Youn-Jea Kim

Mogul-Patterned Elastomeric Substrate for Stretchable Electronics.

A mogul-patterned stretchable substrate with multidirectional stretchability and minimal fracture of layers under high stretching is fabricated by double photolithography and soft lithography. Au layers and a reduced graphene oxide chemiresistor on a mogul-patterned poly(dimethylsiloxane) substrate are stable and durable under various stretching conditions. The newly designed mogul-patterned stretchable substrate shows great promise for stretchable electronics.

A Novel Passive Membrane Pumping Nano Fountain-Pen

In this paper, flow control of nano fountain pen using active membrane pumping is investigated. DPN (Dip Pen Nano- Lithography) has a shortcoming in which is the need of frequent loading and unloading while coating for broadband patterning. This issue is caused by a limit in quantity of ink, which is tied on the tip surface. The control of fluid injection using active membrane pumping in chambers is the answer of the problem. The flow rates in channels with the presence of capillary force are analyzed including the cantilever deflection and the control of mass flow rates by deflection of membrane. Finally, in this paper, the membrane deflection using a nano indentation equipment has been experimentally examined.

Analysis of Line width with Nano Fountain Pen Using Active Membrane Pumping

The intention of this research was investigated the line width that is written by NFP (nano fountain pen) using active membrane pumping in order to understand how to control it. The relationships between velocity of tip, concentration, and ink diffusion with line width were studied; it was found that variation of velocity of tip and concentration of ink affect directly to line width. Therefore, this study is shown a model of verifying line width through two conditions: velocity and diffusion.

Influence of External Forces on the Mechanical Characteristics of the a-IGZO and Graphene Based Flexible Display

Thin film transistors (TFTs) based flexible displays have optically transparent and m echanically flexible properties that are attractive for next-generation display technologies. In particular, amorphous indium-gallium-zinc-oxide (a- IGZO) and graphene have attracted much attention due to the advantages of their excellent unif ormity and compatibility with transparent and flexible substrates. To maintain these characteristics, it is important to confirm the deformation characteristics of TFTs with applied external for ces, such as compressive or tensile stress, distortion effects, and temperature. The mechanical c haracteristics of modeled devices applied to different active layers on TFTs, such as a- IGZO and graphene, were investigated under various external conditions. The distributions of t he stress-strain curve on each active layer and the deformed shapes were assessed graphically.

Boundary layer flow of micropolar fluids past an impulsively started infinite vertical plate

Transient free convective boundary layer flow of micropolar fluids past an impulsively started infinite vertical plate is investigated. The transformed dimensionless governing equations for the flow, microrotation and heat transfer characteristics are solved by using the Laplace transform technique. In particular, the relevant solution of the coupled governing equations was found with the second kind of the Volterra integral equation. The obtained results concerning velocity, microrotation and temperature across the boundary layer are illustrated graphically for different values of the parameters entering into the problem under consideration and the dependence of the flow and temperature fields from these parameters is discussed.

Flow and Mixing Characteristics in an Agitator with a Draught Tube

Because the mixing efficiency is influenced remarkably by varying the geometrical configurations, the study of flow characteristics inside the mechanical agitator is very important to improve the performances. The draught tube in the agitator makes intermixing between the screw and tube by interrupting radial flow, and it makes circulation region in a mixing chamber. In general, the helical screw agitator with a draught tube (HSA) is proved more efficient to mix than the others. Consequently, such as the shapes of helical screw, number of pitches and the variation of angular velocity are the main parameters for improving the capacity of HSA. And also the suspension of the solid particles in the agitator can be determined these parameters. The rate of solids suspension in the mixing chamber was quantified with a statistical average value, of. Numerical analyses were carried out, using a commercial CFD code, Fluent, to obtain the velocity, pressure and particle distributions under steady, laminar flow and no-slip conditions. Results are graphically depicted with various parameters.

A Study on the Plane Couette Flow Using Micropolar Fluid Theory

An analysis of the plane Couette flow between two parallel plates of a viscous, incompressible, micropolar fluid is presented. Especially, the effects of non-zero values of the microgyration boundary condition coefficient and pressure gradient on the flow fields are studied. Numerical results show that the micropolar parameter was found to have much more of an impact on the flow behaviors. It is also observed that the micro-gyration boundary condition coefficient influenced on the coefficients of skin friction and couple stress due to its different effect on the surface stress.

Flow Characteristics in Compact Thermal Spray Coating Systems with Minimum Length Nozzle

In this study, numerical analysis is performed to adopt the equivalence ratio on the high velocity oxygen fuel (HVOF) thermal spray coating systems equipped with a minimum length nozzle. The analysis is applied to investigate the axisymmetric, steady-state, turbulent, and chemically combusting flow both within the torch and in a free jet region between the torch and the substrate to be coated. The combustion is modeled using a single-step and eddy-dissipation model which assumes that the reaction rate is limited by the turbulent mixing rate of the fuel and oxidant. As the diameter of the nozzle throat is increased, the location of the Mach shock disc moves backward from the nozzle exit. As the throat diameter and the divergent portion are 6 mm and 8 mm, respectively, the pressure in the HVOF system is the lowest at the chamber and the expanding gas is steadily maintained with both high velocity and high temperature for different equivalence ratios. Thus, relatively minor amendments of the equivalence ratio and the geometry of HVOF can lead to improved control over coating characteristics.

Effects of Obstacles on the Mixing Performance in Microchannels

The mixing of two or more fluid streams in microchannels needs quite long channel lengths. Therefore, in order to improve the mixing performance, obstacles have been placed in the channel to disrupt flow and to reduce the diffusion path. The disruption to flow velocity field alters the flow direction from one fluid to another. Properly designed geometric parameters, such as layout, angle with main flow direction and aspect ratio of obstacles, will be resulted in improving the mixing performance with only little increase of the pressure drop. In this study, T-type rectangular microchannel is used, which has two inlets with W×H×L = 100×100×100 μm3 and one outlet with W×H×L = 200×100×6950 μm3 . Furthermore, the mixing channel has obstacles which are placed with an angle of inclination and with dimensions W×H×L = 10×100×h μm3 on the lower layer. In order to estimate the performance of the mixing, numerical analyses are carried out with water and ethanol. Especially, the diffusion coefficient, D, is set to 10−10 m2 /s for simulating two-fluid diffusion-convection flow, the mixing efficiency and the pressure drop of microchannel are investigated with various values of the angle of inclination, aspect ratio (h = αH) of obstacle and Reynolds number. When the flow passes through on the obstacles, rotation flow is observed. This flow pattern is repeated at each cycle. Besides, in each case that obstacles are turned to the center of channel and to the side walls, rotational direction is changed reversely. In case of pressure drop, as the Reynolds number, the angle of obstacle (θ) and the aspect ratio (α) are increased, the pressure drop is also increased. Results show that the ratio between the maximum and minimum of pressure drop is the order-of-magnitude of 1 at Re = 1.667. Results also show that the angle of inclination of obstacles has more influence on the mixing performance than the height of obstacles and Reynolds number.Copyright

Flow Control of Nano Fountain Pen Using Active Membrane Pumping

In this paper, flow control of nano fountain pen using active membrane pumping is investigated. This FPN has been integrated with pumping chambers, micro channels, and a high capacity reservoir for continuous ink feeding. The control of fluid injection using active membrane pumping in chambers is the answer of the problem. The flow rates in channels with the presence of capillary force are theoretically analyzed, including the cantilever deflection and the control of mass flow rates by deflection of membrane. Then, the above results are compared with numerical results based on the commercial code, FLUENT