npsm 새물리 New Physics : Sae Mulli

pISSN 0374-4914 eISSN 2289-0041
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  • Research Paper 2021-04-30

    Effect of Raw Material SiO2 Powder Size on the Crystallinity of Sr3SiO5:Eu(3+/2+)(4%) Phosphor and Optical Properties of Eu(3+/2+)

    Purevdulam NANKHAI, Kiwan JANG*

    Abstract : We fabricated a series of Sr2.96SiO5:0.04Eu(2+/3+) phosphors by using powders of a raw-material, SiO2, with various grainsizes, and we studied the effect of grain particle size on optical properties, such as excitation and emission spectra of Eu(2+/3+) ions doped in Sr3SiO5 and the crystallinity of Sr2.96SiO5:0.04Eu(2+/3+). Some of the samples studied using x-ray diffiaction had the same crystal structure as that of the standard sample Sr3SiO5(JCPDS-260984), but the crystallinity and the optical properties of Sr2.96SiO5:0.04Eu(2+/3+) depended greatly on the size of the particles in the SiO2 powder. The studied Sr2.96SiO5:0.04Eu2+ phosphors showed the maximum emission intensity at 582 nm with a full width at half maximum of about 70 nm and had good excitation efficiencies in the 240-500 nm region. Thus, we can conclude that the combination of ultraviolet or blue LED chips with a Sr2.96SiO5:0.04Eu2+ phosphor can be used as a source of warm white light with many potential applications. Through this study, we experimentally confirmed that the fabrication of Sr2.96SiO5:0.04Eu2+ phosphors was very sensitive to the powder size of SiO2 raw material.

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  • Research Paper 2021-04-30

    Ultrasonic Testing to Evaluate the Signal Characteristic for CFRP Composite Lamination

    Yun-Taek Yeom, Hak-Joon Kim, Sung-Jin Song et al.

    Abstract : CFRP (carbon fiber reinforced plastic) composites have superior chemical resistance, vibrationdamping properties, electrical insulation, dimensional safety, etc. than conventional metal materials. Also, applications of these composites are gradually being attempted in various fields, such as the automobile, shipbuilding, medical equipment, and aerospace and aviation industries, and the scope of applications is expanding. CFRP composites have properties such as imbalance and anisotropy because they are manufactured with a desired stacking order and fiber arrangement angle by using a one-way prepreg sheet. In the additive process, defects such as pores, uneven thickness, resin distribution, and micro-cracks can occur due to sliding or stacking defects and can cause the destruction of the fibers and parent materials, interfacial separation, and fracture, Thus, the characteristics for the shape of CFRP Composite lamination must be evaluate, so In this study, an evaluating of the characteristics was performed by analyzing the ultrasonic A-scan (Amplitude-scan) signal and C-scan (Contrast-scan) image for CFRP composite lamination

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  • Research Paper 2021-03-31

    Effect of Synthesis Temperature on Luminescent Properties of Carbon dots Originated from Sucrose

    Woo Tae Hong, Hyun Kyoung Yang

    Abstract : Carbon dots (CDs) originating from sucrose were synthesized by using a solvothermal method. The morphological, structural and luminescent properties of those CDs were analyzed to investigate the effect of the synthesis temperature on the CDs. TEM images of the CDs showed that increasing the synthesis temperature caused an increase in the particle size and aggregation of the CDs. The FT-IR and XPS spectra of the prepared CDs indicated that an increase in the synthesis temperature eliminated the surface functionalized ligands and the defects in CDs fabricated using the solvothermal reduction. Under 400-nm excitation, the PL spectra of the CDs exhibited a blue emission band with a maximum at 477 nm. When the synthesis temperature was 220 °C, the maximum emission intensity of the CDs was the highest. When the synthesis temperature was 250 °C, the dominant emission wavelength and emission intensity decreased due to the removed of defect states in the bandgap. The results in this study, clearly show that the synthesis temperature can be used to control the morphological, structural, luminescent properties of CDs.

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  • Research Paper 2021-03-31

    Defect Detection in XLPE Material Using Terahertz Wave-based Non-destructive Testing

    Min-Gyu BAE, In-Sung LEE, Joong Wook LEE

    Abstract : We used a continuous-wave (CW) terahertz (THz) imaging system to investigated a method for detecting defects in cross-linked polyethylene (XLPE) material for power cable insulation Using the two-dimensional images of coherent CW THz waves, we measured the change in the amplitude of transmission, which directly corresponds to the difference between the phases of THz waves transmitted through bare XLPE and XLPE with defects. We found that defects of less than 0.3 mm size can be detected by the non-destructive testing method based on coherent THz imaging system. The experimental results indicate that the method might be useful for evaluating the reliability, durability and safety of the insulation materials used in electrical components and facilities.

