• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.04a
• /
• pp.1-2
• /
• 2011

Hybrid rockets have lately attracted attention as a strong candidate of small, low cost, safe and reliable launch vehicles. A significant topic is that the first commercially sponsored space ship, SpaceShipOne vehicle chose a hybrid rocket. The main factors for the choice were safety of operation, system cost, quick turnaround, and thrust termination. In Japan, five universities including Hokkaido University and three private companies organized "Hybrid Rocket Research Group" from 1998 to 2002. Their main purpose was to downsize the cost and scale of rocket experiments. In 2002, UNISEC (University Space Engineering Consortium) and HASTIC (Hokkaido Aerospace Science and Technology Incubation Center) took over the educational and R&D rocket activities respectively and the research group dissolved. In 2008, JAXA/ISAS and eleven universities formed "Hybrid Rocket Research Working Group" as a subcommittee of the Steering Committee for Space Engineering in ISAS. Their goal is to demonstrate technical feasibility of lowcost and high frequency launches of nano/micro satellites into sun-synchronous orbits. Hybrid rockets use a combination of solid and liquid propellants. Usually the fuel is in a solid phase. A serious problem of hybrid rockets is the low regression rate of the solid fuel. In single port hybrids the low regression rate below 1 mm/s causes large L/D exceeding a hundred and small fuel loading ratio falling below 0.3. Multi-port hybrids are a typical solution to solve this problem. However, this solution is not the mainstream in Japan. Another approach is to use high regression rate fuels. For example, a fuel regression rate of 4 mm/s decreases L/D to around 10 and increases the loading ratio to around 0.75. Liquefying fuels such as paraffins are strong candidates for high regression fuels and subject of active research in Japan too. Nakagawa et al. in Tokai University employed EVA (Ethylene Vinyl Acetate) to modify viscosity of paraffin based fuels and investigated the effect of viscosity on regression rates. Wada et al. in Akita University employed LTP (Low melting ThermoPlastic) as another candidate of liquefying fuels and demonstrated high regression rates comparable to paraffin fuels. Hori et al. in JAXA/ISAS employed glycidylazide-poly(ethylene glycol) (GAP-PEG) copolymers as high regression rate fuels and modified the combustion characteristics by changing the PEG mixing ratio. Regression rate improvement by changing internal ballistics is another stream of research. The author proposed a new fuel configuration named "CAMUI" in 1998. CAMUI comes from an abbreviation of "cascaded multistage impinging-jet" meaning the distinctive flow field. A CAMUI type fuel grain consists of several cylindrical fuel blocks with two ports in axial direction. The port alignment shifts 90 degrees with each other to make jets out of ports impinge on the upstream end face of the downstream fuel block, resulting in intense heat transfer to the fuel. Yuasa et al. in Tokyo Metropolitan University employed swirling injection method and improved regression rates more than three times higher. However, regression rate distribution along the axis is not uniform due to the decay of the swirl strength. Aso et al. in Kyushu University employed multi-swirl injection to solve this problem. Combinations of swirling injection and paraffin based fuel have been tried and some results show very high regression rates exceeding ten times of conventional one. High fuel regression rates by new fuel, new internal ballistics, or combination of them require faster fuel-oxidizer mixing to maintain combustion efficiency. Nakagawa et al. succeeded to improve combustion efficiency of a paraffin-based fuel from 77% to 96% by a baffle plate. Another effective approach some researchers are trying is to use an aft-chamber to increase residence time. Better understanding of the new flow fields is necessary to reveal basic mechanisms of regression enhancement. Yuasa et al. visualized the combustion field in a swirling injection type motor. Nakagawa et al. observed boundary layer combustion of wax-based fuels. To understand detailed flow structures in swirling flow type hybrids, Sawada et al. (Tohoku Univ.), Teramoto et al. (Univ. of Tokyo), Shimada et al. (ISAS), and Tsuboi et al. (Kyushu Inst. Tech.) are trying to simulate the flow field numerically. Main challenges are turbulent reaction, stiffness due to low Mach number flow, fuel regression model, and other non-steady phenomena. Oshima et al. in Hokkaido University simulated CAMUI type flow fields and discussed correspondence relation between regression distribution of a burning surface and the vortex structure over the surface.

