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41.
Ab‐initio calculations within density functional theory are performed to obtain a more systematic understanding of the electronic structure of iron pnictides. As a prototypical compound we study Ba0.5K0.5Fe2As2 and analyze the changes of its electronic structure when the interaction between the Fe2As2 layers and their surrounding is modified. We find strong effects on the density of states near the Fermi energy as well as the Fermi surface. The role of the electron donor atoms in iron pnictides thus cannot be understood in a rigid band picture. Instead, the bonding within the Fe2As2 layers reacts to a modified charge transfer from the donor atoms by adapting the intra‐layer Fe‐As hybridization and charge transfer in order to maintain an As3‐ valence state. 相似文献
42.
Axisymmetric laser welding of ceramics: comparison of experimental and finite element results 总被引:1,自引:0,他引:1
In this paper, we compare experimental data for a laser spot weld on a ceramic to the solution from an adaptive finite element model of the system. Our focus is on validating the finite element model, which necessarily includes numerous simplifications. We assume an axisymmetric geometry and flow profile, with a flat free surface. Buoyancy and surface tension drive the liquid motion in the molten ceramic pool beneath the laser, which is calculated using the axisymmetric forms of the continuity, momentum and energy equations. Latent heat, temperature-dependent material properties and radiation effects are all included in the formulation. These equations are solved with standard finite element techniques utilizing mesh relocation with a movement indicator based on solution gradients. Comparision with experimental data indicates that the numerical techniques used successfully predicted the depth and diameter of the actual ceramic weld pool. 相似文献
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45.
A series of methyl 4-(4-alkoxystyryl)benzoates was synthesised and studied for liquid crystalline and fluorescence properties. The peculiarity of the reaction scheme involved condensation between 4-alkoxybenzaldehyde and 4-(methoxycarbonyl)benzyltriphenyl phosphonium bromide in dichloromethane without any phase separation. The compounds were found thermally stable up to 200°C. The banded or arced focal-conic fan texture of CrE phase was exhibited on cooling the compounds (with chain length > C4) below the SmA phase. It was observed that increasing chain length up to C10 enhances mesophase stability. No LC behaviour was manifested by small (up to C3) and branched small chain (up to C4) members of the series. 相似文献
46.
Wajiha Khan Muhammad A. Abbasi Aziz-ur Rehman Sabahat Z. Siddiqui Majid Nazir Syed A. Ali Shah Hussain Raza Mubashir Hassan Muhammad Shahid Sung Y. Seo 《Journal of heterocyclic chemistry》2020,57(7):2955-2968
In the current paper, through a convergent multi-step approach, a library of novel indole-phenyltriazole hybrids containing an amide moiety ( 9a-k) was synthesized. The structural verification of all synthesized molecules was accomplished by CHN and spectral analyses data. These synthesized bi-heterocyclic derivatives ( 9a-k ) were evaluated for their anti-ulcer potential by inhibitory action against Jack bean urease enzyme and subsequently their structure-activity relationship was perceived. Moreover, these compounds were inspected for cytotoxic profile by hemolytic activity and it was professed that nearly all the synthesized compounds showed low cytotoxicity. In addition, free radical scavenging activity and kinetic analysis were also carried out for these compounds to understand their mode of inhibition. So, it was summated that these derivatives might lead to further research gateways for obtaining better and safe anti-ulcer agents. 相似文献
47.
Nazir M Saleem M Riaz N Hafeez M Sultan M Jabbar A Ali MS 《Natural product communications》2011,6(11):1651-1652
Two new rotenoids, boerharotenoids A (1) and B (2), and four known compounds, boeravinone (3), 5,7,3'-trihydroxycoumaronochromone (4), boeravinone F (5), and eupalitin-3-O-beta-D-galactopyranoside (6), have been isolated from Boerhavia repens and their structures established by spectroscopic (1D and 2D NMR) and mass spectrometric comparison with literature values. 相似文献
48.
Mojtaba Shamsipur Nazir Fattahi Meghdad Pirsaheb Kiomars Sharafi 《Journal of separation science》2012,35(20):2718-2724
Dispersive liquid–liquid microextraction coupled with high‐performance liquid chromatography‐ultraviolet detection as a fast and inexpensive technique was applied to the simultaneous extraction and determination of traces of three common herbicides, 2,4‐D, alachlor and atrazine, in aqueous samples. The critical experimental parameters, including type of the extraction and disperser solvents as well as their volumes, sample pH, salt addition, extraction time and centrifuging time, and speed were investigated and optimized. Under the optimum conditions, the calibration graphs found to be linear in the range of 0.3–200 μg/L with limits of detection in the range of 0.05–0.1 μg/L. The relative standard deviations were in the range of 4.5–6.2% (n = 7). The relative recoveries of well, tap, and river water samples which have been spiked with different levels of herbicides were 92.0–107.0, 82.0–104.0, and 82.0–86.0%, respectively. 相似文献
49.
Nekrasov-Okounkov identity gives a product representation of the sum over partitions of a certain function of partition hook length. In this paper, we give several generalizations of the Nekrasov-Okounkov identity using the cyclic symmetry of the topological vertex. 相似文献
50.
A. Shaukat Y. Saeed S. Nazir N. Ikram M. Tanveer 《Physica B: Condensed Matter》2009,404(21):3964-3972
Full-potential linearized augmented plane wave method (FP-LAPW) within density functional theory has been used to calculate structural, electronic and optical properties of Ca1−xSrxS, an alkali earth chalcogenide, with varying compositional parameter x in the range 0<x<1. Whereas the structural properties are discussed in terms of charge transfer between the two cations, calculated electronic band structure and density of states have been analyzed in terms of contribution from the S p, Ca d and Sr d states. Furthermore, we have calculated some optical properties such as real and imaginary parts of dielectric constant, ε(ω), and the calculated results have been discussed in comparison with the existing experimental data and other theoretical calculations. 相似文献