• Journal of IKEEE
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• v.21 no.4
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• pp.368-374
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• 2017

In this Paper, we developed a low power type LED security light using LED lighting that substitutes a 220[V] commercial power source for a solar cell module instead of a halogen or a sodium lamp. in addition, a PWM type drive control circuit is designed to minimize the heat generation problem and the drive current of the LED drive controller. in developed system, The light efficiency measurement value is 93.6[lm/W], and a high precision temperature sensor is used inside the controller to control the heat generation of the LED lamp. In order to eliminate the high heat generated from the LED lamp, it is designed to disperse quickly into the atmosphere through the metal insertion type heat sink. The heat control range of LED lighting was $50-55[^{\circ}C]$. The luminous flux and the lighting speed of the LED security lamp were 0.5[s], and the beam diffusion angle of the LED lamp was about $110[^{\circ}C]$ by the light distribution curve based on the height of 6[m].

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.05a
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• pp.85-91
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• 2002

Even though electroless Hi and Sn-Ag-Cu solder are widely used materials in electronic packaging applications, interfacial reactions of the ternary Ni-Cu~Sn system have not been known well because of their complexity. Because the growth of intermetallics at the interface affects reliability of solder joint, the intermetallics in Ni-Cu-Sn system should be identified, and their growth should be investigated. Therefore, in present study, interfacial reactions between electroless Ni UB7f and 95.5Sn-4.0Ag-0.5Cu alloy were investigated focusing on morphology of the IMCs, thermodynamics, and growth kinetics. The IMCs that appear during a reflow and an aging are different each other. In early stage of a reflow, ternary IMC whose composition is Ni$_{22}$Cu$_{29}$Sn$_{49}$ forms firstly. Due to the lack of Cu diffusion, Ni$_{34}$Cu$_{6}$Sn$_{60}$ phase begins growing in a further reflow. Finally, the Ni$_{22}$Cu$_{29}$Sn$_{49}$ IMC grows abnormally and spalls into the molten solder. The transition of the IMCs from Ni$_{22}$Cu$_{29}$Sn$_{49}$ to Ni$_{34}$Cu$_{6}$Sn$_{60}$ was observed at a specific temperature. From the measurement of activation energy of each IMC, growth kinetics was discussed. In contrast to the reflow, three kinds of IMCs (Ni$_{22}$Cu$_{29}$Sn$_{49}$, Ni$_{20}$Cu$_{28}$Au$_{5}$, and Ni$_{34}$Cu$_{6}$Sn$_{60}$) were observed in order during an aging. All of the IMCs were well attached on UBM. Au in the quaternary IMC, which originates from immersion Au plating, prevents abnormal growth and separation of the IMC. Growth of each IMC is very dependent to the aging temperature because of its high activation energy. Besides the IMCs at the interface, plate-like Ag3Sn IMC grows as solder bump size inside solder bump. The abnormally grown Ni$_{22}$Cu$_{29}$Sn$_{49}$ and Ag$_3$Sn IMCs can be origins of brittle failure.failure.

• Journal of the Korean Magnetics Society
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• v.22 no.2
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• pp.37-41
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• 2012

The Ag nanoparticles attached $La_{0.7}Sr_{0.3}Co_{0.3}Fe_{0.7}O_{3-{\delta}}$ (LSCF) perovskites were prepared by plasma method. The Ag nanoparticles with size of several nanometers deposited from the Ag target were coated on the surface of LSCF powders with size range from 0.2 to 3 ${\mu}m$. The agglomeration of Ag particles annealed at $800^{\circ}C$ under inert gas of Ar were rarely observed. The inter-diffusion between surface Ag and core LSCF is effectively strong to prevent aggregation of Ag nanoparticles. The wave number of FT-IR spectra for LSCF were largely shifted as the concentration of Ag on LSCF up to 2.11 wt.%. The ionic states of irons in LSCF were measured by M$\ddot{o}$ssbauer spectroscopy. The small amount of $Fe^{4+}$ ions are converted to $Fe^{3+}$ ions after Ag nanopartcles were coated on LSCF.

