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排序方式: 共有193条查询结果,搜索用时 15 毫秒
51.
Retinoids are a class of synthetic and natural compounds structurally related to retinoic acid. In a search for discovery of a new class of heterocycle‐bridged and conformationally constrained retinoids, here we report the synthesis of 4‐(7,8,9,10‐tetrahydro‐7,7,10,10‐tetramethyl‐4H‐benzo[6,7]chromeno[4,3‐d]thiazole‐2‐yl)benzoic acid ( 10 ) starting from 5,6,7,8‐tetrahydro‐5,5,8,8‐tetramethylnaphthalen‐2‐ol ( 13 ). Several approaches was attempted to obtain target compound 10 . Structure elucidation of synthesized compounds has been made on the basis of elemental analysis and spectral data (1H NMR, IR and MS). 相似文献
52.
Ali Khalafi‐Nezhad Mohammad Navid Soltani Rad A. A. Moosavi‐Movahedi M. Kosari 《Helvetica chimica acta》2007,90(4):730-737
The syntheses of the novel acyclic nucleosides 5a – 5m , carrying different N‐[(benzyloxy)(aryl)methyl] substituents, are described (Scheme). These compounds could be prepared in medium‐to‐good yields by either direct or silyl‐assisted coupling of the electrophiles 6 with either purine or pyrimidine nucleobases, or with different imidazole derivatives. The reactivity of the positively charged electrophilic intermediates derived from 6 upon Cl? abstraction was rationalized by ab initio HF/6‐311G quantum‐mechanic calculations. The positive charge was found to be dispersed differently, depending on the electronic properties of the aryl substituents. 相似文献
53.
Natalija van Well Sitaram Ramakrishnan Ketty Beauvois Navid Qureshi Eric Ressouche Markos Skoulatos Robert Georgii Oksana Zaharko Sander van Smaalen 《Annalen der Physik》2020,532(7):2000147
The triangular antiferromagnetic Cs2CuCl4-xBrx mixed system is studied by neutron single-crystal diffraction in magnetic field. It shows a rich magnetic phase diagram consisting of four regimes depending on the Br concentration and is characterized by different exchange coupling mechanisms. For the investigated compositions from regime I (0 < x ≤ 1.5), a critical magnetic field Bc is found for a Br concentration x = 0.8 at Bc = 8.10(1) T and for x = 1.1 at Bc = 7.73(1) T and from regime IV (3.2 < x < 4) for x = 3.3 at Bc = 0.99(3) T. For magnetic fields larger than the respective Bc, magnetic superlattice reflections of these compounds are not found. The incommensurate magnetic wave vector q = (0, 0.470, 0) appears below the ordering temperature TN = 0.51(1) K for Cs2CuCl3.2Br0.8, and q = (0, 0.418, 0) below TN = 1.00(6) K for Cs2CuCl0.3Br3.7. Neutron diffraction experiments at around 60 mK for x = 3.7 in a magnetic field show the critical magnetic field at Bc = 7.94(16) T and the formation of the second magnetic phase at around 8.5 T depending on the temperature. Inelastic neutron scattering experiments for the compound from regime III (2 < x ≤ 3.2) with x = 2.2 show dynamical correlations at a temperature around 50 mK giving evidence for a spin liquid phase. 相似文献
54.
Leung C Lu Z Esfandiari N Casper RF Sun Y 《IEEE transactions on bio-medical engineering》2011,58(4):935-942
Sperm immobilization is a requisite step in intracytoplasmic sperm injection (ICSI). Conventionally, sperm immobilization is performed manually, which entails long training hours and stringent skills. Manual sperm immobilization also has the limitation of low success rates and poor reproducibility due to human fatigue and skill variations across operators. This paper presents a system for fully automated sperm immobilization to eliminate limitations in manual operation. Integrating computer vision and motion control algorithms, the automated system is able to visually track a sperm and control a micropipette to immobilize the sperm. A robust sperm tail tracking algorithm is developed to locate the optimal position on the sperm tail for sperm immobilization. The system demonstrates: 1) an average sperm tail tracking error of 0.95 μm; 2) a sperm tail visual tracking success rate of 96%; 3) a sperm immobilization success rate of 88.2% (based on 1000 trials); and 4) a speed of 6-7 s per successful immobilization. 相似文献
55.
