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Semi-Lagrangian lattice Boltzmann method for compressible flows

Physical Review E 2020年第5期101卷 053306-053306页

作者： Dominik Wilde Andreas Krämer Dirk Reith Holger Foysi Department of Mechanical Engineering University of Siegen Paul-Bonatz-Straße 9-11 D-57076 Siegen-Weidenau Germany Institute of Technology Resource and Energy-efficient Engineering (TREE) Bonn-Rhein-Sieg University of Applied Sciences Grantham-Allee 20 D-53757 Sankt Augustin Germany National Heart Lung and Blood Institute National Institutes of Health Bethesda Maryland 20892 USA Fraunhofer Institute for Algorithms and Scientific Computing (SCAI) Schloss Birlinghoven D-53754 Sankt Augustin Germany

This work thoroughly investigates a semi-Lagrangian lattice Boltzmann (SLLBM) solver for compressible flows. In contrast to other LBM for compressible flows, the vertices are organized in cells, and interpolation polynomials up to fourth order are used to attain the off-vertex distribution function values. Differing from the recently introduced Particles on Demand (PoD) method [Dorschner, Bösch, and Karlin, Phys. Rev. Lett. 121, 130602 (2018)], the method operates in a static, nonmoving reference frame. Yet the SLLBM in the present formulation grants supersonic flows and exhibits a high degree of Galilean invariance. The SLLBM solver allows for an independent time step size due to the integration along characteristics and for the use of unusual velocity sets, like the D2Q25, which is constructed by the roots of the fifth-order Hermite polynomial. The properties of the present model are shown in diverse example simulations of a two-dimensional Taylor-Green vortex, a Sod shock tube, a two-dimensional Riemann problem, and a shock-vortex interaction. It is shown that the cell-based interpolation and the use of Gauss-Lobatto-Chebyshev support points allow for spatially high-order solutions and minimize the mass loss caused by the interpolation. Transformed grids in the shock-vortex interaction show the general applicability to nonuniform grids.

关键词： Kinetic theory Lattice-Boltzmann methods

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RDM-stars and related topics

arXiv

引用

arXiv 2019年

作者： Nikitin, Igor Fraunhofer Institute for Algorithms and Scientific Computing Schloss Birlinghoven Sankt Augustin53757 Germany

In this paper, we will continue to study the model of black holes coupled to the radial flows of dark matter (RDM-stars). According to recent studies, this model well describes the experimental Rotation Curves (RCs) of spiral galaxies, also, RDM-stars can produce signals with the characteristics of Fast Radio Bursts (FRBs). In this paper, we will perform a combined analysis of experimental data on RCs and FRBs, which will allow to constrain tighter parameters of the model. We will also show that within the framework of the model, the Tully-Fisher relation with a slope of β = 3 − 4 can be obtained. Further, several particular solutions will be considered: tachyonic oven – a solution in which the incoming flow of tachyons turns into an outgoing flow of massive particles;shell condensate – a naked singularity of negative mass covered by a thin shell of positive mass, so that the Schwarzschild solution of negative mass inside is joined to one of positive mass outside;also, an RDM solution with a cosmological constant will be considered. Further, in the model under consideration, Penrose diagrams will be constructed, which share common features with Schwarzschild solutions of positive and negative mass, whose combination the model is. The mechanism of effective formation of negative masses in the model is discussed, which is activated when the density of the central core exceeds the Planck value, similarly to the previously studied quantum bounce effect. Copyright © 2019, The Authors. All rights reserved.

关键词： Stars

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Quantum gravity wormholes and topological teleporter

arXiv

引用

arXiv 2019年

作者： Nikitin, Igor Fraunhofer Institute for Algorithms and Scientific Computing Schloss Birlinghoven Sankt Augustin53757 Germany

The question of a possibility of opening a wormhole due to the deformation of the equation of state of the matter caused by quantum gravity effects is considered. As a wormhole environment, the previously considered model of a galaxy with radial flows of dark matter is selected. The calculation shows, that for a wormhole solution in the framework of this model, after the nominal classical density exceeds a critical value in the Planck range, the components of the energy-momentum tensor become negative in a certain order. First, the mass density becomes negative, then the radial pressure, then the tangential pressure. In this case, at some point the flare-out conditions necessary and sufficient to open the wormhole are fulfilled. Calculations are made to open a wormhole in a model with parameters of the Milky Way galaxy. It is shown that the opening of the wormhole is accompanied by a separation of the bubble of space, completely detached from the wormhole and the outer space. In addition to this solution, a topologically dual one is found, looking like an instant swapping of two volumes in space, which can be interpreted as an event of teleportation. Copyright © 2019, The Authors. All rights reserved.

