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Rapid advancements in Internet of Things (IoT) technology have promoted numerous novel applications that are sensitive to information timeliness. With different applications coexisting in one wireless network, each of which has heterogeneous traffic characteristics, it is of paramount importance while challenging to address how to characterize and optimize the information freshness performance network-wide, particularly in the massive access scenario. This paper casts attention on the heterogeneous slotted Aloha network and uses the Peak Age of Information (PAoI) metric to quantify information freshness. By assuming that the sensors in each group are equipped with unit-sized buffers and Bernoulli packet arrival, we derive the network steady-state point and PAoI. Depending on whether one group or all groups are age-sensitive, we focus on single-group PAoI and global PAoI optimization respectively. When only one single group is age-sensitive, we derive its optimal transmission probability. When all groups are age-sensitive, we propose a heuristic algorithm based on the particle swarm optimization method, where the bi-stability of Aloha network is considered for avoiding the risk of rapid performance deterioration. Extensive simulation results are presented to verify our analysis and the effectiveness of the proposed algorithm.

With the increasing demand for DC transmission from new energy sources and the increasing DC load, the original AC distribution network system cannot meet the demand for power transmission, and AC-DC distribution network has become one of the development directions of future distribution network. When photovoltaic system is connected to AC/DC distribution system, unplanned island operation may occur on both AC and DC sides of the system. When unplanned islanding occurs in the system, maintenance personnel and system equipment fail to detect islanding in time and operate normally, which may pose a great threat to the safety of equipment and personnel. Therefore, it is necessary to accurately identify the operating state of the system, and then provide accurate judgment information for the action of the micro-switch to operate the photovoltaic system with islanding phenomenon through the micro-switch integrated with islanding detection algorithm, so as to ensure the safety and stability of the distribution system and load. In order to identify the running state of the system reliably, this paper analyzes the changes of the system electrical quantity before and after the islanding, and based on this, puts forward an islanding detection method. First of all, this paper uses a variety of data preprocessing techniques to clean and extract the features of the original data, and selects six island characteristic indicators such as voltage, current and output active power as detection features to generate a feature vector set to improve the quality and accuracy of the data. Secondly, this paper adopts three classification algorithms, including KNN, random forest and XGBoost, to integrate and learn the model, so as to improve the accuracy and robustness of the islanding detection task. Finally, it is verified by experiments that the islanding detection method based on multi-classification fusion model proposed in this paper has high fault detection accuracy and robustness, and has a wide application prospect and popularization value in practical application, which can provide performance improvement and stability guarantee for micro-cluster switches.

[Objective] Cracking in the concrete of urban rail transit project underground station side-walls can pose a threat to the structural safety of metro stations. It is essential to analyze the causes of cracking in the concrete of USSW (underground station side-walls) and propose key technologies for controlling it. [Method] Low hydration rate and slightly expansive concrete is prepared by reducing cement usage and adding highly effective anti-cracking agents. Its impacts on structural mechanical properties, thermal insulation temperature rise, and volume deformation are compared before and after the composition optimization, which verifies the improvement of USSW concrete composition crack-resistance performance after optimization. Based on this, a finite element model simulation analysis is carried out on USSW concrete structures, and the influence of different wall thicknesses and segment lengths on crack-resistance safety factor is calculated. Thus, under the premises of satisfying crack-resistance safety factor, the optimal lengths of USSW segmented concrete-pouring for different seasons are determined. Finally, the temperature change law of typical segments in the experimental section of the underground station is monitored to propose temperature control indicators for side-wall concrete. [Result & Conclusion] The contraction of USSW concrete and the constraints on it are the main causes of cracking in USSW concrete. Key crack control measures include introducing highly effective anti-cracking agents to enhance concrete crack-resistance performance, optimizing the USSW segmented concrete-pouring lengths for different seasons to reduce concrete constraints, and strictly controlling concrete temperature indicators. Implementing these key crack control measures significantly reduce the number of cracks in the concrete of USSW.

