• 한국결정성장학회지
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• 제6권3호
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• pp.301-308
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• 1996

Domain structure and properties of LiNbO3 single crystals grown by continuous method (Orr's method) were characterized. It was found that the growth striation of the grown crystals correspond with domain structure and the positive-negative domains were repeated with the perpendicular direction to the C axes. The formation of negative domains were related to the rapid crystal growth rate. The measured dielectric constant of the grown crystal was 140∼150 at 100 kHz at the room temperature and Curie point was 1153℃.

• 한국세라믹학회지
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• 제31권6호
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• pp.617-622
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• 1994

Single crystals of misfit layered (LaS)xVS2(x 1.18) were grown using LaCl3(or I2) as a mineralizer (or transport agent) for the single crystal X-ray diffraction analysis. Procession photographs of (LaS)xVS2(x 1.18) were analyzed as the stacking structure of two kinds of LaS-and VS2-subcell. The result shows that two sublattices have common periodicities along the a*-and c*-axes, respectively, but not along the b*-axis. Sublattice dimensions of LaS and VS2 layers along b-axis were 5.67$\AA$ and 3.42$\AA$, respectively. Their ratio was 1.657 which is very close to 5/3.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제55권12호
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• pp.617-622
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• 2006

It is necessary to measure precisely the magnetic characteristics of electrical steel sheets under rotating magnetic fields, to obtain an accurate numerical performance analysis of electric machines made of electrical steel sheets. In this paper, the two dimensional magnetic characteristics of an electrical steel sheet are measured and explained under rotating magnetic fields using a two-axes-excitation type single sheet tester (SST). Through experiments, the magnetic properties, under rotating magnetic fields, of a non-oriented and grain oriented electrical steel sheet were measured respectively. In addition, the iron losses due to not only the alternating magnetic fields, but also rotating magnetic fields were measured. These experimentally measured results can evidently be applied to the analysis of iron losses in electrical machines.

• 제어로봇시스템학회논문지
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• 제4권1호
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• pp.38-44
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• 1998

The modified maximum likelihood estimation method is used to estimate the nondimensional aerodynamic derivatives of a single turbo-prop aircraft at a specified flight condition for the best deduction of the dynamic characteristics. In wind axes the six degree of freedom equations are algebraically linearized so that the linear state equation contains aerodynamic derivatives in a state-space form and is used in the maximum likelihood method. The simulated data added with the measurement noise is used as a flight test data which is necessary to the estimation of nondimensional aerodynamic derivatives. It is obtained by implementing the 6-DOF nonlinear flight simulation. In the flight simulation, the effects of several control input types, control deflection amplitudes, and the turbulence intensities on the statistical convergence criteria are also examined and quantitative analysis of the results is discussed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.842-848
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• 2013

Developments of Solid-State Gyroscopy during last decades are impressive and were based on thin-walled shell resonators like HRG or CRG made from fused quartz or leuko-sapphire. However, a number of design choices for inertial-grade gyroscopes, which can be used for high-g applications and for mass- or middle-scale production, is still very limited. So, considerations of fundamental physical effects in solids that can be used for development of a miniature, completely solid-state, and lower-cost sensor look urgent. There is a variety of different types of bulk acoustic (elastic) waves (BAW) in anisotropic solids. Shear waves with different variants of their polarization have to be studied especially carefully, because shear sounds in glasses and crystals are sensitive to a turn of the solid as a whole, and, so, they can be used for development of gyroscopic sensors. For an isotropic medium (for a glass or a fine polycrystalline body), classic Lame's theorem (so-called, a general solution of Elasticity Theory or Green-Lame's representation) has been modified for enough general case: an elastic medium rotated about an arbitrary set of axes. Travelling, standing, and mixed shear waves propagating in an infinite isotopic medium (or between a pair of parallel reflecting surfaces) have been considered too. An analogy with classic Foucault's pendulum has been underlined for the effect of a turn of a polarizational plane (i.e., an integration effect for an input angular rate) due to a medium's turn about the axis of the wave propagation. These cases demonstrate a whole-angle regime of gyroscopic operation. Single-crystals are anisotropic media, and, therefore, to reflect influence of the crystal's rotation, classic Christoffel-Green's tensors have been modified. Cases of acoustic axes corresponding to equal velocities for a pair of the pure-transverse (shear) waves have of an evident applied interest. For such a special direction in a crystal, different polarizations of waves are possible, and the gyroscopic effect of "polarizational precession" can be observed like for a glass. Naturally, formation of a wave pattern in a massive elastic body is much more complex due to reflections from its boundaries. Some of these complexities can be eliminated. However, a non-homogeneity has a fundamental nature for any amorphous medium due to its thermodynamically-unstable micro-structure, having fluctuations of the rapidly-frozen liquid. For single-crystalline structures, blockness (walls of dislocations) plays a similar role. Physical nature and kinematic particularities of several typical "drifts" in polarizational BAW gyros (P-BAW) have been considered briefly too. They include irregular precessions ("polarizational beats") due to: non-homogeneity of mass density and elastic moduli, dissymmetry of intrinsic losses, and an angular mismatch between propagation and acoustic axes.

