Table of Content

20 May 2006, Volume 42 Issue 3

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An Improvement on Carry Chain of Conditional Carry Selection

WU Ke,GAN Xuewen,ZHAO Baoying

2006, 42(3):  371-374. 

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An improved conditional carry selection (CCS) circuit is proposed in this paper. The new circuit is compared with the conventional conditional carry selection structure for a 4-bit adder. The two circuits were simulated by SPICE under the same condition and the results show that the propagation time of carry and sum (C₃ and S₃)of 4-bit adder are reduced 34.39% and 33.95%, respectively.

Analysis and Design of Low Power XOR-XNOR Circuits

LAN Jinghong,WANG Fang,JI Lijiu,JIA Song

2006, 42(3):  380-384. 

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Two novel low power pass transistor based XOR-XNOR circuits are proposed, UPPL (Unsymmetrical Push Pull Pass Transistor Logic) and CPPL (Complementary Push Pull Pass Transistor Logic). They both input single rail signals and output dual rail signals, which can get XOR and XNOR signals simultaneously. The output signals are full swing voltage. Hspice simulation under 0.18μm technology 1.8V voltage showed improvement on speed and power-delay product compared with some other circuits. Compared with the latest circuits, which was proposed by Mohamed Elgamel in 2003, the UPPL and CPPL circuits have 61.0% and 58.4% decreases on power delay product respectively without load. And with fanout three, they have 25.3% and 45.3% decreases respectively.

Field Emission Properties of a Tungsten Tip after Discharge Treatment

TAO Xiong,ZHANG Zhaoxiang,WANG Mingsheng,WU Yue,ZHANG Gengmin

2006, 42(3):  385-387. 

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A tungsten tip received discharge treatment under a high voltage over 10kV in a field-emission microscope (FEM). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation showed that some nanometer-scale protrusions resulted from the discharge treatment. The post-treatment tungsten tip delivered a field emission current as high as 1.55mA. The FEM pattern of the tip demonstrated a four-fold symmetry and thus the field emission was attributed to a single protrusion. The dependence of the field emission current on the applied voltage approximately followed the Fowler-Nordheim (F-N) theory. The value of the emission area calculated by the F-N theory is in agreement with that obtained from the TEM observation in the order of magnitude.

A Theoretical Study on a Novel Performance-Tunable Electromagnetic Band-Gap——2-D Ferrite EBG

ZHAO Xiaoying,ZHOU Lezhu

2006, 42(3):  375-379. 

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A novel tunable Electromagnetic Band-Gap, 2-D ferrite EBG, the performance of which can be adjusted by changing applied biased magnetic field, is proposed. The finite element method of the hybrid of edge-elements and node-elements incorporated with vector Floquet Theism is employed for calculating the scattering properties of this kind of EBG. Comparisons and Analysis of the frequency response of the transmitting power for this kind of ferrite EBG with different applied magnetic fields are presented, which shows better characteristic of stop and pass band-gaps，and more importantly the performance of the EBG devices is changeable by adjusting the biased magnetic filed. It indicates the possibility of R/D a novel performance tunable EBG.

Improved Application of JPEG2000 to Image Compression on Space Solar Telescope

XIE Hua,Harald MICHALIK,JIN Shengzhen,AI Guoxia

2006, 42(3):  366-370. 

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A new coding and rate control method for JPEG2000 is proposed to improve its coding efficiency. Through modifying the coding order, the most important passes are coded first in a whole tile. Then, a simple data-stream truncation method is able to both terminate the coding in advance and approximate the optimal rate distortion. At the end, a feasible parallel implementation is proposed and it is to speed up JPEG2000 significantly. The improved algorithm makes JPEG2000 much more beneficial to applications with the restricted computing resource on board. The research satisfies the elementary requirements of image compression of Space Solar Telescope.

A New Adaptive Playout Algorithm Based on E-Model with Packet Loss Dependency Characteristic

HAN Xinhui,SI Duanfeng,ZOU Wei

2006, 42(3):  388-394. 

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Adaptive playout algorithm is an important component of the Internet multiparty real-time communication system. The authors bring forward a new adaptive playout algorithm in the multiparty real-time communication fields based on the consideration of the impact of the packet loss dependency using E model tool. The aim of the algorithm is to give the best voice feeling to users as well as the best voice quality. The experiment results prove the validity of the algorithm. The algorithm can reduce the packet loss probability and delay significantly, and reduce the consecutive packet loss simultaneously.

Using Multilevel Fast Multipole Algorithm to Analyze Electromagnetic Scattering in Resonance Region of 3-D Complex Objects

WANG Pai,DONG Shuo,ZHOU Lezhu,XIA Mingyao

2006, 42(3):  395-400. 

