4,909 research outputs found
A case for inherent geometric and geodetic accuracy in remotely sensed VNIR and SWIR imaging products
Significant aberrations can occur in acquired images which, unless compensated on board the spacecraft, can seriously impair throughput and timeliness for typical Earth observation missions. Conceptual compensations options are advanced to enable acquisition of images with inherent geometric and geodetic accuracy. Research needs are identified which, when implemented, can provide inherently accurate images. Agressive pursuit of these research needs is recommended
Group study of an 'undercover' test for visuospatial neglect: Invisible cancellation can reveal more neglect than standard cancellation
Visual neglect is a relatively common deficit after brain damage, particularly strokes. Cancellation tests provide standard clinical measures of neglect severity and deficits in daily life. A recent single-case study introduced a new variation on standard cancellation. Instead of making a visible mark on each target found, the patient made invisible marks (recorded with carbon paper underneath, for later scoring). Such invisible cancellation was found to reveal more neglect than cancellation with visible marks. Here we test the generality of this. Twenty three successive cases with suspected neglect each performed cancellation with visible or invisible marks. Neglect of contralesional targets was more pronounced with invisible marks. Indeed, about half of the patients only showed neglect in this version. For cases showing more neglect with invisible marks, stronger neglect of contralesional targets correlated with more revisits to ipsilesional targets for making additional invisible marks upon them. These results indicate that cancellation with invisible marks can reveal more neglect than standard cancellation with visible marks, while still providing a practical bedside test. Our observations may be consistent with recent proposals that demands on spatial working memory (required to keep track of previously found items only when marked invisibly) can exacerbate spatial neglect
Audiovisual temporal correspondence modulates human multisensory superior temporal sulcus plus primary sensory cortices
The brain should integrate related but not unrelated information from different senses. Temporal patterning of inputs to different modalities may provide critical information about whether those inputs are related or not. We studied effects of temporal correspondence between auditory and visual streams on human brain activity with functional magnetic resonance imaging ( fMRI). Streams of visual flashes with irregularly jittered, arrhythmic timing could appear on right or left, with or without a stream of auditory tones that coincided perfectly when present ( highly unlikely by chance), were noncoincident with vision ( different erratic, arrhythmic pattern with same temporal statistics), or an auditory stream appeared alone. fMRI revealed blood oxygenation level-dependent ( BOLD) increases in multisensory superior temporal sulcus (mSTS), contralateral to a visual stream when coincident with an auditory stream, and BOLD decreases for noncoincidence relative to unisensory baselines. Contralateral primary visual cortex and auditory cortex were also affected by audiovisual temporal correspondence or noncorrespondence, as confirmed in individuals. Connectivity analyses indicated enhanced influence from mSTS on primary sensory areas, rather than vice versa, during audiovisual correspondence. Temporal correspondence between auditory and visual streams affects a network of both multisensory ( mSTS) and sensory-specific areas in humans, including even primary visual and auditory cortex, with stronger responses for corresponding and thus related audiovisual inputs
An earth pole-sitter using hybrid propulsion
In this paper we investigate optimal pole-sitter orbits using hybrid solar sail and solar electric propulsion (SEP). A pole-sitter is a spacecraft that is constantly above one of the Earth's poles, by means of a continuous thrust. Optimal orbits, that minimize propellant mass consumption, are found both through a shape-based approach, and solving an optimal control problem, using a direct method based on pseudo-spectral techniques. Both the pure SEP case and the hybrid case are investigated and compared. It is found that the hybrid spacecraft allows consistent savings on propellant mass fraction. Finally, is it shown that for sufficiently long missions (more than 8 years), a hybrid spacecraft, based on mid-term technology, enables a consistent reduction in the launch mass for a given payload, with respect to a pure SEP spacecraft
Inclination-Independent Galaxy Classification
We present a new method to classify galaxies from large surveys like the
Sloan Digital Sky Survey using inclination-corrected concentration,
inclination-corrected location on the color-magnitude diagram, and apparent
axis ratio. Explicitly accounting for inclination tightens the distribution of
each of these parameters and enables simple boundaries to be drawn that
delineate three different galaxy populations: Early-type galaxies, which are
red, highly concentrated, and round; Late-type galaxies, which are blue, have
low concentrations, and are disk dominated; and Intermediate-type galaxies,
which are red, have intermediate concentrations, and have disks. We have
validated our method by comparing to visual classifications of high-quality
imaging data from the Millennium Galaxy Catalogue. The inclination correction
is crucial to unveiling the previously unrecognized Intermediate class.
Intermediate-type galaxies, roughly corresponding to lenticulars and early
spirals, lie on the red sequence. The red sequence is therefore composed of two
distinct morphological types, suggesting that there are two distinct mechanisms
for transiting to the red sequence. We propose that Intermediate-type galaxies
are those that have lost their cold gas via strangulation, while Early-type
galaxies are those that have experienced a major merger that either consumed
their cold gas, or whose merger progenitors were already devoid of cold gas
(the ``dry merger'' scenario).Comment: Accepted for publication in ApJ. 7 pages in emulateap
Mission Control Center - Houston
The Mission Control Center - Houston (MCC-H) was designed to control all NASA manned space flights from the first Gemini rendezvous through the Apollo program. The MCC-H is a three-story building which contains 112,000 square feet, and which required 30 months to implement. It has a capability to control a live mission and a simulation simultaneously, or two simulations simultaneously. This capability was provided by locating duplicate operational areas on separate floors. The facility layout is shown in Figures 1, 2, and 3.
