Subjects: Statistics >> Social Statistics submitted time 2024-05-18 Cooperative journals: 《中国科学院院刊》
Abstract： Since the implementation of the major function oriented zoning, the ecological space of key ecological functional areas has continuously expanded, with a significant increase in vegetation coverage. Concurrently, there has been a dual change in population dynamics, characterized by a decrease in total population and an increase in the urban population. Furthermore, significant achievements have been made in economic and social development, and there has been a steady improvement in the functions of ecological security barriers, contributing to an alleviation of tension in human-environment relationships. During the 15th Five-Year Plan period, it is imperative to adhere to the functional orientation primarily focused on providing ecological services or products. While consolidating provisioning, regulating, supporting, and cultural ecosystem services, there is an increased emphasis on enhancing the quality of these services, thereby constructing a more diversified, stable, and sustainable ecological foundation. Furthermore, exploring compatible functions of eco-product development and utilization promote greening and decarbonization, aiming to establish an inclusive conservation approach that advances modernization characterized by harmony between humanity and nature. In the 15th Five-Year Plan period, ecological regions will not only be crucial components of the new territorial security pattern but also pillars of the new territorial development pattern. Optimization recommendations are as follows. From the perspective of strategic patterns, it is necessary to enhance the spatial connection and supply-demand interaction between ecological security barriers and the territorial development pattern. In detail, continued efforts are needed to consolidate the national ecological security barriers, optimize the pattern of key ecological functional areas, integrate the system of natural protected areas, and strictly adhere to ecological conservation red lines. Moreover, a greater focus should be on upgrading quality of ecosystem service functions through classification, fully implementing the holistic approach to protecting and restoring mountains, rivers, forests, farmlands, lakes, grasslands, and sand, actively fostering new growth drivers for green development, accelerating the establishment of a refined zoning control system, and synergistically advancing reforms and innovations of institutions and mechanisms. These measures aim to support high-quality development in ecological regions through high-standard protection.
Subjects: Biology >> Botany >> Applied botany submitted time 2023-12-24 Cooperative journals: 《广西植物》
Abstract： In order to adjust the structure of inefficient Pinus massoniana forest and explore the dynamic changes for DOC during the mixed decomposition process of P. massoniana and native broad-leaved tree species. Our research focuses on the leaf litter of P. massoniana, Cinnamomum camphora and Toona sinensi, and combine them into the 15 treatments (3 single tree treatments + 12 mixed treatments) according to different tree species combinations and mass ratios, and then conducted field decomposition experiments to further explore the optimal combination for DOC release. The results showed that: (1) DOC content of Pinus massoniana and most of mixed treatments (except for PT64) significantly increased during the early stages of decomposition (0-6 months), leading to carbon enrichment. The DOC content of leaf litter decreased with the extension of decomposition time, and also exhibit carbon enrichment in small degree during the middle to late stages of decomposition (12-18 months) or the late stages of decomposition (18-24 months). Mixed leaf litter showed that the higher the proportion of broad leaves, the lower the DOC content in the later stage. (2) The antagonistic effect of DOC release rate in the early stage of decomposition (0-6 months) was strong (58.33%), and its synergistic effect gradually strengthened (91.67%) after 6-18 months. But the synergistic effect of leaf litter weakened (66.67%) during the late stage of decomposition (18-24 months). Among all mixed treatments, PT64 exhibited synergistic effects throughout the entire decomposition period, followed by PT73, PCT622 and PCT613(3/4). (3) Partial Least-Squares Regression (PLS) showed that N content, P content, lignin content, condensed tannin content, C/N, C/N, lignin/N, and lignin/P were important factors affecting the release of DOC from litter in this study area. Overall, the DOC release from mixed P. massoniana and broad-leaved litter was affected by tree species, mixing ratio and decomposition time. Among all of the mixtures, PT64, PT73, PCT622 and PCT613 showed strong synergistic effects for DOC release.
