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   清华大学学报自然科学版(英文版)
  2006年, 第11卷, 第1期 刊出日期:2006-01-20 上一期    下一期
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论文
Mobile Police Information System Based on Web Services 收藏
Hao Yin, Qiang Fu, Chuang Lin, Zhangxi Tan, Rong Ding, Yishu Lin, Yanxi Li, Yanfei Fan
清华大学学报自然科学版(英文版). 2006, (1): 1-7.   DOI: 10.1016/S1007-0214(06)70146-8
摘要 ( 130 )  
The demand for communications anywhere, anytime, and on any device without recording the date is growing with the development of modern information technologies. Current wireless communications enable people to freely exchange information, while web services provide loosely-coupled, language-neutral, and platform-independent ways of linking applications within organizations, across enterprises, and across the Internet. This paper describes a mobile information system for police service, which integrates wireless communication technologies and web service technologies. The system satisfies the special demands of police information systems, such as security and interoperability. Policemen in the system can use various kinds of mobile terminals, such as mobile phones, tablet PCs, personal digital assistants, and laptops equipped with wireless LAN or GPRS to access data in the central database. The system is based on web services with a secure web service architecture and simple object access protocol message passing.
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Linear-in-dB Variable-Gain Downconversion Mixer for Zero Intermediate Frequency Receivers 收藏
Dong Feng, Bingxue Shi
清华大学学报自然科学版(英文版). 2006, (1): 8-11.   DOI: 10.1016/S1007-0214(06)70147-X
摘要 ( 192 )  
In-phase/quadrature (I/Q) mismatch is a key problem in zero intermediate frequency (ZIF) receiver architectures. Although integration and careful layout can alleviate I/Q mismatch, circuit and system level calibrations are also needed due to process variations and variable operating conditions. The amplitude imbalance between I/Q channels was calibrated using a modified R-2R ladder to achieve fine linear-in-dB variable gain. A downconversion mixer working in the 2.4-GHz band was developed for a wireless local area network (WLAN) ZIF receiver using 0.25-μm complementary metal-oxide semiconductor (CMOS). The two-stage mixer configuration relaxes the tradeoff between noise and linearity. Experimental results verify the fine linear-in-dB variable conversion gain of the mixer, which can also be used as part of an automatic gain control (AGC) loop.
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A Fast Method for Heuristics in Large-Scale Flow Shop Scheduling 收藏
Xiaoping Li, Lianchen Liu, Cheng Wu
清华大学学报自然科学版(英文版). 2006, (1): 12-18.   DOI: 10.1016/S1007-0214(06)70148-1
摘要 ( 140 )  
Fast computation methods are needed for the heuristics of flow shop scheduling problems in practical manufacturing environments. This paper describes a generalized flow shop model, which is an extension of the classical model, in which not all machines are available at time zero. The general completion-time computing method is used to compute completion time of generalized flow shops. The transform classical flow shop to generalized shop (TCG) method is used to transform classical schedules into generalized schedules with less jobs. INSERT and SWAP, extended from job-insertion and pair-wise exchange which are fundamental procedures used in most heuristics for classical flow shops, reduce the CPU time by 1/2 and 1/3, respectively. The CPU time of 14 job-insertion and pair-wise exchange-based heuristics are analyzed with and without the TCG method. The results show that TCG considerably reduces the CPU time.
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Performance of Adaptive Subchannel Assignment-Based MIMO/OFDM Systems over Multipath Fading Channels 收藏
Yahan Pan, Khaled Ben Letaief, Zhigang Cao
清华大学学报自然科学版(英文版). 2006, (1): 19-24.   DOI: 10.1016/S1007-0214(06)70149-3
摘要 ( 164 )  
Adaptive antenna arrays at both the base and mobile stations can further increase system capacity and improve the quality of service of conventional orthogonal frequency division multiplexing (OFDM) systems. Conventional adaptive antenna array-based multiple-input multiple-output (MIMO)/OFDM systems use the sub-carriers characterized by the largest eigenvalue to transmit the OFDM symbols. This paper describes the performance of adaptive subchannel assignment-based MIMO/OFDM systems over multipath fading channels. The system adaptively selects the eigenvectors associated with the relatively large subchannel eigenvalues to generate the antenna array weights at the base and mobile stations and then adaptively assigns the corresponding best subchannels to transmit the OFDM symbols. Simulation results show that the proposed system can achieve better performance than the conventional adaptive antenna array-based MIMO/OFDM system over multipath fading channels.
