基于二值化计算鬼成像的盲水印方法

提出了一种基于二值化计算鬼成像的盲水印方法.首先将水印图像经计算关联成像加密系统加密,并将加密数据二值化,然后将其隐藏到宿主图像的离散余弦变换域,实现水印信息的嵌入.水印信息的提取和重建是隐藏和加密的逆过程,分别借助提取密钥和解密密钥获取水印信息.仿真实验证明,该方法具有很好的隐蔽性,在嵌入因子α=10时,嵌入水印仍具有较好的不可感知性,含水印图像的峰值信噪比在38 dB以上;另外,该方法也具有一定的容错能力,提取的加密数据错误率达20%时,重建的水印信息仍能分辨和识别;与传统的计算鬼成像相比,加密数据的二值化为水印嵌入提供了方便,但是并未对重建图像带来严重恶化,其相关系数相差不足0.1;水印信息的提取无需借助原始宿主图像,是一种盲提取方法.     

Creation of multi-frequency terahertz waves by optimized cascaded difference frequency generation

A new scheme which generates multi-frequency terahertz (THz) waves from planar waveguide by the optimized cascaded difference frequency generation (OCDFG) is proposed. A THz wave with frequency ω_T1 is generated by the OCDFG with two infrared pump waves, and simultaneously a series of cascaded optical waves with a frequency interval ω_T1 is generated. The THz wave with a frequency of M-times ω_T1 is generated by mixing the m-th-order and the (m+M)-th-order cascaded optical wave. The phase mismatch distributions of cascaded difference frequency generation (CDFG) are modulated by changing the thickness of planar waveguide step by step, thereby satisfying the phase-matching condition from first-order to high-order cascaded Stokes process step by step. As a result, the intensity of THz wave can be enhanced and modulated by controlling the cascading order of OCDFG.     

具有强剪切流等离子体中离子声波与涡旋的转化

研究了在具有剪切本底流的非磁化等离子体中离子声波的激发及其与涡旋的转化。从流体方程组出发，导出了描述低频静电扰动的微分方程组。采用非模方法，得到了扰动量的剪切傅里叶谐波分量随时间演化的方程组，并对方程组进行了数值分析。结果表明：在强剪切条件下，剪切旋涡可以转化为离子声波；同样地，离子声波也激发剪切旋涡。     

Two-dimensional models of threshold voltage and subthreshold current for symmetrical double-material double-gate strained Si MOSFETs

The two-dimensional models for symmetrical double-material double-gate(DM-DG) strained Si(s-Si) metal–oxide semiconductor field effect transistors(MOSFETs) are presented. The surface potential and the surface electric field expressions have been obtained by solving Poisson's equation. The models of threshold voltage and subthreshold current are obtained based on the surface potential expression. The surface potential and the surface electric field are compared with those of single-material double-gate(SM-DG) MOSFETs. The effects of different device parameters on the threshold voltage and the subthreshold current are demonstrated. The analytical models give deep insight into the device parameters design. The analytical results obtained from the proposed models show good matching with the simulation results using DESSIS.     

THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves

We propose a novel scheme for THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves (HSWs). The repeated frequency conversions are accomplished by oscillations of Stoke waves in resonant cavity (RC) where low-order Stokes waves (LSWs) are converted to high-order Stokes waves again and again. The continuous frequency conversions are accomplished by optimized cascaded difference frequency generation (OCDFG) where the poling periods of the optical crystal are aperiodic leading to the frequency conversions from low-order Stokes waves to high-order Stokes waves uninterruptedly and unidirectionally. Combined with the repeated and continuous frequency conversions, the optical-to-THz energy conversion efficiency (OTECE) exceeds 26% at 300 K and 43% at 100 K with pump intensities of 300 MW/cm².