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ISSN 1000-0585
CN 11-1848/P
Started in 1982
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  • Table of Content
      , Volume 54 Issue 2 Previous Issue    Next Issue
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    Orginal Article
    Improved unbiased grey model for prediction of gas supplies
    Jie YANG, Wenguo WENG
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 145-148.  
    Abstract   HTML   PDF (1237KB) ( 798 )

    An improved unbiased grey model is developed to forecast urban gas supplies to efficiently allocate resources and ensure urban safety. The model uses three-point smoothing and an equal dimension new information model. Comparison of the improved unbiased grey model with the original model to predict the gas supplies indicates that the original model predictions decrease linearly so the differences between the predicted and actual gas supplies increase over time. The improved unbiased grey model gives nonlinear results that are better for mid-to-long term forecasts with the predicted gas supplies in better agreement with actual statistics. The average relative error for gas supplies predicted by the original model is 7.32% while that for the improved model is 5.76%.

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    Representation of emergency case information
    Chao HUANG, Quanyi HUANG, Shifei SHEN, Xueming SHU
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 149-152.  
    Abstract   HTML   PDF (1164KB) ( 1337 )

    Case representation is the basis for case-based reasoning. The representation should efficiently organize large amounts of information which is usually unstructured information, related to the emergency cases. This paper describes the attributes that should be included in emergency case descriptions with a case framework based on analyses of emergency events and information with both structured and unstructured information. The structured information uses fuzzy sets to describe the non-quantitative data using memberships instead of numerical values. The unstructured information is analyzed by three algorithms for keyword extraction with the word co-occurrence approach chosen as the best. The extracted keywords are then used to obtain the proper information segments for the unstructured part of the emergency case. The whole case is represented in a semi-structured form with quantitative attributes used in the case retrieval and text data used in the case reasoning. The results show that this approach gives good results as a foundation for case-based reasoning applications.

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    Distribution of thermo seeds in magnetic induction therapy based on the simulated annealing algorithm
    Dongyang CAI, Zihan ZHUO, Jie WANG, Jian'an WU, Jintian TANG
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 153-158.  
    Abstract   HTML   PDF (1560KB) ( 484 )

    Optimum distribution of the thermo seeds in a tumor is key to magnetic induction therapy planning. The core objective is to achieve the desired temperature distribution using the minimum number of thermo seeds. The optimum distribution of the thermo seeds is found using the simulated annealing (SA) algorithm combined with bio-heat production and transfer theory. This paper describes the calculational method to solve for the distribution of thermo seeds using the SA algorithm, including the design of the thermo seed distribution model, the bio-heat production and transfer model and the SA scheme. The algorithm is designed for the thermo seed distribution, initial temperature, stop condition, evaluation functions, acceptance probability and annealing strategy. The modeling and meshing of the tumor region, the modeling of the thermo seed implantation, the temperature distribution, and the iteration process are all introduced to show the feasibility of solving for the thermo seed distribution using the SA algorithm.

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    Neutron multiplicity counter design and calibration
    Ligao CHEN, Xiaobo LIU, Jian GONG, Kan WANG, Chuanjiang DONG, Ru RONG, Yi LU
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 159-163.  
    Abstract   HTML   PDF (1305KB) ( 749 )

    A neutron multiplicity counter is designed and calibrated with the integrated electronics data acquisition and processing software described here. The predelay time length search equations are developed by balancing the correlated counts and the background counts of Am-Li neutron sources. A deadtime coefficient fitting method minimizes the root mean square. Nine parameters are acquired and two plutonium samples are used to verify the counter performance and parameter calibration algorithm. Test results show that the design and calibration for neutron multiplicity measurements are valid.

