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Song-Jin Im

Publications and source records attributed to Song-Jin Im.

At least 37 records · Page 2Linked to original sources
arXiv2015

Propagation of Acoustical Wave in Finite Cylindrical Solid Bar surrounded by Semi-Infinite Porous Media saturated with Fluid

We established the propagation equation of acoustical wave in media with the solid/porous media cylindrical boundary and obtained the analytic solution. We suggested the boundary condition on solid-porous media cylindrical boundary. Based on that, we introduced the dispersion equation, and constructed the algorithm to perform numerical calculation and analysis of dispersion equation.

cond-mat.mtrl-sci↗
arXiv2015

Infrared absorption property of silicon carbide-silica nanocables synthesized by ethanol pyrolysis

A controllable synthesis method for SiC-SiO$_{2}$ nanocables has been proposed. The diameter of SiC core and thickness of SiO$_{2}$ shell were changed by adjusting the flow ratio between Ar dilution gas and ethanol precursor. With increasing the flow, the enhancement of 1137cm$^{-1}$ peak was observed from fourier transform infrared spectroscopy (FTIR) spectra. This peak is considered to be originated from a highly disordered surface structure of SiO$_{2}$ shell which was enhanced with increasing the flow. The FTIR spectra show the 910cm$^{-1}$ peak which is attributed to surface phonon resonance in the nanostructure of SiC exited by p-polarized field component.

cond-mat.mtrl-sci↗
arXiv2015

Study of the Composition and Spectral Characteristics of a HDG-Prism Disperse System (GRISM) by Refractive Index Phase Matching

The composition and characteristics of a GRISM gained by refractive index matching between a refractive index modulation type HDG and a prism is investigated, the HDG being built by processing silver halide emulsion with halide vapor. The GRISM has been stable under external influences like humidity or ultraviolet light exposure. The mercury atomic spectrum obtained by a GRISM based on a HDG with a spatial frequency of 600mm-1 shows yellow dual lines with the wavelength difference of 2.1nm sufficiently separated.

physics.optics↗
arXiv2015

Investigation of the Cubic Boron Nitride Nucleation under the High Pressure and the High Temperature

In this paper we have theoretically found the activation energy ($420.38kJ/mol$) for the transformation from hBN to cBN in the microscopic viewpoint. We have introduced an analytical formula representing the dependence of nucleus formation time on the activation energy, synthesis pressure and temperature. We have theoretically determined the boundary line of cBN nucleus formation region in the $P-T$ phase diagram on the basis of the diffusion mechanism of cBN nucleus formation. We have found that the cBN crystal nucleus formation time is less than $300ms$ by comparing of the theory and experiment.

cond-mat.mtrl-sci↗
arXiv2015

Intrinsic nonlinear response of surface plasmon polaritons

We offer a model to describe the intrinsic nonlinear response of surface plasmon polaritons (SPPs). Relation of the complex nonlinear coefficient of SPPs to the third-order nonlinear susceptibility of the metal is provided. As reported in a recent study, gold is highly lossy and simultaneously highly nonlinear due to interband absorption and interband thermo-modulation at a wavelength shorter than 700 nm. The effect of the high loss of the metal on the SPP nonlinear propagation is taken into account in our model. With the model we show difference in sign of real and imaginary parts between the nonlinear propagation coefficient and the nonlinear susceptibility of component material for the first time to our knowledge. Our model could have practical importance in studying plasmonic devices utilizing the nonlinear phase modulation and the nonlinear absorption of SPPs. For example, it allows one to extract the complex nonlinear susceptibility of gold through a measurement of SPP nonlinear propagation at the visible range.

physics.optics↗
arXiv2014

$Ab$ $initio$ study of the adsorption and dissociation of nitrogen molecule on Fe(111) surface

The adsorption and dissociation of nitrogen molecule on Fe(111) surface is studied by density functional theory calculations. The simulation results show that the molecule needs to acquire parallel orientation with respect to the surface for the adsorption and dissociation. In addition, Fe(111) surface is more active in dissociating N2 than Fe(100) surface due to its morphology. The interaction between antibonding molecular orbitals of N2 and partially filled $3d$ orbitals of Fe atoms on the surface may be the key to the molecular dissociation of N2. To break down the triple bond of N2, the electron density on the surface needs to be partially transferred to the molecule to fill the antibonding molecular orbitals of the nitrogen molecule. The present result may provide some insights on the dissociation mechanism of molecules over transition metal surfaces.

