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1021 research outputs found
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Power management approach of hybrid energy storage system for electric vehicle charging stations
No full textThe applicability of Hybrid Energy Storage Systems (HESSs) has been shown in multiple application fields, such as Charging Stations (CSs), grid services, and microgrids. HESSs consist of an integration of two or more single Energy Storage Systems (ESSs) to combine the benefits of each ESS and improve the overall system performance. In this work, we propose a novel power management controller called the Hybrid Controller for the efficient HESS’s charging and discharging, considering the State of Charge (SoC) of the HESS and the dynamic supply and load. The Hybrid Controller optimises the use of the HESS, i.e., minimises the amount of energy drawn from and discharged to the grid, thus utilising and prioritising the provided Photovoltaic (PV) power. The performance of our proposal was assessed via simulation using various evaluation metrics, i.e., Autarky, charge/discharge cycle, and Self-Consumption (SC), where we defined 24 scenarios in different locations in Germany
Beyond financial wealth: The experienced utility of collectibles
No full textWe argue that the utility of specific assets, in our case collectibles, is not only derived from the financial outcome, but also from the conditions that prevail until a financial outcome may be realized. Therefore, we derive a multi-attribute utility function that measures financial returns — using a mean-variance utility function — on the one hand, and non-financial returns — using an experienced utility function — on the other. We then reveal the trade-off between financial and non-financial utility by analyzing 363 owners of collectibles. We divide the owners into the group of collectors and the group of investors, based on their self-reported motivation. Our results suggest that collectors receive almost no utility from financial returns, but rather from experience. The opposite is the case for investors. Our findings help to explain the reported financial underperformance of collectibles and suggest to adjust existing models of utility
Teaching advanced topics in econometrics using introductory textbooks : the case of dynamic panel data methods
No full textWe show how to use the introductory econometrics textbook by Stock and Watson (2019) as a starting point for teaching and studying dynamic panel data methods. The materials are intended for undergraduate students taking their second econometrics course, undergraduate students in seminar-type courses, independent study courses, capstone, or thesis projects, and beginning graduate students in a research methods course. First, we distill the methodological core necessary to understand dynamic panel data methods. Second, we design an empirical and a theoretical case study to highlight the capabilities, downsides, and hazards of the method. The empirical case study is based on the cigarette demand example in Stock and Watson (2019) and illustrates that economic and methodological issues are interrelated. The theoretical case study shows how to evaluate current empirical practices from a theoretical standpoint. We designed both case studies to boost students’ confidence in working with technical material and to provide instructors with more opportunities to let students develop econometric thinking and to actively communicate with applied economists. Although we focus on Stock and Watson (2019) and the statistical software R, we also show how to modify the material for use with another introductory textbook by Wooldridge (2020) and Stata, and highlight some possible further pathways for instructors and students to reuse and extend our materials
Pinball boosting of regression quantiles
No full textAn algorithm for boosting regression quantiles using asymmetric least absolute deviations, better known as pinball loss, is proposed. Existing approaches for boosting regression quantiles are essentially equal to least squares boosting of regression means with the single difference that their working residuals are based on pinball loss. All steps of our boosting algorithm are embedded in the well-established framework of quantile regression, and its main components – sequential base learning, fitting, and updating – are based on consistent scoring rules for regression quantiles. The Monte Carlo simulations performed indicate that the pinball boosting algorithm is competitive with existing approaches for boosting regression quantiles in terms of estimation accuracy and variable selection, and that its application to the study of regression quantiles of hedonic price functions allows the estimation of previously infeasible high-dimensional specifications
Ein Manchurian-Kandidat? Der Diskurs der Republikanischen Partei zu Russlands Krieg in der Ukraine
