arXiv subjects

Shixin Liu

Publications and source records attributed to Shixin Liu.

6 recordsLinked to original sources

arXiv2024

Minimizing Upper Confidence Bounds: A Data-Driven Framework for Stochastic Programming

Stochastic programming is often challenged by epistemic uncertainty, where critical probability distributions are poorly characterized or unknown due to a lack of data. To address this, we pioneer a novel framework for stochastic programming that minimizes an upper confidence bound (UCB) on the expected random cost, acting as a robustness-seeking strategy. Our central contribution is the Average Percentile Upper Bound (APUB), a new statistical construct that serves as both a statistically rigorous upper bound for population means and an approximate risk metric for sample means. We rigorously prove the asymptotic correctness and consistency of APUB, establishing a reliable foundation for data-driven decision-making. We also develop practical solution methods, including a bootstrap sampling approximation method and an L-shaped method, to solve APUB optimization problems, with a specific focus on two-stage linear stochastic optimization with random recourse. Empirical demonstrations on a two-stage product mix problem reveal the significant benefits of our APUB optimization framework, which fortifies the process against epistemic uncertainty while reinforcing key decision-making attributes like reliability and consistency. The implementation and source code are available at https://github.com/8Wings/APUB-Optimization.

math.OC↗

arXiv2023

Quantifying the contribution of material and junction resistances in nano-networks

Networks of nanowires and nanosheets are important for many applications in printed electronics. However, the network conductivity and mobility are usually limited by the inter-particle junction resistance, a property that is challenging to minimise because it is difficult to measure. Here, we develop a simple model for conduction in networks of 1D or 2D nanomaterials, which allows us to extract junction and nanoparticle resistances from particle-size-dependent D.C. resistivity data of conducting and semiconducting materials. We find junction resistances in porous networks to scale with nanoparticle resistivity and vary from 5 Ohm for silver nanosheets to 25 GOhm for WS2 nanosheets. Moreover, our model allows junction and nanoparticle resistances to be extracted from A.C. impedance spectra of semiconducting networks. Impedance data links the high mobility (~7 cm2/Vs) of aligned networks of electrochemically exfoliated MoS2 nanosheets to low junction resistances of ~670 kOhm. Temperature-dependent impedance measurements allow us to quantitatively differentiate intra-nanosheet phonon-limited band-like transport from inter-nanosheet hopping for the first time.

cond-mat.mes-hall↗

arXiv2023

Knot Architecture for Biocompatible and Semiconducting Two-Dimensional Electronic Fibre Transistors

In recent years, the rising demand for close interaction with electronic devices has led to a surge in the popularity of wearable gadgets. While wearable gadgets have generally been rigid due to their utilisation of silicon-based technologies, flexible semiconducting fibre-based transistors will be needed for future wearables as active sensing components or within microprocessors to manage and analyse data. Two-dimensional (2D) semiconducting flakes are yet to be investigated in fibre transistors but could offer a route toward high-mobility, biocompatible and flexible fibre-based devices. Here we report the electrochemical exfoliation of semiconducting two-dimensional (2D) flakes of tungsten diselenide (WSe2) and molybdenum disulfide (MoS2). The high aspect ratio (>100) of the flakes achieves aligned and conformal flake-to-flake junctions on polyester fibres enabling transistors with mobilities ~ 1 cm^2 V^-1 s^-1 and a current on/off ratio, Ion/Ioff ~ 10^2 - 10^4. Furthermore, the cytotoxic effects of the MoS2 and WSe2 flakes with human keratinocyte cells are investigated and found to be biocompatible. As an additional step, we create a unique transistor knot architecture by leveraging the fibre diameter to establish the length of the transistor channel, facilitating a route to scale down transistor channel dimensions (100 μm) and utilise it to make MoS2 fibre transistors with a human hair that achieves mobilities as high as μ ~ 15 cm^2 V^-1 s^-1.

cond-mat.mtrl-sci↗

arXiv2023

3D-imaging of Printed Nanostructured Networks using High-resolution FIB-SEM Nanotomography

Networks of solution-processed nanomaterials are important for multiple applications in electronics, sensing and energy storage/generation. While it is known that network morphology plays a dominant role in determining the physical properties of printed networks, it remains difficult to quantify network structure. Here, we utilise FIB-SEM nanotomography to characterise the morphology of nanostructured networks. Nanometer-resolution 3D-images were obtained from printed networks of graphene nanosheets of various sizes, as well as networks of WS2 nanosheets, silver nanosheets and silver nanowires. Important morphological characteristics, including network porosity, tortuosity, pore dimensions and nanosheet orientation were extracted and linked to network resistivity. By extending this technique to interrogate the structure and interfaces within vertical printed heterostacks, we demonstrate the potential of this technique for device characterisation and optimisation.

cond-mat.mes-hall↗

arXiv2019

A Study on the Block Relocation Problem: Lower Bound Derivations and Strong Formulations

The block relocation problem (BRP) is a fundamental operational issue in modern warehouse and yard management, which, however, is very challenging to solve. In this paper, to advance our understanding on this problem and to provide a substantial assistance to practice, we (i) introduce a classification scheme and present a rather comprehensive review on all 16 BRP variants; (ii) develop a general framework to derive lower bounds on the number of necessary relocations and demonstrate its connection to existing lower bounds of the unrestricted BRP variants; (iii) propose and employ a couple of new critical substructures concepts to analyze the BRP and obtain a lower bound that dominates all existing ones; (iv) build a new and strong mixed integer programming (MIP) formulation that is adaptable to compute 8 BRP variants, and design a novel MIP-formulation-based iterative procedure to compute exact BRP solutions; (v) extend the MIP formulation to address four typical industrial considerations. Computational results on standard test instances show that the new lower bound is significantly stronger, and our new MIP computational methods have superior performances over a state-of-the-art formulation.

math.OC↗

arXiv2017

Capacity Expansion Planning of Wind Power Generation in A Market Environment with Topology Control

Wind power integration is an essential problem for modern power industry. In this paper, we develop a novel bilevel mixed integer optimization model to investigate wind power generation planning problem in an electricity market environment with topology control operations. Different from existing formulations, the lower level market clearing problem introduces binary variables to model line switching decisions, which have been proven very effective to improve transmission capability under different load profiles. To solve this challenging bilevel mixed integer program, a recent decomposition method is customized and a couple of enhancement techniques based on grid structure are designed. Through computing instances from typical IEEE test beds, our solution methods demonstrate a strong solution capacity. Also, we observe that applying topology control on a small number of lines could be very helpful to reduce wind power curtailment and improve the wind penetration level.

math.OC↗