ISSN 0253-2778

CN 34-1054/N

2010 Vol. 40, No. 10

Display Method:
Influence of sputtering parameters on the properties of ZnO:Al films prepared by magnetron sputtering
WU Bingjun, HAO Changshan, LI Ming, XIE Bin
2010, 40(10): 991-998. doi: 10.3969/j.issn.0253-2778.2010.10.001
Transparent and conductive ZnO:Al (AZO for short) films with resistivity of order of 10-3Ω·cm and visible lights transmittance >85% were prepared by an industrialized mid-frequency dual-targets magnetron sputtering coater (RAS-1100C) using AZO ceramic targets with Al2O3 content of 27% (mass fraction). Influences of baking temperature, argon flow rate and sputtering power on the electrical properties of the deposited AZO films were analyzed. Meanwhile, differences in the resistivity of AZO films deposited on those substrates fixed in different regions in front of the targets were also studied. Results show that the resistivity of AZO films deposited facing the erosion areas of the targets is on the order of 10-2 Ω·cm while resistivity of samples deposited facing the middle area between the two targets is around 5×10-4Ω·cm, which indicates that the properties of AZO films deposited on the cylindrical substrate holder of RAS exhibit an average mixing result of films deposited in different regions. The key issues for improving the properties of the deposited AZO films depend on the suppression of bombarding implantation effect, which was caused by energetic oxygen ions, and the enhancement of crystallinity of the deposited films.
Fabrication of polyimide nanowires array and research on the wetting mechanism
XU Yun, LI Linbin, GU Ping
2010, 40(10): 999-1003. doi: 10.3969/j.issn.0253-2778.2010.10.002
Polyimide nanowire array was fabricated by wetting alumina templates using polyamic acid solution. SEM was employed to characterize the morphology of nanowires. The flow distance of polymer solution in nanochannels was investigated by measuring the length of generated polymer nanowires, which demonstrates that the flow behaviour of polymer solution on nanoscale is in accordance with Lucas-Washburn equation. The influence of polymer solution concentration on the wetting mechanism and formed structures was discussed to help better control the nanostructure in the template.
Prediction of pKa of organic compounds in acetonitrile with QSPR method
XIE Kun, QIAO Shu, FU Chuan, CHENG Cong
2010, 40(10): 1004-1010. doi: 10.3969/j.issn.0253-2778.2010.10.003
The quantitative structure-property relationships (QSPR) model for pKa values of 43 organic compounds in acetonitrile were established by using electrotopological state indices as descriptors. Leave-one-out cross validation was performed, which confirmed the good stability and powerful prediction of this model. A satisfactory relationship is expressed as
Ablation and micromachining of PZT thick films using femtosecond laser
LIU Shuang, CHU Jiaru, HUANG Wenhao, LI Baojia
2010, 40(10): 1011-1015. doi: 10.3969/j.issn.0253-2778.2010.10.004
Femtosecond laser was used for the ablation and patterning of PZT thick films. The pulse width of the laser was 130 fs, and the repetition rate was 1 kHz. First, based on the relationship between the diameter of the ablated crater and the applied peak fluence, the ablation threshold fluence 100 J/cm2 for PZT was estimated by determining the magnitude of the peek fluence for zero ablated spot diameter (no damage); then, 50 to 300 mW femtosecond laser was used to pattern the PZT thick film actuator accurately and efficiently, the process of which had no heat affected zones and did not need a mask. Under the feed rate of 5 mm/s, the PZT thick film actuator was patterned. The driving ability of the actuator is enhanced by 30% after patterning.
Study of RANS based flamelet/progress variable turbulent combustion model
WU Wen, HUANG Wei, ZHAO Pinghui, YE Taohong
2010, 40(10): 1016-1022. doi: 10.3969/j.issn.0253-2778.2010.10.005
Laminar flamelet library was built up with steady state laminar stretched diffusion flames, indexed by the mixture fraction-progress variable. Then the β PDF of mixture fraction and first-order conditional PDF of the progress variable were employed to generate the mean turbulent flamelet library. By adding the library looking up and solving sections to OpenFOAM, a turbulent combustion solver named ZCFoam was developed based on RANS. A typical turbulent methane/air partially premixed jet flame was studied. The computational results indicate that the FPV approach could satisfactorily predict the flame structure, temperature and species concentration fields.
