Ex) Article Title, Author, Keywords
pISSN 0374-4914
eISSN 2289-0041
pISSN 0374-4914
eISSN 2289-0041
Ex) Article Title, Author, Keywords
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.
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.
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.
Abstract : In this study, we evaluate the dose distributions of $^{4}$He and $^{6}$He ion beams under the same irradiation settings by using the Monte Carlo method. For the simulations, we defined a water phantom that which includes three normal regions and one target region for measuring the dose deposition in various regions. In addition, we define the $^{4}$He and the $^{6}$He ion beams with specified parameters. Then, we obtain the distributions of the doses and the tracks of $^{4}$He and $^{6}$He ion beams and calculate the dose deposited in each region. The calculated results show that in the proximal volume, lateral volume, distal volume, and target volume, the dose depositions of the $^{4}$He ion beam are 73.77%, 31.44%, 73.5%, and 98.50% of that of $^{6}$He ion beam. In conclusion, we can say from the aspect of physical dose distribution, that the $^{4}$He ion beam is more ideal than the $^{6}$He ion beam. To more objectively evaluate the therapatic effects of $^{4}$He and $^{6}$He ion beams, in our need experiment-based study, we will consider the biological effects of $^{4}$He and $^{6}$He ion beams.
Abstract : We have grown nitrogen-doped titanium dioxide thin films by using DC magnetron sputtering methods. During the growth, the nitrogen flow was altered to adjust the amount of nitrogen into the titanium-dioxide films. By a comparative study of X-ray diffraction and Raman spectroscopy results, we found that the insertion of nitrogen led to a reduction in crystal size/volume, distortion of Ti-O bending, and displacement of Ti atoms. As the nitrogen flow was increased, the degradation of crystal quality became more severe. A blue shift of the optical energy bandgap was observed for the titanium-dioxide films with nitrogen, which is possibly related to quantum-confinement effects.
Abstract : We studied the electronic structure of Si$_2$Bi$_2$ through a first-principles calculation based on the density functional theory. Si$_2$Bi$_2$, a van der Waals layered structure, which possesses an in-plane $C_3$ rotational and time-reversal symmetries as well as inversion, exhibits metallic characteristics in equilibrium. Intriguingly, its electronic band structure reveals Dirac cones existing near the Fermi level. In addition, we observed that Si$_2$Bi$_2$ could undergo a phase transition from metallic to topological insulating phases due to in-plane compressive strains, either uniaxial or biaxial. In particular, its band structure evolution under the uniaxial compressive strain along the zigzag direction revealed that a band inversion had occurred. Our hybrid Wannier charge center calculation confirmed that this material, indeed, becomes a topological insulator. Finally, we constructed its topological phase diagram in the parameter space of the in-plane strain fields, which revealed how to control the in-plane strain to realize the topologically different phases of Si$_2$Bi$_2$.
Abstract : Using the cluster expansion methods and first-principles density functional theory calculations, we studied the mixing energy of 1H MoS$_{2-2x}$Te$_{2x}$ and 1T$^{\prime}$ MoS$_{2-2x}$Te$_{2x}$ binary alloys composed of the two-dimensional transition-metal chalcogenides MoS$_{2}$ and MoTe$_{2}$. For 1H MoS$_{2-2x}$Te$_{2x}$, a phase separation is expected due to the positive mixing energies regardless of the relative S and Te content. However, both MoS$_2$ and MoTe$_2$ can form solid solutions at temperatures above the room temperature because the mixing energy is less than 10 meV. In contrast, the mixing energies of 1T$^{\prime}$ MoS$_{2-2x}$Te$_{2x}$, alloys are always negative, resulting in the formation of a solid solution. We expect our theoretical studies to be utilized to guide the design of two-dimensional transition-metal chalcogenide alloys-based novel devices.
