Browsing
     by title


0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

or enter first few letters:   
OK
Full Text
Peer Reviewed
See detailMonostability and multistability of genetic regulatory networks with different types of regulation functions
Pan, Wei UL; Wang, Z; Gao, H. et al

in Nonlinear Analysis : Real World Applications (2010), 11(4), 31703185

Monostability and multistability are proven to be two important topics in synthesis biology and system biology. In this paper, both monostability and multistability are analyzed in a unified framework by ... [more ▼]

Monostability and multistability are proven to be two important topics in synthesis biology and system biology. In this paper, both monostability and multistability are analyzed in a unified framework by applying control theory and mathematical tools. The genetic regulatory networks (GRNs) with multiple time-varying delays and different types of regulation functions are considered. By putting forward a general sector-like regulation function and utilizing up-to-date techniques, a novel Lyapunov–Krasovskii functional is introduced for achieving delay dependence to ensure less conservatism. A new condition is then proposed for the general stability of a GRN in the form of linear matrix inequalities (LMIs) that are dependent on the upper and lower bounds of the delays. Our general stability conditions are applicable to several frequently used regulation functions. It is shown that the existing results for monostability of GRNs are special cases of our main results. Five examples are employed to illustrate the applicability and usefulness of the developed theoretical results. [less ▲]

Detailed reference viewed: 54 (0 UL)
Full Text
Peer Reviewed
See detailMorphological traits essential to electrospun and grafted Nylon-6 nanofiber membranes for capturing submicron simulated exhaled breath aerosols
Reyes, Catherine UL; Frey, Margaret

in Journal of Applied Polymer Science (2017), 134(17), 1-15

As contagious bio-aerosols continue to impact our society, we examine how the morphological traits of large-scale (15 cm x 93 cm), uniformly thick, electrospun Nylon membranes can contribute to the ... [more ▼]

As contagious bio-aerosols continue to impact our society, we examine how the morphological traits of large-scale (15 cm x 93 cm), uniformly thick, electrospun Nylon membranes can contribute to the development of diagnostic, sensor driven face masks for capturing exhaled breath content. In our study, we compare the capture efficiencies of three types of large-scale Nylon-6 nanofiber membranes against those of commercial control textiles for capturing in-lab simulated salt breath aerosols. One of the electrospun membranes was also surface functionalized via grafting technique. The fabrication, functionalization, and exhaled aerosol capture of these large-scale membranes underscores the importance of assessing the lifetime, and usability, of electrospun materials before future integration with diagnostic sensing platforms can be successfully achieved. [less ▲]

Detailed reference viewed: 128 (1 UL)
Full Text
See detailA Multi-agent approach for in silico simulations of micro-biological systems
Proverbio, Daniele UL; Gallo, Luca; Passalacqua, Barbara et al

E-print/Working paper (2019)

A Multi-agent approach forin silicosimulations ofmicro-biological systemsProverbio D., Gallo L., Passalacqua B., Pellegrino J., Maggiora M.AbstractUsing a Multi-agent systems paradigm, the present project ... [more ▼]

A Multi-agent approach forin silicosimulations ofmicro-biological systemsProverbio D., Gallo L., Passalacqua B., Pellegrino J., Maggiora M.AbstractUsing a Multi-agent systems paradigm, the present project develops, validates and exploits a computa-tionaltestbedthat simulates micro-biological complex systems, namely the aggregation patterns of thesocial amoebaDyctiostelium discoideum. We propose a new design and implementation for managingdiscrete simulations with autonomous agents on a microscopic scale, thus focusing on their social be-havior and mutual interactions. Then, the dependence on the main physical variables is tested, namelydensity and number of amoebas; in addition, we analyze the robustness of the dynamics against var-ious noise sources. Along with these results, we suggest a methodology for further studies that makeuse of our validated model. [less ▲]

Detailed reference viewed: 103 (4 UL)
Full Text
See detailMULTI-GNSS ERROR CHARACTERISTICS AND BENEFITS TO LONG-TERM MONITORING APPLICATIONS IN GEOSCIENCES
Abraha, Kibrom Ebuy UL

Doctoral thesis (2018)

