital elevation models (DEMs). Furthermore, low-cost and easy to use drones can be quickly deployed in remote regions to capture blocks of images of local areas. Dense point clouds derived from these methods provide an invaluable data source to fill the gap between globally available low-resolution DEMs and highly accurate terrestrial surveys. Here we investigate the use of archived VHR satellite imagery with approx. 0.5 m GSD as well as low-altitude drone-based imagery with average GSD of better than 0.03 m to generate high-quality DEMs using photogrammetric tools over Tristan da Cunha, a remote island in the South Atlantic Ocean which lies beyond the reach of current commercial manned airborne mapping platforms. This study explores the potentials and limitations to combine this heterogeneous data sources to generate improved DEMs in terms of accuracy and resolution. A cross-validation between low-altitude airborne and spaceborne data sets describes the fit between both optical data sets. No co-registration error, scale difference or distortions were detected, and a quantitative cloud-to-cloud comparison showed an average distance of 0.26 m between both point clouds. Both point clouds were merged applying a conventional georeferenced approach. The merged DEM preserves the rich detail from the drone-based survey and provides an accurate 3D representation of the entire study area. It provides the most detailed model of the island to date, suitable to support practical and scientific applications. This study demonstrates that combination archived VHR satellite and low-altitude drone-based imagery provide inexpensive alternatives to generate high-quality DEMs. [less ▲]

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See detailRemoving the saturation assumption in Bank-Weiser error estimator analysis in dimension three
Bulle, Raphaël UL; Chouly, Franz; Hale, Jack UL et al

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 ▲]

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See detailFully-Actuated Aerial Manipulator for Infrastructure Contact Inspection: Design, Modeling, Localization, and Control
Sanchez Cuevas, Pedro Jesus UL; Gonzalez Morgado, Antonio; Cortes, Nicolas et al

in Sensors (2020)

This paper presents the design, modeling and control of a fully actuated aerial robot for infrastructure contact inspection as well as its localization system. Health assessment of transport ... [more ▼]

This paper presents the design, modeling and control of a fully actuated aerial robot for infrastructure contact inspection as well as its localization system. Health assessment of transport infrastructure involves measurements with sensors in contact with the bridge and tunnel surfaces and the installation of monitoring sensing devices at specific points. The design of the aerial robot presented in the paper includes a 3DoF lightweight arm with a sensorized passive joint which can measure the contact force to regulate the force applied with the sensor on the structure. The aerial platform has been designed with tilted propellers to be fully actuated, achieving independent attitude and position control. It also mounts a “docking gear” to establish full contact with the infrastructure during the inspection, minimizing the measurement errors derived from the motion of the aerial platform and allowing full contact with the surface regardless of its condition (smooth, rough, ...). The localization system of the aerial robot uses multi-sensor fusion of the measurements of a topographic laser sensor on the ground and a tracking camera and inertial sensors on-board the aerial robot, to be able to fly under the bridge deck or close to the bridge pillars where GNSS satellite signals are not available. The paper also presents the modeling and control of the aerial robot. Validation experiments of the localization system and the control system, and with the aerial robot inspecting a real bridge are also included. [less ▲]

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See detailTransparency by Design in Data-Informed Research: a Collection of Information Design Patterns
Rossi, Arianna UL; Lenzini, Gabriele UL

in Computer Law & Security Review (2020), 37(105402),

Oftentimes information disclosures describing personal data-gathering research activities are so poorly designed that participants fail to be informed and blindly agree to the terms, without grasping the ... [more ▼]

Oftentimes information disclosures describing personal data-gathering research activities are so poorly designed that participants fail to be informed and blindly agree to the terms, without grasping the rights they can exercise and the risks derived from their cooperation. To respond to the challenge, this article presents a series of operational strategies for transparent communication in line with legal-ethical requirements. These "transparency-enhancing design patterns" can be implemented by data controllers/researchers to maximize the clarity, navigability, and noticeability of the information provided and ultimately empower data subjects/research subjects to appreciate and determine the permissible use of their data. [less ▲]

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See detailCategorisation of building data in the digital documentation of heritage buildings
Khalil, Ahmed; Stravoravdis, Spyridon; Backes, Dietmar UL

in Applied Geomatics (2020)

The documentation of heritage buildings is the preliminary action to deal with any problem related to the built heritage. The procedure of documentation requires a very diverse range of data (quantitative ... [more ▼]

The documentation of heritage buildings is the preliminary action to deal with any problem related to the built heritage. The procedure of documentation requires a very diverse range of data (quantitative and qualitative) to be obtained and investigated in order to produce an accurate digital representation of the building. This type of work of data capture and interpretation is often conducted in isolation by different stakeholders and for a range of purposes, leading to a lack of communication between different data types, repeated effort and incomplete documentation. Heritage Building Information Modelling (H-BIM) is set to play a key role in the digital documentation of heritage buildings, as it can combine quantitative and qualitative data and facilitate the integration of different stakeholders and specialised data into the digital management of the different phases of dealing with heritage buildings. This paper aims to review the multitude of data types that could be included in the documentation and investigation process of the built heritage, in order to assess the breadth and depth by which heritage buildings can be documented. Four main categories that span the whole documentation data areas are being suggested which vary from outer geometry surveys, to subsurface materials and structural integrity investigations, to data concerning the building performance, as well as the historic records concerning the building’s morphology over time, which can help to create a more in-depth knowledge about the heritage building’s status and performance and can create a solid base for any required restoration and retrofitting processes (Khalil and Stravoravdis 2019a). [less ▲]

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See detailAnalysis of Cooperative Bus Priority at Traffic Signals
Seredynski, Marcin; Laskaris, Georgios UL; Viti, Francesco UL

in IEEE Transactions on Intelligent Transportation Systems (2020), 21(5), 1929-1940

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See detailViviane Reding on her action in the field of the information society and media (2004-2010)
Danescu, Elena UL

in Internet Histories: Digital Technology, Culture and Society (2020)

The following pages are taken from a long interview (more than eight hours of footage in total) that Viviane Reding granted us in 2015 in connection with the “Pierre Werner and Europe” research project ... [more ▼]

The following pages are taken from a long interview (more than eight hours of footage in total) that Viviane Reding granted us in 2015 in connection with the “Pierre Werner and Europe” research project. Drawing on more than 40 years’ experience in politics, Viviane Reding spoke about her career, the role of Luxembourg and Luxembourgers in the European integration process, and various key events in which she played a part. In these extracts, she discusses her role as a member of the first and second Barroso Commissions (2004-2009 and 2010-2014) and her efforts to help build an information and knowledge society in Europe, one that serves citizens and protects their rights and fundamental freedoms. Her achievements in this respect include capping mobile phone roaming charges (they were subsequently abolished in 2017), advocating for the introduction of a single emergency number (112) in all EU countries, launching the Europeana digital library, and spearheading a programme to use technological innovation for climate and energy solutions. She also describes the process of developing a Digital Agenda for Europe to improve the continent’s digital competitiveness compared with the United States, China and Japan – a complex and challenging task given the context of globalisation and the divergent interests of the various stakeholders (research, industry, consumers, etc.). Finally, she mentions the reform of personal data protection that she initiated (leading to the GDPR, adopted in April 2016). [less ▲]

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See detailAgainst mass media trends: Minority growth in cultural globalization
Cosenza, M. G.; Gavidia, Marino UL; Gonzalez-Avella, J. C.

in PLoS ONE (2020)

