Youn-Joong Kim

Size effect of Pt nanoparticle on catalytic activity in oxidation of methanol and formic acid: comparison to Pt(111), Pt(100), and polycrystalline Pt electrodes.

This work presents variation of oxidative catalytic activities of methanol and formic acid on Pt nanoparticles of various sizes and a comparison to the results observed on Pt(111), Pt(100), and polycrystalline Pt. The Pt nanoparticles dispersed on platelet carbon nanofiber are cuboctahedral particles, whose sizes span from 5.6 to 1.1 nm. The electrochemically active surface areas, measured using charges of hydrogen adsorption/desorption and stripping of adsorbed CO, are reasonably consistent with those calculated theoretically with a simple cuboctahedron model. However, Pt nanoparticles with extremely small size (<1.8 nm) aggregate to reduce their surface areas. The size effect of Pt nanoparticles in oxidation of methanol and formic acid is discussed in terms of specific activity (current per unit surface area) and mass activity (current per unit mass).

Flexible and elastic metamaterial absorber for low frequency, based on small-size unit cell

Using a planar and flexible metamaterial (MM), we obtained the low-frequency perfect absorption even with very small unit-cell size in snake-shape structure. These shrunken, deep-sub-wavelength and thin MM absorbers were numerically and experimentally investigated by increasing the inductance. The periodicity/thickness (the figure of merit for perfect absorption) is achieved to be 10 and 2 for single-snake-bar and 5-snake-bar structures, respectively. The ratio between periodicity and resonance wavelength (in mm) is close to 1/12 and 1/30 at 2 GHz and 400 MHz, respectively. The absorbers are specially designed for absorption peaks around 2 GHz and 400 MHz, which can be used for depressing the electromagnetic noise from everyday electronic devices and mobile phones.

Omental torsion:CT features

A 33-year-old male presented to the emergency department complaining of right upper quadrant pain and was initially diagnosed with acute cholecystitis. Abdominal computed tomography showed a whirling pattern of fatty streaks and vessels within the greater omentum, and surgery confirmed infarction of the omentum secondary to torsion. We report a case of surgically and pathologically proven omental torsion that demonstrated the typical whirling appearance on computed tomography.

Metamaterial-based perfect absorbers

Metamaterials are artificially-engineered materials, possessing properties which are not readily observable in materials existing in nature. Since they show very novel properties such as left-handed behavior, negative refractive index, classical analog of electromagnetically-induced transparency, extraordinary transmission, negative Doppler effect, and so on, they can be used for perfect lens, invisibility cloaking, perfect absorption and transmission, etc. Metamaterial-based perfect absorbers (MMPAs) are promising candidates for the practical application of perfect absorbers. MMPA is usually composed of three layers. The first layer is periodically-arranged metallic patterns, whose structure and geometrical parameters should be carefully adjusted to fulfill the impedance-matching condition with the ambient, allowing no reflection of incident electromagnetic (EM) waves. The second layer is a dielectric layer, which allows a space for the EM waves to be dissipated, and sometimes plays a role of resonance cavity to prolong the time taken by the EM waves inside the second layer. Finally, the third layer is a continuous metallic plate, blocking remnant transmission. For practical usage, several aspects of MMPAs are to be considered seriously. Some of them are broadband operation, polarization-independent response, omni-directional response, and tunability. These aspects are basically determined by the structures of MMPA. Another important aspect is flexibility, which is determined by the material used in the fabrication. In this review, the basic operating principles of MMPAs and brief introduction of recent progresses in the field of MMPAs operating in different frequency ranges (GHz, THz and infrared/visible) are presented. Perspectives and future works for the investigation and the real application of MMPAs are also presented.

Radiofrequency thermal ablation of hepatic tumors: pitfalls and challenges

Image-guided radiofrequency (RF) thermal ablation has been accepted as a promising interventional technique to control unresectable hepatic tumors. One important key to maximize the efficacy of RF ablation is to adhere to the therapeutic guidelines and to avoid preventable pitfalls. There are also several challenges obstructing successful ablation: poor approach path; small sonic window during multiple overlapping ablations; incomplete ablation due to the heat sink effect; subcapsular mass (too exophytic or the mass is adjacent to the gastrointestinal tract); focal residual tumors; too isoechoic or small masses; and mistargeting to adjacent another lesion. Knowledge of these challenges and pitfalls in RF ablation is helpful for a successful ablation.

Precise control of quantum dot location within the P3HT-b-P2VP/QD nanowires formed by crystallization-driven 1D growth of hybrid dimeric seeds.

