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Öğe Low field AC susceptibility study of YBCO prepared by top seeded melt growth(Springer New York LLC, 2011) Güçlü, N.; Yeşilkanat, Cafer Mert; Ağıl, F.; Gemçer, A.; Kölemen, U.Superconducting bulk YBa 2 Cu 3 O 7-x (YBCO) material prepared by the melt growth method was characterized by AC susceptibility measurements. The measured susceptibilities were affected by the ac field amplitudes. The measured fundamental susceptibility was compared with the Bean model. An empirical function for the penetration field H p = H α (1 - t) β , where t is the reduced temperature, was obtained. Ac losses were determined at fixed temperatures and compared with theoretical calculations. A qualitative agreement was found between the experimental results and theoretical calculations.Öğe Effects of tree canopy on litter decomposition rates of Abies nordmanniana, Picea orientalis and Pinus sylvestris(Taylor&Francis, 2008) Sarıyıldız, TemelEffects of tree canopy (distance from the stem) on litter decay rates were investigated in the field for 4 years. Needle litter of Nordmann fir [Abies nordmanniana (Stev.) Spach.], Oriental spruce [Picea orientalis (L.) Link] and Scots pine (Pinus sylvestris L.) species were placed at three distances from their stems (<1 m, 1-2 m and >2 m). The litter showed highest decomposition rates at the distance of >2 m and lowest rates at <1 m for all species. Initial lignin concentrations were most strongly correlated with the decay rates, but among the microclimatic and soil factors, forest floor moisture content was the best predictor. The results showed that litter quality variables define the potential rates of microbial decomposition rates within and between trees, but adverse environmental conditions created by a tree canopy can also significantly affect decomposition rates. The closer distance to the stem significantly reduces litter decay rates by changing environmental conditions (especially forest floor moisture content) which can reduce microbial activity, and thus, the effects of tree canopy on litter decomposition rates should be taken into an account when calculating or comparing litter decomposition dynamics of forest ecosystems.
