• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제30회 춘계학술대회논문집
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• pp.321-327
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• 2008

초음속 디퓨져를 사용하는 고도모사 장치에서 기존에 연구되었던 일정단면적 형태를 개선해 2차 목 형태 디퓨져의 효과를 고찰하였다. 기 수행 된 일정단면적 디퓨져 정상상태 해석 결과 및 공압시험 데이터를 바탕으로 본 연구의 해석방법을 검증하고, 2차목에 의한 효과를 정량화시키기 위해 노즐전압력과 2차목 면적에 따른 시동성능과 진공챔버압력 변화에 관하여 해석하였다. 일정단면적 디퓨져 내부 벽면 및 중심축을 따른 압력데이터 비교에서 일치하는 거동을 확인했으며, 2차목의 사용에 의해 시동을 위한 노즐 전압력이 현저히 낮아짐을 알 수 있었다. 저팽창비 노즐 사용으로 인하여 2차목에 의한 진공챔버 내 압력 변화는 거의 없음을 관찰하였다.

• 한국환경교육학회지:환경교육
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• 제19권2호
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• pp.26-47
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• 2006

Environmental problems became bigger and widely known among all parts of the society in the last decade. The broad and sustainable study of the environment is the most basic and primary solution to the problems. For this reason, International Environmental Project Olympiad (INEPO) was organized in 1993. Many countries have participated in this organization. Therefore, the purpose of this study was to revitalize the environmental education and to realize the value of environmental education by making students aware of the environmental problems through the INEPO and Korean Environmental Olympiad (KEO). To achieve these goals, we conducted as follows First, we introduced aims, major contents and rules of the INEPO and grasped problems related to the applying method of students who want to participate in the INEPO in Korea. In addition, we introduced both results of domestic contest for participating in the 14th INEPO and of the 14th INEPO itself opened in 2006. Second, we analysed participants' themes according to project types such as environment-biology, environment-chemistry, environment-physics, environment-health and environment-social sciences from Previous INEPOs. Third, we had interviews with several participants to gather their thoughts on motivation and impression of participation, the reason of theme selection, and the method of environmental education in school, by visiting each booth of INEPO. Finally, we suggested sustainable methods of the KEO to revitalize environmental education, and proposed various methods to revitalize the environmental education through the KEO and INEPO in the primary and secondary schools.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권1호
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• pp.21-40
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• 2018

In this paper, we propose the distributed robust beamforming design scheme in cognitive two-way amplify-and-forward (AF) relay networks with imperfect channel state information (CSI). Assuming the CSI errors follow a complex Gaussian distribution, the objective of this paper is to design the robust beamformer which minimizes the total transmit power of the collaborative relays. This design will guarantee the outage probability of signal-to-interference-plus-noise ratio (SINR) beyond a target level at each secondary user (SU), and satisfies the outage probability of interference generated on the primary user (PU) above the predetermined maximum tolerable interference power. Due to the multiple CSI uncertainties in the two-way transmission, the probabilistic constrained optimization problem is intractable and difficult to obtain a closed-form solution. To deal with this, we reformulate the problem to the standard form through a series of matrix transformations. We then accomplish the problem by using the probabilistic approach based on two sorts of Bernstein-type inequalities and the worst-case approach based on S-Procedure. The simulation results indicate that the robust beamforming designs based on the probabilistic method and the worst-case method are both robust to the CSI errors. Meanwhile, the probabilistic method can provide higher feasibility rate and consumes less power.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.188.1-188.1
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• 2014

Aluminum is widely used as a material for electrode on silicon based devices. Especially, aluminum films are used as backside and front-side electrodes in silicon quantum dot (QD) solar cells. In this point, the diffusion of aluminum is very important for the enhancement of power conversion efficiency by improvement of contact property. Aluminum was deposited on a Si (100) wafer and a Si QD layer by ion beam sputter system with a DC ion gun. The Si QD layer was fabricated by $1100^{\circ}C$ annealing of the $SiO_2/SiO_1$ multilayer film grown by ion beam sputtering deposition. Cs ion beam with a low energy and a grazing incidence angle was used in SIMS depth profiling analysis to obtain high depth resolution. Diffusion behavior of aluminum in the Al/Si and Al/Si QD interfaces was investigated by secondary ion mass spectrometry (SIMS) as a function of heat treatment temperature. It was found that aluminum is diffused into Si substrate at $450^{\circ}C$. In this presentation, the effect of heat treatment temperature and Si nitride diffusion barrier on the diffusion of Al will be discussed.