Herein, we report a simple fabrication of hybrid nanowires (NWs) composed of a p-type conjugated polymer (CP) and n-type inorganic quantum dots (QDs) by exploiting the crystallization-driven solution assembly of poly(3-hexylthiophene)-b-poly(2-vinylpyridine) (P3HT-b-P2VP) rod-coil amphiphiles. The visualization of the crystallization-driven growth evolution of hybrid NWs through systematic transmission electron microscopy experiments showed that discrete dimeric CdSe QDs bridged by P3HT-b-P2VP polymers were generated during the initial state of crystallization. These, in turn, assemble into elongated fibrils, forming the coaxial P3HT-b-P2VP/QDs hybrid NWs. In particular, the location of the QD arrays within the single strand of P3HT-b-P2VP can be controlled precisely by manipulating the regioregularity (RR) values of P3HT block and the relative lengths of P2VP block. The degree of coaxiality of the QD arrays was shown to depend on the coplanarity of the thiophene rings of P3HT block, which can be controlled by the RR value of P3HT block. In addition, the location of QDs could be regulated at the specific-local site of P3HT-b-P2VP NW according to the surface characteristics of QDs. As an example, the comparison of two different QDs coated with hydrophobic alkyl-terminated and hydroxyl-terminated molecules, respectively, is used to elucidate the effect of the surface properties of QDs on their nanolocation in the NW.

Triple-band perfect metamaterial absorption, based on single cut-wire bar

In general metamaterial perfect absorber, the single meta-pattern makes the single absorption band. Therefore, the multi-absorption bands need the corresponding kinds of meta-patterns. Here, we introduce the triple-band metamaterial perfect absorber utilizing only single kind of pattern. We also demonstrate the absorption mechanism of the triple perfect absorption. The first and the second absorption bands were induced by the fundamental magnetic resonance of the major and the minor axes, respectively, of cut-wire bar. The third peak was caused by the third-harmonic magnetic resonance of the major axis. Additionally, the unexpected third band was formed, which was the overlapping of the third absorption peak with another absorption peak, which was made by pairs of antiparallel currents parallel or antiparallel to the incident electromagnetic wave.

Serum VEGF levels in acute ischaemic strokes are correlated with long‐term prognosis

Background and purpose:  We investigated whether serum vascular endothelial growth factor (VEGF) levels in acute‐stage ischaemic stroke patients with small vessel disease (SVD) or large vessel disease (LVD) are correlated with long‐term prognoses, based on the difference in NIH Stroke Scale (NIHSS) scores between acute and chronic stages.

Multipotent Progenitor Cells Derived From Human Umbilical Cord Blood Can Differentiate Into Hepatocyte-Like Cells in a Liver Injury Rat Model

Umbilical cord blood (UCB), a rich source of hematopoietic stem cells, offers practical and ethical advantages. It has been reported that various adult stem cells transplanted into a damaged liver show characteristics of a hepatic lineage. In a previous study, we reported on novel UCB-derived adult stem cells, termed umbilical cord blood-derived multipotent progenitor cells (UCB-MPCs). We demonstrated that these cells were capable of differentiating into hepatocyte- like cells in vitro. To assess the hepatic differentiation capacity of UCB-MPCs, rat models of hepatic injury were generated using carbon tetra-chloride (CCl(4)) with transplantation of cells into the liver. The transplanted cells successfully incorporated into the liver of the recipient animal differentiated into functional hepatocyte-like cells that expressed hepatocyte-specific markers, such as CK-18 and albumin. Moreover, human albumin was detected in the serum of the recipient rat model. These data indicated that UCB-MPCs were capable of displaying similar characteristics to those of functional hepatocytes in a recipient liver. UCB-MPCs may prove to be a useful, transplantable alternative for hepatic progenitor cells in both experimental and therapeutic applications.

Cation Disordering by Rapid Crystal Growth in Olivine-Phosphate Nanocrystals

On the basis of Paulings first rule for ionic bonding, the coordination number of cations with oxygen anions can be determined by comparison of their relative ionic size ratio. In contrast to simple oxides, various site occupancies by multicomponent cations with similar sizes usually occur in complex oxides, resulting in distinct physical properties. Through an unprecedented combination of in situ high-temperature high-resolution electron microscopy, crystallographic image processing, geometric phase analysis, and neutron powder diffraction, we directly demonstrate that while the initial crystallites after nucleation during crystallization have a very high degree of ordering, significant local cation disordering is induced by rapid crystal growth in Li-intercalation metal-phosphate nanocrystals. The findings in this study show that control of subsequent crystal growth during coarsening is of great importance to attain a high degree of cation ordering, emphasizing the significance of atomic-level visualization in real time.