Light scattering from nonspherical airborne particles: experimental and theoretical comparisons

A laser light-scattering instrument has been designed to permit an investigation of the spatial intensity distribution of light scattered by individual airborne particles constrained within a laminar flow, with a view to providing a means of classifying the particles in terms of their shape and size. Ultimately, a means of detecting small concentrations of potentially hazardous particles, such as asbestos fiber, is sought. The instrument captures data relating to the spatial distribution of light scattered from individual particles in flow. As part of an investigation to optimize orientation control over particles within the sample airstream, the instrument has been challenged with nonspherical particles of defined shape and size, and a simple theoretical treatment based on the Rayleigh-Gans formalism has been used to model the spatial intensity distribution of light scattered from these particle types and hence derive particle orientation data. Both experimental and theoretical scattering data arepresented, showing good agreement for all particle types examined.     

Absolute real-time measurement of particle size distribution with the flying light-scattering indicatrix method

The flying light-scattering indicatrix (FLSI, angular dependency of the intensity of light scattered by a moving individual particle) method, based on a scanning flow cytometer (SFC) that permits measurement of individual particle characteristics from light-scattering data, has been used for the determination of size distribution of the following particles: polystyrene latex, milk fat, and spores (Penicillium levitum, Aspergillus pseudoglaucus). The optical system of the SPC and empirical equations provided absolute sizing at the rate of 50 particles/s. Size distributions obtained with the FLSI method and a best-fit procedure using Mie scattering theory have been compared.     

Simultaneous light scattering and intrinsic fluorescence measurement for the classification of airborne particles

We describe a prototype laboratory light-scattering instrument that integrates two approaches to airborne particle characterization: spatial light-scattering analysis and intrinsic fluorescence measurement, with the aim of providing an effective means of classifying biological particles within an ambient aerosol. The system uses a single continuous-wave 266-nm ultraviolet laser to generate both the spatial elastic scatter data (from which an assessment of particle size and shape is made) and the particle intrinsic fluorescence data from particles in the approximate size range of 1-10-mum diameter carried in a sample airflow through the laser beam. Preliminary results suggest that this multiparameter measurement approach can provide an effective means of classifying different particle types and can reduce occurrences of false-positive detection of biological aerosols.     

Computation of light scattering by axisymmetric nonspherical particles and comparison with experimental results

A laboratory prototype of a novel experimental apparatus for the analysis of spherical and axisymmetric nonspherical particles in liquid suspensions has been developed. This apparatus determines shape, volume, and refractive index, and this is the main difference of this apparatus from commercially available particle analyzers. Characterization is based on the scattering of a monochromatic laser beam by particles [which can be inorganic, organic, or biological (such as red blood cells and bacteria)] and on the strong relation between the light-scattering pattern and the morphology and the volume, shape, and refractive index of the particles. To keep things relatively simple, first we focus attention on axisymmetrical particles, in which case hydrodynamic alignment can be used to simplify signal gathering and processing. Fast and reliable characterization is achieved by comparison of certain properly selected characteristics of the scattered-light pattern with the corresponding theoretical values, which are readily derived from theoretical data and are stored in a look-up table. The data in this table were generated with a powerful boundary-element method, which can solve the direct scattering problem for virtually arbitrary shapes. A specially developed fast pattern-recognition technique makes possible the on-line characterization of axisymmetric particles. Successful results with red blood cells and bacteria are presented.     

Analysis of particle sizes, concentration, and refractive index in measurement of light transmittance in the forward-scattering-angle range

A simple method for determining the mean size, the concentration, and the refractive index of the monodispersion and the polydispersion of particles has been presented. The method is based on the empirical inversion of measurements of forward-angle light-scattering transmittance. The effects of particle size distribution and optical constants on forward-angle-scattering transmittance have been considered by using Mie theory. The proposed method has been used successfully for single latex spheres in water and polydispersed weakly absorbing particles of Al(2) O(3) and SiO(2) in the flow of the propane-air flame combustion products.     

Angular structure of radiation scattered by monolayers of particles: experimental study

An experimental study has been made of the angular structure of radiation scattered by monolayers of large nonabsorbing particles. We have investigated three media exhibiting different light-scattering properties: monodisperse polyvinyl toluene latex particles of 3.75-mum diameter suspended in water, polydisperse rice starch particles with a mean diameter of 6.4 mum suspended in water, and a mixture of ethyl and benzoic alcohols. It is shown that for large particles the structure of scattered radiation can be described in a single-scattering approximation. Analysis of the influence of polydispersity and the relative refractive index of particles on the intensity scattered by the monolayer has been performed.     

Neural-network-based spatial light-scattering instrument for hazardous airborne fiber detection

A laser light-scattering instrument has been designed to facilitate the real-time detection of potentially hazardous respirable fibers, such as asbestos, within an ambient environment. The instrument captures data relating to the spatial distribution of light scattered by individual particles in flow by use of a dedicated multielement photodiode detector array. These data are subsequently processed with an artificial neural network that has previously been trained to recognize those features or patterns within the light-scattering distribution that may be characteristic of the specific particle types being sought, such as, for example, crocidolite or chrysotile asbestos fibers. Each particle is thus classified into one of a limited set of classes based on its light-scattering properties, and from the accumulated data a particle concentration figure for each class may be produced and updated at regular intervals. Particle analysis rates in excess of 103 /s within a sample volume flow rate of 1 l /min are achievable, offering the possibility of detecting fiber concentrations at the recommended maximum exposure limit of 0.1 fibers /ml within a sampling period of a few seconds.     

