Compression properties of individual micron-sized acrylic particles

Compression behaviours of individual micron-sized acrylic particles have been studied by using a nanoindentation-based method with a flat-end tip, instead of a commonly used sharp tip. The effect of loading rate on the mechanical properties of the high monodisperse acrylic particles, such as K-value, breaking force and breaking displacement, has been investigated. A wide range of loading rate conditions has been applied to examine the sensitivity of selected mechanical properties. It has been observed that the loading rate has a significant effect on K-value and breaking force whereas breaking displacement is independent of loading rate. These results facilitate the industrial applications of acrylic particles.     

Measurement of rotation of individual spherical particles in cohesive granulates

To explore dynamical processes in granular matter, we use a combination of 3D imaging and mechanical testing. We analyze structural changes using confocal microscopy while applying a compression load simultaneously. Fluorescently labeled polydisperse silica particles were hydrophobized with long alkyl chains and dispersed in an index-matching liquid. The particles show a weak attraction. Photobleaching the central plane of individual particles generates an optical anisotropy without changing particle interaction. In a series of 3D images, we follow trajectories and rotation of single particles. We focus on particle translation and rotation in dependency of the local volume fraction. During compression, restructuring happens predominantly in regions of low packing density. We show that rotation plays an important role and is hence a key parameter for explaining dynamical processes in granular systems.     

Light scattering resonances in small particles with electric and magnetic properties

Lorenz-Mie resonances produced by small spheres are analyzed as a function of their size and optical properties (epsi > or < 0, mu > or < 0). New generalized (mu not equal to 1) approximate and compact expressions of the first four Lorenz-Mie coefficients (a1, b1, a2, and b2) are calculated. With these expressions and for small particles with various values of epsi and mu, the extinction cross section (Q(ext)) is calculated and analyzed, in particular for resonant conditions. The dependence on particle size of the extinction resonance, together with the resonance shape (FWHM), is also analyzed. In addition to the former analysis, a study of the scattering diagrams for some interesting values of epsi and mu is also presented.     

Experimental and theoretical study of light scattering by individual mature red blood cells by use of scanning flow cytometry and a discrete dipole approximation

Elastic light scattering by mature red blood cells (RBCs) was theoretically and experimentally analyzed by use of the discrete dipole approximation (DDA) and scanning flow cytometry (SFC), respectively. SFC permits measurement of the angular dependence of the light-scattering intensity (indicatrix) of single particles. A mature RBC is modeled as a biconcave disk in DDA simulations of light scattering. We have studied the effect of RBC orientation related to the direction of the light incident upon the indicatrix. Numerical calculations of indicatrices for several axis ratios and volumes of RBC have been carried out. Comparison of the simulated indicatrices and indicatrices measured by SFC showed good agreement, validating the biconcave disk model for a mature RBC. We simulated the light-scattering output signals from the SFC with the DDA for RBCs modeled as a disk-sphere and as an oblate spheroid. The biconcave disk, the disk-sphere, and the oblate spheroid models have been compared for two orientations, i.e., face-on and rim-on incidence, relative to the direction of the incident beam. Only the oblate spheroid model for rim-on incidence gives results similar to those of the rigorous biconcave disk model.     

Simultaneous laser-induced fluorescence and scattering detection of individual particles separated by capillary electrophoresis

This technical note describes a detector capable of simultaneously monitoring scattering and fluorescence signals of individual particles separated by capillary electrophoresis. Due to its nonselective nature, scattering alone is not sufficient to identify analyte particles. However, when the analyte particles are fluorescent, the detector described here is able to identify simultaneously occurring scattering and fluorescent signals, even when contaminating particles (i.e., nonfluorescent) are present. Both fluorescent polystyrene particles and 10-nonyl acridine orange (NAO)-labeled mitochondria were used as models. Fluorescence versus scattering (FVS) plots made it possible to identify two types of particles and a contaminant in a mixture of polystyrene particles. We also analyzed NAO-labeled mitochondria before and after cryogenic storage; the mitochondria FVS plots changed with storage, which suggests that the detector reported here is suitable for monitoring subtle changes in mitochondrial morphology that would not be revealed by monitoring only fluorescence or scattering signals.     

