The ASTRO-H X-ray Observatory

The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the high-energy universe via a suite of four instruments, covering a very wide energy range, from 0.3 keV to 600 keV. These instruments include a high-resolution, high-throughput spectrometer sensitive over 0.3-2 keV with high spectral resolution of Delta E < 7 eV, enabled by a micro-calorimeter array located in the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers covering 5-80 keV, located in the focal plane of multilayer-coated, focusing hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12 keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the 40-600 keV band. The simultaneous broad bandpass, coupled with high spectral resolution, will enable the pursuit of a wide variety of important science themes.Comment: 22 pages, 17 figures, Proceedings of the SPIE Astronomical Instrumentation "Space Telescopes and Instrumentation 2012: Ultraviolet to Gamma Ray

Hitomi (ASTRO-H) X-ray Astronomy Satellite

The Hitomi (ASTRO-H) mission is the sixth Japanese x-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E  >  2  keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft x-rays to gamma rays. After a successful launch on February 17, 2016, the spacecraft lost its function on March 26, 2016, but the commissioning phase for about a month provided valuable information on the onboard instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month

Electrochemical Impedance Spectroscopy Part 1: Fundamentals

Electrochemical impedance spectroscopy (EIS) enables the examination of the electrochemical nature of electrodes and electrochemical cells by applying an alternating voltage (or current) and measuring the resulting current (or voltage). The resistance and capacitance components of the electrode can be evaluated by applying an AC voltage and changing the frequency. In particular, analysis using the equivalent circuit can determine important parameters related to the electrochemical reaction of the electrode, such as the charge transfer resistance, electric double-layer capacitance, and Warburg impedance. Moreover, the internal resistance of the cell can be divided into resistances caused by the positive electrode, negative electrode, and electrolyte. Because of these advantages, EIS is a powerful technique used for basic research, such as in identifying the rate-determining step of an electrochemical reaction, and also for applied research, such as characterizing electrochemical devices (e.g., batteries and capacitors). In this paper, the concept of impedance, which represents the relationship between the AC voltage and current, is first explained; then, the AC characteristics of various circuit elements used in equivalent circuits, which are essential for understanding EIS, are described. Finally, treatments of more complex circuits based on transmission-line models (TLMs), which are used to represent equivalent circuits of porous electrodes, are presented. Analyses based on TLMs are the foundation for understanding electrodes for practical applications because porous electrodes are usually used in electrochemical devices

Relationship between Local Structure and Oxide Ionic Diffusion of Nd[2]NiO[4+δ] with K[2]NiF[4] Structure

The relationship between the local structure and oxide ionic conduction of Nd[2]NiO[4+δ]possessing the K[2]NiF[4] structure was investigated. Various oxygen nonstoichiometry samples of Nd[2]NiO[4+δ] prepared with different annealing oxygen partial pressures were examined. The local structure related to oxide ionic conduction was determined by the Nd K-edge extended X-ray absorption fine structure. The oxide ionic conductivity and surface exchange coefficient were estimated using electronic conductivity relaxation methods. The activation energy for the oxide ionic conductivity was found to have a direct correlation to the surface exchange coefficient. The bottleneck size for oxide ion conduction was strongly correlated to the oxide ionic conduction of interstitial oxygen and the oxygen surface exchange rate

High-pressure (GPa) impedance measurements based on an indentation-induced local stress field

International audienceElectrical measurements of conducting and dielectric materials under high pressures (in the order of GPa) reveal important information regarding orbital overlaps, electronic states, changes in transition temperatures, and activation volumes (Delta V). In this study, we demonstrate a new method for high-pressure impedance measurements, up to 4 GPa, utilizing an indentation-induced local stress field. The current system does not require any pressure mediums or pressure calibrations. The Delta V for O2- ion conduction in 10 mol\% Y2O3-doped zirconia at 500 degrees C was estimated to be 3.0 cm(3) mol(-1). Delta V increased with increasing temperatures from 500 to 600 degrees C. The technique also allows the concurrent determination of the effective elastic modulus by fitting the experimental data obtained from the indentation load-depth profile curve with the Hertzian elastic model. The experimental values were consistent with the theoretical values. (C) 2013 Elsevier B.V. All rights reserved

Direct Observation of Rate Determining Step for Nd[2]NiO[4+δ] SOFC Cathode Reaction by operando Electrochemical XAS

The oxygen chemical potential of dense Nd[2]NiO[4+δ] thin films on Zr[0.92]Y[0.08]O[1.96] electrolyte was investigated by operando X-ray absorption spectroscopy (XAS) measurements. Operando XAS at the Ni K-edge was measured under an applied voltage and various oxygen partial pressures at high temperature to simulate the operating conditions of solid oxide fuel cells (SOFCs). The absorption edge energy under various polarizations is similar to those measured under equivalent oxygen partial pressures under open circuit condition. Thus, the oxygen chemical potential changes drastically at the electrode/gas interface and the rate-determining step of this model system is the surface reaction. This study provides direct evidence for the rate-determining step of the SOFC cathode reaction