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31.
Darko Volkov 《计算数学(英文版)》2011,29(5):543-573
We present in this paper a numerical method for hypersingular boundary integral equations.This method was developed for planar crack problems:additional edge si... 相似文献
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33.
Irena ?aleta Ana ?iko? Dinko ?iher Ivica ?ilovi? Marko Duk?i Dubravka Gembarovski Ivan Grgi?evi? Mirjana Bukvi? Kraja?i? Darko Fili? Dubravka Matkovi?-?alogovi? Ivica Malnar Sulejman Alihod?i? 《Structural chemistry》2012,23(6):1785-1796
Macrolide aglycons (E)-9-hydroxyimino-6-O-methylerythronolide A (4), 9a-aza-9-deoxo-9,9-dihydro-9a,11-O-dimethyl-9a-homoerythronolide A (5) and 9a-aza-9-deoxo-9,9-dihydro-9a-homoerythronolide A (6) were prepared by multistep syntheses. A conformational study of these new macrolide aglycons was performed using single crystal X-ray crystallography to gain information about the solid state, while a combination of NMR spectroscopy and molecular modelling was employed to study the solution structures. The crystal structures were found to be stabilised by a complex network of hydrogen bonds and van der Waals interactions. To some extent, the same building motif of infinite molecular chains held together by O?CH···O hydrogen bonds was present in the crystal structure of all three compounds. Thorough analysis and comparison of the obtained solid state structures with their solution counterparts showed no significant differences between them, confirming the constrained flexibility of the macrocyclic ring. Moreover, in all three compounds, in both solution and solid state, the macrolactone ring adopts energetically more favoured folded-out conformations. 相似文献
34.
A. R. Awudu A. Faanu E. O. Darko G. Emi-Reynolds O. K. Adukpo D. O. Kpeglo F. Otoo H. Lawluvi R. Kpodzro I. D. Ali M. K. Obeng B. Agyeman 《Journal of Radioanalytical and Nuclear Chemistry》2012,291(3):635-641
Knowledge of radioactivity levels in human diet is of particular concern for the estimation of possible radiological hazards to human health. However, very few surveys of radioactivity in food have been conducted in Ghana. The natural radionuclides 226Ra, 228Ra, 228Th and 40K were measured in the foodstuffs using gamma ray spectrometry. All samples were found to contain high 40K content in the range 87.77?C368.50?Bq?kg?1. The maximum concentration of 228Th and 40K were found in cassava to be 14.93?±?3.86 and 368.50?±?19.20?Bq?kg?1, respectively. The total annual committed effective dose was estimated to be 4.64?mSv. The daily intake of radionuclides from food consumption reveals that cassava and plantain are the highest contributors, while millet is the lowest. The daily radionuclide intake from the foodstuffs consumed by the general public was 411.32?Bq and the daily internal dose resulting from ingestion of the radionuclides in the foodstuffs was 0.01?mSv. The radionuclide concentrations were comparable with those reported from other countries. 相似文献
35.
Marija argonja Darko Mekterovi Paula
urga Jagoda Ravli‐Gulan Iva Bogdanovi Radovi Gordana
auhar 《X射线光谱测定》2021,50(1):68-79
During metal welding and cutting, large amounts of particulate matter (PM) are produced that might represent a significant health risk for the exposed workers. In the present pilot study, we performed an elemental analysis of fine PM collected in a metal workshop. Also, elemental analysis of the hair and nail samples collected from workers exposed to the workshop dust and control group was done. Concentrations of 15 elements in PM were measured with X‐Ray Fluorescence (XRF) and Particle Induced X‐ray Emission (PIXE), whereas inductively coupled plasma mass spectrometry (ICP‐MS) was used to determine 12 elements in hair and nail samples. Mean 8‐hr concentrations of PM2.5, Fe, and Mn in the vicinity of welders were up to 1803, 860, and 30 μg/m3, respectively, whereas in the nearby city, daily PM2.5 concentrations are on average 11 μg/m3. We found that several elements, especially Fe and Mn, had substantially higher concentrations in hair and nail samples of exposed workers than in the control group, which indicates the accumulation of metals in workers' tissues, although limit values were not exceeded. 相似文献
36.
