325 research outputs found
Fabrication of slender struts for deployable antennas
A procedure for manufacturing long slender graphite tubing is desired. Such tubing has considerable application in truss supported spacecraft applications. The motivation for the selection of the tubing size developed in this program is for use as struts in a NASA, Langley Research Center truss supported antenna concept. The manufacturing procedure uses the LMSC vertical winding machine. A procedure for fabricating graphite epoxy tubing with an aluminum foil inner and outer wrap was also developed. The aluminum foil provides a vapor barrier, significantly improves the thermal conductivity, and provides an excellent thermal control surface
Seamless metal-clad fiber-reinforced organic matrix composite structures and process for their manufacture
A metallic outer sleeve is provided which is capable of enveloping a hollow metallic inner member having continuous reinforcing fibers attached to the distal end thereof. The inner member is then introduced into outer sleeve until inner member is completely enveloped by outer sleeve. A liquid matrix member is then injected into space between inner member and outer sleeve. A pressurized heat transfer medium is flowed through the inside of inner member, thereby forming a fiber reinforced matrix composite material. The wall thicknesses of both inner member and outer sleeve are then reduced to the appropriate size by chemical etching, to adjust the thermal expansion coefficient of the metal-clad composite structure to the desired value. thereby forming a fiber reinforced matrix composite material. The wall thicknesses of both inner member and outer sleeve are then reduced to the appropriate size by chemical etching, to adjust the thermal expansion coefficient of the metal-clad composite structure to the desired value. The novelty of this invention resides in the development of a efficient method of producing seamless metal clad fiber reinforced organic matrix composite structures
Development of assembly and joint concepts for erectable space structures
The technology associated with the on-orbit assembly of tetrahedral truss platforms erected of graphite epoxy tapered columns is examined. Associated with the assembly process is the design and fabrication of nine member node joints. Two such joints demonstrating somewhat different technology were designed and fabricated. Two methods of automatic assembly using the node designs were investigated, and the time of assembly of tetrahedral truss structures up to 1 square km in size was estimated. The effect of column and node joint packaging on the Space Shuttle cargo bay is examined. A brief discussion is included of operating cost considerations and the selection of energy sources. Consideration was given to the design assembly machines from 5 m to 20 m. The smaller machines, mounted on the Space Shuttle, are deployable and restowable. They provide a means of demonstrating the capabilities of the concept and of erecting small specialized platforms on relatively short notice
The Dynamics of Galaxy Pairs in a Cosmological Setting
We use the Millennium Simulation, and an abundance-matching framework, to
investigate the dynamical behaviour of galaxy pairs embedded in a cosmological
context. Our main galaxy-pair sample, selected to have separations under 250
kpc/h, consists of over 1.3 million pairs at redshift z = 0, with stellar
masses greater than 10^9 Msun, probing mass ratios down to 1:1000. We use dark
matter halo membership and energy to classify our galaxy pairs. In terms of
halo membership, central-satellite pairs tend to be in isolation (in relation
to external more massive galaxies), are energetically- bound to each other, and
are also weakly-bound to a neighbouring massive galaxy. Satellite-satellite
pairs, instead, inhabit regions in close proximity to a more massive galaxy,
are energetically-unbound, and are often bound to that neighbour. We find that
60% of our paired galaxies are bound to both their companion and to a third
external object. Moreover, only 9% of our pairs resemble the kind of systems
described by idealised binary merger simulations in complete isolation. In sum,
we demonstrate the importance of properly connecting galaxy pairs to the rest
of the Universe.Comment: 25 pages, 14 figures, accepted by MNRA
What drives galaxy quenching? A deep connection between galaxy kinematics and quenching in the local Universe
We develop a 2D inclined rotating disc model, which we apply to the stellar
velocity maps of 1862 galaxies taken from the MaNGA survey (SDSS public Data
Release 15). We use a random forest classifier to identify the kinematic
parameters that are most connected to galaxy quenching. We find that kinematic
parameters that relate predominantly to the disc (such as the mean rotational
velocity) and parameters that characterise whether a galaxy is rotation- or
dispersion-dominated (such as the ratio of rotational velocity to velocity
dispersion) are not fundamentally linked to the quenching of star formation.
