• Title/Summary/Keyword: angle dependence

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Study on Dynamic Fracture Path Prediction According to Load Point using Cast Iron FC200 (주철 FC200을 이용한 하중점에 따른 동적파괴경로 예측 연구)

  • Jik-Su Yu;Kyu-Chun Jo
    • Journal of the Korean Society of Industry Convergence
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    • v.27 no.4_2
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    • pp.973-980
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    • 2024
  • Dependence of dynamic fracture path on loading velocity was observed from experimental results based on the three point bending fracture in cast iron. In this study, 3D and 2D numerical simulations are used to evaluate singular stress fields near crack tip and fracture mechanics parameters. Moving finite element technique, 2D and 3D Delauney automatic mesh generation and contact-noncontact evaluation is introduced into the numerical method. Dynamic fracture thoughness is decreased with increase of impact loading velocity. Fracture mode-ratio corresponds to initial kink angle of fracture path. The numerical result shows that the maximum hoop stress criterion cannot be applied to dynamic fracture of cast iron.

A Study on the Thermal Boundary Layer Flow of a Micropolar Fluid in the Vicinity of a Wedge (미세극성 유체 유동장에 놓여진 쐐기형 물체주위의 열경계층에 관한 연구)

  • 김윤제
    • The Korean Journal of Rheology
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    • v.11 no.2
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    • pp.122-127
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    • 1999
  • The characteristics of thermal boundary layer flow of a micropolar fluid in the vicinity of a wedge has been studied with constant surface temperature. The similarity variables found by Falkner and Skan are employed to reduce the streamwise-dependence in the coupled nonlinear boundary layer equations. Numerical solutions are presented for the heat transfer characteristics with Pr=1 using the fourth-order Runge-Kutta method and their dependence on the material parameters is discussed. The distributions of dimensionless temperature and Nusselt number across the boundary layer are compared with the corresponding flow problems for a Newtonian fluid over wedges. Numerical results show that for a constant wedge angle with a given Prandtl number, Pr=1, the effect of increasing values of K results in an increasing thermal boundary thickness for a micropolar fluid, as compared with a Newtonian fluid. For the case of the constant material parameter K, however, the heat transfer rate for a micropolar fluid is lower than that of a Newtonian fluid.

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Direction Dependence of the Perception of the Support Rotation While Quiet Standing (정적서기 상태에서 지지면 회전 인지능력의 방향별 차이)

  • Jeon, H.J.;Heo, J.H.;Jeon, H.M.;Yun, J.S.;Kweon, Y.R.;Eom, G.M.
    • Journal of Biomedical Engineering Research
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    • v.38 no.2
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    • pp.57-61
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    • 2017
  • The purpose of this study was to investigate the effect of direction (pitch and roll) on the perception of support surface rotation while standing. Thirty young healthy subjects participated in this study. Support surface was rotated at an unexpected instant in a very slow speed (0.2 deg/s). The direction of support surface rotation was randomly chosen among pitch (forward and backward) and roll (right and left) directions. The experiment was performed with eyes open and closed. Perception performance was evaluated by the perception threshold, defined as the rotation angle of the surface at the instant when a subject recognized that the support surface was moving. Results showed that the perception threshold was smaller for roll directions than pitch directions irrespective of vision and gender (p < 0.01). This indicates that the perception of support surface rotation is more sensitive in roll direction than in pitch direction. Among three sensory functions related to postural perception, the effect of vestibular and visual functions on the direction difference of the perception should be little because of the very slow surface rotation and independence on visual conditions. Therefore, the direction dependence of perception would have been affected mainly by the somatosensory function.

Emission and Structural Properties of Titanium Oxide Nanoparticles-coated a-plane (11-20) GaN by Spin Coating Method

  • Kim, Ji-Hoon;Son, Ji-Su;Baik, Kwang-Hyeon;Park, Jung-Ho;Hwang, Sung-Min
    • Proceedings of the Korean Vacuum Society Conference
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    • 2011.02a
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    • pp.146-146
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    • 2011
  • The blue light emitting diode (LED) structure based on non-polar a-plane (11-20) GaN which was coated TiO2 nanoparticles using spin coating method was grown on r-plane (1-102) sapphire substrates to improve light extraction efficiency. We report on the emission and structural properties with temperature dependence of photoluminescence (PL) and x-ray rocking curves (XRC). From PL results at 13 K of undoped GaN samples, basal plane stacking fault (BSF) and near band edge (NBE) emission peak were observed at 3.434 eV and 3.484 eV, respectively. We also found the temperature-induced band-gap shrinkage, which was fitted well with empirical Varshini's equation. The PL intensity of TiO2 nanoparticles ?coated multiple quantum well (MQW) sample is decayed slower than that of no coating sample with increasing temperature. The anisotrophic strain and azimuth angle dependence in the films were shown from XRC results. The full width at half maximum (FWHM) along the GaN [11-20] and [1-100] directions were 564.9 arcsec and 490.8 arcsec, respectively. A small deviation of FWHM values at in-plane direction is attributed to uniform in-plane strain.

