Tsinghua Science and Technology

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Volume 11 No. 5
20 May 2006

A Modified Cellular Automaton Method for the Modeling of the Dendritic Morphology of Binary Alloys

Ying Liu, Qingyan Xu, Baicheng Liu

2006, 11(5): 495-500. doi:10.1016/S1007-0214(06)70225-5

Abstract ( 159 ) ( 252 )

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A cellular automaton (CA)-based model for the precise two-dimensional simulation of the dendritic morphology of cast aluminum alloys was developed. Compared with previous CA models, the new model considers the solidification process in more detail, solving the solute and heat conservation equations in the modeling domain, including calculation of the solid fraction, the tip velocity, and the solute diffusion process, all of which have significant influence on the dendrite evolution. The rotating...

Forces in Hard Turning of 51CrV4 with Wiper Cutting Tool

Xinfeng He, Su Wu, Hubert Kratz

2006, 11(5): 501-506. doi:10.1016/S1007-0214(06)70226-7

Abstract ( 172 ) ( 300 )

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For precision machining, the hard turning process is becoming an important alternative to some of the existing grinding processes. This paper presents an analytical model for predicting cutting forces in hard turning of 51CrV4 with hardness of 68 HRC. The cutting tool used is made from cubic boron nitride (CBN) with a wiper cutting edge. Formulas for differential chip loads are derived for three different situations, depending on the radial depth of cut. The cutting forces are determined by inte...

Propulsion Challenges for Small Spacecraft: 2005

Vadim Zakirov, Luming Li

2006, 11(5): 507-514. doi:10.1016/S1007-0214(06)70227-9

Abstract ( 177 ) ( 329 )

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Small (<100 kg) spacecrafts are being developed in many countries but their propulsion systems still have many challenges. Although there is demand for small spacecraft propulsion, the number of missions at present is small due to several commercial and technical reasons. Poor performance of existing small spacecraft propulsion systems is one of the main reasons for the small number of missions. Several reasons are given for the poor performance of existing small spacecraft propulsion. Suggested...

Design and Manufacturing of a Composite Lattice Structure Reinforced by Continuous Carbon Fibers

Hualin Fan, Wei Yang, Bin Wang, Yong Yan, Qiang Fu, Daining Fang, Zhuo Zhuang

2006, 11(5): 515-522. doi:10.1016/S1007-0214(06)70228-0

Abstract ( 245 ) ( 317 )

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New techniques have been developed to make materials with a periodic three-dimensional lattice structure. The high stiffness per unit weight and multifunction of such lattice structures make them attractive for use in aeronautic and astronautic structures. In this paper, epoxy-soaked continuous carbon fibres were first introduced to make lattice composite structures, which maximize the specific load carrying capacity. A micromechanical analysis of several designs, each corresponding to a differe...

Heat Transfer Enhancement Due to Marangoni Flow Around Moving Bubbles During Nucleate Boiling

David M. Christopher, Hao Wang, Xiaofeng Peng

2006, 11(5): 523-532. doi:10.1016/S1007-0214(06)70229-2

Abstract ( 176 ) ( 341 )

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Nucleate boiling is a very efficient method for generating high heat transfer rates from solid surfaces; however, the fundamental physical mechanisms governing nucleate boiling heat transfer are not well understood. The heat transfer mechanisms around stationary and moving bubbles on very thin microwires were analyzed numerically to evaluate the effect of the bubble motion on the heat transfer from the wire surface. The numerical analysis accurately models the experimentally observed bubble move...

Scale Factor Determination of Micro-Machined Angular Rate Sensors Without a Turntable

Gaisser Alexander, Zhongyu Gao, Bin Zhou, Rong Zhang, Zhiyong Chen

2006, 11(5): 533-537. doi:10.1016/S1007-0214(06)70230-9

Abstract ( 166 ) ( 313 )

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This paper presents a digital readout system to detect small capacitive signals of a micro-machined angular rate sensor. The flexible parameter adjustment ability and the computation speed of the digital signal processor were used to develop a new calibration procedure to determine the scale factor of a gyroscope without a turntable. The force of gravity was used to deflect the movable masses in the sensor, which resulted in a corresponding angular rate input. The gyroscope scale factor was then...

