JOURNAL OF BEIJING INSTITUTE OF TECHNOLOGY

Structure-preserving algorithms for autonomous Birkhoffian systems

KONG Xin-lei, WU Hui-bin, MEI Feng-xiang

2012, 21(1): 1-7.

[Abstract](882) [PDF 365KB](311)

Abstract:
The Pfaff-Birkhoff variational principle is discretized, and based on the discrete variational principle the discrete Birkhoffian equations are obtained. Taking the discrete equations as an algorithm, the corresponding discrete flow is proved to be symplectic. That means the algorithm preserves the symplectic structure of Birkhoffian systems. Finally, simulation results of the given example indicate that structure-preserving algorithms have great advantage in stability and energy conserving.

Weak Noether symmetry and conserved laws of Birkhoffian systems

XIE Jia-fang, WU Run-heng, ZHANG Zhu, ZOU Jie-tao, LI Guo-fu

2012, 21(1): 8-12.

[Abstract](745) [PDF 301KB](200)

Abstract:
A new kind of weak Noether symmetry is obtained that arises in the study of Birkhoffian systems. The conserved quantities, which includes Noether conserved quantity, Hojman type conserved quantity and new type conserved quantity, are also calculated from this symmetry. Finally, two examples are presented to illustrated the application of these new results.

Numerical study on rock fracture and vibration due to blasting

DAI Kai-da, CHEN Peng-wan, YANG Jun

2012, 21(1): 13-18.

[Abstract](692) [PDF 947KB](265)

Abstract:
Fracture and ground vibration of rock subjected to different decoupling decked charges are investigated based on the numerical simulation. The dynamic pressure value is studied, which demonstrates that simulation of fracture zone is feasible. Attenuation index of dynamic pressure is 2.06, 2.05 and 1.93 for air, water and sand intervals respectively. The small attenuation of sand interval results in the large ground vibration. The predicted vertical vibration waveform and peak particle velocities (PPV) in far-field are in agreement with the monitoring results. The results show that the air and water decked charges can improve the effect of rock fracture in near-field and reduce ground vibration in far-field.

Mechanical properties of dental composite resins containing nanodiamond of different diameters

CHU Ya-qing, TONG Yi, ZHANG Tong-lai, HUANG Feng-lei

2012, 21(1): 19-22.

[Abstract](860) [PDF 265KB](222)

Abstract:
In order to investigate the effect of nanodiamond (ND) on the mechanical properties of dental composite resins, bisphenol-A-glycidyl dimethacrylate(Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), barium glass (BG) powder, DL-camphoroquinone(CQ) and dimethylaminoethylmethacrylate (DMAEMA) were mixed as the matrix for the experiments. NDs of three diameters (100.nm, 220.nm, 500.nm) modified with 3-(trimethoxysilyl)propyl methacrylate ( γ -MPS) were added to the mixture separately in 0.2% to get test samples. The flexural strength and elastic modulus of these samples and the mixture without ND(as the reference group, RG) were characterized with standard specification tests. Results reveal that the mechanical properties and elastic modulus of resins containing 220.nm ND (R-220) and 500.nm ND (R-500) were significantly different from those of RG. R-500 had the highest flexural strength and elastic modulus (by average data), and all of its five specimens were found to have mean flexural strength values greater than the minimum value (80MPa) prescribed by ISO 4049: 2000. Different sizes of diamonds have different effects on mechanical properties of dental composite resins, and the performances of 220.nm and 500.nm diamonds are better than that of 100.nm diamond.

Mathematical modeling of the bellows dispersion system of submunitions

SHI Jiao, TANG Sheng-jing, GAO Feng

2012, 21(1): 23-30.

[Abstract](637) [PDF 388KB](196)

Abstract:
A mathematical model of the bellows dispersion system is developed by combining the interior ballistic theory with structural dynamics theory to describe the deformation course of bellows. By analyzing the physical model of the bellows dispersion system, the dispersion course is divided into three stages. For each stage, mathematical model is built and its terminal conditions are given. The numerical simulation is based on the Runge-Kutta method and differential quadrature method. Simulation results of the model agree with those of the model built by only interior ballistics theory. However, this model is congruous with the actual dispersion course and can more easily determine the dispersion time and submunition displacement.

Application of equivalent information method to high reliability assessment of initiating explosive devices

ZHANG Tian-fei, DONG Hai-ping, CAI Rui-jiao

2012, 21(1): 31-34.

