• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.8
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• pp.29-36
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• 2004

Supersonic inlet buzz can be defined as unstable subcritical operation associated with fluctuating internal pressures and a shock pattern oscillating about the inlet entrance. The flow pulsations could result in flameout in the combustor or even structural damage to the engine. An experimental study was conducted to investigate the phenomenon of supersonic inlet buzz on axisymmetric, external-compression inlet. An inlet model with a cowl lip diameter of 30mm was tested at a free stream Mach number of 2.0. Subcritical instability was investigated by considering the frequency of pressure pulsation and shock wave structure at the inlet entrance. The results obtained show that total pressure recovery ratios were varied from 0.42 to 0.78, and capture area ratio from 0.34 to 0.98. The frequency of the subcritical flow increased with decrease in capture area ratios. Frequency was measured at $224{\sim}240Hz$.

• Journal of the Korean Society of Radiology
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• v.8 no.6
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• pp.287-292
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• 2014

In this study, the neutron capture cross section of $^{180}Ta$(natural existence ratio: 0.012 %) obtain by measuring has been compared with the evaluated data for the capture data. In generally, the neutron capture resonance is defined as Breit-Wigner formula. The formula consists of the resonance parameters such as neutron width, total width and neutron width. However in the case of $^{180}Ta$, these are very poor experimental neutron capture cross section data and resonance information in below 10 eV. Therefore, in the study, we analyzed the neutron resonance of $^{180}Ta$ with the measuring the prompt gamma-ray from the sample. And the resonance was compared with the evaluated data by Mughabghab, ENDF/B-VII, JEFF-3.1 and TENDL 2012. Neutron sources from photonuclear reaction with 46-MeV electron linear accelerator at Research Reactor Institute, Kyoto University used for cross section measurement of $^{180}Ta(n,{\gamma})^{181}Ta$ reaction. $BGO(Bi_4Ge_3O_{12})$ scintillation detectors used for measurement of the prompt gamma ray from the $^{180}Ta(n,{\gamma})^{181}Ta$ reaction. The BGO spectrometer was composed geometrically as total energy absorption detector.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.228-228
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• 2011

낮은 공정비용과 높은 집적도를 가지는 플래시 메모리 소자에 대한 휴대용기기에 응용가능성때문에 연구가 필요하다. 플래시 메모리 중에서도 질화막에 전하를 저장하는 전하 포획 플래시 메모리 소자는 기존의 부유 게이트 플래시 메모리 소자에 비해 공정의 단순하고 비례축소에 용이하며 인접 셀 간의 간섭에 강하다는 장점으로 많은 관심을 갖게 되었다. 소자의 크기가 작아짐에 따라 전하 포획 플래시 메모리 소자 역시 인접 셀 간의 간섭현상과 단채널 효과가 문제를 해결할 필요가 있다. 본 연구에서는 인접 셀 간의 간섭을 최소화 시키기 위하여 metal-oxide-nitride-oxide-silicon (MONOS) 플래시 메모리 소자에 bit-line 방향으로 금속 공간층을 삽입할 구조를 사용하였으며 금속 공간층의 깊이에 따른 전기적 성질을 비교하였다. 게이트 길이는 30 nm, 금속 공간층의 깊이를 채널 표면에서부터 4 nm~12 nm까지 변화하면서 TCAD 시뮬레이션 툴인 Sentaurus를 사용하여 전기적 특성을 계산하였다. 금속 공간층의 깊이가 채널표면에 가까워 질수록 fringing field가 증가하여 드레인 전류가 증가하였고, 금속 공간층의 전기적 차폐로 인해 인접 셀의 간섭현상도 감소하였다. 금속 공간층이 표면에 가까이 위치할수록 전하 저장층을 감싸는 면적이 증가하여 coupling ratio가 높아지기 때문에 subthreshold swing 특성이 향상되었으나, 금속 누설전류가 증가하였다.

• Journal of Ecology and Environment
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• v.29 no.3
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• pp.253-257
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• 2006

The objectives of this paper are to estimate home range and core habitat area of wild bores in Jirisan National Park of Korea. A radio-telemetry study was carried out on 5 wild boar individuals (3 females and 2 males). Except one individual whose enough data could not be collected, the mean home range size of 4 individuals was $5.13km^2$ (95% kernel) and mean core habitat area was $1.18{\pm}0.31km^2$ (50% kernel). Home-range sizes of 2 females were $6.21km^2\;and\;5.45km^2$ each, and that of 2 males were $5.15km^2\;and\;3.72km^2$ each, which means home-ranges of female boars were larger than those of male boars in this research. This result is presumed to have been caused by the fact that the males were sub adult individuals weighing 40 kg and 19 kg when they were captured for this research.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.16-27
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• 2020

For the operation of the scramjet engine in the wide flight range, the design of the inlet must show stable performance in various flight conditions. In this study, the design methods of a 2D fixed inlet for stable performance in wide flight ranges of Mach number 4 to 6 and angle -6° to 6°, is performed. After proposing the design method and design focus, performance prediction and analysis were performed by various initial compression angles and design Mach numbers, which are essential design factors in total pressure recovery and inlet capture area ratio in the wide flight range. Based on the analysis results, we present the selection criteria for the two main design elements to represent stable performance in the wide flight range.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.126-126
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• 2011

