• Journal of The Korean Astronomical Society
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• v.43 no.4
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• pp.105-113
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• 2010

We study the dynamical evolution of the M87 globular cluster (GC) system using the most advanced and realistic Fokker-Planck (FP) model.By comparing our FP models with both mass function (MF) and radial distribution (RD) of the observed GC system, we find the best-fit initial (at M87's age of 2-3 Gyr) MF and RD for three GC groups: all GCs, blue GCs, and red GCs. We estimate the initial total mass in GCs to be $1.8^{+0.3}_{-0.2}{\times}10^{10}M_{\bigodot}$, which is about 100 times larger than that of the Milky Way GC system. We also find that the fraction of the total mass currently in GCs is 34\%. When blue and red GCs are fitted separately, blue GCs initially have a larger total mass and a shallower radial distribution than red GCs. If one assumes that most of the significant major merger events of M87 have ended by the age of 2-3 Gyr, our finding that blue (metal-poor) GCs initially had a shallower radial distribution supports the major merger scenario for the origin of metallicity bimodality.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.2
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• pp.77-82
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• 2002

This Paper describes the dynamic load simulator for high-speed elevator system, which can emulate 3-mass system as well as equivalent 1-mass system. In order to implement the equivalent inertia of entire elevator system the conventional simulators have generally utilized the mechanical inertia(flywheel) with large radius, which makes the entire system large and heavy. In addition, the mechanical inertia should be replaced each time in order to est another elevator system. In this paper, the dynamic load simulation methods using electrical inertia are Presented so hat the volume and weight of simulator system are greatly reduced and the adjustment of inertia value can be achieved easily by software. Experimental results show the feasibility of this simulator system.

• Journal of the Korean institute of surface engineering
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• v.37 no.4
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• pp.220-225
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• 2004

A new ion beam extraction system is designed using a simple ion mass filter and a micro mass balance and a QMS based detecting system. A quadrupole Mass Filter is used for selective ion beam formation from inductively coupled high density plasma sources with appropriate electrostatic lens and final analyzing QMS. Also a quartz crystal microbalance is set between a QMF and a QMS to measure the etching and polymerization rate of the mass selected ion beam. An inductively coupled plasma was used as a ion/radical source which had an electron temperature of 4-8 eV and electron density of $4${\times}$10^{11}$＃/㎤. A computer interfaced system through 12bit AD-DA board can control the pass ion mass of the qmf by setting RF/DC voltage ratio applied to the quadrupoles so that time modulation of pass ion's mass is possible. So the direct measurements of ion - surface chemistry can be possible in a resolution of $1\AA$/sec based on the qcm's sensitivity. A full set of driving software and hardware setting is successfully carried out to get fundamental plasma information of the ICP source and analysed $Ar^{+}$ beam was detected at the $2^{nd}$ QMS.

• Journal of Institute of Control, Robotics and Systems
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• v.12 no.3
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• pp.269-276
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• 2006

Increasing requirements for the high quality of industrial robot performance made the vibration control issue very important because the vibration makes it difficult to achieve quick response of robot motion and may bring mechanical damage to the robot. This paper presents the vibration mechanism of an industrial robot which has flexible joints. The joint flexibility of the robot is modeled as a two-mass system and its dynamic characteristics are analysed. And some characteristics of the two-mass system, especially for the joint of industrial robots, such as disturbance, non-linearity and time-varying characteristics are studied. And finally, some considerations on controller design for the flexible joint of industrial robots are discussed.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.35.1-35.1
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• 2010

Unlike the initial mass function, the initial size distribution of globular cluster (GC) systems is not well known. We calculate the evolution of the mass function (MF), radial distribution (RD), and size distribution (SD) of the Galactic GC system. By comparing the results from this calculation and the present-day MF, RD, and SD of the Galactic GC system, we infer the initial SD of the GC system. We find that a Gaussian distribution of the half-mass radius and a Gaussian distribution of the half-mass to Jacobi radius ratio are the best-fit initial SDs of the Galactic GC system.

