- 毕军;刘冰洋;吴建平;沈燕;
A signature-and-verification-based method, automatic peer-to-peer anti-spoofing (APPA), is proposed to prevent IP source address spoofing. In this method, signatures are tagged into the packets at the source peer, and verified and removed at the verification peer where packets with incorrect signatures are filtered. A unique state machine, which is used to generate signatures, is associated with each ordered pair of APPA peers. As the state machine automatically transits, the signature changes accordingly. KISS random number generator is used as the signature generating algorithm, which makes the state machine very small and fast and requires very low management costs. APPA has an intra-AS (autonomous system) level and an inter-AS level. In the intra-AS level, signatures are tagged into each departing packet at the host and verified at the gateway to achieve finer-grained anti-spoofing than ingress filtering. In the inter-AS level, signatures are tagged at the source AS border router and verified at the destination AS border router to achieve prefix-level anti-spoofing, and the automatic state machine enables the peers to change signatures without negotiation which makes APPA attack-resilient compared with the spoofing prevention method. The results show that the two levels are both incentive for deployment, and they make APPA an integrated anti-spoofing solution.
2009年04期 v.14 413-422页 [查看摘要][在线阅读][下载 675K] [下载次数:91 ] |[网刊下载次数:0 ] |[引用频次:9 ] |[阅读次数:0 ] - 夏尔雷;章毓晋;
Many video surveillance applications rely on efficient motion detection. However, the algorithms are usually costly since they compute a background model at every pixel of the frame. This paper shows that, in the case of a planar scene with a fixed calibrated camera, a set of pixels can be selected to compute the background model while ignoring the other pixels for accurate but less costly motion detection. The calibration is used to first define a volume of interest in the real world and to project the volume of interest onto the image, and to define a spatial adaptive subsampling of this region of interest with a subsampling density that depends on the camera distance. Indeed, farther objects need to be analyzed with more precision than closer objects. Tests on many video sequences have integrated this adaptive subsampling to various motion detection techniques.
2009年04期 v.14 423-433页 [查看摘要][在线阅读][下载 1676K] [下载次数:67 ] |[网刊下载次数:0 ] |[引用频次:0 ] |[阅读次数:0 ] - 杨敬钰;彭义刚;徐文立;戴琼海;
Many algorithms have been proposed to achieve sparse representation over redundant dictionaries or transforms. A comprehensive understanding of these algorithms is needed when choosing and designing algorithms for particular applications. This research studies a representative algorithm for each category, matching pursuit (MP), basis pursuit (BP), and noise shaping (NS), in terms of their sparsifying capability and computational complexity. Experiments show that NS has the best performance in terms of sparsifying capability with the least computational complexity. BP has good sparsifying capability, but is computationally expensive. MP has relatively poor sparsifying capability and the computations are heavily dependent on the problem scale and signal complexity. Their performance differences are also evaluated for three typical applications of time-frequency analyses, signal denoising, and image coding. NS has good performance for time-frequency analyses and image coding with far fewer computations. However, NS does not perform well for signal denoising. This study provides guidelines for choosing an algorithm for a given problem and for designing or improving algorithms for sparse representation.
2009年04期 v.14 434-443页 [查看摘要][在线阅读][下载 816K] [下载次数:165 ] |[网刊下载次数:0 ] |[引用频次:7 ] |[阅读次数:0 ] - 张宇;杨唐文;孙增圻;
A neuro-sliding-mode control (NSMC) strategy was developed to handle the complex nonlinear dynamics and model uncertainties of flexible-link manipulators. A composite controller was designed based on a singularly perturbed model of flexible-link manipulators when the rigid motion and flexible motion are decoupled. The NSMC is employed to control the slow subsystem to track a desired trajectory with a traditional sliding mode controller to stabilize the fast subsystem which represents the link vibrations. A stability analysis of the flexible modes is also given. Simulations confirm that the NSMC performs better than the traditional sliding-mode control for controlling flexible-link manipulators. The control strategy not only gives good tracking performance for the joint angle, but also effectively suppresses endpoint vibrations. The simulations also show that the control strategy has a strong self-adaptive ability for controlling manipulators with different parameters.
