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排序方式: 共有118条查询结果,搜索用时 31 毫秒
1.
Tiit Kaljuvee Merli Keelman Andres Trikkel Vilma Petkova 《Journal of Thermal Analysis and Calorimetry》2013,113(3):1063-1071
Thermooxidative decomposition (TOD) of seven coal samples from different deposits (Bulgaria, Russia, Ukraine) was studied with the aim to determine characteristics of the process and the differences related to the origin of the coal samples studied. The experiments with a Setaram Setsys 1750 or Labsys Evo 1600 thermoanalyzers coupled to a Nicolet 380 FTIR spectrometer or Pfeiffer mass spectrometer, respectively, were carried out under non-isothermal heating conditions up to 1,000 °C at the heating rates of 1, 2, 5, 10, and 20 °C min?1 in an oxidizing atmosphere. A model-free kinetic analysis approach based on the differential isoconversional method of Friedman was used to calculate the kinetic parameters. The combined TG-FTIR and TG-MS study of TOD of the coal samples made it possible to identify a number of gaseous species formed and evolved at that as well as to determine the differences in the thermal behavior of the coal samples and in the emission profiles of these species depending on their origin. The value of activation energy E along the reaction progress α varied more for the samples with higher content of organic matter and, especially, for the samples having at that also quite high content of mineral matter, indicating to the close association of mineral matter with organic matter and fixed carbon. 相似文献
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V. Yu. Baranovskii V. G. Ganev V. B. Petkova Kh. Ch. Voicheva M. V. Dimitrov 《Colloid Journal》2012,74(6):645-648
IR spectroscopy and viscometry data have shown that poly(acrylic acid) and poly(methacrylic acid) form complexes with agar-agar in aqueous solutions as they do with other polysaccharides. The polyacid-agar-agar complexes are typical hydrogels. The swelling index of hydrogels based on the poly(methacrylic acid)-agar-agar complex has been found to be markedly lower than that of poly(acrylic acid)-agaragar complex. The hydrogels based on the complex of cross-linked poly(acrylic acid) with agar-agar can be of practical interest as polymeric carriers for drugs. 相似文献
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O. Kostadinova A. Chrissanthopoulos T. Petkova S.N. Yannopoulos 《Journal of solid state chemistry》2011,184(2):447-454
We report an investigation of the structure and vibrational modes of (AgI)x (AsSe)100−x, bulk glasses using Raman spectroscopy and first principles calculations. The short- and medium-range structural order of the glasses was elucidated by analyzing the reduced Raman spectra, recorded at off-resonance conditions. Three distinct local environments were revealed for the AsSe glass including stoichiometric-like and As-rich network sub-structures, and cage-like molecules (As4Sen, n=3, 4) decoupled from the network. To facilitate the interpretation of the Raman spectra ab initio calculations are employed to study the geometric and vibrational properties of As4Sen molecular units that are parts of the glass structure. The incorporation of AgI causes appreciable structural changes into the glass structure. AgI is responsible for the population reduction of molecular units and for the degradation of the As-rich network-like sub-structure via the introduction of As-I terminal bonds. Ab initio calculations of mixed chalcohalide pyramids AsSemI3−m provided useful information augmenting the interpretation of the Raman spectra. 相似文献
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Roger E. Behrend Paul A. Pearce Valentina B. Petkova Jean-Bernard Zuber 《Nuclear Physics B》2000,570(3):525-589
We develop further the theory of Rational Conformal Field Theories (RCFTs) on a cylinder with specified boundary conditions emphasizing the role of a triplet of algebras: the Verlinde, graph fusion and Pasquier algebras. We show that solving Cardy's equation, expressing consistency of a RCFT on a cylinder, is equivalent to finding integer valued matrix representations of the Verlinde algebra. These matrices allow us to naturally associate a graph G to each RCFT such that the conformal boundary conditions are labelled by the nodes of G. This approach is carried to completion for sl(2) theories leading to complete sets of conformal boundary conditions, their associated cylinder partition functions and the A-D-E classification. We also review the current status for WZW sl(3) theories. Finally, a systematic generalisation of the formalism of Cardy–Lewellen is developed to allow for multiplicities arising from more general representations of the Verlinde algebra. We obtain information on the bulk–boundary coefficients and reproduce the relevant algebraic structures from the sewing constraints. 相似文献
