38 results on '"Keon, Kim"'
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2. A Review on the Latest Advancements and Innovation Trends in Vibration-Based Structural Health Monitoring (SHM) Techniques for Improved Maintenance of Steel Slit Damper (SSD)
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John Mark G. Payawal and Dong-Keon Kim
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Steel slit damper ,structural health monitoring ,vibration-based techniques ,PRISMA 2020 ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 - Abstract
Steel slit damper (SSD) is specifically engineered to absorb and disperse energy to mitigate the possibility of structural damage and collapse during seismic events. However, the effectiveness of these dampers are compromised due to wear, corrosion and other forms of material degradation and failure mechanisms. For this reason, it is important to consistently monitor its condition and conduct maintenance and repairs to guarantee safety and dependability of the structures it is installed with. Now, vibration-based techniques have emerged as a promising structural health monitoring (SHM) strategy. It involves methodologies for detecting changes in functions and analyzing vibrations to discover potential problems. This study entails a comprehensive examination of the most recent advancements and breakthroughs in vibration-based methodologies used in SHM. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020), we identified several key techniques and technologies that show promise in enhancing the maintenance and monitoring of steel– or steel and metal surfaces- slit dampers. The pros and cons of these methods are presented to be applicable when monitoring an SSD. This paper presents notable figures and their corresponding discussions to achieve enhanced understanding of the advancements in SHM towards sensor technologies, monitoring techniques, and applications in civil infrastructure. Furthermore, this paper reviews the applications and functions framework for real-time SHM of SSDs together with their practical implementations and applications using diverse monitoring technologies to promote innovation. Finally, the optimal sensor selection criteria, data gathering methodologies, experimental settings, innovative approaches with comparative analyses, and a proposed maintenance standard for SSDs are described in this study.
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- 2024
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3. Clinical relevance of serum ionized magnesium concentration in dogs with myxomatous mitral valve disease
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Ock‐Kyu Kim, Keon Kim, Sinwook Park, Hayoung Yang, Hyunwoo Kim, Woong‐Bin Ro, and Chang‐Min Lee
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ACVIM ,congestive heart failure ,electrolytes ,hypomagnesemia ,Veterinary medicine ,SF600-1100 - Abstract
Abstract Background Hypomagnesemia is associated with a poor prognosis in humans with congestive heart failure (CHF), but studies in veterinary medicine are limited. Hypothesis Serum ionized magnesium concentration [iMg2+] would decrease as CHF progresses compared with the initial diagnostic levels and that lower [iMg2+] would be negatively associated with prognosis in dogs with CHF. Animals A total of 181 client‐owned dogs with myxomatous mitral valve disease (MMVD) were included. They were classified into the preclinical stage (NO‐CHF, n = 108), stage C (n = 42), and stage D (n = 31) based on the American College of Veterinary Internal Medicine MMVD classification. Methods This is a retrospective study from 2 referral centers. The [iMg2+] was compared among the NO‐CHF, stage C, and stage D groups. Kaplan‐Meier curves and the log‐rank test were used to compare the incidence of death between groups. Multivariable Cox regression analysis was used to estimate the association of hypomagnesemia with the death. Results In the stage D group, the [iMg2+] was lower than that in the NO‐CHF (P
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- 2024
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4. Assessment of the Film-Free Water Decal Method for Speckle Pattern Application in Digital Image Correlation
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Anna Camille Sanchez and Dong-Keon Kim
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film-free water decal ,digital image correlation (DIC) ,speckle pattern ,SS275 steel ,strain measurement ,tensile testing ,Chemical technology ,TP1-1185 - Abstract
Digital Image Correlation (DIC) often encounters challenges with variability and consistency in traditional speckle pattern application techniques, such as spray-painting, affecting measurement accuracy and reliability. This study evaluates a film-free water decal method as an alternative for applying speckle patterns in DIC. SS275 structural steel specimens were prepared with speckle patterns using both the film-free water decal method and traditional spray-painting. The quality of the speckle patterns was assessed, and their effectiveness for DIC was evaluated through tensile testing and a comparison with strain gauge measurements. The film-free water decal method provided enhanced control over speckle pattern application, resulting in high-quality, consistent patterns. Strain measurements obtained using this method closely matched those from traditional methods, confirming its reliability. The film-free water decal method offers a practical and reliable alternative to spray-painting, improving the consistency and accuracy of DIC experiments, with potential applications in various engineering and scientific fields.
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- 2024
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5. A content analysis of YouTube videos on tinnitus in South Korea
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Hee Won Seo, Jung Woo Ha, Jin Hye Kwak, Moo Keon Kim, Hayoung Byun, Seung Hwan Lee, and Jae Ho Chung
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Medicine ,Science - Abstract
Abstract More people use the internet for medical information, especially YouTube. Nevertheless, no study has been conducted to analyze the quality of YouTube videos about tinnitus in Korea. This study aims to review the contents and quality of YouTube videos on tinnitus. The top 100 Korean YouTube videos on tinnitus were reviewed by a tinnitus expert. This study assessed video details: title, creator, length, and popularity indicators—subscribers, views, and likes. The contents of the video clips were analyzed to determine the relevance, understandability, actionability, and quality of information. Out of 100 tinnitus videos, 27 were created by otolaryngologists, 25 by traditional Korean medicine doctors, 25 by other medical professionals, and 3 by lay persons. Sensorineural tinnitus was frequently dealt, and hearing loss, stress, and noise were introduced as main causes of tinnitus. Otolaryngologists' videos covered verified treatments, but others suggested unproven therapies including herbal medicine or acupressure. Otolaryngologists' videos showed significantly higher understandability and quality of information compared to others (p
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- 2023
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6. Validation of the Korean Version of the Clinical Frailty Scale-Adjusted Korean Triage and Acuity Scale for Older Patients in the Emergency Department
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Ho Sub Chung, Yunhyung Choi, Ji Yeon Lim, Keon Kim, Sung Jin Bae, Yoon Hee Choi, and Dong Hoon Lee
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frailty ,triage ,emergency department ,aged ,geriatrics ,Medicine (General) ,R5-920 - Abstract
Background and Objectives: The Clinical Frailty Scale (CFS), used to screen for prehospital frailty in patients aged >65 years, is simple, time-efficient, and has been validated in emergency departments (EDs). In this study, we analyzed whether the Korean Triage and Acuity Scale (KTAS) classification by level in older patients determined to have frailty based on the Korean version of the CFS increases the triage performance of the current KTAS. Materials and Methods: The primary outcome was 30-day in-hospital mortality, and secondary outcomes were hospital and intensive care unit (ICU) admissions. This study retrospectively analyzed prospectively collected data from three ED centers. Patients with a CFS score ranging from five (mildly frail) to nine (terminally ill) were categorized into the frailty group. We upgraded the KTAS classification of the frailty group by one level of urgency and defined this as the CFS-KTAS. Results: The cutoff values for predicting admission were three and two for the KTAS and CFS-KTAS, respectively. A significant difference was observed in the area under the receiver operating characteristic (AUROC) curve between the KTAS and CFS-KTAS. To predict ICU admission, the cutoff score was two for both scales. A significant difference was observed in the AUROC curve between the KTAS and CFS-KTAS. For predicting in-hospital mortality, the cutoff score was two for both scales. A significant difference was observed in the AUROC curve between the KTAS and CFS-KTAS. Conclusions: This study showed that the CFS-adjusted KTAS has a more useful prognostic value than the KTAS alone for predicting hospital outcomes in older patients.