关键词： Galaxies

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RDM-stars and galactic rotation curves

arXiv

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arXiv 2019年

作者： Nikitin, Igor Fraunhofer Institute for Algorithms and Scientific Computing Schloss Birlinghoven Sankt Augustin53757 Germany

The recently formulated model of black holes coupled to the radial flows of dark matter (RDM-stars) is considered and the shape of the galactic rotation curves predicted by the model is evaluated. Under the assumption that the density of black holes is proportional to the density of luminous matter, the model perfectly fits the experimental data, both for the universal rotation curve, describing the spiral galaxies of a general form, and for the grand rotation curve, describing the orbital velocities of Milky Way galaxy in a wide range of distances. The modeling of the galactic gravitational field at large distances from the center and out of the galactic plane is also discussed. Copyright © 2019, The Authors. All rights reserved.

关键词： Stars

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On the convergence of system-AMG in reservoir simulation

On the convergence of system-AMG in reservoir simulation

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作者： Gries, Sebastian Fraunhofer Institute for Algorithms and Scientific Computing Numerical Software Department Germany

System-algebraic multigrid (AMG) provides a flexible framework for linear systems in simulation applications that involve various types of physical unknowns. Reservoir-simulation applications, with their driving elliptic pressure unknown, are principally well-suited to exploit System-AMG as a robust and efficient solver method. However, the coarse grid correction must be physically meaningful to speed up the overall convergence. It has been common practice in constrained-pressure-residual (CPR) -type applications to use an approximate pressure/saturation decoupling to fulfill this requirement. Unfortunately, this can have significant effects on the AMG applicability and, thus, is not performed by the dynamic rowsum (DRS) method. This work shows that the pressure/saturation decoupling is not necessary for ensuring an efficient interplay between the coarse grid correction process and the fine-level problem, demonstrating that a comparable influence of the pressure on the different involved partial- differential equations (PDEs) is much more crucial. As an extreme case with respect to the outlined requirement, linear systems from compositional simulations under the volume-balance formulation will be discussed. In these systems, the pressure typically is associated with a volume balance rather than a diffusion process. It will be shown how System-AMG can still be used in such cases. © 2018 Society of Petroleum Engineers.

关键词： Linear systems

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A multimodal digital biomarker of functional deficits in early-stage Alzheimer’s disease: results of the RADAR-AD study

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Alzheimer's & Dementia 2023年第S15期19卷

作者： Srinivasan Vairavan Manuel Lentzen Marijn Muurling Casper de Boer Alankar Atreya Jelena Curcic Chris Hinds Pauline Conde Margarita Grammatikopoulou Gaetano Scebba Ioulietta Lazarou Spiros Nikolopoulos Anna-Katharine Brem Neva Coello Pieter Jelle Visser Holger Fröhlich Vaibhav A Narayan Gayle Wittenberg Dag Aarsland Janssen Research and Development Titusville NJ USA Correspondece Fraunhofer Institute for Algorithms and Scientific Computing SCAI Sankt Augustin Germany VU University Medical Center Amsterdam Netherlands University of Oxford Oxford United Kingdom Novartis Institutes for BioMedical Research Basel Switzerland King’s College London London United Kingdom Centre for Research & Technology Hellas Thessaloniki Greece Davos Alzheimers Collaborative Wayne PA USA Janssen Research and Development LLC Titusville NJ USA

Background Remote monitoring technologies (RMTs), such as smartphone apps, smartwatches, and in-home sensors, are rapidly changing the way functional and cognitive performance is measured in Alzheimer’s disease (AD) patients. Here, we present results from the European RADAR-AD study on the use of multimodal data streams for the identification of functional deficits across all syndromic stages of AD. Method Four study groups (Healthy controls (HC), preclinical AD (pre. AD), prodromal AD (pro. AD), and mild AD) were included in this cross-sectional study. The RMT features (gait measures from Timed up and Go (TUG), Dual Task Effect (DTE) using physilog, acoustic features from Speech task in Mezurio, neurocognitive function using Altoida, managing finances with Banking app) with in-clinic neuropsychological (NP) tests, activities of daily living with Amsterdam IADL and demographics (age, gender, education years) were analyzed for different combinations of the multimodal digital biomarker of disease stage in AD across different pairwise comparisons. The analysis includes data from 175 participants (HC = 67, *** = 26, *** = 50, Mild AD = 32) collected for 8 weeks. An extreme gradient boosting (XGBoost) machine learning model was trained to obtain a multimodal biomarker of AD disease stage with repeated cross-validation (5-fold with 4 repeats) (Figure 1). This investigation is part of the ongoing RADAR-AD study. Result The multimodal combination of RMTs achieved a mean AUC of > 0.60 in all pairwise comparisons with a mean AUC > 0.65 for HC vs (***, *** and Mild) (Figures 2 and 3). The addition of NP tests increases the performance considerably across all pairwise comparisons except HC vs ***. Conclusion Our results highlight the advantage of combining RMTs to identify functional deficits in the early stage of AD. In particular, in prodromal and mild AD patients, a combined signal shows much more strength compared to individual tests. This work has received s

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scaiView - A semantic search engine for biomedical research utilizing a microservice architecture 14

SCAIView - A semantic search engine for biomedical research ...

