• Title/Summary/Keyword: ablation performance

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Theoretical Modeling of Pulsed Plasma Thruster Performance with Teflon Ablation

  • Cho, Mingyoung;Sung, Hong-Gye
    • International Journal of Aeronautical and Space Sciences
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    • v.18 no.1
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    • pp.138-143
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    • 2017
  • A performance analysis for a pulsed plasma thruster(PPT) has been conducted to predict the thrust and current change. Two models were implemented - a one-dimensional lumped circuit analysis model and the Teflon ablation model provided by Michael Keidar. The circuit model incorporating resistance and inductance models was adapted to predict the magnitude of the discharge current. Numerical simulations like current discharge rates with different voltages were reasonably well compared with experimental data. The effects of Teflon ablation on thruster characteristics were investigated.

Analysis on Ablation of KL-3 Engine Nozzle Throat Using Image Analysis (영상분석을 통한 KL-3 엔진 노즐목 삭마 경향 분석)

  • Kim, Young-Han;Park, Sung-Jin;Ryu, Chul-Sung;Kim, Yong-Wook;Han, Sang-Yeop;Kim, Byung-Hun
    • 한국연소학회:학술대회논문집
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    • 2003.05a
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    • pp.51-55
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    • 2003
  • In this research, authors tried to measure the shape of the nozzle throat of KL-3 engines, which is the main engine of KSR-III rocket, to find the increase of nozzle area caused by the thermal ablation. For the purpose, we invented an image-based method instead of the 3D pointer, which is actually inaccessible to such large scale engines. As a result, our equipment showed satisfactory accuracy and performance. Analysing the results of experiments, we find that the pattern of ablation is determined by the spray pattern and that the process of thermal ablation phenomena can be categorized in three regimes - the first regime that the shape of nozzle throat is maintained and ablation is negligible, the second regime that saw-tooth form is developed and ablation is accelerated, and the third regime that the saw-tooth form is already established and the growth of ablation rate is reduced. Also, we find that the ratio of area increase after 60 seconds combustion is +5.82% and conclude that this figure is acceptable and satisfactory.

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An experimental study on the picosecond laser dressing of bronze-bonded diamond wheels

  • Wang, Yanyi;Chen, Genyu;Hu, Bang;Zhou, Wei
    • Advances in nano research
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    • v.12 no.6
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    • pp.583-592
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    • 2022
  • In this paper, a pulsed picosecond laser dressing method for bronze-bonded diamond wheel is studied systematically and comprehensively. The picosecond laser pulse ablation experiment is carried out, and the ablation thresholds of bronze-bonded and diamond abrasive particle are measured respectively. The results indicate that the single-pulse ablation thresholds of bronze-bonded are 0.89J/cm2, 0.24J/cm2 during strong/weak ablation stages. And the multi-pulse ablation thresholds of diamond abrasive particle are 1.69J/cm2, 0.49J/cm2 during strong/weak ablation stages. Obviously, diamond grains have less thermal damage during the process of gentle ablation. The diamond grains of the grinding wheel surface are graphitized during laser dressing. The bronze-bonded is relatively smooth and organizational stability, and the diamond grits have suitable prominent height, which are beneficial to maintain the good grinding performance of dressed bronze-bonded diamond grinding wheels.

Comparison of Ablation Performance between Octopus Multipurpose Electrode and Conventional Octopus Electrode

