• Journal of the Korean Chemical Society
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• v.33 no.4
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• pp.337-342
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• 1989

Gasless combustion is a vigorous exothermic reaction ignited directly in solid mixture, similar to Thermit reaction. The gasless combustion synthesis has the advantages of rapid processing, energy saving, low processing cost, and high purity of products. The Ti$Si_x$(x = 0.6, 0.8, 1.0, 2.0) systems are prepared by the gasless combustion synthesis without external sintering process. The crystallographic structures of $Ti_5Si_3$, $Ti_5Si_4$ are hexagonal and tetragonal system, respectively. Those of TiSi, $TiSi_2$ are orthorhombic systems. The results of X-ray analysis agree with the JCPDS data. The combustion modes of all combustion reactions are steady state combustions, and the propagation velocities of the combustion waves of $Ti_5Si_3$, $Ti_5Si_4$ and TiSi are greater than 0.6 cm/sec and that of $TiSi_2$ is 0.28 cm/sec.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.23 no.1
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• pp.27-44
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• 1993

This study was performed to investigate the changes of mandibular condyle by low calcium diet and the effects of irradiation on the bone in osteoporotic state. In order to carry out this experiment, 80 seven-week old Sprague-Dawley strain rats weighing about 150 gm were selected and equally divided into one experimental group of 40 rats and one control group with the remainder. The experimental group and the control group were then subdivided into two group and exposed to irradiation. The two irradiation groups received a single dose of 20 Gy on the jaw area only and irradiated with a cobalt-60 teletherapy unit. The rats in the control and experimental groups were serially terminated by fours on the 3rd, the 7th, the 14th, and the 21st day after irradiation. After termination, both sides of the dead rats mandibular condyle were removed and fixed with 10% neutral formalin. The bone mineral density of mandibular condyle was measured by use of dual energy X-ray bone densitometer(model DDX-alpha, Lunn Corp., U. S. A.). The mandibular condyle was radiographed with Hitex HA-80(Hitex Co., Japan). Thereafter, the obtained radiographs were observed, and the mandibular condyle was further decalcified and embedded in paraffin as the general method. The specimen sectioned and stained with hematoxylin-eosin, PAS and Rabbit Anti-Human Tumor Necrosis Factor-a observed by a light microscope. The obtained results were as follows: 1. In the non-irradiated group with the low calcium diet, the bone mineral density of the condyle was markedly decreased after 14 days, and decrease the number of trabeculae of the condyle and resorption of the calcified cartilaginous zone were observed after 3 days. On microscopic observations, the number nd size of trabeculae were decreased after 7 days of experiment. 2. In the irradiated group with the low calcium diet, the bone mineral density of the condyle was markedly decreased after 14 days and resorption of the calcified cartilaginous zone and decrease the number and coarse of the trabeculae of the condyle were observed. These findings were extended rather than in non-irradiated group with low calcium diet. On microscopic observations, many osteoclasts were detected and the number and size of trabeculae were somewhat decreased after 7 days. Also there was degenerative changes of tissues of bone marrow on the 14th day but that condition was restored on the 21st day of experiment. 3. In the irradiated group with normal diet, the bone mineral density of the condyle was somewhat decreased with times and degree of decrease of the number of trabeculae was somewhat larger than in the non-irradiated group with normal diet. On microscopic observations, the tissues of bone marrow were atrophic and degenerative changes but that condition was restored on the 21st day of experiment. 4. In immunocytochemical findings, in the irradiated and non-irradiated groups with low calcium diet, negative or partial positive response to TNF was observed, but positive response in the normal diet groups.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.297-297
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• 2010

Precise control of the position and density of doping elements at the nanoscale is becoming a central issue for realizing state-of-the-art silicon-based optoelectronic devices. As dimensions are scaled down to take benefits from the quantum confinement effect, however, the presence of interfaces and the nature of materials adjacent to silicon turn out to be important and govern the physical properties. Utilization of visible light is a promising method to overcome the efficiency limit of the crystalline Si solar cells. Si quantum dots (QDs) have been proposed as an emission source of visible light, which is based on the quantum confinement effect. Light emission in the visible wavelength has been reported by controlling the size and density of Si QDs embedded within various types of insulating matrix. For the realization of all-Si QD solar cells with homojunctions, it is prerequisite not only to optimize the impurity doping for both p- and n-type Si QDs, but also to construct p-n homojunctions between them. In this study, XPS and SIMS were used for the development of p-type and n-type Si quantum dot solar cells. The stoichiometry of SiOx layers were controlled by in-situ XPS analysis and the concentration of B and P by SIMS for the activated doping in Si nano structures. Especially, it has been experimentally evidenced that boron atoms in silicon nanostructures confined in SiO2 matrix can segregate into the Si/$SiO_2$ interfaces and the Si bulk forming a distinct bimodal spatial distribution. By performing quantitative analysis and theoretical modelling, it has been found that boron incorporated into the four-fold Si crystal lattice can have electrical activity. Based on these findings, p-type Si quantum dot solar cell with the energy-conversion efficiency of 10.2% was realized from a [B-doped $SiO_{1.2}$(2 nm)/$SiO_2(2\;nm)]^{25}$ superlattice film with a B doping level of $4.0{\times}10^{20}\;atoms/cm^2$.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.305-305
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• 2014

