Abstract:Archimedes spiral path, which is widely used in computer-controlled polishing process, always brings about excessively high rotational speed, and consequently excessive machining when polishing central region of the work-piece. To resolve this problem, the characteristics of a universal spiral path are studied first. It shows that the instantaneous rotational speed of the work-piece depends on the local dwell-time density and the local increase rate of the area enclosed by the spiral. Based on this, a novel spiral was proposed as a polishing path. The increase rate of the area enclosed by this new spiral is constant, and therefore, it can be referred to as uniform-area-increment spiral. This spiral path can ensure the stableness of the rotational speed of the work-piece, and reduce the rotational speed in the central region. Consequently, it can reduce the demands on motion performance to machine, and reduce the cost for machine and process. Finally, experimental results verified that Archimedes spiral path causes excessive machining in the central region due to excessive demand for rotational speed, and results in lower precision, while the uniform-area-increment spiral path avoids the excessive machining in the central region and results in higher precision.

Abstract:The algorithm and implementation of Magnetorheological Finishing with spiral scan mode was researched. The algorithm implemented changes the removal function matrix to the coefficient matrices of the linear system of equations for dwell-time calculation. These equations are resolved quickly because the coefficient matrices are sparse. The variations of speed on the spiral path are obtained by the allocation of the dwell time and the work piece can be processed well using the machine that contains the information about the MRF process. An experiment on a K9 circular plane mirror is made on the KDMRF-200 machine developed by us. The RMS surface error is 0.02λ(λ=632.8nm) through the 2nd iteration.

Abstract:With the development of modern optical technology, there has been a basic requirement to control the surface error in all spatial frequency ranges for precision optics. The low spatial frequency range error of the surface can be easily and effectively eliminated by CCOS methods, but for the surface error in the middle and high spatial frequency ranges, there are few effective methods to correct them. Hence it has becomes a universal concern in modern optical manufacturing because of its serious influence on some modern precision optical systems. As is proved previously, the correcting ability of middle and high frequency error can be improved by reducing the size of the polishing lap. Based on this theroy, the small ion beam figuring methode has been intruduced to solve the problem of mid and high frequency error correcting. Firstly, we studied how to gain small and steady ion beams by two methods. Then we designed a series of actual figuring experiment and computer simulation to test the effectivness of those mothods on small scale optic surfaces. The desired results have been gained to reduce the surface error from 0.111λ rms to 0.015λ rms (λ=632.8nm).

Abstract:Applying phase retrieval to mirror metrology can simplify the measurement system and increase the ability of resisting the vibration effects. The capability of phase retrieval testing system for mirrors is described from two aspects: its hardware and algorithm. According to the theory of Fourier optics and geometry optics, the pixel size and the total size of CCD spherically limit the f-number and the departure of a wavefront respectively. The adjustability of phase retrieval algorithm to different figure errors is observed afterward. A series of simulation experiments show that the algorithm is high-powered when the period of figure errors is about 31.4mm, and the performance is weaker when over or under that frequency; but the algorithm is reliable when the RMS value is up to six wavelength or as small as one percent wavelength.

Abstract:A predictive model of removal function in MRF has been established based on an analysis of MRF process. According to the residual surface error before and after finishing as well as the simulative residual surface error, this model can identify the efficiency coefficient of removal function with varieties of material and achieve exact prediction of removal function. Based on this model, the MRF process can be optimized by identifying the efficiency coefficient of removal function. A HIP SiC mirror which isin size had been polished nine times with this optimal MRF process. As a result, its residual surface error decreased from PV 0.72μm and RMS 0.108μm to PV 0.13μm and RMS 0.012μm, tested by sub-aperture stitching technique. The experiments indicate that the predictive model of removal function can optimize MRF process, improve the finishing determinacy and enhance the process flexibility so as to achieve high-precision and deterministic MRF of optical mirror.

