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Tsinghua Science and Technology

Issue 4 • Date Aug. 2006

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Displaying Results 1 - 18 of 18
  • [Front cover]

    Publication Year: 2006 , Page(s): c1
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    Freely Available from IEEE
  • Contents

    Publication Year: 2006 , Page(s): 1
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    Freely Available from IEEE
  • Transmit antenna selection with power and rate allocation for spatial multiplexing in distributed antenna systems

    Publication Year: 2006 , Page(s): 259 - 263
    Cited by:  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    High spectral efficiency distributed antenna systems (DAS) require vertical Bell-Labs layered space-time (V-BLAST) like spatial multiplexing schemes. However, unlike normal point-to-point multiple input multiple output (MIMO) channels, DAS channels have different large-scale fadings from different transmit antennas, thus making equal power and rate transmission that is feasible in MIMO channels unrealistic in DAS channels. This paper proposes a novel transmit antenna selection scheme with power and rate allocation. The scheme is based on large-scale fading (shadow fading and path loss) and is suitable for VBLAST structures with zero-forcing and successive interference cancellation (ZF-SIC) receivers, ensuring balanced average symbol error rate (SER) performance in each layer. On the receiver side, a fixed detection order is used, which is obtained in the transmit antenna selection process. Simulation results show that the proposed scheme gives good performance gains over equal power and rate transmission systems without antenna selection. View full abstract»

    Open Access
  • Two normal basis multiplication algorithms for GF(2n)

    Publication Year: 2006 , Page(s): 264 - 270
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    For software implementations, word-level normal basis multiplication algorithms utilize the full data-path of the processor, and hence are more efficient than the bit-level multiplication algorithm presented in the IEEE standard P1363–2000. In this paper, two word-level normal basis multiplication algorithms are proposed for GF(2n). The first algorithm is suitable for high complexity normal bases, while the second algorithm is fast for type-I optimal normal bases and low complexity normal bases. Theoretical analyses and experimental results both indicate that the presented algorithms are efficient in GF(2233), GF(2283), GF(2409), and GF(2571), which are four of the five binary fields recommended by the National Institute of Standards and Technology (NIST) for the elliptic curve digital signature algorithm (ECDSA) applications. View full abstract»

    Open Access
  • Analytical expression for the MIMO channel capacity

    Publication Year: 2006 , Page(s): 271 - 277
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (327 KB)  

    This paper presents analytical expressions for the multiple-input multiple-output (MIMO) channel capacity in frequency-flat Rayleigh fading environments. An exact analytical expression is given for the ergodic capacity for single-input multiple-output (SIMO) channels. The analysis shows that the SIMO channel capacity can be approximated by a Gaussian random variable and that the MIMO channel capacity can be approximated as the sum of multiple SIMO capacities. The SIMO channel results are used to derive approximate closed-form expressions for the MIMO channel ergodic capacity and the complementary cumulative distribution function (CCDF) of the MIMO channel capacity (outage capacity). Simulations show that these theoretical results are good approximations for MIMO systems with an arbitrary number of transmit or receive antennas. Moreover, these analytical expressions are relatively simple which makes them very useful for practical computations. View full abstract»

    Open Access
  • Adaptive delayed acknowledgement algorithm for mpeg-4 traffic in uwb networks

    Publication Year: 2006 , Page(s): 278 - 286
    Cited by:  Patents (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (259 KB)  

    Although ultra-wideband transmission rates are very high in the physical layer, the bandwidth utilization efficiency is very low in the medium access control (MAC) layer. The bandwidth utilization efficiency can be improved and the quality of service for delay-sensitive variable bit rate traffic such as high rate motion picture experts group (MPEG)-4 traffic can be guaranteed by a simple and efficient algorithm that dynamically sets the burst size of the delayed-acknowledgement (Dly-ACK) based on the IEEE 802.15.3 standard. The burst size was adjusted in response to the wireless channel quality. Furthermore, the burst size was bounded by a maximum acknowledgement burst size setting and the remaining number of un-received blocks of a current supra-block. Simulation results show that the method achieves significant performance enhancement in the job failure rate and throughput compared to immediate-acknowledgement (Imm-ACK) and other fixed burst size Dly-ACK schemes. This algorithm can also be applied in generalized time division multiple access (TDMA) systems by using the block acknowledgement mechanism for delay sensitive traffic. View full abstract»

