微型金柱腔中原位成型制备微孔泡沫

 报道了在μm量级圆柱状金柱腔中原位成型制备微孔泡沫的方法。在直径400 μm、长度700 μm、壁厚20 μm、两端开口的金柱腔中原位成型成功制备出密度为50 mg·cm^-3、蜂窝直径不超过1 μm的多元丙烯酸酯聚合物微孔泡沫。干燥过程中泡沫没有明显收缩,在柱腔中填充紧密,无需后续机械加工。     

Multiple scattering effect in the Young-like interference pattern of an optical wave scattered by a double cylinder

The plane-polarized laser wave with a wavelength of 441.6 nm collides with two close parallel cylinders, called a double cylinder, each of a diameter about 100 or 200 nm at normal incidence. The measured angular distribution of the scattered light intensity, called a Young-like interference pattern, is compared with the rigorous theoretical calculation over a wide range of scattering angles. We have experimentally confirmed the multiple scattering effect of the wave between cylinders in an exact way.     

用全固态激光器和一维CCD测定微粒粒径

建立了一套利用线阵CCD探测散射光强从而测定粒径的实验装置.该装置采用线阵CCD取代传统的同心环探测器，并采用一台小尺寸全固态绿光激光器取代传统的He-Ne激光器.理论上采用全Mie氏散射理论，自行编写了实验数据的计算机拟合程序，可以由实验测得的散射光强角分布反演求出粒径分布信息.对粒径分别为4.91 μm和9.88 μm的聚苯乙烯小球均取得了良好的粒径测量结果.该装置被证实可用于测定的粒径范围为0.7 μm～44.0 μm.     

Direkte Beobachtung einzelner magnetischer Flußquanten in supraleitenden Hohlzylindern. I

By use of electron interferometry in connection with the Aharonov-Bohm effect it was possible to observe directly single magnetic flux quanta, trapped in superconducting tubes with an inner diameter ranging from 0.5 μm to 1 μm. The flux coincided with the fluxoid quantumhc/2e within the experimental error of 4% for thick walled cylinders. The flux distribution along the cylinders was found to be not constant in time and space. Flux quanta down to 8 μm length have been observed. The method permits the observation of flux creep of single flux quanta.     

Monte Carlo simulation of photon transport in a randomly oriented sphere-cylinder scattering medium

A Monte Carlo simulation tool for simulating photon transport in a randomly oriented sphere-cylinder medium has been developed. The simulated medium represents a paper pulp suspension where the constituents are assumed to be mono-disperse micro-spheres, representing dispersed fiber fragments, and infinitely long, straight, randomly oriented cylinders representing fibers. The diameter of the micro-spheres is considered to be about the order of the wavelength and is described by Mie scattering theory. The fiber diameter is considerably larger than the wavelength and the photon scattering is therefore determined by an analytical solution of Maxwell’s equation for scattering at an infinitely long cylinder. By employing a Stokes–Mueller formalism, the software tracks the polarization of the light while propagating through the medium. The effects of varying volume concentrations and sizes of the scattering components on reflection, transmission and polarization of the incident light are investigated. It is shown that not only the size but also the shape of the particles has a big impact on the depolarization.     

Theoretical studies on particle shape classification based on simultaneous small forward angle light scattering and aerodynamic sizing

Particle shape contributes to understanding the physical and chemical processes of the atmosphere and better ascertaining the origins and chemical compositions of the particles. The particle shape can be classified by the aspect ratio,which can be estimated through the asymmetry factor measured with angularly resolved light scattering. An experimental method of obtaining the asymmetry factor based on simultaneous small forward angle light scattering and aerodynamic size measurements is described briefly. The near forward scattering intensity signals of three detectors in the azimuthal angles at 120?offset are calculated using the methods of T-matrix and discrete dipole approximation. Prolate spheroid particles with different aspect ratios are used as the shape models with the assumption that the symmetry axis is parallel to the flow axis and perpendicular to the incident light. The relations between the asymmetry factor and the optical size and aerodynamic size at various equivalent sizes, refractive indices, and mass densities are discussed in this paper. The numerically calculated results indicate that an elongated particle may be classified at diameter larger than 1.0 μm, and may not be distinguished from a sphere at diameter less than 0.5 μm. It is estimated that the lowest detected aspect ratio is around 1.5:1 in consideration of the experimental errors.     

