Show filters Hide filters

Refine your search

Publication Year
Publisher
1-36 out of 42 results
Change view
  • Sort by:
47:23 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

"Extreme Fluids" - Some Examples, Challenges and Simulation Techniques for Flow Problems with Complex Rheology

In this talk we discuss numerical simulation techniques for incompressible fluids with complex rheology which means that local flow characteristics may differ significantly by several orders of magnitude, for instance due to non-isothermal behavior and pressure, resp., shear dependent viscosity. Such fluids usually include viscoplastic as well as viscoelastic effects which is typical for yield-stress fluids, granular material as well as polymer melts and kautschuk. Corresponding applications are relevant for polymer processing, but include also viscoplastic lubrication, fracking and macro encapsulation. In this talk, we present special discretization and solver techniques in which case the coupling between the velocity, pressure and additional variables for the stresses, which leads to restrictions for the choice of the FEM approximation spaces, and the (often) hyperbolic nature of the problem are handled with special Finite Element techniques including stabilization methods. The resulting linearized systems inside of outer Newton-like solvers are (special) nonsymmetric saddle point problems which are solved via geometrical multigrid approaches. We illustrate and analyze numerically the presented methodology for well-known benchmark configurations as well as protoypical industrial applications for several nonlinear flow models.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
52:42 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2017

Machine learning and applications

Since a few years Machine Learning (ML) has broadened the modeling toolbox for the sciences and industry. The talk will first remind the audience of the main ingredients for applying machine learning. Then various ML applications in the sciences namely Brain Computer Interfaces and Quantum Chemistry will be discussed.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
25:03 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

Mathematical knowledge management as a route to sustainability in mathematical modeling and simulation

Mathematical modeling and simulation (MMS) has now been established as an essential part of the scientific work in many disciplines. It is common to categorize the involved numerical data and to some extend the corresponding scientific software as research data. Both have their origin in mathematical models. A holistic approach to research data in MMS should cover all three aspects: models, software, and data. Yet it is unclear, whether a suitable management of the mathematical knowledge related to models is possible and how it would look like. In this talk, we outline an approach to address this problem based on a flexiformal representation of the mathematical knowledge in scientific publications and discuss how this can contribute to sustainable research in MMS.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
42:16 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2017

An introduction to inverse problems with applications in machine learning

The presentation starts with some motivating examples of Inverse Problems before introducing the general setting. We shortly review the most common regularization approaches (Tikhonov, iteration methods) and sketch some recent developments in sparsity and machine learning. Sparsity refers to additional expert information on the desired reconstruction, namely, that is has a finite expension in some predefined basis or frame. In machine learning we focus on 'multi colored' inverse problems, where part of the application can be formulated by a strict analytical framework but some part of the problem needs to modeled by a data driven approach. Those combined problems can be created by data- driven linear low rank approximations or more general black box models. In particular we review deep learning approaches to inverse problems. Finally, machine learning techniques by themselves are often inverse problems. We highlight basis learning techniques and applications to hyperspectral image analysis.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
25:36 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

MRI data models at low SNR

In this talk we elaborate the effect of low SNR on estimated parameters in models for neuroimaging data. We will present a new method for the local estimation of the noise parameter in the signal distribution and demonstrate how this can be used for improved estimation of model parameters. (joint work with Joerg Polzehl).
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
27:38 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

Lost in the Web?

