• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.7
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• pp.202-213
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• 1999

Adaptive Cruise Control (ACC) is one of key features on intelligent Transportation System(ITS). In ACC, the steering is done by a driver, but the engine throttle valve and the brake are controlled electronically. The relative velocity and distance from the preceeding vehicle are measured by radars or image processing units and relevant vehicular spacing is maintained in ACC control systems. In this study, vehicle longitudinal dynamics are modeled to simulate vehicle longitudinal maneuver and to design longtitudinal controllers for ACC vehicles. The control algorithm is designed based on the modeled vehicle longitudinal dynamics using a non-linear sliding mode control method. To verity the performance of the control algorithm, a real time numerical simulation program is developed on a Silicon Graphics workstation using C-language . A real time graphic program is alos develpe and integrated with the numerical simulation program.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.3C
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• pp.243-250
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• 2009

In this paper, a closed-form expression of the ergodic channel capacity for a narrow-band time-reversal communication scheme is analytically formulated. In the time-reversal communication scenario, a transmitter sends a signal and a so-called time-reversal array receives the signal. Then, the received signal is reversed in the time do main and resent to the original transmitter. Here, one transmitter and an antenna array for the time-reversal array are assumed. Since the spacing between the array elements is large, the signals received by each antenna element can be considered independent. For simplicity, the communication channel is assumed stationary, whose properties are not changed for the time-reversal process. Based on the obtained formulation, the channel capacities for the time-reversal and the conventional channels are compared.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.741-750
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• 2004

Air voids in hardened concrete have an important influence on concrete durability such as freeze-thaw resistance, surface scaling resistance, and water permeability, and they have been characterized by spacing factor Linear traverse and point count methods in ASTM standard have been used in estimating an air void system in hardened concrete. However, these methods require lots of time and efforts, further they are not repeatable. Image analysis method could be utilized In estimating an air void systems in hardened concrete with a developments of microscope, digital camera and computer program. The purpose of this study was to develope image analysis method and provide a guideline by comparing the results from ASTM method and image analysis method. The concerns were at air void content and diameter distribution, air voids system as well as spacing factors. The experimental variables included air content by air entrained agent (0, 0.01, $0.03\%$) and depth of specimen (top, middle, bottom). The result showed that it was possible to calculate spacing factor using image analysis technique, as well as air content, air diameter distribution, and air structure. This study also contributed in developing an reasonable and repeatable image analysis method.

• Journal of Bio-Environment Control
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• v.14 no.1
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• pp.7-14
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• 2005

This study was conducted to develop a chain conveyor-type, row-spacing system for a plant factory. The developed system was evaluated for its practical use in growing plants. Results are intended to provide technical suggestions on the row spacing for hydroponically grown vegetables in a plant factory. The designed row-spacing system for a plant factory could be adjusted by four stages with a conveying speed range of $5.3\~15.8cm{\cdot}s^{-1}$ and with a row-space range of 10-25cm. The torque of driving shaft was measured with a torque range of 11.7-33.3 N$\cdot$m according as a trough weight changes with a range of $17\~935$ N. A measured value was $5.9\~9.8\;N{\cdot}m$ lower than a theoretical value. Travel reduction rate was shown up $1.6\~1.9\%$. The conveying time of trough was shown up 2.24 seconds in case that the designed value was 2.26 seconds. The system was evaluated to be functioning effectively according to the initial design factors in the test.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.93-93
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• 1999