Subjects: Digital Publishing >> New Media submitted time 2023-10-08 Cooperative journals: 《中国传媒科技》
Abstract：本文首先简要介绍了毫米波在频谱、产业链等方面的发展情况,然后提出一种基于Opto-DMD的新型光生毫米波装置,装置可生成17.23GHz～137.36GHz频段的毫米波信号,同时对其核心器件Opto-DMD进行了简单介绍,接着对光生毫米波过程中涉及的关键过程进行理论分析,包括游标效应、四波混频和光学外差法等,最后分析了毫米波的优劣势,并提出广电5G毫米波部署场景建议。
Subjects: Library Science，Information Science >> Library Science submitted time 2023-07-26 Cooperative journals: 《图书情报工作》
Abstract： [Purpose/significance] This paper takes the short-term rental shared service platform as an example, and constructs an evaluation index system for the resource information quality of the shared service platform, so as to help platform enterprises effectively identify the resources with information quality problems and improve the information quality.[Method/process] Firstly, using the theory of information dissemination, the paper analyzed the process of information dissemination of the shared service platform. Then, according to the participants, information quality evaluation of the shared service platform, evaluation index system was established from three dimensions, including source quality, content quality and utility. Finally, the information quality evaluation method based on BP neural network was proposed, and 100 sets of collected sample data was used for training and simulation verification by Matlab 2018a software.[Result/conclusion] The evaluation index system for the resource information quality of shared service platform is proposed and validated by BP neural network. Taking the short-term rental platform as an example, the final results prove that the evalution index system has certain feasibility and practicability.
Subjects: Mechanics >> Solid Mechanics submitted time 2023-06-21 Cooperative journals: 《应用力学学报》
Abstract： The finite element method is used to analyze the deformation law and ice-shedding dynamic response law of 750 kV EHV transmission line under uneven icing condition.The model of “insulator string six bundle conductor” is established,and the conductor shape and its ice-shedding dynamic response under uniform icing,three section icing,linear icing and high altitude icing are compared and analyzed.The influences of span number,span length,height difference,icing thickness and ice-shedding rate on the shape change and ice-shedding jump height of conductors under high altitude icing conditions are mainly discussed.The results show that the conductor deformation and ice-shedding jump height increase with the increase of span number,span length and icing thickness.When the height difference of the fourth span increases,the slip along the horizontal direction of the conductor increases,while the ice-shedding jump height decreases.When the fourth span is 1 000 m under uniform icing,the ice shedding jump height of the conductor has a peak value,which is 25.627 m.The above research results show that the UHV transmission line is uniformly covered.
Subjects: Library Science，Information Science >> Information Science submitted time 2023-04-01 Cooperative journals: 《图书情报工作》
Abstract： [Purpose/significance] This paper aimed to analyze the information service contents, co-occurrence relationships and influences of universities libraries' WeChat official accounts.[Method/process] Firstly, this paper summarized the related research of information service and information diffusion influence. And then, analyzing the information service items and constructing a relationship network based on the co-occurrence matrix of nine famous university libraries' WeChat official account; in order to compare the importance of different nodes, the closeness centrality has been calculated. Finally, the WeChat influence index(WCI) of each WeChat official account have been calculated, the impact of different service on WCI has been compared by the analyzing of high-reading contents.[Result/conclusion] The results showed that user information, resource search and information delivery take the relative important positions in the network, but only information delivery service has the highest impact on WCI, resource search, user information, interaction & consultation, and other service have little impact.