No full textThe United States has a longstanding tradition regarding its overall foreign policy, in the form of a bipartisan consensus. This includes—among other things—maintaining alliances and curbing the influence of rivals (e.g., Russia). Since this consensus has been in place, traditionally the Republican Party (GOP) has been especially intent on a less cooperative and more containing or deterring stance towards Russia. With former U.S. President Donald Trump, we can see a turning point in this behaviour by the GOP. Trump’s obvious admiration for Russian president Putin and his statements about Putin being overly favourable, while simultaneously questioning NATO and the United States’ commitment to defend Eastern European partners, show a distinctive shift in the GOP’s discourse. This renunciation has subsequently been picked up by parts of the Republican Party, rendering the bipartisan consensus a contested issue. The full-scale Russian invasion of Ukraine in February 2022 now constitutes an important external shock influencing said discursive shift. By drawing on discourse-bound identity theory and discourse analysis, the GOP’s discourse regarding Russia and NATO is expected to have (substantially) changed in a kind of Zeitenwende —back towards the bipartisan consensus. This article will, therefore, analyse the statements of prominent Republicans after the Russian invasion, compare them to Trump’s positions on these issues, and identify whether the invasion serves as a formative event that creates an overall shift in rhetoric and positions.Die USA haben eine langanhaltende Tradition in ihrer allgemeinen Außenpolitik, in Form des sog. „bipartisan consensus“. Darin enthalten sind u. a. das Erhalten von Allianzen und die Einschränkung des Einflusses von Rivalen (bspw. Russlands). Seit dieser Konsens existiert, verfolgen die Republikaner traditionellerweise einen weniger kooperativen, eher einhegenden und abschreckenden Kurs gegenüber Russland. Mit dem früheren US-Präsidenten Trump kann man hier eine Wende im Verhalten der Partei erkennen. Die Verschiebung des Republikanischen Diskurses zeigt sich klar mit seiner offensichtlichen Bewunderung für Russlands Präsident Putin und seinen lobenden Aussagen über diesen, während er die NATO und die Verteidigungspflicht gegenüber osteuropäischen Partnern hinterfragt. Diese Abkehr von früheren Positionen wurde daraufhin von Teilen der Republikanischen Partei übernommen, wodurch der bisherige „bipartisan consensus“ contestet wird. Die russische Invasion der Ukraine im Februar 2022 stellt hierbei nun einen entscheidenden externen Schock dar, der diesen diskursiven Wandel beeinflussen kann. Unter der Einbeziehung der diskursgebundenen Identitätstheorie und einer Diskursanalyse wird davon ausgegangen, dass sich der Republikanische Diskurs zu Russland und der NATO (erheblich) gewandelt hat – zurück zum „bipartisan consensus“ in einer Art Zeitenwende . Dafür werden in diesem Artikel Aussagen relevanter Republikaner:innen nach der russischen Invasion analysiert, mit den Positionen Trumps zu diesen Themen verglichen und festgestellt, ob es sich demnach um ein formatives Ereignis handelt, durch das ein genereller Wandel in Rhetorik und Einstellungen entsteht
Organizational integration of highly skilled migrants? Social worlds as multiple cultures dismantling conventional framings
No full textThis paper examines the integration of highly skilled migrants into organizations. Whereas prior research has mainly focused on macro-economic and macro-political analysis, little is known about the dynamic process of organizational level integration. Applying Strauss’ theory of social worlds and the concept of multiple cultures, we dismantle the boundaries of an organization describing the integration processes of migrants from the perspective of different social worlds that intersect an organization. We use social worlds which form around a core activity or context of action to describe different levels of cultures within an organization. Via multifaceted identification with these multiple cultures, we suggest that person–organization interaction and mutual intercultural learning processes with colleagues result in organizations conveying values, norms, behavior, language and social contacts that prove valuable and integrative, especially to newcomers. Based on three qualitative case studies in German SMEs, migrants’ experiences during the integration process show the central role organizations play inhibiting previously overlooked multi-cultural social worlds which lead not only to their organizational integration, but to societal integration as well. Organizations thus contribute to different forms of integration. Consequently, this paper extends traditional integration perspectives at the national or transnational level of analysis by differentiating into multiple cultures that provide integrative knowledge both internally and beyond the organization. In particular, interaction with colleagues as socialization agents leads to integration. Theory and practice should draw conclusions from this to consider integration as a multilayered opportunity