양자점(Quantum dots)은 3차원적 운반자 구속과 낮은 전류와 높은 온도에서 작동하는 나노 크기의 전기적, 광학적 소자로 응용이 적합하기 때문에 그 특성을 이용한 단전자 트랜지스터, 적외선 검출기, 레이저, LED, 태양전지 등 반도체 소자로의 응용연구가 활발히 진행되고 있다. 특히 양자점의 낮은 임계전류밀도와 높은 차동 이득(differential gain), 그리고 고온에서 작동이 용이하여 양자점 레이저로 활용되고 있다. 이러한 분야에 양자점을 응용하기 위해서는 양자점의 운반자 동역학을 이해하고 양자점의 모양, 크기, 크기 분포와 같은 특성 조절이 필요하다. 또한 기존의 연구들은 III-V족 화합물 반도체 양자점에 대한 연구가 대부분이며, II-VI족으로 구성된 연구가 미흡한 상황이기 때문에 II-VI족 화합물 반도체 양자점에 대한 많은 연구가 필요한 상황이다. II-VI 족 화합물 반도체 양자점은 기존의 III-V 족 양자점보다 더 큰 엑시톤 결합에너지(exciton binding energy)를 가지고 있으며, 이러한 특성을 가지는 II-VI 족 화합물 반도체 양자점 중에서도 CdTe 양자점은 높은 엑시톤 결합에너지와 녹색 스펙트럼 영역을 필요로 하는 광학적 장치들에 응용 가능성이 높기 때문에 더욱 주목받고 있다. 본 연구에서는 분자 선속 에피 성장법(Molecular Beam Epitaxy; MBE)과 원자 층 교대 성장법(Atomic Layer Epitaxy; ALE)으로 CdTe/ZnTe 나노구조에서 ZnTe 완충층의 두께에 따른 운반자 동역학 및 광학적 특성을 연구 하였다. 저온 광루미네센스 측정(Photoluminescence; PL) 을 통하여 ZnTe 완충층 두께가 증가할수록 양자점의 광루미네센스 피크가 낮은 에너지로 이동함을 알 수 있었는데, 이는 ZnTe 완충층의 두께가 증가할수록 ZnTe 완충층과 CdTe 양자점의 격자 불일치(lattice mismatch)로 인한 구조 변형력이 감소하고 이에 따라 CdTe 양자점으로 가해지는 변형(Strain)이 감소하여 CdTe 양자점의 크기가 증가했기 때문이다. 그리고 ZnTe 완충층의 두께가 증가할수록 PL 세기가 증가함을 알 수 있었는데, 이는 ZnTe 완충층의 두께가 증가할수록 양자 구속 효과로부터 electronic state와 conduction band edge 사이의 에너지 차이의 증가 때문이다. 또한 시분해 광루미네센스 측정 결과 ZnTe의 두께가 증가할수록 양자점의 소멸 시간이 더 길게 측정되었는데, 이는 더 큰 양자점 일수록 엑시톤 오실레이터 강도가 감소하기 때문에 더 긴 소멸 시간을 나타내는 것을 확인할 수 있었다. 결과적으로 본 연구는 ZnTe 두께 변화를 통해 양자점의 에너지 밴드를 제어할 수 있으며, 양자점의 효율 향상을 할 수 있는 좋은 방법임을 제시하고 있다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.528-535
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• 2020

Recently, the protection coordination method of DC systems has been presented because renewable energy and distributed resources are being installed and operated in distribution systems. On the other hand, it is difficult to detect ground faults because there is no significant difference compared to a steady-state current in ungrounded IT systems, such as DC load networks and urban railways. Therefore, this paper formulates the detection principle of IMD (Insulation Monitoring Device) to use it as a protection coordination device in a DC system. Based on the signal injection method of IMD, which is analyzed by a wavelet transform, this paper presents an algorithm of detecting ground faults in a DC system in a fast and accurate manner. In addition, this paper modeled an IMD and an ungrounded DC system using the PSCAD/EMTDC S/W and performed numerical analysis of a wavelet transform with the Matlab S/W. The simulation results of a ground fault case in an ungrounded DC system showed that the proposed algorithm and modeling are useful and practical tools for detecting a ground fault in a DC system.

