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Search Results: 1 - 10 of 44010 matches for " Wu Jitao "
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Texture segmentation based on the use of the structure tensor and the wasserstein distance

xiexiaozhen,wu jitao,

中国图象图形学报 , 2010,
Abstract: 基于区域的非参数活动轮廓模型被广泛地应用于图像分割领域。在结构张量和图像灰度直方图基础上建立的新模型就属于这个范畴, 它被用于灰度和彩色纹理图像的分割。首先,对经典的结构张量进行扩展,使其能表达原始纹理图像的梯度信息和色彩信息。利用扩展的结构张量,使一幅图像生成多个特征通道,从而提取更多的纹理特征。然后,在各个通道中,利用像素点的局部灰度直方图的Wasserstein距离信息分割图像,使图像不同分割区域的灰度分布近似同态。最后,为了有效地降低模型的数值计算复杂度,一些数值计算技巧被引入模型的计算过程,产生了很好的效果。通过大量的实验对比,利用新模型能得到更精确、更稳定的分割结果。
Research on calculation Method of Fractal Dimension Based Topographic Data

Wang Qiao,Wu Jitao,

中国图象图形学报 , 1997,
Abstract: The expression and analysis of topographic data is a difficult question to deal with in the automatic treatmenting of topographic data. In this paper, some new calculation methods of fractal dimension based topographic data are proposed after researching general fractal theory, related characters of these methods are discussed and some actual examples are given lastly.
Region-based active contour model improving the signed pressure force function