Abstract : $[1-x]$Bi$_{1.03}$(Fe$_{0.99}$Al$_{0.01}$)O$_{3}$-$x$BaTiO$_{3}$ ($x$ = 0.30, 0.33, 0.35, and 0.40) lead-free piezoelectric ceramics were prepared through a conventional solid-state reaction method followed by a water-quenching process. A single perovskite structure without any impurity or secondary phase was confirmed for all compositions. The crystal phase, phase transition, microstructure, dielectric, ferroelectric, and piezoelectric properties were investigated. The temperature-dependent dielectric losses ($\tan \delta$) were found to decrease dramatically to 100 -- 200 $^{\circ}$C and then increased sharply at higher temperatures for $x$ = 0.30, 0.33, and 0.35. The ferroelectric properties improved with increasing measurement temperatures and the highest value of $2P_{r}$ = 80.2 $\upmu$C/cm$^{2}$ was observed at $x$ = 0.33 at 100 $^{\circ}$C. It was found that the best piezoelectric charge sensor coefficient ($d_{33}$) was 323 pC/N and the Curie temperature ($T_{C}$) was 452 $^{\circ}$C for $x$ = 0.33. The best piezoelectric actuator coefficient ($d_{33}^{*}$) was 515 pm/V and the $T_{C}$ was 344 $^{\circ}$C for $x$ = 0.40. These results showed that Al-doped BF-BT ceramics have great potential for were in high-temperature lead-free piezoelectric sensor and actuator applications.
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.
Abstract : The equation of state of dense nuclear matter is explored using the KIDS (Korea-IBS-Daegu-Sungkyunkwan) density functional. The equation-of-state parameters, which are coefficients of the energy density expanded in powers of $(\rho - \rho_0)/3\rho_0$ where $\rho$ is the nuclear matter density and $\rho_0$ is its density at saturation, are constrained by using both nuclear data and the mass-radius relation of a neutron star, as determined from modern astronomy data. We find that a combination of both types of data can significantly reduce the uncertainties in the equation-of-state parameters that are determined experimentally. We verify that the newly constrained parameters reproduce with high accuracy the basic properties of spherical magic nuclei. Neutron drip lines, on the other hand, show a non-negligible dependence in the uncertainty of the nuclear symmetry energy.
Abstract : Relativistic Dirac phenomenological analyses are done employing an optical potential model and the collective model for 800-MeV polarized proton scatterings from Sn isotopes, $^{116}$Sn and $^{124}$Sn. Lorentz covariant scalar and time-like vector optical potential parameters using the Woods-Saxon geometry and the deformation parameters are determined to reproduce the experimental data phenomenologically by solving the Dirac coupled channel equations employing a computer code and the results obtained in the Dirac phenomenological calculations are compared with those obtained in the non-relativistic calculations. The Dirac equation is reduced to a Schr\"{o}dinger-like second-order differential equation to get the effective central potentials and the effective spin-orbit optical potentials and the effective potentials are analyzed by considering the mass dependence. The first-oder rotational collective model is used to accomodate the low-lying excited states that belong to the ground state rotational band at the axially-symmetric nuclei, Sn isotopes, and the optical potential parameters and the deformation parameters obtained by using Dirac phenomenological calculations are analyzed by considering the mass dependence.
Abstract : In nuclear and particle physics experiments, muons are used for performance testing during detector commissioning. Therefore, an understanding the flux of muons incident on the detector is very important. In this study, two rectangular, parallelepiped, scintillation detectors were used to measure the muon flux according to their incident angle. In addition, simulations using MATLAB and models based on geometry were performed and the distribution of the number of muons with respect to the angle of incidence was calculated, and the results were confirmed to agree with the experimental values within the statistical uncertainty. This simulation was used to calculate the flux of muons incident on a complex detector, and the results showed that the teching demonstrated in this study can be used to estimate the size of the muon signal required for a complex type detector performance test.
Abstract : This study was conducted as a basic investigation of the concept of energy and to measure the level of understanding of the concept of energy in Science-gifted elementary school students. The subjects of the study were 60 elementary school students participating in classes after having been selected as gifted students at an institute for Science-gifted students. The research results show that the students chose electric and electronic products the most as associations related to energy concepts, followed by the natural environment and resources, means of transportation, and abstract concepts. Furthermore, the study measured the level of understanding of energy concepts demonstrated by dividing the students into four levels, with 6 students (10%) classified as level 1, 25 students (42%) as level 2, 21 students (35%) as level 3, and 8 students(13%) as level 4. The results of this study will be applied to form effective teaching strategies or curricula for energy concept learning in the future by clearly identifying the level of understanding regarding energy concepts on the part of Science-gifted elementary school students.
