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Single-Layer Phase Gradient mmWave Metasurface Lens for Incident Angle Independent Focusing
Lee Wonwoo,Jo Semin,Kim Yongchan,Choi Keun-Yeong,Yun Eseudeo,Lee Ryungyu,Moon Jinho,Kim Hyunwoo,Lee Hojin 한국통신학회 2022 한국통신학회 학술대회논문집 Vol.2022 No.2
Metasurfaces allow the rapid development of flat electromagnetic devices owing to their ability in exploiting the wavefront of electromagnetic waves. Particularly, with respect to the metasurface lenses, wide operating bandwidth and wide incident angle characteristics are critical features for practical applications. Herein, a single-layer phase gradient metasurface lens is presented to realize millimeter-wave focusing at a focal point of 13 mm regardless of the incident angle. The proposed metasurface lens is designed with subwavelength-thick (<λ/10) phase elements composed of two metallic layers separated by a single dielectric substrate that exhibits low-Q resonance properties and a wide phase modulation range with satisfactory transmissivity. By controlling the spatial phase distribution, the proposed metasurface lens realizes effective wavefront manipulation properties and high performance electromagnetic wave focusing characteristics over a wide operating frequency range from 35 to 40 GHz with incident angle independency up to 30°.
Tunneling decay of self-gravitating vortices
Dupuis, É,ric,Gobeil, Yan,Lee, Bum-Hoon,Lee, Wonwoo,MacKenzie, Richard,Paranjape, Manu B.,Yajnik, Urjit A.,Yeom, Dong-han,Gwak, B.,Kang, G.,Kim, C.,Kim, H.-C.,Lee, C.-H.,Lee, J.,Lee, S.,Lee, W. EDP Sciences 2018 The European Physical Journal Conferences Vol.168 No.-
<P>We investigate tunneling decay of false vortices in the presence of gravity, in which vortices are trapped in the false vacuum of a theory of scalar electrodynamics in three dimensions. The core of the vortex contains magnetic flux in the true vacuum, while outside the vortex is the appropriate topologically nontrivial false vacuum. We numerically obtain vortex solutions which are classically stable; however, they could decay via tunneling. To show this phenomenon, we construct the proper junction conditions in curved spacetime. We find that the tunneling exponent for the vortices is half that for Coleman-de Luccia bubbles and discuss possible future applications.</P>
Lee, Byeongno,Kang, Seung Hee,Kang, Donghyeon,Lee, Kyu Hyung,Cho, Jaeheung,Nam, Wonwoo,Han, Oc Hee,Hur, Nam Hwi Royal Society of Chemistry 2011 Chemical communications Vol.47 No.40
<P>A solid hydrazine was isolated as a crystalline powder by reacting aqueous hydrazine with supercritical CO<SUB>2</SUB>. Its structure determined by single crystal X-ray diffraction shows a zwitterionic form of NH<SUB>3</SUB><SUP>+</SUP>NHCO<SUB>2</SUB><SUP>−</SUP>. The solid hydrazine is remarkably stable but is as reactive as liquid hydrazine even in the absence of solvents.</P> <P>Graphic Abstract</P><P>A stable solid hydrazine prepared in supercritical CO<SUB>2</SUB> has a zwitterionic structure, exhibiting superior activity toward carbonyl compounds even in the absence of solvents. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1cc14542h'> </P>
Limited Use of Ridge Retression
Lee, Wonwoo 延世大學校經濟硏究所 1996 延世經濟硏究 Vol.3 No.2
Ridge regression is the most popular approach to the multicollinearity problem when it presents in the multiple linear regression mode. However, it is not a panacea since the performance of ridge regression is dependent upon the values of the parameters.
