检索结果-南通市图书馆

Optimal user scheduling and power control in multi-user cognitive broadcast systems

Science china(Information Sciences) 2012年第6期55卷 1402-1414页

作者： WANG QunHuan 1,2,3,WANG HuiMing 1,2,3 & YIN QinYe 1,3 1 School of Electronic and Information engineering,xi'an jiaotong university,xi'an 710049,china 2.state key Lab for Integrated Services Networks,xidian university,xi'an 710071,china 3 Ministry of Education key Lab for Intelligent Networks and Network Security,xi'an jiaotong university,xi'an 710071,china. 1. School of Electronic and Information engineering Xi’an Jiaotong University Xi’an 710049 China2. State Key Lab for Integrated Services Networks Xidian University Xi’an 710071 China3. Ministry of Education Key Lab for Intelligent Networks and Network Security Xi’an Jiaotong University Xi’an 710071 China

Cognitive radio systems should not only have the ability to sense and exploit "frequency spectrum holes",but also the ability to sense and utilize "spatial spectrum holes".In this paper,we consider the issue of maximizing the throughput of the cognitive systems by fully utilizing "spatial spectrum holes" brought in by multiple cognitive users,in the scenario where a pair of licensed users and a cognitive broadcast system share multiple spectrum *** exploiting the channel reciprocity under the premise that the licensed system adopts the time-division-duplexing (TDD) mode,we propose a more practical cognitive access scheme that can sense the interference at the licensed user caused by the cognitive transmitter,based on the existing feedback signals from the licensed user to the licensed base *** both interferences from the licensed base station to the cognitive receiver and from the cognitive transmitter to the licensed user into consideration,we investigate the optimal user scheduling and power allocation scheme that can maximize the ergodic sum rate of the cognitive *** show that scheduling the user whose channel gain to interference and noise ratio (CGINR) is the largest for each frequency band is *** also derive the dynamic power allocation scheme meeting the three practical constraints,i.e.,the transmitter's average transmission power constraint,the power amplifier's instantaneous transmission power constraint,and the interference power constraint at the licensed *** result shows that in different coherent time intervals and different frequency bands,the power allocation has a multi-level waterfilling *** analysis shows that the strategy scheduling user with the largest CGINR introduces significant performance improvement compared with the traditional strategy scheduling user with the largest channel gain to noise ratio (CGNR).We also illustrate the impact of power constraints and the number of users on system p

关键词： cognitive radio distributed spatial spectrum holes opportunistic scheduling power allocation

来源：

同方期刊数据库评论

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Economical Quadrupedal Multi-Gait Locomotion via Gait-Heuristic Reinforcement Learning

引用

Journal of Bionic engineering 2024年第4期21卷 1720-1732页

作者： Lang Wei Jinzhou Zou xi Yu Liangyu Liu Jianbin Liao Wei Wang Tong Zhang School of power and Mechanical engineering Wuhan UniversityLuojiashanWuhan430072HubeiChina state key laboratory of Information engineering in Surveying Mapping and Remote SensingWuhan UniversityLuojiashanWuhan430072HubeiChina

In order to strike a balance between achieving desired velocities and minimizing energy consumption,legged animals have the ability to adopt the appropriate gait pattern and seamlessly transition to another if *** ability makes them more versatile and efficient when traversing natural terrains,and more suitable for long *** the same way,it is meaningful and important for quadruped robots to master this *** achieve this goal,we propose an effective gait-heuristic reinforcement learning framework in which multiple gait locomotion and smooth gait transitions automatically emerge to reach target velocities while minimizing energy *** incorporate a novel trajectory generator with explicit gait information as a memory mechanism into the deep reinforcement learning *** allows the quadruped robot to adopt reliable and distinct gait patterns while benefiting from a warm start provided by the trajectory ***,we investigate the key factors contributing to the emergence of multiple gait *** tested our framework on a closed-chain quadruped robot and demonstrated that the robot can change its gait patterns,such as standing,walking,and trotting,to adopt the most energy-efficient gait at a given ***,we deploy our learned controller to a quadruped robot and demonstrate the energy efficiency and robustness of our method.

