Privet: A Privacy-Preserving Vertical Federated Learning Service for Gradient Boosted Decision Tables

Vertical federated learning (VFL) has recently emerged as an appealing distributed paradigm empowering multi-party collaboration for training high-quality models over vertically partitioned datasets. Gradient boosting has been popularly adopted in VFL, which builds an ensemble of weak learners (typically decision trees) to achieve promising prediction performance. Recently there have been growing interests in using decision table as an intriguing alternative weak learner in gradient boosting, due to its simpler structure, good interpretability, and promising performance. In the literature, there have been works on privacy-preserving VFL for gradient boosted decision trees, but no prior work has been devoted to the emerging case of decision tables. Training and inference on decision tables are different from that the case of generic decision trees, not to mention gradient boosting with decision tables in VFL. In light of this, we design, implement, and evaluate Privet, the first system framework enabling privacy-preserving VFL service for gradient boosted decision tables. Privet delicately builds on lightweight cryptography and allows an arbitrary number of participants holding vertically partitioned datasets to securely train gradient boosted decision tables. Extensive experiments over several real-world datasets and synthetic datasets demonstrate that Privet achieves promising performance, with utility comparable to plaintext centralized learning.Comment: Accepted in IEEE Transactions on Services Computing (TSC

Understanding Status Update in Microblog: A Perspective on Media Needs

Microblog has grown popularly as a seminal social medium for timely information seeking and sharing. However, the reason why individuals update real-time information in microblog has not been well understood, and empirical research to address this specific information behavior is hardly available. As a felt urge can be conceptualized as a precursor of real-time updating in the microblog, we attempt to capture the underlying mechanism in causing this less reflective behavior urge. We apply the media needs theory to investigate how the individuals’ media needs spark their urge to update personal status in the microblog. In particular, we conceptualize the cognitive needs as related to information uniqueness, personal integrative needs as related to connectivity, social integrative needs as a unidirectional relationship, affective needs as positive emotions and tension release needs as negative emotions. An online survey was employed to validate the proposed model within 523 microblog users in China. The results suggest that the users’ behavior urge is significantly influenced by information uniqueness, connectivity, unidirectional relationship and positive emotions. Furthermore, among the five media needs, the affective and social integrative related factors strongly determine the personal real-time status update in microblog. The theoretical and practical implications are discussed in this paper

Heterogeneous Nucleation and Grain Initiation on a Single Substrate

Recently, we have proposed a new framework for early stages solidification, in which heterogeneous nucleation and grain initiation have been treated as separate processes. In this paper, we extend our atomic-level understanding of heterogeneous nucleation to spherical cap formation for grain initiation on a single substrate using molecular dynamics calculations. We first show that heterogeneous nucleation can be generally described as a three-layer mechanism to generate a two-dimensional (2D) nucleus under a variety of atomic arrangements at the solid/substrate interface. We then introduce the atomistic concept of spherical cap formation at different grain initiation undercoolings (ΔTgi) relative to nucleation undercooling (ΔTn). When ΔTn < ΔTgi, the spherical cap formation is constrained by the curvature of the liquid/solid interface, produces a dormant cap, and further growth is only made possible by increasing undercooling to overcome an energy barrier. However, when ΔTn > ΔTgi, spherical cap formation becomes barrierless and undergoes three distinctive stages: heterogeneous nucleation to produce a 2D nucleus with radius, rn; unconstrained growth to deliver a hemisphere of rN (substrate radius); and spherical growth beyond rN. This is followed by a theoretical analysis of the three-layer nucleation mechanism to bridge between three-layer nucleation, grain initiation and classical nucleation theory

Preface to the Special Issue on “Mathematical Methods for Computer Science”

In the last few decades, the relationship between mathematics and algorithms has become increasingly important and influential in computer science [...

Heterogeneous Nucleation Mechanisms in Systems with Large Lattice Misfit Demonstrated by the Pb(<i>l</i>)/Cu(<i>s</i>) System

Our current understanding of heterogeneous nucleation has been largely confined to the classical nucleation theory (CNT) that was postulated over 100 years ago based on a thermodynamic approach. Further advances in heterogeneous nucleation research requires detailed knowledge of atomistic activities at the liquid/substrate interface. In this work, using a classical molecular dynamics (MD) simulation, we investigated the atomistic mechanisms of heterogeneous nucleation in systems with a large lattice misfit (|f| > 12.5%) demonstrated by the liquid Pb and solid Cu system (denoted as the Pb(l)/Cu(s) system) with a misfit of 27.3%. We found that heterogeneous nucleation in systems with a large misfit takes place in two distinctive steps: (1) Prenucleation creates a coincidence site lattice (CSL) on the substrate surface to accommodate the majority (fcsl) of the initial misfit (f) and (2) Heterogeneous nucleation accommodates the residual misfit fr (fr = misfit − fcsl) at the nucleation temperature to create a plane of the new solid phase (a two-dimensional (2D) nucleus) through either a three-layer dislocation mechanism if fr fr > 0, such as in the case of the Pb(l)/Cu(s) system

