• Korean Journal of Optics and Photonics
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• v.5 no.2
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• pp.298-303
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• 1994

Microlens arrays are fabricated by melting "islands" of thick photoresist on a glass substrate. Microlenses with diameters $25\mu\textrm{m}$, $50\mu\textrm{m}$, $100\mu\textrm{m}$are made. Their surface profiles are obtained by a scanning electron microscope and a mechanical surface profilometer. The wavefront of the microlenses is measured by phase-shifting techniques using a Mach-Zehnder-like configuration. Thereby wavefront errors, focal lengths. point spread functions are obtained. The microlens with the diameter of $100\mu\textrm{m}$ has focal length of $164\mu\textrm{m}$ and spot diameter is less than $5\mu\textrm{m}$..

• Journal of the Korean Society for Heat Treatment
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• v.2 no.2
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• pp.27-32
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• 1989

The effect of quenchant temperature on the surface residual stress was studied for AISI 8620 steel. Specimens were carburized at $900^{\circ}C$ in all case type furnace using a gas-base atmosphere of methanol cracked and liquefied petroleum gas, and then subjected to single reheat quenchant in oil or salt bath in the temperature range of $60^{\circ}C$ to $300^{\circ}C$. After carburizing and reheat Quenching, residual stress was measured by the hole drilling method. Experimental results showed that the surface residual stress was increased as the quenchant temperature was raised. This is in contrast to the fact that the formation of phase of low transformation strain such as bainite results in lower surface compressive stress. The greater compressive stress observed in specimens Quenched at higher temperature may be attributed to the shifting of the transformation start point farther from the surface, as was reported in other carburizing steels.

• Journal of Broadcast Engineering
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• v.20 no.1
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• pp.3-15
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• 2015

Recently terrestrial digital broadcasting systems have experienced a growth with the demand of high data rate. In order to meet such demand, the MIMO technology has received a wide attention. This paper proposes a pre-coding method, which provides high space channel correlation for the improved performance over terrestrial broadcasting channels when the polarized $2{\times}2$ MIMO SM is adopted for DVB-NGH systems. When signals with two different modulation orders are transmitted through two antennas, a method that is based on non-uniform power is also proposed for improved reception performance. To optimize the proposed method, phase shifting values for the pre-coding method and appropriate unequal power ratio are obtained. These obtained parameters are applied to a terrestrial broadcasting system, and then the performance improvement over the conventional SM is shown through computer simulations.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.4
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• pp.393-401
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• 2002

Pipelines in power plants, nuclear facilities and chemical industries are often affected by corrosion effects. It is important to inspect the internal defects in pipelines in oder to guarantee safe operational condition. We have taken relatively much time, cost and manpower to use conventional NDT methods because these methods are contact measuring methods. In this paper, we used digital shearography, a laser-based optical method which allows full-field measurement of surface displacement derivatives. This method has many advantages in practical use, such as low sensitivity to environmental noise, simple optical configuration and real time measurement. The experiment was performed with pressure vessels which has different internal cracks and detected internal cracks in the pressure vessels at a real time using phase shifting method.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.6 s.348
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• pp.1-8
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• 2006

In the asynchrous OFCDM(Orthogonal Frequency and Code Division Multiplexing) system, a three-step cell search algorithm is performed for the initial synchronization in the following three steps: OFCDM symbol timing, i.e., Fast Fourier Transform(FFT) window timing is estimated employing guard interval (GI) correlation in the first step, then the frame timing and CSSC (Cell Specific Scrambling Code) group is detected by taking the correlation of the CPICH(Common Pilot Channel) based on the property yeilded by shifting the CSSC phase in the frequency domain. Finally, the CSSC phase within the group is identified in the third step. This paper proposes a modification code(PCSSCG:Patial Cell Specific Scrambling Code Group) of the conventional CPICH based cell search algorithm in the second step which offers MS(Mobile Station) complexity reductions with the nearly same performance. The proposed method is to be compared and verified through the computer simulation.

