306 research outputs found
Magnetization Oscillation of a Spinor Condensate Induced by Magnetic Field Gradient
We study the spin mixing dynamics of ultracold spin-1 atoms in a weak
non-uniform magnetic field with field gradient , which can flip the spin
from +1 to -1 so that the magnetization is not any more a
constant. The dynamics of Zeeman component , as well as the
system magnetization , are illustrated for both ferromagnetic and polar
interaction cases in the mean-field theory. We find that the dynamics of system
magnetization can be tuned between the Josephson-like oscillation similar to
the case of double well, and the interesting self-trapping regimes, i.e. the
spin mixing dynamics sustains a spontaneous magnetization. Meanwhile the
dynamics of may be sufficiently suppressed for initially imbalanced
number distribution in the case of polar interaction. A "beat-frequency"
oscillation of the magnetization emerges in the case of balanced initial
distribution for polar interaction, which vanishes for ferromagnetic
interaction.Comment: 6 pages, 5 figures, Phys. Rev. A accepte
Quantum tunneling of magnetization in dipolar spin-1 condensates under external fields
We study the macroscopic quantum tunneling of magnetization of the F=1 spinor
condensate interacting through dipole-dipole interaction with an external
magnetic field applied along the longitudinal or transverse direction. We show
that the ground state energy and the effective magnetic moment of the system
exhibit an interesting macroscopic quantum oscillation phenomenon originating
from the oscillating dependence of thermodynamic properties of the system on
the vacuum angle. Tunneling between two degenerate minima are analyzed by means
of an effective potential method and the periodic instanton method.Comment: 2 figures, accepted PR
Vid2Act: Activate Offline Videos for Visual RL
Pretraining RL models on offline video datasets is a promising way to improve
their training efficiency in online tasks, but challenging due to the inherent
mismatch in tasks, dynamics, and behaviors across domains. A recent model, APV,
sidesteps the accompanied action records in offline datasets and instead
focuses on pretraining a task-irrelevant, action-free world model within the
source domains. We present Vid2Act, a model-based RL method that learns to
transfer valuable action-conditioned dynamics and potentially useful action
demonstrations from offline to online settings. The main idea is to use the
world models not only as simulators for behavior learning but also as tools to
measure the domain relevance for both dynamics representation transfer and
policy transfer. Specifically, we train the world models to generate a set of
time-varying task similarities using a domain-selective knowledge distillation
loss. These similarities serve two purposes: (i) adaptively transferring the
most useful source knowledge to facilitate dynamics learning, and (ii) learning
to replay the most relevant source actions to guide the target policy. We
demonstrate the advantages of Vid2Act over the action-free visual RL
pretraining method in both Meta-World and DeepMind Control Suite
(E)-2-[(4-Chloro-1,3-dimethyl-1H-pyrazol-5-yl)methyleneamino]benzamide
In the title compound, C13H13ClN4O, the dihedral angle between the aromatic rings is 33.47 (9)° and an intramolecular N—H⋯N hydrogen bond generates an S(6) ring. In the crystal, inversion dimers linked by pairs of N—H⋯O hydrogen bonds occur, resulting in R
2
2(8) loops
Unsupervised Object-Centric Voxelization for Dynamic Scene Understanding
Understanding the compositional dynamics of multiple objects in unsupervised
visual environments is challenging, and existing object-centric representation
learning methods often ignore 3D consistency in scene decomposition. We propose
DynaVol, an inverse graphics approach that learns object-centric volumetric
representations in a neural rendering framework. DynaVol maintains time-varying
3D voxel grids that explicitly represent the probability of each spatial
location belonging to different objects, and decouple temporal dynamics and
spatial information by learning a canonical-space deformation field. To
optimize the volumetric features, we embed them into a fully differentiable
neural network, binding them to object-centric global features and then driving
a compositional NeRF for scene reconstruction. DynaVol outperforms existing
methods in novel view synthesis and unsupervised scene decomposition and allows
for the editing of dynamic scenes, such as adding, deleting, replacing objects,
and modifying their trajectories
Model-Based Reinforcement Learning with Isolated Imaginations
World models learn the consequences of actions in vision-based interactive
systems. However, in practical scenarios like autonomous driving,
noncontrollable dynamics that are independent or sparsely dependent on action
signals often exist, making it challenging to learn effective world models. To
address this issue, we propose Iso-Dream++, a model-based reinforcement
learning approach that has two main contributions. First, we optimize the
inverse dynamics to encourage the world model to isolate controllable state
transitions from the mixed spatiotemporal variations of the environment.
Second, we perform policy optimization based on the decoupled latent
imaginations, where we roll out noncontrollable states into the future and
adaptively associate them with the current controllable state. This enables
long-horizon visuomotor control tasks to benefit from isolating mixed dynamics
sources in the wild, such as self-driving cars that can anticipate the movement
of other vehicles, thereby avoiding potential risks. On top of our previous
work, we further consider the sparse dependencies between controllable and
noncontrollable states, address the training collapse problem of state
decoupling, and validate our approach in transfer learning setups. Our
empirical study demonstrates that Iso-Dream++ outperforms existing
reinforcement learning models significantly on CARLA and DeepMind Control.Comment: arXiv admin note: substantial text overlap with arXiv:2205.1381
Collaborative World Models: An Online-Offline Transfer RL Approach
Training visual reinforcement learning (RL) models in offline datasets is
challenging due to overfitting issues in representation learning and
overestimation problems in value function. In this paper, we propose a transfer
learning method called Collaborative World Models (CoWorld) to improve the
performance of visual RL under offline conditions. The core idea is to use an
easy-to-interact, off-the-shelf simulator to train an auxiliary RL model as the
online ``test bed'' for the offline policy learned in the target domain, which
provides a flexible constraint for the value function -- Intuitively, we want
to mitigate the overestimation problem of value functions outside the offline
data distribution without impeding the exploration of actions with potential
advantages. Specifically, CoWorld performs domain-collaborative representation
learning to bridge the gap between online and offline hidden state
distributions. Furthermore, it performs domain-collaborative behavior learning
that enables the source RL agent to provide target-aware value estimation,
allowing for effective offline policy regularization. Experiments show that
CoWorld significantly outperforms existing methods in offline visual control
tasks in DeepMind Control and Meta-World
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