• Title, Summary, Keyword: polar

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A Numerical Simulation of Blizzard Caused by Polar Low at King Sejong Station, Antarctica (극 저기압(Polar Low) 통과에 의해 발생한 남극 세종기지 강풍 사례 모의 연구)

  • Kwon, Hataek;Park, Sang-Jong;Lee, Solji;Kim, Seong-Joong;Kim, Baek-Min
    • Atmosphere
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    • v.26 no.2
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    • pp.277-288
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    • 2016
  • Polar lows are intense mesoscale cyclones that mainly occur over the sea in polar regions. Owing to their small spatial scale of a diameter less than 1000 km, simulating polar lows is a challenging task. At King Sejong station in West Antartica, polar lows are often observed. Despite the recent significant climatic changes observed over West Antarctica, adequate validation of regional simulations of extreme weather events such as polar lows are rare for this region. To address this gap, simulation results from a recent version of the Polar Weather Research and Forecasting model (Polar WRF) covering Antartic Peninsula at a high horizontal resolution of 3 km are validated against near-surface meteorological observations. We selected a case of high wind speed event on 7 January 2013 recorded at Automatic Meteorological Observation Station (AMOS) in King Sejong station, Antarctica. It is revealed by in situ observations, numerical weather prediction, and reanalysis fields that the synoptic and mesoscale environment of the strong wind event was due to the passage of a strong mesoscale polar low of center pressure 950 hPa. Verifying model results from 3 km grid resolution simulation against AMOS observation showed that high skill in simulating wind speed and surface pressure with a bias of $-1.1m\;s^{-1}$ and -1.2 hPa, respectively. Our evaluation suggests that the Polar WRF can be used as a useful dynamic downscaling tool for the simulation of Antartic weather systems and the near-surface meteorological instruments installed in King Sejong station can provide invaluable data for polar low studies over West Antartica.

Non-polar and Semi-polar InGaN LED Growth on Sapphire Substrate

  • Nam, Ok-Hyeon
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.51-51
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    • 2010
  • Group III-nitride semiconductors have been widely studied as the materials for growth of light emitting devices. Currently, GaN devices are predominantly grown in the (0001) c-plane orientation. However, in case of using polar substrate, an important physical problem of nitride semiconductors with the wurtzite crystal structure is their spontaneous electrical polarization. An alternative method of reducing polarization effects is to grow on non-polar planes or semi-polar planes. However, non-polar and semipolar GaN grown onto r-plane and m-plane sapphire, respectively, basically have numerous defects density compared with c-plane GaN. The purpose of our work is to reduce these defects in non-polar and semi-polar GaN and to fabricate high efficiency LED on non/semi-polar substrate. Non-polar and semi-polar GaN layers were grown onto patterned sapphire substrates (PSS) and nano-porous GaN/sapphire substrates, respectively. Using PSS with the hemispherical patterns, we could achieve high luminous intensity. In case of semi-polar GaN, photo-enhanced electrochemical etching (PEC) was applied to make porous GaN substrates, and semi-polar GaN was grown onto nano-porous substrates. Our results showed the improvement of device characteristics as well as micro-structural and optical properties of non-polar and semi-polar GaN. Patterning and nano-porous etching technologies will be promising for the fabrication of high efficiency non-polar and semi-polar InGaN LED on sapphire substrate.

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Comparative study of photoluminescences for Zn-polar and O-polar faces of single-crystalline ZnO bulks

  • O, Dong-Cheol;Kim, Dong-Jin;Bae, Chang-Hwan;Gu, Gyeong-Wan;Park, Seung-Hwan
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.39-39
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    • 2010
  • The authors have an extensive study of photoluminescences for Zn-polar and O-polar faces of single-crystalline ZnO bulks. In the photoluminescence (PL) spectra at 10 K, Zn-polar and O-polar faces show a common emission feature: neutral donor-bound excitons and their longitudinal-optical (LO) phonon replicas are strong, and free excitons are very weak. However, in the PL spectra at room temperature (RT), Zn-polar and O-polar faces show extremely different emission characteristics: the emission intensity of Zn-polar face is 30 times larger than that of O-polar face, and the band edge of Zn-polar face is 33 meV red-shifted from that of O-polar face. The temperature dependence of photoluminescence indicates that the PL spectra at RT are closely associated with free excitons and their phonon-assisted annihilation processes. As a result, it is found that the RT PL spectra of Zn-polar face is dominated by the first-order LO phonon replica of A free excitons, while that of O-polar face is determined by A free excitons. This is ascribed that Zn-polar face has larger exciton-phonon coupling strength than O-polar face.

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Introduction to IMO Polar Code - From the perspective of class

  • Suk, Ji-Hoon
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • pp.130-132
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    • 2015
  • The IMO Polar Code was adopted by Res.MSC.385(94) and Res.MEPC.264(68) and will enter into force on 1 January 2017. The Polar Code will affect design and equipment of ships intending to operate in polar areas. In this study, the requirements in the Polar Code are analysed from the perspective of class.

