ArCL: Enhancing Contrastive Learning with Augmentation-Robust Representations

Self-Supervised Learning (SSL) is a paradigm that leverages unlabeled data for model training. Empirical studies show that SSL can achieve promising performance in distribution shift scenarios, where the downstream and training distributions differ. However, the theoretical understanding of its transferability remains limited. In this paper, we develop a theoretical framework to analyze the transferability of self-supervised contrastive learning, by investigating the impact of data augmentation on it. Our results reveal that the downstream performance of contrastive learning depends largely on the choice of data augmentation. Moreover, we show that contrastive learning fails to learn domain-invariant features, which limits its transferability. Based on these theoretical insights, we propose a novel method called Augmentation-robust Contrastive Learning (ArCL), which guarantees to learn domain-invariant features and can be easily integrated with existing contrastive learning algorithms. We conduct experiments on several datasets and show that ArCL significantly improves the transferability of contrastive learning.Comment: Accepted by ICLR 202

Simultaneous copper incorporation in core/shell-structured eco-friendly quantum dots for high-efficiency photoelectrochemical hydrogen evolution

The rational design of elemental incorporation in colloidal eco-friendly core/shell quantum dots (QDs) holds the potential to synergistically tailor their electronic band structure and carrier kinetics for applications in forthcoming “green” and high-efficiency solar energy conversion. Herein, we have conducted simultaneous Cu incorporation in both the core and shell regions of environment-benign AgInSe (AISe)/ZnSe core/shell QDs to realize high-efficiency solar-driven photoelectrochemical (PEC) hydrogen evolution. It is verified that Cu incorporation in AISe core enables an upward shift in the position of the band edge relative to the ZnSe shell, which promoted the electron delocalization and extended the lifetime of exciton. Simultaneously, Cu incorporation in the ZnSe shell further results in the trapping of photoinduced holes from AISe core, leading to a decelerated recombination of carriers. The prepared Cu-AISe/ZnSe:Cu QDs with optimized optoelectronic properties have been successfully employed to fabricate QDs-PEC devices, delivering a maximum photocurrent density of 9.1 mA cm−2 under standard AM 1.5 G illumination (100 mW cm−2). Our findings indicate that synchronous elemental incorporation in eco-friendly core/shell QDs is a promising strategy to achieve future high-performance solar-to-hydrogen conversion systems

High Yield and Packing Density Activated Carbon by One-Step Molecular Level Activation of Hydrophilic Pomelo Peel for Supercapacitors

Highly hydrophilic pomelo peel is used as an activated carbon (AC) precursor so that KOH can be homogeneously absorbed within it. Subsequent cryodesiccation retains the original morphology of the pomelo peel and distribution of KOH, which provides the precondition of the one-step molecular level activation. The resulting AC has a high yield of 16.7% of the pomelo peel. The specific surface area of the AC prepared by the one-step molecular activation of cryodesiccated mixture of pomelo peel and KOH (CAC-1) is 1870 m2 g-1, which is higher than that of the AC by the one-step activation of oven-dried mixture (AC-1) and AC by the two-step calcination (AC-2). CAC-1 has the highest specific capacitance of 219 F g-1 at 1 A g-1 among all the three samples. Importantly, the CAC-1 electrode has a high packing density of 0.63 g cm-3. The aqueous supercapacitor based on CAC-1 has a volumetric cell capacitance of 30.7 F cm-3, which corresponds to 123 F cm-3 for a single electrode. When the ionic liquid of 1-ethyl-3-methyl-imidazolium tetrafluoroborate is used as electrolyte, CAC-1 shows maximum specific energy of 40.5 Wh kg-1 and energy density of 25.5 Wh l-1

Two-Dimensional Octuple-Atomic-Layer M2Si2N4 (M = Al, Ga and In) with Long Carrier Lifetime

Bulk III-nitride materials MN (M = Al, Ga and In) and their alloys have been widely used in high-power electronic and optoelectronic devices, but stable two-dimensional (2D) III-nitride materials, except h-BN, have not been realized yet. A new kind of 2D III-nitride material M2Si2N4 (M = Al, Ga and In) is predicted by choosing Si as the appropriate passivation element. The stability, electronic and optical properties of 2D M2Si2N4 materials are studied systematically based on first-principles calculations. The results show that Al2Si2N4 and Ga2Si2N4 are found to be indirect bandgap semiconductors, while In2Si2N4 is a direct bandgap semiconductor. Moreover, Al2Si2N4 and In2Si2N4 have good absorption ability in the visible light region, while Ga2Si2N4 is an ultraviolet-light-absorbing material. Furthermore, the carrier lifetimes of Ga2Si2N4 and In2Si2N4 are as large as 157.89 and 103.99 ns, respectively. All these desirable properties of M2Si2N4 materials make them attractive for applications in electronics and photoelectronics

Simultaneous copper incorporation in core/shell-structured eco-friendly quantum dots for high-efficiency photoelectrochemical hydrogen evolution

The rational design of elemental incorporation in colloidal eco-friendly core/shell quantum dots (QDs) holds the potential to synergistically tailor their electronic band structure and carrier kinetics for applications in forthcoming “green” and high-efficiency solar energy conversion. Herein, we have conducted simultaneous Cu incorporation in both the core and shell regions of environment-benign AgInSe (AISe)/ZnSe core/shell QDs to realize high-efficiency solar-driven photoelectrochemical (PEC) hydrogen evolution. It is verified that Cu incorporation in AISe core enables an upward shift in the position of the band edge relative to the ZnSe shell, which promoted the electron delocalization and extended the lifetime of exciton. Simultaneously, Cu incorporation in the ZnSe shell further results in the trapping of photoinduced holes from AISe core, leading to a decelerated recombination of carriers. The prepared Cu-AISe/ZnSe:Cu QDs with optimized optoelectronic properties have been successfully employed to fabricate QDs-PEC devices, delivering a maximum photocurrent density of 9.1 mA cm−2 under standard AM 1.5 G illumination (100 mW cm−2). Our findings indicate that synchronous elemental incorporation in eco-friendly core/shell QDs is a promising strategy to achieve future high-performance solar-to-hydrogen conversion systems.Validerad;2024;Nivå 2;2024-02-05 (joosat);Funder: Sichuan Science and Technology Program (2021YFH0054, 2023JDGD0011); National Natural Science Foundation of China (22105031); National Key Research and Development Program of China (2019YFE0121600); Fundamental Research Funds for the Central Universities (2019YFB2203400, ZYGX2020J028); 111 Project (B20030); H2020 Framework program through PNRR iNEST and NEST projects; Ca’ Foscari University of Venice;Full text license: CC BY</p