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Machine Translation Based on Translation Corresponding Tree Structure 收藏
Fai Wong, Mingchui Dong, Dongcheng Hu
清华大学学报自然科学版(英文版). 2006, (1): 25-31.   DOI: 10.1016/S1007-0214(06)70150-X
摘要 ( 147 )  
A representation schema called translation corresponding tree (TCT) has been applied to a Portuguese to Chinese example-based machine translation system. The translation examples are annotated by the representation of the TCT structure. Each TCT describes not only the syntactic structure of the source sentence (i.e., Portuguese in our system) but also the translation correspondences (i.e., Chinese translation). In addition, the TCT nodes describe the corresponding linguistic relationships between the source and target languages. The translation examples can be effectively represented with this annotation schema and organized in the bilingual knowledge database or example base. In the real machine translation process, the target language is synthesized with higher quality by referring to the TCT translation information.
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Performance Analysis of Post-Detection Combining for NFSK and DPSK Systems over Arbitrarily Correlated Nakagami Channels with Distinct Fading Parameters 收藏
Daming Hang, Xiaowei Cui, Zhigang Cao
清华大学学报自然科学版(英文版). 2006, (1): 32-37.   DOI: 10.1016/S1007-0214(06)70151-1
摘要 ( 126 )  
For differential phase shift keying (DPSK) and noncoherent frequency shift keying (NFSK) systems over fading channels, the post-detection combining method is a popular means for improving the bit error performance. However, the bit error performance of such systems over Nakagami channels with an arbitrary covariance matrix and real distinct fading parameters has been seldom described in the literature. This paper studies the problem using a generic correlated Nakagami fading model and presents a closed form solution which is used to study the influence of the fading parameters and the signal-to-noise ratio (SNR) distribution ratios among all the branches on the bit error performance. Moreover, the average SNRs of each branch are not restricted to one value in the analysis. The closed form solution developed for the problem can be used to study the influence of the fading parameters and the SNR distribution ratios on the error performance.
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Design and Implementation of SCSI Target Emulator 收藏
Jiaming Pan, Jiwu Shu, Suqin Zhang, Weimin Zheng
清华大学学报自然科学版(英文版). 2006, (1): 38-43.   DOI: 10.1016/S1007-0214(06)70152-3
摘要 ( 174 )  
A SCSI target emulator is used in a storage area network (SAN) environment to simulate the behavior of a SCSI target for processing and responding to I/O requests issued by initiators. The SCSI target emulator works with general storage devices with multiple transport protocols. The target emulator utilizes a protocol conversion module that translates the SCSI protocols to a variety of storage devices and implements the multi-RAID-level configuration and storage visualization functions. Moreover, the target emulator implements RAM caching, multi-queuing, and request merging to effectively improve the I/O response speed of the general storage devices. The throughput and average response times of the target emulator for block sizes of 4 KB to 128 KB are 150% faster for reads and 67% faster for writes than the existing emulator. With a block size of 16 KB, the I/O latency of the target emulator is only about 20% that of the existing emulator.
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B3A: Prompting Cooperation Among Rational Participants in P2P Bulk File Sharing Environments 收藏
Ming Chen, Guangwen Yang, Xuezheng Liu, Weimin Zheng
清华大学学报自然科学版(英文版). 2006, (1): 44-49.   DOI: 10.1016/S1007-0214(06)70153-5
摘要 ( 120 )  
Peer-to-peer (P2P) file sharing systems assume that their users download files in proportion to their sharing. Unfortunately, users are unlikely to do so without an incentive mechanism. Previous solutions to the problem required some types of centralized control, which strays from the spirit of P2P to provide long-term incentives. This paper presents the balance-based bandwidth allocation, B3A, an incentive framework to inspire participants to share files. In the B3A framework, each peer keeps the differences between the amount of data it has received from each peer and the amount it has sent to that one. When receiving simultaneous requests from various peers, the peer prefers to allocate its limited upload bandwidth to those peers with larger differences. Therefore, the downloading bandwidth perceived by a peer is positively related to its contributions to others, consequently stimulating it to share more files. The B3A framework is fully decentralized, scalable, and secure.
