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

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

Roles of Free Electrons and H2O2 in the Optical Breakdown-Induced Photochemical Reduction of Aqueous [AuCl4]-

Free electrons and H2O2 formed in an optical breakdown plasma are found to directly control the kinetics of [AuCl4]− reduction to form Au nanoparticles (AuNPs) during femtosecond laser-assisted synthesis of AuNPs. The formation rates of both free electrons and H2O2 strongly depend on the energy and duration of the 800 nm laser pulses over the ranges of 10−2400 μJ and 30−1500 fs. By monitoring the conversion of [AuCl4]− to AuNPs using in situ UV−vis spectroscopy during laser irradiation, the first- and second-order rate constants in the autocatalytic rate law, k1 and k2, were extracted and compared to the computed free electron densities and experimentally measured H2O2 formation rates. For laser pulse energies of 600 μJ and lower at all pulse durations, the first-order rate constant, k1, was found to be directly proportional to the theoretically calculated plasma volume, in which the electron density exceeds the threshold value of 1.8 × 1020 cm−3. The second-order rate constant, k2, was found to correlate with the measured H2O2 formation rate at all pulse energies and durations, resulting in the empirical relationship k2 ≈ H2O20.5. We have demonstrated that the relative composition of free electrons and H2O2 in the optical breakdown plasma may be controlled by changing the pulse energy and duration, which may make it possible to tune the size and dispersity of AuNPs and other metal nanoparticle products synthesized with femtosecond laser-based methods

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

The Longitudinal Effects of STEM Identity and Gender on Flourishing and Achievement in College Physics

Background. Drawing on social identity theory and positive psychology, this study investigated women’s responses to the social environment of physics classrooms. It also investigated STEM identity and gender disparities on academic achievement and flourishing in an undergraduate introductory physics course for STEM majors. 160 undergraduate students enrolled in an introductory physics course were administered a baseline survey with self-report measures on course belonging, physics identification, flourishing, and demographics at the beginning of the course and a post-survey at the end of the academic term. Students also completed force concept inventories and physics course grades were obtained from the registrar. Results. Women reported less course belonging and less physics identification than men. Physics identification and grades evidenced a longitudinal bidirectional relationship for all students (regardless of gender) such that when controlling for baseline physics knowledge: (a) students with higher physics identification were more likely to earn higher grades; and (b) students with higher grades evidenced more physics identification at the end of the term. Men scored higher on the force concept inventory than women, although no gender disparities emerged for course grades. For women, higher physics (versus lower) identification was associated with more positive changes in flourishing over the course of the term. High-identifying men showed the opposite pattern: negative change in flourishing was more strongly associated with high identifiers than low identifiers. Conclusions. Overall, this study underlines gender disparities in physics both in terms of belonging and physics knowledge. It suggests that strong STEM identity may be associated with academic performance and flourishing in undergraduate physics courses at the end of the term, particularly for women. A number of avenues for future research are discussed