Dilworth Y. Parkinson

Detection of subsurface structures underneath dendrites formed on cycled lithium metal electrodes

Failure caused by dendrite growth in high-energy-density, rechargeable batteries with lithium metal anodes has prevented their widespread use in applications ranging from consumer electronics to electric vehicles. Efforts to solve the lithium dendrite problem have focused on preventing the growth of protrusions from the anode surface. Synchrotron hard X-ray microtomography experiments on symmetric lithium-polymer-lithium cells cycled at 90 °C show that during the early stage of dendrite development, the bulk of the dendritic structure lies within the electrode, underneath the polymer/electrode interface. Furthermore, we observed crystalline impurities, present in the uncycled lithium anodes, at the base of the subsurface dendritic structures. The portion of the dendrite protruding into the electrolyte increases on cycling until it spans the electrolyte thickness, causing a short circuit. Contrary to conventional wisdom, it seems that preventing dendrite formation in polymer electrolytes depends on inhibiting the formation of subsurface structures in the lithium electrode.

Real-time quantitative imaging of failure events in materials under load at temperatures above 1,600 °C

Ceramic matrix composites are the emerging material of choice for structures that will see temperatures above ~1,500 °C in hostile environments, as for example in next-generation gas turbines and hypersonic-flight applications. The safe operation of applications depends on how small cracks forming inside the material are restrained by its microstructure. As with natural tissue such as bone and seashells, the tailored microstructural complexity of ceramic matrix composites imparts them with mechanical toughness, which is essential to avoiding failure. Yet gathering three-dimensional observations of damage evolution in extreme environments has been a challenge. Using synchrotron X-ray computed microtomography, we have fully resolved sequences of microcrack damage as cracks grow under load at temperatures up to 1,750 °C. Our observations are key ingredients for the high-fidelity simulations used to compute failure risks under extreme operating conditions.

Quantitative 3-D imaging of eukaryotic cells using soft x-ray tomography

Imaging has long been one of the principal techniques used in biological and biomedical research. Indeed, the field of cell biology grew out of the first electron microscopy images of organelles in a cell. Since this landmark event, much work has been carried out to image and classify the organelles in eukaryotic cells using electron microscopy. Fluorescently labeled organelles can now be tracked in live cells, and recently, powerful light microscope techniques have pushed the limit of optical resolution to image single molecules. In this paper, we describe the use of soft X-ray tomography, a new tool for quantitative imaging of organelle structure and distribution in whole, fully hydrated eukaryotic Schizosaccharomyces pombe cells. In addition to imaging intact cells, soft X-ray tomography has the advantage of not requiring the use of any staining or fixation protocols--cells are simply transferred from their growth environment to a sample holder and immediately cryofixed. In this way the cells can be imaged in a near native state. Soft X-ray tomography is also capable of imaging relatively large numbers of cells in a short period of time, and is therefore a technique that has the potential to produce information on organelle morphology from statistically significant numbers of cells.

Quantitative analysis of yeast internal architecture using soft X‐ray tomography

We used soft X‐ray tomography (SXT)—a high‐resolution, quantitative imaging technique—to measure cell size and organelle volumes in yeasts. Cell size is a key factor in initiating cell division in yeasts, whereas the number and volume of the organelles have a profound impact on the function and viability of a cell. Consequently, determining these cell parameters is fundamentally important in understanding yeast biology. SXT is well suited to this type of analysis. Specimens are imaged in a near‐native state, and relatively large numbers of cells can be readily analysed. In this study, we characterized haploid and diploid strains of Saccharomyces cerevisiae at each of the key stages in the cell cycle and determined the relationships that exist cellular and organelle volumes. We then compared these results with SXT data obtained from Schizosaccharomyces pombe, the three main phenotypes displayed by the opportunistic yeast pathogen Candida albicans and from a coff1‐22 mutant strain of S. cerevisiae. This comparison revealed that volumetric ratios were invariant, irrespective of yeast strain, ploidy or morphology, leading to the conclusion these volumetric ratios are common in all yeasts. Copyright

3D spectral imaging with synchrotron Fourier transform infrared spectro-microtomography

We report Fourier transform infrared spectro-microtomography, a nondestructive three-dimensional imaging approach that reveals the distribution of distinctive chemical compositions throughout an intact biological or materials sample. The method combines mid-infrared absorption contrast with computed tomographic data acquisition and reconstruction to enhance chemical and morphological localization by determining a complete infrared spectrum for every voxel (millions of spectra determined per sample).

A comparative study of X-ray tomographic microscopy on shales at different synchrotron facilities: ALS, APS and SLS.

