Fabrication and spectral investigation of Y2O3:Nd3+ nanoparticles

In this study we have synthesized Y₂O₃ (yttria) nanopowders with 1 % Nd³⁺ concentration by using a thermal decomposition method and investigated the effect of annealing temperature on the particle sizes and the effect of particle sizes on the spectroscopic properties of these systems. The particle sizes were effectively controlled by synthesis and annealing temperatures; the sizes were found to vary in the 15–290 nm range. The particle sizes and cubic phase of the yttria were determined by using XRD patterns and confirmed by SEM and TEM measurements. We note that the particle sizes increase by increasing the synthesis and annealing temperatures. Temperature dependence of the width and position of a selected spectral line were successfully fitted with the theoretical expressions. We studied thoroughly the behavior of the samples under pulsed excitation and give plausible explanations of the measured effects.     

YAG : Ce3+发光粉的粒度与LED匹配性

研究了不同粒度的YAG : Ce³⁺发光粉对LED亮度的影响,结果显示:粒度越大,封装后LED亮度越高;造成这种结果的主要原因是发光粉颗粒的晶格完整性不同。计算了发光粉在硅胶中的沉降速度,数据说明粒度越大,沉降速度越快,也就越不利于点胶。综合以上两个方面的结果认为发光粉的颗粒不宜太粗或太细,而且分布应该尽可能的窄,10~20 μm是粒径的理想范围。     

Particle sorting using a subwavelength optical fiber

Size‐based particle sorting using a subwavelength optical fiber was demonstrated with 600‐nm and 1‐μm sizes of polystyrene particles. Optical forces acting on the particles were calculated based on three‐dimensional finite‐difference time‐domain simulations at wavelengths of 808, 1047, and 1310 nm propagating in a subwavelength optical fiber with diameter of 800 nm. Calculations indicate that by launching two counterpropagating laser beams at different wavelengths into the fiber, the directions of the resultant optical scattering forces acting on the two particle sizes can be opposite along the fiber, which leads to a countertransport of the particles. To verify the theoretical prediction, experiments were performed using the 800‐nm fiber to sort the two particle sizes. The results show that with two counterpropagating beams at 808 and 1310 nm, a continuous particle sorting was achieved. Measured particle velocities were in agreement with the theoretical calculations.     

The effect of particle size on the surface composition of microcrystalline alloys

Thin films a Ni?1at%Pd alloy, ranging in thickness from 10 to 100 Å were deposited onto alumina substrates by RF sputtering. The films were subsequently heat treated to produce small particles of the alloy with average sizes in the range 300 to 1000 Å. The surface composition of aggregates of small particles was determined by Auger electron spectroscopy after equilibration of the samples at 650°C. Average particle sizes were determined by analysis of photomicrographs taken by electron microscopy techniques. The results show a strong dependence of surface composition on particle size. A decrease of a factor of five in surface concentration of palladium is observed over the range of particle sizes studied. The dependence of equilibrium surface composition on particle size has been estimated by means of a mass balance model. While this model accounts qualitatively for the effects of particle size on surface composition, discrepancies between model predictions and the experimental results suggest the intervention of other phenomena, possibly related to capillarity effects.     

Effect of the particle sizes of the components on the leakage threshold of the electrical conductivity of a dispersed mixture

The electrical conductivity of a dispersed mixture of sand and graphite of various granulometric compositions (filling factor k=0.74) was investigated. It is shown that for mixtures which have pore sizes in a structure of dense packing of one component do not exceed the particle sizes of the other component and the threshold volume concentration of the conducting phase is completely determined by the ratio of the particle sizes of both phases. An analytic expression relating the volume threshold concentration of the conducting component and the particle sizes of the components is obtained by solving the bond problem.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 10–14, July, 1982.     

Influence of spatial laser energy distribution on evaluated soot particle sizes using two-colour laser-induced incandescence in a flat premixed ethylene/air flame

Time-resolved laser-induced incandescence (LII) has been developed rapidly during the last decade as a useful non-intrusive technique for particle size determination. Still several parameters should be investigated in order to improve the accuracy of LII for particle sizing and the spatial distribution of the laser energy is one of these. Generally a top-hat profile is recommended, as this ensures a uniform heating of all particles in the measurement volume. As it is generally not straightforward to create a uniform beam profile, it is of interest to establish the influence of various profiles on the evaluated particle sizes. In this work we present both an experimental and a theoretical investigation of the influence of the spatial profile on evaluated sizes. All experiments were carried out using a newly developed setup for two-colour LII (2C-LII) which provides online monitoring of both the spatial and temporal profile as well as the laser pulse energy. The LII measurements were performed in a one-dimensional premixed sooting ethylene/air flame, and evaluated particle sizes from LII were compared with thermophoretically sampled soot particles analysed using transmission electron microscopy (TEM). The results show that although there is some influence of the spatial laser energy distribution on the evaluated particle sizes both in modelling and experiments, this effect is substantially smaller than the influence of the uncertainties in gas temperature and the thermal accommodation coefficient.     

