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Highly efficient computer algorithm for identifying layer thickness of atomically thin 2D materials
Lee, Jekwan,Cho, Seungwan,Park, Soohyun,Bae, Hyemin,Noh, Minji,Kim, Beom,In, Chihun,Yang, Seunghoon,Lee, Sooun,Seo, Seung Young,Kim, Jehyun,Lee, Chul-Ho,Shim, Woo-Young,Jo, Moon-Ho,Kim, Dohun,Choi, Hy IOP 2018 Journal of Physics. D, Applied Physics Vol.51 No.11
<P>The fields of layered material research, such as transition-metal dichalcogenides (TMDs), have demonstrated that the optical, electrical and mechanical properties strongly depend on the layer number <I>N</I>. Thus, efficient and accurate determination of <I>N</I> is the most crucial step before the associated device fabrication. An existing experimental technique using an optical microscope is the most widely used one to identify <I>N</I>. However, a critical drawback of this approach is that it relies on extensive laboratory experiences to estimate <I>N</I>; it requires a very time-consuming image-searching task assisted by human eyes and secondary measurements such as atomic force microscopy and Raman spectroscopy, which are necessary to ensure <I>N</I>. In this work, we introduce a computer algorithm based on the image analysis of a quantized optical contrast. We show that our algorithm can apply to a wide variety of layered materials, including graphene, MoS<SUB>2</SUB>, and WS<SUB>2</SUB> regardless of substrates. The algorithm largely consists of two parts. First, it sets up an appropriate boundary between target flakes and substrate. Second, to compute <I>N</I>, it automatically calculates the optical contrast using an adaptive RGB estimation process between each target, which results in a matrix with different integer <I>N</I>s and returns a matrix map of <I>N</I>s onto the target flake position. Using a conventional desktop computational power, the time taken to display the final <I>N</I> matrix was 1.8 s on average for the image size of 1280 pixels by 960 pixels and obtained a high accuracy of 90% (six estimation errors among 62 samples) when compared to the other methods. To show the effectiveness of our algorithm, we also apply it to TMD flakes transferred on optically transparent <I>c</I>-axis sapphire substrates and obtain a similar result of the accuracy of 94% (two estimation errors among 34 samples).</P>
Contribution of Convex Surfaces to Magnetostatic Interaction in Granular Medium
Jehyun Lee,Suess, D.,Schrefl, T.,Eu Sun Yu,You Sub Lee,Kyu Hwan Oh,Fidler, J. IEEE 2009 IEEE transactions on magnetics Vol.45 No.6
<P>Finite element micromagnetic studies on the magnetic behaviors of granular structures are performed to investigate the magnetostatic contributions of the curved surfaces of grains with various film thicknesses. From the result, it is found that the magnetization reversal process in one grain is much faster when the grains have convex surfaces. The magnetization vectors of all convex models are stabilized in shorter time by factor of 10 compared to those of flat models. And, the reversals of each grain are carried out by nucleation and domain wall propagation in the entire granular structure, whereas the grains in flat model are individually reversed. Moreover, the magnetization behaviors of the convex models are closer to the experimental results. Since the geometric and magnetic conditions are same for the two models, the only origin of the more realistic magnetic behavior is the magnetostatic interaction between the grains, enhanced by introducing the convex surfaces. From the further analysis, it is found that the convex surface induces pinning field that suppress other parts' reversal.</P>
Renoprotective antioxidant effect of alagebrium in experimental diabetes.
Park, Jehyun,Kwon, Min Kyung,Huh, Joo Young,Choi, Won Jun,Jeong, Lak Shin,Nagai, Ryoji,Kim, Wan Young,Kim, Jin,Lee, Geun Taek,Lee, Hi Bahl,Ha, Hunjoo Springer International ; Oxford University Press 2011 Nephrology, dialysis, transplantation Vol.26 No.11
<P>Despite the beneficial effects of alagebrium (ALA), a putative advanced glycation end-product (AGE) breaker, on diabetic nephropathy, its renoprotective mechanisms are incompletely understood. Since oxidative stress exacerbates diabetic renal injury through interaction with AGE, the present study examined the antioxidative property of ALA in db/db mice, mesangial cells cultured under high glucose or H(2)O(2) and a test tube.</P>