Facile synthesis of anisotropic Au@SiO2 core-shell nanostructures

Anisotropic Au@SiO(2) core-shell nanostructures have been fabricated from CTABr-stabilized Au nanoparticles with a facile synthesis involving a single growth solution. This procedure circumvents tedious surface modification steps and allows for the SiO(2) shell thickness to be tuned from 5 to 20 nm by modulating the nanoparticle number density and concentration of silica precursor.     

The impact of substituents on the transition states of SN2 and E2 reactions in aliphatic and vinylic systems: remarkably facile vinylic eliminations

For a series of α and β substituted haloethanes and haloethenes, gas-phase experiments and computational modeling have been used to characterize their nucleophilic substitution and elimination reactions. Despite being less thermodynamically favorable, the vinylic eliminations have rate constants and computed barriers that are similar to those of analogous aliphatic eliminations. This is the result of the vinylic systems shifting to more E1(cb)-like transition states and exploiting the inherent greater acidity of vinylic hydrogens. In general, the α-substituents have a greater impact on the S(N)2 pathways and stabilize the transition states via field and polarizability effects. Substantial stabilization is also provided to the E2 transition states by the α-substituents, but they have surprisingly little impact on the geometries of the transition states of either pathway. The β-substituents generally lead to a strong bias toward elimination and greatly affect the synchronicity of the elimination (more E1(cb)-like) as well as its location on the reaction coordinate (early). The experimental and computational data are in good accord, and the full data set provides a comprehensive picture of substituent effects on solvent-free S(N)2 and E2 processes.     

基于枝向量行列式算法的高校教学信息化系统反馈分析

在建立9棵简化流率基本入树模型的基础上,运用SD枝向量行列式算法进行了系统反馈环计算,并运用关键因果链分析对策生成法,对全部反馈环进行结构、极性、关键因果链分析及分类,生成7大类共15条关键因果链,最后根据全部关键作用因果链揭示的主要问题,生成了7条对策,以期为提升高校教学信息化水平组织管理对策的制定与实施提供参考依据。 更多还原     

Effect of steam on the single particle ignition of solid fuels in a drop tube furnace under air and simulated oxy-fuel conditions

This article investigates the effect of steam on the ignition of single particles of solid fuels in a drop tube furnace under air and simulated oxy-fuel conditions. Three solid fuels, all in the size range 125–150 µm, were used in this study; specifically, a low rank sub-bituminous Colombian coal, a low-rank/high-ash sub-bituminous Brazilian coal and a charcoal residue from black acacia. For each solid fuel, particles were burned at a constant drop tube furnace wall temperature of 1475?K, in six different mixtures of O₂/N₂/CO₂/H₂O, which allowed simulating dry and wet conventional and oxy-fuel combustion conditions. A high-speed camera was used to record the ignition process and the collected images were treated to characterize the ignition mode (either gas-phase or surface mode) and to calculate the ignition delay times. The Colombian coal particles ignite predominately in the gas-phase for all test conditions, but under simulated oxy-fuel conditions there is a decrease in the occurrence of this ignition mode; the charcoal particles experience surface ignition regardless of the test condition; and the Brazilian coal particles ignite predominately in the gas-phase when combustion occurs in mixtures of O₂/N₂/H₂O, but under simulated oxy-fuel conditions the ignition occurs predominantly on the surface. The ignition delay times for particles that ignited in the gas-phase are smaller than those that ignited on the surface, and generally the simulated oxy-fuel conditions retard the onset of both gas-phase and surface ignition. The addition of steam decreases the gas-phase and surface ignition delay times of the particles of both coals under simulated oxy-fuel conditions, but has a small impact on the gas-phase ignition delay times when the combustion occurs in mixtures of O₂/N₂/H₂O. The steam gasification reaction is likely to be responsible for the steam effect on the ignition delay times through the production of highly flammable species that promote the onset of ignition.     

A PIXE study of elemental concretions in aortic wall tissue

Calcification of implanted biological heart valves leads to malfunction after a certain period. The substance mainly responsible for accumulated calcium deposits in glutaraldehyde. The study was divided into was phase: chemical detoxification of the tissue by glutaraldehyde extraction to minimize calcification, and a subsequent PIXE analysis of more than 80 aortic wall samples to examine the efficiency of the detoxification process.     

PdCO(OH)-体系中OH-助催化性能的成键能研究

本文使用相对论赝势从头计算方法和成键能判据[1 ] 研究了模型化合物 Pd CO(OH) -的电子结构 ,讨论了 OH-的助催化作用。得出 OH-对 Pd CO的助催化作用既可以通过其与金属 Pd形成化学键 (通过金属 )来实现 ,也可以通过空间电荷静电作用 (通过空间 )来实现。由分子轨道成键能分析指出 CO分子的强成键占据分子轨道 3σ和 1π的削弱是活化 CO的关键。     

From colloidal Co/CoO core/shell nanoparticles to arrays of metallic nanomagnets: surface modification and magnetic properties.

The magnetic properties of nanoparticles can be subject to strong variations as the chemical composition of the particle surface is modified. To study this interrelation of surface chemistry and magnetism, self-assembled layers of colloidal 9.5 nm Co/CoO core/shell nanoparticles were exposed to mild reactive hydrogen and oxygen plasmas. The consecutive oxygen/hydrogen plasma treatment transforms the particle layer into an array of metallic nanomagnets with complete reduction of the oxide and removal of the organic surfactants. The original arrangement of the particle array and the number of Co atoms per particle remains unchanged within the experimental error, and thus this is a possible route for the fabrication of ultrahigh-density magnetic bit structures from colloidal dispersions. The magnetic properties can be tuned by controlling the thickness of the surface oxide layer, which magnetically hardens the particles, as evidenced by element-specific magnetic hysteresis loops.     

Low temperature self-ion irradiation of pure and granular aluminium-films

Al-films, evaporated at room temperature under different oxygen partial pressures, were irradiated with self-ions (500 keV, Al⁺⁺) at low temperature (<7 K). The observed increase of the resistivity and of the superconducting transition temperatureT _c depends strongly on the oxygen contentc ₀ present in the layers. A qualitative different behaviour of the above quantities was found for different fluence ranges of the bombarding ions. For high fluences in all cases an oxygen stabilized disorder state was obtained with correspondingT _c-increases betweenT _c=0.2 K for the purest films (c ₀0.5 at %) andT _c =1.2 K for films with c ₀=40 at %. The annealing behaviour of the irradiated films is also dependent on the oxygen contentc ₀.