- N Max;S Saito;K Watanabe;M Nakajima;
We have simulated a time varying wind field using the lattice Boltzmann model, and its effect on blades of grass with a simple mass-spring model. We present a global illumination model for multiple scattering of incident sun and sky illumination within the field of grass. We model the grass as a continuous distribution of infinitesimal colored scattering flakes and solve a system of differential equations for the radiance transport. We repeat this for a collection of grass bending directions and amounts, and then interpolate the solutions when rendering animations of blowing grass.
2010年02期 v.15 133-137页 [查看摘要][在线阅读][下载 868K] [下载次数：50 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] - Naik A;
In this paper, we briefly address the application of the standard principal component analysis (PCA) technique to fault detection and identification. Based on an analysis of the existing test statistic, we propose a new test statistic, which is similar to the Hawkin’s TH 2 statistic but without the numerical drawback. In comparison with the SPE index, the threshold setting associated with the new statistic is computationally simpler. Our further study is dedicated to the analysis of fault sensitivity. We consider the off-set and scaling faults, and evaluate the test statistic by viewing its sensitivity to the faults. Our final study focuses on identifying off-set and scaling faults. To this end, two algorithms are proposed. This paper also includes some critical remarks on the application of the PCA technique to fault diagnosis.
2010年02期 v.15 138-144页 [查看摘要][在线阅读][下载 316K] [下载次数：248 ] |[网刊下载次数：0 ] |[引用频次：99 ] |[阅读次数：0 ] - V. Van;P.-T. Ho;
The use of microring resonators to assist in the evanescent field coupling between dissimilar waveguides is proposed and analyzed. Theoretical analysis based on the coupled mode theory and nu-merical example show that complete cross power transfers can be obtained near the microring resonances. Applications of the device include power dividers, low-power thermo-optic or electro-optic switches, and modulators.
2010年02期 v.15 145-150页 [查看摘要][在线阅读][下载 756K] [下载次数：16 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] - Sheldon X.-D. Tan;
Model order reduction of interconnect circuits is an important technique to reduce the circuit complexity and improve the efficiency of post-layout verification process in the nanometer VLSI design. Existing works using the Krylov subspace method are very efficient, but the resulting models are less compact and lack global accuracy. Also, existing methods cannot handle interconnect circuits with large input and output ports. Recent advances in reduction techniques using non-Krylov subspace techniques such as truncated balanced realization (TBR) hold some promise to solve these problems. In this paper, we first review the classic TBR-based reduction methods and then present the recent developments in fast TBR-based reduction and techniques such as PMTBR, SBPOR, and ETBR methods. These newly proposed methods try to avoid the expensive computing steps in traditional TBR methods at some cost to accuracy to boost efficiency and scalability, which is critical to reduce large interconnect parasitics modeled as RLCK circuits. The ETBR method can also reduce circuits with massive ports by considering the input signals. We show the pros and cons of each method and compare them on a set of large interconnect circuits, and finally point to some new research directions for this area.
2010年02期 v.15 151-168页 [查看摘要][在线阅读][下载 796K] [下载次数：56 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - Roberto Rodes;Antonio Caballero;Jesper Bevensee Jensen;Timothy Braidwood Gibbon;Neil Guerrero Gonzalez;Idelfonso Tafur Monroy;
We theoretically analyze the channel capacity of a 5th-order Gaussian pulse-based ultra-wideband (UWB) system and experimentally demonstrate 2 Gbit/s UWB-over-fiber transmission systems incorporating wireless transmission. Both electrical and photonic UWB pulse generation methods are employed and its performance is compared. By utilizing optimum UWB pulse design and employing a digital signal processing (DSP) receiver, a bit-error-rate above the forward error correction (FEC) limit for 8 meters of wireless emission is obtained in our photonic generation UWB system. A noticeable increase in the channel capacity is achieved compared to previously reported results.
2010年02期 v.15 169-173页 [查看摘要][在线阅读][下载 641K] [下载次数：57 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 叶思隽;张友民;王新民;姜斌;
The problem of fault-tolerant controller design for a class of polytopic uncertain systems with actuator faults is studied in this paper. The actuator faults are presented as a more general and practical continuous fault model. Based on the affine quadratic stability (AQS), the stability of the polytopic uncertain system is replaced by the stability at all corners of the polytope. For a wide range of problems including H∞ and mixed H 2 /H∞ controller design, sufficient conditions are derived to guarantee the robust stability and performance of the closed-loop system in both normal and fault cases. In the framework of the linear matrix inequality (LMI) method, an iterative algorithm is developed to reduce conservativeness of the design procedure. The effectiveness of the proposed design is shown through a flight control example.
