• Journal of Mechanical Science and Technology
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• v.20 no.2
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• pp.262-270
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• 2006

Direct numerical simulations (DNS) of turbulent channel flows up to $Re_{\tau}=1270$ are performed to investigate an elliptic feature and strain rate field on cross sections of coherent fine scale eddies (CFSEs) in wall turbulence. From DNS results, the CFSEs are educed and the strain rate field around the eddy is analyzed statistically. The principal strain rates (i.e. eigenvalues of the strain rate tensor) at the CFSE centers are scaled by the Kolmogorov length $\eta$ and velocity $U_k$. The most expected maximum (stretching) and minimum (compressing) eigenvalues at the CFSE centers are independent of the Reynolds number in each $y^+$ region (i. e. near-wall, logarithmic and wake regions). The elliptic feature of the CFSE is observed in the distribution of phase-averaged azimuthal velocity on a plane perpendicular to the rotating axis of the CFSE $(\omega_c)$. Except near the wall, phase-averaged maximum $(\gamma^{\ast}/\gamma_c^{\ast})$ and minimum $(\alpha^{\ast}/\alpha_c^{\ast})$ an eigenvalues show maxima on the major axis around the CFSE and minima on the minor axis near the CFSE center. This results in high energy dissipation rate around the CFSE.

• Fisheries and Aquatic Sciences
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• v.21 no.11
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• pp.31.1-31.7
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• 2018

Three economic marine algae that have been used as food and carrageenan sources were collected from Korea during a survey of marine algal flora. They share the generic features of Hypnea, and three major clades supported by the sectional features were confirmed in a phylogenetic tree based on rbcL sequences. The first species, which belongs to a species group corresponding to the sect. Spinuligerae, nests in the same clade with Hypnea yamadae in a genetic distance of 0%. It is morphologically characterized by an entangled base, subcompressed or subterete to terete axes, somewhat percurrent main axis, irregularly alternately branching with wide angle, and rarely hooked spinous branchlets. The second one is also referred to the sect. Spinuligerae and formed the same clade as Hypnea cenomyce. The genetic distance between both sequences was calculated as 0.0-0.1%, which is considered to be intraspecific. This species is distinct by somewhat entangled thallus at the basal part, percurrent axis, short spine-like branchlets densely covering the axis, and medullary lenticular thickenings. The third alga, which forms a species group corresponding to the sect. Pulvinatae, nests in the same clade as Hypnea nidulans (no intraspecific divergence). It shows occasionally epiphytic habitat rather than epilithic habitat of low mat-forming growth and percurrent erect main axes with dense lateral branchlets. Based on these morphological and molecular data, the three Korean species are identified as H. yamadae, H. cenomyce, and H. nidulans. This is the first record of the Hypnea species in Korea.

• The Journal of the Acoustical Society of Korea
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• v.18 no.7
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• pp.67-73
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• 1999

We constructed a class Ⅳ Flextensional transducer, and analyzed the effects of the variation in its material properties and structure on the resonance frequency of the transducer. We used the FEM for the analysis. Major axis length, minor axis length, thickness and material properties of the shell turned out to have large effects, while volume of the insert material, material properties and thickness of the ceramic bar have little. Thickness of the nodal-plate has no effect on the resonance frequency. Results of the present work can be utilized to design Class W Flextensional transducers of various resonance frequency.

• Journal of Biomedical Engineering Research
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• v.16 no.2
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• pp.183-190
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• 1995

The use of ultrasound pulsed Doppler systems has become increasingly popular due to the advantages of easy measurements of blood velocity, volume blood blow, and irregularities of the circulatory system. However, the 2-D Doppler systems have several problems, such as range ambiguity, low signal to noise ratio, and slow frame rate. The mean frequency aliasing problem originating from the pulse repetition frequency is one of major limitations in pulsed Doppler systems. A conventional approach to resolve this problem is tracking the mean frequency close to and beyond the Nyquist frequency along the temporal axis. In this paper, a new concept of tracking the mean frequency along the spatial axis is proposed. The proposed technique is fault tolerant by nature and more suitable for multi gate and 2-D Doppler system than conventional methods.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.875-879
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• 2006

Noise reduction has become a major issue of the duct air-conditioners. This paper describes the reduction of noise and vibration of rotational slim duct system. The design of slim duct system is the most important point of noise reduction in terms of the motor of 2f line noise, resonance noise between forced frequency and natural frequency of Sirocco fan, unbalance noise of motor axis and the noise induced refrigerant. The noise of duct system is mainly measured from diffuser and bottom of duct. The optimal design was implemented after measuring the effect of noise and vibration in each part which is composed of duct system. In this paper, experimental results show that the main elements in air-conditioner duct design. These elements are anti-vibration rubber of motor, axis length of motor, rubber coupler, materials of sirocco fan and control method of motor which are the most vital factors in reducing noise.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.226-227
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• 2008

We constructed a class I Flextensional transducer, and analyzed the variation of the resonance frequency of the transducer in relation to its design variables. We used the FEM for the analysis. Major axis length, minor axis length, thickness and material properties of the shell have large effects on the resonance frequency. In addition, the validation of the FE model was verified by manufacturing and comparison of the impedance analysis.

• International Journal of Aeronautical and Space Sciences
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• v.8 no.1
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• pp.105-114
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• 2007

This article presents the details of a designed control moment gyroscope (CMG) with a constant speed momentum wheel and one-axis-gimbal, and its experimental results performed at Korea Aerospace Research Institute. The CMG which is able to produce a torque of lOO mNm per each, is mounted in a pyramid configuration with four SGCMGs. Each CMG test and a single axis maneuver test with four-CMG cluster configuration are performed to confirm their performance on a ground-test facilities consisted of three major parts: a vibration isolation system, a dynamic force plate (Kistler sensor), and a DSP board. These facilities provide the accurate data of three axial and torques from the control moment gyro. Details of the CMG experimental results are presented with discussion of the experimental errors. The experimental data are compared with theoretical results and both results are used to verify their performance specifications.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.732-735
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• 2002

By forming lens-like shapes on the electrode surfaces in OLEDs, the external quantum efficiency is enhanced. The external quantum efficiency of the proposed structure can be much more increased compared to that of the flat structure by decreasing the length of major axis and increasing the length of minor axis for the lens-like shapes.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.185-190
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• 2005

This work presents a numerical procedure to optimize the elliptic-shaped pin fin arrays to enhance turbulent heat transfer. The response surface method is used as an optimization technique with Reynolds-averaged Navier Stokes analysis of flow and heat transfer. Shear stress transport (SST) turbulence model is used as a turbulence closure. Computational results for average heat transfer rate show a reasonable agreement with the experimental data. Four variables including major axis length, minor axis length, pitch and the pin fin length nondimensionalized by duct height are chosen as design variables. The objective function is defined as a linear combination of heat transfer and friction-loss related terms with weighting factor. D-optimal design is used to reduce the data points, and, with only 28 points, reliable response surface is obtained. Optimum shapes of the pin-fin arrays have been obtained in the range from 0.0 to 0.1 of weighting factor.

• The Korean Journal of Applied Statistics
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• v.16 no.1
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• pp.129-140
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• 2003

This study was to develop a fruit sorting system using statistical image processing. Histogram was used to compare fruit colors to standard fruit color and edge detector using Wilcoxon test was used to calculate an accurate geometrical characteristics of fruit including perimeter, area, major axis and minor axis length and roundness. The experimental result obtained from using our system for sorting apples was presented.