ZIB

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Digitale Medien

A measurement of τ polarization in Z^0 decays (1992-8977)

L3 Collaboration

Amsterdam : Elsevier

Physics Letters B 294 (1992), S. 466-478

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ISSN: 0370-2693

Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Thema: Physik

Materialart: Digitale Medien

URL: http://linkinghub.elsevier.com/retrieve/pii/0370-2693(92)91549-O

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2

Digitale Medien

Measurement of the average lifetime of b hadrons (1993-4325)

L3 Collaboration

Amsterdam : Elsevier

Physics Letters B 317 (1993), S. 474-484

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ISSN: 0370-2693

Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Thema: Physik

Materialart: Digitale Medien

URL: http://linkinghub.elsevier.com/retrieve/pii/0370-2693(93)91027-K

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3

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Γ-convergence of Onsager–Machlup functionals: I. With applications to maximum a posteriori estimation in Bayesian inverse problems (2022)

Ayanbayev, Birzhan ; Klebanov, Ilja ; Lie, Han Cheng ; [weitere]

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Publikationsdatum: 2022-03-11

Sprache: Englisch

Materialart: article , doc-type:article

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4

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Γ-convergence of Onsager–Machlup functionals: II. Infinite product measures on Banach spaces (2022)

Ayanbayev, Birzhan ; Klebanov, Ilja ; Lie, Han Cheng ; [weitere]

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Publikationsdatum: 2022-03-11

Sprache: Englisch

Materialart: article , doc-type:article

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5

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Annual Report 2019 (2022)

Konrad-Zuse-Zentrum für Informationstechnik Berlin

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Publikationsdatum: 2022-01-25

Sprache: Englisch

Materialart: annualzib , doc-type:report

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6

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Spontaneous trail formation in populations of auto-chemotactic walkers (2022)

Mokhtari, Zahra ; Patterson, Robert I. A. ; Höfling, Felix

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Publikationsdatum: 2022-02-03

Sprache: Englisch

Materialart: article , doc-type:article

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7

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Annual Report 2020 (2022)

Konrad-Zuse-Zentrum für Informationstechnik Berlin

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Publikationsdatum: 2022-01-25

Sprache: Englisch

Materialart: annualzib , doc-type:report

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8

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Archivierungsstrategie für audiovisuelles Material (2022)

Dittmann, Antje ; Hasler, Tim ; Oltmanns, Elias

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Publikationsdatum: 2022-03-14

Beschreibung: Im Rahmen ihrer Strategie zur Langzeitarchivierung forscht die Deutsche Kinemathek in einer Kooperation mit dem Zuse-Institut Berlin (ZIB) an der digitalen Langzeitarchivierung von AV-Materialien. Ausgangspunkt des Projektes sind die enormen Dateigrößen und die heterogenen Dateiformate, die einem Werk und einer Fassung zugeordnet werden müssen. Die Verwendung von persistenten Identifikatoren stellt den Lösungsansatz dar.

Sprache: Deutsch

Materialart: reportzib , doc-type:preprint

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9

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An overview of graph covering and partitioning (2022)

Schwartz, Stephan

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Publikationsdatum: 2022-03-29

Beschreibung: While graph covering is a fundamental and well-studied problem, this field lacks a broad and unified literature review. The holistic overview of graph covering given in this article attempts to close this gap. The focus lies on a characterization and classification of the different problems discussed in the literature. In addition, notable results and common approaches are also included. Whenever appropriate, this review extends to the corresponding partitioning problems.

Sprache: Englisch

Materialart: article , doc-type:article

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10

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Timetable Optimization for a Moving Block System (2022)

Schlechte, Thomas ; Borndörfer, Ralf ; Denißen, Jonas ; [weitere]

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Publikationsdatum: 2022-03-30

Beschreibung: We present an optimization model which is capable of routing and ordering trains on a microscopic level under a moving block regime. Based on a general timetabling definition (GTTP) that allows the plug in of arbitrarily detailed methods to compute running and headway times, we describe a layered graph approach using velocity expansion, and develop a mixed integer linear programming formulation. Finally, we present promising results for a German corridor scenario with mixed traffic, indicating that applying branch-and-cut to our model is able to solve reasonably sized instances with up to hundred trains to optimality.

Sprache: Englisch

Materialart: article , doc-type:article

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11

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A quantum key distribution testbed using a plug&play telecom-wavelength single-photon source (2022)

Gao, Timm ; Rickert, Lucas ; Urban, Felix ; [weitere]

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Publikationsdatum: 2022-06-13

Sprache: Englisch

Materialart: article , doc-type:article

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12

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Numerical optimization of single-mode fiber- coupled single-photon sources based on semiconductor quantum dots (2022)

Bremer, Lucas ; Jimenez, Carlos ; Thiele, Simon ; [weitere]

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Publikationsdatum: 2022-06-13

Sprache: Englisch

Materialart: article , doc-type:article

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13

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Improving perovskite/silicon tandem solar cells with optical simulations (2022)

Jäger, Klaus ; Sutter, Johannes ; Tockhorn, Philipp ; [weitere]

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Publikationsdatum: 2022-06-13

Sprache: Englisch

Materialart: conferenceobject , doc-type:conferenceObject

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14

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Source code and simulation results for nanoantennas supporting an enhanced Purcell factor due to interfering resonances (2022)

Colom, Remi ; Binkowski, Felix ; Betz, Fridtjof ; [weitere]

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Publikationsdatum: 2022-06-13

Sprache: Englisch

Materialart: researchdata , doc-type:ResearchData

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15

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Timetable merging for the Periodic Event Scheduling Problem (2022)

Lindner, Niels ; Liebchen, Christian

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Publikationsdatum: 2022-04-28

Beschreibung: We propose a new mixed integer programming based heuristic for computing new benchmark primal solutions for instances of the PESPlib. The PESPlib is a collection of instances for the Periodic Event Scheduling Problem (PESP), comprising periodic timetabling problems inspired by real-world railway timetabling settings, and attracting several international research teams during the last years. We describe two strategies to merge a set of good periodic timetables. These make use of the instance structure and minimum weight cycle bases, finally leading to restricted mixed integer programming formulations with tighter variable bounds. Implementing this timetable merging approach in a concurrent solver, we improve the objective values of the best known solutions for the smallest and largest PESPlib instances by 1.7 and 4.3 percent, respectively.

Sprache: Englisch

Materialart: article , doc-type:article

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16

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Personal Digital Archiving: Eine neue Aufgabe für Öffentliche und Wissenschaftliche Bibliotheken (2022)

Zangerl, Lina Maria ; Peters-Kottig, Wolfgang ; Oßwald, Achim

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Publikationsdatum: 2022-04-25

Beschreibung: Die Sicherung und längerfristige Archivierung persönlich relevanter Dokumente und Dateien, in der Fachliteratur als Personal Digital Archiving (PDA) bezeichnet, ist eine für Privatpersonen zunehmend wichtiger werdende Aufgabe. Praktische Anleitungen und weiterführende Hinweise zur Umsetzung dieser Aufgabe gibt die auf unterschiedliche Nutzer:innenperspektiven ausgerichtete Webseite meinDigitalesArchiv.de, die seit 2020 von der nestor-AG PDA bereitgestellt wird. Mit den Informationen dieser Webseite können und sollten Bibliotheken und andere Einrichtungen, die Informationskompetenz vermitteln, Privatpersonen für die Sicherung ihrer persönlichen digitalen Daten sensibilisieren und schulen. Mit der Umsetzung dieser Aufgabe können Öffentliche wie Wissenschaftliche Bibliotheken zur Sicherung auch gesamtgesellschaftlich relevanter Erinnerungsbausteine beitragen.

Sprache: Deutsch

Materialart: article , doc-type:article

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17

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大規模二次割当問題への挑戦 (2022)

Fujii, Koichi ; Ito, Naoki ; Kim, Sunyoung ; [weitere]

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Publikationsdatum: 2022-05-13

Beschreibung: 二次割当問題は線形緩和が弱いことが知られ，強化のため多様な緩和手法が考案されているが，その一つである二重非負値計画緩和（ DNN 緩和）及びその解法として近年研究が進んでいるニュートン・ブラケット法を紹介し，それらに基づく分枝限定法の実装及び数値実験結果について報告する．

Sprache: Japanisch

Materialart: reportzib , doc-type:preprint

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18

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The tropical and zonotopal geometry of periodic timetables (2022)

Bortoletto, Enrico ; Lindner, Niels ; Masing, Berenike

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Publikationsdatum: 2022-05-10

Beschreibung: The Periodic Event Scheduling Problem (PESP) is the standard mathematical tool for optimizing periodic timetabling problems in public transport. A solution to PESP consists of three parts: a periodic timetable, a periodic tension, and integer periodic offset values. While the space of periodic tension has received much attention in the past, we explore geometric properties of the other two components, establishing novel connections between periodic timetabling and discrete geometry. Firstly, we study the space of feasible periodic timetables, and decompose it into polytropes, i.e., polytopes that are convex both classically and in the sense of tropical geometry. We then study this decomposition and use it to outline a new heuristic for PESP, based on the tropical neighbourhood of the polytropes. Secondly, we recognize that the space of fractional cycle offsets is in fact a zonotope. We relate its zonotopal tilings back to the hyperrectangle of fractional periodic tensions and to the tropical neighbourhood of the periodic timetable space. To conclude we also use this new understanding to give tight lower bounds on the minimum width of an integral cycle basis.

