460 research outputs found
Lessons Learned During the Implementation of a Cold Gas Propulsion System for the SunRISE Mission
The SunRISE mission utilizes a two-phase cold gas propulsion system, which provides several advantages over other cold gas systems but experienced challenges during assembly and testing. Since 2020, Georgia Tech Research Corporation (GTRC), Utah State University Space Dynamics Laboratory (SDL), and the Jet Propulsion Laboratory (FPL) have implemented several improvements to the SunRISE propulsion system.
The SunRISE propulsion system leverages an additively manufactured monolithic structure, commercial off-the-shelf (COTS) valves and transducers, and the benign working fluid R-236fa to provide a suitable propulsion system for the SunRise mission. While the GTRC propulsion system had been developed for other missions, the multi-organizational team found and corrected several previously undetected design issues, including filters with highly variable flow performance, solenoid valve drive circuit issues, and inconsistencies in the tank additive manufacturing process that impacted manufacturing yield, thrust consistency, and quality of seals. Leaks in metallic fittings were also identified, and process improvements were put in place to mitigate them. Solenoid valve stiction was the last issue which was mitigated through valve screening and drive circuit adjustments. In this paper, we present lessons learned from the SunRISE propulsion system effort to aid future teams in identifying and addressing similar issues
Ultrafast adsorbate excitation probed with sub-ps resolution XAS
We use a pump-probe scheme to measure the time evolution of the C K-edge
X-ray absorption spectrum (XAS) from CO/Ru(0001) after excitation by an
ultrashort high-intensity optical laser pulse. Due to the short duration of the
X-ray probe pulse and precise control of the pulse delay, the
excitation-induced dynamics during the first ps after the pump can be resolved
with unprecedented time resolution. By comparing with theoretical (DFT)
spectrum calculations we find high excitation of the internal stretch and
frustrated rotation modes occurring within 200 fs of laser excitation, as well
as thermalization of the system in the ps regime. The ~100 fs initial
excitation of these CO vibrational modes is not readily rationalized by
traditional theories of nonadiabatic coupling of adsorbates to metal surfaces,
e. g. electronic frictions based on first order electron-phonon coupling or
transient population of adsorbate resonances. We suggest that coupling of the
adsorbate to non-thermalized electron-hole pairs is responsible for the
ultrafast initial excitation of the modes.Comment: 16 pages, 16 figures. To be published in Physical Review Letters:
https://journals.aps.org/prl/accepted/c1070Y74M8b18063d9cd0221b000631d50ef7a24
Ultrafast Adsorbate Excitation Probed with Subpicosecond-Resolution X-Ray Absorption Spectroscopy
We use a pump-probe scheme to measure the time evolution of the C K-edge x-ray absorption spectrum from CO/Ru(0001) after excitation by an ultrashort high-intensity optical laser pulse. Because of the short duration of the x-ray probe pulse and precise control of the pulse delay, the excitation-induced dynamics during the first picosecond after the pump can be resolved with unprecedented time resolution. By comparing with density functional theory spectrum calculations, we find high excitation of the internal stretch and frustrated rotation modes occurring within 200 fs of laser excitation, as well as thermalization of the system in the picosecond regime. The ∼100 fs initial excitation of these CO vibrational modes is not readily rationalized by traditional theories of nonadiabatic coupling of adsorbates to metal surfaces, e.g., electronic frictions based on first order electron-phonon coupling or transient population of adsorbate resonances. We suggest that coupling of the adsorbate to nonthermalized electron-hole pairs is responsible for the ultrafast initial excitation of the modes
Atom-Specific Probing of Electron Dynamics in an Atomic Adsorbate by Time-Resolved X-Ray Spectroscopy
The electronic excitation occurring on adsorbates at ultrafast timescales from optical lasers that initiate surface chemical reactions is still an open question. Here, we report the ultrafast temporal evolution of x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES) of a simple well-known adsorbate prototype system, namely carbon (C) atoms adsorbed on a nickel [Ni(100)] surface, following intense laser optical pumping at 400 nm. We observe ultrafast (∼100 fs) changes in both XAS and XES showing clear signatures of the formation of a hot electron-hole pair distribution on the adsorbate. This is followed by slower changes on a few picoseconds timescale, shown to be consistent with thermalization of the complete C/Ni system. Density functional theory spectrum simulations support this interpretation
Applying new biotechnologies to the study of occupational cancer--a workshop summary.
As high-throughput technologies in genomics, transcriptomics, and proteomics evolve, questions arise about their use in the assessment of occupational cancers. To address these questions, the National Institute for Occupational Safety and Health, the National Cancer Institute, the National Institute of Environmental Health Sciences, and the American Chemistry Council sponsored a workshop 8-9 May 2002 in Washington, DC. The workshop brought together 80 international specialists whose objective was to identify the means for best exploiting new technologies to enhance methods for laboratory investigation, epidemiologic evaluation, risk assessment, and prevention of occupational cancer. The workshop focused on identifying and interpreting markers for early biologic effect and inherited modifiers of risk
Atom-Specific Probing of Electron Dynamics in an Atomic Adsorbate by Time-Resolved X-ray Spectroscopy
The electronic excitation occurring on adsorbates at ultrafast time scales
from optical lasers that initiate surface chemical reactions is still an open
question. Here, we report the ultrafast temporal evolution of X-ray absorption
spectroscopy (XAS) and X-ray emission spectroscopy (XES) of a simple well known
adsorbate prototype system, namely carbon (C) atoms adsorbed on a nickel
(Ni(100)) surface, following intense laser optical pumping at 400 nm. We
observe ultrafast (~100 fs) changes in both XAS and XES showing clear
signatures of the formation of a hot electron-hole pair distribution on the
adsorbate. This is followed by slower changes on a few ps time scale, shown to
be consistent with thermalization of the complete C/Ni system. Density
functional theory spectrum simulations support this interpretation.Comment: 33 pages, 12 figures. Submitted to Physical Review Letter
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