视频会议多点控制单元的MCU设计与实现

多点控制单元(MCU)是基于IP网络的视频会议系统的重要组成部件,可提供多点会议的管理功能。文中介绍多点视频会议的分类,给出了集中型多点视频会议中MCU系统的网络结构和软件设计方法。

集中式多点视频会议控制单元MCU的实现

多点控制单元(MCU)是多点视频会议系统的核心,它提供多点会议的管理和控制功能。本文主要讨论IP视频会议多点控制单元的设计和技术实现,提出并采用了MCU的多点会议控制机制、多路语音的混音处理和多画面合成等技术。采用了事件驱动的多线程机制实现音频处理和多路混音,并在压缩域实现四画面和成。

IP网络视频会议系统中MCU的设计与实现

多点控制单元(MCU)是基于IP网络的视频会议系统的重要组成部件,它提供多点会议的管理功能。文章主要介绍用软件方法设计并实现集中型多点会议形式下的MCU,并给出相应的软件测试结果。

矿井地面生产系统采用660V供电技术探讨

随着大型矿井地面生产系统生产能力的扩大,单台设备的电动机容量也随之增大,提高地面生产系统的电压等级势在必行。本文就地面供电电压等级由380V提高到660V电压技术问题进行探讨。

一起主变保护误动事故的分析与处理

通过一次保护误动原因查找和分析,发现了电气回路存在的问题并对定值商榷,从而纠正了运行中的缺陷,保证电网的安全稳定运行。

An Estimate for Distance Between Adjacent Zeroes of Solutions of Neutral Equations

In this paper, we establish a new estimate for the distance between adjacent zeroes of the solution of the first order neutral differential equation

Model test on vertical bearing capacity of X-section concrete pile raft foundation in silica sand

To reveal the bearing capacity of the X-section concrete piles pile raft foundation in silica sand,a series of vertical load tests are carried out.The X-section concrete piles are compared with circular section pile with the same section area.The load−settlement curves,axial force and skin friction,strain on concave and convex edge of the pile,pile-sand stress ratio,distributions of side and tip resistance are presented.The results show that bearing capacity of the X section concrete pile raft foundation is much larger than that of the circular pile raft foundation.Besides,compared with the circular pile,the peak axial force of X-section piles under raft is deeper and smaller while the neutral point of X-section concrete pile is deeper.Moreover,the strain on the concave edge is much larger than that on the convex edge of the pile,and the convex edge has more potential in bearing capacity as the vertical load increases.The X-section pile has higher pile-sand stress ratios and load-sharing between side resistance and tip resistance.Above all,the X-section concrete pile can significantly increase the bearing capacity of pile-raft foundations in silica sand.

Oscillation in a Class of Neutral Differential Equations with Positive and Negative Coefficients

The oscillatory behavior of neutral differential equation with positive and negative coefficients is investigated by mathematics analysis technique and the fixed point principle. Some sufficient conditions for oscillation of neutral differential equation with positive and negative coefficients are obtained.

A Time-dependent Stochastic Grassland Fire Ignition Probability Model for Hulun Buir Grassland of China

Grassland fire is one of the most important disturbance factors in the natural ecosystems.This paper focuses on the spatial distribution of long-term grassland fire patterns in the Hulun Buir Grassland located in the northeast of Inner Mongolia Autonomous Region in China.The density or ratio of ignition can reflect the relationship between grassland fire and different ignition factors.Based on the relationship between the density or ratio of ignition in different range of each ignition factor and grassland fire events,an ignition probability model was developed by using binary logistic regression function and its overall accuracy averaged up to 81.7%.Meanwhile it was found that daily relative humidity,daily temperature,elevation,vegetation type,distance to county-level road,distance to town are more important determinants of spatial distribution of fire ignitions.Using Monte Carlo method,we developed a time-dependent stochastic ignition probability model based on the distribution of inter-annual daily relative humidity and daily temperature.Through this model,it is possible to estimate the spatial patterns of ignition probability for grassland fire,which will be helpful to the quantitative evaluation of grassland fire risk and its management in the future.

Tas the Lewisian Turning Point Arrived in China？- An Empirical Study of China＇s Dual Economy Transition in Labor Market Based on Data of 284 Cities

Labor shortage and the rise of wages in China have generated heated debate on the arrival of the Lewisian Turning Point. Based on an empirical study of macroeconomic data for 284 prefecture-level cities, this paper argues that the dual economy transition in China involves the coexistence of urbanization, industrialization and open economy. However, China has not yet arrived at the Lewisian Turning Point, because wage gaps between different industries and regions still exist and surplus labor is still being attracted to the labor-intensive manufacturing and tertiary industries in the eastern provinces. External economic shock and the mismatch between industrialization and urbanization are the primary causes of the coexistence of labor surplus and labor shortage.

