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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Determination of the Thicknesses and Visualization of Ion-Exchange Waveguides in Glasses by Scanning Electron Microscopy

The formation of a surface layer with silver and sodium concentration gradients in K8-grade glasses as a result of ion exchange is demonstrated by scanning electron microscopy (SEM) and electron probe X-ray microanalysis. The silver ions enriched layers with different thicknesses, depending on the duration of the ion exchange from the silver melt, are visualized in the secondary electrons mode. SEM data on the thickness of the silver enriched layer are in good agreement with the results of calculation from the diffusion equation for silver in glass. The dependence of the silver concentration on the diffusion depth is obtained using elemental composition mapping over the glass cross section. The presence of a layer with a silver concentration gradient leads to formation of a gradient waveguide. Discrete peaks in silver concentration profiles, caused by specific features of mutual diffusion of sodium and silver ions in glasses, are found.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Design of a tapered slot waveguide dielectric laser accelerator for sub-relativistic electrons

We propose a dielectric laser accelerator design based on a tapered slot waveguide structure for sub-relativistic electron acceleration. This tapering scheme allows for straightforward tuning of the phase velocity of the accelerating field along the propagation direction, which is necessary for maintaining synchronization with electrons as their velocities increase. Furthermore, the non-resonant nature of this design allows for better tolerance to experimental errors. We also introduce a method to design this continuously tapered structure based on the eikonal approximation, and give a working example based on realistic experimental parameters.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Amplification-free nucleic acid detection with a fluorescence-based waveguide biosensor

Early detection of pathogens using nucleic acids in clinical samples often requires sensitivity at the single-copy level, which currently necessitates time-consuming and expensive nucleic acid amplification. Here, we describe 1) a redesigned flow cell in the shape of a trapezoid-subtracted geometric stadium, and 2) modified experimental procedures that allow for the measurement of sub-attomolar analytes in microliter quantities on a fluorescence-based waveguide biosensor. We verified our instrumental sensitivity with a 200-μL sample of a fluorescent streptavidin conjugate at 100 zM (100 zeptomolar, or 100·10 −21 mol L −1 ) and theoretically explored the applicability of this modified sensing platform in a sandwich immunoassay format using a Langmuir adsorption model. We present assays that demonstrate specific detection of synthetic influenza A DNA (in buffer) and RNA (in saliva) oligonucleotides at the single-copy level (200 μL at 10 zM) using a fluorescent molecular beacon. Lastly, we demonstrate detection of isolated genomic influenza A RNA at a clinically relevant concentration. This work constitutes a sensitivity improvement of over twelve orders of magnitude compared to our previous nucleic acid detection work, illustrating the significant enhancements that can be gained with optimized experimental design.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Gold Ion Beam Milled Gold Zero-Mode Waveguides

Zero-mode waveguides (ZMWs) are widely used in single molecule fluorescence microscopy for their enhancement of emitted light and the ability to study samples at physiological concentrations. ZMWs are typically produced using photo or electron beam lithography. We report a new method of ZMW production using focused ion beam (FIB) milling with gold ions. We demonstrate that ion-milled gold ZMWs with 200 nm apertures exhibit similar plasmon-enhanced fluorescence seen with ZMWs fabricated with traditional techniques such as electron beam lithography.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Kink Waves in Non-isothermal Stratified Solar Waveguides: Effect of the External Magnetic Field

We study the effect of an external magnetic field on the properties of kink waves, propagating along a thin non-isothermal stratified and diverging magnetic flux tube. A wave equation, governing the propagation of kink waves under the adopted model is derived. It is shown that the vertical gradient of temperature introduces a spatially local cut-off frequency ω {sub c}. The vertical distribution of the cut-off frequency is calculated for the reference VAL-C model of the solar atmosphere and for different values of a ratio of external to internal magnetic fields. The results show that the cut-off frequency is negative below the temperature minimum due to the negative temperature gradient. In the chromosphere the cut-off frequency at a given height is smaller for a stronger external magnetic field. For the appropriate range of a ratio B{sub e} / B{sub i} ≈ 0–0.8, the cutoff lies in the range ω{sub c} ≈ 0.003–0.010 s{sup −1} (periods 600 < P{sub c} < 2000 s). The estimate of the cut-off frequency in the transition region is provided as well. In the propagating wave regime, the effective wave energy flux in the non-isothermal diverging flux tubes is the same as in the straight and homogeneous cylindrical waveguides. The obtained wave equation in the limit β = 0 is used to study the kink oscillations of non-isothermal coronal loops. It is found that the gradient of temperature along the coronal loops reduces the frequency ratio of the first overtone to the fundamental mode, i.e., ω{sub 2}/ ω{sub 1} < 2. This reduction grows for a larger ratio of temperature at the loop top to the temperature at the footpoints. Moreover, the effect of reduction is most pronounced for the steeper temperature profiles.

79 ASTRONOMY AND ASTROPHYSICS↗