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- 2024
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7. Tumor microbiome analysis provides prognostic value for patients with stage III colorectal cancer
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Jae Hyun Kim, Jongwook Yu, Dong Keon Kim, Seunghun Lee, Seung Hyun Lee, Byung Kwon Ahn, Tae Il Kim, and Seun Ja Park
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colorectal cancer ,microbiome ,tissue ,prognosis ,tumor ,Neoplasms. Tumors. Oncology. Including cancer and carcinogens ,RC254-282 - Abstract
IntroductionAlthough patients with colorectal cancer (CRC) can receive optimal treatment, the risk of recurrence remains. This study aimed to evaluate whether the tumor microbiome can be a predictor of recurrence in patients with stage III CRC.MethodsUsing 16S rRNA gene sequencing, we analyzed the microbiomes of tumor and adjacent tissues acquired during surgery in 65 patients with stage III CRC and evaluated the correlation of the tissue microbiome with CRC recurrence. Additionally, the tumor tissue microbiome data of 71 patients with stage III CRC from another center were used as a validation set.ResultsThe microbial diversity and abundance significantly differed between tumor and adjacent tissues. In particular, Streptococcus and Gemella were more abundant in tumor tissue samples than in adjacent tissue samples. The microbial diversity and abundance in tumor and adjacent tissues did not differ according to the presence of recurrence, except for one genus in the validation set. Logistic regression analysis revealed that a recurrence prediction model including tumor tissue microbiome data had a better prediction performance than clinical factors (area under the curve [AUC] 0.846 vs. 0.679, p = 0.009), regardless of sex (male patients: AUC 0.943 vs. 0.818, p = 0.043; female patients: AUC 0.885 vs. 0.590, p = 0.017). When this prediction model was applied to the validation set, it had a higher AUC value than clinical factors in female patients.ConclusionOur results suggest that the tumor microbiome of patients with CRC be a potential predictor of postoperative disease recurrence.
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- 2023
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8. Genome-wide association study of mammary gland tumors in Maltese dogs
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Keon Kim, Jung Eun Song, Jae Beom Joo, Hyeon A Park, Chang Hyeon Choi, Chang Yun Je, Ock Kyu Kim, Sin Wook Park, Yoon Jung Do, Tai-Young Hur, Sang-Ik Park, and Chang-Min Lee
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canine ,genome-wide association study ,Maltese ,mammary gland tumor ,single-nucleotide polymorphism ,Veterinary medicine ,SF600-1100 - Abstract
BackgroundA genome-wide association study (GWAS) is a valuable tool for investigating genetic and phenotypic variation in many diseases.ObjectiveThe objective of this study was to identify variations in the genomes of Maltese dogs that are associated with the mammary gland tumor (MGT) phenotype and to assess the association between each biological condition and MGT phenotype in Maltese dogs.MethodsDNA was extracted from 22 tumor samples and 11 whole blood samples from dogs with MGTs. Genome-wide single-nucleotide polymorphism (SNP) genotyping was performed, and the top 20 SNPs associated with various conditions and genetic variations were mapped to their corresponding gene locations.ResultsThe genotyping process successfully identified 173,662 loci, with an overall genotype completion rate of 99.92%. Through the quality control analysis, 46,912 of these SNPs were excluded. Allelic tests were conducted to generate Manhattan plots, which showed several significant SNPs associated with MGT phenotype in intergenic region. The most prominent SNP, located within a region associated with transcription and linked to the malignancy grade of MGT, was identified on chromosome 5 (p = 0.00001) though there may be lack of statistical significance. Other SNPs were also found in several genes associated with oncogenesis, including TNFSF18, WDR3, ASIC5, STAR, and IL1RAP.ConclusionTo our knowledge, this is the first GWAS to analyze the genetic predisposition to MGT in Maltese dogs. Despite the limited number of cases, these analyzed data could provide the basis for further research on the genetic predisposition to MGTs in Maltese dogs.
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- 2023
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9. Snail acetylation by autophagy‐derived acetyl‐coenzyme A promotes invasion and metastasis of KRAS‐LKB1 co‐mutated lung cancer cells
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Jang Hee Han, Yong Keon Kim, Hakhyun Kim, Jooyoung Lee, Myung Joon Oh, Sang Bum Kim, Minjee Kim, Kook Hwan Kim, Hyun Ju Yoon, Myung‐Shik Lee, John D. Minna, Michael A. White, and Hyun Seok Kim
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snail ,autophagy ,acetyl‐coenzyme A ,epithelial‐to‐mesenchymal transition ,non‐small‐cell lung cancer ,CAMKK2 ,Neoplasms. Tumors. Oncology. Including cancer and carcinogens ,RC254-282 - Abstract
Abstract Background Autophagy is elevated in metastatic tumors and is often associated with active epithelial‐to‐mesenchymal transition (EMT). However, the extent to which EMT is dependent on autophagy is largely unknown. This study aimed to identify the mechanisms by which autophagy facilitates EMT. Methods We employed a liquid chromatography‐based metabolomic approach with kirsten rat sarcoma viral oncogene (KRAS) and liver kinase B1 (LKB1) gene co‐mutated (KL) cells that represent an autophagy/EMT‐coactivated invasive lung cancer subtype for the identification of metabolites linked to autophagy‐driven EMT activation. Molecular mechanisms of autophagy‐driven EMT activation were further investigated by quantitative real‐time polymerase chain reaction (qRT‐PCR), Western blotting analysis, immunoprecipitation, immunofluorescence staining, and metabolite assays. The effects of chemical and genetic perturbations on autophagic flux were assessed by two orthogonal approaches: microtubule‐associated protein 1A/1B‐light chain 3 (LC3) turnover analysis by Western blotting and monomeric red fluorescent protein‐green fluorescent protein (mRFP‐GFP)‐LC3 tandem fluorescent protein quenching assay. Transcription factor EB (TFEB) activity was measured by coordinated lysosomal expression and regulation (CLEAR) motif‐driven luciferase reporter assay. Experimental metastasis (tail vein injection) mouse models were used to evaluate the impact of calcium/calmodulin‐dependent protein kinase kinase 2 (CAMKK2) or ATP citrate lyase (ACLY) inhibitors on lung metastasis using IVIS luciferase imaging system. Results We found that autophagy in KL cancer cells increased acetyl‐coenzyme A (acetyl‐CoA), which facilitated the acetylation and stabilization of the EMT‐inducing transcription factor Snail. The autophagy/acetyl‐CoA/acetyl‐Snail axis was further validated in tumor tissues and in autophagy‐activated pancreatic cancer cells. TFEB acetylation in KL cancer cells sustained pro‐metastatic autophagy in a mammalian target of rapamycin complex 1 (mTORC1)‐independent manner. Pharmacological inhibition of this axis via CAMKK2 inhibitors or ACLY inhibitors consistently reduced the metastatic capacity of KL cancer cells in vivo. Conclusions This study demonstrates that autophagy‐derived acetyl‐CoA promotes Snail acetylation and thereby facilitates invasion and metastasis of KRAS‐LKB1 co‐mutated lung cancer cells and that inhibition of the autophagy/acetyl‐CoA/acetyl‐Snail axis using CAMKK2 or ACLY inhibitors could be a potential therapeutic strategy to suppress metastasis of KL lung cancer.