[Abstract](728) [PDF 290KB](168)

Abstract:
The amount of information required for reliability assessment of success/failure products is defined and the formula of equivalent information method is deduced. Based on the formula, a method for assessing reliability of initiating explosive devices with small sample size is established. Compared with the assessment method for devices with large sample size, the new method is correct and feasible and can be used to assess the reliability of initiating explosive devices with high reliability requirements.

An improved seed growth method for accurate stereo matching in disparity space

LU Pei-yuan, WANG Jian-zhong, LUO Tao

2012, 21(1): 35-40.

[Abstract](694) [PDF 1985KB](213)

Abstract:
Matching is a classical problem in stereo vision. To solve the matching problem that components cannot continue growing on the occlusions region and repetitive patterns, an improved seed growth method is proposed. The method obtains a set of interesting points defined as initial seeds from a rectified image. Through global optimization the seeds and their neighbors can be selected into a match table. Finally the components grow with the matching points and create a semi-dense map under the maximum similar subset according to the principle of the unique constraint. Experimental results show that the proposed method in the grown process can rectify some errors in matching. The semi-dense map has a good performance in the occlusions region and repetitive patterns. This algorithm is faster and more accurate than the traditional seed growing method.

Influence of flange location on axial deformation stability of double-hat structure

WU Xue-yuan, XIA Yong, ZHOU Qing

2012, 21(1): 41-49.

[Abstract](838) [PDF 2128KB](180)

Abstract:
A new structural configuration with better impact stability for increasing energy absorbing efficiency is found. Based on finite element analysis, deformation modes of double-hat structure under axial impact loading are categorized to find the main reasons that affect deformation stability. It is revealed that, in a double-hat structure, the location of the flanges is highly related to the deformation mode and energy absorbing efficiency. Moving the flanges away from their traditional mid-location may result in more regular and stable deformation mode and achieve higher energy absorbing efficiency. The flange offset value needs to be controlled within a certain range, otherwise, the double-hat structure would tend to deform like a top-hat structure and the energy absorbing efficiency could be compromised. These findings and analyses lead to a new structural design configuration-asymmetric flange locations—for enhancing the deformation mode stability in double-hat structures.

Analysis of the compound split transmission based on the four-port power split device

YUAN Shi-hua, LIU Hong, PENG Zeng-xiong, WEI Bin

2012, 21(1): 50-57.

[Abstract](658) [PDF 445KB](230)

Abstract:
In order to identify all the appropriate system schemes for the compound split systems formed primarily with a four-port mechanical power split device, power transmission characteristics of the compound split systems was analyzed. Considering the structural symmetry and according to the different connection arrangement of the four ports, compound split system was classified into four types. Using black-box modeling method, the generalized models of the speed ratio, the torque ratio and the power split ratio were established. Moreover, a semi-invert diagram was used to distinguish the different schemes in each type. The characteristics of the speed ratio, the torque ratio and the power split ratio in each domain were also analyzed and compared. Through the semi-invert diagram, a selection method based on the rated-power speed ranges in different schemes was presented and all suitable compound split systems were identified, which can be used as references for the scheme selection of this kind of continuously variable power split transmission.

Traveling property of wheel-type pipeline robot with different configurations

TANG De-wei, LI Qing-kai, JIANG Sheng-yuan, DENG Zong-quan

2012, 21(1): 58-63.

[Abstract](611) [PDF 1158KB](173)

Abstract:
In order to improve the travelling ability of the wheel-type pipeline robot in elbow section of pipeline, the model of drive ratios is proposed aiming at the pipeline robots with different configurations. Through the movement analysis of the robot with different configurations in elbow section, the pose model of the robot is established, and the coordinates of the wheel centers and the contact points can be got through the calculation of the pose model. Based on the pose model established, the corresponding drive ratios are obtained combining with the relations of the velocities of wheel centers and rotative velocities of wheels under the movement condition with no interference. The virtual simulations and prototype experiments are carried out, and the drive ratios accuracy of the model when the robot moved in elbow without interference is validated.

Building of road boundary map based on laser radar

BAI Cong-min, WANG Chun-xiang, YANG Ming, WANG Bing

2012, 21(1): 64-71.