To get information of mathematical software is sometimes like finding a needle in a haystack. But otherwise, more and more research results will be achieved by using mathematical software. Comprehensive and precise information about software used is also an important condition for the credibility of research results. But software has some unique features which pose new requirements to information infrastructure, especially the dynamic character of software, its encoding in formal languages, dependencies from hardware, other software, and further context information. The information on mathematical software is widely distributed on Web sites, repositories, portals, Web archives, etc., and is not standardized. The talk will address two relevant activities which can significantly improve the information about mathematical software: the initiatives for a citation standard for software, and the development of a comprehensive portal for mathematical software which integrates the existing information about software from the Web. A state of the art report on the swMATH service will illustrate the concepts and approaches.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
19:20 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

On new developments in the discretization theory for PDEs, possibly relevant for GFD & CFD

In this talk, an overview will be given on some new developments in the field of discretization theory for partial differential equations, which are possibly relevant for applications in CFD & GFD. Among them are: pressure-robust schemes for the incompressible Navier-Stokes equations, physically-consistent discretizations, discretizations on polyhedral meshes
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
30:32 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

Modeling decision tree training problems as a Mixed Integer Program (MIP) yields optimal decision trees

The problem of constructing an optimal binary decision tree is known to be NP-complete. Therefore most current implementations base on heuristics where local optimality criteria are used. Our approach optimizes decision trees globally by construction a suitable MIP. In recent years both very high computing power and very efficient branch-and-cut algorithms for solving MIPs make the running time more and more realistic for practical applications. We applied our method for the discrimination of tumor samples into distinct telomere maintenance mechanisms (TMM). Telomeres are at the end of the chromosomes and shorten after each replication serving as a crucial check point for protecting cells from unbound replication. Tumor cells circumvent this by either re-evoking the enzyme for elongation or redirecting DNA-repair mechanisms know as alternative TMM. Our approach allowed classifying the tumor samples with an accuracy of 0.95 when using the experimental gold standard (C-circle assays).
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
24:33 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

Make the most of your audio-visual simulation data

Visualisations of mathematical simulations play an important role in the communication of research results. However, in most cases simulation data is shown in publications either as snapshots or as supplemental videos. Either way, the full potential of visualized simulations is not exploited. This talk will show how the TIB AV-Portal supports researchers to uncover the hidden potential of visualisations such as simulations and animations and how this can help to increase the impact of their publications.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
14:53 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2017

Estimation of cardiovascular system parameter from real data

This talks shows preliminary results for the estimation of some parameters regarding the cardiovascular system (e.g., vessel mechanical properties, vasculature resistance) using real patient data. The mathematical model is based on efficient one-dimensional network for the blood flow simulation and on the unscented Kalman filtering for the parameter estimation.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
25:49 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

Syncretism Distribution Modeling

The morphological analysis of paradigms (morpheme tables) generally proposes a distinction between accidental homophony (to and two represent different concepts, but sound the same) and systematic homophony (you (vs German singular du and plural ihr ) corresponds to the concept `2nd Person'). No specific assumptions are usually made about the distribution of accidental homophony, though. Therefore current assumptions cannot proof satisfactorily what should be regarded as systematic in morphology. We propose that accidental homophony should be assumed to be a random event in the statistical sense with a constant probability across languages and across paradigms. This approach allows us to assign a likelihood to any actual typological distribution of syncretism given a morphological analysis. And by computing such likelihoods for a range of analyses, we can then apply maximum likelihood analysis to determine the best analyses. Hence, the statistical foundation allow us to empirically test morphological analyses that include accidental syncretism. In this paper, we primarily introduce the conceptual and mathematical foundations of a statistical modeling technique, Syncretism Distribution Modeling, and show how it overcomes the problem of accidental homophony. In addition, we apply the technique to show that person paradigms must involve both accidental homophony and systematic syncretism.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
44:53 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2017

Welcome/Opening MMS Days

  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
14:59 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

Consistent 3D turbulence parametrization in circulation models

We present an extension of the Dynamic Smagorinsky model (DSM) to parameterize the subgrid-scale momentum diffusion in global circulation models (GCM) In contrast to the standard approach, the test filter to determine the Smagorinsky parameter is separated from the resolution scale to exclude potential interactions. In addition, in GCMs the horizontal and vertical scales are usually treated differently due to gravity. While for the turbulent vertical diffusion of horizontal momentum a classical Smagorinsky approach is common, the respective horizontal diffusion in the free atmosphere is usually neglected. We show how to formulate the generalized DSM as subgrid-scale horizontal momentum diffusion to run stably a GCM without hyperdiffusion. Furthermore, the idea of stratified turbulence is applied to find a dynamic approach also for the vertical diffusion. Both improvements allow for a realistic spectrum of kinetic energy (almost) up to the resolution scale.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
13:52 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

