Micro-Ramp Flow Control for Oblique Shock Interactions: Comparisons of Computational and Experimental Data

Computational fluid dynamics was used to study the effectiveness of micro-ramp vortex generators to control oblique shock boundary layer interactions. Simulations were based on experiments previously conducted in the 15- by 15-cm supersonic wind tunnel at the NASA Glenn Research Center. Four micro-ramp geometries were tested at Mach 2.0 varying the height, chord length, and spanwise spacing between micro-ramps. The overall flow field was examined. Additionally, key parameters such as boundary-layer displacement thickness, momentum thickness and incompressible shape factor were also examined. The computational results predicted the effects of the microramps well, including the trends for the impact that the devices had on the shock boundary layer interaction. However, computing the shock boundary layer interaction itself proved to be problematic since the calculations predicted more pronounced adverse effects on the boundary layer due to the shock than were seen in the experiment

Dark interlayer plasmons in colloidal gold nanoparticle bi- and few-layers

We demonstrate the excitation of dark plasmon modes with linearly polarized light at normal incidence in self-assembled layers of gold nanoparticles. Because of field retardation, the incident light field induces plasmonic dipoles that are parallel within each layer but antiparallel between the layers, resulting in a vanishing net dipole moment. Using microabsorbance spectroscopy we measured a pronounced absorbance peak and reflectance dip at 1.5 eV for bi- and trilayers of gold nanoparticles with a diameter of 46 nm and 2 nm interparticle gap size. The excitations were identified as dark interlayer plasmons by finite-difference time-domain simulations. The dark plasmon modes are predicted to evolve into standing waves when further increasing the layer number, which leads to 90% transmittance of the incident light through the nanoparticle film. Our approach is easy to implement and paves the way for large-area coatings with tunable plasmon resonance

Chiral selectivity of polyglycerol-based amphiphiles incorporating different aromatic cores

Customized polyglycerol-based surfactants incorporating different aromatic cores are used to isolate and suspend carbon nanotubes in water. Different cores yield suspension with distinct chiral species distribution. Increasing the number of the phenyl rings connecting head and tail, the dispersion of the semiconducting species becomes sharper toward the nanotubes with bigger family index

a Raman scattering study

The longitudinal optical phonon of metallic nanotubes shifts by 23 cm−1 to lower energies when the nanotubes are deposited from a solution onto a substrate. The linewidth increases by 13 cm−1. The changes are explained in terms of shifts in the Fermi energy that influence the Kohn anomaly in the longitudinal optical phonon branch in metallic nanotubes. Using in situ electrochemical Raman measurements we show that the Fermi energy is 0.16 eV below its intrinsic value in metallic nanotubes in solution. Our results impact the application of Raman spectroscopy to distinguish between metallic and semiconducting tubes by examining the high-energy mode line shape

Direct optical excitation of dark plasmons for hot electron generation

An ideal plasmonic system for hot-electron generation allows the optical excitation of plasmons, limits radiation losses, exhibits strong non-radiative electron damping, and is made from scalable and cost-effective materials. Here we demonstrate the optical excitation of dark interlayer plasmons in bilayers of colloidal gold nanoparticles. This excitation is created by an antiparallel orientation of the dipole moments in the nanoparticle layers; it is expected to exhibit strongly reduced radiative damping. Despite the vanishing dipole moment, an incoming electromagnetic wave that is propagating normal to the surface will excite the dark mode due to field retardation. We observe a strong peak in the absorption spectrum of a colloidal gold bilayer (nanoparticle diameter = 46 nm); this peak is absent for a nanoparticle monolayer. The full width at half maximum of the dark mode is 230 meV for an ideal nanoparticle crystal and 320 meV for the structure produced by self-assembly out of solution. The position and width of the dark plasmon are efficiently tailored by the interparticle distance within the layer, nanoparticle size and layer number. We present time-resolved pump and probe experiments of hot-electron generation by bright and dark bilayer nanoparticle modes

