• Restorative Dentistry and Endodontics
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• v.34 no.5
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• pp.424-429
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• 2009

This study aimed to assess the influence of different cross-sectional area on the cyclic fatigue fracture of Ni-Ti rotary files using a fatigue tester incorporating cyclical axial movement. Six brands of Ni-Ti rotary files (ISO 30 size with. 04 taper) of 10 each were tested: Alpha system (KOMET), HeroShaper (MicroMega), K3 (SybronEndo), Mtwo (VDW), NRT (Mani), and ProFile (Dentsply). A fatigue-tester (Denbotix) was designed to allow cyclic tension and compressive stress on the tip of the instrument. Each file was mounted on a torque controlled motor (Aseptico) using a 1:20 reduction contra-angle and was rotated at 300 rpm with a continuous, 6 mm axial oscillating motion inside an artificial steel canal. The canal had a $60^{\circ}$ angle and a 5 mm radius of curvature. Instrument fracture was visually detected and the time until fracture was recorded by a digital stop watch. The data were analyzed statistically. Fractographic analysis of all fractured surfaces was performed to determine the fracture modes using a scanning electron microscope. Cross-sectional area at 3 mm from the tip of 3 unused Ni-Ti instruments for each group was calculated using Image-Pro Plus (Imagej 1.34n, NIH). Results showed that NRT and ProFile had significantly longer time to fracture compared to the other groups (p < .05). The cross-sectional area was not significantly associated with fatigue resistance. Fractographycally, all fractured surfaces demonstrated a combination of ductile and brittle fracture. In conclusion, there was no significant relationship between fatigue resistance and the cross-sectional area of Ni-Ti instruments under experimental conditions.

• The Journal of Engineering Geology
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• v.6 no.1
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• pp.15-22
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• 1996

Frequency content of seismic waves observed in field seismic survey in Korea has almost not exceeded 4kHz(wave length 1m). The limited frequency content not only restricts the minimum size of objects which can be surveyed in seismic tomogrpahic application, but also makes a fundamental limit in the resolution of tomogram. This paper shows the resonable result obtained by confirmimg and resolving the problems which can be occured m measuring procedure for the small - sized section through field application. Seismic tomographic field survey was performed for a concrete construction for railroad bridge in Korea, and to this the tomographic measurements for the stone-build foundation construction for a bell house of church in Germany were compared.

• The Korean Journal of Rheology
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• v.8 no.1
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• pp.11-29
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• 1996

스크류 채널 내에 주기적을 배리어를 설치함으로써 단축 스크류 압출 공정에서의 혼합 성능이 높여질수 있음이 S.J. Kim과 T.H. Kwom에 의해 밝혀진 바있다. 그들은 이새 로운 스크류를 통한 혼합이 카오틱하는 점으로부터 이 새로운 스크류를 카오스 스크류라고 명명했다. 우리는 카오스 스크류가 장착된 단축 압출공정에서 역학계 이론과 혼합운동학을 연계하여 연구를 수행하였다. 포인카레 단면을 통한 연구로부터 우리는 배리어의 배열이 islan의 크기에 대단히 밀접하게 관련되어 있음을 발견하였다. 연속적인 쉘 변형은 카오틱 유동에서 유체 요소를 지수 함수 형태로 늘이는 늘임과 접힘으로 이루어진 카오틱 혼합 메 카니즘을보여준다. 유체요소의 국부 늘임은 원리상으로는 계산되어질수 있으나 수치 해석상 의 어려운 점이 있다. 정규 유동에서와 달리 카오틱 유동에서는 입자 추적이 Runge-Kutta 적분중의 시간간격에 대단히 민감하다. 그래서 실제 사용될수 있는 시간 간격에 의해 계산 된 국부 늘임율 및 혼합효율의 정확도가 보장되어지지 않는다. 이러한 점들을 고려하여 우 리는 새로운 혼합 척도로 $\sigma$z를 제안하는데 이값은 비교적 긴 유체선분이 채널방향을 따라 늘어나는 비에 관련된 값이다. 배리어 영역의 길이가 짧을수록 $\sigma$z는 큰값으로 나타나지만 포인카레 단면에 의한 연구에 따르면 배리어의 주기가 너무 짧다면 두 개의 거대한 island 가 존재하는 것으로 밝혀졌다. 그리고 이러한 사실은 유체요소의 늘임비가 크다는 것이 항 상 좋은 혼합성능을 뜻하는 것은 아니라는 점을 보여준다. 이러한 관점에서 볼 때 혼합 스 크류를 설계하는데 있어서는 포인카레 단면을 병행하여 ${\sigma}_z$의 값을 사용하는 것이 바람직할 것이다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.4
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• pp.1-10
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• 1992