We investigate the collective behavior of a globalized society under the influence of endogenous mass media trends. The mass media trend is a global field corresponding to the statistical mode of the ... [more ▼]

We investigate the collective behavior of a globalized society under the influence of endogenous mass media trends. The mass media trend is a global field corresponding to the statistical mode of the states of the agents in the system. The interaction dynamics is based on Axelrod’s rules for the dissemination of culture. We find situations where the largest minority group, possessing a cultural state different from that of the predominant trend transmitted by the mass media, can grow to almost half of the size of the population. We show that this phenomenon occurs when a critical number of long-range connections are present in the underlying network of interactions. We have numerically characterized four phases on the space of parameters of the system: an ordered phase; a semi-ordered phase where almost half of the population consists of the largest minority in a state different from that of the mass media; a disordered phase; and a chimera-like phase where one large domain coexists with many very small domains. [less ▲]

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See detailEnhancing Bus Holding Control Using Cooperative ITS
Laskaris, Georgios; Seredynski, Marcin; Viti, Francesco UL

in IEEE Transactions on Intelligent Transportation Systems (2020), 21(4), 1767-1778

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See detailGuest Editorial Introduction of the Special Issue on Management of Future Motorway and Urban Traffic Systems
Ciuffo, Biagio; Roncoli, Claudio; Viti, Francesco UL

in IEEE Transactions on Intelligent Transportation Systems (2020), 21(4), 1631-1634

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See detailCybermenaces, enjeux et sécurité : entretien avec Stéphane Bortzmeyer et Mohsen Souissi (Afnic)
Schafer, Valerie UL

in Flux: Cahiers Scientifiques Internationaux Réseaux et Territoires (2020), 2019/4

Si les cyberattaques récentes au Moyen-Orient, menées via les noms de domaine, ont eu un vaste écho médiatique fin février 2019, tandis que la revue Défense et Sécurité Internationale consacrait un ... [more ▼]

Si les cyberattaques récentes au Moyen-Orient, menées via les noms de domaine, ont eu un vaste écho médiatique fin février 2019, tandis que la revue Défense et Sécurité Internationale consacrait un dossier spécial à la techno-guérilla, les menaces qui pèsent sur les réseaux informatiques ne sont pas nouvelles. L’Afnic – Association Française pour le Nommage Internet en Coopération –, gestionnaire historique du .fr, fait partie des acteurs français confrontés au quotidien aux enjeux de sécurité des réseaux Internet et veille notamment à la sécurité des noms de domaine et au bon fonctionnement du .fr, en terme de disponibilité mais aussi d’intégrité. Mohsen Souissi, alors Responsable des Sécurité des Sys- tèmes d’information (RSSI) à l’Afnic, qu’il a intégrée en 2000 et où il était précédemment responsable Recherche et développement (R&D) de 2007 à 2016, et Stéphane Bortzmeyer, auteur de Cyberstructure (C&F Éditions, 2018) et ingénieur à l’Afnic depuis seize ans, après avoir été administrateur pour plusieurs systèmes et réseaux universitaires et de centres de recherche, reviennent sur les cybermenaces et les enjeux de sécurité auxquels ils sont confrontés. [less ▲]

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See detailTowards a European health research and innovation cloud (HRIC)
Aarestrup, FM; Albeyatti, A; Armitage, WJ et al

in Genome Medicine (2020)

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See detailMaking the Case for Evidence-based Standardization of Data Privacy and Data Protection Visual Indicators
Rossi, Arianna UL; Lenzini, Gabriele UL

in Journal of Open Access to Law (2020), 8(1),

Lately, icons have witnessed a growing wave of interest in the view of enhancing transparency and clarity of data processing practices in mandated disclosures. Although benefits in terms of ... [more ▼]

Lately, icons have witnessed a growing wave of interest in the view of enhancing transparency and clarity of data processing practices in mandated disclosures. Although benefits in terms of comprehensibility, noticeability, navigability of the information and user’s attention and memorization can be expected, they should also be supported by decisive empirical evidence about the efficacy of the icons in specific contexts. Misrepresentation, oversimplification, and improper salience of certain aspects over others are omnipresent risks that can drive data subjects to wrong conclusions. Cross-domain and international standardization of visual means also poses a serious challenge: if on the one hand developing standards is necessary to ensure widespread recognition and comprehension, each domain and application presents unique features that can be hardly established, and imposed, in a top-down manner. This article critically discusses the above issues and identifies relevant open questions for scientific research. It also provides concrete examples and practical suggestions for researchers and practitioners that aim to implement transparency-enhancing icons in the spirit of the General Data Protection Regulation (GDPR). [less ▲]

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See detailA review of nature-based solutions for resource recovery in cities
Kisser, Johannes; Wirt, Maria; De Gusseme, Bart 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 ▲]

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See detailIncorporating trip chaining within online demand estimation
Cantelmo, Guido; Qurashi, Moeid; Prakash, Arun et al

in Transportation Research. Part B, Methodological (2020), 132

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See detailWhich App to Choose? An Online Tool that Supports the Decision-making Process of Recreational Runners to Choose an App
Janssen, Mark; Lallemand, Carine UL; Hoes, Kevin et al

in Proceedings of the 6th International Conference on Design4Health Amsterdam 2020 (2020)

In recent years, there has been an exponential increase in the use of health and sports-related smartphone applications (apps). This is also reflected in App-stores, which are stacked with thousands of ... [more ▼]

In recent years, there has been an exponential increase in the use of health and sports-related smartphone applications (apps). This is also reflected in App-stores, which are stacked with thousands of health- and sports-apps, with new apps launched each day. These apps have great potential to monitor and support people’s physical activity and health. For users, however, it is difficult to know which app suits their needs. In this paper, we present an online tool that supports the decision-making process for choosing an appropriate app. We constructed and validated a screening instrument to assess app content quality, together with the assessment of users’ needs. Both served as input for building the tool through various iterations with prototypes and user tests. This resulted in an online tool which relies on app content quality scores to match the users’ needs with apps that score high in the screening instrument on those particular needs. Users can add new apps to the database via the screening instrument, making the tool self supportive and future proof. A feedback loop allows users to give feedback on the recommended app and how well it meets their needs. This feedback is added to the database and used in future filtering and recommendations. The principles used can be applied to other areas of sports, physical activity and health to help users to select an app that suits their needs. Potentially increasing the long-term use of apps to monitor and to support physical activity and health. [less ▲]

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See detailVisualizing Computer-Based Activity on Ambient Displays to Reduce Sedentary Behavior at Work
Brombacher, Hans; Ren, Xipei; Vos, Steven et al

in 32ND AUSTRALIAN CONFERENCE ON HUMAN-COMPUTER INTERACTION (2020)

Workplace health interventions have predominantly been designed around visualizations of physical activity data in the work routine. Yet, contextual factors, such as computer-based activity, appears to be ... [more ▼]

Workplace health interventions have predominantly been designed around visualizations of physical activity data in the work routine. Yet, contextual factors, such as computer-based activity, appears to be crucial to support healthier behaviors at work. In this research, we explore the effect of visualizing computer-based activity to prompt physical activity at work, through desktop-based ambient displays. Based on our prototypes Yamin and Apphia, we conducted an exploratory qualitative user study in a lab setting with office workers (N=16). Results showed that visualizing one’s computer-based activity could potentially increase the awareness, self-reflection, and social interactions for individuals to become physically active. With our findings, we discuss design implications for using computer activity data in a physical form as a motivational factor to encourage physically active workstyles. We present directions for future field studies to gain further insights on this topic. [less ▲]

