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See detailModelling Crystallization
Schilling, Tanja UL

Presentation (2011)

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See detailModelling defeasible and prioritized support in bipolar argumentation
Villata, Serena; Boella, Guido; Gabbay, Dov M. UL et al

in Annals of Mathematics & Artificial Intelligence (2012), 66(1-4), 163-197

Cayrol and Lagasquie-Schiex introduce bipolar argumentation frameworks by introducing a second relation on the arguments for representing the support among them. The main drawback of their approach is ... [more ▼]

Cayrol and Lagasquie-Schiex introduce bipolar argumentation frameworks by introducing a second relation on the arguments for representing the support among them. The main drawback of their approach is that they cannot encode defeasible support, for instance they cannot model an attack towards a support relation. In this paper, we introduce a way to model defeasible support in bipolar argumentation frameworks. We use the methodology of meta-argumentation in which Dung’s theory is used to reason about itself. Dung’s well-known admissibility semantics can be used on this meta-argumentation framework to compute the acceptable arguments, and all properties of Dung’s classical theory are preserved. Moreover, we show how different contexts can lead to the alternative strengthening of the support relation over the attack relation, and converse. Finally, we present two applications of our methodology for modeling support, the case of arguments provided with an internal structure and the case of abstract dialectical frameworks. [less ▲]

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See detailModelling Dependable Collaborative Time-constrained Business Process
Capozucca, Alfredo UL; Guelfi, Nicolas UL

in Enterprise Information Systems (2010), 4(2), 153-214

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See detailModelling dynamic urban structures and air pollution exposure
Schindler, Mirjam UL

Scientific Conference (2013, September)

Despite vast technological improvements and various political control strategies, air pollution is a major concern in urban areas worldwide. Hereby, traffic is acknowledged to be the major source. Several ... [more ▼]

Despite vast technological improvements and various political control strategies, air pollution is a major concern in urban areas worldwide. Hereby, traffic is acknowledged to be the major source. Several studies provide evidence for the influence of travel behaviour and other characteristics on air pollution (e.g. Briggs et al., 2008) and research is increasingly expanding this link by investigating which role urban form plays in the discussion about sustainable cities (Jabareen, 2006). In order to meet sustainable growth, many argue that a compact city is the desirable urban form due to shorter travelling distances and reduced conversion of land, just in contrast to the trend towards urban sprawl (e.g. Stone et al., 2007). However, if energy consumption (Newman & Kenworthy, 2000) and total emissions (Cervero, 2000) can be shown to be reduced with more compact urban forms via reduced car use at regional scale, compactness is still debated (Gordon & Richardson, 1997). Residents often respond to externalities such as pollution primarily through spatial behaviour (location and relocation choices) which may have important impacts on the emerging form of cities. As these forms may not be socially optimal and are currently widely debated, there is a need for further research on welfare-enhancing policies. The question I ask is: if preferences such as exposure to car-related air pollution and the valuation of green space are considered by residents in their choice of residential location, which role do they play in shaping our cities and in overcoming the environmental and social challenge? In order to investigate this, I compare two approaches: first, a simulation approach by developing a system comprising five spatio-dynamic models; second, a micro-economic urban growth modelling approach considering residential preferences. Opposing the simulation to a further simplified model emanating from micro-economic principles provokes the discussion on complexity versus simplicity in urban modelling. The simulation method allows to a) model the growth of an urban area (Caruso et al. (2010), b) model the traffic flow which would be generated by residents commuting on the resulting road network, c) estimate the emissions generated, d) model how these emissions are dispersed by wind and finally e) estimate the average exposure residents are faced with at each residential location. In contrast, the micro-economic approach models residential location in a peri-urban area in mono-centric one-dimensional space. Inspired by works from e.g. Fujita (1989), Arnott et al. (2008), Gubins & Verhoef (2012) and Franceschetti et al. (2013) I aim at complementing existing urban equilibrium models by linking air pollution exposure and traffic congestion externalities with spatiality and residential valuations. Through contrasting the two approaches I take on the discussion of complexity in urban environmental modelling and investigate how policy interactions impact on intra-urban forms and the well-being of residents. [less ▲]

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See detailModelling earnings dynamics and inequality: foreign workers and inequality trends in Luxembourg, 1988--2009
Sologon, Denisa M.; Van Kerm, Philippe UL

in Journal of the Royal Statistical Society. Series A Statistics in Society (2018), 181(2), 409-440

