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28 December 2011, Volume 17 Issue 6
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Communication and Information
Improved Transceiver Structure Based on Per-antenna Rate Control Scheme for Multi-stream MultipleInput Multiple-Output Systems
ZHOU Ji-Ting, XIONG Yong, ZHOU Zhi-Gang
2011, 17(6): 691-695. doi:
10.3969/j.issn.1007-2861.2011.06.001
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Per-antenna rate control (PARC) is an efficient way to increase throughput of multi-stream multipleinput multiple-output (MIMO) systems. In time-varying channels, however, the channel quality indicator (CQI) fed back to the transmitter becomes is outdated. There is a mismatch between the selected transmission scheme and actual situation. Therefore, the system performance may be degraded. We propose an improved transceiver structure for PARC based multi-stream MIMO system considering the channel delay effects of CQI feedback. The minimum mean square error (MMSE) channel predictor based on pilot symbol assisted modulation (PSAM) for MIMO systems is used for prediction. This scheme compensates for the performance degradation caused by transmission delay and offers a more precise application of the modulation and coding set (MCS) selection scheme for modulation and rate control. Simulations are performed to demonstrate the performance for the proposed system.
Optical QPSK Modulation Based on Parallel DD-MZM Scheme in a 40 GHz Radio over Fiber System
CHEN Xiang, LI Ying-Chun, CA You-Mei, JU Shi-Huan
2011, 17(6): 696-701. doi:
10.3969/j.issn.10072861.2011.06.002
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A new millimeter-wave radio over fiber (RoF) system based on optical frequency multiplication (OFM) technique is proposed, in which quadrature phase shift keying (QPSK) is implemented on optical wave in a parallel structure of Mach-Zehnder modulators (MZM). In the center station, light-wave injected into parallel DD-MZM is split into four optical carries, which are phase modulated by four microwave signals respectively, and then combined together. The light-wave is photodetected to generate an electrical signal consisting of harmonics of the microwave signal. The desired millimeter-wave signal is included in the harmonics, and can be maximized just by adjusting the phase modulation index. QPSK modulation is realized while millimeter waves are generated at the base station. This system overcomes the disadvantage of the traditional optical QPSK modulation in an mmRoF system. Simulation results verify the millimeter-wave generation technique, and the signal modulation and demodulation, showing feasibility of the proposed millimeterwave system.
Stability of Fiber Grating Preparation Structure
XIAO Jian-Feng, SHI Jie-Long, LIU Jun-Hui, SUN Wei-Qing
2011, 17(6): 702-707. doi:
10.3969/j.issn.1007-2861.2011.06.003
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We analyze stability and accuracy of fiber Bragg grating with a phaseshift mask in the preparation process. By simulation and experiments, we have verified effects of some parameters that affect stability and accuracy of preparation. Meanwhile, we show the relationship between light sensitivity and exposure in the fiber. We also study how to improve the focus effect and stability of the centre wavelength of fiber Bragg grating. As a result, we provide a new scheme for batch processing temperaturestable fiber grating wit high precision.
Novel Multiband Microstrip Slot Antenna for Mobile Handsets
CHEN Wen-Feng, XIAO Zhong-Yin, XIANG Liang-Liang, MA De-Chen
2011, 17(6): 708-712. doi:
10.3969/j.issn.1007-2861.2011.06.004
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This paper proposes a novel microstrip slot antenna. Multiband is realized for WiFi and GPS applications by etching an inverted-T shape monopole slot in the patch, and wide-band achieved by using phase-delay microstrip feed line. The effects of different parameters on S11 and bandwidth have been investigated. Stimulation results are obtained using the commercial software CST2009. The measured results agree with the simulated ones.
