• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.106-107
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• 2007

We fabricated anodic aluminium oxides (AAO) on Si and sapphire substrates from the electrochemical reactions of thin AI films in an aqueous solution of oxalic acid. The thin AI films have deposited on Si and Sapphire substructure by using E-beam evaporation and thermal evaporation, respectively. The formation of AAO structures has investigated from FE-SEM measurement image and showed randomly distributed phase of nanoholes instead of the periodic lattice of photonic crystals. The AAO structure on sapphire shows the double layers of nanoholes.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1864-1865
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• 2007

In this paper, we proposed pre-filter algorithms which using frequency domain analysis method, for the detections of defects in large-sized Thin Film Transistor-Liquid Crystal Display(TFT-LCD) panel surfaces. We performed frequency analysis with 1-D, 2-D FFT methods for extract periodic patterns of lattice structures in TFT-LCDs. To remove this patterns, band-stop filters were used for eliminating specific frequency components. In order to acquire only defected images, we used 2-D inverse FFT methods which can be reverts images that remains defects.

• Steel and Composite Structures
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• 제17권5호
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• pp.721-734
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• 2014

In the current study, we consider a new class of analytical periodic solution for free nonlinear vibration of mechanical systems. Hamiltonian approach is applied to analyze nonlinear problems which occur in dynamics. The proposed method doesn't have the limitations of the classical methods and leads us to a high accurate solution by only one iteration. Two well known examples are studied to show the convenience and effectiveness of this approach. Runge-Kutta's algorithm is also applied and the results of it are compared with the Hamiltonian approach. High accuracy of the proposed approach reveals that the Hamiltonian approach can be very useful for other nonlinear practical problems in engineering.

• Journal of electromagnetic engineering and science
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• 제19권2호
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• pp.71-81
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• 2019

This paper presents a design methodology for wideband single-layered microwave absorbers with arbitrary absorption at the design center frequency using reactive Salisbury screens. The bandwidth of the absorber increases when the flatness of the reflection response at the design center frequency is maximized. Based on this observation, closed-form design formulas for wideband absorbers are derived. As they are scalable to any design frequency, wideband reactive screens can be systematically realized using two-dimensional periodic crossed-dipole structures patterned on a resistive sheet. Based on this method, a single-layered absorber with a 90% bandwidth improved to 124% of the design center frequency is presented. For the purpose of physical demonstration, an absorber with a design center frequency of 10 GHz is designed and fabricated using a silver nanowire resistive film with a surface resistance of 30 Ω/square. The measured absorption shows a good agreement with both the calculation and the electromagnetic simulation.

• Steel and Composite Structures
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• 제44권5호
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• pp.685-690
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• 2022

In this paper, the equivalent material properties of cellular metamaterials with different types of perforations have been presented using finite element (FE) simulation of tensile test in Abaqus commercial software. To this end, a Representative Volume Element (RVE) has been considered for each type of cellular metamaterial with regular array of circular, square, oval and rectangular perforations. Furthermore, both straight and perpendicular patterns of oval and rectangular perforations have been studied. By applying Periodic Boundary conditions (PBC) on the RVE, the actual behavior of cellular material under uniaxial tension has been simulated. Finally, the effective Young's modulus, Poisson's ratio and mass density of various metamaterials have been presented as functions of relative density of the RVE

• Imaging Science in Dentistry
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• 제54권1호
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• pp.109-113
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• 2024

A 54-year-old male patient presented for a periodic check-up at the dental clinic. A panoramic radiograph showed bilateral ossification of the stylohyoid ligament with an oval radiopacity on the right side. Cone-beam computed tomography revealed a well-defined, homogenous hyperdense entity from the lower third of the ossified stylohyoid ligament on the right side. The differential diagnosis of osteoma on the stylohyoid chain includes Eagle syndrome and benign tumors of the stylohyoid chain and adjacent structures. Osteoma rarely manifests in the neck. Even more infrequent are tumors originating from the stylohyoid chain, with only a single documented case of osteoma reported in the literature in 1993. Due to the asymptomatic status, no surgical intervention was advised, and the case would be monitored periodically. This case report describes the details of an osteoma that emerged from the stylohyoid chain, marking it as the second recorded occurrence of this highly rare condition.

• 한국항행학회논문지
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• 제12권4호
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• pp.332-340
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• 2008

본 논문에서는 OFDM (Orthogonal Frequency Division Multiplexing) 시스템의 주파수 효율 증가를 목적으로 시간 영역에 추가적인 데이터 신호를 중첩시키는 방법들의 성능을 비교한다. 본 저자들이 제안하였던 시간 영역 데이터 중첩 전송 (TDSD : Time Domain Superimposition of Data) 시스템은 기존 중첩 전송 방식들 (SPPT : the Superimposed periodic pilot in the time domain, APSB : the Added Pilot Semi-Blind channel estimation)이 파일롯 신호를 데이터와 중첩하도록 하는 방법과 달리 시간 영역에서 추가 데이터를 중첩시킨다. 그러나 중첩 전송 방식들은 데이터 전송률을 증가시킬 경우, 주파수간 간섭 (ICI)이 증가하는 관계를 갖는다. 하지만 TDSD는 선처리 과정을 통해서 시간 영역 신호와 주파수 영역 신호간의 간섭을 제거함으로써 주파수 효율을 증가시킬 수 있다. 본 논문에서 기존에 제안된 OFDM에서의 중첩 전송 방식들과 여러 모의실험을 통하여 성능을 비교한다. TDSD는 주파수 효율 측면에서 일반적인 OFDM 시스템과 비교할 경우 특정 중첩 전송 변수 사용 (M=16) 시 약 20%의 주파수 효율을 증가 시키는 데 반해 SPPT는 일반적인 OFDM과 비슷한 성능을 갖는다. 그리고 APSB는 비교 대상 중에서 가장 낮은 효율을 보인다.

