• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1495-1508
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• 1990

There are requirement of surface roughness in mechanical elements that has minute surface of several nm degree. When high precision surface roughness measurement is made with stylus type surface roughness measuring apparatus, measuring accuracy depend on the tip radius of diamond stylus. Therefore, ultra precision machining was accomplished using ion sputter machining in order to machining the stylus tip radius less than 0.5.mu.m, which is impossible through lapping machining. In this study, optimal machining condition for the ion sputter machining was obtained through the experiment under the various varing machinbing quantity and condition of diamond stylus. And as the result of applying this optimal condition, the good result was obtained that machining probability of stylus tip radius less than o.5.mu.m is 93%.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.367-368
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• 2006

Today, the Artificial Intervertebral Disc (AID) is being developed by increasing the oblique of the endplate gradually. In other words, Ultra-high Molecular Weight Polyethylene (UHMWPE) which is apply to the sliding core of the AID, does not change the shape but alters the oblique of endplate. However, the unreasonable increase of degree of freedom (DOF) can result in the aggravation of the bone fusion and the initial stability and it can also lead to the increase of the concentrated force in core. For these reasons, it is necessary to develop the advanced techniques, which choose the most adequate DOF. In this study, the new optimized modeling of the sliding core and the endplate, the fatigue characteristics, the crack propagation and the formation mechanism of wearing debris was studied and the minimizing technique will be derived from this research.

• Steel and Composite Structures
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• v.44 no.3
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• pp.407-421
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• 2022

Prefabricated hybrid wind turbine towers (WTTs) are promising due to height increase. This study proposes the use of ultra-high performance concrete (UHPC) to develop a new type of WTT without the need to use reinforcement. It is demonstrated that the UHPC WTT structure without reinforcing bars could achieve performance similar to that of reinforced concrete WTTs. To simplify the design of WTT, a design approach for the calculation of stresses at the horizontal joints of a WTT is proposed. The stress distribution near the region of the horizontal joint of the WTT structure under normal operating conditions and different load actions is studied using the proposed approach, which is validated by the finite element method. A further parametric study shows that the degree of prestressing and the bending moment both significantly affect the principal stress. The shear-to-torsion ratio also shows a significant influence on the principal tensile stress.

• Journal of IKEEE
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• v.24 no.2
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• pp.419-425
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• 2020

The market size of immersive 360-degree video contents, which are noted as one of the main technology of the fourth industry, increases every year. However, since most of the images are distributed through illegal distribution networks such as Torrent after the DRM gets lifted, the damage caused by illegal copying is also increasing. Although filtering technology is used as a technology to respond to these issues in 2D videos, most of those filtering technology has issues in that it has to overcome the technical limitation such as huge feature-point data volume and the related processing capacity due to ultra high resolution such as 4K UHD or higher in order to apply the existing technology to immersive 360° videos. To solve these problems, this paper proposes a feature-point recognition ratio improvement method for immersive 360-degree videos using deep learning technology.

• Journal of Korean Physical Therapy Science
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• v.21 no.1
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• pp.37-43
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• 2014

Background : The purpose of this study is to verify the type of influence on the skin color according to the photoaging symptoms depending on the degree of external activities among the factors that influence the skin due to UV exposure and to obtain the basic study data on the physical therapy of the skin. Methods : In this study, in order to investigate the type of influence on the skin color according to the photoaging symptoms when the body is exposed to the UV rays having various effects on our body, a study was conducted using questionnaires and skin color measurement tool targeting 20 male college soccer students with many external activities and the senior high school students who has relatively less external activities due to the preparation for college entrance. The skin color was measured and the results were compared. Result : In the test group having relatively higher external activities, while they had less use of the sunscreen, they had more degree of UV exposure, and for the recognition of ultraviolet hazard, more were aware that it was harmful. In addition, in the skin color measurement test conducted targeting the son and the father in order to investigate the association between the skin color and the genetic factors, the experimental group showed a significant difference(p<.05) but the control group did not show any significant difference(p>.05). Conclusion : Based on such study results, the UV exposure time and the use of sunscreen are thought to be an important factor in the skin care.