Since the structural system of a prestressed concrete bridge erected by Incremental Launching Method is varying continuosly during construction, the main girder bears alternating stress resultants different from those under a service load condition. The magnitude of these stress resultants depends on span lengths, nose length and stiffness ratios between girder and nose. A parametric study is performed for various span lengths, nose lengths and stiffness ratios. In order to analyze structural systems varying at every launching step two programs are developed; a pre-processor which automatically produces a data file for each stage and a main-processor which can summarize the results of all stages. From the results, the relationships between optimum nose length and stiffness ratio are proposed for various span lengths.

• Computational Structural Engineering
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• v.2 no.3
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• pp.69-75
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• 1989

The primary purpose of using bracings is to improve the lateral rigidity of main structural system, i.e., columns and beams, by reinforciing them with much smaller members. In conventional design methods brackings are considered as tension-only members, since difficulties arise in the analysis when the P-.DELTA. effects and post-buckling behaviour of the bracing members are taken into account. This is particulary true fox X-bracings. Recently, however, both analytical and experimental studies have been conducted to investigate the more precise and real behaviour of bracing members, especially for the nonlinear and plastic behaviour under cyclic loads. In this study, an analytical model is proposed to investigate the nonlinear behavior of steel bracing members subjected to cyclic loads. Results of the analysis were compared with previous experimental results, and good agreements were obtained between these results.

• Journal of the Korean Wood Science and Technology
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• v.37 no.3
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• pp.231-238
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• 2009

Red pine (Pinus densiflora) has been used for structural wood members of Korean traditional residence (HANOK) and historic wooden structures. For these constructions, generally, natural drying has conducted for long time; however, unless drying is conducted sufficiently, it could cause several drying defects such as check or warping. Shrinkage changes of red pine species for small clear specimens and big-size specimens according to the conditions of moisture contents, were examined. For the estimation of volumetric shrinkage at a special moisture content, it was more precise to divide the range of moisture contents into two groups, green to air-dry and air-dry to oven-dry. The volumetric shrinkage had no difference with specimen sizes in sapwood, but decreased as specimen size increased in heartwood.

• Korean Journal of Optics and Photonics
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• v.19 no.1
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• pp.15-19
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• 2008

A fiber-optic interferometric voltage sensor with high sensitivity is investigated. The fiber-optic voltage sensor is composed of an In-Line Michaelson interferometer bonded on a PZT. The In-Line Michaelson interferometer is a hollow optical fiber spliced to a single-mode fiber at one end and cleaved at the other end. The phase shift of the sensor output signal was induced by the applied AC voltage. The relation between the amplitude of the applied voltage and the phase shift of the sensor output signal was approximately linear and the sensitivity was $0.065{\pi}$ radian/V.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.303.1-303.1
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• 2014