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- 2022
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10. DOMAIN ADAPTATION BASED FAULT DIAGNOSIS UNDER VARIABLE OPERATING CONDITIONS OF A ROCK DRILL
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Yong Chae Kim, Taehun Kim, Jin Uk Ko, Jinwook Lee, and Keon Kim
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fault diagnosis ,rock drill ,deep-learning ,domain-adaptation ,Engineering machinery, tools, and implements ,TA213-215 ,Systems engineering ,TA168 - Abstract
Data-driven fault diagnosis is an essential technology for the safety and maintenance of rock drills. However, since the signals acquired from a rock drill have different distributions, which arise due to their variable operating conditions, the classification performance of any data-driven method is diminished; this is called the domain-shift issue. This paper proposes a new domain-adaptation-based fault diagnosis scheme to solve the domain-shift problem. The proposed method introduces a data-cropping technique to mitigate the difference in the length of the data measured from a rock drill for each impact cycle. To extract invariant features for all operating conditions, the proposed method combines two methods: a domain adversarial neural network and minimization of the maximum mean discrepancy (MMD) between the features from different domains. In addition, a soft voting ensemble is used to reduce the model uncertainty. The proposed method shows superior performance when validated with a rock drill dataset; the proposed approach was ranked in 2nd place in the 2022 PHM Conference Data Challenge.
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- 2023
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11. Case report: Successful medical management of adrenocortical carcinoma with metastasis in a Maltese dog
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Sin-Wook Park, Keon Kim, Ock-Kyu Kim, Woong-Bin Ro, and Chang-Min Lee
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adrenal-dependent hyperadrenocorticism ,canine ,adrenal tumor ,metastasis ,trilostane ,Veterinary medicine ,SF600-1100 - Abstract
IntroductionAdrenocortical carcinoma (ACC) with metastasis has a grave prognosis, and adrenalectomy is associated with a high perioperative mortality rate in dogs. A favorable outcome following trilostane treatment in patients with metastatic ACC confirmed by a decreased size of the adrenal tumor and metastatic lesions has not been reported in dogs.Case descriptionA 12-year-old neutered male Maltese dog was diagnosed with a right adrenal tumor and a hepatic mass. Adrenal-dependent hyperadrenocorticism (ADH) was diagnosed based on clinical signs and an adrenocorticotropic hormone stimulation test (ACTHST). In addition, tests for plasma metanephrine and normetanephrine ruled out a pheochromocytoma. Based on cytology and computed tomography, unresectable metastatic ACC was confirmed. The dog was managed with trilostane due to the presence of distant metastasis. Medical management improved the clinical signs and post-ACTHST cortisol concentrations. One year after the first presentation, the clinical signs and ACTHST test showed a favorable outcome. In addition, computed tomography revealed a decreased size of the right adrenal tumor and resolution of the hepatic mass.ConclusionsTrilostane could be considered as a treatment option for unresectable metastatic ACC. A decrease in tumor size following treatment with trilostane has not been reported in dogs. This case report is the first to demonstrate a favorable outcome of metastatic ACC following trilostane mono therapy for >1 year.
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- 2023
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12. Determinants of COVID-19 vaccine Hesitancy: 2020 California Health Interview Survey
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Ingyu Moon, Junghee Han, and Keon Kim
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Vaccine hesitancy ,COVID-19 ,Determinants of health ,Vaccine acceptance ,Public health ,Medicine - Abstract
Although the COVID-19 vaccine is a key intervention against the ongoing COVID-19 pandemic, vaccine hesitancy is a barrier to vaccination coverage, leading to a higher risk of COVID-19-related morbidity and mortality. To reduce vaccine hesitancy, the factors affecting it must be addressed. Based on the determinants of health approach, this study aimed to investigate whether the distribution of determinants of health differed between the vaccine hesitancy group and the vaccine acceptance group and to identify determinants of participants’ hesitancy to receive the COVID-19 vaccine if it was available. This study utilized the 2020 California Health Interview Survey Data collected between May and December 2020. Data were collected using a population-based web and telephone health survey. Data from 21,949 participants in California were included, and 4,183 (23.4 %) showed vaccine hesitancy. The following determinants were positively associated with vaccine hesitancy: female sex, Black and American Indian/Alaskan Native ethnicity, smoking, poverty, U.S.-born citizen, frequent use of social media, food insecurity, and limited healthcare access. Older age, not having severe psychological distress, not having diabetes, and high perceived safety in the neighborhood were negatively associated with COVID-19 vaccine hesitancy. This study also found that higher use of social media potentially threatened vaccine uptake, whereas frequent internet use was negatively associated with vaccine hesitancy. Public health and other relevant service providers should address the determinants of vaccine hesitancy and develop effective strategies and interventions for vaccine-hesitant groups.