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See detailAssessing Two-way and One-way Carsharing: an Agent-Based Simulation Approach
Giorgione, Giulio UL; Bolzani, Luca UL; Viti, Francesco UL

in Transportation Research Procedia (2020), 52

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See detailNon-localised contact between beams with circular and elliptical cross-sections
Magliulo, Marco UL; Lengiewicz, Jakub UL; Zilian, Andreas UL et al

in Computational Mechanics (2020), 65

The key novelty of this contribution is a dedicated technique to e fficiently determine the distance (gap) function between parallel or almost parallel beams with circular and elliptical cross-sections ... [more ▼]

The key novelty of this contribution is a dedicated technique to e fficiently determine the distance (gap) function between parallel or almost parallel beams with circular and elliptical cross-sections. The technique consists of parametrizing the surfaces of the two beams in contact, fixing a point on the centroid line of one of the beams and searching for a constrained minimum distance between the surfaces (two variants are investigated). The resulting unilateral (frictionless) contact condition is then enforced with the Penalty method, which introduces compliance to the, otherwise rigid, beams' cross-sections. Two contact integration schemes are considered: the conventional slave-master approach (which is biased as the contact virtual work is only integrated over the slave surface) and the so-called two-half-pass approach (which is unbiased as the contact virtual work is integrated over the two contacting surfaces). Details of the finite element formulation which is suitably implemented using Automatic Di fferentiation techniques are presented. A set of numerical experiments shows the overall performance of the framework and allows a quantitative comparison of the investigated variants. [less ▲]

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See detailHeuristic methods for minimal controller location set problem in transportation networks
Mazur, Xavier UL; Rinaldi, Marco UL; Viti, Francesco UL

in Transportation Research Procedia (2020), 52

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See detailIsogeometric analysis of thin Reissner-Mindlin shells: locking phenomena and B-bar method
Hu, Qingyuan; Xia, Yang; Natarajan, Sundararajan et al

in Computational Mechanics (2020), 65(5), 1323-1341

We propose a local type of B-bar formulation, addressing locking in degenerated Reissner–Mindlin shell formulation in the context of isogeometric analysis. Parasitic strain components are projected onto ... [more ▼]

We propose a local type of B-bar formulation, addressing locking in degenerated Reissner–Mindlin shell formulation in the context of isogeometric analysis. Parasitic strain components are projected onto the physical space locally, i.e. at the element level, using a least-squares approach. The formulation allows the flexible utilization of basis functions of different orders as the projection bases. The introduced formulation is much cheaper computationally than the classical $$\bar{B}$$B¯ method. We show the numerical consistency of the scheme through numerical examples, moreover they show that the proposed formulation alleviates locking and yields good accuracy even for slenderness ratios of $$10^5$$105, and has the ability to capture deformations of thin shells using relatively coarse meshes. In addition it can be opined that the proposed method is less sensitive to locking with irregular meshes. [less ▲]

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See detailThe stochastic maintenance location routing allocation problem for rolling stock
Tönissen, Denise; Arts, Joachim UL

in International Journal of Production Economics (2020), 230

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See detailQualifying and Measuring Transparency: A Medical Data System Case Study
Spagnuelo, Dayana; Bartolini, Cesare UL; Lenzini, Gabriele UL

in Computers and Security (2020)

Transparency is a data processing principle enforced by the GDPR but purposely left open to interpretation. As such, the means to adhere to it are left unspecified. Article 29 Working Party provides ... [more ▼]

Transparency is a data processing principle enforced by the GDPR but purposely left open to interpretation. As such, the means to adhere to it are left unspecified. Article 29 Working Party provides practical guidance on how to interpret transparency, however there are no defined requirements nor ways to verify the quality of the implementation of transparency. We address this problem. We discuss and define applicable metrics for transparency, propose how measurement can be conducted in an operative system, and suggest a practical way in which these metrics can be interpreted in order to increase confidence that transparency is realised in a system. [less ▲]

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

in Acta Mechanica (2020), 231

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

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

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See detailEffect of Red Blood Cell Aging In Vivo on Their Aggregation Properties In Vitro: Measurements with Laser Tweezers
Ermolinskiy, Petr; Lugovtsov, Andrei; Yaya, Francois et al

in Applied Sciences (2020), 10(21), 7581-10

Red blood cell (RBC) aggregation highly influences hemorheology and blood microcirculation in the human body. The aggregation properties of RBCs can vary due to numerous factors, including RBC age. The ... [more ▼]

Red blood cell (RBC) aggregation highly influences hemorheology and blood microcirculation in the human body. The aggregation properties of RBCs can vary due to numerous factors, including RBC age. The aim of this work was to estimate in vitro the differences in the RBC aggregation properties of different RBC age populations in single-cell experiments using laser tweezers. RBCs from five healthy volunteers were separated into four subpopulations by Percoll density gradient centrifugation. Each subpopulation of the RBC was separately resuspended in autologous plasma or dextran 70 kDa (50 mg/mL). The aggregation force between the single cells was measured with holographic laser tweezers. The obtained data demonstrated an enhancement of RBC aggregation force in doublets with age: the older the cells, the higher the aggregation force. The obtained data revealed the differences between the aggregation and aggregability of RBC in dependence of the RBC in vivo age. [less ▲]

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See detailThe role of microscale solid matrix compressibility on the mechanical behaviour of poroelastic materials
Dehghani, Hamidreza UL; Noll, Isabelle; Penta, Raimondo et al

in European Journal of Mechanics. A, Solids (2020), 83

We present the macroscale three-dimensional numerical solution of anisotropic Biot's poroelasticity, with coefficients derived from a micromechanical analysis as prescribed by the asymptotic ... [more ▼]

We present the macroscale three-dimensional numerical solution of anisotropic Biot's poroelasticity, with coefficients derived from a micromechanical analysis as prescribed by the asymptotic homogenisation technique. The system of partial differential equations (PDEs) is discretised by finite elements, exploiting a formal analogy with the fully coupled thermal displacement systems of PDEs implemented in the commercial software Abaqus. The robustness of our computational framework is confirmed by comparison with the well-known analytical solution of the one-dimensional Therzaghi's consolidation problem. We then perform three-dimensional numerical simulations of the model in a sphere (representing a biological tissue) by applying a given constant pressure in the cavity. We investigate how the macroscale radial displacements (as well as pressures) profiles are affected by the microscale solid matrix compressibility (MSMC). Our results suggest that the role of the MSMC on the macroscale displacements becomes more and more prominent by increasing the length of the time interval during which the constant pressure is applied. As such, we suggest that parameter estimation based on techniques such as poroelastography (which are commonly used in the context of biological tissues, such as the brain, as well as solid tumours) should allow for a sufficiently long time in order to give a more accurate estimation of the mechanical properties of tissues. [less ▲]

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See detailThe DAta Protection REgulation COmpliance Model
Bartolini, Cesare UL; Lenzini, Gabriele UL; Robaldo, Livio UL

in IEEE Security and Privacy (2019), 17(6), 37-45

Understanding whether certain technical measures comply with the General Data Protection Regulation’s (GDPR’s) principles is complex legal work. This article describes a model of the GDPR that allows for ... [more ▼]

Understanding whether certain technical measures comply with the General Data Protection Regulation’s (GDPR’s) principles is complex legal work. This article describes a model of the GDPR that allows for semiautomatic processing of legal text and the leveraging of state-of-the-art legal informatics approaches, which are useful for legal reasoning, software design, information retrieval, or compliance checking. [less ▲]

