• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.6
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• pp.9-15
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• 2004

In this study the development of the two dimensional flowfield around an impulsively translated circular cylinder is numerically simulated using the diffusion vortex method. A detailed streamline pattern of fore wake and main wake of Re=1200, 9500 flowfields are investigated. The results of streamline pattern, the size of main wake and the axial velocities along the rear symmetry axis of the circular cylinder show good agreement with the reported experimental results. The long term wake delvelopment for Re=1200 flowfield was calculated up to ${\tau}=50$. The vortex shedding frequency shows the similar value as that of reported.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1485-1492
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• 1992

While the vibration of circular plates were considered by many researchers, rather less attention is given to elliptical plates. In the present paper, the Rayleigh-Ritz mothod is used to obtain an eigenvalue equation for the free flexural vibration of thin elliptical plates having the classical free, simply suported or clmped boundary condition. Circular plates are included as a special case of the elliptical plates. Products of simple polynomials are used as the admissible functions and a recurrence relationship facilitates the evaluation of the necessary integrals. The analysis is developed for rectilinear orthotropic plates but the numerical results are given for isotropic plates with various aspect ratios.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.8 no.2
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• pp.147-151
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• 2015

In this paper, the performance variation of a planar circular monopole antenna is studied, when this antenna is fabricated to film type and installed in the space between case and PCB of UWB terminal. When the circular monopole part has the 'ㄷ' folded structure, the input impedance and return loss, bandwidth, radiation pattern of this antenna are simulated and measured. Then the performance variation is compared with conventional planar antenna. As the results, the folded type circular antenna is usable as a intenna of UWB communication terminal, because of the good return loss and radiation pattern performance in the 2.6 - 12 GHz including the UWB frequency band.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.913-916
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• 1998

In this paper, to provide the robustness of character recognition, we propose a recognition method using the dilated boundary curve feature which has the invariance characteristics for the shift, scale, and rotation changes of character pattern. And its some characteristics and effectieness are evaluated through the experiments for both the english alphabets and the numeral digits. The feature vector is represented by the fourier descriptor for a boundary curve of the dilated character pattern which is generated by the circular mask dilation method, and is used for a nearest neighbort classifier(NNC) or a nearest neighbor mean classifier(NNMC). These the processing time and the recognition rate, and take also the robustness of recognition for both some internal noise and partial corruption of an image pattern.

• Journal of Plant Biology
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• v.29 no.2
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• pp.135-143
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• 1986

The distributional pattern of the bast fibres strands or bundles in the stems of Sida species represented in Nigeria is studied. Three major patterns of arrangement are recognized, namely aggregation of fibre strands into units with wedge-shaped, or triangular, rectangular, rhomboidal, square and trapezoid outlines; serial arrangement of fibre strands into rings or circular, ovoid, semi-circular or crescentic rows; and intermediate pattern in which both fibre strands-aggregates and serial rows of strands patterns are combined. The first pattern is found in S. linifolia, S. urens and S. scabrida, the second in S. cordifolia, S. pilosa, S. ovata, S. rhombifolia and S. spinosa, and the third in S. garckeana, and S. acuta. A dichotomous key based on these features is presented. Dimensional characteristics of the bast fibre cells are also given.

• Journal of Sensor Science and Technology
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• v.30 no.5
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• pp.273-278
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• 2021

Here, we studied the change in the mechanical stiffness of a diaphragm according to the corrugation pattern. The diaphragm consists of a silicon oxide and nitride double layer; a corrugation pattern was formed by dry etching, and the diaphragm was released by wet etching. The fabrication of the thin film was verified using focused ion beam and scanning electron microscopy images. The mechanical stiffness of the diaphragm was obtained by measuring the surface vibration using a laser Doppler vibrometer while applying external sound pressure. Flat squares, diaphragms with square corrugations, and circular corrugation patterns were measured and compared. The stiffness of the diaphragm with a corrugation structure was found to be smaller than that without a corrugation structure; in particular, circular corrugation showed a better effect because of the high symmetry. Furthermore, the effect of corrugation was theoretically predicted. The proposed corrugated diaphragm showed comparable flexibility with the state-of-the-art MEMS microphone diaphragm.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.1B
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• pp.13-20
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• 2011

The spatio-temporal pattern in precipitation is a significant element in defining characteristics of precipitation. In this study, a new scheme on regionalization utilizing temporal information was introduced on the basis of existing approaches that is mainly based on simple moments of data and geographical information. Given the identified spatio-temporal pattern, this study was extended to characterize regional pattern of annual maximum rainfall over Korea. We have used circular statistics to characterize the temporal distribution on the precipitation, and the circular statistics allow us to effectively assess changes in timing of the extreme rainfall in detail. In this study, a modified K-means method was incorporated with derived temporal characteristics of extreme rainfall in order to better characterize hydrologic pattern for regional frequency analysis. The extreme rainfall was reasonably separated into five categories that considered most attributes in both quantitative and temporal changes in extremes. The results showed that the proposed approach is a promising approach for regionalization in term of physical understanding of extreme rainfall.

• International Journal of Safety
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• v.8 no.1
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• pp.1-5
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• 2009

The CFRP composite has unique properties that offer high strength and stiffness, even though it has light weight. Therefore it can be used in many industrial applications. When mechanical fasteners are used for joining composites, high stress concentrations appear near the edge of holes prepared for accommodating structural bolts and rivets. This presence of high stress concentrations can be a source of damage. The aim of this work is to evaluate fracture behavior and patterns of plain woven CFRP with circular hole and repairing patch element. The maximum strength and pattern for the plain woven carbon composite specimen with the repaired circular hole were examined. From the results, we show that repairing of the CFRP composite specimen with ($\pi$) 3~5 mm of circular hole diameter results in load rising effect and the repairing is more effective as bigger hole specimen.

• Journal of Plant Biology
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• v.36 no.4
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• pp.337-343
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• 1993

Tracheid structure of aerial system in five species of Ophioglossaceae and one species of Osmundaceae was examined with light and scanning electron microscopy. The species were Botrichium multifidum var. robustrum, B. ternatum, strictum, B. virginianum, Ophioglossum vulgatum, and Osmunda japonica. Three types of tracheids could be recognized by the pattern of secondary wall thickening; helical, irregular reticulate and circular bordered pitted tracheids. Among them, the appearance of circular bordered pitted tracheids supported that ophioglossaceous plants might have phylogenetic relationship with progymnosperm-seed plant line. Circular and elliptical bordered pits in shape were observed in five ophioglossaceous species; the former was subdivided into large and small types in size. In conclusion, three types of bordered pits were found: (1) large circular type- O. vulgatum, (2) small circular type- B. multifidum var. robustrum, B. ternatum and (3) elliptical type-B. strictum, B. virginianum. B. strictum and B. virginianum belong to subgenus Osmundopteris had the elliptical bordered pits. Therefore, this group might be interpreted as the most primitive in this family; however, such suggestion did subgenus Osmundopteris was classified into the most advanced group.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.6
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• pp.736-744
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• 2003

This study is conducted to investigate aerodynamic forces and wake structures about the pressure interference of a circular cylinder with slits. An experimental investigation of a circular cylinder with slits is carried out in uniform flow in the range of Reynolds number from 8,000 to 32,000 using X-type hot wire. Flow visualization is executed by smoke-wire method to understand the mechanism of these vortex formation process. Inspection in the wake at X/D=5.5 of the cylinder with the slits suggested that a strong vortex-shedding pattern for these cylinders is revealed compare with a circular cylinder without slits. It is found that the rolling up position of shear layer of the cylinder with slits is shorten compare with a circular cylinder without slits.