[Abstract](881) [PDF 513KB](219)

Abstract:
A method for road boundary detection and tracking using laser ladar with respect to a vehicle’s local coordinates is proposed. It can be applied to different types of road conditions, such as roads with or without curbs, having relatively rough road surface and with obstacles on road surface. In the method, some line segments are extracted after a series of preprocessing on range data. The extracted line segments are combined and further selected. They are then united to match the road models and generate the road boundary points which are tracked by Kalman filter. Then the obtained road boundary points are transformed to build a precise vector map by least squares fitting algorithm. These fitted line segments represent road boundary vectors. The vector map is precise enough to provide ample road information such as the orientation of road, the road width and the passable road region. Finally, extensive experiments conducted in urban and semi-urban environment demonstrate the robustness, effectiveness and viability of the proposed method.

Safety analysis of pedestrian and roadway dimensional-dividing buildings

DANG Yu, ZHAO Hong

2012, 21(1): 72-76.

[Abstract](444) [PDF 341KB](152)

Abstract:
The safety performance of pedestrian and roadway dimensional-dividing buildings under seismic excitations are analysed. Considering the large displacement of the isolator bearing during earthquake, the gravity force becomes the dominant forces because of the accumulated permanent deformations in the building, which results in the structure collapse due to lateral instability. A model is established based on an inelastic time history analysis to considerP-Δeffects in multi-degree-of-freedom. A safety criterion of the system is defined. The influence of the stiffness of an independent column is revealed and compared with the influence of the shear force of the independent column to analyze the safety of the structures. Numerical results show that the special structure of pedestrian and roadway dimensional-dividing buildings can reduce the risk of the building in earthquake. The suitable section and height of the independent column greatly affect the building safety.

Calculation of railway transport capacity in an emergency based on Markov process

MENG Xue-lei, JIA Li-min, QIN Yong, XU Jie, WANG Li

2012, 21(1): 77-80.

[Abstract](724) [PDF 282KB](161)

Abstract:
A method is proposed to calculate the railway transport capacity in an emergency to support the dispatching work of control centers. The effect of an emergency on section transport capacity is analyzed and the basic method to calculate the transport capacity is presented. The results show that the situation-changing process in emergency is actually a Markov process. The calculation rule is presented based on division of the time segment during which the emergency lasts. The algorithm is designed to calculate the transport capacity of each time segment. The pessimistic strategy and the fuzzy strategy are proposed to determine the computing value of the transport capacity of each time segment, to satisfy the calculating requirements in different occasions. Our study shows that the method is reasonable and practical and the method can be embedded in the train dispatching system to support the operation work in an emergency.

Model of desired speed based on vehicle dynamic

GUO Wei-wei, WANG Wu-hong, MAO Yan, XIONG Hui, ZHANG Wei-han

2012, 21(1): 81-84.

[Abstract](795) [PDF 300KB](179)

Abstract:
The desired speed will help the drivers control their driver behavior that could directly influences the traffic safety. This paper presents a basic definition of a driver’s desired speed, and analyzes the effects of road geometer parameter, driver behavior and vehicle performance on the desired speed. By setting the familiar horizontal curve as the research environment, the generating process of the desired speed was described. Then, combined with the desired trajectory, the effect of driver’s identification of vehicle dynamic on the desired speed was highlighted. Based on the vehicle dynamic theory, a desired speed model that consisted of the desired trajectory, the driver’s experience and vehicle parameter was established and numerically analyzed.

Band structures analysis of one-dimensional photonic crystals using plane wave expansion

LI Ping, LI Zhuo

2012, 21(1): 85-90.

[Abstract](488) [PDF 416KB](200)

Abstract:
A theoretical analysis is made, using plane wave expansion, on how the width of the first three band gaps is influenced by filling ratio, dielectric constant ratio, and periodic width in one-dimensional photonic crystals (PhCs). From simulation and analysis, there are one, two, and three peak points on the first, second and third band gaps respectively with the changes of filling ratio under fixed dielectric constant ratio. When filling ratio is fixed, the bandwidth of the first band gap consistently increases with dielectric constant ratio. However, no similar trend is observed in the second and the third band gaps. Because of scaling properties, varying periodic width does not alter the relative bandwidth.

Multi-resolution EMD and classscatter matrix extracting of tank sound

ZHANG Wan-jun, WU Xiao-ying, WANG Xin

2012, 21(1): 91-95.

