• Mass Spectrometry Letters
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• v.12 no.1
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• pp.1-10
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• 2021

A simple, specific, and economical LC-MS/MS method was investigated for the screening of 43 prescribed antihypertensive and related drugs in human urine. The urine samples were simply prepared by diluting and mixing with internal standard before directly introduced to the LC-MS/MS system, which is fast, straightforward, and cost-effective. Fractional factorial, Box-Behnken, and I-optimal design were applied to screen and optimize the mass spectrometric and chromatographic factors. The analysis was carried out on a triple quadrupole mass spectrometer system utilizing multiple reaction monitoring with positive and negative electrospray ionization method. Chromatographic separation was performed on a Thermo Scientific Accucore RP-MS column (50 × 3.0 mm ID., 2.6 ㎛) using two separate gradient elution programs established with the same mobile phases. Chromatographic separation was performed within 12 min. The optimal method was validated based on FDA guideline. The results indicated that the assay was specific, reproducible, and sensitive with the limit of detection from 0.1 to 50.0 ㎍/L. The method was linear for all analytes with coefficient of determination ranging from 0.9870 to 0.9981. The intra-assay precision was from 1.44 to 19.87% and the inter-assay precision was between 2.69 and 18.54% with the recovery rate ranges from 84.54 to 119.78% for all drugs measured. All analytes in urine samples were stable for 24 h at 25℃, and for 2 weeks at -60℃. The developed method improves on currently existing methods by including larger number of cardiovascular medications and better sensitivity of 12 analytes.

• Journal of Advanced Navigation Technology
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• v.24 no.6
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• pp.465-470
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• 2020

Complex materials are widely used in aviation industries where lightweighting is essential because they have lighter properties than metals. However, composite materials can cause defects such as internal void formation, poor adhesive mixing, and non-adhesive parts during the production process, and there is a risk of micro-cracking and interlayer separation due to low energy impact. Therefore, a structural damage test is essential. As a result, structural integrity monitoring using FBG is drawing attention. Compared to conventional electrical sensors, FBG has the advantage of being more corrosion-resistant and multiplexed without being affected by electrical noise. However, interloggers measuring FBG are expensive and have a large disadvantage because they are made on the premise of measuring large structures. In this paper, low-cost interloggers were designed for use in unmanned or small aircraft using optical switche, WDM filter, and LTFs, and compared to conventional high-priced interrogator.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.2
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• pp.1-11
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• 2021

The cavity inside the combustor increases the mixing efficiency of fuel and air by inducing a oscillation of the flow and the recirculation area with a low speed, and enables continuous combustion by maintaining the flame. In this study, the characteristics of the internal flow by change in the shape parameters of the cavity were analyzed through experiments and two-dimensional computational analysis. It was observed that the flow in the supersonic combustor was greatly influenced by various shape parameters of cavity besides L/D. Even with the same L/D, it was confirmed that the flow type varies depending on the depth of the cavity, either open or closed type, and the aft ramp angle of the cavity and the height of the combustor also affect the flow characteristics. As a result, the change in the shape parameters of the cavity had a great influence on the total pressure loss.

• Journal of the Korean GEO-environmental Society
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• v.16 no.12
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• pp.45-52
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• 2015

With the rising interest in the environment, more attention on ecological restoration for damaged slope surface to restore its original state has been drawn. Generally, the most useful method is vegetation based spray work. This method uses green soil including sewage sludge, sawdust, paper sludge, and weathered granite soil. However, because there are neither accurate information nor test values about green soil, green soil is often lost by environmental factors such as rainfalls and strong winds. To solve the problem of green soil, it is necessary to prepare design standards about green soil, and conduct studies to deal with green soil loss in consideration of various variables including basic material property, soil quality of slope surface, and weather. This study was conducted in the mixture of green soil and eco-friendly soil stabilizer. With green soil, basic material property test and compaction test were conducted for the analysis on the basic characteristics of green soil. In the mixture with soil stabilizer at a certain ratio, we conducted shear strength test depending on the ratio in order to analyze the maximum shear strength, cohesion and the change in internal friction angles. Furthermore, in the mixture ratio of green soil and soil stabilizer, which is the same as the ratio in the shear strength test, an inclination of slope surface was made in laboratory for the analysis on erosion and germination rate. Finally, this study evaluated the most effective and economic mixing ratio of soil stabilizer to cope with neighboring environmental factors. According to the test, the shear strength of green soil increased up to 51% rely onto the mixing ratio of and a curing period, and its cohesion and internal friction angle also gradually increases. It is judged that the mixture of soil stabilizer was effective in improving shear strength and thereby increased the stability of green soil.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.1-2
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• 2011

