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Analysis of Excitation Current in DC-Biased Transformer by Wavelet Transform

100%

Zhou X. , Zhou Z. , Ma Y. , Wu D.

2012

tom R. 88, nr 5b

108-112

To analyze the excitation current in DC-Biased Transformer in depth, the thesis deduces the mathematical expression of distortion excitation current, and put forwards the analysis method with wavelet transform principle, which directs at analyzing the boundedness of distortion excitation current using the Fourier Transform. Through sampling the distortion excitation current signal, we resolve its wavelet LF approximation signal and HF detail signal, conclude DC component size of the distortion excitation current, confirm the moment of excitation current waveform distorting, comparatively analyze the results after Fourier Transform, and make clear that the principle is feasibility and superiority. Through analyzing the energy spectrogram in the signal high-frequency band of distortion excitation current and short circuit current are determined. Simulation results show that energy changes in the high frequency band among the different scale. In practice, DC bias can lead to the action of relay protection device, which does harm to the system potentially.

Przedstawiono metodę analizy składowej stałej podmagnesowującej w prądzie magnesującym transformatora. Do analizy wykorzystuje się transformatę falkową I transformatę Fouriera prądu magnesującego.

Carbon storage of cycad and other gymnosperm ecosystems in China: implications to evolutionary trends

63%

Ma Y. , Jiang H. , Wang B. , Zhou G. , Yu S. , Peng S. , Hao Y. , Wei X. , Liu J. , Yu Z.

2009

tom Vol. 57, nr 4 (2

635-646

Cycads are an ancient lineage of plants that originated in the Permian, which are vital to the interpretation of plant ecology. The evidence in the fossil records indicates that the morphological and anatomical features of cycads are remarkably similar to the extant taxa, which has been instrumental in our understanding the connections between the early origins of seed plants and their present-day counterparts. The cycad ecosystem is an important vegetation type throughout geological time. Research on the ecological function of the cycad plays a significant role in the study of evolutionary ecology. In this study, we investigated the biomass, productivity and total carbon storage (total of vegetation, litter, and soil carbon) of cycad (Cycas panzhihuaensis L. Zhou et S.Y. Yang) ecosystems in the National C. panzhihuaensis Reserve of China (latitude 26[degrees]37', longitude 101[degrees]35', at 1635 m altitude) by applying the site-standard tree sampling harvest. Cycads are considered to be rare and endangered species, and are in the list of key protected wild plants in the world. The National C. panzhihuaensis Reserve is in Southwestern China, which area approximately 1358 ha, growing approximately 20 000 C. panzhihuaensis individuals. 20 sample plots, each 5 x 5 m were established in the spring of 2006. The mean height of cycads within the stand was 0.44 m and the mean basal diameter was 23.2 cm. The biomass and productivity data for other communities was compiled from references published over the past 20 years throughout China. The biomass and productivity of cycad ecosystems (8.102 [plus or minus] 6.880 t C ha[^-1] and 1.183 [plus or minus] 0.975 t C ha[^-1] yr[^-1], respectively) are smaller than tree fern (Alsophila spinulosa (Wall. ex Hook.) R. M. Tryon) or gymnosperm (Pinaceae, Cupressaceae or Taxodiaceae for representative) ecosystems. The community biomass of Pinaceae-, Cupressaceae- or Taxodiaceae-dominated ecosystems are 6.8, 5.4, and 5.3 times larger than the cycad ecosystem, respectively. The productivity of each is 2.3, 2.8 and 3.8 times larger than the cycad ecosystem. Cycad is an ancient dioecious plant. However, the results show that the differences between the biomass of male and female cycads, as well as the productivity, are not significant.

Leaf litter decomposition along the temperate - tropical transect (East China) : the influence of stand succession, litter quality and climate

63%

Song X. , Jiang H. , Peng C. , Zhou G. , Chang S. , Yu S. , Ma Y. , Peng S. , Wei X.

2012

tom Vol. 60, nr 2

265-276

The relationship between litter decomposition and forest succession in addition to the influence of climate variables on the rate of litter decomposition in forest ecosystems are poorly understood. In this study, the effects of forest successional stages, climate, and litter quality on litter decomposition rates were investigated in five sites located in China. The selected sites cover 29 degrees of latitude from 18[degrees]N to 47[degrees]N and spans more than 5,000 km in length along a temperature gradient that transverses across eastern China. This zonal gradient includes five climate zones from temperate to subtropical to tropical zones. Forest types include broad-leaved Korean pine, deciduous broad-leaved, evergreen broad-leaved, monsoon evergreen broad-leaved, and tropical rain forests. The North-South Transect of Eastern China (NSTEC) is one of fifteen international standard transects setup by Global Change and Terrestrial Ecosystems (GCTE). NSTEC is a key component of the International Geosphere-Biosphere Programme (IGBP). The litterbag method was used in this study to determine mass loss and annual decomposition rates of eight tree species (Pinus massoniana Lamb., Cunninghamia lanceolata (Lamb.) Hook., Schima superba Gardn. et Champ., Cinnamomum camphora (L.) Presl., Cyclobalanopsis glauca (Thunb.) Oerst., C. gracilis (Rehd. et Wils.) Cheng et T. Hong, Michelia chapensis Dandy, and Castanopsis eyeri (Champ.) Tutch. through a timeframe starting in May, 2006, and ending in May, 2008. Litterbags 15 x 15 cm and 0.5 x 1.0 mm mesh were filled with 10 g of leaf litter collected from the subtropical forest region and then placed onto the forest floor in triplicate samples for each eight species in all five sites. Three litterbags per species were retrieved from each of the five sites at two month intervals during the two year experimental period. Results suggest that species litter in the climax stage (C. glauca, C. gracilis, and M. chapensis) tended to decompose faster than those in the pioneer stage (P. massoniana and C. lanceolata). Initial phosphorous (P) and nitrogen (N) concentrations of leaf litter were the most critical variables of litter quality in relation to the impact on the rate of litter decomposition. Litter decomposition at different successional stages was found to be directly related to climatic variables such as mean annual precipitation (MAP) and mean annual temperature (MAT). MAP and initial P and N concentrations could therefore be considered good indicators of rates of decomposition.