654 research outputs found
Discovering Low-rank Subspaces for Language-agnostic Multilingual Representations
Large pretrained multilingual language models (ML-LMs) have shown remarkable
capabilities of zero-shot cross-lingual transfer, without direct cross-lingual
supervision. While these results are promising, follow-up works found that,
within the multilingual embedding spaces, there exists strong language identity
information which hinders the expression of linguistic factors shared across
languages. For semantic tasks like cross-lingual sentence retrieval, it is
desired to remove such language identity signals to fully leverage semantic
information. In this work, we provide a novel view of projecting away
language-specific factors from a multilingual embedding space. Specifically, we
discover that there exists a low-rank subspace that primarily encodes
information irrelevant to semantics (e.g., syntactic information). To identify
this subspace, we present a simple but effective unsupervised method based on
singular value decomposition with multiple monolingual corpora as input. Once
the subspace is found, we can directly project the original embeddings into the
null space to boost language agnosticism without finetuning. We systematically
evaluate our method on various tasks including the challenging
language-agnostic QA retrieval task. Empirical results show that applying our
method consistently leads to improvements over commonly used ML-LMs.Comment: 17 pages, 7 figures, EMNLP 2022 (main conference
Combustion characteristics of lignite char in a fluidized bed under O2/N2, O2/CO2 and O2/H2O atmospheres
As a possible new focus of oxy-fuel work, O2/H2O combustion has many advantages over O2/CO2 combustion, and has gradually gained increasing attention. The unique physicochemical properties (thermal capacity, diffusivity, reactivity) of H2O significantly influence the char combustion characteristics. In the present work, the combustion and kinetics characteristics of lignite char particle were studied in a fluidized bed (FB) reactor under N2, CO2 and H2O atmospheres with different O2 concentrations (15%–27%) and bed temperatures (Tb, 837–937 °C). Results indicated that the average reaction rate (raverage) and the peak reaction rate (rpeak) of lignite char in H2O atmospheres were slower than those in CO2 atmospheres at low O2 concentrations. However, as the O2 concentration increases, the rpeak and raverage of lignite char in H2O atmospheres significantly improved and exceeded those under CO2 atmospheres. The calculation result for the activation energy based on the shrinking-core model showed that the order of activation energy under different atmospheres is: O2/CO2 (28.96 kJ/mol) > O2/H2O (26.11 kJ/mol) > O2/N2 (23.31 kJ/mol). Furthermore, gasification reactions play an important role in both O2/CO2 and O2/H2O combustion, and should not be ignored. As the Tb increased, the active sites occupied by gasification agent were significantly increased, while the active sites occupied by oxygen decreased correspondingly
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