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T. Petkova B. Monchev O. Kostadinova P. Petkov S.N. Yannopoulos 《Journal of Non》2009,355(37-42):2063-2067
We report a structural investigation of bulk Ge-rich Ge–S–AgI chalcohalide glasses. A vibrational spectroscopic study of the quaternary system (AgI)x (GeS1.5)100−x (0 xAgI 20) has been undertaken using infrared spectroscopy and Fourier transform Raman scattering. It was found that the GeS1.5 Raman spectrum is compatible with a glass structure composed of corner- and edge-sharing mixed GeSnGe4−n (n = 0–4) tetrahedra where units with n = 2–4 dominate, whilst the fraction of corner-sharing units are significantly lower than the corresponding fraction in the stoichiometric GeS2 glass. The addition of AgI has revealed a subtle but systematic effect in the structure of the Ge-rich glass matrix, manifested by mild decrease of the ES units and the concomitant increase of complex GeSnI4−n or GeSnGemI4-n−m tetrahedra whose vibrational modes form a continuum at low frequencies. Although, AgI seems to cause subtle structural changes due to the formation of Ge–I bonds, it is also evident that AgI does not act as a real modifier that would depolymerize appreciably the Ge–S network structure. 相似文献
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The paper consists of two independent parts. First, we review the situationin scale invariant massless QED from an axiomatic standpoint. Assuming that the τ-functions (or, equivalently, the Euclidean Schwinger functions) transform covariantly under dilatations, we deduce that the current jτ(x) has zero n-point Wightman functions, but nonvanishing τ-functions. Assuming in addition conformal invariance of the current-field vertex function, we write down a bootstrap equation similar to the one derived in [7] from the point of view of pertubation theory. Next we consider a non-Lagrangian, conformal invariant model of interacting antisymmetric tensor field Fμv (of scale dimension d) and Dirac field ψ (of dimension d'. The model involves two conserved currents (an “electric” and a “magnetic” one) and two effective coupling constants. We demonstrate that it is free of ultravioletdivergences in the range of dimensions . 相似文献
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Fin A Petkova I Doval DA Sakai N Vauthey E Matile S 《Organic & biomolecular chemistry》2011,9(24):8246-8252
The green-fluorescent protein of the jellyfish operates with the most powerful phenolate donors in the push-pull fluorophore. To nevertheless achieve red fluorescence with the same architecture, sea anemone and corals apply oxidative imination, a process that accounts for the chemistry of vision as well. The objective of this study was to apply these lessons from nature to one of the most compact family of panchromatic fluorophores, i.e. core-substituted naphthalenediimides (cNDIs). We report straightforward synthetic access to hydroxylated cNDI and cPDI cores by palladium-catalyzed cleavage of allyloxy substituents. With hydroxylated cNDIs but not cPDIs in water-containing media, excited-state intramolecular proton transfer yields a second bathochromic emission. Deprotonation of hydroquinone, catechol and boronic ester cores provides access to an impressive panchromism up to the NIR frontier at 640 nm. With cNDIs, oxidative imination gives red shifts up to 638 nm, whereas the expanded cPDIs already absorb at 754 nm upon deprotonation of hydroquinone cores. The practical usefulness of hydroquinone cNDIs is exemplified by ratiometric sensing of the purity of DMF with the "naked eye" at a sensitivity far beyond the "naked nose". We conclude that the panchromatic hypersensitivity toward the environment of the new cNDIs is ideal for pattern generation in differential sensing arrays. 相似文献