Absorption and scattering properties of dense ensembles of nonspherical particles

The purpose of this work is to show that an appropriate multiple T-matrix formalism can be useful in performing qualitative studies of the optical properties of colloidal systems composed of nonspherical objects (despite limitations concerning nonspherical particle packing densities). In this work we have calculated the configuration averages of scattering and absorption cross sections of different clusters of dielectric particles. These clusters are characterized by their refraction index, particle shape, and filling fraction. Computations were performed with the recursive centered T-matrix algorithm (RCTMA), a previously established method for solving the multiple scattering equation of light from finite clusters of isotropic dielectric objects. Comparison of the average optical cross sections between the different systems highlights variations in the scattering and absorption properties due to the electromagnetic interactions, and we demonstrate that the magnitudes of these quantities are clearly modulated by the shape of the primary particles.     

Measurement of transport properties of liquids with equilibrium and nonequilibrium Rayleigh scattering

We have developed an experimental arrangement for measuring Rayleigh scattering in liquids and liquid mixtures that are either in thermal equilibrium or in thermal nonequilibrium states. As an illustrative example we report experimental values for the thermal dilfusivity, the mass diffusion coefficient, the Rayleigh-factor ratio, and the Suret coefficient of an equimolar mixture of liquid toluene andn-hexane.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994 Boulder Colorado U S A     

The effect of clustering of particles on Rayleigh scattering of radiation in a turbulent flow

The effect of clustering of particles under conditions of homogeneous isotropic turbulence on Rayleigh scattering of radiation is analyzed. It is demonstrated that, similarly to the diagnostics of molecular structure of liquid using X-ray scattering, the radial distribution function of macroscopic particles, which characterizes the clustering phenomenon, may be determined by way of measuring the intensity of scattering of infrared or microwave radiation. An approximate relation for clustering coefficient is obtained, which may be employed for estimating the increase in reflected radiation of microwave radar from cumulus clouds owing to turbulent clustering of water drops in the cloud.     

Measurement of optical properties of highly scattering ceramic materials

Radiation transfer in highly scattering ceramics is described by a diffusion approximation based on the asymptotic relation of the radiant flux and the radiant energy density in material depth. In this approximation, a calculation of the effective absorption coefficient k and the radiation diffusion coefficient D is based on the measurement of normal-hemispherical transmission of specimens shaped as various-thickness disks. Taken into account are radiation field, twodimensionality, and the radiation boundary reflection effect. The optical property measurements have been performed on the experimental apparatus based on an integrating sphere, a collimated radiation source, and a twochannel data acquisition and processing system. Results of the measurements of k and D for the silica ceramic are given at room temperature.     

Inelastic scattering on particles with inclusions

The investigation of particles with inclusions is of high interest in many parts of scientific research. Raman scattering is very good at yielding information on the internal composition of the particle. We use a geometrical-optics-based technique to determine the angle dependence of the inelastic scattering on particles with several spherical inclusions.     

Analytical performance of an ultrasonic particle focusing flow cytometer

Creation of inexpensive small-flow cytometers is important for applications ranging from disease diagnosis in resource-poor areas to use in distributed sensor networks. In conventional-flow cytometers, hydrodynamics focus particles to the center of a flow stream for analysis, which requires sheath fluid that increases consumable use and waste while dramatically reducing instrument portability. Here we have evaluated, using quantitative measurements of fluorescent microspheres and cells, the performance of a flow cytometer that uses acoustic energy to focus particles to the center of a flow stream. This evaluation demonstrated measurement precision for fluorescence and side scatter CVs for alignment microspheres of 2.54% and 7.7%, respectively. Particles bearing 7 x 10(3) fluorophores were well resolved in a background of 50 nM free fluorophore. The lower limit of detection was determined to be about 650 fluorescein molecules. Analysis of Chinese hamster cells on the system demonstrated that acoustic focusing had no effect on cellular viability. These results indicate that the ultrasonic flow cytometer has the necessary performance for most flow cytometry applications. Furthermore, through robust engineering approaches and the combination of acoustic focusing with low-cost light sources, detectors, and data acquisition systems, it will be possible to achieve a low-cost, truly portable flow cytometer.     

具有三维聚焦之微型流式细胞/颗粒计数仪

本研究提出一种新式的微型细胞颗粒计数器,此微型细胞颗粒计数器结合二维水力聚焦及微文件流结构(micro-weir structure)于微管道中,可进行高精确度及均一性的细胞或颗粒计数,本研究是利用简单的等向性(isotropie)的湿式蚀刻技术来制作微文件流结构于玻璃基材上,而此微型细胞颗粒计数器的主要构成的组件包含二维边鞘流的聚焦结构,其主要功能为将细胞或颗粒聚焦于x-Y平面上,而微文件流结构的目的在于将细胞或颗粒在z方向的筛选,最后利用雷射诱导荧光系统将细胞或颗粒侦测出.在实验与数值分析的结果,显示此微型细胞颗粒计数器确实可进行高精确度及均一性的细胞或颗粒的计数,并且可以提供一个微型化的生物分析系统.     