Abstract : This study examined the electricity and magnetism (E&M) exhibits at representative science centers in Korea and the United States. I carry out this study in the following two stages: (1) content and design analysis of 24 E\&M exhibits at the Gwacheon National Science Museum and the Exploratorium, and (2) case analysis of the E\&M exhibits with design attributes for students’ engagement in learning. The results of this study indicate that the E\&M exhibits of the two science centers dealt mostly with ‘electromagnetic induction’ and ‘magnetic fields caused by a current’ at the middle and the high school levels, and encouraged students’ cognitive and behavioral engagement by reflecting design attributes that help students understand the exhibits and how to use them. However, design attributes to enhance students’ emotional engagement are rarely observed. Based on these results, I discuss the E\&M exhibit design to foster students’ engagement in learning physics.
Abstract : 이 연구에서는 예비 물리교사들이 양자 현상에 대해 갖고 있는 생각들의 군집과 그 특성을 살펴보았다. 이를 위해 예비 물리교사 160명을 대상으로 선행 연구에서 이미 밝혀진 양자 현상에 대한 다양한 관념들에 대한 그들의 생각을 조사하였으며, 응답 결과를 군집분석과 다차원 척도법을 적용하여 분석하였다. 연구 결과, 첫째 예비 물리교사들의 양자 현상에 대한 개념 이해는 ‘준양자론 관점’, ‘혼합 관점’, ‘비결정론 관점’, ‘기계론 관점’ 등 4개의 개념 군집으로 분류될 수 있으며, 개념 군집의 분포는 ‘이중성’과 ‘불확실성’을 차원으로 갖는 2차원 공간에 지도화할 수 있다. 둘째, 예비 물리교사들은 자신의 개념 이해 군집에 따라 ‘현대적 이해’, ‘혼재된 확신’, ‘혼동 이해’ 집단으로 구분할 수 있다. 혼동 이해 집단이 가장 큰 비중을 차지하며, 현대적 이해와 혼재된 확신 집단이 뒤를 잇는다. 셋째, 양자 현상에 대한 개념 이해 군집에 따라 구분한 예비 물리교사들의 집단 분포는 학년, 성별, 대학에서의 양자물리학 관련 과목 이수 정도에 따라 유의한 차이를 보인다. 이 연구 결과는 양자물리학 개념 이해 분포의 다양성 및 서로 상충되는 개념 이해의 병치 가능성을 드러내었으며, 이는 물리 교사교육에서 양자물리학 교수학습 방향에 대한 시사점을 제공한다.
Abstract : Recently, the quantum cascade laser (QCL) has been spotlighted as a next-generation light source in the mid-infrared region because of its increase in optical power due to the development of manufacturing technology. However, the optical power of a single QCL is limited by the self-heating effect. Therefore, high-efficiency beam combination technology is essential to achieve a high-power mid-IR laser. In this paper, we demonstrate a simple and effective beam combination method that can be used for QCLs in the 3.85 -- 4.15 $\mu$m wavelength region. We achieved a high 89.0% efficiency by combining three QCLs using flat mirrors. In addition, we adjusted the divergence angles of the fast axis and the slow axis equally for easy application in various wavelength regions.
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.
Abstract : Multiple layers formed by multiple objects can be easily found in concrete structures. Defects occurring on the exterior of the structure are typically cracks and leaks in the outer wall, and defects occurring at multiple layers hidden on the back of the outer wall are known as corrosion of reinforcement and the occurrence of voids in concrete. Among them, studies on inspecting voids in concrete at multiple layers are insufficient. Therefore, in this paper, an inspection study was conducted using a microphone, which is a non-contact sensor, to check the differences in signals caused by voids at various void depth. For this purpose, a specimen and blocks capable of implementing various void depths were produced, and an actuator was used as an impact source. For the acoustic signals collected according to void depth, after signal processing to improve the S/N ratio, the acoustic energy for each void depth in the frequency domain was calculated, and an evaluation of voids occurring in the multiple layers was performed through comparison and analysis
Myoung Won CHO*
New Phys.: Sae Mulli 2019; 69(4): 338-347
https://doi.org/10.3938/NPSM.69.338
Yeon-Su LIM, Yun-Taek YEOM, Hak-Joon KIM, Sung-Jin SONG, Woo-Young KANG, Sung-Duk KWON*
New Phys.: Sae Mulli 2019; 69(4): 348-354
https://doi.org/10.3938/NPSM.69.348
Tae Jong HWANG*, Dong Ho KIM
New Phys.: Sae Mulli 2019; 69(4): 355-360
https://doi.org/10.3938/NPSM.69.355
pISSN 0374-4914
