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Ngan Pham

Publications and source records attributed to Ngan Pham.

2 recordsLinked to original sources

Speaking in Words, Thinking in Logic: A Dual-Process Framework in QA Systems

Recent advances in large language models (LLMs) have significantly enhanced question-answering (QA) capabilities, particularly in open-domain contexts. However, in closed-domain scenarios such as education, healthcare, and law, users demand not only accurate answers but also transparent reasoning and explainable decision-making processes. While neural-symbolic (NeSy) frameworks have emerged as a promising solution, leveraging LLMs for natural language understanding and symbolic systems for formal reasoning, existing approaches often rely on large-scale models and exhibit inefficiencies in translating natural language into formal logic representations. To address these limitations, we introduce Text-JEPA (Text-based Joint-Embedding Predictive Architecture), a lightweight yet effective framework for converting natural language into first-order logic (NL2FOL). Drawing inspiration from dual-system cognitive theory, Text-JEPA emulates System 1 by efficiently generating logic representations, while the Z3 solver operates as System 2, enabling robust logical inference. To rigorously evaluate the NL2FOL-to-reasoning pipeline, we propose a comprehensive evaluation framework comprising three custom metrics: conversion score, reasoning score, and Spearman rho score, which collectively capture the quality of logical translation and its downstream impact on reasoning accuracy. Empirical results on domain-specific datasets demonstrate that Text-JEPA achieves competitive performance with significantly lower computational overhead compared to larger LLM-based systems. Our findings highlight the potential of structured, interpretable reasoning frameworks for building efficient and explainable QA systems in specialized domains.

cs.CL

Mobility of single vacancies and adatoms in graphene at room temperature

We investigate the mobility of structural defects, adatoms, and defect-adatom combinations in self-supporting graphene subjected to keV ion irradiation. In the first scenario, homogeneous irradiation using 20 keV Ar$^+$ ions at a dose of $3 \times 10^{14}$ ions/cm$^2$ induces tensile strain of up to 0.8\%. This strain diminishes with increasing defect density at the dose of $5 \times 10^{14}$ ions/cm$^2$, indicating a strain-relaxation mechanism. Contrary to the expected localized behavior, vacancies exhibit long-range interactions, contributing to global strain effects across the lattice. In the second scenario, by employing a nanopore mask, we spatially confined defect generation to periodically aligned circular regions surrounded by non-irradiated material, enabling direct observation of vacancy and adatom dynamics. Selected area electron diffraction (SAED) reveals significant structural damage in areas adjacent to the irradiated regions, suggesting that single vacancies migrate over distances on the order of 100 nm from irradiated to non-irradiated zones even at room temperature. The build-up of lattice strain observed in this study may play a key role in lowering the migration barrier of single vacancies, thereby facilitating their diffusion into pristine lattice regions. Furthermore, the findings highlight the role of pre-existing surface contaminants in preserving lattice integrity through a self-healing mechanism, where adatom-induced lattice reconstruction mitigates defect-induced structural degradation.

cond-mat.mtrl-sci