Background Meadows and shrublands are two major vegetation types on the Qinghai-Tibetan Plateau, but little is known about biochemical characteristics and its relation to decomposability of soil organic carbon (OC) under these two vegetation types. The present study was designed to evaluate effects of aspectvegetation complex on biochemical characteristics and decomposability of soil OC. Methods Two hills were randomly selected; both with vegetation being naturally divided into southward meadows and northward shrublands by a ridge, and soils were sampled at depths of 0-15 and 15-30 cm, along contours traversing the meadow and shrubland sites. Particulate (particle size 2-0.05 mm) OC and nitrogen (N), microbial biomass C and N, non-cellulosic sugars, and CuO lignin were analyzed, and OC mineralization was measured for 49 days at 18 and 25°C under laboratory incubation, respectively. Results More than half of soil OC was present as particulate fraction across all samples, indicating the coarse nature of soil organic matter in the region. Averaging over depths, shrublands contained 87.7−114.1 g OC and 7.7−9.3 g N per kg soil, which were 63−78 and 26−31 % higher than those in meadows, respectively. Meanwhile the C/N ratio of soil organic matter was 11.4 −12.3 under shrublands, being 29−40 % higher than that under meadows. Soil OC under meadows was richer in noncellulosic carbohydrates and microbial biomass in the 0-15 and 15-30 cm depths but contained less lignin in the 15-30 cm depth. Ratios of microbiallyto plant-derived monosaccharides and between acid and aldehyde of the vanillyl units were greater in soils under shrublands, showing more abundant microbiallyderived sugars and microbially-transformed ligneous substances in OC as compared to meadow soils. By the end of 49 days' incubation, total CO 2 -C evolution from soils under meadows was 15.0-16.2 mg g −1 OC averaging over incubation temperatures and soil depths, being 27-55 % greater than that under shrublands.
The receptance function has been studied and applied widely since it interrelates the harmonic excitation and the response of a structure in the frequency domain. This paper presents the derivation of the exact receptance function of continuous cracked beams and its application for crack detection. The receptance curvature is defined as the second derivative of the receptance. The influence of the crack on the receptance and receptance curvature is investigated. It is concluded that when there are cracks the receptance curvature has sharp changes at the crack positions. This can be applied for the crack detection purpose. In this paper, the numerical simulations are provided.
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