Cadmium sulfide photoluminescence in poly(methyl methacrylate)-matrix composites

Poly(methyl methacrylate)-matrix composites containing cadmium, lead, and zinc sulfides and also mixed (cadmium lead and cadmium zinc) sulfides were prepared by reacting metal salts with thioacetamide. The transmission of the composites in the range λ > 500 nm is 92% at absorbing layer thicknesses of ≤5 mm. The photoluminescence (PL) of the composites in the wavelength range 500–820 nm is due to the cadmium sulfide, and that in the wavelength range 300–550 nm arises from the zinc sulfide. It results from radiative recombination at levels of extrinsic structural defects in CdS and ZnS, respectively. The PL excitation spectra contain excitonic absorption bands of cadmium sulfide and zinc sulfide quantum dots. The PL of the cadmium sulfide in the composites is influenced by the presence of lead(II) and zinc(II) ions and the complexation of cations on the surface of the particles.     

Laboratory investigation of the properties of epoxy asphalt rubber (EAR)

Crumb rubber is preliminarily mixed with asphalt in wet process to produce ductile and elastic asphalt rubber (AR), which has been extensively used in high performance bituminous mixtures for road pavement. Epoxy asphalt is a thermosetting polymer modified asphalt with excellent performance and has been widely applied on the pavement of steel bridge decks. Epoxy asphalt rubber (EAR) was prepared by mixing AR with the epoxy (EP). The effect of AR concentration on the phase-separated morphology, viscosity, thermal stability and mechanical properties of the neat EP were compared with that of asphalt. Laser scanning confocal microscopy observations revealed that AR particles disperse in the continuous epoxy phase with co-continuous phase-separated structures in EARs with 40 and 50 wt% AR. However, the phase inverts to continuous asphalt structures with dispersed spherical and co-continuous epoxy phase as AR concentration reaches 60 wt%. The addition of AR increases the viscosity of the neat EP. The thermal stability of the neat EP is improved with the incorporation of AR. The presence of AR decreases the tensile strength of the neat EP, while the elongation at break of the neat EP increases with the increase of AR concentration. The viscosity and mechanical properties of EAR with 50 wt% AR completely satisfy the technical requirement of hot-mix epoxy asphalt binder for steel bridge deck pavements.     

Percolation Segregation in Binary Size Mixtures of Spherical and Angular-Shaped Particles of Different Densities

Percolation segregation in binary size mixtures for two particulate types, urea (spherical) and potash (angular), were studied. Materials chosen are major raw ingredients of blended fertilizer that represent two extremes based on shape and density. In this study, the coarse and fine particles were classified using particle sizes larger and smaller than 2,000 μm, respectively. Three coarse mean sizes (3,675 μm, 3,075 μm, and 2,580 μm) for both spherical and angular particles and three fines mean sizes (2,180 μm, 1,850 μm, and 1,550 μm) for angular particles and two fines mean sizes (2,180 μm and 1,850 μm) for spherical particles were selected for tests. Size ratio for binary size mixture is defined as the ratio of mean size of coarse to fine particles. Binary mixed samples of coarse and fine particles were placed into the shear box of the primary segregation shear cell (PSSC-II) very gently to avoid segregation. Percolation segregation was quantified using PSSC-II. Based on experimental results, the segregated fines mass, normalized segregation rate (NSR), and segregation rate of fines for binary mixtures were higher for larger size ratios as expected (2.4 > 2.0 > 1.7). The NSR is defined as the amount of fines percolated from initial fines present in the binary mixture based on total time of PSSC-II operation (kg/kg-h). Segregation rate was the highest and lowest for mixing ratios 33:67 and 67:33, respectively, when coarse mean size was 3,675 μm, where mixing ratio for binary mixtures is the ratio of the mass of coarse particles to the mass of fine particles. For the same size ratio, segregated fines mass for coarse-fine size combinations in the binary mixtures of urea and potash were significantly different (p < 0.05). Segregated fines mass of potash and urea particles was significantly different for the same size ratio and the same coarse sizes (p < 0.05). Percent segregated fines of angular particles (59%) was higher than that of spherical particles (45%) for the size ratio 2.0 and coarse mean size of 3,675 μm.     