Effect of a wall on flow with dense particles

The behavior of dense gas–solid flows in engineering applications such as fluidized beds and pneumatic conveyers is highly complex and a reliable numerical model is required. Such flows are usually within solid walls that considerably affect the flow fields, and it is important to correctly include this effect in numerical models to improve their prediction capability. The observation of microscopic flows near walls can enhance our understanding of the flow behavior and assist in improving models. In this study, direct simulations are performed to investigate the effect of a wall on flow fields at a microscopic level. The effects of the bulk void fraction, particle Reynolds number, and particle diameter are investigated. The prediction performances of existing correlation equations usually used in mesoscopic model calculations are also investigated. It is found that the Ergun and Beetstra equations produce large discrepancies in the region within a distance equal to the particle diameter from the wall.     

Measurement of wetting properties of individual boron nitride nanotubes with the wilhelmy method using a nanotube-based force sensor

The wetting properties of individual boron nitride nanotubes (BNNTs) were studied with the Wilhelmy method in ambient conditions. A nanotube-based force sensor having a force resolution of 0.1 nN, calibrated with the wetting force method, was used to study the interactions between BNNTs and liquids in situ. The static contact angles of the liquids on BNNTs were evaluated, and the surface tension of the BNNT along with its surface tension components was determined based on the Owens and Wendt method and the van Oss-Chaudhury-Good acid-base theory.     

流式细胞仪样品流速及聚焦流测量方法研究

为提高流式细胞仪的探测分辨率和数据检测的稳定性,需要精确控制样品流速,并分析样品流速和鞘液流速对样品聚焦流的影响,可通过样品聚焦流直径和样品聚焦流在流动室流道中的相对位置来评价样品的聚焦状况。利用蠕动泵运动特点,设计了一种平均流量称重法测量样品流速的方法,并与微流量传感器测量结果作比较;采用最小二乘法线性拟合蠕动泵的控制电压和样品流速之间的函数关系,并采用显微成像法直接测量和分析样品流速和鞘液流速对样品聚焦流直径、偏离流动室流道中心线的距离的影响。实验结果显示,采用平均流量称重法与微流量传感器测得的样品流速的线性相关系数高达0.982 8;蠕动泵的样品流速与其控制电压的线性相关系数高于0.99,说明利用该线性关系可以实现样品流速的精确控制;采用的显微成像法能快速方便地测得样品聚焦流的直径及位置,为流式细胞仪样品流速、鞘液流速的调控以及液流器件组装精度的测试提供了指导方法。     

Reciprocity theorem for the calculation of average scattering properties of agglomerated particles

The reciprocity theorem in light scattering is a general theorem that is verified theoretically and experimentally. However, violation of the reciprocity theorem has been encountered in previous investigations for simulation of light scattering from agglomerates. We demonstrate that the violations of the reciprocity theorem are due to inappropriate orientation averaging or the incorrect formulation of light-scattering quantities. In situ optical diagnostics of aggregated aerosols requires the calculation of the orientation averages of scattering quantities. Thus it is imperative to establish a criterion that can be used to determine a sufficient number of orientations for the reliable calculation of averages for the scattering quantities. It is demonstrated that the reciprocity theorem may serve as such a criterion for typical sizes of agglomerates such as flame soot with fractal dimensions D(f) = 1.8, primary particle size parameter x 相似文献   

Electromagnetic scattering of high-permittivity particles on a substrate

We contribute to the study of the optical properties of high-permittivity nanostructures deposited on surfaces. We present what we believe is a new computational technique derived from the coupled-dipole approximation (CDA), which can accommodate high-permittivity scatterers. The discretized CDA equations are reformulated by use of the sampling theory to overcome different sources of inaccuracy that arise for high-permittivity scatterers. We first give the nonretarded filtered surface Green's tensor used in the new scheme. We then assess the accuracy of the technique by comparing it with the standard CDA approach and show that it can accurately handle scatterers with a large permittivity.     

Estimation of scattering from a moist rough surface with spheroidal dust particles

The scattering from moisture rough surface with spheroidal dust particles having surface with spheroidal dust particles has recently received much attention. In part due to the recent prediction and observation of the spheroidal dust particles in rough surfaces under elastic wave by the Kirchhoff scattering model and scalar approximation with slope. Our analysis shows that the scattering depends on the moisture (2–4·5%) with spheroidal dust particles. At slightly moisture rough surface the dielectric properties increase with change in field amplitude in a rough surface with spheroidal dust particles.