The quasi biennial oscillations ( QBOs) of the Sun-Earth environment are an important research topic in space weather science, and are of great significance for understanding the coupling processes between the solar atmosphere, the solar terrestrial space, and the terrestrial environment. The QBOs phenomenon possesses ubiquitous and extremely diverse observational features in time and space, but its exact physical generation mechanism is still not thoroughly clarified. QBOs exist in all levels of the solar atmosphere, and even in the convection zone. They develop independently in the northern and southern hemispheres. The solar QBOs propagate into interplanetary space through open magnetic flux transport. The strength of the radial heliospheric magnetic field is highly correlated with the total open magnetic flux. The time gap of weakened solar activity near the 11year cyclic maximum can be viewed as a constituent part of the QBOs. For the generation mechanism of QBOs, this paper reviews the latest theoretical generation mechanisms, and discusses the observational features that sup port / refute these theories. As a fundamental property of solar activity, the QBOs are not only important for studying the dynamic processes in the solar dynamo, but also have significant practical implications for space weather forecasting and warning.

Attention to healthy urban development has risen to a national strategic priority in recent years. Scientific assessment of the health index and spatial characteristics of cities is the basis for providing guidance for urban and rural planning and construction. At this stage, the theoretical development of urban health evaluation did not start long ago, and the existing research focuses on single dimension evaluation of urban health, but lacks comprehensive multi dimension integration judgment,and a unified systematic evaluation system has not yet been formed. In addition, existing studies have considered the health characteristics of cities as independent individuals and neglected the assessment of intercity health correlation, which is not conducive to the improvement of the health level of cities through the mutual learning effect. Therefore, this study attempts to optimize the comprehensive evaluation system of Chinas urban health development index from five dimensions, and takes the Pearl River Delta ( PRD) region as an example, combining a complex network approach to scientifically assess the health level and group characteristics of each spatial unit and its neighboring units. The study found that the first tier of the PRD with the highest healthy city index is Guangzhou and Shenzhen, the second tier is Dongguan, Foshan and Zhuhai, and the third tier is Zhongshan and the peripheral cities of Huizhou, Jiangmen and Zhaoqing, which are spatially heterogeneous in terms of different dimensions of their health indicators; meanwhile, the PRD spatial network of health can be classified into five major groups, namely, single type health, dual type health and mixed type health, which pro vides ideas for scientifically identifying the shortcomings of health development in each region and seeks to find more efficient and lower cost benchmarking and learning regions. This study aims to pro vide a systematic research framework for the evaluation of Chinas urban health index, and to provide a reference for the formulation of targeted policies for urban health development.

Since the inception of the “ Guangdong-Hong Kong-Macao” Greater Bay Area initiative, the concept of “ bay area” has attracted increasing attention from both academic circles and broader society. This paper argues that the regional cooperative structure of the “ Guangdong-Hong Kong-Macao” Greater Bay Area needs to be further clarified in the context of this region. While reviewing the regional synergy mechanisms of New York, San Francisco, Tokyo and the Sydney Bay Area, this pa per focuses on the regional synergy experience of the Greater Sydney Bay Area. On this basis, this pa per puts forward the idea of constructing the structure of the Guangdong-Hong Kong-Macao Greater Bay Area Management Committee with “ unified national leadership and multilevel participation” , trying to provide experience and new ideas for the planning, implementation and development of the “ Guangdong-Hong Kong-Macao” Greater Bay Area.

With the rapid development of Dongguan’s economy and urbanization, the land use pattern has significantly changed. To explore the spatial-temporal characteristics and driving factors of land use changes of Dongguan, this study analyzes land use structure, change range and transformation di rection of Dongguan over the past 20 years based on the current land use data in the years 2000, 2005, 2010, 2015 and 2020. Quantitative analysis with the geographic detector was also implemented to the driving factors of land use change in Dongguan. The results show that: ① During 2000 - 2020, the area of cultivated land and forest land in Dongguan decreased by 425 71 km2 and 225 9 km2 respectively; the construction land continued to expand with a total area increase of 680 20 km2 , mainly transferred from the cultivated land and forest land; in contrast, the area of grassland, water, and other land changed to less extent. ② The driving factors have had different influences on land use changes in Dongguan in these 20 years, but the distance from town centers, the distance from major roads, average annual precipitation, average annual temperature and elevation are the main factors; moreover, the interaction between all factors shows a dual factor enhancement which indicates that the interaction has intensified the land use changes in Dongguan.

Hyperspectral data of in situ measurement of water surface and spectral data of satellite im ages are both important data sources in water quality monitoring. There are differences between them in spectral resolution, and their correlation affects the accuracy of water quality retrieval to a certain extent. In order to explore the correlation between the two data sources, this paper takes the coastal waters of the Pearl River Estuary as the research area, and is based on the hyperspectral data of water from four rounds of synchronous measurements in 2020 and 2021 and Sentinel2 images. In addition, the relationships and differences between the image results of different atmospheric correction algorithms and the data of in situ measurements were compared from the perspectives of spectral morphology and reflectance. By comparing equivalent reflectance with Sen2cor and C2RCC ( Case2 Regional / Coast color) atmospheric correction algorithms, the following conclusions are drawn: Sen2cor algorithm performs better in turbid water, and the spectral morphology of the image accords with the in situ spectrum better. The performance of C2RCC algorithm is better in general water or non turbidite water, and the absolute reflectance on the image is closer to the reflectance of in situ measurement.

