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As widely used in data-driven decision-making, recommender systems have been recognized for their capabilities to provide users with personalized services in many user-oriented online services, such as E-commerce (e.g., Amazon, Taobao, etc.) and Social Media sites (e.g., Facebook and Twitter). Recent works have shown that deep neural networks-based recommender systems are highly vulnerable to adversarial attacks, where adversaries can inject carefully crafted fake user profiles (i.e., a set of items that fake users have interacted with) into a target recommender system to promote or demote a set of target items. Instead of generating users with fake profiles from scratch, in this paper, we introduce a novel strategy to obtain “fake” user profiles via copying cross-domain user profiles, where a reinforcement learning-based black-box attacking framework (CopyAttack+) is developed to effectively and efficiently select cross-domain user profiles from the source domain to attack the target system. Moreover, we propose to train a local surrogate system for mimicking adversarial black-box attacks in the source domain, so as to provide transferable signals with the purpose of enhancing the attacking strategy in the target black-box recommender system. Comprehensive experiments on three real-world datasets are conducted to demonstrate the effectiveness of the proposed attacking framework. 

Silicon carbide (SiC) recently emerged as a promising photonic and quantum material owing to its unique material properties. In this work, we carried out an exploratory investigation of the Pockels effect in high-quality-factor (high-Q) 4H-SiC microresonators and demonstrated gigahertz-level electro-optic modulation for the first time. The extracted Pockels coefficients show certain variations among 4H-SiC wafers from different manufacturers, with the magnitudes ofr₁₃andr₃₃estimated to be in the range of (0.3–0.7) pm/V and (0–0.03) pm/V, respectively.

 

Protein translation is tightly and precisely controlled by multiple mechanisms including upstream open reading frames (uORFs), but the origins of uORFs and their role in maize are largely unexplored. In this study, an active transposition event was identified during the propagation of maize inbred line B73. The transposon, which was named BTA for ‘B73 active transposable element hAT’, creates a novel dosage-dependent hypomorphic allele of the hexose transporter gene ZmSWEET4c through insertion within the coding sequence in the first exon, and results in reduced kernel size. The BTA insertion does not affect transcript abundance but reduces protein abundance of ZmSWEET4c, probably through the introduction of a uORF. Furthermore, the introduction of BTA sequence in the exon of other genes can regulate translation efficiency without affecting their mRNA levels. A transposon capture assay revealed 79 novel insertions for BTA and BTA-like elements. These insertion sites have typical euchromatin features, including low levels of DNA methylation and high levels of H3K27ac. A putative autonomous element that mobilizes BTA and BTA-like elements was identified. Together, our results suggest a transposon-based origin of uORFs and document a new role for transposable elements to influence protein abundance and phenotypic diversity by affecting the translation rate.