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Pseudo-Newtonian simulation of a thin accretion disk around a Reissner-Nordström naked singularity

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arXiv 2025年

作者： Čemeljić, Miljenko Kluzniak, Wlodek Mishra, Ruchi Wielgus, Maciek College of Astronomy and Natural Sciences SGMK Nicolaus Copernicus Superior School Nowogrodzka 47A Warsaw00-695 Poland Nicolaus Copernicus Astronomical Center The Polish Academy of Sciences Bartycka 18 Warsaw00-716 Poland Research Center for Computational Physics and Data Processing Institute of Physics Silesian University in Opava Bezručovo nám. 13 OpavaCZ-746-01 Czech Republic Academia Sinica Institute of Astronomy and Astrophysics P.O. Box 23-141 Taipei106 Taiwan Instituto de Astrofísica de Andalucía-CSIC Glorieta de la Astronomía s/n GranadaE-18008 Spain

We present the first numerical simulations of a thin accretion disk around a Reissner-Nordström (RN) naked singularity (a charged point mass). The gravity of the RN naked singularity is modeled with a pseudo-Newtonian potential that reproduces exactly the radial dependence of the RN Keplerian orbital frequency;in particular, orbital angular velocity vanishes at the zero gravity radius and has a maximum at 4/3 of that radius. Angular momentum is transported outwards by viscous stresses only outside the location of this maximum. Nonetheless, even at that radius, accretion proceeds at higher latitudes, the disk having thickened there owing to excess pressure. The accretion stops at a certain distance away from the singularity, with the material accumulating in a toroidal structure close to the zero-gravity sphere. The shape of the structure obtained in our simulations is reminiscent of fluid figures of equilibrium analytically derived in full general relativity for the RN singularity. The presence of a rotating ring, such as the one found in our simulations, could be an observational signature of a naked singularity. For charge to mass ratios close to but larger than unity, the inner edge of the quasi-toroidal inner accretion structure would be located well within the Schwarzschild marginally stable orbit (ISCO), and the maximum orbital frequency in thin accretion disks would be much higher than the Schwarzschild ISCO frequency. © 2025, CC BY.

关键词： Relativity

Accretion disc backflow in resistive MHD simulations

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arXiv 2022年

作者： Mishra, Ruchi Čemeljić, M. Kluźniak, W. Nicolaus Copernicus Astronomical Center The Polish Academy of Sciences Bartycka 18 Warsaw00-716 Poland Academia Sinica Institute of Astronomy and Astrophysics P.O. Box 23-141 Taipei106 Taiwan Research Centre for Computational Physics and Data Processing Silesian University in Opava Bezručovo nám. 13 OpavaCZ-74601 Czech Republic

We investigate accretion onto a central star, with the size, rotation rate, and magnetic dipole of a young stellar object, to study the flow pattern (velocity and density) of the fluid within and outside of the disc. We perform resistive MHD simulations of thin α-discs, varying the parameters such as the stellar rotation rate and magnetic field, and (anomalous) coefficients of viscosity and resistivity in the disc. To provide a benchmark for the results and to compare with known analytic results, we also perform purely hydrodynamic simulations (HD) for the same problem. Although obtained for a different situation with differing inner boundary condition, the disc structure in the HD simulations closely follows the analytic solution of Kluźniak & Kita (2000)—in particular a region of "midplane" backflow exists in the right range of radii, depending on the viscosity parameter. In the MHD solutions, whenever the magnetic Prandtl number does not exceed a certain critical value, the midplane backflow exists throughout the accretion disc, extending all the way down to the inner transition zone where the disc transitions to a magnetic funnel flow. For values of the magnetic Prandtl number close to the critical value the backflow and the inner disc undergo a quasiperiodic radial oscillation, otherwise the backflow is steady, as is the disc solution. From our results, supplemented by our reading of the literature, we conclude that midplane backflow is a real feature of at least some accretion discs, whether HD α-discs or MHD discs, including ones driven by MRI turbulence. Copyright © 2022, The Authors. All rights reserved.