• Bulletin of the Korean Chemical Society
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• 제28권4호
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• pp.567-573
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• 2007

The crystal structure of ZnI2 molecule synthesized in zeolite A (LTA) has been studied by single-crystal X-ray diffraction techniques. A single crystal of |Zn6|[Si12Al12O48]-LTA, synthesized by the dynamic ion-exchange of |Na12|[Si12Al12O48]-LTA with aqueous 0.05 M Zn(NO3)2 and washed with deionized water, was placed in a stream of flowing 0.05 M KI in CH3OH at 294 K for four days. The resulting crystal structure of the product (|K6Zn3(KI)3(ZnI2)0.5|[Si12Al12O48]-LTA, a = 12.1690(10) A) was determined at 294 K by single-crystal X-ray diffraction in the space group Pm3m. It was refined with all measured reflections to the final error index R1 = 0.078 for 431 reflections which Fo > 4σ (Fo). At four crystallographically distinct positions, 3.5 Zn2+ and nine K+ ions per unit cell are found: three Zn2+ and five K+ ions lie on the 3-fold axes opposite 6-rings in the large cavity, two K+ ions are off the plane of the 8-rings, two K+ ions are recessed deeply off the plane of the 8-rings, and the remaining a half Zn2+ ion lie on the 3-fold axes opposite 6-rings in the sodalite cavity. A half Zn2+ ion and an I- ion per unit cell are found in the sodalite units, indicating the formation of a ZnI2 molecule in 50% of the sodalite cavities. Each ZnI2 (Zn-I = 3.35(5) A) is held in place by the coordination of its one Zn2+ ion to the zeolite framework oxygens and by the coordination of its two I- ions to K+ ions through 6-rings (I-K = 3.33(8) A). Three additional I- ions per unit cell are found opposite a 4-ring in the large cavity and form a K3I2+ and two K2ZnI3+ ionic clusters, respectively.

• International Journal of Aeronautical and Space Sciences
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• 제11권3호
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• pp.167-174
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• 2010

The design, dynamics, and control allocation of tri-rotor unmanned aerial vehicles (UAVs) are introduced in this paper. A trirotor UAV has three rotor axes that are equidistant from its center of gravity. Two designs of tri-rotor UAV are introduced in this paper. The single tri-rotor UAV has a servo-motor that is installed on one of the three rotors, which enables rapid control of its motion and its various attitude changes-unlike a quad-rotor UAV that depends only on the angular velocities of four rotors for control. The other design is called 'coaxial tri-rotor UAV,' which has two rotors installed on each rotor axis. Since the tri-rotor type of UAV has the yawing problem induced from an unpaired rotor's reaction torque, it is necessary to derive accurate dynamic and design control logic for both single and coaxial tri-rotors. For that reason, a control strategy is proposed for each type of tri-rotor, and nonlinear simulations of the altitude, Euler angle, and angular velocity responses are conducted by using a classical proportional-integral-derivative controller. Simulation results show that the proposed control strategies are appropriate for the control of single and coaxial tri-rotor UAVs.

• 한국정보통신학회논문지
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• 제19권12호
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• pp.2943-2948
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• 2015

경제성을 얻기 위해 단일 카메라를 이용하여 3차원 복원을 수행한 뒤 그 정보를 토대로 운전자에게 전방에 존재하는 장애물의 통과 여부를 알려줄 수 있는 운전 보조 장치에 관한 연구를 진행한다. 그 결과 depth 정보는 떨어지나 직진상의 장애물을 통과 할 수 있는 정보를 제공할 수 있다. 3차원 복원을 위해서는 내부파라미터를 측정하고, 특징점을 찾아 매칭하여 기본행렬을 계산하고 이를 토대로 삼각측량을 수행하여 얻는다. 실험을 통해 결과를 확인해 보면 depth 정보는 불완전하나, 장애물 통과 여부를 판단 할 수 있는 X, Y 축의 정보는 신뢰성을 가진다.

• Wind and Structures
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• 제21권6호
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• pp.677-691
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• 2015

In this study, the geometrical setup of a turbine blade is tracked. A research-scale rotating turbine blade system is setup with a single 3-axes accelerometer mounted on one of the blades. The turbine system is rotated by a controlled motor. The tilt and rolling angles of the rotating blade under operating conditions are determined from the response measurement of the single accelerometer. Data acquisition is achieved using a prototype wireless sensing system. First, the Rodrigues' rotation formula and an optimization algorithm are used to track the blade rolling angle and pitching angles of the turbine blade system. In addition, the blade flapwise natural frequency is identified by removing the rotation-related response induced by gravity and centrifuge force. To verify the result of calculations, a covariance-driven stochastic subspace identification method (SSI-COV) is applied to the vibration measurements of the blades to determine the system natural frequencies. It is thus proven that by using a single sensor and through a series of coordinate transformations and the Rodrigues' rotation formula, the geometrical setup of the blade can be tracked and the blade flapwise vibration frequency can be determined successfully.

• 한국세라믹학회지
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• 제35권10호
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• pp.1007-1013
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• 1998

The samples of Bi2Sr2Ca1-xNaxCu2O8+y with various carrier concentration were synthesized by substituting Na for Ca ion. The superconducting properties hall coefficients and X-ray powder diffraction were measur-ed the sampled. Single phase samples were obtained for 0$\leq$x<0.3 of Bi2Sr2Ca1-xNaxCu2O8+y In the single phase the critical temperature. {{{{ { T}_{c } }} and carrier concentration increase with the increase of Na concentration pass through a maximum and then decreases. In the range of x$\geq$0.7 to the Na doped samples however we observed the metal-semiconductor transition. The c-axis seemed to decrease and a and b-axes increase with increasing Na concentration in the single phase. Decreasing of c-axis while increasing x is due to the smaller size of {{{{ {Na}^{+1 } }} ions to the {{{{ { Ca}^{+2 } }} ions. In the range of x>0.3 however the trend becomes ambiguous due to the inclusion of the 10K phase and impurity phase.