An online coupled Lagrangian particle dispersion model for COSMO

Lagrangian particle dispersion models (LPDM) are a well-known method for modeling exhaust gas distributions and similar problems. Open accessible LPDM's, e.g., the FLEXPART model are designed for meso-scale simulations and work offline coupled with the coarse frequented output data of any numerical weather prediction model. But the central issue there is that high resolution simulations of small scale phenomena need a high frequency input of meteorological data fields to work accuracy, which can directly be provided by an online coupled model system. Based on the COSMO trajectory module the model LAPASI was developed that integrates an online coupled Lagrangian particle transport into the default COSMO version. It supports any kind of simulation that are possible with the COSMO including idealized cases and can handle a couple Million particles with individual start times, start locations and dry depositions velocities. Thus, LAPASI is a useful extension for COSMO and a necessary addition to the previously existing LPDM's.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
26:33 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

Long-Term Accessibility of Software through Web Archives

Software is widely used and referenced in research and scientific publications. Hence, just like the results published in an article, associated software should be preserved and made long-term accessibly as well. Due to the nature of software and its dynamic aspects, this is rather challenging though. Very commonly, only related materials, such as a software's documentation, parts of its source code or change logs, are freely available. However, these can be very valuable to comprehend or reproduce experiments described in literature. We found that a big portion of this data is provided on the Web. Around 60% of the software webpages we analyzed link to documentation, while another 50% even contain some artifacts of the actual software [1, 2]. Web Archives are a way to preserve this information and allow for long-term accessibility, even if the software and corresponding information change. Although many of those websites are already archived, our study shows that the evolution of a software is not always well captured. Therefore, we are working towards a pro-active approach to archive software on the Web in the future as part of the scientific process. [1] Holzmann, H., Runnwerth, M., Sperber, W.: Linking Mathematical Software in Web Archives. 5th International Congress on Mathematical Software, ICMS 2016. Berlin, Germany (2016). [2] Holzmann, H., Sperber, W., Runnwerth, M.:?Archiving Software Surrogates on the Web for Future Reference.20th International Conference on Theory and Practice of Digital Libraries, TPDL 2016, Hannover, Germany(2016).
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
25:37 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

Thermodynamically consistent modeling of fluids

The motion of fluids is restricted by the 2nd Law of Thermodynamics in multiple manner. This lecture uses historical and contemporary issues to illustrate both the general structure and special properties of thermodynamically consistent modeling.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
18:34 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

Spatial Segmentation Algorithm for Stratified Random Sample considering geometric circumstances

We developed a Segmentation Algorithm, which is based on Region Growing, for Stratified Random Sample. But instead of raster data our algorithm is using vector data! By the use of accurate vector data we can easily implement barriers, like rivers or railways, to control the growing we need to. Also by splitting polygons we achieve a kind of density gradient to slow the grow in unwanted regions, like bridges. As well we had to remove a lot of bottlenecks to reduce runtime and make it performant and practicable. The result are approximately optimal segmented regions, which are met certain conditions regarding the sample design and take consideration to geometric circumstances. In our case it is useful for reduction of costs on Germany-wide field survey for random sample of non-residential building, but is also applicable to any other wanted segmentation.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
14:56 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