• 한국해양공학회지
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• 제17권5호
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• pp.66-75
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• 2003

Long cylinder, subjected to internal pressure, is important in the analysis and design of nuclear fuel rod structures. In many cases, long cylinder problems have been considered as a plane strain condition. However, strictly speaking, long cylinder problems are not plane strain problems, but rather a general plane strain (GPS) condition, which is a combination of a plane strain state and a uniform strain state. The magnitude of the uniform axial strain is required, in order to make the summation of the axial force zero. Although there has been the GPS element, this paper proposes a general technique to solve long cylinder problems, using several pseudo-general plane strain (PGPS) elements. The conventional GPS elements and PGPS elements employed are as follows: axisymmetric GPS element (GA3), axisymmetric PGPS element (PGA8/6), 2-D GPS element (GIO), 3-D PGPS element (PG20/16), and reduced PGPS elements (RPGA6, RPG20/16). In particular, PGPS elements (PGA8/6, PG20/16) can be applied in periodic structure problems. These finite elements are tested, using several kinds of examples, thereby confirming the validity of the proposed finite element models.

• Fisheries and Aquatic Sciences
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• 제1권1호
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• pp.48-62
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• 1998

Seasonal volume transport on the Texas-Louisiana continental shelf is investigated in terms of objectively fitted transport streamfunction fields based on the current meter data of the Texas­Louisiana Shelf Circulation and Transport Processes Study. Adopted here for the objective mapping is a method employing a two-dimensional truncated Fourier representation of the streamfunction over a domain, with the amplitudes determined by least square fit of the observation. The fitting was done with depth-averaged flow rather than depth-integrated flow to reduce the root-mean-square error. The fitting process filters out $11\%$ of the kinetic energy in the monthly mean transport fields. The shelf-wide pattern of streamfunction fields is similar to that of near-surface velocity fields over the region. The nearshore transport, about 0.1 to 0.3 Sv $(1 Sv= 10^6\;m^3/sec)$, is well correlated with the seasonal signal of along-shelf wind stress. The spring transport is weak compared to other seasons in the inner shelf region. The transport along the shelf break is large and variable. In the southwestern shelf break, transport amounts up to 4.7 Sv, which is associated with the activities of the encroaching of energetic anticyclonic eddies originated in Loop Current of the eastern Gulf of Mexico. The first empirical orthogonal function (EOF) of streamfunction variability contains $67.3\%$ of the variance and shows a simple, shelf-wide, along-shelf pattern of transport. The amplitude evolution of the first EOF is highly correlated (correlation coefficient: 0.88) with the evolution of the along-shelf wind stress. This provides strong evidence that the large portion of seasonal variation of the shelf transport is wind-forced. The second EOF contains $23.7\%$ of the variance and shows eddy activities at the southwestern shelf break. The correlation coefficient between the amplitudes of the second EOF and wind stress is 0.42. We assume that this mode is coupled a periodic inner shelf process with a non-periodic eddy process on the shelf break. The third EOF (accounting for $7.2\% of the variance) shows several cell structures near the shelf break associated with the variability of the Loop Current Eddies. The amplitude time series of the third EOF show little correlation with the along-shelf wind.

• Journal of Advanced Marine Engineering and Technology
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• 제38권3호
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• pp.302-311
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• 2014

본 연구에서는 소형화된 투명 플렉시블 무선통신소자 구현을 위해, 주기적 구조를 가지는 fishbone 형태의 전송선로를 PES (polyether sulfone) 박막상에 제작하였으며, 이에 관한 RF 특성을 고찰하였다. 그 결과에 의하면, PES 박막상에 제작된 fishbone 형태의 전송선로는 종래의 코프레너선로에 비해 단파장특성을 보여주었으며, 구체적으로 50 GHz에서 선로파장은 2.23 mm으로, 종래의 코프레너 선로의 56.6%이다. 삽입손실 측정결과에 의하면 fishbone 형태의 전송선로는 50 GHz 까지의 주파수 범위에서 1.31 dB보다 낮은 저손실특성을 보여주었다. 대역폭 추출결과에 의하면, PES 박막상의 fishbone 형태의 전송선로는 통과대역이 608 GHz인 광대역 특성을 보였다. PES 박막상의 fishbone 형태의 전송선로의 특성임피던스는 기존의 주기적 구조와는 달리 매우 적은 주파수 의존성을 나타내었으며, 이로 인해 광대역의 전송선로 및 광대역 분포형 수동소자에 이용될 수 있음을 알 수 있었다.