Leibniz Universität Hannover

The immiscible displacement of a wetting fluid by a non-wetting fluid in rough fractures is crucial in many subsurface applications. Hydrodynamic-scale modeling of such drainage flows is challenging due to the complex interaction between the forces at play, the intricate geometry, and the required modeling of moving contact lines. In addition, a remaining critical open question is to what extent not resolving the films of wetting fluid deposited on fracture walls degrades numerical predictions. We address this question by solving the Navier–Stokes equations, employing the volume-of-fluid method to capture fluid–fluid interfaces and considering numerical meshes that result in either resolved films (RF) or unresolved films (UF) in the simulations. The numerical model, implemented in OpenFOAM, is validated in the classical Saffman–Taylor (ST) viscous instability configuration using the original ST experimental measurements; at capillary numbers (Ca) larger than 10−3, UF simulations overpredict ST finger widths. We then address two synthetic fracture geometries: one with sinusoidally varying apertures and one with stochastic geometric properties typical of geological fractures. Predictions of RF and UF simulations are compared quantitatively for Ca ranging between 10−5 and 10−3. Wetting film thicknesses follow a power law of Ca similar to Bretherton's law. RF and UF approaches both predict similar invasion patterns, but the latter underestimates interfacial lengths and macroscopic pressure drops, as compared to RF simulations, while overpredicting invading fluid saturations and breakthrough times. These discrepancies increase with Ca, whereas the disordered nature of the geological fracture tends to limit them. For Ca<10−5, the discrepancies are negligible.

This paper investigates the behavior of feldspar-based geopolymer mortars under nitric acid, sulfuric acid attack and seawater attacks and provides an understanding of their degradation mechanisms. Geopolymer mortars were cast using feldspar quarry waste (pegmatite) altered with 20–30 wt% of calcined clay and mixed with river sand, then, activated in an alkaline medium. The effect of alteration of calcined clay on the exposure of geopolymer mortars to physical and chemical attacks was investigated via visual observation, mass loss, mechanical strengths, Fourier Transform Infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscope coupled with energy dispersive X-ray spectroscopy (SEM-EDS). From the results, the appearance of samples showed a degradation with the time of exposure and type of solution used from seawater to sulfuric acid. The compressive strength showed a loss after 90 days to seawater, nitric and sulfuric acids attack which decreased from 58.6 MPa to 30.8, 10.8 and 7.9 MPa, respectively. Similarly, significant deterioration of microstructure was observed after immersion in acid solutions, which is more pronounced in sulfuric acid compared to nitric acid. The results demonstrate an overall negative effect of feldspar-based geopolymer mortars due to the weak resistance of geopolymer gels formed under acid attacks. The outcomes of this study hold promise for tailoring geopolymer properties for various applications and provide a basis for further work in this area.

This editorial introduces the Special Collection "Grasslands of Asia" in Vegetation Classification and Survey, highlighting the urgent need for systematic vegetation classification across Asia's diverse grassland ecosystems. Despite their vast ecological, climatic, and cultural significance, Asian grasslands remain underrepresented in global vegetation studies. This gap results from uneven research capacities, methodological fragmentation, limited data accessibility, and complex geopolitical barriers. Grasslands across Asia, which include both natural types like steppes, savannas, and alpine meadows and semi-natural ecosystems, face escalating threats including climate change, overgrazing, land-use changes, habitat fragmentation, and socio-political disruptions. Inspired by discussions at the inaugural Asian Grassland Conference in 2022 and the establishment of the Asian Regional Section of the International Association for Vegetation Science (IAVS), this Special Collection aims to promote standardized vegetation classification methods, enhance cross-regional data sharing, and foster international collaboration. Although only seven contributions from West and Middle Asia were ultimately included, they significantly advance the understanding of grassland typologies in these regions. Moving forward, coordinated efforts at local, regional, and continental scales are essential, supported by platforms such as the Asian Regional Section of IAVS. Strengthening vegetation classification frameworks and regional databases will bridge existing methodological gaps and provide critical support for conservation planning, sustainable management, and biodiversity research in Asia's grassland ecosystems.

