1,492 research outputs found
Computer considerations for real time simulation of a generalized rotor model
Scaled equations were developed to meet requirements for real time computer simulation of the rotor system research aircraft. These equations form the basis for consideration of both digital and hybrid mechanization for real time simulation. For all digital simulation estimates of the required speed in terms of equivalent operations per second are developed based on the complexity of the equations and the required intergration frame rates. For both conventional hybrid simulation and hybrid simulation using time-shared analog elements the amount of required equipment is estimated along with a consideration of the dynamic errors. Conventional hybrid mechanization using analog simulation of those rotor equations which involve rotor-spin frequencies (this consititutes the bulk of the equations) requires too much analog equipment. Hybrid simulation using time-sharing techniques for the analog elements appears possible with a reasonable amount of analog equipment. All-digital simulation with affordable general-purpose computers is not possible because of speed limitations, but specially configured digital computers do have the required speed and consitute the recommended approach
Fast and Slow Rotators in the Densest Environments: a SWIFT IFS study of the Coma Cluster
We present integral-field spectroscopy of 27 galaxies in the Coma cluster
observed with the Oxford SWIFT spectrograph, exploring the kinematic
morphology-density relationship in a cluster environment richer and denser than
any in the ATLAS3D survey. Our new data enables comparison of the kinematic
morphology relation in three very different clusters (Virgo, Coma and Abell
1689) as well as to the field/group environment. The Coma sample was selected
to match the parent luminosity and ellipticity distributions of the early-type
population within a radius 15' (0.43 Mpc) of the cluster centre, and is limited
to r' = 16 mag (equivalent to M_K = -21.5 mag), sampling one third of that
population. From analysis of the lambda-ellipticity diagram, we find 15+-6% of
early-type galaxies are slow rotators; this is identical to the fraction found
in the field and the average fraction in the Virgo cluster, based on the
ATLAS3D data. It is also identical to the average fraction found recently in
Abell 1689 by D'Eugenio et al.. Thus it appears that the average slow rotator
fraction of early type galaxies remains remarkably constant across many
different environments, spanning five orders of magnitude in galaxy number
density. However, within each cluster the slow rotators are generally found in
regions of higher projected density, possibly as a result of mass segregation
by dynamical friction. These results provide firm constraints on the mechanisms
that produce early-type galaxies: they must maintain a fixed ratio between the
number of fast rotators and slow rotators while also allowing the total
early-type fraction to increase in clusters relative to the field. A complete
survey of Coma, sampling hundreds rather than tens of galaxies, could probe a
more representative volume of Coma and provide significantly stronger
constraints, particularly on how the slow rotator fraction varies at larger
radii.Comment: Accepted for publication in MNRA
The Effect of Fertilization on Biomass and Metabolism in North Carolina Salt Marshes: Modulated by Location-Specific Factors
The resilience of salt marshes to sea level rise depends on vertical accretion through belowground biomass production and sediment deposition to maintain elevation above sea level. Increased nitrogen (N) availability from anthropogenic sources may stimulate aboveground biomass production and sediment deposition and, thus, accretion; however, increased N may also negatively impact marsh accretion by decreasing belowground biomass and increasing net CO2 emissions. A study was conducted in Spartina alterniflora‐dominated salt marshes in North Carolina, USA, to determine how responses to fertilization vary across locations with different physical and chemical characteristics. Pore water residence time, inundation time, and proximity to tidal creeks drove spatial differences in pore water sulfide, ammonium, and dissolved carbon concentrations. Although annual respiration and gross primary production were greater at the creek edge than interior marsh sites, net ecosystem CO2 exchange (NEE) was nearly balanced at all the sites. Fertilization decreased belowground biomass in the interior sites but not on the creek edge. Aboveground biomass, respiration, gross primary production, and net CO2 emissions increased in response to fertilization, but responses were diminished in interior marsh locations with high pore water sulfide. Hourly NEE measured by chambers were similar to hourly NEE observed by a nearby eddy covariance tower, but correcting for inundation depth relative to plant height was critical for accurate extrapolation to annual fluxes. The impact of fertilization on biomass and NEE, and thus marsh resilience, varied across marsh locations depending upon location‐specific pore water sulfide concentrations
The SAMI Galaxy Survey: Unveiling the nature of kinematically offset active galactic nuclei
We have observed two kinematically offset active galactic nuclei (AGN), whose
ionised gas is at a different line-of-sight velocity to their host galaxies,
with the SAMI integral field spectrograph (IFS). One of the galaxies shows gas
kinematics very different to the stellar kinematics, indicating a recent merger
or accretion event. We demonstrate that the star formation associated with this
event was triggered within the last 100 Myr. The other galaxy shows simple disc
rotation in both gas and stellar kinematics, aligned with each other, but in
the central region has signatures of an outflow driven by the AGN. Other than
the outflow, neither galaxy shows any discontinuity in the ionised gas
kinematics at the galaxy's centre. We conclude that in these two cases there is
no direct evidence of the AGN being in a supermassive black hole binary system.