Resonant anti-Stokes Raman scattering in single-walled carbon nanotubes

The dependence of the anti-Stokes Raman intensity on the excitation laser energy in carbon nanotubes is studied by resonant Raman spectroscopy. The complete resonant anti-Stokes and Stokes Raman profiles of the high-energy longitudinal phonon (G+) are obtained for (8,3), (7,5), (6,4), and (6,5) single chirality enriched samples. A high asymmetry between the intensity of the incoming and outgoing resonance is observed in the resonant Raman profiles. In contrast to Stokes scattering, anti-Stokes scattering is more intense at the outgoing resonance then at the incoming resonance. The resonance profiles are explained by a Raman process that includes the phonon- mediated interactions with the dark excitonic state. The chirality dependence of the Raman profiles is due to the variation in the exciton-phonon matrix elements, in agreement with tight-binding calculations. Based on the asymmetric Raman profiles we present the resonance factors for the Stokes /anti-Stokes ratios in carbon nanotubes

In situ functionalization of graphene

While the basal plane of graphene is inert, defects in it are centers of chemical activity. An attractive application of such defects is towards controlled functionalization of graphene with foreign molecules. However, the interaction of the defects with reactive environment, such as ambient, decreases the efficiency of functionalization and makes it poorly controlled. Here, we report a novel approach to generate, monitor with time resolution, and functionalize the defects in situ without ever exposing them to the ambient. The defects are generated by an energetic argon plasma and their properties are monitored using in situ Raman spectroscopy. We find that these defects are functional, very reactive, and strongly change their density from ≈1 × 1013 cm−2 to ≈5 × 1011 cm−2 upon exposure to air. We perform the proof of principle in situ functionalization by generating defects using the argon plasma and functionalizing them in situ using ammonia functional. The functionalization induces the n-doping with a carrier density up to 5 × 1012 cm−2 in graphene and remains stable in ambient conditions

Improving Preschoolers’ Theory of Mind Skills With Mobile Games

This single-case research study examined whether interactive touch screen apps enriched with Theory of Mind (ToM)—enhancing language would promote ToM skills in preschoolers. Six typically developing girls between the ages of 46- and 52- months participated in multiple sessions across the three phases of the study: In baseline, participants played games without voice-overs; in the original treatment phase, participants played games with embedded voice-overs; finally, in the modified treatment phase, participants first played games with embedded voice-overs, then engaged in the researcher-led conversation. All sessions across the three phases concluded with ToM assessments: two measures based on a continuous scale. The first measure included three tasks targeting earlier-developing ToM skills (diverse desires, diverse beliefs, and knowledge access), and the other measure had two tasks that assessed a later-developing ToM competency, false belief understanding. Results showed that apps with ToM-embedded language improved children’s earlier-developing ToM skills (i.e., understanding that people can have different desires, beliefs, and knowledge access) in the phase where an adult-led conversation also followed voice-over-enriched app play. Apps with ToM-embedded language without a follow-up discussion were only marginally effective in promoting the earlier-emerging ToM skills. Across the conditions, apps were not effective in promoting children’s later-developing ToM skills—false belief understanding. Our findings indicate that incorporating ToM conducive language in mobile apps can promote ToM development in preschoolers, especially when supplemented by an adult-led conversation

The role of contextual constraints and chronic expectancies on behavior categorizations and dispositional inferences

The authors examined the roles of chronic expectancies and other contextual information in the dispositional inference process within the domain of ability judgments. Prior to viewing a videotaped performance under either cognitive load or no load, participants in Studies 1 and 2 were given additional information designed to constrain their categorizations of the performance. In Study 2, chronic future-event expectancies also were assessed. Analyses revealed that when under cognitive load, participants' ability inferences were assimilated to the constraint information (Studies 1 and 2) and to chronic expectancies (Study 2). Furthermore, Study 2 analyses revealed that these effects were mediated by participants' behavior categorizations. Evidence suggestive of a proceduralized form of correction for task difficulty (Studies 1 and 2) and an effortful, awareness-based correction for the constraint information and for chronic expectancies also was found. Results are examined in light of recent models of the dispositional inference process