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CO_(2)enrichment accelerates successional development of an understory plant community

Journal of Plant Ecology 2010年第1期3卷 33-39页

作者： Lara Souza R.Travis Belote Paul Kardol Jake F.Weltzin Richard J.Norby Environmental Sciences Division Oak Ridge National LaboratoryBuilding 1062PO Box 2008Oak RidgeTN 37831USA Department of Ecology and Evolutionary Biology 569 Dabney HallUniversity of TennesseeKnoxvilleTN 37996USA The Wilderness Society 503 West Mendenhall St BozemanMT 59715USA USA national phenology network National Coordinating officeTucsonAZ 85721USA

Aims Rising concentrations of atmospheric carbon dioxide([CO_(2)])may influence forest successional development and species composition of understory plant communities by altering biomass production of plant species of functional ***,we describe how elevated[CO_(2)](eCO_(2))affects aboveground biomass within the understory community of a temperate deciduous forest at the Oak Ridge national Laboratory sweetgum(Liquidambar styraciflua)free-air carbon dioxide enrichment(FACE)facility in eastern Tennessee,*** asked if(i)CO_(2)enrichment affected total understory biomass and(ii)whether total biomass responses could be explained by changes in understory species composition or changes in relative abundance of functional groups through *** and methods The FACE experiment started in 1998 with three rings receiving ambient[CO_(2)](aCO_(2))and two rings receiving eCO_(2).From 2001 to 2003,we estimated species-specific,woody versus herbaceous and total aboveground biomass by harvesting four 130.5-m subplots within the established understory plant community in each FACE *** 2008,we estimated herbaceous biomass as previously but used allometric relationships to estimate woody biomass across two 535-m quadrats in each FACE *** findings Across years,aboveground biomass of the understory community was on average 25%greater in eCO_(2)than in aCO_(2)*** could not detect differences in plant species composition between aCO_(2)and eCO_(2)***,we did observe shifts in the relative abundance of plant functional groups,which reflect important structural changes in the understory *** 2001-03,little of the understory biomass was in woody species;herbaceous species made up 94%of the total understory biomass across[CO_(2)]*** time,woody species increased in importance,mostly in eCO_(2),and in 2008,the contribution of herbaceous species to total understory biomass was 61%in aCO_(2)and only 33%in eCO_(2)***

关键词： community composition FACE aboveground biomass woody herbaceous sweetgum Microstegium vimineum Lonicera japonica

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Blockchain-based vehicular edge computing networks: the communication perspective

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Science China(Information Sciences) 2023年第7期66卷 253-265页

作者： Lin HE Fuchang LI Haikun XU Wenbo XIA Xuefei ZHANG Xiaofeng TAO Research Institute China United Network Communications Corporation Limited national Engineering Research Center of Mobile network Technologies Beijing University of Posts and Telecommunications

Vehicular edge computing(VEC) networks can satisfy the increasing demands of data processing by offloading the computation tasks to multiple distributed edge computing nodes assisted by servers. These edge servers generally combine with roadside units(RSUs). However, RSUs with edge servers cannot be fully trusted, possibly leading to serious security and privacy problems. Combining blockchain with VEC networks may establish a trusted and decentralized vehicular environment, but the coexistence of multiple communication modes comprising vehicle-to-vehicle(V2V), vehicle-to-RSU(V2R), and RSU-to-RSU(R2R) makes the block propagation patterns have different effects on the block consensus process. In this paper, we study the block propagation patterns between vehicles and RSUs with edge servers under three communication *** first give the closed-form expressions for the single-block and multiblock propagation times in two specific conditions to explore how the priority of a block generated from a specific node affects the block propagation process, in which multiblock propagation embodies competitive propagation due to blockchain ***, an innovative consensus mechanism that fully invokes the communication capability of the nodes is proposed, and the block propagation time and frequency can be substantially reduced under this *** addition, an important finding is that under the conventional and proposed consensus mechanisms, an RSU or a vehicle that creates a new block plays a decisive role in the block propagation pattern.

