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2006 Vol. 32, No. 04

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Volterra series based transonic unsteady aerodynamics modeling
Wu Zhigang, Yang Chao
2006, 32(04): 373-376.
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To implement aeroservoelastic analysis and synthesis in transonic flow, an approach for transonic unsteady aerodynamics modeling by applying Volterra series theory is presented. Based on the assumption of small perturbation, transonic unsteady aerodynamics can be expressed approximately as one-order Volterra series. Using the unsteady aerodynamics step responses due to the structural deformation calculated by CFD(computation fluid dynamics) technique, the Volterra kernels are determined, and the generalized unsteady AIC(aerodynamics influence coefficients) in frequency-domain are obtained. Then the aeroelastic state-space model is built by rational function approximation. To validate the transonic aerodynamics modeling, flutter analysis of a swept wing is executed by the Volterra series approach and is compared with other methods. The results show the aerodynamics model educed by the Volterra series approach can reflect the features of transonic aerodynamics. The Volterra series approach coincides with the CFD-CSD(computation fluid dynamics-computation structure dynamics) method in flutter analysis.
IPACS modeling and dynamical analysis of a flexible spacecraft
Zhang Jun, Xu Shijie
2006, 32(04): 377-381.
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The dynamical equations of a flexible spacecraft with VSCMGs (variable speed control moment gyroscopes) are established via the Lagrange equations in terms of quasi-coordinates and the momentum theorem. The equations are suitable for both attitude control law design and VSCMGs steering law design. Singularity may occur when VSCMGs are used for attitude control and energy storage, which is avoided effectively via momentum management and configuration design of VSCMGs. The dynamical coupling between the IPACS (integrated power/attitude control system) and vibration of flexible spacecraft with VSCMGs is analyzed. The numerical simulation for a large-scale flexible spacecraft with IPACS is carried out. The simulating results show, when either the torque axes of VSCMGs are near singularity (or enter singularity) or the power is conversed, that the motion of VSCMGs markedly influences flexible appendages.
Particle simulation of ion thruster optical system based on PIC method
Liu Chang, Tang Haibin, Gu Zuo, Jiang Haocheng
2006, 32(04): 382-386.
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The plasma particle simulation of ion thruster optical system was carried out by the PIC (particle-in-cell) method. PIC method is an efficient method in plasma particle simulation, in which the SOR(successive over relaxation) method was adopted to calculate the electric field and the leap-frog method was adopted to accelerate the particles. Xenon was used as propellant and only singly charged Xenon ions was included in the simulation. The simulation results include the distribution of the electric potential between the grids and distribution of the electric field strength, and also the distribution of Xenon ion number density. The simulation results show that under the electrical parameters and the geometric parameters used, the ion beam can get across the grid aperture, with no hits on the grid wall. The simulation of the optical system provided an efficient method to analyze the characteristic of the grid erosion and to evaluate the life time of an ion thruster.
Adaptive local time step method for DSMC code
Du Yongle, Yan Chao
2006, 32(04): 387-390.
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Theoretic analysis reveals that, ALTS(adaptive local time step) method offered by Laux, although greatly reducing the execution CPU time needed for the flow to reach to a steady state and thus leading to high simulation efficiency of DSMC(direct simulation of Monte Carlo) method codes, has some drawbacks in complicating molecules’ moving and collision calculations and in requiring additional RAM. Modifications were made to time intervals at which molecular moving and collision are computed, and to the collision sampling method. These modifications simplified molecules’ moving and collision computation, and also avoid the consumption of unnecessary RAM. The modified ALTS method was adopted in the DSMC code. Simulations of rarefied gas flow over a cylinder were performed with and without this modified ALTS method, and the result shows that these modifications result in a significant reduction in the execution CPU time, but introduce little difference on the simulation resolution and the flow structure.
New algorithm of processing multi occultation and its application in infrared radiation calculation of military helicopter
Chen Haitao, Bian Enrong
2006, 32(04): 391-394.
