• 대한소아치과학회지
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• 제31권2호
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• pp.228-235
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• 2004

하악 과두의 발달과 증식은 측두하악관절 부위의 생역학적 환경의 변화에 따라 변경될 수 있다. 이 부위에 전달되는 생역학적 하중은 섭취하는 음식물의 경도를 다르게 함으로써 변화시킬 수 있다. 이번 연구의 목적은 성장 중인 쥐에서 부드러운 음식물의 섭취에 의해 저작력을 변화시키는 것이 하악 과두의 해면골의 형태를 변화시킬 수 있는지 미세전산화 단층촬영을 이용하여 분석하는 것이었다. 생후 21일 된 C57BL/6 쥐 36마리를 무작위로 두 그룹으로 나누었다. 8주 동안 대조군의 쥐들은 일반적인 딱딱한 덩어리의 사료를, 실험군의 쥐들은 덩어리의 사료를 잘게 갈은 후 물과 섞어 부드럽게 만들어 먹였다. 또한 실험군의 쥐들의 하악 절치를 일주일에 두 번씩 잘라서 짧게 만들었다. 8주 후 모든 쥐들을 희생하여 우측 하악 과두를 준비하였다. 미세전산화 단층촬영과 삼차원 영상 분석프로그램을 이용하여 하악 과두 해면골의 bone volume(BV), bone surface(BS), total volume(TV) bone volume fraction(BV/TV), surface to volume ratio(BS/BV), trabecular thickness(Tb. Th.), structure model index(SMI)와 degree of anisotropy(DA)를 측정하고 이들 값으로부터 trabecular number(Tb. N.)와 trabecular separation (Tb. Sp.)을 계산하였다 미세전산화 단층영상을 얻은 후 하악 과두의 조직 표본을 만들었다. 연구 결과는 다음과 같았다. 1. Bone volume fraction(BV/TV), trabecular thickness(Tb. Th.)와 trabecular number(Tb. N.)가 대조군에 비해 부드러운 음식을 먹인 실험군에서 유의하게 감소되었다(p<0.05). 2. Trabecular separation(Tb. Sp.)은 부드러운 음식을 먹인 실험군에서 유의하게 증가하였다(p<0.05). 3. Surface to volume ratio(BS/BV), structure model index(SMI), degree of anisotropy (DA)는 두 군 사이에 유의한 차이를 보이지 않았다(p>0.05). 4. 조직 절편을 관찰한 결과, 부드러운 사료를 먹인 실험군에서 하악 과두의 연골층의 증식 층과 전체 두께가 상당히 감소하였다.

• Advances in concrete construction
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• 제9권3호
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• pp.235-248
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• 2020

Progressive collapse in a structure occurs when load bearing members are failed and the adjoining structural elements cannot resist the redistributed forces and fails subsequently, that leads to complete collapse of structure. Recently, construction using precast concrete technology is adopted increasingly because it offers many advantages like faster construction, less requirement of skilled labours at site, reduced formwork and scaffolding, massive production with reduced amount of construction waste, better quality and better surface finishing as compared to conventional reinforced concrete construction. Connections are the critical elements for any precast structure, because in past, major collapse of precast structure took place because of connection failure. In this study, behavior of four different precast wet connections with U shaped reinforcement bars provided at different locations is evaluated. Reduced 1/3^rd scale precast beam column assemblies having two span beam and three columns with removed middle column are constructed and examined by performing experiments. The response of precast connections is compared with monolithic connection, under column removal scenario. The connection region of test specimens are filled by cast-in-place micro concrete with and without polypropylene fibers. Performance of specimen is evaluated on the basis of ultimate load carrying capacity, maximum deflection at the location of removed middle column, crack formation and failure propagation. Further, Finite element (FE) analysis is carried out for validation of experimental studies and understanding the performance of structural components. Monolithic and precast beam column assemblies are modeled using non-linear Finite Element (FE) analysis based software ABAQUS. Actual experimental conditions are simulated using appropriate boundary and loading conditions. Finite Element simulation results in terms of load versus deflection are compared with that of experimental study. The nonlinear FE analysis results shows good agreement with experimental results.