Light-scattering properties of plate and column ice crystals generated in a laboratory cold chamber

Angular scattering properties of ice crystal particles generated in a laboratory cloud chamber are measured with a lightweight polar nephelometer with a diode laser beam. This cloud chamber produces distinct plate and hollow column ice crystal types for light-scattering experiments and provides a controlled test bed for comparison with results computed from theory. Ice clouds composed predominantly of plates and hollow columns generated noticeable 22 degrees and 46 degrees halo patterns, which are predicted from geometric ray-tracing calculations. With the measured ice crystal shape and size distribution, the angular scattering patterns computed from geometrical optics with a significant contribution by rough surfaces closely match those observed from the nephelometer.     

Characterization of Macromolecular Solutions by a Combined Static and Dynamic Light Scattering Technique

The combination of quasi-elastic light scattering (LS) with integrated scattered intensity measurements in the same sample has been applied to study polymer and polymer–protein aqueous solutions. The molecular weight, the radius of gyration, and the second virial coefficient for thermosensitive polymer [poly(N-isopropylacrylamid)] solutions before and after precipitation transition have been obtained using Zimm plot calculations. The precipitation curve (intensity versus temperature dependence) for polymer solutions has been experimentally obtained using the light scattering setup. For the first time the static and dynamic LS properties of aqueous solutions of antibody–poly(methacrylic acid) and antibody–poly(acrylic acid) conjugates and solutions of their components [antibody, poly(methacrylic acid), and poly(acrylic acid)] at different pH values have been measured. In both cases the parallel comparison of the characteristic size variations allowed us to represent novel structural features of scattered particles (macromolecules, associates, aggregates, conjugates, colloidal particles) in studied systems.     

木质素磺酸钠/三聚氰胺甲醛微球泡沫的制备及表征

利用价格低廉的木质素磺酸钠作为添加剂,制备了具有微球结构的木质素磺酸钠/三聚氰胺甲醛（LS/MF）微球泡沫。采用FTIR研究了微球泡沫固化过程中时间的变化,分析其固化过程,并结合理论计算分析了LS与MF的交联反应机制,研究了LS的添加含量对所制备的LS/MF微球泡沫性能的影响,利用SEM分析了LS/MF微球泡沫的微观形貌。研究表明：添加LS制备的泡沫微球尺寸均匀,直径在3 μm左右,并具有二级结构,大的微球表面有大量的200 nm左右的小微球粒子产生;LS含量为15wt%时,所制备的LS/MF微球泡沫的性能最佳,此时LS/MF泡沫的导热系数低至0.0216 W（mK）^-1,比未添加LS的MF泡沫降低了20%。因此,利用LS替代多聚甲醛制备的LS/MF微球泡沫具有更优异的保温性能,且方法简单,成本低廉,具有潜在的应用前景。     

Inversion of particle-size distribution from angular light-scattering data with genetic algorithms

A stochastic inverse technique based on a genetic algorithm (GA) to invert particle-size distribution from angular light-scattering data is developed. This inverse technique is independent of any given a priori information of particle-size distribution. Numerical tests show that this technique can be successfully applied to inverse problems with high stability in the presence of random noise and low susceptibility to the shape of distributions. It has also been shown that the GA-based inverse technique is more efficient in use of computing time than the inverse Monte Carlo method recently developed by Ligon et al. [Appl. Opt. 35, 4297 (1996)].     

Early physics results

For the past year, experiments at the Large Hadron Collider (LHC) have started exploring physics at the high-energy frontier. Thanks to the superb turn-on of the LHC, a rich harvest of initial physics results have already been obtained by the two general-purpose experiments A Toroidal LHC Apparatus (ATLAS) and the Compact Muon Solenoid (CMS), which are the subject of this report. The initial data have allowed a test, at the highest collision energies ever reached in a laboratory, of the Standard Model (SM) of elementary particles, and to make early searches Beyond the Standard Model (BSM). Significant results have already been obtained in the search for the Higgs boson, which would establish the postulated electro-weak symmetry breaking mechanism in the SM, as well as for BSM physics such as Supersymmetry (SUSY), heavy new particles, quark compositeness and others. The important, and successful, SM physics measurements are giving confidence that the experiments are in good shape for their journey into the uncharted territory of new physics anticipated at the LHC.     

