• 천문학회보
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• 제40권1호
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• pp.41.1-41.1
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• 2015

Hierarchical galaxy formation models under LCDM cosmology predict that the most massive structures such as galaxy clusters (M > $10^{14}M_{\odot}$) appear late (z < 1) in the history of the universe through hierarchical clustering of small objects. Galaxy formation is also expected to be accelerated in overdense environments, with the star formation rate-density relation to be established at z ~ 2. In this talk, we present our search of massive structures of galaxies at 0.7 < z < 4, using the data from GOODS survey and our own imaging survey, Infrared Medium-deep Survey (IMS). From these studies, we find that there are excess of massive structures of galaxies at z > 2 in comparison to the Millennium simulation data. At 1 < z < 2, the number density of massive structures is consistent with the simulation data, but the star formation history is more or less identical between field and cluster. The star formation quenching process is dominated by internal process (stellar mass). The environmental effect becomes important only at z < 1, which contributes to create the well known star formation-density relation in the local universe. Our results suggest that galaxy formation models under LCDM cosmology may require further refinements to match the observation.

• 천문학회보
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• 제38권2호
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• pp.69.2-69.2
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• 2013

A galaxy cluster is an important laboratory to study the large scale structure in the Universe and the galaxy evolution. In order to identify candidate galaxy clusters at z~1, we have used deep and wide optical-NIR datasets based on IMS, UKIDSS DXS and CFHTLS wide covering ${\sim}20deg^2$ in the SA22 field. We measure the angular two-point correlation function of the candidate clusters and investigate the star formation activity of the member galaxies. Based on bias factor and halo mass function, candidate clusters have the average halo mass of > $10^{14}h^{-1}M_{\odot}$. At z~1, the star formation rate of cluster galaxies is similar to that of field galaxies, which indicates the environmental quenching is not so significant at z~1 as the local Universe.

• 열처리공학회지
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• 제7권4호
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• pp.318-327
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• 1994

According to conventional nitriding of tool steels, it was very difficult to produce a high surface hardness. This study has been conducted to investigate the influence of initial structures on the nitriding characteristics of tool steels in gas-nitrided for the improvement in surface hardness. The specimens (SACM645, STD61 steels) have been quenching and tempering at various temperature and then gas-nitrided for 30, 45 and 60hr at 500, 530 and $550^{\circ}C$ respectively in gasatmosphere of 30%$NH_3-70%N_2$ As hardness of initial structure was higher, the nitriding layer was deeper and hardness of the nitriding layer was higher. Deeper nitriding layers was due to higher diffusion rate by fine initial microstructure. Also the reason of high surface hardness was associated with formation of dispersed fine carbonitrides of nitrides.

• 한국해양공학회지
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• 제6권2호
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• pp.113-124
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• 1992

The offshore industry created a need for quality wet weld repairs. Wet welding is a fast method of repair providing sound, structural quality welds. It requires less support equipment than a similar underwater dry weld repair or the alternative mechanical connections. Compared to welds made in air, underwater wet welds are plagued by increased hardness due to rapid quenching by the surrounding water. In this paper is described the experimntal study of improving the cooling rates of wet welds of TMCP steel plate by shielding around weld arc surroundings. The principal results of this experimental investigation can be summarized as follows : By shielding around weld arc surrounding, the cooling rates resulting from wet welds on TMCP steel plate could be lower than that of nonshielded wet welds and the fesibility on high quality of mecanical properties of wet weld on TMCP steel plate was carried out with shielded weld arc surrounding.