Global Navigation Satellite System (GNSS)-derived position solutions are used for crustal deformations for long-term monitoring studies such as correcting sea-level records for vertical land movements and ... [more ▼]

Global Navigation Satellite System (GNSS)-derived position solutions are used for crustal deformations for long-term monitoring studies such as correcting sea-level records for vertical land movements and to determine present-day surface-mass changes. In all these studies scientists rely heavily on precise International GNSS Service (IGS) products. In recent years the IGS products have partly been generated from a rigorous combination of GNSS, such as Global Positioning System (GPS) and Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS) observations. Although combined solutions from two or more GNSS benefit from the diversity and redundancy of having more than one GNSS, the solutions are also subjected to system-specific systematic errors. Applications which demand high-accuracy products, therefore, would profit from evaluations of the benefits and error characteristics of combined GNSS solutions. In response to the increased availability of multi-GNSS observations from a truly global ground network of receivers, the goal of this thesis is to investigate their overall impacts on the derived products. Primarily, the impacts of combined GNSS data processing for stations in a constrained environment with a potential for signal obstructions, is investigated. The effects of signal obstructions on derived parameter time series and station velocity estimates are assessed. The benefits of combined solutions are evaluated for stations in constrained environments. Moreover, the study of the impacts of combined solutions on satellite orbits and station parameters contributes to the understanding of the error characteristics of combined GNSS data processing on derived products. The consistency of the parameters, noise analysis and system-specific periodic errors are assessed. Dominant system specific periodic errors and the impact of combined solutions on reducing the effects are addressed. Unmodelled or insufficiently modelled (sub-)daily errors propagate to longer periods and appear in high-end products coinciding with other longer periods, which in turn may lead to misleading interpretations of the latter. The propagation mechanism mainly depends, among other factors, on data sampling deficiencies and GNSS ground repeat periods. Here, the results of this study show that combined solutions not only reduce system-specific effects but also provide a means to identifying the sources from other compatible elements. [less ▲]

Detailed reference viewed: 47 (10 UL)
Full Text
Peer Reviewed
See detailMulti-robot distributed visual consensus using epipoles
Montijano, E.; Thunberg, Johan UL; Hu, X. et al

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

In this paper we give a distributed solution to the problem of making a team of non-holonomic robots achieve the same heading (attitude consensus problem) using vision sensors with limited field of view ... [more ▼]

In this paper we give a distributed solution to the problem of making a team of non-holonomic robots achieve the same heading (attitude consensus problem) using vision sensors with limited field of view. The use of cameras with constrained field of view limits the information the robots perceive compared to other omnidirectional sensors. This makes the consensus problem more complicated, because the robots will not always be able to observe other robots. By using structure from motion computed from images, the robots can estimate the difference in their headings from common observations of the environment without the necessity of directly observe each other. In this way, the robots achieve the consensus in their headings while observing the environment instead of each other. The contribution of the paper is a new controller that uses the epipoles computed from pairs of images to estimate the misalignment between neighbor robots. In addition, the control is robust to changes in the topology of the network and does not require to know the calibration of the cameras in order to achieve the desired configuration. To the best of our knowledge, this is the first time that the epipoles are used in multi-robot consensus, putting their properties in value. [less ▲]

Detailed reference viewed: 60 (0 UL)
Full Text
Peer Reviewed
See detailMulti-scale methods for fracture: model learning across scales, digital twinning and factors of safety
Bordas, Stéphane UL; Beex, Lars UL; Kerfriden, Pierre et al

Scientific Conference (2015, November 18)

Authors: S. P. A. Bordas, L. A. A. Beex, P. Kerfriden, D. A. Paladim, O. Goury, A. Akbari, H. Rappel  Multi-scale methods for fracture: model learning across scales, digital twinning and factors of safety ... [more ▼]

