Twelve different equiatomic five-metal carbides of group IVB, VB, and VIB refractory transition metals are synthesized via high-energy ball milling and spark plasma sintering. Implementation of a newly developed ab initio entropy descriptor aids in selection of candidate compositions for synthesis of high entropy and entropy stabilized carbides. Phase formation and composition uniformity are analyzed via XRD, EDS, S/TEM-EDS, and EXAFS. Nine of the twelve candidates form true single-phase materials with the rocksalt (B1) structure when sintered at 2473 K and can therefore be investigated as high entropy carbides (HECs). The composition (V 0.2 Nb 0.2 Ta 0.2 Mo 0.2 W 0.2)C is presented as a likely candidate for further investigation as an entropy stabilized carbide. Seven of the carbides are examined for mechanical properties via nanoindentation. The HECs show significantly enhanced hardness when compared to a rule of mixtures average of the constituent binary carbides and to the highest hardness of the binary constituents. The mechanical properties are correlated to the electronic structure of the solid solutions, offering a future route to tunability of the mechanical properties of carbide ceramics via exploration of a new complex composition space.

No abstract

Electron backscatter diffraction (EBSD) is one of the primary tools for crystal structure determination. However, this method requires human input to select potential phases for Hough-based or dictionary pattern matching and is not well suited for phase identification. Automated phase identification is the first step in making EBSD into a high-throughput technique. We used a machine learning–based approach and developed a general methodology for rapid and autonomous identification of the crystal symmetry from EBSD patterns. We evaluated our algorithm with diffraction patterns from materials outside the training set. The neural network assigned importance to the same symmetry features that a crystallographer would use for structure identification.

The Gemini Multi-conjugate Adaptive Optics System -GeMS, a facility instrument mounted on the Gemini South telescope, delivers a uniform, near diffraction limited images at near infrared wavelengths (0.95 µm -2.5 µm) over a field of view of 120 . GeMS is the first sodium layer based multi laser guide star adaptive optics system used in astronomy. It uses five laser guide stars distributed on a 60 square constellation to measure for atmospheric distortions and two deformable mirrors to compensate for it. In this paper, the second devoted to describe the GeMS project, we present the commissioning, overall performance and operational scheme of GeMS. Performance of each sub-system is derived from the commissioning results. The typical image quality, expressed in full with half maximum, Strehl ratios and variations over the field delivered by the system are then described. A discussion of the main contributor to performance limitation is carried-out. Finally, overheads and future system upgrades are described.

A novel scheme for the focusing of high-energy leptons in future linear colliders was proposed in 2001 [P. Raimondi and A. Seryi, Phys. Rev. Lett. 86, 3779 (2001)]. This scheme has many advantageous properties over previously studied focusing schemes, including being significantly shorter for a given energy and having a significantly better energy bandwidth. Experimental results from the ATF2 accelerator at KEK are presented that validate the operating principle of such a scheme by demonstrating the demagnification of a 1.3 GeV electron beam down to below 65 nm in height using an energy-scaled version of the compact focusing optics designed for the ILC collider.