The Tayler instability is a kink-type, current driven instability that plays an important role in plasma physics but might also be relevant in liquid metal applications with high electrical currents. ...In the framework of the Tayler-Spruit dynamo model of stellar magnetic field generation (Spruit 2002 Astron. Astrophys. 381 923-32), the question of spontaneous helical (chiral) symmetry breaking during the saturation of the Tayler instability has received considerable interest (Zahn et al 2007 Astron. Astrophys. 474 145-54; Gellert et al 2011 Mon. Not. R. Astron. Soc. 414 2696-701; Bonanno et al 2012 Phys. Rev. E 86 016313). Focusing on fluids with low magnetic Prandtl numbers, for which the quasistatic approximation can be applied, we utilize an integro-differential equation approach (Weber et al 2013 New J. Phys.15 043034) in order to investigate the saturation mechanism of the Tayler instability. Both the exponential growth phase and the saturated phase are analysed in terms of the action of the and β effects of mean-field magnetohydrodynamics. In the exponential growth phase we always find a spontaneous chiral symmetry breaking which, however, disappears in the saturated phase. For higher degrees of supercriticality, we observe helicity oscillations in the saturated regime. For Lundquist numbers in the order of one we also obtain chiral symmetry breaking of the saturated magnetic field.
Mass and charge transport in liquid metal batteries are closely intertwined because of the fully liquid interior of the cells. We found that charging and discharging cycles may show pronounced ...asymmetries. They are caused by the presence (charge) or absence (discharge) of solutal convection. While the direction of thermal gradients in the positive electrode of a liquid metal battery depends on boundary conditions and thermodynamics in a non-trivial manner, the solutal gradient predictably changes direction from charge to discharge. The unstable density distribution during charge drives a flow strong enough to prevent any concentration polarization. In contrast, during discharge, the stable density gradient suppresses convection and leads to a substantial mass transport overvoltage. We illustrate this scenario by experimental data, numerical simulations and a physical model.
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•Liquid metal positive electrodes have a stable density stratification in discharge.•A diffusion overvoltage is present during the discharge of a liquid metal battery.•Electrorefining light solute from the top of a liquid alloy induces solutal convection.•Solutal convection guarantees a negligible mass transport overvoltage in charge.
The electrical current through an incompressible, viscous and resistive liquid conductor produces an azimuthal magnetic field that becomes unstable when the corresponding Hartmann number exceeds a ...critical value of the order of 20. This Tayler instability (TI), which is not only discussed as a key ingredient of a nonlinear stellar dynamo model (Tayler-Spruit dynamo), but also as a limiting factor for the maximum size of large liquid metal batteries, was recently observed experimentally in a column of a liquid metal (Seilmayer et al 2012 Phys. Rev. Lett. 108 244501). On the basis of an integro-differential equation approach, we have developed a fully three-dimensional numerical code, and have utilized it for the simulation of the Tayler instability at typical viscosities and resistivities of liquid metals. The resulting growth rates are in good agreement with the experimental data. We illustrate the capabilities of the code for the detailed simulation of liquid metal battery problems in realistic geometries.
The New European Union Forest Strategy for 2030 has been controversially discussed by all relevant interest groups: member states, forest owners, forest-related industry, environmental NGOs. The ...analysis reveals two central conflicts characterizing the Strategy: sovereignty vs. increased Union control—the primary concern of member states and forest owners; and commodity vs. amenity—a central issue between forest-based industry and environmental NGOs. In this respect it is interesting to note that, while being competitors over influence in European forest policy, both forest-related industry and environmental NGOs share the demand for clearer definitions in the Strategy. The Commission’s position is discussed in view of the central conflicts with no unequivocal results—while in the first conflict the Commission can be assumed to, indeed, seek to obtain more power vis-à-vis the member states, with regard to the second conflict three assumptions are on the horizon: (i) the Commission tries to balance the demands of commodity and amenity- oriented interest groups; (ii) despite environmental rhetoric used, the Strategy is dominated by economic goals; (iii) the strategic vision of the Commission inclines towards environmental goals.
Holistic and multi-transdisciplinary approaches, where multiple goals are achieved in order to improve resilience in societies and ecosystems in the short, medium, and long term, are ideal, even ...utopian. Hence, science has come together with practical experiences that highlight the importance of working at a ‘landscape’ level. Landscapes, as socio-ecological systems, are key for sustainability and sustainable development, and they represent a realistic unit to interconnect local, national, and ultimately global scales. International efforts regarding holistic natural resources management approaches are not new; however, they are currently pointing to an Integrated Landscape Approach (ILA). Based on a documentation review and analysis, the present article review aims to promote the disambiguation of the ILA concept and provide an updated synthesis knowledge on the ILA. Especially for the forest sector, the ILA has been identified as particularly beneficial, strongly highlighted by the scientific literature, and with an infrastructure of organizations that are encouraging it. The paper presents the rationale of the science behind the concept, as well as the main principles, we identified a variety of definitions with some significant points of overlap, we highlight the inclusion of ILAs in the current international arena and the relationship of ILA’s and Jurisdictional Approaches, and we make a review of the ILA in a challenging world of rapid change. Our review recognizes ILAs socio-ecological management strategy to reconcile conservation, development, climate change, and human well-being goals. ILAs naturally have a social and idealistic construction behind it, which might be just as necessary andsignificant as the journey toward sustainability itself.