关键词： block propagation blockchain consensus VEC network

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Stochastic geometry based analysis for heterogeneous networks: a perspective on meta distribution

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Science China(Information Sciences) 2020年第12期63卷 230-250页

作者： Xinlei YU Qimei CUI Yuanjie WANG Na LI Xiaofeng TAO Mikko VALKAMA national Engineering Laboratory for Mobile network Technologies Beijing University of Posts and Telecommunications national Computer network Emergency Response Technical Team/Coordination Center of China (CNCERT/CC) Department of Electrical Engineering Tampere University

The meta distribution as a new performance metric can provide much more fine-grained information about the individual link reliability, and is of great value for the analysis and design of the future cellular networks. In this paper, we investigate the stochastic geometry based analysis for heterogeneous networks from the perspective on the meta distribution. The comprehensive overview for the fundamental framework of the meta distribution is provided, which involves the concepts of the meta distribution and its related performance metric(e.g., mean local delay and spatial outage capacity) and the efficient calculation methods of the meta distribution. The insights of the meta distribution are also stated by the comparison with standard success probability. The various applications of the meta distribution to heterogeneous networks are summarized and categorized by different types of technologies. Furthermore, some open issues and future work are discussed to promote the development and application of the meta distribution.

关键词： meta distribution stochastic geometry heterogeneous network success probability per-link reliability

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GAGMS: a requirement-driven general address generation and management system

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Science China(Information Sciences) 2018年第9期61卷 126-140页

作者： Ying LIU Lin HE Gang REN Institute for network Sciences and Cyberspace Tsinghua University Tsinghua national Laboratory for Information Science and Technology

IPv6 address generation is closely related to the manageability, security, privacy protection, and traceability of the Internet. There are many kinds of IPv6 address generation and configuration methods in the area of Internet standards and research that may cause certain problems, including the mixed operation problem of multiple IPv6 address generation schemes, the synchronization problem of the change in IPv6 address, the efficiency problem of processing large-scale concurrent IPv6 address requests, and the general model problem for mapping IPv6 addresses to other requirement spaces as identifiers. In this paper, we consider generating and managing IPv6 addresses according to network requirements. After conducting a requirement analysis of most proposed address generation schemes, we propose a general address generation model and a general address management system, which are the cores of the general address generation and management system(GAGMS). This system solves the above problems under the premise of maintaining the diversity and flexibility of the existing IPv6 address generation and configuration methods and allows networks to utilize different address generation schemes according to different requirements in different scenarios. Finally, we design a prototype system and evaluate our GAGMS to demonstrate its effectiveness,manageability, and scalability, and we have conducted trial deployment in campus networks and are trying to standardize this work in IETF.

关键词： IPv6 address generation IPv6 address management requirement analysis DHCPv6 SLAAC

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Secret key generation based on private pilot under man-in-the-middle attack

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Science China(Information Sciences) 2017年第10期60卷 93-106页

作者： Yu HUANG Liang JIN Na LI Zhou ZHONG Xiaoming XU national Digital Switching System Engineering and Technological R&D Center national Engineering Laboratory for Mobile network Technologies Beijing University of Posts and Telecommunications

Given the openness and invariance of public pilot, secret key generation(SKG) based on wireless channels is vulnerable to active attacks. In this paper, we explore man-in-the-middle(MITM) attacks, where the attacker acts as a transparent relay to intercept channel state information and deduce the generated *** prevent this type of attacks, a dynamic private pilot is generated, where legitimate nodes first consider the information authenticated between them as seed information for the private pilot, and then generate the private pilot based on this seed information according to the pilot requirements. Then, both the new seed information and secret keys are dynamicaally derived from wireless channels that are estimated with the private pilot instead of a public pilot. The proposed private pilot encrypts and authenticates wireless channels, allowing an SKG rate close to that without attackers. Analysis and simulation results show that the proposed SKG approach can effectively withstand an MITM attack.

