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service life prediction of AP/Al/HTPB solid rocket propellant with consideration of softening aging behavior

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Chinese Journal of Aeronautics 2019年第2期32卷 361-368页

作者： Walid M.ADEL Guozhu LIANG School of Astronautics Beihang University

The aging behavior of softening composite solid propellant was investigated by measuring its mechanical and ballistic prosperities during prolonged storage at elevated and room temperatures. Accelerated aging was conducted at 65 °C for 231 days while the normal aging was performed at 25 ± 3 °C and relative humidity less than 50% for 8 years. The mechanical properties were obtained from uniaxial tensile tests for the aged propellant specimens while the ballistic properties were determined from static firing tests of subscale motors aged for 112 days at 65 °C. The mechanical results show that the maximum tensile strength and Young's modulus initially increase and subsequently decrease with increasing aging time, while the maximum tensile strain generally increases with increasing aging time. The ballistic properties like burning rate show a small change which cannot affect the ballistic performance. The experimental results show that the changes in the mechanical properties are significant during the aging period, but the burning rate does not undergo significant changes. From this study, it is observed that the propellant ages through a combination of reactions like post-cure, oxidative cross-linking, chain scission, and hydrolysis. The chain scission and the hydrolysis effect are the most significant process, which makes the propellant soft and extendible. The observed aging mechanism has been modeled using an exponential function with two terms which can describe the complex behavior of the aging. By applying Arrhenius equation,the activation energy values were obtained based on the propellant mechanical properties. The shelf life of this propellant formulation at 25 °C is predicted to be 13 years using the modulus as failure criteria and control parameter.

关键词： Aging Hydrolysis service life Softening behavior Solid propellant

service-Driven Coded Forward Scheme Based on Streaming Transmission Model for Lunar Space Communication Networks

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China Communications 2020年第7期17卷 15-26页

作者： Shushi Gu Ye Wang Guoqing Chen Shuo Shi School of Electronic and Information Engineering Harbin Institute of Technology(Shenzhen)Shenzhen 518055China Peng Cheng Laboratory Shenzhen 518055China School of Electronic and Information Engineering Harbin Institute of TechnologyHarbin 150001China

With the rapid development of lunar exploration,a large amount of scientific data and media stream service needs to be transmitted through Lunar Space Communication Networks(LSCNs).Due to limited transmitter power and intermittent,long delay and packet loss connections,the reliable and efficient multi-priority services’transmission in LSCNs becomes an urgent ***,we propose a Streaming Transmission Model(STM)based on temporal and spatial topology graph to describe the delay and energy consumption for data transmission in ***,we further devise a Coded Forward Scheme based on STM,termed CFS-STM,to achieve multi-priority service in two steps:i).Link Stability Function(LSF)is established by solving an optimization problem to choose the appropriate single-hop ***).Raptor code is employed to further save delay and energy with adjustable code-rate according to the different channel *** results show that,CFS-STM can significantly improve the transmission efficiency of multi-service priority streaming delivery in LSCNs.

关键词： Streaming service delay

Future forestation in China should aim to align the temporal service window of the forest carbon sink with the“carbon neutrality”strategy

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Science China Earth Sciences 2023年第12期66卷 2971-2976页

作者： Hao XU Chao YUE Shilong PIAO College of Urban and Environmental Sciences Peking UniversityBeijing 100871China Institute of Soil and Water Conservation Northwest A&F UniversityYangling 712100China Institute of Tibetan Plateau Research Chinese Academy of SciencesBeijing 100101China

*** Carbon sequestration in forest ecosystems worldwide dominates the current global terrestrial carbon sink,offsetting approximately 26% of global anthropogenic carbon emissions annually(Pan et al.,2011).

关键词： service annually forest

Effect of long-term service on the precipitates in P92 steel

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International Journal of Minerals,Metallurgy and Materials 2018年第8期25卷 913-921页

作者： Yan-ping Zeng Jin-dou Jia Wen-he Cai Shu-qing Dong Zhi-chun Wang School of Materials Science and Engineering University of Science and Technology BeijingBeijing 100083China North China Electric Power Research Institute Co. Ltd.Beijing 100045China

The precipitates in P92 steel after long-term service in an ultra-supercritical unit were investigated by field-emission scanning electron microscopy and transmission electron microscopy and were found to mainly consist of M23 C6 carbides,Laves phase,and MX *** Z-phase was observed.M23 C6 carbides and Laves phase were found not only on prior austenite grain boundaries,martensite lath boundaries,and subgrain boundaries but also in lath interiors,where two types of MX carbonitrides—Nb-rich and V-rich particles—were also observed but the "winged" complexes were hardly *** kind of precipitate within the martensite laths exhibited multifarious morphologies,suggesting that a morphological change of precipitates occurred during long-term *** M23 C6 carbides and Laves phase coarsened substantially,and the latter grew faster than the ***,MX carbonitrides exhibited a relatively low coarsening *** effect of the evolution of the precipitate phases on the creep rupture strength of P92 steel was discussed.