不同粒径沙地表面双向反射特性研究

由于自然环境遭到人为因素的破坏,我国沙地面积正在逐步扩大,确定沙地的性质与面积已经成为改善环境的重要的指示性信息.遥感技术以其特有的优势可以为沙地监测提供科学有效的信息.本文以不同粒径沙地表面为研究对象,测量其双向反射信息,分析粒径大小对沙地表面反射特性的影响;基于现有的模型对不同粒径大小沙地表面的反射信息进行计算,与实测信息进行对比.研究结果表明,粒径大小对沙地表面反射的反射分布特性有明显的影响;通过对比测量的反射信息与模型计算的反射信息发现,利用双向反射模型可以准确地计算出不同粒径沙地表面的反射信息.本研究不仅确定了粒径大小对反射信息的影响,也为遥感技术估算沙地表面粒径大小以及研究地表固有光学特性提供参考.     

Size Measurement of Small Magnetic Particles

Many different methods for size measurement are known and since they differ in their physical principles, different results are also obtained. In the recent past, there were rapid developments in new measurement techniques and one can now quickly and routinely determine particle sizes in the very fine range. Smaller particle sizes, on the other hand, tend to increase the probability of agglomeration. The measurement of the particle sizes for magnetic materials is not well understood and this paper reports results regarding the size determination of very fine magnetic materials. Because of their dipole moment, these particles tend to agglomerate even more, which in turn causes certain difficulties during the measurements. Wet and dry laser measurement systems were compared and also magnetic materials with different permeabilities in order to establish the influence of individual factors on the measurement process and on the accuracy of the results obtained.     

颗粒增强金属基复合材料变形强化中的应变梯度效应

 针对单轴压缩实验,根据颗粒增强金属基复合材料中颗粒和基体两相的局部变形协调条件,并通过简单的位错模型,确定出与变形协调相应的几何必需位错密度,进而导出一种颗粒强化-应变梯度律。从中可以清楚地看出,颗粒增强金属基复合材料的强化由材料的微结构特征几何参数l和基体应变梯度联合控制。对于颗粒含量一定的复合材料,颗粒越小,应变梯度越高,强化效果越好。这一结果揭示了,颗粒强化及尺寸效应主要是通过应变梯度效应来表现的。这也同时说明,应变梯度可能是控制材料变形与断裂的重要因素之一。     

不同粒度条件下矿物光谱变化分析

矿物粒度是影响矿物光谱特征的一个重要因素,探索不同粒度下矿物光谱曲线的变化情况以及相同粒度下不同矿物的光谱差异,不仅是高光谱矿物遥感信息识别的关键,也为研究矿物随着粒度变化而产生的光谱差异提供理论基础。利用地物光谱仪对采集的六种矿物进行观测,获取了不同粒度下的反射率光谱曲线,同时生成一阶微分光谱曲线,进而分析了不同粒度下各种矿物的光谱变化特征,对比了相同粒度下不同矿物的光谱差异,探索高光谱遥感识别矿物的可能波段。结果表明：各种矿物的光谱曲线均会随着粒度的改变而产生较大的差异,但变化规律不尽相同,紫苏辉石的整条光谱曲线都会随着粒度的增加而下降,叶蛇纹石、赤铁矿、高岭石、绿泥石的光谱曲线在特定的波长范围内随着粒度的增加而下降,橄榄石的光谱与粒度大小不存在直接的相关性;相同粒度下,不同矿物的光谱反射率在大部分波段范围内差异较大,为实现矿物高精度识别提供了可能;叶蛇纹石、高岭石、绿泥石具有较多的宽度较窄、强度较小的吸收峰,而赤铁矿、橄榄石、紫苏辉石的光谱曲线相对平滑,吸收和反射峰的数量较少。本研究旨在为矿物光谱库的构建以及矿物的高光谱技术识别提供基础数据和理论支撑。     