The production of conventional bricks has negative impact on the environment due to CO 2 emissions. Therefore, the use of alkali-activated by-product materials as partial or full replacement of cement has been promising in producing eco-friendly compressed earth bricks for sustainable construction. This research aims to simulate the thermal behavior of an office building prototype composed of eco-friendly compressed earth brick (CEB) walls using Design Builder software to investigate the impact of CEB walls on the indoor thermal comfort, total energy consumption and CO 2 emissions. In addition to investigate the influence of the type and thicknesses of walls, and thickness of expanded polystyrene (EPS) insulating layer on the total energy consumption and (CO 2 ) emissions. The results indicated that using walls of compressed earth bricks (CEB) made by alkali-activated ground granulated blast furnace slag (GGBS) as soil stabilizer with full replacement of cement is promising for reducing the total energy consumption and CO 2 emissions with competitive compressive strength to those stabilized by cement. The results also revealed the noticeable effect of the type and thicknesses of walls in addition to the thickness of EPS insulating layer in reducing the total energy consumption and CO 2 emissions. This reduction reached about 21–25% for different wall types of thickness 120 mm when EPS thicknesses increased up to 50 mm compared to the same walls without EPS.

Performativity of science refers to the phenomenon that the dissemination of scientific conceptualisations can sometimes affect their target systems or referents. A widely held view in the literature is that scientists ought not to deliberately deploy performative models or theories with the aim of eliciting desirable changes in their target systems. This paper has three aims. First, I cast and defend this received view as a worry about autonomy-infringing paternalism and, to that end, develop a taxonomy of the harms it can impose. Second, I consider various approaches to this worry within the extant literature and argue that these offer only unsatisfactory responses. Third, I propose two positive claims. Manipulation of target systems is (a) not inherently paternalist and can be unproblematic, and is (b) sometimes paternalist, but whenever such paternalism is inescapable, it has got to be justifiable. I generalise an example of modelling international climate change coordination to develop this point.

Zusammenfassung Im Fach Sport hat das Thema des Übens und Konsolidierens unter dem Fokus der Unterstützung der Konsolidierung bisher kaum Beachtung gefunden. Ziel des Beitrags ist es, einen Einblick in die Forschungen zur Unterstützung des Übens und Konsolidierens im Sportunterricht zu geben, konzeptuelle Überlegungen darzustellen und die Bedeutung des Konsolidierens und dessen Unterstützung für den Sportunterricht kritisch zu diskutieren. Ausgehend von den fachlichen Besonderheiten des Sportunterrichts (2) und des motorischen Lernens (3), das in knapper Form aus sportpädagogischer und bewegungswissenschaftlicher Perspektive beleuchtet wird, werden Prämissen für das Konsolidieren und seine Unterstützung abgeleitet. Der nachfolgende Überblick über empirische Befunde zum Üben und der Unterstützung von Konsolidierungsprozessen bezieht neben den wenigen sportunterrichtsbezogenen Studien auch Erkenntnisse des außerschulischen Sports mit ein, da diese die fachdidaktischen Überlegungen sinnvoll ergänzen können (4). Daran schließen konzeptuelle Überlegungen zum „guten“ Üben an (5), die deutschsprachige und internationale Ansätze aufgreifen. Im letzten Abschnitt werden schließlich Vorschläge zur zukünftigen Erforschung und zur Implementierung der Unterstützung des Konsolidierens im Sportunterricht formuliert sowie neuralgische Punkte diskutiert (6).

The need for large amounts of force in the Equal-Channel Angular Pressing (ECAP) process has always caused problems and limitations in conducting it. In the current study, elevated temperature ECAP process is proposed as an approach to reduce force and its effects on the microstructural and mechanical properties of copper metal has been investigated, comprehensively. The research results showed that due to the phenomenon of recrystallization and the creation of refined and equiaxed grains, the microstructure of copper and its resistance to corrosion was improved. Accordingly, the stress concentration created in the triple points was decreased, and, consequently, the fracture toughness of the material increased. Based on the present findings, the crack growth becomes intergranular, so the crack growth path becomes longer. Moreover, only one component of the applied force causes the crack to grow, and as a result, the resistance of the material increases. Therefore, for example, the fatigue crack growth range threshold of the material subjected to the ECAP process was 3.5 times larger than those of the base metal (BM). Also, it can increase ultimate strength up to 65.4%, hardness up to 89%, and impact toughness up to 91.9%. In addition, it was found that if the ECAP process is performed at elevated temperatures, the maximum required force can be reduced by 45.6%.

