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.     

Experimental Study of Liquid Hydrocarbons Pyrolysis to Acetylene in H2/Ar Plasma

Liquid hydrocarbons including n-hexane, cyclohexane and toluene are pyrolyzed in H₂/Ar plasma to investigate the effects of feedstock properties and key operating conditions (e.g., the feedstock specific input power and residence time) on the reaction performance. The experiments verify that the non-aromatic hydrocarbons show better chemical reactivity than partially aromatic substances. Meanwhile, the straight-chain alkanes and cycloalkanes have better yields of ethylene during the pyrolysis. The results also demonstrate that the pyrolysis reactions are almost completed within the first 0.8?ms in Ar/H₂ plasma independent of the feed substances (i.e., liquid hydrocarbons), where the increased feedstock specific input power enhances the reactant conversions and correspondingly raises the yields of acetylene. At a feedstock specific input power of 4.7?×?10⁴?kJ/kg, the n-hexane conversion is over 90?% and the yield of acetylene reaches 70?%. In addition, when using n-hexane as the feedstock, very little coke is formed during the course of reaction. Comprehensive comparisons of the current experiments with the data reported in the literature are made to point out the key influencing factors, i.e., the effective mass ratio of C/H (R _C/H) in the gaseous phase and the quench temperature. Both two factors would need to be enhanced in order to get a better performance. Finally, the improvements on the specific energy requirement of this process are discussed.     

Catalytic palladium nanoparticles supported on nanoscale MOFs: a highly active catalyst for Suzuki–Miyaura cross-coupling reaction

Pd nanoparticles have been successfully supported on nanoscale metal-organic frameworks (NMOFs) by using a simple and effective microwave-assisted impregnation process. The resulting composite, representing as a highly active NMOFs supported metal nanoparticles catalyst for the Suzuki cross-coupling reaction between aryl/heteroaryl halides and arylboronic acids, is well characterized, and its high activity and good recyclability are discussed in details. It reveals that, compared to the corresponding bulk MOFs and conventional active carbon materials, nanoscale MOFs as novel support materials for heterogeneous catalysts can exhibit superior performance in the catalytic reactions.     

非低温法的稀有气体纯化技术概述

稀有气体广泛应用于工业生产中,如离子刻蚀、检漏等。但是它们在地球上的含量比较少,属于稀有资源,因此需要对它们进行纯化以循环再利用。首先介绍了不同气体纯化的原理,然后以实际生产中的不同稀有气体使用范围为例,说明纯化装置的设计方法和需要考虑的问题。为以后气体纯化装置的设计提供借鉴。     

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.     

Red–Green–Blue Trichromophoric Nanoparticles with Dual Fluorescence Resonance Energy Transfer: Highly Sensitive Fluorogenic Response Toward Polyanions

A red–green–blue (RGB) trichromophoric fluorescent organic nanoparticle exhibiting multi‐colour emission was constructed; the blue‐emitting cationic oligofluorene nanoparticle acted as an energy‐donor scaffold to undergo fluorescence resonance energy transfer (FRET) to a red‐emitting dye embedded in the nanoparticle (interior FRET) and to a green‐emitting dye adsorbed on the surface through electrostatic interactions (exterior FRET). Each FRET event occurs independently and is free from sequential FRET, thus the resultant dual‐FRET system exhibits multi‐colour emission, including white, in aqueous solution and film state. A characteristic white‐emissive nanoparticle showed visible responses upon perturbation of the exterior FRET efficiency by acceptor displacement, leading to highly sensitive responses toward polyanions in a ratiometric manner. Specifically, our system exhibits high sensitivity toward heparin with an extremely low detection limit.