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Fuzzy Clustering with Novel Separable Criterion 收藏
Zhonghang Yin, Yuangang Tang, Fuchun Sun, Zengqi Sun
清华大学学报自然科学版(英文版). 2006, (1): 50-53.   DOI: 10.1016/S1007-0214(06)70154-7
摘要 ( 154 )  
Fuzzy clustering has been used widely in pattern recognition, image processing, and data analysis. An improved fuzzy clustering algorithm was developed based on the conventional fuzzy c-means (FCM) to obtain better quality clustering results. The update equations for the membership and the cluster center are derived from the alternating optimization algorithm. Two fuzzy scattering matrices in the objective function assure the compactness between data points and cluster centers, and also strengthen the separation between cluster centers in terms of a novel separable criterion. The clustering algorithm properties are shown to be an improvement over the FCM method's properties. Numerical simulations show that the clustering algorithm gives more accurate clustering results than the FCM method.
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Analysis of Water Management in Proton Exchange Membrane Fuel Cells 收藏
Cheng Bao, Minggao Ouyang, Baolian Yi
清华大学学报自然科学版(英文版). 2006, (1): 54-64.   DOI: 10.1016/S1007-0214(06)70155-9
摘要 ( 152 )  
A two-dimensional, steady-state, isothermal water-management model for a complete proton exchange membrane fuel cell (PEMFC) was developed. The model includes the transport in the diffusion layer and the proton exchange membrane (PEM) with a pseudo-homogeneous model for the cathode catalyst layer. The predicted fuel cell performance with variable cathode porosities compares well with experimental results. The model is then used to investigate the effects of some structural parameters, such as the rib size, the interdigitated flow field, and various operating conditions including the gas flow rate, the cell temperature and pressure, humidification, and the relative humidity at the inlet. Water management is best achieved by tuning the anode operating conditions.
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A Functional Framework for Integrating eCRM with Workflow Management Based on Customer Value 收藏
W.H. Ip, Bocheng Chen, Henry C.W. Lau, Bing Liang
清华大学学报自然科学版(英文版). 2006, (1): 65-73.   DOI: 10.1016/S1007-0214(06)70156-0
摘要 ( 134 )  
eCRM ties customer relationship management with e-business. Very often, eCRM is interfaced with other information systems to form a seamless integration and interchange of information both inside and outside an organization—a work flow management system. This integration of business partners, suppliers, and customers is essential in this global competitive market environment. An effective infrastructure and hence an appropriate framework are required to provide the information exchange and data analysis between eCRM and work flow management. This paper proposes a functional framework of eCRM based on customer value to realize the win-win strategy for both the companies and their customers. Moreover, a workflow management system also forms an integral part of this total solution to facilitate the implementation of a supply chain or extended enterprise.
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Terrain Identification for Prosthetic Knees Based on Electromyographic Signal Features* 收藏
Dewen Jin, Jiankun Yang, Ruihong Zhang, Rencheng Wang, Jichuan Zhang
清华大学学报自然科学版(英文版). 2006, (1): 74-79.   DOI: 10.1016/S1007-0214(06)70157-2
摘要 ( 157 )  
The features of electromyographic (EMG) signals were investigated while people walking on different terrains, including up and down slopes, up and down stairs, and during level walking at different speeds. The features were used to develop a terrain identification method. The technology can be used to develop an intelligent transfemoral prosthetic limb with terrain identification capability. The EMG signals from 8 hip muscles of 13 healthy persons were recorded as they walked on the different terrains. The signals from the sound side of a transfemoral amputee were also recorded. The features of these signals were obtained using data processing techniques with an identification process developed for the identification of the terrain type. The procedure was simplified by using only the signals from three muscles. The identification process worked well in an intelligent prosthetic knee in a laboratory setting.
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Estimates of Identification Result Disturbances in Parallel Mechanism Calibration* 收藏
Meng Gao, Tiemin Li, Xiaoqiang Tang, Guanghong Duan
清华大学学报自然科学版(英文版). 2006, (1): 80-87.   DOI: 10.1016/S1007-0214(06)70158-4
摘要 ( 179 )  
General QR decomposition of the observation matrix is used to solve identification functions to evaluate identification results of every parameter in parallel mechanism calibrations. A relationship between measured information and identification results is obtained by analyzing numerous matrix transforms and QR decompositions. When distributions of measurement error are determined, random distributions of identification result disturbances (IRDs) can be obtained from this relationship as a function of measurement errors. Then the ranges of the IRDs can be effectively estimated, even if true parameter values are unknown. An optimization index based on IRD estimate is presented to select measurement configurations to achieve smaller IRDs. Two simulation examples were carried out with different modes and calibration methods. The results show that the method is effective and that the optimization index is useful. Some regular parameter identification problems can be explained by the IRD estimates.