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  • Research Paper 2021-02-26

    Dependence of the AC loss on Interval and Stacking Number in $z$ Stacked GdBCO Coated Conductor

    Chan KIM, Young-kyoung KIM, Sung-min JEON et al.

    Abstract : The 2G High-$T_{c}$ superconductor-coated conductors (2G HTS CC) with large aspect ratios have large AC losses for a perpendicular external magnetic field. A reduction of the AC loss is an important issue in 2G HTS CC applications. In a previous study, stacking of HTS CC was found to increase the full penetration field $H_{p}$ and to decrease the AC loss. The AC loss for the maximum applied magnetic field $H_{m}$ below $H_{p}$ was affected by the interval $D$ and the staking number $n$. In this study, to reduce the AC loss, we stacked GdBCO-coated conductors with the same geometries and with regular $D$, and we measured the magnetization curves of the stacked samples at a temperature of 83 K ($t = T/T_{c} = 0.88$). The AC losses were calculated using the experimental results, and the AC losses of the stacked samples were compared with phose for the single-layer sample. We investigated the dependences on $D$ and n of the AC losses of the stacked GdBCO CCs. As the interval decreases, the volume normalized AC loss decreased. In the case of $D$ = 0.10 mm, the AC loss was decreased by 16% and 37% in the 2-layer structure and the 3-layer structure, respectively, compared with the 1-layer structure.

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Current Issue

    April, 2021 | Volume 71, No. 4
  • Review Paper 2021-04-30

    Assessment of the Magnetocaloric Effect upon the Magnetic Entropy Change

    Ying De ZHANG, Tien Van MANH, The Long PHAN et al.

    Abstract : The magnetocaloric effect is a dynamic phenomenon associated with a temperature change of a magnetic material when it is subjected to a magnetic-field change. The effect can be assessed through the adiabatic temperature change (ΔTad) or the isothermal magnetic-entropy change (ΔSm). This work reviews some typical methods that are usually used to calculate ΔSm for perovskite-type manganites. These methods was thermodynamic relations and different theoretical models to analyze magnetization isotherms, M(H) data, recorded at temperatures around the ferromagnetic-paramagnetic phase transition (TC), Together with showing the methods for calculating of ΔSm, we also take into account the figures of merit of a MC material.

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  • Review Paper 2021-04-30

    Gamma Ray Bursts and Gravitational Waves: Landscape with Physics

    Hyun Kyu LEE*

    Abstract : The observations of gamma-ray bursts and gravitational waves imply the presence of explosive phenomena in the Universe, which are characterized by the emission of solar-mass-equivalent energies in a time shorter than few seconds (much more luminous than the whole Universe). Compact stars, like black holes and/or neutron stars, are believed to be the main actors at the centers of explosive processes. The mechanism for explosivly emiting energy in system with black holes which includes the gravitational binding energy in inspiral and merging processes and the rotational energy due to the magnetic braking process, and the possible characteristics of the gravitational waves from the center of gamma-ray bursts will be discussed. The properties of compact stars and of hadronic matter at extreme high density can be probed by gamma-ray bursts and gravitational waves.

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  • Research Paper 2021-04-30

    Nitrogen-doped Carbon Nanofiber for use in a Symmetric Supercapacitor

    Gyawali GHANASHYAM, Hae Kyung JEONG*

    Abstract : We synthesized nitrogen-doped carbon nanofiber for supercapacitor applications. Melamine is used as nitrogen source. 4 wt% of nitrogen is doped, and it consists of pyridinium, pyrrole, and quaternary nitrogen The electrochemical surface area increased from 0.28 $\mu$cm$^{2}$ to 0.40 $\mu$cm$^{2}$ due to the nitrogen doping, and the electrochemical impedance decreased from 249 to 63 $\Omega$ at 100 Hz. Finally, the specific capacitance was enhanced from 71 F/g to 192 F/g (at 0.5 A/g), which is almost three times higher, compared to the precursor carbon nanofiber. A high specific energy of 17 Wh/kg with a specific power of 200 W/kg was obtained from a symmetric supercapacitor device. Capacitance retention of 87% and coulombic efficiency of 81% after 3,000 cycles prove relatively good rate capability and cyclic stability.

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  • Research Paper 2021-04-30

    Structural Study on Spontaneous van der Waals Epitaxy of Layered Chalcogenide film

    Jae-Yeol HWANG*

    Abstract : In the layer-structured Bi-Sb-Te (BST) pnictogen chalcogenide film grown on a Al$_2$O$_3$ substrate by using spontaneous van der Waals epitaxy, a structurally correlated in-plane orientation between the 2D BST film and the 3D substrate was found. In order to elucidate the origin of such a peculiar structural feature, we confirmed that well-matched stacking at the van der Waals hetero-interface could be induced by the similar atomic arrangements and surface topographies of Te monolayers. Particularly, the $c-$axis lattice parameter of the BST film was individually manipulated by altering the growth rate of spontaneous van der Waals epitaxy. We found that such a change could be generated by variations in the van der Waals interfaces between BST quintets in a layer-structured pnictogen chalcogenide.