• Journal of Korean Neurosurgical Society
• /
• v.64 no.6
• /
• pp.983-994
• /
• 2021

Objective : The effectiveness of gamma knife radiosurgery (GKR) in the treatment of brain metastases is well established. The aim of this study was to evaluate the efficacy and safety of maximizing the radiation dose in GKR and the factors influencing tumor control in cases of small and medium-sized brain metastases from non-small cell lung cancer (NSCLC). Methods : We analyzed 230 metastatic brain tumors less than 5 mL in volume in 146 patients with NSCLC who underwent GKR. The patients had no previous radiation therapy for brain metastases. The pathologies of the tumors were adenocarcinoma (n=207), squamous cell carcinoma (n=18), and others (n=5). The radiation doses were classified as 18, 20, 22, and 24 Gy, and based on the tumor volume, the tumors were categorized as follows : small-sized (less than 1 mL) and medium-sized (1-3 and 3-5 mL). The progression-free survival (PFS) of the individual 230 tumors and 146 brain metastases was evaluated after GKR depending on the pathology, Eastern Cooperative Oncology Group (ECOG) performance score (PS), tumor volume, radiation dose, and anti-cancer regimens. The radiotoxicity after GKR was also evaluated. Results : After GKR, the restricted mean PFS of individual 230 tumors at 24 months was 15.6 months (14.0-17.1). In small-sized tumors, as the dose of radiation increased, the tumor control rates tended to increase (p=0.072). In medium-sized tumors, there was no statistically difference in PFS with an increase of radiation dose (p=0.783). On univariate analyses, a statistically significant increase in PFS was associated with adenocarcinomas (p=0.001), tumors with ECOG PS 0 (p=0.005), small-sized tumors (p=0.003), radiation dose of 24 Gy (p=0.014), synchronous lesions (p=0.002), and targeted therapy (p=0.004). On multivariate analyses, an improved PFS was seen with targeted therapy (hazard ratio, 0.356; 95% confidence interval, 0.150-0.842; p=0.019). After GKR, the restricted mean PFS of brain at 24 months was 9.8 months (8.5-11.1) in 146 patients, and the pattern of recurrence was mostly distant within the brain (66.4%). The small and medium-sized tumors treated with GKR showed radiotoxicitiy in five out of 230 tumors (2.2%), which were controlled with medical treatment. Conclusion : The small-sized tumors were effectively controlled without symptomatic radiation necrosis as the radiation dose was increased up to 24 Gy. The medium-sized tumors showed potential for symptomatic radiation necrosis without signifcant tumor control rate, when greater than 18 Gy. GKR combined targeted therapy improved the tumor control of GKR-treated tumors.

• The Journal of Korean Society for Radiation Therapy
• /
• v.31 no.1
• /
• pp.43-49
• /
• 2019

Purpose : We apply the Layered Rescanning PBS designed to complement the Pencil Beam Scanning(PBS), which is vulnerable to moving organs with the Moving Phantom, and compare the homogeneity with the single scan PBS. Methods and materials: Matrix X (IBA, Belgium) and Moving Phantom (standard imaging, USA) were used. A dose of 200 cGy was measured in the AP direction on a hypothetical tumor $10{\times}10{\times}5cm$. The plan type was planned as 4 kinds of sinlge scan PBS, rescan number 4, 8, 12 times. Were measured three times for each types. During the measurement, the respiratory cycle of the Moving Phantom was generally set to 4 seconds per cycle, and the movement radius in the S-I direction was set to 2 cm. In addition, beam on time was measured. Results : The mean values of $D_{max}$ in the PTV were $246.47{\pm}18.8cGy$, $223.43{\pm}8.92cGy$, and $222.47{\pm}7.7cGy$, $213.9{\pm}6.11cGy$ and the mean values of $D_{min}$ were $165.53{\pm}4.32cGy$, $173.13{\pm}11.94cGy$, $184.13{\pm}8.04cGy$, $182.67{\pm}4.38cGy$ and the mean values of $D_{mean}$ $192.77{\pm}6.98cGy$, $196.7{\pm}4.01cGy$, $198.17{\pm}4.96cGy$, $195.77{\pm}3.15cGy$ respectively. As the number of rescanning increased, the Homogeneity Index converged to 1. The beam on time was measured as 2:15, 3:15, 4:30, 5:37 on average. In the measurement process, in the low dose layer of the MU, the problem was found that it was not rescanned as many times as the set number of rescan. Conclusions : In the treatment of tumors with long-term movements, the application of layered rescanning PBS showed a more uniform dose distribution than single scan PBS. And as the number of rescan increase, the distribution of homogeneity is uniform. Compared with single scan plan and 12 rescan plan, HI value was improved by 0.32. Further studies are expected to be applicable to patients who can not be treated with respiratory synchronous radiation therapy.