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To solve the problem of calculating visible net area under any direction in infrared radiation calculation for military helicopter, a new algorithm based on stochastic simulation was proposed. By using surface modeling method, the helicopter's three-dimensional model was constructed and discretilized into quad surface elements. The mathematic model for helicopter was represented with the winged-edge structure. Visibility test, depth test and shelter test were applied to find out all the other polygons that have occultation relationship with the researched spatial polygon, then put them into a set. The statistics method of random variable was introduced subsequently to calculate the net area of this polygon. The calculation results of certain military helicopter and simple object show that the percentage error for simple object can be controlled within 5%, and for complex object can meet the engineering requirement by controlling the total polygons and random points reasonably. The algorithm has been used successfully in the calculation software of military helicopter 's infrared radiation. Applications show that the algorithm is stable, reliable and suitable for engineering analyses.
Noise density research in the system-modeling of RF receivers
Wang Qiong, Su Donglin, Xie Shuguo, Dai Fei
2006, 32(04): 395-398.
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A new method of noise analysis in RF (radio frequency) receivers is provided when the system modeling is required while only some limited parameters of the whole RF system are known. The analysis procedure of AWGN(additive white Gaussian noise) through noisy linear circuits is given in detail using the theory of equivalent computation of noise power density. Take a communication station as an example for noise computation and system modeling. Noise parameters of each component such as noise figure in the RF receiver are derived in the condition of limited system parameters of the receiver including SNR (signal noise ratio), sensitivity, RF gain etc. Modeling and simulation are carried out to validate the analysis method and fair agreement between the theoretical and simulated results is obtained. This equivalent computation method of noise power density has a good instructional meaning to noise analysis and proper system modeling of RF receivers.
Series microscopy images fusion based on area wavelet transform
Jiang Zhiguo, Han Dongbing, Xue Bindang, Zhou Xiaokua
2006, 32(04): 399-403.
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Digital image fusion technique based on multi-focus series microscopy images is an effective method to extend the depth of focus. In order to avoid the blocking effect of fused image by spatial domain fusion algorithm when large focusing step is chosen or the image samples are transparent, a series microscopy images fusion algorithm based on area wavelet transform is proposed. Considering the fact that neighboring pixels are related and wavelet transform has the multi-resolution merit, fusion strategies are as follow: fusion operators are different corresponding to different frequency region, and fusion process is based on region coefficients of wavelet transform. Meanwhile, the influences of different wavelet bases on performance of fusion are investigated. Experimental results show that the blur is improved in obtained fused image and the blocking effect is eliminated. The fusion performance of this method is satisfactory.
Product spectrum based target recognition using high resolution radar range profiles
Guo Zunhua, Li Shaohong
2006, 32(04): 404-406.
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To solve the problem of classifying the aircrafts using high resolution radar range profiles, the product spectrum which was used in the speech signal processing community was introduced to the radar target recognition community. The product spectrum was defined as the product of the power spectrum and the group delay, this feature combined the information contained in the magnitude spectrum and the phase spectrum of the range profiles and carried more information about the shape of the aircrafts. A multi-layered feed-forward neural network with resilient propagation (RPROP) algorithm was selected as classifier. The range profiles were obtained by step-frequency technique using the two-dimension backscatters distribution data of four different aircraft models. Simulations were presented to evaluate the classification performance with the product spectrum features. The results show that the product spectrum based features can yield good performance even in noisy conditions for the application of radar target recognition.
Analysis of frequency stability of atomic clock under sinusoidal vibration
Cao Yu, Lü Shanwei, Feng Keming, Dang Qun
2006, 32(04): 407-411.
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Vibration effects on the atomic clock(atomic frequency standard) could be divided into three parts: atomic resonance effects, crystal oscillator effects and servo-loop effects. Within the vibration frequency, the phase noise of crystal oscillator under sinusoidal vibration was only related to acceleration sensitivity, peak acceleration and vibration frequency, and it has no concern with the phase noise in the static state. But above the vibration frequency, the phase noise of crystal oscillator was the same with the value in the static state. By the frequency stability transfer formulas from the atomic clock to crystal oscillator, vibration effects on crystal oscillator was combined with vibration effects on the atomic clock through servo loop. For computing Allan variance directly from integral equation of phase noise, the several analysis formulas were derived by residue theorem. With increased servo loop bandwidth, vibration effects on frequency stability of the atomic clock can be controlled effectively. Two other methods are analyzed to improve the performance of the atomic clock under vibration: reducing vibration frequency and choosing crystal oscillator with smaller acceleration sensitivity.
