Dental amalgams have been used for centuries as major restorative materials for decaying teeth. Amalgams are prepared by mixing alloy particles which contain Ag, Sn, and Cu as the major constituent elements with liquid Hg. The study of microstructure is essential in understanding the setting reactions and improving the properties of amalgams. Until the work reported in this dissertation, optical microscopy (OM), scanning electron microscopy (SEM), and x-ray diffractometry (XRD) were used commonly to analyze amalgam microstructures. No previous systematic transmission electron microscopy (TEM) study has been performed due to sample preparation difficulties and composite structure of dental amalgams. The goal of this research was to carry out detailed microstructural and compositional studies of dental amalgams. This was accomplished using the enhanced spatial resolution of the TEM and its associated microanalytical techniques, namely, scanning transmission electron microscopy (STEM), x-ray energy dispersive spectroscopy (XEDS) and micro-microdiffraction (μμD). A new method was developed for thinning amalgam samples to electron transparency using the "wedge technique." Velvalloy, a low-Cu amalgam, and Tytin, a high-Cu amalgam, were the two amalgams characterized. Velvalloy is composed of a Ag₂Hg₃ (γ₁)/HgSn₇₋₉ (γ₂) matrix surrounding unreacted Ag₃Sn (γ) particles. In addition, hitherto uncharacterized reaction layers between Ag₃Sn(γ)/Ag₂Hg₃ (γ₂) and Ag₂Hg₃ (γ₁)/HgSn₇₋₉ (γ₂) were observed and analyzed. An Ag-Hg-Sn (β₁) phase was clearly identified for the first time. In Tytin, the matrix consists of Ag₂Hg₃ (γ₁) grains. Fine precipitates of Cu₆Sn₅ (η') are embedded inside the γ₁ and at the grain boundaries. These precipitates are responsible for the improved creep resistance of Tytin compared to Velvalloy. The additional Cu has completely eliminated the γ₂ phase which is the weakest component of amalgams. Ag-Hg-Sn (β₁) and large grains of Cu₆Sn₅ (η') are found adjacent to the unreacted alloy particles. Tytin alloy particles contain Cu₃Sn (ε) precipitates in a matrix of Ag₃Sn (γ) and Ag₄Sn (β). SEM was used to correlate the TEM findings in the context of the general microstructure. The results are in good agreement with those published in the literature. The microstructural details reported here, many of which were not previously available, will help provide insight into the deformation mechanisms of dental amalgams.

We propose to interpret Cryogenic Electron Microscopy (CryoEM) data as a supervision for learning parameters of CryoEM microscopes. Following this formulation, we present a differentiable version of Transmission Electron Microscopy (TEM) Simulator that provides differentiability of all continuous inputs in a simulation. We demonstrate the learning capability of our simulator with two examples, detector parameter estimation and denoising. With our differentiable simulator, detector parameters can be learned from real data without time-consuming handcrafting. Besides, our simulator enables new way to denoising micrographs. We develop this simulator with the combination of Taichi and PyTorch, exploiting kernel-based and operator-based parallel differentiable programming, which results in good speed, low memory footprint and expressive code. We call our work as Differentiable TEM Detector as there are still challenges to implement a fully differentiable transmission electron microscope simulator that can further differentiate with respect to particle positions. This work presents first steps towards a fully differentiable TEM simulator. Finally, as a subsequence of our work, we abstract out the fuser that connects Taichi and PyTorch as an open-source library, Stannum, facilitating neural rendering and differentiable rendering in a broader context. We publish our code on GitHub.

While much is known about the attachment of the chlamydiae to the host cell and intracellular events during the developmental cycle, little is known about the mechanism(s) by which elementary bodies exit the cell. In this report, we use the guinea-pig conjunctival model of Chlamydia caviae infection to present in vivo ultrastructural evidence supporting two mechanisms for release of chlamydiae from the mucosal epithelia. Four days after infection, histopathologic observation shows an intense infiltration of polymorphonuclear leukocytes (PMN) in the conjunctival epithelium. Using transmission electron microscopy, a gradient-directed PMN response to chlamydiae-infected epithelial cells was observed. As PMN infiltration intensifies, epithelial hemidesmosome/integrin/focal adhesion adherence with the basal lamina is disconnected and PMNs literally lift off and release infected superficial epithelia from the mucosa. Many of these infected cells appear to be healthy with intact microvilli, nuclei, and mitochondria. While lysis of some infected cells occurs with release of chlamydiae into the extracellular surface milieu, the majority of infected cells are pushed off the epithelium. We propose that PMNs play an active role in detaching infected cells from the epithelium and that these infected cells eventually die releasing organisms but, in the process, move to new tissue sites via fluid dynamics.

No description available.

<p> The fatigue softening behaviour of copper single crystals was investigated as a function of temperature. Copper crystals, prestrained in tension, were softened by "push-pull" cycling at constant plastic strain amplitude, in the low amplitude range, and the cyclic stress-strain curves determined at various temperatures. Transmission electron microscopy was employed to determine the detailed microstructural changes which occured during softening while X-ray and slip line observations were utilized to indicate the overall structural changes on a macroscopic scale. The results were correlated and a rationale, based on dipole production, proposed for the observed softening behaviour. </p> / Thesis / Master of Science (MSc)

