742 research outputs found
Automatic assembly design project 1968/9: report of technical survey committee
An Industrial survey has been carried out to
determine the desired features of an automatic
as machine.
A questionnaire was circulated to industry and
the results of the 38% response obtained were
analysed and plotted. From these, conclusions
were drawn as to the industrial requirements of
an assembly machine
Hydrogen Isocyanide in Comet 73P/Schwassmann-Wachmann (Fragment B)
We present a sensitive 3-sigma upper limit of 1.1% for the HNC/HCN abundance
ratio in comet 73P/Schwassmann-Wachmann (Fragment B), obtained on May 10-11,
2006 using Caltech Submillimeter Observatory (CSO). This limit is a factor of
~7 lower than the values measured previously in moderately active comets at 1
AU from the Sun. Comet 73P/Schwassmann-Wachmann was depleted in most volatile
species, except of HCN. The low HNC/HCN ratio thus argues against HNC
production from polymers produced from HCN. However, thermal degradation of
macromolecules, or polymers, produced from ammonia and carbon compounds, such
as acetylene, methane, or ethane appears a plausible explanation for the
observed variations of the HNC/HCN ratio in moderately active comets, including
the very low ratio in comet 73P/Schwassmann-Wachmann reported here. Similar
polymers have been invoked previously to explain anomalous 14N/15N ratios
measured in cometary CN.Comment: 6 pages, 5 figures, 2 table
Abundance Measurements of Titan's Stratospheric HCN, HCN, CH, and CHCN from ALMA Observations
Previous investigations have employed more than 100 close observations of
Titan by the Cassini orbiter to elucidate connections between the production
and distribution of Titan's vast, organic-rich chemical inventory and its
atmospheric dynamics. However, as Titan transitions into northern summer, the
lack of incoming data from the Cassini orbiter presents a potential barrier to
the continued study of seasonal changes in Titan's atmosphere. In our previous
work (Thelen et al., 2018), we demonstrated that the Atacama Large
Millimeter/submillimeter Array (ALMA) is well suited for measurements of
Titan's atmosphere in the stratosphere and lower mesosphere (~100-500 km)
through the use of spatially resolved (beam sizes <1'') flux calibration
observations of Titan. Here, we derive vertical abundance profiles of four of
Titan's trace atmospheric species from the same 3 independent spatial regions
across Titan's disk during the same epoch (2012 to 2015): HCN, HCN,
CH, and CHCN. We find that Titan's minor constituents exhibit large
latitudinal variations, with enhanced abundances at high latitudes compared to
equatorial measurements; this includes CHCN, which eluded previous
detection by Cassini in the stratosphere, and thus spatially resolved abundance
measurements were unattainable. Even over the short 3-year period, vertical
profiles and integrated emission maps of these molecules allow us to observe
temporal changes in Titan's atmospheric circulation during northern spring. Our
derived abundance profiles are comparable to contemporary measurements from
Cassini infrared observations, and we find additional evidence for subsidence
of enriched air onto Titan's south pole during this time period. Continued
observations of Titan with ALMA beyond the summer solstice will enable further
study of how Titan's atmospheric composition and dynamics respond to seasonal
changes.Comment: 15 pages, 16 figures, 2 tables. Accepted for publication in Icarus,
September 201
Ethyl cyanide on Titan: Spectroscopic detection and mapping using ALMA
We report the first spectroscopic detection of ethyl cyanide (CHCN)
in Titan's atmosphere, obtained using spectrally and spatially resolved
observations of multiple emission lines with the Atacama Large
Millimeter/submillimeter array (ALMA). The presence of CHCN in Titan's
ionosphere was previously inferred from Cassini ion mass spectrometry
measurements of CHCNH. Here we report the detection of 27
rotational lines from CHCN (in 19 separate emission features detected
at confidence), in the frequency range 222-241 GHz. Simultaneous
detections of multiple emission lines from HCN, CHCN and CHCCH were
also obtained. In contrast to HCN, CHCN and CHCCH, which peak in
Titan's northern (spring) hemisphere, the emission from CHCN is found
to be concentrated in the southern (autumn) hemisphere, suggesting a distinctly
different chemistry for this species, consistent with a relatively short
chemical lifetime for CHCN. Radiative transfer models show that most of
the CHCN is concentrated at altitudes 300-600 km, suggesting production
predominantly in the mesosphere and above. Vertical column densities are found
to be in the range (2-5) cm.Comment: Published in 2015, ApJL, 800, L1
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