Metal-Oxide Nanostructures Fabricated from Laser-Assisted Synthesis Technique

Background Rising levels of greenhouse gases in our atmosphere such as CO 2 are contributing to global rises in temperature, acidification of the oceans, and more extreme weather conditions. Hydrogenation of CO 2 to form carbon-based products is of great importance to reduce CO 2 levels and generate carbon-based compounds that can be used for industrial purposes. Copper- and nickel- based nanocatalysts have promising catalytic activity toward CO 2 hydrogenation, and have great interest to replace expensive and rare Pt- and Pd-based catalysts. Methods Focusing high powered laser pulses onto the surface of a silicon wafer immersed in liquid solutions containing nickel nitrate or copper nitrate in alkaline media leads to the formation of Cu, Ni or copper-nickel phyllosilicates (PS). The laser pulses remove Si atoms from the wafer, allowing them to interact with the surrounding liquid where the Cu 2+ or Ni 2+ ions incorporate themselves into the forming phyllosilicate structure. The well-dispersed Cu and Ni atoms throughout the structure lead to a highly catalytically active material. Results The Cu-PS and Ni-PS nanostructures were synthesized, and the formation mechanisms from different experimental parameters were investigated. The Cu-PS selectively converted CO 2 to methanol below 500ºC, and formed methanol and methane above 500ºC. Conclusions The synthesis of Cu-PS and Ni-PS nanostructured catalysts were achieved using a reactive laser ablation in liquid technique, and the products displayed catalytic activity toward the hydrogenation of CO 2 , with temperature-dependent selectivity toward methanol and methane.https://scholarscompass.vcu.edu/gradposters/1095/thumbnail.jp

Model Tests of Jet Induced Lift Effects on a VTOL Aircraft in Hover

Lift loss and jet decay measurements on hovering vertical takeoff aircraft model

Selection for individual recognition and the evolution of polymorphic identity signals in Polistes paper wasps

Individual recognition (IR) requires individuals to uniquely identify their social partners based on phenotypic variation. Because IR is so specific, distinctive phenotypes that stand out from the crowd facilitate efficient recognition. Over time, the benefits of unique appearances are predicted to produce a correlation between IR and phenotypic variation. Here, we test whether there is an association between elevated phenotypic polymorphism and IR in paper wasps. Previous work has shown that Polistes fuscatus use variable colour patterns for IR. We test whether two less variable wasp species, Polistes dominulus and Polistes metricus , are capable of IR. As predicted, neither species is capable of IR, suggesting that highly variable colour patterns are confined to Polistes species with IR. This association suggests that elevated phenotypic variation in taxa with IR may be the result of selection for identity signals rather than neutral processes. Given that IR is widespread among social taxa, selection for identity signalling may be an underappreciated mechanism for the origin and maintenance of polymorphism.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79348/1/j.1420-9101.2009.01923.x.pd

Probing Coherent Vibrations of Organic Phosphonate Radical Cations with Femtosecond Time-Resolved Mass Spectrometry

Organic phosphates and phosphonates are present in a number of cellular components that can be damaged by exposure to ionizing radiation. This work reports femtosecond time-resolved mass spectrometry (FTRMS) studies of three organic phosphonate radical cations that model the DNA sugar-phosphate backbone: dimethyl methylphosphonate (DMMP), diethyl methylphosphonate (DEMP), and diisopropyl methylphosphonate (DIMP). Upon ionization, each molecular radical cation exhibits unique oscillatory dynamics in its ion yields resulting from coherent vibrational excitation. DMMP has particularly well-resolved 45 fs (732 ± 28 cm−1) oscillations with a weak feature at 610–650 cm−1, while DIMP exhibits bimodal oscillations with a period of ∼55 fs and two frequency features at 554 ± 28 and 670–720 cm−1. In contrast, the oscillations in DEMP decay too rapidly for effective resolution. The low- and high-frequency oscillations in DMMP and DIMP are assigned to coherent excitation of the symmetric O–P–O bend and P–C stretch, respectively. The observation of the same ionization-induced coherently excited vibrations in related molecules suggests a possible common excitation pathway in ionized organophosphorus compounds of biological relevance, while the distinct oscillatory dynamics in each molecule points to the potential use of FTRMS to distinguish among fragment ions produced by related molecules

Probing Coherent Vibrations of Organic Phosphonate Radical Cations with Femtosecond Time-Resolved Mass Spectrometry

Organic phosphates and phosphonates are present in a number of cellular components that can be damaged by exposure to ionizing radiation. This work reports femtosecond time-resolved mass spectrometry (FTRMS) studies of three organic phosphonate radical cations that model the DNA sugar-phosphate backbone: dimethyl methylphosphonate (DMMP), diethyl methylphosphonate (DEMP), and diisopropyl methylphosphonate (DIMP). Upon ionization, each molecular radical cation exhibits unique oscillatory dynamics in its ion yields resulting from coherent vibrational excitation. DMMP has particularly well-resolved 45 fs (732 ± 28 cm−1) oscillations with a weak feature at 610–650 cm−1, while DIMP exhibits bimodal oscillations with a period of ∼55 fs and two frequency features at 554 ± 28 and 670–720 cm−1. In contrast, the oscillations in DEMP decay too rapidly for effective resolution. The low- and high-frequency oscillations in DMMP and DIMP are assigned to coherent excitation of the symmetric O–P–O bend and P–C stretch, respectively. The observation of the same ionization-induced coherently excited vibrations in related molecules suggests a possible common excitation pathway in ionized organophosphorus compounds of biological relevance, while the distinct oscillatory dynamics in each molecule points to the potential use of FTRMS to distinguish among fragment ions produced by related molecules