• Journal of Astronomy and Space Sciences
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• 제15권1호
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• pp.83-90
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• 1998

Svechnikow & Kuznetsova (1990)의 Catalogue of Approximate Photometric and Absolute Elements of Eclipsing Variable로 부토 3780개의 식 쌍성들을 이용하여 식 쌍성의 질량-궤도 각 운동량과의 상관 관계를 조사하였다. 그 결과 쌍성이 진화하는 동안 궤도 각 운동량이 보전되지 못하며, 비록 일정한 값을 갖지는 않지만 점진적으로 분리형에서 준분리 형으로 그리고 접촉형으로 진화할수록 그 값이 감소하는 것으로 나타났다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.341-344
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• 2008

The complicated helical flow formed in the regenerative turbomachines is usually decomposed into a peripheral component and a circulatory component. On the basis of the momentum exchange theory, the circulatory flow plays a critical role of imparting angular momentum to the peripheral flow. Therefore, the accuracy of performance prediction is dominated by the circulatory flow modeling. Until now the circulatory flow has been accounted of a standstill flow normal to the peripheral flow. However, the circulatory path from the impeller exit to the re-entrance inlet is exposed to the adverse pressure gradient, so it would be more realistic to describe that the circulatory flow is formed on the skewed plane not perpendicular to the peripheral flow. Present study suggests new circulatory flow loss model including the effect of adverse pressure gradient and modifies the effective circulatory flow rate and circulatory pivot which were previously published.

• 천문학회지
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• 제33권3호
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• pp.173-175
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• 2000

The time-dependence of an $\alpha$-disk model under the influence of collisions of particles is examined. Collisions with viscosity tend to take away angular momentum. Both effects cause the disk to rotate more rapidly. The disk gradually contracts with increasing time.

• 제어로봇시스템학회논문지
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• 제16권11호
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• pp.1104-1109
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• 2010

This paper deals with the attitude control of an underactuated spacecraft that has fewer than three actuators. Even though such spacecrafts are known as uncontrollable, restricted missions are possible with controlling two-axis attitude angles. A variable speed control moment gyroscope is considered as an actuator. It is a kind of momentum exchange device and it shows highly nonlinear dynamical properties. Speed commands are generated by kinematic equations represented by Euler angles. A control law, that is designed to make a spacecraft follow the speed commands, is derived by the backstepping method. Angular speeds are estimated from the attitude measurements. Several estimation methods have been compared.

• Journal of Astronomy and Space Sciences
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• 제18권1호
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• pp.1-6
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• 2001

In this paper we investigate the properties of advection-dominated accretion flows (ADAFs) in case that outflows carry away infalling matter with its angular momentum and energy. Positive Bernoulli number in ADAFs allow a fraction of the gas to be expelled in a form of outflows. The ADAFs are also unstable to convection. We present self-similar solutions for advection-dominated accretion flows in the presence of outflows from the accretion flows(ADIOS). The axisymmetric flow is treated in variables integrated over polar sections and the effects of outflows on the accretion flow are parameterized for possible configurations compatible with the one dimensional self-similar ADAF solution. We explicitly derive self-similar solutions of ADAFs in the presence of outflows and show that the strong outflows in the accretion flows result in a flatter density profile, which is similar to that of the convection-dominated accretion flows(CDAFs) in which convection transports the angular momentum inward and the energy outward. There two different versions of the ADAF model should show similar behaviors in X-ray spectrum to some extent. Even though the two models may show similar behaviors, they should be distinguishable due to different physical properties. We suggest that for a central object of which mass is known these two different accretion flow should have different X-ray flux value due to deficient matter in the wind model.

• 한국전자파학회논문지
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• 제29권1호
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• pp.28-31
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• 2018

본 논문에서는 균일원형배열(UCA) 안테나를 이용한 궤도각운동량(OAM) 다중모드 전송시스템의 채널용량에 대하여지면 반사가 미치는 영향을 수치적으로 분석하였다. 지면 반사는 OAM 다중모드 간 간섭을 유발하고 시스템의 심각한 성능 저하를 가져온다. 전송거리가 증가함에 따라 OAM 다중모드 채널용량은 지면 반사의 영향으로 인하여 매우 작아진다. 지면 반사의 영향을 줄이기 위해서는 UCA의 높이를 높이고, 배열 소자의 지향성을 높이는 것이 필요하다.

