Showing papers by "Xidian University published in 1999"
TL;DR: A new method of phase error estimation that utilizes the weighted least-squares (WLS) algorithm is presented for synthetic aperture radar (SAR)/inverse SAR (ISAR) autofocus applications, and it is robust for many kinds of scene content.
Abstract: A new method of phase error estimation that utilizes the weighted least-squares (WLS) algorithm is presented for synthetic aperture radar (SAR)/inverse SAR (ISAR) autofocus applications. The method does not require that the signal in each range bin be of a certain distribution model, and thus it is robust for many kinds of scene content. The most attractive attribute of the new method is that it can be used to estimate all kinds of phase errors, no matter whether they are of low order, high order, or random. Compared with other methods, the WLS estimation is optimal in the sense that it has the minimum variance of the estimation error. Excellent results have been obtained in autofocusing and imaging experiments on real SAR and ISAR data.
235 citations
TL;DR: In this paper, the authors investigated the self-deflection process of bright screening-photovoltaic solitons by taking diffusion effects into account, and they found that the center of the optical beam moves on a parabolic trajectory and moreover, the central spatial-frequency component shifts linearly with the propagation distance.
Abstract: Steady-state dark (or bright) spatial solitons are predicted for biased photovoltaic–photorefractive materials when the diffraction of an optical beam is exactly compensated for by nonlinear self-defocusing (or self-focusing) that is due both to the photovoltaic effect and to spatially nonuniform screening of the applied field. These solitons differ from previously observed steady-state photorefractive or photovoltaic spatial solitons in their properties and experimental condition. These biased photovoltaic solitons are known as the screening-photovoltaic solitons. If the bias field is much stronger than the photovoltaic field, then the screening-photovoltaic solitons are just like the screening solitons. If the applied field is absent, they degenerate into photovoltaic solitons in the closed-circuit condition. We investigate the self-deflection process of bright screening-photovoltaic solitons by taking diffusion effects into account. By use of perturbation techniques it is found that the center of the optical beam moves on a parabolic trajectory and, moreover, that the central spatial-frequency component shifts linearly with the propagation distance. Both the spatial deflection and the angular deviation are proportional to the sum of two dimensionless quantities that are associated with the bias field and the photovoltaic field, respectively. The drift process and the photovoltaic process play an equivalent role in the self-bending process.
172 citations
TL;DR: The relations between fuzzy entropy, fuzzy Hamming distance, divergence measuredefined by Bhandari and Pal (1993), and divergence measure defined in this paper are studied and quite a general conclusion is obtained.
172 citations
TL;DR: Some subsethood measure formulas are presented from the point of view of set-theoretic approach, and from fuzzy implication operator, and an application of subsethoodMeasure to cluster validity is shown.
103 citations
TL;DR: The proximity measure introduced by Pappis is analyzed and a general definition of proximity measure is given, based on the axiom definition of similarity measure, to simplify the process of comparison of some similarity measures of fuzzy values.
100 citations
TL;DR: In this article, a new line feed structure for a large spherical radio telescope (LSRT) is presented, and nonlinear dynamic analysis of the suspended cable system is carried out with some sensible results that could be useful to the real engineering of LSRT.
93 citations
71 citations
TL;DR: Based on a far-field asymptotic solution of the Helmholtz equation a vector theory to describe the propagation of an off-axis Gaussian wave is developed, and the accurate formulas represented in terms of elementary functions are derived.
Abstract: Based on a far-field asymptotic solution of the Helmholtz equation a vector theory to describe the propagation of an off-axis Gaussian wave is developed, the accurate formulas represented in terms of elementary functions are derived, and the propagation properties such as wave spot size and divergence angle are discussed in detail. The applicable range of scalar theory is also presented. A relative error criterion of optical intensity is given by ∊ = sin2 α.
34 citations
TL;DR: In this paper, single phase and nanosized microstructure Bi 4 Ti 3 O 12 thin films were prepared on fused quartz substrate by metallorganic solution deposition technique using titanium butoxide and bismuth nitrate at relatively low annealing temperature.
29 citations
TL;DR: In this paper, the authors apply the concept of the mazer to the two-photon process and propose the idea of the twophoton mazer, and calculate its emission probability in the special case of a mesa mode function.