  • Sae-Jin Park;Jae Hyun Kim;Jeong Hee Yoon;Jeong Min Lee
    • Korean Journal of Radiology
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    • v.24 no.2
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    • pp.86-94
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    • 2023
  • Objective: To compare Octopus multipurpose (MP) electrodes, which are capable of saline instillation and direct tissue temperature measurement, and conventional electrodes for radiofrequency ablation (RFA) in porcine livers in vivo. Materials and Methods: Sixteen pigs were used in this study. In the first experiment, RFA was performed in the liver for 6 minutes using Octopus MP electrodes (n = 15 ablation zones) and conventional electrodes (n = 12 ablation zones) to investigate the effect of saline instillation. The ablation energy, electrical impedance, and ablation volume of the two electrodes were compared. In the second experiment, RFA was performed near the gallbladder (GB) and colon using Octopus MP electrodes (n = 12 ablation zones for each) with direct tissue temperature monitoring and conventional electrodes (n = 11 ablation zones for each). RFA was discontinued when the temperature increased to > 60℃ in the Octopus MP electrode group, whereas RFA was performed for a total of 6 minutes in the conventional electrode group. Thermal injury was assessed and compared between the two groups by pathological examination. Results: In the first experiment, the ablation volume and total energy delivered in the Octopus MP electrode group were significantly larger than those in the conventional electrode group (15.7 ± 4.26 cm3 vs. 12.5 ± 2.14 cm3, p = 0.027; 5.48 ± 0.49 Kcal vs. 5.04 ± 0.49 Kcal, p = 0.029). In the second experiment, thermal injury to the GB and colon was less frequently noted in the Octopus MP electrode group than that in the conventional electrode group (16.7% [2/12] vs. 90.9% [10/11] for GB and 8.3% [1/12] vs. 90.9% [10/11] for colon, p < 0.001 for all). The total energy delivered around the GB (2.65 ± 1.07 Kcal vs. 5.04 ± 0.66 Kcal) and colon (2.58 ± 0.57 Kcal vs. 5.17 ± 0.90 Kcal) were significantly lower in the Octopus MP electrode group than that in the conventional electrode group (p < 0.001 for all). Conclusion: RFA using the Octopus MP electrodes induced a larger ablation volume and resulted in less thermal injury to the adjacent organs compared with conventional electrodes.

3D CACT-assisted Radiofrequency Ablation Following Transarterial Chemoembolization for Hepatocellular Carcinoma: Early Experience

  • Jiao, De-Chao;Han, Xin-Wei;Wu, Gang;Ren, Jian-Zhuang
    • Asian Pacific Journal of Cancer Prevention
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    • v.16 no.17
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    • pp.7897-7903
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    • 2015
  • Background: To explored the value of 3D C-arm CT (CACT) guidance system in performing radiofrequency ablation (RFA) following transarterial chemoembolizationon (TACE) for hepatocellular carcinomas. Materials and Methods: RFA of hepatocellular carcinomas (HCC) were performed on 15 patients (21 lesions) with the assistance of CACT guidance system. Technical success, procedure time, complications and patient radiation exposure were investigated. The puncture performance level was evaluated on a five-point scale (5-1: excellent-poor). Complete ablation rate was evaluated after two months follow-up using enhanced CT scans. Results: The technical success rate of RFA procedure under CACT navigation system was 100 %. Mean total procedure time was $24.24{\pm}6.53min$, resulting in a mean effective exposure dose of $15.4{\pm}5.1mSv$. The mean puncture performance level rated for CACT guided RFA procedure was $4.87{\pm}0.35$. Complete ablation (CA) was achieved in 20 (95.2%) of the treated 21 tumors after the first RFA session. None of patients developed intra-procedural complications. Conclusions: 3D CACT guidance system enables reliable and efficient needle positioning by providing real-time intraoperative guidance for performing RFA on HCCs.

Comparative Tissue Ablation Study between 532 and 980 nm (가시광선과 근적외선 파장을 이용한 조직 제거 연구)

  • Kang, Hyun Wook;Oh, Junghwan
    • Korean Journal of Optics and Photonics
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    • v.23 no.3
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    • pp.108-112
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    • 2012
  • In this paper, two wavelengths mainly used for laser prostatectomy have been quantitatively compared: 532 and 980 nm. Two lasers at 40 W were employed to ablate bovine liver in vitro. Ablation performance was evaluated in light of number of sweeps, ablation volume, and coagulative necrosis. 532 nm yielded up to four times higher ablation efficiency than 980 nm. Regardless of wavelength, ablation rate per sweep decreased with the number of sweeps. 532 nm generated relatively deeper ablation craters along with thinner coagulation whereas 980 nm created superficial tissue ablation with up to 2 mm thick coagulative necrosis. Due to higher light absorption and effective thermal confinement, 532 nm induced more efficient tissue ablation with a smaller coagulative necrotic zone. The current study demonstrated that 532 nm could be a more ideal wavelength for laser prostatectomy, and the future in vivo investigations will confirm these findings.

