AGE method simulations of a turbulent far‐wake compared to spectral DNS

Turbulent flow simulation methods based on finite differences are attractive for their simplicity, flexibility and efficiency, but not always for accuracy or stability. This paper demonstrates that a good compromise is possible with the advected grid explicit (AGE) method. Starting from the same initial field as a previous spectral DNS, AGE method simulations of a planar turbulent wake were carried out as DNS, and then at three levels of reduced resolution. The latter cases were in a sense large‐eddy simulations (LES), although no specific sub‐grid‐scale model was used. Results for the two DNS methods, including variances and power spectra, were very similar, but the AGE simulation required much less computational effort. Small‐scale information was lost in the reduced resolution runs, but large‐scale mean and instantaneous properties were reproduced quite well, with further large reductions in computational effort. Quality of results becomes more sensitive to the value chosen for one of the AGE method parameters as resolution is reduced, from which it is inferred that the numerical stability procedure controlled by the parameter is acting in part as a sub‐grid‐scale model. Copyright © 2002 John Wiley & Sons, Ltd.     

Dextran-modified iron oxide nanoparticles

Dextran-modified iron oxide nanoparticles were prepared by precipitation of Fe（Ⅱ） and Fe（Ⅲ） salts with ammonium hydroxide by two methods. Iron oxide was precipitated either in the presence of dextran solution, or the dextran solution was added after precipitation. In the second method, the iron oxide particle size and size distribution could be controlled depending on the concentration of dextran in the solution. The nanoparticles were characterized by size-exclusion chromatography, transmission electron microscopy and dynamic light scattering. Optimal conditions for preparation of stable iron oxide colloid particles were determined, The dextran/iron oxide ratio 0-0,16 used in precipitation of iron salts can be recommended for synthesis of nanoparticles suitable for biomedical applications, as the colloid does not contain excess dextran and does not coagulate.     

Sensitivity of depolarized lidar signals to cloud and aerosol particle properties

Measurements from depolarized lidars provide a promising method to retrieve both cloud and aerosol properties and a versatile complement to passive satellite-based sensors. For lidar observations of clouds and aerosols, multiple scattering plays an important role in the scattering process. Monte Carlo simulations are carried out to investigate the sensitivity of lidar backscattering depolarization to cloud and aerosol properties. Lidar parameters are chosen to be similar to those of the upcoming space-based CALIPSO lidar. Cases are considered that consist of a single cloud or aerosol layer, as well as a case in which cirrus clouds overlay different types of aerosols. It is demonstrated that besides thermodynamic cloud phase, the depolarized lidar signal may provide additional information on ice or aerosol particle shapes. However, our results show little sensitivity to ice or aerosol particle sizes. Additionally, for the case of multiple but overlapping layers involving both clouds and aerosols, the depolarized lidar contains information that can help identify the particle properties of each layer.     

Improved holographic particle sizing by using absolute values of the wavelet transform

A new method for sizing particle from in-line particle holograms by using absolute values of the wavelet transform is proposed in order to improve accuracy in measurements. The proposed method provides direct calculation of the particle size by using spatial frequency information of a chirp signal at minima position of an envelope function. Simulation and experimental results are presented.     

短脉冲强激光在稀薄等离子体中传播时的电磁类孤立子

 采用二维粒子模拟方法，研究了短脉冲强激光在稀薄等离子体中传播时电磁类孤立子的产生和时空演化过程。通过分析电磁场与等离子体波的非线性能量交换和激光场的频率谱结构等，给出了电磁类孤立子形成的基本物理图像，讨论了等离子体参数对电磁类孤立子形成的影响。模拟结果表明：类孤立子的形成是由于局部电磁波振荡频率减小至等离子体频率引起的，初始等离子体密度越高越容易形成空间局域结构。     

偏滤器靶板磁预鞘层边界的离子流

利用流体力学模型研究了偏滤器等离子体条件下磁预鞘层边界离子流和预鞘层宽度之间的关系，并分析了粒子碰撞对预鞘层边界离子流的影响。由于粒子碰撞对离子的驱动效益，预鞘层边界离子流速度随着预鞘层宽度的增加而减少；只有当预鞘层宽度趋于零时，边界离子流沿磁力线的速度才趋近于离子声速。在固定预鞘层宽度的条件下，计算了预鞘层边界离子流速度与碰撞频率之间的函数关系。     

分离流动的脉冲热线测量方法研究与应用

1引言分离流动经常出现在许多实际流动中，对流体机械和飞行器产生重大影响。但由于这种流动具有方向性，变化快，给测量带来了困难。到目前为止，主要有以下三种测量方法：山激光多普勒测速治（＊D川；（2）飞行热线（F坊In含＊。卜w让e）；O）脉冲热线技术（PulsedAVire。‘脉冲热线”比“激光多普勒测速仪”价格低一个数量级，操作简单，是一种比较理想的测量技术。其原理最初由Baner山提出，随后经过BradburyP］，Eaton问，Castro＊和Fernholz问等人不断发展与完善，目前国外正推广应用在分离流动的研究中。但在国内，尚不多见其…     

Neutrino astronomy: Present and future

I briefly review the present and future status of the burgeoning field of neutrino astronomy. I outline the astrophysics and particle physics goals, design, and performance of the various current and proposed neutrino telescopes. Also described are present results and future expectations.     

Characterization of spherical particles using high-order neural networks and scanning flow cytometry

We retrieve the radius R, real n and imaginary k parts of the refractive index of homogeneous spherical particles using angular distribution of the light-scattering intensity. To solve the inverse light-scattering problem we use a high-order neural-network technique. The effect of network parameters on optimization is examined. The technique is evaluated for noise-corrupted input data at 0.6 μm<R<10.6 μm, 1.02<n<1.38, and 0<k<0.03. The errors of retrieval for nonabsorbing particles do not exceed 0.05 μm for radius and 0.015 for refractive index. The experimental verification is fulfilled by experimental data retrieved by means of a scanning flow cytometer. The light-scattering profiles of polystyrene beads and spherized red blood cells are processed with the high-order neural networks and a non-linear regression at Mie theory. The parameters retrieved by the high-order neural networks correlate well with the parameters retrieved by the least-square method.     

电子直线加速器束流均方根发射度变化方程

本文导出了考虑外场和束流效应后束流均方根发射度平方变化方程的一般表达式,并就仅考虑外场,仅考虑空间电荷场和仅考虑尾场等三种特殊情况进行了分析。