Application of periodical structure in millimeter waveguide coaxial connecter
Zhou Yan, Su Donglin
2006, 32(04): 412-416.
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Waveguide coaxial connecter has been playing a very important role in microwave & millimeter-wave communications and tests. On the basis of the effects of PBG(photonic band-gap) structure and step impedance conversion structure in transmitting electromagnetic wave system, a novel waveguide coaxial connecter for 8mm has been discussed and studied based on above two structures, the 2D air column structure in dielectric support cushion depress the dissipation of electromagnetic wave in coaxial structure, at the same time, the step impedance conversion structure improve the performance of waveguide to coaxial port, these two conversion structures in designing of 8 mm waveguide coaxial connecter. Simulations and measurement accuracy proved that this structure has the capability of improving the communication performance of millimeter waveguide coaxial connecter and reducing VSWR(voltage standing wave ratio) at a very wide frequency band without additional components used for tuning.
Novel autofocus algorithm based on DCT for SAR images
Ma Lun, Liao Guisheng
2006, 32(04): 417-420.
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A novel autofocus algorithm for SAR(synthetic aperture radar) images is presented, which is based on DCT(discrete cosine transform). The method, which starts with complex phase-degraded SAR image, after phase errors model is introduced into the range-compressed phase-history domain, carries out phase errors correction by changing the focus until the intensity of the weight function of the azimuth profile in the area of high sequencies is maximized. Compared with the PGA autofocus algorithm, this autofocus algorithm needs not isolate prominent point target in image domain and is especially suitable for the images without specific characteristic. This autofocus algorithm is of less computational complexity and easy to implement, because there are fast algorithms for DCT. The simulation and the processing results of the measured data show the validity of the proposed method.
Filter wheel device in solar X-EUV image telescope
Zhang Xin, Su Donglin, Li Baoquan, Wei Fei
2006, 32(04): 421-425.
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The solar X-EUV(X rays-extreme ultraviolet) imaging telescope is a solar shortwave imaging instrument, which can be used to monitor the solar activities and predict space weather. The solar X-EUV imaging telescope operates in the 0.4~10 nm X-ray waveband and the 19.5 nm EUV wavelength, and it can provide the high resolving solar full-disk. The filter wheel is an important part of the solar X-EUV imaging telescope, which can expand the dynamic range of responses, redound to reconstruct the plasma parameters from which different solar activities can be analyzed. Low power consumption is one characteristic of the movement control of the filter wheel, which needs to satisfy the special requirement of space application. In addition, it is the emphasis to develop a method to maintain the accurate position of step motor. There are two types of PECM(photoelectric coding matrix) that can be used to detect positions. And then, one of the types is adopted which is realizable in practice. Furthermore, form the point of view of functional reliability, the failure mode analysis of PECM is performed and the correspondent solution is provided.
Microwave imaging by scattering
Li Liang, Miao Jungang, Jiang Yuesong, Li Zhiping
2006, 32(04): 426-429.
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A microwave imaging method, which can be applied in detection of concealed weapons and contraband and security in public situations, is presented. In the method, the radar scans on a rectangular plane, i.e. synthesizing a rectangular planar aperture.Synthetic aperture processing for radar data can improve resolutions of the image and the detecting ability of radar. The system can be quasi-monostatic and only a monochromatic microwave is required to illuminate the target to be imaged. Utilizing the phase and amplitude information recorded over a two-dimensional(2-D) aperture can reconstruct a focused 2-D image of the target. A fully 2-D image-reconstruction algorithm, which can be applied in near-field, is developed and deduced. The processing results of simulation and measurement data show that the image-reconstruction algorithm can produce a microwave image with high spatial and radiation resolutions, and has the ability to detect in range without three-dimensional imaging.
Fault injection system design based on BIT
Zhang Xiaojie, Wang Xiaofeng, Jin Man
2006, 32(04): 430-434.