Thomas Stönner Darko Hanžel Brigitte Baretzky Klaus-Peter Lieb Peter Schaaf 《Hyperfine Interactions》1998,112(1-4):155-160
Fe-Al intermetallic alloys have been considered as protective materials against corrosion. We have studied the properties of such intermetallic coatings Fe x Al1?x (x ≤ 0.5) on the aluminum-rich side and their oxidation behaviour. The samples were prepared using rf-magnetron sputtering. The composition and layer thickness were determined by Rutherford Backscattering Spectrometry (RBS) and high-resolution scanning electron microscopy (HRSEM). Conversion Electron Mössbauer Spectroscopy (CEMS) and X-Ray Diffraction (XRD) were applied for phase analysis. We report here on the oxidation of such coatings. 相似文献
37.
A new detector for CEMS has been built and optimized with respect to the statistical quality of spectra obtained. The optimization has been performed by measuring Mößbauer and pulse height spectra at in- and off-resonance. Single channel analyzer settings were calculated by a new optimization routine. A comparison of different detector designs has been performed using the statistical utility rate of spectra obtained from a stainless steel foil. A procedure for determining optimal operating parameters for ICEMS gas flow proportional counters is proposed. 相似文献
38.
Andreja Lesac Ute Baumeister Irena Dokli Zdenko Hameršak Trpimir Ivšić Darko Kontrec 《Liquid crystals》2018,45(7):1101-1110
Herein we report a comprehensive study on novel carbonyl- and ethenyl-linked symmetric dimers that combine synthesis, mesomorphic properties and molecular modelling. The study has been focused on the impact of geometry imposed by the linkage group on the incidence of the twist-bend nematic (NTB) phase. Comparison of the mesomorphic properties of these two series complemented with computational studies of conformational space around the linkage group points molecular curvature and intramolecular torsion plays important role in the appearance of the NTB phase and can be regarded as the basic structural requirements for design of new twist-bend nematogen materials. 相似文献
39.
Darko Skorin-Kapov 《Annals of Operations Research》1995,57(1):233-249
A cost allocation problem arising from the Steiner Tree (ST) problem in networks is analyzed. This cost allocation problem is formulated as a cost cooperative game in characteristic function form, referred to as theST-game. The class ofST games generalizes the class of minimum cost spanning tree games which were used in the literature to analyze a variety of cost allocation problems. In general, the core of anST-game may be empty. We construct an efficient Core Heuristic to compute a good lower bound on the maximum fraction of the total cost that can be distributed among users while satisfying the core constraints. Based on the Core Heuristic, we also provide a sufficient condition for a givenST not to be optimal for the linear programming relaxation of an integer programming formulation of theST problem. The Core Heuristic was implemented and tested on 76 data sets from the literature (Wong's, Aneja's and Beasley's Steiner tree problems). Core points were found for 69 of these cases, and points close to the core were computed in the others. 相似文献
40.
Solid solutions in the series (1−x)Ta2O5−xTiO2 with x=0.0-0.1 were prepared by high-temperature ceramic processing methods, and the crystal structure was determined at room temperature by transmission electron microscopy, electron diffraction and high-resolution lattice imaging. A structural model is proposed for the oxygen-deficient tantalum oxide (Ta2O5) phase with high TiO2 doping level (x=0.08). The model is based on edge sharing of an oxygen octahedron-hexagonal bi-pyramid-octahedron molecular building block unit that repeats four times per unit cell. Electron diffraction reveals a monoclinic distortion from a pseudo-tetragonal model structure that is modulated primarily along 〈110〉. The modulation length varies with increasing TiO2 content. Furthermore, by quantitative HREM analysis and matching of lattice images by simulation, it is shown that the modulation is associated with small ionic displacements in specific lattice planes that coincide with Ta ions in the model structure coordinated by oxygen hexagonal bi-pyramids. Based on this evidence, it is suggested that the modulation comes from a replacement of Ta with Ti ions, and the loss of inversion symmetry in the modulated structure is related to the dielectric properties of the material. 相似文献