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141.
Todora Ojkova Donka Stoilova Dimitar Barkov 《Monatshefte für Chemie / Chemical Monthly》2000,131(10):1019-1023
Summary. The solubilities in the systems Rb2SeO4=ZnSeO4=H2O and Cs2SeO4=ZnSeO4=H2O at 25°C were studied by the method of isothermal decrease of supersaturation. Comparatively wide crystallization fields
of the double salts Rb2Zn(SeO4)2ċ6H2O and Cs2Zn(SeO4)2ċ6H2O are observed in the solubility diagrams. The double salts form monoclinic crystals which are isostructural with those of
the corresponding rubidium and cesium zinc sulfate hexahydrates. TG and TDA measurements indicate that the double salts lose
their crystallization water in one step in the temperature intervals of 50–160°C (rubidium salt) and 70–150°C (cesium salt).
Received March 14, 2000. Accepted (revised) June 5, 2000 相似文献
142.
The basic class of the non-integrable almost complex manifolds with a pair of Norden metrics are considered. The interconnections
between corresponding quantities at the transformation between the two Levi-Civita connections are given. A 4-parametric family
of 4-dimensional quasi-K?hler manifolds with Norden metric is characterized with respect to the associated Levi-Civita connection. 相似文献
143.
Albermann C Soriano A Jiang J Vollmer H Biggins JB Barton WA Lesniak J Nikolov DB Thorson JS 《Organic letters》2003,5(6):933-936
[reaction: see text] In an effort to expand the scope of natural product in vitro glycorandomization (IVG), the substrate specificity of NovM was investigated. A test of four aglycon analogues and over 40 nucleotide sugars revealed NovM has a surprisingly stringent substrate specificity and provided only three new "unnatural" natural products. On the basis of the determined substrate specificity, an alternative to the sugar nucleotide biosynthetic dogma and a cautionary note for the general applicability of IVG are introduced. 相似文献
144.
145.
Miloš Svirčev Goran Benedeković Ivana Kovačević Mirjana Popsavin Vesna Kojić Dimitar Jakimov Tatjana Srdić-Rajić Marko V. Rodić Velimir Popsavin 《Tetrahedron》2018,74(36):4761-4768
A series of new conformationally restricted goniofufurone mimics, bearing an additional 1,3-dioxan ring and a halogen, azido or benzoyloxy functionality at the C-7 position has been designed and synthesized. The Appel reaction was used for replacement of 7-OH group with Cl or Br functions in tricyclic lactone (3). 7-Iodo derivative (3d) was prepared by using the Ph3P/I2/2,6-lutidine reagent system. 7-Fluoro group was introduced by treatment of 3 with DAST, while the corresponding 7-azido and 7-benzoyloxy derivatives have been prepared by multistep sequences. Synthesized products were evaluated for their ability to inhibit growth of selected human malignant cell lines. Structure-activity relationships demonstrated that the nature of a substituent at the C-7 position could enhance the antiproliferative activity of the analogues. The preliminary study on the mechanisms indicated that all synthesized compounds induced apoptosis in 61–77% of K562?cells. 相似文献
146.
Ljuan Gurdev Tanja Dreischuh Orlin Vankov Irina Bliznakova Lachezar Avramov Dimitar Stoyanov 《Applied physics. B, Lasers and optics》2014,115(3):427-441
The possibility is studied to develop a straightforward analytical approach to the determination of the optical properties of liquid turbid media having forward-peaked scattering indicatrices. The approach is based on investigating the in-depth behavior of the radius and the axial intensity of a laser radiation beam propagating through the turbid medium. Based on the small-angle approximation, the detected forward-propagating light power spatial distribution, at relatively small or large optical depths along the beam axis, is obtained asymptotically in analytical form allowing one to derive relatively simple expressions of the extinction, reduced-scattering and absorption coefficients and the anisotropy factor of the medium through the characteristics of the propagating light beam. Preliminary experiments have also been performed, using Intralipid dilutions of different relatively low concentrations and measuring the cross-sectional radial distribution of the detected light power at different depths along the beam axis. The corresponding on-axis detected light power profiles have been measured independently as well. The experimental results are consistent with the analytical expressions obtained that allow one to estimate the optical coefficients and the anisotropy factor of the investigated media on the basis of the measured beam characteristics. The values obtained are near those predicted by other researchers. 相似文献
147.
The largest class of Riemannian almost product manifolds, which is closed with respect to the group of the conformal transformations of the Riemannian metric, is the class of the conformal Riemannian P-manifolds. This class is an analogue of the class of the conformal Kähler manifolds in almost Hermitian geometry. The main aim of this work is to obtain properties of manifolds of this class with connections, whose curvature tensors have similar properties as the Kähler tensors in Hermitian geometry. 相似文献
148.
Radina Kralchevska Maria Milanova Petya Kovacheva Jovo Kolev Georgi Avdeev Dimitar Todorovsky 《Central European Journal of Chemistry》2011,9(6):1027-1038
Microcomposites consisting of TiO2 (or Ce-doped TiO2) and ThO2 (0.5–2% of the TiO2 mass) are produced by sol-gel synthesis of TiO2 in presence of ThO2. X-ray diffraction study reveals the effects of ThO2 (compared to the ThO2-free TiO2, obtained by the same method) on the anatase interplanar distances, crystallites size and phase composition. The photocatalytic
tests in presence of the composites under UV irradiation reveal an increase of the Malachite Green degradation rate constant.
The effect depends on the Th relative content, temperature of annealing of the catalyst and addition of other doping agent.
The highest photocatalytic activity is observed for TiO2 obtained at 550°C and containing 1% ThO2. The composite exhibits activity in dark, also. The presence of Ce4+ ions is not an obligatory requirement for the realization of the ThO2 effect. The reported results suggest that the radioactivity of the Th and/or its decay products is one of the main factors
responsible for the increased photocatalytic activity of TiO2.
相似文献