Dynamic Transmissibility of a Complex Nonlinear Coupling Isolator

Ping Yang, Jianming Yang, Jianning Ding

2006, 11(5): 538-542. doi:10.1016/S1007-0214(06)70231-0

Abstract ( 281 ) ( 329 )

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A mathematical model was developed for a complex nonlinear coupling isolator for attenuating vibration which coupled quadratic damping, viscous damping, Coulomb damping, and nonlinear spring forces. The approximate analytical solution for the dynamic transmissibility of the isolator was deduced by combining Fourier transforms and the harmonic balance method with deterministic excitation. The mathematical characteristics of the dynamic transmissibility were analyzed to illustrate the dynamic perf...

Brightness Independent 4-Star Matching Algorithm for Lost-in-Space 3-Axis Attitude Acquisition

Ying Dong, Fei Xing, Zheng You

2006, 11(5): 543-548. doi:10.1016/S1007-0214(06)70232-2

Abstract ( 196 ) ( 330 )

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A star identification algorithm was developed for a charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) autonomous star tracker to acquire 3-axis attitude information for a lost-in-space spacecraft. The algorithm took advantage of an efficient on-board database and an original “4-star matching” pattern recognition strategy to achieve fast and reliable star identification. The on-board database was composed of a brightness independent guide star catalog (mission catalog)...

Safety Implementation of Hydrogen Igniters and Recombiners for Nuclear Power Plant Severe Accident Management

Jianjun Xiao, Zhiwei Zhou, Xingqing Jing

2006, 11(5): 549-558. doi:10.1016/S1007-0214(06)70233-4

Abstract ( 143 ) ( 319 )

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Hydrogen combustion in a nuclear power plant containment building may threaten the integrity of the containment. Hydrogen recombiners and igniters are two methods to reduce hydrogen levels in containment buildings during severe accidents. The purpose of this paper is to evaluate the safety implementation of hydrogen igniters and recombiners. This paper analyzes the risk of deliberate hydrogen ignition and investigates three mitigation measures using igniters only, hydrogen recombiners only or a ...

Optimizing Fiber Topologies for WDM Optical Networks Based on Multi-Granularity Optical Switching Technology

Junjie Li, Bingkun Zhou, Hanyi Zhang, Yanhe Li

2006, 11(5): 559-567. doi:10.1016/S1007-0214(06)70234-6

Abstract ( 177 ) ( 340 )

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For the quality of service (QoS) and fairness considerations, the hop counts of various lightpaths in a wavelength division multiplexing (WDM) optical network should be short and compact. The development of multi-granularity optical switching technology has made it possible to construct various fiber topologies over a fixed physical topology. This paper describes a fiber topology design (FTD) problem, which minimizes the maximum number of required fibers in the physical links for a maximum light...

Joint Maximum-Likelihood and MMSE Channel Estimator for UWB Communications

Lei Zhou, Shidong Zhou, Yan Yao

2006, 11(5): 568-573. doi:10.1016/S1007-0214(06)70235-8

Abstract ( 144 ) ( 304 )

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Channel estimation and synchronization are crucial problems in coherent ultra wideband (UWB) receiver designs. A joint maximum-likelihood (ML) and minimum-mean-square-error (MMSE) channel estimation scheme was developed for more precise channel estimates based on the assumption of exponential multipath decay. The performance improvement was analyzed theoretically with a computer simulation using IEEE 802.15.3a ultra-wideband channel models. Theoretical and simulation results show that the scheme...

Performance Analysis of Hard Iterative Channel Estimation in Turbo Equalization

Yongjun Deng, Zhixing Yang, Changyong Pan, Jun Wang

2006, 11(5): 574-581. doi:10.1016/S1007-0214(06)70236-X

Abstract ( 213 ) ( 296 )

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Reasonable bit error rate performance requires perfect channel state information (CSI) in traditional turbo equalization (TE), which is hard to obtain in practice. Soft and hard iterative algorithms have been developed to address the channel estimation problem with the performance of the soft iterative channel estimate based on the recursive least square algorithm. This paper presents an analysis of the performance of hard iterative channel estimation (HICE) based on the least mean square algori...

