Publikationen

2021

• Teilwicklungsanlauf von Käfigläufermotoren mit kombinierter Stern-Dreieck-Wicklung

  Huth, G., & Löhlein, B. (2021). Teilwicklungsanlauf von Käfigläufermotoren mit kombinierter Stern-Dreieck-Wicklung. http://doi.org/10.1007/s00502-021-00900-6

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  Mit Rücksicht auf die Netzverhältnisse müssen Käfigläufermotoren mit einem geeigneten Anlaufverfahren an das Drehstromnetz geschaltet werden. Liegen, wie zum Beispiel bei Kompressoren, schwere Anlaufbedingungen vor, so kommt neben dem verstärkten Stern-Dreieck-Anlauf häufig der Teilwicklungsanlauf zum Einsatz. Wenn zur Steigerung der Energieeffizienz eine kombinierte Stern-Dreieck-Wicklung zum Einsatz kommt, bietet sich die Drehfeldwicklung zusätzlich auch für den Teilwicklungsanlauf an, wenn die kombinierte Wicklung als Parallelschaltung ausgeführt ist. Die Möglichkeiten hierzu werden unter Berücksichtigung des Oberfeldverhaltens analysiert und am Beispiel von zwei Käfigläufermotoren wird das Betriebsverhalten simulativ untersucht.

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  • 2021
  • Journal Article
  • • Gerhard Huth
    • Bernd Löhlein

• The impact of entrepreneurship on economic, social and environmental welfare and its determinants: a systematic review

  Neumann, T. (2021). The impact of entrepreneurship on economic, social and environmental welfare and its determinants: a systematic review, 71(3), 553–584,. http://doi.org/10.1007/s11301-020-00193-7

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  This paper presents a systematic review of (a) the impact of entrepreneurship on economic, social and environmental welfare and (b) the factors determining this impact. Research over the past 25 years shows that entrepreneurship is one cause of macroeconomic development, but that the relationship between entrepreneurship and welfare is very complex. The literature emphasizes that the generally positive impact of entrepreneurship depends on a variety of associated determinants which affect the degree of this impact. This paper seeks to contribute to the literature in three ways. First, it updates and extends existing literature reviews with the recently emerged research stream on developing countries, and incorporates studies analysing not only the impact of entrepreneurship on economic growth and welfare but also on social and environmental welfare. Second, it identifies and structures the current knowledge on the determinants of this impact. And third, it provides a roadmap for future research which targets the shortcomings of the existing empirical literature on this topic. The review of 102 publications reveals that the literature generally lacks research which (a) goes beyond the common measures of economic welfare, (b) examines the long-term impact of entrepreneurship and (c) focuses on emerging and developing countries. Regarding the determinants of the impact of entrepreneurship, the results highlight the need for empirical research which addresses both already investigated determinants which require more attention (e.g. survival, internationalisation, qualifications) and those which are currently only suspected of shaping the impact of entrepreneurship (e.g. firm performance, the entrepreneur’s socio-cultural background and motivations).

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  • 2021
  • Journal Article
  • • Thomas Neumann

• A Key Manipulation Attack on Some Recent Isogeny-Based Key Agreement Protocols

  Gönen, M. E., Tutdere, S., & Uzunkol, O. (2021). A Key Manipulation Attack on Some Recent Isogeny-Based Key Agreement Protocols. Bulletin of the Iranian Mathematical Society . http://doi.org/10.1007/s41980-021-00534-6

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  Recently, Daghigh et al. proposed some isogeny-based key agreement protocols in Bull. Iran. Math. Soc. 43 (2017), no. 4, 77-88. They claimed that their key exchange protocols based on supersingular isogenies provide the same security level as the Jao et al.’s protocol SIDH. This paper addresses first a vulnerability of these protocols to a key manipulation attack. Hence, unlike the security claims of Daghigh et al., these protocols unfortunately do not provide the same security when compared with SIDH. Second, we show in particular that the secret dual isogenies of the protocols can easily be retrieved by applying our key manipulation attack. We also discuss lastly the countermeasures to this attack.

