Yong Woon Kim

Using Brownian dynamics simulations, we investigate the pumping efficiency of an array of periodically beating semiflexible filaments that are grafted to a surface. Full hydrodynamic interactions among and within filaments and no slip at the surface are considered. Optimal pumping is obtained for a characteristic ratio of applied forward-backward torques and filament persistence length. For independently driven filaments, phase locking between neighboring filaments occurs autonomously via hydrod

Electrokinetic methods are efficient in probing the electrostatic surface properties of charged systems. However, anomalies observed in experiments indicate that the classical electrokinetic theory should be reconsidered. Using Green's function methods and hydrodynamic simulations, we investigate electro-osmosis driven by electric-field-induced ion motion near a charged planar substrate with smooth or rough boundary. First, a reformulation of electro-osmotic theory for planar charged surfaces em

We study the effect of dumbbell-like counterions on the interactions between similarly charged surfaces. Via a systematic study using Monte Carlo simulations and field theory, we fully consider electrostatic correlations and ion structure and find that their intricate coupling determines the equilibrium phase behaviors. In particular, an energetic bridging mechanism is revealed to cause surface attractions for a finite range of surface separations, even in the Poisson-Boltzmann limit.

In order to evaluate the role of visceral and subcutaneous fat tissue in insulin sensitivity and lipid metabolism, we measured the fasting levels of plasma free fatty acid (FFA) and insulin, glucose disappearance rate (Rd), and hepatic glucose production rate (HGP) after surgical removal of visceral (VF) or subcutaneous (SF) fat tissue in monosodium glutamate-obese (MSG-Ob) rats. Monosodium glutamate obesity was induced in rats by neonatal injection of MSG. Surgery to remove fat was done at 15 w

The phenomena resulting from interaction between polymers and membranes pose important problems for biological applications. Based on a scaling theory, we investigate the spontaneous curvature of a membrane induced by either flexible or semiflexible chain adsorption. Irrespective of chain stiffness, a weakly adsorbed polymer induces the membrane to bend away (to have a positive curvature) from the polymer mostly due to increase of the conformational entropy compared with that for a flat surface.

The possibility of observing stochastic resonance (SR) in a periodic potential without a static bias, driven by noise and an oscillating field, is investigated in both limits of damping. It is shown from the matrix continued fraction method that, although an underdamped Brownian particle moving in a periodic potential displays a dynamical resonance facilitated by noise, there is no conventional SR irrespective of damping. The reason such SR cannot be observed in an overdamped regime is demonstra

Membrane fusion is fundamental to diverse biological processes ranging from intercellular and intracellular transport to egg fertilization. We study the effects of coupling between membrane undulation and charge fluctuation on its fusion. We find that, at concentrations of millimolar range, multivalent cations such as calcium in solution induce a strong correlated-charge fluctuation on each membrane, leading to inversion and overcondensation of surface charges. When the charge fluctuation is coo

To evaluate the roles of hyperglycemia and increased plasma FFA level in the development of insulin resistance, we examined the effects of phlorizin and acipimox treatments on tissue sensitivity to insulin in streptozotocin(STZ)-diabetic rats. Insulin sensitivity was assessed with the glucose-insulin clamp technique. Blood glucose concentration was clamped at basal levels of control and diabetic states, and plasma insulin concentrations were clamped at the levels of basal, approximately 60 and a

Abstract In feedback controls, measurement is an essential step in designing protocols according to outcomes. For quantum mechanical systems, measurement has another effect; to supply energy to the measured system. We verify that in feedback-controlled quantum engines, measurement plays a dual role; not only as an auxiliary to perform feedback control but also as an energy supply to drive the engines. We consider a specific engine cycle exploiting feedback control followed by projective measurem

Counterion condensation onto a charged cylinder, known as the Manning transition, has received a great deal of attention since it is essential to understand the properties of polyelectrolytes in ionic solutions. However, the current understanding is still far from complete and poses a puzzling question: While the strong-coupling theory valid at large ionic correlations suggests a discontinuous nature of the counterion condensation, the mean-field theory always predicts a continuous transition at

Close to equilibrium, the exchange of particles and heat between macroscopic systems at different temperatures and different chemical potentials is known to be governed by a matrix of transport coefficients which are positive and symmetric. We investigate the amounts of heat and particles that are exchanged between two small quantum systems within a given time, and find them characterized by a transport matrix which neither needs to be symmetric nor positive. At larger times even spontaneous tra

Based on the two state model, we study the condensation of counterions on oppositely charged membranes in the presence of monovalent salts. Using the Gaussian approximation, we evaluate the contribution of two-dimensional charge fluctuation to the free energy, from which the number of condensed counterions is determined self-consistently. It is shown that charge inversion can occur upon the addition of divalent ions of millimolar range, or of trivalent ions of micromolar range. The driving force

Purpose: Intra-abdominal leiomyosarcoma is an uncommon malignant tumor, and its standard treatment is surgical resection. However, there is no generally preferred treatment for its metastatic mass, especially in the liver. Methods: According to the sarcoma registry, 476 patients were diagnosed as leiomyosarcoma and received treatment in Asan Medical Center, Seoul, Korea. And from 2003 to 2015, surgical resections of liver metastases were performed in 10 patients with leiomyosarcoma. The characte