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The extensive existence of governor deadband has a significant influence on the minimum frequency of power system after a disturbance. However, the strong non-linearity of deadband makes it difficult to quantify its impact on the frequency response. For this end, the backlash non-linearity is adopted to represent for the governor with deadband. The non-linear characteristics of governor with deadband are thus well approximated. The describing function method is applied to linearise the backlash non-linearity. Then a first-order model of governor system is derived to consider the deadband effect quantitatively. Minimum frequency estimation algorithm is proposed based on the first-order model. The proposed algorithm is effective to reflect the effects of various widths of deadbannd on the minimum value of frequency. Case study is conducted to prove its adequate performance in minimum frequency estimation with a practical power grid in China. [ABSTRACT FROM AUTHOR]

An adaptive power system critical eigenvalues tracing approach based on the projected continuation of invariant subspace (CIS) is proposed in this study. The proposed method reduces problem size by applying projections to invariant subspace corresponding to critical eigenvalues to ensure efficiency. An adaptive update strategy is adopted to detect and include new critical eigenvalues, ensuring that eigenvalues of interest are always traced. Testing on New England 39‐ and IEEE‐118 bus systems shows that the proposed approach can detect and trace new critical eigenvalues as soon as they emerge and immediately find bifurcation, thus avoiding missing instability information. It also shows that the proposed approach has an advantage in terms of computational time. [ABSTRACT FROM AUTHOR]

Pseudomonas plecoglossicida is an important pathogen in aquaculture and causes serious economic losses. Our previous study indicated that znuA gene might play an important role in the pathogenicity of P. plecoglossicida. Five shRNAs were designed and synthesized to silence the znuA gene of P. plecoglossicida. Two of the five mutants of P. plecoglossicida exhibited significant reduction in the expression level of znuA mRNA with different efficiencies. The mutant with the highest silencing efficiency of 89.2% was chosen for further studies. Intrapleural injection of the znuA‐RNAi strain at a dose of 105 cfu/fish did not cause the death of Epinephelus coioides, and no significant signs were observed at the spleen surface of infected E. coioides, while the counterpart E. coioides infected by the same dose of wild‐type strain of P. plecoglossicida all died in 5 days post‐infection (dpi). The expression of znuA gene of znuA‐RNAi strain in E. coioides was always lower than that in wild‐type strain of P. plecoglossicida. The pathogen load in the early stage of infection was higher than that in the later stage of infection. Although the infection of the znuA‐RNAi strain of P. plecoglossicida could induce the production of antibodies in E. coioides, it failed to produce a good immune protection against the infection of wild‐type strain of P. plecoglossicida. Compared with the transcriptome data of E. coioides infected by the wild‐type strain of P. plecoglossicida, the transcriptome data of E. coioides infected by the znuA‐RNAi strain of P. plecoglossicida have altered significantly. Among them, KEGG enrichment analysis showed that the focal adhesion pathway was significantly enriched and exhibited the largest number of 302 DEMs (differentially expressed mRNAs). These results showed that the immune response of E. coioides to P. plecoglossicida infection was significantly affected by the RNAi of znuA gene. [ABSTRACT FROM AUTHOR]

In this study, an impurity profiling method was established for the source identification of spilled benzene series compounds. Toluene was used as a case study to demonstrate the feasibility of this approach. Gas chromatography with mass spectrometry was applied for identification and quantification of the impurities including ethyl benzene, p-xylene, m-xylene, and o-xylene in toluene. Impurities in toluene were detected at very low levels by applying mass spectrometry in selected-ion monitoring mode. Eight authentic toluene samples collected from different manufacturers were analyzed by the developed gas chromatography with mass spectrometry method to construct the characteristic impurity profiling of toluene. Then, combined with scatter distribution, similarity analysis and t-test, a suite of diagnostic ratios based on the impurity distribution was used for the differentiation of toluene from different sources. Results indicated that scatter distribution method can discriminate the original toluene samples from different manufacturers. Similarity calculation and t-test methods can identify effectively the weathered toluene samples. The proposed impurity profiling method was useful for discrimination between toluene samples from different sources. Statistical analysis of these impurity profiles demonstrated the potential to investigate whether two questioned spilled toluene samples encountered in forensic casework are from the same source. [ABSTRACT FROM AUTHOR]

Understanding power system dynamics is essential for online stability assessment and control applications. Global positioning system‐synchronised phasor measurement units and frequency disturbance recorders (FDRs) make power system dynamics visible and deliver an accurate picture of the overall operation condition to system operators. However, in the actual field implementations, some measurement data can be inaccessible for various reasons, for example, most notably failure of communication. In this study, a measurement‐based approach is proposed to estimate the missing power system dynamics. Specifically, a correlation coefficient index is proposed to describe the correlation relationship between different measurements. Then, the auto‐regressive with exogenous input identification model is employed to estimate the missing system dynamic response. The US Eastern Interconnection is utilised in this study as a case study. The robustness of the correlation approach is verified by a wide variety of case studies as well. Finally, the proposed correlation approach is applied to the real FDR data for power system dynamic response estimation. The results indicate that the correlation approach could help select better input locations and thus improve the response estimation accuracy. [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]

A simple and rapid solid-phase microextraction approach for the isolation of polycyclic aromatic sulfur heterocycles from the aromatic fraction of crude oil is described. 8-Hydroxyquinoline silica gel impregnated with palladium chloride was used as a sorbent material for extraction. Operational parameters of the extraction solvents have been evaluated and optimized. Benzothiophene, dibenzothiophene, and benzo[ b]naphtho[1,2- d]thiophene and their C1- C4 alkyl derivatives were identified and quantified by GC- MS. Under optimum conditions, the limits of detection for benzothiophene, dibenzothiophene, and benzo[ b]naphtho[1,2- d]thiophene were 0.277, 0.193, and 0.597 μg/g oil, respectively. The recoveries for the polycyclic aromatic sulfur heterocycles ranged from 81.5 to 92.1%, and the linear dynamic range was from 10 to 1000 ng/mL. The developed methodology was tested in the characterization of crude oil samples collected at the DY, SZ, ZH, and HC petroleum oil fields of the Bohai Sea. The results proved that SPE coupled with GC- MS is a promising tool for the quantitative analysis of polycyclic aromatic sulfur heterocycles in crude oils, especially for oil samples with low concentrations of polycyclic aromatic sulfur heterocycles. [ABSTRACT FROM AUTHOR]