Vertical Federated Graph Neural Network for Recommender System

Conventional recommender systems are required to train the recommendation model using a centralized database. However, due to data privacy concerns, this is often impractical when multi-parties are involved in recommender system training. Federated learning appears as an excellent solution to the data isolation and privacy problem. Recently, Graph neural network (GNN) is becoming a promising approach for federated recommender systems. However, a key challenge is to conduct embedding propagation while preserving the privacy of the graph structure. Few studies have been conducted on the federated GNN-based recommender system. Our study proposes the first vertical federated GNN-based recommender system, called VerFedGNN. We design a framework to transmit: (i) the summation of neighbor embeddings using random projection, and (ii) gradients of public parameter perturbed by ternary quantization mechanism. Empirical studies show that VerFedGNN has competitive prediction accuracy with existing privacy preserving GNN frameworks while enhanced privacy protection for users' interaction information.Comment: 17 pages, 9 figure

PrivMVMF: Privacy-Preserving Multi-View Matrix Factorization for Recommender Systems

With an increasing focus on data privacy, there have been pilot studies on recommender systems in a federated learning (FL) framework, where multiple parties collaboratively train a model without sharing their data. Most of these studies assume that the conventional FL framework can fully protect user privacy. However, there are serious privacy risks in matrix factorization in federated recommender systems based on our study. This paper first provides a rigorous theoretical analysis of the server reconstruction attack in four scenarios in federated recommender systems, followed by comprehensive experiments. The empirical results demonstrate that the FL server could infer users' information with accuracy >80% based on the uploaded gradients from FL nodes. The robustness analysis suggests that our reconstruction attack analysis outperforms the random guess by >30% under Laplace noises with b no larger than 0.5 for all scenarios. Then, the paper proposes a new privacy-preserving framework based on homomorphic encryption, Privacy-Preserving Multi-View Matrix Factorization (PrivMVMF), to enhance user data privacy protection in federated recommender systems. The proposed PrivMVMF is successfully implemented and tested thoroughly with the MovieLens dataset

Ultrafast‐Charging Supercapacitors Based on Corn‐Like Titanium Nitride Nanostructures

Ultrahigh rates realized by ALD‐made TiN. The symmetric full‐cell supercapacitors deliver a typical capacitance of 20.7 F cm(−3) at a scan rate of 1 V s(−1), and retain 4.3 F cm(−3) at high rate of 100 V s(−1). The devices can be charged and discharged for 20 000 cycles with negligible capacitance loss and with an ultralow self‐discharge current (≈1 μA). [Image: see text

Ultrafast-Charging Supercapacitors Based on Corn-Like Titanium Nitride Nanostructures

Ultrahigh rates realized by ALD-made TiN. The symmetric full-cell supercapacitors deliver a typical capacitance of 20.7 F cm−3 at a scan rate of 1 V s−1, and retain 4.3 F cm−3 at high rate of 100 V s−1. The devices can be charged and discharged for 20 000 cycles with negligible capacitance loss and with an ultralow self-discharge current (≈1 μA).ASTAR (Agency for Sci., Tech. and Research, S’pore)MOE (Min. of Education, S’pore)Published versio

Low-Cost High-Performance Solid-State Asymmetric Supercapacitors Based on MnO₂ Nanowires and Fe₂O₃ Nanotubes

A low-cost high-performance solid-state flexible asymmetric supercapacitor (ASC) with α-MnO₂ nanowires and amorphous Fe₂O₃ nanotubes grown on flexible carbon fabric is first designed and fabricated. The assembled novel flexible ASC device with an extended operating voltage window of 1.6 V exhibits excellent performance such as a high energy density of 0.55 mWh/cm³ and good rate capability. The ASC devices can find numerous applications as effective power sources, such as powering color-switchable sun glasses and smart windows

Hydrogenated ZnO Core–Shell Nanocables for Flexible Supercapacitors and Self-Powered Systems

Although MnO₂ is a promising material for supercapacitors (SCs) due to its excellent electrochemical performance and natural abundance, its wide application is limited by poor electrical conductivity. Inspired by our results that the electrochemical activity and electrical conductivity of ZnO nanowires were greatly improved after hydrogenation, we designed and fabricated hydrogenated single-crystal ZnO@amorphous ZnO-doped MnO₂ core–shell nanocables (HZM) on carbon cloth as SC electrodes, showing excellent performance such as areal capacitance of 138.7 mF/cm² and specific capacitance of 1260.9 F/g. Highly flexible all-solid-state SCs were subsequently assembled with these novel HZM electrodes using polyvinyl alcohol/LiCl electrolyte. The working devices achieved very high total areal capacitance of 26 mF/cm² and retained 87.5% of the original capacitance even after 10 000 charge/discharge cycles. An integrated power pack incorporating series-wound SCs and dye-sensitized solar cells was demonstrated for stand-alone self-powered systems

Hydrogenated ZnO Core–Shell Nanocables for Flexible Supercapacitors and Self-Powered Systems

Although MnO₂ is a promising material for supercapacitors (SCs) due to its excellent electrochemical performance and natural abundance, its wide application is limited by poor electrical conductivity. Inspired by our results that the electrochemical activity and electrical conductivity of ZnO nanowires were greatly improved after hydrogenation, we designed and fabricated hydrogenated single-crystal ZnO@amorphous ZnO-doped MnO₂ core–shell nanocables (HZM) on carbon cloth as SC electrodes, showing excellent performance such as areal capacitance of 138.7 mF/cm² and specific capacitance of 1260.9 F/g. Highly flexible all-solid-state SCs were subsequently assembled with these novel HZM electrodes using polyvinyl alcohol/LiCl electrolyte. The working devices achieved very high total areal capacitance of 26 mF/cm² and retained 87.5% of the original capacitance even after 10 000 charge/discharge cycles. An integrated power pack incorporating series-wound SCs and dye-sensitized solar cells was demonstrated for stand-alone self-powered systems

Fiber-Based All-Solid-State Flexible Supercapacitors for Self-Powered Systems

All-solid-state flexible supercapacitors based on a carbon/MnO₂ (C/M) core–shell fiber structure were fabricated with high electrochemical performance such as high rate capability with a scan rate up to 20 V s^–1, high volume capacitance of 2.5 F cm^–3, and an energy density of 2.2 × 10^–4 Wh cm^–3. By integrating with a triboelectric generator, supercapacitors could be charged and power commercial electronic devices, such as a liquid crystal display or a light-emitting-diode, demonstrating feasibility as an efficient storage component and self-powered micro/nanosystems

Fiber-Based All-Solid-State Flexible Supercapacitors for Self-Powered Systems

All-solid-state flexible supercapacitors based on a carbon/MnO₂ (C/M) core–shell fiber structure were fabricated with high electrochemical performance such as high rate capability with a scan rate up to 20 V s^–1, high volume capacitance of 2.5 F cm^–3, and an energy density of 2.2 × 10^–4 Wh cm^–3. By integrating with a triboelectric generator, supercapacitors could be charged and power commercial electronic devices, such as a liquid crystal display or a light-emitting-diode, demonstrating feasibility as an efficient storage component and self-powered micro/nanosystems