• Nuclear Engineering and Technology
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• v.21 no.2
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• pp.89-98
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• 1989

The expanding copper mandrel test performed at three strain rates (3.2$\times$10E -5/s, 2.0$\times$10E-6/s and 1.2$\times$10E-7/s) over 553-873 K temperature range by varying the heating rates (8-1$0^{\circ}C$/s, 1-2$^{\circ}C$/s and 0.5$^{\circ}C$/s) in air and in vacuum (5$\times$10E-5 torr). The yield stress peak, the strain rate sensitivity minimum and the activation volume peaks could be explained in terms of the dynamic strain aging. The activation energy for dynamic strain aging obtained from the yield stress peak temperature and strain rate was 196 KJ/mol and this value was in good agreement with the activation energy for oxygen diffusion in $\alpha$-zirconium and Zircaloy-2 (207-220 KJ/mol). Therefore, oxygen atoms are responsible for the dynamic strain aging which appeared between 573 K and 673 K. The yield stress increase due to the oxidation was obtained by comparing the yield stress in air with that in vacuum and represented by the percentage increase of yield stress ( $\sigma$$^{a}$ $_{y}$ - $\sigma$$^{v}$ $_{y}$ / $\sigma$$^{v}$ $_{y}$ ). The slower the strain rate, the greater the percentage increase occurs. In order to estimate the yield stress of PWR fuel cladding material under the service environment, the yield stress in water was obtained by comparing the oxidation rate in air that in water assuming the relationship between the oxygen pick-up amount and the yield stress increase.

• Korean Chemical Engineering Research
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• v.56 no.1
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• pp.1-5
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• 2018

In this work, we study the ion conductivity by analyzing the impedance to the high current density range that the PEMFC (Proton Exchange Membrane Fuel Cell) is actually operated. The effect of GDL (Gas Diffusion Layer)presence on impedance was investigated indirectly by measuring hydrogen permeability. When the RH (Relative Humidity)was higher than 60% in the low current range (< $80mA/cm^2$), the moisture content of the polymer membrane was sufficient and the ion conductivity of the membrane was not influenced by the current change. However, when RH was low, ion conductivity increased due to water production as current density increased. The ion conductivity of the membrane obtained by HFR (High Frequency Resistance) in the high current region ($100{\sim}800mA/cm^2$)was compared with the measured value and simulated value. At RH 100%, both experimental and simulated values showed constant ion conductivity without being influenced by current change. At 30~70% of RH, the ionic conductivity increased with increasing current density and tended to be constant.

• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.1
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• pp.13-23
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• 2008

In coastal region, eutrophication, Do deficit and red tide are frequently occurred by influx of fresh water. When the fresh water containing pollutants is discharged into the sea, the surrounding water is contaminated by dispersion of freshwater flowing into coastal waters. The prediction and analysis about the dispersion process of the discharged fresh water should be conducted. A modeling system using GUI was developed to simulate hydrodynamic flow and fresh water dispersion in coastal waters and to analyze the results efficiently. The modeling module of the system includes a tide model using a finite element method and a fresh water dispersion model using a particle-tracking method. This system was applied to predict the tidal currents and fresh water dispersion in Mokpo coastal zone. To verify accuracy of the hydrodynamic model, the simulation results were compared with observed sea level and time variations of tidal currents showing a good agreement. The fresh water dispersion was verified with observed salinity distribution. The dispersion model also was verified with analytic solutions with advection-diffusion problems in 1-dimensional and 2-dimensional simple domain. The system is operated on GUI environment, to ease the model handling such as inputting data and displaying results. Therefore, anyone can use the system conveniently and observe easily and accurately the simulation results by using graphic functions included in the system. This system can be used widely to decrease the environmental disaster induced by inflow of fresh water into coastal waters.

