• Journal of the Microelectronics and Packaging Society
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• v.17 no.3
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• pp.17-26
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• 2010

Pb-Sn solder is rapidly being replaced by lead-free solder for board-level interconnection in microelectronic package assemblies due to the environmental protection requirement. There is a general lack of mechanical reliability information available on the lead-free solder. In this study, thermo-mechanical behaviors of wire-bond plastic ball grid array (WB-PBGA) package assemblies are characterized by high-sensitivity moire interferometry. Experiments are conducted for two types of WB-PBGA packages that have Pb-Sn solder and lead-free solder as joint interconnections. Using real-time moire setup, fringe patterns are recorded and analyzed for several temperatures. Bending deformations of the assemblies and average strains of the solder balls are investigated and compared for the two type of WB-PBGA package assemblies. Results show that shear strain in #3 solder ball located near the chip shadow boundary is dominant for the failure of the package with Pb-Sn solder, while normal strain in #7 most outer solder ball is dominant for that with lead-free solder. It is also shown that the package with lead-free solder has much larger bending deformation and 10% larger maximum effective strain than the package with Pb-Sn solder at same temperature level.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.1
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• pp.259-264
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• 2014

IEEE 802.15.4 has been emerging as the popular choice for various monitoring and control applications. In this paper, a fault management system for DC power-lines has been designed using IEEE 802.15.4, in order to monitor DC power-lines in real time, and to rapidly detect faults and shut off the line where such faults occur. Numbers were allocated for each node and unslotted CSMA-CA method of IEEE 802.15.4 was used, the performance of which was analyzed by a simulation. For such purpose, a total of 60 bits of the control data consisting of 16 bits of the current, 16 bits of the amplitude, 28 bits of the terminal state data were sent out, and the packet transfer rate and the transmission delay time of the fault management system for DC power-lines were measured and analyzed. When the traffic load was 330 packets per second or lower, the average delay time was shown to be shorter than 0.02 seconds, and when the traffic load was 260 packets per second or lower, the packet transfer rate was shown to be 99.99% or higher. Therefore, it was confirmed that the stringent condition of US Department of Energy (DOE) could be satisfied if the traffic load was 260 packets per second or lower, The results of this study can be utilized as basic data for the establishment of the fault management system for DC power-lines using IEEE 802.15.4.

• Journal of the Korean earth science society
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• v.32 no.3
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• pp.249-264
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• 2011

A multi-Gaussian kriging approach extended to space-time domain is presented for uncertainty modeling as well as time-series mapping of environmental variables. Within a multi-Gaussian framework, normal score transformed environmental variables are first decomposed into deterministic trend and stochastic residual components. After local temporal trend models are constructed, the parameters of the models are estimated and interpolated in space. Space-time correlation structures of stationary residual components are quantified using a product-sum space-time variogram model. The ccdf is modeled at all grid locations using this space-time variogram model and space-time kriging. Finally, e-type estimates and conditional variances are computed from the ccdf models for spatial mapping and uncertainty analysis, respectively. The proposed approach is illustrated through a case of time-series Particulate Matter 10 ($PM_{10}$) concentration mapping in Incheon Metropolitan city using monthly $PM_{10}$ concentrations at 13 stations for 3 years. It is shown that the proposed approach would generate reliable time-series $PM_{10}$ concentration maps with less mean bias and better prediction capability, compared to conventional spatial-only ordinary kriging. It is also demonstrated that the conditional variances and the probability exceeding a certain thresholding value would be useful information sources for interpretation.

• Journal of Korea Water Resources Association
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• v.44 no.12
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• pp.929-940
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• 2011

In this study, the future expected discharges are analyzed for Daecheong and Yongdam Dam Watershed in Geum River watershed using A1B scenario based RCM with 27 km spatial resolutions from Korea Meteorological Agency and SWAT model. The direct use of GCM and RCM data for water resources impact assessment is practically hard because the spatial and temporal scales are different. In this study, the problems of spatial and temporal scales were settled by the spatial and temporal downscaling from watershed scale to weather station scale and from monthly to daily of RCM grid data. To generate the detailed hydrologic scenarios of the watershed scale, the multi-site non-stationary downscaling method was used to examine the fluctuations of rainfall events according to the future climate change with considerations of non-stationary. The similarity between simulation and observation results of inflows and discharges at the Yongdam Dam and Daecheong Dam was respectively 90.1% and 84.3% which shows a good agreement with observed data using SWAT model from 2001 to 2006. The analysis period of climate change was selected for 80 years from 2011 to 2090 and the discharges are increased 6% in periods of 2011~2030. The seasonal patterns of discharges will be different from the present precipitation patterns because the simulated discharge of summer was decreased and the discharge of fall was increased.

