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Abstract An efficient, atom-economic, one-pot protocol has been developed for the synthesis of highly functionalized dihydropyridines via four-component reactions of aromatic aldehydes, arylamines, malononitrile, and dimethylacetylenedicarboxylate in the presence of sodium hydroxide in ethanol. This domino reaction proceeded smoothly in good to excellent yields and offered several advantages, including short reaction time, simple experimental procedure, and applicability to a broad range of substrates. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献
113.
AC Conduction and Time–Temperature Superposition Scaling in a Reduced Graphene Oxide–Zinc Sulfide Nanocomposite
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Koushik Chakraborty Poulomi Das Sankalpita Chakrabarty Dr. Tanusri Pal Dr. Surajit Ghosh 《Chemphyschem》2016,17(10):1518-1523
We report, herein, the results of an in depth study and concomitant analysis of the AC conduction [σ′(ω): f=20 Hz to 2 MHz] mechanism in a reduced graphene oxide–zinc sulfide (RGO–ZnS) composite. The magnitude of the real part of the complex impedance decreases with increase in both frequency and temperature, whereas the imaginary part shows an asymptotic maximum that shifts to higher frequencies with increasing temperature. On the other hand, the conductivity isotherm reveals a frequency‐independent conductivity at lower frequencies subsequent to a dispersive conductivity at higher frequencies, which follows a power law [σ′(ω)∝ωs] within a temperature range of 297 to 393 K. Temperature‐independent frequency exponent ′s′ indicates the occurrence of phonon‐assisted simple quantum tunnelling of electrons between the defects present in RGO. Finally, this sample follows the “time–temperature superposition principle”, as confirmed from the universal scaling of conductivity isotherms. These outcomes not only pave the way for increasing our elemental understanding of the transport mechanism in the RGO system, but will also motivate the investigation of the transport mechanism in other order–disorder systems. 相似文献
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An analysis is made using a four-dimensional mathematical model where there is a constant rate of flow of input nutrient. An organism is introduced in the model which is growing by taking in that nutrient. Two other predators on that organism are also introduced. The predators at the second and third trophic levels belong to the same species, though of different age groups. The predator at the third trophic level exhibits a distinct cannibalistic attitude to the predator of the second trophic level. Our analysis leads to different thresholds in terms of the model parameters acting as conditions under which the species associated with the system cannot thrive even in the absence of competition. Local stability of the system is obtained when one or more of the predators go extinct. Under appropriate circumstances a positive rest point of the system is obtained. Computer simulations have been carried out to illustrate different analytical results. 相似文献
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Jitendra Pal Singh Gagan Dixit R.C. Srivastava Hemaunt Kumar H.M. Agrawal Ravi Kumar 《Journal of magnetism and magnetic materials》2012
In the present work zinc ferrite nanoparticles of different crystallite size were irradiated with 200 MeV Ag15+ ion beam. The structural and magnetic characterization performed for these samples indicate the presence of size dependent irradiation induced changes in the nanoparticles. The superparamgnetic nanoparticles do not alter their behavior after irradiation; however paramagnetic samples exhibit weak ferrimagnetism in the irradiated specimen. Results obtained from these measurements are in agreement with results obtained from the electron paramagnetic resonance spectroscopy. 相似文献
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Dark currents n+/ν/p+ Hg0.69Cd0.31Te mid wave infrared photodiodes were measured at room temperature. The diodes exhibited negative differential resistance at room-temperature, but with increasing leakage currents as a function of reverse bias. The current–voltage characteristics were simulated and fitted by incorporating trap assisted tunneling via traps and Shockley–Read–Hall generation recombination process due to dislocations in the carrier transport equations. The thermal suppression of carriers was simulated by taking energy level of trap (Et), trap density (Nt) and the doping concentrations of n+ and ν regions as fitting parameters. Values of Et and Nt were 0.78Eg and ~6–9 × 1014 cm?3 respectively for most of the diodes. Variable temperature current voltage measurements on variable area diode array (VADA) structures confirmed the fact that variation in zero bias resistance area product (R0A) is related to g–r processes originating from variation in concentration and kind of defects that intersect a junction area. 相似文献
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Palá-Paúl J Pérez-Alonso MJ Velasco-Negueruela A Sanz J 《Journal of chromatography. A》2002,947(2):327-331
The essential oil of Ageratina adenophora Spreng., growing in the Canary Islands was analyzed by GC-MS. A total of 78 volatile compounds was identified and p-cymene (11.6%) was the major component in the oil. The sesquiterpene fraction (44.3%) was higher than the monoterpene one (32.1%). 相似文献