• Transactions of Materials Processing
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• v.26 no.5
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• pp.314-322
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• 2017

In the high-speed forming analysis, dynamic material properties considering a high strain rate are required. The split Hopkinson pressure bar (SHPB) experiment was performed for measuring dynamic material properties under high strain rate. The pulse shaping method was used to improve the accuracy of the SHPB experiment. A pulse shaper attached to the front of the incident bar was used for specimen dynamic stress equilibrium through stress wave control. Numerical analysis and SHPB test were performed to verify whether the pulse shaper affects the dynamic stress equilibrium in copper and Al6061 specimens. The results of SHPB test and numerical analysis show that the pulse shaper contributes to the dynamic stress equilibrium. Based on the improved stress equilibrium using a pulse shaper, the flow stress curves for copper and Al6061 materials were obtained at strain rates of 1344.4/sec and 1291.6/sec, respectively.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1222-1233
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• 1990

The formation and oxidation processes of soot particles in a diesel flame were investigated with a rapid compression machine. A cloud of soot particles was successfully visualized by means of the instantaneous laser shadow photographs technique and the equivalence ratio of the soot formation zone was estimated from a measured fuel concentration distribution in a nonevaporating spray. The temporal and spatial variation of soot concentration in the flame was also correlated with the rate of heat release. Soot particles appears first in a region near the flame tip when diffusion combustion period starts, and its concentration is a maximum at about the end of injection, then decreases due to oxidation. The reason for soot being formed in a fuel lean region near the flame tip is the evaporated fuel requires time to be pyrolized as it travels through the burning fuel rich zone towards the flame tip.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.5
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• pp.31-37
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• 2020

In this paper, we propose a novel sub-wavelength unit cell metamaterial absorber using multi-layer structure. The proposed absorber consists of 4 layers, and each layer has a spiral resonator connected by a via hole. This structure increases inductance of the unit cell, and therefore the resonant frequency can shift to lower frequency. We optimized the proposed absorber, and the electrical size of the unit cell is dramatically reduced to 0.013 times of the wavelength. The performance of the proposed absorber is demonstrated with full-wave simulation and measurement results. An absorption rate exceeding 97% is achieved at 1.74GHz. In addition, the proposed absorber attains a high absorption rate of 90% for different polarization and incident angles.

• Journal of Korean Academy of Fundamentals of Nursing
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• v.17 no.2
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• pp.177-186
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• 2010

Purpose: The purpose of this descriptive study was to investigate the application of physical restraints in ICUs of a university hospital. Method: Data were collected from August 1 to October 1 2009, using a recording tool from Electric Nursing Records and an observation tool for physical restraints and related factors. Frequency, percentage, and paired t-test with the SPSS/WIN 16.0 program were used to analyze the data. Results: The application rate for physical restraints in 5 ICUs was 34.3%, the highest application rate was 48.4% in the neurosurgical ICU. The mean frequency for physical restraint application per patient was 1.14, and the mean hours of restraint application per incident was 113.01 hours. The most common complications of physical restraints were bruising and edema. Conclusion: Many ICU nurses use physical restraints when caring for patients who are at high risk for falls, including patients have high levels of acuity, decreased level of consciousness or increased irritability. When physical restraints are applied, patients show resistance against the use resulting in side effects of bruising and edema. Therefore, nurses should observe changes in restrain sites, perform nursing interventions to prevent complications, and minimize the use of physical restraints.

• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.9
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• pp.1391-1397
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• 2013

As Korea is expected to enter an aging society in near future, the number of patients who need a long-term prescription is expected to increase as well. In particular, Korea shows the highest in both the incident rate and the death rate among OECD member nations. The current situation requires more strict monitoring and management for patients' taking medicine, there are a few practical problems such as personnel expenses. In order to realize the efficient management of medicine administration, this paper proposes a smart pillbox that is developed based on IT technologies. Through the experiments in which actual patients participate, it is proved that the smart pillbox is beneficial to the patients taking medicine.

