• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.14 no.5
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• pp.1-12
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• 2015

Length and the number of tunnels has increased 10% annually. Tunnel construction has positive effect in nature and driving condition. However, the structure of tunnels lead to a greater probability of major accidents. For this reason, tunnel is focusing its attention on the rapid incident handling and disaster management to build a tunnel management system in recently. In this study, tunnel management system adequacy analyzed in terms of operational safety using IPA and AHP analysis. IPA analysis results using the portfolio chart, incident management factors has a large gap between important and satisfaction. Disaster management is analyzed high ranking in priority. However, incident management factors are derived first priority in AHP analysis. This study determined that the results are meaningful to practitioners in the field is determined. In addition, practitioners comments should be reflected primarily for tunnel operational safely.

• Korean Journal of Materials Research
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• v.10 no.5
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• pp.369-374
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• 2000

In order to investigate the effects of addition of 1M sulfuric acid to the etching solution or 1M hydrochloric acid on the etching behavior of aluminum foil for electrolytic capacitors, the changes in the density of etch pit, the length and diameter of etch tunnels and the capacitance were analyzed using SEM, TEM, LCR meter etc. Sulfate ion as a corrosion inhibitor was contributed to the increase of the surface area comparing with chloride ion. By adding sul-furic acid the density of etch pit and the length of etched tunnel increased and the diameter of the tunnel decreased, resulting in the increase of capacitance. It was also shown that the capacitance decreased when the current density was below $0.9A/\textrm{cm}^2$, while remarkably increased in the other case.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.255-255
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• 2010

전하 트랩형 비휘발성 메모리는 10년 이상의 데이터 보존 능력과 빠른 쓰기/지우기 속도가 요구 된다. 그러나 두 가지 특성은 터널 산화막의 두께에 따라 서로 trade off 관계를 갖는다. 즉, 두 가지 특성을 모두 만족 시키면서 scaling down 하기는 매우 힘들다. 이것의 해결책으로 적층된 유전막을 터널 산화막으로 사용하여 쓰기/지우기 속도와 데이터 보존 특성을 만족하는 Tunnel Barrier engineered Memory (TBM)이 있다. TBM은 가운데 장벽은 높고 기판과 전극쪽의 장벽이 낮은 crested barrier type이 있으며, 이와 반대로 가운데 장벽은 낮고 기판과 전극쪽의 장벽이 높은 VARIOT barrier type이 있다. 일반적으로 유전율과 밴드갭(band gap)의 관계는 유전율이 클수록 밴드갭이 작은 특성을 갖는다. 이러한 관계로 인해 일반적으로 crested type의 터널 산화막층은 high-k/low-k/high-k의 물질로 적층되며, VARIOT type은 low-k/high-k/low-k의 물질로 적층된다. 이 형태는 밴드갭이 다른 물질을 적층했을 때 전계에 따라 터널 장벽의 변화가 민감하여 전자의 장벽 투과율이 매우 빠르게 변화하는 특징을 갖는다. 결국 전계에 민감도 향상으로 쓰기/지우기 속도가 향상되며 적층된 유전막의 물리적 두께의 증가로 인해 데이터 보존 특성 또한 향상되는 장점을 갖는다. 본 연구에서는 기존의 TBM과 다른 형태의 staggered tunnel barrier를 제안한다. staggered tunnel barrier는 heterostructure의 에너지 밴드 구조 중 하나로 밴드 line up은 두 밴드들이 같은 방향으로 shift된 형태이다. 즉, 가전자대 에너지 장벽의 minimum이 한 쪽에 생기면 전도대 에너지 장벽의 maximum은 반대쪽에 생기는 형태를 갖는다. 이러한 밴드구조를 갖는 물질을 터널 산화막층으로 하게 되면 쓰기/지우기 속도를 증가시킬 수 있으며, 데이터 보존 능력 모두 만족할 수 있어 TBM의 터널 산화막으로의 사용이 기대된다. 본 연구에서 제작한 staggered TBM소자의 터널 산화막으로는 $Si_3N_4$/HfAlO (Hf:Al=1:3)을 사용하여 I-V(current-voltage), Retention, Endurance를 측정하여 메모리 소자로서의 특성을 분석하였으며, 터널 산화막의 제 1층인 $Si_3N_4$의 두께를 1.5 nm, 3 nm일 때의 특성을 비교 분석하였다.