Study on coupling diffusion of composite dust and cloud-mist dedust technology in fully mechanized driving face of mixed coal-rock roadway

Aiming at addressing the problem of coal dust and rock dust mixed pollution in mixed coal-rock roadways, this study conducted a CFD numerical simulation on the coupling migration and pollution of coal dust and rock dust in the fully mechanized driving face of mixed coal-rock roadway (i.e., roadway section with both coal seam and rock stratum). Research findings: Small coal dust particles mainly migrate backward along the upper space of the roadway, while large coal dust particles mostly diffuse backward along the bottom of the air return side and settle evidently, with the concentration being higher than 1,000 mg/m³. The concentration of rock dust starts to decline significantly to about 350–800 mg/m³ in the middle and rear of the roadway. The concentration of coal dust is relatively high (200–500 mg/m³) in the front of the roadway, and it decreases gradually to around 175 mg/m³ in the middle and rear sections. With the increase of diffusion time T of rock dust and coal dust, the diffusion distance L_D shows a linear increasing trend. Both rock dust and coal dust conform to the linear equation L_D = 0.82 T + 11. After the application of the cloud-mist dedust technology, all the measuring points in the mixed coal-rock roadway witnessed a dust removal efficiency of above 75 %, which is a mark of effectiveness of the technology in improving the underground working environment.     

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.     

Radiative Properties of Silica Nanoporous Matrices

Superinsulating materials are currently of much interest because of the price of energy on the one hand and CO₂ emissions attributed to offices and houses cooling and heating on the other hand. In this work, we aim at understanding and modeling the radiative transfer within silica nanoporous matrices that are the principal components of nanoporous superinsulating materials. We first elaborate samples of various thicknesses from a pyrogenic silica powder. These samples are characterized using two spectrophotometers on the whole wavelength range [250 nm; 20 μm]. Using a parameter identification technique, we compute the radiative properties of the various samples. Then, our samples being made of packed quasi-spherical particles, we use the Mie theory to model the radiative properties of these materials. Due to the observed discrepancies between the experimental radiative properties and those computed from the Mie theory with a uniform value of 10 nm for the scatterer diameter (value derived from TEM images), we determine an effective scatterer diameter that allows a good agreement between the experimental radiative properties and the Mie results. Nevertheless, in the short wavelength range, the Mie theory gives results that significantly differ from the experimental radiative properties. This behavior is attributed to structure effects as the wavelength is of the same order of magnitude as the diameter of the scatterer that is now regarded as an aggregate of nanoparticles. Hence, to take into account these effects, we use the discrete dipole approximation (DDA). The DDA extinction coefficient spectra appear to be much closer to the experimental results than the Mie spectra, and these first results are quite encouraging.     

原位自生TiC颗粒对Al8.5Fe1.4V1.7Si耐热铝合金的组织及性能的影响

利用原位自生技术向Al8.5Fe1.4V1.7Si耐热铝合金中添加一定数量的TiC颗粒,利用金相、X-射线以及透射电镜等手段,分析了材料的组织结构特点,研究了原位TiC粒子对材料的组织结构的影响规律,并测试了材料的力学性能.研究结果表明:原位TiC粒子可以有效地抑制合金中粗大相的产生,促进球状Al12(Fe,V)3Si相的形成;通过添加原位TiC粒子,可以将材料的力学性能提高10%左右,而材料塑性变化不大.     

Estimation of complex refractive index of polydisperse particulate systems from multiple-scattered ultraviolet-visible-near-infrared measurements

A method to extract the complex refractive index of spherical particles from a polydisperse suspension at concentrations where multiple light-scattering effects are significant is presented. The optical constants are estimated from total diffuse reflectance and transmittance measurements and inverting the measurements using the radiative transfer equation (RTE) and the Mie theory for scattering by polydisperse spherical particles. The method is tested by applying it to three different polydisperse polystyrene suspensions and extracting the optical constants of polystyrene particles in the wavelength range of 450-1200 nm. The effect of particle size, concentration, and polydispersity on the estimated values of the optical constants is also discussed.     

