• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.5
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• pp.615-622
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• 2000

Numerical simulation is performed with Denton's code to get pressure loss coefficients in wide range of reverse flow incidence(from -90 degree to +85 degree) for an axial compressor cascade. As a results, it is found that the pressure loss coefficient is increased with incidence and there exist critical incidence which corresponds to the maximum pressure loss coefficient. Pressure loss coefficient with bigger incidence than its critical value is decreased. The effect of increasing incidence in a cascade extremely reduce the mass flow rate by the large flow separation region. Consequently this effect reduce the portion of dynamic pressure in the total pressure loss and beyond the critical incidence the pressure loss coefficient decrease.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.47.1-47.1
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• 2015

The formation mechanism of supermassive black holes (SMBHs) at the center of galaxies remains an open fundamental question. Black holes (BHs) are believed to grow by accretion of gas or by merging with other BHs. Motivated by the observation of luminous quasar around redshift z ~ 7 with SMBH mass up to 109 solar mass, we follow the growth of the early assembly of SMBHs that trace the hierarchical evolution of dark matter halos derived from large cosmological simulations. The initial masses of BH seeds in the first halos were set up according to the BH mass - halo mass relation. We assume that mergers of host galaxies cause loss of angular momentum of gas and trigger episodes of gas accretion onto BHs for available durations and at the end of each episode of accretion, BHs merge immediately. We trace the evolution of BH masses for various scenarios for central gas properties in halos. We estimate the BH to halo mass ratio and BH mass function at each redshift.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.60.3-60.3
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• 2019

Binary systems of a white dwarf showing mass transfer activities are classified into cataclysmic variables and symbiotic stars. In the case of cataclysmic variables, the companion is usually a late type main sequence star filling its Roche lobe, where material is transferred through the inner Lagrangian point to form an accretion disk around the white dwarf. The disk becomes unstable and highly viscous when the surface density exceeds the critical density, leading to dwarf nova outbursts. In contrast, symbiotic stars are wide binary systems having a giant as the mass donor. Some fraction of giant stellar wind is accreted to the white dwarf giving rise to various symbiotic activities. In particular, half of symbiotics show Raman O VI at 6830 and 7088, which are important spectroscopic probe of mass transfer process. Monitoring observations using 1 m class telescopes will produce valuable information regarding the mass loss and mass transfer to white dwarf stars, shedding much light on the last stage of stellar evolution of low and intermediate mass stars.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.8 no.2
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• pp.186-195
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• 1998

The objective of this study was to determine if MWF(metalworking fluids) mass sampled on PVC filter lose during flowing airstream and desiccating and to present direction to correct the underestimated MWF mass. Flowing airstream caused MWF sampled on PVC filter to be breakthrough and lost. Loss of MWF on PVC filter increased in proportion to time of flowing airstream. Meanwhile, loss of MWF was observed during desiccating without flowing airstream. Vapor pressure of MWF is so low that it would not normally be thought to evaporate. However, MWF mist sampled on PVC filter has so great a surface area that loss by flowing airstream and evaporation can be appreciable. Loss between fresh and used MWF was also different. Those study results mean that NIOSH method(#0500 method) to take airborne MWF mist with PVC filter is not valid. Media to sample airborne MWF accurately still have not been introduced. It seems to be needed to estimate how much MWF on PVC filter may be lost during sampling. Regression model between sampling time including 1 day desiccating and total loss of MWF was "Total loss(%)=18.4%+0.06 sampling time(p=0.000, r2=49.6%)". This model help correct MWF lost when one measures airborne MWF using NIOSH # 0500 method.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.145-148
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• 2008

Korea Aeronautics Research Institute (KARI) is developing a turbo pump that has 1-stage impulse turbine and relatively high tip clearance for safety. The objective of this research is to investigate the effect of reaction on tip clearance loss in axial turbines. Both cascades were tested in a subsonic wind tunnel. In each cascade, total pressure was measured for tip clearance ranging from 1% to 20% of chord. In results, increasing tip clearance, total pressure loss in reaction turbines is continually increased but impulse turbines keep almost same level of mass averaged total pressure loss. When tip clearance becomes more than 10% of chord, mass-averaged total pressure loss in impulse turbines is less than in reaction. This means that when tip clearance is more than 10% of chord, impulse turbines have better efficiency than reaction turbines.

• The Journal of Korean Physical Therapy
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• v.15 no.4
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• pp.466-478
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• 2003

This study was to evaluate the body composition and bone mineral density according to aging in adult and investigated the relationship between various parameters such as body mass index(BMI), bone mineral density(BMD), bone mineral content(BMC), lean body mass(LBM), fat mass(FM) and the value obtained from dual energy X-ray absorptiometry(DEXA). The subjects were composed of healthy adult male and female who were $20^{\sim}73$ years old and they were divided three group according to age (A group : 20-39 yrs., B group : 40-59 yrs., C group : more than 60 yrs.). The conclusion derived from statistical analysis was as follows : 1. Bone mineral content and density were significantly affected by lean body mass(relatively, R=0.85 - 0.63). 2. There was significant difference among age groups in total bone mineral density. 3. There was significant difference among age groups in bone mineral content of male and female. 4. Lean body mass is diminished according to age, but there was not significant difference among age groups. 5. Fat mass of A group in male had the highest mass and followed by C group and B group. In female groups, fat mass of A group had the highest mass and followed by B group and C group. Abdominal fat mass is increased according to age. This result suggest that aging was closely relation with loss of muscle mass, bone mineral density and bone mineral content.

