• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.1
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• pp.30-37
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• 2006

A thermal resistance estimation of carbon/carbon composites used as the nozzle throat insert of solid rocket motor was performed using TPEM motor. Three types of TPEM motor and two types of propellant were employed. The ablation rate is higher for the higher chamber pressure and also higher for the higher concentration of oxidizing species in combustion gas, but it is lower for the higher material density.

• Korean Journal of Radiology
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• v.22 no.2
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• pp.179-188
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• 2021

Objective: This study aimed to prospectively compare the efficacy, safety, and mid-term outcomes of dual-switching monopolar (DSM) radiofrequency ablation (RFA) to those of conventional single-switching monopolar (SSM) RFA in the treatment of hepatocellular carcinoma (HCC). Materials and Methods: This single-center, two-arm, parallel-group, randomized controlled study was approved by the Institutional Review Board. Written informed consent was obtained from all patients upon enrollment. A total of 80 patients with 94 HCC nodules were randomized into either the DSM-RFA group or SSM-RFA group in a 1:1 ratio, using a blocked randomization method (block size 2). The primary endpoint was the minimum diameter of the ablation zone per unit time. The secondary endpoints included other technical parameters, complication rate, technique efficacy, and 2-year clinical outcomes. Results: Significantly higher ablation energy per unit time was delivered to the DSM-RFA group than to the SSM-RFA group (1.7 ± 0.2 kcal/min vs. 1.2 ± 0.3 kcal/min; p < 0.001). However, no significant differences were observed between the two groups for the analyzed variables, including primary endpoint, regarding size of the ablation zone and ablation time. Major complication rates were 4.9% in the DSM-RFA group and 2.6% in the SSM-RFA group (p = 1.000). The 2-year local tumor progression (LTP) rates of the HCC nodules treated using DSM-RFA and SSM-RFA were 8.5% and 4.7%, respectively (p = 0.316). The 2-year LTP-free survival rates of patients in the DSM-RFA and SSM-RFA groups were 90.0% and 94.4%, respectively (p = 0.331), and the 2-year recurrence-free survival rates were 54.9% and 75.7%, respectively (p = 0.265). Conclusion: Although DSM-RFA using a separable clustered electrode delivers higher ablation energy than SSM-RFA, its effectiveness failed to show superiority over SSM-RFA in the treatment of HCC.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.8
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• pp.597-604
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• 2013

A coupled thermomechanical analysis of composite structures in pyrolysis and ablation environments is performed. The pyrolysis and ablation models include the effects of mass loss, pore gas diffusion, endothermic reaction energy, surface recession, etc. The thermal and structural analysis interface is based upon a staggered coupling algorithm by using a commercial finite element code. The characteristics of the proposed method are investigated through numerical experiments with carbon/phenolic composites. The numerical studies are carried out to examine the surface recession rate by chemical and mechanical ablation. In addition, the effects of shrinkage or intumescence during the pyrolysis process are shown.

• Journal of Biomedical Engineering Research
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• v.38 no.6
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• pp.285-290
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• 2017

Radiofrequency catheter ablation is the interventional therapy that be employed to eliminate cardiac tissue caused by arrhythmias. During radiofrequency catheter ablation, The thrombus can occur at electrode tip if the temperature of tissue and electrode is excess $100^{\circ}C$. To prevent this phenomenon, we investigated numerical model of electrode for radiofrequency catheter ablation considering saline irrigation and temperature-controlled radiofrequency system. The numerical model is based on coupled electric-thermal-flow problem and solved by COMSOL Multiphysics software. The results of the models show that the dimensions of the thermal lesion are increased if the flow rate of the saline irrigation and the set temperature are increased. The surface width characterized to determine the thermal lesion isn't need to measure in temperature-controlled radiofrequency system due to convective heat transfer by saline irrigation at tissue-electrode interface.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.14
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• pp.5799-5804
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• 2014

