Abstract:Rod-coil diblock copolymers of PPQ-b-PEG containing poly(phenylquinoline) (PPQ) as the rod block and the poly(ethylene glycol) (PEG) as the coil block were designed and synthesized from Methyl-PEG(M_w:2000), butanedioic anydride 4-Aminoacetophenone, 5-acetyl-2-aminobenzophenone. The structures of PPQ-b-PEG are characterized by IR, ¹HNMR. And thermostabilities are studied.The results show that the first decompostion temperature of PPQ-b-PEG is 250℃.The weight of PPQ-b-PEG is reduced by 5% at 250～400℃. It is reduced rapidly at 400～600 ℃.

Abstract:By using directive evaporation, linear arrays of opals are formed inside the microchannels on the flat Si wafer. The results show that the samples have photonic band gaps in the visible region. Compared with flat substrates, the microchannels have confining effect on the growth of opals to some extent.

Abstract:The preparation of the polymer-derived SiC fibers involves a pyrolysis process, in which great weight loss and shrinkage are usually recorded. It causes the bend, which reduces the tensile strength of SiC fibers. The reason of the bend forming is discussed on the basis of the pyrolysis process of PCS fibers; the effect of the bend on the properties of SiC fibers is studied through mechanical analysis. The way of thermal-curing under tension or pyrolysis under tension is brought forward in order to solve the problem, then the properties of SiC fibers can be improved.

Abstract:Finite element software ANSYS7.0 is employed to analyze the interlaminar shearing stresses of C_f/epoxy composite tubes under axial loading. The tubes are fabricated by the flexible expandable mould process. Analysis results show that asymmetry plies increase the hoop interlaminar shearing stresses by 0.43～1.14 times，but no effects on axial interlaminar stresses. The ratio of axial plies to hoop plies plays an important role on the hoop and axial interlaminar shearing stresses, which the stresses reach to a minimum when it's withn the range of 7∶3～4∶1.

Abstract:SiC coating is prepared successfully on C/SiC ceramic matrix composites by the reaction method. The phase structure and components of the coating are investigated by XRD. The profile and surface micrograph are observed by SEM and optical metallography microscopy,and the forming course of SiC coating is analyzed. The result shows the main component of the coating is SiC and a little of Si. There is a good gradient structure and no obvious interface between the uncracked SiC coating and C/SiC substrate. On the contrary, if there were no gradient structure, the SiC coating would crack because of the great residual stress.The uncracked SiC coating prepared by the reaction method matched with CVD SiC coating excellently. At the same time,the CVD SiC coating fabricated on it has no dot defect.

Abstract:A new method of direction determination with a single geostationary satellite is presented. Also an experiment is done in order to validate the method with GPS satellites. The result shows that the precision of direction determination can be higher than 0.05°when the baseline length is about 3 meters long; so it proves that the principle of direction determination with a single geostationary satellite is right and feasible.

Abstract:Fatigue enhancement mechanism of the omni-axis random vibration environment is one of the key techniques to carry out the reliablity enhancement testing. This paper studies the fatigue enhancement mechanism of its broad bandwidth characteristic. At first related spectral parameters of random stresses to influence fatigue are studied. Then it is analyzed how the bandwidth affects the above parameters. Finally the fatigue enhancement mechanism of the broad bandwidth characteristic is illustrated.

Abstract:In order to obtain the appropriate “sample” for “computer experiment”to study molecular dynamics of the shock detonation of solid explosives, we carried out simulation of NVE and NVT molecular dynamics using REBO model. In addition, we carried out the simulation without artificial scale, therein the evolution of the system is absolutely driven by movement functions. Finally, we discuss how to choose the appropriate simulation method for different requirements.

Abstract:Aiming at the demand of the distributed simulation system, this paper has built a common grid-based fault tolerance system. The system consists of three parts: simulation resource monitoring module, data saving module, and error recovery module. The implementation of monitoring module is built on top of grid's MDS, while data saving module, including the saving of the process space and the iterative relationship between processes, and fault recovery are realized based on checkpoint mechanism in the user space. In addition, we analyze the relationship between these three modules and the existing function modules in simulation system. In the end, we design and implement a fault tolerance broker in Client/Sever mode to automate the fault tolerance.

