共查询到18条相似文献,搜索用时 171 毫秒
1.
2.
由于不同海域上空气象条件的不同, 海上蒸发波导在大尺度海面上空发生时通常是区域性非均匀的, 这一特性使得该环境中的电波传播特性相对于水平均匀的蒸发波导环境情况而明显不同, 因此, 进行区域性非均匀的蒸发波导探测反演对正确预测电波传播特性及提高雷达系统的工作性能具有重要的意义. 考虑到实际应用中蒸发波导信息获取手段的多样性, 将中尺度数值气象模式MM5预报的区域性蒸发波导修正折射率剖面作为先验信息, 提出了一种含该先验信息的区域性非均匀蒸发波导的雷达海杂波后验概率估计模型. 该模型使用主分量分析法对蒸发波导的水平非均匀性进行参数化建模, 然后通过贝叶斯理论将修正折射率剖面参数的先验概率分布、后验概率分布和似然函数联系起来, 利用雷达海杂波实现蒸发波导剖面参数的最大后验概率估计反演. 通过我国东海海域的实际区域性非均匀蒸发波导反演测试, 表明该模型能够以更高的精度实现区域性非均匀蒸发波导的反演. 相似文献
3.
海洋蒸发波导自然现象对近海面电磁波的传播有重要影响,获取大面积海域蒸发波导的长时间统计分布规律,对于海上雷达、通信、制导等电磁系统的设计与应用,具有重要意义.针对现有单点局部观测方法的缺点,建立了基于美国环境预报中心再分析数据的大面积海域蒸发波导统计特性计算方法,利用太平洋气象浮标数据、北部湾海岛气象观测数据对分析方法的正确性进行了验证.利用该分析方法和最近18年的美国环境预报中心再分析数据,重点研究了西太平洋蒸发波导的统计规律,获得了蒸发波导高度在不同海域、不同月份的分布特性,建立了空间分辨率约为18
关键词:
蒸发波导
再分析数据
电磁波
统计特性 相似文献
4.
荧光显微成像技术具有标记能力强、信号强度高、实验成本低、成像过程简单且从活体到离体均可成像等特点,在肿瘤细胞成像、药物分布体内探测等生物学分析成像研究中应用广泛,但如何同时兼具宽视场和高分辨率是当前荧光显微成像领域的一大难点.平面硅波导被发现可实现超薄样品大范围成像,然而其需要溅射沉积或是离子束刻蚀等制备工艺,相关工艺复杂且设备昂贵.本文设计了一种基于皮秒激光直写的平面波导型荧光显微装置,利用皮秒激光刻蚀玻璃表层快速制备微米级沟槽,进一步通过旋涂SU-8光刻胶实现低成本、批量化制备玻璃基平面波导.通过调整激光加工功率、频率、扫描速度等参数可以定制波导直径和深度.采用罗丹明B荧光分子的显微探测实验,验证了该激光直写玻璃基平面波导完全满足高分辨率和大视场的生物成像需要,这种简易快速的加工手段能够有效提升荧光成像领域的经济效益和社会效益. 相似文献
5.
采用数值模拟和理论分析方法,研究了圆波导内置n-Si探测结构对X波段几种常用电磁波模式的电场响应。首先基于强电场下的热载流子效应,设计了一种利用n-Si进行高功率脉冲实时测量的圆波导探测结构。接着采用三维并行电磁场时域有限差分方法,模拟研究并分析了TE11(两种极化方向)、TM01和TE01模式作用下圆波导探测结构内的横向电场分布特点。结果表明:不同模式下探测芯片内的横向电场均以径向电场为主,径向和角向电场幅度比约为10,而芯片在圆波导内引入的横向电场驻波比均不大于1.3。最后推导了圆波导探测结构在不同模式电场作用下的灵敏度表达式,理论分析指出了探测结构的最大承受功率与圆波导模式有关,最高可达422MW,响应时间则均为ps量级,初步证实了该探测结构可用于X波段百MW级脉冲波源在线探测的可行性。 相似文献
6.