Authors: S. P. A. Bordas, L. A. A. Beex, P. Kerfriden, D. A. Paladim, O. Goury, A. Akbari, H. Rappel  Multi-scale methods for fracture: model learning across scales, digital twinning and factors of safety Fracture and material instabilities originate at spatial scales much smaller than that of the structure of interest: delamination, debonding, fibre breakage, cell-wall buckling, are examples of nano/micro or meso-scale mechanisms which can lead to global failure of the material and structure. Such mechanisms cannot, for computational and practical reasons, be accounted at structural scale, so that acceleration methods are necessary.  We review in this presentation recently proposed approaches to reduce the computational expense associated with multi-scale modelling of fracture. In light of two particular examples, we show connections between algebraic reduction (model order reduction and quasi-continuum methods) and homogenisation-based reduction. We open the discussion towards suitable approaches for machine-learning and Bayesian statistical based multi-scale model selection. Such approaches could fuel a digital-twin concept enabling models to learn from real-time data acquired during the life of the structure, accounting for “real” environmental conditions during predictions, and, eventually, moving beyond the “factors of safety” era. [less ▲]

Detailed reference viewed: 374 (19 UL)
Full Text
See detailMulti-scale methods for fracture: model learning across scales, digital twinning and factors of safety
: primer on Bayesian Inference
Bordas, Stéphane UL; Hale, Jack UL; Beex, Lars UL et al

Speeches/Talks (2015)

Fracture and material instabilities originate at spatial scales much smaller than that of the structure of interest: delamination, debonding, fibre break- age, cell-wall buckling, are examples of nano ... [more ▼]

Fracture and material instabilities originate at spatial scales much smaller than that of the structure of interest: delamination, debonding, fibre break- age, cell-wall buckling, are examples of nano/micro or meso-scale mechanisms which can lead to global failure of the material and structure. Such mech- anisms cannot, for computational and practical reasons, be accounted at structural scale, so that acceleration methods are necessary. We review in this presentation recently proposed approaches to reduce the computational expense associated with multi-scale modelling of frac- ture. In light of two particular examples, we show connections between algebraic reduction (model order reduction and quasi-continuum methods) and homogenisation-based reduction. We open the discussion towards suitable approaches for machine-learning and Bayesian statistical based multi-scale model selection. Such approaches could fuel a digital-twin concept enabling models to learn from real-time data acquired during the life of the structure, accounting for “real” environmental conditions during predictions, and, eventually, moving beyond the era of factors of safety. [less ▲]

Detailed reference viewed: 139 (4 UL)
Full Text
See detailMulti-scale modelling of fracture
Bordas, Stéphane UL; Kerfriden, Pierre; Beex, Lars et al

Speeches/Talks (2016)

We present recent models on complexity reduction for computational fracture mechanics

Detailed reference viewed: 169 (7 UL)
Full Text
Peer Reviewed
See detailA multifactorial evaluation framework for gene regulatory network reconstruction
Mombaerts, Laurent UL; Aalto, Atte UL; Markdahl, Johan UL et al

in Foundations of Systems Biology in Engineering (2019)

In the past years, many computational methods have been developed to infer the structure of gene regulatory networks from time series data. However, the applicability and accuracy presumptions of such ... [more ▼]

In the past years, many computational methods have been developed to infer the structure of gene regulatory networks from time series data. However, the applicability and accuracy presumptions of such algorithms remain unclear due to experimental heterogeneity. This paper assesses the performance of recent and successful network inference strategies under a novel, multifactorial evaluation framework in order to highlight pragmatic tradeoffs in experimental design. The effects of data quantity and systems perturbations are addressed, thereby formulating guidelines for efficient resource management. Realistic data were generated from six widely used benchmark models of rhythmic and nonrhythmic gene regulatory systems with random perturbations mimicking the effect of gene knock-out or chemical treatments. Then, time series data of increasing lengths were provided to five state-of-the-art network inference algorithms representing distinctive mathematical paradigms. The performances of such network reconstruction methodologies are uncovered under various experimental conditions. We report that the algorithms do not benefit equally from data increments. Furthermore, at least for the studied rhythmic system, it is more profitable for network inference strategies to be run on long time series rather than short time series with multiple perturbations. By contrast, for the non-rhythmic systems, increasing the number of perturbation experiments yielded better results than increasing the sampling frequency. We expect that future benchmark and algorithm design would integrate such multifactorial considerations to promote their widespread and conscientious usage. [less ▲]

