13,108 research outputs found
Chemoselective, Isomerization-Free Synthesis of N-Acylketimines from N?H Imines
No full textN-Acylketimines were synthesized through a ruthenium-catalyzed generation of N?H ketimines from secondary azides and subsequent acylation with mixed anhydrides under mild conditions. The synthetic scope was broad to give N-acylimines having various functional groups, including those with aliphatic groups that are prone to tautomerization to the corresponding enamides. In addition, various acyl moieties were accommodated. The synthetic utility of this chemoselective imine generation was illustrated by a highly diastereoselective nucleophilic addition of a Grignard reagent to a cyclic N-acylimine. (Figure presented.). ? 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim111Nsciescopu
Author's reply: Comments on delay-dependent robust H-infinity control for uncertain systems with a state-delay
No full textIn the above-mentioned comment, the authors point out a technical problem with the paper [Lee, Y. S., Moon, Y. S., Kwon, W. H., & Park, P. G. (2004). Delay-dependent robust H-infinity control for uncertain systems with a state-delay. Automatica, 40(1), 65-72]. We show this technical problem can be solved by changing the proof of Theorem 3.1. (C) 2007 Elsevier Ltd. All rights reserved.X115sciescopu
DFT and TB study of the geometry of hydrogen adsorbed on graphynes
No full textUsing density-functional calculations (DFT) and a tight-binding model, we investigate the origin of distinct favorable geometries which depend on the type of graphyne used. The change in the H geometry is described in terms of the tuning of the hopping between sp(2)-bonded C atoms and sp-bonded C atoms hybridized with the H atoms. We find that the different preferred geometry for each type of graphyne is associated with the electronic effects due to different symmetries rather than a steric effect minimizing the repulsive interaction between the H atoms. The band gaps are significantly tuned as the hopping varies, except in alpha-graphyne, in agreement with the result of our previous DFT study (Koo J et al 2013 J. Phys. Chem. C 117 11960). Our model can be used to describe the geometry and electronic properties of hydrogenated graphynes
Vibration and Aeroelastic Characteristics of advanced Aircrafts in Transonic and Supersonic Region
No full textThis work was supported through funding from the
Korea Ministry of Science and Technology and Korea
Aerospace Industry (KAI). The authors acknowledge the support as the National Research Laboratory
Program and KAI
Computational Analysis of Fluid/Structure Interaction for Flight Vehicle Structures
No full textThis research was supported by the Korea Aerospace Industries, Ltd., the National Research Laboratory Program from the Korea Ministry of Science and Technology, Agency for Defense Development, and Korea Aerospace Research Institute. The authors thank for their supports
Initial-boundary value problems for conservation laws with source terms and the Degasperis-Procesi equation
No full textWe consider conservation laws with source terms in a bounded domain
with Dirichlet boundary conditions. We first prove the existence of
a strong trace at the boundary in order to provide a simple
formulation of the entropy boundary condition. Equipped with this
formulation, we go on to establish the well-posedness of entropy
solutions to the initial-boundary value problem. The proof utilizes
the kinetic formulation and the averaging lemma. Finally, we make
use of these results to demonstrate the well-posedness in a class of
discontinuous solutions to the initial-boundary value problem for
the Degasperis-Procesi shallow water equation, which is a third
order nonlinear dispersive equation that can be rewritten in the
form of a nonlinear conservation law with a nonlocal source term
Rigorous analysis on a U-shaped index fiber for generating cylindrical vector beams in an all-fiber format
No full textWe propose a novel method to generate cylindrical vector beams (CVBs) which can be applied to conventional fiber-laser system configuration. We focus on the relationship between the laser pump power threshold and the power confinement in the high index region of a fiber, and suggest a novel type of index distribution for the desirable operation. We verify our idea by computer simulations and show that the laser threshold of the CV mode can be reduced down below that of the fundamental mode by 3%. The suggested method will be useful for generating cylindrical vector beams in an all-fiber format
An improved bridgeless PFC boost-doubler rectifier with high-efficiency
No full textAn improved bridgeless boost-doubler rectifier is proposed for high-efficiency power-factor correction (PFC). In the proposed rectifier, the conduction losses are reduced by essentially eliminating the full-bridge diode rectifier. A bidirectional switch is used for the power switches, simplifying the overall power circuit structure. The reverse-recovery problems of the rectifying diodes are also reduced by using a simple passive snubber circuit. Zero-current turn-off of the rectifying diodes can be achieved, which removes the reverse-recovery losses of the rectifying diodes in the continuous conduction mode operation. The proposed rectifier provides high power-factor and improves power efficiency for low line voltage applications. The performance of the proposed rectifier is evaluated on an 800W (400V/2A) experimental prototype at 110V rms line voltage.1126sciescopu
Multi-mode MPPT control for improved efficiency
No full textA multi-mode maximum power point tracking (MPPT) control for wide photovoltaic (PV) voltage range and improved efficiency is proposed in this paper. This MPPT control is fitted for the two-stage PV power system which is composed of a step-up converter and a step-down inverter. In the low PV voltage, the step-up converter performs the MPPT. On the other hand, in the high PV voltage, the inverter performs the MPPT control. The proposed MPPT control makes the dc link voltage low as soon as possible and improves the power efficiency under the wide PV voltage range.113sciescopu
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