• Journal of the Korean Geosynthetics Society
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• v.15 no.3
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• pp.1-12
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• 2016

In this study, the impact of sand and weathered granite soil is analyzed by changing the internal temperature from $20^{\circ}C{\sim}70^{\circ}C$C by installing a heating coil inside the triaxial cell. To check the effect on weathered granite soil due to increase of temperature and number of heating-coiling cycles are analyzed by measuring the temperature by using thermometer installed inside the triaxial cell and due to that deviator stress also occurred during the consolidated undrained test. To analyze the effect of weathered granite soil with change of temperature during undrained testing. The deviator stress and pore pressure is measured. As a result, pore pressure increases and the deviator stress decreases with rise of temperature.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1877-1889
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• 1992

Upsetting is performed in open-die press forging to deform metal in all directions in order to enhance soundness of a product and reduce directionality of properties caused by casting. It is necessary to ensure sufficient forging ratio for subsequent cogging operations and consolidate the void along the centerline. To obtain these benefits, the upper die shape (dome and dished shape) is considered as an upsetting parameter. Thermo-viscoplastic finite element analysis has been carried out so as to understand the influence of upper die shape on the effective strain, hydrostatic stress and temperature in the upset-forged ingots without internal defects. The analysis is focused on the investigation into internal void closure in ingots with pipe holes and circular voids. The computational results have shown that the volume fraction of the void is independent of the circular void size and the closure of internal voids is much more influenced by the effective strain than the hydrostatic stress around the void. It is finally suggested that the height reduction must be over 35% for consolidation of internal voids.

• Journal of the Korean Geotechnical Society
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• v.21 no.9
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• pp.53-64
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• 2005

For geotechnical design in practice, soils are, in general, assumed to behave as a linear elastic or perfect plastic material. More realistic geotechnical design, however, should take into account various factors that affect soil behavior in the field, such as non-linearity of stress-strain response, stress history, and water content. In this study, a series of laboratory tests including triaxial and resonant column tests were peformed with sands of various silt contents, relative densities, stress states, OCR and water contents. This aims at investigating effects of various factors that affect strength and stiffness of sands. From the results in this study, it is found that the effect of OCR is significant for the intermediate stress-strain range from the initial to failure, while it may be ignored for the initial stiffness and peak strength. For the effect of water content, it is observed that the initial elastic modulus decreases with increasing water content at lower confining stress and relative density At higher confining stresses, the effect of water content Is found to become small.

• Korean Journal of Materials Research
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• v.25 no.8
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• pp.386-390
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• 2015

Fe-base superalloy powders with $Y_2O_3$ dispersion were prepared by high energy ball milling, followed by spark plasma sintering for consolidation. High-purity elemental powders with different Fe powder sizes of 24 and 50 mm were used for the preparation of $Fe-20Cr-4.5Al-0.5Ti-O.5Y_2O_3$ powder mixtures (wt%). The milling process of the powders was carried out in a horizontal rotary ball mill using a stainless steel vial and balls. The milling times of 1 to 5 h by constant operation (350 rpm, ball-to-powder ratio of 30:1 in weight) or cycle operation (1300 rpm for 4 min and 900 rpm for 1 min, 15:1) were applied. Microstructural observation revealed that the crystalline size of Fe decreased with an increase in milling time by cyclic operation and was about 15 nm after 3 h, forming a FeCr alloy phase. The cyclic operation had an advantage over constant milling in that a smaller-agglomerated structure was obtained. The milled powders were sintered at $1100^{\circ}C$ for 30 min in vacuum. With an increase in milling time, the sintered specimen showed a more homogeneous microstructure. In addition, a homogenous distribution of Y-compound particles in the grain boundary was confirmed by EDX analysis.