Abstract:Reaction wheels are widely used for spacecraft attitude control in missions that require fine pointing accuracy and stabilization nowadays. But the friction produced by the reaction wheel assembly (RWA) itself when crossing zero is one of the most significant sources of disturbance. And it is necessary to eliminate these disturbances, especially for those cases that the wheels are running at low-speed throughout the space mission. The mathematical model of the reaction wheel assembly driven by a DC motor is presented on the base of Dahl friction equations. And a state observer is constructed to estimate the friction torque in order to compensate for it. A numerical simulation model, which assumes the satellite attitude is controlled by three reaction wheels arranged in an orthogonal geometry, is established. The simulation results prove that this method can improve the satellite attitude pointing accuracy and stability efficiently. Finally, the integration of the observer method and a sliding-mode control law is discussed.

Abstract:The impedance matching design is briefly introduced. Three kinds of conductive fibers were prepared. Then the fibers were woven into tabby fabrics. A new kind of multilayer structural radar absorbing material was made with these conductive tabby fabrics. From 8.4GHz to 18GHz, the reflection attenuation of the material exceeds 10dB. The material is light (3.2mm thick and density 1.38g/cm³) and of good mechanical properties (flexural strength 173MPa，toughness 12.53GPa).

Abstract:Carrier-free GPR(Ground-penetrating Radar) is a near-ground-time-domain detecting system using nanosecond pulse, influenced by half-infinite lossy media interface, therefore the analysis of scattering features of the near ground time-domain antenna is extremely difficult. This paper designs a bow-tie antenna loaded with patch resistors. Results of FDTD (Finite-difference Time-domain) calculation show good fidelity of the wave, and exciting radiation features as well as fine effect of shielding. It can be widely used in GPR and other UWB (Ultra-wide-band) systems.

Abstract:A new algorithm for image enhancement based on the dyadic wavelet transform is proposed aiming at minimizing the image noise while amplifying the image feature. By making full use of the shift invariability of the dyadic wavelet transform and correlation of the wavelets coefficients from different scales, the proposed algorithm can efficiently alleviate the amplification of the noise and distortion of edges, which are the most difficult and common problems in image enhancement. Furthermore, the enhancing strategy is highly adaptive and thus applicable to images from many sources. The results of experiments are also given, which show that the new algorithm performs better in both de noising and image feature enhancing compared with the existing multi scale algorithms.

Abstract:A new method for two dimensional damped sinusoids estimation in colored Gaussian noise, called two dimensional fourth order mixed cumulants based on ESPRIT (2d FOMCESPRIT), is presented. The amount of computations is greatly reduced by holding the dimensions of the feature matrix compared with that of the former methods in the presence of a long record. Due to FOMC's auto suppressing Gaussian noise, the SNR threshold is reduced and the precision of the parameter estimation is improved. Simulation results show that this method is of better performance and higher efficiency than the former methods in colored Gaussian noise.

Abstract:Predicated execution improves the performance by eliminating branches but wastes energy due to extra instructions. Nullifying FALSE predicted instruction earlier can save energy. Based on the Itanium 2 microprocessor, we modify the pipeline function; advance the read of predicate and present methods to stall the pipeline on predicates dependency. Simulation results show that the advanced predicate reading and FALSE predicated instruction nullifying can reduce energy waste and improve the efficiency of energy.

Abstract:With the rapid development of communication technology, optical transmit technique demands higher requirement of the core router's forwarding performance. OC192 POS interfaces have made the core router's forwarding engine a new bottleneck. Further development of optical transmit technique has exceeded the maximum accessing ability of DRAM, which makes impossible the design of new forwarding engine with one chip of DRAM. New hardware parallel forwarding engine design is offered on the basis of Gupat's DIR 24 8 BASIC forwarding architecture, taking advantage of the parallel of multiplex DRAM chips. In order to get really performance of the parallel forwarding engine design, IP packet header trace and routing table's dump of Internet core router node are used as the input of the target system's simulator. The result shows that the parallel forwarding engine can achieve linear speedup with the increase of parallel basic forwarding tables.

Abstract:When detecting man made targets hidden in foliage in a FOPEN UWBSAR image, trunk clutter is the primary disturbance. Whether the detection can be performed successfully or not is dependent on the performance of the trunk clutter suppression. Based on Hidden Markov Modeling, a new trunk clutter recognition and suppression method is proposed. From the experiments results, the recognition method proposed in this paper can recognize the trunk clutter in UWBSAR image effectively, and improve the target detection performance in foliage.

