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Olfa Labidi Rose-Noëlle Vannier Jean-Pierre Wignacourt 《Journal of solid state chemistry》2008,181(9):2268-2273
Reinvestigation of PbBiOXO4 (X=V, P, As) thermal behaviour revealed a phase transition for V- and P-compounds, but no transition for the As-compound. As shown by single-crystal X-ray diffraction and high-resolution neutron powder diffraction, α-PbBiOVO4 transforms to β-PbBiOVO4 at 550 °C. The two PbBiOPO4 varieties are isomorph to the vanadate forms, while PbBiOAsO4 adopts the β-type structure whatever the temperature. PbBiP1−xOAsxO4 and PbBiV1−xOMxO4 (M=As, P, Cr, Mn) solid solutions display both triclinic and monoclinic domains, and the α→β transition temperature is a function of the substitution rate. The ionic conductivity of these compounds was investigated by impedance spectroscopy. The analysis of free space in the β-PbBiOVO4 structure allows to propose a one-dimensional oxygen diffusion pathway along [010] when the temperature increases. 相似文献
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Laila Manni Olfa Ghorbel-Bellaaj Kemel Jellouli Islem Younes Moncef Nasri 《Applied biochemistry and biotechnology》2010,162(2):345-357
Chitin is a polysaccharide found in abundance in the shell of crustaceans. In this study, the protease from Bacillus cereus SV1 was applied for chitin extraction from shrimp waste material of Metapenaeus monoceros. A high level of deproteinization 88.8% ± 0.4 was recorded with an E/S ratio of 20. The demineralization was completely achieved
within 6 h at room temperature in HCl 1.25 M, and the residual content of calcium in chitin was below 0.01%. 13C CP/MAS-NMR spectral analysis of chitin prepared by the enzymatic deproteinization of shrimp wastes was found to be similar
to that obtained by alkaline treatment and to the commercial α-chitin. The degree of N-acetylation, calculated from the spectrum,
was 89.5%. Chitin obtained by treatment with crude protease from B. cereus was converted to chitosan by N-deacetylation, and the antibacterial activity of chitosan solution against different bacteria
was investigated. Results showed that chitosan solution at 50 mg/mL markedly inhibited the growth of most Gram-negative and
Gram-positive bacteria tested. Furthermore, the antioxidant potential of the protein hydrolysates obtained during enzymatic
isolation of chitin was evaluated using various in vitro assays. All the samples exerted remarkable antioxidant activities. These results suggest that enzymatic deproteinization
of the shrimp shell wastes, using B. cereus SV1 protease, could be applicable to the chitin production process. 相似文献
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Rafik Aguech Nabil Lasmar Olfa Selmi 《Annals of the Institute of Statistical Mathematics》2019,71(2):389-408
Annals of the Institute of Statistical Mathematics - In this paper, we consider an unbalanced urn model with multiple drawing. At each discrete time step n, we draw m balls at random from an urn... 相似文献
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Olfa Labidi Florence Porcher Rose-Noëlle Vannier 《Journal of solid state chemistry》2008,181(9):2260-2267
Reinvestigation of PbBiOVO4 thermal behaviour revealed a phase transition. As shown by single-crystal X-ray diffraction and high-resolution neutron powder diffraction, α-PbBiOVO4 transforms to β-PbBiOVO4 at 550 °C. At 25 °C, α-PbBiOVO4 is triclinic, S.G. P-1, Z=2, with a=5.6088(3), b=7.1109(3), c=7.2978(3) Å, α=108.957(2), β=111.889(2), and γ=94.833(2)°. Above 550 °C, β-PbBiOVO4 is monoclinic, S.G. C2/m, Z=4, with a=13.61(1), b=5.64(1), c=7.18(1) Å, and β=113.75(1)°. Both structures are built upon (O2Bi2Pb2)∞ chains parallel to the [100] direction in the α polymorph and [001] in the β-polymorph. These chains are undulated in α and linear in β. In both structures, VO4 tetrahedra are organized in two sets of rows parallel to (O2Bi2Pb2)∞ chains, thus building layers of (OBiPb) sandwiched by two layers of VO4 oriented head to tail; VO4 displays different orientations in α- and β-PbBiOVO4. 相似文献
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Ab initio and DFT methods were used to investigate the interconversions of substituted polyacetylene conformers C10H6X6 (X=F, Cl and I) in the vapour phase. The rates of this geometrical isomerization have been calculated and the Arrhenius parameters evaluated. In the case of unsubstituted polyacetylene as the reference, the B3LYP Arrhenius parameters obtained are A1=2.99 × 1017 s–1 and Ea=17.30 kcal mol–1. The values of the equilibrium constant for the reaction have also been determined at various temperatures between 300 and 500 K and the value of the energies change calculated. The results also suggest that the straightforward kinetics characterizing the majority of substituted polyacetylene isomerizations above 300 K. The isomerization energies are positive and the barrier heights ΔEbarrier are expected to be sensitive for the magnitude of halogens effects. According to geometries features the Cis → Trans isomerization in the gas phase occurs by a rotational mechanism. 相似文献
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