cond-mat.mtrl-sci↗
arXiv2014

First-principles study on electron field emission from nanostructures

A first-principles approach is introduced to calculate electron field emission characteristics of nanostructures, based on the nonequilibrium Green function technique combined with the density functional theory. The method employs atomic-like basis orbitals with large confinement radii and lithium anode to describe the electron density in the vacuum between the nanostructure tip and the anode, so takes the presence of emitted current into account. The simulation results on a capped single-walled carbon nanotube reproduce the experimental trend closely, in particular, the current saturation and the deviation from the Fowler-Nordheim behavior.

cond-mat.mes-hall↗
arXiv2014

Study on acoustic radiation impedance at aperture of a waveguide with circular cross section taking account of interaction between different guided modes

In this paper we simulated self- and mutual- acoustic impedances of guided modes at the aperture and estimated accuracy of the piston radiation approximation. We used the Rayleigh integral to simulate the interactions between different guided modes at the aperture, with low time-consuming. This kind of guided-wave technique can be utilized to solve problems in diverse fields of wave science such as acoustics, electromagnetism and optics. For acoustic waves emitted through a horn or a waveguide with an aperture much smaller than the wavelength, there are only plane wave modes in the waveguide and the aperture of horn can therefore be considered as a piston radiator. However if an acoustic wave with high frequency such as ultrasonic wave is radiated, there can exist several guided modes in the duct. For arbitrary shape and size of waveguide, interactions between different modes must be taken into account to evaluate sound field in the duct and total acoustic power from its aperture. In this paper we simulated self- and mutual- acoustic impedances of guided modes at the aperture and estimated accuracy of the piston radiation approximation. We used the Rayleigh integral to simulate the interactions between different guided modes at the aperture, with low time-consuming. This kind of guided-wave technique can be utilized to solve problems in diverse fields of wave science such as acoustics, electromagnetism and optics.

physics.class-ph↗
arXiv2014

Theoretical prediction of the source-detector separation distance suited to the application of the spatially resolved spectroscopy from the near-infrared attenuation data cube of tissues

The modified Beer-Lambert law (MBL) and the spatially resolved spectroscopy are used to measure the tissue oxidation in muscles and brains by the continuous wave near-infrared spectroscopy. The spatially resolved spectroscopy predicts the change in the concentration of the absorber by measuring the slope of attenuation data according to the separation and calculating the absorption coefficients of tissue on the basis of the slop in attenuation at the separation distance satisfying the linearity of this slop. This study analyzed the appropriate source-detector separation distance by using the diffuse approximation resolution for photon migration when predicting the absorption coefficient by the spatially resolved spectroscopy on the basis of the reflective image of the tissue. We imagine the 3 dimensional attenuation image with the absorption coefficient, reduced scattering coefficient and separation distance as its axes and obtained the attenuation data cube by calculating the attenuation on a certain interval of coordinate on the basis of the diffuse approximation expression. We predicted the separation distance appropriate for the application of the spatially resolved spectroscopy by calculating and analyzing the first derivatives and second derivatives of attenuation with respect to the coordinates and also doing the differential pathlength factors and first derivatives of the attenuation with respect to the absorption coefficient from the attenuation data cube. When analyzing the hemoglobin derivatives in tissues, the appropriate separation distances are 3-5cm and the value of its corresponding differential pathlength factors are from 3.5 to 5. These data agree with the preceding experimental data.

physics.optics↗
arXiv2014

Study on the Vibration Displacement Distribution of a Circular Ultrasonic Motor Stator

In this paper is presented a theoretical consideration on the stator's displacement distribution, which is one of the most important problems in defining the structure of the circular ultrasonic motor stator. The results are compared with results obtained utilizing holographic interferometer, laser vibrometer and a FEM (finite element method) simulation. They are in a good agreement with each other.

physics.optics↗
arXiv2014

Study on the Electronic Structure and Stability of Some OPE(oligo-phenylene-ethynylene derivative)-RE3N@C80 Dyads by PM7

