Evaluation of derived concentration guideline levels reflecting the site-specific data for the soil of the Korea research reactor unit 1 and 2.

The purpose of this study is to evaluate the derived concentration guideline levels for unrestricted site reuse the Korea research reactor unit 1 and 2. Distribution coefficients for Co-60 and Sr-90 were derived, and site-specific values of the KRR soil were applied for the DCGLs for the seven target nuclide. The distribution coefficients of Co-60 and Sr-90 were 6,128 and 86.0 mL/g. The DCGLs derived from the dose by age group were 0.053 Bq/g for Co-60 and 45.0 Bq/g for H-3.

Derivation of site-specific derived concentration guideline levels at Korea Research Reactor 1 and 2 sites using probabilistic analysis.

The purpose of this study is to apply a probabilistic method to derive the derived concentration guideline levels for decommissioning of Korea Research Reactor 1 and 2. A total of seven parameters were found to be the sensitive parameters of the target nuclides. The DCGLs of Co-60 and H-3 were 0.063 Bq/g and 85.470 Bq/g, respectively. The concentrations of the gamma ray-emitting nuclides in the actual reactor sites were 7.7-215 times lower than the derived DCGLs for gamma ray-emitting nuclides.

Super-Resolution Fluorescence Imaging for Semiconductor Nanoscale Metrology and Inspection.

The increase in the number and complexity of process levels in semiconductor production has driven the need for the development of new measurement methods that can evaluate semiconductor devices at the critical dimensions of fine patterns and simultaneously inspect nanoscale contaminants or defects. However, conventional optical inspection methods often fail to resolve device patterns or defects at the level of tens of nanometers required for device development owing to their diffraction-limited resolutions. In this study, we used the stochastic optical reconstruction microscopy (STORM) technique to image semiconductor nanostructures with feature sizes as small as 30 nm and detect individual 20 nm-diameter contaminants. STORM imaging of semiconductor nanopatterns is based on the development of a selective labeling method of fluorophores for a negative silicon oxide surface using the charge interaction of positive polyethylenimine molecules. This study demonstrates the potential of STORM for nanoscale metrology and in-line defect inspection of semiconductor integrated circuits.

Studies on Oxygen Permeation Resistance of SiCN Thin Film and RRAM Applications.

In this study, a silicon carbon nitride (SiCN) thin film was grown with a thickness of 5~70 nm by the plasma-enhanced chemical vapor deposition (PECVD) method, and the oxygen permeation characteristics were analyzed according to the partial pressure ratio (PPR) of tetramethylsilane (4MS) to the total gas amount during the film deposition. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and X-ray reflectivity (XRR) were used to investigate the composition and bonding structures of the SiCN film. An atomic force microscope (AFM) was used to examine the surface morphology of the SiCN films to see the porosity. The analysis indicated that Si-N bonds were dominant in the SiCN films, and a higher carbon concentration made the film more porous. To evaluate the oxygen permeation, a highly accelerated temperature and humidity stress test (HAST) evaluation was performed. The films grown at a high 4MS PPR were more susceptible to oxygen penetration, which changed Si-N bonds to Si-N-O bonds during the HAST. These results indicate that increasing the 4MS PPR made the SiCN film more porous and containable for oxygen. As an application, for the first time, SiCN dielectric film is suggested to be applied to resistive random access memory (RRAM) as an oxygen reservoir to store oxygen and prevent a reaction between metal electrodes and oxygen. The endurance characteristics of RRAM are found to be enhanced by applying the SiCN.

LIN28A enhances regenerative capacity of human somatic tissue stem cells via metabolic and mitochondrial reprogramming.

Developing methods to improve the regenerative capacity of somatic stem cells (SSCs) is a major challenge in regenerative medicine. Here, we propose the forced expression of LIN28A as a method to modulate cellular metabolism, which in turn enhances self-renewal, differentiation capacities, and engraftment after transplantation of various human SSCs. Mechanistically, in undifferentiated/proliferating SSCs, LIN28A induced metabolic reprogramming from oxidative phosphorylation (OxPhos) to glycolysis by activating PDK1-mediated glycolysis-TCA/OxPhos uncoupling. Mitochondria were also reprogrammed into healthy/fused mitochondria with improved functional capacity. The reprogramming allows SSCs to undergo cell proliferation more extensively with low levels of oxidative and mitochondrial stress. When the PDK1-mediated uncoupling was untethered upon differentiation, LIN28A-SSCs differentiated more efficiently with an increase of OxPhos by utilizing the reprogrammed mitochondria. This study provides mechanistic and practical approaches of utilizing LIN28A and metabolic reprogramming in order to improve SSCs utility in regenerative medicine.

Super-resolution imaging reveals cytoskeleton-dependent organelle rearrangement within platelets at intermediate stages of maturation.