• Journal of the Korean institute of surface engineering
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• v.29 no.6
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• pp.809-815
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• 1996

$Y_2O_3$-based metal-insulator-semiconductor (MIS) structure on p-Si(100) has been studied. Films were prepared by UHV reactive ionized cluster beam deposition (r-ICBD) system. The base pressure of the system was about $1 \times 10^{-9}$ -9/ Torr and the process pressure $2 \times 10^{-5}$ Torr in oxygen ambience. Glancing X-ray diffraction(GXRD) and in-situ reflection high energy electron diffracton(RHEED) analyses were performed to investigate the crystallinity of the films. The results show phase change from amorphous state to crystalline one with increasingqr acceleration voltage and substrate temperature. It is also found that the phase transformation from $Y_2O_3$(111)//Si(100) to $Y_2O_3$(110)//Si(100) in growing directions takes place between $500^{\circ}C$ and $700^{\circ}C$. Especially as acceleration voltage is increased, preferentially oriented crystallinity was increased. Finally under the condition of above substrate temperature $700^{\circ}C$ and acceleration voltage 5kV, the $Y_2O_3$films are found to be grown epitaxially in direction of $Y_2O_3$(1l0)//Si(100) by observation of transmission electron microscope(TEM). Capacitance-voltage and current-voltage measurements were conducted to characterize Al/$Y_2O_3$/Si MIS structure with varying acceleration voltage and substrate temperature. Deposited $Y_2O_3$ films of thickness of nearly 300$\AA$ show that the breakdown field increases to 7~8MV /cm at the same conditon of epitaxial growing. These results also coincide with XPS spectra which indicate better stoichiometric characteristic in the condition of better crystalline one. After oxidation the breakdown field increases to 13MV /cm because the MIS structure contains interface silicon oxide of about 30$\AA$. In this case the dielectric constant of only $Y_2O_3$ layer is found to be $\in$15.6. These results have demonstrated the potential of using yttrium oxide for future VLSI/ULSI gate insulator applications.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.45 no.5
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• pp.472-479
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• 2012

The formation of volatile fatty acids(VFAs) and changes in pH, oxidation and reduction potential(Eh) and acid volatile sulfide(AVS) with the addition of yellow clay were investigated using microcosm systems to examine the effects of yellow clay dispersion on the anaerobic decomposition of Cochlodinium polykrikoides in marine sediments. The acetate concentration reached a maximum by day 4 and was 1.2-1.8 fold less in the sample treated with yellow clay compared to the untreated sample (224-270 vs. 333 uM). The formate concentration reached a maximum by day 1 and was 1.3-2.8 fold less in the sample treated with yellow clay compared to the untreated sample (202-439 vs. 563 uM). The propionate concentration reached a maximum by day 2 and was 1.5-1.8 fold less in the sample treated with yellow clay compared to the untreated sample (32.6 vs. 57.2 uM). After the amounts of acetate, formate and propionate peaked the levels dropped dramatically due to the utilization by sulfate reducing bacteria. The Eh of the samples treated with yellow clay was similar to the untreated sample on day 0 but was higher in the sample treated with yellow clay(140-206 mV) from days 4 to 17. AVS started to form on day 3 and this was sustained until day 6, and 1.2-2.2 fold less was produced in the sample treated with yellow clay compared to the untreated sample (40.2-69.3 vs. 83.2-93.8 mg/L). Accordingly, during the anaerobic decomposition of C. polykrikoides in marine sediments, yellow clay dispersal seems to suppress the reduction state of Eh and the formation of volatile fatty acids(acetate, formate and propionate) used as an energy source by sulfate reducing bacteria, indicating that this process controls the production of hydrogen sulfide that negatively affects marine organisms and the marine sediment environment.