• Structural Engineering and Mechanics
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• v.86 no.5
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• pp.673-686
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• 2023

Determining the properties of pile from cone penetration test (CPT) is costly, and need several in-situ tests. At the present study, two novel hybrid learning models, namely PSO-RF and HHO-RF, which are an amalgamation of random forest (RF) with particle swarm optimization (PSO) and Harris hawks optimization (HHO) were developed and applied to predict the pile set-up parameter "A" from CPT for the design aim of the projects. To forecast the "A," CPT data along were collected from different sites in Louisiana, where the selected variables as input were plasticity index (PI), undrained shear strength (S_u), and over consolidation ratio (OCR). Results show that both PSO-RF and HHO-RF models have acceptable performance in predicting the set-up parameter "A," with R² larger than 0.9094, representing the admissible correlation between observed and predicted values. HHO-RF has better proficiency than the PSO-RF model, with R² and RMSE equal to 0.9328 and 0.0292 for the training phase and 0.9729 and 0.024 for testing data, respectively. Moreover, PI and OBJ indices are considered, in which the HHO-RF model has lower results which leads to outperforming this hybrid algorithm with respect to PSO-RF for predicting the pile set-up parameter "A," consequently being specified as the proposed model. Therefore, the results demonstrate the ability of the HHO algorithm in determining the optimal value of RF hyperparameters than PSO.

• Geomechanics and Engineering
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• v.36 no.3
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• pp.259-276
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• 2024

The undrained shear strength is widely acknowledged as a fundamental mechanical property of soil and is considered a critical engineering parameter. In recent years, researchers have employed various methodologies to evaluate the shear strength of soil under undrained conditions. These methods encompass both numerical analyses and empirical techniques, such as the cone penetration test (CPT), to gain insights into the properties and behavior of soil. However, several of these methods rely on correlation assumptions, which can lead to inconsistent accuracy and precision. The study involved the development of innovative methods using extreme gradient boosting (XGB) to predict the pile set-up component "A" based on two distinct data sets. The first data set includes average modified cone point bearing capacity (q_t), average wall friction (f_s), and effective vertical stress (σ_vo), while the second data set comprises plasticity index (PI), soil undrained shear cohesion (S_u), and the over consolidation ratio (OCR). These data sets were utilized to develop XGBoost-based methods for predicting the pile set-up component "A". To optimize the internal hyperparameters of the XGBoost model, four optimization algorithms were employed: Particle Swarm Optimization (PSO), Social Spider Optimization (SSO), Arithmetic Optimization Algorithm (AOA), and Sine Cosine Optimization Algorithm (SCOA). The results from the first data set indicate that the XGBoost model optimized using the Arithmetic Optimization Algorithm (XGB - AOA) achieved the highest accuracy, with R2 values of 0.9962 for the training part and 0.9807 for the testing part. The performance of the developed models was further evaluated using the RMSE, MAE, and VAF indices. The results revealed that the XGBoost model optimized using XGBoost - AOA outperformed other models in terms of accuracy, with RMSE, MAE, and VAF values of 0.0078, 0.0015, and 99.6189 for the training part and 0.0141, 0.0112, and 98.0394 for the testing part, respectively. These findings suggest that XGBoost - AOA is the most accurate model for predicting the pile set-up component.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.29 no.1
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• pp.1-9
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• 2007

Purpose: To evaluate the effect of compression on the distracted area in new bone formation during mandibular distraction osteogenesis in rabbits. Materials and method: Sixteen rabbits, weighing approximately 2 Kg, and the prefabricated distraction device were used. With the rabbits under general anesthesia, we performed vertical osteotomies between the anterior and posterior mandibular teeth and then placed the distraction device. After a 5 -day latency period, the mandible was distracted to a length of 10.0 mm at a rate of 1 mm/day and then immediately compressed 4 mm in the experimental group (n=8). In the control group (n=8), the mandible was distracted to a length of 6.0 mm at a rate of 1 mm/day. Rabbits in the control group were killed at 2 and 8 weeks during the consolidation period. The specimens were evaluated with light microscope after H & E stain. Histomorphometric analysis was done at 8 week specimens. Results: All experimental animals showed mandibular elongation on the macroscopical and radiographic evaluations. At 2 week, immature bone formation was observed from the surface of the host bone margins with collagen fibers arranged parallel to the direction of distraction in the control group; in the experimental group, immature bone formation was observed adjacent to the host bone, and the collagen fibers were not arranged uniformly. At 8 week, spindle-shaped new bone formation was seen in the direction of distraction in distracted area of the control group, while in the experimental group, the newly formed bone was arranged in a multidirectional manner, like the pattern of trabeculae. In the histomorphometric analysis of 8 weeks, the area of bone deposition was $2.12{\pm}\;0.75\;inch^2$ in the experimental group and $0.87{\pm}0.51\;inch^2$ in the control group (p<0.01). The bone deposition ratio was $29.60{\pm}10.50%$ in the experimental group and $12.10{\pm}7.17%$ in the control group (p<0.01). Conclusion: These results suggest that compression after over-distraction during the mandibular distraction osteogenesis is an effective method of increasing the amount of newly formed bone in distracted area.

