Table of Content

30 October 2017, Volume 23 Issue 5

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New application of firefly synchronization model in time synchronization of underwater wireless sensor networks

JIN Yanliang, FANG Changli, ZHANG Xiaoshuai, YAO Bin

2017, 23(5):  647-657.  doi:10.12066/j.issn.1007-2861.1765

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Time synchronization is a basic demand for a sensor network. However, in a complex underwater environment, underwater wireless sensor networks (UWSNs) face two challenges: long propagation delay and mobility of nodes. This paper uses a firefly synchronization model to underwater, and proposes an underwater firefly algorithm. It makes use of good characteristics of distribution and phase compensation to effectively improve the effectiveness of time synchronization and shorten synchronization time. A chirp signal is combined with the model since the chirp has strong of anti-Doppler ability. This also contributes more synchronization precision for underwater wireless sensor networks. Good performance of the underwater firefly algorithm model is verified by simulation.

Demodulation for multi vortex beams based on composite diffraction hologram

WANG Yingying, LI Yingchun, SHAO Wei, ZHANG Weibin, SUN Tengfen, ZHU Fuquan

2017, 23(5):  658-665.  doi:10.12066/j.issn.1007-2861.1761

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When projecting a Gauss beam onto the spatial light modulator (SLM) loaded with a composite hologram, several vortex beams are generated simultaneously. On the contrary, when projecting the corresponding vortex beam onto a hologram, the Gauss beam can be restored, realizing demodulation of the vortex beam. Traditionally, a hologram can only demodulate one incident vortex beam. In this paper a vortex beam demodulation method based on composite diffraction hologram that can demodulate several incident vortex beams with only one hologram is proposed, thus having a good chance of applications. An experimental system is set up to achieve generation, transmission and demodulation of vortex beams with 16 quadrature amplitude modulation-orthogonal frequency division multiplexing (QAM-OFDM) signals. After offline processing on the demodulated Gauss beam, constellation and bit error rate of each subcarrier for OFDM signals are acquired. The experiment results show that the bit error rates of all subcarriers are below the forward error correction (FEC) threshold.

Energy efficiency of bidirectional amplify-and-forward relay links

CHEN Fangfang, WANG Tao, SUN Yanzan, WU Yating

2017, 23(5):  666.  doi:10.12066/j.issn.1007-2861.1762

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In this paper, a three-node relay link with bidirectional data transmission is studied. Power consumption of both baseband and radio frequency circuits is taken into account. With an amplify-and-forward relay system and a given bit error rate, the influence of modulation rate on energy efficiency is analyzed. Minimum transmitted power of the radio freqency circuit is derived. An expression of energy efficiency is obtained for the case that the baseband circuit power is related to the modulation rate. The optimization problem is solved using a mathematical optimization method. The effect of modulation rate on energy efficiency is analyzed, and verified by simulation results.

Optimal computation and measurement of permittivity of flake dielectric materials

ZHOU Jianjun, ZHANG Ning, YAN Jinkui

2017, 23(5):  674-681.  doi:10.12066/j.issn.1007-2861.1673

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Based on an open-ended flanged coaxial probe technique, this paper measures complex permittivity of flake dielectric materials loading at the end of a probe. The method compares measured values and theoretically calculated values, the measured values being processed by optimization iteration computation. This paper introduces a theoretical model and the measurement system in detail. Feasibility and rationality of the presented method are shown by measuring some common materials.

Dynamic range compression with local contrast preservation

YAN Ming1, HU Yueli1, HU Yunsheng2

2017, 23(5):  682-689.  doi:10.12066/j.issn.1007-2861.1722

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As partial detail in a high dynamic range image cannot be shown on a common display, a dynamic range compression algorithm with local contrast preservation is presented. This paper addresses the problem that ordinary algorithms reduce local contrast and damage highlighted regions, and proposes a new S shaped luminance mapping curve. Luminance is successfully enhanced by controlling intensity of the curve. Experimental results show that the algorithm can effectively compress the image dynamic range with good visual effect.

Minimum pulse width modulation of current harmonic for three-level inverter

XU Yuan, SONG Wenxiang, FENG Jiuyi, YANG Ying

2017, 23(5):  690-701.  doi:10.12066/j.issn.1007-2861.1724

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Medium voltage transmission systems driven by a high power three-level inverter operating at low switching frequency can reduce switching losses of the power
device. This paper proposes a subsection synchronous current harmonic minimum pulse width modulation (CHMPWM) approach of neutral point clamped three-level (NPC-3L) inverter in low switching frequency operation. A subsection synchronous scheme is obtained with the theoretical calculation at the allowed maximum switching frequency. Genetic algorithm(GA) is used to get high-precision initial values. The expected switching angles are achieved with as sequential quadratic programming (SQP) algorithm. Validity of the theoretical analysis and superiority of CHMPWM are verified via simulation and experiments.

