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"Lee, Dong-Geun"
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Distribution of atherosclerotic stenosis determining early neurologic deterioration in acute ischemic stroke
2017
Early neurologic deterioration (END) during the acute stage of stroke is clinically important because of its association with poor outcomes. The purpose of this study was (1) to investigate variables associated with END, (2) to determine the distribution of atherosclerotic stenosis associated with END, and (3) to clarify the relationship between END and clinical outcomes.
516 patients with acute ischemic stroke were included. The median follow-up period was 31.7 months. END was defined as a ≥2 point increase in the National Institutes of Health Stroke Scale (NIHSS), ≥1 point increase in level of consciousness or motor item of the NIHSS, or the development of any new neurological deficits during the first 72 hours of hospitalization. A signal loss on 1.5-T magnetic resonance angiography exceeding 50% was considered to be significant for the categorization of stenosis pattern.
The prevalence of END was 19.0%. END was associated with intracranial atherosclerotic stenosis (IAS) together with large artery atherosclerosis (LAA) subtype. In particular, stenosis of basilar artery or posterior cerebral artery was independently associated with END. Lesion growth or hypoperfusion was more accountable for END in patients with IAS, whereas intracerebral hemorrhage or edema/herniation was more frequently observed in END patients without IAS. Patients with END had a higher rate of mortality, but a similar rate of further vascular events compared to patients without END.
Pre-stroke IAS and LAA subtype could determine the development of END during the acute stage of ischemic stroke.
Journal Article
Effect of Oxygen on Static Recrystallization Behaviors of Biomedical Ti-Nb-Zr Alloys
by
Lee, Dong-Geun
,
Han, Chan-Byeol
in
beta titanium alloy
,
Biocompatibility
,
Biomedical materials
2024
Titanium alloys that are used in biomedical applications must possess biocompatibility and a low elastic modulus so that they protect host bone tissue without causing stress shielding. As the elastic modulus of beta Ti alloys is close to that of bone (10–30 GPa), these alloys are considered potential orthopedic implant materials. The elastic modulus of the single β-phase Ti-39Nb-6Zr (TNZ40) alloy is approximately 40 GPa, whereas the strength is lower than that of other types of Ti alloys. Interstitial oxygen in a Ti matrix is well known to improve the matrix strength by solid-solution hardening. The desired mechanical properties can be optimized using a thermo-mechanical procedure to maintain a low elastic modulus. In order to enhance the strength, TNZ40 alloys were fabricated with different amounts of oxygen. The TNZ-0.16O and TNZ-0.26O alloys were cold swaged into 11 mm diameter bars, subjected to solution treatment at 900 °C and 950 °C for 2 h, and furnace-cooled to room temperature. As a result, recrystallized grains were clearly observed in the β matrix. The TNZ-0.26O alloy that was cold-worked by swaging followed by solution treatment at 900 °C exhibited the best mechanical properties (Vickers hardness: 247 HV, ultimate tensile strength: 777 MPa, elongation at rupture: 18.6%, and compressive strength: 1187 MPa). This study reports the effects of oxygen content on the recrystallization behavior and mechanical properties of these alloys.
Journal Article
Robust Motor Imagery-Brain-Computer Interface Classification in Signal Degradation: A Multi-Window Ensemble Approach
2025
Electroencephalography (EEG)-based brain-computer interface (BCI) mimics the brain's intrinsic information-processing mechanisms by translating neural oscillations into actionable commands. In motor imagery (MI) BCI, imagined movements evoke characteristic patterns over the sensorimotor cortex, forming a biomimetic channel through which internal motor intentions are decoded. However, this biomimetic interaction is highly vulnerable to signal degradation, particularly in mobile or low-resource environments where low sampling frequencies obscure these MI-related oscillations. To address this limitation, we propose a robust MI classification framework that integrates spatial, spectral, and temporal dynamics through a filter bank common spatial pattern with time segmentation (FBCSP-TS). This framework classifies motor imagery tasks into four classes (left hand, right hand, foot, and tongue), segments EEG signals into overlapping time domains, and extracts frequency-specific spatial features across multiple subbands. Segment-level predictions are combined via soft voting, reflecting the brain's distributed integration of information and enhancing resilience to transient noise and localized artifacts. Experiments performed on BCI Competition IV datasets 2a (250 Hz) and 1 (100 Hz) demonstrate that FBCSP-TS outperforms CSP and FBCSP. A paired t-test confirms that accuracy at 110 Hz is not significantly different from that at 250 Hz (
< 0.05), supporting the robustness of the proposed framework. Optimal temporal parameters (window length = 3.5 s, moving length = 0.5 s) further stabilize transient-signal capture and improve SNR. External validation yielded a mean accuracy of 0.809 ± 0.092 and Cohen's kappa of 0.619 ± 0.184, confirming strong generalizability. By preserving MI-relevant neural patterns under degraded conditions, this framework advances practical, biomimetic BCI suitable for wearable and real-world deployment.