7.
《物理学报》2016,(19)
利用角锥棱镜将准直飞秒高斯光束转变为飞秒贝塞尔光束,利用飞秒贝塞尔光束在石英玻璃样品中刻写了单芯和双芯光波导.实验中首先使用无像散的脉宽50 fs的贝塞尔激光脉冲在石英玻璃中刻写出单芯光波导,研究了波导直径和折射率改变量随激光脉冲能量和脉冲个数的变化关系.通过旋转角锥棱镜,在飞秒贝塞尔光束中引入像散,利用像散飞秒贝塞尔光束在石英玻璃中刻写了双芯光波导.实验发现,当角锥棱镜的转角为1?时,可以制备出双芯间距仅为5.6μm的双芯光波导.当双芯波导沿某一方向移动时,在近场可观察到从双芯输出的光强出现周期性的亮暗变化,这应是由双芯间距较小导致的.当角锥棱镜的转角增大至3?和5?时,制备的波导双芯之间的间距分别增大至9.1μm和16.1μm,此时没有观察到双芯光强随位置改变的往复变化.本文刻写的双芯光波导可用作高灵敏度差分位移传感器(可探测的最小位移小于3μm).与传统的单芯波导的位移传感器相比,双芯波导差分位移传感器一方面大幅提高了探测的灵敏度和信噪比;另一方面也降低了高灵敏度位移传感器的装配难度. 相似文献
8.
9.
10.
11.
Anna Paola Caricato Armando Luches 《Applied Physics A: Materials Science & Processing》2011,105(3):565-582
The matrix-assisted pulsed laser evaporation (MAPLE) technique offers an efficient mechanism to transfer soft materials from
the condensed to the vapor phase, preserving the versatility, ease of use and high deposition rates of the pulsed laser deposition
(PLD) technique. The materials of interest (polymers, biological cells, proteins, …) are diluted in a volatile solvent. Then
the solution is frozen and irradiated with a pulsed laser beam. Here, important results of MAPLE deposition of polymer, biomaterials
and nanoparticle films are summarized. Finally, the MAPLE mechanism is discussed. A review of experimental and theoretical
works points out that the simple model of individual molecule evaporation must be abandoned. Solute concentration, solubility,
evaporation temperature of solvents, laser pulse power density and laser penetration depth emerge as important parameters
to explain the morphology of the MAPLE-deposited films. 相似文献
12.
Experimental verification of effect of horizontal inhomogeneity of evaporation duct on electromagnetic wave propagation 下载免费PDF全文
《中国物理 B》2015,(4)
The evaporation duct which forms above the ocean surface has a significant influence on electromagnetic wave propagation above 2 GHz over the ocean. The effects of horizontal inhomogeneity of evaporation duct on electromagnetic wave propagation are investigated, both in numerical simulation and experimental observation methods, in this paper. Firstly, the features of the horizontal inhomogeneity of the evaporation duct are discussed. Then, two typical inhomogeneous cases are simulated and compared with the homogeneous case. The result shows that path loss is significantly higher than that in the homogeneous case when the evaporation duct height(EDH) at the receiver is lower than that at the transmitter. It is also concluded that the horizontal inhomogeneity of the evaporation duct has a significant influence when the EDH is low or when the electromagnetic wave frequency is lower than 13 GHz. Finally, experimental data collected on a 149-km long propagation path in the South China Sea in 2013 are used to verify the conclusion. The experimental results are consistent with the simulation results. The horizontal inhomogeneity of evaporation duct should be considered when modeling electromagnetic wave propagation over the ocean. 相似文献
13.
P. Martinez-Torres J. J. Alvarado-Gil 《The European physical journal. Special topics》2008,153(1):65-67
The analysis of dynamics of the evaporation process of a
solvent on top of a substrate is investigated using photothermal techniques.