Arc contour detection method based on discrete curvature characteristics

ZHANG Xudong, ZHAO Qijie

2017, 23(5):  702-713.  doi:10.12066/j.issn.1007-2861.1764

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Detection of object shape is the basis of autonomous environment understanding for robots. An object turns into connected domains after color layering and multi-scale filtering segmentation, and therefore it can be easily analyzed. In view of this, a method based on discrete curvature characteristics is proposed to detect the arc shape of objects. This method is based on extraction of object contour, and detection of lines and features. Interferential lines are illuminated, and the arc features are detected according to the discrete curvature changes of the remaining contour points. A system of robot operation is established for experiments. Average precision of arc contour detection is 90.6% and the handling time is 0.75 s. The result shows effectiveness of the proposed method in detecting arc contour of objects.

Finite p-groups with central automorphism almost being inner automorphism

ZHANG Boru, GUO Xiuyun

2017, 23(5):  714-721.  doi:10.12066/j.issn.1007-2861.1744

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Let G be a finite p-group and let K(G) be a subgroup of G consisting of all elements in G fixed by every central automorphism in G. A necessary and sufficient
condition is given on |Aut_c(G) : Inn(G)| = |Z(G) : K(G)| for a finite p-group G of class 2. The condition for |Aut_c(G) : Inn(G)| = p|Z(G) : K(G)| is also studied.

Counting problem in multiplicative subsemigroups of positive integers

ZHU Xiaojie, YAO Weili

2017, 23(5):  722-731.  doi:10.12066/j.issn.1007-2861.1749

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Let S and S' be minimal systems of generators of specific subsemigroups of positive integers N. If A N, then is the subsemigroup generated by A. Let N_A(x):=∑_n∈:n≦_x1. A formula that establishes a connection between N_S(x) and N_{S∪S' (x)} is obtained via elementary methods of changing summation order. With this formula and induction on several variables, an asymptotic estimation of the number of element in a subsemigroup generated by a finite set of primes is obtained.

Bayesian estimation of autoregressive models with time-varying coefficients

CHEN Yunxian, GAO Xingyue, WANG Yuying, HE Youhua

2017, 23(5):  732-741.  doi:10.12066/j.issn.1007-2861.1754

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This paper analyzes a time-varying autoregression model where coeffcients are correlated at different time. When only one sample path is chosen, the Bayesian method is used for estimation. Formulas of estimation of the first order model are presented. This paper also discusses how the estimation is affected by the coeffcient values and the length of samples. To conclude, based on an empirical evidence, it is shown that the statistical results are consistent with the actual data.

Segmenting groups in crowd based on spatiotemporal restraint

YI Xian1,2, DONG Nan2, WEI Jianming2, ZHU Wenhao1

2017, 23(5):  742-751.  doi:10.12066/j.issn.1007-2861.1760

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Pedestrians in crowded scenes can be seen as a collection of groups moving coherently. To segment the crowd into groups and analyze interactions between them, a method using group spatiotemporal relationships is proposed. Spatiotemporal information of crowds by modeling the background and tracking the feature points is acquired. Then the individuals are grouped according to aspatial neighborhood restraint. The groups are further divided by motion correlation over time. These two restraints work with each other effectively, and generate groups with coherent motion. Tests on many videos of real-world pedestrian scenes show that the method can be applied to a variety of scenes with different crowd densities and perspective of videos.

Distribution of PFCs in water and sediment, and toxicity and removal

LIANG Huanhuan1,2, WU Minghong1, XU Gang1, WANG Jiajun1, MAO Wen1, AN Da2

2017, 23(5):  752-761.  doi:10.12066/j.issn.1007-2861.1756

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Perfluorinated compounds (PFCs) in major river, seas and human serum were detected. They have attracted attention from environmental workers worldwide, become a hot research topic in environmental studies in recent years. Human exposure pathways to PFCs include drinking water, food and air-dust inhalation. In this paper, distributions of PFCs in different environmental media, toxic status quo and removal process at home and abroad are briefly surveyed. The existing problems and trends are also discussed to provide directions for researchers of PFCs.

Influence of temperature on swelling characteristics of GMZ bentonite due to wetting

JIANG Jianghong, SUN Dean

2017, 23(5):  762-771.  doi:10.12066/j.issn.1007-2861.1728

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A series of wetting tests on GMZ07 Na-bentonite, taken from Gaomiaozi area, Inner Mongolia, were performed to investigate the swelling characteristics at different temperatures. The influences of temperature and initial dry density were studied under a vertical pressure ranging from 100 to 600 kPa. The test results show that deformation due to wetting is mainly affected by dry density and vertical pressure, and slightly affected by temperature. With the same initial dry density and temperature, the greater the vertical pressure, the less the void ratio after saturation. There is a linear relation between saturated void ratio and logarithm of vertical pressure. At the same temperature and vertical pressure, void ratios after saturation for different initial dry densities are similar. In addition,
swelling pressure decreases slightly with increasing temperature.