Mixed convection of non-Newtonian nanofluid in an H-shaped cavity with cooler and heater cylinders filled by a porous material: Two phase approach

In the present problem, two-phase mixed convection of a non-Newtonian nanofluid in a porous H-shaped cavity is studied. Inside the enclosure there are four rotating cylinders, using the Boussinesq approximation, mixed convection is created. Nanofluid includes H₂O + 0.5% CMC and copper oxide nanoparticles. The mixture model was used to model physical phenomena. Different aspect ratios were used in order to achieve the best heat transfer rate. The Darcy and Richardson numbers ranges are 10⁻⁴ ≤ Da ≤ 10⁻² and 1 ≤ Ri ≤ 100 respectively. Also, the aspect ratio and dimensionless angular velocities of cylinders ranges are 1.4 ≤ AR ≤ 1.6 and −10 ≤ Ω ≤ 10 respectively. Streamlines and isotherm-lines contours have been obtained for the variation of Darcy and Richardson numbers, aspect ratio and angular velocity. The heat transfer rates have been obtained for various aspect ratios, Darcy and Richardson numbers, and the direction of the cylinder's rotation, and are compared with each other. The results show that the direction of cylinders rotation influences the strength and extent of the generation vortices. Also, the use of porous material in high permeability can be a good alternative to lowering the angular velocity of the cylinders and ultimately reducing the need for less energy.     

Correlation Between Physico-Chemical Properties and Cohesive Behavior of Furosemide Crystal Modifications

Abstract

This study reports the influence of changes in crystal form, with subsequent changes in physicochemical properties, on the cohesive properties of furosemide powders. Two known polymorphs and three crystal habits were prepared by changing the crystallisation solvent and velocity. Crystallised products were characterised by their XRD profiles. Powder properties including solid-state photochemical reactivity, particle size and distribution, density, wettability and dissolution were measured. Fine particles of form I, mean size 3 μm, were extremely cohesive, mean size of agglomerates 108 μm, and poorly wettable, contact angle > 90°. Changes in the crystal habit of form I led to the crystallisation of large (mean size > 50 μm) tabular and rod shape, less cohesive but also poorly wettable (contact angle > 90°) particles. These large particles although not cohesive had poor dissolution properties. Milled particles with a mean size of smaller than 10 μm, obtained from the large crystals were again cohesive. The method of preparation of form II produced small plate like crystals, mean size 8 μm, fractionally more wettable, contact angle 75°, and not as cohesive, mean size agglomerates 25 μm. Milling to a mean size of 4 μm increased the cohesive properties because the mean size of agglomerates was then 53 μm. Different crystal habits of form I did not show a difference in degradation during the nucleation period, mean rate constant 1.4×10^?2 h^?1, and the growth period, mean rate constant 2.4×10^?2h^?1. In summary crystal modification improved the wettabillity and cohesive properties of furosemide particles without changing the solid-state stability of the drug. The dissolution properties of larger less cohesive particles were however poor and milling, to increase the surface area available for dissolution, increased the cohesive properties of particles.     

Numerical simulation of mixed aerosols deposition behavior on cylindrical cross fibers

In the actual dust removal process, aerosol particles with distinct physical properties often coexist. Most studies on fiber filtration focused on the particles of a single species, resulting in a poor understanding of the deposition behavior of mixed aerosols. In this study, the dynamic deposition behavior of mixed aerosol particles containing silica (SiO₂) and polystyrene (PS) on cylindrical cross fibers was numerically studied using a lattice Boltzmann model coupled with discrete element method (LB-DEM). The mutual influences between the dynamic particle transport/deposition and the airflow were considered using immersed moving boundary (IMB) scheme. The mixed particles exhibit different deposit morphology and filtration performance from single particulate species mainly in the dendritic filtration stage, where the mixed particles tend to deposit on the lateral sides rather than the front of fibers. The filtration efficiency and pressure drop of mixed aerosols are not a superposition of the individual components. At high particle Stroke number (St), the synergistic deposition of SiO₂ particles and PS particles of low elastic modulus occurs, resulting in filtration efficiencies that are approximately-four times greater than any single particulate species. When St is below 1.0, the filtration efficiency is improved with increasing St, which is similar to that of single species. Moreover, at the same flow velocity, the pressure drop rises faster and the flow is easier to be clogged for mixed particle filtration. The pressure drop rising rates of the mixed filtration at a high St range from 0.013 to 0.020, which is more than three times the rates for PS (0.006) and SiO₂ (0.003).     

