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Ahmad Seif Ehsan Zahedi Goodarz M. Rozbahani 《Central European Journal of Chemistry》2012,10(1):96-104
To investigate the influence of C-doping on the electrostatic structure properties in the frame work of density functional
theory (DFT), we considered beryllium monoxide nanotubes (BeONTs), consisting of 60 Be and 60 O atoms. Full geometry optimizations
are performed for all structures, i.e., all atoms are allowed to relax. Afterwards, the chemical shielding (CS) tensors are
calculated for Be-9, O-17 and C-13 nuclei in the C-doped forms and also pristine models of the (10, 0) zigzag and (5, 5) armchair
BeONTs. Formation energies indicate that C-doping of Be atom (CBe form) could be more favorable than C-doping of O atom (CO
form) in both zigzag and armchair BeONTs. Gap energies and dipole moments detected the effects of dopant in the (5, 5) armchair
models; however, those parameters did not indicate any significant changes in the C-doped (10, 0) zigzag BeONT models. The
results show that the CS values for the Be and O atoms-contributed to the Be-C bonds or those atoms close to the C-doped region-in
the CO form of BeONTs (zigzag and armchair) are changed. The same values only for the O atoms-contributed to the O-C bonds-
in the CBe form of BeONTs (zigzag and armchair) are changed. 相似文献
24.
An accurate pressure–velocity decoupling technique for semi‐implicit rotational projection methods 下载免费PDF全文
Ehsan Tavakoli 《国际流体数值方法杂志》2017,84(5):241-267
In this paper, an accurate semi‐implicit rotational projection method is introduced to solve the Navier–Stokes equations for incompressible flow simulations. The accuracy of the fractional step procedure is investigated for the standard finite‐difference method, and the discrete forms are presented with arbitrary orders or accuracy. In contrast to the previous semi‐implicit projection methods, herein, an alternative way is proposed to decouple pressure from the momentum equation by employing the principle form of the pressure Poisson equation. This equation is based on the divergence of the convective terms and incorporates the actual pressure in the simulations. As a result, the accuracy of the method is not affected by the common choice of the pseudo‐pressure in the previous methods. Also, the velocity correction step is redefined, and boundary conditions are introduced accordingly. Several numerical tests are conducted to assess the robustness of the method for second and fourth orders of accuracy. The results are compared with the solutions obtained from a typical high‐resolution fully explicit method and available benchmark reports. Herein, the numerical tests are consisting of simulations for the Taylor–Green vortex, lid‐driven square cavity, and vortex–wall interaction. It is shown that the present method can preserve the order of accuracy for both velocity and pressure fields in second‐order and high‐order simulations. Furthermore, a very good agreement is observed between the results of the present method and benchmark simulations. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
25.
Alireza Hasaninejad Khodabakhsh Niknam Abdolkarim Zare Ehsan Farsimadan Mohsen Shekouhy 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):147-155
Silphox [POCl3-n(SiO2)n] efficiently catalyzes the condensation of benzene-1,2-diamine with mono and dicarboxylic acids under microwave irradiation to afford benzimidazole derivatives in high yields and short reaction times. 相似文献
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Abolfazl Shiroudi Ehsan Zahedi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5):619-631
Abstract The gas-phase thermal decomposition kinetics of silacyclobutane (1), 1-methyl- silacyclobutane (2), and 1,1-dimethyl-1-silacyclobutane (3) has been theoretically studied at the B3LYP/6-311G**, B3PW91/6-311G**, and MPW1PW91/6-311G** levels. The B3LYP/6-311G** method was found to give a reasonable good agreement with the experimental kinetics and thermodynamic parameters. The decomposition reaction of compounds 1–3 yields ethylene and the corresponding silene. Based on the optimized ground state geometries using B3LYP/6-311G** method, the natural bond orbital (NBO) analysis of donor-acceptor (bonding–antibonding) interactions revealed that the perturbation energies (E2) associated with the electronic delocalization from σSi1–C2 to σ*C4–Si1 orbitals increase from compounds 1 to 3. The σSi1–C2→σ*C4–Si1 resonance energies for compounds 1–3 are 1.17, 1.26, and 1.43 kcal/mol, respectively. Also, the decomposition process in these compounds is controlled by σ→σ* resonance energies. Moreover, the obtained order of energy barriers could be explained by the number of electron-releasing methyl groups substituted to the Sisp2 atom. NBO analysis shows that the occupancies of σSi1–C2 bonds decrease for compounds 1–3 as 3 < 2 < 1, and the occupancies of σ*Si1–C2 bonds increase in the opposite order (3 > 2 > 1). Moreover, these results can fairly explain the decrease of the energy barriers (ΔEo) of the decomposition reaction of compounds 1 to 3. The calculated data demonstrate that in the decomposition process of the studied compounds, the polarization of the C3–C4 bond is the rate determining factor. Analysis of bond orders, NBO charges, bond indexes, synchronicity parameters, and IRC calculations indicate that these reactions are occurring through a concerted and asynchronous four-membered cyclic transition state type of mechanism. 相似文献
27.
Mesoporous CuFe2O4 solid solution nanopowders with high specific surface areas were synthesized by a novel, very simple and inexpensive sol-gel route using propylene oxide as gelation agent, and used as the catalyst in low temperature CO oxidation. The samples were characterized by X-ray diffraction, N2 adsorption-desorption, thermogravimetric/differential thermal analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and temperature-programmed reduction. The results revealed that the samples have a nanocrystalline structure with crystals in the range of 10 to 25 nm, and that all the catalysts have mesoporous pores. The addition of Cu into iron oxide affected its structural and catalytic properties. The sample containing 15 mol% Cu showed the highest specific surface area and catalytic activity, and showed high catalytic stability in low temperature CO oxidation. 相似文献
28.
Mehdi Adib Ehsan Sheikhi Pouyan Haghshenas Saideh Rajai-Daryasarei Hamid Reza Bijanzadeh Long-Guan Zhu 《Tetrahedron letters》2014
A novel one-pot, five-component synthesis of 1-(alkylimino)-5,5-dicyano-3a-aryloctahydro-3-oxacyclobuta[cd]pentalene-1a,2,5a,5b(2H,3aH)-tetracarboxylates is described. A mixture of phenacyl bromide, malononitrile, isocyanide, and two equivalents of a dialkyl acetylenedicarboxylate undergoes a novel 1:1:1:2 addition reaction at ambient temperature in absolute ethanol to produce diastereoselectively the title compounds in good yields. 相似文献
29.
Sharifkhani Samira M. Yaftian Mohammad Reza Hosseini Majid Haji Zolfonoun Ehsan 《Journal of Analytical Chemistry》2022,77(4):505-512
Journal of Analytical Chemistry - In this study, for the first time, the organic gas steam-liquid extraction by a special hand-made cell was used as a simple and inexpensive preconcentration... 相似文献
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