• Korean Journal of Remote Sensing
• /
• v.38 no.5_1
• /
• pp.609-625
• /
• 2022

Validation of satellite data products is critical for subsequent analysis that is based on the data. Particularly, performance of ocean color products in turbid and shallow near-land ocean areas has been questioned for long time for its difficulty that stems from the complex optical environment with varying distribution of water constituents. Furthermore, validation with ship-based or station-based measurements has also exhibited clear limitation in its spatial scale that is not compatible with that of satellite data. This study firstly performed validation of major GOCI-II products such as remote sensing reflectance, chlorophyll-a concentration, suspended particulate matter, and colored dissolved organic matter, using the in-situ measurements collected from ship-based field campaign. Secondly, this study also presents preliminary analysis on the use of drone images for product validation. Multispectral images were acquired from a MicaSense RedEdge camera onboard a UAV to compensate for the significant scale difference between the ship-based measurements and the satellite data. Variation of water radiance in terms of camera altitude was analyzed for future application of drone images for validation. Validation conducted with a limited number of samples showed that GOCI-II remote sensing reflectance at 555 nm is overestimated more than 30%, and chlorophyll-a and colored dissolved organic matter products exhibited little correlation with in-situ measurements. Suspended particulate matter showed moderate correlation with in-situ measurements (R²~0.6), with approximately 20% uncertainty.

• Journal of Space Technology and Applications
• /
• v.3 no.2
• /
• pp.118-143
• /
• 2023

Space is becoming more commercialized. Despite of its delayed start-up, space activities in Korea are attracting more nation-wide supports from both investors and government. May 25, 2023, KSLV II, also called Nuri, successfully transported, and inserted seven satellites to a sun-synchronous orbit of 550 km altitude. However, Starlink has over 4,000 satellites around this altitude for its commercial activities. Hence, it is necessary for us to constantly monitor the collision risks of these satellites against resident space objects including Starlink. Here we report a quantitative research output regarding the conjunctions, particularly between the Nuri satellites and Starlink. Our calculation shows that, on average, three times everyday, the Nuri satellites encounter Starlink within 1 km distance with the probability of collision higher than 1.0E-5. A comparative study with KOMPSAT-5, also called Arirang-5, shows that its distance of closest approach distribution significantly differs from those of Nuri satellites. We also report a quantitative analysis of collision-avoiding maneuver cost of Starlink satellites and a strategy for Korea, being a delayed starter, to speed up to position itself in the space leading countries. We used the AstroOne program for analyses and compared its output with that of Socrates Plus of Celestrak. The two line element data was used for computation.

• Radiation Oncology Journal
• /
• v.21 no.4
• /
• pp.261-268
• /
• 2003

Purpose: To report the results of curative treatment for patients with tonsil cancer by retrospective analysis. Materials and Methods: From Jan. 1995 till Dec. 2000, 27 patients with squamous cell carcinoma of the tonsil received curative treatment at Samsung Medical Center. Therapeutic decision was made through multidisciplinary conference, and curative radiation therapy was favored when, (1) the patient's condition was not fit for general anesthesia and surgery, (2) the patient refused surgery, (3) complete resection was presumed impossible, or (4) too severe disability was expected after surgery. Surgery was the main local modality in 17 patients (S$\pm$RT group), and radiation therapy in 10 (RT$\pm$CT group). The median follow-up period was 41 months. Results: AJCC stages were I/II in four, III in two, and IV in 21 patients. The 5-year disease-free survival rate was 73.3$\%$ in all patients, 70.6$\%$ in the S$\pm$RT group, and 77.8$\%$ in the RT$\pm$CT group. Treatment failure occurred in seven patients, all with stage III/IV, and all the failures occurred within 24 months of the start of treatment. Five patients among the S$\pm$CT group developed treatment failures; 2 local, 2 regional, and 1 distant (crude rate=29.4$\%$). Two patients among the RT$\pm$CT group developed failures; 1 synchronous local and regional, and 1 distant (crude rate=20.0$\%$). The 5-year overall survival rate was 77.0$\%$ in all patients, 80.9$\%$ in the S$\pm$RT group, and 70.0$\%$ in the RT$\pm$CT group. Conclusion: We could achieve favorable results that were comparable to previously reported data with respect to both the rates of local control and of survival by applying S$\pm$RT and RT$\pm$CT. RT$\pm$CT is judged to be an alternative option that can avoid the functional disability after surgical resection.

