• 대한공업교육학회지
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• 제30권1호
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• pp.106-119
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• 2005

Many problems with the offline class, which is the traditional education type in corporations or universities, were indicated and people hoped that e-learning, which is web-based instruction, would solve these problems. However, e-learning also has weak points in that it should be self-paced and media-based in many ways. Therefore, when considering the good and weak points of offline classes and e-learning, blended learning seems to be necessary. Until now, blended learning has usually been used in corporations, and there have been almost no studies on the effectiveness or management of blended learning in universities. Thus, in this study, I would like to design blended classes, manage them at the level of university classes, and verify the effectiveness of blended classes, by comparing academic achievement, student participation, and student satisfaction. The subject students who signed up for Computer & Technology at C University in 2005 were divided into three study groups: offline class, online class, and blended class. The offline class was taught using the traditional class teaching method. For the online class and the blended class, multimedia contents were developed and a different LMS was used. The results of 13 weeks of teaching are as follows. For the academic achievement in the offline, online and blended classes, there was no statistically significant difference (f=2.387, p=.096). But when comparing the average achievement, the average of the blended class was higher than that of the other classes, so that it can be said that the blended class has positive effects on academic achievement. Second, when comparing the learners' participation in the online class and the blended class, the total posts were 85 and 138 respectively, which shows a considerable difference. The hit counts for each post in the online class and the blended class are 10 and 20, respectively. Moreover, the login counts for subjects are 3 in the online class and 4 in the blended class. In the questionnaire for the students' academic satisfaction in the online class and the blended class, all of the 15 items showed higher satisfaction in the blended class. Considering all these results, if adequate media are properly combined, the blended class is better than either the pure online class or the pure offline class.

• 대한수학회지
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• 제55권2호
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• pp.343-372
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• 2018

Let K be an imaginary quadratic field with ring of integers ${\mathcal{O}}_K$. Let E be an elliptic curve with complex multiplication by ${\mathcal{O}}_K$, and let $h_E$ be the Weber function on E. Let $N{\in}\{2,3,4,6\}$. We show that $h_E$ alone when evaluated at a certain N-torsion point on E generates the ray class field of K modulo $N{\mathcal{O}}_K$. This would be a partial answer to the question raised by Hasse and Ramachandra.

• Journal of Power Electronics
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• 제18권1호
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• pp.277-288
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• 2018

Wireless inductive power transfer (IPT) technology is used in many applications today. A compact and high-frequency primary side inverter is one of the most important parts of a WPT system. In this study, a modified class EF-type voltage-fed multi-resonant inverter has been proposed for WPT application at a frequency range of 85-100 kHz. Instead of an infinite input choke inductor, a resonant inductor is used to reduce loss and power density. The peak voltage stress across the MOSFET has been reduced to almost 60% from a class-E inverter using a passive clamping circuit. A simple yet effective design procedure has been presented to calculate the various component values of the proposed inverter. The overall system is simulated using MATLAB/SimPowerSystem to verify the theoretical concepts. A 500-W prototype was built and tested to validate the simulated results. The inverter exhibited 90% efficiency at nearly perfect alignment condition, and efficiency reduced gradually with the misalignment of WPT coils. The proposed inverter maintains zero-voltage switching (ZVS) during considerable load changes and possesses all the inherent advantages of class E-type inverters.

• 호남수학학술지
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• 제15권1호
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• pp.75-85
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• 1993

For A and B, $-1{\leq}B<A{\leq}1$, let P[A, B] be the class of functions p analytic in the unit disk E with P(0) = 1 and subordinate to $\frac{1+Az}{1+Bz}$. We introduce the class $T_{\alpha}[A,B]$ of functions $f:f(z)=z+\sum\limits_{n=2}^{{\infty}}a_nz^n$ which are analytic in E and for $z{\in}E$, ${\alpha}{\geq}0$, $[(1-{\alpha}){\frac{f(z)}{z}}+{\alpha}f^{\prime}(z)]{\in}P[A,B]$. It is shown that, for ${\alpha}{\geq}1$, $T_{\alpha}[A,B]$ consists entirely of univalent functions and the radius of univalence for $f{\in}T_{\alpha}[A,B]$, $0<{\alpha}<1$ is obtained. Coefficient bounds and some other properties of this class are studied. Some radii problems are also solved.

• Journal of Periodontal and Implant Science
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• 제31권4호
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• pp.689-711
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• 2001

The purpose of this study was to compare clinical results of guided tissue regeneration(GTR) using either a nonresorbable ePTFE membrane or a resorbable membrane made from a synthetic copolymer of glycolide and lactide(PLGA) in the treatment of human class Ⅱ furcation defects. The ePTEE membranes were applied to 16 patients with maxillary molar buccal class Ⅱ furcation defects as Group I, PLGA membranes were applied to 15 patients with maxillary molar buccal class Ⅱ furcation defects as Group Ⅱ, ePTFE membranes were applied to 20 patients with mandibular molar buccal class Ⅱ furcation defects as Group Ⅲ and PLGA membranes were applied to 20 patients with mandibular molar buccal class Ⅱ furcation defects as Group Ⅳ and bone graft materials(DFDBA) were applied in all groups. Probing depth, gingival recession, clinical attachment level, tooth mobility and sulcus bleeding index(SBI) were measured at baseline, 3, 6 and 12months postoperatively. In addition, membrane exposure levels were measured at surgery, 1, 2 and 6weeks postoperatively and postoperative complications were evaluated. The results were as follows: In all groups, there were statistically significant differences in probing depth reduction, gain of clinical attachment and mobility reduction at values of 3, 6 and 12months postoperatively compared to values of baseline, whereas no significant differences in SBI except Group I and gingival recession(p<0.05). Membrane exposure levels were increased at 1, 2 and 6weeks postopratively compared to value of baseline in Group I(p<0.05). There were no statistically significant differences between ePTFE and PLGA membrane in probing depth, clinical attachment level and SBI. There were minimal gingival recession and membrane exposure in Group Ⅳ and pain and swelling were the most common postoperative complications in Group Ⅱ, Ⅲ(p<0.05). In conclusion, this study showed that both nonresorbable membrane and resorbable membrane were effective similarly in the treatment of class Ⅱ furcation defects, without statistical differences in clinical measurements.