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See detailData driven discovery of cyber physical systems
Yuan, Ye; Tang, Xiuchuan; Zhou, Wei et al

in Nature Communications (2019)

Cyber-physical systems embed software into the physical world. They appear in a wide range of applications such as smart grids, robotics, and intelligent manufacturing. Cyber-physical systems have proved ... [more ▼]

Cyber-physical systems embed software into the physical world. They appear in a wide range of applications such as smart grids, robotics, and intelligent manufacturing. Cyber-physical systems have proved resistant to modeling due to their intrinsic complexity arising from the combination of physical and cyber components and the interaction between them. This study proposes a general framework for discovering cyber-physical systems directly from data. The framework involves the identification of physical systems as well as the inference of transition logics. It has been applied successfully to a number of real-world examples. The novel framework seeks to understand the underlying mechanism of cyber-physical systems as well as make predictions concerning their state trajectories based on the discovered models. Such information has been proven essential for the assessment of the performance of cyber- physical systems; it can potentially help debug in the implementation procedure and guide the redesign to achieve the required performance. [less ▲]

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See detailTechnical report on data protection and privacy in smart ICT: Internet of Things: Gap analysis between scientific research and technical standardisation: Gap analysis Internet of Things
Samir Labib, Nader UL; Brust, Matthias R. UL; Danoy, Grégoire UL et al

in Technical report on data protection and privacy in smart ICT (2019), 1

With the emergence of new digital trends like the Internet of Things (IoT), more industry actors and technical committees pursue research in utilizing such technologies as they promise better and ... [more ▼]

With the emergence of new digital trends like the Internet of Things (IoT), more industry actors and technical committees pursue research in utilizing such technologies as they promise better and optimized management, improved energy efficiency and better quality living by facilitating a magnitude of value-added services. However, as communication, sensing and actuation become increasingly sophisticated, such promising data-driven IoT systems generate, process, and exchange larger amounts of data, some of which is privacy-sensitive and security-critical. The sustained increase in number of connected devices, catalyzed by IoT, affirms the importance of addressing data protection, privacy and security challenges, as indices of trust, to achieve market acceptance. This consequently, emphasizes the need of a solid technical and regulatory foundation to ensure trustworthiness within the IoT ecosystem. The goal of this study is to first introduce the concept of trustworthiness in IoT with its main pillars, data protection, privacy and security, and then analyze developments in research and standardization for each of these. The study presents a gap analysis on data protection, privacy and security between research and standardization, throughout which the use case of Unmanned Aerial Vehicles (UAVs) is referred to, as a promising value-added service example of mobile IoT devices. The study concludes with suggestions for future research and standardization in order to address the identified gaps. [less ▲]

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See detailFracture mechanism simulation of inhomogeneous anisotropic rocks by extended finite element method
Mohtarami, Ehsan; Baghbanan, Alireza; Hashemolhosseini, Hamid et al

in Theoretical and Applied Fracture Mechanics (2019), 104

The vast majority of rock masses is anisotropic due to factors such as layering, unequal in-situ stresses, joint sets, and discontinuities. Meanwhile, given the frequently asymmetric distribution of pores ... [more ▼]

The vast majority of rock masses is anisotropic due to factors such as layering, unequal in-situ stresses, joint sets, and discontinuities. Meanwhile, given the frequently asymmetric distribution of pores, grain sizes or different mineralogical compounds in different locations, they are often classified as inhomogeneous materials. In such materials, stress intensity factors (SIFs) at the crack tip, which control the initiation of failure, strongly depend on mechanical properties of the material near that area. On the other hand, crack propagation trajectories highly depend on the orthotropic properties of the rock mass. In this study, the SIFs are calculated by means of anisotropic crack tip enrichments and an interaction integral are developed for inhomogeneous materials with the help of the extended finite element method (XFEM). We also use the T-stress within the crack tip fields to develop a new criterion to estimate the crack initiation angles and propagation in rock masses. To verify and validate the proposed approach, the results are compared with experimental test results and those reported in the literature. It is found that the ratio of elastic moduli, shear stiffnesses, and material orientation angles have a significant impact on the SIFs. However, the rate of change in material properties is found to have a moderate effect on these factors and a more pronounced effect on the failure force. The results highlight the potential of the proposed formulation in the estimation of SIFs and crack propagation paths in inhomogeneous anisotropic materials. [less ▲]

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See detailTaylor-Series Expansion Based Numerical Methods: A Primer, Performance Benchmarking and New Approaches for Problems with Non-smooth Solutions
Jacquemin, Thibault Augustin Marie UL; Tomar, Satyendra UL; Agathos, Konstantinos UL et al

in Archives of Computational Methods in Engineering (2019)

We provide a primer to numerical methods based on Taylor series expansions such as generalized finite difference methods and collocation methods. We provide a detailed benchmarking strategy for these ... [more ▼]

We provide a primer to numerical methods based on Taylor series expansions such as generalized finite difference methods and collocation methods. We provide a detailed benchmarking strategy for these methods as well as all data files including input files, boundary conditions, point distribution and solution fields, so as to facilitate future benchmarking of new methods. We review traditional methods and recent ones which appeared in the last decade. We aim to help newcomers to the field understand the main characteristics of these methods and to provide sufficient information to both simplify implementation and benchmarking of new methods. Some of the examples are chosen within a subset of problems where collocation is traditionally known to perform sub-par, namely when the solution sought is non-smooth, i.e. contains discontinuities, singularities or sharp gradients. For such problems and other simpler ones with smooth solutions, we study in depth the influence of the weight function, correction function, and the number of nodes in a given support. We also propose new stabilization approaches to improve the accuracy of the numerical methods. In particular, we experiment with the use of a Voronoi diagram for weight computation, collocation method stabilization approaches, and support node selection for problems with singular solutions. With an appropriate selection of the above-mentioned parameters, the resulting collocation methods are compared to the moving least-squares method (and variations thereof), the radial basis function finite difference method and the finite element method. Extensive tests involving two and three dimensional problems indicate that the methods perform well in terms of efficiency (accuracy versus computational time), even for non-smooth solutions. [less ▲]

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See detailFusing the Seth-Hill strain tensors to fit compressible elastic material responses in the nonlinear regime
Beex, Lars UL

in International Journal of Mechanical Sciences (2019), 163

Strain energy densities based on the Seth-Hill strain tensors are often used to describe the hyperelastic mechanical behaviours of isotropic, transversely isotropic and orthotropic materials for ... [more ▼]

Strain energy densities based on the Seth-Hill strain tensors are often used to describe the hyperelastic mechanical behaviours of isotropic, transversely isotropic and orthotropic materials for relatively large deformations. Since one parameter distinguishes which strain tensor of the Seth-Hill family is used, one has in theory the possibility to t the material response in the nonlinear regime. Most often for compressible deformations however, this parameter is selected such that the Hencky strain tensor is recovered, because it yields rather physical stress-strain responses. Hence, the response in the nonlinear regime is in practise not often tailored to match experimental data. To ensure that elastic responses in the nonlinear regime can more accurately be controlled, this contribution proposes three generalisations that combine several Seth-Hill strain tensors. The generalisations are formulated such that the stress-strain responses for in finitesimal deformations remain unchanged. Consequently, the identifi cation of the Young's moduli, Poisson's ratios and shear moduli is not a ffected. 3D fi nite element simulations are performed for isotropy and orthotropy, with an emphasis on the identifi cation of the new material parameters. [less ▲]