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- 2023
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13. Evaluation of plasma prealbumin as a novel inflammatory biomarker in dogs: a pilot study
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Sin-Wook Park, Keon Kim, Ock-Kyu Kim, Woong-Bin Ro, and Chang-Min Lee
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canine ,biomarkers ,inflammation ,negative acute phase protein ,transthyretin ,Veterinary medicine ,SF600-1100 - Abstract
IntroductionPrealbumin (PAB) is a plasma protein synthesized in the hepatic parenchymal cells. PAB has a short half-life (~2 days), and its concentration is affected by changes in transcapillary escape. Measurement of PAB is widely used in hospitalized patients in human medicine due to its decreasing concentration in states of inflammation and malnutrition. However, only a few studies are available in dogs. The aim of this study is to determine whether the plasma PAB concentration decreases in dogs with inflammation and to evaluate the relationship between the plasma PAB concentration and inflammation-related parameters in dogs.MethodsA total of 94 dogs were divided into healthy (n = 33) and diseased (n = 61) groups. These were further divided into group A (n = 24) and group B (n = 37) according to plasma C-reactive protein (CRP) levels. Group A included dogs with a plasma CRP 0.05). A plasma PAB
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- 2023
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14. Advancements and Future Prospects of Buckling Restrained Braces for Corrosive-Environments: A Comprehensive Literature Review
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Hubdar Hussain and Dong-Keon Kim
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seismic design ,seismic protection devices ,buckling-restrained braces ,anti-corrosive materials ,corrosion-resistant BRBs ,earthquake-prone areas ,Building construction ,TH1-9745 - Abstract
The seismic design of structures is crucial for preventing structural collapse and safeguarding human lives. Buckling-restrained braces (BRBs) have emerged as effective seismic protection devices due to their high stiffness, strength, and exceptional energy absorption capabilities. Typically, a conventional BRB consists of a steel core surrounded by concrete-filled steel tubes, with a separation mechanism ensuring axial-only deformation of the core. However, researchers have been increasingly focusing on developing innovative BRB designs with enhanced performance, incorporating different materials and configurations. This paper presents a comprehensive analysis of the development of novel BRBs introduced in the past 15 years. A systematic review approach is adopted, and the selected articles are categorized based on the shapes, materials, and compositions of the BRB components. Although carbon steel has been widely used in numerous studies, its susceptibility to corrosion and its potential impact on the hysteretic behavior of BRBs remain unexplored. Consequently, future research prospects are identified, highlighting the significance of employing anti-corrosive materials in fabricating BRBs to ensure their stable seismic performance under harsh environmental conditions. Investigating novel materials and configurations can lead to the creation of more robust and corrosion-resistant BRBs, thus enhancing the safety and longevity of structures in earthquake-prone areas.
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- 2023
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15. Evaluation of the Seismic Performance of Single-Plate Metallic Slit Dampers Using Experimental and Numerical Data
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John Mark Go Payawal and Dong-Keon Kim
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passive energy dissipation device ,single-plate metallic slit damper (SPMSD) ,cyclic load ,ABAQUS simulation ,topology optimization ,maximum considered earthquake (MCER) ,Building construction ,TH1-9745 - Abstract
Passive energy dissipation systems and devices are helpful in mitigating the danger of earthquake damage to structures. Metallic slit dampers (MSDs) are one of the most efficient and cost-effective solutions for decreasing seismic energy intake. The potential importance of MSDs in managing vibrations and limiting structural fatigue continues to grow as research advances and new materials and designs are introduced. This study evaluated the seismic performance of single-plate MSDs (SPMSDs) through a combination of numerical simulation and assessment of experimental results. ABAQUS software was used to create an assembly consisting of endplates, bolts, and SPMSDs. A real-world earthquake scenario was simulated using cyclic loads based on ASCE/SEI standards, and displacement-measuring devices such as strain gauges and LVDT were employed to record the behavior of the SPMSDs. The results of the experiment are used to assess the compliance of the SPMSDs and discuss their behavior as they undergo minimum and maximum displacements due to minimum and maximum applied forces. The energy dissipation capabilities of the dampers are presented by analyzing and comparing the area of their hysteresis loops, equivalent viscous damping, and their damping ratios. Actual failure modes are identified and shown to describe the limitations and potential vulnerability of the dampers. The relative error between the lowest and greatest recorded forces from experimental data and numerical simulation ranges from 4.4% to 5.7% for SPMSD 1 and from 1.6% to 2.1% for SPMSD 2, respectively. These deviation values represent a satisfactory level of precision, demonstrating that the numerical simulation accurately predicts the actual performance and behavior of the dampers when subjected to cyclic stress. The topology optimization performed in this study yielded an improved geometry of the SPMSD suited for a corresponding maximum considered earthquake (MCER) displacement of ±33 mm. This research also suggests practical implementations of the investigated and improved SPMSDs.
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- 2023
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16. A Convolutional Transformer Model for Multivariate Time Series Prediction
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Dong-Keon Kim and Kwangsu Kim
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Artificial neural networks ,predictive models ,time series prediction ,Electrical engineering. Electronics. Nuclear engineering ,TK1-9971 - Abstract
This paper presents a multivariate time series prediction framework based on a transformer model consisting of convolutional neural networks (CNNs). The proposed model has a structure that extracts temporal features of input data through CNN and interprets correlations between variables through an attention mechanism. This framework solves the problem of the inability to simultaneously analyze the temporal features of the input data and the correlation between variables, which is a limitation of the forecasting models presented in existing studies. We designed a forecasting experiment using several time series datasets with various data characteristics to precisely evaluate the proposed model. In addition, comparative experiments were performed between the proposed model and several predictive models proposed in recent studies. Furthermore, we conducted ablation studies on the extent to which the proposed CNN structure in the prediction model affects the forecasting results by substituting a specific layer of the model. The results of the experiments showed that the proposed predictive model exhibited good performance in predicting time series data with a clear cycle and high correlation between variables, and improved the accuracy by approximately 3% to 5% compared with that of previous studies’ time series prediction models.
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- 2022
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17. Effect of change of sand properties on travel distance of ricocheted debris
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Yoon Keon Kim and Woo Chun Choi
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Ricochet ,Exploded debirs ,Environmental change ,Sand ,Temperature ,Water content ,Military Science - Abstract
The debris from exploded buildings can ricochet after colliding with the ground, thus increasing the debris travel distance and danger from any associated impacts or collisions. To reduce this danger, the travel distance of ricocheted debris must be accurately predicted. This study analyzed the change in the travel distance of ricocheted concrete debris relative to changes in the properties of a sand medium. Direct shear tests were conducted to measure the change in internal friction angle as a function of temperature and water content of the sand. Finite element analysis (FEA) was then applied to these variables to predict the speed and angle of the debris after ricochet. The FEA results were compared with results of low-speed ricochet experiments, which employed variable temperature and water content. The travel distance of the debris was calculated using MATLAB, via trajectory equations considering the drag coefficient. As the internal friction angle decreased, the shear stress decreased, leading to deeper penetration of the debris into the sand. As the loss of kinetic energy increased, the velocity and travel distance of the ricocheted debris decreased. Changes in the ricochet velocity and travel distance of the debris, according to changes in the internal friction angle, indicated that the debris was affected by the environment.
