Time filter

Source Type

Incheon, South Korea

Long-range transport of and exposure to perfluorinated substances (PFSs) strongly depend on their emission mode. In the present study, watershed-based riverine discharge loads and emission factors are estimated for perfluorooctanoate (PFOA), perfluorononanoate (PFNA), perfluorohexylsulfonate (PFHxS), and perfluorooctylsulfonate (PFOS) by using spatially distributed data of chemical concentrations together with water flows and a geographic information system (GIS). Average per capita emissions (emission factor, μg capita-1d-1) are 75 for PFOA, 36 for PFNA, 17 for PFHxS, and 43 for PFOS, which are several times lower than the estimates for Japan and the European continent. A relatively uniform distribution is observed for PFHxS and PFOS emission factors, while elevated values of PFOA and PFNA predominate in one of eight river basins. This may indicate the leading contribution of diffusive sources (e.g. nonpoint source) for PFHxS and PFOS versus the presence of localized point sources for PFOA and PFNA. The lower-upper bound of total riverine loads discharged annually from the Korean peninsula are in the range of 0.53-1.3tons for PFOA, 0.09-0.60tons for PFNA, 0.07-0.29tons for PFHxS, and 0.19-0.73tons for PFOS, accounting for <1% of global annual emissions. Furthermore, these riverine discharge loads are significantly greater than the discharge loads from a wastewater treatment plant, indicating the necessity of further study of nonpoint sources. © 2012 Elsevier Ltd.

Shim M.S.,Georgia Institute of Technology | Shim M.S.,Incheon National University | Xia Y.,Georgia Institute of Technology
Angewandte Chemie - International Edition | Year: 2013

Stimuli-responsive release: The high levels of reactive oxygen species (ROS) in prostate cancer cells can be exploited to trigger cancer-targeted gene delivery. A ROS-responsive thioketal-based cationic polymer was synthesized and functionalization with a cancer-targeting peptide led to selective and enhanced gene transfection in prostate cancer cells (see scheme). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

This paper presents an optimization method to design a solar water heating (SWH) system based on life cycle cost (LCC). A genetic algorithm is employed to optimize its configuration and sizing as the optimization technique. To ensure that the optimal solution obtained from the proposed method is a practical design, three constraint conditions, including the energy balance, solar fraction, and available space to install solar collectors, have been set. In addition, the real devices available in the marketplace are considered in the optimization process that searches for optimal configuration and sizing, which is represented by the type and number of each component. By using the proposed method, a SWH system in an office building, South Korea has been designed and optimized. It is observed that a low solar fraction does not always present a decrease in the LCC. A trade-offbetween the equipment cost and the energy cost results in an optimal design of the SWH system that yields the minimum LCC. © 2015 by the authors.

A resistive random access memory device having a nano-scale tip and a nanowire is provided. A memory array using the same also is provided and fabrication method thereof. A technique is provided for forming a bottom electrode having an upwardly protruding tapered tip structure through etching a semiconductor substrate and a top electrode being formed of a nanowire and a technique forming a resistive random access memory device at a location intersected with each other in order that an area of each memory cell is minimized and that an electric field is focused on the tip of the bottom electrode across the top electrode.

Sarker A.K.,Incheon National University | Hong J.-D.,Incheon National University
Langmuir | Year: 2012

Multilayer assemblies of uniform ultrathin film electrodes with good electrical conductivity and very large surface areas were prepared for use as electrochemical capacitors. A layer-by-layer self-assembly approach was employed in an effort to improve the processability of highly conducting polyaniline (PANi) and chemically modified graphene. The electrochemical properties of the multilayer film (MF-) electrodes, including the sheet resistance, volumetric capacitance, and charge/discharge ratio, were determined by the morphological modification and the method used to reduce the graphene oxide (GO) to reduced graphene oxide (RGO) in the multilayer films. The PANi and GO concentrations could be modulated to control the morphology of the GO monolayer film in the multilayer assemblies. Optical ellipsometry was used to determine the thickness of the GO film in a single layer (1.32 nm), which agreed well with the literature value (̃1.3 nm). Hydroiodic acid (HI), hydrazine, or pyrolysis were tested for the reduction of GO to RGO. HI was found to be the most efficient technique for reducing the GO to RGO in the multilayer assemblies while minimizing damage to the virgin state of the acid-doped PANi. Ultimately, the MF-electrode, which could be optimized by fine-tuning the nanostructure and selecting a suitable reduction method, exhibited an excellent volumetric capacitance, good cycling stability, and a rapid charge/discharge rate, which are required for supercapacitors. A MFelectrode composed of 15 PANi/RGO bilayers yielded a volumetric capacitance of 584 F/cm3 at a current density of 3.0 A/cm3. Although this value decreased exponentially as the current density increased, approaching a value of 170 F/cm3 at 100 A/cm3, this volumetric capacitance is one of the best yet reported for the other carbon-based materials. The intriguing features of the MF-electrodes composed of PANi/RGO multilayer films offer a new microdimensional design for high energy storage devices for use in small portable electronic devices. © 2012 American Chemical Society.

Discover hidden collaborations