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See detailMultiPluriTrans. Emerging Fields in Educational Ethnography. Introduction to the conference
Bollig, Sabine UL; Neumann, Sascha UL

Scientific Conference (2013, November 21)

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See detailMultiPluriTrans: Oder:Does Educational Ethnography remain what it used to be?
Hekel, Nicole UL; Husen, Onno

in Zeitschrift für Qualitative Forschung (2016), 1

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See detailMultipoint Lax operator algebras. Almost-graded structure and central extensions
Schlichenmaier, Martin UL

in Sbornik: Mathematics (2014), 205(5), 117-160

Recently, Lax operator algebras appeared as a new class of higher genus current type algebras. Based on I.Krichever's theory of Lax operators on algebraic curves they were introduced by I. Krichever and O ... [more ▼]

Recently, Lax operator algebras appeared as a new class of higher genus current type algebras. Based on I.Krichever's theory of Lax operators on algebraic curves they were introduced by I. Krichever and O. Sheinman. These algebras are almost-graded Lie algebras of currents on Riemann surfaces with marked points (in-points, out-points, and Tyurin points). In a previous joint article of the author with Sheinman the local cocycles and associated almost-graded central extensions are classified in the case of one in-point and one out-point. It was shown that the almost-graded extension is essentially unique. In this article the general case of Lax operator algebras corresponding to several in- and out-points is considered. In a first step it is shown that they are almost-graded. The grading is given by the splitting of the marked points which are non-Tyurin points into in- and out-points. Next, classification results both for local and bounded cocycles are shown. The uniqueness theorem for almost-graded central extensions follows. For this generalization additional techniques are needed which are presented in this article [less ▲]

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See detailMultiprecision Multiplication on ARMv8
Liu, Zhe UL; Järvinen, Kimmo; Liu, Weiqiang et al

in IEEE 24th Symposium on Computer Arithmetic - ARITH24 (2017, August 01)

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See detailMultiprofessional collaboration in Finnish schools
Vainikainen, M.-P; Thuneberg, H.; Greiff, Samuel UL et al

in International Journal of Educational Research (2015), 72

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See detailMultirésidences et travail frontalier au Luxembourg et dans la Grande Région Saar-Lor-Lux
Pigeron-Piroth, Isabelle UL

in Hamman, Philippe; Blanc, Maurice; Duchêne-Lacroix, Cédric (Eds.) et al Questionner les mobilités résidentielles à l'aune de la multilocalité (2014)

Définis par un lieu de résidence et un lieu de travail situés dans deux Etats différents « où ils retournent en principe chaque jour ou au moins une fois par semaine » (Règlement CE 883/2004), les ... [more ▼]

Définis par un lieu de résidence et un lieu de travail situés dans deux Etats différents « où ils retournent en principe chaque jour ou au moins une fois par semaine » (Règlement CE 883/2004), les travailleurs frontaliers sont concernés par diverses formes de mobilités domicile-travail ou même résidentielles. Or la définition de la résidence n’est pas toujours évidente et unique, les personnes multirésidentes, c’est-à-dire ayant simultanément plusieurs lieux de résidence ne sont plus marginales. Encore peu étudiée jusqu’alors, la multirésidence des travailleurs frontaliers est riche d’enseignements quant aux rapports qu’ils entretiennent avec l’espace, et plus précisément avec le Luxembourg et les frontières. Nous tenterons par cette communication qui se veut plutôt méthodologique, d’apporter des éléments de compréhension des pratiques de mobilité des travailleurs frontaliers selon leurs profils socio-économiques par exemple. [less ▲]

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See detailMultiscale computational mechanics: industrial applications
Bordas, Stéphane UL; Kerfriden, Pierre; Beex, Lars UL et al

Presentation (2014, November 25)

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See detailA Multiscale DEM-VOF Method for the simulation of three-phase flows
Pozzetti, Gabriele UL; Peters, Bernhard UL

in International Journal of Multiphase Flow (2018), 99

A novel multiscale approach for three-phase flows is presented. The goal of the proposed method is to solve arbitrary three-phase flow configurations in a computationally efficient way, and in particular ... [more ▼]

A novel multiscale approach for three-phase flows is presented. The goal of the proposed method is to solve arbitrary three-phase flow configurations in a computationally efficient way, and in particular taking into account the effects of different length scales while sharply reducing the computational burden. This is particularly important in chemical, environmental, and process engineering, where large-scale quantities are normally of interest, but small-scale dynamics cannot be neglected. The method is based on the definition of two different length scales: the bulk scale, and the fluid fine scale. A dual-grid approach is adopted in order to resolve the bulk scale with information from the fluid fine scale. It is shown that the described method succeeds in delivering more accuracy than a standard approach based on the volume averaging technique, still, it remains suitable for the solution of real interest problems. The method is shown to successfully satisfy experimental results presented in the literature. Examples of three-phase flows simulations are provided to show how the proposed numerical approach can describe the physics of particle-laden, free surface flows with competitive computational cost. It is shown how the proposed method can naturally extend the DEM-VOF method to the presence of complex interface dynamics. [less ▲]