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Multilevel fast multipole algorithm (MLFMA) and preconditioned generalized minimal residual (GMRES) method was employed to analyze electromagnetic scattering characteristics in resonance region of 3-D complex objects in this paper. For the problem of scattering in resonance region, such as 5 to 10 wavelengths, MLFMA needs much less core memory and computing complexity than moment method and fast multipole method. How to choose the optimal parameter L, the multipole number, is discussed. Preconditioned GMRES is used to solve the MLFMA matrix equation with a large number of unknowns, which proves to be more efficient than conventional conjugate gradient (CG) method. Finally, electromagnetic scattering in resonance region of 3-D complex bodies including the missile model and stealthy airplane model are analyzed.

Research on Effects of Dispersion of Signal Transmission on Millimeter-Wave ROF Optical Communication Systems

YANG Xiangyun,HU Weiwei,XU Anshi

2006, 42(3):  401-405. 

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Brief introduction of Radio over Fiber (ROF) communication technology and research on effect of fiber dispersion on ROF optic communication system are given. Dispersion problem of single wavelength and two-wavelength modulation ROF systems is analyzed systematically with theory and simulation experiment, and theoretic analysis accords with simulation experiment results well. Finally, design index of dispersion in ROF optical communication is presented, and fiber dispersion effects of single wavelength and two-wavelength modulation are concluded, compared and summarized.

An Overview of the Application of FEM in Dental Biomechanics

XU Xuejun,ZHENG Yufeng

2006, 42(3):  412-419. 

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Finite element method (FEM) is an effective analyzing method in the simulation of the mechanical behavior of human body. An overview of the application of the FEM in dental biomechanics is provided, including the mechanical simulation of the dental tissues and the optimization of the instruments. Some shortcomings and the extensive research about the reconstruction and related analysis are generalized while the methods, tools and material assumptions are reviewed.

A Queueing System GI^X/M/1/N with Balking and Batch Arrivals

WANG Hao,LI Xiaoming,YAN Wei

2006, 42(3):  406-411. 

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A queueing system GI^X/M/1/N with balking and batch arrivals was discussed. The interarrival and service times are arbitrarily and exponentially distributed, respectively. The distributions of the number of customers in the system at prearrival and arbitrary epochs are obtained. In addition, some performance metrics are given, such as the customer loss rate, the system utilization, the mean and variance of the queue length, the mean of the waiting time. Some application scenarios on computer communication network are discussed concerning this queueing system.

On the General Solution of Anisotropic Piezoelasticity

XU Sipeng,WANG Wei

2006, 42(3):  302-304. 

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The general solution of anisotropic piezoelasticity is obtained constructively. Its completeness and nonuniqueness are also proved.

Wave Propagation and Energy Transportation along Cylindrical Piezoelectric-Piezomagnetic Material

WEI Jianping,SU Xianyue

2006, 42(3):  310-314. 

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The axisymmetric flexural wave in a piezoelectric-piezomagnetic cylinder was studied by applying "rod model". The lower modes, which are classified by Quasi-P wave, Quasi-SV wave and SH wave, are obtained. Then the authors find that the electromagnetic induction, which does not exist in piezoelectric or piezomagnetic material, is in the composite material. And there are high-speed electromagnetic wave and steady stress wave propagation along the cylinder, and the energy transports and inter-changes differently in channels formed by Quasi-P wave and Quasi-SV wave.

Oblique Derivative Problems for Second Order Quasilinear Equations of Mixed Type with Parabolic Degeneracy

WEN Guochun

2006, 42(3):  285-293. 

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It is dealed with that oblique derivative problems for quasilinear equations of mixed type with parabolic degeneracy, which include the Tricomi problem for Chaplygin equation as a special case. Firstly the formulation of the problems is given, and then the existence and uniqueness of solutions for the problems are proved by using a new complex analytic method.

Mechanism Design and Motion Control of Robotic Dolphin

WANG Long,YU Junzhi,HU Yonghui,FAN Ruifeng,HUO Jiyan,XIE Guangming

2006, 42(3):  294-301. 

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This paper is concerned with the design, construction, and control of a novel biomimetic robotic dolphin equipped with mechanical flippers based on an engineered propulsive model. The robotic dolphin is modelled as a three-segment organism composed of rigid anterior body, flexible rear body, and an oscillating fluke. The dorsoventral movement of the tail produces the thrust, and bending of the anterior body in the horizontal plane enables turning maneuvers. Swimming performance of the prototype is tested, and the experimental results confirm the effectiveness of the dolphinlike movement in propulsion and maneuvering.