Investigation of the chemical mixing state of individual Asian dust particles by the combined use of electron probe X-ray microanalysis and Raman microspectrometry

In this work, quantitative electron probe X-ray microanalysis (EPMA) and Raman microspectrometry (RMS) were applied in combination for the first time to characterize the complex internal structure and physicochemical properties of the same ensemble of Asian dust particles. The analytical methodology to obtain the chemical composition, mixing state, and spatial distribution of chemical species within single particles through the combined use of the two techniques is described. Asian dust aerosol particles collected in Incheon, Korea, during a moderate dust storm event were examined to assess the applicability of the methodology to resolve internal mixtures within single particles. Among 92 individual analyzed particles, EPMA and RMS identified 53% of the particles to be internally mixed with two or more chemical species. Information on the spatial distribution of chemical compounds within internally mixed individual particles can be useful for deciphering the particle aging mechanisms and sources. This study demonstrates that the characterization of individual particles, including chemical speciation and mixing state analysis, can be performed more in detail using EPMA and RMS in combination than with the two single-particle techniques alone.     

Dry powder formulation combining bedaquiline with pyrazinamide for latent and drug-resistant tuberculosis

The purpose of this study was to develop an inhalable combination dry powder formulation of bedaquiline and pyrazinamide and study their physicochemical properties and safety since this combination acts synergistically against Mycobacterium tuberculosis while pyrazinamide alone is active against latent TB and bedaquiline alone is active against drug-resistant TB. The cospray-dried powder of bedaquiline and pyrazinamide with 20% w/w of L-leucine consisted of spherical, porous particles of inhalable size with a diameter ≤3.2 µm. The aerosolization efficiency of the combination powder (FPF: >66%) evaluated using a next generation impactor was higher than bedaquiline-only (FPF: 31.3%) and pyrazinamide-only (FPF: 5.1%) powders, which could be due to the differences in the morphology of the powders. The combination powder was stable during storage for one month in a desiccator and 75% RH and also safe to both Calu-3 and A549 cells up to 100 µg/ml. This is the first report on the development of an inhalable combination dry powder formulation of bedaquiline and pyrazinamide with high aerosolization efficiency. This formulation has the potential to improve the treatment of both latent and drug-resistant TB.     

Scattering of Light from Two Interacting Spherical Particles

Abstract

Linear optical properties of two spherical particles interacting via their dipole fields are studied. The dipole susceptibility and cross-sections of extinction, scattering and dissipation are found as functions of susceptibility χ₀ of an isolated particle. The case of arbitrary distance between particles is considered (which include interaction in near-zone, transitional-zone and far-zone). It is shown, that radiative energy losses of an oscillating dipole give rise to a finite phase shift between oscillations of the dipole and it's electromagnetic field in the near-zone. Application of this fact to the problem of two interacting dipoles leads to appearance of two additional resonances of susceptibility of the pair with radiative half-width tending to be zero when r₁₂→0 as (r₁₂/λ)², where r ₁₂ is the distance between particles.     

Synthesis of high tap density spherical micro-size silver particles by liquid-phase reduction using response surface methodology

Mono-disperse and spherical micro-size silver particles with high tap density were prepared by using silver nitrate as metal source, ascorbic acid as reductant, sulfuric acid as dispersant and polyethylene glycol 4000 (PEG4000) as surfactant. The aim of this paper was to study the simultaneous effects of surfactant dosage (PEG4000/AgNO₃ mass ratio), silver nitrate concentration [AgNO₃], deionized water dosage in reductant solution, stirring rate and their interactions on properties of silver particles. For optimizing these parameters, irregular fractional factorial design of experiments was used. As-prepared silver particles were characterized by X-ray diffraction, scanning electron microscopy, laser particle size analyzer and tap density (tap density refers to the stacking density of particles after vibration compaction) meter. The results showed that silver particles were spherical, mono-disperse and with high tap density (>5.0 g/mL), average particle size of about 2–3 μm and narrow particle size distribution. By surveying the experiment results and analysis of variance, two mathematical models were obtained and optimized parameters were determined. Analysis of the variance demonstrated that the interaction of [AgNO₃] and stirring rate were the most significant factor affecting particle size and PEG4000/AgNO₃ mass ratio and [AgNO₃] were main significant factors affecting tap density. The predicted particle size and tap density were respectively 2.5 μm and 5.065 g/mL while the experimental results were 2.52 μm and 5.108 g/mL, which indicated that the models were in good agreement with the experimental data.     