The 3D microstructure of shales is important to assess elastic anisotropic characteristics. In this study, microporosity and mineral components in two shale samples were investigated with X-ray tomographic microscopy at three synchrotron facilities: ALS, APS and SLS, and excellent agreement was observed.

Automatic alignment and reconstruction of images for soft x-ray tomography

Soft X-ray tomography (SXT) is a powerful imaging technique that generates quantitative, 3D images of the structural organization of whole cells in a near-native state. SXT is also a high-throughput imaging technique. At the National Center for X-ray Tomography (NCXT), specimen preparation and image collection for tomographic reconstruction of a whole cell require only minutes. Aligning and reconstructing the data, however, take significantly longer. Here we describe a new component of the high throughput computational pipeline used for processing data at the NCXT. We have developed a new method for automatic alignment of projection images that does not require fiducial markers or manual interaction with the software. This method has been optimized for SXT data sets, which routinely involve full rotation of the specimen. This software gives users of the NCXT SXT instrument a new capability - virtually real-time initial 3D results during an imaging experiment, which can later be further refined. The new code, Automatic Reconstruction 3D (AREC3D), is also fast, reliable, and robust. The fundamental architecture of the code is also adaptable to high performance GPU processing, which enables significant improvements in speed and fidelity.

Nanoimaging Cells Using Soft X-Ray Tomography

Soft X-ray microscopy is ideally suited to visualizing and quantifying biological cells. Specimens, including eukaryotic cells, are imaged intact, unstained and fully hydrated, and therefore visualized in a near-native state. The contrast in soft X-ray microscopy is generated by the differential attenuation of X-rays by the molecules in the specimen-water is relatively transmissive to this type of illumination compared to carbon and nitrogen. The attenuation of X-rays by the specimen follows the Beer-Lambert law, and therefore both linear and a quantitative measure of thickness and chemical species present at each point in the cell. In this chapter, we will describe the procedures and computational methods that lead to 50 nm (or better) tomographic reconstructions of cells using soft X-ray microscope data, and the subsequent segmentation and analysis of these volumetric reconstructions. In addition to being a high-fidelity imaging modality, soft X-ray tomography is relatively high-throughput; a complete tomographic data set can be collected in a matter of minutes. This new modality is being applied to imaging cells that range from small prokaryotes to stem cells obtained from mammalian tissues.

Two-dimensional optical spectroscopy: Two-color photon echoes of electronically coupled phthalocyanine dimers

Two-color photon echo peak shift spectroscopy was used to study electronic coupling in a phthalocyanine homodimer. Two optical parametric amplifiers were used to produce pulses to excite the split lower states of LuPc2-. The existence of a two-color peak shift indicates the existence of correlation between these two dipole-allowed states. The nature of this correlation is discussed based on theoretical predictions of the interactions between exciton and charge resonance states.

Using High Resolution Computed Tomography to Visualize the Three Dimensional Structure and Function of Plant Vasculature

High resolution x-ray computed tomography (HRCT) is a non-destructive diagnostic imaging technique with sub-micron resolution capability that is now being used to evaluate the structure and function of plant xylem network in three dimensions (3D) (e.g. Brodersen et al. 2010; 2011; 2012a,b). HRCT imaging is based on the same principles as medical CT systems, but a high intensity synchrotron x-ray source results in higher spatial resolution and decreased image acquisition time. Here, we demonstrate in detail how synchrotron-based HRCT (performed at the Advanced Light Source-LBNL Berkeley, CA, USA) in combination with Avizo software (VSG Inc., Burlington, MA, USA) is being used to explore plant xylem in excised tissue and living plants. This new imaging tool allows users to move beyond traditional static, 2D light or electron micrographs and study samples using virtual serial sections in any plane. An infinite number of slices in any orientation can be made on the same sample, a feature that is physically impossible using traditional microscopy methods. Results demonstrate that HRCT can be applied to both herbaceous and woody plant species, and a range of plant organs (i.e. leaves, petioles, stems, trunks, roots). Figures presented here help demonstrate both a range of representative plant vascular anatomy and the type of detail extracted from HRCT datasets, including scans for coast redwood (Sequoia sempervirens), walnut (Juglans spp.), oak (Quercus spp.), and maple (Acer spp.) tree saplings to sunflowers (Helianthus annuus), grapevines (Vitis spp.), and ferns (Pteridium aquilinum and Woodwardia fimbriata). Excised and dried samples from woody species are easiest to scan and typically yield the best images. However, recent improvements (i.e. more rapid scans and sample stabilization) have made it possible to use this visualization technique on green tissues (e.g. petioles) and in living plants. On occasion some shrinkage of hydrated green plant tissues will cause images to blur and methods to avoid these issues are described. These recent advances with HRCT provide promising new insights into plant vascular function.