不同粒径对土壤有机质含量可见—近红外光谱预测的影响

土壤有机质(SOM)是表征土壤肥力的重要指标,实现其快速准确检测可为精准农业区域管理提供有效的数据支撑。土壤粒径对SOM 的光谱预测及仪器开发有很大的影响,为了明确不同粒径对 SOM 预测的影响,分别制备了1～2,0.5～1,0.25～0.5,0.1～0.25和<0.1mm 五种均匀粒径及<1mm 混合粒径共计6种粒径土样并进行了可见-近红外(300～2 500nm)光谱数据采集。采用蒙特卡罗交叉验证分别剔除了不同粒径的异常样本,结合Savitzky-Golay卷积平滑法对光谱数据进行平滑去噪处理,比较了不同粒径样品的光谱反射率差异,并对平滑后的原始光谱 R进行倒数IR、对数 LR、一阶导数 FDR等3种光谱变换并分析与SOM 含量的相关性,基于竞争性自适应重加权算法(CARS)对光谱数据进行了特征波长提取,并结合偏最小二乘回归(PLSR)分别建立了相应的SOM 含量预测模型。结果表明,不同粒径土样的平均光谱反射率与变异系数随着粒径的减小逐渐增加,且在大于540nm 波长范围内,差异明显。随着粒径的减小,SOM含量与光谱反射率在全波段范围的相关性变化幅度愈加明显,FDR 变...     

Effect of Al particle size on the reaction kinetics and densification of TiAl intermetallics

The present investigation deals with response of the particle size of aluminum on the reactive sintering of Ti–Al intermetallics and subsequently on their reaction kinetics and densification behavior. Aluminum powders of initial average particle size of 44 μm were milled for various durations in a planetary ball mill to produce average particles sizes of 100, 28 and 7 μm. These aluminum powders of various particle sizes i.e. 100, 28 and 7 μm were mixed with titanium powder of average particles size of 44 μm in the ratio of 1:1 corresponding to the Ti–Al intermetallic composition. The reactive sintering temperatures of the mixtures were determined by DTA and the effect of change in particle Al particle size has been determined for the activation energy ofthe self-propagating reaction. The effect of Al particle size on the sintering was determined by studying density and microstructure.     

Modeling of thermal conductivity of nanofluids by modifying Maxwell’s equation using cell model approach

Nanofluid is an innovative heat transfer fluid with superior potential for enhancing the heat transfer performance of conventional fluids. Though many attempts have been made to investigate the abnormal high thermal conductivity of nanofluids, the existing models cannot precisely predict the same. An attempt has been made to develop a model for predicting the thermal conductivity of different types of nanofluids. The model presented here is derived based on the fact that thermal conductivity of nanofluids depends on thermal conductivity of particle and fluid as well as micro-convective heat transfer due to Brownian motion of nanoparticles. Novelty of the article lies in giving a unique equation which predicts thermal conductivity of nanofluids for different concentrations and particle sizes which also correctly predicts the trends observed in experimental data over a wide range of particle sizes, temperatures, and particle concentrations.     

Effect of interstitial air pressure and particle size on the heat storage coefficient of a two phase system

An expression for the heat storage coefficient (HSC) of loose granular systems at interstitial air pressures is developed in terms of the characteristic pressure. The dependence of the HSC on pore and particle sizes and characteristic pressure is also discussed. To test the validity of the derived expression, the experiments are performed on a number of materials with various particle sizes and interstitial air pressures. The other reported data on the HSC are also compared with predicted values. A good agreement is found between them. This study suggests that the selection of proper particle size and partial evacuation of the pore improves the insulation characteristics of the materials.     

Dependence of diffraction radiation on the energy of an ultrarelativistic particle

The possibility of a strong dependence of the diffraction radiation of an ultrarelativistic charged particle on its Lorentz factor is discussed. It is shown that the distribution of diffraction radiation arising when the ultrarelativistic particle flies parallel to a thin dielectric layer with finite sizes depends strongly on the Lorentz factor of the particle.     

