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Vernov Yu. S. Mnatsakanova M. N. Chubarov M. S. 《Theoretical and Mathematical Physics》1984,59(2):473-477
Theoretical and Mathematical Physics - 相似文献
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The X-ray pattern of ice recorded at −10°C reveals, along with the reflexes of a hexagonal phase, intense diffuse X-ray scattering,
testifying to the presence of a noncrystalline phase in the sample. Heating of ice to a temperature close to the melting point
leads to almost complete decomposition of the crystalline phase. As this takes place, intense diffuse X-ray scattering with
a maximum at 2Θ of 23°C appears in the diffraction pattern, which is typical for a metastable amorphous phase. The first maximums
of the radial distribution function for the metastable amorphous phase of ice appear to be close in their positions to the
first radii of the hexagonal phase coordination spheres. 相似文献
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V. M. Silonov V. V. Chubarov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2014,8(3):509-512
In addition to reflections of the hexagonal phase of ice I h, the intense diffuse scattering of X-rays mainly due to the amorphization of ice is revealed on the X-ray diffraction patterns of water ice samples prepared at liquid nitrogen (studied by the authors earlier) and samples prepared at T = ?10°C (this work). The measurements are performed in the temperature range from ?25 to 0°C. The existence of reflections of the crystalline phase and intense diffuse scattering on the X-ray diffraction patterns makes it possible make a conclusion about the coexistence of crystalline and amorphous structures of ice. Splitting of the first maximum on the electron-density radial distribution function is detected on the basis of an X-ray diffraction pattern recorded at T = ?3°C. This splitting is explained by an increase in the interatomic distances between the nearest-neighbor atoms located at different levels. Similar splitting was also detected on a radial distribution function constructed using an X-ray diffraction pattern recorded at ?10°C. 相似文献
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The features of rock-forming elements determination in powder samples of peat sediments are considered. Based on theoretical calculations and experimental data, the mineralogical and particle size effects on the X-ray fluorescence intensity have been estimated. For routine analysis, powder rock samples are usually milled to a particle size of 10–60 μm. Theoretically, estimated variations of rock-forming elements analytical lines intensities in different minerals are up to 30%, and the particle size effect cannot be eliminated simultaneously for all rock-forming elements. Experimental estimation shows that the impossibility of the particle size distribution control can lead to significant variations in the intensities of the analytical lines (3%–18%) that is mainly corresponding to theoretical estimation. Fine milling allowed us to achieve an average particle size of fewer than 20 μm and reduce the measurement uncertainty by 1.5–2 times. 12 samples of peat sediments with organic matter content up to 70 wt% were analyzed by X-ray fluorescence analysis using different sample preparation techniques, as well as by certified methods. The accuracy of X-ray fluorescence analysis of peat sediments prepared as pressed pellets varies from 1.5 to 11 rel% depending on compound contents. It is more than for samples prepared as fused beads, however, the proposed method can be used to determine the variations of rock-forming elements contents in peat sediments where the content variations exceed the measurement uncertainty, and accuracy of analysis is sufficient for further paleoecological reconstructions. 相似文献
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Institute of Nuclear Research, USSR Academy of Sciences; All-Union Scientific-Research Institute of Physicotechnical and Radio Engineering. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 79, No. 3, pp. 416–422, June, 1989. 相似文献
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M. P. Evstigneev A. O. Rozvadovskaya A. S. Chubarov A. A. Hernandez Santiago D. B. Davies A. N. Veselkov 《Journal of Structural Chemistry》2005,46(1):67-74
Heteroassociation of the antitumor antibiotic daunomycin (DAU) with flavin mononucleotide (FMN) has been investigated by one-and two-dimensional 1H NMR spectroscopy (500 MHz) in a water solution to determine the molecular mechanism of the combined action of the antibiotic and vitamin in the FMN-DAU system. The equilibrium constants of the reactions, induced proton chemical shifts, and thermodynamic parameters (ΔH, ΔS) of heteroassociation were determined from the concentration and temperature dependences of the proton chemical shifts in the interacting aromatic molecules. Analysis of the results indicate that heterocomplexes of riboflavin mononucleotide and daunomycin are formed due to stacking interactions between aromatic chromophores. The most probable spatial structure of the 1:1 DAU-FMN heterocomplex was determined by the molecular dynamics method using the X-PLOR program and the results of the analysis of the induced proton chemical shifts in molecules. Calculation of the relative content of self-and hetero-complexes of daunomycin for different values of the ratio (r) between the concentrations of flavin mononucleotide and daunomycin demonstrated that for r > 3, the contribution of DAU-FMN heterocomplexes to the equilibrium distribution of associates in aqueous solution is dominant. It is concluded that the aromatic molecules of vitamins, in particular, riboflavin, can form energetically strong heteroassociates with antitumor antibiotics in water solution and can thereby affect their medical and biological activity. 相似文献