Journal Article
Association between ischemic stroke and seropositive rheumatoid arthritis in Korea: A nationwide longitudinal cohort study
by
Hong, Je Beom
,
Sheen, Seung Hun
,
Jang, Jae-Won
in
Arthritis
,
Biology and Life Sciences
,
Codes
2021
The purpose of this longitudinal follow-up study was to investigate the risk of ischemic stroke nationwide in patients with seropositive rheumatoid arthritis (RA) and controls who were matched in age and sex. Patient data were collected from the National Health Insurance Service (NHIS) Health Screening (HEALS) cohort. Using the International Classification of Diseases code M05 (seropositive RA), with a prescription of any disease-modifying anti-rheumatic drug (DMARD), RA was identified. A total of 2,765 patients and 13,825 control subjects were included in our study. The 12-year incidence of ischemic stroke in each group was calculated using the Kaplan–Meier method. The risk ratio of ischemic stroke was estimated using Cox proportional hazards regression. Sixty-four patients (2.31%) in the seropositive RA group and 512 (3.70%) in the control group experienced ischemic stroke ( P < 0.001) during the follow-up period. The hazard ratio of ischemic stroke in the seropositive RA group was 1.32 (95% confidence interval (CI), 1.02–1.73) after adjusting for age and sex. The adjusted hazard ratio of ischemic stroke in the seropositive RA group was 1.40 (95% CI, 1.07–1.82) after adjusting for demographics and comorbid medical disorders. According to the subgroup analysis, the hazard ratios of ischemic stroke risks in the female and hypertensive subgroups were 1.44 (95% CI, 1.05–1.97) and 1.66 (95% CI, 1.16–2.38), respectively. In the non-diabetes and non-dyslipidemia subgroups, the corresponding hazard ratios of ischemic stroke were 1.47 (95% CI, 1.11–1.95) and 1.43 (95% CI, 1.07–1.91). Seropositive RA patients have an increased risk of ischemic stroke. In female, hypertension, non-diabetes, and non-dyslipidemia RA subgroups, even without the traditional risk factors for stroke (except for hypertension), increased the risk, which could be potentially attributed to RA.
Journal Article
Effect of Molybdenum Content on Microstructure and Mechanical Properties of Ti-Mo-Fe Alloys by Powder Metallurgy
by
Lee, Dong-Geun
,
Park, Ji-Hwan
,
Hwang, Hyo-Woon
in
Alzheimer's disease
,
beta titanium
,
Biomedical materials
2022
Titanium has many limitations in coverage and frequency of application due to its expensive alloying elements and complex manufacturing process. The biocompatible Ti-Mo-Fe ternary beta titanium alloys were designed by replacing high-cost beta-stabilizer elements (V, Nb, Zr, etc.) with low-cost Mo and Fe elements. In addition, it was attempted to obtain a low-cost, high-strength beta-titanium alloy with 800 MPa or more by applying the powder metallurgy process technology to the Ti-Mo-Fe alloy system. The added Mo element has the effect of reducing the elastic modulus of the titanium alloy without reducing its strength. In this study, Ti-Mo-Fe alloys designed with different Mo contents were fabricated using a powder metallurgy process and analyzed in connection with microstructural properties, phase changes, and mechanical properties. As Mo contents are increased, the α-lath thickness of Widmanstätten decreases and the size of prior β grain decreases. It was confirmed that the hardness and tensile strength were excellent and were compared with the ingot material of the same alloy system.
