• Journal of Dental Rehabilitation and Applied Science
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• v.29 no.4
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• pp.366-376
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• 2013

The purpose of this study is to evaluate the marginal and internal fit of coping made by CAD/CAM using different scanning methods. Zirconia coping was made by each CAD/CAM system followed by intra-oral scanning, model optical scanning and model contact scanning. It was embedded into Epoxy Resin and was cut by buccal to lingual. AMD (Absolute marginal discrepancy), MG (Marginal gap), GA (Gap of axial), GL (Gap of line angle) and GO (Gap of occlusal) of each sample were measured. The result is as followed; 1. The mean value of AMD in Group 1, Group 2, Group 3 are $141.21{\pm}42.94{\mu}m$, $140.63{\pm}31.64{\mu}m$, $109.37{\pm}28.42{\mu}m$. The averages of MG in Group 1, Group 2, Group 3 are $82.52{\pm}43.99{\mu}m$, $90.28{\pm}27.93{\mu}m$, $66.55{\pm}28.77{\mu}m$. Statistically there is no difference in AMD and MG among the three Groups (Anova, P>0.05). 2. GA of Group 2 revealed statistically difference compared with Group 1 and Group 3 (Anova, P<0.05). 3. GL and GO of Group 1 showed statistically significant differences compared with Group 2 and Group 3 (Mann-whitney test (P<0.05). Zirconia copings made by 3 ways of scanning methods have no difference with conventional ceramics in AMD and MG which are known as the most important factors.

• Fire Science and Engineering
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• v.24 no.1
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• pp.90-94
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• 2010

In this study it is intended to review the moving characteristics of smoke by performing visualization simulation for the calculation of the optimal smoke exhaust air volume in case a fire occurs in tunnels where transverse ventilation is applied, and to obtain basic data necessary for the design of smoke exhaust systems by deriving optimal smoke exhaust operational conditions under various conditions. As a result of this study, if it was assumed 0 critical velocity in the tunnel, the smoke exhaust air volume was limited within 250 meter in the road-tunnel disaster prevention indicator and the exhaust efficiency was from 55.1% to 95.8% in the result of this study. If the wind velocity is in the tunnel, the exhaust rate intends to increase rapidly and the exhaust efficiency is decreased. In addition, if the wind velocity is increased, the exhaust rate should be increased in compared with the generation rate of smoke in maximum 1.8 or 1.04 times. In this study, when the wind velocity is in the tunnel, the limited exhaust rate is $84m^3/s{\cdot}250m$. And if it was assumed 1.75 m/s critical velocity in the tunnel, the exhaust rate would be defined $393m^3/s{\cdot}250m$($Q_E$ = 80 + 5Ar).

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.63-63
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• 2000

Deep submicron device contact hole에서의 bottom step coverage의 향상 및 SALICIDE공정의 필요성에 의해 collimated sputtering 및 ionized sputtering 등의 다양한 증착방법이 연구되어왔다. 반도체소자의 고집적화 및 미세화에 따라서 기존의 증착방법보다 더 높은 throughput을 가진 새로운 증착방법의 필요성이 대두되고 있다. Collimated sputtering방식으로 증착한 박막의 경우에는 증착속도가 느리고 collimator의 사용기간에 따른 공정조건의 변화가 단점으로 작용하였고 새로이 ionzied sputtering방식이 개발되었다. ionzied sputtering방식은 증착되는 금속 입자를 이온화시키고 기판에 바이어스를 걸어서 증착되는 입자의 방향성 및 증착속도의 향상을 얻을 수 있었다. 하지만 고집적도가 더욱 증가함에 따라서 더 높은 박막의 증착속도, bottom step coverage의 향상, 방향성의 향상과 더불어 증착되는 입자의 이온화 율의 증가 및 기존의 증착방식에 의한 박막보다 향상된 물성을 가진 박막증착의 필요성에 의해 hollow cathode magnetron sputtering방식이 연구되었다. HCM방식으로 titanium 박막을 증착하여 collimated sputtering 및 ionize sputtering 방식으로 증착한 titanium 박막과 물성을 비교해서 증착방식에 따른 박막물성의 차이를 연구하였다. 증착전에 기판온도는 30$0^{\circ}C$를 유지하였고 base pressure는 5.0$\times$10-9torr, working pressure는 5.7m torr로 유지하였다. power는 30kW를 가하여 50nm두께의 titanium박막을 증착하였다. 증착된 박막의 미세구조는 TEM 및 XRD로 분석하였다. HCM방식으로 증착한 titanium박막은 5nm두께의 비정질 층이 관찰되었고 ionized sputtering방식으로 증착한 titatnium박막에서 나타나는 것으로 보고된 silicon (002)와 titanium (0002) eledtron diffraction spot사이의 (10-10)spot은 관찰되지 않았다. 박막은 크고 작은 grain의 연속적 분포를 가졌고 HCM방식으로 증착한 titanium박막의 in-plane grain size가 다른 증착방식으로 증착한 박막에 비해 크게 관찰됨을 Plan-view TEM 분석을 통해서 확인되었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.1
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• pp.30-39
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• 1997

