Search

When the GaAs/AlGaAs superlattice-based devices are used under irradiation environments, point defects may be created and ultimately deteriorate their electronic and transport properties. Thus, understanding the properties of point defects like vacancies and interstitials is essential for the successful application of semiconductor materials. In the present study, first-principles calculations are carried out to explore the stability of point defects in GaAs/Al0.5Ga0.5As superlattice and their effects on electronic properties. The results show that the interstitial defects and Frenkel pair defects are relatively difficult to form, while the antisite defects are favorably created generally. Besides, the existence of point defects generally modifies the electronic structure of GaAs/Al0.5Ga0.5As superlattice significantly, and most of the defective SL structures possess metallic characteristics. Considering the stability of point defects and carrier mobility of defective states, we propose an effective strategy that AlAs, GaAs, and AlGa antisite defects are introduced to improve the hole or electron mobility of GaAs/Al0.5Ga0.5As superlattice. The obtained results will contribute to the understanding of the radiation damage effects of the GaAs/AlGaAs superlattice, and provide a guidance for designing highly stable and durable semiconductor superlattice-based electronics and optoelectronics for extreme environment applications.

In recent years, the increasing energy crisis and environmental pollution have brought attention to distributed renewable power generation such as photovoltaics and wind power. However, the integration of distributed power sources puts forward higher requirements for the safety, stability and economic operation of the power system. Traditional protection setting methods face greater difficulties in solving the contradiction between action time and protection selectivity under complex conditions including distributed power generation. In many cases, the setting value is not optimal. With the increase in the penetration rate of distributed power sources and the increasingly complex operation of distribution networks, how to achieve the optimal setting of overall protection performance has become a current research hotspot. For this reason, this paper proposes a new scheme based on the Sparrow algorithm to optimize the online protection of distributed power distribution network protection, which is verified by a calculation example.

In rare earth production, improving the fault detection of extraction equipment has a key impact on improving extraction efficiency and product quality. The traditional method is based on the observation of the liquid level, the efficiency and accuracy can’t be guaranteed. In this paper, a fault diagnosis and recognition method for rare earth extraction production line based on wavelet packet and alexnet transfer learning is proposed. Taking six fault states of rare earth extraction production line as the research object, the fault signal is extracted by wavelet packet decomposition, and the corresponding target data set of time-frequency diagram is generated. Then, the pre trained alexnet model is trained and fine tuned on the generated target data set, and finally applied to fault diagnosis of rare earth extraction production line. The results show that the proposed method is more accurate than the traditional convolution neural network, which verifies the effectiveness of the method.

Limited studies focused on the slope rock foundation, and the application results of several methods differ considerably. In this paper, the coefficients of the Bell solution are first reduced by the length ratio of the sliding failure plane and the vertical area ratio of the overloaded soil. Then, the Hoek–Brown criterion for nonlinear failure is introduced, and the tangential line tangent to the Hoek–Brown failure criterion curve is calculated to replace the original M-C failure criterion. A method for determining the instantaneous friction angle and instantaneous cohesion under normal stress with the Bell solution failure mode is established, and the relationship between the instantaneous friction angle, instantaneous cohesion, and normal stress are discussed. The instantaneous friction angle decreases with the increase in normal stress, whereas the instantaneous cohesion increases with normal stress. The influence of geological strength index (GSI) and rock empirical parameter mi on bearing capacity coefficients N σ, N q, and Nγ are also comprehensively analyzed. The coefficients increase with GSI and mi . In addition, the method is used to analyze the bearing capacity of rock foundation of a high and steep slope in an open-pit mine, and the results are compared with the slip-line method, which considers Hoek–Brown failure criterion and finite-element numerical simulation. The comparison demonstrates the acceptability of the proposed method.

The potential-driving model is used to describe the driving potential distribution and to calculate the pre-neutron emission mass distributions for different incident energies in the reaction. The potential-driving model is implemented in Geant4 and used to calculate the fission-fragment yield distributions, kinetic energy distributions, fission neutron spectrum and the total nubar for the reaction. Compared with the built-in G4ParaFissionModel, the calculated results from the potential-driving model are in better agreement with the experimental data and evaluated data. Given the good agreement with the experimental data, the potential-driving model in Geant4 can describe well the neutron-induced fission of actinide nuclei, which is very important for the study of neutron transmutation physics and the design of a transmutation system.