Background: Radiofrequency ablation (RFA) is the most widely used and studied method internationally for the local treatment of liver tumors. However, the extension of coagulation necrosis in one RFA procedure is limited and incomplete coverage of the damaged area can lead to a high local recurrence rate. Objective: In this study, we compared the effects of different solutions in enhancing hepatic radiofrequency by establishing a rabbit VX2 liver cancer model. We also determined the optimal solution to maximise effects on the extent of RFA-induced coagulation necrosis. Methods: Thirty VX2 tumor rabbits were randomly assigned to five groups: group A, RFA alone; group B, RFA with anhydrous ethanol injection; group C, RFA with 5% hypertonic saline injection; group D, RFA with lidocaine injection; and group E, RFA with a mixed solution. Routine ultrasound examinations and contrast-enhanced ultrasound (CEUS) of the ablation areas were performed after RFA. Then, we measured the major axis and transverse diameter and compared the areas of coagulation necrosis induced by RFA. Results: The mean ablation area range increased in groups B, C and especially E, and the scopes were greater compared with group A. Preoperative application of anhydrous ethanol, hypertonic saline, lidocaine and the mixed solution (groups B, C, D and E, respectively) resulted in larger coagulation necrosis areas than in group A (p<0.05). Among the groups, the coagulation necrosis areas in group E was largest, and the difference was statistically significant compared with other groups (p<0.05). Pathological findings were consistent with imaging results. Conclusions: A mixture of dehydrated alcohol, hypertonic saline and lidocaine injected with RFA increases the extent of coagulation necrosis in the liver with a single application, and the mixed solution is more effective than any other injection alone.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.7
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• pp.97-103
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• 2019

Mn+1AXn (MAX) phases are a family of nano-laminated compounds that possess unique combination of typical ceramic properties and typical metallic properties. As a member of MAX-phase, $Ti_2AlN$ bulk materials are attractive for some high temperature applications. In this study, $Ti_2AlN$ bulk with high density were synthesized by spark plasma sintering method. X-ray diffraction, micro-hardness, electrical and thermal conductivity were measured to compare the effect of material properties both $Ti_2AlN$ bulk samples and a conventional Ti-6Al-4V alloy. A femto-second laser conditions were conducted at a repetition rate of 6 kHz and laser intensity of 50 %, 70% and 90 %, respectively, laser confocal microscope were used to evaluate the width and depth of ablation. Consequently, the laser ablation result of the $Ti_2AlN$ sample than that of the Ti-6Al-4V alloys show a considerably good ablation characteristics due to its higher thermal conductivity regardless of to high densification and high hardness.

• Korean Journal of Radiology
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• v.25 no.2
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• pp.199-209
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• 2024

Objective: This study aimed to compare therapeutic efficacy and technical outcomes between adjustable electrode (AE) and conventional fixed electrode (FE) for radiofrequency ablation (RFA) of benign thyroid nodules. Materials and Methods: Between 2013 and 2021, RFA was performed on histologically proven benign thyroid nodules. For the AE method, AE length ≥ 1 cm with higher power and < 1 cm with lower power were utilized for ablating feeding vessels and nodules, especially those near anatomical structures, respectively. The therapeutic efficacy (volume reduction rate [VRR], complication rate, and regrowth rate) and technical outcomes (total energy delivery, ablated volume/energy, RFA time, and ablated volume/time) of FE and AE were compared. Continuous parameters were compared using a two-sample t-test or Mann-Whitney U test, and categorical parameters were compared using a chi-squared test or Fisher's exact test. Results: A total of 182 nodules (FE: 92 vs. AE: 90) in 173 patients (mean age ± standard deviation, 47.0 ± 14.7 years; female, 90.8% [157/173]; median follow-up, 726 days [interquartile range, 441-1075 days]) were analyzed. The therapeutic efficacy was comparable, whereas technical outcomes were more favorable for AE. Both electrodes demonstrated comparable overall median VRR (FE: 92.4% vs. AE: 84.9%, P = 0.240) without immediate major complications. Overall regrowth rates were comparable between the two groups (FE: 2.2% [2/90] vs. AE: 1.1% [1/90], P > 0.99). AE demonstrated a shorter median RFA time (FE: 811 vs. AE: 627 seconds, P = 0.009). Both delivered comparable median energy (FE: 42.8 vs. AE: 29.2 kJ, P = 0.069), but AE demonstrated higher median ablated volume/energy and median ablated volume/time (FE: 0.2 vs. AE: 0.3 cc/kJ, P < 0.001; and FE: 0.7 vs. AE: 1.0 cc/min, P < 0.001, respectively). Conclusion: Therapeutic efficacy between FE and AE was comparable. AE demonstrated better technical outcomes than FE in terms of RFA time, ablated volume/energy, and ablated volume/time.

