Search

Flexible capture has high applicability in the removal of space debris. In this paper, a novel adhesive capture mechanism is proposed, the multibody dynamic modeling method of the capture system is detailed, and an investigation of the adhesive capture process by numerical simulation is presented. First, the passive trigger mechanism of the capture device is described. Second, based on the classical rigid body mechanics and the fully parameterized ANCF beam element, the multibody model of the capture device is detailed. A contact detection algorithm is proposed to take the failure of adhesive connection into account, and its robustness and effectiveness are demonstrated. Finally, investigations of the dynamics during the capture process in two typical capture conditions are described and the impact of some system parameters on the capture effectiveness is discussed. The simulation results provide key parameters for the selection of the adhesive material and show the practical applicability of the capture mechanism.

The tethered-net is one of the most promising flexible space debris cleaning technologies to be developed in recent years. Momentum and geometric analysis were used to select four characteristic parameters of the tethered-net ejection system—the radius of the circumcircle of the net, the ratio of the bullet mass to the net mass, the ejection velocity of the bullet, and the ejection angle—to establish a set of formulas that describe the kinematics of the net deployment. The net deployment performance evaluation criteria were obtained with a concise analytical form. The calculation results of this set of analytical formulas are in good agreement with the numerical simulation results of the mass-spring model. Furthermore, this set of analytical formulas reveals some intrinsic characteristics of the net deployment dynamics. For example, the flying distance of the net from the start of ejection to the largest area is mainly determined by the radius of the circumcircle of the net and ejection angle. It is believed that the analytic formulas proposed are suitable for the preliminary design of a tethered-net system, especially when numerical simulation is time consuming.

Dust storms bring a large quantity of dust aerosols from arid and semi-arid regions of the Earth. However, real-time dust concentration data for dust storms in arid regions, important for wind erosion studies, are still limited. Here, temporal variation of airborne dust concentrations in the Mogao Grottoes, Northwest China, during the monitoring period from February to October 2012 and typical dust storms under different wind directions were analyzed. Results reveal that the monthly mean total suspended particle (TSP), particulate matter less than 10 μm (PM10), and particulate matter less than 2.5 μm (PM2.5) concentrations gradually decreased from February to October. The daily mean dust concentrations fluctuated with the day, with extreme values occurring mainly on February, March, and April. The daily mean PM10/TSP ratio ranged from 0.67 to 0.98 (mean of 0.82), and the PM2.5/PM10 ratio ranged from 0.31 to 0.73 (mean of 0.55), indicating PM10 dominated in TSP. In typical dust storms, the maximum real-time concentrations can reach 16, 000–21, 000 μg TSP m−3, ∼11, 000 μg PM10 m−3, and 3000–3500 μg PM2.5 m−3, and extreme real-time dust concentrations of 50358.03 μg TSP m−3, 33100.86 μg PM10 m−3, and 7502.59 μg PM2.5 m−3 were recorded. Coincidence of the dry climate and windy season and sufficient dust sources in the surrounding environment contributed to the high dust concentrations in the Mogao Grottoes. To achieve the goal of minimizing the damage of falling dust to the murals and statues, establishing a dust storm early warning system and improving the existing sand control system are recommended.

Additional file 2: Table S2. Conserved motifs in the amino acid sequences of CsPP2C proteins.

Additional file 1: Table S1. Selective pressure analysis of PP2C genes family.

Excitonic insulators are long-sought-after quantum materials predicted to spontaneously open a gap by the Bose condensation of bound electron-hole pairs, namely, excitons, in their ground state. Since the theoretical conjecture, extensive efforts have been devoted to pursuing excitonic insulator platforms for exploring macroscopic quantum phenomena in real materials. Reliable evidences of excitonic character have been obtained in layered chalcogenides as promising candidates. However, owing to the interference of intrinsic lattice instabilities, it is still debatable whether those features, such as charge density wave and gap opening, are primarily driven by the excitonic effect or by the lattice transition. Herein, we develop a novel charge-transfer excitonic insulator in organic-inorganic superlattice interfaces, which serves as an ideal platform to decouple the excitonic effect from the lattice effect. In this system, we observe the narrow gap opening and the formation of a charge density wave without periodic lattice distortion, providing visualized evidence of exciton condensation occurring in thermal equilibrium. Our findings identify spontaneous interfacial charge transfer as a new strategy for developing novel excitonic insulators and investigating their correlated many-body physics.

The discrete-time fault-tolerant control method for permanent magnet synchronous motors (PMSMs) is investigated for the first time in this paper based on adaptive fuzzy theory, where the designed controllers consider faults containing both loss of effectiveness and bias. Firstly, with the help of Euler method, the discrete-time model of PMSMs is obtained. Secondly, adaptive fuzzy theory is used to realize fault-tolerant control of PMSMs. Next, dynamic surface control is used to resolve the problems of “explosion of complexity” and noncausal in discrete-time systems caused by backstepping. It is proved that the proposed method can guarantee all signals and states in the closed-loop system are semi-global uniform ultimate bounded when the faults occur and the position tracking error can converge to a small neighborhood of the origin. Finally, simulation results show that the proposed control method has strong fault-tolerant performance and robustness.

