Showing papers by "National University of Defense Technology published in 2004"
TL;DR: The lumped-mass method is applied to study the propagation of elastic waves in two-dimensional binary periodic systems, i.e., periodic soft rubber/epoxy and vacuum/EPoxy composites, for which the conventional methods fail or converge very slowly.
Abstract: The lumped-mass method is applied to study the propagation of elastic waves in two-dimensional binary periodic systems, i.e., periodic soft rubber/epoxy and vacuum/epoxy composites, for which the conventional methods fail or converge very slowly. A comprehensive study is performed for the two-dimensional binary locally resonant phononic crystals, which are composed of periodic soft rubber cylinders immersed in epoxy host. Numerical simulations predict that subfrequency gaps also appear because of the high contrast of mass density and elastic constant of the soft rubber. The locally resonant mechanism in forming the subfrequency gaps is thoroughly analyzed by studying the two-dimensional model and its quasi-one-dimensional mechanical analog. The rule used to judge whether a resonant mode in the phononic crystals can result in a corresponding subfrequency gap or not is found.
337 citations
TL;DR: In this paper, the propagation of longitudinal and transverse elastic waves oblique or perpendicular to the laminations of infinite periodically layered fourfold system is studied for one-dimensional phononic crystals with locally resonant structures.
166 citations
TL;DR: In this paper, a lumped-mass method is introduced to study the propagation of elastic waves in two-dimensional periodic systems, which makes it possible for easy calculations of band structures of phononic crystals with interfaces of large contrast of elastic constants as well as units of any shapes.
Abstract: A lumped-mass method is introduced to study the propagation of elastic waves in two-dimensional periodic systems. First, it is used to calculate the band structure of an array of Pb columns in an epoxy background. Second, the method is applied to the same array of Pb columns in a soft rubber background. The results are compared with those calculated with the well-known plane-wave expansion formalism, where the advantages of the lumped-mass method are pointed out and analyzed. These advantages make it possible for easy calculations of band structures of phononic crystals with interfaces of large contrast of elastic constants as well as units of any shapes.
110 citations
TL;DR: In this article, the authors presented the design and experimental results of a novel overmoded slow-wave high-power microwave (HPM) generator that is featured by its compactness, low-operation magnetic field, and potentially high power and high efficiency.
Abstract: We present the design and experimental results of a novel overmoded slow-wave high-power microwave (HPM) generator that is featured by its compactness, low-operation magnetic field, and potentially high power and high efficiency. The device includes two slow-wave structure (SWS) sections, a resonant cavity, and a tapered waveguide. The resonant cavity was well designed and was used to achieve the axial mode selection and to decrease the length of the SWS sections. The radial mode selection is achieved using the property of "surface wave" of the device to excite the TM/sub 01/ mode while making the higher TM/sub 0n/ modes unexcited. The physical mechanisms of axial and radial mode selections ensure that the microwave is produced with a single mode and a narrow band. The feasibility of low magnetic field operation is also investigated based on the characteristics of the overmoded slow-wave devices. Experiments were carried out at the Spark-2 accelerator. At diode voltage of 474 kV, beam current of 5.2 kA, and guiding magnetic field strength of 0.6 T, a microwave was generated with power of 510 MW, mode of TM/sub 01/, and frequency of 9.54 GHz. The relative half width of the frequency spectrum is /spl Delta/f/f= 0.6%, and the beam-to-microwave efficiency is about 21% in our experiment.
95 citations
TL;DR: This work considers the first level fusion scheme for personal identification using face and palmprint biometrics and finds that the performance is significantly improved in both cases, especially in the case of feature fusion using ICA.