Intercomparison of Inversion Algorithms for Particle‐Sizing Using Mie Scattering

The applicability of different inversion algorithms to retrieve a size distribution of particles in air from light scattering is examined. The investigation is focused on an optical measurement setup with an elliptical mirror as the main optical element. In order to evaluate the capabilities of the individual inversion methods, light scattering by spherical particles is simulated in the size ranges of 0.1 – 10 μm and 0.05 – 1 μm. The distribution of the particle diameters is modeled with three different parametric functions, i.e., RRSB, logarithmic‐normal and a more specific distribution from an ultrasonic nebulizer. Different kinds of noise, e.g., additive and/or multiplicative, are applied in different levels to the simulated scattering measurement to include real physical measurement conditions. The convergence properties of the scattering simulation are investigated with respect to the number of size classes, and thus, information concerning the size resolution required to simulate a measurement for a given particle size distribution is obtained. Further parameters of interest are the minimum angular resolution of the measurements, the number of size classes of the retrieved particle size distribution and the measured polarization of the scattered light.     

A method for investigating the orientational behaviour of fibrous particles in gaseous flow

A method is described by which the angular orientation distribution of fibrous particles carried in a gaseous stream may be investigated. The method is based upon the interpretation of the spatial intensity distribution or scattering profile of laser light scattered by individual fibres. The scattering instrument used to capture the profiles is described, and the mathematical computation required to ascertain the orientation of each particle at the measurement point is detailed. Illustrative results are given for a study of airborne micromachined silicon particles of 12 μm length and 1.0 μm by 1.5 μm cross-section. The method is currently being employed by the authors to investigate ways of improving the orientation control over nonspherical particles in systems such as aerodynamic particle sizers and particle shape classifiers, since lack of particle orientation control is known to adversely affect the measurement accuracy of both these types of instrument.     

Determination of the Disperse Composition of a PbO Suspension Containing Aggregates of Particles of Lamellar Shape by the Laser-Polarimetry Method

The results of measurements of the scattering matrix at a wavelength of 0.63 μm in the range of scattering angles of 10°–155° are presented for an aqueous suspension of lead oxide containing particles of plate form and their aggregates of monomers with dimensions of ~5 nm. The results of the measurements are compared with the results of calculations for axially symmetric scatterers (ellipsoids of rotation, cylinders). It is shown that the presence of aggregates affects the scattering properties of such a medium. The results of reconstructing the distribution of particles of a disperse medium in sizes from the measurements data of the scattering matrix are presented. The reconstruction of the distributions was carried out by solving the problem of optimizing the sum of the squared deviations of the experimental and calculated values of matrix elements in the framework of the model of axially symmetric scatterers. It is shown that the distribution of particles by sizes is more accurately reconstructed by minimizing the sum of the squares of the deviations for the sum of the diagonal elements. The obtained distribution is compared with the distribution measured by the method of dynamic light scattering.     

Infrared and microwave radiative properties of metal coated microfibres

Recent experimental investigations have shown that insulations containing metallised glass or polymer fibres are characterised by an extremely high extinction coefficient for infrared radiation and, as a result, by very good heat shielding properties. This may be explained by the unusual optical properties of single fibres. In this paper, the most general theoretical model for the radiation absorption and scattering by metallised fibres is employed. It is based on the rigorous theory of scattering by an arbitrary oriented two-layer cylinder and may be used for calculations in a wide spectral range. The accuracy of some simple models of metallised fibres is analysed. In particular, the range of applicability of the perfectly conducting cylinder approximation is determined. A comparison with published experimental data shows good agreement between the calculated and the experimental values of the equivalent specific extinction coefficients in the spectral range of 2.5 < λ < 27.5 μm. Computational data on the absorption and scattering of microwave radiation by metallised dielectric fibres are presented for the first time. High values of the absorption efficiency factor for single submicron fibres may be of interest for microwave applications.     