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With the deep research and comprehensive application of BIT(built-in test), exigent demands for the validation and estimate have been brought forward, and this field becomes a new focus on research. Testing the performance of BIT through fault-injection is an effective method to validate its testing level. Based on integrating the relevant domestic and foreign materials, the importance, imminence and practicality of the validation and evaluation of BIT have been analyzed in detail. The design and implementation of fault injection system have been particularly expatiated. Then the block diagram of gross structure, relation diagram of each mold in the system and working process chart of the system implementation have been presented. On the basis of the design and performance of hardware/software, primary experiment of BIT validation had been processed; a certain quantity of fault was injected into tested circuit in order to verify the validity. The result of experiment indicates that the system of fault-injection can suffice the request of BIT design.
SAR imaging formation and geometric correction method based on diving model
Sun Bing, Zhou Yinqing, Chen Jie, Li Chunsheng
2006, 32(04): 435-439.
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The squint SAR(synthetic aperture radar) high resolution imaging formation and geometric correction method based on the diving model were studied. The general three-dimensional geometric model was founded based on the SAR movement mode. The equivalent squint range model was derived from this general geometric model and the echo signal expression was given based on this range model. According to the signal's characteristic, burst work mode was adopted in diving SAR, and a modified ECS(extended chirp scaling) imaging algorithm was utilized to form high resolution image. The imaging formation flow chart and four ECS phase compensation factors were presented. According to the range equation and Doppler positioning equation, geometric correction calculating expressions corresponding to ECS algorithm were derived. The computer simulation results illuminated that the modified ECS algorithm could be used to form high resolution image for diving model SAR and squint SAR, also geometric distortion could be calibrated with this correction method.
Multi-channel Chirp Scaling algorithm for high-resolution multi-channel antenna space-borne SAR imaging
Wang Pengbo, Zhou Yinqing, Chen Jie, Li Chunshen
2006, 32(04): 440-444.
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Based on the analysis of the limitation that exists in the traditional imaging algorithms when processing the echo of high resolution multi-channel antenna space-borne SAR(Synthetic Aperture Radar), a novel MCCS(multi-channel Chirp Scaling algorithm) for high resolution multi-channel antenna space-borne SAR imaging is developed. The algorithm uses a filter banks to realize the conversion fromthe echo of high resolution multi-channel antenna space borne SAR to the echo of strip map SAR. When the filter banks are designed properly, the conversion is strictly equivalent. the ambiguity that caused by inadequately sampling can be completely avoided, and the dependence on DPC(displaced phase center) equivalent condition can be completely removed. But when using the traditional imaging algorithms, the DPC equivalent condition should be strictly satisfied. Then using the Chirp Scaling principle to accomplish imaging, and the precise focusing picture can be realized. Finally, the computer simulation showed the validity of the algorithm.
Quick method of distributed small satellite synthetic aperture radar single-look complex image simulation
Xu Huaping, Chen Jie, Wang Baofa, Zhou Yinqing
2006, 32(04): 445-449.
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The basic requirements for echo simulation of DSS-SAR(distributed small satellite synthetic aperture radar) were concluded. The geometry model and signal model of DSS-SAR were presented. Hill equation was employed to illustrate the configuration of small satellites. Single-look complex image signal model, correlation of DSS-SAR echoes and interferometric phase probability density function were given to show the signal characteristics of DSS-SAR. A quick methodwas proposed to simulate single-look complex images of DSS-SAR. The method calculated positions of small satellites with the position of the central point and the small satellite configuration. It can simulate the single-look complex imagesignal of the arbitrary formation small satellite cluster conveniently. The flat and conical terrains were chosen, and the simulated single-look SAR(sythentic aperture radar) complex images were obtained with the proposed method. Computer simulation results show the simulation method not only satisfies the DSS-SAR signal simulation needs, but adds many kinds of error conveniently and simulates signal realistically.
Investigation of probability failure assessing curve of steel used as pressure vessel material produced in China
Luo Hongyun, Zhang Yubo, Zhong Qunpeng
2006, 32(04): 450-454.
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Along with the development of the theory and the technology of PSA(probabilistic safety assessment),the theory and the technology has been used on the engineering field. But there are many problems that are not clear both in theory and technology of PSA. Probabilize of failure assessment curve is one of the significant problems among them. To solve this problem plenty of probabilistic analysis have been carried on the failure assessment curves of 5 kinds of crack styles of four kinds of steel produced in different Chinese steel makers, different heat and different thickness. Probabilistic assessment curve of four kinds of steel and general steel which has long yield point elongation that manufactured in China on different reliability have been obtained by the three-part analysis way and closing approach. The equations are valuable for the engineering probabilistic safety assessment of the long yield point elongation steel manufactured in China.