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    • Uzunkol, Osmanbey

  • Fachbereich

    • Fachbereich 3: Information und Kommunikation

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  • 2021
  • Journal Article
  • • Mehmet Gönen
    • Seher Tutdere
    • Osmanbey Uzunkol

• Digital Competences of Prospective Engineers and Science Teachers: A Latent Profile and Correspondence Analysis

  Schulze-Heuling, L., Wild, S., & Vest, A. (2021). Digital Competences of Prospective Engineers and Science Teachers: A Latent Profile and Correspondence Analysis. International Journal of Education in Mathematics, Science and Technology (IJEMST), 9(4), 760-782. http://doi.org/https://doi.org/10.46328/ijemst.1831 (Original work published Oktober 2021)

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    • Vest, Anja

  • Fachbereich

    • Fachbereich 2: Energy and Life Science

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  • 2021
  • Journal Article
  • • Lydia Schulze-Heuling
    • Steffen Wild
    • Anja Vest

• The Physical Optimum as an Ideal Reference Value for Balancing Thermodynamic Processes Integrating the Exergetic Evaluation by the Example of Heat Supply

  Volta, D., & Weber, S. (2021). The Physical Optimum as an Ideal Reference Value for Balancing Thermodynamic Processes Integrating the Exergetic Evaluation by the Example of Heat Supply. MDPI Energies, 14(15), 15. http://doi.org/https:// doi.org/10.3390/en14154426 (Original work published Juli 2021)

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  This paper contains the basic definition and application of the physical optimum as a method for process evaluation and optimization. By means of the exemplary balance of a wood pellet-fired boiler, the conventional efficiency is compared to the PhO. Furthermore, this study demonstrates the possibility of applying the thermodynamic state variable exergy as a physical reference property of a system within the PhO method. To explain the approach, the heat generation in the wood pellet-fired boiler is compared to the supply from a heat pump, which itself is connected to a power plant. Furthermore, the process-independent PhO is explained in order to illustrate the limitations of feasible optimization. Additionally, possible research topics such as the inte-gration of dynamic behavior in the method are approached. As a conclusion, the differences be-tween the methods outline the advantage of the PhO in the optimization process.

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    • Volta, Dirk
    • Rohm, Samanta Alena

  • Fachbereich

    • Fachbereich 2: Energy and Life Science

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  • Journal Article
  • • Dirk Volta
    • Samanta Weber
  • • physical optimum
    • PhO
    • reference process
    • energy efficiency
    • energy optimization
    • method comparison
    • energy

• Application of a New Dispatch Methodology to Identify the Influence of Inertia Supplying Wind Turbines on Day-Ahead Market Sales Volumes

  Thiesen, H., & Jauch, C. (2021). Application of a New Dispatch Methodology to Identify the Influence of Inertia Supplying Wind Turbines on Day-Ahead Market Sales Volumes. Energies, 14(5). http://doi.org/10.3390/en14051255 (Original work published Februar 2021)

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  Power system inertia is an essential part of grid frequency control. The number of synchronously connected machines, which inherently provide inertia, is decreasing due to the transition to renewable energies. Conventional generation units are being replaced by renewable generation units which are connected to the grid via frequency converters. Some power systems already suffer from too little power system inertia. Hence, inertia is a valuable yet non-traded commodity. A day-ahead dispatch methodology to secure power system inertia was developed and is applied and assessed in this work. Day-ahead market data of the combined market of the Republic of Ireland and Northern Ireland is used. If the superimposition of sell and buy bids results in insufficient inertia, the dispatch algorithm is applied. In decreasing price order, non-inertia-providing sell bids get replaced by the following sell bids in the merit order. The iterative process is repeated until sufficient inertia is in the system. The provision of synthetic inertia by wind turbines is considered in the process. The costs for additional stored kinetic energy for the assessed time periods and scenarios result in costs ranging from 1.02 to 4.49 EUR/kgm2.

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    • Thiesen, Henning
    • Jauch, Clemens

  • Abteilung/Einrichtung

    • Wind Energy Technology Institute

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  • 2021
  • Journal Article
  • • Henning Thiesen
    • Prof. Dr. Clemens Jauch

• Grid Services and Stress Reduction with a Flywheel in the Rotor of a Wind Turbine

  Jauch, C. (2021). Grid Services and Stress Reduction with a Flywheel in the Rotor of a Wind Turbine. Energies, 14. http://doi.org/10.3390/en14092556

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  Wind power penetration increases in most grids and the sizes of wind turbines increase. This leads to increasingly tough requirements, which are imposed on wind turbines, both from the grid as well as from economics. Some of these partially contradictory requirements can only be satisfied with additional control mechanisms in the wind turbines. In this paper, such a mechanism, i.e., a hydraulic–pneumatic flywheel system in the rotor of a wind turbine, is discussed. This flywheel system supports a wind turbine in providing grid services such as steadying the power infeed, fast frequency response, continuous inertia provision, power system stabilization, and low voltage ride-through. In addition, it can help mitigate the stress on the mechanical structure of a wind turbine, which results from varying operating points, imbalances in the rotor, gravitation that acts on the blades, in-plane vibrations, and emergency braking. The study presented in this paper is based on simulations of a publicly available reference wind turbine. Both the rotor blade design as well as the design of the flywheel system are as previously published. It is discussed how the aforementioned grid services and the stress reduction mechanisms can be combined. Finally, it is concluded that such a flywheel system broadens the range of control mechanisms of a wind turbine substantially, which is beneficial for the grid as well as for the wind turbine itself.