2009年04期 v.14 444-451页 [查看摘要][在线阅读][下载 1368K] [下载次数:67 ] |[网刊下载次数:0 ] |[引用频次:13 ] |[阅读次数:0 ] - 张国艳;王小云;
The scheme introduced by Hwang and Liu in 2008 is shown to be insecure against the key replacement attack. A more practical attack model is introduced, and according to this model, an efficient certificateless encryption scheme is presented which is IND-CCA secure against both Type I and Type II attackers without random oracle. This encryption scheme can defend against the malicious key generation center attack, and can reach Girault's trusted level 3 as in traditional public key infrastructure-based cryptography. This certificateless encryption scheme has a shorter public key than other schemes in the standard model.
2009年04期 v.14 452-459页 [查看摘要][在线阅读][下载 392K] [下载次数:99 ] |[网刊下载次数:0 ] |[引用频次:7 ] |[阅读次数:0 ] <正>Tsinghua University celebrated its 98th anniversary on April 26, 2009, bringing together alumni from around the country and all over the world for a weekend of reunions. The
2009年04期 v.14 459页 [查看摘要][在线阅读][下载 226K] [下载次数:6 ] |[网刊下载次数:0 ] |[引用频次:0 ] |[阅读次数:0 ] - 焦胜才;葛宁;陆建华;蒋明;
A compact antenna with extended band-notched characteristics was designed for ultra wideband (UWB) communications. The antenna consists of a crescent-shaped elliptical patch with a T-shaped stub and a square ground board plane. The antenna is easily integrated with radio-frequency/microwave circuits to reduce the manufacturing cost. The central frequency and the notch bandwidth can be adjusted by changing the size of the T-shaped stub. Simulations verify the design characteristics. Measurements show that the antenna produces the UWB working bandwidth.
2009年04期 v.14 460-464页 [查看摘要][在线阅读][下载 570K] [下载次数:50 ] |[网刊下载次数:0 ] |[引用频次:0 ] |[阅读次数:0 ] - 张浩翔;张林;山秀明;李安国;
Peer-to-peer (P2P) networks aggregate enormous storage and processing resources while minimizing entry and scaling costs. Gnutella-like P2P networks are complex heterogeneous networks, in which the underlying overlay topology has a power-law node degree distribution. While scale-free networks have great robustness against random failures, they are vulnerable to deliberate attacks where highly connected nodes are eliminated. Since high degree nodes play an important role in maintaining the connectivity, this paper presents an algorithm based on random walks to locate high degree nodes in P2P networks. Simulations demonstrate that the algorithm performs well in various scenarios and that heterogeneous P2P networks are very sensitive to deliberate attacks.
2009年04期 v.14 465-469页 [查看摘要][在线阅读][下载 408K] [下载次数:40 ] |[网刊下载次数:0 ] |[引用频次:0 ] |[阅读次数:0 ] - 钱镱;崔晓伟;陆明泉;冯振明;
For certain system models, the structure of the Kalman filter is equivalent to a second-order variable gain digital phase-locked loop (DPLL). To apply the knowledge of DPLLs to the design of Kalman filters, this paper studies the steady-state performance of Kalman filters for these system models. The results show that the steady-state Kalman gain has the same form as the DPLL gain. An approximate simple form for the steady-state Kalman gain is used to derive an expression for the equivalent loop bandwidth of the Kalman filter as a function of the process and observation noise variances. These results can be used to analyze the steady-state performance of a Kalman filter with DPLL theory or to design a Kalman filter model with the same steady-state performance as a given DPLL.
