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Random pinhole attenuator for high-power laser beams

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High Power Laser Science and Engineering 2024年第3期12卷 116-121页

作者： Seong Cheol Park Hyeok Yun Jin woo Yoon Seong Ku Lee Jae Hee Sung il woo choi Chang Hee Nam Kyung Taec Kim Department of Physics and Photon Science Gwangju Institute of Science and TechnologyGwangjuRepublic of Korea Center for Relativistic Laser Science Institute for Basic ScienceGwangjuRepublic of Korea Advanced Photonics Research Institute Gwangju Institute of Science and TechnologyGwangjuRepublic of Korea

The intensity attenuation of a high-power laser is a frequent task in the measurements of optical *** intensity can be attenuated by inserting an optical element,such as a partial reflector,polarizer or absorption *** devices are,however,not always easily applicable,especially in the case of ultra-high-power lasers,because they can alter the characteristics of a laser beam or become easily *** this study,we demonstrated that the intensity of a laser beam could be effectively attenuated using a random pinhole attenuator(RPA),a device with randomly distributed pinholes,without changing the beam *** this device,a multi-PW laser beam was successfully attenuated and the focused beam profile was measured without any alterations of its *** addition,it was confirmed that the temporal profile of a laser pulse,including the spectral phase,was ***,the RPA possesses significant potential for a wide range of applications.

关键词： high-power laser intensity attenuation laser diagnostics

Characterization of the plasma mirror system at the J-KAREN-P facility

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High Power Laser Science and Engineering 2022年第4期10卷 26-35页

作者： Akira Kon Mamiko Nishiuchi Yuji Fukuda Kotaro Kondo Koichi Ogura Akito Sagisaka Yasuhiro Miyasaka Nicholas P.Dover Masaki Kando Alexander S.Pirozhkov Izuru Daito Liu Chang il woo choi Chang Hee Nam Tim Ziegler Hans-Peter Schlenvoigt Karl Zeil Ulrich Schramm Hiromitsu Kiriyama Kansai Photon Science Institute National Institutes for Quantum Science and TechnologyKyoto 619-0215Japan Center for Relativistic Laser Science Institute for Basic ScienceGwangju 61005Republic of Korea Advanced Photonics Research Institute Gwangju Institute of Science and TechnologyGwangju 61005Republic of Korea Department of Physics and Photon Science Gwangju Institute of Science and TechnologyGwangju 61005Republic of Korea Helmholtz-ZentrumDresden-Rossendorf 01328 DresdenGermany Technische Universitat Dresden 01062 DresdenGermany

We report on the design and characterization of the plasma mirror system installed on the J-KAREN-P laser at the Kansai Photon Science Institute,National Institutes for Quantum Science and *** reflectivity of the single plasma mirror system exceeded 80%.In addition,the temporal contrast was improved by two orders of magnitude at 1 ps before the main ***,the laser near-field spatial distribution after the plasma mirror was kept constant at plasma mirror fluence of less than 100 kJ/cm^(2).We also present the results of investigating the difference and the fluctuation in energy,pulse width and pointing stability with and without the plasma mirror system.

关键词： high-powerlasers laser plasma plasma mirror

High-intensity laser-driven particle and electromagnetic wave sources for science, industry, and medicine

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Frontiers of Optoelectronics 2009年第3期2卷 299-303页

作者： Akito SAGISAKA Hiroyuki DAIDO Alexander S.PIROZHKOV Michiaki MORI Akifumi YOGO Koichi OGURA Satoshi ORIMO Mamiko NISHIUCHI Jinglong MA Hiromitsu KIRIYAMA Shuhei KANAZAWA Shuji KONDO Yoshiki NAKAI Takuya SHIMOMURA Manabu TANOUE Atsushi AKUTSU Hajime OKADA Tomohiro MOTOMURA Tetsuya KAWACHI Sergei V.BULANOV Timur Zh.ESIRKEPOV Shigeki NASHIMA Makoto HOSODA Hideo NAGATOMO Yuji OISHI Koshichi NEMOTO il woo choi Seong Ku LEE Jongmin LEE Advanced Photon Research Center and Photo-Medical Research Center Japan Atomic Energy Agency A.M.Prokhorov Institute of General Physics Russian Academy of Sciences Moscow Institute of Physics and Technology Department of Applied Physics Graduate School and Faculty of Engineering Osaka City University Institute of Laser Engineering Osaka University Central Research Institute of Electric Power Industry Advanced Photonics Research Institute Gwangju Institute of Science and Technology

We simultaneously observed both the fast proton generation and terahertz(THz) radiation in the laser pulse interaction with a thin-foil target. The maximum proton energy of ～2.3 Me V and an intense THz radiation were observed at the pulse duration of～30 fs. We also measured the proton beam and UV harmonics from a thin-foil target by changing the laser pulse duration. In the case of the ～500 fs, peaks of UV harmonics up to fourth order appeared. This unique combination of the multiple beams will provide useful applications such as pump-probe experiments.