The paper exploits large-scale administrative data to analyse trends in male earnings inequality in Luxembourg during 20 years of rapid economic growth, industrial redevelopment and massive inflow of ... [more ▼]

The paper exploits large-scale administrative data to analyse trends in male earnings inequality in Luxembourg during 20 years of rapid economic growth, industrial redevelopment and massive inflow of foreign workers. A detailed error components model is estimated to identify persistent and transitory components of (the trends of) log-earnings variance and to disentangle the contributions to it of native, immigrant and cross-border workers. The model is flexible and allows for a high degree of individual, age, time and cohort heterogeneity. We observe a surprising stability in overall earnings inequality as a result of more complex underlying changes, with marked increases in persistent inequality (except among natives), a growing contribution of foreigners and a decrease in earnings instability (primarily for natives). [less ▲]

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See detailModelling Experience Through Multiple Modes in Digital Art
Huemer, Birgit UL

in Jones, Carys; Ventola, Eija (Eds.) From Language to Multimodality. New Developments in the Study of Ideational Meaning (2008)

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See detailModelling Fanconi anemia pathogenesis and therapeutics using integration-free patient-derived iPSCs.
Liu, Guang-Hui; Suzuki, Keiichiro; Li, Mo et al

in Nature communications (2014), 5

Fanconi anaemia (FA) is a recessive disorder characterized by genomic instability, congenital abnormalities, cancer predisposition and bone marrow (BM) failure. However, the pathogenesis of FA is not ... [more ▼]

Fanconi anaemia (FA) is a recessive disorder characterized by genomic instability, congenital abnormalities, cancer predisposition and bone marrow (BM) failure. However, the pathogenesis of FA is not fully understood partly due to the limitations of current disease models. Here, we derive integration free-induced pluripotent stem cells (iPSCs) from an FA patient without genetic complementation and report in situ gene correction in FA-iPSCs as well as the generation of isogenic FANCA-deficient human embryonic stem cell (ESC) lines. FA cellular phenotypes are recapitulated in iPSCs/ESCs and their adult stem/progenitor cell derivatives. By using isogenic pathogenic mutation-free controls as well as cellular and genomic tools, our model serves to facilitate the discovery of novel disease features. We validate our model as a drug-screening platform by identifying several compounds that improve hematopoietic differentiation of FA-iPSCs. These compounds are also able to rescue the hematopoietic phenotype of FA patient BM cells. [less ▲]

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See detailModelling gender-specific regulation of tau in Alzheimer’s disease
Glaab, Enrico UL

Presentation (2016)

Public transcriptomic studies have shown that several genes display pronounced gender differences in their expression in the human brain, which may influence the manifestations and risk for neuronal ... [more ▼]

Public transcriptomic studies have shown that several genes display pronounced gender differences in their expression in the human brain, which may influence the manifestations and risk for neuronal disorders. Here, we apply a transcriptome-wide analysis to discover genes with gender-specific expression and significant alterations in public postmortem brain tissue from Alzheimer’s disease (AD) patients compared to controls. We identify the sex-linked ubiquitin-specific peptidase 9 (USP9) as an outstanding candidate gene with highly significant expression differences between the genders and male-specific underexpression in AD. Since previous studies have shown that USP9 can modulate the phosphorylation of the AD-associated protein MAPT, we investigate functional associations between USP9 and MAPT in further detail. After observing a high positive correlation between the expression of USP9 and MAPT in the public transcriptomics data, we show that USP9 knockdown results in significantly decreased MAPT expression in a DU145 cell culture model and a concentration-dependent decrease for the MAPT orthologs mapta and maptb in a zebrafish model. From the analysis of microarray and qRT-PCR experiments for the knockdown in DU145 cells and prior knowledge from the literature, we derive a data-congruent model for a USP9-dependent regulatory mechanism modulating MAPT expression via BACH1 and SMAD4. Overall, the analyses suggest USP9 may contribute to molecular gender differences observed in tauopathies and provide a new target for intervention strategies to modulate MAPT expression. [less ▲]

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See detailModelling Heterogeneous Reactions In Packed Beds and Its Application to The Upper Shaft of A Blast Furnace
Hoffmann, Florian UL

Doctoral thesis (2014)

Heterogeneous reactions in packed beds such as iron ore reduction or gasification of coke in a blast furnace involve various aspects of thermodynamics, fluid dynamics, chemistry and physics. Unfortunately ... [more ▼]