Detailed reference viewed: 48 (5 UL)
Full Text
Peer Reviewed
See detailA Multilayer Software Architecture for Safe Autonomous Robots
Gribov, Vladislav UL; Voos, Holger UL

in Proceedings of 19th IEEE International Conference on Emerging Technologies and Factory Automation, Barcelona, Spain, 16-19 Sept. 2014 (2014, September)

In this paper a safety-oriented model based software architecture for robotic solutions is proposed. The main focus herein is to consider aspects such as real-time, het- erogeneity, deployment, modeling ... [more ▼]

In this paper a safety-oriented model based software architecture for robotic solutions is proposed. The main focus herein is to consider aspects such as real-time, het- erogeneity, deployment, modeling and analysis of emerging effects as well as functional safety and to combine all aspects into an overall development approach. The architecture shall capture the complexity caused by the autonomy and mobility of the robot and support the developer with a suitable chain of evidence especially suited for the safety relevant functions. A use case comprising a lightweight robotic manipulator which will be integrated in a mobile service robot underlines the feasibility of this approach. [less ▲]

Detailed reference viewed: 138 (6 UL)
Full Text
Peer Reviewed
See detailMultiline holding based control for lines merging to a shared transit corridor
Laskaris, Georgios UL; Cats, Oded; Jenelius, Erik et al

in Transportmetrica B: Transport Dynamics (2018)

In transit corridors, multiple lines share a sequence of consecutive stops to provide higher joint frequency in higher demand areas. A key challenge is to coordinate the transition from single line to ... [more ▼]

In transit corridors, multiple lines share a sequence of consecutive stops to provide higher joint frequency in higher demand areas. A key challenge is to coordinate the transition from single line to joint operation. A holding control strategy aimed at minimizing passenger travel times is introduced for lines merging into a shared corridor, accounting for the coordination of vehicle arrivals from the merging lines as well as the regularity of each line. The criterion is tested using an artificial network and a real-world network to analyze the impact of demand distribution and compare cooperative versus single line control. We illustrate how the real-time strategy yields overall passenger gains, depending on the composition of different user groups. Results are assessed based on operation and passenger performance indicators and show that coordination is achieved. When combined with joint control in the common part, the proposed approach achieves consistentnetwork-wide travel time benefits. [less ▲]

Detailed reference viewed: 79 (4 UL)
Full Text
See detailMultiphysics applications and computational challenges
Zilian, Andreas UL

Scientific Conference (2017, January 24)

Detailed reference viewed: 78 (5 UL)
Full Text
Peer Reviewed
See detailMultiple crack detection in 3D using a stable XFEM and global optimization
Agathos, Konstantinos; Chatzi, Eleni; Bordas, Stéphane UL

in Computational Mechanics (2018)

A numerical scheme is proposed for the detection of multiple cracks in three dimensional (3D) structures. The scheme is based on a variant of the extended finite element method (XFEM) and a hybrid ... [more ▼]

A numerical scheme is proposed for the detection of multiple cracks in three dimensional (3D) structures. The scheme is based on a variant of the extended finite element method (XFEM) and a hybrid optimizer solution. The proposed XFEM variant is particularly well-suited for the simulation of 3D fracture problems, and as such serves as an efficient solution to the so-called forward problem. A set of heuristic optimization algorithms are recombined into a multiscale optimization scheme. The introduced approach proves effective in tackling the complex inverse problem involved, where identification of multiple flaws is sought on the basis of sparse measurements collected near the structural boundary. The potential of the scheme is demonstrated through a set of numerical case studies of varying complexity. [less ▲]

Detailed reference viewed: 165 (7 UL)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 50 (19 UL)
Full Text
See detailMultiscale Modelling of Damage and Fracture in Discrete Materials Using a Variational Quasicontinuum Method
Rokos, Ondrej; Peerlings, Ron; Beex, Lars UL et al

Scientific Conference (2017, September 05)

Detailed reference viewed: 43 (1 UL)
Full Text
Peer Reviewed
See detailA multiscale partitioned reduced order model applied to damage simulation
Goury, Olivier; Kerfriden, Pierre; Bordas, Stéphane UL

Scientific Conference (2013, July)

