Jingxuan Chai, Jie Mei, Youmin Gong, Weiren Wu, Guangfu Ma and Guoming Zhao
Asteroids have the characteristics of noncooperative, irregular gravity and complex terrain on the surface, which cause difficulties in successful landing for conventional…
Abstract
Purpose
Asteroids have the characteristics of noncooperative, irregular gravity and complex terrain on the surface, which cause difficulties in successful landing for conventional landers. The purpose of this paper is to study the trajectory tracking problem of a multi-node flexible lander with unknown flexible coefficient and space disturbance.
Design/methodology/approach
To facilitate the stability analysis, this paper constructs a simplified dynamic model of the multi-node flexible lander. By introducing the nonlinear transformation, a concurrent learning-based adaptive trajectory tracking guidance law is designed to ensure tracking performance, which uses both real-time information and historical data to estimate the parameters without persistent excitation (PE) conditions. A data selection algorithm is developed to enhance the richness of historical data, which can improve the convergence rate of the parameter estimation and the guidance performance.
Findings
Finally, Lyapunov stability theory is used to prove that the unknown parameters can converge to their actual value and, meanwhile, the closed-loop system is stable. The effectiveness of the proposed algorithm is further verified through simulations.
Originality/value
This paper provides a new design idea for future asteroid landers, and a trajectory tracking controller based on concurrent learning and preset performance is first proposed.
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Qinglei Hu and Guangfu Ma
To provide an approach to vibration reduction of flexible spacecraft which operates in the presence of various disturbances, model uncertainty and control input non‐linearities…
Abstract
Purpose
To provide an approach to vibration reduction of flexible spacecraft which operates in the presence of various disturbances, model uncertainty and control input non‐linearities during attitude control for spacecraft designers, which can help them analyze and design the attitude control system.
Design/methodology/approach
The new approach integrates the technique of active vibration suppression and the method of variable structure control. The design process is twofold: first design of the active vibration controller by using piezoelectric materials to add damping to the structures in certain critical modes in the inner feedback loop, and then a second feedback loop designed using the variable structure output feedback control (VSOFC) to slew the spacecraft and satisfy the pointing requirements.
Findings
Numerical simulations for the flexible spacecraft show that the precise attitude control and vibration suppression can be accomplished using the derived vibration attenuator and attitude control controller.
Research limitations/implications
Studies on how to control the flywheel (motor) under the action of the friction are left for future work.
Practical implications
An effective method is proposed for the spacecraft engineers planning to design attitude control system for actively suppressing the vibration and at the same time quickly and precisely responding to the attitude control command.
Originality/value
This paper fulfills a useful source of theoretical analysis for the attitude control system design and offers practical help for the spacecraft designers.
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Yueyong Lv, Qinglei Hu, Guangfu Ma and Jian Zhang
The purpose of this paper is to propose a decentralized output feedback controller for cooperative attitude regulation of spacecraft formation in absence of angular velocity…
Abstract
Purpose
The purpose of this paper is to propose a decentralized output feedback controller for cooperative attitude regulation of spacecraft formation in absence of angular velocity feedback.
Design/methodology/approach
The nonlinear relative attitude dynamic and kinematic equations represented by relative quaternion and relative angular velocity, respectively, are considered in this paper. The lead filter is employed to synthesize virtual angular velocity signal so that the design of output feedback controller is achieved. Lyapunov method is adopted to prove the stability of closed‐loop system. Considering the external disturbance, the theory of L2‐gain disturbance attenuation is employed to improve the designed controller. Numerical simulations are carried out to verify the controllers proposed.
Findings
It is found that the closed‐loop system can be guaranteed asymptotically stable in absence of external disturbance. When disturbance is considered, as long as the sufficient condition proposed is satisfied, the improved controller can render system uniformly ultimately bounded stable.
Practical implications
The proposed output feedback control scheme can be considered as a fall‐back alternative for the case that the angular velocity sensors fail, or seen as another option for the system without angular velocity sensors at all.