• Membrane Journal
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• v.11 no.3
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• pp.109-115
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• 2001

Pore-filled ion-exchange membranes in which polypropylene(PP) microporous membrane was used as a nascent membrane were prepared by an in-situ cross-linking technique. Poly(vinylbenzyl chloride)(PVBCI) reacted with piperazine(PIP) or 1,4-diaminobicyclo[2,2,2]octane(DABCO) in a di-methylforamide(DMF) solution was filled in the pores of the microporous base membrane. After gellation the remaining chloromethyl groups were, then reacted with an amine such as trimethylamine to form positively charged, ammonium site. This will produce the pore-filled anion-exchange membrane. It was shown that this simple 2 step procedure gave dimensionally stable, pore-filled membranes in which the MG of polymer gel and degree of cross-linking could be easily controlled by the concentration of PVBCI and cross-linker in the starting DMF solution. Specially, high water permeability (7.8 kg/$m^2$hr, host membrane: PP3, MG: 73%, degree of cross-linking: 10%, crosslinker: PIP) at ultra low pressure(100 kPa) indicates the produced pore-filled membranes is usable as a water softening membrane.

• Journal of Navigation and Port Research
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• v.37 no.5
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• pp.551-557
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• 2013

In this paper, we manufactured portable inflatable kayak using ultra high pressure drop stitch. by improving inflatable kayaks' performance with a design using the extra-high-voltage special space paper, they were manufactured to go near to performance of hard shell kayaks. The kayaks were manufactured having all merits of the performance of hard shell kayaks and functionality and portability of the inflatable kayaks, and through performance evaluation of test products, the performance was compared with previous hard shell kayaks. About 6 knot of target speed in the verification result of resistance performance, the developed kayak was more excellent than the HOBIE-KONA kayak by 12.33%. In case of same displacement in a result of inclination test, the centroid of the developed kayak was less distributed by 22.7% than the HOBIE-KONA kayak, based on the bottoms of the ships. This makes the difference for righting arm (GZ) lessened to some degree because the developed kayak is lower than the HOBIE-KONA kayak in the centroid. In the dynamic stability of ship bodies, the HOBIE-KONA kayak showed a little excellent performance. However, in rudder force and resistance factor, the developed kayak was more outstanding than the HOBIE-KONA kayak.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.9
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• pp.817-825
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• 2013

The UHDTV system, which provides realistic service with ultra-high definite video and multi-channel audio, has been studied as a next generation broadcasting service. Since the conventional digital terrestrial transmission system is not capable to cover the increased transmission data rate of the UHDTV service, there are great necessity of researches about increase of data rate. Accordingly, the researches has been studied to increase the transmission data rate of the DVB-T2 system using dual-polarized MIMO technique and high order modulation. In order to optimize the MIMO DVB-T2 system where irregular LDPC codes are used, it is necessary to study the design of the bit mapper that matches the LDPC code and QAM symbols in MIMO channel. However, the research related to the design of the bit mapper has been limited to the SISO system. Therefore, this paper defines a new parameter that indicates the VND distribution of MIMO DVB-T2 system and performs the performance analysis according to the parameter which will be helpful for designing a MIMO bit mapper.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1373-1377
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• 2014

Hot-stamping is a method of obtaining ultrahigh-strength steel by simultaneously forming and cooling boron steel in a press die after it has been heated at $900^{\circ}C$ or above. After heat treatment, boron steel has a strength of 1500 MPa or more. This material ensures a high level of quality because it overcomes the spring-back phenomenon, which is a problem associated with high-strength steel materials, and the degree of dimensional precision is improved by 90 or more because of the good formability compared with existing types of steel. In this study, the welding characteristics were identified through the butt and lap welding of hot-stamped steel using a disk laser. Full penetration was obtained at a faster speed with butt welding compared to lap welding, and a white band was observed in every specimen.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.10
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• pp.44-49
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• 2021

Seats in autonomous vehicles must be able to rotate to fully utilize the interior space. Generally, ultra-high strength steel is used for the rotation module because it should have high strength and high rigidity. In addition, the rotating parts are difficult to form because they have complex shapes. In this study, the upper plate of the rotating module, whose complex shape makes it difficult to form, was formed by applying the hot stamping method. The drawing method and the form-drawing method, which are generally used to form components of complex shapes, were compared. We showed that the form-drawing method increased the degree of freedom of the material flow to improve the formability, thus enabling the forming of the plate. In addition, the die and blank shapes were found to be important factors in determining the success of the hot stamping. The validity of the analysis results was confirmed through forming analysis and experiments.