Sprache: Englisch

Materialart: reportzib , doc-type:preprint

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19

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Optimizing transient gas network control for challenging real-world instances using MIP-based heuristics (2022)

Hennings, Felix ; Hoppmann-Baum, Kai ; Zittel, Janina

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Publikationsdatum: 2022-05-24

Beschreibung: Optimizing the transient control of gas networks is a highly challenging task. The corresponding model incorporates the combinatorial complexity of determining the settings for the many active elements as well as the non-linear and non-convex nature of the physical and technical principles of gas transport. In this paper, we present the latest improvements of our ongoing work to solve this problem for real-world, large-scale problem instances: By adjusting our mixed-integer non-linear programming model regarding the gas compression capabilities in the network, we reflect the technical limits of the underlying units more accurately while maintaining a similar overall model size. In addition, we introduce a new algorithmic approach that is based on splitting the complexity of the problem by first finding assignments for discrete variables and then determining the continuous variables as locally optimal solution of the corresponding non-linear program. For the first task, we design multiple different heuristics based on concepts for general time-expanded optimization problems that find solutions by solving a sequence of sub-problems defined on reduced time horizons. To demonstrate the competitiveness of our approach, we test our algorithm on particularly challenging historic demand scenarios. The results show that high-quality solutions are obtained reliably within short solving times, making the algorithm well-suited to be applied at the core of time-critical industrial applications.

Sprache: Englisch

Materialart: reportzib , doc-type:preprint

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20

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Chiral Generation of Hot Carriers for Polarization-Sensitive Plasmonic Photocatalysis with Hybrid Nanostructures (2022)

Negrin-Montecelo, Yoel ; Movsesyan, Artur ; Gao, Jie ; [weitere]

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Publikationsdatum: 2022-06-13

Sprache: Englisch

Materialart: article , doc-type:article

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21

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Optical and Spin Properties of NV Center Ensembles in Diamond Nano-Pillars (2022)

Volkova, Kseniia ; Heupel, Julia ; Trofimov, Sergei ; [weitere]

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Publikationsdatum: 2022-06-13

Sprache: Englisch

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22

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Reconstructing phase aberrations for high-precision dimensional microscopy (2022)

Schneider, Philipp-Immanuel ; Manley, Phillip ; Krüger, Jan ; [weitere]

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Publikationsdatum: 2022-06-13

Sprache: Englisch

Materialart: article , doc-type:article

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23

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Visible wavelength spectral tuning of absorption and circular dichroism of DNA-assembled Au/Ag core-shell nanorod assemblies (2022)

Dass, Mihir ; Kuen, Lilli ; Posnjak, Gregor ; [weitere]

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Publikationsdatum: 2022-06-13

Sprache: Englisch

Materialart: article , doc-type:article

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24

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Toward maximally electromagnetically chiral scatterers at optical frequencies (2022)

Garcia Santiago, Xavier ; Hammerschmidt, Martin ; Sachs, Johannes ; [weitere]

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Publikationsdatum: 2022-06-15

Sprache: Englisch

Materialart: article , doc-type:article

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25

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Plasmonic nanocrystals with complex shapes for photocatalysis and growth: Contrasting anisotropic hot-electron generation with the photothermal effect (2022)

Movsesyan, Artur ; Santiago, Eva Yazmin ; Burger, Sven ; [weitere]

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Publikationsdatum: 2022-06-27

Sprache: Englisch

Materialart: article , doc-type:article

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26

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An analysis of the parameterized complexity of periodic timetabling (2022)

Lindner, Niels ; Reisch, Julian

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Publikationsdatum: 2022-08-08

Beschreibung: Public transportation networks are typically operated with a periodic timetable. The periodic event scheduling problem (PESP) is the standard mathematical modeling tool for periodic timetabling. PESP is a computationally very challenging problem: For example, solving the instances of the benchmarking library PESPlib to optimality seems out of reach. Since PESP can be solved in linear time on trees, and the treewidth is a rather small graph parameter in the networks of the PESPlib, it is a natural question to ask whether there are polynomial-time algorithms for input networks of bounded treewidth, or even better, fixed-parameter tractable algorithms. We show that deciding the feasibility of a PESP instance is NP-hard even when the treewidth is 2, the branchwidth is 2, or the carvingwidth is 3. Analogous results hold for the optimization of reduced PESP instances, where the feasibility problem is trivial. Moreover, we show W[1]-hardness of the general feasibility problem with respect to treewidth, which means that we can most likely only accomplish pseudo-polynomial-time algorithms on input networks with bounded tree- or branchwidth. We present two such algorithms based on dynamic programming. We further analyze the parameterized complexity of PESP with bounded cyclomatic number, diameter, or vertex cover number. For event-activity networks with a special—but standard—structure, we give explicit and sharp bounds on the branchwidth in terms of the maximum degree and the carvingwidth of an underlying line network. Finally, we investigate several parameters on the smallest instance of the benchmarking library PESPlib.

Sprache: Englisch

Materialart: article , doc-type:article

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27

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Adaptive Cut Selection in Mixed-Integer Linear Programming (2022)

Turner, Mark ; Koch, Thorsten ; Serrano, Felipe ; [weitere]

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Publikationsdatum: 2022-08-08

Beschreibung: Cut selection is a subroutine used in all modern mixed-integer linear programming solvers with the goal of selecting a subset of generated cuts that induce optimal solver performance. These solvers have millions of parameter combinations, and so are excellent candidates for parameter tuning. Cut selection scoring rules are usually weighted sums of different measurements, where the weights are parameters. We present a parametric family of mixed-integer linear programs together with infinitely many family-wide valid cuts. Some of these cuts can induce integer optimal solutions directly after being applied, while others fail to do so even if an infinite amount are applied. We show for a specific cut selection rule, that any finite grid search of the parameter space will always miss all parameter values, which select integer optimal inducing cuts in an infinite amount of our problems. We propose a variation on the design of existing graph convolutional neural networks, adapting them to learn cut selection rule parameters. We present a reinforcement learning framework for selecting cuts, and train our design using said framework over MIPLIB 2017. Our framework and design show that adaptive cut selection does substantially improve performance over a diverse set of instances, but that finding a single function describing such a rule is difficult. Code for reproducing all experiments is available at https://github.com/Opt-Mucca/Adaptive-Cutsel-MILP.

Sprache: Englisch

Materialart: reportzib , doc-type:preprint

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28

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Tight Convex Relaxations for the Expansion Planning Problem (2022)

Lenz, Ralf (Dr.) ; Serrano, Felipe (Dr.)

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Publikationsdatum: 2022-08-09

Beschreibung: Secure energy transport is considered as highly relevant for the basic infrastructure of nowadays society and economy. To satisfy increasing demands and to handle more diverse transport situations, operators of energy networks regularly expand the capacity of their network by building new network elements, known as the expansion planning problem. A key constraint function in expansion planning problems is a nonlinear and nonconvex potential loss function. In order to improve the algorithmic performance of state-of-the-art MINLP solvers, this paper presents an algebraic description for the convex envelope of this function. Through a thorough computational study, we show that this tighter relaxation tremendously improves the performance of the MINLP solver SCIP on a large test set of practically relevant instances for the expansion planning problem. In particular, the results show that our achievements lead to an improvement of the solver performance for a development version by up to 58%.

Sprache: Englisch

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29

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Effect of depth discontinuity on interfacial stability of tangential-velocity discontinuity in shallow-water flow (2022)

Le, Thi Thai (Dr.) ; Fukumoto, Yasuhide (Prof. Dr.)

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Publikationsdatum: 2022-08-09

Beschreibung: It is well known as the Kelvin-Helmholtz instability (KHI) that an interface of tangential velocity discontinuity is necessarily unstable, regardless of the velocity difference's strength. However, the KHI is suppressed for shallow water flows if the Froude number, defined by the ratio of the velocity difference to the gravity wave's speed, is sufficiently large. In this investigation, we examine the effect of the depth difference of two fluid layers on the KHI. The depth difference enhances instability. Given the Froude number in the instability range, the growth rate sensitively depends on the depth ratio and increases monotonically with the depth ratio difference from unity. The critical value of the Froude number for stabilization varies with the depth ratio and attains the minimum value √8 for equal depth. This behavior is verified by asymptotic analysis.

Sprache: Englisch

Materialart: article , doc-type:article

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30

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Faster exact solution of sparse MaxCut and QUBO problems (2022)

Rehfeldt, Daniel ; Koch, Thorsten ; Shinano, Yuji

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Publikationsdatum: 2022-08-09

Sprache: Englisch

Materialart: reportzib , doc-type:preprint

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31

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Chiral Bioinspired Plasmonics: A Paradigm Shift for Optical Activity and Photochemistry (2022)

Avalos-Ovando, Oscar ; Santiago, Eva Yazmin ; Movsesyan, Artur ; [weitere]

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Publikationsdatum: 2022-08-03

Sprache: Englisch

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32

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Computation of eigenfrequency sensitivities using Riesz projections for efficient optimization of nanophotonic resonators (2022)

Binkowski, Felix ; Betz, Fridtjof ; Hammerschmidt, Martin ; [weitere]

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Publikationsdatum: 2022-08-10

Sprache: Englisch

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33

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Modeling the transition of the multimodal pan-European energy system including an integrated analysis of electricity and gas transport (2022)

Yueksel-Erguen, Inci ; Most, Dieter ; Wyrwoll, Lothar ; [weitere]

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Publikationsdatum: 2022-09-21

Beschreibung: The European energy system has been through a fundamental transformation since the Paris Agreement to reduce greenhouse gas emissions. The transition involves several energy-generating and consuming sectors emphasizing sector coupling. The increase in the share of renewable energy sources has revealed the need for flexibility in the electri city grid. Thus, holistic planning of pathways towards decarbonized energy systems also involves assessing the gas infrastructure to provide such a flexibility and support for the security of supply. In this paper, we propose a workflow to investigate such optimal energy transition pathways considering sector coupling. This workflow involves an integrated operational analysis of the electricity market, its transmission grid, and the gas grid in high spatio-temporal resolution. In a case study on a pan-European scale between 2020-2050, we show that carbon neutrality can be reached within feasible additional costs and in time. However, the manifestation of the potential pathways strongly depends on political and technological constraints. Sector coupling acts as an enabler of cross-border cooperation to achieve both, decarbonization and security of supply.

