• Korean Journal of Optics and Photonics
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• v.33 no.5
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• pp.218-229
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• 2022

We have investigated reliable inspection methods for finding the defects generated during the manufacturing process of lightweight, large-aperture satellite telescope mirrors using silicon carbide, and we have measured the basic physical properties of the mirrors. We applied the advanced ceramic material (ACM) method, a combined method using liquid-silicon penetration sintering and chemical vapor deposition for the carbon molded body, to manufacture four SiC mirrors of different sizes and shapes. We have provided the defect standards for the reflectors systematically by classifying the defects according to the size and shape of the mirrors, and have suggested effective nondestructive methods for mirror surface inspection and internal defect detection. In addition, we have analyzed the measurements of 14 physical parameters (including density, modulus of elasticity, specific heat, and heat-transfer coefficient) that are required to design the mirrors and to predict the mechanical and thermal stability of the final products. In particular, we have studied the detailed measurement methods and results for the elastic modulus, thermal expansion coefficient, and flexural strength to improve the reliability of mechanical property tests.

• Journal of the Korea Convergence Society
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• v.13 no.5
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• pp.229-236
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• 2022

The goal of this research is to understand the extent to which active seniors' mobile app usage level affects their lifestyle and life satisfaction. For this, we surveyed for 15 days in early December 2021 targeting about 150 users nationwide. As the questionnaire content, the independent variable was "mobile app usage level", the parameter was "lifestyle", and the dependent variable was "life satisfaction". As a result of empirical analysis, reliability and exploratory factors between each variable were verified, and it was confirmed that internal consistency was secured. It was investigated that the concentration validity of each item was generally well confirmed. As a result of hypothesis testing by the structural equation, 'App usage level ⇨ Lifestyle' was 0.244, 'Lifestyle ⇨ Life satisfaction' 0.707, and 'App usage level ⇨ Life satisfaction 0.141' was adopted. This study shows that the higher the level of mobile app usage of active seniors, the higher the lifestyle. Also, the better the lifestyle, the better the quality of life. It is analyzed that life satisfaction will improve as the level of mobile app use increases. Therefore, in order to improve life satisfaction, it seems necessary to increase the level of app use and lifestyle.

• Phonetics and Speech Sciences
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• v.14 no.4
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• pp.45-56
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• 2022

This paper proposes an optimal methodology for automatically diagnosing and predicting the severity of the chronic kidney disease (CKD) using patients' utterances. In patients with CKD, the voice changes due to the weakening of respiratory and laryngeal muscles and vocal fold edema. Previous studies have phonetically analyzed the voices of patients with CKD, but no studies have been conducted to classify the voices of patients. In this paper, the utterances of patients with CKD were classified using the variety of utterance types (sustained vowel, sentence, general sentence), the feature sets [handcrafted features, extended Geneva Minimalistic Acoustic Parameter Set (eGeMAPS), CNN extracted features], and the classifiers (SVM, XGBoost). Total of 1,523 utterances which are 3 hours, 26 minutes, and 25 seconds long, are used. F1-score of 0.93 for automatically diagnosing a disease, 0.89 for a 3-classes problem, and 0.84 for a 5-classes problem were achieved. The highest performance was obtained when the combination of general sentence utterances, handcrafted feature set, and XGBoost was used. The result suggests that a general sentence utterance that can reflect all speakers' speech characteristics and an appropriate feature set extracted from there are adequate for the automatic classification of CKD patients' utterances.

• Composites Research
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• v.20 no.4
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• pp.31-41
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• 2007

Dome shape design methods of Filament Winding (FW) composite pressure vessel, which can suggest various dome contour according to the external loading conditions, were investigated analytically and numerically. The performance indices(PV/W) of the pressure vessels with same cylinder radius and boss opening but different dome shape were evaluated by finite element analysis under the internal pressure loading condition. The analysis results showed that as the dome shape becomes flat, the performance index decreases significantly due to the reduced burst pressure. Especially, for the case of the high value of the parameter ro, the ratio between the radii of the cylinder part and the boss opening, the flat dome is disadvantageous in the aspect of the weight reduction, and additional reinforcing dome design technique should be required to increase the burst pressure. For example, above ro=0.54 condition, the dome shape change according to the loading condition could cause the low burst pressure and increase of composite weight in dome region and is not recommendable except for the special case that maximum inner volume or sufficient space between skirt and dome is the primary design objective. However, at ro=0.35, the dome shape change brings not so significant differences in the performance of FW vessel.

