Single-crystal Ih ice surfaces unveil connection between macroscopic and molecular structure.

Physics and chemistry of ice surfaces are not only of fundamental interest but also have important impacts on biological and environmental processes. As ice surfaces-particularly the two prism faces-come under greater scrutiny, it is increasingly important to connect the macroscopic faces with the molecular-level structure. The microscopic structure of the ubiquitous ice Ih crystal is well-known. It consists of stacked layers of chair-form hexagonal rings referred to as molecular hexagons. Crystallographic unit cells can be assembled into a regular right hexagonal prism. The bases are labeled crystallographic hexagons. The two hexagons are rotated 30° with respect to each other. The linkage between the familiar macroscopic shape of hexagonal snowflakes and either hexagon is not obvious per se. This report presents experimental data directly connecting the macroscopic shape of ice crystals and the microscopic hexagons. Large ice single crystals were used to fabricate samples with the basal, primary prism, or secondary prism faces exposed at the surface. In each case, the same sample was used to capture both a macroscopic etch pit image and an electron backscatter diffraction (EBSD) orientation density function (ODF) plot. Direct comparison of the etch pit image and the ODF plot compellingly connects the macroscopic etch pit hexagonal profile to the crystallographic hexagon. The most stable face at the ice-water interface is the smallest area face at the ice-vapor interface. A model based on the molecular structure of the prism faces accounts for this switch.

Understanding heterogeneity in Genesis diamond-like carbon film using SIMS analysis of implants.

An amorphous diamond-like carbon film deposited on silicon made at Sandia National Laboratory by pulsed laser deposition was one of several solar wind (SW) collectors used by the Genesis Mission (NASA Discovery Class Mission #5). The film was ~1 µm thick, amorphous, anhydrous, and had a high ratio of sp 3-sp 2 bonds (>50%). For 27 months of exposure to space at the first Lagrange point, the collectors were passively irradiated with SW (H fluence ~2 × 1016 ions cm-2; He fluence ~8 × 1014 ions cm-2). The radiation damage caused by the implanted H ions peaked at 12-14 nm below the surface of the film and that of He about 20-23 nm. To enable quantitative measurement of the SW fluences by secondary ion mass spectroscopy, minor isotopes of Mg (25Mg and 26Mg) were commercially implanted into flight-spare collectors at 75 keV and a fluence of 1 × 1014 ions cm-2. The shapes of analytical depth profiles, the rate at which the profiles were sputtered by a given beam current, and the intensity of ion yields are used to characterize the structure of the material in small areas (~200 × 200 ± 50 µm). Data were consistent with the hypothesis that minor structural changes in the film were induced by SW exposure.

Elemental composition, morphology and mechanical properties of calcified deposits obtained from abdominal aortic aneurysms.

Calcified deposits exist in almost all abdominal aortic aneurysms (AAAs). The significant difference in stiffness between these hard deposits and the compliant arterial wall may result in local stress concentrations and increase the risk of aneurysm rupture. Calcium deposits may also complicate AAA repair by hindering the attachment of a graft or stent-graft to the arterial wall or cause vessel wall injury at the site of balloon dilation or vascular clamp placement. Knowledge of the composition and properties of calcified deposits helps in understanding the risks associated with their presence. This work presents results of elemental composition, microscopic morphology, and mechanical property measurements of human calcified deposits obtained from within AAAs. The elemental analyses indicate the deposits are composed primarily of calcium phosphate with other assorted constituents. Microscopy investigations show a variety of microstructures within the deposits. The mechanical property measurements indicate an average elastic modulus in the range of cortical bone and an average hardness similar to nickel and iron.

Gold nanoparticle mediated formation of aligned nanotube composite films.

We report on the formation of highly anisotropic nanotube composite materials, made by the attachment of gold nanoparticles to the surface of the single-walled carbon nanotubes, followed by preparation of an aligned composite film by compression in a Langmuir-Blodgett trough. The gold is attached in a one-step sonication procedure. The gold-modified nanotube material forms a stable suspension in toluene and has been characterized by atomic force and scanning force microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy. The aligned films have highly anisotropic electrical properties, with a factor of approximately 3000 difference in the conductivity between the aligned and perpendicular directions.

Insights into the dissolution and the three-dimensional structure of insensitive munitions formulations.

Two compounds, 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO) are the main ingredients in a suite of explosive formulations that are being, or soon will be, fielded at military training ranges. We aim to understand the dissolution characteristics of DNAN and NTO and three insensitive muntions (IM) formulations that contain them. This information is needed to accurately predict the environmental fate of IM constituents, some of which may be toxic to people and the environment. We used Raman spectroscopy to identify the different constituents in the IM formulations and micro computed tomography to image their three-dimensional structure. These are the first three-dimensional images of detonated explosive particles. For multi-component explosives the solubility of the individual constituents and the fraction of each constituent wetted by water controls the dissolution. We found that the order of magnitude differences in solubility amongst the constituents of these IM formulations quickly produced hole-riddled particles when these were exposed to water. Micro-computed tomography showed that particles resulting from field detonations were fractured, producing conduits by which water could access the interior of the particle. We think that micro-computed tomography can also be used to determine the initial composition of IM particles and to track how their compositions change as the particles dissolve. This information is critical to quantifying dissolution and developing physically based dissolution models.

The diaphragms of fenestrated endothelia: gatekeepers of vascular permeability and blood composition.

