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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>
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.
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>
The nucleation of false vacuum bubbles with compact geometries
Lee, Bum-Hoon,Lee, Chul H.,Lee, Wonwoo,Oh, Changheon World Scientific 2015 International Journal of Modern Physics A Vol.30 No.18
<P> We investigate and classify the possible types of false vacuum bubbles in Einstein gravity. The false vacuum bubbles can occur only if gravity is taken into account. We show that there exist solutions only with compact geometries. The analytic computations for the radius and nucleation rate of a vacuum bubble are evaluated using the thin-wall approximation. We discuss possible cosmological implications of our new solutions. </P>
Fubini instantons and gravity effects
Lee, Bum-Hoon,Lee, Wonwoo,Ro, Daeho World Scientific 2016 International journal of modern physics. A, Partic Vol.31 No.2
<P> We study Fubini instantons of a self-gravitating scalar field, which belongs to the tunneling without a barrier. The instantons describe the decay of a tachyonic vacuum to an arbitrary state. When the gravity is taken into account, there exist various types of unexpected solutions including oscillating bounce solutions. Based on the Fubini instanton solutions in curved space, the issue on the instability of a tachyonic vacuum is discussed with regard to cosmology. </P>
Design and Analysis of Polarization Diversity Antenna for Mobile Terminals
Wonwoo Lee,이병호 한국전자통신연구원 2014 ETRI Journal Vol.36 No.1
This letter presents an antenna design method for anorthogonally-polarized dual antenna for use in mobile stations(MSs) and includes a verification method for improving thelink-level throughput performance of an MS that uses aproposed multiple-input multiple-output antenna. The link-levelthroughput performance of an MS is strongly related to thecorrelation between antenna branches, which is determined bythe cross polarization discrimination of the second branchantenna, both numerically and experimentally.
Vacuum bubbles in a de Sitter background and black hole pair creation
Lee, Bum-Hoon,Lee, Wonwoo Institute of Physics 2009 Classical and quantum gravity Vol.26 No.22
<P>We study the possible types of nucleation of vacuum bubbles. We classify vacuum bubbles in a de Sitter background and present some numerical solutions. The thin-wall approximation is employed to obtain the nucleation rate and the radius of vacuum bubbles. With careful analysis we confirm that Parke's formula is also applicable to the large true vacuum bubbles. The nucleation of the false vacuum bubble in a de Sitter background is also evaluated. The tunneling process in the potential with degenerate vacua is analyzed as the limiting cases of the large true vacuum bubble and false vacuum bubble. Next, we consider the pair creation of black holes in the background of bubble solutions. We obtain the static bubble wall solutions of the junction equation with a black hole pair. The masses of created black holes are uniquely determined by the cosmological constant and the surface tension on the wall. Finally, we obtain the rate of pair creation of black holes.</P>