• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.1175-1180
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• 2000

Recently, the crack of concrete induced by the heat of hydration of cement is a serious problem for more greater, special and higher strength of concrete structures. The increasing concrete's temperature is mainly caused by the heat of hydration of cement and so, to control the thermal stress of concrete structure is desirable to use low heater material of hydration. There are many methods to diminish the increasing of concrete temperature such as using of low heat cement, addition of fly-ash, application of pre-cooling, etc., and in this study, we evaluate the heating and mechanical properties of ultra low heat mass concrete using Low Heat Portland(KS Type IV) cement with 30% of limestone powder. The results of this study will be applied to side wall and bottom of No. 15 and 16 of underground LNG tank in Inchon.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05a
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• pp.356-361
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• 1997

To investigate parametric effect on CHF and to get CHF data, experimental study has been performed with vertical round tubes under the condition of low pressure and low flow (LPLF). Test sections are made of Inconel-625 tube and have the geometry of 8 and 10 mm in diameter, and 0.5 and 1.0 m in heated length. All experiments have been conducted at the pressure of under 9 bar, the mass flux of under 250 kg/$m^2$ and the inlet subcooling of 350 and 450 kJ/kg, for stable upward flow with water as a coolant. Flow regime analysis has been performed for obtained CHF data with Mishima's flow regime map, which reveals that most of the CHF occur in the annular-mist flow regime. General parametric trends of the collected CHF data are consistent with those of previous studies. However, for the pressure effect on CHF, two different are observed; For relatively high mass flux, CHF increases with pressure and far lower mass flux, CHF decrease with pressure. Using modern data regression tool, ACE algorithm, two new CHF correlations for LPLF condition are developed based on local condition and inlet condition, respectively. The developed CHF correlations show better prediction accuracy compared with existing CHF prediction methods.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.45.3-46
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• 2018

Although mass accretion from the disk to the central protostar is a key process of low mass star formation, the accretion mechanism is still poorly understood. To investigate "episodic accretion", which has been suggested as an accretion mechanism in low mass star formation, we have carried out near-infrared spectroscopic observations of three very low-luminosity objects (VeLLOs) and one background source, using InfraRed Camera onboard the AKARI space telescope. The ice absorption features of $H_2O$, $CO_2$, and CO were detected around the wavelengths of 3.0, 4.26, and $4.67{\mu}m$, respectively. In addition, we revealed the XCN ice feature, which is attributed to high energy UV photons produced by the episodic burst accretion. The comparisons of the ice abundances of our targets with those of other YSOs observed previously with AKARI IRC imply that the three VeLLOs had experienced burst accretions although they are now in a very quiescent phase.

• Journal of The Korean Astronomical Society
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• v.29 no.2
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• pp.107-117
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• 1996

We have studied the star forming activities and dust properties of Lynds 1251, a dark cloud located at relatively high galactic latitude. Eleven IRAS point sources identified toward Lynds 1251 are discussed. Estimate of stellar masses, and far-infrared lumnosities of the young stars associated with two prominent IRAS point sources imply that these are T-Tauri stars with masses smaller than $0.3 M_\bigodot$. The low dust temperature of 27 K and low ratio of FIR emission to hydrogen column density are probably due to the lack of internal heating sources. Presumably two low mass young stars do not have enough energy to heat up the dust and gas associated. The dust heating is dominated by the interstellar heating source, and the weaker interstellar radiation field can explain the exceptionally low dust temperatures found in Lynds 1251. The estimated dust mass of Lynds 1251 is just $\~1M_\bigodot$, or about 1/1000 of gas mass, which implies that there must be a substantial amount of colder dust. The infrared flux at $100{\mu}m$ is matching well with $^{13}CO$ peak temperature, while the $^{12}CO$ integrated intensity is matching with the boundary of dust emission. Overall, the dust properties of Lynds 1251 is similar to those of normal dark clouds even though it does have star forming activities.

• Journal of Korea Association of Health Promotion
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• v.2 no.2
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• pp.137-148
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• 2004

Objective : To identify the risk factors for postmenopausal osteoporosis in Korea Materials and methods : Bone mineral density (BMD) at the lumbar spine and femoral neck was measured by dual energy X-ray absorptiometry in 808 apparently normal postmenopausal Korean women. Questions about life style, demographic parameters, medical history and social habits etc. were asked on these women; 2ll women with normal bone mineral density, and 597 women with osteopenia or osteoporosis. Results 'Age of >50 years, low body mass index (BMI; <18.5 kg/m2), long duration of menopause(>10 years), and previous history of fracture were associated with increased prevalence of osteopenia or osteoporosis. Women without the outside activity also showed a higher frequency of low bone mass, Risk for osteopenia or osteoporosis was low in women with high BMI (>23 kg/m2) and women with job. The prevalence of low bone mass appeared to be independent of the following parameters: socioeconomic status, familial history, smoking, drinking, exercise, previous use of oral contraceptive, coffee or milk consumption, and degree of sunlight exposure. Conclusion 'Age, BMI, duration of menopause, previous history of fracture and degree of outside activity are the risk factors for postmenopausal osteoporosis in Korea.

