Structures, energetics and fragmentation pathways of CnH22+ carbodications

Potential energy curves have been calculated for CnH22+ (n = 2−9) ions and results have been compared with data on unimolecular charge-separation reactions obtained by Rabrenović and Beynon. Geometry-optimized, minimum energy, linear CnH22+ structures have been computed for ground and low-lying excited states. These carbodications exist in stable configurations with well depths greater than 3 eV. Decomposition pathways into singly charged fragment ions lead to products with computed kinetic energies in excess of 1 eV. A high degree of correlation exists between experimental information and results computed for linear CnH22+ structures having hydrogen atoms on each end. The exception involves C4H22+reactions where a low-lying doubly charged isomer must be invoked to rationalize the experimental data.

Characterization of vascular cavity coatings and microscopic tube-shaped structures from Upper Cretaceous dinosaur bone: evidence of a bacterial origin for dinosaur blood vessels""

Recent claims of blood vessels extracted from dinosaur fossils challenge classical views of soft-tissue preservation. Alternatively, these structures may represent postdepositional,diagenetic biofilms that grew on vascular cavity surfaces within the fossil. Similar red, hollow, tube-shaped structures were recovered from well-preserved and poorly-preserved (abraded, desiccated, exposed) Upper Cretaceous dinosaur fossils in this study. Integration of light microscopy, scanning electron microscopy, and energy dispersive x-ray spectroscopy was used to compare these vessel structures to the fossils from which they are derived. Vessel structures are typically 100-400 μm long, 0.5-1.5 μm thick, 10-40 μm in diameter and take on a wide range of straight, curved, andbranching morphologies. Interior surfaces vary from smooth to globular and typically contain spheres, rods, and fibrous structures (< 2 μm in diameter) incorporated into the surface. Exterior surfaces exhibit 2-μm-tall converging ridges, spaced 1-3 μm apart, that are sub-parallel to the long axis of the vessel structure. Fossil vascular cavities are typically coated with a smooth or grainy orange layer that shows a wide range of textures including smooth, globular, rough, ropy, and combinations thereof. Coatings tend to overlay secondary mineral crystals and framboids, confirming they are not primary structures of the fossil. For some cavity coatings, the surface that had been in contact with the bone exhibits a ridged texture, similar to that of vessel structures, having formed as a mold of the intravascular bone surface. Thus, vessel structures are interpreted as intact cavity coatings isolated after the fossil is demineralized. The presence of framboids and structures consistent in size and shape with bacteria cells, the abundance of iron in cavity coatings, and the growth of biofilms directly from the fossil that resemble respective cavity coatings support the hypothesis that vessel structures result from ironconsuming bacteria that form biofilms on the intravascular bone surfaces of fossil dinosaur bone. This also accounts for microstructures resembling osteocytes as some fossil lacunae are filled with the same iron oxide that comprises vessel structures andcoatings. Results of this study show that systematic, high-resolution SEM analyses of vertebrate fossils can provide improved insight on microtaphonomic processes, including the role of bacteria in diagenesis. These results conflict with earlier claims of dinosaurblood vessels and osteocytes.

Monitoring and Modeling of the Hydraulic and Sediment Processes at In-Stream Restoration Structures in the Vicinity of a Bridge Crossing

The long-term performance of infrastructure depends on reliable and sustainable designs. Many of Pennsylvania’s streams experience sediment transport problems that increase maintenance costs and lower structural integrity of bridge crossings. A stream restoration project is one common mitigation measure used to correct such problems at bridge crossings. Specifically, in an attempt to alleviate aggradation problems with the Old Route 15 Bridge crossing on White Deer Creek, in White Deer, PA, two in-stream structures (rock cross vanes) and several bank stabilization features were installed along with a complete channel redevelopment. The objectives of this research were to characterize the hydraulic and sediment transport processes occurring at the White Deer Creek site, and to investigate, through physical and mathematical modeling, the use of instream restoration structures. The goal is to be able to use the results of this study to prevent aggradation or other sediment related problems in the vicinity of bridges through improved design considerations. Monitoring and modeling indicate that the study site on White Deer Creek is currently unstable, experiencing general channel down-cutting, bank erosion, and several local areas of increased aggradation and degradation of the channel bed. An in-stream structure installed upstream of the Old Route 15 Bridge failed by sediment burial caused by the high sediment load that White Deer Creek is transporting as well as the backwater effects caused by the bridge crossing. The in-stream structure installed downstream of the Old Route 15 Bridge is beginning to fail because of the alignment of the structure with the approach direction of flow from upstream of the restoration structure.