A simulation study of the performances of HDLC controlled links

Among the exchanging link protocols, HDLC is becoming more and more popular. But the standards which define it contain options and parameters to be selected according to the actual environment.A model of the information exchange phase of a balanced HDLC link is presented. The choice of two parameters (the maximum window width and a timer constant) is discussed with the help of simulation results. Information frames are of random length and two types of Supervisory frames are used (RR and REJ). The link has been simulated in saturated and nonsaturated situations with different transmission error rates. P/F checkpointing is not used, line propagation times are neglected.The illustrated performances include the link efficiency and various delays associated with the transmission of Information frames.     

On the estimation of pulmonary blood flow from CO2 production time series

It may be possible to estimate a nominal pulmonary blood flow (Q) during an exercise stress test via the algorithm used to estimate breath-by-breath alveolar CO2 production. Recently it has been demonstrated that by relating breath-to-breath fluctuations in alveolar CO2 production to breath-to-breath fluctuations in end-tidal CO2, an optimizing parameter related to Q can be determined that can be used to process the CO2 production fluctuations and minimize their variation. However, the reported values of Q using this procedure appear to be biased low. Using a computer simulation of gas exchange, we demonstrate that the estimate of Q is biased low when the nominal lung volume used in the alveolar gas exchange algorithm is too large. Furthermore, alveolar CO2 transport is determined by an integral of alveolar CO2 over the breath time and, thus, is a path-dependent quantity. The use of end-tidal CO2 fluctuations to approximate fluctuations in this integral contributes to an error in the estimation of Q which yields estimates that are biased low. Alternatively, the use of mean alveolar CO2 fluctuations yield more appropriate Q estimates. These results suggest practical implications for estimating effective pulmonary blood flow during an exercise stress test by using breath-to-breath estimates of mean alveolar CO2.     

改进的空间网络密钥交换协议

针对空间网络的特点及空间网络对密钥交换的特殊需求,提出一种适用于空间网络的密钥交换协议。该协议以Internet密钥交换协议为基础,通过增加DH循环队列、提高Cookie计算强度的方法增强其抗拒绝服务攻击的能力,给出抵御中间人攻击、选项攻击及反射攻击的修正方法。理论分析表明,该协议具有更高的安全性和较少的交换次数,更适用于空间网络通信环境。     

Urban flood risk analysis for determining optimal flood protection levels based on digital terrain model and flood spreading model

The objective of the paper is to present a new risk-analysis approach for the assessment of optimal flood protection levels in urban flood risk management, which is based on an active contour method. Although the active contour method is a very popular research topic, there has been no attempt made on deriving a model for simulating flooding and inundating to date, as far as we are aware. We have developed a flooding prototype system, which consists of two main parts: a digital terrain model and a flood simulation model. The digital terrain model is constructed using real world measurement data of GIS, in terms of digital elevation data and satellite image data. A pyramidal data arrangement structure is used for dealing with the requirements of terrain details with different resolutions. A new flooding model has been developed, which is useful for urban flood simulation. It consists of a flooding image spatial segmentation based on an active contour model, a water level calculation process, a standard gradient descent method for energy minimisation. When testing the 3D flood simulation system, the simulation results are very close to the real flood situation, and this method has faster speed and greater accuracy of simulating the inundation area in comparison to the conventional 2D flood simulation models.     

The design of a new remote manipulator for space operation using a 4-cable-driven thrusters-embedded configuration

A new remote manipulator based on cable-driven parallel mechanism (CDPM) is designed for space long-distance operations (e.g. space capture/docking and other long-distance space activities) in this paper. By controlling the cables and thrusters which are equipped on the manipulator simultaneously, the new remote manipulator can achieve expected position, linear velocity, and angular velocity. The new manipulator has a larger controllable workspace compared with usual CDPMs. The structure and characteristics of this manipulator are discussed in this paper. The volume and characteristics of the workspace are also discussed. The influence of the distance on the static equilibrium is studied. The simulation results show that the workspace of this new manipulator is larger than usual CDPM’s. The results also indicate that the cable forces and thruster vectors can completely constrain the manipulator and meet the requirements of space activities. The results of the simulation also show that the controllable workspace of the manipulator is not continuous at some regions. Hence, trajectory planning is necessary.     