    Open Access
  • Networked Control System Simulation Design and Its Application

    Publication Year: 2006 , Page(s): 287 - 294
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (271 KB)  

    This paper presents a framework for networked control system simulation (NCSS) to enable the analysis of the influence of network transmissions on the performance of control systems. The simulation is composed of the network environment simulated using the network simulator, the control system component simulation using Matlab or C/C++, and an external application programming interface. To implement the plant (sensor), controller, and actuator nodes, an agent-based design is introduced, and a multi-agent networked control system is constructed. Therefore, the network simulator 2–26 (NS-2.26) release is extended by modifying the user data protocol (UDP) common header in order to support application data transmission between network nodes. Then, modifying the network topology parameters, networked control system simulations are analyzed for different parameter changes, such as the network bandwidth, the number of plant nodes, and the sampling period. An analysis of the influence of these parameters on network-induced delays and packet drop is made. The results show that the simulation system is an effective tool for the study of networked control systems. View full abstract»

    Open Access
  • Machine translation using constraint-based synchronous grammar

    Publication Year: 2006 , Page(s): 295 - 306
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (381 KB)  

    A synchronous grammar based on the formalism of context-free grammar was developed by generalizing the first component of production that models the source text. Unlike other synchronous grammars, the grammar allows multiple target productions to be associated to a single production rule which can be used to guide a parser to infer different possible translational equivalences for a recognized input string according to the feature constraints of symbols in the pattern. An extended generalized LR algorithm was adapted to the parsing of the proposed formalism to analyze the syntactic structure of a language. The grammar was used as the basis for building a machine translation system for Portuguese to Chinese translation. The empirical results show that the grammar is more expressive when modeling the translational equivalences of parallel texts for machine translation and grammar rewriting applications. View full abstract»

    Open Access
  • MW-obs: An improved pruning method for topology design of neural networks

    Publication Year: 2006 , Page(s): 307 - 312
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (267 KB)  

    Topology design of artificial neural networks (ANNs) is an important problem for large scale applications. This paper describes a new efficient pruning method, the multi-weight optimal brain surgeon (MWOBS) method, to optimize neural network topologies. The advantages and disadvantages of the OBS and unit-OBS were analyzed to develop the method. Actually, optimized topologies are difficult to get within reasonable times for complex problems. Motivating by the mechanism of natural neurons, the MW-OBS method balances the accuracy and the time complexity to achieve better neural network performance. The method will delete multiple connections among neurons according to the second derivative of the error function, so the arithmetic converges rapidly while the accuracy of the neural network remains high. The stability and generalization ability of the method are illustrated in a Java program. The results show that the MWOBS method has the same accuracy as OBS, but time is similar to that of unit-OBS. Therefore, the MWOBS method can be used to efficiently optimize structures of neural networks for large scale applications. View full abstract»

    Open Access
  • Transient flow in rapidly filling air-entrapped pipelines with moving boundaries

    Publication Year: 2006 , Page(s): 313 - 323
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (418 KB)  

    A mathematical model is presented for transient flow in a rapidly filling pipeline with an entrapped air pocket. The influence of transient shear stress between the pipe wall and the flowing fluid is taken into account. A coordinate transformation technique is employed to generate adaptive moving meshes for the multiphase flow system as images of the time-independent computational meshes in auxiliary domains. The method of characteristics is used to reduce the coupled nonlinear hyperbolic partial differential equations governing the motion of the filling fluid, entrapped air, and blocking fluid to ordinary differential equations. Numerical solution of resulting equations shows that the transient shear stresses have only a small damping effect on the pressure fluctuations. The peak pressure in the entrapped air pocket decreases significantly with increasing initial entrapped air volume, but decreases slightly with increasing initial entrapped air pressure. View full abstract»