Hybrid rockets have lately attracted attention as a strong candidate of small, low cost, safe and reliable launch vehicles. A significant topic is that the first commercially sponsored space ship, SpaceShipOne vehicle chose a hybrid rocket. The main factors for the choice were safety of operation, system cost, quick turnaround, and thrust termination. In Japan, five universities including Hokkaido University and three private companies organized "Hybrid Rocket Research Group" from 1998 to 2002. Their main purpose was to downsize the cost and scale of rocket experiments. In 2002, UNISEC (University Space Engineering Consortium) and HASTIC (Hokkaido Aerospace Science and Technology Incubation Center) took over the educational and R&D rocket activities respectively and the research group dissolved. In 2008, JAXA/ISAS and eleven universities formed "Hybrid Rocket Research Working Group" as a subcommittee of the Steering Committee for Space Engineering in ISAS. Their goal is to demonstrate technical feasibility of lowcost and high frequency launches of nano/micro satellites into sun-synchronous orbits. Hybrid rockets use a combination of solid and liquid propellants. Usually the fuel is in a solid phase. A serious problem of hybrid rockets is the low regression rate of the solid fuel. In single port hybrids the low regression rate below 1 mm/s causes large L/D exceeding a hundred and small fuel loading ratio falling below 0.3. Multi-port hybrids are a typical solution to solve this problem. However, this solution is not the mainstream in Japan. Another approach is to use high regression rate fuels. For example, a fuel regression rate of 4 mm/s decreases L/D to around 10 and increases the loading ratio to around 0.75. Liquefying fuels such as paraffins are strong candidates for high regression fuels and subject of active research in Japan too. Nakagawa et al. in Tokai University employed EVA (Ethylene Vinyl Acetate) to modify viscosity of paraffin based fuels and investigated the effect of viscosity on regression rates. Wada et al. in Akita University employed LTP (Low melting ThermoPlastic) as another candidate of liquefying fuels and demonstrated high regression rates comparable to paraffin fuels. Hori et al. in JAXA/ISAS employed glycidylazide-poly(ethylene glycol) (GAP-PEG) copolymers as high regression rate fuels and modified the combustion characteristics by changing the PEG mixing ratio. Regression rate improvement by changing internal ballistics is another stream of research. The author proposed a new fuel configuration named "CAMUI" in 1998. CAMUI comes from an abbreviation of "cascaded multistage impinging-jet" meaning the distinctive flow field. A CAMUI type fuel grain consists of several cylindrical fuel blocks with two ports in axial direction. The port alignment shifts 90 degrees with each other to make jets out of ports impinge on the upstream end face of the downstream fuel block, resulting in intense heat transfer to the fuel. Yuasa et al. in Tokyo Metropolitan University employed swirling injection method and improved regression rates more than three times higher. However, regression rate distribution along the axis is not uniform due to the decay of the swirl strength. Aso et al. in Kyushu University employed multi-swirl injection to solve this problem. Combinations of swirling injection and paraffin based fuel have been tried and some results show very high regression rates exceeding ten times of conventional one. High fuel regression rates by new fuel, new internal ballistics, or combination of them require faster fuel-oxidizer mixing to maintain combustion efficiency. Nakagawa et al. succeeded to improve combustion efficiency of a paraffin-based fuel from 77% to 96% by a baffle plate. Another effective approach some researchers are trying is to use an aft-chamber to increase residence time. Better understanding of the new flow fields is necessary to reveal basic mechanisms of regression enhancement. Yuasa et al. visualized the combustion field in a swirling injection type motor. Nakagawa et al. observed boundary layer combustion of wax-based fuels. To understand detailed flow structures in swirling flow type hybrids, Sawada et al. (Tohoku Univ.), Teramoto et al. (Univ. of Tokyo), Shimada et al. (ISAS), and Tsuboi et al. (Kyushu Inst. Tech.) are trying to simulate the flow field numerically. Main challenges are turbulent reaction, stiffness due to low Mach number flow, fuel regression model, and other non-steady phenomena. Oshima et al. in Hokkaido University simulated CAMUI type flow fields and discussed correspondence relation between regression distribution of a burning surface and the vortex structure over the surface.

• Journal of the Korean Society for Marine Environment & Energy
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• v.17 no.4
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• pp.306-317
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• 2014

This study has been executed to understand the additional and removal processes of nutrients in the Saemangeum Salt-water Lake, and discussed with other monthly-collected environmental parameters such as water temperature, salinity, dissolved oxygen, suspended solids, and Chl-a from 2008 to 2010. $NO_3$-N, TP, $PO_4$-P, and DISi showed the removal processes along with the salinity gradients at the surface water of the lake, whereas $NO_2$-N, $NH_4$-N, and Chl-a showed addition trend. In the bottom water all water quality parameters except $NO_3$-N appeared addition processes indicating evidence of continuous nutrients suppliance into the bottom layer. The mixing modelling approach revealed that the biogeochemical processes in the lake consume $NO_3$-N and consequently added $NH_4$-N and $PO_4$-P to the bottom water during the summer seasons. The $NH_4$-N and $PO_4$-P appeared strong increase at the bottom water of the river-side of the lake and strong concentration gradient difference of dissolved oxygen also appeared in the same time. DISi exhibited continuous seasonal supply from spring to summer. Internal addition of $NH_4$-N and $PO_4$-P in the river-side of the lake were much higher than the dike-side, while the increase of DISi showed similar level both the dike and river sides. The temporal distribution of benthic flux for DISi indicates that addition of nutrients in the bottom water was strongly affected by other sources, for example, submarine ground-water discharge (SGD) through bottom sediment.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.2
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• pp.146-154
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• 2017

