228 research outputs found
Superconductivity and metallic behavior in heavily doped bulk single crystal diamond and graphene/diamond heterostructure
Owing to extremely large band gap of 5.5 eV and high thermal conductivity,
diamond is recognized as the most important semiconductor. The
superconductivity of polycrystalline diamond has always been reported, but
there are also many controversies over the existence of superconductivity in
bulk single crystal diamond and it remains a question whether a metallic state
exists for such a large band gap semiconductor. Herein, we realize a single
crystal superconducting diamond with a Hall carrier concentration larger than
3*1020 cm-3 by co-doped of boron and nitrogen. Furthermore, we show that
diamond can transform from superconducting to metallic state under similar
carrier concentration with tuned carrier mobility degrading from 9.10 cm2 V-1
s-1 or 5.30 cm2 V-1 s-1 to 2.66 cm2 V-1 s-1 or 1.34 cm2 V-1 s-1. Through
integrating graphene on a nitrogen and boron heavily co-doped diamond, the
monolayer graphene can be superconducting through combining Andreev reflection
and exciton mediated superconductivity, which may intrigue more interesting
superconducting behavior of diamond heterostructure
PCR: Proxy-based Contrastive Replay for Online Class-Incremental Continual Learning
Online class-incremental continual learning is a specific task of continual
learning. It aims to continuously learn new classes from data stream and the
samples of data stream are seen only once, which suffers from the catastrophic
forgetting issue, i.e., forgetting historical knowledge of old classes.
Existing replay-based methods effectively alleviate this issue by saving and
replaying part of old data in a proxy-based or contrastive-based replay manner.
Although these two replay manners are effective, the former would incline to
new classes due to class imbalance issues, and the latter is unstable and hard
to converge because of the limited number of samples. In this paper, we conduct
a comprehensive analysis of these two replay manners and find that they can be
complementary. Inspired by this finding, we propose a novel replay-based method
called proxy-based contrastive replay (PCR). The key operation is to replace
the contrastive samples of anchors with corresponding proxies in the
contrastive-based way. It alleviates the phenomenon of catastrophic forgetting
by effectively addressing the imbalance issue, as well as keeps a faster
convergence of the model. We conduct extensive experiments on three real-world
benchmark datasets, and empirical results consistently demonstrate the
superiority of PCR over various state-of-the-art methods.Comment: To appear in CVPR 2023. 10 pages, 8 figures and 3 table
UER: A Heuristic Bias Addressing Approach for Online Continual Learning
Online continual learning aims to continuously train neural networks from a
continuous data stream with a single pass-through data. As the most effective
approach, the rehearsal-based methods replay part of previous data. Commonly
used predictors in existing methods tend to generate biased dot-product logits
that prefer to the classes of current data, which is known as a bias issue and
a phenomenon of forgetting. Many approaches have been proposed to overcome the
forgetting problem by correcting the bias; however, they still need to be
improved in online fashion. In this paper, we try to address the bias issue by
a more straightforward and more efficient method. By decomposing the
dot-product logits into an angle factor and a norm factor, we empirically find
that the bias problem mainly occurs in the angle factor, which can be used to
learn novel knowledge as cosine logits. On the contrary, the norm factor
abandoned by existing methods helps remember historical knowledge. Based on
this observation, we intuitively propose to leverage the norm factor to balance
the new and old knowledge for addressing the bias. To this end, we develop a
heuristic approach called unbias experience replay (UER). UER learns current
samples only by the angle factor and further replays previous samples by both
the norm and angle factors. Extensive experiments on three datasets show that
UER achieves superior performance over various state-of-the-art methods. The
code is in https://github.com/FelixHuiweiLin/UER.Comment: 9 pages, 12 figures, ACM MM202
HPCR: Holistic Proxy-based Contrastive Replay for Online Continual Learning
Online continual learning (OCL) aims to continuously learn new data from a
single pass over the online data stream. It generally suffers from the
catastrophic forgetting issue. Existing replay-based methods effectively
alleviate this issue by replaying part of old data in a proxy-based or
contrastive-based replay manner. In this paper, we conduct a comprehensive
analysis of these two replay manners and find they can be complementary.
Inspired by this finding, we propose a novel replay-based method called
proxy-based contrastive replay (PCR), which replaces anchor-to-sample pairs
with anchor-to-proxy pairs in the contrastive-based loss to alleviate the
phenomenon of forgetting. Based on PCR, we further develop a more advanced
method named holistic proxy-based contrastive replay (HPCR), which consists of
three components. The contrastive component conditionally incorporates
anchor-to-sample pairs to PCR, learning more fine-grained semantic information
with a large training batch. The second is a temperature component that
decouples the temperature coefficient into two parts based on their impacts on
the gradient and sets different values for them to learn more novel knowledge.