Abstract: This paper presents a novel fusion strategy for personal identification using face and palmprint biometrics. In the context of biometrics, three levels of information fusion schemes have been suggested: feature extraction level, matching score level and decision level. This work considers the first level fusion scheme. The purpose of our paper is to investigate whether the integration of face and palmprint biometrics can achieve higher performance that may not be possible using a single biometric indicator alone. Both Principal Component Analysis (PCA) and Independent Component Analysis (ICA) are considered in this feature vector fusion context. We compare the results of the combined biometrics with the results of the individual face and palmprint. It is found that the performance is significantly improved in both cases, especially in the case of feature fusion using ICA obtaining encouraging results with a 99.17% recognition accuracy rate using a test set sized of 40 people.
78 citations
TL;DR: In this article, a scheme for teleporting an arbitrary and unknown two-particle state from a sender to either one of two receivers is presented, where the sender performs two generalized Bell-state measurements and the receiver introduces an appropriate unitary transformation with the help of the other receiver's Hadamard operation and simple measurements.
73 citations
TL;DR: In this article, a high-impedance surface is chosen as EBG structure, and the numerical simulation is performed by periodic Green's functions plus the moment method, both the bandgap curve of the EBG and the scan characteristics of the phased arrays have been calculated.
Abstract: Electromagnetic bandgap (EBG) material is applied in the design of a phased array of rectangular microstrip patches. The surface-waves could be suppressed by the frequency bandgap and, therefore, the scan blindness could be eliminated. A high-impedance surface is chosen as EBG structure, and the numerical simulation is performed by periodic Green's functions plus the moment method. Both the bandgap curve of the EBG structure and the scan characteristics of the phased arrays have been calculated. The elimination of scan blindness is observed.
70 citations
Journal Article•
TL;DR: To characterize the scale-free feature of complex network quantificationally, the concepts of node-importance, network structure entropy and standard network structureropy are proposed and it is indicated that thenetwork structure entropy will be an important tool to research the complex network.
66 citations
TL;DR: In this paper, unique templates such as filters, carbon nanotube, carbon fiber and silica were used to make porous SiC ceramic with special morphologies, such as SiC nano-net, fiber-inverse and beadinverse, from the preceramic precursor, polymethylsilane (PMS).
Abstract: Sacrificial template technique is widely used in producing porous materials with controlled morphologies and tailored properties. In this paper, unique templates such as filters, carbon nanotube, carbon fiber and silica were used to make porous SiC ceramic with special morphologies. Template derived porous ceramic plates, SiC nano-net, fiber-inverse and bead-inverse porous SiC ceramic were successfully prepared from the preceramic precursor, polymethylsilane (PMS). The synthesis procedures were involved with the infiltration of the templates with appropriate concentration of the preceramic polymer, their curing, pyrolysis and subsequent template removal. The synthesized porous SiC was characterized by SEM, TEM, XRD and BET methods.
62 citations
13 Sep 2004
TL;DR: By investigating the reputation systems in P2P networks, some key issues within the design of trust-based incentive in P 2P networks are outlined and some other approaches addressing the incentive of P2p networks are introduced.
Abstract: In the world of Internet technologies, peer-to-peer (P2P) computing is currently receiving considerable interest However, as experience with P2P networks such as Gnutella shows, the selfish behaviors of peers may lead to serious problems of P2P network, such as Free-riding and Tragedy of Commons In order to solve these problems, there are increasingly considerations on incentive design in the study of P2P systems In this paper, we give a brief survey of researches on trust-based incentive in P2P network By investigating the reputation systems in P2P networks, we outline some key issues within the design of trust-based incentive in P2P networks After that we introduce some other approaches addressing the incentive of P2P networks and conclude the paper with a summary and discussion on future research
61 citations
19 Jul 2004
TL;DR: In this article, the authors identify some social premises behind the social conceptions adopted in multi-agent systems and define levels of modeling constructs and classify organizational and social concepts in the AOSE literature into categories according to their organizational abstractions.
