• Transactions of the Korean hydrogen and new energy society
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• v.34 no.5
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• pp.456-464
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• 2023

In this study, a compact hydrogen liquefaction system was constructed with the aim of creating a data storage and monitoring program for liquid hydrogen production. This program was designed to receive and record signals from diverse control equipment through the LabVIEW software. A range of measurement instruments were devised to collect data, encompassing variables such as flow rate, pressure, temperature, and liquid level. As a result, it was possible to directly check the production of liquid hydrogen by obtaining various data of condensed liquid hydrogen. In addition, it was confirmed that long-term storage of liquid hydrogen is possible by developing automatic ON/OFF through the LabVIEW program.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.5
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• pp.131-138
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• 2023

In this paper, a free space optical communication device that can be used in a mobile base station of several km or less was fabricated and its characteristics were investigated. To overcome the loss due to atmospheric transmission, an optical fiber amplifier (EDFA) with an output of 23 dBm or more was used. In order to increase the focusing speed and miniaturization of the laser beam, an optical lens was manufactured, and a transmission lens was designed to have beam divergence within the range of 1.5 to 1.8 [mrad]. A PT module that controls PAN/TILT was fabricated in order to reduce pointing errors and effective automatic alignment between transceiver devices. In this study, Reed-Solomon (RS) code was used to maintain the transmission quality above a certain level. It was manufactured to be able to communicate at a wireless distance of 300m in a weather situation with visibility of 300m. For performance measurement, it was measured using BERT and eye pattern analyzer, and it was confirmed that BER can be maintained at 2.5Gbps.

• The Korean Journal of Applied Statistics
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• v.37 no.3
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• pp.265-282
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• 2024

Research in the area of financial portfolio optimization, with the dual goals of increasing expected returns and reducing financial risk, has actively explored various risk measurement indicators. At the same time, the incorporation of various penalty terms to construct efficient portfolios with limited assets has been investigated. In this study, we present a novel portfolio optimization formula that combines the mean-shortfall portfolio and the SLOPE penalty term. Specifically, we formulate this optimization expression, which differs from linear programming, by introducing new variables and using the alternating direction method of multipliers (ADMM) algorithms. Through simulations, we validate the automatic grouping property of the SLOPE penalty term within the proposed mean-shortfall portfolio. Furthermore, using the model introduced in this paper, we propose and evaluate four different types of portfolio compositions relevant to real-world investment scenarios through empirical data analysis.

• Korean Circulation Journal
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• v.54 no.7
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• pp.382-394
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• 2024

Background and Objectives: Fractional flow reserve (FFR) is an invasive standard method to identify ischemia-causing coronary artery disease (CAD). With the advancement of technology, FFR can be noninvasively computed from coronary computed tomography angiography (CCTA). Recently, a novel simpler method has been developed to calculate onsite CCTA-derived FFR (CT-FFR) with a commercially available workstation. Methods: A total of 319 CAD patients who underwent CCTA, invasive coronary angiography, and FFR measurement were included. The primary outcome was the accuracy of CT-FFR for defining myocardial ischemia evaluated with an invasive FFR as a reference. The presence of ischemia was defined as FFR ≤0.80. Anatomical obstructive stenosis was defined as diameter stenosis on CCTA ≥50%, and the diagnostic performance of CT-FFR and CCTA stenosis for ischemia was compared. Results: Among participants (mean age 64.7±9.4 years, male 77.7%), mean FFR was 0.82±0.10, and 126 (39.5%) patients had an invasive FFR value of ≤0.80. The diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of CT-FFR were 80.6% (95% confidence interval [CI], 80.5-80.7%), 88.1% (95% CI, 82.4-93.7%), 75.6% (95% CI, 69.6-81.7%), 70.3% (95% CI, 63.1-77.4%), and 90.7% (95% CI, 86.2-95.2%), respectively. CT-FFR had higher diagnostic accuracy (80.6% vs. 59.1%, p<0.001) and discriminant ability (area under the curve from receiver operating characteristic curve 0.86 vs. 0.64, p<0.001), compared with anatomical obstructive stenosis on CCTA. Conclusions: This novel CT-FFR obtained from an on-site workstation demonstrated clinically acceptable diagnostic performance and provided better diagnostic accuracy and discriminant ability for identifying hemodynamically significant lesions than CCTA alone.