Abstract:Material removal mechanism in MRF process by nano-sized diamond abrasives is proved to be a plastic shear removal. Process experiments showed the relationship between polishing parameters (rotation speed, gap between polishing wheel and work piece, and intensity of magnetic field) and peak removal rate or surface roughness. Polishing spot is proved to be stable and repeatable. Within 2.5h, the change of peak removal rate is below ±0.3% and the change of volume removal rate is below ±0.5%. One HIP SiC flat (202mm in diameter) is polished with KDMRF-1000F polishing machine and KDMRW-3 water-based MR fluids. After rough polish (30h) and finishing polish (9h), its surface form accuracy peak-to-valley (PV) is 0.13um, root-mean-square (RMS) is 0.012um and roughness RMS is 2.439nm.

Abstract:Slow Slide Servo, in comparison with Fast Slide Servo, is a novel machining process capable of generating freeform optical surfaces or rotationally non-symmetric surfaces at high level of accuracy. It is processed in the polar and cylinder coordinates with the method of C, X and X axes. Micro-optical devices, e.g., micro lenses, micro mirrors, play an important role in high speed data, voice and video signal transmissions. Micro array lens can be treated as a freeform surface and therefore can be machined by slow tool servo method. In the tool radius compensation, the discontinuity of normal direction may cause the lathe motion beyond servo axis' capability. In the current research, servo axes limitation motion capability was analyzed and two tool radius compensation methods were studied. Experiments show that by correctly selecting tool radius compensation method, slow tool servo can manufacture array lens in a single operation and accurate geometry and optical surface finish can be obtain.

Abstract:High precision perpendicularity measurement of internal surfaces of frame parts is one of the most difficult problems in manufacturing. A novel method based on wave-front interferometer to measure the internal surfaces of frame parts is introduced in this paper, and the influencing factors in the measurement are also discussed theoretically. The experiment results show that the method can achieve high perpendicularity measurement accuracy of 0.6". Considering the distribution of the perpendicularity errors derived, the measurement results can be used in error correction machining of the parts.

Abstract:Free-Form optics have complicated surfaces and the fast tool servo（FTS）is a highly effective method to fabricate such parts. With regard to the fact that the piezoelectric FTS actuator has limited fabricating capacity as of its low stroke, a long stroke FTS project driven with voice coil actuator (VCA) was presented. Compared with piezoelectric actuator, the VCA can fabricate broader range of parts owing to its longer stroke. Illustrated with a typical optical freeform part, the key performance parameters of FTS are analyzed. The structure of VCA was given, the theoretical model of VCA was built, the closed-loop controller was designed and the actual performance of VCA actuator was tested. The test results indicate that the designed VCA actuator has long stroke and high frequency response, and the frequency response can reach 300Hz when at stroke of 200μm, More important, at this level of stoke, the frequency response presented is better than similar products abroad.

Abstract:The phase-comparison method in frequency domain is usually used in the angle measurement by the conventional CW radar. Based on amplitude-comparison method in frequency domain, a new algorithm of low-angle measurement by CW radar is proposed. An investigation is made to expose the relationship between phase-comparison method and amplitude-comparison method, with the conclusion that the amplitude-comparison method in frequency domain can be used in the angle measurement by the CW radar. Furthermore, the utility of the C²algorithm is also studied, Additionally, a new algorithm of low-angle measurement of CW radar is given. Experimental results show that the proposed algorithm is effective for tracking the target in low-altitude environment.

Abstract:A processing flow is proposed to suppress the severe clutter in high pulse repetition frequency (PRF) stepped-frequency radar. Firstly, the folded clutter caused by high PRF is attenuated by the intermediate frequency (IF) band-pass filter in the receiver's foreside. Secondly, two methods are brought forward to reject the residual clutter for targets of different velocities in signal processing system. On condition of specific waveform parameters, high range resolution processing eliminates the effect of the clutter to high speed targets. Two high resolution range profiles (HRRP) are utilized to cancel the clutter for low speed targets. The current method of processing need not change the basic stepped-frequency waveform and has the advantages of simplicity and effectiveness. The simulation and experiment results validate the correctness of the method.

Abstract:Lumped resistors are introduced to period structures to absorb the incident wave effectively，and this can reduce the RCS of target. Two absorbing structures, which are designed to be thin and light, are presented. The absorbing principle is analyzed and formulas of reflection coefficient are given. Samples of two absorbing material are fabricated and the absorbing performance is analyzed.