Sprache: Englisch

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Ontogeny of a tessellated surface: carapace growth of the longhorn cowfish Lactoria cornuta (2022)

Eigen, Lennart ; Baum, Daniel ; Dean, Mason N. ; [weitere]

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Publikationsdatum: 2022-08-24

Beschreibung: Biological armors derive their mechanical integrity in part from their geometric architectures, often involving tessellations: individual structural elements tiled together to form surface shells. The carapace of boxfish, for example, is comprised of mineralized polygonal plates, called scutes, arranged in a complex geometric pattern and nearly completely encasing the body. In contrast to artificial armors, the boxfish exoskeleton grows with the fish; the relationship between the tessellation and the gross structure of the armor is therefore critical to sustained protection throughout growth. To clarify whether or how the boxfish tessellation is maintained or altered with age, we quantify architectural aspects of the tessellated carapace of the longhorn cowfish Lactoria cornuta through ontogeny (across nearly an order of magnitude in standard length) and in a high-throughput fashion, using high-resolution microCT data and segmentation algorithms to characterize the hundreds of scutes that cover each individual. We show that carapace growth is canalized with little variability across individuals: rather than continually adding scutes to enlarge the carapace surface, the number of scutes is surprisingly constant, with scutes increasing in volume, thickness, and especially width with age. As cowfish and their scutes grow, scutes become comparatively thinner, with the scutes at the edges (weak points in a boxy architecture) being some of the thickest and most reinforced in younger animals and thinning most slowly across ontogeny. In contrast, smaller scutes with more variable curvature were found in the limited areas of more complex topology (e.g. around fin insertions, mouth, and anus). Measurements of Gaussian and mean curvature illustrate that cowfish are essentially tessellated boxes throughout life: predominantly zero curvature surfaces comprised of mostly flat scutes, and with scutes with sharp bends used sparingly to form box edges. Since growth of a curved, tiled surface with a fixed number of tiles would require tile restructuring to accommodate the surface’s changing radius of curvature, our results therefore illustrate a previously unappreciated advantage of the odd boxfish morphology: by having predominantly flat surfaces, it is the box-like body form that in fact permits a relatively straightforward growth system of this tessellated architecture (i.e. where material is added to scute edges). Our characterization of the ontogeny and maintenance of the carapace tessellation provides insights into the potentially conflicting mechanical, geometric and developmental constraints of this species, but also perspectives into natural strategies for constructing mutable tiled architectures.

Sprache: Englisch

Materialart: article , doc-type:article

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Quantitative Analysis of Nonlinear MultifidelityOptimization for Inverse Electrophysiology (2022)

Chegini, Fatemeh ; Kopanicakova, Alena (Dr.) ; Weiser, Martin (Dr.) ; [weitere]

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Publikationsdatum: 2022-08-29

Beschreibung: The electric conductivity of cardiac tissue determines excitation propagation and is important for quantifying ischemia and scar tissue and for building personalized models. Estimating conductivity distributions from endocardial mapping data is a challenging inverse problem due to the computational complexity of the monodomain equation, which describes the cardiac excitation. For computing a maximum posterior estimate, we investigate different optimization approaches based on adjoint gradient computation: steepest descent, limited memory BFGS, and recursive multilevel trust region methods, which are using mesh hierarchies or heterogeneous model hierarchies. We compare overall performance, asymptotic convergence rate, and pre-asymptotic progress on selected examples in order to assess the benefit of our multifidelity acceleration.

Sprache: Englisch

Materialart: conferenceobject , doc-type:conferenceObject

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Annual Report 2021 (2022)

Konrad-Zuse-Zentrum für Informationstechnik Berlin

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Publikationsdatum: 2022-09-29

Sprache: Englisch

Materialart: annualzib , doc-type:report

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37

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Bayesian Target-Vector Optimization for Efficient Parameter Reconstruction (2022)

Plock, Matthias ; Andrle, Kas ; Burger, Sven ; [weitere]

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Publikationsdatum: 2022-10-14

Sprache: Englisch

Materialart: article , doc-type:article

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38

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Onset of Chirality in Plasmonic Meta-Molecules and Dielectric Coupling (2022)

Martens, Kevin ; Funck, Timon ; Santiago, Eva Y. ; [weitere]

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Publikationsdatum: 2022-10-28

Sprache: Englisch

Materialart: article , doc-type:article

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The Largest Unsolved QAP Instance Tai256c Can Be Converted into A 256-dimensional Simple BQOP with A Single Cardinality Constraint (2022)

Fujii, Koichi ; Kim, Sunyoung ; Kojima, Masakazu ; [weitere]

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Publikationsdatum: 2022-10-28

Beschreibung: Tai256c is the largest unsolved quadratic assignment problem (QAP) instance in QAPLIB; a 1.48% gap remains between the best known feasible objective value and lower bound of the unknown optimal value. This paper shows that the instance can be converted into a 256 dimensional binary quadratic optimization problem (BQOP) with a single cardinality constraint which requires the sum of the binary variables to be 92.The converted BQOP is much simpler than the original QAP tai256c and it also inherits some of the symmetry properties. However, it is still very difficult to solve. We present an efficient branch and bound method for improving the lower bound effectively. A new lower bound with 1.36% gap is also provided.

Sprache: Englisch

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40

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Robust SDE-Based Variational Formulations for Solving Linear PDEs via Deep Learning (2022)

Richter, Lorenz ; Berner, Julius

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Publikationsdatum: 2022-12-08

Beschreibung: The combination of Monte Carlo methods and deep learning has recently led to efficient algorithms for solving partial differential equations (PDEs) in high dimensions. Related learning problems are often stated as variational formulations based on associated stochastic differential equations (SDEs), which allow the minimization of corresponding losses using gradient-based optimization methods. In respective numerical implementations it is therefore crucial to rely on adequate gradient estimators that exhibit low variance in order to reach convergence accurately and swiftly. In this article, we rigorously investigate corresponding numerical aspects that appear in the context of linear Kolmogorov PDEs. In particular, we systematically compare existing deep learning approaches and provide theoretical explanations for their performances. Subsequently, we suggest novel methods that can be shown to be more robust both theoretically and numerically, leading to substantial performance improvements.

Sprache: Englisch

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41

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An optimal control perspective on diffusion-based generative modeling (2022)

Berner, Julius ; Richter, Lorenz ; Ullrich, Karen

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Publikationsdatum: 2022-12-08

Beschreibung: We establish a connection between stochastic optimal control and generative models based on stochastic differential equations (SDEs) such as recently developed diffusion probabilistic models. In particular, we derive a Hamilton-Jacobi-Bellman equation that governs the evolution of the log-densities of the underlying SDE marginals. This perspective allows to transfer methods from optimal control theory to generative modeling. First, we show that the evidence lower bound is a direct consequence of the well-known verification theorem from control theory. Further, we develop a novel diffusion-based method for sampling from unnormalized densities -- a problem frequently occurring in statistics and computational sciences.

Sprache: Englisch

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42

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Progress in Mathematical Programming Solvers from 2001 to 2020 (2022)

Koch, Thorsten ; Berthold, Timo ; Pedersen, Jaap ; [weitere]

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Publikationsdatum: 2022-12-08

Beschreibung: This study investigates the progress made in LP and MILP solver performance during the last two decades by comparing the solver software from the beginning of the millennium with the codes available today. On average, we found out that for solving LP/MILP, computer hardware got about 20 times faster, and the algorithms improved by a factor of about nine for LP and around 50 for MILP, which gives a total speed-up of about 180 and 1,000 times, respectively. However, these numbers have a very high variance and they considerably underestimate the progress made on the algorithmic side: many problem instances can nowadays be solved within seconds, which the old codes are not able to solve within any reasonable time.

Sprache: Englisch

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43

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New Ramsey Multiplicity Bounds and Search Heuristics (2022)

Parczyk, Olaf ; Pokutta, Sebastian ; Spiegel, Christoph ; [weitere]

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Publikationsdatum: 2022-11-29

Beschreibung: We study two related problems concerning the number of monochromatic cliques in two-colorings of the complete graph that go back to questions of Erdős. Most notably, we improve the 25-year-old upper bounds of Thomason on the Ramsey multiplicity of K4 and K5 and we settle the minimum number of independent sets of size 4 in graphs with clique number at most 4. Motivated by the elusiveness of the symmetric Ramsey multiplicity problem, we also introduce an off-diagonal variant and obtain tight results when counting monochromatic K4 or K5 in only one of the colors and triangles in the other. The extremal constructions for each problem turn out to be blow-ups of a finite graph and were found through search heuristics. They are complemented by lower bounds and stability results established using Flag Algebras, resulting in a fully computer-assisted approach. More broadly, these problems lead us to the study of the region of possible pairs of clique and independent set densities that can be realized as the limit of some sequence of graphs.

Sprache: Englisch

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44

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Benders Decomposition for the Periodic Event Scheduling Problem (2022)

Lindner, Niels ; van Lieshout, Rolf

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Publikationsdatum: 2022-11-03

Beschreibung: The Periodic Event Scheduling Problem (PESP) is the central mathematical model behind the optimization of periodic timetables in public transport. We apply Benders decomposition to the incidence-based MIP formulation of PESP. The resulting formulation exhibits particularly nice features: The subproblem is a minimum cost network flow problem, and feasibility cuts are equivalent to the well-known cycle inequalities by Odijk. We integrate the Benders approach into a branch-and-cut framework, and assess the performance of this method on instances derived from the benchmarking library PESPlib.

