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15,278 results on '"TANG, Yi"'

213. Computational Prediction and Experimental Validation of a Bridged Cation Intermediate in Akanthomycin Biosynthesis

Author

Jamieson, Cooper S, Ohashi, Masao, Houk, KN, and Tang, Yi

Subjects
Biological Products, Cations, Cyclization, Pyridones, Chemical Sciences, General Chemistry
Abstract

Here we report a computation-driven chemoenzymatic synthesis and biosynthesis of the natural product deoxyakanthomycin, an atropisomeric pyridone natural product that features a 7-membered carbocycle with five stereocenters, one of which a quaternary center. The one-step synthesis from a biosynthetic precursor is based on computational analysis that predicted a σ-bridged cation mediated cyclization mechanism to form deoxyakanthomycin. The σ-bridged cation rationalizes the observed substrate-controlled selectivity; diastereoselectivity arises from attack of water anti to the σ-bridging, as is generally found for σ-bridged cations. Our studies also reveal a unifying biosynthetic strategy for 2-pyridone natural products that derive from a common o-quinone methide to create diverse structures.

Published
2022

246. Discovery and characterization of a terpene biosynthetic pathway featuring a norbornene-forming Diels-Alderase

Author

Sun, Zuodong, Jamieson, Cooper S, Ohashi, Masao, Houk, KN, and Tang, Yi

Subjects
Biocatalysis, Biosynthetic Pathways, Cycloaddition Reaction, Norbornanes, Terpenes
Abstract

Pericyclases, enzymes that catalyze pericyclic reactions, form an expanding family of enzymes that have biocatalytic utility. Despite the increasing number of pericyclases discovered, the Diels-Alder cyclization between a cyclopentadiene and an olefinic dienophile to form norbornene, which is among the best-studied cycloadditions in synthetic chemistry, has surprisingly no enzymatic counterpart to date. Here we report the discovery of a pathway featuring a norbornene synthase SdnG for the biosynthesis of sordaricin-the terpene precursor of antifungal natural product sordarin. Full reconstitution of sordaricin biosynthesis reveals a concise oxidative strategy used by Nature to transform an entirely hydrocarbon precursor into the highly functionalized substrate of SdnG for intramolecular Diels-Alder cycloaddition. SdnG generates the norbornene core of sordaricin and accelerates this reaction to suppress host-mediated redox modifications of the activated dienophile. Findings from this work expand the scopes of pericyclase-catalyzed reactions and P450-mediated terpene maturation.

Published
2022

247. Video Salient Object Detection via Adaptive Local-Global Refinement

Author

Tang, Yi, Li, Yuanman, and Xing, Guoliang

Subjects
Computer Science - Computer Vision and Pattern Recognition
Abstract

Video salient object detection (VSOD) is an important task in many vision applications. Reliable VSOD requires to simultaneously exploit the information from both the spatial domain and the temporal domain. Most of the existing algorithms merely utilize simple fusion strategies, such as addition and concatenation, to merge the information from different domains. Despite their simplicity, such fusion strategies may introduce feature redundancy, and also fail to fully exploit the relationship between multi-level features extracted from both spatial and temporal domains. In this paper, we suggest an adaptive local-global refinement framework for VSOD. Different from previous approaches, we propose a local refinement architecture and a global one to refine the simply fused features with different scopes, which can fully explore the local dependence and the global dependence of multi-level features. In addition, to emphasize the effective information and suppress the useless one, an adaptive weighting mechanism is designed based on graph convolutional neural network (GCN). We show that our weighting methodology can further exploit the feature correlations, thus driving the network to learn more discriminative feature representation. Extensive experimental results on public video datasets demonstrate the superiority of our method over the existing ones.