SAT Solving Using XOR-OR-AND Normal Forms
No full textThis paper introduces the XOR-OR-AND normal form (XNF) for logical formulas. It is a generalization of the well-known Conjunctive Normal Form (CNF) where literals are replaced by XORs of literals. As a first theoretic result, we show that every CNF formula is equisatisfiable to a formula in 2-XNF, i.e., a formula in XNF where each clause involves at most two XORs of literals. Subsequently, we present an algorithm which converts Boolean polynomials efficiently from their Algebraic Normal Form (ANF) to formulas in 2-XNF. Experiments with the cipher ASCON-128 show that cryptographic problems, which by design are based strongly on XOR-operations, can be represented using far fewer variables and clauses in 2-XNF than in CNF. In order to take advantage of this compact representation, new SAT solvers based on input formulas in 2-XNF need to be designed. By taking inspiration from graph-based 2-CNF SAT solving, we devise a new DPLL-based SAT solver for formulas in 2-XNF. Among others, we present advanced pre- and in-processing techniques. Finally, we give timings for random 2-XNF instances and instances related to key recovery attacks on round reduced ASCON-128, where our solver outperforms state-of-the-art alternative solving approaches
Von Alemann, Ulrich, Nina Basedahl, Gernot Graeßner, und Sabrina Kovacs (2022): Politische Ideen im Wandel der Zeit
No full text"Einführungen in die Politische Theorie und Ideengeschichte, die auch für Studienanfänger*innen verständlich sind und sich zugleich auf der Höhe des Forschungsstands bewegen, sind nach wie vor eine gehörige Herausforderung. Erschwerend kommt hinzu, dass die gängigen autor*innen-, werk- oder diskurszentrierten Formate allesamt ihre blinden Flecken besitzen. Insofern ist die Lösung, die Ulrich von Alemann, Nina Basedahl, Gernot Graeßner und Sabrina Kovacs gefunden haben und die auf eine Kombination aller drei genannten Ansätze hinausläuft, im Prinzip durchaus zu begrüßen.
Periods, power series, and integrated algebraic numbers
No full textPeriods are defined as integrals of semialgebraic functions defined over the rationals. Periods form a countable ring not much is known about. Examples are given by taking the antiderivative of a power series which is algebraic over the polynomial ring over the rationals and evaluate it at a rational number. We follow this path and close these algebraic power series under taking iterated antiderivatives and nearby algebraic and geometric operations. We obtain a system of rings of power series whose coefficients form a countable real closed field. Using techniques from o-minimality we are able to show that every period belongs to this field. In the setting of o-minimality we define exponential integrated algebraic numbers and show that exponential periods and the Euler constant is an exponential integrated algebraic number. Hence they are a good candiate for a natural number system extending the period ring and containing important mathematical constants
Intelligent design of sensor networks for data-driven sensor maintenance at railways
No full textWith rapid advances in digitization, many critical processes in transportation, industries, and our daily life rely on sensor measurements. With time, however, the measurements may get gradually biased and their precision deteriorates, leading to an enhanced risk of major disruptions caused by false sensor measurements. All single sensor measurements are uncertain and deviate from the true value. To detect malfunctioning sensors early on, a set of recent measurements of each sensor has to be constantly cross-checked against the measurements of a given number of other sensors, i.e., sensors should form a diagnosable network.
In this article, we examine the intelligent positioning of safety-relevant sensors at railways such that the installed sensors can constantly cross-check each other and the number of the required sensors is minimized. The arising sensor positioning problem (SPP) belongs to the family of the coordinated set covering problems with two binary matrices: the choice of columns in one matrix implies the selection of specific columns and rows in the other matrix. We formulate an integer program, provide some formal analysis of the SPP and design a customized large neighborhood search metaheuristic RuM, which finds close-to-optimality solutions fast. In our computational experiments, we show that if we ignore the diagnosability requirement, the installed sensors cannot sufficiently cross-check each other in most cases. However, it costs only a few (or even no) additional sensors to ensure the diagnosability of the sensor network