• Journal of Mechanical Science and Technology
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• v.17 no.4
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• pp.581-589
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• 2003

Film absorption involves simultaneous heat and mass transfer in the gas-liquid system. While the non-absorbable gas does not participate directly In the absorption process. its pretence does affect the overall heat and mass transfer. An experimental study was performed to investigate the heat and mass transfer characteristics of LiBr-H$_2$O solution flow ing over 6-row horizontal tubes with the water vapor absorption in the pretence of non-absorbable gases. The volumetric concentration of non-absorbable gas, air, was varied from 0.17 to 10.0%. The combined effects of the solution flow rate and its concentration on the heat and mass transfer coefficients were also examined. The presence of 2％ volumetric concentration of air resulted in a 25% reduction in the Nusselt number and 41% reduction in the Sherwood number Optimum film Reynolds number was found to exist at which the heat and mass transfer reach their maximum value independent of air contents. Reduced Nusselt and Sherwood numbers. defined as the ratio of Nusselt and Sherwood numbers at given non-absorbable gas content to that with pure water vapor, were correlated to account for the reduction in the heat and mass transfer due to non-absorbable gases in a falling film absorption process.

• Earthquakes and Structures
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• v.16 no.2
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• pp.149-163
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• 2019

By integrating an active tuned mass damper (ATMD) and an inerter, the ATMDI has been proposed to attenuate undesirable oscillations of structures under the ground acceleration. Employing the mode generalized system, the dynamic magnification factors (DMF) of the structure-ATMDI system are formulated. The criterion can then be defined as the minimization of maximum values of the DMF of the controlled structure for optimum searching. By resorting to the defined criterion and the particle swarm optimization (PSO), the effects of varying the crucial parameters on the performance of ATMDI have been scrutinized in order to probe into its superiority. Furthermore, the results of both ATMD and tuned mass dampers inerter (TMDI) are included into consideration for comparing. Results corroborate that the ATMDI outperforms both ATMD and TMDI in terms of the effectiveness and robustness. Especially, the ATMDI may greatly reduce the demand on both the mass ratio and inerter mass ratio, thus being capable of further miniaturizing both the ATMD and TMDI. Likewise the miniaturized ATMDI still keeps nearly the same stroke as the TMDI with a larger mass ratio. Hence, the ATMDI is deemed to be a high performance control device with the miniaturization and suitable for super-tall buildings.

• International Journal of High-Rise Buildings
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• v.8 no.2
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• pp.117-123
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• 2019

Tall buildings are prone to wind-induced vibrations due to their slenderness whereby peak structural accelerations may be higher than the recommended maximum value. The common countermeasure is the installation of a tuned mass damper (TMD) near the highest occupied floor. Due to the extremely large modal mass of tall buildings and because of the narrow to broad band type of wind excitation the TMD mass may become inacceptable large - in extreme cases up to 2000 metric tons. It is therefore a need to develop more efficient TMD concepts which provide the same damping to the building but with reduced mass. The adaptive TMD concept described in this paper represents a solution to this problem. Frequency and damping of the adaptive TMD are controlled in real-time by semi-active oil dampers according to the actual structural acceleration. The resulting enhanced TMD efficiency allows reducing its mass by up to 20% compared to the classical passive TMD. The adaptive TMD system is fully fail-safe thanks to a smart valve system of the semi-active oil dampers. In contrast to active TMD solutions the adaptive TMD is unconditionally stable and its power consumption on the order of 1 kW is negligible small as controllable oil dampers are semi-active devices. The adaptive TMD with reduced mass, stable behavior and lowest power consumption is therefore a preferable and cost saving damping tool for tall buildings.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.4
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• pp.101-107
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• 1996

This test was performed on the hydraulic automatic gauge control(AGC) system of adaptive mass flow method. Fundamental purpose of this study are performance evaluation of this AGC system under the actual rolling condition. It was concluded that the response of AGC system depends on the dynamic characteristics of a reel motor or roll position. The test results are as follows : 1) The control method of reel motor current is better than than of the roll position as AGC system. 2) The more steel strip thickness of delivery side is thick, the larger the gauge deviation is large, and the more it is thin, the larger the gauge deviation rate is large. 3) Because the gauge deviation is large at acceleration and deceleration speed than steady speed, so AGC system is better to adopt over 50m/min. By applying this AGC system, not only the accurary in strip thickness were improved but also productivity was improved dramatically.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.11
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• pp.1428-1436
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• 2000

The absorption of vapor involves simultaneous heat and mass transfer in the vapor/liquid system. In this paper, a numerical study for vapor absorption process into LIBr-H$_2$O solution film flowing over helical absorber has been carried out. Axisymmetric cylindrical coordinate system was adopted to model the helical tube and the transport equations were solved by the finite volume method. The effects of operating conditions, such as the cooling water temperature. the system pressure, the film Reynolds number and the solution inlet concentration have been investigated in view of the absorption mass flux and the total absorption mass flux and the total absorption rate. The results for the temperature and concentration profiles, as well as the local absorption mass flux at the helical absorber are presented. It is shown that solution inlet concentration affected other than operation conditions for a mass flux.