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Determining the connectedness of an undirected graph
- TAN Tunzi, GAO Suixiang, YANG Wenguo
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2018, 35 (5):
582-588.
DOI: 10.7523/j.issn.2095-6134.2018.05.002
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Abstract (
1252 )
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Determining the connectedness of an undirected graph is a frequent issue in practical graph mining and regarded as a key subproblem of the graph partitioning problem. Apart from graph partitioning, graph connectedness also plays an imperative role in tracking the spread of disease, VLSI design, social network analysis, and theoretical studies in graph theory such as "Cayley graph". This work reviews several important methods for determining the connectedness of an undirected graph, such as breadth-first search, depth-first search, and the eigenvalues of a graph Laplacian matrix. In addition, we propose several new methods, such as power sum and logical sum of adjacency matrix. We compare all the relevant methods empirically on random graphs with up to 10 000 vertices, and show that the breadth-first search and logical sum methods deliver good performances on large graphs with more than 100 vertices and the logical sum method is the fastest.
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A margin model with liquidity risk
- CHEN Songsong, CHENG Xijun, MA Lijun
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2018, 35 (5):
589-594.
DOI: 10.7523/j.issn.2095-6134.2018.05.003
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Abstract (
327 )
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Existing models can not be used to effectively describe the relationship between the market price risk and liquidity risk of futures portfolio. To solve this problem, this work models the two risks separately. Firstly, we consider the correlation of risks of the same kind among different futures. Secondly, we study the interaction between the market price risk and liquidity risk. Then,we provide a margin model including the liquidity risk.
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Numerical simulation of laminar natural convection heat transfer from three horizontal attached cylinders
- SHI Hongyan, LIU Jie, LU Wenqiang
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2018, 35 (5):
595-601.
DOI: 10.7523/j.issn.2095-6134.2018.05.004
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Abstract (
445 )
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In this study, by applying the new computational model proposed by Bejan, laminar natural convection heat transfer from three horizontal attached cylinders has been studied numerically over the Rayleigh number range 10 ≤ Ra ≤ 106 and at the Prandtl number Pr=0.707 0. The comprehensive results consisting of streamlines, isothermal contours, and local and average Nusselt numbers are presented with different Rayleigh numbers. The obtained results show that a vortex is formed in the space between the adjacent two cylinders. The maximum local Nusselt number appears near θ=140°, and it increases with the Rayleigh number. Furthermore, this work accurately fits the equation dascribing the variation of average Nusselt number of the three cylinders with Rayleigh number. Hence the heat transfer coefficient of natural convection can be determined, and an accurate reference value is provided for industrial application.
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Comparison of the measured morphology parameters of an abdominal aortic aneurysm between the 2D and 3D techniques
- WEI Chijun, QIU Yue, YUAN Ding, ZHENG Tinghui
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2018, 35 (5):
607-611.
DOI: 10.7523/j.issn.2095-6134.2018.05.006
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Abstract (
362 )
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The purpose of this study is to find out the measured morphology differences of a patient-specific abdominal aortic aneurysm (AAA) between the 2D and 3D image technique. The 34 AAA models were reconstructed based on the computed tomography scan images using Mimics software, and the geometry parameters were measured and compared with those values using the 2D images.Compared with the results using the 3D model, the measurement errors in the artery diameters using the 2D images were less than 15%, but the errors in some parameters such as the longest and shortest axes of the maximum cross section of the AAA were significant. In addition, the angle parameters showed big differences between the two different measurement methods. The conclusions are that the parameter values measured using the 2D images were far from the values measured using the 3D models. We suggest to measure the morphology parameters of a patient-specific AAA using the 3D images for clinic practice.
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Power line extraction using airborne LiDAR point clouds characteristics and model fitting method
- YANG Yuan, CHEN Fengxiang, GUO Tao, SHI Lei, WANG Cheng, LUO Xin
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2018, 35 (5):
612-616.