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    Optimal source biased sampling density function for the Monte Carlo method
    Jian SU, Zhi ZENG, Jianping CHENG, Junli LI
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 164-171.  
    Abstract   HTML   PDF (1326KB) ( 659 )

    The source biased sampling method reduces the variance and improves the efficiency of Monte Carlo particle transport calculations. This paper gives a multi-region, multi-weight shooting model to simulate the source in transport processes. The density function gives the minimum variance for source biased sampling. The model is solved using a random numerical method to verify the correctness of the function. A particle transportation problem is then simulated to show the significant effect of the variance reduction. This method can be used as a general variance reduction technique in Monte Carlo particle transport analyses to construct the density function for biased source sampling for various particle source parameters, such as the transmission location and direction. It gives the best partition coefficient with the minimum variance in stratified sampling.

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    Geometric parameter analysis of Chinese cervical discs
    Weiqiang LIU, Ting PU, Hongsheng GU, Zhenhua LIAO, Jinpeng JIANG
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 172-177.  
    Abstract   HTML   PDF (1329KB) ( 878 )

    A protocol is developed for precise measurements of the geometric parameters of cervical discs as a basis for the design of artificial cervical discs for Chinese people and the selection of total disc replacement models. The six key parameters (i.e., the anterior height, the middle height, the posterior height, the intervertebral angle, the sagittal diameter and the transverse diameter) of all the five cervical intervertebral discs, C23, C34, C45, C56 and C67, are measured from a magnetic resonance imaging (MRI) database of normal Chinese discs. Chinese cervical disc geometric characteristics are then analyzed statistically. The height of a normal Chinese cervical disc tends to increase first and then decrease with age, with the maximum at 39-48 years old. All six parameters increase about linearly from the upper to the lower discs except for the intervertebral angle. The parameters for females are about 90% of those for males.

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    Combined analysis method for low-cycle fatigue damage variables in the welded joint of steam turbine rotors
    Zhipeng CAI, Jiandong WU, Zhinan TANG, Boqi ZHANG, Jiluan PAN, Xia LIU
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 178-184.  
    Abstract   HTML   PDF (1463KB) ( 790 )

    Analyses of low-cycle fatigue damage to welded joints in turbine rotors are significant to safety assessments. In this paper, fatigue damage mechanics are used to analyze low-cycle fatigue in a 1:1 simulated sample of a NiCrMoV steel low-pressure (LP) steam turbine welded rotor. The elastic modulus method and the stress amplitude method both cannot accurately represent the fatigue damage variable, so this paper presents a combined analysis method, which considers the material damage during cyclic softening (or hardening) in cyclic softening materials or materials with cyclic hardening followed by softening. The results are better than with previous methods for low-cycle fatigue analyses of NiCrMoV steel LP steam turbine welded rotors.

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    Error correction algorithm for manipulator of wall climbing robot with both ends having magnetic adsorption
    Jiajun LIU, Zhenguo SUN, Wenzeng ZHANG, Qiang CHEN
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 185-190.  
    Abstract   HTML   PDF (1303KB) ( 845 )

    A wall climbing robot with both ends using magnetic adsorption is developed for on-site hydraulic turbine blade repairs. The magnetic mobile platform has a multiple degrees of freedom (DOF) manipulator and an end operating unit. The manipulator has 3 active and 3 passive joints, so the trajectory planning method for a given working path assumes a local curve where the end effector of the manipulator works on a plane. However, simulations for a sphere with a 1.5 m curvature show that the path error due to this assumption is larger than 5 mm. A correction algorithm to reduce the error transforms the error from Cartesian space to the joint space through a Jacobian matrix. Simulations show that the error can be reduced to less than 1 mm by this algorithm.

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    Residual welding stresses in the pipe-bar joints of a rotary drilling rig
    Haiyan ZHAO, Xingquan XU, Xingzhe YU, Xiaowu ZHU
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 191-196.  
    Abstract   HTML   PDF (2141KB) ( 679 )

    The drill rod is one of the most important components of a rotary drilling rig and it is highly stressed. The pipe-bar welded joints are most likely to be damaged. The welding of pipe-bar joints is simulated using the SYSWELD software to calculate the residual welding stresses for comparison with measured residual welding stresses by X-ray diffraction. The calculated results are in good agreement with the measured data. The welding speed is then changed to study its effect on the residual welding stresses. The results show that the maximum tensile stress exists at the heat affected zone. With the increase of welding speed, the maximum tangential compressive stress increases, but the maximum tensile stress has no significant change.

