Joonhyung Park

A polymer gate dielectric for high-mobility polymer thin-film transistors and solvent effects

A polymer gate dielectric of poly(2-hydroxyethyl methacrylate) is introduced to the polymer thin-film transistor (TFT) with poly(3-hexylthiophene) as its active layer. With this polymer dielectric, the field-effect mobility is 0.1cm2V−1s−1. The solvent used in forming the active layer on the polymer dielectric film has pronounced effects on the device performance. These solvent effects are related to the roughness of the dielectric surface a solvent can induce. The solvent that induces the least roughness is found to be the most desirable for better device performance. The roughness can in turn be related to solubility parameter.

An improved method of preparing composite poly(dimethylsiloxane) moulds

Preparing a poly(dimethylsiloxane) (PDMS) mould having a high density pattern with a feature size smaller than 100 nm and an aspect ratio larger than unity has been a challenge yet to be met. A method is presented that permits preparation of such a PDMS mould. Lowering the viscosity of PDMS prepolymer mixture and enhancing the wettability by introducing a properly chosen solvent to the mixture, coupled with the use of an excessive amount of modulator to delay cross-linking, is the key to successfully preparing the mould. While the method is shown to be effective for dense patterns down to 40 nm feature size with an aspect ratio of 1.5, it might also prove to be effective for smaller feature sizes.

Controlled polymer dewetting by physical confinement

We report ordering of polymer drops that takes place when a thin polystyrene film confined by polydimethylsiloxane walls dewets on a silicon substrate. When annealed above the glass transition temperature, the thin polymer film dewets, resulting in the formation of a regular structure inside and outside the confinement. It is found that the ordering becomes strongly suppressed as the film thickness increases and the pattern size decreases due to the physical confinement of the mold. As a result, the ordering can take place only when the wavelength of the capillary wave is smaller than the characteristic length of the physical confinement.

Three-dimensional pattern transfer and nanolithography: modified soft molding

One-step transfer of molded three-dimensional polymer structures into underlying substrate is reported. The one-step transfer is made possible by a molding technique presented here in the form of modified soft molding. Formation of a desired three-dimensional structure in a polymer film by this method, followed by one-step reactive ion etching, is utilized for the transfer. The technique is also shown to be effective in transferring sub-100-nm features.

Polymer thin-film transistors fabricated by dry transfer of polymer semiconductor

A dry transfer technique is applied to the semiconductor layer formation in fabricating polymer thin-film transistors (TFTs). This method removes the solvent compatibility problem that is typically encountered in solution processing of polymer semiconductor and polymer gate dielectric such that any pair of the two polymers can be admitted to the fabrication of polymer TFTs. When the technique is used in place of spin coating of the active layer, the mobility increases by almost an order of magnitude, primarily because the deleterious effects are removed that a solvent can have on the underlying dielectric layer. Annealing of the active layer is also made possible by the method, which results in a significant improvement in the on∕off ratio of the device.

Determination of Secondary Reserve Requirement Through Interaction-dependent Clearance Between Ex-ante and Ex-post

This paper discusses a method for the determination of frequency control reserve requirement with consideration of the interaction between ex-ante planning and real-time balancing. In proposed method, we consider the fact that the delivered energy for tertiary control reserve is determined based on required capacity for secondary control reserve and the expected amount of load errors. Uncertain load errors are derived by Brownian motion, an optimization method is suggested using a stochastic programming. In a short, we propose an interactive dependent method for determining secondary control reserve requirement based on the principle that it satisfies to minimize the total cost. As a result, this paper provides will analyze for an example model to demonstrate the capabilities of the method.

Modified dynamic programming based unit commitment technique

This paper represents a modified dynamic programming solution to the unit commitment (UC) problem. The UC is a complex decision-making process because of multiple constraints which may not be violated while finding the optimal or suboptimal commitment schedule. There are many methods to solve the UC problem gradually. So, before we present our method, we will show the drawbacks of the standard dynamic programming methods which use general purpose optimization techniques to the UC problem. The priority list method, the lagrange relaxation and the mixed integer linear programming (MILP) are possible to apply to a real power system for performing the unit commitment. However, by using these methods, we could not get an optimal solution but only a suboptimal silution. Therefore we propose to get an optimal solution by using dynamic programming. Performing dynamic programming takes a lot of simulation time, so it is not optimal to use in a real power system for performing the unit commitment. Therefore, we need a modified dynamic programming method to satisfy both the simulated and the real power system to get the optimal solution. For those not familiar with UC problem, we introduce the constraints, production cost and start-up cost. The goal of the objective function is in cost minimization, so we use the economic dispatch using the lambda iteration method when we calculate the production costs. Finally, we compare the UC solution by using both methods.

Reliability and Validity of the Korean Version of the Foot Function Index

Although translated versions of the Foot Function Index (FFI) in several languages are available, the absence of a Korean version has precluded comparing the data from Korea with the data from other countries using the FFI. We, therefore, evaluated the reliability and validity of the adapted Korean version of the FFI. We translated the English version of the FFI into Korean and back into English. We mailed the Korean version of the visual analog scale, FFI, and the previously validated Medical Outcomes Study Short-Form 36-item questionnaire (SF-36) to 121 patients with treated foot complaints. To evaluate the test-retest reliability and internal consistency, we used the intraclass correlation coefficient and Cronbachs α, respectively. We also evaluated the concurrent and construct validity of Korean version of the FFI by comparing the visual analog scale and SF-36. Cronbachs α was 0.91 and 0.95 for the pain and disability subscales, respectively. The reproducibility was good, and a strong correlation between the FFI and the SF-36 and visual analog scale with related content was observed, indicating good construct validity.The Korean version of the FFI is a reliable and valid questionnaire for the self-assessment of pain and disability in Korean patients with foot complaints.

Northeast Asia interconnection and virtual power system simulator design

In this paper, a virtual power system simulator (VPSS) using a virtual power plant (VPP) concept is introduced. VPSS efficiently emulates power system operations and electricity transactions in order to protect the access to future electricity markets utilizing the power system interconnections in Northeast Asia (NEA). This paper introduces methods on how to structure and operate the operative mechanism and the simulator design for these proposed inter-regional interconnections in the NEA. The inter-regional power system interconnection structure is expressed by using an interregional scenario performed by the Integrated Inter-Regional Transmission Organization (IIRTO). In these NEA countries, electric power bidding scenarios and price signal scenarios are options that are able to be defined by one VPSS based on the IIRTO parameters.

South Korean power distribution system-based operation, market structure and regulation strategies under distributed generation and smart grid

In this paper, we suggest the operation, market structure, and regulation strategies with distributed generation (DG), demand response (DR), smart grid (SM) in the Korean power distribution system. The strategic business unit (SBU) in the Korea Electric Power Corporation (KEPCO) was introduced as an alternative strategy because of the interruptions in the steps of distribution separation in the power generation sector. The SBU is a system which retains responsibility for its own costs through self-regulation by each unit, thus providing incentives for competition, innovation and learning. In the regulatory perspective data envelopment analysis (DEA), the retail price index (RPI-X) regulation algorithm can be used to evaluate the relative efficiency of each unit in incentive based regulation. A distributed distribution power flow analysis can be performed for the calculation of the boundary values of each SBUs information. In this paper, we will consider diverse strategies involving DG, SM, DR, and market regulation strategies in the South Korean power system.