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See detailA stochastic Galerkin cell-based smoothed finite element method (SGCS-FEM)
Mathew, Tittu; Beex, Lars UL; Bordas, Stéphane UL et al

in International Journal of Computational Methods (2019), 17(8),

In this paper, the cell based smoothed finite element method is extended to solve stochastic partial diff erential equations with uncertain input parameters. The spatial field of Young's moduli and the ... [more ▼]

In this paper, the cell based smoothed finite element method is extended to solve stochastic partial diff erential equations with uncertain input parameters. The spatial field of Young's moduli and the corresponding stochastic results are represented by Karhunen-Lo eve expansion and polynomial chaos expansion, respectively. The Young's Modulus of structure is considered to be random for stochastic static as well as free vibration problems. Mathematical expressions and the solution procedure are articulated in detail to evaluate the statistical characteristics of responses in terms of static displacements and free vibration frequencies. The feasibility and eff ectiveness of the proposed SGCS-FEM method in terms of accuracy and lower requirement on the mesh size in the solution domain over that of conventional FEM for stochastic problems are demonstrated by carefully chosen numerical examples. From the numerical study, it is inferred that the proposed framework is computationally less demanding without compromising accuracy. [less ▲]

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See detailDeriving essential components of lean and industry 4.0 assessment model for manufacturing SMEs
Kolla, Sri Sudha Vijay Keshav UL; Minoufekr, Meysam UL; Plapper, Peter UL

in 52nd CIRP Conference on Manufacturing Systems (CMS) (2019), 81

Quantifying lean and ICT architecture related to Industry 4.0 is a new challenge in Small and Medium Scale Enterprises (SMEs) that needs to be addressed by both research as well as enterprises themselves ... [more ▼]

Quantifying lean and ICT architecture related to Industry 4.0 is a new challenge in Small and Medium Scale Enterprises (SMEs) that needs to be addressed by both research as well as enterprises themselves. Especially in the manufacturing sector, SMEs need to transform themselves into emerging trends such as industry 4.0 while practicing existing manufacturing philosophies such as Lean Production Systems (LPS) to be competitive in global markets. The major concern is that there are many assessment models available to measure the status of an enterprise related to either LPS or Industry 4.0. Often, these models are complex and don’t fulfill the requirements of manufacturing SMEs. On the other hand, most of the models only consider either lean or industry 4.0 elements. The outcomes of this research help to develop a hybrid model including both lean and industry 4.0 features suitable for manufacturing SMEs. The main objective of this research is to provide state of the art literature on existing assessment models and consequently map lean and industry 4.0 components to the specific characteristics of manufacturing SMEs. The paper concludes with a summary and outlook for our future research. [less ▲]

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See detailCoupled molecular-dynamics and finite-element-method simulations for the kinetics of particles subjected to field-mediated forces
Cascio, Michele; Baroli, Davide UL; Bordas, Stéphane UL et al

in Physical Review. E ,Statistical, Nonlinear, and Soft Matter Physics (2019), 99(6),

A computational approach that couples molecular-dynamics (MD) and the-finite-element-method (FEM) technique is here proposed for the theoretical study of the dynamics of particles subjected to ... [more ▼]

A computational approach that couples molecular-dynamics (MD) and the-finite-element-method (FEM) technique is here proposed for the theoretical study of the dynamics of particles subjected to electromechanical forces. The system consists of spherical particles (modeled as micrometric rigid bodies with proper densities and dielectric functions) suspended in a colloidal solution, which flows in a microfluidic channel in the presence of a generic nonuniform variable electric field generated by electrodes. The particles are subjected to external forces (e.g., drag or gravity) which satisfy a particlelike formulation that is typical of the MD approach, along with an electromechanical force that, in turn, requires the three-dimensional self-consistent solutions of correct continuum field equations during the integration of the equations of motion. In the MD-FEM method used in this work, the finite element method is applied to solve the continuum field equations while the MD technique is used for the stepwise explicit integration of the equations of motion. Our work shows the potential of coupled MD-FEM simulations for the study of electromechanical particles and opens a double perspective for implementing (a) MD away from the field of atomistic simulations and (b) the continuum-particle approach to cases where the conventional force evaluation used in MD is not applicable. [less ▲]

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See detailIsotropic–isotropic phase separation and spinodal decomposition in liquid crystal–solvent mixtures
Reyes, Catherine UL; Baller, Jörg UL; Araki, Takeaki et al

in Soft Matter (2019), 15

Phase separation in mixtures forming liquid crystal (LC) phases is an important yet under- appreciated phenomenon that can drastically influence the behaviour of a multi-component LC. Here we demonstrate ... [more ▼]

Phase separation in mixtures forming liquid crystal (LC) phases is an important yet under- appreciated phenomenon that can drastically influence the behaviour of a multi-component LC. Here we demonstrate, using polarising microscopy with active cooling as well as differential scanning calorimetry, that the phase diagram for mixtures of the LC-forming compound 4’-n- pentylbiphenyl-4-carbonitrile (5CB) with ethanol is surprisingly complex. Binary mixtures reveal a broad miscibility gap that leads to phase separation between two distinct isotropic phases via spinodal decomposition or nucleation and growth. On further cooling the nematic phase enters on the 5CB-rich side, adding to the complexity. Significantly, water contamination dramatically raises the temperature range of the miscibility gap, bringing up the critical temperature for spinodal de- composition from ∼ 2◦C for the anhydrous case to > 50◦C if just 3 vol.% water is added to the ethanol. We support the experiments with a theoretical treatment that qualitatively reproduces the phase diagrams as well as the transition dynamics, with and without water. Our study highlights the impact of phase separation in LC-forming mixtures, spanning from equilibrium coexistence of multiple liquid phases to non-equilibrium effects due to persistent spatial concentration gradients. [less ▲]

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See detailStructural shape optimization of three dimensional acoustic problems with isogeometric boundary element methods
Chen, L.L.; Lian, Haojie UL; Chen, H.B. et al

in Computer Methods in Applied Mechanics and Engineering (2019), 355

The boundary element method (BEM) is a powerful tool in computational acoustics, because the analysis is conducted only on structural surfaces, compared to the finite element method (FEM) which resorts to ... [more ▼]

The boundary element method (BEM) is a powerful tool in computational acoustics, because the analysis is conducted only on structural surfaces, compared to the finite element method (FEM) which resorts to special techniques to truncate infinite domains. The isogeometric boundary element method (IGABEM) is a recent progress in the category of boundary element approaches, which is inspired by the concept of isogeometric analysis (IGA) and employs the spline functions of CAD as basis functions to discretize unknown physical fields. As a boundary representation approach, IGABEM is naturally compatible with CAD and thus can directly perform numerical analysis on CAD models, avoiding the cumbersome meshing procedure in conventional FEM/BEM and eliminating the difficulty of volume parameterization in isogeometric finite element methods. The advantage of tight integration of CAD and numerical analysis in IGABEM renders it particularly attractive in the application of structural shape optimization because (1) the geometry and the analysis can be interacted, (2) remeshing with shape morphing can be avoided, and (3) an optimized solution returns a CAD geometry directly without postprocessing steps. In the present paper, we apply the IGABEM to structural shape optimization of three dimensional exterior acoustic problems, fully exploiting the strength of IGABEM in addressing infinite domain problems and integrating CAD and numerical analysis. We employ the Burton–Miller formulation to overcome fictitious frequency problems, in which hyper-singular integrals are evaluated explicitly. The gradient-based optimizer is adopted and shape sensitivity analysis is conducted with implicit differentiation methods. The design variables are set to be the positions of control points which directly determine the shape of structures. Finally, numerical examples are provided to verify the algorithm. [less ▲]

