Search

Voltage-source inverter is a significant part of power supply for various applications. In hard working conditions, the inverter is prone to failure, such as open-circuit (OC) faults, which bring great risk to the safe operation. Therefore, a simple and robust fault diagnosis method for OC faults of voltage-source inverter is proposed. First, the fault principle of OC fault is studied, and a rule of voltage sequence is found that the sequence of positive and negative abnormal voltages is related to the fault position. Then, available line voltages are used as fault diagnosis variables, the fault phase is detected by abnormal values of line voltages, and the fault switch is located according to the fault phase and the rule of voltage sequence. Different from existing OC fault diagnosis methods, the proposed method is immune to phase to phase short-circuit fault, which has not been referred to or discussed in existing literatures yet but can lead to the false diagnosis of OC fault diagnosis methods. Moreover, the proposed method is robust to load variation, switching and fundamental frequencies. The experimental tests are carried out on a dSPACE platform, and the proposed method is verified. [ABSTRACT FROM AUTHOR]

To develop a novel high-temperature microwave absorber, B4C/Al2O3/CNTs composite powders were prepared by a combustion synthesis method. The experiment results show that the products are mainly composed by B4C, α-Al2O3, and residual CNTs. The better crystallinity B4C particles had a grain size about 0.5–1.0 μm and embedded in the Al2O3 matrix, while the CNTs cracked and dispersed in the composite powders. The results of combustion synthesis process illustrated that as CNTs increase, the product zone decreased, and the combustion temperature (Tc), the adiabatic combustion temperature (Tad), and the combustion wave velocity (VC) decreased. The dielectric permittivity of prepared composite powders has been determined in the X band. The results show that the dielectric real part ε´ and dielectric loss tanδ have a growing tendency with the increase of the CNTs. The dielectric real part (ε′) and the loss tangent (tanδ) reached the highest, when the molar excess coefficient of CNTs was 0.2 (CS-2). The different mass ratios of CS-2 and paraffin binder were combined to test their dielectric properties. The results show that both ε′ and tanδ increased with the increase of the CS-2, while the impedance matching ratio decreased. [ABSTRACT FROM AUTHOR]

Multiple stressors associated with global change are influencing the phytoplankton taxonomic composition and biomass in plateau lakes, such as higher levels of ultraviolet radiation (UVR, 280–400 nm) and the risk of eutrophication. Although the restrictive effects of high UVR on phytoplankton are generally recognized, the effects will be impacted by the UVR levels of seasonal changes and the nutrient status. In this study, in situ phytoplankton productivity was measured seasonally under full solar radiation and only visible light (photosynthetically active radiation, PAR) conditions in the plateau oligotrophic Lake Fuxian, Southwest China. To determine the single effects of UVR and nutrient enrichment and their combined impact on phytoplankton communities, a mesocosm experiment (1 month) was conducted outdoors during late summer (rainy season). The interactive experiment was designed with two radiation treatments (UVR + PAR and PAR) and four nutrient treatments (raw water, nitrogen addition, phosphorus addition, nitrogen and phosphorus addition). Our results suggested that the response of phytoplankton to UVR depended largely on nutrient availability, which was embodied in the no significant responses of phytoplankton productivity and total biomass to UVR in the oligotrophic raw water from Lake Fuxian, but the positive responses of total biomass to UVR in the nutrient enrichment treatment. Furthermore, the response of phytoplankton to UVR was also taxa dependent. Chlorophytes and dinoflagellates showed positive response to UVR, whereas chrysophytes were quite sensitive to UVR; diatoms had no significant response to UVR under all nutrient conditions, while the response of cyanobacteria to UVR was highly dependent on nutrient status. This study highlights that the increase in nutrient concentrations in oligotrophic lake not only directly promotes the growth of phytoplankton but also combines with low UVR during summer to benefit the growth of eutrophic taxa based on the non-negative effect of UVR on total phytoplankton biomass and the positive effect on eutrophic taxa. [ABSTRACT FROM AUTHOR]

Here, we demonstrate the synthesis of sheet-shaped Co2P grown on carbon cloth (sheet-shaped Co2P-CC) through a facile route. Electrochemical measurements indicated that sheet-shaped Co2P-CC with a loading of 0.6 mg cm−2 Co2P (denoted Co2P-CC-0.6) exhibits exceptional electrocatalytic activity in the hydrogen evolution reaction (HER), with an overpotential of 94 mV at a current density of 10 mA cm−2 and a small Tafel slope of 80 mV decade−1 in 1 M KOH. Similarly, sheet-shaped Co2P-CC-0.6 was also found to be an excellent electrocatalyst for the HER in 0.5 M H2SO4 and in 0.5 M phosphate buffer solution (PBS), with overpotentials of 95 and 231 mV at a current density of 10 mA cm−2, respectively. Sheet-shaped Co2P has a large surface area, meaning that it can provide a relatively large number of active sites on its surface, and CC is an highly conductive substrate that, when used in conjunction with Co2P, can enhance the conductivity of the electrocatalyst. These outstanding results show that sheet-shaped Co2P-CC could be an excellent candidate for a highly efficient electrocatalyst. [ABSTRACT FROM AUTHOR]

Pyrrolidines and piperidines are important building blocks in organic synthesis. Numerous methods exist for constructing substituted pyrrolidines and piperidines. However, efficient syntheses of pyrrolidines and piperidines bearing chiral tertiary alcohols are limited. Here we report an efficient enantioselective nickel-catalyzed intramolecular reductive cyclization of N-alkynones. A P-chiral bisphosphorus ligand DI-BIDIME is designed and applied in the synthesis of tertiary allylic siloxanes bearing pyrrolidine and piperidine rings in high yields and excellent enantioselectivities, with triethylsilane as reducing reagent. The highest turn over number achieved is 1000 (0.1 mol% catalyst loading) with > 99:1 er. This reaction provides a practical way to synthesize pyrrolidine and piperidine derivatives with chiral tertiary alcohols from easily accessible starting materials under mild conditions. The products can be scaled up and transformed to various useful chiral intermediates. The P-chiral bisphosphorus ligand developed in this study represents one of the few ligands for highly enantioselective cyclization of alkynones. Transition metal-catalyzed cyclization of alkynes and carbonyls offers a useful route to cyclic allylic alcohols, but typically uses precious metal catalysts. Here, enantioselective nickel-catalyzed reductive cyclization of N-alkynones gives tertiary allylic alcohols in up to 99:1 er with catalyst loadings of 0.1 mol% [ABSTRACT FROM AUTHOR]