关键词： Magnetohydrodynamics

Learning ECG Signal Features Without Backpropagation Using Linear Laws

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arXiv 2023年

作者： Pósfay, Péter Kurbucz, Marcell T. Kovács, Péter Jakovác, Antal Department of Computational Sciences Institute for Particle and Nuclear Physics HUN-REN Wigner Research Centre for Physics 29-33 Konkoly-Thege Miklós Street BudapestH-1121 Hungary Department of Statistics Institute of Data Analytics and Information Systems Corvinus University of Budapest 8 Fővám Square BudapestH-1093 Hungary Department of Numerical Analysis Eötvös Loránd University 1/c. Pázmány Péter sétány BudapestH-1117 Hungary

This paper introduces LLT-ECG, a novel method for electrocardiogram (ECG) signal classification that leverages concepts from theoretical physics to automatically generate features from time series data. Unlike traditional deep learning approaches, LLT-ECG operates in a forward manner, eliminating the need for backpropagation and hyperparameter tuning. By identifying linear laws that capture shared patterns within specific classes, the proposed method constructs a compact and verifiable representation, enhancing the effectiveness of downstream classifiers. We demonstrate LLT-ECG’s state-of-the-art performance on real-world ECG datasets from PhysioNet, underscoring its potential for medical applications where speed and verifiability are *** Codes 62H30, 68T10, 62M10, 92C50 © 2023, CC BY.

关键词： Contrastive Learning

PANDORA Project for the study of photonuclear reactions below

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The European Physical Journal A 2023年第9期59卷 1-21页

作者： Tamii, A. Pellegri, L. Söderström, P.-A. Allard, D. Goriely, S. Inakura, T. Khan, E. Kido, E. Kimura, M. Litvinova, E. Nagataki, S. Neumann-Cosel, P. von Pietralla, N. Shimizu, N. Tsoneva, N. Utsuno, Y. Adachi, S. Adsley, P. Bahini, A. Balabanski, D. Baret, B. Bekker, J. A. C. Binda, S. D. Boicu, E. Bracco, A. Brandherm, I. Brezeanu, M. Brummer, J. W. Camera, F. Crespi, F. C. L. Dalal, R. Donaldson, L. M. Fujikawa, Y. Furuno, T. Haoning, H. Higuchi, R. Honda, Y. Gavrilescu, A. Inoue, A. Isaak, J. Jivan, H. Jones, P. Jongile, S. Just, O. Kawabata, T. Khumalo, T. Kiener, J. Kleemann, J. Kobayashi, N. Koshio, Y. Kuşoğlu, A. Li, K. C. W. Malatji, K. L. Molaeng, R. E. Motoki, H. Murata, M. Netshiya, A. A. Neveling, R. Niina, R. Okamoto, S. Ota, S. Papst, O. Parizot, E. Petruse, T. Reen, M. S. Ring, P. Sakanashi, K. Sideras-Haddad, E. Siem, S. Spall, M. Suda, T. Sudo, T. Taniguchi, Y. Tatischeff, V. Utsunomiya, H. Wang, H. Werner, V. Wibowo, H. Wiedeking, M. Wieland, O. Xu, Y. Yang, Z. H. Research Center for Nuclear Physics (RCNP) Osaka University Ibaraki Japan Institute for Radiation Sciences (IRS) Osaka University Toyonaka Japan Department of Physics Osaka University Toyonaka Japan School of Physics University of the Witwatersrand Johannesburg South Africa Themba Laboratory for Accelerator Based Sciences Somerset West South Africa Extreme Light Infrastructure-Nuclear Physics (ELI-NP)/Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH) Bucharest-Măgurele Romania Laboratoire Astroparticule et Cosmologie CNRS Université Paris Cité Paris France Institut d’Astronomie et d’Astrophysique Université Libre de Bruxelles Brussels Belgium Tokyo Institute of Technology Tokyo Japan IJCLab CNRS/IN2P3 Université Paris-Saclay Orsay Cedex France RIKEN Wako Japan Department of Physics Hokkaido University Sapporo Japan Faculty of Science Japan and Nuclear Reaction Data Centre Hokkaido University Sapporo Japan Department of Physics Western Michigan University Kalamazoo USA Institut für Kernphysik Technische Universität Darmstadt Darmstadt Germany Center for Computational Sciences University of Tsukuba Tsukuba Japan Advanced Science Research Center Japan Atomic Energy Agency Tokai Japan Cyclotron and Radioisotope Center Tohoku University Sendai Japan Department of Physics and Astronomy Texas A &M University College Station USA Cyclotron Institute Texas A &M University College Station USA University of Bucharest Bucharest-Măgurele Romania Dipartimento di Fisica dell’Università degli Studi di Milano Milan Italy INFN Sezione di Milano Milan Italy Guru Jambheshwar University of Science and Technology Hisar India Department of Physics Kyoto University Kyoto Japan Politehnica University of Bucharest Bucharest Romania GSI Helmholtzzentrum für Schwerionenforschung Darmstadt Germany Department of Physics Okayama University Okayama Japan Department of Physics Faculty of Science Istanbul University Istanbul Turkey Depart