The method consists on the illumination of an opaque metallic substrate with
a modulated laser and the detection of the heating on the illuminated zone
using photoacoustics. It is shown that at the last stage of the process the
formation of the meniscus must be taken into account. In order to analyze
the experimental data an effective model for the liquid layer is considered
as well as the slowing down of the rate of evaporation due to the meniscus. 相似文献
14.
Spurious illumination penetrating into a gas duct adversely affects the performance of a laser gage measuring the concentration of solid particles dispersed in the air flow. The noise and gas duct vibration caused by the noise and vibration of the flow driver and other sources mechanically connected to the gas duct modulate the spurious radiation so that it may generate a signal that is perceived as a useful one by a photodetector. The noise-and vibration-modulated spurious illumination, as well as its optical-to-electric conversion with consideration for the spectral characteristics and the connection of the photodetector to the laser gage, is analyzed. From the amplitude and frequency properties of real noise and vibration sources causing the gas duct walls, on which the laser gage is mounted, to vibrate, the effect of the parasitic illumination is estimated. The operating parameters of a laser gage with double amplitude modulation and subsequent double synchronous detection, which make it possible to considerably improve its noise immunity, are proposed. 相似文献
15.
Investigation on global positioning system signal scattering and propagation over the rough sea surface 下载免费PDF全文
This paper is devoted to the study of polarization
properties, scattering properties and propagation properties of
global positioning system (GPS) scattering signal over the rough sea
surface. To investigate the polarization and the scattering
properties, the scattering field and the bistatic scattering
coefficient of modified Kirchhoff approximation with using the
tapered incident wave is derived in detail. In modeling the
propagation properties of the GPS scattering signal in the
evaporation duct, the initial field of parabolic equation
traditionally computed by the antenna pattern with using fast
Fourier transform (FFT) is replaced by the GPS scattering field. And
the propagation properties of GPS scattering signal in the
evaporation duct with different evaporation duct heights and
elevation angles of GPS are discussed by the improved discrete mixed
Fourier transform with taking into account the sea surface
roughness. 相似文献
16.
The cavity formation during laser pulse heating of steel, nickel, and tantalum is examined and evaporation rate from the cavity surface is predicted. The mushy zones generated across the vapor–liquid and liquid–solid phases are modeled using the energy method. Temperature-dependent thermal properties are accommodated in the analysis and the laser pulse shape resembling the actual laser pulse is employed in the simulations. A numerical scheme using the control volume method is used to predict the cavity size, recession velocity of the vapor front, and temperature field in the laser irradiated region. It is found that cavity depth for steel is the largest, then follows nickel and tantalum. The recession velocity of the vapor front is high for steel due to the low evaporation temperature and latent heat of evaporation of steel. 相似文献
17.
18.
Near- and mid-infrared laser monitoring of industrial processes, environment and security applications 总被引:3,自引:0,他引:3
Ulrike Willer Mohammad Saraji Alireza Khorsandi Peter Geiser Wolfgang Schade 《Optics and Lasers in Engineering》2006,44(7):699
The advantages of infrared laser monitoring in terms of sensitivity, selectivity and the ability of non-intrusive detection of gases are reviewed. Emphasis is laid on direct absorption spectroscopy and evanescent-field spectroscopy. The performance of the latter for gas detection in the near-infrared is demonstrated for the analysis of volcanic gases. For industrial process control, direct mid-infrared absorption spectroscopy is used to detect CO in the high-temperature atmosphere of a glass melting furnace. For both applications portable, stable, rugged and easy-to-handle laser systems are needed. Mid-infrared absorption spectroscopy is also applied to detect different explosives. Material evaporation is achieved by plasma generation with a pulsed laser at high repetition rate. Energetic materials contain high concentrations of nitrogen; therefore NO is present in the generated plasma. However, the rate at which NO is produced varies in a highly characteristic manner for different energetic materials. This enables the distinction between different types of explosives. 相似文献