CdS Quantum Dots in Glass: “Modification of Photoluminescence by Silver Doping”

Silicate glasses containing CdS and Ag₂O were made by the melt-quenching method. CdS quantum dots (QDs) were precipitated inside the glass matrix by heat treatment at 570–590 °C for 10 h, and the influence of Ag on photoluminescence (PL) of CdS QDs was investigated. The emission located at 478–493 nm in wavelength originated from the direct recombination of electron/hole pairs was quenched due to charger transfer between Ag and CdS QDs. Modification of PL from CdS QDs by Ag provides potentials toward developing the color changing materials for light-emitting diodes (LEDs).     

Antioxidant activities of phlorotannins purified from Ecklonia cava on free radical scavenging using ESR and H2O2-mediated DNA damage

The potential antioxidant activities of three phlorotannins (phloroglucinol, eckol and dieckol) purified from Ecklonia cava collected in Jeju Island were investigated to evaluate their potential value as the natural products for foods or cosmetic application. In this study, antioxidant activities were measured by electron spin resonance spectrometry (ESR) technique for scavenging effects of free radicals such as 1,1-diphenyl-2-picrylhydrazyl (DPPH), alkyl, hydroxyl (HO^•) and superoxide anion radical (O₂ ^•−) and by comet assay for protecting effects against H₂O₂-mediated DNA damage. The results show that all the phlorotannins have the potential DPPH, alkyl, hydroxyl and superoxide radical scavenging activities. Especially, eckol samples scavenged around 93% of DPPH at 0.25, 0.5, 1 mg/mL of concentrations and were higher than the other phlorotannins, such as phloroglucinol and dieckol samples. Also, protecting effects of the phlorotannins against H₂O₂-mediated DNA damage increased with increased concentrations of the samples in the L5178 mouse T-cell lymphoma cell lines (L5178Y-R). In conclusion, these results suggest that the three phlorotannins purified from E. cava have the potential inhibitory effect on H₂O₂-mediated DNA damage and harmful free radicals and can be used as antioxidants in cosmetic, foods and drug industry.     

Influence of helical tube dimensions on open channel natural convection heat transfer

Natural convection heat transfer of a helical tube was investigated experimentally for varying tube diameter, length, height, pitch, radius, and number of turns, in order to determine an appropriate characteristic length to describe the phenomenon. Mass-transfer rates of a CuSO₄–H₂SO₄ electroplating system were measured by replacing the heat transfer system according to the analogy concept. When the pitch-to-diameter ratio was larger than 5 and the pitch-to-radius ratio was smaller than 2.3, the heat transfer rates were very close to those of a horizontal cylinder, and decreased with the diameter of the tube while remaining unaffected by the total length and height. The natural convection heat transfer of the Nth turn of a helical tube was measured for varying pitch-to-diameter ratio and number of turns, and the results were formulated as an empirical correlation.     

Micromagnetic Simulation of Damped Oscillatory Behavior of Domain Wall Propagation in Sinusoidal Ferromagnetic Nanowire

We have investigated a damped oscillatory behavior of domain wall propagation in wavy nanowires under an external field higher than the Walker breakdown field using micromagnetic simulation. In nanowires having sinusoidal edge distortions with variation of wavelengths, domain wall has been observed to pseudomorphically follow the sinusoidal wires with keeping an intrinsic transformational frequency of inner wall spin structure. Oscillation amplitude of the domain wall position decreases as the wavelength of the wire decreases by an interaction between the periodically distributed spins and the propagating domain wall. Oscillatory behavior of the domain wall position is found to decay in a wire having the wavelength well matching with an intrinsic transformational frequency of the propagating domain wall.      

Monolithic carbon structures including suspended single nanowires and nanomeshes as a sensor platform

With the development of nanomaterial-based nanodevices, it became inevitable to develop cost-effective and simple nanofabrication technologies enabling the formation of nanomaterial assembly in a controllable manner. Herein, we present suspended monolithic carbon single nanowires and nanomeshes bridging two bulk carbon posts, fabricated in a designed manner using two successive UV exposure steps and a single pyrolysis step. The pyrolysis step is accompanied with a significant volume reduction, resulting in the shrinkage of micro-sized photoresist structures into nanoscale carbon structures. Even with the significant elongation of the suspended carbon nanowire induced by the volume reduction of the bulk carbon posts, the resultant tensional stress along the nanowire is not significant but grows along the wire thickness; this tensional stress gradient and the bent supports of the bridge-like carbon nanowire enhance structural robustness and alleviate the stiction problem that suspended nanostructures frequently experience. The feasibility of the suspended carbon nanostructures as a sensor platform was demonstrated by testing its electrochemical behavior, conductivity-temperature relationship, and hydrogen gas sensing capability.     

Study on containment safety systems for Korean fusion DEMO plant

The purpose of this study is to review the strategy for radiation barriers in the fusion power plants and to produce simulation data for the conceptual design of safety features to maintain the integrity of such barriers as a part of R&D program through the National Fusion Research Institute of Korea. Even though the amount of radioactive source term in fusion power plants should be much less than that of fission power plants, internal as well as external events can result in damage to facilities such that public can be critically exposed by radiation. In the first part of this study, we reviewed and compared the multiple defenses to protect radioactive hazard in fission and fusion power plants. Containment was characterized as an indispensable physical barrier and the integrity of containment particularly enveloping a fuel cycle which is a major radioactive source term, tritium, should be secured. Since water is assumed as one of the coolant options in the Korean fusion DEMO plant, the thermo-hydraulic analysis was carried out using computer simulations to produce key parameters related with the integrity of containment in the second part. The performance of both of active and passive safety features to control the key parameters was compared to take recent fission technologies into account.     

Characterization and Wideband Modeling of Miniaturized LTCC Helical Inductors

We report fabrication of miniaturized low temperature co-fired ceramic helical (3-D) inductors with more than seven layers of helices and the conductor linewidth of 100mum. We achieve the Q_maxLeff/A product ranging from 200 to 370. Such high values are possible thanks to the drastic reduction of the active area and still acceptably large Q_max and self-resonant frequency. High frequency characterization of the inductors is performed up to 12GHz, and a new equivalent circuit model considering vertical electromagnetic coupling between conductors is shown to reproduce all the measured characteristics