• 한국통신학회논문지
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• 제40권1호
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• pp.9-15
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• 2015

S급 전력 증폭기 응용을 위한 CMOS 대역 통과 델타 시그마 변조기(BPDSM)와 캐스코드 E급 전력 증폭기를 설계 및 제작 하였다. 대역 통과 델타 시그마 변조기는 1 GHz의 샘플링 주파수로 250 MHz의 입력 신호를 펄스폭 변조 방식의 디지털 신호로 변조하며 양자화 잡음을 효과적으로 제거하였다. 대역 통과 델타 시그마 변조기는 25 dB의 SQNR을 가지며 1.2 V 전원 전압에서 24 mW의 전력을 소비한다. 캐스코드 E급 전력 3.3V 전원에서 동작하며 최대 18.1 dBm의 출력 전력을 가지며 25%의 드레인 효율을 보였다. 두 회로 모두 동부 0.11 um RF CMOS 공정으로 제작되었다.

• 호남수학학술지
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• 제20권1호
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• pp.79-88
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• 1998

In this paper we define the concept of $Fr{\acute{e}}chet$ function algebras on hemicompact spaces. So we show that under certain condition they can be represented as a projective limit of Banach function algebras. Then the class of $Fr{\acute{e}}chet$ Lipschitz algebras on hemicompact metric spaces are defined and their relations with the class of lipschitz algebras on compact metric spaces are studied.

• Educational Technology International
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• 제19권2호
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• pp.175-197
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• 2018

Flipped classroom (FC) has gained attention as an active learning approach. Designing effective out-of-class activities to help prepare students for in-class activities is fundamental for successful implementation of FC. This study investigated the effectiveness of Goal-Based Scenarios (GBS) for out-of-class learning in FC. Four out of twelve units in a medical humanities course for Year 2 medical students was redesigned into a FC format, where e-learning modules were designed using a GBS approach for out-of-class activities and classroom debates were implemented for in-class activities. The other eight units were delivered in a conventional classroom debate format, which included reading text materials as pre-class assignments. A formative evaluation study was conducted using questionnaires and interview methods and students' academic achievements were evaluated by comparing their pre- and post-test scores between FC and conventional units. Students had positive perceptions of the e-learning modules in GBS approach and preferred the structure of learning in the FC format. Students' pre-test scores were slightly higher in the FC units, yet their post-test scores were comparable with conventional units. This study illustrates students' perceptions that the learning was bettered structured in FC and that the out-of-class learning using the GBS approach helped them better prepared for in-class activities.

• Journal of Electrochemical Science and Technology
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• 제1권1호
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• pp.19-24
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• 2010

Alloying degree is an important structural factor of PtRu catalysts for direct methanol fuel cells (DMFC). In this work, carbon supported PtRu catalysts were synthesized by reduction method using anhydrous ethanol as a solvent and $NaBH_4$ as a reducing agent. Using anhydrous ethanol as a solvent resulted in high alloying degree and good dispersion. The morphological structure and crystallanity of synthesized catalysts were characterized by X-ray diffraction (XRD), high resolution transmission electron microscope (HR-TEM). CO stripping and methanol oxidation reaction were measured. Due to high alloying degree catalyst prepared in anhydrous ethanol, exhibited low onset potential for methanol oxidation and negative peak shift of CO oxidation than commercial sample. Consequently, samples, applying ethanol as a solvent, exhibited not only enhanced CO oxidation, but also increased methanol oxidation reaction (MOR) activity compared with commercial PtRu/C (40 wt%, E-tek) and 40 wt% PtRu/C prepared in water solution.

• 한국학교수학회논문집
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• 제22권4호
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• pp.395-413
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• 2019

본 연구는 블렌디드 이러닝이 공과대학 학생들의 공학수학 교수·학습에 미치는 영향을 알아보기 위하여 M대학교 기계공학과 3학년 42명을 연구대상자로 선정하였다. 본 연구에서 공학수학 교과목에 블렌디드 이러닝을 적용한 수업은 오프라인에서는 전체 수강생을 대상으로 강의실에서 면대면 수업의 형태로 진행되었고, 수업이 진행되는 동안 수업의 전 과정을 녹화한 후 녹화된 동영상을 LMS에 탑재하여 온라인 상에서 개별 학습이 이루어지도록 하였다. 한 학기 동안 오프라인과 온라인을 혼합한 형태로 수업을 진행하면서 학습자들의 온라인 자료의 활용 실태 및 오프라인 수업에서의 학생들의 태도의 변화 등을 조사하였다. 그 결과 다음과 같은 결론을 얻었다. 첫째, 공학수학에 적용한 블렌디드 이러닝은 학생들의 자기주도적이고 개별화된 학습에 긍정적인 영향을 준다. 둘째, 블렌디드 이러닝은 공학수학 교수·학습에 긍정적인 영향을 준다. 셋째, 블렌디드 이러닝은 학생들의 수업 만족도에 긍정적인 영향을 준다.