Size Measurement of Very Small Spherical Particles by Mie Scattering Imaging (MSI)

The Mie Scattering Imaging method (MSI) gathers out‐of‐focus images of dispersed spherical particles present in a laser light sheet and extracts the individual particle diameter from these images. The general idea of the method has been around for more than a decade and a number of papers has dealt with it over recent years. Our work focuses on small particle sizes from 20 μm down to 2 μm, a range which has not been tackled so far although it is of great importance in particle systems. We present an optical set‐up with a special arrangement of camera lenses that allows to work in this range. An evaluation algorithm based on correlation of the experimental optical information with theoretical Mie scattering was found to give the most accurate results for particle sizing. Besides accuracy measurements on solid spheres the versatility of the method is demonstrated by an example of transient droplet growth between 2–7 μm.     

Shape Estimation of Anisometric Particles Using Size Measurement Techniques

This study was conducted to establish a simple method for evaluating the morphology of fine anisometric particles using size measurement techniques. The size distributions of mica particles and carbon fibers classified into narrower size ranges were measured by gravitational sedimentation and laser diffraction techniques. The ratio of mean diameters determined for flaky particles strongly depended on the aspect ratio, i.e. flatness. The relationship between particle shape and diameter is discussed theoretically. The experimental results were similar to those predicted. The flatness of fine particles can be evaluated by the ratio of the median diameter determined by laser diffraction to that determined by sedimentation.     

镍/铁复合纳米微粒中与粒径相关的控制参数及磁性能分析

根据样品的TEM、EDX和VSM检测结果,分析制备纳米微粒工艺中与粒径相关的水／有机物（摩尔比R）比例对颗粒成核尺寸的影响,以及不同镍／铁比例（摩尔比）对粉末材料磁性能的影响。给出控制颗粒尺寸大小的R取值。     

Measurement of Size,Number Concentration and Velocity of Aerosol Particles using an optical particle counter

An aerosol measurement instrument is presented which allows for the simultaneous measurement of the size distribution, number concentration and velocities of particles. A commercial optical particle counter (OPC) was modified in terms of optics and signal evaluation to provide the required measurement information. The design of this instrument allows the definition of a cubic measuring volume by purely optical means. This is achieved by an aperture/lens system which projects a sharply defined light beam into a stream of aerosol flow. Light scattered from single particles at average angles of 90° is collected by two opposite receiver units, each projecting light on to a separate photomultiplier. The intensity of the scattered light with this instrument is found to be an unambiguous function of the particle size. The total number of particles detected per unit time results in the particle flux. The particle velocity can be calculated, in principle, through the correlation of the signal length and the optical length of the measuring volume, provided that the particles have a straight trajectory through the measuring volume and the measuring volume length in the mean flow direction is well defined. The absence of sharpness in real optical projections effects a border zone of definite length, in which the illumination declines to zero. This leads, together with the low-pass filtering of the particle signals, to an increase in the length of the signal slopes, causing some difficulties in the determination of the signal length. A digital signal evaluation technique was developed that renders possible the clear differentiation between the slope and the kernel region of the signal. The latter represents the motion of particles through the completely illuminated region, which can be a more accurate parameter to define the signal length. In addition to the signal length determination, a cross-correlation technique was tested for its potential to obtain particle velocity. the instrument has two interlaced measuring volumes of nearly the same size, which are shifted for this special application in the main flow direction by 20 μm. The phase difference between the signals from the two photomultipliers, together with the optical distance, yields the particle velocity.     

Critical Angle Refractometry for Simultaneous Measurement of Particles in Flow: Size and Relative Refractive Index

The principle of the optical technique critical angle refractometry, used to determine the size and refractive index of spherical particles (with relative refractive index below unity) in liquid flows, was investigated. This technique is based on the observation of the particle scattering pattern around the critical angle. Similarly to the recent technique developed for rainbow scattering pattern analysis for droplet temperature and size measurements, it is shown that the relative particle refractive index (m_r<1) and size can be determined from the position of the primary diffraction fringe and from the angular spacing between two fringes. Explicit equations for refractive index and particle size measurement were derived from the first-order term of the physical optics approximation. An experimental validation test and numerical computations based on the Lorenz-Mie theory were used to validate the principle of the proposed technique and to estimate its sensitivity, which was shown to be of the same order as that of the rainbow technique. This technique is considered to be useful for various applications in liquid multiphase flows where the particles size and material are to be characterized.     