• Membrane Journal
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• v.24 no.1
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• pp.31-38
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• 2014

Rainwater harvesting is a process by which rainwater collected from rooftop or other catchment is purified so that the water can be directly or indirectly used by human beings for beneficial uses. As rainwater is increasingly considered for high quality purposes, membranes have gained an important place in rainwater treatment. It has advantages such as the production of high quality water, small footprint, and affordable energy consumption. Nevertheless, membrane fouling is regarded as a serious problem similar to the cases of water treatment and wastewater reclamation. In this study, we applied microfiltration (MF) membranes for rainwater treatment. In addition, a low pressure ultraviolet (UV) process was also use as a pretreatment to control notonly. To quantify the effect of UV on organic matters, both total organic carbon (TOC) and UV absorbance (UVA) were measured. Moreover, the effect of UV pretreatment on membrane fouling was investigated. Experimental results indicated that the pretreatment of membranes using LPUV was effective to control fouling of MF membranes only when the rainwater was contaminated by algae. This was attributed the reduction and modification of organics after UV treatments. It is likely that the UV/MF process is a promising option for water treatment in decentralized water treatment such as micro water grid systems.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5879-5884
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• 2013

With the rapid industrialization and economical development, the electricity demands of the industrial facilities and densely populated large cities are continuing to increase in Korea. The increase in the power consumption requires the extension of power facilities, but it is difficult to secure spaces for equipment installation in the limited space of urban areas. In addition, the 154 kV or 345 kV transmission systems in Korea has a short transmission distance, and are connected to one another in network structures that ensure the high reliability and stability of power supply. This structure reduces the impedance during the fault in power system, and increases the magnitude of in the short circuit fault current. The superconducting fault current limiter (SFCL) was devised to effectively address these existing problems. The SFCL is a new-concept eco-friendly protective device that ensures fast operation and recovery time for the fault current and does not need additional fault detection devices. Therefore, many studies are being conducted around the world. In this paper, based on the wiring method the initial fault current characteristics, current limiting characteristics, according to the incident angle and the change in inductance current limiting characteristics were analyzed in a multifaceted methods.

• Journal of the Korean association of regional geographers
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• v.13 no.3
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• pp.301-320
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• 2007

In Korean academic societies, old maps has not yet been properly investigated in terms of their genealogy, classification, detailed place names, historical backgrounds and the other aspects. With publication of the bibliographies and papers on old maps reserved in museum and library, the scope of research enlarged gradually its scope from 1970s. In 1980s, with the development of theoretical geography, scientific analysis were applied to investigate the projection method of Daedongyeo-jido. The 1990s proved a prominent decade for researches. The photo-copies of old maps enabled researchers to investigate the in-depth comparative study. The more important thing is that old maps became to be powerful instrument in the research of historical geography, such as territorial disputes and marine name(東海). And county old maps compiled by region became to be regional-cultural contents of local areas. Important issues in old map research in Korean academic societies are about Cheonha-do which is unique old world map in Korea, grid-system projection in old county maps and the genealogy of Daedongyeo-jido(manuscript and block print edition). This study shows that bibliography of all old maps preserved in each library and museum should be standardized. This could enable the exchange of information of old maps between institutes. The more important thing is that conciliation of human, social and natural sciences should be applied in the research of old maps.

• Journal of the Korean Association of Geographic Information Studies
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• v.16 no.3
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• pp.193-210
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• 2013

This study aims to assess the slope stability variation of Jeollabuk-do drainage areas by RCM model outputs based on A1B climate change scenario and infinite slope stability model based on the specific catchment area concept. For this objective, we downscaled RCM data in time and space: from watershed scale to rain gauge scale in space and from monthly data to daily data in time and also developed the GIS-based infinite slope stability model based on the concept of specific catchment area to calculate spatially-distributed wetness index. For model parameterization, topographic, geologic, forestry digital map were used and model parameters were set up in format of grid cells($90m{\times}90m$). Finally, we applied the future daily rainfall data to the infinite slope stability model and then assess slope stability variation under the climate change scenario. This research consists of two papers: the first paper focuses on the methodologies of climate change scenario preparation and infinite slope stability model development.

• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.2
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• pp.120-128
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• 2016

This paper describes power generation from sea waves by using linear permanent magnet generator. A buoy is placed on the ocean surface and connected to the generator. The wave energy is carried out from the movement of a buoy. An electrical conversion system is needed between the generator and the grid. For an analysis of the power system, the modeling of the linear generator and converter system was proceeded. This paper proposes vector control method for wave power generation system using linear generator. In order to verify the proposed method, simulation and experiment performed and the results support the validity of the control scheme.

• The Journal of Engineering Geology
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• v.24 no.4
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• pp.501-510
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• 2014

Volcanic eruptions alone may lead to serious natural disasters, but the associated release of water from a caldera lake may be equally damaging. There is both historical and geological evidence of the past eruptions of Mt. Baekdusan, and the volcano, which has not erupted for over 100 years, has recently shown signs of reawakening. Action is required if we are to limit the social, political, cultural, and economic damage of any future eruption. This study aims to identify the area that would be inundated following a volcanic flood from the Cheon-Ji caldera lake that lies within Mt. Baekdusan. A scenario-based numerical analysis was performed to generate a flood hydrograph, and the parameters required were selected following a consideration of historical records from other volcanoes. The amount of water at the outer rim as a function of time was used as an upper boundary condition for the downstream routing process for a period of 10 days. Data from the USGS were used to generate a DEM with a resolution of 100 m, and remotely sensed satellite data from the moderate-resolution imaging spectroradiometer (MODIS) were used to show land cover and use. The simulation was generated using the software FLO-2D and was superposed on the remotely sensed map. The results show that the inundation area would cover about 80% of the urban area near Erdaobaihezhen assuming a 10 m/hr collapse rate, and 98% of the area would be flooded assuming a 100 m/hr collapse rate.