Marine carbon dioxide removal (mCDR) and geological carbon storage in the marine environment (mCS) promise to help mitigate global climate change alongside drastic emission reductions. However, the implementable potential of mCDR and mCS depends, apart from technology readiness, also on site‐specific conditions. In this work, we explore different options for mCDR and mCS, using the German context as a case study. We challenge each option to remove 10 Mt CO2 yr⁻¹, accounting for 8%–22% of projected hard‐to‐abate and residual emissions of Germany in 2045. We focus on the environmental, resource, and infrastructure requirements of individual mCDR and mCS options at specific sites, within the German jurisdiction when possible. This serves as an entry point to discuss main uncertainty factors and research needs beyond technology readiness, and, where possible, cost estimates, expected environmental effects, and monitoring approaches. In total, we describe 10 mCDR and mCS options; four aim at enhancing the chemical carbon uptake of the ocean through alkalinity enhancement, four aim at enhancing blue carbon ecosystems' sink capacity, and two employ geological off‐shore storage. Our results indicate that five out of 10 options would potentially be implementable within German jurisdiction, and three of them could potentially meet the challenge. Our exercise serves as an example on how the creation of more tangible and site‐specific CDR options can provide a basis for the assessment of socio‐economic, ethical, political, and legal aspects for such implementations. The approach presented here can easily be applied to other regional or national CDR capacity considerations.

Results of recent publications on machine-learning based gravitational-wave searches vary greatly due to differences in evaluation procedures. The Machine Learning Gravitational-Wave Search Challenge [1] was organized to resolve these issues and produce a unified framework for machine-learning search evaluation. Six teams submitted contributions, four of which are based on machine learning methods and two are state-of-the-art production analyses. This chapter is a modified version of [2], which describes the submission from our team titled TPI FSU Jena and its updated variant. We also apply this algorithm to real O3b data and recover the relevant events of the GWTC-3 catalog. Reprinted with permission from [2]. Copyright (2024) by the American Physical Society.

An important part for material modeling is the consideration of electromagnetic fields. In this paper, we add them to Hamilton’s principle for mechanical and thermal fields. We begin with a brief introduction to the electric and magnetic limit cases, which allows a non-relativistic formulation. After introducing the thermodynamic fundamentals, we present the Hamilton functionals for the limit cases from which we derive our governing system of equations by applying Hamilton’s principle of stationary action. In order to be able to describe the microstructure as well, we also consider general internal variables. After the derivation of the equations for the dominant fields, we show how to obtain the secondary fields. For both limit cases we show an example where the dominant electromagnetic field and the mechanic field are coupled by material properties.

A bstract Interference effects are well founded from the quantum mechanical viewpoint and in principle cannot be ignored in realistic studies of New Physics scenarios. In this work, we investigate the size of interference effects between resonant and non-resonant contributions to di-Higgs production in the singlet extension of the Standard Model, where the additional heavy scalar provides a resonant channel. We find these interference contributions to have a non-negligible effect on the cross-sections and differential distributions. In order to allow for a computationally efficient treatment of these effects via reweighting, we introduce a new tool utilising a matrix-element reweighting method: HHReweighter. In addition to the broadly used di-Higgs invariant mass m hh , we analyse the sensitivity to the interference terms for other kinematic variables, such as the Higgs boson transverse momentum, and find that these also can be sensitive to interference effects. Furthermore, we provide updates on the latest experimental and theoretical limits on the parameter space of the real singlet extension of the Standard Model Higgs sector.

Baeyer–Villiger monooxygenases (BVMOs) are key for the selective oxidation of ketones into diverse (cyclic) esters. However, challenges like oxygen and cofactor dependence and substrate/product inhibition hinder their broader application. To address some of these issues, nonconventional media have been applied; still, they lack certain water required for enzyme hydration and cofactor regeneration, reducing activity and/or stability. Fusion approaches enable efficient cofactor recycling by shortening the diffusion distance between enzyme active sites in cascades, especially under low‐water conditions. Trial‐and‐error linker design and time‐intensive construction of fusion enzymes substantially slow down the development of fusion enzymes. In this study, we present the work on the fusions of cyclohexanone monooxygenase (CHMO) and alcohol dehydrogenase (ADH) with linkers owing varying lengths and flexibility in both orientations in nonconventional media, focusing on understanding the effects of linkers on the structural and catalytic properties of fusion enzymes. As such, 12 new fusion enzymes were constructed and evaluated regarding the kinetics, specific activity, and stability, identifying the optimal ones for the linear oxyfunctionlization cascade in aqueous–organic biphasic systems. The conformation and flexibility of linkers and the spatial arrangement of fusion enzymes were studied with simulations, which provides a deep understanding of linkers’ influence and offers insights into the rational design of fusion enzymes.