Synergetic evolution analysis of building defects under influence of foundation deformation of high loess slopes in Kashgar, Xinjiang

MENG Dan1, PANG Feng2

2017, 23(5):  772-779.  doi:10.12066/j.issn.1007-2861.1717

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To deal with the cracking damage caused by foundation deformation in masonry buildings of the high loess slopes in Kashgar, Xinjiang, the phase change behavior and evolution of order parameter in the loading of buildings are studied by comparing the entropy of the equilibrium phase transformation system to the cooperative system. Order parameter is represented by the angle between vector sums of the crack projected onto the coordinate system. The results show that evolution of the crack in masonry structure is closely related to the free energy of the building. Study on the variation of free energy in the process of building damage and its related factors can help understand the evolution of building damage, and provide a theoretical basis for preventing damage due to foundation
deformation for high loess slopes in Kashgar.

PFC numerical simulation of direct shear tests on standard sand

LI Hang, LU Ye, SUN Kang

2017, 23(5):  780-788.  doi:10.12066/j.issn.1007-2861.1672

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As a common method of indoor soil test, direct shear test is widely used in practice. However research on its shear band, involving the test method and test apparatus, is insufficient. Particle flow code (PFC) is the most used simulation software, which takes particle as a basic unit, and can be used to simulate the particle properties of the material. Accordingly, the effect of particle shape and initial porosity of the sample on the macro mechanical behavior of the direct shear is studied in numerical simulation using PFC. By successfully establishing a numerical model of direct shear test on sands, the coordination number of the particles, particle velocity field and local porosity distribution is analyzed. The shear band in sands is not a straight line, but a slope and curvature. Thickness of the shear band is about 10.37 times the size of mean particle diameter.

Two-stage model for outbound containers’ space allocation assignment using rolling horizon method

LIU Chanjuan, HU Zhihua

2017, 23(5):  789-800.  doi:10.12066/j.issn.1007-2861.1741

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This paper addresses storage location assignment for outbound containers. Considering randomness of the containers’ approach time, this study divides the problem into two phases. The first is distribution of blocks and bays for containers based on a rolling plane. The second is to propose a multi-objective optimization model to minimize reshuffling and balance the number of each stack. The Yalmip toolbox of Matlab is used to solve the problem. Experimental results show that proposed method can effectively solve the space allocation problem for outbound containers, and reduce the amount of yard equipment operations. Efficiency of the terminal operation is significantly improved by reducing reshuffling.

Optimization of distribution system for pharmaceutical cold-chain logistics based on new GSP standard

XIONG Yongjing, YU Liying

2017, 23(5):  801-809.  doi:10.12066/j.issn.1007-2861.1766

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With advances of pharmaceutical and logistics industries, the pharmaceutical cold-chain logistics market has great potential for development. This paper analyzes the progress and criterion, focuses on the distribution of pharmaceutical cold-chain logistics, and builds an optimization model for it. The model uses minimum distribution cost as an objective function with constraints such as co-ordination of supply and demand, capacity of transfer stations, and largest volume of different transportation cycles. An example is used to show that the improved method meets the demand of the new good supply practice(GSP) standard at a lower distribution cost. This work provides ideas for building a system of pharmaceutical cold-chain logistics with high-efficiency, low-cost and low attrition rate.

GREET-based model for analyzing pollutant emissions characteristic of new energy vehicles

WANG Enci1, FAN Song1, WU Xuebin1, PU Xianjuan2, JIAO Zheng1,2, NIE Yongyou1

2017, 23(5):  810-820.  doi:10.12066/j.issn.1007-2861.1723

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Using an evaluation system of from the well-to-wheel (WTW) and the greenhouse gases, regulated emissions, and energy use in transportation (GREET) model proposed by the Argonne National Laboratory, USA, controlling variables, emissions and energy consumption of both traditional and electric vehicles can be calculated. The WTW calculation methods and GREET model put forward by the U.S. Department of Argonne National Laboratory are used to compare environmental and economic implications of conventional, hybrid, electric and hydrogen fuel cell vehicles in their whole life cycle. Four countries are then compared with different energy structures, differences about electric cars can be seen from energy consumption and emissions. Differences in energy consumption and emission exist in pure electric vehicles between countries using fossil energy and countries using new energy. From the data, it can be concluded that countries using new energy is given priority to develop pure electric vehicles with less emissions. Thus energy and power structures affect the environmental implication of new energy vehicles.