1,312 research outputs found
Input noise approximation in tracker modeling
The validity of approximating random Gaussian distributed inputs used in human response modeling by sums of discrete sine waves is studied. An ideal rectangular power density spectrum is simulated using both filtered Gaussian white noise and sums-of-discrete sine waves with three different input cutoff frequencies in the same compensatory tracking task. Resulting normalized tracking error and quality operator observations are used to investigate apparent discrepancies in human operator characteristics. Results show that discrete and continuous input tracking data compare favorable when the power in the crossover region is taken into account
Stellar and Quasar Feedback in Concert: Effects on AGN Accretion, Obscuration, and Outflows
We study the interaction of feedback from active galactic nuclei (AGN) and a
multi-phase interstellar medium (ISM), in simulations including explicit
stellar feedback, multi-phase cooling, accretion-disk winds, and Compton
heating. We examine radii ~0.1-100 pc around a black hole (BH), where the
accretion rate onto the BH is determined and where AGN-powered winds and
radiation couple to the ISM. We conclude: (1) The BH accretion rate is
determined by exchange of angular momentum between gas and stars in
gravitational instabilities. This produces accretion rates ~0.03-1 Msun/yr,
sufficient to power luminous AGN. (2) The gas disk in the galactic nucleus
undergoes an initial burst of star formation followed by several Myrs where
stellar feedback suppresses the star formation rate (SFR). (3) AGN winds
injected at small radii with momentum fluxes ~L/c couple efficiently to the ISM
and have dramatic effects on ISM properties within ~100 pc. AGN winds suppress
the nuclear SFR by factors ~10-30 and BH accretion rate by factors ~3-30. They
increase the outflow rate from the nucleus by factors ~10, consistent with
observational evidence for galaxy-scale AGN-driven outflows. (4) With AGN
feedback, the predicted column density distribution to the BH is consistent
with observations. Absent AGN feedback, the BH is isotropically obscured and
there are not enough optically-thin sightlines to explain Type-I AGN. A
'torus-like' geometry arises self-consistently as AGN feedback evacuates gas in
polar regions.Comment: 17 pages, 12 figures, MNRAS accepted (revised to match published
version
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
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
Insulation Sensitivity Analysis for an Optimized Fabric Shelter Off-grid Hybrid Energy System
During military and disaster relief operations, connecting to an established electrical grid is rarely an option. In these situations, camps consisting of poorly insulated fabric shelters are predominantly powered by inefficient diesel generators that require frequent fuel resupply. In order to reduce the fuel demand of these generators, camps may utilize photovoltaic-battery systems. This paper presents an innovative cost-performance model capable of optimizing solar array size, battery backup system, and shelter insulation type to minimize the operating cost of powering a single fabric shelter. Model performance was evaluated using one year of insolation, weather and energy requirement data from a shelter located in Southwest Asia. For a shelter with R-4.7 insulation, the model generated an optimal system configuration consisting of a 251 m2 solar array and an 86 kWh lithium-ion battery. Over one year, this system would reduce the fuel consumption by 97% and save $1.1 million, including system purchase price, compared to a diesel generator. The results of the case study analysis demonstrate the model’s unique capability to optimize photovoltaic-battery system size and shelter insulation material in order to minimize annual operating costs
Black Holes on FIRE: Stellar Feedback Limits Early Feeding of Galactic Nuclei
We introduce massive black holes (BHs) in the Feedback In Realistic
Environments project and perform high-resolution cosmological hydrodynamic
simulations of quasar-mass halos () down to . These simulations model stellar
feedback by supernovae, stellar winds, and radiation, and BH growth using a
gravitational torque-based prescription tied to resolved properties of galactic
nuclei. We do not include BH feedback. We show that early BH growth occurs
through short (Myr) accretion episodes that can reach or even
exceed the Eddington rate. In this regime, BH growth is limited by bursty
stellar feedback continuously evacuating gas from galactic nuclei, and BHs
remain under-massive relative to the local -
relation. BH growth is more efficient at later times, when the nuclear stellar
potential retains a significant gas reservoir, star formation becomes less
bursty, and galaxies settle into a more ordered state, with BHs rapidly
converging onto the scaling relation when the host reaches . Our results are not sensitive to the details of the
accretion model so long as BH growth is tied to the gas content within pc of the BH. Our simulations imply that bursty stellar feedback has
strong implications for BH and AGN demographics, especially in the early
Universe and for low-mass galaxies.Comment: 5 pages, 3 figures, submitted to MNRA
Cost Analysis of Optimized Islanded Energy Systems in a Dispersed Air Base Conflict
The United States Air Force has implemented a dispersed air base strategy to enhance mission effectiveness for near-peer conflicts. Asset dispersal places many smaller bases across a wide geographic area, which increases resupply requirements and logistical complexity. Hybrid energy systems reduce resupply requirements through sustainable, off-grid energy production. This paper presents a novel hybrid energy renewable delivery system (HERDS) model capable of (1) selecting the optimal hybrid energy system design that meets demand at the lowest net present cost and (2) optimizing the delivery of the selected system using existing Air Force cargo aircraft. The novelty of the model’s capabilities is displayed using Clark Air Base, Philippines as a case study. The HERDS model selected an optimal configuration consisting of a 676-kW photovoltaic array, an 1846-kWh battery system, and a 200-kW generator. This hybrid energy system predicts a 54% reduction in cost and an 88% reduction in fuel usage, as compared to the baseline Air Force system. The HERDS model is expected to support planners in their ongoing efforts to construct cost-effective sites that minimize the transport and logistic requirements associated with remote installations. Additionally, the results of this paper may be appropriate for broader civilian applications
A Deep Learning Approach to Galaxy Cluster X-ray Masses
We present a machine-learning approach for estimating galaxy cluster masses
from Chandra mock images. We utilize a Convolutional Neural Network (CNN), a
deep machine learning tool commonly used in image recognition tasks. The CNN is
trained and tested on our sample of 7,896 Chandra X-ray mock observations,
which are based on 329 massive clusters from the IllustrisTNG simulation. Our
CNN learns from a low resolution spatial distribution of photon counts and does
not use spectral information. Despite our simplifying assumption to neglect
spectral information, the resulting mass values estimated by the CNN exhibit
small bias in comparison to the true masses of the simulated clusters (-0.02
dex) and reproduce the cluster masses with low intrinsic scatter, 8% in our
best fold and 12% averaging over all. In contrast, a more standard core-excised
luminosity method achieves 15-18% scatter. We interpret the results with an
approach inspired by Google DeepDream and find that the CNN ignores the central
regions of clusters, which are known to have high scatter with mass.Comment: 10 pages, 6 figures, accepted for publication in The Astrophysical
Journa
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