Abstract: AOSE methodologies and models borrow abstractions and concepts from organizational and social disciplines. Although they all view multi-agent systems as organized society, the organizational abstractions, assumptions, concepts, and models in them are actually used in different ways. It is therefore desirable to have a systematic way of analyzing and comparing the organizational and social concepts in AOSE. The contribution of this paper is threefold. Firstly, we identify some premises behind the social conceptions adopted in multi-agent systems. Secondly, we define levels of modeling constructs and classify organizational and social concepts in the AOSE literature into categories according to their organizational abstractions. Finally, we analyze two representative AOSE methodologies and their models, explaining how they use organizational and social concepts to analyze and specify multi-agent system, reflecting various social premises at different levels.
TL;DR: In this article, three-dimensional long range ordered macroporous SiC ceramics were prepared using a low molecular weight polymer precursor, polymethylsilane (PMS), by utilizing sacrificial colloidal silica crystalline arrays as templates which were subsequently etched off with HF (45%) after pyrolysis in an argon atmosphere.
Abstract: Three-dimensionally long range ordered macroporous SiC ceramics were prepared using a low molecular weight polymer precursor, polymethylsilane (PMS), by utilizing sacrificial colloidal silica crystalline arrays as templates which were subsequently etched off with HF (45%) after pyrolysis in an argon atmosphere. SEM, TEM, HRTEM and BET were used to specify the morphologies and BET surface areas of the porous materials. The pore sizes of about 84–658 nm and BET surface areas (pore volumes) of about 584.64 m2 g−1
(0.64 cm3 g−1)–299.44 m2 g−1
(0.25 cm3 g−1) of the achieved macroporous SiC ceramic were approximately proportional to the sizes 112–700 nm of the sacrificial silica sphere templates used. It was found for the first time that the unexpectedly high surfaces area and pore volumes of the achieved porous SiC ceramic were related to the microchannels on the walls that were caused by the interfacial diffusion of oxygen or silica from the silica sphere template into the walls of the SiC framework structures.
22 Jul 2004
TL;DR: Experimental results show that the proposed decentralized and localized density control algorithm outperforms the PEAS algorithm and the sponsor area based algorithm with respect to the number of working sensors needed, thus longer system lifetime can be obtained, while preserving completely the sensing coverage of the original network.
Abstract: In wireless sensor networks that consist of a large number of low-power, short-lived, unreliable sensors, one of the important design challenges is to reduce energy consumption and prolong network lifetime. In this paper, we propose a decentralized and localized density control algorithm that prolongs network lifetime by keeping a minimal number of sensors in active mode while not scarifying any sensing coverage. Experimental results show that our algorithm outperforms the PEAS algorithm and the sponsor area based algorithm with respect to the number of working sensors needed (about 30% more off-duty eligible nodes), thus longer system lifetime can be obtained, while preserving completely the sensing coverage of the original network.
TL;DR: A distributed approach is proposed for the control of remote robots, so that the time delay in one control loop does not affect performance of the others, and a vision-based method is developed to monitor and render interactions between the robots.
Abstract: With the rapid development of information technology, the Internet has evolved from a simple data-sharing media to an amazing information world where people can enjoy various services. Recently, the use of the Internet has been expanded to the field of automation, i.e., using the Internet as a tool to control equipment located at remote sites. This work presents a system that enables multiple operators at different sites to cooperatively control multiple robots with real-time force reflecting via the Internet. To overcome instability and reliability problems caused by random time delay of the Internet communication, we adopt an event as the reference for the controller design. To improve real-time efficiency and reduce the complexity of the controller, a distributed approach is proposed for the control of remote robots, so that the time delay in one control loop does not affect performance of the others. A vision-based method is developed to monitor and render interactions between the robots. The usefulness and effectiveness of the developed method and system have been verified by teleoperation experiments on a two-robots cooperative system among Hong Kong, mainland China, and the U.S.
TL;DR: In this article, the character of operators to distinguish the elements of a full product basis set in a multipartite system is analyzed, and it is shown that distinguishing perfectly these product bases needs only local projective measurements and classical communication, and these measurements cannot damage each product basis.