OSCILLATING INSTANTONS AS HOMOGENEOUS TUNNELING CHANNELS
LEE, BUM-HOON,LEE, WONWOO,YEOM, DONG-HAN World Scientific 2013 International journal of modern physics. A, Partic Vol.28 No.18
<P> In this paper, we study Einstein gravity with a minimally coupled scalar field accompanied with a potential, assuming an O(4) symmetric metric ansatz. We call an Euclidean instanton is to be an oscillating instanton, if there exists a point where the derivative of the scale factor and the scalar field vanish at the same time. Then, we can prove that the oscillating instanton can be analytically continued, both as inhomogeneous and homogeneous tunneling channels. Here, we especially focus on the possibility of a homogeneous tunneling channel. For the existence of such an instanton, we have to assume three things: (1) there should be a local maximum and the curvature of the maximum should be sufficiently large, (2) there should be a local minimum and (3) the other side of the potential should have a sufficiently deeper vacuum. Then, we can show that there exists a number of oscillating instanton solutions and their probabilities are higher compared to the Hawking-Moss instantons. We also check the possibility when the oscillating instantons are comparable with the Coleman-de Luccia channels. Thus, for a general vacuum decay problem, we should not ignore the oscillating instanton channels. </P>
A Mn(iv)-peroxo complex in the reactions with proton donors
Lee, Chien-Ming,Sankaralingam, Muniyandi,Chuo, Chi-He,Tseng, Tzu-Hsien,Chen, Peter P.-Y.,Chiang, Ming-Hsi,Li, Xiao-Xi,Lee, Yong-Min,Nam, Wonwoo The Royal Society of Chemistry 2019 Dalton Transactions Vol.48 No.16
<P>Protons play an important role in promoting O-O or M-O bond cleavage of metal-peroxo complexes. Treatment of side-on O2-bound [PPN][Mn<SUP>IV</SUP>(<SUP>TMS</SUP>PS3)(O2)] (1, PPN = bis(triphenylphosphine)iminium and <SUP>TMS</SUP>PS3H3 = 2,2′,2′′-trimercapto-3,3′,3′′-tris(trimethylsilyl)triphenylphosphine) with perchloric acid (HClO4) in the presence of PR3 (R = phenyl or <I>p</I>-tolyl) results in the formation of neutral five-coordinate Mn<SUP>III</SUP>(OPR3)(<SUP>TMS</SUP>PS3) complexes (R = phenyl, 2a; <I>p</I>-tolyl, 2b), which are confirmed by X-ray crystallography. Isotope labelling experiments demonstrate that the oxygen atom in the phosphine oxide product derives from the peroxo ligand of 1. Reactions of 1 with weak proton donors, such as phenylthiol, phenol, substituted phenol and methanol, are also investigated to explore the reactivity of the Mn<SUP>IV</SUP>-peroxo complex, leading to the isolation of a series of five-coordinate [Mn<SUP>III</SUP>(L)(<SUP>TMS</SUP>PS3)]<SUP>−</SUP> complexes (L = phenylthiolate, phenolate or methoxide). Mechanistic aspects of the reactions of the Mn<SUP>IV</SUP>-peroxo complex with proton donors are discussed as well.</P>
Silhouette Segmentation in Multiple Views
Wonwoo Lee,Woontack Woo,Boyer, E IEEE 2011 IEEE transactions on pattern analysis and machine Vol.33 No.7
<P>In this paper, we present a method for extracting consistent foreground regions when multiple views of a scene are available. We propose a framework that automatically identifies such regions in images under the assumption that, in each image, background and foreground regions present different color properties. To achieve this task, monocular color information is not sufficient and we exploit the spatial consistency constraint that several image projections of the same space region must satisfy. Combining the monocular color consistency constraint with multiview spatial constraints allows us to automatically and simultaneously segment the foreground and background regions in multiview images. In contrast to standard background subtraction methods, the proposed approach does not require a priori knowledge of the background nor user interaction. Experimental results under realistic scenarios demonstrate the effectiveness of the method for multiple camera set ups.</P>
Lee, Hogyu,Kim, Jun Hee,Lee, Won Koo,Cho, Jaeheung,Nam, Wonwoo,Lee, Jaedeok,Ha, Hyun-Joon The Royal Society of Chemistry 2013 Organic & Biomolecular Chemistry Vol.11 No.22
<P>Polyhydroxylated pyrrolidines, such as biologically important azafuranoses represented by the natural product (+)-2,5-imino-2,5,6-trideoxy-<I>gulo</I>-heptitol and its C(3)-epimer, were elaborated from a commercially available enantiomerically pure (2<I>R</I>)-hydroxymethylaziridine by highly stereoselective directed reactions in more than 61% overall yield. At first, the nucleophile 2-trimethylsilyloxyfuran was directed to (2<I>R</I>)-aziridine-2-carboxaldehyde by ZnBr<SUB>2</SUB> to yield the unusual <I>anti</I>-addition product as a single isomer via the chelation-controlled transition. The ring opening of aziridine was followed by conjugate addition to give a <I>cis</I>-fused bicycle, which was converted to the target molecule after the required reductive operations.</P> <P>Graphic Abstract</P><P>Azafuranoses represented by the natural product (+)-2,5-imino-2,5,6-trideoxy-gulo-heptitol and its C(3)-epimer were elaborated from a commercially available enantiomerically pure (2<I>R</I>)-hydroxymethylaziridine by highly stereoselective directed reactions.. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3ob27390c'> </P>