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    FPGA based high precision sinusoidal signal generator
    Zhuo PENG, Yan DENG, Cheng MA, Jianping XIONG, Yongli Yin
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 197-201.  
    Abstract   HTML   PDF (1264KB) ( 1192 )

    A 24-bit sigma-delta digital-to-analog converter (DAC) is used to produce high precision sinusoidal signals with low total harmonic distortion (usually less than -106 dB) for seismic data acquisition system self-tests. The key problem is to convert the sinusoid to a sigma-delta bit stream to drive the sigma-delta DAC. This paper presents a field-programmable gate array (FPGA) based bit stream generator which is composed of a sinusoidal data memory, an interpolation filter and a sigma-delta modulator. This paper focuses on the design and simulation methods for the interpolation filter and the sigma-delta modulator and the whole system implementation using the DSP Builder in FPGA. Tests show that the bit stream generator can drive a 24-bit sigma-delta DAC to produce a 31.25 Hz, 3.96 V peak-peak voltage sinusoidal signal with -121.0 dB total harmonic distortion and 111.4 dB signal-to-noise ratio, which meets the needs for seismic use. The design is simple, programmable and easy to implement.

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    Improved resolution for SPR detection systems with angular modulation
    Fuyin DOU, Peng WANG, Xinglong YU
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 202-206.  
    Abstract   HTML   PDF (2415KB) ( 969 )

    Improved system resolutions for surface plasmon resonance (SPR) will enable applications in more fields. This paper shows theoretically that the resolution of SPR with angular modulation is not only improved with increased sensitivity, but also with a narrower half-peak width. The resolutions with Au, Ag and Au-Ag chips show that the resolution of the Au-Ag chip is higher than that of the Au chip. Thus, the system resolution can be improved by using the Au-Ag chip. Measurements of the resolution of Au and Au-Ag chips using NaCl solutions with different mass fractions show that the Au and Au-Ag chip resolutions are 5.2×10-6 and 3.9×10-6 RIU (refractive index unit). Thus, the Au-Ag chip resolution is 1.4 times higher than the Au chip, similar to the theoretical result being 1.6 times higher.

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    Electrical conductivity measurement method using square wave pulse excitation
    Fan MENG, Yonggui DONG
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 207-211.  
    Abstract   HTML   PDF (1401KB) ( 1836 )

    When a square wave pulsed signal is adopted as excitation to obtain electrical impedance information for a conductive medium, the amplitude decay of the higher harmonics in square wave spectrum can have a significant effect. Adding an inductor or capacitor to a first-order resistant-capacitive-type sensing system creates a second-order resonant element that creates a freely damped oscillating signal at both the rising and falling edges of the excitation. The excitation amplitude near the resonant frequency is, therefore, enhanced. The equivalent resistance in the resonant element can be obtained by measuring the first positive peak voltage of the freely damped signal at the falling edge of the pulse. Tests indicate that resistance measurements for frequencies from 30 kHz to 1 MHz can be implemented only by a fixed frequency square wave excitation signal generated by a digital circuit. This method can be used for conductivity measurements of conductive media, such as electrolyte solutions, water and human skin, using both wired and wireless transmitters.

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    Optimization of spray gun speed for pipe painting robots
    Yulong PAN, Guolei WAN, Li ZHU, Yan CHEN, Ken CHEN
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 212-216.  
    Abstract   HTML   PDF (1361KB) ( 987 )

    Paint coating thickness uniformity is investigated with a double beta spray gun model to investigate the coating thickness distribution assuming that the robot spraying coating shape is oval. Then, the coating mechanism is analyzed for the spray gun model. The relationship between the coating thickness variation and the coating transfer efficiency is studied experimentally with a uniform gun motion speed. An optimal spray gun motion speed is found with the best results found for a constant ratio of the spray gun speed to the paint transfer efficiency. The experimental results indicate that the speed optimization method effectively improves the coating thickness uniformity.

