无溶剂Fe3O4纳米流体的制备及表征

采用共沉淀法合成Fe3O4纳米粒子, 将含有硅氧烷基的离子型改性剂二甲基十八烷基氯化铵与Fe3O4纳米粒子进行接枝反应, 再用脂肪醇聚氧乙烯醚磺酸盐的长链阴离子交换Cl-, 在Fe3O4纳米粒子表面生成具有阴、 阳离子双电层结构的表面处理层, 得到无溶剂Fe3O4纳米流体. 研究结果表明, 在Fe3O4纳米粒子表面成功接枝了有机物长链, 改性的Fe3O4纳米粒子呈单分散分布, 其损耗剪切模量G″明显大于储能剪切模量G', 具有明显的流体行为, 在室温下即可流动.     

Monomeric adenine decay dynamics influenced by the DNA environment

We report on‐the‐fly surface‐hopping dynamics simulations of single adenine embedded in solvated DNA oligomers, (dA)₁₀ and (dA)₁₀·(dT)₁₀. Both model systems are found to decay from the S₁ to the S₀ state via distinct monomeric channels, on account of the strong hydrogen‐bonding interactions between the Watson–Crick pair in the double‐stranded oligomer. Surprisingly, the decay times (several picoseconds) for the current models are 10 times longer than those of adenine in the gas or aqueous phase, while matching one of the time constants observed experimentally. We discuss possible reasons for these longer decay times, including steric hindrance in the DNA strands, electronic effects of the environment, and the presence of other local excited‐state minima. We present optimized geometries and relative energies for representative S₀ and S₁ minima as well as conical intersections related to the hopping events. We have also computed steady‐state and time‐dependent fluorescence spectra that may help understand the experimental observations. © 2012 Wiley Periodicals, Inc.     

Thermodynamic study on the complexation of Am(III) and Eu(III) with tetradentate nitrogen ligands: a probe of complex species and reactions in aqueous solution

A thermodynamic investigation has been performed to study the complexation of trivalent metal (M) ions (M = Am(III), Eu(III)) with tetradentate ligands (L), 6,6'-bis(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2'-bipyridines (BTBPs), by using relativistic quantum mechanical calculations. The structures and stabilities of the inner-sphere BTBPs complexes were explored in the presence of various counterions such as NO(3)(-), Cl(-), and ClO(4)(-). According to our calculations, Am(III) and Eu(III) can chelate eight or nine water molecules at most, whereas more stable species like M(NO(3))(3)(H(2)O)(4) tend to be formed in the presence of nitrate ions. The inner sphere of the BTBPs complexes can accommodate four water molecules or three nitrate ions based on our calculations, forming species such as [ML(H(2)O)(4)](3+) and ML(NO(3))(3). Compared with Eu(III) complexes, the Am(III) counterparts have obviously lower binding energies in both the gas phase and solution. In addition, the solvent effect significantly decreases the binding energies of the BTBPs complexes. It has been found that the complexing reactions, in which products and reactants possess the same or close number of nitrate ions, are more favorable for formation of the BTBPs complexes. In short, the reactions of M(NO(3))(3)(H(2)O)(4) → ML(NO(3))(3) and [M(NO(3))(H(2)O)(7)](2+) → [ML(2)(NO(3))](2+) are probably the dominant ones in the Am(III)/Eu(III) separation process.     

基于三角模糊数序列的灰色预测模型

以GM(1,1)模型为代表的灰色预测模型是以精确数序列为基础,难以满足实际需要.为了使灰色模型适应于模糊数序列,具体给出了一种基于三角模糊数序列的建模方法,这种方法也可以实现对二元区间模糊数和梯形模糊数序列的建模.首先由三角模糊数序列得出三个含有等量信息的精确数序列:重心序列、隶属函数的覆盖面积序列和中界点序列,对这三个序列分别建模后,再导出原始三角模糊数序列的三个界点的预测模型.这种建模方法既保持了模糊数的整体性又提高了建模序列的光滑度,提高了预测精度.最后进行了多组随机三角模糊数序列的数据模拟,验证了模型的有效性.     

