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排序方式: 共有122条查询结果,搜索用时 15 毫秒
101.
Taoufik Ben Jomaa Mourad Nouiri Lotfi Béji Abdelaziz Bouazizi 《Current Applied Physics》2013,13(7):1256-1263
Assembled heterojunction was fabricated by spin-coating poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene)] (MEH-PPV) thin layers on straight and porous n+-GaAs substrates. The current–voltage and capacitance–voltage studies have shown an abrupt junction behavior with current conduction governed by SCLC and thermionic modes. Andersons' rules were used to determine depletion width and balance bands discontinuities for both heterojunctions. Capacitance and conductance vs. frequency techniques were used to evaluate the density of interface states. Density values obtained from both techniques were in a good agreement. 相似文献
102.
Viscosity deviations from ideal mixing for 1,4-dioxane + water mixtures over the entire range of composition at temperatures
of (293.15, 303.15 and 313.15) K and atmospheric pressure were calculated from experimental viscosity data presented in a
previous work. The temperature range was extended to 323.15 K with data from the literature. This system exhibits very large
positive deviations due to strong heteromolecular interactions and also due to size differences of the unlike molecules. The
viscosity data as well as their corresponding relative functions were used to test the applicability of two correlative equations:
the reduced Redlich-Kister equation and the recently proposed Herráez equation. These relative functions are important to
reduce the effect of temperature and, consequently, to reveal the effects of different types of interactions. Their correlation
abilities at different temperatures, and using different numbers of parameters, are discussed for the case of limited experimental
data. Generally, good agreement between experimental and calculated data was obtained with both equations provided more than
three parameters were employed. 相似文献
103.
Mazoyer E Szeto KC Basset JM Nicholas CP Taoufik M 《Chemical communications (Cambridge, England)》2012,48(30):3611-3613
The first example of propylene production from 2-butene in promising yield is described by reacting trans-2-butene over tungsten hydrides precursor W-H/Al(2)O(3) at 150 °C and different pressures in a continuous flow reactor. The tungsten carbene-hydride active site operates as a "bi-functional catalyst" through the disfavoured 2-butene isomerisation on W-hydride and 2-butenes/1-butene cross-metathesis on W-carbene. 相似文献
104.
Mazoyer E Merle N de Mallmann A Basset JM Berrier E Delevoye L Paul JF Nicholas CP Gauvin RM Taoufik M 《Chemical communications (Cambridge, England)》2010,46(47):8944-8946
A well-defined, silica-supported tungsten oxo alkyl species prepared by the surface organometallic chemistry approach displays high and sustained activity in propene metathesis. Remarkably, its catalytic performances outpace those of the parent imido derivative, underlining the importance of the oxo ligand in the design of robust catalysts. 相似文献
105.
106.
Sami Lakhdar Dr. François Terrier Prof. Dominique Vichard Guillaume Berionni Nizar El Guesmi Régis Goumont Prof. Taoufik Boubaker Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(19):5681-5690
The reaction of 4,6‐dinitrobenzofuroxan (DNBF) with 1‐trimethylsilyloxybuta‐1,3‐diene ( 8 ) is shown to afford a mixture of [2+4] diastereomeric cycloadducts ( 10 , 11 ) through stepwise addition–cyclization pathways. Zwitterionic intermediate σ‐adduct 9 , which is involved in the processes, has been successfully characterized by 1H and 13C NMR spectroscopy and UV/visible spectrophotometry in acetonitrile. A kinetic study has been carried out in this solvent that revealed that the rate of formation of 9 nicely fits the three‐parameter equation log k=s(E+N) developed by Mayr to describe the feasibility of nucleophile–electrophile combinations. This significantly adds to the NMR spectroscopic evidence that the overall cycloadditions take place through a stepwise mechanism. The reaction has also been studied in dichloromethane and toluene. In these less polar solvents, the stability of 9 is not sufficient to allow direct characterization by spectroscopic methods, but a kinetic investigation supports the view that stepwise processes are still operating. An informative comparison of our reaction with previous interactions firmly identified as prototype stepwise cycloadditions is made on the basis of the global electrophilicity index, ω, defined by Parr within the density functional theory, and highlighted by Domingo et al. as a powerful tool for understanding Diels–Alder reactions. 相似文献
107.
In this paper we study a fractional diffusion Boussinesq model which couples the incompressible Euler equation for the velocity and a transport equation with fractional diffusion for the temperature. We prove global well-posedness results. 相似文献
108.
Rohand T Baruah M Qin W Boens N Dehaen W 《Chemical communications (Cambridge, England)》2006,(3):266-268
The BODIPY chromophore can be easily modified by nucleophilic mono- or disubstitution of 3,5-dichloroBODIPY with O-, N-, S- and C-nucleophiles. Absorption and fluorescence spectral data of the new BODIPY derivatives are also reported. 相似文献
109.
Lakhdar S Westermaier M Terrier F Goumont R Boubaker T Ofial AR Mayr H 《The Journal of organic chemistry》2006,71(24):9088-9095
The kinetics of the coupling of indole (1a), N-methylindole (1b), 5-methoxyindole (1c), and 5-cyanoindole (1d) with a set of reference benzhydryl cations have been investigated in acetonitrile and/or dichloromethane. The second-order rate constants for the reactions correlate linearly with the electrophilicity parameter E of the benzhydryl cations. This allows the determination of the reactivity parameters, N and s, characterizing the nucleophilicity of 1a-d according to the linear free enthalpy relationship log k(20 degrees C) = s(N + E) (Acc. Chem. Res. 2003, 36, 66). The nucleophilicity parameters thus defined describe nicely the reactions of 1a-d with 4,6-dinitrobenzofuroxan (2), a neutral superelectrophilic heteroaromatic whose electrophilicity (E) has been recently determined. On this ground, the kinetics of the coupling of 2 with a large variety of indole structures have been studied in acetonitrile, leading to a ranking of this family of pi-excessive carbon nucleophiles over a large domain of the nucleophilicity scale N. Importantly, two linear and parallel correlations are obtained on plotting the measured N values versus the pK(a)(H(2)O) values for protonation at C-3 of 5-X-substituted indoles and 5-X-substituted 2-methylindoles, respectively. This splitting reveals that the presence of the 2-methyl group causes steric hindrance to the approach of 2 from the adjacent C-3 position of an indole structure. The N vs pK(a)(H(2)O) correlation for 5-X-substituted indoles is used for a rapid determination of the C-3 basicity of indoles whose acidity constants cannot be measured through equilibrium studies in strongly acidic aqueous media. 相似文献
110.