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The ultrafast internal conversion and intersystem crossing dynamics of 2-thiouracil (2TU) and 2-thiothymine (2TT) are studied using time-resolved photoelectron spectroscopy to investigate the effect of methylation on the deactivation mechanism. Like other thiobases, the triplet manifold is populated with high quantum yields via the lowest singlet excited state, which is dark in absorption. This study focuses on the lowest triplet state and the role of two minima, with sulfur-out-of-plane and slightly boat-like geometries, in the intersystem crossing dynamics back to the ground state.

The ultrafast internal conversion (IC) and intersystem crossing (ISC) dynamics of 2-thiouracil (2TU) and 2-thiothymine (2TT) are studied with time-resolved photoelectron spectroscopy (TRPES) to investigate the effect of methylation on the deactivation mechanism.

Photo-oxa-dibenzocyclooctyne (Photo-ODIBO) undergoes photodecarbonylation under UV excitation to its bright S2 state, forming a highly reactive cyclooctyne, ODIBO. Following 321 nm excitation with sub-50 fs actinic pulses, the excited state evolution and cyclopropenone bond cleavage with CO release were characterized using femtosecond stimulated Raman spectroscopy and time-dependent density functional theory Raman calculations. Analysis of the photo-ODIBO S2 CO Raman band revealed multi-exponential intensity, peak splitting and frequency-shift dynamics. This suggests a stepwise cleavage of the two C–C bonds in the cyclopropenone structure that is completed within

Recently, dense passage retrieval has become a mainstream approach to finding relevant information in various natural language processing tasks. A number of studies have been devoted to improving the widely adopted dual-encoder architecture. However, most of the previous studies only consider query-centric similarity relation when learning the dual-encoder retriever. In order to capture more comprehensive similarity relations, we propose a novel approach that leverages both query-centric and PAssage-centric sImilarity Relations (called PAIR) for dense passage retrieval. To implement our approach, we make three major technical contributions by introducing formal formulations of the two kinds of similarity relations, generating high-quality pseudo labeled data via knowledge distillation, and designing an effective two-stage training procedure that incorporates passage-centric similarity relation constraint. Extensive experiments show that our approach significantly outperforms previous state-of-the-art models on both MSMARCO and Natural Questions datasets., ACL 2021

In open-domain question answering, dense passage retrieval has become a new paradigm to retrieve relevant passages for finding answers. Typically, the dual-encoder architecture is adopted to learn dense representations of questions and passages for semantic matching. However, it is difficult to effectively train a dual-encoder due to the challenges including the discrepancy between training and inference, the existence of unlabeled positives and limited training data. To address these challenges, we propose an optimized training approach, called RocketQA, to improving dense passage retrieval. We make three major technical contributions in RocketQA, namely cross-batch negatives, denoised hard negatives and data augmentation. The experiment results show that RocketQA significantly outperforms previous state-of-the-art models on both MSMARCO and Natural Questions. We also conduct extensive experiments to examine the effectiveness of the three strategies in RocketQA. Besides, we demonstrate that the performance of end-to-end QA can be improved based on our RocketQA retriever., Comment: NAACL 2021

Since 2010, the plasmon-driven catalysis using surface-enhanced Raman spectroscopy (SERS) in atmospheric environment has been experimentally reported. Recent experimental results since 2014 revealed that catalysis under aqueous condition is much better than that in atmospheric environment. In this paper, we review plasmon-driven catalysis using SERS under aqueous condition. First, the experimental apparatus developed by ourselves is introduced in detail. Second, we demonstrate the advantages of plasmon-driven catalysis using SERS under aqueous condition compared to that in atmospheric environment. Third, we review recent experimental results using this measurement method in different experimental settings under aqueous condition. The manipulation of reaction environment effectively provided the possibility to reveal the mechanism of surface plasmon catalysis for different reactions. This method has great potential to apply on ultrasensitive spectral analysis for SERS, catalysis, sensor and biology system under aqueous condition. Copyright © 2016 John Wiley & Sons, Ltd.