arXiv subjects

Myong Chol Pak

Publications and source records attributed to Myong Chol Pak.

9 recordsLinked to original sources

arXiv2025

Low Mach number limit for the diffusion approximation model in radiation hydrodynamics at equilibrium-diffusion regime

The low Mach number limit for the compressible viscous diffusion approximation model arising in radiation hydrodynamics is rigorously justified. For the 3-D Cauchy problem, the solutions in an equilibrium diffusion regime are shown to converge to the solutions of an incompressible Navier-Stokes equations locally and globally in time as Mach number goes to zero, when the effect of the small temperature variation upon the limit is taken into account.

math.AP↗

arXiv2024

Methods of Fitting experimental data in several amplifiers for single spot radiometer

Single spot radiometers are widely used to estimate temperature of body heated by high temperature, specially blast furnace, glass fusion, boiler of power plant, and so on. In previous papers on single spot radiometer a heated body was deduced according to interpolation functions between heated body temperature and photocurrent, which had previously measured. However, fitting functions required for current-to-voltage converter, non-inverting amplifier, and logarithmic amplifier have never reported. Therefore, in this paper the fitting functions are reported that can obtain the relationship between radiance temperatures of a body and outputs of amplifiers in single spot radiometer.

physics.ins-det↗

arXiv2021

Microstructure and wear resistance of Fe-Cr-C-Mo-V-Ti-N hardfacing layers

In this paper, to improve wear resistance of components such as screws under severe friction-wear, Fe-Cr-C-Mo-V-Ti-N hardfacing coatings were further developed. The hardfacing coatings were acquired by shielded manual arc welding (SMAW) method. The ferroalloys added into the coating flux of the hardfaced electrode were jointly nitrided. The microstructure of the coatings was carried out using X-ray diffraction(XRD), optical microscope(OM), field emission scanning electron microscope (FESEM) and energy dispersive Xray spectrometry (EDS). In addition, FactSage 7.0 software was employed to calculate the equilibrium phase diagram of the hardfacings. The wear resistance was performed on a pin-on-disc machine. The Fe-Cr-C- Mo-V-Ti-N hardfacings exhibited higher wear resistance than cladding layer without nitrides.

cond-mat.mtrl-sci↗

arXiv2020

Influence of geometric structure, convection, and eddy on sound propagation in acoustic metamaterial with turbulent flow

The problem of reducing noise in the transportation is an important research field to prevent accidents and to provide a civilized environment for people. A material that has recently attracted attention in research to reduce noise is acoustic metamaterial, and most of the research projects so far have been limited to the case of static media without flow. We have studied the sound transmission properties of acoustic metamaterial with turbulent flow to develop acoustic metamaterial that be used in transportation. In this paper, the effect of geometrical structure, the convective effect, and the eddy effect on sound propagation in acoustic metamaterial with turbulent flow are investigated, and the relationships between them are analyzed. The convective effect and the eddy effect both reduce the resonant strength of sound transmission loss resulting from the unique geometry of the acoustic crystal, but shift the resonant frequencies in opposite directions. In addition, when the convective effect and the eddy effect of the airflow, as well as the intrinsic interaction effect generated from the unique geometrical structure of the acoustic metamaterial cannot be ignored, they exhibit competition phenomena with each other, resulting in a widening of the resonance peak. As a result, these three effects cause the shift of the resonance frequency of the sound transmission loss and the widening of the resonance peak. The results of this study show that even in the case of turbulent flow, acoustic metamaterial can be used for transportation by properly controlling the geometric size and shape of the acoustic metamaterial.

cond-mat.mes-hall↗

arXiv2020

On the evaluation of spinnability of metallic materials in the powerful spinning process: a review

