Search

The sudden and unpredictable breach of landslide dams in the Yarlung Tsangpo river basin usually causes megafloods, posing great risks to human lives and infrastructures in the downstream areas. This study proposed an efficient and quantitative risk assessment framework of breach floods caused by landslide dam failures in the mainstream and tributaries of the Yarlung Tsangpo river basin with limited data. The impact of dam breach floods on human risks was evaluated. The flood attenuation along rivers, strategies for mitigating overlapping floods, and sensitivity analysis of human risks were also discussed. The results show that the developed framework successfully assessed flood risks caused by the breach of landslide dams. The flood attenuation ratio increased with river length but decreased with the peak discharge at dam site. A higher peak discharge and a larger inundated area downstream were predicted when the breach floods of two landslide dams, one in mainstream and the other in a tributary, overlapped at the confluence. The overlapping flood could be mitigated by reducing peak discharges of the two landslide dams or increasing time interval between the two peaks. The simulations also outlined the downstream peak discharge resulting from the cascading breach was larger than that of a single dam. However, it was smaller than the combined peak discharges of two separate dams, because the erosion during the breach of the downstream dam incurred energy dissipation. The human risks in the Pasighat village were greater when overlapping flood occurred due to the increased water depth and more hazardous inundated buildings. In the case of multi-peak floods, the warnings for the former peak flood would also warn the peak flood thereafter when individuals were notified multiple peaks. Otherwise, individuals might be misled by the warning of the previous peak flood, resulting in catastrophic flood impacts. A parametric analysis indicated that early evacuation warnings were needed to avoid serious loss of life and flood damages, especially in cases of dam breaches occurring at nighttime or for areas in close proximity to the dam site. [ABSTRACT FROM AUTHOR]

In this paper, we study a stochastic predator–prey model with Beddington–DeAngelis functional response and time-periodic coefficients. By analyzing the stability of the solution on the boundary and some stochastic estimates, the threshold conditions for the time-average persistence in probability and extinction of each population are established. Furthermore, the existence of a unique periodic measure of the model is also presented under the condition of the time-average persistence in probability of the model. Several numerical simulations are given to verify the effectiveness of the theoretical results and to illustrate the effects of the white noises on the persistence and periodic measure of the model. [ABSTRACT FROM AUTHOR]

Recently, layered BeN4 as a novel Dirac semimetal has been fabricated (M. Bykov, T. Fedotenko, S. Chariton et al. Phys. Rev. Lett., 2021, 126, 175501). Motivated by the experiment, we perform first-principles calculations to predict the stability, magnetic configurations, and electronic structures of unsaturated BeN4 nanoribbons with an armchair-terminated edge. The magnetic interactions and electronic properties of BeN4 nanoribbons are sensitively influenced by the edge morphology. The BeN4 nanoribbons with both edges occupied by Be atoms undergo a transition from a ferromagnetic (FM) metal to an antiferromagnetic (AFM) semiconductor with the increase of ribbon width. The configurations with edges situated by Be and N atoms are FM/ferrimagnetic (FIM) metals or nearly half-metals, and the spin polarizability is as high as 85% when the ribbon width is N = 5. The nanoribbons with both edge sites occupied by pentagonal N atoms are nonmagnetic (NM), while the nanoribbons terminated by N atoms in a hexagonal ring are FM metals. We also explore the magnetic properties and band structures of BeN4 nanoribbons with hydrogen passivation. Our results open up a versatile edge engineering avenue to design BeN4-based spintronic and nanoelectronic devices. [ABSTRACT FROM AUTHOR]

