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Choi, Jihoon,Lee, Bobin,Yu, Chan-Mo Royal Society of Chemistry 2011 Chemical communications Vol.47 No.13
<P>An enantioselective synthesis of the homoallenyl alcohols was achieved from the reaction of chiral 2-borylbutadiene with aldehydes through an allylic transfer reaction in good yields and enantioselectivities.</P> <P>Graphic Abstract</P><P>An enantioselective synthesis of the homoallenyl alcohols was achieved from the reaction of chiral 2-borylbutadiene with aldehydes through an allylic transfer reaction in good yields and enantioselectivities. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0cc05751g'> </P>
Choi, Mansoo,Lee, Sang-Hun,Jung, Yang-Il,Jung, Jun-Young,Park, Jung-Soon,Choi, Wang-Kyu,Park, Sang-Yoon,Won, Hui-Jun,Moon, Jei-Kwon,Choi, Jihoon,Kim, Seon-Byeong ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.729 No.-
<P><B>Abstract</B></P> <P>NiFe<SUB>2</SUB>O<SUB>4</SUB> thin film has been prepared by electron beam evaporation method and has been investigated as anode materials providing large reversible Li<SUP>+</SUP> capacity with high cycling performance for lithium ion batteries. The NiFe<SUB>2</SUB>O<SUB>4</SUB> thin film crystallized with annealing process after NiFe<SUB>2</SUB>O<SUB>4</SUB> thin film deposition. In electrochemical measurements, the first discharge and charge capacity of NiFe<SUB>2</SUB>O<SUB>4</SUB> thin film were found to be 1693 mAh g<SUP>−1</SUP> and 1108 mAh g<SUP>−1</SUP>, which is above its theoretical capacity (915 mAh g<SUP>−1</SUP>). In addition, the cycle performance test of NiFe<SUB>2</SUB>O<SUB>4</SUB> thin film also showed steady charge-discharge capacity at 0.1 C during 100 cycles compared to other NiFe<SUB>2</SUB>O<SUB>4</SUB> materials, indicating that the empty space or porous surface of electrode was beneficial for accessibility of electrolyte and served as buffer to alleviate stress.</P> <P><B>Highlights</B></P> <P> <UL> <LI> NiFe<SUB>2</SUB>O<SUB>4</SUB> thin film has been prepared by electron beam evaporation method. </LI> <LI> The first discharge and charge capacity of NiFe<SUB>2</SUB>O<SUB>4</SUB> thin film were found to be 1693 mAh g<SUP>−1</SUP> and 1108 mAh g<SUP>−1</SUP>. </LI> <LI> The cycle performance test of NiFe<SUB>2</SUB>O<SUB>4</SUB> thin film also showed steady charge-discharge capacity at 0.1 C during 100 cycles. </LI> </UL> </P>
Polymer Diffusion from Attractive and Athermal Substrates
Choi, Jihoon,Clarke, Nigel,Winey, Karen I.,Composto, Russell J. American Chemical Society 2017 Macromolecules Vol.50 No.7
<P>Given the exceedingly high interfacial area-to-volume ratios in polymer nanocomposites and the ability to manipulate the polymer/nanoparticle interfacial interactions, manipulating the chain dynamics at these interfaces has immense potential for impacting macroscopic properties. There, the polymer center-of-mass tracer diffusion coefficient (D) from attractive (hydroxyl terminated) and athermal (phenyl-terminated or polymer-grafted) substrates was measured over a range of temperatures and tracer molecular weights using elastic recoil detection. The tracer polymer diffusion slows significantly relative to the bulk when polymers are in direct contact with an attractive substrate and exhibits a weaker molecular weight dependence, D M M. For polymers without direct contacts on the attractive substrates and for athermal substrates, the diffusion coefficients are similar to the bulk case. The temperature dependence of these diffusion coefficients indicates that the slower diffusion at the interfaces is coupled to differences in polymer conformation and smaller fractional free volumes. These deviations from bulk are more pronounced for higher molecular weights and more attractive interfaces.</P>
Linear Fresnel Lens for a Solar Cell with above 85% Focal Efficiency
Jihoon Choi,Heeso Noh,Hyeri Jang,Jeong Seok Kang 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.8
We designed a linear Fresnel lens (LFL) for harvesting solar energy. The optimized LFL was fabricated with dimensions of 100 (W) × 100 (H) × 5 (T) mm^3, a focal length of 100 mm, and a fixed pitch size of 500 μm. The maximum focal efficiency is approximately 91%, and the half width at half maximum (HWHM) value of the focus size is approximately 130 μm. We also investigated the robustness of the LFL to changes in the incident angle, draft angle, and detection position. Simulations revealed a focal efficiency above 85% with an incident angle up to 1°, a draft angle up to 10°, and a detection position up to ±10 mm. We fabricated the LFL by using an injection molding process. The fabricated lens had a maximum focal efficiency of approximately 88% and a full width at half max (FWHM) of about 2.5 mm.
A graph with the partial order competition dimension greater than five
Choi, Jihoon,Eoh, Soogang,Kim, Suh-Ryung Elsevier 2019 Discrete Applied Mathematics Vol.260 No.-
<P><B>Abstract</B></P> <P>In this paper, we use the Erdös–Szekeres lemma to show that there exists a graph with partial order competition dimension greater than five.</P>
Unidirectional incident wave for an electromagnetic wave simulation using the finite element method
Choi Jihoon,Noh Heeso 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.78 No.7
In many simulations, the interference between the reflection from the structure and incident wave makes obtaining the reflectance difficult. This problem can be solved using unidirectional incident waves. This study developed a novel method to generate a unidirectional source using a simulation. For the periodic boundary condition, Gaussian source and nanobeam, we obtained an intensity ratio along the backward and the forward directions of the unidirectional incident wave of up to 0.45% after optimization. The optimized source width for the given wavelength λ was νλ∕(2neff) , where ν was a positive integer and neff the effective refractive index. This study was able to demonstrate that achieving a unidirectional incident wave for the periodic boundary condition, Gaussian source and nanobeam is possible using a simulation. This method can reduce the simulation time and computation memory needed for conventional calculations.
On ( 1 , 2 ) -step competition graphs of bipartite tournaments
Choi, Jihoon,Eoh, Soogang,Kim, Suh-Ryung,Lee, Sojung Elsevier BV, North-Holland 2017 Discrete Applied Mathematics Vol.232 No.-
<P><B>Abstract</B></P> <P>In this paper, we study ( 1 , 2 ) -step competition graphs of bipartite tournaments. A bipartite tournament is an orientation of a complete bipartite graph. We show that the ( 1 , 2 ) -step competition graph of a bipartite tournament has at most one non-trivial component or consists of exactly two complete components of size at least three and, especially in the former, the diameter of the nontrivial component is at most three if it exists. Based on this result, we show that, among the connected non-complete graphs which are triangle-free or the cycles of which are edge-disjoint, <SUB> K 1 , 4 </SUB> is the only graph that can be represented as the ( 1 , 2 ) -step competition graph of a bipartite tournament. We also completely characterize the complete graphs and the disjoint unions of complete graphs which can be represented as the ( 1 , 2 ) -step competition graph of a bipartite tournament. Finally we present the maximum number of edges and the minimum number of edges which the ( 1 , 2 ) -step competition graph of a bipartite tournament might have.</P>