2009年04期 v.14 470-473页 [查看摘要][在线阅读][下载 513K] [下载次数:132 ] |[网刊下载次数:0 ] |[引用频次:17 ] |[阅读次数:0 ] - Richard Huynh;葛宁;杨华中;
Reed-Solomon (RS) codes have been widely adopted in many modern communication systems. This paper describes a new method for error detection in the syndrome calculator block of RS decoders. The main feature of this method is to prove that it is possible to compute only a few syndrome coeffi-cients — less than half — to detect whether the codeword is correct. The theoretical estimate of the prob-ability that the new algorithm failed is shown to depend on the number of syndrome coefficients computed. The algorithm is tested using the RS(204,188) code with the first four coefficients. With a bit error rate of 1×10?4, this method reduces the power consumption by 6% compared to the basic RS(204,188) decoder. The error detection algorithm for the syndrome calculator block does not require modification of the basic hardware implementation of the syndrome coefficients computation. The algorithm significantly reduces the computation complexity of the syndrome calculator block, thus lowering the power needed.
2009年04期 v.14 474-477页 [查看摘要][在线阅读][下载 409K] [下载次数:61 ] |[网刊下载次数:0 ] |[引用频次:4 ] |[阅读次数:0 ] - 胡芝兰;王贵锦;林行刚;严洪;
Skin segmentation is widely used in many computer vision tasks to improve automated visualization. This paper presents a graph cuts algorithm to segment arbitrary skin regions from images. The detected face is used to determine the foreground skin seeds and the background non-skin seeds with the color probability distributions for the foreground represented by a single Gaussian model and for the background by a Gaussian mixture model. The probability distribution of the image is used for noise suppression to alleviate the influence of the background regions having skin-like colors. Finally, the skin is segmented by graph cuts, with the regional parameter γ optimally selected to adapt to different images. Tests of the algorithm on many real world photographs show that the scheme accurately segments skin regions and is robust against illumination variations, individual skin variations, and cluttered backgrounds.
2009年04期 v.14 478-486页 [查看摘要][在线阅读][下载 1851K] [下载次数:85 ] |[网刊下载次数:0 ] |[引用频次:6 ] |[阅读次数:0 ] <正>Harvard University’s Gilbert Butler Professor of Environmental Studies, Michael B. McElroy, delivered a stirring talk in the Tsinghua Forum Lecture Series in the Main Building on April 14, 2009, on the global challenges facing a low-carbon energy future and its potential benefits for air quality and public health.
2009年04期 v.14 486页 [查看摘要][在线阅读][下载 198K] [下载次数:15 ] |[网刊下载次数:0 ] |[引用频次:0 ] |[阅读次数:0 ] - 苏环;张超;陆建华;
A carrier frequency offset (CFO) estimator was developed based on an interference cancellation scheme for an orthogonal frequency division multiplex access uplink. An initial CFO estimate was first obtained based on the received training signals at each user's prescribed subcarrier positions. Then, the received training signals were compensated by using the initial CFO estimates in the frequency domain and the multi-user interferences were estimated. Finally, the interference-cancelled training signals were used to reliably estimate each user's CFO. The CFO estimator performance was evaluated by the bit error rate performances of the CFO compensation-based receivers at the base station. Simulations show that with this optimal interference-cancellation-based CFO compensation receiver, the performance gain with the estimated CFO values is approximately 3 dB better at the 0.1% bit error rate than the initial CFO estimates.
2009年04期 v.14 487-491页 [查看摘要][在线阅读][下载 468K] [下载次数:73 ] |[网刊下载次数:0 ] |[引用频次:1 ] |[阅读次数:0 ] - 曾森;黄双喜;范玉顺;
The service-oriented architecture (SOA) and the model-driven architecture (MDA) have been recognized as major evolutionary steps in enterprise integration (EI) in service-oriented computing environments. Service-oriented enterprise (SOE) networks (SOEN) are emerging with the significant advances of EI, SOA, and MDA. However, the implementation and optimization of SOEN is still lacking integrated SOA, MDA, and performance analysis and optimization (PAO) methods. This paper introduces an integrated solution of SOA and MDA with a simulation-based three-stage PAO method with stage 1 being an analytic hierarchy process (AHP)-based comprehensive performance calculation for service matching and binding, stage 2 being a simulation-based comprehensive performance evaluation for business process/service composition, and stage 3 being a business process simulation-based performance optimization for SOEN. The SOE architecture, performance analysis framework, performance indicators, and performance operators are discussed. The system uses MDA as the system development philosophy, SOA as the system implementation infrastructure, and the simulation-based PAO methods to analyze and optimize the SOEN performance. A case study of the SOEN illustrates the usage of the integrated solution.
