Volume 11

Based on the spread of the new crown epidemic, the use of masks has been popularized, so it has a significant impact on the development of face recognition under the cover. The study of how to improve the performance of face recognition under occlusion conditions is also an important topic in the field of face recognition in the future. At the same time, the neural network model is one of the most important models in deep learning, in the field of image classification, face recognition based on deep network has also been proved to be an efficient feature extraction method, this paper divides the face recognition method based on occlusion into two categories: local feature class based on non-occlusion area and feature class based on recognition occlusion area; The basic processes of these two types of methods are summarized, and the specific cases of these two types of occlusion face recognition methods are analyzed. Further summarize the advantages and disadvantages of each and elaborate them. At the end of the article, the shortcomings and future development trends of the current shielding face recognition research are summarized.

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Out of consideration for sustainable development, photovoltaic power generation system has become a hot research issue in the future energy strategy due to its significant cleanliness and reproducibility. Meanwhile, playing an important role in connecting the PV cell and the grid, the non-isolated photovoltaic inverter not only has the ability to convert energy with great efficiency but also with low loss and cost. In that case, the non-isolated inverter is widely used in the production. However, the leakage current is a big challenge that should be addressed with caution. This paper focuses on the leakage current mitigation strategy and makes a comprehensive analysis of each topology. The author analyses the generation mechanism of leakage current based on the single-phase inverter circuit. After that, the common ground type inverter topology and the H-Bridge type inverter topology will be further analysed for their universal utilization. Specific topologies from the two types of inverters are under comparison based on several perspectives, ranging from the degree of leakage current suppression to the complexity of the circuit structure, from the difficulty of analysis to the economic performance of the inverter. In addition, some improvement measures are proposed.

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With the advancement of modern science and technology, wireless communication technology has grown rapidly. A number of common standards for wireless data transmission have emerged, primarily for long-distance and short-range wireless communication. This paper compares several common wireless communication transmission technologies, including satellite communication, Bluetooth, WiFi, NFC, etc. Wireless communication technology has now entered the 5G stage. From the previous SMS to the current video conference, the transmission rate and transmission accuracy have been greatly improved. Wi-Fi facilities everywhere in the city, Bluetooth transmission, mobile phone NFC payment, etc. are convenient and improve people's lives. Wireless communication technology also has many applications, such as 5G technology, Internet of Things technology, and the development of artificial intelligence technology.

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Based on the existing literature and data, this paper starts from the principle of radio frequency identification technology, analyses the situation of the application field of RFID and predicts its development prospect. The results show that RFID technology is a kind of technology that uses the transmission characteristics of RF signals through space alternating electromagnetic coupling to identify targets and thus realize rapid automatic identification. Since it was developed and used in warfare in the mid-twentieth century, RF identification technology has developed rapidly and developed a variety of applications. Today, with the development of electronic technology and communication technology, RF identification technology already has a wide and irreplaceable role in medicine, military and food safety. It is not difficult to imagine that with more joint applications of new technology, radio frequency-related algorithm improvement, radio frequency tag price reduction, and other conditions, the technology will have a more extensive and profound application in the future.

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This paper discusses the method for artificial potential field in traditional sense. It is based on the algorithm with the planning of physics that guides a robot along a gradient toward a target endpoint by applying forces with gravitation and repulse within a robot environment. The article proposes to improve the potential field method by incorporating the A-star algorithm for the improvement of path planning in accuracy and efficiency. The A-star algorithm uses a cost function to measure the goodness of a node and finds the optimal path totally and thoroughly through heuristic search. The proposed method uses the A-star algorithm to generate the optimal path, which takes potential field and its method as basis, thus repeating the process until the robot reaches the end point. By combining the A-star algorithm and the method based on artificial potential field, the robot's driving route is made more reasonable, and thus testing and verifying how the method works through an experiment with simulation.