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See detailMultiscale fracture across scales and time
Bordas, Stéphane UL; Kerfriden, Pierre

Scientific Conference (2014, November 11)

Multi-scale Computational Mechanics in Aerospace Engineering Flying is today one of the safest ways to spend our time. In the United Kingdom, for example, it is 33,000 times more likely to die from a ... [more ▼]

Multi-scale Computational Mechanics in Aerospace Engineering Flying is today one of the safest ways to spend our time. In the United Kingdom, for example, it is 33,000 times more likely to die from a clinical error than from an air crash. This is probably the consequence of over a century of experience building, starting with the Wright brothers at the beginning of the 20th century to the most recent aerospace developments culminating in technological giants such as the Airbus A380 and the Boeing Dreamliner, through the enlightening catastrophic events of the "Comet Aircraft”, ``Liberty Ships'' and many others. Yet, with the increasing urge to increase flight efficiency, decrease costs and Carbon emissions, airlines have been pushed to drive down the weight of aircraft, whilst guaranteeing their safety. This push for lighter aircraft has progressively seen a reduction in the use of metallic components which have been slowly replaced by composite materials. Such composite materials are made up of two or more phases of which they exploit the mechanical complementarity. For some applications, such as thermal barrier coatings, thermal complementarity is also leveraged. Yet, these novel materials, and especially their failure mechanisms and durability have proven difficult to understand, both through physical and virtual, in silico, experiments. One of the reasons for this is the large ratio between the size of the smallest constituent relevant in the description of failure mechanisms (e.g. 5-10 micron diameter carbon fibres) and the size of the structure (79m wingspan A380). In this presentation, we will briefly review advances in modeling and simulation of failure across the scales. We will discuss non exhaustively some of the recent advances in this field, ranging from adaptive atomistic modeling of fracture to algebraic model reduction methods for severely non-linear problems, including homogenization. We will also discuss the relevance of such simulations in daily engineering practice and claim that devising interactive simula- tors able to let engineers interact with the composite structure of interest and thus develop intuition about these advanced and complex materials. We will conclude by making a parallel between the difficulties encountered in modeling complex aerospace components and those met in personalized medicine, by discussing briefly the concept of Digital Twin. [less ▲]

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See detailMultiscale fracture: a natural connection between reduced order models and homogenisation
Bordas, Stéphane UL; Beex, Lars UL; Chen, Li UL et al

Scientific Conference (2019, May 13)

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See detailMultiscale hedge ratio between the spot and future prices of carbon: Wavelet Based Approach
Nsouadi, Ange; Terraza, Virginie UL

E-print/Working paper (2016)

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See detailMultiscale hydrogeological and hydrogeophysical approach to monitor vadose zone hydrodynamics of a karst system
Watlet, Arnaud; Poulain, Amaël; Francis, Olivier UL et al

Poster (2016)

The vadose zone of karst systems plays an important role on the water dynamics. In particular, temporary perched aquifers can appear in the subsurface due to changes of weather conditions, reduced ... [more ▼]

The vadose zone of karst systems plays an important role on the water dynamics. In particular, temporary perched aquifers can appear in the subsurface due to changes of weather conditions, reduced evapotranspiration and the vertical gradients of porosity and permeability. Although many difficulties are usually encountered when studying karst environments due to their heterogeneities, cave systems offer an outstanding opportunity to investigate vadose zone from the inside. We present a multi-scale study covering two years of hydrogeological and geophysical monitoring of the Lomme Karst System (LKS) located in the Variscan fold-and-thrust belt (Belgium), a region (∼3000 ha) that shows many karstic networks within Devonian limestone units. Hydrogeological data cover the whole LKS and involve e.g. flows and levels monitoring or tracer tests performed in both vadose and saturated zones. Such data bring valuable information on the hydrological context of the studied area at the catchment scale. Combining those results with geophysical measurements allows validating and imaging them at a smaller scale, with more integrative techniques. Hydrogeophysical measurements are focused on only one cave system of the LKS, at the Rochefort site (∼40 ha), taking benefit of the Rochefort Cave Laboratory (RCL) infrastructures. In this study, a microgravimetric monitoring and an Electrical Resistivity Tomography (ERT) monitoring are involved. The microgravimetric monitoring consists in a superconducting gravimeter continuously measuring gravity changes at the surface of the RCL and an additional relative gravimeter installed in the underlying cave located 35 meters below the surface. While gravimeters are sensible to changes that occur in both the vadose zone and the saturated zone of the whole cave system, combining their recorded signals allows enhancing vadose zone’s gravity changes. Finally, the surface ERT monitoring provide valuable information at the (sub)-meter scale on the hydrological processes that occur in the vadose zone. Seasonal water variations and preferential flow path are observed. This helps separating the hydrological signature of the vadose zone from that of the saturated zone. [less ▲]