关键词： Legged robots Deep reinforcement learning Central pattern generator Quadrupedal gait

来源：

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Simulation on the Melt flow in Laser Full Penetration Welding with a Model Including a Non-Rotational Symme-try keyhole Based on Energy Balance

引用

稀有金属材料与工程 2011年第S4期40卷 120-124页

作者： Zhang L J1,Zhang J X1,Wu B1,2,Chen L2,Gong S L2,Wang H R3 1 state key laboratory of Mechanical Behavior for Materials,xi’an jiaotong university,xi’an 710049,china2 power Beam Processing Dept.,Avic Beijing Aeronautical Manufacturing Technology Research Institute,Beijing 100024,china3 School of Energy and power engineering,xi’an jiaotong university,xi’an 710049,china xi An Jiao Tong Univ Sch Energy & Power Engn Xian 710049 Peoples R China xi An Jiao Tong Univ State Key Lab Mech Behav Mat Xian 710049 Peoples R China Avic Beijing Aeronaut Mfg Technol Res Inst Power Beam Proc Dept Beijing 100024 Peoples R China

A three dimensional model including a non-rotational symmetry keyhole of which the geometry is calculated base on the energy balance at keyhole wall is created to simulate the heat transfer and fluid flow within the molten pool during laser full penetration welding of titanium alloy *** order to take into account the effects of multiple reflections within the keyhole,a ray tracing method is employed and the coordinate dependent heat flux obtained is exerted on keyhole wall during the simulation on the heat transfer and fluid flow within molten ***,the computed weld cross sectional profile is compared with the experimental result to verify the model and it is fond that the simulation result is consists with experimental result.

关键词： laser welding titanium alloy non-rotational symmetry keyhole simulation

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

铜钼基硫氧化物催化剂及其光催化产氢性能

引用

太阳能学报 2009年第10期30卷 1331-1334页

作者：梁慧荣郭烈锦西安交通大学动力工程多相流国家重点实验室西安710049

以[NH_4]_2MoS_4和CuCl为原料,合成了一系列铜钼基硫氧化物催化剂,并利用X射线衍射(XRD),UV-Vis漫反射光谱、X射线荧光(XRF)等化学物理手段对其进行了表征,制备的催化剂对光表现出较强的吸收特性,同时研究了该系列催化剂在可见光条件下... 详细信息

以[NH_4]_2MoS_4和CuCl为原料,合成了一系列铜钼基硫氧化物催化剂,并利用X射线衍射(XRD),UV-Vis漫反射光谱、X射线荧光(XRF)等化学物理手段对其进行了表征,制备的催化剂对光表现出较强的吸收特性,同时研究了该系列催化剂在可见光条件下的光催化制氢性能,并考察了反应温度和反应时间对催化剂产氢活性的影响。结果表明,在140℃条件下水热24h合成的催化剂制氢性能最好,平均产氢速率为10.7μmol/h·g。

关键词：硫氧化物催化剂产氢

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Simulation of flow across complicated domain between tube bundles by the discrete vortex method

引用

Progress in Natural Science:Materials International 2003年第3期 55-60页

作者： CHEN Bin, GUO Liejin and YANG xiaogang(state key laboratory of multiphase flow in power engineering, xi’an jiaotong university, xi’an 710049, china) state key laboratory of multiphase flow in power engineering Xi'an J iaotong University Xi'an 710049 China

On the basis of the anaysis of wrical simulation methods for the complicated domain between tube bundles, an im-proved Lagragian discrete vortex method (DVM) and corresponding algorithm are put forward to solve the practical difficulties of flowacross tube bundles. With this method the amount of vortices can be reduced considerably, which makes quick calculation possible. Ap-plied to the practical configuration of horizontal tube bundles, the DVM simulation is carried out and compared with the experimental re-sults. Both the transient flow field and the profile of mean velocity and fluctuations are in good agreement with experimental results, whichindicate that the DVM is suitable for the simulation of single-phase flow across tube bundles.

关键词： tube bundles discrete vortex method numerical simulation.

