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Sarra El Ichi Ferid Limam M. Nejib Marzouki 《Materials science & engineering. C, Materials for biological applications》2009,29(5):1662-1667
Peroxidase X1 (POX1) isoenzyme was purified from garlic bulb (Allium sativum L.). Native-PAGE profile showed two isoforms partially purified (designated POX1A and POX1B). A POX1B-based electrode showed great potential for monitoring hydrogen peroxide in biological samples. Chitosan was used as a matrix for enzyme immobilization. The enzyme activities were studied by photometry. Immobilization was accomplished by either inclusion in a thin film or adsorption to cross-linked microspheres. Two linkage agents were used: glutaraldehyde and glyoxal. The best immobilization and activity yields (82%, 95%) were obtained when POX1B was incorporated within a chitosan/glyoxal film. The effect of temperature on the immobilized enzyme was tested. Results showed that full activity was retained after 40 min incubation at 40 °C. Anchored POX1B inside chitosan was used for biosensor design. Cyclic voltammetry and impedance spectroscopy were employed to analyze electrochemical properties of the modified gold electrode and to monitor hydrogen peroxide. The biosensor was very sensitive and attained a detection limit of 100 nM. 相似文献
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The major task of clustering is to group an heterogeneous population into unknown groups based on a similarity measure. In order to enhance the robustness and the stability of unsupervised classification solutions, clustering ensembles are used; they are considered to be a powerful tool to deal with this issue. Individual clusterers consolidate the process of decision making through the concept of weighting. The aim is to determine an effective combination method that makes use of the benefits of each clusterer while avoiding its weaknesses. In this paper, we study the problem of combining multiple partitioning without accessing the original features. A genetic algorithm is proposed using three different fitness scores. Following three scenarios: Object Distributed Clustering, Feature Distributed Clustering, and Robust Centralized Clustering, the proposed consensus functions algorithm outperforms three existing ones: Cluster-based Similarity Partitioning Algorithm, HyperGraph Partitioning Algorithm and Meta-Clustering Algorithm. 相似文献
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Nonlinear relations between the beam displacement and generalized strain measures, which have basic effects on postbuckling behavior of elastic beams, are presented. The complex coupling phenomena associated with the higher order strain terms is reviewed for the special case of planar and rectilinear pinned-pinned beams. Special consideration was made for the physical assumptions used in the various column-beam models. A natural hierarchy results yielding that all the higher order terms can, for a specific beam formulation, be steadily obtained by dissimilar polynomial approximations of the generalized strains. The asymptotic expansions method and the minimum energy criterion are used to perform analytical calculation of the postbifurcation equilibrium path at the neighborhood of a bifurcation point when only a unique buckling mode is assumed to occur. As a result, postbuckling branches are easily obtained even when accounting for both beam centerline extensional deformation and shear strain. They show that the critical load is scarcely affected by the higher order strain terms unlike the postbuckling paths which are found to be very sensitive to them. 相似文献
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Er3+-doped tellurite glasses with molar compositions of 75TeO2–20ZnO–(5 − x) Na2O–xEr2O3 (x = 0, 0.5, 1, 2, 3, and 4 mol%) have been elaborated from the melt-quenching method. The effects of Er2O3 concentration on the thermal stability and optical properties of tellurite glasses have been discussed. From the differential
scanning calorimetry (DSC) profile, the glass transition temperature T
g, and crystallization onset temperature T
x are estimated. The thermal stability factor, defined as ∆T = T
x − T
g, was higher than 100 °C. It suggests that tellurite glass exhibits a good thermal stability and consequently is suitable
to be a potential candidate for fiber drawing. Furthermore, the stability factor increases with Er2O3 concentration up to 2 mol% then presents a continue decrease suggesting of beginning of crystallization of highly doped tellurite
glasses. The refractive index and extinction coefficient data were obtained by analyzing the experimental spectra of tanΨ
and cos∆ measured by spectroscopic ellipsometry (SE). The complex dielectric functions (ε = ε1 + iε2) of the samples were estimated from regression analysis. The fundamental absorption edge has been identified from the optical
absorption spectra and was analyzed in terms of the theory proposed by Davis and Mott. The values of optical band gap for
direct and indirect allowed transitions have been determined. An important decrease of the optical band gap was found after
