The mobility of nitrogen (N) in the environment is conditioned by its cycling between atmospheric, terrestrial, and marine ecosystems. It is a key element for global biogeochemistry, and although ...isotope analysis has been an integral part of many studies over the past eighty years, the complexity of the nitrogen cycle hinders a correct and detailed understanding of the mechanisms behind its processes. It could be argued that the interpretation of the isotopic signatures of nitrogen in soils is still in its infancy. In Croatia, such research has recently begun and is driven by a need for the comprehensive study of nitrogen isotopes in terrestrial ecosystems. The aim of this study was to compare the abundance of the 15N isotope in soils from continental and coastal parts of Croatia with different types of land use (arable land/crop production, meadows, forests, orchards, ski slopes, urban soil/city roads) and to authenticate the nitrogen origin in soils in relation to different soil management practices. This research was based on 27 soil samples collected at 11 locations in Croatia. The samples differed according to soil type, land use, applied mineral and organic nitrogen fertilization, and climatic condition at each specific location. The determination of δ15NT (T—total nitrogen) values in bulk samples was performed in duplicate with the IRMS (Isotope Ratio Mass Spectrometry) method using an IsoPrime100-Vario PYRO Cube (OH/CHN Pyrolyser/Elemental Analyzer). The results reveal that the mean δ15N abundance in soils according to different land use declines in the following order: crop production (+5.66 ± 1.06‰) > apple orchard (+5.60 ± 0.10‰) > city road (+4.33 ± 0.38‰) > meadow (+3.71 ± 0.85‰) > ski slope (+2.20 ± 0.10‰) > forest (+2.15 ± 1.86‰). The individual values were in the range from 0.00 ± 0.10‰ in the forest soil in continental Croatia to +7.19 ± 0.07‰ in the vegetable garden (crop production) soil in coastal Croatia. Among the investigated soil properties and weather conditions, PCA analysis identified close correlations between P2O5 content and δ115N abundance in arable soils, as well as between soil reaction (pH) and mean annual temperatures, while high C/N ratio values explained the isotopic distribution in non-arable soils (city roads and forests). Despite the long-term application of mineral nitrogen fertilizers, the results represent nitrogen of organic origin in the arable soils (crop production), which partly confirms the sustainable management of those agroecosystems.
Efforts to improve the environmental sustainability of the construction industry involve exploring waste materials, environmentally friendly production processes and high performance materials like ...ultra-high-performance concrete (UHPC). Despite UHPC’s benefits, its widespread use is hampered by its high cost and environmental concerns. To address this, limestone filler and metakaolin were used to replace 30% of the cement, while recycled tyre steel fibres (RTSF) and production waste carbon fibres (CF) replaced the conventional factory-made fibres. Eight mixes underwent various tests in fresh state and hardened state, revealing initial negative effects of supplementary cementitious materials (SCMs) on strength and capillary absorption, which improved considerably over time. Fibres addition, especially hybrid fibres, increased strength and toughness without significantly affecting modulus of elasticity. RTSF at 1 vol% and 1.5 vol% positively impacted compressive strength and toughness, while 1 vol% CF improved flexural strength and capillary water absorption. Optimal contents varied for the hybrid fibre mixes depending on the tested property, with overall best results in compressive strength, toughness and specific energy absorption. The hybrid mixes outperformed the RTSF mixes but lagged behind the CF mixes in terms of flexural strength and capillary water absorption. A multi-criteria analysis was conducted to determine the optimum mix design, taking into account factors such as performance, cost, and environmental impact. This analysis highlighted the potential of the supplementary materials and fibres to improve the environmental and economic efficiency of UHPC while maintaining or even improving the tested properties.
In general, 20-25% of the original fibre weight is considered waste in the production of high-quality textiles for the construction sector. A market analysis has shown that in the Republic of Croatia ...alone, up to 327 tonnes of this waste is produced annually, which is enough to reinforce 50 to 150 thousand m
of cementitious composites. This preliminary study aims to evaluate the contribution of glass, basalt and carbon fibres generated as waste in the local production of high-performance technical textiles, to the fresh and hardened properties of fibre reinforced mortars. In order to investigate the influence of fibres, three types of fibres in two different lengths (5 and 10 mm) were used, while the amount of fibres was constant. The obtained results show that due to the fibre presence, workability is reduced regardless of the type and length of the fibre. The tested fibres have a negligible effect on compressive strength, but the use of basalt and carbon fibres increases the tensile strength. Furthermore, all three types have positive influence on the toughness and volumetric deformations, although to a greater extent in the use of 10 mm long fibres and carbon fibres.