• Nuclear Engineering and Technology
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• v.27 no.2
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• pp.176-188
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• 1995

A particle tracking scheme was developed in order to model radionuclide transport through a tortuous flow Held in a rock fracture. The particle tacking method may be used effectively in a heterogeneous flow field such as rock fracture. The parallel plate representation of the single fracture fails to recognize the spatial heterogeneity in the fracture aperture and thus seems inadequate in describing fluid movement through a real fracture. The heterogeneous flow field une modeled by a variable aperture channel model after characterizing aperture distribution by a hydraulic test. To support the validation of radionuclide transport models, a radionuclide migration experiment was performed in a natural fracture of granite. $^3$$H_2O$ and $^{131}$ I are used as tracers. Simulated results were in agreement with experimental result and therefore support the validity of the transport model. Residence time distributions display multipeak curves caused by the fast arrival of solutes traveling along preferential fracture channels and by the much slower arrival of solutes following tortous routes through the fracture. Results from the modelling of the transport of nonsorbing tracer through the fracture show that diffusion into the interconnected pore space in the rock mass has a significant effect on retardation.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.113-113
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• 2000

직접천이형 wide band gap(3.4eV) 반도체중의 하나인 GaN를 청색 및 자외선 laser diode, 고출력 전자장비 등으로 응용하기 위해서는 낮은 접합저항을 갖는 Ohmic contact이 선행되어야 한다. 그러나 만족할만한 p-type GaN의 Ohmic contact은 아직 실현되고 있지 못하며, 이는 GaN와 접합 금속과의 구체적인 반응의 연구를 필요로 한다. 본 연구에서 앞서 Pt, Pt, Ni등의 late transition metal을 p-GaN에 접합시킨 결과 이들은 접합 당시 비교적 평탄하나 후열 처리과정에서 비교적 낮은 온도에서 기판과 열팽창계수의 차이로 인하여 평탄성을 잃어버리면서 barrier height가 증가한다는 사실을 확인하였다. 따라서 본 연구에서는 이러한 열적 불안정성을 극복하기 위하여 Ni과 Pd를 차례로 증착하고 가열하면서 interfacial reaction, film morphology, Fermi level의 움직임을 monchromatic XPS(x-ray photoelectron spectroscopy) 와 SAM(scanning Auger microscopy) 그리고 ex-situ AFM을 이용하여 밝히고자 하였다. 특히 후열처리에 의한 계면 반응에 수반되는 구성 금속원소 간의 합금현상과 금속 층의 평탄성이 밀접한 관계가 있다는 것을 확인하였다. 이러한 합금과정에서 나타나는 금속원소들의 중심 준위의 이동을 체계적으로 규명하기 위해서 Pd1-xNix와 Pd1-xGax 합금들의 표준시료를 arc melting method로 만들어 농도에 따른 금속원소들의 중심 준위의 이동을 측정하여, Pd/Ni/p-GaN 및 Ni/Pd/p-GaN 계에서 열처리 온도에 따른 interfacial reaction을 확인하였다. 그 결과 두 계가 상온에서 nitride 및 alloy를 형성하지 않고 고르게 증착되고, 열처리 온도를 40$0^{\circ}C$에서 $650^{\circ}C$까지 증가시킴에 따라 계면반응의 부산물인 metallic Ga은 증가하고 있으마 nitride는 여전히 형성되지 않는 것을 확인하였다. 증착당시 Ni이 계면에 있는 Pd/Ni/p-GaN의 경우에는 52$0^{\circ}C$까지의 열처리에 의하여 Ni과 Pd가 골고루 섞이고 그 평탄성도 유지되고 barier height의 변화도 없었다. 더 높은 $650^{\circ}C$ 가열에 의해서는 surface free energy가 작은 Ga의 활발한 편석 현상으로 인해 표면은 Ga이 풍부한 Pd-Ga의 합금층으로 덮이고, 동시에 작은 pinhole들이 발생하며 barrier height도 0.3eV 가량 증가하게 된다. 반면에 증착당시 Pd이 계면에 있는 Ni/Pd/p-GaN의 경우에는 40$0^{\circ}C$의 가열까지는 두 금속이 그들 계면에서부터 섞이나, 52$0^{\circ}C$의 가열에 의해 이미 barrier height가 0.2eV 가량 증가하기 시작하였다. 더 높은 $650^{\circ}C$가열에 의해서는 커다란 pinhole, 0.5eV 가량의 barrier height 증가, Pd clustering이 동시에 관찰되었다. 따라서 Ni과 Pd의 일함수는 물론 thermal expansion coefficient가 거의 같으며 surface free energy도 거의 일치한다는 점을 감안하면, 이렇게 뚜렷한 열적 안정성의 차이는 GaN와 contact metal과의 반응시작 온도(disruption onset temperature)의 차이에 기인함을 알 수 있었다. 즉 계면에서의 반응에 의해 편석되는 Ga에 의해 박막의 strain이 이완되면, pinhole 등의 박막결함이 줄어 들고, 이는 계면의 N의 out-diffusion을 방지하여 p-type GaN의 barrier height 증가를 막게 된다.