• Radiation Oncology Journal
• /
• v.26 no.4
• /
• pp.204-212
• /
• 2008

Purpose: This study was performed to evaluate the disease-free survival and risk factors of recurrence in early breast cancer patients who have undergone breast conserving surgery and radiation therapy. Materials and Methods: From March 1997 to December 2002, 77 breast cancer patients who underwent breast conserving surgery and radiation therapy were reviewed retrospectively. The median follow-up time was 58.4 months (range $43.8{\sim}129.4$ months) and the mean subject age was 41 years. The frequency distribution of the different T stages, based on the tumor characteristics was 38 (49.3%) for T1, 28 (36.3%) for T2, 3 for T3, 7 for T is and 1 for an unidentified sized tumor. In addition, 52 patients (67.5%) did not have axillary lymph metastasis, whereas 14 patients (18.1%) had $1{\sim}3$ lymph node metastases and 3 (0.03%) had more than 4 lymph node metastases. The resection margin was negative in 59 patients, close (${\leq}2\;mm$) in 15, and positive in 4. All patients received radiation therapy at the intact breast using tangential fields with a subsequent electron beam boost to the tumor bed at a total dose ranging from 59.4 Gy to 66.4 Gy. Patients with more than four positive axillary lymph nodes received radiation therapy ($41.4{\sim}60.4\;Gy$) at the axillary and supraclavicular area. Chemotherapy was administered in 59 patients and tamoxifen or fareston was administered in 29 patients. Results: The 5 year overall survival and disease-free survival rates were 98.08% and 93.49%, respectively. Of the 77 patients, a total of 4 relapses (5.2%), including 1 isolated supraclavicular relapse, 1 supraclavicular relapse with synchronous multiple distant relapses, and 2 distant relapses were observed. No cases of local breast relapses were observed. Lymph node metastasis or number of metastatic lymph nodes was not found to be statistically related with a relapse (p=0.3289) nor disease-free survival (p=0.1430). Patients with positive margins had a significantly shorter disease-free survival period (p<0.0001) and higher relapse rates (p=0.0507). However, patients with close margins were at equal risk of relapse and disease-free survival as with negative margins (p=1.000). Patients younger than 40 years of age had higher relapse rates (9.3% vs. 0%) and lower disease-free survival periods, but the difference was not statistically significant (p=0.1255). The relapse rates for patients with tumors was 14% for tumor stage T2, compared to 0% for tumor stage T1 tumors (p=0.0284). A univariate analysis found that disease-free survival and relapse rates, T stage, positive resection margin and mutation of p53 were significant factors for clinical outcome. Conclusion: The results of this study have shown that breast conservation surgery and radiation therapy in early breast cancer patients has proven to be a safe treatment modality with a low relapse rate and high disease-free survival rate. The patients with a positive margin, T2 stage, and mutation of p53 are associated with statistically higher relapse rates and lower disease-free survival.

• Radiation Oncology Journal
• /
• v.18 no.4
• /
• pp.233-243
• /
• 2000

Purpose : First of all, this study was performed to assess the result of curative radiotherapy and to evaluate different possible prognostic factors for squamous cell carcinoma of the supraglottic larynx treated at the Pusan National University Hospital. The second goal of this study was by comparing our data with those of other study groups, to determine the better treatment policy of supraglottic cancer in future. Methods and Material : Thirty-two patients with squamous cell carcinoma of the supraglottic larynx were treated with radiotherapy at Pusan National University Hospital, from August 1985 to December 1996. Minimum follow-up period was 29 months, Twenty-seven patients (84.4$\%$) were followed up over 5 years. Radiotherapy was delivered with 6 MV photons to the primary laryngeal tumor and regional iymphatics with shrinking field technique. Ail patients received radiotherapy under conventional fractionated schedule (once a day). Median total tumor dose was 70.2 Gy (range, 55.8 to 75.6 Gy) on primary or gross tumor lesion. Thirteen patients had Induction chemotherapy with cisplatln and 5-fluorouracil (1-3 cycles). Patient distribution, according to the different stages, were as follows: stage I, 5/32 (15.6$\%$): stage II, 10/32 (31.3$\%$); stage III, 8/32 (25$\%$): stage IV, 9/32 (28.1$\%$). Results :The 5-year overall survival rate of the whole series (32 patients) was 51.7$\%$. The overall survival rate at 5-years was 80$\%$ in stage I, 66.7$\%$ in stage II, 42.9$\%$ in stage III, 25$\%$ in stage IV (p=0.0958). The S-year local control rates after radiotherapy were as fellows: stage I, 100$\%$; stage II, 60$\%$ stage III, 62.5$\%$; stage IV, 44.4$\%$ (p=0.233). Overall vocal preservation rates was 65.6$\%$, 100% In stage I, 70% in stage II, 62.5$\%$ In stage III, 44.4$\%$ in stage IV (p=0.210). There was no statistical significance in survival and local control rate between neoadjuvant chemotherapy followed by radiotherapy group and radiotherapy alone group. Severe laryngeal edema was found in 2 cases after radiotllerapy, emergent tracheostomy was done. Four patients were died from distant metastsis, . three in lung, one in brain. Double primary tumor was found in 2 cases, one in lung (metachronous), another in thyroid (synchronous). Ulcerative lesions were revealed as unfavorable prognostic factor ( p=0.0215), and radiation dose (more or less than 70.2 Gy) was an important factor on survival (p=0.002). Conclusion : The role of radiotherapy treatment of supraglottic carcinoma is to important factor on survival and to preserve the laryngeal function. Based on our data and other studies, early and moderately advanced supragiottic carcinomas could be successfully treated with either consewative surgery or radiotherapy alone. Both modalities showed similar results in survival and vocal preservation. For the advanced cases, radiotherapy alone is Inadequate for curative aim and surgery combined with radiotherapy should be done in operable patients. When patients refuse operation or want to preserve vocal function, or for the patients with inoperable medical conditions, combined chemoradiotherapy (concurrent) or altered fractionated radiotherapy with or without radiosensitizer should be taken into consideration in future.

