High Impedance Arc Fault Modelling in Offshore Oil Platform Power Grid

In offshore oil platform power grid, high impedance arc fault occurs frequently. The fault characteristics of high- impedance arc information are weak and difficult to detect, which may not cause the protection method to activate. Therefore, it is important to detect and clear the high impedance fault. In the high impedance case, usually, the arc fault occurs. In the research, the arc model was established using the typical Cassie model and the high impedance arc fault characteristics in offshore oil platform power grids were analysed. An improved arc fault detection method using the phase angle difference between zero sequence voltage and zero sequence current was proposed to extract fault characteristics. This method requires limited detection information and high accuracy to solve the problem of small current and voltage changes in high-resistance arc faults. The offshore oil platform power grid and the arc were modelled using electromagnetic transients software PSCAD/EMTDC. The simulation results show that the arc model and fault detection method work well

Wideband RCS Reduction Based on Hybrid Checkerboard Metasurface

Traditional stealth technologies all have their problems such as high cost and large thickness. To solve the problems, we used novelty checkerboard metasurface in stealth technology. Checkerboard metasurface does not have as high conversion efficiency as radiation converters, but it has many advantages such as small thickness and low cost. So it is expected to overcome the problems of traditional stealth technologies. Unlike other checkerboard metasurfaces, we improved it further by using two types of polarization converter units to be arranged in turn to form a hybrid checkerboard metasurface. Because the checkerboard metasurface composed of one type of polarization converter units can have a relatively wide radar cross-section (RCS) reduction in bandwidth when two types of polarization converter units are arranged in turn to form a hybrid checkerboard metasurface and mutual compensation of the two polarization converter units can broaden RCS reduction band further. Therefore, by designing the metasurface to be independent from the polarization, the effect of RCS reduction can be insensitive to the polarization of the incoming EM waves. The experiment and simulation results showed the value of this proposed hybrid checkerboard metasurface for RCS reduction. Mutual compensation of the units is a new attempt in the field of checkerboard metasurfaces for stealth technology and proved to be effective

Community Structure of Eukaryotic Phytoplankton in Wetland of Golmud River and Its Lower Reaches and Relative Environmental Factors

Identification of the community structure of phytoplankton is an important link in studying the structure and function of aquatic ecosystems. However, research on the community structure of phytoplankton in the Golmud area is very scarce at present. To explore the composition of phytoplankton in the Golmud area, eukaryotic phytoplankton and environmental parameters were sampled in September 2020. The composition and diversity of the eukaryotic phytoplankton community were determined by microscopic observation and Illumina high-throughput sequencing technology. The results showed that a total of 40 species of eukaryotic phytoplankton from 4 phyla were identified by microscopic observation, and 154 species of eukaryotic phytoplankton from 7 phyla were obtained by high-throughput sequencing, mainly Bacillariophyta and Chlorophyta. The dominant species were Dunaliella sp., Teleaulax sp., Parvodinium mixtum, and Lindavia radiosa. The eukaryotic phytoplankton density in summer was 0.09–12.08 × 105 cells/L, the total biomass was 0.002–0.55 mg/L, and the concentration of chlorophyll-a was 0.00–0.91 μg/L. Multiple α diversity indices showed that the diversity of water in different salinities was in the order of freshwater > brackish > saline. The β diversity results showed that the eukaryotic phytoplankton community composition was more similar in water with the same salinity. The redundancy analysis results of water with different salinities showed that environmental factors susc as salinity, total phosphorus concentration, and dissolved oxygen affected the eukaryotic phytoplankton community structure, among which salinity had the greatest influence

Parameter estimation and fault diagnosis for compensation capacitators in ZPW-2000 jointless track circuit

We propose a parameter estimation approach to fault diagnosis for jointless track circuits in railway transportation, focusing on the compensation capacitors. How to estimate various parameters of the jointless track circuits poses a tremendous challenge, because the existing track circuits do not have sensor networks embedded to the railway network. Assuming the available special inspection train and the measurement data, we analyze how various parameters of the jointless track circuits can be estimated, and how faults in the compensation capacitors can be detected. Our analysis results are illustrated by a numerical example

O2, pH, and redox potential microprofiles around Potamogeton malaianus measured using microsensors.