Ultrasonic Measurement of Sub-Micron Particles

Based on technology described in a Du Pont patent for an offline system, we have developed a prototype in-line ultrasonic cell for measuring particle size distribution. We have used this cell to verify the Allegra-Hawley model of ultrasonic attenuation in dilute (< 5 % vol) slurries of sub-micron ceramic particles, and we are developing a model that can cope with the multiple scattering effects occuring at higher concentrations. In this paper we present the results of attenuation measurements for ultrasound (2–50 MHz) in slurries with concentrations ranging from 0.5 010 to 38 010 (vol). The attenuation is proportional to slurry concentration up to 5 010 (vol) and is predicted by single scattering models. Above approximately 100% concentration, the attenuation is actually lower than expected. For the dilute slurries we find excellent agreement between our measurements and the Allegra-Hawley calculations, and the effects of the particle size distribution are evident in the ultrasonic attenuation spectrum. These ultrasonic data can be inverted to determine the particle size and concentration in aqueous slurries of sub-micron particles.     

On the Size Distribution of Dispersed Fractal Particles

Technical Physics - Using a thermodynamic approach, a disperse system formed by an ensemble of particles with various shapes and volumes is studied. The shape of a particle is set by the value of...     

带电粒子在磁场中运动的几个特征及应用

对带电粒子在磁场中的运动问题,学生对直接用公式解题,一般尚能应付. 但对于较复杂的问题,往往显得办法不多,束手无策.本文介绍几个有关特征,供学生解题时应用.1 带电粒子在磁场中做匀速圆周运动的几个基本特征     

磁传感器与磁场的测量

在中学物理教学中，研究磁场传统的实验方法是用小磁针显示磁场的方向，用小磁针或铁粉显示磁感线分布．磁针和铁粉用来形象描述磁场功不可没，可对磁感强度的定量研究却显得无能为力．学生也只好在题海中领会感受磁感强度B的大小；1特斯拉有多大?在脑子里只有一个模糊抽象的印象．物理学对电磁现象的研究成果为各行各业提供了先进的检测设备，可是在自身的物理教学中对磁场的实验检测仍停留在4大发明的“司南”时代．近来上海的DIS实验(数字化实验系统)，     

On-Line Characterization of the Shape and Size of Particles

An image analysis system for extracting on-line quantitative geometric and densitometric information from images of ore samples is described. The apparatus employs a pulsed semiconductor laser as the light source for illuminating of a flowing stream of particles and a non-interlaced solid-state TV camera as size measurement device in a shadowgraph imaging system. The problem of the sampling volume is discussed and several size distributions of solid particulates are presented. The particle size measurement range is 2–400 μm.     

Propagation and Absorption of ECR Waves in a Low Temperature Toroidal Plasma of Small Size and Magnetic Field

The propagation and absorption of ECR waves in a tokamak plasma with small size and low values of the electron temperature and the toroidal magnetic field is studied numerically. The cold plasma dispersion equation is solved and ray tracing calculations are performed to find the accessibility conditions and the optimal angle of wave launching for maximal ECR absorption. Absorption coefficients are computed in the high density approximation.     

An Ellipsoidal Model for Small Multilayer Particles

This paper presents an ellipsoidal model that is constructed for small layered nonspherical particles and methods for constructing “effective” multilayer ellipsoids, the light-scattering properties of which would be close to the corresponding properties of original particles. In the case of axisymmetric particles, prolate or oblate spheroids (ellipsoids of revolution) are implied. Numerical calculations of the polarizability and scattering cross sections of small layered nonspherical particles, including nonconfocal (similar) spheroids, Chebyshev particles, and pseudospheroids, are performed by different approximate and rigorous methods. Approximate approaches involve the use of an ellipsoidal model, in which the polarizability of a layered particle is determined in two ways. In the first case, the polarizability is calculated in the approximation of confocal spheroids, while, in the second case, it is sought as a linear combination of the polarizabilities of embedded spheroids proportionally to the volumes of layers. Among rigorous methods, the extended boundary conditions method and the generalized separation of variables method are applied. On the basis of a comparison of the results obtained with rigorous and approximate approaches, their drawbacks and advantages are discussed.     