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    Arc-length constrained deformation of characteristic NURBS curves for customized shoe-last CAD system
    Huaiyi REN, Boxiong WANG, Xiuzhi LUO
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 217-222.  
    Abstract   HTML   PDF (1629KB) ( 900 )

    A customized shoe-last system is developed based on the deformation of characteristic NURBS curves for feet or shoe-lasts to enable customized shoes without a shoe-last database. Deformations of the feet or shoe-lasts characteristic curves are used to make new shoe-lasts with constraints of the arc-lengths. The system uses comfort matching rules between the feet and the shoe-lasts with the characteristic curves divided into four types according to their different deformation ways, orders, and constraints. Deformation roadmaps are then given with forward, reverse and bidirectional deformation roadmaps for the II-type curves with arc-length constraints. The bidirectional deformation uses an improved vertex substitution algorithm and a modified variable-parameter 4-point interpolatory subdivision scheme with a new arc-length loss actor and a rigid joint chain model. Customized shoe-last curves are produced from a mother shoe-last through sampling, grading, sectioning, simplifying, deforming, subdividing, and NURBS fitting. For the metatarsophalangeal contour curve, a bidirectional deformation test gives an arc length change of 1.0 mm. With this system, a man's shoe-last can be customized in less than 480 s to give accurate, practical customized shoes without a shoe-last database. This method greatly increases the redesign for customized shoe-lasts.

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    Analysis and parametric design of the dynamics of a dry gas seal for extreme operating conditions using a semi-analytical method
    Xiangfeng LIU, Chen XU, Weifeng HUANG
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 223-228.  
    Abstract   HTML   PDF (1482KB) ( 584 )

    The dynamics of a spiral groove dry gas seal (DGS) are analyzed using extreme operating conditions based on the semi-analytical method developed by Miller and Green. The compressible form of the Reynolds equation is solved numerically with a finite element method for the DGS gas film model to determine the stiffness model for the gas film during the dynamic process by calculating the gas film response to a step jump in the film thickness. Then, the stiffness model is applied to the kinetic model of the seal ring in the frequency domain. The movement of the seal ring in the time domain is obtained by an inverse Laplace transform. The method is used to solve for the transient response of a DGS to both the axial and tilt initial disturbances. The influences of the geometric parameters are evaluated to find reasonable parameters for parametric design to improve dynamic performance of the DGS for turbine compressor spiral groove DGS designs.

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    One-dimensional hydrodynamic model of the recycling valve in a circulating fluidized bed
    Heng FENG, Qinghai LI, Chao GAN, Aihong MENG, Yanguo ZHANG
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 229-234.  
    Abstract   HTML   PDF (1280KB) ( 780 )

    This study focuses on the influence of key factors, such as solids circulation rate and the aeration rate, on the solids height in the standpipe of the recycling valve. A one-dimensional hydrodynamic model is developed based on the hydrodynamics of the gas-solid flow in the loop-seal and the standpipe. The predicted heights agree well with experimental data. Redistribution of the aeration ratio in the standpipe and the discharge chamber increases the solids height in the standpipe to adapt to increasing solids circulation rates and to balance the pressures in the circuit. The results also indicate that if the solids circulation rate is over a critical value, the recycling valve will lose its self-adaptability and the solids will rise out of the standpipe and into the cyclone separator. The self-adaptability can be enhanced and the stable operation range of the recycling valve can be extended by properly increasing the aeration rate. This model is useful for the design and optimization of circulating fluidized bed recycling valves with relatively short standpipes.

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    Pseudo-component model to predict the thermochemical behaviour of combustible solid waste
    Aihong MENG, Yanqiu LONG, Hui ZHOU, Yanguo ZHANG, Qinghai LI
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 235-239.  
    Abstract   HTML   PDF (1209KB) ( 1011 )

    More than 20 kinds of typical solid waste and component compounds were analyzed using a thermogravimetric analyzer (TGA). The waste was divided into 6 groups with a pseudo-component model used to re-configurate their mass loss curves. The principal idea of the pseudo-component model was described and used to define the typical pseudo-component model and its groups. The correlation coefficient for Chinese cabbage and its pseudo-components is higher than 0.92 with similar results for orange peels, aspen branches and leaves. The re-configurated TG curves for the pseudo-components fit well with the experimental curves for the solid waste. The results show that the pseudo-component model and its groups can be used to predict the thermochemical behavior of combustible solid waste based on TGA measurements.

