• 보존과학회지
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• 제31권4호
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• pp.429-441
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• 2015

문화재 복원을 비롯한 회화용으로 많이 사용되는 녹색 안료 중 천연 무기안료인 석록과 뇌록의 물리적 특성 규명을 위하여 본 연구를 수행하였다. 석록은 Malachite가 주 구성광물이고, 뇌록은 Celadonite가 주 구성광물이다. 본 연구를 위하여 K사(社)의 A등급 석록, B등급 석록, 소성석록의 물리적 특성을 평가하였으며, 이와 비교하기 위하여 J사(社)의 송엽녹청, 소녹청을 평가하였다. 뇌록은 K사(社)의 뇌록을 평가하였다. 석록 및 송엽녹청의 소성 여부는 색도를 제외한 다른 물리적 특성에 큰 영향을 미치지 않는 것으로 판단되며, K사(社)의 석록과 소성석록과의 색차가 J사(社)의 송엽녹청과 소녹청의 색차보다 훨씬 높았다. K사(社)는 녹색도 $+a^*$가 J사(社)보다 가로로 넓게 분포하여 녹색의 다양한 색표현이 가능하다. 뇌록은 색도, 비중, 흡유량 등의 물리적 특성이 석록과는 많은 차이를 보였다. 뇌록의 색도는 $a^*$가 0에 가까이 분포하여 석록에 비하여 무채색에 더 가까웠고, 비중은 석록에 비해 작고, 흡유량은 2배 정도 컸다. 또한 뇌록과 암녹은 비록 구성 물질에 차이가 있어도 물리적 특성이 비슷하여 대체하여 사용 가능 할 것으로 보인다. 본 연구결과를 통하여 천연안료의 물리적 특성을 규명하여 품질기준을 확립하고, 문화재 보존, 복원의 선택적 사용에 대한 기초적인 자료로 활용되길 기대한다.

• 천문학회지
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• 제46권1호
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• pp.41-47
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• 2013

I present a simple scheme for the treatment of gravitational interactions on galactic scales. In anal- ogy with known mechanisms of quantum field theory, I assume ad hoc that gravitation is mediated by virtual exchange particles-gravitons-with very small but non-zero masses. The resulting den- sity and mass profiles are proportional to the mass of the gravitating body. The mass profile scales with the centripetal acceleration experienced by a test particle orbiting the central mass, but this comes at the cost of postulating a universal characteristic acceleration $a_0{\approx}4.3{\times}10^{-12}msec^{-2}$ (or $8{\pi}a_0{\approx}1.1{\times}10^{-10}msec^{-2}$). The scheme predicts the asymptotic flattening of galactic rotation curves, the Tully-Fisher/Faber-Jackson relations, the mass discrepancy-acceleration relation of galaxies, the surface brightness-acceleration relation of galaxies, the kinematics of galaxy clusters, and "Renzo's rule" correctly; additional (dark) mass components are not required. Given that it is based on various ad-hoc assumptions and given further limitations, the scheme I present is not yet a consistent theory of gravitation; rather, it is a "toy model" providing a convenient scaling law that simplifies the description of gravity on galactic scales.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.1641-1644
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• 2005

Magnetic actuation utilizes the mechanic torque that is the result of interaction of the current in a coil with an external magnetic field. A main obstacle is, however, that torques can only be produced perpendicular to the magnetic field. In addition, there is uncertainty in the Earth magnetic field models due to the complicated dynamic nature of the field. Also, the magnetic hardware and the spacecraft can interact, causing both to behave in undesirable ways. This actuation principle has been a topic of research since earliest satellites were launched. Earlier magnetic control has been applied for nutation damping for gravity gradient stabilized satellites, and for velocity decrease for satellites without appendages. The three axes of a micro-satellite can be stabilized by using an electromagnetic actuator which is rigidly mounted on the structure of the satellite. The actuator consists of three mutually-orthogonal air-cored coils on the skin of the satellite. The coils are excited so that the orbital frame magnetic field and body frame magnetic field coincides i.e. to make the Euler angles to zero. This can be done using a Neural Network controller trained by PD controller data and driven by the difference between the orbital and body frame magnetic fields.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제6권3호
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• pp.223-231
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• 2006

In high-speed fuzzy control systems applied to intelligent systems such as robot control, one of the most important problems is the improvement of the execution speed of the fuzzy inference. In particular, it is more important to have high-speed operations in the consequent part and the defuzzification stage. To improve the speedup of fuzzy controllers for intelligent systems, this paper presents an integer line mapping algorithm to convert [0, 1] real values of the fuzzy membership functions in the consequent part to a $400{\times}30$ grid of integer values. In addition, this paper presents a method of eliminating the unnecessary operations of the zero items in the defuzzification stage. With this representation, a center of gravity method can be implemented with only integer additions and one integer division. The proposed system is analyzed in the air conditioner control system for execution speed and COG, and applied to the truck backer-upper control system. The proposed system shows a significant increase in speed as compared with conventional methods with minimal error; simulations indicate a speedup of an order of magnitude. This system can be applied to real-time high-speed intelligent systems such as robot arm control.

• 한국소음진동공학회논문집
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• 제26권3호
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• pp.323-330
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• 2016

This paper describes real-time unbalance moment compensation method for line of sight(LOS) stabilization control systems. The factors of system inertia, frictions and unbalance moment affect the control accuracy of drive systems that are equipped to on the move(OTM) platforms requiring LOS stabilization function. In case of the unbalance moment among those factors is continuously changed as variation of relative angle between gravity vector and drive torque vector. Then, consideration of the effect in real-time is very complicate. Therefore, its effect should be designed to be minimized, however, designing it almost zero is impossible in real condition. In other words, it is hard to achieve target performance overcoming stability issue of highly unbalanced systems. To solve these problems, this paper proposes calculation method of unbalance moment by using measured sensor data for LOS stabilization control and its use for control compensation. Also, kinematical converting process and control structure for compensation are explained. The effectiveness of the proposed method as variation of unbalance moment is verified under simulation circumstance modeled by assuming LOS control system with 2-axis gimbal structure.