• Journal of the Korean Society of Safety
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• v.23 no.5
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• pp.73-78
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• 2008

The fire hazards and combustion heat of puzzle mats in group day care home were analysed using variable external irradiation level. The fire hazards such as ignition time, ignition temperature, mass loss rate, and flame temperature profile were measured. Incident heat fluxes of $15kW/m^2$, $20kW/m^2$, $25kW/m^2$, $35kW/m^2$, $50kW/m^2$ and $75kW/m^2$ were selected for these experiments. All samples were tested in the horizontal orientation and were wrapped in a single layer of aluminium foil. Each sample was nominally 20mm thick and 100mm square. Five samples of puzzle mat were tested in the study : Type A, B, C, D and E. Type A, B and C are all general grades whereas Type D and E are both Flame retardant grades. As results, Type E of FR-grade showed the best characteristics in safety of the early fire from ignition time, critical heat flux, and ignition and flame temperature data of this study. All specimen of G-grade(Type A, B and C), however, showed the weak in safety of fire.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.412-414
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• 2003

This paper is about research of scintillator layer, which is used for Hybrid method to increase electric signals in a-Se, the material of Direct method. In case of the thermal evaporation, CsI has column structure which is an disadvantage as scintillator. But it decreases scattering of incident X-ray, has better Light output intensity than other scintillation materials. CsI was made by Thermal evaporation. The Doping material, Na, 0.1, 0.3, 0.5, 0.7g were added in each sample. Analysis of absorbed wavelength, PL(Photoluminescence), Light output intensity, SEM, and XRD analysis were performed to analyze optical characteristics. Doping rate of CsI:Na to use as scintillation layer in a-Se based detector could be optimized.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.1
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• pp.93-99
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• 2011

In this study, a series of laboratory experiments are carried out to analyze fluid behaviors around multi-arranged (2 pieces) floating breakwaters with various parameters such as distance between structures, wave periods and steepness. The rate of wave transmission is shown to be affected directly by wave periods of incident waves and the breakwaters with multi-arranged structures show the highest rate of wave protection compared with other cases. The velocity fields around the breakwaters are measured by using the Laser Doppler Velocimetry system. The transmission coefficients are also measured in laboratory experiments. Finally, laboratory observed data are compared with numerical experimental results and analyzed in detail.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.7
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• pp.2027-2046
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• 2024

Reconfigurable Intelligent Surface (RIS) is an innovative technique to precisely control the phase of incident signals with the help of low-cost passive reflective elements. It shows excellent potential in the sixth generation of mobile communication systems, which not only extends wireless coverage but also boosts channel capacity. Considering that multipath propagation and a high number of antennas are involved in RIS in assisted mega multiple-input multiple-output (MIMO) systems, it suffers from severe channel fading and multipath effects, which in turn lead to signal instability and degradation of transmission performance. To overcome this obstacle, this essay suggests an improved gradient optimization algorithm to dynamically and optimally adjust the phase of the reflective elements to counteract channel fading and multipath effects as a strategy. In order to overcome the optimization problem of falling into local minima, this paper proposes an adaptive learning rate algorithm based on Adagrad improvement, which searches for the global optimal solution more efficiently and improves the robustness of the optimization algorithm. The suggested technique helps to enhance the estimate of channel efficiency of RIS-assisted large MIMO systems, according to simulation results.

• Journal of information and communication convergence engineering
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• v.4 no.4
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• pp.158-161
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• 2006

[ $Bi_2Sr_2Ca_nCu_{n+1}O_y(n{\geq}0)$ ] thin film is fabricatedvia two different processes using an ion beam sputtering method i.e. co-deposition and layer-by-layer deposition. A single phase of Bi2212 can be fabricated via the co-deposition process. While it cannot be obtained by the layer-by-layer process. Ultra-low growth rate in our ion beam sputtering system brings out the difference in Bi element adsorption between the two processes and results in only 30% adsorption against total incident Bi amount by layer-by-layer deposition, in contrast to enough Bi adsorption by co-deposition.