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Electrorheological Effects at High Shear Rate* 收藏
Ling Ren, Keqin Zhu
清华大学学报自然科学版(英文版). 2006, (1): 88-95.   DOI: 10.1016/S1007-0214(06)70159-6
摘要 ( 139 )  
Much attention has been given to electrorheological (ER) fluids because of the ER effect, which has been described by a large number of researchers as a notable increase in the apparent viscosity of a fluid upon the application of an electric field. The description of ER effects is, however, not accurate at high shear rates. To clarify the discrepancy, we analyze and compute the apparent viscosity as a function of shear rate for ER fluid flow between rotating coaxial cylinders in the presence of an electric field. The theoretical predictions show that the increase of electric intensity contributes little to the apparent viscosity enhancement at high shear rates, while ER effects for ER fluids with a higher polarization rate still exist and ER devices possess controllability in this regime. Description of the ER effect by the apparent viscosity leads to an unrealistic conclusion that ER effects disappear at high shear rates, because the apparent viscosity of ER fluids approaches the value for Newtonian fluids. Therefore, it is concluded that the proper description of ER effects, i.e., one that holds uniformly for any strain rate when ER effects exist, is manifested by a remarkable increase in the extra stress rather than in the apparent viscosity of ER fluids.
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Optimization of Unbalanced Multi-stage Logistics Systems Based on Pr黤er Number and Effective Capacity Coding 收藏
Hang Xu, Rong Xu, Qingtai Ye
清华大学学报自然科学版(英文版). 2006, (1): 96-101.   DOI: 10.1016/S1007-0214(06)70160-2
摘要 ( 156 )  
Unbalanced multi-stage logistics systems are optimized using an improved genetic algorithm based on the Pr黤er number and the effective capacity coding. The improved decoding procedure uses the node capacity of the logistics system as an important factor, which influences the decoding procedure. As a result, any Pr黤er number produced stochastically can be decoded to a feasible logistics pattern, which matchs the node capacities of the logistics system. With effective capacity coding, an unbalanced logistics system can be converted to a set of balanced systems. The effective capacity coding was combined with the Pr黤er number to construct the chromosome for the new method to search the whole solution space of the unbalanced multi-stage logistics system. Simulation results show that the new method finds a better solution with less computational time than st-GA. Although using a little more memory, the new method is still an efficient and robust method for optimizing unbalanced multi-stage logistics systems.
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Expected Value Method for Fuzzy Multiple Attribute Decision Making 收藏
Ling Zeng
清华大学学报自然科学版(英文版). 2006, (1): 102-106.   DOI: 10.1016/S1007-0214(06)70161-4
摘要 ( 171 )  
This paper presents a fuzzy multiple attribute decision-making (FMADM) method in which the attribute weights and decision matrix elements (attribute values) are fuzzy variables. Fuzzy arithmetic and the expected value operator of fuzzy variables are used to develop the expected value method to solve the FMADM problem. A numerical example is given to demonstrate the feasibility and effectiveness of the method.
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Parallel Machine Scheduling with Special Jobs 收藏
Zhenbo Wang, Wenxun Xing
清华大学学报自然科学版(英文版). 2006, (1): 107-110.   DOI: 10.1016/S1007-0214(06)70162-6
摘要 ( 145 )  
This paper considers parallel machine scheduling with special jobs. Normal jobs can be processed on any of the parallel machines, while the special jobs can only be processed on one machine. The problem is analyzed for various manufacturing conditions and service requirements. The off-line scheduling problem is transformed into a classical parallel machine scheduling problem. The on-line scheduling uses the FCFS (first come, first served), SWSC (special window for special customers), and FFFS (first fit, first served) algorithms to satisfy the various requirements. Furthermore, this paper proves that FCFS has a competitive ratio of m, where m is the number of parallel machines, and this bound is asymptotically tight, SWSC has a competitive ratio of 2 and FFFS has a competitive ratio of 3–2/m, and these bounds are tight.
