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991.
Hu Yang Weisi Yin Xuxin Kong Min Xu Yefeng Yao Qun Chen Rongshi Cheng 《Colloid and polymer science》2006,284(8):935-940
The compact single-chain (SC) particulates of Poly(N-isopropylacrylamide) (PNIPAM), which have been formed above its lower critical solution temperature in an aqueous solution containing the surfactant of sodium n-dodecyl sulfate (SDS), were recovered from the solution by freeze-drying. Under scanning electron microscopy, the compact particulate appears as a spherical or elliptical particulate individually dispersed in SDS, which acts as a solid solvent to prevent agglomeration. The conformation of the compact SC particulates of PNIPAM dispersed in SDS had been studied by the solid-state high-resolution 13C NMR spectroscopy. The 13C spin-lattice relaxation time T
1 of the SC sample was determined in comparison with that of the original one. It was found that the T
1 of the methyl carbon in the isopropyl group of the SC sample was about 45% higher than that in the original multichain sample, which revealed the differences in the motion of the methyl group in the different condensed states and illuminated the characteristic conformation of the compact SC globular particulates of PNIPAM. 相似文献
992.
溶质在超临界流体中的溶解度与流体的密度密切相关。本文采用微扰硬球链理论对纯CO2及CO2-正戊烷、CO2-正庚烷、CO2-正癸烷体系在不同条件下的密度进行计算,计算值与文献给出的实验值符合很好。 相似文献
993.
Bingzhi Li Min Chen Yang Li Xiaolin Cao Yongxin She Jungang Yin Shuang Cong Ziping Zhang 《Journal of separation science》2022,45(3):752-759
In this paper, a flower-like molybdenum disulfide material was prepared by hydrothermal method and was first used as adsorbents in the solid-phase extraction process for enriching N-nitrosoamines. Molybdenum disulfide exhibited three-dimensional petal-like microspheres with about 500 nm in diameter. The relevant analyte extraction and elution parameters (sample volumes, solution pH, washing solvents, elution solvents, and elution volumes) were optimized to improve the solid-phase extraction efficiency. The solid-phase extraction process coupled with high-performance liquid chromatography-tandem mass spectrometry for determining N-nitrosoamines in environmental water samples was established. The limits of detection were in the range of 0.01–0.05 ng/mL. The satisfactory recoveries (68.9–106.1%) were obtained at three different spiked concentrations (2, 5, and 8 ng/mL) in water samples, and the relative standard deviations were between 1.96 and 8.38%. This proposed method not only showed high sensitivity and good reusability but also provided a new adsorbent for enriching trace N-nitrosoamines in environmental water samples. 相似文献
994.
In situ self-assemblies of new biodegradable triblock PLLA-b-PBS-b-PLLA and PDLA-b-PBS-b-PDLA have been investigated in acetonitrile solution. At first, two series of PLLA-b-PBS-b-PLLA and PDLA-b-PBS-b-PDLA, respectively denoted as the P and Q triblock copolyester series, were prepared with fixed PBS block ((overline) M(n,NMR) = 6.9 kDa) and diverse enantiomeric PLLA/PDLA blocks. Further, their chemical structures and thermal properties were characterized by means of titration, nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), polarimeter, wide-angle X-ray diffraction (WAXD) and thermal analytical instruments. When mixing the synthesized enantiomeric copolyester pairs denoted as P(1)/Q(1) - P(8)/Q(8) in acetonitrile solution at 60 degrees C, in situ self-assemblies were found to happen for the P(4)/Q(4) to P(8)/Q(8) pairs, bearing longer enantiomeric PLA block lengths. DSC and WAXD analysis of the self-assembled microparticles demonstrated that PLLA/PDLA racemic crystals were formed for the P(5)/Q(5) - P(8)/Q(8) systems, as evidenced by their melting points over 200 degrees C, and a new X-ray diffraction peak detected at 2theta = 11.8 degrees . Moreover, morphological studies by scanning electron microscopy (SEM) indicated the formation of disk- or platelet-like microparticles. It was noted that the diameters of the microparticles self-assembled in situ decreased from 1.28-1.50 mum down to 480-660 nm, through tailoring the enantiomeric PLA block length. Other factors, such as a central PBS block, the enantiomeric block length and the preparation conditions were suggested to play important roles in the in situ self-assembly of these enantiomeric triblock copolyesters. These results provide a facile way to self-assemble hydrophobic, biodegradable microparticles, through tuning the important van der Waals stereocomplexation interactions between two enantiomeric blocks in solution. 相似文献
995.
