• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.66.2-66.2
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• 2016

KASI and NAOJ are making collaborating efforts to implement faster mapping capability into the new 275-500 GHz Atacama Submillimeter Telescope Experiment focal plane array (FPA). Feed horn antenna is one of critical parts of the FPA. Required fractional bandwidth is almost 60 % while that of traditional conical horn is less than 50 %. Therefore, to achieve this wideband performance, we adopted a horn of which the corrugation depths have a longitudinal profile. A profiled horn has features not only of wide bandwidth but also of shorter length compared to a linear-tapered corrugated horn, and lower cost fabrication with less error can be feasible. In our design process the flare region is represented by a cubic splined curve with several parameters. Parameters of the flare region and each dimension of the throat region are optimized by a differential evolution algorithm to keep >20 dB return loss and >30 dB maximum cross-polarization level over the operation bandwidth. To evaluate RF performance of the horn generated by the optimizer, we used a commercial mode matching software, WASP-NET. Also, Gaussian beam (GB) masks to far fields were applied to give better GB behavior over frequencies. The optimized design shows >23 dB return loss and >33 dB maximum cross-polarization level over the whole band. Gaussicity of the horn is over 96.6 %. The length of the horn is 12.5 mm which is just 57 % of the ALMA band 8 feed horn (21.96 mm).

• Carbon letters
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• v.12 no.4
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• pp.229-235
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• 2011

Isotactic polyacrylonitrile (PAN) with triad isotacticity of 0.53, which was determined by $^{13}C$ NMR, using dialkylmagnesium as an initiator, was successfully synthesized. Isothermal treatment of iso-PAN was conducted in air at 200, 220, 250 and $280^{\circ}C$. Structural evolutions and chemical changes were studied with Fourier transformation infrared and wide-angle X-ray diffraction during stabilization. A new parameter $CNF={I_{2240cm}}^{-1}/ ({I_{1595cm}}^{-1}+f^*{I_{1595cm}}^{-1})$ was defined to evaluate residual nitrile groups. Crystallinity and crystal size were calculated with X-ray diffraction dates. The results indicated that the nitrile groups had partly converted into a ladder structure as stabilization proceeded. The rate of reaction increased with treatment temperature; crystallinity and crystal size decreased proportionally to pyrolysis temperature. The iso-conversional method coupled with the Kissinger and Flynn-Wall-Ozawa methods were used to determine kinetic parameters via differential scanning calorimetry analysis with different heating rates. The active energy of the reaction was 171.1 and 169.1 kJ/mol, calculated with the two methods respectively and implied the sensitivity of the reaction with temperature.

• BMB Reports
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• v.40 no.6
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• pp.986-1001
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• 2007

Cold acclimation improves freezing tolerance in plants. In higher plants, many advances have been made toward identifying the signaling and regulatory pathways that direct the low-temperature stress response; however, similar insights have not yet been gained for simple nonvascular plants, such as bryophytes. To elucidate the pathways that regulate cold acclimation in bryophytes, we used two PCR-based differential screening techniques, cDNA amplified fragment length polymorphism (cDNA-AFLP) and suppression subtractive hybridization (SSH), to isolate 510 ESTs that are differentially expressed during cold acclimation in Physcomitrella patens. We used realtime RT-PCR to further analyze expression of 29 of these transcripts during cold acclimation. Our results show that cold acclimation in the bryophyte Physcomitrella patens is not only largely similar to higher plants but also displays distinct differences, suggests significant alteration during the evolution of land plants.

• Steel and Composite Structures
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• v.27 no.3
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• pp.297-310
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• 2018

A simple and efficient numerical optimization approach for the lightweight optimal design of composite laminated beams is presented in this paper. The proposed procedure is a combination between the finite element method (FEM) and a global optimization algorithm developed recently, namely Jaya. In the present procedure, the advantages of FEM and Jaya are exploited, where FEM is used to analyze the behavior of beam, and Jaya is modified and applied to solve formed optimization problems. In the optimization problems, the objective aims to minimize the overall weight of beam; and fiber volume fractions, thicknesses and fiber orientation angles of layers are selected as design variables. The constraints include the restriction on the first fundamental frequency and the boundaries of design variables. Several numerical examples with different design scenarios are executed. The influence of the design variable types and the boundary conditions of beam on the optimal results is investigated. Moreover, the performance of Jaya is compared with that of the well-known methods, viz. differential evolution (DE), genetic algorithm (GA), and particle swarm optimization (PSO). The obtained results reveal that the proposed approach is efficient and provides better solutions than those acquired by the compared methods.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.6 s.46
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• pp.53-58
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• 2005

Semi-analytical methodology to examine the dynamic responses of a bridge is developed via the joint probability density function. The evolution of joint probability density function is evaluated by the semi-analytical procedure developed. The joint probability function of the bridge responses can be obtained by solving the path-integral solution of the Fokker-Planet equation corresponding to the stochastic differential equations of the system. The response characteristics are observed from the joint probability density function and the boundary of the envelope of the probability density function can provide the maxima ol the bridge responses.