The MCC-H is comprised of five basic systems: the Display/Control System, the Real Time Computer Complex (RTCC), the Communications System, the Command System, and the Simulation, Checkout, and Training System (SCATS). These systems are designed to provide the flight operations team with the necessary real-time data and associated reference data for rapid assessment of mission progress, and for rapid decisions in the event of abnormal or emergency situations. The reference data are the result of the enormous effort that is spent prior to the mission in analyzing every possible contingency situation that may occur, and contains predicted trend data, mission rules and carefully planned, detailed operational procedures for regulating the mission
A log-quadratic relation for predicting supermassive black hole masses from the host bulge Sersic index
We reinvestigate the correlation between black hole mass and bulge
concentration. With an increased galaxy sample, updated estimates of galaxy
distances, black hole masses, and Sersic indices `n' - a measure of
concentration - we perform a least-squares regression analysis to obtain a
relation suitable for the purpose of predicting black hole masses in other
galaxies. In addition to the linear relation, log(M_bh) = 7.81(+/-0.08) +
2.69(+/-0.28)[log(n/3)] with epsilon_(intrin)=0.31 dex, we investigated the
possibility of a higher order M_bh-n relation, finding the second order term in
the best-fitting quadratic relation to be inconsistent with a value of zero at
greater than the 99.99% confidence level. The optimal relation is given by
log(M_bh) = 7.98(+/-0.09) + 3.70(+/-0.46)[log(n/3)] -
3.10(+/-0.84)[log(n/3)]^2, with epsilon_(intrin)=0.18 dex and a total absolute
scatter of 0.31 dex. Extrapolating the quadratic relation, it predicts black
holes with masses of ~10^3 M_sun in n=0.5 dwarf elliptical galaxies, compared
to ~10^5 M_sun from the linear relation, and an upper bound on the largest
black hole masses in the local universe, equal to 1.2^{+2.6}_{-0.4}x10^9
M_sun}. In addition, we show that the nuclear star clusters at the centers of
low-luminosity elliptical galaxies follow an extrapolation of the same
quadratic relation. Moreover, we speculate that the merger of two such
nucleated galaxies, accompanied by the merger and runaway collision of their
central star clusters, may result in the late-time formation of some
supermassive black holes. Finally, we predict the existence of, and provide
equations for, a relation between M_bh and the central surface brightness of
the host bulge
The nature of the dwarf population in Abell 868
We present the results of a study of the morphology of the dwarf galaxy
population in Abell 868, a rich, intermediate redshift (z=0.154) cluster which
has a galaxy luminosity function with a steep faint-end slope (alpha=-1.26 +/-
0.05). A statistical background subtraction method is employed to study the B-R
colour distribution of the cluster galaxies. This distribution suggests that
the galaxies contributing to the faint-end of the measured cluster LF can be
split into three populations: dIrrs with B-R<1.4; dEs with 1.4<B-R<2.5; and
contaminating background giant ellipticals (gEs) with B-R>2.5. The remvoal of
the contribution of the background gEs from the counts only marginally lessens
the faint-end slope (alpha=-1.22 +/- 0.16). However, the removal of the
contribution of the dIrrs from the counts produces a flat LF (alpha=-0.91 +/-
0.16). The dEs and the dIrrs have similar spatial distributions within the
cluster except that the dIrrs appear to be totally absent within a central
projected radius of about 0.2 Mpc (Ho=75 km/s /Mpc). The number density of both
dEs and dIrrs appear to fall off beyond a projected radius of about 0.35 Mpc.
We suggest that the dE and dIrr populations of A868 have been associated with
the cluster for similar timescales but that evolutionary processes such as
`galaxy harassment' tend to fade the dIrr galaxies while having much less
effect on the dE galaxies. The harassement would be expected to have the
greatest effect on dwarfs residing in the central parts of the cluster.Comment: 6 pages, 6 figures To be published in The Monthly Notices of the
Royal Astronomical Societ
Two-phase galaxy evolution: the cosmic star formation histories of spheroids and discs
From two very simple axioms: (1) that active galactic nucleus activity traces spheroid formation, and (2) that the cosmic star formation history is dominated by spheroid formation at high redshift, we derive simple expressions for the star formation histories of spheroids and discs, and their implied metal enrichment histories.
Adopting a Baldry–Glazebrook initial mass function we use these relations and apply PEGASE.2 to predict the z = 0 cosmic spectral energy distributions (CSEDs) of spheroids and discs. The model predictions compare favourably to the dust-corrected CSED recently reported by the Galaxy And Mass Assembly team from the far-ultraviolet through to the K band. The model also provides a reasonable fit to the total stellar mass contained within spheroid and disc structures as recently reported by the Millennium Galaxy Catalogue team. Three interesting inferences can be made following our axioms: (1) there is a transition redshift at z ≈ 1.7 at which point the Universe switches from what we refer to as ‘hot mode evolution’ (i.e. spheroid formation/growth via mergers and/or collapse) to what we term ‘cold mode evolution’ (i.e. disc formation/growth via gas infall and minor mergers); (2) there is little or no need for any pre-enrichment prior to the main phase of star formation; (3) in the present Universe mass loss is fairly evenly balanced with star formation holding the integrated stellar mass density close to a constant value.
The model provides a simple prediction of the energy output from spheroid and disc projenitors, the build-up of spheroid and disc mass and the mean metallicity enrichment of the Universe
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