Elastic properties for 3 dimensional and 5 directional braided composites
Lu Zixing, Liu Zixian
2006, 32(04): 455-460.
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According to actual braiding process and the micro-structural model of braiding preform, using stiffness averaging method, the stiffness matrix of 3D&5D(3 dimensional and 5 directional) braided composites is deduced and their elastic properties are calculated. On the basis of calculation,the changing characteristics of elastic constants with the braided angle and volume fraction of fibers is described and the difference of elastic properties between 3D&5D and 3D&4D(3 dimensional and 4 directional) braided composites as well as the effect of cross-section size of performs are discussed. Numerical calculation showsthat 3D&5D braided composites not only keep the certain merits of 3D&4D braided composites but also enhance the mechanical properties of axial direction or braided direction. The effect of cross-section size of braiding preform on the elastic properties of braided composites is larger only if the cross-section size is smaller.
Packing density of powder in paste with continuous grain size distribution
Huang Xin, Zhu Baolin, Guo Ye, Ma Baoguo
2006, 32(04): 461-465.
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The experimental result of measuring water requirements in paste under the same fluidity showed that there existed noticeable difference in packing density among the slag powders with different particle size distribution. By regarding the powder particles with the water film wrapping them as compounded particles, the packing density of powder particles in actual paste system was transformed into the packing density of compounded particles in imaginary dry-particle system. Based on Stovall model, a calculation method for packing density of powder with continuous particle size distribution in paste was developed. The parameters in the method were fixed and the validity of this method was verified by experiment. It was proved that with this method the packing density of powder could be calculated as long as the size distribution of powder was known.
Application of improved threshold denoising based on wavelet transform to ultrasonic signal processing
Chen Yi, Li Shu
2006, 32(04): 466-470.
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The signal to noise ratio of ultrasonic echoes signal was low, the echoes signal was submerged easily in ultrasonic testing, and wavelet transforms was an effective method by which the flaw echoes can be extracted. The mathematics model of ultrasonic echoes signal was established, including the flaw echoes and the noise, the traditional soft and hard threshold denoising methods based on wavelet transform was ameliorated, and a middle course method was put forward for signal denoising in ultrasonic testing. At the same time the parameters selection was also optimized with the signal to noise ratio of ultrasonic flaw echoes signal as object function. The simulation experimental results showed that this method was fit for analyzing ultrasonic signal, and it can depress noises well. This method utilized the advantage of the soft and hard threshold denoising methods and avoided their disadvantage in the farthest. Compare to the traditional soft and hard threshold denoising methods, the denoising effect was improved in a certain extent, and the signal to noise ratio of ultrasonic flaw echoes signal was improved by using this method.
Embedded CNC system with the μc/os-Ⅱ OS
Wang Tianmiao, Chen Youdong, Sun Kai, Wei Hongxing
2006, 32(04): 471-474.
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An embedded CNC(computer numerical control) system and its hardware and software platform are presented. The system hardware consists of microcontroller ARM(advanced RISC machines) and FPGA(field programmable gate arrays). The CNC system application runs on the ARM, while FPGA is used to connect IO and generate pulses. The software platform utilizes the μc/os-Ⅱ OS to provide hard real time capabilities. The CNC controller software architecture which applies a generic open architecture model with a software bus is presented. Some important methods for carrying out the implementing of the CNC controller are researched and demonstrated, including thread cutting. Finally, a real machining experiment on the system mentioned above is introduced. The result shows that it can be successfully used in real manufacturing environment.
Process parameters and limits in tube hydro-forming with axial feeding
Li Xinjun, Zhou Xianbin, Lang Lihui
2006, 32(04): 475-480.