Supporting videos attached / The nanoscale structure of fully dense human cortical bone is explored using advanced transmission electron microscopy (TEM) techniques. Studies of fully dense cortical bone are rare because of the sample preparation challenges. In this work, cryogenic ion milling is compared favourably with traditional ultramicrotoming methods because of the clearer imaging results and better preservation of biological structures in the ion milled samples. Ion milled samples were prepared parallel, perpendicular and at a 45 degree angle to the long axis of a human femur. The samples are cooled with liquid nitrogen while being milled to prevent heating damage to the bone structure. Bright-field and dark-field imaging show that mineral mainly occurs as 65 nm wide, 5 nm thick mineral structures, external to the collagen fibrils, and with the long axis of the mineral running parallel to the fibrils. In samples cut parallel to the long axis of the bone, the mineral structures have their c-axes aligned with the collagen fibril long axis. In these sections the mineral structures extend up to 200 nm and are grouped into stripe-like bunches, 53 nm apart. Samples cut perpendicular to the long axis of the bone show open areas roughly 45 nm in diameter. These open areas are assumed to be the location of collagen fibrils within the structure and are tangentially surrounded by 65 nm wide, 5 nm thick mineral structures. On average, there are 22 nm of mineral structures between adjoining collagen fibrils. Samples cut at 45 degrees to the long axis of the bone confirm that the open structure seen in the perpendicular section is not an artefact of sample preparation. By tilting the sample, the 45 degree sample shows the structure of both the parallel and perpendicular sections. The parallel structure strongly resembles images of embryonic bone and other mineralized tissues seen in the literature, so the perpendicular open structure is not caused by sample preparation. An examination of ultramicrotoming’s effect on mineral structure size compared with that of ion milling shows that the mineral structures in ion milled samples are twice as long as in ultramicrotomed samples, indicating that bone mineral may be damaged by the forces applied to the complex composite structure existing in fully dense cortical bone. Using energy dispersive X-ray spectroscopy (EDXS) results and a simplified model of the locations of mineral within the collagen/mineral framework, a calculation of the percentage of external mineral was performed. The result showed that 80+_ 6 % of the mineral in fully dense cortical bone must be external to the collagen fibrils to obtain the EDXS results. Finally, Z-contrast tomography, based on the use of high angle annular darkfield (HAADF) imaging, was used to prepared tomographic reconstructions of the external mineral in fully dense cortical bone. Unlike bright-field tomography, the Z-contrast technique allows examination of crystalline materials as the contrast in HAADF images is mass-thickness dependent instead of diffraction based. These reconstructions again showed the mineral tangentially surrounding 50 nm diameter cylindrical holes, assumed to be the location of collagen fibrils in all directions. This work shows the importance of mineral that is external to the collagen fibrils to the nanoscale structure of fully dense cortical bone. / Thesis / Doctor of Philosophy (PhD)

Schwertmannite, a ferric oxyhydroxysulfate mineral typically found under acidic, high sulfate and iron aqueous conditions, such as acid mine drainage environments, was studied using analytical high resolution transmission electron microscopy (HRTEM). HRTEM offers advantages over bulk techniques such as powder x-ray diffraction and pair distribution function (PDF) analysis of synchrotron data, in its ability to discern multiple phases within poorly crystalline nanominerals. Based on extensive HRTEM observations of both natural and synthetic schwertmannite samples, the authors suggest that schwertmannite should not be described as a single phase mineral with a repeating unit cell, but as a polyphasic nanomineral with crystalline areas spanning less than a few nanometers within an amorphous matrix. The few visible lattice fringes observable in both natural and synthetic schwertmannite agree well with d-spacings of goethite (and jarosite in natural samples) implying that the transformation from schwertmannite to these phases occurs as a gradual structural reordering at the nanoscale. In the synthetic study, the complete transformation from schwertmannite to goethite nanorods and nanoparticles within 24 hours at 75°C was observed, indicating a low energetic barrier to schwertmannite's phase transformation. We also found that amorphous silica can be intimately entrained within natural schwertmannite, and that high concentrations of arsenic can be held in close association of nanocrystalline regions of the mineral. / Ph. D.

No description available.

No description available.

Particle contamination control is a critical issue for the semiconductor industry. In the near future, this industry will be concerned with the chemical identities of contaminant particles as small as 0.01 pm in size. Therefore, analytical techniques with both high chemical sensitivity and spatial resolution are required. Transmission electron microscopy (TEM) provides excellent spatial resolution and yields structural and compositional information. It is rarely used, however, due to the difficulty of sample preparation. The goals of this research are to promote the use of TEM as an ultrafine particle analysis tool by developing new sample preparation methods, and to exploit the new TEM techniques for analysis of particles in semiconductor processing fluids. A TEM methodology for the analysis of particulate contaminants in fluids with an elemental detectability limit as low as 0.1 part per trillion (ppt), and a particle concentration detectability limit as low as 1 particle/ml for particles greater than 0.2 pm was developed and successfully applied to the analysis of particles in HF, H202, de-ionized (DI) water, and on the surface of an electronic device. HF samples from three manufacturers were examined. For HF (B), the maximum particle concentration was 8.3 x 103 particles/ml. Both a viscous material and lath-shaped particles were observed. The Sb concentration was less than 0.6 part per billion (ppb). HF (C) was the cleanest. CaF2 and TiO2 particles were identified in HF (D). For H2 02, iron and tin oxides and hydroxides were identified. The maximum particle concentration was 990 particles/ml. The Sn and Fe concentrations were less than 0.3 ppb. Spherical and dendritic particles were observed. For DI water, spherical and dendritic particles (<2 particles/ml), and particles containing Fe or Si with concentrations less than 0.1 ppt were observed. Contaminants on an electronic device surface were also analyzed. Clusters of small particles were determined to be a mixture of aluminum oxides and aluminum silicates.