Kwangwoon University

About: Kwangwoon University is a education organization based out in Seoul, South Korea. It is known for research contribution in the topics: Thin film & Resonator. The organization has 4020 authors who have published 8217 publications receiving 104365 citations.

Prolonged Release Period of Nitric Oxide Gas for Treatment of Bacterial Keratitis by Amine-Rich Polymer Decoration of Nanoparticles

Abstract: Exogeneous nitric oxide (NO) delivery is a promising therapeutic method because NO is a significant cell signaling molecule to control physiological functions. A major challenge for NO delivery is to control release due to the fast diffusion properties of gaseous molecules with low molecular weight. It is important in biomedical applications to mitigate initial burst emissions because higher concentrations of reactive NO cause cytotoxicity and tissue damage. In this study, a nanoparticle system is developed to control spontaneous gas release on the basis of surface-modified silica nanoparticles (Si NPs) by branched polyethylene imine (BPEI). BPEI is not only a scaffold of N-diazeniumdiolates—a type of NO donor—and but also a stabilizer of donors by molecular interactions with nearby amine groups. With the sustained-release manner, BPEI-coated NO-releasing Si NPs (BPEI-NO NPs) have multifunctional properties, including bactericidal efficacies as well as good cell viability for human cells. An improved ocul...

Piezoelectric energy harvester using impact-driven flexible side-walls for human-limb motion

Abstract: We present a human-limb driven piezoelectric energy harvester using two mass-loaded unimorph piezoelectric beams clamped on two flexible sidewalls. Since vibration generated by human-limb motion has low-frequency and high amplitude characteristics, the energy harvester has been designed to up-convert the low-frequency human-limb vibration by mechanical impact of a spring less spherical metallic ball. However, instead of direct mechanical impact on the power generating elements (unimorph piezoelectric beams), the ball impacts on the bases (flexible sidewalls) of each beam to avoid mechanical wear of the piezo-materials. While excited by human-limb motion, the ball impacts consecutively on the flexible sidewalls which transfer impulsive forces to the loaded mass of the respective unimorph beam. The beam vibrates at its own resonant frequency and causes voltage generation by virtue of piezoelectric effect. A proof-of-concept prototype has been fabricated and tested. At optimum load condition, each unimorph piezoelectric generator generates 96 µW average power while excited at 4.96 Hz frequency and ~2g acceleration. The device with series connected generators is capable of generating maximum 175 µW average power. Improved design and further optimization would be able to increase its power generation capability (as well as power density) to be used in wearable devices applications.

Dynamics of Chain Molecules in Disordered Materials

Abstract: The dynamic behavior of hard chains in disordered materials composed of fixed hard spheres is studied using discontinuous molecular dynamics simulations. The matrix induces entanglements in the chain fluid, i.e., for high matrix densities the diffusion coefficient $D$ scales with the chain length $N$ as $D\ensuremath{\sim}{N}^{\ensuremath{-}2}$. At high matrix densities the rotational relaxation time becomes very large but the translational diffusion is not affected significantly; i.e., the chains display a dynamic heterogeneity reminiscent of probe diffusion in supercooled liquids and glasses. We show that this is because some chains are trapped, and move via a hopping mechanism. There are no signatures of this dynamic heterogeneity in the matrix static structure, however, which is identical to that of a hard-sphere liquid.

Turbo-coded optical direct-detection CDMA system with PPM modulation

Abstract: The performance of an optical code division multiple access (CDMA) system with turbo coding is analyzed and simulated. Turbo codes are parallel concatenated convolutional codes (PCCCs) in which the information bits are first encoded by a recursive systematic convolutional code, and then, after passing through an interleaver, are encoded by a second systematic convolutional encoder. Turbo coding is superimposed on an intensity-modulated optical channel with pulse-position modulation (PPM) and direct detection of the received optical signal, and the performance is evaluated in terms of an upper bound on bit error probability. From the simulation results, it is seen that turbo coding offers considerable coding gain over other methods, with reasonable encoding/decoding complexity. Also, it is demonstrated that, for a fixed code rate, the performance of the optical CDMA system can be substantially improved by increasing the interleaver length and the number of iterations. Serially concatenated convolutional codes (SCCCs) are also considered, and are shown to perform comparably to PCCC in general and better than PCCCs for the case of large signal photocounts. The results in this paper can be applied, for example, to indoor optical wireless LANs.