• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.1
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• pp.44-55
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• 1996

Emerald (3BeO{\cdot}Al$_{2}$O_{3}{\cdot}6SiO_2 : Cr^{3+}$) single crystals were grown by flux method of $Li_2O-MoO_3 - V_2O_5$ system. The composition of starting materials were 1, 3, 5 mole ratio of $MoO_3 - V_2O_5/$Li_2O$, 20 - 15% of emerald content to flux composition and 1% of $Cr_2O_3$ colordopant to emerald composition. After mixing those were melted at $1100^{\circ}C$ in Pt crucible of electric furnace. Single crystal growth was cooled down slowly rate of $3^{\circ}C$/hr from $1100^{\circ}C$ to $650^{\circ}C$, for the cooling period it was controlled and prevented the nucleation of microcrystallite from variation of each thermal fluctuation range. Specially it has been obtained plenty of large emerald single crystal when thermal fluctuation was treated for cooling period at $1050 ~ 950^{\circ}C$, in 3 mole ratio of $V_2O_5 - MoO_3/Li_2O$ flux. Emerald single crystal growing effect and $Cr_{+3}$ ion of substitutional solid solution effect for $Al_{+3}$ ion was good than mole ratio of 5. Emerald single crystals were c (0001) hexagonal rystal face of preferencial direction and m (1010) post side. Emerald was hexagonal columnar greenish transparent and 2.65 ~ 2.66 of specific gravity.

• Journal of the Korean Society of Clothing and Textiles
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• v.21 no.6
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• pp.977-987
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• 1997

The present study was designed to see what the local cooling of different body regions especially head and neck, hands and feet effect physiological responses in cold environment. Four male subjects wore garments covering whole body except face and rested for 20 min and then they rested for 40 min with uncovered head, neck, hands and feet, respectively in a cold environment(10$\pm$1$^{\circ}C$, 50$\pm$5%R.H.) 1. Rectal temperature increased when hands and feet were exposed to cold environment respectively, and when head and neck, hands and feet were exposed to cold environment together. 2. Exposed skin temperatures fell in cold environment. And hands temperature was lower than any other exposed skin temperatures. The hands temperature was significantly lower when head was exposed than when head was covered. And the feet temperature were significantly lower when hands were exposed than when hands were covered. 3. Mean skin temperature was the lowest when head and neck, hands and feet were exposed simultaneously, In conclusion, skin temperatures of extremities were decreased due to exposure to the cold environment. Especially upper extremities were lower than lower extremities by exposed parts of the body. It seemed that the extremities played the role of cold receptors but head and neck didn't. And there were large heat losses from the unprotected head and neck. In cold environment of 1$0^{\circ}C$ , thus, it is suggested for the purpose of thermoregulatory responses that head and neck would be covered and extremities would be exposed, especially upper extremities.

• Journal of the Korean Magnetics Society
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• v.13 no.1
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• pp.41-46
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• 2003

This study deals with the Benard flow of magnetic fluids in a rectangular cavity. The ratio of height to length of the cavity is 1 : 4 and the bottom of the cavity is assumed to be a heating face while the other sides are to be cooling faces. When magnetic field was equally impressed, considering the internal rotation of the elementary ferromagnetic particle, we found the following result from the numerical analysis of the GSMAC algorithm applied to the equations for the magnetic fluid. Benard flow was controled by the intensity and the direction of magnetic fields, and a critical point was appeared when the magnetic field near H=-7000 was applied.

• Journal of computational fluids engineering
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• v.6 no.1
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• pp.1-13
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• 2001

The natural convection heat transfer and solidification in a stratified pool are studied. The flow and heat transfer characteristics in a heat generating pool are compared between single-layered and double-layered pools. And local Nusselt number distributions on outer walls are obtained to consider thermal loads on a vessel wall. The cooling and solidification of Al₂O₃/Fe melt in a hemispherical vessel are simulated to study the mechanism of heat transfer and temperature distribution. A unstructured mesh is chosen for this study because of the non-orthogonality originated from the boundaries of double-layered pool. Interface between the layers is modeled to be fixed. With this assumption mass flux across the interface is neglected, but shear force and heat flux are considered by boundary conditions. The colocated cell-centered finite volume method is used with the Rhie-Chow interpolation to compute cell face velocity. To prevent non-physical solutions near walls in case body force is large the wall pressure is extrapolated by the way to include body force. The numerical solutions calculated by current method show that averaged downward heat flux of the double-layered pool increases compared to single-layered pool and maximum temperature occurs right below the interface of the layers.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.699-702
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• 2001

The increasing demand in industry to produce rectangular cans at the reduction by the rectangular backward extrusion process involves better understanding of this process. In 2-D die deflection and dimensional variation of the component during extrusion, punch retraction, component injection and cooling was conducted using a coupled thermal-mechanical approach for the forward extrusion of aluminum alloy and low-carbon steel in tools of steel. Backward extrusion FE simulation and experimental simulation by physical modeling using wax as a model material have been performed. These simulations gave good results concerning the prediction of th flow modes and the corresponding surface expansions of the material occuring at the contact surface between the can and the punch. There prediction are the limits of the can height, depending on the reduction, the punch geometry, the workpiece material and the friction factor, in order to avoid the risk of damage caused by sticking of the workpiece material to the punch face. The influence of these different parameter on the distribution of the surface expansion along the inner can wall and bottom is already determined. This paper deals with the influence of the geometry changes of the forming tool and the work material in the rectangular backward using the 3-D finite element method.