关键词： private pilot man-in-the-middle attack secret key generation physical layer security

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Compressed sensing based channel estimation used in non-sample-spaced multipath channels of OFDM system

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The Journal of China Universities of Posts and Telecommunications 2015年第2期22卷 31-37页

作者： Chen Baohao Cui Qimei Yang Fan national Engineering Laboratory for Mobile network Security Beijing University of Posts and Telecommunications

By virtue of an increase in spectral efficiency by reducing the transmitted pilot tones, the compressed sensing （CS） has been widely applied to pilot-aided sparse channel estimation in orthogonal frequency division multiplexing （OFDM） systems. The researches usually assume that the channel is strictly sparse and formulate the channel estimation as a standard compressed sensing problem. However, such strictly sparse assumption does not hold true in non-sample-spaced multiple channels. The authors in this article proposed a new method of compressed sensing based channel estimation in which an over-complete dictionary with a finer delay grid is applied to construct a sparse representation of the non-sample-spaced multipath channels. With the proposed, the channel estimation was formulated as the model-based CS problem and a modified model-based compressed sampling matching pursuit （CoSaMP） algorithm was applied to reconstruct the discrete-time channel impulse response （CIR）. Simulation indicates that the new method proposed here outperforms the traditional standard CS-based methods in terms of mean square error （MSE） and bit error rate （BER）.

关键词： channel estimation model-based compressed sensing non-sample-spaced multipath channels

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Responses of an old-field plant community to interacting factors of elevated[CO_(2)],warming,and soil moisture

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Journal of Plant Ecology 2009年第1期2卷 1-11页

作者： E.Cayenne Engel Jake F.Weltzin Richard J.Norby Aimee T.Classen Department of Ecology and Evolutionary Biology University of Tennessee569 Dabney HallKnoxvilleTN 37996-1610USA Environmental Sciences Division Oak Ridge National LaboratoryOne Bethel Valley RoadBuilding 1062Oak RidgeTN 37831-6422USA Present address:USA national phenology network National Coordinating Office1955 East 6th StreetTucsonAZ 85721USA

Aims The direct effects of atmospheric and climatic change factors—atmospheric[CO_(2)],air temperature and changes in precipitation—can shape plant community composition and alter ecosystem *** is essential to understand how these factors interact to make better predictions about how ecosystems may respond to *** investigated the direct and interactive effects of[CO_(2)],warming and altered soil moisture in open-top chambers(OTCs)enclosing a constructed old-field community to test how these factors shape plant *** and methods The experimental facility in Oak Ridge,TN,USA,made use of 4-m diameter OTCs and rain shelters to manipulate[CO_(2)](ambient,ambient+300 ppm),air temperature(ambient,ambient+3.5C)and soil moisture(wet,dry).The plant communities within the chambers comprised seven common old-field species,including grasses,forbs and *** tracked foliar cover for each species and calculated community richness,evenness and diversity from 2003 to *** findings This work resulted in three main findings:(1)warming had speciesspecific effects on foliar cover that varied through time and were altered by soil moisture treatments;(2)[CO_(2)]had little effect on individual species or the community;(3)diversity,evenness and richness were influenced most by soil moisture,primarily reflecting the response of one dominant *** conclude that individualistic species responses to atmospheric and climatic change can alter community composition and that plant populations and communities should be considered as part of analyses of terrestrial ecosystem response to climate ***,prediction of plant community responses may be difficult given interactions between factors and changes in response through time.

关键词： climate change foliar cover multi-factor interactions diversity richness

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A Frameless network Architecture for the Way Forward of C-RAN

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China Communications 2016年第6期13卷 154-166页

作者： Xiaodong Xu Zhao Sun Xun Dai Xiaofeng Tao Ping Zhang national Engineering Laboratory for Mobile network Security Beijing University of Posts and Telecommunications

The key technologies involved in the evolution of the Cloud-based Radio Access network(C-RAN) are discussed in this paper. Taking the Frameless network Architecture(FNA) as a starting point, a cell-lessbased network topology for a multi-tier Heterogeneous network(Het Net) and ultra-dense network is proposed. The FNA network topology modeling is researched with centralized processing and distributed antenna deployments. The Antenna Element(AE) is released as a new dimensional radio resource that is included in the centralized Radio Resource Management(RRM) processes. This contributes to the on-demand user-centric serving-set associations with cell-edge effect elimination. The Control Plane(CP) and User Plane(UP) separation and adaptation are introduced for energy efficiency improvements. The centralized RRM and different optimization goals are discussed for fully exploring the merits from the centralized computing of C-RAN. Considering the complexity, near-optimal approaches for specific users' Quality-of-Service(Qo S) requirements are addressed. Finally, based on the research highlighted above, the way forward of C-RAN evolution is discussed.

