• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 봄 학술발표회 논문집
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• pp.221-228
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• 2002

Thickness of concrete lining, voids at the back of lining or shotcrete are very important elements for inspecting the safety of tunnels. Therefore, the inspection of tunnel lining structure means to investigate the inner layer boundaries of the structure. For this purpose, seismic reflection survey is the most desirable method if it works in good conditions. However, the conventional seismic reflection method can not be properly used for investigating thin layers in the lining structure. In other words, to detect the inner boundaries, it is desirable for the wavelength of source to be less than the thickness of each layer and for the receiver to be capable of detecting high frequency(ultrasonic) signals. To this end, new appropriate source and receiver devices should be developed above all for the ultrasonic reflection survey. This paper deals primarily with the development of source and receiver devices which are essential parts of field measuring system. Interests are above all centered in both the radiation pattern, energy, frequency content of the source and the directional sensitivity of the receiver. With these newly devised ones, ultrasonic physical modeling has been performed on 3-D physical model composed of bakelite, water-proof and concrete, The measured seismograms showed a clear separation of wave arrivals reflected from each layer boundary. Furthermore, it is noteworthy that reflection events from the bottom of concrete below water-proof could be also observed. This result demonstrates the usefulness of the both devices that can be applied to benefit the ultrasonic reflection survey. Future research is being focus on dealing with at first an optimal configuration of source and receiver devices well coupled to tunnel wall, and further an efficient data control system of practical use.

• 화약ㆍ발파
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• 제21권2호
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• pp.21-30
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• 2003

현재 터널 굴착시 기초 지보수단으로 활용되고 있는 숏크리트는 암반의 굴착 특성상 조기에 얇은 두께로 타설하여도 높은 강도를 유지할 수 있다는 장점 때문에 그동안 우수한 장비와 재료가 개발되어 비약적인 발전을 거듭해 오고 있다. 또한, 계측기술의 발달로 지하암반 거동상태도 조기에 자세히 파악되어 강도와 두께 등 거의 정확한 설계가 이루어지고 있으며, 신소재의 보강재료도 지속적으로 개발되고 있다. 국내 석탄 화력발전소에서 발생되는 석탄회에는 fly ash와 bottom ash가 있으며, 이러한 석탄회는 시멘트, 골재, 건축, 토목 및 농수산 분야에 이르기까지 많은 분야에 기술개발이 되었으며, 연구가 활발히 진행 중에 있다. 따라서, 본 연구에서는 fly ash를 혼합한 콘크리트를 숏크리트 재료로서 활용하기 위해 기존의 숏크리트 배합설계에서 fly ash를 시멘트의 대체재로서 사용할 때, 압축강도의 향상 및 굴착면의 타설 리바운드 율을 저하시키는 최적의 함량에 대하여 실험을 실시하였다. 그 결과, fly ash를 시멘트에 15% 중량 치환했을 때, 약 10%의 압축강도의 향상과 리바운드 율이 6%감소되었다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제17권2호
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• pp.260-264
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• 2017

Process variation effect on arch-structured gate stacked array (GSTAR) 3-D NAND flash is investigated. In case of arch-structured GSTAR, a shape of the arch channel is depending on an alignment of photo-lithography. Channel width fluctuates according to the channel hole alignment. When a shape of channel exceeds semicircle, channel width becomes longer, increasing drain current. However, electric field concentration on tunnel oxide decreases because less electric flux converges into a larger surface of tunnel oxide. Therefore, program efficiency is dependent on the process variation. Meanwhile, a radius of channel holes near the bottom side become smaller due to an etch slope. It also affects program efficiency as well as channel width. Larger hole radius has an advantage of higher drain current, but causes degradation of program speed.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2007년도 춘계종합학술대회
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• pp.556-558
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• 2007

최근에 분자 전자 소자로 사용되기에 적합한 많은 분자들이 많은 주목을 받고 있다. 또한 이러한 소자에 사용되는 초박막 물질들은 의용공학용 전자 소자에도 많이 사용되기도 한다. 분자 수준 스위치의 개발에 기초로 한 현재의 많은 시도들은 논리회로와 메모리 소자 등에 응용 될 수 있다. 본 연구에서는 eicosanoic acid 지질막을 이용하여 초박막 소자를 제작하고, 이의 전기적 특성을 측정하였다. 또한 측정된 결과를 통하여 본 연구에서의 분자 소자가 의용 소자로의 응용 가능을 확인하고자 하였다.

• Progress in Superconductivity
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• 제12권2호
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• pp.110-113
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• 2011

We have grown a Nb/Gd bilayer on a$SiO_2$/Si substrate by using a DC magnetron sputtering system, which was fabricated in situ with silicon stencil masks. In order to investigate proximity effect of the Nb/Gd bilayer, we used a planar tunnel junction with an AlOx tunnel barrier by oxidizing the Al ground electrode at the bottom. A $Co_{60}Fe_{40}$ backing of Al was deposited so as to reduce the superconductivity of the Al, ensuring a normal counterelectrode. With a 50-nm-thick Nb layer, we have measured dI/dV (dynamic conductance) by varying the thickness of Gd, which can reveal the density of states (DOS) of the Nb/Gd bilayer as a function of the Gd thickness resulting from the proximity effect of a superconductor/ferromagnet bilayer (S/F). The SF proximity effect in Nb/Gd will be discussed in comparison to our previous results of the CoFe/Nb, Ni/Nb and CuNi/Nb proximity effect; Gd is expected to show different effects since Gd has f-electrons, while CoFe, Ni, and CuNi have only d-electrons. Our studies will focus on the triplet correlation in a superconducting pair.