• Progress in Superconductivity
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• v.14 no.2
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• pp.99-101
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• 2012

Fluorescent yield X-ray absorption fine structure (XAFS) spectroscopy is useful for analyzing local structure of specific elements in matrices. We developed an XAFS apparatus with a 100-pixel superconducting tunnel junction (STJ) detector array with a high sensitivity and a high resolution for light-element dopants in wide-gap semiconductors. An STJ detector has a pixel size of $100{\mu}m$ square, and an asymmetric layer structure of Nb(300 nm)-Al(70 nm)/AlOx/Al(70 nm)-Nb(50 nm). The 100-pixel STJ array has an effective area of $1mm^2$. The XAFS apparatus with the STJ array detector was installed in BL-11A of High Energy Accelerator Research Organization, Photon Factory (KEK PF). Fluorescent X-ray spectrum for boron nitride showed that the average energy resolution of the 100-pixels is 12 eV in full width half maximum for the N-K line, and The C-K and N-K lines are separated without peak tail overlap. We analyzed the N dopant atoms implanted into 4H-SiC substrates at a dose of 300 ppm in a 200 nm-thick surface layer. From a comparison between measured X-ray Absorption Near Edge Structure (XANES) spectra and ab initio FEFF calculations, it has been revealed that the N atoms substitute for the C site of the SiC lattice.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.408-409
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• 2009

The memory characteristics of charge trap memory capacitor with high-k materials were investigated. I-V characteristics of the fabricated device with band gap engineered tunneling gate stacks consisted of $SiO_2$, $ZrO_2$, $Al_2O_3$ dielectrics were evaluated and compared with the one consisted of $SiO_2$ tunneling dielectric. The memory capacitor including engineered tunneling dielectrics of ($Al_2O_3/ZrO_2/SiO_2$) shows the fastest PIE speed and long data retention time.

• Journal of KIISE:Information Networking
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• v.36 no.1
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• pp.43-49
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• 2009

The Mobile IPv6(MIPv6) has a well-known time gap of packet loss between link down and binding update. To minimize such packet loss, this paper proposes a MIPv6-based dual tunneling mechanism, which keeps exploiting the old tunnel while creating a new tunnel. Superiority of the proposed mechanism is evaluated by quantitative analysis on the lost packets and computer simulation, based on two overlay heterogeneous access networks, such as the UMTS and a WLAN.

• Journal of Aerospace System Engineering
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• v.10 no.3
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• pp.39-43
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• 2016

In this paper, a wind-tunnel test is accomplished to investigate the roll characteristics of a variable-span wing flying inside a channel. The factors that affect the roll characteristics of the wing were identified by analyzing the measured data; accordingly, when the wing is flying without both the ground and sidewall effects, the asymmetric wing extension causes the roll moment. Both the ground and the sidewall can increase the roll moment, but when the wing is affected by both the ground and the sidewall, the roll moment does not increase as much as the case where the wing is only affected by the ground. Also, the aerodynamic characteristics of the flying wing inside a channel are the nonlinear function of the wing height and the gap between the wingtip and the sidewall, both of which should be considered in a study of the stability and the flight control of the wing-in-ground effect of the vehicle flying inside a channel.

• Wind and Structures
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• v.26 no.5
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• pp.305-315
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• 2018

A numerical study based on a delayed detached eddy simulation (DDES) is conducted to investigate the aerodynamic mechanism behind the suppression of vortex-induced vibrations (VIVs) of twin box girders by central grids, which have an inhibition effect on VIVs, as evidenced by the results of section model wind tunnel tests. The mean aerodynamic force coefficients with different attack angles are compared with experimental results to validate the numerical method. Next, the flow structures around the deck and the aerodynamic forces on the deck are analyzed to enhance the understanding of the occurrence of VIVs and the suppression of VIVs by the application of central grids. The results show that shear layers are separated from the upper railings and lower overhaul track of the upstream girder and induce large-scale vortices in the gap that cause periodical lift forces of large amplitude acting on the downstream girder, resulting in VIVs of the bridge deck. However, the VIVs are apparently suppressed by the central grids because the vortices in the central gap are reduced into smaller vortices and become weaker, causing slightly fluctuating lift forces on the deck. In addition, the mean lift force on the deck is mainly caused by the upstream girder, whereas the fluctuating lift force is mainly caused by the downstream girder.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.2
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• pp.136-142
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• 2007

A small supersonic wind tunnel was designed and built to study the flow characteristics of a supersonic impulse turbine cascade. The supersonic cascade with a 2-dimensional supersonic nozzle was tested for the axial gap ratio (${\delta}$) of the supersonic turbine that is the one of the turbine design parameter. Firstly, the flow was visualized by a single pass Schlieren system. Next, total and static pressure of the cascade were measured by a pressure scanning system. Highly complicated flow patterns including shocks, nozzle-cascade interaction and shock boundary layer interactions, flow characteristics of the supersonic turbine were observed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.4
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• pp.1458-1471
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• 1996

The present study is concerned with the heat transfer enhancement associated with a symmetrical or asymmetrical horseshoe vortex in front of and around the circular cylinder centered between the side walls of a wind tunnel. The static pressure measurements and the flow visualization in front of and around cylinders have been performed to determine the existence of horseshoe vortex. The hue-capturing method using the thermochromatic liquid crystals with great spatial resolution was used to obtain the local information of the endwall heat transfer coefficients. In case of one cylinder, the convective heat transfer coefficients of the region where the horseshoe vortex exists are larger than those of any other region. In case of two cylinders with tandem arrangement, the heat transfer rate of gap spacing (d/D= 1.5) is higher than that of gap spacings (d/D=2.0 or 2.5).