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Real-time outdoor concealed-object detection with passive millimeter wave imaging.
Yeom, Seokwon,Lee, Dong-Su,Son, Jung-Young,Jung, Min-Kyoo,Jang, Yushin,Jung, Sang-Won,Lee, Seok-Jae Optical Society of America 2011 Optics express Vol.19 No.3
<P>Millimeter wave imaging is finding rapid adoption in security applications such as the detection of objects concealed under clothing. A passive imaging system can be realized as a stand-off type sensor that can operate in open spaces, both indoors and outdoors. In this paper, we address real-time outdoor concealed-object detection and segmentation with a radiometric imaging system operating in the W-band. The imaging system is equipped with a dielectric lens and a receiver array operating at around ??4 GHz. Images are analyzed by multilevel segmentation to identify a concealed object. Each level of segmentation comprises vector quantization, expectation-maximization, and Bayesian decision making to cluster pixels on the basis of a Gaussian mixture model. In addition, we describe a faster process that adopts only vector quantization for the first level segmentation. Experiments confirm that the proposed methods provide fast and reliable detection and segmentation for a moving human subject carrying a concealed gun.</P>
Stabilization of selenium cathodes via in situ formation of protective solid electrolyte layer
Lee, Jung Tae,Kim, Hyea,Nitta, Naoki,Eom, Kwang-sup,Lee, Dong-Chan,Wu, Feixiang,Lin, Huan-Ting,Zdyrko, Bogdan,Cho, Won Il,Yushin, Gleb The Royal Society of Chemistry 2014 Journal of Materials Chemistry A Vol.2 No.44
Designing whispering gallery modes via transformation optics
Kim, Yushin,Lee, Soo-Young,Ryu, Jung-Wan,Kim, Inbo,Han, Jae-Hyung,Tae, Heung-Sik,Choi, Muhan,Min, Bumki Nature Publishing Group, a division of Macmillan P 2016 Nature photonics Vol.10 No.10
<P>In dielectric cavities with a rotational symmetry, whispering gallery modes (WGMs) with an extremely long lifetime (that is, a very high Q factor) can be formed by total internal reflection of light around the rim of the cavities. The ultrahigh Q factor of WGMs has enabled a variety of impressive photonic systems, such as ultralow threshold microlasers(1-3), biosensors with unprecedented sensitivity(4,5) and cavity optomechanical devices(6). However, the isotropic emission of WGMs, which is due to the rotational symmetry, is a serious drawback in applications that require directional light sources. Considerable efforts have thus been devoted to achieving directional emission by intentionally breaking the rotational symmetry(7-9). However, all of the methods proposed so far have suffered from substantial Q-spoiling. Here, we show how the mode properties of dielectric whispering gallery cavities, such as the Q factor and emission directionality, can be tailored at will using transformation optics. The proposed scheme will open a new horizon of applications beyond the conventional WGMs.</P>
Lee, Jung Tae,Zhao, Youyang,Thieme, Sö,ren,Kim, Hyea,Oschatz, Martin,Borchardt, Lars,Magasinski, Alexandre,Cho, Won‐,Il,Kaskel, Stefan,Yushin, Gleb WILEY‐VCH Verlag 2013 ADVANCED MATERIALS Vol.25 No.33
<P><B>Novel nanostructured sulfur (S)–carbide derived carbon (CDC) composites</B> with ordered mesopores and high S content are successfully prepared for lithium sulfur batteries. The tunable pore‐size distribution and high pore volume of CDC allow for an excellent electrochemical performance of the composites at high current densities. A higher electrolyte molarity is found to enhance the capacity utilization dramatically and reduce S dissolution in S‐CDC composite cathodes during cycling.</P>
Kim Nahun,Jung Dawoon,Kim Yushin,Kim Sihoon,Hong Sung Ju,한강희,Bahk Young-Mi 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.1
We investigate simple chemical doping process and the optical characterization of large-area graphene. The large-area graphene is grown on copper foil by chemical vapor deposition method, where carrier density is varied by exposure duration within FeCl3 solution after complete etching of copper. Using terahertz time-domain spectroscopy, we obtain terahertz conductivity with diferent exposure duration. We confrm that the longer exposure time, the higher conductivity, which results from p-type doping due to copper etchant. The result implies that varying etching time during transfer process enables distinguished Fermi levels in graphene sheet, essential for simple fabrication of doping-level-controlled graphene sample.