Sprache: Englisch

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45

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Tropical Neighbourhood Search: A New Heuristic for Periodic Timetabling (2022)

Bortoletto, Enrico ; Lindner, Niels ; Masing, Berenike

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Publikationsdatum: 2022-11-03

Beschreibung: Periodic timetabling is a central aspect of both the long-term organization and the day-to-day operations of a public transportation system. The Periodic Event Scheduling Problem (PESP), the combinatorial optimization problem that forms the mathematical basis of periodic timetabling, is an extremely hard problem, for which optimal solutions are hardly ever found in practice. The most prominent solving strategies today are based on mixed-integer programming, and there is a concurrent PESP solver employing a wide range of heuristics [Borndörfer et al., 2020]. We present tropical neighborhood search (tns), a novel PESP heuristic. The method is based on the relations between periodic timetabling and tropical geometry [Bortoletto et al., 2022]. We implement tns into the concurrent solver, and test it on instances of the benchmarking library PESPlib. The inclusion of tns turns out to be quite beneficial to the solver: tns is able to escape local optima for the modulo network simplex algorithm, and the overall share of improvement coming from tns is substantial compared to the other methods available in the solver. Finally, we provide better primal bounds for five PESPlib instances.

Sprache: Englisch

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22nd Symposium on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems (ATMOS 2022) (2022)

D'Emidio, Mattia ; Lindner, Niels

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Publikationsdatum: 2022-11-03

Beschreibung: OASIcs, Volume 106, ATMOS 2022, Complete Volume

Sprache: Englisch

Materialart: proceedings , doc-type:Other

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47

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Nano-optical designs for high-efficiency monolithic perovskite–silicon tandem solar cells (2022)

Tockhorn, Philipp ; Sutter, Johannes ; Cruz, Alexandros ; [weitere]

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Publikationsdatum: 2022-11-14

Sprache: Englisch

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48

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tgEDMD: Approximation of the Kolmogorov Operator in Tensor Train Format (2022)

Lücke, Marvin ; Nüske, Feliks

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Publikationsdatum: 2022-11-24

Beschreibung: Extracting information about dynamical systems from models learned off simulation data has become an increasingly important research topic in the natural and engineering sciences. Modeling the Koopman operator semigroup has played a central role in this context. As the approximation quality of any such model critically depends on the basis set, recent work has focused on deriving data-efficient representations of the Koopman operator in low-rank tensor formats, enabling the use of powerful model classes while avoiding over-fitting. On the other hand, detailed information about the system at hand can be extracted from models for the infinitesimal generator, also called Kolmogorov backward operator for stochastic differential equations. In this work, we present a data-driven method to efficiently approximate the generator using the tensor train (TT) format. The centerpiece of the method is a TT representation of the tensor of generator evaluations at all data sites. We analyze consistency and complexity of the method, present extensions to practically relevant settings, and demonstrate its applicability to benchmark numerical examples.

Sprache: Englisch

Materialart: article , doc-type:article

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49

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Optimal Connected Subgraphs: Integer Programming Formulations and Polyhedra (2022)

Rehfeldt, Daniel ; Franz, Henriette ; Koch, Thorsten

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Publikationsdatum: 2022-11-24

Sprache: Englisch

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50

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Location, transshipment and routing: An adaptive transportation network integrating long-haul and local vehicle routing (2022)

Hosada, Junko ; Maher, Stephen ; Shinano, Yuji ; [weitere]

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Publikationsdatum: 2022-11-24

Sprache: Englisch

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51

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Rooted Maximum Weight Connected Subgraphs with Balancing and Capacity Constraints (2022)

Borndörfer, Ralf ; Schwartz, Stephan ; Surau, William

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Publikationsdatum: 2022-11-24

Beschreibung: Finding connected subgraphs of maximum weight subject to additional constraints on the subgraphs is a common (sub)problem in many applications. In this paper, we study the Maximum Weight Connected Subgraph Problem with a given root node and a lower and upper capacity constraint on the chosen subgraph. In addition, the nodes of the input graph are colored blue and red, and the chosen subgraph is required to be balanced regarding its cumulated blue and red weight. This problem arises as an essential subproblem in district planning applications. We show that the problem is NP-hard and give an integer programming formulation. By exploiting the capacity and balancing condition, we develop a powerful reduction technique that is able to significantly shrink the problem size. In addition, we propose a method to strengthen the LP relaxation of our formulation by identifying conflict pairs, i.e., nodes that cannot be both part of a chosen subgraph. Our computational study confirms the positive impact of the new preprocessing technique and of the proposed conflict cuts.

Sprache: Englisch

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52

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Kernel Autocovariance Operators of Stationary Processes: Estimation and Convergence (2022)

Mollenhauer, Mattes ; Klus, Stefan ; Schütte, Christof ; [weitere]

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Publikationsdatum: 2022-11-27

Beschreibung: We consider autocovariance operators of a stationary stochastic process on a Polish space that is embedded into a reproducing kernel Hilbert space. We investigate how empirical estimates of these operators converge along realizations of the process under various conditions. In particular, we examine ergodic and strongly mixing processes and obtain several asymptotic results as well as finite sample error bounds. We provide applications of our theory in terms of consistency results for kernel PCA with dependent data and the conditional mean embedding of transition probabilities. Finally, we use our approach to examine the nonparametric estimation of Markov transition operators and highlight how our theory can give a consistency analysis for a large family of spectral analysis methods including kernel-based dynamic mode decomposition.

Sprache: Englisch

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53

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SepFree NMF: A Toolbox for Analyzing the Kinetics of Sequential Spectroscopic Data (2022)

Sechi, Renata ; Fackeldey, Konstantin (PD-DR) ; Chewle, Surahit ; [weitere]

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Publikationsdatum: 2022-11-28

Beschreibung: This work addresses the problem of determining the number of components from sequential spectroscopic data analyzed by non-negative matrix factorization without separability assumption (SepFree NMF). These data are stored in a matrix M of dimension “measured times” versus “measured wavenumbers” and can be decomposed to obtain the spectral fingerprints of the states and their evolution over time. SepFree NMF assumes a memoryless (Markovian) process to underline the dynamics and decomposes M so that M=WH, with W representing the components’ fingerprints and H their kinetics. However, the rank of this decomposition (i.e., the number of physical states in the process) has to be guessed from pre-existing knowledge on the observed process. We propose a measure for determining the number of components with the computation of the minimal memory effect resulting from the decomposition; by quantifying how much the obtained factorization is deviating from the Markovian property, we are able to score factorizations of a different number of components. In this way, we estimate the number of different entities which contribute to the observed system, and we can extract kinetic information without knowing the characteristic spectra of the single components. This manuscript provides the mathematical background as well as an analysis of computer generated and experimental sequentially measured Raman spectra.

Sprache: Englisch

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ICLR 2022 Challenge for Computational Geomerty & Topology: Design and Results (2022)

Myers, Adele ; Utpala, Saiteja ; Talbar, Shubham ; [weitere]

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Publikationsdatum: 2022-11-30

Sprache: Englisch

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The Price of Symmetric Line Plans in the Parametric City (2022)

Masing, Berenike ; Lindner, Niels ; Borndörfer, Ralf

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Publikationsdatum: 2022-12-01

Beschreibung: We consider the line planning problem in public transport in the Parametric City, an idealized model that captures typical scenarios by a (small) number of parameters. The Parametric City is rotation symmetric, but optimal line plans are not always symmetric. This raises the question to quantify the symmetry gap between the best symmetric and the overall best solution. For our analysis, we formulate the line planning problem as a mixed integer linear program, that can be solved in polynomial time if the solutions are forced to be symmetric. The symmetry gap is provably small when a specific Parametric City parameter is fixed, and we give an approximation algorithm for line planning in the Parametric City in this case. While the symmetry gap can be arbitrarily large in general, we show that symmetric line plans are a good choice in most practical situations.

Sprache: Englisch

Materialart: reportzib , doc-type:preprint

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MaRDI - The mathematical Research Data Initiative (2022)

Reidelbach, Marco ; Weber, Marcus

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Publikationsdatum: 2022-12-05

Sprache: Englisch

Materialart: poster , doc-type:Other

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57

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Solving eigenvalue PDEs of metastable diffusion processes using artificial neural networks (2022)

Zhang, Wei (Dr.) ; Li, Tiejun (Prof.) ; Schütte, Christof (Dr.)

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Publikationsdatum: 2022-12-05

Beschreibung: In this paper, we consider the eigenvalue PDE problem of the infinitesimal generators of metastable diffusion processes. We propose a numerical algorithm based on training artificial neural networks for solving the leading eigenvalues and eigenfunctions of such high-dimensional eigenvalue problem. The algorithm is useful in understanding the dynamical behaviors of metastable processes on large timescales. We demonstrate the capability of our algorithm on a high-dimensional model problem, and on the simple molecular system alanine dipeptide.

Sprache: Englisch

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Multiple projection MCMC algorithms on submanifolds (2022)

Lelievre, Tony (Prof.) ; Stoltz, Gabriel (Prof.) ; Zhang, Wei (Dr.)

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Publikationsdatum: 2022-12-05

Beschreibung: We propose new Markov Chain Monte Carlo algorithms to sample probability distributions on submanifolds, which generalize previous methods by allowing the use of set-valued maps in the proposal step of the MCMC algorithms. The motivation for this generalization is that the numerical solvers used to project proposed moves to the submanifold of interest may find several solutions. We show that the new algorithms indeed sample the target probability measure correctly, thanks to some carefully enforced reversibility property. We demonstrate the interest of the new MCMC algorithms on illustrative numerical examples.

Sprache: Englisch

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Statistical Analysis and Modeling for Detecting Regime Changes in Gas Nomination Time Series (2022)

Petkovic, Milena (Dr.) ; Zakiyeva, Nazgul (Dr.) ; Zittel, Janina (Dr.)

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Publikationsdatum: 2022-12-06

Beschreibung: As a result of the legislation for gas markets introduced by the European Union in 2005, separate independent companies have to conduct the transport and trading of natural gas. The current gas market of Germany, which has a market value of more than 54 billion USD, consists of Transmission System Operators (TSO), network users, and traders. Traders can nominate a certain amount of gas anytime and anywhere in the network. Such unrestricted access for the traders, on the other hand, increase the uncertainty in the gas supply management. Some customers’ behaviors may cause abrupt structural changes in gas flow time series. In particular, it is a challenging task for the TSO operators to predict gas nominations 6 to 10 h-ahead. In our study, we aim to investigate the regime changes in time series of nominations to predict the 6 to 10 h-ahead of gas nominations.