Recently, self-healing concrete has been researched as maintenance and repair of concrete structures are important challenges we face. This paper focused on possibility of ion exchange resin as a novelty material directly and actively controlling harmful ions of concrete, whereas most self-healing concrete researches have been focused on methods to automatically filling and repairing internal crack of concrete. Because equilibrium properties between ion exchange resin and harmful ion is important before design of cement mixing proportion, it was conducted to remove chloride or sulfate in saturated $Ca(OH)_2$ solutions containing NaCl or $Na_2SO_4$. The removal performance was analyzed using kinetic equation and isothermal equation. Consequently, the removal properties of anion exchange resin were relatively more dependent on pseudo second reaction equation and Langmuir equation than pseudo first reaction equation and Freundlich equation. And it was concluded that each chloride and sulfate can be removed to the maximum 1068 ppm and 1314 ppm.

• Applied Chemistry for Engineering
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• v.8 no.5
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• pp.763-770
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• 1997

The separation of benzene-cyclohexane mixture using (O/W)/O emulsion liquid membrane was studied. The operating parameters which can affect the selectivity, benzene yield, and emulsion size distribution were examined and determined by the batch type operation. The unsteady state and steady state extraction behavior in continuous pulse stirred reactor(CPSR) were verified. The optimum conditions for benzene selectivity and yield in batch operation were as follows; emulsion mixing intensity 4000 rpm, Tween 80 concentration 0.4%, volume ratio of membrane phase to internal phase 0.75, volume ratio of dispersed phase to continuous phase 0.5, and permeation time 10 minutes, As impeller speed increased and the microdrop holdup decreased, the Sauter mean diameter decreased. Turbulence damping parameter of modified Calabrease correlation considering microdrop holdup was 2.28. The optimum conditions of continuous operation were as follows; agitation speed 300 rpm, pulse frequence 2 times/sec, flow rate of continuous phase 30ml/min, and flow rate of emulsion phase 12.0ml/min.

• Journal of Pharmaceutical Investigation
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• v.35 no.2
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• pp.123-127
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• 2005

An HPLC method was employed for the determination of ethambutol in human plasma. After addition of internal standard (IS, octylamine, $2\;{\mu}g/mL$) and alkalinization of the plasma with 5 M sodium hydroxide, the drug and IS were extracted into the mixture of chloroform and diethyl ether (40:60, v/v). Following a 15-min vortex-mixing and a 10min centrifugation, the organic phase was spiked with $100{\mu}L$ of phenylethylisocyanate $(2000{\mu}g/mL)$ for chemical derivatization, mixed for 5 min and evaporated to dryness under a stream of nitrogen. The residue was reconstituted with $100{\mu}L$ of mobile phase and $20{\mu}L$ was injected into C18 column with a mobile phase consisting of methanol:water (70:30, v/v). The samples were detected utilizing an ultraviolet detector at 200 nm. The method was specific and validated with a limit of $0.15\;{\mu}g/mL$. Intra- and inter-day precision and accuracy were acceptable for all quality control samples including the lower limit of quantification. The applicability of this method was demonstrated by analysis of human plasma after oral administration of a single 1200-mg dose to 20 healthy subjects. From the plasma ethambutol concentration vs. time curves, the mean AUC was $9.61{\pm}1.64\;{\mu}g{\cdot}hr/mL$ and Cmax of $2.68\;{\mu}g/mL$ reached 2.73 hr after administration. The mean biological half-life of ethambutol was $3.46{\pm}1.21$ hr. Based on the results, this simple and validated assay could readily be used in any pharmacokinetic studies using humans.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.2
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• pp.660-667
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• 2018

This study examined the optimal manufacturing conditions of RDF using heat-dried sludge from sewage treatment plant in Cheonan with the oil-drying method. The amounts of oil evaporation and oil drying of the heat-dried sludge were measured at different temperatures to evaluate the value of the product. The performance of the product was then measured using a calorimeter and TGA. In addition, the concentration of odor, NH3, H2S, and TVOC during drying was determined using a portable odor-meter. Ingredient analysis was performed by EDS. Considering mass-production, the oil to heat-dried sludge weight ratio was fixed to 4:1. At $130^{\circ}C$, only physical mixing occurred after the instantaneous drying of internal water. Considering the eco-friendly aspects, there was no significant difference in the drying efficiency between $160^{\circ}C$ and $190^{\circ}C$. Therefore, the optimal conditions were a drying temperature of $160^{\circ}C$ within 5 minutes. Finally, the RDF manufactured in this study and fuel used in the thermal power plants were compared. The calorific value was 4,449kcal/kg, the water content was 2% and the ash content was 34%, which is higher than the fuel of thermal power plants. Therefore, it is believed that coal energy as well as wood pellets can be replaced.