• Current Optics and Photonics
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• v.2 no.3
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• pp.280-285
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• 2018

A new method to design a see-through off-axis head-mounted-display (OA-HMD) optical system with an ellipsoidal surface is proposed, in which a tilted ellipsoidal surface is used as the combiner, which yields the benefits of easier fabrication and testing compared to a freeform surface. Moreover, we realize a coaxial structure in the relay lens group, which is simple and has looser tolerance requirements, thus making assembly easier. The OA-HMD optical system we realize has a simple structure and consists of a combiner and 7 pieces of coaxial relay lenses. It has a $48^{\circ}{\times}36^{\circ}$ field of view (FOV) and 12-mm exit pupil diameter.

• Journal of the Korea Safety Management & Science
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• v.13 no.3
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• pp.1-8
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• 2011

The overall goal of a safety based railroad system is either to eliminate hazards in designing or to minimize the possibility of it. In order to indicate system safety or low risk although it may not be possible to achieve zero risk conditions, first, it shall ensure that any disasters would occur due to system operation because the prescribed specifications are properly fulfilled and there are no failures of any kind. Second, the risk of faults or failures leading to a mishap must be eliminated or minimized by using fault-tolerance or fail-safe procedures. This paper will attempt to summarize the personal and social risk criterion at widely scattered points, presently used as a safety approach in all over EU, in order to establish the step by step procedures of the detailed standard for railway facilities. In addition, we present the new safety analysis method using the SIL-based evaluation standard and the Reachability Graph of the Petri Net.

• Korean Journal of Optics and Photonics
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• v.16 no.1
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• pp.71-78
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• 2005

A null lens system of autostigmatic type, consisting of two mirrors, is designed for testing a large aspherical mirror. The system is theoretically analyzed to determine the limitation of measurement accuracy according to the manufacturing and alignment errors. We confirmed that irregularity of the null lens surface is the principal factor among tolerances in limiting measurement accuracy. Consequently, we can predict that measurement accuracy will be from 5λ/100 to 4λ/1000 according to the amount of this irregularity. That is, we can present the limitation of possible measurement accuracy with actual alignment and manufacturing errors.

• Journal of the Korean Institute of Landscape Architecture
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• v.31 no.6
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• pp.53-63
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• 2004

Planting models for restoration forest on the seaside have been demanded because coastal reclaimed land has increased for habitation sites, industrial complexes and new towns on the west seaside of Korea. The planting models have to consider endurance for bad environmental conditions in order to make a role to protect the urban space against the extreme seaside environment. The dominant species, relative impotance value, individuals and species number were analysed in natural forests that were exposed to extreme seaside conditions in Deokjeok island and Younghung island, Incheon. The native species such as Pinus thunbergii and Pinus densiflora, which survive on the seaside, were mainly recommended because the coastal reclaimed land had extreme environmental conditions. Stable vegetation structures could be made by multi-layer planing by using these species. A diverse vegetation community could be made according to these planting models. The maritime forests made by these planting models might be more effective for environmental adaptation and a windbreak forest than alone tree, and the young trees below 3m height could easily adapt to these conditions.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.1
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• pp.1-5
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• 2020

Solar power generation systems require maximum power point tracking (MPPT) control to operate PV panels at their maximum power point (MPP). Most conventional MPPT algorithms are based on the slope-tracking concept. A typical slope-tracking method is the perturb and observe (P&O) algorithm. The P&O algorithm measures the current and voltage of a PV panel to find the operating point of the voltage at which the calculated power is maximized. However, the measurement error of the sensor causes irregularity in the calculation of the generated power and voltage control. This irregularity leads to the problem of not finding the correct MPP operating point. In this work, the power output of a PV panel based on the P&O algorithm is simulated by considering the insolation profiles from typical clear and cloudy weather conditions and the errors of current and voltage sensors. Simulation analysis suggests the optimal control period and perturbation voltage of MPPT to maximize its target efficiency under real weather conditions with sensor tolerance.

• Journal of the Korean institute of surface engineering
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• v.52 no.6
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• pp.310-315
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• 2019

The use of a silicon carbide (SiC)-based composite ceramic layer for the mold of a curved cover glass was demonstrated. The stress of SiC/VDR/graphite-based mold structure was evaluated via finite element analysis. The results revealed that the maximum tensile stress primarly occured at the edge region. Moreover, the stress can be reduced by employing a relatively thick SiC coating layer and, therefore, layers of various thicknesses were deposited by means of chemical vapor deposition. During growth of the layer, the orientation of the facets comprising the SiC grain became dominant with additional intense SiC(220) and SiC(004). However, the roughness of the SiC layer increased with increasing thickness of the layer and. Hence, the thickness of the SiC layer needs to be adjusted by values lower than the tolerance band of the curved cover glass mold.