Sprache: Englisch

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PIPELINE FOR SINGLE CELL SEQUENCING OF HUMAN CHONDROCYTE PELLET CULTURES TO DELINEATE IL-1β MODULATED CHANGES IN CELL HETEROGENEITY (2022)

Lang, Annemarie ; Vester, Antja ; Ferreira-Gomes, M. ; [weitere]

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Publikationsdatum: 2022-12-09

Sprache: Englisch

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KOBV-Sondernewsletter zum 25-jährigen Jubiläum (2022)

KOBV (Hrsg.)

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Publikationsdatum: 2022-12-09

Beschreibung: Der Kooperative Bibliotheksverbund Berlin-Brandenburg wird heute 25 Jahre alt. Seit dem 1. April 1997 entwickelt der KOBV neue Dienstleistungen für Nutzende und Bibliotheken, baut Informationsinfrastrukturen in Berlin und Brandenburg aus, vernetzt Bibliotheken aus der Region und informiert über aktuelle Themen. Im Sondernewsletter geben uns aktuelle und ehemalige KOBV-Mitarbeitende/Mitglieder Antworten auf Fragen zur Entstehung und Weiterentwicklung des Verbundes. Lesen und feiern Sie mit uns zusammen!

Sprache: Deutsch

Materialart: other , doc-type:Other

Format: application/pdf

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62

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DeepGreen: Eine Infrastruktur für die Open-Access-Transformation (2022)

Boltze, Julia ; Höllerl, Annika ; Kuberek, Monika ; [weitere]

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Publikationsdatum: 2022-12-09

Beschreibung: Mit DeepGreen wurde eine Infrastruktur aufgebaut und etabliert, die Zeitschriftenartikel von wissenschaftlichen Verlagen abholt und berechtigten Bibliotheken zur Veröffentlichung in ihren Repositorien sendet. DeepGreen unterstützt Bibliotheken als Dienstleister für Hochschulen, außeruniversitäre Einrichtungen und die dort tätigen Wissenschaftler*innen, Publikationen auf Open-Access-Repositorien frei zugänglich zu machen und fördert das Zusammenspiel von wissenschaftlichen Einrichtungen und Verlagen. DeepGreen wurde von Januar 2016 bis Juni 2021 von der Deutschen Forschungsgemeinschaft gefördert und wird nun vom Kooperativen Bibliotheksverbund Berlin-Brandenburg, von der Bayerischen Staatsbibliothek und von der Universitätsbibliothek Erlangen-Nürnberg in arbeitsteiliger Eigenleistung für zwei Jahre weiterbetrieben. Der vorliegende Beitrag beleuchtet vielfältige Aspekte bei der Realisierung von DeepGreen und geht auf die Perspektiven dieser zentralen Open-Access-Infrastruktur für deutsche Wissenschaftseinrichtungen ein.

Sprache: Deutsch

Materialart: article , doc-type:article

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63

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DeepGreen: Etablierung und Weiterentwicklung rechtssicherer Workflows zur effizienten Umsetzung von Open-Access-Komponenten in Lizenzvereinbarungen für wissenschaftliche Publikationen – Abschlussbericht (2022)

Bertelmann, Roland ; Koch, Thorsten ; Ceynowa, Klaus ; [weitere]

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Publikationsdatum: 2022-12-09

Beschreibung: DeepGreen wurde vom 01.08.2018 bis zum 30.06.2021 in einer zweiten Projektphase von der Deutschen Forschungsgemeinschaft (DFG) gefördert. DeepGreen unterstützt Bibliotheken als Dienstleister für Hochschulen, außeruniversitäre Forschungseinrichtungen und die dort tätigen Wissenschaftler:innen dabei, Publikationen auf Open-Access-Repositorien frei zugänglich zu machen und fördert das Zusammenspiel von wissenschaftlichen Einrichtungen und Verlagen. An der zweiten Projektphase waren der Kooperative Bibliotheksverbund Berlin-Brandenburg, die Bayerische Staatsbibliothek, der Bibliotheksverbund Bayern, die Universitätsbibliotheken der Friedrich-Alexander-Universität Erlangen-Nürnberg und der Technischen Universität Berlin und das Helmholtz Open Science Office beteiligt. In dem Projekt wurde erfolgreich eine technische und organisatorische Lösung zur automatisierten Verteilung von Artikeldaten wissenschaftlicher Verlage an institutionelle und fachliche Repositorien entwickelt. In der zweiten Projektphase lag der Fokus auf der Erprobung der Datendrehscheibe in der Praxis und der Ausweitung auf weitere Datenabnehmer und weitere Verlage. Im Anschluss an die DFG-geförderte Projektlaufzeit ist DeepGreen in einen zweijährigen Pilotbetrieb übergegangen. Ziel des Pilotbetriebs ist es, den Übergang in einen bundesweiten Real-Betrieb vorzubereiten.

Sprache: Deutsch

Materialart: reportzib , doc-type:preprint

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64

Unbekannt

Determination of the ice composition near the surface of comet 67P/Churyumov-Gerasimenko (2022)

Läuter, Matthias (Dr.) ; Kramer, Tobias (Prof. Dr.) ; Rubin, Martin (Dr.) ; [weitere]

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Publikationsdatum: 2022-12-16

Beschreibung: During the apparition of comet 67P/Churyumov-Gerasimenko (67P/C-G) solar irradiation causes varying rates for sublimation of volatile species from the cometary nucleus. Because sublimation processes take place close to the cometary surface, the relative abundance of volatiles in the coma and the ice composition are related to each other. To quantify this relation we assume a model for the expansion of a collisionless gas from the surface into the surrounding space. We use an inverse model approach to relate the in situ measurements of gas densities from the two Rosetta instruments COPS (COmet Pressure Sensor) and DFMS (Double Focusing Mass Spectrometer) at the positions of the spacecraft to the locations of surface gas emissions during the Rosetta mission 2014-2016. We assume the temporally integrated gas emissions to be representative for the ice composition close to the surface. Our analysis shows characteristic differences in the ice compositions between both hemispheres of 67P/C-G. In particular CO2 ice has a reduced abundance on the northern hemisphere. In contrast to the hemispherical differences, the two lobes do not show significant differences in terms of their ice composition.

Sprache: Englisch

Materialart: conferenceobject , doc-type:conferenceObject

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65

Unbekannt

The near nucleus gas and dust environment around comet 67P/Churyumov-Gerasimenko (2022)

Kramer, Tobias (Prof. Dr.) ; Läuter, Matthias (Dr.)

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Publikationsdatum: 2022-12-16

Beschreibung: The Rosetta mission to comet 67P/C-G provided a detailed view of the near nucleus environment of an active Jupiter family comet. The continuous monitoring of the gas pressure with the ROSINA experiment at the location of the Rosetta spacecraft in combination with the images of the dust environment acquired by the OSIRIS cameras allows one to test different hypotheses about the origin of the dust and gas emissions. In addition the orbital elements and the rotation axis and spin rate of the nucleus are affected by the gas release.

Sprache: Englisch

Materialart: conferenceobject , doc-type:conferenceObject

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66

Unbekannt

Lunar regolith properties derived from LRO/Diviner data and thermophysical modelling (2022)

Bürger, Johanna ; Gundlach, Bastian (Dr.) ; Blum, Jürgen (Prof. Dr.) ; [weitere]

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Publikationsdatum: 2022-12-16

Beschreibung: The Moon as our nearest celestial object is one of the most important bodies for space resource exploration and planetary science. However, knowledge of the physical properties of the lunar regolith is required for the exploitation of lunar resources and for understanding the Moon's geologic history. This knowledge comes mainly from Apollo in-situ experiments and returned samples, but the global distribution of these properties is still poorly understood. Remote sensing measurements offer the opportunity to derive properties of unsampled areas with the help of models. In our study, a microphysical thermal model for the lunar regolith was developed and the simulated surface temperatures were compared with thermal emission measurements from the Diviner radiometer on board the Lunar Reconnaissance Orbiter (LRO) to derive regolith properties. This work expands upon previous investigations of lunar regolith properties using Diviner data, by more directly simulating physical properties such as particle size and porosity.

Sprache: Englisch

Materialart: conferenceobject , doc-type:conferenceObject

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67

Unbekannt

Navigation of Concentric Tube Continuum Robots using Optimal Control (2022)

Dhanakoti, Siva Prasad Chakri ; Maddocks, John (Prof. Dr.) ; Weiser, Martin (Dr.)

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Publikationsdatum: 2022-12-14

Beschreibung: Recently developed Concentric Tube Continuum Robots (CTCRs) are widely exploited in, for example in minimally invasive surgeries which involve navigating inside narrow body cavities close to sensitive regions. These CTCRs can be controlled by extending and rotating the tubes in order to reach a target point or perform some task. The robot must deviate as little as possible from this narrow space and avoid damaging neighbouring tissue. We consider \emph{open-loop} optimal control of CTCRs parameterized over pseudo-time, primarily aiming at minimizing the robot's working volume during its motion. External loads acting on the system like tip loads or contact with tissues are not considered here. We also discussed the inclusion of tip's orientation in the optimal framework to perform some tasks. We recall a quaternion-based formulation of the robot configuration, discuss discretization, develop optimization objectives addressing different criteria, and investigate their impact on robot path planning for several numerical examples. This optimal framework can be applied to any backbone based continuum robots.