A steady supply of platelets maintains their levels in the blood, and this is achieved by the generation of progeny from platelet intermediates. Using systematic super-resolution microscopy, we examine the ultrastructural organization of various organelles in different platelet intermediates to understand the mechanism of organelle redistribution and sorting in platelet intermediate maturation as the early step of platelet progeny production. We observe the dynamic interconversion between the intermediates and find that microtubules are responsible for controlling the overall shape of platelet intermediates. Super-resolution images show that most of the organelles are located near the cell periphery in oval preplatelets and confined to the bulbous tips in proplatelets. We also find that the distribution of the dense tubular system and α granules is regulated by actin, whereas that of mitochondria and dense granules is governed by microtubules. Altogether, our results call for a reassessment of organelle redistribution in platelet intermediates.

Super-resolution imaging of platelet-activation process and its quantitative analysis.

Understanding the platelet activation molecular pathways by characterizing specific protein clusters within platelets is essential to identify the platelet activation state and improve the existing therapies for hemostatic disorders. Here, we employed various state-of-the-art super-resolution imaging and quantification methods to characterize the platelet spatiotemporal ultrastructural change during the activation process due to phorbol 12-myristate 13-acetate (PMA) stimuli by observing the cytoskeletal elements and various organelles at nanoscale, which cannot be done using conventional microscopy. Platelets could be spread out with the guidance of actin and microtubules, and most organelles were centralized probably due to the limited space of the peripheral thin regions or the close association with the open canalicular system (OCS). Among the centralized organelles, we provided evidence that granules are fused with the OCS to release their cargo through enlarged OCS. These findings highlight the concerted ultrastructural reorganization and relative arrangements of various organelles upon activation and call for a reassessment of previously unresolved complex and multi-factorial activation processes.

Improvement of the Electrical Properties of a Cu(In,Ga)Se2 Solar Cell Based on a ZnS Buffer Layer from Radio Frequency Magnetron Sputtering.

We fabricated zinc sulfide (ZnS) buffer layers with a great band gap and small light loss at a short wavelength, and then applied them to copper indium gallium sulphur-selenide (CIGS) thin film solar cells. A CIGS evaporation system was used for fabrication of the CIGS thin films, and a thickness monitor was used to check the evaporation rate at each source. The evaporation rate and deposition time were adjusted to change the composition ratio of the thin films. Also, CIGS thin films were deposited by changing the temperature of the substrates from room temperature (RT) to 150 °C, 250 °C, and 350 °C during ZnS deposition, and among them, the optimal substrate temperature was selected to measure the light conversion efficiency of ZnS-deposited CIGS thin film solar cells. The grown ZnS thin films were analyzed for crystallinity and composition by using X-ray diffraction, and by using a scanning electron microscope, the cross section and surface shape of the thin films were examined. When we applied the ZnS thin film that was fabricated at a temperature of 150 °C with a thickness of 50 nm as a buffer layer for the CIGS solar cells, we obtained a light conversion efficiency of 14.48% without an antireflection layer.

High-Efficiency Cu(In,Ga)Se2 Thin Film Solar Cells Using ZnS and CdS Buffer Layers.

Most of the existing copper indium gallium diselenide (CIGS) thin film solar cells are based on a cadmium sulfide (CdS) buffer layer fabricated using a chemical bath deposition (CBD) process. However, due to environmental pollution caused by material toxicity and the unique wet process's incompatibility with the vacuum process, many studies are now being actively carried out on nontoxic buffer layers. In this study, to replace CdS buffer layers, zinc sulfide (ZnS) buffer layers with a big band gap and a low optical loss at a short wavelength were fabricated using a magnetron sputtering system. For comparative analysis, this study also fabricated CdS buffer layers using the CBD process. Then, the conversion efficiency of CIGS thin film solar cells deposited with ZnS and CdS thin film as buffer layers was measured. The light conversion efficiency of ZnS buffer layer-based CIGS was measured at 14.44%, while that of the CdS buffer layer-based CIGS was measured at 15.71%. Given that both are higher than the minimum conversion efficiency required for commercialization (10%), ZnS buffer layer-based solar cells could have a competitive edge over the existing CdS buffer layer-based solar cells.

Muscular cell proliferative and protective effects of N-acetylcysteine by modulating activity of extracellular signal-regulated protein kinase.

N-acetylcysteine (NAC), an antioxidant and a precursor of glutathione, is currently in clinical use for various pathological conditions. No data is available as to the relationship between NAC and muscular cell proliferation or muscular degenerative disease. In this study, we assessed the effect of NAC on growth of L6 myoblasts, a rat skeletal muscle cell line, under normal or bupivacaine-treated condition. Of interest, under normal growth conditions, NAC treatment concentration-dependently increased viability, cell number, and DNA incorporation of L6 cells. Remarkably, NAC treatment for 12 to 24 h led to increased phosphorylation of ERKs, a family of mitogen-activated protein kinase known to involve in cell proliferation, in L6 cells, and specific inhibition of ERKs by PD98059, a selective inhibitor of ERKs, greatly abolished the ability of NAC to increase the number of L6 cells. More importantly, pretreatment with NAC effectively blocked decrease in the number and ERKs phosphorylation in L6 cells induced by the exposure of bupivacaine, a local anesthetic with myotoxicity. These results collectively suggest that NAC has muscular cell proliferative and protective effects and the effects by NAC appear to be, in part, mediated via increase in ERKs activation.