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Jihyeon Yun,Seunggu Kang 한양대학교 청정에너지연구소 2024 Journal of Ceramic Processing Research Vol.25 No.4
The ZnO-Al2O3-SiO2-Na2O (ZASN) system glass was fabricated and heat-treated to produce glass-ceramics specimenscontaining willemite (Zn2SiO4). The obtained glass revealed the presence of minor phase-separated droplets, each tens ofnanometers in size, serving as nuclei for crystal growth and enabling a direct one-step heat treatment process without theneed for a separate nucleation step. The activation energy (E) for crystallization was calculated from DTA data using theKissinger equation. The resulting Avrami constant (n) was found to be 1.49 when substituted E into the Augis-Bennettequation, indicating surface nucleation, which suggests that controlling the size and distribution of droplets could enhancethe properties of glass-ceramics through induced internal crystallization. Photoluminescence (PL) properties revealed broademission peaks attributed to Zn2+ ions with d10 electronic configuration. CIE color coordinate of glass-ceramics treatedwithin 10 minutes shifted towards darker blue hues with time; exceeding 1 hour shifted towards cyan. The controllability ofcrystallization mechanism and heat treatment process in ZASN glass, along with fine adjustability of luminescent properties,suggests potential for applications in cyan-green luminescent materials.
Downlink Spectrum Sharing of Heterogeneous Communication Systems in LEO Satellite Network
Yun, Jihyeon,An, Taegun,Jo, Haesung,Ku, Bon-Jun,OH, Dae-Sub,Joo, Changhee 한국통신학회 2022 Journal of communications and networks Vol.24 No.6
We study downlink spectrum sharing in low earthorbit (LEO) satellite networks, where wide beam coverage andside lobe beam make it hard to manage mutual interferencebetween satellites. As a first step, we consider a two-satellitesystem of control satellite and interference satellite, which sharethe same frequency spectrum range and are located close enoughto have interference each other. We investigate resource allocationstrategy for the control satellite to maximize its throughputperformance while satisfying interference constraints. Assumingthat the control satellite has no prior knowledge about thebehavior of the interference satellite, we develop online frequencyallocation algorithms that successfully manage the interferenceby employing a learning-based design with UCB index. Underthe proposed algorithms, we can maximize throughput of thecontrol satellite while constraining interference at the interferencesatellite as well as at the control satellite, without any directinformation exchange with the interference satellite. Throughsimulations, we demonstrate that the proposed schemes achievehigh throughput performance satisfying interference constraints.
Jihyeon Yun,Sushmit Sharma Bhattarai,Hyunhwan Kim,나일호 한국아스팔트학회 2023 한국아스팔트학회지 Vol.13 No.2
In this research, the viscoelastic properties and microstructure of asphalt binders modified with two Crumb rubber modifiers (CRM), #50 and #30, using mechanical tests and Atomic force microscopy (AFM) were evaluated. Each modified asphalt binder was prepared by mixing 5% and 15% CRM. The Separation index (SI) of each binder was calculated using rheological measurements (G*/sin δ and % recovery). Additionally, AFM was employed to capture topographical images of the CRM asphalt binders, aiding in a comprehensive assessment for SI. The key findings include (1) enhanced rheological properties in the lower sections of CRM asphalt binders, attributed to density differences between the CRM and the base asphalt; (2) lower SI in #50 CRM binders, correlating with their more uniform particle distribution; and (3) microstructural distinctions observed via AFM, with #50 CRM binders showing uniformity across top and bottom layers, unlike #30 CRM binders. These insights demonstrate that microstructural images can be an effective tool for assessing the storage stability of CRM asphalt binders, thereby contributing significantly to a more in-depth understanding of their stability.
과학적 창의성 관점에서 살펴본 영재교육종합 데이터베이스(GED)의 초등 과학영재교육 프로그램 특징 분석
윤지현 ( Yun Jihyeon ),강훈식 ( Kang Hunsik ) 한국초등과학교육학회 2021 초등과학교육 Vol.40 No.2
This study analyzes the characteristic of elementary science-gifted education winner programs in Gifted Education Database (GED) focusing on scientific creativity. For this purpose, an analysis framework to analyze the programs was developed and a total of 840 inquiry activities from 55 winner programs were analyzed according to the analysis framework. The analysis of the results reveal that ‘scientific inquiry skill’ of the five scientific creativity components was most frequently included in the activities. ‘Scientific knowledge content’ and ‘creative thinking’ were also frequently included. However, ‘problem solving ability’ and ‘common factor’ were a little included. In the aspects of integration, the integrations between two or three components with five or eight types were frequently found. No integrations were also frequently included although less than the previous categories. The integrations among four with four types or five components were also slightly found. ‘Scientific knowledge content’, ‘scientific inquiry skills’, and ‘creative thinking’ with other components were more frequently found. However, the integrations of ‘common factor’ or ‘problem solving ability’ with the other components were less frequently found. Educational implications of these findings are discussed.
F1/F2의 변화가 한국어 /오/, /우/ 모음의 지각판별에 미치는 영향
윤지현(Yun, Jihyeon),성철재(Seong, Cheoljae) 한국음성학회 2013 말소리와 음성과학 Vol.5 No.3
This study examined the perception of two Korean vowels using F1/F2 manipulated synthetic vowels. Previous studies indicated that there is an overlap between the acoustic spaces of Korean /o/ and /u/ in terms of the first two formants. A continuum of eleven synthetic vowels were used as stimuli. The experiment consisted of three tasks: an /o/ identification task (Yes-no), an /u/ identification task (Yes-no), and a forced choice identification task (/o/-/u/). ROC(Receiver Operating Characteristic) analysis and logistic regression were performed to calculate the boundary criterion of the two vowels along the stimulus continuum, and to predict the perceptual judgment on F1 and F2. The result indicated that the location between stimulus no.5 (F1 = 342Hz, F2 = 691Hz) and no.6 (F1 = 336Hz, F2 = 700Hz) was estimated as a perceptual boundary region between /o/ and /u/, while stimulus no.0 (F1=405Hz, F2=666Hz) and no.10 (F1=321Hz, F2=743Hz) were at opposite ends of the continuum. The influence of F2 was predominant over F1 on the perception of the vowel categories.
/오/-/우/ 합성모음 연속체에 대한 중국인 한국어 학습자의 청지각적 경계
윤지현(Yun, Jihyeon),김은경(Kim, EunKyung),성철재(Seong, Cheoljae) 한국음성학회 2015 말소리와 음성과학 Vol.7 No.4
The present study examines the auditory boundary between Korean /o/ and /u/ on a synthesized vowel continuum by Chinese learners of Korean language. Preceding researches reported that the Chinese learners have difficulty pronouncing Korean monophthongs /o/ and /u/. In this experiment, a nine-step continuum was resynthesized using Praat from a vowel token from a recording of a male announcer who produced it in isolated form. F1 and F2 were synchronously shifted in equal steps in qtone (quarter tone), while F3 and F4 values were held constant for the entire stimuli. A forced choice identification task was performed by the advanced learners who speak Mandarin Chinese as their native language. Their experiment data were compared to a Korean native group. ROC (Receiver Operating Characteristic) analysis and logistic regression were performed to estimate the perceptual boundary. The result indicated the learner group has a different auditory criterion on the continuum from the Korean native group. This suggests that more importance should be placed on hearing and listening training in order to acquire the phoneme categories of the two vowels.