粒子场全息分析中的自动判焦与自动阈值选择方法

本文提出一种新的自动判焦与自动阈值选择方法,并在由IBM/PC-XT计算和PCVISION plus图象板组成的系统上实现。通过对实际粒子场全息图的分析,表明该方法效果良好,是一种更一般的、适应性更广的方法。     

Digital particle holographic system for measurements of spray field characteristics

A digital particle holographic system for measurements of spray fields is presented. A double exposure hologram recording system with a synchronization system for time control is established, resulting in digital holograms that can be quickly recorded. To process recorded holograms, the correlation coefficient method is used for focal plane determination of particles. To remove noise and improve the quality of holograms and reconstructed images, a Wiener filter is adopted. The two-threshold and image segmentation methods are used for binary image transformation. For particle pairing, the match probability method is adopted. The proposed system is applied to a spray field, and three-dimensional velocities and sizes of spray droplets are measured. Measurement results from the digital holographic system are compared to those made by laser instruments, which prove the feasibility of the proposed in-line digital particle holographic system as a good measurement tool for spray droplets.     

基于霍夫变换与线性啁啾变换的粒子全息图分析方法研究

基于霍夫变换及线性啁啾变换,提出在空域及频域中分析数字全息图中颗粒粒径大小的方法.在对粒子全息图进行降噪滤波、边缘提取等预处理后,利用弦中点霍夫变换检测粒子的圆心位置,然后以圆心为起点径向扫描出归一化光强分布曲线,求出空域第一个极小值位置.对光强信号做傅里叶变换,结合线性啁啾变换做局部频谱细化,求出频域第一个极小值位置.利用所得极小值位置,代入公式,即可求解颗粒粒径大小.数值计算结果表明,对于粒子间距较大的粒子全息图,该方法误差在2.5%以内.     

Holographic particle sizing using Wigner–Ville distribution

A novel method for measuring size of small objects with high-aspect ratio from in-line holograms by using Wigner–Ville distribution (WVD) is proposed. The proposed method provides direct calculation of the particle size by using local spatial-frequency information at the half length of holograms being analyzed. Feasibility of this method is experimentally verified by analyzing in-line holograms of an optical fiber.     

Computer generated holograms using personal computers

Holography or the method of wave-front reconstruction to produce an image was introduced by D. Gabor in 1948. Normally a laser is necessary to produce holograms in the laboratory. This paper introduces the usage of the high resolution display of the IBM-PC and a graphics printer to generate holograms. The advantages of using this method are that holograms of real or fictitious objects can be made, since all objects can be represented by a collection of points and one does not need an elaborate set up to make the holograms. This method is also useful for making Fourier transform holograms, image plane holograms, spatial filters, optical elements, etc.^1,2     

Periodic orbits for classical particles having complex energy

This Letter revisits earlier work on complex classical mechanics in which it was argued that when the energy of a classical particle in an analytic potential is real, the particle trajectories are closed and periodic, but that when the energy is complex, the classical trajectories are open. Here it is shown that there is a discrete set of eigencurves in the complex-energy plane for which the particle trajectories are closed and periodic.     

Depth-of-focus reduction for digital in-line holography of particle fields

Poor axial precision caused, in part, by large depth of focus (tau) has been a vexing problem in extraction of particle position from digital in-line holograms. A simple method is proposed to combat this depth-of-focus difficulty. The method is based on decoupling of size and position information. With d, Delta, and lambda being particle diameter, CCD pixel size, and the wavelength, respectively, our main theoretical result is the reduction of tau from tau - d2/lambda to tau - Delta2/lambda for particles of known size. This result is confirmed in laboratory experiments with holograms of calibrated glass spheres.     

Three-dimensional solid particle positions in a flow via multiangle off-axis digital holography

We present a new development of digital off-axis (OA) holography for determining the instantaneous solid particle positions in a flow. This holographic imaging method uses a CCD camera for the simultaneous digital recording of two views of digital Fresnel OA holograms on the same support. The reconstruction is obtained numerically. The method provides two orthogonal views of the same flow area of interest at the same instant. It helps to overcome the depth of focus problem existing for the particle image reconstructions and that is inherent to the method. This method has the advantage of being simpler than the methods presently available, and it does not suffer from the flaws of in-line holographic configuration. Furthermore it is completely digital and thus avoids the cumbersome analysis following hologram recording. Digital holograms and digital reconstructions are obtained for solid particles of 200 mum moving into a stirred flow cell of 5 cm(3).     

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.     

Determination of depth-of-focus in lensless in-line digital particle holography

Lensless in-line digital particle holography (DPH) can be thought of as a special case of photography, and its depth of focus (DoF) characteristics combine those of both photography and holography. The effect of important parameters such as the pixel size and the number of pixels in a charge-coupled device (CCD), the object's distance, the wavelength of the laser, and the particle diameter on the DoF of a reconstruction image in lensless in-line DPH was investigated using simulation holograms. The DoF is directly proportional to the object distance and the particle size. As the wavelength of the laser increases, the DoF decreases. The DoF is inversely proportional to the pixel size and to the number of pixels in a CCD. Instead of expressing nonspecific proportional relationships for DoF, the DoF prediction equations for typical CCD cameras were obtained using DoF data from many simulation holograms and efficient data-fitting software. Finally, the DoF prediction equations were verified using real holograms from a calibration target for several cases. Good agreement between measured and predicted values was confirmed.     

Phase signature for particle detection with digital in-line holography

The spatial phase resulting from the digital reconstruction of an in-line hologram of a particle field is shown to yield a unique pattern that can be used for particle detection. This phase signature is present only when viewed along with the reference light. The existence of the phase pattern is verified computationally and confirmed in laboratory experiments with holograms of calibrated glass spheres. The phase signature provides an alternative to the widely used intensity method for particle detection.     

