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The Journal of Machine Learning Research 2024年第1期25卷 3892-3898页

作者： Moritz Wolter Felix Blanke Jochen Garcke Charles Tapley Hoyt High-Performance Computing and Analytics Lab University of Bonn Germany Fraunhofer Institute for Algorithms and Scientific Computing Sankt Augustin Germany Institute for Numerical Simulation University of Bonn and Fraunhofer Institute for Algorithms and Scientific Computing Sankt Augustin Germany Northeastern University Boston

The fast wavelet transform is an important workhorse in signal processing. Wavelets are local in the spatial- or temporal- and the frequency-domain. This property enables frequency domain analysis while preserving some spatiotemporal information. Until recently, wavelets rarely appeared in the machine learning literature. We provide the PyTorch Wavelet Toolbox to make wavelet methods more accessible to the deep learning community. Our PyTorch Wavelet Toolbox is well documented. A pip package is installable with pip install ptwt.

关键词： PyTorch wavelet wavelet-packets wavelet-analysis wavelet-transform

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Stability of dynamic fluid transport simulations 12

Stability of dynamic fluid transport simulations

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12th International Conference on Mathematical Modeling in Physical Sciences, IC-MSQUARE 2023

作者： Anvari, Mehrnaz Baldin, Anton Clees, Tanja Klaassen, Bernhard Nikitin, Igor Nikitina, Lialia Pott, Sabine Fraunhofer Institute for Algorithms and Scientific Computing Sankt Augustin Germany PLEdoc GmbH Essen Germany Hochschule Bonn-Rhein-Sieg University of Applied Sciences Sankt Augustin Germany

Pipeline transport is an efficient method for transporting fluids in energy supply and other technical applications. While natural gas is the classical example, the transport of hydrogen is becoming more and more important;both are transmitted under high pressure in a gaseous state. Also relevant is the transport of carbon dioxide, captured in the places of formation, transferred under high pressure in a liquid or supercritical state and pumped into underground reservoirs for storage. The transport of other fluids is also required in technical applications. Meanwhile, the transport equations for different fluids are essentially the same, and the simulation can be performed using the same methods. In this paper, the effect of control elements such as compressors, regulators and flaptraps on the stability of fluid transport simulations is studied. It is shown that modeling of these elements can lead to instabilities, both in stationary and dynamic simulations. Special regularization methods were developed to overcome these problems. Their functionality also for dynamic simulations is demonstrated for a number of numerical experiments. © 2024 Institute of Physics Publishing. All rights reserved.

关键词： Carbon dioxide

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INDEX: the Intelligent Data Steward Toolbox Utilizing Large Language Model Embeddings for Automated Data Harmonization 15

INDEX: the Intelligent Data Steward Toolbox Utilizing Large ...

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15th International Conference on Semantic Web Applications and Tools for Health Care and Life Sciences, SWAT4HCLS 2024

作者： Adams, Tim Aborageh, Mohamed Salimi, Yasamin Fröhlich, Holger Jacobs, Marc Fraunhofer Institute for Algorithms and Scientific Computing Schloss Birlinghoven Sankt Augustin53757 Germany Bonn-Aachen International Center for IT Rheinische Friedrich-Wilhelms-Universität Bonn Bonn53115 Germany

The data steward, responsible for overseeing data management, plays a pivotal role in evidence-based medicine by ensuring the quality, integrity, and accessibility of data throughout its lifecycle. However, managing medical data poses challenges, including handling diverse structured and unstructured data from various sources in different formats. This data curation process demands significant time and resources. To alleviate these challenges and enhance the efficiency of data stewards, we introduce a novel data stewardship tool and curation workflow utilizing Large Language Models (LLMs). We evaluated our approach by performing automatic pairwise cohort harmonization using data dictionaries of 6 different Parkinson’s Disease (PD) studies and 13 different studies in the context of Alzheimer’s Disease (AD), as well as a mapping task of over 38,000 ICD10 codes using code descriptions obtained from UKBioBank. When compared with a String Matching based baseline method that does not capture the context of variable descriptions, we found that Generative Pre-trained Transformer (GPT) embedding based mappings performed significantly better, reaching a best average accuracy for the application of PD cohort harmonization for an automated initial closest match of 82%. While we found that due to various different formulation and wording issues descriptions could not be automatically matched in all cases, we are confident that our data steward tool can significantly facilitate the work of the data steward in a semi-automatic fashion. © 2024 Copyright for this paper by its authors.

