• Proceedings of the Korean Fiber Society Conference
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• 2003.10b
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• pp.76-79
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• 2003

Recently, many attempts have been made to develop high strength and high modulus fibers from conventional polymers such as poly(vinyl alcohol) (PVA)[1-4] and polyethylene (PE). PVA has potentiality to yield high strength and high modulus fiber, since they have high theoretically attainable moduli because of their planar zig-zag structure. As PVA has a melting temperature as high as 230$^{\circ}C$ in contrast to PE with a low melting temperature such as 130$^{\circ}C$, it seems possible that high strength and high modulus fibers comparable to Aramid can be fabricated from PVA. (omitted)

• 한국정보디스플레이학회:학술대회논문집
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• 2000.01a
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• pp.61-62
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• 2000

We have studied the molecular orientation by the phase transitions of the chiral smectic liquid crystals, 4-(1-Trifluoromethyl-6-ethoxy-hexyloxycarbonlphenyl)-4-nonyloxybiphenyl-4-carbo-xylate (R-TFMEOHPNBC) to seek the original solution of the zig-zag defect using two different experimental techniques; optical system and x-ray scattering. The phase sequence is gamma ferroelectric $(SmC{\gamma}\;^*)$ ${\rightarrow}$ smectic A (SmA) ${\rightarrow}$ isotropic (I). Existence of two layer spacing at chiral smectic phase gives a possibility of the molecular orientation in two different tilt angles, ${\theta}\;_1$ and ${\theta}\;_2$, which are separated each other to the layer normal at a given temperature. The gamma ferroelectric-like phase is, first, discovered in the single compound.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.5
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• pp.848-872
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• 2015

Hydrodynamic derivatives or coefficients are required to predict the maneuvering characteristics of a marine vehicle. These derivatives are obtained numerically for a DTMB 5512 model ship by virtual simulating of captive model tests in a CFD environment. The computed coefficients are applied to predict the turning circle and zig-zag maneuvers of the model ship. The comparison of the simulated results with the available experimental data shows a very good agreement among them. The simulations show that the CFD is precise and affordable tool at the preliminary design stage to obtain maneuverability performance of a marine vehicles.

• Proceedings of the IEEK Conference
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• 2002.06d
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• pp.319-322
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• 2002

In this paper, we present a digital authentication technique using content-based watermarking in digital images. To digest the image contents, Hopfield network is employed on the block-based edge image. The Hopfield function extracts the same tit fur similarly looking blocks so that the values are unlikely to change to the innocuous manipulations while being changed far malicious manipulations. By inputting the extracted bit sequence with secret key to the cryptographic hash function, we generate a watermark for each block by seeding a pseudo random number generator with a hash output Therefore, the proposed authentication technique can distinguish between malicious attacks and innocuous attacks. Watermark embedding is based on the block-based spread spectrum method in DCT domain and the strength of watermark is adjusted according to the local statistics of DCT coefficients in a zig-zag scan line in AC subband. The numerical experiments show that the proposed technique is very efficient in the performance of robust authentication.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.3
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• pp.358-367
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• 1998

Since the performance of cooling tower is strongly dependent on the thermal performance of the packing, the evaluations of heat transfer rate and fan power from various packing have attracted intense interest. In the present study, two new packings have been devised and their performances have been compared with those of two existing packings to find better shape characteristic. It is found that one of the existing packings, which showed high heat transfer rate and medium fan power due to zig -zag flow passages and highly irregular surfaces, should be adapted.

• Korean Journal of Child Studies
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• v.21 no.3
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• pp.107-117
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• 2000

This study examined a portfolio scale for the assessment of the writing of 295 kindergarten children. The data were analyzed by Spradley's Developmental Research Sequence(DRS), using qualitative methods. Results showed that the writing portfolio scale for 4-year-olds includes "a word or write a children's name" "picture or word with shape of letters" and "scribbling or zig-zag". The writing portfolio scale for 5- and 6-year-olds includes "invented spelling" "write according to sound" and "omitted letters" "write a good hand". The writing portfolio scale for 4-, 5-, and 6-year-olds reflects their writing experience in daily life.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.552-555
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• 2001

This paper deal with the power factor improvement of DC power regenerating systems, which are composed of two inverters, zig-zag connected output transformers, and an AC filter. The output voltages of the inverter system are not sinusoidal. Regenerated complex power is analyzed on the basis of fundamental components and therefore the reactive power produced by harmonics is not considered. Therefore, it is needed a new control scheme capable of controlling the reactive power nearly to zero for nonsinusoidal case. Computer simulations are carried out to verify the validity of the proposed control scheme.

• Journal of the Korean Institute of Navigation
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• v.3 no.1
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• pp.1-17
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• 1979

It is very important for both naval architects and ship's officers to know the maneuvering characteristics of their ships. As the abilities of a rudder which controlls a ship can be determined clearly by analyzing the results of Kempf's zig-zag maneuver and directional stability of a ship also known by Dieudonn spiral maneuver, the importance of turning test which takes much time is recently apt to be neglected. But because the test can be executed comparatively more simply than any other maneuvering tests, it gives some informations on the directional stability, and turning characteristics may be expressed simply by the results of the test, it is still often performed. In this paper several assumptions are made to simplify the turning motion of a ship. The equations of initial transient phase, the radius ofsteady turning circle, and the center of the steady turning point are derived by using the hydrodynamic derivatives. And then the approximate method of drawing the turning circle geometrically is suggested.

• Bulletin of the Korean Chemical Society
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• v.5 no.2
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• pp.61-64
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• 1984

The molecular orbital calculations for solid HF are performed by using the pseudolattice method considering the coulomb lattice sum. In order to obtain the reliable net atomic charges and lattice energy of one dimensional chains, the limited counting of interactions terms up to second neighbours for zig-zag chain and third neighbours for linear chain are sufficient in this calculation. In three dimensional solid HF, the contribution of interaction energy between non-hydrogen bonded neighbours to lattice energy is about 3.5% and the lattice energy of nonpolar structure is stablized by 2.05 kcal/mole compared with that of polar structure. And, this method is further tested and compared with the other methods.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.3
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• pp.466-477
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• 2015

In this study, a numerical prediction method on manoeuvrability of Wind Turbine Installation Vessel (WTIV) is presented. Planar Motion Mechanism (PMM) captive test for the bare hull of WTIV is carried out in the model basin and compared with the numerical results using RANS simulation based on Open-source Field Operation And Manipulation (OpenFOAM) calculation to validate the developed method. The manoeuvrability of WTIV with skeg and/or without skeg is investigated using the numerical approach along with the captive model test. In the numerical calculations, the dynamic stability index which indicates the course keeping ability is evaluated and compared for three different hull configurations i.e. bare hull and other two hulls with center skeg and twin skeg. This paper proves that the numerical approach using RANS simulation can be readily applied to estimate the manoeuvrability of WTIV at the initial design stage.