Abstract:Under the condition that only the direct sequence spread spectrum signal and additive Gaussian noise are present at the receiver, the square of amplitude of received signal after DFT is assumed to be exponentially distributed. Based on this assumption, a novel narrowband interference detection and suppression algorithm is proposed. Theoretical analysis and simulation results demonstrate that the algorithm can suppress multi tone jamming and narrowband Gaussian jamming efficiently.

Abstract:To improve the throughput of the tactical Ad Hoc networks, a distributed Location Aided Power Control Algorithm (LAPCA) is developed which computes the number of the neighboring nodes by location prediction, then adjusts transmitting power of the node to maintain an optimal connectivity when nodes are in motion. This algorithm can work as an independent module in company with most of the popular routing protocols. The Reference Point Group Mobility (RPGM) model, which is more suitable for tactical scenarios, is used to generate network simulation scenarios. As shown by the results of simulation, the throughput of the network in almost all the RPGM scenarios can be thus greatly improved with respect to the pure AODV routing protocol.

Abstract:In order to surmount the disadvantage that much time is consumed for feature extraction with traditional K L transform, an improved K L transform method in pattern recognition is presented. This improved method gets covariance matrix with recursion algorithm and computes the eigenvalues and eigenvectors of the covariance matrix with matrix perturbation theory. The simulation results show that compared with the traditional method, the consuming time with this method is sharply decreased, and the computing precision is kept.

Abstract:Pitch modification is an important part in text to speech synthesis and voice conversion. In voice conversion, many authors in favor of realizing the voice conversion by the method based on LPC analysis, with which the spectrum envelope is converted by modifying the LPC coefficients directly or indirectly and the pitch modification is realized by processing the LPC excitation spectrum or LPC residual. Frequency method is proposed to process the LPC residual, then the pitch modified LPC residual is got. This method can also be used in the pitch modification of the text to speech synthesis.

Abstract:A complex C⁴ISR system is composed of many subsystems. We use activity model to create the activity adjacency matrix, and path matrix (accessible matrix) of graph theory to recognize the strongly connected components, so as to get the sets of strongly depended activities. The activities in one set should be rearranged in one subsystem. We adopt this approach to recompose the C⁴ISR system.

Abstract:In order to get the risk on the level of system and to obtain the quantitative decision reference of safety, this paper proposes an analytic method of system safety based on probabilistic risk. This method will divide the system into different subsystems according to some criterion, count the danger sources of all subsystems and build causality diagrams corresponding to danger sources, and at last compute the probabilistic risk on the level of system according to some rules. The difficult problem of computing the probabilistic risk by this method is discussed.

Abstract:An adaptive method for Hamilton-Jacobi equations on unstructured meshes is given,the paper presents the key ingredient to choose smooth indicator. Using non-oscillatory interpolation it gets the essentially non-osscilatory scheme.Extensive numerical experiments show that the adaptive methods can also produce high resolution and improve the accuracy with small grid points if grid adaptation is employed.

Abstract:This paper studies a queueing system wherein the distribution of the m-th interarrival time α_m -α_m-1(m≥1)depends on the number of customers in the system at time  α_m-1. Using the method of supplementary variables,the integral representation of the transient queue length distribution is obtained, of which the integrated term can be calculated recursively under the condition that the interarrival times and service times of the system have density functions.

Abstract:It is very important and diffcult to obtain the ideal regular sequence of polynomial ring. In the lexical order a zero dimension ideal Grǒbner has a maximal orderless regluar sequence. We can obtain the regular sequence owing to the calculability of Grǒbner bases and the method of the primary factor of the radical initial ideal.

Abstract:In order to study a three-axis overhead tracking problems, α-degenerative tracking algorithm is discussed. A completely degenerate tracking and a three-step tracking algorithm are proposed. It is proved theoretically that they can solve overhead tracking problems. Furthermore, by applying the first algorithm, it is simulated that the three-axis tracks to a satellite orbits abou 2000km form the Earth. The simulating data shows that the completely degenerate algorithm keeps the rotation speed of each axis within 0.56 degrees per second. The second tracking algorithm is used in the three-axis automatic tracking experiment. It shows that the three-step tracking can solve the overhead tracking problem.