302 research outputs found
Signatures of Massive Black Hole Merger Host Galaxies from Cosmological Simulations I: Unique Galaxy Morphologies in Imaging
Low-frequency gravitational wave experiments such as the Laser Interferometer
Space Antenna and pulsar timing arrays are expected to detect individual
massive black hole (MBH) binaries and mergers. However, secure methods of
identifying the exact host galaxy of each MBH merger amongst the large number
of galaxies in the gravitational wave localization region are currently
lacking. We investigate the distinct morphological signatures of MBH merger
host galaxies, using the Romulus25 cosmological simulation. We produce mock
telescope images of 201 simulated galaxies in Romulus25 hosting recent MBH
mergers, through stellar population synthesis and dust radiative transfer.
Based on comparisons to mass- and redshift-matched control samples, we show
that combining multiple morphological statistics via a linear discriminant
analysis enables identification of the host galaxies of MBH mergers, with
accuracies that increase with chirp mass and mass ratio. For mergers with high
chirp masses (>10^8.2 Msun) and high mass ratios (>0.5), the accuracy of this
approach reaches >80%, and does not decline for at least >1 Gyr after numerical
merger. We argue that these trends arise because the most distinctive
morphological characteristics of MBH merger and binary host galaxies are
prominent classical bulges, rather than relatively short-lived morphological
disturbances from their preceding galaxy mergers. Since these bulges are formed
though major mergers of massive galaxies, they lead to (and become permanent
signposts for) MBH binaries and mergers that have high chirp masses and mass
ratios. Our results suggest that galaxy morphology can aid in identifying the
host galaxies of future MBH binaries and mergers.Comment: 19 pages, 10 figures. Submitted to Ap
Estimating Cognitive Workload in an Interactive Virtual Reality Environment Using EEG
With the recent surge of affordable, high-performance virtual reality (VR) headsets, there is unlimited potential for applications ranging from education, to training, to entertainment, to fitness and beyond. As these interfaces continue to evolve, passive user-state monitoring can play a key role in expanding the immersive VR experience, and tracking activity for user well-being. By recording physiological signals such as the electroencephalogram (EEG) during use of a VR device, the user\u27s interactions in the virtual environment could be adapted in real-time based on the user\u27s cognitive state. Current VR headsets provide a logical, convenient, and unobtrusive framework for mounting EEG sensors. The present study evaluates the feasibility of passively monitoring cognitive workload via EEG while performing a classical n-back task in an interactive VR environment. Data were collected from 15 participants and the spatio-spectral EEG features were analyzed with respect to task performance. The results indicate that scalp measurements of electrical activity can effectively discriminate three workload levels, even after suppression of a co-varying high-frequency activity
A rumble in the dark: signatures of self-interacting dark matter in supermassive black hole dynamics and galaxy density profiles
We explore for the first time the effect of self-interacting dark matter (SIDM) on the dark matter (DM) and baryonic distribution in massive galaxies formed in hydrodynamical cosmological simulations, including explicit baryonic physics treatment. A novel implementation of supermassive black hole (SMBH) formation and evolution is used, as in Tremmel et al., allowing us to explicitly follow the SMBH dynamics at the centre of galaxies. A high SIDM constant cross-section is chosen, σ = 10 cm2gr−1, to amplify differences from CDM models. Milky Way-like galaxies form a shallower DM density profile in SIDM than they do in cold dark matter (CDM), with differences already at 20 kpc scales. This demonstrates that even for the most massive spirals, the effect of SIDM dominates over the adiabatic contraction due to baryons. Strikingly, the dynamics of SMBHs differs in the SIDM and reference CDM case. SMBHs in massive spirals have sunk to the centre of their host galaxy in both the SIDM and CDM run, while in less massive galaxies about 80 per cent of the SMBH population is off-centred in the SIDM case, as opposed to the CDM case in which ∼ 90 per cent of SMBHs have reached their host’s centre. SMBHs are found as far as ∼9 kpc away from the centre of their host SIDM galaxy. This difference is due to the increased dynamical friction time-scale caused by the lower DM density in SIDM galaxies compared to CDM, resulting in core stalling. This pilot work highlights the importance of simulating in a full hydrodynamical context different DM models combined to the SMBH physics to study their influence on galaxy formation
Morphology parameters for intracranial aneurysm rupture risk assessment
OBJECTIVE—The aim of this study is to identify image-based morphological parameters that
correlate with human intracranial aneurysm (IA) rupture.
METHODS—For 45 patients with terminal or sidewall saccular IAs (25 unruptured, 20 ruptured),
three-dimensional geometries were evaluated for a range of morphological parameters. In addition
to five previously studied parameters (aspect ratio, aneurysm size, ellipticity index, nonsphericity
index, and undulation index), we defined three novel parameters incorporating the parent vessel
geometry (vessel angle, aneurysm [inclination] angle, and [aneurysm-to-vessel] size ratio) and
explored their correlation with aneurysm rupture. Parameters were analyzed with a two-tailed
independent Student's t test for significance; significant parameters (P < 0.05) were further examined
by multivariate logistic regression analysis. Additionally, receiver operating characteristic analyses
were performed on each parameter.
RESULTS—Statistically significant differences were found between mean values in ruptured and
unruptured groups for size ratio, undulation index, nonsphericity index, ellipticity index, aneurysm
angle, and aspect ratio. Logistic regression analysis further revealed that size ratio (odds ratio, 1.41;
95% confidence interval, 1.03−1.92) and undulation index (odds ratio, 1.51; 95% confidence interval,
1.08−2.11) had the strongest independent correlation with ruptured IA. From the receiver operating
characteristic analysis, size ratio and aneurysm angle had the highest area under the curve values of
0.83 and 0.85, respectively.
CONCLUSION—Size ratio and aneurysm angle are promising new morphological metrics for IA
rupture risk assessment. Because these parameters account for vessel geometry, they may bridge the
gap between morphological studies and more qualitative location-based studies
Laser-Spectroscopic Investigation of OH-Radical Concentrations in the Exhaust Plane of Jet Engines
Hydroxyl radical (OH) emissions are relevant for oxidation reactions in the post flame chemistry of exhaust gases emitted from jet engines. No direct measurements of OH concentrations are available to date due to the low abundance and the short lifetime of this radical species. The first application of a combined technique based on Raman scattering and laser_induced fluorescence (LIF) spectrometry is presented here for measurements in the exhaust gases of a commercial jet engine operated in a test rig. From the measurements, upper limits for OH concentrations in the exit plane were determined in the range of 90 ppbv for take off and 80 ppbv for ap_idle. The values are significantly below the predictions of model calculations based on HONO and HNO3 in_flight concentration measurements presented recently. Possibilities for further increase of the detection sensitivity for OH are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86750/1/Sick34.pd
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