Simulating fracture in realistic engineering components is computationally expensive. In the context of early-stage design, or reverse engineering, such simulations might need to be performed for a large ... [more ▼]

Simulating fracture in realistic engineering components is computationally expensive. In the context of early-stage design, or reverse engineering, such simulations might need to be performed for a large range of material and geometric parameters, which makes the solution to the parametric problem of fracture unaffordable. Model order reduction, such as the proper orthogonal decomposition (POD), is one way to reduce significantly the computational time by reducing the number of spatial unknowns. The solution is searched for in a reduced space spanned by a few well-chosen basis vectors only. In the context of solid mechanics involving structural softening, the strong topological changes in the zone where damage localises are extremely sensitive to variations of the parameters, which requires reduced spaces of prohibitively large dimensions in order to approximate the solution with a sufficiently high degree of accuracy. Introduced in [1], partitioned model order reduction is an alternative to global model order reduction that essentially divides up the problem into smaller regions. Each region can then be tackled using a reduced model of appropriate size, if at all, depending on the local material non-linearities in the region. In the context of multiscale homogenization, simulations of representative volume elements (RVE) have to be performed to obtain the material properties in the different elements of a coarse mesh. When considering a nonlinear material, those multiple RVE simulations can be com- putationally very expensive. They however only differ by the history of boundary conditions applied. This contribution proposes to apply partitioned model order reduction to those RVEs with reduced bases parametrized by the boundary conditions. REFERENCES [1] P. Kerfriden, O. Goury, T. Rabczuk, S. Bordas, A partitioned model order reduction approach to rationalise computational expenses in nonlinear fracture mechanics, Computer Methods in Applied Mechanics and Engineering, 256:169–188, 2013. [less ▲]

Detailed reference viewed: 291 (5 UL)
Full Text
See detailMultiscale Quasicontinuum Methods for Dissipative Truss Models and Beam Networks
Beex, Lars UL; Peerlings, Ron; Geers, Marc et al

Presentation (2014, November 05)

Detailed reference viewed: 121 (4 UL)
Full Text
Peer Reviewed
See detailMultistability of genetic regulatory networks
Pan, Wei UL; Zhang, Z.; Liu, H.

in International Journal of Systems Science (2010), 41(1), 107-118

Multistability is found to be an important recurring theme in synthesis biology. In this article, the multistability analysis problem is investigated by applying control theory and mathematical tools ... [more ▼]

Multistability is found to be an important recurring theme in synthesis biology. In this article, the multistability analysis problem is investigated by applying control theory and mathematical tools. Both the modelling and analysis issues are discussed. Specifically, the genetic regulatory networks (GRNs) with multistability are modelled as switched systems with interval time-varying delays and parameter uncertainties, where the piecewise-affine models are used to approximate the inherent non-linearities existing in the GRNs. Then, by using a novel Lyapunov functional approach and linear matrix inequality (LMI) techniques, a few delay-dependent criteria for the multistability of such genetic regulatory networks are established in the form of LMIs, which can be readily verified by using standard numerical software. A three-component network and a genetic toggle switch with bistability are employed to illustrate the applicability and usefulness of the developed theoretical results. [less ▲]

Detailed reference viewed: 86 (0 UL)
Full Text
See detailNASA-FDL Artificial Intelligence in Planetary Science; Lunar Resource Mission
Backes, Dietmar UL

Scientific Conference (2017, December 15)

Detailed reference viewed: 85 (18 UL)
Full Text
See detailNatural frequencies of cracked isotropic & specially orthotropic plates using the extended finite element method
Natarajan, S; Baiz, P; Mahapatra, D Roy et al

Scientific Conference (2011, April)

In this paper, the linear free flexural vibration of cracked isotropic and specially orthotropic plates is studied using the extended finite element method. The mixed interpolation technique of the well ... [more ▼]

In this paper, the linear free flexural vibration of cracked isotropic and specially orthotropic plates is studied using the extended finite element method. The mixed interpolation technique of the well- established MITC4 [1] quadrilateral finite element with 12 standard degrees of freedom per element is used for this study. The natural frequencies of simply supported square plates are computed as a function of crack length and crack location. [less ▲]

Detailed reference viewed: 102 (1 UL)