Two Language Models Using Chinese Semantic Parsing

Mingqin Li, Xia Wang, Zuoying Wang

2006, 11(5): 582-588. doi:10.1016/S1007-0214(06)70237-1

Abstract ( 244 ) ( 337 )

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This paper presents two language models that utilize a Chinese semantic dependency parsing technique for speech recognition. The models are based on a representation of the Chinese semantic structure with dependency relations. A semantic dependency parser was described to automatically tag the semantic class for each word with 90.9% accuracy and parse the sentence semantic dependency structure with 75.8% accuracy. The Chinese semantic parsing technique was applied to structure language models to...

SCSI Target Simulator Based on FC and IP Protocols in TH-MSNS

Bigang Li, Jiwu Shu, Weimin Zheng

2006, 11(5): 589-596. doi:10.1016/S1007-0214(06)70238-3

Abstract ( 190 ) ( 322 )

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Storage area networks (SAN) generally use fiber channel (FC) disks, but they are expensive, hard to scale, and incompatible with previous storage arrays. This paper describes an SCSI interface disk array, which is controlled by a simulated target controller, as the target device of an SAN system. A detailed target-mode SCSI middle level design and implementation is described with interfaces to efficiently supervise the entire target simulator. The target simulator has control flexibility, wide a...

Precoding for Multiuser Spatial Multiplexing MIMO Downlink

Bijun Zhang, Guangxi Zhu, Yingzhuang Liu

2006, 11(5): 597-605. doi:10.1016/S1007-0214(06)70239-5

Abstract ( 151 ) ( 318 )

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Previous precoding algorithms have concentrated on the single user scenario where the precoding scheme assumes perfect channel state information (CSI) at the transmitter or on limited feedback techniques, such as channel quantization or limited feedback signal designs. This paper proposes a novel unitary downlink precoding design scheme for multiuser spatial multiplexing multiple-input multiple-output (MIMO) systems. With the perfect CSI available at the transmitter and the linear decoder at the...

Polling Strategy for Wireless Multimedia LANs

Zhijun Yang, Dongfeng Zhao

2006, 11(5): 606-610. doi:10.1016/S1007-0214(06)70240-1

Abstract ( 140 ) ( 319 )

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Wireless local area networks (WLANs) are a viable technology for multimedia traffic. One of the most common WLANs standards being adopted as a mature technology is the IEEE 802.11 standard. This paper presents a new polling strategy for wireless multimedia LANs with variable packet lengths, which synchronizes polling and transmission of the information packets. A mathematical model based on imbedded Markov chain theory and the generation function was used to predict the mean queue length and inf...

Pattern Recognition of Non-Stationary Time Series with Finite Length

Wanchun Fei, Lun Bai

2006, 11(5): 611-616. doi:10.1016/S1007-0214(06)70241-3

Abstract ( 171 ) ( 312 )

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Statistical learning and recognition methods were used to extract the characteristics of size series measurements of cocoon filaments that are non-stationary in terms of mean and auto-covariance, by using the time varying parameter auto-regressive (TVPAR) model. After the system was taught to recognize the size data, the system correctly recognized the size of series of cocoon filaments as much as 96.95% of the time for a single series and 98.72% of the time for the mean of two series. The corre...

Parameter Uncertainty in CGE Modeling of the Macroeconomic Impact of Carbon Reduction in China

Can Wang, Jining Chen

2006, 11(5): 617-624. doi:10.1016/S1007-0214(06)70242-5

Abstract ( 217 ) ( 319 )

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Formal methods are used to characterize the uncertainty in the computable general equilibrium (CGE) model outputs to assess the use of the CGE model of China (integrated energy-economy-environment dynamic CGE, TEDCGE) for carbon tax policy issues. Monte Carlo experiment was used for the parameter uncertainty propagation and unconditional sensitivity analysis, using the variance of the conditional expectation (VCE) as the importance index to identify critical uncertainties. The results illustrate...