삼차원 구조의 낸드 플래시 메모리 소자는 기존 이차원 구조의 메모리 소자를 비례 축소할 때 발생하는 단채널 효과와 간섭효과를 최소화 하면서 집적도를 높일 수 있는 장점 때문에 많은 연구가 진행되고 있다. 그러나, 삼차원 구조의 낸드 플래시 메모리 소자는 공정 과정이 복잡하고 주변 회로 연결이 어려울 뿐만 아니라 금속 접촉에 필요한 면적이 넓은 단점을 가지고 있다. 이러한 문제점을 해결하기 위해 Vertical-Stacked-Array-Transistor (VSAT) 구조를 갖는 플래시 메모리 소자가 제안되었으나, VSAT 구조 역시 드레인 전류량이 적고 program과 erase 동작 시게이트 양쪽의 전하 트랩층에 전자와 정공을 비효율적으로 포획해야 하는 문제점을 가진다. 본 연구에서는 기존의 VSAT 구조의 문제점을 개선하면서 집적도를 증가한 삼차원 구조의 고집적낸드 플래시 메모리 소자를 제안하였다. 본 연구에서 제안한 플래시 메모리 소자의 구조는 기존 VSAT 구조에서 수직 방향의 두 string 사이에 존재하는 polysilicon을 제거하고 두 string 사이에 절연막을 증착하였다. 삼차원 시뮬레이션 툴인 Sentaurus를 사용하여 이 소자의 동작특성을 시뮬레이션 하였다. 소스와 드레인 사이의 유효 채널 길이가 감소하였기 때문에 기존의 VSAT 구조를 갖는 메모리 소자에 비해 turn-on 상태의 드레인 전류가 증가하였다. 제안한 플래시 메모리 소자의 subthreshold swing (SS)가 기존의 VSAT 구조를 갖는 메모리 소자의 SS 에 비해 낮아, 소자의 스위칭 특성이 향상하였다. 프로그램 전후의 문턱전압의 변화량이 기존의 VSAT 구조를 갖는 메모리 소자에 비해 크기 때문에 멀티 레벨 동작이 가능하다는 것을 확인하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.992-995
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• 2011

A study on the performance design schemes of the supersonic air intakes applied to the supersonic air-breathing propulsion system(Ramjet/Scramjet) was conducted and for two kinds of air intakes, the preliminary configuration designs and the performance analysis models were established. For axisymmetric conical air intake and two dimensional rectangular air intake, the performance effects were assessed according to compression angles and shock wave numbers.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.6
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• pp.53-59
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• 2010

This research aims in finding a more optimal ejector size for evacuating engine exhaust gasses and 20% of the cell cooling air. The remaining 80% of cell cooling air pumped into the test chamber is separately exhausted from the test chamber via a discharge port fitted with flow control valves and vacuum pump. Unlike its predecessor this configuration utilizes a smaller capture area to improve pressure recovery. The modified ejector size has a diameter of 1100mm enough to evacuate 66kg/s jet engine exhaust in addition to about 20%, 24kg/s of the cell cooling air tapped from the sterling chamber. This configurations has an area ratio of the engine exit and ejector inlet of about 1.2. Simulation results of the proposed ejector configuration, indicates improved pressure recovery.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.833-837
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• 2010

This study aims at finding an optimal exhaust diffuser design of a high altitude testing chamber for a low bypass turbofan engine (F404-402) with thrust pound force of 17,700 and air mass flow rate of 66kg/s ejecting at a speed of Mach 1.66. The final proposed ejector size has better pressure recovery characteristics and targets to reduce operational cost at engine performance testing. Conventional high altitude test chamber layout was adopted and first drawn in two dimensions using Autocad software so as to determine the gas path, the ejector frontal size was then determined from gas dynamics equations considering traditional gas ejection method where both the engine exhaust and cell cooling air are exhausted via the ejector. Modification to a smaller ejector with an alternative secondary cell cooling exhaust port was then performed and modelled in 3D using Solid Works software.

• Korean journal of applied entomology
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• v.50 no.2
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• pp.97-105
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• 2011

Understanding the metapopulation structure and movement of a species are required for conserving the species. In this paper, migration patterns and connectivity of patches of a threatened butterfly, Parnassius bremeri Bremer, were postulated using the mark-release-recapture (MRR) technique in a habitat located in the mid-southern region of the Korean peninsula. A total of 194 individuals were captured (137 males and 57 females) and, of them, 93 individuals (73 males and 20 females) were recaptured during the MRR experiment. The migration analysis showed 23-150% immigration and 28-53% emigration. There were high correlations between the migrating individuals and the distance between patches, but there was no correlation between migrating individuals and patch size or between migrating individuals and the number of host plants. Consequently, the migration of butterflies occurred frequently between closer patches, while patch size and quantity of the food plant had minor effects on migration behavior. Additionally, males migrated more frequently than females. Analysis of the migration patterns of P. bremeri showed that the central patch played an important role on linking patch groups and more frequent migrations were monitored between nearby patches than between the remote patches. This study suggested that active migrations take place between the neighboring multiple patches and these are accelerated if there is a stepping-stone patch between them.