34 research outputs found
Can Synthetic Data Boost the Training of Deep Acoustic Vehicle Counting Networks?
In the design of traffic monitoring solutions for optimizing the urban
mobility infrastructure, acoustic vehicle counting models have received
attention due to their cost effectiveness and energy efficiency. Although deep
learning has proven effective for visual traffic monitoring, its use has not
been thoroughly investigated in the audio domain, likely due to real-world data
scarcity. In this work, we propose a novel approach to acoustic vehicle
counting by developing: i) a traffic noise simulation framework to synthesize
realistic vehicle pass-by events; ii) a strategy to mix synthetic and real data
to train a deep-learning model for traffic counting. The proposed system is
capable of simultaneously counting cars and commercial vehicles driving on a
two-lane road, and identifying their direction of travel under moderate traffic
density conditions. With only 24 hours of labeled real-world traffic noise, we
are able to improve counting accuracy on real-world data from to
for cars and from to for commercial vehicles.Comment: Accepted paper: 2024 IEEE International Conference on Acoustics,
Speech and Signal Processing (ICASSP 2024
The Role of Galactic Winds on Molecular Gas Emission from Galaxy Mergers
We assess the impact of starburst and AGN feedback-driven winds on the CO
emission from galaxy mergers, and, in particular, search for signatures of
these winds in the simulated CO morphologies and emission line profiles. We do
so by combining a 3D non-LTE molecular line radiative transfer code with
smoothed particle hydrodynamics (SPH) simulations of galaxy mergers that
include prescriptions for star formation, black hole growth, a multiphase
interstellar medium (ISM), and the winds associated with star formation and
black hole growth. Our main results are: (1) Galactic winds can drive outflows
of masses ~10^8-10^9 Msun which may be imaged via CO emission line mapping. (2)
AGN feedback-driven winds are able to drive imageable CO outflows for longer
periods of time than starburst-driven winds owing to the greater amount of
energy imparted to the ISM by AGN feedback compared to star formation. (3)
Galactic winds can control the spatial extent of the CO emission in post-merger
galaxies, and may serve as a physical motivation for the sub-kiloparsec scale
CO emission radii observed in local advanced mergers. (4) Secondary emission
peaks at velocities greater than the circular velocity are seen in the CO
emission lines in all models. In models with winds, these high velocity peaks
are seen to preferentially correspond to outflowing gas entrained in winds,
which is not the case in the model without winds. The high velocity peaks seen
in models without winds are typically confined to velocity offsets (from the
systemic) < 1.7 times the circular velocity, whereas the models with AGN
feedback-driven winds can drive high velocity peaks to ~2.5 times the circular
velocity.Comment: Accepted by ApJ; Minor revisions; Resolution tests include
Coagulation of small grains in disks: the influence of residual infall and initial small-grain content
Turbulent coagulation in protoplanetary disks is known to operate on
timescale far shorter than the lifetime of the disk. In the absence of
mechanisms that replenish the small dust grain population, protoplanetary disks
would rapidly lose their continuum opacity-bearing dust. This is inconsistent
with infrared observations of disks around T Tauri stars and Herbig Ae/Be
stars, which are usually optically thick at visual wavelengths and show
signatures of small (a<~ 3um) grains. A plausible replenishing mechanism of
small grains is collisional fragmentation or erosion of large dust aggregates,
which model calculations predict to play an important role in protoplanetary
disks. If optically thick disks are to be seen as proof for ongoing
fragmentation or erosion, then alternative explanations for the existence of
optically thick disks must be studied carefully. In this study we explore two
scenarios. First, we study the effect of residual, low-level infall of matter
onto the disk surface. We find that infall rates as low as 10^{-11} Msun/yr
can, in principle, replenish the small grain population to a level that keeps
the disk marginally optically thick. However, it remains to be seen if the
assumption of such inflow is realistic for star+disk systems at the age of
several Myrs, at which winds and jets are expected to have removed any residual
envelope. In summary, fragmentation or erosion still appear to be the most
promising processes to explain the abundant presence of small grains in old
disks.Comment: 10 pages, 4 figures, A&A in pres
Modeling the Dust Properties of z ~ 6 Quasars with ART^2 -- All-wavelength Radiative Transfer with Adaptive Refinement Tree
The detection of large quantities of dust in z ~ 6 quasars by infrared and
radio surveys presents puzzles for the formation and evolution of dust in these
early systems. Previously (Li et al. 2007), we showed that luminous quasars at
z > 6 can form through hierarchical mergers of gas-rich galaxies. Here, we
calculate the dust properties of simulated quasars and their progenitors using
a three-dimensional Monte Carlo radiative transfer code, ART^2 --
All-wavelength Radiative Transfer with Adaptive Refinement Tree. ART^2
incorporates a radiative equilibrium algorithm for dust emission, an adaptive
grid for inhomogeneous density, a multiphase model for the ISM, and a
supernova-origin dust model. We reproduce the SED and dust properties of SDSS
J1148+5251, and find that the infrared emission are closely associated with the
formation and evolution of the quasar host. The system evolves from a cold to a
warm ULIRG owing to heating and feedback from stars and AGN. Furthermore, the
AGN has significant implications for the interpretation of observation of the
hosts. Our results suggest that vigorous star formation in merging progenitors
is necessary to reproduce the observed dust properties of z~6 quasars,
supporting a merger-driven origin for luminous quasars at high redshifts and
the starburst-to-quasar evolutionary hypothesis. (Abridged)Comment: 26 pages, 22 figures, accepted by ApJ. Version with full resolution
images is available at
http://www.cfa.harvard.edu/~yxli/ARTDUST/astroph0706.3706.pd
ART^2 : Coupling Lyman-alpha Line and Multi-wavelength Continuum Radiative Transfer
Narrow-band Lya line and broad-band continuum have played important roles in
the discovery of high-redshift galaxies in recent years. Hence, it is crucial
to study the radiative transfer of both Lya and continuum photons in the
context of galaxy formation and evolution in order to understand the nature of
distant galaxies. Here, we present a three-dimensional Monte Carlo radiative
transfer code, All-wavelength Radiative Transfer with Adaptive Refinement Tree
(ART^2), which couples Lya line and multi-wavelength continuum, for the study
of panchromatic properties of galaxies and interstellar medium. This code is
based on the original version of Li et al., and features three essential
modules: continuum emission from X-ray to radio, Lya emission from both
recombination and collisional excitation, and ionization of neutral hydrogen.
The coupling of these three modules, together with an adaptive refinement grid,
enables a self-consistent and accurate calculation of the Lya properties. As an
example, we apply ART^2 to a cosmological simulation that includes both star
formation and black hole growth, and study in detail a sample of massive
galaxies at redshifts z=3.1 - 10.2. We find that these galaxies are Lya
emitters (LAEs), whose Lya emission traces the dense gas region, and that their
Lya lines show a shape characteristic of gas inflow. Furthermore, the Lya
properties, including photon escape fraction, emergent luminosity, and
equivalent width, change with time and environment. Our results suggest that
LAEs evolve with redshift, and that early LAEs such as the most distant one
detected at z ~ 8.6 may be dwarf galaxies with a high star formation rate
fueled by infall of cold gas, and a low Lya escape fraction.Comment: 20 pages, 16 figures, accepted for publication in MNRA
US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report
This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in
Dark Matter" held at University of Maryland on March 23-25, 2017.Comment: 102 pages + reference