In light of various initiatives taken around the world to convert waste materials into new products, the objective of this paper is to promote the use of steel fibers from recycled car tyres in the ...concrete industry. Hybrid steel fiber reinforced concrete (HSFRC) is a material that combines two or more types of steel fibers, in this case: manufactured steel fibers and recycled steel fibers from waste car tyres in equal proportions. The main objective of the presented research was to investigate the possible application of HSFRC in structural elements with conventional reinforcing bars in order to improve the flexural behavior and to investigate the possibility of partially replacing the conventional reinforcement with steel fibers in terms of service performance. For this purpose, eight slab specimens with different reinforcement ratios were subjected to a four‐point bending test to measure displacements, strength, and crack widths. The addition of a hybrid fiber mix to a conventionally reinforced concrete slab significantly reduced crack widths by up to 53%. The addition of fibers compensated for a conventional reinforcement reduction of 20% by reducing crack widths by up to 38%. It was observed that slightly more cracks opened with smaller widths and at smaller distances from each other in these slab types than in the conventionally reinforced reference slabs. Slabs with hybrid fiber mix and 44% reinforcement reduction showed no improvement in crack control compared to the conventionally reinforced concrete reference slabs. Using numerical models in ABAQUS simulating the flexural test on notched prismatic specimens, a calibration of the material models of plain concrete, and HSFRC was performed based on the test results. These validated material models were used for numerical modeling of slabs. The results of the analyses compared with the experimental results showed good agreement and confirmed the ability of the proposed material model of HSFRC to predict the flexural behavior of slabs with conventional reinforcement.
The temperature increase in oceans reflects on marine ecosystem functioning and surely has consequences on the marine carbon cycle and carbon sequestration. In this study, we examined dissolved ...lipid, lipid classes and dissolved organic carbon (DOC) production in the northern Adriatic Sea, isolated diatom Chaetoceros pseudocurvisetus batch cultures grown in a wide temperature range (10–30 °C) and in contrasting nutrient regimes, phosphorus (P)-depleted and P-replete conditions. Additionally, lipids and DOC were analyzed in the northern Adriatic (NA) in two stations characterized with different P availability, occupied from February to August 2010 that covered a temperature range from 9.3 to 31.1 °C. To gain insight into factors governing lipid and lipid classes' production in the NA, apart from temperature (T), Chlorophyll a, phytoplankton community abundance and structure, nutrient concentrations were measured together with hydrographic parameters. We found enhanced accumulation of dissolved lipids, particulary glycolipids, with increasing T, especially during the highest in situ temperature. The effect of T on enhanced dissolved lipid release is much more pronounced under P-deplete conditions indicating that oligotrophic regions might be more vulnerable to T rise. Temperature between 25 and 30 °C is a threshold T range for C. pseudocurvisetus, at which a significant part of lipid production is directed toward the dissolved phase. Unlike monocultures, there are multiple factors influencing produced lipid composition, distribution and cycling in the NA that may counteract the T influence. The possible role of enhanced dissolved lipid concentration for carbon sequestration at elevated T is discussed. On the one hand, lipids are buoyant and do not sink, which enhances their retention at the surface layer. In addition, they are surface active, and therefore prone to adsorb on sinking particles, contributing to the C sequestration.
•We investigated dissolved lipid production in response to sea surface warming.•We performed diatom Chaetoceros pseudocurvisetus batch culture experiments.•We performed investigations in the northern Adriatic Sea.•Temperature rise increases dissolved lipid content.•Effect of T on lipid release is more pronounced under P-depleted conditions.
Dodavanjem čeličnih vlakana u beton poboljšavaju se njegova svojstva pri zamoru. Opisana su eksperimentalna istraživanja betonskih elemenata s recikliranim čeličnim vlaknima pri cikličkom ...opterećenju. Prikazani su proračunski modeli zamora prema fib Model Code 2010, ACI 215 i JSCE smjernicama. Rezultati proračunskih modela uspoređeni su s rezultatima eksperimentalnog istraživanja. Uočeno je da, u pravilu, svi proračunski modeli podcjenjuju eksperimentalno određenu otpornost betona pri zamoru. Dan je prijedlog korekcije fib Model Code modela.
Two cases of subacute sclerosing panencephalitis (SSPE), diagnosed in Croatia in 2002, were investigated. The coding regions of the matrix (M), hemagglutinin (H) and nucleoprotein (N) genes of ...measles virus were sequenced following direct RT-PCR amplification of viral RNA extracted from brain tissue. Phylogenetic analysis of the sequences of H and N genes, showed that both strains belonged to genotype D6. No vaccine strain was detected although both patients had been previously immunized. The comparison of analyzed sequences of two SSPE causative viruses with corresponding sequences of D6 genotype and with each other revealed a number of mutations in N and H gene sequences. In comparison to the Edmonston reference strain, the M gene of the SSPE viruses showed the characteristic biased hypermutation and a premature termination codon in one of the patients.
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