• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.11
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• pp.1672-1678
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• 1989

Major problems preventing the device-quality GaAs/Si heterostructure are the lattice mismatch of about 4% and difference in thermal expansion coefficient by a factor of 2.64 between Si and GaAs. Ge is a good candidate for the buffer layer because its lattice parameter and thermal expansion coefficient are almost the same as those of GaAs. As a first step toward developing heterostructure such as GaAs/Ge/Si entirely by a home-built PAE (plasma-assisted epitaxy), Ge films have been deposited on p-type Si (100)substrate by the plasma assisted evaporation of solid Ge source. The characteristics of these Ge/Si heterostructure were determined by X-ray diffraction, SEM and Auge electron spectroscope. PAE system has been successfully applied to quality-good Ge layer on Si substrate at relatively low temperature. Furthermore, this system can remove the native oxide(SiO2) on Si substrate with in-situ cleaning procedure. Ge layer grown on Si substrate by PAE at substrate temperature of 450\ulcorner in hydrogen partial pressure of 10mTorr was expected with a good buffer layer for GaAs/Ge/Si heterostructure.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.78.1-78.1
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• 2014

An ionization front (IF) surrounding an H II region is a sharp interface through which a cold neutral gas makes transition to a warm ionized phase by absorbing UV photons from central massive stars. We investigate the structure and instability of a plane-parallel D-type IF threaded by magnetic fields parallel to the front. We find that magnetic fields increase the maximum propagation speed of the IFs, while reducing the expansion factor, defined as the density ratio of neutral to ionized phases. IFs become unstable to distortional perturbations due to gas expansion across the fronts, exactly analogous to the Darrieus-Landau instability of ablation fronts in terrestrial flames. The growth rate of the IF instability is proportional linearly to the perturbation wavenumber as well as the upstream flow speed. The IF instability is stabilized by gas compressibility and becomes completely quenched when the front is D-critical. The instability is also stabilized by magnetic pressure when the perturbations propagate in the direction perpendicular to the fields. When the perturbations propagate in the direction parallel to the fields, on the other hand, it is magnetic tension that reduces the growth rate, completely suppressing the instability when ${\beta}$ < 1.5, with ${\beta}$ denoting the square of the ratio of the sound speed to the Alfven speed in the pre-IF region. When the front experiences an acceleration, the IF instability cooperates with the Rayleigh-Taylor instability to make the front more unstable. We discuss potential effects of IF instability on the evolution and dynamics of IFs in the interstellar medium.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.11a
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• pp.237-239
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• 2011

This study was performed to investigate the influence of curing temperature on the properties of light weight foamed concrete, manufactured on-site construction according to the various experimental factor such as temperature of material, curing temperature in air(5, 10, 20℃), curing time in air(5, 10, 15hour), and target density of hardened state(0.8, 1.2t/㎥). As a result, the influence of the curing temperature on various properties of foamed concrete is greater than curing time. When increasing temperature and time in air curing, progress of hydration is fast and compressive strength is increasing more and more. However, when considering the productivity, minimum curing time is required 15hours at 5℃, 10hours at 10℃, and 5hours at 20℃. If this condition is not required, there is some crack due to volume expansion on the surface of light weight foamed concrete.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1340-1347
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• 2002

Finite element simulations are being widely used to increase the efficiency and effectiveness of design of bulk metal forming processes. In such simulations, proper consideration of friction condition is crucial in obtaining reliable results. For this purpose, tip test based on backward extrusion was proposed recently. In this lest, a cylindrical billet is positioned in a shallow groove of a counter punch for centering purpose and formation of a radial tip is induced on the extruded end of the workpiece. In this study, the effect of centering groove on tip test was investigated. The quantitative ratio of the shear friction factors between the punch and die was numerically determined depending on the shape of centering groove. Also, surface expansion and pressure distribution along the punch and die were considered in order to better understand the reason that friction condition at the punch compared to the one of die was more severe.

• Journal of Biosystems Engineering
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• v.25 no.2
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• pp.107-114
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• 2000

Low temperature storage method is to increase the value of agricultural products by reducing quality loss and regulate consignment time by controlling respiration rates of agricultural products. Respiration rate of agricultural products depends on several factors such as temperature, moisture, gas composition and a microbe inside the storage room. Temperature is the most important factor among these, which affects respiration rate and causes low or high temperature damage. Fuzzy logic was used to control the temperature of a storage room ,which uses information of uncertain facts and mathematical model for room temperature control . Room temperature was controlled better by using fuzzy logic control method rather than on-off control method. Refrigerant flow rates and temperature deviations were measured for on-off system using TEV(temperature expansion valve) and for fuzzy system using EEV(Electrical Expansion Valve) . Temperature of the Storage room was lowered faster by using fuzzy system than on -off system. Temperature deviation was -0.6~+0.9$^{\circ}C$ for on-off system and $\pm$0.2$^{\circ}C$ for fuzzy system developed. Temperature deviation and variation of temperature deviation were used as inout parameters for fuzzy system. The most suitable input and output value were found by experiment. Cooling rate of the storage room decreased while temperature deviation increased for the sampling time of 20 sec.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.5
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• pp.381-389
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• 2014