Quadrature Modulation, Quadrature Exciting, Quadrature Receiving and Quadrature Demodulation in MRI System

JIANG Zhongde,ZU Donglin,GU Xiaofang

2006, 42(3):  320-323. 

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It is clearly clarified the conceptions of quadrature modulation, quadrature exciting, quadrature receiving, and quadrature demodulation in the MRI system. The purpose of quadrature modulation is to generate the SSB RF exciting pulse that avoids exciting it's mirror slice. Quadrature demodulation can distinguish positive and negative frequency so it can overcome position uncertainties on imaging data space. Quadrature exciting and quadrature receiving refer to make use of circular polarization RF coils. These quadrature operations are necessary for the optimization of MRI system and they bring some significant benefit.

Experimental Research on the Mechanism of Reverse Transition in Turbulent Boundary Layer

ZHANG Zhen,SUN Zhili,YAN Dachun

2006, 42(3):  305-309. 

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Experimental research on the phenomenon of reverse transition in the boundary layer under a heated plate is presented, and the mechanism of reverse transition is also explained. During the experiment, the production term, dissipation term as well as absorption term of turbulent energy is measured. Experimental results show that, through the formation of stably stratified structure, the production term of turbulent energy in the range between 400 - 1000 mm away from the leading edge of the plate has become negative, so the region is actually an absorption region of turbulent energy. In the same time, the dissipation term near the wall region is strengthened by smallscale eddy. Under the conjunct effect of the negative production term, the absorption term, as well as the absorption term caused by buoyancy, the turbulent energy in the inner layer of turbulent boundary layer is depleted rapidly, and the turbulent flow in the outer layer changes into passive flow because of the lack of energy source. Finally, the turbulence turns into laminar flow.

Turbulent Fluxes over Heterogeneous Surfaces and the Blending Height

ZHOU Cheng,CHEN Jiayi,CAI Xuhui

2006, 42(3):  315-319. 

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The concept and application of blending height are introduced. Large-eddy simulations were conducted to study the blending height in convective boundary layers over heterogeneously heated surfaces. The influences of heterogeneous length, heterogeneous strength and wind speed on blending height were investigated. The results show that the blending heights are mainly determined by the heterogeneous length and wind speed, while less influenced by the heterogeneous strength. Blending height appears at the height where the spatial standard deviation of heat flux decreases to 5% of that on the surface and can be fitted as Z_b = 1/C_wm * w'θ'_sfc/Θ₀ * L^a_hetero/U^b, with a=1.266, b=0.854, C_wm=3.205×10^-3.

The Recirculation Gas Stripper of PKUAMS

WEI De,GONG Linghua,LIU Kexin,YUAN Jinglin,JIANG Zhengyuan,REN Xiaotang

2006, 42(3):  324-327. 

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The gas stripper system of the EN tandem accelerator at the Peking University is being improved for AMS ¹⁰Be measurements with super high sensitivity. The design of a recirculation gas stripper, including the vacuum system and control system, is presented. The experimental results on a simulation test bench are also described.

Ghost Diffraction from Un－Entangled Photon Pairs

HUA Jing,WANG Ruopeng

2006, 42(3):  334-338. 

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An experimental setup is presented in which the ghost diffraction phenomenon can be observed for two un-entangled photons in the same mode. No quantum non-locality is involved in this case, because the photons are not spatially separated. Therefore the ghost diffraction phenomenon is not an experimental evidence for quantum non-locality.

Measurement of the Field Distribution in a Cold Model of RFQ Resonant Cavity

SONG Xiangxiang,GUO Zhiyu,ZHU Kun,YAN Xueqing,LI Weiguo,FANG Jiaxun

2006, 42(3):  339-342. 

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A cold model measurement system of the RFQ resonant cavity is introduced, which can measure the field distribution of cold model through bead-pull measurement. The system has two advantages. One is that people can write a script and make it automatically accomplish all the procedures, including pulling and positioning the bead and all the data acquisition. The other is that the precision of bead positioning is improved much by using the step-motor. Some measurement results of a D⁺ RFQ cold model are given.

Determination of Atmospheric Boundary Layer Height in Unstable Conditions over the Middle Tibetan Plateau

SONG Xingzhuo,ZHANG Hongsheng,LIU Xinjian,FAN Shaohua,LIU Huizhi,HU Fei,LI Shiming,ZHOU Mingyu,BIAN Lingen,XU Xiangde

2006, 42(3):  328-333. 

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The atmospheric boundary layer (ABL) height z_i in unstable condition was analyzed using turbulence data from Damxung observational station, which was one of the ABL observational stations in the second Tibet Plateau Experiment (TIPEX) in 1998. Together with the observational vertical profiles of temperatures, the authors studied the diurnal and seasonal evolution characteristics of the ABL over the Tibet Plateau, analyzed both differences and similarities of the ABL between dry and wet seasons, and explored the terrain influence on the ABL height. The results show that the ABL over Tibet Plateau has the characteristics of development and lasting over a longer time.

