Ex) Article Title, Author, Keywords
Ex) Article Title, Author, Keywords
Abstract : Potassium silicate solution (PSS) added with Y3Al5O12:Ce3+(YAG:Ce3+) phosphors was synthesized by using a solid-state reaction method. The crystal structure, morphology, and luminescence properties of the phosphors were measured for various PSS concentrations. The X-ray diffraction pattern of the phosphors shows that the addition of PSS promotes the formation of a garnet structure at lower temperature than commercial YAG phosphors. FE-SEM images show that the addition of PSS promotes the growth of particle size and aggregation. With the addition of 10 wt.% of PSS, the PL spectra show that the emission intensity at 533 nm is 20% higher than the normal phosphor. In determining the performance of PSS-added YAG:Ce3+ phosphors, white LEDs were fabricated by combining blue LEDs and phosphors. The phosphor exhibited lower color temperature because of the enhancement of yellow emission. Result shows that PSS can be applied as a flux, which decreases the synthesis temperature of YAG phosphors.
Abstract : For this qualitative study, we conducted an in-depth analysis of unexpected situations that occur in sixth-grade electric circuit lessons in a South Korean elementary school, the causes of these situations, and factors affecting the teacher’s responses. We performed a detailed observation of electric circuit lessons taught by an experienced teacher and carried out pre-lesson and post-lesson interviews. The causes of unexpected situations were found to be students’ neglect of electrical components, poor quality electrical components, images in the textbook, and real-life examples and analogies used by the teacher. The situations considered unexpected by the teacher included an electric circuit that did not light up, incorrect experimental results, and student questions regarding the teacher’s real-life examples. The teacher handled these unexpected situations by explaining that electrical components are consumables, giving real-life examples, providing opportunities for inquiry, and limiting textbook use. These responses originated from the teacher’s belief that science teaching should be student-centered and inquiry-based, and needs to emphasize the relationship between science and real-life experience. The study offers implications for science education in general and the teaching of electric circuits, which presents significant difficulties for elementary school teachers.
Abstract : This paper proposes two methods for calculating current flow through an electric bulb, which is a nonlinear electric device: the graphical method and the optimal auxiliary function method. The currents flowing through an electric bulb of 2.5 V − 0.3 A with room temperature resistance R0 = 1.3 Ω according to the terminal voltages of it are calculated via the methods and are compared with the measured currents. Compared with the measured currents, the currents calculated via the graphical method have error rates below 5.95%, and the currents calculated via the optimal auxiliary function method have error rates below 2.44% in the operating region of the electric bulb. These low error rates demonstrate the validity and practicality of the two methods.
Abstract : Light scattering by small particles enables the characterization of their size, density, and refractive index. For example, a collimated laser beam can be used to detect micrometer-scale particles, such as fine dusts in air or microplastics in water, by measuring the intensity of the light scattered by them. However, millimeter-size laser beams cannot be used to detect particles smaller than 1 μm because the size of these particles is comparable to the wavelength of the laser beam, resulting in low light scattering. In this study, we demonstrated the measurement of light scattering by small particles with diameters of hundreds of nanometers by using a home-built laser microscope. We used two identical objective lenses to achieve optimized light illumination and collection in the measurements. The signal-to-noise ratio was minimized by achieving balanced detection with the lock-in amplifiers. Single particles were clearly revealed in the scanning scattering-intensity map. We expect that our proposed method will be useful for detecting and characterizing nanoscale particles in environment-monitoring systems.
Abstract : A solid-phase synthesis mechanism of CuAlO2 was studied, and a method for suppressing the secondary phases of CuO and CuAl2O4 during synthesis was developed. The p-type electrical characteristics according to the Mg addition amount were analyzed. Results showed that during heating, Cu2O was changed to CuO with high mobility and reactivity formed on the Al2O3 surface. The CuO-Al2O3 interface induced a diffusion reaction depending on the temperature. During heat treatment, Cu loss occurred in the upper and lower layers and CuO phase was observed in the middle layer. This non-uniformity caused Cu loss in the entire sample. After Cu loss was compensated, a single CuAlO2 phase was obtained. CuAlO2 and CuAl(1-x)Mg(x)O2 showed p-type conductivity. The residual amount of CuO and CuAl2O4 phases increased with the Mg doping amount and affected the decrease in hole mobility.
YeonJung PARK, Joonghoe DHO*
New Phys.: Sae Mulli 2021; 71(5): 450-456
https://doi.org/10.3938/NPSM.71.450
Jongwon PARK, Insun LEE*
New Phys.: Sae Mulli 2021; 71(5): 476-489
https://doi.org/10.3938/NPSM.71.476
Chang-Duk KIM*, Younjung JO, Nguyen Tam Nguyen TRUONG
New Phys.: Sae Mulli 2021; 71(5): 422-426
https://doi.org/10.3938/NPSM.71.422