양자점(Quantum dot : QD)를 이용한 소자를 만들기 위해서는 수직방향으로의 적층이 필수적이다. 양자점의 적층은 수직적으로 같은 위치에 정렬하므로, 고려되어야 할 요소로는 양자점간의 파동함수의 중첩(coupling)에 의한 특성변화, 적층의 진행에 따른 변형(strain)의 증가로 기인되는 volcano 모양으로 나타나는 결함등이 있다. 이러한 결함은 nonradiative recombination center로 작용하여 오히려 효율이 떨어지게 되는 현상이 발생하게 되므로 본 연구에서는 적층횟수에 따른 발광효율의 변화를 조사하여 소자응용에 적절한 적층 조건을 조사하였다. 시료성장은 molecular beam epitaxy (MBE) 장치를 이용하여 GAs(100) 기판위에 GaAs buffer를 58$0^{\circ}C$에서 150nm 성장후 InAs/GaAs 양자점과 50$0^{\circ}C$에서 적층회수 1, 3, 6, 10, 15, 20회로 하였으며 적층성장 이후 GaAs cap layer를 성장하였다. GaAs spacing과 cap layer의 성장온도 역시 50$0^{\circ}C$이며 시료의 분석은 photoluminescence (PL)과 scanning transmission electron microscope (STEM)으로 하였다. 적층횟수를 바꾸어 시료를 성장하기 전에 적층횟수를 10회로 고정하고 spacing 두께를 2.8nm, 5.6nm, 11.2nm로 바꾸어 성장하여 PL 특성을 관찰하여본 결과 spacing이 2.8nm인 경우 수직적으로 정렬된 양자점 간에 coupling이 매우 커서 single layer QD의 PL peak에 비해 약 100nm 정도 파장이 증가하였고, spacing의 두께가 11.2nm 일 경우는 single layer QD와 거의 같은 파장의 빛을 방출하여 중첩이 거의 일어나지 않지만 두꺼운 spacing때문에 PL세기가 감소하였다. 한편, 적층회수에 따른 광학적 특성을 PL로 조사하여 본 결과 peak 파장은 적층횟수가 1회에서 3회로 증가했을 때는 blue shift 하다가 이후 적층이 증가함에 따라 red shift 하였다. 그리고 10층 이상의 적층에서는 excited state에서 기인된 peak이 검출되었다. 이렇나 원인은 적층수가 증가함에 따라 carrier life time이 증가하여 exciter state에 carrier가 존재할 확률이 증가하기 때문으로 생각된다. 또한 PL 세기가 다소 증가하다가 10층 이상의 경우는 다시 감소함을 알 수 있었다. 반치폭도 3층과 6층에서 가장 적은 값을 보였다. 이와 같은 결과는 결함생성과 관련하여 STEM 분석으로 해석되어질 수 있는데 6층 적층시는 양자점이 수직적으로 정렬되어 잘 형성됨을 관찰할 수 있었고 적층에 따른 크기 변화도 거의 나타나지 않았다. 그러나 10층 15층 적층시 몇가지 결함이 형성됨을 볼수 있었고 양자점의 정렬도 완전하게 이루어지지 않음을 볼 수 있었다. 그러므로 수직적층된 InAs 양자점의 광학적 특성은 성장조건에 따른 결함생성과 밀접한 관련이 있으며 상세한 논의가 이루어질 것이다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.276-276
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• 2010

Localized surface plasmon resonance (LSPR) has been explored recently as a promising approach to increase energy conversion efficiency in photovoltaic devices, particularly for thin film hydrogenated amorphous silicon (a-Si:H) solar cells. The LSPR is frequently excited via an electromagnetic (EM) radiation in proximate metallic nanostructures and its primary con sequences are selective photon extinction and local EM enhancement which gives rise to improved photogeneration of electron-hole (e-h) pairs, and consequently increases photocurrent. In this work, high-dielectric-constant (k) $ZrO_2$ (refractive index n=2.22, dielectric constant $\varepsilon=4.93$ at the wavelength of 550 nm) is proposed as spacing layer to enhance the LSPR for application to the thin film silicon solar cells. Compared to excitation of the LSPR using $SiO_2$ (n=1.46, $\varepsilon=2.13$ at the wavelength of 546.1 nm) spacing layer with Au nanoparticles of the radius of 45nm, that using $ZrO_2$ dielectric shows the advantages of(i) ~2.5 times greater polarizability, (ii) ~3.5 times larger scattering cross-section and ~1.5 times larger absorption cross-section, (iii) 4.5% higher transmission coefficient of the same thickness and (iv) 7.8% greater transmitted electric filed intensity at the same depth. All those results are calculated by Mie theory and Fresnel equations, and simulated by finite-difference time-domain (FDTD) calculations with proper boundary conditions. Red-shifting of the LSPR wavelength using high-k $ZrO_2$ dielectric is also observed according to location of the peak and this is consistent with the other's report. Finally, our experimental results show that variation of short-circuit current density ($J_{sc}$) of the LSPR enhanced a-Si:H solar cell by using the $ZrO_2$ spacing layer is 45.4% higher than that using the $SiO_2$ spacing layer, supporting our calculation and theory.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.6 no.1
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• pp.65-72
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• 2008

The purpose of the HLW deep geological disposal is to isolate and to delay the radioactive material release to human beings and the environment for a long time so that the toxicity does not affect to the environment. The main requirements for the HLW repository design is to keep the buffer temperature below $100\;^{\circ}C$ in order to maintain its integrity. So the cooling time of spent fuels discharged from the nuclear power plant is the key consideration factors for efficiency and economic feasibility of the repository. The disposal tunnel/disposal hole spacing, the disposal area and thermal capacity required for the deep geological repository layout which satisfies the temperature requirement of the disposal system is analyzed to set the optimized spent fuels cooling time. To do this, based on the reference disposal concept, thermal stability analyses of the disposal system have been performed and the derived results have been compared by setting the spent fuels cooling time and the disposal tunnel/disposal hole spacing in various ways. From these results, desirable spent fuels cooling time in view of disposal area is derived. The results shows that the time reaching the maximum temperature within the design limit of the temperature in the disposal site is likely shortened as the cooling time of spent fuels becomes short. Also it seems that the temperature-rising and-dropping patterns in the disposal site are of smoothly varying form as the cooling time of spent fuels becomes long. In addition, it is revealed that a desirable cooling time of spent fuels is approximately 40-50 years when spent fuels are supposedly disposed in the deep geological disposal site with its structural scale under consideration in this study.

• The Journal of the Acoustical Society of Korea
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• v.18 no.1
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• pp.78-85
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• 1999

In this paper we propose a method to improve the performance of the mel-cepstrum that is widely used in speech recognition. Typically, the met-cepstrum is obtained by critical band filters that have fixed center spacing and bandwidth. However different filter characteristics produce a different mel-cepstrum, resulting in a different performance. In this paper we analyze triangular-shaped and rectangular-shaped filters. By changing the characteristics of filters such as center frequency and bandwidth, we analyze the performance of the met-cepstrum. Then utilizing the simplex method, we propose a method to optimize the critical band filters. Using the dynamic time warping, we performed speaker independent recognition experiments with Korean digit words pronounced by 10 males and 10 females. Experiments show that the rectangular-shaped filters show good performance and the mel-cepstrum obtained by the optimized filters shows better performance than filters that have fixed center spacing and bandwidth.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.1
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• pp.29-40
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• 2005

Formation of nanocrystalline ferrite was investigated using milled powders obtained by planetary ball milling of chips, which were made by high speed mechanical cutting of a low carbon steel(0.15%C-1.1%Mn-0.01%Ti). After 4 hour milling the chips were changed to powders of $50{\mu}m$ in average size, and with increasing milling time the powders were refined to about $3{\mu}m$ for 128 hour and showed more equiaxed shapes. Nanocrystalline(nc) region appeared in the surfaces of powders milled for 1 hour, and the 4 hour milled powders were almost filled with nc region. Hardness of nc region was much higher than that of work-hardened(WH) region. With increasing milling time, ferrite and cementite in pearlite were severely deformed and lamellar spacing was decreased, and then cementites began to disappear after 4 hour milling due to dissolution into ferrite. Deformation bands formed in lightly work-hardened region showed large width and similar crystallographic orientations. Spacing of deformation bands was decreased with deformation and the layered microstructure consisting of narrow deformation bands subdivided into variously oriented small grains was formed by more deformation, and eventually this structure seemed to be evolved to the nc structure by further deformation. It is also conjectured the growth of nc ferrite grains occurred through the coalescence of nanocrystalline ferrites rather than the nucleation and growth of recrystallized grains.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.1-11
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• 2017

In this study, 1/6 small-scale model tests of helical piles were conducted to evaluate their installation time and ultimate capacities. Model sand layers were constructed using sand pluviating method to produce uniform soil relative density. For installation of different helical piles varying locations (vertical center-to-center spacings of 50 mm and 150 mm) of helix plates, two different rotation speeds of 15 rpm and 30 rpm were implemented. Cone penetration equipment was installed within the hallow section of the helical pile to increase ultimate capacity of helical pile and to evaluate soil properties of plugged soils and soils below pile tip after installation of the piles. Based on the test results, the most fasted installation was possible under the condition of "rotation speed of 30 rpm and center-to-center spacing of 50 mm", and the highest ultimate capacity was mobilized under the condition of "rotation speed of 30 rpm and center-to-center spacing of 150 mm with cone penetration implementation."