• Journal of Advanced Navigation Technology
• /
• v.6 no.3
• /
• pp.203-210
• /
• 2002

In this paper, the BER performance of IEEE 802.11a OFDM WLAN system is obtained by simulation and it is shown that the proposed modified channel estimation algorithm improves the channel estimation performance of the system. The wireless channel used in channel simulation includes AWGN and delay spread channel implemented by TDL model. At first, the performance of OFDM WLAN system according to data rate and coding rate defined in standard is evaluated in AWGN channel. Then, imperfect channel estimation in indoor wireless channel is considered. After the performance of conventional channel estimation scheme using only two long training symbols is evaluated, and that of proposed modified channel estimation scheme using additional 8 short training symbol is compared with it. From the simulation results, it is shown that modified channel estimation scheme provides reduced channel estimation error and improves the channel estimation performance due to noise averaging effect with the same preamble format as defined in specification.

• Journal of Distribution Science
• /
• v.18 no.1
• /
• pp.5-13
• /
• 2020

Purpose: The purpose of this study is to examine the growth and change process of Korean cosmetic market that has grown more than three times since 2000. It also examined how the growth and decline of the cosmetics brands are related to the change of the cosmetic distribution structure. Research methodology: This study tried to classify the change of the Korean cosmetics market into four stages based on the market sales information. It analyzed the sales information of Korean cosmetic companies and the relationship with the sales of the brands by distribution channel. Results: One-brand store channel had played a leading role in the market growth, and multi-brand stores have grown and a number of brands also grew through that channel since 2013. Since 2016, multi-brand stores have continued to grow and have dominated the market beyond one-brand store channel. Conclusions: The changes in sales of domestic cosmetics companies have been classified based on the distribution channel type in four stages: the emergence of one-brand store, the growth of one-brand store channel, the growth of multi-brand store channel, and the decline of one-brand store channel. In conclusion, multi-brand store channels have recently grown in the Korean cosmetics market, and this trend is expected to continue.

• Nuclear Engineering and Technology
• /
• v.20 no.2
• /
• pp.80-87
• /
• 1988

Predicted in this paper are flow distributions in average and hot channels of the reactor core during small and large break LOCAs. Also estimated based on REALP5/MOD2 calculations are the effects of cross flow between channels on LOCA analysis results. It has been so far generally accepted that a single average channel is sufficient for small break LOCA core hydraulic modelling. However, based on these calculation results, hot channel modeling (two channel modeling) is found necessary in order to guarantee more reliable and conservative results. In large break LOCA blowdown phase, the hot channel thermal hydraulics is worse than that of average channel in both cases with the without consideration of cross flow.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.12 no.3
• /
• pp.1098-1112
• /
• 2018

Achievable sum rate and energy efficiency (EE) are investigated for the massive multiple-input multiple-output (Massive MIMO) downlink with channel aging in the time varying Ricean fading channel. Specifically, the expression of the achievable sum rate of the system for the maximum ratio transmission (MRT) precoder with aged channel state information (CSI) in the time varying Ricean fading channel is first presented. Based on the expression, the effect of both channel aging and the Ricean factor on the power scaling law are studied. It is found that the transmit power of base station (BS) is scaled down by $1/{\sqrt{M}}$(where M is the number of the BS antennas) when the Ricean factor K is equal to zero (i.e., time varying Rayleigh fading channel), indicating that aged CSI does not affect the power scaling law. However, the transmit power of the BS is scaled down by 1/M for the time varying Ricean fading channel (where $K{\neq}0$) indicating that the Ricean factor affects the power scaling law and sum rate, and channel aging only leads to a reduction of the sum rate. Second, the EE of the system is analyzed based on the general power consumption model. Both the theoretical analysis and the simulations show that the channel aging could degrade the sum rate and the EE of the system, and it does not affect the power scaling law.

• Korean Chemical Engineering Research
• /
• v.53 no.6
• /
• pp.818-823
• /
• 2015

In this study, FT reaction in a microchannel was simulated using computational fluid dynamics(CFD), and sensitivity analyses conducted to see effects of channel geometry variables, namely, process channel width, height, gap between process channel and cooling channel, and gap between process channels on the channel temperature profile. Microchannel reactor considered in the study is composed of five reaction channels with height and width ranging from 0.5 mm to 5.0 mm. Cooling surfaces is assumed to be in isothermal condition to account for the heat exchange between the surface and process channels. A gas mixture of $H_2$ and CO($H_2/CO$ molar ratio = 2) is used as a reactant and operating conditions are the following: GHSV(gas hourly space velocity) = $10000h^{-1}$, pressure = 20 bar, and temperature = 483 K. From the simulation study, it was confirmed that heat removal in an FT microchannel reactor is affected channel geometry variables. Of the channel geometry variables considered, channel height and width have significant effect on the channel temperature profile. However, gap between cooling surface and process channel, and gap between process channels have little effect. Maximum temperature in the reaction channel was found to be proportional to channel height, and not affected by the width over a particular channel width size. Therefore, microchannels with smaller channel height(about less than 2 mm) and bigger channel width (about more than 4 mm), can be attractive design for better heat removal and higher production.

