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Intergroup networks as random threshold graphs

Physical Review E 2014年第4期89卷 042812-042812页

作者： Sudipta Saha Niloy Ganguly Animesh Mukherjee Tyll Krueger Department of Computer Science and Engineering Technical University of Wroclaw Poland

Similar-minded people tend to form social groups. Due to pluralistic homophily as well as a sort of heterophily, people also participate in a wide variety of groups. Thus, these groups generally overlap with each other; an overlap between two groups can be characterized by the number of common members. These common members can play a crucial role in the transmission of information between the groups. As a step towards understanding the information dissemination, we perceive the system as a pruned intergroup network and show that it maps to a very basic graph theoretic concept known as a threshold graph. We analyze several structural properties of this network such as degree distribution, largest component size, edge density, and local clustering coefficient. We compare the theoretical predictions with the results obtained from several online social networks (LiveJournal, Flickr, YouTube) and find a good match.

关键词： thresholding algorithms HOMOPHILY theory (Communication) OVERLAP integral CLUSTER theory (Nuclear physics) ONLINE social networks

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Representative elementary volume assessment of three-dimensional x-ray microtomography images of heterogeneous materials: Application to limestones

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Physical Review E 2014年第5期89卷 053304-053304页

作者： O. Rozenbaum S. Rolland du Roscoat Institut des Sciences de la Terre d'Orléans (ISTO) UMR 7327–CNRS/Universitéd'Orléans 45071 Orléans BRGM BP36009 45060 France Université Grenoble Alpes 3SR Lab CNRS 38041 Grenoble Cedex 9 France

Over the last 15 years, x-ray microtomography has become a useful technique to obtain morphological, structural, and topological information on materials. Moreover, these three-dimensional (3D) images can be used as input data to assess certain properties (e.g., permeability) or to simulate phenomena (e.g., transfer properties). In order to capture all the features of interest, high spatial resolution is required. This involves imaging small samples, raising the question of the representativity of the data sets. In this article, we (i) present a methodology to analyze the microstructural properties of complex porous media from 3D images, (ii) assess statistical representative elementary volumes (REVs) for such materials; and (iii) establish criteria to delimit these REVs. In the context of cultural heritage conservation, a statistical study was done on 30 quarry samples for three sorts of stones. We first present the principles of x-ray microtomography experiments and emphasize the care that must be taken in the 3D image segmentation steps. Results show that statistical REVs exist for these media and are reached for the image sizes studied (1300 × 1300 × 1000 voxels) for two characteristics: porosity and chord length distributions. Furthermore, the estimators used (porosity, autocorrelation function, and chord length distributions) are sufficiently sensitive to quantitatively distinguish these three porous media from each other. Lastly, this study puts forward criteria based on the above-mentioned estimators to evaluate the REVs. These criteria avoid having to repeat the statistical study for each new material studied. This is particularly relevant to quantitatively monitor the modifications in materials (weathering, deformation …) or to determine the smallest 3D volume for simulation in order to reduce computing time.

关键词： X-ray computed microtomography MICROSTRUCTURE thresholding algorithms AUTOCORRELATION (Statistics) CALCITE SILICA

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Sparse Recovery by Semi-Iterative Hard thresholding Algorithm

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MATHEMATICAL PROBLEMS IN ENGINEERING 2013年第1期2013卷 1-6页

作者： Zhou, Xueqin Feng, Xiangchu Jing, Mingli Xidian Univ Sch Sci Xian 710071 Shaanxi Peoples R China Xi An Jiao Tong Univ Sch Elect & Informat Engn Xian 710049 Shaanxi Peoples R China Xian Univ Finance & Econ Sch Stat Xian 710100 Shaanxi Peoples R China

We propose a computationally simple and efficient method for sparse recovery termed as the semi-iterative hard thresholding (SIHT). Unlike the existing iterative-shrinkage algorithms, which rely crucially on using negative gradient as the search direction, the proposed algorithm uses the linear combination of the current gradient and directions of few previous steps as the search direction. Compared to other iterative shrinkage algorithms, the performances of the proposed method show a clear improvement in iterations and error in noiseless, whilst the computational complexity does not increase.