Abstract: Nonlocality without entanglement is an interesting field. A manifestation of quantum nonlocality without entanglement is the possible local indistinguishability of orthogonal product states. In this paper we analyze the character of operators to distinguish the elements of a full product basis set in a multipartite system, and show that distinguishing perfectly these product bases needs only local projective measurements and classical communication, and these measurements cannot damage each product basis. Employing these conclusions one can discuss local distinguishability of the elements of any full product basis set easily. Finally we discuss the generalization of these results to the locally distinguishability of the elements of incomplete product basis set.
TL;DR: Three-dimensional long range ordered hollow SiC and filled SiCN sphere assemblies were prepared for the first time by embedding low molecular weight pre-ceramic polymers of polymethylsilane and polysilazane into sacrificial 3DOM carbon templates which were subsequently burned out in air after pyrolysis under a nitrogen atmosphere.
06 Jun 2004
TL;DR: A novel workflow model named Service/Resource Net (SRN) is proposed for Web service composition, which is an extended Petri-net-based model with some new elements, such as time, resource taxonomy, condition, etc.
Abstract: The emergence of Web services has led to more interest into Web service composition, which is an active area of research. The formidable problem of efficient and effective composition of existing Web services is the subject of much current attention. The study of workflow model is one of the most important parts and a key layer of Web service composition. The existing approaches have difficulties in modeling dynamic and complex service composition process, so we propose a novel workflow model named Service/Resource Net (SRN) for Web service composition, which is an extended Petri-net-based model with some new elements, such as time, resource taxonomy, condition, etc. To establish formal concept system of Web service taxonomy in SRN, we present Web service semigroup based on group theory. Moreover, meta-service is proposed based on the definition of generating element in cyclic monoid. As the supplement of traditional analysis methods of basic Petri net, some new methods based on graph theory are presented for SRN analyzing and evaluating. For system and methodology validation purpose, SRN is applied to a case study in our research project.
29 Sep 2004
TL;DR: This paper follows Hong's Gabor filter based enhancement scheme but uses a circle support filter and tunes the filter’s frequency and size differently and does improve the performance of minutiae detection.
Abstract: Fingerprint minutiae are prevalently used in AFISs. The extraction of fingerprint minutiae is heavily affected by the quality of fingerprint images. This leads to the incorporation of a fingerprint enhancement module in AFIS to make the system robust with respect to the quality of input fingerprint images. Most of existing enhancement methods suffer from mainly two kinds of defects: (1) time consuming and thus unusable in time critical applications; and (2) blocky effect in the enhanced image. This paper follows Hong’s Gabor filter based enhancement scheme (IEEE Trans. PAMI, vol.20, no.8, pp. 777-789, 1998) but uses a circle support filter and tunes the filter’s frequency and size differently. This scheme can enhance the fingerprint image rapidly and overcome the blocky effect effectively and does improve the performance of minutiae detection.
TL;DR: In this article, the exclusive semileptonic decays of the p-wave excited mesons were investigated in the framework of heavy quark effective theory. And the decay rates and branching ratios were computed with the inclusion of corrections of order 1/m{1/m}{Q}$ with respect to the Isgur-Wise functions up to the sub-leading order of the light quark expansion.
Abstract: We study the exclusive semileptonic decays ${B}_{s}\ensuremath{\rightarrow}{D}_{s0}^{*}\mathcal{l}\overline{\ensuremath{
u}}$ and ${B}_{s}\ensuremath{\rightarrow}{D}_{s1}^{*}\mathcal{l}\overline{\ensuremath{
u}},$ where p-wave excited ${D}_{s0}^{*}$ and ${D}_{s1}^{*}$ states are identified with the newly observed ${D}_{\mathrm{sJ}}(2317)$ and ${D}_{\mathrm{sJ}}(2460)$ states Within the framework of heavy quark effective theory the Isgur-Wise functions up to the subleading order of the heavy quark expansion are calculated by QCD sum rules The decay rates and branching ratios are computed with the inclusion of corrections of order ${1/m}_{Q}$ We point out that investigation of ${B}_{s}$ semileptonic decays to excited ${D}_{s}$ mesons may provide some information about the nature of the new ${D}_{\mathrm{sJ}}^{*}$ mesons
TL;DR: The piecewise linear current density recursive convolution (PLCDRC) finite-difference time-domain (FDTD) method for isotropic dispersive media greatly improves accuracy over recursive convolutions (RC) and CDRC FDTD approaches but retains its speed and efficiency advantages as discussed by the authors.