聚硅氧烷微球/PMMA光散射材料的 制备与光学性能

采用共混法以聚硅氧烷微球作为光散射剂,聚甲基丙烯酸甲酯为基材制备光散射材料.研究了聚硅氧烷微球的粒径与浓度对光散射材料总光透过率与扩散率的影响并与理论模拟值进行了对比分析.研究结果表明,聚硅氧烷微球与聚甲基丙烯酸甲酯折射率匹配良好,较好地解决了光散射材料透光率与扩散率之间的矛盾,实现了高透射与高雾度的双重要求.当微球粒径为5 μm,填充浓度为0.6 wt%时,厚度为1 mm的光散射材料总光透过率为88.5%,扩散率为89.5%.可见光波段总光透过率基本不受光源波长变化影响.选取合适粒径,扩散率随光源波长变化也可降至最低,有效避免了波长色散现象.实验数据与理论模拟结果符合良好.     

聚硅氧烷微球/PMMA光散射材料的制备与光学性能

采用共混法以聚硅氧烷微球作为光散射剂,聚甲基丙烯酸甲酯为基材制备光散射材料.研究了聚硅氧烷微球的粒径与浓度对光散射材料总光透过率与扩散率的影响并与理论模拟值进行了对比分析.研究结果表明,聚硅氧烷微球与聚甲基丙烯酸甲酯折射率匹配良好,较好地解决了光散射材料透光率与扩散率之间的矛盾,实现了高透射与高雾度的双重要求.当微球粒径为5μm,填充浓度为0.6wt%时,厚度为1mm的光散射材料总光透过率为88.5%,扩散率为89.5%.可见光波段总光透过率基本不受光源波长变化影响.选取合适粒径,扩散率随光源波长变化也可降至最低,有效避免了波长色散现象.实验数据与理论模拟结果符合良好.     

核爆炸光辐射探测中的大气传输性能研究

从核爆炸光辐射特点出发, 结合我国中纬度地区大气特点,研究了(0.2～1.2)μm波段大气传输性能。通过实际测量数据分析可知,大气对（0.2～1.2)μm光辐射起主要作用的成分有水蒸气、二氧化碳和臭氧的分子吸收和散射以及气溶胶大粒子的散射。综合考虑这些因素,改进了水平路径传输上（0.2～1.2）μm光辐射大气传输经验方程。计算机仿真结果表明：该方程能体现我国中纬度地区光辐射的传输情况,对（0.4～0.8）μm可见光波段能很好地吻合。将（0.4～0.8）μm波段光辐射大气传输定量计算结果直接应用到基于可见光辐射探测的核爆炸探测子系统中,模拟核爆炸探测,实验结果表明：与传统大气传输计算软件的定性结果相比,该方法的测量精度有明显的提高。     

Global Rainbow Thermometry for Mean Temperature and Size Measurement of Spray Droplets

Global rainbow thermometry is a new technique for measuring the average size and temperature of spray droplets. For data inversion a global rainbow pattern is employed, which is formed by constructive interference of laser light scattered by an ensemble of spherical droplets. The non‐spherical droplets and liquid ligaments provide a uniform background and hence do not influence the interference pattern from which average size and temperature are derived. This is a large improvement with respect to standard rainbow thermometry, investigated since 1988, which is strongly influenced by particle shape. Moreover, the technique is applicable to smaller droplets than the standard technique because the global pattern is not spoiled by a ripple structure. Data inversion schemes based on inflection points, minima and maxima are discussed with respect to spray dispersion and droplet flux. The temperature derivation from inflection points appears to be independent of spray dispersion. Preliminary measurements in a heated water spray are reported. The mean diameter obtained from the rainbow pattern is smaller than the arithmetic mean diameter measured by phase‐Doppler anemometry. The accuracy of the temperature measurement by global rainbow thermometry is shown to be a few degrees Celsius.     

Wave diffraction by a finite set of azimuthally magnetized ferrite cylinders

The article is devoted to the problem of scattering of plane linear and circular electromagnetic waves by a set of ferrite-coated cylinders. Particular attention is paid to the possibility of controlling the scattering pattern by the azimuthal magnetic field induced in the ferrite by the dc current in metal core of cylinders. It is shown that the best sensitivity can be obtained for the magnetic field, which provides the magnetic resonance inside ferrite layer. Relevant scattering patterns are also presented.     