Ultrasonic guided wave inspection is one of the non-destructive testing (NDT) techniques available for the structural health monitoring (SHM) of engineering structures. Compared with other NDT techniques, guided waves can propagate over tens of metres with a relatively high sensitivity to defects in the structure. The general sensitivity range of the operation is up to 3% reduction of the cross-sectional area, depending on the signal-to-noise ratio. However, optimisation of guided wave testing method is still a requirement, as the technique is currently subject to a complex analysis due to wide number of guided wave modes generated. This can be done by optimising the transducer array design. In this paper, it is described the behaviour of a set of piezoelectric transducer arrays upon excitation in a tubular structure with simulated defects. This is achieved through a combination of finite element analysis (FEA) and experimental testing. The core objective of the work is to optimise the design of transducer arrays aimed at exciting the T(0,1) mode with a significant level of mode purity. This will significantly reduce the complexity of guided wave analysis, enhancing effectively the structural health of structures and subsequently reduce the industry maintenance cost.

Using non-equilibrium molecular dynamics simulations, we investigate thermal rectification (TR) in graphene/hexagonal boron nitride (h-BN) hybrid structures. Two different structural models, partially substituting graphene into h-BN (CBN) and partially substituting h-BN into graphene (BNC), are considered. It is found that CBN has a significant TR effect while that of BNC is very weak. The observed TR phenomenon can be attributed to the resonance effect between out-of-plane phonons of graphene and h-BN domains in the low-frequency region under negative temperature bias. In addition, the influences of ambient temperature, system size, defect number and substrate interaction are also studied to obtain the optimum conditions for TR. More importantly, the TR ratio could be effectively tuned through chemical and structural diversity. A moderate C/BN ratio and parallel arrangement are found to enhance the TR ratio. Detailed phonon spectra analyses are conducted to understand the thermal transport behavior. This work extends hybrid engineering to 2D materials for achieving TR.

As one of the most important key technologies for future advanced light source based on the energy recovery linac, a photocathode dc electron gun is supported by Institute of High Energy Physics (IHEP) to address the technical challenges of producing very low emittance beams at high average current. Construction of the dc gun is completed and a preliminary high voltage conditioning is carried out up to 440 kV. The design, construction and preliminary HV conditioning results for the dc gun are described.

We present a scheme that is capable of detecting photon numbers during the quantum key distribution (QKD) based on an improved differential phase shift (DPS) system without Trojan horse attack. A time-multiplexed detector (TMD) is set in for the photon-number resolution. Two fibre loops are used for detecting photon numbers as well as distributing keys. The long-term stabilization is guaranteed by two Faraday mirrors (FM) at Bob's site to automatically compensate for polarization defect. Our experimental study (90km QKD is completed) indicates that such a system is stable and secure which nearly reaches the performance of a single photon scheme.

Damage identification in civil engineering structures using vibration measurements has become an important area of research. A reliable and cost effective method is required to detect and quantify local damage in the structures. The objective of this new proposed method is to identify structural damage in real time at a more detailed level directly from the vibration measurements. Structural damage is assumed to be associated with a proportional reduction of element stiffness matrix. Dynamics characteristics of the structure are calculated by using N ewmark's numerical integration method based on measured acceleration data. The change in the stiffness matrix caused by structural damage is implemented into the equation of motion of the dynamic system. A system of governing equations is derived, where the difference between the vibration data of undamaged and damaged structures can be directly adopted. The changes in the stiffness matrix are represented by the changes in the coefficients associated with element stiffness matrixes. Those coefficients can be used as damage parameters in structural damage detection. Both the location and extent of the damage are then determined based on the inverse calculations of damage parameters of the individual elements. Finally, a numerical example is utilised to demonstrate the effectiveness of the proposed approach for on-line structural damage assessment.

High-spin states in 84Rb have been studied by using the 70Zn (18O, p3n) 84Rb reaction at a beam energy of 75 MeV. The γ - γ coincidence, excitation function and ratios for directional correlation of oriented states were performed. A new level scheme was established in which the positive and negative parity bands have been extended up to 17+ and 17- with excitation energy about 7 MeV. The signature splitting and signature inversion of the positive parity yrast bands were observed and are discussed.

