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排序方式: 共有111条查询结果,搜索用时 2 毫秒
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2.
G. N. Dolenko E. N. Deryagina L. P. Turchaninova V. P. Elin E. I. Basina T. O. Pavlova V. K. Voronov 《Heteroatom Chemistry》1995,6(6):623-629
Some aspects of the spatial and electronic structure of disulfides XSSX (X = H, Alk, Ph, Hal) are considered. It is shown that the growth of the geminal ns-σSX* conjugation efficiency leads to a shortening of the SS bond that is more than three times as large as the simultaneous SX bond lengthening. The positive effective charge on the sulfur atom also increases as a result of this conjugation. These effects increase with the growth of - I and + M abilities of the substituents X. The SKa line shifts and the HOMO bonding degree (Delta;nS) have been measured by the X-ray fluorescence spectroscopy method for dialkyl disulfides (Alk = Me, Et, Pr, i-Pr, Bu, i-Bu, t-Bu, C5H11, C8H17, H2NCH2CH2, CH2CH CH2, CH2Ph) and S8. With the help of ΔnS values that are proportional to the nS–σSC* conjugation efficiency, the sequence of the enhancement of the geminal conjugation efficiency has been established for the disulfides investigated. In the framework of the nS–σSS* geminal conjugations, the shortening of the SS bonds in S8 is explained. © John Wiley & Sons, Inc. 相似文献
3.
Elin Julianti Hana Oh Hyi-Seung Lee Dong-Chan Oh Ki-Bong Oh Jongheon Shin 《Tetrahedron letters》2012,53(23):2885-2886
Acremolin (1), a novel modified base, was isolated from the culture broth of the marine fungus Acremonium strictum. Based on combined spectroscopic analyses, the structure of this compound was that of a methyl guanine base containing an isoprene unit. In addition, the presence of a 1H-azirine moiety is unprecedented among natural products. This compound exhibited weak cytotoxicity against an A549 cell line. 相似文献
4.
Graff BA Benjaminsen IC Melås EA Brurberg KG Rofstad EK 《Magnetic resonance imaging》2005,23(9):961-966
The purpose of this study was to use dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to search for systematic intratumor heterogeneity in blood perfusion in human melanoma xenografts growing intradermally in BALB/c-nu/nu mice. Six xenografted tumors of an amelanotic human melanoma line (A-07) were included in the study. DCE-MRI was performed daily for 5 days by using spoiled-gradient recalled sequences. Tumor images of E.F (E is initial extraction fraction and F is perfusion) were produced by subjecting DCE-MRI data to Kety analysis. E.F was used as a measure of tumor blood perfusion, since comparative studies have shown that E.F is closely related to blood perfusion in A-07 tumors. The E.F images indicated that the intratumor heterogeneity in blood perfusion was similar in all investigated tumors. The blood perfusion was low in the center of the tumors and increased toward the tumor periphery in the dorsal and ventral direction by a factor of 3-4, but not in the lateral and medial direction. The magnitude of the heterogeneity increased by a factor of approximately 2 during tumor growth. In conclusion, intradermal human melanoma xenografts show significant systematic intratumor heterogeneity in blood perfusion. 相似文献
5.
G. N. Dolenko V. P. Elin A. L. Litvin O. Kh. Poleshchuk E. V. Dolenko 《Russian Chemical Bulletin》1989,38(11):2311-2313
We propose an x-ray spectral criterion as a characteristic of organic and inorganic thiocyanates and isothiocyanates. We establish the lack of interaction between the level of the unshared electron pair of sulfur and the cC-orbitals in thiocyanates.Translated from Izvestiya Akademii Nauk SSSR, Seriya, Khimicheskaya, No. 11, pp. 2519–2521, November, 1989. 相似文献
6.