Sprache: Englisch

Materialart: conferenceobject , doc-type:conferenceObject

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68

Unbekannt

Active Segmentation: Differential Geometry meets Machine Learning (2022)

Prodanov, Dimiter ; Vohra, Sumit Kumar

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Publikationsdatum: 2022-12-13

Beschreibung: Image segmentation is an active area of research for more than 30 years. Traditional image segmentation algorithms are problem-specific and limited in scope. On the other hand, machine learning offers an alternative paradigm where predefined features are combined into different classifiers, providing pixel-level classification and segmentation. However, machine learning only can not address the question as to which features are appropriate for a certain classification problem. This paper presents a project supported in part by the International Neuroinformatics Coordination Facility through the Google Summer of code. The project resulted in an automated image segmentation and classification platform, called Active Segmentation for ImageJ (AS/IJ). The platform integrates a set of filters computing differential geometrical invariants and combines them with machine learning approaches.

Sprache: Englisch

Materialart: conferenceobject , doc-type:conferenceObject

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69

Unbekannt

Mathematical modelling of follicular growth and ovarian stimulation (2022)

Fischer-Holzhausen, Sophie ; Röblitz, Susanna (Prof. Dr.)

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Publikationsdatum: 2022-12-20

Sprache: Englisch

Materialart: article , doc-type:article

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70

Unbekannt

Enhanced Purcell factor for nanoantennas supporting interfering resonances (2022)

Colom, Remi ; Binkowski, Felix ; Betz, Fridtjof ; [weitere]

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Publikationsdatum: 2022-12-21

Sprache: Englisch

Materialart: article , doc-type:article

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71

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Parallelization of large-scale agent-based epidemiological simulations (2022)

Fürst, Steffen ; Rakow, Christian

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Publikationsdatum: 2022-12-19

Beschreibung: Agent-based epidemiological models have been applied widely successfully during the SARS-CoV-2 pandemic and assisted policymakers in assessing the effectiveness of intervention strategies. The computational complexity of agent-based models is still challenging, and therefore it is important to utilize modern multi-core systems as good as possible. In this paper, we are presenting our work on parallelizing the epidemiological simulation model MATSim Episim. Episim combines a large-scale person-centric human mobility model with a mechanistic model of infection and a person-centric disease progression model. In general, the parallelization of agent-based models with an inherent sequential structure — in the case of epidemiological models, the temporal order of the individual movements of the agents — is challenging. Especially when the underlying social network is irregular and dynamic, they require frequent communication between the processing elements. In Episim, however, we were able to take advantage of the fact that people are not contagious on the same day they become infected, and therefore immediate health synchronization is not required. By parallelizing some of the most computationally intensive submodels, we are now able to run MATSim Episim simulations up to eight times faster than the serial version. This makes it feasible to increase the number of agents, e.g. to run simulations for the whole of Germany instead of just Berlin as before.

Sprache: Englisch

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72

Buch

Computing : archives for informatics and numerical computation; Supplementum (1977-2003)

Wien [u.a.] :Springer, ; 1.1977 - 16.2003; damit Ersch. eingest.

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Titel: Computing : archives for informatics and numerical computation; Supplementum

Verlag: Wien [u.a.] :Springer,

Erscheinungsjahr: 1977-2003

Erscheinungsverlauf: 1.1977 - 16.2003; damit Ersch. eingest.

Materialart: Buch

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Zuse-Institut Berlin

73

Online-Ressource

Journal of molecular modeling (1996-2002)

Berlin ; Heidelberg :Springer, ; 1.1995(1996) - 8.2002

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Titel: Journal of molecular modeling

Verlag: Berlin ; Heidelberg :Springer,

Erscheinungsjahr: 1996-2002

Erscheinungsverlauf: 1.1995(1996) - 8.2002

ISSN: 0949-183X

Materialart: Online-Ressource

Sprache: Unbestimmte Sprache

Nachfolgender Titel: Forts. ---〉:Journal of molecular modeling

Anmerkung: Kumuliert jeweils den abgeschlossenen Jg. der Internetausg.

Paralleltitel: Druckausg. ---〉:Molecular modeling annual

URL: http://www.springerlink.com/content/100529

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Zuse-Institut Berlin

74

Zeitschrift/Serie

SIGBIO newsletter / (ab 1969-2001)

Association for Computing Machinery / Special Interest Group on Biomedical Computing

New York, NY :ACM, ; 1.1969 - 7.1975/76; N.S. 1.1976 - 21.2001,1; damit Ersch. eingest.

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Titel: SIGBIO newsletter /

Autor: Association for Computing Machinery / Special Interest Group on Biomedical Computing

Verlag: New York, NY :ACM,

Erscheinungsjahr: 1969-2001

Erscheinungsverlauf: 1.1969 - 7.1975/76; N.S. 1.1976 - 21.2001,1; damit Ersch. eingest.

ISSN: 0163-5697

Materialart: Zeitschrift/Serie

Sprache: Unbestimmte Sprache

Paralleltitel: Internetausg. ---〉:Biomedical computing

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Zuse-Institut Berlin

75

Zeitschrift/Serie

¬The¬ journal of logic programming (ab 1984-2000)

New York, NY :North-Holland, ; 1.1984 - 46.2000

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Titel: ¬The¬ journal of logic programming

Verlag: New York, NY :North-Holland,

Erscheinungsjahr: 1984-2000

Erscheinungsverlauf: 1.1984 - 46.2000

ISSN: 0743-1066

Materialart: Zeitschrift/Serie

Sprache: Unbestimmte Sprache

Nachfolgender Titel: Forts. ---〉:¬The¬ journal of logic and algebraic programming

Paralleltitel: Internetausg. ---〉:¬The¬ journal of logic and algebraic programming

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Zuse-Institut Berlin

76

E-Ressource

Medical image analysis CD : an international journal of computer vision, visualization and image- guided intervention in medicine (1996-1999)

Oxford :Univ. Press, ; 1.1996/97 - 3.1999; damit Ersch. eingest.

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Titel: Medical image analysis CD : an international journal of computer vision, visualization and image- guided intervention in medicine

Verlag: Oxford :Univ. Press,

Erscheinungsjahr: 1996-1999

Erscheinungsverlauf: 1.1996/97 - 3.1999; damit Ersch. eingest.

ISSN: 1361-8431

Materialart: Elektronische Ressource

Sprache: Unbestimmte Sprache

Paralleltitel: Druckausg. ---〉:Medical image analysis

Paralleltitel: Internetausg. ---〉:Medical image analysis

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Zuse-Institut Berlin

77

Zeitschrift/Serie

CWI quarterly (ab 1988-1999)

Centrum voor Wiskunde en Informatica 〈Amsterdam〉

Amsterdam :CWI, ; 1.1988 - 12.1999; damit Ersch. eingest.

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Titel: CWI quarterly

Autor: Centrum voor Wiskunde en Informatica 〈Amsterdam〉

Verlag: Amsterdam :CWI,

Erscheinungsjahr: 1988-1999

Erscheinungsverlauf: 1.1988 - 12.1999; damit Ersch. eingest.

ISSN: 0168-826X , 0922-5366

Materialart: Zeitschrift/Serie

Sprache: Unbestimmte Sprache

Vorheriger Titel: Vorg. ---〉:Centrum voor Wiskunde en Informatica 〈Amsterdam〉: CWI newsletter

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Zuse-Institut Berlin

78

Buch

Computer personnel : a quarterly publ. of the Special Interest Group on Computer Personnel Research, SIGCPR (1971-1999)

New York, NY :ACM, ; Nachgewiesen 2.1971 - 20.1999,4; damit Ersch. eingest.

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Titel: Computer personnel : a quarterly publ. of the Special Interest Group on Computer Personnel Research, SIGCPR

Verlag: New York, NY :ACM,

Erscheinungsjahr: 1971-1999

Erscheinungsverlauf: Nachgewiesen 2.1971 - 20.1999,4; damit Ersch. eingest.

ISSN: 0160-2497

Materialart: Buch

Paralleltitel: Internetausg. ---〉:Computer personnel

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Zuse-Institut Berlin

79

Zeitschrift/Serie

Computer networks and ISDN systems : the international journal of computer and telecommunications networking (ab 1985-1998)

Amsterdam [u.a.] :Elsevier [u.a.], ; 9.1985 - 30.1998

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Titel: Computer networks and ISDN systems : the international journal of computer and telecommunications networking

Verlag: Amsterdam [u.a.] :Elsevier [u.a.],

Erscheinungsjahr: 1985-1998

Erscheinungsverlauf: 9.1985 - 30.1998

ISSN: 0169-7552 , 0376-5075

Materialart: Zeitschrift/Serie

Sprache: Unbestimmte Sprache

Nachfolgender Titel: Vorg. u. Forts. ---〉:Computer networks

Anmerkung: Computer networks for research in Europe

Suppl.: In 14,1=15 von:Networkshop: Conference report

Suppl.: 16,1/2=4; 17,4/5=5 von:European Networkshop: European Networkshop

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Zuse-Institut Berlin

80

Zeitschrift/Serie

SIGNUM newsletter (ab 1969-1998)

Association for Computing Machinery / Special Interest Group on Numerical Mathematics

New York, NY :ACM, ; 4.1969 - 33.1998,2; damit Ersch. eingest

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Titel: SIGNUM newsletter

Autor: Association for Computing Machinery / Special Interest Group on Numerical Mathematics

Verlag: New York, NY :ACM,

Erscheinungsjahr: 1969-1998

Erscheinungsverlauf: 4.1969 - 33.1998,2; damit Ersch. eingest

ISSN: 0163-5778

Materialart: Zeitschrift/Serie

Vorheriger Titel: Vorg. ---〉:Association for Computing Machinery / Special Interest Committee on Numerical Mathematics: SICNUM newsletter

Suppl.: 16,3=3,2 von:Association for Computing Machinery / Technical Committee on Fortran: FORTEC forum

Paralleltitel: Internetausg. ---〉:Numerical mathematics

URL: Nur Table of Contents.