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By using the viscous media, tube hydro forming with axial feeding was investigated. Based on the diffusion instability and plasticity theory, the distribution rules of the internal pressure were indicated and the relationship between the internal pressure and the axial loading were obtained with axial symmetrical part. After creating the loading function to control the loads, the method to control the axial feeding was proposed and the loading mode was optimized. Based on the localized instability theory, the limits of the internal pressure were calculated, and the UDL(uniform deformation limitation) and the concept of LSR(limited stress ratio) were proposed to check the basic workability of parts. After analyzing the features of stress variation during forming, the mechanism that the stress state changes quickly from the tension-compression to the dual-tension was carried out. Through the experiment and numerical simulation, the forming process of the tube hydro forming with axial feeding was conducted and it proves that the results from the theoretical analysis keep a reasonable agreement with the reality.
Numerical simulation of influence of two different hand-figures on swim propulsive efficiency
Kang Honglin, Yuan Wu, Gao Ruize, Yan Chao
2006, 32(04): 481-483.
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In order to find which hand-figures could provide higher propulsive efficiency for swimming, two different 3D unstructured grid models of a native woman swimmer’s hand and forearm were generated based on two hand-figures-fingers splaying and fingers holding together. The numerical technique of computational fluid dynamics (CFD) was applied to calculate the steady flow around the swimmer's hand and forearm in two different hand-figures at various speeds when angle of attack was 90°. The drags, lifts and corresponding coefficients were computed for the hand and forearm, and the flow fields around the hand and forearm were analyzed based on the calculated data, which showed the influence of hand-figures on swimming propulsive efficiency. The results show that the forcescaused by pressure difference are the major part of the propulsive forces, swimming with fingers holding together provides higher propulsive efficiency than swimming with fingers splaying when the angle of attack is 90°.
Research and implement of a grid job manager
Wang Yong, Xia Xianbo, Wan Yu, Hu Chunming
2006, 32(04): 484-488.
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With the development of grid and grid applications, more and more flow jobs have appeared. Definition, execution and management of jobs need the support of software system and the job manager is the core component. The job manager interprets the job definition and provides the monitor function. A job description language is proposed and a job manager is designed based on early work of Web service composition. The job manager is composed of invoker, conversation manager, instance manager, job instance, activity instance and activity invoker. The job manager provides an executing engine for grid jobs. The layered architecture of the job manager simplifies the message processing. Three different conversation mechanisms supported by the job manager satisfy the requirement of the conversation between jobs and between jobs and component services. Event-based message exchange mechanism makes the relation among components of the job manager clearer and meets the requirement of the object-oriented design.
Fast algorithm for pseudo random number generation in Linux user space
Gao Xiaopeng, Zhang Zhe, Liu Guoliang, Long Xiang
2006, 32(04): 489-493.
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RNGs(random number generators) are important building blocks for algorithms in security applications. They are paramount in construction of encryption keys. For security applications with key exchange in high frequency, the two RNGs provided by Linux kernel are not acceptable because of their low efficiency. An algorithms for fast pseudo random number generation as proposed is implemented in Linux user space. The source of random number is a high-frequency 64 bit counter. The lowest 4 bytes of the counter are added in a pool, then the pool is hashed with SHA(security hash algorithm). The first 16 bytes of the hash are output. This process is repeated until the requested number of random number is achieved. Several statistical tests are employed to investigate the randomness of RNGs. The results show that the quality of random number generated are guaranteed. Due to its running in Linux user space, this algorithm has much higher efficiency than Linux’s two RNGs.
User oriented availability model of ethernet
Shi Jian, Wang Shaoping, Wei Zhenjin
2006, 32(04): 494-498.
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Carrier sensing random multiple access with collision detection protocol (CSMA/CD) can solve competition effectively and provide high throughput and low delay, so it has become an attractive protocol to the designers of local area net (LAN). Based on LAN’s CSMA/CD protocol analysis, the user oriented availability model of Ethernet is put forward. By defining the workstation operating mode as congesting model and idle mode, the availability model based on bandwidth and time slot is established. The probability of LAN sending packets successfully in specified time is defined as the availability measure of Ethernet. By analyzing the effect of different parameters which include the number of workstations in Ethernet, average length of packets, packets arrival rate and retransmission rate on availability, it is show that the LAN’s availability will decrease synchronously with workstation number in network increasing. With packets arrival rate increasing, availability will improve to maximum firstly, then decrease subsequently. It also shows that increasing retransmission rate can improve LAN’s availability. By setting parameters reasonably, the higher LAN’s availability can be obtained.

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