Mass transfer is of paramount importance for an efficient operation of liquid metal batteries. We show for the first time that electrodynamically driven flow can indeed improve mixing of liquid ...electrodes, and reduces concentration polarisation substantially. Simulating the discharge of a realistic Li||Bi cell at 1 A/cm2, the corresponding overpotential reduces by up to 62%. Moreover, the formation of intermetallic phases is delayed, which improves capacity usage. Finally, we demonstrate that vertical magnetic fields – which are originating from external sources – change the flow structure entirely, and will homogenise the positive electrode even better.
The importance of local forests as places of recreation and human well-being depends very much on their visual impact on human perception. Forest managers, therefore, seek to achieve structural ...elements or attributes that can be used to enhance the visual aesthetics of managed forest ecosystems. The following survey was undertaken in the Tharandter Forest in Saxony (Germany). The field interviews were focussed on visual aesthetics and acceptance. The statements of the 53 participants in the survey were used to analyse views concerning typical Norway spruce forest types: with the regeneration of deciduous tree species in the background, without regeneration, and with European beech as a second layer in the foreground. The evaluation of the questionnaires confirmed a clear ranking. The forest view with the regeneration of deciduous tree species received the highest number of positive scores, followed by the forest view with beech as a second layer. The forest view characterised by pure and dense Norway spruce trees received the worst rating, differing significantly from the other two, on the basis of the spatial arrangement, visual diversity and acceptance. Linear mixed models demonstrated that visual aesthetics was mostly explained by visual diversity as a result of tree species diversity or mixtures and age structures, the diversity of surrounding structures and colours, ground vegetation or visibility.
This paper provides a comparison of current visions, missions and strategies of three international forest research organizations: European Forest Institute (EFI), Center for International Forest ...Research (CIFOR) and International Union of Forest Research Organizations (IUFRO). Against the background of theoretical conceptions of visions, missions and strategies, a qualitative tabular content analysis is applied. A special focus lies on the thematic work areas of the organizations and their connection to the Sustainable Development Goals (SDGs).
Visions and missions provide an important guidance for employees and other people in the organization, but also for communication to outsiders. Within strategies, Non-Profit Organizations can define their mission and vision as well as strategic goals. Recent missions and visions of EFI, CIFOR and IUFRO are analyzed with a textual analysis, while for their strategies a summarizing content analysis is used.
The comparison discloses differences between the three organizations with regard to their orientation towards societal impact and/or advancement of science. However, all of them strive for improving living conditions for people. CIFOR clearly focuses on the SDGs and covers all of them, while IUFRO and EFI do this only partially. Except for doublings, EFI and IUFRO together address 12 SDGs out of 17 SDGs. This finding is especially important in the light of the current cooperation between EFI and IUFRO. Both organizations signed a Memorandum of Understanding in 2019, where they claim to account for achieving the SDGs by strengthening the role of forest conservation and sustainable forest management.
•This study examines the perception of urban residents regarding the services and disservices of urban trees in the Garden City of West Africa.•The most important services provided by urban trees are ...related to health and climate improvement, energy, aesthetics and environmental benefits.•Key challenges identified include poor management of urban trees, infrastructure damage, and safety issues, such as parks and gardens serving as hideouts for criminals.•Institutional assistance and changes in the legislative structure are recommended to address these challenges and sustain urban forestry.
The growth of trees in urban areas brings forth an extensive array of services and disservices, the comprehension of which can assist urban forestry professionals in advancing a more sustainable urban forest ecosystem. This paper assesses the perception of urban residents on the services and disservices from urban trees in a less represented geographic area. Using a mixed method approach, primary data was gathered from 396 urban inhabitants in the study area. Exploratory factor analysis was used to assess perception of services and disservices from the urban trees. Using a principal component analysis, it was found out that the most important services provided by urban trees were health and climate improvement as well as energy, esthetic and environmental benefits. These services explained 50.8% of citizens’ perception variance and are linked to basic human needs. Additionally, the Monte Carlo parallel analysis-based on exploratory factor analysis revealed that the underlying problems that needs to be addressed were related to poor management and maintenance of urban trees, destruction of infrastructure by trees and issues related to safety including parks and gardens serving as hideouts for criminals in the city. These components were predicting 53.3% of the problems and disservices of urban trees. The results provide a valuable insight for urban forestry professionals. The findings imply that institutional assistance should be increased, and the legislative structure changed to address these challenges to sustain urban forestry.
This work sets out to apply the Policy Coherence Framework (PCF) to the case of climate policy, taking into account the European, German and Thuringian political levels of analysis. It combines an ...analysis of vertical coherence between these levels and horizontal coherence within and between different sectoral policies. The study demonstrates disparities between coherence within climate policy itself and between other policy sectors as regards forest area development. It further reveals some contradictions between economic and ecological goals in German climate policy, particularly as concerns the role of forests. According to the authors, this observation can, at least in part, be explained by the national security obligations of Germany as a nation state. This assumption is supported by the observation that the regional level of Thuringia is more consistent with the supranational level of the European Union, both of which can “afford” to favour ecology over economy due to not being nation states. Another finding suggests that the broad and ambiguous definition of climate policy causes many contradictions, leading to an “omnipresence” of climate policy, and in doing so, strips it of its meaning and, consequently, practical relevance.
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