• Journal of the Korean Ceramic Society
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• v.26 no.1
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• pp.59-66
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• 1989

Single crystals of the superconducting Y-Ba-Cu oxide were grown by a flux technique. Stoichiometric mixture with excess BaO and CuOcontent was melted at 130$0^{\circ}C$, followed by fast cooling to 108$0^{\circ}C$ to prevent crystallizing of CuO. It was then reheated to 110$0^{\circ}C$ followed by being held at this temperature to control the number of nuclei, and cooled by 5$^{\circ}C$/hr to 80$0^{\circ}C$. This procedure was repeated with various compositions and crystals were obtained in cavity. Molten solution was seperated to two parts : the upper part of almost CuO and the rest of different composition. Appropriate composition of flux was 30mol% BaO and 70mol% CuO due to the seperation of molten solution. Single crystals have the habit of thin plate with good developed (001) crystal face, XRD, EDAX and single crystal X-ray investigations were carried out. The grown crystals have tetragonal structure with the lattice parameters a=b=3.84$\AA$, c=11.7$\AA$, and the space group P4/mmm. The crystal surface were observed by SEM.

• Nuclear Engineering and Technology
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• v.50 no.4
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• pp.542-552
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• 2018

Operators face challenges to plan alternative countermeasures when no procedure exists to address the current plant state. A model-based approach is desired to aid operators in acquiring plant resources and deriving response plans. Multilevel flow modeling (MFM) is a functional modeling methodology that can represent intentional knowledge about systems, which is essential in response planning. This article investigates the capabilities of MFM to plan alternatives. It is concluded that MFM has a knowledge capability to represent alternative means that are designed for given ends and a reasoning capability to identify alternative functions that can causally influence the goal achievement. The second capability can be applied to find originally unassociated means to achieve a goal. This is vital in a situation where all designed means have failed. A technique of procedure synthesis can be used to express identified alternatives as a series of operations. A case of station blackout occurring at the boiling water reactor is described. An MFM model of a boiling water reactor is built according to the analysis of goals and functions. The accident situations are defined by the model, and several alternative countermeasures in terms of operating procedures are generated to achieve the goal of core cooling.

• Journal of the Korea Institute of Building Construction
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• v.4 no.2
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• pp.143-149
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• 2004

The recycle of domestic waste concrete is, however, still in an early stage, and it has been only partially being used for the road fillers. As a counter-plan of activating recycled concrete, we have confirmed the hydration possibility of the waste concrete powder from the experiment on recycling the aggregate powder since 2000. Though that study, we have known that the strength is increasing when the baking time is longer, and baking temperature maintain in $700^{\circ}C$. Also, the quality is lowered because of the fine aggregate powder which has a bad influence on flowability & compression strength by adhesion of mortar on the aggregate face. Therefore, mortar and interfacial separation of aggregate are large in proper quality for concrete recycling is expected that affect. The purpose of this study is to investigate effective aggregate separation and to determine the most suitable production method controlling the duration of baking time for recycled cement from the compressive strength, X-ray diffraction and ingredient analysis test.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.764-769
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• 2001

Brake-induced vibrations of a vehicle such as brake judder are determined by the excitation of brake torque variations and by their transfer to the driver's contact points via suspension, body and steering system. The formation of brake torque variation is mainly determined by static and dynamic disk thickness variations. The vibration transfer from the excitation by brake torque variation to the perception by the driver depends on the kinematic and dynamic behaviour of the components in the transfer path. Optimization of the judder performance can be achieved either by minimizing the excitation or by reduction of the judder sensitivity of the vehicle. In this paper, the optimization process of a front rotor is suggested to reduce brake judder considering the cooling performance of the rotor, the judder sensitivity of the vehicle and durability of the rotor.

• Korean Journal of Materials Research
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• v.9 no.2
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• pp.199-204
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• 1999

As the engine design change to get high efficiency and performance of commercial diesel engine, surface wear of the cam follower becomes an important issues as applied load increasing at the contact face between cam follower and cam. Purpose of this study is the developing of the ceramic cam follower made of silicon nitride ceramic which is more wear resistant than the cast iron and sintered cam follower. Ceramic cam follower was made by direct brazing of thin ceramic disk to steel can follower body using active bracing alloy. Effect of joining condition on the interfacial phases and joining strength wer examined at bvarious joining temperatures, times, and cooling rates. Crowning resulted from the difference of thermal expansion coefficient after direct brazing without using any stress-relieving inter layer was measured. Interfacial phases are mainly titanium silicide and titanium nitride which are the products between active metal(Ti) in brazing alloy and silicon nitiride. Maximum joining strength of the ceramic metal joint, measured by DBS method, was 334MPa. Crowning(R) of the prototype ceramic cam follower was 1595mm. As machining for crowning is not necessary, production cost can be reduced.