Boundary Fractal Dimensions from Sections of a Particle Profile

The fractal dimension of particles is commonly evaluated from complete particle boundaries. In this work, a study has been made of the self-similar nature of complete and incomplete boundary profiles of a range of morphologically different copper powders. Boundary images were captured from SEM micrographs of particle boundaries at a range of magnifications up to nearly 14000X. An algorithm was developed to compute the fractal dimension of boundary segments. This algorithm was tested against the Koch Island fractal, and was found to give excellent estimates of the fractal dimension. For the particle system studied, the boundary fractal was found to be sensitive to magnification with appreciable drops in value at high magnification. This demonstrates that the particles studied did not have true fractal boundaries and the use of fractal theory to study particle surface roughness must be used with caution.     

Modelling tunnel diodes for computer aided design

A SPICE macromodel for simulating tunnel diode current-voltage characteristic is presented. An example is given to verify the model.     

计算机辅助彩色立体图像生成中的误差分析与处理

柱透镜光栅的计算机辅助立体成像的基本原理是将二维序列图像进行切分和重组,使之以三维模型的形式展现,使合成的图像在柱透镜光栅下观察时具有"纵深感"。该项技术在广告、摄影、电影制作中具有广泛的应用。但是长期以来,在图像切分时并不能保证像素一定被整除,这意味着剩余像素的出现,合成的立体图像必然存在误差。如何处理剩余像素的问题一直是个难题,阻碍了该技术的推广。针对立体图像生成方法中的剩余像素问题,详尽地分析了误差的形成,并提出了强行取整算法和误差分散算法两种误差处理方法。实验表明,这两种算法能较好的处理剩余像素,增强了合成图像的立体效果,这将有助于立体成像技术的进一步推广。     

Fractal Dimensions of Correlation Clusters for Conformal Fields

The fractal dimensions of correlation clusters at the critical point of continuous phase transition are studied within the framework of conformal field theory. The generalized dimensions D_n(n = 2,3, …), the singularity strength a and its distribution f(α) are derived rigorously, and their meanings are discussed.     

Fractal Dimensions for Repellers of Maps with Holes

In this work we study the Hausdorff dimension and limit capacity for repellers of certain non-uniformly expanding maps f defined on a subset of a manifold. This subset is covered by a finite number of compact domains with pairwise disjoint interiors (the complement of the union of these domains is called hole) each of which is mapped smoothly to the union of some of the domains with a subset of the hole. The maps are not assumed to be hyperbolic nor conformal. We provide conditions to ensure that the limit capacity of the repeller is less than the dimension of the ambient manifold. We also prove continuity of these fractal invariants when the volume of the hole tends to zero.     

Obtaining Fractal Dimensions and Examining Boundaries by Coordinate Averaging

Problems with automated techniques for measuring boundary fractal dimensions using structured walks are described and a new method is proposed, coordinate averaging. The actual polygon generated by a structured walk is variable and depends upon the chosen starting point. This noise is apparent in the resulting Richardson plots. The use of multiple starting points enhances the Fast (equipaced) method but is less productive with the Hybrid (fixed step) method because the paths followed around the perimeter tend to converge. Coordinate averaging uses perimeters that have been mapped as a list of sequential coordinates. They are then examined by averaging every coordinate with an increasing number of neighbours. The resulting family of shapes progressively shed detail and can be used to generate fractal dimensions. Coordinate averaging appears to be free from the noise found with structured walks and is able to examine highly convoluted shapes. In addition it appears well suited to the examination of the homogeneity of boundaries and can follow the detailed evolution of individual features.     

An image source computer model for room acoustics analysis and electroacoustic simulation

A computer program for the determination of the impulse response of rooms, using the mirror image method, has been developed. It is intended for acoustical planning of auditoria and the simulation of sound fields. The computer also generates the necessary information for the automatic mixer, delay unit and reverberation unit, which makes it possible to change sound field simulations in a short time.The program allows arbitrary room shapes to be analyzed by representing curved surfaces with plane approximations. The program also calculates energy time gaps, radiation angles and angles of incidence for the investigated source and receiver positions. The absorption coefficients of the reflecting surfaces are also taken into account. The source and the receiver may be positioned anywhere in the room. Compared with other programs described in the literature, this program yields more information, necessary particularly for electroacoustic room acoustics simulation and acoustical planning.     

A computer aided system for research on the quantitative laser spectroscopy of ethylene

Spectral line strength, self- and N₂-broadened widths of 28_2,27–28_1,27 transition of ethylene v₇ band have been obtained at room temperature and were agree well with the results of theoritical calculation. With those spectral parameters, the temperature dependence of C₂H₄ absorption coefficients at CO₂laser transition 10P(14)were measured. The results showed that the temperature dependence of the linewidth was close to T^–0.4. A computer aided system was used so that the accuracy of the measurement was well improved than that we did before.     