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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 detailMultiscale model of dynamic neuromodulation integrating neuropeptide-induced signaling pathway activity with membrane electrophysiology.
Makadia, Hirenkumar K.; Anderson, Warren D.; Fey, Dirk et al

in Biophysical journal (2015), 108(1), 211-23

We developed a multiscale model to bridge neuropeptide receptor-activated signaling pathway activity with membrane electrophysiology. Typically, the neuromodulation of biochemical signaling and biophysics ... [more ▼]

We developed a multiscale model to bridge neuropeptide receptor-activated signaling pathway activity with membrane electrophysiology. Typically, the neuromodulation of biochemical signaling and biophysics have been investigated separately in modeling studies. We studied the effects of Angiotensin II (AngII) on neuronal excitability changes mediated by signaling dynamics and downstream phosphorylation of ion channels. Experiments have shown that AngII binding to the AngII receptor type-1 elicits baseline-dependent regulation of cytosolic Ca(2+) signaling. Our model simulations revealed a baseline Ca(2+)-dependent response to AngII receptor type-1 activation by AngII. Consistent with experimental observations, AngII evoked a rise in Ca(2+) when starting at a low baseline Ca(2+) level, and a decrease in Ca(2+) when starting at a higher baseline. Our analysis predicted that the kinetics of Ca(2+) transport into the endoplasmic reticulum play a critical role in shaping the Ca(2+) response. The Ca(2+) baseline also influenced the AngII-induced excitability changes such that lower Ca(2+) levels were associated with a larger firing rate increase. We examined the relative contributions of signaling kinases protein kinase C and Ca(2+)/Calmodulin-dependent protein kinase II to AngII-mediated excitability changes by simulating activity blockade individually and in combination. We found that protein kinase C selectively controlled firing rate adaptation whereas Ca(2+)/Calmodulin-dependent protein kinase II induced a delayed effect on the firing rate increase. We tested whether signaling kinetics were necessary for the dynamic effects of AngII on excitability by simulating three scenarios of AngII-mediated KDR channel phosphorylation: (1), an increased steady state; (2), a step-change increase; and (3), dynamic modulation. Our results revealed that the kinetics emerging from neuromodulatory activation of the signaling network were required to account for the dynamical changes in excitability. In summary, our integrated multiscale model provides, to our knowledge, a new approach for quantitative investigation of neuromodulatory effects on signaling and electrophysiology. [less ▲]

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See detailMultiscale model of sintering: diffusion and plastic flow
Kabore, Brice Wendlassida UL; Peters, Bernhard UL

Scientific Conference (2017, September 27)

Impacting particles or static aggregated particles at high temperature may undergo a permanent change of shape modifying the microstructure. Two particles in contact can develop some bonds within sub ... [more ▼]

Impacting particles or static aggregated particles at high temperature may undergo a permanent change of shape modifying the microstructure. Two particles in contact can develop some bonds within sub-second time. This fast sintering force in the particular case of the snow contribute to the rheological behavior and grain rearrangement [1]. Understanding the kinetics of sintering in granular material is of great importance in some engineering applications. For decades, diffusional processes have received more attention in investigations related to the mechanisms behind sintering [2]. Some works have suggested that the plastic flow might be neglected in sintering process for stresses are not high enough to cause dislocation. However, some studies have showed that stresses experienced in fine particles necks can be high enough and even lead to plasticity driven sintering. The importance of each mechanism in the sintering process may lie in the temporal and spatial scale of interest. Increasing importance is being accorded to the role of plastic flow in sintering. however, several investigations have proved that the conventional plasticity theory may fail to predict plastic activity at micro-scale, The objective of this work is to develop adequate computational model that includes instantaneous and time-dependent plastic flow at micro-scale. We aim at extending existing models of sintering and plasticity to cope with multiple spatial and temporal scales simulations using Extended Discrete Element Method. The numerical results are compare to experimental data on snow. [less ▲]

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See detailMultiscale Modeling of Discrete Mesomodels for Dry-Woven Fabrics
Magliulo, Marco UL; Beex, Lars UL; Zilian, Andreas UL

Scientific Conference (2018, March)

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See detailMultiscale modeling of metabolism and macromolecular synthesis in E. coli and its application to the evolution of codon usage.
Thiele, Ines UL; Fleming, Ronan MT UL; Que, Richard et al

in PLoS ONE (2012), 7(9), 45635

Biological systems are inherently hierarchal and multiscale in time and space. A major challenge of systems biology is to describe biological systems as a computational model, which can be used to derive ... [more ▼]

