• Journal of Information Processing Systems
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• v.13 no.4
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• pp.677-688
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• 2017

In order to solve the undetected probability of multiple targets in ultra-wideband (UWB) through-the-wall radar imaging (TWRI), a time-delay and amplitude modified back projection (BP) algorithm is proposed. The refraction point is found by Fermat's principle in the presence of a wall, and the time-delay is correctly compensated. On this basis, transmission loss of the electromagnetic wave, the absorption loss of the refraction wave, and the diffusion loss of the spherical wave are analyzed in detail. Amplitude compensation is deduced and tested on a model with a single-layer wall. The simulating results by finite difference time domain (FDTD) show that it is effective in increasing the scattering intensity of the targets behind the wall. Compensation for the diffusion loss in the spherical wave also plays a main role. Additionally, the two-layer wall model is simulated. Then, the calculating time and the imaging quality are compared between a single-layer wall model and a two-layer wall model. The results illustrate the performance of the time-delay and amplitude-modified BP algorithm with multiple targets and multiple-layer walls of UWB TWRI.

• Fire Science and Engineering
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• v.10 no.4
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• pp.13-18
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• 1996

A general description of sprinkler activation time in compartment-fire-generated smoke layers is made. For calculation of the time hot layer temperature is obtained from two-layer zonal model and time constant of sprinkler is measured. Upper-layer thickness at the instant of sprinkler activation is also presented with changes of opening area. The output of the present study provide inputs for the interaction modeling of sprinkler spray and compartment fire environment, which simulates fire suppression phenomena. Futhermore, experiments are performed in mock-up with gasoline pool fire in order to evaluate the reliability of the model.

• JSTS:Journal of Semiconductor Technology and Science
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• v.13 no.6
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• pp.668-675
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• 2013

We investigate the effect of the ageing time and etching time on the etching rate of SiGe mixed etching solution, namely 1 vp HF (6%), 2 vp $H_2O_2$ (30%) and 3 vp $CH_3COOH$ (99.8%). For this etching solution, we found that the etch rate of SiGe layer is saturated after the ageing time of 72 hours, and the selectivity of $Si_{0.8}Ge_{0.2}$ layer and Si layer is 20:1 at ageing time of 72 hours. The collapse was appeared at the etching time of 9min with etching solution of after saturation ageing time.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.11 s.254
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• pp.1348-1357
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• 2006

In a hybrid three-layer control architecture(deliberative, sequencing, and reflexive), the lowest reflexive layer consists of resources, actions, an action coordinator, and motion controllers. Because the execution of individual components in the reflexive layer should be done in real-time, each component has to be simple and, due to this reason, the Linux-RTAI(Real-Time Application Interface for Linux) has been used as an operating system. In this paper, a navigation control architecture, which combines the components in the reflexive layer and the navigation-related modules in the sequencing layer, is proposed. And then, as basic components, four actions(Goto, Avoid, Move, and EmergencyStop) are designed. Experimental results confirm the effectiveness of the proposed architecture and the performance of individual associated actions.

• Journal of Pharmaceutical Investigation
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• v.25 no.4
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• pp.339-345
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• 1995

For the effective treatment of aphthous stomatitis, the matrix type mucoadhesive patches containing triamcinolone acetonide have been formulated. The drug layer was obtained by drying the polymer gel which was prepared with carbomer 934P, ammoniomethacrylate copolymer, titanium dioxide and polyethylene glycol 400. The effects of the content of additives on physical characteristics of the polymer gel and the drug layer were evaluated. The addition of carbomer increased the yield point and the zero-shear viscosity of polymer gel as well as the thickness, the water absorption ratio, the adhesive time and $T_{50%}$ of drug layer. The adhesive time and the water absorption ratio of drug layer were also improved by the addition of ammoniomethacrylate copolymer, but the addition of titanium dioxide had decreased the zero-shear viscosity of polymer gel and the adhesive time of drug layer.