    Open Access
  • Application of method-of-lines to charging-up process in pipelines with entrapped air

    Publication Year: 2006 , Page(s): 324 - 331
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (361 KB)  

    A mathematical model is presented for the charging-up process in an air-entrapped pipeline with moving boundary conditions. A coordinate transformation technique is employed to reduce fluid motion in time-dependent domains to ones in time-independent domains. The nonlinear hyperbolic partial differential equations governing the unsteady motion of fluid combined with an equation for transient shear stress between the pipe wall and the flowing fluid are solved by the method of lines. Results show that ignoring elastic effects overestimates the maximum pressure and underestimates the maximum front velocity of filling fluid. The peak pressure of the entrapped air is sensitive to the length of the initial entrapped air pocket. View full abstract»

    Open Access
  • Wave damping over a perforated plate with water chambers

    Publication Year: 2006 , Page(s): 332 - 338
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (277 KB)  

    The movement of waves propagating over a horizontally submerged perforated plate with water-filled chambers bellow the plate was investigated by using linear potential theory. The analytical solution was compared with laboratory experiments on wave blocking. The analysis of the wave energy dissipation on the perforated bottom surface shows that the effects of the perforated plate on the wave motion depend mainly on the plate porosity, the wave height, and the wave period. The wave number is a complex number when the wave energy dissipation on the perforated plate is considered. The real part of the wave number refers to the spatial periodicity while the imaginary part represents the damping modulus. The characteristics of the wave motion were explored for several possible conditions. View full abstract»

    Open Access
  • Socio-economic impact assessment of intelligent transport systems

    Publication Year: 2006 , Page(s): 339 - 350
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (293 KB)  

    A general review of the socio-economic impact of the intelligent transport system (ITS) is presented with a case study to demonstrate the data envelopment analysis method. Cost-benefit analyses are still the dominant method for evaluating ITS and other transport engineering projects, while cost effective analyses and multi-criteria appraisals are widely used to define and prioritize objectives by providing useful information for the most promising policy decisions. Both cost-benefit analyses and a data envelopment analysis method are applied to analyze the socio-economic impact of convoy driving systems. The main findings are that a convoy provides a worthwhile benefit-cost ratio when more than 30% of the traffics in the convoys and the traffic load exceeds 5500 vehicles/h for a three-lane motorway. The results also show that for a fixed percentage of convoys, increased demand will increase the data envelopment analysis method relative efficiency and that the neglect of certain output indicators of an ITS may result in underestimation of the system effects. View full abstract»

    Open Access
  • Disaggregate traffic mode choice model based on combination of revealed and stated preference data

    Publication Year: 2006 , Page(s): 351 - 356
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    The conventional traffic demand forecasting methods based on revealed preference (RP) data are not able to predict the modal split. Passengers' stated intentions are indispensable for modal split forecasting and evaluation of new traffic modes. This paper analyzed the biases and errors included in stated preference data, put forward the new stochastic utility functions, and proposed an unbiased disaggregate model and its approximate model based on the combination of RP and stated preference (SP) data, with analysis of the parameter estimation algorithm. The model was also used to forecast rail transit passenger volumes to the Beijing Capital International Airport and the shift ratios from current traffic modes to rail transit. Experimental results show that the model can greatly increase forecasting accuracy of the modal split ratio of current traffic modes and can accurately forecast the shift ratios from current modes to the new mode. View full abstract»

    Open Access
  • Credit assessment of contractors: A rough set method

    Publication Year: 2006 , Page(s): 357 - 362
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (219 KB)  

    A rough set method is presented in this paper to assess the credit of contractors. Unlike traditional methods, the rough set method deduces credit-classifying rules from actual data to predict new cases. The method uses a contractors' database with a genetic algorithm and an exhaustive reduction implemented using ROSETTA software that integrates rough set method. The classification accuracy of the rough set model is not as good as that of a decision tree, logistic regression, and neural network models, but the rough set model more accurately predicts contractors with bad credit. The results show that the rough set model is especially useful for detecting corporations with bad credit in the currently disordered Chinese construction market. View full abstract»

