• Transactions of Materials Processing
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• v.29 no.3
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• pp.163-171
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• 2020

We present a multi-step cold drawing for a non-equiatomic Co₁₀Cr₁₅Fe₂₅Mn₁₀Ni₃₀V₁₀ high entropy alloy (HEA) with a simple face-centered cubic (FCC) crystal structure. The distribution of strain in the cold-drawn Co₁₀Cr₁₅Fe₂₅Mn₁₀Ni₃₀V₁₀ HEA wires was analyzed by the finite element method (FEM). The effective strain was expected to be higher as it was closer to the surface of the wire. However, the reverse shear strain acted to cause a transition in the shear strain behavior. The critical effective strain at which the shear strain transition behavior is completely shifted was predicted to be 4.75. Severely cold-drawn Co₁₀Cr₁₅Fe₂₅Mn₁₀Ni₃₀V₁₀ HEA wires up to 96% of the maximum cross-sectional reduction ratio were successfully manufactured without breakage. With the assistance of electron back-scattering diffraction and transmission electron microscope analyses, the abundant deformation twins were found in the region of high effective strain, which is a major strengthening mechanism for the cold-drawn Co₁₀Cr₁₅Fe₂₅Mn₁₀Ni₃₀V₁₀ HEA wire.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.4
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• pp.415-424
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• 2001

The destructive method is reliable and widely used for the estimation of material degradation but, it have time-consuming and a great difficulty in preparing specimens from in-service industrial facilities. Therefore, the estimation of degraded structural materials by nondestructive evaluation is strongly desired. In this paper, the use of guided wave was suggested for the evaluation on thermally damaged 2.25Cr-1Mo steel as an alternative way to compensate for limitations of fracture tests. The observation of microstructure variations of the material including carbide precipitation increase and spheroidization near grain boundary was conducted and the correlation with the guided wave features such as energy loss ration and group velocity changes was investigated. Through this study, the feasibility of ultrasonic guided wave evaluation for thermally damaged materials was explored.

• Journal of Breast Cancer
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• v.21 no.4
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• pp.382-390
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• 2018

Purpose: PIK3CA mutation is considered to be a possible cause for resistance to neoadjuvant chemotherapy (NAC) in human epidermal growth factor receptor 2 (HER2)-positive breast cancer. We investigated the association between PIK3CA mutations and the outcome of NAC in HER2-positive breast cancers. Methods: A total of 100 HER2-positive breast cancer patients who had undergone NAC and surgery between 2004 and 2016 were examined. Mutation status was sequentially assessed in pre-NAC, post-NAC, and recurrent specimens taken from these patients. Results: PIK3CA mutations were identified in the sequential specimens of 17 patients (17.0%). These 17 patients experienced shorter disease-free survival (DFS) than the rest of the patients (58.3 months vs. 119.3 months, p=0.020); however, there was no significant difference in pathologic complete response (pCR) and overall survival (OS) (pCR, 17.6% vs. 33.7%, p=0.191; OS, 84.5 months vs. 118.0 months, p=0.984). While there was no difference in pCR between the wild-type and mutant PIK3CA groups in pre-NAC specimens (25.0% vs. 31.8%, p=0.199), PIK3CA mutations correlated with lower pCR in postNAC specimens (0.0% vs. 24.3%, p<0.001). Multivariate analysis revealed significantly worse DFS in the mutant PIK3CA group than in the wild-type group (hazard ratio, 3.540; 95% confidence interval, 1.001-12.589; p=0.050). Moreover, the DFS curves of the change of PIK3CA mutation status in sequential specimens were significantly different (p=0.016). Conclusion: PIK3CA mutation in HER2-positive breast cancer was correlated with a lower pCR rate and shorter DFS. These results suggest that PIK3CA mutation is a prognostic marker for NAC in HER2-positive breast cancer, especially in post-NAC specimens.

• Bulletin of the Society of Naval Architects of Korea
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• v.6 no.1
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• pp.25-34
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• 1969