(0, mf-k+1)-图中具有正交(0,f)-因子分解的子图

设G是一个简单图, f是定义在V(G)上的整数值函数,且m是大于等于2的整数. 讨论(0, mf-k+1)-图G的正交因子分解, 并且证明了对任意的1≤k≤m, (0, mf-k+1)-图G中存在着一个子图R, 使得R有一个(0,f)-因子分解正交于图G中的任意一个k-子图H.     

Highly efficient Cherenkov radiation generation in the irregular point of hollow-core photonic crystal fiber

Highly efficient Cherenkov radiation(CR) is generated by the soliton self-frequency shift(SSFS) in the irregular point of a hollow-core photonic crystal fiber(HC-PCF) in our laboratory.The impacts of pump power and wavelength on the CR are investigated,and the corresponding nonlinear processes are discussed.When the average power of the 120 fs pump pulse increases from 500 mW to 700 mW,the Raman soliton shifts from 2210 nm to 2360 nm,the output power of the CR increases by 2.3 times,the maximum output power ratio of the CR at 539 nm to that of the residual pump is calculated to be 24.32:1,the width of the output optical spectrum at the visible wavelength broadens from 35 nm to 62 nm,and the conversion efficiency η of the CR in the experiment can be above 32%.     

A High-Efficiency Spectral Method for Two-Dimensional Ocean Acoustic Propagation Calculations

The accuracy and efficiency of sound field calculations highly concern issues of hydroacoustics. Recently, one-dimensional spectral methods have shown high-precision characteristics when solving the sound field but can solve only simplified models of underwater acoustic propagation, thus their application range is small. Therefore, it is necessary to directly calculate the two-dimensional Helmholtz equation of ocean acoustic propagation. Here, we use the Chebyshev–Galerkin and Chebyshev collocation methods to solve the two-dimensional Helmholtz model equation. Then, the Chebyshev collocation method is used to model ocean acoustic propagation because, unlike the Galerkin method, the collocation method does not need stringent boundary conditions. Compared with the mature Kraken program, the Chebyshev collocation method exhibits a higher numerical accuracy. However, the shortcoming of the collocation method is that the computational efficiency cannot satisfy the requirements of real-time applications due to the large number of calculations. Then, we implemented the parallel code of the collocation method, which could effectively improve calculation effectiveness.     

In-cylinder tumble flows and performance of a motorcycle engine with circular and elliptic intake ports

The temporal and spatial evolution processes of the flows in the cylinder of a four-valve, four-stroke, single cylinder, reciprocating motorcycle engine installed with the elliptic and circular intake ports were experimentally studied by using the particle image velocimetry (PIV). The engine was modified to fit the requirements of PIV measurement. The velocity fields measured by the PIV were analyzed and quantitatively presented as the tumble ratio and turbulence intensity. In the symmetry plane, both the circular and elliptic intake ports could initiate a vortex around the central region during the intake stroke. During the compression stroke, the central vortex created in the cylinder of the engine with the circular intake port disappeared, while that in the engine cylinder with the elliptic intake port further developed into the tumble motion. In the offset plane, weak vortical structures were initiated by the bluff-body effect of the intake valves during the intake stroke. The vortical structures induced by the elliptic intake port were more coherent than those generated by the circular intake port; besides, this feature extends to the compression stroke. The cycle-averaged tumble ratio and the turbulence intensity of the engine with the elliptic intake port were dramatically larger than those of the engine with the circular intake port. The measured engine performance was improved a lot by installing the elliptic intake port. The correlation between the flow features and the enhancement of the engine performance were argued and discussed.     

关于时空标架变换和物质标架无关性原理

建立了欧几里德标架无关性的一般表述与某一参考标架\phi下作相对刚体运动的一般曲线坐标、分量表述之间的关系,从而使欧几里德标架无关性的张量表述有相应的分量表述形式.建立这种联系的基础是, 参考标架\phi^\ast 下描述的运动在参考标架\phi 中某坐标系下的分量结果, 对应于\phi下另一相对该坐标系作相同刚体运动的坐标系下描述\phi观测的运动的分量结果. 通过例子说明了Truesdell和Noll用等价动力过程,关于物质标架无关性原理的陈述,比Svendsen和Bertram及Liu的本构关系在参考标架变换下的形式不变性更合理且方便,尤其是对微分方程形式的本构关系更是如此.