• Advances in aircraft and spacecraft science
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• 제6권1호
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• pp.31-49
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• 2019

Flutter is a dangerous phenomenon encountered in flexible structures subjected to aerodynamic forces. This includes aircraft, helicopter blades, engine rotors, buildings and bridges. Flutter occurs as a result of interactions between aerodynamic, stiffness and inertia forces on a structure. The conventional method for designing a rotor blade to be free from flutter instability throughout the helicopter's flight regime is to design the blade so that the aerodynamic center (AC), elastic axis (EA) and center of gravity (CG) are coincident and located at the quarter-chord. While this assures freedom from flutter, it adds constraints on rotor blade design which are not usually followed in fixed wing design. Periodic Structures have been in the focus of research for their useful characteristics and ability to attenuate vibration in frequency bands called "stop-bands". A periodic structure consists of cells which differ in material or geometry. As vibration waves travel along the structure and face the cell boundaries, some waves pass and some are reflected back, which may cause destructive interference with the succeeding waves. In this work, we analyze the flutter characteristics of a helicopter blades with a periodic change in their sandwich material using a finite element structural model. Results shows great improvements in the flutter forward speed of the rotating blade obtained by using periodic design and increasing the number of periodic cells.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.578-595
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• 2020

Submarine pressure hulls must withstand high hydraulic pressure and be free of defects. To improve the precision of defect detection, we herein examined different probes for optimal defect assessment by applying the Phased Array Ultrasonic Testing (PAUT) method. Two sets of probe design parameters were selected by considering pressure hull characteristics and analyzed through modeling. PAUT probes were applied, and defect assessment results were compared based on ultrasonic signals of various simulated defects in specimens designed to be the same as actual pressure hulls. The final selected design parameters for the submarine probe, which were designed to minimize the grating lobe of wave interference effect and improve the ultrasonic resolution of pressure hull welds, were identified through the experiment. The improvement in the probe's ability to detect defects in a pressure hull was verified. Furthermore, the accuracy of defect length measurement was improved, enhancing the applicability of the technique.

• Nuclear Engineering and Technology
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• 제54권2호
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• pp.423-428
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• 2022

Very low contents (in the range of 10^-9 g/g) of Ir in mantle-derived rock samples (komatiites) were non-destructively determined by INAA coupled with coincidence gamma-ray spectrometry using 16 Ge detectors. Aliquots of the same samples were analyzed by NiS fire-assay ICP-MS for Ir and other platinum group elements. Because the INAA procedure used in this study is non-destructive and is almost free from spectral interference in gamma-ray spectrometry, the INAA values of Ir contents obtained in this study can be highly reliable. Iridium values obtained by ICP-MS were consistent with the INAA values, implying that the ICP-MS values of Ir obtained in this study are equally reliable. Under the present experimental conditions, detection limits were estimated to be 1 pg/g, which corresponds to 0.1 pg for a sample mass of 0.1 g. These levels can be even lowered by an order of magnitude, if necessary, which cannot be achieved by ICP-MS carried out in this study.

• Journal of Species Research
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• 제12권1호
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• pp.55-67
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• 2023

Two new records of marine nematodes, belonging to the family Ironidae de Man, 1876, are reported based on the specimens collected from intertidal sediments from the west coast of Korea. Conilia sinensis is characterized by a relatively long body length, a well-developed buccal cavity with three claw-like teeth, the presence of a single spicule with transverse striations, the presence of rib-shaped telamons, and single precloacal supplement. Pheronous donghaiensis is distinguished from other species of the genus by a well-developed buccal cavity with four claw-like solid teeth and minute denticles, relatively short and thick spicules with the central septum, the presence of 8-9 curved tubular-shaped precloacal supplements, and a sharp pointed tail with three small tubular supplements arranged into two rows in males. In this report, we provide a taxonomic description and illustrations of two unrecorded species of the family Ironidae by differential interference contrast microscopy. This is the first taxonomic report on the species of the family Ironidae from Korea.

• Journal of Microbiology and Biotechnology
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• 제33권12호
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• pp.1692-1697
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• 2023

Staphylococcus aureus integrated with mecA gene, which codes for penicillin-binding protein 2a, is resistant to all penicillins and other beta-lactam antibiotics, resulting in poor treatment expectations in skin and soft tissue infections. The development of a simple, sensitive and portable biosensor for mecA gene analysis in S. aureus is urgently needed. Herein, we propose a dual-toehold-probe (sensing probe)-mediated exonuclease-III (Exo-III)-assisted signal recycling for portable detection of the mecA gene in S. aureus. When the target mecA gene is present, it hybridizes with the sensing probe, initiating Exo III-assisted dual signal recycles, which in turn release numerous "3" sequences. The released "3" sequences initiate catalytic hairpin amplification, resulting in the fixation of a sucrase-labeled H2 probe on the surface of magnetic beads (MBs). After magnet-based enrichment of an MB-H1-H2-sucrase complex and removal of a liquid supernatant containing free sucrase, the complex is then used to catalyze sucrose to glucose, which can be quantitatively detected by a personal glucose meter. With a limit of detection of 4.36 fM for mecA gene, the developed strategy exhibits high sensitivity. In addition, good selectivity and anti-interference capability were also attained with this method, making it promising for antibiotic tolerance analysis at the point-of-care.