Subjects: Other Disciplines >> Synthetic discipline submitted time 2023-03-28 Cooperative journals: 《中国科学院院刊》
Abstract： There have been rapid progresses in biodiversity science of China in recent two decades. These progresses have been achieved in six key respects: species catalogue, origination and evolution of biodiversity, biodiversity maintenance and its relationships with ecosystem functioning and services, threats to biodiversity and biodiversity’s responses to global change, biodiversity and ecological security, and construction of research platforms. However, we still lack theoretical breakthrough in biodiversity science. For further progresses, we propose to: (1) translate basic biodiversity research into biodiversity conservation for sustainable utilization; (2) strengthen application of advanced technologies, including high-throughput sequencing, genomics, and remote sensing; and (3) strengthen and expand international collaborations.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Advanced aero and power generation industry needs high-performance gas turbine. As key parts of gas turbine directionally solidified (DS) columnar grain and single crystal (SX) blades operate in heavy stress and high temperature conditions. The continuous demand for increasing turbine inlet temperature and aggressive environment has pushed alloy designers to develop DS and SX Ni-based blade alloys that contain high amount of alloying elements. DS process of blades using such alloys has become a challenging task. The small DS and SX blades are usually produced by high rate solidification (HRS) process. However, the growth of large DS and SX blades requires directional solidification with a sustained thermal gradient along the DS direction. By increasing the thermal gradient, the dendrites are refined, which results in a mechanically-superior DS and SX with reduced defects. One method to achieve consistent and higher thermal gradients is the utilization of the liquid metal cooling (LMC) process. In this method, heat extraction from the outer surface of the mold during DS relies on heat conduction rather than radiation in the conventional HRS process. The optimization of the LMC process is difficult and costly by experimental methods, especially for the complexly shaped industry gas turbine (IGT) blades because of the complicated process parameters associated with the technique. Numerical simulation is an efficient method to solve this problem. In this work, directionally solidified industry gas turbine hollow blades were prepared by high gradient LMC process. Liquid Sn was used as cooling medium. The temperature fields, macrostructures, primary dendrite arm spacing (PDAS) at various withdrawal rates during LMC process have been calculated with ProCAST software. The impact of withdrawal rate on formation of stray grains and freckles was predicted. The calculated results and the experimental observations agreed well. The solidification rates and cooling rates were found to increase with the increase of withdrawal rate. The axial thermal gradient was high and stable during the LMC process. It was found that stray grains would not block the growth of original grains at optimized withdrawal rate. No freckles were observed in the industry gas turbine hollow blades prepared by LMC technique due to the high cooling rate. Though the mean diameters of columnar grains in LMC blades were almost identical to that observed in HRS blades, the PDAS were more than 50% refined in LMC blades than those in HRS blades.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Ni-based single crystal (SX) superalloys are widely used for production of blades in gas turbines and aircraft engines for their superior mechanical performance at high temperatures. To obtain high cooling efficiency, most of the SX blades consist of thin wall with cooling holes. However, thermal fatigue cracks are usually observed in blades with this kind of structures. Thus, it must be valuable to investigate the crack initiation and propagation around a hole during thermal fatigue tests in a SX superalloy. In the present work a second generation SX Ni-based superalloy was used. Plate specimens that parallel to directional solidification (DS) direction and along (100) or (110) planes were prepared. A hole with diameter of 0.5 mm was drilled vertical to the surface in the middle of the plate by electro-discharge machining (EDM). Thermal fatigue tests were performed between room temperature and 1100 ℃. Effect of crystal orientation on the crack initiation and propagation was investigated and the reasons were analyzed. It was found that a thin recast layer was produced around holes of EDM drilled. The thickness of the recast layer was 15 mm in the maximum. Crystal orientation has great effect on the crack initiation sites and propagation kinetics. After 80 cyc thermal fatigue tests, in (110) specimens cracks initiated at the edge of the holes that vertical to the DS direction, then grew quickly and propagated along directions about 45° from the DS direction. After 200 cyc tests, cracks developed to more than 2 mm in length. While in (100) specimens no cracks could be observed even after 200 cyc thermal fatigue tests. This difference was mainly due to the combined effects of different thermal stress caused by the anisotropy of single crystals and of the microstructure characteristics.
Subjects: Computer Science >> Integration Theory of Computer Science submitted time 2020-09-28 Cooperative journals: 《计算机应用研究》
Abstract： This paper presented a novel discriminative K-SVD network (DKSVDN) for face recognition. It embedded discriminative information into traditional K-SVD algorithm by special design of dictionary as well as sparse representation coefficients on the dictionary. The dictionary consisted of label specific atoms and descriptive atoms, while sparse codes contained one-hot label vectors and descriptive codes. In addition, as sparse representation algorithms were time-consuming, DKSVDN attached a co-trained feed-forward neural network to discriminative dictionary learning model to predict sparse codes. Moreover, with generative module in DKSVDN, this work also designed a new dreaming training phase to improve the robustness of DKSVDN for unknown pattern in known class. The experiment results on public face image datasets verified effectiveness of this method.