Split-explicit methods for low Mach number flows with cut cell discretization

Split-explicit methods are a common integration method in numerical weather prediction. They combine two explicit methods to integrate different parts of the right hand side with different time steps. Common combinations are for the slow part Leap-Frog, Runge-Kutta, or Adams-method and for the fast part a Verlet-type integration method. For Runge-Kutta methods as the slow integrator Wensch et.al give a generalization (MIS-method) and analysed this new method in case of an exact integration of the fast part. When the orography is represented by a cut cell approach the splitting has to respect also the small cell problem. Modifications are described, which represent the fast part by a local linear operator and use a special implicit-explicit method for the integration of this linear differential equation. We will compare our new integrators and known methods for the two-dimensional compressible Euler-equations for examples with different Mach-numbers and grid configurations.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
24:27 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2017

On perspectives for common research in the Leibniz MMS network in the field of Computational and Geophysical Fluid Dynamics

Computational Fluid Dynamics (CFD) and Geophysical Fluid Dynamcis (GFD) are common research topics of different Leibniz institutes, where very similar mathematical and physical modelling approaches are used. Therefore, CFD & GFD seem to be obvious candidates for interdisciplinary research in the Leibniz Association. In the talk, an overview is given about the first common MMS research activities in the field of (CFD & GFD), and some perspectives for common research are presented.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
23:27 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

zbMATH beyond publications

Today, mathematical research information extends far beyond the classical publication format. This is especially true in the area of modelling and simulation, where the theoretical aspects of modelling are naturally connected with research data, mathematical software, and computational results. While all these components are essential in the process of research, they are not always similarly reflected in the publications. We describe how zbMATH currently supports the needs for documentation, information, and reputation management of research beyond texts. We also outline some approaches for future developments.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
16:44 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

Combining linear Support Vector Machines by constraining them to use the same set of features improves consistency in biomarker discovery for blood infections

Blood infection is highly prevalent in critical ill patients and can lead to sepsis and often death. It can be caused by bacteria or fungi and for appropriate treatment it is mandatory to identify the type of infection early. To find discriminating biomarkers, in situ high throughput gene expression profiling of immune cells after fungal or bacterial infection have been performed. However, these studies showed very heterogeneous results. To find a generic gene signature with discriminative power across all datasets, we implemented linear SVMs basing on Mixed Integer Linear Programming. We combined classifiers constraining them to use the same set of features. Learning with one pair of datasets and applying to the rest of the datasets showed 43?mprovement in consistency of the selected features (genes) while non-decreased classification performance (accuracy: 0.96). The final biomarkers comprised of 19 genes mostly involved in ERK-MAPK signalling being central in immune response.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
14:53 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) German 2017

Investigation of phenomena in the Western Baltic Sea

To understand the processes of local phenomena over the Baltic Sea such as Coastal Upwelling or Salinity Inversion, we are coupling an atmosphere and ocean model with the Earth System Modelling Framework (ESMF). For the atmospheric part the operational model of the German Weather Service (ICON) is utilized in a nested limited area mode. The General Estuarine Turbulence Model (GETM) has been chosen for the local ocean model. Typical coupling issues are the different grid schemes of the models and hence, a set and choice of suitable interpolation/regridding methods is required. Within our framework, the state variables (e.g. temperature) and flux data (e.g. heat flux) has to be interpolated from the unstructured triangular grid of ICON to the structured rectangular latitude longitude grid of GETM and vice versa. Furthermore, due to different grids, the land sea masking of each model has to be considered for the interpolation. Additionally, when using a parallel infrastructure, the number of processes has to be chosen such that the coupled model runs well balanced. Since we are using the concurrent structure ESMF is providing, the focus is on the reduce of possible waiting time for each model. The presentation shall give an overview about these issues, how we are addressing them within our coupled model framework and some results of first runs.
  • Published: 2017
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: German
40:47 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

Key Note Lecture: Why is the desert not flat? The interesting physics of windblown sand.