Originality/value
Unlike most classical works in the field of output feedback which focus on centralized scheme and neglect the disturbance, the controller proposed in this paper is able to handle the output feedback control problem of multi‐agent formation in a decentralized fashion, so as to avoid the single failure point of a centralized scheme. Meanwhile, the capability of L2‐gain disturbance attenuation is also achieved simultaneously.
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Jiale Zhang and Farzana Quoquab
Although the metaverse has gained popularity in recent days, research on metaverse tourism in urban destinations is still lacking. Drawing on existing cases in Chinese urban…
Abstract
Purpose
Although the metaverse has gained popularity in recent days, research on metaverse tourism in urban destinations is still lacking. Drawing on existing cases in Chinese urban destinations, this paper aims to provide valuable insights into the development of metaverse tourism in China and provides managerial implications for future urbanmetaverse tourismplayers.
Design/methodology/approach
Literature from Chinese and international sources was reviewed to highlight the current status of metaverse tourism in the context of Chinese urban tourism. This paper also draws on information provided by online materials, especially the official websites of tour organizers and news media.
Findings
This paper outlines important aspects of metaverse in Chinese urban tourism. First, cities are the hotbeds of metaverse development, and the metaverse has become a new way to attract urban tourists and a significant element in various exhibitions. Second, the combination of metaverse with China’s extensive and profound traditional culture has made urban tourism full of vitality. Third, China’s game companies are progressively empowering the metaverse tourism industry.
Originality/value
This paper contributes to the existing knowledge on metaverse tourism based on the Chinese urban tourism context. Furthermore, it highlights the state of the metaverse in Chinese urban tourism during and after the pandemic situation. Lastly, it provides thoughtful implications for tourism players and future tourism development.
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Lei Guo, Lien Zhu, Lei Ma, Jian Zhang, QiuYu Meng, Zheng Jin, Meihua Liu and Kai Zhao
The purpose of this paper is to prepare a spherical modifier-modified activated carbon fiber of high specific capacitance intended for electrode materials of supercapacitor.
Abstract
Purpose
The purpose of this paper is to prepare a spherical modifier-modified activated carbon fiber of high specific capacitance intended for electrode materials of supercapacitor.
Design/methodology/approach
In this study, phenolic-based microspheres are taken as modifiers to prepare PAN-based fiber composites by electrospinning, pre-oxidation and carbonization. Pearl-chain structures appear in RFC/ACF composites, and pure polyacrylonitrile fibers show a dense network. The shape and cross-linking degree are large. After the addition of the phenolic-based microspheres, the composite material exhibits a layered pearlite chain structure with a large porosity, and the RFC/ACF composite material is derived because of the existence of a large number of bead chain structures in the composite material. The density increases, the volume declines and the mass after being assembled into a supercapacitor as a positive electrode material decreases. The specific surface area of RFC/ACF composites is increased as compared to pure fibers. The increase in specific surface area could facilitate the diffusion of electrolyte ions in the material. Owing to the large number of bead chains, plenty of pore channels are provided for the diffusion of electrolyte ions, which is conducive to enhancing the electrochemical performance of the composite and improving the RFC/ACF composite and the specific capacitance of the material. The methods of electrochemical testing on symmetric supercapacitors (as positive electrodes) are three-electrode cyclic voltammetry, alternating current impedance and cycle stability.
Findings
The specific capacitance value of the composite material was found to be 389.2 F/g, and the specific capacitance of the electrode operating at a higher current density of 20 mA/cm2 was 11.87 F/g (the amount of the microsphere modifier added was 0.3 g). Using this material as a positive electrode to assemble into asymmetrical supercapacitor, after 2,000 cycles, the specific capacitance retention rate was 87.46 per cent, indicating excellent cycle stability performance. This result can be attributed to the fact that the modifier embedded in the fiber changes the porosity between the fibers, while improving the utilization of the carbon fibers and making it easier for electrolyte ions to enter the interior of the composites, thereby increasing the capacitance of the composites.