关键词： Neurodegenerative diseases

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On Advanced Modeling of Compressors and Weighted Mix Iteration for Simulation of Gas Transport Networks 1

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11th International Conference on Simulation and Modeling Methodologies, Technologies and Applications, SIMULTECH 2021

作者： Baldin, Anton Cassirer, Kläre Clees, Tanja Klaassen, Bernhard Nikitin, Igor Nikitina, Lialia Pott, Sabine Fraunhofer Institute for Algorithms and Scientific Computing Schloss Birlinghoven Sankt Augustin53754 Germany Bonn-Rhine-Sieg University of Applied Sciences Grantham-Allee 20 Sankt Augustin53754 Germany

ISBN: (数字)9783031231490

ISBN: (纸本)9783031231483

In this paper, the modeling of gas compressors with detailed representation of their calibrated characteristics is considered. A method is developed for transforming the characteristics from the space of calibration data to the space of transport variables in which the network problem is actually solved. This transformation satisfies the general stability conditions necessary for the convergence of Newtonian iterations in solving large scale network problems. In addition, a stabilization method of weighted relaxation for mixing iterations is presented, used to find the detailed gas composition. The tests on a large number of realistic gas networks demonstrate nearly 100% convergence of the methods. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.

关键词： Linear systems

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Retrofit of a combined heat and power plant with gas and steam turbines to hydrogen with special consideration of the balance of plant

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International Journal of Hydrogen Energy 2025年

作者： Schiffer, Barbara Pfennig, Malte Clees, Tanja Grantham-Allee 20 Sankt Augustin53757 Germany Fraunhofer Institute for Algorithms and Scientific Computing SCAI Schloss Birlinghoven Sankt Augustin53757 Germany

In 2020, around 44% of natural gas in Germany was used in combined heat and power as well as in combined cycle gas turbines plants. As district heating will play an important role in future heating planning, the retrofit of these plants to hydrogen is a viable option. This paper analyzes a typical combined cycle power plant, including its balance of plant under consideration of different hydrogen blends. We show that retrofits are limited by the gas turbines in many cases. For instance, the preheater in the fuel gas system must be dimensioned higher than with natural gas. While pressure losses are very low, materials could be a problem due to higher volume flows. Additionally, the higher combustion temperatures in the gas turbine can compensate for possible efficiency losses in the Heat Recovery System Generator (HRSG) and steam turbine making this a suitable approach for electricity-led plants. However, for heat-led plants this leads to a reduction in the district heating output. Therefore, the performance of the HRSG must be considered as a limiting factor for heat-driven plants and the change in flue gas must be analyzed. Currently, hydrogen blends of 20–40 vol.-% appear feasible without major adjustments. The water content in the exhaust gas can also lead to problems in the HRSG and flue gas aftertreatment due to changes in the dew point. For higher hydrogen blends, a plant specific analysis is recommended. © 2025 The Authors

关键词： Steam turbines

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New dark matter scenarios with low energy photons and neutrinos

arXiv

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arXiv 2023年

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

In this paper, a cosmological model is considered, in which dark matter is emitted by T-symmetric quasi-black holes distributed over galaxies. Low energy photons and neutrinos are taken as candidates for dark matter particles. Photon case can be closed due to the suppression of electromagnetic waves by interstellar/intergalactic medium. For neutrinos, two scenarios are considered. In the first, light neutrinos pair to bosonic quasiparticles that form massive halos around galaxies. In the second, heavier sterile neutrinos form massive halos without pairing. At the observables level, both scenarios turn out to be equivalent to the standard LambdaCDM model. At the same time, the considered model possesses additional sources – quasi-black holes – that can produce the required number of neutrinos in addition to the Big Bang. This opens up additional possibilities for cosmological constructions. The matching of the model with early cosmology and ongoing neutrino experiments is discussed. In addition, the possibility of solving general cosmological problems, including horizon, flatness and cosmological constant problems, as well as Hubble tension, within the framework of the considered model, is discussed. © 2023, CC BY.

关键词： Photons

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On dark stars, galactic rotation curves and fast radio bursts 9

On dark stars, galactic rotation curves and fast radio burst...

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9th International Conference on Mathematical Modeling in Physical Sciences, IC-MSQUARE 2020

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

This paper is a continuation of our recent work on Radial Dark Matter stars (RDM-stars), black holes, coupled with radial flows of dark matter. As a galaxy model, it produces flat rotation curves, approximately valid for many galaxies far from the center. In this paper, more detailed modeling is carried out, including the vicinity of the galactic center. Assuming that the distribution of stellar black holes repeats the distribution of luminous matter, we get a perfect match between the model rotation curves and the observed ones. Further, using numerical integration, we examine the gravitational field of an individual RDM-star. The computation shows the event horizon being erased and rapidly increasing mass density arising instead (mass inflation). In this regime, we apply the previously constructed Planck star model, where at high densities a repulsive force occurs (quantum bounce). In our stationary model, the evolution of a Planck star has stopped under the pressure of dark matter flows. This system is considered as a possible source of Fast Radio Bursts (FRBs). In a scenario involving an asteroid falling onto an RDM-star, the model reproduces the correct frequency range of FRBs. Their total energy, coherence and short duration are explained as well. © Published under licence by IOP Publishing Ltd.