来源：

同方期刊数据库评论

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Observation and verification of surface electrical explosion driven by radial-distributed pulsed current in laboratory lightning strike test

引用

High Voltage 2024年第1期9卷 137-149页

作者： Ruoyu Han Yuchen Cao Yakun Liu xi Chen Ting Li Chen Li Pengfei Li state key laboratory of Explosion Science and Technology Beijing Institute of TechnologyBeijingChina School of Mechatronical engineering Beijing Institute of TechnologyBeijingChina Department of Electrical engineering Shanghai Jiaotong UniversityShanghaiChina Beijing Institute of Astronautical System engineering BeijingChina Aerospace Research Institute of Materials and Processing Technology BeijingChina

The laboratory lightning test is essential for assessing the effectiveness of lightning strike protection(LSP).Particularly,direct lightning strike damage can be performed with pulsed current injection into the *** paper focuses on the dynamic process of arc plasma and shock wave behaviour in the vicinity of the‘strike’point.A rod-plate discharge load is built for testing aluminium and coated plate under 40-kA-level pulsed *** visualisation of the luminous discharge plasma and its flow field via high-speed photography(from different angles)is meticulously designed and implemented,synchronised with electro-physical *** results indicate some new mechanisms for lightning strike damage,apart from the impulse heat loading from the thermal *** transient current injection through the arc root concentrates on a thin skin layer(skin-depth effect),with the radial-attenuated current density,driving asynchronously electrical explosions on the plate *** inhomogeneous Joule heating of the plate leads to outwardly propagating phase transition and shock wave along the conductive *** addition,the electro-thermal instability is observed and regarded as the seed of irregular erosion *** information reveals two different plasma states of main discharge arc channel and adjacent surface electrical *** correspondence of the physical mechanism of electrical explosion and optical radiation is *** images for different regions depict erosion characteristics and summarise influencing factors,further confirming the mechanism *** research clarifies the role of skin-depth effect in transaction arc erosion for electrode,complements the electrical explosion theory with unevenly distributed current and helps optimise strategies of LSP.

关键词： electrical lightning radial

来源：

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Nitrogen isotopic composition of plant-soil in the Loess Plateau and its responding to environmental change

引用

Chinese Science Bulletin 2009年第2期54卷 272-279页

作者： LIU WeiGuo1,2 & WANG Zheng1,3 1 state key laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, xi’an 710075, china 2 xi’an jiaotong university, School of Human Settlement and Civil engineering, xi’an 710049, china 3 Graduate university of Chinese Academy of Sciences, Beijing 100049, china Chinese Acad Sci Inst Earth Environm State Key Lab Loess and Quaternary Geol Xian 710075 Peoples R China.

The nitrogen isotope of soil is of emerging significance as an indicator of climatic change and biogeochemical cycle of nitrogen in nature systems. In this paper, the nitrogen content and isotopic composition of modern ecosystems from arid and semiarid Loess Plateau in northwestern china, including plant roots and surface soil, were determined to investigate trends in δ15N variation of plant roots and soil along a precipitation and temperature gradient in northwestern china under the East Asian Monsoon climate condition. The δ15N values of surface soil from the study area vary from ?1.2‰ to 5.8‰, but from -5.1‰ to 1.9‰ in the plant roots. Our results indicate that (1) although the isotopic compositions of both plant roots and surface soil change with a similar trend along the climate gradient, the apparent nitrogen difference between plant roots and soil existed, with -δ15N values ranging from 0.3‰ to 7.2‰ with average of 4.1‰; and (2) mean annual precipitation (MAP) is the dominant factor for isotopic composition of plant-soil nitrogen in the Loess Plateau, and the δ15N values are less correlated with MAT; we suggest that nitrogen isotopic composition of soil is a potential tracer for environmental changes.