Su Rina,Wu Jitao,

中国图象图形学报 , 2011,
Abstract: By using the local regional information which has the ability to enhance the image, a new SPF function has been defined. The edge stopping function in the GAC model is replaced by the SPF function, and a new region-based active contour model is put forward by improving the GAC model. Therefore, images with intensity inhomogeneities and weak boundaries can be processed. The Selective Binary and Gaussian Filtering Level Set (SBGFRLS) method is continuously used in the new model which is simplified by avoiding the process of reinitializing the level set function. Experiments on real and synthetic images indicate that the new model has the same segmentation results as the LBF model, while the computational efficiencies improve significantly. The new model not only can segment images with intensity inhomogeneities and weak boundaries, but also has the properties such as sub-pixel accuracy, anti-noise nature, selective local or global segmentation, etc.
A novel terahertz time-domain spectroscopic endoscope based on a single photoconductive antenna chip
Jitao Zhang
Physics , 2013,
Abstract: The common terahertz time-domain spectroscopy (THz-TDS) based on photoconductive antenna (PCA) needs two separate PCA chips. One PCA works as an emitter, and the other works as a receiver. For a reflection-type measurement, the technique called 'attenuated total reflection' usually is needed to enhance the reflection sensitivity. These make the system bulk and complicated for the reflection-type measurement. In this paper, we propose a novel THz-TDS endoscope that is specifically designed for reflection-type measurement. This THz-TDS endoscope is benefited from an integrated photoconductive antenna (we call it iPCA), which integrates the emitter and receiver on a single antenna chip. Therefore, the dimension of the endoscope can be shrunk as much as possible for practical usage. We present the design and working principle of this THz-TDS endoscope in details. It may open a promising way for the THz-TDS application in biomedical fields.
Enhanced terahertz radiation from an elliptical-beam-illuminated sawtooth photoconductive antenna: design and numerical analysis
Jitao Zhang
Physics , 2014,
Abstract: The enhanced terahertz radiation from a new photoconductive antenna (PCA) has been predicted by numerical simulation. Different from the conventional PCA, the proposed PCA has electrodes with sawtooth structures on the edge, which will introduce stronger localized bias field than common electrode (e.g. strip-line structure). In addition, the elliptical beam of the laser source is used to illuminate the sawtooth structure of the PCA, so that the effective region of the terahertz excitation is enlarged and higher laser power can be applied before saturation effect occurs. The design of the proposed PCA is presented, and its performance is predicated by numerical analysis based on the full-wave finite-difference-time-domain method. The simulated result shows that, comparing with a conventional PCA, the proposed PCA achieves $1.4$ times enhancement of the THz radiation field(i.e. peak of the time-domain THz pulse) at the same condition. Further enhancement as high as $2$ times can be achieved when considering the upper limit of the power density of the incoming laser beam.
Numerical analysis of the emission properties of terahertz photoconductive antenna by finite-difference-time-domain method
Jitao Zhang
Physics , 2014,
Abstract: The emission properties of terahertz(THz) photoconductive antenna (PCA) have been numerically studied by three-dimensional finite-difference-time-domain method based on the full-wave model. The dependence of the THz radiation on various parameters, such as laser power, bias voltage, substrate's material, pulse duration of the laser, beam spot's size, dimension of the antenna, were comprehensively simulated and analyzed. This work, on one hand, reveals the internal relationship between the THz radiation of a PCA and the involved parameters, so that one can have a better understanding of the PCA. On the other hand, it can inspire new PCA's design that aims at improved performance, such as high radiation power, enhanced optics-to-THz conversion efficiency, and broadband spectrum.
Design and performance of a terahertz photoconductive antenna with nano-crossfinger structure
Jitao Zhang
Physics , 2014,
Abstract: Improving terahertz(THz) radiation power and/or optics-to-THz efficiency of the photoconductive antenna(PCA) is widely recognized as one of the most attractive and challenging missions in THz community. In this work, the design of a THz PCA with nano-crossfinger structure in the active region is proposed. The THz radiation properties of this PCA was demonstrated by finite-difference-time-domain method based on full-wave model. As a comparison, the PCA with nano-finger structure that promises enhanced THz radiation than conventional PCA was also analyzed numerically. The results indicate that the nano-crossfinger PCA can radiate even higher THz field than the nano-finger PCA, primarily due to the enhanced bias field within the nano-structure.
Characterization of the terahertz photoconductive antenna by three-dimensional finite-difference time-domain method
Jitao Zhang
Physics , 2014,
Abstract: We numerically describe the physical mechanism underlying the terahertz photoconductive antenna (PCA) by the finite-difference time-domain method in three-dimension. The feature of our approach is that the multi-physical phenomena happening in the PCA, such as light-matter interaction, photo-excited carrier dynamics and full-wave propagation of the THz radiation, are considered and embodied in the simulation. The method has been verified by comparing with existing commercial softwares. In addition, we use this simulation tool to characterize the parameter-dependent performance of a PCA,thereby the design of novel PCA with enhanced optics-to-THz efficiency can be inspired.
The C-V model with motion factor

WANG Xiaotao,WU Jitao,

中国图象图形学报 , 2010,
Abstract: One advantage of C-V model among the variational level set methods is that it can detect image boundaries which were not defined by gradient. However, when detecting these type boundaries, the C-V model only consider the mean value of each region without local information, so though the C-V model can get non-gradient defined image boundary, its segmentation result contains errors. The above problem is solved by importing the motion factor to the C-V model in this paper. Where, the motion factor is defined as a function of local convexities of image. By adjusting parameters of the motion factor, the novel model can adjust the height of its 0-level set, i.e., can make the 0-level set get close to the plane which the target belongs to, so can eliminate the partition errors. We present the partial differential model, and experiments validate the quality of the segmentations obtained.


红外与毫米波学报 , 1991,
Abstract: SiC_xN_y: H thin films with continuously variable compositions have been preparedby using the plasma-enhanced chemical vapor-deposition (PECVD) method. The composition of the films is analyzed by using FTIR and AES. The experimental results show that the ratio of N/(N+C)in the SiC_xN_y: H films can be obtained rapidly from the FTIR absorption spectrum. Analyses of films thermally annealed rapidly by using FTIR indicate that the passivated films, which have been prepared by PECVD, have good thermal stabilities.
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