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11.
V. S. Ptuskin V. N. Zirakashvili A. A. Georgieva E. G. Klepach 《Bulletin of the Russian Academy of Sciences: Physics》2007,71(4):461-463
Propagation of cosmic rays in the interstellar medium after their emergence from sources—supernova remnants—may be accompanied by the development of flow instability which forms high magnetohydrodynamic turbulence and leads to nonlinear cosmic ray diffusion. A self-similar solution to the nonlinear diffusion equations is found and it is shown that the noted mechanism leads to an effective diffusion coefficient of cosmic rays, which coincides with the empirical value. 相似文献
12.
Velyana Georgieva Dilyana Zvezdova Lyubomir Vlaev 《Journal of Thermal Analysis and Calorimetry》2013,111(1):763-771
Thermogravimetric studies of chitin in air atmosphere were carried out at six rates of linear increase of the temperature. The kinetics and mechanism of the thermal decomposition reaction were evaluated from the TG data by iso-conversional calculation procedure of Kissinger–Akahira–Sunose recommended from ICTAC kinetics committee, as well as 27 mechanism functions. The comparison of the results obtained showed that they strongly depend on the selection of proper mechanism function for the process. Therefore, it is very important to determine the most probable mechanism function. In this respect, the iso-conversion calculation procedure turned out to be the most appropriate one. In the present work, the values of the apparent activation energy E, pre-exponential factor A in Arrhenius equation, as well as the changes of entropy ΔS ≠, enthalpy ΔH ≠, and Gibbs free energy ΔG ≠ for the formation of the activated complex from the reagent are calculated. All the calculations were performed using programs compiled by ourselves. 相似文献
13.
Dr. Georgian Melinte Dr. Veselina Georgieva Dr. Marie‐Anne Springuel‐Huet Dr. Andreï Nossov Prof. Ovidiu Ersen Dr. Flavien Guenneau Prof. Antoine Gedeon Dr. Ana Palčić Dr. Krassimir N. Bozhilov Dr. Cuong Pham‐Huu Prof. Shilun Qiu Dr. Svetlana Mintova Dr. Valentin Valtchev 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(50):18316-18327
The principle aspects and constraints of the dynamics and kinetics of zeolite nucleation in hydrogel systems are analyzed on the basis of a model Na‐rich aluminosilicate system. A detailed time‐series EMT‐type zeolite crystallization study in the model hydrogel system was performed to elucidate the topological and temporal aspects of zeolite nucleation. A comprehensive set of analytical tools and methods was employed to analyze the gel evolution and complement the primary methods of transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR) spectroscopy. TEM tomography reveals that the initial gel particles exhibit a core–shell structure. Zeolite nucleation is topologically limited to this shell structure and the kinetics of nucleation is controlled by the shell integrity. The induction period extends to the moment when the shell is consumed and the bulk solution can react with the core of the gel particles. These new findings, in particular the importance of the gel particle shell in zeolite nucleation, can be used to control the growth process and properties of zeolites formed in hydrogels. 相似文献
14.
Albena Bachvarova-Nedelcheva Stancho Yordanov Reni Iordanova Irina Stambolova Angelina Stoyanova Nelly Georgieva Veronica Nemska 《Molecules (Basel, Switzerland)》2021,26(13)
TiO2 nanopowders modified by Nd and Sm were prepared using the sol-gel technique. It was found by XRD analysis that the samples containing Sm are amorphous up to 300 °C, while those with Nd preserve a mixed organic-inorganic amorphous structure at higher temperatures (400 °C). The TiO2 (rutile) was not detected up to 700 °C in the presence of both modified oxides. TiO2 (anatase) crystals found at about 400 °C in the Sm-modified sample exhibited an average crystallite size of about 25–30 nm, while doping with Nd resulted in particles of a lower size—5–10 nm. It was established by DTA that organic decomposition is accompanied by significant weight loss occurring in the temperature range 240–350 °C. Photocatalytic tests showed that the samples heated at 500 °C possess photocatalytic activity under UV irradiation toward Malachite green organic dye. Selected compositions exhibited good antimicrobial activity against E. coli K12 and B. subtilis. 相似文献
15.
