490 research outputs found
Steady and dynamic magnetic phase transitions in interacting quantum dots arrays coupled with leads
We apply the Hubbard model, non-equilibrium Green's function (NEGF) theory,
exact diagonalization (ED) and the hierarchical equations of motion (HEOM)
method to investigate abundant magnetic phase transitions in the 1D interacting
quantum dots arrays (QDA) sandwiched by non-interaction leads. The spin
polarization phase transitions are firstly studied with a mean-field
approximation. The many-body calculation of the ED method is then used to
verify such transitions. We find with the weak device-leading couplings, the
anti-ferromagnetic (AF) state only exists in the uniform odd-numbered QDA or
the staggered-hopping QDA systems. With increasing the coupling strength or the
bias potentials, there exists the magnetism-to non-magnetism phase transition.
With the spin-resolved HEOM method we also investigate the detailed dynamic
phase transition process of these lead-QDA-lead systems.Comment: 17 pages, 6 figure
Joint event extraction based on hierarchical event schemas from framenet
Event extraction is useful for many practical applications, such as news summarization and information retrieval. However, the popular automatic context extraction (ACE) event extraction program only defines very limited and coarse event schemas, which may not be suitable for practical applications. FrameNet is a linguistic corpus that defines complete semantic frames and frame-to-frame relations. As frames in FrameNet share highly similar structures with event schemas in ACE and many frames actually express events, we propose to redefine the event schemas based on FrameNet. Specifically, we extract frames expressing event information from FrameNet and leverage the frame-to-frame relations to build a hierarchy of event schemas that are more fine-grained and have much wider coverage than ACE. Based on the new event schemas, we propose a joint event extraction approach that leverages the hierarchical structure of event schemas and frame-to-frame relations in FrameNet. The extensive experiments have verified the advantages of our hierarchical event schemas and the effectiveness of our event extraction model. We further apply the results of our event extraction model on news summarization. The results show that the summarization approach based on our event extraction model achieves significant better performance than several state-of-the-art summarization approaches, which also demonstrates that the hierarchical event schemas and event extraction model are promising to be used in the practical applications
ProtoEM: A Prototype-Enhanced Matching Framework for Event Relation Extraction
Event Relation Extraction (ERE) aims to extract multiple kinds of relations
among events in texts. However, existing methods singly categorize event
relations as different classes, which are inadequately capturing the intrinsic
semantics of these relations. To comprehensively understand their intrinsic
semantics, in this paper, we obtain prototype representations for each type of
event relation and propose a Prototype-Enhanced Matching (ProtoEM) framework
for the joint extraction of multiple kinds of event relations. Specifically,
ProtoEM extracts event relations in a two-step manner, i.e., prototype
representing and prototype matching. In the first step, to capture the
connotations of different event relations, ProtoEM utilizes examples to
represent the prototypes corresponding to these relations. Subsequently, to
capture the interdependence among event relations, it constructs a dependency
graph for the prototypes corresponding to these relations and utilized a Graph
Neural Network (GNN)-based module for modeling. In the second step, it obtains
the representations of new event pairs and calculates their similarity with
those prototypes obtained in the first step to evaluate which types of event
relations they belong to. Experimental results on the MAVEN-ERE dataset
demonstrate that the proposed ProtoEM framework can effectively represent the
prototypes of event relations and further obtain a significant improvement over
baseline models.Comment: Work in progres
A revisit of superconductivity in 4-TaSSe single crystals
Previous investigations of 4-TaSSe mainly focused on the
direct competition between superconductivity and charge density wave (CDW).
However, the superconductivity itself, although has been prominently enhanced
by isovalent Se substitution, has not been adequately investigated. Here, we
performed a detailed electrical transport measurement down to 0.1 K on a series
of 4-TaSSe single crystals. A systematic fitting of the
temperature-dependent resistance demonstrates that the decreased Debye
temperatures () and higher electron-phonon coupling constants
() at the optimal Se doping content raise the superconducting
transition temperature (). Additionally, we discovered that the
incorporation of Se diminishes the degree of anisotropy of the
superconductivity in the highly layered structure. More prominently, a
comprehensive analysis of the vortex liquid phase region reveals that the
optimally doped sample deviates from the canonical 2D Tinkham prediction but
favors a linear trend with the variation of the external magnetic field. These
findings emphasize the importance of interlayer interaction in this segregated
superconducting-Mott-insulating system.Comment: 11 pages, 5 figure
An In-Context Schema Understanding Method for Knowledge Base Question Answering
The Knowledge Base Question Answering (KBQA) task aims to answer natural
language questions based on a given knowledge base. As a kind of common method
for this task, semantic parsing-based ones first convert natural language
questions to logical forms (e.g., SPARQL queries) and then execute them on
knowledge bases to get answers. Recently, Large Language Models (LLMs) have
shown strong abilities in language understanding and may be adopted as semantic
parsers in such kinds of methods. However, in doing so, a great challenge for
LLMs is to understand the schema of knowledge bases. Therefore, in this paper,
we propose an In-Context Schema Understanding (ICSU) method for facilitating
LLMs to be used as a semantic parser in KBQA. Specifically, ICSU adopts the
In-context Learning mechanism to instruct LLMs to generate SPARQL queries with
examples. In order to retrieve appropriate examples from annotated
question-query pairs, which contain comprehensive schema information related to
questions, ICSU explores four different retrieval strategies. Experimental
results on the largest KBQA benchmark, KQA Pro, show that ICSU with all these
strategies outperforms that with a random retrieval strategy significantly
(from 12\% to 78.76\% in accuracy)
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