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41.
Youssef Naït-Si Jean-Dominique Fourneron 《Monatshefte für Chemie / Chemical Monthly》2004,135(10):1319-1326
Summary. Hypericin and pseudohypericin in extracts of St. Johns Wort (Hypericum perforatum) are assayed using UV-Vis, measuring the absorbance at 588nm of a methanolic solution of the compounds. The value of the absorption coefficient is difficult to define insofar as none of the routine purity criteria can be applied to these two compounds. Analysis of the entire UV-Vis spectrum from 220 to 740nm would seem to be a reliable way of comparing different samples. A UV-Vis spectrum was recorded for each of the compounds using a Photodiode array detection system. A more accurate way of determining the levels of hypericin and pseudohypericin in extracts of St. Johns Wort using these reference spectra is described. 相似文献
42.
In the present paper, we report the first results concerning a centimetre cantilever driven through non-linear effects in thin magnetostrictive films. Bimorph centimetre beams (24 mm x 5 mm) were designed using 160 microns thick glass and 0.4 micron thick multilayer TbFe/Fe films deposited via RF sputtering, using several sputtering conditions. Dynamic magneto-elastic excitations were studied experimentally on the few eigenresonance modes of the cantilevers. Sub-harmonic excitation at half or one-third of the frequency of an eigenresonance mode has been achieved near the spin reorientation transition and the efficiency is as good as for eigenfrequency excitation. Specific magnetic properties of the samples led to a model of the thermodynamic potentials and behaviour of the excited resonator. 相似文献
43.
A self-consistent approach is used to estimate the internal stresses induced by moisture absorption in composite materials
with a viscoelastic matrix and linear elastic fibers. A strong influence of the behavior of the viscoelastic matrix and humidity
on the internal stresses in the structures at macroscopic and local scales is found to exist. 相似文献
44.
H. M. Youssef 《Computational Mathematics and Modeling》2008,19(2):201-216
In this work, we will consider a half-space filled with an elastic material, which has constant elastic parameters. The governing
equations are taken in the context of the theory of two-temperature generalized thermoelasticity. A linear temperature ramping
function is used to more realistically model thermal loading of the half-space surface. The medium is assumed initially quiescent.
Laplace and Fourier transform techniques are used to obtain the general solution for any set of boundary conditions. The general
solution obtained is applied to a specific problem of a half-space subjected to ramp-type heating. The inverse Fourier transforms
are obtained analytically while the inverse Laplace transforms are computed numerically using a method based on Fourier expansion
techniques. Some comparisons have been shown in figures to estimate the effect of the ramping parameter of heating. 相似文献
45.
46.
Allal Ghanmi Youssef Hantout Ahmed Intissar Changgui Zhang Azzouz Zinoun 《The Ramanujan Journal》2008,16(3):271-284
In this paper, we introduce a notion of similarly self dual lattice in a d-dimensional Euclidean space and a classical Jacobi theta function is associated to such a lattice. We establish identities
of arithmetic type between values of this theta function and its successive derivatives. This work can be related to the spectral
theory of the Landau operators.
相似文献
47.
Eric R. Kaufmann Nickolai Kosmatov Youssef N. Raffoul 《Nonlinear Analysis: Theory, Methods & Applications》2008,69(9):2924-2929
We study a second-order nonlinear differential equation on an unbounded domain with solutions subject to impulsive conditions and the Sturm–Liouville type boundary conditions. The existence results are obtained via applications of Krasnosel’ski?’s fixed point theorem for the sum of a completely continuous operator and a contraction. 相似文献
48.
49.
Nabil Smichi Ahmed Fendri Raja Chaabouni Faouzi Ben Rebah Youssef Gargouri Nabil Miled 《Applied biochemistry and biotechnology》2010,162(5):1483-1496
A lipolytic activity was located in the sardine digestive glands (pyloric caeca), from which a sardine digestive lipase (SaDL)
was purified. Pure SaDL has a molecular mass of 43 kDa as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis
analysis. The enzyme was found to be more active on short-chain triacylglycerols than on long-chain ones. SaDL does not present
the interfacial activation phenomenon. Control experiments were performed under the same experimental conditions, with dromedary
and turkey pancreatic lipases and showed a positive interfacial activation phenomenon. Sodium deoxycholate (NaDC) has an inhibitory
effect on the lipase activity. The pure enzyme lost 40% of its activity in presence of 8 mM NaDC. SaDL was found to be mostly
stable at low pH values. Interestingly, no colipase was detected in the sardine pyloric caeca. Analogous results were reported
for the scorpion and the crab digestive systems. This is in line with the idea that colipase might has evolved in mammal animals
simultaneously with the appearance of an exocrine pancreas. No similarity was found between the NH2-terminal amino acid residues of SaDL and those of lipases from the digestive tract of other species. Altogether, these results
suggest that SaDL is a member of a new group of lipases belonging to aquatic species. 相似文献
50.
In this paper, we characterize the d-symmetric d-orthogonal polynomials of Brenke type. We obtain two new families of polynomials and the moments of the corresponding d-dimensional vectors of linear functionals. Weights, providing integral representations for these moments, were also given. 相似文献