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91.
设n为自然数,σ(n)表示n的所有正因子和函数.令d是n的真因子,若n满足σ(n)=2n-d,则称n为亏因子为d的亏完全数.本文给出了具有四个素因子的奇亏完全数的一些性质的刻画. 相似文献
92.
S变换在分析非平稳信号时能有效地反映出频率随时间的变化,但由于其窗函数是固定不变的,在实际中应用受到了限制.从基本理论出发,推导出一种改进的S变换形式,并对合成信号分别进行傅立叶变换、s变换和改进的S变换,通过对比发现:改进的s变换方法能够更好地分辨非平稳信号的频率特性,比S变换具有更高的分辨率.最后应用改进的s变换方法对地震背景噪声数据进行了去噪处理,取得了较好的结果. 相似文献
93.
TBAI‐Catalyzed/Water‐Assisted Double C−S Bond Formations: An Efficient Approach to Sulfides through Metal‐Free Three‐Component Reactions 下载免费PDF全文
Xue‐Qiang Chu Prof. Dr. Xiao‐Ping Xu Prof. Dr. Shun‐Jun Ji 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14181-14185
An aqueous catalytic method for double C?S bond formations that involves alcohol derivatives, organic halides, and sodium thiosulfate has been developed. A diverse range of functionalized sulfides, including pharmaceutical and biological derivatives, can be obtained in an efficient and eco‐friendly manner under air. The mechanistic studies revealed that this tetrabutylammonium‐iodide‐catalyzed/water‐assisted reaction generated a mercaptan species as the key intermediate. 相似文献
94.
《Applied Mathematical Modelling》2014,38(5-6):1607-1611
In this paper, He’s homotopy perturbation method (HPM) is applied for solving linear programming (LP) problems. This paper shows that some recent findings about this topic cannot be applied for all cases. Furthermore, we provide the correct application of HPM for LP problems. The proposed method has a simple and graceful structure. Finally, a numerical example is displayed to illustrate the proposed method. 相似文献
95.
96.
Pilar G. Rodríguez Ortega Prof. Manuel Montejo Prof. Fernando Márquez Prof. Juan J. López González 《Chemphyschem》2015,16(7):1416-1427
The implementation of a strategy comprising the use of vibrational circular dichroism spectroscopy and DFT calculations allows determination of the solution‐state conformational distribution in (?)‐S‐cotinine, giving further proof of the extra conformer‐discriminating potential of this experimental technique, which may offer unique molecular fingerprints of subtly dissimilar molecular conformers of chiral samples. Natural bond orbital electronic structure calculations of the rotational barrier height between the two main conformers of the species indicate that hyperconjugative effects are the key force governing the conformational equilibrium. The negligible effect of the solvent’s polarity over both structure and conformational energy profile supports this result. 相似文献
97.
Chemical investigation of the ethanol extract of the roots of Cudrania cochinchinensis led to the isolation of a new flavonoid, (6S,12S,13R)-1-methoxy cyanomaclurin (1), together with seven known compounds, 1,3,5-trihydroxy-4-(3′-hydroxy-3′-methylbutyl)xanthone (2), 1,3,6-trihydroxy-4-prenylxanthone (3), 1,3,6,7-tetrahydroxyxanthone (4), 1,3,5,6-tetrahydroxyxanthone (5), 1,3,6-trihydroxy-5-methoxyxanthone (6), resveratrol (7) and oxyresveratrol (8). The structure of compound 1 was elucidated on the basis of 1D and 2D NMR spectra and the HR-ESI-MS data. The absolute stereochemistry was deduced via Rh2(OCOCF3)4-induced CD and NOESY spectra. 相似文献
98.
Method development for the determination of 24S‐hydroxycholesterol in human plasma without derivatization by high‐performance liquid chromatography with tandem mass spectrometry in atmospheric pressure chemical ionization mode 下载免费PDF全文
Hiroshi Sugimoto Masaaki Kakehi Yoshinori Satomi Hidenori Kamiguchi Fumihiro Jinno 《Journal of separation science》2015,38(20):3516-3524
We developed a highly sensitive and specific high‐performance liquid chromatography with tandem mass spectrometry method with an atmospheric pressure chemical ionization interface to determine 24S‐hydroxycholesterol, a major metabolite of cholesterol formed by cytochrome P450 family 46A1, in human plasma without any derivatization step. Phosphate buffered saline including 1% Tween 80 was used as the surrogate matrix for preparation of calibration curves and quality control samples. The saponification process to convert esterified 24S‐hydroxycholesterol to free sterols was optimized, followed by liquid–liquid extraction using hexane. Chromatographic separation of 24S‐hydroxycholesterol from other isobaric endogenous oxysterols was successfully achieved with gradient mobile phase comprised of 0.1% propionic acid and acetonitrile using L‐column2 ODS (2 μm, 2.1 mm id × 150 mm). This assay was capable of determining 24S‐hydroxycholesterol in human plasma (200 μL) ranging from 1 to 100 ng/mL with acceptable intra‐ and inter‐day precision and accuracy. The potential risk of in vitro formation of 24S‐hydroxycholesterol by oxidation from endogenous cholesterol in human plasma was found to be negligible. The stability of 24S‐hydroxycholesterol in relevant solvents and human plasma was confirmed. This method was successfully applied to quantify the plasma concentrations of 24S‐hydroxycholesterol in male and female volunteers. 相似文献
99.
Dr. Junhong Zhao Youjuan Zhang Zhen Run Pengwei Li Qifei Guo Prof. Huan Pang 《ChemistryOpen》2015,4(3):274-277
Uniformly sized and shape-controlled nanoparticles are important due to their applications in catalysis, electrochemistry, ion exchange, molecular adsorption, and electronics. Several ferric phosphate hydroxide (Fe4(OH)3(PO4)3) microstructures were successfully prepared under hydrothermal conditions. Using controlled variations in the reaction conditions, such as reaction time, temperature, and amount of hexadecyltrimethylammonium bromide (CTAB), the crystals can be grown as almost perfect hyperbranched microcrystals at 180 °C (without CTAB) or relatively monodisperse particles at 220 °C (with CTAB). The large hyperbranched structure of Fe4(OH)3(PO4)3 with a size of ∼19 μm forms with the “fractal growth rule” and shows many branches. More importantly, the magnetic properties of these materials are directly correlated to their size and micro/nanostructure morphology. Interestingly, the blocking temperature (TB) shows a dependence on size and shape, and a smaller size resulted in a lower TB. These crystals are good examples that prove that physical and chemical properties of nano/microstructured materials are related to their structures, and the precise control of the morphology of such functional materials could allow for the control of their performance. 相似文献
100.
Jonathan H. Brown Lisa Orloff Clark Astrid an Huef 《Journal of Pure and Applied Algebra》2017,221(10):2458-2481
The graph groupoids of directed graphs E and F are topologically isomorphic if and only if there is a diagonal-preserving ring ?-isomorphism between the Leavitt path algebras of E and F. 相似文献