Our study demonstrates that selecting kinematically offset AGN from
single-fibre spectroscopy provides, by definition, samples of kinematically
peculiar objects, but IFS or other data are required to determine their true
nature.Comment: MNRAS accepted. 14 pages, 11 figure
The SAMI Galaxy Survey: Towards a unified dynamical scaling relation for galaxies of all types
We take advantage of the first data from the Sydney-AAO Multi-object Integral
field (SAMI) Galaxy Survey to investigate the relation between the kinematics
of gas and stars, and stellar mass in a comprehensive sample of nearby
galaxies. We find that all 235 objects in our sample, regardless of their
morphology, lie on a tight relation linking stellar mass () to internal
velocity quantified by the parameter, which combines the contribution
of both dispersion () and rotational velocity () to the
dynamical support of a galaxy (). Our
results are independent of the baryonic component from which and
are estimated, as the of stars and gas agree remarkably
well. This represents a significant improvement compared to the canonical
vs. and vs. relations. Not only is no sample
pruning necessary, but also stellar and gas kinematics can be used
simultaneously, as the effect of asymmetric drift is taken into account once
and are combined. Our findings illustrate how the
combination of dispersion and rotational velocities for both gas and stars can
provide us with a single dynamical scaling relation valid for galaxies of all
morphologies across at least the stellar mass range
8.511. Such relation appears to be more general and at
least as tight as any other dynamical scaling relation, representing a unique
tool for investigating the link between galaxy kinematics and baryonic content,
and a less biased comparison with theoretical models.Comment: 6 pages, 4 figures. Accepted for publication in ApJ Letter
The SAMI Galaxy Survey: Gas Streaming and Dynamical M/L in Rotationally Supported Systems
Line-of-sight velocities of gas and stars can constrain dark matter (DM)
within rotationally supported galaxies if they trace circular orbits
extensively. Photometric asymmetries may signify non-circular motions,
requiring spectra with dense spatial coverage. Our integral-field spectroscopy
of 178 galaxies spanned the mass range of the SAMI Galaxy Survey. We derived
circular speed curves (CSCs) of gas and stars from non-parametric Diskfit fits
out to . For 12/14 with measured H I profiles, ionized gas and H I
maximum velocities agreed. We fitted mass-follows-light models to 163 galaxies
by approximating the radial starlight profile as nested, very flattened mass
homeoids viewed as a S\'ersic form. Fitting broad-band SEDs to SDSS images gave
median stellar mass/light 1.7 assuming a Kroupa IMF vs. 2.6 dynamically.
Two-thirds of the dynamical mass/light measures were consistent with
star+remnant IMFs. One-fifth required upscaled starlight to fit, hence
comparable mass of unobserved baryons and/or DM distributed similarly across
the SAMI aperture that came to dominate motions as the starlight CSC declined
rapidly. The rest had mass distributed differently from starlight. Subtracting
fits of S\'ersic profiles to 13 VIKING Z-band images revealed residual weak
bars. Near the bar PA, we assessed m = 2 streaming velocities, and found
deviations usually <30 km/s from the CSC; three showed no deviation. Thus,
asymmetries rarely influenced our CSCs despite co-located shock-indicating,
emission-line flux ratios in more than 2/3.Comment: 21 pages, 15 figures. Accepted to MNRA
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