• The Korean Journal of Physiology and Pharmacology
• /
• v.2 no.5
• /
• pp.549-553
• /
• 1998

Using the planar lipid bilayer method, we investigated the effect of d-tubocurarine (dTC) on the extracellular side of large-conductance $Ca^{2+}-activated\;K^+$ channel from rat brain. When the initial open probability (Po) of the channel was relatively high, dTC decreased channel activity in a concentration dependent manner. In contrast, when the initial Po was lower, sub-micro molar dTC increased channel activity by destabilizing the closed states of the channel. Further addition of dTC up to micro molar range decreased channel activity. This dual effect of dTC implicates that there exist at least two different binding sites for dTC.

• The Research Journal of the Costume Culture
• /
• v.26 no.3
• /
• pp.346-359
• /
• 2018

Currently, dramatic change had led to the growth of the distribution environment and the retailer's distribution channel. This change had shifted the 'single channel' to 'multi channel', and from 'cross channel' to 'omni channel'. While fashion companies using omni channel are rapidly growing, few research regarding omni channel had been done in academic field. In this study, we examined the influence of omni channel characteristics on consumers' perceived risk as well as consumers' perceived risk toward attitude and intention to use omni channel. We surveyed 696 male and female respondents aged 20 to 40 who lived in Seoul and the metropolitan area. Using AMOS 20.0, factor analysis, reliability analysis, and structural equation model analysis were performed to verify the model of this study. The results were as follows. First, omni channel's instant connectivity, location-based provability, interactivity, and entertainment factors did not decrease impacts on the perceived risk related to privacy and annoyance. Second, omni channel's instant connectivity and entertainment did not increase effects on the perceived financial risk, and location-based provability and interactivity did not increase effect on perceived financial risk. Third, the perceived risk concerning omni channel did not decrease on consumer attitude toward omni channel. Fourth, consumer attitude toward omni channel influenced the intention to use omni channel significantly.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2006.05a
• /
• pp.199-200
• /
• 2006

It will not be an exaggeration to say that one of the most important features of RT (Rapid Tooling) technology is to easy manufacturing complex shape of cooling channel in injection mold. That is, RT technology is hardly influenced complex shape of tool, Therefore, mold designer can optimize the position and shape of cooling channel whatever they want. In this study, we optimized cooling channel through CAE analysis to solve the problem; prototype-connector-mold applied conventional cooling channel, locally warped by internal stress: The effect of three-dimensional cooling channel was supported by simulation result. But it is impossible to produce injection mold applied three-dimensional cooling channel through machining operation. Therefore, we produced the prototype-connector-mold with three-dimensional cooling channel using Direct Metal Laser Sintering (DMLS) process, and get good-quality prototype-connector without warpage.

• Journal of Mechanical Science and Technology
• /
• v.16 no.8
• /
• pp.1144-1153
• /
• 2002

A hybrid performance prediction method is proposed in the present study. A channel diffuser is divided into four subregions: vaneless space, semi-vaneless space, channel, and channel exit region. One-dimensional compressible core flow and boundary layer calculation of each region with an incidence loss model and empirical correlation of residuary pressure recovery coefficient of a channel predict the performance of diffusers. Three channel diffusers are designed and tested for validating the developed prediction method. The pressure distributions from an impeller exit to the channel diffuser exit are measured and discussed for various operating conditions from choke to nearly surge conditions. The strong non-uniform pressure distribution which is caused by impeller-diffuser interaction is obtained over the vaneless and semi-vaneless spaces. The predicted performance shows good agreement with the measured performance of diffusers at a design condition as well as at off-design conditions.

• Speech Sciences
• /
• v.11 no.1
• /
• pp.43-52
• /
• 2004

This paper concerns an effective dual-channel noise reduction method to increase the performance of speech recognition in a car environment. While various single channel methods have already been developed and dual-channel methods have been studied somewhat, their effectiveness in real environments, such as in cars, has not yet been formally proven in terms of achieving acceptable performance level. Our aim is to remedy the low performance of the single and dual-channel noise reduction methods. This paper proposes an effective dual-channel noise reduction method based on a high-pass filter and front-end processing of the eigendecomposition method. We experimented with a real multi-channel car database and compared the results with respect to the microphones arrangements. From the analysis and results, we show that the enhanced eigendecomposition method combined with high-pass filter indeed significantly improve the speech recognition performance under a dual-channel environment.