Published
2021

248. Vector dark matter from split SU(2) gauge bosons

Author

Hu, Zexi, Cai, Chengfeng, Tang, Yi-Lei, Yu, Zhao-Huan, and Zhang, Hong-Hao

Subjects
High Energy Physics - Phenomenology, Astrophysics - Cosmology and Nongalactic Astrophysics, High Energy Physics - Experiment
Abstract

We propose a vector dark matter model with an exotic dark SU(2) gauge group. Two Higgs triplets are introduced to spontaneously break the symmetry. All of the dark gauge bosons become massive, and the lightest one is a viable vector DM candidate. Its stability is guaranteed by a remaining Z_2 symmetry. We study the parameter space constrained by the Higgs measurement data, the dark matter relic density, and direct and indirect detection experiments. We find numerous parameter points satisfying all the constraints, and they could be further tested in future experiments. Similar methodology can be used to construct vector dark matter models from an arbitrary SO(N) gauge group., Comment: 25 pages, 5 figures

Published
2021
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249. Phase transition gravitational waves from pseudo-Nambu-Goldstone dark matter and two Higgs doublets

Author

Zhang, Zhao, Cai, Chengfeng, Jiang, Xue-Min, Tang, Yi-Lei, Yu, Zhao-Huan, and Zhang, Hong-Hao

Subjects
High Energy Physics - Phenomenology, Astrophysics - Cosmology and Nongalactic Astrophysics, General Relativity and Quantum Cosmology
Abstract

We investigate the potential stochastic gravitational waves from first-order electroweak phase transitions in a model with pseudo-Nambu-Goldstone dark matter and two Higgs doublets. The dark matter candidate can naturally evade direct detection bounds, and can achieve the observed relic abundance via the thermal mechanism. Three scalar fields in the model obtain vacuum expectation values, related to phase transitions at the early Universe. We search for the parameter points that can cause first-order phase transitions, taking into account the existed experimental constraints. The resulting gravitational wave spectra are further evaluated. Some parameter points are found to induce strong gravitational wave signals, which have the opportunity to be detected in future space-based interferometer experiments LISA, Taiji, and TianQin., Comment: 35 pages, 8 figures, accepted for publication in JHEP

Published
2021
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250. Website fingerprinting on early QUIC traffic

Author

Zhan, Pengwei, Wang, Liming, and Tang, Yi

Subjects
Computer Science - Cryptography and Security, Computer Science - Machine Learning, Computer Science - Networking and Internet Architecture
Abstract

Cryptographic protocols have been widely used to protect the user's privacy and avoid exposing private information. QUIC (Quick UDP Internet Connections), including the version originally designed by Google (GQUIC) and the version standardized by IETF (IQUIC), as alternatives to the traditional HTTP, demonstrate their unique transmission characteristics: based on UDP for encrypted resource transmitting, accelerating web page rendering. However, existing encrypted transmission schemes based on TCP are vulnerable to website fingerprinting (WFP) attacks, allowing adversaries to infer the users' visited websites by eavesdropping on the transmission channel. Whether GQUIC and IQUIC can effectively resist such attacks is worth investigating. In this paper, we study the vulnerabilities of GQUIC, IQUIC, and HTTPS to WFP attacks from the perspective of traffic analysis. Extensive experiments show that, in the early traffic scenario, GQUIC is the most vulnerable to WFP attacks among GQUIC, IQUIC, and HTTPS, while IQUIC is more vulnerable than HTTPS, but the vulnerability of the three protocols is similar in the normal full traffic scenario. Features transferring analysis shows that most features are transferable between protocols when on normal full traffic scenario. However, combining with the qualitative analysis of latent feature representation, we find that the transferring is inefficient when on early traffic, as GQUIC, IQUIC, and HTTPS show the significantly different magnitude of variation in the traffic distribution on early traffic. By upgrading the one-time WFP attacks to multiple WFP Top-a attacks, we find that the attack accuracy on GQUIC and IQUIC reach 95.4% and 95.5%, respectively, with only 40 packets and just using simple features, whereas reach only 60.7% when on HTTPS. We also demonstrate that the vulnerability of IQUIC is only slightly dependent on the network environment., Comment: This work has been accepted by Elsevier Computer Networks for publication

Published
2021
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