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Zuse-Institut Berlin

81

Zeitschrift/Serie

Computers in physics / (ab 1987-1998)

American Institute of Physics

Woodbury, NY :AIP, ; 1.1987,1(Nov./Dez.); 2.1988 - 12.1998

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Titel: Computers in physics /

Beteiligte Person(en): American Institute of Physics

Verlag: Woodbury, NY :AIP,

Erscheinungsjahr: 1987-1998

Erscheinungsverlauf: 1.1987,1(Nov./Dez.); 2.1988 - 12.1998

ISSN: 0894-1866

Materialart: Zeitschrift/Serie

Sprache: Unbestimmte Sprache

Nachfolgender Titel: Forts. ---〉:Computing in science & engineering

URL: http://www.aip.org/cip/

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Zuse-Institut Berlin

82

Zeitschrift/Serie

SIGART bulletin : a quarterly publ. of the Special Interest Group on Artificial Intelligence (ab 1990-1998)

Association for Computing Machinery / Special Interest Group on Artificial Intelligence

New York, NY :ACM, ; 1.1990 - 9.1998

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Titel: SIGART bulletin : a quarterly publ. of the Special Interest Group on Artificial Intelligence

Autor: Association for Computing Machinery / Special Interest Group on Artificial Intelligence

Verlag: New York, NY :ACM,

Erscheinungsjahr: 1990-1998

Erscheinungsverlauf: 1.1990 - 9.1998

ISSN: 1053-4830

Materialart: Zeitschrift/Serie

Sprache: Unbestimmte Sprache

Vorheriger Titel: Vorg. ---〉:Association for Computing Machinery / Special Interest Group on Artificial Intelligence: SIGART newsletter

Nachfolgender Titel: Forts. ---〉:Intelligence

Paralleltitel: Internetausg. ---〉:Artificial intelligence

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Zuse-Institut Berlin

83

Zeitschrift/Serie

Unix review : the publication for the Unix community (ab 1983-1998)

San Francisco, Calif. :Miller Freeman, ; 1.1983 - 16.1998,3

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Titel: Unix review : the publication for the Unix community

Verlag: San Francisco, Calif. :Miller Freeman,

Erscheinungsjahr: 1983-1998

Erscheinungsverlauf: 1.1983 - 16.1998,3

ISSN: 0742-3136

Materialart: Zeitschrift/Serie

Sprache: Unbestimmte Sprache

Nachfolgender Titel: Forts. ---〉:Unix review's performance computing

Paralleltitel: Internetausg. ---〉:Unix review.com

URL: Zugriff lizenzfrei

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Zuse-Institut Berlin

84

Zeitschrift/Serie

Annals of numerical mathematics : journal edition (ab 1994-1997)

Basel :Baltzer, ; 1.1994 - 4.1997; damit Ersch. eingest

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Titel: Annals of numerical mathematics : journal edition

Verlag: Basel :Baltzer,

Erscheinungsjahr: 1994-1997

Erscheinungsverlauf: 1.1994 - 4.1997; damit Ersch. eingest

ISSN: 1021-2655

Materialart: Zeitschrift/Serie

Sprache: Unbestimmte Sprache

Paralleltitel: Internetausg. : Annals of numerical algorithms

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Zuse-Institut Berlin

85

Zeitschrift/Serie

SIGICE bulletin : a monthly publication of the ACM Special Interest Group on Individual Computing Environments (ab 1994-1997)

Association for Computing Machinery / Special Interest Group on Individual Computing Environments

New York, NY :ACM, ; 19.1993/94,3(1994) - 23.1997/98,2(1997); damit Ersch. eingest.

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Titel: SIGICE bulletin : a monthly publication of the ACM Special Interest Group on Individual Computing Environments

Autor: Association for Computing Machinery / Special Interest Group on Individual Computing Environments

Verlag: New York, NY :ACM,

Erscheinungsjahr: 1994-1997

Erscheinungsverlauf: 19.1993/94,3(1994) - 23.1997/98,2(1997); damit Ersch. eingest.

Materialart: Zeitschrift/Serie

Sprache: Unbestimmte Sprache

Vorheriger Titel: Vorg. ---〉:Association for Computing Machinery / Special Interest Group on Small and Personal Computing Systems and Applications: SIGSMALL - PC notes

Paralleltitel: Internetausg. ---〉:Association for Computing Machinery / Special Interest Group on Individual Computing Environments: ACM SIGICE bulletin

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Zuse-Institut Berlin

86

Zeitschrift/Serie

Supercomputer : bimonthly magazine on supercomputing in the Netherlands (ab 1984-1997)

Amsterdam :Amsterdam Universities Computing Centre, ; Nr. 1.1984 - 69.1997; damit Ersch. eingest.

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Titel: Supercomputer : bimonthly magazine on supercomputing in the Netherlands

Verlag: Amsterdam :Amsterdam Universities Computing Centre,

Erscheinungsjahr: 1984-1997

Erscheinungsverlauf: Nr. 1.1984 - 69.1997; damit Ersch. eingest.

ISSN: 0168-7875

Materialart: Zeitschrift/Serie

Sprache: Unbestimmte Sprache

Anmerkung: Teils auch mit Jg.-Zählung

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Zuse-Institut Berlin

87

Zeitschrift/Serie

LISP and symbolic computation : an internat. journal ; a forum for current and envolving symbolic computing, focusing on LISP and object-oriented programming (ab 1988-1997)

Dordrecht [u.a.] :Kluwer Acad. Publ., ; 1.1988 - 10.1997

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Titel: LISP and symbolic computation : an internat. journal ; a forum for current and envolving symbolic computing, focusing on LISP and object-oriented programming

Verlag: Dordrecht [u.a.] :Kluwer Acad. Publ.,

Erscheinungsjahr: 1988-1997

Erscheinungsverlauf: 1.1988 - 10.1997

ISSN: 0892-4635

Materialart: Zeitschrift/Serie

Sprache: Unbestimmte Sprache

Nachfolgender Titel: Forts. ---〉:Higher order and symbolic computation

Paralleltitel: Internetausg. ---〉:Higher-order and symbolic computation

URL: Zugriff nur bis zu den Abstracts möglich.

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Zuse-Institut Berlin

88

Zeitschrift/Serie

World Wide Web journal : W3J; a publication of the World Wide Web Consortium (ab 1995-1997)

Sebastopol, CA, ; 1.1995/96 - 2.1997,4; damit Ersch. eingest.

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Titel: World Wide Web journal : W3J; a publication of the World Wide Web Consortium

Verlag: Sebastopol, CA,

Erscheinungsjahr: 1995-1997

Erscheinungsverlauf: 1.1995/96 - 2.1997,4; damit Ersch. eingest.

ISSN: 1085-2301

Materialart: Zeitschrift/Serie

Sprache: Unbestimmte Sprache

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Zuse-Institut Berlin

89

E-Ressource

Software 〈Chichester〉 : practice & experience ; SP & E ; SP & E archive (1994-1997)

Chichester [u.a.] :Wiley, ; 1/20.1971/90(1994) - 21/25.1991/95(1997); damit Ersch. eingest.

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Titel: Software 〈Chichester〉 : practice & experience ; SP & E ; SP & E archive

Verlag: Chichester [u.a.] :Wiley,

Erscheinungsjahr: 1994-1997

Erscheinungsverlauf: 1/20.1971/90(1994) - 21/25.1991/95(1997); damit Ersch. eingest.

ISSN: 0038-0644

Materialart: Elektronische Ressource

Sprache: Unbestimmte Sprache

Suppl.: 1/20=3; 21/25=5 von:Software 〈Chichester〉 / Special

Paralleltitel: Druckausg. ---〉:Software 〈Chichester〉

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Zuse-Institut Berlin

90

Zeitschrift/Serie

¬The¬ international journal of supercomputer applications and high performance computing (ab 1987-1997)

Thousand Oaks, Calif. :Sage Science Press, ; 1.1987 - 11.1997

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Titel: ¬The¬ international journal of supercomputer applications and high performance computing

Verlag: Thousand Oaks, Calif. :Sage Science Press,

Erscheinungsjahr: 1987-1997

Erscheinungsverlauf: 1.1987 - 11.1997

ISSN: 1078-3482 , 0890-2720

Materialart: Zeitschrift/Serie

Nachfolgender Titel: Forts. ---〉:¬The¬ international journal of high performance computing applications

Paralleltitel: Internetausg. ---〉:¬The¬ international journal of high performance computing applications

URL: Zugriff auf diese Zeitschrift für die Jahrgänge 3. 1989 - 11. 1997 innerhalb der ZIB Domain (IP Adressen: 130.73.*.*) möglich.