Prenucleation at the Liquid/Substrate Interface: An Overview

Prenucleation refers to the phenomenon of substrate-induced atomic ordering in the liquid adjacent to the liquid/substrate interface at temperatures above the nucleation temperature. We investigated the effects of the physical and chemical properties of the substrate on prenucleation, using the classical molecular dynamics (MD) and ab initio MD simulations. We found that the physical origin of prenucleation is structural templating, which is affected significantly by the lattice misfit between the solid and the substrate, chemical interaction between the solid and the substrate, and the substrate surface roughness at the atomic level. Prenucleation ultimately determines the nucleation potency of a substrate and provides a precursor for heterogeneous nucleation at the nucleation temperature. In this paper, we provide an overview of the recent advances in the understanding of prenucleation made by the LiME Research Hub. After a brief review of the historical research on atomic ordering at the liquid/substrate interface in the literature, we present an overview of the recent advances in understanding prenucleation, covering the concept of prenucleation, the effect of temperature, lattice misfit and substrate chemistry, and substrate surface roughness at the atomic level. Our discussions will be focused on the effect of prenucleation on heterogeneous nucleation and its consequences on grain refinement

Seeing is not Believing: An Identity Hider for Human Vision Privacy Protection

Massive captured face images are stored in the database for the identification of individuals. However, these images can be observed intentionally or unintentionally by data managers, which is not at the will of individuals and may cause privacy violations. Existing protection schemes can maintain identifiability but slightly change the facial appearance, rendering it still susceptible to the visual perception of the original identity by data managers. In this paper, we propose an effective identity hider for human vision protection, which can significantly change appearance to visually hide identity while allowing identification for face recognizers. Concretely, the identity hider benefits from two specially designed modules: 1) The virtual face generation module generates a virtual face with a new appearance by manipulating the latent space of StyleGAN2. In particular, the virtual face has a similar parsing map to the original face, supporting other vision tasks such as head pose detection. 2) The appearance transfer module transfers the appearance of the virtual face into the original face via attribute replacement. Meanwhile, identity information can be preserved well with the help of the disentanglement networks. In addition, diversity and background preservation are supported to meet the various requirements. Extensive experiments demonstrate that the proposed identity hider achieves excellent performance on privacy protection and identifiability preservation

A New Atomistic Mechanism for Heterogeneous Nucleation in the Systems with Negative Lattice Misfit: Creating a 2D Template for Crystal Growth

Heterogeneous nucleation is a widespread phenomenon in both nature and technology. However, our current understanding is largely confined to the classical nucleation theory (CNT) postulated over a century ago, in which heterogeneous nucleation occurs stochastically to form a spherical cap facilitated by a substrate. In this paper, we show that heterogeneous nucleation in systems with negative lattice misfit completes deterministically within three atomic layers by structural templating to form a two-dimentional template from which the new phase can grow. Using molecular dynamics (MD) simulations of a generic system containing metallic liquid (Al) and a substrate of variable lattice misfit (fcc lattice with fixed Al atoms), we found that heterogeneous nucleation proceeds layer-by-layer: the first layer accommodates misfit through a partial edge dislocation network; the second layer twists an angle through a partial screw dislocation network to reduce lattice distortion; and the third layer creates a crystal plane of the solid (the 2D nucleus) that templates further growth. The twist angle of the solid relative to the substrate as a signature of heterogeneous nucleation in the systems with negative lattice misfit has been validated by high resolution transmission electron microscopic (HRTEM) examination of TiB2/Al and TiB2/α-Al15(Fe, Mn)3Si2 interfaces in two different Al-alloys

Metaverse: Security and Privacy Concerns

The term "metaverse", a three-dimensional virtual universe similar to the real realm, has always been full of imagination since it was put forward in the 1990s. Recently, it is possible to realize the metaverse with the continuous emergence and progress of various technologies, and thus it has attracted extensive attention again. It may bring a lot of benefits to human society such as reducing discrimination, eliminating individual differences, and socializing. However, everything has security and privacy concerns, which is no exception for the metaverse. In this article, we firstly analyze the concept of the metaverse and propose that it is a super virtual-reality (VR) ecosystem compared with other VR technologies. Then, we carefully analyze and elaborate on possible security and privacy concerns from four perspectives: user information, communication, scenario, and goods, and immediately, the potential solutions are correspondingly put forward. Meanwhile, we propose the need to take advantage of the new buckets effect to comprehensively address security and privacy concerns from a philosophical perspective, which hopefully will bring some progress to the metaverse community.Comment: This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl