• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.5
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• pp.389-398
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• 2019

In this paper, we propose a method to detect small unmanned aerial vehicles(UAVs) flying in a real-world environment. Small UAV signals are frequently obscured by clutter signals because UAVs usually fly at low altitudes over urban or mountainous terrain. Therefore, to obtain a desirable detection performance, clutter signals must be considered in addition to noise, and thus, a performance analysis of each clutter removal technique is required. The proposed detection process uses clutter removal and pulse integration methods to suppress clutter and noise signals, and then detects small UAVs by utilizing a constant false alarm rate detector. After applying three clutter removal techniques, we analyzed the performance of each technique in detecting small UAVs. Based on experimental data acquired in a real-world outdoor environment, we found it was possible to derive a clutter removal method suitable for the detection of small UAVs.

• Korean Journal of Optics and Photonics
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• v.34 no.5
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• pp.202-209
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• 2023

A KRISS-type small integrating sphere with a high spatial radiance uniformity was made using pressed polytetrafluoroethylene (PTFE) and a reflective rod to calibrate the spectral radiance responsivity of absolute radiant thermometers. The spatial radiance uniformity of the KRISS-type small integrating sphere was ±0.009%, five times higher than the best value reported by foreign national metrology institutions thus far. In addition, we improved the spatial radiance uniformity of a commercial sintered PTFE integrating sphere by a factor of 10.

• Korean Journal of Optics and Photonics
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• v.29 no.6
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• pp.233-240
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• 2018

In this paper, a design method to reduce fabrication errors in reflector shape of a test lamp for a flame detector is carried out. Although the test lamp should be operated in parallel with a high-intensity light, it is difficult to fix the small reflector that controls the central light during fabrication. To solve these problems, a small spherical reflector is designed to minimize the performance degradation for a light loss factor of less than 5%, even during tilt and decenter, and a spherical shape is proposed for a small reflector with little effect on the error when designing the optical system.

• Journal of The Korean Society of Grassland and Forage Science
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• v.20 no.1
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• pp.67-76
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• 2000

An experiment was conducted to evaluate the effects of lime, zeolite, and rock phosphate as coating materials and coated seed size on germination, establishment, and early growth of pasture species at the experimental livestock farm, Yonam College of Agriculture in 1997. Germinating energy and germination of coated tall fescue and orchardgrass seeds were lower than those of non-coated seeds. Coated seed of tall fescue with 70% lime and 15% rock phosphate was the best in germination. The germination of small size seed (< ${\varnothing}2$ mm) was better than those of medium (> ${\varnothing}2$ mm and < ${\varnothing}2$ mm) and large size seeds (> ${\varnothing}2$ mm). Germination of coated orchardgrass seed with 55% lime and 30% rock phosphate treatment was higher than that of other coated seeds, and germination of small size seed was higher than those of medium and large size seeds (p<0.05). Germination energy and germination of coated alfalfa and birdsfoot trefoil seeds were lower than those of non-coated seeds. Germination of coated alfalfa seed with 70% lime and 15% rock phosphate, and 45% lime and 55% rock phosphate was higher compared with other coated seeds. Germination of medium size seed was higher than those of small and large size seeds (p<0.05). Among coated birdsfoot trefoil seed, 45% lime and 40% rock phosphate treatment resulted in higher germinating energy and germination than other treatments. There was no significant difference in establishment and early growth of coated tall fescue and orchardgrass seeds. However, tall fescue and orchardgrass coated with 45 % lime and 40% phosphate rock showed higher establishment and early growth. There was also no significant difference in establishment and early growth of coated alfalfa among the treatments. Among coated treatments, establishment and early growth of alfalfa coated with 75% lime and 10% rock phosphate were the highest and showed 46.4% and $72.6\;g/\textrm{m}^2$, respectively. Establishment and early growth of coated birdsfoot trefoil with 55% lime and 30% rock phosphate were the highest among coated birdsfoot trefoil seed (p<0.05) and recorded 46.4% and $44.6\;g/\textrm{m}^2$, respectively. Results of this study indicate that the germination of coated grass and legume seed may be improved by increasing the percentage of rock phosphate and decreasing that of lime. With regard to seed size, the germination of pasture species with small seed size (< ${\varnothing}2$ mm) may be better than medium and large size seeds except alfalfa. Establishment and early growth of grasses can be also improved by increasing the percentage of rock phosphate and decreasing that of lime.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.1C
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• pp.29-38
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• 2011

The smaller diameter cone penetrometer has been widely used to estimate the characteristics of local area due to high vertical resolution. The half-bridge cirucits have been adopted to measure the mechnical strength of soil through the smaller diameter cone penetrometer due to the limitation of the areas for configuring the full-bridge circuit. The half-bridge circuit, however, is known as being easily affected to the temperature variation. The objective of this study suggests the temperature-compensated method in mini-cones. The diameter and length of the mini-cone is designed to 15mm and 56mm. The load cell of the mini-cone is extended about 54mm on the behind of the mini-cone to reflect the only temperature variation. The full-bridge circuit is installed to measure the temperature-compensated values in the mini-cone and the half-bridge circuit is also organized to compare the temperature compensated values with uncompensated values. The seasonal variation tests are performed to define the effect of temperature variation under summer and winter temperature condition. The densification tests are also carried out to investigate temperature effects during penetration. The measured mechanical resistances with temperature-compensated method show more reliable and reasonable values than those measured by thermal uncompensated system. This study suggests that the temperature-compensated method of the mini-cone may be a useful technique to obtain the more reliable resistances with minimizing the temperature effect.

• The Journal of the Acoustical Society of Korea
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• v.20 no.8
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• pp.31-37
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• 2001

Following the recent trends of reducing the size of multimedia devices, we tried for the development of a compact-sized speaker to produce low-frequency sounds efficiently. For this work, equivalent-circuit analysis was used to get fundamental resonant frequency and then the structure of speaker components has been changed appropriately. As a result, an 80mm small-sized speaker was developed. The performance test showed that the resonant frequency of our system is 79 Hz while that of numerical analysis was 81Hz. At a distance of 1m from our speaker, the frequency ranges 80 Hz to 15kHz and the average sound pressure was found to be 84±2 dB. The second (at 400 Hz) and the third (at 100 Hz) high-frequency distortions of our system were 0.5% and 1.8% respectively, which is to be compared with the distortions of 0.9% and 6% in conventional speakers.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.4
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• pp.65-70
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• 2010

A small unmanned aerial vehicle(UAV), which uses a propulsion system consisting of electric motor and battery, weighs less than 8 kg, capable of hand launch. Because it is easy to operate and able to transmit image information in real time, the use of small UAV has been increasing. However, very few analysis methods or analysis results on flight performance of the small UAV have been known so far. In this paper, the performance analysis methods of a small UAV, which is manufactured to study an electric powered UAV, are suggested and their results are achieved. Aerodynamic data of the vehicle are obtained by making use of gliding performance from actual flight test, and required thrust and required power by flight speed are predicted. In addition, the methods to predict range and endurance in case of using battery as power source are suggested and their results are achieved.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.192-195
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• 2008

A sensor fault detection method for small turbo shaft engine considering multiple trim conditions is proposed. This engine is used in a helicopter. Firstly, under multiple trim conditions, we derive the linearized models from a nonlinear model which includes engine, rotor and feedback control loop. As a fault detection method, we adopt the Kalman filter based method. To keep continuity of estimates between the changes of trim conditions, we reconfigure the initial values of state variables at trim changes. We detect the faults with two steps that when the first filter does not alarm the faults for some sensors, the second filter is runned for other sensor. Via some simulations we show that the proposed method works well under multiple trim conditions.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 2011.04a
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• pp.231-235
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• 2011

The purpose of this study was to analyze the types and characteristics of temporary small-sized housing units for single-person households. A document research method and case studies were used to analyze and classified the spatial characteristics and types of the temporary dwelling spaces since 2000. Findings of this study were as follows: temporary and simplified dwelling spaces were developed by the concept of impermanence for single-person households in modern society. In order to conform the concept of temporary dwelling for small-sized housing units of single-person households, the characteristics were divided into three aspects. 'Transporting' by wheel and rotation and vehicles, 'Transforming' by adapting, assembling disassembling, and folding unfolding, and 'Wearing Carrying' by inflatable and tented types. It attempted to resolve the concept of temporarity through the experiment so that they might apply to the space of contemporary city.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.2
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• pp.214-220
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• 2012

About 12 million people of the mobility handicapped were increased by the end of 2009 year. Universal design concept has been implemented in developed countries. Since 2004 low-floor buses are in Korea. In this study, there is no provision for mobility handicapped and small buses that can be comfortable riding car ramp design presented. The gate of a small buses lowered height of 200mm. Install the ramp in the center of the ramp by an air cylinder moves from side to side. The slope of the ramp was controlled by a hinge. Air cylinder thin type applicable in the narrow space of the slide cylinder was used.