Study of microstructure of carbon-based materials in plasma wind tunnel testing

  • Kang, Bo-Ram;Lim, Hyeon-Mi;Oh, Phil-Yong;Hong, Bong Guen
    • Proceedings of the Korean Vacuum Society Conference
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    • 2016.02a
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    • pp.200.2-200.2
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    • 2016
  • Carbon-based materials have been known as ablative material and have been used for thermal protection systems. Ablation is an erosive phenomenon that results in thermochemical and thermomechanical changes on materials. Ablation resistance is one of the key properties that determines performance and life-time of the thermal protection material under ablative conditions. In this study, ablation properties of graphite, 3-dimensional (C/C) composites (needle-punched type and rod type) were investigated byusing a plasma wind tunnel which produce a supersonic plasma flow from a segmented arc heater with the power level of 0.4 MW. The mass losses and surface roughness changes which contain main result of the ablation are measured. A morphological analysis ofthe carbon-based materials, before and after the ablation test, are performed through field emission scanning electron microscopy (FE-SEM) and non-contact 3D surface measuring system. Electronic balance and a portable surface roughness tester were used for evaluation of the recession and mass loss of the test samples.

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Microstructure and Ablation Performance of CNT-phenolic Nanocomposites (삭마 효과에 대한 CNT-페놀 나노복합재료의 미세구조 분석)

  • Wang, Zuo-Jia;Kwon, Dong-Jun;Park, Jong-Kyoo;Lee, Woo-Il;Park, Joung-Man
    • Composites Research
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    • v.26 no.5
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    • pp.309-314
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    • 2013
  • Highly ablation resistant carbon nanotube (CNT)-phenolic composites were fabricated by the addition of low concentrations of CNT nanofiller. Tensile and compressive properties as well as ablative resistance were significantly improved by the addition of only 0.1 and 0.3 wt% of uniformly dispersed CNTs. An oxygen-kerosene-flame torch and a field emission scanning electron microscope (FE-SEM) were used to evaluate the ablative properties and microstructures of these CNT-phenolic composites. Thermal gravimetric analysis (TGA) revealed that the ablation rate was lower for the 0.3 wt% CNT-phenolic composites than for neat phenolic or the composite with 0.1 wt% CNT. Ablative mechanisms for all three materials were investigated using this TGA in conjunction with microstructural studies using a FE-SEM. The microstructural studies revealed that CNT acted as an ablation resistant phase at high temperatures, and that the uniformity of dispersion of the CNT played an important role in this resistance to ablation.

Role of radiofrequency ablation in advanced malignant hilar biliary obstruction

  • Mamoru Takenaka;Tae Hoon Lee
    • Clinical Endoscopy
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    • v.56 no.2
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    • pp.155-163
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    • 2023
  • Malignant hilar biliary obstruction (MHO), an aggressive perihilar biliary obstruction caused by cholangiocarcinoma, gallbladder cancer, or other metastatic malignancies, has a poor prognosis. Surgical resection is the only curative treatment for biliary malignancies. However, the majority of patients with MHO cannot undergo surgery on presentation because of an advanced inoperable state or a poor performance state due to old age or comorbid diseases. Therefore, palliative biliary drainage is mandatory to improve symptomatic jaundice and the quality of life. Among the drainage methods, endoscopic biliary drainage is the current standard for palliation of unresectable advanced MHO. In addition, combined with endoscopic drainage, additional local ablation therapies, such as photodynamic therapy or radiofrequency ablation (RFA), have been introduced to prolong stent patency and survival. Currently, RFA is commonly used as palliative therapy, even for advanced MHO. This literature review summarizes recent studies on RFA for advanced MHO.

Micro Sampling System for Highly Radioactive Specimen by Laser Ablation (Laser Ablation에 의한 고방사성시편의 미세영역 시료채취 장치개발)

  • Han Sun Ho;Ha Yeong Keong;Han Ki Chul;Park Yang Soon;Jee Kwang Yong;Kim Won Ho
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.3 no.1
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    • pp.17-21
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    • 2005
  • Shielded laser ablation system composed of laser system, image analyser, XYZ translator with motion controller, ablation chamber, manipulator and various optics was designed. Nd:YAG laser which can be tunable from 1064 nm to 266 m was selected as light source. CCD camera(< $\pm$200) was chosen to analyze a crater less than 50 un in diameter. XYZ translator was composed of three linear stage which can travel 50 w with a minimum movement of 1 um and motion controller. Before the performance test, each part of system was optically aligned. To perform the ablation test, the specimen was ablated by 50 um interval and observed by image analyser The shape of crater was almost round, indicating laser beam has homogeneous energy distribution. The resolution and magnification of image system were compatible with the design.

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