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Aktuellste Veröffentlichungen

A robust test for equal predictive accuracy
(2026) Demetrescu, Matei; Hanck, Christoph; Hoga, Yannick
This paper studies what we call a "robust" Diebold–Mariano type test. The unique feature of our test is that - even in the absence of any knowledge of the forecasting method - it is robust to estimation noise in the forecasts, i.e., size is kept irrespective of estimation effects induced by model fitting. We obtain this feature by a test statistic that is based on rolling-window means whose length is a vanishing fraction of the total evaluation sample. This leads to non-standard Gumbel limit laws. Other desirable features of our test are that it is easily robustified against time-varying volatility, and that it naturally uncovers time-varying differences in predictive ability under the alternative. Simulations demonstrate the benefits of our multiply robust implementation vis-à-vis several competitors. An empirical application to forecasts for several variables, horizons, vintages and methods from the Survey of Professional Forecasters illustrates the relevance of the new approach, allowing us to identify forecasters with superior models. Such conclusions are in fact impossible to infer by extant tests, since information on the models and estimation procedures behind the forecasts are typically proprietary and, hence, estimation effects cannot be factored out.
(Food) justice in the interim? Temporary urban gardening, welfare activation, and plural valuation
(2026-06-01) Bakunowitsch, Julija
Across European cities, temporary urban gardening is used to address vacancy, sustainability, and social inclusion. Yet little is known about how justice is enacted when such initiatives are embedded in welfare and labor‐market activation policies. This article examines a publicly funded urban gardening project in Dortmund, Germany, implemented as a labor‐market activation measure on temporarily available land targeting employable welfare recipients. Drawing on qualitative data from interviews, participant observation, and document analysis, the study combines the concept of “food justice” with valuation studies to analyze how labor, land, and exchange are valued in everyday practice. Rather than using food justice as a normative benchmark, the article explores how notions of justice are produced and negotiated through institutional frameworks, daily routines, and actors’ evaluative judgments. The findings reveal tensions between empowerment and dependency, care and control, and social recognition and material precarity. While participants experience gardening as meaningful work and a source of social participation and belonging, these valuations remain bounded by welfare regulations, temporary land tenure, and charity‐based forms of food distribution. The article argues that temporary urban gardening projects function as spaces of plural and negotiated valuation, where justice is enacted provisionally through everyday practices, contributing to debates on temporary urban land use, food practices under welfare governance, and the limits of inclusion‐oriented sustainability interventions.
Integrating artificial intelligence in investigating magneto-bioconvection flow of oxytactic microorganisms and nano-enhanced phase change material in H-type cavity
(2024-03-01) Hussain, Shafqat; Aly, Abdelraheem M.; Alsedias, Noura; Çolak, Andaç Batur
Nano-enhanced phase change materials is an effective way to improve the thermal characteristics and to minimize energy consumption. The bioconvection flow of nano-enhanced phase change materials is gaining more attention in recent investigations due to its significant applications in engineering and medical sciences. The present study aims to numerically explore magneto-bioconvection flow of nano-enhanced phase change materials in H-type cavity including oxytactic microorganisms. The cavity is constantly heated from the left and a right wall is maintained at cold temperature. The major focus of the current investigation is analyzing the flow and thermal features of the suspension of nano-enhanced phase change materials and a host fluid. The governing system is reduced to the dimensionless form by applying the appropriate transformation. Impact of pertinent parameters, porosity, cavity aspect ratio, Darcy, Hartmann, Lewis, Rayleigh, bioconvection Rayleigh numbers, radiation parameter, and Péclet number on bioconvection flow of oxytactic microorganisms in H-type cavity has been analyzed. Six various artificial neural network models are explored in order to estimate critical parameters with an artificial intelligence approach. It is found that the variations of a cavity aspect ratio are enhancing the bioconvection flow and phase change material. Increasing Hartmann number reduces the nanofluid velocity and distributions of oxygen and microorganisms. The Rayleigh and bioconvection Rayleigh numbers are playing an importance role in enhancing bioconvection flow and varying phase change material.As Ha increases from 10 to 100, at γ=900, there is a 1.67% decrease in the values of Nuavg and a 0.247% increase in Shavg. Among the study findings, the developed artificial neural networks can predict each parameter with high accuracy.
