Abstract:The pressure vibration failure of the large flux pressure reducing valve (PRV) was analyzed. A dynamic mathematical model of the PRV system was developed to simulate this failure, and a simple and effective method of reducing the area of the control cavity inlet to enhance the stability of the pressure output response of the PRV was found by the simulation and validated by the experiments. The result of the simulation shows that the vibration problems of the large flux PRV are related not only to the design parameters of the PRV, but also to the backward tubes connecting to the PRV.

Abstract:In order to investigate the influence of multi-cavity on gas fuel distribution in scramjet combustor, the numerical simulation was used to analyze the pilot hydrogen jet, which was used to pilot kerosene into cold flow in scramjet. The analysis was conducted in three aspects: firstly, dual-cavity combustor with cavities in tandem was compared with single-cavity combustor, with the result showing that the center of hydrogen jet leans to the main stream because of the downstream cavity. Secondly, in dual-cavity combustor with cavities in tandem, upstream cavity was compared with downstream cavity in fuel distribution. The result reveals that hydrogen spreads more extensively in the Z axis direction in upstream cavity, while it spreads wider in Y axis direction in downstream cavity. Finally, the dual-cavity combustor with cavities in parallel was compared with single-cavity combustor. The result indicates that cavity which is in the bottom wall has no influence on gas fuel distribution.

Abstract:The spacecraft on highly elliptic orbit flies over their apogee in the most part of one period. So this kind of orbit can be used to realize long term communication and airborne early warning for high latitude areas, which is significant if applied in military. The kinematics of multi-spacecraft formation is required to deal with space missions such as the exploration of space magnetic fields and the information interference. Formulations of the relative motion on highly elliptic orbits are developed by kinematic method which takes the relative orbit elements as the variable, and then the precision of the formation is analyzed. Based on the formation, several special relative formations including the linear circular elliptical and isosceles triangle ones are discovered, and the conditions to form these formations are presented. Under the circumstance of two-body, the results from simulation show that the more close of the spacecrafts, the more accurate of the formations.

Abstract:The autonomous orbit determination of navigation constellation is one of the key techniques of the Compass Navigation Satellite System (CNSS). There, howerver， is a deficiency problem of the datum mark when only intersatelite measurements of range is used. To solve this problem, this paper presents a new method that a few ground-based radio emitters should work randomly to offer the benchmark, and the constellation satellites should estimate their position and velocity for the whole network, based on the fusion of crosslink pseudo-range measurements and ground-based measurements. It is aimed to improve the orbit determination accuracy ulteriorly. Finally, the simulation results prove the rationality and validity of this method.

Abstract:Extracting the linear parameters of the runway is the precondition for airborne vision based auto-landing. Firstly it is required to obtain a lot of short lines by gradient direction grouping on the edge map. Secondly according to the angle between two lines and the distance between the ends of two lines, and the gray average on both sides of lines, a rule to quantitatively characterize the affinity between two short lines is advanced, then the short lines on the same line end-to-end by the value of affinity will be linked. Finally the longest lines are left to choose, and priori knowledge, namely the contrast information of shades between the internal and external runway is applied to distinguish the two lines lying on the two edges of the same runway. The method has been tested valid by many actual images.

Abstract:Because of the fixed orbit of the space station in inertia space, it is important to design the trans-lunar trajectory of the probe based on the space station assembly. In this paper, considering the kinematic law of the moon, an integrated mathematical model for trans-lunar trajectory design is established, and the constraint conditions are presented according to practical situations in engineering. Then the main problem for orbit design is to solve the orbit dynamics equation in some constraint conditions. Appropriate object function and constraint conditions are chosen, and the equation is solved by using genetic algorithm and SQP method. The parameters of trans-lunar trajectory are calculated by using numerical method. Finally, by a comparison with the data gained from STK, the results are validated.

