214 research outputs found
On the Observability of Optically Thin Coronal Hyperfine Structure Lines
We present Cloudy calculations for the intensity of coronal hyperfine lines
in various environments. We model indirect collisional and radiative
transitions, and quantify the collisionally-excited line emissivity in the
density-temperature phase-space. As an observational aid, we also express the
emissivity in units of the continuum in the 0.4--0.7 keV band. For most
hyperfine lines, knowledge of the X-ray surface brightness and the plasma
temperature is sufficient for rough estimates. We find that the radiation
fields of both Perseus A and Virgo A can enhance the populations of highly
ionized species within 1 kpc. They can also enhance line emissivity within the
cluster core. This could have implications for the interpretation of spectra
around bright AGN. We find the intensity of the Fe XXIV {\lambda}3.068
mm to be about two orders of magnitude fainter than previously thought, at
about 20 {\mu}K. Comparably bright lines may be found in the infrared. Finally,
we find the intensity of hyperfine lines in the Extended Orion Nebula to be
low, due to the shallow sightline. Observations of coronal hyperfine lines will
likely be feasible with the next generation of radio and sub-mm telescopes.Comment: 48 pages; 13 figures; 9 tables; additional images available at the
online journa
Fluid Routing System: Industrial Automation and Simulation
Newport News Shipbuilding (NNS) builds the biggest ships in the world. These ships store and deliver millions of gallons of fluids via computer-controlled networks of pipes, valves, pumps, and tanks. A working, small scale demonstrator of these systems is needed for NNS to use in training and educational demonstrations. The demonstrator needs to allow for functional control of physical parameters by implementing a working instrumentation and control (I&C) system. Core components of this system are a programmable logic controller (PLC), a software development platform, a simulator, and a graphical user interface (GUI) on a human machine interface (HMI).
Project deliverables are the physically built demonstrator, as well as the PLC code with algorithm, HMI, GUI, simulator hardware and all of the applicable connections and driver boards. The demonstrator and all accessory equipment needs to be tabletop size while also being complex enough to show valid path finding techniques of the coded algorithm.
The students went with a simplified yet still multifaceted design based on four tanks, twenty-one electric valves and two pumps. With this degree of complexity, the demonstrator exemplifies how shipboard systems work, while also showing the routing algorithm’s ability to help increase efficiency in a larger network. The project’s simulator can be used to model arbitrarily complex networks, while the project’s routing algorithm can determine ideal paths through these modeled networks. The future of the project could see an interface that allows for more control of physical system that would have the ability to dynamically change due to conditions, such as sensed flow rates and blockages.
The routing algorithm could improve the efficiency of any fluid routing system. It also could allow for the reduction in the level of manual intervention needed during emergency situations, thus reducing the possibility of human error.https://scholarscompass.vcu.edu/capstone/1105/thumbnail.jp
The size of the X-ray emitting region in SWIFT J2127.4+5654 via a broad line region cloud X-ray eclipse
We present results obtained from the time-resolved X-ray spectral analysis of
the Narrow-Line-Seyfert 1 galaxy SWIFT J2127.4+5654 during a ~130 ks XMM-Newton
observation. We reveal large spectral variations, especially during the first
~90 ks of the XMM-Newton exposure. The spectral variability can be attributed
to a partial eclipse of the X-ray source by an intervening low-ionization/cold
absorbing structure (cloud) with column density N_H = 2.0^{+0.2}_{-0.3}e22
cm^-2 which gradually covers and then uncovers the X-ray emitting region with
covering fraction ranging from zero to ~43 per cent. Our analysis enables us to
constrain the size, number density, and location of the absorbing cloud with
good accuracy. We infer a cloud size (diameter) of $D_c < 1.5e13 cm,
corresponding to a density of n_c > 1.5e9 cm^-3 at a distance of R_c > 4.3e16
cm from the central black hole. All of the inferred quantities concur to
identify the absorbing structure with one single cloud associated with the
broad line region of SWIFT J2127.4+5654. We are also able to constrain the
X-ray emitting region size (diameter) to be D_s < 2.3e13 cm which, assuming the
black hole mass estimated from single-epoch optical spectroscopy (1.5e7 M_sun),
translates into D_s < 10.5 gravitational radii (r_g) with larger sizes (in r_g)
being associated with smaller black hole masses, and viceversa. We also confirm
the presence of a relativistically distorted reflection component off the inner
accretion disc giving rise to a broad relativistic Fe K emission line and small