Journal Article
Relationship between Kidney Dysfunction and Ischemic Stroke Outcomes: Albuminuria, but Not Estimated Glomerular Filtration Rate, Is Associated with the Risk of Further Vascular Events and Mortality after Stroke
2016
Estimated glomerular filtration rate (eGFR) and albuminuria are known to be associated with ischemic stroke outcomes. In this study, we investigated the longitudinal relationships of the two markers with mortality, vascular events and functional outcomes in a stroke cohort.
A total of 295 patients with acute ischemic stroke were prospectively recruited in a single center between May 2012 and February 2015. Renal dysfunction was defined as a decreased eGFR (<60 mL/min/1.73 m2) or albuminuria (urine albumin-to-creatinine ratio ≥ 30 mg/g). Good functional outcome at 6 months was defined as a modified Rankin scale score ≤ 2, and the occurrence of major vascular events (stroke, acute coronary syndrome or peripheral artery occlusion) or death was monitored. The associations between renal dysfunction and mortality, major vascular events, and 6-month functional outcome were evaluated by the Cox proportional hazards model and logistic regression analysis. Unadjusted and adjusted hazards ratios (HRs), odds ratios (ORs), and 95% confidence intervals (CIs) were obtained. A Kaplan-Meier survival curve for composite adverse events (major vascular events or death) was also computed according to the presence or absence of albuminuria.
Albuminuria, not eGFR, was significantly associated with mortality (P = 0.028; HR 2.15; 95% CI 1.09-4.25) and major vascular events (P = 0.044; HR 2.24; 95% CI 1.02-4.94) in the multivariate Cox proportional hazards models adjusting for age, sex, diabetes, hypertension, current smoking, atrial fibrillation, previous stroke, alcohol history, initial National Institutes of Health Stroke Scale (NIHSS) score and eGFR. In addition, albuminuria was negatively associated with 6-month functional outcome in the multivariate logistic regression analysis adjusting for age, sex, diabetes, hypertension, current smoking, atrial fibrillation, previous stroke, alcohol history and eGFR (P = 0.001; OR 0.36; 95% CI 0.20-0.65), but the association disappeared when NIHSS score was additionally adjusted (P = 0.519; OR 0.79; 95% CI 0.39-1.60). Furthermore, the patients with albuminuria had a significantly higher rate of composite adverse events than the patients without albuminuria (P < 0.001 by log-rank test).
Albuminuria seems a more useful clinical indicator than eGFR in evaluating the risk of adverse outcomes including further vascular events and death in patients with ischemic stroke.
Journal Article
Control of Hybrid Active Power Filter to Reduce Harmonics of 3-Phase Cap-Less Inverter
by
Kim, Rae-Young
,
Lee, Dong-Geun
in
Capacitors
,
Electrical Engineering
,
Electrical Machines and Networks
2023
Recently, material cost competitiveness in various fields, by applying a cap-less inverter technology that uses a small capacity film capacitor to the dc link, the harmonics of input current increase and the power factor decreases compared to the motor drive inverter that uses the existing large capacitor. The increase in harmonics must be installed by expanding the power facility capacity, and the installation of communication facilities sensitive to harmonics is limited. In addition, the decrease in power factor increases the reactive power component, which requires a large current compared to the actual operating capacity, and causes a problem of reducing the operating range of the product. The hybrid active power filter proposed in this paper reduces high order harmonics by applying L filter to the dc side of a 3 phase cap-less inverter for motor driving. The load harmonic compensation current for overall order harmonics through the active power filter. The input current harmonic is reduced by injecting with the current harmonic by inverting the phase. The IEC 61000-3-2 Class A of international harmonics regulations was met and verified using the proposed harmonic reduction system.