Investigating the influence of B, C, and N on the tribo-mechanical properties of the chemically complex TiSiBCN thin films using design of experiments
(2024-12-10) Tillmann, Wolfgang; Urbanczyk, Julia; Ebady, Ahmad Zahid; Thewes, Alexander; Bräuer, Günter; Lopes Dias, Nelson Filipe
TiSiBCN thin films show promising properties like high hardness and improved tribological behavior. Adjusting the chemical composition can tailor the properties of these thin films. To investigate this influence, usually one element is varied. However, the interplay and influence of especially the light elements B, C, and N on the tribo-mechanical properties of chemical complex TiSiBCN thin films remain unclear. Therefore, a design of experiment using a central composite design (CCD) was employed to investigate the influences of these light elements on the tribo-mechanical properties of TiSiBCN thin films. TiSiBCN with varying chemical compositions were grown in a magnetron sputtering process by adjusting the cathode power of TiB2/TiSi2 composite targets and the gas flow rates of C2H2 and N2. X-ray diffraction (XRD) analysis revealed crystalline phases based on Ti, TiN, TiC, and TiB, with varying degrees of crystallinity dependent on the chemical composition, where the TiSiBCN thin films demonstrate a broad spectrum of mechanical properties, with hardness and elastic modulus ranging from 20.2 to 39.7 GPa and from 222.3 to 405.0 GPa, respectively. Notably, the B content significantly affects the mechanical properties, with the highest hardness and elastic modulus observed at 46.0 at.-% B. In tribometer tests against an Al2O3 ball under dry friction at room temperature, the TiSiBCN thin films also exhibit a broad spectrum of tribological properties, with the coefficients of friction (CoF) between 0.62 and 0.89 and wear rates between 6.4 × 10−5 and 12.2 × 10−5 mm3/Nm. The lowest CoF of 0.62 with a wear rate of 7.7 × 10−5 mm3/Nm is obtained for TiSiBCN with high amounts of 31.1 at.-% C and 33.5 at.-% N, while high 31.7 at.-% C and low 11.2 at.-% N contents favor the lowest wear rate of 6.4 × 10−5 mm3/Nm with a CoF of 0.74. The tribological results reveal the significant influence of C and N on friction and wear, with TiSiBCN displaying reduced friction and wear tending to have lower hardness. Consequently, TiSiBCN thin films with either high hardness or enhanced friction and wear performance are attainable by adjusting the chemical composition. Depending on the application requirements, the content of the light elements is decisive for the properties of TiSiBCN thin films. The CCD provides insights into the intricate interplay between the chemical composition and tribo-mechanical performance of TiSiBCN. Adjusting the concentrations of B, C, and N within TiSiBCN is crucial for tailoring the tribo-mechanical behavior to meet the specific requirements of applications.
Incumbent responses to anticipated discontinuous regulatory change: the case of Scope 3 CO2 reporting in the European steel industry
(2024-10-28) Hettler, Maximilian; Graf-Vlachy, Lorenz
Regulatory change can be highly discontinuous for organizations. Yet, despite the vast discontinuous change and institutionalism literatures, our understanding of incumbent behavior in response to anticipated discontinuous regulatory change is limited. To address this issue, we conducted a qualitative analysis in the European steel industry, which is facing prospective discontinuous regulatory change on Scope 3 reporting. Our findings offer new insights into this understudied field by elaborating on incumbents' expectations for the future, their ensuing motivations, and their taken or planned actions. We find evidence for heterogenous adaptation behavior that manifests in three motivational patterns: Incentives for early movers, reasons for hesitation, and disincentives preventing implementation. These patterns are a result of incumbents’ varying expectations of future circumstances, opportunities, and risks, and they lead to different actions incumbents plan or take in response to the anticipated change. Our study contributes to the theoretical understanding of regulatory change as a distinct form of discontinuous change, sheds light on incumbent behavior at an early stage of a discontinuous change prior to its actual occurrence, and highlights that adaptation to a discontinuous regulatory change can have both positive and negative effects on incumbents. Our process model enables practitioners to make more informed decisions in the context of discontinuous regulatory change and policymakers may use our findings to improve the regulatory design process and subsequent compliance. Finally, our study opens up numerous pathways for future research.