关键词： SPARSE matrices ITERATIVE methods (Mathematics) thresholding algorithms SIGNAL processing COMPUTATIONAL complexity ELECTRONIC data processing

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Comparison of automatic thresholding methods for snow-cover mapping using Landsat TM imagery

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INTERNATIONAL JOURNAL OF REMOTE SENSING 2013年第19期34卷 6529-6538页

作者： Yin, Dameng Cao, Xin Chen, Xuehong Shao, Yijie Chen, Jin Beijing Normal Univ State Key Lab Earth Surface Proc & Resource Ecol Beijing 100875 Peoples R China

Knowledge of snow cover is essential to understanding the global water and energy cycle. thresholding the normalized difference snow index (NDSI) image is a method frequently used to map snow cover from remotely sensed data. However, the threshold is dependent on the scenario and needs to be determined accordingly. In this study, nine automatic thresholding methods were tested on the NDSI. Comparisons of the automatic thresholding methods, optimal threshold, and support vector machine (SVM) classification show that Otsu's and Nie's methods appear to be the most robust among the nine automatic thresholding methods, achieving comparable accuracies with the latter two approaches. In addition, NDSI from the digital number (DN) can be an efficient substitution for NDSI obtained from atmospherically or topographically corrected data, with similar accuracy.

关键词： SNOW cover LANDSAT satellites thresholding algorithms REMOTE sensing SUPPORT vector machines COMPARATIVE studies

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Wavelet-denoising on hardware devices with Perfect Reconstruction, low latency and adaptive thresholding

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COMPUTERS & ELECTRICAL ENGINEERING 2013年第4期39卷 1300-1311页

作者： Ballesteros L, Dora M. Moreno, Juan M. Univ Politecn Cataluna Dept Elect Engn Barcelona Spain Univ Mil Nueva Granada Dept Telecommun Engn Bogota Colombia

This paper introduces a wavelet denoising architecture with adaptive thresholding for real-time 1D-systems and without the use of external memories for storing input data or wavelet coefficients. The Discrete Wavelet Transform (DWT) is executed sample-by-sample by a polyphase scheme of the biorthogonal base 5/3. Since the weights of the filters are represented by integer terms and the quantization error is quasi-zero, the principle of Perfect Reconstruction is satisfied. The adaptive threshold is based on a real-time sorting process which calculates the median of the detail coefficients. Simulations are presented to measure the delay, latency, quantization error and hardware cost. A comparison with related works is also provided in order to show the strengths of the current proposal. The good trade-off among reconstruction error, latency, delay and hardware cost permits to use the proposed architecture in a wide variety of signals that require good fidelity and prompt response. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： WAVELETS (Mathematics) SIGNAL denoising COMPUTER input-output equipment thresholding algorithms REAL-time clocks (Computers) ERROR analysis (Mathematics) TIME delay systems

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Hierarchical Artificial Bee Colony Optimizer with Divide-and-Conquer and Crossover for Multilevel Threshold Image Segmentation

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DISCRETE DYNAMICS IN NATURE AND SOCIETY 2014年第1期2014卷 1-22页

作者： He, Maowei Hu, Kunyuan Zhu, Yunlong Ma, Lianbo Chen, Hanning Song, Yan Chinese Acad Sci Shenyang Inst Automat Dept Informat Serv & Intelligent Control Shenyang 110016 Peoples R China Univ Chinese Acad Sci Beijing 100039 Peoples R China

This paper presents a novel optimization algorithm, namely, hierarchical artificial bee colony optimization (HABC), for multilevel threshold image segmentation, which employs a pool of optimal foraging strategies to extend the classical artificial bee colony framework to a cooperative and hierarchical fashion. In the proposed hierarchical model, the higher-level species incorporates the enhanced information exchange mechanism based on crossover operator to enhance the global search ability between species. In the bottom level, with the divide-and-conquer approach, each subpopulation runs the original ABC method in parallel to part-dimensional optimum, which can be aggregated into a complete solution for the upper level. The experimental results for comparing HABC with several successful EA and SI algorithms on a set of benchmarks demonstrated the effectiveness of the proposed algorithm. Furthermore, we applied the HABC to the multilevel image segmentation problem. Experimental results of the new algorithm on a variety of images demonstrated the performance superiority of the proposed algorithm.

关键词： BEES algorithm MULTILEVEL models (Statistics) SEGMENTATION (Image processing) thresholding algorithms INFORMATION sharing

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Automatic detection of field furrows from very high resolution optical imagery

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INTERNATIONAL JOURNAL OF REMOTE SENSING 2013年第9-10期34卷 3467-3484页

作者： Le Hegarat-Mascle, S. Ottle, C. Univ Paris 11 IEF ACCIS F-91405 Orsay France LSCE IPSL F-91191 Gif Sur Yvette France