Predicting the performance of microfluidic fuel cells
LU Zhaosheng, KONG Wei, LI Jiayu, CHEN Daifen, DOU Xuan, WU Ping, HE Liqun
2010, 40(10): 1023-1028. doi: 10.3969/j.issn.0253-2778.2010.10.006
The performance of microfluidic-based fuel cells was predicted numerically by Fluent, where liquid fuel and liquid oxidant flow side by side in a channel at microscale and the current of electricity is achieved by electrochemical reactions at electrodes on channel walls. The obtained polarization curves were found to be in good agreement with experiments, and with the increase in the volumetric flow rate, the cell performance rises gradually. In our case, the cell performance is very sensitive to the content of oxygen in the cathode stream, while it is insensitive to the concentration of formic acid in the anode stream, confirming the cathode limited performance in microfluidic fuel cell as reported by others.
Numerical simulation of pulsating aviation fuel flame spread
CHEN Guoqing, ZHOU Jiebo, WANG Changjian, LU Shouxiang
2010, 40(10): 1029-1035. doi: 10.3969/j.issn.0253-2778.2010.10.007
A model was set up to describe the flame spreading oscillation on an aviation fuel oil pool. The chemical kinetic parameter was deduced by simulation, and, based on the measurement of flame temperature, the average reaction rates of flammable mixture were calculated and taken as a criterion for ignition. The large eddy simulation and mixture fraction model were applied to calculate the oscillations of aviation fuel flame spreading, and the pulsating of flame spread was divided into the development step and the fading step. The result indicated that there are mainly two combustion modes: diffusion and premix. The model for prediction of flame pulsating frequency was also established.
Control effect of smoke in different opening situations in a high-building stairwell
XU Xiaoyuan, LI Yuanzhou, XU Zhaoyu, LI Zheng
2010, 40(10): 1036-1042. doi: 10.3969/j.issn.0253-2778.2010.10.008
Experiments were carried out in a one-third scale model of a twelve-storey stairwell in order to investigate the control effect of smoke spreading in the stairwell under different opening conditions. The fire source was located on the 6th floor. The smoke temperature distribution along the stairwell, the inflow or outflow velocity at the openings and the rising-time of smoke front under different opening conditions were discussed. The results show that the smoke temperature takes on an exponential decay along the vertical direction when the smoke reaches a certain height, and that the neutral plane height varies under various opening conditions. In general, when vents are opened on floors near the fire, smoke temperature decreases faster, the smoke spreads more slowly, and the effect of smoke control is better.
A method for freehand sketch retrieval based on affine adaptive skeleton
QIAN Jing, WANG Zengfu
2010, 40(10): 1043-1053. doi: 10.3969/j.issn.0253-2778.2010.10.009
A novel freehand sketch retrieval method was presented, which is based on affine transformation adaptive shape and skeleton features. Firstly, a Fourier-based approach to dimensionality reduction and smoothing was employed to process object contour data. And, after normalization, the sampled contour data was used to extract contours and regional features of objects. Then, a new affine adaptive skeletonization algorithm was presented to extract the skeletons of objects and a new skeleton tree descriptor and matching algorithm were derived. At last, a new sketch retrieval method combining contour region and skeleton features was presented. The experimental results show that the method is robust to object affine transformation (translation, scaling, rotation) and noise corruptions.
HMAC: An energy efficient MAC protocol for wireless sensor networks
SU Yu, QU Yugui, LIN Zhiting
2010, 40(10): 1054-1064. doi: 10.3969/j.issn.0253-2778.2010.10.010
Duty-cycle MAC protocols widely used in wireless sensor networks lead to extra end-to-end delivery latency, while the existing solutions, such as RMAC (the Routing enhanced MAC protocol), are only applicable to light-load traffic. A new MAC protocol called HMAC is proposed, which avoids the unnecessary energy consumption caused by loss events without sacrificing the performance of packet delivery latency. By using two scheduling frames, HMAC realizes efficient multihop packet delivery in a single cycle, and ensures that bad link conditions do not impact the downstream nodes. Compared with S-MAC and RMAC, it is shown that HMAC outperforms these protocols in a heavy-load traffic scenario, with higher energy efficiency and lower delivery latency.