Cultural differences in sport have been studied according to the perspective of “culture of inter-normative differences”. Taking the promotion of traditional sports in tourism as an example, the aim is to strengthen the protection and development of athletes who do not know the culture and arts, and to provide theoretical advice to support the development of sports. It was found that the symbols of cultural spaces, sports and tourism products of ethno-cultural combination appeared in four areas: space-temporality, presence, openness and drama. National cultural and artistic leadership and tourism cooperation together are making a difference in the development of the “cultural zone”. Creating a cultural landscape that integrates national culture, sports culture, and tourism services in a unified and symbiotic way will promote the transition from the formation of social leadership trends to individual leadership knowledge and beliefs, and finally to the realization of social development. national sports culture. Those. The combination of national cultural sports and tourism products, and the construction of the epidemic cultural landscape is a process of digging up the traditional culture of a nation to the public and creating tourism products that tourists can use and experience. In this case, it is planned to create a cultural zone for the integration and symbiosis of ethnic culture, sports and tourism services.

The national and regional basketball professional league is a complex system that multiple organizations and industries influence. Its development is restricted and influenced by many factors. The basketball profession in ethnic areas is studied. The goal is to explore the correlation between each factor and its strength using PESTEL analysis and statistics. It is found that the potential and core strength of reserve talents, first-line players, coaches, and other talents are important conditions for their development at the micro level. The management system, business operation, and the professionalization of referees in the league are major factors affecting the league’s development. At the larger level, politics, economics, and culture are secondary factors. There are some obvious problems with sports development in the minority areas of China.

To extend the service life of 316L stainless steel components in harsh environments, this study utilized laser cladding technology to enhance the hardness, wear resistance, and corrosion resistance of the 316L stainless steel surface. Nickel-based and cobalt-based cladding layers were prepared on the surface of the 316L stainless steel, and the microstructure and phases of the layers were analyzed using scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. In addition, the hardness of the substrate and the cladding layers was tested with a microhardness tester, the frictional wear performance was tested with a pin on disc wear tester, and the corrosion resistance was tested with an electrochemical workstation. The experimental results indicate that the nickel-based cladding layer primarily comprises the γ-(Fe, Ni), Cr7C3, and Ni3Si phases, with equiaxed and dendritic grains being the predominant morphologies. By contrast, the cobalt-based cladding layer mainly comprises the γ-Co, Cr7C3, and Co7W6 phases, with columnar and dendritic grains being the predominant morphologies. Both cladding layers displayed a significantly better microhardness, wear resistance, and corrosion resistance than the substrate. Between the two cladding layers, the nickel-based cladding layer demonstrated a superior microhardness, whereas the cobalt-based cladding layer slightly outperformed in wear resistance and corrosion resistance. The findings from our results are important for understanding the performance of laser-cladding layers and laying a scientific basis for the promotion and optimization of laser cladding technology in industrial applications. Moreover, our results showed that laser cladding technology is increasingly important in extending the service life of components and improving the material performance.

Low power wide area network (LPWAN) technologies have become an integral part of Internet-of-Things (IoT) applications due to their ability to meet key requirements such as long range, low cost, massive device numbers, and low energy consumption. Among all available LPWAN technologies, LoRaWAN has garnered significant interest from both industry and academia. Due to wide communication range of LoRaWAN, the coverage of gateway (GW) may overlap and the packet transmissions from nodes in the overlapping area would collide, which deteriorates the network performance. How to tune the backoff parameter settings to reduce collision and maximize the network throughput in multi-GW LoRaWAN is still an open issue. To solve this issue, in this paper, we first propose a low-complexity model for multi-GW LoRaWAN, which divides nodes into different groups based on GWs they can communicate with. Key performance metrics, i.e., the network throughput, access delay and the probability of successful transmission, are derived as functions of backoff parameter and input rate. As the throughput performance crucially depends on whether each group is saturated or not, we propose an iterative algorithm to analyze the stability of the multi-GW LoRaWAN, based on which we further develop an iterative algorithm to tune the backoff parameter of each group iteratively for the network throughput optimization. The simulation results validate the effectiveness of the proposed algorithms and reveal the trade-off between fairness and efficiency.

