• Journal of Ecology and Environment
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• v.46 no.4
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• pp.282-291
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• 2022

Background: The Arctic permafrost stores enormous amount of carbon (C), about one third of global C stocks. However, drastically increasing temperature in the Arctic makes the stable frozen C stock vulnerable to microbial decomposition. The released carbon dioxide from permafrost can cause accelerating C feedback to the atmosphere. Soil organic matter (SOM) composition would be the basic information to project the trajectory of C under rapidly changing climate. However, not many studies on SOM characterization have been done compared to quantification of SOM stocks. Thus, the purpose of our study is to determine soil properties and molecular compositions of SOM in four different Arctic regions. We collected soils in different soil layers from 1) Cambridge Bay, Canada, 2) Council, Alaska, USA, 3) Svalbard, Norway, and 4) Zackenberg, Greenland. The basic soil properties were measured, and the molecular composition of SOM was analyzed through pyrolysis-gas chromatography/mass spectrometry (py-GC/MS). Results: The Oi layer of soil in Council, Alaska showed the lowest soil pH and the highest electrical conductivity (EC) and SOM content. All soils in each site showed increasing pH and decreasing SOC and EC values with soil depth. Since the Council site was moist acidic tundra compared to other three dry tundra sites, soil properties were distinct from the others: high SOM and EC, and low pH. Through the py-GC/MS analysis, a total of 117 pyrolysis products were detected from 32 soil samples of four different Arctic soils. The first two-axis of the PCA explained 38% of sample variation. While short- and mid-hydrocarbons were associated with mineral layers, lignins and polysaccharides were linked to organic layers of Alaska and Cambridge Bay soil. Conclusions: We conclude that the py-GC/MS results separated soil samples mainly based on the origin of SOM (plants- or microbially-derived). This molecular characteristics of SOM can play a role of controlling SOM degradation to warming. Thus, it should be further investigated how the SOM molecular characteristics have impacts on SOM dynamics through additional laboratory incubation studies and microbial decomposition measurements in the field.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.1
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• pp.48-55
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• 2022

This study uses the recovered water as mixing water and artificial lightweight aggregate pre-wetting water as part of a study to increase the recycling rate and reduce greenhouse gas of the ready-mixed concrete recovered during the concrete transport process, and cement fine powder of blast furnace slag(BFS) and fly ash(FA). The engineering characteristics of the three-component lightweight aggregate mortar used as a substitute were reviewed. For this purpose, the flow, dry unit mass, compressive strength, drying shrinkage, neutralization depth, and chloride ion penetration resistance of the three-component lightweight aggregate mortar were measured. When used together with the formulation, when 15 % of BFS and 5 % of FA were used, it was found to be positive in improving the compressive strength and durability of the mortar.

• Journal of Aerospace System Engineering
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• v.16 no.5
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• pp.26-34
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• 2022

The propulsion system of geostationary orbiting satellites is typically used to raise the orbit into a transfer orbit, maintain the orbital position in the south/north, east/west direction in regular operation, and accumulate momentum in the south/north and east/west direction. Recently, when an electric propulsion system is used in a geostationary orbit satellite, the payload capacity can be increased by about 40% compared to a chemical propulsion system. However, despite these advantages, using an electric propulsion system has several limitations that should apply to all geostationary orbiting satellites. This paper discusses the operational constraints to consider when developing an indigenous geostationary satellite using a fully electric propulsion, radiation exposure, and control mechanism design due to unit displacement and floating ground-design. A high-voltage control unit for electric drives were analyzed.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1999.10a
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• pp.59-59
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• 1999

In this study, planer inductively coupled $Cl_2$ based plasmas were used to etch InGaN and the effects of plasma conditions on the InGaN etch properties have been characterized using quadrupole mass spectrometry(QMS) and optical emission spectroscopy(OES). As process conditions used to study the effects of plasma characteristics on the InGaN etch properties, $Cl_2$ was used as the main etch gas and $CHF_3,{\;}CH_4$, and Ar were used as additive gases. Operational pressure was varied from SmTorr to 3OmTorr, inductive power and bias voltage were varied from 400W to 800W and -50V to -250V, respectively while the substrate temperature was fixed at 50 centigrade. For the $Cl_2$ plasmas, selective etching of GaN to InGaN was obtained regardless of plasma conditions. The small addition of $CHF_3$ or Ar to $Cl_2$ and the decrease of pressure generally increased InGaN etch rates. The selective etching of InGaN to GaN could be obtained by the reduction of pressure to l5mTorr in $CI_2/IO%CHF_3{\;}or{\;}CI_2/IO%Ar$ plasma. The enhancement of InGaN etch rates was related to the ion bombardment for $CI_2/Ar$ plasmas and the formation of $CH_x$ radicals for $CI_2/CHF_3(CH_4)$ plasmas.

