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Impact of Extra Nitrogen on Ecological Stoichiometry of Alpine Grasslands on Tibetan Plateau : Meta-Analysis

Zhang H. R., Sun W., Li S. W., Han F. S., Yu C. Q., Zhang X. Z., Wang J. S., He Y. T., Zhong Z. M.

Polish Journal of Ecology

2018

Vol. 66, nr 4

315--324

The general impact of extra nitrogen on ecological stoichiometry was examined in alpine grasslands on the Tibetan Plateau. Extra nitrogen increased the ratio of nitrogen to phosphorus (N:P ratio) in leaves and aboveground parts of plants by 43.4% and 32.7%, respectively. In contrast, extra nitrogen reduced the ratio of carbon to nitrogen (C:N ratio) in leaves by 30.6%. Extra nitrogen decreased soil C:N ratio by 9.1% in alpine meadows, but increased soil C:N ratio by 3.4% in alpine steppes. Extra urea had a stronger positive impact on aboveground vegetation N:P ratio than did extra ammonium nitrate. Extra urea rather than ammonium nitrate decreased aboveground vegetation C:N ratio and soil C:N ratio. The impact of extra nitrogen on aboveground vegetation N:P ratio was positively correlated with latitude, mean annual temperature and precipitation, nitrogen application rate and accumulated amount, but negatively correlated with elevation, duration and aboveground vegetation N:P ratio of the control plots. The impact of extra nitrogen on leaves N:P ratio was positively correlated with nitrogen application rate and accumulated amount. The impact of extra nitrogen on leaves C:N ratio was positively correlated with latitude, but negatively correlated with mean annual temperature and precipitation, nitrogen application rate, accumulated amount, duration and leaves C:N ratio of the control plots. Therefore, nitrogen enrichment caused by human activities will most likely alter element balance and alpine plants from nitrogen limitation to phosphorus limitation. This effect may weaken with time, and increase with climatic warming, increased precipitation and nitrogen input rate.

An improved PO and immune MPPT method for PV generating system under partially shaded conditions

Liu L. Q., Liu C. X., Yang G. T., Zheng X. Y., Wang J. S.

Przegląd Elektrotechniczny

2013

R. 89, nr 1a

235--238

The maximum power point tracking (MPPT) for photovoltaic (PV) generating system study on the tracking method at partial shading is very important to improve the output efficiency of costly PV, the objective is to improve the respond speed and extract maximum power under different weather and partial shading conditions. The output characteristics of PV system get more complex than same irradiation because of the continually changing of atmospheric conditions and frequently partially shaded in actual woke state. The nonlinear and multiple local peaks characteristics of PV system at partial shading are considered by using perturbation and observation (PO) method to gain the actual global peak of PV system, and the conventional PO method is improved by using the perturb Pulse-Width Modulation (PWM) method at ideal irradiation and partial shading, and then the artificial immune theory is used to accelerate the response speed and robustness. The proposed improved PO and immune method has an excellent dynamic performance and small oscillation as compared to the traditional PO method under partially shaded conditions.

W artykule opisano algorytm śledzenia maksymalnego punktu pracy (MPPT) dla system paneli fotowoltaicznych, w warunkach częściowego zacienienia. W celu wyznaczenia punktu globalnego MPPT, zastosowano metodę perturbacji i obserwacji (PO). Metoda PO została ulepszona poprzez zastosowanie zmodyfikowanej modulacji PWM przy braku nasłonecznienia i częściowym zacienieniu. W celu zwiększenia dynamiki i odporności algorytmu wykorzystano teorię sztucznej odporności. Proponowana metoda gwarantuje bardzo dobrą efektywność.