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In this era of information explosion, the improvement of communication capacity has become an urgent problem, and the improvement of transmission speed and the reduction of channel spacing are near the limit, so widening the available bandwidth of fiber optic transmission is the most feasible method. The research progress of fiber optic amplifiers is analyzed, and the outlook is presented. Researchers are working to find breakthroughs in C++ band, L++ band, and C+L band, starting with amplifier’s materials, structures, and designs. The EDFA targeted C++ and L++ band have been widely studying these years while different types of amplifiers have been invented to simultaneously work on C+L band. Also, as quantum dot is introduced to design innovated fiber amplifier, more new amplifiers need to be invented to achieve better amplification. This paper presents the recent research results of the above-mentioned research directions, and the next goal of researchers is to stabilize all these amplifiers’ gain flatness and production implement ability.

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Research on optical fiber amplifiers has gotten much more in-depth in recent years as a direct result of the emergence of the information age. The most effective of these materials are optical fibers that have been doped with rare earth elements. Lasers that have gain media composed of rare-earth doped optical fibers find widespread use in fields such as optical communication, medicine, and the processing of materials. For different rare earth ions, especially for bismuth-doped fiber amplifiers, bismuth-doped fiber has a good prospect in fiber amplifiers and lasers due to its unique luminescence characteristics and ultra-wideband near-infrared luminescence of bismuth. Therefore, for bismuth-doped fiber amplifiers, in this paper, the pump wavelength is designed for the signal wavelength range, energy level structure, and electron transition process. The corresponding rate equation and power equation are established. At the same time, the gain spectrum changes with the fiber length and doping concentration are calculated using Matlab programming, and the maximum and minimum gain differences are minimized using Matlab calculations.

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Optical fiber amplifier technology is to incorporate rare earth elements that can produce a laser into the fiber core, and the DC light excitation provided by the laser makes the amplification through the light signal. Neodymium-doped fiber laser was first developed and received much attention early on. Neodymium doped fibers had the highest pumping efficiency around 920 nm, 1060 nm and 1350 nm. The simulated annealing algorithm belongs to a stochastic optimization algorithm, which is mainly used to find the optimal global solution of the objective function. The author considers that this algorithm can be used to find the full capacity of the fiber amplifier, that is, a new method to find the full capacity, to develop new applications of this algorithm. In this paper, the fiber length and doped concentration were optimized to calculate the maximum power of the neodymium-doped fiber amplifier 1250-1350 nm by using the Matlab modeling and simulated annealing algorithm. The gain was most significant at a fiber length of 2.4 m and a doping concentration of 3.2*(10^25). The maximum profit is: 53.2182dB.

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In this research, the performance of thulium-doped fiber lasers is analyzed and a mathematical model is established. Thulium-doped fiber amplifiers are the focus of this article. A large number of simulations have been carried out in the MATLAB simulation environment, and the main work and innovation points are as follows: firstly, the energy level structure characteristics of thulium were studied, and its spectral characteristics were analyzed. After consulting some information, 3H4 to 3H6 energy level has been selected in modeling. Secondly, use the rate equations and the power propagation equations to provide a theoretical analysis of the pumping mode of thulium-doped fiber lasers. And a mathematical model of a thulium-doped fiber laser was established. The parameters such as fiber length and doping concentration in the model are discussed. Finally, to find the appropriate parameters, the genetic optimization algorithm is used to optimize the fiber length and doping concentration, and then we can get the parameters corresponding to the maximum output power of the thulium-doped fiber amplifier.

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Nowadays, with the development of the space technology and the maturity of traditional launch vehicle technology, there are sufficient foundations for the research of higher-level space vehicles. As space vehicles gradually enter the commercial market, the demand for better cost control and higher carry capacity has been put forward. The recovery and reuse of space vehicles, especially launch vehicle, often means higher resource utilization and effective cost control, which has unprecedented advantages in business mode. Many countries and organizations have shown concern about the reusable vehicles. In order to facilitate the further research of reusable rocket technology, this article summaries the research and developments of reusable vehicles over the years and sorts out the overall scheme and key technologies of it. In particular, in view of the successful case of Falcon 9, this article analyses the commercialization experience of SpaceX reusable rockets and its business model. This article may offer a reference for the reusable rocket technology development.

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