    Open Access
  • Effect of methyl jasmonic acid on baccatin III biosynthesis

    Publication Year: 2006 , Page(s): 363 - 367
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (369 KB)  

    As baccatin III is an immediate diterpenoid precursor of taxol, the increase of baccatin III is beneficial to the biosynthesis of taxol. Addition of methyl jasmonic acid (MJ) enhances the activity of 10-deaceyle baccatin (DAB) III acetyl transferase which catalyzes the bioconversion from 10-DAB III to beccatin III. In this paper, the baccatin III content was increased by 174% by the addition of 100 μmol/L, MJ in suspension cultures of Taxus cuspidate. Induction by MJ also increased the expression of a 49.0-kDa protein. This paper describes the cell free acetylation of 10-DAB III in crude extracts of enzyme from the suspension cultures of Taxus cuspidate. The reaction product was confirmed by high performance liquid chromatograph (HPLC). About 25.0% of the 10-DAB III was acetylized into baccatin II on the 4th day with 100 μmol/l, MJ. The 10-DAB III acetyl transferase activity reached a peak on the 2nd day with 100 μmol/L, MJ, with 54.7% of the 10-DAB III transformed into baccatin III. The baccatin III content increased with the increase of 10-DAB III acetyl transferase activity, although the biosynthesis was delayed by more than 24 h. The remarkable induction of MJ on baccatin III biosynthesis shows a promising way to increase the production of taxol. View full abstract»

    Open Access
  • Isothermal kinetics of the pentlandite exsolution from mss/pyrrhotite using model-free method

    Publication Year: 2006 , Page(s): 368 - 373
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (343 KB)  

    The pentlandite exsolution from monosulfide solid solution (mss)/pyrrhotite exsolution is a complex multi-step process, including nucleation, new phase growth and atomic diffusion, and lamellae coarsening. Some of these steps occur in sequence, others simultaneously. These make its kinetic analysis difficult, as the mechanisms cannot be elucidated in detail. In mineral reactions of this type, the true functional form of the reaction model is almost never known, and the Arrhenius parameters determined by the classic Avrami method are skewed to compensate for errors in the model. The model-free kinetics allows a universal determination of activation energy. Kinetic study of pentlandite exsolution from mss/pyrrhotite was performed over the temperature range 200 to 300°C. For mss/pyrrhotite with bulk composition (Feo.77Nio.19)S, activation energy of pentlandite exsolution, Ea, varies from 49.6 kJ·mol−1 at the beginning of reaction (nucleation is dominant) to 20.7 kJ·mol−1 at the end (crystal growth is dominant). In general, the activation energy varies during the course of solid reaction with the extent of reaction. The surrounding environment of reactant at-oms affects the atom's activity and more or less accounts for changes of activation energy Ea. View full abstract»

    Open Access
  • Ultrasonic enhancement of industrial sludge settling ability and dewatering ability

    Publication Year: 2006 , Page(s): 374 - 378
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    This paper investigates the treatment of chromium (Cr) contaminated industrial sludge from a tanning process with ultrasound to enhance the sludge settling ability and dewatering ability. Ultrasound at various frequencies, intensities, and time was tested to optimize the operation. The results show that treatment with 30 kHz, 12 W/L ultrasound for 120 s shortened the sludge settling time from 3 h to 1 h and reduced the supernatant Cr concentration. The ultrasonic treatment also reduced the sludge volume from 4.02 mL/g to 2.58 mL/g and increased the sludge Cr concentration by 2/3. The treated sludge could then be reused in the tanning operation. Proper ultrasonic treatment can significantly reduce the sludge volume and enhance the Cr reuse. View full abstract»

    Open Access

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Tsinghua Science and Technology (Tsinghua Sci Technol) aims to highlight scientific achievements in computer science, electronic engineering, and other IT fields. Contributions all over the world are welcome.

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