Advanced characterization techniques for high-angular and high-spatial resolutions in the scanning electron microscope

High-angular resolution electron diffraction-based techniques aim at measuring relative lattice rotations and elastic strains with an accuracy about 1.10-4 (<0.01°) in the scanning electron microscope (SEM). These metrics are essential for the fine characterization of deformation structures in terms of grain internal disorientations and geometrically necessary dislocation densities. To this purpose, relative deformations between electron diffraction patterns are retrieved with subpixel accuracy using digital image correlation (DIC) techniques. Here, a novel DIC approach is proposed. It relies on a linear homography [1], i.e., a geometric transformation often met in photogrammetry to model projections. The method is implemented in ATEX-software [2], developed at the University of Lorraine. Its performances are illustrated from both a semi-conductor and a metal. First, lattice rotation and elastic strain fields are investigated in the vicinity of a giant screw dislocation in GaN single crystal using the electron backscattered diffraction technique (Fig. 1). Second, the proposed method is coupled with the on-axis Transmission Kikuchi Diffraction (TKD) configuration to characterize a nanocrystalline aluminium obtained by severe plastic deformation. On-axis TKD consists in observing a thin foil in transmission in the SEM, using a scintillator is placed beneath the specimen, perpendicularly to the electron beam. Thanks to this coupling, high-spatial (3-6 nm) and high-angular (~0.01°) resolutions are simultaneously achieved in SEM. [3]

Monte-Carlo Go Developments

We describe two Go programs, and , developed by a Monte-Carlo approach that is simpler than Bruegmann&apos;s (1993) approach. Our method is based on Abramson (1990). We performed experiments to assess ideas on (1) progressive pruning, (2) all moves as first heuristic, (3) temperature, (4) simulated annealing, and (5) depth-two tree search within the Monte-Carlo framework. Progressive pruning and the all moves as first heuristic are good speed-up enhancements that do not deteriorate the level of the program too much. Then, using a constant temperature is an adequate and simple heuristic that is about as good as simulated annealing. The depth-two heuristic gives deceptive results at the moment. The results of our Monte-Carlo programs against knowledge-based programs on 9x9 boards are promising. Finally, the ever-increasing power of computers lead us to think that Monte-Carlo approaches are worth considering for computer Go in the future

Monte-Carlo Proof-Number Search for Computer Go

Abstract. In the last decade, proof-number search and Monte-Carlo methods have successfully been applied to the combinatorial-games domain. Proof-number search is a reliable algorithm. It requires a well defined goal to prove. This can be seen as a disadvantage. In contrast to proof-number search, Monte-Carlo evaluation is a flexible stochastic evaluation for game-tree search. In order to improve the efficiency of proof-number search, we introduce a new algorithm, Monte-Carlo Proof-Number search. It enhances proof-number search by adding the flexible Monte-Carlo evaluation. We present the new algorithm and evaluate it on a sub-problem of Go, the Life-and-Death problem. The results show a clear improvement in time efficiency and memory usage: the test problems are solved two times faster and four times less nodes are expanded on average. Future work will assess the possibility of applying this method to enhanced proof-number techniques.

Grain refinement of TiAl alloys by isomorphic self-inoculation

International audienceGrain refinement by inoculation relies upon particles which act as heterogeneous nucleation sites. A novel concept of grain refinement by isomorphic self-inoculation is introduced in this paper. The inoculant particles have the same crystallographic structure as the solidifying phase, and the nucleation stage is replaced by direct epitaxial growth compared to classical inoculation. This concept has been successfully applied to a Ti-Al alloy, where classical inoculants (borides, carbides) can be embrittling in the as-cast state. Casting trials were successful in reducing the as-cast grain size as well as increasing the equiaxed grain fraction. It is shown that, opposed to classical inoculation theory, the particle size distribution has no influence and only the number of inoculant particles introduced impacts the final grain size. Moreover, the results suggest that each introduced particle can be responsible for multiple grains found in the as-cast ingot

Single-player monte-carlo tree search

Abstract. Classical methods such as A * and IDA * are a popular and successful choice for one-player games. However, they fail without an accurate admissible evaluation function. In this paper we investigate whether Monte-Carlo Tree Search (MCTS) is an interesting alternative for one-player games where A * and IDA * methods do not perform well. Therefore, we propose a new MCTS variant, called Single-Player Monte-Carlo Tree Search (SP-MCTS). The selection and backpropagation strategy in SP-MCTS are different from standard MCTS. Moreover, SP-MCTS makes use of a straightforward Meta-Search extension. We tested the method on the puzzle SameGame. It turned out that our SP-MCTS program gained the highest score so far on the standardized test set.