Abstract: We apply the concept of the mazer to the two-photon process and propose the idea of the two-photon mazer. We establish the general quantum theory of the two-photon mazer and calculate its emission probability in the special case of a mesa mode function. We study not only the case in which the cavity field is initially in a number state, but also the case in which the cavity field is initially in a coherent state. Under the condition of an initial coherent field, the emission probability shows the collapse-revival phenomena, which have different features in different regimes. In the thermal-atom regime, the collapse revivals are similar to that in the two-photon Jaynes-Cummings model. In the critical regime, the collapse revivals look like that in the one-photon Jaynes-Cummings model. In the ultracold-atom regime, the collapse revivals are different from those in the above two regimes. The reasons for these results have been analyzed.
18 citations
TL;DR: A new attack on block ciphers is introduced, which is termed integral cryptanalysis, which relies on similar principles to differential crypt analysis, but is based on different statistics.
Abstract: A new attack on block ciphers is introduced, which is termed integral cryptanalysis. It relies on similar principles to differential cryptanalysis, but is based on different statistics. It is shown that this method is more effective than differential cryptanalysis in attacking SAFER+.
31 Oct 1999
TL;DR: A new algorithm for network probabilistic connectivity is presented, and a new method to construct sub-graphs for the obtained events is proposed, which can greatly reduce the dimensions of network states space.
Abstract: A new algorithm for network probabilistic connectivity is presented. In this algorithm, the multi-step decomposition algorithm of the network states space is given. A new method to construct sub-graphs for the obtained events is proposed, which can greatly reduce the dimensions of network states space. An iterative computation is used to approximate lower bound of the value of the probabilistic connectivity. Compared with other algorithms, ours is characterized by its fast computing and converging speed, and is most suitable for approximating computation.
TL;DR: In this paper, a novel adaptive multi-wavelet prefilter is presented which is designed to overcome the low-pass property of a scaling function in conventional wavelet transforms, and simulation results show that the approximation accuracy of the prefiltering algorithm is satisfactory.
Abstract: In conventional wavelet transforms, prefiltering is not necessary due to the lowpass property of a scaling function. This is no longer true for multiwavelet transforms. A novel adaptive multiwavelet prefilter is presented which is designed to overcome this problem. Simulation results show that the approximation accuracy of the prefiltering algorithm is satisfactory.
TL;DR: An information criterion is introduced for extracting the minor component associated with the covariance matrix of an input process and an adaptive stepsize learning algorithm (ASMCEX) is proposed that has an equilibrium point.
Abstract: An information criterion is introduced for extracting the minor component associated with the covariance matrix of an input process. An adaptive stepsize learning algorithm (ASMCEX) is proposed. The analysis shows that the ASMCEX algorithm has an equilibrium point. The simulations show that the ASMCEX algorithm can improve the convergence speed significantly.
TL;DR: Based on this method, the verification of the protocols becomes independent of model checking tools and is illustrated with an example on the Needham-Schroeder public-key protocol.
Abstract: A general method, which can be used to verify the two-party cryptographic protocols, is present in this paper. Our approach makes use of running modes of the two-party cryptographic protocols to analyze the protocols. Based on this method, the verification of the protocols becomes independent of model checking tools. Finally, this approach is illustrated with an example on the Needham-Schroeder public-key protocol.
13 Oct 1999
TL;DR: This paper presents an instantaneous adaptive bit-assignment (IABA) algorithm for lossless compression of multichannel electroencephalograms (EEGs) that features random data access, real-time decoding, and approximately half storage reduction.
Abstract: This paper presents an instantaneous adaptive bit-assignment (IABA) algorithm for lossless compression of multichannel electroencephalograms (EEGs). This algorithm features random data access, real-time decoding, and approximately 50% storage reduction.
TL;DR: The problem of parameters selection for potential function used to initialize cluster centers is discussed, and two formulas are given for determining these parameters.
Abstract: The problem of parameters selection for potential function used to initialize cluster centers is discussed, and two formulas are given for determining these parameters. Then a new potential function to initialize cluster centers is also given which is computational effective. Finally, a set of compared experiments is presented to show the effectiveness of the proposed methods.
TL;DR: In this article, a multiphase linear induction coilgun (LIL) and a 4-stage reconnection coilgun were designed and analyzed for use in microgravity experimental research, and the results showed that the requirement of very low acceleration is difficult, because the acceleration fluctuation of both designs is large.
Abstract: Variants of the coilgun are considered for use in microgravity experimental research. Subscale point designs are described for a payload of 50 kg and muzzle velocity of 30 to 40 m/s. A multiphase linear induction coilgun (LIL) (one stage with six coils and constant pitch) and a 4-stage reconnection coilgun were designed and analyzed. The results show that the requirement of very low acceleration is difficult, because the acceleration fluctuation of both designs is large. But differences between them are revealed. The induced current in the armature of the reconnection gun distributes much more unevenly than in the LIL, and this will cause mechanical and thermal problems. The efficiency of energy transformation in the connection gun is better than LIL of this specific design. Mechanical structural analysis results of the reconnection coilgun are also presented. The results show the coils are structurally sound. The armature is a nonlinear problem of both material and geometry so the available code Super SAP is adopted. However, the armature requires structural reinforcement.