• Investigative Magnetic Resonance Imaging
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• v.26 no.1
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• pp.10-19
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• 2022

Purpose: To evaluate whether the added value of contrast leakage information from dynamic susceptibility contrast magnetic resonance imaging (DSC MRI) is a better prognostic imaging biomarker than the cerebral blood volume (CBV) value in distinguishing true progression from pseudoprogression in glioblastoma patients. Materials and Methods: Forty-nine glioblastoma patients who had undergone MRI after concurrent chemoradiotherapy with temozolomide were enrolled in this retrospective study. Twenty features were extracted from the normalized relative CBV (nCBV) and extraction fraction (EF) map of the contrast-enhancing region in each patient. After univariable analysis, we used multivariable stepwise logistic regression analysis to identify significant predictors for differentiating between pseudoprogression and true progression. Receiver operating characteristic (ROC) analysis was employed to determine the best cutoff values for the nCBV and EF features. Finally, leave-one-out cross-validation was used to validate the best predictor in differentiating between true progression and pseudoprogression. Results: Multivariable stepwise logistic regression analysis showed that MGMT (O⁶-methylguanine-DNA methyltransferase) and EF max were independent differentiating variables (P = 0.004 and P = 0.02, respectively). ROC analysis yielded the best cutoff value of 95.75 for the EF max value for differentiating the two groups (sensitivity, 61%; specificity, 84.6%; AUC, 0.681 ± 0.08; 95% CI, 0.524-0.837; P = 0.03). In the leave-one-out cross-validation of the EF max value, the cross-validated values for predicting true progression and pseudoprogression accuracies were 69.4% and 71.4%, respectively. Conclusion: We demonstrated that contrast leakage information parameter from DSC MRI showed significance in differentiating true progression from pseudoprogression in glioblastoma patients.

• Korean Journal of Radiology
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• v.23 no.7
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• pp.720-731
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• 2022

Objective: We aimed to develop and test a deep learning algorithm (DLA) for fully automated measurement of the volume and signal intensity (SI) of the liver and spleen using gadoxetic acid-enhanced hepatobiliary phase (HBP)-magnetic resonance imaging (MRI) and to evaluate the clinical utility of DLA-assisted assessment of functional liver capacity. Materials and Methods: The DLA was developed using HBP-MRI data from 1014 patients. Using an independent test dataset (110 internal and 90 external MRI data), the segmentation performance of the DLA was measured using the Dice similarity score (DSS), and the agreement between the DLA and the ground truth for the volume and SI measurements was assessed with a Bland-Altman 95% limit of agreement (LOA). In 276 separate patients (male:female, 191:85; mean age ± standard deviation, 40 ± 15 years) who underwent hepatic resection, we evaluated the correlations between various DLA-based MRI indices, including liver volume normalized by body surface area (LV_BSA), liver-to-spleen SI ratio (LSSR), MRI parameter-adjusted LSSR (aLSSR), LSSR × LV_BSA, and aLSSR × LV_BSA, and the indocyanine green retention rate at 15 minutes (ICG-R15), and determined the diagnostic performance of the DLA-based MRI indices to detect ICG-R15 ≥ 20%. Results: In the test dataset, the mean DSS was 0.977 for liver segmentation and 0.946 for spleen segmentation. The Bland-Altman 95% LOAs were 0.08% ± 3.70% for the liver volume, 0.20% ± 7.89% for the spleen volume, -0.02% ± 1.28% for the liver SI, and -0.01% ± 1.70% for the spleen SI. Among DLA-based MRI indices, aLSSR × LV_BSA showed the strongest correlation with ICG-R15 (r = -0.54, p < 0.001), with area under receiver operating characteristic curve of 0.932 (95% confidence interval, 0.895-0.959) to diagnose ICG-R15 ≥ 20%. Conclusion: Our DLA can accurately measure the volume and SI of the liver and spleen and may be useful for assessing functional liver capacity using gadoxetic acid-enhanced HBP-MRI.

• Korean Journal of Radiology
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• v.20 no.4
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• pp.683-692
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• 2019

Objective: We aimed to evaluate correlations between computed tomography (CT) parameters and pulmonary function test (PFT) parameters according to disease severity in patients with chronic obstructive pulmonary disease (COPD), and to determine whether CT parameters can be used to predict PFT indices. Materials and Methods: A total of 370 patients with COPD were grouped based on disease severity according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) I-IV criteria. Emphysema index (EI), air-trapping index, and airway parameters such as the square root of wall area of a hypothetical airway with an internal perimeter of 10 mm (Pi10) were measured using automatic segmentation software. Clinical characteristics including PFT results and quantitative CT parameters according to GOLD criteria were compared using ANOVA. The correlations between CT parameters and PFT indices, including the ratio of forced expiratory volume in one second to forced vital capacity (FEV1/FVC) and FEV₁, were assessed. To evaluate whether CT parameters can be used to predict PFT indices, multiple linear regression analyses were performed for all patients, Group 1 (GOLD I and II), and Group 2 (GOLD III and IV). Results: Pulmonary function deteriorated with increase in disease severity according to the GOLD criteria (p < 0.001). Parenchymal attenuation parameters were significantly worse in patients with higher GOLD stages (P < 0.001), and Pi10 was highest for patients with GOLD III (4.41 ± 0.94 mm). Airway parameters were nonlinearly correlated with PFT results, and Pi10 demonstrated mild correlation with FEV1/FVC in patients with GOLD II and III (r = 0.16, p = 0.06 and r = 0.21, p = 0.04, respectively). Parenchymal attenuation parameters, airway parameters, EI, and Pi10 were identified as predictors of FEV₁/FVC for the entire study sample and for Group 1 (R² = 0.38 and 0.22, respectively; p < 0.001). However, only parenchymal attenuation parameter, EI, was identified as a predictor of FEV₁/FVC for Group 2 (R² = 0.37, p < 0.001). Similar results were obtained for FEV₁. Conclusion: Airway and parenchymal attenuation parameters are independent predictors of pulmonary function in patients with mild COPD, whereas parenchymal attenuation parameters are dominant independent predictors of pulmonary function in patients with severe COPD.