• 한국전자파학회논문지
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• 제16권8호
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• pp.815-824
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• 2005

본 논문에서 우리는 새로운 방식의 IMT-2000 대역 DGS(Defected Ground Structure) 도허 티 증폭기를 제안하였다. 근본적으로 도허티 증폭기의 능동 로드-풀 회로 해석 기법은 이상적인 고조파 단락 상태를 가정한다. 그러나 기존의 논문에서는 대부분 이러한 이상적인 고조파 단락을 간과하고 있었다. 우리는 도허티 주 증폭기의 부하 변조 동작에 필수적인 출력단의 임피던스 변환 전송 선로와 보조 증폭기의 출력 임피던스 보정을 위한 오프셋 전송 선로에 DGS를 적용함으로써 이러한 가정을 만족시킴과 동시에 이득, 효율 그리고 최대 출력 전력을 개선하였으며, 선형성 개선과 상당한 크기 감소 효과도 얻을 수 있었다. 제안된 DGS 도허티 증폭기의 2차, 3차 고조파는 비교 대상으로 제작된 일반적인 도허티 증폭기에 비해 각각 44.92 dB, 23.77 dB 이상 차단되었다. 그 결과로서 얻어진 DGS 도허티 증폭기의 P1 dB는 0.42 dB 증가하였고 드레인 효율은 최대 $13.4\%,$ 이득은 0.33 dB 증가하였으며, WCDMA 1 FA 신호에 대한 ACPR 특성이 최대 5.4 dEc 개선되었다. 게다가 주 증폭기와 보조 증폭기 경로에서 각각 $90^{\circ}$ 전기각에 해당하는 길이를 줄일 수 있어 전체 회로의 크기를 상당히 줄일 수 있었다.

• 한국재료학회지
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• 제16권12호
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• pp.777-781
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• 2006

Recently, there are a lot of study to alternate polycarbonate which is being used as storage material in CD, DVD. In this study, we alternated polycarbonate with glass. We observed the change of shape in a surface of the glass which was focused by Nd:YAG Laser. The change of shape and property was studied by thermal mechanical analysis (TMA), UV-Vis spectrometer, AFM and SEM. According to Laser power and quantity of additives, the Bump's size and shape are showed differently. In high energy, the Bump will be transformed into Pit. And also according to CTE, $T_d$ and absorption ratio of glass, difference between Bump and Pit is confirmed. From these investigation, we could control that the minimum size of bump which is more useful shape than pit's is about 1.3 $\mu$m, H 70 nm, and it is near same the spot size.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권5호
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• pp.396-401
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• 1999

In this study, $Ar^+$ ion laser etching process of single/poly-crystalline Si with $CCl_2F_2$ gas is investigated for MEMS applications. In general, laser direct etching process is useful in microelectronic process, fabrication of micro sensors and actuators, rapid prototyping, and complementary processing because of the advantages of 3D micromachining, local etching/deposition process, and maskless process with high resolution. In this study, a pyrolytic method, in which $CCl_2F_2$ gasetches molten Si by the focused laser, was used. In order to analyze the temperature profile of Si by the focused laser, the 3D heat conduction equation was analytically solved. In order to investigate the process parameters dependence of etching characteristics, laser power, $CCl_2F_2$ gas pressure, and scanning speed were varied and the experimental results were observed by SEM. The aspect ratio was measured in multiple scanning and the simple 3D structure was fabricated. In addition, the etching characteristics of $6\mum$ thick poly-crystalline Si on the insulator was investigated to obtain flat bottom and vertical side wall for MEMS applications.

