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881.
Vladimir Kurenok 《Transactions of the American Mathematical Society》2008,360(2):925-938
Let be of the form where is a symmetric stable process of index with . We obtain various -estimates for the process . In particular, for and any measurable, nonnegative function we derive the inequality As an application of the obtained estimates, we prove the existence of solutions for the stochastic equation for any initial value .
882.
Chemical surface modifications of microfibrillated cellulose 总被引:1,自引:0,他引:1
Per Stenstad Martin Andresen Bjørn Steinar Tanem Per Stenius 《Cellulose (London, England)》2008,15(1):35-45
Microfibrillated cellulose (MFC) was prepared by disintegration of bleached softwood sulphite pulp through mechanical homogenization.
The surface of the MFC was modified using different chemical treatments, using reactions both in aqueous- and organic solvents.
The modified MFC was characterized with fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS)
and transmission electron microscopy (TEM). Epoxy functionality was introduced onto the MFC surface by oxidation with cerium
(IV) followed by grafting of glycidyl methacrylate. The length of the polymer chains could be varied by regulating the amount
of glycidyl methacrylate added. Positive charge was introduced to the MFC surface through grafting of hexamethylene diisocyanate,
followed by reaction with the amines. Succinic and maleic acid groups could be introduced directly onto the MFC surface as
a monolayer by a reaction between the corresponding anhydrides and the surface hydroxyl groups of the MFC. 相似文献
883.
The concerted mechanism of free radical SH2′ reaction of 2‐substituted allyl chloride was suggested again by inverse secondary α‐deuterium isotope effect. The transition state of free radical SH2′ reaction of allyl chlorides seems to be symmetrical and is not as early as that of a free radical addition reaction. 相似文献
884.
LLDPE was blended with esterified styrene-maleic anhydride (ESMA) to improve the environmental degradation characteristics of LLDPE. ESMA was synthesized by esterifying styrene maleic anhydride (SMA) with n-decanol. LLDPE was blended with ESMA (EDP blends) and SMA separately in a single screw extruder by melt mixing. Composition of ESMA was varied from 20 to 40 wt% in the blends. LLDPE grafted with glycidyl methacrylate (LLDPE-g-GMA) was used as compatibilizer to improve the compatibility. Scanning electron photomicrograph (SEM) of cryofractured impact specimens showed significant reduction in domain size and uniform distribution of ESMA in LLDPE matrix in presence of compatibilizer in 70/30 blends. Environmental degradability was assessed by subjecting the films to soil burial test and exposure to buffer solution of different pH. Environmental degradation was followed by measuring the periodic change in weight of the blend samples. Films were exposed to accelerated and natural weathering and photodegradation was assessed by noting the embrittlement time of the film. Films of compatibilized blends fragmented at a faster rate than the films of uncompatibilized blend. Carbonyl index of films subjected to natural weathering was also found to be higher than that for the virgin LLDPE films. 相似文献
885.
Takayoshi Ishimoto Masanori Tachikawa Umpei Nagashima 《International journal of quantum chemistry》2008,108(3):472-481
To optimize the exponent values in protonic and deuteronic Gaussian‐type functions (GTF) by the elimination of translational and rotational motions, we have proposed the new scheme of an analytical gradient formula with respect to the exponent values in the multi‐component molecular orbital scheme, which can take into account the quantum effects of protons and deuterons, under the Hartree‐Fock level of theory. Numerical assessment of H2 and D2 molecules confirms that there is a clear difference between distributions of protonic and deuteronic orbitals following the elimination of translational and rotational motions. In particular, the d‐type GTF in the protonic orbital drastically improves the total energy. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献
886.