2010年02期 v.15 174-183页 [查看摘要][在线阅读][下载 786K] [下载次数：163 ] |[网刊下载次数：0 ] |[引用频次：23 ] |[阅读次数：0 ] - 姜敏;黄旭;周一鸣;
Teleportation schemes based on probabilistic channels usually rely heavily on the implementation of high-dimensional unitary operations. Since high-dimensional unitary operations are very difficult to directly implement in physics experiments, methods are used to avoid high-dimensional unitary operations during the teleportation process. This paper describes how to construct a deterministic teleportation channel and a control channel using Bell state measurements only instead of high-dimensional unitary operations. Here, the general four-particle and five-particle class states are used as the potential quantum channel and the control channel for deterministic teleportation even without access to the relevant parameters. The results show that this scheme makes physical realization of teleportation more reasonable.
2010年02期 v.15 184-189页 [查看摘要][在线阅读][下载 440K] [下载次数：43 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] - 顾弘;赵光宙;裘君;
One-class support vector machines (one-class SVMs) are powerful tools that are widely used in many applications. This paper describes a semi-supervised one-class SVM that uses supervision in terms of relative comparisons. The analysis uses a hypersphere version of one-class SVMs with a penalty term appended to the objective function. The method simultaneously finds the minimum sphere in the feature space that encloses most of the target points and considers the relative comparisons. The result is a standard convex quadratic programming problem, which can be solved by adapting standard methods for SVM training, i.e., sequential minimal optimization. This one-class SVM can be applied to semi-supervised clustering and multi-classification problems. Tests show that this method achieves higher accuracy and better generalization performance than previous SVMs.
2010年02期 v.15 190-197页 [查看摘要][在线阅读][下载 546K] [下载次数：169 ] |[网刊下载次数：0 ] |[引用频次：9 ] |[阅读次数：0 ] - 孙月;徐连宇;彭超;李正斌;
The transmission matrix method is used to analyze the influence of incident light on coupled resonators. Two different types of incident light on the same coupled resonator geometry are shown to lead to different system transmission features. The EIT-like phenomenon occurs in the type I case with the transmission being symmetric around the zero-single-pass-phase-shift frequency. In the type II case the resonant frequency has a blue shift corresponding to the increasing coupling strength between the two ring resonators. Also, the critical-coupling-like condition exists in the type II configuration to maintain the zero-single pass-phase-shift frequency. The incident light, as well as the geometry, partially determine the mode interference in the coupled ring resonator system.
2010年02期 v.15 198-201页 [查看摘要][在线阅读][下载 562K] [下载次数：30 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 应蓓华;刘勇攀;汪蕙;
Previous studies have indicated that data compression in wireless sensor networks is not always beneficial to energy conservation due to the additional computational energy costs. This work gives an energy-efficient arbitration mechanism that enhances the performance of compression algorithms by avoiding unnecessary energy losses. The adaptive compression arbitration system uses a new prediction modeling and adaptation. Tests show that the modeling method gives better predictions with the adaptive mechanism needing less data for modeling, which allows on-line prediction modeling instead of an off-line training process. Moreover, adaptive adjustments of the model parameters enable the system to keep good arbitration precision even as the data characteristics or applications change.
2010年02期 v.15 202-208页 [查看摘要][在线阅读][下载 663K] [下载次数：72 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 肖红江;戴琼海;季向阳;
An opportunistic automatic repeat request (ARQ) scheme was developed to support high-quality video transmission over cooperative decode-forward networks. The opportunistic ARQ is implemented in the form of distributed space-time block codes (STBCs) and the desired STBC for a certain channel state is de-termined by the diversity-multiplexing tradeoff principle. With good channel states, the source and relay may jointly retransmit the lost video packets using high-rate low-diversity codes while with bad channel states they will retransmit the lost video packets using low-rate high-diversity codes. Furthermore, an adaptive packet dropping mechanism was introduced by considering the delay constraint and layer dependency characteristics of scalable video streaming. Test results show that the scheme significantly improves the throughput and video quality compared with other schemes. Tests also indicate that the source-relay link condition plays an important role in affecting the scheme performance.
