• Journal of the Korean Society of Safety
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• v.15 no.1
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• pp.36-42
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• 2000

An experimental study was carried out to investigate the effects of inclined angles of channel on thermal stability of electronic components. In this study, it is focused on the natural convection heat transfer from an inclined parallel channel with discrete protruding heat sources. The material used for the inclined parallel channel was epoxy-resin, while air as the cooling fluid. Heat transfer phenomena for inclined angles of $\psi$=$15^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$ and for the range of $9.52{\times}10^5/ were analyzed. The thermal fields in the channel were visualized by Mach-Zehnder interferometer. Also, local temperatures were measured by thermocouples along the channel wall and heat sources surface. As a result, for the range of $4.29{\times} 10^5/, a useful correlation of mean Nusselt number was proposed as a function of modified channel Rayleigh number.

• Solar Energy
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• v.19 no.3
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• pp.29-41
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• 1999

Three-dimensional natural convective heat transfer in a vertical channel with a protruding single module was investigated experimentally. The particular interest was in the removal of thermal energy from the module by convective heat transfer. Hence radiative and conductive heat losses were estimated by using thermocouples and heat flux sensor respectively. The flow fields in the channel were visualized by means of a smoke-method. Also, local temperatures were measured by thermocouples inside the channel, along the vertical wall and module surface. It is found that convective heat transfer was promoted at the lower comer of the module and was decreased at the upper comer due to a recirculation zone. A general correlation of the critical channel ratios was found as a function of Rayleigh number. For the range of $8.28{\times}10^3<Ra^*_c<3.48{\times}10^6$, a useful correlation for the mean Nusselt number was proposed as a function of modified channel Rayleigh number.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.12
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• pp.1774-1783
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• 1998

The transition from steady laminar to chaotic convection in a glass melting furnace specified by upper surface temperature distribution has been studied by the direct numerical analysis of the two and three-dimensional time dependent Navier-Stokes equations. The thermal instability of convection roll may take place when modified Rayleigh number($Ra_m$) is larger than $9.71{\times}10^4$. It is shown that the basic flows in a glass melting furnace are steady laminar, unsteady periodic, quasi-periodic or chaotic flow. The dimensionless time scale of unsteady period is about the viscous diffusion time, ${\tau}_d=H^2/{\nu}_0$. Through primary and secondary instability analyses the fundamental unsteady feature in a glass melting furnace is well defined as the unsteady periodic or weak chaotic flow.

• Nuclear Engineering and Technology
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• v.48 no.4
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• pp.925-931
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• 2016

In this study, laminar natural circulation and heat transfer in a tall rectangular enclosure with disconnected vertical partitions inside were investigated. Analytical expressions were developed to predict the circulation flow rate and the average Nusselt number in a partially partitioned enclosure with isothermal side walls at different temperatures and insulated top and bottom walls. The proposed formulas are then validated against numerical results for modified Rayleigh numbers of up to $10^6$. The impacts of the governing parameters are also examined along with a discussion of the heat transfer regimes.

• The KIPS Transactions:PartD
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• v.15D no.3
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• pp.313-320
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• 2008

A typical software development life cycle consists of a series of phases, each of which has some ability to insert and detect defects. To achieve desired quality, we should progress the defect removal with the all phases of the software development. The well-known model of phase-based defect profile is Gaffney model. This model assumes that the defect removal profile follows Rayleigh curve and uses the parameters as the phase index number. However, these is a problem that the location parameter cannot present the peak point of removed defects when you apply Gaffney model to the actual situation. Therefore, Gaffney model failed to represent the actual defect profile. This paper suggests two different models: One is modified Gaffney model that introduce the parameter of Putnam's SLIM model to replace of the location parameter, the other is the growth function model because the cumulative defect profile shows S-shaped. Suggested model is analyzed and verified by the defect profile sets that are obtained from 5 different software projects. We could see from the experiment, the suggested model performed better result than Gaffney model.

• Journal of Communications and Networks
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• v.10 no.1
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• pp.44-54
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• 2008

In this paper, an iterative multiple symbol differential detection for turbo coded differential unitary space-time modulation using a posteriori probability (APP) demodulator is investigated. Two approaches of different complexity based on linear prediction are presented to utilize the temporal correlation of fading for the APP demodulator. The first approach intends to take account of all possible previous symbols for linear prediction, thus requiring an increase of the number of trellis states of the APP demodulator. In contrast, the second approach applies Viterbi algorithm to assist the APP demodulator in estimating the previous symbols, hence allowing much reduced decoding complexity. These two approaches are found to provide a trade-off between performance and complexity. It is shown through simulation that both approaches can offer significant BER performance improvement over the conventional differential detection under both correlated slow and fast Rayleigh flat-fading channels. In addition, when comparing the first approach to a modified bit-interleaved turbo coded differential space-time modulation counterpart of comparable decoding complexity, the proposed decoding structure can offer performance gain over 3 dB at BER of $10^{-5}$.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.1
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• pp.117-124
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• 2015

Recently an opportunistic incremental relaying (OIR) system has been studied for improving the performance degradation in fading channel. However there are few studies on power control in the system, and the studies are assumed perfect knowledge of the all channels at transmitters. The assumption that the source know all channel information is difficult in practical channels. Therefore, in this paper we assume that the source knows partial channel information and propose a modified truncated channel inversion (TCI) power control scheme for the OIR system. We derive the channel capacity of the proposed system and perform Monte Carlo simulation. It is noticed that the proposed OIR system has better capacity than that of the power controlled system with direct path only, and the capacity increases with the number of relays. The power controlled OIR system gained more capacity of 29.7%, 32.7%, and 33.5% than that of the system with direct path only for the number of relays of 1, 3, and 5, respectively. The results from this paper can be applied to the estimation of a theoretical capacity for the currently operating cellular systems when they adopt the IOR system.