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See detailAn implicit potential method along with a meshless technique for incompressible fluid flows for regular and irregular geometries in 2D and 3D
Bourantas, Georgios UL; Loukopoulos, V. C.; Chowdhury, H. A. et al

in Engineering Analysis with Boundary Elements (2017), 77

We present the Implicit Potential (IPOT) numerical scheme developed in the framework of meshless point collocation. The proposed scheme is used for the numerical solution of the steady state ... [more ▼]

We present the Implicit Potential (IPOT) numerical scheme developed in the framework of meshless point collocation. The proposed scheme is used for the numerical solution of the steady state, incompressible Navier-Stokes (N-S) equations in their primitive variable (u-v-w-p) formulation. The governing equations are solved in their strong form using either a collocated or a semi-staggered type meshless nodal configuration. The unknown field functions and derivatives are calculated using the Modified Moving Least Squares (MMLS) interpolation method. Both velocity-correction and pressure correction methods applied ensure the incompressibility constraint and mass conservation. The proposed meshless point collocation (MPC) scheme has the following characteristics: (i) it can be applied, in a straightforward manner to: steady, unsteady, internal and external fluid flows in 2D and 3D, (ii) it equally applies to regular an irregular geometries, (iii) a distribution of points is sufficient, no numerical integration in space nor any mesh structure are required, (iv) there is no need for pressure boundary conditions since no pressure constitutive equation is solved, (v) it is quite simple and accurate, (vi) results can be obtained using collocated or semi-staggered nodal distributions, (vii) there is no need to compute the velocity potential nor the unit normal vectors and (viii) there is no need for a curvilinear system of coordinates. Simulations of fluid flow in 2D and 3D for regular and irregular geometries indicate the validity of the proposed methodology. [less ▲]

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

in Selected Areas in Cryptography (2008)

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

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

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See detailAn improved sampling rule for mapping geopotential functions of a planet from a near polar orbit
Weigelt, Matthias UL; Sneeuw, Nico; Schrama, E.J.O. et al

in Journal of Geodesy (2013), 87(2), 127-142

One of the limiting factors in the determination of gravity field solutions is the spatial sampling. Especially during phases, when the satellite repeats its own track after a short time, the spatial ... [more ▼]

One of the limiting factors in the determination of gravity field solutions is the spatial sampling. Especially during phases, when the satellite repeats its own track after a short time, the spatial resolution will be limited. The Nyquist rule-of-thumb for mapping geopotential functions of a planet, also referred to as the Colombo–Nyquist rule-of-thumb, provides a limit for the maximum achievable degree of a spherical harmonic development for repeat orbits. We show in this paper that this rule is too conservative, and solutions with better spatial resolutions are possible. A new rule is introduced which limits the maximum achievable order (not degree!) to be smaller than the number of revolutions if the difference between the number of revolutions and the number of nodal days is of odd parity and to be smaller than half the number of revolutions if the difference is of even parity. The dependence on the parity is reflected in the eigenvalue spectrum of the normal matrix and becomes especially important in the presence of noise. The rule is based on applying the Nyquist sampling theorem separately in North–South and East–West direction. This is only possible for satellites in highly inclined orbits like champ and grace. Tables for these two satellite missions are also provided which indicate the passed and (in case of grace) expected repeat cycles and possible degradations in the quality of the gravity field solutions. [less ▲]

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See detailImproving the accuracy of OD estimation from traffic counts employing a partial observabillity maximizing methodology
Rinaldi, Marco UL; Fakhraeiroudsari, Farzad; Viti, Francesco UL et al

Scientific Conference (2016, January)

Detailed reference viewed: 55 (1 UL)
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See detailImproving the conditioning of XFEM/GFEM for fracture mechanics problems through enrichment quasi-orthogonalization
Agathos, Konstantinos; Bordas, Stéphane UL; Chatzi, Eleni

in Computer Methods in Applied Mechanics and Engineering (2018)

Partition of unity enrichment is known to significantly enhance the accuracy of the finite element method by allowing the incorporation of known characteristics of the solution in the approximation space ... [more ▼]

Partition of unity enrichment is known to significantly enhance the accuracy of the finite element method by allowing the incorporation of known characteristics of the solution in the approximation space. However, in several cases it can further cause conditioning problems for which a number of remedies have been proposed in the framework of the extended/generalized finite element method (XFEM/GFEM). Those solutions often involve significant modifications to the initial method and result in increased implementation complexity. In the present work, a simple procedure for the local near-orthogonalization of enrichment functions is introduced, which significantly improves the conditioning of the resulting system matrices, while requiring only minor modifications to the initial method. Although application to different types of enrichment functions is possible, the resulting scheme is specialized for the singular enrichment functions used in linear elastic fracture mechanics and tested through benchmark problems. [less ▲]

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See detailIMPROVING THE CONVERGENCE OF BOUNDS FOR EFFECTIVE ELASTIC PARAMETERS OF HETEROGENEOUS MATERIALS
Heaney, Claire; Kerfriden, Pierre; Bordas, Stéphane UL

Scientific Conference (2014)

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

Scientific Conference (2011)

Detailed reference viewed: 64 (1 UL)
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See detailIn-silico Robust Reconstruction of the Per-Arnt-Sim Kinase Pathway using Dynamical Structure Functions
Chetty, V.; Adebayo, J.; Mathis, A. et al

Scientific Conference (2012, October)

Detailed reference viewed: 53 (1 UL)
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See detailIncentives and gaming environments for changing commuter behaviour
Kracheel, Martin UL; McCall, Roderick UL; Koenig, Vincent UL et al

