分支通道内液-液自发渗吸规律研究

自发渗吸过程中两相界面在分支通道内的破裂和汇合为强非稳态过程, 难以用经典理论及常规数值计算方法准确描述。本文采用格子玻尔兹曼方法研究孔隙结构分支通道基本单元内的液-液自发渗吸行为, 对比出入口通道大小、两相黏度差异对液-液自发渗吸行为的影响。入口通道的大小对两相界面破裂进入分支通道内的竞争自发渗吸行为起控制作用, 而两相流体黏度控制了自发渗吸整体行为。本研究为复杂孔隙结构内液-液自发渗吸行为定量表征提供研究基础。     

5-Aza-2′-deoxycytidine reactivates the CDH1 gene without influencing methylation of the entire CpG island or histone modification in a human cancer cell line

It is well-recognized that DNA methylation and histone modifications play critical roles in epigenetic regulation of gene activity through the alteration of chromatin structure. Recent studies have shown that in a subset of cancer cells, the silencing of the human E-cadherin (CDH1) gene is associated with hypermethylation of the CpG island. However, the associated molecular mechanism remains unclear. To understand the mechanism, we have investigated the alteration of CpG island methylation and histone modifications during the reactivation of the CDH1 gene by treatment with 5-aza-2′-deoxycytidine (5-aza-dC). Although the CDH1 gene expression was recovered by treatment with 5-aza-dC in a liver cancer cell line Li21, the methylation status of the entire CpG island and acetylation and methylation status of associated histones were not significantly altered. These results demonstrate that the silenced CDH1 gene can be reactivated without apparent alteration of histone modification or CpG island methylation.     

Regio-controlled ring-opening polymerization of perfluoroalkyl-substituted epoxides

Highly fluorinated epoxides were polymerized under mild conditions regioregularly, which gave easy access to isotactic polymers by using optically pure epoxides.     

A comparative spectroscopic investigation of21Ne and21F by pickup reactions

The reactions²²Ne(d, t)²¹Ne and²²Ne(d, τ)²¹F have been investigated in a parallel experiment atE _d=52MeV. Energy spectra of tritons andτ particles have been measured up to excitation energies of 18MeV in both²¹Ne and²¹F nuclei. Thel values could be determined, and spectroscopic factors have been obtained by a DWBA analysis of the measured angular distributions. Together with the results from a preceding \({}^{22}Ne(\vec d, \tau ){}^{21}F\) experiment, several spins could be determined in²¹F. From a comparison of the triton andτ particle spectra,T=3/2 states in²¹Ne could be identified and on this basis the new information on spins of²¹F states could be transferred to their analog states in²¹Ne. The completeT _< andT _> parts of the (2s, 1d) strengths could be observed. The 1p strength is highly fragmented. Of theT _< part only 60% of the 1p1/2 and 40% of the lp3/2 strength could be found, but the totalT _> part of the 1p strength could be localized. The spectroscopic results for positive parity states are in qualitatively good agreement with shell model predictions.     

LOWLAD: a locally weightedL 1 smoothing spline algorithm with cross validated choice of smoothing parameters

The computation ofL ₁ smoothing splines on large data sets is often desirable, but computationally infeasible. A locally weighted, LAD smoothing spline based smoother is suggested, and preliminary results will be discussed. Specifically, one can seek smoothing splines in the spacesW _m (D), with [0, 1] ⁿ D. We assume data of the formy _i =f(t _i )+ _i ,i=1,..., N with {t _i } _i=1 ^N D, the _i are errors withE( _i )=0, andf is assumed to be inW _m . An LAD smoothing spline is the solution,s , of the following optimization problem

Sidelobe suppression of spectral response in holographic optical filter

In order to suppress sidelobes of holographic filter’s spectral response we propose to use weighting of grating intensity distribution along light propagation. This can be realized in photorefractive material (for example in LiNbO₃:Fe) by using spatial selective decaying of conventional uniform grating by illumination of light through some transparent mask. Experimental results show that it is able to obtain 8 dB improvement of sidelobe level compared to uniform grating. But it is accompanied by 1.7 times expansion of main lobe and two times decrease of diffraction efficiency.     

基于任意形状颗粒集合二值图像的体积估算模型

基于任意形状颗粒集合的二值图像,提出了估计其体积(或质量)的方法.首先利用发光背景台面获取的颗粒灰度图像变换为相应的二值图像,得到颗粒的边界轮廓.然后再基于其边界信息,定义与颗粒形状特征相关的描述量,并将其无量纲化.将由此定义的无量纲参变量作为回归变量建立一个多元线性回归(multiple linear regression)模型用以估计颗粒集合的扁平度,进而估算颗粒体积.回归变量的系数由随机采样的501个样本颗粒(尺寸范围为4.75～25 mm)用误差最小平方和求得.将模型应用于由具有相似统计分布特征的其他颗粒集合,并将得到的体积估计值与其体积真实值相比较,实验结果显示模型的相对误差在±2%以内.     

Geometrical limitations in the intramolecular addition of unsymmetrical allylsilanes to enones

The geometrical constraints of the fluoride-initiated and Lewis acid-catalyzed intramolecular addition of allylsilanes to enone systems were shown to be governed by kinetic-ring-size preferences. Molecules containing adjacent quaternary carbon atoms can be prepared using this method.     

Direct mono-insertion of isocyanides into terminal alkynes catalyzed by rare-earth silylamides

Rare-earth silylamide complexes, Ln[N(SiMe3)2]3 (Ln = Y, La, Sm, Yb), effectively catalyzed the coupling reaction of isocyanides with both aliphatic and aromatic terminal alkynes under mild conditions.