Estimating reaction parameters in mechanism-enabled population balance models of nanoparticle size distributions: A Bayesian inverse problem approach

In order to quantitatively predict nano- as well as other particle-size distributions, one needs to have both a mathematical model and estimates of the parameters that appear in these models. Here, we show how one can use Bayesian inversion to obtain statistical estimates for the parameters that appear in recently derived mechanism-enabled population balance models (ME-PBM) of nanoparticle growth. The Bayesian approach addresses the question of “how well do we know our parameters, along with their uncertainties?.” The results reveal that Bayesian inversion statistical analysis on an example, prototype nanoparticle formation system allows one to estimate not just the most likely rate constants and other parameter values, but also their SDs, confidence intervals, and other statistical information. Moreover, knowing the reliability of the mechanistic model's parameters in turn helps inform one about the reliability of the proposed mechanism, as well as the reliability of its predictions. The paper can also be seen as a tutorial with the additional goal of achieving a “Gold Standard” Bayesian inversion ME-PBM benchmark that others can use as a control to check their own use of this methodology for other systems of interest throughout nature. Overall, the results provide strong support for the hypothesis that there is substantial value in using a Bayesian inversion methodology for parameter estimation in particle formation systems.     

Growth kinetic study of ionic liquid mediated synthesis of gold nanoparticles using Elaeis guineensis (oil palm) kernels extract under microwave irradiation

Gold nanoparticles (AuNPs) are the most studied nanomaterials due to their promising applications. However, surface capping of AuNPs is essential to protect aggregation for enhanced colloidal stability. In this study, a single step method was established to synthesize stable AuNPs using oil palm kernel (OPK) extract prepared in IL[EMIM][OAc] (1-ethyl-3-methylimidazolium acetate). Ionic liquids were used for phytochemicals extraction along with capping and stabilizing of AuNPs after their synthesis. The OPK extract reduced the gold precursor, and UV–vis spectroscopy revealed a sharp surface plasmon (SPR) peaks in the region of 524–529 nm, which confirmed the formation of AuNPs. UV–vis and TEM analysis indicated that microwave assisted synthesis was rapid to synthesize well dispersed and small sized AuNPs in comparison with conventional heating. FTIR analysis of kernels extract before and after its reaction with gold precursor identified the involvement of CH aromatic groups, polyphenolic OH groups, and carbonyl amide groups that are responsible for reduction of trivalent gold ions to AuNPs. EDAX and XPS analysis were performed to identify the elemental gold and its surface interaction with ILs and other organic moieties. Colloidal AuNPs kept at room temperature for periods of six months were remained stable. The change of pristine nanostructure arises due to involvement of different driving forces during growth of nanoparticles. Thermodynamically instability of nanomaterials may leads to Ostwald Repining (OR) or adopt complex pattern of growth and undergo coalesce and orientation attachment (OA). These models were fitted to compare the theoretically growth of particles along with actual increase of particles size. Experimental results suggested that OA growth was originated in early phase, however, it substituted and mainly controlled by OR growth pattern over time.     

Curing of a maleimide model compound

A monofunctional maleimide-ended model compound was synthesized and purified. The thermal curing of this compound was followed by size exclusion chromatography and the molecular masses of the oligomers formed during the curing reaction were determined by mass spectroscopy. It was found that high molecular mass species were not thermally stable. At high temperature and after enough time, a strong decrease in the polydispersity of the oligomers and a significantly preferential formation of trimer were observed. From ¹³C-NMR characterization, a five membered ring structure was found for the trimer, which explains the thermal stability of this species. © 1995 John Wiley & Sons, Inc.     

激光窗口热效应和应力双折射的分析

 分析了平板窗口在激光加热和内外压强差作用下对光束带来的附加相移，详细讨论了应力双折射部分的相移，计算了CaF₂窗口的温升、应力、附加相移、远场Strehl比和退偏度等的分布。结果表明：窗口变形和折射率随温度变化是产生附加相移的主要原因，窗口的非均匀温升将导致光束质量下降，应力双折射部分的相移与窗口表面Miller指数有关，对入射光产生一定的退偏效应，从而影响光束质量。     

高能工业CT用新型X射线源焦斑测量

 为了获得较高的空间分辩率，设计了一种新型小束斑驻波电子直线加速器，该加速器取消了加速腔中的鼻锥结构，而在耦合腔中设置鼻锥结构。用狭缝法代替小孔法测得X射线源的焦斑尺寸为1.4mm。讨论了射线源焦点对成像质量的影响，分析了在高能条件下小孔法不适合用于焦点测量的物理原因，用4种测量方法测量了该高能X射线源的参数，测得该系统的成像极限分辩率为2.5 lp/mm，最后对实验结果进行了分析。     