• Proceedings of the KOSOMBE Conference
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• v.1993 no.11
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• pp.51-54
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• 1993

The purpose of this research is to investigate the relationship between the blood flow and autonomic nervous system which regulates the circulation system. After the oral glucose tolerance test(GTT) the velocity changes of the blood flow were measured from the normal, hyperglycemia and diabetic neuropathy using the laser doppler. The FFT analyses showed that the spectrums were concentrated around the particular bands(0.02-0.166Hz, 0.8-1.1Hz) for the normal, while almost uniform distribution of the spectrums was observed for the abnormal. The blood glucose affects the compliance of the blood vessels and viscosity and finally causes the resistance problem in the blood vessels. An index PG was introduced, which was determined by the ratio of the change or the integral power spectrum in the range between 0.02 and 0.166Hz to change of the blood glucose before and after GTT. The index shows 1.0. 0.3 and 0.1 for the normal, hyperglycemia and diabetic neuropathy, respectively. As a conclusion, this spectrum analysis shows the potential of checking the progress or the diabetic, also car be used to evaluate the vasomotion which are regulated by the autonomic nervous system.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.6
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• pp.516-521
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• 2009

X-ray system which is usefully used in diagnosis of the patient, being bombed of radioactivity is a big weak point when irradiates a X-ray to the human body so that ICRP restricted the radiation exposure tolerance of the human body. In order to reduce being bombed, the many research and development is now advanced. A lots of diagnostic X-ray machines have currently used due to the increase of occurrence efficiency of X-ray and precisely the output control by using the inverter which is a high speed switching semiconductors. For getting the confidence of the X-ray machine, the same radiation occurrence, same evaluation, and same irradiation condition are necessary when evaluates X-ray irradiation. It is the most important part for the accuracy of the test result and the patient safety. This research has produced the high voltage occurrence system of full-wave rectification method by using the LC resonance inverter, and evaluated the irradiation reproducibility in order to use it in diagnosis of the patient.

• Journal of Korean Society for Quality Management
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• v.44 no.1
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• pp.77-94
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• 2016

Purpose: This paper reviews Type 1 Gage study, Gage R&R study, and procedure of ISO 22514-7 for assessing a measurement system, and discusses some relationships between the measurement capability indices. Methods: The gage capability index $C_g$ of Type 1 Gage study, precision-to-tolerance ratio PTR of Gage R&R study, and measurement performance ratio $Q_{MS}$ and $Q_{MP}$ of ISO 22514-7 are considered in this paper. Results: This paper derives the relationships between $C_g$ and $Q_{MS}$, PTR and $Q_{MP}$, and $Q_{MS}$ and $Q_{MP}$, respectively, and discusses the acceptance conditions for each procedures. Conclusion: The measurement capability analysis is the first step for the quality improvement of the manufacturing processes. Therefore the result of this study provides a helpful guidelines for assessing the measurement system, enabling proper evaluation of manufacturing processes.

• Proceedings of the Korea Water Resources Association Conference
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• 1987.07a
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• pp.113-122
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• 1987

A numerical simulation technique of three-dimensional finite difference model is developed to study the groundwater flow system in Dcjima, an upland area which faces Kasumigaura Lake. For general perspectives of the groundwater flow system, a steady state three-dimentional model is simulated. For the sedimentary mud formations which are found in the representative formation, three situations of hydraulic conductivity are considered, representing an isotropic condition and situations where the horizontal permeability is equal to 10 times and 100times of the vertical one. The finite difference grid used in the simulation has 60x50x30=90,000 nodes. A converged solution with a tolerance of 0.001 meter of hydraulic head is set. Having determined the flow net by using a steady state three-dimensional model. the results for the three cases of hydraulic conductivity are compared with the results of tracer methods (Bae and Kayane 1987) With the aid of four representative vertical cross-sections, groundwater flow systems in the study area are assumed. Water balances for the three cases indicate very good agreement between total recharge and discharge in each case Analyses of groundwater flow system based on the tritium concentrations and water quality measurements (Bae and Kayane 1987) are confirmed by the numerical simulation and the results obtained by these two methods appeared to be in close agreement.