3,557 research outputs found
Score-based Conditional Generation with Fewer Labeled Data by Self-calibrating Classifier Guidance
Score-based Generative Models (SGMs) are a popular family of deep generative
models that achieves leading image generation quality. Earlier studies have
extended SGMs to tackle class-conditional generation by coupling an
unconditional SGM with the guidance of a trained classifier. Nevertheless, such
classifier-guided SGMs do not always achieve accurate conditional generation,
especially when trained with fewer labeled data. We argue that the issue is
rooted in unreliable gradients of the classifier and the inability to fully
utilize unlabeled data during training. We then propose to improve
classifier-guided SGMs by letting the classifier calibrate itself. Our key idea
is to use principles from energy-based models to convert the classifier as
another view of the unconditional SGM. Then, existing loss for the
unconditional SGM can be adopted to calibrate the classifier using both labeled
and unlabeled data. Empirical results validate that the proposed approach
significantly improves the conditional generation quality across different
percentages of labeled data. The improved performance makes the proposed
approach consistently superior to other conditional SGMs when using fewer
labeled data. The results confirm the potential of the proposed approach for
generative modeling with limited labeled data
Orbital Magnetization under an Electric Field and Orbital Magnetoelectric Polarizabilty for a Bilayer Chern System
In the the real space formalism of orbital magnetization (OM) for a Chern
insulator without an external electric field, it is correct to average the
local OM either over the bulk region or over the whole sample. However for a
layered Chern insulator in an external electric field, which is directly
related to the nontrivial nature of orbital magnetoelectric coupling, the role
of boundaries remains ambiguous in this formalism. Based on a bilayer model
with an adjustable Chern number at half filling, we numerically investigate the
OM with the above two different average types under a nonzero perpendicular
electric field. The result shows that in this case, the nonzero Chern number
gives rise to a gauge shift of the OM with the bulk region average, while this
gauge shift is absent for the OM with the whole sample average. This indicates
that only the whole sample average is reliable to calculate the OM under a
nonzero electric field for Chern insulators. On this basis, the orbital
magnetoelectric polarizablity (OMP) and the Chern-Simons orbital
magnetoelectric polarizablity (CSOMP) with the whole sample average are
studied. We also present the relationship between the OMP (CSOMP) and the
response of Berry curvature to the electric field. The stronger the response of
Berry curvature to electric field, the stronger is the OMP (CSOMP). Besides
clarify the calculation methods, our result also provides an effective method
to enhance OMP and CSOMP of materials.Comment: 11 pages, 11 figure
- …