Abstract:Feasibility of hole-drilling method for the measurement of residual stresses in short carbon fiber enhanced silicon carbide (C/SiC) composites was studied. Based on the disadvantage of conventional hole-drilling method and good electric conductance of high-hardness C/SiC composite, electric sparkle method (ESM), an alternative method, was presented and proved suitable. Then an experimental procedures for residual stresses of C/SiC composites were established. Finally the established ESM method was used for the measurement of residual stresses in two C/SiC samples with different machined surface. Results show that difference of residual stresses between two samples displays good distinguishing ability of the ESM method. Less intrinsic residual stresses and mechanically introduced residual stresses bring the advantage of surface figure stability for C/SiC composites used for reflecting mirror.

Abstract:With the development of high-speed spacecrafts, the properties and heat transfer simulation of thermal protection materials used by the spacecrafts are of great significance. This study aims to study the properties of silica aerogel composites and heat transfer simulation. The results indicate that thermal conductivity of the silica aerogel composites is only 0.018W/m?K and transient heat transfer simulation shows good agreement with the experimental data. Thus the simulation method can forecast the experimental conclusions and optimize the geometric structure of the composites.

Abstract:The enthalpies of phase change have been studied by means of CDR-34p Differential Scanning Calorimetry(DSC) and Phase diagram for Na₂SO₄-H₂O system. The current study found that latent heat for inorgonic hydrated salt is made of reaction enthalpies, dissolution heats, integral dissolution heats. In addicition, the latent heat of phase change was calculated. Compared with experimental data, the relative error of the calculated results is just 2%.

Abstract:Considering the specific constrains of electromagnetic detection satellite (EDS), a multi-satellites scheduling model is established and a scheduling algorithm based on genetic algorithm is proposed. To deal with some specific constraints, a punish function method is introduced. In order to conquer the difficulty of punish coefficient setting, a mechanism of punish coefficient self-adaptive adjustment is designed. Finally, some experiments are conducted to verify the correctness and practicability of our scheduling algorithms.

Abstract:We present a quantum secure direct communication protocol where the channels are not the maximally entangled states. The communication parties utilize decoy photons to check eavesdropping. After ensuring the security of the quantum channel, the sender encodes the secret message and transmits it to the receiver by using controlled-NOT operation and von Neumann measurement. The protocol is efficient in that all pure entangled states are used to transmit the secret message. As for the experimental feasibility, our protocol can be realized with today's technologies. The protocol is also verified to be secure for a noise quantum channel.

Abstract:Crosstalk of arbitrary layout transmission line is analyzed using BLT equation. Transmission line is cut in discrete pieces, Ideal Junction is imported to calculate the scattering parameters, and the transmission line is made equivalent to multiconductor transmission line network. The cases of non-parallel line and cross line are emphasized. The numerical examples indicate the validity of the method, and the method can offer theoretical instruction for the crosstalk analysis in electromagnetic compatibility.

Abstract:Two types of tasks, the spot and polygon targets, are requested in remote sensing. However, great difference exists between the two request tasks and it is difficult to schedule the two kinds of requests within one model. In this paper, a novel model is proposed to tackle it by the following method. The spot requests are regarded as special polygon and they are also partitioned into subtasks. All of the subtasks generated by the requests are mapping into atomic task, and two types of request were unified in atomic task level. Finally, two evaluation functions were proposed to deal with there difference. Simulation results demonstrate the validity of the current approach.

Abstract:For a 3-D distributed space-borne SAR, small area antenna leads to serious Doppler ambiguity. Joint processing of all echoes from multiple antennas is able to eliminate Doppler ambiguity and obtain high resolution and wide swath. This paper firstly builds the echo model for the formation of one transmitting and two receivings. Then the relationship between the two received echoes is analyzed. After compensation for envelope difference and part of phase difference, the analytic expression which describes the frequency spectrum relationship between two echoes can be obtained accordingly. Based on this equation, two weight functions are designed to eliminate the Doppler ambiguity. Finally, a conventional imaging algorithm is used to get SAR images.

