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이학준 ( Lee¸ Hakjun ),우정한 ( Woo¸ Jeonghan ) 대구대학교 한국특수교육문제연구소 2021 특수교육저널 : 이론과 실천 Vol.22 No.3
[목적] 이 연구의 목적은 특수교육에서 코로나19 연구현황을 분석하는 것이다. [방법] 이를 위하여 국내 특수교육에서 진행된 코로나19 학술지 논문 17편을 분석하였다. [결과] 그 결과는 다음과 같다. 특수교육에서 코로나19는 비대면, 비접촉, 사회적 거리 두기라는 특성을 보여주었다. 첫째, 연구 대상은 특수교사와 장애 학생이 많았다. 둘째, 연구주제는 장애학생과 특수교사의 온라인수업 경험에 관한 연구가 다수를 차지하였고 그 외는 인식 및 실태, 시사점 순이다. 셋째, 연구 방법은 질적연구가 다른 연구 방법보다 많았다. 향후 연구과제는 온라인수업 인식 및 실태, 보편적 학습설계 기반 수업, 정책적 지원 등이다. [결론] 특수교육에서 코로나19 연구현황 분석은 특수교육에서 해결해야 할 우선순위를 결정하는데 기초자료가 된다. 현재 특수교육 분야에서 절실한 고민은 코로나19 상황에서의 특수교육대상자에 대한 효과적인 수업일 것이다. 그 방법은 교사와 학생 그리고 학부모 등 모든 구성원이 함께 해결해야 할 과제라고 할 수 있다. [Purpose] The purpose of this study was to review the current status of research on special education during the COVID-19 pandemic in Korea. [Method] The research method was a quantitative research method. [Result] During the COVID-19 pandemic in Korea, special education had characteristics of non-face-to-face, non-contact, and social distancing. Most of the studies are related to online classes, while others are related to a variety of different topics. [Conclusion] The results of this study suggest that pending issues of special education should be prioritized during the COVID-19 pandemic. The most urgent task is to ensure effective classes for all special education students during the pandemic. This is a problem that all relevant parties, including teachers, students, and parents, must solve together.
Hakjune Lee,Duk-Jae Woo,Sangwook Nam IEEE 2016 IEEE antennas and wireless propagation letters Vol.15 No.-
<P>A novel compact and broadband asymmetric coplanar wave guide (ACPW) antenna is presented. A method to extend the bandwidth of a metamaterial-inspired antenna based on a composite right/left-handed transmission line (CRLH-TL) and a modified ground plane is proposed. The ACPW antenna has a broadband characteristic by placing the zeroth-order resonance (ZOR), first-positive-order resonance (FPOR) of short-ended CRLH-TL and the modified ground plane's two resonances, which are half and one lambda resonances, at all different frequencies with proper frequency intervals. The prototype of the proposed antenna has been implemented and measured. The measured -10-dB fractional bandwidth is 109.1% (from 2.69 to 9.15 GHz) with high efficiency of over 65% and a low profile of 0.32 lambda(0) x 0.19 lambda(0) (where lambda(0) is the free-space wavelength at the first resonant frequency).</P>
Hakjun Lee,Jinsuk Choi,Wookyong Kwon 제어로봇시스템학회 2022 제어로봇시스템학회 국제학술대회 논문집 Vol.2022 No.11
While operating a mobile manipulator on uneven terrain, the manipulator experiences severe degradation in control performance owing to an unexpected motion. To resolve this problem, this paper proposes an effective composite control scheme for the mobile manipulator with a robust control scheme and an inertial measurement unit (IMU) sensor. First, the IMU sensor is used to estimate the tilt angle of the robot and compensate for the effects of these rotational movements on the end-effector. In addition, we employ a robust control based on a time delay-control with a disturbance observer to compensate for model uncertainty and exogenous disturbance caused by uneven terrain. It is demonstrated through a simulation that the proposed control scheme compensates well for the effect of the uneven terrain on the mobile manipulator.