Journal Article
Effect of Aging Treatment on the Microstructure and Mechanical Properties of Ti-3Al-8V-6Cr-4Mo-4Zr Alloy
2024
The mechanical properties of beta titanium alloys can be improved by precipitating the α phase in the β-phase matrix and controlling the microstructure via appropriate aging treatments. In this study, heat treatment in the range of 400 to 550 °C is performed to optimize the aging of Ti-3Al-8V-6Cr-4Mo-4Zr alloys. The increase in the aging temperature and holding time increases the hardness and compressive yield strength owing to the precipitation of the secondary α phase in the β matrix. The precipitation driving force at 400 °C is low because of the slow diffusion rate, and therefore the improvements in the hardness and strength are small. At temperatures above 500 °C, phase separation occurs rapidly (β → β + β′), and the β′ phase acts as a nucleation site for the secondary α phase. The phase transformation from the β′ to the secondary α phase is promoted at 500 °C, resulting in the highest hardness (406.3 HV) and compressive yield strength (1433.8 MPa) at 24 h. At 550 °C, the secondary α phase grows and the hardness and compressive yield strength degrade. These results can be effectively applied to manufacture springs with excellent formability and mechanical properties.
Journal Article
Video-assisted thoracoscopic lobectomy is feasible for selected patients with clinical N2 non-small cell lung cancer
2020
Few studies have evaluated the usefulness of video-assisted thoracoscopic surgery (VATS) for advanced-stage lung cancer. We aimed to evaluate the feasibility of VATS for treating clinical N2 (cN2) lung cancer. A retrospective cohort analysis was performed with data from 268 patients who underwent lobectomy for cN2 disease from 2007 to 2016. Using propensity score-based inverse probability of treatment weighting (IPTW), perioperative and long-term survival outcomes were compared. We performed VATS and open thoracotomy on 121 and 147 patients, respectively. Overall, VATS was preferred for patients with peripherally located tumors (
p
< 0.001). After IPTW-adjustment, all preoperative information became similar between the groups. Compared to thoracotomy, VATS was associated with shorter hospitalization (7.7 days vs. 9.1 days,
p
= 0.028), despite equivalent complete resection rates (92.6% vs. 90.5%,
p
= 0.488) and dissected lymph nodes (mean, 31.9 vs. 29.4,
p
= 0.100). On IPTW-adjusted analysis, overall survival (50.5% vs. 48.4%,
p
= 0.127) and recurrence-free survival (60.5% vs 44.6%,
p
= 0.069) at 5 years were also similar between the groups. Among selected patients with resectable cN2 disease and peripherally located tumors, VATS is feasible, associated with shorter hospitalization and comparable perioperative and long-term survival outcomes, compared with open thoracotomy.
Journal Article
Comparison of the Accuracy of Intraoral Scanners Based on the Type of Tooth Preparation for a Single Crown
2021
The purpose of this study was to evaluate the accuracy of intraoral scanners in 10 abutments (five premolars and five molars) obtained in a dental clinic and to analyze the impacts of the volume and area of abutments on scanning accuracy. Abutment casts were scanned five times with a 3D contact scanner (DS10; Renishaw plc). The five scan files were lined up and then merged, and one high-resolution computer-aided design reference model (CRM) was obtained. To obtain a computer-aided design test model (CTM), three types of intraoral scanners (CS3600 (Carestream Dental), i500 (Medit), and EZIS PO (DDS)) and one type of laboratory scanner (E1; 3Shape) were employed. Using 3D analysis software (Geomagic control X; 3D Systems), the accuracy of the scanners was evaluated, including optimal overlap by optimal alignment. The conformity of the overlapped data was calculated by the root mean square (RMS) value, using the 3D compare function for evaluation. As for statistical analysis, testing was conducted, using one-way and two-way ANOVA and the Tukey HSD test (α = 0.05) for the comparison of the groups. To analyze the correlations of the volume and area of the abutments with accuracy, Pearson’s correlation analysis was conducted (α = 0.00625). Both premolar and molar abutments showed a lower RMS value on the laboratory scanner than on the intraoral scanners, and the RMS value was lower in premolars than in molars (p < 0.001). In the intraoral scanner group, CS3600 showed the best accuracy (p < 0.001). There were significant positive correlations for the volume and area of the abutments with accuracy (p < 0.001). The type, volume, and area of the clinically applicable abutments may affect the accuracy of intraoral scanners; however, the scanners used in the present study showed a clinically acceptable accuracy range, regardless of the type of abutment.
Journal Article