关键词： Stars

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Mathematical modeling and visualization of topologically non-trivial solutions in general relativity 9

Mathematical modeling and visualization of topologically non...

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9th International Conference on Mathematical Modeling in Physical Sciences, IC-MSQUARE 2020

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

In general relativity, there is a class of solutions that currently do not have observed analogues, but on which the theory is shaped, giving an understanding what is fundamentally possible within its framework. Such solutions include wormholes, tunnels that connect distant regions in spacetime. Although not a single wormhole has yet been discovered, there is a large number of works devoted to their study, thanks to which wormholes as a class of solutions become firmly established in modern science. In this paper, we consider two topologically nontrivial types of solutions related to wormholes. First: wormholes that can open and close. In this relation, we will discuss topological censorship theorems, which under certain conditions prohibit changing topology. We will also discuss known ways to circumvent these theorems. Using analytical and numerical methods, as well as visualization, we will construct an example of an opening and closing wormhole with the dimensions of the central black hole in the Milky Way galaxy. Our construction continues the work by Kardashev, Novikov and Shatskiy, in which a static wormhole with the same parameters was considered. The second type is a modification of Visser's dihedral wormhole solution for a dynamic case. © Published under licence by IOP Publishing Ltd.

关键词： Visualization

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Galactic model with a phase transition from dark matter to dark energy 24

Galactic model with a phase transition from dark matter to d...

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24th Workshop What Comes Beyond the Standard Models

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

This work continues the construction of a recently proposed model of dark matter stars. In this model, dark matter quanta are sterile massless particles that are emitted from the central regions of the galaxy in the radial direction. As a result, at large distances r from the center of the galaxy, the mass density of dark matter has the form ρ ∼ r-2, in contrast to the homogeneous model ρ = Const. In the cosmological context, the homogeneous model with massless particles corresponds to the radiation epoch of the expansion of the universe, while the proposed inhomogeneous model turns out to be equivalent to ΛCDM. In this paper, scenarios will be considered in which the radial emission of dark matter is brought into hydrostatic equilibrium with a uniform background. It is shown that solutions exist if the uniform background has an equation of state typical for dark energy. Thus, this model describes a phase transition from dark matter inside the galaxy to dark energy outside of it. The specific mechanism for such a transition could be Bose-Einstein condensation. In addition, the question of what happens if dark matter particles are not sterile, for example, are photons of the Standard Model, is considered. © 2021 DMFA zaloznistvo. All rights reserved.

关键词： Galaxies

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A landscape analysis of standardisation in the field of artificial intelligence

Journal of ICT Standardization

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Journal of ICT Standardization 2020年第2期8卷 151-184页

作者： Ziegler, Wolfgang Fraunhofer Institute for Algorithms and Scientific Computing SCAI Sankt Augustin Germany

While projects, developments and applications addressing and using artificial intelligence (AI) are rather multifaceted and their number is constantly increasing, the standardisation activities in the field of artificial intelligence are limited, their number is significantly lower and does not increase at the same pace. The European funded project *** aims at supporting European experts' presence in and contributions to international standardisation activities in ICT. The focus of the project is on the 5 priority domains identified by the European Commission (Cloud computing, IoT, Big Data, Cyber Security, 5G) and on Artificial Intelligence while being open for other relevant topics defined in the annual European Rolling Plan for ICT Standardisation. The project has two main outcomes: (i) increased contribution of European experts in international standardisation through support by providing grants for planned contributions of successful applications of experts, and (ii) an online observatory of published standards and ongoing standardisation activities in the areas mentioned before. This observatory (called Standards Watch) is accessible through the project's web site and open for contributions and comments from registered users. As part of the effort for the Standards Watch the projects has prepared a comprehensive analysis of the international standardisation landscape in the AI field, that comprises a description of the ICT standards and ongoing work at international level in the field of AI across the standardisation organisations already active in the field. In this article we will present results of our work where we have analysed the work of the 5 international and European Standards Development Organisations (SDOs) IEEE,1 ISO/IEC,2 ITU-T,3 ETSI4 and CEN-CENELEC5 developing standards in the field of AI. The first 4 bodies have already been active several years in AI standardisation at the time of writing this article. CEN-CENELEC has launched a focu

关键词： Watches

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