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    Effect of bubble coalescence on the wall heat transfer during subcooled pool boiling
    Coulibaly Abdoulaye, Xipeng LIN, Jingliang BI, M. Christopher David
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 240-246.  
    Abstract   HTML   PDF (3558KB) ( 1104 )

    This study experimentally investigated the effects of bubble coalescence on nucleate pool boiling. A micro heater array was used to generate vapor bubbles in FC-72 liquid with constant surface temperature boundary conditions while the heat flux at selected locations was measured using a high speed data acquisition system. The heat flux for boiling with coalescence was found to fluctuate much more than when only a single bubble formed on the surface due to the vaporization of the liquid layer trapped between the bubbles and oscillation of the bubbles after coalescence. These oscillations significantly increased the average heat transfer by increasing the frequency of rewetting of the heated surfaces compared to single bubble nucleation. The observations also showed that very fast coalescence events were not accompanied by an increase in the heat transfer rate as the liquid layer between the bubbles was physically pushed away by the rapid bubble growth during the inertial bubble growth stage instead of evaporating. The results show that the heat transfer increases for the dimensionless coalescence number, Ncoal, more than 0.2 but decreases for Ncoal less than 0.2.

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    Biofouling growth model and force analysis
    Qianpeng YANG, Xiaodong CHEN, Lei TIAN, Lin SHI
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 247-252.  
    Abstract   HTML   PDF (3515KB) ( 554 )

    Biofouling on heat exchanger surfaces reduces the heat transfer rate and the system security. Thus, more investigations are needed on biofouling growth mechanisms and the forces acting on the biofouling. This study uses a three dimensional cellular automata model to simulate biofouling growth. Reciprocal inhibition between different bacteria strains is also simulated. A shape factor concept is then used to describe the various biofouling shapes to analyze the forces on the biofouling. The cellular automata model simulates Bacillus subtilis and Aeromonas ichthiosmia as typical heat exchanger bacteria strains. The model simulates the biofouling growth and reciprocal inhibition to show that the heat exchanger biofouling inhibition should focus on Bacillus subtilis. The shape factors for three typical shapes used in this work accurately model the biofouling shapes. The shape factors simplify the force analyses and are useful for comparing different biofouling shapes.

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    Modified rigid finite element method for wind turbine dynamics
    Fenghao ZHANG, Rong HE
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 253-258.  
    Abstract   HTML   PDF (1440KB) ( 856 )

    The two-stage-division method used by the rigid finite element method has some defects that restrict analyses for wind turbine dynamics. A modified method is developed which replaces the two-stage-division method by distributing the spring damping elements as in the real structure. The action range of the spring damping element is also adjusted. The displacement and frequency results computed by the modified method are very close to precise results. The modified method is flexible with easily applied boundary conditions, so this method can be widely used. A wind turbine dynamic model developed using the modified method gives accurate results.

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    Wavelet de-noising method with threshold selection rules based on SNR evaluations
    Jianjun ZHONG, Jian SONG, Changxi YOU, Xinqiao YIN
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 259-263.  
    Abstract   HTML   PDF (1269KB) ( 1409 )

    Acceleration signals from automotive automatic transmission bench tests need to be de-noised. Wavelet threshold de-noising requires a relatively small amount of computations and has better filtering. However, different wavelet basic functions and different threshold rules produce different noise signal de-noising results. Optimal matching parameters are found for simulated signals that approximate an observed signal through de-noising tests using the signal-to-noise ratio (SNR) and root-mean-square error (RMSE) of the de-noised signal as the evaluation index. The results are combined with the angular acceleration signal de-noise processing obtained in a bench test for the filtering. The wavelet transform de-noising is efficient, stable and not easily distorted when dealing with noise signals. The effect of the wavelet de-noising noisy signal can be evaluated using SNR combined with RMSE for the objective evaluation. Different signals may need to use different wavelet basis functions with different threshold rules.

