Publications by authors named "Sun Kyoung Kim"

7 Publications

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Rapid Numerical Estimation of Pressure Drop in Hot Runner System.

Micromachines (Basel) 2021 Feb 18;12(2). Epub 2021 Feb 18.

Department of Mechanical System Design Engineering, Seoul National University of Science and Technology, Seoul 01811, Korea.

To determine dimensions in the hot runner systems, given a material, it is necessary to predict the pressure drop according to them. Although modern injection molding simulators are able to evaluate such pressure drops, they are expensive and demanding to be employed as a design utility. This work develops a computer tool that can calculate a pressure drop from the sprue to the gate assuming a steady flow of a generalized Newtonian fluid. For a four drop hot runner system, the accuracy has been verified by comparing the obtained results with those by a commercial simulator. This paper presents how to utilize the proposed method in the hot runner design process.
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http://dx.doi.org/10.3390/mi12020207DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7922069PMC
February 2021

High-Throughput Synthesis of Liposome Using an Injection-Molded Plastic Micro-Fluidic Device.

Micromachines (Basel) 2021 Feb 9;12(2). Epub 2021 Feb 9.

Department of Mechanical System Design Engineering, Seoul National University of Science and Technology, 232 Gongreung-Ro, Nowon-Gu, Seoul 01811, Korea.

For mass production of liposomes, we designed a plastic micro-channel device on the basis of 5 μm of micro-nozzle array forming T-junction with 100 μm depth of micro-channel. A micro-channel unit for synthesizing liposomes consisted of two micro-nozzle arrays for mixing two solutions as well as delivery and recovery channels for supplying solutions and collecting liposome suspension. The number of micro-nozzles was approximately 2400 for a micro-channel unit, and seven units were applied independently on a micro-channel plate. The plastic micro-channel plate was injection-molded for mass production using a micro-channel stamper previously fabricated by UV lithography and nickel electroforming process. A plastic cover plate with seven pairs of inlet and outlet ports was machined by mechanical milling and drilling and was assembled with a micro-channel plate using a holder to form a liposome synthesizing device. Flow and mixing of solutions in the micro-channels were tested using colored water to check the micro-fluidic characteristics of the device. Finally, a L-α-phosphatidylcholine (SOY PC) liposome was synthesized using EtOH solution of SOY PC (95%) and saline (0.85% NaOH solution) to find that the liposomes were around 230 and 260 nm in diameter, depending on the flow rate of the lipid solution.
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http://dx.doi.org/10.3390/mi12020170DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7915932PMC
February 2021

Optimal Dummy Pattern Design Method for PWB Warpage Control Using the Human-Based Genetic Algorithm.

Micromachines (Basel) 2020 Aug 25;11(9). Epub 2020 Aug 25.

Department of Mechanical System Design Engineering, Seoul National University of Science and Technology, Seoul 02421, Korea.

In this work, a method that minimizes printed wiring board (PWB) warpage by dummy pattern design is proposed. This work suggests that dummy patterns are placed on a preset discretized location in the PWB to reduce the warpage. On each discretized candidate area, the dummy pattern can be set or unset. The warpage is numerically simulated based on direct modeling of the as-is PWB patterns to evaluate the warpage alongside the dummy pattern design set. The optimal pattern that minimizes warpage is determined using the human-based genetic algorithm where the objective function is evaluated by the structural simulation. The optimization method is realized in a spreadsheet that allows scripting language with which the input and output files of the simulation tool can be modified and read. Two different cases have been tested and the results show that the method can determine the optimal dummy patterns. The measured and simulated deflections agree well with each other. Moreover, it has been shown that certain dummy pattern designs that should reduce the warpage can be sought by the optimization.
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http://dx.doi.org/10.3390/mi11090807DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7569826PMC
August 2020

Enhancement of struvite purity by re-dissolution of calcium ions in synthetic wastewaters.

J Hazard Mater 2013 Oct 8;261:29-37. Epub 2013 Jul 8.

Research Division for Industry & Environment, Korea Atomic Energy Research Institute, 1266 Sinjeong, Jeongeup, Jeollabuk-do, 580-185, Republic of Korea.

Although it is widely known that the presence of Ca ions inhibits the nucleation and growth of struvite, which consists of NH4(+), PO4(3-), and Mg(2+), there is a lack of knowledge on actual Ca contents in struvite co-precipitates at various N and P concentrations and the corresponding effects on the sizes of the precipitates. Therefore, to address this challenge, this study designed synthetic wastewaters including the variety of N and P concentrations, and conducted batch experimental reactions with each wastewater to investigate Ca precipitation and size distributions of the precipitates. The molar ratio of Mg:P:N was confined to 1:1:7, while the initial Ca(2+) concentrations were chosen to be 30-60 mg/L, which are typical Ca concentrations in real wastewaters. The result of the batch experiments confirmed that the presence of Ca caused smaller solids than struvite as indicated in previous studies, and there was competition between Ca-phosphate and Mg-N- PO4 (struvite) reactions, as expected. At the beginning of the experiment (∼1 min), fast Ca-phosphate precipitation was dominant because free Ca and P ions were quickly removed while Mg and N concentrations gradually reduced. However, as the nucleation and crystal growth processes elapsed, dissolved Mg and N concentrations continuously decreased, but dissolved Ca concentrations could rise again at high N and P concentration conditions. The interesting phenomenon is that such increases of Ca concentrations probably results from the thermodynamic energy differences between struvite and Ca-phosphate formations. A high thermodynamic driving force of struvite precipitation could drive the re-dissolution of Ca-ions from the Ca-phosphate compounds with low saturation states. This result is expected to be applied for increasing the struvite purity by the Ca re-dissolution through the thermodynamic spontaneity without additional energy input.
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http://dx.doi.org/10.1016/j.jhazmat.2013.06.072DOI Listing
October 2013