Abstract: The piecewise linear current density recursive convolution (PLCDRC) finite-difference time-domain (FDTD) method for isotropic dispersive media greatly improves accuracy over recursive convolution (RC) and current density recursive convolution (CDRC) FDTD approaches but retains its speed and efficiency advantages. This letter extends this approach to anisotropic magnetoactive plasmas which incorporates both anisotropy and frequency dispersion at the same time, enabling the transient solutions of electromagnetic wave propagation in anisotropic magnetoactive plasmas. The high efficiency and accuracy of the method are confirmed by computing the reflection and transmission through a magnetized plasma layer, with the direction of propagation parallel to the direction of the biasing field. A comparison to frequency-domain analytic results and CDRC FDTD results is included.
13 Dec 2004
TL;DR: A new distributed clustering algorithm for dynamically organizing mobile nodes into clusters in which the probability of path availability can be bounded is presented and a data replication policy is proposed to improve data availability during network partitioning.
Abstract: In Mobile Ad Hoc Networks (MANET), network partitioning occurs when nodes move freely and cause disconnections frequently. Network partitioning is a wide-scale topology change that can cause sudden and severe disruptions to ongoing data access, and consequently data availability is decreased. A new distributed clustering algorithm is presented in this paper for dynamically organizing mobile nodes into clusters in which the probability of path availability can be bounded. Based on this clustering algorithm, a data replication policy is proposed to improve data availability during network partitioning. Through theoretic analysis our algorithm has proper complexity. Simulation results show that the clusters created by our clustering algorithm have desirable properties and our algorithms improve the data availability effectively in MANET environment.
TL;DR: It is proved that the Neimark-Sacker bifurcation occurs when the bifURcation parameter exceeds a critical value.
TL;DR: Using the supercell plane wave method, a bend-shaped linear defect in a two-dimensional acoustic band-gap material consisting of water cylinders in mercury background was investigated in this paper.
TL;DR: In this paper, the authors present the results of an experimental investigation concerning composite structure models for hypervelocity impact-resistant composites, which involve several material systems, dual-wall configurations, fabric-reinforced silicon carbide ceramic-matrix composite as impact-facing sheet, hollow sphere energy-absorption materials, carbon fabric and Kevlar fabric reinforced epoxy matrix composites as pressure walls.
TL;DR: The author proposes a novel method, the contoured correlation-fringe-pattern (CCFP) method, by which speckle-noise-free fringe patterns can be generated for ESPI, and eliminates the two main disadvantages of the phase-shifting (stepping) methods of ESPI.
Abstract: Speckle fringe patterns of electronic speckle pattern interferometry (ESPI) are full of high-level speckle noise and are mainly processed by phase-shifting methods that normally require three speckle fringe patterns or more. The author proposes a novel method, the contoured correlation-fringe-pattern (CCFP) method, by which speckle-noise-free fringe patterns can be generated for ESPI. The application of this novel method is extended to the phase-shifting or phase-stepping for ESPI after its improvement. It generates speckle-noise-free phase fringes and remains valid for single phase-step condition, thus eliminates the two main disadvantages of the phase-shifting (stepping) methods of ESPI.
13 Dec 2004
TL;DR: A new feature extraction method for palmprint recognition using the discrete Meyer wavelet transform to replace the “a trous” transform and the ridgelet transform, which is applied to each block which is subbanded after the digital curvelet transform.
