npsm 새물리 New Physics : Sae Mulli

pISSN 0374-4914 eISSN 2289-0041
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  • Research Paper 2020-08-31

    Calculation of the Stacking Fault Energy by Using the Anisotropic Next-Nearest Neighbor Ising Model

    Byeong-Hyeon JEONG, Ji-Sang PARK*

    Abstract : A stacking fault is a type of extended defect formed in a material. It is known to prohibit the transport of charges in semiconductor materials and promote the recombination of charges; therefore, the performance of electronic devices can be suppressed. For investigating of the stability of stacking faults, first-principles calculations are widely performed, which can be also described using an anisotropic next-nearest-neighbor Ising model (ANNNI) and can be constructed using the total energy of polytypes obtained from the first-principles calculations. In this study, we constructed the ANNNI model for diamond Si and zinc-blende CdTe, ZnS, and GaAs. Our models consider the interactions between two and three layers, resulting in a lower error than the models using only two-layer interactions. The predicted stacking fault energy was similar to that from the first-principles calculations, indicating that the stacking fault energy can be obtained using the ANNNI model.

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  • Research Paper 2020-08-31

    Study of the Electronic Structure for Ce(Fe$_{0.4}$Co$_{0.6}$)$_2$ and CeCo$_2$ Compounds

    En-Jin CHO*, Byung-Hee choi, Jai-Kwan JUNG et al.

    Abstract : For Ce(Fe$_{0.4}$Co$_{0.6}$)$_{2}$ and CeFe$_{2}$ compounds, we obtained Fe/Co $3d$ and Ce $4f$ spectra by using photoelectron spectroscopy. With the Anderson impurity Hamiltonian, we analyzed theoretically the Ce $4f$ spectra of two compounds. Not only a bulk contribution but also a surface contribution to the Ce $4f$ spectrum is needed to explain the experimental Ce $4f$ spectrum, For the Ce(Fe$_{0.4}$Co$_{0.6}$)$_{2}$ compound, we obtained a theoretical bulk $4f$ spectrum by using a bare $f$ electron binding energy, $\epsilon_{f}^ B $, to be 0.90 eV and the average hybridization between a $f$ and conduction electrons, $\Delta_{av}^B$, to be 47.6 meV. From the theoretical results of the Ce(Fe$_{0.4}$Co$_{0.6}$)$_{2}$ compound, the number of $4f$ electrons, $n_{f}^B$, is 0.88 and the Kondo temperature, $T_{K}$, is 261K. For the CeCo$_{2}$ compound, we obtained a theoretical bulk $4f$ spectrum, $n_{f}^B$=0.80 and $T_{K}$=691K with $\epsilon_{f}^ B $=0.90 eV and $\Delta_{av}^B$=61.5 meV.

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  • Research Paper 2020-08-31

    Calculation of the off-axes Magnetic Field for Finite-length Solenoids

    Taehun JANG, Yun Kyung SEO, Sang Ho SOHN* et al.

    Abstract : In this study, we derived an approximate analytic function for the off-axis magnetic field of a finite-length solenoid by using the magnetic vector potential of a circular current loop. We verified that the derived analytic function reduced to a well-known magnetic field formula on the vertical axis of the solenoid and also inferred the magnetic field on the horizontal axis of the solenoid. Furthermore, we investigated the magnetic field at arbitrary points satisfying the approximate conditions through a simulation performed using Wolfram Mathematica.

  • Research Paper 2020-07-31

    Study of the Scintillation Properties of a CsI:Tl Crystal and Pulse Shape Discrimination Study

    Sang Hyeok IM, HongJoo KIM*, Phan Quoc VUONG

    Abstract : Scintillators are widely used in and studied for particle physics, nuclear physics and astroparticle physics detection. In this study, we estimated the scintillation properties of a CsI:Tl crystal and determined the best method to discriminate $\alpha$-particles, which is an important component of the cosmic-ray background, from $\gamma$-rays. We studied the scintillation properties of the CsI:Tl crystal and the pulse shape discrimination capability by using an $^{241}$Am $\alpha$-particle source and a $^{137}$Cs $\gamma$-ray source. For the pulse shape discrimination study, we used these well-known methods: the mean time method, charge integration method and optimum filter method. To determine which method was best for discrimination, we calculated the FOM value for each method under various conditions. Consequently, the optimum filter method was found to give the best value of the FOM. If we use the optimum filter method when we are observing $\gamma$-rays from the sky, we can distinguish the background of ion particles, such as $\alpha$-particles, from $\gamma$-rays.