This study uses remote sensing data to calculate enhanced nighttime light urban index( ENUI) and remote sensing ecological index ( RSEI) . Secondly, the coupling coordination degree( CCD) between ENUI and RSEI is analyzed by using the coupling coordination degree model( CCDM) , expecting to provide reference for the sustainable development of urban agglomeration. The results show that: ① The ENUI of the five major urban agglomerations generally shows an upward trend. The ENUI of the Pearl River Delta is the highest and has the fastest growth rate, followed by the Yangtze River Delta urban agglomerations; ②The RSEI values of the five major urban agglomerations are distributed in the range of 0.4 ~ 0. 8, and the RSEI values of the three major urban agglomerations of Beijing Tianjin Hebei, Yangtze River Delta and Pearl River Delta rise first and then fall; However, the middle reaches of the Yangtze River and the Chengdu Chongqing urban agglomeration are a continuously rising process; ③The overall coordination index fluctuates between 0 and 0 2, and both keep an upward trend. The coordination degree of urban agglomerations in Yangtze River Delta and Pearl River Delta is higher than that of the other three urban agglomerations, and there are significant differences in coordination between urban agglomerations.

This paper proposes an offset-free model predictive control ( MPC) algorithm for constrained nonlinear systems, by utilizing an artificial disturbance to replace the modeling error. The algorithm is based on a new expanded system structure and the dual part control law consisting of the linear stabilizing control and the dynamic predictive control. Compared with previous techniques, there is no need for calculating the steady state input, state targets and using an observer for augmented states. Other characteristics of this algorithm include controllable expanded system model and handling model mismatch. By consideration of the state and input constraints, design of the MPC controller not only achieves the aim of offset free control but also guarantees the constraint satisfaction in the presence of disturbance and model mismatch. The particular characteristics of the pro posed algorithm are illustrated via a simulation using a continuous nonlinear jacketed stirred tank reactor( CSTR) model.

In order to improve the hydrogen permeation resistance of stainless steel under high temperature and high pressure in nuclear reactors, composite ceramic coatings of different αAl2 O3 , La2 O3 , and SiO2 metal oxides were prepared on the surface of stainless steel using the slurry method and high-temperature melting method. The surface morphology, phase structure, and surface composition of oxide ceramic coatings were characterized by scanning electron microscopy ( SEM) , X-ray diffraction( XRD) , and energy dispersive X-ray spectroscopy ( EDS) . The hydrogen permeation performance of the coatings was tested using a gas driven permeation device. The results indicate that the coating preparation process in this work is simple and can be applied to the surfaces of complex structural components. The coating has high uniformity and density. With increasing temperature, the hydrogen permeation resistance of the coatings to deuterium kept constant. At 650 ℃ , the permeation resistance factor ( PRF) for coatings with an oxide content of 20% was around 295, while coatings with an oxide content of 15% achieved a PRF of approximately 512, demonstrating optimal hydrogen permeation resistance.

Particle Swarm Optimizer ( PSO) has the problems of long running time and easy to fall in to local optimality when dealing with the optimization of large data. In this paper, based on the traditional particle swarm optimization algorithm, the feature selection method based on factor space is used to optimize the combination of feature data and reduce the running time of the algorithm. The fuzzy multi-population particle swarm optimization algorithm based on factor space is proposed by combining the idea of multi-population particle swarm optimization model with the idea of fuzzy mathematics, which enhances the global optimization ability of the algorithm and speeds up the convergence rate, thus achieving the overall optimization of the algorithm. The traditional particle swarm optimization algorithm is easy to converge to the local optimal defect. The results show that compared with the traditional particle swarm optimization algorithm, dynamic multi-population particle swarm optimization algorithm and multi-population particle swarm optimization algorithm based on density peak, the fuzzy multi-population particle swarm optimization algorithm based on factor space proposed in this pa per has a better ability to find the global optimal solution and convergence speed.

The paper deals with the existence of solutions for a class of Volterra integral-differential equations. By using the fixed point method in Banach space, two theorems were obtained to give sufficient conditions for the existence of uncountable bounded positive solutions of the equation. The conclusions generalize these results. Finally, an example is given to illustrate the application of the theorems.

This paper studies transitive compactness and its relationships with other forms of transitivity for dynamical systems with semigroup actions. Main results are as follows: ① if ( S, X) is weakly mixing where S is an Abelian semigroup, then ( S, X) is transitively compact; ② if ( S, X) is elastic, then ( S, X) is completely transitive; ③ we prove that n-transitivity ( n≥2) , weakly mixing and elastic are equivalent mutually when S is an Abelian semigroup.

In order to avoid rear end accidents of cars, an anti-rear-end control method based on the longitudinal dynamics model of cars is designed. Firstly, by analyzing the braking process of a vehicle, a mathematical model of safety distance is established to obtain a dynamic warning distance and danger distance. Secondly, in order to maintain a safe distance for vehicles, an overall model of the system is established based on vehicle longitudinal dynamics. Using Lyapunov stability theory, combined with dynamic warning distance and danger distance, a control method is designed using the Backstepping method to make the system gradually stable. Finally, through simulation, the following conclusions were drawn: The designed control method can enable the vehicle to better track the expected speed and expected displacement, and the relative distance between the vehicle and the vehicle in front is always greater than the dangerous distance during braking, ensuring the safety of the two vehicles, and achieving the design goal of vehicle rear-end collision prevention.