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11.
A systematic theoretical DFT study of the bonding between the cation Fe3+ and the anion was carried out. The role of water ligands is presented. Several isomers with tetrahedral, bipyramidal and octahedral environments around the iron ion were investigated. 5-fold coordination of the Fe3+ cation is found when 5 and 6 water molecules are included. Calculated infrared spectra are also presented. 相似文献
12.
A model based on the thermodynamics of relaxations of continuous media (called DNLR as Distribution of nonlinear relaxations)
is used to describe the tension/torsion progressive strain phenomenon. The proposed model is compared to the experimental
data obtained by Benham on mild steel at room temperature with satisfactory results. We discuss the capacities and the relevance
of the model obtained. 相似文献
13.
The present study concerns the rheological behavior of the Jebel Shemsi clay dispersions (Shp). Shp is an interstratified illite/smectite clay from southern Tunisia. The influences of clay concentration, NaCl, and xanthan-a semirigid polymer-on the yield stress, the elastic modulus, and the xanthan adsorption were investigated. The sol-gel transition and the scale laws of rheometric properties are established. Progressive addition of NaCl to the clay dispersions decreases the thickness of the diffuse double layer, which makes the system rigid, increasing the yield and the elastic modulus. In the presence of xanthan, the negative surface charges become higher and the repulsive interparticle interactions increase; consequently the yield and the elastic modulus increase. The xanthan adsorption on the clay particle surface increases slightly with the NaCl concentration. The particle aggregation due to the salt and the particle dispersion due to the polymer are observed. The behavior of this interstratified clay is compared to that found for pure smectite. The 15% illite stratified with smectite in the Shp clay does not change the gels' rheological properties significantly. Meanwhile the amount of Shp clay needed to obtain a gel is more important than in the case of a pure smectite. 相似文献
14.
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
15.
Abdelhak Ayadi Sana Elgasri Abderrazek Mezghani Mickaël Castro Foued Elhaouani 《ournal of non Newtonian Fluid Mechanics》2011,166(12-13):661-666
The gross melt fracture defect is related to the flow instabilities developed in the contraction region. To mitigate these upstream instabilities, a convergent radial flow in the die entrance has been created. In fact, the ultimate objective of the present work is to examine the effect of the clearance width of radial flow on the appearance and development of gross melt fracture defect. So, capillary rheometer experiments were performed with linear polydimethylsiloxane (PDMS) oil.As for the influence of radial flow width on the morphology of gross melt fracture defect, extrudate photographs show that this imperfection can be mitigated since its frequency is higher and amplitude smaller when the gap of radial flow decreases. Such results may be related both to shear and elongational components of radial flow. Actually, when gap width is very small compared to the external diameter of radial flow, shear deformations become more enhanced with respect to the elongational deformations and thus the helical gross melt fracture becomes more like a surface defect than volume defect. 相似文献
16.
We have applied harmonic expansion to derive an analytical solution for the Lorenz-Haken equations. This method is used to describe the regular and periodic self-pulsing regime of the single mode homogeneously broadened laser. These periodic solutions emerge when the ratio of the population decay rate ? is smaller than 0:11. We have also demonstrated the tendency of the Lorenz-Haken dissipative system to behave periodic for a characteristic pumping rate “2C P ”[7], close to the second laser threshold “2C 2th ”(threshold of instability). When the pumping parameter “2C” increases, the laser undergoes a period doubling sequence. This cascade of period doubling leads towards chaos. We study this type of solutions and indicate the zone of the control parameters for which the system undergoes irregular pulsing solutions. We had previously applied this analytical procedure to derive the amplitude of the first, third and fifth order harmonics for the laser-field expansion [7, 17]. In this work, we extend this method in the aim of obtaining the higher harmonics. We show that this iterative method is indeed limited to the fifth order, and that above, the obtained analytical solution diverges from the numerical direct resolution of the equations. 相似文献
17.
Talha Achouri Mekki Ayadi Khaled Omrani 《Numerical Methods for Partial Differential Equations》2009,25(3):668-684
In this article, a fully discrete Galerkin scheme based on a nonlinear Crank–Nicolson method to approximate the solution of the DGRLW equation is constructed. Some a priori bounds are proved as well as error estimates. Then, a linearized modification scheme by an extrapolation method is discussed. The two schemes are time second order convergence. The last part is devoted to some numerical results. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009 相似文献
18.
Plants of two wheat species (Triticum aestivum cv. Tanit and T. durum cv. Ben Bachir), differing in their sensitivity to NaCl were cultivated in the presence or absence of 100 mM NaCl for 21 days. Soluble proteins extracted from leaves were analyzed by two-dimensional electrophoresis in order to detect NaCl-induced changes in the polypeptide patterns. In all, 500 spots were detected. Results showed species-dependent differences. The greatest alterations in the polypeptide profiles following salt stress were found in the most sensitive cultivar: among the 12 spots (molecular mass, 15-31 kDa) specifically considered in the acidic region of the gel, 11 declined, even disappeared in the NaCl-sensitive leaf profiles, while in the tolerant species only five spots were affected by the salt treatment and five remained untouched; moreover in the latter, two new polypeptides were shown to be induced by NaCl. 相似文献
19.
Faycal Abidi Mekki Ayadi Khaled Omrani 《Journal of Applied Mathematics and Computing》2008,27(1-2):293-305
A finite difference scheme is derived for the initial-boundary problem for the nonlinear equation system $$\frac{\partial u}{\partial t}=A\frac{\partial^{2}u}{\partial x^{2}}+f(u),$$ where A is a complex diagonal matrix, f is a complex vector function. The stability and convergence in discrete L ∞-norm of proposed Crank-Nicolson type finite difference schemes is proved. No restrictions on the ratio of time and space grid steps are assumed. Some numerical experiments have been conducted in order to validate the theoretical results. 相似文献
20.