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- 2021
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18. Dynamic Response of Drill Floor to Fire Subsequent to Blowout
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Teak-Keon Kim, Seul-Kee Kim, and Jae-Myung Lee
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offshore structure ,drilling ,blowout ,fire ,fire protection ,Ocean engineering ,TC1501-1800 - Abstract
Explosions and fires on offshore drilling units and process plants, which cause loss of life and environmental damage, have been studied extensively. However, research on drilling units increased only after the 2010 Deepwater Horizon accident in the Gulf of Mexico. A major reason for explosions and fires on a drilling unit is blowout, which is caused by a failure to control the high temperatures and pressures upstream of the offshore underwater well. The area susceptible to explosion and fire due to blowout is the drill floor, which supports the main drilling system. Structural instability and collapse of the drill floor can threaten the structural integrity of the entire unit. This study simulates the behavior of fire subsequent to blowout and assesses the thermal load. A heat transfer structure analysis of the drill floor was carried out using the assessed thermal load, and the risk was noted. In order to maintain the structural integrity of the drill floor, passive fire protection of certain areas was recommended.
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- 2020
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19. Effects of Entrance Shape and Blast Pocket on Internal Overpressure Mitigation for Protective Tunnels Exposed to External Detonation on the Ground
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Jinwon Shin, Seungki Pang, and Dong-Keon Kim
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protective tunnel ,blast overpressure mitigation ,entrance shape ,blast pocket ,Technology ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Biology (General) ,QH301-705.5 ,Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
This study presents a numerical analysis to reduce the overpressure inside protective tunnels for external detonations. A three-dimensional computational fluid dynamics model of a tunnel subjected to detonation for a hemispherical charge with a charge weight of 555 kg and a standoff distance of 7.6 m was established, based on a mesh sensitivity study to obtain an optimal element size, stability analysis of overpressure, and validation study to evaluate the accuracy of the numerical results based on Unified Facilities Criteria (UFC) 3-340-02. A parametric analysis was performed using the validated numerical model to investigate the effects of the entrance shape and blast pockets on the reduction in the maximum overpressure. The maximum overpressures were effectively reduced as the slope angle of the tunnel entrance decreased and the length of the blast pocket divided by the tunnel width decreased. An optimized shape of the tunnel was proposed based on the numerical results, where the peak overpressures were reduced by a maximum of 64.5%. This study aims to protect facilities, personnel, and equipment and further reduce construction costs by lowering the overpressure rating of blast valves in protective tunnels.
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- 2023
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20. Image-Based Structural Health Monitoring: A Systematic Review
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John Mark Go Payawal and Dong-Keon Kim
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structural health monitoring ,PRISMA ,image-based SHM ,Technology ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Biology (General) ,QH301-705.5 ,Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
The early discovery of factors that compromise a civil infrastructure’s structural integrity allows for safety monitoring, timely prevention, and a prompt remedy to the discovered problem. As a result, researchers have been researching various methodologies and types of structural health monitoring (SHM). A systematic search was performed following the updated Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA 2020) in Scopus and ScienceDirect from Elsevier, Google Scholar, MDPI, Springer, Wiley Online and ASCE Library, EOP and IOP Science, IEEE, and other databases with the reliable peer review process. From 1480 identified pieces of literature, one hundred and nine (109) sources met the criteria for inclusion and exclusion and were used to produce our findings. This study presents the identified purpose and application of image-based SHM, which includes: (1) identifying and discovering; (2) measuring and monitoring; (3) automating and increasing efficiency; and (4) promoting development and creating 3D models. Furthermore, the responsibilities and relevance of components and parameters for implementing image-based SHM devices and systems, and their issues, are covered in this paper. Future research can benefit from the stated applications for innovation and the requirements of image-based SHM.
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- 2023
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21. Transmission of wireless backhaul signal in a cellular system with small moving cells
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Hyoung-Keon Kim, Yong-Suk Byun, Geon-Woong Jung, and Yong-Hwan Lee
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MIMO ,Moving cell ,Backhaul ,Telecommunication ,TK5101-6720 ,Electronics ,TK7800-8360 - Abstract
Abstract Deployment of small moving cells (SMCs) has been considered in advanced cellular systems, where wireless backhaul links are required between base stations and SMCs. In this paper, we consider signal transmission by means of multiuser beamforming in the wireless backhaul link. We generate the beam weight in an eigen-direction of weighted combination of short- and long-term channel information of the backhaul link. The beam weight can maximize the average signal-to-leakage-plus-noise ratio (SLNR), while providing the transmission robust to SMC mobility. We analyze the performance of the proposed scheme in terms of the average signal-to-interference-plus-noise ratio (SINR) and optimize the transmit power by iterative water-filling. Finally, we verify the performance of the proposed scheme by computer simulation.
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- 2019
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22. A Comparison of Emergency Department Revisit Rates of Pediatric Patients between Pre-COVID-19 and COVID-19 Periods
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Myeong Namgung, Dong Hoon Lee, Sung Jin Bae, Ho Sub Chung, Ji Young Park, Keon Kim, Choung Ah Lee, Duk Ho Kim, Eui Chung Kim, Jee Yong Lim, Sang Soo Han, and Yoon Hee Choi
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revisit to emergency department ,COVID-19 ,pediatric patients ,Pediatrics ,RJ1-570 - Abstract
Unscheduled revisits to emergency departments (EDs) are important because they indicate the quality of emergency care. However, the characteristics of pediatric patients visiting EDs changed during the coronavirus disease (COVID-19) pandemic, and these changes may have affected their revisit patterns. Therefore, we aimed to compare the ED revisit patterns of pediatric patients between the pre-COVID-19 and COVID-19 periods. This retrospective multicenter study included patients aged below 18 years who visited the ED in the pre-COVID-19 and COVID-19 periods. ED revisit rates were analyzed using five age groups and three visit-revisit intervals. In the pre-COVID-19 period, the revisit rates decreased with increasing age. In the COVID-19 period, the revisit rates were the lowest for the group aged 4–6 years, and the rates increased for those aged ≥7 years. In conclusion, there were changes in the patterns of revisit rates of pediatric patients according to age between the pre-COVID-19 and COVID-19 periods. Therefore, it is necessary to identify the reasons for revisits according to age and establish strategies to reduce the revisit rates of pediatric patients.