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    • Jauch, Clemens

  • Fachbereich

    • Fachbereich 2: Energy and Life Science

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  • 2021
  • Journal Article
  • • Prof. Dr. Clemens Jauch

• Financial performance and firm efficiency of automotive manufacturers and their suppliers A longitudinal data envelopment analysis

  Brandenburg, M., & Hahn, G. J. (2021). Financial performance and firm efficiency of automotive manufacturers and their suppliers A longitudinal data envelopment analysis. Logistics Research, 14(1), 26. http://doi.org/10.23773/2021_01

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  A data envelopment analysis (DEA) is presented to assess evolutions of firm efficiency and financial performance in automotive supply chains. A sample of 32 decision-making units (DMUs), 17 globally operating original equipment manufacturers (OEMs) and 15 key suppliers from the automotive industry, is in focus of this analysis in which cost levels and capital requirements are put into relation to sales growth and profit. Cost of goods sold, operating capital, and net fixed assets represent the financial input of a company while sales growth and earnings before interest and taxes (EBIT) reflect the financial output. The financial performance of a firm is indicated by its efficiency, calculated by an input-oriented variable returns to scale model. A multiple linear regression analysis reveals which operational performance factors are predictors of financial performance. A longitudinal DEA approach that covers the years from 2003 to 2017 is chosen to reveal performance evolutions over time. In order to analyze the stability of relationships between efficient firms (peers) and inefficient ones (followers) over time, changes in the performance relationship network are assessed in a graph-theoretic approach. In this study, geographical and structural specifics of DMU groups are taken into account. The study reveals similarities and differences between OEMs and their suppliers regarding the importance of value drivers and detects periods of performance losses and recovery from the global economic crisis.

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    • Brandenburg, Marcus

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  • 2021
  • Journal Article
  • • Marcus Brandenburg
    • Gerd Hahn
  • • Automotive industry
    • Data Envelopment Analysis
    • Financial performance
    • Supply networks

• Arbeiten Frauen aufgrund des Ehegattensplittings weniger? — Eine empirische Untersuchung für Deutschland

  Chirvi, M. (2021). Arbeiten Frauen aufgrund des Ehegattensplittings weniger? — Eine empirische Untersuchung für Deutschland. Steuer und Wirtschaft, 98(2). http://doi.org/10.9785/stuw-2021-980207

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  Der Beitrag soll zur Klärung der Frage beitragen, ob das Ehegattensplitting, wie vielfach behauptet wird, einen negativen Einfluss auf das Arbeitsverhalten verheirateter Frauen hat. Hierzu kommt für Deutschland erstmals ein von Quasi-Experimenten inspirierter Ansatz zum Einsatz, bei dem anhand des allgemeinen Effekts der Heirat auf das Erwerbsverhalten der heiratenden Frauen die Wirkung des Ehegattensplittings geschätzt wird. Die Veränderung des Arbeitsverhaltens heiratender Frauen wird dabei der Veränderung bei jenen Frauen gegenübergestellt, die im gleichen Zeitraum weiterhin mit ihrem festen Partner zusammenleben, ohne zu heiraten (Kontrollgruppe). Die Ergebnisse sprechen eindeutig gegen einen unmittelbaren negativen Effekt des Ehegattensplittings auf das Erwerbsverhalten von Frauen. Jedoch reduzieren heiratende und zeitgleich ein Kind bekommende Frauen ihre Erwerbstätigkeit stärker als gebärende Frauen in der Kontrollgruppe. In Folge einer lediglich teilweisen Abschaffung des Ehegattensplittings, die in den Entwürfen zu Parteiprogrammen zur Bundestagswahl 2021 teilweise gefordert wird, sind sogar noch geringere Effekte auf das Arbeitsverhalten zu erwarten.

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    • Chirvi, Malte

  • Fachbereich

    • Fachbereich 4: Wirtschaft

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  • 2021
  • Journal Article
  • • Malte Chirvi

• \# Covid-19: An Exploratory Investigation of Hashtag Usage on Twitter

  Petersen, K., & Gerken, J. M. (2021). \# Covid-19: An Exploratory Investigation of Hashtag Usage on Twitter. Health Policy.

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    • Petersen, Kai
    • Gerken, Jan

  • Abteilung/Einrichtung

    • FLAIR - Flensburg Artificial Intelligence Research

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  • 2021
  • Journal Article
  • • Kai Petersen
    • Jan Gerken