Heterogeneous reactions in packed beds such as iron ore reduction or gasification of coke in a blast furnace involve various aspects of thermodynamics, fluid dynamics, chemistry and physics. Unfortunately, inaccessible and hostile process environments make it very difficult to gain insights into such reactors and to operate the industrial processes. To address this problem extensive research has been undertaken in the past to develop numerical methods and models. However, little effort has been made to describe the complex thermochemical processes inside such reactors starting from the particle and especially intra-particle scale. The objectives of this thesis are to introduce a coupled approach which allows for the physical and chemical interaction of a granular material with a surrounding gas phase and to apply it to the reduction processes in the upper shaft of a blast furnace. Furthermore, a suitable model to investigate the gas-solid thermochemical interaction within a single particle and within a packed bed of particles was to be established. Thus, the classical discrete element method (DEM) was extended by thermodynamic state variables such as temperature, composition and chemical reactions. In addition, a coupling between the particulate phase and a continuous gas phase for convective heat and mass transfer was implemented. It should be noted that the application of the presented methodology is not only restricted to the blast furnace, but rather represents a rigorous approach that can be applied to other packed bed reactors as well. A validation study on the particle scale using experimental results shows that the dis- crete particle model accurately predicts the progress of indirect reduction of a pellet. The particle model is shown to be capable of resolving radial gradients on the particle scale avoiding rigorous assumptions or mathematical fits to a specific experimental setup. These qualities of the model permit its usage in the presented analysis of indirect reduc- tion within the shaft of a blast furnace where each particle is subjected to time-varying boundary conditions. On the packed bed scale heat and mass transfer from the discrete to the continuous phase was validated using experimental data. Moreover, the model showed accurate results when compared to experimental reduction data from a lab scale bed of iron ore particles. Finally, the reduction processes in the upper shaft of a blast furnace were analysed: Firstly, isothermal reduction of a packed bed of pellets according to ISO standards were analysed in terms of heterogeneity in temperature and reduction degree inside the cylindrical reactor. Results indicate that radial gradients inside the packed bed are caused by the higher mass flow rate close to the reactor wall. Axial gradients develop due reduction reactions and the direction of the fluid flow. The formation of these axial gradients is found to be inherent to the process of indirect reduction of iron oxides due to the sequence of exothermic and endothermic reaction steps. Secondly, a complex packed bed with a layered structure of coke and iron ore particles is analysed under time-varying reducing gas conditions simulating the journey of a packed bed column through the upper shaft of a blast furnace. Results highlight that the gas and the solid phase are highly coupled in space and time during the process of indirect reduction. Axial gradients in temperature and composition form due to the heat and mass transfer between the packed bed and the streaming gas. Energy released or consumed by the indirect reduction provides an opposing trend to the gradients formed from the hot gas stream, thus reducing axial gradients within the bed and the gas phase. The results indicate the mechanisms involved during the formation of the thermal reserve zones inside the blast furnace shaft due to the complex interaction of convective heat and mass transfer in conjunction with energy consumption and release by the reactions. Considering the findings presented, this thesis is understood to contribute to the better understanding of heterogeneous reactions in packed beds and as a particular example of such the upper part of the blast furnace. [less ▲]

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See detailModelling hydraulic fractures in porous media using flow cohesive interface elements
Nguyen, Vinh Phu; Lian, Haojie; Rabczuk, Timon et al

in Engineering Geology (2017), 225

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See detailModelling implicit dynamic introduction of function symbols in mathematical texts
Cramer, Marcos UL

in de Paiva, Valeria; et al. (Eds.) Joint Proceedings of the Second Workshop on Natural Language and Computer Science (NLCS’14) & 1st International Workshop on Natural Language Services for Reasoners (NLSR 2014) Affliated to RTA-TLCA, VSL 2014 July 17-18, 2014 Vienna, Austria. (2014)

The specialized language of mathematics has a number of linguistically and logically interesting features. One of them, which to our knowledge has not been systematically studied before, is the implicit ... [more ▼]

The specialized language of mathematics has a number of linguistically and logically interesting features. One of them, which to our knowledge has not been systematically studied before, is the implicit dynamic introduction of function symbols, exemplified by constructs of the form "for every x there is an f(x) such that ...". We present an extension of Groenendijk and Stokhof's Dynamic Predicate Logic – Typed Higher-Order Dynamic Predicate Logic – which formally models this feature of the language of mathematics. Furthermore, we illustrate how the implicit dynamic introduction of function symbols is treated in the proof checking algorithm of the Naproche system. [less ▲]