This study is concerned with the estimation of vibration-field of a cylindrical structure by modal expansion method(MEM). MEM is a technique that identifies modal participation factors using some of vibration signals and natural modes of the structure: The selection of sensor locations has a big influence on predicted vibration results. Therefore, this paper deals with four optimal sensor placement( OSP) methods, EFI, EFI-DPR, EVP, AutoMAC, for the estimation of vibration field. It also finds optimal sensor locations of the cylindrical structure by each OSP method and then performs MEMs. Predicted vibration results compared with reference ones obtained by forced response analysis. The standard deviations of errors between reference and predicted results were also calculated. It is utilized to select the most suitable OSP method for estimation of vibration field of the cylindrical structure.

• Journal of Applied Reliability
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• v.9 no.4
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• pp.275-290
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• 2009

This paper considers accelerated thermal degradation tests which are performed for rubber seal materials used for undersea tunnels constructed by immersion method. Three types of rubber seals are tested; rubber expansion seal, omega seal, and shock absorber hose. Main ingredient of rubber expansion seal is EPDM(Ethylene Propylene Diene Monomer) and that of both omega seal and shock absorber hose is SBR(Styrene Butadiene Rubber). The accelerated stress is temperature and an Arrhenius model is introduced to describe the relationship between the lifetime and the stress. From the accelerated degradation tests, dominant failure mode of the rubber seals is found to be the loss of elongation. The lifetime distribution and the service life of the rubber seals at use condition are estimated from the test results. The acceleration factor for three types of rubber seals are also investigated.

• Journal of The Korea Institute of Healthcare Architecture
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• v.16 no.2
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• pp.17-28
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• 2010

The considerable increase of the elderly with dementia is expected annually and when we think about the family members' and the patients' suffering, it could be painful. Above all things, it imposes heavy economic burdens on the family members that have patients who suffer from diseases of age like dementia or paralysis that caring them at home and also, it is not desirable for those old people in point of physical or environmental circumstances for medical care. Thus, it is needed urgently that the expansion of specified facilities and improvement of services for these old people. Under this present condition, it is the special feature that the subject of research is people/facilities that offer services, not the elderly with dementia-the main user of those facilities. This proposal aims to make a study of expansion and improvement the old people's welfare facilities by using remodeled closed Small and Midium Hospitals which are the bad effect of economic growth. Also, it can save money with re-using abolished buildings which is property of the nation and protect environment too. In this study, We examine the present conditions of old people's welfare institution, and research a factor of remodeling for welfare facilities. Then we will verify remodeling-possibility which is concrete and working by using the product of this study.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.05b
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• pp.57-60
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• 2009

In ultra-high-strength concrete, autogenous shrinkage is larger than dry shrinkage due to the consume of a large amount of cement and cementitous material, and this is a factor deteriorating the quality of structures. Thus, we need a new technology for minimizing the shrinkage strain for ultra-high-strength concrete. So, this paper have prepared super-high-strength concrete with specified mixing design strength of over 150MPa and have evaluated a method of reducing autogenous shrinkage by utilizing expander and shrinkage-reducing agent. According to the results of this study, with regard to the change in length by autogenous shrinkage, an expansion effect was observed until the age of seven days. The expansion effect was higher when the contents of the expander material were higher. In addition, ultra-high-strength concrete showed a shrinkage rate that slowed down with time, and the effect of the addition of expander material on compressive strength was insignificant. That is shown that required more database to be accumulated through experimental research for the shrinkage strain of members.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.3
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• pp.225-235
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• 2010

There are many types of the geometric transitions such as dent, bulge, protrusion, expansion, etc, on the inner and outer surfaces of heat exchanger tubes, steam generator tubes, and condenser tubes of nuclear power plants. Such geometric transition causes a local residual stress in heat exchanger tubes and acts as a structural factor accelerating the evolution of defects, in particular stress corrosion cracks. In the conventional eddy current test methods, the bobbin coil profilometry can provide 2-dimensional geometric information on the variation of the average inner diameter along the tube length, but the 3-dimensional distribution and the quantitative size of a local geometric transition existing in the tube cannot be measured. In this paper, a new eddy current probe, developed for the 3-dimensional profile measurement, is introduced and its superior performance is compared with that from the conventional bobbin coil profilometry for the various types of geometric transition. Also, the accuracy of the probe for the quantitative profile measurement is verified by comparing the results with that from the laser profilometry. It is expected that the new eddy current probe and techniques can be effectively used for an optimization of the tube expansion process, and the management of tubes with geometric transitions in service.