关键词： precipitate P92 steel long-term service ultra supercritical unit

Cloud service selection using cloud service brokers: approaches and challenges

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Frontiers of Computer Science 2019年第3期13卷 599-617页

作者： Meysam VAKILI Neda JAHANGIRI Mohsen SHARIFI Department of Computer Engineering University of Science and Culture Tehran 14619-68151 Iran School of Computer Engineering Iran University of Science and Technology Tehran 16846-13114 Iran

Cloud computing users are faced with a wide variety of services to choose from. Consequently, a number of cloud service brokers (CSBs) have emerged to help users in their service selection process. This paper reviews the recent approaches that have been introduced and used for cloud service brokerage and discusses their challenges accordingly. We propose a set of attributes for a CSB to be considered effective. DifFerent CSBs' approaches are classified as either single service or multiple service models. The CSBs are then assessed, analyzed, and compared with respect to the proposed set of attributes. Based on our studies, CSBs with multiple service models that support more of the proposed effective CSB attributes have wider application in cloud computing environments.

关键词： cloud service broker (CSB) cloud service selection cloud computing quality of service (QoS)

Research advances on blockchain-as-a-service:architectures,applications and challenges

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Digital Communications and Networks 2022年第4期8卷 466-475页

作者： Jie Song Pengyi Zhang Mohammed Alkubati Yubin Bao Ge Yu Software College Northeastern University Shenyang110819China School of Computer Science and Engineering Northeastern UniversityShenyang110819China

Due to the complexity of blockchain technology,it usually costs too much effort to build,maintain and monitor a blockchain system that supports a targeted *** this end,the emerging“Blockchain as a service”(BaaS)makes the blockchain and distributed ledgers more accessible,particularly for businesses,by reducing costs and *** combines the high computing power of cloud computing,the pervasiveness of IoT and the decentralization of blockchain,allowing people to build their own applications while ensuring the transparency and openness of the *** paper surveys the research outputs of both academia and ***,it introduces the representative architectures of BaaS systems and then summarizes the research contributions of BaaS from the technologies for service provision,roles,container and virtualization,interfaces,customization and *** typical applications of BaaS in both academic and practical domains are also *** present,the research on the blockchain is abundant,but research on BaaS is still in its *** challenges of BaaS are concluded in this paper for further study directions.

关键词： Blockchain as a service Blockchain service Internet of things Cloud computing

Performance Analyses of Production Inventory Systems Considering service Time and Product Returns of Online Shopping

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Journal of Systems Science & Complexity 2019年第3期32卷 888-906页

作者： QIN Yaling YUE Dequan School of Economics and Management Yanshan University Qinhuangdao 066004 China LiRen College Yanshan University Qinhuangdao 066004 China College of Science Yanshan University Qinhuangdao 066004 China

This paper considers a production inventory system with service time and product returns, dependent on the characteristics of online shopping beliaviors. The customers arrive according to a Poisson process, in which the arriving customer requires an item in the inventory, as well as a server service that the service time is exponentially distributed. Moreover, there is one production facility to produce items according to (s, S) policy, and the production time also follows an exponential (listribution. In the beginning, the stationary joint distribution is obtained in the product form for the queue length and the on-hand inventory level. Additionally, the resulting distribution is applied to derive some performance measures, which can be adopted to numerically calculate the optimal (s, S) policy. Finally, numerical analyses are processed to investigate the effects of some system parameters on the performance measures. The numerical results clearly indicate that the product return rate has a significantly monotonic effect on the optimal policy and optimal cost.

关键词： Online shopping production inventory return service time (s, S) policy

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service refinement

Science in China(Series F) 2008年第6期51卷 661-682页

作者： HE JiFeng Software Engineering Institute Shanghai key Laboratory of Trustworthy Computing East China NormalUniversity Shanghai 200062 China

This paper presents a refinement calculus for service components. We model the behaviour of individual service by a guarded design, which enables one to separate the responsibility of clients from the commitment made by the system, and to identify a component by a set of failures and divergences. Protocols are introduced to coordinate the interactions between a component with the external environment. We adopt the notion of process refinement to formalize the substitutivity of components, and provide a complete proof method based on the notion of simulations.

关键词： service component refinement

Pricing and service Strategies for Two-sided Platforms

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Journal of Systems Science and Systems Engineering 2019年第3期28卷 299-316页

作者： Xiaogang Lin Chuanying Chen Zhaozhan Lin Yongwu Zhou School of Business Administration South China University of TechnologyGuangzhou 510641China

Nowadays,more and more transactions or interactions like online dating and shopping are completed on two-sided platforms involving two groups of *** these two-sided platforms,there often exist cross-network effects,i.e., the benefits that agents at one side receive are positively related to the number of agents at the other side,and vice *** paper considers such two-sided platforms,where the platforms offer a certain service to attract agents of both sides to join the platforms,and then charge agents who join the platforms a lump-sum fee to gain the *** present service and pricing strategies for both monopolistic and duopolistic platforms,*** also investigate the impact of platforms'life cycle on their service and pricing *** managerial implications are shown.

关键词： Two-sided markets cross-network effects service level platform pricing multi-homing