The key to narrow-band interference excision in frequency domain is to determine the excision thresh- old in direct-sequence spread-spectrum （DS-SS） systems. The excision threshold is a non-linear function related t...The key to narrow-band interference excision in frequency domain is to determine the excision thresh- old in direct-sequence spread-spectrum （DS-SS） systems. The excision threshold is a non-linear function related to the number and the power of interference, and attempting to get the exact relation of threshold related to the number and the power of interference is almost impossible. The N-sigma algorithm determines the excision threshold using subsection function; however, the excision threshold determined by this method is not exact. A new method to determine the threshold of N-sigma algorithm is proposed. The new method modifies the scale factor N by use of the membership function. The threshold determined by this method is consecutive and smooth, and it is closer to the fact than that of the initial N-sigma algorithm. The GPS signal and single-tone （CW） interference （that is, typical narrow-band interference） are implemented in the simulation, and the results are presented to demonstrate the validity of the new algorithm.展开更多
This paper presents a secure spread-spectrum watermarking algorithm for digital images in discrete wavelet transform (DWT) domain. The algorithm is applied for embedding watermarks like patient identification /source ...This paper presents a secure spread-spectrum watermarking algorithm for digital images in discrete wavelet transform (DWT) domain. The algorithm is applied for embedding watermarks like patient identification /source identification or doctors signature in binary image format into host digital radiological image for potential telemedicine applications. Performance of the algorithm is analysed by varying the gain factor, subband decomposition levels, size of watermark, wavelet filters and medical image modalities. Simulation results show that the proposed method achieves higher security and robustness against various attacks.展开更多
南海中央海盆海底扩张活动结束之后,出现了频繁的岩浆活动。由于海盆被海水覆盖,针对活跃的岩浆活动开展实测调查非常困难。本文利用二维地震剖面资料,结合拖网样品资料及有关钻探资料的研究成果,在建立岩浆活动与沉积作用关系模型的基...南海中央海盆海底扩张活动结束之后,出现了频繁的岩浆活动。由于海盆被海水覆盖,针对活跃的岩浆活动开展实测调查非常困难。本文利用二维地震剖面资料,结合拖网样品资料及有关钻探资料的研究成果,在建立岩浆活动与沉积作用关系模型的基础上,通过解释地震剖面反射特征和地震相特征,较全面地分析了南海中央海盆扩张期后岩浆活动的特征与期次。结果表明,南海中央海盆的岩浆活动具有脉动期,形成大量的海底山和岩浆底辟,即以多期次间隙性喷发和浅层侵入为特征。南海中央海盆后扩张期的岩浆活动主要有4个期次,其中11.6、7.5、5.3 Ma 3个期次的分析结果与岩石样品的测年结果吻合,而且进一步确定1.6 Ma左右的岩浆活动时间较长,一直延续至近代,分布范围广;2.6~1.6 Ma期间曾被认为是南海中央海盆岩浆活动静默期,本研究首次发现岩浆活动的踪迹;这一时期既有一次性活动形成的岩浆底辟和海底火山,也有通过多次火山活动而形成的规模较大的岩浆底辟和海底火山。展开更多
文摘The key to narrow-band interference excision in frequency domain is to determine the excision thresh- old in direct-sequence spread-spectrum （DS-SS） systems. The excision threshold is a non-linear function related to the number and the power of interference, and attempting to get the exact relation of threshold related to the number and the power of interference is almost impossible. The N-sigma algorithm determines the excision threshold using subsection function; however, the excision threshold determined by this method is not exact. A new method to determine the threshold of N-sigma algorithm is proposed. The new method modifies the scale factor N by use of the membership function. The threshold determined by this method is consecutive and smooth, and it is closer to the fact than that of the initial N-sigma algorithm. The GPS signal and single-tone （CW） interference （that is, typical narrow-band interference） are implemented in the simulation, and the results are presented to demonstrate the validity of the new algorithm.
文摘This paper presents a secure spread-spectrum watermarking algorithm for digital images in discrete wavelet transform (DWT) domain. The algorithm is applied for embedding watermarks like patient identification /source identification or doctors signature in binary image format into host digital radiological image for potential telemedicine applications. Performance of the algorithm is analysed by varying the gain factor, subband decomposition levels, size of watermark, wavelet filters and medical image modalities. Simulation results show that the proposed method achieves higher security and robustness against various attacks.
文摘南海中央海盆海底扩张活动结束之后,出现了频繁的岩浆活动。由于海盆被海水覆盖,针对活跃的岩浆活动开展实测调查非常困难。本文利用二维地震剖面资料,结合拖网样品资料及有关钻探资料的研究成果,在建立岩浆活动与沉积作用关系模型的基础上,通过解释地震剖面反射特征和地震相特征,较全面地分析了南海中央海盆扩张期后岩浆活动的特征与期次。结果表明,南海中央海盆的岩浆活动具有脉动期,形成大量的海底山和岩浆底辟,即以多期次间隙性喷发和浅层侵入为特征。南海中央海盆后扩张期的岩浆活动主要有4个期次,其中11.6、7.5、5.3 Ma 3个期次的分析结果与岩石样品的测年结果吻合,而且进一步确定1.6 Ma左右的岩浆活动时间较长,一直延续至近代,分布范围广;2.6~1.6 Ma期间曾被认为是南海中央海盆岩浆活动静默期,本研究首次发现岩浆活动的踪迹;这一时期既有一次性活动形成的岩浆底辟和海底火山,也有通过多次火山活动而形成的规模较大的岩浆底辟和海底火山。