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See detailModelling interfacial cracking with non-matching cohesive interface elements
Nguyen, Viet Ha UL; Nguyen, Chi Thanh; Bordas, Stéphane UL et al

in Computational Mechanics (2016), 58(5), 731-746

Interfacial cracking occurs in many engineering problems such as delamination in composite laminates, matrix/interface debonding in fibre reinforced composites etc. Computational modelling of these ... [more ▼]

Interfacial cracking occurs in many engineering problems such as delamination in composite laminates, matrix/interface debonding in fibre reinforced composites etc. Computational modelling of these interfacial cracks usually employs compatible or matching cohesive interface elements. In this paper, incompatible or non-matching cohesive interface elements are proposed for interfacial fracture mechanics problems. They allow non-matching finite element discretisations of the opposite crack faces thus lifting the constraint on the compatible discretisation of the domains sharing the interface. The formulation is based on a discontinuous Galerkin method and works with both initially elastic and rigid cohesive laws. The proposed formulation has the following advantages compared to classical interface elements: (i) non-matching discretisations of the domains and (ii) no high dummy stiffness. Two and three dimensional quasi-static fracture simulations are conducted to demonstrate the method. Our method not only simplifies the meshing process but also it requires less computational demands, compared with standard interface elements, for problems that involve materials/solids having a large mismatch in stiffnesses. [less ▲]

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See detailModelling Metabolic Interactions in the Legume-Rhizobia Symbiosis
Pfau, Thomas UL

Doctoral thesis (2013)

With the emergence of “omics” techniques, it has become essential to develop tools to utilise the vast amount of data produced by these methods. Genome-scale metabolic models represent the mathematical ... [more ▼]

With the emergence of “omics” techniques, it has become essential to develop tools to utilise the vast amount of data produced by these methods. Genome-scale metabolic models represent the mathematical essence of metabolism and can easily be linked to the data from omics sources. Such models can be used for various analyses, including the investigation of metabolic responses to changing environmental conditions. Legumes are known for their ability to form a nitrogen-fixing symbiosis with rhizobia, a vital process that provides the biosphere with the majority of its nitrogen content. In the present thesis, a genome-scale metabolic model for the legume Medicago truncatula was reconstructed, based on the annotated genome sequence and the MedicCyc database. A novel approach was employed to define the compartmentalisation of the plant’s metabolism. The model was used to calculate the biosynthetic costs of biomass precursors (e.g. amino acids, sugars, fatty acids, nucleotides), and its capability to produce biomass in experimentally observed ratios was demonstrated using flux balance analysis. Further investigation was carried out into how the biosynthesis fluxes and costs change with respect to different nitrogen sources. The precise charge balancing of all reactions in the model allowed the investigation of the effects of charge transport over the cellular membrane. The simulations showed a good agreement with experimental data in using different sources of nitrogen (ammonium and nitrate) to minimise the charge transport of the membrane. To allow the investigation of the symbiotic relationship, two rhizobial models were used. The first model, for Sinorhizobium meliloti, was reconstructed from the MetaCyc database (MC-model); the second model was a recently published model for S. meliloti specialised for symbiotic nitrogen fixation (SNF-model). Combined models were created for both rhizobial networks using a specialised nodule submodel of the plant model. Potential interactions were extracted from the literature and investigated, with the analysis suggesting that oxygen availability is the main limitation factor in symbiotic nitrogen fixation. Within the analysis the SNF-model appeared to be too restricted and lacking the potential for sufficient nitrogen fixation; therefore, further analysis was carried out using the MC-model, upon which it was observed that the availability of oxygen can also influence how nitrogen is supplied to the plant. At high oxygen concentrations ammonia is the primary form of nitrogen supplied by the rhizobium. However, the simulations, in accordance with experimental data, show that at lower concentrations of oxygen, alanine takes precedence. The findings also support the concept of amino acid cycling as a potential way to improve nitrogen fixation. The more flexible MetaCyc based model has allowed other potential genetic engineering approaches for higher nitrogen fixation yields to be proposed. [less ▲]

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See detailModelling Metrics for Transparency in Medical Systems
Pierina Brustolin Spagnuelo, Dayana UL; Bartolini, Cesare UL; Lenzini, Gabriele UL

in Proceedings of TrustBus 2017 (2017, July)

Detailed reference viewed: 148 (19 UL)
See detailModelling of crack growth behaviour in composite materials using the extended finite element method (XFEM)
Cahill, L.; Natarajan, S.; McCarthy, C. et al