Improved shape context based on 1-D fourier transformation
LI Shanshan, WU Xiuqing
2010, 40(10): 1065-1073. doi: 10.3969/j.issn.0253-2778.2010.10.011
A new shape feature descriptor was proposed, which considers shape context features as an array of 1-D signals. The 1-D Fourier transformation was then performed on every signal. The new feature descriptor has been proved theoretically to be invariant for scaling, translation and rotation, with acceptable computational complexity. Shape point matching experiment shows the efficiency and effectiveness of the new feature descriptor.
An audio steganalysis method for echo hiding based on statistical features of power cepstrums
WANG Yujie, GUO Li, WANG Cuiping
2010, 40(10): 1074-1081. doi: 10.3969/j.issn.0253-2778.2010.10.012
An audio steganalysis method for echo hiding based on statistical features of power cepstrums was proposed. In this scheme, audio signals were first divided into little segments and a hanning window was applied to each segment, then average power cepstrums of the windowed audio segments were calculated, and based on the feature that the average power cepstrums of echo hiding signals can generate peaks at echo delays, variances of differences and flatness of the average power cepstrums were calculated as statistical features, and, finally, support vector machine (SVM) was implemented as a classifier. This steganalysis method can not only detect the basic single echo kernel, but also be applied to the improved echo kernels. Experimental results show that the performance of the proposed method is satisfactory, achieving high classification accuracy even with low attenuation coefficients and regardless of the length of the embedded segments of audio signals.
Principle and theoretical analysis of all-fiber circular polarizers
YANG Li, LI Cheng, SU Jue, QIAN Jingren
2010, 40(10): 1082-1086. doi: 10.3969/j.issn.0253-2778.2010.10.013
A new suggestion of making chiral fiber gratings and all-fiber circular polarizers by spinning strain-induced high birefringence fibers was presented. By means of coupled-mode theory, it is shown that a circular polarizer might be achieved by using a spun Bow-Tie fiber or Panda fiber with short pitches of less than one millimeter. Unlike the special chiral fibers previously mentioned, these strain-induced high birefringence fibers are commercially available and are easy to be spliced with common fibers. The coupled-mode analysis also reveals the scheme of polarization-selectivity between coupled modes and the necessary conditions for achieving polarizers in these kinds of chiral fiber gratings. A numerical simulation was done on a spun Panda fiber, and it is shown that in a right-handed rotating birefringent fiber with a numerical aperture of 0.186 5, a beat length of 125 millimeter, a rotation pitch of 0375 millimeter and a fiber length of 332 millimeter, a left-circular polarization light would output at the wavelength of 155 micron.
Replication strategy based on incentive mechanism in peer-to-peer networks
GUO Liangmin, YANG Shoubao, LU Weina, ZHANG Rui, WU Bin
2010, 40(10): 1087-1095. doi: 10.3969/j.issn.0253-2778.2010.10.014
To encourage peers in P2P network to provide their storage space saving replications and strengthen cooperation between them, the replication strategy based on incentive mechanism was put forward using information economics about principal-agent relationship and the incentive concept for reference. The experimental results show that the proposed replication strategy can weaken the negative effect brought about by noncooperation between peers as far as possible to create replications successfully, and indeed improve search performance of P2P networks to a certain extent. Compared with classical replication strategies, the new method can reduce search response time, promote search success ratio and balance peers load.
Intrusion detection system design in wireless LANs based on optimized BP algorithm
LIU Fengchun, ZHOU Hao, ZHAO Baohua
2010, 40(10): 1096-1100. doi: 10.3969/j.issn.0253-2778.2010.10.015
In view of the existence of slightly curved surfaces and local minima problems with the application of the BP neural network algorithm, ergodic BP algorithm based on minimal point escape was proposed to achieve better convergence effect. The improved BP algorithm was applied to the wireless network intrusion detection system. Experiments show that, the improved BP algorithm enhances the accuracy and real time of intrusion detection systems.