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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.

The urban wetland is a precious wealth of the city, which has a very important role and value for the development of human and society. Zhuzhou is a traditional industrial city in China, which is located in the lower reaches of the Xiangjiang River and rich in urban wetland resources. In order to protect, utilize and manage urban wetland resources scientifically, based on LCM model platform, using Landsat series remote sensing images and other data, this paper systematically analyses the land use change process of Zhuzhou urban wetland from 2006 to 2016 and simulates and forecasts the urban wetland landscape pattern in 2021. The prediction results show that the urban wetland in Zhuzhou city will change continuously in 2021, but the overall change is relatively small, which is basically consistent with the change trend and regain of urban wetland in 2006~2016. Among them, the change of paddy fields area is the largest, with a total decrease of 1364.8ha; the increase of reservoirs area is 82.4ha; the decrease of pond area is 34.6ha, while riverine wetland is basically unchanged. In addition, Zhuzhou urban wetland landscape pattern change is affected by both natural and human factors, while human activities have a more significant impact on the wetland, with both positive and negative effects.

Zhuzhou is an important part of the Changsha-Zhuzhou-Xiangtan city group in southern China. To grasp the economic benefits of urban wetland resources value in Zhuzhou City, strengthen wetland conservation and utilization, and ensure the sustainable development of cities, this paper takes Zhuzhou 2016 wetland remote sensing image interpretation map and multi-source data as the foundation, and build urban wetland ecosystem service evaluation system. Through deduplicate double counting, this paper evaluates the value of urban wetland ecosystem service in Zhuzhou City employing shadow project method, replacement cost method, travel cost method, conditional value method and other economic value evaluation methods. The results indicate: (a) The total value of urban wetland ecosystem services is $1,527,908,900 in 2016. (b) The ultimate value of urban wetland services ranked as follows: water storage regulation value ($539,566,265), climate regulation value ($424,930,361), tourism recreation value ($174,543,328), water supply value ($133,183,901), biological product value ($121,987,952), atmospheric composition regulation value ($92,111,687), soil erosion prevention value ($15,799,608), water purification value ($14,598,298), and aesthetic heritage value ($10,075,346); (c) The value of different types of wetlands ranked as follows: paddy fields ($526,111,672), riverine wetland ($526,111,672), ponds ($329,628,343), reservoirs ($149,275,241), wastewater treatment plant ($207,831/a); (d) The value per unit area of different types of wetlands ranked as follows: reservoirs ($240,919/ha), riverine wetland ($236,627/ha), pond ($145,693/ha), paddy fields ($26,551/ha) and wastewater treatment plant ($17,003/ha). The evaluation results reveal the great contribution of urban wetland system service to the Zhuzhou city with numbers, that not only provides data basis for wetland conservation and management but also provides a reference for the refined evaluation of urban wetland ecosystem service value.

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.

When using HBase to store tiles of remote sensing images, the spatial position of a tile is often used as the first part of the tile's rowkey so that tiles with high spatial correlations are stored close together to improve query efficiency. We refer to this storage method as the Geo-First model. However, Geo-First models have two problems: the load between nodes is unbalanced, and the accumulation of time-series remote sensing images has a negative impact on storage and query efficiency. Considering these two problems, we proposed a method for storing remote sensing images based on Google S2 and HBase. In our method, two strategies are adopted to eliminate these problems: the balanced placement strategy (BPS) and the periodic storage strategy (PSS). We evaluated our method by focusing on the effectiveness of BPS and PSS. The results show that our method achieves higher tile storage and query efficiency than three Geo-First models based on latitude and longitude, Geohash code, and Google S2 code. BPS effectively balances the load between nodes, while PSS alleviates the negative impact of the accumulation of time-series remote sensing images. Both BPS and PSS greatly improve tile storage and query efficiency.

To improve the corrosion resistance of LY12 aluminum alloy, a novel Mo–Zr–Ti composite conversion coating on its surface was prepared. The surface morphology, elements distribution, phase compositions and the corrosion resistance were systematically determined, and the relation between them were established. The results indicate that the optimal conversion temperature and conversion time are 40 °C and 15 min, respectively. The surface morphology of the composite coating under the best conversion condition is continuous and dense. The major elements are Mo, Zr, Ti, Al, O and F, and their distribution between the inner and outer coating are distinction. The phase compositions mainly consist of MoO _3 , Mo _2 O _5 , TiO _2 , ZrO _2 , Al _2 O _3 , AlF _3 ∙3H _2 O, Na _3 AlF _6 and ZrF _4 , and the nucleation and growth mechanisms are proposed. Additionally, the composite coating can significantly reduce the I _corr and increase the film resistance R _f in the temperature range from 0 to 60 °C through electrochemical test, and its activation energy E _a increases from 25.7 to 34.5 kJ ∙ mol ^−1 . Compared with Al matrix, the average corrosion rate of the composite coating is reduced by 65% to 85% in the full immersion test. Therefore, the composite conversion coating greatly improves the corrosion resistance of Al matrix.

Based on the petrological study, according to single factor analysis and multifactor comprehensive mapping method, the quantitative lithofacies palaeogeography of the Upper Permian Changxing Stage of the Middle and Upper Yangtze Region was studied. The Changxing Stage in the Middle and Upper Yangtze Region is mainly composed of carbonate rocks; in addition, clastic and siliceous rocks occur with rare coals and pyroclastic rocks. Lithofacies can be divided into five types, including clastic rock assemblage, clastic rock–limestone assemblage, limestone assemblage, limestone–siliceous rock assemblage, and siliceous rock–clastic rock assemblage. Four fundamental ecological types and five fossil assemblages were recognized in the Changxing Stage. On the basis of the petrological and palaeoecological study, eight single factors were chosen including thickness, content of marine rocks, content of shallow water carbonate rocks, content of bioclasts with limemud matrix, content of bioclasts with sparry cement, distribution of reefs, content of thin bedded siliceous rocks and content of deep water sedimentary rocks. And eight single factor maps and one lithofacies paleogeographic map of the Changxing Stage were compiled. Paleoenvironments from west to east include an erosional area, fluvial plain, clastic platform, carbonate platform and reefs that developed there, slope and basin, low energy organic banks, and high energy organic banks. Sedimentary environments have an obvious control on the development of the source rocks, and the excellent source rocks are developed in the Dalong Formation. Changxing Stage reservoirs should be dominated by the reef and platform surrounding the Guangyuan–Liangping Basin rim area, and is the most favorable exploration area of the reef petroleum reservoirs of the Changxing Formation.

One of the purposes of Internet of Things (IoT) is to reach more deeper perception. For this purpose, the efficient energy consumption is necessary among intelligent devices that make up the part of Opportunistic Networks (ONs). It is irrational for an ONs without any sleep scheduling because of awful user experience. We explore a sleeping schedule which is based on duty cycling for mobile devices to reduce energy consumption of ONs. To see how schedule affects the performance of ONs, we took a series of simulations and the results indicated that the sleeping schedule is an efficient method for prolonging the network life time in ONs. The successful delivery ratio can increase two to three times when factor Tr equal 0.2. We also observed that the network matrices are acceptable, and the network survival time can be extended effectively in ONs.