• Journal of Korea Water Resources Association
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• v.47 no.4
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• pp.371-384
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• 2014

This study developed a new algorithm of extreme rainfall extraction based on the Communication, Ocean and Meteorological Satellite (COMS) and the Tropical Rainfall Measurement Mission (TRMM) Satellite image data and evaluated its applicability for the heavy rainfall event in July-2011 in Seoul, South Korea. The power-series-regression-based Z-R relationship was employed for taking into account for empirical relationships between TRMM/PR, TRMM/VIRS, COMS, and Automatic Weather System(AWS) at each elevation. The estimated Z-R relationship ($Z=303R^{0.72}$) agreed well with observation from AWS (correlation coefficient=0.57). The estimated 10-minute rainfall intensities from the COMS satellite using the Z-R relationship generated underestimated rainfall intensities. For a small rainfall event the Z-R relationship tended to overestimated rainfall intensities. However, the overall patterns of estimated rainfall were very comparable with the observed data. The correlation coefficients and the Root Mean Square Error (RMSE) of 10-minute rainfall series from COMS and AWS gave 0.517, and 3.146, respectively. In addition, the averaged error value of the spatial correlation matrix ranged from -0.530 to -0.228, indicating negative correlation. To reduce the error by extreme rainfall estimation using satellite datasets it is required to take into more extreme factors and improve the algorithm through further study. This study showed the potential utility of multi-geostationary satellite data for building up sub-daily rainfall and establishing the real-time flood alert system in ungauged watersheds.

• Korean Journal of Environment and Ecology
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• v.32 no.3
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• pp.303-312
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• 2018

This study was conducted to investigate the relationship between the decrease of forest biomass by forest thinning and the change of temperature in the natural forest by measuring forest biomass and temperature before and after forest thinning in the Pusan National University forest where afforestation had been carried out. We intended to investigate the relationship between the forest biomass, estimated by calculating the Basal area, Crown area and Crown volume using the same formula to the same quadrat before and after forest thinning, and the forest temperature. Temperature measurement was carried out on April 20, 2016 through 28 before forest thinning, July 26, 2016 through November 4 around the time of forest thinning, and April 15, 2017 through May 8 after forest thinning. A temperature data logger was installed to point north at the height of 2.0 m above the ground in the center of the quadrat to record data every 10 minutes during the measurement periods. We used the AWS (Automatic Weather Station) data of the Dongnae-gu area located in the nearby city because it was difficult to set the control group since the whole forest was the subject to the forest thinning. The analysis of the relationship between forest biomass change and temperature showed that the change in temperature inside the forest was the greatest in the midday (12:00 - 15: 00) and was highly correlated with the Crown volume in the forest biomass. The temperature increase was much larger (average $1.91^{\circ}C$) 1 year after forest thinning than immediately after forest thinning (average $0.74^{\circ}C$). The comparison of the decrease rate of Crown volume and the increase in temperature showed that the Pitch pine community, which showed the highest decrease of Crown volume by 15.4%, recorded the highest temperature rise of $1.06^{\circ}C$ immediately after forest thinning and $2.49^{\circ}C$ 1 year after forest thinning. The Pitch pine-Korean red pine community, which showed the lowest Crown volume reduction rates with 5.0%, recorded no significant difference immediately after forest thinning but a temperature rise of $0.92^{\circ}C$ 1 year after forest thinning. The results confirmed that the decrease of forest biomass caused by forest thinning led to a rapid increase of the internal temperature. The fact that the temperature increase was more severe after 1 year than immediately after forest thinning confirmed that the microclimate changes due to the removed biomass cannot be recovered in a short time.

