• Advances in aircraft and spacecraft science
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• 제6권2호
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• pp.169-187
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• 2019

This work presents a practical detailed finite element (FE) approach for the three-dimensional (3D) free-vibration analysis of actual aircraft and spacecraft-type lightweight and thin honeycomb sandwich panels. It consists of calling successively in $MATLAB^{(R)}$, via a developed user-friendly GUI, a detailed 3D meshing tool, a macrocommands language translator and a commercial FE solver($ABAQUS^{(R)}$ or $ANSYS^{(R)}$). In contrary to the common practice of meshing finely the faces and core cells, the proposed meshing tool represents each wall of the actual hexagonal core cells as a single two-dimensional (2D) 4 nodes quadrangularshell element or two 3 nodes triangular ones, while the faces meshes are obtained simply using the nodes at the core-faces interfaces. Moreover, as the same 2D FE interpolation type is used for meshing the core and faces, this leads to an automatic handling of their required FE compatibility relations. This proposed approach is applied to a sample made of very thin glass fiber reinforced polymer woven composite faces and a thin aluminum alloy hexagonal honeycomb core. The unknown or incomplete geometric and materials properties are first collected through direct measurements, reverse engineering techniques and experimental-FE modal analysis-based inverse identification. Then, the free-vibrations of the actual honeycomb sandwich panel are analyzed experimentally under different boundary conditions and numerically using different mesh basic cell shapes. It is found that this approach is accurate for the first few modes used for pre-design purpose.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1317-1322
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• 2014

Membrane disruption by an antimicrobial peptide (AMP) was investigated by measuring the $^2H$ solid-state nuclear magnetic resonance spectra of 1-palmitoyl-$d_{31}$-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC_$d_{31}$) in mixtures of POPC_$d_{31}$/cholesterol and either magainin 2 or aurein 3.3 deposited on thin cover-glass plates. The line shapes of the experimental $^2H$ solid-state nuclear magnetic resonance (SSNMR) spectra were best simulated by assuming the coexistence of a mosaic spread of bilayers containing pore structures and a fasttumbling isotropic phase or a hexagonal phase. Within a few days of incubation in a hydration chamber, an isotropic phase and a pore structure were induced by magainin 2, while in case of aurein 3.3 only an isotopic phase was induced in the presence of a bilayer phase. After an incubation period of over 100 days, alignment of the bilayers increased and the amount of the pore structure decreased in case of magainin 2. In contrast with magainin 2, aurein 3.3 induced a hexagonal phase at the peptide-to-lipid ratio of 1/20 and, interestingly, cholesterol was not found in the hexagonal phase induced by aurein 3.3. The experimental results indicate that magainin 2 is more effective in disrupting lipid bilayers containing cholesterol than aurein 3.3.

• 한국세라믹학회지
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• 제17권3호
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• pp.121-128
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• 1980

In order to obtain the fundamental data for the preparation of ferroxplana $Zn_2Y(Ba_2Zn_2Fe_{12}O_{22})$, which is useful for GHz-band communication, the optimum coprecipitation condition of $Zn(NO_3)_2-6FeCl_3$ in $NH_4OH$ solution and the formation process of the hexagonal ferrite were investigated. By the hot-petroleum-drying and calcining the coprecipitated hydroxide mixture $Zn(OH)_2 +Ba(OH)_2+ 6Fe(OH)_3$, the fine and uniform powder was obtained , whose phase composition and microstructure were studied by X.R.D. and electron microscope. In results, it was found that $Zn_2Y$, BaM and $Zn_2W$ were the representative phases in calcined specimens whose activation energies of crystal growth were about 3, 8, 2.5, $5.4{\times}10^4$ J/mole , respectively. The sintered specimens would be appreciated as useful magnetic cores for the high frequency communication.

• Journal of electromagnetic engineering and science
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• 제6권1호
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• pp.53-61
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• 2006

In this paper, we present parametric studies for the optimum design of a hexagonal plate monopole antenna. The dependence of the antenna performance on various geometric parameters is investigated using a commercial electromagnetic software, from which an optimum design of a hexagonal plate monopole antenna is derived. Guidelines for determining initial parameter values are given. The diameter of the circular ground plane is minimized tlo 1/5 wavelength at the lowest operating frequency. The antenna impedance matching is controlled by adjusting the gap between the plate and the ground plane, the plate base width, and the base bevel angle. The antenna proposed in. this paper shows a reflection coefficient less than -10 dB and a $2.0{\sim}6.2$ dBi gain over $3{\sim}20$ GHz frequencies.

• 한국인터넷방송통신학회논문지
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• 제22권1호
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• pp.121-126
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• 2022

본 연구는 변형된 힐버트 커브 프랙탈 모노폴 구조를 단순화하여 육각형 대칭 패턴을 가지면서 모노폴 형태로 구현한 안테나에 대한 것이다. 힐버트 커브 프랙탈 모노폴 구조를 단순화하여 소형화했을 뿐 아니라 성능 개선을 모색하기 위해 복사기 구조를 육각형 대칭 패턴으로 구현했다. 기판 유전체의 비유전율은 4.7이며, 미앤더 형태로 대칭 구조를 갖는 총 선로길이는 59 mm이다. 안테나의 크기는 10 mm × 10 mm × 0.8 mm이고, 선폭은 0.4 mm이다. 안테나 측정 지그의 크기는 64 mm × 21 mm × 1 mm이다. 공진주파수는 1.57 GHz 이고, 주파수 범위는 1.51 ~ 1.615 GHz이다. 주파수대역폭은 105 MHz이다. 안테나 이득은 YZ-plane의 측정이득은 2.32 dBi 이고, XZ-plane의 경우 -1.03 dBi를 얻었다. 결과적으로 육각형 대칭 패턴 프랙탈 구조를 이용하여 안테나 소형화를 이루었으며, 복사기 구조 변화로 안테나 성능 개선이 용이함을 확인했다.