01 Oct 1999
TL;DR: In this article, a recursive algorithm for decoding turbo codes with a convolutional interleaver is proposed, based on a symbol-by-symbol maximum a posteriori probability algorithm.
Abstract: A novel type of recursive algorithm for decoding turbo codes with a convolutional interleaver is proposed, based on a symbol-by-symbol maximum a posteriori probability algorithm. It requires only a forward recursion which can be performed in parallel, and the number of variables to be stored does not increase with decoding delay. This algorithm can be used in continuous decoding for both recursive and nonrecursive encoders. Simulation results of demonstrating its performance are presented.
TL;DR: In this article, the internal strain in Bi4Ti3O12 thin films was calculated from peak shifts and broadening of XRD patterns with an increase in annealing temperature, the uniform strain decreased from positive to zero and then to negative, and the non-uniform strain decreased and was negative.
Abstract: Ferroelectric Bi4Ti3O12 thin films with single phase and nanosized microstructure were prepared on Pt/Ti/SiO2/Si(111) substrate by metalorganic solution deposition using titanium butoxide and bismuth nitrate at relatively low annealing temperatures The internal strain in Bi4Ti3O12 thin films was calculated from the peak shifts and broadening of XRD patterns With increase in annealing temperature, the uniform strain decreased from positive to zero and then to negative, and the non-uniform strain decreased and was negative The total strain was negative and in the range of -02%–-10%, from which the stress of the films was calculated to be about -14×109 N/m2 The mode values of strain decreased with increase in annealing temperature and increased with increase in film thickness The dielectric constant increased with increase in annealing temperature and film thickness The dielectric properties were interpreted by considering the influence of strain, grain size, and grain boundaries The strain lowered the polarization and increased the dielectric constant The larger the grain size and the thinner the grain boundary, the greater the dielectric constant The influence of grain size and grain boundary was stronger than that of the strain
TL;DR: Cyclotron-resonance energy gain of injected electrons subjected to an intense circularly polarized laser field and the magnetic field induced in a low-density plasma is investigated theoretically and limits to the energy gain are discussed.
Abstract: Cyclotron-resonance energy gain of injected electrons subjected to an intense circularly polarized laser field and the magnetic field induced in a low-density plasma is investigated theoretically. By considering the inverse Faraday effect (IFE), where a circularly polarized finite area laser beam induces an axial magnetic field in a plasma, it is found that very interesting energy gains can be obtained by Doppler-shifted cyclotron resonance in this field for the appropriate injection velocity. This same IFE field also acts to confine these electrons radially and, on exiting the plasma adiabatically, it is in this way that the transverse electron energy is converted to axial energy. Two limits to the energy gain are discussed: (i) cyclotron radius of the energetic electrons becoming comparable to the beam, and (ii) axial dephasing.
TL;DR: Researchers seek a means of constructing a powerful code with the same performance as long codes so as to enable ML decoding to be broken down into simpler partial decoding steps.
Abstract: Researchers seek a means of constructing a powerful code with the same performance as long codes so as to enable ML decoding to be broken down into simpler partial decoding steps. Turbo codes represent one of the most successful methods; they consist of two simple constituent encoders linked by an interleaver. The interleaver performs a permutation function and changes the weight distribution of the code, helping to increase the minimum distance and lower the error coefficient. The influence of interleavers on the performance of turbo codes is investigated.
TL;DR: In this article, a novel orthogonal prefilter satisfying the Strang-fix condition was designed for common orthonormal compactly supported multiscaling functions for GHM 2 wavelets.
Abstract: A novel orthogonal prefilter satisfying the Strang-Fix condition is designed for common orthonormal compactly supported multiscaling functions Compared with the method given by Xia (see IEEE Trans Signal Process, vol 46, p 1558-1570, 1998) for GHM 2 wavelets, the /spl phi/(/spl omega/) of the /spl phi/(t) constructed using the proposed method has second-order flatness at /spl omega/=0
TL;DR: A novel method is proposed to optimize co-redundancy degree which is then used to construct a family of nearly semi-orthogonal interpolating wavelets, and by performing the local orthogonalization on the obtained wavelet functions the scheme is efficient in designing practical wavelet systems with good performance indexes.