• The Korean Journal of Nuclear Medicine Technology
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• v.16 no.1
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• pp.44-49
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• 2012

Purpose: In the whole body PET/CT scan, it is natural to lift the patient's arm for its quality improvement. However, when the lesion is located in head and neck, the arms should be located lower. This study was designed to compare the CT effective dose for each arm position applying Automatic Exposure Control (AEC). Materials and Methods: 45 patients who had $^{18}F$-FDG whole body PET/CT scan were studied with Biograph Truepoint 40 (SIEMENS, GERMANY), Biograph Sensation 16 (SIEMENS, GERMANY), Discovery STe 8 (GE healthcare, USA). The CT effective dose of 15 patients for each equipment was measured and comparatively analyzed in both arm-lifted position and lower-arm position. ImPACT v1.0 program was used as the method of measurement for CT effective dose. For the statistics analysis, Paired t-test which paired with SPSS 18.0 statistic program was applied. Results: In the case of arm-lifted, it was measured as $6.33{\pm}0.93mSv$ for Biograph Sensation 16, $8.01{\pm}1.34mSv$ for Biograph Truepoint 40, and $9.69{\pm}2.32mSv$ for Discovery STe 8. When arms are located lower position, it was measure as $6.97{\pm}0.76mSv$, $8.95{\pm}1.85mSv$, $13.07{\pm}2.87mSv$ for each. CT effective dose according to the arm position was 9.2% for Biograph Truepoint 40, 10.5% for Biograph Sensation 16, and 25.9% for Discovery Ste 8. The statistics analysis showed the meaningful difference ($p$<0.05). Conclusion: For the whole body PET/CT case, CT effective dose applying AEC was decreased the radiation exposure of the patients when the arm was lifted for 15.2% of average value. The patient who has no lesion in head and neck would decrease the artifact occurrence in objective part and lower the CT effective dose. Also, for the patient who had lesion in head and neck, the artifact in objective part can be lower by putting the arms down, the fact that CT effective dose increases should be concerned in its whole body PET/CT scan.

• The Korean Journal of Nuclear Medicine
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• v.36 no.6
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• pp.381-391
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• 2002

Purpose: The presence of perfusion defect may influence the left ventricular mass (LVM) measurement by quantitative gated myocardial perfusion SPECT (QGS), and ischemic myocardium, usually showing perfusion defect may produce post-stress LV dysfunction. This study was aimed to evaluate the effects of extent and reversibility of perfusion defect on the automatic measurement of LVM by QGS and to investigate the effect of reversibility of perfusion defect on post-stress LV dysfunction. Subjects and Methods: Forty-six patients (male/female=34:12, mean age=64years) with perfusion defect on myocardial perfusion SPECT underwent rest and post-stress QGS. Forty patients (87%) showed reversible defect. End-diastolic volume (EDV), end-systolic volume (ESV), LV ejection fraction (EF), and LV myocardial volume were obtained from QGS by AutoQUANT program, and LVM was calculated by multiplying the LV myocardial volume by the specific gravity of myocardium. Results: LVMs measured at rest and post-stress QGS showed good correlation, and higher correlation was founded in the subjects with fixed perfusion defect and with small defect (smaller than 20%). There were no significant differences in EDVs, ESVs and EFs between obtained by rest and post-stress QGS un patients with fixed myocardial defect. Whereas, EF obtained by post-stress QGS was lower than that by rest QGS in patients with reversible defect and 10 (25%) of them showed decreases in EF more than 5% in post-stress QGS, as compared to that of rest QGS. Excellent correlations of EDVs, ESVs, EFs between rest and post-stress QGS were noted. Patients with fixed defect had higher correlation between EDVs, ESVs, EFs than patients with reversible defect. Conclusion: These results suggest that perfusion defect can affect LVM measurement by QGS and patients with reversible defect shows post-stress LV dysfunction more frequently than patients with fixed perfusion defect.

