• Journal of Educational Research in Mathematics
• /
• v.27 no.4
• /
• pp.833-855
• /
• 2017

This study aims to reinvestigate the reason for introducing radian as a new unit to express the size of angles, what is the meaning of radian measures to use arc lengths as angle measures, and why is the domain of trigonometric functions expanded to real numbers for expressing general angles. For this purpose, it was conducted historical, mathematical and applied mathematical analyzes in order to research at multidisciplinary analysis of the radian concept. As a result, the following were revealed. First, radian measure is intrinsic essence in angle measure. The radian is itself, and theoretical absolute unit. The radian makes trigonometric functions as real functions. Second, radians should be aware of invariance through covariance of ratios and proportions in concentric circles. The orthogonality between cosine and sine gives a crucial inevitability to the radian. It should be aware that radian is the simplest standards for measuring the length of arcs by the length of radius. It can find the connection with sexadecimal method using the division strategy. Third, I revealed the necessity by distinction between angle and angle measure. It needs justification for omission of radians and multiplication relationship strategy between arc and radius. The didactical suggestions derived by these can reveal the usefulness and value of the radian concept and can contribute to the substantive teaching of radian measure.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2013.10a
• /
• pp.67-68
• /
• 2013

In this paper, a super wideband printed dipole antenna operating in the band of 1-15 GHz is studied. A semi-circular-shaped dipole element is used to obtain a super wideband characteristic. Optimal design parameters are obtained by analyzing the effects of the gap between the two arms of the semi-circular-shaped dipole and the radius of the semi-circle on the input reflection coefficient and gain characteristics. The optimized printed semi-circular-shaped dipole antenna is fabricated on an FR4 substrate with a dimension of $100mm{\times}100mm$. Experimental results show that the antenna has a desired super wideband characteristic with a frequency band of 1-15 GHz (bandwidth ration 15:1, 175%) for a VSWR < 2.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.15 no.4
• /
• pp.85-93
• /
• 2011

A parametric study is conducted for the design of segmented arc plasma torch with the input power and current of 0.4 MW and 300 A, respectively. For this purpose, we use the analytical relationship between input power, current condition, plasma temperature, inner diameter (R) and length (L) of the torch constrictor based on arc channel model. The results reveal that arc plasma temperatures increase monotonically as ��L increases or R decreases for the ranges of R ${\leq}$ 7.5 mm and L ${\leq}$ 1.25 m. For larger valuse of ��R and L than 7.5 mm and 1.25 m, respectively, however, they show non-linear behavior corresponding to the variations of ��L, which stands for the generation of unstable arc plasma. From this parametric study, optimum ranges of R and L are suggested as 5.5 mm ${\leq}$ R ${\leq}$ 7.5 mm and 0.25 m ${\leq}$ L ${\leq}$ 0.5 m for 0.4 MW class segmented arc plasma torch, under which stable arc plasma can be achieved at the input currents of ~300 A.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.14 no.5
• /
• pp.431-436
• /
• 2003

In this paper, simulation results of an electromagnetic field and mode distributions in a cylindrical reverberation chamber were presented. Reverberation chamber is an alternative test facility for a semi anechoic chamber, which is widely used for the analysis and measurement of electromagnetic interference and immunity tests. The method of computing the number of modes in a cylindrical reverberation chamber was presented and the number of modes in a cylindrical reverberation chamber with the same volume was compared with the different ratio of radius to height. The FDTD method was used to produce field characteristics inside of rectangular, right-angled isosceles triangular, and cylinder type reverberation chambers with the same test volume.

• The KIPS Transactions:PartA
• /
• v.12A no.1 s.91
• /
• pp.7-12
• /
• 2005

Scattered look-ahead(SLA) pipelining method can be efficiently used for high-speed or low-power applications of digital II R filters. Although the pipelined filters are guaranteed to be stable by this method, these filters suffer from large roundoff noise when the poles are crowded within some critical regions. An angle and radius constrained II R fille. design approach using modified Remez exchange algorithm and least squares algorithm is proposed to avoid tight pole-crowding in pipelined filters, resulting in improved frequency responses and reduced coefficient sensitivities. Experimental results demonstrate that our proposed method leads to chip area reduction by $33{\%}$ and low power by $45{\%}$ against the conventional method.