Space net capture is an innovative concept for active debris removal that provides a prospective method for the removal of large, non-cooperative space targets. The design of a space net capture system must meet two basic requirements: maximizing the capture ability and minimizing the system cost. This paper presents an inexpensive multi-objective optimization framework to solve this design problem. In this framework, a design optimization approach using a lumped parameter modelling method as well as an improved inexpensive multi-objective optimization algorithm is proposed. The system mass and effective distance are chosen as objectives of this optimization problem. The simulation results reveal that the multi-objective optimization framework is feasible and effective for the design of a space net capture system, and the designer preferred solutions that enhance system design are reliably identified.

A thermal analysis of AlGaN/GaN high electron mobility transistors (HEMTs) with Graphene is investigated using Silvaco and Finite Element Method. Two thermal management solutions are adopted; first ...

In this study, a new cooling strategy for a proton exchange membrane (PEM) fuel cell stack is investigated using a three-dimensional (3D) multiphase non-isothermal model. The new cooling strategy follows that of the Honda's Clarity design and further extends to a cooling unit every five cells in stacks. The stack consists of 5 fuel cells sharing the inlet and outlet manifolds for reactant gas flows. Each cell has 7-path serpentine flow fields with a counter-flow configuration arranged for hydrogen and air streams. The coolant flow fields are set at the two sides of the stack and are simplified as the convective heat transfer thermal boundary conditions. This study also compares two thermal boundary conditions, namely limited and infinite coolant flow rates, and their impacts on the distributions of oxygen, liquid water, current density and membrane hydration. The difference of local temperature between these two cooling conditions is as much as 6.9 K in the 5-cell stack, while it is only 1.7 K in a single cell. In addition, the increased vapor concentration at high temperature (and hence water saturation pressure) dilutes the oxygen content in the air flow, reducing local oxygen concentration. The higher temperature in the stack also causes low membrane hydration, and consequently poor cell performance and non-uniform current density distribution, as disclosed by the simulation. The work indicates the new cooling strategy can be optimized by increasing the heat transfer coefficient between the stack and coolant to mitigate local overheating and cell performance reduction.

Early fault detection is increasingly important for the reliable and secure operation of power plant fans. In this paper, we propose an early fault detection strategy for power plant fans based on dynamic neural network. First, the nonlinear autoregressive (NARX) with exogenous inputs network is utilized to predict the behavior of fans by using normal operating data, and the discrete particle swarm optimization (DPSO) is utilized to optimize the hyper-parameters of NARX network to enhance prediction accuracy. Then, the fault alarm strategy is proposed by the prediction deviations and generalized extreme value (GEV) theory. Finally, the proposed method is applied to a forced draft (FD) fan in a coal-fired power plant. Experiment results show that the proposed model has high prediction accuracy on normal operations and produces large prediction errors when a failure occurs. Furthermore, it can detect early faults accurately and timely before the failure occurs.

Rod-tubing wear and suck rod failure are two serious problems in many oil fields, which take 45% of the whole workover. Because of the problem, in some area, the average mean-time-between-failure is only 200 days. The workover costs lots of money, not including the loss of oil production. A rodless artificial lift system, electric submersible progressive cavity pump (ESPCP), was developed and had been successfully deployed. This paper focuses on the ESPCP technology and field application. The system included a progressive cavity pump driven by a downhole permanent magnet synchronous motor, which allowed adjusting the rotation speed between 50-500 rpm. a motor protector and a flexible shaft connecting the pump and the motor protector. More than 20 ESPCP systems has been deployed. The power of these motors was 9-15 kilowatts. The average pump setting depth was 1100 meters and the average production rate was 7-70 cubic meters per day. The application results showed that the average pump efficiency was 75.2% and the system could save more than 20% of the electricity power. In some area, the average time between workovers from 192 days of the traditional sucker rod pump to more than 400 days. The longest running life was more than 500 days. By using this technology, the production and workover cost could be greatly saved and increased production days can be increased accordingly. Moreover, the system was located at the bottom of oil well, so less site occupation, more safety and less noise pollution to the environment were achieved. The ESPCP system is of great of significance for some special wells such as directional well, highly-deviated well, it also can avoid the pollution in wetland and floodplain field.

This Chapter aims to calculate the students’ drop-out rates caused by various diseases and make the comparison between the drop-out rates of primary and secondary schools (χ2 test) and to understand the current situation of drop-out due to diseases in key primary and secondary schools of Lubei district of Tangshan city from 2003 to 2008. The results show that mental illness led to the lowest drop-out rate of students, while cardiovascular disease led to the highest. And drop-out rates caused by various diseases was lower than 5‰ in total. There were no significant differences between the drop-out rates of primary and secondary schools. The disease spectrum in children and adolescents has changed, and cardiovascular disease has replaced infectious disease to be the main disease, causing students to drop-out. So it is imperative to strengthen the prevention and treatment of cardiovascular disease.

Morphologies and characteristics of the surface and interface of TaSi2/Si and TaSi2/poly‐Si structures reactively formed by furnace annealing and rapid thermal annealing (RTA) have been investigated thoroughly. Scanning electron microscopy and transmission electron microscopy (cross section) results show that the morphologies of the annealed samples were uneven, but the surface and interface of RTA samples were better than that of furnace annealed samples. The specific contact resistivity of TaSi2 to n+ ‐Si substrates with Kelvin structure was measured. The contact resistivity increased as the annealing temperature increased, but was lower for RTA samples than for furnace annealed samples. Sheet resistance measurement, x‐ray diffraction, and Auger electron spectroscopy analysis techniques were used to monitor the formation of TaSi2 films.