• Analytical Science and Technology
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• v.17 no.6
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• pp.496-513
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• 2004

This study was carried out to evaluate the performance of sampling and analytical methodology used for the measurement of toxic volatile organic compounds (VOCs) in the ambient air. VOCs were determined by the adsorbent tube sampling and automatic thermal desorption coupled with GC/MSD analysis. Target analytes were 33 compounds including major aromatic compounds such as BTEX, and halogenated compounds. The methodology was investigated with a wide range of different adsorbents which are commercially available and have been frequently adopted for the VOC measurement. A total of 10 adsorbents were tested in this study: 6 carbon-based adsorbents such as Carbotrap, Carbopack B, Carbosieve S-III, Carboxen 1000, Carbotrap C, Activated Charcoal; and 4 polymer-based adsorbents including Tenax, Porapak Q, Chromosorb 102, and Chromosorb 106. The sampling performance was evaluated with respect to the sampling capacity of VOCs with single-adsorbent and multiple-adsorbents methods for standard samples and field samples. As a result, the best adsorbents for single-adsorbent method in the sampling of toxic organic compounds (including benzene, toluene, xylenes etc.) appeared to be Carbotrap, Carbopack B and Tenax TA. On the other hand, Chromosorb 102, Chromosorb 106 and Porapak Q were found to be unsuitable adsorbents for VOC measurement based on thermal desorption method. Multi-adsorbent packings were evaluated with 4 carbon-based adsorbents, which classified by 3 combination sets of double adsorbents and 2 combination sets of triple adsorbents. The results indicated that the most suitable combination for toixc VOC measurements is Carbotrap C with Carbotrap. Multi-sorbents tubes packed with a strong adsorbent such as Carbosieve S-III or Carboxen 1000 were found to be relatively unsuitable for several compounds, not only owing to the effect of migration of adsorbed compounds from weaker adsorbent to stronger adsorbent, but to hydrophobic nature of the adsorbents. Therefore, it should be addressed that selection of a proper adsorbent (or combination of multi sorbents) is extremely important to obtain reliable data for the concentrations of toxic VOCs in indoor and outdoor environments.

• Progress in Medical Physics
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• v.22 no.1
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• pp.42-51
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• 2011

Nuclear medicine images (SPECT, PET) were widely used tool for assessment of myocardial viability and perfusion. However it had difficult to define accurate myocardial infarct region. The purpose of this study was to investigate methodological approach for automatic measurement of rat myocardial infarct size using polar map with adaptive threshold. Rat myocardial infarction model was induced by ligation of the left circumflex artery. PET images were obtained after intravenous injection of 37 MBq $^{18}F$-FDG. After 60 min uptake, each animal was scanned for 20 min with ECG gating. PET data were reconstructed using ordered subset expectation maximization (OSEM) 2D. To automatically make the myocardial contour and generate polar map, we used QGS software (Cedars-Sinai Medical Center). The reference infarct size was defined by infarction area percentage of the total left myocardium using TTC staining. We used three threshold methods (predefined threshold, Otsu and Multi Gaussian mixture model; MGMM). Predefined threshold method was commonly used in other studies. We applied threshold value form 10% to 90% in step of 10%. Otsu algorithm calculated threshold with the maximum between class variance. MGMM method estimated the distribution of image intensity using multiple Gaussian mixture models (MGMM2, ${\cdots}$ MGMM5) and calculated adaptive threshold. The infarct size in polar map was calculated as the percentage of lower threshold area in polar map from the total polar map area. The measured infarct size using different threshold methods was evaluated by comparison with reference infarct size. The mean difference between with polar map defect size by predefined thresholds (20%, 30%, and 40%) and reference infarct size were $7.04{\pm}3.44%$, $3.87{\pm}2.09%$ and $2.15{\pm}2.07%$, respectively. Otsu verse reference infarct size was $3.56{\pm}4.16%$. MGMM methods verse reference infarct size was $2.29{\pm}1.94%$. The predefined threshold (30%) showed the smallest mean difference with reference infarct size. However, MGMM was more accurate than predefined threshold in under 10% reference infarct size case (MGMM: 0.006%, predefined threshold: 0.59%). In this study, we was to evaluate myocardial infarct size in polar map using multiple Gaussian mixture model. MGMM method was provide adaptive threshold in each subject and will be a useful for automatic measurement of infarct size.