arXiv subjects

Meng-Lin Tsai

Publications and source records attributed to Meng-Lin Tsai.

3 recordsLinked to original sources

arXiv2026

Incorporating circular economy policies into product supply chains using bilevel optimization -- A case study on coffee packaging

Transitioning to a Circular Economy requires policies to drive sustainable practices. This study proposes a bilevel optimization framework to evaluate the combined use of carbon taxes and subsidies in promoting circular supply chains under varying budget levels. A case study of the coffee packaging supply chain with an Extended Producer Responsibility scenario is used to demonstrate this approach. The framework captures the hierarchical interaction between a regional government (upper level), which aims to minimize environmental impacts, and coffee companies (lower level), which seek to minimize costs. Two bilevel optimization problems are formulated based on two environmental objectives: (1) minimization of greenhouse gas (GHG) emissions, and (2) maximization of circularity. The model integrates mixed-integer linear programming (MILP) with life cycle assessment (LCA), techno-economic assessment (TEA) and circularity assessment. Results demonstrate that subsidies effectively drive supply chain shifts toward low-emission and high-circularity configurations, while carbon taxes alone have a more limited impact. Sensitivity analyses highlight the influence of key parameters, such as glass washing distance and loss rates, on policy effectiveness. Overall, the study provides a bilevel optimization framework with quantitative insights to support policy design for sustainable circular supply chains.

math.OC↗

arXiv2026

Parametric Region Search: A Mixed-Integer Bilevel Optimization Problem Primal Heuristic

Bilevel optimization is a mathematical modeling formulation for hierarchical systems and two-player interactions, with wide-ranging applications in environmental, energy, and control engineering. Despite its utility, the mixed-integer bilevel optimization (MIBO) problem is exceptionally challenging to solve. While numerous exact and metaheuristic methods exist, the development of specialized primal heuristics for MIBO, aimed at quickly identifying high-quality feasible solutions, remains an underexplored area. This paper introduces the Parametric Region Search (PRS), a new primal heuristic for MIBO. The PRS method leverages insights from multi-parametric optimization by iteratively exploring regions defined by the lower-level problem's critical regions. We formally define the MIBO structure and the necessary parametric region formulations, and then detail the proposed heuristic's initialization and iterative search mechanism. Computational results demonstrate that the PRS heuristic consistently locates high-quality primal solutions compared to established derivative-free metaheuristics, including DOMINO-COBYLA and DOMINO-ISRES. Furthermore, we illustrate how the PRS can be effectively integrated with other heuristics like DOMINO-COBYLA to enhance the overall solution discovery process for MIBO.

math.OC↗

arXiv2013

Ultrahigh-Gain Phototransistors Based on Graphene-MoS2 Heterostructures

Due to its high carrier mobility, broadband absorption, and fast response time, graphene is attractive for optoelectronics and photodetection applications. However, the extraction of photoelectrons in conventional metal-graphene junction devices is limited by their small junction area, where the typical photoresponsivity is lower than 0.01 AW-1. On the other hand, the atomically thin layer of molybdenum disulfide (MoS2) is a two-dimensional (2d) nanomaterial with a direct and finite band gap, offering the possibility of acting as a 2d light absorber. The optoelectronic properties of the heterostructure of these two films is therefore of great interest. The growth of large-area graphene using chemical vapour deposition (CVD) has become mature nowadays. However, the growth of large-area MoS2 monolayer is still challenging. In this work, we show that a large-area and continuous MoS2 monolayer is achievable using a CVD method. Both graphene and MoS2 layers are transferable onto desired substrates, making possible immediate and large-scale optoelectronic applications. We demonstrate that a phototransistor based on the graphene/MoS2 heterostructure is able to provide a high photoresponsivity greater than 107 A/W while maintaining its ultrathin and planar structure. Our experiments show that the electron-hole pairs are produced in the MoS2 layer after light absorption and subsequently separated across the layers. Contradictory to the expectation based on the conventional built-in electric field model for metal-semiconductor contacts, photoelectrons are injected into the graphene layer rather than trapped in MoS2 due to the alignment of the graphene Fermi level with the conduction band of MoS2. The band alignment is sensitive to the presence of a perpendicular electric field arising from, for example, Coulomb impurities or an applied gate voltage, resulting in a tuneable photoresponsivity.

cond-mat.mtrl-sci↗