Analysis of image of objective for formation of nanostructures by computer isophotometry method

The possibilities of using the computer isophotometry method to estimate the image quality of high-resolution projection objectives are considered. An experimental setup for measuring the point spread function is developed. A two-mirror objective of the Schwarzschild type with a numerical aperture of 0.36 designed for the use in an experimental nanolithographer is studied. Control measurements by the computer isophotometry method show that, at a wavelength of 13.4 nm, this objective is capable of resolving image features with a size of no larger than 50 nm.     

Automated Digital Image Based Measurement of Boundary Fractal Dimension for Complex Nanoparticles

There is a growing realization that complex nanoparticles produced by combustion reaction, precipitation, and spray technology using supercritical fluids, are fractally structured. The boundary fractal dimension is linked to the flow, packing and consolidation dynamics of nanopowders. It also contains information on the formation dynamics of the nanoparticles produced by various methods. Extraction of the fractal dimension information embodied in the nanoparticle's fractal structure is hampered by the lack of automated characterization algorithms for processing images of particles. This paper describes an efficient algorithm for analyzing digitized images of fractally structured nanoparticles and presents a computer program that automates the procedure using digital image processing techniques. The program functionality is demonstrated and discussed using digital images of typical pigment, ceramic and pharmaceutical powders.     

Fractal sorting vector-based least significant bit chaotic permutation for image encryption

The image's least significant bit(LSB) covers lots of the details that have been commonly used in image encryption analysis. The newly proposed fractal sorting vector(FSV) and FSV-based LSB chaotic permutation(FSV-LSBCP) is a novel chaotic image encryption cryptosystem introduced in this article. The FSV-LSBCP effectively strengthens the security of the cryptographic scheme concerning the properties of the FSV. Key analysis, statistical analysis, resistance differential attack analysis, and resistance to cropping attacks and noise attacks are the focus of the suggested image encryption cryptosystem. The security experiment shows that the cryptosystem is adequate to achieve the desired degree of security.     

Grey level on axis computer holograms for incoherent image processing

We present a method for the simple production of a pair of real non-negative pupil functions p?₁,p?₂, that act together to yield a bipolar system spread function P>(x) = |p₁|p² ? |p₂|p². The subtraction can be perf ormed by electronic means.     

泰曼-格林干涉仪干涉条纹计算机图像处理实验系统

介绍了利用CCD摄像头和Matlab图像处理软件与传统的泰曼-格林干涉仪相结合构建的干涉条纹计算机图像处理实验系统,实现了测量信号的自动化处理,可用于物理光学现场实验教学．     

Improvement of the conditions of use of a EDXRD diffractometer by means of computer aided position sensors

Abstract

The conditions of use of a EDXRD diffractometer have been made easier by means of a series of computer aided position sensors. These devices are able to detect and to measure with an accuracy of few micrometers any displacement of one of the main parts of the diffractometer with respect to a reference position. A special program has been made for this purpose.     

Strategies for baryon resonance analysis

The analytic properties of scattering amplitudes provide a meeting point for experimental and theoretical investigations of baryon resonances. Pole positions and residues allow for a parameterization of resonances in a well-defined way which relates different reactions. The recent progress made within the Jiilich model is summarized.     

Strategies for baryon resonance analysis

The analytic properties theoretical investigations of baryon of scattering amplitudes provide a meeting point for experimental and resonances. Pole positions and residues allow for a parameterization of resonances in a well-defined way which relates different reactions. The recent progress made within the Jiilich model is summarized.     

Boundary layer analysis for non-equilibrium phase transitions

In this review, we discuss some of the recent developments in understanding various boundary induced phase transitions in asymmetric simple exclusion processes using boundary layer analysis. The boundary layer analysis is shown to be useful in gaining a lot of physical insights regarding the formation of shock, the critical point and the dual boundary transition.     

采用连续/不连续单元边界元法的声学灵敏度分析

采用连续单元与不连续单元混合离散建模的方法,将源点与场点分别划分为连续单元与不连续单元,由于两种网格节点互不重合,从而可以有效避免边界元法中奇异积分的问题。该方法简单易执行,利于工程应用。将该边界元公式应用于声学灵敏度分析中,所得的公式可以用来计算设计参数的改变而导致的场点声压改变量,为验证这一方法的正确性,以脉动球为例进行声灵敏度计算,并与常单元方法比较,证实了该方法的准确性。