Abstract:A new method is proposed to select optimal initial cluster centers. By searching parameters' histogram peak values, the number of cluster centers can be estimated, and these optimal initial cluster centers are selected in the columns or cells where the histogram peaks exist. Because these optimal initial cluster centers are near to real cluster centers, the iterations of clustering are reduced efficiently. Theoretical analysis demonstrates that the compute complexity of new method is lower than some conventional techniques. The improved K-Means algorithm is applied to sort frequency-hopping signals, and the simulation results demonstrate that the algorithm is effective.

Abstract:Kylin is a server operating system focusing on high performance and security. In this paper, a hierarchical kernel structure for Kylin operating system is proposed. Under this structure, Kylin is organized into two layers. The basic kernel layer is responsible for initializing the hardware and providing basic memory management and task management while the system service layer is based on FreeBSD providing UFS2 file system and BSD network protocols. In terms of this conception, the motivation for this novel hierarchical operating system kernel model is discussed. Then the kernel's infrastructure is introduced. Last, the performance comparison of Kylin, Redhat 9.0 and FreeBSD 5.3 with standard benchmarks is presented. Finally, a discussion of the future directions of Kylin operating system is made.

Abstract:The responses of voltage-controlled oscillators (VCOs) to single-event transients (SETs) were investigated. A classic differential VCO with symmetrical loads was implemented in a 180nm bulk CMOS process. Modeling the charge deposition and collection from ion strikes as a current source, the transient SET responses of this VCO were achieved by circuit-level simulation. Simulations and analysis indicated SET responses were not only dependent on incident energy and the frequency of oscillation, but also dependent on striking time, which can increase the phase displacement by up to 300 degrees. Additionally, some nodes in the bias generation circuit are most sensitive to SET. Strikes in these nodes were amplified and resulted in an approximate 7 clock cycles distortion.

Abstract:The resilient S-boxes have applications in fault tolerant distributed computing, quantum cryptographic key distribution and random sequence generation for stream ciphers. Based on the use of linear error correcting codes together with highly nonlinear S-Boxes, a new construction of highly nonlinear resilient S-boxes with given degree is provided. A contribution of the construction is that the nonlinearity of the resilient S-boxes can be calculated with the parameter of the linear code. As a result, the construction provides currently the best results in the aspect of nonlinearity.

Abstract:It is significant to mine Top-K most-frequent patterns in dataset. The existing algorithms usually use the k-most frequent items as the initial items, and use the support of item with lowest frequency in initial items as the initial border support. In fact, since the number of items in Top-K most-frequent patterns is much less than k, the efficiency of the existing algorithms is restricted. To solve this problem, an efficient mixed-searching based algorithm for mining Top-K most-frequent patterns, MTKFP is presented. The algorithm firstly mines some short item sets by breadth-first searching, and uses short item sets to obtain the scope of the initial items (the number of initial items is less than k) and the higher initial border support; then it obtains all Top-K most-frequent patterns by depth-first searching. The experimental results show that the number of initial items of MTKFP is 70% lower than that of existing algorithms, and the initial border support of MTKFP is higher than that of existing algorithms. Hence the performance of MTKFP is superior to that of the best existing algorithm.

Abstract:Group theory is a sort of strong mathematics tool for the researches of the symmetry property. Chaos is the internal randomicity put up by the definite non-linear dynamical system. It has several properties, including the limitary, the nonperiodic and the dependence on initial condition and parameters. The discrete sequences produced by chaos system are often used to encrypt data such as digital pictures. In former papers, the relationship of Group theory and Chaotic system has seldom been studied. In this paper, it proves the result that the scrambling transform of two-dimensional chaotic scrambling arrays will form permutation groups. It is proposed on the basic theory of Group and Chaos and is proved in theoretical and experiment ways. According to the result, it is demonstrated invalid to use two-dimensional chaotic scrambling arrays created by different chaotic system and different initial values to encrypt multimedia data such as digital images and videos.