[Abstract](598) [PDF 303KB](160)

Abstract:
The acoustic vibration signal of tank is disassembled into the sum of intrinsic mode function (IMF) by multi-resolution empirical mode decomposition (EMD) method. The instantaneous frequency is obtained, and feature transformation matrix is figured out by class scatter matrix. Multi-dimensional scale energy vector is mapped into low-dimensional eigenvector, and classification extraction is realized. This method sufficiently separates of different sound target features. The test result indicates that it is effective.

Beam pointing correction of variable polarization MMW/IR combined detection

LIU Jian-xun, ZHANG Wei, DENG Hong, SUN Hou-jun, LÜ Xin

2012, 21(1): 96-100.

[Abstract](568) [PDF 351KB](168)

Abstract:
A kind of beam-scanning algorithm of variable polarization millimeter array antenna based on the phased array technology is put forward in this paper. The algorithm can be successfully applied to deal with beam directivities inconsistency of millimeter wave/infrared( MMW/IR ) multimode detector, it can keep electric axis and optical axis coincident. Accordingly, this method can decrease the data fusion difficulty and improve the accuracy of angle measurement. Simulation results show that variable polarization millimeter array antenna has flexible beam-scanning abibility within ±0.5° after the algorithm was adopted, simultaneously, antenna polarization purity is better than 20.dB within the half power beamwidth, sidelobe imbalance keeps high available and antenna gain of the sum beam is over 26.8.dB.

Recognition of vortex structures in turbulent refractive index field using wavelet transformation

QI Zhen-qiang, FENG Hao-nan

2012, 21(1): 101-105.

[Abstract](748) [PDF 704KB](224)

Abstract:
When the light wave propagates through the hypersonic flow field, the aero-optic distortion happens. It is necessary to recognize the vortex structure for studying the light propagation model. A new vortex structure recognition method is proposed in this paper. Firstly, the refractive index field, which is transformed from the turbulent density field, is changed to gray scale images with abundant texture information equivalently. Then, wavelet transform is performed to decompose these images and the entropy values of the wavelet base coefficients are calculated. Comparing the entropy value to a given threshold, the modules with lower entropy are considered to be the large-scale vortex modules while those with higher entropy are small-scale vortex modules. The computer simulation results show that the proposed method is valid to recognize the vortex structures. This paper provides basis for investigation on the optics propagation model in terms of the turbulence vortex structures.

Distributed optimal relay selection for spectral efficiency improvement in underlay-paradigm based cognitive radio networks

CHEN Dan, JI Hong

2012, 21(1): 106-111.

[Abstract](640) [PDF 435KB](204)

Abstract:
A distributed best-relay node selection scheme is investigated for cooperative communications with adaptive modulation and coding (MAC) strategy over underlay-paradigm based cognitive radio (CR) networks. The scheme aims to maximize the average spectral efficiency and meanwhile to guarantee that the primary link is provided with a minimum-rate for a certain percentage of time. Simulation results demonstrate that the proposed scheme can significantly improve the spectral efficiency compared with other existing schemes.

Hollow calcium carbonate microspheres prepared in the presence of polyoxyethylene (20) sorbitan monolaurate and sodium dodecyl sulfate

YOU Chao, ZHANG Qiang, ZHAO Yun, JIAO Qing-ze

2012, 21(1): 112-117.

[Abstract](779) [PDF 6000KB](201)

Abstract:
Hollow calcium carbonate (CaCO₃) microspheres were prepared in aqueous solution with the presence of polyoxyethylene (20) sorbitan monolaurate (Tween20) and sodium dodecyl sulfate (SDS). The microspheres were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The X-ray diffraction data showed that the hollow CaCO₃microsphere consisted of calcite crystals. The influence of Tween20 and SDS concentrations on the morphology of CaCO₃crystals was investigated. The results suggested that the"core-shell model"of Tween20/SDS micelle aggregated as templates, which could control the growth of hollow CaCO₃microspheres. The interaction between mixed surfactants and calcium ions played a critical role in organizing calcium carbonate in microscopic level.

Synthesis and characterization functionalized poly(ether ether ketone)s with carboxylic groups

WANG Dong, GAO Hong, JIANG Zhen-hua

2012, 21(1): 118-121.