Soil Fertility Self-development Under Ecological Restoration in the Zhuxi Watershed in the Red Soil Hilly Region of China

Current methods that utilize simple data or models to judge whether soil fertility can selfdevelop are not sufficiently rigorous. A new framework has been set up using catastrophe theory, laboratory experiment, field work, and 3S(Geographic information system, Global positioning system, and Remote sensing) to explore soil fertility catastrophe under ecological restoration, discriminate whether soil fertility can self-develop, and propose adjustment of ecological restoration measures in the Zhuxi watershed of Changting County, Fujian Province, China, which is a typical representative of the red soil hilly region of China. The results show that: 1) the soil fertility is obviously improved through the four ecological restoration measures, which impels soil fertility catastrophe. Among 89 soil samples, catastrophic soil samples and stable soil samples account for 26(29.21%) and 63(70.79%) of the samples, respectively. The four ecological restoration measures are listed in the order lowquality forest improvement > arbor–bush–herb mixed plantation > orchard improvement > closing measures according to the proportions of catastrophic soil samples. A typical soil sample in Bashilihe that can self-develop is selected as the criterion to judge the upper lobe and lower lobe of soil fertility in the process surface of the Cusp catastrophe model. Twenty-six(29.21%) were in the middle lobe, 10(11.24%) were in the upper lobe, and 53(70.79%) were in the lower lobe. The catastrophic direction of 26 catastrophic soil samples is to the upper lobe according to soil and water loss change as well as fieldwork. There is a significant positive correlation of Δ with soil and water loss change, and the lower soil and water loss relates to higher catastrophic probability. 2) Soil fertility self-development could be regionalized as "Soil fertility can self-develop" whose area was 12.74 km2(28.33%) distributed mainly in the leftmost and rightmost parts, "Soil fertility tends to self-develop" whose area was 11.63 km2(25.89%) distributed mainly in the middle part, and "Soil fertility cannot self-develop" whose area was 20.58 km2(45.78%) distributed mainly between the above two types. 3) There is no need to take ecological restoration measures and excessive human interference should be avoided in the future in regions of "Soil fertility can self-develop" and "Soil fertility tends to self-develop," and ecological restoration measures should be taken in region of "Soil fertility cannot self-develop." 4) We suggest withdrawal and implementation of ecological restoration measures should be incorporated into the evaluation criteria of ecological restoration to avoid misuse of funds.

Transient Performance of an Isolated Induction Generator under Unbalanced Loading Conditions

This paper presents a new transient model ofa standalone （isolated） self excited induction generator （SEIG）. This model is based on direct phase quantities and is suitable to study the performance of the generator under any balanced or unbalanced conditions. It includes a general load as well as general excitation capacitor model. The model has the advantage of connecting or disconnecting the neutral points of the generator electrical system with both excitation capacitors and load. Furthermore, a more accurate magnetization curve is used. Moreover, the simulation results have been verified experimentally.

Secure planar convex hull protocol for large-scaled point sets in semi-honest model

Efficiency and scalability are still the bottleneck for secure multi-party computation geometry （SMCG）. In this work a secure planar convex hull （SPCH） protocol for large-scaled point sets in semi-honest model has been proposed efficiently to solve the above problems. Firstly, a novel priva- cy-preserving point-inclusion （PPPI） protocol is designed based on the classic homomorphic encryp- tion and secure cross product protocol, and it is demonstrated that the complexity of PPPI protocol is independent of the vertex size of the input convex hull. And then on the basis of the novel PPPI pro- tocol, an effective SPCH protocol is presented. Analysis shows that this SPCH protocol has a good performance for large-scaled point sets compared with previous solutions. Moreover, analysis finds that the complexity of our SPCH protocol relies on the size of the points on the outermost layer of the input point sets only.

An Iterative Clustering-Based Localization Algorithm for Wireless Sensor Networks

In wireless sensor networks,node localization is a fundamental middleware service.In this paper,a robust and accurate localization algorithm is proposed,which uses a novel iterative clustering model to obtain the most representative intersection points between every two circles and use them to estimate the position of unknown nodes.Simulation results demonstrate that the proposed algorithm outperforms other localization schemes (such as Min-Max,etc.) in accuracy,scalability and gross error tolerance.

Association of upper gastrointestinal symptoms with functional and clinical characteristics in the elderly

