• Journal of Applied Reliability
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• v.12 no.4
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• pp.275-285
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• 2012

This paper presents a changes of luminescence property for converted white LEDs with the commercially available silicate phosphor. If silicate phosphor's quantity increase step by step. luminescence property will be changing. we analyze luminescence property for these change and carry out the high temperature aging test for 7,000 hours, the high temperature and humidity aging test for 7,000 hours for reliability. LED degradation not only results in reduced light output but also in color changes. so we monitor correlated color temperature (CCT), chromaticity coordinates(x, y) and spectrum intensity. Those results suggest that humidity factor more bad effect in color changes than temperature factor and Lighting quality is related with quantity of phosphor.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.59-62
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• 2001

Flow induced vibration in steam generators has caused dynamic interactions between tubes and contacting materials resulting in fretting wear . Series of experiments have been performed to examine the wear properties of Inconel 690 steam generator tubes in various environmental conditions. For the present study, the test rig was designed to examine the fretting wear and rolling wear properties in high temperature(room temperature - 290。C) water. The test was performed at constant applied load and sliding distance to investigate the effect of test temperature on wear properties of the steam generator tube materials. To investigate the wear mechanism of material, the worn was observed using scanning electron microscopy. The weight loss increase at higher test temperature was caused by the decrease of water viscosity and the mechanical property change of tube material. The mechanical property changes of steam generator tube material, such as decrease of hardness or yield stress in the high temperature tests. From the SEM observation of worn surfaces, the severe wear scars were observed in specimens tested at the higher temperature.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.93-98
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• 1994

The property of concrete at different places in mass concrete is affected by the age under the same curing temperature. For more accurate analysis of thermal stress in mass cocnrete, it is necessary to obtain the property of concrete with age and curing temperature. In this study, the effects of curing temperature and age (Maturity) on the development of the property of concrete were investigated by using concrete specimens made with type I cement. The curing temperatures are 23$^{\circ}C$, 5$0^{\circ}C$, and 8$0^{\circ}C$, respectively. As the maturity increases, the strength of concrete was increased. The results obtained experimentlly was compapred with the previous models, and good agreements was obtained.

• Korean Journal of Materials Research
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• v.25 no.12
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• pp.678-682
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• 2015

The electrical property of polymer matrix composites with added carbon powder is studied based on the temperature dependency of the conduction mechanism. The temperature coefficient of the resistance of the polymer matrix composites below the percolation threshold (x) changed from negative to positive at 0.20 < x < 0.21; this trend decreased with increasing of the percolation threshold. The temperature dependence of the electrical property(resistivity) of the polymer matrix composites below the percolation threshold can be explained by using a tunneling conduction model that incorporates the effect of the thermal expansion of the polymer matrix composites into the tunneling gap. The temperature coefficient of the resistance of the polymer matrix composites above the percolation threshold has a positive value; its absolute value increased with increasing volume fraction of carbon powder. By assuming that the electrical conduction through the percolating paths is a thermally activated process and by incorporating the effect of thermal expansion into the volume fraction of the carbon power, the temperature dependency of the resistivity above the percolation threshold can be well explained without violating the universal law of conductivity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.11
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• pp.777-783
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• 2012

The hardness and strength test was performed to make the manufacturing process of SA213 P92 boiler pipe steel. And the microstructure change was studied to find out the cause of room temperature property of P92 steel, ie, low hardness and strength property. The room temperature property of P92 steel depends on the improper normalizing and cooling rate. Especially, Ferrite was formed and the steel had low hardness when the temperature was decreased slowly under the cooling rate $1^{\circ}C$/min after normalizing at the temperature around $A_{c1}$ to $A_{c3}$. The critical heat treatment temperature and cooling rate was over $900^{\circ}C$ and over $10^{\circ}C$/min to satisfy the minimum yield and tensile stress which was laid down by ASME Code.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.22-24
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• 2002

This paper introduces the real-time soil thermal property analyzer and temperature measuring system which is combined with radio telecommunication technique. To measure the thermal parameters in real-time, the radio telecommunication technique are used the personal communication service (PCS) which is in the world-wide serviced commercially firstly by CDMA. The thermal property analyzer has an ability of measuring thermal resistivity, thermal diffusivity and thermal stability. To estimate the soil thermal properties, the curve fitting algorithm by means of the least square method are used. TCP/IP protocol and MTM are used to install the real-time soil thermal property and temperature measurement system at multiple locations along routes of the underground power cables and to reduce the cost of telecommunication.