• Composites Research
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• v.37 no.5
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• pp.427-433
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• 2024

As the automotive industry transitions from internal combustion engine vehicles (ICEV) to battery electric vehicles (BEVs), customers are becoming increasingly aware of and demanding solutions to squeak noises, especially from audio, video, and navigation (AVN) components. These noises occur under relatively high load and low speed conditions and cannot be reproduced on commercial friction test equipment. Therefore, a new friction testing machine was developed and evaluated in this study. This machine is a pin-on-disk type tribometer that can set up the squeak noises test conditions for AVN component materials and quantitatively measure acceleration, sound pressure, and displacement due to friction. The developed equipment was evaluated through two types of tests: the noise evaluation of well-known contact pairs, and the comparison test of the friction coefficient repeatability. The test results confirm that the developed test machine can be utilized for the evaluation of the squeak noise. In addition, it was also found that the characteristics of squeak noise in high load and low speed conditions can be defined as groan noise. Moreover, displacement, friction force, acceleration was found to have a relationship with sound amplitude with relation of more than R² = 0.75. Acceleration can be a key parameter to predict squeak noise, since it has a strong correlation (R² = 0.94) in high load low speed conditions.

• Investigative Magnetic Resonance Imaging
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• v.18 no.2
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• pp.120-132
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• 2014

Purpose : To compare dynamic susceptibility contrast imaging, diffusion-weighted imaging, and susceptibility-weighted imaging (SWI) for the differentiation of tumor recurrence and delayed radiation therapy (RT)-related changes in patients treated with RT for primary brain tumors. Materials and Methods: We enrolled 24 patients treated with RT for various primary brain tumors, who showed newly appearing enhancing lesions more than one year after completion of RT on follow-up MRI. The enhancing-lesions were confirmed as recurrences (n=14) or RT-changes (n=10). We calculated the mean values of normalized cerebral blood volume (nCBV), apparent diffusion coefficient (ADC), and proportion of dark signal intensity on SWI (proSWI) for the enhancing-lesions. All the values between the two groups were compared using t-test. A multivariable logistic regression model was used to determine the best predictor of differential diagnosis. The cutoff value of the best predictor obtained from receiver-operating characteristic curve analysis was applied to calculate the sensitivity, specificity, and accuracy for the diagnosis. Results: The mean nCBV value was significantly higher in the recurrence group than in the RT-change group (P=.004), and the mean proSWI was significantly lower in the recurrence group (P<.001). However, no significant difference was observed in the mean ADC values between the two groups. A multivariable logistic regression analysis showed that proSWI was the only independent variable for the differentiation; the sensitivity, specificity, and accuracy were 78.6% (11 of 14), 100% (10 of 10), and 87.5% (21 of 24), respectively. Conclusion: The proSWI was the most promising parameter for the differentiation of newly developed enhancing-lesions more than one year after RT completion in brain tumor patients.

• Korean Journal of Acupuncture
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• v.30 no.4
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• pp.252-263
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• 2013

Objectives : Skin color deformation by cupping has been widely used as a diagnostic parameter in Traditional Korean Medicine(TKM). Skin color deformation such as ecchymoses and purpura is induced by local vacuum in a suction cup. Since existing studies have relied on a visual diagnostic method, there is a need to use the quantitative measurement method. Methods : We conducted an analysis of cross-polarization photographic images to assess the changes in skin color deformation. The skin color variation was analyzed using $L^*a^*b^*$ space and the skin erythema index(E.I.). The meridian theory in TKM indicates that the condition of primary internal organs is closely related to the skin color deformation at special acupoints. Before conducting these studies, it is necessary to evaluate whether or not skin color deformation is influenced by muscle condition. Hence, we applied cupping at BL13, BL15, BL18, BL20 and BL23 at Bladder Meridian(BL) and measured blood lactate at every acupoint. Results : We confirmed the high system measurement accuracy, and observed the diverse skin color deformations. Moreover, we confirmed that the $L^*$, $a^*$ and E.I. had not changed after 40 minutes(p>0.05). The distribution of blood lactate levels at each part was observed differently. Blood lactate level and skin color deformation at each part was independent of each other. Conclusions : The negative pressure produced by the suction cup induces a reduction in the volumetric fraction of melanosomes and subsequent reduction in epidermal thickness. The relationship between variations of tissue and skin properties and skin color deformation degree must be investigated prior to considering the relationship between internal organ dysfunction and skin color deformation.