A typical flywheel energy storage system (FESS) includes an electrical machine, a flywheel, and magnetic bearings, which are independent of each other. Therefore, the structure of FESS is complicated, which leads to the problems of high cost and low integration. This article presents a novel stator PM excitation solid rotor machine (SPE-SRM) for FESS, which integrates an electrical machine, flywheels, and a magnetic bearing. The design method of the SPE-SRM is presented specifically. First, the structure and operation principle of the SPE-SRM are illustrated. Second, the design and optimization of the flywheel-rotor are presented with considering of power, energy storage, and mechanical strength. Third, the magnetic equivalent circuit of the SPE-SRM is established to simplify the design. Besides, the armature reaction and leakage flux factor are investigated. Fourth, the performance indexes, including torque, suspension force, no-load back electromotive force (back-EMF), losses, and temperature rise are fully analyzed by the finite element analysis. Finally, a 22 kW prototype is manufactured and tested. The rationality of the concept and design is validated by experiments. The SPE-SRM has the merits of high integration, robust structure, and low cost, so it has the potential for wide application in FESS. [ABSTRACT FROM AUTHOR]

The development of low-cost and high-efficiency hydrogen evolution reaction (HER) electrocatalysts has become extremely essential to address global energy issues. Herein, we have fabricated arrays of nitrogen and sulfur co-doped CoMoO4 ultrathin nanosheets grown on nickel foam (N, S-CoMoO4/NF400). The experimental results demonstrate that modulating the electronic structure of CoMoO4 by co-doping N and S atoms is one of the most powerful methods to boost the performance of HER. N, S-CoMoO4/NF400 displays superior HER activity under alkaline environment, with overpotentials of 58 and 119 mV at 10 and 100 mA cm−2. The excellent performance of the N, S-CoMoO4/NF400 electrode proves that the N, S co-doping engineering can significantly improve the catalytic activity of transition metal-based oxide HER. [ABSTRACT FROM AUTHOR]

Homopolar inductor machine (HIM) has caught much attention in the field of flywheel energy storage system (FESS) due to its merits of robust rotor, brushless exciting, and high reliability. Compared with permanent magnet HIM (PM-HIM), the HIM with field winding (FW-HIM) can effectively eliminate the idling loss caused by the no-load magnetic field by cutting off the excitation current, while the charge/discharge efficiency of the HIM would be decreased due to the copper loss of field winding. To address this contradiction, a novel PM-HIM with a mechanical flux modulator (MFM-HIM) is proposed to achieve low idling loss and high charge/discharge efficiency. First, the special structure and operation principle of the MFM-HIM are investigated. Afterwards, the characteristic of the equivalent magnetic circuit of the MFM-HIM is analyzed and the key structure parameters of it are derived and optimized. Moreover, the electromagnetic performance indexes of the MFM-HIM, including back electromotive force, flux weakening ability, losses, etc. are fully analyzed. Finally, a prototype of the MFM-HIM is designed, manufactured, and tested. Experiment results confirm those obtained by simulations. Results show that the proposed MFM-HIM inherits the merits of high charge/discharge efficiency of PM-HIM and almost no idling electromagnetic loss of FW-HIM. The MFM-HIM could be a promising candidate for the application of FESS. [ABSTRACT FROM AUTHOR]

Permanent magnet (PM) machines have attracted much attention in the field of flywheel energy storage system (FESS) due to their merits of high power density and high efficiency. However, the flux generated by the PMs would cause large stator core loss during the idling state of FESS, which would reduce the energy conversion ratio and limit the application of FESS in long-term energy storage occasions. Addressing this issue, a novel dual-rotor single-stator coreless PM machine (DSSCPMM) with dual-flywheel is proposed in this article. The stator of the DSSCPMM is made of ceramic material, which can effectively eliminate the stator core loss. The rotor of the DSSCPMM contains inner and outer rotors, which are used as the flywheels and can be helpful to improve the energy storage density. First, the structure and operation principle of the proposed DSSCPMM are illustrated. Then, the influences of the key structure parameters and arrangement of PMs, winding configurations, and magnetization method on the electromagnetic performance of the proposed DSSCPMM are investigated. Finally, the optimized structure of the DSSCPMM is obtained and the efficiency is calculated. The result shows that the proposed DSSCPMM is a promising candidate for the application of FESS. [ABSTRACT FROM AUTHOR]

