Video temporal localization aims to locate a period that semantically matches a natural language query in a given untrimmed video. We empirically observe that although existing approaches gain steady progress on sentence localization, the performance of phrase localization is far from satisfactory. In principle, the phrase should be easier to localize as fewer combinations of visual concepts need to be considered; such incapability indicates that the existing models only capture the sentence annotation bias in the benchmark but lack sufficient understanding of the intrinsic relationship between simple visual and language concepts, thus the model generalization and interpretability is questioned. This paper proposes a unified framework that can deal with both sentence and phrase-level localization, namely Phrase Level Prediction Net (PLPNet). Specifically, based on the hypothesis that similar phrases tend to focus on similar video cues, while dissimilar ones should not, we build a contrastive mechanism to restrain phrase-level localization without fine-grained phrase boundary annotation required in training. Moreover, considering the sentence's flexibility and wide discrepancy among phrases, we propose a clustering-based batch sampler to ensure that contrastive learning can be conducted efficiently. Extensive experiments demonstrate that our method surpasses state-of-the-art methods of phrase-level temporal localization while maintaining high performance in sentence localization and boosting the model's interpretability and generalization capability. Our code is available at https://github.com/sizhelee/PLPNet. CCS CONCEPTS• Computing methodologies → Visual content-based indexing and retrieval; Activity recognition and understanding.

Utilizing the anti-Zeno effect, we demonstrate that the resonances of ultracold molecular interactions can be selectively controlled by modulating the energy levels of molecules with a dynamic magnetic field. We show numerically that the inelastic scattering cross section of the selected isotopic molecules in the mixed isotopic molecular gas can be boosted for 2-3 orders of magnitude by modulation of Zeeman splittings. The mechanism of the resonant anti-Zeno effect in the ultracold scattering is based on matching the spectral modulation function of the magnetic field with the Floquet engineered resonance of the molecular collision. The resulting insight provides a recipe to implement resonant anti-Zeno effect in control of molecular interactions, such as selection of reaction channels between molecules involving shape and Feshbach resonances, and external field assisted separation of isotopes.

In this paper, we address the problem of video temporal sentence localization, which aims to localize a target moment from videos according to a given language query. We observe that existing models suffer from a sheer performance drop when dealing with simple phrases contained in the sentence. It reveals the limitation that existing models only capture the annotation bias of the datasets but lack sufficient understanding of the semantic phrases in the query. To address this problem, we propose a phrase-level Temporal Relationship Mining (TRM) framework employing the temporal relationship relevant to the phrase and the whole sentence to have a better understanding of each semantic entity in the sentence. Specifically, we use phrase-level predictions to refine the sentence-level prediction, and use Multiple Instance Learning to improve the quality of phrase-level predictions. We also exploit the consistency and exclusiveness constraints of phrase-level and sentence-level predictions to regularize the training process, thus alleviating the ambiguity of each phrase prediction. The proposed approach sheds light on how machines can understand detailed phrases in a sentence and their compositions in their generality rather than learning the annotation biases. Experiments on the ActivityNet Captions and Charades-STA datasets show the effectiveness of our method on both phrase and sentence temporal localization and enable better model interpretability and generalization when dealing with unseen compositions of seen concepts. Code can be found at https://github.com/minghangz/TRM.