Polycrystal deformation analysis by high energy synchrotron X-ray diffraction on the I12 JEEP beamline at Diamond Light Source

Better understanding of the distribution of elastic and plastic strains in deformed polycrystalline, multiphase materials is important for structural engineering. The deformation response depends upon the interaction of grains of different orientations, and the anisotropy associated with each phase. Strain partitioning and tensile-compressive hardening asymmetry arises due to mismatches in modulus and ductility between grains and phases in alloys such as Ti-6Al-4V that displays both strong anisotropy within one phase and significant differences of properties between phases. Simple four-point bent beam samples were studied using the newly available energy-dispersive X-ray diffraction setup at the high energy white-beam synchrotron beamline I12 (JEEP) at Diamond Light Source. Diffraction patterns from the bent polycrystalline Ti6Al4V samples were collected using the new 23-cell “horseshoe” detector and interpreted using Pawley refinement to extract unit cell parameters, thus allowing elastic strain to be determined. The tensile-compressive hardening asymmetry was quantified for the grains oriented with the basal plane perpendicular to the loading direction. Initial evaluation of the performance of the new instrument is reported.     

A two-level distributed multiple hypothesis decision system

A two-level distributed decision system consisting of a number of local decision makers (LDMs) connected to a global decision maker (GDM) is considered. The LDMs share a common M-hypothesis testing problem, have their own observations independent of each other, and employ likelihood ratios for their decision making. Each LDM transmits its inference to the GDM where the final decision is derived. The local inferences consist of the ranking of the candidate hypotheses and a degree of confidence based on likelihood ratios. Using a maximum distance criterion, the optimum confidence-based subpartitioning of local decision space is studied. It is shown that the presented system can greatly outperform one in which LDM provides a single-hypothesis hard decision and can perform nearly as well as the optimum centralized system     

Geothermal exploration of kos island, Greece: Magnetotelluric and microseismicity studies

This paper reports the results of magnetotelluric (MT) and microseismicity studies, conducted as part of a multi-disciplinary project to explore the geothermal potential of the island of Kos, Greece. The MT survey, comprising 18 soundings, was carried out in the bandwidth 128 Hz–40 s, in order to determine the deep conductivity structure in the geothermally prospective western part of the island. Rigorous dimensionality analysis has indicated that the geoelectric structure could adequately be approximated with 1-D interpretation tools. Two significant and seemingly communicating conductive zones of potential geothermal interest were found within the first 2 km. The first is extensive and shallow, detected at depths of 400–600 m; the second is deeper (1000–1300 m), but of considerably smaller lateral dimensions. A very deep relative conductor (<25 Ωm) was also detected at depths of 7–10 km, which is thought to comprise part of an old magma chamber with brine-saturated rocks. The microseismicity studies revealed the partial or total attenuation of shear waves in many microearthquake records. The analysis of these observations determined the vertical and lateral extent of that attenuation zone, the greatest part of which is located underneath the marine area between western Kos and Nissyros island to the south, extending approximately from near the surface to about 1.5 km depth. The nature of this zone is discussed in terms of fluid concentration due to the geothermal system of the area.     

Interphasial viscoelastic behavior of CNT reinforced nanocomposites studied by means of the concept of the hybrid viscoelastic interphase

In this study the effect of carbon nanotubes content as well as of the tensile stress level applied upon the linear viscoelastic creep response of carbon nanotube polymer nanocomposites was investigated. Experimental findings were modeled by means of the newly developed hybrid viscoelastic interphase model, which constitutes an extension of the previously developed hybrid interphase model. According to this model, the viscoelastic interphase thickness has not of constant value but is dependent upon the property considered at the time as well as on the creep time. In addition, the parameter of imperfect bonding is introduced through the degree of adhesion. Experimental findings combined with analytical results gave a better understanding of the viscoelastic response of epoxy resin carbon nanotubes nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The Oxford-Diamond In Situ Cell for studying chemical reactions using time-resolved X-ray diffraction

A versatile, infrared-heated, chemical reaction cell has been assembled and commissioned for the in situ study of a range of chemical syntheses using time-resolved energy-dispersive X-ray diffraction (EDXRD) on Beamline I12 at the Diamond Light Source. Specialized reactor configurations have been constructed to enable in situ EDXRD investigation of samples under non-ambient conditions. Chemical reactions can be studied using a range of sample vessels such as alumina crucibles, steel hydrothermal autoclaves, and glassy carbon tubes, at temperatures up to 1200 °C.     

Transform-based graph topology similarity metrics

Neural Computing and Applications - Graph signal processing has recently emerged as a field with applications across a broad spectrum of fields including brain connectivity networks, logistics and...     

High-resolution X-ray fluorescence microtomography of homogeneoussamples

First experimental results of fluorescence microtomography with 6 μm resolution obtained at ESRF, Grenoble, France, are described. The setup comprises high-quality optics (monochromator, mirror, focusing lenses) coupled to the high-energy/brilliance/coherence of the ID 22 undulator beamline. The tomographic setup allows precise measurements in the “pencil-beam” geometry. The image reconstruction is based on a modification of the algebraic reconstruction method but includes simplifications of the model. The quality and precision of the two-dimensional reconstructed elemental images of a phantom sample are encouraging. The method will be further refined and applied for the analysis of more complex inhomogeneous samples     

Experimental,analytical, and numerical investigation of interphasial stress and strain fields in MWCNT polymer composites

In this investigation, the effect of polymer matrix‐MWCNT interphase on the stress and strain fields developed at the close vicinity of MWCNT was studied. The recently developed concept of the hybrid interphase (Papanicolaou et al., 2002) was applied. According to this concept, the interphase thickness depends on the property considered at the time. The parameter of imperfect bonding between the primary constituent materials is also introduced by means of the degree of adhesion. Experimental findings combined with analytical and numerical results gave a better understanding of the structural and mechanical performance of epoxy resin‐carbon nanotubes composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011