• Journal of Yeungnam Medical Science
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• v.23 no.1
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• pp.10-18
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• 2006

Epithelial to mesenchymal transition (EMT) is an important etiologic factor for the development of peritoneal fibrosis in CAPD patients. Mesothelial cells are main source of trans-differentiated fibroblasts under stress from the bioincompatible peritoneal dialysate. In our study there was no difference in dialysate TGF-${\beta}$ and VEGF between the low and high GDP groups during an initial 12 months. However, after adjusting with D-CA125, the low GDPs group showed a significantly lower D-TGF-${\beta}$/D-CA125 and D-VEGF/CA125 during the initial 12 months. Among the adjusted peritoneal growth factors for CA125, VEGF/CA125 and TGF-b/CA125 were factors significantly associated with greater EMT in this study. Adjustment of the peritoneal growth factor for effluent CA125 (surrogate for mass of HPMCs) revealed significant association with EMT suggesting that the fibroblastoid transition from HPMCs could be affected by the amount of intraperitoneal growth factors (TGF-b, VEGF) per unit mass of HPMCs. There was significant improvement in both cell score and D-CA125 at the sixth and 12th months after switching from a high GDPs solution to a low GDPs solution. Use of icodextrin solution in patients who had average peritoneal transport showed not only better systemic effects such as decreased glucose absorption via dialysate but also preservation of the peritoneum, including less EMT and high mesothelial bulk mass. In conclusion, Therapy with low GDP solution including icodextrin may positively impact preservation of the peritoneal membrane integrity and prevention of peritoneal fibrosis with time on PD.

• Publications of The Korean Astronomical Society
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• v.33 no.2
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• pp.21-30
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• 2018

Formation processes of high-mass stars have been long-standing issues in astronomy and astrophysics. This is mainly because of major difficulties in observational studies such as a smaller number of high-mass young stellar objects (YSOs), larger distances, and more complex structures in young high-mass clusters compared with nearby low-mass isolated star-forming regions (SFRs), and extremely large opacity of interstellar dust except for centimeter to submillimeter wavelengths. High resolution and high sensitivity observations with Atacama Large Millimeter/Submillimeter Array (ALMA) at millimeter/submillimeter wavelengths will overcome these observational difficulties even for statistical studies with increasing number of high-mass YSO samples. This review will summarize recent progresses in high-mass star-formation studies with ALMA such as clumps and filaments in giant molecular cloud complexes and infrared dark clouds (IRDCs), protostellar disks and outflows in dense cores, chemistry, masers, and accretion bursts in high-mass SFRs.

• Publications of The Korean Astronomical Society
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• v.25 no.3
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• pp.65-69
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• 2010

Observations of large samples of galaxies from low to high redshifts are composing a picture of remarkable simplicity: (1) The star formation rate (SFR) of starforming galaxies scales almost linearly with mass, strongly decline with cosmic time, and exhibits very small scatter around the average relation. (2) Due to the high observed SFRs the mass of galaxies at high redshifts must increase very rapidly, and yet the mass function of star forming galaxies evolves only very slightly with redshift. (3) At all redshifts the fraction of quenched (passively evolving) galaxies increases with galactic stellar mass and with local overdensity, with the remarkable property that the relative efficiency of "mass quenching" is independent of environment, and that of "environment quenching" is independent of mass. In a recent paper by the zCOSMOS collaboration, Peng et al. (2010) demonstrate that these three empirical facts suffice to account for the observed evolution of the galaxy mass function and naturally generate the "double-Schechter" mass function for quenched galaxies.

• Journal of Welding and Joining
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• v.19 no.4
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• pp.406-412
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• 2001

This study is focussed on the numerical prediction of the thermal fatigue life of a ${\mu}BGA$(Micro Ball Grid Array) solder joint. Numerical method is used to perform three-dimensional finite element analysis for Sn-37mass%Pb. Sn-3.5mass%Ag solder alloys during the given thermal cycling. Strain values, along with the result of mechanical fatigue tests for solder alloys were then used to predict the solder joint fatigue life using the Coffin-Manson equation. In this study, a practical correlation for the prediction of the thermal fatigue life is suggested by using the dimensionless variable $\gamma$. As a result. it could be found that Sn-3.5mass%Ag has longer fatigue life than Sn-37mass%Pb in low cycle fatigue. In addition. the result with ${\gamm}ashow$a good agreement with the FEA results.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.267-270
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• 2005

We investigate the spectral energy distributions (SEDs) of low mass-loss rate O-rich asymptotic giant branch (AGB) stars using the infrared observational data including the Infrared Space Observatory (ISO) data. Comparing the results of detailed radiative transfer model calculations with observations, we find that the dust formation temperature is much lower than 1000 K for standard dust shell models. We find that the superwind model with a density-enhanced region can be a possible alternative dust shell model for LMOA stars.