• Korean Journal of Radiology
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• v.23 no.4
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• pp.479-487
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• 2022

Objective: To prospectively evaluate the efficacy of lauromacrogol injection for ablation (LIA) of benign predominantly cystic thyroid nodules and its related factors. Materials and Methods: A total of 142 benign predominantly cystic thyroid nodules (median volume, 12.5 mL; range, 0.4-156 mL) in 137 patients (male:female sex ratio, 36:101; mean age ± standard deviation [SD], 49 ± 13 years) were treated with LIA after being confirmed as benign via cytology. The volume reduction rate (VRR) of the nodules and cosmetic score were evaluated during follow-up at 1, 3, and 6 months after treatment and every 6 months thereafter. A VRR of ≥ 50% at the 12-month follow-up was considered to indicate effective treatment. The associations between the clinical factors and nodular ultrasound features, including the initial nodule volume, proportion of solid components, vascularity grade and ineffective treatment (VRR of < 50% at the 12-month follow-up), and regrowth were analyzed. Results: All patients completed follow-up for at least 12 months. The average ± SD follow-up period was 32 ± 11 months (range, 12-54 months). The effective treatment rate was 73.2% (104/142), while the regrowth rate was 12.0% (17/142) at the last follow-up. Grade 2-3 intranodular vascularity in the solid components of the nodules was the only independent factor associated with ineffective treatment, with an odds ratio (reference category, grade 0-1) of 3.054 (95% confidence interval, 1.148-8.127) (p = 0.025). Conclusion: LIA is an effective treatment for predominantly cystic thyroid nodules. Grade 2-3 intranodular vascularity in the solid components of nodules is the only independent risk factor for ineffective LIA.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.887-890
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• 1997

Recently micromachining using DPSSL(Diode Pumped Solid State Laser) with 3rd harmonic wavelength is actively studied in laser machining area. Micromachining using DPSSL have outstanding advantages as UV source comparing with excimer laser in various aspect such a maintenance cost, maskless machining, high repetition rate and so on. In this study micro-drilling of PCB type substrate which consists of Cu-PI-Cu layer was performed using DPSS Nd:YAG laser(355nm, wavelength) in vector scanning method. Experimental and numerical method(Matlab simulation, FEM) are used to optimize process parameter and control machining depth. The man mechanism of this process is laser ablation. It is known that there is large gap between energy threshold of copper and that of PI. Matlab simulation considering energy threshold of material is performed to effect of duplication of pulse and FEM thermal analysis is used to predict the ablation depth of copper. This study could be widely used in various laser micromachining including via hole microdrilling of PCB, and micromachining of semiconductor components, medical parts and printer nozzle and so on.

• Journal of Energy Engineering
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• v.23 no.3
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• pp.21-26
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• 2014

EU-APR1400, the Korean nuclear reactor design for European market adopts a so-called core catcher for ex-vessel molten corium retention and cooling as a severe-accident mitigation system. Sacrificial material, which controls melt properties and modifies melt conditions favorable for corium cooling and retention, is usually employed to protect core catcher body from molten corium. Since molten corium can be ejected through a breach of a reactor pressure vessel and impinged on the sacrificial material with enhanced heat transfer at a severe accident, it is very important to predict ablation rate of sacrificial material due to corium jet impingement accurately for core catcher design. In this paper, sacrificial-material ablation model based on boundary layer theory is suggested and compared with the experimental results by KAERI.