Windblown sand creates a distinct hierarchy of mobile landforms on Earth on some celestial bodies, ranging from tapestries of meticulously carved ripples to vast fields of shifting dunes. They are often perceived as aesthetically appealing, yet economically and ecologically threatening. But how do they form, and what determines their characteristic shapes, sizes, and migration dynamics? I will sketch three crucial physical mechanisms that govern this whole phenomenology: spontaneous turbulent symmetry breaking, broken scale invariance due to an emergent mesoscale, and aeolian sand sorting. Together they give rise to the notion of a forbidden wavelength gap between ripples and dunes and explain why it can (only) be inhabited by a peculiar bedform known as megaripples, which might actually be better characterized as mini-dunes. K. Kroy, G. Sauermann, H. J. Herrmann, Minimal model for sand dunes, Physical Review Letters 88 (2002) 054301. M. Lämmel, K. Kroy, Analytical mesoscale modeling of aeolian sand transport, Physical Review E 96 (2017) 052906. M. Lämmel, A. Meiwald, H. Yizhaq, H. Tsoar, I. Katra, and K. Kroy, Aeolian sand sorting and megaripple formation, Nature Physics, to appear.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
25:33 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

Discretization of generalized Coriolis and friction terms on the deformed hexagonal C-grid

The talk discusses the generalized Coriolis and friction terms from two perspectives: (i) within the linearized discretized momentum equations on an equilateral grid, and (ii) as nonlinear terms on a distorted mesh. The discrete linearized momentum equations are formulated using a trivariate coordinate system. The tendencies of the different forcing terms for each wind component must be linear dependent. This constraint determines unique discretizations for each term. The linearized vorticity flux term around a zonal mean current requires only the four rhombus PVs next to an edge. The vector Laplacian must be formulated with the vorticity on vertices defined as the average of three rhombus vorticities. A modified generalized Coriolis term is defined on the deformed mesh. The baroclinic wave test on the sphere does not reveal any sign of a non-linear Hollingsworth instability, even though it is demonstrated that the Lamb form and the advective form of momentum advection are not equivalent. Physical constraints determine the shape of the stress tensor. These are invariance to the addition of solid body rotation and a resulting positive definite dissipation rate. An appropriate stress tensor formulation does not deliver a Laplacian momentum diffusion in the linear case. On the deformed mesh, parts of this stress tensor are obtained by a least squares reconstruction of wind gradients. This approach avoids spurious deformations diagnosed for constant flow in the vicinity of pentagon cells. It is impossible for both terms to meet all physical requirements and the additional numerical linear dependency constraint. The topic is of general interest, because the linear dependency of overspecified dynamics may play a role also in other modeling fields.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
21:32 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

Modelling turbulent fluid-, thermo-, and droplet dynamics in the Leipzig Aerosol Cloud Interaction Simulator (LACIS-T)

The turbulent Leipzig Aerosol Cloud Interaction Simulator (LACIS-T) is a Göttingen-type moist-air wind tunnel designed for investigating interactions between turbulence and cloud microphysics under reproducible and well defined thermo- and fluid dynamic conditions. To draw reliable conclusions from measurements at the wind tunnel it is necessary to have precise knowledge about the flow field and turbulent fluctuations of velocity, temperature, and water vapour concentration. For this reason, the flow inside the measurement section of LACIS-T is simulated with OpenFOAM, employing a Large Eddy Simulation model for turbulence. Different boundary conditions for water vapour concentration and temperature are considered and the results are compared to measurements. Furthermore, particles are tracked through the domain using a Lagrangian approach. Thereto, a suitable growth model is implemented to calculate particle/droplet growth due to the condensation of water vapour from the gas phase. Joint work with D. Niedermeier, J. Voigtländer, and F. Stratmann.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
22:04 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

Numerical simulation of large atmospheric multiphase mechanisms and detailed combustion kinetics

