排序方式: 共有147条查询结果,搜索用时 15 毫秒
31.
The aim of the present work is the numerical computation of the average magnetic induction in the cross-section of a non-oriented 3% Si-Fe sheet by solving the magnetic diffusion equation. Jiles’ dynamic model is used to describe the magnetization law. The obtained results are compared with those of the measurements carried out for frequencies of 0.5, 50, 200 and 500 Hz. A satisfactory agreement is obtained between both types of results. 相似文献
32.
Hakim Mazrou Zahir Idiri Tassadit Sidahmed Malika Allab 《Journal of Radioanalytical and Nuclear Chemistry》2010,284(2):253-263
A new approach has been suggested to establish reliable response matrix of a CRNA Bonner Sphere Spectrometer equipped with
a high efficiency 10 mm diameter × 2 mm thick 6LiI (Eu) scintillation detector from thermal neutron energy up to 20 MeV. It combines the experimental response functions
obtained using a continuous neutron spectrum emitted from an 241Am-Be neutron source of known emission, with those obtained by Monte-Carlo (MC) calculations. Sensitivity analysis has been
performed to check the influence of pertinent parameters on the MC computed detector response. The parameters of interest
are the density of polyethylene moderators, the cross section library used in MCNP5 and two computing models depending on
the interactions of the neutrons in the detector. The calculated responses of the spectrometer to the 241Am-Be neutron source showed discrepancies depending on the sphere diameter when compared to our measured responses. However,
this difference was smaller compared with the experiments available in the literature. The enhancement achieved in the present
study is partly due to improved modeling in the MC calculations. To correct for the differences observed, a fitting factor
has been deduced for each sphere diameter and used to adjust the MC responses to the experimental ones. The obtained results
were subsequently compared to the experimental data of GSF-G spheres system obtained for a typical 4 mm diameter × 4 mm thick
6LiI scintillator for four ISO-8529 selected neutron energies (144.0 keV, 565 keV, 2.5 and 14.8 MeV). The present responses
were similar in shape but higher, in absolute values, by about two and half times for all spheres owing essentially to the
increase in active part of the detector. Finally, the CRNA-BSS response matrix containing 48 energy points from 0.01 eV to
20 MeV for 22 sphere diameters with a mean polyethylene density of 0.944 g/cm3 was constructed by applying a spline interpolation method. The released response matrix was then compared to data available
in the literature evaluated by Monte-Carlo calculations for a 4 mm × 4 mm 6LiI crystal scintillator. The obtained response matrix is intended for radiation protection applications at CRNA. 相似文献
33.
A stereoselective synthesis of pentacyclic steroids has been achieved. Starting from commercially available cholic acid 1, followed by asymmetric epoxidation and by stereoselective epoxide ring opening, employing nucleophilic species, the corresponding products were afforded in good yields. The compounds were being evaluated for their biological activity. 相似文献
34.
Fouzia Gudira Malika Saidi Idrissi Harald Krautscheid Lahcen El Ammari 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(12):m530-m532
In the title compound, μ‐3,4′‐bi‐1,2,4‐triazole‐di‐μ‐chloro‐copper(II) monohydrate, {[CuCl2(C4H4N6)]·H2O}n, the Cu atom is located in a distorted octahedron consisting of two N atoms and four Cl atoms. The structural unit is an infinite chain in which octahedral groups, connected by shared edges, are also linked by bitriazole molecules. The bitriazole ligand, the Cu atom and the water O atom all lie on independent twofold axes. The structure is held together by hydrogen bonds between the water molecules and the non‐coordinated N atoms of the ligand, and by van der Waals forces. 相似文献
35.
36.