关键词：氮同位素物理性质化学性质环境论

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A mathematical model and numerical simulation of pressure wave in horizontal gas-liquid bubbly flow

引用

Progress in Natural Science:Materials International 2004年第4期 58-63页

作者： HUANG Fei, BAI Bofeng and GUO Liejin(state key laboratory of multiphase flow in power engineering, xi’an jiaotong university, xi’an 710049, china) statekeylaboratoryofmultiphaseflowinpowerengineering Xi＇anJiaotongUniversityXi＇an710049China

By using an ensemble-averaged two-fluid model, with valid closure conditions of interfacial momentum exchange due to virtual mass force, viscous shear stress and drag force, a model for pressure wave propagation in a horizontal gas-liquid bubbly flow is proposed. According to the small perturbation theory and solvable condition of one-order linear uniform equations, a dispersion equation of pressure wave is induced. The pressure wave speed calculated from the model is compared and in good agreement with existing data. According to the dispersion equation, the propagation and attenuation of pressure wave are investigated systemically. The factors affecting pressure wave, such as void fraction, pressure, wall shear stress, perturbation frequency, virtual mass force and drag force, are analyzed. The result shows that the decrease in system pressure, the increase in void fraction and the existence of wall shear stress, will cause a decrease in pressure wave speed and an increase in the attenuation coefficie

关键词： pressure wave two-fluid model gas-liquid bubbly flow dispersion speed attenuation.

来源：

同方期刊数据库评论

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

A MODEL FOR LIQUID SLUG LENGTH DISTRIBUTION IN VERTICAL GAS-LIQUID SLUG flow

引用

Journal of Hydrodynamics 2009年第4期21卷 491-498页

作者： xiA Guo-dong CUI Zhen-zhen LIU Qing ZHOU Fang-de HU Ming-sheng College of Environmental and Energy engineering Beijing University of Technology Beijing 100124 China state key laboratory of multiphase flow in power engineering Xi＇an Jiaotong University Xi＇an 710049 China

The slug length and the trailing Taylor bubble velocity in an upward vertical slug flow were measured by using the optical probes and the EKTAPRO 1000 high speed motion analyzer. The correlation between the trailing bubble velocity and the length of liquid slug ahead of that bubble is derived from the experimental data. Based on this correlation as well as the bubble overtaking mechanism, a model for the slug length distribution at any designated locations along the pipe is proposed. The predicted results are in agreement with the experimental data.

关键词： gas-liquid two-phase flow slug flow Taylor bubble liquid slug

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A NUMERICAL PRESSURE TRANSIENT MODEL FOR MULTILAYERED GAS RESERVOIRS WITH PSEUDOSTEADY state FORMATION CROSSflow

引用

Journal of Hydrodynamics 2002年第2期14卷 71-77页

作者： Sun He-dong, Wang Yue-she, Zhou Fang-de state key laboratory of multiphase flow in power engineering, xi’an jiaotong university, xi’an 710049, china Gao Cheng-tai xi’an Petroleum Institute, xi’an 710065, china Zhao Hai-hong china Oil and Gas Pipel state key laboratory of multiphase flow in power engineering Xi'an Jiaotong University Xi'an 710049 China xi'an Petroleum Institute Xi'an 710065 China china Oil and Gas Pipeline Scientific Research Institute Langfang 065000 China

Reservoir deposition occurs over geologic periods of time. Although reservoirs are assumed to be homogenous for simplicity of analysis, most reservoirs are heterogeneous in nature. Some common forms of hetergeneity are the presence of layers and the presence of different zones of fluids and/or rock in the formation. A modified semi-permeable model for multi-layered gas reservoirs with pseudo-steady state interlayer crossflow was developed. The model accounted for the effect of skin and wellbore storage, considers all layers open to a single well, which flows at constant total rate. This new numerical solution was proved to be computationally very efficient, and it has been validated by comparing the results with those of some simple, well known models in the well testing literature. The effects of the reservoir parameters such as permeability, vertical permeability, skin, wellbore storage on the wellbore response, pressure and layer production rate were investigated. Numerical solutions of the problem for the modified semi-permeable model were used to find the structure of crossflow in typical cases.

关键词： layered reservoir semi-permeable model transient well testing numerical simulation crossflow

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

欢迎您,

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案：

请选择收藏分类：

通借通还

欢迎您,

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：