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The role of saturated thermal conduction in shaping electric current dynamics in jet-launching disks

Journal of High Energy Astrophysics 2025年 47卷

作者： Rezgui, Ghassen Preiner, Reinhold Department of Physics Faculty of Sciences of Tunis University of Tunis El Manar Campus Universitaire Tunis El Manar 2092 Tunisia Institute of Computer Graphics and Knowledge Visualization Graz University of Technology Inffeldgasse 16c Graz A-8010 Austria

This study investigates the dynamics of jet formation from a viscous, resistive accretion disk around a young stellar object using MHD simulations with the PLUTO code. We conducted an in-depth analysis of electric currents from various perspectives to elucidate how their dynamics, influenced by saturated thermal conduction, impact jet acceleration and collimation processes. Our simulations confirm the butterfly topology of electric current lines, as predicted by earlier analytic models. Crucially, increasing the saturation parameter ϕ_s alters the current line topology: higher saturation enhances collimation in the inner disk regions while inducing decollimation in the outer regions. By the end of our simulations (t=700, ∼112 rotational periods), higher ϕ_s results in a faster and more collimated jet compared to its lower ϕ_s counterpart, whereas at earlier times (t=200, ∼32 rotational periods), the jet exhibits lower acceleration despite enhanced collimation. In our reference case, we find that the electric current lines connect the launching region to the Alfvén and fast magnetosonic surfaces from early times, confirming the effectiveness of the acceleration mechanism at the onset of jet formation. Our study reveals that the upper jet regions are transitioning toward Kelvin–Helmholtz instability (KHI), while the jet base continues to exhibit wave activity. At t=700, doubling the saturation parameter reduces these oscillations and suppresses KHI, indicating faster plasma propagation. Analysis of the vertical profile of the current density, J_z, shows a clear correlation between increased saturation and both enhanced jet acceleration and current density. Furthermore, the ratio of electric currents at the Alfvén point, I_A, and sub-magnetosonic point, I_sm, indicates that higher saturation significantly improves the efficiency of matter propulsion and energy transfer within the jet. © 2025 Elsevier B.V.

关键词： Electric current Jet dynamics Magnetohydrodynamics simulations Saturated thermal conduction Young stellar objects

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End-to-end Color 3D reproduction of cultural heritage artifacts: Roseninsel replicas

End-to-end Color 3D reproduction of cultural heritage artifa...

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2019 Eurographics Workshop on graphics and Cultural Heritage, GCH 2019

作者： Domajnko, M. Tanksale, T. Tausch, R. Ritz, M. Knuth, M. Santos, P. Fellner, D.W. TU Darmstadt and Fraunhofer Institute for Computer Graphics Research Germany Graz University of Technology Institute of Computer Graphics and Knowledge Visualization Austria

ISBN: (纸本)9783038680826

Planning exhibitions of cultural artifacts is always challenging. Artifacts can be very sensitive to the environment and therefore their display can be risky. One way to circumvent this is to build replicas of these artifacts. Here, 3D digitization and reproduction, either physical via 3D printing or virtual, using computer graphics, can be the method of choice. For this use case we present a workflow, from photogrammetric acquisition in challenging environments to representation of the acquired 3D models in different ways, such as online visualization and color 3D printed replicas. This work can also be seen as a first step towards establishing a workflow for full color end-to-end reproduction of artifacts. Our workflow was applied on cultural artifacts found around the "Roseninsel" (Rose Island), an island in Lake Starnberg (Bavaria), in collaboration with the Bavarian State Archaeological Collection in Munich. We demonstrate the results of the end-to-end reproduction workflow leading to virtual replicas (online 3D visualization, virtual and augmented reality) and physical replicas (3D printed objects). In addition, we discuss potential optimizations and briefly present an improved state-of-the-art 3D digitization system for fully autonomous acquisition of geometry and colors of cultural heritage objects. © 2019 Eurographics Association.

关键词： Color

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Automated 3D mass digitization for the GLAM sector

Automated 3D mass digitization for the GLAM sector

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Archiving 2020 Online: Digitization, Preservation, and Access

作者： Santos, Pedro Tausch, Reimar Domajnko, Matevz Ritz, Martin Knuth, Martin Fellner, Dieter Fraunhofer Institute for Computer Graphics Research TU-Darmstadt Germany Graz University of Technology Institute of Computer Graphics and Knowledge Visualization Austria

The European Cultural Heritage Strategy for the 21st century has led to an increased demand for fast, efficient and faithful 3D digitization technologies for cultural heritage artefacts. Yet, unlike the digital acquisition of cultural goods in 2D which is widely used and automated today, 3D digitization often still requires significant manual intervention, time and money. To overcome this, the authors have developed CultLab3D, the world's first fully automatic 3D mass digitization technology for collections of three-dimensional objects. 3D scanning robots such as the CultArm3D-P are specifically designed to automate the entire 3D digitization process thus allowing to capture and archive objects on a large-scale and produce highly accurate photo-realistic representations. © 2020 Society for Imaging Science and Technology

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Bridging the Distance in Education: Design and Implementation of a Synchronous, Browser-Based VR Remote Teaching Tool

Bridging the Distance in Education: Design and Implementatio...