AIM： To evaluate the prevalence of upper gastrointestinal symptoms and their association with clinical and functional characteristics in elderly outpatients. METHODS： The study involved 3238 outpatients ≥ 60 years consecutively enrolled by 107 general practitioners. Information on social, behavioral and de- mographic characteristics, function in the activities of daily living （ADL）, co-morbidities and drug use were collected by a structured interview. Upper gastroin- testinal symptom data were collected by the 15-items upper gastro-intestinal symptom questionnaire for the elderly, a validated diagnostic tool which includes the following five symptom clusters： （1） abdominal pain syndrome; （2） reflux syndrome; （3） indigestion syn- drome; （4） bleeding, and （5） non-specific symptoms. Presence and severity of gastrointestinal symptoms were analyzed through a logistic regression model. RESULTS： 3100 subjects were included in the final analysis. The overall prevalence of upper gastrointes- tinal symptoms was 43.0%, i.e. cluster （1） 13.9%, （2） 21.9%, （3） 30.2%, （4） 1.2%, and （5） 4.5%. Upper gastrointestinal symptoms were more frequently re- ported by females （P 〈 0.0001）, with high number of co-morbidities （P 〈 0.0001）, who were taking higher number of drugs （P 〈 0.0001） and needed assistance in the ADL. Logistic regression analysis demonstrated that female sex （OR = 1.39, 95% CI： 1.17-1.64）, dis- ability in the ADL （OR = 1.47, 95% CI： 1.12-1.93）, smoking habit （OR = 1.29, 95% C]： 1.00-1.65）, and body mass index （OR = 1.06, 95% CI： 1.04-1.08）, as well as the presence of upper （OR = 3.01, 95% C]： 2.52-3.60） and lower gastroenterological diseases （OR = 2.25, 95%CI： 1.70-2.97）, psychiatric （OR = 1.60, 95% CI： 1.28-2.01） and respiratory diseases （OR = 1.25, 95% C]： 1.01-1.54） were significantly associated with the presence of upper gastrointestinal symptoms. CONCLUSION： Functional and clinical characteristics are associated with upper gastrointestinal symptoms. A multidimensional comprehensive evaluation may be useful when approaching upper gastrointestinal symp- toms in older subjects.

Combining CLUE-S and SWAT Models to Forecast Land Use Change and Non-point Source Pollution Impact at a Watershed Scale in Liaoning Province, China

Non-point source(NPS) pollution has become a major source of water pollution. A combination of models would provide the necessary direction and approaches designed to control NPS pollution through land use planning. In this study, NPS pollution load was simulated in urban planning, historic trends and ecological protection land use scenarios based on the Conversion of Land Use and its Effect at Small regional extent(CLUE-S) and Soil and Water Assessment Tool(SWAT) models applied to Hunhe-Taizi River Watershed, Liaoning Province, China. Total nitrogen(TN) and total phosphorus(TP) were chosen as NPS pollution indices. The results of models validation showed that CLUE-S and SWAT models were suitable in the study area. NPS pollution mainly came from dry farmland, paddy, rural and urban areas. The spatial distribution of TN and TP exhibited the same trend in 57 sub-catchments. The TN and TP had the highest NPS pollution load in the western and central plains, which concentrated the urban area and farm land. The NPS pollution load would increase in the urban planning and historic trends scenarios, and would be even higher in the urban planning scenario. However, the NPS pollution load decreased in the ecological protection scenario. The differences observed in the three scenarios indicated that land use had a degree of impact on NPS pollution, which showed that scientific and ecologically sound construction could effectively reduce the NPS pollution load in a watershed. This study provides a scientific method for conducting NPS pollution research at the watershed scale, a scientific basis for non-point source pollution control, and a reference for related policy making.

INCENTIVE MECHANISMS FOR TRUSTWORTHY ROUTING BASED ON GAME MODEL OF THE STRATEGIES OF NODES IN P2P NETWORKS

The trustworthiness and security of routing in the existing Peer-to-Peer (P2P) networks can not be ensured because of the diversity of the strategies of P2P nodes. This paper firstly uses game theory to establish game model of the strategies and profits of various types of routing nodes. Then,two incentive mechanisms for the corresponding stages of P2P trustworthy routing are proposed,namely trust associated mechanism and trust compensated mechanism. Simulation results show that the incentive mechanisms proposed in this paper will encourage cooperation actions of good nodes and restrain malicious actions of bad nodes,which ensure the trustworthiness of routing consequently.

Model predictive control of three-level active front-end converter with low switching frequency

In medium voltage-high power(MV-HP)applications,the high switching frequency of power converter will result in unnecessary energy losses,which directly affect efficiency.To resolve this issue,a novel finite control set-model predictive control(FCS-MPC)with low switching frequency for three-level neutral point clamped-active front-end converters(NPC-AFEs)is proposed.With this approach,the prediction model of three-level NPC-AFEs is established inα-βreference frame,and the control objective of low average switching frequency is introduced into a cost function.The proposed method not only achieves the desired control performance under low switching frequency,but also performs the efficient operation for the three-level NPC-AFEs.The simulation results are provided to verify the effectiveness of proposed control scheme.

MODELING THE IMPACT OF VOLUNTARY TESTING AND TREATMENT ON TUBERCULOSIS TRANSMISSION DYNAMICS

A deterministic model for evaluating the impact of voluntary testing and treatment on the transmission dynamics of tuberculosis is formulated and analyzed. The epidemio- logical threshold, known as the reproduction number is derived and qualitatively used to investigate the existence and stability of the associated equilibrium of the model system. The disease-free equilibrium is shown to be locally-asymptotically stable when the reproductive number is less than unity, and unstable if this threshold parameter exceeds unity. It is shown, using the Centre Manifold theory, that the model undergoes the phenomenon of backward bifurcation where the stable disease-free equilibrium co- exists with a stable endemic equilibrium when the associated reproduction number is less than unity. The analysis of the reproduction number suggests that voluntary tuber- culosis testing and treatment may lead to effective control of tuberculosis. Furthermore, numerical simulations support the fact that an increase voluntary tuberculosis testing and treatment have a positive impact in controlling the spread of tuberculosis in the community.