A Case Study of a Black Storm at the Northern Foothills of Tianshan Mountains

MA Yu,WANG Xu,XIAO Kaiti,LIU Xiaomei,TAN Jiang

2006, 42(3):  343-350. 

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Using conventional observational data, autographic records and satellite images, the authors studied a black storm caused by a dry squall line associated with a southern cold front at the northern foothills of Tianshan Mountains in Xinjiang on April 18, 1998. The results show that winds, pressure, temperatures and humidity all have abrupt changes when the black storm passes through meteorological stations, changes associated with the black storm are much stronger than that with dust storms. The dust wall is almost isothermal, with horizontal thickness of about 4-9km. Strong surface winds were mainly caused by rapid intensification of the cold front and the cold advection. Meanwhile, the development of a upper level jet and strong downward transport of momentum by the sinking branch of the upper level jet's secondary circulation are also important for the formation of strong surface winds. The mixed layer is the crucial stratification factor affecting the formation of black storm because it can minimize the energy required to develop the deep dry convection and so is favorable for the formation of black storm in drought region. In this case primary reason that the black storm occurres at the northern foothills of Tianshan Mountain is the formation of deep mixed layer, which is induced by the surface heating for a long time. So the deep dry convection can be developed when the cold front passes and the black storm occurres there.

Numerical Simulations of Mountain Gravity Waves Generated by Multi-Layer Flow over an Isolated Mountain

LI Ziliang

2006, 42(3):  351-356. 

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Characteristics of non-linear mountain gravity waves and atmospheric ship waves generated by three-dimensional multi-layer flow over an isolated mountain were investigated using the numerical model, ARPS. Results show that the transverse and diverging modes of atmospheric ship waves generated by two layer flow over an isolated mountain are the same as that of mountain gravity waves in linear models. However, non-linear mountain gravity waves and atmospheric ship waves generated by three-dimensional three-layer flow over an isolated mountain show completely different characteristics from linear mountain gravity waves. In the nonlinear case, due to non-linear interactions there exist two ship waves involving in two diverging modes on the lee side, which propagate downstream. These ship wave modes have more complex wave characteristics compared with that in two layer and linear models.

Growth of MgB₂ Thin Film Fabricated on Mg Substrate by Hybrid Physical-Chemical Vapor Deposition

YAO Dan,ZHUANG Chenggang,ZHANG Kaicheng,YU Zengqiang,FENG Qingrong,WANG Furen

2006, 42(3):  357-360. 

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Superconducting MgB₂ thin films were fabricated on Mg substrate by using the hybrid physical-chemical vapor deposition (HPCVD) technique. The film has a T_c(onset)＝39.5K. The SEM images demonstrate that crystallite is compact. X-ray diffraction pattern indicates the film is polycrystalline with no preferring growing direction. The grain size is about 400nm-1.0μm. These results show that it is feasible to deposit MgB₂ thin films directly on Mg by HPCVD technique. It is advantaged to fabricate MgB₂ fibers directly on SiC carrier and MgB₂ superconductive wires.

Effect of Nanometer-Sized B Powder on Phase Formation of Polycrystalline MgB₂

AN Ling,CHENG Chinping,WANG Bo,ZHUANG Chenggang,LI Xingguo,ZHOU Zengjun,FENG Qingrong

2006, 42(3):  361-365. 

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The size effect of the raw B powder on the MgB₂ phase formation is studied by the technique of in-situ high temperature resistivity (HT-ρT) measurement. The onset temperature, T_onset, and the completion temperature, T_PF, of the phase formation are determined directly during the ongoing thermal process. These two temperatures, T_onset and T_PF of the sample synthesized using nanometer B and Mg powders (NanoB-MgB₂) are 440 and 490℃, respectively, the same as those of the sample using micrometer B and nanometer Mg powders (MicroB-MgB₂). This indicates that the phase formation temperature of MgB₂ do not depend on the B powder size. The upper limit of the sintering temperature, T_N, above which the sample loses superconductivity, is below 750℃ for NanoB-MgB₂, much lower than 980℃ for the MgB₂ prepared using micron-sized B powder and millimeter sized Mg powder (DM-MgB₂). In comparison with the sample directly sintered at 650℃<T_N, an interesting, irreversible transformation in the crystal structure of the MgB₂ phase is observed with the sample going through the stages of initial sintering at 750℃, then re-sintering at 650℃ in an Mg-rich environment after the processes of regrinding and pressing.