State Academy of science

Pyongyang, South Korea

State Academy of science

Pyongyang, South Korea
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Kim K.-H.,State Academy of science | Choe S.-H.,State Academy of science
Applied Physics B: Lasers and Optics | Year: 2016

We propose diamond nanoparticle Raman laser operating in the spectral range of deep ultraviolet. High Raman gain and low cavity loss of diamond nanoparticles enable low-threshold Raman lasing. Based on the coupled-mode theory, we numerically study its lasing dynamics. For the diamond nanoparticle with a radius of about 130 nm, the lasing threshold energy is below 10 pJ for a pump spot size of 1 μm. © 2016, Springer-Verlag Berlin Heidelberg.

HONG H.,State Academy of science | WANG T.,Beijing Forestry University
Acta Mathematica Scientia | Year: 2017

Abstract For the general gas including ideal polytropic gas, we study the zero dissipation limit problem of the full 1-D compressible Navier-Stokes equations toward the superposition of contact discontinuity and two rarefaction waves. In the case of both smooth and Riemann initial data, we show that if the solutions to the corresponding Euler system consist of the composite wave of two rarefaction wave and contact discontinuity, then there exist solutions to Navier-Stokes equations which converge to the Riemman solutions away from the initial layer with a decay rate in any fixed time interval as the viscosity and the heat-conductivity coefficients tend to zero. The proof is based on scaling arguments, the construction of the approximate profiles and delicate energy estimates. Notice that we have no need to restrict the strengths of the contact discontinuity and rarefaction waves to be small. © 2017 Wuhan Institute of Physics and Mathematics

Hong H.,State Academy of science | Wang T.,Beijing Forestry University
Nonlinearity | Year: 2017

In this paper, we investigate the one-dimensional motion of compressible viscous and heat-conductive fluid on the half line R+= (0,+∞). The largetime behavior of the superposition of the transonic (or degenerate) boundary layer solution, 1-rarefaction wave, 2-viscous contact wave and 3-rarefaction wave is established for the inflow problem of full compressible Navier-Stokes system under a large initial perturbation for any adiabatic exponent γ > 1, provide the wave strength is suitable small. © 2017 IOP Publishing Ltd & London Mathematical Society Printed in the UK.

Ri M.-H.,State Academy of science
Annali dell'Universita di Ferrara | Year: 2017

In this paper we show that a Leray–Hopf weak solution u to 3D Navier–Stokes initial value problem is smooth if there is some (Formula presented.) such that (Formula presented.) is suitably smooth, where (Formula presented.). © 2017 Università degli Studi di Ferrara

Ri J.-H.,State Academy of science | Hong H.-S.,State Academy of science
Archive of Applied Mechanics | Year: 2017

Linear matching method has been widely used for the numerical analysis of limit and shakedown. It has been proved theoretically that linear matching method could offer the monotonically reducing sequence of upper bound. Nevertheless, it still remains open whether linear matching method can obtain the conversed and reliable lower bound or not. Thus, an elastic compensation method is used generally for the evaluation of lower bound, but limit analysis using linear matching method and elastic compensation method needs double iterative computations. Moreover, the convergence can be checked only after the computation is finished because linear matching method and elastic compensation method cannot be performed simultaneously. From this, we propose a simple method in order to improve the numerical solution of lower bound by linear matching method. The Young’s modulus varying spatially is determined in every iteration such that not only the stress state lies on the yielding surface but also the strain state does not exceed a certain value of reference strain, leading to the evaluation of lower bound based on the strain state but not the stress one. The proposed method can improve the numerical solution of lower bound by linear matching method without any affection on the upper bound. ANSYS UserMat is used for implementing the current method. The limit analysis is performed like the general elastic finite element analysis in ANSYS. Some numerical examples are considered in order to confirm the effectiveness of proposed approach. Numerical examples showed the validity and improvement of numerical accuracy of our approach. It should be mentioned that our approach can predict the lower bound and upper one simultaneously within the framework of only linear matching method without using the elastic compensation method. © 2017 Springer-Verlag Berlin Heidelberg

Kim K.-H.,State Academy of science | Yurkin M.A.,Novosibirsk State University
Optics Express | Year: 2015

