Sangtae Kim

Microhydrodynamics: Principles and Selected Applications presents analytical and numerical methods for describing motion of small particles suspended in viscous fluids. The text first covers the fundamental principles of low-Reynolds-number flow, including the governing equations and fundamental theorems; the dynamics of a single particle in a flow field; and hydrodynamic interactions between suspended particles. Next, the book deals with the advances in the mathematical and computational aspect

The permeability of a random array of fixed spheres has been calculated over the range of volume fractions from dilute to almost closest packing, by assuming pairwise-additive (low-Reynolds-number) hydrodynamic interactions within an effective medium. Non-convergent pair interactions arising from the long-range decay of the Stokeslet were removed by renormalizing the Stokes equation to determine the permeability of the effective medium, i.e. to include the mean screening effect of the other sphe

The resistance and mobility functions which completely characterize the linear relations between the force, torque, and stresslet and the translational and rotational velocities of two spheres in low-Reynolds-number flow have been calculated using a boundary collocation technique. The ambient velocity field is assumed to be a superposition of a uniform stream and a linear (vorticity and rate-of-strain) field. This is the first compilation of accurate expressions for the entire set of functions.

To understand the difference in reversible energy storage capacity between the O3-type layered Na and Li compounds, we use first principles calculations to study and contrast the effect of two well-known destabilization mechanisms, transformation into the spinel-type structures and cation mixing due to transition metal migration. This study is performed on the layered oxides at the A(0.5)MO(2) composition, where A = (Na, Li) and M is a 3d transition metal. We find that while all Li(0.5)MO(2) com

Efficient mechanical energy harvesters enable various wearable devices and auxiliary energy supply. Here we report a novel class of mechanical energy harvesters via stress-voltage coupling in electrochemically alloyed electrodes. The device consists of two identical Li-alloyed Si as electrodes, separated by electrolyte-soaked polymer membranes. Bending-induced asymmetric stresses generate chemical potential difference, driving lithium ion flux from the compressed to the tensed electrode to gener

In terms of the state-dependent Riccati equation (SDRE) control framework, a nonlinear motion control is investigated for the two-wheeled inverted pendulum (TWIP) mobile robot platform. As a critical design issue, the state dependent coefficient matrix is established based on the sound understanding of dynamic characteristics of the TWIP robot. The developed SDRE control solution has the merit of robust posture stabilization when the inverted pendulum robot experiences strong nonlinear behaviors

Semiconducting inorganic materials with band gaps ranging between 0 and 5 eV constitute major components in electronic, optoelectronic and photovoltaic devices. Since the band gap is a primary material property that affects the device performance, large band-gap databases are useful in selecting optimal materials in each application. While there exist several band-gap databases that are theoretically compiled by density-functional-theory calculations, they suffer from computational limitations s

Reverse electrodialysis (RED) directly harvests renewable energy from salinity gradients, and the achievable potential power heavily relies on the ion exchange membranes. Graphene oxides (GOs) are considered a solid candidate for the RED membrane because the laminated GO nanochannels with charged functional groups provide an excellent ionic selectivity and conductivity. Yet, a high internal resistance and poor stability in aqueous solutions limit the RED performance. Here, we develop a RED membr

The hydrodynamic interaction between two spheres in a Brinkman medium has been calculated using both the method of reflections and the boundary collocation technique. In particular, calculation of the forces and dipoles for two spheres in a uniform stream and linear field show that the method of reflections converges more rapidly than in the Stokes case, owing to screening of interactions, and that the boundary collocation technique produces accurate solutions at almost all separations (except t

The roles of graphene oxide scaffolds in the nucleation and growth of Mg nanocrystals and the consequent hydrogen storage properties are revealed. This work lays the foundation for design guidelines towards more optimized hydrogen storage composites.