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45th Annual Conference on European Association for computer graphics, EUROgraphics 2024

作者： Pehlić, Abdulmelik Augsdörfer, Ursula Graz University of Technology Institute of Computer Graphics and Knowledge Visualization Austria

ISBN: (纸本)9783038682387

The rapid shift to remote education has presented numerous challenges for educators and students alike. Virtual Reality (VR) has emerged as a promising solution, offering immersive and interactive learning experiences. We design and implement a synchronous, browser-based VR teaching tool. The tool is compatible with budget VR equipment and enables meaningful engagement between teachers and students in a virtual setting, as well as active participation and interaction across a range of platforms, thus solving a range of disadvantages of current approaches. © 2024 The Authors.

关键词： Virtual environments

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A repository for 3D model production and interpretation in culture and beyond 11

A repository for 3D model production and interpretation in c...

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11th International Symposium on Virtual Reality, Archaeology and Intelligent Cultural Heritage, VAST 2010

作者： Doerr, M. Tzompanaki, K. Theodoridou, M. Georgis, Ch. Axaridou, A. Havemann, S. Institute of Computer Science FORTH Crete Greece Institute of Computer Graphics and Knowledge Visualization Graz University of Technology Austria

ISBN: (纸本)9783905674293

In order to support the work of researchers in the production, processing and interpretation of complex digital objects and the dissemination of valuable and diverse information to a broad spectrum of audience there is need for an integrated high performance environment that will combine knowledge base features with content management and information retrieval (IR) technologies. In this paper we describe the design and implementation of an integrated repository to ingest, store, manipulate, and export 3D Models, their related digital objects and metadata and to enable efficient access, use, reuse and preservation of the information, ensuring referential and semantic integrity. The repository design is based on an integrated coherent conceptual schema that models complex metadata regarding provenance information, structured models, formats, compatibility of 3D models, historical events and real world objects. This repository is not implemented just to be a storage location for digital objects;it is meant to be a working integrated platform for distant users who participate in a process chain consisting of several steps. A first prototype, in the field of Cultural Heritage, has already been implemented in the context of 3D-COFORM project, an integrated research project funded by the European Community's Seventh Framework Programme (FP7/2007-2013, no 231809) and the results are satisfactory, proving the feasibility of the design decisions which are absolutely new, ambitious, and extraordinarily generic for e-science. © The Eurographics Association 2010.

关键词： Metadata

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Elastic flattening of painted pottery surfaces

Elastic flattening of painted pottery surfaces

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2018 Eurographics Workshop on graphics and Cultural Heritage, GCH 2018

作者： Preiner, Reinhold Karl, Stephan Baye, Paul Schreck, Tobias Graz University of Technology Institute of Computer Graphics and Knowledge Visualization Austria University of Graz Department of Archaeology Austria

ISBN: (纸本)9783038680574

Generating flat images from paintings on curved surfaces is an important task in Archaeological analysis of ancient pottery. It allows comparing styles and painting techniques, e.g, for style and workshop attribution, and serves as basis for domain publications which typically use 2d images. To obtain such flat images from scanned textured 3d models of the pottery objects, current practice is to perform so-called rollouts using approximating shape primitives like cones or spheres, onto which the mesh surfaces are projected. While this process provides in intuitive deformation metaphor for the users, it naturally introduces unwanted distortions in the mapping of the surface, especially for vessels with high-curvature profiles. In this work, we perform an elastic flattening of these projected meshes, where stretch energy is minimized by simulating a physical relaxation process on a damped elastic spring model. We propose an intuitive contraction-directed physical setup which allows for an efficient relaxation while ensuring a controlled convergence. Our work has shown to produce images of significantly improved suitability for domain experts' tasks like interpretation, documentation and attribution of ancient pottery. © 2018 GCH 2018 - Eurographics Workshop on graphics and Cultural Heritage. All rights reserved.

关键词： Textures

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Robust shape fitting and semantic enrichment 21

Robust shape fitting and semantic enrichment

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21st International CIPA Symposium 2007

作者： Ullrich, Torsten Fellner, Dieter W. Institute of Computer Graphics and Knowledge Visualization Graz University of Technology Inffeldgasse 16c GrazA-8010 Austria

A robust fitting and reconstruction algorithm has to cope with two major problems. First of all it has to be able to deal with noisy input data and outliers. Furthermore it should be capable of handling multiple data set mixtures. The decreasing exponential approach is robust towards outliers and multiple data set mixtures. It is able to fit a parametric model to a given point cloud. As parametric models use a description which may not only contain a generative shape but information about the inner structure of an object, the presented approach can enrich measured data with an ideal description. This technique offers a wide range of applications. © 2007 International Society for Photogrammetry and Remote Sensing. All rights reserved.

