检索结果-南通市图书馆

Load-balance cell association for improving network capacity in heterogeneous cellular networks

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

The Journal of China Universities of Posts and Telecommunications 2014年第3期21卷 56-61,70页

作者： CHEN Lei LI Xi JI Hong LIU Gang School of Telecommunication Engineering Beijing University of Posts and Telecommunications

Heterogeneous cellular networks improve the spectrum efficiency and coverage of wireless communication networks by deploying low power base station （BS） overlapping the conventional macro cell. But due to the disparity between the transmit powers of the macro BS and the low power BS, cell association strategy developed for the conventional homogeneous networks may lead to a highly unbalanced traffic loading with most of the traffic concentrated on the macro BS. In this paper, we propose a load-balance cell association scheme for heterogeneous cellular network aiming to maximize the network capacity. By relaxing the association constraints, we can get the upper bound of optimal solution and convert the primal problem into a convex optimization problem. Furthermore we propose a Lagrange multipliers based distributed algorithm by using Lagrange dual theory to solve the convex optimization, which converges to an optimal solution with a theoretical performance guarantee. With the proposed algorithm, mobile terminals （MTs） need to jointly consider their traffic type, received signal-to-interference-noise-ratios （SINRs） from BSs, and the load of BSs when they choose server BS. Simulation results show that the load balance between macro and pico BS is achieved and network capacity is improved significantly by our proposed cell association algorithm.

关键词： heterogeneous cellular networks load balance cell association Lagrange dual problem

Investigation of the deterioration of passive films in H_2S-containing solutions

在线全文

学校读者我要写书评

暂无评论

International Journal of Minerals,Metallurgy and Materials 2017年第8期24卷 943-953页

作者： Zhu Wang Lei Zhang Xian Tang Zhao-yang Cui Jun-peng Xue Min-xu Lu Institute of Advanced Materials and Technology University of Science and Technology Beijing Safetech Research Institute

The effect of H_2S on the corrosion behavior of 316 L stainless steel was investigated using electrochemical methods by changing the gas condition from CO_2 to H_2S and then back to CO_2. The presence of H_2S showed an acceleration effect on the corrosion of 316 L stainless steel in comparison with CO_2. The acceleration effect remained even after the complete removal of H_2S by CO_2, indicating that the passive film was irreversibly damaged. X-ray photoelectron spectroscopy(XPS) analysis indicated that the passive film was composed of Cr_2O_3, Fe_2O_3, and FeS_2 after being immersed in H_2S-containing solutions. The semiconducting property of the passive film was then investigated by using the Mott–Schottky approach. The presence of sulfides resulted in higher acceptor and donor densities and thus was responsible for the deterioration of passive films.

关键词： stainless steel passive films hydrogen sulfide corrosion

Attitude coordination for spacecraft formation with multiple communication delays

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2015年第2期28卷 527-534页

作者： Guo Yaohua Lu Pingli Liu Xiangdong School of Automation Beijing Institute of Technology

Communication delays are inherently present in information exchange between space- craft and have an effect on the control performance of spacecraft formation. In this work, attitude coordination control of spacecraft formation is addressed, which is in the presence of multiple communication delays between spacecraft. Virtual system-based approach is utilized in case that a constant reference attitude is available to only a part of the spacecraft. The feedback from the virtual systems to the spacecraft formation is introduced to maintain the formation. Using backstepping control method, input torque of each spacecraft is designed such that the attitude of each spacecraft converges asymptotically to the states of its corresponding virtual system. Furthermore, the back- stepping technique and the Lyapunov-Krasovskii method contribute to the control law design when the reference attitude is time-varying and can be obtained by each spacecraft. Finally, effectiveness of the proposed methodology is illustrated by the numerical simulations of a spacecraft formation.