Hydrodynamic pair attractions between driven colloidal particles

Colloidal spheres driven through water along a circular path by an optical ring trap display unexpected dynamical correlations. We use Stokesian dynamics simulations and a simple analytical model to demonstrate that the path's curvature breaks the symmetry of the two-body hydrodynamic interaction, resulting in particle pairing. The influence of this effective nonequilibrium attraction diminishes as either the temperature or the stiffness of the radial confinement increases. We find a well-defined set of dynamically paired states whose stability relies on hydrodynamic coupling in curving trajectories.     

Cartesian Ovals as Phase Trajectories of Relativistic Charged Particles

For a relativistic charged particle interacting with a circularly polarized stationary electromagnetic wave running along a uniform magnetostatic field, it is shown that the plane on which the set of trajectories of the particle coincides with a set of Cartesian ovals can serve as a phase space, provided that certain conditions are fulfilled. The cases of both decelerated and accelerated waves are investigated, and the results obtained confirm the statement that the mentioned plane is the most natural phase surface for a particle in the system of fields under consideration.     

Chaotic motion of test particles in the Ernst space-time

Trajectories of test particles in the Ernst space-time are studied. The Poincaré surfaces of section are constructed and Lyapunov characteristic exponents are evaluated for a selected set of trajectories. This approach indicates that the number of isolating integrals is not sufficient to separate equations of motion and the particle trajectories are not integrable.     

Behavior of the warm ocean water at the south coast of Kyushu

The warm ocean water filaments are emanated periodically in winter from the meandering Kuroshio Current at the East China Sea. They bring the intermittent warm ocean water intrusion into the Kagoshima Bay well known as ‘Kyucho’ phenomenon. From the satellite SST images, the warm water intrusion is also observed at the Fukiage Seashore. In addition to the warm water intrusions, the cold-water mass at the Osumi Strait is observed. In this study, the numerical analysis is performed to understand these phenomena. A density current is calculated by a multi-leveled finite difference method (FDM). Then, particle trajectories are calculated by the Lagrangian particle tracking method by using the previous current result. Particles are dealt with as passive tracers to be a model of plankton and hyponeuston (i.e. larva, eggs or seeds) of an open sea. Calculated results of the warm water mass show similar features of the SST images, i.e. the warm water intrusions into the bay and the cold-water mass generation. The warm water intrusion occurs when it reaches the mouth of the bay or the edge of the coast. The cold-water mass is concerned with a horizontal vortex shed from the edge of the cape. The cold-water mass is produced in a stagnation region by a horizontal vortex rather than upwelling from the deep ocean. The particle trajectories have a tendency to pile up in the bay and a stagnation region behind of the peninsula. These results supply the fundamental knowledge that contributes to biological problems at the south of Kyushu in winter adequately.     

Focal plane location using integrated gray-level gradient method in digital particle holography

To accurately locate the focal plane of the object in digital particle holography, the integrated gray-level gradient method is presented. This method consists of a conventional edge-sharpness [Es] method and a new method, namely, overall-sharpness [Os] method which is an efficient supplement of the former. The respective scopes of application of above criterions were discussed by using numerical simulation holograms of particles. At last, the integrated gray-level gradient method was applied to the real holograms of dot array target, calibration target and glass bead. The experiment results demonstrate that this method can effectively extract the focal plane of particle.     

宽筛分煤粉颗粒间相互作用的数值研究

本文采用颗粒轨道模型,对不同直径的细小煤粉颗粒绕流单个球形大颗粒后的运动轨迹进行了数值模拟,研究了宽筛分条件下大颗粒的尾涡作用对小颗粒运动情况的影响．同时将计算结果同激光全息的实验结果进行了对照,二者符合得较好．结果表明,只有当煤粉颗粒的尺寸小到一定程度时,大颗粒的尾涡才对其运动轨迹产生显著影响．     

Localizing and Characterizing Colloidal Particles Scattering Using Lens-free Holographic Microscopy

Lens-free holographic microscopy could achieve both improved resolution and field of view(FOV), which has huge potential applications in biomedicine, fluid mechanics and soft matter physics. Unfortunately, due to the limited sensor pixel size, target objects could not be located to a satisfactory level. Recent studies have shown that electromagnetic scattering can be fitted to digital holograms to obtain the 3 D positions of isolated colloidal spheres with nanometer precision and millisecond temporal resolution. Here, we describe a lens-free holographic imaging technique that fits multi-sphere superposition scattering to digital holograms to obtain in situ particle position and model parameters: size and refractive index of colloidal spheres. We show that the proposed method can be utilized to analyze the location and character of colloidal particles under large FOV with high density.     

Modeling and experimental validation of hydrodynamics in an ultrasonic batch reactor

Simulation of hydrodynamics in ultrasonic batch reactor containing immobilized enzymes as catalyst is done. A transducer with variable power and constant frequency (24 kHz) is taken as source of ultrasound (US). Simulation comprises two steps. In first step, acoustic pressure field is simulated and in second step effect of this field on particle trajectories is simulated. Simulation results are compared with experimentally determined particle trajectories using PIV Lab (particle image velocimetry). Effect of varying ultrasonic power, positioning and number of ultrasonic sources on particle trajectories is studied. It is observed that catalyst particles tend to orientate according to pattern of acoustic pressure field. An increase in ultrasonic power increases particle velocity and also brings more particles into motion. Simulation results are found to be in agreement with experimentally determined data.