Fenestral and stomatal diaphragms are endothelial subcellular structures of unknown function that form on organelles implicated in vascular permeability: fenestrae, transendothelial channels, and caveolae. PV1 protein is required for diaphragm formation in vitro. Here, we report that deletion of the PV1-encoding Plvap gene in mice results in the absence of diaphragms and decreased survival. Loss of diaphragms did not affect the fenestrae and transendothelial channels formation but disrupted the barrier function of fenestrated capillaries, causing a major leak of plasma proteins. This disruption results in early death of animals due to severe noninflammatory protein-losing enteropathy. Deletion of PV1 in endothelium, but not in the hematopoietic compartment, recapitulates the phenotype of global PV1 deletion, whereas endothelial reconstitution of PV1 rescues the phenotype. Taken together, these data provide genetic evidence for the critical role of the diaphragms in fenestrated capillaries in the maintenance of blood composition.

Phase contrast microscopy analysis of breast tissue: differences in benign vs. malignant epithelium and stroma.

OBJECTIVE: To assess how optical scatter properties in breast tissue, as measured by phase contrast microscopy and interpreted pathophysiologically, might be exploited as a diagnostic tool to differentiate cancer from benign tissue. STUDY DESIGN: We evaluated frozen human breast tissue sections of adipose tissue, normal breast parenchyma, benign fibroadenoma tumors and noninvasive and invasive malignant cancers by phase contrast microscopy through quantification of grayscale values, using multiple regions of interest (ROI). Student's t tests were performed on phase contrast measures across diagnostic categories testing data from individual cases; all ROI data were used as separate measures. RESULTS: Stroma demonstrated significantly higher scatter intensity than did epithelium, with lower scattering in tumor-associated stroma as compared with normal or benign-associated stroma. Measures were comparable for invasive and noninvasive malignant tumors but were higher than those found in benign tumors and were lowest in adipose tissue. CONCLUSION: Significant differences were found in scatter coefficient properties of epithelium and stroma across diagnostic categories of breast tissue, particularly between benign and malignant-associated stroma. Improved understanding of how scatter properties correlate with morphologic criteria used in routine pathologic diagnoses could have a significant clinical impact as developing optical technology allows macroscopic in situ phase contrast imaging.

Elemental compositions of comet 81P/Wild 2 samples collected by Stardust.

We measured the elemental compositions of material from 23 particles in aerogel and from residue in seven craters in aluminum foil that was collected during passage of the Stardust spacecraft through the coma of comet 81P/Wild 2. These particles are chemically heterogeneous at the largest size scale analyzed ( approximately 180 ng). The mean elemental composition of this Wild 2 material is consistent with the CI meteorite composition, which is thought to represent the bulk composition of the solar system, for the elements Mg, Si, Mn, Fe, and Ni to 35%, and for Ca and Ti to 60%. The elements Cu, Zn, and Ga appear enriched in this Wild 2 material, which suggests that the CI meteorites may not represent the solar system composition for these moderately volatile minor elements.

Monitoring angiogenesis in brain using steady-state quantification of DeltaR2 with MION infusion.

An MRI method for quantification of cerebral blood volume (CBV) in time-course studies of angiogenesis is described. Angiogenesis was stimulated by acclimation to hypoxia. The change in relaxation rate, R2, which is relatively sensitive to the microvasculature, was quantified before and after infusion of a superparamagnetic vascular contrast agent (MION). The DeltaR2 was measured in serum and brain parenchyma with a multiecho sequence. In vitro and in vivo calibration curves of MION concentration vs. R2 were approximated by a linear function. CBV was 3.14 +/- 0.32% (mean +/- SE, n=13) and 6.42 +/- 0.54% (n=4) before and after acclimation. A second acclimated group was hemodiluted to control for polycythemia. CBV was not significantly different between hemodiluted and nonhemodiluted groups. In animals where NMR measurements were taken before and after acclimation, there was a 120% increase in CBV. The NMR technique was validated using quantitative morphometrics, which showed an increase of 147% in CBV with acclimation. We found a linear correlation between MRI and the morphometric results for CBV, as well as demonstrating a quantitative equivalence for relative changes in CBV. This article describes a simple, repeatable method of imaging brain microvascular volume using a plasma-based contrast agent that can be applied to longitudinal studies of angiogenesis.

Analysis of the microvasculature and tissue type ratios in normal vs. benign and malignant breast tissue.

OBJECTIVE: To analyze the microvasculature and tissue type ratios in normal vs. benign and malignant breast tissue to establish a baseline for expected values against which future imaging studies can be benchmarked. STUDY DESIGN: Using computer-assisted techniques on immunostained breast tissue (normal [n = 28], fibrocystic [n = 37], fibroadenomas [n = 19], invasive carcinomas [n = 19]), values were obtained for microvessel density (MVD), mean vessel area (MVA), vessel orientation (shape) and epithelial:stromal ratio (E:S). Measurement reproducibility and the effects of fibroadenoma stromal hyalinization and fibrocystic disease severity were also tested. RESULTS: Value ranges for the 4 diagnostic groups were significantly different (P < .001). For invasive breast carcinomas, E:S and MVD were significantly higher (P < .001) but MVA was smaller as compared to that in fibroadenomas. Peripherally vs. centrally there was no significant difference in MVD, MVA or vessel shape in the neoplasms. Decreases in E:S and MVD correlated with fibroadenoma stromal hyalinization. Increases in E:S and MVA correlated with more severe fibrocystic disease. Correlation coefficients for measurement reproducibility were high across the diagnostic categories. CONCLUSION: This study established a specific, reproducible, computer-assisted technique and baseline of expected values for morphologic criteria in normal, benign and malignant breast tissue that may be used in the future to correlate new breast imaging responses with these underlying biologic properties.