2,062 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
An eccentrically perturbed Tonks-Girardeau gas
We investigate the static and dynamic properties of a Tonks-Girardeau gas in
a harmonic trap with an eccentric -perturbation of variable strength.
For this we first find the analytic eigensolution of the single particle
problem and use this solution to calculate the spatial density and energy
profiles of the many particle gas as a function of the strength and position of
the perturbation. We find that the crystal nature of the Tonks state is
reflected in both the lowest occupation number and momentum distribution of the
gas. As a novel application of our model, we study the time evolution of the
the spatial density after a sudden removal of the perturbation. The dynamics
exhibits collapses and revivals of the original density distribution which
occur in units of the trap frequency. This is reminiscent of the Talbot effect
from classical optics.Comment: Comments and suggestions are welcom
Complex diffuse radio emission in the merging PLANCK ESZ cluster Abell 3411
We present VLA radio and Chandra X-ray observations of the merging galaxy
cluster Abell 3411. For the cluster, we find an overall temperature of 6.4 keV
and an X-ray luminosity of 2.8 x 10^{44} erg s^{-1} between 0.5 and 2.0 keV.
The Chandra observation reveals the cluster to be undergoing a merger event.
The VLA observations show the presence of large-scale diffuse emission in the
central region of the cluster, which we classify as a 0.9 Mpc size radio halo.
In addition, a complex region of diffuse, polarized emission is found in the
southeastern outskirts of the cluster, along the projected merger axis of the
system. We classify this region of diffuse emission as a radio relic. The total
extent of this radio relic is 1.9 Mpc. For the combined emission in the cluster
region, we find a radio spectral index of -1.0 \pm 0.1 between 74 MHz and 1.4
GHz. The morphology of the radio relic is peculiar, as the relic is broken up
into five fragments. This suggests that the shock responsible for the relic has
been broken up due to interaction with a large-scale galaxy filament connected
to the cluster or other substructures in the ICM. Alternatively, the complex
morphology reflects the presence of electrons in fossil radio bubbles that are
re-accelerated by a shock.Comment: Accepted for publication in ApJ, 8 pages, 5 figure
Rate of improvement of CF life expectancy exceeds that of general population: observational death registration study
Background: It is unclear why cystic fibrosis (CF) survival has improved. We wished to quantify increases in CF median age of death in the context of general population survival improvement.
Method: Death registration data analysis (US, England & Wales (E&W)â1972â2009).
Results: CF median age of death is higher in US than E&W and greater for males, opposite to that of death from all causes. CF median age of death has increased by 0.543 life years per year (E&W, US combined (95% confidence interval 0.506, 0.582)). The difference in median age at death between those dying from all causes and CF decreased in both territories. CF median age of death for males is greater than for females in both territories. This gap has not narrowed.
Conclusion: The median age of death of people with CF is improving more rapidly than that of the general population in US and E&W
From LTL and Limit-Deterministic B\"uchi Automata to Deterministic Parity Automata
Controller synthesis for general linear temporal logic (LTL) objectives is a
challenging task. The standard approach involves translating the LTL objective
into a deterministic parity automaton (DPA) by means of the Safra-Piterman
construction. One of the challenges is the size of the DPA, which often grows
very fast in practice, and can reach double exponential size in the length of
the LTL formula. In this paper we describe a single exponential translation
from limit-deterministic B\"uchi automata (LDBA) to DPA, and show that it can
be concatenated with a recent efficient translation from LTL to LDBA to yield a
double exponential, \enquote{Safraless} LTL-to-DPA construction. We also report
on an implementation, a comparison with the SPOT library, and performance on
several sets of formulas, including instances from the 2016 SyntComp
competition
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 alternifloraâdominated 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 locationâspecific pore water sulfide concentrations
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