Er doping. It was assigned to structural changes induced from the formation of non-bridging oxygen. The absorption coefficient
just below the absorption edge varies exponentially with photon energy indicating the presence of Urbach’s tail. The origin
of the Urbach energy is associated with the phonon-assisted indirect transitions. 相似文献
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The problem of inelastic bending and collapse of tubes in the presence of internal pressure is investigated using experiments and analyses. The experiments involve 1.5-inch diameter, D/t=52 stainless steel tubes bent to failure at fixed values of pressure. The moment-curvature response is governed by the inelastic characteristics of the material. Bending induces some ovalization to the tube cross section while, simultaneously, the internal pressure causes the circumference to grow. Following some inelastic deformation, small amplitude axial wrinkles appear on the compressed side of the tube, and their amplitude grows stably as bending progresses. Eventually, wrinkling localizes, causing catastrophic failure usually in the form of an outward bulge. Internal pressure stabilizes the structure, it increases the wavelength of the wrinkles and can increase significantly the curvature at collapse. The onset of wrinkling is established by a custom bifurcation buckling formulation. The evolution of wrinkling and its eventual localization are simulated successfully using a FE shell model. The material is represented as an anisotropic elastic-plastic solid using the flow theory, while the models are assigned initial geometric imperfections with the wavelength of the wrinkling bifurcation mode. It is demonstrated that successful prediction of collapse requires very accurate representation of the material inelastic properties including yield anisotropies, and that as expected, the collapse curvature is sensitive to the imperfection amplitude and wavelength imposed. 相似文献
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The third-generation architectures have to support multiple mobile virtual network operators (MVNOs). They have also to host different types of these virtual operators. Virtualizing these architectures will allow the MVNOs to rapidly deploy their equipment. It will separate the management domain between them and the mobile host operator. It will also allow sharing resources and reducing the deployment cost. Motivated by these requirements, we propose some MVNO distributed architectures. First of all, we evaluate the physical and virtual deployment time, then we define the utility function of the equipment for the different types of MVNOs. The utility function evaluates the gain in deployment time for each type of MVNO. This function has to be maximized. Our study demonstrates that the data calls type is the best MVNO candidate for virtualization. This latter consistently yields the best overall utility across an important number of network equipment to be virtualized by varying the time required for software installation and the time spent to determine the physical position of the equipment. 相似文献
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Effects of Extraction Solvents and Provenances on Phenolic Contents and Antioxidant Activities of Cumin (Cuminum cyminum L.) Seeds 总被引:1,自引:0,他引:1
Iness Bettaieb Rebey Soumaya Bourgou Imen Ben Slimen Debez Iness Jabri Karoui Ibtissem Hamrouni Sellami Kamel Msaada Ferid Limam Brahim Marzouk 《Food and Bioprocess Technology》2012,5(7):2827-2836
Polyphenol contents and 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) scavenging activity of cumin (Cuminum cyminum L.) seed extracts were compared depending on their geographical origin (Tunisia and India: TCS and ICS, respectively) and the extraction solvent polarity. The ??-carotene bleaching assay, the chelating ability and the reducing power of the most promising solvent extracts were also assessed. In addition, TCS and ICS extracts were acid-hydrolyzed and the phenolics identified by reversed-phase high-performance liquid chromatography (HPLC). Seed phenolic contents and antioxidant activity appeared to be accession and solvent dependent. Extraction with 80% acetone led to the highest polyphenol (18.60 and 16.50?mg gallic acid equivalents (GAE)/g dry weight (DW)), flavonoid (5.91 and 4.99?mg catechin equivalents (CE)/g DW) and tannin (83.23 and 80.23?mg CE/g DW) contents, respectively for TCS and ICS. DPPH scavenging activity, ??-carotene bleaching assay, chelating ability and reducing power were maximal in 80% acetone for both TCS and ICS. HPLC analysis revealed several phenolic compounds in C. cyminum seeds, with p-coumaric (4.83 and 2.33?mg/g DW), trans-2-dihydrocinnamic (1.09 and 1.20?mg/g DW) and rosmarinic (0.70 and 1.04?mg/g DW) acids as major phenolics in TCS and ICS, respectively. Thus, phenolic composition of cumin seeds is also origin dependent. Taken together, our findings indicate that cumin might constitute a rich and novel source of natural antioxidants as food additives in food industry and that acetone 80% would be the most appropriate solvent for seed extraction. 相似文献