Photonuclear reactions of light nuclei below a mass of $$A=60$$ are planned to be studied experimentally and theoretically with the PANDORA (Photo-Absorption of Nuclei and Decay Observation for Reactions in Astrophysics) project. Two experimental methods, virtual photon excitation by proton scattering and real photo absorption by a high-brilliance $$\gamma $$ -ray beam produced by laser Compton scattering, will be applied to measure the photoabsorption cross sections and decay branching ratio of each decay channel as a function of the photon energy. Several nuclear models, e.g. anti-symmetrized molecular dynamics, mean-field and beyond-mean-field models, a large-scale shell model, and ab initio models, will be employed to predict the photonuclear reactions. The uncertainty in the model predictions will be evaluated based on the discrepancies between the model predictions and experimental data. The data and predictions will be implemented in the general reaction calculation code, TALYS. The results will be applied to the simulation of the photo-disintegration process of ultra-high-energy cosmic rays in inter-galactic propagation.

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Inner dusty regions of protoplanetary discs - III. The role of non-radial radiation pressure in dust dynamics

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arXiv 2024年

作者： Vinković, Dejan Čemeljić, Miljenko Science and Society Synergy Institute Bana Josipa Jelačića 22 ČakovecHR-40000 Croatia Oraclum Intelligence Systems Ltd. 23 Arnold Close Hauxton CambridgeCB22 5FN United Kingdom SGMK Nicolaus Copernicus Superior School College of Astronomy and Natural Sciences Nowogrodzka 47A Warsaw00-697 Poland Research Centre for Computational Physics and Data Processing Institute of Physics Silesian University in Opava Bezručovo nám. 13 OpavaCZ-74601 Czech Republic Nicolaus Copernicus Astronomical Center Polish Academy of Sciences Bartycka 18 Warsaw00-716 Poland Academia Sinica Institute of Astronomy and Astrophysics P.O. Box 23-141 Taipei106 Taiwan

We explore dynamical behaviour of dust particles that populate the surface of inner optically thick protoplanetary discs. This is a disc region with the hottest dust and of a great importance for planet formation and dust evolution, but we still struggle to understand all the forces that shape this environment. In our approach we combine results from two separate numerical studies - one is the wind velocity and density distributions obtained from magnetohydrodynamical simulations of accretion discs, and the other is a high-resolution multigrain dust radiation transfer. In our previous paper in the series, we described the methodology for utilising these results as an environmental input for the integration of dust trajectories driven by gravity, gas drag, and radiation pressure. Now we have two improvements - we incorporate time changes in the wind density and velocity, and we implement the non-radial radiation pressure force. We applied our analysis on Herbig Ae and T Tau stars. We confirm that the radiation pressure force can lead to dust outflow, especially in the case of more luminous stars. Additionally, it opposes dust accretion at the inner disc edge and reduces dust settling. These effects are enhanced by the disc wind, especially in the zone where the stellar and the disc magnetic fields meet. Our results suggest that dust grains can stay in the hottest disc region for an extended period and then can end up ejected into the outer disc regions. Copyright © 2024, The Authors. All rights reserved.

关键词： Dust

Unsupervised Behaviour Analysis of News Consumption in Turkish Media

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arXiv 2022年

作者： Makaroğlu, Didem Cakir, Altan Töreyin, Behçet Uğur Demirören Teknoloji A.S. İstanbul Turkey Signal Processing for Computational Intelligence Group Informatics Institute Istanbul Technical University Istanbul Turkey Physics Engineering Faculty of Science and Letters Istanbul Technical University Istanbul Turkey Istanbul Technical University Artificial Intelligence Data Science Research and Application Center Istanbul Turkey