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On a Reduction of the Kadomtsev-Petviashvili Hierarchy 收藏
Ting Xue
清华大学学报自然科学版(英文版). 2006, (1): 111-116.   DOI: 10.1016/S1007-0214(06)70163-8
摘要 ( 130 )  
This paper analyzes the reduction of the well known Kadomtsev-Petviashvili hierarchy. The reduction yields a previously unknown dispersion counterpart of the dispersionless hierarchy which has a Lax function of the form p+u(x)(p??)?1+v(x)(p??)?2. This paper also describes the bihamiltonian structure of the reduced hierarchy using Dirac reduction and proves that the approximation for the reduced hierarchy up to the second order of the dispersion parameter coincides with the hierarchy of integrable systems constructed from a particular two-dimensional Frobenius manifold using the approach of Dubrovin and Zhang.
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Large Eddy Simulations of Three-Dimensional Flows Around a Spur Dike 收藏
Xuelin Tang, Xiang Ding, Zhicong Chen
清华大学学报自然科学版(英文版). 2006, (1): 117-123.   DOI: 10.1016/S1007-0214(06)70164-X
摘要 ( 161 )  
Large eddy simulations were used to model the three-dimensional flows around a non-submerged spur dike. Based on the rigid lid assumption, all these vortex flows around the spur dike, which probably affected the whole flow field, were numerically simulated and analyzed. The largest circulating flow region caused by the spur dike behind it was weak, which would naturally lead to sedimentation for silt-laden twophase flows. Based on the Smagorinsky model, the finite volume method was used to discretize the NavierStokes equations, and the SIMPLEC algorithm was used to solve them. Meanwhile, these flows were investigated experimentally in a 0.5-m wide flume with a dike placed as a barrier. The computational results are in a fairly good agreement with the experimental data.
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Push-Over Analysis of the Seismic Behavior of a Concrete-Filled Rectangular Tubular Frame Structure 收藏
Jianguo Nie, Kai Qin, Yan Xiao
清华大学学报自然科学版(英文版). 2006, (1): 124-130.   DOI: 10.1016/S1007-0214(06)70165-1
摘要 ( 202 )  
To investigate the seismic behavior of concrete-filled rectangular steel tube (CFRT) structures, a push-over analysis of a 10-story moment resisting frame (MRF) composed of CFRT columns and steel beams was conducted. The results show that push-over analysis is sensitive to the lateral load patterns, so the use of at least two load patterns that are expected to bound the inertia force distributions is recommended. The M-? curves and N-M interaction surfaces of the CFRT columns calculated either by Han's formulae or by the USC-RC program (reinforced concrete program put forward by University of Southern Califonia) are suitable for future push-over analyses of CFRT structures. The P-? effect affects the MRF seismic behavior seriously, and so should be taken into account in MRF seismic analysis. In addition, three kinds of RC structures were analyzed to allow a comparison of the earthquake resistance behavior of CFRT structures and RC structures. The results show that the ductility and seismic performance of CFRT structures are superior to those of RC structures. Consequently, CFRT structures are recommended in seismic regions.
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Three-Dimensional Stress and Stress Intensity for Tensioned Flat Plates with Edge Cracks 收藏
Yuanqing Wang, Yanmin Wu, Yongjiu Shi, Jianjing Jiang
清华大学学报自然科学版(英文版). 2006, (1): 131-136.   DOI: 10.1016/S1007-0214(06)70166-3
摘要 ( 114 )  
The stress in the thickness direction is an important factor influencing the fracture behavior of structural members. A stress σy tensioned flat plate with edge cracks is widely used as an analysis model. The stresses σx and σy for the plate model can be acquired from Neuber's solution. However, the solution is applicable only for a perfect plane stress or plane strain state. As a consequence of the thickness of the plate a three-dimensional (3-D) stress state will arise near the crack tip, resulting in a variation of the distribution of σx and σy stresses. A full analysis for the 3-D stress fields for a tensioned flat plate with edge cracks has been therefore carried out. The results show that the 3-D stress field near the crack tip is mainly determined by two factors: the thickness of the plate and the curvature radius at the crack tip. A further analysis has been carried out for the stress intensity near the crack tip. In this paper we give some equations matching to the 3-D stress and stress intensity, which describe precisely the stress state near the crack tip, and which can be applied effectively in engineering analysis.
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