• KIPS Transactions on Computer and Communication Systems
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• v.5 no.9
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• pp.211-216
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• 2016

Worldwide casualties caused by earthquakes, floods, fire or other disaster has been increasing. So many researchers are being actively done technical studies to ensure golden-time. In this paper if a disaster occurs, use the IoT technologies in order to secure golden-time and transmits the message after to find the user of the accident area first. When the previous job is finished, gradually finds a user of the surrounding area and transmits the message. For national emergency information, OPEN API of Korea Meteorological Administration was used. To collect detailed information on a relevant area in real time, this study established the system that connects and integrates Crowd Sensing technology with BLE (Bluetooth Low Energy) Beacon technology. Up to now, the CBS based on base station has been applied. However, this study designed and mapped DB in the integration of Beacon based user positioning and national administrative address system in order to estimate local users. In this experiment, the accuracy and speed of information dif6fusion algorithm were measured with a rise in the number of users. The experiments were conducted in a manner that increases the number of users by one thousand and was measured the accuracy and speed of the message spread transfer algorithm. Finally, became operational in less than one second in 20,000 users, it was confirmed that the notification message is sent.

• Korean Journal of Metals and Materials
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• v.50 no.3
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• pp.256-262
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• 2012

This study investigated the hydrogen storage properties of Zr-Based $AB_{2-x}M_x$ metal hybride made by HCS (Hydriding Combustion Synthesis). The materials were prepared by HCS 80 wt% $AB_2$-15 wt% Mg-5 wt% Mm, HCS 80 wt% $AB_2$-20 wt% Mg and pure Zr-Based $AB_2$, These materials were activated at 298 K under 20 bar. Both HCS 80 wt% $AB_2$-20 wt% Mg and HCS 80 wt% $AB_2$-15 wt% Mg-5 wt% Mm were absorbed within 1 minute. In the case of the $AB_2$, it was perfectly absorbed within 6 minutes. Then, the materials were evaluated to obtain P-C-T (Pressure-Composition-Temperature) curves at 298K. As a result, the hydrogen storage capacity of HCS 80 wt% $AB_2$-20 wt% Mg, HCS 80 wt% $AB_2$-15 wt% Mg-5 wt% Mm and pure Zr-Based $AB_2$ were determined to be 1.2, 1.6 and 1.74 wt%, respectively. The activation energy and rate controlling step were calculated by the Johnson-Mehl Avrami equation. The activation energies of HCS 80 wt% $AB_2$-20 wt% Mg, HCS 80 wt% $AB_2$-15 wt% Mg-5 wt% Mm and pure Zr-Based $AB_2$ were 26.91, 20.45, and 60.41 kJ/mol, respectively. Also, the values of ${\eta}$ in the Johnson-Mehl Avrami equation for HCS 80 wt% $AB_2$-20 wt% Mg, HCS 80 wt% $AB_2$-15 wt% Mg-5 wt% Mm and pure Zr-Based $AB_2$ are 0.60, 0.51, and 0.44. So, the rate controlling steps which indicate hydrogen storage mechanism are an one dimensional diffusion process.