排序方式: 共有49条查询结果,搜索用时 15 毫秒
41.
Djamila Oukacha-Hikem Malika Makhloufi-Chebli Anissa Amar Houria Bouherrou Yahia Rachedi Hacène Meghezzi 《合成通讯》2017,47(6):590-598
The synthesis of new 2-pyrone-based hydrazones has been prepared by the coupling of 6-methyl-2H-furo[3,2-c]pyran-3,4-dione with diazonium salts, obtained by diazotization of aniline derivatives. The structure of all compounds was established by spectroscopic methods, and the structure of the more stable conformer was theoretically confirmed by the potential energy profile analysis. The prepared 2-pyrone-based hydrazone dyes were acetylated and both groups of compounds showed moderate to good radical scavenging activity. 相似文献
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43.
Khelifa Bouacem Amel Bouanane-Darenfed Nawel Boucherba Manon Joseph Mohammed Gagaoua Wajdi Ben Hania Mouloud Kecha Said Benallaoua Hocine Hacène Bernard Ollivier Marie-Laure Fardeau 《Applied biochemistry and biotechnology》2014,174(5):1969-1981
To date, xylanases have expanded their use in many processing industries, such as pulp, paper, food, and textile. This study aimed the production and partial characterization of a thermostable xylanase from a novel thermophilic anaerobic bacterium Caldicoprobacter algeriensis strain TH7C1T isolated from a northeast hot spring in Algeria. The obtained results showed that C. algeriensis xylanase seems not to be correlated with the biomass growth profile whereas the maximum enzyme production (140.0 U/ml) was recorded in stationary phase (18 h). The temperature and pH for optimal activities were 70 °C and 11.0, respectively. The enzyme was found to be stable at 50, 60, 70, and 80 °C, with a half-life of 10, 9, 8, and 4 h, respectively. Influence of metal ions on enzyme activity revealed that Ca+2 enhances greatly the relative activity to 151.3 %; whereas Hg2+ inhibited significantly the enzyme. At the best of our knowledge, this is the first report on the production of xylanase by the thermophilic bacterium C. algeriensis. This thermo- and alkaline-tolerant xylanase could be used in pulp bleaching process. 相似文献
44.
In this study, by the use of Yuan and Lee’s definition of the fuzzy group based on fuzzy binary operation we give a new kind
of fuzzy ring. The concept of fuzzy subring, fuzzy ideal and fuzzy ring homomorphism are introduced, and we make a theoretical
study their basic properties analogous to those of ordinary rings.
相似文献
45.
In a recent work, the authors have used Bertrand's postulate to give a partial answer to the conjecture of Mez? which says that the hyperharmonic numbers – iterations of partial sums of harmonic numbers – are not integers. In this Note, using small intervals containing prime numbers, we prove that a great class of hyperharmonic numbers are not integers. 相似文献
46.
Donnan dialysis has been investigated in this work in the order to exhibit the influence of the composition of solution on the performance of commercial cation exchange membrane toward metallic ions. Transference fluxes have been determined either as experimental values or calculated according to theoretical models. A good agreement between theoretical and experimental flows has been obtained principally in the case of CMV membrane which presents a lower thickness. It has been demonstrated that addition of thiourea causes an increase of separation properties of membrane. The separation is mainly due to the complex formation between Ag+ and Cu+ ions and thiourea. Monovalent copper ion is obtained after reduction of Cu2+ and oxidation of thiourea and formation of bisulfide of formamidine which constitute a barrier to monovalent complex transference. 相似文献
47.
Design of computationally efficient yet perceptually realistic room auralisation algorithms require a careful selection of the early reflections to be auralised. A perception-based simplification algorithm is presented for the selection of the early reflections using a criterion which depends both on the arrival time and on the angle of incidence of the early reflection with respect to the listener. Results of two subjective tests for the evaluation of the proposed algorithm are presented. The proposed algorithm is shown to provide a significant reduction in the number of early reflections without significantly affecting the tested localisational or spatial qualities of auralisation. 相似文献
48.
Kaan Atak Ozgur O. Aybar Gokhan ?ahin Avadis Hac?nl?yan Yani Skarlatos 《Central European Journal of Physics》2009,7(3):568-574
Polyethylene Glycol has an irregular current characteristic under constant voltage and slowly varying relative humidity. The
current through a thin film of Gamma-isocyanatopropyltriethoxysilane added Polyethylene glycol (PEG-Si), its hydrogenated
and hydrophobically modified forms, as a function of increasing relative humidity at equal time steps is analyzed for chaoticity.
We suggest that the irregular behavior of current through PEG-Si thin films as a function of increasing relative humidity
could best be analyzed for chaoticity using both time series analysis and detrended uctuation analysis; the relative humidity
is kept as a slowly varying parameter. The presence of more then one regime is suggested by the calculation of the maximal
Lyapunov exponents. Furthermore, the maximal Lyapunov exponent in each of the regimes was positive, thus confirming the presence
of low dimensional chaos. DFA also confirms the presence of at least two different regimes, in agreement with the behavior
of the maximal Lyapunov exponent in the time series analysis. We also suggest that the irregular behavior of the current through
PEG-Si can be reduced by hydrogenating and hydrophobically modifying PEG-Si and the improvement in stability can be confirmed
by our study.
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49.
This research investigates the effect of uncertain material parameters on the stochastic, dynamic response of a rock-fill dam-foundation system subjected to non-stationary random excitation. The uncertain material parameter of particular interest is the shear modulus, developed from a lognormal distribution model. The stochastic seismic response model of the dam-foundation system, with uncertain material parameters and subjected to random loads is the result of a Monte Carlo simulation method. The nonlinear behavior model arises from an equivalent linear method, which considers the nonlinear variation of soil shear modulus and soil damping as a function of shear strain. Specification of the non-stationary stochastic process arises from a simulation method, which generates artificial earthquake accelerograms obtained from the product of a deterministic function of time and a stationary process. The artificial earthquake ground acceleration records reflect the characteristics of soft, medium and firm soil types. Comparison of the numerical results from these approaches provides stochasticity in earthquake seismic excitation and randomness in material parameter (shear modulus) cases. Further, the results indicate that both these cases generally influence the nonlinear dynamic response of rock-fill dams to a non-stationary seismic excitation. 相似文献