Abstract:Data distribution is one of the key factors that affect the performance of programs running on distributed memory multiprocessors. This paper presents a 0-1 integer programming based approach for effective data distribution using data transformation techniques. This approach uses data transformations to change memory layouts and hence makes effective data distribution possible. Moreover, it also uses data distribution graphs to describe how programs are parallelized and how arrays are accessed, and transforms global data distribution problems into the problems of finding optimal paths in data distribution graphs. Therefore, 0-1 integer programming can be used to solve optimal path problems. The approach can effectively distribute multidimensional arrays with affine subscripts accessed in multiple loop nests and can exploit the parallelisms of loop nests as much as possible. In addition, it can also solve offset alignment problems. Thus data communication overheads can be reduced as much as possible. The experimental results show that the approach presented in this paper is effective.

Abstract:Based on Chip Multi-Processor(CMP), this paper presents optimization of cluster join in Radix-Join algorithm. In order to solve the problem of serious cache may miss during the multithreaded cluster join execution, and to improve the performance of cache access, we adopt preload thread to read the clusters whose thread will access from memory to L2-Cache. Furthermore, based on the cost model of cluster join execution, the framework of cluster join execution and various thread parameters have been optimized. In the experiments, we implement the algorithm in EaseDB. The results show that cluster join performance is improved.

Abstract:With the development of the intrusion technology and the uncertainty, complexity and diversity character of the network attack, the next direction will be characterized as large scale, collaboration and multilayered. As a result, modeling of network attack has been the focus of attention. In the current study, firstly, the research background of modeling of network attack and the concept of attack graph are presented. Then the represented network attack graph generating method and its algorithmic complexity are discussed. Finally, the application of network attack graph is given. In conclusion, some major problems and research trends in this area are addressed.

Abstract:Protein-protein interaction network is one of the research hotspot in post-genome era. Several representative methods of clustering in protein-protein interaction network are reviewed. The characteristics of the methods are summarized and the difficulties and challenge are discussed. Finally, the development prospect is proposed.

Abstract:Spaceborne SAR-GMTI Systems have the ability to detect, track and relocate moving targets of the ground or the sea. The systems may provide high quality information for battlefield command, pinpoint strike and state evaluation, which is an important technique for space based reconnaissance. In this paper, Spaceborne SAR-GMTI Systems and relevant research process are introduced. The significant researches and development status quo in this field are discussed, and their limitations and key techniques are analyzed. Finally, the technique challenge and research emphasis are proposed.

Abstract:Regarding the fact that ambiguous high resolution range profiles of stepped frequency radar is cycle extension, a new method to achieve unambiguous range profiles equivalent to mixing process is proposed, and the range of local mixing frequency is presented. Finally, the validity of this method is verified by simulation.

Abstract:Interaction between two interleaved installation cavities in supersonic flow was experimentally investigated with high speed camera and schlieren system. Results revealed that shock interaction was main affection between two cavities, shock interaction between two cavities lead to the change of cavities flowfield；double cavities with same length range(short or long) will strengthen the compression shock or expansion shock; different length cavities combine will decrease the flow strength.

Abstract:Super-low frequency flexibility during motion is an important issue for a large space manipulator,which involves not only the bending vibration of arm exists, but also the joint torsional vibration. In joint control, what is important is to stabilize and suppress low flexible vibration of joint and arm while joint position is being controlled. How gear ratio parameters for joint structure affect vibration suppression is also a required problem to analyze in joint design of space manipulator, on which gear ratio parameters depend. Combined dynamics of flexible joint and arm for space manipulator was modeled with concentrated parameter method, one strategy of suppressing joint vibration and arm vibration simultaneously was put forward, the effect of gear ratio on vibration suppression was analyzed by numerical simulation and theoretical analysis. This will be useful in design and research of large space flexible manipulator.