关键词： Attitude coordination Backstepping Delay control systems Formation Lyapunov-Krasovskii

Field corrosion characterization of soil corrosion of X70 pipeline steel in a red clay soil

在线全文

学校读者我要写书评

暂无评论

Progress in Natural Science:Materials International 2015年第3期25卷 242-250页

作者： Shengrong Wang Cuiwei Du Xiaogang Li Zhiyong Liu Min Zhu Dawei Zhang Corrosion and Protection Center Key Lab of Minstry of Education University of Science and Technology Beijing

The corrosion behavior of X70 pipeline steel buried in red soil environment has been studied. The surface morphology and elemental distribution were determined by scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDS), and X-ray diffraction(XRD).The corrosion kinetics was evaluated by weight loss measurement. The results show that in red soil, the corrosion rate of X70 steel decreases with time, and follows the exponential decay law. General corrosion with non-uniform and localized pitting occurred on the steel surface. α-Fe OOH was the dominate products during corrosion in whole buried periods, and the corrosion products exhibited well protective properties. The potentiodynamic polarization tests revealed that icorrdecreased with time, indicating the improvement of corrosion resistance. The results of Electrochemical impendence spectroscopy(EIS) are consistent with potentiodynamic polarization tests.

关键词： X70 steel Soil corrosion Corrosion kinetics Non-uniform corrosion Pitting corrosion

Fully Bayesian reliability assessment of multi-state systems with overlapping data

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Systems Engineering and Electronics 2017年第1期28卷 187-198页

作者： Zhipeng Hao Jianbin Guo Shengkui Zeng Aircraft Airworthiness Institute China Academy of Civil Aviation Science and TechnologyBeijing 100028China School of Reliability and Systems Engineering Beihang UniversityBeijing 100191China Science and Technology on Reliability and Environmental Engineering Laboratory Beijing 100191China

The failure data at the system level are often limited, resulting in high uncertainty to system reliability assessment. Integrating data drawn from various structural levels of the target system (e.g. the system, subsystems, assemblies and components), i.e. the multi-level data, through Bayesian analysis can improve the precision of system reliability assessment. However, if the multi-level data are overlapping, it is challenging for Bayesian integration to develop the likelihood function. Especially for multi-state systems (MSS), the Bayesian integration with overlapping data is even more difficult. The major disadvantage of previous approaches is the intensive computation for the development of the likelihood function caused by the workload to opt the appropriate combinations of the vectors of component states consistent with the overlapping data. An improved fully Bayesian integration approach from a geometric perspective is proposed for the reliability assessment of MSS with overlapping data. In this method, a specific combination of component states is regarded as a state vector, which leads to a specific system state of the MSS, and all state vectors generate a system state space. The overlapping data are regarded as the constraints which create hyperplanes in the system state space. And a point in a hyperplane corresponds to a particular combination of the state vectors. In the light of the features of the constraints, the proposed approach introduces space partition and hyperplane segmentation, which reduces the selection workload significantly and simplifies the likelihood function for overlapping data. Two examples demonstrate the feasibility and efficiency of the proposed approach. © 1990-2011 beijing Institute of Aerospace Information.

关键词： Geometry Integration Reliability Reliability analysis Reliability theory Satellites Vector spaces Vectors

Improved ant colony-based multi-constrained QoS energy-saving routing and throughput optimization in wireless Ad-hoc networks

在线全文

学校读者我要写书评

暂无评论

The Journal of China Universities of Posts and Telecommunications 2014年第1期21卷 43-53,59页

作者： WANG Ya-li SONG Mei WEI Yi-fei WANG Ying-he WANG Xiao-jun School of Electronic Engineering Beijing University of Posts and Telecommunications Chinese Academy of Science Shanghai Institute of Microsystem and Information Technology School of Electronic Engineering Dublin City University

In order to establish a route supporting multi-constrained quality of service（QoS）, increase network throughput and reduce network energy consumption, an improved ant colony-based multi-constrained QoS energy-saving routing algorithm（IAMQER） is proposed. The ant colony algorithm, as one of the available heuristic algorithms, is used to find the optimal route from source node to destination node. The proposed IAMQER algorithm, which is based on the analysis of local node information such as node queue length, node forwarding number of data packets and node residual energy, balances the relationship between the network throughput and the energy consumption, thus improving the performance of network in multi-constrained QoS routing. Simulation results show that this IAMQER algorithm can find the QoS route that reduce average energy consumption and improves network packet delivery ratio under the end-to-end delay and packet loss ratio constraints.