This study aimed to elucidate the effects of periphyton on the microprofiles of oxygen (O2), pH, and oxidation-reduction potential around the stems and leaves of a submerged macrophyte Potamogeton malaianus and on the plant growth in the eutrophic shallow Taihu Lake, China. The microprofiles were measured using a motorized microprofiling system equipped with microsensors. The leaf age of the macrophyte and periphyton exerted significant effects on the microprofiles of O2, pH, and oxidation-reduction potential. O2 concentration and pH increased whereas the oxidation-reduction potential decreased with decreasing distance to the stem/leaf surface. The fluctuation amplitudes of O2, pH, and oxidation-reduction potential were the largest in the microprofiles of mature leaves and the lowest in senescent leaves. The periphyton increased the thickness of the broad diffusive boundary layer and fluctuation amplitudes of O2, pH, and oxidation-reduction potential. When the periphyton was removed, the thickness of the broad diffusive boundary layer in the microprofiles of stems, senescent leaves, and mature leaves reduced by 29.0%, 49.72%, and 70.34%, and the O2, pH, and oxidation-reduction potential fluctuation amplitudes also declined accordingly. Our results suggest that a thick periphyton exerted negative effects on the growth of macrophytes by providing extensive shading and creating a barrier that hindered the transport of dissolved substances such as O2, and led to premature decline in macrophytes in the eutrophic Taihu Lake. The consequent implications can help to elucidate the control mechanism of the broad diffusive boundary layer around macrophytes on nutrient cycling in eutrophic waters and to better understand the role of this layer in the Taihu Lake and other similar eutrophic waters

Study on Frequency Stability of an Independent System Based on Wind-Photovoltaic-Energy Storage-Diesel Generator

Wind and photovoltaic power generation connected to the independent power system can save fuel, reduce carbon emissions, and provide significant economic and environmental benefits. Influenced by the characteristics of light resources and wind resources, the wind and photovoltaic output active power is characterized by volatility and randomness, which affects the frequency stability of the independent power system. In order to evaluate the frequency stability, in this paper, the simulation model of an independent power system is established, and the simulation model of a diesel generator, wind and photovoltaic are connected. Through droop calculation and Simulink simulation, the frequency characteristics of an independent power system under different working conditions are analyzed, and the maximum absorption capacity of wind and photovoltaic is studied. In an independent power system, when the new energy output is 25% of the total output, all the new energy output is cut off, the frequency drops by 0.5 Hz, and the frequency fluctuation is within the specified range

Multiple and prolonged porphyry Cu–Au mineralization and alteration events in the Halasu deposit, Chinese Altai, Xinjiang, northwestern China

The Halasu area is located in the southeastern margin of the Chinese Altai in Xinjiang, China. It is part of the Altaid orogenic collage where a number of porphyry-type Cu–Mo–Au deposits have been discovered in recent years. Geological mapping and drilling indicate the presence of various mineralized porphyritic intrusions in the Halasu Cu–Au deposit, which is currently under exploration. U–Pb dating of zircon crystals from four different mineralized porphyries reveals three significantly different ages of magmatic intrusion, i.e., ca. 372–382 Ma granodioritic porphyry and porphyritic granite, ca. 266 Ma quartz monzonitic porphyry, and ca. 216 Ma quartz dioritic porphyry. Re–Os dating of molybdenite from veinlet-dissemination ores in the granodioritic porphyry yields an age of mineralization of ca. 377 Ma, and Ar–Ar dating of K-feldspar from K-feldspar–quartz–chalcopyrite veins produces ages of ca. 269 and ca. 198 Ma. The mineralization (and alteration) ages correspond broadly to the three episodes of magmatic intrusion, suggesting three overprinting porphyry mineralization events that are significantly separated in time. The first episode of porphyry intrusion and mineralization may be related to the magmatic arc being above a plate subduction zone, and the second was formed in a late-collisional environment during the closing of the Junggar Ocean, whereas the third episode of mineralization took place in the post-collisional stage. This case study suggests that in orogens where major porphyry deposits have been found in magmatic arc environments, the potential of discovering late- to post-collisional porphyry deposits cannot be neglected; conversely, in orogens where most porphyry deposits have late- to post-collisional ages, more attention should be paid to porphyries that were formed earlier in magmatic arc environments

Phylotranscriptomic and Evolutionary Analyses of Oedogoniales (Chlorophyceae, Chlorophyta)

This study determined the transcriptomes of eight Oedogoniales species, including six species from Oedogonium and two species from Oedocladium to conduct phylotranscriptomic and evolutionary analyses. 155,952 gene families and 192 single-copy orthogroups were detected. Phylotranscriptomic analyses based on single-copy orthogroups were conducted using supermatrix and coalescent-based approaches. The phylotranscriptomic analysis results revealed that Oedogonium is polyphyletic, and Oedocladium clustered with Oedogonium. Together with the transcriptomes of the OCC clade in the public database, the phylogenetic relationship of the three orders (Oedogoniales, Chaetophorales, Chaetopeltidales) is discussed. The non-synonymous (dN) to synonymous substitution (dS) ratios of single-copy orthogroups of the terrestrial Oedogoniales species using a branch model of phylogenetic analysis by maximum likelihood were estimated, which showed that 92 single-copy orthogroups were putative rapidly evolving genes. Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analyses results revealed that some of the rapidly evolving genes were associated with photosynthesis, implying that terrestrial Oedogoniales species experienced rapid evolution to adapt to terrestrial habitats. The phylogenetic results combined with evolutionary analyses suggest that the terrestrialization process of Oedogoniales may have occured more than once