The third is a distillation component that constrains the learning process to
keep more historical knowledge. Experiments on four datasets consistently
demonstrate the superiority of HPCR over various state-of-the-art methods.Comment: 18 pages, 11 figure
MetaDiff: Meta-Learning with Conditional Diffusion for Few-Shot Learning
Equipping a deep model the abaility of few-shot learning, i.e., learning
quickly from only few examples, is a core challenge for artificial
intelligence. Gradient-based meta-learning approaches effectively address the
challenge by learning how to learn novel tasks. Its key idea is learning a deep
model in a bi-level optimization manner, where the outer-loop process learns a
shared gradient descent algorithm (i.e., its hyperparameters), while the
inner-loop process leverage it to optimize a task-specific model by using only
few labeled data. Although these existing methods have shown superior
performance, the outer-loop process requires calculating second-order
derivatives along the inner optimization path, which imposes considerable
memory burdens and the risk of vanishing gradients. Drawing inspiration from
recent progress of diffusion models, we find that the inner-loop gradient
descent process can be actually viewed as a reverse process (i.e., denoising)
of diffusion where the target of denoising is model weights but the origin
data. Based on this fact, in this paper, we propose to model the gradient
descent optimizer as a diffusion model and then present a novel
task-conditional diffusion-based meta-learning, called MetaDiff, that
effectively models the optimization process of model weights from Gaussion
noises to target weights in a denoising manner. Thanks to the training
efficiency of diffusion models, our MetaDiff do not need to differentiate
through the inner-loop path such that the memory burdens and the risk of
vanishing gradients can be effectvely alleviated. Experiment results show that
our MetaDiff outperforms the state-of-the-art gradient-based meta-learning
family in few-shot learning tasks.Comment: Accepted by AAAI 202
Direct-Current Generator Based on Dynamic Water-Semiconductor Junction with Polarized Water as Moving Dielectric Medium
There is a rising prospective in harvesting energy from water droplets, as
microscale energy is required for the distributed sensors in the interconnected
human society. However, achieving a sustainable direct-current generating
device from water flow is rarely reported, and the quantum polarization
principle of the water molecular remains uncovered. Herein, we propose a
dynamic water-semiconductor junction with moving water sandwiched between two
semiconductors as a moving dielectric medium, which outputs a sustainable
direct-current voltage of 0.3 V and current of 0.64 uA with low internal
resistance of 390 kilohm. The sustainable direct-current electricity is
originating from the dynamic water polarization process in water-semiconductor
junction, in which water molecules are continuously polarized and depolarized
driven by the mechanical force and Fermi level difference, during the movement
of the water on silicon. We further demonstrated an encapsulated portable
power-generating device with simple structure and continuous direct-current
voltage, which exhibits its promising potential application in the field of
wearable electronic generators
Rabies virus pseudotyped with CVS-N2C glycoprotein as a powerful tool for retrograde neuronal network tracing
Abstract
Background: Efficient viral vectors for mapping and manipulating long projection neuronal circuits are crucial in brain structural and functional studies. The glycoprotein gene-deleted SAD strain rabies virus pseudotyped with the N2C glycoprotein (SAD-RV(ΔG)-N2C(G)) shows high neuro-tropism in cell culture, but its in vivo retrograde infection efficiency and neuro-tropism have not been systematically characterized.
Methods: SAD-RV(ΔG)-N2C(G) and two other broadly used retrograde tracers, SAD-RV(ΔG)-B19(G) and rAAV2-retro were respectively injected into the VTA or DG in C57BL/6 mice. The neuron numbers labeled across the whole brain regions were counted and analyzed by measuring the retrograde infection efficiencies and tropisms of these viral tools. The labeled neural types were analyzed using fluorescence immunohistochemistry or GAD67-GFP mice.
Result: We found that SAD-RV (ΔG)-N2C (G) enhanced the infection efficiency of long-projecting neurons by ~ 10 times but with very similar neuro-tropism, compared with SAD-RV (ΔG)-B19(G). On the other hand, SAD-RV(ΔG)-N2C(G) showed comparable infection efficiency with rAAV2-retro, but had a more restricted diffusion range, and broader tropism to different types and regions of long-projecting neuronal populations.
Conclusions: These results demonstrate that SAD-RV(ΔG)-N2C(G) can serve as an effective retrograde vector for studying neuronal circuits.
Key words:Viral vector, N2C Glycoprotein, Neuronal circuits, Retrograde tracin
- …