In this paper, we investigated the electronic structure and stability of some mesomorphic OPE-RE3N@C80 dyads from the oligo-phenylene-ethynylene derivatives (OPE) and the trimetallic nitride template endohedral fullerenes (TNT-EMFs) - RE3N@C80 (RE=Sc,Y,La) by using PM7, the updated version of the semi-empirical Hartree-Fock method. In OPE-RE3N@C80, the fullerene cages were modified to have the opened cage (fulleroid) structure by addition of OPE on the [6,6] position of the fullerene cages. There was no considerable charge transfer between OPE and fullerene cage, but the fullerene cages had the remarkable minus charges mainly due to the electron transfer from RE3N to the cage. The calculated electronic spectra showed that light absorption bands of OPE-C80 were more red-shifted than that of OPE-RE3N@C80 and all of OPE-RE3N@C80 seem to have a couple of Vis-NIR absorption peaks.

physics.chem-ph↗
arXiv2014

Plasmonic amplification and suppression in nanowaveguide coupled to gain-assisted high-quality plasmon resonances

We theoretically study transmission in nanowaveguide coupled to high-quality plasmon resonances for which the metal loss is overcompensated by gain. The on-resonance transmission can vary widely from lower than --20dB to higher than 20dB for a range of gain coefficient. A reversible transition between the high-quality amplification and the suppression can be induced by a quite small change of gain coefficient for a moderately increased distance between the waveguide and the resonator. It is expected that in practice a small change of gain coefficient can be made by flexibly controlling pumping rate or utilizing nonlinear gain. Additionally, based on the frequency-dependant model for gain-transition susceptibility, it is shown that the wide variation of the on-resonance transmission can also be observed for defferent detuning of the gain-transition line-center. Such a widely controllable on-resonance transmission is promising for applications such as well-controlled lumped amplification of surface plasmon-polariton as well as plasmonic switching.

physics.optics↗
arXiv2014

All-optical control in metal nanocomposites due to a reversible transition between the local-field-enhancement and a local-field-depression upon irradiation by ultrashort control-pulses of light

We theoretically study on non-perturbative effective nonlinear responses of metal nanocomposites based on the intrinsic third-order nonlinear response of metal nanoparticles. The large intrinsic third-order nonlinear susceptibility of metal nanoparticles and an irradiation by ultrashort control pulse of light with a sufficiently high peak intensity and moderate fluence can induce a local-field-depression and a saturated plasmon-bleaching in metal nanoparticles. If the control pulse is on, the metal nanocomposites can behave like a dielectric due to the local-field-depression, while if the control pulse is off, the metal nanocomposites can behave like a metal showing a high absorption due to the local-field-enhancement at the plasmon-resonance. This phenomenon can be applied to an ultrafast and remote control of light in metal nanocomposites.

physics.optics↗
arXiv2014

Micro-joule sub-10-fs VUV pulse generation by MW pump pulse using highly efficient chirped-four-wave mixing in hollow-core photonic crystal fibers

We theoretically study chirped four-wave mixing for VUV pulse generation in hollow-core photonic crystal fibers. We predict the generation of sub-10-fs VUV pulses with energy of up to hundreds of microjoule by broad-band chirped idler pulses at 830 nm and MW pump pulses with narrow-band at 277 nm. MW pump could be desirable to reduce the complexity of the laser system or use a high repetition rate-laser system. The energy conversion efficiency from pump pulse to VUV pulse reaches to 30%. This generation can be realized in kagome-lattice hollow-core PCF filled with noble gas of high pressure with core-diameter less than 40 micrometers which would enable technically simple or highly efficient coupling to fundamental mode of the fiber.

physics.optics↗
arXiv2013

Generating Functional in String Field Theory

In our paper, we introduce a path integral of general functional field in order to build the path integral formalism in string field theory from the fact that a string field is a functional field, and describe a method for calculating it in the case of "Gauss-type". We also obtain the generating functional of an open bosonic string and the corresponding Feynman diagram.

physics.gen-ph↗
arXiv2013

Influence of Pulse width and Rabi frequency on the Population dynamics of three-level system in two-photon absorption process

We investigate the population dynamics of the three-level system in the two-photon absorption (TPA) process, mainly focusing the influence of pulse width and Rabi frequency on the population dynamics of the system. We observe the dependency of the population with the Rabi frequency and the pulse width. We also show that the arbitrary superposition state consisted in two states, upper state and lower state, is possible by controlling the pulse width and Rabi frequency. The results obtained can be used to the case of more complex multilevel system and they can be valuable for coherent quantum control in quantum information processing.

physics.optics↗