Two-dimensional imaging of edge-localized modes in KSTAR plasmas unperturbed and perturbed by n=1 external magnetic fields

The temporal evolution of edge-localized modes (ELMs) has been studied using a 2-D electron cyclotron emission imaging system in the KSTAR tokamak. The ELMs are observed to evolve in three distinctive stages: the initial linear growth of multiple filamentary structures having a net poloidal rotation, the interim state of regularly spaced saturated filaments, and the final crash through a short transient phase characterized by abrupt changes in the relative amplitudes and distance among filaments. The crash phase, typically consisted of multiple bursts of a single filament, involves a complex dynamics, poloidal elongation of the bursting filament, development of a fingerlike bulge, and fast localized burst through the finger. Substantial alterations of the ELM dynamics, such as mode number, poloidal rotation, and crash time scale, have been observed under external magnetic perturbations with the toroidal mode number n = 1. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3694842]X1125sciescopu

Appearance and Dynamics of Helical Flux Tubes under Electron Cyclotron Resonance Heating in the Core of KSTAR Plasmas

Dual (or sometimes multiple) flux tubes (DFTs) have been observed in the core of sawtoothing KSTAR tokamak plasmas with electron cyclotron resonance heating. The time evolution of the flux tubes visualized by a 2D electron cyclotron emission imaging diagnostic typically consists of four distinctive phases: (1) growth of one flux tube out of multiple small flux tubes during the initial buildup period following a sawtooth crash, resulting in a single dominant flux tube along the m/n = 1/1 helical magnetic field lines, (2) sudden rapid growth of another flux tube via a fast heat transfer from the first one, resulting in approximately identical DFTs, (3) coalescence of the two flux tubes into a single m/n = 1/1 flux tube resembling the internal kink mode in the normal sawteeth, which is explained by a model of two currentcarrying wires confined on a flux surface, and (4) fast localized crash of the merged flux tube similar to the standard sawtooth crash. The dynamics of the DFTs implies that the internal kink mode is not a unique prerequisite to the sawtooth crash, providing a new insight on the control of the sawtooth.X112217Ysciescopu

Acute Hypoglycemia Induces Retinal Cell Death in Mouse

BACKGROUND: Glucose is the most important metabolic substrate of the retina and maintenance of normoglycemia is an essential challenge for diabetic patients. Glycemic excursions could lead to cardiovascular disease, nephropathy, neuropathy and retinopathy. A vast body of literature exists on hyperglycemia namely in the field of diabetic retinopathy, but very little is known about the deleterious effect of hypoglycemia. Therefore, we decided to study the role of acute hypoglycemia in mouse retina. METHODOLOGY/PRINCIPAL FINDINGS: To test effects of hypoglycemia, we performed a 5-hour hyperinsulinemic/hypoglycemic clamp; to exclude an effect of insulin, we made a hyperinsulinemic/euglycemic clamp as control. We then isolated retinas from each group at different time-points after the clamp to analyze cells apoptosis and genes regulation. In parallel, we used 661W photoreceptor cells to confirm in vivo results. We showed herein that hypoglycemia induced retinal cell death in mouse via caspase 3 activation. We then tested the mRNA expression of glutathione transferase omega 1 (Gsto1) and glutathione peroxidase 3 (Gpx3), two genes involved in glutathione (GSH) homeostasis. The expression of both genes was up-regulated by low glucose, leading to a decrease of reduced glutathione (GSH). In vitro experiments confirmed the low-glucose induction of 661W cell death via superoxide production and activation of caspase 3, which was concomitant with a decrease of GSH content. Moreover, decrease of GSH content by inhibition with buthionine sulphoximine (BSO) at high glucose induced apoptosis, while complementation with extracellular glutathione ethyl ester (GSHee) at low glucose restored GSH level and reduced apoptosis. CONCLUSIONS/SIGNIFICANCE: We showed, for the first time, that acute insulin-induced hypoglycemia leads to caspase 3-dependant retinal cell death with a predominant role of GSH content

Oxidative stress causes ERK phosphorylation and cell death in cultured retinal pigment epithelium: Prevention of cell death by AG126 and 15-deoxy-delta 12, 14-PGJ(2)

BACKGROUND: The retina, which is exposed to both sunlight and very high levels of oxygen, is exceptionally rich in polyunsaturated fatty acids, which makes it a favorable environment for the generation of reactive oxygen species. The cytotoxic effects of hydrogen peroxide (H(2)O(2)) induced oxidative stress on retinal pigment epithelium were characterized in this study. METHODS: The MTT cell viability assay, Texas-Red phalloidin staining, immunohistochemistry and Western blot analysis were used to assess the effects of oxidative stress on primary human retinal pigment epithelial cell cultures and the ARPE-19 cell line. RESULTS: The treatment of retinal pigment epithelial cells with H(2)O(2 )caused a dose-dependent decrease of cellular viability, which was preceded by a significant cytoskeletal rearrangement, activation of the Extracellular signal-Regulated Kinase, lipid peroxidation and nuclear condensation. This cell death was prevented partially by the prostaglandin derivative, 15d-PGJ(2 )and by the protein kinase inhibitor, AG126. CONCLUSION: 15d-PGJ(2 )and AG126 may be useful pharmacological tools in the future capable of preventing oxidative stress induced RPE cell death in human ocular diseases

