• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.1
• /
• pp.47.1-47.1
• /
• 2011

We studied the evolution of the two mass components system with NFW initial density distribution by direct integration of the Fokker-Planck equations. The low mass component is regarded the dark matter particles while the high mass component is assumed to be conglomerates of baryonic matter in order to depict the 'stars'. While the true mass ratio between these two types of particles should be extremely large, our adopted mass ratio is about 1000 beyond which the dynamical evolution and density distribution tend to converge. Since the dynamical evolution is dominated by the dynamical friction, the high mass component slowly moves toward the central part, and eventually undergoes the core collapse. The system reaches the core-collapse at about $7.1{\times}10^{-3}$ $t_{fh}$ in NFW models, where $t_{fh}$is the dynamical friction time at half-mass radius. The distribution of the high mass component is well fitted by the Sersic profiles or modified Hubble profile when the mass segregation is established. From these results, the surface brightness of elliptical galaxies may be explained by the high mass component experiencing dynamical friction by the dark matter particles. In order for the mass segregation to be effective within Hubble time, the mass of the luminous component should be greater than $10^5M_{\bigodot}$.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
• /
• v.27 no.1
• /
• pp.87-97
• /
• 1997

The purpose of this study was to evaluate the method for quantitative assessment of bone mass from aluminum-equivalent value of hydroxyapatite by using digital imaging system consisted of Power Macintosh 7200/120, 15-inch color monitor, and GT-9000 scanner with transparency unit. After aluminum-equivalent image made from correlation between aluminum thickness and grey scale, the accuracy of conversion to mass from aluminum-equivalent value was evaluated. Measured bone mass was compared with converted bone mass from aluminum-equivalent value of hydroxyapatite block by correlation formula between aluminum-equivalent value of hydroxyapatite block and hydroxyapatite mass. The results of this study were as follow; 1. Correlation between aluminum thickness and grey level for obtaining aluminum-equivalent image was high positively associated(r²=0.99). Converted masses from aluminum-equivalent value were very similar to measured masses. There was, statistically, no significant difference(P<0.05) between them 2. Correlation between hydroxyapatite aluminum-equivalent and hydroxyapatite mass was shown to linear relation (r²=0.95). 3. Converted masses from aluminum-equivalent value of 3 dry mandible segments were similar to measured masses. The difference between the exposure directions was not significantly different(P<0.05).

• Structural Engineering and Mechanics
• /
• v.16 no.3
• /
• pp.341-360
• /
• 2003

The goal of this paper is to determine the eigenvalues of a uniform rectangular plate carrying any number of spring-damper-mass systems using an analytical-and-numerical-combined method (ANCM). To this end, a technique was presented to replace each "spring-damper-mass" system by a massless equivalent "spring-damper" system with the specified effective spring constant and effective damping coefficient. Then, the mode superposition approach was used to transform the partial differential equation of motion into the matrix equation, and the eigenvalues of the complete system were determined from the associated characteristic equation. To verify the reliability of the presented theory, all numerical results obtained from the ANCM were compared with those obtained from the conventional finite element method (FEM) and good agreement was achieved. Since the order of the property matrices for the equation of motion obtained from the ANCM is much lower than that obtained from the FEM, the CPU time required by the ANCM is much less than that by the FEM.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.10 no.3
• /
• pp.79-86
• /
• 2011

The dynamic instability and natural frequency of elastically restrained pipe conveying fluid with the attached mass and crack are investigated. The pipe system with a crack is modeled by using extended Hamilton's Principle with consideration of bending energy. The crack on the pipe system is represented by a local flexibility matrix and two undamaged beam segments are connected. In this paper, the influence of attached mass, its position and crack on the dynamic stability of a elastically restrained pipe system is presented. Also, the critical flow velocity for the flutter and divergence due to the variation in the position and stiffness of supported spring is studied. Finally, the critical flow velocities and stability maps of the pipe conveying fluid with the attached mass are obtained by the changing parameters.