In this paper, a new practical coherent detection scheme for biorthogonal signals, which uses multi-symbol observation interval, is proposed and its performances are analyzed and simulated. The technique jointly estimates both the demondulated data and the channel from received signal only while reducing computation complexity by an approximate maximum-likelihood sequence estimation rather than symbol-by-symbol detection as in previous noncoherent detection. The scheme achieves performance close to that of ideal coherent detection with perfect channel estimates when select the appropriate observation symbol interval N in the given symbol alphabet wize M. What is particularly interesting is that the requeired average signal-to-noise ratio per bit ${\gamma}_{b}$ can be reducedd by as much as 1.4dB and the capacity can be increase by as much as 38% when we use this system in the CDMA cellular reverse link.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.1016-1023
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• 1998

DS-CDMA system requeires a power-efficient transmission and reception scheme to increase capacity. In this paper, coherent detection of DS-CDMA system with M-ary orthogonal signaling is considered, and multistage decision-directed channel estimator is proposed. The multistage decision-directed channel estimator is based on the fact that better channel estimation can be obtained by using the final decisions of the detector with a conventional decision-directed channel estimator. In this scheme, symbol detector and channel estimator operate algernaely. by simulation, it is shown that the proposed method achieves performance gain capare to conventional method, specially at low signal to noise ratio over fast time-variant channel with diversity.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.3
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• pp.18-27
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• 2000

Signal attenuation of Ka-band satellite communication system due to rain fading is more severe than those of conventional frequency band system, thus an efficient rain fade countermeasure technique is absolutely required. In this paper, we design an improved adaptive modulation system, which switches the modulation mode according to the channel condition, and propose the novel synchronization algorithms. We assume that the modulation scheme is M-ary PSK and the receiver is TDMA burst mode. And the transponder model is the same with KOREASAT-3. By using the adaptive modulation scheme, we satisfy the BER and mean spectral efficiency requirements, simultaneously, which is impossible by using the fixed modulation scheme.

• Journal of Satellite, Information and Communications
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• v.12 no.2
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• pp.15-20
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• 2017

A conventional TV relay broadcast is a method of transmitting a program by means of a microwave, a leased wire, or a satellite. With the latest advances in LTE network, a relay approach using LTE mobile communications network has become increasingly competing with the traditional TV relay broadcast method. Since 2012, TV Chosun has been using the LTE network for marathon production, and channel A has also broadcast a marathon production broadcast using the LTE network. Therefore in this paper, we investigated the marathon relay method using LTE mobile communications network and compared with the traditional TV marathon relay method, and then suggested the optimum method for the marathon relay.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.05a
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• pp.192-193
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• 2015

음극방식은 피방식체를 일정 전위로 음극분극 하는 원리로써 외부전원을 인가하거나 비전위의 금속을 희생양극으로 연결하여 방식하는 방법이다. 해수 중에서 음극방식을 실시할 경우 음극 표면에 용존산소 환원반응과 수소발생반응이 일어나 $OH^-$ 이온이 발생하게 된다. 이러한 반응에 의해 생성되는 석회질 피막 (Calcareous deposit)은 강구조물의 부식방지를 위한 물리적인 방호벽 역할을 하면서 용존산소의 확산 및 이동을 억제하며, 전류밀도를 감소시킨다. Potentiostat 및 rectifier를 이용하여 정전위 및 정전류 조건에서 형성된 석회질 피막을 SEM, EDS, XRD를 통해 분석하고 이를 바탕으로 양극의 종류(Al, Zn) 및 1, 5, $10mA/m^2$의 전류밀도 조건에서 실제 강관에 형성된 석회질 피막의 메커니즘을 해명하였다. 또한 석회질 피막 형성 시 Steel Wire Mesh를 설치하여 그 영향에 대해서도 분석하였다. 석회질 피막의 내구성은 침지-자연전위 및 밀착성 테스트를 통해 평가되었다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.9
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• pp.1672-1678
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• 2007

The communication systems and characteristics of transmit are very importance a serious view of ubiquitores society. The high rate systems have to construct for data of voice, graphics and moving-video with the multimedia to transmit on the low frequency band. The rate of data are relation that there are the bandwidth of line and channels, the bit per second and communication-systems. This paper study for the error performance of 2, 4 8 level FSK to transmit amount of data in the communication systems and design to FDM system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.7
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• pp.663-679
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• 1991

본 논문에서는 다중 경로 페이딩 채널에서 최대 다중 경로 지연폭이 한 비트 폭보다 큰 경우 발생할 수 있는 심볼간 간섭을 극복하기 위해 M-ary 신호 방식과 절환 신호 방식을 채용한 다중 경로 다이버시티 수신 noncoherent F나 ds / SSMA 통신 시스템의 평균 오율을 평가하였다. 시스템의 평균 오율은 가우스 근사법을 이용해 채널 파라메타와 PN 시퀀스의 길이와 같은 시스템 파라메타에 대한 식으로 표현하였고, 이러한 결과식을 이용해 M-ary FSK 시스템과 두 종류의 절환 수신기에 대한 FSK시스템의 평균 오율을 수치적으로 분석하였다.