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  • 2020-07-31

    Dependences Comparison of the Polarization Spectroscopy Signal on Pump Beam Intensity and Temperature for closed transition lines of $^{85}\text{Rb}$ and $^{87}\text{Rb}$

    Jeongyoun JEONG, Sanglok LEE, Geol MOON*

    Abstract : We investigate the dependence of the polarization spectroscopy signal on the pump beam intensity and the vapor cell temperature around the $F_g=3\rightarrow F_e=4$ closed transition line of $^{85}$Rb and the $F_g=2\rightarrow F_e=3$ closed transition line of $^{87}$Rb, and we analyze the amplitudes of those signals. We observe that the temperature dependences of the polarization spectroscopy signal around the closed transition lines of $^{85}$Rb and $^{87}$Rb shows different tendencies, and that the temperature dependence of the polarization spectroscopy signal on the pump beam intensity. Interestingly the different temperature dependence of two isotopes comes from the difference in energy spacing between its hyperfine structure energy levels. It was theoretically confirmed that the signal amplitude of the closed transition line is affected by overlapping with the cross-over signal due to the increase in line width of the cross-over spectral signal depending on the temperature dependence.

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Current Issue

    August, 2020 | Volume 70, No. 8
  • Research Paper 2020-08-31

    Calculation of the Stacking Fault Energy by Using the Anisotropic Next-Nearest Neighbor Ising Model

    Byeong-Hyeon JEONG, Ji-Sang PARK*

    Abstract : A stacking fault is a type of extended defect formed in a material. It is known to prohibit the transport of charges in semiconductor materials and promote the recombination of charges; therefore, the performance of electronic devices can be suppressed. For investigating of the stability of stacking faults, first-principles calculations are widely performed, which can be also described using an anisotropic next-nearest-neighbor Ising model (ANNNI) and can be constructed using the total energy of polytypes obtained from the first-principles calculations. In this study, we constructed the ANNNI model for diamond Si and zinc-blende CdTe, ZnS, and GaAs. Our models consider the interactions between two and three layers, resulting in a lower error than the models using only two-layer interactions. The predicted stacking fault energy was similar to that from the first-principles calculations, indicating that the stacking fault energy can be obtained using the ANNNI model.

    Show More  
  • Research Paper 2020-08-31

    Study of the Electronic Structure for Ce(Fe$_{0.4}$Co$_{0.6}$)$_2$ and CeCo$_2$ Compounds

    En-Jin CHO*, Byung-Hee choi, Jai-Kwan JUNG et al.

    Abstract : For Ce(Fe$_{0.4}$Co$_{0.6}$)$_{2}$ and CeFe$_{2}$ compounds, we obtained Fe/Co $3d$ and Ce $4f$ spectra by using photoelectron spectroscopy. With the Anderson impurity Hamiltonian, we analyzed theoretically the Ce $4f$ spectra of two compounds. Not only a bulk contribution but also a surface contribution to the Ce $4f$ spectrum is needed to explain the experimental Ce $4f$ spectrum, For the Ce(Fe$_{0.4}$Co$_{0.6}$)$_{2}$ compound, we obtained a theoretical bulk $4f$ spectrum by using a bare $f$ electron binding energy, $\epsilon_{f}^ B $, to be 0.90 eV and the average hybridization between a $f$ and conduction electrons, $\Delta_{av}^B$, to be 47.6 meV. From the theoretical results of the Ce(Fe$_{0.4}$Co$_{0.6}$)$_{2}$ compound, the number of $4f$ electrons, $n_{f}^B$, is 0.88 and the Kondo temperature, $T_{K}$, is 261K. For the CeCo$_{2}$ compound, we obtained a theoretical bulk $4f$ spectrum, $n_{f}^B$=0.80 and $T_{K}$=691K with $\epsilon_{f}^ B $=0.90 eV and $\Delta_{av}^B$=61.5 meV.