Light scattering and absorption by soot in the presence of sulfate aerosols

The radiative properties of aerosol-soot mixtures, both internal and external, are determined in the visible and near-infrared bands by use of exact indirect mode-matching solutions to electromagnetic-wave scattering from a sphere with an eccentric spherical inclusion and from a cluster of spheres. Spherical sulfate droplets are assumed to represent aerosol particles. Soot particles are represented by volume-equivalent carbon spheres, the size distribution of which is obtained from the number distribution of the primary carbon particles that aggregate into soot grains. The mean gram-specific absorption cross section and the mean albedo of aerosol-soot mixtures are obtained by integration of the corresponding characteristics of composite sulfate-carbon particles over the size range of carbon spheres. Enhanced absorption of light by soot in aerosol-soot mixtures, a result of lensing by sulfate droplets, is highlighted by maps of the electromagnetic field in a sulfate-carbon particle.     

Micro-craters in aluminum foils: Implications for dust particles from comet Wild 2 on NASA's Stardust spacecraft

Dust impacts on aluminum foils during encounter of comet 81P/Wild 2 by the Stardust spacecraft in January 2004 have been simulated using spherical projectiles of monodispersive polymer, glass, and metals, and polydispersive mineral powders of diverse grain shapes. The encounter speed of the cometary particles was a constant and modest 6.1 km s⁻¹, well within the capabilities of light gas guns, permitting high fidelity experiments to infer dust size, density, and mass from quantitative dimensional analysis of both natural and experimental impact features. Specific interest focused on exceptionally small impactors, all <100 μm and some as small as 1.5 μm. To simulate the compound shape of many Stardust craters required novel, artificial aggregate projectiles of heterogeneous mass distribution. We demonstrate that the dimensional scaling obtained previously for millimeter sized impactors extends to particles as small as 10 μm at 6.1 km s⁻¹, all yielding a constant relationship for spherical soda lime glass projectiles of diameter (Dp) to crater diameter (Dc) in Al1100 of Dc = 4.6 Dp; however, this ratio seems to decrease for projectiles ?10 μm. The overwhelming majority of the Stardust craters are <20 μm in diameter, and substantial challenges remain in quantifying the exact size-frequency distribution of the Wild 2 comet dust. Nevertheless, the current experiments provide improved insights into some of the particles' physical properties.     

Preparation of fine particles of carnegieite by a mist decomposition method

A mist of a hydrosol consisting of silica, alumina/NaAlO₂ and sodium hydroxide was produced by a supersonic atomization, and treated successively in three furnaces of different temperatures. The temperatures of the furnaces were adjusted for the evaporation of water, the dehydration and the crystallization of the mixed oxide, respectively. The spherical particles ( 0.5m) of carnegieite were found to be formed in a narrow composition range of the raw materials at temperatures of 650 to 900° C. The factors affecting the properties of the particles were investigated.     

Characterization and sintering behaviour of submicrometre titanium dioxide spherical particles obtained by gas-phase hydrolysis of titanium tetrabutoxide

Spherical fine (∼0.7 μm) titania powders were prepared by vapour-phase hydrolysis of a titanium tetrabutoxide/butanol solution. Powder X-ray diffraction showed that as-prepared powders were amorphous and crystallized to anatase when calcined at 450°C. Although the spherical titania particles shrank on calcination and retained the spherical shape, the primary particles grew to a notable extent after calcining. The individual calcined titania spheres were constituted by microporous agglomerates of about 13 nm primary anatase particles. When isopressed at 200 MPa, the titania spheres were crushed to form dense green bodies (∼55% theoretical density). These green compacts gave dense bodies (>99%) of rutile when sintered at 1030°C for 2 h with a submicrometre and quite uniform microstructure. This revised version was published online in November 2006 with corrections to the Cover Date.     

Reevaluation of the quondam dust trend in the middle atmosphere

Quondam lunar eclipse photometry data offered valuable information on the optical properties of the middle atmosphere, including dust particles. However, in comparison with nonspherical grains, the simple model of spherical particles has a different effect on solar radiation penetrating horizontally through the atmosphere. It is shown that the systems, in which the smallest size fraction of dust particles dominates, reduce irradiation of the Earth's shadow more efficiently if the grains are of irregular shape. In contrast, the populations contaminated by a certain amount of large particles cause an opposite effect. Depending on the actual form of the size distribution function of the irregular grains, the irradiance within the center of the Earth's shadow may change by 2 orders of magnitude in the visible spectrum. It is therefore evident that dust properties retrieved in the past are eligible candidates for reevaluation to correct a view on the dust trend in the middle atmosphere. Sample calculations are presented for the lunar eclipse observed on 19 January 1954.