基于无约束非线性优化算法的光强自相关函数拟合

在光子相关光谱(PCS)颗粒测量技术中非线性累积反演方法是一种重要的算法。采用无约束非线性优化算法对反演过程中相关曲线的拟合问题进行了分析和研究, 实现了从任意初始值开始获取最优非线性拟合解, 并给出了算法的实现步骤。采用此方法对50 nm, 100 nm, 200 nm和500 nm的标准聚苯乙烯乳胶颗粒的实测光强自相关函数数据进行了拟合, 并反演了颗粒粒径, 与其他曲线拟合算法相比, 本算法不但对初始值的依赖性小, 而且得到的颗粒粒径更接近乳胶颗粒的标称直径, 测量误差更小。     

微颗粒X射线荧光强度MCNPX模拟与WDXRF实验

为研究样品微颗粒在X射线荧光(XRF)分析中对测量结果的影响,运用蒙特卡罗模型MCNPX对X射线荧光仪进行建模,研究了样品颗粒粒径对X射线荧光特征峰强度、峰总比和源峰探测效率的影响,并设计波长色散X射线荧光光谱法(WDXRF)分析实验对模拟结果进行了检验。结果表明：对于样品微颗粒X射线荧光强度与粒径尺寸的关系,MCNPX模拟值与理论计算值保持一致;MCNPX模拟结果与WDXRF实验结果存在一定差异,这取决于MCNPX模型对待测样品状态的假设与实际情况存在一定的差异性;运用样品粉碎、研磨至小颗粒并进行压片处理的办法,可使WDXRF实测结果尽可能的减小与MCNPX理论模拟结果的差异性;在待测样品的颗粒粒径达到一定尺寸时,其峰总比、源峰探测效率、特征峰X射线荧光计数均趋于稳定值;颗粒粒径在某一特定尺寸范围之内,颗粒度效应的影响不容忽视;除此之外,颗粒度效应的影响基本可以忽略。论文充分考虑了待测样品颗粒粒径对XRF分析结果的影响,为减小因颗粒度效应引起分析结果的不确定性提供了一种可行的研究思路,该方法也可为X射线分析的生产实践提供一定的技术参考。     

Kinetic stability of hematite nanoparticles: the effect of particle sizes

Nanoparticles are ubiquitous in environment and are potentially important in many environmental processes such as sorption, coprecipitation, redox reactions, and dissolution. To investigate particle size effects on nanoparticle aggregation and stability, this study tested aggregation behavior of 12(±2), 32(±3), and 65(±3) nm (hydrated radius) hematite particles under environmental relevant pH and ionic strength conditions. The results showed that at the same ionic strength and pH conditions, different particle sizes show different tendency to aggregate. At the same ionic strength, aggregation rates are higher for smaller particles. The critical coagulation concentration also depends on particle size, and decreases as particle size decreases. As the particle size decreases, fast aggregation shifted to lower pH. This may be related to a dependence of PZC on particle size originating from change of structure and surface energy characteristics as particle size decreases. Under the same conditions, aggregation occurs faster as particle concentration increases. Even though the nanoparticles of different sizes show different response to the same pH and ionic strength, DLVO theory can be used to qualitatively understand hematite nanoparticle aggregation behavior.     

Heat and mass transfer at the ignition of a liquid substance by a single “Hot” particle

The results of a numerical solution to the problem of heat and mass transfer at the ignition of a liquid flammable substance by a single particle heated to a high temperature located on its surface are presented. The problem is solved within the framework of a gas phase model of ignition. A mathematical model is formulated. It describes the following processes in a two-dimensional statement: the heat conduction and evaporation of a flammable liquid and the diffusion and convection of the combustible vapors in the oxidizer medium in the system “particle heated to a high temperature-liquid flammable substance-air.” The numerical investigations established the relation between the ignition delay time, the particle temperature and sizes, and the particle minimum temperature and sizes at which ignition of a combustible liquid is possible.     

Optical properties of hybrid plasmonic nanofluid based on core/shell nanoparticles

The plasmonic effect is used in nanofluid to help capture and absorb sunlight. The optical absorption is significantly enhanced as plasmonic effect excited. To obtain an enhanced absorption in a broad band, the hybrid plasmonic nanofluid is developed. It is composed of core/shell nanoparticles of different sizes. The overall absorption of hybrid nanofluid is examined. Compared to the nanofluid of single particle size, the hybrid nanofluid exhibits a broadband absorption. As particle size increases, the plasmon resonance peak is shifted to longer wavelength. The variation in the sizes of core/shell nanoparticles can broaden the absorption spectrum. In the near-infrared region, the proportion of different size particles has an obvious influence. With the increase of proportion of larger particles, the absorption band is broadened. Since the suspended nanoparticles have different sizes, the particle distribution in base fluid also has an effect on absorption of light. The large particle in upper has a broadband absorption, however, less energy can be transmitted to lower after the absorption of upper particles. The contribution from the particles in lower is relatively weak.