13 Aug 1999
TL;DR: A parametric RELAX-based algorithm to extract the target features when there are MTRC errors in radar imaging is proposed and the results show that the mean squared errors of the parameter estimates obtained by the algorithm can approach the corresponding CRB's.
Abstract: In this paper, we establish a data model for the feature extraction of point scatterers in the presence of motion through resolution cell (MTRC) errors and unknown noise, the data model is a sum of 2-dimensional sinusoidal signals with quadratic phase errors, which are caused by 'range walk' and 'variable range rate' respectively. Based on the data model, we propose a parametric RELAX-based algorithm to extract the target features when there are MTRC errors in radar imaging. The algorithm minimizes a complicated nonlinear least-squares (NLS) cost function, and it is performed alternately by letting only the parameters and errors of one scatterer vary and freezing all others at their most recently determined values. The Cramer-Rao bounds (CRB's) for the parameters of the data model are also derived. We compare the performance of the proposed algorithm with the CRB's by simulation. And the results show that the mean squared errors of the parameter estimates obtained by the algorithm can approach the corresponding CRB's. Then we apply the algorithm to the simulated radar data with MTRC errors. The proposed algorithm generates 'focused' point image with higher resolution, which conforms the algorithm and the data model.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
17 May 1999
TL;DR: In this paper, the prerequisite courses and contents of a course in EMC given in the Department of Microwave Telecommunication Engineering at Xidian University, China are described and the resource extension technique taken during teaching the EMC course is presented in detail.
Abstract: This paper describes the prerequisite courses and contents of a course in EMC given in the Department of Microwave Telecommunication Engineering at Xidian University, China. The resource extension technique taken during teaching the EMC course is presented in detail, meanwhile, the aim and effect of the course are outlined in this paper.
01 Jan 1999
TL;DR: In this paper, an entropy-based topological optimization method for truss structures is presented, where the density distribution of energy is defined first, and then the energy distribution is found, optimal cross-sectional areas are found.
Abstract: This paper presents an entropy – based topological optimization method for truss structures. A group of variables meaning the density distribution of energy is defined first, so that a bridge between energy distribution and topological optimization is built. After the energy distribution is found, optimal cross – sectional areas are found. Then the above two steps are executed in turn till the convergence is reached. Next, the stiffness and strength reliability corresponding to the final topology are computed with reasonable results.
TL;DR: Theoretical analysis shows that the OWBE convergences faster than the conventional LMS based linear equalizer(LE), while the increase in the computational complexity is very slow.
Abstract: An orthonomal wavelets based equalizer (OWBE) is presented. The equalizer is represented by a set of orthonomal wavelets and the corresponding coefficients. The paper gives the structure and also the adaption algorithm of the OWBE. Theoretical analysis shows that the OWBE convergences faster than the conventional LMS based linear equalizer(LE), while the increase in the computational complexity is very slow. Several simulations are performed to evaluate the behavior of the OWBE.
TL;DR: In this article, a hybridization method of moment (MOM) and equivalent edge currents (EECs) is presented to study the electromagnetic (EM) scattering from the slot antennas fed by the waveguides with arbitrary termination.
Abstract: In this paper, a hybridization method of moment (MOM) and equivalent edge currents (EECs) is presented to study the electromagnetic (EM) scattering from the slot antennas fed by the waveguides with arbitrary termination. The EECs is applied to calculate the EM scattering of a conducting plane, including the diffraction of edge, while the MOM is used to obtain the fields in the slots and deal with the coupling between them In conjunction with them, the EM scattering of the slot antennas can be evaluated quickly. Several results are presented, demonstrating the applicability of this technique.
TL;DR: Study of the discrete time Markov decision processes (MDP) with expected discounted total reward, where the state space is countable, the action space is measurable, the reward function is extended real-valued, and the discount rate may be any real number.
Abstract: This paper studies the discrete time Markov decision processes (MDP) with expected discounted total reward, where the state space is countable, the action space is measurable, the reward function is extended real-valued, and the discount rate may be any real number. Two conditions (GC) and (C) are presented, which are weaker than that presented in literature. By eliminating some worst actions, the state space S can be partitioned into sets S
∞, S
−∞, S
0, on which the optimal value function equals +∞ , −∞ or is finite, respectively. Furthermore, the validity of the optimality equation is shown when its right hand side is well defined, especially, when it is restricted to the subset S
0. The reward function r (i, a) is finite and bounded above in a for each i∈S
0. Finally, some sufficient conditions for (GC) and (C) are given.