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71.
Ren Berger Janis Kliava El-Mostapha Yahiaoui Jean-Claude Bissey Paul K. Zinsou Pierre Bziade 《Journal of Non》1995,180(2-3):151-163
Electron paramagnetic resonance (EPR) spectra of lithium borate glass (1 - x)(0.63B2O3 · 0.37Li2O) · xFe2O3, with x varying from 0.001 to 0.1, were measured at different microwave frequencies and temperatures. For low Fe3+ concentrations (Fe2O3 molar contents from 0.001 to 0.01), X-band EPR spectra, consisting of a gef = 4.3 peak accompanied by a shoulder continuing down to gef = 9.7, are computer simulated on the basis of a ‘rhombic’ spin-Hamiltonian with Zeeman and fine-structure terms. A good fit to the experimental spectra for various Fe2O3 contents is observed with the same values of the spin-Hamiltonian parameters and assuming a Lorentzian lineshape and a linewidth increasing linealry with the concentration of Fe3+ ions. It is concluded that the spectrum is due to diluted Fe3+ ions in a relatively strong crystal field of orthorhombic symmetry, with largely distributed fine-structure parameters. From the concentration dependence of the line width, by extending to glasses a theoretical EPR linewidth expression derived for polycrystalline systems, the minimum distance between diluted Fe3+ ions is estimated as 4.9 Å. A diluted state of Fe3+ ions in the glass network in this range is also confirmed by the temperature dependence of the gef = 4.3 resonance which follows a Curie law. For intermediate concentrations of Fe3+ ions (Fe2O3 molar contents from 0.01 to 0.1), the width of the gef = 4.3 line is proportional to the square root of concentration, still indicating dipolar interactions. On the other hand, the microwave frequency dependence of a broad gef ≈ 2 line, which coexists at these concentrations with the gef = 4.3 line, shows that the former line is due to pairs or small clusters of exchange-coupled Fe3+ ions. The temperature dependence of the gef ≈ 2 line intensity in 0.1 mol Fe2O3 glass is consistent with a more antiferromagnetic character by comparison with the 0.05 mol Fe2O3 glass, which is attributed to an appearance, at higher Fe2O3 contents, of iron-containing microclusters not incorporated in the random glass network, with smaller distances between the paramagnetic ions. These microcluster are probably the origin of a new narrow line superposed with the broad gef ≈ 2 line in the low-temperature EPR spectra. 相似文献
72.
Oussama Kamal Tarik Eljaddi El Houssine EL Atmani Imane Touarssi Laurent Lebrun Miloudi Hlaïbi 《先进技术聚合物》2017,28(4):541-548
To conduct experiments related to the facilitated extraction phenomenon and recovery of vanadium ions VO2+, two grafted polymer membranes were prepared; containing respectively cholic acid and azithromycin as extractive agents and the obtained membranes were characterized. All experiments for the facilitated extraction phenomenon of these ions were carried out. Kinetic and thermodynamic models, based on the interaction of the substrate S (VO2+) with the extractive agent T, and the diffusion of the formed entity (TS) through the membrane were developed, to determine the macroscopic parameters, permeability P and initial fluxes J0, and the microscopic parameters, association constants Kass and apparent diffusion coefficients D*, related to the formation of entities TS and their diffusion. A clear evolution of these parameters, depending on various factors (substrate concentration C0, extractive agent concentration and feed and receiving phases temperature), and high permeabilities for this extraction phenomenon of VO2+ ions were observed for this membrane type. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
73.
Oussama Boumezgane 《International Journal of Polymer Analysis and Characterization》2017,22(5):463-471
Poly(ethylene glycol) (PEG) blends photo-curable and thermal activated shape-memory polymers (SMPs), with different activation temperature (Tswitch), have been synthesized and characterized. PEG blends with different molecular weights were chain-end functionalized with isocyanate ethyl methacrylate and photo-cured with UV lamp. Degree of cross-linking of the blend network, determined by gel content measurement, resulted as higher than 95%. The thermal and thermomechanical properties of these SMPs PEG blends were characterized by differential scanning calorimetry and dynamic mechanical analysis. The shape-memory properties of the networks were quantified using thermomechanical three-point bending experiments and showed strain fixity rates higher than 99% and a minimum strain recovery ratio of 82%. 相似文献
74.
Rashidi M. M. Mahariq Ibrahim Alhuyi Nazari Mohammad Accouche Oussama Bhatti Muhammad Mubashir 《Journal of Thermal Analysis and Calorimetry》2022,147(22):12301-12311
Journal of Thermal Analysis and Calorimetry - Heat exchangers (HEs) are used for several applications including chemical processes, power plants, air conditioning systems, etc. The performance of... 相似文献
75.
76.