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See detailA Structured Argumentation Framework for Modeling Debates in the Formal Sciences
Cramer, Marcos; Dauphin, Jérémie UL

in Journal for General Philosophy of Science (2019)

Scientific research in the formal sciences comes in multiple degrees of formality: fully formal work; rigorous proofs that practitioners know to be formalizable in principle; and informal work like rough ... [more ▼]

Scientific research in the formal sciences comes in multiple degrees of formality: fully formal work; rigorous proofs that practitioners know to be formalizable in principle; and informal work like rough proof sketches and considerations about the advantages and disadvantages of various formal systems. This informal work includes informal and semi-formal debates between formal scientists, e.g. about the acceptability of foundational principles and proposed axiomatizations. In this paper, we propose to use the methodology of structured argumentation theory to produce a formal model of such informal and semi-formal debates in the formal sciences. For this purpose, we propose ASPIC-END, an adaptation of the structured argumentation framework ASPIC+ which can incorporate natural deduction style arguments and explanations. We illustrate the applicability of the framework to debates in the formal sciences by presenting a simple model of some arguments about proposed solutions to the Liar paradox, and by discussing a more extensive - but still preliminary - model of parts of the debate that mathematicians had about the Axiom of Choice in the early 20th century. [less ▲]

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See detailEstimating fibres' material parameter distributions from limited data with the help of Bayesian inference
Rappel, Hussein UL; Beex, Lars UL

in European Journal of Mechanics. A, Solids (2019), 75

Numerous materials are essentially structures of discrete fibres, yarns or struts. Considering these materials at their discrete scale, one may distinguish two types of intrinsic randomness that affect ... [more ▼]

Numerous materials are essentially structures of discrete fibres, yarns or struts. Considering these materials at their discrete scale, one may distinguish two types of intrinsic randomness that affect the structural behaviours of these discrete structures: geometrical randomness and material randomness. Identifying the material randomness is an experimentally demanding task, because many small fibres, yarns or struts need to be tested, which are not easy to handle. To avoid the testing of hundreds of constituents, this contribution proposes an identification approach that only requires a few dozen of constituents to be tested (we use twenty to be exact). The identification approach is applied to articially generated measurements, so that the identified values can be compared to the true values. Another question this contribution aims to answer is how precise the material randomness needs to be identified, if the geometrical randomness will also influence the macroscale behaviour of these discrete networks. We therefore also study the effect of the identified material randomness to that of the actual material randomness for three types of structures; each with an increasing level of geometrical randomness. [less ▲]

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See detailWeak and strong from meshless methods for linear elastic problem under fretting contact conditions
Kosec, Gregor; Slak, Jure; Depolli, Matja et al

in Tribology International (2019), 138

We present numerical computation of stresses under fretting fatigue conditions derived from closed form expressions. The Navier-Cauchy equations, that govern the problem, are solved with strong and weak ... [more ▼]

We present numerical computation of stresses under fretting fatigue conditions derived from closed form expressions. The Navier-Cauchy equations, that govern the problem, are solved with strong and weak form meshless numerical methods. The results are compared to the solution obtained from well-established commercial package ABAQUS, which is based on finite element method (FEM). The results show that the weak form meshless solution exhibits similar behavior as the FEM solution, while, in this particular case, strong form meshless solution performs better in capturing the peak in the surface stress. This is of particular interest in fretting fatigue, since it directly influences crack initiation. The results are presented in terms of von Mises stress contour plots, surface stress profiles, and the convergence plots for all three methods involved in the study. [less ▲]

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See detailAvailability-based dynamic pricing on a round-trip carsharing service: an explorative analysis using agent-based simulation 
Giorgione, Giulio UL; Ciari, Francesco; Viti, Francesco UL

in Transportation Research Procedia (2019)

Carsharing companies aim to customize their service to increase fleet usage and revenues with different pricing schemes and offer types. Dynamic pricing policies can be designed to adjust and balance ... [more ▼]

Carsharing companies aim to customize their service to increase fleet usage and revenues with different pricing schemes and offer types. Dynamic pricing policies can be designed to adjust and balance temporally and spatially cars availability but may pose some question on customers’ fairness. In this paper, we propose an explorative analysis of how an availability-based dynamic pricing scheme impacts the demand and the supply performance. The policy is simulated in MATSim and compared to a fixed pricing policy scheme. This simulation consists of analyzing the behavior of a synthetic population of car-sharing members for Berlin and the surrounding region in which is applied an availability-based dynamic pricing in which price depends on vehicle availability in booking stations. Results show that when the dynamic pricing is applied there is a light decrease in the number of bookings and people with low value of time tend to abandon the carsharing mode in favor of other modes of transportation. [less ▲]

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See detailGraft materials provide greater static strength to medial opening wedge high tibial osteotomy than when no graft is included
Belsey, James; Diffo Kaze, Arnaud UL; Jobson, Simon et al

in Journal of Experimental Orthopaedics (2019), 6(13),

Background The purpose of this study was to compare the stability of medial opening-wedge high tibial osteotomy (MOWHTO) with and without different graft materials. Good clinical and radiological outcomes ... [more ▼]

Background The purpose of this study was to compare the stability of medial opening-wedge high tibial osteotomy (MOWHTO) with and without different graft materials. Good clinical and radiological outcomes have been demonstrated when either using or not using graft materials during MOWHTO. Variations in the biomechanical properties of different graft types, regarding the stability they provide a MOWHTO, have not been previously investigated. Methods A 10 mm biplanar MOWHTO was performed on 15 artificial sawbone tibiae, which were fixed using the Activmotion 2 plate. Five bones had OSferion60 wedges (synthetic group), five had allograft bone wedges (allograft group), and five had no wedges (control group) inserted into the osteotomy gap. Static compression was applied axially to each specimen until failure of the osteotomy. Ultimate load, horizontal and vertical displacements were measured and used to calculate construct stiffness and valgus malrotation of the tibial head. Results The synthetic group failed at 6.3 kN, followed by the allograft group (6 kN), and the control group (4.5 kN). The most valgus malrotation of the tibial head was observed in the allograft group (2.6°). The synthetic group showed the highest stiffness at the medial side of the tibial head (9.54 kN·mm− 1), but the lowest stiffness at the lateral side (1.59 kN·mm-1). The allograft group showed high stiffness on the medial side of the tibial head (7.54 kN·mm− 1) as well as the highest stiffness on the lateral side (2.18 kN·mm− 1). Conclusions The use of graft materials in MOWHTO results in superior material properties compared to the use of no graft. The static strength of MOWHTO is highest when synthetic grafts are inserted into the osteotomy gap. Allograft wedges provide higher mechanical strength to a MOWHTO than when no graft used. In comparison to the synthetic grafts, allograft wedges result in the stiffness of the osteotomy being more similar at the medial and lateral cortices. [less ▲]

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See detailA gradient weighted extended finite element method (GW-XFEM) for fracture mechanics
Feng, S. Z.; Bordas, Stéphane UL; Han, X. et al

in Acta Mechanica (2019), 230

In this study, a gradient weighted extended finite element method (GW-XFEM) is presented for the analysis of fracture problems. For this method, the domain discretization is the same as the standard XFEM ... [more ▼]

