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Performance Investigation of Space-Time Block Coded Multicarrier DS-CDMA in Time-Varying Channels

  • Narzullaev, Anvar;Ryu, Kwan-Woong;Park, Yong-Wan
    • ETRI Journal
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    • v.28 no.5
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    • pp.684-687
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    • 2006
  • In this letter, we evaluate the system performance of a space-time block coded (STBC) multicarrier (MC) DS-CDMA system over a time selective fading channel, with imperfect channel knowledge. The average bit error rate impairment due to imperfect channel information is investigated by taking into account the effect of the STBC position. We consider two schemes: STBC after spreading and STBC before spreading in the MC DS-CDMA system. In the scheme with STBC after spreading, STBC is performed at the chip level; in the scheme with STBC before spreading, STBC is performed at the symbol level. We found that these two schemes have various channel estimation errors, and that the system with STBC before spreading is more sensitive to channel estimation than the system with STBC after spreading. Furthermore, derived results prove that a high spreading factor (SF) in the MC DS-CDMA system with STBC before spreading leads to high channel estimation error, whereas for a system with STBC after spreading this statement is not true.

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Menu Structure Design using Asymmetric Spreading Activation in Mobile Phone (비대칭 활성화 확산 이론을 이용한 휴대폰 메뉴 구조 디자인)

  • Oh, Se-Eung;Myung, Ro-Hae
    • Journal of the Ergonomics Society of Korea
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    • v.28 no.1
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    • pp.1-7
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    • 2009
  • As products are getting more diverse and new products are entering the market faster, customers have trouble learning how to use them. User-oriented menu structures may solve this problem. In order to design user-oriented menu structures, spreading activation theory has been studied. The spreading activation test shows that the strong associative relationship between words has shorter response times. Based on the spreading activation test, asymmetric spreading activation was introduced and a hypothesis that in a well-designed menu structure, association between upper-low menu pairs is not affected by an activation direction was tested for this study. In this study the menu of a cellular phone (Model: SPH-w2900) was extracted, and underwent 1st spreading activation tests. Then, on each menu pair, response time differences (asymmetric transition) by accuracy and directions were analyzed to find out problems in labels and improve menu structures and vocabulary. Second spreading activation tests were conducted to check whether asymmetric transitions decreased. The results showed that response time differences (asymmetric transition) for activation directions were found to be dropped significantly. Asymmetric transitions in spreading activation presented in this study will be helpful to define user-oriented menu structures.

Review : Continuous Fiber Tow Spreading Technologies and Its Applications (연속 섬유의 펼침에 대한 기술 현황 및 적용)

  • Roh, Jeong U;Lee, Woo Il
    • Composites Research
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    • v.26 no.3
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    • pp.155-159
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    • 2013
  • This paper reviewed the continuous fiber tow spreading technologies and its applications. The effect of the continuous fiber tow spreading in manufacturing process of continuous fiber reinforced thermoplastic composite was introduced theoretically. The fiber tow spreading technologies were categorized according to the spreading medium and its order during manufacturing process. The general principles, the applications, and the merits and demerits of fiber tow spreading technologies were introduced. Furthermore, the proposal for future direction of research on this issue was considered in this study.

An experimental Investigation on Flame spreading over liquid fuel surface (액체 연료 표면에서의 화염확장기구에 관한 실험적 연구)

  • 김한석
    • Fire Science and Engineering
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    • v.7 no.1
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    • pp.5-10
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    • 1993
  • Flame spreading over liquid fuel surface has been investigated using thermocouple and schlieren photograph. Without forced convection, it was clearly found that the flame spreading is mainly controlled by surface flow which is maybe generated by change of surface tension. Furthermore, the radiative heat transfer is dominant over a conductive heat transfer in kerosene. But the latter was found more influential than the former in diesel. Oscillation of flame spreading was found. It maybe cause of surface flow.

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An Experimental Investigation on Flame Spreading Over Liquid Fuel Surface (액체연료표면에서의 화염 확장에 관한 연구)

  • 김한석;백승욱;문정기
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.2
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    • pp.271-276
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    • 1989
  • Flame spreading over a hydrocarbon fuel surface has been investigated for liquid fuels such as kerosene and diesel, using thermocouple. Without forced convection, it was clearly found that the flame spreading was mainly controlled by the liquid fuel surface flow. Furthermore, the radiative heat transfer was dominant over a conductive heat transfer in kerosene. But in diesel the latter was found to be more influential than the former, when the direction of windflow was the same as that of flame spreading. The oscillation period and amplitude of the flame spreading velocity increase if the windflow is blowing in the direction of the flame spreading velocity, and decrease if the direction of windflow is blowing against the flame spreading direction.

