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Distributed cooperative deployment strategy in multi-UAVs assisted heterogeneous networks

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The Journal of China Universities of Posts and Telecommunications 2021年第3期28卷 11-19页

作者： Zhang Yi Zhang Heli ji Hong Li xi School of Information and Communication Engineering Beijing University of Posts and TelecommunicationsBeijing 100876China

Unmanned aerial vehicle base stations(UAV-BSs)can provide a fast network deployment scheme for heterogeneous ***,unmanned aerial vehicle(UAV)has limited capability and cannot assist the base station(BS)*** ability of a UAV to assist the BSs is limited,and the cluster deployment relies on the leading *** dispersive deployment of multiple UAVs(multi-UAVs)need a macro base station(MBS)to determine their positions to prevent collisions or ***,a distributed cooperative deployment scheme is proposed for UAVs to solve this *** scheme can increase the ability of UAVs to assist users and reduce the pressure on BSs to deploy ***,the randomly distributed users are *** the placement problem was modeled as a circle expansion problem and a pre-clustering radius expansion algorithm was *** the constraint of users'data rates,it provides services for more ***,the proposed algorithm was compared with the density-aware placement *** simulation results show that the proposed algorithm can provide services for more users and improve the coverage rate of users while ensuring the data rates.

关键词： unmanned aerial vehicle base stations(UAV-BSs) distributed cooperative pre-clustering radius expansion algorithm unmanned aerial vehicles(UAVs)deployment

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A Holomorphic Operator Function Approach for the Transmission Eigenvalue Problem of Elastic Waves

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Communications in Computational Physics 2022年第7期32卷 524-546页

作者： Yingxia xi xia ji School of Mathematics and Statistics Nanjing University of Science and TechnologyNanjing 210094China School ofMathematics and Statistics Beijing Institute of TechnologyBeijing 100081China Beijing Key Laboratory onMCAACI Beijing Institute of TechnologyBeijing 100081China

The paper presents a holomorphic operator function approach for the transmission eigenvalue problem of elastic waves using the discontinuous Galerkin *** use the abstract approximation theory for holomorphic operator functions,we rewrite the elastic transmission eigenvalue problem as the eigenvalue problem of a holomorphic Fredholm operator function of index *** convergence for the discontinuous Galerkin method is proved following the abstract theory of the holomorphic Fredholm *** spectral indicator method is employed to compute the transmission *** numerical examples are presented to validate the theory.

关键词： Discontinuous Galerkin method transmission eigenvalue problem elastic waves Fredholm operator

Parallel-batch scheduling with deterioration and rejection on a single machine

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Applied Mathematics(A Journal of Chinese Universities) 2020年第2期35卷 141-156页

作者： LI Da-wei LU xi-wen School of Science East China University of Science and TechnologyShanghai 200237China.

The single machine parallel-batch scheduling with deteriorating jobs and rejection is considered in this paper.A job is either rejected,in which a rejection penalty should be paid,or accepted and processed on the *** job’s processing time is an increasing linear function of its starting *** machine can process any number of jobs simultaneously as a *** processing time of a batch is equal to the largest processing time of the jobs in the *** objectives are to minimize the makespan and the total weighted completion time,respectively,under the condition that the total rejection penalty cannot exceed a given upper bound *** show that both problems are NP-complete and present dynamic programming algorithms and fully polynomial time approximation schemes(FPTASs)for the considered problems.