关键词： Mixtures

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Using SVG for an user-interface to a digital library

Using SVG for an user-interface to a digital library

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10th International Conference on Electronic Publishing, ELPUB 2006

作者： Krottmaier, Harald Scherngell, Christian Institute for Computer Graphics and Knowledge Visualization Graz University of Technology Infeldgasse 16c 8010 Graz Austria

ISBN: (纸本)9789541600405

Interfaces for users on the web are usually created using standard HTML-technologies. Although dynamic text-based features are widely available on the web (e.g. by using DHTML) there are still some limitations in the user experience when using dynamic graphical elements. In this article we focus on a GUI-prototype using Scalable Vector graphics (SVG) as an interface to an existing Digital Library. First we describe the current situation of the running system and explain some of the limitations in the GUI. Thereafter we compare the document-format with other electronic formats. An overview of the prototype and a description of the used framework will be given in the main section of this article. Finally we are going to show an improved version of a search task using an SVG-category viewer. The currently supported SVG-recommendation (SVG 1.1) by the SVG-plugins have some limitations. The upcoming release will solve some of the problems and introduce new features related to data-handling and database access. An outlook of these new features and lessons learned in implementing the prototype will close the article.

关键词： Graphical user interfaces

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Implicit mesh generation using volumetric subdivision 13

Implicit mesh generation using volumetric subdivision

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13th Workshop on Virtual Reality Interactions and Physical Simulations, VRIPHYS 2017

作者： Altenhofen, C. Schuwirth, F. Stork, A. Fellner, D. TU Darmstadt Germany Fraunhofer IGD Germany Graz University of Technology Institute of Computer Graphics and Knowledge Visualization Austria

ISBN: (纸本)9783038680321

In this paper, we present a novel approach for a tighter integration of 3D modeling and physically-based simulation. Instead of modeling 3D objects as surface models, we use a volumetric subdivision representation. Volumetric modeling operations allow designing 3D objects in similar ways as with surface-based modeling tools. Encoding the volumetric information already in the design mesh drastically simplifies and speeds up the mesh generation process for simulation. The transition between design, simulation and back to design is consistent and computationally cheap. Since the subdivision and mesh generation can be expressed as a precomputable matrix-vector multiplication, iteration times can be greatly reduced compared to common modeling and simulation setups. Therefore, this approach is especially well suited for early-stage modeling or optimization use cases, where many geometric changes are made in a short time and their physical effect on the model has to be evaluated frequently. To test our approach, we created, simulated and adapted several 3D models. Additionally, we measured and evaluated the timings for generating and applying the matrices for different subdivision levels. For comparison, we also measured the tetrahedral meshing functionality offered by CGAL for similar numbers of elements. For changing topology, our implicit meshing approach proves to be up to 70 times faster than creating the tetrahedral mesh only based on the outer surface. Without changing the topology and by precomputing the matrices, we achieve a speed-up of up to 2800. © 2017 The Author(s) Eurographics Proceedings 2017 The Eurographics Association.

关键词： Mesh generation

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Efficient Point Cloud Skeletonization with Locally Adaptive L1-Medial Projection 30

Efficient Point Cloud Skeletonization with Locally Adaptive ...

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30th International Conference in Central Europe on computer graphics, visualization and computer Vision, WSCG 2022

作者： Lengauer, Stefan Houska, Peter Preiner, Reinhold Institute of Computer Graphics and Knowledge Visualization Graz University of Technology Inffeldgasse 16c Graz8010 Austria

ISBN: (纸本)9788086943336

3D line skeletons are simplistic representations of a shape's topology which are used for a wide variety of geometry-processing tasks, including shape recognition, retrieval, and reconstruction. Numerous methods have been proposed to generate a skeleton from a given 3D shape. While mesh-based methods can exploit existing knowledge about the shape's topology and orientation, point-based techniques often resort to precomputed per-point normals to ensure robustness. In contrast, previously proposed techniques for unprocessed point clouds either exhibit inferior robustness or require expensive operations, which in turn increases computation time. In this paper, we present a new and highly efficient skeletonization approach for raw point cloud data, which produces overall competitive results compared to previous work, while exhibiting much lower computation times. Our algorithm performs robustly in the face of noisy and fragmented inputs, as they are usually obtained from real-world 3D scans. We achieve this by first transferring the input point cloud into a Gaussian mixture model (GMM), obtaining a more compact representation of the surface. Our method then iteratively projects a small subset of the points into local L1-medians, yielding a rough outline of the shape's skeleton. Finally, we present a new branch detection technique to obtain a coherent line skeleton from those projected points. We demonstrate the capabilities of our proposed method by extracting the line skeletons of a diverse selection of input shapes and evaluating their visual appearance as well as the efficiency compared to alternative state-of-the-art methods. © 2022 University of West Bohemia. All rights reserved.

关键词： Topology

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