• Korean Journal of Construction Engineering and Management
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• v.5 no.6 s.22
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• pp.146-153
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• 2004

The purposes of this study are to survey unfair aspects of specific provisions in the construction contract, and to suggest counterplans and institutional reformations. The research method of this study includes judicial precedent analysis and a questionnaire survey, The results of this study are as follows: 1) the main problems of unfair specific provisions are payment condition, shifting of the responsibility and adjustment in the contract sum. 2) counterplans ate suggested according to the construction phase : bid, construction and completion phase. 3) institutional reformations include firming up regulations, supervision, invigoration of claim, development of variation guideline, and so on.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.916-922
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• 2014

Diode rectifiers have been widely used for an AC to DC converter. But a big problem is that they include large harmonics components in the input currents. A 12-pulse configuration with phase shifting transformer is useful for reducing them. however, it still includes the ($12{\pm}1$)th (m; integer) harmonics in the input currents. In this paper, we propose a single-phase square wave auxiliary voltage supply which is inserted in the middle DC bus. It reduces harmonics especially the 11th and 13th and the harmonic characteristic becomes almost equivalent to a 24-pulse rectifier. Theoretical analysis of the combined 12-pulse diode rectifier with the auxiliary supply is presented and a control method of the auxiliary supply is proposed. The reduction in the input current harmonics is verified by simulation using software PSIM.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.1
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• pp.16-24
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• 1999

Residual stress is one of the causes which make defects in engineering components and materials. And interest in the measurement of residual stress exists in many industries. There are commonly used methods by which residual stresses are currently measured. But these methods have a little demerits. time consumption and other problems. Therefore we devised a new experimental technique to measure residual stress in materials with a combination of laser speckle pattern interferometry, finite element method and spot heating. The speckle pattern interferometer measures in-plane deformations while the heating provides for very localized stress relief. FEM is used for determining heat temperature and other parameters. The residual stresses are determined by the amount of strain that is measured subsequent to the heating and cool-down of the region being interrogated. A simple model is presented to provide a description of the method. In this paper, the ambiguity problem for the fringe patterns has solved by a phase shifting method.

• Transactions of the Society of Information Storage Systems
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• v.2 no.4
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• pp.224-229
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• 2006

There has been studied flow to minimize the spot size to increase data capacity. Optical data storage devices are being developed near practical limits with wavelength and NA of 405nm and 0.85. There has been studied many types of next generation storage devices such as blu-ray multilayer system, probe based data storage and holographic data storage. Among these data storage devices, solid immersion lens(SIL) based near field recording (NFR) has been widely studied. In this system, SIL is the key component that focuses the laser beam with a very small size which enables ultra high data capacity. Therefore, optical performance evaluation system is required for SIL assembly. In this dissertation, a simple and accurate SIL assembly measurement method is proposed with wedge plate lateral shearing interferometer(LSI). Wedge plate LSI is cheaper than commercialized interferometer, robust to the vibration and the moving distance for phase shifting is large that is order of micrometer. We designed the thickness, wedge angle, material, surface quality and wavelength of wedge plate as 1mm, 0.02degree, fused silica, lamda/10(10-5) and 405nm, respectively. Also, we confirmed simulation and experimental results with quantitative analysis. This simple wedge plate LSI can be applied to different types of SIL such as solid immersion mirror(SIM), hemispherical, super-hemispherical and elliptical SIL.

• Journal of Internet Computing and Services
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• v.22 no.1
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• pp.109-135
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• 2021

his study classified the development process of artificial intelligence (AI) speakers through analysis of the news text of artificial intelligence (AI) speakers shown in traditional news reports, and identified the characteristics of each product by period. The theoretical background used in the analysis are news frames and topic frames. As analysis methods, topic modeling and semantic network analysis using the LDA method were used. The research method was a content analysis method. From 2014 to 2019, 2710 news related to AI speakers were first collected, and secondly, topic frames were analyzed using Nodexl algorithm. The result of this study is that, first, the trend of topic frames by AI speaker provider type was different according to the characteristics of the four operators (communication service provider, online platform, OS provider, and IT device manufacturer). Specifically, online platform operators (Google, Naver, Amazon, Kakao) appeared as a frame that uses AI speakers as'search or input devices'. On the other hand, telecommunications operators (SKT, KT) showed prominent frames for IPTV, which is the parent company's flagship business, and 'auxiliary device' of the telecommunication business. Furthermore, the frame of "personalization of products and voice service" was remarkable for OS operators (MS, Apple), and the frame for IT device manufacturers (Samsung) was "Internet of Things (IoT) Integrated Intelligence System". The econd, result id that the trend of the topic frame by AI speaker development period (by year) showed a tendency to develop around AI technology in the first phase (2014-2016), and in the second phase (2017-2018), the social relationship between AI technology and users It was related to interaction, and in the third phase (2019), there was a trend of shifting from AI technology-centered to user-centered. As a result of QAP analysis, it was found that news frames by business operator and development period in AI speaker development are socially constituted by determinants of media discourse. The implication of this study was that the evolution of AI speakers was found by the characteristics of the parent company and the process of co-evolution due to interactions between users by business operator and development period. The implications of this study are that the results of this study are important indicators for predicting the future prospects of AI speakers and presenting directions accordingly.