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Zuse-Institut Berlin

91

Buch

Online : erfolgreiches Informationsmanagement, ADI-Nachrichten, ÖVD ; Organ d. ADI - Anwenderverband Deutscher Informationsverarbeiter e.V (1973-1997)

Anwenderverband Deutscher Informationsverarbeiter

Bergheim :DATACOM-Zeitschriften-Verl., | Köln Müller -1993,9 ; 11.1973 - 14.1976; 19.1981 - 20.1982; 1983 - 1994; 32.1995 - 34.1997,10

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Titel: Online : erfolgreiches Informationsmanagement, ADI-Nachrichten, ÖVD ; Organ d. ADI - Anwenderverband Deutscher Informationsverarbeiter e.V

Beteiligte Person(en): Anwenderverband Deutscher Informationsverarbeiter

Verlag: Bergheim :DATACOM-Zeitschriften-Verl., , Köln Müller -1993,9

Erscheinungsjahr: 1973-1997

Erscheinungsverlauf: 11.1973 - 14.1976; 19.1981 - 20.1982; 1983 - 1994; 32.1995 - 34.1997,10

ISSN: 0340-1545 , 0179-6623 , 0342-9393

Materialart: Buch

Sprache: Unbestimmte Sprache

Vorheriger Titel: Vorg. ---〉:Zeitschrift für Datenverarbeitung

Nachfolgender Titel: 15.1977 - 18.1980 ---〉:ADL-Verband für Informationsverarbeitung: ADL-Nachrichten, Online

Nachfolgender Titel: Aufgeg. in ---〉:Information week

Anmerkung: Später ohne Zählung

Suppl.: Beil. ---〉:Drucker spezial

Suppl.: Beil. ---〉:Online / special

Suppl.: Darin ---〉:Anwenderverband Deutscher Informationsverarbeiter: ADI-Nachrichten, ÖVD

Suppl.: Beil. ---〉:Pro info

Suppl.: Beil. ---〉:Online-Info

Suppl.: 1996 darin ---〉:Datacom-Special

Paralleltitel: 19.1981 auch in ---〉:Öffentliche Verwaltung und Datenverarbeitung

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Zuse-Institut Berlin

92

Digitale Medien

Properties of thermal flare plasmas (3×106–3×107 K): Observational results (1996)

Feldman, Uri

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 3203-3241

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: One of the most violent while best observed phenomena occurring in the solar upper atmosphere is flare emission in the 3×106 to 3×107 K temperature range. This emission, commonly called thermal flare emission, can vary in intensity by more than five orders of magnitude, and exhibits regular and predictable properties. A wealth of observational data regarding thermal solar flares has been collected. Through these data the morphological properties of thermal flares have been determined. Plasma properties such as electron temperatures, electron densities, mass motions, and variations in elemental abundances during the course of the flare are well established. Observational data have also been used to determine relationships between peak fluxes and maximum flare temperatures as well as general properties of the light curve of flares.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871605

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93

Digitale Medien

Perpendicular ion acceleration by localized high frequency electric fields in magnetized plasmas (1996)

Reitzel, K. J. ; Morales, G. J.

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 3251-3266

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A basic process capable of explaining observations of fast perpendicular ions in a wide range of plasma environments is described. Spatial symmetry breaking perpendicular to the confining magnetic field is shown to cause irreversible energy gain for ions gyrating through an electric field having a nonuniform amplitude. The efficiency depends on the ratio of the ion Larmor radius to the scale length of the amplitude gradient, and on the scaled frequency ν≡ω/Ωi. A Landau resonance is not required, and there is no lower threshold on the electric field, because the mechanism is active in the linear regime. Theory, numerics, and particle-in-cell simulations are used to illustrate the interaction for electrostatic fields in the lower-hybrid range of frequencies, but the process does not depend on a particular type of mode. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871608

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94

Digitale Medien

l=1 electrostatic instability induced by electron-neutral collisions in a nonneutral electron plasma interacting with background neutral gas (1996)

Davidson, Ronald C. ; Chao, Edward H.

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 3279-3287

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: This paper investigates theoretically the electrostatic stability properties of a nonneutral electron plasma interacting with background neutral gas through elastic collisions with constant collision frequency νen. The model treats the electrons as a strongly magnetized fluid (ωpe2/ωce2(very-much-less-than)1) immersed in a uniform magnetic field B0eˆz, and assumes small-amplitude perturbations with azimuthal mode number l=1 and negligible axial variation (∂/∂z=0). The analysis also assumes weak electron collisions with νen/ωce=ε(very-much-less-than)1, and that the process of heat conduction is sufficiently fast that the electrons have relaxed through electron-electron collisions to a quasiequilibrium state with scalar pressure P(r,θ,t)=n(r,θ,t)T, and isothermal temperature T. Assuming that perturbed quantities vary with time according to exp(−iωt), the detailed stability analysis carried out to first order in νen/ωce(very-much-less-than)1 shows that the real oscillation frequency and growth rate for the l=1 diocotron mode are given, respectively, by the simple expressions Re ω=ω0 and Im ω=(νen/ωce)ω0. Here, ω0=Nec/r2wB0, where rw is the perfectly conducting wall radius, and N=∫d2x n is the number of electrons per unit axial length. This analysis suggests that a measurement of the oscillation frequency and growth rate for the l=1 diocotron mode can be used to infer νen, and thereby serve as a sensor for the background neutral pressure. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871610

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95

Digitale Medien

Analysis of the self-oscillations instability due to the plasma coupling with an emissive hot cathode sheath (1996)

Arnas Capeau, C. ; Prasad, G. ; Bachet, G. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 3331-3336

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Experimental results are reported showing that plasma self-oscillations appear when the ion flux arriving at the hot emissive cathode double sheath boundary from a continuous plasma discharge is not high enough to sustain the discharge. Using the stability criterion of a double sheath and the particle balance equations, different conditions for the plasma stability are stated, in good qualitative agreement with experimental results. A nonlinear analysis giving the noninteger correlation dimension in a chaotic self-oscillations regime is also reported, showing that a complete understanding of this instability may be reached by a finite set of nonlinear equations. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871602

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96

Digitale Medien

Theory-based transport modeling of the gyro-radius experiments (1996)

Kinsey, Jon E. ; Bateman, Glenn

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 3344-3357

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Self-consistent predictive transport simulations of temperature and density profiles have been carried out for ten dimensionally similar low (L) mode discharges from the Tokamak Fusion Test Reactor (TFTR) [D. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)], Doublet III-D Tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], and the Joint European Torus [P. H. Rebut, R. J. Bickerton, and B. E. Keen, Nucl. Fusion 25, 1011 (1985)], where only the normalized Larmor radius was allowed to vary. It is found that a purely gyro-Bohm transport model predicts temperature and density profiles that match the experimental data from these ρ* scans very well. In particular, a combination of theoretically derived transport models is used in these simulations, including the Weiland model for transport due to drift waves (ion temperature gradient and trapped electron modes) and the Guzdar–Drake model for transport due to resistive ballooning modes. These gyro-Bohm transport models depend very sensitively on the shapes as well as the magnitudes of the profiles. As the magnetic field, density and temperature are changed in each dimensionally similar series of discharges, the penetration length of neutrals from the edge varies considerably. This effect causes the shape of the density profiles to change near the edge of the plasma, which causes the scaling of our transport model diffusivities to differ significantly from their fundamentally gyro-Bohm scaling. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871604

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97

Digitale Medien

A threshold for excitation of neoclassical tearing modes (1996)

Gorelenkov, N. N. ; Budny, R. V. ; Chang, Z. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 3379-3385

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Stability criterion for neoclassical tearing modes is obtained from the drift kinetic equation. A finite amplitude of a magnetic island is required for mode excitation. The threshold is determined by the ratio of the transversal and the parallel transport near the island when the flattening of the pressure profile eliminates the bootstrap current. A number of supershots from the database of the Tokamak Fusion Test Reactor (TFTR) [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)] are compared with the theory. In cases where the modes were observed in experiment the stability criterion was violated. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871614

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98

Digitale Medien

Velocity–space asymmetry of the trapping boundary of charged particles at and near the magnetic axis of a tokamak (1996)

Chu, T. K.

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 3397-3409

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: In tokamaks, the trajectory of a trapped particle has a pair of poloidal turning points where Vz reverses direction. They form a stagnation point when coalescing on the equatorial plane. The trajectories traversing the stagnation point, because of the finite Larmor radius and hence the banana width, have a threefold degeneracy: a pinch orbit and a kidney orbit of a trapped particle, and a loop orbit of a passing particle. When traversing the stagnation point from a pinch orbit, the trajectory of a negative-V(parallel) particle must change to a loop orbit and the particle becomes passing, and that of a positive-V(parallel) particle must change to a kidney orbit and the particle remains trapped. The trapping boundary is asymmetric in V(parallel). The percentage of trapped particles in a species in a local Maxwellian plasma depends on the radial distance r as well as on the Larmor radius of its thermal particle. At the axis the trapping ratio is finite and more ions than electrons are trapped; for typical parameters in Princeton Beta Experiment-Modification [Bell et al., Phys. Fluids B 2, 1271 (1990)], for example, 2.2% of electrons and 8.6% of deuterons are trapped. Up to a radial distance of ∼10 times the Larmor radius of a thermal particle, the trapping ratio increases as r2. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871616

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99

Digitale Medien

Short-pulse laser harmonics from oscillating plasma surfaces driven at relativistic intensity (1996)

Lichters, R. ; Meyer-ter-Vehn, J. ; Pukhov, A.

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 3425-3437

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The generation of harmonics by interaction of an ultrashort laser pulse with a step boundary of a plane overdense plasma layer is studied at intensities Iλ2=1017–1019 W cm−2 μm2 for normal and oblique incidence and different polarizations. Fully relativistic one-dimensional particle-in-cell (PIC) simulations are performed with high spectral resolution. Harmonic emission increases with intensity and also when lowering the plasma density. The simulations reveal strong oscillations of the critical surface driven by the normal component of the laser field and by the ponderomotive force. It is shown that the generation of harmonics can be understood as reflection from the oscillating surface, taking full account of retardation. Describing the oscillations by one or more Fourier components with adjustable amplitudes, model spectra are obtained that well reproduce the PIC spectra. The model is based on relativistic cold plasma equations for oblique incidence. General selection rules concerning polarization of odd and even harmonics depending on incident polarization are derived. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871619

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100

Digitale Medien

Electron cyclotron resonance heating near the turning point in inhomogeneous magnetic field (1996)

Tatematsu, Y. ; Kiwamoto, Y. ; Saito, T. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 3318-3323

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Cyclotron resonance heating of electrons in a magnetic beach is studied by rigorous numerical analysis of the electron trajectories. It is confirmed that a heating response function [Y. Kiwamoto et al., Phys. Plasmas 1 834 (1994)] connecting the velocity distributions in both sides of the resonance layer can be applied over a wider range of electron velocities than originally expected. For electrons mirror-reflected close to the resonance layer, however, the electron velocity distribution after heating substantially deviates from the prediction of the response function. The deviation is quantitatively evaluated to obtain a criterion of applicability of the response function. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871600

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