996.
Coupling characteristics of high birefringence dual-core As2S3 rectangular lattice photonic crystal fiber 下载免费PDF全文
A type of As2S3 chalcogenide glass mid-infrared dual-core photonic crystal fiber has been proposed.The dualcore photonic crystal fiber(PCF) consists of two asymmetric cores.The high polarization property and the coupling characteristics have been studied by using the finite element method and mode coupling theory.Numerical results show that the birefringence at wavelength λ = 10 μm is up to 0.01386 and the coupling length can reach wavelength λ = 5 μm,261 μm and 271.44 μm for x-polarized mode and y-polarized mode,respectively.It demonstrates that a 6.786-mm-long fiber can exhibit an extinction ratio of better than 10 dB and a bandwidth of 180 nm. 相似文献
997.
JUNA团队计划利用CJPL所提供的极低本底条件和400 kV高压平台上2.45 GHz ECR离子源产生的毫安量级束流首次在天体物理能区对关键核反应进行直接测量。实验需要10 emA的质子束流和He+束流以及2 emA的He2+束流。使用2.45 GHz离子源产生毫安量级的He2+束流是离子源制造的难点。由于离子源分析磁铁分辨能力有限,无法区分He2+和H+2离子,本文首次使用核反应法对离子源产生的A/q=2的束流进行了鉴别,结果显示,JUNA项目2.45 GHz ECR离子源无法产生毫安量级的He2+束流。该研究成果为JUNA项目离子源的设计提供了重要的参考依据。JUNA团队另外研制了一台微波频率为14.5 GHz的ECR离子源并成功产生2 emA的He2+束流来满足实验需求。 相似文献
998.
荒漠植物含水量的光谱特征分析 总被引:3,自引:0,他引:3
用美国SVC的HR-768便携光谱仪现地测定了9种荒漠植物的高光谱并在实验室使用烘干法测定相应植物的含水率,对测定的光谱数据使用ENVI软件去除包络线,运用相关系数法分析植物含水率与反射光谱之间的关系,结果表明:978~1 030 nm波段与植物含水率相关性一般,1 133~1 266 nm波段与植物含水率相关性较好,1 374~1 534 nm波段与植物含水率相关性最好,是表达植物含水率大小的特征波段.对1 374~1 534 nm波段光谱数据进行聚类分析,可将测定的植物划分为含水率较高(>70%)、中等(50%~70%)、较低(<50%)3个等级.以上研究揭示了荒漠植物含水量大小和光谱数据之间的关系,为荒漠区生境分析和利用遥感数据进行荒漠植物监测提供了参考依据. 相似文献
999.
A novel method of synthesizing Ti3+-doped TiO2 was proposed. Ti3+-doped TiO2 hollow spheres were prepared with different thickness of carbon shell by using atmospheric pressure plasma jet generated by dual-frequency power sources. The as-synthesized Ti3+-doped TiO2 hollow microspheres were characterized by X-ray diffraction (XRD) pattern, scanning electron microscope (SEM) images, high-resolution transmission electron microscopy (HRTEM) images, Raman spectra, X-ray photoelectron spectroscopy (XPS), and UV–vis spectra. These results indicated that these samples had mixed phases of anatase and rutile and the structure of hollow sphere varied with different thickness of carbon shell. The Ti-O-C chemical bond was the connection between the TiO2 hollow sphere and carbon layer. Amount of Ti3+ ions were found, which were accompanied with the formation of oxygen vacancies. Meantime, the as-synthesized catalysts also display strong absorption in the visible light region and have a narrow band energy gap. Optical emission spectroscopy (OES) was used to observe different excited species in the discharge area. These results showed that the oxygen content had a significant impact on the number of oxygen vacancies. Finally, the photocatalytic activities of as-prepared samples were evaluated by decomposition of rhodamine B aqueous solution, which showed better photocatalytic activity under UV–vis light irradiation. 相似文献
1000.