A simulation tool for the numerical solution of large kinetic systems with special emphasis on examples from atmospheric chemistry and combustion is presented. The chemical mechanism has to be provided in readable ASCII format, whereas the program is able to read the TROPOS syntax for chemical systems and also the widely used ChemKin format. From this, a system of ordinary differential equations is generated internally and solved numerically by Rosenbrock-type methods. Efficiency is obtained by carefully exploiting the sparsity structures of the Jacobian. Additionally, another approach is implemented, where the direct evaluation of the Jacobian is no longer required. The effects of both strategies are investigated by simulating detailed atmospheric multiphase mechanisms and gas-phase combustion mechanisms.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
30:13 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

High resolution Magnetic Resonance Imaging experiments - lessons in nonlinear statistical modeling

Recent advances in neuro-imaging attempt to enable in-vivo histology of the brain. Doing so requires increased spatial resolution up to a situation where the signal meets the noise floor. The talk will cover research conducted at WIAS, in collaboration with MR physicists, on statistical issues in modeling imaging data characterized by low signal-to-noise ratio (SNR). I'll cover several specific, but interrelated problems: - characterization of the signal distribution in MR experiments, - effects of preprocessing on the signal distribution, - estimation of the noise profile in MR images, - use of spatial information for variance reduction in (collections of) MR images, - bias due to incorrect modeling in MR experiments. I'll consider two specific imaging experiments to illustrate problems, characterize effects that are due to high measurment noise and provide solutions for: - diffusion weighted MR, with an analysis based on data of the Human Connectome Project, - multi-parameter mapping, using data measured at the Wellcome Trust Center for Neuroimaging, London. Literature: S. Becker, K. Tabelow, S. Mohammadi, N. Weiskopf and J. Polzehl, Adaptive smoothing of multi-shell diffusion-weighted MR data by msPOAS, NeuroImage, 95 (2014) pp. 90--105. K. Tabelow, H.U. Voss and J. Polzehl, Local estimation of the noise level in MRI using structural adaptation, Medical Image Analysis, 20 (2015) pp. 76--86. J. Polzehl and K. Tabelow, Low SNR in dMRI models, JASA, 11 (2016) pp. 1480--1490. K. Tabelow, Ch. D'Alonzo, L. Ruthotto, M. F. Callaghan, N. Weiskopf, J. Polzehl and S. Mohammadi, Removing the estimation bias due to the noise floor in multi-parameter maps, ISMRM annual meeting 2017.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
24:01 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

Handling research software: recommendations to users, developers and research managers.

A working group initiated by a joint initiative of German research and funding organizations developed a "helping hand" paper providing recommendations on important aspects of research software developmement and maintenance [1]. It is addressed to the different stakeholders in the hierarchy of an research organization. The talk will introduce the main points of this document. Based on the personal experience of the speaker a number of steps necessary to introduce these guidelines into the everyday practice of a research institution will be discussed. [1] Katerbow, Matthias / Feulner, Georg (2018): Handreichung zum Umgang mit Forschungssoftware. Herausgegeben von der AG Forschungssoftware im Rahmen der Schwerpunktinitiative Digitale Information der Allianz der deutschen Wissenschaftsorganisationen. Unter Mitarbeit von Mathias Bornschein, Björn Brembs, Michael Erben-Russ, Konrad Förstner, Michael Franke, Bernadette Fritzsch, Jürgen Fuhrmann, Michael Goedicke, Stephan Janosch, Uwe Konrad, Dennis Zielke.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
42:45 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

Key Note Lecture: Managing research software development - better software, better research

In a 2014 survey of UK research-intensive universities, 92% of researchers said they used research software and 68% said their research would be impossible without software. Yet 71% have had no formal software training, and few are ready to apply many of the things we consider as best practice in research software development. The UK's Software Sustainability Institute has worked at the forefront of activity to address these issues, providing guidance and training whilst developing ways of supporting sustainable communities of practice. My talk will challenge the workshop attendees to understand how they can work with their own communities to improve the ways that software is used and developed, including infrastructure, incentives, overcoming fears and increasing adoption, and planning for change.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
28:04 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