2009年04期 v.14 492-503页 [查看摘要][在线阅读][下载 903K] [下载次数:113 ] |[网刊下载次数:0 ] |[引用频次:9 ] |[阅读次数:0 ] - 岳耀;张春明;王海欣;白国强;陈弘毅;
Most existing system-on-chip (SoC) architectures are for microprocessor-centric designs. They are not suitable for computing intensive SoCs, which have their own configurability, extendibility, performance, and data exchange characteristics. This paper analyzes these characteristics and gives design principles for computing intensive SoCs. Three architectures suitable for different situations are compared with selection criteria given. The architectural design of a high performance network security accelerator (HPNSA) is used to elaborate on the design techniques to fully exploit the performance potential of the architectures. A behavior-level simulation system is implemented with the C++ programming language to evaluate the HPNSA performance and to obtain the optimum system design parameters. Simulations show that this architecture provides high performance data transfer.
2009年04期 v.14 504-511页 [查看摘要][在线阅读][下载 408K] [下载次数:37 ] |[网刊下载次数:0 ] |[引用频次:2 ] |[阅读次数:0 ] - 戚昀;刘连池;王骥;陈应华;
Erns is a highly glycosylated envelope protein of classical swine fever virus (CSFV) with RNase activity. Erns can induce neutralizing antibodies and provide immune protection against CSFV infection. In this study, the RNase domain of the Erns was produced in Escherichia coli. Its reactivity with CSFV-positive sera and its ability to induce antibodies and to provide protective immunity were then investigated. The serological tests showed that the prokaryotically expressed RNase domain of the Erns retained its antigenicity and induced high titers of humoral responses. However, only partial protection and a limited amount of neutralizing antibodies were demonstrated by an in vitro neutralization test and an immunization/challenge test. The results suggest that other essential factors rather than simply enhancing the immunogenicity of Erns should be taken into consideration when Erns is enrolled as one of the components of a candidate vaccine.
2009年04期 v.14 512-518页 [查看摘要][在线阅读][下载 585K] [下载次数:64 ] |[网刊下载次数:0 ] |[引用频次:2 ] |[阅读次数:0 ] - 赵玉男;申佳;苏慧;黄玉芳;邢东明;杜力军;
Corticosterone, a principal glucocorticoid synthesized in the rodent adrenal cortex, can be cumulatively toxic to hippocampal neurons, the cause of which is not known. The present study determined whether the cytosol adenylate kinase (AK) system was involved in the neuronal damage induced by long-term exposure to high corticosterone levels. We investigated the effects of long-term exposure to high corticosterone levels on AK1 activity, AK1 mRNA expression, and energy levels in cultured hippocampal neurons. The results show that long-term exposure to high corticosterone levels induces a reduction of the cultured hippocampal neuron viability, significantly reduces energy levels, and causes a time-dependant reduction of the AK1 activity. These findings indicate that changes in the AK system might be the mechanism underlying neuronal damage induced by long-term exposure to high corticosterone levels.
2009年04期 v.14 519-527页 [查看摘要][在线阅读][下载 497K] [下载次数:49 ] |[网刊下载次数:0 ] |[引用频次:4 ] |[阅读次数:0 ] - 蒋玉凤;罗雪春;王玺玫;方蕾;黄启福;
The effects of salvianolic acid B (SalB) on the mitochondrial membrane potential (MMP), calcium, and apoptosis of neurons with cerebral ischemia in mice were investigated using an acute cerebral ischemia model established by ligating the bilateral common carotid arteries in mice. The MMP, the intracellular calcium concentration, and the apoptosis rate of cortical neurons were measured at 6 min, 12 min, 18 min, 24 min, and 30 min after cerebral ischemia by a flow cytometer. The experiments show that SalB increases the MMP and reduces the intracellular calcium and the apoptosis rate at different stages of the cerebral ischemia in mice. The results show that the protective mechanism of SalB on cerebral ischemia enhances the MMP and maintains intracellular calcium homeostasis.
