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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>
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>
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>
Lee, Wonwoo,Ko, Kyeong Ryang,Kim, Hyun-keun,Lim, Seonung,Kim, Sunyoung Elsevier 2018 Biochemical and biophysical research communication Vol.495 No.3
<P><B>Abstract</B></P> <P>Estrogen deficiency results in an imbalance between the levels of bone-resorping osteoclasts and bone-forming osteoblasts, eventually leading to overall bone loss. Dehydrodiconiferyl alcohol (DHCA), a lignan compound originally isolated from <I>Cucurbita moschata</I>, has been shown to bind to estrogen receptor, and indeed exhibits various activities of estrogen, such as anti-inflammatory and anti-oxidative stress effects. In this study, we tested whether synthetic DHCA could affect the BMP-2-induced osteoblastogenesis in vitro. In MC3T3-E1 cells, DHCA promoted BMP-2-induced differentiation of osteoblasts. Consistently, the expression of three osteoblastogenic genes known to be induced by BMP-2, ALP, osteocalcin and OPG, was up-regulated by DHCA treatment. DHCA was also shown to activate the production of RUNX2 by activating Smad1/5/9 and AMPK. Data from transient transfection assays suggested that DHCA might activate the estrogen receptor signaling pathway. Effects of DHCA on BMP-2-induced osteoblastogenesis were reduced when cells were treated with a specific siRNA to ERα or ERβ. Taken together, our results suggest that DHCA may be developed as an efficient therapeutic for osteoporosis by regulating osteoblastogenesis through its estrogenic effects.</P> <P><B>Highlights</B></P> <P> <UL> <LI> DHCA promotes BMP-2-induced osteoblasts differentiation. </LI> <LI> DHCA upregulated the production of RUNX2 by activating Smad1/5/9 and AMPK. </LI> <LI> DHCA exerted its osteoblastogenic activities through acting as an agonist of both estrogen receptor alpha and beta. </LI> </UL> </P>
Lee, Wonwoo,Cho, Hyo Min,Oh, Chung Seok,Kim, Eun Hae,Sun, Woong Korean Society of Microscopy 2014 Applied microscopy Vol.44 No.2
With wide use of nano-materials, it is increasingly important to address their potential toxicity to mammalian cells. However, toxic effects of these materials have been mainly assessed by the cell survival assays. Considering that mitochondrial morphology and quality are highly sensitive to the condition of the cells, and the impairment of mitochondrial function greatly affect the survival of cells, here we tested the impact of multi-walled carbon nanotubes (MWNT) on the survival, mitochondrial morphology, and their membrane potential in HeLa cells. Interestingly, although MWNT did not induce cell death until 24 hours as assessed by pyknotic cell assay, mitochondrial length was elongated and the mitochondrial membrane potential was significantly reduced by exposure of HeLa cells to MWNT. These results suggest that MWNT exposure is potentially harmful to the cell, and the mechanism how MWNT alters mitochondrial quality should be further explored to assess the safety of MWNT use.
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>
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>
Video-Based In Situ Tagging on Mobile Phones
Wonwoo Lee,Youngmin Park,Lepetit, V.,Woontack Woo IEEE 2011 IEEE transactions on circuits and systems for vide Vol.21 No.10
<P>We propose a novel way to augment a real-world scene with minimal user intervention on a mobile phone; the user only has to point the phone camera to the desired location of the augmentation. Our method is valid for horizontal or vertical surfaces only, but this is not a restriction in practice in manmade environments, and it avoids going through any reconstruction of the 3-D scene, which is still a delicate process on a resource-limited system like a mobile phone. Our approach is inspired by recent work on perspective patch recognition, but we adapt it for better performances on mobile phones. We reduce user interaction with real scenes by exploiting the phone accelerometers to relax the need for fronto-parallel views. As a result, we can learn a planar target in situ from arbitrary viewpoints and augment it with virtual objects in real-time on a mobile phone.</P>