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Gate-Controlled Spin-Orbit Interaction Parameter in a GaSb Two-Dimensional Hole gas Structure

  • Park, Youn Ho;Koo, Hyun Cheol;Shin, Sang-Hoon;Song, Jin Dong;Kim, Hyung-Jun;Chang, Joonyeon;Han, Suk Hee;Choi, Heon-Jin
    • Proceedings of the Korean Vacuum Society Conference
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    • 2013.02a
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    • pp.382-383
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    • 2013
  • Gate-controlled spin-orbit interaction parameter is a key factor for developing spin-Field Effect Transistor (Spin-FET) in a quantum well structure because the strength of the spin-orbit interaction parameter decides the spin precession angle [1]. Many researches show the control of spin-orbit interaction parameter in n-type quantum channels, however, for the complementary logic device p-type quantum channel should be also necessary. We have calculated the spin-orbit interaction parameter and the effective mass using the Shubnikov-de Haas (SdH) oscillation measurement in a GaSb two-dimensional hole gas (2DHG) structure as shown in Fig 1. The inset illustrates the device geometry. The spin-orbit interaction parameter of 1.71×10111.71×1011 eVm and effective mass of 0.98 m0m0 are obtained at T=1.8 K, respectively. Fig. 2 shows the gate dependence of the spin-orbit interaction parameter and the hole concentration at 1.8 K, which indicates the spin-orbit interaction parameter increases with the carrier concentration in p-type channel. On the order hand, opposite gate dependence was found in n-type channel [1,2]. Therefore, the combined device of p- and n-type channel spin transistor would be a good candidate for the complimentary logic device.

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Dependence of Surface Morphology of Transparent Hydrophobic Anti-Reflective Coating (투명 발수 반사방지 코팅의 표면 형상 의존성)

  • Kim, Ki-Chul
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.18 no.10
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    • pp.771-776
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    • 2017
  • The cover glass of mobile displays and photovoltaic cells needs a functional coating, such as an anti-reflection and self-cleaning coating. Numerous studies have been conducted on the engineering application of biomimetic functional surfaces, such as moth eye and lotus leaf Anti-reflection coantings of silica nanoparticles could enhance the light transmittance. TiO2TiO2 photocatalyst coatings have been applied to self-cleaning functional films. In this study, transparent hydrophobic anti-reflective coatings consisting of thin layers of SiO2/TiO2SiO2/TiO2 nanoparticles were fabricated on a slide glass substrate by the sol-gel process and dip-coating process. The dependence of the surface morphology of the functional coatings was investigated by the atomic force microscopy (AFM), contact angle measurement, and UV-visible spectroscopy. It was found that the coating of TiO2TiO2 nanoparticles exhibited a high average transmittance comparable to that of the bare slide glass substrate in the visible light range. The bi-layered functional coating of 7 nm SiO2SiO2/7nm TiO2TiO2 nanoparticles exhibits a transparent hydrophobic surface with a contact angle of 110110 and an improvement of the average transmittance of 2.3% compared to the bare slide glass substrate in the visible light range.

The Study on the Fragment Ejection Velocity and Spray Angle from a High Explosive Cylindrical Warhead (실린더형 HE 탄두 폭발 시 파편의 속도 및 발사각 추정방법 연구)

  • Hwang, Changsu;Park, Younghyun;Park, Seikwon;Jung, Daehan;Lee, Moonsik;Kang, Sunbu;Kim, Deuksu
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.47 no.12
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    • pp.904-912
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    • 2019
  • We have studied the numerical analysis about the fragment ejection velocity and spray angle when the High Explosive warhead detonated at proximity distance at an aircraft. To study the physical quantities about the warhead components is very important to assessment the vulnerability of aircraft. Generally, the physical quantities about the components of a warhead such as the mass, length, diameter and charge to mass ratio are unknown. Therefore, it is required to estimate the physical quantities by using physical continuities of similar threats. The empirical formulas to understand the dependence among charge to mass ratio, length and diameter ratio were driven by using the physical parameters of similar threatening such as terrier, sparrow. As a result, we confirmed that the dead mass ratio was closed to 20% of warhead mass since the metal case of the proximity threat acts as a simple carrier. This implies that the effective length and diameter of High Explosive Compound is smaller than the length and diameter of warhead, and become a key to understand the large ejection gradient velocity and small spray angle of fragments within 6 degree.