• Bulletin of the Korean Chemical Society
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• v.20 no.12
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• pp.1457-1463
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• 1999

Structure and their redox property of the vanadium oxides prepared by decomposing NH₄VO₃ at various temperatures were studied by XRD, SEM, XPS, and temperature programmed reduction/temperature programmed oxidation (TPR/TPO) experiment. All TPR profiles have two sharp peaks in the temperature range 650-750℃, and the area ratio of the two sharp peaks changed from sample to sample. There were three redox steps in TPR/TPO profiles. The oxidation proceeded in the reverse order of the reduction process, and both the reactions proceeded via quite a stable intermediates. The changes of the morphological factor $(I_{(101)}/I_{(010)})$, the ratio of $O_{1S}$ peak area (O$_{1S}$( α)/O$_{1S}$( β)) in the XPS results, and the ratio of hydrogen consumption in TPR profiles with various vanadium oxides showed the distinct relationship between the structural property and their redox property of vanadium oxides. The change of the specific yield of phthalic anhydride with various vanadium oxides showed a very similar trend to those of the peak area ratio in TPR profiles, which meant that the first reduction step related to the partial oxidation of o-xylene on the vanadium oxide catalyst.

• Korean Journal of Acupuncture
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• v.19 no.2
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• pp.35-39
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• 2002

Objective : The purpose of this study was to investigate the Effect of Acupuncture Stimulation of Sohae(H3) and Sobu(H8) Acupoint on Skin Temperature of Sochung Acupint(H9, the end acupoint of Heart Meridian). Sohae and Sobu acupoint has a property of water and fire in the Five agents on Heart Meridian. Methods : Subjects were four healthy oriental medical students volunteers(male, mean age-28). One group(two subjects) received acupuncture on Sohae acupoint(H3) and the other group(two subjects) on Sobu acupoint(H8) while resting. Skin temperature was measured on Sochung acupoint(H9) before, during, and after acupunture stimulation. Each test took 15minutes. The initial 5minutes were definded as BAS(Before Acupuncture Stimulation) period, the following 5minutes as DAS(During Acupuncture Stimulation) period, the last 5minutes as AAS(After Acupuncture Stimulation) period. This test was performed twice in order to increase the statistical authenticity. Results : Our result indicates that acupuncrue stimulation of Sohae acupoint(H3) decreased and Sobu acupoint(H8) increased skin temperature on Sochung acupoint(H9) in the DAS period. The changes remained throughout the AAS period. Our conculusion are that stimulaton of the Water and Fire property-acupoint(H3, H8) on Heart changes the skin temperature on Sochung acupoint on the same Heart Meridian. However this study has no authenticity because it had no regard for many factors effecting on the result and the result of the study was the very reverse of our expectation.

• Korean Journal of Materials Research
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• v.14 no.12
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• pp.863-869
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• 2004

The purpose of this research is to investigate the mechanical property and ductile-brittle transition temperature of Ti-Nb-P added extra low carbon interstitial free steel having a tensile strength of 440 MPa. The mechanical property and transition temperature of hot rolled steel sheets were more influenced by the coiling temperature rather than by the small amount of alloying element. Further, at the same composition, the property of the specimen coiled at low temperature was superior to that obtained at higher coiling temperature. The fracture surface of 0.005C-0.2Si-1.43Mn steel coiled at $630^{\circ}C$ showed a ductile fracture mode at $-100^{\circ}C$, but coiling at $670^{\circ}C$ showed a transgranular brittle fracture mode at $-90^{\circ}C$. The galvannealed 0.006C-0.07Si-1.33Mn steel sheet annealed at $810^{\circ}C$ has tensile strength and elongation of 442.8 MPa and $36.6\%$, respectively. The transition temperature of galvannealed 0.006C-0.07Si-1.33Mn steel sheet was increased with a drawing ratio, and the transition temperature of the galvannealed 0.006C-0.07Si-1.33Mn steel was $-60^{\circ}C$ at a drawing ratio of 1.8

• Progress in Superconductivity and Cryogenics
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• v.14 no.4
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• pp.16-19
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• 2012

In power cables as one of the important power applications adopting HTS tapes, a good insulation should be kept at its optimum performance. As an insulation material for superconducting device applications, polypropylene laminated paper (PPLP) is now widely used instead of the conventional Kraft paper. In addition to its dielectric property, the insulation material should also possess superior mechanical property at cryogenic temperatures and operability that is necessary for the insulation winding process. This study aims to evaluate the mechanical property of the PPLP material at ambient and cryogenic temperatures. At cryogenic temperature, the failure stress of PPLP increased significantly as compared with that at ambient temperature. The failure stress at both temperatures depended upon the sample orientation to the load application.