From viewpoints of over-all ship economy the straight framed V-bottom hull forms with chines are considered to be attractive even for usual commercial vessels, because increments of resistance over that of round hull forms, if any, can be well compensated with reduction in construction cost.[1] To investigate the influences of both prismatic coefficient and chine elevation on resistance performance, three models of straight-framed V-bottom hull forms which are similar to Prof. C. Ridgely-Nevitt's W-18, W-8, and W-20[2],[3] in size and hull form coefficients were tested at the SNU Ship Model Towing Tank for resistance measurements. They are of Cp=0.60, 0.65 and 0.70 and of ${\Delta}/(0.01L)^3=300$. Influence of variation of chine elevation on resistance performance were observed with the test results obtained at normal condition, and at the trimed by the stern by 2% and 4% of $L_{bp}$ at normal condition under same displacement. The hull form characteristics are shown in Table 1, and in Fig. 1, 2, 3, 4 and 5. The test results are shown in Fig 8, 9 and 10 in the form of Cr vs. $V/\sqrt{L}$ curves taking Cp as a parameter for normal condition, trim by the stern in 2% and 4% $L_{bp}$ at normal condition , respectively. Cr vs. $V/\sqrt{L}$ curves taking trim condition as a parameter are also shown in Fig 11, 12 and 13 for Cp=0.60 and 0.70, respectively. The best and the worst trim condition at given $V/\sqrt{L}$ in viewpoint of Cr are plotted for each Cp-value as shown in Fig 14, 15 and 16. From the above results the following conclusions are derived: (1) In general, the resistance performance of the straight-framed V-bottom hull forms are not inferior to those of round hull forms. At a certain range of $V/\sqrt{L}$ the former gives less resistance than the latter. (2) Regarding influences of Cp on Cr, it is observed that, at $V/\sqrt{L}$ less than about 0.925, the greater Cp-value gives the more increment of Cr, and that, at $V/\sqrt{L}$ greater than about 0.925 the smaller Cp-value gives the more increment of Cr. It is also noteworthy that the model of Cp=0.70 has remarkable hump on Cr vs. $V/\sqrt{L}$ curve between $V/\sqrt{L}=0.80$ and 0.90. (3) For higher speed within the test range, the chine elevation having the steeper slope around bow and the easier slope around amidship and stern, refered to watering, give the better results in resistance performance. (4) Assuming the chine elevations adopted for the tested models were not of the best, we would expect further improvement of resistance performance for such form. Hence, a systematic study on chine elevation is very disirable to prepare design data of general purpose for the such hull forms.

• Journal of the Korean institute of surface engineering
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• v.41 no.1
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• pp.38-42
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• 2008

316L stainless steel welding tube was electrolytically polished and the inner surface characteristics of the tube were tested. Electro-polishing variables such as current, voltage, concentration of electrolyte and electropolishing time were changed to seek for optimum condition. These makes a optimum conditions for the electro-polishing as 4000 A, 9 V, 1.7 specific gravity of electrolyte, and 30 minute of electro-polishing time. It makes the surface roughness as Ra < $0.25{\mu}m$. XPS test resulted as the ratio of CrO/FeO equals or more to 3/1. AES test resulted as the thickness of CrO film of $38{\AA}$. DTA test resulted as the tube did not react with $N_2,\;H_2\;and\;O_2$ gas below 1073K. As summarize above results, the electro- polished 316L stainless steel welding tube satisfied the conditions to apply as a pipeline for semi- conductor production facility and clean room.

• Proceedings of the KSMRM Conference
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• 2002.11a
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• pp.80-80
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• 2002

Purpose： Three tesla high field MR has been important to those disciplines that are SNR limited, such as MR spectroscopy. Additionally, increased spectral dispersion is critical for minimizing spectral overlap and simplifying resonance structures. The purpose of this study was to assess clinical proton MR spectroscopy (MRS) as a noninvasive method for evaluating brain tumor malignancy at 3T high field system Materials and Methods： Using 3T MRI/MRS system, localized water-suppressed single-voxel technique in patients with brain tumors was employed to evaluate spectra with peaks of N-acetyl aspartate (NAA), choline-containing compounds (Cho), creatine/phosphocreatine (Cr) and lactate. On the basis of Cr, these peak areas were quantificated as a relative ratio.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.68 no.1
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• pp.90-97
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• 2019

The charge redistribution digital-to-analog converter(CR-DAC) is often used for successive approximation register analog-to-digital converter(SAR ADC) that requiring low power consumption and small circuit area. However, CR-DAC is required 2 to the power of N unit capacitors to generate reference voltage for successive approximation of the N-bit SAR ADC, and many unit capacitors occupy large circuit area and consume more power. In order to improve this problem, this paper proposes SAR ADC using series capacitor DAC. The series capacitor DAC is required 2(1+N) unit capacitors to generate reference voltage for successive approximation and charges only two capacitors of the reference generation block. Because of these structural characteristics, the SAR ADC using series capacitor DAC can reduce the power consumption and circuit area. Proposed SAR ADC was designed in CMOS 180nm process, and at 1.8V supply voltage and 500kS/s sampling rate, proposed 6-bit SAR ADC have signal-to-noise and distortion ratio(SNDR) of 36.49dB, effective number of bits(ENOB) of 5.77-bit, power consumption of 294uW.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.6
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• pp.446-453
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• 2013

Clustering schemes have been adopted as an efficient solution to prolong network lifetime and improve network scalability. In such clustering schemes cluster ratio is represented by the rate of the number of cluster heads and the number of total nodes, and affects the performance of clustering schemes. In this paper, we mathematically analyze an optimal clustering ratio in wireless sensor networks. We consider a multi-hop to one-hop transmission case and aim to provide the optimal cluster ratio to minimize the system hop-count and maximize packet reception ratio between nodes. We examine its performance through a set of simulations. The simulation results show that the proposed optimal cluster ratio effectively reduce transmission count and enhance energy efficiency in wireless sensor networks.