关键词： parallel-batch scheduling rejection deterioration FPTAS NP-complete

Energy efficiency based multi-relay selection and power allocation in OFDM cooperation networks

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The Journal of China Universities of Posts and Telecommunications 2014年第3期21卷 10-17页

作者： WANG Rui ji Hong LI xi Key Laboratory of Universal Wireless Communications Beijing University of Posts and Telecommunications

Getting along with the improvement of green communications, the energy efficiency （EE） of wireless network becomes more and more important. However, in nmlti-relay-assisted systems, the related work obviously depends on the end-to-end performance, whereas EE of relays has not attracted enough attention. The authors propose an orthogonal frequency division multiplexing （OFDM） multi-relay system based on amplify and forward （AF） mode. Taking incorporating EE and remaining energy as factor, decision criteria of attending cooperation is designed. The EE based asynchronous power iteration method is presented, and the existence and convergence of nash equilibrium （NE） is proven. Furthermore, a joint algorithm in subcarrier pairing, relay selection and power allocation is given. Genetic algorithm （GA） and iteration method are integrated to improve the convergence speed additionally. Simulation demonstrates the obvious improvement of EE, decrease of power consumption and increase of lifetime in relays of this algorithm with the constraint of minimum data transmission rate.

关键词： EE OFDM Multi-relay selection power allocation subcarrier pairing

Embodied energy consumption and carbon emissions evaluation for urban industrial structure optimization

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Frontiers of Earth Science 2014年第1期8卷 32-43页

作者： xi ji Zhanming CHEN jinkai LI School of Economics Peking University Beijing 100871 China Department of Energy Economics School of Economics Renmin University of China Beijing 100872 China Guanghua School of Management Peking University Beijing 100871 China

Cities are the main material processors asso- ciated with industrialization. The development of urban production based on fossil fuels is the major contributor to the rise of greenhouse gas density, and to global warming. The concept of urban industrial structure optimization is considered to be a solution to urban sustainable develop- ment and global climate issues. Enforcing energy con- servation and reducing carbon emissions are playing key roles in addressing these issues. As such, quantitative accounting and the evaluation of energy consumption and corresponding carbon emissions, which are by-products of urban production, are critical, in order to discover potential opportunities to save energy and to reduce emissions. Conventional evaluation indicators, such as ＂energy consumption per unit output value＂ and ＂emissions per unit output value＂, are concerned with immediate consumptions and emissions; while the indirect consump- tions and emissions that occur throughout the supply chain are ignored. This does not support the optimization of the overall urban industrial system. To present a systematic evaluation framework for cities, this study constructs new evaluation indicators, based on the concepts of ＂embodied energy＂ and ＂embodied carbon emissions＂, which take both the immediate and indirect effects of energy consumption and emissions into account. Taking Beijing as a case, conventional evaluation indicators are compared with the newly constructed ones. Results show that the energy consumption and emissions of urban industries are represented better by the new indicators than by conventional indicators, and provide useful information for urban industrial structure optimization.

关键词： embodied carbon emissions embodied energy industrial structure optimization urban economy

Momentum distribution and non-local high order correlation functions of 1D strongly interacting Bose gas

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Chinese Physics B 2018年第7期27卷 138-151页

作者： EJKP Nandani xi-wen Guan Wuhan Institute of Physics and Mathematics Chinese Academy of Sciences Wuhan 430071 China University of Chinese Academy of Sciences Beijing 100049 China Department of Mathematics University of Ruhuna Matara 81000 Sri Lanka Department of Theoretical Physics Research School of Physics and Engineering Australian National University Canberra ACT 0200 Australia

The Lieb-Liniger model is a prototypical integrable model and has been turned into the benchmark physics in theoretical and numerical investigations of low-dimensional quantum systems. In this note, we present various methods for calculating local and nonlocal M-particle correlation functions, momentum distribution, and static structure factor. In particular, using the Bethe ansatz wave function of the strong coupling Lieb-Liniger model, we analytically calculate the two-point correlation function, the large moment tail of the momentum distribution, and the static structure factor of the model in terms of the fractional statistical parameter a = 1 - 2/γ, where γ, is the dimensionless interaction strength. We also discuss the Tan＇s adiabatic relation and other universal relations for the strongly repulsive Lieb-Liniger model in terms of the fractional statistical parameter.