2010年02期 v.15 209-215页 [查看摘要][在线阅读][下载 566K] [下载次数：70 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] - 魏宇平;季向阳;张乃尧;戴琼海;
Motion compensation with adaptive interpolation filters (AIF) was developed to compensate for temporary varieties in the aliasing of video signals and improve the coding efficiency. The AIF achieves better RD performance than common static interpolation filtering by exploiting the statistics in the reference frames’ local auto-correlation and the local cross-correlation between the current encoding frame and the reference frames. This paper presents an interpolation filter buffering structure that derives the current encoding frame’s interpolation filters from the filters of previous frames. The number of encoding bits for the filter coefficients is reduced by encoding only the differences between the current filter coefficients and the corresponding buffered filter coefficients. Experimental results show that in comparison with the AIF in the current "key technical area" (KTA) reference software, this interpolation filter buffering structure further improves all the test sequences (with up to 2.87% bit rate saving) with negligible computational increase.
2010年02期 v.15 216-220页 [查看摘要][在线阅读][下载 392K] [下载次数：74 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] - 魏琦;韩丹丹;杨华中;
This paper describes a 12-bit 40-MS/s and 8-bit 80-MS/s dual-mode low power pipelined analog-to-digital converter (ADC). An improved multiplying digital-to-analog converter is used to provide the dual-mode operation. A pre-charged fast power-on switched operational amplifier is used to reduce the power consumption of the pipelined ADC to 28.98 mW/32.74 mW at 40 MHz/80 MHz sampling rates. The ADC was designed in a 1.8-V 1P6M 0.18-μm CMOS process. Simulations indicate that the ADC exhibits a spurious free dynamic range of 90.24 dB/58.33 dB and signal-to-noise-and-distortion ratio of 73.81 dB/47.85 dB at 40 MHz/80 MHz sampling frequencies for a 19-MHz input sinusoidal signal.
2010年02期 v.15 221-227页 [查看摘要][在线阅读][下载 773K] [下载次数：108 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] - 刘婧瑶;孟华东;张颢;王希勤;
It is an important issue to study sea clutter suppression because it could interfere with the detection of targets above the sea surface severely. Spatial spectrum analyses show that the majority of sea clutter has low-frequency characteristics, compared to the high-frequency characteristics of the targets. This paper proposes a frequency-based spatial tracking filter to suppress sea clutter to facilitate targets identification. Experimental results show that the signal-to-clutter ratio can increase by more than 10 dB after filtering and the algorithm is feasible for practical use. In addition, the filtering equation can be optimized to maximize the signal-to-clutter ratio improvement. The equation parameters can also be adjusted to give a proper cut-off frequency for different targets and clutter.
2010年02期 v.15 228-234页 [查看摘要][在线阅读][下载 817K] [下载次数：107 ] |[网刊下载次数：0 ] |[引用频次：6 ] |[阅读次数：0 ] - 张晶;黄京华;陈俊全;
The mobile search, a combination of a web search engine and a mobile communication system, is viewed as the most influential application in the 3G era. Therefore, mobile search service providers are eager to know which factors most influence user acceptance of mobile searches. Based on the characteristics of mobile searches and a review of previous information technology acceptance research, this study integrates the task technology fit model and the unified theory of acceptance and use of technology model to develop a mobile search acceptance model and empirically tests this model. This study finds that, for mobile searches, the performance expectancy, social influence, and perceived cost all significantly influence use intention and the performance expectancy increases with the increasing user’s experience and higher task technology fit degree. The effort expectancy is found to not affect the use intention of mobile searches and the users’ gender does not have a significant moderating effect on the use intention. The results are then used to develop suggestions for mobile search providers to promote their application and development.
2010年02期 v.15 235-245页 [查看摘要][在线阅读][下载 594K] [下载次数：221 ] |[网刊下载次数：0 ] |[引用频次：19 ] |[阅读次数：0 ] - 饶毓;陈盛博;陈巍;刘序明;
This paper addresses the optimal number of simultaneous data transmissions that maximize the system throughput in an MIMO WLAN. To facilitate simultaneous packet transmissions, both transceivers have to exchange preambles to calculate the channel state information. This exchange is combined with the RTS (request to send)/CTS (clear to send) handshake which is used to contend for the channel in WLANs. This study presents an expression for the optimal number of simultaneous data transmissions under the distributed coordinate function mechanism derived using the Markov chain model, as well as an analytical formula for the optimal system throughput given the length of the contention window and the number of nodes in the network. The analytical results show that the system throughput cannot be enhanced by simply increasing the number of simultaneous data transmissions.
2010年02期 v.15 246-250页 [查看摘要][在线阅读][下载 487K] [下载次数：102 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] -
<正>Tsinghua Science and Technology (Tsinghua Sci Technol), a comprehensive academic journal sponsored by Tsinghua University, is published bimonthly.
2010年02期 v.15 251页 [查看摘要][在线阅读][下载 781K] [下载次数：15 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] 下载本期数据