Precipitation is not limiting for xylem formation dynamics and vessel development in European beech from two temperate forest sites

We investigated the dynamics of xylem differentiation processes and vessel characteristics in Fagus sylvatica L. to evaluate the plasticity of xylem structures under different environmental conditions. In 2008-10, analyses were performed on microcores collected weekly from two temperate sites: Menina planina (1200 m above sea level (a.s.l.)) and Panska reka (400 m a.s.l.). The duration between the onset and end of major cell differentiation steps and vessel characteristics (i.e., density, VD; mean diameter, MVD; mean area, MVA; and theoretic conductivity area, TCA) were analysed in the first and last quarters of the xylem rings, also in respect of local weather conditions (precipitation, temperature). Although the onset, duration and end of xylem formation phases differed between the two sites, the time spans between the successive wood formation phases were similar. Significant differences in MVD, MVA and TCA values were found between the first and last quarters of xylem increment, regardless of the site and year. Vessel density, on the other hand, depended on xylem-ring width and differed significantly between the sites, being about 30% higher at the high elevation site, in beech trees with 54% narrower xylem rings. Vessel density in the first quarter of the xylem ring showed a positive correlation with the onset of cell expansion, whereas a negative correlation of VD with the cessation of cell production was found in the last quarter of xylem increment. This may be explained by year-to-year differences in the timing of cambial reactivation and leaf development, which effect hormonal regulation of radial growth. No significant linkage between intra-annual weather conditions and conduit characteristics was found. It can thus be presumed that precipitation is not a limiting factor for xylem growth and cell differentiation in beech at the two temperate study sites and sites across Europe with similar weather conditions

How does the Grundnorm fare? : towards a theory less pure

Defence date: 25 September 2018Examining Board: Professor Nehal Bhuta, European University Institute (Supervisor); Professor Peter Drahos, European University Institute; Professor Hans Lindahl, Tilburg University; Professor Alexander Somek, University of ViennaThis thesis advances the argument that Kelsen‘s pure theory of law still has the potential to inform and inspire critical legal research in the postmodern world. The common view that pure theory represents an outdated, state-centric theory of law is rejected through a creative re-reading of Kelsen‘s seminal theory, which traces both its critical iconoclastic ambitions, and the limitations imposed on these ambitions by Kelsen‘s purist methodology. To illustrate this tension, the thesis focuses on Kelsen‘s Grundnorm (basic norm) concept. The Grundnorm represents the presupposed foundation of law, a feigned ground of objective legal validity representing law‘s binding power, mode of existence, and unity. The Grundnorm concept is a positivist answer to the theories that derive legal validity from substantial – yet elusive – natural law. Kelsen‘s Grundnorm does not prescribe the content of a legal order, and this position is often interpreted as dangerous, even nihilistic. Many attempts have been made to rearticulate the formal Grundnorm into a substantial concept grounding law in the values of liberalism. This project, in contrast, embraces the emptiness of the Grundnorm as pure theory‘s commitment to the critical treatment of law. Kelsen insists that law is a human-made and thus constantly transforming phenomenon – a phenomenon potentially dangerous or redeeming. Pure theory is, accordingly, envisioned as a dynamic theory of law. Nevertheless, owning to the rigorous epistemological norms enforced by Kelsen, the Grundnorm remains trapped in a linear conception of time and is spatially imagined as a single point supporting a legal system. To engage with both critical potentialities and limitations of pure theory and its Grundnorm, this thesis reads them through the works of Heidegger, Derrida, and Nietzsche. In this process, the Grundnorm is simultaneously affirmed and destroyed – rearticulated as a multiplicity, a perspectivist Grundnorm(s) that nevertheless retains the most important critical insights of pure theory

Dominance of Fagus sylvatica in the Growing Stock and Its Relationship to Climate—An Analysis Using Modeled Stand-Level Climate Data