DOI: 10.7523/j.issn.2095-6134.2018.05.007
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Abstract (
438 )
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Digital power line is a core part of digital grid construction and smart line security inspection. Airborne LiDAR has a unique advantage for power line reconstruction because it is capable of accurately and quickly obtaining 3-D information. We propose a new method for automatically and rapidly extracting power lines from airborne LiDAR data in the transmission corridor. Firstly, the power line points were roughly extracted based on the spatial distribution of raw point clouds, and the noise points were removed by using the improved Hough transform and RANSAC parabolic fitting method. Then, the power lines were distributed on the horizontal plane and the vertical plane. Finally, the points of power line were extracted by the model growth method, which was based on the assumption that the plane model of single power line was linear and the model on the vertical plane was parabolic. The experimental results show that the extraction accuracy of power line reaches 99.6% using the proposed method.
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Effects of red mud and the combinations on lead, cadmium, and arsenic availability in contaminated soil
- SHI Lizheng, CHEN Huikang, WU Chuan, HUANG Liu, CUI Mengqian, XUE Shengguo
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2018, 35 (5):
617-626.
DOI: 10.7523/j.issn.2095-6134.2018.05.008
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Abstract (
356 )
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The soil incubation experiment was conducted to investigate the effects of red mud, acid-modified red mud, zeolite, gypsum, and ferrous sulfate each and their combinations on the available lead, cadmium, and arsenic concentrations in contaminated soils. The results are showed as follows. In the acid-modified red mud, aluminum, calcium, and iron atoms were further exposed with the changes of surface structures than in the red mud. Additions of 0.5% acid-modified red mud, the combination of red mud and ferrous sulfate, and the combination of acid-modified red mud and zeolite decreased soil available lead contents by 1.96%~76.47%, 4.94%~75.01%, and 5.47%~68.44%, respectively, during the incubation. Additions of the 0.5% acid-modified red mud and the combination of red mud and ferrous sulfate decreased soil available cadmium concentrations with the maximal reductions of 27.78% and 15.04%, respectively. The combination of red mud and gypsum and the combination of red mud and ferrous sulfate were more effective than other amendments in reducing the available arsenic, with reductions of 0.41%, 37.87%, 5.41%, and 3.72% and 55.60%, 13.81%, 37.85%, and 25.36% in 7, 15, 30, and 60 incubation days, respectively. The overall effect of the combination of red mud and ferrous sulfate was the best for the immobilization of lead, cadmium, and arsenic in heavy metal contaminated soils.
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Application of improved set pair analysis model for considering the influence of stochastic observation error in water quality fuzzy evaluation
- SHU Chikai, HOU Xingfu, WANG Jianjin, YANG Kan
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2018, 35 (5):
627-634.
DOI: 10.7523/j.issn.2095-6134.2018.05.009
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Abstract (
236 )
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In order to better deal with the uncertain information in the process of water quality evaluation, the theory of set pair analysis is used. Considering the water quality classification level refinement, we divide the diversity factor in set pair analysis theory into good-difference and bad-difference and divide the reverse factor into good-reverse and bad-reverse. The weight of the index is calculated by the combining weighting method and corrected by considering the influence of stochastic observation error. The difference coefficient and correlation are used to optimize the index system. This model is applied in the evaluation of ground water functional zone in Yixing. The results are compared with those obtained using the artificial neural network, gray theory, and projection pursuit methods. When the evaluation results of the four methods are different in some sections, we find that the results using this model are in the best agreement with the water quality monitoring data.
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Loading and stability analyses of viscous debris flow check dam
- SUN Hao, YOU Yong, LIU Jinfeng, LIN Xueping
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2018, 35 (5):
635-644.
DOI: 10.7523/j.issn.2095-6134.2018.05.010
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Abstract (
433 )
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As a counter measure, check dam has been constructed widely because of its obvious advantages. Stability analysis is one of the most important contents in engineering designs of a check dam. Based on analysis of loading combination in this work, a mathematical expression of stability coefficient has been reduced when reservoir of check dam has or has not a deposition. The expression shows a decreasing variation in stability coefficient basically in intercepting process. Through the contrastive analyses of different working conditions of check dam, the results show that check dam having a deposition in reservoir is more dangerous than that harving no deposition, when intercepting earlier arrays of debris flow. The thicker the deposition behind check dam is the more dangerous. Finally the relationship between stability and upstream slope of check dam has been discussed. The results indicate that the effect of upstream slope of check dam decreases when intercepting debris flow continuously. Then a fold-line shaped upstream slope of check dam, which is gentle in the downside and steep in the upside, is suggested for engineering design.
