• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.1
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• pp.1-8
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• 2011

In this paper, a water tank experiment using Binary Frequency Shift Keying (BFSK) method for text transmission performance by water surface fluctuation is conducted. Water surface fluctuation and delay spread which affect the channel coherence bandwidth is a limiting factor in underwater acoustic communication. The amplitude fluctuation and delay spread the smooth surface and fluctuation surface, were identified. The effective delay spread of both cases are 5ms, 4ms corresponding to the coherence bandwidth of 200Hz, 250Hz, respectively. The bit error rate of BFSK modulated text transmission is about $10^{-4}$ in less than 200bps in smooth surface but less than 250bps in fluctuation surface. Therefore, this experiment shows that the water surface fluctuation is important factor determining the performance of the underwater acoustic transmission.

• The KIPS Transactions:PartC
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• v.9C no.4
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• pp.581-588
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• 2002

In this paper, we newly propose the optical CDMA routing scheme for the radio access network. At the radio base station (RBS), the received radio signals are multiplied by the PN codes and converted to the CDMA radio signals. In the next optical CDMAS are performed and multiplxed by using the PN codes which are the addresses of the routing mobile switching center (MSC). At the MSC, the CDMA radio signals are routined to another MSC by the CDM receiver at the routing node. In the case MSC is equal to the desired MSC, the radio signal is correlated by the two-layerd spectrum despreading at a time. Finally we theoretically analyze the signal-to-interference and noise power ratio of regenerated signal and the routing error probability and show the availability of proposed scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.5
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• pp.992-998
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• 2017

For local advertising based on D2D communications, sources want advertisement messages to be diffused to unspecified users as many as possible. It is one of challenging issues to select target-areas for advertising if users are uniformly distributed. In this paper, we propose D2D based advertisement dissemination algorithm using user clustering with expectation-maximization. The user distribution of each cluster can be estimated by principal components (PCs) obtained from each cluster. That is, PCs enable the target-areas and routing paths to be properly determined according to the user distribution. Consequently, advertisement messages are able to be disseminated to many users. We evaluate performances of our proposed algorithm with respect to coverage probability and average reception number per user.

• Journal of Korea Technology Innovation Society
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• v.21 no.2
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• pp.684-714
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• 2018

Contrary to predictions, the market diffusion of smartwatch is proceeding slowly. Smartwatch companies should pursue new strategies to overcome this so-called chasm; however, little is known about smartwatch attributes valuable for target consumers. This study investigates beneficial and sacrificial features influencing overall perceived value of smartwatch, which in turn affects usage intention, and considers moderating effect of personal innovativeness. A total of 323 usable data were analysed using partial least squares. The results show that two benefits (utilitarian and hedonic) and three sacrifices (usability, performance, and finance) significantly impact on usage intention via perceived value. A significant effect of personal innovativeness as a moderator is also observed. Interestingly, the influence of social benefits on perceived value is not supported, which means strengthening image improvement strategies might not be appropriate for the diffusion. In order to overcome the chasm, suitable strategies should be used, and focusing on consumers who are highly innovative are strongly recommended.

• Korean Chemical Engineering Research
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• v.57 no.3
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• pp.358-367
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• 2019

Adsorption equilibrium and intraparticle diffusion characteristics of benzene, toluene, and xylene vapors on activated carbon and zeolite 13X were investigated. Static adsorption experiments were carried out under the pressure range of 0.01~0.07 bar while changing the adsorption temperature to 293.15 K, 303.15 K, and 313.15 K, respectively. Adsorption equilibrium was analyzed by Langmuir, Freundlich and Toth models. The adsorption energy was 5.26~31.0 kJ/mol representing physical adsorption characteristics. The maximum adsorption capacity on activated carbon was the largest for benzene, and the smallest for xylene. Toluene was in between. In the case of zeolite 13X, the maximum adsorption capacity was the largest for xylene, and the smallest for benzene as opposed to activated carbon. The effective diffusion coefficients of gas adsorbate were measured to be about $10^{-5}{\sim}10^{-4}cm^2/s$, and increased with temperature. As the pressure increased, the effective diffusion coefficients were decreased. The dependence of effective diffusion coefficients on temperature and pressure was greater in zeolite 13X particles than in activated carbon. Therefore, it is necessary to express the diffusion coefficients as a function of pressure in order to predict the precise dynamic behavior of the adsorption process using zeolite 13X where the pressure fluctuation occurs abruptly.

• The Journal of the Acoustical Society of Korea
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• v.42 no.6
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• pp.491-499
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• 2023

Scattering by Sea surface roughness occurs due to sea level roughness, communication performance deteriorates by causing frequency spread in communication signals and time variation in communication channels. In order to compare the difference in time variation of underwater acoustic communication channel according to the surface roughness, an experiment was performed in a tank owned by Hanyang University Ocean Acoustics Lab. Artificial surface roughness was created in the tank and communication signals with three bandwidths were used (8 kHz, 16 kHz, 32 kHz). The measured surface roughness was converted into a Rayleigh parameter and used as a roughness parameter, and statistical analysis was performed on the time-varying channel characteristics of the surface path using Doppler spread and correlation time. For the Doppler spread of the surface path, the Weighted Root Mean Square Doppler spread (w_fσ_ν) that corrected the effect of the carrier frequency and bandwidth of the communication signal was used. Using the correlation time of the surface path and the energy ratio of the direct path and the surface path, the correlation of total channels was simulated and compared with the measured correlation time of total channels. In this study, we propose a method for efficient communication signal design in an arbitrary marine environment by using the time-varying characteristics of the sea surface path according to the sea surface roughness.