• Journal of Advanced Marine Engineering and Technology
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• 제13권4호
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• pp.40-53
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• 1989

Boiling heat transfer phenomena is widely applied to BWR and electrical heating system because of its high heat transfer coefficient. In these systems, steady state heat transfer is dependent on nucleate boiling. When the heat generating rate is sharply increased or the cooling capacity of coolant is sharply decreased, sharp wall temperature rise is occurred under the critical heat flux(CHF) condition. This paper presents the simple wall temperature fluctuation model of transition mechanism in the repeating process of overheating and quenching, when coalescent bubble passes relatively slowly on the wall and simultaneously the transition from nucleate boiling to film boiling is carried at especially onset of the CHF state. The values calculated by the present model are resulted comparatively good with the measured.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.160-165
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• 2007

It is well recently recognized that quench is one of the serious problems for the integrity of superconducting magnets, which is mainly attribute to the rapid temperature rising in the magnet due to some extrinsic factors such as conductor motion, crack initiation etc. In order to apply acoustic emission(AE) technique effectively to monitor and diagnose superconducting magnets, it is essential to identify the sources of acoustic emission. In this paper, an acoustic emission technique has been used to monitor and diagnose quenching phenomenon in racetrack shaped superconducting magnets at cryogenic environment of 4.2K. For these purposes special attention was paid to detect AE signals associated with the quench of superconducting magnets. The characteristics of AE parameters have been analyzed by correlating with quench number, winding tension of superconducting coil and charge rate by transport current.

• 한국연소학회지
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• 제10권3호
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• pp.17-24
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• 2005

A sub-millimeter scale catalytic combustor with a simple plate-shaped combustion chamber was fabricated. A porous ceramics support coated with platinum catalyst was placed in the chamber. The combustor has a gallium arsenide window on the top that is transparent to infrared ray. The temperature distribution in the combustion chamber was measured using infrared thermal imager while hydrogen-air premixture is steadily supplied to the combustor. The area where the catalytic reaction took place broaden for higher flow rate and lower equivalence ratio made activated area in the combustion chamber broaden. The amount of coated platinum catalyst did not affect the reaction. Stop of reaction, which is similar to flame quenching of conventional combustion, was investigated. Large content of heat generation and broad activated area are essential criteria to prevent stop of reaction that has a bad effect on the combustor performance.

• 한국초전도ㆍ저온공학회논문지
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• 제1권2호
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• pp.8-14
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• 1999

In this study, acoustic emission(AE) technique has been applied to detecting quench which is one of the serious peoblems to assure the integrity of superconducting coil at cryogenic temperature. The characteristics of AE parameters have been analyzed by correlating with the number of quenches, whinding tension of superconducting coil and charge rate of transport current. The quench localization was also performed using AE signals and there was also good correlation between quench current and AE parameters such as AE energy and AE events. In this study, it was confirmed that AE signals were mainly due to the conductor motion which caused by premature quenching. It was also found that optimized winding tension at superconducting coil was needed to prevent quench caused by conductor motion.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.252-257
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• 1991

This paper proposed that the eddy-current measurement method can be used a means of in-process measuring the hardening depth in Laser surface treatment process. Also, this paper deal with the numerical analysis of magnetic flux distribution and experimental result of measurement. In Laser heat treatment process of steels, a thin layer of the substrate is rapidly heated to austenitizing temperature and subsequently cooled at a very fast rate due to the self-quenching by heat conduction into the bulk body, to produce a martensite structure which have low magnetic permeability. The eddy-current measurement method depends on the properties of material to be measured such as electric conductivity, magnetic permeability and geometry. In this paper, the hardening depth was measured by detecting relevant magnetic permeability changes caused by heat treatment of steels.

• 천문학회보
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• 제42권2호
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• pp.40.1-40.1
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• 2017

Massive early-type galaxies (ETG) have been spectroscopically confirmed up to z>3 which, together with their ages and abundances at z>1.5, implies that their progenitors must have converted gas into stars on short timescales. The termination of star formation in these galaxies can occur through several channels, but they remain largely conjectural, in part due to the current lack of direct measurements of the amount of residual gas in high redshift ETGs. Here I will present constraints on the star formation rate and dust/gas content of z=1.4-2.5 ETGs. These galaxies, close to their epoch of quenching, contained more than 2 orders of magnitude more dust than their local counterparts, which suggests the presence of substantial amounts of gas and a low star formation efficiency.