Subjects: Computer Science >> Integration Theory of Computer Science submitted time 2018-12-13 Cooperative journals: 《计算机应用研究》
Abstract： RPL (IPv6 Routing Protocol for Low power and Lossy Networks) is a routing layer protocol for IPv6 low-power lossy wireless networks. The lack of a strong security protection mechanism and running on resource-constrained IoT devices make it vulnerable to network attacks. When performing intrusion detection, it is necessary to minimize the consumption of device resources. Against the above question, this paper analyzed the network topology structure of RPL, the intrusion detection technology of RPL and the principle of common network attacks. Then, this paper expounded and proposed an adaptive energy-saving algorithm. It could reduce equipment power and network load. Finally, this paper implemented the algorithm in Contiki3 . 0, and verified the effectiveness by Cooja. Simulation experiments show that the algorithm can select effective detection nodes according to the network topology and reduce the average power of the devices by about 12% with the same true positive rate.
Subjects: Dynamic and Electric Engineering >> Engineering Thermophysics submitted time 2017-11-07 Cooperative journals: 《工程热物理学报》
Abstract：采用ssT k-w模型对冷却条件下超临界压力co2在水平管内的对流换热进行了数值研究，分析了流体物性、热流密度、直径以及浮升力等对其在拟临界点附近的流动换热特性的影响，并从场协同的角度分析了超临界压力co2的传热机理。结果表明:浮力效应使流体在流动截面上出现温度场不对称和二次流现象;下壁面的对流换热系数比上壁面先达到峰值，但换热系数小于上壁面;增大热流密度对换热系数的影响较小但能够使换热系数的峰值向入口段移动;增大热流密度和增大直径能够增强浮力效应对流体换热特性的影响;场协同原理可以解释同一截面处的换热不均匀现象。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：选用某第二代镍基单晶高温合金，制备了平行于定向凝固方向且分别沿(100)面和(110)面的2组板式试样,采用电火花方法在试样中心垂直于板面加工孔径为0.5 mm的圆孔。采用室温到1100 ℃的冷热疲劳实验，研究了冷热循环过程中不同晶体学平面的板式试样上圆孔周围裂纹萌生及扩展行为。结果表明，位于不同晶体学平面的板式试样中，电火花方法加工圆孔周围产生了一薄层再铸层，再铸层最厚处约15 um。板式试样所在晶体学平面对圆孔周围裂纹萌生及扩展行为影响显著。冷热循环80 cyc后, (110)面试样中，裂纹在与枝晶生长方向垂直的孔边产生，之后，迅速沿与枝晶生长方向呈45°角扩展。而对于(100)面试样，即使经过200 cyc冷热循环后孔边也未观察到裂纹，造成此差异的本质原因是单晶高温合金晶体结构的各向异性导致的热应力差别与微观组织特征共同作用的结果。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：利用高温度梯度定向凝固-液态金属冷却(LMC)技术制备了重型燃机定向结晶空心高压涡轮叶片，采用ProCAST有限元模拟软件计算了LMC定向凝固工艺下，不同抽拉速率时空心定向结晶叶片凝固过程的温度场、晶粒组织以及一次枝晶间距(PDAS)，预测了抽拉速率对杂晶、雀斑等缺陷的影响。结果表明，模拟结果与实验结果吻合良好。随着抽拉速率增加，叶片的凝固速率、冷却速率均增加，远高于高速凝固法(HRS)的凝固速率、冷却速率；叶片不同部位达到最大纵向温度梯度时的抽拉速率不同，纵向温度梯度是评价定向工艺的有效方法；LMC工艺制备的燃机叶片消除了雀斑缺陷，PDAS远小于HRS工艺。
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