Abstract:Survivability helps ensure that underwater monitoring systems provide essential services under conditions of attacks, failures, and accidents. To evaluate the survivability of such systems accurately, definition of survivability and its model is proposed in this paper. Survivability, the ability of a system to meet user's requirement of service when the system is affected by some events in a specified environment, and is computed by mathematical expectation of services performance. This method will have more precise result than others in judging whether system design achieves the criteria of survivability. To the survivability model based on multi-state system, service performance is the function of state of all subsystems, which is related to structure function of system. Probability distribution of subsystem's states is decided by reliability and security. In the end, an illustrative example is presented to prove the effective of the survivability model is presented in the end.

Abstract:A dwell time algorithm for magnetorheological finishing (MRF) process of optics is developed in this paper. Firstly, the vector of residual heights of the control nodes is calculated, and the removal rate of the “polishing spot” at each control node is written into a removal matrix. Then, a nonnegative least-squares method is used to obtain the optimal solution of the dwell time. With this algorithm, a spherical surface (145mm aperture) is polished on the MRF machine developed by ourselves. After two iterations, PV values λ/15, RMS values λ/125, and Ra ，0.57nm.

Abstract:Subsurface damage (SSD) may still exist in polished elements, which influences laser induced damage threshold and optical performance. Therefore, SSD must be reduced and finally removed from the polished surface to improve the service performance of optical elements. Hence it is required to make the accurate detection and characterization of the polishing SSD. In the current approach, firstly, the depth of hydrolyzed layer and embedded polishing contaminants were detected with constancy chemical etch rate technique and secondary ion mass spectrography, respectively. Then, dimension of subsurface plastic scratches was measured with atomic force microscope. Furthermore, the development of surface roughness with depth was analyzed, in order to discuss the correlation among superficial flow layer, hydrolyzed layer, and subsurface plastic scratches. Finally, the SSD model in polishing process was established, and, material removal mechanism was proposed on the basis of the model. The results show that hydrolyzed layer contains superficial flow layer, plastic scratches, and polishing contaminants. The depth of hydrolyzed layer on polished fused silica surface ranges from 76nm to 105nm. Optical polishing process is responsible for the corporate effects of hydrolyzed action, mechanical removal, and plastic flow.

Abstract:In order to achieve an optimal trade-off between the robustness against unknown inputs and the fault detectability, an observer-based residue generation and fault detection method applying sliding mode observer is presented in this paper. Taking advantage of the essential feature of sliding mode variable structure technology, being completely insensitive to unknown input disturbances, the generated residue of the designed fault detection system is not affected by the unknown input, but still keeps high sensitivity to the fault signal. Simulation results show the effectiveness of the proposed approach.

Abstract:The stiffness coefficient on the contact point of the gear pairs is defined based on the Hertz Elastic Contact Theory, which can be used to calculate the meshing force of the gear pairs. Then, the characteristics of the working flanks of the involute ring tooth spherical gear are analyzed and the equations to calculate the master curvature radius are derived. Afterwards, the contact ratio, a key factor in the calculation of the stiffness coefficient, is studied and the method on how to find the position of inverse meshing point is given. Finally, the result of an example is presented to demonstrate the time-variable characteristic of the stiffness coefficient in spherical gears transmission.

Abstract:An ultrasonic obstacle detection system for mounting on the front bumper of an automobile was designed. Using an omnibus ultrasonic transducer array and ultrasonic pulse coding techniques, an algorithm for collision identification was formulated based on a synthetic aperture to discriminate between echoes constituting real threats and those that do not. Theoretical calculation and test results show that the detectable diameter of flat boards is 15mm, and the active range is between 0.2～25m. Furthermore, the multiple obstacles in front of the automobile can be located simultaneously.

Abstract:This paper is aimed to study the dynamics of a class of non-autonomous parabolic equation with time delays and alpha-translation exponential external function. The existence of pullback attractor for the non-autonumous infinite-dimensional dynamical systems generated by the non-autonomous parabolic equation with time delays is obtained in the space L²(Ω)×C(［-r,0］; L²(Ω)).