soft excess (small because of the high Galactic column density), supporting the
measurement of an intermediate black hole spin in SWIFT J2127.4+5654 that was
obtained from a previous Suzaku observation.Comment: 8 pages, 7 figures, accepted for publication in MNRA
Processing Energy Modeling for Neural Network Based Image Compression
Nowadays, the compression performance of neural-networkbased image
compression algorithms outperforms state-of-the-art compression approaches such
as JPEG or HEIC-based image compression. Unfortunately, most neural-network
based compression methods are executed on GPUs and consume a high amount of
energy during execution. Therefore, this paper performs an in-depth analysis on
the energy consumption of state-of-the-art neural-network based compression
methods on a GPU and show that the energy consumption of compression networks
can be estimated using the image size with mean estimation errors of less than
7%. Finally, using a correlation analysis, we find that the number of
operations per pixel is the main driving force for energy consumption and
deduce that the network layers up to the second downsampling step are consuming
most energy.Comment: 5 pages, 3 figures, accepted for IEEE International Conference on
Image Processing (ICIP) 202
Broad-band X-ray observation of broad-line radio galaxy 3C 109
We present a study of the central engine in the broad-line radio galaxy 3C
109. To investigate the immediate surrounding of this accreting, supermassive
black hole, we perform a multi-epoch broad-band spectral analysis of a joint
NuSTAR/XMM observation (2017), an archival xmm observation (2005) and the
105-month averaged Swift-BAT data. We are able to clearly separate the spectrum
into a primary continuum, neutral and ionized absorption, and a reflection
component. The photon index of the primary continuum has changed since 2005
(), while
other components remain unchanged, indicative of minimal geometric changes to
the central engine. We constrain the high-energy cutoff of 3C 109
(E\,keV ) for the first time. The
reflector is found to be ionized (log = )
but no relativistic blurring is required by the data. SED analysis confirms the
super-Eddington nature of 3C 109 initially ( 2.09). However,
we do not find any evidence for strong reflection (R = ) or a steep power law index, as expected from a super-Eddington source.
This puts the existing virial mass estimate of 2 M
into question. We explore additional ways of estimating the Eddington ratio,
some of which we find to be inconsistent with our initial SED estimate. We
obtain a new black hole mass estimate of 9.3 M, which
brings all Eddington ratio estimates into agreement and does not require 3C 109
to be super-Eddington.Comment: 13 pages, 8 figure
Reorienting MHD colliding flows: a shock physics mechanism for generating filaments normal to magnetic fields
We present numerical simulations of reorienting oblique shocks that form in the collision layer between magnetized colliding flows. Reorientation aligns post-shock filaments normal to the background magnetic field. We find that reorientation begins with pressure gradients between the collision region and the ambient medium. This drives a lateral expansion of post-shock gas, which reorients the growing filament from the outside-in (i.e. from the flow/ambient boundary, towards the colliding flows axis). The final structures of our simulations resemble polarization observations of filaments in Taurus and Serpens South, as well as the integral-shaped filament in Orion A. Given the ubiquity of colliding flows in the interstellar medium, shock reorientation may be relevant to the formation of filaments normal to magnetic fields
Production of adaptive movement patterns via an insect inspired spiking neural network central pattern generator
Navigation in ever-changing environments requires effective motor behaviours. Many insects have developed adaptive movement patterns which increase their success in achieving navigational goals. A conserved brain area in the insect brain, the Lateral Accessory Lobe, is involved in generating small scale search movements which increase the efficacy of sensory sampling. When the reliability of an essential navigational stimulus is low, searching movements are initiated whereas if the stimulus reliability is high, a targeted steering response is elicited. Thus the network mediates an adaptive switching between motor patterns. We developed Spiking Neural Network models to explore how an insect inspired architecture could generate adaptive movements in relation to changing sensory inputs. The models are able to generate a variety of adaptive movement patterns, the majority of which are of the zig-zagging kind, as seen in a variety of insects. Furthermore, these networks are robust to noise. Because a large spread of network parameters lead to the correct movement dynamics, we conclude that the investigated network architecture is inherently well suited to generating adaptive movement patterns
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