- Published
- 2022
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23. Ricochet of steel spheres on sand with varying water content
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Yoon Keon Kim and Woo Chun Choi
- Subjects
Mechanical engineering and machinery ,TJ1-1570 - Abstract
The explosion of a building generates plenty of debris that flies far away. The flying debris is hazardous because it contains large amounts of kinetic energy. Therefore, determining the safety distance from the debris is essential. However, debris ricochet that collides onto the ground affects the safety distance because the ricochet phenomenon is influenced by the condition of the medium. In this study, experiments and finite element analysis were performed to investigate the ricochet based on the water content of sand. From a direct shear test, the internal friction angle and cohesion of sand were obtained based on the water content. The effects of internal friction angle and adhesion on the yield stress and ricochet were investigated. The results indicated that as the water content increased, the internal friction angle increased and then decreased, and the cohesion continued to decrease. The yield stress was proportional to the internal friction angle and inversely proportional to adhesion. Therefore, lower yield stress resulted in deeper penetration of debris, leading to higher energy loss, which increased the kinetic energy loss factor. Thus, the condition of the medium should be considered for setting a proper safety distance suitable for the surrounding environment of the building.
- Published
- 2020
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24. Farnesyl diphosphate synthase is important for the maintenance of glioblastoma stemness
- Author
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Hee Yeon Kim, Dong Keon Kim, Seung-Hyun Bae, HyeRan Gwak, Ji Hoon Jeon, Jong Kwang Kim, Byung Il Lee, Hye Jin You, Dong Hoon Shin, Young-Ho Kim, Soo Youl Kim, Sung-Sik Han, Jin-Kyoung Shim, Ji-Hyun Lee, Seok-Gu Kang, and Hyonchol Jang
- Subjects
Medicine ,Biochemistry ,QD415-436 - Abstract
Brain cancer: Enzyme target for potential therapy A drug that targets a key enzyme in aggressive brain cancer tumors could help tackle resistance to existing treatments. Glioblastoma is the most aggressive form of brain cancer and remains difficult to treat because the cancer cells can survive chemotherapy and radiotherapy. Certain cells within glioblastoma tumors have ‘stemness’ – unique stem cell-like metabolic characteristics that allow them to rapidly repair DNA damage and trigger relapse. Hyonchol Jang at the National Cancer Center in Goyang, South Korea and co-workers discovered that an enzyme called farnesyl diphosphate synthase (FDPS) helps maintain stemness in glioblastoma. The team then treated patient-derived glioblastoma cells with existing drugs known to inhibit FDPS. One such drug, which is already used to treat osteoporosis, inhibited the formation of secondary glioblastoma and may prove valuble in the treatment of brain cancer.
- Published
- 2018
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25. Dynamic Contrast-Enhanced CT Findings of a Extrapleural Solitary Fibrous Tumor in the Spleen: A Case Report and Literature Review
- Author
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Tae Keon Kim, Hyun Young Han, and Ju Heon Kim
- Subjects
solitary fibrous tumors ,hemangiopericytoma ,spleen ,computed tomography ,x-ray ,calcification ,pathologic ,Medical physics. Medical radiology. Nuclear medicine ,R895-920 - Abstract
Extrapleural solitary fibrous tumor, formerly referred to as "hemangiopericytoma" is a rare soft tissue vascular tumor which has elevated malignancy potential arising from the capillary pericytes. Extrapleural solitary fibrous tumors, originating from the spleen, are extremely rare. We report on a rare case of a patient presenting with splenic extrapleural solitary fibrous tumors with intratumoral irregular calcification detected by dynamic contrast-enhanced computed tomography.
- Published
- 2018
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26. A Study on TiO2 Surface Texturing Effect for the Enhancement of Photocatalytic Reaction in a Total Phosphorous Concentration Measurement System
- Author
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Jae Keon Kim, Seung Deok Kim, Jae Yong Lee, Chang Hee Kim, Hyeon-Su Lee, Seong Mo Koo, YoungJin Lee, Jong-Hoo Paik, Da Ye Kim, and Seong Ho Kong
- Subjects
total phosphorus ,surface texturing ,sandblast ,photocatalysis ,Mechanical engineering and machinery ,TJ1-1570 - Abstract
Powerful sunlight, a high water temperature, and stagnation in the water flow induce eutrophication in rivers and lakes, which destroys the aquatic ecosystem and threatens the downstream water supply systems. Accordingly, it is very important to perform real-time measurements of nutrients that induce algal growth, especially total phosphorus, to preserve and manage the aquatic ecosystem. To conduct quantitative analysis of the total phosphorus in the aquatic ecosystem, it is essential to perform a pretreatment process and quickly separate the phosphorus, combined with organic and inorganic materials, into a phosphate. In this study, the sandblasting process was used for the physical etching of the wafer, and photocatalytic materials were deposited on the surface with various roughness in order to improve the photocatalytic reaction surface and efficiency. The photocatalytic reaction was applied to combine the pretreated sample with the coloring agent for color development, and the absorbance of the colored sample was analyzed quantitatively to compare and evaluate the characteristics, followed by the surface increase in the photocatalytic materials. In addition, the pretreatment and measurement parts were materialized in a single chip to produce a small and light total phosphorus analysis sensor.
- Published
- 2021
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27. Modeling of Ductile Fracture for SS275 Structural Steel Sheets
- Author
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Yonghyun Cho, Changkye Lee, Jurng-Jae Yee, and Dong-Keon Kim
- Subjects
ductile fracture ,digital image correlation: hybrid experimental–finite element method ,stress triaxiality ,Technology ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Biology (General) ,QH301-705.5 ,Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
A series of earthquake events give impetus to research on the ductile fracture behavior of steel materials. In the last decades, many fracture models have been developed and utilized in the mechanical or aerospace engineering. Nevertheless, very little application to structural members used in the construction industry has been made due to the lack of a suitable model for the fracture behavior of constructional steel. This paper presents the experimental and finite element (FE) technique to predict ductile fracture in mild carbon structural steel (SS275) sheets, which has been widely used in building structures. The post-necking true stress–strain responses were successfully estimated using the weighted-average method. The Bao and Wierzbicki (BW) model, which requires only two model parameters, was selected for the identification of fracture locus. Each model parameter was calibrated from uniaxial tension and in-plane shear specimens with the aid of digital image correlation (DIC) and finite element analysis. Fracture simulation was then performed and validated based on the experimental results of the specimens under combined tension and shear stress state.
- Published
- 2021
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28. Characteristics of Elderly Long-Term Care Residents Who Were Injured and Transferred to Hospital Emergency Departments in Korea: A Retrospective Multicenter Study
- Author
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Myeong Namgung, Keon Kim, Dong Hoon Lee, Ho Young Yune, Jung Hee Wee, Duk Ho Kim, Eui Chung Kim, and Jee Yong Lim
- Subjects
Medical emergencies. Critical care. Intensive care. First aid ,RC86-88.9 - Abstract
The objective of this retrospective multicenter study was to investigate the mechanism and characteristics of trauma experienced by patients aged ≥65 years who were transferred from a long-term care hospital to one of five university hospital emergency departments. Of 255,543 patients seen in one of the five emergency departments, 79 were transferred from a long-term care hospital because of trauma. The most common trauma mechanism was slipping down, with 33 (58.9%) patients, followed by falling from a bed (17.9%), striking an object such as a wall or corner (10.7%), overextending a joint (8.9%), and unknown mechanisms (3.6%). Many cases of slip (39.4%) occurred in relation to the bathroom. Comparing slip and fall from a bed, we found more hip fractures (95.2%) because of slipping down than falling from a bed (57.1%); traumatic brain injury only occurred in slip cases. These traumas cause significant morbidity in elderly patients; therefore, we sought to identify strategies that prevent slip in long-term care hospitals.