• Advances in aircraft and spacecraft science
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• 제4권4호
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• pp.401-419
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• 2017

This paper presents the main outcomes of the preliminary development of the Anuloid, an innovative disk-shaped VTOL aircraft. The Anuloid has three main features: lift is provided by a ducted fan powered by a turboshaft; control capabilities and anti-torque are due to a system of fixed and movable surfaces that are placed in the circular internal duct and the bottom portion of the aircraft; the Coanda effect is exploited to enable the control capabilities of such surfaces. In this paper, results from CFD analyses and wind tunnel tests are presented. Horizontal and vertical flights were considered, including accelerated flight. Particular attention was paid to the experimental analysis of the Coanda effect via a reduced scale 3D printed model. The results suggest that the Coanda effect is continuously present at the lower surface of the Anuloid and may be exploited for the control of the aircraft. Also, very complex 3D flows may develop around the aircraft.

• JSTS:Journal of Semiconductor Technology and Science
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• 제9권2호
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• pp.91-97
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• 2009

The performance of GaInP/GaAs tandem solar cells with AlInP growth temperatures of 680$^{\circ}C$ and 700 $^{\circ}C$ on n-type GaAs (100) substrate with 2$^{\circ}$ and 6$^{\circ}$ tilt angles has been investigated. The series resistance and open circuit voltage of the fabricated tandem solar cells are affected by the substrate tilt angles and the growth temperatures of the window layer when zinc is doped in the tunnel diode. With carbon doping as a p-type doping source in the tunnel diode and the effort of current matching between top and bottom cells, GaInP/GaAs tandem solar cell has been exhibited 25.58% efficiency.

• 대한기계학회논문집B
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• 제22권9호
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• pp.1229-1237
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• 1998

Experiments of shock-wave/turbulent boundary layer interaction were conducted by using a supersonic wind tunnel. Nominal Mach number was varied in the range of 1.6 to 3.0 by means of different nozzles. The objective of the present study is to investigate the effects of boundary layer suction on normal shock-wave oscillations caused by shock wave/boundary layer interaction in a straight duct. Two-dimensional slits were installed on the top and bottom walls of the duct to bleed turbulent boundary layer flows. The bleed flows were measured by an orifice. The ratio of the bleed mass flow to main mass flow was controlled below the range of 11 per cent. Time-mean and fluctuating wall pressures were measured, and Schlieren optical observations were made to investigate time-mean flow field. Time variations in the shock wave displacement were obtained by a high-speed camera system. The results show that boundary layer suction by slits considerably reduce shock-wave oscillations. For the design Mach number of 2.3, the maximum amplitude of the oscillating shock-wave reduces by about 75% compared with the case of no slit for boundary layer suction.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 추계학술대회 논문집(제1권)
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• pp.509-514
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• 2006

본 연구는 준설선을 이용하여 가덕수도를 횡단하며 준설공사를 하는 동안의 선박들의 안전한 통항방안을 제시하는 것을 목적으로 한다. 부산${\sim}$거제간 연결도로 건설공사 중 가덕수도의 해저로 횡단하는 침매터널을 건설하기 위해서는 준설작업이 필요하다. 이에 따라 불가피하게 준설선이 가덕수도 항로를 횡단하며 준설을 해야 한다. 이는 상대적으로 가덕수도를 통항하는 선박들의 잠재적인 위험상황으로 충돌 등의 해난사고가 발생할 가능성이 있다. 따라서 이에 대한 선박의 안전통항방안을 모색하고 대책을 제시하였다.

• Wind and Structures
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• 제36권4호
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• pp.263-275
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• 2023

As a new kind of construction facility for high rise buildings, the integral steel platform scaffold system (ISPS) consisting of the steel skeleton and suspended scaffold faces high wind during the construction procedure. The lattice structure type and existence of core tubes both make it difficult to estimate the wind load and calculate the wind-induced responses. In this study, an aeroelastic model with a geometry scale ratio of 1:25 based on the ISPS for Shanghai Tower, with the representative square profile, is manufactured and then tested in a wind tunnel. The first mode of the prototype ISPS is a torsional one with a frequency of only 0.68 Hz, and the model survives under extreme wind speed up to 50 m/s. The static wind load and wind vibration factors are derived based on the test result and supplementary finite element analysis, offering a reference for the following ISPS design. The spacer at the bottom of the suspended scaffold is suggested to be long enough to touch the core tube in the initial status to prevent the collision. Besides, aerodynamic wind loads and cross-wind loads are suggested to be included in the structural design of the ISPS.