Loop Parallelization using the 3D Iteration Space Visualizer

A 3D iteration space visualizer (ISV) is presented to analyze the parallelism in loops and to find loop transformations which enhance the parallelism. Using automatic program instrumentation, the iteration space dependency graph (ISDG) is constructed, which shows the exact data dependencies of arbitrarily nested loops. Various graphical operations such as rotation, zooming, clipping, coloring and filtering, permit a detailed examination of the dependence relations. Furthermore, an animated dataflow execution shows the maximal parallelism and the parallel loops are indicated automatically by an embedded data dependence analysis. In addition, the user may discover and indicate additional parallelism for which a suitable unimodular loop transformation is calculated and verified. The ISV has been applied to parallelize algorithmic kernel programs, a computational fluid dynamics (CFD) simulation code, the detection of statement-level parallelism and loop variable privatization. The applications show that the visualizer is a versatile and easy to use tool for the high-performance application programmer.     

Remote-sensing image analysis and geostatistics

The random function theory forms the basis of geostatistics and allows modelling of the uncertainty associated with spatial estimation and simulation. Remote sensing involves gathering information about an object by measuring signals composed of radiation, particles and fields emanating from an object with a sensor that is not in direct contact with it. This article reviews the present state of the art of how geostatistics is used in remote-sensing studies by reviewing the 2000–2010 literature in this field. This article first addresses the issue of stationarity in the context of image analysis and reviews whether this holds as it is a basic assumption of most geostatistical techniques. Ways to relax the assumption are discussed. Following is the use of variograms to quantify image structure and texture, and the use of variograms to address issues of optimal scale of observation. Next, various kriging-based estimation techniques (parametric and non-parametric) and how these can be used to enhance image information, fill missing pixel information and downscale information through super-resolution techniques (e.g. downscaling with preservation of spatial structure at the finer resolution) are discussed. Cokriging techniques are discussed to enable the combination of various variables at different support sizes and to link field and image data. To address issues of uncertainty and to characterize landscape heterogeneity, stochastic simulation techniques are discussed. A bibliometric analysis is presented which places the field of ‘remote sensing and geostatistics’ in a broader geosciences context and explores who are the key scientists and research groups that have contributed to the development of this field. It is concluded that the field of remote sensing and geostatistics has further developed the use of various pre-existing numerical techniques, which has led to new application areas. However, few new geostatistical techniques have been developed for use in remote sensing. In particular, aspects of scale and spatial sampling have been extensively addressed, but issues related to monitoring and space–time analysis have been largely neglected.     

Computer aided model building and CAL

Model building has become an educational objective at the tertiary and the secondary level. There are reservations in regard to the suitability of computer simulations for integrating modelling into the education process. Interactive simulation systems can be designed to meet educational requirements, presenting a preprogrammed simulation environment which only has to be supplied with the model itself. The model can be supplied as a set of statements (“missinglink” program) or as a block diagram representing the structure of the system. Examples are presented for both possibilities and their respective characteristics are discussed.     

Data exchange between distributed spectral databases

Spectral databases constitute one of the components of a complete observing system, storing in situ spectroscopic measurements plus associated metadata and providing data for the validation, calibration, and simulation of imaging spectrometer products. Such databases may be employed by physically or organisationally separate entities. Consequently, methods for data exchange between distributed spectral databases are required, allowing the transfer of defined subsets of spectral data including their full metadata context from a source to a target system. The data exchange comprises generic approaches to the sequential steps of ordered table row export, relational storage in XML files, and nonconflicting import into the target database. The SPECCHIO spectral database system was used as a test bed for the data exchange between databases of identical schemata and according import/export functionality has been added to the SPECCHIO application. Import and export speeds were assessed using test cases of different metadata space densities, a score for the density with which associated metadata are detailed, and the potential utility as a quantitative rating for quality. Future spectral databases should allow the exchange between heterogeneous systems, ideally implementing a common subset of metadata parameters and thus supporting the long-term usability and data sharing between research partners.     

The Study of RAIM Performance by Simulation

1 Introduction Global Positioning System (GPS) is a satellite based navigation system. One concern of GPS users is system integrity, which is the ability of the system to provide timely warnings to users when the system should not be used for navigation. GPS integrity is very important in civil aviation in order to guarantee the flight safety. RAIM is a technique used to provide a measure of the trust which can be placed in the correctness of the information supplied by the total system[…     

Transient analysis of superposed GSPNs

The paper considers transient analysis using randomization for superposed generalized stochastic Petri nets (GSPNs). Since state space explosion implies that space is the bottleneck for numerical analysis, superposed GSPNs profit from the structured representation known for its associated Markov chain. This moves the bottleneck for analysis from space for generator matrices to space for iteration vectors. Hence a variation of randomization is presented which allows to reduce space requirements for iteration vectors. An additional and welcome side effect is that during an initial phase, this algorithm avoids useless multiplications involving states with zero probability. Furthermore, it accommodates to adaptive randomization in a natural way. Although the algorithm has been developed for superposed GSPNs, it applies to continuous time Markov chains in a more general setting     