Liquid-phase synthesis of cobalt oxide nanoparticles

Various liquid-phase syntheses of CoO and Co3O4 nanoparticles have been studied. The experiments focus on two synthesis routes: the coprecipitation and the sol-gel methods combined with thermal decomposition. The effect of synthesis route, the type of precursors (cobalt nitrate/chloride) and precipitation agent (carbonate, hydroxide, oxalic acid, and ammonia), the chemical compositions, pH, application of surfactants (PDMS, Triton X-100, NaDS, NaDBS, TTAB, ethyl acetate, citric acid), and the heat treatments on the properties of particles were investigated. The particle size and distribution have been determined by dynamic light scattering (DLS). The phases and the morphology of products have been analysed by XRD and SEM. The coprecipitation technique is less able to shape the particles than sol-gel technique. PDMS can be applied efficiently as surfactant in preparation methods. The finest particles (around 85 nm) with narrow polydispersity (70-100 nm) and spherical shape could be achieved by using sol-gel technique in medium of 1-propanol and ethyl acetate.     

Particle size determination of a three-component suspension using a laser-scattering particle size distribution analyzer

In this study, a rapid and accurate particle size determination method using a light-scattering particle size analyzer was developed to measure the particle size and size distribution of a suspension containing three solid components: clotrimazole, triamcinolone, and sarafloxacin, which have different refractive indices. To ensure that data represent the size distribution of the primary particles of the suspension, the optimal sonication prior to and during measurement was determined. It was found that the results obtained using the average relative refractive index (RRI) of the three components agreed with the results obtained using three individual RRIs. In addition, the results from two analysts demonstrated good reproducibility of this method. The size distribution data of the suspension were also compared to those of the bulk drugs. The results showed that the median particle size of this three-component suspension is relatively close to that of clotrimazole, which accounts for 80% of solid particles in the suspension. Furthermore, the results obtained using the light-scattering technique were comparable to those obtained using a polarized light microscope equipped with an image analyzer, indicating acceptable accuracy of this technique.     

Particle Size Determination of a Three-Component Suspension Using a Laser-Scattering Particle Size Distribution Analyzer

In this study, a rapid and accurate particle size determination method using a light-scattering particle size analyzer was developed to measure the particle size and size distribution of a suspension containing three solid components: clotrimazole, triamcinolone, and sarafloxacin, which have different refractive indices. To ensure that data represent the size distribution of the primary particles of the suspension, the optimal sonication prior to and during measurement was detemined. It was found that the results obtained using the average relative refractive index (RRI) of the three components agreed with the results obtained using three individual RRIs. In addition, the results from two analysts demonstrated good reproducibility of this method. The size distribution data of the suspension were also compared to those of the bulk drugs. The results showed that the median particle size of this three-component suspension is relatively close to that of clotrimazole, which accounts for 80% of solid particles in the suspension. Furthermore, the results obtained using the light-scattering technique were comparable to those obtained using a polarized light microscope equipped with an image analyzer, indicating acceptable accuracy of this technique.     

Time-resolved studies of the interactions between pulsed lasers and aerosols

Studies of the interaction between a pulsed CO2 laser and micrometer-sized aqueous and organic particles by use of light-scattering methods and step-scan Fourier-transform infrared (FTIR) spectroscopy are reported. Visible two-color extinction experiments indicate primary particle shattering, accompanied by a high fraction of vaporization, followed by secondary particle evaporation. The extent of the latter depends on the pulse intensity and particle composition. Angle-resolved light-scattering investigations provide insight into the aerosol size distribution and temperature following the pulsed heating event. The time dependence of the vapor plume, monitored with step-scan FTIR spectroscopy, confirms that a large fraction of the initial particle is quickly evaporated during the shattering event, followed by secondary fragment evaporation and thermal expansion.     

Sizing of colloidal particles with light scattering: corrections for beginning multiple scattering

Static light scattering is widely used for sizing of particles with radii in the range of 50 nm up to several micrometers. These experiments usually require very low particle concentrations (<10(-4)) for prevention of multiple scattering. As a consequence, nonabsorbing samples that are suited for light-scattering investigations must be transparent so that the transmittance of the incident light is typically above 95%. Investigations of less translucent samples require corrective terms for the beginning of multiple scattering to retrieve the particle-size distribution successfully. We applied a computationally convenient first-order approximation for the multiple-scattering problem that has Hartel's approach in its first steps. When incorporated into our inversion technique, this approximation functions well for samples with transmittances above 30%. We present examples of applications to experimental data.     

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.     

PARTICLE SIZE DISTRIBUTION STUDY OF LANTHANUM-DOPED YTTRIA POWDERS BY SEM-IMAGE ANALYSIS AND LASER LIGHT-SCATTERING METHODS

Particle size analysis of lanthana-doped yttria powders by automatic image analysis (IA) has been used to improve the quality of sizing data obtained using classical laser light scattering methods. A calibration test using monomodal, standard polystyrene spheres confirmed that the IA method provides a narrower distribution and improved size resolution compared to that obtained by light scattering. To ensure that the light-scattering distributions obtained in a study of lanthana-doped yttria powders were accurate, image analysis methods were used to obtain particle size distribution data from which corrected parameters for data reduction of the light-scattering data were obtained. In one case, a bimodal distribution obtained by light-scattering data was found to be artifactural when compared to the distribution obtained from IA measurements. It is concluded that direct particle size distribution analysis by image analysis can be successfully applied in light-scattering studies of yttria powders and can be extended to sizing studies of other powder types.