Originality/value
The modified PAN-based activated carbon fibers in the study had high specific surface area and significantly high specific capacitance, which makes it applicable as an efficient and environment-friendly absorbent, as well as an advanced electrode material for supercapacitor.
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This study aims to explore the following questions: What are resources for humans and what are not? How does nature “become” a resource? Does the result of cultural resources'…
Abstract
Purpose
This study aims to explore the following questions: What are resources for humans and what are not? How does nature “become” a resource? Does the result of cultural resources' re‐identification and utilization benefit cultural conservation?
Design/methodology/approach
The main methods used were participant observation (from 2005 to 2007) and in‐depth interviews. In‐depth interviews included local elites, wetland farmers, and local tourism business owners.
Findings
The process of culture becoming resources includes three stages: resource identification, meaning‐giving, and social reduction. The achievement of each stage is a result of the interactions of local powers. When the aims of the identification and utilization of cultural resources excessively combine with some interests of capitalism, there is often a conflict between preservation and development.
Practical implications
The results of the analysis suggest that, if this program could acquire local consensus and local participation, it could really benefit cultural resource conservation.
Originality/value
This study proposes the “indigenous concept of resource” as a critical viewpoint on the current concept of resource.
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Dayong Zhang, Xiaohui Liu, Xuefeng Bai, Gang Wang, Liping Rong, Ying Zhao, Xin Li, Jinhua Zhu and Changhong Mi
The purpose of this study is to investigate the heat resistance and heat-resistant oxygen aging of 4-nitrophthalonitrile-etherified cardanol-phenol-formaldehyde (PPCF) to further…
Abstract
Purpose
The purpose of this study is to investigate the heat resistance and heat-resistant oxygen aging of 4-nitrophthalonitrile-etherified cardanol-phenol-formaldehyde (PPCF) to further use and develop the resin as the matrix resin of high-temperature resistant adhesives and coatings.
Design/methodology/approach
PPCF resin was synthesized by 4-nitrophthalonitrile and cardanol-phenol-formaldehyde (PCF). The structures of PPCF and PCF were investigated by Fourier transform infrared, differential scanning calorimetry and proton nuclear magnetic resonance. In addition, the heat resistance and processability of PPCF and PCF resins were studied by dynamic mechanical analysis, thermogravimetric analysis, scanning electronic microscopy (SEM), X-ray diffraction (XRD) techniques and rheological studies.
Findings
The results reveal that PPCF forms a cross-linked network at a lower temperature. PPCF resin has excellent resistance under thermal aging in an air atmosphere and that it still had a certain residual weight after aging at 500°C for 2 h, whereas the PCF resin is completely decomposed.
Originality/value
4-Nitrophthalonitrile was introduced into PCF resin, and XRD and SEM were used to investigate the high temperature residual carbon rate and heat-resistant oxygen aging properties of PPCF and PCF resins.
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In recent years, a great deal of work has emerged on eco-cities in China. Specifically, writers have discussed the role of the entrepreneurial state in the construction of…
Abstract
In recent years, a great deal of work has emerged on eco-cities in China. Specifically, writers have discussed the role of the entrepreneurial state in the construction of eco-cities and have noted the role of these cities in the production of high-end real estate and new forms of capital accumulation and land acquisition. Whilst this chapter supports these arguments, we argue that the emergence of eco-cities in China is tied up with broader socioeconomic and cultural discourses and discourses of governance. We explore these ideas through a qualitative investigation of an eco-city known as the North Lake (Beihu) Ecological New Town (NLENT) located in the city of Jining, Shandong province. Specifically, this project, which involved the collection of documents, photographs and 20 semi-structured interviews, aims to understand the role that discourses of class, taste and consumption play in the fashioning of Chinese eco-cities. In exploring discourses of ‘green conduct’, this chapter also seeks to understand the role of eco-cities in the governmental fashioning of Chinese subjects and bodies. In this regard, this chapter suggests that whilst new forms of green development have played a part in urban expansion, new green real estate zones such as the NLENT have a powerful role to play in the construction and shaping of Chinese identity and behaviour.
