김석 교수

Reversible control of adhesion is an important feature of many desired, existing, and potential systems, including climbing robots, medical tapes, and stamps for transfer printing. We present experimental and theoretical studies of pressure modulated adhesion between flat, stiff objects and elastomeric surfaces with sharp features of surface relief in optimized geometries. Here, the strength of nonspecific adhesion can be switched by more than three orders of magnitude, from strong to weak, in a

Being inspired by gecko foot hairs, microfibers with flat spatulate tips are proposed as repeatable adhesives. They are fabricated by molding a master template fabricated using deep reactive ion etching and the notching effect. Fabricated polyurethane fiber arrays with 4.5μm fiber and 9μm tip diameter demonstrated macroscale adhesion pressures up to 18N∕cm2 and overall work of adhesion up to 11J∕m2 on a 6mm diameter glass hemisphere for a preload pressure of 12N∕cm2. These results show around fo

We calculate the superconformal index for N=6 Chern–Simons-matter theory with gauge group U(N)k×U(N)−k at arbitrary allowed value of the Chern–Simons level k. The calculation is based on localization of the path integral for the index. Our index counts supersymmetric gauge invariant operators containing inclusions of magnetic monopole operators, where latter operators create magnetic fluxes on 2-sphere. Through analytic and numerical calculations in various sectors, we show that our result perfe

This work reports thin-film terminated micro-fibrillar adhesives made of adhesive polymers and shape memory polymers as reversible dry adhesives with thermally controllable adhesion. Structurally different adhesives were fabricated by coating a continuous thin layer of an elastomeric adhesive polymer onto either a flat or a fibrillar shape memory polymer surface. Experimental results exhibited that pull-off forces of the adhesives can be up to four times different depending on thermal conditions

We report that hydrophilic polyurethane mushroom shaped microfiber arrays possess wet self-cleaning ability using the lotus effect as biologically inspired synthetic fibrillar adhesives. In comparison with a flat surface made of the same polyurethane, the fiber array exhibited almost 100% wet self-cleaning without any degradation of adhesive strength. We attribute this cleaning ability to the mushroom shaped tip ending geometry of the fiber array, which causes the fiber array to be apparently hy

Previous studies have demonstrated that gecko foot-hair inspired elastomer microfibers with spatulate tips have significant adhesion enhancement compared to the flat elastomer surface. In this study, we report the friction enhancement of these highly adhesive fibers and analyze the relation between adhesion and friction of elastomer microfiber arrays with spatulate tips. Fabricated polyurethane fiber arrays with spatulate tips demonstrate macroscale static friction pressures up to 41N∕cm2 for a

We empirically analyze the effects of a company’s community of practice and knowledge management system on knowledge management activities and management performance. We gather data by administering surveys to large- and mid-sized companies in Seoul, Gyeonggi, and other regions of Korea. The company samples collected are statistically analyzed using methods: hierarchical analysis and structural equation modeling. First, the community of practice has a positive effect on the knowledge management

A bstract We study the asymptotic behavior of the (modified) superconformal index for 4d $$ \mathcal{N} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>N</mml:mi> </mml:math> = 1 gauge theory. By considering complexified chemical potential, we find that the ‘high-temperature limit’ of the index can be written in terms of the conformal anomalies 3 c − 2 a . We also find macroscopic entropy from our asymptotic free energy when the Hofman-Maldacena bound 1/2 &lt; a / c &lt; 3/2

We study a family of 2d $$ \mathcal{N}=\left(0,\ 4\right) $$ gauge theories which describes at low energy the dynamics of E-strings, the M2-branes suspended between a pair of M5 and M9 branes. The gauge theory is engineered using a duality with type IIA theory, leading to the D2-branes suspended between an NS5-brane and 8 D8-branes on an O8-plane. We compute the elliptic genus of this family of theories, and find agreement with the known results for single and two E-strings. The partition functi

The effect of the backing layer thickness on adhesion was investigated for single-level elastomer fibrillar adhesives. Polyurethane microfiber arrays with spatulated tips on a 160μm thick backing layer show nine times greater adhesion strength (around 22N∕cm2) than those with a 1120μm thick backing. A theoretical model is proposed to explain this difference in which very thin backing layers promote equal load sharing, maximizing adhesion, while very thick backings can lead to reduced adhesion du