A. Kirov N. Nenoff E. Georgieva C. Necheva I. Ephtimov 《Zeitschrift für Physik A Hadrons and Nuclei》1993,345(3):285-292
Cross sections for the reactions152Sm(n, p)152g,m1,m2 Pm,154Sm(n, p)154g,m Pm,178Hf(n, p)178m,g Lu,154Sm(n, d)153Pm and152Sm(n, α)149Nd were measured at 14.5 MeV neutron energy by the activation method. On the basis of these cross sections, the associated isomeric ratios in154Pm,152Pm,178Lu and the comparison with the predictions of different compound and precompound models, conclusions are drawn about the role of the preequilibrium processes in 14.5 MeV neutron induced reactions. Calculations for equal angular momentum removal by equilibrium and preequilibrium emitted particles better reproduced the experimental isomeric ratios, than for higher angular momentum removal in the preequilibrium phase. The isomeric ratios may be used as a source of additional information about the spin of the isomeric states in152Pm and154Pm for which the spectroscopic information is uncertain. 相似文献
16.
Ohne Zusammenfassung 相似文献
17.
N. Georgieva 《Archive for Mathematical Logic》1974,16(3-4):187-189
18.
Georgieva I Trendafilova N Bauer G 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,63(2):403-415
The paper presents a detailed experimental and theoretical study of five metal complexes of glyoxilic acid oxime (gaoH2), Cu(gaoH)2(H2O)2 (1), Zn(gaoH)2(H2O)2 (2), Co(gaoH)2(H2O)2 (3), Ni(gaoH)2(H2O)2 (4) and [Cd(gaoH)2(H2O)2].H2O (5). The electronic and vibrational spectra were measured and discussed as to the most sensitive to the M-L binding bands. Two different types of coordination were considered for gaoH- ligand: bidentate through the carboxylic oxygen and oxime nitrogen in 1-4 and mixed bidentate and bridging through the COO group in 5. It is shown that the spectral behavior of the nu(COO) modes can be used to predict bridging ligand coordination. DFT(B3LYP/6-31++G(d,p)) calculations on model compounds: neutral, anionic and radical forms of gao and Cu(gaoH)2, have been carried out to correlate geometries, electronic and vibrational structures. The results obtained were used to assist the electronic and vibrational analysis of the complexes studied. The effect of the metal-ligand interactions (electrostatic and covalent) on the geometry structure of the ligand was investigated. 相似文献
19.
Angelina T. Georgieva Vijay Pappu Vijay Krishna Pando G. Georgiev Ion Ghiviriga Paul Indeglia Xin Xu Z. Hugh Fan Ben Koopman Panos M. Pardalos Brij Moudgil 《Journal of nanoparticle research》2013,15(7):1-18
Characterization of C60 polyhydroxyfullerenes (PHF) prepared in alkaline media, preparation facilitated by phase-transfer catalyst, presents challenges in determining the chemical structure resulting from the possibility of multiple isomers or analogs with greater or fewer hydroxyl groups from a single reaction mixture. This paper presents the utilization of analytical methods employed in tandem, especially X-ray photoelectron spectroscopy, nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy for semi-quantitative analysis on the number of hydroxyl groups present in PHF. Capillary Electrophoresis was used for purity estimation of the material. Multiple spectra and electropherograms were analyzed using a new simultaneous curve fitting method. The most accurate estimate of hydroxyl groups for C60 polyhydroxy fullerenes obtained is between 16 and 18 allylic hydroxyl groups by combining analytical methods’ results with 5 % accuracy. High precision (reproducibility) of the experiments is observed. Purity of 98 % is estimated by capillary electrophoresis. The size of PHF nanoparticles or aggregates has been determined by atomic force microscopy to be 7.4–14.2 nm. According to the elemental analysis the average probable empirical formula for the most pure PHF at pH 7.1 is C60O17H12Na5(NaHCO3)3(H2O)13 and the average formula weight is 1,605.9 g/mol. This is the first thorough characterization of PHF in terms of purity. 相似文献
20.
Dimiter L. Tsalev E. I. Tserovski A. G. Raitcheva A. I. Barzev R. G. Georgieva Z. K. Zaprianov 《光谱学快报》2013,46(2):331-346
An analytical scheme for the determination of up to fifteen trace elements in nails and hair has been proposed. Samples were solubilized by means of aqueous tetraalkylammonium hydroxide (alkyl = methyl or ethyl). Cadmium, Cr, Cu, Fe, Mn, Pb and Zn were determined by pulse-nebulization flame AAS, employing the Slotted Tube Atom Trap (STAT) for Cd and Pb. Suitable chemical modifiers have been applied in electrothermal AAS (ETAAS) determinations of Cd and Pb (ammonium hydrogen phosphate), As, Sb, Se and Sn (palladium), while no modifier was needed in determinations of Al, Co, Cr, Mn, Mo and Ni. Calibration was performed by means of matrix-matched standards and the technique was verified by standard additions, comparison with neutron activation and analysis of hair reference material. The usefulness of this technique for occupational exposure monitoring is briefly discussed. 相似文献