Analyzing paradigmatic language change by visual correlation

Paradigmatic language change occurs, when paradigmatically related words with similar usage rise or fall together. Such change is the rule rather than an exception. Words rarely increase or decrease in isolation but together with similar words. In the short term, this is usually due to thematic change, but in the longer term, also grammatical preferences change. We present an approach to visually explore paradigmatic change by reducing the dimensionality of and correlating the two main factors involved: Frequency change and distributional semantics of words. Frequency change is reduced to one dimension by means of fitting the logistic growth curves to the observed word frequencies in fixed intervals (e.g. year or decade). Semantics of words reduced to two dimensions such that words with similar usage contexts are positioned closely together. This is accomplished by reducing the very high dimensional representation of word usage context in two steps. Neural network based word embeddings and t-Distributed Stochastic Neighbour Embedding.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
26:48 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

On the role of the Helmholtz-Leray projector in the space discretization of the Navier-Stokes equations

Recent progress on pressure-robust mixed methods for the incompressible Navier-Stokes equations and the connection to the Helmholtz-Leray projector is presented. It is argued that and how pressure-robust methods allow to decrease the (formal) approximation order of the used discretizations. As applications, electrolytes and stagnation point flows are emphasized.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
33:36 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

Model pathway diagrams for the representation of mathematical models

Mathematical modeling and simulation (MMS) has now been established as an essential part of the scientific work in many disciplines. It is common to categorize the involved numerical data and to some extent the corresponding scientific software as research data. But both have their origin in mathematical models, therefore any holistic approach to research data in MMS should cover all three aspects: data, software, and models. However, finding an appropriate representation for models is far less obvious than for numerical data and software. The current practice of representing models is a mixture of mathematical formulae and natural language in scientific publications. This (rigorous, but) informal approach creates ambiguity, potential incompleteness of the presentation, less reproducibility and often "re-invention of the wheel". We present a concept for a machine-actionable as well as human-understandable of mathematical models based on Model Pathway Diagrams (MPD). MPDs specify the physical quantities that are described in the model as well as the relations between them (laws, constitutive equations) and informal documentation about them. MPDs provide a visual tool for understanding the structural properties of models as well as algorithms for numerical simulations. For a formalized representation of mathematical models and their underlying physics, we use the OMDoc/MMT, a special machine-readable description language for mathematical documents, that allows specifying the mathematical vocabulary of models, i.e. the concepts, their properties, and relations. We illustrate our approach by application to the van Roosbroeck system describing the carrier transport in semiconductors by drift and diffusion. We introduce an approach for the block-based composition of models from simpler components.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
22:28 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

Software information and the swMATH service

Scientific software is an indensible tool for the automatization and control of complex problems. But what is software? Software is a entirety of different kinds of objects which is developing dynamically and cannot be reduced to software code. Moreover, software plays a special role: Software is in the middle between models and simulations. The distributed development of software and the access to the software have led to new concepts and tools for maintaining software and software information. The swMATH service is a portal for mathematical software. It provides landing pages for each software entry. These landing pages contain general information about the software products and links to a lot of resources which describe or use the software, e.g., websites of the software, repositories, Internet archives, and publications citing a software. The integration and analysis of different resources allows a nearly complete overview about the Web information of a software. In the talk, new features and future extensions of the swMATH service are presented.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
34:11 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