(3R,4R)-2-(4-Chloro-3-(4-(((S)-tetrahydrofuran-3-yl)oxy)benzyl)phenyl)-5-((R)-1,2-dihydroxyet... To a solution of Et SB 3 sb SiH(1.5 g, 11.2 mmol) and BF SB 3 sb -Et SB 2 sb O(15.5 g, 109.2 mmol) in DCM, was added the solution of B 18 b (see above) at 5-10 °C. To a solution of B 6e b (20 g, 91.1 mmol) in DCM (150 mL), was added PCC (26.5 g, 122.6 mmol), and the mixture was stirred at rt for 20 h, then filtered to remove the solid, and the filter cake was washed with DCM (20 mL). Small amounts of water in the tetrahydrofuran (THF) solution of B 13 b and ( I S i )-3-hydroxytetrahydrofuran can lead to the production of degradation products B 15a b and B 15b b (Scheme 1), as previously noted in the literature.[11],[12] Briefly, impurity B 15b b was removed by washing with a sodium bicarbonate solution. (2S,3R,4S,5S,6R)-2-(4-Chloro-3-(4-(((S)-tetrahydronfuran-3-yl)oxy)benzyl)phenyl)-6-(hydroxyme... To a solution of B 16 b (200 g, 546.4 mmol) in THF (600 mL) was slowly added 1.1 eq n-BuLi (240 ml, 2.5 mol/L hexane solution, 600.0 mol) at -75 °C over 40 min. [Extracted from the article]

In this article, we present an adaptive broadband thyristor-controlled impedance matching network (TCIMN) for increasing power utilization from a power amplifier to the loads. Different from the conventional passive impedance matching methods, the proposed one can achieve load impedance matching under a wide frequency range of power amplifiers. First, the operation principle of TCIMN is introduced mathematically. Based on that, the parameter design method is proposed based on the required frequency range. Moreover, the operating range and harmonic analyses are provided to give the TCIMN firing angle operating ranges under different frequencies and alleviate the potential harmonic problem caused by thyristors. To control the proposed TCIMN, the dynamic impedance identification is applied to match the load reactive power adaptively. Finally, the simulation and experimental results of a prototype are given to demonstrate the validity of the proposed TCIMN, analysis, and control method. The results clearly show that the proposed TCIMN can adaptively match the load impedance for the different loads and broadband frequency range. More importantly, the power amplifier power utilization factor is significantly improved without causing harmonic pollutions. [ABSTRACT FROM AUTHOR]

The urban rail transit system has the characteristics of wide voltage fluctuation, intermittent and strong impact load, limited heat dissipation capacity. The high-speed flywheel energy storage system (FESS) is used to provide network voltage stability and regenerative braking energy recovery due to its high power density, unlimited number of charge-discharge cycles, fast response and environmental friendliness. When considering the design of high-speed FESS converter with 3.6 kHz fundamental frequency and 330 kW rated power used in 1500 VDC urban rail transit system, the two-stage topological converter reduces the efficiency and increase the cost and size, meanwhile, the series-connected converters and the multilevel converter increase the difficulties of control and insulation, so the two-level and I-type three-level converters of high-speed FESS are designed and evaluated. Several comparisons are made by detailed experimental data from the perspective of the traction load characteristics of the 1500 VDC urban rail transit system and the technical and economical requirements of the high-speed FESS. It is found that the three-level converter has significant advantages in matching the traction load characteristics for its higher duty cycle capability, as well as improving the technical and economical performances such as efficiency, du/dt value, THD, voltage stability, and reducing the cost by 40% when compared to the two-level converter. While in the future MW class high-speed FESS development, the maximum output power capacity of the three-level FESS is relatively lower than that of the two-level FESS. The theoretical analyses were verified by experiments. [ABSTRACT FROM AUTHOR]