LabVIEW与PIMS数据接口及应用

本文通过分析虚拟仪器系统开发平台LabVIEW和过程信息管理系统(PIMS)软件的特点,结合实际工程应用,通过DDE(动态数据交换)实现这两种软件间数据接口的方法。该方法是将HART协议智能仪表采集到的数据引入到PIMS系统中,从而和DCS上使用的数据共同进行组态,绕过了开发专用DCS-HART转换卡的不便,扩展了过程信息管理系统组态软件的开发功能。     

基于改进模拟植物生长算法的配电网重构

针对模拟植物生长算法所存在的需遍历搜索区域进行寻优导致计算量太大的问题。将支路交换算法中所用的启发式交换规则与之相结合。提出一种用于配电网重构的改进模拟植物生长算法。所提方法的主要优点,是在保留模拟植物生长算法所具备的全局寻优能力的同时,大大减少每一步计算中所产生的生长点集的数量,因而减少相应的潮流计算、目标函数值计算及形态素浓度计算的次数即计算量．对IEEE33节点系统的计算结果,验证所提方法的有效性。     

CIM algorithm for approximating three-dimensional polygonal curves

The polygonal approximation problem is a primary problem in computer graphics,pattern recognition,CAD/CAM,etc.In R^2,the cone intersection method(CIM) is one of the most efficient algorithms for approximating polygonal curves,With CIM Eu and Toussaint,by imposing an additional constraint and changing the given error criteria,resolve the three-dimensional weighted minimum number polygonal approximation problem with the parallel-strip error criterion(PS-WMN)under L2 norm.In this paper,without any additional constraint and change of the error criteria,a CIM solution to the same problem with the line segment error criterion(LS-WMN)is presented,which is more frequently encountered than the PS-WMN is .Its time complexity is O(n^3),and the space complexity is O(n^2) .An approximation algorithm is also presented,which takes O(n^2) time and O(n) space.Results of some examples are given to illustrate the efficiency of these algorithms.     

A numerical study of floe in Athens area using the MIUU model

The flow regime in Greater Athens Area (GAA) io numerically investigated by a mesoscale, higher-order turbulence closure model. The model is three-dimensional, hydrostatic, and with a terrain following coordinate system. It has been developed at the Department of Meteorology in Uppsala (MIUU).The numerical investigation was performed within the frame of the Athenian Photochemical Smog Intercomparison of Simulations (APSIS) and the day chosen for simulation is May 25, 1990.Although the geostrophic wind was kept constant throughout the simulation period, the simulated wind fields in the lower layers are quite variable both in time as well as in space. The major characteristics of the flow field during day-hours, are identified and discussed.     

无线传感器网络目标跟踪机制的研究与改进

文章对无线传感器网络(WSN)目标跟踪机制进行了研究,针对层次型的WSN,提出一种高效的跟踪机制,包括双层的预测机制,以及泛洪(flooding)扩散的恢复机制,并对这两种机制进行了详细的分析。仿真结果表明,该改进后的目标跟踪机制不仅耗费较少的能量,而且能够获得较高的跟踪精度。     

碰撞检测技术及在桥梁视景仿真中的应用

碰撞检测(Collision Detection)及优化是视景仿真技术中一项非常重要的技术,文中通过对碰撞检测理论的论述,概要介绍了碰撞检测算法关于时间域与空间域的不同分类方法,并讨论如何优化碰撞检测的方法,以减少运算时间与复杂度。通过视景仿真中桥梁碰撞检测的实例对碰撞检测理论及优化算法进行了验证。     

系统参数和状态联合估计

文［１］提出了多变量系统所有参数同时估计的联合辨识算法。本文将讨论系统参数和状态的联合估计算法。其特点是在估计系统参数的同时，可获得系统状态的估计，这为状态反馈设计控制器提供了极大方便。文中还给出了仿真例子。     

传感器网络中基于角度域的洪泛路由算法

针对传感器网络的特点,在洪泛算法的基础上给出了一种基于角度域的路由算法。其基本思想是使洪泛时产生的分组被限制在一个构造的有限角度域中。新算法有效降低了路由开销,而且实现简单。理论分析和仿真结果均表明新算法具有良好的路由性能。     

一种基于BP神经网络的SIP DoS洪泛攻击检测方法

为了检测IMS网络中的SIP洪泛攻击,提出一种基于BP神经网络的洪泛攻击检测方法,并分析产生SIP洪泛攻击的原因,由此确定BP神经网络特征输入量,仿真试验结果表明该方法具有较好的检测性能。