In this study, a gradient weighted extended finite element method (GW-XFEM) is presented for the analysis of fracture problems. For this method, the domain discretization is the same as the standard XFEM. However, the gradient field is constructed by considering the influences of the element itself and its adjacent elements. Based on the Shepard interpolation, the weighted strain filed can be obtained, which will be utilized to construct the discretized system equations. The validity of the presented method is fully investigated through several numerical examples. From these results, it is shown that compared with standard XFEM, the presented method can achieve much better accuracy, efficiency and higher convergence, when dealing with fracture analysis. [less ▲]

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See detailA unified polygonal locking-free thin/thick smoothed plate element
Katili, Irwan; Maknun, Imam Jauhari; Katili, Andi Makarim et al

in Composite Structures (2019), 219

A novel cell-based smoothed finite element method is proposed for thin and thick plates based on Reissner-Mindlin plate theory and assumed shear strain fields. The domain is discretized with arbitrary ... [more ▼]

A novel cell-based smoothed finite element method is proposed for thin and thick plates based on Reissner-Mindlin plate theory and assumed shear strain fields. The domain is discretized with arbitrary polygons and on each side of the polygonal element, discrete shear constraints are considered to relate the kinematical and the independent shear strains. The plate is made of functionally graded material with effective properties computed using the rule of mixtures. The influence of various parameters, viz., the plate aspect ratio and the material gradient index on the static bending response and the first fundamental frequency is numerically studied. It is seen that the proposed element: (a) has proper rank; (b) does not require derivatives of shape functions and hence no isoparametric mapping required; (c) independent of shape and size of elements and (d) is free from shear locking. [less ▲]

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See detailIncorporating trip chaining within online demand estimation
Cantelmo, Guido; Qurashi, Moeid; Prakash, Arun et al

in Transportation Research. Part B, Methodological (2019)

Time-dependent Origin–Destination (OD) demand flows are fundamental inputs for Dy- namic Traffic Assignment (DTA) systems and real-time traffic management. This work in- troduces a novel state-space ... [more ▼]

Time-dependent Origin–Destination (OD) demand flows are fundamental inputs for Dy- namic Traffic Assignment (DTA) systems and real-time traffic management. This work in- troduces a novel state-space framework to estimate these demand flows in an online con- text. Specifically, we propose to explicitly include trip-chaining behavior within the state- space formulation, which is solved using the well-established Kalman Filtering technique. While existing works already consider structural information and recursive behavior within the online demand estimation problem, this information has been always considered at the OD level. In this study, we introduce this structural information by explicitly representing trip-chaining within the estimation framework. The advantage is twofold. First, all trips belonging to the same tour can be jointly calibrated. Second, given the estimation during a certain time interval, a prediction of the structural deviation over the whole day can be obtained without the need to run additional simulations. The effectiveness of the proposed methodology is demonstrated first on a toy network and then on a large real-world net- work. Results show that the model improves the prediction performance with respect to a conventional Kalman Filtering approach. We also show that, on the basis of the estimation of the morning commute, the model can be used to predict the evening commute without need of running additional simulations. [less ▲]

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See detailA unified enrichment approach addressing blending and conditioning issues in enriched finite elements
Agathos, Konstantinos; Chatzi, Eleni; Bordas, Stéphane UL

in Computer Methods in Applied Mechanics and Engineering (2019), 349

We present a combination of techniques to improve the convergence and conditioning properties of partition of unity (PU) enriched finite element methods. By applying these techniques to different types of ... [more ▼]

We present a combination of techniques to improve the convergence and conditioning properties of partition of unity (PU) enriched finite element methods. By applying these techniques to different types of enrichment functions, namely polynomial, discontinuous and singular, higher order convergence rates can be obtained while keeping condition number growth rates similar to the ones corresponding to standard finite elements. [less ▲]

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See detailModel order reduction accelerated Monte Carlo stochastic isogeometric method for the analysis of structures with high-dimensional and independent material uncertainties
Ding, Chensen UL; Deokar, Rohit R.; Ding, Yanjun et al

in Computer Methods in Applied Mechanics and Engineering (2019), 349

Structural stochastic analysis is vital to engineering. However, current material related uncertainty methods are mostly limited to low dimension, and they mostly remain unable to account for spatially ... [more ▼]

Structural stochastic analysis is vital to engineering. However, current material related uncertainty methods are mostly limited to low dimension, and they mostly remain unable to account for spatially uncorrelated material uncertainties. They are not representative of realistic and practical engineering situations. In particular, it is more serious for composite structures comprised of dissimilar materials. Therefore, we propose a novel model order reduction via proper orthogonal decomposition accelerated Monte Carlo stochastic isogeometric method (IGA-POD-MCS) for stochastic analysis of exactly represented (composite) structures. This approach particularly enables high-dimensional material uncertainties wherein the characteristics of each element are independent. And the novelties include: (1) the structural geometry is exactly modeled thanks to isogeometric analysis (IGA), as well as providing more accurate deterministic and stochastic solutions, (2) we innovatively consider high-dimensional and independent material uncertainties by separating the stochastic mesh from the IGA mesh, and modeling different stochastic elements to have different (independent) uncertainty behaviors, (3) the classical Monte Carlo simulation (MCS) is employed to universally solve the high-dimensional uncertainty problem. However, to circumvent its computational expense, we employ model order reduction via proper orthogonal decomposition (POD) into the IGA coupled MCS stochastic analysis. In particular, we observe that this work decouples all IGA elements and hence permits independent uncertainty models easily, thereby the engineering problem is modeled to be more realistic and authentic. Several illustrative numerical examples verify the proposed IGA-POD-MCS approach is effective and efficient; and the larger the scale of the problem is, the more advantageous the method will become. [less ▲]

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See detailA simple and robust computational homogenization approach for heterogeneous particulate composites
Bansal, Manik; Singh, I.V.; Patil, R.U. et al

in Computer Methods in Applied Mechanics and Engineering (2019), 349

In this article, a computationally efficient multi-split MsXFEM is proposed to evaluate the elastic properties of heterogeneous materials. The multi-split MsXFEM is the combination of multi-split XFEM ... [more ▼]

In this article, a computationally efficient multi-split MsXFEM is proposed to evaluate the elastic properties of heterogeneous materials. The multi-split MsXFEM is the combination of multi-split XFEM with multiscale finite element methods (MsFEM). The multi-split XFEM is capable to model multiple discontinuities in a single element which leads to reduction in the number of mesh elements, whereas MsFEM helps in reducing the computational time. Strain energy based homogenization has been implemented on an RVE (having volume fraction of heterogeneities up to 50%) for evaluating the elastic properties. From macro-element size analysis, we estimate that the RVE edge length must be 5 times the edge length of the macro-element. The directional analysis has been performed to verify the isotropic behavior of the material, whereas contrast analysis has been done to check the numerical accuracy of the proposed scheme. A level set correction (LSC) based on higher order shape functions has been proposed to reduce mapping errors of level set values. It is also observed that multi-split MsXFEM is about 16 times computationally more efficient than MsXFEM for 50% volume of heterogeneities. [less ▲]

