First high-pressure XAFS results at the bending-magnet-based energy-dispersive XAFS beamline BL-8 at the Indus-2 synchrotron facility

The static focusing optics of the existing energy-dispersive XAFS beamline BL-8 have been advantageously exploited to initiate diamond anvil cell based high-pressure XANES experiments at the Indus-2 synchrotron facility, India. In the framework of the limited photon statistics with the 2.5 GeV bending-magnet source, limited focusing optics and 4 mm-thick diamond windows of the sample cell, a (non-trivial) beamline alignment method for maximizing photon statistics at the sample position has been designed. Key strategies include the selection of a high X-ray energy edge, the truncation of the smallest achievable focal spot size to target size with a slit and optimization of the horizontal slit position for transmission of the desired energy band. A motor-scanning program for precise sample centering has been developed. These details are presented with rationalization for every step. With these strategies, Nb K-edge XANES spectra for Nb2O5 under high pressure (0–16.9 GPa) have been generated, reproducing the reported spectra for Nb2O5 under ambient conditions and high pressure. These first HPXANES results are reported in this paper. The scope of extending good data quality to the EXAFS range in the future is addressed. This work should inspire and guide future high-pressure XAFS experiments with comparable infrastructure.

Microwave Sintering of Alumina at 915 MHz: Modeling, Process Control, and Microstructure Distribution

Microwave energy can be advantageously used for materials processing as it provides high heating rates and homogeneous temperature field distribution. These features are partly due to the large microwave penetration depth into dielectric materials which is, at room temperature, a few centimeters in most dielectric materials. However, up to now, this technology is not widely spread for high-temperature material processing applications (>1200 °C), because its reproducibly and ability to sinter large size samples (>30 cm3) still needs to be improved. In this context, this paper describes both an empirically designed 915 MHz single-mode cavity made from SiC susceptors and refractory thermal insulation, and the 3D modeling of the process in order to improve our understanding of it. Different susceptors geometries and coupling slit position were numerically tested in order to better understand how these parameters impact the field homogeneity and the process stability. It was found that positioning the largest surface of the susceptors parallel to the electrical field allows a very uniform and hybrid heating of the material, while avoiding plasma or thermal instabilities. This was correlated to the 3D modeling results. Finally, thanks to a fully-automatized system this apparatus was used to sinter large size (~30 cm3) low-loss dielectric alumina samples. The sintered materials were subsequently characterized in terms of density, grain size distribution, and homogeneity. The reproducibility was also discussed, demonstrating the process efficiency and reliability.

Simulation of Separation Control in Axisymmetric Diffuser Flow

Large–Eddy Simulations were performed for the separated turbulent flow in an axisymmetric diffuser. An active control technique was investigated in order to decrease the size of the separation region. The technique was based on periodic perturbation using sinusoidal blowing and suction through slits on the diffuser’s circumference. The slit position and slit geometry were varied as well as the frequency and the amplitude of the control flow. The length of the separation region could be reduced by up to 37%, along with a 20% reduction of pressure loss in the diffuser. A vortex visualization technique was applied to detect changes in the turbulent structures of the flow in the axisymmetric expansion.

Optical design of the U7 undulator beamline at the Pohang Light Source

The first insertion-device beamline at the Pohang Light Source is designed for high-resolution spectroscopy and spectromicroscopy. The beamline will contain a variable-included-angle plane-grating monochromator (VIA-PGM) using a grating substrate which has seven different grooves with different depths. The advantages of this scheme will be the fixed exit-slit position and the mechanical stability of the grating scan mechanism while changing the photon energy range. The beamline is designed to cover the photon energy range 20–2000 eV. The estimated spectral resolution, E/ΔE, is above 8000 in the photon energy range below 500 eV, and above 4000 for the remaining photon energy range. The estimated flux at the end-station is of the order of 1012 photons s−1 (0.1% bandwidth)−1.

Unusual Emission Line Profiles of M1-1

In order to seek out intrinsically compact PN, we have observed high-excitation and angularly small PN, M1-1, with the intensified Reticon system (one-dimensional 1024 pixel-array) at the Coude focus of the 188 cm telescope. We have obtained highly resolved emission line profiles of [NII]λ6583, Hα, [OIII]λ5007, and HeIIλ4686 at several slit position angles. These lines were analyzed with the aid of Multiple Gaussian Method. From the analysis of their radial velocities and decomposed profiles, we can summarize our observational results as follows, (a) HeII were fitted by three Gaussians, those are main blue and red-components and an extremely red-shifted sub-component. Hα and [OIII] were decomposed into blue and red components. [NII] were fitted by single Gaussian.