In the future, climate change is expected to affect the spatial distribution of most tree species in Europe. The European beech (Fagus sylvatica), a drought-sensitive tree species, is currently distributed throughout Europe, where it is an ecologically and economically important species. In Slovenia, the European beech represents 33% of the growing stock, but such a proportion greatly varies across Europe. Whether such a variation is related to the climate environmental gradients or because of historical or management decisions is an as-yet unexplored question. For this study, we employed the Slovenian Forests Service inventory, where the proportion of beech in the forest stock has been monitored in 341,341 forest stands across the country. Modeled climate data from the SLOCLIM database, calculated for each of the stands, was also used to test the hypothesis that although beech forests have always been influenced by human activity, the dominance of beech trees in forest stands is at least partially dictated by the climate. The results showed the distribution of the main climate variables (annual precipitation, the share of summer and spring precipitation, and annual maximum and minimum temperatures) and how they affect the current dominance of beech trees at the stand level. Due to the large number and variability of forest stands studied, the results should be transferable to better understand and manage the climatic suitability and risks of Fagus sylvatica. The modeled data is publicly available in the web repository Zenodo

SLOCLIM: a high-resolution daily gridded precipitation and temperature dataset for Slovenia

We present a new publicly available daily gridded dataset of maximum and minimum temperature and precipitation data covering the whole territory of Slovenia from 1950 to 2018. It represents the great variability of climate at the crossroads between the Mediterranean, Alpine and continental climatic regimes with altitudes between 0-2864ma.s.l. We completely reconstructed (quality control and gap filling) the data for the three variables from 174 observatories (climatological, precipitation and automatic stations) with the original records all over the country. A comprehensive quality control process based on the spatial coherence of the data was applied to the original dataset, and the missing values were estimated for each day and location independently. Using the filled data series, a grid of 1 x 1 km spatial resolution with 20 998 points was created by estimating daily temperatures (minimum and maximum) and precipitation, as well as their corresponding uncertainties at each grid point. In order to show the potential applications, four daily temperature indices and two on precipitation were calculated to describe the spatial distribution of (1) the absolute maximum and minimum temperature, (2) the number of frost days, (3) the number of summer days, (4) the intensity of precipitation and (5) the maximum number of consecutive dry days. The use of all the available information, the complete quality control and the high spatial resolution of the grid allowed for an accurate estimate of precipitation and temperature that represents a precise spatial and temporal distribution of daily temperatures and precipitation in Slovenia. The SLOCLIM dataset is publicly available at https://doi.org/10.5281/zenodo.4108543 and http://www.sloclim.eu (last access: 10 June 2021) and can be cited as Skrk et al. (2020)

14 MeV calibration of JET neutron detectors-phase 1: calibration and characterization of the neutron source

In view of the planned DT operations at JET, a calibration of the JET neutron monitors at 14 MeV neutron energy is needed using a 14 MeV neutron generator deployed inside the vacuum vessel by the JET remote handling system. The target accuracy of this calibration is ±10% as also required by ITER, where a precise neutron yield measurement is important, e.g. for tritium accountancy. To achieve this accuracy, the 14 MeV neutron generator selected as the calibration source has been fully characterised and calibrated prior to the in-vessel calibration of the JET monitors. This paper describes the measurements performed using different types of neutron detectors, spectrometers, calibrated long counters and activation foils which allowed us to obtain the neutron emission rate and the anisotropy of the neutron generator, i.e. the neutron flux and energy spectrum dependence on emission angle, and to derive the absolute emission rate in 4π sr. The use of high resolution diamond spectrometers made it possible to resolve the complex features of the neutron energy spectra resulting from the mixed D/T beam ions reacting with the D/T nuclei present in the neutron generator target. As the neutron generator is not a stable neutron source, several monitoring detectors were attached to it by means of an ad hoc mechanical structure to continuously monitor the neutron emission rate during the in-vessel calibration. These monitoring detectors, two diamond diodes and activation foils, have been calibrated in terms of neutrons/counts within ±5% total uncertainty. A neutron source routine has been developed, able to produce the neutron spectra resulting from all possible reactions occurring with the D/T ions in the beam impinging on the Ti D/T target. The neutron energy spectra calculated by combining the source routine with a MCNP model of the neutron generator have been validated by the measurements. These numerical tools will be key in analysing the results from the in-vessel calibration and to derive the response of the JET neutron detectors to DT plasma neutrons starting from the response to the generator neutrons, and taking into account all the calibration circumstances.EURATOM 63305

Living on the edge: contrasted wood-formation dynamics in Fagus sylvatica and Pinus sylvestris under Mediterranean conditions