Hamidreza Ali-Asgari Dehaghi Saeedeh Mazinani Davood Zaarei Mohammadreza Kalaee Hamed Jabari Navid Sedaghat 《Journal of Thermal Analysis and Calorimetry》2013,114(1):185-194
Systematic study about the effect of acrylonitrile–butadiene rubber (NBR) concentration on the fracture toughness and thermal behavior of epoxy resin is conducted in this study. NBR is solved in an aromatic hydrocarbon solvent and is added to epoxy resin. We used diethylene-teriamin as the curing agent for epoxy resin. Tensile test results, performed followed by molding procedure, show that the toughness is improved owing to the increase of rubber content. Scanning electron microscopy (SEM) and atomic force microscopy besides thermogravimetric analysis (TG) are used to investigate the epoxy/rubber interface and chemical decomposition of the resultant mixture. The thermal behavior of cured epoxy resin was analyzed via TG instrument at different heating rates. Thermogravimetry curves showed that the thermal decomposition of epoxy system was occurred in only one stage regardless of the rubber content. The apparent activation energies of the rubber/epoxy systems containing 0, 5, and 10 phr of rubber were determined by Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Friedman methods. The results prove that the thermal stability of epoxy resin was decreased with enhancing the rubber content. However, the trend of changing activation energy versus conversions is totally different followed by adding the elastomer to the system compared to neat epoxy resin. Moreover, the results obtained via our proposed facile solution blending method are compared to those of resins modified with nano-powdered elastomer. 相似文献
56.
Hamid R. Zare Zahra Ghanbari Navid Nasirizadeh Ali Benvidi 《Comptes Rendus Chimie》2013,16(3):287-295
In this study, ruthenium oxide nanoparticles were electrochemically deposited on the surface of a glassy carbon electrode (RuON-GCE). Electrochemical studies indicate that a modified electrode (RuON-GCE) plays the role of an excellent bifunctional electrocatalyst for the oxidation of adrenaline (AD) and uric acid (UA) in two different potentials. The charge transfer coefficient (α) and the heterogeneous charge transfer rate constant (k′) between the analytes and the electrodeposited nanoparticles were determined using cyclic voltammetry experiments. Through a different pulse voltammetric (DPV) method, the plot of the electrocatalytic current versus AD and UA concentrations emerged to be constituted of two linear segments with different sensitivities. Furthermore, the detection limits of AD and UA were estimated. In DPV, RuON-GCE could separate the oxidation peak potentials of AD, UA, and cysteine (Cys) present in the same solution though, at the bare GCE, the peak potentials were indistinguishable. Finally, the modified electrode activity was studied for the electrocatalytic determination of AD in an injection solution and UA in a human urine sample. The results were found satisfactory. 相似文献
57.
58.
Mohammad Navid Soltani Rad Ali Khalafi-Nezhad Mohammad Ali Faghihi Abolfath Parhami 《Tetrahedron》2008,64(8):1778-1785
A convenient and efficient one-pot N-alkylation of nucleobases from alcohols using N-(p-toluenesulfonyl)imidazole (TsIm) is described. In this method, treatment of alcohols with a mixture of purine or pyrimidine nucleobase, TsIm, K2CO3, and triethylamine in refluxing DMF regioselectively furnishes the corresponding N-alkyl nucleobases in good yields. This methodology is highly efficient for various structurally diverse primary alcohols. 相似文献
59.
Afzal Asif Yashawantha K. M. Aslfattahi Navid Saidur R. Abdul Razak R. K. Subbiah Ram 《Journal of Thermal Analysis and Calorimetry》2021,145(4):2129-2149
Journal of Thermal Analysis and Calorimetry - Back-propagation modeling of viscosity and shear stress of Ionic-MXene nanofluid is carried out in this work. The data for Ionic-MXene nanofluid of... 相似文献
60.
Rueping M Sugiono E Theissmann T Kuenkel A Köckritz A Pews-Davtyan A Nemati N Beller M 《Organic letters》2007,9(6):1065-1068
The enantioselective Br?nsted acid catalyzed addition of methyleneaminopyrrolidine to N-Boc imines has been achieved in the presence of chiral phosphoric acids derived from 3,3'-di(phenanthryl)-H8-BINOL. The corresponding aminohydrazones have been isolated in good yields with enantiomeric excesses up to 90%. [reaction: see text] 相似文献