关键词： C-RAN frameless network architecture user-centric control plane and user plane adaptation centralized radio resource management optimization

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A trust framework based smart aggregation for machine type communication

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Science China(Information Sciences) 2017年第10期60卷 78-92页

作者： Tabinda SALAM Waheed ur REHMAN Xiaofeng TAO Yu CHEN Ping ZHANG national Engineering Laboratory for Mobile network Technologies Beijing University of Posts and Telecommunication Department of Computer Science University of Peshawar

Machine type communication(MTC) is one of the significant communication paradigms in the fifth generation networks. The existing cellular networks are not designed for massive access of the MTC ***, data aggregation and relaying are advocated to reduce the massive MTC access besides other physical layer solutions. In this paper, we propose a secured multiple mobile relay selection algorithm that smartly aggregates data from adjacent MTC devices through multiple user equipments and transmits it to the base station(BS). The paper also presents a framework for the selection of trusted relays to cooperatively aggregate MTC data and render two-hop connectivity to the BS. Our proposed algorithm is compared with existing algorithms on the basis of energy efficiency, system capacity, communication delay and outage probability. Our proposed algorithm outperforms the other schemes by improving outage probability and communication delay by 33% and 25%, respectively.

关键词： D2D communication data aggregation machine type communication(MTC) mobile relay MTC offloading

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Simulating Error-Opening of Pressure Relief Valves of a Station on a Continuous Undulating Oil Pipeline with Large Elevation Difference

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Energy Engineering 2022年第4期119卷 1439-1452页

作者： Xiaohua Chen Caifu Lan Honghao Zheng Wang Li Chao Zhao Wenjun Dang national Pipeline network Group Southwest Pipeline Co.Ltd.Chengdu610094China national Pipeline network Group North Pipeline CompanyLangfang065000China national Pipeline network Group West-to-East Gas Transmission CompanyShanghai200000China

For oil pipeline in mountain areas,high hydrostatic pressure in the pipeline may cause error-opening of pressure relief valves,and oil is discharged from the pipeline to the pressure relief tanks,bringing spilling-over risk of the pressure relief ***,simulating the error-opening situations of the pressure relief valves and investigating the oil discharge process are necessary for checking the possibility of the spilling-over accident and then proposing measures to improve the pressure relief *** research focuses on a continuous undulating oil pipeline with large elevation difference and a station along this pipeline,which is named B station in this paper,is *** OLGA software,simulation model of the pressure relief system of B station is established,and the accuracy of the model is verified by reconstructing a real accident and making a comparison with the actual accident *** maximum discharge rate reached 8284 m3/h when the pressure relief valve was opened by mistake in the inlet and outlet of the *** accumulated filling time of the two pressure relief tanks is 200 s,which is in good agreement with the accident *** this basis,for error-opening of the pressure relief valves at the inlet and outlet of B station,simulation is performed to investigate variations of the discharge velocity,discharge flow rate,accumulated discharge volume and ventilation volume of the vent *** discharge velocity is found to be over the maximum velocity allowed for safety *** to the accumulated discharge volume,it is inferred that spilling over of the pressure relief tanks will be caused once error-opening of the pressure relief valve *** it is judged that the existing breathing valve can not satisfy the ventilation requirement in case of failure of the pressure relief *** these simulation results,it is proposed that increasing the number of vent valves,replacing the manual valves with electrically operate

关键词： Continuous undulating oil pipeline large elevation difference pressure relief system error-opening oil dis-charge improvement measure

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