3,045 research outputs found
Correcting the Sub-optimal Bit Allocation
In this paper, we investigate the problem of bit allocation in Neural Video
Compression (NVC). First, we reveal that a recent bit allocation approach
claimed to be optimal is, in fact, sub-optimal due to its implementation.
Specifically, we find that its sub-optimality lies in the improper application
of semi-amortized variational inference (SAVI) on latent with non-factorized
variational posterior. Then, we show that the corrected version of SAVI on
non-factorized latent requires recursively applying back-propagating through
gradient ascent, based on which we derive the corrected optimal bit allocation
algorithm. Due to the computational in-feasibility of the corrected bit
allocation, we design an efficient approximation to make it practical.
Empirical results show that our proposed correction significantly improves the
incorrect bit allocation in terms of R-D performance and bitrate error, and
outperforms all other bit allocation methods by a large margin. The source code
is provided in the supplementary material
NeRRF: 3D Reconstruction and View Synthesis for Transparent and Specular Objects with Neural Refractive-Reflective Fields
Neural radiance fields (NeRF) have revolutionized the field of image-based
view synthesis. However, NeRF uses straight rays and fails to deal with
complicated light path changes caused by refraction and reflection. This
prevents NeRF from successfully synthesizing transparent or specular objects,
which are ubiquitous in real-world robotics and A/VR applications. In this
paper, we introduce the refractive-reflective field. Taking the object
silhouette as input, we first utilize marching tetrahedra with a progressive
encoding to reconstruct the geometry of non-Lambertian objects and then model
refraction and reflection effects of the object in a unified framework using
Fresnel terms. Meanwhile, to achieve efficient and effective anti-aliasing, we
propose a virtual cone supersampling technique. We benchmark our method on
different shapes, backgrounds and Fresnel terms on both real-world and
synthetic datasets. We also qualitatively and quantitatively benchmark the
rendering results of various editing applications, including material editing,
object replacement/insertion, and environment illumination estimation. Codes
and data are publicly available at https://github.com/dawning77/NeRRF
Query-Policy Misalignment in Preference-Based Reinforcement Learning
Preference-based reinforcement learning (PbRL) provides a natural way to
align RL agents' behavior with human desired outcomes, but is often restrained
by costly human feedback. To improve feedback efficiency, most existing PbRL
methods focus on selecting queries to maximally improve the overall quality of
the reward model, but counter-intuitively, we find that this may not
necessarily lead to improved performance. To unravel this mystery, we identify
a long-neglected issue in the query selection schemes of existing PbRL studies:
Query-Policy Misalignment. We show that the seemingly informative queries
selected to improve the overall quality of reward model actually may not align
with RL agents' interests, thus offering little help on policy learning and
eventually resulting in poor feedback efficiency. We show that this issue can
be effectively addressed via near on-policy query and a specially designed
hybrid experience replay, which together enforce the bidirectional query-policy
alignment. Simple yet elegant, our method can be easily incorporated into
existing approaches by changing only a few lines of code. We showcase in
comprehensive experiments that our method achieves substantial gains in both
human feedback and RL sample efficiency, demonstrating the importance of
addressing query-policy misalignment in PbRL tasks.Comment: The first two authors contributed equall
Conditional Perceptual Quality Preserving Image Compression
We propose conditional perceptual quality, an extension of the perceptual
quality defined in \citet{blau2018perception}, by conditioning it on user
defined information. Specifically, we extend the original perceptual quality
to the conditional perceptual quality
, where is the original image, is the
reconstructed, is side information defined by user and is
divergence. We show that conditional perceptual quality has similar theoretical
properties as rate-distortion-perception trade-off \citep{blau2019rethinking}.
Based on these theoretical results, we propose an optimal framework for
conditional perceptual quality preserving compression. Experimental results
show that our codec successfully maintains high perceptual quality and semantic
quality at all bitrate. Besides, by providing a lowerbound of common randomness
required, we settle the previous arguments on whether randomness should be
incorporated into generator for (conditional) perceptual quality compression.
The source code is provided in supplementary material
Synthesis of hollow poly(aniline-co-pyrrole)-Fe3O4 composite nanospheres and their microwave absorption behavior
Hollow poly(aniline-co-pyrrole)-Fe3O4 (HPAP-Fe3O4) nanospheres with significant electromagnetic properties were successfully prepared via the oxidative polymerization of a mixture of aniline and pyrrole in the presence of a magnetic fluid, using a non-ionic surfactant as a template. The products were characterized by field emission scanning electron microscopy, transmission electron microscopy. Fourier transform infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis and Xray photoelectron spectroscopy. The electromagnetic (EM) and microwave absorbing properties of the nanocomposites were also investigated. The HPAP-Fe3O4 nanospheres exhibit superparamagnetic properties, and the conductivity increases with Fe3O4 content. The reflection loss evaluation based on the absorbing wall theory at 2 mm thickness shows that the reflection loss is reinforced in the frequency range of 0.5-10 GHz by the presence of Fe3O4 nanoparticles, and the frequency of minimum reflection loss shifts to a higher value with increasing Fe3O4 content. HPAP-Fe-06 exhibits the best microwave absorbing property between 0.5 and 10 GHz.ArticleSYNTHETIC METALS. 162(3-4):337-343 (2012)journal articl
Enhancement of baryon-to-meson ratios around jets as a signature of medium response
We present a unique signal of jet-induced medium excitations: the enhancement
of baryon-to-meson ratios around the quenched jets. To illustrate this, we
study jet-particle correlations and the distributions of jet-induced identified
particles with respect to the jet direction in Pb+Pb collisions at the LHC via
a multi-phase transport model. We find a strong enhancement of baryon-to-meson
ratios for associated particles at intermediate transverse momentum around the
triggered jets in Pb+Pb collisions relative to p+p collisions, due to the
coalescence of jet-excited medium partons. Since the lost energy from jets can
diffuse to large angles, such baryon-to-meson-ratio enhancement is more
pronounced for larger relative distance from the jet axis. We argue that the
experimental confirmation of the enhancement of jet-induced baryon-to-meson
ratios around the jets will provide an unambiguous evidence for the medium
response to jet quenching in heavy-ion collisions.Comment: 6 pages, 3 figure
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