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A Modified Cryopreservation Method of Psychrophilic Chlorophyta Pyramimonas sp. from Antarctica

  • Hong, Sung-Soo;Lee, Soo-Young;Kim, Young-Nam;Kang, Sung-Ho;Kim, Hak-Jun
    • Ocean and Polar Research
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    • v.33 no.3
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    • pp.303-308
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    • 2011
  • Polar psychrophiles which thrive under extreme conditions such as cold temperature, high salinity, and high dose ultraviolet light, emerge as novel targets for biotechnology. To prevent genetic drift and the possibility of contamination by subculturing, cryopreservation was employed for two psychrophilic microalgae, Porosira sp. (KOPRI AnM0008) and Pyramimonas sp. (KOPRI AnM0046), which have anti-freeze activities. Five cryoprotectants (dimethyl sulphoxide, ethylene glycol, glycerol, methanol and propylene glycol) showed toxicity at 20-30% (v/v). The optimal cryoprotectant concentration and equilibration time were less than 20% and 10 min, respectively. Cryopreservation was carried out in the presence of cryoprotectants either by direct freezing in liquid nitrogen ($LN_2$) or controlled freezing using a controlled rate freezer followed by storage in the $LN_2$ tank. As a result, Pyramimonas sp. (KOPRI AnM0046), a psychrophilic chlorophyta was revived. Cryopreserved Porosira sp. was not revived from either freezing protocols probably due to the silicic cell wall and its relatively large cell size. In the case of Pyramimonas sp. (KOPRI AnM0046), the controlled freezing method showed higher revival yield than the direct freezing method.

A Study on the Development of Curriculum of Polar safety training (극지기초안전교육과정 개발에 관한 연구)

  • LEE, Jin-Woo;KIM, E-Wan;WOO, Young-Jin;LEE, Chang-Hee
    • Journal of Fisheries and Marine Sciences Education
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    • v.28 no.4
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    • pp.1031-1041
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    • 2016
  • Interests in the Polar Regions have been growing due to various factors such as depletion of natural resources and advanced resource development technologies, accelerated rate of polar ice melting as a result of global warming, etc. In particular, demand for the workforce related to vessel passage using the Northern Sea Route and polar studies is still expanding. The International Maritime Organization adopted the Polar Code in 2015 for the safety of ship operation in polar waters and it will enter into force from 2017. But education and training section in the code has been prescribed only for the safe navigation in the ice covered waters intended for navigational offices. There is no basic safety training requirement that applies commonly for all personnel exposed to the risk of the polar regions and the relevant study or discussion has not been made so far. Therefore, this study provides basic data for developing safety training courses for crew and other personnel by analyzing relevant regulations on polar safety training and the contents of relevant safety training in offshore industry required by the costal states adjacent to arctic ocean.

Cryobiological Perspectives on the Cold Adaptation of Polar Organisms (극지 생물의 저온적응 기작과 저온 생물학적 응용 연구)

  • Kang, Sung-Ho;Joo, Hyung-Min;Park, Seung-Il;Jung, Woong-Sic;Hong, Sung-Soo;Seo, Ki-Won;Jeon, Mi-Sa;Choi, Han-Gu;Kim, Hak-Jun
    • Ocean and Polar Research
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    • v.29 no.3
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    • pp.263-271
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    • 2007
  • The survival strategies of polar organisms at permanently or extremely cold temperatures and their application to cryobiology were reviewed here. In addition, ongoing studies on psychrophiles also were described. Psychrophiles are extremophiles that can grow and reproduce in cold temperatures, typically at -10 to $20^{\circ}C$. These organisms developed various mechanisms of adaptation to extremely cold environments. Polar organisms cope with these extreme physicochemical conditions using strategies such as avoidance, protection and partnership with other organisms. Understanding on the strategies adopted by polar organisms may provide insight on the physiological process that cells can go through during freezing. Cryopreservation may be able to take advantage of the findings described above. Currently, genomes of many cold-loving organisms have been sequenced and comparative genomics has revealed, at a molecular level, the characteristics of these organisms. The investigation of microorganisms on the polar glaciers may expand our understanding on the origin of life on Earth and other planets.

Polar Body: Indicator of Oocyte's Maturation, Have Any Function on Oocyte?

  • Dibyendu, Biswas;Hyun, Sang-Hwan
    • Journal of Embryo Transfer
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    • v.24 no.4
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    • pp.249-251
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    • 2009
  • Polar body was usually used as a determinant of oocyte's maturation. Polar body morphology could reflect the embryo quality and implantation competence. This review only focuses on morphology of the first polar body and embryo developmental rate in the presence or absence of polar body. However, it is very difficult to describe whether polar body has any effects on embryo development in vitro or in vivo. Further intensive research is needed to determine its function on embryo development.