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  • Research Paper 2021-04-30

    Effect of Raw Material SiO2 Powder Size on the Crystallinity of Sr3SiO5:Eu(3+/2+)(4%) Phosphor and Optical Properties of Eu(3+/2+)

    Purevdulam NANKHAI, Kiwan JANG*

    Abstract : We fabricated a series of Sr2.96SiO5:0.04Eu(2+/3+) phosphors by using powders of a raw-material, SiO2, with various grainsizes, and we studied the effect of grain particle size on optical properties, such as excitation and emission spectra of Eu(2+/3+) ions doped in Sr3SiO5 and the crystallinity of Sr2.96SiO5:0.04Eu(2+/3+). Some of the samples studied using x-ray diffiaction had the same crystal structure as that of the standard sample Sr3SiO5(JCPDS-260984), but the crystallinity and the optical properties of Sr2.96SiO5:0.04Eu(2+/3+) depended greatly on the size of the particles in the SiO2 powder. The studied Sr2.96SiO5:0.04Eu2+ phosphors showed the maximum emission intensity at 582 nm with a full width at half maximum of about 70 nm and had good excitation efficiencies in the 240-500 nm region. Thus, we can conclude that the combination of ultraviolet or blue LED chips with a Sr2.96SiO5:0.04Eu2+ phosphor can be used as a source of warm white light with many potential applications. Through this study, we experimentally confirmed that the fabrication of Sr2.96SiO5:0.04Eu2+ phosphors was very sensitive to the powder size of SiO2 raw material.

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  • Research Paper 2021-04-30

    Dirac Coupled Channel Analyses of $^{120}$Sn (p,p$^\prime$)

    Sugie SHIM*

    Abstract : Unpolarized proton inelastic scatterings of 800-MeV from $^{120}$Sn are analyzed using an optical potential model and the first-order collective model in relativistic Dirac coupled channel calculations. The theoretical results for the differential cross sectioons obtained in the Dirac phenomenological calculations are compared with the experimental data and with the results obtained in non-relativistic calculations. The channel coupling effects between the excited states that belong to the ground state rotational band are investigated, and the deformation parameters for several of the lowest-lying excited state, as obtained using Dirac approaches, are analyzed and compared with those calculated by using non-relativistic approaches.

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  • Research Paper 2021-04-30

    Conceptual Changes of Elementary Science-gifted Students Through Analogy Between the Current in an Electric Circuit and Mechanical Motion

    Jiseon KIM, Hyejung KWAK, Jung Bog KIM*

    Abstract : The purpose of this study was to analyze the conceptual changes, as related to electric current of elementary science-gifted students through analogy between the motion of charge and mechanical motion in gravity. This study developed an analogy considering reasoning for the motion of charge to help students understand the reason charge moves in an electrical circuit, the reason a bulb lights up, and the factors influencing the speed of charge. As a result of this research, the average Hake-gain for each of the 6 categories was 0.92, and that fot all students was a high of 0.94, The analogy between the reasoning for the motion of charge and mechanucal motion in gravity was confirme to be a highly effective teaching approach for changing the misconceptions of elementary gifted students about electric current to more scientific concepts. Especially, students who discovered the fact that while particles (charges) are passing through a light bulb, particles go faster, hit an obstacle, and slow down repeatedly, understood that the speed of particles before and after passing through the light bulb was the same, so the current consumption model and the sequential consumption model were changed to a scientific model.

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  • Research Paper 2021-04-30

    Scientific Inquiry Activity to Measure the Conductivity of a Conductor by Using Magnetic Levitation

    Sungwook HONG*

    Abstract : In this study, the forces on a permanent magnet near a vertically rotating Cu plate were analyzed, and a method of measuring the conductivity of a conductor, such as Cu, was devised. The magnetic levitation force, $F_{L}$, and the drag force, $F_{D}$, act spontaneously on the magnet. $F_{L}$ and $F_{D}$ were determined by using a pendulum, that was designed to restrict the degree of freedom of one of the two angles to measure two angles in dividually. When the distance between the Cu surface and the magnet was constant, the higher the rotational linear velocity of Cu was, the greater the $F_{D}$ was. However, when the linear velocity was constant, $F_{D}$ was inversely proportional to the square of the distance. Because the distance increased when the linear velocity of the Cu plate increased, the magnetic levitation force $F_{L}$ can be expressed as a function of the velocity and the distance. $F_{D}$ decreased with decreasing linear velocity of Cu when measured under the same measurement conditions as $F_{L}$, and the conductivity of Cu was found to be $\sigma = 5.92 \pm 0.35 \times 10^{7} \Omega^{-1}$m$^{-1}$ based on the relationship between $F_{L}$ and $F_{D}$.