Abstract:Two styles of inner bypass structure, the annulus style and gear style, were numerically studied. The fuel was HTPB while the overall reaction process and Eddy-Dissipation Model were adapted. It was concluded that the combustion in the dump afterburning chamber of annulus style was still controlled by diffuse. The gear style could induce couples of symmetrical vortexs in the head of dump afterburning chamber, which could enhance the mixing effect of unburned fuel and bypass air, and the total pressure loss was approximately approaching the annulus style, thus the combustion performance of gear style performs better.

Abstract:The figure of the relative kinematical track of the coplanar flying-around satellites is an ellipse. However, the configuration of the formation flying will change because of the disturbing force. A new formation keeping strategy based on combined maneuver was developed. In Hill orbital coordinates, through the measurement of the relative position components of the flying-around satellites, the combined control of the tangential impulse thrust and the constant continuous radial thrust eliminated the phase excursion of the center of the relative kinematical ellipse. Then the method considering the J₂perturbations was applied to improve the control accuracy. Simulation results show that this control strategy has nice performance on formation keeping.

Abstract:A two-phase reaction model of the secondary combustor was established to study the effect of water-fuel ratio on engine performance of magnesium-based water ramjet with twice water penetration. The change tendency of specific impulse, temperature and velocity of nozzle exit were obtained with water-fuel ratio. Direct-connected tests were carried out in order to validate the correctness of the numerical simulation. The result shows that there exists the optimum water-fuel ratio, which can improve the performance of water ramjet.

Abstract:A study is presented on a three Dimensional carbon fiber cloth reinforced silicon oxycarbide (3D C_f/Si-O-C) composites with low cost silicon resin as precursors and 3D C_f as reinforcement. Effects of adding SiC powder(SiCp) on the structure, mechanical properties and anti-oxidation properties of 3D C_f/Si-O-C composites were investigated. The results showed that adding SiCP filler could reduce the porosity and improve the interface bonding, therefore increase the properties of composites. But when the content was excessive, it was difficult to dense the matrix of composites at the further cycles and pores existed in the matrix. As a result, the mechanical properties of the composites decreased. It was found that when fabricated with 18.2 weight percent SiCp, the composites exhibited the highest mechanical properties, and the flexural strength and fracture toughness reached 421.3MPa and 13.0 MPa·m^1/2, respectively. Meanwhile, the anti-oxidation properties were improved with the increase of the SiCp content. When fabricated with 25.0 weight percent SiCp, the composites exhibited best oxidation resistance properties, and the composites retained 89.5% of original flexural strength.

Abstract:A parallel one-dimensional model for transient thermal analysis of the metallic thermal protection system (MTPS) for reusable launch vehicle (RLV) is established. Firstly, several heat roads are defined according the structure of the MTPS. The implicit differential formulation of single heat road is given after the discretization of heat roads. Then, the local control equations for series-wound and parallel public nodes are given with the heat equilibrium method. Furthermore, the uniform formulas of the usual boundary conditions are presented. Finally, the global control equation is gained. The transient temperature field is obtained with numerical calculation. The results show that the heat transfer process can be predicted more credibly and accurately by the adoption of the parallel one-dimensional model, which can also provide a more valuable reference for the optimization design of MTPS.

Abstract:CNTs/AlN ceramics were fabricated by hot-pressure sintering, and the effect of sintering aids kinds, contents on the microstructure and properties of CNTs/AlN ceramics was investigated. The phase constitution, fracture morphology and microstructure were analyzed by XRD, SEM and TEM. The result shows that sintering aids (Y₂O₃+CaF₂) were more efficient for the densification of CNTs/AlN ceramics than sintering aids (YF₃+CaF₂). As the contents of sintering aids (Y₂O₃+CaF₂) increased, the density of CNTs/AlN ceramics improved, while the properties of mechanics and thermal-conductivity decreased.

Abstract:In equipment demonstration, it is a difficult task to map vague operational requirements onto quantitative requirements of operational performances logically and reasonably. A requirements analysis approach based on the Quality Function Development (QFD) and Analytic Network Process(ANP) is proposed to solve this problem. It can help analysts to understand the causal relationship between factors and make reasonable judgments. Operational performance ratings can be obtained in the structured operational requirements analysis procedure. Finally, an example is presented to validate the proposed method.