Fundamentals of Tight fitted Contact Lens Movement (Tight Fit 콘택트렌즈 운동의 기초)

  • Kim, Dae Soo
    • Journal of Korean Ophthalmic Optics Society
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    • v.14 no.3
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    • pp.17-27
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    • 2009
  • Purpose: This review article was written to determine the effects of parameters characterizing a hard contact lens (RGP included), such as BCs, diameters, edge angles, on the time interval for tight fitted lens to return to the equilibrium when it was decentered from blinking. Methods: A mathematical formulation was established to relate or calculate the restoring forces and thickness of lacrimal layer beneath the cornea with the various lens parameters when the tight fitted lens was decentered from blinking. Based on this formulation the differential equations and their numerical solution program were set up to describe the time dependence of the lens on the position and to estimate the time for the lens's return to the equilibrium after blink. Results: It is found that the time interval for the tight fitted lens to return to the equilibrium decreases as either the BC decreases or the diameter increases because both the reduction in BC and increase in diameter result in the increase in the lacrimal layer thickness between the lens and cornea increase which yielded the lowering of the viscous friction in the lens motion. As the edge angle of tight fitted lens increases the time for recentering decreases due to the increase in restoring force without change in lacrimal thickness beneath the lens. In the case of flat fitted hard lens (RGP included), the lacrimal layer thickness under the lens increases as either BC or diameter increases which results in reduction in viscous friction so that the time for the lens's return to the equilibrium were to decrease. The edge angle of flat fitted lens does not affect the lens motion. Conclusions: The effect of BCs on the lens motion (time to approach the equilibrium) was concluded to be significant with both tight and flat fitted lens where its results are contrary with each other. The edge angle of lens only affects the motion in tight fitted lenses.

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The Initiation of Slip on Frictional Fractures (마찰 전단면의 전단거동과 에너지방출률)

  • Park, Chi-Hyun
    • Tunnel and Underground Space
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    • v.20 no.5
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    • pp.344-351
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    • 2010
  • Slip along a frictional fracture can be approached as initiation and propagation of a mode II crack along its own plane. Fracture mechanics theories predict that under pure mode II loading initiation will occur when the energy release rate of the fracture attains a critical value (GIICGIIC), which is generally taken as a material property. For the past few years the rock mechanics group at Purdue University has investigated experimentally the dependence of GIICGIIC on normal stress and on the frictional characteristics of a fracture. A number of experiments has been conducted first on acrylic, a material that, using photoelastic methods, allows visualization of the stress field ahead of the fracture tip; and later on gypsum, a rock model material with relatively low unconfined compression strength. The experimental investigation has been expanded to include other frictional materials with higher unconfined compression strength. Direct shear tests have been conducted on specimens made with cement paste. New observations together with previous experiments indicate that GIICGIIC can only be considered a material property when the peak friction angle of the discontinuity is similar to the residual friction angle; otherwise the critical energy release rate increases with normal stress.

Magnetic and Magneto-Optical Properties of Mn1xCrxPt3Mn1xCrxPt3 Ordered Alloy Films (Mn1xCrxPt3Mn1xCrxPt3 박막의 자기 및 자기광학 특성)

  • 박문기;조재경
    • Journal of the Korean Magnetics Society
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    • v.8 no.6
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    • pp.374-379
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    • 1998
  • Mn1xCrxPt3Mn1xCrxPt3 alloy films have been prepared by depositing (Mn, Cr)/Pt multilayers using a rf magnetron sputterer followed by heat treatment. Small and wide angle x-ray diffractometry, magnetic hysteresis loops and Kerr rotation angle spectra of the films have been measured and used to investigate structural, magnetic and magneto-optic properties of the films. The films had a crystal structure of ordered AuCu33 type and the strong preferred orientation of a (111)plane parallel to the film surface. The saturation magnetization of the films was decreased with Cr content reaching almost zero near x=0.58 and then increased for further increasement of Cr content up to x=0.77 over that stayed almost constant. This indicated that Cr atoms were antiferromagnetically coupled with Mn atoms. The magnetic easy axis of MnPt33(x=0) film was parallel to the film surface but those of the films with x0.58 increased as Cr content increased reaching about 4 kOe at x=1(CrPt33). The dependence of the Kerr rotation angle on the Cr content was similar to that of the saturation magnetization on the Cr content. The films with x=0.77 and x=1 showed the larger Kerr rotation angle at the wavelengths of near infrared compared to the magneto-optic recording medium, TbFeCo, currently being used.

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