• Composites Research
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• v.19 no.3
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• pp.23-28
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• 2006

Carbon nanotubes reinforced copper matrix laminated nanocomposites were developed and the mechanical properties were evaluated by using micro-tensile testing system. Sandwich-type laminated structure constituted with carbon nanotube layers as a reinforcement and electroplated copper matrix were fabricated by a new processing approach based on selective dip-coating of carbon nanotubes. The mechanical properties of nanocomposites were improved due to an enhanced load sharing capacity of carbon nanotubes homogeneously distributed within the in-plane direction, as well as a bridging effect of carbon nanotubes along the out-of-plane direction between the upper and lower matrices. The universality of the layering approach is applicable to a wide range of functional materials, and here we demonstrate its potential use in reinforcing composite materials.

• Journal of the Korea Society of Computer and Information
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• v.14 no.1
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• pp.135-143
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• 2009

Recently, in the mobile device, the increase of the need for encoding and decoding of high-resolution images requires an efficient implementation of the image codec. This paper proposes a time-optimized color conversion method for the JPEG decoder, which reduces the number of calculations in the color conversion by the rearrangement of arithmetic operations being possible due to the linearity of the IDCT and the color conversion matrices and brings down the time complexity of the color conversion itself by the integer mapping replacing floating-point operations to the optimal fixed-point shift and addition operations, eventually reducing the time complexity of the JPEG decoder. And the proposed method compensates a decline of image quality incurred by the quantification error of the operation arrangement and the integer mapping by using the multi-mode chrominance reconstruction. The performance evaluation performed on the development platform of embedded systems showed that, compared to previous color conversion methods, the proposed method greatly reduces the image decoding time, minimizing the distortion of decoded images.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6D
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• pp.895-904
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• 2008

CWR (Continuous Welded Rail) may be broken when a temperature drop below the neutral temperature changes in axial force, causing tensile fracture and rail gap, in winter. Rail-breaks may lead to the damage of the rail and wheel by dynamic load, and the reduction of running safety if not detected before the passage of a train. In this study, the track and train coupled model with open gap for dynamic interaction analysis, is proposed. Linear track and train systems is coupled by the nonlinear Herzian contact spring and the complete system matrices of total track-train system is constructed. And the interaction phenomenon considering open gap, was defined by assigning the irregularity functions between the two sides of a gap. Time history analysis, which have an iteration scheme such as $Newmark-{\beta}$ method based on Modified Newton-Raphson methods, was performed to solve the nonlinear equation. Finally, numerical studies are performed to assess the effect of various parameters of system, apply to various speeds, open gap size and the support stiffness of rail.

• Journal of Radiation Protection and Research
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• v.48 no.2
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• pp.90-99
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• 2023

Background: Quantitative risk assessments should be accompanied by uncertainty analyses of the risk models employed in the calculations. In this study, we aim to develop a computational code named SUMRAY for use in cancer risk projections from radiation exposure taking into account uncertainties. We also aim to make SUMRAY publicly available as a resource for further improvement of risk projection. Materials and Methods: SUMRAY has two versions of code written in R and Python. The risk models used in SUMRAY for all-solid-cancer mortality and incidence were those published in the Life Span Study of a cohort of the atomic bomb survivors in Hiroshima and Nagasaki. The confidence intervals associated with the evaluated risks were derived by propagating the statistical uncertainties in the risk model parameter estimates by the Monte Carlo method. Results and Discussion: SUMRAY was used to calculate the lifetime or time-integrated attributable risks of cancer under an exposure scenario (baseline rates, dose[s], age[s] at exposure, age at the end of follow-up, sex) specified by the user. The results were compared with those calculated using another well-known web-based tool, Radiation Risk Assessment Tool (RadRAT; National Institutes of Health), and showed a reasonable agreement within the estimated confidential interval. Compared with RadRAT, SUMRAY can be used for a wide range of applications, as it allows the risk projection with arbitrarily specified risk models and/or population reference data. Conclusion: The reliabilities of SUMRAY with the present risk-model parameters and their variance-covariance matrices were verified by comparing them with those of the other codes. The SUMRAY code is distributed to the public as an open-source code under the Massachusetts Institute of Technology license.

• Journal of Sensor Science and Technology
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• v.32 no.4
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• pp.223-231
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• 2023

An integrated-optical biochemical sensor structure that can perform homogeneous and surface sensing using a 2×2 balanced-bridge Mach-Zehnder interference structure based on the optimized SOI slot optical waveguide was described, and its performance and characteristics were evaluated. Equations for the two output optical powers were derived and examined using the transfer matrices of a 3-dB coupler and phase shifter (channel waveguide). The length of the 3-dB coupler was determined such that the two output optical powers were same using these formulas. In homogeneous sensing, the effect of the refractive index of an analyte in the range of 1.33-1.36 on the two output optical power distributions was numerically derived, and the sensitivity was calculated based on each output and the difference between the two outputs, the former and the latter being 7.5796-19.0305 [au/RIU] and 15.2601-38.1351 [au/RIU], respectively. In the case of surface sensing, the sensitivity range of the refractive index of 1.337 based on each of the two outputs was calculated as -2.2490--3.5854 [au/RIU] and 1.2194-3.8012 [au/RIU], and the sensitivity range of 4.8048-7.0694 [au/RIU] was confirmed based on the difference between the two outputs.