- Published
- 2019
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29. Finite Element Analysis on Block Shear Mechanism of Lean Duplex Stainless Steel Welded Connections
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YongHyun Cho, Dong-Keon Kim, JunSu Kim, and TaeSoo Kim
- Subjects
finite element analysis ,welded connection ,lean duplex stainless steel ,stress triaxiality ,block shear fracture ,Technology ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Biology (General) ,QH301-705.5 ,Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
The block shear equations specified in the current AISC specification for structural steel buildings and North American cold-formed steel design specifications are based on research results of carbon steel bolted connections. These equations were found to be inapplicable for the welded connections in the literature. This issue is primarily associated with the use of the incorrect assumption on block shear failure mechanism. The present paper examines the accuracy of various block shear equations available in the design specifications and in the literature. The paper also examines the shear hardening capacity and the level of tensile stress over the critical net area with the results of finite element analysis, in which the fracture simulation is considered. It shows that the block shear capacities of lean duplex stainless steel welded connections can be predicted accurately using tensile stress equal to 1.25Fu, as proposed in the literature.
- Published
- 2021
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30. Respiratory and Systemic Toxicity of Inhaled Artificial Asian Sand Dust in Pigs
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Keon Kim, Seon-Deuk Kim, Tae-Hoon Shin, Chun-Sik Bae, Taeho Ahn, Sung-Shik Shin, Ha-Jung Kim, Chang-Min Lee, and Guk-Hyun Suh
- Subjects
Asian sand dust ,domestic animal model ,respiratory toxicity ,systemic inflammation ,Science - Abstract
Air pollution, particularly caused by Asian sand dust (ASD) and particulate matter (PM), has become one of the leading threats to public health. However, the majority of studies have primarily focused on epidemiological assessment, and in vivo toxicities of certain air pollutants have been poorly elucidated in medium/large-size laboratory animals. To investigate the impact of ASD in domestic animals, 16 Landrace pigs were exposed to an artificial ASD sandstorm for 6 h. All animals were divided in four cages, and a commercial yellow soil was used for generating artificial mineralogical particles. Blood samples were collected, and necropsies were performed before exposure and 6, 12, 24, and 72 h after exposure. Complete blood cell count and the levels of serum biochemical enzymes, blood gas, electrolytes, and a variety of inflammatory cytokines were evaluated. In addition, histopathological examination was conducted. Various test results proved acute lower airway disorders with systemic inflammation in pigs. To our knowledge, this study is the first to describe experimental research in domestic animals concerning the damage caused by artificial ASD exposure. The results of this study suggest that ASD has importance in terms of not only public health but also of ultimate economic losses in the pork industry.
- Published
- 2021
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- View/download PDF
31. Dynamic Response of Drill Floor Considering Propagation of Blast Pressure Subsequent to Blowout
- Author
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Teak-Keon Kim, Seul-Kee Kim, and Jae-Myung Lee
- Subjects
drilling ,drill floor ,gas explosion ,blast pressure propagation ,dynamic structural response ,finite element method ,Technology ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Biology (General) ,QH301-705.5 ,Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
Explosions and fire have very critical safety hazard impacts on offshore oil and gas facilities since they are mostly located in remote areas and could induce serious environmental issues. Explosion risk assessment and structure blast analysis are essential for these production facilities, and research studies have been carried out. Explosion due to blowout during drilling operation is also a critical risk for drilling units, and this has not been researched much until the accident of the drilling unit in the Gulf of Mexico in 2010. This paper provides the risk and evaluation of explosion and structure under blast pressure during the drilling operation, whereas previous research studies have mainly been interested in process plants. This study suggests weight saving in drilling units through the consideration of the actual behavior of gas explosion. Weight saving is the priority of offshore unit design due to payload. This research also gives guidelines to select the material-grade-appropriate anti-explosion system through the comparison of several materials by design and result.
- Published
- 2020
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32. Relationship between occupational stress and depressive mood among interns and residents in a tertiary hospital, Seoul, Korea
- Author
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Keon Kim, Sunhwa Lee, and Yoon Hee Choi
- Subjects
occupational stress ,internship and residency ,depression ,Medical emergencies. Critical care. Intensive care. First aid ,RC86-88.9 - Abstract
Objective Occupational stress can have a harmful effect on the individual both physically and psychologically. In Korea, occupational stress of physician is rarely demonstrated. Although it is well reported that physicians tend to have a high incidence of minor psychiatric disorders, the magnitude of the problem remains unclear. Interns and residents are thought to be under substantial amount of stress, and tend to have psychiatric disorder. In this paper, we aimed to evaluate the relationship between the occupational stress and depression of residents. Methods The participants of this study were surgical and medical residents in a tertiary hospital in Korea. For measurement of occupational stress, we used an occupational stress scale. In addition, to evaluate the prevalence of depression, we used the Beck Depression Inventory. Results Female doctors showed higher degree of occupational stress than the males. The interns and chief residents showed higher degree of occupational stress than the other residents. Interestingly, in this study, most of the participants experienced a depressive mood. Compared with the general population, job demand and culture of workplace were high. Occupational stress was the only significant predictor of a depressive mood. Conclusion Hospital residents experience a high degree of occupational stress leading to a depressed mood due to various risk factors. Therefore, it is essential to recognize the occupational stress of residents early, to encourage positive competition and peer and social support, and to help improve the residents’ ability to cope with stress.