• Computers and Concrete
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• 제32권1호
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• pp.61-74
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• 2023

This article investigates the wave propagation analysis of the imperfect functionally graded (FG) sandwich plates based on a novel simple four-variable integral quasi-3D higher-order shear deformation theory (HSDT). The thickness stretching effect is considered in the transverse displacement component. The presented formulation ensures a parabolic variation of the transverse shear stresses with zero-stresses at the top and the bottom surfaces without requiring any shear correction factors. The studied sandwich plates can be used in several sectors as areas of aircraft, construction, naval/marine, aerospace and wind energy systems, the sandwich structure is composed from three layers (two FG face sheets and isotropic core). The material properties in the FG faces sheet are computed according to a modified power law function with considering the porosity which may appear during the manufacturing process in the form of micro-voids in the layer body. The Hamilton principle is utilized to determine the four governing differential equations for wave propagation in FG plates which is reduced in terms of computation time and cost compared to the other conventional quasi-3D models. An eigenvalue equation is formulated for the analytical solution using a generalized displacements' solution form for wave propagation. The effects of porosity, temperature, moisture concentration, core thickness, and the material exponent on the plates' dispersion relations are examined by considering the thickness stretching influence.

• 재활복지공학회논문지
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• 제7권2호
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• pp.13-18
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• 2013

본 논문에서는 8비트 전류 구동형 DAC를 설계하여 뉴런 신호를 자극하기 위한 전류자극기로 활용하였다. 제안하는 회로는 10KS/s의 샘플링 주파수와 3.3V의 구동전압을 가지며, 0.35um Magna Chip CMOS 공정을 이용하여 설계하였고 Full-Custom 방식의 레이아웃을 수행하였다. 글리치 잡음을 줄이고 해상도를 높이기 위해 상위 3비트의 온도계 코드 디코더 입력과, 하위 5비트의 이진 입력의 혼합된 구조를 적용하였다. 이로 인해 글리치 에너지는 이진 입력으로만 구성된 DAC에 비해 $10nV{\bullet}sec$ 감소하였다. 또한 LSB전류가 $0.8{\mu}m$로 작기 때문에 저전력 전류 자극기로 활용될 수 있다. 제안된 전류 자극기는 MCU와 연결하여 바이패이즈 신호를 형성 할 수 있으며, 신호의 주기와 진폭을 MCU코드를 변경하며 조절할 수 있다. 측정결과 INL은 +0.56/-0.38 LSB이고 DNL은 +0.3/-0.4 LSB로서 우수한 선형성을 나타내었고 소모전력은 6.6mW로 측정되었다.

• 대한의용생체공학회:의공학회지
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• 제15권1호
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• pp.1-8
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• 1994

Electrofusion of cabbage protoplasts was performed with a developed equipment which consists of a parallel wire electrode, a AC field generator, and a pulse generator. Exposure of protoplasts to an alternating current field of 450 KHz causes attraction to each other which leads to chains of protoplasts extending from the electrode. Intra-specific protoplast fusion was effectively induced within the pearl chains by the additional application of a single high-intensity DC square wave pulse of 1 KV/cm for 1-3 msec. To improve the performance, micro fusion electrode fabricated from the semiconductor technology and microcontroller based field an, d pulse generator was proposed. The viability of protoplasts after an application of electric field at optimum condition was reduced by only 5 % compared with that of pre-application. A prototype of fusion electrode, which consists of insulator-structure, was successfully fabricated by using photosensitive polyimide.

• 대한기계학회논문집A
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• 제27권6호
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• pp.997-1006
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• 2003

LICA technique evolved as a basic fabrication process fur micro-structure. The present report deals with the basic technological features in the sequence of the LIGA technique such as deep x-ray lithography(DXRL), electroplating, and moulding processes at Pohang Light Source (PLS). We designed 3-D structured master for fabrication of polymeric optical wavegude and manufactured polymeric optical wavegude with the same using hot embossing process. Polymeric optical waveguide could be produced with ${\pm}$ 1 $\mu\textrm{m}$ accuracy and good surface roughness.

• JSTS:Journal of Semiconductor Technology and Science
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• 제6권4호
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• pp.275-280
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• 2006

We propose Doherty power amplifier structure which can be integrated in Silicon RF ICs. Doherty power amplifiers are widely used in RF transmitters, because of their high Power Added Efficiency (PAE) and good linearity. In this paper, it is proposed that a method to replace the quarter wavelength coupler with IQ up-conversion mixers to achieve 90 degree phase shift, which allows on-chip Doherty amplifier. This idea is implemented and manufactured in CMOS 5 GHz band direct-conversion RF transmitter. We measured a 3dB improvement output RF power and linearity.