On the basis of perfect PC2D simulation to the measured current density vs voltage (J–V) curve of the best selective emitter (SE) solar cell fabricated by the CSG Company using the screen printing phosphoric paste method, we systematically investigated the effect of the parameters of gridline, base, selective emitter, back surface field (BSF) layer and surface recombination rate on performance of the SE solar cell. Among these parameters, we identified that the base minority carrier lifetime, the front and back surface recombination rate and the ratio of the sheet-resistance of heavily and lightly doped region are the four largest efficiency-affecting factors. If all the parameters have ideal values, the SE solar cell fabricated on a p-type monocrystalline silicon wafer can even obtain the efficiency of 20.45%. In addition, the simulation also shows that fine gridline combining dense gridline and increasing bus bar number while keeping the lower area ratio can offer the other ways to improve the efficiency.

Sea defence structures are expected to protect coasts for a long period, hence requiring reliable performance assessment strategies, in order to ensure their integrity and functionality. It has been demonstrated that rising sea level together with changing wave height can lead to increase risks of the failure to coastal defence structures. This paper presents a method for assessing the risk of wave overtopping failure, analysing the joint probability of sea water level and significant wave height under future hydraulic conditions due to climate change. Monte Carlo simulations are utilised to analyse the time-dependant overtopping failure probability of a seawall in the UK subjected to sea level rise. The numerical results for the flood defence example show that the seawall subjected to the sea level rise with high emission scenario could face to a significant increase of the frequency and the rate of overtopping discharge in comparison with the present date conditions without consideration of seawall crest settlement.

Structural performance deterioration of reinforced concrete structures has been extensively investigated, but very limited studies have been carried out to investigate the effect of reinforcement corrosion on time-dependent reliability with consideration of the influence of mechanical characteristics of the bond interface due to corrosion. This paper deals with how corrosion in reinforcement creates different types of defects in concrete structure and how they are responsible for the structural capacity deterioration of corrosion affected reinforced concrete structures during their service life. Cracking in cover concrete due to reinforcement corrosion is investigated by using rebar-concrete model and realistic concrete properties. The flexural strength deterioration is analytically predicted on the basis of bond strength evolution due to reinforcement corrosion, which is examined by the experimental data available. The time-dependent reliability analysis is undertaken to calculate the life time structural reliability of corrosion damaged concrete structures by stochastic deterioration modelling of reinforced concrete. The results from the numerical example show that the proposed approach is capable of evaluating the damage caused by reinforcement corrosion and also predicting the structural reliability of concrete structures during their lifecycle.

From the first-principles calculation, we investigate the electronic transport properties of centrosymmetric carbon nanotube heterojunction with different lengths coupled with between two identical Al(100) electrodes. The results show that the conductance can be modulated with the length of central regular carbon nanotube. The current ratios of different heterojunctions decrease exponentially with the external bias voltage, which provides us a new idea of combination functional element of the next generation of computers. A detailed analysis is proposed.

The tuning system plays a very important role when a superconducting cavity is in operation. It cooperates with other control loops to adjust the cavity frequency with high precision, reduce the reflection power, guarantee the stability of beam, and ensure the safety of the superconducting cavity. This paper focuses mainly on the tuning system working principle, the working state and problems that Beijing Electron Positron Collider (BEPC II) has encountered during operation.

A fibre optic extrinsic Fabry–Perot interferometric (EFPI) displacement sensor for fault measurement in geomechanics is experimentally demonstrated. By using a metal tube and metal bars the EFPI displacement sensor can demonstrate high strength and high stability, as the effects of the harsh environment are mitigated. The sensor is fixed to a long stainless steel pipe which is inserted into a drilled hole and placed across the fault zone. In this way, the sensor can be placed easily and accurately in the fault zone. In order to eliminate the influence of temperature two metal bars of different materials, and therefore with different thermal expansion coefficients, are used. Thus, the sensor itself is capable of compensating for temperature. The experimental results show that the ratio of the cavity length to the temperature reduces from 0.142 to −0.045 µm °C−1. In a continuous test, the measurement results vary over a range of 4.954 µm and the standard deviation is 1.196 µm, when the temperature is changed from 17 to 80 °C.