Heat treated electrolytic manganese dioxide for Li/MnO<inf>2</inf> batteries: Effect of precursor properties

The present study demonstrates that the properties of heat-treated electrolytic manganese dioxide (EMD) materials can be linked to the key properties of the precursor EMD used. The investigation holds particular significance for the informed selection of precursor EMD materials that result in superior performing heat treated materials in Li/MnO2 batteries. Kinetic analysis is used to determine the precise heating regime necessary to, theoretically, completely remove structural water from six different EMD samples. It was found that the oxidation of Mn(III) to Mn(IV) occurred to a greater extent for samples with initially high pyrolusite content and a low fraction of cation vacancies after heat treatment at low temperatures. This same Mn(III) to Mn(IV) conversion was also enhanced after high temperature treatment for those samples with a higher manganese content and low cation vacancy fraction. Additionally, at low heat treatment temperatures the parent -MnO 2 structure and cation vacancies were better retained in samples with low starting BET surface area. Finally, this work determined that samples with high BET surface area tend to lose proportionally less of this value as a consequence of heat treatment, compared to those with low initial values. © 2011 The Electrochemical Society

Thermal expansion of manganese dioxide using higherature in situ X-ray diffraction

Higherature in situ X-ray diffraction is used to determine the thermal expansion behaviour of manganese dioxide in air at temperatures between 298 and 673K, the range accessible prior to material decomposition. Two manganese dioxide samples of different origins are investigated to observe the effect of synthesis conditions and resultant material properties on the thermal response. β-MnO2 prepared by a chemical pathway is found to expand linearly over the temperature window with thermal expansion coefficients (in units of K -1) of a = 9.3(4) × 10-6, c = 7.0(2) × 10 -6 and β = 25.6(8) × 10-6. Conversely, the thermal expansion of heat-treated electrolytic manganese dioxide is disjointed about 473K in the a direction and for the overall unit-cell volume, and about 523K in the c direction. Coefficients are therefore given (in units of K -1) as a = 23(4) × 10-6 (298-473K), 10(3) × 10-6 (473-673K); c = 0.2(9) × 10-6 (298-523K), 10(1) × 10-6 (523-673K); and β = 49(9) × 10-6 (298-473K), 26(5) × 10-6 (473-673K). © 2013 International Union of Crystallography Printed in Singapore - all rights reserved

Optimizing Li/MnO <inf>2</inf> batteries: Relating manganese dioxide properties and electrochemical performance

The electrochemical performance of heat treated manganese dioxide in lithium batteries is for the first time directly related to the numerous physical properties which characterize this battery material. The effect of discharge rate on these relationships is also investigated. Three of these properties are considered, revealing that at low discharge rates heat treated manganese dioxide is optimized by a pyrolusite fraction of ∼0.65, high Mn(IV), and low surface area; while at high discharge rates slightly higher pyrolusite content (∼0.73), high Mn(IV), and surface area around 44 m 2 g -1 are most beneficial. The relationships described here will assist in directing the synthesis and preparative treatment of manganese dioxides for higher performing lithium batteries. © 2012 Elsevier B.V. All rights reserved

Heat treated electrolytic manganese dioxide for primary Li/MnO<inf>2</inf> batteries: Effect of manganese dioxide properties on electrochemical performance

The primary capacity of heat treated manganese dioxide in Li/MnO 2 batteries is directly related to the numerous physical properties which characterize this material. A statistical model is employed to isolate the influence of material structure, composition and morphology on the electrochemical performance at the discharge rates 2, 5, 10 and 20 mA g -1. Among the most influential parameters are the pyrolusite content, Mn(IV) percentage, cation vacancy fraction and surface area. Some of the materials investigated show higher specific capacities than literature materials, with further improvement to the performance of these materials anticipated through the intelligent selection of heat treated manganese dioxide which exhibit the ideal properties outlined in this study. © 2013 Published by Elsevier Ltd

Thermal treatment effects on manganese dioxide structure, morphology and electrochemical performance

Kinetic analysis is used to determine the required isothermal heating time at various temperatures to theoretically completely remove water from an electrolytic manganese dioxide (EMD) sample. The effect of the heat treatment regime on material structure, morphology and composition is investigated using various physical techniques, including X-ray diffraction and gas adsorption. Further, the electrochemical performance of heat treated EMD (HEMD) samples at a range of discharge rates finds that material properties such as retention of the γ-MnO2 structure and high surface area for the sample heat treated at 250°C, and extensive structural conversion and micro-pore closure in the case of the 350°C material, lead to higher capacity and power output. Conversely, significant amounts of structural water in the 200°C sample, and the compromise in structural rearrangement and surface area loss for the material prepared at 300°C, result in poor electrochemical behaviour, especially at high discharge rates. Particularly evident from this study is the complex interplay between the heat treatment regime, resulting HEMD properties and electrochemical performance. © 2011 The Electrochemical Society