• 지구물리와물리탐사
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• 제15권2호
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• pp.92-101
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• 2012

평탄한 자유표면을 갖는 소규모 반구형 분지에서 임의의 전단변형 점진원에 대한 3차원 유한차분 모의를 수행하였다. 자유표면 경계조건을 다루기 위한 새로운 방법을 고안하였다. 분지에서 지반운동 응답에 대한 주요한 특징들을 파악하기 위하여 분지특성 변수를 조사하였다. 분지에서 지반운동의 주파수 함량을 분석하기 위하여, 각 주파수에 대한 진폭을 분지 주변 4개의 위치에서 계산하고 서로 비교하였다. 또한 어떤 종류의 파가 이들 각 지점에서의 지반운동 응답에 우세한 역할을 하는지 보기 위하여 입자운동을 분석하였다. 계산 결과, 지진파 에너지가 진원으로부터 먼 쪽의 분지 경계부에서 집중되는 것을 알 수 있었다. 이러한 집중 효과는 주로 직접 S-파와 분지 경계에서 생성된 표면파의 보강간섭으로 인한 것이다. 또한, 분지의 가장 깊은 곳 상부에서의 지반운동 증폭은 얕은 깊이의 분지 경계 부에 비하여 상대적으로 작게 나타났다. 이러한 결과로부터, 상대적으로 단순한 기반암 경계를 갖는 소규모 분지에서의 지반운동 증폭은 분지의 깊이 보다는 진원의 방위 또는 분지 내부로 입사하는 파의 진행방향에 더 많은 관계가 있다는 것을 추정할 수 있다.

• 인터넷정보학회논문지
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• 제15권3호
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• pp.63-69
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• 2014

IEEE 802.11p 차량 네트워크 환경 (WAVE)에서는 차량 운전자의 안전을 위해서 주기적으로 안전 메시지를 전송하도록 되어 있다. 차량 안전 메시지의 전송을 통해 도로상의 안전과 주행 효율을 제공하기 위해서 WAVE 표준에서는 멀티 채널 멀티 라디오 환경을 제안하고 있다. 그러나 WAVE 표준안은 안전메세지를 하나의 물리 디바이스에 하나의 채널을 이용하여 제어하고 전송하는 것으로 정의되어 있어서 다중 라디오 환경과 안전 메시지 전송 효율성을 고려하지 않았다. 또한 네트워크 무선상에서 서로 충돌이 일어나지 않는 채널을 할당하는 채널 할당은 네트워크 망구성방식을 잘 알고 있거나 모든 노드들이 같은 전송률을 가지는 무선 대역에 있어도 NP-hard한 문제로 잘 알려져 있다. 본 논문에서는 최신 802.11p와 1609.4 802.11p 표준을 이용해서 다중 채널 다중 라디오 WAVE 환경을 무선 메쉬 네트워크로 가정하여 Nash 협상 게임을 통해서 서로 간섭이 없는 채널을 할당하는 방법을 제안하고자 한다. 본 제안된 알고리즘은 시뮬레이션을 통해서 검증하였고 해당 알고리즘이 8채널 3 라디오 환경에서 랜덤 채널 할당 방법이나 Tabu 알고리즘 보다 효율성이 좋다는 것을 입증하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.115-116
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• 2012

