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31.
A parallel is considered between Burnat's “algebraic” approach [restricted to a genuine nonlinearity] and Martin's “differential” approach regarding their contribution to describing some nondegenerate one-dimensional gasdynamic regular interaction solutions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
32.
The linear equivalence method (LEM), introduced by [Bull. Math. Soc. Sci. Math. de la Roumanie 24 (72) (1980) 4417; An. Univ. Bucure
ti, ser. Matematica 31 (1982) 75] to get solutions of nonlinear ODEs, was used so far to get differential type representations. New LEM representations of integral type are presented here and used for the study of the nonlinear elastic bar; a good approximating formula for the rotation of the cross-section at the bar end is also obtained, in case of a simply supported bar. A parallel old–new results is made by means of a programming code. 相似文献
33.
The results of magnetic measurements performed on Ni0.8Cu0.2-xGex solid solutions, with x ? 0.10 are reported. The saturation magnetization, Curie temperature and effective nickel moments decrease nearly linear when substituting Cu by Ge. The ferromagnetic resonance measurements show that the g values are not dependent on composition. Finally, the magnetic behaviour of nickel in these solid solutions is analysed. 相似文献
34.
This study focuses on the characterization and classification of 42 medicinal plants extracts according to their antioxidant activity. Principal component analysis (PCA), cluster analysis (CA) and the combination of PCA with linear discriminant analysis (PCA-LDA) were used as multivariate exploratory techniques for chromatographic data analysis. For the separation of the compounds a mobile phase containing ethyl acetate: toluene: formic acid: water (30:1.5:4:3 v/v/v/v) and different HPTLC plates (Silica gel 60 and HPTLC Silica gel 60?F254) were used. The chromatographic plates were evaluated using the images obtained after spraying the plates with 2-aminoethyldiphenylborate solution (NTS, 0.2% in ethanol) and also after their reaction with 2, 2-diphenyl-1-picrylhydrazyl solution (DPPH?) (0.2% in ethanol). The score projection on the plane defined by first two components (PC1 and PC2) revealed two large groups of the investigated samples depicted according to their antioxidant capacity. A better classification of samples according to their antioxidant capacity was obtained using the CA and PCA-LDA methodology in all cases. The excellent results obtained in this study concerning the classification of medicinal plants according to their antioxidant capacity using the PCA-LDA methodology applied to TLC chromatograms might lead to a new paradigm in the field of medicinal plant holistic evaluation. 相似文献
35.
Smichowski P Farías S Valiente L Iribarren ML Vodopivez C 《Analytical and bioanalytical chemistry》2004,378(2):465-469
Total arsenic in nine species Antarctic macro algae has been measured, by electrothermal atomic absorption spectrometry using a Pd/Mg(NO3)2 matrix modifier, to determine their capacity to accumulate the element. Macro algae were collected in February during the 2000 austral summer season at Jubany Station (Argentinean scientific station) around Potter Cove, King George Island. An optimized two-step microwave (MW) program was used to digest the samples. Dried samples were treated with HNO3, H2O2, and HF, left overnight, then subjected to the first MW cycle. After cooling HNO3 and HClO4 were added and samples were subjected to the second MW cycle of digestion treatment. The effect of power and time on As recovery was examined. The analytical features of the method were: detection limit, 0.24 g g–1 (dry mass); precision (RSD), 4.2–5.7%; recovery 91–105%. A wide range of As-retention capacity (41.0–447 g g–1 dry mass) was observed among the different species. The highest levels of As were found in Phaeurus antarcticus (447 g g–1 dry mass). This organism satisfies several prerequisites to be considered for consideration as a biomonitor in future studies. 相似文献
36.
37.
Ileabethoxazole (1), a new perhydroacenaphthene-type diterpene alkaloid containing the uncommon benzoxazole moiety, was isolated from the Caribbean sea whip Pseudopterogorgia elisabethae. The structure of 1 was elucidated by extensive spectroscopic data interpretation. Ileabethoxazole showed 92% inhibition of Mycobacterium tuberculosis (H37Rv) at the concentration range of 128-64 μg/mL. 相似文献
38.
Michael W. Lufaso Terrell A. Vanderah Ileana M. Pazos Robert S. Roth Virgil Provenzano 《Journal of solid state chemistry》2006,179(12):3900-3910
Subsolidus phase relations have been determined for the Bi2O3-Fe2O3-Nb2O5 system in air (900-1075 °C). Three new ternary phases were observed—Bi3Fe0.5Nb1.5O9 with an Aurivillius-type structure, and two phases with approximate stoichiometries Bi17Fe2Nb31O106 and Bi17Fe3Nb30O105 that appear to be structurally related to Bi8Nb18O57. The fourth ternary phase found in this system is pyrochlore (A2B2O6O′), which forms an extensive solid solution region at Bi-deficient stoichiometries (relative to Bi2FeNbO7) suggesting that ≈4-15% of the A-sites are occupied by Fe3+. X-ray powder diffraction data confirmed that all Bi-Fe-Nb-O pyrochlores form with positional displacements, as found for analogous pyrochlores with Zn, Mn, or Co instead of Fe. A structural refinement of the pyrochlore 0.4400:0.2700:0.2900 Bi2O3:Fe2O3:Nb2O5 using neutron powder diffraction data is reported with the A cations displaced (0.43 Å) to 96g sites and O′ displaced (0.29 Å) to 32e sites (Bi1.721Fe0.190(Fe0.866Nb1.134)O7, Fd3¯m (#227), ). This displacive model is somewhat different from that reported for Bi1.5Zn0.92Nb1.5O6.92, which exhibits twice the concentration of small B-type cations on the A-sites as the Fe system. Bi-Fe-Nb-O pyrochlores exhibited overall paramagnetic behavior with large negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. The single-phase pyrochlore with composition Bi1.657Fe1.092Nb1.150O7 exhibited low-temperature dielectric relaxation similar to that observed for Bi1.5Zn0.92Nb1.5O6.92; at 1 MHz and 200 K the relative permittivity was 125, and above 350 K conductive effects were observed. 相似文献
39.
40.
Mihaela Matache Cristian Dobrota Niculina D. Bogdan Lavinia L. Ruta Ileana C. Farcasanu Daniel P. Funeriu 《Tetrahedron》2009,65(31):5949-3817
A new efficient approach for the synthesis of functionalized dihydro-pyrimido[4,3-d]coumarins is described. Use of benzyl- or tert-butyl acetoacetate and various salicyl aldehydes in typical Biginelli multicomponent reactions provides esters that can be easily deprotected to yield the corresponding hydroxy acids. Annelation of the latter leads to the target dihydro-pyrimido[4,3-d]coumarins. Formation of some unexpected oxo-bridged tetrahydro-pyrimidines is also described. Spectral properties of the synthesized dihydro-pyrimido[4,3-d]coumarins indicate the necessity to revisit some compounds previously reported as products of direct one-pot Biginelli condensation involving 4-hydroxycoumarin as dicarbonyl component. 相似文献