Recent Developments in Recommender Systems: A Survey

In this technical survey, we comprehensively summarize the latest advancements in the field of recommender systems. The objective of this study is to provide an overview of the current state-of-the-art in the field and highlight the latest trends in the development of recommender systems. The study starts with a comprehensive summary of the main taxonomy of recommender systems, including personalized and group recommender systems, and then delves into the category of knowledge-based recommender systems. In addition, the survey analyzes the robustness, data bias, and fairness issues in recommender systems, summarizing the evaluation metrics used to assess the performance of these systems. Finally, the study provides insights into the latest trends in the development of recommender systems and highlights the new directions for future research in the field

Lattice piecewise affine approximation of explicit nonlinear model predictive control with application to trajectory tracking of mobile robot

To promote the widespread use of mobile robots in diverse fields, the performance of trajectory tracking must be ensured. To address the constraints and nonlinear features associated with mobile robot systems, we apply nonlinear model predictive control (MPC) to realize the trajectory tracking of mobile robots. Specifically, to alleviate the online computational complexity of nonlinear MPC, this paper devises a lattice piecewise affine (PWA) approximation method that can approximate both the nonlinear system and control law of explicit nonlinear MPC. The kinematic model of the mobile robot is successively linearized along the trajectory to obtain a linear time-varying description of the system, which is then expressed using a lattice PWA model. Subsequently, the nonlinear MPC problem can be transformed into a series of linear MPC problems. Furthermore, to reduce the complexity of online calculation of multiple linear MPC problems, we approximate the optimal solution of the linear MPC by using the lattice PWA model. That is, for different sampling states, the optimal control inputs are obtained, and lattice PWA approximations are constructed for the state control pairs. Simulations are performed to evaluate the performance of our method in comparison with the linear MPC and explicit linear MPC frameworks. The results show that compared with the explicit linear MPC, our method has a higher online computing speed and can decrease the offline computing time without significantly increasing the tracking error

Experimental Investigation and Exergy Analysis of Dehumidification Performances for a Cascaded Phase Change Heat Storage Dehumidifier

In the humidification and dehumidification solar desalination system, the recovery of vapor condensation latent heat is the key problem. Using a cascaded phase change heat storage method to recover vapor condensation latent heat can improve the phase change heat storage rate and the water production performance of dehumidifier. The exergy analysis and experimental methods are used to study the cascaded phase change storage dehumidifier. The results show that the more stages of phase change materials in the cascaded phase change heat storage device, the greater the exergy efficiency will be. The heat transfer performance of phase change materials increases with the increase of hot and wet air temperature and flow at the inlet of the dehumidifier. The exergy efficiency and gain output ratio of three-stage phase change heat storage are higher than that of the single-stage. The three-stage one is recommended. If the heat recovered by the cascaded phase change heat storage device is supplied to the passive humidification dehumidification desalinator for secondary water output, the water output and gain output ratio will increase by 25% and the water production cost will be reduced by 20%. The results can provide a basis for the design and application of a cascaded phase change heat storage dehumidifier

Study on Heat Transfer Process and Fresh Water Output Performance of Phase Change Heat Storage Dehumidifier

In the humidification-dehumidification solar desalination process, using phase change materials to recover water vapor condensation latent heat in the dehumidification can improve heat utilization and water production performances. When sodium thiosulfate pentahydrate and paraffin were used as phase change materials respectively in the phase change heat storage dehumidifier, by means of numerical simulation and experiment, the heat transfer process, entropy generation, and water production performances of heat pipes and copper wire meshes coupled phase change materials in the dehumidifier were studied. The results showed that sodium thiosulfate pentahydrate has stronger heat transfer ability, higher thermal entropy generation, and heat storage capacity than paraffin; adding copper wire meshes into the phase change material can accelerate heat transfer and shorten the time required for monitoring points to reach phase change temperature; increasing the wet air temperature at inlet of phase change heat storage dehumidifier, using copper wire meshes in the phase change material, increasing the diameter of copper wire mesh, and using a passive basin desalinator for secondary water production can improve water production performances. In brief, the use of sodium thiosulfate pentahydrate and copper wire meshes in the phase change heat storage dehumidifier leads to better heat storage and heat transfer effects

Experimental Investigation and Exergy Analysis of Dehumidification Performances for a Cascaded Phase Change Heat Storage Dehumidifier

In the humidification and dehumidification solar desalination system, the recovery of vapor condensation latent heat is the key problem. Using a cascaded phase change heat storage method to recover vapor condensation latent heat can improve the phase change heat storage rate and the water production performance of dehumidifier. The exergy analysis and experimental methods are used to study the cascaded phase change storage dehumidifier. The results show that the more stages of phase change materials in the cascaded phase change heat storage device, the greater the exergy efficiency will be. The heat transfer performance of phase change materials increases with the increase of hot and wet air temperature and flow at the inlet of the dehumidifier. The exergy efficiency and gain output ratio of three-stage phase change heat storage are higher than that of the single-stage. The three-stage one is recommended. If the heat recovered by the cascaded phase change heat storage device is supplied to the passive humidification dehumidification desalinator for secondary water output, the water output and gain output ratio will increase by 25% and the water production cost will be reduced by 20%. The results can provide a basis for the design and application of a cascaded phase change heat storage dehumidifier

Optimal frequency control for wind power-integrated power system based on parameter identification

Frequency control based on wind power is required by the grid code for maintaining system inertia level as well as frequency stability. However, synchronous generator (SG)-emulated frequency control of wind power will result in a nadir and second dip of frequency trajectory after a disturbance, which may threaten system safety. Optimizing the frequency trajectory of system to improve the nadir and avoid second dip usually relies on grid-wide information. But the information is hardly perfectly acquired in advance for real power system since it may change anytime. To address these problems, an optimal frequency control method for wind power-integrated power system based on parameter identification is proposed. Frequency characteristics of wind power-integrated are firstly analyzed based on the common frequency theory. Then the control framework of proposed method to eliminate the nadir and second dip of frequency trajectory is introduced. To realize this framework, system equivalent parameters like inertia and damp coefficient are identified by the extended Kalman smoother algorithm after each disturbance. These parameters are furtherly utilized to shape the transfer function of wind power-integrated power system as a first-order system. Finally, the implementation steps of proposed method are presented. The effectiveness of proposed method is verified by case studies

Zhou Yi : 10 juan 周易 : 十卷

Blockprint, Double leaves, oriental style, in cas

Simultaneously improved strength and ductility in aluminum matrix composite with heterogeneous structures under impact loadings

Heterostructured composites with the coexistence of hard and soft phases can achieve a superior strength-ductility synergy. However, the deformation and fracture mechanisms of these composites under impact loading has not been comprehensively understood. In this work, an in-situ TiB2/2024 Al composite was adopted to investigate the role of heterogeneous structures on the tensile mechanical responses at different strain rates and temperatures. Surprisingly, a simultaneously enhancement of strength and ductility was found in the composite under impact loading. To explore the underlying mechanisms responsible for the observed mechanical behavior, microstructural analyses were performed on the samples before and after deformation. Results reveal that the composite has obvious heterogeneous structure consist of particle-rich regions (regard as hard phase) and particle-lean regions (soft phase). The interaction between the two phases can affect the strain hardening behavior of the composites at different plastic deformation stages. Compared with the strain rate insensitive matrix, the particle-induced constraint makes the flow stress of the composite increases substantially with an increase in strain rate. Meanwhile, the tortuous crack propagation paths induced by the cooperation of hard and soft phases contribute to the improved ductility at high strain rates