关键词： electromagnetic wave high-intensity laser plasma proton thin-foil target

First Record of the Blue-banded Sea Krait(Laticauda laticaudata,Reptilia:Squamata:Elapidae:Laticaudinae)on Jeju Island,South Korea

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Asian Herpetological Research 2017年第2期18卷 131-136页

作者： Jaejin PARK Kyo-Soung KOO il-Hun KIM woo-Jin choi Daesik PARK Department of Biology Kangwon National UniversityChuncheonKangwon 24341South Korea National Marine Biodiversity Institute of Korea SeocheonChungnam 33662South Korea Division of Science Education Kangwon National UniversityChuncheonKangwon 24341South Korea

We report the first recorded capture of a blue-banded sea snake（Laticauda laticaudata Linnaeus, 1758, Jobeuntti Kun Badabam in Korean） in South Korea based on one male specimen collected from Marado-ri, Seogwiposi, Jeju-do on 20 October 2016. The morphological features of the lateral nostrils, the much wider ventrals than adjacent dorsals, the horizontally undivided rostral, the two prefrontals, and the uniform black bands on the body indicate that the specimen is L. laticaudata. An analysis of the partial mitochondrial cytochrome b gene sequence indicated that the specimen fits well into the known L. laticaudata phylogenetic group, which confirms that the sea krait is L. laticaudata. Including this report, five species of sea snakes（L. laticaudata, L. semifasciata, Hydrophis platurus, H. cyanocinctus, and H. melanocephalus） have now been reported in Korean waters.

关键词： sea snake Hydrophiinae Laticaudinae blue-banded sea snake Laticauda laticaudata

Effect of change of sand properties on travel distance of ricocheted debris

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Defence Technology（防务技术） 2021年第4期17卷 1486-1495页

作者： Yoon Keon Kim woo Chun choi Department of Mechanical Engineering Korea University145 Anam-roSeongbuk-guSeoul02841Republic of Korea

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 *** reduce this danger,the travel distance of ricocheted debris must be accurately *** study analyzed the change in the travel distance of ricocheted concrete debris relative to changes in the properties of a sand *** shear tests were conducted to measure the change in internal friction angle as a function of temperature and water content of the *** element analysis(FEA)was then applied to these variables to predict the speed and angle of the debris after *** FEA results were compared with results of low-speed ricochet experiments,which employed variable temperature and water *** travel distance of the debris was calculated using MATLAB,via trajectory equations considering the drag *** the internal friction angle decreased,the shear stress decreased,leading to deeper penetration of the debris into the *** the loss of kinetic energy increased,the velocity and travel distance of the ricocheted debris *** 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.

关键词： Ricochet Exploded debirs Environmental change Sand Temperature Water content Internal friction angle Travel distance

Grade-4 commercially pure titanium with ultrahigh strength achieved by twinning-induced grain refinement through cryogenic deformation

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Journal of Materials Science & Technology 2021年第7期66卷 193-201页

作者： Seong-woo choi Jae Sukjeong Jong woo Won Jae Keun Hong Yoon Suk choi Titanium Department.Korea Institute of Materials Science Changwon51508Republic of Korea School of Materials Science and Engineering Pusan National UniversityPusan.46241Republic of Korea Materials and Manufacturing Development Team Doosan Heavy Industries and ConstructionChangwon51711Republic of Korea

The yield strength of commercially pure(CP) Ti of ASTM grade 4, the strongest among all the CP-Ti grades, is too low for structural applications that require high-strength materials. Here, we demonstrate the strengthening of grade-4 CP Ti by cryogenic-temperature rolling(CTR), which enables deformation twinning in grade-4 CP Ti to achieve twinning-induced grain refinement. CTR activated {11.22} twinning and {10.12} twinning, which are the most common twinning systems in pure Ti, whereas room-temperature rolling(RTR) did not activate any twinning system. CTR with imposing an area reduction of just 30% significantly increased the yield strength of the CP Ti to 946 MPa, which is not achievable through typical processes performed at or above room temperature and is comparable to that of commercial Ti-6 Al-4 V. The significant increase in strength was due to microstructural strengthening caused by twinning-induced grain refinement, combined with dislocation accumulation. In contrast to RTR, CTR greatly increased the stress concentration at grain boundaries(GBs), which caused the unusual activation of twinning in the grade-4 CP Ti by facilitating twin nucleation at GBs. The stress concentration increased because CTR activated the slip to a lesser extent compared to RTR, thereby reducing the strain compatibility between neighboring grains. These results will contribute to development of ultrahigh-strength CP Ti and may thereby extend its use to structural applications that require high-strength materials.