Small angle X-ray scattering by spherical particles of Polystyrene and Polyvinyltoluene

The high intensity, high resolution multiple reflection diffractometer has been applied to make accurate measurements of the small angle X-ray scattering of eight different Dow Chemical latexes with stated diameters 2.051, 1.305, 0.814, 0.557, 0.365, 0.264, 0.126, and 0.088 μm. Using thin dry samples, the measured intensities of diffraction extrema with orders higher than the third were found to agree well with the simple Rayleigh-Gans theory which neglects multiple scattering as well as interparticle interference. Orders below the fourth showed a distinct effect of interparticle interference. This effect could be demonstrated to vanish when a liquid solution sample was used instead of a dry one. Scattering curves of thick dry samples had strongly decreased contrast between maxima and minima, an effect which is known to be due to multiple scattering. The following particle diameters were determined from the measured scattering curves: 2.102±0.013 μm, 1.313±0.008 μm, 0.823±0.004 μm, 0.552±0.002 μm, 0.352±0.002 μm, 0.254±0.002 μm, 0.119±0.001 μm and 0.078±0.001 μm. The discrepancies between these and the stated sizes are larger for the smaller particles. It is believed that the X-ray measurements are more accurate than the stated sizes which are based on measurements in the electron microscope. Therefore, as secondary standards, the diameter obtained from the X-ray measurements should be used.     

Constraints on PSC particle microphysics derived from lidar observations

Based on extensive T-matrix computations of light scattering by polydispersions of randomly oriented, rotationally symmetric nonspherical particles, we analyze existing lidar observations of polar stratospheric clouds (PSCs) and derive several constraints on PSC particle microphysical properties. We show that sharp-edged nonspherical particles (finite circular cylinders) exhibit less variability of lidar backscattering characteristics with particle size and aspect ratio than particles with smooth surfaces (spheroids). For PSC particles significantly smaller than the wavelength, the backscatter color index and the depolarization color index β are essentially shape independent. Observations for type Ia PSCs can be reproduced by spheroids with aspect ratios larger than 1.2, oblate cylinders with diameter-to-length ratios greater than 1.6, and prolate cylinders with length-to-diameter ratios greater than 1.4. The effective equal-volume-sphere radius for type Ia PSCs is about 0.8 μm or larger. Type Ib PSCs are likely to be composed of spheres or nearly spherical particles with effective radii smaller than 0.8 μm. Observations for type II PSCs are consistent with large ice crystals (effective radius greater than 1 μm) modeled as cylinders or prolate spheroids.     

On the Sizing Accuracy of Laser Optical Particle Counters

The performance of a narrow-angle and a wide-angle, forward scattering laser aerosol spectrometer has been studied as a function of particle size and refractive index. The results have been compared with theoretical calculations based on light scattering theory. The results indicate that for the narrow-angle instrument, the scattered-light intensity is not a monotonic function of particle size for transparent particles (a monotonic relationship is required for unambiguous particle size measurement) above 0.7 μm. The instrument is therefore limited in its useful range to size distribution measurement between 0.2 μm – its lower particle size limit – and 0.7 μm for transparent particles. In the case of the wide-angle instrument, the instrument output is a monotonic function of particle size for transparent particles, but the output is severely attenuated for light absorbing particles above 0.3 μm. The instrument, therefore, cannot be used for accurate size measurements above 0.3 μm for light absorbing particles.     

Scattering properties of aqueous suspensions with absorbing dispersed phase

Scattering matrices of aqueous suspensions of copper oxide and graphite the particles of which are characterized by strong absorption at a wavelength of 0.63 μm have been measured in the scattering angle range of 10°–155°. The results of the measurements are compared with calculation data for axially symmetric scatterers (ellipsoids of revolution and cylinders). It is shown that, if the size parameter equals 4–6, even under conditions of strong radiation absorption by particles of the dispersive medium, deviation of their shape from axial symmetry has an effect on the scattering properties of the medium.     

高散射媒质中的光程可分割动态光散射研究

为研究散射光强度随光子在散射媒质中散射光程的变化,基于单散射理论与扩散波光谱理论,采用了低相干动态光散射装置对不同粒径大小的聚苯乙烯悬浮液进行研究。将测量得到的背散射光光场强度谱的线宽与相应的理论计算结果相比较发现,在短光程区域,考虑容器壁附近拖曳效应的影响后,对于不同粒径的颗粒,光程为约5倍粒子平均自由程的区域可看成为单散射区域;对于光程大于225 m的区域可看成为扩散光波区域。实验结果表明低相干动态光散射法可实现高散射媒质从单散射区域到低次散射再到扩散区域的全光程的可分割的光场强度谱测量。