Clickstream data, which come with a massive volume generated by human activities on websites, have become a prominent feature for identifying readers’ characteristics by newsrooms after the digitization of news outlets. It is essential to have elastic architectures to process the streaming data, particularly for unprecedented traffic, enabling conducting more comprehensive analyses, such as recommending mostly related articles to readers. Although the nature of clickstream data has a similar logic within websites, it has inherent limitations to recognize human behaviours when looking from a broad perspective, which brings the need to limit the problem in niche areas. This study investigates the anonymized readers’ click activities on the organizations’ websites to identify news consumption patterns following referrals from Twitter, who incidentally reach but propensity is mainly routed news content. The investigation is widened to a broad perspective by linking the log data with news content to enrich the insights rather than sticking into the web journey. Methodologies for ensemble cluster analysis with mixed-type embedding strategies are applied and compared to find similar reader groups and interests independent of time. Various internal validation perspectives are used to determine the optimality of the quality of clusters, where the Calinski Harabasz Index (CHI) is found to give a generalizable result. Our findings demonstrate that clustering a mixed-type dataset approaches the optimal internal validation scores, which we define to discriminate the clusters and algorithms considering applied strategies, when embedded by Uniform Manifold Approximation and Projection (UMAP) and using a consensus function as a key to access the most applicable hyper parameter configurations in the given ensemble rather than using consensus function results directly. Evaluation of the resulting clusters highlights specific clusters repeatedly present in the separated monthly sample

关键词： Digital storage

Feature space reduction method for ultrahigh-dimensional, multiclass data: Random forest-based multiround screening (RFMS)

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arXiv 2023年

作者： Hanczár, Gergely Stippinger, Marcell Hanák, Dávid Kurbucz, Marcell T. Törteli, Olivér M. Chripkó, Ágnes Somogyvári, Zoltán Cursor Insight Ltd. 20-22 Wenlock Road LondonN17GU United Kingdom Department of Computational Sciences Wigner Research Centre for Physics 29-33 Konkoly Thege Miklós Street BudapestH-1121 Hungary Institute of Data Analytics and Information Systems Corvinus University of Budapest 8 Fővám Square H-1093 Hungary

In recent years, numerous screening methods have been published for ultrahigh-dimensional data that contain hundreds of thousands of features;however, most of these features cannot handle data with thousands of classes. Prediction models built to authenticate users based on multichannel biometric data result in this type of problem. In this study, we present a novel method known as random forest-based multiround screening (RFMS) that can be effectively applied under such circumstances. The proposed algorithm divides the feature space into small subsets and executes a series of partial model builds. These partial models are used to implement tournament-based sorting and the selection of features based on their importance. To benchmark RFMS, a synthetic biometric feature space generator known as BiometricBlender is employed. Based on the results, the RFMS is on par with industry-standard feature screening methods while simultaneously possessing many advantages over these *** Codes 62G05, 68T01, 62H30 © 2023, CC BY.

关键词： Authentication

Manifestation of kaonium in the e+e− → K+K− process

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arXiv 2020年

作者： Lichard, Peter Institute of Physics Research Centre for Computational Physics and Data Processing Silesian University in Opava Opava746 01 Czech Republic Institute of Experimental and Applied Physics Czech Technical University in Prague Prague128 00 Czech Republic

We analyze the precise data obtained by the CMD-3 experiment on the e+e− annihilation into two charged kaons in the vicinity of the φ peak. A perfect fit is obtained only if a pole on the real axis below the reaction threshold is assumed. This can be interpreted as proof of the existence of the 2p-state of kaonium, a compound of K+ and K−. To determine the binding energy, more data points with the same, or better, precision would be needed. The possibility of discovering 2p kaonium in the e+e− → π+π− process is discussed. The indication of the 2p-state of K0-onium on the basis of the (formula presented) data is inconclusive. Copyright © 2020, The Authors. All rights reserved.

关键词： Binding energy

Possible manifestation of the 2p pionium in particle physics processes

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arXiv 2020年

We suggest a few particle physics processes in which excited 2p pionium A′2π may be observed. They include the e+e− → π+π− annihilation, the V 0 → π0+− and K± → π±+− ( = e, µ) decays, and the photoproduction of two neutral pions from nucleons. We analyze available experimental data and find that they, in some cases, indicate the presence of 2p pionium, but do not provide definite proof. Copyright © 2020, The Authors. All rights reserved.

关键词： Hadrons