Real-Time Optimal State Estimation Scheme With Delayed and Periodic Measurements
Lee, Hakjun,Kang, Suwon,Han, Soohee IEEE 2018 IEEE transactions on industrial electronics Vol.65 No.7
<P>This paper proposes an efficient real-time optimal estimation scheme that uses accurate but delayed measurements obtained periodically from high-performance sensing devices. For real-time optimal estimation, we employ two Kalman filters: one to conventionally estimate the current state and the other to precompute for the future state estimation to be carried out, when a new, accurate but delayed measurement arrives. The precomputing Kalman filter does the necessary computation in advance, for the future state estimation, from the available measurements for distributing the computational burden over time, thereby obtaining an optimal estimate in real time. By optimally incorporating accurate but delayed measurements, the optimality is preserved at all times, without imposing a heavy computational burden in a short sampling time interval. It is demonstrated through experiments that the proposed scheme can significantly improve the estimation performance with the least detriment to the real-time computation and memory size, when delayed and periodic measurements are available.</P>
A Dual-Polarized 1-D Tightly Coupled Dipole Array Antenna
Hakjune Lee,Sangwook Nam Institute of Electrical and Electronics Engineers 2017 IEEE transactions on antennas and propagation Vol.65 No.9
<P>A dual-polarized 1-D tightly coupled dipole array (TCDA) antenna is proposed in this paper. To apply the TCDA design concept to a 1-D array, we place a conducting wall with slits and ferrite sheets along the 1-D dipole array. The simulated dual-polarized 1-D infinite TCDA antenna has a wide overlapped bandwidth of 2.83:1 (from 1 to 2.83 GHz) with VSWR < 2, high isolation (> 25 dB) between the horizontal and vertical polarizations (VPs), and low height of 1/5 lambda at the lowest operating frequency. A prototype of the proposed array is fabricated and measured, which consists of nine horizontal polarization (HP) dipoles and eight VP dipoles interleaved between the HP dipoles. The measured results show high gains > 7.2 dB when scanning up to 30 degrees and a wide half-power beamwidth in the yz plane > 61 degrees over the operating frequency band for both polarizations, consistent with the simulation result.</P>
Cylindrical Tightly Coupled Dipole Array Antenna
Hakjune Lee,Minyoung Yoon,Sangwook Nam 한국전자파학회JEES 2019 Journal of Electromagnetic Engineering and Science Vol.19 No.2
A cylindrical tightly coupled dipole array antenna (C-TCDA) based on Munk’s planar TCDA theory, the elements of which are placed on the surface of a cylinder, is introduced and analyzed in this study. The explicit field components of the transverse electromagnetic (TEM) waves existing in the C-TCDA for both polarizations are given. Moreover, the embedding impedance characteristics of the CTCDA are presented and compared with those of planar TCDA. Analysis results show that the C-TCDA has similar impedance characteristics to the planar TCDA and thus can be implemented in a similar manner. The design of a dual-polarized omnidirectional octagonal TCDA, which has a 3.08:1 bandwidth (from 0.73 ㎓ to 2.25 ㎓) with a voltage standing wave radiation (VSWR) of less than 2 and a low gain variation of less than 1.8 ㏈ at broadside for both polarizations, is also proposed. When scanning up to ±30° in the θ-direction, the array operates in the same frequency band with a VSWR of less than 2.05 and a low gain variation of less than 2 ㏈ for both polarizations.
Lee, Yongwoo,Shabbir, Saira,Lee, Sinyoung,Ahn, Hyunsoek,Rhee, Hakjune The Royal Society of Chemistry 2015 GREEN CHEMISTRY Vol.17 No.6
<P>Poly(NIPAM-<I>co</I>-4-VP) undergoes a phase transition at the low critical solution temperature with a change from the hydrophilic to the hydrophobic core in a hydrophilic solvent. Palladium nanoparticles supported on such a thermoresponsive polymer support were demonstrated to catalyze the Tsuji–Trost reaction for the arylation of various cinnamyl carbonates by arylboronic acids. Therefore, a protocol developed using mild reaction conditions demonstrates the recyclability of the catalyst in an eco-friendly solvent such as water.</P> <P>Graphic Abstract</P><P>Palladium nanoparticles were supported on a thermoresponsive polymer and used as catalysts for the allylic arylation of cinnamyl carbonates in water. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5gc00745c'> </P>
Lee Hakjun,Hwang Kyo Min,Kim Ki Ju,Song You Na,Kim Young Kwan,Kim Taekyung 한국정보디스플레이학회 2022 Journal of information display Vol.23 No.1
In phosphor-sensitized-fluorescent organic light-emitting diodes (PSF-OLEDs), triplet excitons generated in the emitting layer (EML) are harvested by the sensitizer and the excitonic energy is efficiently transferred to the fluorescent dopant molecules. Since a phosphorescent sensitizer is typically doped at around 10 wt.%, the sensitizer not only affects cascade energy transfer but also electrical transporting in the PSF-OLEDs. However, the electrical role of phosphorescent metal complex molecules in the EML is unclear. In this study, we report the impact of the phosphorescent sensitizer on the electrical properties of PSF-OLEDs. Through a comprehensive analysis using impedance spectroscopy in conjunction with current density (J)-voltage (V)-luminance (L) properties of the PSF-OLED, it was revealed that 10 wt.% phosphorescent sensitizer forms an electron transporting pathway inside the EML. Thus, the sensitizer molecules transform a unipolar single host into a bipolar mixed host. In other words, the phosphorescent sensitizer is an n-type host in the PSF-OLEDs. As a result, the charge balance and the operating voltage were simultaneously and significantly improved in the PSF-OLEDs.