좋은 전기적 특성을 가지면서 소자의 크기를 줄이기에 용이한 Gate-all-around (GAA) twin Si nanowire field-effect transistors (TSNWFETs)의 연구가 많이 진행되고 있다. Switching 특성과 단채널 효과가 없는 TSNWFETs의 특성은 GAA 구조의 본질적인 특성이다. TSNWFETs는 기존의 single Si nanowire TSNWFETs와 bulk FET에 비하여 Drive current가 nanowire의 지름에 많은 영향을 받지 않는다. 그러나 TSNWFETs의 전체 on-current는 훨씬 작고 nanowire의 지름이 작아지면서 줄어들게 되면서 소자의 sensing speed와 sensing margin 특성의 악화를 가지고 온다. GAA TSNWFETs의 제작 및 전기적 실험에 대한 연구는 많이 진행되었으나, GAA TSNWFETs의 전기적 특성에 대한 이론적 연구는 매우 적다. 본 연구에서는 GAA TSNWFETs의 nanowire 크기에 따른 전기적 특성을 관찰하였다. GAA TSNWFETs와 bulk FET의 전기적 특성을 양자역학을 고려하여 3차원 TCAD 시뮬레이션을 툴을 이용하여 계산하였다. GAA TSNWFETs와 bulk FET의 전류-전압 특성 계산을 통해 on-current 크기, subthreshold swing, drain-induced barrier lowering (DIBL), gate-induced drain leakage를 보았다. 전류가 흐르는 경로와 전기적 특성의 물리적 의미에 대한 연구를 위해 TSNWFETs에서의 전류 밀도, conduction band edge, potential 특성을 분석하였다. 시뮬레이션 결과를 통해 Switching 특성, 단채널 효과에 대한 면역 특성, nanowire의 단면적에 따른 전류 흐름을 보았다. nanowire의 크기가 작아지면서 DIBL이 증가하고 문턱전압과 전체 on-current는 감소하면서 소자의 특성이 악화된다. 이러한 결과는 GAA TSNWFETs의 전기적 특성을 이해하고 좋은 소자 특성을 위한 구조를 연구하는데 많은 도움이 될 것이다.

• Journal of the Korea Concrete Institute
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• v.21 no.2
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• pp.169-178
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• 2009

An equation for calculating confining reinforcement amount of RC bridge columns, specified in the current bridge design codes, has been made to provide additional load-carrying strength for concentrically loaded columns. The additional load-carrying strength will be equal to or slightly greater than the resistant strength of a column against axial load, which is lost because the cover concrete spalls off. The equation considers concrete compressive strength, yield strength of transverse reinforcement, and the section area ratio as major variables. Among those variables, the section area ratio between the gross section and the core section, varying by cover thickness, is a variable which considers the strength in the compression-controlled region. Therefore, the cross section ratio does not have a large effect in the aspect of ductile behavior of the tension-controlled region, which is governed by bending moment rather than axial force. However, the equation of the design codes for calculating confining reinforcement amount does not directly consider ductile behavior, which is an important factor for the seismic behavior of bridge columns. Consequently, if the size of section is relatively small or if the section area ratio becomes excessively large due to the cover thickness increased for durability, too large an amount of confining reinforcement will be required possibly deteriorating the constructability and economy. Against this backdrop, in this study, comparison and analysis were performed to understand how the cover thickness influences the equation for calculating the amount of confining reinforcement. An equation for calculating the amount of confining reinforcement was also modified for reasonable seismic design and the safety. In addition, appropriateness of the modified equation was examined based on the results of various test results performed at home and abroad.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2008.03a
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• pp.51-68
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• 2008

When the train enters into a tunnel a high speed, pressure waves are generated inside the tunnel. The pressure waves at propagate in a form of compression wave toward the tunnel exit and a fraction of the compression waves that arrives at the exit of the tunnel are discharged to outside of the tunnel and the remainder is reflected into the tunnel as expansion waves. The compression waves emitted from the tunnel does not radiate in a specific direction but in all directions. If the amplitude of the compression wave is great, it causes noise and vibration, and it is called "Micro-Pressure Wave." "Micro-Pressure Wave" must be considered as a decision for the optimum tunnel cross-section as the amplitude of the compression wave depends on train speed, tunnel length, area of tunnel and train. Therefore, this paper introduces the case study of Micro-Pressure Wave characteristics for determination of tunnel cross section in Honam high speed railway, the pressure inside the tunnel and the micro-pressure waves at tunnel exit were measured at Hwashin 5 tunnel in Kyungbu HSR line. At the same time. a test of train operation model was performed and then the measurement results and test results were compared to verify that the various parameters used as input conditions for the numerical simulations, which were appropriate. Also a model test was performed, in order to analysis of the Micro-Pressure Wave Mitigation Performance by Type of Hood at Entrance Portal.