• 한국자동차공학회논문집
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• 제2권5호
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• pp.101-109
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• 1994

Recently, four-wheel steering systems have been developed and studied as one of the latest automotive technologies for improving the handling characteristics of a vehicle. In much of the proposed four-wheel steering systems, the side slip angle at the vehicle's center of gravity is maintained at zero. This approach allows the greater maneuverability at low speed by means of counter-phase rear steering and the improved stability at high speed through same-phase rear steering. In this paper, the effects of several four-wheel steering systems are studied and discussed on the responsiveness and stability of the vehicle by using the linear analysis. Especially, the effects of the cornering stiffnesses of both front and rear wheels are investigated on the yaw velocity gain and critical speed of the vehicle.

• 한국추진공학회지
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• 제11권3호
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• pp.65-72
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• 2007

화재는 인류가 우주 여행을 하거나 우주에서 체류하고자 할 경우, 특히 조심해서 신경을 써야 할 부분이다. 지구상에서와는 달리, 우주에서는 화재를 피하여 외부로 도망을 칠 수도 없고, 진화를 위해 소방서에 도움을 요청할 수도 없다. 따라서 최선책은 화재를 미연에 방지하는 것이 될 것이다. 그러나, 우주에서는 화재가 발생하였을 때, 그 화염의 행태가 지구상에서와는 다른 양상을 띄게 된다. 그 이유는, 지구상에 있는 모든 물질에 작용하는 중력이 우주에서는 없거나 작기 때문이다. 본 논문에서는 미소 중력하에서의 화염의 행태에 대하여 중요한 부분의 연구 결과를 소개하고, 이에 근거하여 유인 우주 탐사선과 우주 정거장 등에서 화염을 방지, 감지, 진화하는 연구에 대하여 미국 NASA의 FPDS 프로그램을 바탕으로 하여 소개하였다.

• Nuclear Engineering and Technology
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• 제26권4호
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• pp.562-569
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• 1994

이 연구에서는 피동형원자로의 과도현상을 분석하기 위한 KOTRAC 코드의 모델을 수정한 것이다. 이 코드에서 열수력학 모델로 도입하고 있는 mixture drift flux model은 피동형원자로와 같이 비상냉각수가 중력으로 주입되는 경우를 잘 모사할 수 있으나, 만일 가압기 밀림관 또는 수평관에서 상의 완전분리가 일어나게 될 때에는 증기상에서의 거의 영에 가까운 밀도로 인해 상당한 어려움이 존재하는 것이 밝혀졌다. 이 연구에서는 이러한 어려움을 극복하기 위해 일부 모델을 개선하였는데 가장 두드러진 것은 KOTRAC에서 사용하고 있는 flow distribution parameter를 Ishii 상관식으로 대체하여 코드를 수정하고 해석하였다. 이렇게 수정된 코드를 사용한 결과는 과도상태 해석코드인 RELAP5 /MOD3 계산결과와 비교적 잘 일치함을 볼 수 있었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.963-971
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• 2008

Unsaturated soil mechanics has been often used to find out a cause of failure (tensile failure) of retaining walls and hill slopes containing sandy soils. Checking shear strength is a popular method by considering suction stress developed form pore water menisci among the grains and saturated pockets of pore water under negative pressure. Linear Mohr-Coulomb failure criterion is generally adopted as a failure criterion. However, depending on relative density, stress history, and the magnitude of stress, the failure behavior of sand may not follow linear M-C frictional behavior. For stress in the large compressive ranges, say from tens to hundreds of kPa, the linear M-C criterion is an adequate representation for the shear strength behavior of sand. However, less than tens of kPa, the M-C criterion often can not be accurately represented. Depending on failure criterion, the uniaxial tensile strength is different over 100% relative error. For sand behavior under small compression regimes, therefore, such as under low or zero gravity, or under undergoing tensile failure in the crest area of hill slopes or behind retaining walls, it is important to consider the non-linear behavior.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
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• pp.34.1-34.1
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• 2009

After SNIa and WMAP observations during the last decade, the discovery of the accelerated expansion of the universe is a major challenge to particle physics and cosmology. There are currently three candidates for the dark energy which results in this accelerated expansion: $\cdot$ a non-zero cosmological constant, $\cdot$ a dynamical cosmological constant (quintessence scalar field), $\cdot$ modifications of Einstein's theory of gravity. The scalar field model like quintessence is a simple model with time-dependent w, which is generally larger than -w1. Because the different w lead to a different expansion history of the universe, the geometrical measurements of cosmic expansion through observations of SNIa, CMB and baryon acoustic oscillations (BAO) can give us tight constraints on w. One of the interesting ways to study the scalar field dark-energy models is to investigate the coupling between the dark energy and the other matter fields. In fact, a number of models which realize the interaction between dark energy and dark matter, or even visible matter, have been proposed so far. Observations of the effects of these interactions will offer an unique opportunity to detect a cosmological scalar field. In this talk, after briefly reviewing the main idea of the three possible candidates for dark energy and their cosmological phenomena, we discuss the interactinng dark-energy model, paying particular attention to the interacting mechanism between dark energy with a hot dark matter (neutrinos). In this so-called mass-varying neutrino (MVN) model, we calculate explicitly the cosmic microwave background (CMB) radiation and large-scale structure (LSS) within cosmological perturbation theory. The evolution of the mass of neutrinos is determined by the quintessence scalar field, which is responsible for the cosmic acceleration today.