174,001 research outputs found
Emissivity coatings for low-temperature space radiators Quarterly progress report no. 1, 1 Jul. - 30 Sep. 1965
Emissivity coatings for low temperature spacecraft radiator
The existence and detection of optically dark galaxies by 21cm surveys
One explanation for the disparity between Cold Dark Matter (CDM) predictions
of galaxy numbers and observations could be that there are numerous dark
galaxies in the Universe. These galaxies may still contain baryons, but no
stars, and may be detectable in the 21cm line of atomic hydrogen. The results
of surveys for such objects, and simulations that do/do not predict their
existence, are controversial. In this paper we use an analytical model of
galaxy formation, consistent with CDM, to firstly show that dark galaxies are
certainly a prediction of the model. Secondly, we show that objects like
VIRGOHI21, a dark galaxy candidate recently discovered by us, while rare are
predicted by the model. Thirdly, we show that previous 'blind' HI surveys have
placed few constraints on the existence of dark galaxies. This is because they
have either lacked the sensitivity and/or velocity resolution or have not had
the required detailed optical follow up. We look forward to new 21cm blind
surveys (ALFALFA and AGES) using the Arecibo multi-beam instrument which should
find large numbers of dark galaxies if they exist
Responding to accents after experiencing interactive or mediated speech
Very little known is about how speakers learn
about and/or respond to speech experienced
without the possibility for interaction. This paper
reports an experiment which considers the effects
of two kinds of exposure to speech (interactive or
non-interactive mediated) on Scottish English
speakers’ responses to another accent (Southern
British English), for two processing tasks,
phonological awareness and speech production.
Only marginal group effects are found according to
exposure type. The main findings show a
difference between subjects according to exposure
type before exposure, and individual shifts in
responses to speech according to exposure type
Collision Integrals for the Exponential Attractive Potential
Numerical integration calculation of collision integrals for exponential attractive potential of gase
Droplet impact on a thin fluid layer
The initial stages of high-velocity droplet impact on a shallow water layer are described, with special emphasis given to the spray jet mechanics. Four stages of impact are delineated, with appropriate scalings, and the successively more important influence of the base is analysed. In particular, there is a finite time before which part of the water in the layer remains under the droplet and after which all of the layer is ejected in the splash jet
Study of fuel cells using storable rocket propellants quarterly report no. 2, 18 may - 17 aug. 1965
Catalysts for Aerozine-50 reforming and nitrogen tetroxide decomposition for development of rocket fuel cells operating on storable propellan
Attack of the Flying Snakes : Formation of Isolated HI Clouds By Fragmentation of Long Streams
The existence of long (> 100 kpc) HI streams and small (< 20 kpc)
free-floating HI clouds is well-known. While the formation of the streams has
been investigated extensively, and the isolated clouds are often purported to
be interaction debris, little research has been done on the formation of
optically dark HI clouds that are not part of a larger stream. One possibility
is that such features result from the fragmentation of more extended streams,
while another idea is that they are primordial, optically dark galaxies. We
test the validity of the fragmentation scenario (via harassment) using
numerical simulations. In order to compare our numerical models with
observations, we present catalogues of both the known long HI streams (42
objects) and free-floating HI clouds suggested as dark galaxy candidates (51
objects). In particular, we investigate whether it is possible to form compact
features with high velocity widths (> 100 km/s), similar to observed clouds
which are otherwise intriguing dark galaxy candidates. We find that producing
such features is possible but extremely unlikely, occurring no more than 0.2%
of the time in our simulations. In contrast, we find that genuine dark galaxies
could be extremely stable to harassment and remain detectable even after 5 Gyr
in the cluster environment (with the important caveat that our simulations only
explore harassment and do not yet include the intracluster medium, heating and
cooling, or star formation). We also discuss the possibility that such objects
could be the progenitors of recently discovered ultra diffuse galaxies.Comment: 46 pages, 27 figures, accepted for publication in MNRA
Spaceborne power systems preference analyses. Volume 2: Decision analysis
Sixteen alternative spaceborne nuclear power system concepts were ranked using multiattribute decision analysis. The purpose of the ranking was to identify promising concepts for further technology development and the issues associated with such development. Four groups were interviewed to obtain preference. The four groups were: safety, systems definition and design, technology assessment, and mission analysis. The highest ranked systems were the heat-pipe thermoelectric systems, heat-pipe Stirling, in-core thermionic, and liquid-metal thermoelectric systems. The next group contained the liquid-metal Stirling, heat-pipe Alkali Metal Thermoelectric Converter (AMTEC), heat-pipe Brayton, liquid-metal out-of-core thermionic, and heat-pipe Rankine systems. The least preferred systems were the liquid-metal AMTEC, heat-pipe thermophotovoltaic, liquid-metal Brayton and Rankine, and gas-cooled Brayton. The three nonheat-pipe technologies selected matched the top three nonheat-pipe systems ranked by this study
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