We develop the time-domain discrete dipole approximation (DDA), describing the temporal evolution of electric field in plasmonic nanostructures. The main equation is obtained by taking the inverse Fourier transform of the Taylor expansion of the frequency-domain DDA in terms of frequency deviation from the central frequency. Thus we assume that incident wavefronts of different frequencies accumulate relatively small phase difference when passing the particle. This assumption is always valid for nanoparticles much smaller than the wavelength. Being the time-domain method, the proposed approach also requires an analytic frequency dependence of electric permittivity, e.g. The Drude model. We present numerical results of application of the time-domain DDA to silver nanosphere, rod, and disk, which agree well with that obtained with its frequency-domain counterpart and the finite-difference time-domain method. Moreover, the time-domain DDA is the fastest of the three methods for incident pulses of several-femtoseconds width. Thus, it can effectively be applied for modeling the temporal responses of plasmonic nanostructures. © 2015 Optical Society of America.

Kim K.-H.,Max Born Institute For Nichtlineare Optik Und Kurzzeitspektroskopie | Kim K.-H.,State Academy of science | Griebner U.,Max Born Institute For Nichtlineare Optik Und Kurzzeitspektroskopie | Herrmann J.,Max Born Institute For Nichtlineare Optik Und Kurzzeitspektroskopie
Optics Express | Year: 2012

We theoretically study femtosecond pulse generation by passive mode-locking of semiconductor disk lasers operating in the blue spectral range using metal nanocomposites as slow saturable absorbers. By using the relation for the nonlinear dielectric response of a layer of silica glass doped with spherical silver nanoparticles and the master equation for modelocking we investigate the dynamics of pulse formation and the achievable pulse parameters and predict the generation of pulses as short as 50 fs at 420 nm in such lasers. ©2012 Optical Society of America.

Kim K.-H.,State Academy of science | Choe S.-H.,State Academy of science
Plasmonics | Year: 2016

We present a theoretical approach for calculating the ultrafast nonlinear optical responses of dielectric composite materials containing metal nanoparticles with different sizes and shapes, taking silica glasses doped with silver nanospheres and nanorods. The approach is based on the model for nonlinear responses of metal nanoparticles combined with time-domain discrete dipole approximation for total field and the effective medium approximation. We numerically study the dependencies of the nonlinear transmittance of those composite films on several parameters such as sizes and aspect ratios of metal nanoparticles, pulse fluences and wavelengths of pump. © 2016 Springer Science+Business Media New York

We develop a theoretical model for the nondegenerate nonlinear optical susceptibility of dielectric composite materials containing metal nanoparticles. The model is based on the theory of transient nonlinear response of metal nanoparticles in combination with the effective medium approximation and the discrete dipole approximation. Its validity is confirmed by comparison with a preceding experimental result. Through numerical simulations, we demonstrate that for off-plasmon-resonant pumping the imaginary part of nondegenerate third-order nonlinear susceptibility becomes negative over a wide spectral range of signal. We additionally show the saturation effect of nondegenerate susceptibility depending on pump intensity and wavelength. © 2013 Astro Ltd.

Kim K.-H.,State Academy of science | Kim S.-H.,State Academy of science | Bae M.-C.,State Academy of science
Applied Optics | Year: 2015

We demonstrate that pronounced Fano resonance can be obtained by dipole-hexapole coupling in a χ-shaped plasmonic nanostructure. The confined local field in the vicinity of dipole-resonant nanorods excites and coherently couples to the hexapolar mode in the rod perpendicular to the polarization direction of the incident wave, leading to strong Fano resonance. By using the discrete dipole approximation, we numerically investigate the behavior of Fano resonance by dipole-hexapole coupling in the plasmonic nanostructure. We obtain the parameters relevant to Fano resonance by fitting the coupled oscillator model equation to the calculated extinction data and investigate their dependencies on the structural parameters. The results demonstrate the possibility of obtaining high-contrast Fano resonance with narrow features by using this plasmonic nanostructure, which has potential applications for highly sensitive biological sensing, low-loss metamaterials, and others. © 2015 Optical Society of America.

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