Particle Size Classification of Glass Particles Using Aerodynamic Jet Vectoring

An experimental demonstration of a new, non‐contact particle characterization technique called Aerodynamic Vectoring Particle Sorting (AVPS) is presented. AVPS uses secondary blowing and suction control flows–flows that are a fraction of the jet flow rate–to sharply change the direction of a planar, particle‐laden jet. As the jet is vectored, particles present in the flow experience a resultant drag force, dependent upon their size, that balances inertia. Since this balance determines the particle's trajectory, vectoring the flow leads to a separation of particles downstream. This simple, low‐pressure‐drop sorting technique classifies particles with less risk of damage or contamination than currently available sorting devices. Particles from 10–40 μm and 2.5 times the density of water have been sorted to an accuracy of 1.5 μm. Sorting of heavy particles such as these is accomplished at very low speeds, reducing the tendency of damage to the particles. Lighter particles are sorted at higher speeds. Particles from 5–40 μm and 0.6 times the density of water were sorted to an accuracy of 6.6 μm. AVPS is also shown to be capable of concentrating aerosols. Our measurements indicate that an air sample containing water‐like particles can be concentrated by a factor of 10 using AVPS.     

Magnetic Anisotropic Particles: Toward Remotely Actuated Applications

The latest breakthroughs in the synthetic preparation of nanomaterials have led to an expanding library of novel, complex and shape controlled structures with unique characteristics. Anisotropic Janus particles (JPs) are asymmetrical and are able to endow diverse chemical and physical characteristics with directionality within a single particle. They are typically distributed into three classes, viz polymeric, inorganic and polymeric‐inorganic and is made in a variation of morphologies including spherical, mushroom, snowman shaped, rod or cylindrical. Herein, we focus on JPs with a magnetic component, with emphasis on their fabrication, unique characteristics and recent applications.     

On-line Measurement of Solids Concentration or the Mean Particle Size in a Saturated Slurry Containing Background Particles Using a Turbidity Method

An on-line double-sensor turbidimeter for estimating the solids concentration or the mean particle size in a saturated slurry system in the presence of foreign insoluble particles is proposed. The correlation representing the operation of the double-sensor turbidimeter for on-line implementation is also developed. The technique relies on measuring the transmittance of an infrared light beam through the suspension, once in the presence of soluble particles and a second time when the soluble particles have completely dissolved. The device can be easily implemented on a crystallization system for monitoring and control applications. The maximum errors for solids concentration and mean particle size measurements were 13% and 7%, respectively.     

On Quantum Systems of Particles with Singular Magnetic Interaction

Abstract

For systems of particles with singular magnetic interation for special choice of a selfadjoint extension of the Hamiltoniam equilibrium reduced density matrices are calculated in the thermodynamic limit for simplest pair magnetic potentials.     

Optical In Situ Size and Concentration Measurement of Particles Dispersed in Gases at Temperatures up to 1000°C

Based on previous experience, an optical particle counter has been designed which allows the direct measurement of the size and concentration of dust particles in gas flows at high temperatures. The instrument features a new optical measuring volume definition together with a signal control to avoid border‐zone error effects. The instrument has a free working distance of 200 mm. Hence it is possible to make true in situ measurements in pipe flows with a cross‐section of ca. 60 cm² and additionally to protect the device against heat and dust precipitation on the optical windows. The instrument was initially used to examine the separation behaviour of cake‐forming rigid ceramic barrier filters at temperatures up to 1000 °C. In particular, the fractional efficiencies and the time‐related concentration changes on the clean gas side caused by a pulse jet cleaning event could be determined. The results obtained so far demonstrate that ceramic barrier filters show basically the same behaviour as conventional filters, but possess a substantially higher separation efficiency at a corresponding higher pressure drop (fractional penetration values between 10⁻⁵ and 10⁻⁹ depending on the type of filter material and the cake formation).     

Magnetic Resonance of Ferritin Crystalline Particles in Tumor Tissue

Lyophilized samples of human tumor tissue exposed and not exposed to radiation therapy were investigated by magnetic resonance spectroscopy. The measurements were taken in the temperature range of 4–280 K on an X-band electron paramagnetic resonance spectrometer. Two types of ferromagnetic resonance signals were detected. The first type signals (g _eff ≈ 2.1 ÷ 2.4) were detected in the spectra of 25% of the samples. The orientational dependence of these signals has been found. The temperature dependences of the first type signals were measured. Specific features were observed near the temperature of 125 K. They are evidently typical for the Verwey phase transition in magnetite. We suppose that the first type signals may belong to arrays or chains of ferritin particles with the crystal core in the form of magnetite. The temperature dependences of magnetic resonance characteristics of ferritin in tumors are differ from those of the same characteristics of ferritin in healthy tissue investigated before. In spectra of irradiated tumors, the second type signals at low fields were detected which may be due to aggregates of different iron particles in cell lysosomes.