(Article begins on next page) Anyone can freely access the full text of works made available as \"Open Access\". Works made available under a Creative Commons license can be used according to the terms and conditions of said license. Use of all other works requires consent of the right holder (author or publisher) if not exempted from copyright protection by the applicable law. Availability: This is the author's manuscript

/pdf/reactivity-of-surface-species-in-heterogeneous-catalysts-1vtf7rqr9y.pdf

Reactivity of Surface Species in Heterogeneous Catalysts Probed by In Situ X-ray Absorption Techniques

This paper aims at illustrating the potential of X-ray tomography for studying the mechanical behaviour of materials through in situ experiments. Typical experimental tomography set ups which use laboratory and synchrotron X ray sources are described; advantages and limitations of both types of sources are presented. Dedicated experimental devices which allow deformation and/or temperature changes to be applied to various types of materials are described. Examples of results of in situ mechanical experiments are presented and discussed; they include monotonic tensile testing of steel fiber entanglements, high temperature compression and room temperature fatigue of Al alloys. Examples of quantitative assessment of localisation of deformation in the interior of optically opaque samples under mechanical loading are also described.

In Situ Experiments with X ray Tomography: an Attractive Tool for Experimental Mechanics

(Received 27 June 2011; revised 26 October 2011; accepted for publication 22 November 2011;published 21 December 2011)Purpose: Measured values of ultrasound attenuation in bone represent a combination of differentloss mechanisms. As a wave is transmitted from a ﬂuid into bone, reﬂections occur at the interface.In the bone, mode conversion occurs between longitudinal and shear modes and the mechanicalwave is scattered by its complex internal microstructure. Finally, part of the wave energy isabsorbed by the bone and converted into heat. Due to the complexity of the wave propagation andthe difﬁculty in performing measurements that are capable of separating the various loss mecha-nisms, there are currently no estimates of the absorption in bone. The aim of this paper is, thus, toquantify the attenuation, scattering, and thermal absorption in bone.Methods: An attenuating model of wave propagation in bone is established and used to develop athree-dimensional ﬁnite difference time domain numerical algorithm. Hydrophone and optical het-erodyne interferometer measurements of the acoustic ﬁeld as well as a x-ray microtomography ofthe bone sample are used to drive the simulations and to measure the attenuation. The acousticmeasurements are performed concurrently with an infrared camera that can measure the tempera-ture elevation during insonication. A link between the temperature and the absorption via a three-dimensional thermal simulation is then used to quantify the absorption coefﬁcients for longitudinaland shear waves in cortical bone.Results: We demonstrate that only a small part of the attenuation is due to absorption in bone andthat the majority of the attenuation is due to reﬂection, scattering, and mode conversion. In the ninesamples of a human used for the study, the absorption time constant for cortical bone was deter-mined to be 1.04 ls628%. This corresponds to a longitudinal absorption of 2.7 dB/cm and a shearabsorption of 5.4 dB/cm. The experimentally measured attenuation across the approximately 8 mmthick samples was 13.360.97 dB/cm.Conclusions: This ﬁrst measurement of ultrasound absorption in bone can be used to estimate theamount of heat deposition based on knowledge of the acoustic ﬁeld.

Attenuation, scattering, and absorption of ultrasound in the skull bone

The principles of a novel technique for nondestructive and simultaneous mapping of the three-dimensional grain and the absorption microstructure of a material are explained. The technique is termed X-ray diffraction contrast tomography, underlining its similarity to conventional X-ray absorption contrast tomography with which it shares a common experimental setup. The grains are imaged using the occasionally occurring diffraction contribution to the X-ray attenuation coefficient each time a grain fulfils the diffraction condition. The three-dimensional grain shapes are reconstructed from a limited number of projections using an algebraic reconstruction technique. An algorithm based on scanning orientation space and aiming at determining the corresponding crystallographic grain orientations is proposed. The potential and limitations of a first approach, based on the acquisition of the direct beam projection images only, are discussed in this first part of the paper. An extension is presented in the second part of the paper [Johnson, King, Honnicke, Marrow & Ludwig (2008). J. Appl. Cryst. 41, 310–318], addressing the case of combined direct and diffracted beam acquisition.

/pdf/x-ray-diffraction-contrast-tomography-a-novel-technique-for-4ymyzuvc73.pdf

X-ray diffraction contrast tomography: a novel technique for three-dimensional grain mapping of polycrystals. I. Direct beam case

X-ray diffraction contrast tomography (DCT) is a technique for mapping grain shape and orientation in plastically undeformed polycrystals. In this paper, we describe a modified DCT data acquisition strategy which permits the incorporation of an innovative Friedel pair method for analyzing diffraction data. Diffraction spots are acquired during a 360 degrees rotation of the sample and are analyzed in terms of the Friedel pairs ((hkl) and (hkl) reflections, observed 180 degrees apart in rotation). The resulting increase in the accuracy with which the diffraction vectors are determined allows the use of improved algorithms for grain indexing (assigning diffraction spots to the grains from which they arise) and reconstruction. The accuracy of the resulting grain maps is quantified with reference to synchrotron microtomography data for a specimen made from a beta titanium system in which a second phase can be precipitated at grain boundaries, thereby revealing the grain shapes. The simple changes introduced to the DCT methodology are equally applicable to other variants of grain mapping.

/pdf/three-dimensional-grain-mapping-by-x-ray-diffraction-20r03pknbe.pdf

Three-dimensional grain mapping by x-ray diffraction contrast tomography and the use of Friedel pairs in diffraction data analysis.

Originally conceived and developed at the European Synchrotron Radiation Facility (ESRF) as an "area" detector for rapid x-ray imaging studies, the fast readout low noise (FReLoN) detector of the ESRF [J.-C. Labiche, ESRF Newsletter 25, 41 (1996)] has been demonstrated to be a highly versatile and unique detector. Charge coupled device (CCD) cameras at present available on the public market offer either a high dynamic range or a high readout speed. A compromise between signal dynamic range and readout speed is always sought. The parameters of the commercial cameras can sometimes be tuned, in order to better fulfill the needs of specific experiments, but in general these cameras have a poor duty cycle (i.e., the signal integration time is much smaller than the readout time). In order to address scientific problems such as time resolved experiments at the ESRF, a FReLoN camera has been developed by the Instrument Support Group at ESRF. This camera is a low noise CCD camera that combines high dynamic range, high readout speed, accuracy, and improved duty cycle in a single image. In this paper, we show its application in a quasi-one-dimensional sense to dynamic problems in materials science, catalysis, and chemistry that require data acquisition on a time scale of milliseconds or a few tens of milliseconds. It is demonstrated that in this mode the FReLoN can be applied equally to the investigation of rapid changes in long range order (via diffraction) and local order (via energy dispersive extended x-ray absorption fine structure) and in situations of x-ray hardness and flux beyond the capacity of other detectors.

http://xrm.phys.northwestern.edu/research/pdf_papers/2007/labiche_rsi_2007.pdf

Invited article: The fast readout low noise camera as a versatile x-ray detector for time resolved dispersive extended x-ray absorption fine structure and diffraction studies of dynamic problems in materials science, chemistry, and catalysis

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Invited article: The fast readout low noise camera as a versatile x-ray detector for time resolved dispersive extended x-ray absorption fine structure and diffraction studies of dynamic problems in materials science, chemistry, and catalysis