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Evolution of rural land in developed areas within the context of population shrinkage: evidence from Changshu City of Jiangsu Province
- TIAN Xiuqin, GAO Jinlong, CHEN Wen, CHEN Jianglong
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2018, 35 (5):
645-653.
DOI: 10.7523/j.issn.2095-6134.2018.05.011
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Abstract (
510 )
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Rural land remains sustained growth against the background of population shrinkage in many rural areas. Based on the land use survey data as well as the high resolution multi-temporal satellite images from 2009 to 2013, this study investigates the evolution of rural land in Changshu and discusses the land expansion mechanism through the lens of supply and demand. This study classifies the rural land into commercial-residential land, industrial land, and other rural land. The results are given as follows.1) Form 2009 to 2013, industrial land growth is the main reason for rural land expansion with a net increase of 53.92%. Commercial-residential land, mainly residential land, increases by 17.88%.2) The continuous growth of residential land in Changshu results from excessive compensation from the local government for the rural construction, while the rapid expansion of industrial land arises from the continuous promotion of rural industrialization, profit-seeking of establishments, and the financial bonus of local government motivated by economic growth. Taking the values of countryside into consideration, it is urgent to attach more importance to rural transition and intensive landuse. Rational centralization of living space, further intensification of production space, and preservation and improvement of ecological space are the three critical approaches to realize the functional integration of rural spaces.
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Study of coupling relationship between industry innovation and industry structure optimization and upgrading in Wuhan East Lake High-tech Development Zone
- CHEN Yufan, WANG Kaiyong
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2018, 35 (5):
654-662.
DOI: 10.7523/j.issn.2095-6134.2018.05.012
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Abstract (
408 )
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This paper establishes a coupling model between industrial innovation and industrial structure optimization and upgrading in development zones. Wuhan East Lake High-tech Development Zone is selected as the study area, and the empirical analysis is carried out. The coupling degree and coupling scheduling for the 2003-2015 industry comprehensive system of East Lake High-tech Development Zone are calculated, and relevant suggestions and countermeasures are put forward. The research shows that there is a coupling relationship between industry innovation and industry structure upgrading in East Lake High-tech Development Zone. The coupling correlation and coordination degree both increased from 2003 to 2015 and the change in coordination degree was prominent. However, there is still much room for improvement in the coupling correlation. The dynamic process of change is closely related to local policies. According to the contributions of industrial innovation subsystems and the industrial structure optimization and upgrading subsystems, the development of the zone should be dominated by innovation factors. Moreover, the integration of different industries and the optimization of resource allocation and resource reorganization should be further promoted so as to enhance the level of industrial development of the park and realize the sustainable development of the park economy.
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Characteristics and influence factors of urban sprawl of Dar es Salaam from 2002 to 2012
- ZHANG Jiaqi, CHEN Shuang, Damas W. Mapunda
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2018, 35 (5):
663-673.
DOI: 10.7523/j.issn.2095-6134.2018.05.013
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Abstract (
249 )
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Based on the land-use classification data (2002, 2007, and 2012) and field investigation, the pattern and influence factors of the urban sprawl of Dar es Salaam were studied. Sector analysis, concentric circle analysis, elasticity ratio of urban land growth, and expansion intensity index were employed in the analysis. The results are showed as follows. 1) The sprawl of Dar es Salaam was characterized by high expansion degrees and increasing expansion speeds from 2002 to 2012, which presented the rapid urban-rural mixed development accompanied by the continuous growing of informal settlements. The occupied lands during the expansion were mainly bare lands and vegetation. 2) The built-up areas mainly spread along the arterial roads and around the city center from 2002 to 2007, while the spread was characterized by filling the open areas between arterial roads or along the urban edges from 2007 to 2012. Therefore, the urban space-form evolved from finger-like to block-shaped. 3) The built-up areas spread mainly towards northwest, west, southwest, and southeast, and the southeast of the city became an important area of spreading. Furthermore, the urban sprawl showed a significant distance attenuation feature. 4) The urban sprawl of Dar es Salaam was mainly affected by the growth of the population and economy, the improvement of traffic conditions, the policy changes, and the land tenure system. Transportation facilities played an important role in guiding the spatial expansion pattern.
