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31.
Nonactivated aziridine with an electron-donating group at the ring nitrogen should be activated to an aziridinium ion prior to being converted to cyclic and acyclic nitrogen-containing molecules. This review describes ways to generate aziridinium ions and their utilization for synthetic purposes. Specifically, the intra- and intermolecular formation of aziridinium ions with proper electrophiles are classified, and their regio- and stereoselective transformations with nucleophiles are described on the basis of recent developments. 相似文献
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Ranjith R. Tirunagari 《Combustion Theory and Modelling》2016,20(5):834-865
We investigated the behaviour of the composition probability density function (PDF) model equations used in a large-eddy simulation (LES) of turbulent combustion in the direct numerical simulation (DNS) limit; that is, in the limit of the LES resolution length scale Δ (and the numerical mesh spacing h) being small compared to the smallest flow length scale, so that the resolution is sufficient to perform a DNS. The correct behaviour of a PDF model in the DNS limit is that the resolved composition fields satisfy the DNS equations, and there are no residual fluctuations (i.e. the PDF is everywhere a delta function). In the DNS limit, the treatment of molecular diffusion in the PDF equations is crucial, and both the ‘random-walk’ and ‘mean-drift’ models for molecular diffusion are investigated. Two test cases are considered, both of premixed laminar flames (of thickness δL). We examine the solutions of the model PDF equations for these test cases as functions of Δ/δL and h/δL. Each of the two PDF models has advantages and disadvantages. The mean-drift model behaves correctly in the DNS limit, but it is more difficult to implement and computationally more expensive. The random-walk model does not have the correct behaviour in the DNS limit in that it produces non-zero residual fluctuations. However, if the specified mixing rate Ω normalised by the reaction timescale τc is sufficiently large (Ωτc ? 1), then the residual fluctuations are less than 10% and the observed flame speed and thickness are close to their laminar values. Away from the DNS limit (i.e. h/δL ? 1), the observed flame thickness scales with the mesh spacing h, and the flame speed scales with Ωh. For this case it is possible to construct a non-general specification of the mixing rate Ω such that the flame speed matches the laminar flame speed. 相似文献
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Mahua Das R. Ranjith C. Bittencourt S. B. Krupanidhi J. J. Pireaux S. A. Shivashankar 《Applied Physics A: Materials Science & Processing》2009,95(2):523-536
We report the fabrication of assembled nanostructures from the pre-synthesized nanocrystals building blocks through optical
means of exciton formation and dissociation. We demonstrate that Li
x
CoO2 nanocrystals assemble to an acicular architecture, upon prolonged exposure to ultraviolet–visible radiation emitted from
a 125 W mercury vapor lamp, through intermediate excitation of excitons. The results obtained in the present study clearly
show how nanocrystals of various materials with band gaps appropriate for excitations of excitons at given optical wavelengths
can be assembled to unusual nanoarchitectures through illumination with incoherent light sources. The disappearance of exciton
bands due to Li
x
CoO2 phase in the optical spectrum of the irradiated film comprising acicular structure is consistent with the proposed mechanism
of exciton dissociation in the observed light-induced assembly process. The assembly process occurs through attractive Coulomb
interactions between charged dots created upon exciton dissociation. Our work presents a new type of nanocrystal assembly
process that is driven by light and exciton directed. 相似文献
35.
R. Ranjith 《Journal of Physics and Chemistry of Solids》2010,71(8):1140-1143
BiFeO3 has been studied extensively due to its room temperature multiferroic features and has been proven as a promising candidate for device applications. But BiFeO3 possesses some drawbacks like high leakage current and complicated magnetic ordering, giving rise to a canted antiferromagnetic behavior. Hence, a superlattice approach of BiFeO3 and BaTiO3 with a good lattice matching was fabricated and the room temperature ferroelectric and ferromagnetic properties were studied. The macroscopic and local probe studies reveal a ferroelectric nature at room temperature, and most importantly a weak ferromagnetic like behavior was observed. The ferromagnetic behavior is expected to arise due to the variation introduced in the spin modulation of single BiFeO3 layer due to the superstructure formation. 相似文献
36.