Effects of electron beam irradiation and temperature on the treatment of swine wastewater using an ion exchange biological reactor.

Bioresour Technol 2013 Jun 21;137:233-8. Epub 2013 Mar 21.

Research Division for Industry & Environment, Korea Atomic Energy Research Institute, Jeongeup, Jeollabuk-do, Republic of Korea.

Swine wastewater was treated using an ion exchange biological reactor (IEBR). Organic matter and nutrient in swine wastewater were pre-treated by electron beam irradiation. The optimal dose for solubilization of organic matter in swine wastewater ranged from 20 kGy to 75 kGy. The carbohydrates, proteins, and lipids were investigated as proteins and lipids mainly contained the solubilized organic matter. The solubilization of organic matter in swine wastewater was affected by the combination effects of temperature and dose. The maximum chemical oxygen demand (COD) and ammonia removal efficiencies were 74.4% and 76.7% at a dose of 0 kGy under room temperatures (23.0°C). The removal of ammonia was significantly affected by low temperature (15.3°C). On the other hand, the removal of phosphorus was not a function of electron beam irradiation or temperature because struvite is one of the main removal mechanisms under anoxic conditions.
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http://dx.doi.org/10.1016/j.biortech.2013.03.083DOI Listing
June 2013

Antibiotic resistance in bacteria isolated from freshwater aquacultures and prediction of the persistence and toxicity of antimicrobials in the aquatic environment.

J Environ Sci Health B 2013 ;48(6):495-504

Research Division for Industry & Environment, Korea Atomic Energy Research Institute, Jeongeup, Republic of Korea.

The occurrence of antibiotic-resistant bacteria isolated from freshwater aquaculture effluents was investigated. The bacterial strains were collected from four different freshwater aquaculture effluents (catfish, trout, eel, and loach). Based on sequence of 16S rRNA, a total of 20 bacterial strains was isolated and one half of the isolated bacteria were Aeromonas sp. The antimicrobial sensitivity test was performed using the disc diffusion method. Individual antibiotic-resistant bacteria to antimicrobials were 41.7% and multiple antibiotic resistant bacteria were 58.3%. The disinfection of antibiotic-resistant bacteria by electron beam (E-beam) irradiation was carried out using an electron accelerator. Antibiotic-resistant bacteria were effectively disinfected by E-beam irradiation. The isolated bacteria were completely disinfected at a dose of less than 2 kGy. The persistence and toxicity of each antimicrobial in the aquatic environment was estimated due to the human health and ecosystems. In order to estimate the persistence and toxicity of antimicrobials in the aquatic environment, two quantitative structure activity relationship (QSAR) models were used. The persistence and toxicity of each antimicrobial were influenced on its hydrophobicity. In addition, QSAR models showed that isoelectric point and hydrogen bonding acceptor are key parameters to estimate the persistence and toxicity of antimicrobials in the aquatic environment.
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http://dx.doi.org/10.1080/03601234.2013.761911DOI Listing
August 2013

Interface analysis of embedded chip resistor device package and its effect on drop shock reliability.

J Nanosci Nanotechnol 2012 Apr;12(4):3186-90

System Packaging Research Center, Korea Electronics Technology Institute, #68 Yatap-Dong, Bundang-Gu, Seongnam-Si, Gyeonggi-Do 463-816, Korea.

In this study, the drop reliability of an embedded passive package is investigated under JESD22-B111 condition. Chip resistors were buried in a PCB board, and it was electrically interconnected by electroless and electrolytic copper plating on a tin pad of a chip resistor without intermetallic phase. However tin, nickel, and copper formed a complex intermetallic phase, such as (Cu, Ni)6Sn5, (Cu, Ni)3Sn, and (Ni, Cu)3Sn2, at the via interface and via wall after reflow and aging. Since the amount of the tin layer was small compared with the solder joint, excessive intermetallic layer growth was not observed during thermal aging. Drop failures are always initiated at the IMC interface, and as aging time increases Cu-Sn-Ni IMC phases are transformed continuously due to Cu diffusion. We studied the intermetallic formation of the Cu via interface and simulated the stress distribution of drop shock by using material properties and board structure of embedded passive boards. The drop simulation was conducted according to the JEDEC standard. It was revealed that the crack starting point related to failure fracture changed due to intermetallic phase transformation along the via interface, and the position where failure occurs experimentally agrees well with our simulation results.
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http://dx.doi.org/10.1166/jnn.2012.5613DOI Listing
April 2012