5,081 research outputs found
Three-dimensional imaging of direct-written photonic structures
Third harmonic generation microscopy has been used to analyze the morphology
of photonic structures created using the femtosecond laser direct-write
technique. Three dimensional waveguide arrays and waveguide-Bragg gratings
written in fused-silica and doped phosphate glass were investigated. A
sensorless adaptive optical system was used to correct the optical aberrations
occurring in the sample and microscope system, which had a lateral resolution
of less than 500 nm. This non-destructive testing method creates volume
reconstructions of photonic devices and reveals details invisible to other
linear microscopy and index profilometry techniques.Comment: 8 pages, 3 color figures, 2 hyper-linked animation
Direct synthesis of hydrogen peroxide in water at ambient temperature
The direct synthesis of hydrogen peroxide (H2O2) from hydrogen and oxygen has been studied using an Au–Pd/TiO2 catalyst. The aim of this study is to understand the balance of synthesis and sequential degradation reactions using an aqueous, stabilizer-free solvent at ambient temperature. The effects of the reaction conditions on the productivity of H2O2 formation and the undesirable hydrogenation and decomposition reactions are investigated. Reaction temperature, solvent composition and reaction time have been studied and indicate that when using water as the solvent the H2O2 decomposition reaction is the predominant degradation pathway, which provides new challenges for catalyst design, which has previously focused on minimizing the subsequent hydrogenation reaction. This is of importance for the application of this catalytic approach for water purification
Simulations of the Mg II k and Ca II 8542 lines from an AlfvÉn Wave-heated Flare Chromosphere
We use radiation hydrodynamic simulations to examine two models of solar flare chromospheric heating:
Alfven wave dissipation and electron beam collisional losses. Both mechanisms are capable of strong chro- ´
mospheric heating, and we show that the distinctive atmospheric evolution in the mid-to-upper chromosphere
results in Mg ii k-line emission that should be observably different between wave-heated and beam-heated simulations.
We also present Ca ii 8542Ă… profiles which are formed slightly deeper in the chromosphere. The
Mg ii k-line profiles from our wave-heated simulation are quite different from those from a beam-heated model
and are more consistent with IRIS observations. The predicted differences between the Ca ii 8542Ă… in the two
models are small. We conclude that careful observational and theoretical study of lines formed in the mid-toupper
chromosphere holds genuine promise for distinguishing between competing models for chromospheric
heating in flares
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