Search

Summary: An improved dynamic power flow (DPF) model considering governor nonlinearity is presented. The proposed DPF model is intended for the analysis of post‐contingency power flow after primary frequency regulation. During the regulation process, the governors play an important role while it is difficult to involve the nonlinear segments in the static method. So in this paper, the governor model with amplitude‐limit and deadband is simplified and included in DPF model. Using the describing function method, the effect of deadband is equivalent to an increment of regulation coefficient. The amplitude‐limit is handled by iterative correction. Applying the algorithm to a three‐node system, a case study of load variation proves the effectiveness of the algorithm. Simulations on a practical grid in southern China further demonstrates the practicability and applicability. The algorithm enhances the accuracy of post‐contingency power flow analysis and provides effective analysis for the static security of power system. [ABSTRACT FROM AUTHOR]

Flavonoids are the main active components of natural medicinal plants with many physiological functions. In this study, an HPLC fingerprinting method based on the distribution and relative amount of 11 bioactive flavonoids was established for the quality evaluation of commercially available wild Jujube leaf tea ( JLT) from China. Separation of the crude flavonoid extract was achieved on a column filled with C18 material with a high carbon content. The flavonoids in wild JLT were identified based on UV spectroscopy and accurate mass measurements by TOF- MS. Twenty-one batches of practical samples collected from different habitats were analyzed by using the developed HPLC method to construct the HPLC characteristic fingerprint of wild JLT. Then, combined with clustering and similarity analyses, the HPLC characteristic fingerprint was used for the authentication and quality evaluation of commercial wild JLT. Results indicated that the proposed HPLC characteristic fingerprint reflected the inherent characteristics of wild JLT collected from different regions. Authenticity identification and quality control of commercially available wild Jujube tea were achieved based on the HPLC characteristic fingerprint analysis. This new approach to bioactive component profiling provided a promising reference method for the quality evaluation of commercial wild flower and plant tea. [ABSTRACT FROM AUTHOR]

The extent of organochlorine pesticides (OCPs) contamination in coastal waters around LaiZhou Bay and JiaoZhou Bay in Shandong Peninsula, northern China, was investigated. The areas around the two bays are both densely populated, thrived with intensive agriculture and industrial activities. Multi-techniques including GC–MS, GC–μECD coupled with chemical peak confirmation and strict QC procedures were used for the quantitative determination of 15 OCPs including alpha, beta, gamma and delta isomers of hexachlorocyclohexane (HCH), pentachloronitrobenzene (PCNB), heptachlor, aldrin, endosulfan, p,p′-DDE, dieldrin, endrin, p,p′-DDD, o,p′-DDT, p,p′-DDT and methoxychlor. The survey results show that contaminations by OCP residues remain widespread in the areas, but the averaged concentration levels are all below the regulatory limits, e.g., CMC limits (acute criterion values) specified in US Environmental Protection Agency (USEPA) and China national standards. Average concentration of OCPs in water samples were from undetectable to 3. 8ngl−1 in LaiZhou Bay and from 0. 1 to 3. 9ngl−1 in JiaoZhou Bay, respectively. A comparison between the current and historical data shows a rapidly decreasing trend of OCPs over the past twenty years in the study areas. [Copyright &y& Elsevier]

The Bashang Plateau, which is an ecologically fragile agro-pastoral zone in Hebei Province in China, plays an important role in protecting the Beijing-Tianjin-Hebei region from wind and sand erosion. Over the last four decades, it has been the target of extensive afforestation campaigns to promote improved ecosystem services. Though the benefits and costs of afforestation and its effectiveness within forestry have been widely investigated, few studies have focused on local households' willingness to accept (WTA) compensation relating to afforestation policies. Moreover, despite their importance in ensuring effective afforestation policies, the factors influencing WTA values have seldom been examined. We administered a direct questionnaire survey of households on the Bashang Plateau and applied a contingent valuation analysis to estimate their WTA values for compensation associated with ecological protection policies. We obtained 249 valid questionnaires, evidencing a high response rate (92.22%). New indicators of factors influencing respondents' WTA has been conducted including social, economic and ecological aspects, especially the improvement of ecological factors which consists of respondents' perceptions regarding the importance of ES and their satisfaction levels, and other environmental awareness factors. Additionally, in the case where many studies performed only one single regression analysis, this study performed a two-stage regression analysis and compared the results with those obtained using the Tobit model. A reasonable compensation standard facilitates a positive relationship between economic development and protection of natural environments. The findings showed that a certain amount of compensation (approximately 477.91 CNY/mu/year) was likely to prompt households' participation in afforestation projects. Compared with compensation standards for other ecological projects, the reported standard for afforestation projects on the Bashang Plateau is low, indicating that there is room for improvement. High annual household incomes are a key factor influencing households' WTA regarding their participation in afforestation activities. The results also revealed households' environmental awareness. Among respondents who participated in afforestation, those who valued forests for protecting environments and improving ecosystem services opted for lower compensation amounts. Our findings contribute valuable inputs for formulating ecological compensation standards and can serve as a reference for analyses of WTA and factors that drive it in other similar economically backward and ecologically fragile regions. • Households' WTA for afforestation projects was calculated by contingent valuation method. • Tobit model and a double-hurdle regression model were used to analyze influencing factors of WTA. • High annual household incomes are a key factor influencing households' WTA. • Respondents who valued forests for improving ecosystem services opted for lower WTA. [ABSTRACT FROM AUTHOR]