光敏感双亲性梳状SMA聚合物的合成及其胶束化 总被引:1,自引:0,他引:1
以含香豆素型苯乙烯类光敏单体(coumarin-containing styrene monomer, CS)与苯乙烯(St)、马来酸酐(MA)为反应单体, 以偶氮二异丁腈(AIBN)为引发剂制备了光敏感三元苯乙烯-马来酸酐共聚物(SMA)双亲交替聚合物P(St/CS-alt-MA), 再利用羧酸酐基元与正辛胺的室温胺解反应获得光敏感双亲性梳状聚合物P(St/CS-alt-MAA8). 用傅立叶变换红外光谱(FTIR)、凝胶渗透色谱(GPC)、1H核磁共振(1H-NMR)等对该双亲梳状聚合物进行结构表征. 通过香豆素基元的光二聚作用, 使梳状聚合物溶解在DMSO中进行光照预交联; 非交联与预交联聚合物分别在选择性溶剂中自组装形成胶束; 利用羧酸基元与NaOH的离子化作用改变聚合物胶束的亲疏水性质. 动态激光光散射(DLS)与芘荧光探针实验表明预交联聚合物胶束较非交联胶束粒径大, 负载芘的能力强; 离子化作用使聚合物胶束解离重组成粒径更小的胶束, 但预交联胶束较非交联胶束小, 离子化后胶束疏水微区更加紧密, 负载芘的能力也增大. 相似文献
887.
Xinwei Zhao Dongping Yu Weijia Zhou Long Yu Han Zhou Yanfang Liu Zhimou Guo Aijing Shen Ziwei Han Chaoran Wang Jixia Wang Xinmiao Liang 《Journal of separation science》2023,46(10):2200704
Ziziphi spinosae semen has been widely used to treat insomnia and anxiety. To profile its chemical components, an online comprehensive two-dimensional liquid chromatography-mass spectrometry was developed. In this two-dimensional liquid chromatography system, a novel phthalic anhydride-bonded stationary phase column was combined with a C18 column. As a result, this new stationary phase exhibited remarkable differences in separation selectivity from C18, achieving a good orthogonality of 83.3%. Moreover, this new stationary phase with weaker hydrophobicity than C18 realized solvent compatibility in the online configuration. Coupled with tandem MS, 154 compounds were identified, including 51 unreported compounds. Compared with one-dimensional liquid chromatography-mass spectrometry, this online two-dimensional liquid chromatography-mass spectrometry system exhibited a much higher resolving power in isomer separation. This work provided an effective separation and characterization method for the material basis of Ziziphi spinosae semen. This strategy provides ideas for the material basis research of other traditional Chinese medicines. 相似文献
888.
采用紫外光接枝法对聚醚醚酮(PEEK)表面进行化学修饰和生物分子固定化.首先向PEEK表面引入亲水性的丙烯酰胺,并以此为反应位点通过戊二醛将胶原和胶原蛋白固定在PEEK表面.用接触角测定仪、扫描电镜、荧光标记和X射线光电子能谱等对改性薄膜进行了表征.结果表明,PEEK上丙烯酰胺的接枝密度高达50.9μg/cm~2;改性薄膜表面浸润性显著提高,水接触角最低降至(22±3)°.荧光标记胶原固定的PEEK薄膜荧光发射光谱强度最高,并在X射线光电子能谱中检测到N元素,表明胶原已固定化,固定胶原蛋白的浓度为10.2μg/cm~2. 相似文献
889.
Artūrs Škute Sergejs Osipovs Davids Vardanjans 《International journal of environmental analytical chemistry》2016,96(1):1-14
Nitrogen isotope ratio of nitrate provides a powerful tool to investigate nitrate sources and cycling mechanisms. Although the use of an isotope ratio method for 15N/14N allows identifying the nitrate sources in rivers by estimating a seasonal variation of N-NO3 concentration, however, there are some restrictions. Nitrification, the conversion of NH4+ to NO3-, can proceed with significant nitrogen isotope fractionation, preferentially accumulating 14N in the produced NO3-, and can make it difficult to identify the nitrate source with a high proportion of the isotope δ15N. However, the uptake and assimilation of NH4+ and NO3- have the capability of affecting isotopic compositions of riverine nitrogen compounds, and this may hinder the determination of whether the impact of the nitrate source with a high proportion of the isotope δ15N reduces. In addition, this study demonstrates that nitrate nitrogen concentration may correlate with δ15NNO3 values both positively and negatively. Such correlations are the result of isotope effects during nitrogen transformation processes (e.g. nitrification and assimilation) and isotopic variability in the various nitrate sources. A comparison of NO3- concentration and δ15NNO3 can be used to further distinguish mixing from biological processing. However, in order to get a more precise answer regarding the nitrate sources, it would be useful to take both the data of nitrogen isotopes and data of oxygen isotopes present in nitrates. 相似文献
890.