Yun Tai Kim

Crystal structure and atomic arrangement of the metastable Ge2Sb2Te5 thin films deposited on SiO2∕Si substrates by sputtering method

The Ge2Sb2Te5 thin films deposited by a sputtering method on SiO2∕Si substrates were annealed through a rapid thermal annealing process and performed a high-resolution transmission electron microscopy study in order to investigate the atomic arrangement of the metastable Ge2Sb2Te5. The metastable rocksalt structure having face-centered-cubic lattice was confirmed by high-resolution transmission electron microscopy images and simulated images on the directions of ⟨100⟩, ⟨110⟩, and ⟨211⟩ zone axes. According to the position of Ge and Sb in the metastable rocksalt structure, the atomic distribution alters when observed in different direction and this causes change in the charge-density distribution, resulting in different images in a high-resolution transmission electron microscopy. It is expected that as the crystallization proceeds, the Ge and Sb atoms tend to position themselves on a specific plane. From this aspect, the ordered structure model of the metastable Ge2Sb2Te5 was proposed by varying the posit...

Selective blockade of PGE2 EP1 receptor protects brain against experimental ischemia and excitotoxicity, and hippocampal slice cultures against oxygen-glucose deprivation

Cyclooxygenase-2 (COX-2) enzyme increases abnormally during excitotoxicity and cerebral ischemia and promotes neurotoxicity. Although COX-2 inhibitors could be beneficial, they have significant side effects. We and others have shown that the EP1 receptor is important in mediating PGE2 toxicity. Here, we tested the hypothesis that pretreatment with a highly selective EP1 receptor antagonist, ONO-8713, would improve stroke outcome and that post-treatment would attenuate NMDA-induced acute excitotoxicity and protect organotypic brain slices from oxygen-glucose deprivation (OGD)-induced toxicity. Male C57BL/6 mice were injected intracerebroventricularly with ONO-8713 before being subjected to 90-min middle cerebral artery occlusion (MCAO) and 96-h reperfusion. Significant reduction in infarct size was observed in groups given 0.1 (25.9 ± 4.7%) and 1.0 nmol (27.7 ± 2.8%) ONO-8713 as compared with the vehicle-treated control group. To determine the effects of ONO-8713 post-treatment on NMDA-induced excitotoxicity, mice were given a unilateral intrastriatal NMD A injection followed by one intraperitoneal injection of 10 µg/kg ONO-8713, 1 and 6 h later. Significant attenuation of brain damage (26.6 ± 4.9%) was observed at 48 h in the ONO-8713-treated group. Finally, brain slice cultures were protected (25.5 ± 2.9%) by the addition of ONO-8713 to the medium after OGD. These findings support the notion that the EP1 receptor propagates neurotoxicity and that selective blockade could be considered as a potential preventive and/or therapeutic tool against isch-emic/hypoxic neurological conditions.

Prostaglandin FP receptor inhibitor reduces ischemic brain damage and neurotoxicity

Bioactive lipids such as the prostaglandins have been reported to have various cytoprotective or toxic properties in acute and chronic neurological conditions. The roles of PGF(2α) and its receptor (FP) are not clear in the pathogenesis of ischemic brain injury. Considering that this G-protein coupled receptor has been linked to intracellular calcium regulation, we hypothesized that its blockade would be protective. We used FP antagonist (AL-8810) and FP receptor knockout (FP(-/-)) mice in in vivo and in vitro stroke models. Mice that were treated with AL-8810 had 35.7±6.3% less neurologic dysfunction and 36.4±6.0% smaller infarct volumes than did vehicle-treated mice after 48h of permanent middle cerebral artery occlusion (pMCAO); FP(-/-) mice also had improved outcomes after pMCAO. Blockade of the FP receptor also protected against oxygen-glucose deprivation (OGD)-induced cell death and reactive oxygen species formation in slice cultures. Finally, we found that an FP receptor agonist dose dependently increased intracellular Ca(2+) levels in cultured neurons and established that FP-related Ca(2+) signaling is related to ryanodine receptor signaling. These results indicate that the FP receptor is involved in cerebral ischemia-induced damage and could promote development of drugs for treatment of stroke and acute neurodegenerative disorders.