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Numerical analysis of influence of water level fluctuation of Dadu River on Guzan borehole strain meter
- REN Tianxiang, YANG Shaohua, DONG Peiyu, CHENG Huihong, SHI Yaolin
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2018, 35 (5):
674-680.
DOI: 10.7523/j.issn.2095-6134.2018.05.014
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Abstract (
302 )
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Four-component borehole strain gauges detect deformation in four orientations in the borehole to monitor long-term variation of earth stresses, with large frequency coverage including signals from earthquakes, solid earth tides, and secular changes. However, the records also contain disturbances from factors other than tectonic stresses. Therefore, it is an important task to investigate the causes of these disturbances. Guzan station, which is in Sichuan Province, is located on the bottom of a steep valley of Dadu River. This station has recorded not only obvious annual changes of amplitude up to 10-6, but also irregular fluctuations following the rise of river water level in the wet season every year. In this study, stresses generated by the change of river water level are calculated using numerical method of elastic mechanics. Preliminary calculation results indicate that water level fluctuation of several meters in Dadu River produces stress variation of kPa magnitude. The fact that borehole strain meter can be used to record changes in river water level is significant. On the one hand, the fact shows that the borehole strain gauges indeed detect the very small change in stress variation, which indicates the high sensitivity of the instrument. On the other hand, the fact shows that the location of the strain meter station should be away from steep valleys as far as possible, in order to reduce the interference and highlight the true tectonic stress changes. Observations of improved quality can be applied in the study on relations between earth stress and seismicity.
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Multi-wavelet NMO correction
- LIN Luchun, XIE Mengyu, SHI Baoping, AN Ping
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2018, 35 (5):
681-688.
DOI: 10.7523/j.issn.2095-6134.2018.05.015
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Abstract (
308 )
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The conventional normal moveout (NMO) correction that processes the seismic data sample-by-sample results in the well-known decrease in frequency content and amplitude distortion through stretch, which lowers the seismic resolution. This work proposes multi-wavelet NMO correction to reduce NMO-stretch effects. Multi-wavelet NMO corrects the data wavelet-by-wavelet rather than sample-by-sample. With the multi-wavelet decomposition technique, a seismic trace is decomposed into a series or a set of wavelets. Multi-wavelet NMO correction is implemented on a wavelet-by-wavelet basis. The moveout is applied to these wavelets to avoid stretch and maintain the seismic resolution. We test the algorithm on two synthetic models and a 2D real seismic section, and compare our results with those obtained using conventional NMO.
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Optimization aeromagnetic compensation method based on power spectrum estimation
- WU Peilin, ZHANG Qunying, CHEN Luzhao, FEI Chunjiao, ZHU Wanhua, FANG Guangyou
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2018, 35 (5):
689-695.
DOI: 10.7523/j.issn.2095-6134.2018.05.016
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Abstract (
306 )
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Aeromagnetic exploration is one of the most important methods in geophysics. Magnetic fields are typically measured by using optically pumped magnetometer mounted on an aircraft. However, any aircraft produces significant levels of magnetic interference. Therefore, aeromagnetic compensation is essential. In this work, power spectrum estimation is proposed to process the signal of the maneuver flight. The optimal bandwidth for the computation of compensation coefficients is obtained by using the method. The optimal compensation coefficients lead to more accurate aeromagnetic compensation. A calibration experiment is designed. In the experiment more accurate optimal compensation coefficients and higher improvement radio are obtained. The validity of the proposed method is demonstrated by the experimental results.