Key Note Lecture: Challenges of atmospheric data assimilation

The initial state for atmospheric numerical models is produced by combining available observational data with a short range model simulation using a data assimilation algorithm. This gives us an initial state from which we can run a deterministic model to produce predictions of the future. The main goal of data assimilation is to produce the best analysis (best initial condition) for the numerical model; that is, the estimate that gives the best prediction for the time scales that we are focusing on. This is a challenging problem since high-resolution numerical models of the atmosphere in use today resolve highly nonlinear dynamics and physics, making them in short runs very sensitive to proper initial and boundary conditions. In this talk, we present the mechanisms of the data assimilation algorithms.. We focus on the ensemble Kalman filter algorithm to estimate the atmospheric state as well as its necessary modifications for our application. Most of the current algorithms used in practice for combining data and previous model forecasts (prior estimates) use Gaussian error assumptions. These assumptions are not appropriate for nonlinear dynamics, since only in the case of linear dynamics will Gaussian errors remain Gaussian in time, not in case of estimating variables that need to be positive or in certain ranges as, for example, rain. Consequently, data assimilation for numerical weather prediction models that resolve many scales of motion and for observations of higher temporal/spatial density/resolution requires re-evaluating and improving the methodology that is currently inherited from less nonlinear applications. We argue that relaxing underlying assumptions of the data assimilation algorithms might be possible by improving the link between the data assimilation and the model. For example, the stronger connection can be established by constraining the analysis with imposing conservation laws and other physical constraints. Applications are illustrated on the convective scale data assimilation example.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
24:52 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

Modeling and simulation of electrically driven quantum light emitters

The design of electrically driven quantum light sources based on semiconductor quantum dots, such as single-photon emitters and nanolasers, asks for modeling approaches combining classical device physics with cavity quantum electrodynamics. In particular, one has to connect the well-established fields of semi-classical semiconductor transport theory and the theory of open quantum systems. We present a first step in this direction by coupling the van Roosbroeck system with a quantum master equation in Lindblad form. The resulting hybrid quantum-classical system obeys the fundamental laws of non-equilibrium thermodynamics and provides a comprehensive description of quantum dot devices on multiple scales: It enables the calculation of quantum optical figures of merit (e.g. the second order intensity correlation function) together with the spatially resolved simulation of the current flow in realistic semiconductor device geometries in a unified way.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
26:17 Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB) English 2018

Czochralski Growth of Ge Computed by Using the Finite Element Tool Elmer

The Czochralski method is widely used for growing single crystals as e.g. silicon crystals. Typically, the thermal field and related ones such as thermal stress is computed for certain stages of the growth. Here we present the successive computations starting from inital state up to nearly the end by combining a perl script and the finite element solver Elmer. The shape of the crystal is given by input and can be taken either from experimental result or by own definition. The numerical computed interface is compared with the one observed by LPS at the crystal grown.
  • Published: 2018
  • Publisher: Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS), Technische Informationsbibliothek (TIB)
  • Language: English
out of 2 pages
Loading...
Feedback

Timings

  195 ms - page object
  104 ms - search
    4 ms - highlighting
    0 ms - highlighting/35348
    3 ms - highlighting/21917
    1 ms - highlighting/21905
    2 ms - highlighting/30617
    4 ms - highlighting/35357
    2 ms - highlighting/35355
    2 ms - highlighting/35354
    2 ms - highlighting/35350
    1 ms - highlighting/21916
    1 ms - highlighting/21900
    1 ms - highlighting/21901
    4 ms - highlighting/35359
    4 ms - highlighting/21918
    4 ms - highlighting/35360
    1 ms - highlighting/35428
    3 ms - highlighting/21908
    2 ms - highlighting/35364
    1 ms - highlighting/21909
    2 ms - highlighting/21910
    2 ms - highlighting/21914
    1 ms - highlighting/21913
    0 ms - highlighting/30616
    2 ms - highlighting/21912
    0 ms - highlighting/21911
    2 ms - highlighting/21907
    2 ms - highlighting/21906
    2 ms - highlighting/35427
    1 ms - highlighting/35358
    2 ms - highlighting/21903
    2 ms - highlighting/21899
    2 ms - highlighting/35352
    1 ms - highlighting/35363
    2 ms - highlighting/35353
    0 ms - highlighting/21915
    0 ms - highlighting/21902
    1 ms - highlighting/21904

Version

AV-Portal 3.7.0 (943df4b4639bec127ddc6b93adb0c7d8d995f77c)