arXiv subjects

Tingting Gao

Publications and source records attributed to Tingting Gao.

75 records · Page 5Linked to original sources

arXiv2022

Domain Generalization via Shuffled Style Assembly for Face Anti-Spoofing

With diverse presentation attacks emerging continually, generalizable face anti-spoofing (FAS) has drawn growing attention. Most existing methods implement domain generalization (DG) on the complete representations. However, different image statistics may have unique properties for the FAS tasks. In this work, we separate the complete representation into content and style ones. A novel Shuffled Style Assembly Network (SSAN) is proposed to extract and reassemble different content and style features for a stylized feature space. Then, to obtain a generalized representation, a contrastive learning strategy is developed to emphasize liveness-related style information while suppress the domain-specific one. Finally, the representations of the correct assemblies are used to distinguish between living and spoofing during the inferring. On the other hand, despite the decent performance, there still exists a gap between academia and industry, due to the difference in data quantity and distribution. Thus, a new large-scale benchmark for FAS is built up to further evaluate the performance of algorithms in reality. Both qualitative and quantitative results on existing and proposed benchmarks demonstrate the effectiveness of our methods. The codes will be available at https://github.com/wangzhuo2019/SSAN.

cs.CV↗

arXiv2014

A criterion of the non-existence of surface states in a semi-infinite crystal

An infinite crystal can be constructed by an infinite number of parallel two-dimensional (hkl) crystal planes coupled to each other. For crystals with negligible spin-orbit coupling, we report a rigorous proof of a criterion on the non-existence of surface states in a semi-infinite crystal with the crystal symmetry. The forward transfer to be the same as the backward one, called as F-B dynamical symmetry, is key to realize the criterion. Based on lattice model Hamiltonian with coupling between the nearest neighbor crystal planes only, we prove that a cut crystal will not be able to accommodate any surface states if the original infinite crystal has reflection symmetry about every crystal plane which results in F-B symmetry. The criterion provide a platform to simply conclude whether surface states exist or not in a cut crystal. For any such crystals, the non-existence or existence of surface states depends on the cut direction of the crystal plane. Since the spin-orbit coupling breaks the chiral symmetry, resulting in the F-B asymmetry, surface states can emerge in the (hkl) cut crystal with spin-orbit coupling.

cond-mat.mes-hall↗

arXiv2011

Uncovering Social Network Sybils in the Wild

Sybil accounts are fake identities created to unfairly increase the power or resources of a single malicious user. Researchers have long known about the existence of Sybil accounts in online communities such as file-sharing systems, but have not been able to perform large scale measurements to detect them or measure their activities. In this paper, we describe our efforts to detect, characterize and understand Sybil account activity in the Renren online social network (OSN). We use ground truth provided by Renren Inc. to build measurement based Sybil account detectors, and deploy them on Renren to detect over 100,000 Sybil accounts. We study these Sybil accounts, as well as an additional 560,000 Sybil accounts caught by Renren, and analyze their link creation behavior. Most interestingly, we find that contrary to prior conjecture, Sybil accounts in OSNs do not form tight-knit communities. Instead, they integrate into the social graph just like normal users. Using link creation timestamps, we verify that the large majority of links between Sybil accounts are created accidentally, unbeknownst to the attacker. Overall, only a very small portion of Sybil accounts are connected to other Sybils with social links. Our study shows that existing Sybil defenses are unlikely to succeed in today's OSNs, and we must design new techniques to effectively detect and defend against Sybil attacks.

cs.SI↗