• 한국운동역학회지
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• 제16권4호
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• pp.135-145
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• 2006

The aim of this study was to find out the differences of biomechanical factors from touching down the vaulting board to landing when techniques of 1/1Turn, stretched, and Tucked were performed on the old vaulting horse and on the new vaulting table. Three national representative men gymnasts were sampled for this study. Three dimension motion analyses by means of six Sony PD-150 video cameras with the velocity of 60 fps were used. As a result of analyzing the kinetic data from two kind of vaulting table, the following conclusions were made. 1. There was not significant differences of angular momentum between the old and the new vaulting table in all three techniques except the phase of stepping on the vaulting board and contacting the vaulting horse in the Tucked technique. IN the two phases above, the angular momentum in the new vaulting table was greater than that of the old vaulting horse. 2. There were few significant differences between the old and the new vaulting horses in the horizontal and vertical reaction force according to techniques when stepping was performed. However, it appeared tendency that the horizontal and vertical reaction force in the new vaulting table was a little greater than that of the old vaulting horse when the 1/1Turn, the Stretched and the Tucked were performed.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.431-438
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• 2009

A Large Eddy Simulation (LES) of the flow in an inducer is carried out under flow rate oscillations. The present study focuses on the dynamic response of the backflow and the unsteady pressure performance to the flow rate fluctuations under non-cavitation conditions. The amplitude of angular momentum fluctuation evaluated by LES is larger than that evaluated by RANS. However, the phase delay of backflow is nearly the same as RANS calculation. The pressure performance curve exhibits a closed curve caused by the inertia effect associated with the flow rate fluctuations. Compared with simplified one dimensional evaluation of the inertia component, the component obtained by LES is smaller. The negative slope of averaged performance curve becomes larger under unsteady conditions. From the conservations of angular momentum and energy, an expression useful for the evaluation of unsteady pressure rise was obtained. The examination of each term of this expression show that the apparent decrease of inertia effects is caused by the response delay of Euler's head and that the increase of negative slope is caused by the delay of inertial term associated with the delay of backflow response. These results are qualitatively confirmed by experiments.

• 천문학회보
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• 제36권2호
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• pp.57.1-57.1
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• 2011

Using high-resolution numerical simulations, we investigate the formation of gaseous substructures and mass inflow rates in barred spiral galaxies in the presence of both bar and spiral potentials. The gaseous medium is assumed to be infinitesimally-thin, isothermal, unmagnetized, and non-self-gravitating. To consider various galactic situations, we vary the pattern speed and strength of spiral arms as well as the black hole mass. We find that spiral arms with pattern speed smaller than that of the bar remove angular momentum from the gas outside corotation which transports to the bar region, making the dust lanes strong and live long. When the arm pattern speed is identical to that of the bar, on the other hand, the gas outside corotation gains angular momentum and thus moves outward, without affecting the bar region. Overall gaseous morphologies in simulations match well with observed IR images of barred spiral galaxies such as NGC 1097, when the arms and bar are in phase at the corotation radius. The presence of spiral arms increases the mass inflow rate as well, making it larger than $0.01M_{\odot}/yr$ when MBH is $4{\times}10^7M_{\odot}$, possibly explaining AGN activities in Seyfert galaxies.

• Bulletin of the Korean Chemical Society
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• 제27권11호
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• pp.1752-1756
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• 2006

This study explores and interprets in a new way the complex solvent and the temperature dependence of the NMR shifts for the N-$CH_2$ protons in tris(N,N-diethyldithiocarbamato) iron(III) in acetone, benzene, carbon disulfide, chloroform, dimethylformamide and pyridine. The NMR shifts are interpreted in terms of the Fermi contact interaction and the dipolar term from the multipole expansion of the interaction of the electron orbital angular momentum and the electron spin dipolar-nuclear spin angular momentum. This analysis yields a direct measure of the effect of the solvent system on the environment of the transition metal ion. The results are analysed in terms of the crystal field environment of the transition metal ion with contributions from (a) the dithiocarbamate ligand (b) the solvent molecules and (c) the interaction of the effective dipole moment of the polar solvent molecule with the transition metal ion complex.