Abstract: In this paper, we present a new feature extraction method for palmprint recognition The digital curvelet transform is revised here and used to extract the palmprint features In our algorithm, we use the discrete Meyer wavelet transform to replace the “a trous” transform, then apply the ridgelet transform to each block which is subbanded after the discrete Meyer wavelet transform from the palmprint image Our work is carried on the PolyU Palmprint Database Dealing with the palmprint image sized of 64 × 64, our new strategy acquires 4 × 128 × 128 curvelet coefficients Based on the system performance, the best coefficients threshold can be obtained With this threshold the curvelet coefficients are filtered and less than 2% of coefficients are selected With this compressed coefficients set, the correct recognition rate of our palmprint identification experiment is up to 95.25%.
25 Oct 2004
TL;DR: A Gauss-Poisson joint distribution model for degradation failure, which is more precise than the Weibull model in processing degradation failure data, is presented, which can assess and verify the reliability level of the capacitors and also save testing cost.
Abstract: A high-energy-density self-healing metallized film pulse capacitor is the key component of the inertial confinement laser fusion facility. The reliability level of capacitors is connected with operating reliability and maintenance expenses of the entire system. By analyzing the degradation mechanism and characteristics of performance of metallized pulse capacitors, and by comparing to the Weibull distribution, this paper presents a Gauss-Poisson joint distribution model for degradation failure, which is used to model nondestructive testing. The Gauss-Poisson model is more precise than the Weibull model in processing degradation failure data. This technique can assess and verify the reliability level of the capacitors and also save testing cost. In addition, this model can be applied to evaluate and identify the reliability of other equipment with respect to the degradation mechanism.
TL;DR: In this article, the synthesis feasibility of nanocrystalline AlN via a modified carbothermal reduction-nitridation route from a low-temperature combustion precursor containing alumina and carbon was studied in detail.
TL;DR: The general picture of Grid computing in China is provided, and shows the great efforts, devotion and confidence in China to use Grid technology to boost the society, economics and scientific research.
Abstract: Grid computing presents a new trend to distributed computation and Internet applications, which can construct a virtual single image of heterogeneous resources, provide uniform application interface and integrate widespread computational resources into super, ubiquitous and transparent aggregation. In the adoption of Grid computing, China, who is facing more resource heterogeneity and other specific demands, has put much effort on both research and practical utilization. In this paper, we introduce the major China Grid research projects and their perspective applications. First we give the overview of the four government-sponsored programs in Grid, namely the China National Grid, ChinaGrid, NSFC Grid, and ShanghaiGrid. Then we present six representative ongoing Grid systems in details, which are categorized into Grid middleware and Grid application. This paper provides the general picture of Grid computing in China, and shows the great efforts, devotion and confidence in China to use Grid technology to boost the society, economics and scientific research.
TL;DR: A novel method to generate aspeckle-noise-free fringe pattern from a single speckle fringe pattern and to extract the phase field from the new pattern and the resultant fringe pattern is normalized automatically so that the full phase field can be extracted from this single fringe pattern by the single-image phase-shifting method.
Abstract: Speckle fringe patterns of ESPI are full of high-level speckle noise and normally are processed by phase shifting methods that require multi speckle fringe patterns. We propose a novel method to generate a speckle-noise-free fringe pattern from a single speckle fringe pattern and to extract the phase field from the new pattern. With the new method, the correlation between two speckle patterns is performed only within contour windows instead of rectangular windows and this contoured correlation results in a smooth, normalized fringe pattern without speckle noise. The new ESPI fringe patterns are speckle-noise-free and of comparable quality to that of moire and hologram, which is unimaginable with traditional ESPI methods. In addition to the smoothness, the resultant fringe pattern is normalized automatically so that the full phase field can be extracted from this single fringe pattern by the single-image phase-shifting method.