253 research outputs found
Satellite Alignment: I. Distribution of Substructures and Their Dependence On Assembly History From N-Body Simulations
Observations have shown that the spatial distribution of satellite galaxies
is not random, but aligned with the major axes of central galaxies. This
alignment is dependent on galaxy properties, such that red satellites are more
strongly aligned than blue satellites. Theoretical work done to interpret this
phenomena has found that it is due to the non-spherical nature of dark matter
halos. However, most studies over-predict the alignment signal under the
assumption that the central galaxy shape follows the shape of the host halo. It
is also not clear whether the color dependence of alignment is due to an
assembly bias or an evolution effect. In this paper we study these problems
using a cosmological N-body simulation. Subhalos are used to trace the
positions of satellite galaxies. It is found that the shape of dark matter
halos are mis-aligned at different radii. If the central galaxy shares the same
shape as the inner host halo, then the alignment effect is weaker and agrees
with observational data. However, it predicts almost no dependence of alignment
on the color of satellite galaxies, though the late accreted subhalos show
stronger alignment with the outer layer of the host halo than their early
accreted counterparts. We find that this is due to the limitation of pure
N-body simulations that satellites galaxies without associated subhalos
('orphan galaxies') are not resolved. These orphan (mostly red) satellites
often reside in the inner region of host halos and should follow the shape of
the host halo in the inner region.Comment: 12 pages, 11 figures, Published on Ap
The Distribution of Satellites Around Central Galaxies in a Cosmological Hydrodynamical Simulation
Observations have shown that the spatial distribution of satellite galaxies
is not random, but rather is aligned with the major axes of central galaxies
(CGs). The strength of the alignment is dependent on the properties of both the
satellites and centrals. Theoretical studies using dissipationless N-body
simulations are limited by their inability to directly predict the shape of
CGs. Using hydrodynamical simulations including gas cooling, star formation,
and feedback, we carry out a study of galaxy alignment and its dependence on
the galaxy properties predicted directly from the simulations.We found that the
observed alignment signal is well produced, as is the color dependence: red
satellites and red centrals both show stronger alignments than their blue
counterparts. The reason for the stronger alignment of red satellites is that
most of them stay in the inner region of the dark matter halo where the shape
of the CG better traces the dark matter distribution. The dependence of
alignment on the color of CGs arises from the halo mass dependence, since the
alignment between the shape of the central stellar component and the inner halo
increases with halo mass. We also find that the alignment of satellites is most
strongly dependent on their metallicity, suggesting that the metallicity of
satellites, rather than color, is a better tracer of galaxy alignment on small
scales. This could be tested in future observational studies.Comment: ApJ Letter, accepted. Four figures, no table. The resolution of Fig 1
was downgraded due to the limitation of file size. Updated to match the
version in pres
Telepath: Understanding Users from a Human Vision Perspective in Large-Scale Recommender Systems
Designing an e-commerce recommender system that serves hundreds of millions
of active users is a daunting challenge. From a human vision perspective,
there're two key factors that affect users' behaviors: items' attractiveness
and their matching degree with users' interests. This paper proposes Telepath,
a vision-based bionic recommender system model, which understands users from
such perspective. Telepath is a combination of a convolutional neural network
(CNN), a recurrent neural network (RNN) and deep neural networks (DNNs). Its
CNN subnetwork simulates the human vision system to extract key visual signals
of items' attractiveness and generate corresponding activations. Its RNN and
DNN subnetworks simulate cerebral cortex to understand users' interest based on
the activations generated from browsed items. In practice, the Telepath model
has been launched to JD's recommender system and advertising system. For one of
the major item recommendation blocks on the JD app, click-through rate (CTR),
gross merchandise value (GMV) and orders have increased 1.59%, 8.16% and 8.71%
respectively. For several major ads publishers of JD demand-side platform, CTR,
GMV and return on investment have increased 6.58%, 61.72% and 65.57%
respectively by the first launch, and further increased 2.95%, 41.75% and
41.37% respectively by the second launch.Comment: 8 pages, 11 figures, 1 tabl
Sub-Nyquist optical pulse sampling for photonic blind source separation
We propose and experimentally demonstrate an optical pulse sampling method for photonic blind source separation. The photonic system processes and separates wideband signals based on the statistical information of the mixed signals, and thus the sampling frequency can be orders of magnitude lower than the bandwidth of the signals. The ultra-fast optical pulses collect samples of the signals at very low sampling rates, and each sample is short enough to maintain the statistical properties of the signals. The low sampling frequency reduces the workloads of the analog to digital conversion and digital signal processing systems. In the meantime, the short pulse sampling maintains the accuracy of the sampled signals, so the statistical properties of the under-sampled signals are the same as the statistical properties of the original signals. The linear power range measurement shows that the sampling system with ultra-narrow optical pulse achieves a 30dB power dynamic range
Sub-Nyquist optical pulse sampling for photonic blind source separation
We propose and experimentally demonstrate an optical pulse sampling method for photonic blind source separation. The photonic system processes and separates wideband signals based on the statistical information of the mixed signals, and thus the sampling frequency can be orders of magnitude lower than the bandwidth of the signals. The ultra-fast optical pulses collect samples of the signals at very low sampling rates, and each sample is short enough to maintain the statistical properties of the signals. The low sampling frequency reduces the workloads of the analog to digital conversion and digital signal processing systems. In the meantime, the short pulse sampling maintains the accuracy of the sampled signals, so the statistical properties of the under-sampled signals are the same as the statistical properties of the original signals. The linear power range measurement shows that the sampling system with ultra-narrow optical pulse achieves a 30dB power dynamic range
Egocentric Audio-Visual Noise Suppression
This paper studies audio-visual suppression for egocentric videos -- where
the speaker is not captured in the video. Instead, potential noise sources are
visible on screen with the camera emulating the off-screen speaker's view of
the outside world. This setting is different from prior work in audio-visual
speech enhancement that relies on lip and facial visuals. In this paper, we
first demonstrate that egocentric visual information is helpful for noise
suppression. We compare object recognition and action classification based
visual feature extractors, and investigate methods to align audio and visual
representations. Then, we examine different fusion strategies for the aligned
features, and locations within the noise suppression model to incorporate
visual information. Experiments demonstrate that visual features are most
helpful when used to generate additive correction masks. Finally, in order to
ensure that the visual features are discriminative with respect to different
noise types, we introduce a multi-task learning framework that jointly
optimizes audio-visual noise suppression and video based acoustic event
detection. This proposed multi-task framework outperforms the audio only
baseline on all metrics, including a 0.16 PESQ improvement. Extensive ablations
reveal the improved performance of the proposed model with multiple active
distractors, over all noise types and across different SNRs.Comment: Under Review at ICASSP 202
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