To optimize the support for massive machine type communication (mMTC) services with different traffic characteristics, packet-based random access (PBRA) scheme coexists with the connection-based random access (CBRA) scheme in 5G networks.Yet, given the traffic characteristic of mMTC, which random access scheme should be chosen is still an open issue.To address this issue, the network throughput and signaling overhead analysis of mMTC with PBRA and CBRA were presented, and the problem of throughput maximization while maintaining the signaling-to-throughput ratio below a certain level was solved.Based on this, the optimal access scheme selection strategy and the corresponding optimal network parameter configuration were obtained and verified via simulations.

Shortening the packet length has been a consensus in wireless network design for supporting the ultra-low latency Internet of Things (IoT) applications. Yet, with short-packet transmission, the rate loss would occur, which further depends on the blocklength, making the network optimization notoriously difficult, especially for random access networks. This paper focuses on the representative random access network, i.e., Aloha, with short packet transmission, namely, short-packet Aloha. Specifically, we aim to optimize the sum rate and access delay of short-packet Aloha. By deriving the probability of successful transmissions of packets, both the network sum rate and the probability generating function of access delay are obtained as explicit functions of key system parameters. The maximum sum rate and the minimum mean access delay are further derived by jointly tuning the packet transmission probability and the blocklength of packets. The effect of system parameters on the optimal sum rate and access delay performance is investigated. It is shown that the maximum sum rate is insensitive to the retry limit $M$ , while deteriorates as the information bits per packet $k$ decreases. In contrast, the optimal delay performance can be improved with a small $M$ or $k$ . The reliability performance is also evaluated and shown to be enhanced with a large retry limit $M$ . The analysis sheds important light on the access design of practical short-packet Aloha networks. By taking LTE-M as an example, it is found that to improve access delay performance, the information bits per packet $k$ should not exceed an upperbound, which polynomially decreases as the network size increases.

This paper aims to explore a new-type Mo-based composite conversion coating on 6061 aluminum alloy, systematically evaluate its corrosion resistance, and further reveal the formation mechanism. The effects of pH, conversion time (CTI) and H2ZrF6 content on the corrosion resistance were determined by the dropping test and electrochemical tests, and the average corrosion rate (ACR) in neutral 3.5 wt.% NaCl solution under different temperatures was calculated by the immersion test. The micro-morphology and phase compositions were systematically investigated by SEM, EDS and XPS. The results showed that the optimal pH and CTI were 4.5 and 12 min respectively, and the most suitable addition amount of H2ZrF6 was 1.2 mL/L. The micro-morphology of the Mo/Ti/Zr conversion coating (MoTiZrCC) under the best conversion condition was relatively smooth and dense, and its phase compositions mainly consisted of MoO3, Mo2O5, TiO2, ZrO2 and Al2O3. The MoTiZrCC could significantly improve corrosion resistance with the lower icorr and higher Rp, and the ACR of the MoTiZrCC could be reduced to 16.7% of the Al alloy matrix. Additionally, based on the above results, the formation mechanism for the MoTiZrCC was logically deduced.

This paper aimed to develop synchronous chemical conversion coating on multi-metal substrates with good corrosion resistance to meet the primer process of new energy light vehicle bodies. Titanium/zirconium-based chemical conversion coatings were prepared on 6061 aluminum alloy/7075 aluminum alloy/galvanized steel substrates. By measuring the open circuit potential (OCP), the formation of a muti-metal synchronous conversion coating can be roughly divided into three steps. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques showed that the self-corrosion current density of the conversion coating decreased significantly while the resistance increased. The surface morphology and composition of the conversion coatings were observed by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Additionally, the micro-zone characteristics of conversion coatings were analyzed by an electron probe microanalyzer (EPMA). The synchronous conversion coatings exhibit uniformity and relative smoothness. Additionally, a number of tiny cracks, pores, intermetallic compounds, enrichments and inclusions provide efficient active sites for the nucleation of chemical conversion. Consequently, in the synchronous conversion coating, the structure of aluminum alloy mainly consists of Al2O3/TiO2/ZrO2/ZrF4, while the structure of conversion coating of galvanized steel contains TiO2/Fe2O3/ZrO2.