融合用户行为和内容的微博用户影响力方法

为了模拟信息在微博环境中的传播情况,根据微博用户行为(发布、关注、转发和评论等)和微博内容,提出一种融合用户行为和内容的微博用户影响力算法。通过对微博用户行为的分析,得到行为因子数据,进而计算出用户影响力的权值。利用微博用户内容建立词共现矩阵,继而运用狄利克雷分配(LDA)模型进行潜在主题分布的识别,通过KL(Kullback Leibler)散度的方法得到用户之间的相似性,最后结合用户影响力权值,得到用户的影响力。实验表明,此算法较为有效。     

Understanding dengue fever dynamics: a study of seasonality in vector-borne disease models

Dengue fever dynamics show seasonality, with the disease transmission being higher during the warmer seasons. In this paper, we analyse seasonally forced epidemic models with and without vector dynamics. We assume small seasonal effects and obtain approximations for the real response of each state variable and also for the corresponding amplitude and phase via decomposition of the sinusoidal forcing into imaginary exponential functions. The analysis begins with the simplest susceptible-infected-susceptible (SIS) model, followed by the simplest model with vector dynamics, susceptible-infected-susceptible for hosts and uninfected-vector (SISUV). Finally, we compare the more complex susceptible-infected-recovered (SIR) and susceptible-infected-recovered for hosts and uninfected-vector (SIRUV) models and conclude that the models give basically the same information when we replace, in the SIR model, the human infectivity by a function of both human and mosquito infectivities.     

Evaluation of Landsat 8 OLI imagery for unsupervised inland water extraction

The successful launch of the Landsat 8 satellite continues the Earth observation of the Landsat series, which has been taking place for nearly 40 years. With the increase in the band number and the improved spectral range compared with the previous Landsat imagery, it will be possible to expand the application of the new Landsat 8 imagery. The purpose of this study is to explore water extraction based on the new Landsat 8 Operational Land Imager (OLI) imagery. According to the specific inland water conditions (clear water, turbid water, and eutrophic water), a number of highly adaptable water indices are assessed for water extraction using Landsat OLI imagery. The results show that clear water is the easiest to extract among the different types of waterbodies, with the highest average accuracy of 97%. The highest-accuracy methods are the automated water extraction index for shadow pixels (AWEI_sh), the normalized difference water index using bands 4 and 7 (NDWI₄₇), and the normalized difference water index using bands 3 and 7 (NDWI₃₇), with accuracies of 98.55%, 95.50%, and 96.61%, corresponding to clear water, turbid water, and eutrophic water, respectively. Through the analysis of the different methods for optimal band selection, the seventh band OLI7 (shortwave infrared 2, SWIR-2) of Landsat OLI shows the best performance in water identification. When applying the water indices to water extraction, Otsu’s algorithm has been used to automatically select the water threshold. Using extensive experiments with Otsu’s algorithm and a manual method, it was found that Otsu’s algorithm can replace manual selection and has the ability to select an accurate threshold for water extraction.     

PolSAR anisotropic diffusion filter with a refined similarity measure and an adaptive fidelity constraint

The presence of speckle complicates the tasks of interpreting and analysing polarimetric synthetic aperture radar (PolSAR) images. The nonlinear anisotropic diffusion (AD) method has been found to perform well in removing image noise. In this article, we propose a new AD method for PolSAR speckle reduction. An iterative refinement method is employed to measure the similarity between pixels and construct the diffusion coefficient in the iteration process, by considering both information in the original speckled image and the restored image of the last iteration. In addition, to alleviate the over-smoothing problem the conventional AD methods often encounter, an adaptive fidelity constraint is added into the diffusion equation by considering local heterogeneity information and the amount of noise. Experiments on both simulated and real PolSAR images confirm the ability of the proposed method to both suppress speckle and retain image details.     

Appearance Harmonization for Single Image Shadow Removal

Shadow removal is a challenging problem and previous approaches often produce de‐shadowed regions that are visually inconsistent with the rest of the image. We propose an automatic shadow region harmonization approach that makes the appearance of a de‐shadowed region (produced using any previous technique) compatible with the rest of the image. We use a shadow‐guided patch‐based image synthesis approach that reconstructs the shadow region using patches sampled from non‐shadowed regions. This result is then refined based on the reconstruction confidence to handle unique textures. Qualitative comparisons over a wide range of images, and a quantitative evaluation on a benchmark dataset show that our technique significantly improves upon the state‐of‐the‐art.     