• Tuberculosis and Respiratory Diseases
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• v.44 no.5
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• pp.1083-1093
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• 1997

Background : So far, there have been numerous reports on organ damage due to cryptococcosis, however, cases of lung localization have been infrequently reported. Recently pulmonary cryptococcosis has been reported more frequently than before due to enhanced diagnostic techniques and increased underlying diseases. Method : The author, therefore, analyzed the clinical manifestations of 5 cryptococcosis cases that we experienced at Hanyang University Hospital from 1985 to 1996 and 9 cases reported in Korea from 1984 and 1996 retrospectively. The following results were obtained. Results : Cryptococcosis occurred frequently over sixth decade and the male to female ratio was 3.6 : 1. Underlying diseases included acute rejection after kidney transplantation, rheumatoid arthritis, autoimmune hepatitis, diabetes mellitus and state of bilateral adrenalectomy. Remaining 8 cases had no evidence of an underlying disease. Because the symptoms were subacute & nonspecific, and not improved by conventional antibiotics, 6 patients of 14 pulmonary cryptococcosis patients were treated as pulmonary tuberculosis before correct diagnosis was made. There were three asymptomatic cases. According to the results of CXR, solitary alveolar consolidation was the most common finding(8 cases) followed by diffuse infiltration(5 cases). It also showed pleural effusion, hilar lymphadenopathy and cavity formation that was rarely reported in world literature. The diagnasis was made through fine needle aspiration biopsy in 10 cases, open thoracotomy in 2 cases, transbronchial lung biopsy in 1 case. and thoracentesis with pleural biopsy in 1 case. Only one case showed positive result in sputum stain and culture, serum latex agglutination test for cryptococcus neoformans. Treatment modalities were various such as fluconazole, amphotericin B, flucytosine, ketoconazole, surgery and it's combination. After 1990 year, there was a trend that fluconazole or ketoconazole are more used than other therapeutic modalities. Conclusion : Because the symptoms are subacute & nonspecific and not improved by conventional antibiotics, pulmonary cryptococcosis is likely to misdiagnosis as pulmonary tuberculosis in Korea. Because the diagnosic yield of sputum stain, culture and serologic test for pulmonary cryptococcosis is low, histologic diagnosis is need in most pulmonary cryptococcosis.

• Tuberculosis and Respiratory Diseases
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• v.44 no.2
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• pp.232-240
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• 1997

Background : Postprimary pulmonary tuberculosis is located mainly in upper lobes. The tuberculous lesion involving the lower lobes usually arises from the upper lobe cavity through endobronchial spread. When tuberculosis is confined to the lower lung field, it often masquerades as pneumonia, lung cancer, bronchiectasis, or lung abscess. Thus the correct diagnosis may be sometimes delayed for a long time. Methods : We carried out, retrospectively, a clinical study on 50 patients confirmed with lower lung field tuberculosis who visited the Department of Pulmonary Medicine at Hanyang University Hospital from January 1992 to December 1994. The following results were obtained. Results : Lower lung field tuberculosis without concomitant upper lobe disease occurred in fifty patients representing 6.9% of the total admission with active pulmonary tuberculosis over a period of 3 years. It occurred most frequently in the third decade but age distribution was relatively even. The mean age was 43 years old. Female was more frequently affected than male (male to female ratio 1 : 1.9). The most common symptom was cough(68%), followed by sputum(52%), fever(38%), and chest discomfort(30%). On chest X-ray of the 50patients, consolidation was the most common finding in 52%, followed by solitary nodule(22%) collapse(16%), cavitary lesion(10%), in decreasing order. The disease confined to the right side in 25 cases, left side 20 cases, and both sides 5 cases. Endobronchial tuberculosis (1) Endobronchial involvement was proved by bronchoscopic examination in 20 of 50patients. (2) Mean age was 44years old and female was more affected than man (male to female ratio 1 : 3). Sputum AFB stain and Mycobacterium tuberculosis culture were positive only in 50% of cases unlikely upper lobe tuberculosis, additional diagnostic methods were needed. In our study, bronchoscopic examination and percutaneous fine needle aspiration biopsy increased diagnostic yield by 18% and 32%, respectively. The most common associated condition was diabetes mellitus(18%) and others were anemia, anorexia nervosa, stomach cancer, and systemic steroid usage. Conclusion : When we find a lower lung field lesion, we should suspect tuberculosis if the patient has diabetes mellitus, anemia, systemic steroid usage, malignancy or other immune suppressed states. Because diagnostic yield of sputum AFB smear & Mycobacterium tuberculosis culture was low, additional diagnostic methods such as bronchoscopy and fine needle aspiration biopsy were needed.

