6,711 research outputs found
Exact results of one-dimensional repulsive Hubbard model
We present analytical results of fundamental properties of one-dimensional
(1D) Hubbard model with a repulsive interaction, ranging from fractional
excitations to universal thermodynamics, interaction-driven criticality,
correlation functions, Contact susceptibilities and quantum cooling. Using the
exact solutions of the Bethe Ansatz equations of the Hubbard model, we first
rigorously calculate the gapless spin and charge excitations, exhibiting exotic
features of fractionalized spinons and holons. Based on the analysis on the
fractional charge and spin excitations, the spin-incoherent Luttinger liquid
with only the charge propagation mode is elucidated by the asymptotic of the
two-point correlation functions with the help of the conformal field theory.
Near quadruple critical point, we then further analytically obtain the
thermodynamical properties, dimensionless ratios and scaling functions near
quantum phase transitions in terms of chemical potential, magnetic field and
interaction. In particular, we determine additivity rules of spin and charge
susceptibilities, and derive explicit forms of thermodynamics of
spin-incoherent Luttinger liquid. Finally, in order to capture deeper insight
into the Mott insulator and interaction driven criticality, we further study
the double occupancy and its associated Contact and Contact susceptibilities
through which an adiabatic cooling scheme upon the quantum criticality is
introduced.Comment: slight changes, 50 pages +18 figures, new analytical result
Spin incoherent liquid and interaction-driven criticality in 1D Hubbard model
A rigorous understanding of the spin incoherent Tomonaga-Luttinger liquid
(TLL), which displays solely a propagating charge mode but not a spin mode, and
the interaction-driven quantum phase transitions in one-dimensional (1D)
systems still remain elusive. In this Letter, we report the universal
properties of spin incoherent TLL and interaction-driven criticality of the 1D
repulsive Hubbard model by means of fractional charge and spin excitations,
asymptotic of correlation functions as well as the lattice Contact. We build up
an essential connection of Contact susceptibilities to the variations of
density, magnetization and entropy with respect to the interaction strength,
providing a rigorous understanding of interaction-driven phase transitions,
Mott insulator and quantum cooling in the model. These relations hold true for
higher dimensional systems.Comment: 4 figures 6 page
Not All Instances Contribute Equally: Instance-adaptive Class Representation Learning for Few-Shot Visual Recognition
Few-shot visual recognition refers to recognize novel visual concepts from a
few labeled instances. Many few-shot visual recognition methods adopt the
metric-based meta-learning paradigm by comparing the query representation with
class representations to predict the category of query instance. However,
current metric-based methods generally treat all instances equally and
consequently often obtain biased class representation, considering not all
instances are equally significant when summarizing the instance-level
representations for the class-level representation. For example, some instances
may contain unrepresentative information, such as too much background and
information of unrelated concepts, which skew the results. To address the above
issues, we propose a novel metric-based meta-learning framework termed
instance-adaptive class representation learning network (ICRL-Net) for few-shot
visual recognition. Specifically, we develop an adaptive instance revaluing
network with the capability to address the biased representation issue when
generating the class representation, by learning and assigning adaptive weights
for different instances according to their relative significance in the support
set of corresponding class. Additionally, we design an improved bilinear
instance representation and incorporate two novel structural losses, i.e.,
intra-class instance clustering loss and inter-class representation
distinguishing loss, to further regulate the instance revaluation process and
refine the class representation. We conduct extensive experiments on four
commonly adopted few-shot benchmarks: miniImageNet, tieredImageNet, CIFAR-FS,
and FC100 datasets. The experimental results compared with the state-of-the-art
approaches demonstrate the superiority of our ICRL-Net
PartSeg: Few-shot Part Segmentation via Part-aware Prompt Learning
In this work, we address the task of few-shot part segmentation, which aims
to segment the different parts of an unseen object using very few labeled
examples. It is found that leveraging the textual space of a powerful
pre-trained image-language model (such as CLIP) can be beneficial in learning
visual features. Therefore, we develop a novel method termed PartSeg for
few-shot part segmentation based on multimodal learning. Specifically, we
design a part-aware prompt learning method to generate part-specific prompts
that enable the CLIP model to better understand the concept of ``part'' and
fully utilize its textual space. Furthermore, since the concept of the same
part under different object categories is general, we establish relationships
between these parts during the prompt learning process. We conduct extensive
experiments on the PartImageNet and PascalPart datasets, and the
experimental results demonstrated that our proposed method achieves
state-of-the-art performance
Is exponential gravity a viable description for the whole cosmological history?
Here we analysed a particular type of gravity, the so-called
exponential gravity which includes an exponential function of the Ricci scalar
in the action. Such term represents a correction to the usual Hilbert-Einstein
action. By using Supernovae Ia, Barionic Acoustic Oscillations, Cosmic
Microwave Background and data, the free parameters of the model are well
constrained. The results show that such corrections to General Relativity
become important at cosmological scales and at late-times, providing an
alternative to the dark energy problem. In addition, the fits do not determine
any significant difference statistically with respect to the CDM
model. Finally, such model is extended to include the inflationary epoch in the
same gravitational Lagrangian. As shown in the paper, the additional terms can
reproduce the inflationary epoch and satisfy the constraints from Planck data.Comment: 20 pages, 6 figures, analysis extended, version published in EPJ
Double Scattering Effect in Transverse Momentum Distribution of Inclusive Production in Photo-Nucleus Collision
In terms of multiple scattering picture, we calculate the double scattering
effect in the transverse momentum distribution of photoproduction.
Applying the generalized factorization theorem, we find that the contributions
from double scattering can be expressed in terms of twist-4 nuclear parton
correlation functions, which is the same as that used to explain the nuclear
dependence in di-jet momentum imbalance and in direct photon production. Using
the known information on the twist-4 parton correlation functions, we estimate
that the double scattering contributes a small suppression in
photoproduction. In the analysis we only take into account the leading order in
the small velocity expansion for the nonperturbative parts related to the
quarkonium.Comment: 23 pages LaTex (9 figures included), to appear in Nucl. Phys.
FedABC: Targeting Fair Competition in Personalized Federated Learning
Federated learning aims to collaboratively train models without accessing
their client's local private data. The data may be Non-IID for different
clients and thus resulting in poor performance. Recently, personalized
federated learning (PFL) has achieved great success in handling Non-IID data by
enforcing regularization in local optimization or improving the model
aggregation scheme on the server. However, most of the PFL approaches do not
take into account the unfair competition issue caused by the imbalanced data
distribution and lack of positive samples for some classes in each client. To
address this issue, we propose a novel and generic PFL framework termed
Federated Averaging via Binary Classification, dubbed FedABC. In particular, we
adopt the ``one-vs-all'' training strategy in each client to alleviate the
unfair competition between classes by constructing a personalized binary
classification problem for each class. This may aggravate the class imbalance
challenge and thus a novel personalized binary classification loss that
incorporates both the under-sampling and hard sample mining strategies is
designed. Extensive experiments are conducted on two popular datasets under
different settings, and the results demonstrate that our FedABC can
significantly outperform the existing counterparts.Comment: 9 pages,5 figure
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