• Progress in Superconductivity
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• 제8권2호
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• pp.175-180
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• 2007

High temperature superconductor $YBa_2Cu_3O_{7-x}$ (YBCO) films have been grown by in-situ electron beam evaporation on artificial metal tapes such as ion-beam assisted deposition (IBAD) and rolling assisted biaxially textured substrates (RABiTS). Deposition rate of the YBCO films is $10{\sim}100{\AA}/sec$. X-ray diffraction shows that the films are grown epitaxially but have inter-diffusion phases, like as $BaZrO_3\;or\;BaCeO_3$, at their interfaces between YBCO and yttrium-stabilized zirconia (YSZ) or $CeO_2$, respectively. Secondary ion mass spectroscopy depth profile of the films confirms diffused region between YBCO and the buffer layers, indicating that the growth temperature ($850{\sim}900^{\circ}C$) is high enough to cause diffusion of Zr and Ba. The films on both the substrates show four-fold symmetry of in-plane alignment but their width in the -scan is around $12{\sim}15^{\circ}$. Transmission electron microscopy shows an interesting interface layer of epitaxial CuO between YBCO and YSZ, of which growth origin may be related to liquid flukes of Ba-Cu-O. Resistivity vs temperature curves of the films on both substrates were measured. Resistivity at room temperature is between 300 and 500 cm, the extrapolated value of resistivity at 0 K is nearly zero, and superconducting transition temperature is $85{\sim}90K$. However, critical current density of the films is very low, ${\sim}10^3A/cm^2$. Cracking of the grains and high-growth-temperature induced reaction between YBCO and buffer layers are possible reasons for this low critical current density.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1998년도 제14회 학술발표회 논문개요집
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• pp.20-20
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• 1998

I Ion beam technology has recently attracted much interest because it has exciting t technological p아:ential for surface analysis, ion beam mixing, surface cleaning and etching i in thin film growth and semiconductor fabrication processes, etc. Es야~cially, ion beam s sputtering has been widely used for sputter depth profiling with x-photoelectron S spectroscopy (XPS) , Auger electron s$\pi$~troscopy(AES), and secondary-ion mass S야i따oscopy(SIMS). However, The problem of surface compositional ch없1ge due to ion b bombardment remains to be understo여 없ld solved. So far sputtering processes have been s studied by s따face an외ysis tools such as XPS, AES, and SIMS which use the sputtering p process again. It would be improbable to measure the modified surface composition profiles a accurately due to ion beam bombardment with surface analysis techniques based on sputter d depth profiling. However, recently Medium energy ion scattering spectroscopy(MEIS) has b been applied to study the sputtering of solid surface at ion bombardment and has been p proved that it has been extremely valuable in probing the surface composition 뻐d s structure nondestructively and quantita디vely with less than 1.0 nm depth resolution. To u understand the sputtering processes of solid surface at ion bombardment, The Molecular D Dynamics(MD) and Monte Carlo(MC) simulation has been used and give an intimate i insight into the sputtering processes of solid surfaces. In this presentation, the sputtering processes of alloys and compound samples at ion b bombardment will be reviewed and the MEIS results for the Ar+ sputter induced altered l layer of the TazOs thin film 뻐dd없nage profiling of Ar+ ion sputt얹"ed Si(100) surface will b be discussed with the results of MD and MC simulation.tion.

• 한국재료학회지
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• 제27권3호
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• pp.144-148
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• 2017

The effects of an excess of Bi on the piezoelectric and dielectric properties of $0.60Bi_{1+x}FeO_3-0.40BaTiO_3$ (x = 0, 0.01, 0.03, 0.05, 0.07) were investigated. The ceramics were processed through a conventional solid state reaction method and then quenched after sintering at different temperatures in the range of $980{\sim}1070^{\circ}C$. A single perovskite structure without any secondary phase was confirmed for all compositions and temperatures. It was found that excess Bi reduced the sintering temperatures, acted as a sintering aid and enhanced the properties in combination with quenching. Curie temperature ($T_C$) was found to slightly increase due to the presence of excess Bi; electrical properties were also improved by quenching. At x = 0.03 and $1030^{\circ}C$, remnant polarization ($2P_r$) was as high as $45.4{\mu}C/cm^2$ and strain at 40 kV/cm was up to 0.176 %.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.274-274
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• 2012

