In this paper, taking its turbulent exchange coefficient as a function of the Lagrangian time scale and standard variance of the turbulence in atmosphere, the atmospheric dispersion PDF models are obtained on the basi...In this paper, taking its turbulent exchange coefficient as a function of the Lagrangian time scale and standard variance of the turbulence in atmosphere, the atmospheric dispersion PDF models are obtained on the basis of atmospheric diffusion K-theory. In the model the statistics of wind speed are directly used as its parameters instead of classic dispersion parameters. The bi- Gaussian PDF is derived in convective boundary layer (CBL), from the statistics of vertical velocity in both of the downdraft and updraft regions that are investigated theoretically in the other part of this paper. Giving the driven parameters of the CBL (including the convective velocity scale w* and the mixing depth h_i) and the time-averaged wind speed at release level, the PDF model is able to simulate the distribution of concentration released at any levels in the CBL. The PDF's simulations are fairly consistent with the measurements in CONDORS experiment or the results brought out by some numerical simulations.展开更多
Developing a watermarking method that is robust to cropping attack is a challenging task in image watermarking. The moment-based watermarking schemes show good robustness to common signal processing attacks and some g...Developing a watermarking method that is robust to cropping attack is a challenging task in image watermarking. The moment-based watermarking schemes show good robustness to common signal processing attacks and some geometric attacks but are sensitive to cropping attack. In this paper, we modify the moment-based approach to deal with cropping attack. Firstly, we find the probability density function （PDF） of the pixel value distribution from the original image. Secondly, we reshape and normalize the pdf of the pixel value distribution （PPVD） to form a two dimensional image. Then, the moment invariants are calculated from the PPVD image. Since PPVD is insensitive to cropping, the proposed method is robust to cropping attack. Besides, it also has high robustness against other common attacks. Theoretical analysis and experimental results demonstrate the effectiveness of the proposed method.展开更多
基金This paper supported by the National Natural Science Foundation of China under Grant No.49475247.
文摘In this paper, taking its turbulent exchange coefficient as a function of the Lagrangian time scale and standard variance of the turbulence in atmosphere, the atmospheric dispersion PDF models are obtained on the basis of atmospheric diffusion K-theory. In the model the statistics of wind speed are directly used as its parameters instead of classic dispersion parameters. The bi- Gaussian PDF is derived in convective boundary layer (CBL), from the statistics of vertical velocity in both of the downdraft and updraft regions that are investigated theoretically in the other part of this paper. Giving the driven parameters of the CBL (including the convective velocity scale w* and the mixing depth h_i) and the time-averaged wind speed at release level, the PDF model is able to simulate the distribution of concentration released at any levels in the CBL. The PDF's simulations are fairly consistent with the measurements in CONDORS experiment or the results brought out by some numerical simulations.
基金partially funded by the Australian Research Council(No.DP110102076)
文摘Developing a watermarking method that is robust to cropping attack is a challenging task in image watermarking. The moment-based watermarking schemes show good robustness to common signal processing attacks and some geometric attacks but are sensitive to cropping attack. In this paper, we modify the moment-based approach to deal with cropping attack. Firstly, we find the probability density function （PDF） of the pixel value distribution from the original image. Secondly, we reshape and normalize the pdf of the pixel value distribution （PPVD） to form a two dimensional image. Then, the moment invariants are calculated from the PPVD image. Since PPVD is insensitive to cropping, the proposed method is robust to cropping attack. Besides, it also has high robustness against other common attacks. Theoretical analysis and experimental results demonstrate the effectiveness of the proposed method.