• Korean Journal of Environmental Agriculture
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• v.41 no.4
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• pp.288-309
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• 2022

BACKGROUND: The objective of this study was to develop a comprehensive and simple method for the simultaneous determination of 59 veterinary drug residues in livestock products for safety management. METHODS AND RESULTS: For sample preparation, we used a modified liquid extraction method, according to which the sample was extracted with 80% acetonitrile followed by incubation at -20℃ for 30 min. After centrifugation, an aliquot of the extract was evaporated to dryness at 40℃ and analyzed using liquid chromatography combined with tandem mass spectrometry. The method was validated at three concentration levels for beef, pork, chicken, egg, and milk in accordance with the Codex Alimentarius Commission/Guidelines 71-2009. Quantitative analysis was performed using a matrix-matched calibration. As a results, at least 52 (77.6%) out of 66 compounds showed the proper method validation results in terms of both recovery of the target compound and coefficient of variation required by Codex guidelines in livestock products. The limit of quantitation of the method ranged from 0.2 to 1119.6 ng g-1 for all matrices. CONCLUSION(S): This method was accurate, effective, and comprehensive for 59 veterinary drugs determination in livestock products, and can be used to investigate veterinary drugs from different chemical families for safety management in livestock products.

• Analytical Science and Technology
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• v.21 no.5
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• pp.397-402
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• 2008

Uranium dioxide was dissolved with nitric acid and a trace amount of HF. The analytical conditions of a spectrophotometer were investigated to determine a trace amount of silicon in the uranium matrices without a separation process. The effects of a trace amount of HF on the determination of silicon were examined. Boric acid was used to eliminate HF the interference in the colorimetric process. The recovery of silicon in the presence of a trace amount of HF in uranium solutions with or without saturated boric acid was $103.3{\pm}0.8$ and $76.6{\pm}6.8%$, respectively. The amount of saturated boric acid did not affect the recovery of the silicon. Therefore it was possible for this procedure to measure a trace amount of silicon in a uranium matrix without a separation by a UV-VIS spectrophotometry.

• Analytical Science and Technology
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• v.20 no.2
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• pp.131-137
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• 2007

The urania-gadolinia fuels were dissolved with nitric acid. The analytical conditions of ICP-AES for the direct determinations of gadolinium in the uranium matrices without separation process were investigated. Based on the effect of uranium on gadolinium intensity, the best wavelength for gadolinium was 336.223 nm. The relative deviation of two methods, direct and indirect measurements with anion exchange chromatography, was less than 5 %. Therefore it was possible for this procedure directly to measure 5~10 wt.% of gadolinium in urania-gadolinia fuels without separation by ICP-AES.

• Korean Journal of Materials Research
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• v.33 no.7
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• pp.295-301
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• 2023

Thermoelectric (TE) energy harvesting, which converts available thermal resources into electrical energy, is attracting significant attention, as it facilitates wireless and self-powered electronics. Recently, as demand for portable/wearable electronic devices and sensors increases, organic-inorganic TE films with polymeric matrix are being studied to realize flexible thermoelectric energy harvesters (f-TEHs). Here, we developed flexible organic-inorganic TE films with p-type Bi_0.5Sb_1.5Te₃ powder and polymeric matrices such as poly(3,4-eethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and poly (vinylidene fluoride) (PVDF). The fabricated TE films with a PEDOT:PSS matrix and 1 wt% of multi-walled carbon nanotube (MWCNT) exhibited a power factor value of 3.96 µW·m^-1·K^-2 which is about 2.8 times higher than that of PVDF-based TE film. We also fabricated f-TEHs using both types of TE films and investigated the TE output performance. The f-TEH made of PEDOT:PSS-based TE films harvested the maximum load voltage of 3.4 mV, with a load current of 17.4 µA, and output power of 15.7 nW at a temperature difference of 25 K, whereas the f-TEH with PVDF-based TE films generated values of 0.6 mV, 3.3 µA, and 0.54 nW. This study will broaden the fields of the research on methods to improve TE efficiency and the development of flexible organic-inorganic TE films and f-TEH.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.162-162
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• 2022

Stormwater management is an essential component of land-use planning and development. Due to the additional challenges posed by climate change and urbanization, various stormwater management schemes have been developed to limit flood damages and ease water quality concerns. Nature-based solutions (NBS) are increasingly used as cost-effective measures to manage stormwater runoff from various land uses. Specifically, constructed wetlands were already considered as socially acceptable green stormwater infrastructures that are widely used in different countries. There is a large collection of published literature regarding the effectiveness or efficiency of constructed wetlands in treating stormwater runoff; however, metadata analyses using bibliographic information are very limited or seldomly explored. This study was conducted to determine the trends of publication regarding stormwater treatment wetlands using a bibliometric analysis approach. Moreover, the research productivity of various countries, authors, and institutions were also identified in the study. The Web of Science (WoS) database was utilized to retrieve bibliographic information. The keywords ("constructed wetland*" OR "treatment wetland*" OR "engineered wetland*" OR "artificial wetland*") AND ("stormwater*" or "storm water*") were used to retrieve pertinent information on stormwater treatment wetlands-related publication from 1990 up to 2021. The network map of keyword co-occurrence map was generated through the VOSviewer software and the contingency matrices were obtained using the Cortext platform (www.cortext.net). The results obtained from this inquiry revealed the areas of research that have been adequately explored by past studies. Furthermore, the extensive collection of published scientific literature enabled the identification of existing knowledge gaps in the field of stormwater treatment wetlands.