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Zhou Yang, Minghe Chi, Xiaorui Zhang, Jiahao Shi, Xue Sun, Xiaoman Zhang and Qingguo Chen
Epoxy resin (EP) is a thermosetting resin commonly characterized by its inherent brittleness, which limits its widespread application. To overcome this limitation, a novel…
Abstract
Purpose
Epoxy resin (EP) is a thermosetting resin commonly characterized by its inherent brittleness, which limits its widespread application. To overcome this limitation, a novel flexible chain-blocking hyperbranched polyester (HBP) was conceptualized and synthesized to enhance the toughness and dielectric properties of EP.
Design/methodology/approach
Using P-toluene sulfonic acid (p-TSA) as the catalyst and Bis(hydroxymethyl)propionic acid (DMPA) as the branching unit with pentaerythritol (PER) as the core, an experimental synthesis was conducted. Subsequently, n-hexanoic acid was introduced separately to produce hyperbranched polyester with n-hexanoic acid capped structures. Microstructural, mechanical, insulating and dielectric analyses of the composite were performed to determine the optimal proportion of HBP.
Findings
Recent research has demonstrated that the flexible segments within hyperbranched polyester create an interpenetrating network structure with the molecular chains of epoxy resin, thereby effectively augmenting the toughness of the epoxy resin. Additionally, HBP has reduced the ε and tgδ values of the epoxy-anhydride cured product by decreasing the number of polar groups per unit volume of EP through the introduction of free volumes.
Originality/value
Currently, HBP serves as an innovative toughening strategy and modifier for epoxy resin. The toughening mechanism involves the generation of free volume by HBP, providing space for EP molecules to maneuver under load. Additionally, the free volume contributes to a reduction in the dielectric constant of EP by diminishing the polarizable group content. Simultaneously, the incorporation of HBP features flexible chains grafted onto the epoxy resin.
Details
Keywords
Jiahao Shi, Ling Weng, Xiaoming Wang, Xue Sun, Shuqiang Du, Feng Gao and Xiaorui Zhang
Epoxy resin (EP) is a kind of thermosetting resin, and its application is usually limited by poor toughness. In this case, a type of new flexible chain blocking hyperbranched…
Abstract
Purpose
Epoxy resin (EP) is a kind of thermosetting resin, and its application is usually limited by poor toughness. In this case, a type of new flexible chain blocking hyperbranched polyester (HBP) was designed and synthesized. The purpose of this study is to enhance the toughness and dielectric properties of EP.
Design/methodology/approach
P-toluene sulfonic acid was used as the catalyst, with dimethy propionic acid as the branch unit and pentaerythritol as the core in the experiment. Then, n-hexanoic acid and n-caprylic acid were, respectively, put to gain HBP with a n-hexanoic acid and n-caprylic acid capped structure. The microstructure, mechanical properties, insulation properties and dielectric properties of the composite were characterized for the purpose of finding the appropriate proportion of HBP.
Findings
HBP enhanced the toughness of epoxy-cured products by interpenetrating polymer network structure between the flexible chain of HBP and the EP molecular chain. Meanwhile, HBP reduced the ε and tgδ of the epoxy anhydride-cured product by reducing the number of polar groups per unit volume of the EP through free volumes.
Research limitations/implications
Yet EP is a kind of thermosetting resin, which is widely used in coating, aerospace, electronics, polymer composites and military fields, but it is usually limited by poor toughness. In a word, it is an urgent priority to develop new EP with better toughness and mechanical properties.
Originality/value
At present, HBP has been applied as a new kind of toughening strategy and as a modifier for EP. According to the toughening mechanism of HBP modified EP, the free volume of HBP creates a space for the EP molecule to move around when loaded. Moreover, the free volume could cause the dielectric constant of EP to diminish by reducing the content of polarizable groups. Meanwhile, the addition of HBP with flexible chains grafted to the EP could develop an interpenetrating network structure, thus further enhancing the toughness of EP