Ki Hong Kim

Synthesis of Thermally Stable Organosilicate for Exfoliated Poly(ethylene terephthalate) Nanocomposite with Superior Tensile Properties

AbstractsA poly(ethylene terephthalate) (PET)/organosilicate nanocomposite, with enhanced mechanical properties, has been prepared using the melt intercalation method. For this purpose, a new organic modifier has been synthesized for the preparation of organosilicate, which is thermally stable and compatible with PET. The use of the new organosilicate yielded almost exfoliated PET nanocomposite; whereas, the PET nanocomposites prepared by use of commercial organoclays (Cloisite 15A and 30B) show only an intercalated morphology. Particularly, the use of the new organosilicate showed an enhanced tensile modulus, andwithout sacrifice of the tensile strength and elongation on breaking, while the use of commercial organoclays only exhibit a trade-off between those mechanical properties.

Polythiophene-graft-PMMA as a dispersing agent for multi-walled carbon nanotubes in organic solvent

Since their discovery, carbon nanotubes (CNTs) with remarkable properties have attracted enormous interest from both academia and industry due to their potential applications in various fields such as field emission devices, electrochemical devices, and polymer composites. However, as-produced CNTs are insoluble in most of organic solvents and aqueous media, since CNTs self-assemble in aggregated bundles where individual CNTs are held together by van der Waals attraction. Thus, the poor solubility of CNTs in solvents has imposed many limitations on their potential applications. Therefore, much effort on improving the solubility of CNTs in solvents has recently been made, which is mainly based on covalent functionalization of the surface of CNTs. Although this approach is very effective to improve the solubility of CNTs in some organic solvents, it inevitably requires complicated chemical reactions. Furthermore, it usually destroys the π-electron system of CNTs, which very often results in detrimental effect on the intrinsic properties of CNTs. As an alternative, non-covalent functionalization which is more facile approach has recently been used to improve the solubility of CNTs in common organic solvents, where the surface of CNTs is functionalized with various polymeric dispersing agents via π-π interaction or van der Waals interaction. In particular, the use of conjugated polymers as a dispersing agent for CNTs have recently attracted much attention owing to their ability to strongly adsorb on the surface of CNTs via π-π interaction. However, development of new dispersing agents must be pursued for better and effective dispersion of MWCNTs. In this study, a graft copolymer (P3HT-g-PMMA) composed of poly(3-hexylthiopene) (P3HT) backbone and poly(methyl methacrylate) (PMMA) graft was synthesized and used as an effective dispersing agent for multi-walled carbon nanotube (MWCNT) in organic solvent. Particularly, we investigate the effect of the graft density of PMMA in P3HT-gPMMA on the capability to disperse and stabilize the pristine MWCNT in organic solvent. For this purpose, we first synthesize two P3HT-g-PMMAs with different graft density of PMMA and then the dispersion capability of these two P3HT-g-PMMAs for pristine MWCNT is compared and discussed.

Xmas: an extensible main-memory storage system for high-performance applications

Xmas is an extensible main-memory storage system for high-performance embedded database applications. Xmas not only provides the core functionality of DBMS, such as data persistence, crash recovery, and concurrency control, but also pursues an extensible architecture to meet the requirements from various application areas. One crucial aspect of such extensibility is that an application developer can compose application-specific, high-level operations with a basic set of operations provided by the system. Called composite actions in Xmas, these operations are processed by a customized Xmas server with minimum interaction with application processes, thus improving the overall performance. This paper first presents the architecture and functionality of Xmas, and then demonstrates a simulation of mobile communication service.

The impact of investment lags on investment decision

This paper suggests a valuation framework for an investment project through the concept of real options. Generally, in real asset world, decision time and its payment time are not identical. This so-called investment lag problem should be considered when valuing real assets. When investment lags exist, firms accommodation capacities play important roles. In this paper, the real effect of investment lag on investment value is tested upon various conditions. We show the valuation process of real assets under the risk-neutral world. The closed-form formula is also provided for valuing real assets, including R&D project.