• Journal of the Korean Vacuum Society
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• v.2 no.1
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• pp.99-108
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• 1993

저압화학증착법에 의해 제조된 hemispheircal 및 rugged Si 박막들은 64 Mbit DRAM 이상의 캐패시터에 사용하기 위해 개발되었다. 이 공정을 사용하므로써 종래에 사용되던 Si 전극의 평평한 표면이 hemispherical 혹은 rugged 박막 형태의 표면으로 변한다. 위와 같은 박막은 비정질 Si 표면에서 핵생성되며 Si 원자 확산에 의해 결정립들이 결정체로 성장한다. 화학증착의 변수, 열처리 및 in-situ doping process들은 hemispherical 및 rugged Si 박막의 미세구조에 영향을 준다. 동일 두께에서는 고온에서 이루어질 때 혹은 동일 온도일 경우에는 얇은 박막층일 때에 하부전극의 표면들이 rugged poly Si 형상을 나타내며 이렇게 됨으로써 유효면적은 2.1배로 증가한다. 이와 같은 캐패시터 유효면적 증가는 대체로 높은 신뢰성을 갖는 두꺼운 절연막을 사용하면서 stack 캐패시터 구조의 높이를 감소시킬 수 있다. 따라서 이러한 제조기술은 차세대 캐패시터에 적용될 수 있다.

• Proceedings of the Korea Information Processing Society Conference
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• 2011.11a
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• pp.706-709
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• 2011

모바일 네트워크 고도화 및 네트워크와 단말기의 비약적인 발전으로 모바일 기기의 보급이 확산되고, 시장의 경쟁 본격화에 따른 개방형 플랫폼 증가와 애플리케이션 및 모바일 웹의 활성화가 이뤄지고 있다. 또한 모바일 환경에서의 개발이 표준화 되어가면서 제작 및 배포가 용이해지고 있다. 이러한 환경적인 영향으로 모바일 웹 및 어플리케이션에 대한 보안 위협은 더욱 가중되고 있으며 공격의 규모 및 피해가 증가될 것으로 예상된다. 본 논문에서는 이러한 모바일 환경에서 인증 보안을 강화하기 위해 인증 서비스에 위치정보를 활용하는 방안을 제안하고 개인별로 특화된 인증에 관련된 LBS(Location-Based Service)를 제공할 수 있는 시스템을 구현한다. 이 시스템의 구현을 통해 사용자 위치에 따라 인증 유효성 여부를 체크함으로써 현재의 인증시스템에서 신뢰성과 유효성을 추가적으로 확보 할 수 있음을 증명하고 구체적인 활용 방안을 제안한다.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1406_1407
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• 2009

Fowler-Nordheim의 전자 방출과 열전자 방출 메카니즘을 이용하여 절연유체 내 전계에 의한 도체의 음극에서 전자 방출현상과 열에 의한 열전자 방출현상을 고려하고 유한요소법(Finite Element Method)을 이용하여 해석하였다. 절연유체 내 공간전하에 대한 해석기법으로 푸아송 방정식, 양이온, 음이온, 전자에 대한 전하연속 방정식, 온도에 대한 열 확산 방정식으로 이루어진 5개의 지배방정식에 Fowler-Nordheim의 전계 방출과 Richardson-Dushman의 열전자 방출을 경계조건으로 부여하였다. 단자 전류는 유한요소법과 잘 부합하는 에너지법으로 계산되었다. 쌍 곡선형 PDE의 공간전하 전파에 대한 지배 방정식은 일반적으로 수치적인 불안정성을 가지므로 인공 확산 항을 고려하여 이를 해결하였다. 제안된 해석법은 세 개의 캐리어를 가진 x-y 좌표축의 2차원 평판 모델에 적용하여 그 유효성을 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1720-1730
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• 1995

Finite-difference analysis was conducted to study the natural convection of a stably stratified salt-water solution in an annulus due to lateral heating. The main purpose of this study is to examine in detail the multi-layered flow structure. Calculation was thus made for R $a_{\eta}$=2*10$^{5}$ and 6.5*10$^{5}$ . Formation of layered flow structure, merging process of layers, the corresponding temperature and concentration distributions, Nusselt number variations with time are examined. Numerical results show that in each layer, the temperature profile looks 'S`-shaped and the concentration profile is uniform due to the convective mixing. The formation of the roll and the layer is governed by natural convection due to the temperature gradient and the merging process of the layer by diffusion of the concentration.ation.