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  • Research Paper 2020-08-31

    A Self-Consistent Crank-Nicolson Method for Solving Time-Dependent Kohn-Sham Equation in a Localized Atomic Orbital Basis Set

    Junhyeok BANG*

    Abstract : The excited state dynamics of electrons in materials is crucial for understanding various phenomena in nature and applications. However, time-dependent density functional theory, which is a first-principles method for studying electronic dynamics, requires extensive computational power, which makes theoretical study difficult. In this work, we studied how to improve the computational speed of TDDFT. A Crank-Nicolson approximation for a time evolution operator of the time-dependent Kohn-Sham equation preserves unitarity and preforms a high-speed calculation in a localized atomic orbital basis. By including a self-consistent loop in the Crank-Nicolson approximation, we were able to increase the calculational speed by more than tenfold while maintaining the calculational accuracy and stability. In this way, we made possible the application of the first-principles method to the study of excited state dynamics on a long time scale.

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  • 2020-08-31

    Comparative Study on the Middle School Physics Curriculum of China and Korea

    Xue-Mei CUI, Seung Kee HAN*

    Abstract : The present study takes 2011 middle school physics curriculum standards in China and the physics field of the 2015 science curriculum standards in South Korea as the research objects, and compares the objectives of science (physics) education and the composition of middle school physics curriculum contents in the two countries. The research results are as follows: 1. In terms of science (physics) education goals, both countries aim to improve scientific literacy, aiming to cultivate students' inquiry ability and innovative consciousness on practical issues in nature and life; The curriculum standards in China stress learning basic physics, basic skills, and research method, while the curriculum standards in South Korea stress understanding the core concepts of science. 2. In terms of the content of middle school physics courses, in a quantitative comparison of the breadth and the depth of the content standards, we found that the middle school physics courses in China are more extensive than those of South Korea, but not as deep than those of South Korea. This result reflects the fact that science education in South Korea does not focus on the quantity of knowledge, but on the development of science core competence by learning an appropriate number of science core concepts. The results of this study provide references for the revision of middle school physics curriculum standards and the development of teaching materials in the future, as sell as useful enlightenment for the further improvement of middle school physics education.

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  • Research Paper 2020-08-31

    Physics Teachers' Perception of IT Convergence-based Physics Education

    Wonkun OH*

    Abstract : In line with the recent increase in social interest in the 4th Industrial Revolution, the demand for various types of IT-based education, such as AI and robots, is also increasing in the science classes of schools. The physics subject in secondary school has already been revised from the 2009 National Curriculum so that this IT-based modern science and technology can be meaningfully fused in line with the development of modern physics. However, foundations for such convergent education in teacher education or re-education in schools, are still insufficient. In this study, an IT convergence-based physics education training course developed for teacher re-education was conducted, and based on the results, the teacher's perception on how IT convergence-based physics education is applicable was investigated. The results are reported based on the positive and the negative responses from teachers.

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  • Research Paper 2020-08-31

    Calculation of the off-axes Magnetic Field for Finite-length Solenoids

    Taehun JANG, Yun Kyung SEO, Sang Ho SOHN* et al.

    Abstract : In this study, we derived an approximate analytic function for the off-axis magnetic field of a finite-length solenoid by using the magnetic vector potential of a circular current loop. We verified that the derived analytic function reduced to a well-known magnetic field formula on the vertical axis of the solenoid and also inferred the magnetic field on the horizontal axis of the solenoid. Furthermore, we investigated the magnetic field at arbitrary points satisfying the approximate conditions through a simulation performed using Wolfram Mathematica.

  • Research Paper 2020-08-31

    Symmetry Transformation and Distorted Black Holes

    Dal Ho PARK*

    Abstract : The distortion of Schwarzschild black holes by external matter in axially symmetric spacetime can generally be described by using the harmonic function, and the distortion of charged black holes or rotating black holes is usually obtained by symmetrically transforming the distorted Schwarzschild black holes. However, a previous paper has shown that both the external matter and the black hole have the same mass-to-charge ratio in the distorted Reissner-Nordstr\"om black hole obtained by using the Harrison transformation. This paper further shown that a specific relationship for the angular momentum must be established between the external matter and the black hole in distorted Kerr black holes obtained by using the B\"acklund transformation and the Cl\'ement transformation. Therefore, the symmetry transformation method should not be used to obtain the distortion of black holes by external matter with arbitrary charge or angular momentum.

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  • Research Paper 2020-08-31

    Fiber-Optic Pulsed Ultraviolet Light Sensor for Defective Insulator Monitoring

    Su-Jeong PARK, Young-min KO, Jong-Ju MOON et al.

