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Shiwei Wang

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Published work

5 published item(s)

preprint2026arXiv

ASTRA-QA: A Benchmark for Abstract Question Answering over Documents

Document-based question answering (QA) increasingly includes abstract questions that require synthesizing scattered information from long documents or across multiple documents into coherent answers. However, this setting is still poorly supported by existing benchmarks and evaluation methods, which often lack stable abstract references or rely on coarse similarity metrics and unstable head-to-head comparisons. To alleviate this issue, we introduce ASTRA-QA, a benchmark for AbSTRAct Question Answering over documents. ASTRA-QA contains 869 QA instances over academic papers and news documents, covering five abstract question types and three controlled retrieval scopes. Each instance is equipped with explicit evaluation annotations, including answer topic sets, curated unsupported topics, and aligned evidence. Building on these annotations, ASTRA-QA assesses whether answers cover required key points and avoid unsupported content by directly scoring topic coverage and curated unsupported content, enabling scalable evaluation without exhaustive head-to-head comparisons. Experiments with representative Retrieval-Augmented Generation (RAG) methods spanning vanilla, graph-based, and hierarchical retrieval settings show that ASTRA-QA provides reference-grounded diagnostics for coverage, hallucination, and retrieval-scope robustness. Our dataset and code are available at https://xinyangsally.github.io/astra-benchmark.

preprint2026arXiv

Characterizations of Tilt-Stable Local Minimizers of a Class of Matrix Optimization Problems

Tilt stability plays a pivotal role in understanding how local solutions of an optimization problem respond to small, targeted perturbations of the objective. Although quadratic bundles are a powerful tool for capturing second-order variational behavior, their characterization remains incomplete beyond well-known polyhedral and certain specialized nonpolyhedral settings. To help bridge this gap, we propose a new point-based criterion for tilt stability in prox-regular, subdifferentially continuous functions by exploiting the notion of minimal quadratic bundles. Furthermore, we derive an explicit formula for the minimal quadratic bundle associated with a broad class of general spectral functions, thus providing a practical and unifying framework that significantly extends existing results and offers broader applicability in matrix optimization problems.

preprint2022arXiv

A CMOS-based Characterisation Platform for Emerging RRAM Technologies

Mass characterisation of emerging memory devices is an essential step in modelling their behaviour for integration within a standard design flow for existing integrated circuit designers. This work develops a novel characterisation platform for emerging resistive devices with a capacity of up to 1 million devices on-chip. Split into four independent sub-arrays, it contains on-chip column-parallel DACs for fast voltage programming of the DUT. On-chip readout circuits with ADCs are also available for fast read operations covering 5-decades of input current (20nA to 2mA). This allows a device's resistance range to be between 1k$Ω$ and 10M$Ω$ with a minimum voltage range of $\pm$1.5V on the device.

preprint2022arXiv

Local convergence analysis of augmented Lagrangian method for nonlinear semidefinite programming

The augmented Lagrangian method (ALM) has gained tremendous popularity for its elegant theory and impressive numerical performance since it was proposed by Hestenes and Powell in 1969. It has been widely used in numerous efficient solvers to improve numerical performance to solve many problems. In this paper, without requiring the uniqueness of multipliers, the local (asymptotic Q-superlinear) Q-linear convergence rate of the primal-dual sequences generated by ALM for the nonlinear semidefinite programming (NLSDP) is established by assuming the second-order sufficient condition (SOSC) and the semi-isolated calmness of the Karush-Kuhn-Tucker (KKT) solution under some mild conditions.

preprint2016arXiv

Oxygen vacancy induced room temperature metal-insulator transition in nickelates films and its potential application in photovoltaics

Oxygen vacancy is intrinsically coupled with magnetic, electronic and transport properties of transition-metal oxide materials and directly determines their multifunctionality. Here, we demonstrate reversible control of oxygen content by post-annealing at temperature lower than 300 degree centigrade and realize the reversible metal-insulator transition in epitaxial NdNiO3 films. Importantly, over six orders of magnitude in the resistance modulation and a large change in optical band gap are demonstrated at room temperature without destroying the parent framework and changing the p-type conductive mechanism. Further study revealed that oxygen vacancies stabilized the insulating phase at room temperature is universal for perovskite nickelates films. Acting as electron donors, oxygen vacancies not only stabilize the insulating phase at room temperature, but also induce a large magnetization of ~50 emu/cm3 due to the formation of strongly correlated Ni2+ t2g6eg2 states. The band gap opening is an order of magnitude larger than that of the thermally driven metal-insulator transition and continuously tunable. Potential application of the newly found insulating phase in photovoltaics has been demonstrated in the nickelates-based heterojunctions. Our discovery opens up new possibilities for strongly correlated perovskite nickelates.