Surface features such as furrows are here detected using high spatial resolution images such as those provided by IKONOS (pixel size 1 mx1 m in panchromatic mode) and WorldView-1 instruments (pixel size 0.5 mx0.5 m), through a new detection methodology based on image analysis. This methodology includes four different steps. First, segmentation of the whole image is performed in order to label each agricultural field individually. Then, for each field, mathematical morphological processes are applied (erosion followed by functional geodesic reconstruction) in order to enhance the image contrast. Then, an automatic thresholding process is applied to construct a binary image of the furrows or other features in the field. In order to reduce the noise due to the overlap between the classes of furrow and background, the a priori information that furrows are straight lines exhibiting regular patterns is introduced. The Hough transform is applied to detect straight lines (represented in polar coordinates) and furrow directions as accumulations on the angle axis in the Hough space. The proposed method was applied on a WorldView-1 image acquired over the Lokna catchment within the Plava watershed in Russia (around 180 km(2)) and validated against ground truth observations.

关键词： OPTICAL images IMAGE analysis thresholding algorithms WATERSHEDS

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Efficient foreground detection for real-time surveillance applications

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ELECTRONICS LETTERS 2013年第18期49卷 1143-1144页

作者： Gruenwedel, S. Petrovic, N. I. Jovanov, L. Nino-Casta-neda, J. O. Pizurica, A. Philips, W. Univ Ghent TELIN IPI iMinds B-9000 Ghent Belgium

The problem of foreground detection in real-time video surveillance applications is addressed. Proposes is a framework, which is computationally cheap and has low memory requirements. It combines two simple processing blocks, both of which are essentially background subtraction algorithms. The main novelty of the approach is a combination of an autoregressive moving average filter with two background models having different adaptation speeds. The first model, having a lower adaptation speed, models long-term background and detects foreground objects by finding areas in the current frame which significantly differ from the proposed background model. The second model, with a higher adaptation speed, models the short-term background and is responsible for finding regions in the scene with a high foreground object activity. The final foreground detection is built by combining the outputs from these building blocks. The foreground obtained by the long-term modelling block is verified by the output of the short-term modelling block, i.e. only the objects exhibiting significant motion are detected as real foreground objects. The proposed method results in a very good foreground detection performance at a low computational cost.

关键词： ELECTRONIC surveillance SECURITY systems DEMODULATION (Electronics) SURVEILLANCE detection SURVEILLANCE radar thresholding algorithms SIGNAL processing

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Influence of the interface trap location on the performance and variability of ultra-scaled MOSFETs

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MICROELECTRONICS RELIABILITY 2013年第9-11期53卷 1243-1246页

作者： Velayudhan, V. Gamiz, F. Martin-Martinez, J. Rodriguez, R. Nafria, M. Aymerich, X. Univ Autonoma Barcelona Dept Engn Elect E-08193 Barcelona Spain Univ Granada Dept Elect & Tecnol Comp E-18071 Granada Spain

The study reported herein examines the influence of the location of the interface traps along the channel in an nMOSFET on the device performance. Device simulations were performed to understand the effect of a single interface trap on the device band structure and electrical characteristics. The dependence of the biasing conditions on the study was also considered. Variability in the device performance due to the randomness in the trap location was also investigated. The study was helpful in identifying the critical device location where traps are more effective. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： METAL oxide semiconductor field-effect transistors -- Performance COMPUTER simulation ELECTRONIC instruments thresholding algorithms CHANNELS (Hydraulic engineering) ATOM trapping

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Multilevel thresholding Segmentation Based on Harmony Search Optimization

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JOURNAL OF APPLIED MATHEMATICS 2013年第unknown期2013卷 1-24页

作者： Oliva, Diego Cuevas, Erik Pajares, Gonzalo Zaldivar, Daniel Perez-Cisneros, Marco Univ Complutense Fac Informat Dept Ingn Software & Inteligencia Artificial E-28040 Madrid Spain Univ Guadalajara CUCEI CU TONALA Dept Ciencias Computac Guadalajara 44430 Jalisco Mexico

In this paper, a multilevel thresholding (MT) algorithm based on the harmony search algorithm (HSA) is introduced. HSA is an evolutionary method which is inspired in musicians improvising new harmonies while playing. Different to other evolutionary algorithms, HSA exhibits interesting search capabilities still keeping a low computational overhead. The proposed algorithm encodes random samples from a feasible search space inside the image histogram as candidate solutions, whereas their quality is evaluated considering the objective functions that are employed by the Otsu's or Kapur's methods. Guided by these objective values, the set of candidate solutions are evolved through the HSA operators until an optimal solution is found. Experimental results demonstrate the high performance of the proposed method for the segmentation of digital images.

关键词： MULTILEVEL models (Statistics) SEGMENTATION (Image processing) thresholding algorithms SEARCH algorithms MATHEMATICAL optimization HARMONY in music MUSICIANS

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