• ETRI Journal
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• v.27 no.4
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• pp.377-384
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• 2005

We investigate near-infrared light (NIR) propagation in a model of an adult head using an extensive Monte Carlo (MC) simulation. The adult head model is a four-layered slab which consists of a surface layer, a cerebrospinal fluid layer, a gray-matter layer, and a white-matter layer. We study the effects of a refractive index mismatch on the model, calculating the intensity of detected light, mean flight time, and partial mean flight time of each layer for various refractive indices of the cerebrospinal fluid layer as functions of source-detector spacing. The Monte Carlo simulation shows that the refractive index mismatch presents very rich results including rapidly decaying intensity of detected light and a peak and cross-over in the partial mean flight time with source-detector spacing. We also investigate spatial sensitivity profiles at various source-detector spacings, discussing the index mismatch effect on the model.

• Journal of applied mathematics & informatics
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• v.22 no.1_2
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• pp.501-515
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• 2006

The IEEE 802.11 protocol is the most mature technology for WLANs(Wireless Local Area Networks). However, as the number of stations increases, the delay and throughput performance of IEEE 802.11 MAC(Medium Access Control) degrades severely. In this paper, we present the comprehensive performance analysis of IEEE 802.11 MAC protocol by investigating the MAC layer packet service time when arrival packet sizes have a general probability distribution. We obtain the discrete probability distribution of the MAC layer service time. By using this, we analyze the system throughput and the MAC layer packet service time of IEEE 802.11 MAC protocol in wireless LAN environment. We take some numerical examples for the system throughput and the mean packet service time for several special distributions of arrival packet sizes.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.203.1-203.1
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• 2013

Zinc oxide (ZnO) nanocrystalline thin films on various growth temperatures for active layer and different buffer layer thickness were grown by plasma-assisted molecular beam epitaxy (PA-MBE) on Si substrates. The ZnO active layer were grown with various growth temperature from 500 to $800^{\circ}C$ and the ZnO buffer layer were grown for different time from 5 to 40 minutes. To investigate the structural and optical properties of the ZnO thin films, scanning electron microscope (SEM), X-ray diffractometer (XRD), and photoluminescence (PL) spectroscopy were used, respectively. In the SEM images, the ZnO thin films have high densification of grains and good roughness and uniformity at $800^{\circ}C$ for active layer growth temperature and 20 minutes for buffer layer growth time, respectively. The PL spectra of ZnO buffer layers and active layers display sharp near band edge (NBE) emissions in UV range and broad deep level emissions (DLE) in visible range. The intensity of NBE peaks for the ZnO thin films significantly increase with increase in the active layer growth temperature. In addition, the NBE peak at 20 minutes for buffer layer growth time has the largest emission intensity and the intensity of DLE peaks decrease with increase in the growth time.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.805-808
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• 2002

This study is designed to reduction of hydration heat of 4 layer division-placed mass concrete considering the difference of setting time of super retarding agent. According to the results, peak temperature of plain concrete by hydration heat show $63^{\circ}C$ around the age of 1 days. Hydration heat is lowest in the bottom layer, and highest in the middle of 3rd layer from the bottom. Hydration heat of mock up structure, which is division-placed at the same interval of 1 and 2 days by setting time difference of super retarding agent, is highest in the bottom layer because after peak temperature of 4th layer, hydration reaction progresses in order of 3rd, 2nd and 1st layer. But in mock up structure which is division-placed at the various interval. peak temperature by hydration heat is reduced by about $13^{\circ}C$, compared with plain concrete because after first peak hydration heat of 4th layer (plain concrete), hydration reaction progresses after the drop of hydration heat in order of 3rd, 2nd and 1st layer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1229-1237
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• 1998

Experiments of shock-wave/turbulent boundary layer interaction were conducted by using a supersonic wind tunnel. Nominal Mach number was varied in the range of 1.6 to 3.0 by means of different nozzles. The objective of the present study is to investigate the effects of boundary layer suction on normal shock-wave oscillations caused by shock wave/boundary layer interaction in a straight duct. Two-dimensional slits were installed on the top and bottom walls of the duct to bleed turbulent boundary layer flows. The bleed flows were measured by an orifice. The ratio of the bleed mass flow to main mass flow was controlled below the range of 11 per cent. Time-mean and fluctuating wall pressures were measured, and Schlieren optical observations were made to investigate time-mean flow field. Time variations in the shock wave displacement were obtained by a high-speed camera system. The results show that boundary layer suction by slits considerably reduce shock-wave oscillations. For the design Mach number of 2.3, the maximum amplitude of the oscillating shock-wave reduces by about 75% compared with the case of no slit for boundary layer suction.