Leader-following consensus of nonlinear multi-agent systems with switching topologies and unreliable communications

In this paper, distributed leader-following consensus for a class of nonlinear multi-agent systems with switching topologies and unreliable communications is studied. Each possible topology contains a directed spanning tree rooted at the leader. Agents share the information only with their neighbors on some disconnected time intervals due to the unreliable communications. By designing suitable distributed controllers, all follower nodes asymptotically synchronize to the leader node if the communication rate is larger than a threshold value for each time interval. By using multiple Lyapunov functions theory and linear matrix inequalities technique, some sufficient conditions are given to guarantee the consensus. Moreover, based on the theoretical results, the admissible communication rate and convergence rate of the whole systems are adjusted by the feedback gain matrix, which provides helpful design guidelines in practical applications. Finally, a simulation example is given to verify the effectiveness of the proposed method.     

TO焦距测试与自动激光焊接系统

在分析BOSA器件结构的基础上,提出一种基于图像分析的TO焦距测试与自动激光焊接方案. TO由气缸驱动从初始点向上单步移动,通过图像系统采集光斑图像,并基于OpenCV分析,通过比较分析结果,得到期望的TO位置.移动T0使焦点落在插芯与圆方管体的贴合面,并在此处进行激光焊接.实验表明,该系统具有良好的准确性和实用性.     

A simple robust control for global asymptotic position stabilization of underactuated surface vessels

Global asymptotic stabilization of underactuated surface vessels is generally achieved only by designing complicated controllers. This paper proposes a very simple control law that globally asymptotically stabilizes the position of underactuated surface vessel to a desired constant location and its velocities to zero. The proposed controller is independent of velocity signals and is robust to model parameters. It neither includes an observer nor an adaptive/sliding‐mode law. Controller development and stability analysis rely on a novel Lyapunov function and LaSalle's theorem. Furthermore, by extending the proposed control strategy, a saturated control law is also obtained ensuring the semiglobal asymptotic stability of position error system. Effectiveness of the proposed control schemes is demonstrated by simulation examples. Copyright © 2017 John Wiley & Sons, Ltd.     

Enhanced charge generation in doped organic/organic p–n heterojunction for improving the performance of tandem organic light emitting diode

The doped organic/organic p–n heterojunctions have been applied as charge generation structure (CGS) in tandem organic light emitting diodes (TOLEDs). It is found that the field‐induced charge generation takes place more efficiently at the interface between Li₂CO₃ n‐doped bathocuproine (BCP:Li₂CO₃) and MoO₃ p‐doped 4,4′‐N ,N′‐dicarbazole‐biphenyl (CBP:MoO₃) than at the interface between BCP:Li₂CO₃ and MoO₃ p‐doped 4,4‐bis[N‐1‐naphthyl‐N‐phenylamino]biphenyl (NPB:MoO₃). It is because the process of electrons tunneling through the depletion zone from the highest occupied molecular orbit (HOMO) of CBP:MoO₃ to the lowest unoccupied molecular orbit (LUMO) of BCP:Li₂CO₃ is more efficient than that from the HOMO of NPB:MoO₃ to the LUMO of BCP:Li₂CO₃. Compared to the TOLED using the conventional CGS of 10‐nm BCP:Li₂CO₃/20‐nm NPB:MoO₃, the one using the CGS of 10‐nm BCP:Li₂CO₃/10‐nm CBP:MoO₃/10‐nm NPB:MoO₃ shows increased device performance. In addition, the interconnecting property of CGS of 10‐nm BCP:Li₂CO₃/x nm CBP:MoO₃/20 ? x nm NPB:MoO₃ shows a strong dependence on the thickness of CBP:MoO₃. We provide a new insight on optimizing Ohmic loss in the CGSs, useful for improving the performance of TOLEDs.     

A Hybrid Heat Rate Forecasting Model Using Optimized LSSVM Based on Improved GSA

Heat rate value is considered as one of the most important thermal economic indicators, which determines the economic, efficient and safe operation of steam turbine unit. At the same time, an accurate heat rate forecasting is core task in the optimal operation of steam turbine unit. Recently, least squares support vector machine (LSSVM) is being proved an effective machine learning technique for solving nonlinear regression problem with a small sample set. However, it has also been proved that the prediction precision of LSSVM is highly dependent on its parameters, which are hardly choosing for the LSSVM. In the paper, an improved gravitational search algorithm (AC-GSA) is presented to further enhance optimal performance of GSA, and it is employed to serve as an approach for pre-selecting LSSVM parameters. Then, a novel soft computing method, based on LSSVM and AC-GSA, is therefore proposed to forecast heat rate of a 600 MW supercritical steam turbine unit. It combines the merits of the high accuracy of LSSVM and the fast convergence of GSA in order to build heat rate prediction model and obtain a well-generalized model. Results indicate that the developed AC-GSA–LSSVM model demonstrates better regression precision and generalization capability.