Effect of oxygen annealing on Pr0.7Ca0.3MnO3 thin film for colossal electroresistance at room temperature

We studied an appropriate annealing condition of Pr0.7Ca0.3MnO3 (PCMO) thin film that can show good resistive switching characteristics for resistance random access memory applications and also tried to elucidate the mechanism of the resistive switching of PCMO thin film at room temperature. We could observe that crystal structure of PCMO film was changed by oxygen annealing. From x-ray photoelectron spectroscopy measurements, we can conclude that the excess of oxygen by oxygen annealing of PCMO film leads to an increase of Mn4+ content at the PCMO surface with a subsequent change in the Mn4+∕Mn3+ ratio at the PCMO surface. The resistance ratio of high resistance state and low resistance state was increased by oxygen annealing of PCMO thin film. This can be explained as follows. The change of the Mn4+∕Mn3+ ratio at the PCMO surface by oxygen annealing leads to the change of characteristics of Au-PCMO interface domain and therefore results in the change of the resistance ratio.

Neuroprotection and Enhancement of Spatial Memory by Herbal Mixture HT008-1 in Rat Global Brain Ischemia Model

To investigate whether HT008-1, a prescription used in traditional Korean medicine to treat mental and physical weakness, has a neuroprotective effect on a rat model of global brain ischemia and an enhancing effect against memory deficit following ischemia. Global brain ischemia was induced for 10 min by using 4-vessel occlusion (4-VO). HT008-1 was orally administered at doses of 30, 100, and 300 mg/kg respectively twice at 0 and 90 min after ischemia. The effect on memory deficit was investigated by using a Y-maze neurobehavioral test 4 days after brain ischemia, and the effect on neuronal damage was measured 7 days after ischemia. The mechanism of action was studied immunohistochemically using an anti-CD11b (OX-42) antibody. The oral administration of HT008-1 at 100 and 300 mg/kg significantly reduced hippocampal neuronal cell death by 49% and 53%, respectively, compared with a vehicle-treated group, and also improved spatial memory function in the Y-maze test. Immunohistochemically, HT008-1 inhibited OX-42 expression in the hippocampus. The effects of HT008-1 were more pronounced than those of its individual herb components. The herbal mixture HT008-1 protects the most vulnerable CA1 pyramidal cells of the hippocampus and enhances spatial memory function against global brain ischemia; an anti-inflammatory effect may be one of the mechanisms of action.

Crystal Structure and Atomic Arrangement of δ-Phase Sb–Te Binary Alloy

The composition modulated Sb–Te binary thin films deposited by a RF sputtering method on SiO2/Si substrates annealed through a rapid thermal annealing process and conducted a high-resolution transmission electron microscopy (HR-TEM) study in order to investigate the atomic arrangement of the δ-phase Sb–Te binary alloys which contain Te from 16 to 37 at. %. Through the comparison with HR-TEM image and diffraction patterns viewed along and direction, we have revealed that the δ-phase Sb–Te alloy crystallized into P3m1 or R3m space group whether the number of layers is the multiple of three or not. We also expect from analogous Bi–Te system in earlier reports that as the Sb/Te ratio increases, total number of Sb layers in a unit cell increases. Therefore, based on above result, we suggested the atomic arrangement model composed of appropriate Sb2 and Sb2Te3 layer and obtained simulated images of zone axis.

Neuroprotective effect of HT008-1, a prescription of traditional Korean medicine, on transient focal cerebral ischemia model in rats.

HT008‐1 is one of the prescriptions used in Traditional Korean Medicine for the treatment of mental and physical weakness. It is composed of Panax ginseng, Acanthopanax senticosus, Angelica sinensis and Scutellaria baicalensis, which have been reported to have various pharmacological effects on the central nervous system. The study investigated whether HT008‐1 has neuroprotective effects in a focal cerebral ischemia rat model. Stroke was induced in rats by 2 h of middle cerebral artery occlusion (MCAo) followed by 22 h of reperfusion. HT008‐1 (30, 100 and 300 mg/kg) and the component herbs (300 mg/kg) were administered orally twice at 0 and 2 h after ischemia. Oral administration of 300 mg/kg HT008‐1 reduced brain infarction by 45.7%, prolonged the latency time by 24.8% in the rotarod test, and enhanced the score by 17.0% in the balance beam test. Only P. ginseng and S. baicalensis showed protective effects, and HT008‐1 showed a greater effect than its component herbs. HT008‐1 down‐regulated the COX‐2 and OX‐42 expression in the penumbra region. In conclusion, the results show that HT008‐1 may be effective in a rat stroke model by an antiinflammatory mechanism and may improve sensory‐motor function by reducing damage in the cortex and caudoputamen. Copyright