• Journal of The Korean Society of Grassland and Forage Science
• /
• v.3 no.2
• /
• pp.100-111
• /
• 1983

The research results reported herein had the objectives to understand and analyze the present problems of saemaeul woodland joint cattle grazing system in Kang Won Do and to take steps of improvement. The study results on actual management conditions, problems analyzed and improvement plan of total 208 joint cattle grazing area which was established 105 area in 1981 and 103 area in 1982 were summarized as follows: 1. the effectiveness of joint cattle grazing projects 1) Average daily weight gain of cattle during joint cattle grazing period was 0.4kg, showing higher daily than the conventional feeding of 0.33kg. 2) Increase of total farm income over the conventional feeding system were \1,031,357,320 during the grazing period from May to October in 1982 by adapting the 208 joint cattle grazing system, of which effectiveness of weight gain was \293,075,300 and labor saving was \543,838,750. 3) According to the results of questionaire investigation from 208 joint cattle grazing area, effectiveness of joint cattle grazing system over the conventional system were (1) labor saving, (2) feed cost saving, (3) reduced diseases, (4) increase of number of feeding, (5) inspiration of joint endeavor, (6) effect of more gain, (7) easiness of feeding and feed cost savings. 2. Problems of joint cattle grazing system. 1) Shortages of grass were a problem at second year of joint cattle grazing period due to the low regrowth rate of wild grass. 2) Proper land for woodland joint cattle grazing is belonging to land of Government ownership and it is very hard to get the permission from office of forestry for cattle grazing purpose. 3) It is also difficult to find a proper time of breeding in grazing area by the difficulty of estrus detection. 4) There are a difficulty to give a proper vaccination and medical examination for the grazing cattle. 3. Improvement plans for woodland joint cattle grazing projects. 1) Obtain sufficient roughages by hoof cultivation and oversowing pasture from the second year of joint cattle grazing period. 2) In order to increase the beef production and to use for a calf production area, Government should arrange that all proper grazing land of Government owned in Kang Won Do convert into woodland joint cattle grazing area. 3) Make a good reproductive record by mixed grazing with a excellent breeding cow in a remote area. And carry out the collective artificial insemination with synchronous puberty induced by injection of puberty stimulation hormone. 4) Make a preventive injection for blackleg, twice medication of fasciola hepatica in a year, and spray and medication of tick insecticide. 4. A policy towards upbringing of woodland joint cattle grazing area. 1) Government should thoroughly investigate about a proper land for woodland joint cattle grazing from all forests. 2) When the area is suitable for the woodland joint cattle grazing, though it is national forest or restricted area, government should make it possible to establish a grazing area. 3) On the proper land foe joint cattle grazing in the remote place, Government should support for the road construction and electric fence equipments by using of national funds. 4) There should be an administrative consideration for well promotion of the project that make woodland joint cattle grazing suitable to the characteristics of Kang Won Do. 5) In order to improve the reproduction record, Government should reform the insufficiency of artificial insemination in the joint cattle grazing area. 6) In order to maintain a proper price of cow, Government should carry out the price plan. 7) When there is any request for grassland formation in the woodland joint cattle grazing area, Government should permit it with preference.