Instead, we find overwhelmingly that it is the absolute level of velocity
dispersion (a property that relates primarily to a galaxy's bulge/spheroidal
component) that is most important for separating star forming and quenched
galaxies. Furthermore, a partial correlation analysis shows that many commonly
discussed correlations between galaxy properties and quenching are spurious,
and that the fundamental correlation is between quenching and velocity
dispersion. In particular, we find that at fixed velocity dispersion, there is
only a very weak dependence of quenching on the disc properties, whereby more
discy galaxies are slightly more likely to be forming stars. By invoking the
tight relationship between black hole mass and velocity dispersion, and noting
that black hole mass traces the total energy released by AGN, we argue that
these data support a scenario in which quenching occurs by preventive feedback
from AGN. The kinematic measurements from this work are publicly available
Mapping galaxy encounters in numerical simulations: The spatial extent of induced star formation
We employ a suite of 75 simulations of galaxies in idealised major mergers
(stellar mass ratio ~2.5:1), with a wide range of orbital parameters, to
investigate the spatial extent of interaction-induced star formation. Although
the total star formation in galaxy encounters is generally elevated relative to
isolated galaxies, we find that this elevation is a combination of intense
enhancements within the central kpc and moderately suppressed activity at large
galacto-centric radii. The radial dependence of the star formation enhancement
is stronger in the less massive galaxy than in the primary, and is also more
pronounced in mergers of more closely aligned disc spin orientations.
Conversely, these trends are almost entirely independent of the encounter's
impact parameter and orbital eccentricity. Our predictions of the radial
dependence of triggered star formation, and specifically the suppression of
star formation beyond kph-scales, will be testable with the next generation of
integral-field spectroscopic surveys.Comment: 12 pages, 8 figures, accepted by MNRA
Bulge mass is king: The dominant role of the bulge in determining the fraction of passive galaxies in the Sloan Digital Sky Survey
We investigate the origin of galaxy bimodality by quantifying the relative
role of intrinsic and environmental drivers to the cessation (or `quenching')
of star formation in over half a million local Sloan Digital Sky Survey (SDSS)
galaxies. Our sample contains a wide variety of galaxies at z=0.02-0.2, with
stellar masses of 8 < log(M*/M_sun) < 12, spanning the entire morphological
range from pure disks to spheroids, and over four orders of magnitude in local
galaxy density and halo mass. We utilise published star formation rates and add
to this recent GIM2D photometric and stellar mass bulge + disk decompositions
from our group. We find that the passive fraction of galaxies increases steeply
with stellar mass, halo mass, and bulge mass, with a less steep dependence on
local galaxy density and bulge-to-total stellar mass ratio (B/T). At fixed
internal properties, we find that central and satellite galaxies have different
passive fraction relationships. For centrals, we conclude that there is less
variation in the passive fraction at a fixed bulge mass, than for any other
variable, including total stellar mass, halo mass, and B/T. This implies that
the quenching mechanism must be most tightly coupled to the bulge. We argue
that radio-mode AGN feedback offers the most plausible explanation of the
observed trends.Comment: Accepted to MNRAS. 32 pages, 27 figures. [This version is virtually
identical to v1
AGN have Underweight Black Holes and Reach Eddington
Eddington outflows probably regulate the growth of supermassive black holes
(SMBH) in AGN. I show that effect of the Rayleigh--Taylor instability on these
outflows means that SMBH masses are likely to be a factor of a few below the relation in AGN. This agrees with the suggestion by Batcheldor (2010)
that the relation defines an upper limit to the black hole mass. I
further argue that observed AGN black holes must spend much of their lives
accreting at the Eddington rate. This is already suggested by the low observed
AGN fraction amongst all galaxies despite the need to grow to the masses
required by the Soltan relation, and is reinforced by the suggested low SMBH
masses. Most importantly, this is the simplest explanation of the recent
discovery by Tombesi et al (2010a, b) of the widespread incidence of massive
ultrafast X--ray outflows in a large sample of AGN.Comment: MNRAS, in pres
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