The temperature dependence of carrier transport properties of AlxGa 1−x N/InyGa 1−y N/GaN and AlxGa 1−x N/GaN heterostructures has been investigated.It is shown that the Hall mobility in Al 0.25 Ga 0.75 N/In 0.03 Ga 0.97 N/GaN heterostructures is higher than that in Al 0.25 Ga 0.75 N/GaN heterostructures at temperatures above 500 K, even the mobility in the former is much lower than that in the latter at 300 K. More importantly, the electron sheet density in Al 0.25 Ga 0.75 N/In 0.03 Ga 0.97 N/GaN heterostructures decreases slightly, whereas the electron sheet density in Al 0.25 Ga 0.75 N/GaN heterostructures gradually increases with increasing temperature above 500 K. It is believed that an electron depletion layer is formed due to the negative polarization charges at the InyGa 1−y N/GaN heterointerface induced by the compressive strain in the InyGa 1−y N channel, which effectively suppresses the parallel conductivity originating from the thermal excitation in the underlying GaN layer at high temperatures.
As a prototypical transition-metal dichalcogenide semiconductor, MoS2 possesses strong spin–orbit coupling, which provides an ideal platform for the realization of interesting physical phenomena. Here, we report the magnetotransport properties in NbN–MoS2–NbN sandwich junctions at low temperatures. Above the critical temperature around ∼11 K, the junction resistance shows weak temperature dependence, indicating a tunneling behavior. While below ∼11 K, nearly zero junction resistance is observed, indicating the superconducting state in the MoS2 layer induced by the superconducting proximity effect. When a perpendicular magnetic field ∼1 T is applied, such proximity effect is suppressed, accompanying with insulator-like temperature-dependence of the junction resistance. Intriguingly, when further increasing the magnetic field, the junction conductance is significantly enhanced, which is related to the enhanced single particle tunneling induced by the decrease of the superconducting energy gap with increasing magnetic fields. In addition, the possible Majorana zero mode on the surface of MoS2 can further lead to the enhancement of the junction conductance.
Based on the theories of the gas seepage in coal seams and the deformation of the coal-rock medium, the gas seepage field in coal-rock mass is coupled with the deformation field of the coal-rock mass to establish a fluidstructure interaction model for the interaction between coal gas and coal-rock masses. The outburst process in coal-rock masses under the joint action of gas pressure and crustal stress is simulated using the material point method. The simulation results show the changes in gas pressure, velocity distribution, maximum principal stress distribution, and damage distribution during the process of the coal and gas outburst, as well as the movement and accumulation of coal-rock masses after the occurrence of the outburst. It was found that the gas pressure gradient was greatest at the working face after the occurrence of the outburst, the gas pressures and pressure gradients at each location within the coal seam gradually decreased with time, and the damage distribution was essentially the same as the minimum principal stress distribution. The simulation further revealed that the outburst first occurred in the middle of the tunnel excavation face and that the speed at which particles of coal mass were ejected was highest at the center and decreased toward the upper and lower sides. The study provides a scientific basis for enhancing our understanding of the mechanism behind coal and gas outbursts, as well as their prevention and control.
In power transformation and distribution system, unplanned blackouts caused by high voltage circuit breaker faults accounted for more than 60% of the total accidents [, most of the circuit breaker faults are caused by mechanical faults. Base on circuit breaker electrical characteristics, this paper present a method of circuit breaker mechanical faults on-line monitoring. Switching on-off of circuit breakers contacts can be equivalent to a time-varying capacitance, based on equivalent circuit model, the relationship between reactive component and time can be concluded. Processing circuit breakers contacts electric signals with orthogonal decomposition and least squares curve fitting method to highlight the main characteristics of the mechanical faults. These processed data collected from different running state can create a database, taking this database as diagnostic basis to diagnose whether mechanical faults occur to circuit breaker.
There are many factors that can lead to partial discharge in the internal of switchgear. High-frequency current will be generated on the inner wall of switchgear when the electromagnetic wave generated by partial discharge reaches the enclosure of switchgear. In the same way, more complex current signal will be produced on the outer wall of the switchgear because of the electromagnetic radiation outside the enclosure. These two currents will flow to earth through the switchgear ground wire. We can determine whether the switchgear exist partial discharge and the severity of the partial discharge by comparing the current flowing through the outer wall and the total current flowing through the ground line.
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