Biological systems are inherently hierarchal and multiscale in time and space. A major challenge of systems biology is to describe biological systems as a computational model, which can be used to derive novel hypothesis and drive experiments leading to new knowledge. The constraint-based reconstruction and analysis approach has been successfully applied to metabolism and to the macromolecular synthesis machinery assembly. Here, we present the first integrated stoichiometric multiscale model of metabolism and macromolecular synthesis for Escherichia coli K12 MG1655, which describes the sequence-specific synthesis and function of almost 2000 gene products at molecular detail. We added linear constraints, which couple enzyme synthesis and catalysis reactions. Comparison with experimental data showed improvement of growth phenotype prediction with the multiscale model over E. coli's metabolic model alone. Many of the genes covered by this integrated model are well conserved across enterobacters and other, less related bacteria. We addressed the question of whether the bias in synonymous codon usage could affect the growth phenotype and environmental niches that an organism can occupy. We created two classes of in silico strains, one with more biased codon usage and one with more equilibrated codon usage than the wildtype. The reduced growth phenotype in biased strains was caused by tRNA supply shortage, indicating that expansion of tRNA gene content or tRNA codon recognition allow E. coli to respond to changes in codon usage bias. Our analysis suggests that in order to maximize growth and to adapt to new environmental niches, codon usage and tRNA content must co-evolve. These results provide further evidence for the mutation-selection-drift balance theory of codon usage bias. This integrated multiscale reconstruction successfully demonstrates that the constraint-based modeling approach is well suited to whole-cell modeling endeavors. [less ▲]

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See detailMultiscale modeling of mitochondria
Garcia, Guadalupe Clara UL

Doctoral thesis (2019)

Life is based on energy conversion by which cells and organisms can adapt to the environment. The involved biological processes are intrinsically multiscale phenomena since they are based on molecular ... [more ▼]

Life is based on energy conversion by which cells and organisms can adapt to the environment. The involved biological processes are intrinsically multiscale phenomena since they are based on molecular interactions on a small scale leading to the emerging behavior of cells, organs and organisms. To understand the underlying regulation and to dissect the mechanisms that control system behavior, appropriate mathematical multiscale models are needed. Such models do not only offer the opportunity to test different hypothesized mechanisms but can also address current experimental technology gaps by zooming in and out of the dynamics, changing scales, coarse-graining the dynamics and giving us distinct views of the phenomena. In this dissertation substantial efforts were done to combine different computational modeling strategies based on different assumptions and implications to model an essential system of eukaryotic life -- the energy providing mitochondria -- where the spatiotemporal domain is suspected to have a substantial influence on its function. Mitochondria are highly dynamic organelles that fuse, divide, and are transported along the cytoskeleton to ensure cellular energy homeostasis. These processes cover different scales, in space and time, where on the more global scale mitochondria exhibit changes in their molecular content in response to their physiological context including circadian modulation. On the smaller scales, mitochondria show also faster adaptation by changing their morphology within minutes. For both processes, the relation between the underlying structure of either their regulating network or the spatial morphology and the functional consequences are essential to understand principles of energy homeostasis and their link to health and disease conditions. This thesis focuses on different scales of mitochondrial adaptation. On the small scales, fission and fusion of mitochondria are rather well established but substantial evidence indicates that the internal structure is also highly variable in dependence on metabolic condition. However, a quantitative mechanistic understanding how mitochondrial morphology affects energetic states is still elusive. In the first part of this dissertation I address this question by developing an agent-based dynamic model based on three-dimensional morphologies from electron microscopy tomography, which considers the molecular dynamics of the main ATP production components. This multiscale approach allows for investigating the emergent behavior of the energy generating mechanism in dependence on spatial properties and molecular orchestration. Interestingly, comparing spatiotemporal simulations with a corresponding space-independent approach, I found only minor space dependence in equilibrium conditions but qualitative difference in fluctuating environments and in particular indicate that the morphology provides a mechanism to buffer energy at synapses. On the more global scale of the regulation of mitochondrial protein composition, I applied a data driven approach to explore how mitochondrial activity is changing during the day and how food intake restrictions can effect the structure of the underlying adaptation process. To address the question if at different times of the day, the mitochondrial composition might adapt and have potential implications for function, I analyzed temporal patterns of hepatic transcripts of mice that had either unlimited access to food or were hold under temporal food restrictions. My analysis showed that mitochondrial activity exhibits a temporal activity modulation where different subgroups of elements are active at different time points and that food restriction increases temporal regulation. Overall, this thesis provides new insights into mitochondrial biology at different scales by providing an innovative computational modeling framework to investigate the relation between morphology and energy production as well as by characterizing temporal modulation of the regulatory network structure under different conditions. [less ▲]

Detailed reference viewed: 116 (12 UL)