Currently, the rapidly developing powerful spinning processes of metals are widely used in many industrial sectors including those requiring high precision processing of metal materials, and the types and production of spun part are increasing. Evaluating the spinnability (flow formability) of material is very important for expanding the application of flow-forming process for producing a lot of products. The spinnability of metal is an important basic data that predicts defects that may appear in the processing of products in advance, makes it possible to create rational processes, and guarantees product quality. In this paper, we comprehensively analyze the data studied so far on the spinnability evaluation during powerful spinning conducted at room temperature, it was described with respect to the test methods and the theoretical methods for evaluating spinnability of metallic materials, and the effect of various factors on the spinnability.

cond-mat.mtrl-sci↗

arXiv2020

Spin Transport in the heterogeneous structure containing Topological Insulator and Diluted Magnetic Semiconductor

In this paper, we discuss spin transport in topological insulator (TI) and diluted magnetic semiconductor (DMS) heterogeneous structures. In DMS / FM (Ferromagnetic Metal) heterogeneous structure, the spin injection efficiency changes according to the electric field and Fermi energy were investigated. The higher electric field, the stronger spin injection efficiency, and its velocity of increase gets lower and approaches to the equilibrium state. Additionally, the higher interface conductivity, the weaker spin injection efficiency, and the transmission due to Fermi energy of spin up and spin down is different from each other. In the same structure, the spin injection efficiency changes depending on the magnetic field, and the spin injection efficiency vibrates sensitively according to the magnetic field. In TI / DMS heterogeneous structure, the spin current changes according to magnetic field were investigated. Here, when the magnetic field is low, the spin current oscillates, and as the magnetic field increases, the vibration is attenuated. It also decreases with increasing temperature and weakens vibrations. This is due to the competitive effect of the chiral properties of Dirac type quasiparticles in the topological insulator and the unique properties of exchange interaction between electrons and ions in DMS. This result allows us to expect the possibility of spintronic devices with high sensitivity to magnetic field.

cond-mat.mes-hall↗

arXiv2020

New discrete method for investigating the response properties in finite electric field

In this paper we develop a new discrete method for calculating the dielectric tensor and Born effective charge tensor in finite electric field by using Berry's phase and the gauge invariance. We present a new method to overcome non-periodicity of the potential in finite electric field due to the gauge invariance, and construct the dielectric tensor and Born effective charge tensor that satisfy translational symmetry in finite electric field. In order to demonstrate the correctness of this method, we also perform calculations for the semiconductors AlAs and GaAs under the finite electric field to compare with the preceding method and the experiment.

cond-mat.mtrl-sci↗

arXiv2020

Recrystallization Characteristics of Catalytic Alloy and Graphite in Diamond Synthesis

We first consider the recrystallization characteristics of catalysis alloy and graphite in the process of diamond synthesis under the condition of super high pressure and high temperature in catalysis method. In the process of diamond synthesis catalysis metal is plastically deformed by increase of pressure and then recrystallized as increasing the temperature. As catalysis metal is recrystallized, the shape of graphite particle is in spherical shape in the region contacting with the catalyst but in any shape in the opposite region. In addition, we calculate the electron charge density distribution and cohesive energies of cementite structure using the first principle method to investigate the reciprocal interaction between transient metal elements and carbon atoms in high-temperature catalyst synthesis. After determination of lattice constant parameters, we obtain the cohesive energy by subtracting the total energy of the crystal from the summation of total energies of atoms composing the crystal and dividing it by the number of atoms. Therefore, the effect of the catalyst on the diamond synthesis is to be analyzed theoretically.

cond-mat.mtrl-sci↗

arXiv2019

Phonon Dispersion Relationship and Oxygen Isotope Effect in Superconductor LaFeAsO

In this paper we calculate ab initially the phonon dispersion relationship of the superconductor LaFeAsO and investigate a main property in the superconductor, the oxygen isotope effect. Based on this phonon dispersion relationship, we find the fact that an important reason of the oxygen isotope effect is connected with the phonon. This result agrees well with the experimental data where the power index of the oxygen isotope effect in the superconductor LaFeAsO is small.

cond-mat.supr-con↗