• Journal of the Korea Organic Resources Recycling Association
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• v.20 no.1
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• pp.23-30
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• 2012

In the state that re-evaluation of calculating optimum amount of incineration in the future is needed, as considering the amount of waste, increase of heat value and change in floating population in each area in city B, the purpose of this research was to predict optimum available capacity in incineration plant and to study alternatives for the amount of disposal in each incineration plant based on the available capacity that was predicted. As a result of predicting the change in population based on progress of population in city B in the past, it is expected that an overall population is decreasing, but in some areas, population is concentrated due to increased apartment complexes, showing similar figures as the present. Moreover, when predicting the amount of waste through forecasting population, it is considered that the amount of waste by decreased population is also decreasing. However, the amount of combustible component among a total amount of waste is expected to increase, so it is predicted that the amount of incineration and combustible component will be reasonable except D incineration plant, Therefore, D incinerating plant showed 72.7% of rate of utilization of incineration facility compared to 59.1% of national rate. However, if shortfall of waste in the future can be used wisely in other areas, the use of renewable energy using burner useless heat can be maximized.

• Journal of Environmental Impact Assessment
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• v.27 no.1
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• pp.56-72
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• 2018

North Korea has been in ecologically deficit state since 1966, despite of lack of energy and food resources. Trends of the Biocapacity (BC), the Ecological Footprint (EF), and the Ecological Deficit (ED) of North Korea were shown and five factors influencing on the Overshoot Rate (OSR) which is the ratio of the BC and the EF in North Korea was analyzed in this study. The five factors consist of two factors affecting to the EF and three factors affecting to the BC in North Korea. Two of the five factors are affecting to the EF those are population, the EF per capita (EFPC) which indicates the individual environmental consumption intensity, and three are affecting to the BC those are the land area, the yield factor, and the value multiplying the equivalence factor and the intertemporal yield factor. The EF has contributed more than the BC to the OSR. From 1966 to mid-1990s, the EFPC was the most contributing factor at about 60%, and after mid-1990s, population at about 40~60%. Contribution ratio of land area and the yield factor have increased after mid-1990s up to 15% and 18%, respectively. The BC of cropland which has decreased due to a decrease in productivity. In order to reduce the ED of North Korea, improvement of productivity of cropland and restoration of forest. Forest area has decreased significantly since 1990 in NK. And ways to solve the food shortage problem which influences on decrease of both productivity of cropland and forest area.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.835-841
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• 2013

Modern solid-state gyroscopes (HRG) with hemispherical resonators from high-purity quartz glass and special surface superfinishing and ultrathin gold coating become the best instruments for precise-grade inertial reference units (IRU) targeting long-term space missions. Designing of these sensors could be a notable contribution into development of Korea as a space nation. In participial, 40mm diameter thin-shell resonator from high-purity fused quartz, fabricated as a single-piece with its supporting stem has been designed, machined, etched, tuned, tested, and delivered by STM Co. (ATS of Ukraine) several years ago; an extremely-high Q-factor (upto 10~20 millions) has been shown. Understanding of the best way how to match such a unique sensor with inner glass assembly of the gyro means how to use the high potential in a maximal extent; and this has become the urgent task. Inner quartz glass assembly has a very thin indium (In) layer soldered the resonator and its silica base (case), but effects of internal resonances between operational modal pair of the shell-cup and its side (parasitic) modes can notable degrade the potential of the sensor as a whole, instead of so low level of resonator's intrinsic losses. Unfortunately, there are special combinations of dimensions of the parts (so-called, "resonant sizes"), when intensive losses of energy occurs. The authors proposed to use the length of stem's fixture as an additional design parameter to avoid such cases. So-called, a cyclic scheme of finite element method (FEM) and ANSYS software were employed to estimate different combinations of gyro assembly parameters. This variant has no mismatches of numerical origin due to FEM's discrete mesh. The optimum length and dangerous "resonant lengths" have been found. The special attention has been paid to analyses of 3D effects in a cup-stem transient zone, including determination of a difference between the positions of geometrical Pole of the resonant hemisphere and of its "dynamical Pole", i.e., its real zone of oscillation node. Boundary effects between the shell (cup) and 3D short "beams" (inner and outer stems) have been ranged. The results of the numerical experiments have been compared with the classic model of a quasi-hemispherical shell band with inextensional midsurface, and the solution using Rayleigh's functions of the $1^{st}$ and $2^{nd}$ kinds. To guarantee the truth of the recommended sizes to a designer of the real device, the analytical and FEM results have been compared with experimental data for a party of real resonators. The consistency of the results obtained by different means has been shown with errors less than 5%. The results notably differ from the data published earlier by different researchers.