关键词： wireless Ad-hoc networks multi-constrained QoS routing ant colony algorithm energy-saving throughput optimization

A local pseudo arc-length method for hyperbolic conservation laws

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2014年第6期30卷 956-965页

作者： Xing Wang Tian-Bao Ma Hui-Lan Ren Jian-Guo Ning State Key Laboratory of Explosion Science and Technology Beijing Institute of Technology

A local pseudo arc-length method（LPALM）for solving hyperbolic conservation laws is presented in this *** key idea of this method comes from the original arc-length method,through which the critical points are bypassed by transforming the computational *** method is based on local changes of physical variables to choose the discontinuous stencil and introduce the pseudo arc-length parameter,and then transform the governing equations from physical space to arc-length *** order to solve these equations in arc-length coordinate,it is necessary to combine the velocity of mesh points in the moving mesh method,and then convert the physical variable in arclength space back to physical *** examples have proved the effectiveness and generality of the new approach for linear equation,nonlinear equation and system of equations with discontinuous initial ***-oscillation solution can be obtained by adjusting the parameter and the mesh refinement number for problems containing both shock and rarefaction waves.

关键词： Numerical method Local pseudo arc-length method Hyperbolic conservation laws Mesh adaptation

Synthesis and crystal structure of bis (1,3-diisopropyl-4,5-dimethylimidazolium) hexatungstate

在线全文

学校读者我要写书评

暂无评论

Journal of beijing Institute of Technology 2014年第2期23卷 265-269页

作者：马小莉孙帅 School of Chemical Engineering and Environment Beijing Institute of Technology

The title compound bis（1,3-diisopropyl-4,5-dimethylimidazolium） hexatungstate,[C11H21N2]2[W6O19],was synthesized and characterized by single-crystal X-ray diffraction,IR and elemental *** crystallizes in the monoclinic system,space group P21/n with a=1.112 84（14）,b=1.283 84（17）,c=1.293 28（17）nm,β=96.410（2）°,V=1.836 2（4）nm^3,C22H42N4O19W6,Mr=1 769.70,Dc=3.201 g/cm3,F（000）=1 596,Z=2,μ（Mo Kα）=18.797 mm-1,the final R=0.031 3,wR=0.059 8for observed reflections（I〉2σ（I））.

关键词： hexatungstate N-heterocyclic carbenes crystal structure

Inorganic Nanotube/Organic Nanoparticle Hybrids for Enhanced Photoelectrochemical Properties

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2017年第7期33卷 728-733页

作者： Yingzhi Chen Aoxiang Li Ming Jin Lu-Ning Wang Zheng-Hong Huang Key Laboratory of Advanced Materials （MOE） School of Materials Science and Engineering Tsinghua University Beijing 100084 China

Inorganic/organic nanohybrids composed of arrayed TiO_2 nanotubes（Ti NTs）/porphyrin nanoparticles（NPs） have been fabricated via a wet chemical approach. The inorganic component, particularly the arrayed one-dimensional（1D） nanostructures, provides high charge-carrier mobility and rapid charge transport. The organic component exhibits extensive visible light absorption and good solution processability. Additionally, the geometric restraint by supramolecular assembly renders an improved photostability. A combination of these two components could thus allow for an efficient solar energy conversion. In this work, a colloid of porphyrin NPs prepared by a solvent exchange method is coated on anodic Ti NTs by means of a dip-coating treatment to form inorganic/organic hybrids. The hybrids exhibit an improvement on solar absorption and a significant enhancement on photocurrent generation at a small bias compared with individual component. Herein, the inorganic/organic nanohybrids are proved to be excellent photoanodes highly responsive to visible light and thus pave a way to discover new inorganic/organic assemblies for high-performance optoelectronic applications, as well as for device integration.

关键词： Anodic TiO_2 nanotubes Porphyrin nanoparticles Inorganic/organic nanohybrid Photoelectrochemical water splitting