- Published
- 2015
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33. Gossypol Suppresses Growth of Temozolomide-Resistant Glioblastoma Tumor Spheres
- Author
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Hee Yeon Kim, Byung Il Lee, Ji Hoon Jeon, Dong Keon Kim, Seok-Gu Kang, Jin-Kyoung Shim, Soo Youl Kim, Sang Won Kang, and Hyonchol Jang
- Subjects
bcl2 ,dehydrogenase ,glioblastoma ,gossypol ,temozolomide resistance ,Microbiology ,QR1-502 - Abstract
Temozolomide is the current first-line treatment for glioblastoma patients but, because many patients are resistant to it, there is an urgent need to develop antitumor agents to treat temozolomide-resistant glioblastoma. Gossypol, a natural polyphenolic compound, has been studied as a monotherapy or combination therapy for the treatment of glioblastoma. The combination of gossypol and temozolomide has been shown to inhibit glioblastoma, but it is not clear yet whether gossypol alone can suppress temozolomide-resistant glioblastoma. We find that gossypol suppresses the growth of temozolomide-resistant glioblastoma cells in both tumor sphere and adherent culture conditions, with tumor spheres showing the greatest sensitivity. Molecular docking and binding energy calculations show that gossypol has a similar affinity to the Bcl2 (B-cell lymphoma 2) family of proteins and several dehydrogenases. Gossypol reduces mitochondrial membrane potential and cellular ATP levels before cell death, which suggests that gossypol inhibits several dehydrogenases in the cell’s metabolic pathway. Treatment with a Bcl2 inhibitor does not fully explain the effect of gossypol on glioblastoma. Overall, this study demonstrates that gossypol can suppress temozolomide-resistant glioblastoma and will be helpful for the refinement of gossypol treatments by elucidating some of the molecular mechanisms of gossypol in glioblastoma.
- Published
- 2019
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34. Tunable Fabry-Perot Interferometer Designed for Far-Infrared Wavelength by Utilizing Electromagnetic Force
- Author
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Dong Geon Jung, Jun Yeop Lee, Jae Keon Kim, Daewoong Jung, and Seong Ho Kong
- Subjects
FPI ,IR detector ,optical filter ,Chemical technology ,TP1-1185 - Abstract
A tunable Fabry-Perot interferometer (TFPI)-type wavelength filter designed for the long-wavelength infrared (LWIR) region is fabricated using micro electro mechanical systems (MEMS) technology and the novel polydimethylsiloxane (PDMS) micro patterning technique. The structure of the proposed infrared sensor consists of a Fabry-Perot interferometer (FPI)-based optical filter and infrared (IR) detector. An amorphous Si-based thermal IR detector is located under the FPI-based optical filter to detect the IR-rays filtered by the FPI. The filtered IR wavelength is selected according to the air etalon gap between reflectors, which is defined by the thickness of the patterned PDMS. The 8 μm-thick PDMS pattern is fabricated on a 3 nm-thick Al layer used as a reflector. The air etalon gap is changed using the electromagnetic force between the permanent magnet and solenoid. The measured PDMS gap height is about 2 μm, ranging from 8 μm to 6 μm, with driving current varying from 0 mA to 600 mA, resulting in a tunable wavelength range of 4 μm. The 3-dB bandwidth (full width at half maximum, FWHM) of the proposed filter is 1.5 nm, while the Free Spectral Range (FSR) is 8 μm. Experimental results show that the proposed TFPI can detect a specific wavelength at the long LWIR region.
- Published
- 2018
- Full Text
- View/download PDF
35. Multi-axis Response of a Thermal Convection-based Accelerometer
- Author
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Jae Keon Kim, Maeum Han, Shin-Won Kang, Seong Ho Kong, and Daewoong Jung
- Subjects
accelerometer ,frequency ,acceleration ,heat convection ,Mechanical engineering and machinery ,TJ1-1570 - Abstract
A thermal convection-based accelerometer was fabricated, and its characteristics were analyzed in this study. To understand the thermal convection of the accelerometer, the Grashof and Prandtl number equations were analyzed. This study conducted experiments to improve not only the sensitivity, but also the frequency band. An accelerometer with a more voluminous cavity showed better sensitivity. In addition, when the accelerometer used a gas medium with a large density and small viscosity, its sensitivity also improved. On the other hand, the accelerometer with a narrow volume cavity that used a gas medium with a small density and large thermal diffusivity displayed a larger frequency band. In particular, this paper focused on a Z-axis response to extend the performance of the accelerometer.
- Published
- 2018
- Full Text
- View/download PDF
36. Sensitivity and Frequency-Response Improvement of a Thermal Convection–Based Accelerometer
- Author
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Maeum Han, Jae Keon Kim, Jin-Hyoung Park, Woojin Kim, Shin-Won Kang, Seong Ho Kong, and Daewoong Jung
- Subjects
accelerometer ,frequency ,acceleration ,heat convection ,Chemical technology ,TP1-1185 - Abstract
This paper presents a thermal convection–based sensor fabricated using simple microelectromechanical systems (MEMS)-based processes. This sensor can be applied to both acceleration and inclination measurements without modifying the structure. Because the operating mechanism of the accelerometer is the thermal convection of a gas medium, a simple model is proposed and developed in which the performance of the thermal convection–based accelerometer is closely associated with the Grashof number, Gr and the Prandtl number, Pr. This paper discusses the experiments that were performed by varying several parameters such as the heating power, cavity size, gas media, and air pressure. The experimental results demonstrate that an increase in the heating power, pressure, and cavity size leads to an increase in the accelerometer sensitivity. However, an increase in the pressure and/or cavity size results in a decrease in the frequency bandwidth. This paper also discusses the fact that a working-gas medium with a large thermal diffusivity and small kinematic viscosity can widen the frequency bandwidth and increase the sensitivity, respectively.
- Published
- 2017
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37. Development of a Liquid Scintillator Using Water for a Next Generation Neutrino Experiment
- Author
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Sun Heang So, Kyung Kwang Joo, Ba Ro Kim, Bong Keon Kim, Seung Chan Kim, Chang Dong Shin, and In Sung Yeo
- Subjects
Physics ,QC1-999 - Abstract
A feasibility study on a new type of liquid scintillator based on water has been performed. Mainly due to the differences in polarities between water and oil, organic solvents are not mixed in water. In order to make a liquid scintillator based on water, a surfactant that contains hydrophilic and hydrophobic groups is used. The surfactant keeps water and organic solvents apart in solution. Good physical and optical parameters and long-term stability are required to use liquid scintillator based on water in massive detector for the next generation neutrino experiments. In this paper, we report the characteristics and the possibility of liquid scintillators using water with various new surfactants.
- Published
- 2014
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38. A Two-Surface Viscoplastic Model for the Structural Steel
- Author
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Dong-Keon Kim and Jinkyu Kim
- Subjects
Two-surface model ,Viscoplasticity ,Numerical simulation ,Mechanics of engineering. Applied mechanics ,TA349-359 ,Descriptive and experimental mechanics ,QC120-168.85 - Abstract
Abstract As extension of the previous two-surface model in plasticity, a two-surface model for viscoplasticity is presented herein. In order to validate and investigate the performance of the proposed model, several numerical simulations are undertaken especially for structural steel under monotonic and cyclic loading cases, where experimental results and numerical results from the rate dependent kinematic hardening model are also provided for the reference. For all the cases studied, the proposed model can appropriately account for the rate-effects in both maximum stress and hysteretic shapes.
- Full Text
- View/download PDF
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