• Journal of Korea Water Resources Association
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• v.32 no.4
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• pp.417-426
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• 1999

A series of numerical experiments is performed to compare the characteristics of outflow hydrograph using linear and nonlinear Muskingum-Cunge methods for two cases: (a) sinusoidal inflow hydrographs and (b) rainfall inputs. The nonlinear method shows the steepening of the rising limb, coupled with a corresponding flattening of the receding limb. The linear method conserves mass exactly. In contrast, the nonlinear method is subject to a gain and a loss of mass. The loss of mass and the subsidence of peak outflow increases with a mild slope, a small baseflow $q_b$ and a large peak inflow to baseflow ratio $q_p/q_b$. A shock wave and associated numerical instability results in the increase of mass for a steep slope and a large $q_p/q_b$ ratio. While the linear method depends on the reference flow per unit-width, the nonlinear method depends on a baseflow and the $q_p/q_b$ ratio. It is found that, unlike for the sinusoidal inflow, the outflow for the rainfall inputs conserves mass fairly exactly in the nonlinear method.

• Journal of the korean academy of Pediatric Dentistry
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• v.29 no.3
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• pp.469-477
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• 2002

One of the major deficiencies of composite restorative resins is their insufficient resistance to wear. Of the multitude of factors that have been associated with wear, subsurface degradation within the restoration is considered to be one. The aim of this study was to evaluate the resistance to degradation of four commercial composite resins in an alkaline solution. The brands studied were Z100(3M), Clearfil AP-X(Kuraray), Tetric Ceram(Vivadent), Aelit flo(Bisco). Resistance to degradation was evaluated on the basis of the following parameters: (a) mass loss(%) - determined from pre-and post-exposure specimen weights: (b) Si loss(ppm) - obtained from ICP-AE analysis of solution exposed to specimens; and (c) degradation depth(${\mu}m$) - measured microscopically (SEM) from polished circular sections of exposed specimens. The results were as follows: 1. The sequence of the mass loss was in ascending order by AE, EL, TC, Z100. There was statistically significant difference of mass loss between AE, CL group and TC, Z100 group(p<0.05). 2. The sequence of the degree of degradation layer depth was in ascending order by AE, CL, TC, Z100. But there was no statistically significant difference of degree of degradation layer depth between AE and CL(p<0.05). 3. For the Si concentration, Z100 was the highest of all. 4. The correlation coefficient between mass loss and degradation depth was relatively high(r=0.71 p<0.05).

• Journal of the korean academy of Pediatric Dentistry
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• v.29 no.3
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• pp.430-438
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• 2002

The aim of this study was to evaluate the resistance to degradation of four commercial composite resins-Prodigy(Kerr, USA), Vitalescence(Ultradent, USA), Z 250(3M, USA), Filtek flow(3M, USA)- in an alkaline solution. Resistance to degradation was evaluated on the basis of following parameters: (a) mass loss(%), (b) Si loss(ppm), (c) degradation depth($\mu}m$). The results were as follows: 1. There was no significant difference between Prodigy and Vitalescence, also Z 250 and Filtek flow. But, there was significant difference between former group and latter group. 2. The sequence of the degree of degradation layer depth was in descending order by Z 250, Filtek flow, Prodigy, Vitalescence. There was significant difference among the materials. 3. The sequence of the Si loss was in descending order by Filtek flow, Z 250, Prodigy, Vitalescence. There was significant difference among the materials. 4. The correlation coefficient between mass loss and degradation layer depth(r=0.714, p<0.05), mass loss and Si loss(r=0.770, p<0.05), and degradation layer depth and Si loss(r=0.930, p<0.05) were relatively high. 5. When observed with SEM, destruction of bonding was observed between resin matrix and filler. 6. When observed with CLSM, degradation layer depth of composite resin surface was observed.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.2
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• pp.136-148
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• 1997

The present study has been carried out to develop a computational procedure for the analysis of the off-design performance in centrifugal compressors with vaneless diffusers by integrating empirical loss models and analytical equations. Losses in centrifugal compressors stem from a number of sources and their exact calculation is not yet possible. This study investigates several modeling schemes and shows that a fairly good prediction can be achieved by a proper selection of the most important flow parameters resulting form a meanline one-dimensional analysis. The performance maps for compressors are calculated and compared with measured performance maps. The off-design performance characteristics in terms of the pressure ratio vs. mass flow produced have generally correct forms. However, no universal means have been found to predict accurately the onset of surge. The prediction method developed through this study can serve as a tool to ensure good matching between parts and it can assist the understanding of the operational characteristics of general purpose centrifugal compressors.