Preparation of SAN/silicate nanocomposites using PMMA as a compatibilizer

Polymer/silicate nanocomposites were prepared via two-step manufacturing process: a master batch preparation and then mixing with matrix polymer. A hybrid of PMMA and Na-MMT with exfoliated structure was first prepared by emulsion polymerization of MMA in the presence of Na-MMT. For the case that SAN24, miscible with PMMA, is used as matrix, we could prepare a nanocomposite with exfoliated structure. However, SAN31 nanocomposite shows the aggregation and/or reordering of the silicate layers due to the immiscibility between SAN31 and PMMA.

Efficient Web-based access to multiple geographic databases through automatically generated wrappers

With the proliferation of various geographic database servers on the Internet, the need to access them simultaneously through the Web arises frequently for high-level decision making. The ongoing OpenGIS standard addresses many of the interoperability issues to make such global utilization of geographic databases possible. Based on the OpenGIS standard, the paper presents an object oriented architecture for the efficient Web based access to multiple geographic databases on the Internet. Called MEADOW, it provides a pair of automatically generated modules: the OpenGIS wrapper on the server side and the matching transparent access provider (TAP) on the client side. In cooperation with the wrapper, TAP supports an applications efficient access to the databases through prefetching and caching of remote objects.

A Middleware Architecture for Transparent Access to Multiple Spatial Object Databases

The need to access multiple databases arises frequently in geographic information processing because a single spatial object database may not contain all the information at the desired level of abstraction, completeness, and accuracy. For example, in planning the extension of underground urban utility networks such as gas and telecommunication lines, it is necessary to access databases of existing and planned utility networks. Such databases are usually maintained independently by individual operating companies. It is also common that these independent databases maintain much geographic information redundantly with different levels of abstraction, completeness, and accuracy. Many high-level decision making processes can take advantage of such redundancy to unify the content of one database with those of others. This unification of spatial objects in multiple databases is expected to extend the solution space that would otherwise be very limited or nonexistent.

A High-Performance Spatial Storage Based on Main-Memory Database Architecture

Newly emerging spatial applications such as the intelligent transportation system require high-performance access to databases. Although research prototypes and spatial extensions on top of commercial DBMSs have been built, the high-performance requirement is difficult to satisfy because most of them employ the traditional disk-based database architecture. With the steadily increasing memory capacity of computer systems, the main-memory database architecture becomes a feasible approach to meeting the requirement, and a few commercial products are developed recently. However, there has been little work on applying the main-memory database to the spatial domain. This paper presents Xmas-SX, a high-performance spatial storage system based on the main-memory database architecture. It provides the core subset of the OpenGIS geometry types, operators, and spatial indexes. Variable-length spatial data are efficiently managed by storing each of them as a sequence of fixed-size fragments. An experiment shows that, compared with a disk-based ODBMS with data fully cached, Xmas-SX shows only 6% better performance for the spatial range query. Before data fully cached, however, the performance gap is much bigger. For the update, Xmas-SX outperforms the ODBMS by more than ten times.

Multi-Physics Modeling Based on Combustion of Energetic Materials

We present an innovative method of multi-physics application involving energetic materials. Energetic materials are related to reacting flows in extreme environments such as fires and explosions. They typically involve high pressure, high temperature, strong non-linear shock waves, and high strain rate deformation of metals. We use an Eulerian methodology to address these problems. Our approach is naturally free from large deformation of materials that makes it suitable for high strain-rate multi-material interaction problems. Furthermore we eliminate the possible interface smearing by using the level sets. We have devised a new level set based tracking framework that can elegantly handle large gradients typically found in reacting gases and metals. We show several work-in-progress applications of our algorithm including the Taylor impact test, explosive venting and additional confined explosion problems of modern interest.

Inactivation efficiency of DNA and RNA viruses during chitin-to-chitosan conversion

Joseph P. Park, Mi-Young Koh, Pil Soo Sung, Keumyeon Kim, Min Sun Kim, Moon Sue Lee, Eui-Cheol Shin*, Ki Hong Kim*, and Haeshin Lee* 1Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea 2Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea 3R & D Center, InnoTherapy Inc., Daejeon 305-732, Korea 4Department of Aquatic Life Medicine, Pukyoug National University, Busan 608-737, Korea