This review covers the anelastic deformation observed under electric loading (electroplasticity) of metals and ceramics. The interplay of various complex mechanisms beyond trivial Joule heating leading to enhanced plasticity is discussed in the context of both materials classes. In the case of metals, electromechanical coupling resulting in forces being exerted on atoms and dislocations is elucidated. In the case of ceramics, change in the grain boundary structure is proposed to justify the enhanced plasticity. Microstructural evidence is analyzed in correlation with the deformation behavior.

Philosophers of science have recently started to discuss the role of scientific methods for their field. Those tendencies have immediate methodological implications for Integrated History and Philosophy Science (&HPS) as an area that contributes to philosophy of science while drawing heavily on historical case studies. This paper addresses the questions whether and if so in which way scientific methods can be useful for research in &HPS by discussing the usefulness of one such method, namely network analysis. By focusing on the example of model transfer in science, I argue that network analysis is particularly useful for doing research in &HPS because it allows for addressing a set of methodological issues arising from the use of case studies. More specifically, my claim is that network analysis can enhance the core functions of case studies in &HPS, namely those of concept generation, of concept refinement, and of empirical justification of concepts. While I discuss the advantages of network analysis for &HPS, I close by cautioning that it cannot replace more traditional philosophical methods. Rather, network analysis must rely on them to fully develop its potentials.

A common goal in clinical trials is to conduct tests on estimated treatment effects adjusted for covariates such as age or sex. Analysis of Covariance (ANCOVA) is often used in these scenarios to test the global null hypothesis of no treatment effect using an ‐test. However, in several samples, the ‐test does not provide any information about individual null hypotheses and has strict assumptions such as variance homoscedasticity. We extend the method proposed by Konietschke et al. [“Analysis of Covariance Under Variance Heteroscedasticity in General Factorial Designs,” Statistics in Medicine 40 (2021): 4732–4749] to a multiple contrast test procedure (MCTP), which allows us to test arbitrary linear hypotheses and provides information about the global‐ as well as the individual null hypotheses. Further, we can calculate compatible simultaneous confidence intervals for the individual effects. We derive a small sample size approximation of the distribution of the test statistic via a multivariate t‐distribution. As an alternative, we introduce a Wild‐bootstrap method. Extensive simulations show that our methods are applicable even when sample sizes are small. Their application is further illustrated within a real data example.

The Saharo-Arabian Desert is one of the largest biogeographical barriers on Earth, impeding dispersals between Africa and Eurasia, including movements of past hominins. Recent research suggests that this barrier has been in place since at least 11 million years ago¹. In contrast, fossil evidence from the late Miocene epoch and the Pleistocene epoch suggests the episodic presence within the Saharo-Arabian Desert interior of water-dependent fauna (for example, crocodiles, equids, hippopotamids and proboscideans)2, 3, 4, 5–6, sustained by rivers and lakes7,8 that are largely absent from today’s arid landscape. Although numerous humid phases occurred in southern Arabia during the past 1.1 million years⁹, little is known about Arabia’s palaeoclimate before this time. Here, based on a climatic record from desert speleothems, we show recurrent humid intervals in the central Arabian interior over the past 8 million years. Precipitation during humid intervals decreased and became more variable over time, as the monsoon’s influence weakened, coinciding with enhanced Northern Hemisphere polar ice cover during the Pleistocene. Wetter conditions likely facilitated mammalian dispersals between Africa and Eurasia, with Arabia acting as a key crossroads for continental-scale biogeographic exchanges.

The spectral theory of semigroup generators is a crucial tool for analysing the asymptotic properties of operator semigroups. Typically, Tauberian theorems, such as the ABLV theorem, demand extensive information about the spectrum to derive convergence results. However, the scenario is significantly simplified for positive semigroups on Banach lattices. This observation extends to the broader class of eventually positive semigroups—a phenomenon observed in various concrete differential equations. In this paper, we investigate the spectral and asymptotic properties of eventually positive semigroups, focusing particularly on the persistently irreducible case. Our findings expand upon the existing theory of eventual positivity, offering new insights into the cyclicity of the peripheral spectrum and asymptotic trends. Notably, several arguments for positive operators and semigroups do not apply in our context, necessitating the use of ultrapower arguments to circumvent these challenges.