Wood formation in European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.) was intra-annually monitored to examine plastic responses of the xylem phenology according to altitude in one of the southernmost areas of their distribution range, i.e., in the Moncayo Natural Park, Spain. The monitoring was done from 2011 to 2013 at 1180 and 1580 m a.s.l., corresponding to the lower and upper limits of European beech forest in this region. Microcores containing phloem, cambium and xylem were collected biweekly from twenty-four trees from the beginning of March to the end of November to assess the different phases of wood formation. The samples were prepared for light microscopy to observe the following phenological phases: onset and end of cell production, onset and end of secondary wall formation in xylem cells and onset of cell maturation. The temporal dynamics of wood formation widely differed among years, altitudes and tree species. For Fagus sylvatica, the onset of cambial activity varied between the first week of May and the third week of June. Cambial activity then slowed down and stopped in summer, resulting in a length of growing season of 48–75 days. In contrast, the growing season for P. sylvestris started earlier and cambium remained active in autumn, leading to a period of activity varying from 139-170 days. The intra-annual wood-formation pattern is site and species-specific. Comparison with other studies shows a clear latitudinal trend in the duration of wood formation, positive for Fagus sylvatica and negative for P. sylvestris.Publishe

Annual cambial rhythm in Pinus halepensis and Pinus sylvestris as indicator for climate adaptation

To understand better the adaptation strategies of intra-annual radial growth in Pinus halepensis and Pinus sylvestris to local environmental conditions, we examined the seasonal rhythm of cambial activity and cell differentiation at tissue and cellular levels. Two contrasting sites differing in temperature and amount of precipitation were selected for each species, one typical for their growth and the other represented border climatic conditions, where the two species coexisted. Mature P. halepensis trees from Mediterranean (Spain) and sub-Mediterranean (Slovenia) sites, and P. sylvestris from sub-Mediterranean (Slovenia) and temperate (Slovenia) sites were selected. Repeated sampling was performed throughout the year and samples were prepared for examination with light and transmission electron microscopes. We hypothesized that cambial rhythm in trees growing at the sub-Mediterranean site where the two species co-exist will be similar as at typical sites for their growth. Cambium in P. halepensis at the Mediterranean site was active throughout the year and was never truly dormant, whereas at the sub-Mediterranean site it appeared to be dormant during the winter months. In contrast, cambium in P. sylvestris was clearly dormant at both sub-Mediterranean and temperate sites, although the dormant period seemed to be significantly longer at the temperate site. Thus, the hypothesis was only partly confirmed. Different cambial and cell differentiation rhythms of the two species at the site where both species co-exist and typical sites for their growth indicate their high but different adaptation strategies in terms of adjustment of radial growth to environmental heterogeneity, crucial for long-term tree performance and survival

The integrated engineering design concept of the upper limiter within the EU-DEMO LIMITER system

The EU-DEMO first wall protection relies on a system of limiters. Although they are primarily designed for facing the energy released by a limited plasma during transients, their design should safely withstand a combination of loads relevant for in-vessel components (IVCs) during steady-state operation. They are not meant to breed tritium, nor to provide plasma stability. However, sitting in place of blanket portions, they should ensure an adequate shielding function to vacuum vessel and magnets while withstanding both their dead weight and the electro-mechanical loads arising from the interaction between current induced in the conductive structure and magnetic field. During plasma disruptions they will be subjected to halo currents flowing from/to the plasma and the grounded structures, whose effects must be added to the eddy current ones. Disruption-induced electro-mechanical loads are hence IVC design-driving, despite the uncertainties in both eddy and halo currents' magnitude and distribution, which depend on IVC design, electrical connectivity, plasma temperature and halo width. The integrated design of the limiter is made of two actively water-cooled sub-components: the Plasma-Facing Wall (PFW) directly exposed to the plasma, and the Shielding Block (SB) devoted to hold the PFW while providing neutronic shielding. The PFW design is driven by disruptive heat loads. Disruption-induced electro-magnetic loads are instead SB design drivers, meaning that the design details (i.e. geometry, electrical connections, attachments) affect the loads acting on it, which, in turn, are affected by the mechanical response of the structure. The present paper describes the design workflow and assessment of the Upper Limiter (UL), resulting from a close and iterative synergy among different fields. Built on static-structural and energy balance hand calculations based on, respectively, preliminary electro-magnetic and neutronic loads, the UL integrated design performance has then been verified against electro-magnetic, neutronic, thermal-hydraulic and structural assessment under the above-mentioned load combination. The outcome will be taken as reference for future limiter engineering designs