• Journal of the korean Society of Automotive Engineers
• /
• v.5 no.3
• /
• pp.45-55
• /
• 1983

This paper discussed about Application Technique of Numerical Methods for large structure. The dynamic behaviours of a vehicle were investigated through finite element modelling. After dividing a vehicle body into three substructures, Basic Mass System was composed of 60 flexual modes which was obtained from the dynamic characteristics of each substructure using Modal Synthesis Method. Engine, transmission and rear axle, etc. were added to Basic Mass Model, consequently Full Mass System was constructed by 72 degree of freedoms. Full Mass System was analyzed over the frequency range 0.5-50.0 Hz under the loading conditions which were Stationary Gaussian Random Process. Results and discussions provided the guidelines to eliminate resonances among the parts and to improve the Ride Quality. The Absorbed Power was used as a standard to determine the Ride Quality. The RMS value of driver's vertical acceleration was obtained 0.423g from the basic model and 0.415g from the modified model.

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

• Journal of radiological science and technology
• /
• v.26 no.3
• /
• pp.13-17
• /
• 2003

By converting movable indirect mass chest X-ray devices for vehicles into digital systems and upgrading it to share information with the hospital's medical image information system, excellencies have been confirmed as a result of installing and running this type of system and are listed hereinafter. 1. Upgrading analog systems, such as indirect mass chest X-ray devices dependent on printed film, to digital systems allows them to be run and managed much more efficiently, contributing to the increase in the stability and the efficiency of the system. 2. Unlike existing images, communication based on DICOM standards allow images to be compatible with the hospital's outer and inner network PACS systems, extending the scope of the radiation departments information system. 3. Assuming chest-exclusive indirect mass chest X-rays, a linked development of CAD (Computer Aided Diagnosis, Detector) becomes possible. 4. By applying wireless Internet, Web-PACS for movable indirect mass chest X-ray devices for vehicles will become possible. Research in these fields must continue and if the superior image quality and convenience of digital systems are confirmed, I believe that the conversion of systems still dependent on analog images to modernized digital systems is a must.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.21 no.8
• /
• pp.433-438
• /
• 2009

Experimental results for performance characteristics of small $NH_3$ absorption chiller/ heater are presented. The apparatus consists of 7RT water-cooled absorption system, solution pump, boiler, cooling tower and peripheral devices. The effect of experimental parameters, such as refrigerant mass flow rate, solution mass flow rate and cooling water temperature have been investigated in view of the system performance. The capacity of each heat exchanger increased as refrigerant mass flow rate increased in cooling mode. Also, a cooling capacity increased as a strong solution mass flow rate increased. The cooling and heating COP show 0.5, 1.5 regardless of refrigerant mass flow rate, respectively. The results focus on the evaluation for performance characteristics of system with respect to variation of refrigerant mass flow rate under standard design conditions.

• Tunnel and Underground Space
• /
• v.4 no.3
• /
• pp.215-227
• /
• 1994

Rock Mass classifications have been developed in many European countries. The most widely used classification methods are the Rock Mass Rating (RMR) system proposed by Bieniawski(1973) and the Q-system developed By Barton et al. (1974). These methods are also adopted at many mountain tunnels and subway sites in our country. Here, a geomechanical classification for slopeds in rock, the "Slope Mass Rating"(SMR) is presented for the preliminary assessment of slope stabiliyt. This method can be applied to excavation and support design in the front part of tunnel and cutting area as a guide line and recommendation on support methods which allow a systemmetic use of geomechanical classification for rock slopes.

• Korean System Dynamics Review
• /
• v.13 no.4
• /
• pp.33-55
• /
• 2012

The research is to identify important diffusion factors and their effects on green car diffusion process using system dynamics perspectives and a causal-loop analysis. Through a deep review on previous research, we have found the important factors of green car diffusion process. Price, driving range, network effect, recharge system, fuel cost had important facilitation on consumer attraction and green car diffusion. Based on the review, we have constructed a causal loop diagram explaining hybrid car diffusion process. We have found 3 important reinforcing loops in the causal loop diagram. Loop for learning & economies of scale(supply side), loop for network effect(consumer side), and loop for battery development(technology side) had most significant roles in the whole diffusion process. Through a deliberate analysis on the 3 causal loops, we have found meaningful results. First, there seems to exist a critical mass in the diffusion. Second, of the 3 loops, the battery technology had most significant role. Third, not consumer installed base but sales must be a standard to decide whether the critical mass is achieved or not. Based on these findings, several meaningful implications are suggested for the government and corporations related to the green car industries.