• Tuberculosis and Respiratory Diseases
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• v.43 no.5
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• pp.671-682
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• 1996

Background : Endobronchial tuberculosis is definded as tuberculous infection of the tracheobronchial tree with microbiological and histopathological evidence. Endobronchial tuberculosis has clinical significance due to its sequela of cicatrical stenosis which causes atelectasis, dyspnea and secondary pneumonia and may mimic bronchial asthma and pulmanary malignancy. Method : The authors carried out, retrospectively, a clinical study on 201 patients confirmed with endobronchial tuberculosis who visited the Department of Pulmonary Medicine at Hangyang University Hospital from January 1990 10 April 1996. The following results were obtained. Results: 1) Total 201 parients(l9.5%) were confirmed as endobronchial tuberculosis among 1031 patients who had been undergone flexible bronchofiberscopic examination. The number of male patients were 55 and that of female patients were 146. and the male to female ratio was 1 : 2.7. 2) The age distribution were as follows: there were 61(30.3%) cases in the third decade, 40 cases(19.9%) in the fourth decade, 27 cases(13.4%) in the sixth decade, 21 cases(10.4%) in the fifth decade, 19 cases(9.5%) in the age group between 15 and 19 years, 19 cases(9.5%) in the seventh decade, and 14 cases(7.0%) over 70 years, in decreasing order. 3) The most common symptom, in 192 cases, was cough 74.5%, followed by sputum 55.2%, dyspnea 28.6%, chest discomfort 19.8%, fever 17.2%, hemoptysis 11.5%, in decreasing order, and localized wheezing was heard in 15.6%. 4) In chest X-ray of 189 cases, consolidation was the most frequent finding in 67.7%, followed by collapse 43.9%. cavitary lesion 11.6%, pleural effusion 7.4%, in decreasing order, and there was no abnormal findings in 3.2%. 5) In the 76 pulmanary function tests, a normal pattern was found in 44.7%, restrictive pattern in 39.5 %, obstructive pattern in 11.8%, and combined pattern in 3.9%. 6) Among total 201 patients, bronchoscopy showed caseous pseudomembrane in 70 cases(34.8%), mucosal erythema and edema in 54 cases(26.9%), hyperplastic lesion in 52 cases(25.9%), fibrous s.enosis in 22 cases(10.9%), and erosion or ulcer in 3 cases(1.5%). 7) In total 201 cases, bronchial washing AFB stain was positive in 103 cases(51.2%), bronchial washing culture for tuberculous bacilli in 55 cases(27.4%). In the 99 bronchoscopic biopsies, AFB slain positive in 36.4%. granuloma without AFB stain positive in 13.1%, chronic inflammation only in 36.4%. and non diagnostic biopsy finding in 14.1%. Conclusions : Young female patients, whose cough resistant to genenal antitussive agents, should be evaluated for endobronchial tuberculosis, even with clear chest roentgenogram and negative sputum AFB stain. Furthermore, we would like to emphasize that the bronchoscopic approach is a substantially useful means of making a differential diagnosis of atelectasis in older patients of cancer age. At this time we have to make a standard endoscopic classification of endobronchial tuberculosis, and well designed prospective studies are required to elucidate the effect of combination therapy using antituberculous chemotherapy with steroids on bronchial stenosis in patients with endobronchial tuberculosis.