关键词： correlation function momentum distributions structure factor contact

Energy-efficient joint relay node selection and power allocation over multihop relaying cellular networks toward LTE-Advanced

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The Journal of China Universities of Posts and Telecommunications 2011年第3期18卷 1-7页

作者： CHEN Dan ji Hong LI xi College of Information and Communication Engineering Beijing University of Posts and Telecommunications Beijing 100876 China

Cooperative relaying is emerging as an effective technology to fulfill requirements on high data rate coverage in next-generation cellular networks, like long term evolution-advanced （LTE-Advanced）. In this paper, we propose a distributed joint relay node （RN） selection and power allocation scheme over multihop relaying cellular networks toward LTE-Advanced, taking both the wireless channel state and RNs＇ residual energy into consideration. We formulate the multihop relaying cellular network as a restless bandit system. The first-order finite-state Markov chain is used to characterize the time-varying channel and residual energy state transitions. With this stochastic optimization formulation, the optimal policy has indexability property that dramatically reduces the computational complexity. Simulation results demonstrate that the proposed scheme can efficiently enhance the expected system reward, compared with other existing algorithms.

关键词： cooperative relaying LTE-Advanced relay selection power allocation residual energy restless bandit

Artificial Generation of High Harmonics via Nonrelativistic Thomson Scattering in Metamaterial

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Research 2019年第1期2019卷 1155-1164页

作者： Yongzheng wen ji Zhou State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China

High harmonic generation allows one to extend the frequency of laser to a much broader regime and to study the electron dynamics of ***,severely limited by the vague high-order process in natural material and the unfriendly state of the commonly applied gas and plasma media,the ambitious goal of custom-design high harmonics remains exceptionally ***,we demonstrate that high harmonics can be artifcially designed and tailored based on a metamaterial *** the localized reconstruction of magnetic feld in a metamaterial,the nonlinear Tomson scattering,a ubiquitous electromagnetic process which people used to believe that it only occurs with the relativistic velocity,can be stimulated in a nonrelativistic limit,which drives anharmonic oscillation of free electrons and generates high *** explicit physical model and the numerical simulations perfectly demonstrate the artifcial generation and tailoring of the high *** novel mechanism is entirely dominated by the artifcial structure instead of the natural nonlinear *** not only provides unprecedented design freedom to the high harmonic generation but breaks the rigorous prerequisite of the relativistic velocity of the nonlinear Tomson scattering process,which ofers fascinating possibilities to the development of new light source and ultrafast optics,and opens up exciting opportunities for the advanced understanding of electrodynamics in condensed matters.

关键词： relativistic harmonics harmonic

Comparative study on flow and heat transfer characteristics of sinusoidal and zigzag channel printed circuit heat exchangers

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Science China(Technological Sciences) 2020年第4期63卷 655-667页

作者： wen Zhe-xi LV Yi-Gao LI Qing School of Energy Science and EngineeringCentral South UniversityChangsha 410083China

Printed circuit heat exchangers(PCHEs)are promising candidates for recuperators in supercritical CO2 Brayton cycles.A comparative study is given in this paper on the flow and heat transfer characteristics of PCHEs with sinusoidal and zigzag *** mass flow rates of 0.6–1.8 kg/h and the bend angles of 15°–30°,the thermal-hydraulic performance of the PCHEs is *** show that the sinusoidal channel is superior to the zigzag channel in its comprehensive *** bend angles result in greater reductions in pressure drop if sinusoidal channels are used instead of zigzag channels and a maximum of 48.4%reduction can be obtained in the considered working ***,the inlet sections should be carefully optimized since these sections account for up to 31%and 17%of the total pressure drop in the sinusoidal and zigzag channels,*** corner shape of the zigzag channel can be specially designed to further reduce the pressure *** nonuniform density and heat flux distributions in both channels are found to be related to the periodic changes of flow directions and the centrifugal forces should not be ignored when optimizing the sinusoidal and zigzag channels.

关键词： printed circuit heat exchanger supercritical CO2 thermal-hydraulic performance sinusoidal channel numerical simulation