关键词： Titanium Twinning Cryogenic deformation Grain refinement Tensile properties

Characteristics of machined surface controlled by cutting tools and conditions in machining of brittle material

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中国有色金属学会会刊：英文版 2009年第B9期19卷 194-201页

作者： Yong-woo KIM Soo-Chang choi Jeung-woo PARK Deug-woo LEE Department of Nano Fusion Technology Pusan National University Department of Mechanical Design Engineering Chosun University Department of Nanosystem and Nanoprocess Engineering Pusan National University

One of the ultra-precision machining methods was adapted for brittle material as well as soft material by using multi-arrayed diamond tips and high speed spindle. Conventional machining method is too hard to control surface roughness and surface texture against brittle material because the particles of grinding tools are irregular size and material can be fragile. Therefore, we were able to design tool paths and machine controlled pattern on surface by multi-arrayed diamond tips with uniform size made in MEMS fabrication and high speed spindle, and the maximum speed was about 3×105 r/min. We defined several parameters that can affect the machining surface. Those were multi-array of diamond tips (n×n), speed of air spindle and feeding rate. The surface roughness and surface texture can be controlled by those parameters for micro machining.

关键词：加工表面脆性材料条件控制刀具路径表面粗糙度特征高速主轴加工方法

Effect of dietary vitamin C on gastric cancer risk in the Korean population

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World Journal of Gastroenterology 2016年第27期22卷 6257-6267页

作者： Bach Viet Hoang Jeonghee Lee il Ju choi Young-woo Kim Keun Won Ryu Jeongseon Kim Department of Cancer Control and Policy Graduate School of Cancer Science and Policy National Cancer Center Molecular Epidemiology Branch Research Institute National Cancer Center Center for Gastric Cancer National Cancer Center Hospital National Cancer Center

AIM: To investigate the effects of dietary vitamin C and foods containing vitamin C on gastric cancer ***: Our study included 830 control subjects and 415 patients. Data regarding demographics, medical history, and lifestyle, including dietary and nutrient intake, were collected using reliable selfadministered questionnaires. Dietary intake information was collected from the participants using a food frequency questionnaire that has been previously reported as reliable and valid. A rapid urease test and a histological evaluation were used to determine the presence of Helicobacter pylori(H. pylori) infection. Twenty-three vitamin C-contributing foods were selected, representing over 80% of the cumulative vitamin C contribution. RESULTS: In analyses adjusted for first-degree family history of gastric cancer, education level, job, household income, smoking status, and regular exercise, an inverseassociation between vitamin C intake and gastric cancer risk was observed for the highest(≥ 120.67 mg/d) vs the lowest(< 80.14 mg/d) intake category [OR(95%CI): 0.64(0.46-0.88)], with a significant trend across the three intake categories(P = 0.007). No protective effect of vitamin C was detected after stratification by gender. No effect of vitamin C intake on the gastric cancer incidence was found in either men or women infected with H. pylori. Vitamin C-contributing foods, including cabbage [0.45(0.32-0.63), 0.50(0.34-0.75), 0.45(0.25-0.81)], strawberries [0.56(0.40-0.78), 0.49(0.32-0.74), 0.52(0.29-0.93)], and bananas [0.40(0.29-0.57), 0.41(0.27-0.62), 0.34(0.19-0.63)], were protective factors against the risk of gastric cancer based on the results of the overall adjusted analyses and the results for men and women, ***: A protective effect of vitamin C and vitamin C-contributing foods against gastric cancer was observed. Further studies using larger sample sizes are required to replicate our results.

关键词： Vitamin C Vitamin C-contributing foods Helicobacter pylori Gastric cancer Korean population

Optical coherence tomography imaging of cranial meninges post brain injury in vivo

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Chinese Optics Letters 2017年第9期15卷 16-19页

作者： woo June choi Ruikang K.Wang Department of Bioengineering University of WashingtonSeattleWA 98195USA

We report a new application of optical coherence tomography（OCT） to investigate the cranial meninges in an animal model of brain injury in vivo. The injury is induced in a mouse due to skull thinning, in which the repeated and excessive drilling exerts mechanical stress on the mouse brain through the skull, resulting in acute and mild brain injury. Transcranial OCT imaging reveals an interesting virtual space between the cranial meningeal layers post skull thinning, which is gradually closed within hours. The finding suggests a promise of OCT as an effective tool to monitor the mechanical trauma in the small animal model of brain injury.

关键词： Optical coherence tomography imaging of cranial meninges post brain injury in vivo