Saida Azzouzi Rachid Jalal Malika El Messaoudi Luis R. Domingo M'hamed Esseffar M. José Aurell 《Journal of Physical Organic Chemistry》2007,20(4):245-254
A novel heterocyclic compound 3‐mesityl‐5‐methyl‐4,5,11,11a‐tetrahydro‐6H‐[1,2,4]oxadiazolo [5,4‐b][1,3,4]benzotriazépin‐6‐one 4 has been synthesised by a 1,3 dipolar cycloaddition (13DC) reaction of 1,3,4‐benzotriazepin‐5‐one 1 with mesitylnitrile oxide 3 . The reaction, beside its synthetic interest, has shown to be completely chemo‐ and regioselective. The structure of the compound was determined by X‐ray crystallography and analysed by spectral methods (NMR and mass spectrometry). The molecular mechanism for the reaction has been studied using quantum mechanical calculations at the B3LYP/6‐31G* theory level. Two mechanisms are possible for the formation of the cycloadduct 4 . The first one involves a 13DC reaction between 1 , as dipolarophile and 3 , as dipole. Analysis of the results indicates that it takes place along asynchronous concerted bond‐formation process with a very low polar character. The regioselectivity obtained from the calculations are in complete agreement with the unique formation of the cycloadduct 4 . The second mechanism is initiated by the nucleophilic attack of the N3 nitrogen of the tautomer form of 2 , to the C5 carbon of the nitrile oxide 3 to yield an amidoxime. However, the large energy involved in this addition prevents this mechanism. The large energy difference between the tautomers 1 and 2 , makes that only the C?N site of benzotriazepin‐5‐one 1 could act as a dipolarophile site. This fact makes the 13DC reaction to be chemoselective. The analysis of global electrophilicity of the reagents allows explaining the low polar character of these 13DC reactions. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
37.
Qourzal S Tamimi M Assabbane A Ait-Ichou Y 《Journal of colloid and interface science》2005,286(2):621-626
The photocatalytic oxidation of 2-naphthol has been investigated at room temperature in a dynamic photoreactor with system UV/O2 (air) and aqueous suspension of titanium dioxide TiO2 irradiated under a variety of conditions. The kinetics of disappearance of pollutant were affected by several operating parameters such as TiO2 mass, concentration of the substrate and reaction pH. The experiments were measured by high performance liquid chromatography. A Langmuir-Hinshelwood model was found to be accurate for photocatalytic degradation and indicates that adsorption of the solute on the surface of semiconductor particles plays a role in photocatalytic reaction. 相似文献
38.
Malika Berredjem Zine Regainia Georges Dewynter Jean Louis Montero Nour‐Eddine Aouf 《Heteroatom Chemistry》2006,17(1):61-65
A series of new chiral N,N′‐sulfonyl bis‐oxazolidin‐2‐ones were synthesized starting from 2‐aminoalcohols, sulfuryl chloride, and diethyl carbonate. This method utilizes natural amino acids as a source of chirality for the preparation of oxazolidinones. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:61–65, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20183 相似文献
39.
A framework to model micro-cracked bodies based on the theory of continua with microstructure is presented: assuming a crack embedded in each material element, a field is considered characterising size and orientation of the crack, in addition to the usual placement in the Euclidian space. To deal with crack evolutions, we call upon configurational forces which, in the present case, occur at the level of the microstructure. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
40.
Enolizable Carbonyls and N,O‐Acetals: A Rational Approach for Room‐Temperature Lewis Superacid‐Catalyzed Direct α‐Amidoalkylation of Ketones and Aldehydes 下载免费PDF全文
Bahria Touati Dr. Abderrahman El Bouakher Dr. Catherine Taillier Dr. Raja Ben Othman Prof. Dr. Malika Trabelsi‐Ayadi Dr. Sylvain Antoniotti Dr. Elisabet Duñach Prof. Dr. Vincent Dalla 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(17):6012-6022
An efficient catalytic room‐temperature direct α‐amidoalkylation of carbonyl donors, that is, ketones and aldehydes with unbiased N,O‐acetals, is described. Sn(NTf2)4 is an optimal catalyst to promote this challenging transformation at low loading and the reaction shows promising scope. A comprehensive and rational evaluation of this reaction has led to the establishment of an empirical scale of nucleophilic reactivity for a broad set of ketones that should be helpful in the synthetic design and development of carbonyl α‐functionalization methods. 相似文献