The demand for flexible electronic systems such as wearable computers, E-paper, and flexible displays has increased due to their advantages of excellent portability, conformal contact with curved surfaces, light weight, and human friendly interfaces over present rigid electronic systems. This seminar introduces three recent progresses that can extend the application of high performance flexible inorganic electronics. The first part of this seminar will introduce a RRAM with a one transistor-one memristor (1T-1M) arrays on flexible substrates. Flexible memory is an essential part of electronics for data processing, storage, and radio frequency (RF) communication and thus a key element to realize such flexible electronic systems. Although several emerging memory technologies, including resistive switching memory, have been proposed, the cell-to-cell interference issue has to be overcome for flexible and high performance nonvolatile memory applications. The cell-to-cell interference between neighbouring memory cells occurs due to leakage current paths through adjacent low resistance state cells and induces not only unnecessary power consumption but also a misreading problem, a fatal obstacle in memory operation. To fabricate a fully functional flexible memory and prevent these unwanted effects, we integrated high performance flexible single crystal silicon transistors with an amorphous titanium oxide (a-TiO2) based memristor to control the logic state of memory. The $8{\times}8$ NOR type 1T-1M RRAM demonstrated the first random access memory operation on flexible substrates by controlling each memory unit cell independently. The second part of the seminar will discuss the flexible GaN LED on LCP substrates for implantable biosensor. Inorganic III-V light emitting diodes (LEDs) have superior characteristics, such as long-term stability, high efficiency, and strong brightness compared to conventional incandescent lamps and OLED. However, due to the brittle property of bulk inorganic semiconductor materials, III-V LED limits its applications in the field of high performance flexible electronics. This seminar introduces the first flexible and implantable GaN LED on plastic substrates that is transferred from bulk GaN on Si substrates. The superb properties of the flexible GaN thin film in terms of its wide band gap and high efficiency enable the dramatic extension of not only consumer electronic applications but also the biosensing scale. The flexible white LEDs are demonstrated for the feasibility of using a white light source for future flexible BLU devices. Finally a water-resist and a biocompatible PTFE-coated flexible LED biosensor can detect PSA at a detection limit of 1 ng/mL. These results show that the nitride-based flexible LED can be used as the future flexible display technology and a type of implantable LED biosensor for a therapy tool. The final part of this seminar will introduce a highly efficient and printable BaTiO3 thin film nanogenerator on plastic substrates. Energy harvesting technologies converting external biomechanical energy sources (such as heart beat, blood flow, muscle stretching and animal movements) into electrical energy is recently a highly demanding issue in the materials science community. Herein, we describe procedure suitable for generating and printing a lead-free microstructured BaTiO3 thin film nanogenerator on plastic substrates to overcome limitations appeared in conventional flexible ferroelectric devices. Flexible BaTiO3 thin film nanogenerator was fabricated and the piezoelectric properties and mechanically stability of ferroelectric devices were characterized. From the results, we demonstrate the highly efficient and stable performance of BaTiO3 thin film nanogenerator.

• 한국해안해양공학회지
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• 제18권3호
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• pp.189-197
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• 2006

수치해석을 통하여 이어도 종합해양과학기지 구조물이 대기 유동에 미치는 영향을 분석하였고, 이 결과를 바탕으로 과학기지에 설치된 풍속센서에서의 측정값 오차를 평가하는 연구를 수행하였다. 과학기지 형상을 3차원으로 모델링하였고 수치해석을 위한 격자를 생성하여, Navier-Stokes 방정식 및 난류모델을 적용하여 수치해석을 수행하였다. 선정된 자유류의 풍속과 풍향 조건에 대하여 과학기지 구조물에 의해 변화된 유동장을 계산하고, 실제 풍속센서가 설치된 위치에서의 풍속/풍향 정보와 자유류를 비교하였다. 이를 통하여 자유류 방향 및 측정 위치에 따른 데이터의 정확도와 신뢰할 수 있는 데이터 범위를 알아보았다. 본 연구 결과로 관측된 해상풍 데이터의 구조물 간섭에 의한 오차 범위를 정량적으로 파악할 수 있었으며, 과학기지가 위치한 지점의 정확한 해상풍 데이터 제공을 위한 기초 자료로 활용될 것으로 기대된다.

• 전자공학회논문지S
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• 제36S권2호
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• pp.96-107
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• 1999

GSC(generalized sidelobe conceller)들은 어레이 레이다에서 간섭신호를 제거하기 위하여 이용된다. GSC들 중에서 주파수영역 GSC들은 주파수영역 LMS(least mean square) 알고리즘으로 간섭신호간 상관성을 제거함으로써 시간영역 GSC들보다 빠른 수렴특성을 가진다. 그러나 기존의 주파수영역 GSC의 장점을 충분히 이용하지 못했다. 본 논문은 일정오경보율(constant false-alarm rate: CFAR) 검출기에 근거하여 가중치를 갱신할 빈을 결정하는 새로운 주파수영역 GSC를 제안한다. 본 방법은 간섭신호가 존재해서 전력이 큰 주파수 빈에 대해서만 가중치를 갱신한다. 새로운 GSC는 컴퓨터 모의실험에서 기존의 GSC를 보다 100 반복주기 이상 수렴속도와 5 dB 이상의 출력 신호대 잡음비(singnal-to-noise ratio; SNR)를 개선하였고, 갱신 가중치의 수도 현저히 줄어듬을 확인하였다.