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Lynda Idjouadiene Toufik A. Mostefaoui Hocine Djermoune Letizia Bonizzoni 《X射线光谱测定》2019,48(5):505-512
The North African regions boast a multimillenary tradition of pottery production that represents a decisive progress in all societies. In this paper, we present the analysis of several fragments of pottery dating from the Middle Ages and collected in the archaeological site of Gouraya in Béjaïa (Algeria). Energy-dispersive X-ray fluorescence measurements were performed to obtain the elemental composition of the clays and to attempt a classification of the samples through multivariate analysis methods, connecting them to the archaeological information about the sites. Hierarchical clusters analysis (HCA) identified two possible different groups, related to different production sites, even if only one source of clay seem to be used, consistently with the geological contest. Based on the results, a tentative provenance interpretation could be proposed on historical bases. We put in place a strategy that made it possible to perform provenance studies respecting sample integrity as we aim to extend our research also to integer and well-preserved object from museum, to create a database for Algerian production of in the Middle Ages. 相似文献
43.
The Herschel–Bulkley rheological parameters of an environmentally friendly drilling fluid formulated based on an Algerian bentonite and two polymers—hydroxyethyl cellulose and polyethylene glycol—have been optimized using a genetic algorithm. The effect of hydroxyethyl cellulose, temperature, pH and sodium chloride (NaCl) on the three-parameter Herschel-Bulkley model was also studied. The genetic algorithm technique provided improved rheological parameter characterization compared to the nonlinear regression, especially in the case of drilling fluids formulated with sodium chloride making it a better choice. Furthermore, the oscillatory test offered more reliable yield stress values. The rheological parameters were found to be very sensitive to different conditions. Yield stress and consistency index increased with increasing the hydroxyethyl cellulose concentration, reaching maximum at a temperature of 65 °C and decreased with decreasing pH and also when adding sodium chloride to the drilling fluid. The flow index changed inversely to yield stress and consistency index. The physical origins of these changes in rheological parameters were discussed and correlation between variation in rheological parameters and bentonite suspension properties were concluded. Based on these results, it is recommended to use the proposed formulation of drilling fluid at high temperature and when the formation of alkaline pH is encountered due to the gelation mechanism and to select the optimum concentration of NaCl to avoid degradation of the rheological parameters. 相似文献
44.
Hamiltonism and Partially Square Graphs 总被引:10,自引:0,他引:10
Given a graph G, we define its partially square graph G
* as the graph obtained by adding edges uv whenever the vertices u and v have a common neighbor x satisfying the condition N
G[x]⊆N
G[u]∪N
G [v], where N
G[x]=N
G(x)∪{x}. In particular, this condition is satisfied if x does not center a claw (an induced K
1,3). Obviously G⊆G
*⊆G
2, where G
2 is the square of G. We prove that a k-connected graph (k≥2) G is hamiltonian if the independence number α(G
*) of G
* does not exceed k. If we replace G
* by G we get a well known result of Chvátal and Erdo?s. If G is claw-free and G
* is replaced by G
2 then we obtain a result of Ainouche, Broersma and Veldman. Relationships between connectivity of G and independence number of G
* for other hamiltonian properties are also given in this paper.
Received: June 17, 1996 Revised: October 30, 1998 相似文献
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Hocine Aichaoui Daniel Lesieur Jean-Pierre Hnichart 《Journal of heterocyclic chemistry》1992,29(1):171-175
Benzoxazolinone derivatives have been found to exhibit various pharmacological properties and 6-acyl-2(3H)-benzoxazolones are considered as key starting materials for the preparation of these compounds. Reported here are the optimal conditions for a regioselective acylation at the 6-position of the benzoxazolinone ring. A general method leading to the expected products in excellent yields consists in using a mixture of aluminum chloride-dimethylformamide as catalyst and acid anhydrides or chlorides as acylating agents. 相似文献
49.
D. Amar, I. Fournier, A. Germa, R. Haggkvist, and C. Thomassen conjectured that the vertices of a k-connected graph with stability number α can be covered by α/k cycles. We prove this conjecture. 相似文献
50.
Takuro Miki Takumi Ogawa Tetsuhiko Isobe Hocine Sfihi 《Journal of Sol-Gel Science and Technology》2004,32(1-3):73-77
Acetylcellulose (AC)/silica and polyvinylpyrrolidone (PVP)/silica composites were prepared by the sol–gel method from Si(OCH3)4-AC-HNO3-H2O-tetrahydrofuran-CH3OC2H4OH and Si(OCH3)4-PVP-(CH3COOH or NH3)-H2O-CH3OH-CH3OC2H4OH solutions. AC/silica composites were composed of micrometer-sized particles rich in silica and a matrix rich in AC, while PVP/silica composites were single-phase on the SEM length scale. The AC/silica composites exhibited elastic-plastic behavior, and had excellent machinability without chipping on cutting with an electric saw while the PVP/silica composites showed less plasticity and machinability. Youngs modulus and bending strength were increased by post-drying, 1.8–2.8 GPa and 49–88 MPa, respectively, for the AC/silica composites, and 1.0–3.9 GPa and 17–79 MPa, respectively, for the PVP/silica composites. 相似文献