Ranjith R. Tirunagari Michael W. A. Pettit Andreas M. Kempf Stephen B. Pope 《Flow, Turbulence and Combustion》2017,98(1):131-153
A new methodology is developed to specify inflow boundary conditions for the velocity field at the nozzle exit planes in turbulent counterflow simulations. The turbulent counterflow configuration consists of two coaxial opposed nozzles which emit highly-turbulent streams of varying species compositions depending on the mode considered. The specification of velocity inflow boundary conditions at the nozzle exits in the counterflow configuration is non-trivial because of the unique turbulence field generated by the turbulence generating plates (TGPs) upstream of the nozzle exits. In the method presented here, a single large-eddy simulation (LES) is performed in a large domain that spans the region between the TGPs of the nozzles, and the time series of the velocity fields at the nozzle exit planes are recorded. To provide inflow boundary conditions at the nozzle exit planes for simulations under other conditions (e.g., different stream compositions, bulk velocity, TGP location), transformations are performed on the recorded time series: the mean and r.m.s. (root-mean-square) quantities of velocity, as well as the longitudinal integral length scale on the centerline, at the nozzle exits in simulations are matched to those observed in experiments, thereby matching the turbulent Reynolds number R e t . The method is assessed by implementing it in coupled large-eddy simulation/probability density function (LES/PDF) simulations on a small cylindrical domain between the nozzle exit planes for three different modes of the counterflow configuration: N 2 vs. N 2; N 2 vs. hot combustion products; and C H 4/N 2 vs. O 2. The inflow method is found to be successful as the first and second moments of velocity from the LES/PDF simulations agree well with the experimental data on the centerline for all three modes. This simple yet effective inflow strategy can be applied to eliminate the computational cost required to simulate the flow field upstream of the nozzle exits. It is also emphasized that, in addition to the predicted time series data, the availability of experimental data close to the nozzle exit planes plays a key role in the success of this method. 相似文献
37.
Kinetics of Lifetime Changes in Bimetallic Nanocatalysts Revealed by Quick X‐ray Absorption Spectroscopy
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Dr. Matthias Filez Dr. Hilde Poelman Dr. Evgeniy A. Redekop Dr. Vladimir V. Galvita Dr. Konstantinos Alexopoulos Dr. Maria Meledina Dr. Ranjith K. Ramachandran Dr. Jolien Dendooven Prof. Christophe Detavernier Prof. Gustaaf Van Tendeloo Dr. Olga V. Safonova Dr. Maarten Nachtegaal Prof. Bert M. Weckhuysen Prof. Guy B. Marin 《Angewandte Chemie (International ed. in English)》2018,57(38):12430-12434
38.
P. Mohan B. Ranjith G. Paruthimal Kalaignan 《Journal of Solid State Electrochemistry》2014,18(8):2183-2192
Spinel LiMn2O4 and Sm, La co-substituted LiSm x La0.2-x Mn1.80O4 (x?=?0.05, 0.10 and 0.15) cathode materials were synthesized by sol–gel method using aqueous solutions of metal nitrates and tartaric acid as chelating agent at 600 °C for 10 h. The structure and electrochemical properties of the synthesized materials were characterized by using thermogravimetric/differential thermal analysis, X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, charge/discharge and electrochemical impedance spectroscopy studies. XRD analysis indicated that all the prepared samples were mainly belong to cubic crystal form with Fd3m space group. LiSm0.10La0.10Mn1.80O4 exhibits capacity retention of 90 % and 82 % after 100 cycles at room temperature (30 °C) and at elevated temperature (50 °C) at a rate of 0.5-C, respectively, much higher than those of the pristine LiMn2O4 (74 % and 60 %). Among all the compositions, LiSm0.10La0.10Mn1.80O4 cathode has improved the structural stability, high-capacity retention, better elevated temperature performance and excellent electrochemical performances of the rechargeable lithium-ion batteries. 相似文献
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1,3-Dipolar cycloaddition of C-aryl-N-phenylnitrones to 3,5-bis-(arylidene)-1-methylpiperidin-4-ones affords novel mono- and bis-spiroisoxazolidines in moderate yields. In general, this reaction predominantly yields mono-spiroisoxazolidine, wherein the oxygen of the nitrone is linked to the β-carbon of the benzylidene moiety, while 3,5-bis-(2-chloro- and 3-nitro-benzylidene)-1-methylpiperidin-4-ones afford predominantly bis-spiroisoxazolidines. The cycloaddition of mono-spiroisoxazolidines occurs with facial diastereoselectivity to furnish bis-spiroisoxazolidines. The nitrogen in the heterocyclic ring of the 3,5-bis-(arylidene)-1-methylpiperidin-4-ones facilitates the cycloaddition through transannular (NCO) and/or homoconjugative (NCC) interactions. 相似文献