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    Human safety estimates in hot environments based on a thermal manikin
    Chao ZHAN, Tingxin QIN, Su WU, Jinyu WANG
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 264-269.  
    Abstract   HTML   PDF (1457KB) ( 937 )

    Human safety protection in hot environments is required in many fields, such as high-temperature industrial operations and fire fighting. This paper presents a method to estimate human safety in hot environments. The method combines the bio-heat theoretical model and experimental simulations. The hot experimental environment uses a high-temperature cabin heated by an infrared thermal radiation board. The body temperature and required perspiration rate are calculated by the theoretical model for the real-time experimental parameters. The balance between the warming and the sensible heat released by perspiration is simulated using a NEWTON thermal manikin. The bio-heat response of the body temperature and the perspiration rate due to the heating is studied for 30-40 oC thermal environments. The human safety is estimated for both hyperthermia and dehydration. The results show that this method can accurately simulate the human thermal physiological response and estimate the human safety status in hot environments.

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    Polarimetric feature for registration of polarimetric SAR images
    Wenting MA, Jian YANG, Wei GAO, Guangyi ZHOU
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 270-274.  
    Abstract   HTML   PDF (2282KB) ( 753 )

    The registration of multi-band polarimetric synthetic aperture radar (SAR) images is a key problem for image fusion. This paper presents a feature based on the polarimetric scattering mechanism for registration using the scale invariant feature transform (SIFT) algorithm. The feature represents information for the main scattering component and the influence of the other scattering components distribution and has good consistency for multi-band polarimetric SAR images. Tests demonstrate that the feature difference between multi-band polarimetric SAR images is less than the total scattered power (Span) difference. The SIFT algorithm is then used to get more key points, more correct registration points, and better spatial distribution of the correct registration points. The registration efficiency is remarkably increased by this feature.

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    Efficient frequency division multi-service based on DTMB-A systems
    Bo HAO, Jun WANG, Zhaocheng WANG
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 275-280.  
    Abstract   HTML   PDF (1491KB) ( 567 )

    An efficient frequency division multi-service allocation is designed to provide high data rates and mobile support for broadcasting communication. The transceiver structure design is based on advanced digital terrestrial multimedia broadcasting (DTMB-A). The fixed service uses a 32 × 1024 fast Fourier transform (FFT) and 256 quadrature amplitude modulation (QAM) to provide the static receivers with high definition programs, while the mobile service is flexibly configured according to the channel characteristics with offset-QAM modulation and the isotropic orthogonal transfer algorithm (IOTA) as the shaping filter. Simulations show 20 dB gain for the out-of-band interference for the fixed service and better performance in the Doppler environment. As a result, this method simultaneously meets the needs of both mobile and fixed receivers.

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    On-the-fly translation algorithm from linear temporal logic to Büchi automata
    Laixiang SHAN, Zheng QIN, Xinye LU, Zhengcai LU
    Journal of Tsinghua University(Science and Technology). 2014, 54 (2): 281-288.  
    Abstract   HTML   PDF (1206KB) ( 793 )

    Translations of linear temporal logic to Büchi automata are key to explicit model checking, with the Tableau-based algorithm commonly used for the translation. This paper describes an improved Tableau-based algorithm which converts linear temporal logic to transition-based Büchi automata. The satisfaction information of the U-formula for the states and transitions is used to judge whether the automata is acceptable using only one acceptance condition set, rather than multiple sets. Thus, the algorithm gives an on-the-fly degeneralization mechanism that can expand the state nodes while detecting their validity and removing invalid nodes. The algorithm combines equivalent states and transitions and avoids simplifications after forming the final automata. Comparisons with other conversion tools show that this algorithm runs faster with less states and transitions in the automaton.

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