Simulating Ion Microtomography Data for Improving Reconstruction Quality

Ion Microtomography (IMT) provides quantitative, fine resolution density imaging of samples for materials characterization. Reconstructed tomographic images are obtained by application of a filtered backprojection algorithm to the collected data. The attainable resolution and data acquisition rate are affected by several parameters. These include the number of ions measured per spot, using either the mean or median residual energy, utilizing Bragg additivity, changing the number of rays or the number of projections and oversampling the data. A tomography simulation computer program is described and used to study the contributions from these effects on the numerical reconstruction of an array of silicon pillars

A mechanistic model linking insect (Hydropsychidae) silk nets to incipient sediment motion in gravel‐bedded streams

Plants and animals affect stream morphodynamics across a range of scales, yet including biological traits of organisms in geomorphic process models remains a fundamental challenge. For example, laboratory experiments have shown that silk nets built by caddisfly larvae (Trichoptera: Hydropsychidae) can increase the shear stress required to initiate bed motion by more than a factor of 2. The contributions of specific biological traits are not well understood, however. Here we develop a theoretical model for the effects of insect nets on the threshold of sediment motion, τ * crit , that accounts for the mechanical properties, geometry, and vertical distribution of insect silk, as well as interactions between insect species. To parameterize the model, we measure the tensile strength, diameter, and number of silk threads in nets built by two common species of caddisfly, Arctopsyche californica and Ceratopsyche oslari . We compare model predictions with new measurements of τ * crit in experiments where we varied grain size and caddisfly species composition. The model is consistent with experimental results for single species, which show that the increase in τ * crit above the abiotic control peaks at 40–70% for 10–22 mm sediments and declines with increasing grain size. For the polyculture experiments, however, the model underpredicts the measured increase in τ * crit when two caddisfly species are present in sediments of larger grain sizes. Overall, the model helps explain why the presence of caddisfly silk can substantially increase the forces needed to initiate sediment motion in gravel‐bedded streams and also illustrates the challenge of parameterizing the behavior of multiple interacting species in a physical model. Key Points Caddisfly silk nets are incorporated into a model of incipient sediment motion Silk nets increase critical shear stress in gravel‐bedded streams Species‐specific silk and behaviors control the range of grain sizes affectedPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109329/1/jgrf20303.pd

Technical developments for computed tomography on the CENBG nanobeam line

The use of ion microbeams as probes for computedtomography has proven to be a powerful tool for the three-dimensional characterization of specimens a few tens of micrometers in size. Compared to other types of probes, the main advantage is that quantitative information about mass density and composition can be obtained directly, using specific reconstruction codes. At the Centre d’Etudes Nucléaires de Bordeaux Gradignan (CENBG), this technique was initially developed for applications in cellular biology. However, the observation of the cell ultrastructure requires a sub-micron resolution. The construction of the nanobeamline at the Applications Interdisciplinaires des Faisceaux d’Ions en Region Aquitaine (AIFIRA) irradiation facility has opened new perspectives for such applications. The implementation of computedtomography on the nanobeamline of CENBG has required a careful design of the analysis chamber, especially microscopes for precise sample visualization, and detectors for scanning transmission ion microscopy (STIM) and for particle induced X-ray emission (PIXE). The sample can be precisely positioned in the three directions X, Y, Z and a stepper motor coupled to a goniometer ensures the rotational motion. First images of 3D tomography were obtained on a reference sample containing microspheres of certified diameter, showing the good stability of the beam and the sample stage, and the precision of the motion

Diffusion of titanium and niobium in b.c.c. Ti-Nb alloys

The diffusion coefficients for titanium and niobium radioactive tracers were simultaneously measured in Ti, Ti94.6, Ti80.4, Nb19.6 and Ti64.3Nb35.7 over the temperature range from 9S0°C to 1511°C using 643 3S standard lathe sectioning techniques. The samples were initially heat treated by annealing above the a-B phase transition temperature and then either cooling slowly to room temperature or quenching. The room temperature crystal morphology was then examined using x-ray diffraction. Alloy concentrations were chosen both to suppress the B-a transition and to obtain the metastable w-phase. [DATA]The hypothesized enhancement of diffusion by w-phase fluctuations or effects of the h.c.p. to b.c.c. phase transformation cannot be ruled out by this work, but are certainly not supported directly by the present results.U of I OnlyThesi

Neural Correlates of DéJà Vu and Dissociation: the Roles of the Amygdala and Hippocampus in the Prevalence of Deja Vu Used as an Indicator for the Severity of Dissociation and Posttraumatic Stress Disorder

The phenomenon of déjà vu is one that is poorly understood while posttraumatic stress disorder (PTSD) is a complex diagnosis and presentation of symptoms. Both of these presentations are influenced by amygdala and hippocampus regions of the brain. As such, this study demonstrated through correlational analyses that there are significant relationships between components of each that can be utilized to aid in determining the likely-hood of PTSD and dissociative symptoms. A unique negative relationship was also presented between deǰa vu and PTSD and dissociative assessment scores. Discussion of these relationships and future investigations are also discusse

Diffusion of Titanium and Niobium in Bcc Titanium - Niobium Alloys

84 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1978.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

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