The use of custom-made solid-phase microextraction (SPME) fibers coated with a perfluorosulfonated ionomer, Nafion, was investigated for nitrogen isotopic analysis of ammonium in aqueous solutions. Aqueous ammonium was converted to ammonia by addition of a base, followed by absorption from the headspace, desorption in the injection port of a gas chromatograph, and analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Fibers coated with a Nafion tubing were chosen due to a higher fiber-gas distribution constant and a higher Nafion thickness than fibers coated with Nafion solution, both leading to a higher amount of ammonia absorbed at equilibrium. The Nafion membrane-coated fiber absorbed approximately 20 times more than a commercial polydimethylsiloxane (PDMS) fiber. The isotopic fractionation between fiber and gas was 1.0117 +/- 0.0009 (standard deviation, SD, of all measurements) at an initial ammonia gas concentration of 21-210 microM. At 390 microM initial gas concentration it was slightly lower. When sampling from liquid samples, an ammonium concentration of 10 mM was needed to obtain a sufficient amount of ammonia absorbed. Modeling of the absorption at different temperatures showed that the absorption was approximately constant in the temperature range suitable for SPME experiments. Absorption at room temperature was therefore used for simplicity. A pilot study was conducted in which absorption was achieved from a single 9 microL droplet of sample. The preliminary results showed that delta(15)N analysis was possible for only 0.4-0.5 micromol of ammonium with a SD of 0.8 per thousand (n = 5). 相似文献
7.
Mark Elin Simeon Reich David Shoikhet Fiana Yacobzon 《Complex Analysis and Operator Theory》2008,2(1):55-86
We study the asymptotic behavior of one-parameter continuous semigroups of holomorphic mappings. We present angular characteristics
of their trajectories at their Denjoy–Wolff points, as well as at their regular repelling points (whenever they exist). This
enables us to establish new rigidity properties of holomorphic generators via the asymptotic behavior of the semigroups they
generate.
Received: May 11, 2007. Accepted: July 22, 2007. 相似文献
8.
A multiblock/multilevel algorithm with local refinement for general two‐ and three‐dimensional fluid flow is presented. The patched‐based local refinement procedure is presented in detail and algorithmic implementations are also presented. The multiblock implementation is essentially block‐unstructured, i.e. each block having its own local curvilinear co‐ordinate system. Refined grid patches can be put anywhere in the computational domain and can extend across block boundaries. To simplify the implementation, while still maintaining sufficient generality, the refinement is restricted to a refinement of the grid successively halving the grid size within a selected patch. The multiblock approach is implemented within the framework of the well‐known SIMPLE solution strategy. Computational experiments showing the effect of using the multilevel solution procedure are presented for a sample elliptic problem and a few benchmark problems of computational fluid dynamics (CFD). Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
9.
Alban A. Letailleur Sergey Yu Grachev Elin Søndergård Christophe Couteau Gilles Lérondel Emmanuelle Peter 《Journal of luminescence》2011,131(12):2646-2651
The application of alumina-doped ZnO (AZO) films as luminescent material for large area lighting sources has been evaluated. Thin films were grown on quartz using magnetron sputtering and subsequently annealed under argon atmosphere in a rapid thermal annealing experiment. Below 550 °C, red-shift of the optical band gap and increase of the visible emission are observed in agreement with Al diffusion and formation of interstitial oxygen atoms. At temperatures higher than 800 °C, diffusion is activated and Ostwald ripening leads to the formation of larger grains and an increase of the crystalline phase. The photoluminescence (PL) intensity is enhanced, specifically in the UV range. As a result the emission spectrum of AZO thin films can be adjusted by the annealing conditions, with equal contributions from the UV and orange parts of the PL spectrum resulting in an efficient white emission as quantified using the color space map of the Commission Internationale de l'Éclairage. 相似文献
10.
In previous work we have introduced the idea of preparing ambient pressure dried silica aerogels by increasing the wet gels' stiffness by aging in a TEOS solution until shrinkage during drying is almost eliminated. The present work elucidates the possibilities for obtaining ambient pressure dried aerogels employing this idea, however, cheap water soluble sodium silicate (water glass) precursors have been used to increase the economic feasibility of the process.We have shown how the G modulus of water glass based gels can be increased by aging in TEOS solution and gels with a density down to 0.2 g/cm3 can be obtained. These wet gels show a higher reactivity towards TEOS compared to TEOS based gels. We have also introduced the idea of aging wet gels in a solution where the monomers are provided from water glass instead of TEOS and some initial results on G modulus and density are included. 相似文献