Scientific Conference (2010)

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See detailModelling of early-age complex crack propagation in cement-based materials using phase field method
Nguyen, Thanh Tung UL; Waldmann, Danièle UL

in 6th European Conference on Computational Mechanics (2018)

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See detailModelling of Fluid-Structure Interaction – Effects of Added Mass, Damping and Stiffness
Zilian, Andreas UL

in Irschik, Hans; Belyaev, Alexander K. (Eds.) Dynamics of Mechanical Systems with Variable Mass (2014)

Fluid-flow around mechanical structures can sometimes lead to catastrophic failures. Improved modelling of fluid/structure interaction is required for safety and mechanical considerations. In this ... [more ▼]

Fluid-flow around mechanical structures can sometimes lead to catastrophic failures. Improved modelling of fluid/structure interaction is required for safety and mechanical considerations. In this contribution, concepts for modelling the interaction of structures and fluids are presented. Starting from excitation mechanisms and associated classifications, various model depth approaches are compared. Among them, the use of added coefficients for quasi-steady problems is discussed. On the basis of potential flow theory, different approaches for determining fluid-induced additional mass are established and illustrated using an analytical example. Given the limitations of simplifying the engineering models, the second part of the paper provides a brief overview on computational methods for fluid-structure interaction and presents a monolithic modelling approach using space-time finite elements for discretisation of both fluid and structure. Applications from aero- and hydro-elasticity show the applicability of computational methods for problems involving flow-induced added mass, damping, and stiffness. [less ▲]

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See detailModelling of frictional soil damping in finite element analysis
Van Baars, Stefan UL

in The Second International Symposium on Computational Geomechanic (2011, April)

In soil dynamics, the soil is often described as a viscous material. In a viscous material however, the dissipated energy is assumed to be proportional to the wave frequency, which is absolutely not ... [more ▼]

In soil dynamics, the soil is often described as a viscous material. In a viscous material however, the dissipated energy is assumed to be proportional to the wave frequency, which is absolutely not applicable to soils. It is therefore better to use a concept of damping based on dry particle friction. A non-viscous model based on this concept results in a damping ratio that becomes constant for small deformations for both sand and clay, and is also independent of frequency or shear strain amplitude. This behaviour corresponds with laboratory measurements and requires only one damping parameter which can be obtained from laboratory tests. This model is implemented in Plaxis as a User-Defined Soil Model to analyse the problem of a strip footing subjected to a dynamic load. The initial results are rather remarkable. . For example, a Power Spectral Density plot of the velocities shows that not all frequencies seem to be damped equally and at some distance the input frequency is not even present. [less ▲]

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See detailModelling of inter- and transgranular stress corrosion crack propagation in polycrystalline material by using phase field method
Nguyen, Thanh Tung UL; Réthoré, J.; Bolivar, J. et al

in Journal of the Mechanical Behavior of Materials (2018), 26

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See detailModelling of interfacial crack propagation in strongly heterogeneous materials by using phase field method
Nguyen, Thanh-Tung; Yvonnet, Julien; Waldmann, Danièle UL et al

in Proceedings of the 8th GACM Colloquium on Computational Mechanics for Young Scientists from Academia and Industry (2019, August 28)

Phase field model has been proved to be a useful tool to study the fracture behaviors in heterogeneous materials. This method is able to model complex, multiple crack fronts, and branching in both 2D/3D ... [more ▼]

Phase field model has been proved to be a useful tool to study the fracture behaviors in heterogeneous materials. This method is able to model complex, multiple crack fronts, and branching in both 2D/3D without ad-hoc numerical treatments. In this study, a new interfacial cracking model in the phase field framework is proposed. The effects of both stiff and soft interphases on the fracture response of composite materials are considered. A dimensional-reduced model based on a rigorous asymptotic analysis is adapted to derive the null thickness imperfect interface models from an original configuration containing thin interphase. The idea of mixing the bulk and interfacial energy within the phase field framework is then used to describe the material degradation both on the interface and in bulk. Moreover, in order to ensure the physical crack propagation patterns, a unilateral contact condition is also proposed for the case of spring imperfect interface. The complex cracking phenomena on interfaces such as initiation, delamination, coalescence, deflection, as well as the competition between the interface and bulk cracking are successfully predicted by the present method. Concerning the numerical aspect, the one-pass staggered algorithm is adapted, providing an extremely robust approach to study interfacial cracking phenomena in a broad class of heterogeneous materials. [less ▲]

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