• Design & Manufacturing
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• 제8권1호
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• pp.10-13
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• 2014

Plastic products are producted more than 70% of total processes by the injection molding. The injection molding process has 4 processes such as filling, packing, cooling and ejecting. It spends most of times in the cooling process. Therefore, it is important to control the mold temperature in producing plastic products. The time and system of cooling affect the product's quality and productivity. Especially, cooling time has about 60% of total injection cycle time. Therefore, we can improve a productivity by shortening cooling time. This study shows comparative study about cooling efficiency of spiral channel and baffle and observed the variation of time to freeze of molding As the result of CAE experiments, cooling rate by spiral channel had faster than baffle and as freeze time was decreased. Results of this study will be used widely to design for cooling system of injection mold.

• Bulletin of the Korean Chemical Society
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• 제23권2호
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• pp.267-270
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• 2002

Photodissociations of o-, m-, and p-iodotoluene radical cations were investigated by using Fourier-transform ion cyclotron resonance (FT-ICR) spectrometry. Iodotoluene radical cations were prepared in an ICR cell by a photoionization charge-transfer method. The time-resolved one-photon dissociation spectra were obtained at 532 nm and the identities of $C_7H_7^+$ products were determined by examining their bimolecular reactivities toward toluene-$d_8$. The two-photon dissociation spectra were also recorded in the wavelength range 615-670 nm. The laser power dependence, the temporal variation, and the identities of $C_7H_7^+$ were examined at 640 nm. The mechanism of unimolecular dissociation of iodotoluene radical cations is elucidated: the lowest barrier rearrangement channel leads exclusively to the formation of the benzyl cation, whereas the direct C-I cleavage channel yields the tolyl cations that rearrange to both benzyl and tropylium cations with dissimilar branching ratios among o-, m-, and p-isomers. With a two-photon energy of 3.87 eV at 640 nm, the direct C-I cleavage channel results in the product branching ratio, [tropylium cation]/[benzyl cation], in descending order, 0.16 for meta >0.09 for ortho >0.05 for para.

• Design & Manufacturing
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• 제6권1호
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• pp.1-4
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• 2012

Plastic products are producted more than 70% of total processes in the injection molding. The injection molding process has 4 processes such as filling, packing, cooling and ejecting. It spends most of times in the cooling process. Therefore, it is important to control the mold temperature in producing plastic products. The time and system of cooling affect the product's quality and productivity. Especially, cooling time has about 60% of total injection cycle time. Therefore, we can improve a productivity by shortening cooling time. In this study, it was made a comparative study about cooling of linear channels and baffles and observed the variation of mold temperature on the coolant's temperature. As the result, the linear channel's cooling rate had faster than baffles and as coolant's temperature was increased, difference of cooling time was increased. Result of this study will be used widely to design for cooling system of injection mold.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권4호
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• pp.767-783
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• 2013

This paper aims at designing a selective demodulation scheme based on Log-likelihood Ratio threshold (SDLT) instead of the conventional adaptive demodulation (ADM) scheme, by using rateless codes. The major difference is that the Log-likelihood ratio (LLR) threshold is identified as a key factor to control the demodulation rate, while the ADM uses decision region set (DRS) to adjust the bit rate. In the 16-QAM SDLT scheme, we deduce the decision regions over an additive white Gaussian channel, corresponding to the variation of LLR threshold and channel states. We also derived the equations to calculate demodulation rate and bit error rate (BER), which could be proven by simulation results. We present an adaptation strategy for SDLT, and compare it with ADM and adaptive modulation (AM). The simulation results show that our scheme not only significantly outperforms the ADM in terms of BER, but also achieves a performance as good as the AM scheme. Moreover, the proposed scheme can support much more rate patterns over a wide range of channel states.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.1453-1454
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• 2011

We have investigated the effect of silicon contents (0~0.4 molar ratios) on the performance of solution processed silicon-indium-zinc oxide (SIZO) thin-film transistors (TFTs). Despites its solution processed channel layer, low annealed temperature below $200^{\circ}C$ in air has been used for SIZO-TFTs. The $V_{th}$ is shifted from -4.04 to 5.15 V as increasing Si ratio in the SIZO-TFTs. The positive shift of $V_{th}$ as increasing Si contents in SIZO system indicates that Si suppresses the carrier generation in the active channel layer since $V_{th}$ is defined as the voltage required accumulating sufficient charge carriers to form a conductive channel path.

