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The twinning-detwinning behavior and the associated internal strain/stress evolution in a strongly textured magnesium alloy, ZK60A, were investigated under cyclic loading using neutron and synchrotron diffraction/./ The initial preferred orientation in most grains with their c-axes perpendicular to the loading axis favors extension twinning under compression but not under tension, when the alloy is loaded along the extrusion direction. The unique orientation relationship between the parent grains and the twin grains facilitates detwinning during the subsequent strain reversal. The results indicate that such twinning and detwinning alternates with cyclic loading, i.e., most twins formed during compression are removed when the load is reversed. The study of internal strain/stress evolution shows that once the matrix grains twin, the (00.2) matrix and twin grains are relaxed relative to the neighbors. This stress redistribution between the soft- and hard-grain orientations is a result of plastic anisotropy. The twins formed during the initial compression sustain a tensile stress along their c-axes, when the applied compressive stress is unloaded to less than ~ 80 MPa. This local (intergranular) tensile stress is a result of the stress redistribution between different grain orientations, and hypothesized to be effective for driving the detwinning event under a macroscopic compressive stress field.
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Coherent diffractive imaging (CDI) represents a different way of thinking about image formation in microscopy. In the place of an image-forming lens or lens-analogue--e.g., a Fresnel zone plate--this "lens-less" method relies on some easily obtained a priori sample information and a scattering measurement, which are used in an iterative algorithm. The algorithm recovers the complex wave in the sample plane that can be used to form a traditional absorption image or manipulated to reveal addition information. Since its initial demonstration in 1999, the method has provided images of a wide variety of samples at resolutions of order 20 nm.

In this seminar, I will briefly describe the method and recall a few representative results, including images of condensed matter, electronics, and biological samples. From this basis, recent modifications to the method will be discussed. In particular, the so-called Fresnel CDI method utilizes a well-characterized diverging beam to illuminate the sample, which provides practical benefit in stabilizing the iterative algorithm as well widening the applicability of the method to extended samples by overcoming the necessity to create an isolated one.

Finally, I will present some recent advances to CDI and summarize the current research effort surrounding the new Partner-User microscope at Sector 2-ID-B.
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The main advantage of combining Brillouin spectroscopy (BS) with high-resolution x-ray diffraction (XRD) techniques is the ability to perform simultaneous measurements of velocities and elastic moduli (by Brillouin spectroscopy) and the volume/density (by XRD), independent of any pressure standard. With this unique system, located in the 13BM-D station (GSECARS, APS), it is now possible to study materials with BS and XRD in-situ at high pressure-temperature conditions that provide information essential for interpreting seismic observations and constraining models of the composition and evolution of the Earth. Although the system is designed to be very user-friendly, successful BS measurements at high pressure using diamond anvils requires special preparation and a thorough understanding of the peculiarities of the on-line high pressure BS technique. To help our users make the best use of this exceptional technique, we are organizing this COMPRES/GSECARS-supported workshop focusing on the major topics relevant to high pressure research using Brillouin spectroscopy combined with high-resolution x-ray diffraction techniques.
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