• Composites Research
• /
• v.13 no.5
• /
• pp.18-30
• /
• 2000

In order to optimize the design of unidirectional fiber reinforced composite C-rings, a viscoelastic load relaxation behavior was analyzed under a point load. Initially, the deflection and bending stiffness were calculated based on the elastic beam theory and the viscoelastic relaxation and creep behaviors were derived from the elastic solution using the correspondence theorem. Besides the orthotropic mechanical properties of the composite, asymmetric mechanical property due to the different tensile and compressive properties were also considered. Except the deviation affected by the relatively large thickness of the specimen compared to the radius, the calculated relaxation showed good agreement with the experimental result.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.3
• /
• pp.337-344
• /
• 1989

The upper bound elemental technique (UBET) is used to simulate the bulk flow characteristics in axisymmetric closed die forging process. Internal flow inside the cavity is predicted using a kinematically admissible velocity field that minimizes the rate of energy consumption. Application of the technique includes an assessment of the formation of flash and of degree of filling in rib-web type cavity using billets with various aspect rations. The technique considering bulging effect is performed in an incremental manner. The results of simulation show how it can be used for the prediction of forging load, metal flow, and free surface profile. The experiments are carried out with plasticine. There are good agreements in forging load and material flow in cavity between the simulation and experiment. The developed program using UBET can be effectively applied to the various forging problems.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.338-338
• /
• 2012

유기물을 이용하여 제작한 비휘발성 메모리 소자는 저전력으로 구동하고 공정이 간단할 뿐만아니라 구부림이 가능한 소자를 만들 수 있다는 장점 때문에 많은 연구가 진행되고 있다. 비록 다양한 유기물 나노 클러스터를 포함한 고분자 박막을 사용한 비휘발성 메모리 소자에 대한 연구가 많이 진행되었으나 [6,6]- phenyl-C85 butyric acid methyl ester (PCBM) 나노 클러스터가 고분자 박막에 분산되어 있는 메모리 소자의 휘어짐에 따른 전기적 특성의 변화에 대한 것은 연구되지 않았다. 본 연구에서는 스핀코팅 방법으로 PCBM 나노 클러스터가 polymethyl methacrylate (PMMA) 박막에 분산되어 있는 소자를 제작하여 휘어짐에 따른 전기적 특성의 변화에 대한 관찰을 수행하였다. 소자를 제작하기 위해서 PCBM 나노 클러스터와 PMMA를 클로로벤젠에 용해시킨 후에 초음파 교반기를 사용하여 PCBM 나노 클러스터와 PMMA가 고르게 섞인 용액을 형성하였다. 전극이 되는 Indium Tin Oxide (ITO) 유리기판 위에 PCBM 나노 클러스터와 PMMA가 섞인 용액을 스핀 코팅하고, 열을 가해 용매를 제거하여 PCBM 나노 클러스터가 PMMA에 분산되어 있는 박막을 형성하였다. PCBM 나노 클러스터가 분산된 PMMA 박막 위에 Al을 상부전극으로 열증착하여 메모리 소자를 완성하였다. 제작한 소자의 휘어짐에 따른 전기적 특성을 알아보기 위해서 10 mm 의 반지름을 갖는 휘어진 홀더를 제작 한 후에 소자를 구부리기 전과 후의 전류-전압 (I-V)을 각각 측정하였다. 또한 소자의 휘어짐에 따른 포획된 전하유지능력과 안정성을 알아보기 위해 $1{\times}105$번의 반복적인 읽기 전압을 가한 후 전기적 특성을 측정하였다. 실험 결과들을 토대로 메모리 소자의 휘어짐에 따른 전기적 특성 변화에 대해서 분석하고 그 원인에 대해서 규명하였다.

• Composites Research
• /
• v.26 no.2
• /
• pp.85-90
• /
• 2013

This paper presents the fabrication and 3-point flexion testing of carbon fiber reinforced polymer (CFRP) composite face/aluminum honeycomb core sandwich panels. Specimen sandwich panels were fabricated with three honeycomb types (3.18 mm, 4.76 mm, and 6.35 mm cell size) and three panel radii (flat, r = 1.6 m, r = 1.3 m). The curved sandwiches were fabricated normally with the core in the W-direction. The tensile mechanical properties of the CFRP $2{\times}2$ twill fabric face laminate were evaluated (modulus, strength, Poisson's ratio). The measured values are comparable to other CFRP fabric laminates. The flat sandwich 3-point flexion test core shear strength results were 11-30% lower than the manufacturer published data; the test set-up used may be the cause. With a limited sample size, the 1.3 meter panel curvature appeared to cause a 0.8-3.8% reduction in ultimate core shear strength compared to a flat panel.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.45 no.6
• /
• pp.8-12
• /
• 2008

A ring resonator based band-pass filter enabling enhanced sideband suppression was proposed and demonstrated. It is composed of a single-ring based band-pass section combined with a band-rejection section based on two different coupled rings. The sideband region of the transfer characteristics of the first band-pass filter section was selectively suppressed by means of the band-rejection section without causing any excessive insertion loss. As a result, the overall transfer characteristics of the proposed filter was unproved so that its sideband suppression was elevated to allow for sharper roll-off and narrower bandwidth. In this work, a conventional single-ring band-pass filter and a proposed filter including the band-rejection section were designed and fabricated. As for the achieved device performance, with the center frequency at about 4 GHz, the sideband suppression ratio was increased as much as 8 dB and the 3-dB bandwidth was reduced from 98 MHz to 48 MHz by about 51% with no remarkable excessive insertion loss as expected. And the quality factor of the device was increased by about 105%.