Effects of Current Spreading in GaN-based Light-emitting Diodes Using ITO Spreading Pad

  • Kim, Jang Hyun;Kim, Garam;Park, Euyhwan;Kang, Dong Hoon;Park, Byung-Gook
    • JSTS:Journal of Semiconductor Technology and Science
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    • v.15 no.1
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    • pp.114-121
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    • 2015
  • In conventional LEDs, a mesa-structure is usually used and it causes the current to be overcrowded in a specific region. We propose a novel structure of GaN-based LED to overcome this problem. In order to distribute the current in an active region, a spreading pad is inserted at the p-type region in the GaN based LED device. The inserted spreading pad helps the current flow because it is more conductive than the p-type GaN layer. By performing electrical and optical simulations, the effects of the spreading pad insertion are confirmed. The results of electrical simulation show that the current spreads more uniformly and more radiative recombination is produced as well. Moreover, from the optical simulation, it is revealed that the ITO is less absorptive material than p-GaN if the condition of specific wavelength sources is satisfied. Considering all of the results, we can conclude that the luminescent power is enhanced by the spreading pad.

Reflection Seismology in the Southern Ayu Trough, a Slow-spreading Divergent Boundary

  • Hong, Jong-Kuk;Lee, Sang-Mook
    • Ocean and Polar Research
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    • v.24 no.3
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    • pp.189-196
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    • 2002
  • A multichannel seismic survey was conducted in the southern Ayu Trough which is the only spreading boundary between the Philippine Sea and Caroline plates. The seismic system used in this study comprises of 2.46-l sleeve gun and a 12-channel streamer with a group interval of 6.25m. Migration technique was used to analyze seismic velocity, and poststack depth migration was applied to the stacked data. The sediment thickness obtained from the depth section tends to increase with distance from the spreading axis. Sedimentation rates are poorly constrainted in the study area. The apparent half-spreading rates estimated from the sediment thickness and sedimentation rate from DSDP hole on the caroline plate are 4.7mm/yr and 7.9mm/yr at $1^{\circ}24'N\;and\;0^{\circ}42'N$, respectively, which are fester than Previously suggested. On the basis of new oblique spreading geometry, the recalculated spreading rates are 5.4mm/yr and 9.1mm/yr at $1^{\circ}24'N\;and\;0^{\circ}42'N$, respectively. Seismic sections show that the topography is asymmetric across the Ayu Trough and the acoustic basement is rough. These features are consistent with the earlier suggestion that the Ayu Trough is a slow-spreading divergent boundary. A detailed examination of seismic profiles away from the axis shows that sediments can be divided into two layers which implies a possible change in the spreading rate anuor sedimentation condition during the formation of the trough.

Experimental Study of the Evaporation of Spreading Liquid Nitrogen (확산하는 액체질소의 증발에 관한 실험적 연구)

  • KIM, MYUNGBAE;CHOI, BYUNGIL;KIM, TAE-HOON;DO, KYHYUNG;HAN, YONGSHIK;CHUNG, KYUNGYUL
    • Transactions of the Korean hydrogen and new energy society
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    • v.29 no.5
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    • pp.466-472
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    • 2018
  • The investigation of cryogenic liquid pool spreading is an essential procedure to assess the hazard of cryogenic liquid usage. In this experimental study, to measure the evaporation velocity when the pool is spreading, liquid nitrogen was continuously released onto unconfined concrete ground. Almost all of the reported results are based on a non-spreading pool in which cryogenic liquid is instantaneously poured onto bounded ground for a very short period of time. A simultaneous measurement of the pool location using thermocouples and of the pool mass using a digital balance was carried out to measure the evaporation velocity and the pool radius. A greater release flow rate was found to result in a greater average evaporation velocity, and the evaporation velocity decreased with the spreading time and the pool radius.

Cell-based Discrete Event and Discrete Time Simulation for the Prediction of Oil Slick Movement and Spreading in Ocean Environment (해상에서의 원유 확산 과정 예측을 위한 격자 기반 이산 사건 및 이산 시간 시뮬레이션)

  • Ha, Sol;Cha, Ju-Hwan;Ku, Nam-Kug;Lee, Kyu-Yeul
    • Korean Journal of Computational Design and Engineering
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    • v.17 no.1
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    • pp.45-53
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    • 2012
  • In this paper, oil spreading simulation model is proposed for analyzing the oil spreading phenomenon rapidly when the ocean is polluted by the oil from a stranded ship. The space occupied by the ocean is converted into the latticed cell, and the each cell contains the information, such as the quantity of the oil, the temperature of the ocean, and the direction of current and wind. Two states, such as "clean" and "polluted" are defined in the each cell, and the oil in the cell spreads to the neighbor cells by the spreading rules. There are three spreading rules. First, the oil in the certain cell only spreads to the neighbor cells that contain larger oil than the certain cell. Second, the oil evaporates in proportion to the temperature of the ocean at the every time step. Third, the oil spreading property is affected by the direction and the speed of the current and the wind. The oil spreading simulation model of the each cell is defined by using the combined discrete event and discrete time simulation model architecture with the information and the spreading rules in the cell. The oil spreading simulation is performed when the oil of 10,000 kL is polluted in the ocean environment of 300 m by 300 m with various current and wind.