[Abstract](484) [PDF 302KB](186)

Abstract:
A novel type of aromatic poly(ether ether ketone)s with carboxyl groups were prepared by polycondensation of 4,4-bis(4-hydroxyphenyl)pentanoic acid with difluoro-monomers. Their molecular structures were determined by¹H-NMR and IR, respectively. Their molecular weights were measured by gel permeation chromatography (GPC), which showed that all the polymers had high molecule weights (>42.000). Due to the long side chains of polymers, all the polymers had good solubility (soluble in NMP, DMAc, THF, etc.). The differential scanning calorimeter (DSC) detected their excellent glass transition temperatures (T_g) up to 195.℃. TheT_gincreased with the content of carboxylic units in the polymer chains, because the interactions of H bonds increased with increasing content of carboxylic. The polymers could form transparent and flexible films, which make them a candidate for membrane materials.

First-principles investigation of the phase stability of MgAl₂compounds

CHEN Rong, CHEN Jing-chao, PAN Yong

2012, 21(1): 122-127.

[Abstract](667) [PDF 799KB](183)

Abstract:
First-principles have been calculated to investigate the phase stabilities of the intermetallic phase of MgAl₂compounds by electronic structures and the charge distribution maps. The first-principles employed the norm-conserving pseudo potential density functional method. They were calculated both with the Ceperley and Alder data as parameterized by Perdew and Zunger(CA-PZ) of local-density approximation (LDA) and with the Perdew Burke Eruzerh(PBE) form of gradient-corrected approximation (GGA). A better method was found by comparing results from these two ultrasoft pseudo potentials. The present calculations indicate that LDA is better than GGA compared with references. This work also compared the lattice parameters, cohesive energy, formation enthalpy and electronic structure between theoretical results and experimental measurements (where available). The calculations indicate that the unit cell volume get smaller after optimized and cohesive energy and formation enthalpy of C14 structure is the highest. The calculated structures are stable and the stability is aligned as C36

Forward heuristic breadth-first reasoning based on rule match for biomass hybrid soft-sensor modeling in fermentation process

AN Li, WANG Jian-lin

2012, 21(1): 128-133.

[Abstract](581) [PDF 472KB](154)

Abstract:
Biomass is a key parameter in fermentation process, directly influencing the performance of the fermentation system as well as the quality and yield of the targeted product. Hybrid soft-sensor modeling is a good method for on-line estimation of biomass. Structure of hybrid soft-sensor model is a key to improve the estimating accuracy. In this paper, a forward heuristic breadth-first reasoning approach based on rule match is proposed for constructing structure of hybrid model. First, strategy of forward heuristic reasoning about facts is introduced, which can reason complex hybrid model structure in the event of few known facts. Second, rule match degree is defined to obtain higher estimating accuracy. The experiment results of Nosiheptide fermentation process show that the hybrid mode1ing process can estimate biomass with higher accuracy by adding transcendental knowledge and partial mechanism to the process.

A double weighted LS-SVM model for data estimation in wireless sensor networks

XIE Ying-xin, CHEN Xiang-guang, ZHAO Jun

2012, 21(1): 134-139.

[Abstract](660) [PDF 521KB](151)

Abstract:
In wireless sensor networks, data missing is a common problem due to sensor faults, time synchronization, malicious attacks, and communication malfunctions, which may degrade the network’s performance or lead to inefficient decisions. Therefore, it is necessary to effectively estimate the missing data. A double weighted least squares support vector machines (DWLS-SVM) model for the missing data estimation in wireless sensor networks is proposed in this paper. The algorithm first applies the weighted LS-SVM (WLS-SVM) to estimate the missing data on temporal domain and spatial domain respectively, and then uses the weighted average of these two candidates as the final estimated value. DWLS-SVM considers the possibility of outliers in the dataset and utilizes spatio-temporal dependencies among sensor nodes fully, which makes the estimate more robust and precise. Experimental results on real world dataset demonstrate that the proposed algorithm is outlier robust and can estimate the missing values accurately.

Synthesis and characterization of 3,4-dinitropyrazole

ZHANG Qiao-ling, LI Yong-xiang, CAO Duan-lin

2012, 21(1): 140-142.

[Abstract](977) [PDF 268KB](233)

Abstract:
Nitro-heterocyclic compounds are good candidates for developing new insensitive high-energy explosives with low melting points. A new nitro-heterocyclic compound, 3,4-dinitropyrazole (DNP), was synthesized. With low melting point, it can be used as an explosive. The compound was characterized by IR, elemental analysis, mass spectrometry and nuclear magnetic resonance spectroscopy. Its thermal decomposition and phase change were also analyzed with DSC and its melting point was 85-87.℃. Because of its low melting point and good thermal stability, DNP could be used for the design of novel insensitive melt-cast explosive.

2012 Vol. 21, No. 1