• Investigative Magnetic Resonance Imaging
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• v.17 no.2
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• pp.110-122
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• 2013

Purpose : To compare the image quality and ligament traceability in ankle images obtained using Volume Isotropic Turbo Spin Echo Acquisition (VISTA) MRI with and without fat suppression. Materials and Methods: The signal-to-noise ratios (SNRs) in images from a phantom and from the ankle of a volunteer were compared. Ten ankles from 10 non-symptomatic volunteers were imaged for comparisons of contrast ratio (CR) and ligament traceability. All examinations were performed using VISTA sequences with and without fat suppression on a 3T MRI scanner. The SNRs were obtained from images with subjects and without subjects (noise-only). Contrast ratios from images of the 10 ankles were acquired between fluid and tendon (F-T), F-cartilage (C), F-ligament (L), fat (f)-T, f-C and f-L. Two musculoskeletal radiologists independently scored the traceability of 7 ligaments, in sagittal, axial and coronal images respectively, based on a 4-point scale (1 as not traceable through 4 as clearly traceable). The Wilcoxon signed-rank test was used to compare the CR. Fisher's exact test and Pearson's chi-squared test were used to compare the ligament traceability. Results: The SNRs did not differ significantly between the two sequences except in bone marrow. VISTA SPAIR showed the higher CR only in F-T (p = 0.04), whereas VISTA showed higher CR in f-T (p = 0.005), f-C (p = 0.005) and f-L (p = 0.005). The calcaneofibular ligament traceability with VISTA was superior to that obtained with VISTA SPAIR (p < 0.05) in all planes. Conclusion: VISTA showed significant superiority to VISTA SPAIR in tracing CFL due to the superior CR between fat and ligament.

• Horticultural Science & Technology
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• v.34 no.3
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• pp.433-441
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• 2016

Clubroot caused by the protist Plasmodiophora brassicae is one of the most destructive diseases of Brassica crops. Developing Chinese cabbage cultivars with durable clubroot resistance (CR) is an important goal of breeding programs, which will require new genetic resources to be identified and introduced. In this study, we evaluated resistance to P. brassicae race 4 using 26 Chinese cabbage (B. rapa ssp. pekinensis ) cultivars compared to the clubroot-susceptible Chinese cabbage inbred line 'BP079' and the clubroot-resistant European turnip (B. rapa ssp. rapifera ) inbred line 'IT033820'. No symptoms of clubroot disease were found in 'IT033820' infected with P. brassicae race 4, whereas the Chinese cabbage cultivars exhibited disease symptoms to various degrees. The Chinese cabbage cultivars that were reported to be clubroot-susceptible were susceptible to P. brassicae race 4; however, seven of the 20 cultivars reported to be clubroot-resistant were susceptible to this race of P. brassicae to varying degrees. Resting spores of P. brassicae were abundant within the infected root tissues of 'BP079', as revealed by light microscopy and scanning electron microscopy (SEM), but they were not detected in root tissues of 'IT033820'. Although resting spores were not detected by light microscopy in root tissues of the clubroot-resistant Chinese cabbage cultivar 'Kigokoro 75', a few spores were observed by SEM. The $F_1$ hybrids from a cross between 'IT033820' and 'BP079' showed no disease symptoms, and all $BC_1P_1$ progenies from a cross between the $F_1$ hybrid and 'IT033820' exhibited a resistance phenotype. In the $BC_1P_2$ population from a cross between the $F_1$ hybrid and 'BP079', this trait segregated at a ratio of 3(R):1(S) (${\chi}^2=1.333$, p = 0.248) at a 5% significance level. Inoculated $BC_1P_2$ plants were either highly resistant or highly susceptible to the pathogen, indicating that the CR to race 4 of P. brassicae carried by 'IT033820' is dominant. In the $F_2$ population, this trait segregated at a ratio of 15(R):1(S) (${\chi}^2=0.152$, p = 0.696) at a 5% significance level, suggesting that CR in 'IT033820' is mainly controlled by two dominant genes. Therefore, 'IT033820' represents a promising genetic resource for developing durable CR breeding lines in Chinese cabbage.