Improved Adaptive Domain Decomposition Finite Difference Time- Domain Method for Solving 3D EM Problems
LI Feng, MENG Lian-Qin
2011, 17(6): 713-718. doi:
10.3969/j.issn.1007-2861.2011.06.005
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This paper proposes an improved adaptive domain decomposition finite-difference time-domain (IADD-FDTD) method. We apply an adaptive boundary test to the voltage on the boundary. The new algorithm avoids computational error caused by instability of electric field intensity on the test boundaries, and can get more sub-domains than the original adaptive domain decomposition finite difference time domain (ADD-FDTD) and increase computation speed. Analysis results of some 3-D multilayer interconnected structures show that the proposed algorithm is correct and efficient.
Active Control of Body Weight for Gait Training Robot
FANG Ban, CHEN Lin-Yong, ZHANG E-Nan, JIAN Jin-Wu
2011, 17(6): 719-723. doi:
10.3969/j.issn.1007-2861.2011.06.006
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Partial body-weight supported gait training is an important rehabilitation means in curing lower extremity walking drawback resulting from nerve diseases. As the patient is unable to support his/her own body weight and keep the body in balance during the treadmill training, the body weight support system that help the patient reduce the body weight and keep the body in balance is import for rehabilitation equipment. This paper describes a control method for the body weight support system designed in the laboratory, builds a control system and demonstrates its feasibility by experiments. Experimental results show that the proposed method can meet the requirements of the body weight support system.
Mathematics.Physics and Chemistry
Alternating Direction Implicit Legendre Spectral Element Method
CENG Fan-Hai, MA He-Beng, DIAO Ting-Gang
2011, 17(6): 724-727. doi:
10.3969/j.issn.1007-2861.2011.06.007
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An alternating direction implicit (ADI) Legendre spectral element method for the two dimensional Schrodinger equation is developed, and the optimal H
1
error estimate for the linear case is given. This method converts the two dimensional computation to one dimension with domain decomposition so that the size of problem and the storage are reduced. The main advantage of the method is its high degree of parallel computation. By choosing appropriate base functions, strip sparse matrices are derived. Numerical experiments show validity of the method.
Computer Prediction of P311 Protein and Metallothionein ⅡA Protein Interaction Sites
XUE Xiao-Yi, FENG Tie-Nan, WANG Qun-Qun, WANG Yi-Fei
2011, 17(6): 728-734.
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P311 was identified by suppressive subtraction hybridization as potentially involved in smooth muscle myogenesis. The P311 expression is regulated at multiple levels by pathways that control cellular transformation. It has been demonstrated in the literature that metallothionein ⅡA （MT2A） is associated with the expression of P311, and it is critical in the regulation. Therefore, it has been considered that interaction between P311 and MT2A exists. A 3D model of P311 protein by homology modeling is constructed, and the related residues for interaction are analyzed with Autodock 4.0. The results show that amino acids such as GLU14, SER48 and GLU56 are important in binding, which forms a basis for further experiments.
Synchronizing Improper Fractional Chen Chaotic System
HU Jian-Bing, XIAO Jian, DIAO Ling-Dong
2011, 17(6): 734-739. doi:
10.3969/j.issn.1007-2861.2011.06.009
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This paper proposes a concept of proper and improper fractional systems. A fractional system can be studied individually based on proper and improper fractional systems. A stable theorem of improper fractional system is given. Synchronization of improper fractional systems is studied, and synchronization of an improper fractional Chen chaotic system realized by designing a controller. Numerical simulation shows effectiveness of the method.
Nonparametric Statistical Analysis of Structural Change Point in Volatility Models for Dependent Time Series
JU Mei-Gong, CHENG Jian-Jiang, HE Yao-Hua
2011, 17(6): 740-745.
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Based on a stationary β-mixed process, this paper proposes a method for nonparametric estimation of structural change point in volatility models with unknown regression and conditional variance functions. Asymptotic normality of test statistic is proven, and a corresponding test method presented. Effectiveness of the method is shown with simulations.
Stress Relaxation in Prepreg Composites Due to Z-pinning
SHU Xiao-Guang, ZHANG Dun-Gan
2011, 17(6): 746-750. doi:
10.3969/j.issn.1007-2861.2011.06.011
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The microstructure of laminates is changed by z-pinning. In order to understand the fiber stress distribution in prepreg composites with insertion of z-pins, finite element analyses are conducted based upon the micromechanics model. The uncured resin matrix is modeled by viscoleastic constitutive equations. The fiber stress relaxation behavior with time is revealed.