• 전기전자학회논문지
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• 제26권1호
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• pp.129-132
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• 2022

본 논문에서는 위상배열안테나의 부엽레벨을 최소화할 수 있는 부배열 시스템 구조의 최적화에 관한 기술을 제안하였다. 제안된 배열안테나 구조의 최적화는 6개의 육각배열을 한 개의 부배열과 육각 부배열의 육각형 배열 구조를 이용하여, 부배열의 배열간격과 부배열 사이의 배열 간격을 조절하여, 전체 위상배열안테나 시스템의 방사패턴을 최적화하였다. 제안된 기술은 2차원 평명배열안테나 시스템에 비하여, 24.3 dBi의 이득과 8.46도의 반치각은 변화없이 유지하며, 오직 x축과 y축 방향으로 각각 -3.4 dB와 -6.5 dB를 감소시켰다.

• 한국항공우주학회지
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• 제39권12호
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• pp.1124-1132
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• 2011

본 논문에서는 2차원 공간에서 기동하는 고정익 무인항공기의 장애물 회피를 위한 부드러운 경로궤적을 생성하는 문제를 다룬다. 2차원 장애물맵의 이산화 모델링을 위해 육각형 격자를 채택하였고, 이는 사각형 격자에 비해 연결성이 높아 부드러운 경로궤적 생성이 가능하도록 하였다. 특히 본 논문에서 제안된 경로템플릿 기법은 일정거리 단위로 조합 가능한 대표경로들(경로템플릿)을 사용하여 무인항공기의 기준경로를 생성하는 방법이고, 온라인 경로궤적 생성에서 계산량을 줄여 메모리 및 연산리소스가 제한되는 소형 오토파일럿에서도 적용이 가능하다는 장점이 있다.

• Nuclear Engineering and Technology
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• 제56권3호
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• pp.772-784
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• 2024

The hexagonal nodal code RENUS has been enhanced to handle irregularly deformed hexagonal assemblies. The underlying RENUS methods involving triangle-based polynomial expansion nodal (T-PEN) and corner point balance (CPB) were extended in a way to use line and surface integrals of polynomials in a deformed hexagonal geometry. The nodal calculation is accelerated by the coarse mesh finite difference (CMFD) formulation extended to unstructured geometry. The accuracy of the unstructured nodal solution was evaluated for a group of 2D SFR core problems in which the assembly corner points are arbitrarily displaced. The RENUS results for the change in nuclear characteristics resulting from fuel deformation were compared with those of the reference McCARD Monte Carlo code. It turned out that the two solutions agree within 18 pcm in reactivity change and 0.46% in assembly power distribution change. These results demonstrate that the proposed unstructured nodal method can accurately model heterogeneous thermal expansion in hexagonal fueled cores.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2002년도 International Meeting on Information Display
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• pp.815-818
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• 2002

Mn doped hexagonal phase of ZnS has been studied as a yellow-orange phosphor for the application to fluorescent displays operated at low voltages. It was found that luminescence from $Mn^{2+}$ was increased as the Mn concentration was increased up to1.2 mol% of host lattice. This study has been attempted by adding trivalent ions such as $Al^{3+}$ or $Bi^{3+}$ to ZnS:Mn as an agent to do the efficient incorporation of Mn ions into ZnS:Mn lattice, resulting in a significant improvement in the phosphor performance, especially at low voltages.

• Bulletin of the Korean Chemical Society
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• 제29권4호
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• pp.817-821
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• 2008

We have investigated the influence of the crystal structure on the chemical bonding nature and photocatalytic activity of cubic and hexagonal perovskite A[$Cr_{1/2}Ta_{1/2}$]O3 (A = Sr, Ba) compounds. According to neutron diffraction and field emission-scanning electron microscopy, the crystal structure and particle size of these compounds are strongly dependent on the nature of A-site cations. Also, it was found that the face-shared octahedra in the hexagonal phase are exclusively occupied by chromium ions, suggesting the presence of metallic (Cr-Cr) bonds. X-ray absorption and diffuse UV-vis spectroscopic analyses clearly demonstrated that, in comparison with cubic Sr[$Cr_{1/2}Ta_{1/2}$]$O_3$ phase, hexagonal Ba[$Cr_{1/2}Ta_{1/2}$]$O_3$ phase shows a decrease of Cr oxidation state as well as remarkable changes in interband Cr d-d transitions, which can be interpreted as a result of metallic (Cr-Cr) interactions. According to the test of photocatalytic activity, the present semiconducting materials have a distinct activity against the photodegradation of 4-chlorophenol. Also the Srbased compound was found to show a higher photocatalytic activity than the Ba-based one, which is attributable to its smaller particle size and its stronger absorption in visible light region.