• Journal of Industrial Technology
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• v.19
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• pp.107-113
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• 1999

The microstructural evolution during mechanical alloying of elemental Fe and Si powders, average composition $Fe_{30}Si_{70}$ and $Fe_{50}Si_{50}$, has been investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Differential scanning calorimetry (DSC). Mechanical alloying was performed by using a SPEX 8000 Mixer/Mill under argon atmosphere with/without hexane as a process control agent (PCA). In the presence of PCA, the milling process was dominated by fracture resulting in the decrease in particle size to about $1{\mu}m$. The structural development with milling time depended on the average composition of starting powders. The mixture of $Fe_{50}Si_{50}$ and $Fe_{30}Si_{70}$ resulted in the formation of FeSi(${\varepsilon}$ - phase) and $FeSi_2$(${\beta}$ - phase), respectively. In the case of $Fe_{33.3}Si_{66.7}$, a mixture and $FeSi_2({\beta})$ was formed. These results were discussed by considering the thermodynamics and kinetics concerning the milling process.

• The Plant Pathology Journal
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• v.18 no.5
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• pp.237-243
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• 2002

A survey of virus infection in garlic plants cultivated in Korea was conducted for three years. Most virus-infected garlic plants (Allium sativum) showed typical symptoms on the leaves such as yellow mosaic, stripes, and distortion. Through immunosorbent electron micro-scopy and RT-PCR analysis, the complex mixtures of viruses including garlic viruses of the genus Allerivirus, gaylic strain of Leek yellow stripe virus of the genus Potyvirus, and Garlic latent virus of the genus Carlavirus were identified in the virus-infected garlic plants. Among these viruses, Allexivirus was the most frequently detect-ed in the regions surveyed. Using sets of differential primers for Allexivirus genomes, two members of the genus were amplified and sequenced from the purified viruses. The deduced amino acid sequences for the coat proteins and the nucleic acid binding proteins of two viruses showed high homologies to Garlic virus A (CarV-A) and Garlic virus D (GarV-D) of Allekivirus. This is the first report of GarV-A and GarV-D in Korea. This suggests that Allexivirus in gavlic plants in Korea was mixed and varied. Phylogenetic analyses showed that the genus Allexivirus was diversi(ied by the processes of accumulation and evolution of viruses in garlic plants due to the long period of repeated vegetative propagation.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.4
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• pp.263-273
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• 2011

The diffuse interface model of Saurel et al. (2008) is used for the computation of compressible cavitating flows around underwater missiles. Such systems use gas injection and natural cavitation to reduce drag effects. Consequently material interfaces appear separating liquid and gas. These interfaces may have a really complex dynamics such that only a few formulations are able to predict their evolution. Contrarily to front tracking or interface reconstruction method the interfaces are computed as diffused numerical zones, that are captured in a routinely manner, as is done usually with gas dynamics solvers for shocks and contact discontinuity. With the present approach, a single set of partial differential equations is solved everywhere, with a single numerical scheme. This leads to very efficient solvers. The algorithm derived in Saurel et al. (2009) is used to compute cavitation pockets around solid bodies. It is first validated against experiments done in cavitation tunnel at CNU. Then it is used to compute flows around high speed underwater systems (Shkval-like missile). Performance data are then computed showing method ability to predict forces acting on the system.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.5
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• pp.517-525
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• 2007

This paper presents how to approximate an optimal shape of roll bending process in the fabrication of a curved shell plate. The roll bending process usually makes the cylindrical or conic shape from an initial flat plate. It means that the final shape is developable or its surface representation has zero Gaussian curvature. The fabrication shape is important in order to find process parameters of roil bending. An optimal concept is used to determine the developable fabrication shape which is in the closest proximity to the design surface or the given shell plate and is subject to developability. The results and the efficiency of this algorithm are evaluated by applying to some shell plates. Furthermore, the fabrication shape will be fundamental information for other process parameters of roll bending such as the vertical displacement of the center roller and the rolling directions.

• Korean Journal of Materials Research
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• v.14 no.5
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• pp.315-321
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• 2004

The void evolution in direct bonding process of $Si/Si_3$$N_4$ ∥ $SiO_2$/Si silicon wafer pairs has been investigated with an infrared camera. The voids that formed in the premating process grew in the conventional furnace annealing process at a temperature of $600^{\circ}C$. The voids are never shrunken even with the additional annealing process at the higher temperatures. We observed that the voids became smaller and disappeared with sequential scanning by our newly proposed fast linear annealing(FLA). FLA irradiates the focused line-shape halogen light on the surface while wafer moves from one edge to the other. We also propose the void shrinking mechanism in FLA with the finite differential method (FDM). Our results imply that we may eliminate the voids and enhance the yield for the direct bonding of wafer pairs by employing FLA.