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This letter has studied the gate reliability of p-GaN high electron mobility transistors (HEMTs) influenced by the Mg doping level at the initial growth stage of p-GaN layer. Normally-off HEMTs with p-GaN gate fabricated with relatively low and high Mg doping concentration have been analyzed and compared based on their performances at various statuses of as-fabricated, forward step-stressed, reverse step-stressed and long-term reverse stressed. It reveals that Mg over-doping has a detrimental effect on the p-GaN gate reliability through degrading the PIN diode formed by p-GaN/AlGaN/GaN structure. Severe drain current reduction, threshold voltage instability and gate leakage increase have been observed after being negatively stressed due to the high-density defects acting as apparent acceptor-like traps induced by Mg over-doping. The detailed studies on the p-GaN gate performance with various Mg concentrations give a greater depth of understanding to realize high gate reliability of p-GaN gate HEMTs.

It is of great significance to study the crashworthiness of LNG carrier to improve its crashresistance and enhance its operation safety. In this paper, the collision process between the bulbous bow of the container ship and the side structure of the LNG ship is analyzed by using nonlinear finite element numerical simulation. Collision performance of LNG carrier and collision indicators during the collision, the impact force, velocity and displacement and energy absorption in the process of collision by changing parameters of the major velocity, impact angle and impact location and others are studied. The relevant research results have a strong practical significance for analyzing the deformation, strengthening measures and structural repair of ship side structure impact damage.

In this paper, the load transfer analysis method is used. Firstly, the magnetic thermal coupling analysis model is established and the material parameters are determined in ANSYS software. Secondly, the direction of applied current is determined by studying the influence of current direction on the temperature field in the electrified wire. Then, the relationship between current frequency, current magnitude and temperature field and the change of temperature at typical points with time are studied respectively. Finally, the parameters of temperature field for high frequency induction heater to produce better plastic deformation are determined. The research content of this paper can provide a reference for the subsequent research of electromagnetic thermal structure coupling numerical simulation technology of mobile inductor.

Soil contamination by heavy metals is often caused by industrial and agricultural activities, which directly affects environment quality and food safety, especially for farmlands. To develop indicators for making proper decisions regarding land use, the Soil Heavy Metal Contamination Evaluation System including the Single Pollution Index (Pi), the Nemerow Pollution Index (PINemerow), the Potential Ecological Risk Index (RI), and the Contamination Severity Index (CSI) was developed using data from 499 samples collected from an area of 2017 km2. A risk assessment zoning solution based on PPRC (the Soil Heavy Metal Contamination Evaluation System including Pi, PINemerow, RI and CSI) was proposed, and the study area was mapped for four risk assessment zones as follows: no risk zone, very low risk zone, low risk zone, and intermediate risk zone. Four land use strategies (priority protection, protection, comprehensive monitoring, and warning and control) were proposed. Generally, the risk assessment zoning solution based on PPRC-defined minimizes the potential ecological risk to the land for the scientific evaluation of heavy metal pollution in areas of intensive agricultural activity.

Under the background of big data era, network information has become an important part in the development of modern society. At the same time, computer information security has also suffered an unprecedented impact, corporate secrets stolen, personal privacy has been exposed and other incidents emerge in endlessly. It is an urgent time to strengthen information security protection. Therefore, this paper puts forward the research work of information security protection strategy based on computer big data technology. This paper makes an in-depth investigation on the current situation of computer information security protection. According to the investigation, most enterprises think it is necessary to strengthen the information security protection, but few of them are actually applied to the work. The analysis shows that the main reason is that the information security protection is difficult, the influencing factors are complex, and the investment cost is high. In view of these problems, this paper makes an investigation on the factors affecting the computer network information security, and puts forward effective improvement measures. This measure strengthens the construction of protection software and emphasizes the cultivation of enterprise’s information protection awareness. Through the relevant investigation, we can see that after adopting the information security protection measures, the enterprise’s computer information security has been effectively guaranteed.

In recent years, big data technology has been developed rapidly. While big data technology has been successfully applied in many industries, it has also completely changed the traditional education and teaching mode. Using big data technology for internet teaching is a mainstream trend at present, which makes up for many deficiencies in traditional teaching. As the current Internet teaching technology is still not perfect, this paper establishes the application research of computer big data in Internet learning. This paper makes an in-depth study on the current Internet learning. Through the survey, it can be seen that the popularity rate of Internet learning is very high, and the teaching effect has been affirmed in many aspects. However, because the technology is still in the initial stage of application, there are still many technical shortcomings, such as the information data security is not high, the teaching platform performance is not stable, the platform student management is not scientific and so on. For this reason, this paper gives the relevant suggestions for these deficiencies, as well as optimization and improvement measures. Moreover, through the in-depth study on the application form and application process of Internet learning, this paper believes that Internet learning is the major trend in the future teaching reform and development, and more attention should be paid to the students’ experience and the optimization and upgrading of related technologies in the process of reform and development.