• Geomechanics and Engineering
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• v.34 no.6
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• pp.697-726
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• 2023

Brittleness as an important property of rock plays a crucial role both in the failure process of intact rock and rock mass response to excavation in engineering geological and geotechnical projects. Generally, rock brittleness indices are calculated from the mechanical properties of rocks such as uniaxial compressive strength, tensile strength and modulus of elasticity. These properties are generally determined from complicated, expensive and time-consuming tests in laboratory. For this reason, in the present research, an attempt has been made to predict the rock brittleness indices from simple, inexpensive, and quick laboratory test results namely dry unit weight, porosity, slake-durability index, P-wave velocity, Schmidt rebound hardness, and point load strength index using multiple linear regression, exponential regression, support vector machine (SVM) with various kernels, generating fuzzy inference system, and regression tree ensemble (RTE) with boosting framework. So, this could be considered as an innovation for the present research. For this purpose, the number of 39 rock samples including five igneous, twenty-six sedimentary, and eight metamorphic were collected from different regions of Iran. Mineralogical, physical and mechanical properties as well as five well known rock brittleness indices (i.e., B₁, B₂, B₃, B₄, and B₅) were measured for the selected rock samples before application of the above-mentioned machine learning techniques. The performance of the developed models was evaluated based on several statistical metrics such as mean square error, relative absolute error, root relative absolute error, determination coefficients, variance account for, mean absolute percentage error and standard deviation of the error. The comparison of the obtained results revealed that among the studied methods, SVM is the most suitable one for predicting B₁, B₂ and B₅, while RTE predicts B₃ and B₄ better than other methods.

• Steel and Composite Structures
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• v.46 no.3
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• pp.385-401
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• 2023

Steel is becoming increasingly popular due to its high strength, excellent ductility, great assembly performance, and recyclability. In reality, steel structures serving for a long time in atmospheric, industrial, and marine environments inevitably suffer from corrosion, which significantly decreases the durability and the service life with the exposure time. For the mechanical properties of corroded steel, experimental studies are mainly conducted. The existing numerical analyses only evaluate the mechanical properties based on corroded morphology at the isolated time-in-point, ignoring that this morphology varies continuously with corrosion time. To solve this problem, the relationships between pit depth expectation, standard deviation, and corrosion time are initially constructed based on a large amount of wet-dry cyclic accelerated test data. Successively, based on that, an in-situ pitting evolution method for evaluating the residual tensile strength of corroded steel is proposed. To verify the method, 20 repeated simulations of mass loss rates and mechanical properties are adopted against the test results. Then, numerical analyses are conducted on 135 models of corrosion pits with different aspect ratios and uneven corrosion degree on two corroded surfaces. Results show that the power function with exponents of 1.483 and 1.091 can well describe the increase in pit depth expectation and standard deviation with corrosion time, respectively. The effect of the commonly used pit aspect ratios of 0.10-0.25 on yield strength and ultimate strength is negligible. Besides, pit number ratio α equating to 0.6 is the critical value for the strength degradation. When α is less than 0.6, the pit number increases with α, accelerating the degradation of strength. Otherwise, the strength degradation is weakened. In addition, a power function model is adopted to characterize the degradation of yield strength and ultimate strength with corrosion time, which is revised by initial steel plate thickness.

• Restorative Dentistry and Endodontics
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• v.45 no.4
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• pp.45.1-45.8
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• 2020

Objective: The aim of this study was to introduce a gelatin/bovine serum albumin (BSA) tissue standard, which provides dissolution properties identical to those of biological tissues. Further, the study evaluated whether the utilization of endodontic activating devices led to enhanced phantom dissolution rates. Materials and Methods: Bovine pulp tissue was obtained to determine a benchmark of tissue dissolution. The surface area and mass of samples were held constant while the ratio of gelatin and BSA were varied, ranging from 7.5% to 10% gelatin and 5% BSA. Each sample was placed in an individual test tube that was filled with an appropriate sodium hypochlorite solution for 1, 3, and 5 minutes, and then removed from the solution, blotted dry, and weighed again. The remaining tissue was calculated as the percent of initial tissue to determine the tissue dissolution rate. A radiopaque agent (sodium diatrizoate) and a fluorescent dye (methylene blue) were added to the phantom to allow easy quantification of phantom dissolution in a canal block model when activated using ultrasonic (EndoUltra) or sonic (EndoActivator) energy. Results: The 9% gelatin + 5% BSA phantom showed statistically equivalent dissolution to bovine pulp tissue at all time intervals. Furthermore, the EndoUltra yielded significantly more phantom dissolution in the canal block than the EndoActivator or syringe irrigation. Conclusions: Our phantom is comparable to biological tissue in terms of tissue dissolution and could be utilized for in vitro tests due to its injectability and detectability.