In-depth analysis by secondary ion mass spectrometry (SIMS) is very important for the development of electronic devices using multilayered structures, because the quantity and depth distribution of some elements are critical for the electronic properties. Correct determination of the interface locations is critical for the calibration of the depth scale in SIMS depth profiling analysis of multilayer films. However, the interface locations are distorted from real ones by the several effects due to sputtering with energetic ions. In this study, the determination of interface locations in SIMS depth profiling of multilayer films was investigated by Si/Ge and Ti/Si multilayer systems. The original SIMS depth profiles were converted into compositional depth profiles by the relative sensitivity factors (RSF) derived from the atomic compositions of Si-Ge and Si-Ti alloy reference films determined by Rutherford backscattering spectroscopy. The thicknesses of the Si/Ge and Ti/Si multilayer films measured by SIMS depth profiling with various impact energy ion beam were compared with those measured by TEM. There are two methods to determine the interface locations. The one is the feasibility of 50 atomic % definition in SIMS composition depth profiling. And another one is using a distribution of SiGe and SiTi dimer ions. This study showed that the layer thicknesses measured with low energy oxygen and Cs ion beam and, by extension, with method of 50 atomic % definition were well correlated with the real thicknesses determined by TEM.

• Nuclear Engineering and Technology
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• 제52권10호
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• pp.2410-2414
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• 2020

Heavy ions have a high potential for destroying deep tumors that carry the highest dose at the peak of Bragg. The peak caused by a single-energy carbon beam is too narrow, which requires special measures for improvement. Here, carbon-12 (¹²C) ion with different energies has been used as a source for calculating the dose distribution in the water phantom, soft tissue and bone by the code of Monte Carlobased FLUKA code. By increasing the energy of the initial beam, the amount of absorbed dose at Bragg peak in all three targets decreased, but the trend for this reduction was less severe in bone. While the maximum absorbed dose per bone-mass unit in energy of 200 MeV/u was about 30% less than the maximum absorbed dose per unit mass of water or soft tissue, it was merely 2.4% less than soft tissue in 400 MeV/u. The simulation result showed a good agreement with experimental data at GSI Darmstadt facility of biophysics group by 0.15 cm average accuracy in Bragg peak positioning. From 200 to 400 MeV/u incident energy, the Bragg peak location increased about 18 cm in soft tissue. Correspondingly, the bone and soft tissue revealed a reduction dose ratio by 2.9 and 1.9. Induced neutrons did not contribute more than 1.8% to the total energy deposited in the water phantom. Also during ¹²C ion bombardment, secondary fragments showed 76% and 24% of primary 200 and 400 MeV/u, respectively, were present at the Bragg-peak position. The combined treatment of carbon ions with neutron or electron beams may be more effective in local dose delivery and also treating malignant tumors.

• 대한기계학회논문집B
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• 제21권5호
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• pp.679-690
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• 1997

Oil spill over the sea and the river become a serious problem in these days. Two different approaches are used to clean up the spilled oil by means of chemical dispersion and mechanical devices. If it is possible, removing spilled oil using mechanical devices are highly desirable in order not to worry about the secondary contamination from chemical treatment. One of the major unsolved problems using mechanical devices has been the recovery of highly viscous oil spill. So, the systematic experimental data for treating very viscous oil are still wanting. In the present study a series of experiments were carried out to study the effect of the rotational direction of the belt skimmer on the rate of oil recovery using Bunker C oil. Three different situations, namely, upward, downward and up-and-downward pickup rate have been investigated for variable belt speed. The results showed that the rate of oil recovery for downward pickup was much higher than that for upward pickup. The major mechanism to recover the oil using a belt skimmer has been confirmed that oil sticks to the belt surface while moving to the water rather than moving upward. For the removal of spilled oil the optimal belt speed under the present experimental conditions was found to be about 200 ~ 270 mm/s just before the starvation started. The present experimental results would provide the basis for understanding the performance characteristics and physics of various types of skimmers.