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Energy-efficient hybrid precoding design based on RF chains selection for millimeter wave MIMO systems
- SUN Jihan, QIU Ling
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2018, 35 (5):
696-703.
DOI: 10.7523/j.issn.2095-6134.2018.05.017
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Abstract (
487 )
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In order to reduce the radio frequency (RF) chains cost and satisfy the high capacity demand for communication systems, millimeter wave hybrid precoding with limited RF chains is proposed to make a tradeoff between hardware cost and system performance. In this work, we study the energy-efficient hybrid precoding design problem based on RF chains selection for a millimeter wave multi-user multiple-input multiple-output (MIMO) system. First, we use the predesigned analog precoding codebook to reformulate the original problem as a sparse digital precoding problem. Then we solve it iteratively using successive convex approximation (SCA) method combined with fractional programming method. The simulation results show that our proposed algorithm gives the performance very close to that of the exhaustive search and better than those of the other existed algorithms.
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Spatial variability in degree-day factors in Yarlung Zangbo River Basin in China
- LIU Jinping, ZHANG Wanchang
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2018, 35 (5):
704-711.
DOI: 10.7523/j.issn.2095-6134.2018.05.018
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Abstract (
678 )
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Degree-day model, based on a linear relationship between glacier/snow ablation and positive accumulated temperature, is widely used for estimating glacier and snow melt for its simplicity and outstanding performance. However, degree-day factor (DDF), as the most important parameter in this model, is difficult to obtain in an extensive region, especially in Yarlung Zangbo River Basin, which is the highest basin in the world and characterized by rugged and complex terrain. With the development of distributed hydrological model, increasing demand for spatial dataset of DDFs has become a challenging issue in the relevant fields. The objective of this study is to develop an algorithm to spatially estimate the positive DDFs based on available observed DDFs. Topographical factors are fully taken into account to correlate with DDFs, and spatial DDFs in moderate resolution are generated by stepwise and neighboring mean filtering improved in this study. Finally, the produced DDFs are indirectly validated by snow lines in different orientations, and the correlation coefficient of up to 0.82 proves that the DDFs generated in the present study are reasonable in applications. The spatial distribution of DDFs in Yarlung Zangbo River Basin shows that DDFs in downstream were lower than those in upstream and midstream, which is probably because there is less precipitation and more solar radiation in upstream and midstream than in downstream, due to monsoon from India Ocean. To better estimate glacial meltwater runoff and manage water resources in Yarlung Zangbo River Basin, further studies on spatial variability in DDFs are yet needed.
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Chemical reactions and effects of slick water fracturing fluid on the pore structures of shale reservoirs in different deposition environments
- SUN Zepeng, WANG Yongli, WU Baoxiang, ZHUO Shengguang, WEI Zhifu, WANG Gen, XU Liang
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2018, 35 (5):
712-719.
DOI: 10.7523/j.issn.2095-6134.2018.05.019
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Abstract (
352 )
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In order to study the effects of slick water fracturing fluid on the pore structures of different deposition environments (marine, continental, and marine-continental transitional) shale reservoirs in the process of shale gas exploration, the deep basin fluid-rock interaction experimental device was used to simulate the interaction between the slick water fracturing fluid and different shales in the condition of formation (100 ℃, 50 MPa). Through comparing the changes in mineral composition, pore volume, and specific surface area of three different deposition environment shales before and 72 h after reaction, the transformation effects of pore structure were analyzed. The results showed that the mineral composition and pore structure of different deposition environment shales changed after reaction with fracturing fluid. After reaction, the carbonate minerals (calcite and dolomite) of marine shale were corroded and many dissolution pores with diameter of 2-8 μm occurred, which caused the reduction in pore volume and specific surface of nanopore. Because of the continental shale and marine-continental shale contain a large amount of mixed-layer illite/smectite mineral which is liable to dispersion and swelling when reacting with slick water fracturing fluid, the pore volume and specific surface area of these shales decreased after reaction. The results of this study provide scientific basis for study of the physical and chemical interactions between slick water fracturing fluid and different deposition environment shale reservoirs and of the transformation of fracturing fluid.