2009年04期 v.14 528-533页 [查看摘要][在线阅读][下载 497K] [下载次数:51 ] |[网刊下载次数:0 ] |[引用频次:4 ] |[阅读次数:0 ] -
<正>At an inauguration ceremony on April 10, 2009, Tsinghua University unveiled its Research Center for Japanese Studies, an inter-college research institute which aims to promote mutual understanding as well as academic and student exchanges and cooperation between China and Japan through cross-disciplinary research.
2009年04期 v.14 533页 [查看摘要][在线阅读][下载 263K] [下载次数:15 ] |[网刊下载次数:0 ] |[引用频次:0 ] |[阅读次数:0 ] - 黄雪竹;徐勇;李茜茜;刘破资;杨元;张付全;郭田友;杨闯;郭兰婷;
Previous pharmacological, human genetics, and animal models have implicated the nicotinic acetylcholine receptor α4 subunit (CHRNA4) gene in the pathogenesis of attention deficit/hyperactivity disorder (ADHD). The objective of this study is to examine the genetic association between single nucleotide polymorphisms in the CHRNA4 gene (rs2273502, rs1044396, rs1044397, and rs3827020 loci) and ADHD. Both case-control and family-based designs are used. Children aged 6 to 16 years were interviewed and assessed with the children behavior checklist and the revised conner' parent rating scale to identify probands. No significant differences in the frequency distribution of genotypes or alleles were found between the case and control groups. However, further haplotype analyses showed the CCGG haplotype on risk for ADHD in 164 case-control samples and the standard transmission disequilibrium test analyses suggest that the allele C of rs2273502 was over-transferred in 98 ADHD parent-offspring trios. These findings suggest that the CHRNA4 gene may play a role in the pathogenesis of ADHD.
2009年04期 v.14 534-540页 [查看摘要][在线阅读][下载 384K] [下载次数:86 ] |[网刊下载次数:0 ] |[引用频次:0 ] |[阅读次数:0 ] - 李昊;张辉;郭晓莲;胡广书;
A method was developed to restore degraded images to some extent after the pixel binning pro-cess in image sensors to improve the resolution. A pixel binning model was used to approximate the original un-binned image. Then, the least squares error criterion was used as a constraint to reconstruct the re-stored pixel values from the binning model. The technique achieves about a one-decibel increase in the peak signal-to-noise ratio compared with the original estimated image. The technique has good detail pre-servation performance as well as low computation load. Thus, this restoration technique provides valuable improvements in practical, real time image processing.
2009年04期 v.14 541-545页 [查看摘要][在线阅读][下载 457K] [下载次数:120 ] |[网刊下载次数:0 ] |[引用频次:6 ] |[阅读次数:0 ] - 袁翼;连彦青;
Polystyrene/polyaniline core-shell structure microspheres were synthesized in the presence of poly(sodium 4-styrenesulfonate) as stabilizer and hydrochloric acid as dopant to improve the processibility of conducting polyaniline. After the one-pot reacting process, the product was easily purified by washing with water. The polyaniline shell covering the polystyrene sphere surface was confirmed with FT-IR and X-ray photoelectron spectroscopy. The conductivity of the polyaniline-coated polystyrene particles was 0.0017 S/cm and increased to 0.1 S/cm after being doped in the HCl vapor. The morphology of the microspheres was characterized by TEM and SEM. The particles show a more uniform and smooth surface than previous particles.
2009年04期 v.14 546-550页 [查看摘要][在线阅读][下载 988K] [下载次数:107 ] |[网刊下载次数:0 ] |[引用频次:6 ] |[阅读次数:0 ] -
<正>Tsinghua Science and Technology (Tsinghua Sci Technol), a comprehensive academic journal sponsored by Tsinghua University, is published bimonthly. This journal aims at presenting the up-to-date scientific achievements with high creativity and great significance in various
2009年04期 v.14 551页 [查看摘要][在线阅读][下载 705K] [下载次数:14 ] |[网刊下载次数:0 ] |[引用频次:0 ] |[阅读次数:0 ] 下载本期数据