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Abstract: This study presents the in-situ synthesis of hydroxyapatite (HAp) within the structure of beech and pine wood. The modification process utilized a two-step vacuum-pressure impregnation coupled with chemical precipitation using calcium nitrate tetrahydrate and diammonium hydrogen phosphate solutions, followed by exposure to ammonium hydroxide vapors. While the initial focus was on the overall physicochemical changes, microstructural characteristics and fire behavior of the mineralized wood, the main aim is to specifically investigate the effects of leaching. Because HAp synthesis produces water-soluble ammonium nitrate (NH4NO3) as a by-product, this research systematically addresses how the removal of this component affects the final properties of wood. HAp formation was confirmed by FTIR and X-ray diffraction, while scanning electron microscopy and microcomputed tomography revealed HAp deposits primarily in the cell lumen of both wood species. Fire behavior was evaluated using thermal analysis and the cone calorimeter. The incorporation of non-flammable HAp synthesized within the wood structure may act as a barrier and mass transfer during pyrolysis. This results to comparable or slightly enhanced key fire performance parameters when comparing leached HAp synthesized samples with leached reference samples. In contrast, the unleached HAp synthesized samples, which still contained residual NH4NO3, showed deterioration in fire growth rate (FIGRA) and heat release rate (HRR) parameters, confirming that NH4NO3 acts as an oxidant. However, this oxidative property also leads to improvements in total heat release (THR) and total smoke production (TSP) parameters compared to unleached references, representing a complex interaction when studying the fire properties of mineralized wood.
Keywords: chemical precipitation method, fire retardancy, hydroxyapatite, HAp, leaching process, wood
Published in DiRROS: 17.04.2026; Views: 142; Downloads: 142
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Abstract: The study investigated the floristic composition of 12 pasture areas in the Danube Delta, and their neighbouring regions, and the relationships between the floristic composition and the environmental variables. The vegetation analysis was carried out based on the mean percentage values corresponding to the scale developed by the Braun-Blanquet. For the syntaxonomic assignment, 50 phytocoenological relevés were made. The relevés were analyzed using Agglomerative Hierarchical Clustering (flexible β algorithm and Bray-Curtis dissimilarity). The relationship between floristic composition and environmental variables was assessed using Detrended Correspondence Analysis (DCA) and Canonical Correlation Analysis (CCA) in CANOCO. Our results showed that the analyzed species are mostly mesoxerophilic, oligo-mesotrophic, and poorly exploited as fodder, with moderate tolerance to grazing and medium anthropogenic influence, predominantly urbanophobic. Numerical analysis identified eight well-defined communities, which correspond to associations described in the taxonomic literature, based on their diagnostic species. The predominant plant association is Hordeo murini-Cynodontetum dactyloni. The variation of the floristic composition is influenced by annual precipitation.
Keywords: Danube Delta, agro-biological indices, vegetation analysis, phytocoenological relevés, annual precipitation, Cynodon dactylon
Published in DiRROS: 24.01.2026; Views: 375; Downloads: 209
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Abstract: Long-term monitoring of stable isotopes in precipitation (δ18O, δ2 H), alongside meteorological data, is key to understanding how large-scale hydroclimate variability influences regional and local climate. This study presents one of the longest records in Central and Southeastern Europe: the multi-decadal (1981–2024) dataset of monthly composite precipitation stable isotope records from Ljubljana, Slovenia. The δ18O, δ2 H, and d-excess values are increasing (+0.02 ‰, +0.18 ‰, and +0.05 ‰ per year, respectively), consistent with regional warming. Seasonal patterns were evident, with elevated d-excess values during autumn. The decomposition of the δ18O, δ2 H and d-excess time series using Hilbert-Huang Transform revealed statistically significant annual oscillations in all variables. These oscillations correlated strongly with the annual oscillation of temperature, but a lag of 2–3 months was identified for d-excess. Lower-frequency (multi-year) oscillations of d-excess were also observed. HYSPLIT back-trajectory analysis confirmed a significant contribution of Mediterranean-sourced air masses to autumn precipitation, but did not explain d-excess oscillations. Similar results were observed also for coastal (Portoroˇz, Slovenia) and continental (Vienna, Austria) stations. The findings imply an accelerating, exponential-like isotopic response to warming that has already propagated into the water cycle, providing isotope evidence that precipitation-surface water-groundwater interactions in investigated region changed in last decade.
Keywords: precipitation stable isotopes, trend analysis, Hilbert-Huang transform, ensemble empirical mode decomposition, HYSPLIT
Published in DiRROS: 19.11.2025; Views: 461; Downloads: 234
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Abstract: Dry and warm climate conditions in southern Europe represent clear limits for European beech (Fagus sylvatica) growth near the species southern distribution limit, but it is unclear how aridification and changes in seasonal precipitation regimes will affect these forests at the individual level. We explored climate-growth relationships and the seasonality of peak climate signals in European beech using daily climate data and a large collection of tree-ring width series from southern and southeastern Europe through Generalised Linear Mixed Models (GLMMs). In most cases we found a positive and significant influence of precipitation on tree growth, and a significant negative effect of maximum temperature. Predictions from the GLMMs revealed a positive impact of precipitation during an 88 day window from spring to early summer (mid-April to mid-July), for an average tree across our network. This critical growing time window ranged from 75 days in warmer and drier conditions, and extended up to 100 days in areas with mild temperatures and moderate summer precipitation. Maximum temperatures negatively affected trees for an average of 27 day window in summer (June-July). This period was reduced to <10 days in locations with wetter and colder summers, rising up to 45 days in sites with drier and warmer summers. The positive effect of precipitation on growth was stronger and commenced earlier in larger trees. Similarly, the negative effects of maximum temperatures were more pronounced for larger trees. The use of daily climate data and a tree-centred approach allowed for capturing critical temporal dynamics in climate-growth relationships that are often overlooked by conventional methods. These insights significantly enhance our understanding of climatic factors influencing individual beech growth at the edge of its distribution range and their seasonal variations.
Keywords: European beech, daily climatic variables, precipitation, maximum temperature, tree-ring width, range limit
Published in DiRROS: 06.06.2025; Views: 808; Downloads: 461
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Keywords: gross primary product, regression model, remote sensing, temperature, precipitation, digital elevation model
Published in DiRROS: 03.09.2024; Views: 1781; Downloads: 435
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