Design Flattening Filter of Medical Accelerator Using Monte Carlo Method
BO Fu-Xin, LUO Wen-Yun, ZHOU Shi-Qing, DONG Xiao-Qiang, WANG Chuan-Shan-
2011, 17(6): 751-756. doi:
10.3969/j.issn.1007-2861.2011.06.012
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Using BEAMnrc to model the beam geometry of medical linear accelerator treatment head, X-ray dose distribution for a field sized 10 cm×10 cm is calculated after the X-ray passed through a flattening filter consisting of single material or multimaterial. By comparing the results of the off-axial ratio (OAR), the offaxis dose distribution and off-axis energy fluence distribution curves under GB 15213—94, a multi-material flattening filter with better flatness is designed. Angular distribution of particles, X-ray dose rate and charged particles pollution are discussed. The results show that this flattening filter has advantages including good flatness, satisfactory forward shooting property of particles, and low pollution of charged particles.
Material Science
Preparation of Metal Niobium with Electrodeoxidation of Nb
2
O
5
WANG Xin-Qiang, XIE Da-Hai, CHEN Wei
2011, 17(6): 757-761. doi:
10.3969/j.issn.1007-2861.2011.06.013
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A novel technique of electrodeoxidation was studied for preparation of metal niobium. Nb
2
O
5
was electrodeoxided in a eutectic melt of CaC1
2
-NaCl with a sintered compact as a cathode and graphite as an anode. Nb
2
O
5
cathodes with different density were prepared by sintered and influence of density of the cathodes on electrodeoxidation was investigated. The results show that density of sintered Nb
2
O
5
cathodes has important effect on electrodeoxidaion of Nb
2
O
5
in a eutectic melt of CaC1
2
NaCl. The lower the density of sintered Nb
2
O
5
cathode, the larger the electricity is started at the beginning of and during electrodeoxidation. Valence of the residual oxide niobium in the same time of electrolysis was lowered with decrease of the density of sintered Nb
2
O
5
cathode. It had better electrochemistry activity and was reduced by electrolysis at 850 ℃ for 150 minutes for the sintered Nb
2
O
5
cathode prepared under the condition of compaction of Nb
2
O
5
powder at 8 MPa pressure and sintering at 1 150 ℃ for 8 hours. The reactive rate of electrodeoxidation gradually became low with increasing electrolyzing time. The experiment indicates that electrodeoxidation is a process of interconnection between electrolyte and oxide powder particle, and between reaction and ionization. The electrodeoxidation reaction of oxide niobium is a step-by-step progress from high valence to low valence and to pure metal, i.e. Nb
5+
→Nb
4+
→Nb
2+
→Nb.
Improving Water-Wettability of Graphite Using SiO
2
Sol-Gel Coatings
GAO Rui-Juan, HANG Jian-Zhong, SHI Li-Yi, SHU Chang, HU Huo-Gen
2011, 17(6): 762-767.
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On the base of the heat treatment on graphite, the modification of surface properties of flake graphite was made via sol-gel and ball milling methods using tetraethoxysilane(TEOS) as precursor. IR analysis showed that some hydrophobic groups, such as ketone and double bond, disappeared and hydrophilic carboxyl groups were formed after heat treatment. The results indicated that the hydrophilicity of the modification graphite was improved. TGA-DSC analysis revealed that the weight loss was reduced from 100% to 70%, as well as the oxidation resistance of graphite was improved greatly. SEM and EDS showed that a dense network silicon oxide layer formed on the surface of modified graphite
Effect of Cu on New Cr22 Economical Duplex Stainless Steels
DAN Lu-Lu, MA Zheng-Huan, CUI Shi-Yun, LI Jun, XIAO Hua-Shan, DIAO Jun-Liang
2011, 17(6): 768-773. doi:
10.3969/j.issn.1007-2861.2011.06.015
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Influence of Cu on microstructure, mechanical and corrosion properties of a new family of Cr22 duplex stainless steels (DSSs) is investigated. The results indicate that Cu can greatly increase volume fraction of austenite and enhance elongation and corrosion resistance. The yield stress and tensile strength of new economical Cr22 DSSs reach approximately 490 and 750 MPa respectively. The mechanical properties and corrosion resistance of the new economical Cr22 DSSs are better than those of AISI304.