引用

Posters and Demos Track of the 14th International Conference on Semantic Systems, SEMPDS 2018

作者： Dörpinghaus, Jens Klein, Jürgen Darms, Johannes Madan, Sumit Jacobs, Marc Fraunhofer Institute for Algorithms and Scientific Computing Schloss Birlinghoven Sankt Augustin Germany

Biological and medical researchers explore the mechanisms of living organisms and tend to gain a better understanding of underlying fundamental biological processes of life. To tackle such complex tasks they constantly need to gather and accumulate new knowledge by performing experiments and studying scientific literature. We will present the novel semantic search engine "scaiView" for knowledge discovery and retrieval and, additionally, discuss the most recent paradigm shifts in communication technologies, which leads to a completely new architecture that improves scalability, achieves better interoperability, and also increases fault-tolerance. © 2018 CEUR-WS. All Rights Reserved.

关键词： Fault tolerance

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Improving document retrieval with a clustering based relevance feedback system 11

Improving document retrieval with a clustering based relevan...

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11th IADIS International Conference Information Systems 2018, IS 2018

作者： Darms, Johannes Dörpinghaus, Jens Fraunhofer Institute for Algorithms and Scientific Computing Schloss Birlinghoven Sankt Augustin Germany

ISBN: (纸本)9789898533746

Relevance feedback for document retrieval systems is a technique where user feedback is used to improve a query response. In this work we propose a system that uses multiple clusterings and a semi-supervised heuristic to improve a query response. The heuristic creates an optimal cluster w.r.t. the relevance feedback based on multiple clusterings. We justify the explicit separation of the optimization process and the clustering process by time and space constrains. The evaluation of the heuristic on a corpus containing 1.660 documents from MEDLINE showed promising results. We were able to obtain better results as a single clustering after a few iterations. © 2018 IADIS. All rights reserved.

关键词： Search engines

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Universal translation algorithm for formulation of transport network problems 8

Universal translation algorithm for formulation of transport...

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8th International Conference on Simulation and Modeling Methodologies, Technologies and Applications, SIMULTECH 2018

作者： Baldin, Anton Cassirer, Kläre Clees, Tanja Klaassen, Bernhard Nikitin, Igor Nikitina, Lialia Torgovitskaia, Inna Fraunhofer Institute for Algorithms and Scientific Computing Schloss Birlinghoven Sankt Augustin53754 Germany

ISBN: (纸本)9789897583230

The formulation of transport network problems is represented as a translation between two domain specific languages: From a network description language, used by network simulation community, to a problem description language, understood by generic non-linear solvers. A universal algorithm for this translation is developed, an estimation of its computational complexity given, and an efficient application of the algorithm demonstrated on a number of realistic examples. Typically, for a large gas transport network with about 10K elements the translation and solution of non-linear system together require less than 1 sec on the common hardware. The translation procedure incorporates several preprocessing filters, in particular, topological cleaning filters, which accelerate the solution procedure by factor 8. Copyright © 2018 by SCITEPRESS-Science and Technology Publications, Lda. All rights reserved.

关键词： Complex networks

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Informed machine learning - A taxonomy and survey of integrating prior knowledge into learning systems

arXiv

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arXiv 2019年

作者： von Rueden, Laura Mayer, Sebastian Beckh, Katharina Georgiev, Bogdan Giesselbach, Sven Heese, Raoul Kirsch, Birgit Pfrommer, Julius Pick, Annika Ramamurthy, Rajkumar Walczak, Michal Garcke, Jochen Bauckhage, Christian Schuecker, Jannis The Fraunhofer IAIS Institute for Intelligent Analysis and Information Systems Sankt Augustin53757 Germany The Fraunhofer SCAI Institute for Algorithms and Scientific Computing Sankt Augustin53757 Germany The Fraunhofer ITWM Institute for Industrial Mathematics Kaiserslautern67663 Germany The Fraunhofer IOSB Institute for Optronics System Technologies and Image Exploitation Karlsruhe76131 Germany

Despite its great success, machine learning can have its limits when dealing with insufficient training data. A potential solution is the additional integration of prior knowledge into the training process which leads to the notion of informed machine learning. In this paper, we present a structured overview of various approaches in this field. We provide a definition and propose a concept for informed machine learning which illustrates its building blocks and distinguishes it from conventional machine learning. We introduce a taxonomy that serves as a classification framework for informed machine learning approaches. It considers the source of knowledge, its representation, and its integration into the machine learning pipeline. Based on this taxonomy, we survey related research and describe how different knowledge representations such as algebraic equations, logic rules, or simulation results can be used in learning systems. This evaluation of numerous papers on the basis of our taxonomy uncovers key methods in the field of informed machine learning. © 2019, CC BY.

关键词： Surveys

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