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See detailThe Enthusiast, the Interested, the Sceptic, and the Cynic: Understanding User Experience and Perceived Value in Location-Based Cultural Heritage Games Through Qualitative and Sentiment Analysis
Jones, Catherine UL; Theodosis, Efstathios UL; Lykourentzou, Ioanna

in Journal on Computing and Cultural Heritage (2019), 12(1),

We discuss the user study of a mobile cultural heritage game, designed to stimulate reflection about a city’s history. Aided by location-aware technology, the game fosters the serendipitous discovery of ... [more ▼]

We discuss the user study of a mobile cultural heritage game, designed to stimulate reflection about a city’s history. Aided by location-aware technology, the game fosters the serendipitous discovery of Points-Of-Interest, historical images and stories, whilst players wander the city. This exploration differs from the typical pre-calculated path recommendations used by other location-based applications. It triggers reflection about the city’s past that is as unique as its visitors. Ours is one of the first studies to attempt an understanding of the effects of serendipitous urban discovery and historic reflection-triggering technologies on user experience. We combined field trials with controlled experiments, analysing perceptions of the experience and value using responses expressed in open-ended questionnaire items. Using thematic coding and sentiment analysis, we observed types of emotional responses, indicating four potential profiles of their likelihood towards future technology adoption. Enthusiastic and Interested users appreciated the freedom of movement choice that created an autonomous experience that fostered a sense of personal accomplishment. The interface interactions of the game, designed to stimulate reflection, supported a feeling of connectedness to others. In contrast, Cynical and Sceptical users were less tolerant of perceived technological issues, and required more perfection in functionality and design. These users are less likely to be the early adopters of serendipitous location-based apps. The game was developed as part of a large cultural informatics project, but unlike typical evaluations, we conducted this study midway through the project and not at its end. This approach (1) gave the team the possibility to take stock, pause and reflect and (2) provided insight on future design improvements for increasing the perceived value of serendipitous urban discovery applications. Our results contribute towards a grounded understanding of user experience, and help progress the development of cultural heritage applications that incorporate elements of reflection and/or place-based exploration into their functionalities. [less ▲]

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See detailB-Spline FEM for Time-Harmonic Acoustic Scattering and Propagation
Khajah, Tahsin; Antoine, Xavier; Bordas, Stéphane UL

in Journal of Theoretical and Computational Acoustics (2019), 27

We study the application of a B-splines Finite Element Method (FEM) to time-harmonic scattering acoustic problems. The infinite space is truncated by a fictitious boundary and second-order Absorbing ... [more ▼]

We study the application of a B-splines Finite Element Method (FEM) to time-harmonic scattering acoustic problems. The infinite space is truncated by a fictitious boundary and second-order Absorbing Boundary Conditions (ABCs) are applied. The truncation error is included in the exact solution so that the reported error is an indicator of the performance of the numerical method, in particular of the size of the pollution error. Numerical results performed with high-order basis functions (third or fourth order) showed no visible pollution error even for very high frequencies. To prove the ability of the method to increase its accuracy in the high frequency regime, we show how to implement a high-order Padé-type ABC on the fictitious outer boundary. The above-mentioned properties combined with exact geometrical representation make B-Spline FEM a very promising platform to solve high-frequency acoustic problems. [less ▲]

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See detailCombating non-communicable diseases: potentials and challenges for community health workers in a digital age, a narrative review of the literature
Mishra, Shiva Raj; Lygidakis, Charilaos UL; Neupane, Dinesh et al

in Health Policy and Planning (2019)

The use of community health workers (CHWs) has been explored as a viable option to provide home health education, counselling and basic health care, notwithstanding their challenges in training and ... [more ▼]

The use of community health workers (CHWs) has been explored as a viable option to provide home health education, counselling and basic health care, notwithstanding their challenges in training and retention. In this manuscript, we review the evidence and discuss how the digitalization affects the CHWs programmes for tackling non-communicable diseases (NCDs) in low- and middle-income countries (LMICs). We conducted a review of literature covering two databases: PubMED and Embase. A total of 97 articles were abstracted for full text review of which 26 are included in the analysis. Existing theories were used to construct a conceptual framework for understanding how digitalization affects the prospects of CHW programmes for NCDs. The results are divided into two themes: (1) the benefits of digitalization and (2) the challenges to the prospects of digitalization. We also conducted supplemental search in non-peer reviewed literature to identify and map the digital platforms currently in use in CHW programmes. We identified three benefits and three challenges of digitalization. Firstly, it will help improve the access and quality of services, notwithstanding its higher establishment and maintenance costs. Secondly, it will add efficiency in training and personnel management. Thirdly, it will leverage the use of data generated across grass-roots platforms to further research and evaluation. The challenges posed are related to funding, health literacy of CHWs and systemic challenges related to motivating CHWs. Several dozens of digital platforms were mapped, including mobile-based networking devices (used for behavioural change communication), Web-applications (used for contact tracking, reminder system, adherence tracing, data collection and decision support), videoconference (used for decision support) and mobile applications (used for reminder system, supervision, patients’ management, hearing screening and tele-consultation). The digitalization efforts of CHW programmes are afflicted by many challenges, yet the rapid technological penetration and acceptability coupled with the gradual fall in costs constitute encouraging signals for the LMICs. Both CHWs interventions and digital technologies are not inexpensive, but they may provide better value for the money when applied at the right place and time. [less ▲]

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See detailRobotic system for inspection by contact of bridge beams using UAVs
Sanchez Cuevas, Pedro Jesus UL; Ramon Soria, Pablo; Arrue, Begoña et al

in Sensors (2019)

This paper presents a robotic system using Unmanned Aerial Vehicles (UAVs) for bridge-inspection tasks that require physical contact between the aerial platform and the bridge surfaces, such as beam ... [more ▼]

This paper presents a robotic system using Unmanned Aerial Vehicles (UAVs) for bridge-inspection tasks that require physical contact between the aerial platform and the bridge surfaces, such as beam-deflection analysis or measuring crack depth with an ultrasonic sensor. The proposed system takes advantage of the aerodynamic ceiling effect that arises when the multirotor gets close to the bridge surface. Moreover, this paper describes how a UAV can be used as a sensor that is able to fly and touch the bridge to take measurements during an inspection by contact. A practical application of the system involving the measurement of a bridge’s beam deflection using a laser tracking station is also presented. In order to validate our system, experiments on two different bridges involving the measurement of the deflection of their beams are shown. [less ▲]

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See detailA one point integration rule over star convex polytopes
Francis, Amrita; Natarajan, Sundararajan; Atroshchenko, Elena et al

in Computers and Structures (2019), 215

In this paper, the recently proposed linearly consistent one point integration rule for the meshfree methods is extended to arbitrary polytopes. The salient feature of the proposed technique is that it ... [more ▼]

In this paper, the recently proposed linearly consistent one point integration rule for the meshfree methods is extended to arbitrary polytopes. The salient feature of the proposed technique is that it requires only one integration point within each n-sided polytope as opposed to 3n in Francis et al. (2017) and 13n integration points in the conventional approach for numerically integrating the weak form in two dimensions. The essence of the proposed technique is to approximate the compatible strain by a linear smoothing function and evaluate the smoothed nodal derivatives by the discrete form of the divergence theorem at the geometric center. This is done by Taylor’s expansion of the weak form which facilitates the use of the smoothed nodal derivatives acting as the stabilization term. This translates to 50% and 30% reduction in the overall computational time in the two and three dimensions, respectively, whilst preserving the accuracy and the convergence rates. The convergence properties, the accuracy and the efficacy of the one point integration scheme are discussed by solving few benchmark problems in elastostatics. [less ▲]

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