We give optimal lower bounds for the hypersurface Diracoperator in terms of the Yamabe number, the energy-momentum tensor andthe mean curvature. In the limiting case, we prove that the hypersurfaceis an Einstein manifold with constant mean curvature. 相似文献
77.
G. Graham Allan Angel P. Stoyanov Masahiro Ueda Amar Yahiaoui 《Cellulose (London, England)》2001,8(2):127-138
The incorporation of sucrose or some other disaccharides (cellobiose, -lactose or trehalose) into the cell wall of pulp fibers increases the tearing resistance of the resultant sugar-containing paper relative to that of its sugar-free counterpart, but only when the fiber is well-refined. Maltose and -lactose do not exhibit this effect. By the use of a high cellulose pulp the increase is shown not to be due to the presence of hemicelluloses. Differential scanning calorimetry indicates that the interaction between the sucrose molecules and the cellulosic fibers changes and becomes more uniform as the fibers are refined. Although the azo dye Congo red bonds strongly with cellulose the analogous reaction with disaccharides and cyclodextrins, established spectrophotometrically, could not be used to predict the physical outcome of the interactions with added disaccharides or cyclodextrins. From a consideration of the stereochemistry of the impregnant disaccharides the augmentation of the fiber strength is attributed to the interlamellar hydrogen bonding of impregnant molecules having hydroxy endgroups in the cis conformation and separated by about 10Å. The incorporation of cyclodextrins further demonstrates that the conformation and the separation distance between the OH groups located in the interlamellar sugar molecule play an important role in strengthening the sugar-impregnated fiber and in augmenting the tearing resistance of sugar-containing papers. 相似文献
78.
On a spin quaternionic-Kähler manifold M4m, we give the spectral decomposition of the spin bundle the action of the fundamental 4-form Ω. Moreover, we compute the eigenvalues of Ω which, in the compact case, play an essential role in the problem of estimating the eigenvalues of the Dirac operator. The proof is based on the decomposition of the spin representation into irreducible components under the action of the group Sp(1) × Sp(m). We show that this algebraic results induces a Whitney decomposition of the spin bundle which, when restricted to the fibres, is the spectral decomposition under the action of Ω. 相似文献
79.
Burress CN Bodine MI Elbjeirami O Reibenspies JH Omary MA Gabbaï FP 《Inorganic chemistry》2007,46(4):1388-1395
As part of our efforts to discover simple routes to room-temperature phosphors, we have investigated the interaction of bis(pentafluorophenyl)mercury (1) or trimeric perfluoro-o-phenylene mercury (2) with selected arenes (naphthalene, biphenyl, and fluorene). Solution studies indicate that 2, unlike 1, quenches the fluorescence of naphthalene. When compared to 1, the high quenching efficiency of 2 may be correlated to the higher affinity that 2 displays for arenes as well as to more acute external heavy-atom effects caused by the three mercury atoms. In the crystal, the adducts [1.naphthalene], [1.biphenyl], [1.fluorene], and [2.fluorene] form supramolecular binary stacks in which the arene approaches the mercury centers of 1 or 2 to form Hg-C pi-interactions. Analysis of the electrostatic potential surfaces of the individual components supports the involvement of electrostatic interactions. The luminescence spectra of the adducts show complete quenching of the fluorescence and display heavy-atom-induced emission whose energies and vibronic progressions correspond to the phosphorescence of the respective pure arene. The phosphorescence lifetimes are shortened by 3 or 4 orders of magnitude when compared with those of the free arenes. Taken collectively, the structural, photophysical, and computational results herein suggest that the proximity of the three mercury centers serves to enhance the Lewis acidity of 2, which becomes a better acceptor and a more effective heavy-atom effect inducer than 1. 相似文献
80.
W. TerouziM. De Luca A. BolliA. Oussama M. PatumiG. Ioele G. Ragno 《Vibrational Spectroscopy》2011,56(2):123-128
Four cultivars of olives picked up in the Moroccan region of Beni Mellal were subjected to a characterization and classification study. Analytical data were collected by Fourier transform infrared spectroscopy (FTIR), applied on the mesocarp of the fresh olives without any preliminary treatment. The spectral data were pre-treated by derivative elaboration based on the Savitzky-Golay algorithm to reduce noise and increase analytical information. Partial least squares discriminant analysis (PLS-DA) was performed to elaborate the measurement data and assess the discriminant features of the four cultivars. The PLS model was optimized by applying the Martens’ uncertainty test which provided to select the vibrational frequencies giving the most useful information. The optimized model resulted able to separate the four classes and classify new objects into the appropriate defined classes with a percentage prediction of 97%. The proposed method represents a real novelty to classify olives of different varieties by means of a rapid, inexpensive and reliable procedure. 相似文献