• Ocean and Polar Research
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• 제33권spc3호
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• pp.325-336
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• 2011

Seasonal to inter-annual variations of water properties in the western channel of the Korea Strait are investigated using quasi-monthly hydrographic observations collected during 2006-2010. Weak vertical temperature and salinity gradients are observed during the winter months and these remain until May. At the upper layer, temperature increases from March and reaches a maximum in August, while salinity decreases during the same period. Near-bottom water shows low temperatures during late winter and fall with a minimum peak in September. Korea Strait Bottom Cold Water produces thick layers (>20 m) in 2006 and 2010, while it is observed very near the bottom with relatively high temperature in 2008 and 2009.

• 한국콘텐츠학회논문지
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• 제8권6호
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• pp.34-42
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• 2008

무선망에서 다양한 트래픽의 종단간 서비스의 질을 보장하기 위해서는 매체접근제어가 요구된다. 무선망에서 다양한 트래픽이 채널에서 통합될 때 매체접근제어 프로토콜의 주요 단점은 한정된 대역폭을 어떻게 효율적으로 멀티 클래스 트래픽을 위해 지원할 수 있는가이다. 본 논문에서는 실시간 트래픽의 서비스의 질을 향상시키기 위해 동적 대역 슬롯 기법을 제안하였다. 제안된 기법에서는 동적파라미터를 전송하기 위해서 인 밴드 방식을 사용하였으며, 버퍼의 크기와 지연변이를 고려하여 이동국에서는 2상태 비트를 기지국으로 전송될 수 있도록 하였다. 제안된 기법은 실시간 트래픽의 서비스의 질을 보장하고 전송효율을 높일 수 있도록 하였다.

• ETRI Journal
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• 제31권4호
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• pp.399-407
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• 2009

In this paper, we present a robust $H_{\infty}$ distributed power control scheme for wireless CDMA communication systems. The proposed scheme is obtained by optimizing an objective function consisting of the user's performance degradation and the network interference, and it enables a user to address various user-centric and network-centric objectives by updating power in either a greedy or energy efficient manner. The control law is fully distributed in the sense that only its own channel variation needs to be estimated for each user. The proposed scheme is robust to channel fading due to the immediate decision of the power allocation of the next time step based on the estimations from the $H_{\infty}$ filter. Simulation results demonstrate the robustness of the scheme to the uncertainties of the channel and the excellent performance and versatility of the scheme with users adapting transmit power either in a user-centric or a network-centric efficient manner.

• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.1131-1137
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• 2015

Gallium nitride (GaN) is a promising material for next-generation high-power applications due to its wide bandgap, high breakdown field, high electron mobility, and good thermal conductivity. From a structure point of view, the vertical device is more suitable to high-power applications than planar devices because of its area effectiveness. However, it is challenging to obtain a completely upright vertical structure due to inevitable sidewall slope in anisotropic etching of GaN. In this letter, we design and analyze the enhancement-mode n-channel vertical GaN MOSFET with variation of sidewall gate angle by two-dimensional (2D) technology computer-aided design (TCAD) simulations. As the sidewall slope gets closer to right angle, the device performances are improved since a gradual slope provides a leakage current path through the bulk region.

• The Journal of the Acoustical Society of Korea
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• 제27권3E호
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• pp.69-76
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• 2008

Measurements of bubble size and distribution in the surface layer of the sea, wind speed, and variation of ocean environments were made continually over a four-day period in an experiment conducted in the South Sea of Korea during 17-20 September 2007. Theoretical background of bubble population model indicates that bubble population is a function of the depth, range and wind speed and bubble effects on sound speed shows that sound speed varies with frequency. Observational evidence exhibited that the middle size bubble population fit the model very well, however, smaller ones can not follow the model probably due to their short lifetime. Meanwhile, there is also a hysteresis effect of void fraction. Observational evidence also indicates that strong changes in sound speed are produced by the presence of swarms of micro bubbles especially from 7 kHz to 50 kHz, and calculation results are consistent with the measured data in the high frequency band, but inconsistent in the low frequency band. Based on the measurements of the sound speed and high frequency transmission configuration in the bubble layer, we present an estimation of underwater acoustic channel capacity in the bubble layer.