Scientific Conference (2014, September 30)

The project aims to produce a pervasive, gamified system that tries to incentivize mobility behaviour change by offering alternative activities in contrast to usual journeys in such way that it will ... [more ▼]

The project aims to produce a pervasive, gamified system that tries to incentivize mobility behaviour change by offering alternative activities in contrast to usual journeys in such way that it will reduce traffic, emissions and, in the end, save money. The alternatives, for example, such as taking different modes of transport, are incentivised through gamification. In order to develop this pervasive system, we analysed existing mobility patterns of commuters in Luxembourg. The methodology that we developed consists of a questionnaire, a smartphone application and focus group interviews. This paper presents the findings of the questionnaire and how they influence the design of the gamified pervasive application. [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 detailIncorporating trip chaining within online demand estimation
Cantelmo, Guido; Qurashi, Moeid; Prakash, Arun et al

in Transportation Research Procedia (2019), 38

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

Time-dependent Origin–Destination (OD) demand flows are fundamental inputs for Dynamic Traffic Assignment (DTA) systems and real-time traffic management. This work introduces a novel state-space framework to estimate these demand flows in an online context. 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 network. 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 ▲]

Detailed reference viewed: 86 (3 UL)
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See detailIndoor positioning and floor plan based ground truth: Can you really click where you are?
Popleteev, Andrei UL

in 15th International Conference on Mobile and Ubiquitious Multimedia (MUM-2016) (2016, December)

The increasing accuracy of indoor positioning systems requires an appropriately accurate evaluation, which compares system outputs with the known coordinates of test locations --- the ground truth ... [more ▼]

The increasing accuracy of indoor positioning systems requires an appropriately accurate evaluation, which compares system outputs with the known coordinates of test locations --- the ground truth. Although ground truth data are rarely (if ever) tested, they are traditionally assumed to be perfectly accurate. However, even small errors introduced by inaccurate ground truth need to be taken into account for fair evaluation and comparison between modern high-resolution positioning systems. In this paper we analyze the quality of ground truth data provided by clicking on an interactive floor plan (a method employed by such classical systems as RADAR and Horus). Experimental results show that this method has high precision but low accuracy, and high systematic errors make it unsuitable for evaluation of fine-grained localization systems. [less ▲]

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See detailIndustry 4.0 – Implementation of an automated assembly line in a wooden modular house production plant: The case Leko Labs
de Vincenzo, Vincenzo UL; Hichri, Bassem UL; Plapper, Peter UL

in De vincenzo, Vincenzo; Hichri, Bassem; Plapper, Peter (Eds.) Robotix-Academy Conference for Industrial Robotics (RACIR) 2018 (2018, November)

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See detailInference of switched biochemical reaction networks using sparse bayesian learning
Pan, Wei UL; Yuan, Y.; Sootla, A. et al

in The proceedings of the 7th European Conference on Machine Learning and Principles and Practice of Knowledge Discovery in Databases (ECML/PKDD) (2014)

This paper proposes an algorithm to identify biochemical reaction networks with time-varying kinetics. We formulate the problem as a nonconvex optimisation problem casted in a sparse Bayesian learning ... [more ▼]

This paper proposes an algorithm to identify biochemical reaction networks with time-varying kinetics. We formulate the problem as a nonconvex optimisation problem casted in a sparse Bayesian learning framework. The nonconvex problem can be efficiently solved using Convex-Concave programming. We test the effectiveness of the method on a simulated example of DNA circuit realising a switched chaotic Lorenz oscillator. [less ▲]

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See detailThe influence of fracture geometry variation on non-Darcy flow in fractures under confining stresses
Chen, Yuedu; Lian, Haojie UL; Liang, Weiguo et al

in International Journal of Rock Mechanics and Mining Sciences (2018), 113

To investigate the influence of geometric characteristics of deformable rough fractures under confining stresses on the behaviors of non-Darcy flow, four fractured sandstone specimens were used for ... [more ▼]

To investigate the influence of geometric characteristics of deformable rough fractures under confining stresses on the behaviors of non-Darcy flow, four fractured sandstone specimens were used for hydraulic tests in the experiments. According to the experimental results of the relationships between the hydraulic gradient and the flow rate, it is demonstrated that the Forchheimer's equation can offer a good description of the non-Darcy flow in rough fractures. In addition, the coefficients A and B in Forchheimer's equation are sensitive to the fracture geometric characteristics, and their values also increase as the confining stress rises, mainly owing to the reduction of the hydraulic aperture and the heterogeneous distribution of the interconnected void areas with the confining stress rising. Then, the surface and interior geometric properties of rough fractures were quantitatively characterized with the peak asperity height and the box-counting fractal dimension of the heterogeneous distribution of the interconnected void areas, respectively. Furthermore, an empirical relationship between the fractal dimension D and the fracture apertures was constructed according to the experimental results. Lastly, a quantitative model was proposed to represent the relationship between the fracture geometric characteristics and the non-Darcy coefficient . This model was further used to link the non-linear coefficient of Forchheimer's equation and the critical Reynold number with the fracture geometric characteristics. The proposed models were validated by the experimental data and would be helpful to characterize the non-Darcy flow behavior in rough fractures under various confining stresses. [less ▲]

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

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

Detailed reference viewed: 41 (3 UL)
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See detailInfluence of piston position on the scavenging and swirling flow in two-stroke Diesel engines
Obeidat, Anas UL; Haider, S.; Meyer, K.E. et al

in EUROMECH Colloquium 525 - Instabilities and transition in three-dimensional flows with rotation (2011, June 21)

Detailed reference viewed: 37 (8 UL)