3-D Shoreline Extraction from IKONOS Satellite Imagery

Shorelines are recognized as unique features on Earth. They have valuable properties for a diverse user community. At present, photogrammetry is the most popular technique used to capture a shoreline. With improved resolution and accuracy, commercial high-resolution satellite imagery is demonstrating a great potential in the photogrammetry application domain. One example is the utilization of IKONOS satellite imagery in shoreline extraction. IKONOS panchromatic imagery has a resolution of approximately one meter as well as the capabilities of stereo imaging. This article presents the results of an experiment in which we attempted to improve IKONOS Rational Functions (RF) for a better ground accuracy and to employ the improved RF for 3-D shoreline extraction using 1-meter panchromatic stereo images in a Lake Erie coastal area. Two approaches were investigated. One was to rectify the ground coordinates derived from vendor-provided RF coefficients using ground control points (GCPs). The other was to refine the RF coefficients using the GCPs. We compare the results from these two approaches. An assessment of the shoreline extracted from IKONOS images compared with the existing shoreline is also conducted to demonstrate the potential of the IKONOS imagery for shoreline mapping.     

海洋生态系统动力学研究的相关网上资源

分４部分介绍互联网上与海洋生态系统动力学研究有关的信息资源、主要网址及其主要内容：（１）海洋生态系统模拟研究;（２）海洋科学研究组织和国际研究计划;（３）网上新闻讨论组;（４）海洋生态杂志。     

关于台风风场研究进展的若干问题探讨

台风是对我国造成严重危害的中尺度天气系统,随着沿海地区经济的发展以及越来越多的海洋开发工程的进行,对台风的研究也日益受到重视。本文从台风的观测、理论和数值研究几个方面综合分析了台风研究中的若干问题,并对现阶段存在的问题进行了讨论。     

Difference-frequency ultrasound generation from microbubbles under dual-frequency excitation

The difference-frequency (DF) ultrasound generated by using parametric effect promises to improve detection depth owing to its low attenuation, which is beneficial for deep tissue imaging. With ultrasound contrast agents infusion, the harmonic components scattered from the microbubbles, including DF, can be generated due to the nonlinear vibration. A theoretical study on the DF generation from microbubbles under the dual-frequency excitation is proposed in formula based on the solution of the RPNNP equation. The optimisation of the DF generation is discussed associated with the applied acoustic pressure, frequency, and the microbubble size. Experiments are performed to validate the theoretical predictions by using a dual-frequency signal to excite microbubbles. Both the numerical and experimental results demonstrate that the optimised DF ultrasound can be achieved as the difference frequency is close to the resonance frequency of the microbubble and improve the contrast-to-tissue ratio in imaging.     

相变存储材料Ge1Sb2Te4和Ge2Sb2Te5薄膜的结构和电学特性研究

采用射频磁控溅射方法制备了两种用于相变存储器的Ge₁Sb₂Te₄和Ge₂Sb₂Te₅相变薄膜材料,对其结构、电学输运性质和恒温下电阻随时间的变化关系进行了比较和分析.X射线衍射(XRD)和原子力显微镜(AFM)的结果表明:随着退火温度的升高,Ge₁Sb₂Te₄薄膜逐步晶化,由非晶态转变为多晶态,表面出现均匀的、     

阶变折射率轴棱锥产生局域空心光束

提出利用折射率成阶跃性变化的轴棱锥产生局域空心光束(bottle beam).讨论了折射率沿径向成阶跃式减小或增加两种模型,从几何光学角度分析了它们产生bottle beam的原理,利用衍射积分理论数值模拟两种轴棱锥光传输的光场分布和不同距离处的二维光斑图,研究结果表明折射率沿径向阶跃减小的轴棱锥产生单个bottle beam,而折射率沿径向阶跃增加的轴棱锥产生具有周期再现的bottle beams.bottle beam在原子引导和囚禁、光学俘获及光镊等方面有广泛的应用, 因此本文的研究对bottle     

非稳腔主动式直接获取纳秒近似无衍射贝塞尔绿光

通过对基于轴棱锥的贝塞尔谐振腔和贝塞尔-高斯谐振腔的研究,设计了一台腔内倍频Nd:YAG纳秒近似无衍射贝塞尔绿光激光器. 非稳激光器谐振腔由轴棱锥和凸面镜组成. 实验采用单灯脉冲抽运激光增益介质Nd:YAG晶体,倍频晶体选用KTP. 当抽运电压为350 V时,由主动式直接产生纳秒近似零阶贝塞尔绿光,其脉冲宽度为55.1 ns,波长为532 nm,线宽为0.8 nm,近似无衍射零阶贝塞尔绿光的中心光斑直径为192 μm. 利用Fresnel-Kirchhoff 衍射积分和Fox-Li迭代法,通过数值计算得出     

(2+1)维 Korteweg-de Vries 方程的传播孤子及混沌行为

利用一个投射方程和变量分离法,得到了(2+1)维 Korteweg-de Vries (KdV) 方程的新显式精确解.根据得到的孤立波解,构造出 KdV 方程的传播孤子结构. 利用一个新的混沌系统研究了孤子的混沌行为.     

增强型AlGaN/GaN高电子迁移率晶体管高温退火研究

深入研究了两种增强型AlGaN/GaN高电子迁移率晶体管(HEMT)高温退火前后的直流特性变化.槽栅增强型AlGaN/GaN HEMT在500 ℃ N₂中退火5 min后,阈值电压由0.12 V正向移动到0.57 V,器件Schottky反向栅漏电流减小一个数量级.F注入增强型AlGaN/GaN HEMT在 400 ℃ N₂中退火2 min后,器件阈值电压由0.23 V负向移动到-0.69 V,栅泄漏电流明显增大.槽栅增强型器件退火过程中Schottky有效势垒     

Higher-harmonic focused-wave forces on a vertical cylinder

This paper considers higher-harmonic forces due to wave focusing on a vertical circular cylinder. A series of experiments has been conducted in a wave flume. The first six-harmonic components of the measured wave forces are analyzed using the scale-averaged wavelet spectrum. It is noted that due to the transient nature of focused (freak) waves, Fourier analysis would not provide equivalent information to that gleaned from the analyses used herein. The results for the experiments with very steep wave crests show significant amplitudes at the fourth and fifth harmonics. These harmonics exhibit amplitudes that are the same order as the second harmonic, but much larger than those of the third harmonic. The wavelet-based bicoherence is used to detect the quadratic nonlinearity of the measured forces. And the bicoherence spectra reveal the primary mathematical reason for the existence of the striking amplitudes of the fourth and fifth harmonics: the interaction between the lower-harmonic components couple more strongly with the fourth and fifth harmonics, thus the fourth and fifth harmonics glean more energy than those of the third-harmonic components. However, the physical explanation for this remains elusive.