    Abstract : A fiber-optic pulsed ultraviolet (UV) light sensor, based on a functional polymer-coated optical fiber and butt-coupling of the waveguides, is proposed. The azobenzene polymer was prepared by mixing an azobenzene compound and an UV curing agent. The polymer was applied as a coating on one of two optical fibers and aligned in an alumina fiber ferrule by using a UV curing process. This coating was reversibly stretched by UV light, and in the coated region, the UV light along the fiber induced tensile strains. The strain induced a gap variation between the fibers that resulted in a variation in the optical coupling ratio. The coupling intensity was measured using lock-in amplification to suppress the system noises. We achieved fast detection of UV light, pulsed with a time duration of 0.1 s. This sensing technique is an initial step required to monitor instantaneous UV light in a defective insulator.

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  • Research Paper 2020-08-31

    Characteristics of Radiation in a Free-electron Laser with Two-section Wiggler

    TaeHoon KIM, Yun Seong PARK, Soon-Kwon NAM*

    Abstract : We developed an extended time-dependent free-electron laser by using a two-section wiggler code to analyze the effect of the wiggler wave number ratio ($\alpha$). We studied the intensity of radiation for different ratios of various wiggler wave numbers in a two-section wiggler by using an extended time-dependent simulation code that we developed. For the simulations, we used a 1$^\text{st}$ section wiggler length of 0.4 m -- 0.8 m and 2nd section wiggler length of 1.2 -- 1.6 m. The intensity of radiation was analyzed at various times from -10 $\mu$s to 10 $mu$s and various detuning parameters from -2.5% to 2.5% for the ratio of the wiggler wave number. The radiation intensity was optimized at wiggler wave number ratio ($\alpha$) of 0.25 at time, $t$ = 2.0 $\mu$s for a detuning parameter of 1.0% by using a time-dependent FEL code with two-section wiggler.

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  • Research Paper 2020-08-31

    Analysis of an Ultraviolet Polarizer by Using a Pile of Fused Quartz Plates

    Seung-Eun KIM, Jong-Rak PARK*

    Abstract : For ambient contrast ratio enhancement, liquid crystal retardation films coated on top of a photo-alignment layer can be used as constituents of a wide-band circular polarizer in organic light-emitting diode displays. For the production of polarized ultraviolet (UV) light for photo alignment, a wire-grid or pile-of-plates polarizer can be utilized. Employing a large-scale UV polarizer is essential for manufacturing large-area film. The pile-of-plates polarizer is superior to the wire-grid polarizer in terms of fabrication cost and scalability. In this study, we performed polarization ray tracing simulations for optical configurations in which a pile of fused quartz plates was placed at the Brewster's angle under a UV lamp module used for the UV curing process. Two types of polarizer structures (one-body and partitioned-body) were examined for three polarization directions (0$^{\circ}$, 15$^{\circ}$, and 75$^{\circ}$ relative to the machine direction). We found that total UV power on the receiver decreased and polarization efficiency increased with the increasing of quartz plates. In addition, the partitioned- body type structure exhibited better illuminance uniformity than the one-body type structure.

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  • Research Paper 2020-08-31

    Study on the Improvement of the Color Rendering Index of White LEDs by Using red Quantum dots

    Seung Chan HONG, Juheon BAEK, Heonguk LEE et al.

    Abstract : Red quantum-dot (QD) walls and films were applied to conventional 6-inch white LED (light-emitting diode) lightings, consisting of blue LED chips and yellow phosphors, to improve the color rendering index (CRI). The emission spectra, the CRI, the illuminance, and the luminance properties of six different configurations were investigated. The vertical QD wall surrounding the LED chips and defining the emission area played an important role in improving the R9 CRI for strong, saturated red while the QD film laminated on either the bottom or the top surface of the diffuser plate formed a vertical cavity, enhanced the color conversion efficiency, and increased the average CRI Ra and Re. This study clearly suggests that appropriate QD configuration can be used to increase the CRI of conventional white LED lightings at nearly no expense to the luminous efficiency.

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  • Research Paper 2020-08-31

    Subsidiary Maxima in Multiple Slit Interference: Algebraic Equations

    Heung-Ryoul NOH*

    Abstract : We present an analytical and numerical study on the subsidiary maxima in multiple slit interference with slit numbers between 12 and 31. By using the equation for the existing condition of the subsidiary maxima, we express the intensities at the maxima in a succinct analytical form. We also obtain algebraic equations for the phases for the subsidiary maxima with slit numbers between 12 and 31.

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Current Issue

August, 2020
Vol.70 No.8

pISSN 0374-4914
eISSN 2289-0041

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pISSN 0374-4914
eISSN 2289-0041