Mechanical Properties and Nitriding Characteristics of Novel Cr-Mo-V Nitriding Steel
LIAO Jian-Xiong, MIN Yong-An, HUANG Ze-Min, LI Yang
2011, 17(6): 774-778. doi:
10.3969/j.issn.1007-2861.2011.06.016
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A new non-aluminum nitriding steels microalloyed with niobium were developed, and mechanical properties and nitriding properties investigated. The results show that the tested steel has good strength, plasticity and toughness. Under the same nitriding condition, the tested steel exhibits good nitriding performance with a deep nitriding layer and gentle hardness gradient.
Civil Engineering
Analysis of Horizontal Vibration of Pile-Soil-Superstructure System in Layered Liquefiable Soil
YANG Xiao, HE Guang-Hui
2011, 17(6): 779-784. doi:
10.3969/j.issn.1007-2861.2011.06.017
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According to the characteristics of liquefiable soil in earthquake, we divide the liquefiable soil layer into a top liquefied layer and a bottom nonliquefied layer. Based on the Winkler model for the pilesoil interaction and treating the pile as a Rayleigh beam, the governing equations and the corresponding boundary conditions for interaction of the single pilesoilsuperstructure are established. This is done by taking into account the mass and inertia moment of the superstructure, and the inertia moment and the axial force of the pile. A closedform solution is obtained in the frequency domain, of which results are in agreement with experiments. Influences of the geometrical and physical parameters on the displacement amplification factor and the dynamic amplification factor are investigated. It is shown that the axial force drives the first natural frequency of the system to approach the dominant frequency of earthquake. Soil liquefaction increases the system’s dynamic response, and the critical load of the pile decreases with the degree of soil liquefaction, leading to unstable failure of the pile.
Pull-out Test on Interface Characteristics of Grid Reinforcement of Denti-inclusions
DIAO Gang-Fei, ZHANG Meng-Chi, CA Chun
2011, 17(6): 785-791. doi:
10.3969/j.issn.1007-2861.2011.06.018
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A new soil reinforcement method using mesh with teeth is proposed based on horizontal-vertical (H-V) reinforcement. First, holes and vertical bars are set on the perspex material to constitute a three-dimensional reinforcement material. A series of pull-out tests of perspex with holes geosynthetics are performed to investigate the interface behavior between sand and perspex with hole inclusions in terms of different forms of reinforcements. The impact of tooth height and hole size of reinforcement for ultimate pull-out resistance is discussed. Test results show that the up-limited pull-out force of perspex with teeth is significantly larger than the ordinary ones in the same normal stress. The up-limited pull-out resistance increases with the tooth height, and is significantly influenced by the hole size. Coefficient of apparent pull-out friction is evaluated. A theoretical formula is proposed to determine the pullout resistance. The theoretical values and experimental results are in good agreement.
Physical and Mechanical Behavior of Soil with Construction Waste
YANG De-Sheng, ZHANG Meng-Chi, CUI Zhen-Qing, DIAO Gang-Fei, BI Jun
2011, 17(6): 792-798. doi:
10.3969/j.issn.1007-2861.2011.06.019
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The physical and mechanical behavior of soil with construction waste is different from those of ordinary soils. Experimental studies on these properties have been carried out. Apart from soil, soil with construction waste contains gravel, cracked bricks, glass, plastic, etc. Based on the experiments, soil with construction waste is defined as a kind of loose and incoherent soil with high bearing capacity and shear strength. The shear strength parameters c and φ are heightened compared to the ordinary soil. Consolidation test results show that this kind of soil has high compressibility.
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