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  • Research Paper 2021-04-30

    Measurement of Dielectric Constants of Liquids Using a Parallel Plate Capacitor

    Gun Hee KIM, Hye Jin HA, Sang Ho SOHN* et al.

    Abstract : To estimate the dielectric constants of liquids we designed, a hollow acrylic box and derived formulas for the capacitance and the dielectric constant in a parallel plate capacitor with a hollow acrylic box. The dielectric constants of acrylic, distilled water, and sodium chloride aqueous solutions were obtained and compared with theoretical values. Due to the fringing effect, the measured capacitances of the parallel plate capacitor were found to have values different from the theoretical ones. Because our formulas for the capacitance do not involve the fringing effect, the experimental capacitance values should be corrected using the ratio of the experimental value to the theoretical value to lessen the error rates. By doing so, we obtained meaningful data for the dielectric constants and confirmed that the dielectric constant decreased linearly with increasing concentration of sodium chloride in an aqueous sodium-chloride solution.

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  • Research Paper 2021-04-30

    Study of Lasing Characteristics of Passively Q-switched Nd:YAG Laser On Incidence Angle of Cr:YAG

    Jaeyeol LEE, Jin Seog GWAG, Jonghoon YI*

    Abstract : The passive Q-switching characteristics of a Nd:YAG laser pumped by using a fiber coupled laser diode were analyzed. The pulse energy from the passively Q-switched laser was calculated as a function of the initial transmittance of the Cr:YAG saturable absorber and the reflectance of the output mirror. The ratio of the TEM$_{00}$ mode size in the Nd:YAG crystal to the TEM$_{00}$ mode size in the Cr:YAG crystal was calculated as a function of the incidence angle of the Cr:YAG crystal and the curvature of the resonator mirror. From the calculated ratio of the TEM$_{00}$ mode sizes, the pulse energy of the Q-switched laser was obtained. When the angle of incidence was changed between 20$^{\circ}$ and 70$^{\circ}$, the pulse energy was controlled to be in the range from 14 mJ to 32 mJ for a 40% initial transmittance, and in the range from 0 to 15 mJ for a 90% initial transmittance.

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  • Research Paper 2021-04-30

    Ultrasonic Testing to Evaluate the Signal Characteristic for CFRP Composite Lamination

    Yun-Taek Yeom, Hak-Joon Kim, Sung-Jin Song et al.

    Abstract : CFRP (carbon fiber reinforced plastic) composites have superior chemical resistance, vibrationdamping properties, electrical insulation, dimensional safety, etc. than conventional metal materials. Also, applications of these composites are gradually being attempted in various fields, such as the automobile, shipbuilding, medical equipment, and aerospace and aviation industries, and the scope of applications is expanding. CFRP composites have properties such as imbalance and anisotropy because they are manufactured with a desired stacking order and fiber arrangement angle by using a one-way prepreg sheet. In the additive process, defects such as pores, uneven thickness, resin distribution, and micro-cracks can occur due to sliding or stacking defects and can cause the destruction of the fibers and parent materials, interfacial separation, and fracture, Thus, the characteristics for the shape of CFRP Composite lamination must be evaluate, so In this study, an evaluating of the characteristics was performed by analyzing the ultrasonic A-scan (Amplitude-scan) signal and C-scan (Contrast-scan) image for CFRP composite lamination

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  • Research Paper 2021-04-30

    Feasibility Study on the Calculation of Tritium Breeding Ratio using Geant4 ToolKit

    Byung Chul KIM* 

    Abstract : For fusion power generation, the reliable production of tritium, one of the fuels, is a critical challenge. The calculation of the tritium breeding ratio and the design of devices to optimize that ratio are essential when designing fusion demonstration reactor. Usually, MCNP codes are mainly used to calculate the tritium breeding ratio, but in this review, the feasibility of using Geant4, which is mainly used in the field of high-energy physics research, to examine tritium breeding ratio calculation was studied. Comparisons of tritium breeding ratios calculated using MCNP and Geant4 code in simple 1-D models with the same geometry and material properties showed agreement within a range of 1%. Comparisons of other variables (Flux, Energy Deposition) available from Monte Carlo computer simulations was also performed to consider the potential for expanding the utilization area of the Geant4 toolkit.

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Current Issue

April, 2021
Vol.71 No.4

pISSN 0374-4914
eISSN 2289-0041

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pISSN 0374-4914
eISSN 2289-0041