Wook Ki Jung

Encapsulated monoclinic sulfur for stable cycling of li-s rechargeable batteries.

Monoclinic S8 , an uncommon allotrope of sulfur at room temperature, can be formed when common orthorhombic S8 is heat-treated under enclosed environments in nanometer dimensions. Monoclinic S8 prevents the formation of soluble polysulfides during battery operation, resulting in unprecedented cycling performance over 1000 cycles under the highest sulfur content to date.

A dynamic grid services deployment mechanism for on-demand resource provisioning

Recently grid computing has started to leverage Web services technology by proposing OGSI-standard. OGSI standard defines the grid service, which presents unified interfaces to every participant of grid. In current Glubus Toolkit3(GT3),which is an implementation of OGSI, grid service factories should be deployed manually into resources to provide grid services. However, it is necessary to dynamically allocate proper amount of resource, since the demand for resource of service provider changes over time. In this paper, we propose a architecture to enable on-demand resource provisioning. We develop universal factory service (UFS) that provides a dynamic grid service deployment mechanism and a resource broker called door service. Through the experiments, we show that grid services can adaptively exploit resources according to the request rates.

A novel approach of an infrared transparent Er:Y2O3–MgO nanocomposite for eye-safe laser ceramics

Er3+ ion doped eye-safe lasers operating at a wavelength of 1.5 μm have attracted attention for use in many applications requiring protection from accidental retina exposure. For eye-safe lasers, it is considered important to improve the thermal and mechanical stability of the host materials for high power operation. Transparent Y2O3 is the most representative example among different types of host materials due to its low maximum phonon energy. However, this host shows low thermal conductivity with increasing dopant concentration. Herein, we prepare an Er:Y2O3–MgO nanocomposite as a new host material candidate that shows excellent optical, mechanical and thermal properties. By limiting domain coalescence and eliminating residual pores during sintering, outstanding optical transmittance is demonstrated for the Er:Y2O3–MgO nanocomposite. We also investigated the fluorescence spectrum and cross-section values to evaluate the possibility of using the Y2O3–MgO nanocomposite as a laser gain medium. The Er:Y2O3–MgO nanocomposite also shows excellent mechanical and thermal properties at high Er3+ ion dopant concentrations. The results indicate that Y2O3–MgO nanocomposite ceramics are promising candidate materials for use as high-power infrared laser hosts.

Understanding the role of oxygen ion (O2−) activity in 1-D crystal growth of rutile TiO2 in molten salts

Controlled synthesis of nanostructured materials using facile and easily scalable synthesis techniques is highly attractive for large-scale production of nanomaterials. In this regard, molten salt synthesis is a well-established technique for large-scale production of nanostructured materials. Few reports have demonstrated the applicability of the molten salt technique for high-aspect-ratio one-dimensional rutile TiO2 synthesis. However, the crystal growth mechanism of 1-D TiO2 in the molten salt is not well understood. Here, various sets of experiments have been delivered to investigate 1-D rutile TiO2 crystal growth starting from anatase TiO2 precursors in molten NaCl with the presence of various inorganic oxy-additives. It was found that the oxygen ion (O2−) activity of the molten salt matrix, which can be controlled by oxy-additives, is the decisive factor for the formation of the 1-D structure. The (NaPO3)6 additive, which reduces the O2− activity of the molten salt matrix, increased the solubility of anatase TiO2. The increased solubility facilitates the easy mobility of ions to the growth site where the crystallographic surface energy is high. The natural tendency to minimize the total surface energy causes the crystal to grow in a particular direction, which eventually leads to 1-D rutile TiO2 nanoparticles.

Batteries: Encapsulated Monoclinic Sulfur for Stable Cycling of Li–S Rechargeable Batteries (Adv. Mater. 45/2013)

On page 6547 Do Kyung Kim, Jang Wook Choi and co-workers describe a highly aligned and carbon-encapsulated sulfur cathode synthesized with an AAO template that exhibits a high and long cycle life, and the best rate capability based on the complete encapsulation of sulfur (physical) and implementation of the monoclinic sulfur phase (chemical).