With “improving quality, reducing total amounts and preventing risks” as the mainline, Hefei adheres to ecological priority and the concept of symbiosis between cities and lakes, accelerates the transition towards green production methods, lifestyles and consumption patterns, and strides into a beautiful Hefei where “all lands are green, all waters are lucid, all seasons are scented with flowers and all places are resonant with singing birds”. This paper analyses the unique measures taken by Hefei for green development. On the basis of reviewing the main achievements and problems of Hefei’s green development, it proposes suggestions for reducing the excessive consumption of resources, comprehensively promoting industrial upgrading, disseminating ecological culture, strengthening the rule of law, environmental protection and eco-governance, and pushing forward the continuous improvement of ecological and environmental quality, so as to provide the decision-making basis for building Hefei as a green development demonstration city which realizes comprehensive, coordinated and sustainable development on economic, social and ecological aspects.

With the innovation of mobile internet technology and the popularization of smart phones, China enters a Micro-blog and WeChat Era. The government’s supervision of public opinion will also focus on micro-blogging, WeChat - messaging and other network media platforms. Youth is the main force of the emergence of network public opinion, and improving their media literacy is an important issue at present. This research provides countermeasures and suggestions for improving youth media literacy in the new era.

This paper proposes a new nature based on deep deterministic policy gradient for deep reinforcement learning in continuous state and action space, which can greatly accelerate the emergence of artificial intelligence training and solving problem: state-action permissibility. The proposed method is integrated into the latest DDPG algorithm to guide its training and is applied to solve the lane keeping (steering control) problem in autonomous driving or automatic driving. Finally, the TORCS which is the open racing car simulator simulation software builds various simulation environments, including different tracks to verify the effectiveness of the algorithm. The results show that the proposed method can significantly speed up the algorithm training speed of the lane keeping task.

In this paper, 5A06 aluminum alloy was filled with friction stir spot welding. Mechanical properties and metallographic tests were carried out on the welded joint. By observing the microstructure of the weld, the effects of different welding parameters on the mechanical properties and cross section formation of the filler friction stir spot welded joint were analyzed. The results show that the welding time has the greatest influence on the shear resistance and tensile properties of the friction spot welding joint, and the increase of the rotation speed of the spot welding tool will enhance the tensile properties of the joint.

Many numerical methods are carried out to study the nonlinear failure behaviors of the rock; however, the numerical simulation methods for the failed rock are still in the research stage. This paper establishes the damage constitutive equation by combining the bilinear strain softening constitutive model with energy dissipation principles, as well as the energy failure criterion of mesoscopic elements based on the strain energy density theory. When the strain energy stored by an element exceeds a fixed value, the element enters the damage state and the damage degree increases with increasing energy dissipation. Simultaneously, the material properties of the damaged element change until it becomes an element with certain residual strength. As the load increases, the damage degree of an element increases. When the strain energy stored by an element exceeds the established value of the energy criterion, the element is defined to be failed. As the number of failed elements constantly increases, failed elements interconnect and form macrocracks. The rock fracture calculation program on the basis of the preceding algorithm is successfully applied to the fracture simulation process in Brazilian splitting and intermediate crack tensile tests. This method completes the nonlinear calculation process with linear calculation, avoids singularity of numerical calculation in element fracture, and simulates the rock post-peak fracture behaviors. The simulation results agree well with the test results, indicating the accuracy and feasibility of this method for simulating the rock fracture process.

Luminescent downconversion is a promising way to harvest ultraviolet sunlight and transform it into visible light that can be absorbed by solar cells, and has potential to improve their photoelectric conversion efficiency. In this work, the uniform hollow spheres and well dispersed CaF2 phosphors doped with rare-earth Ce3+ and Tb3+ ions are prepared by a one-step hydrothermal synthesis method. Benefiting from the stronger ability of absorption and emission and excellent transparency property, we demonstrate that the application of the doped nanocrystals can efficiently improve visible light transmittance. The chosen phosphors are added in the SiO2 sols so as to get the anti-reflection coatings with wavelength conversion bi-functional films, promoting the optical transmittance in the visible and near-infrared range which matches with the range of the band gap energy of silicon semiconductor. Optimized photoelectric conversion efficiency of 14.35% and the external quantum efficiency over 70% from 450 to 950 nm are obtained through the silicon solar cells with 0.10 g phosphors coating. Compared with the pure glass devices, the photoelectric conversion efficiency is enhanced by 0.69%. This work indicates that fluorescent downconversion not only can serve as proof of principles for improving photoelectric conversion efficiency of solar cells but also may be helpful to practical application in the future.

It is shown that a novel anomaly associated with transverse Ward-Takahashi identity exists for pseudo-tensor current in QED, and the anomaly gives rise to a topological index of Dirac operator in terms of Atiyah-Singer index theorem., Comment: 4 pages. Submitted to "Chinese Physics C"

The polycrystalline complex compounds of PLZT, the formula (Pb1-xLax)(Zr0.52Ti0.48)O3 (x = 0.10, 0.15, 0.20 and 0.25), were fabricated by sol-gel method. the influence of La content on the microstructure, optical properties and electrical properties of PLZT materials were studied. Phase characterization and crystal orientation of the PLZT films was investigated by X-ray diffraction analysis. The extinction coefficient k of the films drops dramatically in the range of 300-500 nm, and reduces to 0.0355, 0.0357 and 0.0451 with the La concentration of 15%, 20% and 25%, respectively, when the wavelength is larger than 550 nm. The remnant polarization of the films decreases with the La content increasing.