83 research outputs found
Relationship between Intelligence and Criterion Task Set Performance1
↵1 This research was sponsored in part by the Workload and Ergonomics Branch of the Armstrong Aerospace Medical Research Laboratory, United States Air Force, under Contract F33615-85-D-0514 through the Southeastern Center for Electrical Engineering Education (SCEEEHER/86-9). The United States Government is authorized to reproduce and distribute reprints for government purposes notwithstanding any copyright notation hereon. The authors wish to thank Gary Reid for his interest and support in the completion of this projectYeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
Impression creep testing for evaluation of grade 22 ex-service hot reheat piping seam weld
U.S. electric power production is significantly dependent on the operation of coal-fired steam generation units and a large majority of these units are reaching ages over 50+ years with concerns for operating component integrity and remaining life. This paper discusses a small sample testing technique (impression creep) that was used to estimate the remaining life of a hot reheat seam welded piping system that saw about 322,000 hours of operation at nominally 4170 kPa (605psig) and 538°C (1000°F) steam conditions. Two different life assessments using experimental impression creep data are discussed and findings compared to a previous preliminary study of the same piping system using operational data, reported measured piping thickness values (from UT measurements), and published creep rupture data. Impression creep tests were conducted in unaffected base metal, weld metal and the heat-affected zone. Impression creep rates of the various zones showed no creep mismatch. Minimal creep mismatch, proper design, fabrication and operation, combined with proper metallurgy have successfully demonstrated that even low-alloy seam welds can operate 300,000+ hours and still exhibit useful remaining life
Cosmic-Ray Tracks in Astrophysical Ices: Modeling with the Geant4-DNA Monte Carlo Toolkit
Cosmic rays are ubiquitous in interstellar environments, and their bombardment of dust-grain ice mantles is a possible driver for the formation of complex, even prebiotic molecules. Yet, critical data that are essential for accurate modeling of this phenomenon, such as the average radii of cosmic-ray tracks in amorphous solid water (ASW) remain unconstrained. It is shown that cosmic-ray tracks in ASW can be approximated as a cylindrical volume with an average radius that is mostly independent of the initial particle energy. Interactions between energetic ions and both low-density amorphous (LDA) and high-density amorphous (HDA) ice targets are simulated using the Geant4-DNA Monte Carlo toolkit, which allows for tracking secondary electrons down to subexcitation energies in the material. We find the peak track-core radii, r cyl, for LDA and HDA ices to be 9.9 nm and 8.4 nm, respectively-somewhat less than double the value of 5 nm often assumed in astrochemical models. © 2020. The American Astronomical Society. All rights reserved
Detection of Interstellar HCNC and an Investigation of Isocyanopolyyne Chemistry under TMC-1 Conditions
We report an astronomical detection of HCNC for the first time in the
interstellar medium with the Green Bank Telescope toward the TMC-1 molecular
cloud with a minimum significance of . The total column density
and excitation temperature of HCNC are determined to be
cm and K,
respectively, using the MCMC analysis. In addition to HCNC, HCCNC is
distinctly detected whereas no clear detection of HCNC is made. We propose
that the dissociative recombination of the protonated cyanopolyyne,
HCNH, and the protonated isocyanopolyyne, HCNCH, are the main
formation mechanisms for HCNC while its destruction is dominated by
reactions with simple ions and atomic carbon. With the proposed chemical
networks, the observed abundances of HCNC and HCCNC are reproduced
satisfactorily.Comment: Accepted in the Astrophysical Journal Letter
Detection of Two Interstellar Polycyclic Aromatic Hydrocarbons via Spectral Matched Filtering
Ubiquitous unidentified infrared emission bands are seen in many astronomical
sources. Although these bands are widely, if not unanimously, attributed to the
collective emission from polycyclic aromatic hydrocarbons, no single species
from this class has been detected in space. We present the discovery of two -CN
functionalized polycyclic aromatic hydrocarbons, 1- and 2-cyanonaphthalene, in
the interstellar medium aided by spectral matched filtering. Using radio
observations with the Green Bank Telescope, we observe both bi-cyclic ring
molecules in the molecular cloud TMC-1. We discuss potential in situ gas-phase
formation pathways from smaller organic precursor molecules
Searches for Interstellar HCCSH and H₂CCS
A longstanding problem in astrochemistry is the inability of many current models to account for missing sulfur content. Many relatively simple species that may be good candidates to sequester sulfur have not been measured experimentally at the high spectral resolution necessary to enable radioastronomical identification. On the basis of new laboratory data, we report searches for the rotational lines in the microwave, millimeter, and submillimeter regions of the sulfur-containing hydrocarbon HCCSH. This simple species would appear to be a promising candidate for detection in space owing to the large dipole moment along its b-inertial axis, and because the bimolecular reaction between two highly abundant astronomical fragments (CCH and SH radicals) may be rapid. An inspection of multiple line surveys from the centimeter to the far-infrared toward a range of sources from dark clouds to high-mass star-forming regions, however, resulted in nondetections. An analogous search for the lowest-energy isomer, H₂CCS, is presented for comparison, and also resulted in nondetections. Typical upper limits on the abundance of both species relative to hydrogen are 10^(−9)–10^(−10). We thus conclude that neither isomer is a major reservoir of interstellar sulfur in the range of environments studied. Both species may still be viable candidates for detection in other environments or at higher frequencies, providing laboratory frequencies are available
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