• The Korean Journal of Food And Nutrition
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• v.36 no.6
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• pp.543-550
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• 2023

Mulberry fruit is a superior source of polyphenols, especially anthocyanin, and has a long history of use as an edible fruit and traditional medicine. The anthocyanin composition of mulberry fruit from 15 Korean cultivars was analyzed by ultra-performance liquid chromatography diode array detector with quadrupole time of flight/mass spectrometry (UPLC-DAD-QToF/MS) based on a cyanin internal standard. The four glycosides were identified by comparison with authentic standards and published reports. The major anthocyanin was cyanidin 3-O-glucoside (71.7%), followed by cyanidin 3-O-rutinoside (26.6%). The minor components (total of 1.7%) were pelargonidin 3-O-glucoside and pelargonidin 3-O-rutinoside. The total anthocyanin content (mg/100 g, dry weight) of mulberry fruit varied by cultivar and ranged from 471.5±4.0 (Su Hong) to 4,700.2±54.0 (Gwa Sang2). Among the 15 cultivars examined, Gwa Sang2 showed the highest level of cyanidin 3-O-glucoside (3,133.4±32.6), which was 9-fold higher than that of Su Hong (351.5±3.4). In conclusion, anthocyanin profiles, including pelargonidin 3-O-glucoside and pelargonidin 3-O-rutinoside, were reported for the first time from 15 Korean mulberry fruit cultivars. The results will contribute valuable information on pharmaceutical properties, breeding superior mulberry cultivars, and food industries.

• The Korean Journal of Food And Nutrition
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• v.36 no.6
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• pp.506-514
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• 2023

Reported positive ion fragmentation of phenolic acid derivatives in rice (Oryza sativa L.) were summarized based on the literature. A total of eight phenolic acids (4 derivatives of ferulic acid, 3 derivatives of sinapic acid and p-coumaric acid) were isolated and identified from rice (raw and steamed) using UPLC-DAD-QToF/MS. Results revealed that 6-O-feruloylsurose was the major component with 3'-O-sinapoylsucorse being tentatively identified in Oryza sativa L. for the first time as a new hydroxycinnamoyl derivative in rice grains. In our study, raw brown rice had the highest phenolic acid contents with Samkwang showing higher phenolic acid content than Saeilmi and Sindongjin (12.41 vs. 7.89 and 3.10 mg/100 g dry weight, respectively). Of all varieties, brown rice had higher phenolic acid contents than white rice. These contents decreased considerably when rice was steamed whereas, p-coumaric acid and ferulic acid contents were increased. Additionally, contents of rice (raw and steamed) can be used as a fundamental report for new rice varieties.

• Journal of the Korean Wood Science and Technology
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• v.52 no.1
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• pp.13-30
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• 2024

Swietenia mahagoni is one of the commercial timbers in Indonesia. Mahogany heartwood is an important characteristic as it relates to the natural durability and aesthetics of the wood. Lipophilic extractives are known to be involved in the heartwood formation process. Therefore, this study aims to determine the lipophilic compounds associated with heartwood formation. The n-hexane extract from sapwood and heartwood samples (1 to 5 years) was analyzed by gas chromatography-mass spectrometry. The results showed that the content of n-hexane extract ranged from 0.76% to 2.45% based on dry wood. The main group of compounds identified in the lipophilic fraction consisted of sterols (β-sitosterol, stigmasterol, campasterol, and cyclolaudenol), fatty acids (palmitic, oleic, linoleic, and stearic acid), and hydrocarbons (pentadecane, 1-octadecane, hexadecane, cyclotetracosane, cycloeicosane, and cyclooctacosane) after heartwood formation. In addition, the hydrocarbon fraction was the largest, followed by sterols, fatty acids, and 1-heneicosanol. In the radial variation, the distribution of fatty acids was greater in the sapwood than in the heartwood (4-year-old). However, the reverse pattern was found at the age of 5 years. The lipophilic fraction was generally more abundant in the heartwood compared to the sapwood, especially at 5 years of age, with much higher levels than when the heartwood was forming (4 years). These findings show that when the heartwood formation begins, the lipid composition was not fully metabolized at the beginning of heartwood formation compared to 5-year-old trees.