Use of a long-spacer-side-chain liquid crystalline polysiloxane containing a crown ether as a stationary phase for capillary gas chromatography

A new kind of side chain liquid crystalline polysiloxane containing a crown ether with a longer spacer (PSC-11) has been prepared and coated on a fused silica capillary column. The main chroma-tographic characteristics including efficiency, polarity, and selectivity have been examined. The phase exhibits the retention properties of both liquid crystal and crown ether stationary phases and possesses higher efficiency and better selectivity than PSC-3, which has a shorter spacer between the main polysiloxane chain and liquid crystalline side chain.     

条件泛函及其导数非参数估计的强一致收敛速度

研究了条件泛函及其导数的非参数估计,对随机与固定设计的条件泛函,分别利用核估计和非参数加权估计,在核函数及权函数满足一定条件下,证明了估计一致强收敛于待估函数的速度可达到最优。从而进一步推广和发展了Hrdle,etal.(1988)、Severini,etal.(1992)的许多结果。     

Patterned uniformly orientated silicon nanocrystallite films and efficient field emission characteristics

Patterned uniformly (100)-orientated silicon nanocrystallite (SiNC) films were fabricated based on hydrogen ion implantation technique and typical electrochemical anodic etching method. The surface morphology and microstructure characteristics of the films were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and atomic force microscopy. The efficient field emission with low turn-on field of about 3.2 V/μm at current density of 0.1 μA/cm² was obtained. The emission current density from the SiNC films reached 1 mA/cm² under a bias field of about 11 V/μm. The experimental results demonstrate that the SiNC films have great potential applications for flat panel displays.     

Extended X-ray absorption fine structure studies of thulium doped GaN epilayers

The local structure of Tm³⁺ ions incorporated into GaN epilayers was studied by means of Extended X-ray Absorption Fine Structure. The samples were doped either in situ during growth by Molecular Beam Epitaxy or by ion implantation of layers grown by Metal Organic Chemical Vapour Deposition. The implantation was done at ion energy of 300 keV and different nominal fluences of 3×10¹⁵, 4×10¹⁵ cm⁻² and 5×10¹⁵ cm⁻². The concentration of Tm in the samples studied was measured by Wavelength Dispersive X-ray analysis. For the in situ doped sample with concentration of 0.5%, and for all of the implanted samples, Tm was found on the Ga site in GaN. The ion implanted sample and an in situ doped sample with a similar concentration of Tm showed the same local structure, which suggests that the lattice site occupied by Tm does not depend on the doping method. When the average Tm concentration for in situ doped samples is increased to 1.2% and 2.0%, Tm is found to occupy the Ga substitutional site and the presence of a substantial number of Tm ions in the second coordination sphere indicates dopant clustering in the films. The formation of pure TmN clusters was found in an in situ doped sample with a dopant concentration of 3.4%.     

Synthesis and characterization of novel thermoresponsive‐co‐biodegradable hydrogels composed of N‐isopropylacrylamide,poly(L‐lactic acid), and dextran

A series of novel multifunctional hydrogels that combined the merits of both thermoresponsive and biodegradable polymeric materials were designed, synthesized, and characterized. The hydrogels were copolymeric networks composed of N‐isopropylacrylamide (NIPAAM) as a thermoresponsive component, poly(L‐lactic acid) (PLLA) as a hydrolytically degradable and hydrophobic component, and dextran as an enzymatically degradable and hydrophilic component. The chemical structures of the hydrogels were characterized by an attenuated total reflection–Fourier transform infrared spectroscopy (ATR–FTIR) technique. The hydrogels were thermoresponsive, showing a lower critical solution temperature (LCST) at approximately 32 °C, and their swelling properties strongly depended on temperature changes, the balance of the hydrophilic/hydrophobic components, and the degradation of the PLLA component. The degradation of the hydrogels caused by hydrolytic cleavage of ester bonds in the PLLA component was faster at 25 °C below the LCST than at 37 °C above the LCST, determined by the ATR–FTIR technique. Due to their multifunctional properties, the designed hydrogels show great potential for biomedical applications, including drug delivery and tissue engineering. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5054–5066, 2004     

Unexpected end‐groups of poly(acrylic acid) prepared by RAFT polymerization

Low‐molecular‐weight poly(acrylic acid) (PAA) was synthesized by reversible addition fragmentation chain transfer polymerization with a trithiocarbonate as chain‐transfer agent (CTA). With a combination of NMR spectroscopy and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, the PAA end‐groups of the polymer were analyzed before and after neutralization by sodium hydroxide. The polymer prior to neutralization is made up of the expected trithiocarbonate chain‐ends and of the H‐terminated chains issued from a reaction of transfer to solvent. After neutralization, the trithiocarbonates are transformed into thiols, disulfides, thiolactones, and additional H‐terminated chains. By quantifying the different end‐groups, it was possible to demonstrate that fragmentation is the rate limiting step in the transfer reaction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5439–5462, 2004     

Influence of Particle Morphology and Flow Conditions on the Dispersion Behavior of Fumed Silica in Silicone Polymers

The dispersion behavior of agglomerates of several grades of fumed silica in poly(dimethyl siloxane) liquids has been studied as a function of particle morphology and applied flow conditions. The effects of primary particle size and aggregate density and structure on cohesivity were probed through tensile and shear strength tests on particle compacts. These cohesivity tests indicated that the shear strength of particle compacts was two orders of magnitude higher than the tensile strength at the same overall packing density. Experiments carried out in both steady and time‐varying simple‐shear flows indicate that dispersion occurs through tensile failure. In the steady‐shear experiments,enhanced dispersion was obtained at higher levels of applied stress and, at comparable levels of applied stress, dispersion was found to proceed faster at higher shear rates. Experiments conducted in time‐varying flows further corroborated the results obtained in tensile cohesivity tests. Experiments in which the mean and maximum stresses in the time‐varying flows were matched to the stresses produced in steady shear flows highlight the influence of flow dynamics on dispersion behavior.     

信息化对区域经济影响的数理分析

本文以信息化与经济指标资料为基础,运用加权回归、因子分析和聚类分析等方法,讨论了全国31个省(市、区)信息化水平及其与经济发展关系,给出地区综合发展水平的排行榜。并提出若干促进信息化建设的建议。     

一类含有非线性传染率的传染病模型的全局稳定性

讨论了一类带有非线性传染率的SIRS型传染病模型,得到了无病平衡点和地方病平衡点存在的阈值条件,借助构造Dulac函数和Liapunov函数,找到了两类平衡点全局渐近稳定的充要条件.     

UV curing of a novel resin derived from poly(ethylene terephthalate)

The synthesis and characterization of photopolymerizable unsaturated polyester resins based on PET waste are described. The resins came from a depolymerization process based on the glycolysis of PET by diethylene glycol (DEG). Different molecular weights of glycolysates were synthesized. Then, the latter was functionalized by a methyl hemiester of maleic acid to obtain unsatured α,ω‐bismaleate PET oligomers. In the presence of an electron donor monomer, such as triethylene glycol divinyl ether, these electron acceptor oligomers were copolymerized by way of charge‐transfer complexes under UV irradiation. The reaction was monitored in situ by real‐time IR spectroscopy to study the kinetics of photopolymerization. This one was studied in relation with the physical and chemical characteristics of oligoesters and the composition of mixtures containing divinyl ethers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1324–1335, 2007