激光器窗口的旋转效应

通过数值计算比较研究了静止、同心旋转、偏心旋转三种模式下高能激光器窗口工作过程中温度场和应力场的特征及其演变规律。研究表明，旋转式激光器窗口不但可使温度场和应力场轴对称化，且可降低最高温升、最大拉应力和最大剪应力；一定偏心距的偏心旋转可以起到消去拉应力、减小剪切应力的作用，从而使激光器窗口的抗激光损伤的能力有较大幅度的提高。     

Finite size effect on the Raman frequency of phonons in nano-semiconductors

A comprehensive study on Raman spectroscopy with different excitation wavelengths, sample sizes, and sample shapes for optic phonons (OPs) and acoustic phonons (APs) in polar and non-polar nano-semiconductors has been performed. The study affirms that the finite size effect does not appear in the OPs of polar nano-semiconductors, while it exists in all other types of phonons. The absence of the FSE is confirmed to originate from the long-range Fr¨ohlich interaction and the breaking of translation symmetry. The result indicates that the Raman spectra of OPs cannot be used as a method to characterize the scale and crystalline property of polar nano-semiconductors.     

Kinetic Monte Carlo simulation of low-pressure chemical vapor deposition of silicon nitride: Impact of gas flow rate and temperature on silicon cluster size and density

In the present study, the deposition process of SiN_x thin films obtained by a low-pressure chemical vapor deposition technique with a mixture of disilane (Si₂H₆) and ammonia (NH₃) was simulated by using the kinetic Monte Carlo method. A new pattern describing the distribution of ammonia molecules in the simulation matrix was proposed. The influences of the NH₃/Si₂H₆ gas flow ratio and the deposition temperature on the obtained films structure in terms of silicon cluster size and density were analyzed. The simulation results indicate that an increase in the gas flow ratio leads to the deposition of amorphous silicon clusters characterized by small sizes. Nevertheless, an increase in the temperature values of the process provokes an enhancement in the silicon cluster size along with a decrease in their density.     

Firm size distribution and mobility of the top 500 firms in China,the United States and the world

This paper considers the macroscopic and microscopic statistical features of the top 500 firms in China, the United States and the world, denoted as China 500 (CH500), Fortune 500 (US500) and Fortune Global 500 (FG500). From a macroscopic perspective, the firm size distribution of each category, when measured by revenue, is steadily distributed over the observed period, even during periods of financial crises. As is evidenced by the Gini coefficient, divergences between firm scales are most significant for the CH500. From a microscopic perspective, the underlying micro-dynamics are volatile and often turbulent due to the exit and entry of firms as well as shifts in their revenues and ranks. Such fluctuations, or mobility, are visualized in rank/revenue/share clocks. We also propose a revenue/rank/share mobility index that is a quantitative measurement of mobility. Among these, we find that the share mobility acts as an effective indicator of economic status; where there is a share mobility spike, there is an ailing economy. The share mobility indexes indicate that the 2008 Financial Crisis had little impact on the Chinese economy, while it triggered violent changes in the top 500 firms in the United States and the world.     

Dynamic release process of pollutants during suspended sediment transport in aquatic system

Pollutants release is highly consistent with suspended sediment concentration （SSC） in water column, especially during re-suspension and transport events. The present research focuses on pollutant dynamic release from re-suspended sediment, especially the vertical distribution relationship between them. The sediment erosion experiments on a series of uniform flow are conducted in a circulate flume. Reactive tracer （phosphorus） is used as the contaminant in fine-grained sediments to identify the release characteristic length and time. Experimental results show that the flow condition near-bed depends on the sediment surface roughness. The region with high turbulent intensities corresponds to a high concentration sediment layer. In addition, the SSC decreases with the distance, water depth, and particle grain size. The sediment in a smaller grain size takes much more time to reach equilibrium concentration. Total phosphorus （TP） concentration changes along the water depth as SSC in the initial re-suspension stage, appearing in two obvious concentration regimes： the upper low-concentration layer and the high-concentration near-bottom layer. This layered phenomenon remains for about 3 hours until SSC distri- bution tends to be uniform. Longitudinal desorption plays an important role in long-way transport to reduce the amount of suspended sediment in water column.